A significant limitation of many in vitro assays is their limited metabolism of test substances.
The aim of this project was to address the general lack of knowledge concerning the intrinsic metabolic capacity of the different cell lines used in the various in vitro assays for endocrine disruption, as well as evaluate methods for incorporating metabolism in different currently used in vitro assays.
Specifically we have evaluated the endogenous metabolic potential of the CHO-K1 and H295R cell lines, the cells used in two in vitro OEDC test guidelines (TG458 and TG456) for endocrine disruption.
Following enzyme induction, in order to increase potential metabolic activity, we only saw an increased expression of genes for a few Phase I enzymes in the H295R cells. No significant induction of any of the major Phase I or Phase II enzymes were seen in the CHO-K1 cells.
In order to add a metabolic module to the AR and H295R in vitro assays, pre-incubation of test compounds with rat liver S9 was used as an add-on to the cell-based in vitro assays.
Our conclusion that the application of S9 liver fractions is a promising method for incorporating metabolism in vitro assays is supported by others in recently published studies, and we believe that with further optimizations and eventually validated protocols the inclusion of a metabolising system in vitro testing will strengthen the use of in vitro tests in the risk assessment of chemicals.
