Phosphoethanolamine-N-methyltransferase is a potential biomarker for the diagnosis of P. knowlesi and P. falciparum malaria

Analysis of diagnostic biomarkers for malaria: Prospects on rapid diagnostic test (RDT) development

Accurate malaria diagnosis remains a formidable challenge in remote regions of malaria-endemic areas globally. Existing diagnostic methods predominantly rely on microscopy and rapid diagnostic tests (RDTs). While RDTs offer advantages such as rapid results and reduced dependence on highly skilled technicians compared to microscopy, persistent challenges emphasize the critical need to identify novel diagnostic biomarkers to further enhance RDT based malaria diagnosis. This comprehensive review presents a range of promising diagnostic targets. These targets could be useful in developing more robust, accurate, and effective diagnostic tools. Such tools are crucial for the detection of the Plasmodium falciparum (P.falcipaum) malaria parasite. The potential biomarkers discussed here significantly address the challenges posed by HRP2 gene deletion in P.falciparum. Researchers, RDT manufacturers, industrial and other stakeholders involved in malaria diagnosis can harness the crucial information described in this article, to drive the development of advanced RDTs as viable alternatives. By diversifying the available tools for diagnosis, we can attempt to enhance our ability to knock out malaria effectively and contribute to better health outcomes for people residing in malaria-endemic regions. This review serves as a valuable resource for advancing research and development in the field of malaria diagnostics, ultimately aiding to the global fight against this devastating ancient disease.

Expression and copper binding studies of a Plasmodium falciparum protein with Cox19 copper binding motifs

Copper can exist in an oxidized and a reduced form, which enables the metal to play essential roles as a catalytic co-factor in redox reactions in many organisms. Copper confers redox activity to the terminal electron transport chain cytochrome c oxidase protein. Cytochrome c oxidase in yeast obtains copper for the Cu_B site in the Cox1 subunit from Cox11 in association with Cox19. When copper is chelated in growth medium, Plasmodium falciparum parasite development in infected red blood cells is inhibited and excess copper is toxic for the parasite. The gene of a 26 kDa Plasmodium falciparum PfCox19 protein with two Cx₉C Cox19 copper binding motifs, was cloned and expressed as a 66 kDa fusion protein with maltose binding protein and affinity purified (rMBP-PfCox19). rMBP-PfCox19 bound copper measured by: a bicinchoninic acid release assay; an in vivo bacterial host growth inhibition assay; ascorbate oxidation inhibition and differential scanning fluorimetry. The native protein was detected by antibodies raised against rMBP-PfCox19. PfCox19 binds copper and is predicted to associate with PfCox11 in the insertion of copper into the Cu_B site of Plasmodium cytochrome c oxidase. Characterisation of the proteins involved in Plasmodium spp. copper metabolism will help us understand the role of cytochrome c oxidase and this essential metal in Plasmodium homeostasis.

Metabolic Labeling-Based Chemoproteomics Establishes Choline Metabolites as Protein Function Modulators

Choline is an essential nutrient for mammalian cells. Our understanding of the cellular functions of choline and its metabolites, independent of their roles as choline lipid metabolism intermediates, remains limited. In addition to fundamental cellular physiology, this knowledge has implications for cancer biology because elevated choline metabolite levels are a hallmark of cancer. Here, we establish a mammalian choline metabolite-interacting proteome by utilizing a photocrosslinkable choline probe. To design this probe, we performed metabolic labeling experiments with structurally diverse choline analogues that resulted in the serendipitous discovery of a choline lipid headgroup remodeling mechanism involving sequential dealkylation and methylation steps. We demonstrate that phosphocholine inhibits the binding of one of the proteins identified, the attractive anticancer target p32, to its endogenous ligands and to the promising p32-targeting anticancer agent, Lyp-1. Our results reveal that choline metabolites play vital roles in cellular physiology by serving as modulators of protein function.

Expression and copper binding characteristics of Plasmodium falciparum cytochrome c oxidase assembly factor 11, Cox11

Background

Copper is an essential metal for living organisms as a catalytic co-factor for important enzymes, like cytochrome c oxidase the final enzyme in the electron transport chain. Plasmodium falciparum parasites in infected red blood cells are killed by excess copper and development in erythrocytes is inhibited by copper chelators. Cytochrome c oxidase in yeast obtains copper for the Cu_B site in the Cox1 subunit from Cox11.

Methods

A 162 amino acid carboxy-terminal domain of the P. falciparum Cox11 ortholog (PfCox11Ct) was recombinantly expressed and the rMBPPfCox11Ct affinity purified. Copper binding was measured in vitro and in Escherichia coli host cells. Site directed mutagenesis was used to identify key copper binding cysteines. Antibodies confirmed the expression of the native protein.

Results

rMBPPfCox11Ct was expressed as a 62 kDa protein fused with the maltose binding protein and affinity purified. rMBPPfCox11Ct bound copper measured by: a bicinchoninic acid release assay; atomic absorption spectroscopy; a bacterial host growth inhibition assay; ascorbate oxidation inhibition and in a thermal shift assay. The cysteine 157 amino acid was shown to be important for in vitro copper binding by PfCox11whilst Cys 60 was not. The native protein was detected by antibodies against rMBPPfCox11Ct.

Conclusions

Plasmodium spp. express the PfCox11 protein which shares structural features and copper binding motifs with Cox11 from other species. PfCox11 binds copper and is, therefore, predicted to transfer copper to the Cu_B site of Plasmodium cytochrome c oxidase. Characterization of Plasmodium spp. proteins involved in copper metabolism will help sceintists understand the role of cytochrome c oxidase and this essential metal in Plasmodium homeostasis.

A microfluidic paper analytical device using capture aptamers for the detection of PfLDH in blood matrices

Background

The prevalence and death rate arising from malaria infection, and emergence of other diseases showing similar symptoms to malaria require the development of malaria-specific and sensitive devices for its diagnosis. To address this, the design and fabrication of low-cost, rapid, paper-based analytical devices (µPAD) using surface-immobilized aptamers to detect the presence of a recombinant malarial biomarker—Plasmodium falciparum lactate dehydrogenase (rPfLDH)—is reported in this study.

Methods

Test zones on paper surfaces were created by covalently immobilizing streptavidin to the paper, subsequently attaching biotinylated aptamers to streptavidin. Aptamers selectively bound rPfLDH. The measurement of captured rPfLDH enzyme activity served as the means of detecting this biomarker. Enzyme activity across three replicate sensors was digitally quantified using the colorimetric Malstat assay.

Results

Screening of several different aptamers reported in the literature showed that aptamers rLDH7 and 2008s immobilized in this manner specifically recognised and captured PfLDH. Using rLDH7, the sensitivity of the µPAD sensor was evaluated and the µPAD sensor was applied for preferential detection of rPfLDH, both in buffered solutions of the protein and in spiked serum and red blood cell lysate samples. In buffered solutions, the test zone of the µPAD sensor exhibited a K_D of 24 ± 11 nM and an empirical limit of detection of 17 nM, respectively, a limit similar to commercial antibody-based sensors exposed to rPfLDH. The specific recognition of 133 nM rPfLDH in undiluted serum and blood samples was demonstrated by the µPAD.

Conclusion

The reported µPAD demonstrates the potential of integrating aptamers into paper-based malarial rapid diagnostic tests.

Graphical Abstract

Plasmodium knowlesi: the game changer for malaria eradication

Plasmodium knowlesi is a zoonotic malaria parasite that has gained increasing medical interest over the past two decades. This zoonotic parasitic infection is prevalent in Southeast Asia and causes many cases with fulminant pathology. Despite several biogeographical restrictions that limit its distribution, knowlesi malaria cases have been reported in different parts of the world due to travelling and tourism activities. Here, breakthroughs and key information generated from recent (over the past five years, but not limited to) studies conducted on P. knowlesi were reviewed, and the knowledge gap in various research aspects that need to be filled was discussed. Besides, challenges and strategies required to control and eradicate human malaria with this emerging and potentially fatal zoonosis were described.

A Dual, Systematic Approach to Malaria Diagnostic Biomarker Discovery

Background

The emergence and spread of Plasmodium falciparum parasites that lack HRP2/3 proteins and the resulting decreased utility of HRP2-based malaria rapid diagnostic tests (RDTs) prompted the World Health Organization and other global health stakeholders to prioritize the discovery of novel diagnostic biomarkers for malaria.

Methods

To address this pressing need, we adopted a dual, systematic approach by conducting a systematic review of the literature for publications on diagnostic biomarkers for uncomplicated malaria and a systematic in silico analysis of P. falciparum proteomics data for Plasmodium proteins with favorable diagnostic features.

Results

Our complementary analyses led us to 2 novel malaria diagnostic biomarkers compatible for use in an RDT format: glyceraldehyde 3-phosphate dehydrogenase and dihydrofolate reductase-thymidylate synthase.

Conclusions

Overall, our results pave the way for the development of next-generation malaria RDTs based on new antigens by identifying 2 lead candidates with favorable diagnostic features and partially de-risked product development prospects.

Account and Utilization of Blood Lipid Profiles: Lipid Levels Predicted Hemosporidian Infection in Migrating Northern Saw-Whet Owls of Eastern North America

Noting lipidomic changes following the parasitism of migrating birds, the metabolic needs of which are primarily fueled by lipids, can deepen our understanding of host-parasite interactions. We identified lipids of migrating Northern saw-whet owls (Aegolius acadicus) using collision-induced dissociation mass spectrometry, compared the lipidomic signatures of hemoparasite-infected and noninfected individuals, and performed cross-validation analyses to reveal associations between parasite infection and lipid levels. We found significantly lower levels of lipid classes phosphatidic acid (PA), phosphatidylglycerol (PG), phosphatidylinositol (PI), phosphatidylserine (PS), phosphatidylethanolamine (PE), phosphatidylcholine (PC), and sphingomyelin (SM) in infected Northern saw-whet owls than in the noninfected individuals. Conversely, we found higher levels for certain lysoPS and lysoPE species, and variable lipid level changes for free fatty acid (FFA) species. Reporting lipidomic changes observed between hemosporidian-infected and noninfected Northern saw-whet owls can strengthen our understanding of the mechanisms governing parasite proliferation in this species. Furthermore, our analysis indicated that lipidomic signatures are better predictors of parasite infection than the log-adjusted mass/wing chord body index, a metric commonly used to assess the influence of hemosporidia infection on the health of birds. Establishing a lipidomic profile for Northern saw-whet owls that provides baseline lipid levels during fall migration may assist future studies assessing causes of reductions in breeding brought about from subtle differences in behaviors such as delayed migration.

Antimalarial Properties of Isoquinoline Derivative from Streptomyces hygroscopicus subsp. Hygroscopicus: An In Silico Approach

Malaria is one of the life-threatening diseases in the world. The spread of resistance to antimalarial drugs is a major challenge, and resistance to artemisinin has been reported in the Southeast Asian region. In the previous study, the active compound of Streptomyces hygroscopicus subsp. Hygroscopicus (S. hygroscopicus), eponemycin, has been shown to have antimalarial effects. To further analyze the effects of other active compounds on the Plasmodium parasite, identifying and analyzing the effectiveness of compounds contained in S. hygroscopicus through instrumentation of liquid chromatography/mass spectrometry (LC/MS) and in silico studies were very useful. This study aimed at identifying other derivative compounds from S. hygroscopicus and screening the antimalarial activity of the compound by assessing the binding affinity, pharmacokinetic profile, and bond interaction. The derivative compounds were identified using LC/MS. Protein targets for derivative compounds were found through literature studies, and the results of identification of compounds and protein targets were reconstructed into three-dimensional models. Prediction of pharmacokinetic profiles was carried out using Swiss ADME. Screening of protein targets for the derivative compound was carried out using the reverse molecular docking method. Analyzing bond interaction was done by LigPlot. One compound from S. hygroscopicus, i.e., 6,7-dinitro-2-[1, 2, 4]triazole-4-yl-benzo[de]isoquinoline-1,3-dione, was successfully identified using LC/MS. This compound was an isoquinoline derivative compound. Through literature studies with inclusion criteria, thirteen protein targets were obtained for reverse molecular docking. This isoquinoline derivative had the potential to bind to each protein target. The pharmacokinetic profile showed that this compound had the drug-likeness criteria. Conclusion. 6,7-Dinitro-2-[1, 2, 4]triazole-4-yl-benzo[de]isoquinoline-1,3-dione has antimalarial activity as shown by reverse molecular docking studies and pharmacokinetic profiles. The best inhibitory ability of compounds based on bond affinity is with adenylosuccinate synthetase.

Isolation of Nile crocodile (Crocodylus niloticus) serum immunoglobulin M and Y (IgM and IgY)

Crocodile immunity has not been fully characterised with more studies on crocodile innate immunity than cell-mediated or humoral immunity. Crocodile immunoglobulin genes have been described but immunoglobulin proteins have not been isolated or studied biochemically. Two large proteins proposed to be crocodile IgM and IgY were isolated and purified from Crocodylus niloticus sera using two different protocols. A 50% (w/v) ammonium sulfate and a 15% (w/v) polyethylene glycol precipitation step was followed by Cibacron blue F3GA affinity- and Sephacryl-S300 gel filtration chromatography. An alternate purification protocol, with only two steps, involved thiophilic affinity- and Sephacryl-S300 gel filtration chromatography. The purified crocodile IgM resolved on reducing SDS-PAGE with an apparent mass of 180 kDa. Purified crocodile IgY resolved at 180 kDa alongside chicken IgY on a non-reducing SDS-PAGE gel, and is deduced to consist of two 66 kDa heavy and two 23 kDa light chains under reducing conditions. The thiophilic/gel filtration two-step protocol gave three-fold higher yields of isolated protein than the four-step precipitation/chromatography protocol. Antibodies against the isolated crocodile IgM and IgY were raised in chickens and affinity purified. The chicken antibodies differentiated between crocodile IgM and IgY and have the potential for use in the diagnosis of crocodile infections. The purified crocodile antibodies can be biochemically characterised and compared to mammalian and avian antibodies to give a better understanding of crocodile humoral immunity.

Computational and experimental elucidation of Plasmodium falciparum phosphoethanolamine methyltransferase inhibitors: Pivotal drug target

INTRODUCTION

Plasmodium falciparum synthesizes phosphatidylcholine for the membrane development through serine decarboxylase-phosphoethanolamine methyltransferase pathway for growth in human host. Phosphoethanolamine-methyltransferase (PfPMT) is a crucial enzyme for the synthesis of phosphocholine which is a precursor for phosphatidylcholine synthesis and is considered as a pivotal drug target as it is absent in the host. The inhibition of PfPMT may kill malaria parasite and hence is being considered as potential target for rational antimalarial drug designing.

METHODS

In this study, we have used computer aided drug designing (CADD) approaches to establish potential PfPMT inhibitors from Asinex compound library virtually screened for ADMET and the docking affinity. The selected compounds were tested for in-vitro schizonticidal, gametocidal and cytotoxicity activity. Nontoxic compounds were further studied for PfPMT enzyme specificity and antimalarial efficacy for P. berghei in albino mice model.

RESULTS

Our results have identified two nontoxic PfPMT competitive inhibitors ASN.1 and ASN.3 with better schizonticidal and gametocidal activity which were found to inhibit PfPMT at IC50 1.49μM and 2.31μM respectively. The promising reduction in parasitaemia was found both in orally (50 & 10 mg/kg) and intravenous (IV) (5& 1 mg/kg) however, the better growth inhibition was found in intravenous groups.

CONCLUSION

We report that the compounds containing Pyridinyl-Pyrimidine and Phenyl-Furan scaffolds as the potential inhibitors of PfPMT and thus may act as promising antimalarial inhibitor candidates which can be further optimized and used as leads for template based antimalarial drug development.