The covalent binding of reactive intermediates to macromolecules might have potential involvement in severe adverse drug reactions. Thus, quantification of reactive metabolites is necessary during the early stage of drug discovery to avoid serious toxicity. In this study, the relationship between covalent binding and glutathione (GSH) conjugate formation in rat and human liver microsomes were investigated using 10 representative radioactive compounds that have been reported as hepatotoxic or having other toxicity derived from their reactive intermediates: acetaminophen, amodiaquine, carbamazepine, clozapine, diclofenac, furosemide, imipramine, indomethacin, isoniazid, and tienilic acid, all at a concentration of 10 microM. The GSH conjugate formation rate correlates well with the covalent binding of radioactivity (both rat and human, r2 = 0.93), which suggests that quantification of the GSH conjugate can be used to estimate covalent binding. To quantify the GSH-conjugation rate with non-radiolabeled compounds in vitro, the validation study for the determination of GSH conjugate formation using 35S-GSH by radio-HPLC was useful to predict metabolic activation. Following oral administration of 20 mg/kg of the radiolabeled compounds to rats, radioactivity that covalently bound to plasma and liver proteins was determined. The in vivo maximum covalent binding level in liver based on the free fraction of plasma area under the concentration curve (AUC) and in vitro covalent binding rate was found to correlate well (r2 = 0.79). Therefore, this model for in vitro covalent binding studies in human and rat and in vivo rat studies might be useful in predicting human metabolic activation of compounds.

Interspecies allometric scaling is a useful tool for calculating human pharmacokinetic (PK) parameters from data in animals. In this study, in order to determine the scaling exponent in a simple allometric equation that can predict human clearance (CL) and distribution volume at steady state (Vss) of monoclonal antibodies (mAbs) from monkey data alone, PK data of 24 mAbs were collected and analyzed according to the types of targeted antigens (soluble or membrane-bound antigens). Based on the observed PK data in humans (at clinical doses) and monkeys (at >1 mg/kg), where the PK is expected to be linear, the mean scaling exponents in the allometric equation for CL and Vss, respectively, against body weight were calculated to be 0.79 and 1.12 [95% confidence intervals (CIs): 0.69-0.89 and 0.96-1.28] for soluble antigens, and 0.96 and 1.00 (95% CIs: 0.83-1.09 and 0.87-1.13) for membrane-bound antigens. Using these exponents and monkey PK data (at >1 mg/kg) alone, both human CL and Vss of mAbs can be predicted with reasonable accuracy, i.e., within 2-fold of the observed values. Compared with traditional allometric scaling using PK data from three or more preclinical species, this approach is simple, quick, resource-saving, and useful in drug discovery and development.

Objectives. We determined the serum bile acid (BA) composition in patients with liver diseases and healthy volunteers to investigate the relationship between the etiologies of liver disease and BA metabolism. Material and Methods. Sera from 150 patients with liver diseases and 46 healthy volunteers were obtained. The serum concentrations of the 16 different BAs were determined according to the LC-MS/MS method and were compared between the different liver diseases. Results. A total of 150 subjects, including patients with hepatitis C virus (HCV) (n = 44), hepatitis B virus (HBV) (n = 23), alcoholic liver disease (ALD) (n = 21), biliary tract disease (n = 20), nonalcoholic fatty liver disease (NAFLD) (n = 13), and other liver diseases (n = 29), were recruited. The levels of UDCA and GUDCA were significantly higher in the ALD group, and the levels of DCA and UDCA were significantly lower in the biliary tract diseases group than in viral hepatitis group. In the UDCA therapy (−) subgroup, a significantly lower level of TLCA was observed in the ALD group, with lower levels of CDCA, DCA, and GLCA noted in biliary tract diseases group compared to viral hepatitis group. Conclusions. Analysis of the BA composition may be useful for differential diagnosis in liver disease.

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