Protective effect of 2-hydroxyestrone and 2-hydroxyestradiol against chemically induced hepatotoxicity in vitro and in vivo

4-Hydroxyestrogen metabolites strongly prevent chemically-induced ferroptotic hepatocyte injury in vitro and in vivo

Ferroptosis is a regulated cell death characterized by excessive accumulation of toxic lipid reactive oxygen species (ROS). Ferroptosis is an underlying cause in some human diseases, including the drug-induced liver injury. The present study aims to determine whether 4-hydroxyestrone (4-OH-E1) and 4-hydroxyestradiol (4-OH-E2), two endogenous catechol estrogens, can prevent chemically-induced ferroptotic hepatocyte injury in vitro and in vivo. The induction of ferroptotic cell death by erastin and RSL3 in rat H-4-II-E and human HuH-7 hepatoma cells is used as in vitro models. 4-OH-E1 and 4-OH-E2 each exhibit a strong protection against erastin/RSL3-induced ferroptosis in H-4-II-E hepatoma cells, and they also strongly abrogate erastin/RSL3-induced accumulation of cellular NO, ROS and lipid-ROS. A similar protective effect is observed with 4-OH-E1 and 4-OH-E2 in RSL3-induced ferroptosis in HuH-7 cells. Mechanistically, these two catechol estrogens protect hepatoma cells against chemically-induced ferroptosis mainly through binding to cellular PDI protein with a high affinity, which leads to inhibition of PDI-catalyzed NOS dimerization (activation), thereby preventing the accumulation of cellular NO, ROS and lipid-ROS. In addition, the direct antioxidant activity of these two estrogens may also partially contribute to their cytoprotective effect. In vivo animal studies show that 4-OH-E1 and 4-OH-E2 also have a strong protective effect against acetaminophen-induced liver injury in a mouse model. Together, the results of this study demonstrate that 4-OH-E1 and 4-OH-E2 are endogenous factors with a strong protective activity against chemically-induced hepatocyte injury both in vitro and in vivo.