HMOX1 and cervical squamous intraepithelial neoplasia: HO-1 induction results in degradation of prooxidant heme, releasing iron, carbon monoxide (CO), and biliverdin; biliverdin is converted to bilirubin, an antioxidant; iron is sequestered by ferritin; the products of the HO-1 reaction have antioxidant, anti-inflammatory, vasodilatory, and antiapoptotic effects, leading to attenuation of CIN [24].