Baicalein and baicalin alleviate acetaminophen-induced liver injury by activating Nrf2 antioxidative pathway: The involvement of ERK1/2 and PKC

Acetaminophen (APAP)-induced hepatotoxicity is the main cause of drug-induced liver injury. This study investigated the protection of baicalin and its aglycone baicalein against APAP-induced hepatotoxicity and its mechanism. Baicalein and baicalin alleviated APAP-induced hepatotoxicity both in vitro and in vivo. Moreover, this baicalin-provided protection was not diminished in hepatocytes or mice treated with beta-glucuronidase inhibitor. Results of liver glutathione (GSH) and reactive oxygen species (ROS) formation demonstrated the alleviation of baicalein and baicalin on APAP-induced liver oxidative stress injury. Baicalein and baicalin induced the activation of nuclear factor erythroid 2-related factor 2 (Nrf2) and increased the expression of its downstream antioxidant genes. Baicalein and baicalin-provided protection was diminished after the application of Nrf2 siRNA in hepatocytes and Nrf2 knock-out mice. Molecular docking results indicate the potential interaction of baicalein and baicalin with kelch-like ECH-associated protein-1 (Keap1). Baicalein and baicalin induced the sustained phosphorylation of extracellular regulated protein kinases (ERK)1/2 and protein kinase C(PKC). Moreover, ERK1/2 and PKC inhibitors both abrogated Nrf2 phosphorylation and its subsequent activation, and the protection against APAP-induced hepatotoxicity induced by baicalein and baicalin. In summary, baicalein and baicalin alleviate APAP-induced hepatotoxicity by activating Nrf2 via blocking the binding of Nrf2 with Keap1 and inducing Nrf2 phosphorylation. ERK1/2 and PKC are both critical for regulating the phosphorylation of Nrf2 induced by baicalein or baicalin.