HMOX1 and endothelial dysfunction: The cytoprotective actions of HO-1—breaking down heme into biliverdin, carbon monoxide (CO), and free iron—are important for responding to oxidative stress.210–212 Both CO and biliverdin possess antioxidant activity, and studies have shown that these products of HO-1 activity can reverse endothelial dysfunction and decrease atherosclerotic lesion size in vivo.