Direct inhibition of human and rat 11β-hydroxysteroid dehydrogenase 2 by per- and polyfluoroalkyl substances: Structure-activity relationship and in silico docking analysis

Per- and polyfluoroalkyl substances (PFAS) are persistent in the environment and may disrupt the endocrine system. Our previous study showed that perfluorooctanoic acid (PFOA, C8) and perfluorooctanesulfonic acid (PFOS, C8S) can inhibit 11β-hydroxysteroid dehydrogenase 2 (11β-HSD2) activity leading to an active glucocorticoid accumulation. In this study, we extended investigation for 17 PFAS, including carboxylic and sulfonic acids, with different carbon-chain lengths, to determine their inhibitory potency and structure-activity relationship in human placental and rat renal 11β-HSD2. C8-C14 PFAS at 100 μM significantly inhibited human 11β-HSD2 with a potency as C10 (half-maximal inhibitory concentration, IC50, 9.19 μM) > C11 (15.09 μM) > C12 (18.43 μM) > C9 (20.93 μM) > C13 (124 μM) > C14 (147.3 μM) > other C4-C7 carboxylic acids, and C8S > C7S = C10S > other sulfonic acids. For rat 11β-HSD2, only C9 and C10 and C7S and C8S PFAS exhibited significant inhibitory effects. PFAS are primarily mixed/competitive inhibitors of human 11β-HSD2. Preincubation and simultaneous incubation with the reducing agent dithiothreitol significantly increased human 11β-HSD2 but not rat 11β-HSD2, and preincubation but not simultaneous incubation with dithiothreitol partially reversed C10-mediated inhibition on human 11β-HSD2. Docking analysis showed that all PFAS bound to the steroid-binding site and carbon-chain length determined the potency of inhibition, with the optimal molecular length (12.6 Å) for potent inhibitors PFDA and PFOS, which is comparable to the molecular length (12.7 Å) of the substrate cortisol. The length between 8.9 and 17.2 Å is the probable threshold molecular length to inhibit human 11β-HSD2. In conclusion, the carbon-chain length determines the inhibitory effect of PFAS on human and rat 11β-HSD2, and the inhibitory potency of long-chain PFAS on human and rat 11β-HSD2 showed V-shaped pattern. Long-chain PFAS may partially act on the cysteine residues of human 11β-HSD2.