scholarly journals Knockout Studies Reveal an Important Role of Plasmodium Lipoic Acid Protein Ligase A1 for Asexual Blood Stage Parasite Survival

PLoS ONE ◽  
2009 ◽  
Vol 4 (5) ◽  
pp. e5510 ◽  
Author(s):  
Svenja Günther ◽  
Kai Matuschewski ◽  
Sylke Müller
Keyword(s):  
Lipoic Acid ◽  
Blood Stage ◽  
Asexual Blood Stage ◽  
Acid Protein ◽  
Parasite Survival ◽  
Stage Parasite ◽  
Blood Stage Parasite

Parasite killing in murine malaria does not require nitric oxide production

Parasitology ◽  
1999 ◽  
Vol 118 (2) ◽  
pp. 139-143 ◽  
Author(s):  
N. FAVRE ◽  
B. RYFFEL ◽  
W. RUDIN
Keyword(s):  
Nitric Oxide ◽  
Blood Stage ◽  
No Production ◽  
Nos Inhibitor ◽  
Oxide Synthase ◽  
Deficient Mice ◽  
Stage Parasite ◽  
Blood Stage Malaria ◽  
Inducible Nitric Oxide

Nitric oxide (NO) production has been suggested to play a role as effector molecule in the control of the malarial infections. However, the roles of this molecule are debated. To assess whether blood-stage parasite killing is NO dependent, we investigated the course of blood-stage Plasmodium chabaudi chabaudi (Pcc) infections in inducible nitric oxide synthase (iNOS)-deficient mice. Parasitaemia, haematological alterations, and survival were not affected by the lack of iNOS. To exclude a role of NO produced by other NOS, controls included NO suppression by oral administration of aminoguanidine (AG), a NOS inhibitor. As in iNOS-deficient mice, no difference in the parasitaemia course, survival and haematological values was observed after AG treatment. Our results indicate that NO production is not required for protection against malaria in our murine experimental model. However, C57BL/6 mice treated with AG lost their resistance to Pcc infections, suggesting that the requirement for NO production for parasite killing in murine blood-stage malaria might be strain dependent.

scholarly journals Distinct patterns of blood-stage parasite antigens detected by plasma IgG subclasses from individuals with different level of exposure to Plasmodium falciparum infections

2010 ◽  
Vol 9 (1) ◽  
pp. 296 ◽  
Author(s):  
Cathrine Olesen ◽  
Karima Brahimi ◽  
Brian Vandahl ◽  
Susana Lousada-Dietrich ◽  
Prajakta S Jogdand ◽  
...  
Keyword(s):  
Plasmodium Falciparum ◽  
Igg Subclasses ◽  
Blood Stage ◽  
Stage Parasite ◽  
Blood Stage Parasite

scholarly journals The NTP generating activity of pyruvate kinase II is critical for apicoplast maintenance in Plasmodium falciparum

eLife ◽  
2020 ◽  
Vol 9 ◽  
Author(s):  
Russell P Swift ◽  
Krithika Rajaram ◽  
Cyrianne Keutcha ◽  
Hans B Liu ◽  
Bobby Kwan ◽  
...  
Keyword(s):  
Plasmodium Falciparum ◽  
Pyruvate Kinase ◽  
Reducing Power ◽  
Enzymatic Characterization ◽  
Parasite Survival ◽  
Nucleotide Triphosphates ◽  
Bypass Line ◽  
Stage Parasite ◽  
Blood Stage Parasite

The apicoplast of Plasmodium falciparum parasites is believed to rely on the import of three-carbon phosphate compounds for use in organelle anabolic pathways, in addition to the generation of energy and reducing power within the organelle. We generated a series of genetic deletions in an apicoplast metabolic bypass line to determine which genes involved in apicoplast carbon metabolism are required for blood-stage parasite survival and organelle maintenance. We found that pyruvate kinase II (PyrKII) is essential for organelle maintenance, but that production of pyruvate by PyrKII is not responsible for this phenomenon. Enzymatic characterization of PyrKII revealed activity against all NDPs and dNDPs tested, suggesting that it may be capable of generating a broad range of nucleotide triphosphates. Conditional mislocalization of PyrKII resulted in decreased transcript levels within the apicoplast that preceded organelle disruption, suggesting that PyrKII is required for organelle maintenance due to its role in nucleotide triphosphate generation.

scholarly journals Potential and Limitations of Cross-Protective Vaccine against Malaria by Blood-Stage Naturally Attenuated Parasite

Vaccines ◽  
2020 ◽  
Vol 8 (3) ◽  
pp. 375
Author(s):  
Takashi Imai ◽  
Kazutomo Suzue ◽  
Ha Ngo-Thanh ◽  
Chikako Shimokawa ◽  
Hajime Hisaeda
Keyword(s):  
Malaria Vaccine ◽  
Vaccination Strategy ◽  
Plasmodium Yoelii ◽  
Blood Stage ◽  
Plasmodium Berghei Anka ◽  
Complete Protection ◽  
Vaccine Trials ◽  
Multiple Species ◽  
Stage Parasite ◽  
Blood Stage Parasite

Human malaria vaccine trials have revealed vaccine efficacy but improvement is still needed. In this study, we aimed to re-evaluate vaccination with blood-stage naturally attenuated parasites, as a whole-organism vaccine model against cross-strain and cross-species malaria, to establish a better vaccination strategy. C57BL/6 mice controlled blood-stage Plasmodium yoelii 17XNL (PyNL) within 1 month of infection, while mice with a variety of immunodeficiencies demonstrated different susceptibilities to PyNL, including succumbing to hyperparasitemia. However, after recovery, survivors had complete protection against a challenge with the lethal strain PyL. Unlike cross-strain protection, PyNL-recovered mice failed to induce sterile immunity against Plasmodium berghei ANKA, although prolonged survival was observed in some vaccinated mice. Splenomegaly is a typical characteristic of malaria; the splenic structure became reorganized to prioritize extra-medullary hematopoiesis and to eliminate parasites. We also found that the peritoneal lymph node was enlarged, containing activated/memory phenotype cells that did not confer protection against PyL challenge. Hemozoins remained in the spleen several months after PyNL infection. Generation of an attenuated human blood-stage parasite expressing proteins from multiple species of malaria would greatly improve anti-malaria vaccination.

scholarly journals Chemoprophylaxis Vaccination: Phase I Study to Explore Stage-specific Immunity to Plasmodium falciparum in US Adults

2019 ◽  
Vol 71 (6) ◽  
pp. 1481-1490
Author(s):  
Sara A Healy ◽  
Sean C Murphy ◽  
Jen C C Hume ◽  
Lisa Shelton ◽  
Steve Kuntz ◽  
...  
Keyword(s):  
Plasmodium Falciparum ◽  
Phase I ◽  
Malaria Infection ◽  
Blood Smear ◽  
Blood Stage ◽  
Controlled Human Malaria Infection ◽  
Smear Negative ◽  
Parasite Exposure ◽  
Stage Parasite ◽  
Blood Stage Parasite

Abstract Background Chemoprophylaxis vaccination with sporozoites (CVac) with chloroquine induces protection against a homologous Plasmodium falciparum sporozoite (PfSPZ) challenge, but whether blood-stage parasite exposure is required for protection remains unclear. Chloroquine suppresses and clears blood-stage parasitemia, while other antimalarial drugs, such as primaquine, act against liver-stage parasites. Here, we evaluated CVac regimens using primaquine and/or chloroquine as the partner drug to discern whether blood-stage parasite exposure impacts protection against homologous controlled human malaria infection. Methods In a Phase I, randomized, partial double-blind, placebo-controlled study of 36 malaria-naive adults, all CVac subjects received chloroquine prophylaxis and bites from 12–15 P. falciparum–infected mosquitoes (CVac-chloroquine arm) at 3 monthly iterations, and some received postexposure primaquine (CVac-primaquine/chloroquine arm). Drug control subjects received primaquine, chloroquine, and uninfected mosquito bites. After a chloroquine washout, subjects, including treatment-naive infectivity controls, underwent homologous, PfSPZ controlled human malaria infection and were monitored for parasitemia for 21 days. Results No serious adverse events occurred. During CVac, all but 1 subject in the study remained blood-smear negative, while only 1 subject (primaquine/chloroquine arm) remained polymerase chain reaction–negative. Upon challenge, compared to infectivity controls, 3/3 chloroquine arm subjects displayed delayed patent parasitemia (P = .01) but not sterile protection, while 3/11 primaquine/chloroquine subjects remained blood-smear negative. Conclusions CVac-primaquine/chloroquine is safe and induces sterile immunity to P. falciparum in some recipients, but a single 45 mg dose of primaquine postexposure does not completely prevent blood-stage parasitemia. Unlike previous studies, CVac-chloroquine did not produce sterile immunity. Clinical Trials Registration NCT01500980.

scholarly journals Deciphering the targets of retroviral protease inhibitors in Plasmodium berghei

2018 ◽  
Author(s):  
Noah Machuki ◽  
Reagan Mogire ◽  
Loise Ndung’u ◽  
Peter Mwitari ◽  
Francis Kimani ◽  
...  
Keyword(s):  
Molecular Docking ◽  
Protease Inhibitors ◽  
Plasmodium Berghei ◽  
Parasite Growth ◽  
Blood Stage ◽  
Asexual Blood Stage ◽  
Parasite Fitness ◽  
Retroviral Protease ◽  
Stage Parasite ◽  
Aspartyl Proteases

AbstractRetroviral protease inhibitors (RPIs) such as lopinavir (LP) and saquinavir (SQ) are active against Plasmodium parasites. However, the exact molecular target(s) for these RPIs in the Plasmodium parasites remains poorly understood. We hypothesised that LP and SQ suppress parasite growth through inhibition of aspartyl proteases. Using reverse genetics approach, we embarked on separately generating knockout (KO) parasite lines lacking Plasmepsin 4 (PM4), PM7, PM8, or DNA damage-inducible protein 1 (Ddi1) in the rodent malaria parasite Plasmodium berghei ANKA. We then tested the suppressive profiles of the LP/Ritonavir (LP/RT) and SQ/RT as well as antimalarials; Amodiaquine (AQ) and Piperaquine (PQ) against the KO parasites in the standard 4-day suppressive test. The Ddi1 gene proved refractory to deletion suggesting that the gene is essential for the growth of the asexual blood stage parasites. Our results revealed that deletion of PM4 significantly reduces normal parasite growth rate phenotype (P = 0.003). Unlike PM4_KO parasites which were less susceptible to LP and SQ (P = 0.036, P = 0.030), the suppressive profiles for PM7_KO and PM8_KO parasites were comparable to those for the WT parasites. This finding suggests a potential role of PM4 in the LP and SQ action. On further analysis, modelling and molecular docking studies revealed that both LP and SQ displayed high binding affinities (-6.3 kcal/mol to -10.3 kcal/mol) towards the Plasmodium aspartyl proteases. We concluded that PM4 plays a vital role in assuring asexual stage parasite fitness and might be mediating LP and SQ action. The essential nature of the Ddi1 gene warrants further studies to evaluate its role in the parasite asexual blood stage growth as well as a possible target for the RPIs.Author summaryThe antiretroviral drugs (ARVs) such as LP or SQ that inhibit viral proteases reduce the rate of multiplication of the malaria parasites. The mode of action of these drugs against the parasites is however poorly understood. The proteases are among the enzymes that play essential roles in Plasmodium parasites. We sought to investigate the possible mode of action of these drugs by generating mutant parasites lacking specific aspartyl proteases namely PM4, PM7, PM8 or Ddi1 and then evaluate the susceptibility of the mutants to LP and SQ. We successfully generated parasites lacking either PM4, PM7 or PM8 but Ddi1 gene was refractory to deletion. From our data, we demonstrate that, unlike PM7 and PM8, the PM4 and Ddi1 are essential enzymes for asexual blood stage parasite fitness and survival and that the PM4 might be a target for the viral protease inhibitors in reducing parasite growth and multiplication. Further experiments using molecular docking tools show that LP or SQ have a high binding affinity for the Plasmodium aspartyl proteases.

scholarly journals Identification of the asymptomatic Plasmodium falciparum and Plasmodium vivax gametocyte reservoir under different transmission intensities

2021 ◽  
Vol 15 (8) ◽  
pp. e0009672
Author(s):  
Cristian Koepfli ◽  
Wang Nguitragool ◽  
Anne Cristine Gomes de Almeida ◽  
Andrea Kuehn ◽  
Andreea Waltmann ◽  
...  
Keyword(s):  
Plasmodium Falciparum ◽  
Light Microscopy ◽  
Papua New Guinea ◽  
Parasite Density ◽  
Solomon Islands ◽  
Age Groups ◽  
Blood Stage ◽  
Cross Sectional ◽  
Stage Parasite ◽  
Blood Stage Parasite

Background Understanding epidemiological variables affecting gametocyte carriage and density is essential to design interventions that most effectively reduce malaria human-to-mosquito transmission. Methodology/Principal findings Plasmodium falciparum and P. vivax parasites and gametocytes were quantified by qPCR and RT-qPCR assays using the same methodologies in 5 cross-sectional surveys involving 16,493 individuals in Brazil, Thailand, Papua New Guinea, and Solomon Islands. The proportion of infections with detectable gametocytes per survey ranged from 44–94% for P. falciparum and from 23–72% for P. vivax. Blood-stage parasite density was the most important predictor of the probability to detect gametocytes. In moderate transmission settings (prevalence by qPCR>5%), parasite density decreased with age and the majority of gametocyte carriers were children. In low transmission settings (prevalence<5%), >65% of gametocyte carriers were adults. Per survey, 37–100% of all individuals positive for gametocytes by RT-qPCR were positive by light microscopy for asexual stages or gametocytes (overall: P. falciparum 178/348, P. vivax 235/398). Conclusions/Significance Interventions to reduce human-to-mosquito malaria transmission in moderate-high endemicity settings will have the greatest impact when children are targeted. In contrast, all age groups need to be included in control activities in low endemicity settings to achieve elimination. Detection of infections by light microscopy is a valuable tool to identify asymptomatic blood stage infections that likely contribute most to ongoing transmission at the time of sampling.

scholarly journals Evidence for a Common Role for the Serine-Type Plasmodium falciparum Serine Repeat Antigen Proteases: Implications for Vaccine and Drug Design

2007 ◽  
Vol 75 (12) ◽  
pp. 5565-5574 ◽  
Author(s):  
Joanne E. McCoubrie ◽  
Susanne K. Miller ◽  
Tobias Sargeant ◽  
Robert T. Good ◽  
Anthony N. Hodder ◽  
...  
Keyword(s):  
Plasmodium Falciparum ◽  
Functional Redundancy ◽  
Blood Stage ◽  
Parasite Development ◽  
Serine Residue ◽  
Human Malaria Parasite ◽  
Knock Out ◽  
Genetic Deletion ◽  
Stage Parasite ◽  
Blood Stage Parasite

ABSTRACT Serine repeat antigens (SERAs) are a family of secreted “cysteine-like” proteases of Plasmodium parasites. Several SERAs possess an atypical active-site serine residue in place of the canonical cysteine. The human malaria parasite Plasmodium falciparum possesses six “serine-type” (SERA1 to SERA5 and SERA9) and three “cysteine-type” (SERA6 to SERA8) SERAs. Here, we investigate the importance of the serine-type SERAs to blood-stage parasite development and examine the extent of functional redundancy among this group. We attempted to knock out the four P. falciparum serine-type SERA genes that have not been disrupted previously. SERA1, SERA4, and SERA9 knockout lines were generated, while only SERA5, the most strongly expressed member of the SERA family, remained refractory to genetic deletion. Interestingly, we discovered that while SERA4-null parasites completed the blood-stage cycle normally, they exhibited a twofold increase in the level of SERA5 mRNA. The inability to disrupt SERA5 and the apparent compensatory increase in SERA5 expression in response to the deletion of SERA4 provides evidence for an important blood-stage function for the serine-type SERAs and supports the notion of functional redundancy among this group. Such redundancy is consistent with our phylogenetic analysis, which reveals a monophyletic grouping of the serine-type SERAs across the genus Plasmodium and a predominance of postspeciation expansion. While SERA5 is to some extent further validated as a target for vaccine and drug development, our data suggest that the expression level of other serine-type SERAs is the only barrier to escape from anti-SERA5-specific interventions.

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