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Pathways of 1-carbon metabolism in the cytoplasm. The 4 B vitamins, folate, B 2 , B 6 , and B 12 , each serve important roles as cofactors. MTHFR, methylenetetrahydrofolate reductase; MS, methionine synthase; GMT, general methyltransferase family; SAM, S-adenosylmethionine; SAH, S-adenosylhomocysteine; THF, tetrahydrofolate; DHF, dihydrofolate.
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The Wnt pathway is a pivotal signaling cascade in colorectal carcinogenesis. The purpose of this work is to determine whether depletion of folate and other metabolically related B vitamins induces in vivo activation of intestinal Wnt signaling and whether this occurs in parallel with increased tumorigenesis. A hybrid mouse was created by crossing a...
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... would be expected from an animal possessing a defective Apc allele, there were a large number of Wnt elements whose expressions changed in the BAT- LacZApc1638N animals compared with the BAT-LacZ animals; 33 of 84 genes in the microarray underwent significant change (Supplemental Fig. S1). The ob- served changes in gene expression are nearly all con- sistent with Wnt activation in the Apc1638N colon; for instance, Apc gene expression was decreased in the Apc1638N mouse model, and downstream genes whose expression increases with Wnt signaling, such as Pitx2, Jun, and Cyclin D1, were each significantly up-regulated. ...
Citations
... Subsequent studies have further elucidated the role of VitB12 in supplementation, showing that it can downregulate NF-κB and consequently decrease the level of TNF-α in the peripheral nervous system [93]. Moreover, an increase in the Jun mRNA levels was observed in VitB12-deficient mice, which could potentially lead to an increase in the JUN protein, forming the AP-1 heterodimer alongside FOS [97]. This could potentially contribute to increased neuroinflammation, considering AP-1 to be a pivotal regulator of gene transcription encoding cytokines, chemokines, and other proteins crucial for T-cell recruitment and ROS production [98]. ...
Vitamin B12 (VitB12) is a micronutrient and acts as a cofactor for fundamental biochemical reactions: the synthesis of succinyl-CoA from methylmalonyl-CoA and biotin, and the synthesis of methionine from folic acid and homocysteine. VitB12 deficiency can determine a wide range of diseases, including nervous system impairments. Although clinical evidence shows a direct role of VitB12 in neuronal homeostasis, the molecular mechanisms are yet to be characterized in depth. Earlier investigations focused on exploring the biochemical shifts resulting from a deficiency in the function of VitB12 as a coenzyme, while more recent studies propose a broader mechanism, encompassing changes at the molecular/cellular levels. Here, we explore existing study models employed to investigate the role of VitB12 in the nervous system, including the challenges inherent in replicating deficiency/supplementation in experimental settings. Moreover, we discuss the potential biochemical alterations and ensuing mechanisms that might be modified at the molecular/cellular level (such as epigenetic modifications or changes in lysosomal activity). We also address the role of VitB12 deficiency in initiating processes that contribute to nervous system deterioration, including ROS accumulation, inflammation, and demyelination. Consequently, a complex biological landscape emerges, requiring further investigative efforts to grasp the intricacies involved and identify potential therapeutic targets.
... These reports have been thoroughly reviewed elsewhere [2][3][4][5][6][7][8][9]. Studies have linked inadequate folate consumption with an increased risk of cancer, specifically colorectal cancer (CRC) [10][11][12][13][14]. Others have reported that folate restriction can inhibit colorectal tumorigenesis [15][16][17][18]. ...
... The absence of a standard animal model, variations in dietary interventions, and variations in study designs created challenges in drawing parallels across studies. An overview of rodent studies examining the impact of folic acid on CRC revealed that the interventions differed in the use of animal models, diets, folic acid supplementation, antibiotic use, and the type of caging [12][13][14][19][20][21][22][23][24][25]. Of particular importance, the timing, duration, and type of dietary interventions varied considerably, which make comparisons across studies nearly impossible. ...
... The diets either contained no folates (0 mg folic acid/kg diet), no folates with antibiotics (0 mg folic acid/kg diet + 1% SST), a folate adequate diet (2 mg folic acid/kg diet), and a folate adequate diet with antibiotics (2 mg folic acid/kg diet + 1% SST). To avoid over-supplementation in our main study, we used the standard recommended folic acid amount of 2 mg/kg for the AIN−93G diet in our folate adequate groups (FA) [13]. ...
Diet plays a crucial role in the development of colorectal cancer (CRC). Of particular importance, folate, present in foods and supplements, is a crucial modulator of CRC risk. The role of folate, and, specifically, the synthetic variant, folic acid, in the primary prevention of CRC has not been fully elucidated. Animal studies varied considerably in the timing, duration, and supplementation of folates, leading to equivocal results. Our work attempts to isolate these variables to ascertain the role of folic acid in CRC initiation, as we previously demonstrated that folate restriction conferred protection against CRC initiation in a β-pol haploinsufficient mouse model. Here we demonstrated that prior adaptation to folate restriction altered the response to carcinogen exposure in wild-type C57BL/6 mice. Mice adapted to folate restriction for 8 weeks were protected from CRC initiation compared to mice placed on folate restriction for 1 week, irrespective of antibiotic supplementation. Through analyses of mTOR signaling, DNA methyltransferase, and DNA repair, we have identified factors that may play a critical role in the differential responses to folate restriction. Furthermore, the timing and duration of folate restriction altered these pathways differently in the absence of carcinogenic insult. These results represent novel findings, as we were able to show that, in the same model and under controlled conditions, folate restriction produced contrasting results depending on the timing and duration of the intervention.
... Interestingly, neither the cumulative intake over the entire duration of follow-up nor intake 0-12 years prior to the diagnosis of cancer were associated with the risk; rather, the latency analyses pinpointed folate intake 12-24 years before the occurrence of cancer as the window of time that significantly predicted the risk, thus defining a "lag period" between folate intake and cancer risk. This is consistent with the concept that colon cancer evolves gradually over 10 or more years, as well as with animal studies that indicate that the preventive effect of folate is expressed at the earliest stages of carcinogenesis (10,13). ...
... 85 Another study showed that a slight reduction of vitamins such as B2, B6, B12, and folate in APC mutant mice can lead to CRC progression by activating the Wnt signaling pathway. 86 ...
Dysbiosis in the gut microbiota composition due to environmental or genetic variations can disrupt the immune system and may promote several diseases such as colorectal cancer (CRC). Gut microbiota can alter the toxicity and efficiency of an extensive range of CRC treatment methods, especially surgery, chemotherapy, radiotherapy, and immunotherapy. The recent scientific evidence suggested that gut microbiota modulation exhibits an essential positive influence on inhibition and treatment of CRC. The literature survey revealed that modulating the gut microbiota composition by probiotics, prebiotics, and diets protects CRC patients from treatment‐associated adverse effects. This review summarizes the recent advancements in the association between interventions on gut microbiota and CRC to provide innovative strategies for enhancing the safety and efficiency of CRC therapy.
... To understand the role of gut microbiome in linking obesity with inflammation, Wnt pathway and tumorigenesis, we sought to examine how high fat diet and obesity per se drive gut dysbiosis, promote intestinal inflammation, activate the Wnt pathway, and thereby enhance intestinal tumorigenesis using the Apc +/1638N mouse model, the tumorigenic phenotype of which is particularly sensitive to dietary modifications (18,19). ...
... Though this model develops tumors predominantly in the small intestine rather than the colorectum, it is the nature of other genetically-engineered rodent models of CRC such as the widely used Apc Min mouse. Nevertheless, the Apc +/1638N model has a mildly tumorigenic phenotype that sensitively responds to dietary modification and the predilection to developing these small intestinal tumors responds to dietary perturbations in the same manner that diet modifies CRC risk in the human, underscoring the relevance of this model to human colonic tumorigenesis (18,19). Since the tumors predominantly occur in the small intestine in this mouse model, the small intestinal microbial constitution is more reflective of the tumor microenvironment, and therefore in this paper we focused on the microbial composition, inflammatory status and expression of Wnt pathway-specific genes in the small intestine as opposed to the large intestine. ...
Obesity is an established risk factor for colorectal cancer (CRC). Our previous study indicated that obesity increases activity of the pro-tumorigenic Wnt-signaling. Presently, we sought to further advance our understanding of the mechanisms by which obesity promotes CRC by examining associations between microbiome, inflammation and Wnt-signaling in Apc+/1638N mice whose obesity was induced by one of two modalities, diet- or genetically-induced obesity. Three groups were employed: Apc+/1638NLepr+/+ fed a low fat diet (10% fat), Apc+/1638NLepr+/+ fed a high fat diet (60% fat, diet-induced obesity), and Apc+/1638NLeprdb/db fed a low fat diet (genetically-induced obesity). All animals received diets for 16 weeks from 8 to 24 weeks of age. The abundance of 19 bowel cancer-associated bacterial taxa were examined by real-time PCR. The abundance of Turicibacter and Desulfovibrio decreased, but F. prausnitizii increased, in diet-induced obese mice (p < 0.05). In contrast, in genetically-induced obese mice, Bifidobacterium, A. muciniphila and E. rectale decreased, but Peptostrptococcus, and E. coli increased (p < 0.05). Both diet- and genetically-induced obesity altered the expression of genes involved in bacterial recognition (MyD88) and increased inflammation as indicated by elevated levels of cytokines (IFNγ and TNF-α for genetically-induced obesity, and IL-6 for diet-induced obesity). The elevated inflammation was associated with altered expression of genes that are integral components of the Wnt-signaling cascade in a fashion indicating its activation. These findings demonstrate that the composition of the small intestinal microbiome is affected differently in diet- and genetically-induced obesity, but both are associated with elevated intestinal inflammation and alterations of the Wnt pathway towards enhancing tumorigenesis.
... Studying the effect of folic acid and vitamins B2, B6 and B12 on the expression of the gene encoding p53 protein in mice, Liu et al. [29] found that a 10-week deficit of all of these compounds resulted in a much greater effect compared to a deficit of only folic acid in terms of the induction of DNA damage in the p53 gene region vulnerable to mutations, hypomethylation and a significant reduction of its expression and the expression of its regulator MDM2. The same author, in a later work [30] on carcinogenesis in mice BAT-LacZxApc1638N showed that the deficit of all these B vitamins in animals induced the activation of the major signaling Wnt pathway in rectal carcinogenesis as well as mutations in the suppressor gene Apc, together with an increase in the expression of Jun and Pitx2 genes involved in the processes relevant to the development of tumors, i.e. cell proliferation, transformation and apoptosis. The participation of vitamins B2 and B6 in the metabolism of homocysteine, which is involved in the etiology of colorectal cancer, justifies the recognized inverse correlation between the doses of these vitamins consumed during the day and a decrease of the risk of this cancer, as demonstrated in the Women's Health Initiative Observational Study conducted in the USA [27]. ...
The importance of vitamins in the prevention of cancer has attracted the attention of consumers, nutritionists and scientists for decades. The mechanisms of carcinogenesis, extended in the context of the function of vitamins, i.e. regulation of and participation in metabolic processes in the cell, suggest a substantial impact of these compounds on the initial stages of carcinogenesis. One-carbon metabolism involving folic acid, vitamins B2, B6 and B12, and folate metabolism doesn't only generate methyl groups, thus determining epigenetic processes, modifications of the genome and carcinogenesis. It also provides the compounds involved in the DNA synthesis and repair processes, especially the synthesis of purines and pyrimidines and the conversion of dUMP (2-deoxyuridine monophosphate) to dTMP (2-deoxythymidine monophosphate). In light of these pathways, folate, together with vitamins B2, B6 and B12, became a subject of interest as compounds whose deficit or surplus can potentially have an impact on the processes of carcinogenesis. Literature reports, however, do not fully confirm that the influence on the synthesis of nucleotides is connected with the inhibition of carcinogenesis. The impact of individual vitamins involved in one-carbon metabolism on carcinogenesis and their role in the prevention of these conditions depend on the type of cancer and the dose administered. Nevertheless, the research conducted makes it possible to conclude a considerable and probably long-underestimated role of these compounds in the prevention of serious, difficult to treat or incurable diseases.
... Mice possessing one allele with this mutation in the Apc gene (amino acid 1638) spontaneously develop small intestinal neoplasms beginning at approximately 10 weeks of age, some of which remain as adenomas and some which advance to adenocarcinomas over the ensuing 6-8 weeks [24]. Although the predilection for developing small, rather than large, intestinal tumors is a common phenomenon in genetically-engineered models of CRC-such as the widely utilized Apc min mouse -the small intestinal tumorigenesis in the Apc 1638N mouse is an appropriate tool for modelling CRC because its latency, burden and response to dietary perturbations such as inadequacy of 1-carbon nutrients and obesity [25,26] closely match the situation in the human colon. ...
... Combining pups of both genotypes, paternal diet had no impact on weaning weight for male or female offspring (p>0.05). Considering the growth curve of the Apc mice retained for tumor studies between group differences in body weight became apparent; female offspring of DEF and SUPP fathers were significantly lighter than those of CTRL fathers over the entire 25 week study (Repeated measures ANOVA p<0.05). At the final time point the weight of DEF and Values are mean ± SEM. * Significantly different from CTRL (p<0.05). ...
Background:
The importance of maternal nutrition to offspring health and risk of disease is well established. Emerging evidence suggests paternal diet may affect offspring health as well.
Objective:
In the current study we sought to determine whether modulating pre-conception paternal B vitamin intake alters intestinal tumor formation in offspring. Additionally, we sought to identify potential mechanisms for the observed weight differential among offspring by profiling hepatic gene expression and lipid content.
Methods:
Male Apc1638N mice (prone to intestinal tumor formation) were fed diets containing replete (control, CTRL), mildly deficient (DEF), or supplemental (SUPP) quantities of vitamins B2, B6, B12, and folate for 8 weeks before mating with control-fed wild type females. Wild type offspring were euthanized at weaning and hepatic gene expression profiled. Apc1638N offspring were fed a replete diet and euthanized at 28 weeks of age to assess tumor burden.
Results:
No differences in intestinal tumor incidence or burden were found between male Apc1638N offspring of different paternal diet groups. Although in female Apc1638N offspring there were no differences in tumor incidence or multiplicity, a stepwise increase in tumor volume with increasing paternal B vitamin intake was observed. Interestingly, female offspring of SUPP and DEF fathers had a significantly lower body weight than those of CTRL fed fathers. Moreover, hepatic trigylcerides and cholesterol were elevated 3-fold in adult female offspring of SUPP fathers. Weanling offspring of the same fathers displayed altered expression of several key lipid-metabolism genes. Hundreds of differentially methylated regions were identified in the paternal sperm in response to DEF and SUPP diets. Aside from a few genes including Igf2, there was a striking lack of overlap between these genes differentially methylated in sperm and differentially expressed in offspring.
Conclusions:
In this animal model, modulation of paternal B vitamin intake prior to mating alters offspring weight gain, lipid metabolism and tumor growth in a sex-specific fashion. These results highlight the need to better define how paternal nutrition affects the health of offspring.
... Frederick, MD); heterozygosity for this Apc mutation (codon 1638) results in the formation of 1-5 small bowel adenomas or carcinomas by 8 months of age. Although the predilection for developing small, rather than large, intestinal tumors is a common phenomenon in genetically-engineered models of CRC-such as the widely utilized Apc min mouse-the small intestinal tumorigenesis in the Apc 1638N animal appears to be highly relevant to colonic carcinogenesis since it responds to dietary modifications like obesity and 1-carbon nutrient depletion in the same fashion as to what occurs in the colon [18,19]. ...
Obesity is a risk factor for colorectal cancer (CRC), and alterations in the colonic microbiome and metabolome may be mechanistically involved in this relationship. The relative contribution of diet and obesity per se are unclear. We compared the effect of diet- and genetically-induced obesity on the intestinal microbiome and metabolome in a mouse model of CRC. Apc1638N mice were made obese by either high fat (HF) feeding or the presence of the Leprdb/db (DbDb) mutation. Intestinal tumors were quantified and stool microbiome and metabolome were profiled. Genetic obesity, and to a lesser extent HF feeding, promoted intestinal tumorigenesis. Each induced distinct microbial patterns: taxa enriched in HF were mostly Firmicutes (6 of 8) while those enriched in DbDb were split between Firmicutes (7 of 12) and Proteobacteria (5 of 12). Parabecteroides distasonis was lower in tumor-bearing mice and its abundance was inversely associated with colonic Il1b production (p<0.05). HF and genetic obesity altered the abundance of 49 and 40 fecal metabolites respectively, with 5 in common. Of these 5, adenosine was also lower in obese and in tumor-bearing mice (p<0.05) and its concentration was inversely associated with colonic Il1b and Tnf production (p<0.05). HF and genetic obesity differentially alter the intestinal microbiome and metabolome. A depletion of adenosine and P.distasonis in tumor-bearing mice could play a mechanistic role in tumor formation. Adenosine and P. distasonis have previously been shown to be anti-inflammatory in the colon and we postulate their reduction could promote tumorigenesis by de-repressing inflammation.
... For example, we have found the Apc 1638N mouse useful in studying nutritional modulation of CRC as it has both an intermediate tumor burden and latency. In our hands 70% on these mice mouse develops 1-3 small intestinal tumors by the age of 7-8 months and tumorigenesis can be modulated by dietary B vitamin intake [11] and maternal B vitamin intake [12]. Furthermore, similar to the human situation others have shown that obesity promotes tumorigenesis in this model [13]. ...
Several genetically engineered mouse (GEM) models of colorectal cancer have been developed and are a mainstay in our efforts to identify means of preventing and treating this disease. Many of these models involve a germline disruption of the adenomatous polyposis coli (Apc) tumor suppressor gene and share the limitation that the great preponderance of tumors appear in the small rather than large intestine. In recent years efforts have been made to increase the similarity of these models to human sporadic colorectal cancer by disrupting Apc in a tissue-specific fashion using the Cre-Lox system so that the genetic aberrations are confined to the colonic epithelium. These models have shown great promise but reproducible and high penetrance colon-specific tumorigenesis has not yet been achieved without invasive techniques to introduce the Cre enzyme. We therefore sought to create a new model with high penetrance colon-specific tumorigenesis but without the need for exogenous Cre administration. We utilized existing mice possessing a conditional knock out for the Apc gene and a latent activated Kras allele and crossed them with mice expressing Cre recombinase solely in the large intestine. Using this approach we generated mice that developed 1- 9 colonic adenomas per mouse (average 4.3) but without any tumors in the small intestine or cecum. No invasive tumors were observed. Despite the apparent lack of invasion, the geographical correctness, complete penetrance and intermediate tumor burden make this model a promising addition to our toolkit for the study of colorectal cancer treatment and prevention.
... After 8 weeks of feeding, rats exhibit Apc +/+ crossed to SHMT genotype as indicated ( a 35% decrease in colon folate levels [83], but after 20 weeks there is a 72% decline [75]. The data in mice seems odd, in that the colon folate levels are more depleted after 5 weeks of dietary intervention [68] than after 16 weeks [84], but these studies are confounded by alterations in choline and other B vitamins. Further, these mouse studies were carried out in the absence of methods for reducing assimilation of microbial-produced folates in the colon, and there is a possibility that with the extended intervention time (16 weeks) animals adapt to reduced dietary availability of nutrients through increased coprophagy. ...
... Further evidence for the importance of severe dietary restrictions to induce a meaningful decline in folate status is the finding that 32 weeks of feeding 0.5 mg/kg folate without antibiotics or wirebottom cages resulted in no change in blood folate status [78]. It would be useful to have data on the impact of folate depletion on colonic folate status with and without contribution from microbially produced folates, but that information is not available without the confounding of choline deficiency [68] or riboflavin, B6, and B12 deficiencies [84]. A systematic evaluation of dietary factors on target tissue folate status would be informative. ...
Fortification of grains has resulted in a positive public health outcome vis-a-vis reduced incidence of neural tube defects. Whether folate has a correspondingly beneficial effect on other disease outcomes is less clear. A role for dietary folate in the prevention of colorectal cancer has been established through epidemiological data. Experimental data aiming to further elucidate this relationship has been somewhat equivocal. Studies report that folate depletion increases DNA damage, mutagenesis, and chromosomal instability, all suggesting inhibited DNA repair. While these data connecting folate depletion and inhibition of DNA repair are convincing, we also present data demonstrating that genetic inhibition of DNA repair is protective in the development of preneoplastic colon lesions, both when folate is depleted and when it is not. The purpose of this paper is to (1) give an overview of the data demonstrating a DNA repair defect in response to folate depletion, and (2) critically compare and contrast the experimental designs utilized in folate/colorectal cancer research and the corresponding impact on tissue folate status and critical colorectal cancer endpoints. Our analysis suggests that there is still an important need for a comprehensive evaluation of the impact of differential dietary prescriptions on blood and tissue folate status.
