Background and purpose: The holotoxin A(1) , isolated from Apostichopus japonicus, exhibits potent antifungal activities, but the mechanism and efficacy against candidiasis are unclear. In this study we have studied the antifungal effects and mechanism of holotoxin A(1) against Candida albicans and in murine oropharyngeal and intra-abdominal candidiasis. Experimental approach: The antifungal effect of holotoxin A(1) against C. albicans was tested in vitro. To explore the antifungal mechanism of holotoxin A(1) , the transcriptome, ROS levels, and mitochondrial function of C. albicans was evaluated. Effectiveness and systematic toxicity of holotoxin A(1) in vivo was assessed in the oropharyngeal and intra-abdominal candidiasis models in mice. Key results: Holotoxin A(1) was a potent fungicide against C. albicans SC5314, clinical strains and drug-resistant strains. Holotoxin A(1) inhibited oxidative phosphorylation and induced oxidative damage by increasing intracellular accumulation of ROS in C. albicans. Holotoxin A(1) induced dysfunction of mitochondria by depolarizing the mitochondrial membrane potential and reducing the production of ATP. Holotoxin A(1) directly inhibited the enzymatic activity of mitochondrial complex I and antagonized with the rotenone, an inhibitor of complex I, against C. albicans. Meanwhile, the complex I subunit NDH51 null mutants showed a decreased susceptibility to holotoxin A(1) . Furthermore, holotoxin A(1) significantly reduced fungal burden and infections with no significant systemic toxicity in oropharyngeal and intra-abdominal candidiasis in murine models. Conclusion and implications: Holotoxin A(1) is a promising candidate for the development of novel antifungal agents against both oropharyngeal and intra-abdominal candidiasis, especially when caused by drug-resistant strains.
