Pyridinium quaternary ammonium disinfectants inhibit neurosteroid biosynthesis as human and rat 5α-reductase 1 inhibitors

Pyridinium quaternary ammonium disinfectants (PYRs) are cationic surfactants widely used as disinfectants, antiseptics, and preservatives since COVID-19 and their potential effects on neurosteroidogenesis remain unknown. This study explored the inhibitions of eleven PYRs (C1-C20) on human and rat 5α-reductase 1 (5α-R1), identifying carbon-chain length dependent inhibition on human enzyme, with a V-shaped pattern, increasing potency from C12 (nadir activity, IC 50  = 97.87 μM) to C16 (peak activity, 5.78 μM) and then decreases to C20 (IC 50  = 75.93 μM). Enzyme kinetics and SPR (Surface Plasmon Resonance) showed similar high binding of PYRs to human 5α-R1 (C16's KD  = 5.24 μM, C18's KD  = 19.4 μM). Mechanistic analysis revealed that they exerted mixed/noncompetitive inhibition via binding to the NADPH binding pocket. SAR/QSAR modeling highlighted lipophilicity (LogP), molecular weight, carbon chain length and heavy atoms as key determinants of potency. Notably, these chemicals showed stronger inhibition in human 5α-R1 than in rat, underscoring species-specific pharmacodynamics. Molecular docking confirmed interactions with critical residues in NADPH binding site. Despite exhibiting greater microsomal activity compared to C14 PYR, the efficacy of C16 PYR in intact SF126 cells was diminished relative to C14 PYR due to its limited cellular permeability. The findings provide insights into 5α-R1 inhibition and support the identification of these disinfectants as neurosteroid endocrine disrupting actions.