Benzalkonium disinfectants as emerging endocrine disruptors: Inhibition of 11β-Hydroxysteroid dehydrogenase 2 in human and rat models via steric and hydrophobic mechanisms: SPR and docking and enzymatic analysis.

Quaternary ammonium compounds, including benzalkonium chlorides (BACs), have broad uses as disinfectants, preservatives, and surfactants. The escalating application of QACs as disinfectants post-COVID-19 raises significant public health concerns regarding their potential as endocrine disruptors. To investigate this, a systematic literature review was conducted using PubMed, Web of Science, and Scopus databases for the period 2000-2026, identifying a critical gap regarding BAC's effects on glucocorticoid metabolism. The current study therefore aims to explore the suppressive effects of nine BACs on human and rat 11β-hydroxysteroid dehydrogenase type 2 (11β-HSD2), a steroidogenic enzyme for glucocorticoid inactivation, in human and rat microsomes (placental and renal sources) using HPLC-MS/MS technique and Surface Plasmon Resonance (SPR) assays. BACsblocked 11β-HSD2 depending on alkyl group, with C10+ derivatives exhibiting marked activity for human and C12+ derivatives for rat enzyme. C16 BAC emerged as the strongest suppressor (IC50 = 4.22 μM against human enzyme; 24.74 μM against rat homolog). SPR assay showed that C16 BAC had a high affinity binding with KD of 1.95 μM while C18 had moderate affinity with KD of 19.5 μM against human 11β-HSD2. Mechanistic studies identified BACs as mixed/noncompetitive inhibitors of 11β-HSD2 in both species. In intact human BeWo cells, C10-C18 BACs effectively suppressed cortisol metabolism at 1-100 μM. Pearson correlation analysis linked inhibitory potency to structural features (LogP, molecular weight, alkyl carbon count, heavy atoms, flex, Fsp3, volume, Sterimol L) for both enzymes. A 3D-QSAR highlighted apolar interactions are critical. Molecular docking further elucidated binding mechanisms, showing that BACs occupy the NAD+-binding site via van der Waals, H-bonds, apolar contacts, and charges. Collectively, this study reveals a novel mechanism by which BACs disrupt glucocorticoid metabolism through inhibiting 11β-HSD2. The findings underscore BACs as potent environmental endocrine disruptors, warranting urgent re-evaluation of their safety guidelines.