A toxic gas eases IBD

A study on page 1703 might help explain why active smokers rarely suffer from an inflammatory bowel disease (IBD) known as ulcerative colitis. Hegazi and colleagues show that carbon monoxide (CO) gas, a component of cigarette smoke, shuts down the production of a disease-promoting cytokine, thus easing chronic bowel inflammation in mice.

CO is both a toxic air pollutant and a normal byproduct of cellular heme metabolism. Although CO's asphyxiant properties have earned it a bad reputation, the ubiquitous tissue expression of the natural CO-producing enzyme heme oxygenase-1 (HO-1) suggests that the effects of CO must not be all bad.

Indeed, recent studies have shown that CO, at least at low concentrations, has a redeeming quality: it acts as an antiinflammatory agent. Low dose inhaled CO is therapeutic in many...