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Guard, not crook

Can a substance that isn’t good for your hair and skin be good for overall well being? Well, if it is hydrogen peroxide, a by-product of the metabolic activity that goes inside your body, the answer maybe “yes”. So thinks Paula Ludovico, a biologist at the University of Minho in Portugal.

Implicated in the greying of hair and skin damage, hydrogen peroxide or H2O2 has a dubious distinction. For a good part of the last 50 years, when the “free radicals theory” reigned, H2O2 was viewed as a villain. The theory postulates that atoms with unpaired electrons, which are highly reactive, contribute to aging as they donate or grab electrons from important biomolecules. Now, however, a new study has turned this assumption on its head, helping the molecule recover from its tarnished image.

Led by Ludovico, the scientists — who worked with the yeast, Saccharomyces cerevisiae — found that the microorganism managed to live longer than usual despite having relatively higher levels of hydrogen peroxide when put on a low-calorie diet. It also lived longer when catalases, enzymes that control the levels of hydrogen peroxide, were knocked out. This, together with an earlier finding by Rochelle Buffenstein of the City University of New York and others prompted the Portuguese researchers to get to the bottom of the mystery. The latter study showed that the naked mole rat, a burrowing rodent, despite having very high levels of H2O2, has exceptional longevity.

Billions of free radicals are produced by our cells every day as part of metabolism. In a healthy and active individual, such free radicals — also called oxidants — that cause oxidative damage are taken care of by antioxidants produced by the body. But with aging and external factors like smoking and pollution, the body’s antioxidant machinery fails to catch up with the rising demand, leading to an increase in oxidative damage. The multi-billion dollar anti-aging, antioxidant industry capitalises on this premise.

At best, the free radicals theory looks incomplete, says Ludovico. Though hydrogen peroxide is not a free radical but one belonging to the reactive oxygen species, the proponents of the theory clubbed it with free radicals such as superoxide anions as it is perceived to contribute to oxidative damage, the root cause of aging. Superoxide anions are oxygen atoms with unpaired electrons and are capable of interfering with many biochemical reactions that take place in cells.

“Our study shows the two molecules have totally different roles in the aging process,” says Ludovico. “Superoxide anions seem to be the ‘bad’ guys whereas hydrogen peroxide seems to be crucial in triggering mechanisms that reduce the levels of the former and hence can promote longevity,” she told KnowHow.

Their work, which appeared recently in the Proceedings of National Academy of Sciences, showed that hydrogen peroxide helps increase the activity of an enzyme called superoxide dismutase, which decreases the levels of superoxide anions.

When the researchers quantified the amount of hydrogen peroxide in the yeast that lived longer, they were in for a surprise. Contrary to the prevailing belief, the levels of H2O2 within the yeast actually increased with lifespan.

To prove this, the scientists knocked down two catalases or antioxidant proteins, which are responsible for regulating H2O2 levels in living organisms. They saw that the yeast that lacked the proteins not only had high levels of hydrogen peroxide but could also live longer, even without food.

The two findings suggested that hydrogen peroxide could be the reason for the increased longevity. As a final confirmation, the scientists allowed the yeast to grow in a medium abundant in hydrogen peroxide and saw that the microorganism lived longer than usual, proving that the substance could, in fact, slow down aging.

How do the findings impact the antioxidant industry? The work, feels Ludovico, serves as a caution that not all oxidants can be seen in the same light.

“The aging process is far more complex,” she says.

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