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Islet amyloid polypeptide ? a novel controversy in diabetes research
Abstract
The discovery of a previously unknown polypeptide in the islet Beta cells was unexpecled. This putative hormone, named islet amyloid polypeptided (IAPP) or amylin, has beer implicated in the normal regulation of glucose melabolism and has beer proposed to have a role in the pathogenesis of Type 2 (non-insulin-dependent) diabetes mellitus. IAPP is therefore of great interest in the field of diabetes research at present
... However, the possible role of IAPP in the modification of insulin effects on peripheral tissues is still controversial, and it cannot be excluded that IAPP has an important function in the fine tuning, that is difficult to demonstrate experimentally. These effects, and possible effects, direct or indirect, on the liver and adipose tissues have been reviewed several times (59,65,401,414) and will not be repeated here in detail. ...
... The pathological deposition of IAPP-derived amyloid in the islets of Langerhans occurs not only in humans but also in some other mammalian species. One important reason for the earlier relative lack of interest in islet amyloid may be the fact that it does not occur in the animals commonly used in diabetes research, such as the rat and mouse (401). Rat and mouse IAPP (which are identical) lack fibrillogenicity in vivo and in vitro. ...
... First, its importance in health and disease as a hormone has been vigorously discussed. Second, the role of aggregated IAPP in the development of the -cell lesion in type 2 diabetes has not yet become generally accepted (60,401). However, recent results from transplantation of human and transgenic animal islets firmly indicate that IAPP fibrils or oligomers have a crucial role in the progressive failure of -cells in transplants and thereby also indirectly support a similar mechanism in type 2 diabetes. ...
Islet amyloid polypeptide (IAPP, or amylin) is one of the major secretory products of β-cells of the pancreatic islets of Langerhans. It is a regulatory peptide with putative function both locally in the islets, where it inhibits insulin and glucagon secretion, and at distant targets. It has binding sites in the brain, possibly contributing also to satiety regulation and inhibits gastric emptying. Effects on several other organs have also been described. IAPP was discovered through its ability to aggregate into pancreatic islet amyloid deposits, which are seen particularly in association with type 2 diabetes in humans and with diabetes in a few other mammalian species, especially monkeys and cats. Aggregated IAPP has cytotoxic properties and is believed to be of critical importance for the loss of β-cells in type 2 diabetes and also in pancreatic islets transplanted into individuals with type 1 diabetes. This review deals both with physiological aspects of IAPP and with the pathophysiological role of aggregated forms of IAPP, including mechanisms whereby human IAPP forms toxic aggregates and amyloid fibrils.
... With the passing of time, however, as insulin resistance exacerbates and pancreatic insulin reserve depletes, insulin secretion is no longer sufficient to ensure carbohydrate homeostasis [42]. Long-term hyperglycemia impairs the ability of pancreatic β-cells to secrete insulin by, e.g., the dysregulation of cellular processes that determine glucose-dependent insulin secretion or by intracellular deposition of substances co-secreted with insulin, such as IAPP (islet amyloid polypeptide) [28,43,44]. The subsequent depletion of β-cell insulin secretory capacity results in the clinical manifestation of insulin resistance, manifesting from both relative but also absolute insulin deficiency that develops in long-standing T2DM. ...
... The effectiveness of therapy is greater if supervised by an interdisciplinary team of various specialists (diabetologists experienced in obesity management, primary care physicians, registered dietitians, diabetes counselors, etc.) compared to interventions undertaken by physicians alone. [44] Therapeutic meetings with healthcare providers should be frequent: ≥16 sessions over 6 months (ADA) or 12-26 sessions over 6-12 months (EASD) [14,19]. ...
Obesity, a chronic disease with multifactorial etiopathogenesis, is characterized by excessive accumulation of adipose tissue. Obesity prevalence is growing globally at an alarming rate. The overwhelming majority of obesity cases are caused by inappropriate lifestyles, such as overconsumption of food and inadequate physical activity. Metabolic and biochemical changes due to increased adiposity resulted in numerous comorbidities, increased all-cause mortality, and reduced quality of life. T2DM (type 2 diabetes mellitus) and obesity have many common pathogenetic points and drive each other in a vicious cycle. The aim of this article is to review obesity management guidelines and highlight the most important points. Management of both obesity-related and T2DM complications incur enormous expenses on healthcare systems. It is, therefore, paramount to provide streamlined yet custom-tailored weight management in order to avoid the negative ramifications of both diseases. Efficient obesity treatment leads to better diabetes control since some antidiabetic medications support weight reduction. Obesity treatment should be overseen by a multi-disciplinary team providing indispensable information and individually tailored regimens to patients. Weight management should be multimodal and consist chiefly of MNT (medical nutrition therapy), physical activity, and lifestyle changes. A comprehensive approach to obesity treatment may give tangible results to quality of life and comorbidities.
... The ability of lAPP to form amyloid fibrils is related to the amyloidogenic sequence in the 25-28 region. lAPP is co-stored with insulin in the secretory granule and in response to glucose and other secretagogues, it is secreted together with insulin into the extracellular space (Westermark et al. 1992). In the fasting state the serum LAPP concentration is about 10% of the insulin level. ...
... The biological function of lAPP is unknown. At pharmacological concentrations lAPP has been demonstrated to inhibit glucose-stimulated insulin release and to impair basal and insulin-stim ulated glucose disposal by reducing glucose transport, inhibiting glycogen synthase and stimulating glycogen phosphorylase activities (Westermark et al. 1992). However, these effects are not observed at physiological concentrations. ...
Non-insulin dependent diabetes (NIDDM) is characterised by disturbances in insulin action and insulin secretion with hyperproinsulinaemia, but the primary defect remains unknown. The pathogenesis has a strong genetic component and first-degree relatives of patients with NIDDM constitute a population at-risk. Metabolic abnormalities identified in this predisposed group, whilst glucose tolerance is still normal, may represent the primary cause of NIDDM. With this aim this thesis has investigated insulin secretion and insulin sensitivity in glucose-tolerant first-degree relatives from three ethnic groups. In the progress of this work, three new methods for measuring insulin sensitivity were developed: the low dose short insulin tolerance test; glycerol turnover measured in response to low dose insulin using stable isotopic tracers and a glycerol clamp. Relatives of patients of Asian (Indian-subcontinent) origin had raised fasting circulating immunoreactive insulin and glycerol levels and impaired suppression of glycerol and non-esterified fatty acid concentrations following oral glucose. This suggested insulin resistance, which was confirmed using the short insulin tolerance test. Relatives of European patients possessed more subtle abnormalities; when glycerol turnover was measured isotopically in response to low dose insulin infusion, insulin-induced suppression of lipolysis was impaired; these relatives also demonstrated increased levels of 32, 33 split proinsulin following intravenous glucose, indicating a defect in insulin processing. Afro-Caribbean relatives exhibited disturbed pancreatic B cell processing as well with exaggerated intact and 32, 33 split proinsulin responses to intravenous glucose, but a coexistent defect in insulin sensitivity was also apparent. No abnormality in serum lipoprotein concentrations was identified in any ethnic group, suggesting that the dyslipidaemia of NIDDM is a secondary phenomenon. Insulin insensitivity to lipolysis was present in relatives of all ethnic groups despite normal glucose tolerance, suggesting that this is one of the earliest metabolic abnormalities in the pathogenesis of NIDDM. Insulin processing defects identified in European and Afro-Caribbean subjects may also be of aetiological significance.
... A high proportion of NIDDM patients have pancreatic amyloid deposits made up of islet amyloid polypeptide (IAPP) 339 , also called amylin 340 . IAPP was identified at autopsy in the pancreata of 77% of diabetic Pima Indians but in only 7% of controls 341 , comparable to other ethnic groups. ...
... This could occur if IAPP made peripheral skeletal muscle insulin resistant, while maintaining relative adipose sensitivity to insulin-mediated glucose disposal. Although substantial evidence for such a mechanism exists 339,345 , it has been obtained only at pharmacologic levels of IAPP infusion, calling its relevance into question. IAPP levels do not differ among persons with varying degrees of glucose intolerance 346 , nor do they differ between first-degree relatives of persons with NIDDM and controls, unless the relatives were also glucose intolerant 347 . ...
SUMMARY T here is no single cause of non-insulin-de- pendent diabetes mellitus (NIDDM). More than 60 specific diseases have been associ- ated with the NIDDM phenotype, but these account for
... Chronic hyperglycemia, which induces insulin resistance, was found to reduce the insulin-secreting capacity of pancreatic beta cells by altering metabolic pathways, causing endoplasmic reticulum stress, altering intracellular Ca 2+ levels and altering the activity of K +− ATP channels [43]. Furthermore, diabetic patients were found to have decreased levels of islet amyloid polypeptide (IAPP), which is another pancreatic peptide co-secreted with insulin [44]. This occurs due to the accumulation of IAPP in the pancreas; IAPP then forms insoluble toxic oligomers that deposit in the β-cells, resulting in its dysfunction. ...
Diabetes mellitus (DM) is a chronic illness with an increasing global prevalence. More than 537 million cases of diabetes were reported worldwide in 2021, and the number is steadily increasing. The worldwide number of people suffering from DM is projected to reach 783 million in 2045. In 2021 alone, more than USD 966 billion was spent on the management of DM. Reduced physical activity due to urbanization is believed to be the major cause of the increase in the incidence of the disease, as it is associated with higher rates of obesity. Diabetes poses a risk for chronic complications such as nephropathy, angiopathy, neuropathy and retinopathy. Hence, the successful management of blood glucose is the cornerstone of DM therapy. The effective management of the hyperglycemia associated with type 2 diabetes includes physical exercise, diet and therapeutic interventions (insulin, biguanides, second generation sulfonylureas, glucagon-like peptide 1 agonists, dipeptidyl-peptidase 4 inhibitors, thiazolidinediones, amylin mimetics, meglitinides, α-glucosidase inhibitors, sodium-glucose cotransporter-2 inhibitors and bile acid sequestrants). The optimal and timely treatment of DM improves the quality of life and reduces the severe burden of the disease for patients. Genetic testing, examining the roles of different genes involved in the pathogenesis of DM, may also help to achieve optimal DM management in the future by reducing the incidence of DM and by enhancing the use of individualized treatment regimens.
... Amylin is stored in the insulin-secreting granules of pancreatic β cells and is co-secreted with insulin. Its serum concentration is about 1/10 of that of insulin; in the pancreas of many T2DM patients, the content of amylin increases [103]. Pancreatic exosomes from normal people can reduce the formation of amylin by peptide clearance, but pancreatic exosomes and serum exosomes from T2DM patients have no similar effect, and the ratio of C-peptide and lipid composition are different from normal people [104]. ...
Diabetes mellitus (DM) is a first-line priority among the problems facing medical science and public health in almost all countries of the world. The main problem of DM is the high incidence of damage to the cardiovascular system, which in turn leads to diseases such as myocardial infarction, stroke, gangrene of the lower extremities, blindness and chronic renal failure. As a result, the study of the molecular genetic mechanisms of the pathogenesis of DM is of critical importance for the development of new diagnostic and therapeutic strategies. Molecular genetic aspects of the etiology and pathogenesis of diabetes mellitus are intensively studied in well-known laboratories around the world. One of the strategies in this direction is to study the role of exosomes in the pathogenesis of DM. Exosomes are microscopic extracellular vesicles with a diameter of 30-100 nm, released into the intercellular space by cells of various tissues and organs. The content of exosomes depends on the cell type and includes mRNA, non-coding RNAs, DNA, and so on. Non-coding RNAs, a group of RNAs with limited transcriptional activity, have been discovered to play a significant role in regulating gene expression through epigenetic and posttranscriptional modulation, such as silencing of messenger RNA. One of the problems of usage exosomes in DM is the identification of the cellular origin of exosomes and the standardization of protocols for molecular genetic studies in clinical laboratories. In addition, the question of the target orientation of exosomes and their targeted activity requires additional study. Solving these and other problems will make it possible to use exosomes for the diagnosis and delivery of drugs directly to target cells in DM. This study presents an analysis of literature data on the role of exosomes and ncRNAs in the development and progression of DM, as well as the prospects for the use of exosomes in clinical practice in this disease.
... MFG-E8 protein has therapeutic effects in many diseases but has also some limitations in development. For example, MFG-E8 contains a medin site [36], known to cause Alzheimer's [37], type 2 diabetes [38], and aging [39], and glycosylation sites that make it difficult to synthesize with potential immunogenicity after administration in the body; both of these are present in the C2 region. Thus, through the truncation of the C2 domain in MFG-E8, NP-011 might be free from the above concerns in clinical applications. ...
Milk fat globule-EGF factor 8 (MFG-E8) protein is known as an immunomodulator in various diseases, and we previously demonstrated the anti-fibrotic role of MFG-E8 in liver disease. Here, we present a truncated form of MFG-E8 that provides an advanced therapeutic benefit in treating liver fibrosis. The enhanced therapeutic potential of the modified MFG-E8 was demonstrated in various liver fibrosis animal models, and the efficacy was further confirmed in human hepatic stellate cells and a liver spheroid model. In the subsequent analysis, we found that the modified MFG-E8 more efficiently suppressed transforming growth factor β (TGF-β) signaling than the original form of MFG-E8, and it deactivated the proliferation of hepatic stellate cells in the liver disease environment through interfering with the interactions between integrins (αvβ3 & αvβ5) and TGF-βRI. Furthermore, the protein preferentially delivered in the liver after administration, and the safety profiles of the protein were demonstrated in male and female rat models. Therefore, in conclusion , this modified MFG-E8 provides a promising new therapeutic strategy for treating fibrotic diseases.
... Despite islet amyloid relevance in T2D, and in other diseases, this issue remained poorly investigated for many years, probably because IAPP aggregation does not occur spontaneously in animals commonly used in research, such as rodents (P. Westermark et al., 1992). In contrast, human, nonhuman primate, and cat IAPP are prone to form amyloid (Betsholtz et al., 1989). ...
Islet amyloid polypeptide (IAPP or amylin) is a hormone co-secreted with insulin by pancreatic β-cells and is the major component of islet amyloid. Islet amyloid is found in the pancreas of patients with type 2 diabetes (T2D) and may be involved in β-cell dysfunction and death, observed in this disease. Thus, investigating the aspects related to amyloid formation is relevant to the development of strategies towards β-cell protection. In this sense, IAPP misprocessing, IAPP overproduction, and disturbances in intra-and extracellular environments seem to be decisive for IAPP to form islet amyloid. Islet amyloid toxicity in β-cells may be triggered in intra-and/or extracellular sites by membrane damage, endoplasmic reticulum stress, autophagy disruption, mitochondrial dysfunction, inflammation, and apoptosis. Importantly, different approaches have been suggested to prevent islet amyloid cytotoxicity, from inhibition of IAPP aggregation to attenuation of cell death mechanisms. Such approaches have improved β-cell function and prevented the development of hyperglycemia in animals. Therefore, counteracting islet amyloid may be a promising therapy for T2D treatment. K E Y W O R D S amylin, cell death, diabetes, islet amyloid polypeptide, pancreatic β-cells
... Одни ученые полагают, что в основе данных нарушений лежит резистентность периферических тканей к инсулину [8,26,27], а развитие СД 2-го типа, артериальной гипертензии и ИБС реализуется через гиперинсулинемию и нарушение липидного и углеводного обменов. Другие исследователи [21,29,30] отмечают, что СД 2-го типа развивается только при истощении островкового аппарата поджелудочной железы, возникающем под влиянием наследственной предрасположенности и действия факторов внешней среды. При этом создается ложное впечатление о наличии гиперинсулинемии, так как иммунорадиометрические методы не являются совершенными и дают наряду с инсулином перекрестные реакции с проинсулинами. ...
Investigation of pathogenetic correlation of abdominal adisposity and II-type pancreatic diabetes (PD) has been made with the aim to reveal the importance of carbohydrate metabolism disturbances at above said pathology combination in cardiac abnormalities. 30 white alley rats at the age of 8-12 months have been included into the experimental group. Control group has been formed of 30 animals. Used methods of investigation: simulation of II-type PD in rats with streptozotocin and study of carbohydrate metabolism indices in entire organism as well as contractile function indices and indices of isolated and contracting heart metabolism. As a result it has been revealed that the weight of rats with II-type PD and abdominal adisposity, the level of glucose and glycated haemoglobin in blood, of lactate and pyruvate had been increased surely. The normal level of blood serum C-peptide has confirmed the absence of mass death of β-cells. The hearts taken from diabetic animals have responded to the increase of contraction frequency with the decrease of advanced pressure, i.e. the negative inotropic effect has been observed. Therefore the peripheral insulin resistance plays the leading role in the development of metabolic and functional abnormality complex at II-type PD and abdominal adisposity. Accumulation of lactate, metabolic acidosis, decrease of glucose efficiency and dysfunction of cardiac hystiocyte calcium pump with the development of diastolic myocardium dysfunction contribute to the development of metabolic disturbances.
... However, pancreatic autopsy series from T2D patients show a reduction in b-cell mass [49], with relics of activated UPR apoptotic markers. In addition, human type 2 diabetic islets contain protein aggregates in the form of amyloid [50]. Islet amyloid is composed of a 37-residue amyloidogenic polypeptide called islet amyloid polypeptide (IAPP). ...
Background:
Myriad challenges to the proper folding and structural maturation of secretory pathway client proteins in the endoplasmic reticulum (ER) - a condition referred to as "ER stress" - activate intracellular signaling pathways termed the unfolded protein response (UPR).
Scope of review:
Through executing transcriptional and translational programs the UPR restores homeostasis in those cells experiencing manageable levels of ER stress. But the UPR also actively triggers cell degeneration and apoptosis in those cells that are encountering ER stress levels that exceed irremediable thresholds. Thus, UPR outputs are "double-edged". In pancreatic islet β-cells, numerous genetic mutations affecting the balance between these opposing UPR functions cause diabetes mellitus in both rodents and humans, amply demonstrating the principle that the UPR is critical for the proper functioning and survival of the cell.
Major conclusions:
Specifically, we have found that the UPR master regulator IRE1α kinase/endoribonuclease (RNase) triggers apoptosis, β-cell degeneration, and diabetes, when ER stress reaches critical levels. Based on these mechanistic findings, we find that novel small molecule compounds that inhibit IRE1α during such "terminal" UPR signaling can spare ER stressed β-cells from death, perhaps affording future opportunities to test new drug candidates for disease modification in patients suffering from diabetes.
... These same pathways were also dysregulated in fetal islets in a sheep model of hyperthermia-induced IUGR, pointing to the pathways' importance in the pathogenesis of islet dysfunction in diabetes (14). Interestingly, amyloidosis was another enriched pathway in 10-week-old IUGR islets and humans, indicating that although amyloid deposition does not occur in rodent models of diabetes (93), the underlying mechanism contributing to this defect also occurs in IUGR rats. Although IUGR is one of many factors contributing to type 2 diabetes risk, the overlap of pathways associated with islet dysfunction in IUGR rats and in humans strongly suggests that the diverse etiologies of type 2 diabetes converge mechanistically to disrupt islet function. ...
Intrauterine growth restriction (IUGR) increases the risk of developing Type 2 Diabetes in adulthood. Previous studies employing bilateral uterine artery ligation in a rat model of IUGR have revealed age-associated decline in glucose homeostasis and islet function. To elucidate novel mechanisms contributing to IUGR pathogenesis, the islet transcriptome was sequenced at 2 weeks of age, when in vivo glucose tolerance is mildly impaired, and at 10 weeks of age, when rats are hyperglycemic and have reduced β-cell mass. RNA sequencing and functional annotation with Ingenuity Pathway Analysis reveal novel temporal changes in IUGR islets. For instance, gene expression involving amino acid metabolism was significantly reduced primarily at 2 weeks of age but ion channel expression, specifically those involved in cell-volume regulation, was more disrupted in adult IUGR islets. Additionally, we observed alterations in the microenvironment of IUGR islets with ECM genes being significantly increased at 2 weeks of age and significantly decreased at 10 weeks. Specifically, hyaluronan synthase 2 expression and hyaluronan staining was increased in IUGR islets at 2 weeks of age (p<0.05). Mesenchymal stromal cell-derived factors that have been shown to preserve islet allograft function, such as Anxa1, Cxcl12, and others, were also increased at 2 weeks and decreased in adult islets. Finally, comparisons of differentially expressed genes to those of type 2 diabetic human islets support a role for these pathways in human diabetic patients. Taken together, these data point to new mechanisms in the pathogenesis of IUGR-mediated islet dysfunction in type 2 diabetes.
... As an expectation from a polypeptide hormone, IAPP is preserved along evolution, and the molecule has been determined in mammals, birds, and teleostanfishes [50]. Particularly, the NH2-and COOH-terminal parts of IAPP are conserved (Figure 4). ...
The Human Diabetes Proteome Project (HDPP) mentioned more than 1000 diabetes associated proteins. 400 diabetes associated proteins whose structure is not analyzed yet are selected from the database. Each proteins structure is analyzed via prediction tools in order to reveal structural similarity with IAPP (Islet Amyloid Polypeptide) whose role is well characterized in diabetes. Through similarity analysis between proteins and in region of disulfide bridge formation, we aimed to find similar possible misfolding patterns in other diabetes associated proteins. Result indicates that Calcitonin Gene Related Peptide I is the only proteins who shows high structural and conformational similarity with IAPP. We believe that one of the possible enrolments of the protein Calcitonin Gene Related Peptide 1 to the diabetes can be similar conformational changes due to disulfide bridge formation break. Finally we propose that the accumulation of misfolded Calcitonin Gene Related Peptide 1 is similar to other protein based conformational diseases. Further structural analyses needs to be performed to confirm these results.
... ArchCandy is able to correctly predict this effect. It has also been established that rat, hamster and degu amylins do not form fibrils (Westermark et al. 1992). ArchCandy scores for these peptides are below the 0.6 threshold being in agreement with the experiment. ...
A broad range of human diseases are linked to the formation of insoluble, fibrous, protein aggregates called amyloid fibrils. They include, but are not limited to, type II diabetes, rheumatoid arthritis, and perhaps most importantly, debilitating neurodegenerative diseases such as Alzheimer's disease, Parkinson's disease, and Huntington's disease. There currently exists no cure, and no means of early diagnosis for any of these diseases. Numerous studies have shown that the ability to form amyloid fibrils is an inherent property of the polypeptide chain. This has lead to the development of a number of computational approaches to predict amyloidogenicity by amino acid sequences. Although these methods perform well against short peptides (about 6 residues), they generate an unsatisfactory high number of false positives when tested against longer sequences of the disease-related peptides and proteins. The main objective of this thesis was to develop an improved bioinformatics based approach to predict amyloidogenic regions from protein sequence.Recently new experimental techniques have shed light on the structure of amyloids showing that the core element of a majority of disease-related amyloid fibrils is a columnar structure (β--arcade) produced by stacking of β-strand-loop-β-strand motifs called "β-arches". Using this structural insight, we have created a bioinformatics based approach to predict amyloidogenic regions from protein sequence information. Data from the analysis of the known and modeled β-arcade structures was incorporated into a rule based algorithm implemented in the Java programming language to create the ArchCandy program. Testing it against a set of protein and peptide sequences known to be related to diseases has shown that it correctly predicts most of these sequences and a number of mutated sequences related to the familial diseases. In addition to the prediction of regions with high amyloidogenic potential, a structural arrangement of the amyloid fibril is also suggested for each prediction. As whole genome sequencing becomes cheaper, our method provides opportunity to create individual risk profiles for the neurodegenerative, age-related and other diseases ushering in an era of personalized medicine.
... However, pancreatic autopsy series from type 2 diabetic patients clearly show a reduction in b-cell mass (Yoon et al. 2003) concomitant with activation in UPR apoptotic markers. In addition, human type 2 diabetic islets contain protein aggregates in the form of amyloid (Westermark et al. 1992). Islet amyloid is composed of a 37-residue amyloidogenic polypeptide called islet amyloid polypeptide (IAPP). ...
Overwhelming of protein folding in the endoplasmic reticulum (ER)-referred to as "ER stress"-activates a set of intracellular signaling pathways termed the unfolded protein response (UPR). Beneficial outputs of the UPR promote adaptation in cells experiencing manageably low levels of ER stress. However, if ER stress reaches critically high levels, the UPR uses destructive outputs to trigger programmed cell death. Genetic mutations in various UPR components cause inherited syndromes of diabetes mellitus in both rodents and humans, implicating the UPR in the proper functioning and survival of pancreatic islet β cells. Markers of chronically elevated ER stress, terminal UPR signaling, and apoptosis are evident in β cells in these rare disorders; these markers are similarly present in islets of human patients with common forms of diabetes. These findings promise to enhance our molecular understanding of human diabetes significantly and may lead to new and effective therapies.
Type 2 diabetes (T2D) is a chronic metabolic disease characterized by insulin resistance and a progressive loss of pancreatic islet β-cell mass, which leads to insufficient secretion of insulin and hyperglycemia. Emerging evidence suggests that toxic oligomers and fibrils of human islet amyloid polypeptide (hIAPP) contribute to the death of β-cells and lead to T2D pathogenesis. These observations have opened new avenues for the development of islet amyloid therapies for the treatment of T2D. The peptide-based inhibitors are of great value as therapeutic agents against hIAPP aggregation in T2D owing to their biocompatibility, feasibility of synthesis and modification, high specificity, low toxicity, proteolytic stability (modified peptides), and weak immunogenicity as well as the large size of involved interfaces during self-aggregation of hIAPP. An understanding of what has been done and achieved will provide key insights into T2D pathology and assist in the discovery of more potent drug candidates for the treatment of T2D. In this article, we review various peptide-based inhibitors of hIAPP aggregation, including those derived from the hIAPP sequence and those not based on the sequence, consisting of both natural as well as unnatural amino acids and their derivatives. The present review will be beneficial in advancing the field of peptide medicine for the treatment of T2D.
Exosome is a kind of nanoscale-size extracellular vesicles secreted by the means of cell active stimulation with outer membrane structure of vacuoles corpuscle. It can carry and transfer a lot of biological molecules, such as DNA fragments, circular RNA (circRNA), messenger RNA (mRNA), microRNA (miRNA), functional proteins, transcription factors, etc., so as to achieve the goal of information transmission between cells. The relationship between exosomes and diabetes has received extensive attention in recent years. The exosomes play an important role in insulin sensitivity, glucose homeostasis and vascular endothelial function. This paper reviews the role of exosomes in the occurrence and development of diabetes and its complications, and discusses the role and prospect of exosomes as a target for diabetes treatment and its role in the diagnosis and treatment of diabetes.
The histopathological hallmark of type 2 diabetes is islet amyloid implicated in the developing treatment options. The major component of human islet amyloid is 37 amino acid peptide known as amylin or islet amyloid polypeptide (IAPP). Amylin is an important hormone that is co-localized, copackaged, and co-secreted with insulin from islet β cells. Physiologically, amylin regulates glucose homeostasis by inhibiting insulin and glucagon secretion. Furthermore, amylin modulates satiety and inhibits gastric emptying via the central nervous system. Normally, human IAPP is soluble and natively unfolded in its monomeric state. Pathologically, human IAPP has a propensity to form oligomers and aggregate. The oligomers show misfolded α-helix conformation and can further convert themselves to β-sheet-rich fibrils as amyloid deposits. The pathological findings and physiological functions of amylin have led to the introduction of pramlintide, an amylin analog, for the treatment of diabetes. The history of amylin’s discovery is a representative example of how a pathological finding can translate into physiological exploration and lead to pharmacological intervention. Understanding the importance of transitioning from pathology to physiology and pharmacology can provide novel insight into diabetes mellitus and Alzheimer's disease.
Islet amyloid polypeptide (IAPP), also known by the name amylin, and adrenomedullin (ADM) are related neurohormonal peptides, which belong to the calcitonin family (Fig. 1). Structurally, IAPP is more closely related to the other peptides of the calcitonin family than is ADM. IAPP shows approx 50% homology to the calcitonin gene-related peptides (a-and 13-CGRP) and, like the CGRPs, it consists of 37 amino acids, is C-terminally amidated, and has a disulfide bridge between amino acids 2 and 7 (1). In contrast, ADM is a longer peptide, consisting of 52 or 50 amino acids in humans and rats, respectively, and its structural resemblances to the other peptides of the calcitonin family are confined to the C-terminal part of the peptide. Here, ADM displays approx 25% homology to CGRP/IAPP, the aforementioned disulfide bridge in the corresponding position, and the C-terminal amidation also being present (2).
Determining the cause of human calcitonin (hCT) aggregation could be of help in the effort to utilize hCT for treatment of hypercalcemia. Here we report that a dimer model of hCT13-32 aggregated to a greater degree than native hCT under aqueous 2,2,2-trifluoroethanol conditions. Analyses using circular dichroism spectroscopy, thioflavine-T binding assays and atomic force microscopy suggest that the α-helical portion of hCT is important for initiation of the aggregation process, which yields long fibrils. Dimerization, which stabilizes the β-sheet structure of hCT, enhances aggregation potency. Dimerization of hCT stabilizes the α-helix under aqueous TFE conditions, leading to the long fibril formation. Up to now, there have been no reports of using a dimer model to investigate the properties of hCT aggregation. Our findings could potentially serve as the basis for development of novel hCT derivatives that could be utilized for treatment of hypercalcemia, as well as for development of novel therapeutics for other ailments caused by amyloid peptides. Copyright © 2016 European Peptide Society and John Wiley & Sons, Ltd.
Carcinoma of the exocrine pancreas is today the fifth leading cause of cancer death in Western society, with an age-adjusted mortality rate of about 7–9/100 000 in Europe and the USA (57,66). The outcome of the disease is still grim, and has just marginally improved compared with the early part of this century (78). In fact, pancreatic cancer has one of the lowest survival rates of all cancer sites (47), with a 5-year survival of less than 3% (57,78).
Amyloid deposits occur in pancreatic islets in non-insulin-dependent diabetes mellitus (NIDDM) and insulinomas.1–3 Islet amyloid may contribute to the progressive worsening of B-cell function that is observed in NIDDM,4 since its presence is associated with decreased B-cell function in monkeys5 and amyloid was recently demonstrated to cause death of pancreatic islet cells in vitro.6 While it is known that the major constituent of islet amyloid is a 37 amino acid peptide termedislet amyloid polypeptide (IAPP or amylin7,8), it is not known why IAPP forms amyloid in NIDDM. The inherent amyloidogenicity of the peptide is thought to reside in the midsection of the molecule (amino acids 20–29), which is predicted to form beta-pleated sheets and does so in vitro.9 Several species, including primates and cats, produce amyloidogenic forms of IAPP and are prone to islet amyloid development in NIDDM-like syndromes. In species in which non-amyloidogenic IAPP is produced, such as rats and mice, islet amyloid deposits are not observed. However, it appears that production of amyloidogenic IAPP is in itself insufficient for islet amyloid formation to occur, since dog IAPP contains the necessary amyloidogenic sequence, yet amyloid deposits have not been observed in hyperglycemic dogs.10 This finding suggests that some fundamental alteration in B-cell function, perhaps one common to NIDDM and insulinomas,11 must be present for IAPP to deposit as islet amyloid. Alternatively, it has been suggested that overproduction of amyloidogenic IAPP may lead to islet amyloid formation.12
The identification of the messenger phenotype of neuroendocrine cells is crucial for the understanding of neuroendocrine mechanisms. Neuroendocrine cells generally express several neurohormonal peptide messengers—sometimes together with non-peptide messengers—and this expression may be subject to alterations during ontogeny and under pathological conditions. In addition, the level of messenger expression is regulated in response to physiological stimuli. At present, several techniques can be used to assess messenger expression in neuroendocrine cells. Immunocytochemistry, using antibodies directed at these messengers and applied as single, double or triple immunostaining, reveals the localization and co-localization of neurohormonal peptides. In situ hybridization, using probes designed to hybridize with a target mRNA in tissue sections, demonstrates the cellular localization of peptide mRNA; in situ hybridization can be combined with immunocytochemistry and, thus, simultaneously demonstrate the site of expression of both mRNA and peptide. Furthermore, in situ hybridization can, by the aid of computerized image analysis, be used to quantitate levels of mRNA in tissue sections and thereby monitor alterations in gene expression under different conditions. Collectively, these techniques have greatly expanded the present-day knowledge of the neuroendocrine system. In this review, we focus on the recently discovered islet hormone candidate—islet amyloid polypeptide (IAPP or amylin)—to illustrate the use and relevance of these techniques. Protocols for in situ hybridization are given and discussed from a practical standpoint. IAPP is structurally related to calcitonin gene-related peptide (CGRP) and adrenomedullin and is predominantly co-expressed with insulin in pancreatic islets; in some species, such as rat, IAPP is also expressed in islet somatostatin cells. Moreover, IAPP is expressed in gastrointestinal neuroendocrine cells, most of which co-express somatostatin, and in a population of CGRP-containing sensory neurons. Under diabetes-like experimental conditions induced by dexamethasone or streptozotocin, the islet expression of IAPP and insulin dissociate, in that IAPP is over-expressed relative to insulin. The implications of the dissociated expression of IAPP and insulin remain unclear but may be relevant to the pathogenesis and course of diabetes, due to the metabolic and paracrine effects of IAPP-restraining insulin action and release. The role of IAPP in the gastrointestinal tract and in sensory neurons remains to be clarified.
Non-insulin-dependent diabetes mellitus (NIDDM) is a major cause of cardiovascular mortality and morbidity and recent data indicate that the incidence of retinopathy and nephropathy in NIDDM is similar to that in insulin-dependent diabetes mellitus (IDDM). Furthermore, the incidence of neuropathy is very high in NIDDM and this, along with vascular disease, is a major etiologic factor in amputations. Because of these factors as well as epidemiologic data indicating that impaired glucose tolerance is a risk factor for cardiovascular disease, prevention of impaired glucose tolerance (IGT) and prevention of deterioration to NIDDM are important goals for new approaches to NIDDM.
To determine whether chronic overproduction of islet amyloid polypeptide alters beta-cell function, we studied a line of transgenic mice which overexpress islet amyloid polypeptide in their beta-cells. At 3 months of age, these transgenic mice had greater pancreatic content of both islet amyloid polypeptide and insulin. Further, basal and glucose-stimulated secretion of both islet amyloid polypeptide and insulin were also elevated in the perfused pancreas of the transgenic animals. These findings demonstrate that chronic overproduction and secretion of islet amyloid polypeptide are associated with increased insulin storage and enhanced secretion of insulin in vitro. This increase in insulin storage and secretion may be due to a direct effect of islet amyloid polypeptide on the beta-cell or a beta-cell adaptation to islet amyloid polypeptide-induced insulin resistance.-
Non-insulin-dependent diabetes mellitus (NIDDM), also called type 2 diabetes mellitus, is a common metabolic disorder that afflicts 2%–5% of the adult population of most Western countries, with, however, wide international variation (King et al. 1993). Furthermore, NIDDM is often undiagnosed even in the Western countries (Hortulanus-Beck et al. 1990), and numerous data indicate that undiagnosed NIDDM is not a benign condition (Harris 1993). Certainly, NIDDM is a leading cause of disability and death in developed and developing nations (Songer 1992).
The requirements for amyloidogenesis, as it is currently understood, include an adequate amyloid precursor pool, a nidus for fibrillogenesis, interactions with a set of common components (most of which are involved in basement membrane structure) and amyloid turnover. These factors serve as the basis for therapeutic attack. General strategies focusing on each of these factors are presented with examples from the experimental and clinical literature. These include reducing the amyloid precursor protein pool in familial amyloid polyneuropathy by liver transplantation, inhibiting nidus formation in familial Mediterranean fever by the use of colchicine, inhibiting amyloid precursor protein/heparan sulphate interaction in experimental inflammation-associated amyloidosis by the use of novel small molecule anionic sulphates and sulphonates, and the use of new analogues of doxorubicin in light chain amyloidosis to accelerate amyloid removal.
The potential significance of local and systemic amyloid deposits is discussed in the light of new information on the genetics of Alzheimer’s disease, observations made in patients receiving long term dialysis for renal failure, and the potential involvement of amyloid deposits in the pathogenesis of non—insulin-dependent diabetes mellitus.
Neuropeptide Y (NPY) occurs in adrenergic as well as in non-adrenergic nerves innervating the islets of Langerhans and inhibits
glucose-stimulated insulin secretion. Recently we demonstrated that NPY is expressed within islet beta cells of the rat pancreas
following treatment with dexamethasone in vivo. In this study we examined the cellular expression of NPY following dexamethasone treatment of the insulin-producing cell
line RINm5F, which under control conditions does not express or release NPY. The cells were cultured with or without dexamethasone
(100 nm) for 5 days. Over the 5-day culture period, dexamethasone time dependently induced an increased release of NPY with a concomitant
decrease in the release of insulin. Northern blot andin situ hybridization revealed a corresponding time-dependent increase in the amount of NPY transcripts and in the number of cells
labeled for NPY mRNA, whereas immunocytochemistry for NPY revealed only a few immunoreactive cells, indicating a rapid release
of the formed peptide. Following 5 days of culture with dexamethasone, acute stimulation withd-glyceraldehyde (10 mm) or KCl (20 mm) Ca2+ dependently stimulated the release of insulin. In contrast neither stimulation withd-glyceraldehyde or KCl nor removal of extracellular Ca2+ affected the release of NPY. Furthermore thed-glyceraldehyde- and KCl-induced increase in cytosolic Ca2+, evident in control RINm5F cells, was impaired after dexamethasone treatment. We conclude that RINm5F cells show steroid-sensitive
plasticity and express NPY after dexamethasone treatment concomitantly with a decreased insulin secretion and impaired increase
in cytosolic Ca2+ upon depolarization with KCl or stimulation with d-glyceraldehyde. We also conclude that NPY and insulin secretion are regulated differently and suggest that the inability
of the removal of extracellular Ca2+ to inhibit NPY secretion and the failure of d-glyceraldehyde and KCl to stimulate NPY secretion reflect a constitutive release of this peptide from the cells in contrast
to the regulated release of insulin.
Amyloidosis is the generic term for a heterogeneous group of disorders characterised by the common finding of amyloid deposition. The various acquired and hereditary syndromes are classified according to the identity of the respective amyloid fibril sub-unit protein. Systemic amyloidosis and some local forms are progressive diseases that are frequently fatal. The diagnosis of systemic amyloidosis is only occasionally suspected on clinical grounds alone, and is more often considered when an associated disorder such as a chronic inflammatory disease or monoclonal gammopathy is present. No blood test is diagnostic of amyloidosis but routine haematological and biochemical investigations have important roles in defining the underlying metabolic disturbance and evaluating function of affected organs. The diagnosis can only be confirmed by demonstrating the presence of tissue amyloid deposits. Traditionally this required histology but the recent introduction of labelled serum amyloid P component scintigraphy is a specific alternative that provides a quantitative macroscopic whole body survey of amyloid deposits.No treatment specifically causes the resolution of amyloid but therapy which reduces the supply of amyloid fibril precursor proteins can improve survival and preserve organ function. Major regression of amyloid occurs in at least a proportion of such cases suggesting that clinical improvement reflects mobilisation of amyloid.
Insulin is the most important anabolic hormone and of most importance for the acute regulation of carbohydrate metabolism. It is therefore expected that insulin secretion from the β-cells be carefully regulated by a variety of factors. The main regulator of insulin secretion is glucose. The relationship between circulating glucose and insulin secretion is sigmoidal. When glucose levels subsequently decline, the stimulus for insulin secretion is reduced and therefore circulating insulin returns to baseline. Although glucose is the main regulator of insulin secretion, other regulators exist as well, and these factors may be more important than glucose under certain conditions. The nonglucose factors that modulate glucose-stimulated insulin secretion in a potentiating or inhibiting direction are of endocrine, neurocrine, paracine, or autocrinenature. The anatomical basis for the multiregulated integrated influence on insulin secretion by these factors is the microorganization of the pancreatic islets. The messages modulating insulin secretion are integrated at the level of the cells, enabling an optimal discharge of insulin from each individual cell. The modulating factors interact with signaling pathways in the β-cells that are of importance for the exocytosis of the secretory granules containing insulin.
Two major mechanisms, peripheral insulin resistance and impaired insulin secretion participate concomitantly but to a variable extent to the pathogenesis of non-insulin-dependent diabetes, whose heterogeneity, suspected/or a long time, is now confirmed by the recent discoveries of the molecular biology. Mutations of several genes governing key-steps of the recognition of the glucose signal, insulin secretion or its peripheral effect have been found in some particular cases, but presently not at a large scale among non insulin-dependent diabetic patients. The tendency to worsening of the metabolic disturbances with the time, even under adequate therapy, can be explained by the vicious circle of glucose toxicity, but other mechanisms like amylin, responsible of the deposition of amyloid in the islets, may play a role. So, despite the acquisition of many new knowledges, the pathogenesis of non-insulin-dependent diabetes keeps nowadays a part of its mystery.
Amyloid deposits are common in certain polypeptide-producing tissues and are sometimes a characteristic feature of diseases affecting these tissues. Recent years have given us increasing knowledge about the nature of this type of amyloid and its pathogenesis.
A hyaline stroma, different in appearance from collagen, was observed in some endocrine tissues and tumors at an early date'2. Fairly soon, the amyloid nature of this stroma was discussed and designations like “atypical amyloid” or “paraamyloid” 3 were used. For a long time, the amyloid was regarded as a non-specific product of degeneration but when the nature of some systemic amyloids started to become elucidated in 1971, there was a growing suspicion that the amyloid in endocrine tissues reflected a specific pathologic event. This suspicion was verified in 1976 with the clarification of the hormonal nature of the amyloid (calcitonin derived) in a medullary carcinoma of the thyroid. Since then, three more polypeptide hormones have been identified as major amyloid fibril proteins, (islet amyloid polypeptide (1APP); atrial natriuretic factor derived amyloid (ANF); insulin derived amyloid).
The amyloidogemc peptides, amyloid-� (A�) and human amylin, are the major constituents of amyloid deposits found in patients with the chrome degenerative disorders Alzheimer's disease (AD) and type 2 diabetes, respectively. Recent studies have shown that a variety of inflammatory proteins such as cytokines are associated with the amyloid deposits of AD brain tissues. Therefore, in the present study, we sought to determine whether Aand/or human amylin could modulate the various inflammatory activities of eosinophils. We observed that human amylin but not Afpeptides inhibited the in vitro interleukin-5 (IL- 5)-mediated survival of cord blood-derived eosino- phils (CBEs) in a concentration-dependent manner. By contrast, rat amylin, a nonamyloidogeme peptide that is highly homologous to human amylin, failed to affect the IL-5-mediated survival of CBEs. Similar inhibitory effects of human amylin were observed for peripheral blood eosinophils. Human amylin also en- hanced the release of the cytokine granulocyte- macrophage colony-stimulating factor by CBEs that were stimulated with the calcium ionophore A23 187 but was incapable of directly stimulating CBEs to release cytokines. In addition, the A23 187-induced release of the inflammatory lipid mediator leuk- otriene C4 by CBEs was augmented by human amylin. These results suggest that the amyloidogenic peptide human amylin is capable of amplifying the various inflammatory activities of eosinophils. J. Leukoc. Biol. 58: 526-532; 1995.
Diabetes mellitus is a metabolic disorder of glucose homeostasis and associated with long-term vascular complications leading to morbidity and mortality. It is the fastest growing non-communicable disease throughout the world. The pathophysiology of diabetes is complex and multifactorial. Understanding pathological mechanisms of disease can help clinicians to identify and treat the factors involved effectively, and design preventive strategies so as to halt the pandemic of this deadly disorder.
Diabetes is considered to be a genetically and environmentally based chronic metabolic and vascular syndrome caused by a partial or total insulin deficiency with alteration in the metabolism of lipids, carbohydrates and proteins culminating with different manifestations in different organisms. In humans hyperglycemia is the main consequence of defects in the secretion and/or action of insulin, and its deregulation can produce secondary lesions in various organs, especially kidneys, eyes, nerves, blood vessels and immune systems.
Periodontal disease is an entity of localized infection that involves tooth-supporting tissues. The first clinical manifestation of periodontal disease is the appearance of periodontal pockets, which offer a favorable niche for bacterial colonization. The etiology of periodontal disease is multifactorial, being caused by interactions between multiple micro-organisms (necessary but not sufficient primary etiologic factors), a host with some degree of susceptibility and environmental factors. According to current scientific evidence, there is a symbiotic relationship between diabetes and periodontitis, such that diabetes is associated with an increased incidence and progression of periodontitis, and periodontal infection is associated with poor glycaemic control in diabetes due to poor immune systems. Hence, for a good periodontal control it is necessary to treat both periodontal disease and glycaemic control.
A case of severe cardiac involvement is reported in a patient affected with familial amyloidotic polyneuropathy due to the Portuguese type I variant (Val→Met30) of the transthyretin (prealbumin) molecule. Echocardiographic and hemodynamic studies suggested the presence of a progressive infiltrative cardiomyopathy that was later confirmed by endomyocardial biopsy. Amyloid deposits were found in both intra- and extra-myofiber location and thought to be related to primary involvement of the heart. Norepinephrine content of myocardial bioptic specimens was about threefold lower than normal, indicating that autonomic denervation may contribute to the maintenance and progression of cardiomyopathy. A sample obtained from the sural nerve showed a loss of myelinated fibers along with accumulation of amyloid masses in the endoneurial space. This histopathologic pattern correlated with a sharp decrease in the activity of the enzyme subserving electrochemical conduction through the axonal membrane, Na+, K+-ATPase.
Neuropeptide Y (NPY) occurs in adrenergic as well as in non-adrenergic nerves innervating the islets of Langerhans and inhibits
glucose-stimulated insulin secretion. Recently we demonstrated that NPY is expressed within islet beta cells of the rat pancreas
following treatment with dexamethasone in vivo. In this study we examined the cellular expression of NPY following dexamethasone treatment of the insulin-producing cell
line RINm5F, which under control conditions does not express or release NPY. The cells were cultured with or without dexamethasone
(100 nm) for 5 days. Over the 5-day culture period, dexamethasone time dependently induced an increased release of NPY with a concomitant
decrease in the release of insulin. Northern blot andin situ hybridization revealed a corresponding time-dependent increase in the amount of NPY transcripts and in the number of cells
labeled for NPY mRNA, whereas immunocytochemistry for NPY revealed only a few immunoreactive cells, indicating a rapid release
of the formed peptide. Following 5 days of culture with dexamethasone, acute stimulation withd-glyceraldehyde (10 mm) or KCl (20 mm) Ca2+ dependently stimulated the release of insulin. In contrast neither stimulation withd-glyceraldehyde or KCl nor removal of extracellular Ca2+ affected the release of NPY. Furthermore thed-glyceraldehyde- and KCl-induced increase in cytosolic Ca2+, evident in control RINm5F cells, was impaired after dexamethasone treatment. We conclude that RINm5F cells show steroid-sensitive
plasticity and express NPY after dexamethasone treatment concomitantly with a decreased insulin secretion and impaired increase
in cytosolic Ca2+ upon depolarization with KCl or stimulation with d-glyceraldehyde. We also conclude that NPY and insulin secretion are regulated differently and suggest that the inability
of the removal of extracellular Ca2+ to inhibit NPY secretion and the failure of d-glyceraldehyde and KCl to stimulate NPY secretion reflect a constitutive release of this peptide from the cells in contrast
to the regulated release of insulin.
The sections in this article are:
The age-associated (or senile) amyloidoses encompass a heterogeneous group of systemic or localized forms of amyloidosis. In this paper we present an overview of three age-associated amyloid forms derived from transthyretin, apolipoprotein AI and islet amyloid polypeptide. Mutations in the respective genes give rise to transthyretin and apolipoprotein AI forms of familial amyloidosis while senile forms of amyloid are associated with the wild-type proteins. Different mechanisms are probably of importance in the fibrillogenesis associated with these three amyloid types. It is also possible that different amyloidogenic pathways exist for a single amyloidogenic protein. Thus, limited proteolysis may be necessary in the fibrillogenesis in senile transthyretin amyloidosis but not in most familial transthyretin amyloidoses. Other factors in the pathogenesis of amyloidosis such as local concentration, nidus formation and glycation are also discussed.
Primary sensory neurons serve a dual role as afferent neurons, conveying sensory information from the periphery to the central
nervous system, and as efferent effectors mediating, e.g., neurogenic inflammation. Neuropeptides are crucial for both these
mechanisms in primary sensory neurons. In afferent functions, they act as messengers and modulators in addition to a principal
transmitter; by release from peripheral terminals, they induce an efferent response, “neurogenic inflammation,” which comprises
vasodilatation, plasma extravasation, and recruitment of immune cells. In this article, we introduce two novel members of
the sensory neuropeptide family: pituitary adenylate cyclase-activating polypeptide (PACAP) and islet amyloid polypeptide
(IAPP). Whereas PACAP, a vasoactive intestinal polypeptide-resembling peptide, predominantly occurs in neuronal elements,
IAPP, which is structurally related to calcitonin gene-related peptide, is most widely known as a pancreatic β-cell peptide;
as such, it has been recognized as a constituent of amyloid deposits in type 2 diabetes. In primary sensory neurons, under
normal conditions, both peptides are predominantly expressed in small-sized nerve cell bodies, suggesting a role in nociception.
On axotomy, the expression of PACAP is rapidly induced, whereas that of IAPP is reduced. Such a regulation of PACAP suggests
that it serves a protective role during nerve injury, but that of IAPP may indicate that it is an excitatory messenger under
normal conditions. In contrast, in localized adjuvant-induced inflammation, expression of both peptides is rapidly induced.
For IAPP, studies in IAPP-deficient mice support the notion that IAPP is a pronociceptive peptide, because these mutant mice
display a reduced nociceptive response when challenged with formalin.
Islet amyloid polypeptide (IAPP or amylin) is predominantly expressed by insulin cells, but occurs also in primary sensory neurons in the rat. Here, using mice targeted for a null mutation in the IAPP gene, we establish murine expression of IAPP in sensory neurons; its distribution in a population of calcitonin gene-related peptide-containing neurons in the spinal cord and dorsal root ganglion is similar to that previously described in the rat. We also report the IAPP mutant mice display a reduced pain response in the paw formalin test. Adjuvant-induced joint inflammation was not altered in IAPP mutants, arguing against a peripheral inflammatory abnormality. These findings lead us to suggest that IAPP has a pro-nociceptive function in primary sensory neurons.
The O-acyl isopeptide (1) of islet amyloid polypeptide (IAPP), which contains an ester moiety at both Ala8-Thr9 and Ser19-Ser20, was prepared by sequential segment condensation based on the O-acyl isopeptide method. Isopeptide 1 possessed nonaggregative properties, retaining its random coil structure under the acidic conditions; this suggests that the insertion of the O-acyl isopeptide structures in IAPP suppressed aggregation of the molecule. As a result of the rapid O-to-N acyl shift of 1 under neutral pH, in situ-formed IAPP adopted a random-coil structure at the start of the experiment, and then underwent conformational change to α-helix/β-sheet mixed structures as well as aggregation. The click peptide strategy with the nonaggregative precursor molecule 1 could be a useful experimental tool to identify the functions of IAPP, by overcoming the handling difficulties that arise from IAPP's intense and uncontrollable self-assembling nature.
Aortic medial amyloid is a form of localized amyloid that occurs in virtually all individuals older than 60 years. The importance and impact of the amyloid deposits are unknown. In this study we have purified a 5.5-kDa aortic medial amyloid component, by size-exclusion chromatography and RP-HPLC, from three individuals, and we have shown by amino acid sequence analysis that the amyloid is derived from an integral proteolytic fragment of lactadherin. Lactadherin is a 364-aa glycoprotein, previously known to be expressed by mammary epithelial cells as a cell surface protein and secreted as part of the milk fat globule membrane. The multidomain protein has a C-terminal domain showing homology to blood coagulation factors V and VIII. We found that the main constituent of aortic medial amyloid is a 50-aa-long peptide, here called medin, that is positioned within the coagulation factor-like domain of lactadherin. Our result is supported by the specific labeling of aortic medial amyloid in light and electron microscopy with two rabbit antisera raised against two synthetic peptides corresponding to different parts of medin. By using in situ hybridization we have shown that lactadherin is expressed by aortic medial smooth muscle cells. Furthermore, one of the synthetic peptides forms amyloid-like fibrils in vitro. Lactadherin was not previously known to be an amyloid precursor protein or to be expressed in aortic tissue. The structure of lactadherin may implicate an important regulatory function in the aorta.
Type 2 diabetes mellitus is a multifactorial metabolic disorder. It is characterized by chronic hyperglycemia, insulin resistance, and a relative insulin secretion defect. The prevalence of type 2 diabetes mellitus has risen worldwide in large part because of an increase in obesity and sedentary lifestyles. The underlying pathophysiology and complications of type 2 diabetes mellitus are still being elucidated. Recent advances in diabetes research have helped us to gain a better understanding about insulin resistance and insulin secretion defects. The evolving understanding about the influence of the incretin effect, insulin signal transduction, adipose tissue, intra-islet cell communication, and inflammation is changing the way in which we view type 2 diabetes mellitus. This new understanding will eventually provide us with new treatment approaches to help patients who have type 2 diabetes mellitus. This article gives a review of the current and emerging concepts of the pathophysiology of type 2 diabetes mellitus.
Amyloid fibrils created by misfolding and aggregation of proteins are a major pathological feature in a variety of degenerative diseases. Therapeutic approaches including amyloid vaccines and anti-aggregation compounds in models of amyloidosis point to an important role for amyloid in disease pathogenesis. Amyloid deposits derived from the beta-cell peptide islet amyloid polypeptide (IAPP or amylin) are a characteristic of type 2 diabetes and may contribute to loss of beta-cells in this disease.
We developed a cellular model of rapid amyloid deposition using cultured human islets and observed a correlation between fibril accumulation and beta-cell death. A series of overlapping peptides derived from IAPP was generated.
A potent inhibitor (ANFLVH) of human IAPP aggregation was identified. This inhibitory peptide prevented IAPP fibril formation in vitro and in human islet cultures leading to a striking increase in islet cell viability.
These findings indicate an important contribution of IAPP aggregation to beta-cell death in situ and point to therapeutic applications for inhibitors of IAPP aggregation in enhancing beta-cell survival.
Anti-amyloid compounds could potentially reduce the loss of beta-cell mass in type 2 diabetes and maintain healthy human islet cultures for beta-cell replacement therapies.
BACE2 is a protease homologous to BACE1 protein, an enzyme involved in the amyloid formation of Alzheimer disease (AD). However, despite the high homology between these two proteins, the biological role of BACE2 is still controversial, even though a few studies have suggested a pathogenetic role in sporadic inclusion-body myositis and hereditary inclusion-body myopathy, which are characterized by vacuolization of muscular fibers with intracellular deposits of proteins similar to those found in the brain of AD patients. Although BACE2 has also been identified in the pancreas, its function remains unknown and its specific localization in different pancreatic cell types has not been definitively ascertained. For these reasons, the authors have investigated the cellular and subcellular localization of BACE2 in normal rodent pancreases. BACE2 immunoreactivity was found in secretory granules of beta cells, co-stored with insulin and IAPP, while it was lacking in the other endocrine and exocrine cell types. The presence of BACE2 in secretory granules of beta cells suggests that it may play a role in diabetes-associated amyloidogenesis.
A stromal hyaline change has been known for a long time to occur in some hormone producing tissues. Most commonly this has been seen in the islets of Langerhans and in medullary carcinoma of the thyroid. The very localized nature of the hyaline change together with some difficulties in staining contributed to the delay in accepting this hyaline change as a form of amyloid. Contemporary analyses and definitions have made it clear, however, that these alterations fullfil the criteria for amyloid. It was not until 1976 that the molecular nature of one of the “endocrine amyloids”, that in the medullary carcinoma of the thyroid, was clarified, showing the polypeptide hormone derivation of the fibrils (1). Since then, three other polypeptide hormone-derived amyloid forms have been analyzed by amino acid sequence analysis. This short overview deals with these four amyloid forms (for more detailed reviews, see 2,3). After this brief review of the four forms, I will discuss some possible mechanisms that might be of importance in the pathogenesis of these localized form of endocrine amyloid deposition.
Hothersall J.S., Muirhead R.P., Wimalawansa S.J.
The two peptides calcitonin gene related peptide (CGRP) and amylin at 1 uM levels in an isolated rat diaphragm preparation inhibited insulin stimulated 2-deoxy[3H]glucose transport by 30 and 60 percent, respectively; this was the case at maximal (1 uM) and sub-maximal (0.5 mU) insulin concentrations. No effect was measured on the basal level of 2-deoxy[3H]glucose transport.
The pancreatic β-cell hormone amylin acts in isolated rat skeletal muscle to decrease insulin-stimulated incorporation of glucose into glycogen. It also increases blood levels of lactate and glucose in fasted rats in vivo. However, it remained uncertain whether amylin exerts direct effects to stimulate muscle glycogenolysis. We now report that amylin caused a dose-dependent increase in activity of muscle glycogen phosphorylase in isolated rat soleus muscle by stimulating phosphorylase a. Insulin inhibited amylin-stimulated activation of phosphorylase. Effects of amylin to stimulate muscle glycogenolysis are consistent with observed effects of amylin in vivo and could be a major mechanism whereby amylin modulates carbohydrate metabolism.
(1) Congenital syphilitic pancreatitis retards the development of the glandular acini but does not affect the islands of Langerhans. Embedded in the stroma, but not invaded by it, the latter maintain their continuity with the small ducts and acini with which they have a common origin.
(2) Two types of chronic interstitial inflammation affecting the developed pancreas are distinguishable:
(a) Interlobular Pancreatitis.—In the interlobular variety the inflammatory process is localized chiefly at the periphery of the lobule and implicates the islands of Langerhans only when the sclerotic process has reached a very advanced grade. When pancreatitis has followed obstruction of the ducts, the islands long remain unaltered though embedded in dense scar-like tissue.
(b) Interacinar Pancreatitis.—In the interacinar type the process is diffuse, invading the lobules and separating individual acini. The inflammatory change invades the islands of Langerhans.
(3) A relationship has been observed between lesions of the islands of Langerhans and the occurrence of diabetes mellitus.
(a) In one of eleven cases of interlobular panereatitis diabetes of mild intensity occurred. The sclerosis, which in this case followed obstruction of the ducts by calculi, was far advanced and affected the islands of Langerhans.
(b) In two of three cases of interacinar pancreatitis, diabetes was present. The third case was associated with a condition, hæmochromatosis, which at a later stage is associated with diabetes, the result of pancreatic lesion.
(c) In a fourth case of diabetes, hyaline deposit between the capillaries and the parenchymatous cells had so completely altered the islands of Langerhans that they were no longer recognizable.
Unlabelled:
Amylin is a polypeptide of 37 amino acids, predominantly synthesized in pancreatic Beta cells. The peptide was suggested to be dysregulated in Type 2 (non-insulin-dependent) diabetes mellitus and it antagonized certain actions of insulin in vitro in rat muscle. This led to speculation that amylin is involved in the pathogenesis of Type 2 diabetes. We have examined the in vivo effects of rat amylin, amidated at the carboxy-terminus, on insulin-mediated carbohydrate metabolism in conscious rats, using the hyperinsulinaemic (+/- 1 nmol/l) euglycaemic (6 mmol/l) clamp technique combined with [3-3H]-glucose infusion. Basal plasma amylin levels were less than or equal to 75 pmol/l. Applied amylin levels of 220 +/- 75 pmol/l (infusion rate of 12.5 pmol/min) antagonized only the insulin action on liver, resulting in a 100% increase of hepatic glucose output. Amylin levels of 4750 +/- 750 pmol/l (infusion rate of 125 pmol/min) induced a 250% increase of insulin-inhibited hepatic glucose output and, in addition, a 30% decrease of insulin-stimulated peripheral glucose up-take. Amylin did not affect: 1) the metabolic clearance rate of insulin, 2) the levels of plasma glucagon, epinephrine, norepinephrine, and corticosterone, 3) in vitro insulin binding and insulin-stimulated receptor autophosphorylation. This suggests that amylin antagonizes insulin action via binding to a yet unknown receptor.
In conclusion:
amylin causes in vivo insulin resistance and the liver seems the predominant organ regulated by this hormone. The in vivo effects of amylin mimic the pathophysiological abnormalities of insulin action in Type 2 diabetes.
Amylin, a peptide copackaged with insulin in beta-cell granules, was measured in the effluent of the perfused rat pancreases by means of a newly developed specific radioimmunoassay. Its secretion parallels that of insulin in response to 20 mM glucose, 10 mM arginine, or the combination thereof. The relative molar amount of secreted amylin was estimated to be 25-37% that of insulin. Treatment with a borderline diabetogenic dose of streptozotocin reduced amylin response without significantly changing the insulin response. A severely diabetogenic dose of streptozotocin totally abolished amylin release and markedly reduced insulin release. The selective impairment of amylin secretion in streptozotocin-treated rats could represent an early manifestation of beta-cell depletion or injury.
Islet amyloid polypeptide (IAPP), a putative polypeptide hormone, is a product of pancreatic beta-cells and the major constituent of the amyloid deposits seen mainly in islets of type 2 diabetic humans and diabetic cats. The connection between IAPP amyloid formation and diabetes is unknown, but a limited segment of the IAPP molecule, positions 20-29, seems responsible for the aggregation to fibrils. Differences in the amino acid sequence of this region probably determine whether or not islet amyloid can develop in a particular species. Amyloid fibril formation can be mimicked in vitro with the aid of synthetic peptides. With this technique we show that peptides corresponding to IAPP positions 20-29 of human and cat, species that develop IAPP-derived islet amyloid, form amyloid-like fibrils in vitro. The corresponding IAPP segment from three rodent species that do not develop IAPP-derived amyloid did not give rise to fibrils. Substitution of the human IAPP-(20-29) decapeptide with one or two amino acid residues from species without islet amyloid generally reduced the capacity to form fibrils. We conclude that the sequence Ala-Ile-Leu-Ser-Ser, corresponding to positions 25-29 of human IAPP, is strongly amyloidogenic and that a proline-for-serine substitution in position 28, as in several rodents, almost completely inhibits formation of amyloid fibrils.
Cats and humans, unlike most rodent species, develop amyloid in the islets of Langerhans in conjunction with non-insulin-dependent diabetes mellitus. The amyloid consists of a 37-amino acid polypeptide referred to as islet amyloid polypeptide (IAPP). The primary structures of IAPP from human and three rodent species have previously been determined. Sequence divergence was seen in the region corresponding to amino acid residues 20-29, which in human IAPP has been suggested to confer the amyloidogenic properties to the molecule. Using polymerase chain-reaction methodology, we determined the primary sequence of cat IAPP. Amino acid region 20-29 shows specific similarities and differences compared with human and rodent IAPP, respectively. A synthetic cat IAPP20-29 decapeptide formed amyloid fibrils spontaneously in vitro. Comparison between the structure and amyloid fibril-forming activity of various synthetic peptides suggests that the amino acid residues at positions 25-26 in mature IAPP are important for the amyloidogenic properties of the molecule.
Studies have indicated that the 20-29 segment of islet amyloid polypeptide (IAPP) determines the fibril formation. Variations between species in this region explain why only some species develop islet amyloid. This assumption is strongly supported by our study where we have used synthetic peptides in an fibril formation test system. The sequence AILS (IAPP25–28) is the most important amyloido-genic part of the IAPP molecule.
We report the isolation and characterization of the human gene encoding islet amyloid polypeptide (IAPP). Previously characterized cDNA sequences correspond to three exons of which the first is noncoding. A functional promoter region was identified in the 5' flanking DNA; however, this was farther upstream than expected. Northern blot analysis of human insulinoma RNA revealed three IAPP mRNAs of sizes 1.2, 1.8 and 2.1 kb, in agreement with three polyadenylation signals present in the 3' end of the gene. In situ hybridization to metaphase chromosomes resulted in two distinct peaks on chromosome 12, at 12p12-p13 and 12q13-q14. Southern blot analysis of genomic DNA suggested a single IAPP locus but also indicated the presence of additional homologous sequences in human genomic DNA.
Amylin is a new member of the calcitonin/CGRP family: it is a 37 amino acid polypeptide which was recently isolated from amyloid deposits in pancreatic islets obtained from type II diabetics. In the present study we investigated the effect of amylin and amylin-amide on calcium metabolism in the rat and rabbit. Two main methods were used: in vivo hypocalcaemic activity was assessed by measuring plasma calcium levels after injection of the peptide in 50 g rats; and in vitro resorption of cortical bone by disaggregated rat osteoclasts was quantified by scanning electron microscopy together with image analysis. We demonstrate that amylin and amylin-amide have calcitonin-like effects: both are powerful inhibitors of osteoclastic resorption and as a consequence lower plasma calcium in both rats and rabbits. We speculate that the peptide may exert systemic or local regulatory effects on bone cells.
Islet amyloid polypeptide (IAPP) or amylin is a pancreatic islet hormone which was first found in amyloid in insulinomas and in pancreases of patients with type 2 diabetes. In rat a similar polypeptide occurs; however, pancreatic amyloid in this species has not been described. Here we report the structure of the rat and human IAPP gene. Both consist of three exons and two introns which are very similar. The upstream sequence of the rat IAPP gene contains a TATA-box, a CCAAT-sequence and a GT-element, whereas the upstream sequence of the human IAPP gene contains a TATA-box and a rat insulin enhancer-like sequence. This suggests that the rat and human IAPP gene may be controlled differently at the transcriptional level.
The islets of Langerhans of diabetic and non-diabetic patients with different degrees of islet amyloidosis were studied by electron microscopy. The islet amyloid exhibited the typical fine fibrillar ultrastructure and was mainly located interstitially. Adjacent to the β cells the amyloid fibrils were often highly orientated perpendicularly to the cell surface and bundles of amyloid fibrils entered in deep plasmalemmal invaginations of the cells. This was more rarely seen in other types of cell. The epithelial cells exhibited no signs of increased activity. Macrophages were common in the amyloid masses. Amyloid occurred in invaginations of these cells but usually the fibrils showed no orientation. The capillaries, the fibrocytes and the mast cells were not so closely related to the amyloid. These findings probably indicate that the amyloid of the islets of Langerhans is a product of degenerating β cells even if other possibilities are not excluded.
The effect of synthetic rat amylin (10,100,1000 pmol/l) on glucose (10 mmol/) and arginine (10 mmol/l) -stimulated islet hormone release from the isolated perfused rat pancreas and on amylase release from isolated pancreatic acini was investigated. Amylin stimulated the insulin release during the first (+76%) and the second secretion period (+42%) at 1 nmol/l. The first phase of the glucagon release was inhibited concentration dependently by amylin and completely suppressed during the second phase. Amylin diminished the somatostatin release in a concentration dependent manner. This effect was more pronounced at the first than the second secretion period (1 nmol amylin: 1.phase: −60%, 2.phase: −22%). Amylin was without any effect on basal and CCK stimulated amylase release from isolated rat pancreatic acini. Our data suggest amylin, a secretory product of pancreatic B-cells, as a peptide with strong paracrine effects within the Langerhans islet. Therefore, amylin might be involved in the regulation of glucose homeostasis.
We have cloned and sequenced a human islet amyloid polypeptide (IAPP) cDNA. A secretory 89 amino acid IAPP protein precursor is predicted from which the 37 amino acid IAPP molecule is formed by amino- and carboxyterminal proteolytic processing. The IAPP peptide is 43–46% identical in amino acid sequence to the two members of the calcitonin gene-related peptide (CGRP) family. Evolutionary conserved proteolytic processing sites indicate that similar proteases are involved in the maturation of IAPP and CGRP and that the LAPP amyloid polypeptide is identical to the normal proteolytic product of the IAPP precursor. A synthetic peptide corresponding to a carboxyteminal fragment of human IAPP is shown to spontaneously form amyloid-like fibrils in vitro. Antibodies against this peptide cross-react with IAPP from species that develop amyloid in pancreatic islets in conjunction with age-related diabetes mellitus (human, cat, racoon), but do not cross-react with IAPP from other tested species (mouse, rat, guinea pig, dog). Thus, a species-specific structural motif in the putative amyloidogenic region of IAPP is associated with both amyloid formation and the development of age-related diabetes mellitus. This provides a new molecular clue to the pathogenesis of this disease.
Deposition of amyloid is the most constantly present alteration in the islets of Langerhans in type 2 diabetes mellitus and is also quite common in insulin-producing tumors of the pancreas and it is very likely that these two amyloids are identical. We have isolated amyloid fibrils from an insulin-secreting human tumour and purified the fibrillar protein. N-terminal amino acid sequence of the protein is unique and does not resemble insulin or its precursors. Instead it has about 50% homology with the neuropeptide CGRP (calcitonin gene related peptide).
Pancreatic islet volumes of patients with and without maturity onset diabetes mellitus were estimated. The islet volume of the diabetic patients was 1.01 +/- 0.12 cm3 (SEM) and that of the non-diabetic patients 1.60 +/- 0.16 cm3 with considerable overlap between the two groups. Islet amyloidosis was found in all the diabetic and in 9 of the 15 non-diabetic patients. When the amyloid deposits were excluded, the islet volume of the diabetic patients was 0.89 +/- 0.10 cm3, while that of the non-diabetic patients was unchanged, 1.60 +/- 0.16 cm3. There was still some overlapping. Since amyloid deposits seem to destroy the B cell membranes, it was postulated that a comparison of the volumes of islets completely free of amyloid might give a more true picture of the quantitative islet alterations in maturity onset diabetes. It was found that this islet volume of the diabetics was only 0.41 +/- 0.05 cm3 and that of the non-diabetic patients 1.58 +/- 0.16 cm3. These values correspond better to the altered insulin secretion in maturity-onset diabetes mellitus.
Amyloid in the islets of Langerhans increases with increasing severity of diabetes mellitus in Macaca nigra. The amount of insular amyloid was quantified, and diabetic monkeys averaged eight times more islet amyloid than did normal monkeys. The quantity of insular amyloid correlated significantly with glucose clearance in intravenous glucose tolerance tests and with serum glucose, triglycerides, immunoreactive insulin, and prebetallipoprotein measured after an overnight fast. As with human beings, insular amyloid appeared to be more prevalent in aging monkeys. The results support the hypothesis that the interrelated islet pathologic and metabolic events, which result in the appearance of insular amyloid concomitant with islet cell necrosis, may contribute more to maturity-onset diabetes in aging individuals than has been heretofore realized.
Human islet amyloid polypeptide, at concentrations of 1-100 nmol/l, has been demonstrated to inhibit the insulin-stimulated increase in rat muscle glycogen content. However, at physiological concentrations (1-10 pmol/l) of islet amyloid polypeptide, no effects have been reported. We tested the effect of a wide range of concentrations of human islet amyloid polypeptide on insulin- and phorbol ester-stimulated 3-0-methylglucose transport in in vitro incubated human skeletal muscle. Muscle specimens from the quadriceps femoris muscle were obtained from 23 healthy subjects with the use of a newly-developed open muscle biopsy technique. Human islet amyloid polypeptide at a concentration of 100 nmol/l had no effect on basal glucose transport, but inhibited the stimulatory effect of a maximal insulin concentration (1000 microU/ml) by 69% (p less than 0.001). The presence of human islet amyloid polypeptide at 1, 10 and 100 nmol/l decreased the effect of 100 microU/ml of insulin on glucose transport by 61% (p less than 0.05), 78% (p less than 0.05) and 76% (p less than 0.05), respectively. Similarly, human islet amyloid polypeptide at a concentration of 10 nmol/l inhibited phorbol ester-stimulated glucose transport by 100% (p less than 0.05). The inhibitory effects of human islet amyloid polypeptide on glucose transport were present in the muscle strips despite no net changes in glycogen content. Human islet amyloid polypeptide at 10 and 100 pmol/l had no effect on the rate of insulin-stimulated glucose transport.(ABSTRACT TRUNCATED AT 250 WORDS)
Two distinct binding sites for [125I]human calcitonin gene-related peptide (hCGRP) were found in rat brain, skeletal muscle, and liver. Each tissue had a high affinity site with an average Kd of 46 pM and a low affinity site with an average Kd of 22 nM. Islet amyloid polypeptide (IAPP), which has N- and C-terminal sequence homology to CGRP and is produced by islet beta-cells, bound to both sites but had a potency closer to that of CGRP at the low affinity binding site. A C-terminal fragment of IAPP competed for [125I]hCGRP binding at the low affinity site with potency comparable to that of hIAPP. No specific binding to membrane preparations was found in experiments using [125I]rIAPP, which was iodinated at the C-terminal tyrosyl residue. These results suggest that some of the previously reported biological effects occurring at nM or microM concentrations of IAPP may be mediated by IAPP binding to low affinity CGRP receptors. This study further indicates that the C-terminal region of IAPP is important for binding to low affinity CGRP receptors, and suggests that C-terminal fragments of IAPP may be of biological importance.
The intrahypothalamic injection of rat amylin reduced feeding in schedule-fed rats for eight hours. Specificity of this anorectic response was indicated by an appropriate dose-response relationship and the absence of effect of human amylin. Amylin-induced anorexia was accompanied by alterations in neurotransmitter metabolism similar to those observed in anorectic tumor-bearing rats. These results indicate that amylin may inhibit feeding by acting directly on hypothalamic neurons to alter metabolism of neurotransmitter systems known to affect feeding behavior.
Type 2 (non-insulin-dependent) diabetes is associated with the deposition of islet amyloid. The major formative peptide, islet amyloid polypeptide, has recently been characterised and an abnormality of the structure or expression of this gene is a possible candidate for the inherited component of Type 2 diabetes. A restriction fragment length polymorphism of the gene has been identified with Pvu II. To study the relationship between the islet amyloid polypeptide gene and Type 2 diabetes, two distinct genetic approaches have been undertaken. Firstly, non-linkage has been demonstrated in four pedigrees, with four normoglycaemic first degree relatives having an allele associated with diabetes in other family members, and one affected relative not having the putatively associated allele. The LOD score taking age-related penetrance into account was -1.68, making linkage unlikely (p = 0.02). Secondly, in a population-based restriction fragment length polymorphism survey, no linkage disequilibrium of the alleles was found between a population of unrelated Caucasian subjects with Type 2 diabetes and a normal population. A mutation in or near the islet amyloid polypeptide gene is thus unlikely to be a common cause of Type 2 diabetes.
Rats from four experimental treatment groups, including fed controls, 24- to 30-h fasted, dexamethasone-treated, and intraperitoneal glucose-treated, were used to assess the effects of these treatments on the immunohistochemically detectable islet amyloid polypeptide (IAPP) content in the pancreatic islets. Isolated perfused pancreases from additional animals in these groups were used to assess insulin and IAPP secretion and relative amounts of these hormones secreted into the perfusate under low-glucose (2.75 mM) and high-glucose (16.7 mM) conditions. Insulin and IAPP concentrations in the perfusate were measured by radioimmunoassays. Titration of immunohistochemical staining revealed the highest levels of IAPP in the dexamethasone- and glucose-treated groups, followed by the fed controls; the least amount was observed in the fasted group. In the perfusion experiments, the dexamethasone-treated group had significantly higher IAPP secretion than did all of the other groups under stimulation with 16.7 mM glucose. In addition, both dexamethasone treatment and glucose treatment increased the relative amount of IAPP to insulin secretion during 16.7 mM glucose stimulation in comparison with fed controls and fasted groups. Fasting tended to have the opposite effect and significantly decreased the relative amount of IAPP to insulin secreted under stimulation with 16.7 mM glucose. In all groups, IAPP and insulin secretion were generally parallel, which is consistent with their colocalization in the beta-cell secretory vesicle and co-release after glucose stimulation. However, significant differences in the insulin-IAPP ratios between experimental groups is consistent with the hypothesis that production of IAPP and insulin are regulated differently in the beta-cell.(ABSTRACT TRUNCATED AT 250 WORDS)
Although the novel pancreatic peptide amylin has been shown to induce insulin resistance and decrease glucose uptake, the mechanism of amylin's actions is unknown. The following study evaluated the effect of amylin on glycogen metabolism in isolated soleus muscles in the presence and absence of insulin (200 microU/ml). Total glycogen, glycogen phosphorylase and glycogen synthases activities, and cAMP levels were measured. Total glycogen levels were significantly decreased by amylin (100 nM) in fed or fasted muscles under conditions of insulin stimulation. Amylin (100 nM) activated glycogen phosphorylase by as much as 100% and decreased glycogen synthase activity by over 60%, depending on the metabolic state of the muscles. These effects where comparable to those of the beta adrenergic agonist isoproterenol. A lower concentration of amylin (1 nM) did not significantly affect glycogen levels, glycogen phosphorylase, or glycogen synthase activity. Cyclic AMP levels were increased two-fold by isoproterenol but were unaffected by amylin. In conclusion, amylin induces glycogenolysis by decreasing glycogen synthesis and increasing breakdown. The effect of amylin on enzyme activity is consistent with a phosphorylation-dependent mechanism. It is likely that these events are mediated via a cAMP independent protein kinase.
Human calcitonin gene-related peptide (hCGRP-1) and human amylin (hA) have been reported to increase hepatic glucose output in vivo and to bind with high affinity to rat liver plasma membranes, resulting in increased cAMP production. These observations have led to the hypothesis that CGRP or amylin may be physiological regulators of liver glucose metabolism. Liver plasma membranes are derived from several cell types, including parenchymal (hepatocyte), Kupffer, endothelial, lipid storage, and smooth muscle cells. Because the parenchymal cell is responsible for the contribution of the liver to whole-body glucose homeostasis, it is important to verify the location and activity of the CGRP/amylin receptor to this cell. These studies separate liver cells prepared by collagenase digestion into parenchymal and nonparenchymal fractions by metrizamide gradient and differential centrifugation. 125I-labeled [Tyr-0]hCGRP-1 bound with high affinity to nonparenchymal cell fraction and was displaced by both hCGRP-1 and hA. hCGRP-1 bound with greater affinity than hA (Kd = 2.1 +/- 1.6 x 10(-11) vs. 2.6 +/- 1.2 x 10(-8) M) in a manner similar to the binding reported for liver plasma membrane fraction. Linear regression of receptor concentration against nonparenchymal cell count per milliliter was significant (r = 0.999, P = 0.026), leading to an estimate of 3000 receptors/cell. The parenchymal cell fraction bound very little 125I-[Tyr-0]hCGRP-1, and regression of receptor concentration against parenchymal cell count per milliliter was not significant (r = -0.708, P = 0.29), suggesting that binding was not due to parenchymal cells but instead to contamination by nonparenchymal cells.(ABSTRACT TRUNCATED AT 250 WORDS)
The pancreatic beta-cell is a major site of islet amyloid polypeptide (IAPP) biosynthesis, and the peptide is coreleased with insulin. We have analyzed the expression of IAPP (mRNA and protein) in various cell types in normal and transformed murine islet cell cultures by Northern blot analyses and immunocytochemistry. IAPP is primarily coexpressed with insulin in the beta-cell of GH-promoted primary rat islet cell cultures. Additionally, a small population of non-beta-cells exhibited a prominent IAPP expression, and double staining experiments showed colocalization with glucagon or somatostatin in some of these cells. IAPP mRNA was confined to the beta-cell phenotype when analyzing the phenotypically stable in vivo tumor lines, MSL-G2-IN (insulinoma) and MSL-G-AN (glucagonoma), and the transgenic mouse islet cell lines, beta-Tc and alpha-Tc. However, IAPP and insulin expression were completely uncoupled in unstable heterogeneous clones such as NHI-6F. This clone is composed of primarily glucagon-producing cells in vitro, but insulin gene expression becomes dominant after passage in vivo. Interestingly, IAPP was hyperexpressed with glucagon under in vitro conditions in this clone. We conclude that the tissue specificity of expressions of IAPP and insulin are controlled differently, and that coexpression of IAPP with hormones different from insulin may be a marker for pluripotent transformed rat islet cell clones, which are able to activate insulin gene transcription during passage in vivo.
We determined islet amyloid polypeptide (IAPP) response in plasma to oral and intravenous glucose administration and intravenous insulin injection in nondiabetic subjects. Moreover, we studied the effect of somatostatin analogue SMS 201-995 on glucose-induced IAPP secretion in nondiabetic subjects. Plasma IAPP concentration was determined by radioimmunoassay. Oral administration of 75 g glucose (n = 8) significantly increased plasma IAPP levels from 4.5 +/- 0.7 to 14.0 +/- 1.7 pM (P less than 0.01) 60 min after administration. Intravenous administration of 10 g glucose (n = 7) also caused a significant increase in plasma IAPP from 5.0 +/- 0.4 to 11.6 +/- 0.9 pM (P less than 0.01) 5 min after injection. Plasma IAPP significantly decreased from 5.1 +/- 0.4 to 2.9 +/- 0.4 pM (P less than 0.01) 60 min after intravenous insulin injection (n = 8). Pretreatment with SMS 201-995 completely abolished IAPP and insulin secretion to intravenous glucose injection. A significant correlation was found between plasma IAPP and insulin levels in oral and intravenous glucose administration and between plasma IAPP and C-peptide levels during insulin-induced hypoglycemia. These results suggest that IAPP is cosecreted with insulin in response to a glucose load and secretion of IAPP is inhibited by hypoglycemia and somatostatin. IAPP may serve as a novel pancreatic hormone to control carbohydrate metabolism.
Seven canine pancreatic endocrine tumors were evaluated immunohistochemically for the presence of islet amyloid polypeptide (IAPP), calcitonin gene-related peptide (CGRP), and several other pancreatic hormones. Four tumors contained cells with IAPP immunoreactivity, and four had cells with CGRP immunoreactivity. IAPP and CGRP immunoreactivities were localized to distinctly different cell populations in three tumors in which both peptides were detected; however, IAPP immunoreactivity consistently was found in cells that also contained insulin immunoreactivity. Amyloid deposits, which were found in three of the seven tumors, showed strong immunoreactivity with antiserum against IAPP and weaker immunoreactivity with antiserum to CGRP. These results indicate that amyloid deposits in canine pancreatic endocrine tumors are likely derived from IAPP, as is amyloid found in human pancreatic endocrine tumors and pancreatic islet amyloid in aged and diabetic persons and cats.
The structure of human calcitonin gene-related peptide 1 (hCGRP-1) has been determined by 1H NMR in a mixed-solvent system of 50% trifluoroethanol/50% H2O at pH 3.7 and 27 degrees C. Complete resonance assignment was achieved by using two-dimensional methods. Distance restraints for structure calculations were obtained by semiquantitative analysis of intra- and interresidue nuclear Overhauser effects; in addition, stereospecific or X1 rotamer assignments were obtained for certain side chains. Structures were generated from the distance restraints by distance geometry, followed by refinement using molecular dynamics, and were compared with experimental NH-C alpha H coupling constants and amide hydrogen exchange data. The structure of hCGRP-1 in this solvent comprises an amino-terminal disulfide-bonded loop (residues 2-7) leading into a well-defined alpha-helix between residues 8 and 18; thereafter, the structure is predominantly disordered, although there are indications of a preference for a turn-type conformation between residues 19 and 21. Comparison of spectra for the homologous hCGRP-2 with those of hCGRP-1 indicates that the conformations of these two forms are essentially identical.
The role of islet amyloid polypeptide, also known as amylin, in insulin resistance and in the etiology of diabetes has been a subject of debate. Increased plasma amylin levels have been observed in both obese and type II diabetic patients. However, data on endogenous amylin levels with relation to pharmacological interventions have not been reported. In this study, chronic treatment of obese-diabetic viable yellow mice with ciglitazone was shown to significantly alter various parameters. Blood glucose and plasma insulin, triglyceride, and amylin levels were reduced and glucose tolerance in the presence of exogenous insulin was improved. Insulin/amylin ratios which were found to be significantly elevated in diabetic mice as compared to normal controls, were decreased after ciglitazone treatment. However, observed decreases in both amylin and insulin concentrations due to ciglitazone treatment and their subsequent increases upon withdrawal of treatment were correlated, suggesting cosecretion.
We examined the in vivo mechanisms of amylin-induced resistance in concious rats (n = 18). During 180-min euglycemic insulin-clamp (21.5 pmol.kg-1.min-1) studies, amylin (50, 200, or 500 pmol.kg-1.min-1; plasma concentration from 3 x 10(-10) to 9 x 10(-9) M) infusion determined a 19-27% reduction in glucose uptake (117.8 +/- 7.0 vs. 145.8 +/- 11.0, 107.1 +/- 9.2 vs. 145.1 +/- 6.7, and 105.0 +/- 7.2 vs. 144.4 +/- 7.0 mumol.kg-1.min-1 at 50, 200, or 500 pmol.kg-1.min-1, respectively, P less than 0.01) versus insulin alone, whereas 10-pmol.kg-1.min-1 amylin infusion (plasma concn 5 x 10(-11) M) failed to affect insulin-mediated glucose disposal. After amylin infusion, the contribution of whole-body glycolysis to overall glucose disposal increased from 43-48 to 62-79%, whereas muscle glycogen synthesis decreased significantly at all peptide concentrations greater than 3 x 10(-10) M, completely accounting for the decrease in glucose uptake. Skeletal muscle glucose-6-phosphate concentration rose from 0.219 +/- 0.038 mumol/g (insulin alone) to 0.350 +/- 0.018, 0.440 +/- 0.020, and 0.505 +/- 0.035 mumol/g (insulin plus amylin at 50, 200, or 500 pmol.kg-1.min-1, P less than 0.01). Suppression of hepatic glucose production by insulin was unaffected by a 50-pmol.kg-1.min-1 amylin infusion (18.5 +/- 4.3 vs. 21.7 +/- 2.9 mumol.kg-1.min-1), whereas it was slightly but significantly impaired by amylin infusion at 200 pmol.kg-1.min-1 (17.8 +/- 3.9 vs. 24.7 +/- 4.5 mumol.kg-1.min-1, P less than 0.05).(ABSTRACT TRUNCATED AT 250 WORDS)
Amylin is a 37-amino acid pancreatic polypeptide, probably involved in the pathophysiology of Type 2 (non-insulin-dependent) diabetes mellitus. We have determined amylin in human plasma by extraction-based radioimmunoassay (Sep-Pak C18). Of 23 healthy control subjects plasma amylin was determined as 11.9 +/- 3.5 ng/l. Of 27 patients with Type 2 diabetes receiving insulin the amylin levels were lower, and in 16 patients with Type 2 diabetes on oral medication they were higher than in the control subjects; 8.2 +/- 4.4 ng/l (p less than 0.01) vs 18.8 +/- 9.9 ng/l (p less than 0.05). In 14 Type 1 (insulin-dependent) diabetic patients we found extremely low mean amounts of amylin: 2.9 +/- 1.9 ng/l (p less than 0.002). Thus, basal amylin appears to be associated with the capacity to release insulin. An oral glucose load stimulated the release of amylin, this was more pronounced in patients with Type 2 diabetes than in healthy subjects. An excellent correlation of mean amylin with mean insulin concentrations was obtained (r = 0.949). In patients with Type 2 diabetes amylin was reduced congruent to decreases in C-peptide during a hyperinsulinaemic, euglycaemic glucose clamp experiment (r = 0.971 for linear correlation between C-peptide levels and amylin). We conclude, that amylin and insulin are co-secreted in humans, and that the amylin release is under feedback-control by insulin.
1. Islet amyloid isolated from the pancreas of a 20-year-old cougar (Felis concolor) was dissolved and purified by gel permeation and reversed phase HPLC for amino acid sequence analysis. 2. N-Terminal amino acid sequence analysis of the purified protein revealed a primary structure (positions 1-28) identical to islet amyloid polypeptide (IAPP) from domesticated cats. 3. IAPP from the cougar, like IAPP from the human and domesticated cat, incorporates an inherently amyloidogenic AILS sequence at positions 25-28.
Fasting plasma islet amyloid polypeptide concentrations and their responses to an oral glucose load were determined in non-diabetic control subjects and patients with abnormal glucose tolerance in relation to the responses of insulin or C-peptide. Plasma islet amyloid polypeptide was measured by radioimmunoassay. In the non-diabetic control subjects, fasting plasma islet amyloid polypeptide was 6.4 +/- 0.5 fmol/ml (mean +/- SEM) and was about 1/7 less in molar basis than in insulin. The fasting islet amyloid polypeptide level rose in obese patients and fell in patients with Type 1 (insulin-dependent) diabetes mellitus. In non-obese patients with impaired glucose tolerance and Type 2 (non-insulin-dependent) diabetic patients without insulin therapy, the level was equal to that of the control subjects, but a low concentration of islet amyloid polypeptide relative to insulin or C-peptide was observed in the non-obese Type 2 diabetic group. The patterns of plasma islet amyloid polypeptide responses after oral glucose were similar to those of insulin or C-peptide. However, compared to non-obese patients, a hyper-response of islet amyloid polypeptide relative to C-peptide was noted in obese patients who had a hyper-response of insulin relative to C-peptide. This study suggests that basal hypo-secretion of islet amyloid polypeptide relative to insulin exists in non-obese Type 2 diabetes and that circulating islet amyloid polypeptide may act physiologically with insulin to modulate the glucose metabolism.
An immunohistochemical study for islet amyloid polypeptide (IAPP) was made on the gastrointestinal (GI) tract and pancreas of man and rat, using antisera raised against a synthetic peptide of C-terminal human IAPP (24-37) and a synthetic peptide of rat IAPP (18-37). A large number of IAPP-immunoreactive cells were found in the pyloric antrum, and a small number in the body of the stomach in both man and rat. Cytoplasmic processes extended out from the bipolar peripheral region of the immunoreactive cells, rather like neuronal processes, and some appeared to make contact with other immunoreactive cells. In addition, small numbers of immunoreactive cells were also seen in the duodenum and rectum, whereas they were absent from the jejunum, ileum and large intestine. An examination was made for evidence of colocalization of IAPP-immunoreactive material with material immunoreactive for gastrin, somatostatin, vasoactive intestinal polypeptide, pancreatic polypeptide, insulin, and glucagon, but none was found. IAPP-immunoreactive cells were also found in the pancreas of non-diabetic and non-insulin-dependent diabetic patients, but they were completely absent from a patient with insulin-dependent diabetes mellitus despite the presence of IAPP in the plasma. The results of these studies suggest that the peptide may have a biological role in situ in the GI tract and, in addition to the pancreas, may be a possible source of plasma IAPP.
To identify islet amyloid polypeptide (IAPP) present in normal human pancreas, we isolated the peptide from a soluble peptide fraction of amyloid deposit-free pancreata of two non-diabetic patients by using reverse-phase high performance liquid chromatography coupled with a radioimmunoassay specific for human IAPP. IAPP(1-37) and IAPP(17-37) were isolated and their complete amino acid sequences were determined up to the C-terminus. Identification of IAPP in normal human pancreas suggests the possible biological function of IAPP as a novel pancreatic hormone in humans.
Both human and rat islet amyloid polypeptide with COOH-terminal amide (IAPP-NH2) dose-dependently displaced the specific binding of 125I-labeled [Tyr0] rat alpha-calcitonin gene-related peptide (CGRP) to rat liver plasma membranes, whereas human IAPP (IAPP-COOH) had no effect. Conversely, human or rat IAPP-NH2 but not human IAPP-COOH evoked dose-dependent activation of adenylate cyclase in the membranes, and these effects were significantly inhibited by the CGRP-receptor antagonist human CGRP-1(8-37). Moreover, the dose of human or rat IAPP-NH2 necessary for producing half-maximal activation of adenylate cyclase was comparable with that for producing a half-maximal inhibition of the label binding. Thus, IAPP-NH2 but not IAPP-COOH appears to induce adenylate cyclase activation via CGRP receptors on rat liver plasma membranes.
Amylin-amide has been implicated in the pathogenesis of type II diabetes due to its proposed inhibitory effect on insulin release from beta cells of the pancreatic islets, and on glucose uptake by the skeletal muscle. In experiments with rats and rabbits we failed to demonstrate these anti-insulin actions of amylin and amylin-amide. A single bolus dose of the two peptides (500 pmol) administered i.v. failed to suppress plasma insulin levels or to elevate blood glucose levels. The continuous infusion of amylin-amide into rabbits also failed to suppress the release of insulin in response to hyperglycaemia produced by an i.v. bolus injection of glucose. These in vivo observations imply that the amylin peptides may not have a primary physiological role in carbohydrate metabolism, but in view of our previous findings, we speculate that the peptide has a more prominent role in calcium homeostasis.
Islet amyloid polypeptide (IAPP) has been implicated by in vitro studies as an inhibitor of insulin-stimulated glucose utilization by skeletal muscle cells and also as an inhibitor of insulin-stimulated insulin secretion by beta cells. Increased expression and production of IAPP by beta cells, as has been suggested to occur in cats with impaired glucose tolerance, could thus contribute substantially to the development of the insulin resistance and impaired insulin release which are the hallmarks of Type 2 diabetes mellitus. The effects of IAPP with respect to glucose metabolism in living animals, however, have not been previously reported. In the present in vivo study we show that synthetic amidated IAPP induced impaired glucose tolerance in each of the 3 cats studied, with dramatic impairment (increases in glucose to T1/2 values of 124% and 234%) in 2 of the 3 cats. Impaired insulin responses were also evident in the 2 cats with the most dramatic states of glucose intolerance. These results provide the most direct evidence to-date that IAPP may have an important role in the development of Type 2 diabetes mellitus.
Islet amyloid polypeptide is a 37 amino acid hormone-like peptide which is the major protein component of islet amyloid deposits commonly found in patients with Type 2 (non-insulin-dependent) diabetes mellitus. Recent studies indicate that a physiologically active form of this peptide appears to be carboxyamidated and secreted from the insulin-producing beta cell. In order to clarify the possible in vivo actions of islet amyloid polypeptide, we have studied the effects of synthesized islet amyloid polypeptide-amide on peripheral glucose utilization by performing hyperinsulinaemic euglycaemic glucose clamp studies on dogs. Exogenously administered islet amyloid polypeptide-amide (an infusion from 1.0 to 100 micrograms.kg-1.h-1, over 2 h) inhibited the insulin-stimulated glucose disposal rate in a dose dependent manner. Twenty-five micrograms.kg-1.h-1 of islet amyloid polypeptide-amide infused via a peripheral vein significantly lowered the glucose disposal rate by 20% (from 17.4 +/- 1.7 to 14.4 +/- 1.7 mg.kg-1.min-1, n = 5, p less than 0.01). These findings suggest that islet amyloid polypeptide-amide causes peripheral insulin resistance in vivo.
Islet amyloid polypeptide (IAPP) has been identified as the major constituent of the pancreatic amyloid of non-insulin-dependent diabetes mellitus (NIDDM) and is also present in normal beta-cell secretory granules. To determine whether IAPP is a pancreatic secretory product, we measured the quantity of IAPP-like immunoreactivity (IAPP-LI), insulin, and glucagon released into 5 ml of incubation medium during a 2-h incubation of monolayer cultures (n = 5) of neonatal (3- to 5-day-old) Sprague-Dawley rat pancreases under three conditions: 1.67 mM glucose, 16.7 mM glucose, and 16.7 mM glucose plus 10 mM arginine and 0.1 mM isobutylmethylxanthine (IBMX). The quantity of IAPP-LI, insulin, and glucagon in the cell extract was also determined. Mean +/- SE IAPP-LI in the incubation medium increased from 0.041 +/- 0.003 pmol in 1.67 mM glucose to 0.168 +/- 0.029 pmol in 16.7 mM glucose (P less than 0.05) and 1.02 +/- 0.06 pmol in 16.7 mM glucose plus arginine and IBMX (P less than 0.05 vs. 1.67 or 16.7 mM glucose). Insulin secretion increased similarly from 4.34 +/- 0.27 to 20.2 +/- 0.6 pmol (P less than 0.05) and then to 135 +/- 5 pmol (P less than 0.05 vs. 1.67 or 16.7 mM glucose). Glucagon release tended to decrease with the increase in glucose concentration (0.39 +/- 0.01 vs. 0.33 +/- 0.02 pmol, P less than 0.1), whereas with the addition of arginine and IBMX to high glucose, glucagon release increased to 1.32 +/- 0.03 pmol (P less than 0.05 vs. 1.67 or 16.7 mM glucose).(ABSTRACT TRUNCATED AT 250 WORDS)
Amylin, a 37 amino acid C-terminal amidated peptide is an integral part of secretory granules of pancreatic beta-cells. Utilizing a specific radioimmunoassay system we demonstrate in the present study a cosecretion of amylin and insulin from the isolated rat pancreas. The secretion pattern of both peptides during glucose or glucose plus arginine stimulation is identical. The molar ratio of amylin amounts to 10% of that of insulin. The biological significance of amylin is still unknown, but a paracrine/endocrine role in glucose homeostasis is speculated.
Recent interest has focused on the potential role of amylin in the pathogenesis of non-insulin-dependent diabetes mellitus (NIDDM). This 37-amino acid peptide is found in extracellular amyloid deposits in approximately 50% of pancreatic islets of patients with NIDDM and has been shown to inhibit skeletal muscle glycogen synthesis in vitro. Immunocytochemical studies have colocalized amylin and insulin within beta-cell secretory granules in nondiabetic humans, provoking the following questions. Is amylin cosecreted with insulin? Are circulating amylin concentrations higher in patients with NIDDM either before or after food ingestion? To answer these questions, we developed a sensitive and specific immunoassay to measure plasma concentrations of amylin in humans. Use of this assay indicated that, in lean nondiabetic subjects, glucose ingestion resulted in an increase (P less than 0.001) in the plasma concentration of amylin (from 2.03 +/- 0.22 to 3.78 +/- 0.39 pM) and insulin (from 48.3 +/- 3.1 to 265 +/- 44 pM). There was a significant correlation between the concentrations of insulin and amylin (r = 0.74, P less than 0.001) and the increase in insulin and amylin concentration (r = 0.65, P less than 0.005). Fasting concentrations of amylin did not differ in diabetic and weight-matched nondiabetic subjects and showed a similar pattern of change after ingestion of a mixed meal. We conclude that amylin is secreted in response to ingestion of either glucose or a mixed meal and circulates at concentrations that do not differ in patients with NIDDM and nondiabetic subjects. It remains to be determined whether amylin at physiological concentrations influences carbohydrate metabolism and if so whether its effects differ in diabetic and nondiabetic humans.
We examined the effects of rat islet amyloid polypeptide (IAPP) on insulin biosynthesis and secretion by isolated rat islets of Langerhans. Culture of islets for 24 h in the presence of 10(-6) M IAPP and 5.5 mM glucose had no effect on insulin mRNA levels. Similarly, the rates of proinsulin biosynthesis were not altered in islets incubated in 10(-4)-10(-9) M IAPP and 5.5 mM glucose, nor was the rate of conversion of proinsulin to insulin changed at 10(-6) M IAPP. Addition of 10(-5) M IAPP to islets incubated in 11 mM glucose decreased the fractional insulin secretion rate; however, the secretion of newly synthesized proinsulin and insulin was not affected. These data indicate that it is unlikely that IAPP is a physiologically relevant modulator of insulin biosynthesis or secretion.
Islet amyloid polypeptide (IAPP) is a recently discovered pancreatic islet hormone which is stored with insulin in beta cell granules. IAPP may have a significant role in the development of Type 2 diabetes mellitus due to its propensity to form islet cell-disrupting amyloid deposits, and by opposing the action of insulin in peripheral tissues. Most evidence to-date suggests that an intrinsic structural motif of IAPP is linked to the amyloidogenicity of IAPP, and that this motif occurs only in those species (e.g., humans and cats) that also develop age-associated or Type 2 diabetes We utilized polymerase chain reaction methodology in this study to obtain the IAPP nucleotide and protein sequences of the dog, a species not known to develop islet amyloid. We show that dog IAPP contains the same putative amyloidogenic sequence (GAILS) at residues 24-28 as human and cat IAPP, and that although dogs do not develop islet amyloid they do develop IAPP-derived amyloid in association with neoplastic beta cells (i.e., insulinomas). These results provide strong evidence that the amyloidogenicity of IAPP is linked to at least two prerequisites: a species-specific amyloidogenic structural motif, and aberrations in the synthesis (or processing) of IAPP which leads to increased concentration of IAPP in the local milieau.
1. The effects of synthetic human amylin on basal and insulin-stimulated (100 and 1000 microunits/ml) rates of lactate formation, glucose oxidation and glycogen synthesis were measured in the isolated rat soleus muscle preparation incubated in the presence of various concentrations of glucose (5, 11 and 22 mM). 2. The rate of glucose utilization was increased by about 2-fold by increasing the glucose concentration from 5 to 22 mM. 3. Synthetic human amylin (10 nM) significantly inhibited (by 46-56%) glycogen synthesis, irrespective of the concentration of insulin or glucose present in the incubation medium. 4. Amylin (10 nM) did not affect insulin-stimulated rates of 2-deoxy[3H]glucose transport and phosphorylation. 5. Intraperitoneal administration of insulin (100 micrograms/kg) to rats in vivo stimulated the rate of [U-14C]glucose incorporation into glycogen in the diaphragm by about 80-fold. This rate was decreased (by 28%) by co-administration of amylin (66 micrograms/kg).
Islet amyloid polypeptide (IAPP) is a recently discovered pancreatic islet hormone which is stored with insulin in the secretory vesicles of beta cells. Several lines of evidence suggested that IAPP might affect glucose-stimulated insulin secretion and, therefore, might play a role in the development of impaired insulin secretion which is typical of type 2 diabetes. In this study, the effects of human IAPP (amide) on glucose-stimulated insulin secretion was evaluated in the isolated perfused rat pancreas. IAPP in concentrations from 5 x 10(-12) to 10(-7) M had no significant effects on insulin secretion. IAPP, therefore, does not appear to be a significant modulator of glucose-stimulated insulin secretion at concentrations that are physiologically relevant.
Islet amyloid polypeptide (IAPP) is a 37 amino acid peptide present in pancreatic β-cells. Pancreatic and circulating IAPP concentrations in rat models of diabetes were measured using a specific radioimmunoassay. Pancreatic IAPP-like immunoreactivity (IAPP-IR) in dexamethasone-treated rats was twice that of the control rats (1571±137 vs 657±176 ( s.e.m. ; n = 6) pmol/g), and this was reflected by similar changes in the plasma IAPP-IR (272±17 vs 102±10 pmol/l). In streptozotocin-treated rats, pancreatic IAPP-IR (200±90 pmol/g) was reduced compared with controls. There was a significant positive correlation between pancreatic and plasma IAPP-IR and insulin, with r values of 0·82 and 0·91 for the plasma and pancreas respectively. Characterization of pancreatic immunoreactivity, using gel chromatography, revealed two peaks of IAPP-IR, one which coeluted with synthetic human amidated IAPP and another peak, presumably a fragment or breakdown product, which eluted later. Chromatography of the plasma IAPP-IR revealed that >90% of the IAPP-IR eluted in the void volume, although the remaining IR coeluted with the synthetic IAPP standard. These results are not straightforwardly compatible with the suggested role for IAPP as a hormonal, paracrine or autocrine inhibitory regulator of insulin secretion in the maintenance of carbohydrate homeostasis.
Journal of Endocrinology (1990) 126, 425–429