Chain Length-Dependent Inhibition of Human and Rat Placental Aromatase by Benzalkonium Disinfectants: Experimental, Quantitative Structure–Activity Relationship, and In Silico Docking Insights

Benzalkonium chloride (BAC) compounds are a subclass of cationic surfactants widely used as disinfectants. The current research explored the inhibition of BACs on human and rat aromatase activity, revealing a structure-dependent mechanism. In human placental microsomes, BACs (C10, C12, C14, C16, and C18) significantly suppressed aromatase activity with IC₅₀ and <i>K</i>_<i>i</i> values following the order C10 > C12 > C14 > C16 > C18, indicating that inhibitory potency increases with alkyl chain length. Enzyme kinetics and Lineweaver-Burk analyses suggested mixed/noncompetitive inhibition, where BACs bind both free enzyme and enzyme-substrate complexes. Similar trends were observed in rat aromatase, though only BAC-C12 and BAC-C14 showed significant inhibition. In human BeWo cells, BACs reduced estradiol secretion, with BAC-C12 exhibiting comparable inhibition to BAC-C18 despite lower aromatase inhibition in microsomes, suggesting that membrane permeability also influences cellular effects. Molecular docking revealed that BACs bind near the heme site, forming hydrogen bonds and HY interactions, with binding affinity increasing with chain length (Δ<i>G</i>: C10 > C12 > C14 > C16 > C18) against human aromatase. 3D-QSAR pharmacophore modeling identified HY regions as critical for inhibition of human aromatase. Pharmacokinetics predictions indicated poor intestinal absorption for BAC-C16 and BAC-C18, while BAC-C12 and BAC-C14 showed better solubility. These findings highlight the structural dependence of BAC-mediated aromatase inhibition, with implications for endocrine disruption risk assessment.