The use of isolated rainbow trout enterocytes to estimate extrahepatic metabolism of commercial chemicals

Thousands of chemicals are awaiting categorization for bioaccumulation potential. An in vitro test was developed to measure the biotransformation rates of bioaccumlative commercial chemicals (benzo[a]pyrene, chrysene, 9-methylanthracene, and PCB-209) by freshly isolated rainbow trout (Oncorhynchus mykiss) enterocytes. The enterocyte isolation procedure was optimized to yield 4x108+5x106 million cells per fish by systematically investigating pH (7.3-7.4), filtration steps, aeration (air), and DTT (1.0 mM) and collagenase (0.5 mg/ml for 5 min) concentrations. Immunofluorescence microscopy using antibodies to cytokeratin confirmed epithelial origin. Biotransformation rates of test chemicals were not different from control cells in uninduced and β-naphthoflavone-induced fish. In uninduced fish, CYP3A27 and CYP1A1 activity was 5- and 40-fold higher in hepatocytes compared to enterocytes, respectively. CYP1A1 activity was 2-fold higher versus uninduced enterocytes. The findings of this study showed that of enterocyte metabolism of CYP1A1 substrates can be ignored when estimating overall bioaccumulation potential whereas CYP3A27 substrates should be further investigated.