Fungal cell membrane-promising drug target for antifungal therapy

The steroid derivative 6-aminocholestanol inhibits the DEAD-box helicase eIF4A (LieIF4A) from the Trypanosomatid parasite Leishmania by perturbing the RNA and ATP binding sites

The antifungal agent 6-aminocholestanol targets the production of ergosterol, which is the principle sterol in many fungi and protozoans; ergosterol serves many of the same roles as cholesterol in animals. We found that it also is an effective inhibitor of the translation-initiation factor eIF4AI from mouse (eIF4AI_Mus) and the Trypanosomatid parasite Leishmania (LieIF4A). The eIF4A proteins belong to the DEAD-box family of RNA helicases, which are ATP-dependent RNA-binding proteins and RNA-dependent ATPases. DEAD-box proteins contain a commonly-shared core structure consisting of two linked domains with structural homology to that of recombinant protein A (RecA) and that contain conserved motifs that are involved in RNA and ATP binding, and in the enzymatic activity. The compound inhibits both the ATPase and helicase activities by perturbing ATP and RNA binding, and it is capable of binding other proteins containing nucleic acid-binding sites as well. We undertook kinetic analyses and found that the Leishmania LieIF4A protein binds 6-aminocholestanol with a higher apparent affinity than for ATP, although multiple binding sites were probably involved. Competition experiments with the individual RecA-like domains indicate that the primary binding sites are on RecA-like domain 1, and they include a cavity that we previously identified by molecular modeling of LieIF4A that involve conserved RNA-binding motifs. The compound affects the mammalian and Leishmania proteins differently, which indicates the binding sites and affinities are not the same. Thus, it is possible to develop drugs that target DEAD-box proteins from different organisms even when they are implicated in the same biological process.

Make azoles active again: chalcones as potent reversal agents of transporters-mediated resistance in Candida albicans

AIM

Resistance against antifungals used for Candida albicans (Ca) treatment is mediated by two multidrug transporters, Mdr1p and Cdr1p, which are of enormous interest to the development of modulators combined with antifungals.

EXPERIMENTAL

A set of chalcones was synthesized by condensation reactions in laboratory and was then subject to biological assays to evaluate the effects on different yeast strains.  Results: The obtained chalcones were screened using the checkerboard liquid chemosensitization assays. Compounds 4, 10, 12 and 18, when combined with fluconazole, triggered strong sensitization on yeast strains overexpressing CaMdr1p and CaCdr1p, whereas displaying no cytotoxicity by themselves towards control strains and transporter-expressing yeast cells. In the Nile Red transport assay, the two most active compounds, 12 and 18 showed moderate-to-high accumulation of Nile Red with different behaviors towards the two transporters.

CONCLUSION

Chalcones are promising drug candidates for further development to make azole antifungals active again.

In Vitro Anticandidal Activity and Mechanism of a Polyoxovanadate Functionalized by Zn-Fluconazole Complexes

The rise in the number of fungal infections is requiring the rapid development of novel antifungal agents. A new polyoxovanadate functionalized by Zn-fluconazole coordination complexes, Zn₃(FLC)₆V₁₀O₂₈·10H₂O (ZnFLC) (FLC = fluconazole) has been synthesized and evaluated for in vitro antifungal against Candida species. The identity of ZnFLC were confirmed by elemental analysis, IR spectrum, and single-crystal X-ray diffraction. The antifungal activities of ZnFLC was screened in 19 Candida species strains using the microdilution checkerboard technique. The minimum inhibitory concentration (MIC₈₀) value of ZnFLC is 4 μg/mL on the azole-resistant clinical isolates of C. albicans HL973, which is lower than the positive control, FLC. The mechanism of ZnFLC against C. albicans HL973 showed that ZnFLC damaged the fungal cell membrane and reduced the ergosterol content. The expression of ERG1, ERG7, ERG11 ERG27, and ERG28, which have effects on the synthesis of ergosterol, were all significantly upregulated by ZnFLC.

Antifungal Therapy in Birds: Old Drugs in a New Jacket

The use of antifungals in birds is characterized by interspecies and interindividual variability in the pharmacokinetics, affecting drug safety and efficacy. Oral antifungal drug absorption is a complex process affected by drug formulation characteristics, gastrointestinal anatomy, and physiology. New antifungal drug delivery systems can enhance drug stability, reduce off-target side effects, prolong residence time in the blood, and improve efficacy. Topical administration of antifungals through nebulization shows promising results. However, therapeutic output is highly influenced by drug formulation and type of nebulizer, indicating these factors should be taken into account when selecting this medication route.

Biogenic nanosilver synthesized in Metarhizium robertsii waste mycelium extract - As a modulator of Candida albicans morphogenesis, membrane lipidome and biofilm

Due to low efficacy of classic antimicrobial drugs, finding new active preparations attracts much attention. In this study an innovative, cost-effective and environmentally friendly method was applied to produce silver nanoparticles (AgNPs) using filamentous fungi Metarhizium robertsii biomass waste. It was shown that these NPs possess prominent antifungal effects against C. albicans, C. glabrata and C. parapsilosis reference strains. Further detailed studies were performed on C. albicans ATCC 90028. AgNPs kill curve (CFU method and esterase-mediated reduction of fluorescein diacetate); fractionally inhibitory concentration index (FICI) with fluconazole (FLC); effect on fungal cell membrane permeability (propidium iodide (PI) staining), membrane lipids profile (HPLC-MS), yeast morphotypes and intracellular reactive oxygen species level (H₂DCFDA probe) were investigated. Anti-adhesive and anti-biofilm properties of AgNPs (alone and in combination with FLC) were also tested. Biosafety of AgNPs use was assessed in vitro in cytotoxicity tests against L929 fibroblasts, pulmonary epithelial A549 cell line, and red blood cells. Significant reduction in the viability of yeast cells treated with AgNPs was shown within 6 h. The proportion of C. albicans PI-positive cells increased in a dose and time-dependent manner. Changes in the qualitative and quantitative profile of cell membrane lipids, including significant decline in the quantity of most phospholipid species containing C18:2 and an increase in the amount of phospholipids containing C18:1 acyl species were observed after yeast exposure to AgNPs. CLSM images showed an enhancement in ROS intracellular accumulation in C. albicans treated with biogenic nanosilver. C. albicans transformation from yeast to hyphal forms was also reduced. AgNPs decreased adhesion of yeast to abiotic surfaces, as well as acted synergistically with FLC against sessile population. At fungicidal and fungistatic concentrations, they were non-toxic to mammalian cells. Obtained results confirm suitability of our “green synthesis” method to produce AgNPs with therapeutic potential against fungal infections.

PS, It's Complicated: The Roles of Phosphatidylserine and Phosphatidylethanolamine in the Pathogenesis of Candida albicans and Other Microbial Pathogens

The phospholipids phosphatidylserine (PS) and phosphatidylethanolamine (PE) play important roles in the virulence of Candida albicans and loss of PS synthesis or synthesis of PE from PS (PS decarboxylase) severely compromises virulence in C. albicans in a mouse model of systemic candidiasis. This review discusses synthesis of PE and PS in C. albicans and mechanisms by which these lipids impact virulence in this fungus. This is further compared to how PS and PE synthesis impact virulence in other fungi, parasites and bacteria. Furthermore, the impact of PS asymmetry on virulence and extracellular vesicle formation in several microbes is reviewed. Finally, the potential for PS and PE synthases as drug targets in these various kingdoms is also examined.

High-Temperature Induced Changes of Extracellular Metabolites in Pleurotus ostreatus and Their Positive Effects on the Growth of Trichoderma asperellum

Pleurotus ostreatus is a widely cultivated edible fungus in China. Green mold disease of P. ostreatus which can seriously affect yield is a common disease during cultivation. It occurs mostly after P. ostreatus mycelia have been subjected to high temperatures. However, little information is available on the relationship between high temperature and green mold disease. The aim of this study is to prove that extracellular metabolites of P. ostreatus affected by high temperature can promote the growth of Trichoderma asperellum. After P. ostreatus mycelia was subjected to high temperature, the extracellular fluid of P. ostreatus showed a higher promoting effect on mycelial growth and conidial germination of T. asperellum. The thiobarbituric acid reactive substance (TBARS) content reached the maximum after 48 h at 36°C. A comprehensive metabolite profiling strategy involving gas chromatography-mass spectrometry (GC/MS) combined with liquid chromatography-mass spectrometry (LC/MS) was used to analyze the changes of extracellular metabolites in response to high temperature. A total of 141 differential metabolites were identified, including 84.4% up-regulated and 15.6% down-regulated. Exogenous metabolites whose concentrations were increased after high temperature were randomly selected, and nearly all of them were able to promote the mycelial growth and conidial germination of T. asperellum. The combination of all selected exogenous metabolites also has the promotion effects on the mycelial growth and conidial germination of T. asperellum in a given concentration range in vitro. Overall, these results provide a first view that high temperature affects the extracellular metabolites of P. ostreatus, and the extensive change in metabolites promotes T. asperellum growth.

In vitro and in vivo antifungal activities and mechanism of heteropolytungstates against Candida species

The antifungal activities of heteropolytungstates, α-1,2,3-K₆H[SiW₉V₃O₄₀] (SiW-3), K₁₃[Ce(SiW₁₁O₃₉)₂]·17H₂O (SiW-5), K₁₃[Eu(SiW₁₁O₃₉)₂]·25H₂O (SiW-10), K₆PV₃W₉O₄₀ (PW-6), α-K₄PVW₁₁O₄₀ (PW-8), were screened in 29 Candida albicans, 8 Candida glabrata, 3 Candida krusei, 2 Candida parapsilosis, 1 Candida tropicalis, and 1 Cryptococcus neoformans strains using the CLSI M27-A3 method. SiW-5 had the highest efficacy with a minimum inhibitory concentration (MIC) values of <0.2–10.2 μM in vitro. The antifungal mechanism, acute toxicity and in vivo antifungal activity of SiW-5 were then evaluated in C. albicans. The results showed that SiW-5 damaged the fungal cell membrane, reduce the ergosterol content and its main mode of action was through inhibition of ergosterol biosynthesis. Real-time PCR showed that ERG1, ERG7, ERG11 and ERG28 were all significantly upregulated by SiW-5. An acute toxicity study showed the 50% lethal dose (LD₅₀) of SiW-5 for ICR mice was 1651.5 mg/kg. And in vivo antifungal studies demonstrated that SiW-5 reduced both the morbidity and fungal burden of mice infected with C. albicans. This study demonstrates that SiW-5 is a potential antifungal candidate against the Candida species.

Combining two antifungal agents does not enhance survival of Galleria mellonella larvae infected with Madurella mycetomatis

OBJECTIVE

To determine whether combination therapy would improve therapeutic outcome in eumycetoma caused by Madurella mycetomatis.

METHODS

Survival, colony-forming units (CFU), melanisation and histopathology in M. mycetomatis-infected Galleria mellonella larvae treated with amphotericin B, itraconazole, terbinafine or combinations thereof were determined.

RESULTS

Compared to larvae treated with 5% glucose, enhanced survival was obtained when M. mycetomatis-infected larvae were treated with amphotericin B, but not when they were treated with itraconazole or terbinafine. Combination therapy did not increase survival compared to 5% glucose-treated larvae, itraconazole-treated larvae or terbinafine-treated larvae. Compared to amphotericin B monotreatment, a significant decrease in survival was noted when this therapy was combined with either itraconazole or terbinafine. CFU, melanisation and histopathology did not differ between monotherapy, combination therapy or 5% glucose-treated larvae.

CONCLUSIONS

Combining different classes of antifungal agents did not enhance the survival of M. mycetomatis-infected G. mellonella larvae. Instead of improving the therapeutic outcome, combining either itraconazole or terbinafine with amphotericin B resulted in significantly lower survival rates of infected larvae than amphotericin B monotherapy. This experimental study does not provide support for the use of combined amphotericin B and itraconazole, combined itraconazole and terbinafine or combined terbinafine and amphotericin B and should be confirmed in other animal models.