In news that could give smokers yet another reason to kick the habit, researchers have found that a nicotine by-product known as nornicotine modifies the body's proteins in potentially harmful ways. The results of their study, published online yesterday by the Proceedings of the National Academy of Sciences, indicate that the chemical may contribute to aging and to the development of a number of diseases.

Specifically, report Tobin J. Dickerson and Kim D. Janda of the Scripps Research Institute in La Jolla, Calif., nornicotine appears to encourage good proteins to go bad by chemically "cooking" them. The modified proteins then interact with other chemicals in the body and can form troublesome compounds known as advanced glycation endproducts (AGEs). "These advanced glycation endproducts are not supposed to be [present in your body] naturally," Dickerson explains. "Your body is not prepared for them." Indeed, previous work has implicated AGEs in a variety of diseases, including diabetes, cancer and Alzheimer's.

Importantly, the team found that smokers had more nornicotine-modified proteins--and more AGEs--in their blood than nonsmokers did. The researchers also discovered that nornicotine reacts with the commonly prescribed steroids cortisone and prednisone, hinting that it could compromise drug safety and efficacy.