Promising Antifungal Targets Against Candida albicans Based on Ion Homeostasis

Influence of Zinc on Histoplasma capsulatum Planktonic and Biofilm Cells

Histoplasma capsulatum causes a fungal respiratory disease. Some studies suggest that the fungus requires zinc to consolidate the infection. This study aimed to investigate the influence of zinc and the metal chelator TPEN on the growth of Histoplasma in planktonic and biofilm forms. The results showed that zinc increased the metabolic activity, cell density, and cell viability of planktonic growth. Similarly, there was an increase in biofilm metabolic activity but no increase in biomass or extracellular matrix production. N'-N,N,N,N-tetrakis-2-pyridylmethylethane-1,2 diamine (TPEN) dramatically reduced the same parameters in the planktonic form and resulted in a decrease in metabolic activity, biomass, and extracellular matrix production for the biofilm form. Therefore, the unprecedented observations in this study highlight the importance of zinc ions for the growth, development, and proliferation of H. capsulatum cells and provide new insights into the role of metal ions for biofilm formation in the dimorphic fungus Histoplasma, which could be a potential therapeutic strategy.

Chemical composition, antifungal, and anti-virulence action of the stem bark of Hancornia speciosa Gomes (Apocynaceae) against Candida spp

ETHNOPHARMACOLOGICAL RELEVANCE

Hancornia speciosa Gomes is a fruit and medicinal species used for treating infectious diseases of the genitourinary system. However, its mechanism of action against microbes is still not fully understood. Infections in the genitourinary system caused by Candida spp. are associated with its fungal resistance and pathogenicity. New plant-derived compounds are an alternative to fight these Candida infections.

AIM OF THE STUDY

The objective of this study was to evaluate the anti-Candida effects of extracts of the stem bark of H. speciosa. This research investigated the chemical composition of sulfuric ether (EEHS) and methanolic (MEHS) extracts, their drug-modifying action on fluconazole, and their anti-virulence action on the morphological transition of Candida species.

MATERIALS AND METHODS

The extracts (EEHS and MEHS) of the stem bark of H. speciosa were chemically characterized via qualitative phytochemical screening and by liquid chromatography coupled with mass spectrometry (UPLC-MS-ESI-QTOF). The extracts were evaluated regarding their antifungal effects and fluconazole-modifying activity against Candida albicans, Candida krusei, and Candida tropicalis using the broth microdilution method. Additionally, the study evaluated the inhibition of fungal virulence in Candida species through morphological transition assays.

RESULTS

The phytochemical screening revealed the presence of anthocyanidins, anthocyanins, aurones, catechins, chalcones, flavones, flavonols, flavanones, leucoanthocyanidins, tannins (condensed and pyrogallic), and xanthones in both extracts of the stem bark of H. speciosa. The UPLC-MS-ESI-QTOF analysis identified the same compounds in both extracts, predominating phenolic compounds. Some compounds were first time recorded in this species: gluconic acid, cinchonain IIb, cinchonain Ib isomer, and lariciresinol hexoside isomers. Most of the intrinsic antifungal activity was observed for the MEHS against C. krusei (IC50: 58.41 μg/mL). At subinhibitory concentrations (MC/8), the EEHS enhanced the action of fluconazole against all Candida strains. The MEHS exhibited greater efficacy than fluconazole inhibiting C. krusei growth. The EEHS completely inhibited hyphae appearance and reduced pseudohyphae formation in C. albicans.

CONCLUSION

The stem bark of H. speciosa is a rich source of bioactive compounds, especially phenolic. Phenolic compounds can have important roles in fighting infectious diseases of the genitourinary system, such as candidiasis. The extracts of H. speciosa improved the action of the drug fluconazole against Candida species, inhibited hyphae appearance, and reduced pseudohyphae formation. The results of this study can support the development of new therapeutics against resistant strains of Candida.

Transcriptomic meta-analysis to identify potential antifungal targets in Candida albicans

BACKGROUND

Candida albicans is a fungal pathogen causing human infections. Here we investigated differential gene expression patterns and functional enrichment in C. albicans strains grown under different conditions.

METHODS

A systematic GEO database search identified 239 "Candida albicans" datasets, of which 14 were selected after rigorous criteria application. Retrieval of raw sequencing data from the ENA database was accompanied by essential metadata extraction from dataset descriptions and original articles. Pre-processing via the tailored nf-core pipeline for C. albicans involved alignment, gene/transcript quantification, and diverse quality control measures. Quality assessment via PCA and DESeq2 identified significant genes (FDR < = 0.05, log2-fold change > = 1 or <= -1), while topGO conducted GO term enrichment analysis. Exclusions were made based on data quality and strain relevance, resulting in the selection of seven datasets from the SC5314 strain background for in-depth investigation.

RESULTS

The meta-analysis of seven selected studies unveiled a substantial number of genes exhibiting significant up-regulation (24,689) and down-regulation (18,074). These differentially expressed genes were further categorized into 2,497 significantly up-regulated and 2,573 significantly down-regulated Gene Ontology (GO) IDs. GO term enrichment analysis clustered these terms into distinct groups, providing insights into the functional implications. Three target gene lists were compiled based on previous studies, focusing on central metabolism, ion homeostasis, and pathogenicity. Frequency analysis revealed genes with higher occurrence within the identified GO clusters, suggesting their potential as antifungal targets. Notably, the genes TPS2, TPS1, RIM21, PRA1, SAP4, and SAP6 exhibited higher frequencies within the clusters. Through frequency analysis within the GO clusters, several key genes emerged as potential targets for antifungal therapies. These include RSP5, GLC7, SOD2, SOD5, SOD1, SOD6, SOD4, SOD3, and RIM101 which exhibited higher occurrence within the identified clusters.

CONCLUSION

This comprehensive study significantly advances our understanding of the dynamic nature of gene expression in C. albicans. The identification of genes with enhanced potential as antifungal drug targets underpins their value for future interventions. The highlighted genes, including TPS2, TPS1, RIM21, PRA1, SAP4, SAP6, RSP5, GLC7, SOD2, SOD5, SOD1, SOD6, SOD4, SOD3, and RIM101, hold promise for the development of targeted antifungal therapies.

The role of ion homeostasis in adaptation and tolerance to acetic acid stress in yeasts

Maintenance of asymmetric ion concentrations across cellular membranes is crucial for proper yeast cellular function. Disruptions of these ionic gradients can significantly impact membrane electrochemical potential and the balance of other ions, particularly under stressful conditions such as exposure to acetic acid. This weak acid, ubiquitous to both yeast metabolism and industrial processes, is a major inhibitor of yeast cell growth in industrial settings and a key determinant of host colonization by pathogenic yeast. Acetic acid toxicity depends on medium composition, especially on the pH (H+ concentration), but also on other ions' concentrations. Regulation of ion fluxes is essential for effective yeast response and adaptation to acetic acid stress. However, the intricate interplay among ion balancing systems and stress response mechanisms still presents significant knowledge gaps. This review offers a comprehensive overview of the mechanisms governing ion homeostasis, including H+, K+, Zn2+, Fe2+/3+, and acetate, in the context of acetic acid toxicity, adaptation, and tolerance. While focus is given on Saccharomyces cerevisiae due to its extensive physiological characterization, insights are also provided for biotechnologically and clinically relevant yeast species whenever available.

Antimicrobial peptide LL-37 disrupts plasma membrane and calcium homeostasis in Candida albicans via the Rim101 pathway

IMPORTANCE

Candida albicans is a major human fungal pathogen, and antimicrobial peptides are key components of innate immunity. Studying the interplay between C. albicans and human antimicrobial peptides would enhance a better understanding of pathogen-host interactions. Moreover, potential applications of antimicrobial peptides in antifungal therapy have aroused great interest. This work explores new mechanisms of LL-37 against C. albicans and reveals the complex connection among calcium homeostasis, oxidative stress, signaling, and possibly organelle interaction. Notably, these findings support the possible use of antimicrobial peptides to prevent and treat fungal infections.

Helium Cold Atmospheric Plasma Causes Morphological and Biochemical Alterations in Candida albicans Cells

(1) Background: Previous studies reported the promising inhibitory effect of cold atmospheric plasma (CAP) on Candida albicans. However, the exact mechanisms of CAP's action on the fungal cell are still poorly understood. This study aims to elucidate the CAP effect on C. albicans cell wall, by evaluating the alterations on its structure and biochemical composition; (2) Methods: C. albicans cells treated with Helium-CAP were analyzed by atomic force microscopy (AFM) and Fourier transform infrared spectroscopy (FTIR) in order to detect morphological, topographic and biochemical changes in the fungal cell wall. Cells treated with caspofungin were also analyzed for comparative purposes; (3) Results: Expressive morphological and topographic changes, such as increased roughness and shape modification, were observed in the cells after CAP exposure. The alterations detected were similar to those observed after the treatment with caspofungin. The main biochemical changes occurred in polysaccharides content, and an overall decrease in glucans and an increase in chitin synthesis were detected; (4) Conclusions: Helium-CAP caused morphological and topographic alterations in C. albicans cells and affected the cell wall polysaccharide content.

Sub-lethal concentrations of chlorhexidine inhibit Candida albicans growth by disrupting ROS and metal ion homeostasis

Candida albicans is a normal resident of the human oral cavity. It is also the most common fungal pathogen, causing various oral diseases, particularly in immunocompromised individuals. Chlorhexidine digluconate (CHG) is a broad-spectrum antimicrobial agent widely used in dental practice and has been recommended to treat oral candidiasis. However, its action mechanism against the fungal pathogen C. albicans remains poorly understood. The aim of the present study was to investigate the effect of CHG at sub-lethal concentrations against C. albicans. CHG inhibited the growth of C. albicans in a dose- and time-dependent manner. Cells treated with CHG exhibited altered membrane permeability, reduced metabolic activity, and enhanced metal ion and reactive oxygen species (ROS) accumulation. Copper-sensing transcription factor Mac1, iron-sensing transcription factors Sfu1 and Sef2, and copper transporter Ctr1 regulated intracellular metal ion and ROS homeostasis in response to CHG. Deletion of MAC1, SFU1, or SEF2 increased intracellular ROS production and cell susceptibility to CHG. This study revealed a novel mechanism by which CHG induced apoptosis of C. albicans cells through the disruption of metal ion and ROS homeostasis, which may help to identify new targets for fungal infections.

Analysis of possible pathways on the mechanism of action of minocycline and doxycycline against strains of Candida spp. resistant to fluconazole

Species of the genus Candida, characterized as commensals of the human microbiota, are opportunistic pathogens capable of generating various types of infections with high associated costs. Considering the limited pharmacological arsenal and the emergence of antifungal-resistant strains, the repositioning of drugs is a strategy used to search for new therapeutic alternatives, in which minocycline and doxycycline have been evaluated as potential candidates. Thus, the objective was to evaluate the in vitro antifungal activity of two tetracyclines, minocycline and doxycycline, and their possible mechanism of action against fluconazole-resistant strains of Candida spp. The sensitivity test for antimicrobials was performed using the broth microdilution technique, and the pharmacological interaction with fluconazole was also analysed using the checkerboard method. To analyse the possible mechanisms of action, flow cytometry assays were performed. The minimum inhibitory concentration obtained was 4-427 µg ml-1 for minocycline and 128-512 µg ml-1 for doxycycline, and mostly indifferent and additive interactions with fluconazole were observed. These tetracyclines were found to promote cellular alterations that generated death by apoptosis, with concentration-dependent reactive oxygen species production and reduced cell viability. Therefore, minocycline and doxycycline present themselves as promising study molecules against Candida spp.

Significance of the plasma membrane H+-ATPase and V-ATPase for growth and pathogenicity in pathogenic fungi

Pathogenic fungi are widespread and cause a variety of diseases in human beings and other organisms. At present, limited classes of antifungal agents are available to treat invasive fungal diseases. With the wide use of the commercial antifungal agents, drug resistance of pathogenic fungi are continuously increasing. Therefore, exploring effective antifungal agents with novel drug targets is urgently needed to cope with the challenges that the antifungal area faces. pH homeostasis is vital for multiple cellular processes, revealing the potential for defining novel drug targets. Fungi have evolved a number of strategies to maintain a stable pH internal environment in response to rapid metabolism and a dramatically changing extracellular environment. Among them, plasma membrane H+-ATPase (PMA) and vacuolar H+-ATPase (V-ATPase) play a central role in the regulation of pH homeostasis system. In this chapter, we will summarize the current knowledge about pH homeostasis and its regulation mechanisms in pathogenic fungi, especially for the recent advances in PMA and V-ATPase, which would help in revealing the regulating mechanism of pH on cell growth and pathogenicity, and further designing effective drugs and identify new targets for combating fungal diseases.

In vitro antifungal and antibiofilm activities of novel sulfonyl hydrazone derivatives against Candida spp

BACKGROUND

The aim of this study was to investigate the antifungal and antibiofilm activity of the new sulfonyl hydrazones compound derived from sulphonamides.

METHODS

In this study, new sulfonyl hydrazone series were synthesized via a green chemistry method. The structures of the synthesized compounds were characterized by elemental analyses and spectroscopic methods. The antifungal activities of the Anaf compounds against Candida strains under planktonic conditions were tested. The biofilm-forming ability of Candida strains was determined and the inhibitory effects of Anaf compounds on Candida biofilms compared with fluconazole were measured by MTT assay. Expression analysis of biofilm-related genes was investigated with qRT-PCR. The statistical analysis was performed using a one-way ANOVA test. CANDIDA: strains was determined and the inhibitory effects of Anaf compounds on Candida biofilms compared with fluconazole were measured by MTT assay. Expression analysis of biofilm-related genes was investigated with qRT-PCR. The statistical analysis was performed using a one-way ANOVA test.

RESULTS

A total of 16 (45.7%) out of 35 Candida isolates were determined as strong biofilm producers in this study. C. albicans was the most biofilm producer, followed by C. krusei and C. lusitaniae. The Anaf compounds had a broad spectrum of activity with MIC values ranging from 4 μg/ml to 64 μg/ml. Our data indicated that the Anaf compound had a significant effect on inhibiting biofilm formation in both fluconazole-susceptible and -resistant strains. The expression levels of hypha-specific genes als3, hwp1, ece1 and sap5 were downregulated by Anaf compounds.

CONCLUSIONS

Our study revealed that the Anaf compounds had antifungal activity and inhibited fungal biofilms, which may be related to the suppression of C. albicans adherence and hyphal formation. These results suggest that Anaf compounds may have therapeutic potential for the treatment and prevention of biofilm-associated Candida infections.

Hexyl-Aminolevulinate Ethosomes: a Novel Antibiofilm Agent Targeting Zinc Homeostasis in Candida albicans

Substantial drug resistance afforded by Candida albicans biofilms results in ineffective treatment with conventional drugs and persistent infection. Our previous study showed that hexyl-aminolevulinate ethosomes (HAL-ES) act against C. albicans biofilms and weaken their drug resistance and pathogenicity; however, the mechanism involved remains unclear. Here, we systematically evaluated the effects and mechanisms of HAL-ES on biofilm formation and drug resistance. We found that, in addition to mediating antifungal photodynamic therapy, HAL-ES inhibited the early, developmental, and mature stages of biofilm formation compared with fluconazole, HAL, or ES. Notably, adhesion and hyphal formation were significantly inhibited by postdrug effects even after brief exposure (2 h) to HAL-ES. Its therapeutic effect in vivo also has been demonstrated in cutaneous candidiasis. RNA sequencing and quantitative PCR showed that HAL-ES inhibited ribosome biogenesis by disrupting zinc homeostasis in C. albicans, thereby reducing the translation process during protein synthesis. Furthermore, HAL-ES downregulated the expression of multidrug resistance genes and increased fluconazole susceptibility in C. albicans. Our findings provide a novel and efficient method for the treatment of biofilm resistance in C. albicans infection as well as a basis for the application of HAL-ES. We also describe a new strategy for the treatment of biofilm-related infections via zinc restriction. IMPORTANCE Candida albicans is the most prevalent fungal species of the human microbiota. The medical impact of C. albicans on its human host depends on its ability to form biofilms. The intrinsic resistance conferred by biofilms to conventional antifungal drugs makes biofilm-based infections a significant clinical challenge. In this study, we demonstrate the attenuating effect of HAL-ES on C. albicans biofilm formation and drug resistance. Furthermore, we propose that HAL-ES inhibits protein translation by disrupting zinc homeostasis in C. albicans. This study not only provides a novel and effective therapeutic strategy against C. albicans biofilm but also proposes a new strategy to resolve C. albicans biofilm infection by disrupting zinc homeostasis.

The Promotional Effect of GW4869 on C. albicans Invasion and Cellular Damage in a Murine Model of Oral Candidiasis

Candida albicans (C. albicans) is one of the most common fungi in the human body; it is an opportunistic pathogen and can cause candidiasis. Extracellular vesicles (EVs) derived from the host cells have a potentially protective effect against pathogens and can be developed as vaccine formulations. GW4869 can inhibit the production and release of EVs. Previous studies have indicated that GW4869 can alter the immune and inflammatory responses of the host. However, the effect of GW4869 on Candida infection and the anti-Candida response of the host has not been investigated. We evaluated the effect of GW4869 on C. albicans invasion, biofilm formation, and cellular damage in a murine model of oral candidiasis. In this study, C. albicans-infected mice were injected with or without GW4869. The results proven by macroscopic, microscopic, and ultramicroscopic methods showed that GW4869 treatment exacerbated the oral candidiasis of mice, promoted C. albicans invasion and biofilm formation, and aggravated oral mucosal inflammation and cellular ultrastructural damage. The results are beneficial in the further exploration of the immune mechanism of C. albicans infection.

Inferring Therapeutic Targets in Candida albicans and Possible Inhibition through Natural Products: A Binding and Physiological Based Pharmacokinetics Snapshot

Despite being responsible for invasive infections, fungal pathogens have been underrepresented in computer aided therapeutic target mining and drug design. Excess of Candida albicans causes candidiasis, causative of thrush and vaginal infection due to off-balance. In this study, we attempted to mine drug targets (n = 46) using a subtractive proteomic approach in this pathogenic yeast and screen natural products with inhibition potential against fructose-bisphosphate aldolase (FBA) of the C. albicans. The top compound selected on the basis of best docking score from traditional Indian medicine/Ayurvedic library was (4-Hydroxybenzyl)thiocarbamic acid, from the ZINC FBA inhibitor library was ZINC13507461 (IUPAC name: [(2R)-2-hydroxy-3-phosphonooxypropyl] (9E,12E)-octadeca-9,12-dienoate), and from traditional Tibetan medicine/Sowa rigpa was Chelerythrine (IUPAC name: 1,2-Dimethoxy-12-methyl-9H-[1,3]benzodioxolo[5,6-c]phenanthridin-12-ium), compared to the control (2E)-1-(4-nitrophenyl)-2-[(4-nitrophenyl)methylidene]hydrazine. No Ames toxicity was predicted for prioritized compounds while control depicted this toxicity. (4-Hydroxybenzyl)thiocarbamic acid showed hepatotoxicity, while Chelerythrine depicted hERG inhibition, which can lead to QT syndrome, so we recommend ZINC13507461 for further testing in lab. Pharmacological based pharmacokinetic modeling revealed that it has low bioavailability and hence, absorption in healthy state. In cirrhosis and renal impairment, absorption and plasma accumulation increased so we recommend further investigation into this occurrence and recommend high dosage in further tests to increase bioavailability.

Synergistic Effect of the Combination of Deferoxamine and Fluconazole In Vitro and In Vivo against Fluconazole-Resistant Candida Spp

The opportunistic fungal infections are an increasing threat to humans due to the increasing number of patients with immunodeficiency, in which the most popular fungal pathogen is Candida albicans . Fluconazole (FLC) is the common drug for treating C. albicans infections, but increasing drug resistance has limited its clinical use.

Pharmacokinetic profile of sarcin and thionin from Aspergillus giganteus and in vitro validation against human fungal pathogen

Fungal infections are more predominant in agricultural and clinical fields. Aspergillosis caused by Aspergillus fumigatus leads to respiratory failure in patients along with various illnesses. Due to the limitation of antifungal therapy and antifungal drugs, there is an emergence to develop efficient antifungal compounds (AFCs) from natural sources to cure and prevent fungal infections. The present study deals with the investigation of the mechanism of the active compounds from Aspergillus giganteus against aspergillosis. Primarily, the bioavailability and toxicological properties of antifungal proteins such as, sarcin, thionin, chitinase and their derivatives have proved the efficiency of pharmacokinetic properties of selected compounds. Molecular interactions of selected compounds from A. giganteus with the virulence proteins of A. fumigatus (UDP-N-acetylglucosamine pyrophosphorylase, N-myristoyl transferase and Chitinase) have exhibited a good glide score and druggable nature of the AFCs. The antagonistic potential of AFCs on the pathogen was confirmed by SEM analysis where the shrunken and damaged spores of AFCs treated pathogen were observed. The integrity of A. fumigatus cell membrane and nuclear membrane treated with AFCs were analyzed by determining the release of cellular materials. The effective concentration of AFCs was found to be 250 µg/ml (P<0.0001). The GC-MS profiling has revealed the volatile bioactive metabolites present in A. giganteus. Further, interaction studies might provide more information on the synergism activity with the non-volatile metabolites which leads to the development of novel drugs for the treatment of aspergillosis.

A scFv phage targeting the C. albicans cell wall screened from a bacteriophage-based library of induced immune protection in mice

C. albicans is the most prevalent opportunistic fungal and can cause life-threatening systemic infections under certain circumstances. The inefficiency and resistance of traditional therapy make the development of novel techniques indispensable. The main components, proteins and glycoproteins, of the C. albicans cell wall are highly immunogenic and very different from those of the host, making it an ideal source of targets for antifungal drug development. This study aimed to screen and identify specific peptides that bind to the C. albicans cell wall using a phage-display peptide library, and to develop a peptide-based therapy targeted to C. albicans. After four rounds of screening, JC-1 ScFv was found to bind to the C. albicans cell wall specifically, inhibit C. albicans growth and viability in vitro, and protect mice from C. albicans infection in vivo. Further study showed that JC-1 could provoke an immune response in C. albicans-infected mice. These results indicated that JC-1 ScFv screened from a phage-display peptide library had the potential to be developed as a vector for targeting C. albicans.

Pharmacokinetic/Pharmacodynamic Modeling and Application in Antibacterial and Antifungal Pharmacotherapy: A Narrative Review

Pharmacokinetics and pharmacodynamics are areas in pharmacology related to different themes in the pharmaceutical sciences, including therapeutic drug monitoring and different stages of drug development. Although the knowledge of these disciplines is essential, they have historically been treated separately. While pharmacokinetics was limited to describing the time course of plasma concentrations after administering a drug-dose, pharmacodynamics describes the intensity of the response to these concentrations. In the last decades, the concept of pharmacokinetic/pharmacodynamic modeling (PK/PD) emerged, which seeks to establish mathematical models to describe the complete time course of the dose-response relationship. The integration of these two fields has had applications in optimizing dose regimens in treating antibacterial and antifungals. The anti-infective PK/PD models predict the relationship between different dosing regimens and their pharmacological activity. The reviewed studies show that PK/PD modeling is an essential and efficient tool for a better understanding of the pharmacological activity of antibacterial and antifungal agents.

Novel avenues for identification of new antifungal drugs and current challenges

INTRODUCTION

: Some of otherwise useful fungi are pathogenic to humans, and unfortunately, the number of these pathogens is increasing. In addition to common skin infections, these opportunistic pathogens are able to cause severe, often incurable, systemic mycoses.

AREAS COVERED

: The number of antifungal drugs is limited, especially drugs that can be used for systemic administration, and resistance to these drugs is very common. This review summarizes various approaches to the discovery and development of new antifungal drugs, provides an overview of the most important molecules in terms of basic (laboratory) research and compounds currently in clinical trials, and focuses on drug repurposing strategy, while providing an overview of drugs of other indications that have been tested in vitro for their antifungal activity for possible expansion of antifungal drugs and/or support of existing antimycotics.

EXPERT OPINION

: Despite the limitations of the research of new antifungal drugs by pharmaceutical manufacturers, in addition to innovated molecules based on clinically used drugs, several completely new small entities with unique mechanisms of actions have been identified. The identification of new molecular targets that offer alternatives for the development of new unique selective antifungal highly effective agents has been an important outcome of repurposing of non-antifungal drugs to antifungal drug. Also, given the advances in monoclonal antibodies and their application to immunosuppressed patients, it may seem possible to predict a more optimistic future for antifungal therapy than has been the case in recent decades.

Unique roles of aminophospholipid translocase Drs2p in governing efflux pump activity, ergosterol level, virulence traits, and host-pathogen interaction in Candida albicans

Infections caused by Candida albicans are rising due to increment in drug resistance and a limited arsenal of conventional antifungal drugs. Thus, elucidating the novel antifungal targets still represent an alternative that could overcome the problem of multidrug resistance (MDR). In this study, we have uncovered the distinctive effect of aminophospholipid translocase (Drs2p) deletion on major MDR mechanisms of C. albicans. We determined that efflux activity was diminished in Δdrs2 mutant as revealed by extracellular rhodamine 6G (R6G) efflux and flow cytometry. Moreover, we further unveiled that Δdrs2 mutant displayed decreased ergosterol content and increased membrane fluidity. Furthermore, Drs2p deletion affects the virulence attributes and led to inhibited hyphal growth and reduced biofilm formation. Additionally, THP-1 cell lines' mediated host-pathogen interaction studies revealed that Δdrs2 mutant displayed enhanced phagocytosis and altered cytokine production leading to increased IL-6 and decreased IL-10 production. Taken together, the present study demonstrates the relevance of Drs2p in C. albicans and consequently disrupting pathways known for mediating drug resistance and immune recognition. Comprehensive studies are further required to authenticate Drs2p as a novel antifungal drug target.

Natural Compound 2-Chloro-1,3-dimethoxy-5-methylbenzene, Isolated from Hericium Erinaceus, Inhibits Fungal Growth by Disrupting Membranes and Triggering Apoptosis

In this study, 2-chloro-1,3-dimethoxy-5-methylbenzene (CDM), a natural product with anti-Candida albicans activity, was discovered from the Hericium erinaceus mycelium. The minimum inhibitory concentration of CDM was 62.5 μg/mL. Moreover, structural analogues of CDM obtained from chemical synthesis were applied to explore the structure-activity relationship (SAR) of CDM against C. albicans. It was found that methoxy groups, halogen atoms (except fluorine atoms), and methoxy-meta-position methyl groups in the structure of CDM were the key active groups. Furthermore, we investigated the anti-C. albicans mechanism of CDM. Experiments suggested that CDM destroyed the cell membrane of C. albicans, including the cytoplasmic membrane and mitochondrial membrane, and caused the accumulation of reactive oxygen species and mitochondrial dysfunction, which ultimately led to apoptosis of C. albicans. In addition, CDM had no toxicity on human normal gastric mucosal epithelial cells exposed to a concentration of 125 μg/mL. Experiments showed that CDM reduced the damage of C. albicans to the visceral tissue of infected mice and improved the survival rate of mice. Our research provides a scientific basis for the discovery of effective and safe anti-C. albicans drugs from H. erinaceus.

Candida albicans SR-Like Protein Kinases Regulate Different Cellular Processes: Sky1 Is Involved in Control of Ion Homeostasis, While Sky2 Is Important for Dipeptide Utilization

Protein kinases play a crucial role in regulating cellular processes such as growth, proliferation, environmental adaptation and stress responses. Serine-arginine (SR) protein kinases are highly conserved in eukaryotes and regulate fundamental processes such as constitutive and alternative splicing, mRNA processing and ion homeostasis. The Candida albicans genome encodes two (Sky1, Sky2) and the Candida glabrata genome has one homolog (Sky1) of the human SR protein kinase 1, but their functions have not yet been investigated. We used deletion strains of the corresponding genes in both fungi to study their cellular functions. C. glabrata and C. albicans strains lacking SKY1 exhibited higher resistance to osmotic stress and toxic polyamine concentrations, similar to Saccharomyces cerevisiae sky1Δ mutants. Deletion of SKY2 in C. albicans resulted in impaired utilization of various dipeptides as the sole nitrogen source. Subsequent phosphoproteomic analysis identified the di- and tripeptide transporter Ptr22 as a potential Sky2 substrate. Sky2 seems to be involved in Ptr22 regulation since overexpression of PTR22 in the sky2Δ mutant restored the ability to grow on dipeptides and made the cells more susceptible to the dipeptide antifungals Polyoxin D and Nikkomycin Z. Altogether, our results demonstrate that C. albicans and C. glabrata Sky1 protein kinases are functionally similar to Sky1 in S. cerevisiae, whereas C. albicans Sky2, a unique kinase of the CTG clade, likely regulates dipeptide uptake via Ptr22.

Candida albicans Potassium Transporters

Potassium is basic for life. All living organisms require high amounts of intracellular potassium, which fulfils multiple functions. To reach efficient potassium homeostasis, eukaryotic cells have developed a complex and tightly regulated system of transporters present both in the plasma membrane and in the membranes of internal organelles that allow correct intracellular potassium content and distribution. We review the information available on the pathogenic yeast Candida albicans. While some of the plasma membrane potassium transporters are relatively well known and experimental data about their nature, function or regulation have been published, in the case of most of the transporters present in intracellular membranes, their existence and even function have just been deduced because of their homology with those present in other yeasts, such as Saccharomyces cerevisiae. Finally, we analyse the possible links between pathogenicity and potassium homeostasis. We comment on the possibility of using some of these transporters as tentative targets in the search for new antifungal drugs.

Selective Metal Chelation by a Thiosemicarbazone Derivative Interferes with Mitochondrial Respiration and Ribosome Biogenesis in Candida albicans

Metal chelation is generally considered as a promising antifungal approach but its specific mechanisms are unclear. Here, we identify 13 thiosemicarbazone derivatives that exert broad-spectrum antifungal activity with potency comparable or superior to that of fluconazole in vitro by screening a small compound library comprising 89 thiosemicarbazone derivatives as iron chelators. Among the hits, 19ak exhibits minimal cytotoxicity and potent activity against either azole-sensitive or azole-resistant fungal pathogens. Mechanism investigations reveal that 19ak inhibits mitochondrial respiration mainly by retarding mitochondrial respiratory chain complex I activity through iron chelation, and further reduces mitochondrial membrane potential and ATP synthesis in Candida albicans. In addition, 19ak inhibits fungal ribosome biogenesis mainly by disrupting intracellular zinc homeostasis. 19ak also stimulates the activities of antioxidant enzymes and decreases reactive oxygen species formation in C. albicans, resulting in an increase in detrimental intracellular reductive stress. However, 19ak has minor effects on mammalian cells in depleting intracellular iron and zinc. Moreover, 19ak exhibits low capacity to induce drug resistance and in vivo efficacy in a Galleria mellonella infection model. These findings uncover retarded fungal mitochondrial respiration and ribosome biogenesis as downstream effects of disruption of iron and zinc homeostasis in C. albicans and provide a basis for the thiosemicarbazone 19ak in antifungal application. IMPORTANCE The increasing incidence of fungal infections and resistance to existing antifungals call for the development of broad-spectrum antifungals with novel mechanisms of action. In this study, we demonstrate that a thiosemicarbazone derivative 19ak selectively inhibits mitochondrial respiration mainly by retarding mitochondrial respiratory chain complex I activity through iron chelation and inhibits ribosome biogenesis mainly by disrupting intracellular zinc homeostasis in C. albicans. In addition, 19ak exhibits low capacity to induce fungal resistance, minimal cytotoxicity, and in vivo antifungal efficacy. This study provides the basis of thiosemicarbazone derivative 19ak as a metal chelator for the treatment of fungal infections.

A novel antimicrobial peptide derived from human BPIFA1 protein protects against Candida albicans infection

Bactericidal/permeability-increasing fold containing family A, member 1 (BPIFA1) is an innate immunity defense protein. Our previous studies proved its antibacterial and antiviral effects, but its role in fungi remains unknown. The study aimed to identify antifungal peptides (AFP) derived from BPIFA1, and three antimicrobial peptides (AMP1-3) were designed. The antifungal effects were proved by growth inhibition assay. AMP3 activity was confirmed by germ tube growth experiment and XTT assay. Its effects on cell wall and membrane of Candida albicans were assessed by tannic acid and Annexin V-FITC/PI double staining, respectively. Additionally, scanning electron microscope (SEM) and transmission electron microscopy (TEM) were used for morphological and ultrastructural observation. The expression of ALS1, EAP1, and SUN41 was tested by qPCR. Ultimately, three AMPs could fight against C. albicans in vitro, and AMP3 was highly effective. It functioned by destroying the integrity of cell wall and normal structure of cell membrane. It also inhibited biofilm formation of C. albicans. In addition, AMP3 down-regulated the expression of ALS1, EAP1, and SUN41, those are known to be involved in virulence of C. albicans. Altogether, the study reported successful development of a novel AFP, which could be used as a new strategy for antifungal therapy.

Hinokitiol chelates intracellular iron to retard fungal growth by disturbing mitochondrial respiration

Introduction

The increasing morbidity of fungal infections and the prevalence of drug resistance highlighted the discovery of novel antifungal agents and investigation of their modes of action. Iron chelators have been used to treat superficial fungal infections or potentiate the efficacy of certain antifungal drugs. Hinokitiol exhibits potent antifungal activity and iron-chelating ability. However, their relationships have not been established.

Objectives

This study aims to explore the selectivity of hinokitiol against fungal cells and mammalian cells and determine the role of iron-chelating for the antifungal activity of hinokitiol.

Methods

Iron probe FeRhonox-1 was used to determine intracellular Fe²⁺ content. 5-Cyano-2,3-ditolyl tetrazolium chloride probe and Cell Counting Kit-8 were used to detect the mitochondrial respiratory activities. Quantitative real-time PCR and rescue experiments were performed to determine the effect of iron on the antifungal activity of hinokitiol. The effects of hinokitiol on fungal mitochondria were further evaluated using reactive oxygen species probes and several commercial Assay Kits. The ability of hinokitiol to induce resistance in Candida species was carried out using a serial passage method. The in vivo therapeutic effect of hinokitiol was evaluated using Galleria mellonella as an infectious model.

Results

Hinokitiol was effective against a panel of Candida strains with multiple azole-resistant mechanisms and persistently inhibited Candida albicans growth. Mechanism investigations revealed that hinokitiol chelated fungal intracellular iron and inhibited the respiration of fungal cells but had minor effects on mammalian cells. Hinokitiol further inhibited the activities of mitochondrial respiratory chain complexes I and II and reduced mitochondrial membrane potential, thereby decreasing intracellular ATP synthesis and increasing detrimental intracellular reductive stress. Moreover, hinokitiol exhibited low potential for inducing resistance in several Candida species and greatly improved the survival of Candida-infected Galleria mellonella.

Conclusions

These findings suggested the potential application of hinokitiol as an iron chelator to treat fungal infections.

The Importance of Vacuolar Ion Homeostasis and Trafficking in Hyphal Development and Virulence in Candida albicans

The vacuole of Candida albicans plays a significant role in many processes including homeostasis control, cellular trafficking, dimorphic switching, and stress tolerance. Thus, understanding the factors affecting vacuole function is important for the identification of new drug targets needed in response to the world’s increasing levels of invasive infections and the growing issue of fungal drug resistance. Past studies have shown that vacuolar proton-translocating ATPases (V-ATPases) play a central role in pH homeostasis and filamentation. Vacuolar protein sorting components (VPS) regulate V-ATPases assembly and at the same time affect hyphal development. As well, vacuolar calcium exchange systems like Yvc1 and Pmc1 maintain cytosolic calcium levels while being affected by V-ATPases function. All these proteins play a role in the virulence and pathogenesis of C. albicans. This review highlights the relationships among V-ATPases, VPS, and vacuolar calcium exchange proteins while summarizing their importance in C. albicans infections.

The Transient Receptor Potential Channel Yvc1 Deletion Recovers the Growth Defect of Calcineurin Mutant Under Endoplasmic Reticulum Stress in Candida albicans

Transient receptor potential (TRP) channel Yvc1 was related with hyphal growth, oxidative stress response, and pathogenicity. Calcineurin subunit Cnb1 was activated immediately in yeasts when exposed to severe stimulation. However, the relationship between Yvc1 and Cnb1-governed calcium ions and endoplasmic reticulum (ER) stress response remains unrevealed. In this study, we found that the mutant cnb1Δ/Δ was sensitive to TN, which was related with the overexpression of membrane calcium ion channels that could increase the cytosol calcium concentration. However, the growth of the cnb1Δ/Δyvc1Δ/Δ mutant was recovered and its cell vitality was better than the cnb1Δ/Δ strain. Meanwhile, the cellular calcium concentration was decreased and its fluctuation was weakened under ER stress in the cnb1Δ/Δyvc1Δ/Δ strain. To verify the regulation role of Yvc1 in the calcium concentration, we found that the addition of CaCl₂ led to the worse viability, while the growth state was relieved under the treatment of EGTA in the cnb1Δ/Δ strain. In conclusion, the deletion of YVC1 could reduce the cellular calcium and relieve the ER stress sensitivity of the cnb1Δ/Δ strain. Thereby, our findings shed a novel light on the relationship between the Yvc1-governed cellular calcium concentration and ER stress response in C. albicans.

Antifungal Effects and Potential Mechanisms of Benserazide Hydrochloride Alone and in Combination with Fluconazole Against Candida albicans

Purpose

The resistance of C. albicans to traditional antifungal drugs brings a great challenge to clinical treatment. To overcome the resistance, developing antifungal agent sensitizers has attracted considerable attention. This study aimed to determine the anti-Candida activity of BEH alone or BEH–FLC combination and to explore the underlying mechanisms.

Materials and Methods

In vitro antifungal effects were performed by broth microdilution assay and XTT reduction assay. Infected Galleria mellonella larvae model was used to determine the antifungal effects in vivo. Probes Fluo-3/AM, FITC-VAD-FMK and rhodamine 6G were used to study the influence of BEH and FLC on intracellular calcium concentration, metacaspase activity and drug efflux of C. albicans.

Results

BEH alone exhibited obvious antifungal activities against C. albicans. BEH plus FLC not only showed synergistic effects against planktonic cells and preformed biofilms within 8 h but also enhanced the antifungal activity in infected G. mellonella larvae. Mechanistic studies indicated that antifungal effects of drugs might be associated with the increasement of calcium concentration, activation of metacaspase activity to reduce virulence and anti-biofilms, but were not related to drug efflux.

Conclusion

BEH alone or combined with FLC displayed potent antifungal activity both in vitro and in vivo, and the underlying mechanisms were related to reduced virulence factors.

Fluorescent toys 'n' tools lighting the way in fungal research

Although largely overlooked compared to bacterial infections, fungal infections pose a significant threat to the health of humans and other organisms. Many pathogenic fungi, especially Candida species, are extremely versatile and flexible in adapting to various host niches and stressful situations. This leads to high pathogenicity and increasing resistance to existing drugs. Due to the high level of conservation between fungi and mammalian cells, it is hard to find fungus-specific drug targets for novel therapy development. In this respect, it is vital to understand how these fungi function on a molecular, cellular as well as organismal level. Fluorescence imaging allows for detailed analysis of molecular mechanisms, cellular structures and interactions on different levels. In this manuscript, we provide researchers with an elaborate and contemporary overview of fluorescence techniques that can be used to study fungal pathogens. We focus on the available fluorescent labelling techniques and guide our readers through the different relevant applications of fluorescent imaging, from subcellular events to multispecies interactions and diagnostics. As well as cautioning researchers for potential challenges and obstacles, we offer hands-on tips and tricks for efficient experimentation and share our expert-view on future developments and possible improvements.

CDATA[Recent Advances in the Development of 1,2,3-Triazole-containing Derivatives as Potential Antifungal Agents and Inhibitors of Lanoster ol 14α-Demethylase

1,2,3-Triazole, a five-membered heterocyclic nucleus, is widely recognized as a key chromophore of great value in medicinal chemistry for delivering compounds possessing innumerable biological activities, including antimicrobial, antitubercular, antidiabetic, antiviral, antitumor, antioxidants, and anti-inflammatory activities. Mainly, in the past years, diverse conjugates carrying this biologically valuable core have been reported due to their attractive fungicidal potential and potent effects on various infective targets. Hence, hybridization of 1,2,3-triazole with other antimicrobial pharmacophores appears to be a judicious strategy to develop new effective anti-fungal candidates to combat the emergence of drug-sensitive and drug-resistant infectious diseases. Thus, the current review highlights the recent advances of this promising category of 1,2,3-triazole-containing hybrids incorporating diverse varieties of bioactive heterocycles such as conozole, coumarin, imidazole, benzimidazole, pyrazole, indole, oxindole, chromene, pyrane, quinazoline, chalcone, isoflavone, carbohydrates, and amides. It underlies their inhibition behavior against a wide array of infectious fungal species during 2015-2020.

Design, synthesis and biological evaluation of a series of iron and copper chelating deferiprone derivatives as new agents active against Candida albicans

Candida albicans, in specific conditions, is responsible of severe invasive systemic candidiasis that are related to its ability to produce biofilm on biological and artificial surfaces. Many studies reported the role of iron in fungal growth and virulence and the ability of metal chelating agents to interfere with C. albicans metabolism, virulence and biofilm formation. Here we report the activity of 3-hydroxy-1,2-dimethyl-4(1H)-pyridinone (deferiprone) derivatives against C. albicans planktonic cells and biofilm. Some of the studied compounds (2b and 3b) were able to chelate Fe(III) and Cu(II), and showed an interesting activity on planktonic cells (MIC₅₀ of 32 μg/mL and 16 μg/mL respectively) and on biofilm formation (BMIC₅₀ of 32 μg/mL and 16 μg/mL respectively) in cultured ATCC 10,231C. albicans; this activity was reduced, in a concentration dependent way, by the addition of Fe(III) and Cu(II) to the culture media. Furthermore, the most active compound 3b showed a low toxicity on Galleria mellonella larvae.

Calcium-calcineurin signaling pathway in Candida albicans: A potential drug target

Increased morbidity and mortality of candidiasis are a notable threat to the immunocompromised patients. At present, the types of drugs available to treat C. albicans infection are relatively limited. Moreover, the emergence of antifungal drug resistance of C. albicans makes the treatment of C. albicans infection more difficult. The calcium-calcineurin signaling pathway plays a crucial role in the survival and pathogenicity of C. albicans and may act as a potential target against C. albicans. In this review, we summarized functions of the calcium-calcineurin signaling pathway in several biological processes, compared the differences of this signaling pathway between C. albicans and humans, and described anti-C. albicans activity of inhibitors of this signaling pathway. We believe that targeting the calcium-calcineurin signaling pathway is a promising strategy to cope with C. albicans infection.

Cation Transporters of Candida albicans-New Targets to Fight Candidiasis?

Candidiasis is the wide-spread fungal infection caused by numerous strains of yeast, with the prevalence of Candida albicans. The current treatment of candidiasis is becoming rather ineffective and costly owing to the emergence of resistant strains; hence, the exploration of new possible drug targets is necessary. The most promising route is the development of novel antibiotics targeting this pathogen. In this review, we summarize such candidates found in C. albicans and those involved in the transport of (metal) cations, as the latter are essential for numerous processes within the cell; hence, disruption of their fluxes can be fatal for C. albicans.

Candida albicans targets that potentially synergize with fluconazole

Fluconazole has characteristics that make it widely used in the clinical treatment of C. albicans infections. However, fluconazole has only a fungistatic activity in C. albicans, therefore, in the long-term treatment of C. albicans infection with fluconazole, C. albicans has the potential to acquire fluconazole resistance. A promising approach to increase fluconazole's efficacy is identifying potential targets of drugs that can enhance the antifungal effect of fluconazole, or even make the drug fungicidal. In this review, we systematically provide a global overview of potential targets of drugs synergistic with fluconazole in C. albicans, identify new avenues for research on fluconazole potentiation, and highlight the promise of combinatorial strategies with fluconazole in combatting C. albicans infections.

Understanding How Microorganisms Respond to Acid pH Is Central to Their Control and Successful Exploitation

Microbes from the three domains of life, Bacteria, Archaea, and Eukarya, share the need to sense and respond to changes in the external and internal concentrations of protons. When the proton concentration is high, acidic conditions prevail and cells must respond appropriately to ensure that macromolecules and metabolic processes are sufficiently protected to sustain life. While, we have learned much in recent decades about the mechanisms that microbes use to cope with acid, including the unique challenges presented by organic acids, there is still much to be gained from developing a deeper understanding of the effects and responses to acid in microbes. In this perspective article, we survey the key molecular mechanisms known to be important for microbial survival during acid stress and discuss how this knowledge might be relevant to microbe-based applications and processes that are consequential for humans. We discuss the research approaches that have been taken to investigate the problem and highlight promising new avenues. We discuss the influence of acid on pathogens during the course of infections and highlight the potential of using organic acids in treatments for some types of infection. We explore the influence of acid stress on photosynthetic microbes, and on biotechnological and industrial processes, including those needed to produce organic acids. We highlight the importance of understanding acid stress in controlling spoilage and pathogenic microbes in the food chain. Finally, we invite colleagues with an interest in microbial responses to low pH to participate in the EU-funded COST Action network called EuroMicropH and contribute to a comprehensive database of literature on this topic that we are making publicly available.

Advances in Fungal Peptide Vaccines

Vaccination is one of the greatest public health achievements in the past century, protecting and improving the quality of life of the population worldwide. However, a safe and effective vaccine for therapeutic or prophylactic treatment of fungal infections is not yet available. The lack of a vaccine for fungi is a problem of increasing importance as the incidence of diverse species, including Paracoccidioides, Aspergillus, Candida, Sporothrix, and Coccidioides, has increased in recent decades and new drug-resistant pathogenic fungi are emerging. In fact, our antifungal armamentarium too frequently fails to effectively control or cure mycoses, leading to high rates of mortality and morbidity. With this in mind, many groups are working towards identifying effective and safe vaccines for fungal pathogens, with a particular focus of generating vaccines that will work in individuals with compromised immunity who bear the major burden of infections from these microbes. In this review, we detail advances in the development of vaccines for pathogenic fungi, and highlight new methodologies using immunoproteomic techniques and bioinformatic tools that have led to new vaccine formulations, like peptide-based vaccines.

Antifungal Activity and Potential Mechanism of Panobinostat in Combination With Fluconazole Against Candida albicans

Invasive fungal infections are an emerging problem worldwide, which bring huge health challenges. Candida albicans, the most common opportunistic fungal pathogen, can cause bloodstream infections with high mortality in susceptible hosts. At present, available antifungal agents used in clinical practice are limited, and most of them also have some serious adverse effects. The emergence of drug resistance because of the wide use of antifungal agents is a new limitation to successful patient therapy. Drug combination therapy is increasingly becoming a way to enhance antifungal efficacy, and reduce drug resistance and potential toxicity. Panobinostat, as a pan-histone deacetylase inhibitor, has been approved by the United States Food and Drug Administration as novel antitumor agents. In this study, the antifungal effects and mechanisms of panobinostat combined with fluconazole (FLC) against C. albicans were explored for the first time. The results indicated that panobinostat could work synergistically with FLC against resistant C. albicans, the minimal inhibitory concentration (MIC) of panobinostat could decrease from 128 to 0.5–2 μg/ml and the MIC of FLC could decrease from >512 to 0.25–0.5 μg/ml, and the fractional inhibitory concentration index (FICI) value ranged from 0.0024 to 0.0166. It was not only synergized against planktonic cells but also against C. albicans biofilms performed ≤8 h when panobinostat is combined with fluconazole; the sessile MIC (sMIC) of panobinostat could decrease from >128 to 0.5–8 μg/ml and the sMIC of FLC from >1024 to 0.5–2 μg/ml, and the FICI value was <0.5. The Galleria mellonella infection model was used to evaluate the in vivo effect of the drug combination, and the result showed that the survival rate could be improved obviously. Finally, we explored the synergistic mechanisms of the drug combination. The hyphal growth, which plays roles in drug resistance, was found to be inhibited, and metacaspase which is related to cell apoptosis was activated (p < 0.01), whereas the synergistic effects were proven not to be related to the efflux pumps (p > 0.05). These findings might provide novel insights into the antifungal drug discovery and the treatment of candidiasis caused by C. albicans.

Synergistic Effect of Berberine Hydrochloride and Fluconazole Against Candida albicans Resistant Isolates

The emergence of resistant Candida albicans has made clinical fluconazole (FLC) treatment difficult. Improving sensitivity to FLC is an effective way to treat resistant isolates. Berberine hydrochloride (BBH) is a commonly used traditional Chinese medicine with antimicrobial effects, especially in resistant isolates. We investigated the molecular mechanisms underlying BBH and FLC synergism on biofilm-positive FLC-resistant C. albicans inhibition. Checkerboard microdilution assays and time-kill assays showed a strong synergistic effect between BBH and FLC in resistant C. albicans isolates, causing a significant 32–512-fold reduction in minimum inhibitory concentrations. BBH combined with FLC inhibited intracellular FLC efflux due to key efflux pump gene CDR1 downregulation, whereas FLC alone induced high CDR1 transcription in resistant strains. Further, BBH + FLC inhibited yeast adhesion, morphological hyphae transformation, and biofilm formation by downregulating the hyphal-specific genes ALS3, HWP1, and ECE1. BBH caused cytoplasmic Ca²⁺ influx, while FLC alone did not induce high intracellular Ca²⁺ levels. The vacuolar calcium channel gene YVC1 was upregulated, while the vacuolar calcium pump gene PMC1 was downregulated in the BBH + FLC and BBH alone groups. However, vacuolar calcium gene expression after FLC treatment was opposite in biofilm-positive FLC-resistant C. albicans, which might explain why BBH induces Ca²⁺ influx. These results demonstrate that BBH + FLC exerts synergistic effects to increase FLC sensitivity by regulating multiple targets in FLC-resistant C. albicans. These findings further show that traditional Chinese medicines have multi-target antimicrobial effects that may inhibit drug-resistant strains. This study also found that the vacuolar calcium regulation genes YVC1 and PMC1 are key BBH + FLC targets which increase cytoplasmic Ca²⁺ in resistant isolates, which might be critical for reversing biofilm-positive FLC-resistant C. albicans.

The effects of clioquinol in morphogenesis, cell membrane and ion homeostasis in Candida albicans

Background

Candida albicans is the most prevalent opportunistic fungal pathogen. Development of antifungals with novel targets is necessary for limitations of current antifungal agents and the emergence of drug resistance. The antifungal activity of clioquinol was widely accepted while the precise mechanism was poorly understood. Hence, we aimed to seek for the possible mechanism of clioquinol against Candida albicans in the present study.

Results

Clioquinol could inhibit hyphae formation in a concentration-dependent manner in multiple liquid and solid media. The concentration and time-dependent anti-biofilm activities were observed in different incubation periods quantitatively and qualitatively. Further investigation found that clioquinol disrupted cell membrane directly in high concentration and induced depolarization of the membrane in low concentration. As for the influence on ion homeostasis, the antifungal effects of clioquinol could be reversed by exogenous addition of metal ions. Meanwhile, the minimum inhibitory concentration of clioquinol was increased in media supplemented with exogenous metal ions and decreased in media supplemented with exogenous metal chelators. We also found that the cellular labile ferrous iron level decreased when fungal cells were treated with clioquinol.

Conclusion

These results indicated that clioquinol could inhibit yeast-hyphae transition and biofilm formation in Candida albicans. The effect on the cell membrane was different depending on different concentrations of clioquinol. Meanwhile, clioquinol could interfere with ion homeostasis as metal chelators for zinc, copper and iron, which was quite different with current common antifungal agents. All in all, clioquinol can be a new promising antifungal agent with novel target though more studies are needed to better understand the precise antifungal mechanism.

Type I Interferons Ameliorate Zinc Intoxication of Candida glabrata by Macrophages and Promote Fungal Immune Evasion

Host and fungal pathogens compete for metal ion acquisition during infectious processes, but molecular mechanisms remain largely unknown. Here, we show that type I interferons (IFNs-I) dysregulate zinc homeostasis in macrophages, which employ metallothionein-mediated zinc intoxication of pathogens as fungicidal response. However, Candida glabrata can escape immune surveillance by sequestering zinc into vacuoles. Interestingly, zinc-loading is inhibited by IFNs-I, because a Janus kinase 1 (JAK1)-dependent suppression of zinc homeostasis affects zinc distribution in macrophages as well as generation of reactive oxygen species (ROS). In addition, systemic fungal infections elicit IFN-I responses that suppress splenic zinc homeostasis, thereby altering macrophage zinc pools that otherwise exert fungicidal actions. Thus, IFN-I signaling inadvertently increases fungal fitness both in vitro and in vivo during fungal infections. Our data reveal an as yet unrecognized role for zinc intoxication in antifungal immunity and suggest that interfering with host zinc homeostasis may offer therapeutic options to treat invasive fungal infections.

Performance of a new Candida anti-mannan IgM and IgG assays in the diagnosis of candidemia

Candida is one of the most frequent pathogens of bloodstream infections, which is associated with high morbidity and mortality rates. Rapid immunological detection methods are essential in the early diagnosis of candidemia. Anti-mannan is one of host-derived biomarkers against cell wall components of Candida. We conducted this study to evaluate the diagnostic performance of two anti-mannan assays (IgM, IgG) for candidemia through the analysis of 40 candidemia patients, 48 participants with Candida colonization and 213 participants with neither Candida colonization nor Candida infections (13 patients with other bloodstream infections, 145 hospitalized patients and 55 healthy controls). The performance of the two assays were evaluated by calculating their sensitivity and specificity. The sensitivity ranged from 0.78 to 0.80 for the IgM assay and 0.68 to 0.75 for the IgG assay. The specificity ranged from 0.97 to 0.98 for the IgM assay and 0.91 to 0.94 for the IgG assay. The diagnostic performance of the anti-mannan IgM assay was better than that of IgG, with higher sensitivity and specificity. Combining the two assays (positive results of single or both assays are both considered as positive) could improve the sensitivity up to 0.93 (0.79-0.98) and only slightly reduce the specificity (0.93(0.89-0.95)). The anti-mannan IgM, IgG assays are rapid and cost-effective assays that may be probably useful in the diagnosis of candidemia.

Gemini quaternary ammonium compound PMT12-BF4 inhibits Candida albicans via regulating iron homeostasis

Quaternary ammonium compounds (QACs) are classified as cationic surfactants, and are known for their biocidal activity. However, their modes of action are thus far not completely understood. In this study, we synthesized a gemini QAC, PMT12-BF4 and found that it exerted unsurpassed broad-spectrum antifungal activity against drug susceptible and resistant Candida albicans, and other pathogenic fungi, with a minimal inhibitory concentration (MIC) at 1 or 2 μg/mL. These results indicated that PMT12-BF4 used a mode of action distinct from current antifungal drugs. In addition, fungal pathogens treated with PMT12-BF4 were not able to grow on fresh YPD agar plates, indicating that the effect of PMT12-BF4 was fungicidal, and the minimal fungicidal concentration (MFC) against C. albicans isolates was 1 or 2 μg/mL. The ability of yeast-to-hyphal transition and biofilm formation of C. albicans was disrupted by PMT12-BF4. To investigate the modes of action of PMT12-BF4 in C. albicans, we used an RNA sequencing approach and screened a C. albicans deletion mutant library to identify potential pathways affected by PMT12-BF4. Combining these two approaches with a spotting assay, we showed that the ability of PMT12-BF4 to inhibit C. albicans is potentially linked to iron ion homeostasis.

Type I Interferon Response Dysregulates Host Iron Homeostasis and Enhances Candida glabrata Infection

Type I interferons (IFNs-I) fulfil multiple protective functions during pathogenic infections, but they can also cause detrimental effects and enhance immunopathology. Here, we report that IFNs-I promote the dysregulation of iron homeostasis in macrophages during systemic infections with the intracellular pathogen Candida glabrata, leading to fungal survival and persistence. By engaging JAK1, IFNs-I disturb the balance of the transcriptional activator NRF2 and repressor BACH1 to induce downregulation of the key iron exporter Fpn1 in macrophages. This leads to enhanced iron accumulation in the phagolysosome and failure to restrict fungal access to iron pools. As a result, C. glabrata acquires iron via the Sit1/Ftr1 iron transporter system, facilitating fungal intracellular replication and immune evasion. Thus, IFNs-I are central regulators of iron homeostasis, which can impact infection, and restricting iron bioavailability may offer therapeutic strategies to combat invasive fungal infections.

The Synergistic Antifungal Effect and Potential Mechanism of D-Penicillamine Combined With Fluconazole Against Candida albicans

Over the last few decades, candidiasis has exhibited an increasing incidence worldwide, causing high mortality in immunocompromised patients. Candida albicans is one of the leading opportunistic fungal pathogens. However, due to the increased use of antifungal agents, resistance of C. albicans to conventional agents, especially fluconazole, has frequently emerged. Therefore, research on the use of combinations of current drugs to sensitize antifungal agents and overcome fungal resistance has attracted considerable attention. This study demonstrated for the first time that D-penicillamine (PCA) combined with fluconazole showed a synergistic effect against C. albicans. PCA combined with fluconazole not only showed synergistic effects against planktonic cells of C. albicans, but also showed synergistic effects against C. albicans biofilms formed within 12 h in vitro. In addition, a Galleria mellonella infection model was used to evaluate the in vivo effects of this drug combination. The results showed that the combination of the two drugs could improve the survival rate, decrease the fungal burden, and reduce the tissue invasion of G. mellonella larvae. Finally, we explored the potential synergistic mechanisms of the drug combination, mainly including inhibition of the morphological transformation, reduction of the intracellular calcium concentration, and the activation of metacaspase, which is closely related to cell apoptosis. These findings might provide novel insights into antifungal drug discovery and the treatment of candidiasis caused by C. albicans.

Potential of Gallium as an Antifungal Agent

There are only few drugs available to treat fungal infections, and the lack of new antifungals, along with the emergence of drug-resistant strains, results in millions of deaths/year. An unconventional approach to fight microbial infection is to exploit nutritional vulnerabilities of microorganism metabolism. The metal gallium can disrupt iron metabolism in bacteria and cancer cells, but it has not been tested against fungal pathogens such as Aspergillus and Candida. Here, we investigate in vitro activity of gallium nitrate III [Ga(NO₃)₃] against these human pathogens, to reveal the gallium mechanism of action and understand the interaction between gallium and clinical antifungal drugs. Ga(NO₃)₃ presented a fungistatic effect against azole-sensitive and -resistant A. fumigatus strains (MIC_50/90 = 32.0 mg/L) and also had a synergistic effect with caspofungin, but not with azoles and amphotericin B. Its antifungal activity seems to be reliant on iron-limiting conditions, as the presence of iron increases its MIC value and because we observed a synergistic interaction between gallium and iron chelators against A. fumigatus. We also show that an A. fumigatus mutant (ΔhapX) unable to grow in the absence of iron is more susceptible to gallium, reinforcing that gallium could act by disrupting iron homeostasis. Furthermore, we demonstrate that gallium has a fungistatic effect against different species of Candida ranging from 16.0 to 256.0 mg/L, including multidrug-resistant Candida auris, C. haemulonii, C. duobushaemulonii, and C. glabrata. Our findings indicate that gallium can inhibit fungal pathogens in vitro under iron-limiting conditions, showing that Ga(NO₃)₃ could be a potential therapy not only against bacteria but also as an antifungal drug.

Synthesis, antimicrobial activity, and determination of the lipophilicity of ((cyclohex-3-enylmethylene)hydrazinyl)thiazole derivatives

Synthesis and investigation of antimicrobial activity of fifteen novel thiazoles containing cyclohexene moiety are presented. Among the derivatives, compounds 3a–3d, 3f, 3n, and 3o showed very strong activity against the reference Candida spp. strains with MIC = 0.015–3.91 µg/ml. The activity of these compounds is similar and even higher than the activity of nystatin used as positive control. Compounds 3d, 3f, 3n, 3o showed the highest activity with very strong effect towards most of yeasts isolated from clinical materials with MIC = 0.015–7.81 µg/ml. The cytotoxicity studies for the most active compounds showed that Candida spp. growth was inhibited at noncytotoxic concentrations for the mammalian L929 fibroblast. In addition, a good correlation was obtained between lipophilicity of compounds determined using reversed phase thin-layer chromatography and their antifungal activity.

Solidago graminifolia L. Salisb. (Asteraceae) as a Valuable Source of Bioactive Polyphenols: HPLC Profile, In Vitro Antioxidant and Antimicrobial Potential

Solidago species are often used in traditional medicine as anti-inflammatory, diuretic, wound-healing and antimicrobial agents. Still, the bioactive compounds and biological activities of some species have not been studied. The present work aimed to investigate the polyphenolic profile and the biological properties of Solidago graminifolia L. Salisb., a poorly explored medicinal plant. The hydroalcoholic extracts from aerial parts were evaluated for total phenolic content (TPC), total flavonoid content (TFC) and the polyphenolic compounds were investigated by HPLC-MS. The antioxidant potential in vitro was determined using DPPH and FRAP assays. Antibacterial and antifungal effects were evaluated by dilution assays and MIC, MBC and MFC were calculated. The results showed that Solidago graminifolia aerial parts contain an important amount of total phenolics (192.69 mg GAE/g) and flavonoids (151.41 mg RE/g), with chlorogenic acid and quercitrin as major constituents. The hydroalcoholic extracts showed promising antioxidant and antimicrobial potential, with potent antibacterial activity against Staphylococcus aureus and important antifungal effect against Candida albicans and C. parapsilosis. The obtained results indicated that the aerial parts of Solidago graminifolia could be used as novel resource of phytochemicals in herbal preparations with antioxidant and antimicrobial activities.

Zinc and Iron Homeostasis: Target-Based Drug Screening as New Route for Antifungal Drug Development

The incidence of fungal diseases is on the rise and the number of fatalities is still unacceptably high. While advances into antifungal drug development have been made there remains an urgent need to develop novel antifungal agents targeting as-yet unexploited pathways, such as metal ion homeostasis. Here we report such an approach by developing a metal sensor screen in the opportunistic human fungal pathogen Candida albicans. Using this reporter strain, we screened a library of 1,200 compounds and discovered several active compounds not previously described as chemical entities with antifungal properties. Two of these, artemisinin and pyrvinium pamoate, have been further characterized and their interference with metal homeostasis and potential as novel antifungal compounds validated. Lastly, we demonstrate that the same strain can be used to report on intracellular conditions within host phagocytes, paving the way toward the development of novel screening platforms that could identify compounds with the potential to perturb ion homeostasis of the pathogen specifically within host cells.