Carbon Chain Length Determines Inhibitory Potency of Perfluoroalkyl Sulfonic Acids on Human Placental 3- Hydroxysteroid Dehydrogenase 1: Screening, Structure- Activity Relationship, and In Silico Analysis

Objective This study aimed to compare 9 perfluoroalkyl sulfonic acids (PFSA) with carbon chain lengths (C4-C12) to inhibit human placental 3 beta-hydroxysteroid dehydrogenase 1 (3 beta-HSD1), aromatase, and rat 3 beta-HSD4 activities.Methods Human and rat placental 3 beta-HSDs activities were determined by converting pregnenolone to progesterone and progesterone secretion in JEG-3 cells was determined using HPLC/MS-MS, and human aromatase activity was determined by radioimmunoassay.Results PFSA inhibited human 3 beta-HSD1 structure-dependently in the order: perfluorooctanesulfonic acid (PFOS, half-maximum inhibitory concentration, IC50: 9.03 +/- 4.83 mu mol/L) > perfluorodecanesulfonic acid (PFDS, 42.52 +/- 8.99 mu mol/L) > perfluoroheptanesulfonic acid (PFHpS, 112.6 +/- 29.39 mu mol/L) > perfluorobutanesulfonic acid (PFBS) = perfluoropentanesulfonic acid (PFPS) = perfluorohexanesulfonic acid (PFHxS) = perfluorododecanesulfonic acid (PFDoS) (ineffective at 100 mu mol/L). 6:2FTS (1H, 1H, 2H, 2H-perfluorooctanesulfonic acid) and 8:2FTS (1H, 1H, 2H, 2H-perfluorodecanesulfonic acid) did not inhibit human 3 beta-HSD1. PFOS and PFHpS are mixed inhibitors, whereas PFDS is a competitive inhibitor. Moreover, 1-10 mu mol/L PFOS and PFDS significantly reduced progesterone biosynthesis in JEG-3 cells. Docking analysis revealed that PFSA binds to the steroid-binding site of human 3 beta-HSD1 in a carbon chain length-dependent manner. All 100 mu mol/L PFSA solutions did not affect rat 3 beta-HSD4 and human placental aromatase activity.Conclusion Carbon chain length determines inhibitory potency of PFSA on human placental 3 beta-HSD1 in a V-shaped transition at PFOS (C8), with inhibitory potency of PFOS > PFDS > PFHpS > PFBS = PFPS = PFHxS = PFDoS = 6:2FTS = 8:2FTS.