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RSC Advances Dec 2023Development and discovery of new antimalarial drugs are needed to overcome the multi-resistance of parasites to commercially available drugs. Modifying the...
Development and discovery of new antimalarial drugs are needed to overcome the multi-resistance of parasites to commercially available drugs. Modifying the substitutions on the amine groups has been shown to increase antimalarial activities and decrease cross-resistance with chloroquine. In this study, we have synthesized several chalcone derivatives the substitution of aminoalkyl groups into the aromatic chalcone ring using the Mannich-type reaction. The chalcone derivatives were evaluated for their antimalarial properties against A1H1 and 3D7, as well as their molecular docking on dihydrofolate reductases-thymidylate synthase (PfDHFR-TS). Data from evaluation showed that chalcone Mannich-type base derivatives 2a, 2e, and 2h displayed potential antimalarial activities against with EC of 2.64, 2.98, and 0.10 μM, respectively, and 3D7 with EC of 0.08, 2.69, and 0.15 μM, respectively. The synthesized compounds 2a, 2e, and 2h exerted high selectivity index (SI > 10) values on the A1H1 and 3D7 strains. The molecular docking analysis on PfDHFR-TS supported the assay of 2a, 2e, and 2h by displaying CDOCKER energy of -48.224, -43.292, and -45.851 kcal mol. Therefore, the evidence obtained here supports that PfDHFR-TS is a putative molecular target for the synthesized compound.
PubMed: 38090066
DOI: 10.1039/d3ra05361j -
PLoS Neglected Tropical Diseases Jan 2021Plasmodium knowlesi is a simian malaria parasite currently recognized as the fifth causative agent of human malaria. Recently, naturally acquired P. cynomolgi infection...
Plasmodium knowlesi is a simian malaria parasite currently recognized as the fifth causative agent of human malaria. Recently, naturally acquired P. cynomolgi infection in humans was also detected in Southeast Asia. The main reservoir of both parasites is the long-tailed and pig-tailed macaques, which are indigenous in this region. Due to increased urbanization and changes in land use, there has been greater proximity and interaction between the long-tailed macaques and the general population in Singapore. As such, this study aims to determine the prevalence of simian malaria parasites in local macaques to assess the risk of zoonosis to the general human population. Screening for the presence of malaria parasites was conducted on blood samples from 660 peridomestic macaques collected between Jan 2008 and Mar 2017, and 379 wild macaques collected between Mar 2009 and Mar 2017, using a Pan-Plasmodium-genus specific PCR. Positive samples were then screened using a simian Plasmodium species-specific nested PCR assay to identify the species of parasites (P. knowlesi, P. coatneyi, P. fieldi, P. cynomolgi, and P. inui) present. All the peridomestic macaques sampled were tested negative for malaria, while 80.5% of the 379 wild macaques were infected. All five simian Plasmodium species were detected; P. cynomolgi being the most prevalent (71.5%), followed by P. knowlesi (47.5%), P. inui (42.0%), P. fieldi (32.5%), and P. coatneyi (28.5%). Co-infection with multiple species of Plasmodium parasites was also observed. The study revealed that Singapore's wild long-tailed macaques are natural hosts of the five simian malaria parasite species, while no malaria was detected in all peridomestic macaques tested. Therefore, the risk of simian malaria transmission to the general human population is concluded to be low. However, this can be better demonstrated with the incrimination of the vectors of simian malaria parasites in Singapore.
Topics: Animals; Macaca; Macaca fascicularis; Malaria; Monkey Diseases; Plasmodium; Plasmodium knowlesi; Polymerase Chain Reaction; Prevalence; Singapore; Zoonoses
PubMed: 33493205
DOI: 10.1371/journal.pntd.0009110 -
Tropical Medicine and Infectious Disease Oct 2023() causes zoonotic malaria and is known as the "fifth human malaria parasite". malaria is an emerging threat because infections are increasing and can be fatal. While... (Review)
Review
() causes zoonotic malaria and is known as the "fifth human malaria parasite". malaria is an emerging threat because infections are increasing and can be fatal. While most infections are in Southeast Asia (SEA), especially Malaysia, travelers frequently visit this region and can present with malaria around the world. So, clinicians need to know (1) patients who present with fever after recent travel to SEA might be infected with and (2) is often misdiagnosed as (which typically causes less severe malaria). Here we review the history, pathophysiology, clinical features, diagnosis, and treatment of malaria. Severe disease is most common in adults. Signs and symptoms can include fever, abdominal pain, jaundice, acute kidney injury, acute respiratory distress syndrome, hyponatremia, hyperparasitemia, and thrombocytopenia. Dengue is one of the diseases to be considered in the differential. Regarding pathophysiologic mechanisms, when parasites invade mature red blood cells (RBCs, i.e., normocytes) and reticulocytes, changes in the red blood cell (RBC) surface can result in life-threatening cytoadherence, sequestration, and reduced RBC deformability. Since molecular mechanisms involving the erythrocytic stage are responsible for onset of severe disease and lethal outcomes, it is biologically plausible that manual exchange transfusion (ET) or automated RBC exchange (RBCX) could be highly beneficial by replacing "sticky" parasitized RBCs with uninfected, deformable, healthy donor RBCs. Here we suggest use of special -resistant donor RBCs to optimize adjunctive manual ET/RBCX for malaria. "Therapeutically-rational exchange transfusion" (T-REX) is proposed in which -resistant RBCs are transfused (instead of disease-promoting RBCs). Because expression of the Duffy antigen on the surface of human RBCs is essential for parasite invasion, T-REX of Duffy-negative RBCs-also known as Fy(a-b-) RBCs-could replace the majority of the patient's circulating normocytes with invasion-resistant RBCs (in a single procedure lasting about 2 h). When sequestered or non-sequestered iRBCs rupture-in a 24 h asexual life cycle-the released merozoites cannot invade Fy(a-b-) RBCs. When Fy(a-b-) RBC units are scarce (e.g., in Malaysia), clinicians can consider the risks and benefits of transfusing plausibly -resistant RBCs, such as glucose-6-phosphate dehydrogenase deficient (G6PDd) RBCs and Southeast Asian ovalocytes (SAO). Patients typically require a very short recovery time (<1 h) after the procedure. Fy(a-b-) RBCs should have a normal lifespan, while SAO and G6PDd RBCs may have mildly reduced half-lives. Because SAO and G6PDd RBCs come from screened blood donors who are healthy and not anemic, these RBCs have a low-risk for hemolysis and do not need to be removed after the patient recovers from malaria. T-REX could be especially useful if (1) antimalarial medications are not readily available, (2) patients are likely to progress to severe disease, or (3) drug-resistant strains emerge. In conclusion, T-REX is a proposed optimization of manual ET/RBCX that has not yet been utilized but can be considered by physicians to treat malaria patients.
PubMed: 37888606
DOI: 10.3390/tropicalmed8100478 -
Emerging Infectious Diseases Aug 2020Most malaria in Malaysia is caused by Plasmodium knowlesi parasites through zoonotic infection from macaque reservoir hosts. We obtained genome sequences from 28...
Most malaria in Malaysia is caused by Plasmodium knowlesi parasites through zoonotic infection from macaque reservoir hosts. We obtained genome sequences from 28 clinical infections in Peninsular Malaysia to clarify the emerging parasite population structure and test for evidence of recent adaptation. The parasites all belonged to a major genetic population of P. knowlesi (cluster 3) with high genomewide divergence from populations occurring in Borneo (clusters 1 and 2). We also observed unexpected local genetic subdivision; most parasites belonged to 2 subpopulations sharing a high level of diversity except at particular genomic regions, the largest being a region of chromosome 12, which showed evidence of recent directional selection. Surprisingly, we observed a third subpopulation comprising P. knowlesi infections that were almost identical to each other throughout much of the genome, indicating separately maintained transmission and recent genetic isolation. Each subpopulation could evolve and present a broader health challenge in Asia.
Topics: Animals; Asia; Borneo; Genetic Variation; Malaysia; Metagenomics; Plasmodium knowlesi
PubMed: 32687018
DOI: 10.3201/eid2608.190864 -
Bio-protocol Sep 2020Malaria remains a major cause of morbidity and mortality globally. Clinical symptoms of the disease arise from the growth and multiplication of parasites within the...
Malaria remains a major cause of morbidity and mortality globally. Clinical symptoms of the disease arise from the growth and multiplication of parasites within the blood of the host. Thus assays to determine how drug, antibody and genetic perturbations affect the growth rate of parasites are essential for the development of new therapeutics and improving our understanding of parasite biology. As both and can be maintained in culture with human red blood cells, the effect of antimalarial drugs and inhibitory antibodies that target the invasion capacity of parasites are routinely investigated by using multiplication assays or growth inhibition assays against these two species. This protocol gives detailed step-by-step procedures to carry out flow cytometry-based multiplication assays and growth inhibition activity assays to test neutralizing antibodies based on the activity of the parasite enzyme lactate dehydrogenase of adapted to human red blood cell culture. Whilst similar assays are well established for is more closely related to all other human infective species ( Pacheco , 2018 ) and so can be used as a surrogate for testing drugs and vaccines for other malaria species such as , which is the most widespread cause of malaria outside of Africa, but cannot yet be cultured under laboratory conditions.
PubMed: 33659403
DOI: 10.21769/BioProtoc.3743 -
Computational and Structural... 2022Malaria is a tropical disease caused by spp. and transmitted by the bite of infected mosquitoes. Protein kinases (PKs) play key roles in the life cycle of the...
Malaria is a tropical disease caused by spp. and transmitted by the bite of infected mosquitoes. Protein kinases (PKs) play key roles in the life cycle of the etiological agent of malaria, turning these proteins attractive targets for antimalarial drug discovery campaigns. As part of an effort to understand parasite signaling functions, we report the results of a bioinformatics pipeline analysis of PKs of eight species. To date, no and kinome assemble has been conducted. We classified, curated and annotated predicted kinases to update kinomes published to date, as well as report for the first time the kinomes of and . Overall, from 76 to 97 PKs were identified among all spp. kinomes. Most of the kinases were assigned to seven of nine major kinase groups: AGC, CAMK, CMGC, CK1, STE, TKL, OTHER; and the group FIKK. About 30% of kinases have been deeply classified into group, family and subfamily levels and only about 10% remained unclassified. Furthermore, updating and comparing the kinomes of and allowed for the prioritization and selection of kinases as potential drug targets that could be explored for discovering new drugs against malaria. This integrated approach resulted in the selection of 37 protein kinases as potential targets and the identification of investigational compounds with moderate activity against asexual (3D7 and Dd2 strains) stages that could serve as starting points for the search of potent antimalarial leads in the future.
PubMed: 35891792
DOI: 10.1016/j.csbj.2022.07.003 -
Malaria Journal Dec 2023Plasmodium knowlesi is an established experimental model for basic and pre-clinical malaria vaccine research. Historically, rhesus macaques have been the most common...
BACKGROUND
Plasmodium knowlesi is an established experimental model for basic and pre-clinical malaria vaccine research. Historically, rhesus macaques have been the most common host for malaria vaccine studies with P. knowlesi parasites. However, rhesus are not natural hosts for P. knowlesi, and there is interest in identifying alternative hosts for vaccine research. The study team previously reported that pig-tailed macaques (PTM), a natural host for P. knowlesi, could be challenged with cryopreserved P. knowlesi sporozoites (PkSPZ), with time to blood stage infection equivalent to in rhesus. Here, additional exploratory studies were performed to evaluate PTM as potential hosts for malaria vaccine studies. The aim was to further characterize the parasitological and veterinary health outcomes after PkSPZ challenge in this macaque species.
METHODS
Malaria-naïve PTM were intravenously challenged with 2.5 × 10 PkSPZ and monitored for blood stage infection by Plasmodium 18S rRNA RT-PCR and thin blood smears. Disease signs were evaluated by daily observations, complete blood counts, serum chemistry tests, and veterinary examinations. After anti-malarial drug treatment, a subset of animals was re-challenged and monitored as above. Whole blood gene expression analysis was performed on selected animals to assess host response to infection.
RESULTS
In naïve animals, the kinetics of P. knowlesi blood stage replication was reproducible, with parasite burden rising linearly during an initial acute phase of infection from 6 to 11 days post-challenge, before plateauing and transitioning into a chronic low-grade infection. After re-challenge, infections were again reproducible, but with lower blood stage parasite densities. Clinical signs of disease were absent or mild and anti-malarial treatment was not needed until the pre-defined study day. Whole blood gene expression analysis identified immunological changes associated with acute and chronic phases of infection, and further differences between initial challenge versus re-challenge.
CONCLUSIONS
The ability to challenge PTM with PkSPZ and achieve reliable blood stage infections indicate this model has significant potential for malaria vaccine studies. Blood stage P. knowlesi infection in PTM is characterized by low parasite burdens and a benign disease course, in contrast with the virulent P. knowlesi disease course commonly reported in rhesus macaques. These findings identify new opportunities for malaria vaccine research using this natural host-parasite combination.
Topics: Animals; Plasmodium knowlesi; Malaria Vaccines; Macaca nemestrina; Macaca mulatta; Antimalarials; Malaria
PubMed: 38093306
DOI: 10.1186/s12936-023-04788-9 -
Malaria Journal Feb 2021Plasmodium falciparum malaria increases plasma levels of the cytokine Fms-like tyrosine kinase 3 ligand (Flt3L), a haematopoietic factor associated with dendritic cell...
BACKGROUND
Plasmodium falciparum malaria increases plasma levels of the cytokine Fms-like tyrosine kinase 3 ligand (Flt3L), a haematopoietic factor associated with dendritic cell (DC) expansion. It is unknown if the zoonotic parasite Plasmodium knowlesi impacts Flt3L or DC in human malaria. This study investigated circulating DC and Flt3L associations in adult malaria and in submicroscopic experimental infection.
METHODS
Plasma Flt3L concentration and blood CD141 DC, CD1c DC and plasmacytoid DC (pDC) numbers were assessed in (i) volunteers experimentally infected with P. falciparum and in Malaysian patients with uncomplicated (ii) P. falciparum or (iii) P. knowlesi malaria.
RESULTS
Plasmodium knowlesi caused a decline in all circulating DC subsets in adults with malaria. Plasma Flt3L was elevated in acute P. falciparum and P. knowlesi malaria with no increase in a subclinical experimental infection. Circulating CD141 DCs, CD1c DCs and pDCs declined in all adults tested, for the first time extending the finding of DC subset decline in acute malaria to the zoonotic parasite P. knowlesi.
CONCLUSIONS
In adults, submicroscopic Plasmodium infection causes no change in plasma Flt3L but does reduce circulating DCs. Plasma Flt3L concentrations increase in acute malaria, yet this increase is insufficient to restore or expand circulating CD141 DCs, CD1c DCs or pDCs. These data imply that haematopoietic factors, yet to be identified and not Flt3L, involved in the sensing/maintenance of circulating DC are impacted by malaria and a submicroscopic infection. The zoonotic P. knowlesi is similar to other Plasmodium spp in compromising DC in adult malaria.
Topics: Acute Disease; Adult; Dendritic Cells; Female; Humans; Malaria; Malaria, Falciparum; Male; Membrane Proteins; Middle Aged; Plasma; Plasmodium falciparum; Plasmodium knowlesi; Young Adult
PubMed: 33593383
DOI: 10.1186/s12936-021-03642-0 -
Microorganisms Jan 2022Cysteine proteases belonging to the falcipain (FP) family play a pivotal role in the biology of malaria parasites and have been extensively investigated as potential...
Cysteine proteases belonging to the falcipain (FP) family play a pivotal role in the biology of malaria parasites and have been extensively investigated as potential antimalarial drug targets. Three paralogous FP-family cysteine proteases of , termed malapains 2-4 (MP2-4), were identified in PlasmoDB. The three MPs share similar structural properties with the FP-2/FP-3 subfamily enzymes and exhibit a close phylogenetic lineage with vivapains (VXs) and knowpains (KPs), FP orthologues of and . Recombinant MP-2 and MP-4 were produced in a bacterial expression system, and their biochemical properties were characterized. Both recombinant MP-2 and MP-4 showed enzyme activity across a broad range of pH values with an optimum activity at pH 5.0 and relative stability at neutral pHs. Similar to the FP-2/FP-3 subfamily enzymes in other species, recombinant MP-2 and MP-4 effectively hydrolyzed hemoglobin at acidic pHs. They also degraded erythrocyte cytoskeletal proteins, such as spectrin and band 3, at a neutral pH. These results imply that MP-2 and MP-4 are redundant hemoglobinases of and may also participate in merozoite egression by degrading erythrocyte cytoskeletal proteins. However, compared with other FP-2/FP-3 enzymes, MP-2 showed a strong preference for arginine at the P2 position. Meanwhile, MP-4 showed a primary preference for leucine at the P2 position but a partial preference for phenylalanine. These different substrate preferences of MPs underscore careful consideration in the design of optimized inhibitors targeting the FP-family cysteine proteases of human malaria parasites.
PubMed: 35056641
DOI: 10.3390/microorganisms10010193 -
MedRxiv : the Preprint Server For... Apr 2024Malaria remains a major public health concern with substantial morbidity and mortality worldwide. In Malaysia, the emergence of has led to a surge in zoonotic malaria...
INTRODUCTION
Malaria remains a major public health concern with substantial morbidity and mortality worldwide. In Malaysia, the emergence of has led to a surge in zoonotic malaria cases and deaths in recent years. Signs of cerebral involvement have been observed in a non-comatose, fatal case of severe knowlesi infection, but the potential impact of this malaria species on the brain remains underexplored. To address this gap, we investigated circulating levels of brain injury, inflammation, and vascular biomarkers in a cohort of knowlesi-infected patients and controls.
METHODS
Archived plasma samples from 19 patients with confirmed symptomatic knowlesi infection and 19 healthy, age-matched controls from Peninsular Malaysia were analysed. A total of 52 plasma biomarkers of brain injury, inflammation, and vascular activation were measured using Luminex and SIMOA assays. Wilcoxon tests were used to examine group differences, and biomarker profiles were explored through hierarchical clustering heatmap analysis.
RESULTS
Bonferroni-corrected analyses revealed significantly elevated brain injury biomarker levels in knowlesi-infected patients, including S100B (p<0.0001), Tau (p=0.0007), UCH-L1 (p<0.0001), αSyn (p<0.0001), Park7 (p=0.0006), NRGN (p=0.0022), and TDP-43 (p=0.005). Compared to controls, levels were lower in the infected group for BDNF (p<0.0001), CaBD (p<0.0001), CNTN1 (p<0.0001), NCAM-1 (p<0.0001), GFAP (p=0.0013), and KLK6 (p=0.0126). Hierarchical clustering revealed distinct group profiles for circulating levels of brain injury and vascular activation biomarkers.
CONCLUSIONS
Our findings highlight for the first time the impact of infection on the brain, with distinct alterations in cerebral injury and endothelial activation biomarker profiles compared to healthy controls. Further studies are warranted to investigate the pathophysiology and clinical significance of these altered surrogate markers, through both neuroimaging and long-term neurocognitive assessments.
PubMed: 38712121
DOI: 10.1101/2024.04.25.24306382