Physical Interaction of Sodium Houttuyfonate With β-1,3-Glucan Evokes Candida albicans Cell Wall Remodeling

Candida albicans is a commonly isolated opportunistic yeast and can endanger immune-compromised human health. As increasingly isolated strains present resistance to currently used antifungals, it is necessary to develop novel antimycotics. In a previous study, sodium houttuyfonate (SH) alone or in combination with fluconazole revealed relatively strong antifungal potential against C. albicans, and the underlying mechanism might be likely to be associated with beta-glucan synthesis and transportation (Shao et al., 2017). In the present experiment, we used a standard C. albicans isolate and a phr1 mutant (phr1-/-) to investigate the interaction of SH with beta-glucan, one of the critical components in cell wall and biofilm matrix. We showed that lyticase was the most effective enzyme that could significantly increase the antifungal inhibition of SH at 64 mu g/mL in C. albicans SC5314 but became futile in phr1-/-. Although the minimum inhibitory concentrations (MICs) of SH were comparable in the two Candida strains used, phr1-/- appeared to be more susceptible to SH compared with C. albicans SC5314 in biofilms (64 versus 512 mu g/mL). The peak areas of SH decreased markedly by 71.6, 38.2, and 62.6% in C. albicans SC5314 and by 70% and 53.2% in phr1-/- by ultra-performance liquid chromatography (UPLC) analysis after co-incubation of SH with laminarin, extracellular matrix (EM) and cell wall. The chitin appeared to not interact with SH. We further demonstrated that sub-MIC SH (8 mu g/mL) was able to induce cell wall remodeling by unmasking beta-1,3-glucan and chitin in both C. albicans SC5314 and phr1-/-. Based on these findings, we propose that beta-1,3-glucan can block the entrance of SH through non-specific absorption, and then the fungus senses the interaction of SH with beta-1,3-glucan and exposes more beta-1,3-glucan that contributes to SH blocking in turn.