Miltefosine: A Miracle Drug for Meningoencephalitis Caused by Free-Living Amoebas

Development and immunological evaluation of an mRNA-based vaccine targeting Naegleria fowleri for the treatment of primary amoebic meningoencephalitis

More than 95% of patients fall victim to primary amoebic meningoencephalitis (PAM), a fatal disease attacking the central nervous system. Naegleria fowleri, a brain-eating microorganism, is PAM's most well-known pathogenic ameboflagellate. Despite the use of antibiotics, the fatality rate continues to rise as no clinical trials have been conducted against this disease. To address this, we mined the UniProt database for pathogenic proteins and selected assumed epitopes to create an mRNA-based vaccine. We identified thirty B-cell and T-cell epitopes for the vaccine candidate. These epitopes, secretion boosters, subcellular trafficking structures, and linkers were used to construct the vaccine candidate. Through predictive modeling and confirmation via the Ramachandran plot (with a quality factor of 92.22), we assessed secondary and 3D structures. The adjuvant RpfE was incorporated to enhance the vaccine construct's immunogenicity (GRAVY index: 0.394, instability index: 38.99, antigenicity: 0.8). The theoretical model of immunological simulations indicated favorable responses from both innate and adaptive immune cells, with memory cells expected to remain active for up to 350 days post-vaccination, while the antigen was eliminated from the body within 24 h. Notably, strong interactions were observed between the vaccine construct and TLR-4 (- 11.9 kcal/mol) and TLR-3 (- 18.2 kcal/mol).

Virtual Screening of Alkaloid and Terpenoid Inhibitors of SMT Expressed in Naegleria sp

The pathogenic form of thermophilic Naegleria sp. i.e., Naegleria fowleri, also known as brain eating amoeba, causes primary amoebic encephalitis (PAM) with a >97% fatality rate. To date, there are no specific drugs identified to treat this disease specifically. The present antimicrobial combinatorial chemotherapy is hard on many patients, especially children. Interestingly, Naegleria fowleri has complex lipid biosynthesis pathways like other protists and also has a strong preference to utilize absorbed host lipids for generating energy. The ergosterol biosynthesis pathway provides a unique drug target opportunity, as some of the key enzymes involved in this pathway are absent in humans. Sterol 24-C Methyltransferase (SMT) is one such enzyme that is not found in humans. To select novel inhibitors for this enzyme, alkaloids and terpenoids inhibitors were screened and tested against two isozymes of SMT identified in N. gruberi (non-pathogenic) as well as its homolog found in yeast, i.e., ERG6. Five natural product derived inhibitors i.e., Cyclopamine, Chelerythrine, Berberine, Tanshinone 2A, and Catharanthine have been identified as potential drug candidates based on multiple criteria including binding affinity, ADME scores, absorption, and, most importantly, its ability to cross the blood brain barrier. This study provides multiple leads for future drug exploration against Naegleria fowleri.

Novel Antiamoebic Tyrocidine-Derived Peptide against Brain-Eating Amoebae

Acanthamoeba castellanii (A. castellanii) can cause Acanthamoeba keratitis, a sight-threatening infection, as well as a fatal brain infection termed granulomatous amoebic encephalitis, mostly in immunocompromised individuals. In contrast, Naegleria fowleri (N. fowleri) causes a deadly infection involving the central nervous system, recognized as primary amoebic encephalitis, mainly in individuals partaking in recreational water activities or those with nasal exposure to contaminated water. Worryingly, mortality rates due to these infections are more than 90%, suggesting the need to find alternative therapies. In this study, antiamoebic activity of a peptide based on the structure of the antibiotic tyrocidine was evaluated against A. castellanii and N. fowleri. The tyrocidine-derived peptide displayed significant amoebicidal efficacy against A. castellanii and N. fowleri. At 250 μg/mL, the peptide drastically reduced amoebae viability up to 13% and 21% after 2 h of incubation against N. fowleri and A. castellanii., whereas, after 24 h of incubation, the peptide showed 86% and 94% amoebicidal activity against A. castellanii and N. fowleri. Furthermore, amoebae pretreated with 100 μg/mL peptide inhibited 35% and 53% A. castellanii and N. fowleri, while, at 250 μg/mL, 84% and 94% A. castellanii and N. fowleri failed to adhere to human cells. Amoeba-mediated cell cytopathogenicity assays revealed 31% and 42% inhibition at 100 μg/mL, while at 250 μg/mL 75% and 86% A. castellanii and N. fowleri were inhibited. Assays revealed inhibition of encystation in both A. castellanii (58% and 93%) and N. fowleri (73% and 97%) at concentrations of 100 and 250 μg/mL respectively. Importantly, tyrocidine-derived peptide depicted minimal cytotoxicity to human cells and, thus, may be a potential candidate in the rational development of a treatment regimen against free-living amoebae infections. Future studies are necessary to elucidate the in vivo effects of tyrocidine-derived peptide against these and other pathogenic amoebae of importance.

Case Report: Recognition of Devastating Primary Amoebic Meningoencephalitis (PAM) Caused by Naegleria fowleri: Another Case in South China Detected via Metagenomics Next-Generation Sequencing Combined With Microscopy and a Review

Introduction

Primary amoebic meningoencephalitis (PAM) caused by Naegleria fowleri is seldom reported in mainland China.

Methods

One case from South China was presented, and the clinical features of the PAM, especially the early CT features, were compared to those in the literatures from PubMed/Web of Science/China National Knowledge internet (CNKI).

Case Presentation and Results

A 47-year-old man with a high fever came to the fever clinic. Twelve hours later, the man lost consciousness and exhibited generalized tonic-clonic seizures and needed ventilator-controlled ventilation. Then, he was admitted to the neurology intensive care unit (NICU). The opening pressure of his cerebrospinal fluid (CSF) was over 500 mm H2O with highly increased leukocyte/protein levels and very low glucose levels. Three days after admission, high copy numbers of Naegleria fowleri amoebae were detected by metagenomics next-generation sequencing (mNGS) and cysts were visible with wet mount microscopy. Four days after admission, the patient experienced brain death. However, the relatives of the patient did not want to give up, and he received amphotericin B (AmB). During hospitalization, he suffered from severe damage to the liver and kidneys and electrolyte disorders that required continuous renal replacement therapy (CRRT).

Review

All 20 included PAM patients suffered from fever. Seventeen of them had headache and neck stiffness. Ten of them showed generalized brain edema. To date, 7 cases of PAM have been reported in China. Only one patient survived. Most of the patients showed generalized brain edema. Only the surviving patient showed focal edema. He died three months later.

Conclusion

Rapidly progressive meningoencephalitis in which the CSF results are similar to those suffered from a bacterial infection should be considered a possible case of PAM. It can be rapidly detected with microscopy in CSF wet mounts but needs further molecular investigation for confirmation, and mNGS should be a new method used for rapid and precise identification. Moreover, CRRT may prolong the survival time of PAM patients with multiple organ failure.