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Photomicrographs of the substantia nigra and locus ceruleus
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Purpose: Mitochondrial dysfunction has been implicated in the development of idiopathic Parkinson's disease. In this study, it was aimed to investigate the relationship between mitochondrial respiratory chain enzyme deficiency and variants in ND2 and ND4 region of Complex I and expressions of these genes. Complex IV activity and glutathione level were also studied. Methods: Activities of Complex I, Complex IV, citrate synthase and glutathione levels were measured from muscle biopsy samples of 19 idiopathic Parkinson's Disease patients. Entire ND2 and ND4 regions of Complex I were screened by sequencing and expression levels of these regions were also examined by using relative quantitative RT-PCR. Results: A significant decrease in Complex I and IV activities was found in Parkinson's Disease patients (19.73 ± 8.24 U/mg protein, 11.51 ± 6.45 U/mg protein) compared with the control group (31.48 ± 8.28 U/mg protein, 30.02 ± 14.76 U/mg protein), respectively. Although several sequence variants were detected in ND2 and ND4 genes, they didn't account for the decrease in Complex I activity. ND2 (19 % and 21 %) and ND4 (14 % and 13 %) mRNA expressions were reduced in two of 19 patients. Conclusion: Taken together, Complex I and IV dysfunctions and mitochondrial abnormalities might be the result of oxidative stress contributing to the pathogenesis of idiopathic Parkinson's Disease since we found that reduced glutathione levels were decreased 47% in these patients. 2009
Reaction of some picolines 5 with 1-chloro-2,4-dinitrobenzene (6) in acetone furnished methyl-substituted 2,4-dinitrophenylpyri-dinium chlorides 7. Further reaction with phenyl(pyridyl)carbonyl hydrazides 8 at room temperature furnished isolable 2,4-dinitroanilino derivatives 9, which were then refluxed in a water:dioxane mixture (1:4, v/v) to furnish the methyl-substituted phenyl(pyridyl)carbonyl iminopyridinium ylides 10. Reduction of the ylides with NaBH4 finally gave rise to the desired methyl-substituted phenyl(pyridyl)carbonylamino-1,2,3,6-tetrahydropyridines 11. The anti-inflammatory activities of 11a–11l were determined with the carrageenan-soaked sponge model of inflammation in Sprague-Dawley rats, and the analgesic effects of these derivatives were assessed by suppression of acetic acid-induced writhing in male Swiss albino mice. All compounds tested showed moderate to good anti-inflammatory and analgesic effects compared with indomethacin. Compound 11k was the most active analgesic, and 11h was the most effective anti-inflammatory agent among the methyl-substituted tetrahy-dropyridines.
The mitochondrial respiratory chain and oxidative phosphorylation system are responsible for the production of ATP by aerobic metabolism. Defects of the respiratory chain are increasingly recognised as important causes of human disease, and neurodegenerative disorders in particular. This article will seek to review the clinical and biochemical effects of respiratory chain defects, and summarise what is known about the molecular mechanisms that underlie them. Increasing age is also associated with a decline in mitochondrial function. The biochemical correlates of this dysfunction and the possible molecular defects that may cause it will also be reviewed.
Idiopathic Parkinson's disease (PD) involves a documentable decline in the activity of mitochondrial complex I in substantia nigra (1-3). We have EPR spectroscopy to investigate complex I in human substantia nigra and globus pallidus. EPR signals characteristic of the iron-sulfur centers of complexes I and II were observed with globus pallidus, with no significant difference between control and PD. These complex 1 signals could not be clearly observed in substantia nigra. Instead, nitric oxide (NO.) radicals in PD nigra were detected at g approximately 2.08, 1.98 due to [haem-NO] formation. Although an EPR signal indicative of haem-NO was observed with control nigra, it lacked the distinctive g approximately 1.98 trough observed with PD nigra. As PD is associated with a reactive gliosis, the difference in the haem-NO EPR signal, between control and PD nigra, may result from cytotoxic NO. generated by microglia in PD substantia nigra.
Complex I deficiency, either specific or associated with other respiratory chain defects, has been identified in myopathies, encephalomyopathies and in three 'neurodegenerative' disorders: Parkinson's disease, dystonia and Leber's hereditary optic neuropathy. The complex I defect is expressed in blood in all these three but, to date, only in LHON have specific mitochondrial DNA mutations been identified. Recent work with rho degrees cybrids indicates that, in a subgroup of patients at least, the complex I deficiency is determined by mtDNA, in contrast to dystonia where a nuclear gene defect or toxic influence appears a more likely cause. The actions of specific toxins, e.g., MPTP continue to play an important role in our understanding of pathogenesis of neurodegeneration, particularly in PD.
Respiratory chain dysfunction has been identified in several neurodegenerative disorders. In Friedreich's ataxia (FA) and Huntington's disease (HD), where the respective mutations are in nuclear genes encoding non-respiratory chain mitochondrial proteins, the defects in oxidative phosphorylation are clearly secondary. In Parkinson's disease (PD) the situation is less clear, with some evidence for a primary role of mitochondrial DNA in at least a proportion of patients. The pattern of the respiratory chain defect may provide some clue to its cause; in PD there appears to be a selective complex I deficiency; in HD and FA the deficiencies are most severe in complex II/III with a less severe defect in complex IV. Aconitase activity in HD and FA is severely decreased in brain and muscle, respectively, but appears to be normal in PD brain. Free radical generation is thought to be of importance in both HD and FA, via excitotoxicity in HD and abnormal iron handling in FA. The oxidative damage observed in PD may be secondary to the mitochondrial defect. Whatever the cause(s) and sequence of events, respiratory chain deficiencies appear to play an important role in the pathogenesis of neurodegeneration. The mitochondrial abnormalities induced may converge on the function of the mitochondrion in apoptosis. This mode of cell death is thought to play an important role in neurodegenerative diseases and it is tempting to speculate that the observed mitochondrial defects in PD, HD and FA result directly in apoptotic cell death, or in the lowering of a cell's threshold to undergo apoptosis. Clarifying the role of mitochondria in pathogenesis may provide opportunities for the development of treatments designed to reverse or prevent neurodegeneration.
1-Methyl-4-phenyl-1,2,3,6-tetrahydropyridine (MPTP) treatment leads to marked depletion of dopamine (DA) levels in the nigrostriatal pathway and dopaminergic neuronal degeneration in caudate-putamen and substantia nigra. MPTP is believed to inhibit complex I of the electron transport system leading to the generation of reactive oxygen species. We sought to test the hypotheses that MPTP treatment: (1) leads to dopamine depletion; (2) causes extensive mitochondrial DNA damage, and (3) that these effects would be age dependent. The levels of dopamine and its metabolites, DOPAC and HVA were analyzed by HPLC equipped with electrochemical detection. DNA damage was measured by quantitative PCR in both mitochondrial and nuclear (beta-polymerase) targets from the caudate-putamen, substantia nigra and cerebellum regions of control and MPTP-treated mice. The age groups studied were 22 days and 12 months. MPTP produced no significant effect on the levels of dopamine and its metabolites in young mice whereas in old, there was a significant decrease in this neurotransmitter system after MPTP administration. These 12-month-old mice, when compared to the young mice, showed a significant increase in mitochondrial DNA damage in the caudate-putamen and cerebellum. The latter region also displayed a significant increase in DNA damage in a nuclear gene. After treatment with MPTP, there was an age-dependent increase in DNA damage in mitochondria of the caudate-putamen while there was no significant DNA damage in the nuclear target. MPTP treatment led to damage in both mitochondrial and nuclear DNA of the substantia nigra, while there was no damage in either mitochondria or nucleus in cerebellum which was used as a negative control.
This review attempts to summarize our present state of knowledge of mitochondria in relation to a number of areas of biology, and to indicate where future research might be directed. In the evolution of eukaryotic cells mitochondria have for a long time played a prominent role. Nowadays their integration into many activities of a cell, and their dynamic behavior as subcellular organelles within a cell and during cell division are a major focus of attention. The crystal structures of the major complexes of the electron transport chain (except complex I) have been established, permitting increasingly detailed analyses of the important mechanism of proton pumping coupled to electron transport. The mitochondrial genome and its replication and expression are beginning to be understood in considerable detail, but more questions remain with regard to mutations and their repair, and the segregation of the mtDNA in oogenesis and development. Much emphasis and a large effort have recently been devoted to understand the role of mitochondria in programmed cell death (apoptosis). The understanding of their central role in mitochondrial diseases is a major achievement of the past decade. Finally, various drugs have traditionally played a part in understanding biochemical mechanisms within mitochondria; the repertoire of drugs with novel and interesting targets is expanding.
