Fungicidal drugs induce a common oxidative-damage cellular death pathway

Machine learning-assisted SERS approach enables the biochemical discrimination in Bcl-2 and Mcl-1 expressing yeast cells treated with ketoconazole and fluconazole antifungals

Antifungal medications are important due to their potential application in cancer treatment either on their own or with traditional treatments. The mechanisms that prevent the effects of these medications and restrict their usage in cancer treatment are not completely understood. The evaluation and discrimination of the possible protective effects of the anti-apoptotic members of the Bcl-2 family of proteins, critical regulators of mitochondrial apoptosis, against antifungal drug-induced cell death has still scientific uncertainties that must be considered. Novel, simple, and reliable strategies are highly demanded to identify the biochemical signature of this phenomenon. However, the complex nature of cells poses challenges for the analysis of cellular biochemical changes or classification. In this study, for the first time, we investigated the probable protective activities of Bcl-2 and Mcl-1 proteins against cell damage induced by ketoconazole (KET) and fluconazole (FLU) antifungal drugs in a yeast model through surface-enhanced Raman spectroscopy (SERS) approach. The proposed SERS platform created robust Raman spectra with a high signal-to-noise ratio. The analysis of SERS spectral data via advanced unsupervised and supervised machine learning methods enabled unquestionable differentiation (100 %) in samples and biomolecular identification. Various SERS bands related to lipids and proteins observed in the analyses suggest that the expression of these anti-apoptotic proteins reduces oxidative biomolecule damage induced by the antifungals. Also, cell viability assay, Annexin V-FITC/PI double staining, and total oxidant and antioxidant status analyses were performed to support Raman measurements. We strongly believe that the proposed approach paves the way for the evaluation of various biochemical structures/changes in various cells.

Azoles activate type I and type II programmed cell death pathways in crop pathogenic fungi

Triazoles are widely used to control pathogenic fungi. They inhibit the ergosterol biosynthetic pathway, but the precise mechanisms leading to fungicidal activities in many fungal pathogens are poorly understood. Here, we elucidate the mode of action of epoxiconazole and metconazole in the wheat pathogen Zymoseptoria tritici and the rice blast fungus Magnaporthe oryzae. We show that both azoles have fungicidal activity and reduce fluidity, but not integrity, of the plasma membrane. This impairs localisation of Cdc15-like F-BAR proteins, resulting in defective actin ring assembly and incomplete septation. However, mutant studies and pharmacological experiments in vitro and in planta show that azole lethality is due to a combination of reactive oxygen species-induced apoptosis and macroautophagy. Simultaneous inhibition of both programmed cell death pathways abolishes azole-induced cell death. Other classes of ergosterol biosynthesis inhibitors also induce apoptosis and macroautophagy, suggesting that activation of these two cell death pathways is a hallmark of ergosterol synthesis-targeting fungicides. This knowledge will inform future crop protection strategies.

Pitavastatin Calcium Confers Fungicidal Properties to Fluconazole by Inhibiting Ubiquinone Biosynthesis and Generating Reactive Oxygen Species

Fluconazole (FLC) is extensively employed for the prophylaxis and treatment of invasive fungal infections (IFIs). However, the fungistatic nature of FLC renders pathogenic fungi capable of developing tolerance towards it. Consequently, converting FLC into a fungicidal agent using adjuvants assumes significance to circumvent FLC resistance and the perpetuation of fungal infections. This drug repurposing study has successfully identified pitavastatin calcium (PIT) as a promising adjuvant for enhancing the fungicidal activity of FLC from a comprehensive library of 2372 FDA-approved drugs. PIT could render FLC fungicidal even at concentrations as low as 1 μM. The median lethal dose (LD50) of PIT was determined to be 103.6 mg/kg. We have discovered that PIT achieves its synergistic effect by inhibiting the activity of 3-hydroxy-3-methylglutaryl-coenzyme A (HMG-CoA) reductase, thereby impeding ubiquinone biosynthesis, inducing reactive oxygen species (ROS) generation, triggering apoptosis, and disrupting Golgi function. We employed a Candida albicans strain that demonstrated a notable tolerance to FLC to infect mice and found that PIT effectively augmented the antifungal efficacy of FLC against IFIs. This study is an illustrative example of how FDA-approved drugs can effectively eliminate fungal tolerance to FLC.

Natural Substances as Valuable Alternative for Improving Conventional Antifungal Chemotherapy: Lights and Shadows

Fungi are eukaryotic organisms with relatively few pathogenic members dangerous for humans, usually acting as opportunistic infections. In the last decades, several life-threatening fungal infections have risen mostly associated with the worldwide extension of chronic diseases and immunosuppression. The available antifungal therapies cannot combat this challenge because the arsenal of compounds is scarce and displays low selective action, significant adverse effects, and increasing resistance. A growing isolation of outbreaks triggered by fungal species formerly considered innocuous is being recorded. From ancient times, natural substances harvested from plants have been applied to folk medicine and some of them recently emerged as promising antifungals. The most used are briefly revised herein. Combinations of chemotherapeutic drugs with natural products to obtain more efficient and gentle treatments are also revised. Nevertheless, considerable research work is still necessary before their clinical use can be generally accepted. Many natural products have a highly complex chemical composition, with the active principles still partially unknown. Here, we survey the field underlying lights and shadows of both groups. More studies involving clinical strains are necessary, but we illustrate this matter by discussing the potential clinical applications of combined carnosic acid plus propolis formulations.

In Vitro and In Vivo Anti-Candida albicans Activity of a Scorpion-Derived Peptide

The increasing infection and drug resistance frequency has encouraged the exploration of new and effective anti-Candida albicans agents. In this study, CT-K3K7, a scorpion antimicrobial peptide derivative, effectively inhibit the growth of C. albicans. CT-K3K7 killed C. albicans cells in a dose-dependent manner, mainly by damaging the plasma membrane. CT-K3K7 could also disrupt the nucleus and interact with nucleic acid. Moreover, CT-K3K7 induced C. albicans cells necrosis via a reactive oxygen species (ROS)-related pathway. Furthermore, CT-K3K7 inhibited the hyphal and biofilm formation of C. albicans. In the mouse skin subcutaneous infection model, CT-K3K7 significantly prevented skin abscess formation and reduced the number of C. albicans cells recovered from the infection area. Taken together, CT-K3K7 has the potential to be a therapeutic for C. albicans skin infections.

Fungicide-tolerant persister formation during cryptococcal pulmonary infection

Bacterial persisters, a subpopulation of genetically susceptible cells that are normally dormant and tolerant to bactericides, have been studied extensively because of their clinical importance. In comparison, much less is known about the determinants underlying fungicide-tolerant fungal persister formation in vivo. Here, we report that during mouse lung infection, Cryptococcus neoformans forms persisters that are highly tolerant to amphotericin B (AmB), the standard of care for treating cryptococcosis. By exploring stationary-phase indicator molecules and developing single-cell tracking strategies, we show that in the lung, AmB persisters are enriched in cryptococcal cells that abundantly produce stationary-phase molecules. The antioxidant ergothioneine plays a specific and key role in AmB persistence, which is conserved in phylogenetically distant fungi. Furthermore, the antidepressant sertraline (SRT) shows potent activity specifically against cryptococcal AmB persisters. Our results provide evidence for and the determinant of AmB-tolerant persister formation in pulmonary cryptococcosis, which has potential clinical significance.

Halofantrine Hydrochloride Acts as an Antioxidant Ability Inhibitor That Enhances Oxidative Stress Damage to Candida albicans

Candida albicans, a prominent opportunistic pathogenic fungus in the human population, possesses the capacity to induce life-threatening invasive candidiasis in individuals with compromised immune systems despite the existence of antifungal medications. When faced with macrophages or neutrophils, C. albicans demonstrates its capability to endure oxidative stress through the utilization of antioxidant enzymes. Therefore, the enhancement of oxidative stress in innate immune cells against C. albicans presents a promising therapeutic approach for the treatment of invasive candidiasis. In this study, we conducted a comprehensive analysis of a library of drugs approved by the Food and Drug Administration (FDA). We discovered that halofantrine hydrochloride (HAL) can augment the antifungal properties of oxidative damage agents (plumbagin, menadione, and H2O2) by suppressing the response of C. albicans to reactive oxygen species (ROS). Furthermore, our investigation revealed that the inhibitory mechanism of HAL on the oxidative response is dependent on Cap1. In addition, the antifungal activity of HAL has been observed in the Galleria mellonella infection model. These findings provide evidence that targeting the oxidative stress response of C. albicans and augmenting the fungicidal capacity of oxidative damage agents hold promise as effective antifungal strategies.

Antifungal efficacy of scorpion derived peptide K1K8 against Candida albicans in vitro and in vivo

As an alternative class of antimicrobial agents, antimicrobial peptides (AMPs) have gained significant attention. In this study, K1K8, a scorpion AMP derivative, showed effective activity against Candida albicans including clinically resistant strains. K1K8 killed C. albicans cells mainly by damaging the cell membrane and inducing necrosis via an ROS-related pathway. K1K8 could also interact with DNA after damaging the nuclear envelope. Moreover, K1K8 inhibited hyphal development and biofilm formation of C. albicans in a dose-dependent manner. In the mouse skin infection model, K1K8 significantly decreased the counts of C. albicans cells in the infection area. Overall, K1K8 is a potential anti-infective agent against skin infections caused by C. albicans.

Regulation of copper uptake by the SWI/SNF chromatin remodeling complex in Candida albicans affects susceptibility to antifungal and oxidative stresses under hypoxia

Candida albicans is a human colonizer and also an opportunistic yeast occupying different niches that are mostly hypoxic. While hypoxia is the prevalent condition within the host, the machinery that integrates oxygen status to tune the fitness of fungal pathogens remains poorly characterized. Here, we uncovered that Snf5, a subunit of the chromatin remodeling complex SWI/SNF, is required to tolerate antifungal stress particularly under hypoxia. RNA-seq profiling of snf5 mutant exposed to amphotericin B and fluconazole under hypoxic conditions uncovered a signature that is reminiscent of copper (Cu) starvation. We found that under hypoxic and Cu-starved environments, Snf5 is critical for preserving Cu homeostasis and the transcriptional modulation of the Cu regulon. Furthermore, snf5 exhibits elevated levels of reactive oxygen species and an increased sensitivity to oxidative stress principally under hypoxia. Supplementing growth medium with Cu or increasing gene dosage of the Cu transporter CTR1 alleviated snf5 growth defect and attenuated reactive oxygen species levels in response to antifungal challenge. Genetic interaction analysis suggests that Snf5 and the bona fide Cu homeostasis regulator Mac1 function in separate pathways. Together, our data underlined a unique role of SWI/SNF complex as a potent regulator of Cu metabolism and antifungal stress under hypoxia.

Toxic risk evaluation of effluents from a swine biodigester in the plant models Lactuca sativa and Allium cepa

Pig farming is recognized as an activity with great polluting potential. The aim was to investigate possible environmental risks of effluents from the stabilization pond (SP) and the raw effluent (RE) from the biodigestion process of swine residues, in different concentrations in the models Lactuca sativa and Allium cepa. Seeds were germinated in different dilutions, 100% (C1), 50% (C2), 25% (C3), 12.5% (C4), 6.25% (C5), 3.12% (C6), 0.78% (C7), and 0.39% (C8). Distilled water was used as the negative control (CN) and trifluralin (0.84 g/L-1) as the positive control. Germination (GR), root growth (RG), cell cycle, and oxidative stress (OS) were analyzed. To assess OS, the activity of the enzymes superoxide dismutase (SOD), catalase (CAT), and glutathione S-transferase (GST) and the quantification of glutathione (GSH) and lipid peroxidation (LPO) were analyzed. Data were submitted to ANOVA (one way), followed by the Kruskal-Wallis mean test (P ≤ 0.05). Chemical analysis showed high values of Cu, Fe, Mn, and Zn. Dilutions (C1, C2, C3 RE) and (C1 and C2 SP) inhibited GR and RG of L. sativa and A. cepa than other concentrations. The mitotic index showed a reduction in C5 (RE), C6, and C7 (SP) of L. sativa and C3 and C4 (SP) of A. cepa in relation to CN and higher frequencies of chromosomal alterations. Regarding the OS, only the concentrations of SP treatment showed statistical difference in relation to the NC: in L. sativa model, GSH at (C5 and C8) concentrations and LPO (C7); in A. cepa model, SOD (C3 and C4), GST (C4, C5 and C6), GSH (C5 and C8), and CAT (C3 and C7). The alterations in metabolism are possibly related to the metals, such as zinc and copper, observed in high amounts in the raw waste. The results allowed us to conclude that the raw and stabilization pond effluents offer environmental risks, requiring caution and monitoring in the use of these effluents.

Unexpected Inhibitory Effect of Octenidine Dihydrochloride on Candida albicans Filamentation by Impairing Ergosterol Biosynthesis and Disrupting Cell Membrane Integrity

Candida albicans filamentation plays a significant role in developing both mucosal and invasive candidiasis, making it a crucial virulence factor. Consequently, exploring and identifying inhibitors that impede fungal hyphal formation presents an intriguing approach toward antifungal strategies. In line with this anti-filamentation strategy, we conducted a comprehensive screening of a library of FDA-approved drugs to identify compounds that possess inhibitory properties against hyphal growth. The compound octenidine dihydrochloride (OCT) exhibits potent inhibition of hyphal growth in C. albicans across different hyphae-inducing media at concentrations below or equal to 3.125 μM. This remarkable inhibitory effect extends to biofilm formation and the disruption of mature biofilm. The mechanism underlying OCT's inhibition of hyphal growth is likely attributed to its capacity to impede ergosterol biosynthesis and induce the generation of reactive oxygen species (ROS), compromising the integrity of the cell membrane. Furthermore, it has been observed that OCT demonstrates protective attributes against invasive candidiasis in Galleria mellonella larvae through its proficient eradication of C. albicans colonization in infected G. mellonella larvae by impeding hyphal formation. Although additional investigation is required to mitigate the toxicity of OCT in mammals, it possesses considerable promise as a potent filamentation inhibitor against invasive candidiasis.

Inorganic Nanoparticles: Tools to Emphasize the Janus Face of Amphotericin B

Amphotericin B is the oldest antifungal molecule which is still currently widely used in clinical practice, in particular for the treatment of invasive diseases, even though it is not devoid of side effects (particularly nephrotoxicity). Recently, its redox properties (i.e., both prooxidant and antioxidant) have been highlighted in the literature as mechanisms involved in both its activity and its toxicity. Interestingly, similar properties can be described for inorganic nanoparticles. In the first part of the present review, the redox properties of Amphotericin B and inorganic nanoparticles are discussed. Then, in the second part, inorganic nanoparticles as carriers of the drug are described. A special emphasis is given to their combined redox properties acting either as a prooxidant or as an antioxidant and their connection to the activity against pathogens (i.e., fungi, parasites, and yeasts) and to their toxicity. In a majority of the published studies, inorganic nanoparticles carrying Amphotericin B are described as having a synergistic activity directly related to the rupture of the redox homeostasis of the pathogen. Due to the unique properties of inorganic nanoparticles (e.g., magnetism, intrinsic anti-infectious properties, stimuli-triggered responses, etc.), these nanomaterials may represent a new generation of medicine that can synergistically enhance the antimicrobial properties of Amphotericin B.

Reactive oxidant species induced by antifungal drugs: identity, origins, functions, and connection to stress-induced cell death

Reactive oxidant species (ROS) are unstable, highly reactive molecules that are produced by cells either as byproducts of metabolism or synthesized by specialized enzymes. ROS can be detrimental, e.g., by damaging cellular macromolecules, or beneficial, e.g., by participating in signaling. An increasing body of evidence shows that various fungal species, including both yeasts and molds, increase ROS production upon exposure to the antifungal drugs currently used in the clinic: azoles, polyenes, and echinocandins. However, the implications of these findings are still largely unclear due to gaps in knowledge regarding the chemical nature, molecular origins, and functional consequences of these ROS. Because the detection of ROS in fungal cells has largely relied on fluorescent probes that lack specificity, the chemical nature of the ROS is not known, and it may vary depending on the specific fungus-drug combination. In several instances, the origin of antifungal drug-induced ROS has been identified as the mitochondria, but further experiments are necessary to strengthen this conclusion and to investigate other potential cellular ROS sources, such as the ER, peroxisomes, and ROS-producing enzymes. With respect to the function of the ROS, several studies have shown that they contribute to the drugs' fungicidal activities and may be part of drug-induced programmed cell death (PCD). However, whether these "pro-death" ROS are a primary consequence of the antifungal mechanism of action or a secondary consequence of drug-induced PCD remains unclear. Finally, several recent studies have raised the possibility that ROS induction can serve an adaptive role, promoting antifungal drug tolerance and the evolution of drug resistance. Filling these gaps in knowledge will reveal a new aspect of fungal biology and may identify new ways to potentiate antifungal drug activity or prevent the evolution of antifungal drug resistance.

Mitochondrial Membrane-Associated Protein Mba1 Confers Antifungal Resistance by Affecting the Production of Reactive Oxygen Species in Aspergillus fumigatus

Azole resistance in the human fungal pathogen Aspergillus fumigatus is becoming a major threat to global health. To date, mutations in the azole target-encoding cyp51A gene have been implicated in conferring azole resistance, but a steady increase in the number of A. fumigatus isolates with azole resistance resulting from non-cyp51A mutations has been recognized. Previous studies have revealed that some isolates with non-cyp51A mutation-induced azole resistance are related to mitochondrial dysfunction. However, knowledge of the molecular mechanism underlying the involvement of non-cyp51A mutations is limited. In this study, using next-generation sequencing, we found that nine independent azole-resistant isolates without cyp51A mutations had normal mitochondrial membrane potential. Among these isolates, a mutation in a mitochondrial ribosome-binding protein, Mba1, conferred multidrug resistance to azoles, terbinafine, and amphotericin B but not caspofungin. Molecular characterization verified that the TIM44 domain of Mba1 was crucial for drug resistance and that the N terminus of Mba1 played a major role in growth. Deletion of mba1 had no effect on Cyp51A expression but decreased the fungal cellular reactive oxygen species (ROS) content, which contributed to mba1-mediated drug resistance. The findings in this study suggest that some non-cyp51A proteins drive drug resistance mechanisms that result from reduced ROS production induced by antifungals.

Nail Society of India (NSI) Recommendations for Pharmacologic Therapy of Onychomycosis

Onychomycosis (OM) is the commonest cause of dystrophic nails, responsible for upto 50% of cases. Apart from significantly damaging the nails, quality of life, and self-image of the sufferer, it also acts as a reservoir of fungal infections carrying important implications for emerging recalcitrant dermatophytoses. Treatment of OM is based on guidelines released almost a decade back, in addition to published literature and personal preferences. Hence, an expert group of nail society of India (NSI) worked towards drafting these guidelines aimed at compiling recommendations for pharmacologic treatment of OM, based on scientific evidence, along with practical experience. The group did an extensive analysis of available English language literature on OM published during the period 2014-2022. The evidence compiled was graded and discussed to derive consensus recommendations for practice. Special focus was placed on combination therapies and adjunct therapies, including experience of members, to improve treatment outcomes.

The antifungal effect induced by itraconazole in Candida parapsilosis largely depends on the oxidative stress generated at the mitochondria

In Candida parapsilosis, homozygous disruption of the two genes encoding trehalase activity increased the susceptibility to Itraconazole compared with the isogenic parental strain. The fungicidal effect of this azole can largely be counteracted by preincubating growing cells with rotenone and the protonophore 2,4-Dinitrophenol. In turn, measurement of endogenous reactive oxygen species formation by flow cytometry confirmed that Itraconazole clearly induced an internal oxidative stress, which can be significantly abolished in rotenone-exposed cells. Analysis of the antioxidant enzymatic activities of catalase and superoxide dismutase pointed to a moderate decrease of catalase in trehalase-deficient mutant cells compared to the wild type, with an additional increase upon addition of rotenone. These enzymatic changes were imperceptible in the case of superoxide dismutase. Alternative assays with Voriconazole led to a similar profile in the results regarding cell growth and antioxidant activities. Collectively, our data suggest that the antifungal action of Itraconazole on C. parapsilosis is dependent on a functional mitochondrial activity. They also suggest that the central metabolic pathways in pathogenic fungi should be considered as preferential antifungal targets in new research.

Insight into the Antifungal Effects of Propolis and Carnosic Acid—Extension to the Pathogenic Yeast Candida glabrata: New Propolis Fractionation and Potential Synergistic Applications

Fungi have traditionally been considered opportunistic pathogens in primary infections caused by virulent bacteria, protozoan, or viruses. Consequently, antimycotic chemotherapy is clearly less developed in comparison to its bacterial counterpart. Currently, the three main families of antifungals (polyenes, echinocandins, and azoles) are not sufficient to control the enormous increase in life-threatening fungal infections recorded in recent decades. Natural substances harvested from plants have traditionally been utilized as a successful alternative. After a wide screening of natural agents, we have recently obtained promising results with distinct formulations of carnosic acid and propolis on the prevalent fungal pathogens Candida albicans and Cryptococcus neoformans. Here, we extended their use to the treatment against the emerging pathogenic yeast Candida glabrata, which displayed lower susceptibility in comparison to the fungi mentioned above. Taking into account the moderate antifungal activity of both natural agents, the antifungal value of these combinations has been improved through the obtention of the hydroethanolic fractions of propolis. In addition, we have demonstrated the potential clinical application of new therapeutical designs based on sequential pre-treatments with carnosic/propolis mixtures, followed by exposure to amphotericin B. This approach increased the toxic effect induced by this polyene.

Functional Characterization of a Bacillus-Derived Novel Broad-Spectrum Antifungal Lipopeptide Variant against Candida tropicalis and Candida auris and Unravelling Its Mode of Action

Limited treatment options, recalcitrance, and resistance to existing therapeutics encourage the discovery of novel antifungal leads for alternative therapeutics. Antifungal lipopeptides have emerged as potential candidates for developing new and alternative antifungal therapies. In our previous studies, we isolated and identified the lipopeptide variant AF4 and purified it to homogeneity via chromatography from the cell-free supernatant of Bacillus subtilis. AF4 was found to have broad-spectrum antifungal activity against more than 110 fungal isolates. In this study, we found that clinical isolates of Candida tropicalis and Candida auris exposed to AF4 exhibited low MICs of 4 to 8 mg/L. Time-kill assays indicated the in vitro pharmacodynamic potential of AF4. Biocompatibility assays demonstrated ~75% cell viability at 8 mg/L of AF4, indicating the lipopeptide's minimally cytotoxic nature. In lipopeptide-treated C. tropicalis and C. auris cells, scanning electron microscopy revealed damage to the cell surface, while confocal microscopy with acridine orange(AO)/propidium iodide (PI) and FUN-1 indicated permeabilization of the cell membrane, and DNA damage upon DAPI (4',6-diamidino-2-phenylindole) staining. These observations were corroborated using flow cytometry (FC) in which propidium iodide, 2',7'-dichlorodihydrofluorescein diacetate (DCFH-DA), and rhodamine 123 (Rh123) staining of cells treated with AF4 revealed loss of membrane integrity, increased reactive oxygen species (ROS) production, and mitochondrial membrane dysfunction, respectively. Membrane perturbation was also observed in the 1,6-diphenyl-1,3,5-hexatriene (DPH) fluorescence study and the interaction with ergosterol was observed by an ergosterol binding assay. Decreased membrane dipole potential also indicated the probable binding of lipopeptide to the cell membrane. Collectively, these findings describe the mode of action of AF4 against fungal isolates by membrane disruption and ROS generation, demonstrating its antifungal potency. IMPORTANCE C. tropicalis is a major concern for candidiasis in India and C. auris has emerged as a resistant yeast causing difficult-to-treat infections. Currently, amphotericin B (AMB) and 5-flucytosine (5-FC) are the main therapeutics for systemic fungal infections; however, the nephrotoxicity of AMB and resistance to 5-FC is a serious concern. Antifungal lead molecules with low adverse effects are the need of the hour. In this study, we briefly describe the antifungal potential of the AF4 lipopeptide and its mode of action using microscopy, flow cytometry, and fluorescence-based assays. Our investigation reveals the basic mode of action of the investigated lipopeptide. This lipopeptide with broad-spectrum antifungal potency is apparently membrane-active, and there is a smaller chance that organisms exposed to such a compound will develop drug resistance. It could potentially act as a lead molecule for the development of an alternative antifungal agent to combat candidiasis.

Pol32, an accessory subunit of DNA polymerase delta, plays an essential role in genome stability and pathogenesis of Candida albicans

Candida albicans is a pathobiont that inflicts serious bloodstream fungal infections in individuals with compromised immunity and gut dysbiosis. Genomic diversity in the form of copy number alteration, ploidy variation, and loss of heterozygosity as an adaptive mechanism to adverse environments is frequently observed in C. albicans. Such genomic variations also confer a varied degree of fungal virulence and drug resistance, yet the factors propelling these are not completely understood. DNA polymerase delta (Polδ) is an essential replicative DNA polymerase in the eukaryotic cell and is yet to be characterized in C. albicans. Therefore, this study was designed to gain insights into the role of Polδ, especially its non-essential subunit Pol32, in the genome plasticity and life cycle of C. albicans. PCNA, the DNA clamp, recruits Polδ to the replication fork for processive DNA replication. Unlike in Saccharomyces cerevisiae, the PCNA interaction protein (PIP) motif of CaPol32 is critical for Polδ's activity during DNA replication. Our comparative genetic analyses and whole-genome sequencing of POL32 proficient and deficient C. albicans cells revealed a critical role of Pol32 in DNA replication, cell cycle progression, and genome stability as SNPs, indels, and repeat variations were largely accumulated in pol32 null strain. The loss of pol32 in C. albicans conferred cell wall deformity; Hsp90 mediated azoles resistance, biofilm development, and a complete attenuation of virulence in an animal model of systemic candidiasis. Thus, although Pol32 is dispensable for cell survival, its function is essential for C. albicans pathogenesis; and we discuss its translational implications in antifungal drugs and whole-cell vaccine development.

Revealing the Mechanisms for Linalool Antifungal Activity against Fusarium oxysporum and Its Efficient Control of Fusarium Wilt in Tomato Plants

Fusarium oxysporum f. sp. radicis-lycopersici (Forl) is a destructive soil-borne phytopathogenic fungus that causes Fusarium crown and root rot (FCRR) of tomato, leading to considerable field yield losses. In this study, we explored the antifungal capability of linalool, a natural plant volatile organic component, against Forl and its role in controlling FCRR symptoms in tomatoes. Our results showed that Forl mycelial growth was inhibited by the linalool treatment and that the linalool treatment damaged cell membrane integrity, enhanced reactive oxygen species levels, depleted glutathione, and reduced the activities of many antioxidant enzymes in Forl. Transcriptomic and proteomic analyses demonstrated that linalool also downregulated metabolic biosynthetic pathways at the transcript and protein levels, including redox, transporter activity, and carbohydrate metabolism in Forl. Moreover, linalool significantly decreased the expression of many Forl pathogenic genes, such as cell wall degrading enzymes (CWDEs) and G proteins, which is likely how a Forl infection was prevented. Importantly, exogenously applied linalool activated the salicylic acid (SA) and jasmonic acid (JA) defensive pathways to improve disease resistance and relieved the negative effects of Forl on plant growth. Taken together, we report that linalool is an effective fungicide against Forl and will be a promising green chemical agent for controlling FCRR.

Updated Perspectives on the Diagnosis and Management of Onychomycosis

Onychomycosis is the most common nail disease encountered in clinical practice and can cause pain, difficulty with ambulation, and psycho-social problems. A thorough history and physical examination, including dermoscopy, should be performed for each patient presenting with nail findings suggestive of onychomycosis. Several approaches are available for definitive diagnostic testing, including potassium hydroxide and microscopy, fungal culture, histopathology, polymerase chain reaction, or a combination of techniques. Confirmatory testing should be performed for each patient prior to initiating any antifungal therapies. There are several different therapeutic options available, including oral and topical medications as well as device-based treatments. Oral antifungals are generally recommended for moderate to severe onychomycosis and have higher cure rates, while topical antifungals are recommended for mild to moderate disease and have more favorable safety profiles. Oral terbinafine, itraconazole, and griseofulvin and topical ciclopirox 8% nail lacquer, efinaconazole 10% solution, and tavaborole 5% solution are approved by the Food and Drug Administration for treatment of onychomycosis in the United States and amorolfine 5% nail lacquer is approved in Europe. Laser treatment is approved in the United States for temporary increases in clear nail, but clinical results are suboptimal. Oral fluconazole is not approved in the United States for onychomycosis treatment, but is frequently used off-label with good efficacy. Several novel oral, topical, and over-the-counter therapies are currently under investigation. Physicians should consider the disease severity, infecting pathogen, medication safety, efficacy and cost, and patient age, comorbidities, medication history, and likelihood of compliance when determining management plans. Onychomycosis is a chronic disease with high recurrence rates and patients should be counseled on an appropriate plan to minimize recurrence risk following effective antifungal therapy.

iTRAQ-based proteomics revealed baicalein enhanced oxidative stress of Candida albicans by up-regulating CPD2 expression

Baicalein could inhibit the growth and biofilm formation of Candida albicans, the most common clinical fungal pathogen. However, the antifungal mechanism of baicalein has not been elucidated. In this study, isobaric tags for relative and absolute quantification (iTRAQ) was used to verify the mechanism of antifungal fluconazole and baicalein. A total of 58 common proteins were detected in cells treated with fluconazole. These proteins encompassed fluconazole-targeted sterol synthesis pathway, including Erg11p, Erg6p, Erg3p, Erg25p, Erg5p, Erg10p and Ncp1p. Next, iTRAQ was applied to the comparison of baicalein-treated C. albicans proteins, which detected 16 common proteins. The putative NADH dehydrogenase Cpd2p and the ATP-binding cassette transporter Snq2p were the most up-regulated proteins with the treatment of baicalein. Our results showed that CPD2 disruption elevated C. albicans resistance to baicalein significantly both in vitro and in vivo. Further in-depth studies revealed that CPD2 disruption reduced the activation of C. albicans metacaspase and partially restored the mitochondrial membrane potential reduction caused by the treatment of baicalein, which indicated that CPD2 was involved in the apoptosis induced by baicalein. Consistently, under the treatment of baicalein, CPD2Δ/Δ mutant produced lower reactive oxygen species (ROS) that was critical in causing oxidative damage and apoptosis in C. albicans. These results indicated that baicalein could increase intracellular oxidative damage by up-regulating the expression of Cpd2p so as to inhibit the growth of C. albicans, which provides new insights for investigating the antifungal target of baicalein.

The Anti-Fungal Activity of Nitropropenyl Benzodioxole (NPBD), a Redox-Thiol Oxidant and Tyrosine Phosphatase Inhibitor

Phylogenetically diverse fungal species are an increasing cause of severe disease and mortality. Identification of new targets and development of new fungicidal drugs are required to augment the effectiveness of current chemotherapy and counter increasing resistance in pathogens. Nitroalkenyl benzene derivatives are thiol oxidants and inhibitors of cysteine-based molecules, which show broad biological activity against microorganisms. Nitropropenyl benzodioxole (NPBD), one of the most active antimicrobial derivatives, shows high activity in MIC assays for phylogenetically diverse saprophytic, commensal and parasitic fungi. NPBD was fungicidal to all species except the dermatophytic fungi, with an activity profile comparable to that of Amphotericin B and Miconazole. NPBD showed differing patterns of dynamic kill rates under different growth conditions for Candida albicans and Aspergillus fumigatus and was rapidly fungicidal for non-replicating vegetative forms and microconidia. It did not induce resistant or drug tolerant strains in major pathogens on long term exposure. A literature review highlights the complexity and interactivity of fungal tyrosine phosphate and redox signaling pathways, their differing metabolic effects in fungal species and identifies some targets for inhibition. A comparison of the metabolic activities of Amphotericin B, Miconazole and NPBD highlights the multiple cellular functions of these agents and the complementarity of many mechanisms. The activity profile of NPBD illustrates the functional diversity of fungal tyrosine phosphatases and thiol-based redox active molecules and contributes to the validation of tyrosine phosphatases and redox thiol molecules as related and complementary selective targets for antimicrobial drug development. NPBD is a selective antifungal agent with low oral toxicity which would be suitable for local treatment of skin and mucosal infections.

Epigenetic Regulation of Antifungal Drug Resistance

In medical mycology, epigenetic mechanisms are emerging as key regulators of multiple aspects of fungal biology ranging from development, phenotypic and morphological plasticity to antifungal drug resistance. Emerging resistance to the limited therapeutic options for the treatment of invasive fungal infections is a growing concern. Human fungal pathogens develop drug resistance via multiple mechanisms, with recent studies highlighting the role of epigenetic changes involving the acetylation and methylation of histones, remodeling of chromatin and heterochromatin-based gene silencing, in the acquisition of antifungal resistance. A comprehensive understanding of how pathogens acquire drug resistance will aid the development of new antifungal therapies as well as increase the efficacy of current antifungals by blocking common drug-resistance mechanisms. In this article, we describe the epigenetic mechanisms that affect resistance towards widely used systemic antifungal drugs: azoles, echinocandins and polyenes. Additionally, we review the literature on the possible links between DNA mismatch repair, gene silencing and drug-resistance mechanisms.

Reactive oxygen and nitrogen species are crucial for the antifungal activity of amorolfine and ciclopirox olamine against the dermatophyte Trichophyton interdigitale

Onychomycosis is a nail infection caused by Trichophyton interdigitale and other fungi, which can be treated with topical amorolfine (AMR) and ciclopirox olamine (CPX). Although these drugs are widely used, little is known about the role of reactive oxygen (ROS) and nitrogen (RNS) in their mechanism of action. Aiming to better understand the effects of AMR and CPX in dermatophytes, we evaluated whether they act through the production of ROS and peroxynitrite (PRN). We tested a set of strains, all susceptible to AMR and CPX, and these antifungals significantly reduced T. interdigitale viability within 24 hours. This effect occurred concomitantly with reduced ergosterol, increased production of ROS and PRN, and consequently increased lipid peroxidation. Together, these mechanisms lead to cell damage and fungal death. These fungicidal effects were abolished when PRN and superoxide scavengers were used in the assays, demonstrating the role of these species in the mechanism of action. We also studied the antioxidant system when T. interdigitale was exposed to AMR and CPX. Interestingly, superoxide dismutase and catalase inhibition lead to altered ROS and PRN production, lipid peroxidation, and ergosterol levels. In fact, the combination of AMR or CPX with a superoxide dismutase inhibitor was antagonistic. Together, these data demonstrate the importance of ROS and PRN in the antifungal action of AMR and CPX against the evaluated T. interdigitale strains.

In vitro and in vivo Activity of Phibilin Against Candida albicans

The increase in the occurrence of antifungal-resistant Candida albicans infections necessitates more research to explore alternative effective and safe agents against this fungus. In this work, Phibilin, a new antimicrobial peptide obtained from Philomycus bilineatus and used in traditional Chinese medicine, effectively inhibits the growth and activities of C. albicans, including the clinical resistant strains. Phibilin is a fungicidal antimicrobial peptide that exhibited its antimicrobial effect against C. albicans mainly by disrupting the membrane and interacting with the DNA of the fungi. In particular, Phibilin induces the necrosis of C. albicans via the ROS-related pathway. Moreover, this antifungal compound inhibited the biofilm formation of C. albicans by preventing the development of hyphae in a dose-dependent manner. Furthermore, Phibilin and clotrimazole displayed a synergistic effect in inhibiting the growth of the fungi. In the mouse cutaneous infection model, Phibilin significantly inhibited the formation of skin abscesses and decreased the counts of C. albicans cells in the infected area. Overall, Phibilin is potentially an effective agent against skin infections caused by C. albicans.

Lack of Functional Trehalase Activity in Candida parapsilosis Increases Susceptibility to Itraconazole

Central metabolic pathways may play a major role in the virulence of pathogenic fungi. Here, we have investigated the susceptibility of a Candida parapsilosis mutant deficient in trehalase activity (atc1Δ/ntc1Δ strain) to the azolic compounds fluconazole and itraconazole. A time-course exposure to itraconazole but not fluconazole induced a significant degree of cell killing in mutant cells compared to the parental strain. Flow cytometry determinations indicated that itraconazole was able to induce a marked production of endogenous ROS together with a simultaneous increase in membrane potential, these effects being irrelevant after fluconazole addition. Furthermore, only itraconazole induced a significant synthesis of endogenous trehalose. The recorded impaired capacity of mutant cells to produce structured biofilms was further increased in the presence of both azoles, with itraconazole being more effective than fluconazole. Our results in the opportunistic pathogen yeast C. parapsilosis reinforce the study of trehalose metabolism as an attractive therapeutic target and allow extending the hypothesis that the generation of internal oxidative stress may be a component of the antifungal action exerted by the compounds currently available in medical practice.

Antifungal Mechanisms of a Chinese Herbal Medicine, Cao Huang Gui Xiang, Against Candida Species

Cao Huang Gui Xiang (CHGX) formula, a Chinese herbal medicine, has been empirically used for the treatment of Candida infections. In the present study, we discovered that the CHGX showed potent antifungal activities against the major human fungal pathogen Candida albicans and other clinical Candida species. Besides, we indicated that CHGX had in vivo efficacy on treating C. albicans infection in mice without noticeable toxicity at the clinical therapeutic concentration. We then set out to investigate the antifungal mechanisms of CHGX against C. albicans. We found that CHGX played an important role in inhibiting biofilm formation and filament development, two critical virulence factors of C. albicans. We further demonstrated that CHGX disrupted cell membrane integrity, triggered the accumulation of reactive oxygen species (ROS) and consumption of adenosine triphosphate (ATP), followed by a rapid fungal cell death in C. albicans. Multiple pathways, including the conserved Ras1-cAMP pathway and mitochondrial protein Mcu1 are involved in CHGX-induced cell death. Our finding expands the understanding of antifungal mechanism of CHGX against C. albicans, and provides new insights in treating patients with Candida infections in clinical practice.

A detailed insight on the molecular and cellular mechanism of action of the antifungal drugs used in the treatment of superficial fungal infections

Background:

Dermatomycosis, a type of fungal infection that can infect human skin, hair, and nails; day by day the growth of fungal infections ranging from superficial to systemic infection is alarming. Common causative agents included are Candida, Cryptococcus, Aspergillus, and Pneumocystis species.

Objective:

The effective treatment of the fungal infection includes the use of proper antifungal drug therapy. Antifungal drugs are classified into various classes. This paper focuses on understanding and interpreting the detailed molecular and cellular mechanism of action of various classes of an anti-fungal drug along with their important characteristics along with the safety and efficacy data of individual drugs of the particular class.

Methods:

The data selection for carrying out the respective study has been done by studying the combination of review articles and research papers from different databases like Research Gate, PubMed, MDPI, Elsevier, Science Direct, and Med Crave ranging from the year 1972 to 2019 by using the keywords like “anti-fungal agents”, “dermatophytes”, “cutaneous candidiasis”, “superficial fungal infections”, “oral candidiasis”, “amphotericin”, “echinocandins”, “azoles”, “polyenes” “ketoconazole”, “terbinafine”, “griseofulvin”, “azoles”.

Result:

Based on interpretation, we have concluded that the different classes of antifungal drugs follow the different mechanisms of action and target the fungal cell membrane, and are efficient in reducing fungal disease by their respective mechanism.

Conclusion:

The prevention and cure of fungal infections can be done by oral or topical antifungal drugs that aim to destroy the fungal cell membrane. These drugs show action by their respective pathways that are either preventing the formation of ergosterol or squalene or act by inhibiting β-1,3-glucan synthase enzyme. All the drugs are effective in treating fungal infections.

The effect of antifungal resistance development on the virulence of Candida species

In recent years, the relevance of diseases associated with fungal pathogens increased worldwide. Members of the Candida genus are responsible for the greatest number of fungal bloodstream infections every year. Epidemiological data consistently indicate a modest shift toward non-albicans species, albeit Candidaalbicans is still the most recognizable species within the genus. As a result, the number of clinically relevant pathogens has increased, and, despite their distinct pathogenicity features, the applicable antifungal agents remained the same. For bloodstream infections, only three classes of drugs are routinely used, namely polyenes, azoles and echinocandins. Antifungal resistance toward all three antifungal drug classes frequently occurs in clinical settings. Compared with the broad range of literature on virulence and antifungal resistance of Candida species separately, only a small portion of studies examined the effect of resistance on virulence. These studies found that resistance to polyenes and echinocandins concluded in significant decrease in the virulence in different Candida species. Meanwhile, in some cases, resistance to azole type antifungals resulted in increased virulence depending on the species and isolates. These findings underline the importance of studies aiming to dissect the connections of virulence and resistance in Candida species.

Coordinated Regulation of Membrane Homeostasis and Drug Accumulation by Novel Kinase STK-17 in Response to Antifungal Azole Treatment

The emergence of antifungal resistance, especially to the most widely used azole class of ergosterol biosynthesis inhibitors, makes fungal infections difficult to treat in clinics and agriculture. When exposed to azoles, fungi can make adaptive responses to alleviate azole toxicity and produce azole tolerance. However, except for azole efflux pumps and ergosterol biosynthesis genes, the role of most azole responsive genes in azole resistance is unknown. In this study, STK-17, whose transcription is upregulated by azoles, was characterized as a novel kinase that is required for azole resistance. Deletion or dysfunction of STK-17 led to azole hypersensitivity in Neurospora crassa and to other ergosterol biosynthesis inhibitors such as amorolfine, terbinafine, and amphotericin B, but not fatty acid and ceramide biosynthesis inhibitors. STK-17 was also required for oxidative stress resistance, but this was not connected to azole resistance. RNA-seq results showed that stk-17 deletion affected the basal expression and the response to ketoconazole of some membrane protein genes, indicating functional association of STK-17 with the membrane. Notably, deletion of stk-17 affected the normal response to azoles of erg genes, including the azole target-encoding gene erg11, and erg2, erg6, and erg24, and led to abnormal accumulation of sterols in the presence of azoles. HPLC-MS/MS analysis revealed increased intracellular azole accumulation in the stk-17 mutant, possibly due to enhanced azole influx and reduced azole efflux that was independent of the major efflux pump CDR4. Importantly, STK-17 was widely distributed and functionally conserved among fungi, thus providing a potential antifungal target.

IMPORTANCE Antifungal resistance is increasing worldwide, especially to the most widely used azole class of ergosterol biosynthesis inhibitors, making control of fungal infections more challenging. A lot of effort has been expended in elucidating the mechanism of azole resistance and revealing potential antifungal targets. In this study, by analyzing azole-responsive genes in Neurospora crassa, we discovered STK-17, a novel kinase, that is required for azole resistance in several types of fungi. It has a role in regulating membrane homeostasis, responses to azole by ergosterol biosynthesis genes and azole accumulation, thus, deepening our understanding on the mechanism of azole stress response. Additionally, STK-17 is conserved among fungi and plays important roles in fungal development and stress resistance. Kinase inhibitors are broadly used for treating diseases, and our study pinpoints a potential drug target for antifungal development.

D319 induced antifungal effects through ROS-mediated apoptosis and inhibited isocitrate lyase in Candida albicans

BACKGROUND

Candida albicans (C. albicans) is an opportunistic pathogen that can cause superficial and life-threatening systemic infections in immunocompromised patients. However, the available clinically antifungals are limited. Therefore, the development of effective antifungal agents and therapies is urgently needed. Quinoline type of compounds were reported to possess potent anti-fungal effect. A series of quinoline derivatives were synthesized. Moreover their inhibitory activities and mechanisms on C. albicans were evaluated in this study.

METHODS

The structure of D319 was identified by extensive spectroscopic analysis. The antifungal activity of D319 on C. albicans was evaluated using conventional methods, including the inhibition zone diameters with filter paper, Clinical Laboratory Standard Institute (CLSI) broth microdilution method in vitro, and in a murine model in vivo. Flow cytometry, fluorescence microscopy, western blot, knockout mutant and revertant strain techniques, and molecular modeling were applied to explore the mechanism of action of D319 in anti-Candida.

RESULTS

D319 exhibited potent anti-Candida activity with Minimum Inhibitory Concentration value of 2.5 μg/mL in vitro. D319 significantly improved survival rate and reduced fungal burden compared to vehicle control in a murine model in vivo. The treatment of C. albicans with D319 resulted in fungal apoptosis through reactive oxygen species (ROS) accumulation in C. albicans. Furthermore, D319 inhibited the glyoxylate enzyme isocitrate lyase (ICL) of C. albicans, which was also confirmed by docking analysis.

CONCLUSIONS

Quinoline compound D319 exhibited strong anti-Candida activities in vitro and in vivo models through inhibiting ICL activity and ROS accumulation in C. albicans.

GENERAL SIGNIFICANCE

This study showed that compound D319 as a novel isocitrate lyase inhibitor, would be a promising anti-Candida lead compound, which provided a potential application of this type of compounds in fighting clinical fungal infections. Furthermore, this study also supported ICL as a potential target for anti-Candida drug discovery.

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 Elevated Endogenous Reactive Oxygen Species Contribute to the Sensitivity of the Amphotericin B-Resistant Isolate of Aspergillus flavus to Triazoles and Echinocandins

Aspergillus flavus has been frequently reported as the second cause of invasive aspergillosis (IA), as well as the leading cause in certain tropical countries. Amphotericin B (AMB) is a clinically important therapy option for a range of invasive fungal infections including invasive aspergillosis, and in vitro resistance to AMB was associated with poor outcomes in IA patients treated with AMB. Compared with the AMB-susceptible isolates of A. terreus, the AMB-resistant isolates of A. terreus showed a lower level of AMB-induced endogenous reactive oxygen species (ROS), which was an important cause of AMB resistance. In this study, we obtained one AMB-resistant isolate of A. flavus, with an AMB MIC of 32 μg/mL, which was sensitive to triazoles and echinocandins. This isolate presented elevated endogenous ROS levels, which strongly suggested that no contribution of decreased AMB-induced endogenous ROS for AMB-resistance, opposite to those observed in A. terreus. Further, we confirmed that the elevated endogenous ROS contributed to the sensitivity of the AMB-resistant A. flavus isolate to triazoles and echinocandins. Further investigation is needed to elucidate the causes of elevated endogenous ROS and the resistance mechanism to AMB in A. flavus.

Clotrimazole-Induced Oxidative Stress Triggers Novel Yeast Pkc1-Independent Cell Wall Integrity MAPK Pathway Circuitry

Azoles are one of the most widely used drugs to treat fungal infections. To further understand the fungal response to azoles, we analyzed the MAPK circuitry of the model yeast Saccharomyces cerevisiae that operates under treatment with these antifungals. Imidazoles, and particularly clotrimazole, trigger deeper changes in MAPK phosphorylation than triazoles, involving a reduction in signaling through the mating pathway and the activation of the MAPKs Hog1 and Slt2 from the High-Osmolarity Glycerol (HOG) and the Cell Wall Integrity (CWI) pathways, respectively. Clotrimazole treatment leads to actin aggregation, mitochondrial alteration, and oxidative stress, which is essential not only for the activation of both MAPKs, but also for the appearance of a low-mobility form of Slt2 caused by additional phosphorylation to that occurring at the conserved TEY activation motif. Clotrimazole-induced ROS production and Slt2 phosphorylation are linked to Tpk3-mediated PKA activity. Resistance to clotrimazole depends on HOG and CWI-pathway-mediated stress responses. However, Pkc1 and other proteins acting upstream in the pathway are not critical for the activation of the Slt2 MAPK module, suggesting a novel rewiring of signaling through the CWI pathway. We further show that the strong impact of azole treatment on MAPK signaling is conserved in other yeast species.

Do Multiple Drug Resistance Transporters Interfere with Cell Functioning under Normal Conditions?

Eukaryotic cells rely on multiple mechanisms to protect themselves from exogenous toxic compounds. For instance, cells can limit penetration of toxic molecules through the plasma membrane or sequester them within the specialized compartments. Plasma membrane transporters with broad substrate specificity confer multiple drug resistance (MDR) to cells. These transporters efflux toxic compounds at the cost of ATP hydrolysis (ABC-transporters) or proton influx (MFS-transporters). In our review, we discuss the possible costs of having an active drug-efflux system using yeast cells as an example. The pleiotropic drug resistance (PDR) subfamily ABC-transporters are known to constitutively hydrolyze ATP even without any substrate stimulation or transport across the membrane. Besides, some MDR-transporters have flippase activity allowing transport of lipids from inner to outer lipid layer of the plasma membrane. Thus, excessive activity of MDR-transporters can adversely affect plasma membrane properties. Moreover, broad substrate specificity of ABC-transporters also suggests the possibility of unintentional efflux of some natural metabolic intermediates from the cells. Furthermore, in some microorganisms, transport of quorum-sensing factors is mediated by MDR transporters; thus, overexpression of the transporters can also disturb cell-to-cell communications. As a result, under normal conditions, cells keep MDR-transporter genes repressed and activate them only upon exposure to stresses. We speculate that exploiting limitations of the drug-efflux system is a promising strategy to counteract MDR in pathogenic fungi.

LncRNA DINOR is a virulence factor and global regulator of stress responses in Candida auris

The emergent fungal pathogen Candida auris exhibits high resistance to antifungal drugs and environmental stresses, impeding treatment and decontamination^1-3. The fungal factors mediating this stress tolerance are largely unknown. In the present study, we performed piggyBac, transposon-mediated, genome-wide mutagenesis and genetic screening in C. auris, and identified a mutant that grew constitutively in the filamentous form. Mapping the transposon insertion site revealed the disruption of a long non-coding RNA, named DINOR for DNA damage-inducible non-coding RNA. Deletion of DINOR caused DNA damage and an upregulation of genes involved in morphogenesis, DNA damage and DNA replication. The DNA checkpoint kinase Rad53 was hyperphosphorylated in dinorΔ mutants, and deletion of RAD53 abolished DNA damage-induced filamentation. DNA-alkylating agents, which cause similar filamentous growth, induced DINOR expression, suggesting a role for DINOR in maintaining genome integrity. Upregulation of DINOR also occurred during exposure to the antifungal drugs caspofungin and amphotericin B, macrophages, H₂O₂ and sodium dodecylsulfate, indicating that DINOR orchestrates multiple stress responses. Consistently, dinorΔ mutants displayed increased sensitivity to these stresses and were attenuated for virulence in mice. Moreover, genome-wide genetic interaction studies revealed links between the function of DINOR and TOR signalling, an evolutionarily conserved pathway that regulates the stress response. Identification of the mechanism(s) by which DINOR regulates stress responses in C. auris may provide future opportunities for the development of therapeutics.

Shared evolutionary footprints suggest mitochondrial oxidative damage underlies multiple complex I losses in fungi

Oxidative phosphorylation is among the most conserved mitochondrial pathways. However, one of the cornerstones of this pathway, the multi-protein complex NADH : ubiquinone oxidoreductase (complex I) has been lost multiple independent times in diverse eukaryotic lineages. The causes and consequences of these convergent losses remain poorly understood. Here, we used a comparative genomics approach to reconstruct evolutionary paths leading to complex I loss and infer possible evolutionary scenarios. By mining available mitochondrial and nuclear genomes, we identified eight independent events of mitochondrial complex I loss across eukaryotes, of which six occurred in fungal lineages. We focused on three recent loss events that affect closely related fungal species, and inferred genomic changes convergently associated with complex I loss. Based on these results, we predict novel complex I functional partners and relate the loss of complex I with the presence of increased mitochondrial antioxidants, higher fermentative capabilities, duplications of alternative dehydrogenases, loss of alternative oxidases and adaptation to antifungal compounds. To explain these findings, we hypothesize that a combination of previously acquired compensatory mechanisms and exposure to environmental triggers of oxidative stress (such as hypoxia and/or toxic chemicals) induced complex I loss in fungi.

Fingolimod Potentiates the Antifungal Activity of Amphotericin B

Candida albicans (C. albicans) is an opportunistic human fungal pathogen that can cause severe infection in clinic. Its incidence and mortality rate has been increasing rapidly. Amphotericin B (AMB), the clinical golden standard antifungal agent, has severe side effects that limit its clinical application. Thus, lowering the concentration and increasing the efficacy of AMB in a combinatorial antifungal therapy have been pursued by both industry and academia. Here we identify that fingolimod (FTY720), an immunomodulatory drug used for oral treatment of relapsing-remitting multiple sclerosis, can potentiate the efficacy of AMB against C. albicans growth synergistically. Furthermore, we observe an antifungal efficacy of FTY720 in combination with AMB against diverse fungal pathogens. Intriguingly, cells treated with both drugs are hypersensitive to endothelial endocytosis and macrophage killing. This is later found to be due to the hyperaccumulation of reactive oxygen species and the corresponding increase in activities of superoxide dismutase and catalase in the cells that received combinatorial treatment. Therefore, the combination of AMB and FTY720 provides a promising antifungal strategy.

Toxicogenetic of tebuconazole based fungicide through Lactuca sativa bioassays

The rampant use of pesticides can cause serious environmental problems. They can be contaminating surface water and groundwater, affecting the surrounding micro and macro biota. In this sense, this work aimed to evaluate the effects of a tebuconazole-based fungicide through endpoints accessed in Lactuca sativa bioassays. Germinated-seeds with roots upon 2 mm were treated with a fungicide containing Tebuconazole (TBZ) as active compound. The final concentration of TBZ in the tested solutions were 0.025 (C1); 0.05 (C2); 0.1 (C3); 0.2 (C4) and 0.4 g/L (C5). L. sativa roots were exposed for 24 h to these solutions and Petri dishes containing the treated seeds were kept in incubation chamber at 24 °C. Two positive controls (PC,) the herbicide trifluralin (0.84 mg/L) and Methanesulfonate (4 ×10-4 mol/L), were applied. Distilled water was negative control (NC). The following endpoints were analyzed: root growth (RG), cytogenotoxic potential by cell cycle analysis, induction of DNA damage through TUNEL and comet assays. The obtained data were submitted to one-way variance analysis (ANOVA) and then to Tukey or Kruskal Wallis (P < 0.05) tests. The concentrations (C1, C2, C4 and C5) affected negatively the RG of L. sativa, in comparison with the NC. The mitotic index was reduced by 25% from NC to C1 and in the rest of treatments it did not present significant modifications. However, from C3 to C5 great amount of chromosome alterations were observed, in comparison with the NC. TBZ-based fungicide also induced DNA fragmentation as measured by TUNEL and comet assays. Thus, TBZ-based fungicide in some concentrations can have phytotoxic, cytotoxic and genotoxic effects in roots and meristematic cells of L. sativa.

Effects of antifungal agents on the fungal proteome: informing on mechanisms of sensitivity and resistance

INTRODUCTION

Antifungal agents are essential in the fight against serious fungal disease, however emerging resistance is threatening an already limited collection of therapeutics. Proteomic analyses of effects of antifungal agents can expand our understanding of multifactorial mechanisms of action and have also proven valuable to elucidate proteomic changes associated with antifungal resistance.

AREAS COVERED

This review covers the application of proteomic techniques to examine sensitivity and resistance to antifungals including commonly used therapeutics, amphotericin B, echinocandins and the azoles, based predominantly on studies involving Aspergillus fumigatus, Candida albicans and Candida glabrata from the last 10 years. In addition, non-clinical antimicrobial agents are also discussed, which highlight the potential of proteomics to identify new antifungal targets.

EXPERT COMMENTARY

Fungal proteomics has evolved in the last decade with increased genome availability and developments in mass spectrometry. Collectively, these have led to the advancement of proteomic techniques, allowing increased coverage of the proteome. Gel-based proteomics laid the foundation for these types of studies, which has now shifted to the more powerful gel-free proteomics. This has resulted in the identification of key mediators and potential biomarkers of antifungal resistance, as well as elucidating the mechanisms of action of novel and established antifungal agents.

Base Excision Repair AP-Endonucleases-Like Genes Modulate DNA Damage Response and Virulence of the Human Pathogen Cryptococcus neoformans

Pathogenic microbes are exposed to a number of potential DNA-damaging stimuli during interaction with the host immune system. Microbial survival in this situation depends on a fine balance between the maintenance of DNA integrity and the adaptability provided by mutations. In this study, we investigated the association of the DNA repair response with the virulence of Cryptococcus neoformans, a basidiomycete that causes life-threatening meningoencephalitis in immunocompromised individuals. We focused on the characterization of C. neoformansAPN1 and APN2 putative genes, aiming to evaluate a possible role of the predicted Apurinic/apyrimidinic (AP) endonucleases 1 and 2 of the base excision repair (BER) pathway on C. neoformans response to stress conditions and virulence. Our results demonstrated the involvement of the putative AP-endonucleases Apn1 and Apn2 in the cellular response to DNA damage induced by alkylation and by UV radiation, in melanin production, in tolerance to drugs and in virulence of C. neoformans in vivo. We also pointed out the potential use of DNA repair inhibitor methoxy-amine in combination with conventional antifungal drugs, for the development of new therapeutic approaches against this human fungal pathogen. This work provides new information about the DNA damage response of the highly important pathogenic fungus C. neoformans.

Polarization-sensitive stimulated Raman scattering imaging resolves amphotericin B orientation in Candida membrane

Ergosterol-targeting amphotericin B (AmB) is the first line of defense for life-threatening fungal infections. Two models have been proposed to illustrate AmB assembly in the cell membrane; one is the classical ion channel model in which AmB vertically forms transmembrane tunnel and the other is a recently proposed sterol sponge model where AmB is laterally adsorbed onto the membrane surface. To address this controversy, we use polarization-sensitive stimulated Raman scattering from fingerprint C═C stretching vibration to visualize AmB, ergosterol, and lipid in single fungal cells. Intracellular lipid droplet accumulation in response to AmB treatment is found. AmB is located in membrane and intracellular droplets. In the 16 strains studied, AmB residing inside cell membrane was highly ordered, and its orientation is primarily parallel to phospholipid acyl chains, supporting the ion channel model. Label-free imaging of AmB and chemical contents offers an analytical platform for developing low-toxicity, resistance-refractory antifungal agents.

The Fungicidal Action of Micafungin is Independent on Both Oxidative Stress Generation and HOG Pathway Signaling in Candida albicans

In fungi, the Mitogen-Activated Protein kinase (MAPK) pathways sense a wide variety of environmental stimuli, leading to cell adaptation and survival. The HOG pathway plays an essential role in the pathobiology of Candida albicans, including the colonization of the gastrointestinal tract in a mouse model, virulence, and response to stress. Here, we examined the role of Hog1 in the C. albicans response to the clinically relevant antifungal Micafungin (MF), whose minimum inhibitory concentration (MIC) was identical in the parental strain (RM100) and in the isogenic homozygous mutant hog1 (0.016 mg/L). The cell viability was impaired without significant differences between the parental strain, the isogenic hog1 mutant, and the Hog1⁺ reintegrant. This phenotype was quite similar in a collection of hog1 mutants constructed in a different C. albicans background. MF-treated cells failed to induce a relevant increase of both reactive oxygen species (ROS) formation and activation of the mitochondrial membrane potential in parental and hog1 cells. MF was also unable to trigger any significant activation of the genes coding for the antioxidant activities catalase (CAT1) and superoxide dismutase (SOD2), as well as on the corresponding enzymatic activities, whereas a clear induction was observed in the presence of Amphotericin B (AMB), introduced as a positive control of Hog1 signaling. Furthermore, Hog1 was not phosphorylated by the addition of MF, but, notably, this echinocandin caused Mkc1 phosphorylation. Our results strongly suggest that the toxic effect of MF on C. albicans cells is not mediated by the Hog1 MAPK and is independent of the generation of an internal oxidative stress in C. albicans.

Activity of monoterpenoids on the in vitro growth of two Colletotrichum species and the mode of action on C. acutatum

Essential oils and their main compounds, monoterpenoids, are considered as alternative control systems for phytopathogenic fungi, particularly those related to late diseases of fruits and vegetables, like anthracnose caused by Colletotrichum species. In this context, we studied the effect of twenty monoterpenoids on Colletotrichum fructicola and C. acutatum to elucidate their effectiveness and mechanisms of action. Thus, we analyzed mycelial growth and conidial inhibitory concentration, as well as the effect of selected monoterpenoids on membrane integrity and cell vitality, reactive oxygen species (ROS) accumulation, and mitochondrial membrane potential by flow cytometry. The results showed that oxygenated monoterpenoids (alcohols and aldehydes) exhibited higher antifungal activity than their corresponding hydrocarbons, esters, and cyclic counterparts. Indicating that OH^- and O^- radicals react with cellular components affecting fungal homeostasis. In this sense, selected monoterpenoids (citral, citronellol, geraniol, carvacrol, and thymol) inhibited conidial germination of C. acutatum in a dose-dependent manner. The inhibition of conidial germination is associated with a loss of membrane integrity, a decrease of cell metabolism, and a dose-dependent accumulation of ROS, which was non-directly associated with modifications on mitochondrial membrane potential. Membrane dysfunction and ROS accumulation may be responsible for the necrotic behavior induced by high monoterpenoids concentrations, and possible apoptotic response in sub dosages of these compounds.

Safety of current therapies for onychomycosis

INTRODUCTION

Onychomycosis is the most common nail disease seen in clinical practice. Treatment options include systemic and topical therapies, as well as devices. Following clinical and mycologic diagnosis, treatment must be individualized, accounting for disease severity, infecting organism(s), comorbidities, patient characteristics and drug/device efficacy. Safety is the most important consideration in choosing the most appropriate therapeutic modality.

AREAS COVERED

This review covers currently available treatments for onychomycosis, with an emphasis on safety and tolerability. Medications and devices were analyzed for side effects, drug-drug interactions, and safety during pregnancy and breastfeeding.

EXPERT OPINION

Systemic antifungals offer greater efficacy for onychomycosis treatment but are limited by risks of systemic toxicity and drug-drug interactions. The risk of terbinafine-induced hepatotoxicity is negligible in healthy patients. Systemic therapies, especially azole antifungals, are associated with numerous drug-drug interactions, some of which are life-threatening and fatal. Thus, a detailed medication history is critical before prescribing these medications. Topical antifungals are well tolerated and generally safe, with only potential local side effects. Systemic and topical onychomycosis treatments should not be prescribed during pregnancy and breastfeeding. Laser therapy is likely less effective than systemic and topical therapies, but may be safely used during pregnancy and breastfeeding.

A New Antifungal Agent (4-phenyl-1, 3-thiazol-2-yl) Hydrazine Induces Oxidative Damage in Candida albicans

A gradual rise in immunocompromised patients over past years has led to the increasing incidence of invasive fungal infections. Development of effective fungicides can not only provide new means for clinical treatment, but also reduce the occurrence of fungal resistance. We identified a new antifungal agent (4-phenyl-1, 3-thiazol-2-yl), hydrazine (numbered as 31C) which showed high-efficiency, broad-spectrum and specific activities. The minimum inhibitory concentration of 31C against pathogenic fungi was between 0.0625-4 μg/ml in vitro, while 31C had no obvious cytotoxicity to human umbilical vein endothelial cells with the concentration of 4 μg/ml. In addition, 31C of 0.5 μg/ml could exhibit significant fungicidal activity and inhibit the biofilm formation of C. albicans. In vivo fungal infection model showed that 31C of 10 mg/kg significantly increased the survival rate of Galleria mellonella. Further study revealed that 31C-treatment increased the reactive oxygen species (ROS) in C. albicans and elevated the expression of some genes related to anti-oxidative stress response, including CAP1, CTA1, TRR1, and SODs. Consistently, 31C-induced high levels of intracellular ROS resulted in considerable DNA damage, which played a critical role in antifungal-induced cellular death. The addition of ROS scavengers, such as glutathione (GSH), N-Acetyl-L-cysteine (NAC) or oligomeric proanthocyanidins (OPC), dramatically reduced the antifungal activities of 31C and rescued the 31C-induced filamentation defect. Collectively, these results showed that 31C exhibited strong antifungal activity and induced obvious oxidative damage, which indicated that compounds with a structure similar to 31C may provide new sight for antifungal drug development.

Identification of Genomewide Alternative Splicing Events in Sequential, Isogenic Clinical Isolates of Candida albicans Reveals a Novel Mechanism of Drug Resistance and Tolerance to Cellular Stresses

The emergence of resistance in Candida albicans, an opportunistic pathogen, against the commonly used antifungals is becoming a major obstacle in its treatment. The necessity to identify new drug targets demands fundamental insights into the mechanisms used by this organism to develop drug resistance. C. albicans has introns in 4 to 6% of its genes, the functions of which remain largely unknown. Using the RNA-sequencing data from isogenic pairs of azole-sensitive and -resistant isolates of C. albicans, here, we show how C. albicans uses modulations in mRNA splicing to overcome antifungal drug stress.

Alternative splicing (AS)—a process by which a single gene gives rise to different protein isoforms in eukaryotes—has been implicated in many basic cellular processes, but little is known about its role in drug resistance and fungal pathogenesis. The most common human fungal pathogen, Candida albicans, has introns in 4 to 6% of its genes, the functions of which remain largely unknown. Here, we report AS regulating drug resistance in C. albicans. Comparative RNA-sequencing of two different sets of sequential, isogenic azole-sensitive and -resistant isolates of C. albicans revealed differential expression of splice isoforms of 14 genes. One of these was the superoxide dismutase gene SOD3, which contains a single intron. The sod3Δ/Δ mutant was susceptible to the antifungals amphotericin B (AMB) and menadione (MND). While AMB susceptibility was rescued by overexpression of both the spliced and unspliced SOD3 isoforms, only the spliced isoform could overcome MND susceptibility, demonstrating the functional relevance of this splicing in developing drug resistance. Furthermore, unlike AMB, MND inhibits SOD3 splicing and acts as a splicing inhibitor. Consistent with these observations, MND exposure resulted in increased levels of unspliced SOD3 isoform that are unable to scavenge reactive oxygen species (ROS), resulting in increased drug susceptibility. Collectively, these observations suggest that AS is a novel mechanism for stress adaptation and overcoming drug susceptibility in C. albicans.

IMPORTANCE The emergence of resistance in Candida albicans, an opportunistic pathogen, against the commonly used antifungals is becoming a major obstacle in its treatment. The necessity to identify new drug targets demands fundamental insights into the mechanisms used by this organism to develop drug resistance. C. albicans has introns in 4 to 6% of its genes, the functions of which remain largely unknown. Using the RNA-sequencing data from isogenic pairs of azole-sensitive and -resistant isolates of C. albicans, here, we show how C. albicans uses modulations in mRNA splicing to overcome antifungal drug stress.