Nitric oxide at war with homocysteine?

The gaseous molecule nitric oxide plays a variety of roles in the body, many of which researchers are just beginning to understand. Nitric oxide apparently plays a part in the immune system, attacking a wide range of infectious microorganisms.

Actually, the derivatives of nitric oxide, each with different abilities, do this dirty work, says Ferric C. Fang of the University of Colorado Health Sciences Center in Denver. One called S-nitrosothiol may combat Salmonella typhimurium by placing infected cells into "a state of suspended animation" that prevents the bacterium from replicating, says Fang.

Fang and his colleagues suggest in the April 19 Science that the bacteria try to ward off this attack by synthesizing the compound homocysteine, which appears to bind directly to S-nitrothiol. Since the human body makes both nitric oxide and homocysteine, Fang suggests that S-nitrosothiol could govern homocysteine concentrations in the bloodstream. If proved, such an interaction could have therapeutic implications. Epidemiological studies have linked elevated concentrations of homocysteine to increased risk of atherosclerosis.

"These are intriguing results, but we have to be cautious about overinterpreting them," says Jonathan Stamler of Duke University Medical Center in Durham, N.C., who has also shown that forms of nitric oxide interact with homocysteine.