Summary
Carbon monoxide (CO) is emerging as an important signaling molecule that exerts a myriad of biological effects that are only recently being uncovered. CO is a diatomic gas that is generated predominantly from heme degradation by the enzyme heme oxygenase. Traditionally considered a biological “waste product” of heme metabolism and, at high doses, lethal, CO clearly has diverse functions including the modulation of neural signals, inflammation, cell proliferation, cell death, and smooth muscle contractility. Interestingly, at concentrations well below those that would otherwise create toxic effects, CO has beneficial effects in various models of injury and inflammation. The precise mechanisms of these CO-mediated effects are yet unknown but are becoming the focus of intense investigations. This chapter reviews the known signal transduction pathways of CO with a special emphasis on the roles of guanylate cyclase, the mitogen-activated protein kinases, and nuclear factor-κB.