Protein and lipid binding parameters in rainbow trout (Oncorhynchus mykiss) blood and liver fractions to extrapolate from an in vitro metabolic degradation assay to in vivo bioaccumulation potential of hydrophobic organic chemicals

Beate I. Escher, Christina E. Cowan-Ellsberry, Scott Dyer, Michelle R. Embry, Susan Erhardt, Marlies Halder, Jung-Hwan Kwon, Karla Johanning, Mattheus T T Oosterwijk, Sibylle Rutishauser, Helmut Segner, John Nichols

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Binding of hydrophobic chemicals to colloids such as proteins or lipids is difficult to measure using classical microdialysis methods due to low aqueous concentrations, adsorption to dialysis membranes and test vessels, and slow kinetics of equilibration. Here, we employed a three-phase partitioning system where silicone (polydimethylsiloxane, PDMS) serves as a third phase to determine partitioning between water and colloids and acts at the same time as a dosing device for hydrophobic chemicals. The applicability of this method was demonstrated with bovine serum albumin (BSA). Measured binding constants (K BSAw) for chlorpyrifos, methoxychlor, nonylphenol, and pyrene were in good agreement with an established quantitative structure-activity relationship (QSAR). A fifth compound, fluoxypyr-methyl-heptyl ester, was excluded from the analysis because of apparent abiotic degradation. The PDMS depletion method was then used to determine partition coefficients for test chemicals in rainbow trout (Oncorhynchus mykiss) liver S9 fractions (K S9w) and blood plasma (K bloodw). Measured K S9w and K bloodw values were consistent with predictions obtained using a mass-balance model that employs the octanol-water partition coefficient (K ow) as a surrogate for lipid partitioning and K BSAw to represent protein binding. For each compound, K bloodw was substantially greater than K S9w, primarily because blood contains more lipid than liver S9 fractions (1.84% of wet weight vs 0.051%). Measured liver S9 and blood plasma binding parameters were subsequently implemented in an in vitro to in vivo extrapolation model to link the in vitro liver S9 metabolic degradation assay to in vivo metabolism in fish. Apparent volumes of distribution (V d) calculated from the experimental data were similar to literature estimates. However, the calculated binding ratios (f u) used to relate in vitro metabolic clearance to clearance by the intact liver were 10 to 100 times lower than values used in previous modeling efforts. Bioconcentration factors (BCF) predicted using the experimental binding data were substantially higher than the predicted values obtained in earlier studies and correlated poorly with measured BCF values in fish. One possible explanation for this finding is that chemicals bound to proteins can desorb rapidly and thus contribute to metabolic turnover of the chemicals. This hypothesis remains to be investigated in future studies, ideally with chemicals of higher hydrophobicity.

Original languageEnglish
Pages (from-to)1134-1143
Number of pages10
JournalChemical Research in Toxicology
Issue number7
Publication statusPublished - 2011 Jul 18
Externally publishedYes


ASJC Scopus subject areas

  • Toxicology

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