Hydrophobicity-driven inhibition of human and rat 11β-hydroxysteroid dehydrogenase 2 by isothiazolinone biocides: Insights from enzyme kinetics and SPR interactions.

Isothiazole (IT) derivatives are a class of broad-spectrum antimicrobial agents. Despite their widespread use, their effects on the glucocorticoid endocrine system remain unclear. This study investigates the potential interaction of IT biocides with 11β-hydroxysteroid dehydrogenase 2 (11β-HSD2), a key enzyme in glucocorticoid metabolism. The inhibitory strength and structure-activity relationship (SAR)/3D-QSAR of IT and its 6 derivatives on human (placental) and rat (renal) 11β-HSD2 were assessed. The results demonstrated that the IT biocides exhibited a range of inhibitory potencies against human 11β-HSD2, with half-maximal inhibitory concentration (IC₅₀) values spanning from 11.76 μM to greater than 100 μM. These IT biocides inhibited rat 11β-HSD2 in a similar order. Surface Plasmon Resonance analysis revealed that dichlorooctylisothiazolinone (KD = 12.1 μM) had higher affinity to human 11β-HSD2 than benzisothiazolinone (KD = 14.9 μM). Bivariate correlation analysis demonstrated a positive correlation between pIC50 values and hydrophobicity, molecular weight, heavy atom number, volume, and Log D. Molecular docking analysis indicated that these IT biocides bind to cofactor binding sites or between the steroid and cofactor interface. Additionally, 3D-QSAR modeling highlighted the influence of hydrogen bond acceptors and hydrophobic regions on the inhibitory activity of these compounds. The suppression of cortisol metabolism in intact placental BeWo cells is influenced not only by their inhibitory potency on human 11β-HSD2 but also by their cell membrane permeability. These findings provide valuable insights into the endocrine-disrupting potential of IT biocides and their interactions with 11β-HSD2.