scholarly journals Identification of Heparin Modifications and Polysaccharide Inhibitors of Plasmodium falciparum Merozoite Invasion That Have Potential for Novel Drug Development

2017 ◽  
Vol 61 (11) ◽  
Author(s):  
Michelle J. Boyle ◽  
Mark Skidmore ◽  
Benjamin Dickerman ◽  
Lynsay Cooper ◽  
Anthony Devlin ◽  
...  
Keyword(s):  
Plasmodium Falciparum ◽  
Drug Development ◽  
Inhibitory Activity ◽  
Sulfated Polysaccharides ◽  
Merozoite Invasion ◽  
Content Type ◽  
Molecular Weights ◽  
Falciparum Merozoite ◽  
Successful Control ◽  
Novel Drug

ABSTRACT Despite recent successful control efforts, malaria remains a leading global health burden. Alarmingly, resistance to current antimalarials is increasing and the development of new drug families is needed to maintain malaria control. Current antimalarials target the intraerythrocytic developmental stage of the Plasmodium falciparum life cycle. However, the invasive extracellular parasite form, the merozoite, is also an attractive target for drug development. We have previously demonstrated that heparin-like molecules, including those with low molecular weights and low anticoagulant activities, are potent and specific inhibitors of merozoite invasion and blood-stage replication. Here we tested a large panel of heparin-like molecules and sulfated polysaccharides together with various modified chemical forms for their inhibitory activity against P. falciparum merozoite invasion. We identified chemical modifications that improve inhibitory activity and identified several additional sulfated polysaccharides with strong inhibitory activity. These studies have important implications for the further development of heparin-like molecules as antimalarial drugs and for understanding merozoite invasion.

scholarly journals Defining the Timing of Action of Antimalarial Drugs against Plasmodium falciparum

2013 ◽  
Vol 57 (3) ◽  
pp. 1455-1467 ◽  
Author(s):  
Danny W. Wilson ◽  
Christine Langer ◽  
Christopher D. Goodman ◽  
Geoffrey I. McFadden ◽  
James G. Beeson
Keyword(s):  
Flow Cytometry ◽  
Plasmodium Falciparum ◽  
Inhibitory Activity ◽  
Antimalarial Activity ◽  
Trichostatin A ◽  
Mechanisms Of Action ◽  
Trophozoite Stage ◽  
Merozoite Invasion ◽  
Content Type

ABSTRACTMost current antimalarials for treatment of clinicalPlasmodium falciparummalaria fall into two broad drug families and target the food vacuole of the trophozoite stage. No antimalarials have been shown to target the brief extracellular merozoite form of blood-stage malaria. We studied a panel of 12 drugs, 10 of which have been used extensively clinically, for their invasion, schizont rupture, and growth-inhibitory activity using high-throughput flow cytometry and new approaches for the study of merozoite invasion and early intraerythrocytic development. Not surprisingly, given reported mechanisms of action, none of the drugs inhibited merozoite invasionin vitro. Pretreatment of erythrocytes with drugs suggested that halofantrine, lumefantrine, piperaquine, amodiaquine, and mefloquine diffuse into and remain within the erythrocyte and inhibit downstream growth of parasites. Studying the inhibitory activity of the drugs on intraerythrocytic development, schizont rupture, and reinvasion enabled several different inhibitory phenotypes to be defined. All drugs inhibited parasite replication when added at ring stages, but only artesunate, artemisinin, cycloheximide, and trichostatin A appeared to have substantial activity against ring stages, whereas the other drugs acted later during intraerythrocytic development. When drugs were added to late schizonts, only artemisinin, cycloheximide, and trichostatin A were able to inhibit rupture and subsequent replication. Flow cytometry proved valuable forin vitroassays of antimalarial activity, with the free merozoite population acting as a clear marker for parasite growth inhibition. These studies have important implications for further understanding the mechanisms of action of antimalarials, studying and evaluating drug resistance, and developing new antimalarials.

scholarly journals The Central Role of cAMP in Regulating Plasmodium falciparum Merozoite Invasion of Human Erythrocytes

2014 ◽  
Vol 10 (12) ◽  
pp. e1004520 ◽  
Author(s):  
Amrita Dawn ◽  
Shailja Singh ◽  
Kunal R. More ◽  
Faiza Amber Siddiqui ◽  
Niseema Pachikara ◽  
...  
Keyword(s):  
Plasmodium Falciparum ◽  
Human Erythrocytes ◽  
Merozoite Invasion ◽  
Falciparum Merozoite

scholarly journals Plasmodium falciparum Line-Dependent Association ofIn VitroGrowth-Inhibitory Activity and Risk of Malaria

2012 ◽  
Vol 80 (5) ◽  
pp. 1900-1908 ◽  
Author(s):  
Josea Rono ◽  
Anna Färnert ◽  
Daniel Olsson ◽  
Faith Osier ◽  
Ingegerd Rooth ◽  
...  
Keyword(s):  
Plasmodium Falciparum ◽  
Inhibitory Activity ◽  
Content Type ◽  
Phenotypic Differences ◽  
Erythrocyte Invasion ◽  
Growth Inhibitory ◽  
Growth Inhibitory Activity ◽  
Control Study

ABSTRACTPlasmodium falciparum's ability to invade erythrocytes is essential for its survival within the human host. Immune mechanisms that impair this ability are therefore expected to contribute to immunity against the parasite. Plasma of humans who are naturally exposed to malaria has been shown to have growth-inhibitory activity (GIA)in vitro. However, the importance of GIA in relation to protection from malaria has been unclear. In a case-control study nested within a longitudinally followed population in Tanzania, plasma samples collected at baseline from 171 individuals (55 cases and 116 age-matched controls) were assayed for GIA using threeP. falciparumlines (3D7, K1, and W2mef) chosen based on their erythrocyte invasion phenotypes. Distribution of GIA differed between the lines, with most samples inhibiting the growth of 3D7 and K1 and enhancing the growth of W2mef. GIA to 3D7 was associated with a reduced risk of malaria within 40 weeks of follow-up (odds ratio, 0.45; 95% confidence interval [CI], 0.21 to 0.96;P= 0.04), whereas GIA to K1 and W2mef was not. These results show that GIA, as well as its association with protection from malaria, is dependent on theP. falciparumline and can be explained by differences in erythrocyte invasion phenotypes between parasite lines. Our study contributes knowledge on the biological importance of growth inhibition and the potential influence ofP. falciparumerythrocyte invasion phenotypic differences on its relationship to protective immunity against malaria.

scholarly journals Comparative Immunogenicities of Full-Length Plasmodium falciparum Merozoite Surface Protein 3 and a 24-Kilodalton N-Terminal Fragment

2011 ◽  
Vol 18 (8) ◽  
pp. 1221-1228 ◽  
Author(s):  
Maryam Imam ◽  
Yengkhom Sangeeta Devi ◽  
Akhilesh K. Verma ◽  
Virander Singh Chauhan
Keyword(s):  
Plasmodium Falciparum ◽  
Surface Protein ◽  
Merozoite Surface Protein ◽  
Terminal Region ◽  
Content Type ◽  
Conserved Domain ◽  
Terminal Fragment ◽  
Falciparum Merozoite ◽  
Form Part ◽  
Parasite Lysate

ABSTRACTRecombinantPlasmodium falciparummerozoite surface protein 3 (PfMSP3F) and a 24-kDa fragment from its N terminus (MSP3N) that includes the essential conserved domain, which elicits the maximum antibody (Ab)-dependent cellular inhibition (ADCI), were expressed as soluble proteins inEscherichia coli. Both proteins were found to be stable in both soluble and lyophilized forms. Immunization with MSP3F and MSP3N formulated separately with two human-compatible adjuvants, aluminum hydroxide (Alhydrogel) and Montanide ISA 720, produced significant antibody responses in mice and rabbits. Polyclonal Abs against both antigens recognized native MSP3 in the parasite lysate. These two Abs also recognized two synthetic peptides, previously characterized to possess B cell epitopes from the N-terminal region. Antibody depletion assay showed that most of the IgG response is directed toward the N-terminal region of the full protein. Anti-MSP3F and anti-MSP3N rabbit antibodies did not inhibit merozoite invasion or intraerythrocytic development but significantly reduced parasitemia in the presence of human monocytes. The ADCI demonstrated by anti-MSP3N antibodies was comparable to that exhibited by anti-MSP3F antibodies (both generated in rabbit). These results suggest that the N-terminal fragment of MSP3 can be considered a vaccine candidate that can form part of a multigenic vaccine against malaria.

scholarly journals Stepwise dissection of Plasmodium falciparum merozoite invasion of the human erythrocyte

2010 ◽  
Vol 9 (S2) ◽  
Author(s):  
David Riglar ◽  
Dave Richard ◽  
Michelle Boyle ◽  
Danny Wilson ◽  
Fiona Angrisano ◽  
...  
Keyword(s):  
Plasmodium Falciparum ◽  
Human Erythrocyte ◽  
Merozoite Invasion ◽  
Falciparum Merozoite

scholarly journals RALP1 Is a Rhoptry Neck Erythrocyte-Binding Protein of Plasmodium falciparum Merozoites and a Potential Blood-Stage Vaccine Candidate Antigen

2013 ◽  
Vol 81 (11) ◽  
pp. 4290-4298 ◽  
Author(s):  
Daisuke Ito ◽  
Tomoyuki Hasegawa ◽  
Kazutoyo Miura ◽  
Tsutomu Yamasaki ◽  
Thangavelu U. Arumugam ◽  
...  
Keyword(s):  
Plasmodium Falciparum ◽  
Vaccine Candidate ◽  
Binding Protein ◽  
Blood Stage ◽  
Merozoite Invasion ◽  
Free System ◽  
Content Type ◽  
Vaccine Candidate Antigen ◽  
Erythrocyte Binding ◽  
Candidate Antigen

ABSTRACTErythrocyte invasion by merozoites is an obligatory stage ofPlasmodiuminfection and is essential to disease progression. Proteins in the apical organelles of merozoites mediate the invasion of erythrocytes and are potential malaria vaccine candidates. Rhoptry-associated, leucine zipper-like protein 1 (RALP1) ofPlasmodium falciparumwas previously found to be specifically expressed in schizont stages and localized to the rhoptries of merozoites by immunofluorescence assay (IFA). Also, RALP1 has been refractory to gene knockout attempts, suggesting that it is essential for blood-stage parasite survival. These characteristics suggest that RALP1 can be a potential blood-stage vaccine candidate antigen, and here we assessed its potential in this regard. Antibodies were raised against recombinant RALP1 proteins synthesized by using the wheat germ cell-free system. Immunoelectron microscopy demonstrated for the first time that RALP1 is a rhoptry neck protein of merozoites. Moreover, our IFA data showed that RALP1 translocates from the rhoptry neck to the moving junction during merozoite invasion. Growth and invasion inhibition assays revealed that anti-RALP1 antibodies inhibit the invasion of erythrocytes by merozoites. The findings that RALP1 possesses an erythrocyte-binding epitope in the C-terminal region and that anti-RALP1 antibodies disrupt tight-junction formation, are evidence that RALP1 plays an important role during merozoite invasion of erythrocytes. In addition, human sera collected from areas in Thailand and Mali where malaria is endemic recognized this protein. Overall, our findings indicate that RALP1 is a rhoptry neck erythrocyte-binding protein and that it qualifies as a potential blood-stage vaccine candidate.

scholarly journals Analysis of Antibodies to Newly Described Plasmodium falciparum Merozoite Antigens Supports MSPDBL2 as a Predicted Target of Naturally Acquired Immunity

2013 ◽  
Vol 81 (10) ◽  
pp. 3835-3842 ◽  
Author(s):  
Kevin K. A. Tetteh ◽  
Faith H. A. Osier ◽  
Ali Salanti ◽  
Gathoni Kamuyu ◽  
Laura Drought ◽  
...  
Keyword(s):  
Plasmodium Falciparum ◽  
Risk Ratio ◽  
Statistical Significance ◽  
Clinical Malaria ◽  
Content Type ◽  
Type Antigen ◽  
Falciparum Merozoite ◽  
Merozoite Antigens ◽  
Allelic Type

ABSTRACTProspective studies continue to identify malaria parasite genes with particular patterns of polymorphism which indicate they may be under immune selection, and the encoded proteins require investigation. Sixteen new recombinant protein reagents were designed to characterize three such polymorphic proteins expressed inPlasmodium falciparumschizonts and merozoites: MSPDBL1 (also termed MSP3.4) and MSPDBL2 (MSP3.8), which possess Duffy binding-like (DBL) domains, and SURFIN4.2, encoded by a member of the surface-associated interspersed (surf) multigene family. After testing the antigenicities of these reagents by murine immunization and parasite immunofluorescence, we analyzed naturally acquired antibody responses to the antigens in two cohorts in coastal Kenya in which the parasite was endemic (Chonyi [n= 497] and Ngerenya [n= 461]). As expected, the prevalence and levels of serum antibodies increased with age. We then investigated correlations with subsequent risk of clinical malaria among children <11 years of age during 6 months follow-up surveillance. Antibodies to the polymorphic central region of MSPDBL2 were associated with reduced risk of malaria in both cohorts, with statistical significance remaining for the 3D7 allelic type after adjustment for individuals' ages in years and antibody reactivity to whole-schizont extract (Chonyi, risk ratio, 0.51, and 95% confidence interval [CI], 0.28 to 0.93; Ngerenya, risk ratio, 0.38, and 95% CI, 0.18 to 0.82). For the MSPDBL1 Palo Alto allelic-type antigen, there was a protective association in one cohort (Ngerenya, risk ratio, 0.53, and 95% CI, 0.32 to 0.89), whereas the other antigens showed no protective associations after adjustment. These findings support the prediction that antibodies to the polymorphic region of MSPDBL2 contribute to protective immunity.

scholarly journals Fucosylated Chondroitin Sulfate Inhibits Plasmodium falciparum Cytoadhesion and Merozoite Invasion

2014 ◽  
Vol 58 (4) ◽  
pp. 1862-1871 ◽  
Author(s):  
Marcele F. Bastos ◽  
Letusa Albrecht ◽  
Eliene O. Kozlowski ◽  
Stefanie C. P. Lopes ◽  
Yara C. Blanco ◽  
...  
Keyword(s):  
Endothelial Cells ◽  
Plasmodium Falciparum ◽  
Chondroitin Sulfate ◽  
Parasite Development ◽  
Flow Conditions ◽  
Inhibitory Effects ◽  
Merozoite Invasion ◽  
Content Type ◽  
Life Threatening ◽  
Lung Endothelial Cells

ABSTRACTSequestration ofPlasmodium falciparum-infected erythrocytes (Pf-iEs) in the microvasculature of vital organs plays a key role in the pathogenesis of life-threatening malaria complications, such as cerebral malaria and malaria in pregnancy. This phenomenon is marked by the cytoadhesion of Pf-iEs to host receptors on the surfaces of endothelial cells, on noninfected erythrocytes, and in the placental trophoblast; therefore, these sites are potential targets for antiadhesion therapies. In this context, glycosaminoglycans (GAGs), including heparin, have shown the ability to inhibit Pf-iE cytoadherence and growth. Nevertheless, the use of heparin was discontinued due to serious side effects, such as bleeding. Other GAG-based therapies were hampered due to the potential risk of contamination with prions and viruses, as some GAGs are isolated from mammals. In this context, we investigated the effects and mechanism of action of fucosylated chondroitin sulfate (FucCS), a unique and highly sulfated GAG isolated from the sea cucumber, with respect toP. falciparumcytoadhesion and development. FucCS was effective in inhibiting the cytoadherence of Pf-iEs to human lung endothelial cells and placenta cryosections under static and flow conditions. Removal of the sulfated fucose branches of the FucCS structure virtually abolished the inhibitory effects of FucCS. Importantly, FucCS rapidly disrupted rosettes at high levels, and it was also able to block parasite development by interfering with merozoite invasion. Collectively, these findings highlight the potential of FucCS as a candidate for adjunct therapy against severe malaria.

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