Due to reverse electron transfer, mitochondrial H2O2 release increases with age in human vastus lateralis muscle although oxidative capacity is preserved.
Age-related changes in mitochondrial H2O2 release (MHR) could be responsible for an increase in oxidative stress in skeletal muscle and participate in the development of sarcopenia. We compared MHR in vastus lateralis biopsies obtained from young (23.5+/-2.0 year, n=6) and elderly (67.3+/-1.5 year, n=6) healthy sedentary men. Isolated mitochondria were incubated in the presence of glutamate/malate/succinate, with or without rotenone. Muscle fat oxidative capacity, citrate synthase, complex II, complex III, and cytochrome c oxidase activities were also measured. In parallel, we analyzed in gastrocnemius of young male Wistar rats (n=6), the impact of lidocaine (local anesthetic used in humans) on mitochondrial respiration and MHR. In humans, muscle oxidative capacity was preserved with age but muscle MHR was markedly enhanced in elderly subjects compared to young adults (+175%, P<0.05). Rotenone abolished this increase, demonstrating that it was due to a free radical release during reverse electron transfer from complex II towards complex I. Lidocaine can interfere with MHR measurements (intra-muscular injection in rats) but it can be avoided by minimizing contact with muscle (small multiple subcutaneous injections in humans). Physiologic consequences of the observed increase in muscle MHR with aging remain to be determined.