Antifungal activity of emodin against the Cryptococcus neoformans / Cryptococcus gattii complexes: an effect on the enzyme superoxide dismutase

The Cryptococcus neoformans/Cryptococcus gattii species complexes include encapsulated yeasts that cause cryptococcosis. Emodin has demonstrated antimicrobial activity. This study evaluated emodin’s antifungal activity against both planktonic cells and mature biofilms of the Cryptococcus neoformans/Cryptococcus gattii complexes, and its interaction with superoxide dismutase (SOD). Planktonic susceptibility was assessed by broth microdilution (CLSI; M27-A4). Mature biofilms were treated with emodin (128–1024 µg mL −1 ) and evaluated by crystal violet staining for biomass and the 3-(4,5-dimethylthiazol-2yl)-2,5-diphenyl tetrazolium (MTT) assay for metabolic activity. Confocal laser microscopy (CLSM) and LIVE/DEAD™ staining were used to analyze viability and structure. Molecular docking assays with AutoDock Vina showed emodin’s potential to bind SOD, and this was validated through the nitro blue tetrazolium (NBT) reduction assay. Emodin had inhibitory effects on planktonic cells, with MIC values ranging from 256 to 512 µg mL −1 . Against mature biofilms, emodin at 1024 µg mL −1 reduced biomass by 72% and metabolic activity by 99% compared to the drug-free control. Additionally, emodin reduced structural parameters of biofilms and SOD activity, supporting its role in oxidative stress induction. These findings highlight emodin’s potential antifungal activity against Cryptococcus neoformans/Cryptococcus gattii complexes biofilms and inhibitory effect on SOD activity as a potential mechanism of action.