[Heme oxygenase and carbon monoxide: the protection or the injury of cells?].

Heme oxygenase (HO) catalyzes the conversion of heme to carbon monoxide, iron, and biliverdin, which is immediately reduced to bilirubin. Three HO active isozymes exist: HO-1, an inducible heat shock protein (HSP32), and HO-2 and HO-3, which are constitutive and highly concentrated in neurons, spleen and liver. Heme oxygenase-1 is an inducible enzyme that catalyzes heme degradation and has been proposed to play a role in protecting cells against oxidative stress-related injury. The mechanism(s) of protection is not completely elucidated, although it is suggested that one or more of the catalytic by-products provide antioxidant functions either directly or indirectly. The role played by heme oxygenase in tissue pathology is determined by a delicate balance between the injurious and protective actions of heme, bilirubin, CO, and Fe2+. Authors review the functional role of HO and its derivates in cells biology and its real potential application to pathological conditions.