Interference of Paraben Compounds with Estrogen Metabolism by Inhibition of 17β-Hydroxysteroid Dehydrogenases

Parabens are effective preservatives widely used in cosmetic products and processed food, with high human exposure. Recent evidence suggests that parabens exert estrogenic effects. This work investigated the potential interference of parabens with the estrogen-activating enzyme 17-hydroxysteroid dehydrogenase (17 beta-HSD) 1 and the estrogen-inactivating 17 beta-HSD2. A ligand-based 17 beta-HSD2 pharmacophore model was applied to screen a cosmetic chemicals database, followed by in vitro testing of selected paraben compounds for inhibition of 17 beta-HSD1 and 17 beta-HSD2 activities. All tested parabens and paraben-like compounds, except their common metabolite p-hydroxybenzoic acid, inhibited 17 beta-HSD2. Ethylparaben and ethyl vanillate inhibited 17 beta-HSD2 with IC50 values of 4.6 +/- 0.8 and 1.3 +/- 0.3 mu M, respectively. Additionally, parabens size-dependently inhibited 17 beta-HSD1, whereby hexyl- and heptylparaben were most active with IC50 values of 2.6 +/- 0.6 and 1.8 +/- 0.3 mu M. Low micromolar concentrations of hexyl- and heptylparaben decreased 17 beta-HSD1 activity, and ethylparaben and ethyl vanillate decreased 17 beta-HSD2 activity. However, regarding the very rapid metabolism of these compounds to the inactive p-hydroxybenzoic acid by esterases, it needs to be determined under which conditions low micromolar concentrations of these parabens or their mixtures can occur in target cells to effectively disturb estrogen effects in vivo.