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

Objective: This study aimed to compare 9 perfluoroalkyl sulfonic acids (PFSA) with carbon chain lengths (C4-C12) to inhibit human placental 3β-hydroxysteroid dehydrogenase 1 (3β-HSD1), aromatase, and rat 3β-HSD4 activities.

Methods: Human and rat placental 3β-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 3β-HSD1 structure-dependently in the order: perfluorooctanesulfonic acid (PFOS, half-maximum inhibitory concentration, IC : 9.03 ± 4.83 μmol/L) > perfluorodecanesulfonic acid (PFDS, 42.52 ± 8.99 μmol/L) > perfluoroheptanesulfonic acid (PFHpS, 112.6 ± 29.39 μmol/L) > perfluorobutanesulfonic acid (PFBS) = perfluoropentanesulfonic acid (PFPS) = perfluorohexanesulfonic acid (PFHxS) = perfluorododecanesulfonic acid (PFDoS) (ineffective at 100 μmol/L). 6:2FTS (1H, 1H, 2H, 2H-perfluorooctanesulfonic acid) and 8:2FTS (1H, 1H, 2H, 2H-perfluorodecanesulfonic acid) did not inhibit human 3β-HSD1. PFOS and PFHpS are mixed inhibitors, whereas PFDS is a competitive inhibitor. Moreover, 1-10 μmol/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 3β-HSD1 in a carbon chain length-dependent manner. All 100 μmol/L PFSA solutions did not affect rat 3β-HSD4 and human placental aromatase activity.

Conclusion: Carbon chain length determines inhibitory potency of PFSA on human placental 3β-HSD1 in a V-shaped transition at PFOS (C8), with inhibitory potency of PFOS > PFDS > PFHpS > PFBS = PFPS = PFHxS = PFDoS = 6:2FTS = 8:2FTS.