Fungal Infection in the Brain: What We Learned from Intravital Imaging

From Skin and Gut to the Brain: The Infectious Journey of the Human Commensal Fungus Malassezia and Its Neurological Consequences

The human mycobiome encompasses diverse communities of fungal organisms residing within the body and has emerged as a critical player in shaping health and disease. While extensive research has focused on the skin and gut mycobiome, recent investigations have pointed toward the potential role of fungal organisms in neurological disorders. Among those fungal organisms, the presence of the commensal fungus Malassezia in the brain has created curiosity because of its commensal nature and primary association with the human skin and gut. This budding yeast is responsible for several diseases, such as Seborrheic dermatitis, Atopic dermatitis, Pityriasis versicolor, Malassezia folliculitis, dandruff, and others. However recent findings surprisingly show the presence of Malassezia DNA in the brain and have been linked to diseases like Alzheimer's disease, Parkinson's disease, Multiple sclerosis, and Amyotrophic lateral sclerosis. The exact role of Malassezia in these disorders is unknown, but its ability to infect human cells, travel through the bloodstream, cross the blood-brain barrier, and reside along with the lipid-rich neuronal cells are potential mechanisms responsible for pathogenesis. This also includes the induction of pro-inflammatory cytokines, disruption of the blood-brain barrier, gut-microbe interaction, and accumulation of metabolic changes in the brain environment. In this review, we discuss these key findings from studies linking Malassezia to neurological disorders, emphasizing the complex and multifaceted nature of these cases. Furthermore, we discuss potential mechanisms through which Malassezia might contribute to the development of neurological conditions. Future investigations will open up new avenues for our understanding of the fungal gut-brain axis and how it influences human behavior. Collaborative research efforts among microbiologists, neuroscientists, immunologists, and clinicians hold promise for unraveling the enigmatic connections between human commensal Malassezia and neurological disorders.

Evolutionary trends in antifungal resistance: a meta-analysis

The present paper includes a meta-analysis of literature data on 318 species of fungi belonging to 34 orders in their response to 8 antifungal agents (amphotericin B, caspofungin, fluconazole, itraconazole, ketoconazole, posaconazole, terbinafine, and voriconazole). Main trends of MIC results at the ordinal level were visualized. European Committee on Antimicrobial Susceptibility Testing and Clinical & Laboratory Standards Institute (CLSI) clinical breakpoints were used as the staff gauge to evaluate MIC values ranging from resistance to susceptibility, which were subsequently compared with a phylogenetic tree of the fungal kingdom. Several orders (Hypocreales, Microascales, and Mucorales) invariably showed resistance. Also the basidiomycetous orders Agaricales, Polyporales, Sporidiales, Tremellales, and Trichosporonales showed relatively high degrees of azole multi-resistance, while elsewhere in the fungal kingdom, including orders with numerous pathogenic and opportunistic species, that is, Onygenales, Chaetothyiales, Sordariales, and Malasseziales, in general were susceptible to azoles. In most cases, resistance vs susceptibility was consistently associated with phylogenetic distance, members of the same order showing similar behavior.

IMPORTANCE

A kingdom-wide the largest set of published wild-type antifungal data comparison were analyzed. Trends in resistance in taxonomic groups (monophyletic clades) can be compared with the phylogeny of the fungal kingdom, eventual relationships between fungus-drug interaction and evolution can be described.

Preclinical Models for Cryptococcosis of the CNS and Their Characterization Using In Vivo Imaging Techniques

Infections caused by Cryptococcus neoformans and Cryptococcus gattii remain a challenge to our healthcare systems as they are still difficult to treat. In order to improve treatment success, in particular for infections that have disseminated to the central nervous system, a better understanding of the disease is needed, addressing questions like how it evolves from a pulmonary to a brain disease and how novel treatment approaches can be developed and validated. This requires not only clinical research and research on the microorganisms in a laboratory environment but also preclinical models in order to study cryptococci in the host. We provide an overview of available preclinical models, with particular emphasis on models of cryptococcosis in rodents. In order to further improve the characterization of rodent models, in particular the dynamic aspects of disease manifestation, development, and ultimate treatment, preclinical in vivo imaging methods are increasingly used, mainly in research for oncological, neurological, and cardiac diseases. In vivo imaging applications for fungal infections are rather sparse. A second aspect of this review is how research on models of cryptococcosis can benefit from in vivo imaging methods that not only provide information on morphology and tissue structure but also on function, metabolism, and cellular properties in a non-invasive way.

Roles for Microglia in Cryptococcal Brain Dissemination in the Zebrafish Larva

Cryptococcal infection begins in the lungs, but yeast cells subsequently access the bloodstream, from which they can reach the central nervous system (CNS). The resulting meningoencephalitis is the most common presentation and is very difficult to treat. How this fungus interacts with the blood-brain barrier (BBB) and establishes growth in the brain parenchyma remains a central question in fungal pathogenesis. We and others have developed the zebrafish larva as a model host for cryptococcosis and demonstrated that hematogenous CNS infection is replicated in this model. Here, we have used this model to examine the details of BBB crossing and the events immediately before and after. We have observed multiple mechanisms of BBB crossing and found that microglia, the resident phagocytes of the brain, likely have multiple roles. First, microglia either actively transfer yeast cells across the BBB or take up a significant proportion of them immediately after crossing. Second, microglia are capable of clearing individual cryptococcal cells at a developmental stage before adaptive immune cells have emerged. Third, microglia serve to maintain endothelial integrity, preventing other, phagocyte-independent forms of crossing. These proposed microglial functions during infection in the zebrafish larva generate new hypotheses concerning the establishment and control of cryptococcal meningoencephalitis. IMPORTANCE Cryptococcal meningitis is a fungal infection of the brain and a major cause of death in people with uncontrolled HIV. Infection begins in the lungs but can enter the bloodstream and disseminate to the brain. A structure called the blood-brain barrier must be crossed for the fungus to enter and cause meningitis. Learning how Cryptococcus crosses the blood-brain barrier will be crucial to understanding and possibly preventing brain infection. Using the zebrafish larva as a model host, we show that microglia, the resident phagocytes of the brain, potentially play multiple previously unappreciated roles in cryptococcal infection of the brain. These roles include reinforcing the integrity of the blood-brain barrier, clearing cryptococcal cells after they have crossed, and possibly participating directly in crossing via a previously unknown mechanism.

Cryptococcal Immune Reconstitution Inflammatory Syndrome: From Clinical Studies to Animal Experiments

Cryptococcus neoformans is an encapsulated pathogenic fungus that initially infects the lung but can migrate to the central nervous system (CNS), resulting in meningoencephalitis. The organism causes the CNS infection primarily in immunocompromised individuals including HIV/AIDS patients, but also, rarely, in immunocompetent individuals. In HIV/AIDS patients, limited inflammation in the CNS, due to impaired cellular immunity, cannot efficiently clear a C. neoformans infection. Antiretroviral therapy (ART) can rapidly restore cellular immunity in HIV/AIDS patients. Paradoxically, ART induces an exaggerated inflammatory response, termed immune reconstitution inflammatory syndrome (IRIS), in some HIV/AIDS patients co-infected with C. neoformans. A similar excessive inflammation, referred to as post-infectious inflammatory response syndrome (PIIRS), is also frequently seen in previously healthy individuals suffering from cryptococcal meningoencephalitis. Cryptococcal IRIS and PIIRS are life-threatening complications that kill up to one-third of affected people. In this review, we summarize the inflammatory responses in the CNS during HIV-associated cryptococcal meningoencephalitis. We overview the current understanding of cryptococcal IRIS developed in HIV/AIDS patients and cryptococcal PIIRS occurring in HIV-uninfected individuals. We also describe currently available animal models that closely mimic aspects of cryptococcal IRIS observed in HIV/AIDS patients.

Neuroinflammation in neurodegeneration via microbial infections

Recent epidemiological studies show a noticeable correlation between chronic microbial infections and neurological disorders. However, the underlying mechanisms are still not clear due to the biological complexity of multicellular and multiorgan interactions upon microbial infections. In this review, we show the infection leading to neurodegeneration mediated by multiorgan interconnections and neuroinflammation. Firstly, we highlight three inter-organ communications as possible routes from infection sites to the brain: nose-brain axis, lung-brain axis, and gut-brain axis. Next, we described the biological crosstalk between microglia and astrocytes upon pathogenic infection. Finally, our study indicates how neuroinflammation is a critical player in pathogen-mediated neurodegeneration. Taken together, we envision that antibiotics targeting neuro-pathogens could be a potential therapeutic strategy for neurodegeneration.

Fungal brain infection modelled in a human-neurovascular-unit-on-a-chip with a functional blood-brain barrier

The neurovascular unit, which consists of vascular cells surrounded by astrocytic end-feet and neurons, controls cerebral blood flow and the permeability of the blood-brain barrier (BBB) to maintain homeostasis in the neuronal milieu. Studying how some pathogens and drugs can penetrate the human BBB and disrupt neuronal homeostasis requires in vitro microphysiological models of the neurovascular unit. Here we show that the neurotropism of Cryptococcus neoformans-the most common pathogen causing fungal meningitis-and its ability to penetrate the BBB can be modelled by the co-culture of human neural stem cells, brain microvascular endothelial cells and brain vascular pericytes in a human-neurovascular-unit-on-a-chip maintained by a stepwise gravity-driven unidirectional flow and recapitulating the structural and functional features of the BBB. We found that the pathogen forms clusters of cells that penetrate the BBB without altering tight junctions, suggesting a transcytosis-mediated mechanism. The neurovascular-unit-on-a-chip may facilitate the study of the mechanisms of brain infection by pathogens, and the development of drugs for a range of brain diseases.

Quantitative analysis reveals internalisation of Cryptococcus neoformans by brain endothelial cells in vivo

Migration of Cryptococcus neoformans from the blood to the brain parenchyma is crucial to cause fatal meningoencephalitis. Although mechanisms involved in brain migration of C. neoformans have been widely studied in vitro, less is known about how the fungus crosses the blood-brain barrier (BBB) in vivo. This is in part because of the lack of an approach to quantitatively analyse the dynamics of fungal transmigration into the brain across the BBB in vivo. In this study, we report a novel approach to quantitatively analyse the interactions between C. neoformans and brain endothelial cells in a mouse model using flow cytometry. Using this system, we show that C. neoformans was internalised by brain endothelial cells in vivo and that mice infected with acapsular or heat-killed C. neoformans yeast cells displayed a lower frequency of brain endothelial cells containing the yeast cell compared to mice infected with wild-type or viable yeast cells, respectively. We further demonstrate that brain endothelial cells were invaded by serotype A strain (H99 strain) at a higher rate compared to serotype D strain (52D strain). Our experiments established that internalisation of C. neoformans by brain endothelial cells occurred in vivo and offered a powerful approach to quantitatively analyse fungal migration into the brain.

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.

Central Nervous System Mold Infections in Children with Hematological Malignancies: Advances in Diagnosis and Treatment

The incidence of invasive mold disease (IMD) has significantly increased over the last decades, and IMD of the central nervous system (CNS) is a particularly severe form of this infection. Solid data on the incidence of CNS IMD in the pediatric setting are lacking, in which Aspergillus spp. is the most prevalent pathogen, followed by mucorales. CNS IMD is difficult to diagnose, and although imaging tools such as magnetic resonance imaging have considerably improved, these techniques are still unspecific. As microscopy and culture have a low sensitivity, non-culture-based assays such as the detection of fungal antigens (e.g., galactomannan or beta-D-glucan) or the detection of fungal nucleic acids by molecular assays need to be validated in children with suspected CNS IMD. New and potent antifungal compounds helped to improve outcome of CNS IMD, but not all agents are approved for children and a pediatric dosage has not been established. Therefore, studies have to rapidly evaluate dosage, safety and efficacy of antifungal compounds in the pediatric setting. This review will summarize the current knowledge on diagnostic tools and on the management of CNS IMD with a focus on pediatric patients.

The Trojan Horse Model in Paracoccidioides: A Fantastic Pathway to Survive Infecting Human Cells

Paracoccidioidomycosis (PCM) is the most relevant systemic endemic mycosis limited to Latin American countries. The etiological agents are thermally dimorphic species of the genus Paracoccidioides. Infection occurs via respiratory tract by inhalation of propagules from the environmental (saprophytic) phase. In the lung alveoli the fungus converts to the characteristic yeast phase (parasitic) where interact with extracellular matrix proteins, epithelial cells, and the host cellular immunity. The response involves phagocytic cells recognition but intracellular Paracoccidioides have demonstrated the ability to survive and also multiply inside the neutrophils, macrophages, giant cells, and dendritic cells. Persistence of Paracoccidioides as facultative intracellular pathogen is important in terms of the fungal load but also regarding to the possibility to disseminate penetrating other tissues even protected by the phagocytes. This strategy to invade other organs via transmigration of infected phagocytes is called Trojan horse mechanism and it was also described for other fungi and considered a factor of pathogenicity. This mini review comprises a literature revision of the spectrum of tools and mechanisms displayed by Paracoccidioides to overcame phagocytosis, discusses the Trojan horse model and the immunological context in proven models or the possibility that Paracoccidioides apply this tool for dissemination to other tissues.

Targeting Unconventional Pathways in Pursuit of Novel Antifungals

The impact of invasive fungal infections on human health is a serious, but largely overlooked, public health issue. Commonly affecting the immunocompromised community, fungal infections are predominantly caused by species of Candida, Cryptococcus, and Aspergillus. Treatments are reliant on the aggressive use of pre-existing antifungal drug classes that target the fungal cell wall and membrane. Despite their frequent use, these drugs are subject to unfavorable drug-drug interactions, can cause undesirable side-effects and have compromised efficacy due to the emergence of antifungal resistance. Hence, there is a clear need to develop novel classes of antifungal drugs. A promising approach involves exploiting the metabolic needs of fungi by targeted interruption of essential metabolic pathways. This review highlights potential antifungal targets including enolase, a component of the enolase-plasminogen complex, and enzymes from the mannitol biosynthesis and purine nucleotide biosynthesis pathways. There has been increased interest in the enzymes that comprise these particular pathways and further investigation into their merits as antifungal targets and roles in fungal survival and virulence are warranted. Disruption of these vital processes by targeting unconventional pathways with small molecules or antibodies may serve as a promising approach to discovering novel classes of antifungals.

[Invasive candidiasis: A view to central nervous system infection]

Candidemia is the most frequent invasive mycosis in hospitalized patients worldwide. Fungal infection in central nervous system is a life-threatening complication which aggravates patients' prognosis. This article summarizes relevant aspects on the clinical characteristics of this pathology, mechanisms of fungus invasion, local immune response to Candida albicans and the impact of genetic defects on innate immune receptors that increase susceptibility to the acquisition of this form of mycosis.

Candida meningitis in neurosurgical patients: a single-institute study of nine cases over 7 years

Candida meningitis in neurosurgical patients is relatively unusual but is associated with a high mortality rate. We present our experience with this infection and discuss the clinical characteristics, treatment options and outcomes. We retrospectively reviewed neurosurgical patients with multiple positive cerebrospinal fluid (CSF) culture results in our hospital from January 2013 to December 2019. Nine patients were available for review according to our inclusion and exclusion criteria. Four species of Candida were isolated from the CSF samples and Candida albicans accounted for half of all infections. Eight infections were associated with ventricle peritoneal shunt, lumbar cistern peritoneal shunt or external ventricular drain. All of these foreign intracranial materials were removed or changed and all the patients received antifungal treatment, including fluconazole and/or voriconazole. It is associated with severe long-term outcomes in survivors and a mortality rate that reaches 11.1%. Prior treatments with broad-spectrum and high-grade antibiotics and anaemia are possible risk factors for Candida meningitis. We advise that foreign intracranial material should be removed or changed as early as possible and the timing of re-shunt operation can be 1 month after control of Candida meningitis has been achieved, with several negative CSF culture results.

Fungal dissemination is limited by liver macrophage filtration of the blood

Fungal dissemination into the bloodstream is a critical step leading to invasive fungal infections. Here, using intravital imaging, we show that Kupffer cells (KCs) in the liver have a prominent function in the capture of circulating Cryptococcus neoformans and Candida albicans, thereby reducing fungal dissemination to target organs. Complement C3 but not C5, and complement receptor CRIg but not CR3, are involved in capture of C. neoformans. Internalization of C. neoformans by KCs is subsequently mediated by multiple receptors, including CR3, CRIg, and scavenger receptors, which work synergistically along with C5aR signaling. Following phagocytosis, the growth of C. neoformans is inhibited by KCs in an IFN-γ independent manner. Thus, the liver filters disseminating fungi from circulation via KCs, providing a mechanistic explanation for the enhanced risk of cryptococcosis among individuals with liver diseases, and suggesting a therapeutic strategy to prevent fungal dissemination through enhancing KC functions.

Patients with liver diseases are at increased risk of fungal infections. Here the authors show that Kupffer cells are critical for the filtration of fungi out of the blood and thereby for liver-mediated protection against disseminating fungal infection.

Nonlytic exocytosis of Cryptococcus neoformans from neutrophils in the brain vasculature

Background

Cryptococcus neoformans (C. neoformans) is an encapsulated budding yeast that causes life-threatening meningoencephalitis in immunocompromised individuals, especially those with acquired immunodeficiency syndrome (AIDS). To cause meningoencephalitis, C. neoformans circulating in the bloodstream must first be arrested in the brain microvasculature. Neutrophils, the most abundant phagocytes in the bloodstream and the first leukocytes to be recruited to an infection site, can ingest C. neoformans. Little is known about how neutrophils interact with arrested fungal cells in the brain microvasculature.

Methods

A blood-brain barrier (BBB) in vitro model was established. The interactions between neutrophils adhering to brain endothelial cells and fungi were observed under a live cell imaging microscope. A flow cytometry assay was developed to explore the mechanisms. Immunofluorescence staining of brain tissues was utilized to validate the in vitro phenomena.

Results

Using real-time imaging, we observed that neutrophils adhered to a monolayer of mouse brain endothelial cells could expel ingested C. neoformans without lysis of the neutrophils or fungi in vitro, demonstrating nonlytic exocytosis of fungal cells from neutrophils. Furthermore, nonlytic exocytosis of C. neoformans from neutrophils was influenced by either the fungus (capsule and viability) or the neutrophil (phagosomal pH and actin polymerization). Moreover, nonlytic exocytosis of C. neoformans from neutrophils was recorded in brain tissue.

Conclusion

These results highlight a novel function by which neutrophils extrude C. neoformans in the brain vasculature.

Graphical abstract

Electronic supplementary material

The online version of this article (10.1186/s12964-019-0429-0) contains supplementary material, which is available to authorized users.

Silkworm as an experimental animal for research on fungal infections

Silkworm, Bombyx mori, has various advantages as an experimental animal, such as the low cost for rearing and fewer ethical problems. Models utilizing silkworms of infection with pathogenic bacteria have been established for identification of genes encoding virulence factors by large-scale in vivo screening. In this review, we describe recent progress in the study of silkworm infection models for elucidating the mechanisms of fungi infection. Silkworm infection models have been established for Candida albicans, Candida tropicalis, Candida glabrata and Cryptococcus neoformans, which are yeast type fungi, and Aspergillus fumigatus, Arthroderma vanbreuseghemii, Arthroderma benhamiae, Microsporum canis, Trichophyton rubrum, and Rhizopus oryzae, which are filamentous fungi. Novel genes encoding virulence factors in C. albicans and C. glabrata have been identified by using the silkworm infection models. We here outline the benefits of using silkworm infection models and a strategy for identifying the genes responsible for pathogenicity of microorganisms such as fungi. © 2019 The Authors. Microbiology and Immunology Published by The Societies and John Wiley & Sons Australia, Ltd.

Yeast and Filaments Have Specialized, Independent Activities in a Zebrafish Model of Candida albicans Infection

Candida albicans dimorphism is a crucial virulence factor during invasive candidiasis infections, which claim the lives of nearly one-half of those afflicted. It has long been believed that filaments drive tissue invasion and yeast mediates bloodstream dissemination, but observation of these activities during infection has been prevented by technical limitations. We used a transparent zebrafish infection model to analyze more comprehensively how C. albicans utilizes shape to disseminate and invade. This model facilitated the use of diverse, complementary strategies to manipulate shape, allowing us to monitor dissemination, invasion, and pathogenesis via intravital imaging of individual fungal cells throughout the host. To control fungal cell shape, we employed three different strategies: gene deletion (efg1Δ/Δ cph1Δ/Δ, eed1Δ/Δ), overexpression of master regulators (NRG1 or UME6), and modulation of the infection temperature (21°C, 28°C, or 33°C). The effects of these orthogonal manipulations were consistent, support the proposed specialized roles of yeast in dissemination and filaments in tissue invasion and pathogenesis, and indicate conserved mechanisms in zebrafish. To test if either morphotype changes the effectiveness of the other, we infected fish with a known mixture of shape-locked strains. Surprisingly, mixed-strain infections were associated with additive, but not synergistic, filament invasion and yeast dissemination. These findings provide the most complete view of morphotype-function relationships for C. albicans to date, revealing independent roles of yeast and filaments during disseminated candidiasis.

Neuroinfections caused by fungi

BACKGROUND

Fungal infections of the central nervous system (FIs-CNS) have become significantly more common over the past 2 decades. Invasion of the CNS largely depends on the immune status of the host and the virulence of the fungal strain. Infections with fungi cause a significant morbidity in immunocompromised hosts, and the involvement of the CNS may lead to fatal consequences.

METHODS

One hundred and thirty-five articles on fungal neuroinfection in PubMed, Google Scholar, and Cochrane databases were selected for review using the following search words: "fungi and CNS mycoses", CNS fungal infections", "fungal brain infections", " fungal cerebritis", fungal meningitis", "diagnostics of fungal infections", and "treatment of CNS fungal infections". All were published in English with the majority in the period 2000-2018. This review focuses on the current knowledge of the epidemiology, clinical presentations, diagnosis, and treatment of selected FIs-CNS.

RESULTS

The FIs-CNS can have various clinical presentations, mainly meningitis, encephalitis, hydrocephalus, cerebral abscesses, and stroke syndromes. The etiologic factors of neuroinfections are yeasts (Cryptococcus neoformans, Candida spp., Trichosporon spp.), moniliaceous moulds (Aspergillus spp., Fusarium spp.), Mucoromycetes (Mucor spp., Rhizopus spp.), dimorphic fungi (Blastomyces dermatitidis, Coccidioides spp., Histoplasma capsulatum), and dematiaceous fungi (Cladophialophora bantiana, Exophiala dermatitidis). Their common route of transmission is inhalation or inoculation from trauma or surgery, with subsequent hematogenous or contiguous spread. As the manifestations of FIs-CNS are often non-specific, their diagnosis is very difficult. A fast identification of the etiological factor of neuroinfection and the application of appropriate therapy are crucial in preventing an often fatal outcome. The choice of effective drug depends on its extent of CNS penetration and spectrum of activity. Pharmaceutical formulations of amphotericin B (AmB) (among others, deoxycholate-AmBd and liposomal L-AmB) have relatively limited distribution in the cerebrospinal fluid (CSF); however, their detectable therapeutic concentrations in the CNS makes them recommended drugs for the treatment of cryptococcal meningoencephalitis (AmBd with flucytosine) and CNS candidiasis (L-AmB) and mucormycosis (L-AmB). Voriconazole, a moderately lipophilic molecule with good CNS penetration, is recommended in the first-line therapy of CNS aspergillosis. Other triazoles, such as posaconazole and itraconazole, with negligible concentrations in the CSF are not considered effective drugs for therapy of CNS fungal neuroinfections. In contrast, clinical data have shown that a novel triazole, isavuconazole, achieved considerable efficacy for the treatment of some fungal neuroinfections. Echinocandins with relatively low or undetectable concentrations in the CSF do not play meaningful role in the treatment of FIs-CNS.

CONCLUSION

Although the number of fungal species causing CNS mycosis is increasing, only some possess well-defined treatment standards (e.g., cryptococcal meningitis and CNS aspergillosis). The early diagnosis of fungal infection, accompanied by identification of the etiological factor, is needed to allow the selection of effective therapy in patients with FIs-CNS and limit their high mortality.

Gliotoxin penetrates and impairs the integrity of the human blood-brain barrier in vitro

Cerebral fungal infections represent an important public health concern, where a key element of pathophysiology is the ability of the fungi to cross the blood-brain barrier (BBB). Yet the mechanism used by micro-organisms to cross such a barrier and invade the brain parenchyma remains unclear. This study investigated the effects of gliotoxin (GTX), a mycotoxin secreted by Aspergillus fumigatus, on the BBB using brain microvascular endothelial cells (BMECs) derived from induced pluripotent stem cells (iPSCs). We observed that both acute (2 h) and prolonged (24 h) exposure to GTX at the level of 1 μM or higher compromised BMECs monolayer integrity. Notably, acute exposure was sufficient to disrupt the barrier function in iPSC-derived BMECs, resulting in decreased transendothelial electrical resistance (TEER) and increased fluorescein permeability. Further, our data suggest that such disruption occurred without affecting tight junction complexes, via alteration of cell-matrix interactions, alterations in F-actin distribution, through a protein kinase C-independent signaling. In addition to its effect on the barrier function, we have observed a low permeability of GTX across the BBB. This fact can be partially explained by possible interactions of GTX with membrane proteins. Taken together, this study suggests that GTX may contribute in cerebral invasion processes of Aspergillus fumigatus by altering the blood-brain barrier integrity without disrupting tight junction complexes.

Extract of Syzygium aromaticum suppress eEF1A protein expression and fungal growth

AIMS

Clove extract has therapeutic potential as an antifungal drug, yet the mechanism of action remains ambiguous. Current study aimed to address the molecular process of the antifungal activity exerted by clove extract.

METHODS AND RESULTS

The antifungal assay results showed that clove extract had some effects on all of the tested yeast. Propidium iodide staining assay showed cell membrane damage in Saccharomyces cerevisiae after treatment of clove extract for 30 h. Interestingly, SDS-polyacrylamide gel electrophoresis assays revealed that the protein expression of eukaryotic elongation factor 1 alpha (eEF1A) was suppressed significantly after treatment with clove extract (not pure eugenol). Transcriptional analyses revealed that the TEF1 and TEF2 genes (translation elongation factor EF-1 alpha) encoding eEF1A were not disturbed with the addition of clove extract; however, the expression of related genes EFB1 (translation elongation factor 1 subunit beta), ENO2 (phosphopyruvate hydratase ENO2), GSP1 (Ran GTPase GSP1), RPP0 (ribosomal protein P0), YEF3 (translation elongation factor EF-3), TEF4 (translation elongation factor EF1B gamma), and RPS2 (ribosomal 40S subunit protein S2) increased significantly.

CONCLUSIONS

These results suggest that clove extract plays a role in disrupting growth and affecting yeast metabolism. eEF1A was affected by clove extract at the protein level but not at the transcriptional level.

SIGNIFICANCE AND IMPACT OF THE STUDY

This study is based on a detailed study of antifungal action exerted by clove extract, and proposed that down-regulation of eEF1A protein expression may contribute to its antifungal activity. These results may have clinical significance for future application of clove extract as a natural antifungal agent.

Role of microglia in fungal infections of the central nervous system

Most fungi are capable of disseminating into the central nervous system (CNS) commonly being observed in immunocompromised hosts. Microglia play a critical role in responding to these infections regulating inflammatory processes proficient at controlling CNS colonization by these eukaryotic microorganisms. Nonetheless, it is this inflammatory state that paradoxically yields cerebral mycotic meningoencephalitis and abscess formation. As peripheral macrophages and fungi have been investigated aiding our understanding of peripheral disease, ascertaining the key interactions between fungi and microglia may uncover greater abilities to treat invasive fungal infections of the brain. Here, we present the current knowledge of microglial physiology. Due to the existing literature, we have described to greater extent the opportunistic mycotic interactions with these surveillance cells of the CNS, highlighting the need for greater efforts to study other cerebral fungal infections such as those caused by geographically restricted dimorphic and rare fungi.