Abstract
Duck hepatitis A virus type 1 (DHAV-1) is the main pathogen of duck viral hepatitis, but the efficacy of the licensed commercial vaccine needs to be further improved. Therapeutic measures of specific drugs for DHAV-1-infected ducklings need to be urgently developed. Baicalin possesses good antiviral effects. This study aims to investigate the mechanism of baicalin in protecting hepatic mitochondrial function from DHAV-1. The ELISA method was used to detect changes of hepatic and mitochondrial catalase (CAT), superoxide dismutase (SOD), glutathione peroxidase (GPX), inducible nitric oxide synthase (iNOS), adenosine triphosphate (ATP), and malondialdehyde (MDA) levels in vivo and vitro. Hematoxylin and eosin sections and transmission electron microscopy were used to observe liver pathological changes and mitochondrial structural changes. The changes in mitochondrial membrane potential were detected by JC-1 staining method. Western blot and quantitative real-time PCR were employed to analyze the gene and protein expressions in the nuclear erythroid 2-related factor 2 (Nrf2)/antioxidant responsive element (ARE) pathway in duck embryonic hepatocytes infected with DHAV-1. Results showed the administration of baicalin increased the survival rate of ducklings, and alleviated hepatic damage caused by DHAV-1 by enhancing the antioxidant enzyme activities of the liver and mitochondria, including SOD, GPX, CAT, and reducing lipid peroxidative damage (MDA content) and iNOS activities. The mitochondrial ultrastructure changed and the significant increase of ATP content showed that baicalin maintained the structural integrity and ameliorated mitochondrial dysfunction after DHAV-1 infection. In vitro, DHAV-1 infection led to loss of mitochondrial membrane potential and lipid peroxidation and decreased antioxidative enzyme activities (SOD, GPX) and mitochondrial respiratory chain complex activities (succinate dehydrogenase, cytochrome c oxidase). Baicalin relieved the above changes caused by DHAV-1 and activated the gene and protein expressions of Nrf2, which activated ARE-dependent genes including heme oxygenase-1 (HO-1), nicotinamide adenine dinucleotide phosphate quinone oxidoreductase 1 (NQO1), SOD-1, and GPX-1. In addition, baicalin increased the protein expressions of antioxidative enzymes (SOD, GPX). Hence, baicalin protects the liver against oxidative stress in hepatic mitochondria caused by DHAV-1 via activating the Nrf2/ARE signaling pathway.