Antifungal effect and mode of action of glochidioboside against Candida albicans membranes

Glochidioboside was obtained from Sambucus williamsii and its biological effect has not been reported. Its antifungal activity against pathogenic fungi and the mode of action involved in its effect were examined. Glochidioboside exerted antifungal effect with almost no hemolytic effect against human erythrocytes. To understand its antifungal mechanisms, membrane studies were done. Using two dyes, 3,3′-dipropylthiacarbocyanine iodide [DiSC ₃(5)] and propidium iodide, membrane depolarization and permeabilization by glochidioboside were confirmed. Furthermore, the membrane-active mechanism was proven by synthesizing a model membrane, calcein-encapsulating large unilamellar vesicles (LUVs), and also by observing the influx of different sized fluorescent dyes, such as calcein, FD4 and FD10, into the fungal cells. The membrane-active action was pore-forming action with radii between 1.4 and 2.3 nm. Finally, three dimensional (3D) flow cytometric analysis showed the shrinkage of the fungal cells from the membrane damage. In conclusion, this study suggests that glochidioboside exerts an antifungal activity through a membrane-disruptive mechanism.