Thesis (Ph.D.)--Chulalongkorn University, 2009

In the present study, the protective activity of phyllanthin (a principal constituent of Phyllanthus amarus Schum. et Thonn.) and its possible hepatoprotective mechanisms were investigated against ethanol-induced hepatotoxicity in primary cultures of rat hepatocytes. Primary culture of rat hepatocytes (24 h culturing) were incubated with phyllanthin (1, 2, 3, 4 μg/ml) for 24 h prior to 2 h exposure with ethanol (80 μl/ml). Ethanol decreased %cell viability, increased the release of transaminases (ALT and AST) with the increase in the production of intracellular ROS and lipid peroxidation. Phyllanthin exhibited protective effect by attenuating on changes induced by ethanol. Phyllanthin also restored the antioxidant capability of rat hepatocytes including level of total glutathione and activities of superoxide dismutase (SOD) and glutathione reductase (GR) which were reduced by ethanol. Phyllanthin did not affect the activities of ethanol-metabolizing enzymes ADH and ALDH which ALDH activity was suppressed by ethanol. Twenty four hours pretreatment with phyllanthin effectively induced the activation of transcription factor Nrf2 which was reduced by acute ethanol treatment. This was concomitant with the increase in protein expression of antioxidant enzymes: SOD1 (Cu-ZnSOD), SOD2 (MnSOD), GR and GPx in hepatocytes pretreated with phyllanthin before giving ethanol. These results suggested the hepatoprotective effect of phyllathin against ethanol-induced oxidative stress causing rat liver cell damage due to its antioxidant activity through the activation of transcription factor Nrf2 and induction of protein expression especially antioxidant enzymes SOD and GR under the control of Nrf2