Model for the role of heme and heme oxygenase in inflammation.

Free heme interacts with the endothelial cell membrane (thick black line), resulting in oxidative stress, vasopermeability, adhesion molecule induction, leukocyte binding–migration, and HO-1 expression. In contrast, HO-1, the heme-degrading enzyme, acts as a feedback modulator by antagonizing the oxidative and inflammatory actions of heme through the formation of vasodilator carbon monoxide and antioxidants biliverdin/bilirubin.