Activity of thonningianin A against Candida albicans in vitro and in vivo

Fungal infections are increasing rapidly, and antifungal agents used in clinics are limited. Therefore, novel antifungal agents with high efficiency are urgently required. In this study, we investigated the antifungal activity of thonningianin A (THA), a natural compound that is widely found in plants. We first determined the activity of THA against Candida albicans, one of the most common fungal pathogens, and found that THA showed antifungal activity against all C. albicans tested, including several fluconazole-resistant isolates. THA also inhibits the growth of non- Candida albicans species. In addition, THA displayed antibiofilm activity and could not only inhibit biofilm formation but also destroy mature biofilms. The in vivo antifungal efficacy of THA was confirmed in a Galleria mellonella infection model. Further studies revealed that THA could enhance intracellular reactive oxygen species (ROS) production and regulate the transcription of several redox-related genes. Specifically, caspase activity and expression of CaMCA1, a caspase-encoding gene in C. albicans , were remarkably increased upon THA treatment. Consistent with this, in the presence of THA, the Camca1 null mutant displayed higher survival rates and reduced caspase activity compared to the wild-type or CaMCA1-reintroduced strains, indicating an important role of CaMCA1 in the antifungal activity of THA. Taken together, our results indicate that THA possesses excellent antifungal activity and may be a promising novel antifungal candidate. Key points • THA exhibits activity against Candida species, including fluconazole-resistant isolates • THA inhibits biofilm formation and destroys mature biofilm • Elevated ROS production and CaMCA1-mediated caspase activity are involved in the antifungal mechanisms of THA