Disruption of MDCK cell tight junctions by the free-living amoeba Naegleria fowleri

Lactoferrin and Lysozyme Inhibit the Proteolytic Activity and Cytopathic Effect of Naegleria fowleri Enzymes

Naegleria fowleri is a ubiquitous free-living amoeba that causes primary amoebic meningoencephalitis. As a part of the innate immune response at the mucosal level, the proteins lactoferrin (Lf) and lysozyme (Lz) are secreted and eliminate various microorganisms. We demonstrate that N. fowleri survives the individual and combined effects of bovine milk Lf (bLf) and chicken egg Lz (cLz). Moreover, amoebic proliferation was not altered, even at 24 h of co-incubation with each protein. Trophozoites' ultrastructure was evaluated using transmission electron microscopy, and these proteins did not significantly alter their organelles and cytoplasmic membranes. Protease analysis using gelatin-zymograms showed that secreted proteases of N. fowleri were differentially modulated by bLf and cLz at 3, 6, 12, and 24 h. The bLf and cLz combination resulted in the inhibition of N. fowleri-secreted proteases. Additionally, the use of protease inhibitors on bLf-zymograms demonstrated that secreted cysteine proteases participate in the degradation of bLf. Nevertheless, the co-incubation of trophozoites with bLf and/or cLz reduced the cytopathic effect on the MDCK cell line. Our study suggests that bLf and cLz, alone or together, inhibited secreted proteases and reduced the cytopathic effect produced by N. fowleri; however, they do not affect the viability and proliferation of the trophozoites.

Understanding the mechanisms underlying the disruption of the blood-brain barrier in parasitic infections

Parasites have a significant impact on the neurological, cognitive, and mental well-being of humans, with a global population of over 1 billion individuals affected. The pathogenesis of central nervous system (CNS) injury in parasitic diseases remains limited, and prevention and control of parasitic CNS infections remain significant areas of research. Parasites, encompassing both unicellular and multicellular organisms, have intricate life cycles and possess the ability to infect a diverse range of hosts, including the human population. Parasitic illnesses that impact the central and peripheral nervous systems are a significant contributor to morbidity and mortality in low- to middle-income nations. The precise pathways through which neurotropic parasites infiltrate the CNS by crossing the blood-brain barrier (BBB) and cause neurological harm remain incompletely understood. Investigating brain infections caused by parasites is closely linked to studying neuroinflammation and cerebral impairment. The exact molecular and cellular mechanisms involved in this process remain incomplete, but understanding the exact mechanisms could provide insight into their pathogenesis and potentially reveal novel therapeutic targets. This review paper explores the underlying mechanisms involved in the development of neurological disorders caused by parasites, including parasite-derived elements, host immune responses, and modifications in tight junctions (TJs) proteins.

Pro-inflammatory cytokine responses to Naegleria fowleri infection

Naegleria fowleri, or the “brain-eating amoeba,” is responsible for a rare, but lethal, infection known as primary amoebic meningoencephalitis (PAM). Confirmed PAM cases have seen both a rise in numbers, as well as expansion of geographic range over the past several decades. There is no effective therapy for PAM and the clinical prognosis remains grim with a mortality rate over 95%. The role of the immune response in disease prevention and disease severity remains unclear. In this review, we explore potential roles of inflammatory immune responses to N. fowleri in disease pathogenesis with a primary focus on pro-inflammatory cytokines IL-1, IL-6, and TNFα. We also discuss modulating proinflammatory cytokines as an additional immune therapy in PAM treatment.

Role of cathepsin B of Naegleria fowleri during primary amebic meningoencephalitis

Naegleria fowleri causes primary amoebic meningoencephalitis in humans and experimental animals. It has been suggested that cysteine proteases of parasites play key roles in metabolism, nutrient uptake, host tissue invasion, and immune evasion. The aim of this work was to evaluate the presence, expression, and role of cathepsin B from N. fowleri in vitro and during PAM. Rabbit-specific polyclonal antibodies against cathepsin B were obtained from rabbit immunization with a synthetic peptide obtained by bioinformatic design. In addition, a probe was designed from mRNA for N. fowleri cathepsin B. Both protein and messenger were detected in fixed trophozoites, trophozoites interacted with polymorphonuclear and histological sections of infected mice. The main cathepsin B distribution was observed in cytoplasm or membrane mainly pseudopods and food-cups while messenger was in nucleus and cytoplasm. Surprisingly, both the messenger and enzyme were observed in extracellular medium. To determine cathepsin B release, we used trophozoites supernatant recovered from nasal passages or brain of infected mice. We observed the highest release in supernatant from recovered brain amoebae, and when we analyzed molecular weight of secreted proteins by immunoblot, we found 30 and 37 kDa bands which were highly immunogenic. Finally, role of cathepsin B during N. fowleri infection was determined; we preincubated trophozoites with E-64, pHMB or antibodies with which we obtained 60%, 100%, and 60% of survival, respectively, in infected mice. These results suggest that cathepsin B plays a role during pathogenesis caused by N. fowleri mainly in adhesion and contributes to nervous tissue damage.

Three encephalitis-causing amoebae and their distinct interactions with the host

Naegleria fowleri, Balamuthia mandrillaris, and Acanthamoeba spp. can cause devastating brain infections in humans which almost always result in death. The symptoms of the three infections overlap, but brain inflammation and the course of the disease differ, depending on the amoeba that is responsible. Understanding the differences between these amoebae can result in the development of strategies to prevent and treat these infections. Recently, numerous scientific advancements have been made in the understanding of pathogenicity mechanisms in general, and the basic biology, epidemiology, and the human immune response towards these amoebae in particular. In this review, we combine this knowledge and aim to identify which factors can explain the differences between the lethal brain infections caused by N. fowleri, B. mandrillaris, and Acanthamoeba spp.

Acanthamoeba mauritaniensis genotype T4D: An environmental isolate displays pathogenic behavior

Acanthamoeba spp. are free-living amoebae with a worldwide distribution. These amoebae can cause granulomatous amoebic encephalitis and amoebic keratitis in humans. Proteases are considered virulence factors in pathogenic Acanthamoeba. The objective of this study was to evaluate the behavior of Acanthamoeba mauritaniensis, a nonpathogenic amoeba. We analyzed the cytopathic effect of A. mauritaniensis on RCE1(5 T5) and MDCK cells and compared it to that of Acanthamoeba castellanii. A partial biochemical characterization of proteases was performed in total crude extracts (TCE) and conditioned medium (CM). Finally, we evaluated the effect of proteases on tight junction (TJ) proteins and the transepithelial electrical resistance of MDCK cells. The results showed that this amoeba can induce substantial damage to RCE1(5T5) and MDCK cells. Moreover, the zymograms and Azocoll assays of amoebic TCE and CM revealed different protease activities, with serine proteases being the most active. Furthermore, A. mauritaniensis induced the alteration and degradation of MDCK cell TJ proteins with serine proteases. After genotyping this amoeba, we determined that it is an isolate of Acanthamoeba genotype T4D. From these data, we suggest that A. mauritaniensis genotype T4D behaves similarly to the A. castellanii strain.

Host Invasion by Pathogenic Amoebae: Epithelial Disruption by Parasite Proteins

The epithelium represents the first and most extensive line of defence against pathogens, toxins and pollutant agents in humans. In general, pathogens have developed strategies to overcome this barrier and use it as an entrance to the organism. Entamoeba histolytica, Naegleriafowleri and Acanthamoeba spp. are amoebae mainly responsible for intestinal dysentery, meningoencephalitis and keratitis, respectively. These amoebae cause significant morbidity and mortality rates. Thus, the identification, characterization and validation of molecules participating in host-parasite interactions can provide attractive targets to timely intervene disease progress. In this work, we present a compendium of the parasite adhesins, lectins, proteases, hydrolases, kinases, and others, that participate in key pathogenic events. Special focus is made for the analysis of assorted molecules and mechanisms involved in the interaction of the parasites with epithelial surface receptors, changes in epithelial junctional markers, implications on the barrier function, among others. This review allows the assessment of initial host-pathogen interaction, to correlate it to the potential of parasite invasion.

An In Vitro Model of the Blood-Brain Barrier: Naegleria fowleri Affects the Tight Junction Proteins and Activates the Microvascular Endothelial Cells

Naegleria fowleri causes a fatal disease known as primary amoebic meningoencephalitis. This condition is characterized by an acute inflammation that originates from the free passage of peripheral blood cells to the central nervous system through the alteration of the blood-brain barrier. In this work, we established models of the infection in rats and in a primary culture of endothelial cells from rat brains with the aim of evaluating the activation and the alterations of these cells by N. fowleri. We proved that the rat develops the infection similar to the mouse model. We also found that amoebic cysteine proteases produced by the trophozoites and the conditioned medium induced cytopathic effect in the endothelial cells. In addition, N. fowleri can decrease the transendothelial electrical resistance by triggering the destabilization of the tight junction proteins claudin-5, occludin, and ZO-1 in a time-dependent manner. Furthermore, N. fowleri induced the expression of VCAM-1 and ICAM-1 and the production of IL-8, IL-1β, TNF-α, and IL-6 as well as nitric oxide. We conclude that N. fowleri damaged the blood-brain barrier model by disrupting the intercellular junctions and induced the presence of inflammatory mediators by allowing the access of inflammatory cells to the olfactory bulbs.

Nf-GH, a glycosidase secreted by Naegleria fowleri, causes mucin degradation: an in vitro and in vivo study

AIM

The aim of this work was to identify, characterize and evaluate the pathogenic role of mucinolytic activity released by Naegleria fowleri.

MATERIALS & METHODS

Zymograms, protease inhibitors, anion exchange chromatography, MALDI-TOF-MS, enzymatic assays, Western blot, and confocal microscopy were used to identify and characterize a secreted mucinase; inhibition assays using antibodies, dot-blots and mouse survival tests were used to evaluate the mucinase as a virulence factor.

RESULTS

A 94-kDa protein with mucinolytic activity was inducible and abolished by p-hydroxymercuribenzoate. MALDI-TOF-MS identified a glycoside hydrolase. Specific antibodies against N. fowleri-glycoside hydrolase inhibit cellular damage and MUC5AC degradation, and delay mouse mortality.

CONCLUSION

Our findings suggest that secretory products from N. fowleri play an important role in mucus degradation during the invasion process.

Biology and pathogenesis of Naegleria fowleri

Naegleria fowleri is a protist pathogen that can cause lethal brain infection. Despite decades of research, the mortality rate related with primary amoebic meningoencephalitis owing to N. fowleri remains more than 90%. The amoebae pass through the nose to enter the central nervous system killing the host within days, making it one of the deadliest opportunistic parasites. Accordingly, we present an up to date review of the biology and pathogenesis of N. fowleri and discuss needs for future research against this fatal infection.

Naegleria fowleri after 50 years: is it a neglected pathogen?

It has been 50 years since the first case of primary amoebic meningoencephalitis (PAM), an acute and rapidly fatal disease of the central nervous system (CNS), was reported in Australia. It is now known that the aetiological agent of PAM is Naegleria fowleri, an amoeba that is commonly known as 'the brain-eating amoeba'. N. fowleri infects humans of different ages who are in contact with water contaminated with this micro-organism. N. fowleri is distributed worldwide and is found growing in bodies of freshwater in tropical and subtropical environments. The number of PAM cases has recently increased, and the rate of recovery from PAM has been estimated at only 5 %. Amphotericin B has been used to treat patients with PAM. However, it is important to note that there is no specific treatment for PAM. Moreover, this amoeba is considered a neglected micro-organism. Researchers have exerted great effort to design effective drugs to treat PAM and to understand the pathogenesis of PAM over the past 50 years, such as its pathology, molecular and cellular biology, diagnosis and prevention, and its biological implications, including its pathogenic genotypes, its distribution and its ecology. Given the rapid progression of PAM and its high mortality rate, it is important that investigations continue and that researchers collaborate to gain better understanding of the pathogenesis of this disease and, consequently, to improve the diagnosis and treatment of this devastating infection of the CNS.

Pathogens penetrating the central nervous system: infection pathways and the cellular and molecular mechanisms of invasion

The brain is well protected against microbial invasion by cellular barriers, such as the blood-brain barrier (BBB) and the blood-cerebrospinal fluid barrier (BCSFB). In addition, cells within the central nervous system (CNS) are capable of producing an immune response against invading pathogens. Nonetheless, a range of pathogenic microbes make their way to the CNS, and the resulting infections can cause significant morbidity and mortality. Bacteria, amoebae, fungi, and viruses are capable of CNS invasion, with the latter using axonal transport as a common route of infection. In this review, we compare the mechanisms by which bacterial pathogens reach the CNS and infect the brain. In particular, we focus on recent data regarding mechanisms of bacterial translocation from the nasal mucosa to the brain, which represents a little explored pathway of bacterial invasion but has been proposed as being particularly important in explaining how infection with Burkholderia pseudomallei can result in melioidosis encephalomyelitis.

Biochemical and cellular mechanisms regulatingAcanthamoeba castellaniiadherence to host cells

Free-living amoebae belonging to the genusAcanthamoebaare the causative agents of infections such as amoebic keratitis (AK), granulomatous amoebic encephalitis (GAE) and cutaneous lesions. The mechanisms involved in the establishment of infection are unknown. However, it is accepted that the initial phase of pathogenesis involves adherence to the host tissue. In this work, we analysed surface molecules with an affinity for epithelial and neuronal cells from the trophozoites ofAcanthamoeba castellanii. We also investigated the cellular mechanisms that govern the process of trophozoite adhesion to the host cells. We first used confocal and epifluorescence microscopy to examine the distribution of theA. castellaniiactin cytoskeleton during interaction with the host cells. The use of drugs, as cytochalasin B (CB) and latrunculin B (LB), revealed the participation of cytoskeletal filaments in the adhesion process. In addition, to identify the proteins and glycoproteins on the surface ofA. castellanii, the trophozoites were labelled with biotin and biotinylated lectins. The results revealed bands of surface proteins, some of which were glycoproteins with mannose andN-acetylglucosamine residues. Interaction assays of biotinylated amoebae proteins with epithelial and neuronal cells showed that some surface proteins had affinity for both cell types. The results of this study provide insight into the biochemical and cellular mechanisms of theAcanthamoebainfection process.