Cytotoxicity and mitochondrial dysfunction of 2,3,7,8-tetrachlorodibenzo- p-dioxin (TCDD) in isolated rat hepatocytes

Abstract

2,3,7,8-Tetrachlorodibenzo- p-dioxin (TCDD) is an environmental contaminant that induces hepatic and extrahepatic oxidative stress and the mechanisms of TCDD-induced reactive oxygen species are not fully investigated. Moreover, the potential toxicity of TCDD in isolated rat hepatocytes is not fully explored. The aim of the current study was to explore the possible cytotoxic effect of TCDD on primary rat hepatocytes and to explore the impact of mitochondria in TCDD-induced toxicity. Hepatocytes were isolated from adult rat liver and incubated with 0, 5, 10 or 15 nM of TCDD for 24, 48 and 72 h. Cell viability, lactate dehydrogenase (LDH) leakage into media along with reactive oxygen species (ROS) generation and hydrogen peroxide (H 2O 2) production, mitochondrial membrane potential (Δψ m), superoxide dismutase (SOD), catalse (CAT), glutathione peroxidase (GPx), glutathione reductase (GR), total thiol contents, hepatic aryl hydrocarbon hydroxylase (AHH), and ethoxyresorufin O-deethylase (EROD) were performed in hepatocytes. In addition, superoxide anion generation, lipid peroxidation (LPO), mitochondrial protein carbonyl content and respiratory chain complexes II and IV were assayed in hepatocyte mitochondria. Cell viability was significantly decreased while LDH leakage into media was significantly increased in a dose and time related manner. ROS generation and H 2O 2 production along with EROD and AHH activities were significantly increased in hepatocytes in the same pattern. The antioxidant enzymes SOD, CAT, GPx and GR and the non-enzymatic protein thiols, in addition to Δψ m were significantly decreased in hepatocytes in a concentration and time dependent pattern. On the other side, mitochondrial superoxide anion along with LPO and mitochondrial protein carbonyl content were significantly increased while the respiratory chain complexes II and IV activities were significantly decreased in hepatocyte mitochondria. This effect may lead to disruption in the functional integrity of hepatocytes and hepatocyte mitochondria. In conclusion, our data clearly show that TCDD induces hepatocyte toxicity and mitochondrial dysfunction by a mechanism involving generation of ROS. Mitochondria might be the primary source of (or at least contribute to) the oxidative stress response and resulting toxicological outcomes elicited by TCDD.