Hepatotoxicity Induced By Arsenic Drinking Water Exposure And Mechanisms Of Oxidative Damage In Mice

1. Introduction Arsenic is a naturally occurring element present in the environment in both inorganic and organic forms. Inorganic arsenic is considered to be the principal form of arsenic in groundwater, surface water, soil, and many foods. Arsenic in well water usually originates from natural geological sources. In several countries and areas, including India, China, Taiwan China, Mexico, Argentina, and Chile, the people are exposed to high arsenic concentrations through their drinking water. Epidemiology studies show that chronic arsenic exposure produces tumors of the skin, urinary bladder, lung, liver, prostate, kidney, and possibly other organs. Arsenic and arsenic compounds were classified as a group 1 carcinogen to humans based on the strong epidemiological evidence by IARC at 1971. The primary source of arsenic exposure in humans is from the drinking water where inorganic forms predominate. In recent years studies have suggested that arsenic contamination of drinking water has induced liver oxidative damage, but the mechanisms are not very clear. In this study, we had investigated the high arsenic drinking water induced hepatotoxicity and oxidative damage in the liver from in vivo and in vitro. 2. Methods In vivo, forty-eight KM mice (female and male in half) were randomly divided into four groups. Mice were treated with arsenite exposure at 0 , 7,20 and 60 ppm in the drinking water which were provided ad libitum for 9 weeks. Then the mice were killed and liver samples were collected. The following indices were observed and determined: body weight, water consumption, liver index and changes in malondialdehyde (MDA), contents of Glutathione (GSH), activity of superoxide dismutase (SOD), and the histological changes. And 8-hydroxydeoxyguanosine (8-OHdG) was detected by immunohistochemical method. In vitro, HepG2 cells were used as experimental system. Cytotoxicity was determined by MTT colorimetric assay. DNA damage was determined by single cell gel electrophoresis assay (SCGE), and reactive oxygen radicals (ROS) were measured by fluorescence method. 3. Result There were no significant changes of mice body weight , water consumption and liver index compared with control after 9 weeks drinking water arsenite exposure, but some oxidative damage effects were found, including the significant increase of MDA and the significant decrease of contents of GSH and the activity of SOD between arsenite exposure groups and control. The pathological changes were also found in the liver of mice exposured in drinking water with 20ppm and 60pmm aresnite. In vitro, after HepG2 cells were treated by different concentrations of sodium arsenite (NaAsO₂) for 24h, NaAsO₂ produced the dose-dependent cytotoxocity and the production of ROS was significantly increased after hepG2 cells were treated by 0¹00μmol/L NaAsO2 for a 1 h. Single cell gel electrophresis assay showed that NaAsO₂ above 10μmol/L induced DNA strand breaks.4. Conclusion After 9 weeks exposure with arsenite in drinking water, significant increase of the MDA level and significant decrease in GSH content and SOD activity were noted in hepatic tissues of the mice, the pathological changes and positive immunolabeling for 8-OHdG were also observed in the arsenite-treated mice liver. Single cell gel electrophoresis assay showed NaAsO2 induced DNA strand breaks. These results indicate that increase of generation of the ROS results in decrease of antioxidative functions and DNA oxidative damage in liver cells. The oxidative damages could be involved in hepatotoxicity induced by arsenite.