Amphotericin B induces apoptosis-like programmed cell death in Naegleria fowleri and Naegleria gruberi

Utilizing metagenomic next-generation sequencing and phylogenetic analysis to identify a rare pediatric case of Naegleria fowleri infection presenting with fulminant myocarditis

Background

Naegleria fowleri (N. fowleri), a rare and typically lethal amoeba, most commonly causes primary amoebic meningoencephalitis (PAM). This case report describes an exceptionally rare presentation of fulminant myocarditis as the primary manifestation in a 6-year-old child, diverging from the typical neurological pathogenesis associated with N. fowleri infection. Beyond neurological afflictions, the child developed arrhythmias and cardiac failure, necessitating treatment with extracorporeal membrane oxygenation (ECMO).

Methods

Diagnosis was confirmed via metagenomic next-generation sequencing (mNGS) of both blood and cerebrospinal fluid (CSF). This analysis not only substantiated the infection but also revealed a potential new genotype of N. fowleri, designated k39_3, suggesting broader genetic diversity than previously recognized.

Results

Immediate treatment with Amphotericin B (Am B) and rifampin was initiated upon diagnosis. Despite aggressive management and supportive care, the patient failed to maintain hemodynamic stability, continued to show a decrease in cardiac output, and exhibited relentless progression of central nervous system failure, culminating in death within 72 h.

Conclusion

Our report documents a rare pediatric case of N. fowleri infection presenting with fulminant myocarditis, revealing an unexpected clinical manifestation and broadening the known spectrum of its effects. This emphasizes the need for enhanced surveillance and targeted research to understand the pathogenic mechanisms and improve treatment strategies.

Flucofuron as a Promising Therapeutic Agent against Brain-Eating Amoeba

Primary amoebic meningoencephalitis (PAM) is a rare and fulminant neurodegenerative disease caused by the free-living amoeba Naegleria fowleri. Currently, there is a lack of standardized protocols for therapeutic action. In response to the critical need for effective therapeutic agents, we explored the Global Health Priority Box, a collection of 240 compounds provided by the Medicines for Malaria Venture (MMV). From this pool, flucofuron emerged as a promising candidate, exhibiting high efficacy against trophozoites of both N. fowleri strains (ATCC 30808 IC50 : 2.58 ± 0.64 μM and ATCC 30215 IC50: 2.47 ± 0.38 μM), being even active against the resistant cyst stage (IC50: 0.88 ± 0.07 μM). Moreover, flucofuron induced diverse metabolic events that suggest the triggering of apoptotic cell death. This study highlights the potential of repurposing medications for treating challenging diseases, such as PAM.

Next generation imidazothiazole and imidazooxazole derivatives as potential drugs against brain-eating amoebae

Managing primary amoebic meningoencephalitis, induced by Naegleria fowleri poses a complex medical challenge. There is currently no specific anti-amoebic drug that has proven effectiveness against N. fowleri infection. Ongoing research endeavours are dedicated to uncovering innovative treatment strategies, including the utilization of drugs and immune modulators targeting Naegleria infection. In this study, we explored the potential of imidazo[2,1-b]thiazole and imidazooxazole derivatives that incorporate sulfonate and sulfamate groups as agents with anti-amoebic properties against N. fowleri. We assessed several synthesized compounds (1f, 1m, 1q, 1s, and 1t) for their efficacy in eliminating amoebae, their impact on cytotoxicity, and their influence on the damage caused to human cerebral microvascular endothelial (HBEC-5i) cells when exposed to the N. fowleri (ATCC 30174) strain. The outcomes revealed that, among the five compounds under examination, 1m, 1q, and 1t demonstrated notable anti-parasitic effects against N. fowleri (P ≤ 0.05). Compound 1t exhibited the highest anti-parasitic activity, reducing N. fowleri population by 80%. Additionally, three compounds, 1m, 1q, and 1t, significantly mitigated the damage inflicted on host cells by N. fowleri. However, the results of cytotoxicity analysis indicated that while 1m and 1q had minimal cytotoxic effects on endothelial cells, compound 1t caused moderate cytotoxicity (34%). Consequently, we conclude that imidazo[2,1-b]thiazole and imidazooxazole derivatives containing sulfonate and sulfamate groups exhibit a marked capacity to eliminate amoebae viability while causing limited toxicity to human cells. In aggregate, these findings hold promise that could potentially evolve into novel therapeutic options for treating N. fowleri infection.

Natural Terpenes Inhibit the Cytopathogenicity of Naegleria fowleri Causing Primary Amoebic Meningoencephalitis in the Human Cell Line Model

Naegleria fowleri is one of the free-living amoebae and is a causative agent of a lethal and rare central nervous system infection called primary amoebic meningoencephalitis. Despite the advancement in antimicrobial chemotherapy, the fatality rate in the reported cases is more than 95%. Most of the treatment drugs used against N. fowleri infection are repurposed drugs. Therefore, a large number of compounds have been tested against N. fowleri in vitro, but most of the compounds showed high toxicity. To overcome this, we evaluated the effectiveness of naturally occurring terpene compounds against N. fowleri. In this study, we evaluated the antiamoebic potential of natural compounds including Thymol, Borneol, Andrographolide, and Forskolin againstN. fowleri. Thymol showed the highest amoebicidal activity with IC50/24 h at 153.601 ± 19.6 μM. Two combinations of compounds Forskolin + Thymol and Forskolin + Borneol showed a higher effect on the viability of trophozoites as compared to compounds alone and hence showed a synergistic effect. The IC50 reported for Forskolin + Thymol was 81.30 ± 6.86 μM. Borneol showed maximum cysticidal activity with IC50/24 h at 192.605 ± 3.01 μM. Importantly, lactate dehydrogenase release testing revealed that all compounds displayed minimal cytotoxicity to human HaCaT, HeLa, and SH-SY5Y cell lines. The cytopathogenicity assay showed that Thymol and Borneol also significantly reduced the host cell cytotoxicity of pretreated amoeba toward the human HaCaT cell line. So, these terpene compounds hold potential as therapeutic agents against infections caused by N. fowleri and are potentially a step forward in drug development against this deadly pathogen as these compounds have also been reported to cross the blood-brain barrier. Therefore, an in vivo study using animal models is necessary to assess the efficacy of these compounds and the need for further research into the intranasal route of delivery for the treatment of these life-threatening infections.

The anti-amoebic potential of carboxamide derivatives containing sulfonyl or sulfamoyl moieties against brain-eating Naegleria fowleri

Naegleria fowleri is a free-living thermophilic flagellate amoeba that causes a rare but life-threatening infection called primary amoebic meningoencephalitis (PAM), with a very high fatality rate. Herein, the anti-amoebic potential of carboxamide derivatives possessing sulfonyl or sulfamoyl moiety was assessed against pathogenic N. fowleri using amoebicidal, cytotoxicity and cytopathogenicity assays. The results from amoebicidal experiments showed that derivatives dramatically reduced N. fowleri viability. Selected derivatives demonstrated IC50 values at lower concentrations; 1j showed IC50 at 24.65 μM, while 1k inhibited 50% amoebae growth at 23.31 μM. Compounds with significant amoebicidal effects demonstrated limited cytotoxicity against human cerebral microvascular endothelial cells. Finally, some derivatives mitigated N. fowleri-instigated host cell death. Ultimately, this study demonstrated that 1j and 1k exhibited potent anti-amoebic activity and ought to be looked at in future studies for the development of therapeutic anti-amoebic pharmaceuticals. Further investigation is required to determine the clinical relevance of our findings.

Kaempferol induces programmed cell death in Naegleria fowleri

BACKGROUND

Naegleria fowleri is a brain-eating amoeba causing a fatal brain infection called primary amoebic meningoencephalitis (PAM). Despite its high mortality over 95%, effective therapeutic drug for PAM has not been developed yet. Therefore, development of an effective and safe therapeutic drug for PAM is urgently needed. In this study, we investigated anti-amoebic effect of kaempferol (KPF) against N. fowleri and its underlying anti-amoebic molecular mechanisms.

METHODS

Anti-amoebic activity of KPF against N. fowleri trophozoites, as well as cytotoxicity of KPF in C6 glial cells and CHO-K1 cells were investigated. The programmed cell death mechanisms in KPF-treated N. fowleri were also analyzed by apoptosis-necrosis assay, mitochondrial dysfunction assay, TUNEL assay, RT-qPCR, and CYTO-ID assay.

RESULTS

KPF showed anti-amoebic activity against N. fowleri trophozoites with an IC50 of 29.28 ± 0.63 μM. However, it showed no significant cytotoxicity to mammalian cells. KPF induced significant morphological alterations of the amoebae, resulting in death. Signals associated with apoptosis were detected in the amoebae upon treatment with KPF. KPF induced an increase of intracellular reactive oxygen species level, loss of mitochondrial membrane potential, increases of expression levels of genes associated with mitochondria dysfunction, and reduction of ATP levels in the amoebae. Autophagic vacuole accumulations with increased expression levels of autophagy-related genes were also detected in KPF-treated amoebae.

CONCLUSION

KPF induces programmed cell death in N. fowleri trophozoites via apoptosis-like pathway and autophagy pathway. KPF could be used as a candidate of anti-amoebic drug or supplement compound in the process of developing or optimizing therapeutic drug for PAM.

Repurposing of Nitroxoline as an Alternative Primary Amoebic Meningoencephalitis Treatment

Among the pathogenic free-living amoebae (FLA), Naegleria fowleri is the etiological agent of a fatal disease known as primary amoebic meningoencephalitis (PAM). Once infection begins, the lesions generated in the central nervous system (CNS) result in the onset of symptoms leading to death in a short period of time. Currently, there is no standardized treatment against the infection, which, due to the high virulence of the parasite, results in a high case fatality rate (>97%). Therefore, it is essential to search for new therapeutic sources that can generate a rapid elimination of the parasite. In recent years, there have already been several successful examples of drug repurposing, such as Nitroxoline, for which, in addition to its known bioactive properties, anti-Balamuthia activity has recently been described. Following this approach, the anti-Naegleria activity of Nitroxoline was tested. Nitroxoline displayed low micromolar activity against two different strains of N. fowleri trophozoites (IC50 values of 1.63 ± 0.37 µM and 1.17 ± 0.21 µM) and against cyst stages (IC50 of 1.26 ± 0.42 μM). The potent anti-parasitic activity compared to the toxicity produced (selectivity index of 3.78 and 5.25, respectively) in murine macrophages and human cell lines (reported in previous studies), together with the induction of programmed cell death (PCD)-related events in N. fowleri make Nitroxoline a great candidate for an alternative PAM treatment.

Marine Meroterpenoids Isolated from Gongolaria abies-marina Induce Programmed Cell Death in Naegleria fowleri

Naegleria fowleri is the causative agent of a central nervous system affecting disease called primary amoebic meningoencephalitis. It is a fulminant disease with a rapid progression that affects mainly children and young adults who report previous water exposure. Current treatment options are not totally effective and involve several side effects. In this work, six meroterpenoids isolated from the brown algae Gongolaria abies-marina were evaluated against N. fowleri. Gongolarone B (1), 6Z-1'-methoxyamentadione (2), and 1'-methoxyamentadione (3) were the most active molecules against N. fowleri with IC₅₀ values between 13.27 ± 0.96 µM and 21.92 ± 1.60 µM. However, cystomexicone B (6) was the molecule with the highest selectivity index (>8.5). Moreover, all these compounds induced different cellular events compatible with the apoptosis-like PCD process, such as chromatin condensation, damages at the mitochondrial level, cell membrane disruption, and production of reactive oxygen species (ROS). Therefore, G. abies-marina could be considered as a promising source of active molecules to treat the N. fowleri infections.

Cyanomethyl Vinyl Ethers Against Naegleria fowleri

Naegleria fowleri is a pathogenic amoeba that causes a fulminant and rapidly progressive disease affecting the central nervous system called primary amoebic meningoencephalitis (PAM). Moreover, the disease is fatal in more than 97% of the reported cases, mostly affecting children and young people after practicing aquatic activities in nontreated fresh and warm water bodies contaminated with these amoebae. Currently, the treatment of primary amoebic meningoencephalitis is based on a combination of different antibiotics and antifungals, which are not entirely effective and lead to numerous side effects. In the recent years, research against PAM is focused on the search of novel, less toxic, and fully effective antiamoebic agents. Previous studies have reported the activity of cyano-substituted molecules in different protozoa. Therefore, the activity of 46 novel synthetic cyanomethyl vinyl ethers (QOET-51 to QOET-96) against two type strains of N. fowleri (ATCC 30808 and ATCC 30215) was determined. The data showed that QOET-51, QOET-59, QOET-64, QOET-67, QOET-72, QOET-77, and QOET-79 were the most active molecules. In fact, the selectivity index (CC₅₀/IC₅₀) was sixfold higher when compared to the activities of the drugs of reference. In addition, the mechanism of action of these compounds was studied, with the aim to demonstrate the induction of a programmed cell death process in N. fowleri.

Chamigrane-Type Sesquiterpenes from Laurencia dendroidea as Lead Compounds against Naegleria fowleri

Naegleria fowleri is an opportunistic protozoon that can be found in warm water bodies. It is the causative agent of the primary amoebic meningoencephalitis. Focused on our interest to develop promising lead structures for the development of antiparasitic agents, this study was aimed at identifying new anti-Naegleria marine natural products from a collection of chamigrane-type sesquiterpenes with structural variety in the levels of saturation, halogenation and oxygenation isolated from Laurencia dendroidea. (+)-Elatol (1) was the most active compound against Naegleria fowleri trophozoites with IC50 values of 1.08 μM against the ATCC 30808™ strain and 1.14 μM against the ATCC 30215™ strain. Furthermore, the activity of (+)-elatol (1) against the resistant stage of N. fowleri was also assessed, showing great cysticidal properties with a very similar IC50 value (1.14 µM) to the one obtained for the trophozoite stage. Moreover, at low concentrations (+)-elatol (1) showed no toxic effect towards murine macrophages and could induce the appearance of different cellular events related to the programmed cell death, such as an increase of the plasma membrane permeability, reactive oxygen species overproduction, mitochondrial malfunction or chromatin condensation. Its enantiomer (−)-elatol (2) was shown to be 34-fold less potent with an IC50 of 36.77 μM and 38.03 μM. An analysis of the structure–activity relationship suggests that dehalogenation leads to a significant decrease of activity. The lipophilic character of these compounds is an essential property to cross the blood-brain barrier, therefore they represent interesting chemical scaffolds to develop new drugs.

Isobenzofuran-1(3H)-one derivatives: Amoebicidal activity and program cell death in Acanthamoeba castellanii Neff

The genus Acanthamoeba is characterized by being a group of ubiquitous and free-living amoebae that inhabit a variety of environments. Generally, human infections by this parasite are associated with Acanthamoeba keratitis, especially in contact lens wearers, and with chronic but fatal granulomatous amoebic meningoencephalitis. Current treatments used for eradication of amoeba from infection sites represent a challenge for pharmacotherapy, due to the lack of effective treatment and the amoebae highly resistant to anti-amoebic drugs. In this study, we describe the results of the assessment of the IC₅₀ of 10 isobenzofuran-1(3H)-one derivatives (QOET) against four Acanthamoeba strains. The compounds QOET-3 and QOET-9 were the selected derivatives with the lowest IC₅₀ in A. castellanii Neff trophozoites (73.71 ± 0.25 and 69.99 ± 15.32 µM, respectively). Interestingly, analysis of the compound effects on the cell apoptosis-like features showed that both active molecules triggered programmed cell death (PCD) in A. castellanii Neff. The results obtained in this study highlights that isobenzofuranone derivatives could represent an interesting source for developing novel antiamoebic drugs.

The therapeutic potential of novel isobenzofuranones against Naegleria fowleri

The Free-Living Amoeba species, Naegleria fowleri is the causative agent of a lethal encephalitis known as Primary Amoebic Encephalitis (PAM). Moreover, most of the reported cases are often related to swimming and/or diving in aquatic environments. In addition, the current therapeutic options against PAM are not fully effective and hence, there is an urgent need to develop novel therapeutic agents against this disease. Previously isobenzofuranones compounds have been reported to present antiprotozoal and antifungal activity among others. However, to the best of our knowledge, these molecules have not been previously tested against N. fowleri. Therefore, the aim of this study was to evaluate the activity of 14 novel isobenzofuranones against this pathogenic amoeba. The most active and less toxic molecules, were assayed in order to check induction of Programmed Cell Death (PCD) in the treated amoebae. The obtained results showed that these molecules were able to eliminate N. fowleri trophozoites and also induced PCD. Therefore, the tested isobenzofuranones could be potential therapeutic candidates for the treatment of PAM.

Repurposing in vitro approaches for screening anti-parasitic drugs against the brain-eating amoeba Naegleria fowleri

Naegleria fowleri is both a pathogenic and a free-living microbial eukaryote, responsible for the development of primary amoebic meningoencephalitis (PAM) in humans. PAM is a rapid, severe and fatal underestimated infectious disease, which has been reported in countries with warmer climates. The major drawbacks with PAM are the lack of effective therapies and delay in diagnosis. The current frontline treatment presents a low rate of recovery (5%) and severe adverse effects. For example, many drug candidates lack efficacy, since they do not effectively cross the blood-brain-barrier. Consequently, more effective drugs are urgently needed. Herein, we report a new in vitro method suitable for medium- and high-throughput drug discovery assays, using the closely related Naegleria gruberi as a model. We have subsequently used this method to screen a library of 1175 Food and Drug Administration-approved drugs. As a result, we present three drugs (camptothecin, pyrimethamine, and terbinafine) that can be repurposed, and are anticipated to readily cross the blood-brain-barrier with activity against Naegleria species in therapeutically achievable concentrations. Successively, we integrated several in vitro assays that resulted in identifying fast-acting and high amoebicidal drugs. In conclusion, we present a new approach for the identification of anti-Naegleria drugs along with three potential drug candidates for further development for the treatment of PAM.

Naphthyridine Derivatives Induce Programmed Cell Death in Naegleria fowleri

Primary amoebic encephalitis (PAM) caused by the opportunistic pathogen Naegleria fowleri is characterized as a rapid and lethal infection of the brain which ends in the death of the patient in more than 90% of the reported cases. This amoeba thrives in warm water bodies and causes infection after individuals perform risky activities such as splashing or diving, mostly in non-treated water bodies such as lakes and ponds. Moreover, the infection progresses very fast and no fully effective molecules have currently been found to treat PAM. In this study, naphthyridines fused with chromenes or chromenones previously synthetized by the group were tested in vitro against the trophozoite stage of two strains of N. fowleri. In addition, the most active molecule was evaluated in order to check the induction of programmed cell death (PCD) in the treated amoebae. Compound 3 showed good anti-Naegleria activity (61.45 ± 5.27 and 76.61 ± 10.84 µM, respectively) against the two different strains (ATCC^® 30808 and ATCC^® 30215) and a good selectivity compared to the cytotoxicity values (>300 µM). In addition, it was able to induce PCD, causing DNA condensation, damage at the cellular membrane, reduction in mitochondrial membrane potential and ATP levels, and ROS generation. Hence, naphthyridines fused with chromenes or chromenones could be potential therapeutic agents against PAM in the near future.

Primary Amoebic Meningoencephalitis by Naegleria fowleri: Pathogenesis and Treatments

Naegleria fowleri is a free-living amoeba (FLA) that is commonly known as the "brain-eating amoeba." This parasite can invade the central nervous system (CNS), causing an acute and fulminating infection known as primary amoebic meningoencephalitis (PAM). Even though PAM is characterized by low morbidity, it has shown a mortality rate of 98%, usually causing death in less than two weeks after the initial exposure. This review summarizes the most recent information about N. fowleri, its pathogenic molecular mechanisms, and the neuropathological processes implicated. Additionally, this review includes the main therapeutic strategies described in case reports and preclinical studies, including the possible use of immunomodulatory agents to decrease neurological damage.

A Search for Anti-Naegleria fowleri Agents Based on Competitive Exclusion Behavior of Microorganisms in Natural Aquatic Environments

Naegleria fowleri causes deadly primary amoebic meningoencephalitis (PAM) in humans. Humans obtain the infection by inhaling water or dust contaminated with amebae into the nostrils, wherefrom the pathogen migrates via the olfactory nerve to cause brain inflammation and necrosis. Current PAM treatment is ineffective and toxic. Seeking new effective and less toxic drugs for the environmental control of the amoeba population to reduce human exposure is logical for the management of N. fowleri infection. On the basis of the concept of competitive exclusion, where environmental microorganisms compete for resources by secreting factors detrimental to other organisms, we tested cell-free culture supernatants (CFSs) of three bacteria isolated from a fresh water canal, i.e., Pseudomonas aeruginosa, Pseudomonas otitidis, and Enterobacter cloacae, were tested against N. fowleri. The CFSs inhibited growth and caused morphological changes in N. fowleri. At low dose, N. fowleri trophozoites exposed to P. aeruginosa pyocyanin were seen to shrink and become rounded, while at high dose, the trophozoites were fragmented. While the precise molecular mechanisms of pyocyanin and products of P. otitidis and E. cloacae that also exert anti-N. fowleri activity await clarification. Our findings suggest that P. aeruginosa pyocyanin may have a role in the control of amphizoic N. fowleri in the environment.

Laurinterol from Laurencia johnstonii eliminates Naegleria fowleri triggering PCD by inhibition of ATPases

Primary amoebic encephalitis (PAM) is a lethal disease caused by the opportunistic pathogen, Naegleria fowleri. This amoebic species is able to live freely in warm aquatic habitats and to infect children and young adults when they perform risk activities in these water bodies such as swimming or splashing. Besides the need to increase awareness of PAM which will allow an early diagnosis, the development of fully effective therapeutic agents is needed. Current treatment options are amphotericin B and miltefosine which are not fully effective and also present toxicity issues. In this study, the in vitro activity of various sesquiterpenes isolated from the red alga Laurencia johnstonii were tested against the trophozoite stage of a strain of Naegleria fowleri. Moreover, the induced effects (apoptotic cell death) of the most active compound, laurinterol (1), was evaluated by measuring DNA condensation, damages at the mitochondrial level, cell membrane disruption and production of reactive oxygen species (ROS). The obtained results demonstrated that laurinterol was able to eliminate the amoebae at concentrations of 13.42 ± 2.57 µM and also to induced programmed cell death (PCD) in the treated amoebae. Moreover, since ATP levels were highly affected and laurinterol has been previously reported as an inhibitor of the Na⁺/K⁺-ATPase sodium–potassium ion pump, comparison with known inhibitors of ATPases were carried out. Our results points out that laurinterol was able to inhibit ENA ATPase pump at concentrations 100 times lower than furosemide.

Evaluation of Indolocarbazoles from Streptomyces sanyensis as a Novel Source of Therapeutic Agents against the Brain-Eating Amoeba Naegleria fowleri

Naegleria fowleri is an opportunistic pathogenic free-living amoeba which is able to rapidly colonize the central nervous system (CNS) and causes a lethal infection known as primary amoebic meningoencephalitis (PAM). Furthermore, more than 98% of the known cases of PAM are fatal and affect mainly children under 12 and young adults. Until now, no fully effective therapeutic agents against N. fowleri are available and hence the urgent need to find novel agents to treat PAM. At present, PAM therapy is based on the combination of amphotericin B, miltefosine, among others, with unwanted toxic effects. Recently, our team isolated various indolocarbazoles (ICZs) from the culture of a mangrove strain of Streptomyces sanyensis which showed activity against kinetoplastids and the Acanthamoeba genus. Hence, in this study, the activity of the previously isolated ICZs, staurosporine (STS), 7-oxostaurosporine (7OSTS), 4′-demethylamino-4′-oxostaurosporine, and streptocarbazole B, was evaluated against two type strains of N. fowleri. Furthermore, the performed activity assays revealed that STS was the most active ICZ presenting an inhibitory concentration 50 (IC₅₀) of 0.08 ± 0.02 µM (SI 109.3). Moreover, STS induced programmed cell death (PCD) in the treated amoebae by triggering DNA condensation, mitochondrial disfunction, cell membrane disruption, and reactive oxygen species (ROS) generation. Therefore, STS could be a promising therapeutic agent against PAM.

Brain-eating Amoebae Infection: Challenges and Opportunities in Chemotherapy

Pathogenic free-living amoeba are known to cause a devastating infection of the central nervous system and are often referred to as "brain-eating amoebae". The mortality rate of more than 90% and free-living nature of these amoebae is a cause for concern. It is distressing that the mortality rate has remained the same over the past few decades, highlighting the lack of interest by the pharmaceutical industry. With the threat of global warming and increased outdoor activities of public, there is a need for renewed interest in identifying potential anti-amoebic compounds for successful prognosis. Here, we discuss the available chemotherapeutic options and opportunities for potential strategies in the treatment and diagnosis of these life-threatening infections.