In addition to damaging DNA directly, free radicals can also act indirectly. They begin by converting linoleic acid, the major polyunsaturated fatty acid in sunflower, grape, and safflower cooking oils, as well as the major polyunsaturated fatty acid in human plasma, into another compound called a lipid hydroperoxide. When certain metal ions are present to act as catalysts, the lipid hydroperoxides degrade further, into DNA-damaging agents called "genotoxins."

These compounds react with DNA, switching one base for another in mutations that have been found in human tumors.

Scientists, including Blair and his colleagues, have suspected that vitamin C might also be capable of making lipid hydroperoxides degrade into genotoxins, in place of the transition metal ions.

To investigate, the Science authors added vitamin C to solutions of lipid hydroperoxides in the lab. They used concentrations comparable to those found in the human body, assuming a person would take 200 milligrams a day.

The vitamin was more than twice as efficient as transition metal ions at inducing the formation of genotoxins, including a particularly potent variety.

The researchers' next step is to see whether vitamin C produces significant amounts of genotoxins in intact cells, and whether they generate cancer-causing mutations.

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Contact: Cherita Gonzales
cgonzale@aaas.org
202-326-6414
American Association for the Advancement of Science
14-Jun-2001