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In vitro to in vivo extrapolation of hepatic metabolism in fish: An inter-laboratory comparison of in vitro methods - presentation
Citation:
Embry, M., K. Fay, M. Bernard, I. Bischof, J. Davis, J. Domoradzki, M. Halder, J. Hu, K. Johanning, H. Laue, J. Nichols, H. Peterson, C. Schlechtriem, H. Segner, AND J. Weeks. In vitro to in vivo extrapolation of hepatic metabolism in fish: An inter-laboratory comparison of in vitro methods - presentation. SETAC North America, Orlando, FL, November 06 - 10, 2016.
Impact/Purpose:
not applicable
Description:
Chemical biotransformation represents the largest source of uncertainty in chemical bioaccumulation assessments. Model-based estimates of chemical bioconcentration in fish may be greatly improved by including biotransformation rates, as measured in vitro. Substrate depletion assays with trout hepatocytes or liver subcellular fractions (S9) have been successfully employed to this end. Building on previous work, a multi-laboratory ring trial was coordinated by the ILSI Health and Environmental Sciences Institute (HESI). The specific aims of the ring trial were to determine the reliability of these assays within and across laboratories, compare the performance of substrate depletion assays using the two biological systems, and support the development of two OECD test guidelines (OECD Project 3.13). Six laboratories conducted substrate depletion assays for 6 test chemicals (pyrene, 4-n-nonylphenol, fenthion, cyclohexyl salicylate, deltamethrin, methoxychlor) using both trout liver S9 fractions and trout hepatocytes to determine in vitro intrinsic clearance (CL in vitro,int ). Using either test system, participating laboratories measured similar rates of metabolism for each test chemical, and the rates for each chemical exhibited similar variability. The intra-laboratory agreement for each test chemical in CL in vitro,int averaged 15-23 %CV for the hepatocyte assays and 5-29 %CV for the S9 assays. The inter-laboratory agreement was somewhat less, ranging from 22-40 %CV for the hepatocyte assays and 10-29 %CV for the S9assays. Variability in predicted hepatic clearance values, and by extension modeled BCF estimates, was lower than variability exhibited by the in vitro data sets due to blood flow limitations on clearance. For all test chemicals, hepatic clearance values determined by the two test systems were in good agreement (within 2-fold). Bioaccumulation predictions generated using the in vitro data had closer agreement with empirical BCF values than traditional modeled estimates, even for the more slowly metabolized compounds. Results of this ring trial firmly establish the reliability of these methods and provide strong support for use of this information in modeled BCF assessments for fish.