Reactive oxygen species (ROS) primarily arise as by-products of normal metabolic activities and are thought to influence the etiology of age-related diseases. If ROS contribute to aging, then the aging process would be slowed if either the production of ROS were reduced or the endogenous anti-oxidant or repair activities were increased. Indeed, genetic mutations and manipulations that confer resistance to oxidative stress also cause extended life-span; however, dietary antioxidant supplements have been shown to have very limited effects on longevity.
It was decided to test the oxygen radical theory of aging by the development of synthetic catalytic compounds that ameliorate oxidative stress in several disease models and partially rescue mice that are mutant for mitochondrial superoxide dismutase (SOD). It was tested the effect of two mimetics, EUK-8 and EUK-134, on life span in Caenorhabditis elegans. In vitro, these compounds exhibit both SOD- and catalase-like activities (they are SOD/catalase mimetics). EUK-134 is an analog of EUK-8, with increased catalase activity and equivalent SOD activity (13).
Synchronous adult hermaphrodite populations of worms were treated in S medium with various concentrations of mimetics and maintained those populations concurrently with control populations of untreated wild-type worms and, in some experiments, of long-lived age-l(hx546) mutant worms. In every experiment, treatment of wild-type worms with SOD/catalase mimetics significantly increased mean and maximum life span. Treatment of wild-type worms with 0.05mM EUK-134 resulted in an increase in mean life span of 54%. Higher concentrations of EUK-134 and various concentrations of ELK-8 also extended life span. No overall dose response was observed. These compounds probably enter the worm through ingestion alone. As the worms age, they feed less, and consequently there is likely to be an increasing limitation on the amount of drug taken up.
Genetic approach was performed in order to determine the mode of action of the mimetics. It was examined the effects of EUK-134 on the life span of a mutant worm strain that exhibits accelerated aging. Mutation of the mev-l gene, encoding the cytochrome b subunit of succinate dehydrogenase (complex 11) of the electron transport chain, results in an elevated accumulation of oxidative damage during aging, an increased sensitivity to oxygen, and a life-span shortened by 37%. Treatment with 0.5mM EUK-134 restored a normal life-span to the mev-l(kn1) mutants by increasing their life-span by 67%. These results are consistent with amelioration of an endogenous and chronic oxidative stress.
Genetic manipulation of the life span is generally associated with pleiotropic effects on life history traits such as reduced fertility and altered growth rate. Consequently, it was tested whether the SOD/catalase mimetics affected such trails. Treatment of wild-type worms with mimetics did not significantly alter either hermaphrodite self-fertility or body size measured at two stages during development. These results suggest that the mimetic-associated life-span increase is not due to a nonspecific reduction in metabolism. This is consistent with the observation that the treated worms did not appear moribund until close to the end of the extended life span.
It was demonstrated that treatment of adult hermaphrodite worms with SOD/catalase mimetics causes a large increase in life span. In addition, these compounds rescue the life-span defect of the mev-l(kn1) mutation. It could be stated that EUK-8 and ELK-134 extend life span by augmenting natural antioxidant defenses without having any overt effects on other trails. These results suggest that endogenous oxidative stress is a major determinant of the rate of aging.