Distinct antifungal mechanisms: beta-defensins require Candida albicans Ssa1 protein, while Trk1p mediates activity of cysteine-free cationic peptides

Applications of β-defensins against infectious pathogenic microorganisms

INTRODUCTION

Antimicrobial peptides (AMPs) are polypeptides with potent antimicrobial activity against a broad range of pathogenic microorganisms. Unlike conventional antibiotics, AMPs have rapid bactericidal activity, a low capacity for inducing resistance, and compatibility with the host immune system. A large body of data supports the antimicrobial activities of a large body of data supports the antimicrobial activities of the class of AMPs known as β-defensins. This review provides a comprehensive analysis of the effects of β-defensins against various pathogenic microorganism: bacteria, fungi, viruses, Mycoplasmas and Chlamydiae. The primary mechanisms of β-defensins against pathogenic microorganisms include inhibition of biofilms formations, dissolution of membranes, disruption of cell walls, and inhibition of adhesion and receptor binding. Although further study and structural modifications are needed, β-defensins are promising candidates for antimicrobial therapy.

AREAS COVERED

This review describes the inhibitory effects of β-defensins on various pathogenic microorganisms. Additionally, we focus on elucidating the mechanisms underlying their actions to provide, providing valuable references for the further study of β-defensins.

EXPERT OPINION

The biological activities and modes of action of β-defensins provide powerful resources for clinical microbial infection management. Addressing the salt sensitivity and toxicity of β-defensins may further enhance their potential applications.

Human β-defensins and their synthetic analogs: Natural defenders and prospective new drugs of oral health

As a family of cationic host defense peptides, human β-defensins (HBDs) are ubiquitous in the oral cavity and are mainly synthesized primarily by epithelial cells, serving as the primary barrier and aiming to prevent microbial invasion, inflammation, and disease while maintaining physiological homeostasis. In recent decades, there has been great interest in their biological functions, structure-activity relationships, mechanisms of action, and therapeutic potential in oral diseases. Meanwhile, researchers are dedicated to improving the properties of HBDs for clinical application. In this review, we first describe the classification, structural characteristics, functions, and mechanisms of HBDs. Next, we cover the role of HBDs and their synthetic analogs in oral diseases, including dental caries and pulp infections, periodontitis, peri-implantitis, fungal/viral infections and oral mucosal diseases, and oral squamous cell carcinoma. Finally, we discuss the limitations and challenges of clinical translation of HBDs and their synthetic analogs, including, but not limited to, stability, bioavailability, antimicrobial activity, resistance, and toxicity. Above all, this review summarizes the biological functions, mechanisms of action, and therapeutic potential of both natural HBDs and their synthetic analogs in oral diseases, as well as the challenges associated with clinical translation, thus providing substantial insights into the laboratory development and clinical application of HBDs in oral diseases.

Pathophysiological microenvironments in oral candidiasis

Oral candidiasis (OC), a prevalent opportunistic infection of the oral mucosa, presents a considerable health challenge, particularly in individuals with compromised immune responses, advanced age, and local predisposing conditions. A considerable part of the population carries Candida in the oral cavity, but only few develop OC. Therefore, the pathogenesis of OC may depend on factors other than the attributes of the fungus, such as host factors and other predisposing factors. Mucosal trauma and inflammation compromise epithelial integrity, fostering a conducive environment for fungal invasion. Molecular insights into the immunocompromised state reveal dysregulation in innate and adaptive immunity, creating a permissive environment for Candida proliferation. Detailed examination of Candida species (spp.) and their virulence factors uncovers a nuanced understanding beyond traditional C. albicans focus, which embrace diverse Candida spp. and their strategies, influencing adhesion, invasion, immune evasion, and biofilm formation. Understanding the pathophysiological microenvironments in OC is crucial for the development of targeted therapeutic interventions. This review aims to unravel the diverse pathophysiological microenvironments influencing OC development focusing on microbial, host, and predisposing factors, and considers Candida resistance to antifungal therapy. The comprehensive approach offers a refined perspective on OC, seeking briefly to identify potential therapeutic targets for future effective management.

IκBζ is an essential mediator of immunity to oropharyngeal candidiasis

Fungal infections are a global threat; yet, there are no licensed vaccines to any fungal pathogens. Th17 cells mediate immunity to Candida albicans, particularly oropharyngeal candidiasis (OPC), but essential downstream mechanisms remain unclear. In the murine model of OPC, IκBζ (Nfkbiz, a non-canonical NF-κB transcription factor) was upregulated in an interleukin (IL)-17-dependent manner and was essential to prevent candidiasis. Deletion of Nfkbiz rendered mice highly susceptible to OPC. IκBζ was dispensable in hematopoietic cells and acted partially in the suprabasal oral epithelium to control OPC. One prominent IκBζ-dependent gene target was β-defensin 3 (BD3) (Defb3), an essential antimicrobial peptide. Human oral epithelial cells required IκBζ for IL-17-mediated induction of BD2 (DEFB4A, human ortholog of mouse Defb3) through binding to the DEFB4A promoter. Unexpectedly, IκBζ regulated the transcription factor Egr3, which was essential for C. albicans induction of BD2/DEFB4A. Accordingly, IκBζ and Egr3 comprise an antifungal signaling hub mediating mucosal defense against oral candidiasis.

Ssa1-targeted antibody prevents host invasion by Candida albicans

INTRODUCTION

Candida albicans is a commensal fungus that colonizes most healthy individuals' skin and mucosal surfaces but can also cause life-threatening invasive infections, particularly in immunocompromised patients. Despite antifungal treatment availability, drug resistance is increasing, and mortality rates remain unacceptably high. Heat shock protein Ssa1, a conserved member of the Hsp70 family in yeast, is a novel invasin that binds to host cell cadherins, induces host cell endocytosis, and enables C. albicans to cause maximal damage to host cells and induces disseminated and oropharyngeal disease.

RESULT

Here we discovered a mouse monoclonal antibody (mAb 13F4) that targeting C. albicans Ssa1 with high affinity (EC50 = 39.78 ng/mL). mAb 13F4 prevented C. albicans from adhering to and invading human epithelial cells, displayed antifungal activity, and synergized with fluconazole in proof of concept in vivo studies. mAb 13F4 significantly prolonged the survival rate of the hematogenous disseminated candidiasis mice to 75%. We constructed a mAb 13F4 three-dimensional structure using homology modeling methods and found that the antigen-binding fragment (Fab) interacts with the Ssa1 N-terminus.

DISCUSSION

These results suggest that blocking Ssa1 cell surface function may effectively control invasive C. albicans infections and provide a potential new treatment strategy for invasive fungal infections.

Fungicidal activity of human antimicrobial peptides and their synergistic interaction with common antifungals against multidrug-resistant Candida auris

Emergence of Candida auris, a multidrug-resistant yeast, demonstrates the urgent need for novel antifungal agents. Human antimicrobial peptides (AMPs) are naturally occurring molecules with wide spectrum antimicrobial activity, particularly against a variety of fungi. Therefore, this study examined the antifungal activity of seven different human AMPs against C. auris following the CLSI guidelines. The antifungal activity was further assessed using time kill curve and cell viability assays. For combination interaction, effectiveness of these peptides with three antifungals, fluconazole, amphotericin B, and caspofungin was done following standard protocols. To elucidate the antifungal mechanism, the effects of peptides on membrane permeability were investigated using propidium iodide staining method and confocal imaging. Antifungal susceptibility results showed that all the examined peptides possessed fungicidal effect against C. auris at different levels, with human β-defensin-3 being the most potent antifungal with MIC values ranging from 3.125 to 12.5 µg/ml. Time kill curves further confirmed the killing effect of all the tested peptides. Viability assay showed a significant decrease in the percentage of viable cells exposed to different inhibitory and fungicidal concentrations of each peptide (p < 0.01). Furthermore, peptides showed mostly synergistic interaction when combined with conventional antifungal drugs, with caspofungin showing 100% synergy when combined with different AMPs. As antifungal mechanism, peptides disrupted the membrane permeability at concentrations that correlated with the inhibition of growth. Overall, the findings of this study point towards the application of the tested peptides as a monotherapy or as a combination therapy with antifungal drugs to treat multidrug-resistant C. auris infections.

Defensins: defenders of human reproductive health

BACKGROUND

Reproductive tract infection is an important factor leading to male and female infertility. Among female infertility factors, microbial and viral infections are the main factors affecting female reproductive health and causing tubal infertility, ectopic tubal pregnancy and premature delivery. Among male infertility factors, 13-15% of male infertility is related to infection. Defensins are cationic antibacterial and antiviral peptides, classified into α-defensins, β-defensins and θ-defensins. Humans only have α-defensins and β-defensins. Apart from their direct antimicrobial functions, defensins have an immunomodulatory function and are involved in many physiological processes. Studies have shown that defensins are widely distributed in the female reproductive tract (FRT) and male reproductive tract (MRT), playing a dual role of host defence and fertility protection. However, to our knowledge, the distribution, regulation and function of defensins in the reproductive tract and their relation to reproduction have not been reviewed.

OBJECTIVE AND RATIONALE

This review summarizes the expression, distribution and regulation of defensins in the reproductive tracts to reveal the updated research on the dual role of defensins in host defence and the protection of fertility.

SEARCH METHODS

A systematic search was conducted in PubMed using the related keywords through April 2022. Related data from original researches and reviews were integrated to comprehensively review the current findings and understanding of defensins in the human reproductive system. Meanwhile, female and male transcriptome data in the GEO database were screened to analyze defensins in the human reproductive tracts.

OUTCOMES

Two transcriptome databases from the GEO database (GSE7307 and GSE150852) combined with existing researches reveal the expression levels and role of the defensins in the reproductive tracts. In the FRT, a high expression level of α-defensin is found, and the expression levels of defensins in the vulva and vagina are higher than those in other organs. The expression of defensins in the endometrium varies with menstrual cycle stages and with microbial invasion. Defensins also participate in the local immune response to regulate the risk of spontaneous preterm birth. In the MRT, a high expression level of β-defensins is also found. It is mainly highly expressed in the epididymal caput and corpus, indicating that defensins play an important role in sperm maturation. The expression of defensins in the MRT varies with androgen levels, age and the status of microbial invasion. They protect the male reproductive system from bacterial infections by neutralizing lipopolysaccharide and downregulating pro-inflammatory cytokines. In addition, animal and clinical studies have shown that defensins play an important role in sperm maturation, motility and fertilization.

WIDER IMPLICATIONS

As a broad-spectrum antimicrobial peptide without drug resistance, defensin has great potential for developing new natural antimicrobial treatments for reproductive tract infections. However, increasing evidence has shown that defensins can not only inhibit microbial invasion but can also promote the invasion and adhesion of some microorganisms in certain biological environments, such as human immunodeficiency virus. Therefore, the safety of defensins as reproductive tract anti-infective drugs needs more in-depth research. In addition, the modulatory role of defensins in fertility requires more in-depth research since the current conclusions are based on small-size samples. At present, scientists have made many attempts at the clinical transformation of defensins. However, defensins have problems such as poor stability, low bioavailability and difficulties in their synthesis. Therefore, the production of safe, effective and low-cost drugs remains a challenge.

Antimicrobial Peptides with Anti-Candida Activity

Mycoses are accountable for millions of infections yearly worldwide. Invasive candidiasis is the most usual, presenting a high morbidity and mortality. Candida albicans remains the prevalent etiologic agent, but the incidence of other species such as Candida parapsilosis, Candida glabrata and Candida auris keeps increasing. These pathogens frequently show a reduced susceptibility to commonly used antifungal drugs, including polyenes, triazoles and echinocandins, and the incidence of emerging multi-drug-resistant strains of these species continues to increase. Therefore, the need to search for new molecules that target these pathogenic species in a different manner is now more urgent than ever. Nature is an almost endless source of interesting new molecules that could meet this need. Among these molecules, antimicrobial peptides, present in different sources in nature, possess some advantages over conventional antifungal agents, even with their own drawbacks, and are considered as a promising pharmacological option against a wide range of microbial infections. In this review, we describe 20 antimicrobial peptides from different origins that possess an activity against Candida.

Oral Cavity and Candida albicans: Colonisation to the Development of Infection

Candida colonisation of the oral cavity increases in immunocompromised individuals which leads to the development of oral candidiasis. In addition, host factors such as xerostomia, smoking, oral prostheses, dental caries, diabetes and cancer treatment accelerate the disease process. Candida albicans is the primary causative agent of this infection, owing to its ability to form biofilm and hyphae and to produce hydrolytic enzymes and candialysin. Although mucosal immunity is activated, from the time hyphae-associated toxin is formed by the colonising C. albicans cells, an increased number and virulence of this pathogenic organism collectively leads to infection. Prevention of the development of infection can be achieved by addressing the host physiological factors and habits. For maintenance of oral health, conventional oral hygiene products containing antimicrobial compounds, essential oils and phytochemicals can be considered, these products can maintain the low number of Candida in the oral cavity and reduce their virulence. Vulnerable patients should be educated in order to increase compliance.

Opportunistic yeast pathogen Candida spp.: Secreted and membrane-bound virulence factors

Candidiasis is a fungal infection caused by Candida spp. especially Candida albicans, C. glabrata, C. parapsilosis and C. tropicalis. Although the medicinal therapeutic strategies have rapidly improved, the mortality rate due to candidiasis has continuously increased. The secreted and membrane-bound virulence factors (VFs) are responsible for fungal invasion, damage and translocation through the host enterocytes besides the evasion from host immune system. VFs such as agglutinin-like sequences (Als), heat shock protein 70, phospholipases, secreted aspartyl proteinases (Sap), lipases, enolases and phytases are mostly hydrolases which degrade the enterocyte membrane components except for candidalysin, the VF acts as a peptide toxin to induce necrotic cell lysis. To date, structural studies of the VFs remain underexplored, hindering their functional analyses. Among the VFs, only secreted aspartyl proteinases and agglutinin-like sequences have their structures deposited in Protein Data Bank (PDB). Therefore, this review scrutinizes the mechanisms of these VFs by discussing the VF-deficient studies of several Candida spp. and their abilities to produce these VFs. Nonetheless, their latest reported sequential and structural analyses are discussed to impart a wider perception of the host-pathogen interactions and potential vaccine or antifungal drug targets. This review signifies that more VFs structural investigations and mining in the emerging Candida spp. are required to decipher their pathogenicity and virulence mechanisms compared to the prominent C. albicans.

LAY ABSTRACT

Candida virulence factors (VFs) including mainly enzymes and proteins play vital roles in breaching the human intestinal barrier and causing deadly candidiasis. Limited VFs' structural studies hinder deeper comprehension of their mechanisms and thus the design of vaccines and antifungal drugs against fungal infections.

Membrane-Interacting Antifungal Peptides

The incidence of invasive fungal infections is increasing worldwide, resulting in more than 1.6 million deaths every year. Due to growing antifungal drug resistance and the limited number of currently used antimycotics, there is a clear need for novel antifungal strategies. In this context, great potential is attributed to antimicrobial peptides (AMPs) that are part of the innate immune system of organisms. These peptides are known for their broad-spectrum activity that can be directed toward bacteria, fungi, viruses, and/or even cancer cells. Some AMPs act via rapid physical disruption of microbial cell membranes at high concentrations causing cell leakage and cell death. However, more complex mechanisms are also observed, such as interaction with specific lipids, production of reactive oxygen species, programmed cell death, and autophagy. This review summarizes the structure and mode of action of antifungal AMPs, thereby focusing on their interaction with fungal membranes.

Regulation and activity of CaTrk1, CaAcu1 and CaHak1, the three plasma membrane potassium transporters in Candida albicans

Wild-type cells of Candida albicans, the most common human fungal pathogen, are able to grow at very low micromolar concentrations of potassium in the external milieu. One of the reasons behind that behaviour is the existence of three different types of K⁺ transporters in their plasma membrane: Trk1, Acu1 and Hak1. This work shows that the transporters are very differently regulated at the transcriptional level upon exposure to saline stress, pH alterations or K⁺ starvation. We propose that different transporters take the lead in the diverse environmental conditions, Trk1 being the "house-keeping" one, and Acu1/Hak1 dominating upon K⁺ limiting conditions. Heterologous expression of the genes coding for the three transporters in a Saccharomyces cerevisiae strain lacking its endogenous potassium transporters showed that all of them mediated cation transport but with very different efficiencies. Moreover, expression of the transporters in S. cerevisiae also affected other physiological characteristics such as sodium and lithium tolerance, membrane potential or intracellular pH, being, in general, CaTrk1 the most effective in keeping these parameters close to the usual wild-type physiological levels.

Effect of Disulfide Cyclization of Ultrashort Cationic Lipopeptides on Antimicrobial Activity and Cytotoxicity

Ultrashort cationic lipopeptides (USCLs) are considered to be a promising class of antimicrobials with high activity against a broad-spectrum of microorganisms. However, the majority of these compounds are characterized by significant toxicity toward human cells, which hinders their potential application. To overcome those limitations, several approaches have been advanced. One of these is disulfide cyclization that has been shown to improve drug-like characteristics of peptides. In this article the effect of disulfide cyclization of the polar head of N-palmitoylated USCLs on in vitro biological activity has been studied. Lipopeptides used in this study consisted of three or four basic amino acids (lysine and arginine) and cystine in a cyclic peptide. In general, disulfide cyclization of the lipopeptides resulted in peptides with reduced cytotoxicity. Disulfide-cyclized USCLs exhibited improved selectivity between Candida sp., Gram-positive strains and normal cells in contrast to their linear counterparts. Interactions between selected USCLs and membranes were studied by molecular dynamics simulations using a coarse-grained force field. Moreover, membrane permeabilization properties and kinetics were examined. Fluorescence and transmission electron microscopy revealed damage to Candida cell membrane and organelles. Concluding, USCLs are strong membrane disruptors and disulfide cyclization of polar head can have a beneficial effect on its in vitro selectivity between Candida sp. and normal human cells.

Antivirulence and avirulence genes in human pathogenic fungi

Opportunistic commensal and environmental fungi can cause superficial to systemic diseases in humans. But how did these pathogens adapt to infect us and how does host-pathogen co-evolution shape their virulence potential? During evolution toward pathogenicity, not only do microorganisms gain virulence genes, but they also tend to lose non-adaptive genes in the host niche. Additionally, virulence factors can become detrimental during infection when they trigger host recognition. The loss of non-adaptive genes as well as the loss of the virulence potential of genes by adaptations to the host has been investigated in pathogenic bacteria and phytopathogenic fungi, where they are known as antivirulence and avirulence genes, respectively. However, these concepts are nearly unknown in the field of pathogenic fungi of humans. We think that this unnecessarily limits our view of human-fungal interplay, and that much could be learned if we applied a similar framework to aspects of these interactions. In this review, we, therefore, define and adapt the concepts of antivirulence and avirulence genes for human pathogenic fungi. We provide examples for analogies to antivirulence genes of bacterial pathogens and to avirulence genes of phytopathogenic fungi. Introducing these terms to the field of pathogenic fungi of humans can help to better comprehend the emergence and evolution of fungal virulence and disease.

An IL-17F.S65L Knock-In Mouse Reveals Similarities and Differences in IL-17F Function in Oral Candidiasis: A New Tool to Understand IL-17F

Oropharyngeal candidiasis (OPC) is an opportunistic infection of the oral mucosa caused by the commensal fungus Candida albicans IL-17R signaling is essential to prevent OPC in mice and humans, but the individual roles of its ligands, IL-17A, IL-17F, and IL-17AF, are less clear. A homozygous IL-17F deficiency in mice does not cause OPC susceptibility, whereas mice lacking IL-17A are moderately susceptible. In humans, a rare heterozygous mutation in IL-17F (IL-17F.S65L) was identified that causes chronic mucocutaneous candidiasis, suggesting the existence of essential antifungal pathways mediated by IL-17F and/or IL-17AF. To investigate the role of IL-17F and IL-17AF in more detail, we exploited this "experiment of nature" by creating a mouse line bearing the homologous mutation in IL-17F (Ser65Leu) by CRISPR/Cas9. Unlike Il17f^-/- mice that are resistant to OPC, Il17f^S65L/S65L mice showed increased oral fungal burdens similar to Il17a ^-/- mice. In contrast to humans, however, disease was only evident in homozygous, not heterozygous, mutant mice. The mutation was linked to modestly impaired CXC chemokine expression and neutrophil recruitment to the infected tongue but not to alterations in oral antimicrobial peptide expression. These findings suggest mechanisms by which the enigmatic cytokine IL-17F contributes to host defense against fungi. Moreover, because these mice do not phenocopy Il17f^-/- mice, they may provide a valuable tool to interrogate IL-17F and IL-17AF function in vivo in other settings.

Candida albicans Interactions with Mucosal Surfaces during Health and Disease

Flexible adaptation to the host environment is a critical trait that underpins the success of numerous microbes. The polymorphic fungus Candida albicans has evolved to persist in the numerous challenging niches of the human body. The interaction of C. albicans with a mucosal surface is an essential prerequisite for fungal colonisation and epitomises the complex interface between microbe and host. C. albicans exhibits numerous adaptations to a healthy host that permit commensal colonisation of mucosal surfaces without provoking an overt immune response that may lead to clearance. Conversely, fungal adaptation to impaired immune fitness at mucosal surfaces enables pathogenic infiltration into underlying tissues, often with devastating consequences. This review will summarise our current understanding of the complex interactions that occur between C. albicans and the mucosal surfaces of the human body.

β-Defensins: Farming the Microbiome for Homeostasis and Health

Diverse commensal populations are now regarded as key to physiological homeostasis and protection against disease. Although bacteria are the most abundant component of microbiomes, and the most intensively studied, the microbiome also consists of viral, fungal, archael, and protozoan communities, about which comparatively little is known. Host-defense peptides (HDPs), originally described as antimicrobial, now have renewed significance as curators of the pervasive microbial loads required to maintain homeostasis and manage microbiome diversity. Harnessing HDP biology to transition away from non-selective, antibiotic-mediated treatments for clearance of microbes is a new paradigm, particularly in veterinary medicine. One family of evolutionarily conserved HDPs, β-defensins which are produced in diverse combinations by epithelial and immune cell populations, are multifunctional cationic peptides which manage the cross-talk between host and microbes and maintain a healthy yet dynamic equilibrium across mucosal systems. They are therefore key gatekeepers to the oral, respiratory, reproductive and enteric tissues, preventing pathogen-associated inflammation and disease and maintaining physiological normality. Expansions in the number of genes encoding these natural antibiotics have been described in the genomes of some species, the functional significance of which has only recently being appreciated. β-defensin expression has been documented pre-birth and disruptions in their regulation may play a role in maladaptive neonatal immune programming, thereby contributing to subsequent disease susceptibility. Here we review recent evidence supporting a critical role for β-defensins as farmers of the pervasive and complex prokaryotic ecosystems that occupy all body surfaces and cavities. We also share some new perspectives on the role of β-defensins as sensors of homeostasis and the immune vanguard particularly at sites of immunological privilege where inflammation is attenuated.

Self-assembly and biological activities of ionic liquid crystals derived from aromatic amino acids

The self-assembly of amino acid-derived ionic liquid crystals (ILCs) into lamellar or micellar-like aggregates suggests that they might interact with biological membranes. To get some insight, guanidinium chlorides derived from the natural l-amino acids phenylalanine (Phe), tyrosine (Tyr) and 3,4-dihydroxyphenylalanine (DOPA) were synthesized and their mesomorphic properties were investigated via polarizing optical microscopy (POM), differential scanning calorimetry (DSC) and X-ray diffraction (SAXS, WAXS). Mesophase types depended on the number of alkoxy side chains. Phe- and Tyr-based ILCs with one and two side chains, respectively, self-assembled into smectic A bilayers (SmA2), while Dopa-derived ILCs with three side chains formed columnar (Colh) mesophases. The mesophase ranges for Phe ILCs increased steadily with side chain length, for Tyr- and Dopa-based ILCs, however, size matching effects were observed. To clarify whether the mesomorphic behaviour has an impact on biological properties, cytotoxic and antibacterial activities of the ILCs were studied. Phe and Tyr ILCs exhibited much higher cytotoxicities (against the L-929 mouse fibroblast cell line) and/or antibacterial activities (against Staphylococcus aureus) than Dopa ILCs, which were mostly inactive. Furthermore, within each series, the side chain length largely influenced the biological activity. Thus, the bulk mesophase behaviour appeared to correlate with the biological properties, in particular, the interactions with membranes, as shown by measuring the intracellular Ca2+ concentration in human monocytic U937 cells after treatment with the amino acid-based ILCs.

Adaptation of Candida albicans during gastrointestinal tract colonization

Purpose of Review

Colonization of the gastrointestinal (GI) tract with Candida albicans (CA), the most common human fungal pathogen, is the first step towards the development of invasive infection. Yet the fungal virulence factors and host factors that modulate CA GI colonization are still poorly understood. In this review, we will review emerging evidence of the importance of select CA genetic determinants and CA's interaction with the host that contribute to its successful adaptation as a pathobiont in the human GI tract.

Recent Findings

Recent data reveal the importance of 1) CA genetic determinants; 2) host factors; and 3) environmental factors in modulating CA GI colonization in humans.

Summary

As evidence continues to grow supporting the notion that the GI tract and its resident microbiota are an integral part of the host immune system, it will be critical for studies to interrogate the interaction of CA with the host (including both the host innate and adaptive immune system as well as the endogenous gut microbiota) in order to dissect the mechanisms of CA pathogenesis and thus lay the foundation for novel therapeutic approaches to prevent and/or treat invasive fungal infections.

Perspectives for clinical use of engineered human host defense antimicrobial peptides

Infectious diseases caused by bacteria, viruses or fungi are among the leading causes of death worldwide. The emergence of drug-resistance mechanisms, especially among bacteria, threatens the efficacy of all current antimicrobial agents, some of them already ineffective. As a result, there is an urgent need for new antimicrobial drugs. Host defense antimicrobial peptides (HDPs) are natural occurring and well-conserved peptides of innate immunity, broadly active against Gram-negative and Gram-positive bacteria, viruses and fungi. They also are able to exert immunomodulatory and adjuvant functions by acting as chemotactic for immune cells, and inducing cytokines and chemokines secretion. Moreover, they show low propensity to elicit microbial adaptation, probably because of their non-specific mechanism of action, and are able to neutralize exotoxins and endotoxins. HDPs have the potential to be a great source of novel antimicrobial agents. The goal of this review is to provide an overview of the advances made in the development of human defensins as well as the cathelicidin LL-37 and their derivatives as antimicrobial agents against bacteria, viruses and fungi for clinical use.

Candida albicans Heat Shock Proteins and Hsps-Associated Signaling Pathways as Potential Antifungal Targets

In recent decades, the incidence of invasive fungal infections has increased notably. Candida albicans (C. albicans), a common opportunistic fungal pathogen that dwells on human mucosal surfaces, can cause fungal infections, especially in immunocompromised and high-risk surgical patients. In addition, the wide use of antifungal agents has likely contributed to resistance of C. albicans to traditional antifungal drugs, increasing the difficulty of treatment. Thus, it is urgent to identify novel antifungal drugs to cope with C. albicans infections. Heat shock proteins (Hsps) exist in most organisms and are expressed in response to thermal stress. In C. albicans, Hsps control basic physiological activities or virulence via interaction with a variety of diverse regulators of cellular signaling pathways. Moreover, it has been demonstrated that Hsps confer drug resistance to C. albicans. Many studies have shown that disrupting the normal functions of C. albicans Hsps inhibits fungal growth or reverses the tolerance of C. albicans to traditional antifungal drugs. Here, we review known functions of the diverse Hsp family, Hsp-associated intracellular signaling pathways and potential antifungal targets based on these pathways in C. albicans. We hope this review will aid in revealing potential new roles of C. albicans Hsps in addition to canonical heat stress adaptions and provide more insight into identifying potential novel antifungal targets.

Role of Soluble Innate Effector Molecules in Pulmonary Defense against Fungal Pathogens

Fungal infections of the lung are life-threatening but rarely occur in healthy, immunocompetent individuals, indicating efficient clearance by pulmonary defense mechanisms. Upon inhalation, fungi will first encounter the airway surface liquid which contains several soluble effector molecules that form the first barrier of defense against fungal infections. These include host defense peptides, like LL-37 and defensins that can neutralize fungi by direct killing of the pathogen, and collectins, such as surfactant protein A and D, that can aggregate fungi and stimulate phagocytosis. In addition, these molecules have immunomodulatory activities which can aid in fungal clearance from the lung. However, existing observations are based on in vitro studies which do not reflect the complexity of the lung and its airway surface liquid. Ionic strength, pH, and the presence of mucus can have strong detrimental effects on antifungal activity, while the potential synergistic interplay between soluble effector molecules is largely unknown. In this review, we describe the current knowledge on soluble effector molecules that contribute to antifungal activity, the importance of environmental factors and discuss the future directions required to understand the innate antifungal defense in the lung.

Antifungal Effects of Synthetic Human Beta-defensin-3-C15 Peptide on Candida albicans-infected Root Dentin

INTRODUCTION

The aim of this study was to assess the antifungal efficacy of a synthetic human beta-defensin-3-C15 peptide (HBD3-C15) in Candida albicans-infected human root dentin.

METHODS

Standardized root dentin blocks were prepared (6-mm thick, 0.7-mm-wide canal) from single-rooted human permanent premolars and infected with C. albicans for 3 weeks. They were randomly divided into 4 groups (n = 8/group), and their canals were filled with calcium hydroxide (CH), HBD3-C15 peptide, or chlorhexidine digluconate (CHX, 2%) as disinfectants or saline as control. After 1 week of disinfection, dentinal debris were harvested at depths of 200 and 400 μm from the canal lumen, and incubated in Yeast broth for 72 hours at 37°C. Then, colony-forming units (CFU) were measured to assess the antifungal efficacy of each medicament and analyzed statistically.

RESULTS

All medicaments showed significantly lower CFU than saline (P < .05), and their antifungal efficacies were similar at both 200- and 400-μm tubular depths (P > .05). HBD3-C15 had similar antifungal efficacy to that of CHX at both depths (P > .05), and both medicaments had significantly lower CFU than CH at both depths (P < .05).

CONCLUSIONS

In this ex vivo model of C. albicans-infected human root dentin, the antifungal efficacy of synthetic HBD3-C15 was comparable with CHX.

Fungal Strategies to Evade the Host Immune Recognition

The recognition of fungal cells by the host immune system is key during the establishment of a protective anti-fungal response. Even though the immune system has evolved a vast number of processes to control these organisms, they have developed strategies to fight back, avoiding the proper recognition by immune components and thus interfering with the host protective mechanisms. Therefore, the strategies to evade the immune system are as important as the virulence factors and attributes that damage the host tissues and cells. Here, we performed a thorough revision of the main fungal tactics to escape from the host immunosurveillance processes. These include the composition and organization of the cell wall, the fungal capsule, the formation of titan cells, biofilms, and asteroid bodies; the ability to undergo dimorphism; and the escape from nutritional immunity, extracellular traps, phagocytosis, and the action of humoral immune effectors.

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.

The antifungal plant defensin AtPDF2.3 from Arabidopsis thaliana blocks potassium channels

Scorpion toxins that block potassium channels and antimicrobial plant defensins share a common structural CSαβ-motif. These toxins contain a toxin signature (K-C₄-X-N) in their amino acid sequence, and based on in silico analysis of 18 plant defensin sequences, we noted the presence of a toxin signature (K-C₅-R-G) in the amino acid sequence of the Arabidopsis thaliana defensin AtPDF2.3. We found that recombinant (r)AtPDF2.3 blocks K_v1.2 and K_v1.6 potassium channels, akin to the interaction between scorpion toxins and potassium channels. Moreover, rAtPDF2.3[G36N], a variant with a KCXN toxin signature (K-C₅-R-N), is more potent in blocking K_v1.2 and K_v1.6 channels than rAtPDF2.3, whereas rAtPDF2.3[K33A], devoid of the toxin signature, is characterized by reduced K_v channel blocking activity. These findings highlight the importance of the KCXN scorpion toxin signature in the plant defensin sequence for blocking potassium channels. In addition, we found that rAtPDF2.3 inhibits the growth of Saccharomyces cerevisiae and that pathways regulating potassium transport and/or homeostasis confer tolerance of this yeast to rAtPDF2.3, indicating a role for potassium homeostasis in the fungal defence response towards rAtPDF2.3. Nevertheless, no differences in antifungal potency were observed between the rAtPDF2.3 variants, suggesting that antifungal activity and K_v channel inhibitory function are not linked.

Antifungal peptides: To be or not to be membrane active

Most antifungal peptides (AFPs), if not all, have membrane activity, while some also have alternative targets. Fungal membranes share many characteristics with mammalian membranes with only a few differences, such as differences in sphingolipids, phosphatidylinositol (PI) content and the main sterol is ergosterol. Fungal membranes are also more negative and a better target for cationic AFPs. Targeting just the fungal membrane lipids such as phosphatidylinositol and/or ergosterol by AFPs often translates into mammalian cell toxicity. Conversely, a specific AFP target in the fungal pathogen, such as glucosylceramide, mannosyldiinositol phosphorylceramide or a fungal protein target translates into high pathogen selectivity. However, a lower target concentration, absence or change in the specific fungal target can naturally lead to resistance, although such resistance in turn could result in reduced pathogen virulence. The question is then to be or not to be membrane active - what is the best choice for a successful AFP? In this review we deliberate on this question by focusing on the recent advances in our knowledge on how natural AFPs target fungi.

Antifungal effects of synthetic human β-defensin 3-C15 peptide

OBJECTIVES

The purpose of this ex vivo study was to compare the antifungal activity of a synthetic peptide consisting of 15 amino acids at the C-terminus of human β-defensin 3 (HBD3-C15) with calcium hydroxide (CH) and Nystatin (Nys) against Candida albicans (C. albicans) biofilm.

MATERIALS AND METHODS

C. albicans were grown on cover glass bottom dishes or human dentin disks for 48 hr, and then treated with HBD3-C15 (0, 12.5, 25, 50, 100, 150, 200, and 300 µg/mL), CH (100 µg/mL), and Nys (20 µg/mL) for 7 days at 37℃. On cover glass, live and dead cells in the biomass were measured by the FilmTracer Biofilm viability assay, and observed by confocal laser scanning microscopy (CLSM). On dentin, normal, diminished and ruptured cells were observed by field-emission scanning electron microscopy (FE-SEM). The results were subjected to a two-tailed t-test, a one way analysis variance and a post hoc test at a significance level of p = 0.05.

RESULTS

C. albicans survival on dentin was inhibited by HBD3-C15 in a dose-dependent manner. There were fewer aggregations of C. albicans in the groups of Nys and HBD3-C15 (≥ 100 µg/mL). CLSM showed C. albicans survival was reduced by HBD3-C15 in a dose dependent manner. Nys and HBD3-C15 (≥ 100 µg/mL) showed significant fungicidal activity compared to CH group (p < 0.05).

CONCLUSIONS

Synthetic HBD3-C15 peptide (≥ 100 µg/mL) and Nys exhibited significantly higher antifungal activity than CH against C. albicans by inhibiting cell survival and biofilm.

How Chemotherapy Increases the Risk of Systemic Candidiasis in Cancer Patients: Current Paradigm and Future Directions

Candida albicans is a fungal commensal and a major colonizer of the human skin, as well as of the gastrointestinal and genitourinary tracts. It is also one of the leading causes of opportunistic microbial infections in cancer patients, often presenting in a life-threatening, systemic form. Increased susceptibility to such infections in cancer patients is attributed primarily to chemotherapy-induced depression of innate immune cells and weakened epithelial barriers, which are the body’s first-line defenses against fungal infections. Moreover, classical chemotherapeutic agents also have a detrimental effect on components of the adaptive immune system, which further play important roles in the antifungal response. In this review, we discuss the current paradigm regarding the mechanisms behind the increased risk of systemic candidiasis in cancer patients. We also highlight some recent findings, which suggest that chemotherapy may have more extensive effects beyond the human host, in particular towards C. albicans itself and the bacterial microbiota. The extent to which these additional effects contribute towards the development of candidiasis in chemotherapy-treated patients remains to be investigated.

β-Defensin 1 plays a role in acute mucosal defense against Candida albicans

Candida is an opportunistic fungal pathogen that colonizes the mucosal tract of humans. Pathogenic infection occurs in the presence of conditions causing perturbations to the commensal microbiota or host immunity. Early innate immune responses by the epithelium, including antimicrobial peptides (AMPs) and cytokines, are critical for protection against overgrowth. Reduced salivary AMP levels are associated with oral Candida infection, and certain AMPs, including human β-defensins 1-3, have direct fungicidal activity. In this study, we demonstrate that murine β-defensin 1 (mBD1) is important for control of early mucosal Candida infection and plays a critical role in the induction of innate inflammatory mediators. Mice deficient in mBD1, as compared with wild-type mice, exhibit elevated oral and systemic fungal burdens. Neutrophil infiltration to the sites of mucosal Candida invasion, an important step in limiting fungal infection, is significantly reduced in mBD1-deficient mice. These mice also exhibit defects in the expression of other AMPs, including mBD2 and mBD4, which may have direct anti-Candida activity. We also show that mBD1 deficiency impacts the production of important antifungal inflammatory mediators, including IL-1β, IL-6, KC, and IL-17. Collectively, these studies demonstrate a role for the mBD1 peptide in early control of Candida infection in a murine model of mucosal candidiasis, as well as in the modulation of host immunity through augmentation of leukocyte infiltration and inflammatory gene regulation.

Properties and mechanisms of action of naturally occurring antifungal peptides

Antimicrobial peptides are a vital component of the innate immune system of all eukaryotic organisms and many of these peptides have potent antifungal activity. They have potential application in the control of fungal pathogens that are a serious threat to both human health and food security. Development of antifungal peptides as therapeutics requires an understanding of their mechanism of action on fungal cells. To date, most research on antimicrobial peptides has focused on their activity against bacteria. Several antimicrobial peptides specifically target fungal cells and are not active against bacteria. Others with broader specificity often have different mechanisms of action against bacteria and fungi. This review focuses on the mechanism of action of naturally occurring antifungal peptides from a diverse range of sources including plants, mammals, amphibians, insects, crabs, spiders, and fungi. While antimicrobial peptides were originally proposed to act via membrane permeabilization, the mechanism of antifungal activity for these peptides is generally more complex and often involves entry of the peptide into the cell.

Bcr1 functions downstream of Ssd1 to mediate antimicrobial peptide resistance in Candida albicans

In order to colonize the host and cause disease, Candida albicans must avoid being killed by host defense peptides. Previously, we determined that the regulatory protein Ssd1 governs antimicrobial peptide resistance in C. albicans. Here, we sought to identify additional genes whose products govern susceptibility to antimicrobial peptides. We discovered that a bcr1Δ/Δ mutant, like the ssd1Δ/Δ mutant, had increased susceptibility to the antimicrobial peptides, protamine, RP-1, and human β defensin-2. Homozygous deletion of BCR1 in the ssd1Δ/Δ mutant did not result in a further increase in antimicrobial peptide susceptibility. Exposure of the bcr1Δ/Δ and ssd1Δ/Δ mutants to RP-1 induced greater loss of mitochondrial membrane potential and increased plasma membrane permeability than with the control strains. Therefore, Bcr1 and Ssd1 govern antimicrobial peptide susceptibility and likely function in the same pathway. Furthermore, BCR1 mRNA expression was downregulated in the ssd1Δ/Δ mutant, and the forced expression of BCR1 in the ssd1Δ/Δ mutant partially restored antimicrobial peptide resistance. These results suggest that Bcr1 functions downstream of Ssd1. Interestingly, overexpression of 11 known Bcr1 target genes in the bcr1Δ/Δ mutant failed to restore antimicrobial peptide resistance, suggesting that other Bcr1 target genes are likely responsible for antimicrobial peptide resistance. Collectively, these results demonstrate that Bcr1 functions downstream of Ssd1 to govern antimicrobial peptide resistance by maintaining mitochondrial energetics and reducing membrane permeabilization.

Chemical genomic screening of a Saccharomyces cerevisiae genomewide mutant collection reveals genes required for defense against four antimicrobial peptides derived from proteins found in human saliva

To compare the effects of four antimicrobial peptides (MUC7 12-mer, histatin 12-mer, cathelicidin KR20, and a peptide containing lactoferricin amino acids 1 to 11) on the yeast Saccharomyces cerevisiae, we employed a genomewide fitness screen of combined collections of mutants with homozygous deletions of nonessential genes and heterozygous deletions of essential genes. When an arbitrary fitness score cutoffs of 1 (indicating a fitness defect, or hypersensitivity) and -1 (indicating a fitness gain, or resistance) was used, 425 of the 5,902 mutants tested exhibited altered fitness when treated with at least one peptide. Functional analysis of the 425 strains revealed enrichment among the identified deletions in gene groups associated with the Gene Ontology (GO) terms "ribosomal subunit," "ribosome biogenesis," "protein glycosylation," "vacuolar transport," "Golgi vesicle transport," "negative regulation of transcription," and others. Fitness profiles of all four tested peptides were highly similar, particularly among mutant strains exhibiting the greatest fitness defects. The latter group included deletions in several genes involved in induction of the RIM101 signaling pathway, including several components of the ESCRT sorting machinery. The RIM101 signaling regulates response of yeasts to alkaline and neutral pH and high salts, and our data indicate that this pathway also plays a prominent role in regulating protective measures against all four tested peptides. In summary, the results of the chemical genomic screens of S. cerevisiae mutant collection suggest that the four antimicrobial peptides, despite their differences in structure and physical properties, share many interactions with S. cerevisiae cells and consequently a high degree of similarity between their modes of action.

Antimicrobial activity of human β-defensin 4 analogs: insights into the role of disulfide linkages in modulating activity

Human β-defensins (HBDs) are cationic antimicrobial peptides that are components of the innate immune system. They are characterized by three disulfide bridges. However, the number of cationic residues as well as the presence of lysine and arginine residues vary. In HBD4, the cationic residues occur predominantly in the N-terminal segment, unlike in HBD1-3. We have examined the antimicrobial activity of peptides spanning the N- and C-terminal segments of HBD4. We have introduced one, two and three disulfide bridges in the peptides corresponding to the N-terminal segments. Peptides corresponding to the N-terminal segment had identical sequences and variation was only in the number and spacing of cysteines and disulfide bridges. Antimicrobial activity to varying extents was observed for all the peptides. When two disulfide bridges were present, decrease in antimicrobial potency as well as sensitivity of activity to salt was observed. Enhanced antimicrobial activity was observed when three disulfide bridges were present. The antimicrobial potency was similar to HBD4 except against Escherichia coli and was attenuated in the presence of salt. While the presence of three disulfide bridges did not constrain the peptide to a rigid β-sheet, the activity was considerably more as compared to the peptides with one or two disulfide bridges. The peptides enter bacterial and fungal cells rapidly without membrane permeabilization and appear to exert their activity inside the cells rather than at the membrane.

Human beta-defensin 3 is up-regulated in cutaneous leprosy type 1 reactions

Background

Leprosy, a chronic granulomatous disease affecting the skin and nerves, is caused by Mycobacterium leprae (M. leprae). The type of leprosy developed depends upon the host immune response. Type 1 reactions (T1Rs), that complicate borderline and lepromatous leprosy, are due to an increase in cell-mediated immunity and manifest as nerve damage and skin inflammation. Owing to the increase in inflammation in the skin of patients with T1Rs, we sought to investigate the activation of the innate immune system during reactionary events. Specifically, we investigated the expression levels of human beta-defensins (hBDs) 2 and 3 in the skin of patients with T1Rs, in keratinocytes, and in macrophages stimulated with M. leprae and corticosteroids.

Results

Skin biopsies from twenty-three patients with Type 1 reactions were found to have higher transcript levels of hBD3 as compared to fifteen leprosy patients without Type 1 reactions, as measured by qPCR. Moreover, we observed that keratinocytes but not macrophages up-regulated hBD2 and hBD3 in response to M. leprae stimulation in vitro. Corticosteroid treatment of patients with T1Rs caused a suppression of hBD2 and hBD3 in skin biopsies, as measured by qPCR. In vitro, corticosteroids suppressed M. leprae-dependent induction of hBD2 and hBD3 in keratinocytes.

Conclusions

This study demonstrates that hBD3 is induced in leprosy Type 1 Reactions and suppressed by corticosteroids. Furthermore, our findings demonstrate that keratinocytes are responsive to M. leprae and lend support for additional studies on keratinocyte innate immunity in leprosy and T1Rs.

Trial Registration

Controlled-Trials.com ISRCTN31894035

Leprosy, caused by Mycobacterium leprae (M. leprae), is a chronic infection leading to potentially debilitating nerve damage. Although the infection is curable with multi-drug therapy, many patients continue to suffer from episodes of inflammation, called Type 1 reactions. These reactions may lead to nerve damage and deformation. Patients with Type 1 reactions are treated with corticosteroids to reduce the inflammation. Elucidating the immune factors contributing to leprosy Type 1 reactions will further clarify why many leprosy patients develop nerve and skin inflammation. We conducted a study to understand whether the antimicrobial peptides, human beta-defensins (hBD) 2 and 3, are increased in the skin of leprosy patients with Type 1 reactions. We also investigated keratinocyte expression of hBD2 and hBD3 in response to M. leprae. In this study, we found that hBD3 was significantly increased in the skin of leprosy patients with Type 1 reactions. Moreover, we demonstrated that corticosteroid treatment reduced the expression of hBD3 in patients with Type 1 reactions. We also found that keratinocytes incubated with M. leprae upregulated hBD2 and hBD3 in vitro; corticosteroids were found to suppress this response. These studies suggest a role for the innate immune system in leprosy Type 1 reactions.

Biology of the heat shock response and protein chaperones: budding yeast (Saccharomyces cerevisiae) as a model system

The eukaryotic heat shock response is an ancient and highly conserved transcriptional program that results in the immediate synthesis of a battery of cytoprotective genes in the presence of thermal and other environmental stresses. Many of these genes encode molecular chaperones, powerful protein remodelers with the capacity to shield, fold, or unfold substrates in a context-dependent manner. The budding yeast Saccharomyces cerevisiae continues to be an invaluable model for driving the discovery of regulatory features of this fundamental stress response. In addition, budding yeast has been an outstanding model system to elucidate the cell biology of protein chaperones and their organization into functional networks. In this review, we evaluate our understanding of the multifaceted response to heat shock. In addition, the chaperone complement of the cytosol is compared to those of mitochondria and the endoplasmic reticulum, organelles with their own unique protein homeostasis milieus. Finally, we examine recent advances in the understanding of the roles of protein chaperones and the heat shock response in pathogenic fungi, which is being accelerated by the wealth of information gained for budding yeast.

Salivary defense proteins: their network and role in innate and acquired oral immunity

There are numerous defense proteins present in the saliva. Although some of these molecules are present in rather low concentrations, their effects are additive and/or synergistic, resulting in an efficient molecular defense network of the oral cavity. Moreover, local concentrations of these proteins near the mucosal surfaces (mucosal transudate), periodontal sulcus (gingival crevicular fluid) and oral wounds and ulcers (transudate) may be much greater, and in many cases reinforced by immune and/or inflammatory reactions of the oral mucosa. Some defense proteins, like salivary immunoglobulins and salivary chaperokine HSP70/HSPAs (70 kDa heat shock proteins), are involved in both innate and acquired immunity. Cationic peptides and other defense proteins like lysozyme, bactericidal/permeability increasing protein (BPI), BPI-like proteins, PLUNC (palate lung and nasal epithelial clone) proteins, salivary amylase, cystatins, prolin-rich proteins, mucins, peroxidases, statherin and others are primarily responsible for innate immunity. In this paper, this complex system and function of the salivary defense proteins will be reviewed.

Comparative activity and mechanism of action of three types of bovine antimicrobial peptides against pathogenic Prototheca spp

The yeast-like algae of the genus Prototheca are ubiquitous saprophytes causing infections in immunocompromised patients and granulomatous mastitis in cattle. Few available therapies and the rapid spread of resistant strains worldwide support the need for novel drugs against protothecosis. Host defence antimicrobial peptides inactivate a wide array of pathogens and are a rich source of leads, with the advantage of being largely unaffected by microbial resistance mechanisms. Three structurally diverse bovine peptides [BMAP-28, Bac5 and lingual antimicrobial peptide (LAP)] have thus been tested for their capacity to inactivate Prototheca spp. In minimum inhibitory concentration (MIC) assays, they were all effective in the micromolar range against clinical mastitis isolates as well as a Prototheca wickerhamii reference strain. BMAP-28 sterilized Prototheca cultures within 30-60 min at its MIC, induced cell permeabilization with near 100% release of cellular adenosine triphosphate and resulted in extensive surface blebbing and release of intracellular material as observed by scanning electron microscopy. Bac5 and LAP inactivated Prototheca following 3-6 h incubation at fourfold their MIC and did not result in detectable surface damage despite 70-90% killing, suggesting they act via non-lytic mechanisms. In circular dichroism studies, the conformation of BMAP-28, but not that of Bac5 or LAP, was affected by interaction with liposomes mimicking algal membranes. Our results indicate that BMAP-28, Bac5 and LAP kill Prototheca with distinct potencies, killing kinetics, and modes of action and may be appropriate for protothecal mastitis treatment. In addition, the ability of Bac5 and LAP to act via non-lytic mechanisms may be exploited for the development of target-selective drugs.

Expression of mouse beta defensin 2 in escherichia coli and its broad-spectrum antimicrobial activity

Mature mouse beta defensin 2 (mBD2) is a small cationic peptide with antimicrobial activity. Here we established a prokaryotic expression vector containing the cDNA of mature mBD2 fused with thioredoxin (TrxA), pET32a-mBD2. The vector was transformed into Escherichia Coli (E. coli) Rosseta-gami (2) for expression fusion protein. Under the optimization of fermentation parameters: induce with 0.6 mM isopropylthiogalactoside (IPTG) at 34°C in 2×YT medium and harvest at 6 h postinduction, fusion protein TrxA-mBD2 was high expressed in the soluble fraction (>95%). After cleaved fusion protein by enterokinase, soluble mature mBD2 was achieved 6 mg/L with a volumetric productivity. Purified recombinant mBD2 demonstrated clear broad-spectrum antimicrobial activity for fungi, bacteria and virus. The MIC of antibacterial activity of against Staphylococcus aureus was 50 μg/ml. The MIC of against Candida albicans (C. albicans) and Cryptococcus neoformans (C. neoformans) was 12.5μg/ml and 25μg/ml, respectively. Also, the antimicrobial activity of mBD2 was effected by NaCl concentration. Additionally, mBD2 showed antiviral activity against influenza A virus (IAV), the protective rate for Madin-Darby canine kidney cells (MDCK) was 93.86% at the mBD2 concentration of 100 μg/ml. These works might provide a foundation for the following research on the mBD2 as therapeutic agent for medical microbes.

IL-1β and ADAM17 are central regulators of β-defensin expression in Candida esophagitis

Candida albicans resides on epithelial surfaces as part of the physiological microflora. However, under certain conditions, it may cause life-threatening infections, including Candida sepsis. We have recently shown that human β-defensins (hBDs) hBD-2 and hBD-3 are upregulated in Candida esophagitis and that this antifungal host response is distinctly regulated by NF-κB and MAPK/activator protein-1 (AP-1) pathways. Here, we show that C. albicans induces hBD-2 through an autocrine IL-1β loop and that activation of the epidermal growth factor receptor (EGFR) by endogenous transforming growth factor-α (TGF-α) is a crucial event in the induction of hBD-3. To further dissect upstream signaling events, we investigated expression of the central sheddases for EGFR ligands ADAM10 and ADAM17 in the healthy and infected esophagus. Next, we used pharmaceutical inhibitors and small-interfering RNA-mediated knock down of ADAM10 and ADAM17 to reveal that ADAM17-induced shedding of TGF-α is a crucial step in the induction of hBD-3 expression in response to Candida infection. In conclusion, we describe for the first time an autocrine IL-1β loop responsible for the induction of hBD-2 expression and an ADAM17-TGF-α-EGFR-MAPK/AP-1 pathway leading to hBD-3 upregulation in the course of a Candida infection of the esophagus.

Antimicrobial peptides in healthy skin and atopic dermatitis

Antimicrobial Peptides and Proteins (AMPs) represent effector molecules of the innate defense system in all organisms. AMPs are either constitutively or inducibly produced mainly by various epithelial cells, including keratinocytes. This report reviews our current knowledge about the major yet known keratinocyte-derived AMPs, its role in healthy skin and atopic dermatitis.

Fungicidal activity of human lactoferrin-derived peptides based on the antimicrobial αβ region

Owing to the increasing number of infections in hospitalised patients caused by resistant strains of fungi, there is a need to develop new therapeutic agents for these infections. Naturally occurring antimicrobial peptides may constitute models for developing such agents. A modified peptide sequence (CFQWKRAMRKVR; HLopt2) based on amino acid residues 20-31 of the N-terminal end of human lactoferrin (hLF) as well as a double-sized human lactoferricin-like peptide (amino acid residues 16-40; HLBD1) were investigated for their antifungal activities in vitro and in vivo. By in vitro assay, HLopt2 was fungicidal at concentrations of 12.5-25 μg/mL against Cryptococcus neoformans, Candida albicans, Candida krusei, Candida kefyr and Candida parapsilosis, but not against Candida glabrata. HLopt2 was demonstrated to have ≥ 16-fold greater killing activity than HLBD1. By inducing some helical formation caused by lactam bridges or by extending the assay time (from 2h to 20 h), HLBD1 became almost comparable with HLopt2 in its fungicidal activity. Killing of C. albicans yeast cells by HLopt2 was rapid and was accompanied by cytoplasmic and mitochondrial membrane permeabilisation as well as formation of deep pits on the yeast cell surface. In a murine C. albicans skin infection model, atopic treatment with the peptides resulted in significantly reduced yields of Candida from the infected skin areas. The antifungal activities of HLopt2 in vitro and in vivo suggest possible potential as a therapeutic agent against most Candida spp. and C. neoformans. The greatly improved antifungal effect of the lactam-modified HLBD1 indicates the importance of amphipathic helix formation for lethal activity.

Host cell invasion and virulence mediated by Candida albicans Ssa1

Candida albicans Ssa1 and Ssa2 are members of the HSP70 family of heat shock proteins that are expressed on the cell surface and function as receptors for antimicrobial peptides such as histatins. We investigated the role of Ssa1 and Ssa2 in mediating pathogenic host cell interactions and virulence. A C. albicans ssa1Δ/Δ mutant had attenuated virulence in murine models of disseminated and oropharyngeal candidiasis, whereas an ssa2Δ/Δ mutant did not. In vitro studies revealed that the ssa1Δ/Δ mutant caused markedly less damage to endothelial cells and oral epithelial cell lines. Also, the ssa1Δ/Δ mutant had defective binding to endothelial cell N-cadherin and epithelial cell E-cadherin, receptors that mediate host cell endocytosis of C. albicans. As a result, this mutant had impaired capacity to induce its own endocytosis by endothelial cells and oral epithelial cells. Latex beads coated with recombinant Ssa1 were avidly endocytosed by both endothelial cells and oral epithelial cells, demonstrating that Ssa1 is sufficient to induce host cell endocytosis. These results indicate that Ssa1 is a novel invasin that binds to host cell cadherins, induces host cell endocytosis, and is critical for C. albicans to cause maximal damage to host cells and induce disseminated and oropharyngeal disease.

Prediction of the clinical outcome in invasive candidiasis patients based on molecular fingerprints of five anti-Candida antibodies in serum

Better prognostic predictors for invasive candidiasis (IC) are needed to tailor and individualize therapeutic decision-making and minimize its high morbidity and mortality. We investigated whether molecular profiling of IgG-antibody response to the whole soluble Candida proteome could reveal a prognostic signature that may serve to devise a clinical-outcome prediction model for IC and contribute to known IC prognostic factors. By serological proteome analysis and data-mining procedures, serum 31-IgG antibody-reactivity patterns were examined in 45 IC patients randomly split into training and test sets. Within the training cohort, unsupervised two-way hierarchical clustering and principal-component analyses segregated IC patients into two antibody-reactivity subgroups with distinct prognoses that were unbiased by traditional IC prognostic factors and other patients-related variables. Supervised discriminant analysis with leave-one-out cross-validation identified a five-IgG antibody-reactivity signature as the most simplified and accurate IC clinical-outcome predictor, from which an IC prognosis score (ICPS) was derived. Its robustness was confirmed in the test set. Multivariate logistic-regression and receiver-operating-characteristic curve analyses demonstrated that the ICPS was able to accurately discriminate IC patients at high risk for death from those at low risk and outperformed conventional IC prognostic factors. Further validation of the five-IgG antibody-reactivity signature on a multiplexed immunoassay supported the serological proteome analysis results. The five IgG antibodies incorporated in the ICPS made biologic sense and were associated either with good-prognosis and protective patterns (those to Met6p, Hsp90p, and Pgk1p, putative Candida virulence factors and antiapoptotic mediators) or with poor-prognosis and risk patterns (those to Ssb1p and Gap1p/Tdh3p, potential Candida proapoptotic mediators). We conclude that the ICPS, with additional refinement in future larger prospective cohorts, could be applicable to reliably predict patient clinical-outcome for individualized therapy of IC. Our data further provide insights into molecular mechanisms that may influence clinical outcome in IC and uncover potential targets for vaccine design and immunotherapy against IC.

Epithelial cells and innate antifungal defense

The human pathogenic fungus Candida albicans is the predominant cause of both superficial and invasive forms of candidiasis. Clinical observations indicate that mucocutaneous Candida infections are commonly associated with defective cell-mediated immune responses. The importance of the innate immune system as a first-line defense against pathogenic challenge has long been recognized. Over the last decade, many key molecules mediating innate host defense have been identified. Central to these developments is the discovery of pattern recognition receptors such as Toll-like receptors and C-type lectin-receptors that induce innate immune responses and also modulate cellular and humoral adaptive immunity during Candida infections. Although a large amount of information is now available in systemic infections, little is known about localized infections. We address the most relevant pattern recognition receptors and their signaling mechanisms in oral epithelial cells, to gain a better understanding of their contributions to antifungal innate immunity.

Th17 cytokines and host-pathogen interactions at the mucosa: dichotomies of help and harm

The mucosal surfaces are often the first site of interaction between pathogenic microorganisms and the host. Activation of the mucosal immune response has the important function of containing an infection and preventing dissemination of pathogens to systemic sites (barrier function). Numerous lines of evidence suggest that the barrier function is orchestrated by a subset of cytokines (interleukin (IL-)17 and IL-22), which belong to the Th17 family. IL-17 and IL-22 induce expression of antimicrobial peptides and neutrophil chemoattractants at mucosal sites, and thus play an important role in controlling mucosal infections. However, there is increasing evidence that mucosal pathogens achieve greater colonization during inflammation because they are resistant to a subset of these antimicrobial responses. In this review we compare the antimicrobial responses elicited by Th17 cytokines during mucosal infections with four different pathogens: Klebsiella pneumoniae, Citrobacter rodentium, Candida albicans and Salmonella typhimurium. We will then discuss which responses may constitute the mucosal barrier, thus providing a benefit to the host, and which ones may promote the colonization of pathogens, thereby providing a benefit to the microbes.

Proteomic analysis of cytoplasmic and surface proteins from yeast cells, hyphae, and biofilms of Candida albicans

Candida albicans is a human commensal and opportunistic pathogen that participates in biofilm formation on host surfaces and on medical devices. We used DIGE analysis to assess the cytoplasmic and non-covalently attached cell-surface proteins in biofilm formed on polymethylmethacrylate and planktonic yeast cells and hyphae. Of the 1490 proteins spots from cytoplasmic and 580 protein spots from the surface extracts analyzed, 265 and 108 were differentially abundant respectively (>or=1.5-fold, p <0.05). Differences of both greater and lesser abundance were found between biofilms and both planktonic conditions as well as between yeast cells and hyphae. The identity of 114 cytoplasmic and 80 surface protein spots determined represented 73 and 25 unique proteins, respectively. Analyses showed that yeast cells differed most in cytoplasmic profiling while biofilms differed most in surface profiling. Several processes and functions were significantly affected by the differentially abundant cytoplasmic proteins. Particularly noted were many of the enzymes of respiratory and fermentative pentose and glucose metabolism, folate interconversions and proteins associated with oxidative and stress response functions, host response, and multi-organism interaction. The differential abundance of cytoplasmic and surface proteins demonstrated that sessile and planktonic organisms have a unique profile.

Trifluoromethanesulfonic acid-based proteomic analysis of cell wall and secreted proteins of the ascomycetous fungi Neurospora crassa and Candida albicans

Cell wall proteins from purified Candida albicans and Neurospora crassa cell walls were released using trifluoromethanesulfonic acid (TFMS) which cleaves the cell wall glucan/chitin matrix and deglycosylates the proteins. The cell wall proteins were then characterized by SDS-PAGE and identified by proteomic analysis. The analyses for C. albicans identified 15 cell wall proteins and six secreted proteins. For N. crassa, the analyses identified 26 cell wall proteins and nine secreted proteins. Most of the C. albicans cell wall proteins are found in the cell walls of both yeast and hyphae cells, but some cell type-specific cell wall proteins were observed. The analyses showed that the pattern of cell wall proteins present in N. crassa vegetative hyphae and conidia (asexual spores) are quite different. Almost all of the cell wall proteins identified in N. crassa have close homologs in the sequenced fungal genomes, suggesting that these proteins have important conserved functions within the cell wall.