Role of biotransformation in 3-(3,5-dichlorophenyl)-2,4-thiazolidinedione-induced hepatotoxicity in Fischer 344 rats

Cytochrome P450 (CYP)-mediated metabolism in the thiazolidinedione (TZD) ring may contribute to the hepatotoxicity of the insulin-sensitizing agents such as troglitazone. We were interested in determining if biotransformation could also be a factor in the liver damage associated with another TZD ring containing compound, 3-(3,5-dichlorophenyl)-2,4-thiazolidinedione (DCPT). Therefore, hepatotoxic doses of DCPT (0.6 or 1.0mmol/kg, i.p.) were administered to male Fischer 344 rats after pretreatment with vehicle, 1-aminobenzotriazole (ABT, non-selective CYP inhibitor) and troleandomycin (TAO, CYP3A inhibitor). Alternatively, rats were pretreated with vehicle or the CYP3A inducer dexamethasone (DEX) prior to a non-toxic DCPT dose (0.2mmol/kg, i.p.). Vehicle-, ABT-, TAO- and DEX-only control groups were also run. Toxicity was assessed 24h after DCPT administration. Both hepatotoxic doses of DCPT induced elevations in serum alanine aminotransferase (ALT) levels that were attenuated by ABT or TAO pretreatment. Liver sections from rats that received vehicle+DCPT revealed areas of gross necrosis and neutrophil invasion, whereas sections from ABT+DCPT and TAO+DCPT rats showed minor changes compared to controls. DEX pretreatment potentiated ALT levels associated with the non-toxic DCPT dose. Furthermore, DEX+DCPT rat liver sections exhibited hepatic injury when compared against rats that received vehicle+DCPT. Blood urea nitrogen levels, urinalysis and kidney morphology were not markedly altered by any combination of pretreatments or treatments. Enzyme activity and Western blotting experiments with rat liver microsomes confirmed the effects of the various pretreatments. Our results suggest that hepatic CYP3A isozymes may be involved in DCPT-induced liver damage in male rats. We believe this is the first report demonstrating that modulation of the biotransformation of a TZD ring-containing compound can alter hepatotoxicity in a common animal model.