Forget The Antioxidants? Researchers Cast Doubt On Role Of Free Radicals In Aging (2/17/09)
Author summary of the open-access paper:
Deletion of the Mitochondrial Superoxide Dismutase sod-2 Extends Lifespan in Caenorhabditis elegans
For more than 40 years, the prevailing explanation of why we get old has been tied to what is called oxidative stress. This theory postulates that when molecules like free radicals, oxygen ions and peroxides build up in cells, they overwhelm the cells' ability to repair the damage they cause, and the cells age.
An industry of "alternative" antioxidant therapies -- such as Vitamin E or CoQ10 supplements in megadose format -- has sprung up as the result of this theory. However, clinical trials have not shown that these treatments have statistically significant effects.
And now researchers at McGill University, in a study published in the February issue of the journal PLoS Genetics, are calling the entire oxidative stress theory into question. Their results show that some organisms actually live longer when their ability to clean themselves of this toxic molecule buildup is partially disabled. Collectively, these molecules are known as reactive oxygen species, or ROS for short.
Author summary of the open-access paper:
Deletion of the Mitochondrial Superoxide Dismutase sod-2 Extends Lifespan in Caenorhabditis elegans
In this paper, we examine the oxidative stress theory of aging using C. elegans as a model system. This theory proposes that aging results from the accumulation of molecular damage caused by reactive oxygen species (ROS). To test this theory, we examined the effect of deleting each of the five individual superoxide dismutase (SOD) genes on lifespan and sensitivity to oxidative stress. Since SOD acts to detoxify ROS, the oxidative stress theory predicts that deletion of sod genes should increase oxidative stress and decrease lifespan. However, in contrast to yeast, flies, and mice, where loss of either cytoplasmic or mitochondrial SOD results in decreased lifespan, we find that none of the sod deletion mutants in C. elegans exhibits a shortened lifespan despite increased sensitivity to oxidative stress. Surprisingly, we find that sod-2 mutant worms have extended lifespan and even worms with the primary cytoplasmic, mitochondrial, and extracellular sod genes deleted can live longer than wild-type worms. By examining genetic interactions with other genes known to extend lifespan and by comparing the phenotype of worms lacking sod-2 to that of known long-lived mitochondrial mutants such as clk-1 or isp-1, we provide evidence that the loss of sod-2 extends lifespan through alteration of mitochondrial function.