Cryptococcus-Epithelial Interactions

Ethanolic Extract Propolis-Loaded Niosomes Diminish Phospholipase B1, Biofilm Formation, and Intracellular Replication of Cryptococcus neoformans in Macrophages

Secretory phospholipase B1 (PLB1) and biofilms act as microbial virulence factors and play an important role in pulmonary cryptococcosis. This study aims to formulate the ethanolic extract of propolis-loaded niosomes (Nio-EEP) and evaluate the biological activities occurring during PLB1 production and biofilm formation of Cryptococcus neoformans. Some physicochemical characterizations of niosomes include a mean diameter of 270 nm in a spherical shape, a zeta-potential of -10.54 ± 1.37 mV, and 88.13 ± 0.01% entrapment efficiency. Nio-EEP can release EEP in a sustained manner and retains consistent physicochemical properties for a month. Nio-EEP has the capability to permeate the cellular membranes of C. neoformans, causing a significant decrease in the mRNA expression level of PLB1. Interestingly, biofilm formation, biofilm thickness, and the expression level of biofilm-related genes (UGD1 and UXS1) were also significantly reduced. Pre-treating with Nio-EEP prior to yeast infection reduced the intracellular replication of C. neoformans in alveolar macrophages by 47%. In conclusion, Nio-EEP mediates as an anti-virulence agent to inhibit PLB1 and biofilm production for preventing fungal colonization on lung epithelial cells and also decreases the intracellular replication of phagocytosed cryptococci. This nano-based EEP delivery might be a potential therapeutic strategy in the prophylaxis and treatment of pulmonary cryptococcosis in the future.

Tetrahydrocurcumin (THC) enhanced the clearance of Cryptococcus deneoformans during infection in vivo

Cryptococcal species often cause lung infections and are the main cause of fungal meningitis. Claudin-4 appears to be a major structural component that maintains a tight alveolar barrier and prevents fluid and electrolyte leakage into the alveolar space. We aimed to determine whether S7-tetrahydrocurcumin (THC) could clearance of C. deneoformans and regulate claudin-4 expression during C. deneoformans infection. We investigated the effect of THC on C. deneoformans infection and its possible mechanism in vivo. Transmission electron microscopy was used to observe the ultrastructure of the lung tissue and the invasion of Cryptococcus. To clarify the effect of THC, we examined claudin-4, c-Jun, and Smad2 expression. We also measured claudin-4 expression in pulmonary specimens from clinical patients. THC reduced cryptococcal cell invasion in the lungs, improved alveolar exudation, and reduced inflammation. Pretreatment with THC suppressed c-Jun and Smad2 expression, resulting in significantly increased claudin-4 levels. In contrast, the expression of claudin-4 in clinical specimens from patients with cryptococcal infection was higher than that in normal specimens. THC enhanced the clearance of C. deneoformans during infection in vivo. We investigated the expression of claudin-4 and the possible mechanism of THC against C. deneoformans infection.

Importance of Clinical Isolates in Cryptococcus neoformans Research

The human pathogenic fungus Cryptococcus neoformans is a global health concern. Previous research in the field has focused on studies using reference strains to identify virulence factors, generate mutant libraries, define genomic structures, and perform functional studies. In this review, we discuss the benefits and drawbacks of using reference strains to study C. neoformans, describe how the study of clinical isolates has expanded our understanding of pathogenesis, and highlight how studies using clinical isolates can further develop our understanding of the host-pathogen interaction during C. neoformans infection.

Effects of altered N-glycan structures of Cryptococcus neoformans mannoproteins, MP98 (Cda2) and MP84 (Cda3), on interaction with host cells

Cryptococcus neoformans is an opportunistic human fungal pathogen causing lethal meningoencephalitis. It has several cell wall mannoproteins (MPs) identified as immunoreactive antigens. To investigate the structure and function of N-glycans assembled on cryptococcal cell wall MPs in host cell interactions, we purified MP98 (Cda2) and MP84 (Cda3) expressed in wild-type (WT) and N-glycosylation-defective alg3 mutant (alg3Δ) strains. HPLC and MALDI-TOF analysis of the MP proteins from the WT revealed protein-specific glycan structures with different extents of hypermannosylation and xylose/xylose phosphate addition. In alg3Δ, MP98 and MP84 had truncated core N-glycans, containing mostly five and seven mannoses (M5 and M7 forms), respectively. In vitro adhesion and uptake assays indicated that the altered core N-glycans did not affect adhesion affinities to host cells although the capacity to induce the immune response of bone-marrow derived dendritic cells (BMDCs) decreased. Intriguingly, the removal of all N-glycosylation sites on MP84 increased adhesion to host cells and enhanced the induction of cytokine secretion from BMDCs compared with that on MP84 carrying WT N-glycans. Therefore, the structure-dependent effects of N-glycans suggested their complex roles in modulating the interaction of MPs with host cells to avoid nonspecific adherence to host cells and host immune response hyperactivation.

Cryptococcus: History, Epidemiology and Immune Evasion

Cryptococcosis is a disease caused by the pathogenic fungi Cryptococcus neoformans and Cryptococcus gattii, both environmental fungi that cause severe pneumonia and may even lead to cryptococcal meningoencephalitis. Although C. neoformans affects more fragile individuals, such as immunocompromised hosts through opportunistic infections, C. gattii causes a serious indiscriminate primary infection in immunocompetent individuals. Typically seen in tropical and subtropical environments, C. gattii has increased its endemic area over recent years, largely due to climatic factors that favor contagion in warmer climates. It is important to point out that not only C. gattii, but the Cryptococcus species complex produces a polysaccharidic capsule with immunomodulatory properties, enabling the pathogenic species of Cryptococccus to subvert the host immune response during the establishment of cryptococcosis, facilitating its dissemination in the infected organism. C. gattii causes a more severe and difficult-to-treat infection, with few antifungals eliciting an effective response during chronic treatment. Much of the immunopathology of this cryptococcosis is still poorly understood, with most studies focusing on cryptococcosis caused by the species C. neoformans. C. gattii became more important in the epidemiological scenario with the outbreaks in the Pacific Northwest of the United States, which resulted in phylogenetic studies of the virulent variant responsible for the severe infection in the region. Since then, the study of cryptococcosis caused by C. gattii has helped researchers understand the immunopathological aspects of different variants of this pathogen.

Antifungal activity of [K3]temporin-SHa against medically relevant yeasts and moulds

Few antifungal agents are currently available for the treatment of fungal infections. Antimicrobial peptides (AMPs), which are natural molecules involved in the innate immune response of many organisms, represent a promising research method because of their broad killing activity. The aim of this study was to assess the activity of a frog AMP, [K³]temporin-SHa, against some species of yeasts and moulds, and to further explore its activity against Candida albicans. MIC determinations were performed according to EUCAST guidelines. Next, the activity of [K³]temporin-SHa against C. albicans was explored using time-killing curve experiments, membrane permeabilization assays, and electron microscopy. Finally, chequerboard assays were performed to evaluate the synergy between [K³]temporin-SHa and amphotericin B or fluconazole. [K³]temporin-SHa was found to be active in vitro against several yeasts with MIC between 5.5 and 45 µM. [K³]temporin-SHa displayed rapid fungicidal activity against C. albicans (inoculum was divided into two in less than an hour and no viable colonies were recovered after 5 h) with a mechanism that could be due to membrane permeabilization. [K³]temporin-SHa was synergistic with amphotericin B against C. albicans (FICI = 0.303). [K³]temporin-SHa could represent an additional tool to treat several Candida species and C. neoformans.

Effects of cigarette smoke extract on bronchial epithelial cells stimulated with Cryptococcus neoformans

In the airways, the adhesion of Cryptococcus neoformans with airway epithelial cells is crucial for the establishment of cryptococcosis. Tobacco smoke is considered a risk factor for cryptococcosis. Here, we evaluated the effects of cigarette smoke extract (CSE) on human bronchial epithelial cells (BEAS-2B) stimulated with C. neoformans. Multiplicities of infection (MOIs) of 1-100 of C. neoformans per cell led to increased IL-8 production and no cytotoxic effects when compared to those of controls. C. neoformans (MOI 100) also significantly increased the concentration of IL-6. In cells stimulated with CSE doses (1.0, 2.5 and 5.0%) from one or five cigarettes, increased IL-1β production was observed only in doses from one (1.0%) and five (2.5%) cigarettes when compared to that of controls. However, only 1.0% CSE failed to show cytotoxic effects. In addition, CSE significantly increased the concentration of IL-8. Cells stimulated with both CSE and C. neoformans demonstrated a reduction in IL-6/STAT3 signalling compared to that in cells stimulated by C. neoformans. In addition, a significant increase in IL-10 production was also observed. No alterations in NF-kB or ICAM-1 expression were observed among the groups. The combination of CSE and C. neoformans favoured the increase of fungal numbers and extracellular adhering of C. neoformans on BEAS-2B cells. In addition, the internalization of C. neoformans on BEAS-2B cells was reduced after CSE stimulation. In conclusion, the association of CSE and C. neoformans induced an anti-inflammatory effect in bronchial epithelial cells, which might favour the development of C. neoformans infection in the airways.

Opportunistic Fungal Infection Associated With COVID-19

We report 2 cases of severe coronavirus disease 2019 requiring prolonged hospitalization complicated by the late onset of opportunistic fungal infections, histoplasmosis, and cryptococcosis.

Mechanisms of fungal dissemination

Fungal infections are an increasing threat to global public health. There are more than six million fungal species worldwide, but less than 1% are known to infect humans. Most of these fungal infections are superficial, affecting the hair, skin and nails, but some species are capable of causing life-threatening diseases. The most common of these include Cryptococcus neoformans, Aspergillus fumigatus and Candida albicans. These fungi are typically innocuous and even constitute a part of the human microbiome, but if these pathogens disseminate throughout the body, they can cause fatal infections which account for more than one million deaths worldwide each year. Thus, systemic dissemination of fungi is a critical step in the development of these deadly infections. In this review, we discuss our current understanding of how fungi disseminate from the initial infection sites to the bloodstream, how immune cells eliminate fungi from circulation and how fungi leave the blood and enter distant organs, highlighting some recent advances and offering some perspectives on future directions.

Fine Particulate Matter (PM2.5) Promotes CD146 Expression in Alveolar Epithelial Cells and Cryptococcus neoformans Pulmonary Infection

Air pollution is a leading cause of increasing infectious lung diseases. Pulmonary cryptococcosis is a fatal fungal pneumonia in acquired immunodeficiency syndrome patients. In some cases, the pathogen Cryptococcus neoformans also develops dormant nodules in immunocompetent individuals. In the present study, we demonstrated that fine particulate matter (PM₂.₅) increased CD146 expression in alveolar epithelial cells and promoted C. neoformans pulmonary infection. Aryl hydrocarbon receptor (AhR) signaling was required for increased expression of CD146 in epithelial cells treated with PM₂.₅. In a murine model of pulmonary infection, PM₂.₅ promoted fungal infection, and CD146 deficiency decreased the fugal burden of C. neoformans. Our study may highlight the importance of air pollution to lung mycosis and CD146 as a target for preventing infectious lung diseases.

Animal Models of Cryptococcus neoformans in Identifying Immune Parameters Associated With Primary Infection and Reactivation of Latent Infection

Cryptococcus species are environmental fungal pathogens and the causative agents of cryptococcosis. Infection occurs upon inhalation of infectious particles, which proliferate in the lung causing a primary infection. From this primary lung infection, fungal cells can eventually disseminate to other organs, particularly the brain, causing lethal meningoencephalitis. However, in most cases, the primary infection resolves with the formation of a lung granuloma. Upon severe immunodeficiency, dormant cryptococcal cells will start proliferating in the lung granuloma and eventually will disseminate to the brain. Many investigators have sought to study the protective host immune response to this pathogen in search of host parameters that keep the proliferation of cryptococcal cells under control. The majority of the work assimilates research carried out using the primary infection animal model, mainly because a reactivation model has been available only very recently. This review will focus on anti-cryptococcal immunity in both the primary and reactivation models. An understanding of the differences in host immunity between the primary and reactivation models will help to define the key host parameters that control the infections and are important for the research and development of new therapeutic and vaccine strategies against cryptococcosis.

Host and Pathogen Communication in the Respiratory Tract: Mechanisms and Models of a Complex Signaling Microenvironment

Chronic lung diseases are a leading cause of morbidity and mortality across the globe, encompassing a diverse range of conditions from infections with pathogenic microorganisms to underlying genetic disorders. The respiratory tract represents an active interface with the external environment having the primary immune function of resisting pathogen intrusion and maintaining homeostasis in response to the myriad of stimuli encountered within its microenvironment. To perform these vital functions and prevent lung disorders, a chemical and biological cross-talk occurs in the complex milieu of the lung that mediates and regulates the numerous cellular processes contributing to lung health. In this review, we will focus on the role of cross-talk in chronic lung infections, and discuss how different cell types and signaling pathways contribute to the chronicity of infection(s) and prevent effective immune clearance of pathogens. In the lung microenvironment, pathogens have developed the capacity to evade mucosal immunity using different mechanisms or virulence factors, leading to colonization and infection of the host; such mechanisms include the release of soluble and volatile factors, as well as contact dependent (juxtracrine) interactions. We explore the diverse modes of communication between the host and pathogen in the lung tissue milieu in the context of chronic lung infections. Lastly, we review current methods and approaches used to model and study these host-pathogen interactions in vitro, and the role of these technological platforms in advancing our knowledge about chronic lung diseases.

Comparison of MIC Test Strip and Sensititre YeastOne with the CLSI and EUCAST Broth Microdilution Reference Methods for In Vitro Antifungal Susceptibility Testing of Cryptococcus neoformans

We compared MIC test strip (MTS) and Sensititre YeastOne (SYO) methods with EUCAST and CLSI methods for amphotericin B, 5-fluocytosine, fluconazole, voriconazole, and isavuconazole against 106 Cryptococcus neoformans isolates. The overall essential agreement between the EUCAST and CLSI methods was >72% and >94% at ±1 and ±2 dilutions, respectively. The essential agreements between SYO and EUCAST/CLSI for amphotericin B, 5-flucytosine, fluconazole, and voriconazole were >89/>93% and between MTS and EUCAST/CLSI were >57/>75%. Very major error rates were low for amphotericin B and fluconazole (<3%) and a bit higher for the other drugs (<8%).

Cryptococcal Traits Mediating Adherence to Biotic and Abiotic Surfaces

Several species in the genus Cryptococcus are facultative intracellular pathogens capable of causing disease associated with high mortality and morbidity in humans. These fungi interact with other organisms in the soil, and these interactions may contribute to the development of adaptation mechanisms that function in virulence by promoting fungal survival in animal hosts. Fungal adhesion molecules, also known as adhesins, have been classically considered as cell-surface or secreted proteins that play critical roles in microbial pathogenesis or in biofilm formation as structural components. Pathogenic Cryptococcus spp. differ from other pathogenic yeasts in having a polysaccharide capsule that covers the cell wall surface and precludes interactions of those structures with host cell receptors. Hence, pathogenic Cryptococcus spp. use unconventional tools for surface attachment. In this essay, we review the unique traits and mechanisms favoring adhesion of Cryptococcus spp. to biotic and abiotic surfaces. Knowledge of the traits that mediate adherence could be exploited in the development of therapeutic, biomedical, and/or industrial products.

Host-Pathogen Interactions Mediated by MDR Transporters in Fungi: As Pleiotropic as it Gets!

Fungal infections caused by Candida, Aspergillus, and Cryptococcus species are an increasing problem worldwide, associated with very high mortality rates. The successful prevalence of these human pathogens is due to their ability to thrive in stressful host niche colonization sites, to tolerate host immune system-induced stress, and to resist antifungal drugs. This review focuses on the key role played by multidrug resistance (MDR) transporters, belonging to the ATP-binding cassette (ABC), and the major facilitator superfamilies (MFS), in mediating fungal resistance to pathogenesis-related stresses. These clearly include the extrusion of antifungal drugs, with C. albicans CDR1 and MDR1 genes, and corresponding homologs in other fungal pathogens, playing a key role in this phenomenon. More recently, however, clues on the transcriptional regulation and physiological roles of MDR transporters, including the transport of lipids, ions, and small metabolites, have emerged, linking these transporters to important pathogenesis features, such as resistance to host niche environments, biofilm formation, immune system evasion, and virulence. The wider view of the activity of MDR transporters provided in this review highlights their relevance beyond drug resistance and the need to develop therapeutic strategies that successfully face the challenges posed by the pleiotropic nature of these transporters.

Mechanisms of Cryptococcus neoformans-Mediated Host Damage

Cryptococcus neoformans is not usually considered a cytotoxic fungal pathogen but there is considerable evidence that this microbe can damage host cells and tissues. In this essay, we review the evidence that C. neoformans damages host cells and note that the mechanisms involved are diverse. We consider C. neoformans-mediated host damage at the molecular, cellular, tissue, and organism level. Direct mechanisms of cytotoxicity include lytic exocytosis, organelle dysfunction, phagolysosomal membrane damage, and cytoskeletal alterations. Cytotoxicity contributes to pathogenesis by interfering with immune effector cell function and disrupting endothelial barriers thus allowing dissemination. When C. neoformans-mediated and immune-mediated host damage is sufficient to affect homeostasis, cryptococcosis occurs at the organism level.

Mechanisms of Pulmonary Escape and Dissemination by Cryptococcus neoformans

Cryptococcus neoformans is a common environmental saprophyte and human fungal pathogen that primarily causes disease in immunocompromised individuals. Similar to many environmentally acquired human fungal pathogens, C. neoformans initiates infection in the lungs. However, the main driver of mortality is invasive cryptococcosis leading to fungal meningitis. After C. neoformans gains a foothold in the lungs, a critical early step in invasion is transversal of the respiratory epithelium. In this review, we summarize current knowledge relating to pulmonary escape. We focus on fungal factors that allow C. neoformans to disseminate from the lungs via intracellular and extracellular routes.