Inhibitory effects and mode of antifungal action of isobavachalcone on Candida albicans growth and virulence factors

The fungus Candida albicans causes various kinds of human infections, including oral thrush, vulvovaginitis and life-endangering bloodstream infections, the incidence of which are rising. Worsening this, the clinical antifungals are limited to a few, highlighting the necessity to develop novel antifungal therapies. In this study, the antifungal activities of isobavachalcone against C. albicans SC5314 and nine C. albicans clinical isolates were tested. The effects of isobavachalcone (IBC) on C. albicans virulence factors, such as hyphal formation, adhesion, biofilm formation and extracellular phospholipase production, as well as the underlying mechanism, were also evaluated. Antifungal susceptibility test revealed that IBC has significant anti-Candida activities, with both MIC and MFC being 4-5 μg/mL against all strains tested. Hyphal formation in RPMI-1640, Spider and GlcNAc medium, adhesion to abiotic polystyrene surfaces and surfaces of A549 cells, could be inhibited by IBC. Most important, IBC could inhibit the C. albicans biofilm formation and development. PI staining tests showed that IBC could increase the cell membrane permeability, suggesting the damages to the fungal cell membrane. IBC was further demonstrated to induce excessive ROS production in C. albicans planktonic cells and its mature biofilms, as revealed by DCFH fluorescence detection through flowcytometry and relative fluorescence intensity analysis (with a microplate reader). The roles of ROS in the antifungal activity of IBC were further confirmed through antioxidant rescue assays in MIC and biofilm formation tests. Compared to its antifungal activity, the cytotoxicity against mammalian cells was low, indicating its potential in developing antifungal therapies.