Abstract

Ethnopharmacological relevance Usnic acid (UA) is one of the well-known lichen metabolites that induces liver injury. It is mainly extracted from Usnea longissima and U. diffracta in China or from other lichens in other countries. U. longissima has been used as traditional Chinese medicine for treatment of cough, pain, indigestion , wound healing and infection. More than 20 incidences with hepatitis and liver failure have been reported by the US Food and Drug Administration since 2000. UA is an uncoupler of oxidative phosphorylation causing glutathione and ATP depletion. Previous histological studies observed extensive cell and organelle swellings accompanied with hydrotropic vacuolization of hepatocytes. Aim of the study This study was to investigate the mechanism of UA-induced liver toxicity in normal human L02 liver cells and ICR mice using various techniques, such as immunoblotting and siRNA transfection. Materials and methods Assays were performed to evaluate the oxidative stress and levels of GSH, MDA and SOD . Double flouresencence staining was used for the detection of apoptotic cell death . The protein expressions, such as glutathione S transferase , glutathione reductase , glutathione peroxidase 4 , catalase , c-Jun N-terminal protein kinase , caspases , gastamin-D and porimin were detected by Western blotting. Comparisons between transfected and non-transfected cells were applied for the elucidation of the role of porimin in UA-induced hepatotoxicity. Histopathological examination of mice liver tissue, serum total bilirubin and hepatic enzymes of alanine aminotransferase and aspatate aminotransferase were also studied. Results The protein expressions of glutathione reductase, glutathione S transferase and glutathione peroxidase-4 were increased significantly in normal human L02 liver cells. Catalase expression was diminished in dose-dependent manner. Moreover, (+)-UA did not induce the activation of caspase-3, cas