SEARCH · Search PubMed
Search indexed PubMed citations on genomics, clinical trials, systematic reviews and public health. Explore titles, authors and supplied subject terms, then open the PubMed record.
Quote a phrase for an exact phrase match. Source license links do not imply unrestricted reuse.
Erythrocytes infected with chloroquine-sensitive Plasmodium falciparum bind chloroquine with an apparent intrinsic association constant of 1.5 x 10(7) liters per mole. Such high-affinity binding of chloroquine is absent or deficient in uninfected erythrocytes and in erythrocytes infected with chloroquine-resistant Plasmodium falciparum.
Erythrocytic stages of the malaria parasite Plasmodium falciparum rely on glycolysis for their energy supply and it is unclear whether they obtain energy via mitochondrial respiration albeit enzymes of the tricarboxylic acid (TCA) cycle appear to be expressed in these parasite stages. Isocitrate dehydrogenase (ICDH) is either an integral part of the mitochondrial TCA cycle or is involved in providing NADPH for reductive reactions in the cell. The gene encoding P. falciparum ICDH was cloned and analysis of the deduced amino-acid sequence revealed that it possesses a putative mitochondrial targeting sequence. The protein is very similar to NADP+-dependent mitochondrial counterparts of higher eukaryotes but not Escherichia coli. Expression of full-length ICDH generated recombinant protein exclusively expressed in inclusion bodies but the removal of 27 N-terminal amino acids yielded appreciable amounts of soluble ICDH consistent with the prediction that these residues confer targeting of the native protein to the parasites' mitochondrion. Recombinant ICDH forms homodimers of 90 kDa and its activity is dependent on the bivalent metal ions Mg2+ or Mn2+ with apparent Km values of 13 micro m and 22 micro m, respectively. Plasmodium ICDH requires NADP+ as cofactor and no activity with NAD+ was detectable; the for NADP+ was found to be 90 micro m and that of d-isocitrate was determined to be 40 micro m. Incubation of P. falciparum under exogenous oxidative stress resulted in an up-regulation of ICDH mRNA and protein levels indicating that the enzyme is involved in mitochondrial redox control rather than energy metabolism of the parasites.
BACKGROUND: Previous experience with unacceptable adverse effects with mefloquine as treatment for uncomplicated Plasmodium falciparum malaria prompted an evaluation of the effectiveness and side effects of atovaquone-proguanil (Malarone) in a hospital setting. METHODS: Atovaquone-proguanil was given as standard treatment (1,000/400 mgq.d. for 3 days) to 50 adults who had traveled in Africa and returned with uncomplicated Plasmodium falciparum malaria. Half of the treated patients were African and had lived outside Africa for varying periods of time; the other half were Danish-born persons without any previous immunity towards malaria. RESULTS: All patients treated with Malarone were cured without complications. The mean fever clearance times differed among the groups and according to various degrees of prior exposure to malaria and ranged from 1.3 to 2.2 days. Adverse effects during treatment were mild, and were likely to be due to the malaria itself. Fourteen people who had acquired falciparum malaria in spite of taking proguanil-chloroquine prophylaxis were also cured uneventfully without recrudescence. CONCLUSIONS: Malarone appears to be an effective, safe and acceptable oral treatment for uncomplicated malaria.
In 1983, the first African cases of malaria due to Plasmodium falciparum resistant to sulfadoxine/pyrimethamine, were described. Currently, this resistance is frequently found in Kenya and Tanzania. It has also been described in other African countries. A young Spanish woman contracted Plasmodium falciparum malaria in Senegal and was treated in our hospital with sulfadoxine/pyrimethamine. Fever and symptoms disappear within two days. The thick smears taken on the eighth and thirteenth days of treatment contained an abundance of gametocytes, but neither trophozoites nor schizonts. As the risk of transmission of malaria to the rest of the community was considered practically nil, no other treatment was administered. A month late, she was admitted to the hospital due to fever, shivering, fatigue, loss of appetite and hemolytic anaemia. The thick smear test again showed trophozoites of P. Falciparum. Thus, it proved to be a delayed grade I resistance to sulfadoxine/pyrimethamine, detected in far west Africa. An oral dose of mefloquine was administered as well as a red cell transfusion. Both fever and symptoms finally disappeared.
The human malaria parasite, Plasmodium falciparum, maintains at least two distinct types, A and S, of developmentally controlled ribosomal RNAs. To investigate specific functions associated with these rRNAs, we replaced the Saccharomyces cerevisiae GTPase domain of the 25S rRNA with GTPase domains corresponding to the Plasmodium A- and S-type 28S rRNAs. The A-type rRNA differs in a single nonconserved base pair from the yeast GTPase domain. The S-type rRNA GTPase domain has three additional changes in highly conserved residues, making it unique among all known rRNA sequences. The expression of either A- or S-type chimeric rRNA in yeast increased translational accuracy. Yeast containing only A-type chimeric rRNA and no wild-type yeast rRNA grew at the wild-type level. In contrast, S-type chimeric rRNA severely inhibited growth in the presence of wild-type yeast rRNA, and caused lethality in the absence of the wild-type yeast rRNA. We show what before could only be hypothesized, that the changes in the GTPase center of ribosomes present during different developmental stages of Plasmodium species can result in fundamental changes in the biology of the organism.
The increasing resistance of the malaria parasite Plasmodium falciparum to currently available drugs demands a continuous effort to develop new antimalarial agents. In this quest, the identification of antimalarial effects of drugs already in use for other therapies represents an attractive approach with potentially rapid clinical application. We have found that the extensively used antimycotic drug clotrimazole (CLT) effectively and rapidly inhibited parasite growth in five different strains of P. falciparum, in vitro, irrespective of their chloroquine sensitivity. The concentrations for 50% inhibition (IC(50)), assessed by parasite incorporation of [(3)H]hypoxanthine, were between 0.2 and 1.1 microM. CLT concentrations of 2 microM and above caused a sharp decline in parasitemia, complete inhibition of parasite replication, and destruction of parasites and host cells within a single intraerythrocytic asexual cycle (approximately 48 hr). These concentrations are within the plasma levels known to be attained in humans after oral administration of the drug. The effects were associated with distinct morphological changes. Transient exposure of ring-stage parasites to 2.5 microM CLT for a period of 12 hr caused a delay in development in a fraction of parasites that reverted to normal after drug removal; 24-hr exposure to the same concentration caused total destruction of parasites and parasitized cells. Chloroquine antagonized the effects of CLT whereas mefloquine was synergistic. The present study suggests that CLT holds much promise as an antimalarial agent and that it is suitable for a clinical study in P. falciparum malaria.
The human malaria parasite Plasmodium falciparum, one of the world's most devastating pathogens, has an astonishing array of sequences and genes that play key roles in pathogenesis and immune evasion. We must understand the functions of these elements if the chronicity and unpredictable virulence of Plasmodium is to be explained.
We tested the clinical reactions to a synthetic, Plasmodium falciparum, circumsporozoite multiple antigen peptide (MAP) vaccine in 39 volunteers immunized two to three times over 2-8 months using a dose escalation design. Immediate pain at the injection site was associated with the adjuvant QS-21 (P<0.001), and delayed local inflammatory reactions were associated with high-titered circulating IgG anti-MAP antibody (P=0.03). Because two volunteers developed acute, systemic urticaria after the third immunization associated with development of serum IgE MAP antibody, we employed immediate-type hypersensitivity skin tests (ITH-STs) using intradermal injections of diluted MAP vaccine to identify persons sensitized to the vaccine. ITH-STs were negative in seven volunteers tested 27 days after the first vaccination, but six of these individuals developed positive wheal and flare reactions when tested 14 or 83 days after the second vaccination; IgE MAP antibody was detected in only one of them. Another cohort of 16 volunteers, including the 2 allergic individuals, were ITH-ST negative when first tested late after their second or third vaccination at 6-7 months. Five of five non-immunized persons were also ITH-ST negative. ITH-STs may help identify individuals sensitized to malaria peptides and at potential risk of developing systemic allergic reactions after re-vaccination.
Serum-free media were used to culture Plasmodium falciparum. A commercial preparation, Daigo's GF21 developed as a growth-promoting factor for many kinds of mammalian cells, and consisting of the 55-70% ammonium sulphate fraction of adult bovine serum, insulin, transferrin, ethanolamine and sodium selenite, was found to sustain growth of the parasite when Daigo's T was employed as a basal medium. The optimal Daigo's GF21 concentration for parasite growth was between 5 and 20% (v/v), with the best results at 10%. Differential counts indicated that Daigo's GF21 is essential for schizogony. Established serum-free medium, GIT, consisting of Daigo's T basal medium and Daigo's GF21, yielded good parasite growth without any supplementation. Growth-promoting factor derived from adult bovine serum in Daigo's GF21 was shown to be crucial to parasite growth. The results presented here will not only be of practical value, but will provide important information about the developmental requirements for the parasite.
Sera from donors exposed to malaria were tested for their ability to block the transmission of isolates from Cameroonian Plasmodium falciparum gametocyte carriers. Sera were selected from amongst Cameroonian and Gambian donors who had positive antibody reactivity against the surface of activated gametes and against epitopes of Pfs 48/45 (a potential transmission-blocking vaccine candidate antigen). Aliquots of washed blood from gametocyte carriers were resuspended in test and control sera and fed to An. gambiae mosquitoes via a membrane feeder. Comparisons of the prevalence and intensity of infections is dissected mosquitoes showed variations in the ability of sera to block the transmission of the different isolates. Sera were identified that had little or no blocking effect on the transmission of isolates unless the isolate was poorly infectious. Some sera completely blocked the transmission of some isolates whilst having little or no effect on others. The observed variation in transmission-modulating activity may have implications for the development of a transmission-blocking vaccine.
Tumor necrosis factor-alpha (TNF-alpha), interleukin (IL)-1beta, and IL-6 are implicated in the pathogenesis of severe Plasmodium falciparum malaria. In this study, the effect of IL-10 on their production by peripheral blood mononuclear cells (PBMC) from acutely infected patients was examined. Exogenous IL-10 inhibited malarial antigen-induced cytokine production by reducing mRNA accumulation. Maximal inhibition occurred when IL-10 was added in the first 2 h of stimulation. Conversely, the addition of anti-IL-10 markedly enhanced TNF-alpha, IL-1beta, and IL-6 production. The effect was significantly greater on PBMC from patients with uncomplicated infection than PBMC from patients with severe disease. Kinetics studies showed that TNF-alpha, IL-6, and IL-1beta were produced within 2-4 h of stimulation, while IL-10 was first detectable after 8 h. These findings suggest that IL-10 counter-regulates the proinflammatory response to P. falciparum. Severe falciparum malaria may be associated with an inadequate negative feedback response by IL-10.
The genome of the human malaria parasite Plasmodium falciparum is extremely AT-rich such that it is particularly difficult to design standard probes to identify and quantify specific transcripts. Biased AT genome contents (70%-80%) lead to a high proportion of short repetitions and a low free energy of binding between target sequences and their specific probes during hybridization. This causes nonspecific annealing and high background noise. We constructed molecular beacon probes with dual-function stems to avoid nonspecific detection and establish identical melting patterns for use with several fluorescent probes for the analysis of mRNA expression in P. falciparum in real-time reverse transcription PCR (RT-PCR) assays. The method proved highly efficient at detecting low transcript levels in P. falciparum microcultures. Conditions were established for two types of real-time instruments, demonstrating that molecular beacons with dual-function stems are a useful tool for the functional analysis of high AT genomes. The procedure could be adapted to high-throughput gene expression protocols for the biomolecular screening of the P. falciparum and other AT-rich genomes.
The humoral immune response against synthetic peptides of two Plasmodium falciparum blood-stage antigens, Pf155/ring-infected erythrocyte surface antigen (RESA) (EENV)6 and Pf332 (SVTEEIAEEDK)2, in individuals belonging to three sympatric ethnic groups (Mossi, Rimaibe, and Fulani) living in the same conditions of hyperendemic transmission in a Sudan savanna area northeast of Ouagadougou, Burkina Faso were examined. The Mossi and Rimaibe are Sudanese Negroid populations with a long tradition of sedentary farming, while the Fulani are nomadic pastoralists partly settled and characterized by non-Negroid features of possible Caucasoid origin. A total of 764 subjects (311 Mossi, 273 Rimaibe, and 180 Fulani) were tested. A lower P. falciparum prevalence was observed in the Fulani of all age groups. The serologic results clearly indicate the existence of interethnic differences in the capacity to respond to these two P. falciparum antigens. The Mossi and Rimaibe showed similar responses, whereas the Fulani displayed consistently higher prevalences and levels of antibodies against both epitopes tested. The anti-(EENV)6 and anti-(SVTEEIAEEDK)2 seroprevalences were 29.9% and 38.9% in Mossi, 29.7% and 39.2% in Rimaibe, 86.1% and 76.1% in Fulani (all P values of Fulani-Mossi and Fulani-Rimaibe comparisons << 0.001). Anti-RESA and anti-Pf332 antibody levels were approximately 65% (P << 0.001) and 45% (P << 0.001), respectively, higher in seropositive Fulani than in seropositive Mossi and Rimaibe, who showed very similar values. The observed differences cannot be explained in terms of interethnic heterogeneity of malaria exposure since these communities have lived in the same area for more than 30 years and the P. falciparum inoculation rate, measured during two consecutive years, was substantially uniform for the three ethnic groups. The possibility of remarkable heterogeneities in the capacity to mount immune responses against P. falciparum antigens among populations with different genetic backgrounds must be taken into account in the development of anti-malaria vaccines.
In a malaria-endemic area of the Coast of Kenya with chloroquine resistant Plasmodium falciparum, we determined the prevalence and density of falciparum infection in gravid women and assessed the in vivo and in vitro parasite response to a regimen of chloroquine 25 mg/kg body weight divided over three days. P. falciparum infections were present in 65 (21.7%) of 300 pregnant women. The proportion of primigravidae who were parasitaemic was 41.8% which was significantly higher than that of the multigravidae (17.1, P less than 0.01). Primigravidae did not show a significantly higher mean parasite density than the multigravidae. The in vivo tests showed that 45.9% of all the P. falciparum infections were resistant to chloroquine predominantly at RI and RII levels with percentages 36.1% and 8.2%, respectively.
Single nucleotide polymorphisms (SNPs) in the Plasmodium falciparum dihydrofolate reductase (dhfr), and dihydropteroate synthetase (dhps), and chloroquine resistance transporter (Pfcrt) genes are used as molecular markers of P. falciparum resistance to sulfadoxine/pyrimethamine and chloroquine. However, to be a practical tool in the surveillance of drug resistance, simpler methods for high-throughput haplotyping are warranted. Here we describe a quick and simple technique that detects dhfr, dhps, and Pfcrt SNPs using polymerase chain reaction (PCR)- and enzyme-linked immunosorbent assay (ELISA)-based technology. Biotinylated PCR products of dhfr, dhps, or Pfcrt were captured on streptavidin-coated microtiter plates and sequence-specific oligonucleotide probes (SSOPs) were hybridized with the PCR products. A stringent washing procedure enabled detection of remaining bound SSOPs and distinguished between the SNPs of dhfr, dhps, and Pfcrt with high specificity. The SSOP-ELISA compared well with a standard PCR-restriction fragment length polymorphism procedure, and gave identical positive results in more than 90% of the P. falciparum slide-positive samples tested. The SSOP-ELISA of all dhfr, dhps, or Pfcrt SNPs on 88 samples can be performed in a single day and provides quick and reproducible results. The system can potentially be modified to detect SNPs in other genes.
Chloroquine-resistant Plasmodium falciparum has been spreading rapidly after its emergence in 1988 in Yekepa. The in vivo and in vitro susceptibilities to quinine and quinidine, compared to chloroquine, were studied by investigating the number of treatment days required for radical cure and estimating the quinine concentrations concomitantly. The minimal inhibitory concentrations (MIC) for schizont maturation in all successful in vitro tests were 5.12 x 10(-6) mol/l for quinine and 1.28 x 10(-6) mol/l for quinidine, indicating that all 50 isolates were sensitive to the two drugs. The IC50 and IC90 values were 0.22 and 0.78 x 10(-6) mol/l for quinine and 0.07 and 0.26 x 10(-6) mol/l for quinidine, respectively. In vitro inhibition of parasites by 1.6 x 10(-6) mol/l of chloroquine was obtained in 31 out of 47 isolates, 16 (34%) being resistant. The IC50, IC90 and geometrical mean MIC for quinine were all about two times higher for the chloroquine-resistant than for the chloroquine-sensitive isolates (P = 0.006). P. falciparum infected children (n = 64) were randomly allocated to four groups and treated with quinine (10 mg/kg body weight twice daily) for 1 day (3 doses), 2, 4 and 7 days, respectively. All cleared their parasitaemias by day 4 but 5 out of 15 of those treated with only three doses showed a recurrence of parasitaemia between days 7 and 14; these were considered to be recrudescences. In the other groups, recurrent parasitaemias only occurred between days 17 and 28 and were considered to be reinfections.(ABSTRACT TRUNCATED AT 250 WORDS)
Plasmodium falciparum susceptibility to chloroquine in vivo and to chloroquine and mefloquine in vitro was investigated in children living in Ouagadougou area (Burkina Faso) in October 1991. The 7-day WHO in vivo field test was used, with follow-up on days 2, 4, 7 after treatment with 25 mg base of chloroquine per kg body weight given over 3 days, on children aged 2-8 years with monospecific P. falciparum infection (parasite density higher than 800 asexual parasites/microliters of blood), and negative Bergqvist urine tests. At the same time, the in vitro response was assessed using WHO standard test kits. Chloroquine treatment in vivo resulted in parasite clearance in 47 subjects (92.2%) within 7 days (S/RI responses). Parasitaemia did not clear in 4 cases (7.8% of RII responses). There were no RIII responses. The sensitivity study in vitro showed a low degree of chloroquine resistance in 2 out of 12 isolates tested and a mean 50% effective dose (EC50) and EC99 of 0.12 mumol and 1.47 mumol/litre of blood, respectively. All isolates tested were inhibited by mefloquine at 1.6 mumol/litre of blood, indicating full sensitivity. The present study demonstrates that first-line treatment with chloroquine is still satisfactorily effective in the study area of Burkina Faso.
The rapid acquisition of resistance by Plasmodium falciparum to antimalarial drugs has focused worldwide efforts on vaccine development. The definition of critical antigens involved in the induction of protective immunity against disease is essential. Our previous studies have characterized a synthetic peptide complex (SPf70), derived from a 70 kDa P. falciparum exoantigen, in terms of its immunogenicity and antigenic reactivity. In the present study total anti-P. falciparum asexual blood-stage antibodies and antibodies to the Pf70 antigen were measured by immunofluorescence (IFA) and ELISA, respectively, in children and adults (n = 160) of Kinshasa, Zaire, an area with continuous and intense malaria transmission. All of the subjects tested had IFA antibodies and 90% (143/160) had antibodies to Pf70 antigen. Antibody levels against Pf70 were significantly higher among children with low parasitemias (p < 0.05). These results suggest that antibodies to Pf70 antigen may have a protective role against P. falciparum infection. Further studies are needed to define the functional nature of the protective mechanism(s).