MECHANISM OF PROTECTION OF LOBENZARIT AGAINST PARACETAMOL-INDUCED TOXICITY IN RAT HEPATOCYTES

The protective effects of lobenzarit, an antioxidative agent and antir heumatic drug, on the cytotoxicity of paracetamol in rat hepatocytes w ere studied, as well as the inhibitory effects of lobenzarit on cytoch rome P-450s and glutathione S-transferases (GSTs) in rat liver. Parace tamol was selected as a model toxin, since it is known to be bioactiva ted by specific cytochrome P-450s presumably to N-acetyl-p-benzoquinon eimine, a reactive metabolite which upon overdosage of paracetamol cau ses protein and non-protein thiol depletion, lipid peroxidation and cy totoxicity measurable as LDH leakage. At concentrations of lobenzarit of 0.2 and 0.3 mM, added 30 min before paracetamol, the drug prevented paracetamol-induced leakage of lactate dehydrogenase (LDH) almost com pletely and lipid peroxidation (LPO) and depletion of glutathione (GSH ) substantially and also the formation of the 3-glutathionyl conjugate of paracetamol. However, at a concentration of 0.05 mM lobenzarit did not protect anymore against the paracetamol toxicity. When added to t he hepatocytes 1 h and 2 h before paracetamol, 0.05 and 0.2 and 0.3 mM concentrations of lobenzarit did not protect against the cytotoxicity induced by paracetamol either. Lobenzarit did not inhibit cytochromes P-450 1A1/1A2, 2B1/2B2 and 2E1 which were measured as ethoxyresorufin O-deethylation (EROD) activity in beta-naphthoflavone-induced rat liv er microsomes, as pentoxyresorufin de-pentylation (PROD) activity in p henobarbital-induced microsomes and as p-nitrophenol hydroxylation (PN PH) activity in pyrazol-induced microsomes. Lobenzarit did not show in hibition of glutathione S-transferase (GST) activity towards 1-chloro- 2,4-dinitrobenzene (CDNB) in cytosol from liver of rats treated with p henobarbital, pyrazol and beta-naphthoflavone either. It is concluded that the cytoprotective effect of lobenzarit is most likely due to its antioxidant effects and/or to its ability to stimulate GSH reductase.