Magazine article Science News

How Antioxidants Defend Cells

Magazine article Science News

How Antioxidants Defend Cells

Article excerpt

Antioxidants in the body act as chemical scavengers, intercepting reactive molecules called free radicals before they have a chance to damage cells. Two recent studies shed some light on how such protective mechanisms work.

In one study, researchers examined how vitamin E, vitamin C, and carotenoids such as beta carotene collaborate to get rid of free radicals, whose harmful effects arise from their readiness to grab an electron from another molecule. The scheme the chemists propose works something like a bucket brigade, with the dangerous chemical property being passed from one molecule to the next.

First, vitamin E reacts with the free radicals, restoring them to their less harmful state. This reaction, however, turns vitamin E into a potentially damaging radical, which the carotenoids then inactivate. Finally, vitamin C repairs the resulting carotenoid radicals, and the water-soluble vitamin C radicals eventually wash out of the body.

The mechanism, says T. George Truscott of Keele University in England, may help explain the puzzling results of clinical studies showing that beta carotene supplements boost the incidence of cancer in smokers. The Beta Carotene and Retinol Efficacy Trial (CARET), funded by the National Institutes of Health, was halted early because of this finding (SN: 1/27/96, p. 55).

According to the researchers' proposed scheme, smokers tend to be low in vitamin C, so they don't have enough of the vitamin to scavenge carotenoid radicals. Giving smokers supplements of carotenoids only adds to the radicals in the body, he says.

"This [cascade] occurs in test tubes, but the proof will be in human trials" using combinations of antioxidants, Truscott says. He and his colleagues report their findings in the Jan. 22 Journal of the American Chemical Society.

Beta carotene, for example, seemed very promising in the laboratory, says Gilbert S. …

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