Caloric restriction decreases mitochondrial free radical generation at complex I and lowers oxidative damage to mitochondrial DNA in the rat heart

The effect of caloric restriction (CR) (40%) on the rates of mitochondrial H2O2 production and oxygen consumption and oxidative damage to nuclear DNA (nDNA) and mitochondrial DNA (mtDNA) was studied for short-term (6-wk) and long-term (1-year) periods in the heart of young and old rats. Short-term CR did not change any of the parameters measured. However, long-term CR significantly decreased the rate of mitochondrial H2O2 generation (by 45%) and significantly lowered oxidative damage to mtDNA (by 30%) without modifying damage to nDNA. The decrease in H2O2 production occurred exclusively at the complex I free radical generator of the respiratory chain. The mechanism allowing that decrease was not a simple decrease in mitochondrial oxygen consumption. Instead, the mitochondria of caloric-restricted animals released fewer oxygen radicals per unit electron flow in the respiratory chain. This was due to a decrease in the degree of reduction of the complex I generator in caloric-restricted mitochondria. The results are consistent with die concept that CR decreases the aging rate at least in part by decreasing the rate of mitochondrial oxygen radical generation and then the rate of attack on mtDNA.