Vitamin E's bloody role.

Among the vitamin cognoscenti, vitamin E has built a solid reputation as a free radical fighter, ridding the body of the highly reactive molecules that may cause cancer and other woes (SN: 4/22/95, p.248). Indeed, vitamin E's recently reported ability to help prevent strokes and heart attacks has usually been attributed to its skill at mopping up reactive forms of oxygen molecules and other free radicals (SN: 8/1/92, p.76).

But when taken in megadoses, vitamin E also "makes you prone to bleed," notes Paul Dowd of the University of Pittsburgh. This anticoagulant effect, he suspects, might also help prevent clots that can generate heart attacks and strokes.

In the Aug. 29 Proceedings of the National Academy of Sciences, he and colleague Zhizhen Barbara Zheng report that the usual commercial form of vitamin E is relatively ineffective at thinning blood. But vitamin E quinone, a molecule that forms naturally when the vitamin reacts with oxygen in the body, proved a potent anticoagulant.

Vitamin E quinone apparently inhibits carboxylase, an enzyme that must modify a variety of proteins in order for blood clots to form. "This is a busy enzyme," says Dowd. He and Zheng propose that vitamin E quinone inhibits carboxylase by binding to the site on the enzyme where vitamin K--which activates the blood clotting cascade--normally attaches.

"It's a chemical explanation for what we saw," says Robert E. Olson of the University of South Florida College of Medicine in Tampa, who led a group which had shown that megadoses of vitamin E inhibited carboxylase enzymes in mice. Indeed, he says, they've "gone a step further than we did to show a reasonable mechanism."

Dowd believes that investigators should explore whether vitamin E quinone may offer a safe alternative to anticoagulant drugs, such as warfarin, which are sometimes slow to act.