Antifungal activity and potential mechanism of Asiatic acid alone and in combination with fluconazole against Candida albicans.

Candida albicans (C. albicans) infection remains a challenge to clinicians due to the limited available antifungals. With the widespread use of antifungals in the clinic, the drug resistance has been emerging continuously, especially fluconazole. Therefore, searching for new antifungals, active constituents of natural or traditional medicines, and approaches to overcome antifungals resistance is needed. This study investigated the activity of Asiatic acid (AA) alone and in combination with fluconazole (FLC) against C. albicans in vitro and in vivo. The in vitro studies indicated that the drug combination had a synergistic effect on FLC-resistant C. albicans, with fractional inhibitory concentration index (FICI) of 0.25. And when AA at the dose of 32 µg/mL, the drug combination group could decrease the sessile minimum inhibitory concentration (sMIC) of FLC from > 1024 µg/mL to 0.125-0.25 µg/mL within 8 h against C. albicans biofilms, even with the FICI > 0.5. In vivo, the antifungal efficacy of AA used alone and in combination with FLC was evaluated by Galleria mellonella (G. mellonella) larvae. The drug combination group prolonged the survival rate and reduced tissue invasion of larvae infected with resistant C. albicans. Furthermore, mechanism studies indicated that the antifungal effects of AA in combination with FLC might be associated with the inhibition of drug efflux pump, the accumulation of reactive oxygen species (ROS) and the inhibition of hyphal growth. These findings might provide novel insights for overcoming drug resistance of C. albicans and bring new reference data for the development and application of AA in future.