No abstract

1. The thiazolidinedione (TZD) ring present in drugs available for type II diabetes may contribute to hepatic injury. Another TZD ring-containing compound, 3-(3,5dichlorophenyl)-2,4-thiazolidinedione (DCPT), produces liver damage in rats. Accordingly, the effects of gender, dose and time on DCPT hepatotoxicity were therefore evaluated. 2. Male rats were more sensitive to DCPT (0.4-1.0 mmol/kg by i.p. administration) as shown by increased serum alanine aminotransferase (ALT) levels and altered hepatic morphology 24 h post-dosing. Effects in both genders were dose-dependent. In males, DCPT (0.6 mmol/kg) produced elevations in ALTs and changes in liver sections 3 h after dosing that progressively worsened up to 12 h. DCPT-induced renal effects were mild. 3. We conclude that male rats are more susceptible to DCPT hepatotoxicity and that damage occurs rapidly. DCPT primarily affects the liver and may be a useful compound to investigate the role of the TZD ring in hepatic injury. However, the gender dependency and rapid onset of DCPT hepatotoxicity require further investigation.

The thiazolidinedione (TZD) ring is a constituent of the glitazones that are used to treat type II diabetes. Liver injury has been reported following chronic glitazone use; however, they do not produce hepatic damage in common laboratory animal species. In contrast, 3-(3,5-dichlorophenyl)-2,4-thiazolidinedione (DCPT) causes hepatotoxicity in rats. DCPT toxicity is dependent upon the presence of an intact TZD ring and cytochrome P450 (CYP)-mediated biotransformation. To further investigate TZD ring-induced toxicity, DCPT and several structural analogues or potential metabolites were tested in vitro using wild type human hepatoma HepG2 and HepG2 cells stably transfected with the CYP3A4 isozyme. CYP3A4 activity was confirmed by measuring testosterone 6β-hydroxylation. Both cell lines were treated with 0-250 μM of the compounds in Hanks' balanced salt solution. Cell viability was measured after 24 hrs. DCPT and S-(3,5-dichlorophenyl)aminocarbonyl thioglycolic acid (DCTA) were the most toxic compounds of the series. Furthermore, DCPT was significantly more toxic in transfected cells (LC50 = 160.2 ± 5.9 μM) than in wild type cells (LC50 = 233.0 ± 19.7 μM). Treatment with a CYP3A4 inhibitor or inducer attenuated or potentiated DCPT cytotoxicity, respectively. These results suggest that DCPT-induced cytotoxicity in the transfected HepG2 cells is partially dependent on CYP3A4.

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 1.0 mmol/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 (0.2 mmol/kg, i.p.). Vehicle-, ABT-, TAO-and DEX-only control groups were also run. Toxicity was assessed 24 hours 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.

Glitazones, used for type II diabetes, have been associated with liver damage in humans. A structural feature known as a 2,4-thiazolidinedione (TZD) ring may contribute to this toxicity. TZD rings are of interest since continued human exposure via the glitazones and various prototype drugs is possible. Previously, we found that 3-(3,5-dichlorophenyl)-2,4-thiazolidinedione (DCPT) was hepatotoxic in rats. To evaluate the importance of structure on DCPT toxicity, we therefore studied two series of analogues. The TZD ring was replaced with: a mercaptoacetic acid group ([[[(3,5-dichlorophenyl)amino]carbonyl]thio]acetic acid, DCTA); a methylated TZD ring (3-(3,5-dichlorophenyl)-5-methyl-2,4-thiazolidinedione, DPMT); and isomeric thiazolidinone rings (3-(3,5-dichlorophenyl)-2- and 3-(3,5-dichlorophenyl)-4-thiazolidinone, 2-DCTD and 4-DCTD, respectively). The following phenyl ring-modified analogues were also tested: 3-phenyl-, 3-(4-chlorophenyl)-, 3-(3,5-dimethylphenyl)- and 3-[3,5-bis(trifluoromethyl)phenyl]-2,4-thiazolidinedione (PTZD, CPTD, DMPT and DFMPT, respectively). Toxicity was assessed in male Fischer 344 rats 24 hours after administration of the compounds. In the TZD series only DPMT produced liver damage, as evidenced by elevated serum alanine aminotransferase (ALT) activities at 0.6 and 1.0 mmol/kg (298.6 ± 176.1 and 327.3 ± 102.9 Sigma-Frankel units/ml, respectively) versus corn oil controls (36.0 ± 11.3) and morphological changes in liver sections. Among the phenyl analogues, hepatotoxicity was observed in rats administered PTZD, CPTD and DMPT; with ALT values of 1196.2 ± 133.6, 1622.5 ± 218.5 and 2071.9 ± 217.8, respectively (1.0 mmol/kg doses). Morphological examination revealed severe hepatic necrosis in these animals. Our results suggest that hepatotoxicity of these compounds is critically dependent on the presence of a TZD ring and also the phenyl substituents.