vitamin-b-12 and Mitochondrial-Diseases

The active site of oxidative phosphorylation and adenosine triphosphate (ATP) biosynthesis is proposed to consist of thioretinaco, a complex of two molecules of thioretinamide with cobalamin, oxidized to the disulfonium derivative, thioretinaco ozonide, and complexed with oxygen, nicotinamide adenine dinucleotide, inorganic phosphate and ATP. Reduction of the active site complex by electrons from mitochondrial electron transport complexes releases ATP from binding to the active site, producing nicotinamide riboside and hydroperoxide and generating a membrane potential from proton transport to the active site. Opening of the mitochondrial permeability transition pore from decreased mitochondrial melatonin leads to loss of the active site complex from mitochondrial membranes, as observed in aging and dementia. Loss of the active site complex from mitochondria also results from opening of the permeability transition pore and from decomposition of the disulfonium active site by electrophilic carcinogens, oncogenic viruses and microbes which cause depletion of adenosyl methionine because of increased biosynthesis of polyamines, and by free radical oxygen species generated by ionizing radiation, and by catecholamines. Thus the loss of thioretinaco ozonide from mitochondria produces the impaired oxidative phosphorylation, oxidative stress, calcium influx, apoptosis, aerobic glycolysis, and mitochondrial dysfunction that are observed in chemical carcinogenesis, microbial carcinogenesis, traumatic brain injury, aging and dementia.

Topics: Adenosine Triphosphate; Carcinogenesis; Catalytic Domain; Heterocyclic Compounds; Homocysteine; Humans; Mitochondria; Mitochondrial Diseases; Neoplasms; Oxidation-Reduction; Oxidative Phosphorylation; Oxidative Stress; Oxygen; Reactive Oxygen Species; Vitamin B 12

Classical (or isolated) methylmalonic acidemia (MMA) is a heterogeneous inborn error of metabolism most typically caused by mutations in the vitamin B12-dependent enzyme methylmalonyl-CoA mutase (MUT). With the improved survival of individuals with MMA, chronic kidney disease has become recognized as part of the disorder. The precise description of renal pathology in MMA remains uncertain.. Light microscopy, histochemical, and ultrastructural studies were performed on the native kidney obtained from a 19-year-old patient with mut MMA who developed end stage renal disease and underwent a combined liver-kidney transplantation.. The light microscopy study of the renal parenchyma in the MMA kidney revealed extensive interstitial fibrosis, chronic inflammation, and tubular atrophy. Intact proximal tubules were distinguished by the widespread formation of large, circular, pale mitochondria with diminished cristae. Histochemical preparations showed a reduction of cytochrome c oxidase and NADH activities, and the electron microscopy analysis demonstrated loss of cytochrome c enzyme activity in these enlarged mitochondria.. Our results demonstrate that the renal pathology of MMA is characterized by megamitochondria formation in the proximal tubules in concert with electron transport chain dysfunction. Our findings suggest therapies that target mitochondrial function as a treatment for the chronic kidney disease of MMA.

Topics: Amino Acid Metabolism, Inborn Errors; Atrophy; Diet, Protein-Restricted; Female; Humans; Kidney; Kidney Diseases; Kidney Tubules, Proximal; Metabolism, Inborn Errors; Methylmalonyl-CoA Mutase; Mitochondria; Mitochondrial Diseases; Nephritis; Vitamin B 12; Young Adult