Potential antiandrogenic effects of parabens and benzophenone-type UV-filters by inhibition of 3α-hydroxysteroid dehydrogenases.

Parabens and UV-filters are frequently used additives in cosmetics and body care products that prolong shelf-life. They are assessed for potential endocrine disrupting properties. Antiandrogenic effects of parabens and benzophenone-type UV-filters by blocking androgen receptor (AR) activity have been reported. Effects on local androgen formation received little attention. Local 5α-dihydrotestosterone (DHT) production with subsequent AR activation is required for male external genitalia formation during embryogenesis. We investigated whether parabens and benzophenone-type UV-filters might cause potential antiandrogenic effects by inhibiting oxidative 3α-hydroxysteroid dehydrogenases (3α-HSDs) involved in the backdoor pathway of DHT formation. Five different 3α-HSDs were assessed for their efficiency to catalyze the 3α-oxidation reaction to form DHT and activate AR. 17β-hydroxysteroid dehydrogenase type 6 (HSD17B6), retinol dehydrogenases type 5 and 16 were further assessed using a radiometric in vitro activity assay to determine the conversion of 5α-androstane-3α-ol-17-one to 5α-androstane-3,17-dione in lysates of overexpressing HEK-293 cells. All parabens tested, except p-hydroxybenzoic acid (a main metabolite) inhibited HSD17B6 activity. Hexyl- and heptylparaben, as well as benzophenone (BP)-1 and BP-2, showed the highest inhibitory potencies, with nanomolar IC values. Molecular modeling predicted binding modes for the inhibitory parabens and BPs and provided an explanation for the observed structure-activity-relationship. Our results propose a novel mechanism of antiandrogenic action for commercially used parabens and BP UV-filters by inhibiting HSD17B6 and lowering DHT synthesis. Follow-up studies should assess BP-3 metabolism after topical application and whether the identified inhibitors reach concentrations in liver, testis, or prostate to inhibit HSD17B6, thereby causing antiandrogenic effects.