Oral epithelium?Candida glabrata interactions in vitro

Host's Immunity and Candida Species Associated with Denture Stomatitis: A Narrative Review

Denture-related Candida stomatitis, which has been described clinically in the literature, is either localized or generalized inflammation of the oral mucosa in connection with a removable prosthesis. During this inflammatory process, the mycobacterial biofilm and the host’s immune response play an essential role. Among microorganisms of this mixed biofilm, the Candida species proliferates easily and changes from a commensal to an opportunistic pathogen. In this situation, the relationship between the Candida spp. and the host is influenced by the presence of the denture and conditioned both by the immune response and the oral microbiota. Specifically, this fungus is able to hijack the innate immune system of its host to cause infection. Additionally, older edentulous wearers of dentures may experience an imbalanced and decreased oral microbiome diversity. Under these conditions, the immune deficiency of these aging patients often promotes the spread of commensals and pathogens. The present narrative review aimed to analyze the innate and adaptive immune responses of patients with denture stomatitis and more particularly the involvement of Candida albicans sp. associated with this pathology.

Histone H4 dosage modulates DNA damage response in the pathogenic yeast Candida glabrata via homologous recombination pathway

Candida glabrata, a nosocomial fungal bloodstream pathogen, causes significant morbidity and mortality in hospitals worldwide. The ability to replicate in macrophages and survive a high level of oxidative stress contributes to its virulence in the mammalian host. However, the role of DNA repair and recombination mechanisms in its pathobiology is still being discovered. Here, we have characterized the response of C. glabrata to the methyl methanesulfonate (MMS)-induced DNA damage. We found that the MMS exposure triggered a significant downregulation of histone H4 transcript and protein levels, and that, the damaged DNA was repaired by the homologous recombination (HR) pathway. Consistently, the reduced H4 gene dosage was associated with increased HR frequency and elevated resistance to MMS. The genetic analysis found CgRad52, a DNA strand exchange-promoter protein of the HR system, to be essential for this MMS resistance. Further, the tandem-affinity purification and mass spectrometry analysis revealed a substantially smaller interactome of H4 in MMS-treated cells. Among 23 identified proteins, we found the WD40-repeat protein CgCmr1 to interact genetically and physically with H4, and regulate H4 levels, HR pathway and MMS stress survival. Controlling H4 levels tightly is therefore a regulatory mechanism to survive MMS stress in C. glabrata.

The cellular hereditary material DNA is present in a compact ordered form in eukaryotic cells which involves its winding around an octamer of four basic histone proteins, H2A, H2B, H3 and H4. DNA-protein (including histones) complexes form chromatin, with the chromatin structure, open or closed, modulating gene expression. Any change in histone levels impacts chromatin architecture and functions. Here, we have studied the effect of diminished histone H4 levels on viability, DNA damage response and virulence of the pathogenic yeast Candida glabrata. C. glabrata, a constituent of the normal microflora of healthy humans, causes both superficial and invasive infections in immunocompromised individuals. Despite it being the second most common cause of Candida bloodstream infections in USA after C. albicans, its pathogenesis determinants are yet to deciphered in full. We report that the reduced histone H4 gene dosage in C. glabrata results in elevated resistance to the DNA alkylating agent, methyl methanesulfonate, increased homologous recombination (HR) and attenuated virulence. We also show that the H4 interacting protein CgCmr1 regulates HR probably through maintaining H4 levels. Overall, our data underscore the H4 protein abundance as a cue to express virulence factors and regulate DNA metabolism in pathogenic fungi.

Effects of Candida albicans infection on defense effector secretion by human oral mucosal epithelial cells

OBJECTIVE

The aim of this study was to investigate the effects of Candida albicans on the production of defense effector molecules by human oral mucosal epithelial cells in vitro.

DESIGN

Immortalized human oral mucosal epithelial (Leuk-1) cells and C. albicans strain 5314 were cocultured at different cell-to-C. albicans ratios. The viability of Leuk-1 cells was determined by MTT and RTCA measurements. The secretory levels of multiple defense effector molecules were determined by Enzyme-linked immunosorbent assay (ELISA).

RESULTS

Our results indicated that C. albicans significantly decreased the secretion of IgG, cystatin C, lactoferrin, and TGF-β1 in a dose-dependent manner and remarkably reduced the production of IgA independent of the cell-to-C. albicans ratio. However, C. albicans clearly enhanced the secretion of IgM, galectin-3, P-selectin, granzyme B and perforin.

CONCLUSION

These results suggest that C. albicans may exert a regulatory role in the defense response of oral mucosal epithelial cells by altering secretory levels of defense effector molecules.

Candida glabrata Has No Enhancing Role in the Pathogenesis of Candida-Associated Denture Stomatitis in a Rat Model

Many denture wearers suffer from Candida-associated denture stomatitis (DS), a fungal infection of the hard palate in contact with dentures. Biofilm formation by Candida albicans on denture/palate surfaces is considered a central process in the infection onset. Although Candida glabrata is frequently coisolated with C. albicans, its role in DS pathogenesis is unknown. We show here, using a contemporary rat model that employed a patented intraoral denture system, that C. glabrata established stable colonization on the denture/palate. However, in contrast to C. albicans inoculated rats, rats inoculated with C. glabrata exhibited minimal changes in weight gain or palatal tissue damage. Likewise, coinoculation with the two Candida species resulted in no exacerbation of C. albicans-induced DS pathology. Together, our findings indicate that C. glabrata has no inducing/enhancing role in DS pathogenesis.

Denture stomatitis (DS) is a condition characterized by inflammation of the oral mucosa in direct contact with dentures and affects a significant number of otherwise healthy denture wearers. Candida-associated DS is predominantly caused by Candida albicans, a dimorphic fungus that readily colonizes and forms biofilms on denture materials. Previous studies showed a requirement for Candida biofilm formation on both palate and dentures in infection and identified fungal morphogenic transcription factors, Efg1 and Bcr1, as key players in DS pathogenesis. While both C. albicans and Candida glabrata are frequently coisolated in mucosal candidiasis, a pathogenic role for C. glabrata in DS remains unknown. Using an established rat model of DS, we sought to determine whether C. glabrata alone or coinoculation with C. albicans establishes colonization and causes palatal tissue damage and inflammation. Rats fitted with custom dentures were inoculated with C. albicans and/or C. glabrata and monitored over a 4-week period for fungal burden (denture/palate), changes in body weight, and tissue damage via lactate dehydrogenase (LDH) release as well as palatal staining by hematoxylin and eosin (H&E) and immunohistochemistry for myeloperoxidase (MPO) as measures of inflammation. C. glabrata colonized the denture/palate similarly to C. albicans. In contrast to C. albicans, colonization by C. glabrata resulted in minimal changes in body weight, palatal LDH release, and MPO expression. Coinoculation with both species had no obvious modulation of C. albicans-mediated pathogenic effects. These data suggest that C. glabrata readily establishes colonization on denture and palate but has no apparent role for inducing/enhancing C. albicans pathogenesis in DS.

IMPORTANCE Many denture wearers suffer from Candida-associated denture stomatitis (DS), a fungal infection of the hard palate in contact with dentures. Biofilm formation by Candida albicans on denture/palate surfaces is considered a central process in the infection onset. Although Candida glabrata is frequently coisolated with C. albicans, its role in DS pathogenesis is unknown. We show here, using a contemporary rat model that employed a patented intraoral denture system, that C. glabrata established stable colonization on the denture/palate. However, in contrast to C. albicans inoculated rats, rats inoculated with C. glabrata exhibited minimal changes in weight gain or palatal tissue damage. Likewise, coinoculation with the two Candida species resulted in no exacerbation of C. albicans-induced DS pathology. Together, our findings indicate that C. glabrata has no inducing/enhancing role in DS pathogenesis.

Candida glabrata: A Lot More Than Meets the Eye

Candida glabrata is an opportunistic human fungal pathogen that causes superficial mucosal and life-threatening bloodstream infections in individuals with a compromised immune system. Evolutionarily, it is closer to the non-pathogenic yeast Saccharomyces cerevisiae than to the most prevalent Candida bloodstream pathogen, C. albicans. C. glabrata is a haploid budding yeast that predominantly reproduces clonally. In this review, we summarize interactions of C. glabrata with the host immune, epithelial and endothelial cells, and the ingenious strategies it deploys to acquire iron and phosphate from the external environment. We outline various attributes including cell surface-associated adhesins and aspartyl proteases, biofilm formation and stress response mechanisms, that contribute to the virulence of C. glabrata. We further discuss how, C. glabrata, despite lacking morphological switching and secreted proteolytic activity, is able to disarm macrophage, dampen the host inflammatory immune response and replicate intracellularly.

Role of salivary and candidal proteins in denture stomatitis: an exploratory proteomic analysis

Denture stomatitis, inflammation and redness beneath a denture, affects nearly half of all denture wearers. Candidal organisms, the presence of a denture, saliva, and host immunity are the key etiological factors for the condition. The role of salivary proteins in denture stomatitis is not clear. In this study 30 edentulous subjects wearing a maxillary complete denture were recruited. Unstimulated whole saliva from each subject was collected and pooled into two groups (n = 15 each), healthy and stomatitis (Newton classification II and III). Label-free multidimensional liquid chromatography/tandem mass spectrometry (2D-LC-MS/MS) proteomics on two mass spectrometry platforms were used to determine peptide mass differences between control and stomatitis groups. Cluster analysis and principal component analysis were used to determine the differential expression among the groups. The two proteomic platforms identified 97 and 176 proteins (ANOVA; p < 0.01) differentially expressed among the healthy, type 2 and 3 stomatitis groups. Three proteins including carbonic anhydrase 6, cystatin C, and cystatin SN were found to be the same as previous study. Salivary proteomic profiles of patients with denture stomatitis were found to be uniquely different from controls. Analysis of protein components suggests that certain salivary proteins may predispose some patients to denture stomatitis while others are believed to be involved in the reaction to fungal infection. Analysis of candidal proteins suggests that multiple species of candidal organisms play a role in denture stomatitis.

Beyond Candida albicans: Mechanisms of immunity to non-albicans Candida species

The fungal genus Candida encompasses numerous species that inhabit a variety of hosts, either as commensal microbes and/or pathogens. Candida species are a major cause of fungal infections, yet to date there are no vaccines against Candida or indeed any other fungal pathogen. Our knowledge of immunity to Candida mainly comes from studies on Candida albicans, the most frequent species associated with disease. However, non-albicans Candida (NAC) species also cause disease and their prevalence is increasing. Although research into immunity to NAC species is still at an early stage, it is becoming apparent that immunity to C. albicans differs in important ways from non-albicans species, with important implications for treatment, therapy and predicted demographic susceptibility. This review will discuss the current understanding of immunity to NAC species in the context of immunity to C. albicans, and highlight as-yet unanswered questions.

Intracellular survival of Candida glabrata in macrophages: immune evasion and persistence

Candida glabrata is a successful human opportunistic pathogen which causes superficial but also life-threatening systemic infections. During infection, C. glabrata has to cope with cells of the innate immune system such as macrophages, which belong to the first line of defense against invading pathogens. Candida glabrata is able to survive and even replicate inside macrophages while causing surprisingly low damage and cytokine release. Here, we present an overview of recent studies dealing with the interaction of C. glabrata with macrophages, from phagocytosis to intracellular growth and escape. We review the strategies of C. glabrata that permit intracellular survival and replication, including poor host cell activation, modification of phagosome maturation and phagosome pH, adaptation to antimicrobial activities, and mechanisms to overcome the nutrient limitations within the phagosome. In summary, these studies suggest that survival within macrophages may be an immune evasion and persistence strategy of C. glabrata during infection.

Oral lactoferrin protects against experimental candidiasis in mice

AIMS

To determine the role of human lactoferrin (hLF) in protecting the oral cavities of mice against Candida albicans infection in lactoferrin knockout (LFKO(-/-)) mice was compared to wild-type (WT) mice. We also aim to determine the protective role of hLF in LFKO(-/-) mice.

METHODS AND RESULTS

Antibiotic-treated immunosuppressed mice were inoculated with C. albicans (or sham infection) by oral swab and evaluated for the severity of infection after 7 days of infection. To determine the protective role of hLF, we added 0·3% solution of hLF to the drinking water given to some of the mice. CFU count, scoring of lesions and microscopic observations were carried out to determine the severity of infection. LFKO(-/-) I mice showed a 2 log (P = 0·001) higher CFUs of C. albicans in the oral cavity compared to the WT mice infected with C. albicans (WTI). LFKO(-/-) I mice given hLF had a 3 log (P = 0·001) reduction in CFUs in the oral cavity compared to untreated LFKO(-/-) I mice. The severity of infection, observed by light microscopy, revealed that the tongue of the LFKO(-/-) I mice showed more white patches compared to WTI and LFKO(-/-) I + hLF mice. Scanning electron microscopic observations revealed that more filiform papillae were destroyed in LFKO(-/-) I mice when compared to WTI or LFKO(-/-) I + hLF mice.

CONCLUSIONS

Human LF is important in protecting mice from oral C. albicans infection. Administered hLF may be used to prevent C. albicans infection.

SIGNIFICANCE AND IMPACT OF THE STUDY

Human LF, a multifunctional iron-binding glycoprotein can be used as a therapeutic active ingredient in oral healthcare products against C. albicans.

Effects of bovine lactoferrin to oral Candida albicans and Candida glabrata isolates recovered from the saliva in elderly people

The effects of bovine lactoferrin (bLF) on the growth of Candida species and on inflammatory cytokine production in gingival keratinocytes, NDUSD-1 co-cultured with Candida strains were investigated. The results showed that bLF at 10 and 100 μg/mL significantly inhibits the growth of two C. albicans strains and two C. glabrata strains isolated from the saliva of elderly people requiring nursing care, respectively. The levels of inflammatory cytokines, interleukin (IL)-6, and IL-8 in NDUSD-1 co-cultured with each of these four Candida strains were measured. C. albicans tend to have a more potent capacity than C. glabrata to induce the production of the inflammatory cytokines in NDUSD-1. The levels of IL-6 and IL-8 in NDUSD-1 co-cultured with each of Candida species were measured after addition of bLF. bLF at concentrations from 1 to 100 μg/mL significantly inhibited the production of these cytokines in NDUSD-1 co-cultured with Candida species. These findings suggest that bLF may be useful in reducing the risk of aspiration pneumonia among elderly people requiring care for whom oral care is difficult.

Anticandidal activity and biocompatibility of a rechargeable antifungal denture material

OBJECTIVES

Candida-associated denture stomatitis is a recurrent and debilitating oral mucosal disease. Development of anticandidal denture materials represents a promising strategy to manage this condition. We have previously shown that miconazole incorporated in methacrylic acid (MAA) copolymerized diurethane dimethacrylate (UDMA) denture materials has long-term anticandidal activity. In this study, we examined the ability of culture medium conditioned with drug-free- or miconazole-MAA-UDMA discs to prevent Candida infection in an in vitro oral epithelial cell/Candida albicans coculture system.

MATERIALS AND METHODS

Candida albicans (C. albicans)-induced OKF6/TERT-2 cell damage was quantified by the release of lactate dehydrogenase from epithelial cells, cytokine production was quantified using protein cytokine arrays, and the expression of C. albicans genes was measured by RT-qPCR.

RESULTS

Candida albicans had limited growth with altered expression levels of secreted aspartyl proteinase-2 and -5 in culture medium conditioned by miconazole-MAA-UDMA discs. Significantly, the ability of C. albicans to induce oral epithelial cell damage and trigger epithelial proinflammatory cytokine production was also inhibited by miconazole disc conditioned media.

CONCLUSION

Miconazole released from MAA-UDMA denture materials effectively prevents the development of candidal infection in an in vitro oral epithelial system. Further characterization of this drug-rechargeable denture material is warranted.

Candida albicans cell wall glycosylation may be indirectly required for activation of epithelial cell proinflammatory responses

Oral epithelial cells discriminate between the yeast and hyphal forms of Candida albicans via the mitogen-activated protein kinase (MAPK) signaling pathway. This occurs through phosphorylation of the MAPK phosphatase MKP1 and activation of the c-Fos transcription factor by the hyphal form. Given that fungal cell wall polysaccharides are critical in host recognition and immune activation in myeloid cells, we sought to determine whether β-glucan and N- or O-glycosylation was important in activating the MAPK/MKP1/c-Fos hypha-mediated response mechanism and proinflammatory cytokines in oral epithelial cells. Using a series of β-glucan and N- and O-mannan mutants, we found that N-mannosylation (via Δoch1 and Δpmr1 mutants) and O-mannosylation (via Δpmt1 and Δmnt1 Δmnt2 mutants), but not phosphomannan (via a Δmnn4 mutant) or β-1,2 mannosylation (via Δbmt1 to Δbmt6 mutants), were required for MKP1/c-Fos activation, proinflammatory cytokine production, and cell damage induction. However, the N- and O-mannan mutants showed reduced adhesion or lack of initial hypha formation at 2 h, resulting in little MKP1/c-Fos activation, or restricted hypha formation/pseudohyphal formation at 24 h, resulting in minimal proinflammatory cytokine production and cell damage. Further, the α-1,6-mannose backbone of the N-linked outer chain (corresponding to a Δmnn9 mutant) may be required for epithelial adhesion, while the α-1,2-mannose component of phospholipomannan (corresponding to a Δmit1 mutant) may contribute to epithelial cell damage. β-Glucan appeared to play no role in adhesion, epithelial activation, or cell damage. In summary, N- and O-mannosylation defects affect the ability of C. albicans to induce proinflammatory cytokines and damage in oral epithelial cells, but this may be due to indirect effects on fungal pathogenicity rather than mannose residues being direct activators of the MAPK/MKP1/c-Fos hypha-mediated immune response.

Activation of MAPK/c-Fos induced responses in oral epithelial cells is specific to Candida albicans and Candida dubliniensis hyphae

Oral epithelial cells detect the human pathogenic fungus Candida albicans via NF-κB and a bi-phasic mitogen-activated protein kinase (MAPK) signaling response. However, discrimination between C. albicans yeast and hyphal forms is mediated only by the MAPK pathway, which constitutes activation of the MAPK phosphatase MKP1 and the c-Fos transcription factor and is targeted against the hyphal form. Given that C. albicans is not the only Candida species capable of filamentation or causing mucosal infections, we sought to determine whether this MAPK/MKP1/c-Fos mediated response mechanism was activated by other pathogenic Candida species, including C. dubliniensis, C. tropicalis, C. parapsilosis, C. glabrata and C. krusei. Although all Candida species activated the NF-κB signaling pathway, only C. albicans and C. dubliniensis were capable of inducing MKP1 and c-Fos activation, which directly correlated with hypha formation. However, only C. albicans strongly induced cytokine production (G-CSF, GM-CSF, IL-6 and IL-1α) and cell damage. Candida dubliniensis, C. tropicalis and C. parapsilosis were also capable of inducing IL-1α and this correlated with mild cell damage and was dependent upon fungal burdens. Our data demonstrate that activation of the MAPK/MKP1/c-Fos pathway in oral epithelial cells is specific to C. dubliniensis and C. albicans hyphae.

Comparative Proteomic Analysis of Candida albicans and Candida glabrata

Introduction

Candida albicans and Candida glabrata are the two most common opportunistic pathogens which are part of the normal flora in humans. Clinical diagnosis of infection by these organisms is still largely based on culturing of these organisms. In order to identify species-specific protein expression patterns, we carried out a comparative proteomic analysis of C. albicans and C. glabrata.

Methods

We used “isobaric tag for relative and absolute quantitation” (iTRAQ) labeling of cell homogenates of C. albicans and C. glabrata followed by LC-MS/MS analysis using a quadrupole time-of-flight mass spectrometer. The MS/MS data was searched against a protein database comprised of known and predicted proteins reported from these two organisms. Subsequently, we carried out a bioinformatics analysis to group orthologous proteins across C. albicans and C. glabrata and calculated protein abundance changes between the two species.

Results and Conclusions

We identified 500 proteins from these organisms, the large majority of which corresponded to predicted transcripts. A number of proteins were observed to be significantly differentially expressed between the two species including enolase (Eno1), fructose-bisphosphate aldolase (Fba1), CCT ring complex subunit (Cct2), pyruvate kinase (Cdc19), and pyruvate carboxylase (Pyc2). This study illustrates a strategy for investigating protein expression patterns across closely related organisms by combining orthology information with quantitative proteomics.

Enhanced enzymatic activity of Candida species responsible for oral candidiasis in renal transplant recipients

Renal transplant recipients (RTRs) are regarded to be predisposed to oral candidiasis. This study was undertaken to evaluate the activity of hydrolytic enzymes in strains causing oral candidiasis in RTR. A total of 123 Candida albicans and 10 Candida krusei strains were isolated from 200 RTRs (39 RTRs suffered from symptomatic candidiasis, the remaining patients had no clinical symptoms of infection). All fungi were identified based on routine mycological procedures. Because of a small number of non-albicans strains, only C. albicans isolates were compared for enzymatic activity. The activity of 19 hydrolytic enzymes was assessed by API ZYM(®) test. The usage of mycophenolate mofetil was connected with higher ratio of clinically apparent oral candidiasis compared to immunosuppressive regimens without this drug (74.4% vs. 46.8%, respectively, P < 0.01). Candida albicans from RTRs showed higher enzymatic activity compared with strains from immunocompetent patients. Only two enzymes were found to be more active in C. albicans causing symptomatic candidiasis in RTRs (cystine arylamidase: P = 0.001, and α-fucosidase: P = 0.01) compared with saprophytic strains. Atrophic candidiasis showed higher activity of esterase lipase (C8) and α-mannosidase compared with the pseudomembraneous type. We suggest that the enhanced enzymatic activity is responsible for higher invasiveness of Candida residing in the oral cavity of RTRs.

Candida glabrata tryptophan-based pigment production via the Ehrlich pathway

Pigments contribute to the pathogenicity of many fungi, mainly by protecting fungal cells from host defence activities. Here, we have dissected the biosynthetic pathway of a tryptophan-derived pigment of the human pathogen Candida glabrata, identified key genes involved in pigment production and have begun to elucidate the possible biological function of the pigment. Using transcriptional analyses and a transposon insertion library, we have identified genes associated with pigment production. Targeted deletion mutants revealed that the pigment is a by-product of the Ehrlich pathway of tryptophan degradation: a mutant lacking a tryptophan-upregulated aromatic aminotransferase (Aro8) displayed significantly reduced pigmentation and a recombinantly expressed version of this protein was sufficient for pigment production in vitro. Pigment production is tightly regulated as the synthesis is affected by the presence of alternative nitrogen sources, carbon sources, cyclic AMP and oxygen. Growth of C. glabrata on pigment inducing medium leads to an increased resistance to hydrogen peroxide, an effect which was not observed with a mutant defective in pigmentation. Furthermore, pigmented yeast cells had a higher survival rate when exposed to human neutrophils and caused increased damage in a monolayer model of human epithelia, indicating a possible role of pigmentation during interactions with host cells.

Epithelial GM-CSF induction by Candida glabrata

The main cytokine induced by the interaction of oral epithelial cells with C. glabrata is granulocyte monocyte colony-stimulating factor (GM-CSF); however, the mechanisms regulating this response are unknown. Based on previously published information on the interactions of C. albicans with oral epithelial cells, we hypothesized that interaction with viable C. glabrata triggers GM-CSF synthesis via NF-kappaB activation. We found that C. glabrata-induced GM-CSF synthesis was adhesion-dependent, enhanced by endocytosis, and required fungal viability. NF-kappaB activation was noted during interaction of epithelial cells with C. glabrata, and pre-treatment with an NF-kappaB inhibitor partly inhibited GM-CSF synthesis. Blocking TLR4 with anti-TLR4 antibody did not inhibit GM-CSF production. In contrast, an anti-CDw17 antibody triggered significant inhibition of NF-kappaB activation and GM-CSF synthesis. beta-glucans did not stimulate GM-CSF synthesis, suggesting that the CDw17/NF-kappaB/GM-CSF pathway may be beta-glucan-independent. This study provides new insights into the mechanism of GM-CSF induction by C. glabrata.

Immune defence mechanisms and immunoenhancement strategies in oropharyngeal candidiasis

The prevalence of oropharyngeal candidiasis continues to be high, mainly because of an increasing population of immunocompromised patients. Traditional treatment of oropharyngeal candidiasis has relied on the use of antimicrobial drugs. However, unsatisfactory results with drug monotherapy and the emergence of resistant strains have prompted investigations into the potential use of adjunctive immunoenhancing therapies for the treatment of these infections. Here we review the host-recognition systems of Candida albicans, the immune and inflammatory response to infection, and antifungal effector mechanisms. The potential of immune modulation as a therapeutic strategy in oropharyngeal candidiasis is also discussed.