Synergistic effects of dioscin and amphotericin B against Candida albicans: a promising strategy for antifungal therapy

The emerging antifungal resistance exacts deteriorating effects on the availability of drugs for treating fungal infections, calling for novel therapies. Although amphotericin B (AmB) is clinically effective and rarely causes resistance, its severe side effects warrant further reduction. Enhancing or potentiating AmB efficacy with other agents to lower the dose of AmB is appealing to reduce AmB toxicity. Dioscin, a steroidal saponin from the <i>Dioscorea</i> genus, has shown multiple pharmacological activities, including anticancer, antifungal, hepatoprotective, and nephroprotective effects. As combinational therapy has multiple advantages, it is interesting to explore the effects of dioscin and AmB combination in <i>C. albicans</i>, which is the most common fungal pathogen in humans. In this study, through a checkerboard assay, we found that dioscin and AmB produced synergistic effects in inhibiting the planktonic growth of <i>C. albicans</i>, <i>Candida krusei</i>, and <i>Candida tropicalis</i> at 24 h. Dioscin (1 μg/mL) and AmB (0.625 μg/mL) synergistically inhibited the biofilm formation (97%) and development (60%) of <i>C. albicans</i> (SC5314), significantly superior to either agent alone (<i>p</i> < 0.01). Time-killing assay revealed that the combination of dioscin (1 μg/mL) and AmB (0.625 μg/mL) greatly enhanced the killing efficacy compared to either agent alone. The hyphal formation and adhesion to abiotic surfaces of <i>C. albicans</i> were also suppressed by this combination. The damages to the cell membrane caused by this combination were revealed by the cell membrane integrity assay and cell membrane potential assay using fluorescent dyes. Cell membrane damage was further confirmed by results from the transmission electron microscope and scanning electron microscope. Overall, our results suggested that the synergistic combination of dioscin and AmB causes cell membrane damage and holds great potential for future development as anti-<i>Candida</i> therapies.