In this study, the antifungal activity and mode of action(s) of hibicuslide C derived from Abutilon theophrasti were investigated. Antifungal susceptibility testing showed that hibicuslide C possessed potent activities toward various fungal strains and less hemolytic activity than amphotericin B. To understand the antifungal mechanism(s) of hibicuslide C in Candida albicans, flow cytometric analysis with propidium iodide was done. The results showed that hibicuslide C perturbed the plasma membrane of the C. albicans. The analysis of the transmembrane electrical potential with 3,3'-dipropylthiacarbocyanine iodide [DiSC3(5)] indicated that hibicuslide C induced membrane depolarization. Furthermore, model membrane studies were performed with calcein encapsulating large unilamellar vesicles (LUVs) and FITC-dextran (FD) loaded LUVs. These results demonstrated that the antifungal effects of hibicuslide C on the fungal plasma membrane were through the formation of pores with radii between 2.3 nm and 3.3 nm. Finally, in three dimensional flow cytometric contour plots, a reduced cell sizes by the pore-forming action of hibicuslide C were observed. Therefore, the present study suggests that hibicuslide C exerts its antifungal effect by membrane-active mechanism.
Keywords: 3,3′-dipropylthiacarbocyanine; 3-(4,5-dimethyl-2-thiazolyl)-2,5-diphenyl-2H-tetrazolium bromide; ATCC; American Type Culture Collection; Antifungal effect; CH(2)Cl(2); CLSI; Candida albicans; Clinical and Laboratory Standards Institute; DiSC(3)(5); EtOAc; FD; FITC; FITC–dextran; Hibicuslide C; KCTC; Korean Collection For Type Cultures; LUV; MIC; MTT; MeOH; Membrane-active mechanism; PBS; PC; PE; PI; Phytochemical; dichloromethane; ethyl acetate; fluorescein isothiocyanate; large unilamellar vesicle; methanol; minimum inhibitory concentration; phosphate buffered saline; phosphatidylcholine; phosphatidylethanolamine; phosphatidylinositol.
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