A Comparison of the Cytotoxicity of 3-(3,5-Dichlorophenyl)-2,4-thiazolidinedione (DCPT) in HepG2 and MDCK Cells

Thiazolidinedione drugs, such as troglitazone, were developed for the treatment of type 2 diabetes mellitus and act as peroxisome proliferator-activated receptor gamma (PPAR-gamma) agonists. However, chronic use of troglitazone in humans can result in severe liver damage, although no hepatotoxicity was demonstrated in experimental trials in laboratory animals. The toxicity of these drugs may be due to the presence of the thiazolidinedione (TZD) ring in their structures. Similar to troglitazone, 3-(3,5- dichlorophenyl)-2,4-thiazolidinedione (DCPT) also contains the TZD structure; however, in contrast to troglitazone, DCPT is known to cause hepatotoxicity in rats in vivo. In addition, DCPT and its hydrolytic metabolites cause cytotoxicity in wild-type human hepatoma HepG2 cells and CYP3A4-transfected HepG2 cells, but do not appear to be cytotoxic in MDCK cells in vitro. Therefore, DCPT may provide valuable insight on the potential hepatotoxicity associated with the TZD ring structure. Previous in vitro studies focused exclusively on the cytotoxic effects of DCPT when treated to the apical surface of the cell monolayer; however, the cytotoxic effects of DCPT when treated to the basolateral surface of the cell monolayer should also be investigated to gain better insight on DCPT cytotoxicity and the possible transport mechanisms that may be involved. Also, current in vitro studies use polystyrene plastic as an extracellular matrix (ECM) for cell adhesion and growth. Although polystyrene has proven to be a successful extracellular matrix in vitro, it is not truly representative of the internal biological environment. In contrast to polystyrene, collagen is an endogenous biological material found naturally throughout the body. To investigate the cell morphology of HepG2 cells and MDCK cells and the effects of ECM on the cytotoxicity of DCPT, cells were treated and prepared for scanning electron microscopy (SEM) using both a plastic and collagen (Type I) ECM. Improved cellular adhesion and growth were observed in cells cultured on the collagen ECM when compared to the plastic ECM. Cellular damage, changes in morphology, and overall cytotoxicity were observed in HepG2 cells cultured on both the plastic and collagen surfaces after treatment with 200 muM DCPT; however, minimal damage and morphology changes were observed in MDCK cells cultured on both surfaces after DCPT treatment. Overall, the collagen ECM did not significantly affect DCPT cytotoxicity. In addition, the apical and basolateral surface treatments did not significantly affect DCPT cytotoxicity; therefore, cellular transport mechanisms do not appear to influence the cytotoxicity of DCPT. Insignificant changes in transepithelial electrical resistance (TEER) were also observed when MDCK cells were treated with DCPT.