Holotoxin A1 from Apostichopus japonicus inhibited oropharyngeal and intra-abdominal candidiasis by inducing oxidative damage in Candida albicans

Background and Purpose: The holotoxin A1, isolated from Apostichopus japonicus, has shown potent antifungal activities with unclear mechanism and efficacy against candidiasis. This study aimed to reveal the antifungal effects and mechanism of holotoxin A1 against Candida albicans in vitro and in candidiasis murine models for the first time. Experimental Approach: The antifungal effect of holotoxin A1 against C. albicans was tested in vitro. To explore the antifungal mechanism of holotoxin A1, the transcriptome, ROS levels, and mitochondrial function of C. albicans was evaluated. The oropharyngeal and intra-abdominal candidiasis mouse models were used to verify the effectiveness and systematic toxicity in vivo. Key Results: Holotoxin A1 was a potent fungicide against C. albicans SC5314, clinical strains and drug-resistant strains. Holotoxin A1 inhibited the oxidative phosphorylation and induced oxidative damage by increasing intracellular accumulation of ROS in C. albicans. Holotoxin A1 caused the disfunction of mitochondria by depolarizing the mitochondrial membrane potential and reducing the production of ATP. Holotoxin A1 directly inhibited the enzymatic activity of mitochondrial complex I (CI) and antagonized with the rotenone, an inhibitor of CI, against C. albicans. Meanwhile, the CI subunit NDH51 null mutants showed the decreased susceptibility to holotoxin A1. Furthermore, holotoxin A1 significantly reduced fungal burden and infections with no significant systemic toxicity in oropharyngeal and intra-abdominal candidiasis murine models. Conclusions and Implications: Holotoxin A1 was a promising candidate for the development of novel antifungal drug against both oropharyngeal and intra-abdominal candidiasis, especially caused by the drug resistant strains.