Usefulness of in vitro combination assays of mitochondrial dysfunction and apoptosis for the estimation of potential risk of idiosyncratic drug induced liver injury.

Drug-induced liver injury (DILI) is one of the serious and frequent drug-related adverse events. This adverse event is a main reason for regulatory action pertaining to drugs, including restrictions in clinical indications and withdrawal from clinical trials or the marketplace. Idiosyncratic DILI especially has become a major clinical concern because of its unpredictable nature, frequent hospitalization, need for liver transplantation and high mortality. The estimation of the potential for compounds to induce idiosyncratic DILI is very difficult in non-clinical studies because the precise mechanism of idiosyncratic DILI is still unknown. Recently, many in vitro assays which indicate a possibility of the prediction of the idiosyncratic DILI have been reported. Among these, some in vitro assays focus on the effects of compounds on mitochondrial function and the apoptotic effects of compounds on human hepatocytes. In this study, we measured oxygen consumption rate (OCR) and caspase-3/7 activity as an endpoint of mitochondrial dysfunction and apoptosis, respectively, with human hepatocytes after treatment with compounds causing idiosyncratic DILI (troglitazone, leflunomide, ranitidine and diclofenac). Troglitazone and leflunomide decreased the OCR but did not affect caspase-3/7 activity. Ranitidine increased caspase-3/7 activity but did not affect the OCR. Diclofenac decreased the OCR and increased caspase-3/7 activity. Acetaminophen and ethanol, which are also hepatotoxicants but do not induce idiosyncratic DILI, did not affect the OCR or caspase-3/7 activity. These results indicate that a combination assay of mitochondrial dysfunction and apoptosis is useful for the estimation of potential risk of compounds to induce idiosyncratic DILI.