Renal Pathology in Owl Monkeys Vaccinated with Plasmodium falciparum Asexual Blood-Stage Synthetic Peptide Antigens

ABSTRACTThe design of new antimalarial combinations to treatPlasmodium falciparuminfections requires drugs that, in addition to resolving disease symptoms caused by asexual blood stage parasites, can also interrupt transmission to the mosquito vector. Gametocytes, which are essential for transmission, develop as sexual blood stage parasites in the human host over 8 to 12 days and are the most accessible developmental stage for transmission-blocking drugs. Considerable effort is currently being devoted to identifying compounds active against mature gametocytes. However, investigations on the drug sensitivity of developing gametocytes, as well as screening methods for identifying inhibitors of early gametocytogenesis, remain scarce. We have developed a luciferase-based high-throughput screening (HTS) assay using tightly synchronous stage I to III gametocytes from a recombinantP. falciparumline expressing green fluorescent protein (GFP)-luciferase. The assay has been used to evaluate the early-stage gametocytocidal activity of the MMV Malaria Box, a collection of 400 compounds with known antimalarial (asexual blood stage) activity. Screening this collection against early-stage (I to III) gametocytes yielded 64 gametocytocidal compounds with 50% inhibitory concentrations (IC50s) below 2.5 μM. This assay is reproducible and suitable for the screening of large compound libraries, with an average percent coefficient of variance (%CV) of ≤5%, an average signal-to-noise ratio (S:N) of >30, and a Z′ of ∼0.8. Our findings highlight the need for screening efforts directed specifically against early gametocytogenesis and indicate the importance of experimental verification of early-stage gametocytocidal activity in the development of new antimalarial candidates for combination therapy.

Download Full-text

Renal Pathology in Owl Monkeys in Plasmodium falciparum Vaccine Trials

American Journal of Tropical Medicine and Hygiene ◽

10.4269/ajtmh.1990.43.130 ◽

1990 ◽

Vol 43 (2) ◽

pp. 130-138 ◽

Cited By ~ 2

Author(s):

Motohiro Iseki ◽

Keith G. Pirl ◽

Ikuo Igarashi ◽

William E. Collins ◽

Masamichi Aikawa ◽

...

Keyword(s):

Plasmodium Falciparum ◽

Renal Pathology ◽

Vaccine Trials ◽

Owl Monkeys

Download Full-text

5116755 Asexual blood stage antigens of plasmodium falciparum which encode a rhoptry protein

Biotechnology Advances ◽

10.1016/0734-9750(92)90416-7 ◽

1992 ◽

Vol 10 (3) ◽

pp. 471

Keyword(s):

Plasmodium Falciparum ◽

Blood Stage ◽

Asexual Blood Stage ◽

Rhoptry Protein

Download Full-text

Pre-erythrocytic antibody profiles induced by controlled human malaria infections in healthy volunteers under chloroquine prophylaxis

Scientific Reports ◽

10.1038/srep03549 ◽

2013 ◽

Vol 3 (1) ◽

Cited By ~ 55

Author(s):

Philip L. Felgner ◽

Meta Roestenberg ◽

Li Liang ◽

Christopher Hung ◽

Aarti Jain ◽

...

Keyword(s):

Plasmodium Falciparum ◽

Life Cycle ◽

Healthy Volunteers ◽

Protective Immunity ◽

Circumsporozoite Protein ◽

Blood Stage ◽

Asexual Blood Stage ◽

Liver Stage ◽

Human Malaria ◽

Life Cycle Stages

Abstract Complete sterile protection to Plasmodium falciparum (Pf) infection mediated by pre-erythrocytic immunity can be experimentally induced under chloroquine prophylaxis, through immunization with sporozoites from infected mosquitoes' bites (CPS protocol). To characterize the profile of CPS induced antibody (Ab) responses, we developed a proteome microarray containing 809 Pf antigens showing a distinct Ab profile with recognition of antigens expressed in pre-erythrocytic life-cycle stages. In contrast, plasma from naturally exposed semi-immune individuals from Kenya was skewed toward antibody reactivity against asexual blood stage antigens. CPS-immunized and semi-immune individuals generated antibodies against 192 and 202 Pf antigens, respectively, but only 60 antigens overlapped between the two groups. Although the number of reactive antigens varied between the CPS-immunized individuals, all volunteers reacted strongly against the pre-erythrocytic antigens circumsporozoite protein (CSP) and liver stage antigen 1 (LSA1). Well classified merozoite and erythrocytic antigens were strongly reactive in semi-immune individuals but lacking in the CPS immunized group. These data show that the antibody profile of CPS-immunized and semi-immune groups have quite distinct profiles reflecting their protective immunity; antibodies from CPS immunized individuals react strongly against pre-erythrocytic while semi-immune individuals mainly react against erythrocytic antigens.

Download Full-text

Protein ubiquitylation is essential for the schizont to merozoite transition in Plasmodium falciparum blood-stage development

10.1101/755439 ◽

2019 ◽

Author(s):

Yang Wu ◽

Vesela Encheva ◽

Judith L. Green ◽

Edwin Lasonder ◽

Adchara Prommaban ◽

...

Keyword(s):

Plasmodium Falciparum ◽

Homology Model ◽

Food Vacuole ◽

Blood Stage ◽

Parasite Development ◽

Parasite Line ◽

Schizont Stage ◽

Post Translational Modification ◽

Asexual Blood Stage ◽

Erythrocyte Invasion

AbstractUbiquitylation is a common post translational modification of eukaryotic proteins and in the human malaria parasite, Plasmodium falciparum (Pf) overall ubiquitylation increases in the transition from intracellular schizont to extracellular merozoite stages in the asexual blood stage cycle. Here, we identify specific ubiquitylation sites of protein substrates in three intracellular parasite stages and extracellular merozoites; a total of 1464 sites in 546 proteins were identified (data available via ProteomeXchange with identifier PXD014998). 469 ubiquitylated proteins were identified in merozoites compared with only 160 in the preceding intracellular schizont stage, indicating a large increase in protein ubiquitylation associated with merozoite maturation. Following merozoite invasion of erythrocytes, few ubiquitylated proteins were detected in the first intracellular ring stage but as parasites matured through trophozoite to schizont stages the extent of ubiquitylation increased. We identified commonly used ubiquitylation motifs and groups of ubiquitylated proteins in specific areas of cellular function, for example merozoite pellicle proteins involved in erythrocyte invasion, exported proteins, and histones. To investigate the importance of ubiquitylation we screened ubiquitin pathway inhibitors in a parasite growth assay and identified the ubiquitin activating enzyme (UBA1 or E1) inhibitor MLN7243 (TAK-243) to be particularly effective. This small molecule was shown to be a potent inhibitor of recombinant PfUBA1, and a structural homology model of MLN7243 bound to the parasite enzyme highlights avenues for the development of P. falciparum specific inhibitors. We created a genetically modified parasite with a rapamycin-inducible functional deletion of uba1; addition of either MLN7243 or rapamycin to the recombinant parasite line resulted in the same phenotype, with parasite development blocked at the late schizont stage. These results indicate that the intracellular target of MLN7243 is UBA1, and this activity is essential for the final differentiation of schizonts to merozoites. The ubiquitylation of many merozoite proteins and their disappearance in ring stages are consistent with the idea that ubiquitylation leads to their destruction via the proteasome once their function is complete following invasion, which would allow amino acid recycling in the period prior to the parasite’s elaboration of a new food vacuole.

Download Full-text