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At least 721 records · Page 40Linked to original sources
PubMed1986

A new technique for drug susceptibility tests for Plasmodium falciparum by ethidium bromide fluoroassay.

When Plasmodium falciparum parasites were stained with the fluorescent dye ethidium bromide, the fluorescence intensity of the solubilized parasites was correlated with the amount of nucleic acid present. It was possible to monitor development of the parasites from ring form to schizont by the fluoroassay. The assay system was applied to in vitro drug susceptibility tests on malaria parasites.

Chloroquine↗
PubMed2006

Functional genomics of Plasmodium falciparum through transposon-mediated mutagenesis.

Plasmodium falciparum is the causative agent for the most lethal form of human malaria, killing millions annually. Genetic analyses of P. falciparum have been relatively limited due to the lack of robust techniques to manipulate this parasite. Development of transfection technologies and whole genome analyses have helped in understanding the complex biology of this parasite. Even with this wealth of information functional genomics approaches are still very limited in P. falciparum due to the cumbersome and inefficient methods of genetic manipulation. This review focuses on a recently developed, highly efficient method for transposon-based mutagenesis and transgene expression in P. falciparum that will allow functional genomics studies to be performed proficiently on this deadly malaria parasite. By using a piggyBac-based transposition system, multiple random integrations have been obtained into the genome of the parasite. This technique could hence be employed to set up several biological screens in this lethal protozoan parasite that may lead to identification of novel drug targets and vaccine candidates.

Animals↗
PubMed1983

A labour-saving method for the in vitro culture of Plasmodium falciparum.

The in vitro cultivation of Plasmodium falciparum requires at least daily changes of medium (Trager and Jensen, 1976). Addition of 50 mg per litre of hypoxanthine to medium RPMI 1640 permits to postpone the change of medium for up to 72 hours. A single subculture step is required to remove unlabelled hypoxanthine prior to the use of the cultured material in 3H-hypoxanthine incorporation assays. The method constitutes a considerable saving of time and medium.

Animals↗
PubMed2002

Fate of haem iron in the malaria parasite Plasmodium falciparum.

Chemical analysis has shown that Plasmodium falciparum trophozoites contain 61+/-2% of the iron within parasitized erythrocytes, of which 92+/-6% is located within the food vacuole. Of this, 88+/-9% is in the form of haemozoin. (57)Fe-Mössbauer spectroscopy shows that haemozoin is the only detectable iron species in trophozoites. Electron spectroscopic imaging confirms this conclusion.

Animals↗
PubMed1979

Observations on gametogenesis in Plasmodium falciparum from continuous culture.

Gametocytes of Plasmodium falciparum were produced in continuous cultures but eventually declined in numbers after 3--4 months in vitro. Their development progressed in a consistent pattern, from small rounded, through triangular, to ellipsoidal, and finally after 8 days to crescentic forms. Morphologic maturity occurred at 8--9 days, but the gametocytes would not exflagellate in vitro, even after 14--18 days of development. Thus, current culture methods cannot produce a continuous supply of functional gametes for further studies.

Adolescent↗
PubMed2006

Synthesis, solution structure and immune recognition of an epidermal growth factor-like domain from Plasmodium falciparum merozoite surface protein-1.

The Plasmodium falciparum merozoite surface protein-1 19 kDa fragment (MSP-1(19)) comprises two closely packed EGF-like domains (EGF=epidermal growth factor), each stabilized by three disulfide bonds. The native conformation of this protein is important for eliciting P. falciparum growth inhibitory antibodies. Here we show that the N-terminal EGF domain alone can be chemically synthesized and efficiently refolded to a native-like state, as shown by its solution structure as determined by NMR spectroscopy. In order to study its immunogenicity, the domain was coupled through its N terminus to a phospholipid and incorporated into reconstituted influenza virus-like particles (virosomes). When used to immunize mice, the peptide-loaded virosomes elicited potent humoral immune responses that were shown by Western blots and immunofluorescence assays to cross-react with native MSP-1 on the surfaces of P. falciparum blood stage parasites. This opens the way for a medicinal chemistry-oriented approach to the study and optimization of the antigenicity of the protein as a potential malaria vaccine candidate, whilst exploiting the immunopotentiating properties of influenza virosomes as a delivery vehicle.

Amino Acid Sequence↗
PubMed1987

Safety and efficacy of a recombinant DNA Plasmodium falciparum sporozoite vaccine.

A recombinant DNA Plasmodium falciparum sporozoite vaccine produced in Escherichia coli (FSV-1) was tested in doses of 10 micrograms to 800 micrograms protein in fifteen volunteers. No serious adverse reactions occurred. Antibodies that reacted with P falciparum sporozoite antigens by enzyme-linked immunoassay developed in twelve of the volunteers. The highest antibody titres induced were similar to those resulting from lifelong natural exposure to sporozoite-infected mosquitoes. Postimmunization serum samples from a majority of volunteers mediated the circumsporozoite (CS) precipitation reaction and inhibited sporozoite invasion of hepatoma cells in vitro. Serum from the three volunteers who received 800 micrograms doses reacted with the surface of sporozoites in an immunofluorescence assay. Six immunised volunteers receiving a fourth dose of FSV-1 and two non-immunised controls were challenged by bites of mosquitoes infected from cultured P falciparum gametocytes. Parasitaemia did not develop in the volunteer with the highest titre of CS antibodies, and parasitaemia was delayed in two other immunised volunteers. This study confirms that human beings can be protected by CS protein subunit vaccines and provides a framework for the further development and testing of more immunogenic sporozoite vaccines.

Adult↗
PubMed2001

Sialic acid-dependent binding of baculovirus-expressed recombinant antigens from Plasmodium falciparum EBA-175 to Glycophorin A.

The Plasmodium falciparum Erythrocyte Binding Antigen-175, EBA-175, is a soluble merozoite stage parasite protein which binds to glycophorin A surface receptors on human erythrocytes. We have expressed two conserved cysteine-rich regions, region II and region VI, of this protein as soluble His-tagged polypeptides in insect cell culture, and have tested their function in erythrocyte and glycophorin A binding assays. Recombinant region II polypeptides comprised of the F2 sub-domain or the entire region II (F1 and F2 sub-domains together) bound to erythrocytes and to purified glycophorin A in a manner similar to the binding of native P. falciparum EBA-175 to human red cells. Removal of sialic acid residues from the red cell surface totally abolished recombinant region II binding, while trypsin treatment of the erythrocyte surface reduced but did not eliminate recombinant region II binding. Synthetic peptides from three discontinuous regions of the F2 sub-domain of region II inhibited human erythrocyte cell binding and glycophorin A receptor recognition. Immune sera raised against EBA-175 recombinant proteins recognized native P. falciparum-derived EBA-175, and sera from malaria-immune adults recognized recombinant antigens attesting to both the antigenicity and immunogenicity of proteins. These results suggest that the functionally-active recombinant region II domain of EBA-175 may be an attractive candidate for inclusion in multi-component asexual blood stage vaccines.

Amino Acid Sequence↗
PubMed1995

Interactions of atovaquone with other antimalarial drugs against Plasmodium falciparum in vitro.

A series of Plasmodium falciparum in vitro drug sensitivity studies were conducted in order to evaluate atovaquone in combination with other antimalarial drugs and thus to identify a potential partner for a fixed combination. The derived isobolograms indicated that drug interactions ranged from antagonism through addition to synergy. Of particular note were the quinolines and artemisinin analogues, which were all antagonistic, and the biguanides and tetracycline, which showed synergy. Proguanil emerged as the most promising of the current antimalarials as a partner for atovaquone in a fixed combination, with tetracycline as back-up.

Animals↗
PubMed1991

[Molecular recognition between glycophorin A and Plasmodium falciparum merozoites].

By using purified human erythrocyte membrane glycophorin A (GPA) and glycopeptide of GPA, antibodies against GPA and against GPA-glycopeptide, and SPA-colloidal gold, Plasmodium falciparum FCC-1/HN merozoites were immunolabeled. The labeled samples were observed under transmission electron microscope (TEM). The TEM pictures showed that colloidal gold pellets were distributed over all of the merozoite surface. This is the first report on the direct experimental evidence of molecular recognition and combination between GPA (or glycopeptide of GPA) and Plasmodium falciparum merozoites. The results strongly support the hypothesis that GPA is involved as a recognized receptor on erythrocytes for Plasmodium falciparum and the glycopeptide domain of GPA is the receptor site for Plasmodium falciparum.

Animals↗
PubMed2002

A randomized comparison of chloroquine, amodiaquine and their combination with pyrimethamine-sulfadoxine in the treatment of acute, uncomplicated, Plasmodium falciparum malaria in children.

The increasing resistance of Plasmodium falciparum to antimalarial monotherapy (MT) has created an urgent need for the evaluation of alternative effective, safe, cheap, readily available and affordable, combination treatments (CT) with antimalarial drugs. In the present study, the efficacies of chloroquine (CQ) or amodiaquine (AQ) in the oral treatment of acute, symptomatic, uncomplicated, Plasmodium falciparum malaria were compared with those of oral treatments with the combination of CQ or AQ with pyrimethamine-sulfadoxine (PS). The CQ and AQ were each given at a dose of 10 mg/kg.day for 3 days (days 0, 1 and 2), with or without PS given as a single dose (25 mg sulfadoxine/kg) at presentation (day 0). Overall, 303 children aged 0.5-10 years (74 given CQ, 82 AQ, 72 CQPS and 75 AQPS) were evaluated. The fever-clearance time (FCT) was significantly shorter in those treated with AQPS than in those treated with CQ or CQPS. The proportions of patients with complete clearance of their parasitaemias on days 1 and 2 were significantly larger and the parasite-clearance times (PCT) were all significantly shorter with the drug combinations than with their corresponding MT. For example, the mean (S.D.) PCT were 2.6 (0.8) days for CQ v. 2.1 (0.8) days for CQPS (P=0.0002), and 2.6 (0.7) days for AQ v. 2.1 (0.7) days for AQPS (P=0.00001). The cure 'rates' on days 14, 21 and 28 were also significantly higher with AQ, CQPS and AQPS than with CQ; those on day 28, for example, were 47.2%, 98.7%, 100% and 100% for CQ, AQ, CQPS and AQPS, respectively (P=0.000001). Gametocyte carriages on day 3 or on days 3, 7 and/or 14 combined were significantly lower in those treated with CQPS than in those given CQ; there was no gametocyte carriage in the CT groups on day 28. In the CQ group, eight of 13 children with gametocytaemia on day 3 had a response indicative of resistance. However, the five CQ-resistant infections that were re-treated with AQPS responded promptly, with a PCT significantly shorter than that during the initial treatment with CQ and with a cure 'rate' of 100% on day 28. Adverse reactions to treatment were similar on the first and subsequent days of treatment and were tolerable except for pruritus, which was significantly more common in children treated with CQ alone than in the other treatment groups. Haematological and biochemical parameters were not adversely affected by any treatment. The CQPS and AQPS combinations appear to be well tolerated and may be useful as alternatives to monotherapy with CQ or AQ as resistance to the single drugs develops.

Acute Disease↗
PubMed1983

Stage-specific protein synthesis by asexual blood stage parasites of Plasmodium falciparum.

Highly synchronised cultures of cloned Plasmodium falciparum (clone T9-94) were metabolically radiolabelled with [35S]methionine during eight consecutive non-overlapping intervals, while parasites developed from young rings to mature schizonts. Analysis of equal amounts of trichloroacetic acid precipitable radioactivity from each interval by sodium dodecyl sulphate-polyacrylamide gel electrophoresis fluorography allowed the stage specificity of protein synthesis to be investigated. More than forty polypeptides with molecular weights of 20 000 to 200 000 can be distinguished. While some proteins are synthesised throughout erythrocytic schizogony many are shown to be stage-specific. Among these are a range of high molecular weight proteins synthesised only during nuclear division. Detailed morphological information permits correlations to be made between synthesis of particular polypeptides and parasite structure.

Animals↗
PubMed2003

Glyoxalase I of the malarial parasite Plasmodium falciparum: evidence for subunit fusion.

Recombinant Plasmodium falciparum glyoxalase I (PfGlx I) was characterized as monomeric Zn(2+)-containing enzyme of 44 kDa. The K(M) value of the methylglyoxal-glutathione adduct is 77+/-15 microM, the k(cat) value being 4000 min(-1) at 25 degrees C and pH 7.0. PfGlx I consists of two halves, each of which is homologous to the small 2-domain glyoxalase I of man. Both parts of the pfglx I gene were overexpressed; the C-terminal half of PfGlx I was found to be a stable protein and formed an enzymatically active dimer. These results support the hypothesis of domain-swapping and subunit fusion as mechanisms in glyoxalase I evolution.

Amino Acid Sequence↗
PubMed1977

Ultrastructure and viability of cryopreserved Plasmodium falciparum.

Cryopreserved chimpanzee erythrocytes infected with Plasmodium falciparum were examined by electron microscopy directly and after a period of culture. Light microscopic observations on the viability of cryopreserved parasites in culture were also made. Parasitaemia data from a chimpanzee infected with parasites cryostored for more than 2(1/2) years are presented. Varying degrees of damage were apparent as the parasites were examined in vitro, for viability, and by electron microscopy. Schizonts appear not to survive the process, whereas the ability of "ring" trophozoite forms to develop into large trophozoites in vitro varies from 20% to 100% in different preparations. Cryopreserved material examined by electron microscope showed degenerative changes in most of the parasites, but after 72 h of cultivation most of the parasites appeared normal. These findings suggest that some organisms may sustain reversible damage during cryostorage.

Animals↗
PubMed2006

Ammonia permeability of the aquaglyceroporins from Plasmodium falciparum, Toxoplasma gondii and Trypansoma brucei.

Plasmodium falciparum uses amino acids from haemoglobin degradation mainly for protein biosynthesis. Glutamine, however, is mostly oxidized to 2-oxoglutarate to restore NAD(P)H + H+. In this process two molecules of ammonia are released. We determined an ammonia production of 9 mmol h(-1) per litre of infected red blood cells in the early trophozoite stage. External application of ammonia yielded a cytotoxic IC50 concentration of 2.8 mM. As plasmodia cannot metabolize ammonia it must be exported. Yet, no biochemical or genomic evidences exist that plasmodia possess classical ammonium transporters. We expressed the P. falciparum aquaglyceroporin (PfAQP) in Xenopus laevis oocytes and examined whether it may serve as an exit pathway for ammonia. We show that injected oocytes: (i) acidify the medium due to ammonia uptake, (ii) take up [14C]methylamine and [14C]formamide, (iii) swell in solution with formamide and acetamide and (iv) display an ammonia-induced NH4+-dependent clamp current. Further, a yeast strain lacking the endogenous aquaglyceroporin (Fps1) is rescued by expression of PfAQP which provides for the efflux of toxic methylamine. Ammonia permeability was similarly established for the aquaglyceroporins from Toxoplasma gondii and Trypanosoma brucei. Apparently, these aquaglyceroporins are important for the release of ammonia derived from amino acid breakdown.

Ammonia↗
PubMed1988

Uptake of antibiotics by Plasmodium falciparum in culture.

The ability of Plasmodium falciparum to accumulate 3H-clindamycin, 3H-tetracycline, and 3H-dihydrostreptomycin was determined in synchronized trophozoites and schizonts in 87% parasitemia 5% hematocrit cultures. Accumulation was time-dependent and modestly concentration-dependent. At 0.1 mM initial external drug concentration, the ratio of drug concentration in cells:medium after 120 min was 5.5 for 3H-clindamycin, 2.8 for 3H-tetracycline, and 0.95 for 3H-dihydrostreptomycin. Corresponding values for uninfected erythrocytes were 3.2, 2.3, and 0.78, respectively. These data may explain the lack of antimalarial activity of the aminoglycosides and may partially explain the slow onset of therapeutic action of clindamycin and tetracycline. The low intracellular concentrations attained for the latter two drugs have important implications for understanding the kinetics and mechanism of their antiplasmodial effects.

Animals↗
PubMed1988

Immunity in malaria: depression of delayed hypersensitivity reaction in acute Plasmodium falciparum infection.

The effect of acute Plasmodium falciparum malaria infection on the cell-mediated immune response of 30 Nigerian children attending the General Out-patient (GOP) Clinic of the University College Hospital, Ibadan, Nigeria, was assessed in a controlled study. Delayed-type hypersensitivity skin reaction to five tuberculin units (5 TU) of purified protein derivative (PPD) was used as an indicator of cell-mediated immunity. The results showed marked depression of delayed hypersensitivity reaction to PPD in 27 (90%) of the malarious children, compared with four (16%) of the 25 control healthy subjects (P less than 0.0005). This depression was observed despite evidence of previous BCG vaccination in 38 (69.1%) of the 55 children in the study. The possible clinical significance of these observations in tropical paediatric practice, and the immunopathological implications, are discussed.

Acute Disease↗
PubMed1989

Generalized immunological recognition of the major merozoite surface antigen (gp195) of Plasmodium falciparum.

The antibody response to the Plasmodium falciparum major merozoite surface antigen (gp195) of congenic mouse strains differing in H-2 haplotype has been examined. All seven strains of mice were capable of producing gp195-specific antibodies. Generalized immune recognition of gp195 by mice of diverse H-2 haplotypes distinguished gp195 from the P. falciparum circumsporozoite protein and the 230-kDa and 48/45-kDa gamete surface antigens. However, the H-2 genetic locus appeared to influence the specificity of gp195-specific antibodies. Immunoblot patterns of mouse sera with parasite antigens revealed a complex pattern of reactivity with terminal and intermediate processing fragments of gp195. The majority of immunoblot bands observed were similar for all of the mouse strains; however, there were several strains that additionally recognized a few unique fragments or displayed more intense reactivities with specific processing fragments. These results suggest that while individuals of diverse major histocompatibility complex makeup are capable of recognizing the gp195 antigen, the recognition of specific gp195 B-cell and T-cell epitopes may be under control of the major histocompatibility complex.

Animals↗