Hepatoprotective Effect of Apigenin Against Liver Injury via the Non-canonical NF-κB Pathway In Vivo and In Vitro

Apigenin, a flavonoid found in many plants, has various biological properties. We aimed to investigate the anti-inflammatory and anti-oxidative activity of apigenin against carbon tetrachloride (CCl4)-induced acute liver injury in mice and hydrogen peroxide (H2O2)-induced oxidative stress in HepG2 cells and possible mechanism. In vivo, apigenin significantly reduced alanine aminotransferase (ALT) and aspartate aminotransferase (AST) activity in serum of mice challenged by CCl4 and markedly alleviated the lipid peroxidation as indicated by the increased level of superoxide dismutase (SOD), reduced glutathione (GSH), glutathione peroxidases (GSH-Px) and catalase (CAT), and the decreased malondialdehyde (MDA) in liver tissue. Apigenin also ameliorated inflammation by downregulating tumor necrosis factor-alpha (TNF-alpha), interleukin-6 (IL-6), and upregulating IL-10. Consistently, the elevated ALT and AST level; the impaired balance between SOD, GSH activity, and excessive ROS; and the increased gene expression of TNF-alpha and IL-6 resulting from H2O2-induced oxidative stress were restored by apigenin. Moreover, the results from Western blot, real-time qPCR, and immunofluorescence assay indicated that apigenin enhanced the activity of TNF receptor-associated factor (TRAF) 2/3 and cellular inhibitor of apoptosis protein (c-IAP) 1, ameliorated NF-kappa B-inducing kinase (NIK), and mediated the nuclear translocation of NF-kappa B2, therefore had an inhibitory effect on the non-canonical NF-kappa B pathway which was activated in both models. siNIK canceled the protective effect of apigenin on H2O2-induced HepG2 cells. Altogether, our results demonstrated that apigenin mitigated liver injury by ameliorating inflammation and oxidative stress through suppression of the non-canonical NF-kappa B pathway, indicating the potential of apigenin for treatment of the liver injury.