Hepatotoxicity of thiazolidinedione antidiabetic drugs: a structural toxicity relationship study

Abstract

Troglitazone (TGZ) was an orally active thiazolidinedione (TZD) hypoglycemic agent which was used for the treatment of non?insulin?dependent diabetes mellitus and withdrawn from the market in 2000 due to its hepatotoxicity. Pioglitazone (PGZ) and rosiglitazone (RGZ), the other two analogues of the TZD ring are non?toxic and still in the market. While the exact mechanism of TGZ toxicity remains unknown, it has been postulated that the formation of toxic reactive metabolites (RMs) may play an important role in the hepatotoxicity. On the other hand, the sulfation at 6?hydroxyl group of the chroman ring of TGZ may be partially responsible for hepatotoxicity. PGZ and RGZ also produce RMs but they are non?toxic in nature due to lower doses. Few cases of hepatotoxicity of RGZ and PGZ had also been published recently. The purpose of this study is to investigate the role of sulfur moiety of the TZD nucleus in inducing liver toxicity. To achieve this goal, the TZD analogues were synthesized chemically where the sulfur moiety of the TZD ring was replaced by the methylene group of the pyrrolidinedione (PRD) ring. Both these analogues were incubated independently with human liver microsomes and glutathione (GSH). In a separate experiment, the TZD and PRD analogues were incubated with normal human hepatocytes (THLE-2 cells). Reactive metabolite glutathione (RM-GSH) adducts were formed during incubation which were separated by ultra performance liquid chromatography (UPLC) and identified using mass spectrometry (MS). 3-(4,5-Dimethylthiazol-2-yl)-2,5-diphenyltetrazolium (MTT), glutathione (GSH) and protein carbonyl (PC) assays were performed to check the mechanism of toxicity of both these analogues using THLE?2 cells. Finally, peroxisome proliferator activated receptor gamma (PPAR?) binding activity and aP2 gene expression assays were performed to check the binding affinities of both these analogues. Our results indicated collectively that the TZD analogues were more toxic than the PRD analogues in THLE?2 cells. As both analogues were shown to bind to PPAR?, the substitution of the TZD ring by the PRD ring may be beneficial from a drug design perspective. Furthermore, we synthesized sulfo?conjugated troglitazone (TGZS) and toxicity studies were performed using THLE?2 cells. Our MTT, GSH and PC results suggested that TGZS was more toxic than its parent TGZ and may be partially responsible for TGZ?induced hepatotoxicity via the oxidative stress mechanism. In conclusion, our study suggested that the TZD antidiabetic drugs may be partially responsible for its liver toxicity in humans via oxidative stress mechanism through the RMs formation.