Oxidative damage to DNA: relation to species metabolic rate and life span.

Oxidative damage to DNA is caused by reactive by-products of normal metabolism, as well as by radiation. Oxidized DNA bases excised by DNA repair enzymes and excreted in urine were measured in four different species to determine the relation between specific metabolic rate (ml of O2 consumed per gram of body weight per hr) and oxidative DNA damage. An average of 6.04 nmol of thymine glycol per kg/day and 2.58 nmol of thymidine glycol per kg/day were found in mouse urine and 1.12 nmol of thymine glycol per kg/day and 0.95 nmol of thymidine glycol per kg/day were found in monkey urine. On a body weight basis, mice excrete 18 times more thymine glycol plus thymidine glycol than do humans, and monkeys excrete 4 times more thymine glycol plus thymidine glycol than do humans. When results among mice, rats, monkeys, and humans are compared, specific metabolic rate correlates highly with oxidative DNA damage. These findings are consistent with the theory that free radical-induced DNA damage may play a central role in the aging process.