Tangeretin and 4′-demethyltangeretin prevent damage to mouse hepatocytes from oxidative stress by activating the Nrf2-related antioxidant pathway via an epigenetic mechanism

Polymethoxyflavones (PMFs) in citrus fruits have a variety of biological activities, including antioxidant, anti-inflammatory, anticancer, and anti-atherosclerotic effects. The liver is the major detoxifying organ of the human body; however, factors such as acetaminophen (APAP) overdose may increase oxidative stress in liver cells and lead to severe liver failure. In this study we examined the effects of tangeretin (TAN), a common citrus PMF, and its metabolite 4′-demethyltangeretin (4′-OH-TAN) on activation of the Nrf2 antioxidant system in mouse AML-12 hepatocytes through regulation by epigenetic mechanisms. The ability of TAN and 4′-OH-TAN to inhibit APAP-induced hepatotoxicity was also evaluated. The results showed that TAN and 4′-OH-TAN significantly increased the mRNA and protein levels of Nrf2 and Nrf2-mediated antioxidant and detoxifying enzymes (UGT1A, HO-1, and NQO1) in AML-12 cells. TAN and 4′-OH-TAN also suppressed protein expression of histone deacetylases (HDACs) and DNA methyltransferases (DMNTs) and reduced DNA methylation of the nrf2 promoter. Furthermore, TAN and 4′-OH-TAN prevented APAP-induced injury and inhibited APAP-induced ROS generation in AML-12 cells. Based on these results, we conclude that TAN and 4′-OH-TAN may increase the antioxidant capacity of liver cells by regulating epigenetic alteration to activate the Nrf2-related antioxidant system, thereby preventing liver cells from being damaged by APAP-induced oxidative stress.