Alternative approaches to antifungal therapies

Anti-fungal peptides: an emerging category with enthralling therapeutic prospects in the treatment of candidiasis

Candida infections, particularly invasive candidiasis, pose a serious global health threat. Candida albicans is the most prevalent species causing candidiasis, and resistance to key antifungal drugs, such as azoles, echinocandins, polyenes, and fluoropyrimidines, has emerged. This growing multidrug resistance (MDR) complicates treatment options, highlighting the need for novel therapeutic approaches. Antifungal peptides (AFPs) are gaining recognition for their potential as new antifungal agents due to their diverse structures and functions. These natural or recombinant peptides can effectively target fungal virulence and viability, making them promising candidates for future antifungal development. This review examines infections caused by Candida species, the limitations of current antifungal treatments, and the therapeutic potential of AFPs. It emphasizes the importance of identifying novel AFP targets and their production for advancing treatment strategies. By discussing the therapeutic development of AFPs, the review aims to draw researchers' attention to this promising field. The integration of knowledge about AFPs could pave the way for novel antifungal agents with broad-spectrum activity, reduced toxicity, targeted action, and mechanisms that limit resistance in pathogenic fungi, offering significant advancements in antifungal therapeutics.

Malassezia: Zoonotic Implications, Parallels and Differences in Colonization and Disease in Humans and Animals

Malassezia spp. are commensals of the skin, oral/sinonasal cavity, lower respiratory and gastrointestinal tract. Eighteen species have been recovered from humans, other mammals and birds. They can also be isolated from diverse environments, suggesting an evolutionary trajectory of adaption from an ecological niche in plants and soil to the mucocutaneous ecosystem of warm-blooded vertebrates. In humans, dogs and cats, Malassezia-associated dermatological conditions share some commonalities. Otomycosis is common in companion animals but is rare in humans. Systemic infections, which are increasingly reported in humans, have yet to be recognized in animals. Malassezia species have also been identified as pathogenetic contributors to some chronic human diseases. While Malassezia species are host-adapted, some species are zoophilic and can cause fungemia, with outbreaks in neonatal intensive care wards associated with temporary colonization of healthcare worker’s hands from contact with their pets. Although standardization is lacking, susceptibility testing is usually performed using a modified broth microdilution method. Antifungal susceptibility can vary depending on Malassezia species, body location, infection type, disease duration, presence of co-morbidities and immunosuppression. Antifungal resistance mechanisms include biofilm formation, mutations or overexpression of ERG11, overexpression of efflux pumps and gene rearrangements or overexpression in chromosome 4.

Alternative Treatment Strategies for Secondary Bacterial and Fungal Infections Associated with COVID-19

Antimicrobials are essential for combating infectious diseases. However, an increase in resistance to them is a major cause of concern. The empirical use of drugs in managing COVID-19 and the associated secondary infections have further exacerbated the problem of antimicrobial resistance. Hence, the situation mandates exploring and developing efficient alternatives for the treatment of bacterial and fungal infections in patients suffering from COVID-19 or other viral infections. In this review, we have described the alternatives to conventional antimicrobials that have shown promising results and are at various stages of development. An acceleration of efforts to investigate their potential as therapeutics can provide more treatment options for clinical management of drug-resistant secondary bacterial and fungal infections in the current pandemic and similar potential outbreaks in the future. The alternatives include bacteriophages and their lytic enzymes, anti-fungal enzymes, antimicrobial peptides, nanoparticles and small molecule inhibitors among others. What is required at this stage is to critically examine the challenges in developing the listed compounds and biomolecules as therapeutics and to establish guidelines for their safe and effective application within a suitable time frame. In this review, we have attempted to highlight the importance of rational use of antimicrobials in patients suffering from COVID-19 and boost the deployment of alternative therapeutics.

Salivary Histatin 5 Level in Women with Vaginal Candidiasis

Histatins (Hsts) are considered a prominent member of antimicrobial peptides rich in histidine, bearing antifungal activity against Candida species. Hst5 is the most effective among them. Although Hst5 is not found in the cervicovaginal fluid, it has been detected in the human serum. Saliva acts as a mirror, reflecting the cause and effect relationship between several diseases. We aimed to show the salivary Hst5 levels with vaginal candidiasis. Women in the reproductive age group (18-50 years) were enrolled in the study. Patients and controls were classified based on the presence or absence of vaginal discharge suggestive of candidiasis, respectively. Vaginal and salivary samples were collected from all the women. Vaginal samples were cultured for the growth of Candida species. Salivary samples were tested by protein electrophoresis to detect Hst5 levels, and the results were compared between the two groups. A total of 80 women were included in this study. The mean age of women in vaginal candidiasis and control groups was 34.25 ± 8.06 and 36.83 ± 7.29 years, respectively. Candida species were isolated from the vaginal samples of the patient group (34 C. albicans, 6 non-Candida albicans) but not from the control group. Hst5 levels in the patient and control group were found to be 0.0571 ± 0.003 ng/mL and 0.0641 ± 0,0031 ng/mL, respectively. Hst5 levels were found to be significantly lower in the vaginal candidiasis group (p=0.001). We conclude that decreased salivary Hst5 levels in women are associated with vaginal candidiasis. Candida infection is a cause or result of lower salivary Hst5 levels, and it may be an important finding for the etiopathogenesis, diagnosis, and treatment of the disease, but further analysis is needed.

Conventional therapy and new antifungal drugs against Malassezia infections

Malassezia yeasts are commensal microorganisms occurring on the skin of humans and animals causing dermatological disorders or systemic infections in severely immunocompromised hosts. Despite attempts to control such yeast infections with topical and systemic antifungals, recurrence of clinical signs of skin infections as well as treatment failure in preventing or treating Malassezia furfur fungemia have been reported most likely due to wrong management of these infections (e.g., due to early termination of treatment) or due to the occurrence of resistant phenomena. Standardized methods for in vitro antifungal susceptibility tests of these yeasts are still lacking, thus resulting in variable susceptibility profiles to azoles among Malassezia spp. and a lack of clinical breakpoints. The inherent limitations to the current pharmacological treatments for Malassezia infections both in humans and animals, stimulated the interest of the scientific community to discover new, effective antifungal drugs or substances to treat these infections. In this review, data about the in vivo and in vitro antifungal activity of the most commonly employed drugs (i.e., azoles, polyenes, allylamines, and echinocandins) against Malassezia yeasts, with a focus on human bloodstream infections, are summarized and their clinical implications are discussed. In addition, the usefulness of alternative compounds is discussed.

Antifungal Activity of the Sesquiterpene Lactones from Psephellus bellus

Due to increasing resistance of pathogenic fungi to antifungal treatments, new types of drugs are needed. For this purpose, active substances with antifungal properties occurring in natural compounds should be considered. The herb Psephellus bellus shows strong antifungal activity and is characterized by unique guaianolides, which have an ester on C-2. Thus, a specialized method of isolation and testing was applied to assess the pharmacological effects of these guaianolides. After phytochemical analysis (chromatography and spectral methods), selected lipophilic compounds and the herb extract of this species containing 26 sesquiterpene lactones were tested. The antifungal effect of the herbal compounds was determined on clinical strains of fungi Candida, Rhodotorula, Trichophyton, Microsporum, and Scopulariopsis using a diffusion test. The MTT assay was employed to study the cytotoxic effects of the extract against human fibroblasts. Statistical analysis was performed. All analyzed compounds exhibited antifungal activity in cultivations suitable for assessment. Most lipophilic cebellins from Psephellus bellus prevent the growth of most fungal strains.

Dehydroepiandrosterone derived imidazolium salts and their antimicrobial efficacy

Hybrid molecules consisting of steroid-imidazolium salts reveal interesting biological properties, especially regarding antimicrobial activities. Novel dehydroepiandrosterone derived imidazolium salts (11 salts) with side chains of different lengths were obtained in an efficient and straightforward synthetic route. Antimicrobial properties of new salts were examined by determining their minimum inhibitory concentrations (MICs). They were studied against several strains of bacteria, including clinical isolates of MRSA, and fungi. New compounds showed high activity against Gram-positive bacteria and Candida albicans as well as good compatibility with the representatives of the host cells when applied at concentrations corresponding to MIC value. The studies indicated high antimicrobial efficacy of imidazolium salts against the above-mentioned microorganisms with low hemolytic activity at a concentration that restricts the growth of the microorganisms. The interference of salts with the immune defense system, the influence on the biological activity of monocytes/macrophages measured by their viability and metabolic activity was also studied. The new compounds have shown immunoprotective properties.

Innate Inspiration: Antifungal Peptides and Other Immunotherapeutics From the Host Immune Response

The purpose of this review is to describe antifungal therapeutic candidates in preclinical and clinical development derived from, or directly influenced by, the immune system, with a specific focus on antimicrobial peptides (AMP). Although the focus of this review is AMP with direct antimicrobial effects on fungi, we will also discuss compounds with direct antifungal activity, including monoclonal antibodies (mAb), as well as immunomodulatory molecules that can enhance the immune response to fungal infection, including immunomodulatory AMP, vaccines, checkpoint inhibitors, interferon and colony stimulating factors as well as immune cell therapies. The focus of this manuscript will be a non-exhaustive review of antifungal compounds in preclinical and clinical development that are based on the principles of immunology and the authors acknowledge the incredible amount of in vitro and in vivo work that has been conducted to develop such therapeutic candidates.

Studying the Gene Expression of Penicillium rubens Under the Effect of Eight Essential Oils

Essential oils (EOs) are well-known for their beneficial properties against a broad range of microorganisms. For the better understanding of their mechanism of action in fungi, a microarray approach was used in order to evaluate the gene expression of Penicillium chrysogenum (recently renamed P. rubens) exposed to the indirect contact (vapors) of eight EOs. The selection of assayed EOs was based on their antifungal activity. The extraction of RNA and the microarray hybridization procedure were optimized for the analysis of P. rubens. Gene ontology annotation was performed to investigate the functional analysis of the genes. To uncover the metabolic pathway of these differentially expressed genes, they were mapped into the KEGG BRITE pathway database. The transcriptomic analysis showed that, from a total of 12,675 genes, only 551 genes are annotated, and the other 12,124 genes encoded hypothetical proteins. Further bioinformatic analysis demonstrated that 1350 genes were upregulated and 765 downregulated at least with half (four) of the utilizing EOs. A microarray investigation has confirmed the main impact of EOs to metabolic processes in P. rubens involved in vital functions. Presumably, this is the first time that a microarray hybridization analysis was performed in order to evaluate the gene expression of P. rubens exposed to various EOs.

RNase 1, 2, 5 & 8 role in innate immunity: Strain specific antimicrobial activity

The increase in microbial resistance to conventional antimicrobial agents is driving research for the discovery of new antibiotics and antifungal agents. The greatest challenge in this endeavor is to find antimicrobial agents with broad antimicrobial activity and low toxicity. Antimicrobial peptides, for example, RNases, are one of the promising areas. The production of RNases increases during infection, but their role is still being explored. Whereas the enzymatic activity of RNases is well documented, their physiological function is still being investigated. This study aimed to evaluate the antimicrobial activity of RNase 1, 2, 5, and 8 against E. coli strains, S. aureus, Streptococcus thermophilus, P. aeruginosa, Candida albicans, and Candida glabrata. The results demonstrated that RNases have a strain-specific antimicrobial activity. RNase 1 had the highest antimicrobial activity compared to other RNases. All the microorganisms screened had varying levels of susceptibility to RNases, except P. aeruginosa and E. coli DR115. RNase 1 showed dose-dependent activity against C. albicans. The RNase killed Candida albicans by lowering the mitochondrial membrane potential but did not damage the cell membrane. We concluded that strain-specific antimicrobial activity is one of the physiological roles of RNases.

Piperine Impedes Biofilm Formation and Hyphal Morphogenesis of Candida albicans

Candida albicans is the primary etiological agent associated with the pathogenesis of candidiasis. Unrestricted growth of C. albicans in the oral cavity may lead to oral candidiasis, which can progress to systemic infections in worst scenarios. Biofilm of C. albicans encompasses yeast and hyphal forms, where hyphal formation and yeast to hyphal morphological transitions are contemplated as the key virulence elements. Current clinical repercussions necessitate the identification of therapeutic agent that can limit the biofilm formation and escalating the susceptibility of C. albicans to immune system and conventional antifungals. In the present study, a plant-derived alkaloid molecule, piperine, was investigated for the antibiofilm and antihyphal activities against C. albicans. Piperine demonstrated a concentration-dependent antibiofilm activity without exerting negative impact on growth and metabolic activity. Inhibition in the hyphal development was witnessed through confocal laser-scanning microscopy and scanning electron microscopy. Interestingly, piperine displayed a tremendous potential to inhibit the virulence-associated colony morphologies, such as filamentation and wrinkling. Furthermore, piperine regulated morphological transitions between yeast and hyphal forms by inhibiting hyphal extension and swapping hyphal phase to yeast forms yet under filamentation-inducing circumstances. Remarkably, piperine-challenged C. albicans exhibited low potential for spontaneous antibiofilm resistance development. In addition, piperine effectively reduced in vivo colonization and prolonged survival of C. albicans-infected Caenorhabditis elegans, thereby expounding the distinct antivirulent potential. Transcriptomic analysis revealed piperine significantly downregulating the expression of several biofilm related and hyphal-specific genes (ALS3, HWP1, EFG1, CPH1, etc.). Furthermore, no acute toxicity was observed in the HBECs and nematodes exposed to piperine. Altogether, results from this study reveals the potential of piperine to inhibit biofilm and hyphal morphogenesis, and its in vivo efficacy and innocuous nature to HBECs suggests that piperine may be considered as a potential candidate for the treatment of biofilm-associated C. albicans infection, especially for oral candidiasis.

In vitro models of dermatophyte infection to investigate epidermal barrier alterations

Fungal infections of the skin, known as dermatophytoses, are initiated at the epidermal barrier and lead to dysfunctions of the stratum corneum and cornified skin appendages. Dermatophytosis affects a significant part of the human population and, despite the availability of effective treatments, its prevalence is still increasing. Numerous dermatophyte species are able to induce lesions in both animals and humans, with different clinical pictures and host inflammatory responses. The understanding of the infectious process and of tissue responses has been impeded by discrepancies between observations in vivo or in research models. Indeed, cells cultured as monolayers do not undergo the keratinization process required to study the adherence and invasion of dermatophytes. Animal models lack relevance to study human dermatophytosis because of species-specific differences in the development of lesions and inflammatory responses. This review focuses on the recent development of cultured human skin equivalents, which partly overcomes those limitations and allows improved understanding of the pathogenesis of dermatophytosis in human being, especially the impacts of infection on epidermal barrier integrity.

Novel Sulfones with Antifungal Properties: Antifungal Activities and Interactions with Candida spp. Virulence Factors

Since candidiasis is so difficult to eradicate with an antifungal treatment and the existing antimycotics display many limitations, hopefully new sulfone derivatives may overcome these deficiencies. It is pertinent to study new strategies such as sulfone derivatives targeting the virulence attributes of C. albicans that differentiate them from the host. During infections, the pathogenic potential of C. albicans relies on the virulence factors as follows: hydrolytic enzymes, transcriptional factors, adhesion, and development of biofilms. In the article we explored how the above-presented C. albicans fitness and virulence attributes provided a robust response to the environmental stress exerted by sulfones upon C. albicans; C. albicans fitness and virulence attributes are fungal properties whose inactivation attenuates virulence. Our understanding of how these mechanisms and factors are inhibited by sulfones has increased over the last years. As lack of toxicity is a prerequisite for medical approaches, sulfones (non-toxic as assessed in vitro and in vivo) may prove to be useful for reducing C. albicans pathogenesis in humans. The antifungal activity of sulfones dealing with these multiple virulence factors and fitness attributes is discussed.

Dual RNA-Seq Analysis of Trichophyton rubrum and HaCat Keratinocyte Co-Culture Highlights Important Genes for Fungal-Host Interaction

The dermatophyte Trichophyton rubrum is the major fungal pathogen of skin, hair, and nails that uses keratinized substrates as the primary nutrients during infection. Few strategies are available that permit a better understanding of the molecular mechanisms involved in the interaction of T. rubrum with the host because of the limitations of models mimicking this interaction. Dual RNA-seq is a powerful tool to unravel this complex interaction since it enables simultaneous evaluation of the transcriptome of two organisms. Using this technology in an in vitro model of co-culture, this study evaluated the transcriptional profile of genes involved in fungus-host interactions in 24 h. Our data demonstrated the induction of glyoxylate cycle genes, ERG6 and TERG_00916, which encodes a carboxylic acid transporter that may improve the assimilation of nutrients and fungal survival in the host. Furthermore, genes encoding keratinolytic proteases were also induced. In human keratinocytes (HaCat) cells, the SLC11A1, RNASE7, and CSF2 genes were induced and the products of these genes are known to have antimicrobial activity. In addition, the FLG and KRT1 genes involved in the epithelial barrier integrity were inhibited. This analysis showed the modulation of important genes involved in T. rubrum–host interaction, which could represent potential antifungal targets for the treatment of dermatophytoses.

Candida Infections and Therapeutic Strategies: Mechanisms of Action for Traditional and Alternative Agents

The Candida genus comprises opportunistic fungi that can become pathogenic when the immune system of the host fails. Candida albicans is the most important and prevalent species. Polyenes, fluoropyrimidines, echinocandins, and azoles are used as commercial antifungal agents to treat candidiasis. However, the presence of intrinsic and developed resistance against azole antifungals has been extensively documented among several Candida species. The advent of original and re-emergence of classical fungal diseases have occurred as a consequence of the development of the antifungal resistance phenomenon. In this way, the development of new satisfactory therapy for fungal diseases persists as a major challenge of present-day medicine. The design of original drugs from traditional medicines provides new promises in the modern clinic. The urgent need includes the development of alternative drugs that are more efficient and tolerant than those traditional already in use. The identification of new substances with potential antifungal effect at low concentrations or in combination is also a possibility. The present review briefly examines the infections caused by Candida species and focuses on the mechanisms of action associated with the traditional agents used to treat those infections, as well as the current understanding of the molecular basis of resistance development in these fungal species. In addition, this review describes some of the promising alternative molecules and/or substances that could be used as anticandidal agents, their mechanisms of action, and their use in combination with traditional drugs.

Oropharyngeal Candidosis in HIV-Infected Patients-An Update

Oropharyngeal candidosis (OPC) is an opportunistic fungal infection that is commonly found in HIV-infected patients, even in the twenty-first century. Candida albicans is the main pathogen, but other Candida species have been isolated. OPC usually presents months or years before other severe opportunistic infections and may indicate the presence or progression of HIV disease. The concept of OPC as a biofilm infection has changed our understanding of its pathobiology. Various anti-fungal agents (both topical and systemic) are available to treat OPC. However, anti-fungal resistance as a result of the long-term use of anti-fungal agents and recurrent oropharyngeal infection in AIDS patients require alternative anti-fungal therapies. In addition, both identifying the causative Candida species and conducting anti-fungal vulnerability testing can improve a clinician's ability to prescribe effective anti-fungal agents. The present review focuses on the current findings and therapeutic challenges for HIV-infected patients with OPC.

Antifungal properties of essential oils for improvement of indoor air quality: a review

Concerns regarding indoor air quality, particularly the presence of fungi and moulds, are increasing. The potential for essential oils to reduce, control or remove fungi, is gaining interest as they are seen as a "natural" alternative to synthetic chemical fungicides. This review examines published research on essential oils as a method of fungal control in indoor environments. It was difficult to compare the relative performances of essential oils due to differences in research methods and reporting languages. In addition, there are limited studies that scale up laboratory results and assess the efficacy of essential oils within building environments. However, generally, there appears to be some evidence to support the essential oils clove oil, tea tree oil, oregano, thyme and lemon as potential antifungal agents. Essential oils from heartwood, marjoram, cinnamon, lemon basil, caraway, bay tree, fir, peppermint, pine, cedar leaf and manuka were identified in at least one study as having antifungal potential. Future studies should focus on comparing the effectiveness of these essential oils against a large number of fungal isolates from indoor environments. Studies will then need to focus on translating these results into realistic application methods, in actual buildings, and assess the potential for long-term antifungal persistence.

Impact of Brief Exposure to Drugs with Antifungal Properties on the Susceptibility of Oral Candida dubliniensis Isolates to Lysozyme and Lactoferrin

OBJECTIVE

Lysozyme and lactoferrin have anti-candidal activity. Candida dubliniensis is associated with oral candidiasis. Candida infections are managed with nystatin, amphotericin B, caspofungin, ketoconazole, fluconazole, and chlorhexidine. Candida species undergo a brief exposure to therapeutic agents in the mouth. There is no data on the influence of limited exposure to antimycotics on the sensitivity of C. dubliniensis to lactoferrin and lysozyme. Hence, this study observed the changes in the sensitivity of C. dubliniensis to anti-candidal action of lactoferrin and lysozyme after transitory exposure to sub-lethal concentrations of antifungals.

MATERIALS AND METHODS

After determination of the minimum inhibitory concentration (MIC), 20 C. dubliniensis isolates were exposed to twice the concentration of MIC of nystatin, amphotericin B, caspofungin, ketoconazole, fluconazole, and chlorhexidine for 1 h. Drugs were removed by dilution and thereafter the susceptibility of these isolates to lysozyme and lactoferrin was determined by colony-forming unit quantification assay.

RESULTS

Exposure of C. dubliniensis to nystatin, amphotericin B, caspofungin, ketoconazole, fluconazole, and chlorhexidine resulted in an increase in susceptibility to lysozyme by 9.45, 30.82, 30.04, 50.64, 55.60, and 50.18%, respectively (p < 0.05 to p < 0.001). Exposure of C. dubliniensis to nystatin, amphotericin B, caspofungin, ketoconazole, fluconazole, and chlorhexidine resulted in an increase in susceptibility to lactoferrin by 13.54, 16.43, 17.58, 19.60, 21.32, and 18.73, respectively (p < 0.05 to p < 0.001).

CONCLUSION

Brief exposure to nystatin, amphotericin B, caspofungin, ketoconazole, fluconazole, and chlorhexidine enhances the antifungal effect of lysozyme and lactoferrin on C. dubliniensis isolates in vitro.

Natural Antimicrobial Peptides as Inspiration for Design of a New Generation Antifungal Compounds

Invasive fungal infections are associated with high mortality rates, despite appropriate antifungal therapy. Limited therapeutic options, resistance development and the high mortality of invasive fungal infections brought about more concern triggering the search for new compounds capable of interfering with fungal viability and virulence. In this context, peptides gained attention as promising candidates for the antimycotics development. Variety of structural and functional characteristics identified for various natural antifungal peptides makes them excellent starting points for design novel drug candidates. Current review provides a brief overview of natural and synthetic antifungal peptides.

Antifungal activity of essential oils against fungi isolated from air

Fungal contamination of indoor air is an issue of increasing public health concern. Essential oils have been demonstrated to have antifungal capabilities, but there are limited studies investigating the efficacy of essential oils against fungi relevant to air quality. This study provides a preliminary screening of the antifungal properties of clove, lavender and eucalyptus essential oils against a range of fungal species isolated from environmental air samples. The ability of the essential oils to inhibit fungal growth was examined using the disk diffusion assay on malt extract agar and was compared with vinegar, bleach and limonene, with phenol as a positive control. Results identified essential oils which demonstrated antifungal potential against species of environmental origin. Clove oil was found to be most efficacious, with eucalyptus and lavender oils showing some antifungal potential albeit less broad spectrum and with less persistence over time in this assay. All essentials oils performed better than traditional cleaning compounds such as vinegar. Clove oil would be a suitable candidate for further research to validate its use in improving indoor air quality. Further research should next take into consideration the practical application method, concentration and long-term persistence of antifungal properties.

Integrated Activity and Genetic Profiling of Secreted Peptidases in Cryptococcus neoformans Reveals an Aspartyl Peptidase Required for Low pH Survival and Virulence

The opportunistic fungal pathogen Cryptococcus neoformans is a major cause of mortality in immunocompromised individuals, resulting in more than 600,000 deaths per year. Many human fungal pathogens secrete peptidases that influence virulence, but in most cases the substrate specificity and regulation of these enzymes remains poorly understood. The paucity of such information is a roadblock to our understanding of the biological functions of peptidases and whether or not these enzymes are viable therapeutic targets. We report here an unbiased analysis of secreted peptidase activity and specificity in C. neoformans using a mass spectrometry-based substrate profiling strategy and subsequent functional investigations. Our initial studies revealed that global peptidase activity and specificity are dramatically altered by environmental conditions. To uncover the substrate preferences of individual enzymes and interrogate their biological functions, we constructed and profiled a ten-member gene deletion collection of candidate secreted peptidases. Through this deletion approach, we characterized the substrate specificity of three peptidases within the context of the C. neoformans secretome, including an enzyme known to be important for fungal entry into the brain. We selected a previously uncharacterized peptidase, which we term Major aspartyl peptidase 1 (May1), for detailed study due to its substantial contribution to extracellular proteolytic activity. Based on the preference of May1 for proteolysis between hydrophobic amino acids, we screened a focused library of aspartyl peptidase inhibitors and identified four high-affinity antagonists. Finally, we tested may1Δ strains in a mouse model of C. neoformans infection and found that strains lacking this enzyme are significantly attenuated for virulence. Our study reveals the secreted peptidase activity and specificity of an important human fungal pathogen, identifies responsible enzymes through genetic tests of their function, and demonstrates how this information can guide the development of high affinity small molecule inhibitors.

Many pathogenic organisms secrete peptidases. The activity of these enzymes often contributes to virulence, making their study crucial for understanding host-pathogen biology and developing therapeutics. In this report, we employed an unbiased, activity-based profiling assay to examine the secreted peptidases of a fungal pathogen, Cryptococcus neoformans, which is responsible for 40% of AIDS-related deaths. We discovered which peptidases are secreted, identified their substrate specificity, and interrogated their biological functions. Through this analysis, we identified a principal enzyme responsible for the extracellular peptidase activity of C. neoformans, May1, and demonstrated its importance for growth in acidic environments. Characterization of its substrate preferences allowed us to identify compounds that are potent substrate-based inhibitors of May1 activity. Finally, we found that the presence of this enzyme promotes virulence in a mouse model of infection. Our comprehensive study reveals the expression, regulation and function of C. neoformans secreted peptidases, including evidence for the role of a novel aspartyl peptidase in virulence.

Anti-fungal activity of Ctn[15-34], the C-terminal peptide fragment of crotalicidin, a rattlesnake venom gland cathelicidin

Crotalicidin (Ctn), a 34-residue cathelicidin from a South American rattlesnake, and its fragment (Ctn[15-34]) have shown anti-infective and cytotoxic activities against Gram-negative bacteria and certain tumor lines, respectively. The extent of such effects has been related to physicochemical characteristics such as helicity and hydrophobicity. We now report the anti-fungal activity of Ctn and its fragments (Ctn[1-14]) and (Ctn[15-34]). MIC determination and luminescent cell viability assays were used to evaluate the anti-infective activity of Ctn and its fragments (Ctn[1-14]) and (Ctn[15-34]) as anti-fungal agents against opportunistic yeast and dermatophytes. Cytotoxicity towards healthy eukaryotic cells was assessed in vitro with healthy human kidney-2 (HK-2) cells and erythrocytes. The checkerboard technique was performed to estimate the effects of combining either one of the peptides with amphotericin B. Ctn was the most active peptide against dermatophytes and also the most toxic to healthy eukaryotic cells. Fragments Ctn[1-14] and Ctn[15-35] lost activity against dermatophytes, but became more active against pathogenic yeasts, including several Candida species, both clinical isolates and standard strains, with MICs as low as 5 μm. Interestingly, the two peptide fragments were less cytotoxic to healthy HK-2 cells and less hemolytic to human erythrocytes than the standard-of-care amphotericin B. Also noteworthy was the synergy between Ctn peptides and amphotericin B, with consequent reduction in MICs of both drug and peptides. Altogether, Ctn and its fragments, particularly Ctn[15-34], are promising leads, either alone or in combined regimen with amphotericin B, for the treatment of fungal diseases.

Corpora Amylacea of Brain Tissue from Neurodegenerative Diseases Are Stained with Specific Antifungal Antibodies

The origin and potential function of corpora amylacea (CA) remains largely unknown. Low numbers of CA are detected in the aging brain of normal individuals but they are abundant in the central nervous system of patients with neurodegenerative diseases. In the present study, we show that CA from patients diagnosed with Alzheimer's disease (AD) contain fungal proteins as detected by immunohistochemistry analyses. Accordingly, CA were labeled with different anti-fungal antibodies at the external surface, whereas the central portion composed of calcium salts contain less proteins. Detection of fungal proteins was achieved using a number of antibodies raised against different fungal species, which indicated cross-reactivity between the fungal proteins present in CA and the antibodies employed. Importantly, these antibodies do not immunoreact with cellular proteins. Additionally, CNS samples from patients diagnosed with amyotrophic lateral sclerosis (ALS) and Parkinson's disease (PD) also contained CA that were immunoreactive with a range of antifungal antibodies. However, CA were less abundant in ALS or PD patients as compared to CNS samples from AD. By contrast, CA from brain tissue of control subjects were almost devoid of fungal immunoreactivity. These observations are consistent with the concept that CA associate with fungal infections and may contribute to the elucidation of the origin of CA.

Inactivation of human kininogen-derived antimicrobial peptides by secreted aspartic proteases produced by the pathogenic yeast Candida albicans

Ten secreted aspartic proteases (Saps) of Candida albicans cleave numerous peptides and proteins in the host organism and deregulate its homeostasis. Human kininogens contain two internal antimicrobial peptide sequences, designated NAT26 and HKH20. In our current study, we characterized a Sap-catalyzed cleavage of kininogen-derived antimicrobial peptides that results in the loss of the anticandidal activity of these peptides. The NAT26 peptide was effectively inactivated by all Saps, except Sap10, whereas HKH20 was completely degraded only by Sap9. Proteolytic deactivation of the antifungal potential of human kininogens can help the pathogens to modulate or evade the innate immunity of the host.

Design and studies of multiple mechanism of anti-Candida activity of a new potent Trp-rich peptide dendrimers

PURPOSE

Eight peptide dendrimers were designed as structural mimics of natural cationic amphiphilic peptides with antifungal activity and evaluated for their anti-Candida potential against the wild type strains and mutants.

METHODS

Dendrimer 14 containing four Trp residues and dodecyl tail and a slightly smaller dendrimer 9 decorated with four N-methylated Trp that displayed 100 and 99.7% of growth inhibition at 16 μg/mL respectively, were selected for evaluation against the Candida albicans mutants with disabled biosynthesis of aspartic proteases responsible for host tissue colonization and morphogenesis during biofilm formation (sessile model). Flow cytometry method was employed to detect apoptotic cells with membrane alterations (phosphatidylserine translocation), and differentiation of apoptotic from necrotic cells was also performed. Simultaneous staining of cell surface phosphatidylserine with Annexin-V-Fluorescein and necrotic cells with propidium iodide was conducted.

RESULTS

14 at 16 μg/mL caused C. albicans cells to undergo cellular apoptosis but its increasing concentrations induced necrosis. 14 influenced C. albicans biofilm viability as well as hyphal and cell wall morphology. Confocal microscopy and cell wall staining with calcofluor white revealed that in epithelial model the cell surface structure was perturbed at MIC of peptide dendrimer. It appears that tryptophan or 1-methyltryptophan groups displayed at the surface and positive charges hidden in the dendrimer tree along with hydrocarbon tail located at C-terminus are important for the anti-Candida activity since dendrimers containing tryptamine at C-terminus showed only a moderate activity.

CONCLUSIONS

Our results suggest that membranolytic dendrimer 14, targeting cellular apoptotic pathway and impairing the cell wall formation in mature biofilm, may be a potential multifunctional antifungal lead compound for the control of C. albicans infections.

Rapid and simple purification of lysozyme from the egg shell membrane

Lysozyme (EC 3.2.1.17) is a hydrolytic enzyme that cleaves the β-(1,4)-glycosidic bond between N-acetylmuramic acid and N-acetylglucosamine in peptidoglycan, a major bacterial cell wall polymer. In the food industry, lysozyme is used as an additive mainly in the production of wine and beer. Lysozyme was found to be localized in the egg shell membrane. In this study, we found that lysozyme was easily purified from the egg shell membrane and that the enzyme also had antibacterial activity. Furthermore, we found that the antibacterial activity of purified lysozyme from the egg shell membrane was lower than that of purified lysozyme from the egg white at alkaline pH. The method for rapid purification of lysozyme developed in this study should contribute to the food industry.

Signaling domains of mucin Msb2 in Candida albicans

Candida albicans adapts to the human host by environmental sensing using the Msb2 signal mucin, which regulates fungal morphogenesis and resistance characteristics. Msb2 is anchored within the cytoplasmic membrane by a single transmembrane (TM) region dividing it into a large N-terminal exodomain, which is shed, and a small cytoplasmic domain. Analyses of strains carrying deleted Msb2 variants revealed an exodomain segment required for cleavage, shedding, and all functions of Msb2. Phosphorylation of the mitogen-activated protein kinase (MAP kinase) Cek1 was regulated by three distinct regions in Msb2: in unstressed cells, N-terminal sequences repressed phosphorylation, while its induction under cell wall stress required the cytoplasmic tail (C-tail) and sequences N-terminally flanking the TM region, downstream of the proposed cleavage site. Within the latter Msb2 region, overlapping but not identical sequences were also required for hyphal morphogenesis, basal resistance to antifungals, and, in unstressed cells, downregulation of the PMT1 transcript, encoding protein O-mannosyltransferase-1. Deletion of two-thirds of the exodomain generated a truncated Msb2 variant with a striking ability to induce hyperfilamentous growth, which depended on the presence of the Msb2-interacting protein Sho1, the MAP kinase Cek1, and the Efg1 transcription factor. Under cell wall stress, the cytoplasmic tail relocalized partially to the nucleus and contributed to regulation of 117 genes, as revealed by transcriptomic analyses. Genes regulated by the C-tail contained binding sites for the Ace2 and Azf1 transcription factors and included the ALS cell wall genes. We concluded that Msb2 fulfills its numerous functions by employing functional domains that are distributed over its entire length.

Mitigation of human-pathogenic fungi that exhibit resistance to medical agents: can clinical antifungal stewardship help?

Reducing indiscriminate antimicrobial usage to combat the expansion of multidrug-resistant human-pathogenic bacteria is fundamental to clinical antibiotic stewardship. In contrast to bacteria, fungal resistance traits are not understood to be propagated via mobile genetic elements, and it has been proposed that a global explosion of resistance to medical antifungals is therefore unlikely. Clinical antifungal stewardship has focused instead on reducing the drug toxicity and high costs associated with medical agents. Mitigating the problem of human-pathogenic fungi that exhibit resistance to antimicrobials is an emergent issue. This article addresses the extent to which clinical antifungal stewardship could influence the scale and epidemiology of resistance to medical antifungals both now and in the future. The importance of uncharted selection pressure exerted by agents outside the clinical setting (agricultural pesticides, industrial xenobiotics, biocides, pharmaceutical waste and others) on environmentally ubiquitous spore-forming molds that are lesserstudied but increasingly responsible for drug-refractory infections is considered.

Cationic membrane-active peptides - anticancer and antifungal activity as well as penetration into human skin

Cationic antimicrobial peptides are ancient natural broad-spectrum antibiotics, and several compounds also exhibit anticancer activity. However, most applications pertain to bacterial infections, and treatment for skin cancer is less frequently considered. The cytotoxicity of melittin, cecropin A, protegrin-1 and histatin 5 against squamous skin cancer cell lines and normal human keratinocytes was evaluated and compared to established drugs. The results show that melittin clearly outperforms 5-fluorouracil regarding antitumor activity. Importantly, combined melittin and 5-fluorouracil enhanced cytotoxic effects on cancer cells and reduced toxicity on normal keratinocytes. Additionally, minimum inhibitory concentrations indicate that melittin also shows superior activity against clinical and laboratory strains of Candida albicans compared to amphotericin B. To evaluate its potential for topical applications, human skin penetration of melittin was investigated ex vivo and compared to two non-toxic cell-penetrating peptides (CPPs), low molecular weight protamine (LMWP) and penetratin. The stratum corneum prevents penetration into viable epidermis over 6 h; however, the peptides gain access to the viable skin after 24 h. Inhibition of digestive enzymes during skin penetration significantly enhances the availability of intact peptide. In conclusion, melittin may represent an innovative agent for non-melanoma skin cancer and infectious skin diseases. In order to develop a drug candidate, skin absorption and proteolytic digestion by skin enzymes need to be addressed.

Interplay between Candida albicans and the antimicrobial peptide armory

Antimicrobial peptides (AMPs) are key elements of innate immunity, which can directly kill multiple bacterial, viral, and fungal pathogens. The medically important fungus Candida albicans colonizes different host niches as part of the normal human microbiota. Proliferation of C. albicans is regulated through a complex balance of host immune defense mechanisms and fungal responses. Expression of AMPs against pathogenic fungi is differentially regulated and initiated by interactions of a variety of fungal pathogen-associated molecular patterns (PAMPs) with pattern recognition receptors (PRRs) on human cells. Inflammatory signaling and other environmental stimuli are also essential to control fungal proliferation and to prevent parasitism. To persist in the host, C. albicans has developed a three-phase AMP evasion strategy, including secretion of peptide effectors, AMP efflux pumps, and regulation of signaling pathways. These mechanisms prevent C. albicans from the antifungal activity of the major AMP classes, including cathelicidins, histatins, and defensins leading to a basal resistance. This minireview summarizes human AMP attack and C. albicans resistance mechanisms and current developments in the use of AMPs as antifungal agents.

The interaction of aurein 2.5 with fungal membranes

Aurein 2.5 (GLFDIVKKVVGAFGSL-NH2) is an antimicrobial peptide, which was seen to have activity against Stachybotris chartarum, Penicillium roseopurpureum and Aspergillus flavus with minimum fungicidal concentrations in the range 250-500 μM. S. chartarum showed enhanced susceptibility to lysis as compared to P. roseopurpureum and A. flavus, (44, 26 and 28 % respectively). Monolayers formed from lipid membrane extracts derived from S. chartarum, P. roseopurpureum and A. flavus showed maximal surface pressure changes of 13.5, 10.3 and 10.2 mN m(-1) respectively. However, aurein 2.5 adopted similar levels of α-helical structure (circa 45 %) in the presence of vesicles formed from membrane lipid extracts derived from all three fungi. These data imply that differential activity is not due to targeting and membrane association but linked to the ability of the bound peptide to lyse the cells. At sterol levels mimetic of eukaryotic systems, high levels of α-helical structure (circa 50 %) were also observed and hence similar binding. However, enhanced sterol levels (>0.6) led to a reduction in monolayer membrane interaction, suggesting that the sterols influence efficacy. Consistent with this suggestion, thermodynamic analysis showed that the peptide was able to destabilise model fungal monolayers, as indicated by negative values of ∆Gmix.

Defensins: antifungal lessons from eukaryotes

Over the last years, antimicrobial peptides (AMPs) have been the focus of intense research toward the finding of a viable alternative to current antifungal drugs. Defensins are one of the major families of AMPs and the most represented among all eukaryotic groups, providing an important first line of host defense against pathogenic microorganisms. Several of these cysteine-stabilized peptides present a relevant effect against fungi. Defensins are the AMPs with the broader distribution across all eukaryotic kingdoms, namely, Fungi, Plantae, and Animalia, and were recently shown to have an ancestor in a bacterial organism. As a part of the host defense, defensins act as an important vehicle of information between innate and adaptive immune system and have a role in immunomodulation. This multidimensionality represents a powerful host shield, hard for microorganisms to overcome using single approach resistance strategies. Pathogenic fungi resistance to conventional antimycotic drugs is becoming a major problem. Defensins, as other AMPs, have shown to be an effective alternative to the current antimycotic therapies, demonstrating potential as novel therapeutic agents or drug leads. In this review, we summarize the current knowledge on some eukaryotic defensins with antifungal action. An overview of the main targets in the fungal cell and the mechanism of action of these AMPs (namely, the selectivity for some fungal membrane components) are presented. Additionally, recent works on antifungal defensins structure, activity, and cytotoxicity are also reviewed.

Antibiotic development challenges: the various mechanisms of action of antimicrobial peptides and of bacterial resistance

Antimicrobial peptides (AMPs) are natural antibiotics produced by various organisms such as mammals, arthropods, plants, and bacteria. In addition to antimicrobial activity, AMPs can induce chemokine production, accelerate angiogenesis, and wound healing and modulate apoptosis in multicellular organisms. Originally, their antimicrobial mechanism of action was thought to consist solely of an increase in pathogen cell membrane permeability, but it has already been shown that several AMPs do not modulate membrane permeability in the minimal lethal concentration. Instead, they exert their effects by inhibiting processes such as protein and cell wall synthesis, as well as enzyme activity, among others. Although resistance to these molecules is uncommon several pathogens developed different strategies to overcome AMPs killing such as surface modification, expression of efflux pumps, and secretion of proteases among others. This review describes the various mechanisms of action of AMPs and how pathogens evolve resistance to them.

C. albicans growth, transition, biofilm formation, and gene expression modulation by antimicrobial decapeptide KSL-W

Background

Antimicrobial peptides have been the focus of much research over the last decade because of their effectiveness and broad-spectrum activity against microbial pathogens. These peptides also participate in inflammation and the innate host defense system by modulating the immune function that promotes immune cell adhesion and migration as well as the respiratory burst, which makes them even more attractive as therapeutic agents. This has led to the synthesis of various antimicrobial peptides, including KSL-W (KKVVFWVKFK-NH₂), for potential clinical use. Because this peptide displays antimicrobial activity against bacteria, we sought to determine its antifungal effect on C. albicans. Growth, hyphal form, biofilm formation, and degradation were thus examined along with EFG1, NRG1, EAP1, HWP1, and SAP 2-4-5-6 gene expression by quantitative RT-PCR.

Results

This study demonstrates that KSL-W markedly reduced C. albicans growth at both early and late incubation times. The significant effect of KSL-W on C. albicans growth was observed beginning at 10 μg/ml after 5 h of contact by reducing C. albicans transition and at 25 μg/ml by completely inhibiting C. albicans transition. Cultured C. albicans under biofilm-inducing conditions revealed that both KSL-W and amphotericin B significantly decreased biofilm formation at 2, 4, and 6 days of culture. KSL-W also disrupted mature C. albicans biofilms. The effect of KSL-W on C. albicans growth, transition, and biofilm formation/disruption may thus occur through gene modulation, as the expression of various genes involved in C. albicans growth, transition and biofilm formation were all downregulated when C. albicans was treated with KSL-W. The effect was greater when C. albicans was cultured under hyphae-inducing conditions.

Conclusions

These data provide new insight into the efficacy of KSL-W against C. albicans and its potential use as an antifungal therapy.

Antimicrobial activity of aurein 2.5 against yeasts

Fungal infections with multiple resistance to conventional antifungals are increasingly becoming a medical problem, and there is an urgent need for new antifungal compounds with novel mechanisms of action. Here, we show that aurein 2.5, a naturally occurring peptide antibiotic, displays activity against the fungal strains: Rhodotorula rubra and Schizosaccharomyces pombe (MICs < 130 μM). The peptide adopted high levels of membrane-interactive α-helical structure (> 65%) in the presence of lipid membranes derived from these organisms and showed strong propensities to penetrate (π ≥ 13 mN m(-1) ) and lyse them (> 70%). Based on these data, we suggest that aurein 2.5 kills yeasts via membranolytic mechanisms and may act as a template for the development of therapeutically useful antifungal agents.