Microcystin-LR and nodularin induce intracellular glutathione alteration, reactive oxygen species production and lipid peroxidation in primary cultured rat hepatocytes

Microcystin-LR (MCYST-LR) and nodularin (NOD) produced by cyanobacteria are potent specific hepatotoxins. However, the mechanisms of their hepatotoxicity have not been fully elucidated. In the present study the effect of non cytotoxic low concentrations of MCYST-LR and NOD on intracellular reduced glutathione (GSH) alteration, reactive oxygen species (ROS) production and lipid peroxidation was investigated in primary cultured rat hepatocytes. Cell viability was determined by the methylthiazoltetrazolium (MTT) dye assay, reduced GSH was evaluated by enzymatic methods, ROS were evaluated by the dichlorofluorescein diacetate (H2DCF-DA) fluorescent probe and lipid peroxidation by dosing malondialdehyde (MDA) by the thiobarbituric acid method. The 24 It LC50 values of MCYST-LR and NOD were 48 and 62 ng/ml, respectively. Exposure of freshly isolated rat hepatocytes to MCYST-LR or NOD at non cytotoxic low concentrations (2, 10 ng/ml) for 3, 24 and 48 h periods resulted in a significant rise of GSH levels and production of ROS. NOD significantly induced in a time- and concentration-dependent lipid peroxidation. However, MCYST-LR treatment did result in a significant decrease in MDA levels compared with controls. Although MCYST-LR and NOD are closely related in terms of structure and inhibition of protein phosphatases, they induce differently the oxidative stress at non cytotoxic low concentrations. Therefore, the results indicate that oxidative stress mediated by reactive intermediates may be a mechanism by which these cyanotoxins induce their hepatotoxic effect. (C) 2003 Elsevier Ireland Ltd. All rights reserved.