SOD1 and vitamin D deficiency: Interestingly, vitamin D deficiency further increased alcohol-induced upregulation of hepatic NADPH oxidase subunits and significantly attenuated alcohol-induced upregulation of hepatic antioxidant enzymes gshpx and sod1. HO-1, an inducible form of the rate-limiting enzyme that catabolizes free heme, could regulate the content of downstream antioxidant enzymes and inhibit inflammatory response.