Hương Giang Lê

Background/Objectives: Naegleria fowleri is an opportunistic pathogen causing primary amoebic meningoencephalitis (PAM), a fatal neuroinflammatory disease with a high mortality rate of over 97%, in humans. Currently, there are no approved therapeutics for PAM, underscoring the urgent necessity of developing effective and safe drugs. This study aimed to evaluate the potential of ginsenosides Rb3 and Rc as alternative or supplementary drug candidates for PAM by assessing their anti-amoebic activities against N. fowleri. Methods: Anti-N. fowleri activities of ginsenosides Rb3 and Rc and their cytotoxicity to C6 glial cells were evaluated by cell viability assay. The underlying anti-amoebic mode of action of Rb3 and Rc was analyzed by a series of assays for apoptosis–necrosis, TUNEL, intracellular reactive oxygen species (ROS), mitochondrial dysfunction, ATP production, caspase-3, and autophagy. The expression profiles of apoptosis- and autophagy-related genes were also analyzed. Results: Rb3 and Rc effectively induced death of N. fowleri trophozoites with IC₅₀ values of 94.71 ± 1.63 μM and 126.99 ± 1.88 μM, respectively. However, Rb3 and Rc showed no significant cytotoxicities against C6 glial cells, suggesting their selective anti-N. fowleri activities. Typical apoptosis signals, such as apopxin staining and DNA fragmentation, were detected in amoebae upon treatment with Rb3 or Rc. These two ginsenosides enhanced ROS production and induced mitochondrial dysfunction in the amoebae. Enhanced caspase-3 activity and autophagy formation were also identified in amoebae treated with Rb3 or Rc. Conclusions: These results provide the first evidence that ginsenosides Rb3 and Rc induce apoptosis-like programmed cell death in N. fowleri, suggesting that they are potential candidates in developing novel therapeutic strategies against PAM.

Plasmodium vivax merozoite surface protein-1 (PvMSP-1) is one of the major polymorphic markers for molecular epidemiological purposes. In particular, the interspecies conserved block 5–6 (ICB 5–6) of PvMSP-1 is a region exhibiting extensive genetic polymorphism. In this study, we analyzed polymorphic characters of the pvmsp-1 ICB 5–6 region from P. vivax isolates collected in 4 provinces of Vietnam (Dak Lak, Dak Nong, Gia Lai, and Khanh Hoa) between 2018 and 2022. A comparative analysis of pvmsp-1 ICB 5–6 sequences was also conducted between Vietnam and other endemic regions. A total of 139 pvmsp-1 ICB 5–6 sequences were obtained from 117 Vietnamese P. vivax isolates. Vietnam pvmsp-1 ICB 5–6 were clustered into 34 distinct haplotypes at the amino acid level, with the recombinant types being predominant. The pvmsp-1 ICB 5–6 from the Central Highlands, Dak Lak, Dak Nong, and Gia Lai, exhibited high genetic polymorphism, while the sequences from the South-Central region, Khanh Hoa, were less polymorphic. Highly diverse patterns of poly-glutamine (poly-Q) variants were identified in Vietnam pvmsp-1 ICB 5–6. Comparable features of genetic polymorphism were also identified in the global pvmsp-1 ICB 5–6 populations. Phylogenetic analysis of global pvmsp-1 ICB 5–6 revealed no significant country- or region-specific clustering. This study suggests that Vietnam pvmsp-1 ICB 5–6 exhibited a substantial genetic diversity with regional variations, implying the genetic heterogeneity of the Vietnamese P. vivax population. These findings emphasize the importance of continuous molecular surveillance to understand the genetic nature of the parasite in the country.

Cysteine proteases play key roles in the biology of Plasmodium parasites and are recognized as antimalarial drug targets. Because these enzymes are involved in diverse biological functions, precise regulation is required to prevent unnecessary damage to both parasites and hosts. In this study, we identified an endogenous inhibitor of cysteine protease of Plasmodium vivax (PvICP) and characterized its biochemical properties. PvICP was found to share highly similar structural characteristics with orthologous proteins from other Plasmodium species. Recombinant PvICP (rPvICP) expressed in Escherichia coli showed a broad range of inhibitory activity against falcipain family cysteine proteases, including vivapain-3, vivapain-4, falcipain-3, malapain-2, and malapain-4, with more potent inhibitory activity against vivapain-3 and vivapain-4. rPvICP’s inhibitory activity was not significantly affected by pH, suggesting its broad biological functions. These findings provide new insights into PvICP and lay the groundwork for future studies exploring its biological significance and potential as a therapeutic target in malaria research.

Asymptomatic malaria infection is a major concern in the fight against malaria, as it can act as a significant reservoir for its silent spread or transmission. Therefore, surveillance to detect asymptomatic subjects, particularly in regions with high malaria endemicity, is essential. This study aimed to investigate the status of asymptomatic submicroscopic malaria infections in Gia Lai province, Vietnam, and to analyze molecular profiles of antimalarial drug resistance in the parasites from the asymptomatic carriers. A total of 2171 individuals were included from three districts of Gia Lai province, Vietnam, an area where malaria is endemic. Asymptomatic submicroscopic infection was confirmed by quantitative real-time PCR, and the infected Plasmodium species were confirmed by sequencing. Antimalarial drug-resistant genes, including pfk13, pfcrt, pvmdr-1, and pvcrt-o, were analyzed in the parasites from asymptomatic cases. The rate of asymptomatic submicroscopic malaria infection was 2.67%. P. falciparum and P. vivax mono-infections, as well as mixed infections of P. falciparum and P. vivax, were identified, with P. vivax being more prevalent, a significant observation given the challenge of P. vivax relapses and its contribution to sustained malaria transmission. Adults, including young, middle-aged, and older adults, were the predominant affected groups. Asymptomatic infections were more common in females than in males. Interestingly, high frequencies of mutations in genetic markers associated with antimalarial drug resistance, particularly pfk13 (C580Y, 100%), pfcrt (M74I/N75E/K76T, 100%), and pvmdr-1 (F1076L, 100%), were observed in asymptomatic individuals, which may increase the risk of spreading drug resistance. These findings emphasize the urgent necessity for improved surveillance and targeted intervention to prevent the silent spread of malaria, supporting the National Malarial Control and Elimination Program in formulating malaria elimination strategies for Vietnam.

Background/Objectives: Naegleria fowleri is a free-living amoeba that invades brain tissues causing fatal primary amoebic meningoencephalitis (PAM). An effective and tolerable therapeutic agent is still lacking. Methods: A series of conformationally restricted analogs of miltefosine with varied restriction positions, stereochemical configuration and lengths of alkyl chain was investigated to discover more effective and less toxic agents than miltefosine. Results: Among tested compounds, derivatives 2a, 3b and 3d featuring 1,2- or 2,3-positional restriction with trans-configuration and tridecyl or behenyl alkyl chains were discovered as more potent and less cytotoxic agents. Compounds 2a, 3b and 3d elicited 3.49-, 3.58- and 6.03-fold relative potencies to miltefosine and 7.53, 3.90 and 3.49 selectivity indices, respectively. Furthermore, compounds 2a and 3b showed IC₉₀ values for N. fowleri lower than CC₅₀ against glial C6 cells. Compounds 2a, 3b and 3d induced morphological changes and programmed cell death of N. fowleri via the apoptosis-like pathway. The induced death of N. fowleri involved DNA fragmentation along with the loss of mitochondrial membrane potential. Conclusions: The current research presents compounds 2a and 3b as more potent, selective and effective agents than miltefosine against N. fowleri for further development.