Oxidative damage to mitochondrial DNA and its relationship to diabetic complications

Increased oxidative stress induced by hyperglycemia may contribute to the pathogenesis of diabetic complications. Oxidative stress is known to increase the conversion of deoxyguanosine (dG) to 8-hydroxydeoxyguanosine (8-OHdG) in DNA, which is linked to increased mitochondrial DNA (mtDNA) deletions. We investigated mtDNA deletions and 8-OHdG in the muscle DNA of non-insulin-dependent diabetes mellitus (NIDDM) patients. mtDNA deletion of 4977 bp (delta mtDNA4977) and the content of 8-OHdG in the muscle DNA of the NIDDM patients were much higher than those of the control subjects. There was a significant correlation between delta mtDNA4977 and the 8-OHdG content (P < 0.0001). Both delta mtDNA4977 and the 8-OHdG content were also correlated with the duration of diabetes. Delta mtDNA4977 and the 8-OHdG content in muscle DNA increased in proportion to the severity of diabetic nephropathy and retinopathy. This is the first report that an increase in delta mtDNA4977 and 8-OHdG is proportional to the severity of diabetic complications. Oxidative mtDNA damage is speculated to contribute to the pathogenesis of diabetic complications though a defect in mitochondrial oxidative phosphorylation or other mechanisms. 8-OHdG and delta mtDNA4977 are useful markers to evaluate oxidative mtDNA damage in the diabetic patients.