A radical role for dietary fish oils.

A radical role for dietary fish oils

Numerous recent studies in animals and humans link consumption of marine fish and their oils with a decreased risk of heart disease. But the mechanisms accounting for these associations have remained unclear. Now biochemists at the Cleveland Clinic Research Institute report evidence suggesting a possible explanation of how fish oils may reduce artery-clogging atherosclerosis. And the surprise is that free radicals (reactive oxygen species) -- and not the oils' highly touted omega-3 fatty acids -- may lie behind the oils' beneficial effects.

One factor contributing to the development of atherosclerotic lesions is the proliferation of smooth-muscle cells near the interior surface of arteries. Previously, Paul E. DiCorleto and colleagues at the University of Washington in Seattle showed that endothelial cells, which make up the interior surface of arteries and veins, produce a biological factor -- known as PDGFc -- that promotes the growth of smooth-muscle cells. In the July 22 SCIENCE, Paul L. Fox and DiCorleto, now at the Cleveland Clinic, report fish oils can inhibit PDGFc formation. And the inhibition of this protein was selective, Fox notes: With the exception of PDGFc, the cultured cells' protein synthesis was normal.

"What we're now speculating," Fox says, "is that the production of this growth factor in humans might be inhibited by eating fish oil." If that's true, he adds, then it's also possible that the growth of smooth-muscle cells might fall, limiting atherosclerosis development.

What tends to distinguish marine-fish oils from other fats is their high level of omega-3 fatty acids. However, "while we can't yet preclude that the effect we saw is due to omega-3, we feel rather strongly that oxidation is responsible," Fox told SCIENCE NEWS. One reason, he explains, is that safflower oil -- a fat containing almost no omega-3 -- also suppressed PDGFc formation, although with only a tenth or twentieth the potency of fish oil. Safflower oil is mildly susceptible to oxidation, however, and fish oil extremely so. Moreover, when antioxidants were added to the cells cultured with fish oil, PDGFc production was normal.

William Lands, who studies the bio-chemistry of atherosclerosis at the University of Illinois at Chicago, calls the findings "very interesting." However, Lands adds, one has to question how relevant these findings are to modeling fish oils' role in the body, where antioxidants can abound. That's true, Fox concedes. He adds, however, that there is still some question about the levels of antioxidants present in the arterial wall. And that, he notes, is where their research suggests PDGFc production might be affected.