Carbon monoxide: Innovative anti-inflammatory properties of an age-old gas molecule

Observations of the effects of carbon monoxide (CO) on mammalian systems have been known for thousands of years. To be sure, CO is deadly under certain conditions and concentrations, but perhaps as the data presented here will make clear, it also possesses other diverse functional and immunomodulatory properties. This review, together with the other reviews in this issue, will detail that over the past three decades, fundamental functional role(s) for this gas molecule are beginning to emerge. This review outlines that at low concentrations, exogenously administered CO is a molecule involved in the regulation of the inflammatory response in a variety of disease models. CO has been shown to modulate such cellular functions as cytokine production, cell proliferation and apoptosis, protecting the lungs and hearts of rodents from such stressors as endotoxin, ischemia/reperfusion injury, cardiac xenograft rejection, and asthma. Although the mechanism by which this simple diatomic gas provides this protection remains obscure, the conclusions are the same: CO at low concentrations, concentrations that are well below those that would otherwise create toxic effects, is proving beneficial in models of acute injury. CO, akin to nitric oxide, is proving to be an extraordinary signaling molecule generated by the cell that is vital in the regulation of cellular homeostasis.