Inhibitory Effect of Sorbus aucuparia Extracts on the Fusarium proliferatum and F. culmorum Growth and Mycotoxin Biosynthesis.

Fungal infections are among the most common diseases of crop plants. Various species of the Fusarium spp. are naturally prevalent and globally cause the qualitative and quantitative losses of farming commodities, mainly cereals, fruits, and vegetables. In addition, Fusarium spp. can synthesize toxic secondary metabolites-mycotoxins under high temperature and humidity conditions. Among the strategies against Fusarium spp. incidence and mycotoxins biosynthesis, the application of biological control, specifically natural plant extracts, has proved to be one of the solutions as an alternative to chemical treatments. Notably, rowanberries taken from Sorbus aucuparia are a rich source of phytochemicals, such as vitamins, carotenoids, flavonoids, and phenolic acids, as well as minerals, including iron, potassium, and magnesium, making them promising candidates for biological control strategies. The study aimed to investigate the effect of rowanberry extracts obtained by supercritical fluid extraction (SFE) under different conditions on the growth of Fusarium (F. culmorum and F. proliferatum) and mycotoxin biosynthesis. The results showed that various extracts had different effects on Fusarium growth as well as ergosterol content and mycotoxin biosynthesis. These findings suggest that rowanberry extracts obtained by the SFE method could be a natural alternative to synthetic fungicides for eradicating Fusarium pathogens in crops, particularly cereal grains. However, more research is necessary to evaluate their efficacy against other Fusarium species and in vivo applications.

Adaptative responses of Neurospora crassa by histidine kinases upon the attack of the arthropod Sinella curviseta.

Histidine kinases (HKs) are important sensor proteins in fungi and play an essential role in environmental adaptation. However, the mechanisms by which fungi sense and respond to fungivores attack via HKs are not fully understood. In this study, we utilized Neurospora crassa to investigate the involvement of HKs in responding to fungivores attack. We found that the 11 HKs in N. crassa not only affected the growth and development, but also led to fluctuations in antioxidant production. Ten mutants in the genes encoding HKs (except ∆phy1) showed increased production of reactive oxygen species (ROS), especially upon Sinella curviseta attack. The ROS burst triggered changes in conidia and perithecial beaks formation, as well as accumulation of ß-glucan, ergothioneine, ergosterol, and carotenoids. ß-glucan was increased in ∆hk9, ∆os1, ∆hcp1, ∆nik2, ∆sln1, ∆phy1 and ∆phy2 mutants compared to the wild-type strain. In parallel, ergothioneine accumulation was improved in ∆phy1 and ∆hk16 mutants and further increased upon attack, except in ∆os1 and ∆hk16 mutants. Additionally, fungivores attack stimulated ergosterol and dehydroergosterol production in ∆hk9 and ∆os1 mutants. Furthermore, deletion of these genes altered carotenoid accumulation, with wild-type strain, ∆hk9, ∆os1, ∆hcp1, ∆sln1, ∆phy2, and ∆dcc1mutants showing an increase in carotenoids upon attack. Taken together, HKs are involved in regulating the production of conidia and antioxidants. Thus, HKs may act as sensors of fungivores attack and effectively improve the adaptive capacity of fungi to environmental stimuli.

Discovery and Optimization of Ergosterol Peroxide Derivatives as Novel Glutaminase 1 Inhibitors for the Treatment of Triple-Negative Breast Cancer.

In this study, novel ergosterol peroxide (EP) derivatives were synthesized and evaluated to assess their antiproliferative activity against four human cancer cell lines (A549, HepG2, MCF-7, and MDA-MB-231). Compound 3g exhibited the most potent antiproliferative activity, with an IC50 value of 3.20 µM against MDA-MB-231. This value was 5.4-fold higher than that of the parental EP. Bioassay optimization further identified 3g as a novel glutaminase 1 (GLS1) inhibitor (IC50 = 3.77 µM). In MDA-MB-231 cells, 3g reduced the cellular glutamate levels by blocking the glutamine hydrolysis pathway, which triggered reactive oxygen species production and induced caspase-dependent apoptosis. Molecular docking indicated that 3g interacts with the reaction site of the variable binding pocket by forming multiple interactions with GLS1. In a mouse model of breast cancer, 3g showed remarkable therapeutic effects at a dose of 50 mg/kg, with no apparent toxicity. Based on these results, 3g could be further evaluated as a novel GLS1 inhibitor for triple-negative breast cancer (TNBC) therapy.

[Anti-breast cancer effect of a mitochondrion-targeted derivative of ergosterol peroxide in vitro and in vivo].

This study aims to explore the effect and mechanism of a mitochondrion-targeted derivative of ergosterol peroxide(Mito-EP) on breast cancer. The methyl thiazolyl tetrazolium(MTT) assay was employed to examine the proliferation of MDA-MB-231 cells treated with different concentrations(0, 0.075, 0.15, 0.3, 0.6, 1.2, and 2.4 µmol·L~(-1)) of Mito-EP. Cells were grouped for treatment with water(blank control), low, medium, and high concentrations(0.15, 0.3, and 0.6 µmol·L~(-1)) of Mito-EP, and ergosterol peroxide(EP)(0.6 µmol·L~(-1)). After the cells were treated for 48 h, flow cytometry was employed to examine the apoptosis rate, reactive oxygen species(ROS) level, mitochondrial membrane potential, and cell cycle distribution, and the apoptosis, ROS, and mitochondrial membrane potential were observed by laser confocal microscopy. A mouse model bearing subcutaneous xenograft tumor was established by injecting 4T1 cell suspension and used to study the inhibitory effect of Mito-EP on breast cancer. Western blot was employed to determine the protein levels of B-cell lymphoma 2(Bcl-2), Bcl-2-associated X protein(Bax), cytochrome C(Cyt C), cleaved caspase-7, and cleaved caspase-9 in cells and the tumor tissue. The results showed that Mito-EP reduced the proliferation rate of MDA-MB-231 cells in a concentration-dependent manner. Compared with the blank control group, EP(0.6 µmol·L~(-1)) caused slight changes in the apoptosis rate, ROS level, and mitochondrial membrane potential. However, Mito-EP increased the apoptosis rate, elevated the ROS level, decreased mitochondrial membrane potential, up-regulated the protein levels of Bax, Cyt C, cleaved caspase-7, and cleaved caspase-9, and down-regulated the protein level of Bcl-2(all P<0.05). Moreover, Mito-EP reduced the tumor volume and weight. In summary, Mito-EP may promote apoptosis in breast cancer cells by activating the mitochondrial apoptosis pathway.

Nickel tolerance is channeled through C-4 methyl sterol oxidase Erg25 in the sterol biosynthesis pathway.

Nickel (Ni) is an abundant element on Earth and it can be toxic to all forms of life. Unlike our knowledge of other metals, little is known about the biochemical response to Ni overload. Previous studies in mammals have shown that Ni induces various physiological changes including redox stress, hypoxic responses, as well as cancer progression pathways. However, the primary cellular targets of nickel toxicity are unknown. Here, we used the environmental fungus Cryptococcus neoformans as a model organism to elucidate the cellular response to exogenous Ni. We discovered that Ni causes alterations in ergosterol (the fungal equivalent of mammalian cholesterol) and lipid biosynthesis, and that the Sterol Regulatory Element-Binding transcription factor Sre1 is required for Ni tolerance. Interestingly, overexpression of the C-4 methyl sterol oxidase gene ERG25, but not other genes in the ergosterol biosynthesis pathway tested, increases Ni tolerance in both the wild type and the sre1Δ mutant. Overexpression of ERG25 with mutations in the predicted binding pocket to a metal cation cofactor sensitizes Cryptococcus to nickel and abolishes its ability to rescue the Ni-induced growth defect of sre1Δ. As overexpression of a known nickel-binding protein Ure7 or Erg3 with a metal binding pocket similar to Erg25 does not impact on nickel tolerance, Erg25 does not appear to simply act as a nickel sink. Furthermore, nickel induces more profound and specific transcriptome changes in ergosterol biosynthetic genes compared to hypoxia. We conclude that Ni targets the sterol biosynthesis pathway primarily through Erg25 in fungi. Similar to the observation in C. neoformans, Ni exposure reduces sterols in human A549 lung epithelial cells, indicating that nickel toxicity on sterol biosynthesis is conserved.

A Multi-Year Study of Mycotoxin Co-Occurrence in Wheat and Corn Grown in Ontario, Canada.

Mycotoxin emergence and co-occurrence trends in Canadian grains are dynamic and evolving in response to changing weather patterns within each growing season. The mycotoxins deoxynivalenol and zearalenone are the dominant mycotoxins detected in grains grown in Eastern Canada. Two potential emerging mycotoxins of concern are sterigmatocystin, produced by Aspergillus versicolor, and diacetoxyscirpenol, a type A trichothecene produced by a number of Fusarium species. In response to a call from the 83rd Joint Expert Committee on Food Additives and Contaminants, we conducted a comprehensive survey of samples from cereal production areas in Ontario, Canada. Some 159 wheat and 160 corn samples were collected from farms over a three-year period. Samples were extracted and analyzed by LC-MS/MS for 33 mycotoxins and secondary metabolites. Ergosterol was analyzed as an estimate of the overall fungal biomass in the samples. In wheat, the ratio of DON to its glucoside, deoxynivalenol-3-glucoside (DON-3G), exhibited high variability, likely attributable to differences among cultivars. In corn, the ratio was more consistent across the samples. Sterigmatocystin was detected in some wheat that had higher concentrations of ergosterol. Diacetoxyscirpenol was not detected in either corn or wheat over the three years, demonstrating a low risk to Ontario grain. Overall, there was some change to the mycotoxin profiles over the three years for wheat and corn. Ongoing surveys are required to reassess trends and ensure the safety of the food value chain, especially for emerging mycotoxins.

Mechanistic insights into antifungal potential of Alexidine dihydrochloride and hexachlorophene in Candida albicans: a drug repurposing approach.

Candida albicans has been listed in the critical priority group by the WHO in 2022 depending upon its contribution in invasive candidiasis and increased resistance to conventional drugs. Drug repurposing offers an efficient, rapid, and cost-effective solution to develop alternative therapeutics against pathogenic microbes. Alexidine dihydrochloride (AXD) and hexachlorophene (HCP) are FDA approved anti-cancer and anti-septic drugs, respectively. In this study, we have shown antifungal properties of AXD and HCP against the wild type (reference strain) and clinical isolates of C. albicans. The minimum inhibitory concentrations (MIC50) of AXD and HCP against C. albicans ranged between 0.34 and 0.69 µM and 19.66-24.58 µM, respectively. The biofilm inhibitory and eradication concentration of AXD was reported comparatively lower than that of HCP for the strains used in the study. Further investigations were performed to understand the antifungal mode of action of AXD and HCP by studying virulence features like cell surface hydrophobicity, adhesion, and yeast to hyphae transition, were also reduced upon exposure to both the drugs. Ergosterol content in cell membrane of the wild type strain was upregulated on exposure to AXD and HCP both. Biochemical analyses of the exposed biofilm indicated reduced contents of carbohydrate, protein, and e-DNA in the extracellular matrix of the biofilm when compared to the untreated control biofilm. AXD exposure downregulated activity of tissue invading enzyme, phospholipase in the reference strain. In wild type strain, ROS level, and activities of antioxidant enzymes were found elevated upon exposure to both drugs. FESEM analysis of the drug treated biofilms revealed degraded biofilm. This study has indicated mode of action of antifungal potential of alexidine dihydrochloride and hexachlorophene in C. albicans.

Mitochondrial targeted modification and anticancer mechanism of natural product ergosterol peroxide.

Ergosterol peroxide (EP) isolated from the edible medicinal fungus Pleurotus ferulae has a wide range of anti-tumor activity, but poor water solubility and low bioavailability limit further application. In this study, EP was structurally modified using triphenylphosphine (TPP+), which combines mitochondrial targeting, amphiphilicity, and cytotoxicity. A series of TPP+-conjugated ergosterol peroxide derivatives (TEn) with different length linker arms were synthesized. The structure-activity relationship showed that the anticancer activity of TEn gradually decreased with the elongation of the linker arm. The compound TE3 has the optimal and broadest spectrum of antitumor effects. It mainly through targeting mitochondria, inducing ROS production, disrupting mitochondrial function, and activating mitochondria apoptosis pathway to exert anti-cervical cancer activity. Among them, TPP+ only acted as a mitochondrial targeting group, while EP containing peroxide bridge structure served as an active group to induce ROS. In vivo experiments have shown that TE3 has better anti-cervical cancer activity and safety than the first-line anticancer drug cisplatin, and can activate the immune response in mice. Although TE3 exhibits some acute toxicity, it is not significant at therapeutic doses. Therefore, TE3 has the potential for further development as an anti-cervical cancer drug.

Rational selection of morphological phenotypic traits to extract essential similarities in chemical perturbation in the ergosterol pathway.

Terbinafine, fluconazole, and amorolfine inhibit fungal ergosterol synthesis by acting on their target enzymes at different steps in the synthetic pathway, causing the accumulation of various intermediates. We found that the effects of these three in- hibitors on yeast morphology were different. The number of morphological parameters commonly altered by these drugs was only approximately 6% of the total. Using a rational strategy to find commonly changed parameters,we focused on hidden essential similarities in the phenotypes possibly due to decreased ergosterol levels. This resulted in higher apparent morphological similarity. Improvements in morphological similarity were observed even when canonical correlation analysis was used to select biologically meaningful morphological parameters related to gene function. In addition to changes in cell morphology, we also observed differences in the synergistic effects among the three inhibitors and in their fungicidal effects against pathogenic fungi possibly due to the accumulation of different intermediates. This study provided a comprehensive understanding of the properties of inhibitors acting in the same biosynthetic pathway.

With age comes resilience: how mitochondrial modulation drives age-associated fluconazole tolerance in Cryptococcus neoformans.

Cryptococcus neoformans (Cn) is an opportunistic fungal microorganism that causes life-threatening meningoencephalitis. During the infection, the microbial population is heterogeneously composed of cells with varying generational ages, with older cells accumulating during chronic infections. This is attributed to their enhanced resistance to phagocytic killing and tolerance of antifungals like fluconazole (FLC). In this study, we investigated the role of ergosterol synthesis, ATP-binding cassette (ABC) transporters, and mitochondrial metabolism in the regulation of age-dependent FLC tolerance. We find that old Cn cells increase the production of ergosterol and exhibit upregulation of ABC transporters. Old cells also show transcriptional and phenotypic characteristics consistent with increased metabolic activity, leading to increased ATP production. This is accompanied by increased production of reactive oxygen species, which results in mitochondrial fragmentation. This study demonstrates that the metabolic changes occurring in the mitochondria of old cells drive the increase in ergosterol synthesis and the upregulation of ABC transporters, leading to FLC tolerance. IMPORTANCE: Infections caused by Cryptococcus neoformans cause more than 180,000 deaths annually. Estimated 1-year mortality for patients receiving care ranges from 20% in developed countries to 70% in developing countries, suggesting that current treatments are inadequate. Some fungal cells can persist and replicate despite the usage of current antifungal regimens, leading to death or treatment failure. Aging in fungi is associated with enhanced tolerance against antifungals and resistance to killing by host cells. This study shows that age-dependent increase in mitochondrial reactive oxygen species drive changes in the regulation of membrane transporters and ergosterol synthesis, ultimately leading to the heightened tolerance against fluconazole in old C. neoformans cells. Understanding the underlying molecular mechanisms of this age-associated antifungal tolerance will enable more targeted antifungal therapies for cryptococcal infections.

Insights into the antifungal mechanism of Bacillus subtilis cyclic lipopeptide iturin A mediated by potassium ion channel.

Fungal infections pose severe and potentially lethal threats to plant, animal, and human health. Ergosterol has served as the primary target for developing antifungal medications. However, many antifungal drugs remain highly toxic to humans due to similarity in cell membrane composition between fungal and animal cells. Iturin A, lipopeptide produced by Bacillus subtilis, efficiently inhibit various fungi, but demonstrated safety in oral administration, indicating the existence of targets different from ergosterol. To pinpoint the exact antifungal target of iturin A, we used homologous recombination to knock out and overexpress erg3, a key gene in ergosterol synthesis. Saccharomyces cerevisiae and Aspergillus carbonarius were transformed using the LiAc/SS-DNNPEG and Agrobacterium-mediated transformation (AMT), respectively. Surprisingly, increasing ergosterol content did not augment antifungal activity. Furthermore, iturin A's antifungal activity against S. cerevisiae was reduced while it pre-incubation with voltage-gated potassium (Kv) channel inhibitor, indicating that Kv activation was responsible for cell death. Iturin A was found to activate the Kv protein, stimulating K+ efflux from cell. In vitro tests confirmed interaction between iturin A and Kv protein. This study highlights Kv as one of the precise targets of iturin A in its antifungal activity, offering a novel target for the development of antifungal medications.

Deletion of the Candida albicans TLO gene family results in alterations in membrane sterol composition and fluconazole tolerance.

Development of resistance and tolerance to antifungal drugs in Candida albicans can compromise treatment of infections caused by this pathogenic yeast species. The uniquely expanded C. albicans TLO gene family is comprised of 14 paralogous genes which encode Med2, a subunit of the multiprotein Mediator complex which is involved in the global control of transcription. This study investigates the acquisition of fluconazole tolerance in a mutant in which the entire TLO gene family has been deleted. This phenotype was reversed to varying degrees upon reintroduction of representative members of the alpha- and beta-TLO clades (i.e. TLO1 and TLO2), but not by TLO11, a gamma-clade representative. Comparative RNA sequencing analysis revealed changes in the expression of genes involved in a range of cellular functions, including ergosterol biosynthesis, mitochondrial function, and redox homeostasis. This was supported by the results of mass spectrometry analysis, which revealed alterations in sterol composition of the mutant cell membrane. Our data suggest that members of the C. albicans TLO gene family are involved in the control of ergosterol biosynthesis and mitochondrial function and may play a role in the responses of C. albicans to azole antifungal agents.

Mechanism of action and synergistic effect of Eugenia uniflora extract in Candida spp.

The limited arsenal of antifungal drugs have prompted the search for novel molecules with biological activity. This study aimed to characterize the antifungal mechanism of action of Eugenia uniflora extract and its synergistic activity with commercially available antifungal drugs on the following Candida species: C. albicans, C. tropicalis, C. glabrata, C. parapsilosis and C. dubliniensis. In silico analysis was performed to predict antifungal activity of the major compounds present in the extract. Minimal inhibitory concentrations (MICs) were determined in the presence of exogenous ergosterol and sorbitol. Yeast cells were grown in the presence of stressors. The loss of membrane integrity was assessed using propidium iodide staining (fluorescence emission). Synergism between the extract and antifungal compounds (in addition to time kill-curves) was determined. Molecular docking revealed possible interactions between myricitrin and acid gallic and enzymes involved in ergosterol and cell wall biosynthesis. Candida cells grown in the presence of the extract with addition of exogenous ergosterol and sorbitol showed 2 to 8-fold increased MICs. Strains treated with the extract revealed greater loss of membrane integrity when compared to their Fluconazole counterparts, but this effect was less pronounced than the membrane damage caused by Amphotericin B. The extract also made the strains more susceptible to Congo red and Calcofluor white. A synergistic action of the extract with Fluconazole and Micafungin was observed. The E. uniflora extract may be a viable option for the treatment of Candida infections.

Ergosterol inhibits the proliferation of breast cancer cells by suppressing AKT/GSK-3beta/beta-catenin pathway.

Breast cancer is a prevalent malignancy affecting women globally, necessitating effective treatment strategies. This study explores the potential of ergosterol, a bioactive compound found in edible mushrooms, as a candidate for breast cancer treatment. Breast cancer cell lines (MCF-7 and MDA-MB-231) were treated with ergosterol, revealing its ability to inhibit cell viability, induce cell cycle arrest, and suppress spheroid formation. Mechanistically, ergosterol demonstrated significant inhibitory effects on the Wnt/beta-catenin signaling pathway, a critical regulator of cancer progression, by attenuating beta-catenin translocation in the nucleus. This suppression was attributed to the inhibition of AKT/GSK-3beta phosphorylation, leading to decreased beta-catenin stability and activity. Additionally, ergosterol treatment impacted protein synthesis and ubiquitination, potentially contributing to its anti-cancer effects. Moreover, the study revealed alterations in metabolic pathways upon ergosterol treatment, indicating its influence on metabolic processes critical for cancer development. This research sheds light on the multifaceted mechanisms through which ergosterol exerts anti-tumor effects, mainly focusing on Wnt/beta-catenin pathway modulation and metabolic pathway disruption. These findings provide valuable insights into the potential of ergosterol as a therapeutic candidate for breast cancer treatment, warranting further investigation and clinical application.

[Ergosterol peroxide inducing apoptosis of human hepatocellular carcinoma by regulating mitochondrial apoptosis pathway].

This study aims to investigate the effect of ergosterol peroxide(EP) on the apoptosis of human hepatocellular carcinoma and its mechanism of action. The cell viability of HepG2 and SK-Hep-1 cells with 0(blank control), 2.5, 5, 10, 20, 40, and 80 µmol·L~(-1) of EP after 24, 48, and 72 h of action was detected by using CCK-8 assay, and the half inhibitory concentrations(IC_(50)) at 24, 48, and 72 h were calculated. Formal experiments were performed to detect the effect of EP on intracellular reactive oxygen species(ROS) using DCFH-DA staining, the effect of EP on intracellular mitochondrial membrane potential using JC-1 staining, the number of apoptotic cells using Annexin V-FITC/PI double-staining after HepG2 cells were co-cultured with 0(blank control), 10, 20, 40 µmol·L~(-1) EP for 48 h. The effects of EP at different concentrations on apoptotic morphology were detected using AO/EB staining. The effects of different concentrations of EP on the protein expression of mitochondrial apoptosis pathway-related proteins B cell lymphoma 2(Bcl-2), cytochrome C(Cyt-C), Bcl-2-related X protein(Bax), caspase-3, cleaved caspase-3, caspase-9, and cleaved caspase-9 were examined by using Western blot. The results showed that different concentrations of EP could inhibit the proliferation of hepatocellular carcinoma with concentration-and time-dependent trends. Compared with the blank control group, the ROS level in the EP-treated group increased significantly(P<0.05). The mitochondrial membrane potential decreased significantly(P<0.05). The total apoptosis rate increased significantly(P<0.05). The expression of Bcl-2 protein was significantly down-regulated, and the expression of Cyt-C, Bax, cleaved caspase-9, and cleaved caspase-3 were significantly up-regulated(P<0.05). In summary, EP may inhibit the proliferation of hepatocellular carcinoma by modulating the mitochondria-mediated apoptosis pathway and induce apoptosis.

[Mechanism of ergosterol peroxide on MCF-7 breast cancer cells based on network pharmacology and in vitro experiments].

This study investigated the effects of ergosterol peroxide(EP) on the proliferation and apoptosis of MCF-7 breast cancer cells, explored its possible mechanisms of action, and verified the effects and mechanisms by in vitro experiments. Network pharmaco-logy was used to screen the target proteins of EP and construct target networks and protein-protein interaction(PPI) networks to predict the potential target proteins and related pathways involved in EP anti-breast cancer effects. The MTT assay was performed to measure the inhibitory effect of EP on MCF-7 cell proliferation, and the colony formation assay was used to assess the cell cloning ability. Flow cytometry and laser confocal microscopy were employed to evaluate cell apoptosis, mitochondrial membrane potential and reactive oxygen species(ROS) levels. Western blot analysis was conducted to examine the expression levels of B-cell lymphoma 2(Bcl-2), Bcl-2-associated X protein(Bax), cytochrome C(Cyt C), caspase-7, cleaved caspase-7, phosphatidylinositol 3-kinase(PI3K), and se-rine/threonine kinase B(AKT) in MCF-7 cells treated with EP. The results of network pharmacology prediction yielded 173 common targets between EP and breast cancer; the results of Kyoto Encyclopedia of Genes and Genomes(KEGG) enrichment analysis showed that EP treatment for breast cancer mainly affected the signaling pathways such as cancer pathway, PI3K-AKT signaling pathway, cellular senescence signaling pathway, and viral carcinogenesis pathway; and the MTT assay results showed that the viability of MCF-7 cells in the EP group was significantly lower than that in the control group, exhibiting a time-and concentration-dependent trend, and EP can inhibit colony formation of MCF-7 breast cancer cells. Treatment with 10, 20, and 40 µmol·L~(-1) EP for 24 h resulted in a significant increase in the total apoptosis rate of MCF-7 cells, a significant decrease in mitochondrial membrane potential, and a significant increase in ROS levels. In addition, treatment with EP led to an upregulation of Cyt C, Bax, and cleaved caspase-7 protein expression, and a downregulation of p-PI3K, p-AKT, and Bcl-2 protein expression in MCF-7 cells. Studies have shown that EP inhibits MCF-7 breast cancer cell proliferation and reduces colony formation by a mechanism that may be related to the PI3K-AKT pathway mediating the mitochondrial apoptotic pathway.

Sterol 14-alpha demethylase (CYP51) activity in Leishmania donovani is likely dependent upon cytochrome P450 reductase 1.

Liposomal amphotericin B is an important frontline drug for the treatment of visceral leishmaniasis, a neglected disease of poverty. The mechanism of action of amphotericin B (AmB) is thought to involve interaction with ergosterol and other ergostane sterols, resulting in disruption of the integrity and key functions of the plasma membrane. Emergence of clinically refractory isolates of Leishmania donovani and L. infantum is an ongoing issue and knowledge of potential resistance mechanisms can help to alleviate this problem. Here we report the characterisation of four independently selected L. donovani clones that are resistant to AmB. Whole genome sequencing revealed that in three of the moderately resistant clones, resistance was due solely to the deletion of a gene encoding C24-sterol methyltransferase (SMT1). The fourth, hyper-resistant resistant clone (>60-fold) was found to have a 24 bp deletion in both alleles of a gene encoding a putative cytochrome P450 reductase (P450R1). Metabolic profiling indicated these parasites were virtually devoid of ergosterol (0.2% versus 18% of total sterols in wild-type) and had a marked accumulation of 14-methylfecosterol (75% versus 0.1% of total sterols in wild-type) and other 14-alpha methylcholestanes. These are substrates for sterol 14-alpha demethylase (CYP51) suggesting that this enzyme may be a bona fide P450R specifically involved in electron transfer from NADPH to CYP51 during catalysis. Deletion of P450R1 in wild-type cells phenocopied the metabolic changes observed in our AmB hyper-resistant clone as well as in CYP51 nulls. Likewise, addition of a wild type P450R1 gene restored sterol profiles to wild type. Our studies indicate that P450R1 is essential for L. donovani amastigote viability, thus loss of this gene is unlikely to be a driver of clinical resistance. Nevertheless, investigating the mechanisms underpinning AmB resistance in these cells provided insights that refine our understanding of the L. donovani sterol biosynthetic pathway.

Ten ring-B aromatized ergosterols from Aspergillus spectabilis.

Spectasterols F-O (1-10), ten interesting ergosterols with an aromatized B ring, were obtained from Aspergillus spectabilis. Their structures and absolute configurations were determined using a combination of high-resolution electrospray ionization mass spectrometry (HR-ESI-MS), nuclear magnetic resonance (NMR) spectroscopy, single-crystal X-ray diffraction analyses, and electronic circular dichroism (ECD) calculations. Structurally, these aromatic ergosterols feature versatile side chains. Notably, compound aromatic ergosterols featured versatile side chains, and compound 4 is an unusual C23 ergosterol characterized by a shorter side chain due to oxidative cleavage between C-23 and C-24. All compounds were evaluated for their neuroprotective activities, with compound 8 showing a dose-dependent ability to reduce apoptosis and protect mitochondrial function in glutamate-induced SH-SY5Y cells.

Toxic eburicol accumulation drives the antifungal activity of azoles against Aspergillus fumigatus.

Azole antifungals inhibit the sterol C14-demethylase (CYP51/Erg11) of the ergosterol biosynthesis pathway. Here we show that the azole-induced synthesis of fungicidal cell wall carbohydrate patches in the pathogenic mold Aspergillus fumigatus strictly correlates with the accumulation of the CYP51 substrate eburicol. A lack of other essential ergosterol biosynthesis enzymes, such as sterol C24-methyltransferase (Erg6A), squalene synthase (Erg9) or squalene epoxidase (Erg1) does not trigger comparable cell wall alterations. Partial repression of Erg6A, which converts lanosterol into eburicol, increases azole resistance. The sterol C5-desaturase (ERG3)-dependent conversion of eburicol into 14-methylergosta-8,24(28)-dien-3ß,6α-diol, the "toxic diol" responsible for the fungistatic activity against yeasts, is not required for the fungicidal effects in A. fumigatus. While ERG3-lacking yeasts are azole resistant, ERG3-lacking A. fumigatus becomes more susceptible. Mutants lacking mitochondrial complex III functionality, which are much less effectively killed, but strongly inhibited in growth by azoles, convert eburicol more efficiently into the supposedly "toxic diol". We propose that the mode of action of azoles against A. fumigatus relies on accumulation of eburicol which exerts fungicidal effects by triggering cell wall carbohydrate patch formation.

UPC2 mutations and development of azole resistance in Candida albicans hospital isolates from Lebanon.

OBJECTIVES: This study evaluated the role of Upc2 in the development of azole resistance in Candida albicans isolates from Lebanese hospitalized patients and determined a correlation between resistance and virulence. METHODS: The UPC2 gene which codes for an ergosterol biosynthesis regulator was sequenced and analysed in two azole-resistant and one azole-susceptible C. albicans isolates. An amino acid substitution screening was carried out on Upc2 with a focus on its ligand binding domain (LBD) known to interact with ergosterol. Then, Upc2 protein secondary structure prediction and homology modelling were conducted, followed by total plasma membrane ergosterol and cell wall chitin quantifications. For virulence, mouse models of systemic infection were generated and an agar adhesion and invasion test was performed. RESULTS: Azole-resistant isolates harboured novel amino acid substitutions in the LBD of Upc2 and changes in protein secondary structures were observed. In addition, these isolates exhibited a significant increase in plasma membrane ergosterol content. Resistance and virulence were inversely correlated while increased cell wall chitin concentration does not seem to be linked to resistance since even though we observed an increase in chitin concentration, it was not statistically significant. CONCLUSIONS: The azole-resistant C. albicans isolates harboured novel amino acid substitutions in the LBD of Upc2 which are speculated to induce an increase in plasma membrane ergosterol content, preventing the binding of azoles to their target, resulting in resistance.