Liver mitochondrial DNA damage and genetic variability of Cytochrome b - a key component of the respirasome - drive the severity of fatty liver disease.

BACKGROUND AND AIMS: The progression of nonalcoholic fatty liver disease (NAFLD) into severe histological forms (steatohepatitis - NASH) is paralleled by the occurrence of complex molecular processes. Mitochondrial dysfunction is a hallmark feature of advanced disease. Mitochondrially encoded cytochrome B (cytochrome b, MT-CYB), a member of the oxidative phosphorylation system, is a key component of the respirasome supercomplex. Here, we hypothesized that NAFLD severity is associated with liver tissue cytochrome b mutations and damaged mitochondrial DNA (mtDNA). METHODS: We included 252 liver specimens of NAFLD patients - in whom histological disease ranged from mild to severe - which were linked to clinical and biochemical information. Tissue molecular explorations included MT-CYB sequencing and analysis of differential mtDNA damage. Profiling of circulating Krebs cycle metabolites and global liver transcriptome was performed in a subsample of patients. Tissue levels of 4-hydroxynonenal - a product of lipid peroxidation and 8-hydroxy-2'-deoxyguanosine, a marker of oxidative damage - were measured. RESULTS: Compared to simple steatosis, NASH is associated with a higher level of MT-CYB variance, 12.1 vs. 15.6 substitutions per 103  bp (P = 5.5e-10). The burden of variants was associated with increased levels of 2-hydroxyglutarate, branched-chain amino acids, and glutamate, and changes in the global liver transcriptome. Liver mtDNA damage was associated with advanced disease and inflammation. NAFLD severity was associated with increased tissue levels of DNA oxidative adducts and lipid peroxyl radicals. CONCLUSION: NASH is associated with genetic alterations of the liver cellular respirasome, including high cytochrome b variation and mtDNA damage, which may result in broad cellular effects.

Retrospective biochemical screening of fatty acid oxidation disorders in postmortem livers of 418 cases of sudden death in the first year of life.

OBJECTIVE: Fatty acid oxidation (FAO) disorders are frequently reported as the cause of sudden and unexpected death, but their postmortem recognition remains difficult. We have devised a biochemical protocol in which informative findings in liver tissue are microvesicular steatosis, elevated concentrations of C8-C16 fatty acids, glucose depletion, and low carnitine concentration. STUDY DESIGN: We analyzed 27 cases representing five FAO disorders and compared the results with those obtained in a retrospective blinded analysis of 418 cases of sudden infant death (313 SIDS, 45 infections, and 34 accidents and abuse). RESULTS: All cases of accidents and abuse correctly tested negative. Among the others, 25 (6%) showed at least two abnormal findings. Of these, 14 closely matched the biochemical profiles seen in specific FAO disorders. These included 2 cases with medium-chain acyl-CoA dehydrogenase deficiency, 4 cases consistent with glutaric acidemia type 2, 4 cases with either very long-chain acylcoenzyme A dehydrogenase deficiency or long-chain 3-hydroxy-acyl-coenzyme A dehydrogenase deficiency, and 4 cases predicted to be affected with carnitine uptake defect. CONCLUSION: The results of this study support the view that approximately 5% of all cases of sudden infant death are likely caused by an FAO disorder.

Glutaric aciduria type I: unusual biochemical presentation.

We describe a patient with glutaryl-coenzyme A dehydrogenase deficiency, demonstrated by a residual enzyme activity of only 1% in cultured fibroblasts. Although the clinical presentation was typical of glutaric aciduria type I, the urine concentrations of glutaric, glutaconic, and 3-hydroxyglutaric acids remained normal, even during episodes of clinical decompensation. An increased free glutarate level was demonstrated only in cerebrospinal fluid.