Establishment of an in vitro cholestasis risk assessment system using two-dimensional cultured HepaRG cells and 12 bile acids.

Drug-induced liver injury (DILI) is a major cause of market withdrawal or drug-development discontinuation because of safety concerns. In this study, we focused on drug-induced cholestasis (DIC) to establish an in vitro cytotoxicity test system and analyze its sensitivity using two-dimensional (2-D) cultured HepaRG cells and 12 types of bile acids (BAs) present in the human serum. First, to detect the cytotoxicity associated with cholestasis effectively, non-toxic BA concentrations were investigated and determined to be 100-fold the human serum value (455 µM total BAs). Next, the cytotoxicity of 31 compounds that can inhibit the bile acid export pump (BSEP) and were categorized as no-DILI-concern, less-DILI-concern, and most-DILI-concern was examined. None of the no-DILI-concern compounds yielded cytotoxicity, whereas almost all less-DILI-concern compounds (with the exception of simvastatin) and most-DILI-concern compounds (with the exception of bosentan) exhibited cytotoxicity. An investigation of the cause of cytotoxicity using 3H-taurocholic acid revealed that most-DILI-concern and less-DILI-concern compounds, but not no-DILI-concern compounds, triggered the accumulation of radioactivity in the cell lysates. Thus, the onset of cytotoxicity seemed to be associated with cholestasis. The established HepaRG cytotoxicity assessment system (sensitivity of 89%, specificity of 100%, and accuracy of 97%) was mostly superior to the Css/BSEP IC50 (> 0.1) assessment system (sensitivity of 83%, specificity of 100%, and accuracy of 72%). Therefore, the assay method using 2-D cultured HepaRG cells and 12 BAs established here can be widely applicable as a model for the in vitro potential assessment of DIC.

The uracil breath test in the assessment of dihydropyrimidine dehydrogenase activity: pharmacokinetic relationship between expired 13CO2 and plasma [2-13C]dihydrouracil.

PURPOSE: Dihydropyrimidine dehydrogenase (DPD) deficiency is critical in the predisposition to 5-fluorouracil dose-related toxicity. We recently characterized the phenotypic [2-(13)C]uracil breath test (UraBT) with 96% specificity and 100% sensitivity for identification of DPD deficiency. In the present study, we characterize the relationships among UraBT-associated breath (13)CO(2) metabolite formation, plasma [2-(13)C]dihydrouracil formation, [2-(13)C]uracil clearance, and DPD activity. EXPERIMENTAL DESIGN: An aqueous solution of [2-(13)C]uracil (6 mg/kg) was orally administered to 23 healthy volunteers and 8 cancer patients. Subsequently, breath (13)CO(2) concentrations and plasma [2-(13)C]dihydrouracil and [2-(13)C]uracil concentrations were determined over 180 minutes using IR spectroscopy and liquid chromatography-tandem mass spectrometry, respectively. Pharmacokinetic variables were determined using noncompartmental methods. Peripheral blood mononuclear cell (PBMC) DPD activity was measured using the DPD radioassay. RESULTS: The UraBT identified 19 subjects with normal activity, 11 subjects with partial DPD deficiency, and 1 subject with profound DPD deficiency with PBMC DPD activity within the corresponding previously established ranges. UraBT breath (13)CO(2) DOB(50) significantly correlated with PBMC DPD activity (r(p) = 0.78), plasma [2-(13)C]uracil area under the curve (r(p) = -0.73), [2-(13)C]dihydrouracil appearance rate (r(p) = 0.76), and proportion of [2-(13)C]uracil metabolized to [2-(13)C]dihydrouracil (r(p) = 0.77; all Ps < 0.05). CONCLUSIONS: UraBT breath (13)CO(2) pharmacokinetics parallel plasma [2-(13)C]uracil and [2-(13)C]dihydrouracil pharmacokinetics and are an accurate measure of interindividual variation in DPD activity. These pharmacokinetic data further support the future use of the UraBT as a screening test to identify DPD deficiency before 5-fluorouracil-based therapy.