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.

Synergistic activity of clioquinol with voriconazole and amphotericin B against fungi of interest in eye infections

Keratoplasty represents a risk factor for fungal eye infections, despites the antibacterial actives in the corneal tissue preservation means, it does not contain active substances with antifungal action. Among the most commonly associated fungal agents are the species belonging to the genera Fusarium and Candida. These agents can trigger an infectious process characterized by swift progression associated with high rates of morbidity, causing irreversible damage. Polyene and azole antifungals are the main agents of ocular therapy, however, they demonstrate some limitations, such as their toxicity and fungal resistance. In this context, drug repositioning and the combination of antifungals may be an alternative. Hence, the goal of this study was to investigate the potential activity of clioquinol (CLQ), a derivative of 8-hydroxyquinoline with previously described antifungal activity, along with its triple and quadruple combinations with antifungal agents commonly used in ophthalmic fungal therapy, natamycin (NAT), voriconazole (VRC), and amphotericin B (AMB), against main fungal pathogens in eye infections. The MICs for CLQ ranged from 0.25 to 2.0 μg/mL, for NAT from 4.0 to 32.0 μg/mL, for AMB it ranged from 0.25 to 16.0 μg/mL and for VRC from 0.03125 to 512.0 µg/mL. Among the tested combinations, the VRC-AMB-CLQ combination stands out, which showed a synergistic effect for more than 50 % of the tested strains and did not present antagonistic results against any of them. Toxicity data were similar to those antifungals already used, even with lower potential toxicity. Therefore, both clioquinol and the triple combination VCR-AMB-CLQ exhibited promising profiles for use as active components in corneal tissue preservation medium.

Plasma activated Ezhangfeng Cuji as innovative antifungal agent and its inactivation mechanism

Candida albicans is a highly drug-resistant fungus for which new treatments are urgently needed due to the lack of clinically effective options. In this study, we evaluated the antifungal activity and mechanism of plasma-activated Ezhangfeng Cuji (PAEC) against Candida albicans and compared it with physiological saline (PS), plasma-activated physiological saline (PAPS) and Ezhangfeng Cuji (EC). After dielectric barrier discharge (DBD) plasma treatment with EC for 20 min followed by a 10 min immersion of Candida albicans, the fungus was reduced by approximately 3 orders of magnitude. High performance liquid chromatography (HPLC) results showed an increase of 41.18% and 129.88% in the concentration of oxymatrine and rhein, respectively, after plasma-treated EC. The concentrations of reactive species (RS), such as H₂O₂, [Formula: see text], and O₃, were found to be higher and the pH value was getting lower in PS after plasma treatment. Detailed analysis of intracellular material leakage, reactive oxygen species (ROS), apoptosis for Candida albicans and observation by transmission electron microscopy (TEM) and scanning electron microscopy (SEM) demonstrated that PAPS, EC and PAEC disrupt the morphological structure of Candida albicans to varying degrees.Additionally, specific analyses on Candida albicans virulence factors, such as adhesion to tissue surfaces, cell surface hydrophobicity (CSH), the transition of yeast-phase cells to mycelium-phase cells, and the secretion of hydrolytic enzymes for Candida albicans were conducted and found to be inhibited after PAPS/EC/PAEC treatment. In our investigation, the inhibitory effects on Candida albicans were ranked from strong to weak as follows: PAEC, EC, PAPS, and PS.

Chelerythrine reverses the drug resistance of resistant Candida albicans and the biofilm to fluconazole

Aim: To evaluate the antifungal activity of chelerythrine in combination with fluconazole against planktonic Candida albicans strains and preformed biofilm. Materials & methods: A broth microdilution assay was used to reveal the antifungal activity of chelerythrine combined with fluconazole against C. albicans and the preformed biofilm. A fractional inhibitory concentration index model was used to evaluate the interaction. Results: Chelerythrine strongly synergized with fluconazole against fluconazole-resistant C. albicans and the biofilm preformed for less than 12 h. In addition, chelerythrine combined with fluconazole exhibited a synergistic effect against C. albicans morphogenesis. Conclusion: Chelerythrine could reverse the drug resistance of resistant C. albicans and its biofilm to fluconazole, providing new insights for overcoming the drug resistance of C. albicans.

8-hydroxyquinoline and quinazoline derivatives as potential new alternatives to combat Candida spp. biofilm

Often associated to the colonization by Candida spp. biofilm, the catheter-related infections are a serious health problem since the absence of a specific therapy. Hence, the main objective of this work was to evaluate the activity of 8-hydroxyquinoline and quinazoline derivatives on Candida spp. biofilms. A quinazoline derivative (PH100) and an 8-hydroxyquinoline derivative (PH157) were tested against nine strains of C. albicans, C. tropicalis and C. parapsilosis, and their biofilms in polystyrene microtitre plates and on polyurethane central venous catheter. The PH157 compound was incorporated into a film-forming system-type formulation and its capacity to inhibit biofilm formation on catheters was evaluated. The compounds were active against planktonic and sessile cells, as well as against the tested biofilms. PH157 compound performed better than the PH100 compound. The formulation containing PH157 presented results very similar to those of the compound in solution, which indicates that its activity was preserved. Both compounds showed activity against Candida spp. strains and their biofilm, with better PH157 activity. The formulation preserved the action of the PH157 compound, in addition, it facilitates its application on the catheter. The structural modifications that these compounds allow can generate compounds that are even more active, both against planktonic cells and biofilms.

Effect of antifungal agents, lysozyme and human antimicrobial peptide LL-37 on clinical Candida isolates with high biofilm production

Introduction. Candida species can form biofilms on tissues and medical devices, making them less susceptible to antifungal agents.Hypothesis/Gap Statement. Antifungal combination may be an effective strategy to fight against Candida biofilm.Aim. In this study, we investigated the in vitro activity of fluconazole, caspofungin and amphotericin B, alone and in combination, against 17 clinical Candida tropicalis and 6 Candida parapsilosis isolates with high biofilm formation. We also tested LL-37 and lysozyme for anti-biofilm activity against a selected C. tropicalis isolate.Methodology. Candida biofilms were prepared using the 96-well plate-based method. The minimum biofilm eradication concentrations were determined for single and combined antifungal drugs. The activity of LL-37 and lysozyme was determined by visual reading for planktonic cells and using the XTT assay for biofilms.Results. Under biofilm conditions, fluconazole plus caspofungin showed synergistic effects against 60.9% (14 of 23) of the tested isolates, including 70.6% of C. tropicalis [fractional inhibitory concentration index (FICI), 0.26-1.03] and 33.3% of C. parapsilosis (FICI, 0.04-2.03) isolates. Using this combination, no antagonism was observed. Amphotericin B plus caspofungin showed no effects against 78.3% (18 of 23) of the tested isolates. Amphotericin B plus fluconazole showed no effects against 65.2% (15 of 23) of the tested isolates and may have led to antagonism against 2 C. tropicalis and 2 C. parapsilosis isolates. LL-37 and lysozyme had no effect on biofilms of the selected C. tropicalis isolate.Conclusions. We found that fluconazole plus caspofungin led to a synergistic effect against C. tropicalis and C. parapsilosis biofilms. The efficacy of the antifungal combination therapies of the proposed schemes against biofilm-associated Candida infections requires careful and constant evaluation.

Candida albicans biofilms and polymicrobial interactions

Candida albicans is a common fungus of the human microbiota. While generally a harmless commensal in healthy individuals, several factors can lead to its overgrowth and cause a range of complications within the host, from localized superficial infections to systemic life-threatening disseminated candidiasis. A major virulence factor of C. albicans is its ability to form biofilms, a closely packed community of cells that can grow on both abiotic and biotic substrates, including implanted medical devices and mucosal surfaces. These biofilms are extremely hard to eradicate, are resistant to conventional antifungal treatment and are associated with high morbidity and mortality rates, making biofilm-associated infections a major clinical challenge. Here, we review the current knowledge of the processes involved in C. albicans biofilm formation and development, including the central processes of adhesion, extracellular matrix production and the transcriptional network that regulates biofilm development. We also consider the advantages of the biofilm lifestyle and explore polymicrobial interactions within multispecies biofilms that are formed by C. albicans and selected microbial species.

Anti-Candida Activity of Essential Oils from Lamiaceae Plants from the Mediterranean Area and the Middle East

Extensive documentation is available on plant essential oils as a potential source of antimicrobials, including natural drugs against Candida spp. Yeasts of the genus Candida are responsible for various clinical manifestations, from mucocutaneous overgrowth to bloodstream infections, whose incidence and mortality rates are increasing because of the expanding population of immunocompromised patients. In the last decade, although C. albicans is still regarded as the most common species, epidemiological data reveal that the global distribution of Candida spp. has changed, and non-albicans species of Candida are being increasingly isolated worldwide. The present study aimed to review the anti-Candida activity of essential oils collected from 100 species of the Lamiaceae family growing in the Mediterranean area and the Middle East. An overview is given on the most promising essential oils and constituents inhibiting Candida spp. growth, with a particular focus for those natural products able to reduce the expression of virulence factors, such as yeast-hyphal transition and biofilm formation. Based on current knowledge on members of the Lamiaceae family, future recommendations to strengthen the value of these essential oils as antimicrobial agents include pathogen selection, with an extension towards the new emerging Candida spp. and toxicological screening, as it cannot be taken for granted that plant-derived products are void of potential toxic and/or carcinogenic properties.

Candida Biofilms: An Update on Developmental Mechanisms and Therapeutic Challenges

Fungi of the genus Candida are important etiological agents of superficial and life-threatening infections in individuals with a compromised immune system. One of the main characteristics of Candida is its ability to form highly drug tolerance biofilms in the human host. Biofilms are a dynamic community of multiple cell types whose formation over time is orchestrated by a network of transcription regulators. In this brief review, we provide an update of the processes involved in biofilm formation by Candida spp. (formation, treatment, and control), as well as the transcriptional circuitry that regulates its development and interactions with other microorganisms. Candida albicans is known to build mixed species biofilms with other Candida species and with various other bacterial species in different host niches. Taken together, these properties play a key role in Candida pathogenesis. In addition, this review gathers recent studies with new insights and perspectives for the treatment and control of Candida biofilms.

Rational selection of antifungal drugs to propose a new formulation strategy to control Candida biofilm formation on venous catheters

INTRODUCTION

Infections associated with medical devices are often related to colonization by Candida spp. biofilm; in this way, numerous strategies have been developed and studied, mainly in order to prevent this type of fungal growth.

AIM

Considering the above, the main objective of the present study is to make a rational choice of the best antifungal therapy for the in vitro treatment of the biofilm on venous catheters, proposing an innovative formulation of a film-forming system to coat the surface in order to prevent the formation of biofilms.

METHODOLOGY

Anidulafungin, fluconazole, voriconazole, ketoconazole, amphotericin B, and the association of anidulafungin and amphotericin B were tested against biofilms of C. albicans, C. tropicalis, and C. parapsilosis strains in microtiter plates and in a polyurethane catheter. Besides, anidulafungin, amphotericin B, and the combination of both were incorporated in a film-forming system and were evaluated against biofilm.

RESULTS

The superior activity of anidulafungin was demonstrated in relation to the other antifungal agents. Although amphotericin B showed good activity, high concentrations were required. The combination showed a synergistic action, in solution and in the formulation, showing excellent results, with activity above 90%.

CONCLUSION

Due to the superiority of anidulafungin and the synergistic activity of the combination, these alternatives were the most promising options for use in a formulation proposal as a new strategy to combat the Candida spp. biofilm. These formulations demonstrated high in vitro performance in the prevention of biofilms, indicating that they are candidates with great potential for in vivo tests.

Synergistic Effects and Mechanisms of Combined Treatment With Harmine Hydrochloride and Azoles for Resistant Candida albicans

Several studies have demonstrated the significant antiviral, antimicrobial, antiplasmodial, antioxidative, antifungal, antimutagenic, and antitumor properties of harmine hydrochloride (HMH). The main objective of the present study was to investigate the antifungal effects and underlying mechanisms of HMH when combined with azoles to determine whether such combinations act in a synergistic manner. As a result, we found that HMH exhibits synergistic antifungal effects in combination with azoles against resistant Candida albicans (C. albicans) planktonic cells, as well as resistant C. albicans biofilm in the early stage. Antifungal potential of HMH with fluconazole was also explored in vivo using an invertebrate model. Our results suggest that HMH combined with azoles is synergistic against resistant C. albicans in vitro and in vivo. No synergy is seen with azole sensitive C. albicans strains nor with other Candida species. Such synergistic mechanisms on resistance C. albicans are involved in increasing intracellular azoles, inhibiting hyphal growth, disturbing cytosolic calcium concentration, and inducing apoptosis of resistant C. albicans cells.

Antifungal Proteins with Antiproliferative Activity on Cancer Cells and HIV-1 Enzyme Inhibitory Activity from Medicinal Plants and Medicinal Fungi

A variety of fungi, plants, and their different tissues are used in Traditional Chinese Medicine to improve health, and some of them are recommended for dietary therapy. Many of these plants and fungi contain antifungal proteins and peptides which suppress spore germination and hyphal growth in phytopathogenic fungi. The aim of this article is to review antifungal proteins produced by medicinal plants and fungi used in Chinese medicine which also possess anticancer and human immunodeficiency virus-1 (HIV-1) enzyme inhibitory activities.

SOCS3 ablation enhances DC-derived Th17 immune response against Candida albicans by activating IL-6/STAT3 in vitro

AIMS

Enhancing the potency of dendritic cells (DCs) by downregulating negative immunoregulatory pathways may provide immunotherapeutic possibilities against candidiasis.

MAIN METHODS

In this study, a si-RNA method is used to repress expression of the cytokine signaling-3 suppressor (SOCS3) in murine bone marrow-DCs, and then the maturation of DCs and the subsequent T-cell response after exposure to C. albicans are monitored in vitro.

KEY FINDINGS

Along with a higher expression of the DC maturation markers CD40, CD86 and MHC-II, IL-6/STAT3 is markedly upregulated in the SOCS3 siRNA-treated DCs after exposure to C. albicans as compared with control DCs. In response to DCs maturation, CD4⁺ T cells have an increased expression of Th17 cell markers -- including the retinoic acid-related orphan nuclear hormone receptors γt (RORγt), IL-17A and IL-23R -- and increased release of IL-17. We note that this enhanced Th17 cell differentiation induced by siSOCS3-treated DCs in presence of C. albicans can be partly offset when anti-IL-6 antibody is added into the co-culture.

SIGNIFICANCE

As with SOCS1 in our previous report, suppression of SOCS3 alone also has the potential to fully activate DCs maturation. However, while SOCS1 knockdown in DCs during C. albicans infection specifically augments Th1 differentiation, SOCS3 silencing particularly increases Th17 differentiation.

Antifungal Compounds against Candida Infections from Traditional Chinese Medicine

Infections caused by Candida albicans, often refractory and with high morbidity and mortality, cause a heavy burden on the public health while the current antifungal drugs are limited and are associated with toxicity and resistance. Many plant-derived molecules including compounds isolated from traditional Chinese medicine (TCM) are reported to have antifungal activity through different targets such as cell membrane, cell wall, mitochondria, and virulence factors. Here, we review the recent progress in the anti-Candida compounds from TCM, as well as their antifungal mechanisms. Considering the diverse targets and structures, compounds from TCM might be a potential library for antifungal drug development.

A Linear 19-Mer Plant Defensin-Derived Peptide Acts Synergistically with Caspofungin against Candida albicans Biofilms

Public health problems are associated with device-associated biofilm infections, with Candida albicans being the major fungal pathogen. We previously identified potent antibiofilm combination treatment in which the antifungal plant defensin HsAFP1 is co-administered with caspofungin, the preferred antimycotic to treat such infections. In this study, we identified the smallest linear HsAFP1-derived peptide that acts synergistically with caspofungin or anidulafungin against C. albicans as HsLin06_18, a 19-mer peptide derived from the C-terminal part of HsAFP1. The [caspofungin + HsLin06_18] combination significantly reduced in vitro biofilm formation of Candida glabrata and C. albicans on catheters, as well as biofilm formation of a caspofungin-resistant C. albicans strain. The [caspofungin + HsLin06_18] combination was not cytotoxic and reduced biofilm formation of C. albicans in vivo using a subcutaneous rat catheter model, as compared to control treatment. Mode of action research on the [caspofungin + HsLin06_18] combination pointed to caspofungin-facilitated HsLin06_18 internalization and immediate membrane permeabilization. All these findings point to broad-spectrum antibiofilm activity of a combination of HsLin06_18 and caspofungin.

Gentamicin synergises with azoles against drug-resistant Candida albicans

Candida spp. are the primary opportunistic pathogens of nosocomial fungal infections, causing both superficial and life-threatening systemic infections. Combination therapy for fungal infections has attracted considerable attention, especially for those caused by drug-resistant fungi. Gentamicin (GM), an aminoglycoside antibiotic, has weak antifungal activity against Fusarium spp. The aim of this study was to investigate the interactions of GM with azoles against Candida spp. and the underlying mechanisms. In a chequerboard assay, GM was found not only to work synergistically with azoles against planktonic cells of drug-resistant Candida albicans with a fractional inhibitory concentration index (FICI) of 0.13-0.14, but also synergised with fluconazole (FLC) against C. albicans biofilms pre-formed in <12 h. Synergism of GM with FLC was also confirmed in vivo in a Galleria mellonella infection model. In addition, mechanism studies showed that GM not only suppressed the efflux pump of resistant C. albicans in a dose-dependent manner but also inhibited extracellular phospholipase activity of resistant C. albicans when combined with FLC. These findings suggest that GM enhances the efficacy of azoles against resistant C. albicans via efflux inhibition and decreased activity of extracellular phospholipase.

Antifungal plant defensins: increased insight in their mode of action as a basis for their use to combat fungal infections

Plant defensins are small, cationic peptides with a highly conserved 3D structure. They have been studied extensively in the past decades. Various biological activities have been attributed to plant defensins, such as anti-insect and antimicrobial activities, but they are also known to affect ion channels and display antitumor activity. This review focuses on the structure, biological activity and antifungal mode of action of some well-characterized plant defensins, with particular attention to their fungal membrane target(s), their induced cell death mechanisms as well as their antibiofilm activity. As plant defensins are, in general, not toxic to human cells, show in vivo efficacy and have low frequencies of resistance occurrence, they are of particular interest in the fight against fungal infections.

The in vitro and in vivo efficacy of fluconazole in combination with farnesol against Candida albicans isolates using a murine vulvovaginitis model

Farnesol is a quorum-sensing molecule that inhibits biofilm formation in Candida albicans. Previous in vitro data suggest that, in combination with certain antifungals, farnesol may have an adjuvant anti-biofilm agent. However, the in vivo efficacy of farnesol is very questionable. Therefore, the in vitro and in vivo activity of fluconazole combined with farnesol was evaluated against C. albicans biofilms using fractional inhibitory concentration index (FICI) determination, time-kill experiments and a murine vulvovaginitis model. The median biofilm MICs of fluconazole-sensitive C. albicans isolates ranged between 4 -> 512 mg/L and 150-300 μM for fluconazole and farnesol, respectively. These values were 512 -> 512 mg/L and > 300 μM for fluconazole-resistant clinical isolates. Farnesol decreased the median MICs of fluconazole by 2-64-fold for biofilms. Based on FICI, synergistic interaction was observed only in the case of the sessile SC5314 reference strain (FICIs: 0.16-0.27). In time-kill studies, only the 512 mg/L fluconazole and 512 mg/L fluconazole + 75 μM farnesol reduced biofilm mass significantly at each time point in the case of all isolates. The combination reduced the metabolic activity of biofilms for all isolates in a concentration- and time-dependent manner. Our findings revealed that farnesol alone was not protective in a murine vulvovaginitis model. Farnesol was not beneficial in combination with fluconazole for fluconazole-susceptible isolates, but partially increased fluconazole activity against one fluconazole-resistant isolate, but not the other one.

Identification of survival-promoting OSIP108 peptide variants and their internalization in human cells

The plant-derived decapeptide OSIP108 increases tolerance of yeast and human cells to apoptosis-inducing agents, such as copper and cisplatin. We performed a whole amino acid scan of OSIP108 and conducted structure-activity relationship studies on the induction of cisplatin tolerance (CT) in yeast. The use of cisplatin as apoptosis-inducing trigger in this study should be considered as a tool to better understand the survival-promoting nature of OSIP108 and not for purposes related to anti-cancer treatment. We found that charged residues (Arg, His, Lys, Glu or Asp) or a Pro on positions 4-7 improved OSIP108 activity by 10% or more. The variant OSIP108[G7P] induced the most pronounced tolerance to toxic concentrations of copper and cisplatin in yeast and/or HepG2 cells. Both OSIP108 and OSIP108[G7P] were shown to internalize equally into HeLa cells, but at a higher rate than the inactive OSIP108[E10A], suggesting that the peptides can internalize into cells and that OSIP108 activity is dependent on subsequent intracellular interactions. In conclusion, our studies demonstrated that tolerance/survival-promoting properties of OSIP108 can be significantly improved by single amino acid substitutions, and that these properties are dependent on (an) intracellular target(s), yet to be determined.