Heme oxygenase: colors of defense against cellular stress

The discovery of the gaseous molecule nitric oxide in 1987 unraveled invest igations on its functional role in the pathogenesis of a wide spectrum of b iological and pathological processes. At that time, the novel concept that an endogenous production of a gaseous substance such as nitric oxide can im part such diverse and potent cellular effects proved to be very fruitful in enhancing our understanding of many disease processes including lung disor ders. Interestingly, we have known for a longer period of time that there e xists another gaseous molecule that is also generated endogenously; the hem e oxygenase (HO) enzyme system generates the majority if not all of the end ogenously produced carbon monoxide. This enzyme system also liberates two o ther by-products, bilirubin and ferritin, each possessing important biologi cal functions and helping to define the uniqueness of the HO enzyme system. In recent years, interest in HO has emerged in numerous disciplines includ ing the central nervous system, cardiovascular physiology, renal and hepati c systems, and transplantation. We review the functional role of HO in lung biology and its real potential application to lung diseases.