Metabolic clearance of physicochemically diverse pharmaceuticals in cultured fish hepatocytes

Fish are inherently susceptible to the exposure and effects of pharmaceutical pollutants in aquatic ecosystems and are often used to quantify the bioaccumulation and effects of active pharmaceutical ingredients (APIs) during environmental risk assessment. While metabolism and transport are major determinants of an API's ability to bioaccumulate, a sound understanding of these processes in fish and how they compare to those seen in mammals is lacking. Primary hepatocyte cultures comprise a promising in vitro tool that can be applied to help fill these knowledge gaps, while also contributing to the refinement, reduction, and eventual replacement of animal testing in ecotoxicology. Here we apply the well-established rainbow trout (Oncorhynchus mykiss) primary hepatocyte monolayer model to assess the hepatic clearance of five diverse APIs, namely propranolol, quetiapine, mycophenolic acid, clozapine, and olaparib. We also explore the effects of these APIs on the transcription of selected transport- and metabolism-related genes (abcb1, mrp2, cyp1a, and cyp3a) and metabolic enzyme (cytochrome P4501A) activity in fish hepatocytes. The hepatocyte monolayers were found to clear all the studied APIs, with the majority showing comparable extrapolated clearance rates to those measured in humans. Transcript profiling and enzyme activity assay results, on the other hand, showed both differences and similarities to currently available human data, emphasizing the fact that the clearance and effects of APIs on metabolic and transport systems cannot be assumed to be directly comparable between fish and humans. Our data further support the good utility and replicability of the rainbow trout hepatocyte monolayer model and, in turn, its use in hazard identification and building risk profiles for APIs with wide-ranging properties.