Antifungal Effect of Vitamin D3 against Cryptococcus neoformans Coincides with Reduced Biofilm Formation, Compromised Cell Wall Integrity, and Increased Generation of Reactive Oxygen Species

Verapamil enhances the activity of Caspofungin against Cryptococcus neoformans， coinciding with inhibited Ca2+/CN pathway and damage to cell wall integrity

OBJECTIVES

Given the challenges posed by toxicity and drug resistance in the treatment of cryptococcal infections, we sought to explore the antifungal potential of verapamil (VER), a calcium channel blocker, against Cryptococcus neoformans (C. neoformans), and its potential synergy with antifungals, specifically caspofungin (CAS).

MATERIALS AND METHODS

In vitro and in vivo (Galleria mellonella) models were employed to assess VER's antifungal activity and its interaction with CAS. Mechanisms underlying the synergism were explored through analysis of cell wall integrity, membrane permeability, and gene expression related to the calcineurin pathway. Additionally, the influence of Ca2+ on chitin deacetylase activity was investigated.

RESULTS

VER exhibited a pronounced antifungal effect on C. neoformans and synergized with CAS, enhancing antifungal efficacy in Galleria mellonella. VER reduced chitosan content and disrupted cell wall integrity, evidenced by melanin leakage and fluorescence staining. VER+CAS modified membrane permeability, triggering intracellular ROS accumulation and mitochondrial membrane potential alterations. VER mitigated CAS-induced calcium fluctuations and downregulated calcineurin pathway genes. Furthermore, it was found that the enzyme activity of chitin deacetylase of C. neoformans is significantly influenced by the presence of Ca2+, suggesting that the use of VER may affect this activity.

CONCLUSIONS

The synergistic antifungal effect of VER and CAS represents a promising therapeutic strategy for cryptococcal infections. The multifaceted mechanisms, including disruption of cell wall integrity and modulation of membrane permeability, and regulation of intracellular calcium signaling pathways, offer new insights into antifungal drug development.

Contrasting effects of NADPH oxidases on the fungal hyphae growth and immune responses in Pleurotus ostreatus

Pleurotus ostreatus is one of the most consumed mushroom species, as it serves as a high-quality food, favors a rich secondary metabolism, and has remarkable adaptability to the environment and predators. In this study, we investigated the function of two key reactive oxygen species producing enzyme NADPH oxidase (PoNoxA and PoNoxB) in P. ostreatus hyphae growth, metabolite production, signaling pathway activation, and immune responses to different stresses. Characterization of the Nox mutants showed that PoNoxB played an important role in the hyphal formation of the multicellular structure, while PoNoxA regulated apical dominance. The ability of P. ostreatus to tolerate a series of abiotic stress conditions (e.g., osmotic, oxidative, membrane, and cell-wall stresses) and mechanical damage repair was enhanced with PoNoxA over-expression. PoNoxB had a greater responsibility in regulating the polysaccharide composition of the cell wall and methyl jasmonate and gibberellin GA1 biosynthesis, and improved mushroom resistance against Tyrophagus putrescentiae. Moreover, mutants were involved in the jasmonate and GA signaling pathway, and toxic protein defense metabolite production. Our findings shed light on how the oyster mushroom senses stress signals and responds to adverse environments by the complex regulators of Noxs.

Antifungal activity of the repurposed drug disulfiram against Cryptococcus neoformans

Fungal infections have become clinically challenging owing to the emergence of drug resistance in invasive fungi and the rapid increase in the number of novel pathogens. The development of drug resistance further restricts the use of antifungal agents. Therefore, there is an urgent need to identify alternative treatments for Cryptococcus neoformans (C. neoformans). Disulfiram (DSF) has a good human safety profile and promising applications as an antiviral, antifungal, antiparasitic, and anticancer agent. However, the effect of DSF on Cryptococcus is yet to be thoroughly investigated. This study investigated the antifungal effects and the mechanism of action of DSF against C. neoformans to provide a new theoretical foundation for the treatment of Cryptococcal infections. In vitro studies demonstrated that DSF inhibited Cryptococcus growth at minimum inhibitory concentrations (MICs) ranging from 1.0 to 8.0 μg/mL. Combined antifungal effects have been observed for DSF with 5-fluorocytosine, amphotericin B, terbinafine, or ketoconazole. DSF exerts significant protective effects and synergistic effects combined with 5-FU for Galleria mellonella infected with C. neoformans. Mechanistic investigations showed that DSF dose-dependently inhibited melanin, urease, acetaldehyde dehydrogenase, capsule and biofilm viability of C. neoformans. Further studies indicated that DSF affected C. neoformans by interfering with multiple biological pathways, including replication, metabolism, membrane transport, and biological enzyme activity. Potentially essential targets of these pathways include acetaldehyde dehydrogenase, catalase, ATP-binding cassette transporter (ABC transporter), and iron-sulfur cluster transporter. These findings provide novel insights into the application of DSF and contribute to the understanding of its mechanisms of action in C. neoformans.