Aging and high concentrations of glucose potentiate injury to mitochondrial DNA

Deletions of mitochondrial DNA (mtDNA) are associated with aging and several chronic diseases. We have reported heterogeneous mutations between base pair 8468 and 13446 in mtDNA, the region known as the "common" deletion, in muscle of older humans with impaired glucose tolerance or diabetes mellitus. To further characterize potential effects of age and glycemia on mtDNA integrity, we studied corpulent JCR:LA-cp rats that are characterized by insulin resistance, hyperinsulinemia, and hyperlipidemia, factors strongly associated with both aging and cardiovascular disease. In addition to skeletal muscle, we isolated vascular smooth muscle cells (VSMC) from aortas of 6-, 12-, and 17-month-old rats and exposed them to 5-, 25-, 62-, and 100-mM glucose or a combination of hypoxanthine (100 microM) and xanthine oxidase (0.025 U/ml) to generate reactive oxygen species in separate cultures. Long- and short-fragment and nested polymerase chain reaction was used to detect mutations in the common deletion region. The data demonstrate that aging and the cp genotype confer susceptibility to mtDNA deletions in vivo and that high glucose concentrations can induce mtDNA mutations in vitro. Accordingly, aging and glucose-related oxidative stress and possibly hyperinsulinemia may contribute to alterations in mitochondrial gene integrity and the cp genotype appears to increase the susceptibility of muscle to the age-related accumulation of mtDNA mutations.