Candida albicans-epithelial interactions and induction of mucosal innate immunity

Molecular mechanism of host-yeast interactions and prevention by nanoformulation approaches

Fungal infections are a major source of morbidity and mortality in people with compromised immune systems, such as those with human immunodeficiency virus, cancer, organ transplant recipients, and patients undergoing chemotherapy in healthcare settings. According to a recent World Health Organization (WHO) fungal priority pathogens list, Cryptococcus spp., Candida spp., Aspergillus spp., and Candia auris cause severe invasive infections in humans. These opportunistic pathogens cause a significant number of mycoses, which affect over a billion people annually. Around two million infections can be fatal, especially for those with compromised immune systems. To diagnose and treat mycoses, we need to understand the complex interactions between the fungus and the host during pathogenesis, the virulence-causing traits of the fungus, and how the host fights infection through the immune system. Although several antifungal drugs are available to treat fungal infections, their effectiveness is highly variable with adverse effects. In addition, the increasing resistance to traditional antifungal treatments poses serious risks to the healthcare industry. Therefore, new therapeutic strategies are required to combat these potentially fatal fungal infections. Nanostructure-based formulations can improve the therapeutic efficacy of conventional medications by broadening their activities, decreasing toxicity, enhancing bioactivity, and improving biodistribution. The review highlights host and fungus interaction and how nanoformulations can be targeted against fungal infections.

Candidalysin biology and activation of host cells

Candida albicans is an opportunistic fungal pathogen that can cause life-threatening systemic infections and distressing mucosal infections. A major breakthrough in understanding C. albicans pathogenicity was the discovery of candidalysin, the first cytolytic peptide toxin identified in a human pathogenic fungus. Secreted by C. albicans hyphae and encoded by the ECE1 gene, this 31-amino acid peptide integrates into and permeabilizes host cell membranes, causing damage across diverse cell types. Beyond its cytolytic activity, candidalysin can trigger potent innate immune responses in epithelial cells, macrophages, and neutrophils. Additionally, candidalysin plays a key role in nutrient acquisition during infection. This review explores the biology of candidalysin, its role in host cell activation, and extends the discussion to non-candidalysin Ece1p peptides, shedding light on their emerging significance.

Commensalism and pathogenesis of Candida albicans at the mucosal interface

Fungi are important and often underestimated human pathogens. Infections with fungi mostly originate from the environment, from soil or airborne spores. By contrast, Candida albicans, one of the most common and clinically important fungal pathogens, permanently exists in the vast majority of healthy individuals as a member of the human mucosal microbiota. Only under certain circumstances will these commensals cause infections. However, although the pathogenic behaviour and disease manifestation of C. albicans have been at the centre of research for many years, its asymptomatic colonization of mucosal surfaces remains surprisingly understudied. In this Review, we discuss the interplay of the fungus, the host and the microbiome on the dualism of commensal and pathogenic life of C. albicans, and how commensal growth is controlled and permitted. We explore hypotheses that could explain how the mucosal environment shapes C. albicans adaptations to its commensal lifestyle, while still maintaining or even increasing its pathogenic potential.

Candida albicans impacts carbohydrate metabolism of Enterococcus faecalis in interkingdom biofilms

Objectives

This study investigated the transcriptional and physiological responses of Enterococcus faecalis, an opportunistic pathogen linked to endodontic infections, when cultivated in dual-species biofilms with Candida albicans, a yeast pathobiont found in the oral cavity.

Methods

Forty-eight-hour E. faecalis OG1RF biofilms were developed in BHI medium as mono- or dual-species with C. albicans SC5314. Biofilms were assessed for biomass, colony-forming units (CFUs), and architecture using confocal microscopy. RNA sequencing was performed on an Illumina platform. Mannose-PTS activity and glycerol quantification assays were conducted to investigate changes in carbohydrate metabolism.

Results

Transcriptomic analysis revealed 149 E. faecalis genes differentially expressed in dual-species biofilms. Genes linked to mannose-PTS and glycerol metabolism were notably upregulated. Mannose-PTS activity was significantly higher in dual-species biofilms. Mannose, as the sole carbohydrate source, increased E. faecalis CFUs and decreased C. albicans CFUs in co-culture, while glucose had no effect. As C. albicans is a glycerol net producer, glycerol levels were always higher when C. albicans was present, likely contributing to the upregulation of glycerol metabolism genes in E. faecalis when in co-cultures.

Conclusions

The presence of C. albicans alters E. faecalis gene expression and metabolism, suggesting metabolic crosstalk that may influence their pathogenicity and role in oral infections.

Cas5 Regulates the Exposure of β-Glucan, the Cell Surface Hydrophobicity, and the Expression of Cell Wall Proteins to Remodel the Candida albicans Cell Wall and Participates in the Recruitment of Neutrophils

Candida albicans (C. albicans) is a major opportunistic fungal pathogen that causes life-threatening infections, particularly in immunocompromised individuals, underscoring the critical need to understand its pathogenic mechanisms. This study investigates the role of Cas5, a key transcription factor, in regulating C. albicans cell wall remodeling, virulence, and host interactions. Genetic manipulation and biochemical assays were used to examine the effects of Cas5 depletion on C. albicans cell wall structure, adhesion to host cells, morphology transition, innate immune cells recruitment, and pathogenicity in a BALB/C mouse model of oropharyngeal candidiasis (OPC). The results showed that the Cas5 depletion mediated β-glucan exposure and enhanced C. albicans's ability to recruit neutrophils in vivo. Additionally, Cas5-mediated changes in cell surface hydrophobicity (CSH), CWP expressions, and morphological transition promoted C. albicans adhesion to biologically active surfaces (host cells) and increased fungal burden in the mouse model of OPC. In conclusion, Cas5 modulates C. albicans cell wall remodeling by masking cell wall β-glucan, altering CSH, and regulating the expression of cell wall proteins (CWPs). Additionally, Cas5 participates in inhibiting neutrophil recruitment and enhancing the C. albicans adhesion to host cells, as well as facilitating morphological transitions. These actions promote the colonization and invasion of C. albicans in OPC pathogenesis.

Strain background interacts with chromosome 7 aneuploidy to determine commensal and virulence phenotypes in Candida albicans

The human fungal pathobiont Candida albicans displays extensive genomic plasticity, including large-scale chromosomal changes such as aneuploidy. Chromosome trisomy appears frequently in natural and laboratory strains of C. albicans. Trisomy of specific chromosomes has been linked to large phenotypic effects, such as increased murine gut colonization by strains trisomic for chromosome 7 (Chr7). However, studies of whole-chromosome aneuploidy are generally limited to the SC5314 genome reference strain, making it unclear whether the imparted phenotypes are conserved across C. albicans genetic backgrounds. Here, we report the presence of a Chr7 trisomy in the "commensal-like" oral candidiasis strain, 529L, and dissect the contribution of Chr7 trisomy to colonization and virulence in 529L and SC5314. These experiments show that strain background and homolog identity (i.e., AAB vs ABB) interact with Chr7 trisomy to alter commensal and virulence phenotypes in multiple host niches. In vitro filamentation was the only phenotype altered by Chr7 trisomy in similar ways across the two strain backgrounds. Oral colonization of mice was increased by the presence of a Chr7 trisomy in 529L but not SC5314; conversely, virulence during systemic infection was reduced by Chr7 trisomy in SC5314 but not 529L. Strikingly, the AAB Chr7 trisomy in the SC5314 background rendered this strain avirulent in murine systemic infection. Increased dosage of NRG1 failed to reproduce most of the Chr7 trisomy phenotypes. Our results demonstrate that aneuploidy interacts with background genetic variation to produce complex phenotypic patterns that deviate from our current understanding in the genome reference strain.

A molybdenum sulfide based nitric oxide controlled release oral gel for rapid healing of oral mucosal ulcers

Oral mucosal ulcer is the most prevalent oral mucosal lesion, affecting over 25 % of general population. The current treatment regimens lack efficacy in addressing challenges such as wound bleeding, bacterial infection and inflammation on a continuous basis. Hence, a multi-functional oral gel (termed MPCST) with a long-acting duration is designed. It is based on a tannic acid-thioctic acid (TATA) supramolecular hydrogel which absorbs tissue exudate while exhibiting robust tissue adhesion properties. To form MPCST, TATA is loaded with MPCS, which are composed of polydopamine (PDA)-coated molybdenum disulfide (MoS2) nanoflakes (MoS2@PDA) with high photothermal conversion efficiency, nitric oxide (NO) precursor nitroprusside (SNP) and cerium oxide (CeO2) with high reactive oxygen species (ROS) scavenging rate. Upon exposure to 808 nm near-infrared (NIR) irradiation, MPCS rapidly heats up and releases NO to promote angiogenesis, while exhibiting strong ROS scavenging, antibacterial (including oral common Streptococcus mutans), and anti-inflammatory properties. Animal experiments show that the MPCST oral gel, composed of MPCS and TATA hydrogel, exhibits superior therapeutic efficacy compared to the commonly used dexamethasone patch.

Microbial adaptive pathogenicity strategies to the host inflammatory environment

Pathogenic microorganisms can infect a variety of niches in the human body. During infection, these microbes can only persist if they adapt adequately to the dynamic host environment and the stresses imposed by the immune system. While viruses entirely rely on host cells to replicate, bacteria and fungi use their pathogenicity mechanisms for the acquisition of essential nutrients that lie under host restriction. An inappropriate deployment of pathogenicity mechanisms will alert host defence mechanisms that aim to eradicate the pathogen. Thus, these adaptations require tight regulation to guarantee nutritional access without eliciting strong immune activation. To work efficiently, the immune system relies on a complex signalling network, involving a myriad of immune mediators, some of which are quite directly associated with imminent danger for the pathogen. To manipulate the host immune system, viruses have evolved cytokine receptors and viral cytokines. However, among bacteria and fungi, selected pathogens have evolved the capacity to use these inflammatory response-specific signals to regulate their pathogenicity. In this review, we explore how bacterial and fungal pathogens can sense the immune system and use adaptive pathogenicity strategies to evade and escape host defence to ensure their persistence in the host.

Elimination of oral foci of infection might lead to clinical improvement of Graves' orbitopathy

PURPOSE

Graves' disease (GD) and Graves' orbitopathy (GO) are multifactorial disorders with links to the gut microbiome and autoimmunity. It is observed that patients with GD exhibit altered gut microbiome diversity. However, little is known about the role of oral microbiota in GD and GO. This study aims to investigate the impact of oral health and oral sanitation on the clinical course of GO in patients disqualified from glucocorticoid treatment due to oral infections.

METHODS

We reviewed 188 admissions of 127 patients with GO, hospitalized in a tertiary university hospital. Clinical, biochemical, imaging, ophthalmological, and oral health assessment data from each admission were analyzed. Patients excluded from the glucocorticoids (GCs) therapy due to oral foci of infection had the clinical activity score (CAS) reassessed after three months, and they were divided into two groups: with and without improvement.

RESULTS

Finishing dental treatment in the meantime was the only factor significantly correlated with improvement in these patients (p = 0.041). The secondary finding was that anti-thyroid peroxidase antibodies titer was significantly higher in the group with oral foci of infection considered as a contraindication for GCs (medians 28.50 vs 128.00; p = 0.026), and those patients were more likely to smoke than the group without oral issues (p = 0.024).

CONCLUSIONS

The results of our study suggest that monitoring and treating oral diseases may be pertinent in patients with GO and might serve as a supportive treatment strategy for managing the condition.

KEY MESSAGES

What is known: There is a recognized link between gut dysbiosis and the autoimmune processes in Graves' Disease (GD) and Graves' Orbitopathy (GO).

WHAT IS NEW

Elevated levels of TPOAb have been observed in patients with GO who also have oral foci of infection. Dental treatment has been shown to lead to significant clinical improvements in patients with GO. Maintaining oral hygiene might serve as a supportive treatment strategy for managing GO.

Multifunctional hydrogels for the healing of oral ulcers

Oral ulcers are one of the most common oral diseases in clinical practice. Its etiology is complex and varied. Due to the dynamic nature of the oral environment, the wound surface is painful due to contact and wear, which seriously affects the quality of life of patients. Oral ulcers are often treated with topical drug therapy. Studies have shown that functional hydrogels play a positive role in promoting wound healing, showing unique advantages in wound dressings. In this paper, the causes and healing characteristics of oral ulcers are discussed in depth, and then the common treatment methods for oral ulcers are summarized and compared. Finally, the potential of functional hydrogels in the treatment of oral ulcers is discussed and projected through a review of the literature in recent years.

Peptides from Galleria mellonella against Cryptococcus spp: toxicity in three-dimensional cell cultures and G. mellonella

Aim: This work aimed to test peptides against the planktonic and biofilm form of Cryptococcus spp. and in vitro toxicity using three-dimensional (3D) cells characterized and evaluate in vivo toxicity in Galleria mellonella.Materials & methods: Susceptibility tests were conducted on the planktonic form and biofilm formation. The toxicity of the peptides was evaluated in lung and brain cells in monolayer (2D) and 3D mono- and co-culture, in addition to in vivo analysis with G. mellonella.Results: Susceptibility values ranged from 31.25 to over 250 µg/ml with a fungicidal profile. Regarding toxicity, the PepM2 peptide was not toxic in 3D culture (500 µg/ml). G. mellonella, showed a survival rate of more than 85% In assays with brain and lung cell lines, concentrations ranged from 4 × 104 to 4 × 103 cells/well for brain cells and 1 × 103 cells/well for lung cells. Cocultures used 1 × 105 brain and 1 × 103 lung cells.Conclusion: This study shows that the peptides have great potential against cryptococcosis, and all spheroids were characterized as having a spheroidal and compact structure.

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.

Modulation of C. albicans-Induced Immune Response in Vaginal Epithelial Cells by Garcinoic Acid

Vulvovaginal candidiasis (VVC) is a prevalent women's infection characterized by excessive inflammation and damage of the vaginal epithelium that, in its recurrent form (RVVC), causes more than three symptomatic episodes per year, impacting nearly 8% of women globally. Current antifungal treatments alleviate symptoms but often fail to restore the inflammatory homeostasis of mucosal tissue and prevent recurrences. α-Tocopherol (α-TOH) and garcinoic acid (GA), a vitamin E metabolite, with immunomodulatory properties, were investigated for the first time in vaginal epithelial cells exposed to C. albicans infection to assess their effects on inflammatory signaling parameters important to restore cellular homeostasis. For this purpose, the protein kinases MKK3/6, p38 stress kinase (SAPK), and ERK1/2 were studied together with c-Fos transcription factor and IL-6, IL-1α, and IL-1β secretion in A-431 vaginal epithelial cells pre-treated with GA or with α-TOH and then infected with C. albicans. GA, differently from α-TOH, significantly reduced the C. albicans-induced activation of p38-SAPK while increasing pro-survival MAPK ERK1/2 activity. This resulted in a significant reduction in the secretion levels of the inflammatory cytokines IL-6 and IL-1α, as well as IL-1β. Overall, our data indicate that GA holds potential for restoring the immuno-metabolic properties of the vaginal epithelium exposed to C. albicans infection, which may help to treat inflammatory symptoms in VVC/RVVC.

Candida albicans Induces Oral Microbial Dysbiosis and Promotes Oral Diseases

Candida albicans are ubiquitous fungal organisms that colonize the oral cavity of healthy individuals without causing disease. C. albicans is an opportunistic microorganism with several virulent factors that influence the inflammatory process and allow it to invade tissues, evade host defense mechanisms, and release toxins, facilitating proliferation and degradation. At present, increasing emphasis is placed on polymicrobial interactions between C. albicans and various bacterial pathogens. Such interaction is mutually beneficial for both parties: it is competitive and antagonistic. Their complex interaction and colonization in the oral cavity serve as the basis for several oral diseases. The dispersion of C. albicans in saliva and the systemic circulation is noted in association with other bacterial populations, suggesting their virulence in causing disease. Hence, it is necessary to understand fungal-bacterial interactions for early detection and the development of novel therapeutic strategies to treat oral diseases. In this paper, we review the mutualistic interaction of C. albicans in oral biofilm formation and polymicrobial interactions in oral diseases. In addition, C. albicans virulence in causing biofilm-related oral diseases and its presence in saliva are discussed.

A Brg1-Rme1 circuit in Candida albicans hyphal gene regulation

Major Candida albicans virulence traits include its ability to make hyphae, to produce a biofilm, and to damage host cells. These traits depend upon expression of hypha-associated genes. A gene expression comparison among clinical isolates suggested that transcription factor Rme1, established by previous studies to be a positive regulator of chlamydospore formation, may also be a negative regulator of hypha-associated genes. Engineered RME1 overexpression supported this hypothesis, but no relevant rme1Δ/Δ mutant phenotype was detected. We reasoned that Rme1 may function within a specific regulatory pathway. This idea was supported by our finding that an rme1Δ/Δ mutation relieves the need for biofilm regulator Brg1 in biofilm formation. The impact of the rme1Δ/Δ mutation is most prominent under static or "biofilm-like" growth conditions. RNA sequencing (RNA-seq) of cells grown under biofilm-like conditions indicates that Brg1 activates hypha-associated genes indirectly via repression of RME1: hypha-associated gene expression levels are substantially reduced in a brg1Δ/Δ mutant and partially restored in a brg1Δ/Δ rme1Δ/Δ double mutant. An rme1Δ/Δ mutation does not simply bypass Brg1, because iron homeostasis genes depend upon Brg1 regardless of Rme1. Rme1 thus connects Brg1 to the targets relevant to hypha and biofilm formation under biofilm growth conditions.IMPORTANCECandida albicans is a major fungal pathogen of humans, and its ability to grow as a surface-associated biofilm on implanted devices is a common cause of infection. Here, we describe a new regulator of biofilm formation, RME1, whose activity is most prominent under biofilm-like growth conditions.

NLRP3 inflammasome: a key player in the pathogenesis of life-style disorders

Proinflammatory cytokines and chemokines play a crucial role in regulating the inflammatory response, which is essential for the proper functioning of our immune system. When infections or threats to the body's defense mechanisms are detected, the innate immune system takes the lead. However, an excessive inflammatory response can lead to the production of high concentrations of cytotoxic molecules, resulting in tissue damage. Inflammasomes are significant contributors to innate immunity, and one of the most extensively studied inflammasome complexes is NOD-like receptor 3 (NLRP3). NLRP3 has a wide range of recognition mechanisms that streamline immune activation and eliminate pathogens. These cytosolic multiprotein complexes are composed of effector, adaptor, and sensor proteins, which are crucial for identifying intracellular bacterial breakdown products and initiating an innate immune cascade. To understand the diverse behavior of NLRP3 activation and its significance in the development of lifestyle-related diseases, one must delve into the study of the immune response and apoptosis mediated by the release of proinflammatory cytokines. In this review, we briefly explore the immune response in the context of lifestyle associated disorders such as obesity, hyperlipidemia, diabetes, chronic respiratory disease, oral disease, and cardiovascular disease.

Candida albicans and Candida glabrata: global priority pathogens

SUMMARYA significant increase in the incidence of Candida-mediated infections has been observed in the last decade, mainly due to rising numbers of susceptible individuals. Recently, the World Health Organization published its first fungal pathogen priority list, with Candida species listed in medium, high, and critical priority categories. This review is a synthesis of information and recent advances in our understanding of two of these species-Candida albicans and Candida glabrata. Of these, C. albicans is the most common cause of candidemia around the world and is categorized as a critical priority pathogen. C. glabrata is considered a high-priority pathogen and has become an increasingly important cause of candidemia in recent years. It is now the second most common causative agent of candidemia in many geographical regions. Despite their differences and phylogenetic divergence, they are successful as pathogens and commensals of humans. Both species can cause a broad variety of infections, ranging from superficial to potentially lethal systemic infections. While they share similarities in certain infection strategies, including tissue adhesion and invasion, they differ significantly in key aspects of their biology, interaction with immune cells, host damage strategies, and metabolic adaptations. Here we provide insights on key aspects of their biology, epidemiology, commensal and pathogenic lifestyles, interactions with the immune system, and antifungal resistance.

Transcriptomics Reveals Effect of Pulsatilla Decoction Butanol Extract in Alleviating Vulvovaginal Candidiasis by Inhibiting Neutrophil Chemotaxis and Activation via TLR4 Signaling

The Pulsatilla decoction is a well-known herbal remedy used in clinical settings for treating vulvovaginal candidiasis (VVC). However, the specific mechanism that makes it effective is still unclear. Recent studies have shown that in cases of VVC, neutrophils recruited to the vagina, influenced by heparan sulfate (HS), do not successfully engulf Candida albicans (C. albicans). Instead, they release many inflammatory factors that cause damage to the vaginal mucosa. This study aims to understand the molecular mechanism by which the n-butanol extract of Pulsatilla decoction (BEPD) treats VVC through transcriptomics. High-performance liquid chromatography was used to identify the primary active components of BEPD. A VVC mouse model was induced using an estrogen-dependent method and the mice were treated daily with BEPD (20 mg/kg, 40 mg/kg, and 80 mg/kg) for seven days. The vaginal lavage fluid of the mice was analyzed for various experimental indices, including fungal morphology, fungal burden, degree of neutrophil infiltration, and cytokines. Various assessments were then performed on mouse vaginal tissues, including pathological assessment, immunohistochemistry, immunofluorescence, Western blot (WB), quantitative real-time PCR, and transcriptome assays. Our results showed that BEPD reduced vaginal redness and swelling, decreased white discharge, inhibited C. albicans hyphae formation, reduced neutrophil infiltration and fungal burden, and attenuated vaginal tissue damage compared with the VVC model group. The high-dose BEPD group even restored the damaged vaginal tissue to normal levels. The medium- and high-dose groups of BEPD also significantly reduced the levels of IL-1β, IL-6, TNF-α, and LDH. Additionally, transcriptomic results showed that BEPD regulated several chemokine (CXCL1, CXCL3, and CXCL5) and S100 alarmin (S100A8 and S100A9) genes, suggesting that BEPD may treat VVC by affecting chemokine- and alarmin-mediated neutrophil chemotaxis. Finally, we verified that BEPD protects the vaginal mucosa of VVC mice by inhibiting neutrophil recruitment and chemotaxis in an animal model of VVC via the TLR4/MyD88/NF-κB pathway. This study provides further evidence to elucidate the mechanism of BEPD treatment of VVC.

The yeast-human coevolution: Fungal transition from passengers, colonizers, and invaders

Fungi are the cause of more than a billion infections in humans every year, although their interactions with the host are still neglected compared to bacteria. Major systemic fungal infections are very unusual in the healthy population, due to the long history of coevolution with the human host. Humans are routinely exposed to environmental fungi and can host a commensal mycobiota, which is increasingly considered as a key player in health and disease. Here, we review the current knowledge on host-fungi coevolution and the factors that regulate their interaction. On one hand, fungi have learned to survive and inhabit the host organisms as a natural ecosystem, on the other hand, the host immune system finely tunes the response toward fungi. In turn, recognition of fungi as commensals or pathogens regulates the host immune balance in health and disease. In the human gut ecosystem, yeasts provide a fingerprint of the transient microbiota. Their status as passengers or colonizers is related to the integrity of the gut barrier and the risk of multiple disorders. Thus, the study of this less known component of the microbiota could unravel the rules of the transition from passengers to colonizers and invaders, as well as their dependence on the innate component of the host's immune response. This article is categorized under: Infectious Diseases > Environmental Factors Immune System Diseases > Environmental Factors Infectious Diseases > Molecular and Cellular Physiology.

The evil companion of OSCC: Candida albicans

OBJECTIVE

Microbial dysbiosis and microbiome-induced inflammation may play a role in the etiopathogenesis of oral squamous cell carcinoma (OSCC). Candida albicans (C. albicans) is the most prevalent opportunistic pathogenic fungus in the oral cavity, and Candida infection is considered as one of its high-risk factors. Although oral microbiota-host interactions are closely associated with the development of OSCC, the interrelationship between fungi and OSCC is poorly understood compared to that between bacteria and viruses.

RESULTS

We accumulated knowledge of the evidence, pathogenic factors, and possible multiple mechanisms by which C. albicans promotes malignant transformation of OSCC, focusing on the induction of epithelial damage, production of carcinogens, and regulation of the tumor microenvironment. In addition, we highlight the latest treatment strategies for Candida infection.

CONCLUSION

This review provides a new perspective on the interrelationship between C. albicans and OSCC and contributes to the establishment of a systematic and reliable clinical treatment system for OSCC patients with C. albicans infection.

Wet adhesive hydrogels based on niobium carbide for experimental research of oral mucosal impairment

Oral mucosal impairment is a prevalent oral disease that frequently causes pain for patients. Conventional treatments have limited effectiveness and can cause adverse reactions. Furthermore, the moist and dynamic nature of the oral mucosal environment makes persistent adherence of conventional materials challenging, which can affect treatment efficacy. In this study, we investigated the potential of a NbC/TA-GelMA hydrogel system, where niobium carbide (NbC) and tannic acid (TA) were added to gelatin methacryloyl (GelMA), for repairing oral mucosal impairment. The wet adhesion properties of NbC/TA-GelMA hydrogels were confirmed by the inclusion of TA with a catechol-rich group. In addition, the photothermal effect of NbC/TA-GelMA hydrogel under near-infrared light, synergizing with TA, provided sustained antibacterial action. Furthermore, the NbC/TA-GelMA hydrogel effectively healed damaged oral mucosa of rats.

One-Step Synthesis of Hydrogel Adhesive with Acid-Responsive Tannin Release for Diabetic Oral Mucosa Defects Healing

The complex preparation, weak wet tissue adhesion, and limited biological activity of traditional oral wound dressings usually impede their efficient treatment and healing for diabetic oral mucosal defects. To overcome these problems, a novel hydrogel adhesive (named CFT hydrogel) is rapidly constructed using a one-step method based on dual-dynamic covalent cross-linking. Compared with the commercial oral patches, the CFT hydrogel shows superior in vivo (rat tongue) wet tissue adhesion performance. Additionally, the CFT hydrogel exhibits unique acid-responsive properties, thereby facilitating the release of bioactive molecule tannic acid in the acidic diabetic wound microenvironment. And a series of in vitro experiments substantiate the favorable biocompatibility and bioactivity properties (including antibacterial, antioxidative, anti-inflammatory, and angiogenetic effects) exhibited by CFT hydrogel. Moreover, in vivo experiments conducted on a diabetic rat model with oral mucosal defects demonstrate that the CFT hydrogel exhibits significant efficacy in protecting against mucosal wounds, alleviating inflammatory reactions, thereby facilitating the wound-healing process. Taken together, this study provides a promising and comprehensive therapeutic option with great potential for the clinical management of oral mucosa defects in diabetic patients.

Nanobody-mediated neutralization of candidalysin prevents epithelial damage and inflammatory responses that drive vulvovaginal candidiasis pathogenesis

Candida albicans can cause mucosal infections in humans. This includes oropharyngeal candidiasis, which is commonly observed in human immunodeficiency virus infected patients, and vulvovaginal candidiasis (VVC), which is the most frequent manifestation of candidiasis. Epithelial cell invasion by C. albicans hyphae is accompanied by the secretion of candidalysin, a peptide toxin that causes epithelial cell cytotoxicity. During vaginal infections, candidalysin-driven tissue damage triggers epithelial signaling pathways, leading to hyperinflammatory responses and immunopathology, a hallmark of VVC. Therefore, we proposed blocking candidalysin activity using nanobodies to reduce epithelial damage and inflammation as a therapeutic strategy for VVC. Anti-candidalysin nanobodies were confirmed to localize around epithelial-invading C. albicans hyphae, even within the invasion pocket where candidalysin is secreted. The nanobodies reduced candidalysin-induced damage to epithelial cells and downstream proinflammatory responses. Accordingly, the nanobodies also decreased neutrophil activation and recruitment. In silico mathematical modeling enabled the quantification of epithelial damage caused by candidalysin under various nanobody dosing strategies. Thus, nanobody-mediated neutralization of candidalysin offers a novel therapeutic approach to block immunopathogenic events during VVC and alleviate symptoms.IMPORTANCEWorldwide, vaginal infections caused by Candida albicans (VVC) annually affect millions of women, with symptoms significantly impacting quality of life. Current treatments are based on anti-fungals and probiotics that target the fungus. However, in some cases, infections are recurrent, called recurrent VVC, which often fails to respond to treatment. Vaginal mucosal tissue damage caused by the C. albicans peptide toxin candidalysin is a key driver in the induction of hyperinflammatory responses that fail to clear the infection and contribute to immunopathology and disease severity. In this pre-clinical evaluation, we show that nanobody-mediated candidalysin neutralization reduces tissue damage and thereby limits inflammation. Implementation of candidalysin-neutralizing nanobodies may prove an attractive strategy to alleviate symptoms in complicated VVC cases.

Hyphal-associated protein expression is crucial for Candida albicans-induced eicosanoid biosynthesis in immune cells

Candida albicans causes opportunistic infections ranging from mucosal mycoses to life-threatening systemic infections in immunocompromised patients. During C. albicans infection, leukotrienes and prostaglandins are formed from arachidonic acid by 5-lipoxygenase (5-LOX) and cyclooxygenases, respectively to amplify inflammatory conditions, but also to initiate macrophage infiltration to achieve tissue homeostasis. Since less is known about the cellular mechanisms triggering such lipid mediator biosynthesis, we investigated the eicosanoid formation in monocyte-derived M1 and M2 macrophages, neutrophils and HEK293 cells transfected with 5-LOX and 5-LOX-activating protein (FLAP) in response to C. albicans yeast or hyphae. Leukotriene biosynthesis was exclusively induced by hyphae in neutrophils and macrophages, whereas prostaglandin E2 was also formed in response to yeast cells by M1 macrophages. Eicosanoid biosynthesis was significantly higher in M1 compared to M2 macrophages. In HEK_5-LOX/FLAP cells only hyphae activated the essential 5-LOX translocation to the nuclear membrane. Using yeast-locked C. albicans mutants, we demonstrated that hyphal-associated protein expression is critical in eicosanoid formation. For neutrophils and HEK_5-LOX/FLAP cells, hyphal wall protein 1 was identified as the essential surface protein that stimulates leukotriene biosynthesis. In summary, our data suggest that hyphal-associated proteins of C. albicans are central triggers of eicosanoid biosynthesis in human phagocytes.

Candidiasis in breast cancer: Tumor progression or not?

Candida albicans is an "opportunistic fungal agent" in cancer patients that can become colonized in both mucosal and deep tissues and cause severe infections. Most evidence has shown that C. albicans can enhance the progress of different cancers by several mechanisms such as generating virulence factors, participation in endogenous production of pro-inflammatory mediators, and stimulating a wide range of immune cells in the host. The main idea of this review is to describe a range of Candida-used mechanisms that are important in candidiasis-associated malignant processes and cancer development, particularly breast cancer. This review intends to provide a detailed discussion on different regulatory mechanisms of C. albicans that undoubtedly help to open new therapeutic horizons of cancer therapy in patients with fungal infection. The current therapeutic approach is not fully effective in immunocompromised and cancer patients, and further studies are required to find new products with effective antifungal properties and minimal side effects to increase the susceptibility of opportunistic fungal infections to conventional antifungal agents. So, in this situation, a special therapy should be considered to control the infection and simultaneously have the most therapeutic index on tumor patients.

Decoding the host-pathogen interspecies molecular crosstalk during oral candidiasis in humans: an in silico analysis

Introduction: The objective of this study is to investigate the interaction between Candida albicans and human proteins during oral candidiasis, with the aim of identifying pathways through which the pathogen subverts host cells. Methods: A comprehensive list of interactions between human proteins and C. albicans was obtained from the Human Protein Interaction Database using specific screening criteria. Then, the genes that exhibit differential expression during oral candidiasis in C. albicans were mapped with the list of human-Candida interactions to identify the corresponding host proteins. The identified host proteins were further compared with proteins specific to the tongue, resulting in a final list of 99 host proteins implicated in oral candidiasis. The interactions between host proteins and C. albicans proteins were analyzed using the STRING database, enabling the construction of protein-protein interaction networks. Similarly, the gene regulatory network of Candida proteins was reconstructed using data from the PathoYeastract and STRING databases. Core module proteins within the targeted host protein-protein interaction network were identified using ModuLand, a Cytoscape plugin. The expression levels of the core module proteins under diseased conditions were assessed using data from the GSE169278 dataset. To gain insights into the functional characteristics of both host and pathogen proteins, ontology analysis was conducted using Enrichr and YeastEnrichr, respectively. Result: The analysis revealed that three Candida proteins, HHT21, CYP5, and KAR2, interact with three core host proteins, namely, ING4 (in the DNMT1 module), SGTA, and TOR1A. These interactions potentially impair the immediate immune response of the host against the pathogen. Additionally, differential expression analysis of fungal proteins and their transcription factors in Candida-infected oral cell lines indicated that Rob1p, Tye7p, and Ume6p could be considered candidate transcription factors involved in instigating the pathogenesis of oral candidiasis during host infection. Conclusion: Our study provides a molecular map of the host-pathogen interaction during oral candidiasis, along with potential targets for designing regimens to overcome oral candidiasis, particularly in immunocompromised individuals.

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.

Artemisinins inhibit oral candidiasis caused by Candida albicans through the repression on its hyphal development

Candida albicans is the most abundant fungal species in oral cavity. As a smart opportunistic pathogen, it increases the virulence by switching its forms from yeasts to hyphae and becomes the major pathogenic agent for oral candidiasis. However, the overuse of current clinical antifungals and lack of new types of drugs highlight the challenges in the antifungal treatments because of the drug resistance and side effects. Anti-virulence strategy is proved as a practical way to develop new types of anti-infective drugs. Here, seven artemisinins, including artemisinin, dihydroartemisinin, artemisinic acid, dihydroartemisinic acid, artesunate, artemether and arteether, were employed to target at the hyphal development, the most important virulence factor of C. albicans. Artemisinins failed to affect the growth, but significantly inhibited the hyphal development of C. albicans, including the clinical azole resistant isolates, and reduced their damage to oral epithelial cells, while arteether showed the strongest activities. The transcriptome suggested that arteether could affect the energy metabolism of C. albicans. Seven artemisinins were then proved to significantly inhibit the productions of ATP and cAMP, while reduced the hyphal inhibition on RAS1 overexpression strain indicating that artemisinins regulated the Ras1-cAMP-Efg1 pathway to inhibit the hyphal development. Importantly, arteether significantly inhibited the fungal burden and infections with no systemic toxicity in the murine oropharyngeal candidiasis models in vivo caused by both fluconazole sensitive and resistant strains. Our results for the first time indicated that artemisinins can be potential antifungal compounds against C. albicans infections by targeting at its hyphal development.

Vaginal homeostasis features of Vulvovaginal Candidiasis through vaginal metabolic profiling

Vulvovaginal candidiasis (VVC) is an inflammatory disease primarily infected by Candida albicans. The condition has good short-term treatment effects, high recurrence, and seriously affects the quality of life of women. Metabolomics has been applied to research a variety of inflammatory diseases. In the present study, the vaginal metabolic profiles of VVC patients and healthy populations (Cnotrol (CTL)) were explored by a non-targeted metabolomics approach. In total, 211 differential metabolites were identified, with the VVC group having 128 over-expressed and 83 under-expressed metabolites compared with healthy individuals. Functional analysis showed that these metabolites were mainly involved in amino acid metabolism and lipid metabolism. In addition, network software analysis indicated that the differential metabolites were associated with mitogen-activated protein kinase (MAPK) signaling and NF-κB signaling. Further molecular docking suggested that linoleic acid can bind to the acyl-CoA synthetase 1 (ACSL1) protein, which has been shown to be associated with multiple inflammatory diseases and is an upstream regulator of the MAPK and NF-κB signaling pathways that mediate inflammation. Therefore, our preliminary analysis results suggest that VVC has a unique metabolic profile. Linoleic acid, a significantly elevated unsaturated fatty acid in the VVC group, may promote VVC development through the ACSL1/MAPK and ACSL1/NF-κB signaling pathways. This study's findings contribute to further exploring the mechanism of VVC infection and providing new perspectives for the treatment of Candida albicans vaginal infection.

Living together: The role of Candida albicans in the formation of polymicrobial biofilms in the oral cavity

The oral cavity of humans is colonized by diversity of microbial community, although dominated by bacteria, it is also constituted by a low number of fungi, often represented by Candida albicans. Although in the vast minority, this usually commensal fungus under certain conditions of the host (e.g., immunosuppression or antibiotic therapy), can transform into an invasive pathogen that adheres to mucous membranes and also to medical or dental devices, causing mucosal infections. This transformation is correlated with changes in cell morphology from yeast-like cells to hyphae and is supported by numerous virulence factors exposed by C. albicans cells at the site of infection, such as multifunctional adhesins, degradative enzymes, or toxin. All of them affect the surrounding host cells or proteins, leading to their destruction. However, at the site of infection, C. albicans can interact with different bacterial species and in its filamentous form may produce biofilms-the elaborated consortia of microorganisms, that present increased ability to host colonization and resistance to antimicrobial agents. In this review, we highlight the modification of the infectious potential of C. albicans in contact with different bacterial species, and also consider the mutual bacterial-fungal relationships, involving cooperation, competition, or antagonism, that lead to an increase in the propagation of oral infection. The mycofilm of C. albicans is an excellent hiding place for bacteria, especially those that prefer low oxygen availability, where microbial cells during mutual co-existence can avoid host recognition or elimination by antimicrobial action. However, these microbial relationships, identified mainly in in vitro studies, are modified depending on the complexity of host conditions and microbial dominance in vivo.

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.

The Interplay between Candida albicans, Vaginal Mucosa, Host Immunity and Resident Microbiota in Health and Disease: An Overview and Future Perspectives

Vulvovaginal candidiasis (VVC), which is primarily caused by Candida albicans, is an infection that affects up to 75% of all reproductive-age women worldwide. Recurrent VVC (RVVC) is defined as >3 episodes per year and affects nearly 8% of women globally. At mucosal sites of the vagina, a delicate and complex balance exists between Candida spp., host immunity and local microbial communities. In fact, both immune response and microbiota composition play a central role in counteracting overgrowth of the fungus and maintaining homeostasis in the host. If this balance is perturbed, the conditions may favor C. albicans overgrowth and the yeast-to-hyphal transition, predisposing the host to VVC. To date, the factors that affect the equilibrium between Candida spp. and the host and drive the transition from C. albicans commensalism to pathogenicity are not yet fully understood. Understanding the host- and fungus-related factors that drive VVC pathogenesis is of paramount importance for the development of adequate therapeutic interventions to combat this common genital infection. This review focuses on the latest advances in the pathogenic mechanisms implicated in the onset of VVC and also discusses novel potential strategies, with a special focus on the use of probiotics and vaginal microbiota transplantation in the treatment and/or prevention of recurrent VVC.

Dual-light defined in situ oral mucosal lesion therapy through a mode switchable anti-bacterial and anti-inflammatory mucoadhesive hydrogel

Oral mucosal ulcer is the most prevalent oral mucosal lesion, affecting the quality of life. Due to the moist and highly dynamic oral lining, the existing oral mucoadhesives are unable to serially address the challenges of residency, hemorrhage, bacterial infection and inflammatory reaction. Herein, a dual-light defined oral mucoadhesive (ZPTA-G/HMA) was proposed, with a methacrylate gelatin-methacrylate hyaluronic acid (GelMA-HAMA, G/HMA) double network hydrogel as a matrix, tannic acid (TA) as a high content anchor moiety provider for the moist oral mucosa, and polydopamine modified zinc oxide (ZnO@PDA, ZP) as a photocatalytic antibacterial substance. This platform had good adhesive and hemostatic properties both in vitro and in vivo. Under 520 nm green light (GL) irradiation, ZPTA-G/HMA would anchor to the wet mucosa surface by crosslinking and exert broad-spectrum antibacterial ability (even including Candida albicans) by in situ producing reactive oxygen species (ROS). Moreover, under 808 nm near-infrared (NIR) irradiation, the increased release of TA combined with the photothermal effect of ZP endowed ZPTA-G/HMA with enhanced anti-inflammatory and pro-healing performance. Collectively, ZPTA-G/HMA could be switched by light sources to achieve the dual-mode real-time adjustment of in situ anti-bacterial function and controlled anti-inflammation, combined with ideal mucosal residence, thus promising in developing personalized sequential strategies for varied oral mucosal lesions.

Of Mycelium and Men: Inherent Human Susceptibility to Fungal Diseases

In medical mycology, the main context of disease is iatrogenic-based disease. However, historically, and occasionally, even today, fungal diseases affect humans with no obvious risk factors, sometimes in a spectacular fashion. The field of “inborn errors of immunity” (IEI) has deduced at least some of these previously enigmatic cases; accordingly, the discovery of single-gene disorders with penetrant clinical effects and their immunologic dissection have provided a framework with which to understand some of the key pathways mediating human susceptibility to mycoses. By extension, they have also enabled the identification of naturally occurring auto-antibodies to cytokines that phenocopy such susceptibility. This review provides a comprehensive update of IEI and autoantibodies that inherently predispose humans to various fungal diseases.

Calcitermin-Loaded Smart Gels Activity against Candida albicans: A Preliminary In Vitro Study

Calcitermin is an antimicrobial peptide of 15 amino acids found in human nasal fluid characterized by antifungal and antibacterial properties. Candida albicans is the most common human fungal pathogen affecting many tissues, such as vaginal mucosa. In this study a formulation suitable for calcitermin administration on vaginal mucosa was developed for the treatment of fungal infections. To favor topical application, mucosal adhesion, and permanence, gels based on poloxamer 407 and xanthan gum were designed and compared with regard to their rheological behavior, erosion, and leakage. The selected gel was loaded with calcitermin, whose release kinetic was evaluated in vitro by Franz cells. An antifungal activity assay was conducted to assess the calcitermin anticandidal potential and the effect of its inclusion in the selected gel. The rheological study revealed the elastic and viscous moduli behavior as a function of poloxamer 407 and xanthan gum concentration. Xanthan gum presence decreased the transition temperature of the gel, while prolonging its erosion and leakage. Particularly, poloxamer 407, 18% and xanthan gum 0.4% were chosen. The calcitermin loading in the selected gel resulted in a transparent and homogeneous formulation and in a 4-fold decrease of the release rate with respect to the calcitermin solution, as evidenced by Franz cell study. The anticandidal activity tests demonstrated that calcitermin-loaded gel was more active against Candida albicans with respect to the peptide solution.

The Candida glabrata Parent Strain Trap: How Phenotypic Diversity Affects Metabolic Fitness and Host Interactions

Reference strains improve reproducibility by standardizing observations and methodology, which has ultimately led to important insights into fungal pathogenesis. However, recent investigations have highlighted significant genotypic and phenotypic heterogeneity across isolates that influence genetic circuitry and virulence within a species. Candida glabrata is the second leading cause of candidiasis, a life-threatening infection, and undergoes extensive karyotype and phenotypic changes in response to stress. Much of the work conducted on this pathogen has focused on two sequenced strains, CBS138 (ATCC 2001) and BG2. Few studies have compared these strains in detail, but key differences include mating type and altered patterns of expression of EPA adhesins. In fact, most C. glabrata isolates and BG2 are MATa, while CBS138 is MATα. However, it is not known if other phenotypic differences between these strains play a role in our understanding of C. glabrata pathogenesis. Thus, we set out to characterize metabolic, cell wall, and host-interaction attributes for CBS138 and BG2. We found that BG2 utilized a broader range of nitrogen sources and had reduced cell wall size and carbohydrate exposure than CBS138, which we hypothesized results in differences in innate immune interactions and virulence. We observed that, although both strains were phagocytosed to a similar extent, BG2 replicated to higher numbers in macrophages and was more virulent during Galleria mellonella infection than CBS138 in a dose-dependent manner. Interestingly, deletion of SNF3, a major nutrient sensor, did not affect virulence in G. mellonella for BG2, but significantly enhanced larval killing in the CBS138 background compared to the parent strain. Understanding these fundamental differences in metabolism and host interactions will allow more robust conclusions to be drawn in future studies of C. glabrata pathogenesis. IMPORTANCE Reference strains provide essential insights into the mechanisms underlying virulence in fungal pathogens. However, recent studies in Candida albicans and other species have revealed significant genotypic and phenotypic diversity within clinical isolates that are challenging paradigms regarding key virulence factors and their regulation. Candida glabrata is the second leading cause of candidiasis, and many studies use BG2 or CBS138 for their investigations. Therefore, we aimed to characterize important virulence-related phenotypes for both strains that might alter conclusions about C. glabrata pathogenesis. Our study provides context for metabolic and cell wall changes and how these may influence host interaction phenotypes. Understanding these differences is necessary to support robust conclusions about how virulence factors may function in these and other very different strain backgrounds.

Tacrolimus inhibits stress responses and hyphal formation via the calcineurin signaling pathway in Trichosporon asahii

The pathogenic fungus Trichosporon asahii causes fatal deep-seated mycosis in immunocompromised patients. Calcineurin, which is widely conserved in eukaryotes, regulates cell growth and various stress responses in fungi. Tacrolimus (FK506), a calcineurin inhibitor, induces sensitivity to compounds that cause stress on the cell membrane and cell wall integrity. In this study, we demonstrated that FK506 affects stress responses and hyphal formation in T. asahii. In silico structural analysis revealed that amino acid residues in the binding site of the calcineurin-FKBP12 complex that interact with FK506 are conserved in T. asahii. The growth of T. asahii was delayed by FK506 in the presence of SDS or Congo red but not in the presence of calcium chloride. FK506 also inhibited hyphal formation in T. asahii. A mutant deficient of the cnb gene, which encodes the regulatory subunit B of calcineurin, exhibited stress sensitivities on exposure to SDS and Congo red and reduced the hyphal forming ability of T. asahii. In the cnb-deficient mutant, FK506 did not increase the stress sensitivity or reduce hyphal forming ability. These results suggest that FK506 affects stress responses and hyphal formation in T. asahii via the calcineurin signaling pathway.

Candidalysin: Connecting the pore forming mechanism of this virulence factor to its immunostimulatory properties

Candida albicans is a deadly pathogen responsible for millions of mucosal and systemic infections per year. The pathobiology of C. albicans is largely dependent on the damaging and immunostimulatory properties of the peptide candidalysin (CL), a key virulence factor. When CL forms pores in the plasma membrane of epithelial cells, it activates a response network grounded in activation of the epidermal growth factor receptor. Prior reviews have characterized the resulting CL immune activation schemas but lacked insights into the molecular mechanism of CL membrane damage. We recently demonstrated that CL functions by undergoing a unique self-assembly process; CL forms polymers and loops in aqueous solution prior to inserting and forming pores in cell membranes. This mechanism, the first of its kind to be observed, informs new therapeutic avenues to treat Candida infections. Recently, variants of CL were identified in other Candida species, providing an opportunity to identify the residues that are key for CL to function. In this review, we connect the ability of CL to damage cell membranes to its immunostimulatory properties.

Antifungal Activity of Plant Secondary Metabolites on Candida albicans: An Updated Review

Fungal infections have been increasing continuously worldwide, especially in immunocompromised individuals. Fungi, regarded as eukaryotic pathogens, have many similarities to the host cells, which inhibit anti-fungal drug development progress. Various fungal model systems have been studied, and it was concluded that Candida spp. is the most common disease-causing fungus. Candida species are well known to cause infections not only in our mouth, skin, and vagina, but they are also a frequent cause of life-threatening hospital bloodstream infections. The morphological and developmental pathways of Candida have been studied extensively, providing insight into the fungus development. Candida albicans is known to be the most pathogenic species responsible for a variety of infections in humans. Conventional anti-fungal drugs, mainly azoles drugs available in the market, have been used for years developing resistance in C. albicans. Hence, the production of new anti-fungal drugs, which require detailed molecular knowledge of fungal pathogenesis, needs to be encouraged. Therefore, this review targets the new approach of "Green Medicines" or the phytochemicals and their secondary metabolites as a source of novel anti-fungal agents to overcome the drug resistance of C. albicans, their mechanism of action, and their combined effects with the available anti-fungal drugs.

The IL-20RB receptor and the IL-20 signaling pathway in regulating host defense in oral mucosal candidiasis

Pseudomembranous candidiasis (thrush), erythematous candidiasis, and fungal esophagitis are infections of the barrier mucosa of the upper gastrointestinal tract. The majority of these infections are caused by Candida albicans, an opportunistic fungal pathogen that frequently exists as a harmless commensal on mucosal surfaces lining the gastrointestinal tract. Oral infections are initiated in the superficial stratified squamous epithelium, in which keratinocytes are the most abundant host cells and are the initial points of contact with C. albicans present in saliva. Intrinsic features of oral keratinocytes are likely to play important roles in host defense and tissue homeostasis in oral candidiasis. One understudied pathway that may be important for modulating oral candidiasis is the IL-20 cytokine signaling pathway that employs keratinocyte IL-20RB receptors as ligands for IL-19, IL-20, and IL-24. We report that production of human oral keratinocyte il24 mRNA and protein are stimulated during co-culture with C. albicans. To test the role of the IL-20 family signaling pathway in oral candidiasis, Il20rb^-/- mice (lacking the IL-20RB receptor) were compared to wild-type mice in a murine model of oropharyngeal candidiasis. Fungal burdens and percent loss in body weight were determined. Despite comparable fungal burdens, the Il20rb^-/- mice exhibited less weight loss over the course of their infection compared to the B6 mice, suggestive of reduced overall disease consequences in the mutant mice. Interference with IL-20 family cytokine signaling may be useful for augmenting the ability of the host to defend itself against pathogens.

Epidermal clearance of Candida albicans is mediated by IL-17 but independent of fungal innate immune receptors

IL-17 plays important roles in host defense against Candida albicans at barrier surfaces and during invasive infection. However, the role of IL-17 in host defense after colonization of the epidermis, a main site of C. albicans infection, remains poorly understood. Using a murine model of epicutaneous candidiasis without skin abrasion, we found that skin inflammation triggered by epidermal C. albicans colonization was self-limiting with fungal clearance completed by day 7 after inoculation in wild-type mice or animals deficient in IL-17A or IL-17F. In contrast, marked neutrophilic inflammation in the epidermis and impaired fungal clearance were observed in mice lacking both IL-17A and IL-17F. Clearance of C. albicans was independent of Dectin-1, Dectin-2, CARD9 (caspase-recruitment domain family, member 9), TLR2 (Toll-like receptor 2) and MyD88 in the epidermal colonization model. We found that group 3 innate lymphoid cells (ILC3s) and γδT cells were the major IL-17 producers in the epicutaneous candidiasis model. Analyses of Rag2-/- mice and Rag2-/-Il2rg-/- mice revealed that production of IL-17A and IL-17F by ILC3s was sufficient for C. albicans clearance. Finally, we found that depletion of neutrophils impaired C. albicans clearance in the epidermal colonization model. Taken together, these findings indicate a critical and redundant function of IL-17A and IL-17F produced by ILC3s in host defense against C. albicans in the epidermis. The results also suggest that epidermal C. albicans clearance is independent of innate immune receptors or that these receptors act redundantly in fungal recognition and clearance.

Small, Cationic Antifungal Proteins from Filamentous Fungi Inhibit Candida albicans Growth in 3D Skin Infection Models

The emerging resistance of human-pathogenic fungi to antifungal drugs urges the development of alternative therapeutic strategies. The small, cationic antifungal proteins (AFPs) from filamentous ascomycetes represent promising candidates for next-generation antifungals. These bio-molecules need to be tested for tolerance in the host and efficacy against fungal pathogens before they can be safely applied in humans. Testing of the efficacy and possible adverse effects of new drug candidates in three-dimensional (3D) human-cell based models represents an advantageous alternative to animal experiments. In, this study, as a proof-of-principle, we demonstrate the usefulness of 3D skin infection models for screening new antifungal drug candidates for topical application. We established a cutaneous infection with the opportunistic human-pathogenic yeast Candida albicans in a commercially available 3D full-thickness (FT) skin model to test the curative potential of distinct AFPs from Penicillium chrysogenum (PAFopt, PAFB, and PAFC) and Neosartorya (Aspergillus) fischeri (NFAP2) in vitro. All tested AFPs were comparably well tolerated by the skin models. The infected 3D models exhibited reduced epidermal permeability barriers, allowing C. albicans to colonize the epidermal and dermal layers, and showed increased secretion of the pro-inflammatory cytokine IL-6 and the chemokine IL-8. AFP treatment diminished the fungal burden and penetration depth of C. albicans in the infected models. The epidermal permeability barrier was restored and the secretion of IL-8 was decreased following AFP treatment. In summary, our study proves that the tested AFPs exhibit antifungal potential against cutaneous C. albicans infection in a 3D FT skin model. IMPORTANCE Candida albicans represents one of the most prevalent opportunistic fungal pathogens, causing superficial skin and mucosal infections in humans with certain predisposing health conditions and life-threatening systemic infections in immunosuppressed patients. The emerging drug resistance of this human-pathogenic yeast and the limited number of antifungal drugs for prevention and treatment of infections urgently demands the identification of new antifungal compounds with novel mechanisms of action. Small, cationic antifungal proteins (AFPs) from filamentous fungi represent promising candidates for next-generation antifungals for topical application. These bio-molecules need to be tested for tolerance by the host and efficacy in pathogen clearance prior to being involved in clinical trials. In a proof-of-principle study, we provide evidence for the suitability of 3D human-cell based models as advantageous alternatives to animal experiments. We document the tolerance of specific AFPs and their curative efficacy against cutaneous C. albicans infection in a 3D skin model.

The Bacillary Postbiotics, Including 2-Undecanone, Suppress the Virulence of Pathogenic Microorganisms

Secreted molecules from probiotic Bacilli have often been considered potential pharmaceuticals to fight infections caused by bacterial or yeast pathogens. In the present study, we investigated the antagonistic potential of secreted probiotic filtrates (hereafter, postbiotics) derived from Lactobacillus plantarum cells against pathogenic microorganisms, such as Escherichia coli, Staphylococcus aureus, and Candida albicans. We found that the postbiotics mitigate the biofilms of the tested pathogens with no notable effect on their planktonic growth. In addition, the postbiotics suppressed some virulence traits, for instance, the dendrite swarming motility of E. coli and yeast-to-hyphal switch in C. albicans. Further assays with an active constituent produced by the L. plantarum cells–2-undecanone revealed two significant findings: (i) 2-undecanone inhibits C. albicans biofilms and hyphae in vitro and in a Caenorhabditis elegans model, and (ii) it interacts specifically with Gln 58 amino acid residue of hyphal wall protein-1 (Hwp-1) in molecular docking analysis. The results suggest the targeted mode of antagonistic action of 2-undecanone against C. albicans biofilm. In total, the findings of the study depict an appealing strategy to use postbiotics, including specific ketone molecules, produced by L. plantarum for developing novel antibiofilm and anti-hyphal pharmaceuticals.

The Candida albicans toxin candidalysin mediates distinct epithelial inflammatory responses through p38 and EGFR-ERK pathways

The fungal pathogen Candida albicans secretes the peptide toxin candidalysin, which damages epithelial cells and drives an innate inflammatory response mediated by the epidermal growth factor receptor (EGFR) and mitogen-activated protein kinase (MAPK) pathways and the transcription factor c-Fos. In cultured oral epithelial cells, candidalysin activated the MAPK p38, which resulted in heat shock protein 27 (Hsp27) activation, IL-6 release, and EGFR phosphorylation without affecting the induction of c-Fos. p38 activation was not triggered by EGFR but by two nonredundant pathways involving MAPK kinases (MKKs) and the kinase Src, which differentially controlled p38 signaling outputs. Whereas MKKs mainly promoted p38-dependent release of IL-6, Src promoted p38-mediated phosphorylation of EGFR in a ligand-independent fashion. In parallel, candidalysin also activated the EGFR-ERK pathway in a ligand-dependent manner, resulting in c-Fos activation and release of the neutrophil-activating chemokines G-CSF and GM-CSF. In mice, early clearance events of oral C. albicans infection required p38 but not c-Fos. These findings delineate how candidalysin activates the pathways downstream of the MAPKs p38 and ERK that differentially contribute to immune activation during C. albicans infection.

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.

Antifungal Activity and Biocompatibility of α-AgVO3, α-Ag2WO4, and β-Ag2MoO4 Using a Three-Dimensional Coculture Model of the Oral Mucosa

Fungal infections have become a major concern in the medical community, especially those caused by Candida spp. Within this species, Candida albicans stands out for being an opportunistic commensal fungus that can cause superficial and invasive infections. Current antifungal therapy involves the local and/or systemic use of drugs such as azoles, polyenes, and echinocandins. These antifungals are based on highly specific target sites, and the development of resistance may occur with changes in the enzymatic pathways that serve as the drug targets. Thus, the development of new antifungal drugs is highly recommended to prevent drug resistance. The present investigation evaluated the antifungal activity of silver-containing microcrystals such as silver vanadate (α-AgVO₃), silver tungstate (α-Ag₂WO₄), and silver molybdate (β-Ag₂MoO₄). In addition to having antimicrobial activity, such compounds should not cause damage to underlying tissues. Thus, to better assess the biocompatibility of new compounds, a new three-dimensional (3D) coculture model involving three cell lines was developed. The validation of the model was based on fluorescent markers and confocal laser microscopy. The biocompatibility of silver-containing microcrystals was evaluated by MTT (3-(4,5-dimethylthiazol-2-yl)-2,5-diphenyltetrazolium bromide) assay. 3D coculture was infected with C. albicans biofilm and challenged with α-AgVO₃, α-Ag₂WO₄, and β-Ag₂MoO₄. The action of microcrystals on C. albicans biofilm was evaluated by colony-forming units (CFU/ml) and LIVE/DEAD staining. In addition, production of proinflammatory cytokines interleukin 6 (IL-6), IL-8, IL-1β, and tumor necrosis factor α (TNF-α) was measured by cytometric bead array kit using flow cytometry. The 3D coculture model described here proved to be adequate to assess both the biocompatibility of the new materials and the infectious processes. Regarding the biocompatibility of the microcrystals, only α-AgVO₃ (15.62 µg/ml) showed a decrease in cell viability. The antibiofilm activity of α-Ag₂WO₄ was similar to that of the standard drug (fluconazole). Although α-Ag₂WO₄ was able to induce the production of IL-6, IL-8, and IL-1β, no differences in cytokine production were observed between noninfected and infected models treated with this microcrystal. β-Ag₂MoO₄ inhibits the production of TNF-α in the infected model; however, it showed no antibiofilm activity. Based on the biocompatibility and antifungal findings, α-Ag₂WO₄ is a promising material for treating C. albicans infection.

[Research Updates: The Role of Interaction between Oral Microbiota, Immune Cells, and Epithelial Barrier in Oral Mucosal Homeostasis and Pathogenesis]

In a healthy state, the interaction between the oral microorganisms, mucosal immune cells and epithelial barrier can maintain the oral microecological stability. However, the oral microecology is disrupted under a diseased state and various pathogenic bacteria and their virulence factors and metabolites irritate the immune system, which causes direct or indirect damage to the epithelial barrier, promotes the pathogenesis and progression of oral mucosal diseases, and triggers immune inflammatory response or the irreversible transformation from inflammation into cancer. We herein reviewed the interaction between oral microorganisms, immune cells and epithelial barrier from two perspectives, the maintenance of the oral homeostasis and the pathogenesis of oral mucosal diseases. We intended to gain further understanding of the oral mucosal homeostasis and the mechanism of action of the pathogenesis and progression of oral mucosal diseases, and to provide thereby ideas and scientific and theoretical basis for developing new strategies for the diagnosis and treatment of oral mucosal diseases through re-establishing mucosal homeostasis.

A call for further research on the relation between type 2 diabetes and oral candidiasis

OBJECTIVE

This study aimed to evaluate the relationship between oral candidiasis with salivary features, neutrophil function, and glycemic control in type 2 diabetes (T2D).

DESIGN

Twenty-nine individuals were included, 16 with T2D and 13 without the disease. The participants underwent clinical examination, neutrophilic function tests, fasting glycemia and glycated hemoglobin (A1c), stimulated and unstimulated saliva collection, and swab and exfoliative cytology. Salivary flow, pH, and total fungi count were evaluated on saliva, and identification of the Candida species was performed in saliva and swab samples.

RESULTS

There was no difference in unstimulated salivary flow and pH of the stimulated and unstimulated saliva for participants with T2D and controls (P > .05). Individuals from both groups presented no candidal lesions. The salivary fungal growth in the T2D group was higher than that in controls (P < .05). Only individuals with T2D presented alterations in the neutrophilic functions (14/16; 87.5%; P < .05). There was no relationship between high A1c values and neutrophil dysfunction with the presence of Candida spp. in both saliva and mucosa (P > .05).

CONCLUSIONS

High A1c level, reduction in neutrophil activity, salivary flow and pH, and increase in total salivary Candida spp. counts were not related to oral candidiasis in patients with T2D.