Determination of xenobiotic intrinsic clearance in freshly isolated hepatocytes from rainbow trout (Oncorhynchus mykiss) and rat and its application in bioaccumulation assessment

Bioaccumulation in fish depends on the dynamics of various processes that involve fish uptake, storage, and elimination of xenobiotics. Elimination via fish biotransformation is a primary process that can be evaluated in an in vitro system to improve the performance of the prediction of xenobiotic bioaccumulation potentials. In this study, values of intrinsic clearance (CLint) of seven reference compounds (atrazine, molinate, 4,4-bis(dimethylamino)-enzophenone, 4-nonylphenol, 2,4-di-tert-butylphenol, trifluralin, benzo(a) pyrene) in hepatocytes freshly isolated from rainbow trout and rat were determined using a substrate depletion approach. Atrazine was metabolized in rat hepatocytes with a CLint value of 3.81 +/- 1.96 mL/h/ 106 cells, whereas in trout hepatocytes, the clearance was not significant until very high cell concentration was used and the rate was estimated to be approximately 0.002 mL/h/106 cells. Intrinsic clearance values for all other compounds were 5.5-78.5-fold lower in trout hepatocytes than those in rat hepatocytes. Trout hepatic clearance (CLH) values were extrapolated from the CLint values using a well-stirred liver model. Biotransformation rate constants (k(MET)) of the compounds in trout were subsequently estimated and used as inputs to a kinetic model for the prediction of bioconcentration factors (BCF) in fish. Compared to the BCF values predicted without consideration of fish biotransformation, the inclusion of estimated k(MET) values significantly improved fish BCF predictions for the reference compounds. This study demonstrates a framework for future bioaccumulation assessment of xenobiotics using combined information of the physical-chemical properties of the compounds and the biotransformation potentials of the compounds in fish.