Nitric oxide is an important regulator of heme oxygenase-1 expression in the lipopolysaccharide and interferon-γ-treated murine macrophage-like cell line J774.1/JA-4.

Heme oxygenase-1 (HO-1) catabolizes the degradation of heme into bilirubin, carbon monoxide, and iron ions. The HO-1 products provide antioxidant cytoprotection in addition to having potent antiinflammatory and immunomodulatory functions. HO-1 is induced by its substrate heme and environmental factors including oxidative and heat stresses.