HO1

HO-1, or heme oxygenase-1, is an enzyme that catalyzes the first step in heme degradation, converting heme to biliverdin, iron, and carbon monoxide. It is encoded by the HMOX1 gene in humans and is one of two mammalian heme oxygenases, the other being HO-2. HO-1 is inducible, with low basal expression that increases in response to oxidative stress, hypoxia, inflammation, heavy metals, heat shock, and certain drugs. The enzyme is predominantly associated with the endoplasmic reticulum and is widely expressed in tissues such as liver, spleen, vascular endothelium, and brain. HO-1 is also known as heat shock protein 32 (Hsp32) in some contexts.

The products of HO-1 activity have protective roles. Biliverdin is rapidly reduced to bilirubin, both of which have antioxidant properties; iron released from heme is sequestered by ferritin; and carbon monoxide acts as a signaling molecule with anti-inflammatory and vasodilatory effects. Through these mechanisms, HO-1 contributes to cytoprotection against oxidative injury, inflammation, and apoptosis.

Clinical and research relevance: HO-1 plays a role in cardiovascular, neurodegenerative, and inflammatory diseases. Increased HO-1 expression is generally associated with protective outcomes in experimental models, while insufficient induction can worsen injury in some settings. Polymorphisms in the HMOX1 promoter, including GT repeats, influence inducibility and disease risk in various populations. Because of its protective properties, HO-1 is investigated as a potential therapeutic target and biomarker in conditions such as ischemia–reperfusion injury, transplantation, and metabolic disorders.