The component of green tea, L-theanine protects human hepatic L02 cells from hydrogen peroxide-induced apoptosis

L-theanine is a natural amino acid in green tea and it has been well known for its activities of relieving depression and neuroprotection. However, cytoprotective effect and its mechanism of L-theanine on hepatocytes have not been reported. The objective of this work was to investigate the hepatoprotective effect of L-theanine as well as its mechanism by using the human hepatic L02 cells injured by hydrogen peroxide (H2O2). Results showed that L-theanine dose dependently decreased H2O2-induced cell viability loss and lactate dehydrogenase (LDH) release. L-theanine pretreatment improved nuclear morphology of the cells injured by H2O2. By using flow cytometric analysis, we found that L-theanine significantly inhibited H2O2-induced cell apoptosis. Further, L-theanine attenuated H2O2-induced reduction in pro-caspase3 and cleavage of poly (adenosine diphosphate-ribose) polymerase (PARP). H2O2-activated p38 mitogen-activated protein kinase (MAPK) was also inhibited by L-theanine. These data suggest that L-theanine could protect L02 cells against H2O2-induced apoptosis via suppression of p38 MAPK. L-theanine might potentially be useful in the prevention and treatment of liver diseases.