Synergistic and Antagonistic Mechanisms of Arctium lappa L. Polyphenols on Human Neutrophil Elastase Inhibition: Insights from Molecular Docking and Enzymatic Kinetics

This study systematically investigated the inhibitory mechanism of <i>Arctium lappa</i> L. polyphenols (ALP) against human neutrophil elastase (HNE). Molecular docking techniques were employed to predict the binding patterns and inhibition types between polyphenolic components and HNE, complemented by in vitro enzymatic tests to validate inhibitory efficacy. Combination index (CI) analysis was applied to evaluate synergistic effects. Through preliminary in vitro screening, chlorogenic acid, quercetin, and isochlorogenic acid A were identified as key bioactive constituents. Experimental results demonstrated that the half-inhibitory concentration (IC₅₀) of individual compounds against HNE ranged from 46.4 to 203.3 μM, while ALP extract exhibited dose-dependent inhibition (IC₅₀ = 0.99 mg/mL). Drug combination ratios based on individual IC₅₀ values revealed synergistic effects (CI < 1) in chlorogenic acid-quercetin and isochlorogenic acid A-quercetin combinations, whereas antagonism (CI > 1) was observed in chlorogenic acid-isochlorogenic acid A pairs. The molecular docking results predicted that chlorogenic acid and isochlorogenic acid A competitively occupy the same binding site of the target protein (HNE) to exert inhibitory effects, thereby explaining the antagonism produced by their combination. In contrast, quercetin may inhibit HNE with a binding site different from that of chlorogenic acid or isochlorogenic acid A, which accounts for the observed synergistic effects. This study provides the first systematic elucidation of synergistic mechanisms of ALP as natural HNE inhibitors, providing theoretical foundations for developing novel natural HNE inhibitors with potential applications in acute lung injury, COVID-19-associated inflammatory conditions, and chronic inflammatory diseases.