Inhibitory effects and kinetics of Sudan dyes on human carboxylesterases

Sudan dyes, widely used as industrial colorants and occasionally added illegally to foods, have been reported to act as environmental endocrine disruptors with adverse effects on metabolic processes. This study investigated the inhibitory effects of Sudan dyes on the predominant human carboxylesterases CES1 and CES2 using an in vitro system based on human liver microsomes, aiming to elucidate the mechanisms underlying Sudan dye-related metabolic toxicity. All Sudan dyes significantly inhibited CES1 and CES2 activities, with CES1 strongly inhibited by Sudan II, Para Red, and Sudan Red 7B, and CES2 by Sudan III, Sudan IV, and Sudan Red G, showing inhibition ratios exceeding 70%. Kinetic analyses combined with in vitro-in vivo extrapolation suggested potential interference of Sudan dyes with CES-mediated hydrolytic metabolism in vivo. Molecular docking revealed hydrophobic interactions and azo-group-mediated hydrogen bonding as key determinants of binding, and molecular dynamics simulations confirmed the formation of stable and compact enzyme-dye complexes. These findings provide new experimental evidence for understanding the toxicity of Sudan dyes mediated through CES inhibition and indicate a potential contribution to metabolic disorders, particularly in relation to lipid metabolism.