HMOX1 and hepatocellular carcinoma: On the other hand, ROS also appear to have a stimulatory effect on HO-1 expression, as demonstrated by the inhibition of HO-1 formation by NAC, e.g., in renal tubule epithelial [45], umbilical vein endothelial [48], smooth muscle [47] and HepG2 hepatoma cells [46].