Anti-cryptococcus Activity and Mechanism of Essential Oil from Coreopsis tinctoria Flowering on Cryptococcus

The essential oil (EO) extracted from the flower of Coreopsis tinctoria Nutt. is a kind of plant-derived natural therapeutics against Cryptococcus neoformans. In our study, the anti-cryptococcal effects of the EO were observed from various aspects, such as minimal inhibitory concentration, minimum fungicidal concentration, germ tube formation, and biomass. The results indicated that the EO had potent antifungal activities on C. neoformans and that it was more effective than the commonly used antifungal agents fluconazole and amphotericin B. To further elucidate the mechanism of the antifungal action, the effect of the EO on the plasma membrane and the mitochondria of C. neoformans were investigated. The lesion in the plasma membrane was detected through flow cytometry and was further verified through the inhibition of ergosterol synthesis. The essential oil caused morphological changes in the cells of C. neoformans and a reduction in the ergosterol quantity. Moreover, mitochondrial membrane potential, mitochondrial ATPase, succinate dehydrogenase (SDH), and malate dehydrogenase (MDH) were detected. The reactive oxygen species (ROS) accumulation was examined through fluorometric assay. Decreased SDH, MDH, and ATPase in C. neoformans cells were also observed in a dose-dependent manner. The above dysfunctions of the mitochondria caused ROS accumulation in C. neoformans. A reduction in cell viability was prevented through the addition of L-cysteine, and this reduction indicates that ROS is an important mediator of the antifungal action of the EO. In summary, EO from C. tinctoria flower showed anti-cryptococcus activity. Its mechanism of action is to disrupt the permeability barrier of the plasma membrane and the mitochondrial dysfunction-induced ROS accumulation in C. neoformans. With better antifungal activity than the commonly used antifungal agents and less possibility to induce drug resistance, the EO can be used as a potential anti-cryptococcal agent.