Biotransformation of genistein and bisphenol A in cell lines used for screening endocrine disruptors

In vitro assays provide the opportunity for generating alerts for chemicals which interact with hormone receptors and are also valuable tools for mechanistic research. However, the limited capabilities of in vitro models to metabolically activate or inactivate xenobiotics may lead to misinterpretation of the in vitro data if such information is not taken into account. The aim of this study was to investigate the metabolic capabilities of human HepG2, human MCF7 and mouse HC11 cell lines used for testing endocrine disruptors (EDs) toward radiolabelled bisphenol A and genistein, two estrogenic compounds for which metabolic pathways in vivo as in vitro are well known. Incubations were performed during 12-48 h with 250.10(3) cells in 12 wells plates and 5-25 microM of substrates. The kinetics of formation of the metabolites were studied. Rat liver slices were used as reference for comparison with the metabolic capabilities of the cell lines. HC11 cells did not show any biotransformation capability while the major biotransformation pathways in HepG2 and MCF7 cells were conjugation to sulfate and to a lesser extent to glucuronic acid. We detected no phase I metabolite, even in rat liver slices. These results suggest that HC11 cells should be a valuable cellular system to study the intrinsic estrogenic activity of the tested compound, while HepG2 and MCF7 cells can help to take into account part of the metabolic fate of the tested compound that occur in vivo. However, since phase I enzymes are poorly or not at all expressed in these systems, their use in endocrine disruptor testing may result in false negative for compounds for which bioactivation is a prerequisite.