Age-related increase of superoxide generation in the brains of mammals and birds

Oxidative stress, an imbalance between endogenous levels of oxygen radicals and antioxidative defense, increases with aging. However, it is not clear which of these two factors is the more critical. To clarify the production of oxygen radicals increases with age, we examined oxygen radical-dependent chemiluminescent signals in ex vivo brain slices using a novel photonic imaging method. The chemiluminescent intensity was significantly decreased by the membrane permeable superoxide dismutase (SOD)/catalase mimic, but not by Cu,Zn-SOD. Inhibitors for complex I, III, and IV of the mitochondrial electron transport chain transiently enhanced the chemiluminescent signal. The superoxide-dependent chemiluminescent intensity in senescence accelerated mouse (SAM) brain tissues increases with age. Moreover, the slope of the age-dependent increase was steeper in SAMP10, a strain characterized by a short lifespan and atrophy in the frontal cerebral cortex, than the senescence-resistant strain SAMR1, which has a longer lifespan. An increase in chemiluminescence with age was also observed in C57/BL6 mice, Wistar rats, and pigeons, although levels of chemiluminescence were lower in the pigeons than murines. The rate of age-related increases of superoxide-dependent chemiluminescence was inversely related to the maximum lifespan of the animals. The activity of superoxide dismutase was unchanged during the aging process in the brain. This suggested that superoxide production itself may increase with age. We speculated that reactive oxygen may be a signal to determine the aging process.