WITHDRAWN: Baicalein protects against Staphylococcus aureus pneumonia in a mouse model via inhibition of the self-assembly of α-hemolysin heptamers

α-Hemolysin (α-HL) is secreted by Staphylococcus aureus as a water-soluble monomer that assembles in the lipid bilayers of susceptible host cells to form cylindrical heptameric pores. In this study, we found that baicalein (BAE), a natural compound with weak anti-S. aureus activity, could inhibit the hemolytic activity of α-HL at low concentrations. Further, molecular dynamics simulations, free energy calculations, and mutagenesis assays were carried out to determine the potential mode of action. The data revealed that BAE could directly bind to α-HL, restricting the conformation of the critical Loop region in α-HL and preventing the formation of α-HL heptameric transmembrane pore, thereby inhibiting the hemolytic activity of α-HL. This mechanism was confirmed by experimental data based on a deoxycholate-induced oligomerization assay. Moreover, in vivo tests indicated that BAE provides protection against lethal S. aureus pneumonia in a mouse model system. The mortality, bacterial load and histopathologic manifestation in lung tissue, percent neutrophils and cytokine levels in the bronchoalveolar lavage fluids were significantly decreased following treatment with BAE. These findings indicate that BAE hinders the lysis activity of α-HL through a novel mechanism, which should facilitate the development of novel therapeutics that target S. aureus α-HL.