Isothiazole Disinfectants Inhibit Neurosteroid Production by Targeting Human and Rat 5α-Reductase Type 1

Isothiazole disinfectants are widely used antimicrobial preservatives found in various consumer products, raising concerns about their potential effects on human health. This study investigated the inhibitory effects of seven isothiazole disinfectants on human and rat steroid 5α-reductase type 1 (SRD5A1), a key enzyme in neurosteroid biosynthesis. Among the tested compounds, dichlorooctylisothiazole exhibited the strongest suppression on human SRD5A1 with an IC₅₀ value of 3.23 μM, followed by octylisothiazole (5.10 μM), butylbenzo[d]isothiazol-3(2H)-one (16.51 μM), benzisothiazole (31.64 μM), and methylchloroisothiazole (42.65 μM). Enzyme kinetics and molecular docking analyses revealed that these compounds acted through mixed/noncompetitive inhibition by binding to the NADPH-binding pocket via van der Waals and hydrogen bonds. Cell-based studies in human SF126 glioblastoma cells confirmed that these compounds penetrated cell membranes and reduced dihydrotestosterone production. Structure-activity relationship analysis showed that compounds with higher LogP, molecular weight, volume, heavy atom number, and apolar desolvation exhibited stronger inhibitory activity. 3D quantitative structure-activity relationship analysis incorporated hydrogen bond acceptor and hydrophobicity domain features. Additionally, dichlorooctylisothiazole showed significant inhibition of rat SRD5A1 with an IC₅₀ of 21.47 μM. In conclusion, these findings reveal some isothiazole disinfectants as potential endocrine disruptors targeting neurosteroid biosynthesis via SRD5A1 and highlight clear structure-activity relationship and species-dependent variance.