Effects of Magnolol and Honokiol on Adhesion, Yeast-Hyphal Transition, and Formation of Biofilm by Candida albicans

BackgroundThe first step in infection by Candida albicans is adhesion to host cells or implanted medical devices and this followed by hyphal growth and biofilm formation. Yeast-to-hyphal transition has long been identified as a key factor in fungal virulence. Following biofilm formation, C. albicans is usually less sensitive or insensitive to antifungals. Therefore, development of new antifungals with inhibitory action on adhesion, yeast-hyphal transition and biofilm formation by C. albicans is very necessary.MethodsThe effects of magnolol and honokiol on hypha growth were investigated using different induction media. Their inhibitory effects were determined using the 2,3-bis(2-methoxy-4-nitro-5-sulfophenyl)-2H-tetrazolium-5- carboxanilide assay, and biofilm thickness and viability were observed by a confocal scanning laser microscope. Mammalian cells were used in adhesion assays. Genes related to hyphae development and cell adhesions were analyzed by real-time reverse transcription-polymerase chain reaction. The exogenous cyclic adenosine monophosphate was used to determine the mechanisms of action of magnolol and honokiol. Caenorhabditis elegans was used as an in vivo model to estimate the antifungal activities of magnolol and honokiol.Results and conclusionsMagnolol and honokiol inhibited adhesion, the transition from yeast to hypha, and biofilm formation by C. albicans through the Ras1-cAMP-Efg1 pathway. Moreover, magnolol and honokiol prolonged the survival of nematodes infected by C. albicans. Magnolol and honokiol have potential inhibitory effects against biofilm formation by C. albicans.General SignificanceThis study provides useful information towards the development of new strategies to reduce the incidence of C. albicans biofilm-associated infection.

【背景】白色念珠菌（Candida albicans）感染的首要步骤是黏附于宿主细胞或植入式医疗器械，随后将发生菌丝生长与生物膜形成。长期以来，酵母相-菌丝相转换被认定为真菌致病力的关键影响因素。生物膜形成后，白色念珠菌通常对抗真菌药物的敏感性降低，甚至完全耐药。因此，开发能够抑制白色念珠菌黏附、酵母相-菌丝相转换以及生物膜形成的新型抗真菌药物具有重要的现实意义。

【方法】本研究借助不同诱导培养基，探究了厚朴酚（magnolol）与和厚朴酚（honokiol）对菌丝生长的调控效果；采用2,3-双(2-甲氧基-4-硝基-5-磺苯基)-2H-四唑-5-甲酰苯胺实验测定二者的抑菌活性，通过共聚焦扫描激光显微镜观察生物膜的厚度与活性；利用哺乳动物细胞开展黏附实验；通过实时逆转录聚合酶链反应（real-time reverse transcription-polymerase chain reaction）分析与菌丝发育及细胞黏附相关的基因表达情况；使用外源性环磷酸腺苷（cyclic adenosine monophosphate）解析厚朴酚与和厚朴酚的作用机制；以秀丽隐杆线虫（Caenorhabditis elegans）作为体内感染模型，评估厚朴酚与和厚朴酚的抗真菌活性。

【结果与结论】厚朴酚与和厚朴酚可通过Ras1-cAMP-Efg1通路抑制白色念珠菌的黏附、酵母相-菌丝相转换以及生物膜形成；此外，二者能够延长受白色念珠菌感染的线虫的存活时长。厚朴酚与和厚朴酚对白色念珠菌生物膜的形成具有潜在的抑制作用。

【研究意义】本研究为开发降低白色念珠菌生物膜相关感染发生率的新型防治策略提供了极具价值的参考依据。