In vitro investigation of the glutathione S - transferase M 1 and T 1 null genotypes as risk factors for troglitazone - induced liver injury

This article has not been copyedited and formatted. The final version may differ from this version. This article has not been copyedited and formatted. The final version may differ from this version. Abstract The double null mutation of glutathione S-transferase, GSTM1 and GSTT1 is reported to influence troglitazone-associated abnormal increases of ALT/AST. However, no non-clinical data have hitherto been reported with a bearing on the clinical outcomes and underlying mechanisms. To investigate whether deficiency in GSTM1 and/or GSTT1 is related to troglitazone hepatotoxicity in vitro, the covalent binding level (CBL, an index of reactive metabolite formation) and cytotoxicity of troglitazone and rosiglitazone, another thiazolidinedione but with low-hepatotoxicity, were examined using human liver samples phenotyped for cytochrome P450s (CYPs) and genotyped for GSTM1 and GSTT1. Despite addition of GSH, CBLs of troglitazone and rosiglitazone in human liver microsomes were correlated with CYP3A (or CYP2C8) and CYP2C8 activities, respectively. With addition of recombinant GSTM1, the microsomal CBLs of troglitazone and rosiglitazone decreased. However, the CBLs of troglitazone in GSTM1/GSTT1 wild-type hepatocytes were unexpectedly higher than those in null hepatocytes. Although this discrepancy is not fully explained, the GSTM1 and GSTT1 null mutations increased the cytotoxicity of troglitazone, independent of CYP3A or CYP2C8 activities. Furthermore, a GSH adduct of troglitazone, M2 was detected limited to GSTM1 wild-type hepatocytes. Of clear interest, GSTM1 and/or This article has not been copyedited and formatted. The final version may differ from this version. GSTT1 null mutation-dependent cytotoxicity, and higher exposure to the reactive metabolite trapped as M2 as for troglitazone, were not observed for rosiglitazone. This might at least partly explain the findings related to clinical hepatotoxicity, suggesting that measurement of GSH adducts or cytotoxicity using GSTM1-and GSTT1-genotyped hepatocytes might offer an important in vitro system to assist in better prediction of idiosyncratic hepatotoxicity. This article has not been copyedited and formatted. The final version may differ from this version.