Anti-Candida albicans effect and mechanism of Pachysandra axillaris Franch

Ethnopharmacological relevance: Pachysandra axillaris Franch., a traditional herbal medicine in Yunnan, has been used to treat traumatic injuries and stomach ailments, some of which were related to microbial infections in conventional applications, but, to the best of our knowledge, the antifungal bioactivity of this plant and its main antifungal components have not been previously reported.

Aim of the study: To identify the antifungal compounds of P. axillaris against fluconazole-resistant C. albicans in vitro and in vivo, and then elucidate the underlying mechanism of action.

Materials and methods: The antifungal compounds were obtained by bioguided isolation, and then they were investigated in vitro by MIC, growth curves, time-kill assay, and drug resistance induction. The antifungal mechanism was explored using combined network pharmacology and metabolomic analysis, and further supported by analyzing sterol composition using LC-MS/MS, scanning and transmission electron microscopy observation of fungal cell morphology, examining its effects on cell membranes using the fluorescent probes and RT-qPCR. Additionally, the antifungal effect in vivo was evaluated by a murine C. albicans skin infection model.

Results: Three bioactive compounds from P. axillaris efficiently inhibited fluconazole-resistant C. albicans (MIC = 4 μg/mL), in which the major compound, pachysamine M, affected the ergosterol biosynthesis pathway by inhibiting ERG genes (ERG1, ERG4, ERG7, ERG9, and ERG24), leading to the accumulation of squalene, lanosterol, and zymosterol. So, pachysamine M targeted cell membranes in vitro by reducing the ergosterol level, to avoid drug resistance. In addition, it promoted wound healing, reduced fungal load, and alleviated inflammation in vivo.

Conclusions: Pachysamine M, an antifungal compound without reported before, inhibited fluconazole-resistant C. albicans efficiently in vitro and in vivo, and its mechanism targeted cell membranes, reducing the risk of drug resistance, which validated the traditional use of P. axillaris for the treatment of fungal skin infections.