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P Ringwald

Publications and source records attributed to P Ringwald.

At least 19 recordsLinked to original sources
PubMed2000

In vitro antimalarial activity of limonoids from Khaya grandifoliola C.D.C. (Meliaceae).

The crude extract from the bark and seeds of Khaya grandifoliola was active in vitro against Plasmodium falciparum with an IC50 value of 13.23 microg/ml. The extract was purified to obtain seven limonoids--methylangolensate (1), 6-methylhydroxyangolensate (2), gedunin (3), 7-deacetylkhivorin (5), 1-deacetylkhivorin (6), swietenolide (7), 6-acetylswietenolide (8)--and one flavonoid, catechin (4). Five limonoids (1, 3, 5, 6, 8) were active with IC50 values between 1.25 and 9.63 microg/ml. Catechin was practically devoid of activity. The most active limonoid, gedunin, exhibited an additive effect when combined with chloroquine.

Animals↗
PubMed2000

Molecular epidemiology of malaria in Yaounde, Cameroon. VI. Sequence variations in the Plasmodium falciparum dihydrofolate reductase-thymidylate synthase gene and in vitro resistance to pyrimethamine and cycloguanil.

Pyrimethamine and cycloguanil, the major human metabolite of proguanil, are inhibitors of dihydrofolate reductase that play a key role in the treatment and prevention of chloroquine-resistant Plasmodium falciparum infections in sub-Saharan Africa. Resistance to these antifolate drugs has emerged in some areas of Africa. Earlier molecular studies have demonstrated that point mutations at key positions of the dihydrofolate reductase-thymidylate synthase gene are strongly associated with antifolate resistance. However, whether the same or distinct mutations are involved in the development of resistance to both pyrimethamine and cycloguanil has not been well established in naturally occurring P. falciparum isolates. In this study, the in vitro responses to both antifolate drugs were measured in 42 Cameroonian isolates and compared with the complete sequence of the dihydrofolate reductase domain of the gene (from 34 of 42 isolates) to analyze the genotype that may distinguish between pyrimethamine and cycloguanil resistance. The wild-type profile (n = 11 isolates) was associated with low 50% inhibitory concentrations (IC50s) ranging from 0.32 to 21.4 nanamole for pyrimethamine and 0.60-6.40 nM for cycloguanil. Mutant isolates had at least one amino acid substitution, Asn-108. Only three mutant codons were observed among the antifolate-resistant isolates: Ile-51, Arg-59, and Asn-108. The increasing number of point mutations was associated with an increasing level of pyrimethamine IC50 and, to a much lesser extent, cycloguanil IC50. These results support a partial cross-resistance between pyrimethamine and cycloguanil that is based on similar amino acid substitutions in dihydrofolate reductase and suggest that two or three mutations, including at least Asn-108, may be necessary for cycloguanil resistance, whereas a single Asn-108 mutation is sufficient for pyrimethamine resistance.

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PubMed1999

Chloroquine resistance in Plasmodium falciparum and polymorphism of the CG2 gene.

A distinct genotype (designated Dd2-type profile) consisting of 12 point mutations and 3 repetitive regions of the CG2 gene, a candidate gene for chloroquine resistance, has been associated with in vitro resistance in laboratory-adapted strains of Plasmodium falciparum. The DNA sequence of clinical isolates, characterized by in vitro and in vivo tests, was analyzed to evaluate whether the genotype corresponds to the phenotype in naturally occurring parasites. Eight of 11 chloroquine-resistant isolates had the Dd2 genotype. One resistant isolate (by in vitro assay) with a sensitive CG2 genotype was sensitive in vivo. Two resistant isolates and 6 sensitive isolates were multiple infections with mixed alleles. No typical CG2 genotype was found corresponding to the chloroquine-sensitive isolates. These results suggest a strong association between the drug-resistant and CG2 genotypes and support the hypothesis that the CG2 gene may be implicated in chloroquine resistance.

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PubMed1999

In vitro activities of pyronaridine, alone and in combination with other antimalarial drugs, against Plasmodium falciparum.

The in vitro activities of pyronaridine, alone and in combination with established antimalarial drugs, were assessed by isotopic microtest. Pyronaridine was highly active against all Cameroonian isolates. A positive correlation was observed between the response to pyronaridine and that to chloroquine. Drug combination studies showed synergy between pyronaridine and primaquine, additive effects with 4-aminoquinolines, and weak antagonism with dihydroartemisinin, antifolates, or amino alcohols.

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PubMed1999

In vitro culture and drug sensitivity assay of Plasmodium falciparum with nonserum substitute and acute-phase sera.

The short-term in vitro growth of Plasmodium falciparum parasites in the asexual erythrocytic stage and the in vitro activities of eight standard antimalarial drugs were assessed and compared by using RPMI 1640 medium supplemented with 10% nonimmune human serum, 10% autologous or homologous acute-phase serum, or 0.5% Albumax I (lipid-enriched bovine serum albumin). In general, parasite growth was maximal with autologous (or homologous) serum, followed by Albumax I and nonimmune serum. The 50% inhibitory concentrations (IC50s) varied widely, depending on the serum or serum substitute. The comparison of IC50s between assays with autologous and nonimmune sera showed that monodesethylamodiaquine, halofantrine, pyrimethamine, and cycloguanil had similar IC50s. Although the IC50s of chloroquine, monodesethylamodiaquine, and dihydroartemisinin were similar with Albumax I and autologous sera, the IC50s of all test compounds obtained with Albumax I differed considerably from the corresponding values obtained with nonimmune serum. Our results suggest that Albumax I and autologous and homologous sera from symptomatic, malaria-infected patients may be useful alternative sources of serum for in vitro culture of P. falciparum isolates in the field. However, autologous sera and Albumax I do not seem to be suitable for the standardization of isotopic in vitro assays for all antimalarial drugs.

Adolescent↗
PubMed1999

In vitro activity of dihydroartemisinin against clinical isolates of Plasmodium falciparum in Yaounde, Cameroon.

The in vitro activities of dihydroartemisinin (the biologically active metabolite of artemisinin derivatives), chloroquine, monodesethylamodiaquine (the biologically active metabolite of amodiaquine), quinine, mefloquine, halofantrine, and pyrimethamine were assessed in 65 African isolates of Plasmodium falciparum from Yaounde, Cameroon using an isotopic microtest. The 50% inhibitory concentration (IC50) values for dihydroartemisinin were within a narrow range from 0.25 to 4.56 nM, with a geometric mean of 1.11 nM (95% confidence interval = 0.96-1.28 nM). Dihydroartemisinin was equally active (P > 0.05) against the chloroquine-sensitive isolates (geometric mean IC50 = 1.25 nM, 95% confidence interval = 0.99-1.57 nM) and the chloroquine-resistant isolates (geometric mean IC50 = 0.979 nM, 95% confidence interval = 0.816-1.18 nM). A significant positive correlation was observed between the responses to dihydroartemisinin and mefloquine (r = 0.662) or halofantrine (r = 0.284), suggesting in vitro cross-resistance. There was no correlation between the responses to dihydroartemisinin and other antimalarial drugs.

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PubMed1999

Short report: effects of pyronaridine on gametocytes in patients with acute uncomplicated falciparum malaria.

The effects of pyronaridine and chloroquine on mature Plasmodium falciparum gametocytes were compared in 161 patients treated with chloroquine or pyronaridine. Neither pyronaridine nor chloroquine showed gametocytocidal activity. The relative risks of post-treatment gametocytemia after pyronaridine and chloroquine treatment in the presence of chloroquine-resistant isolates were 1.25 and 11.5, respectively, suggesting that the use of chloroquine was associated with a high risk of favoring post-therapeutic gametocytemia in chloroquine-resistant infections.

Adolescent↗
PubMed1999

Immune responses against Plasmodium falciparum asexual blood-stage antigens and disease susceptibility in Gabonese and Cameroonian children.

The frequency and level of cellular and humoral responses to seven synthetic peptides from asexual blood stages of Plasmodium falciparum were measured in two cohorts of children living in areas highly endemic for malaria in Gabon and Cameroon. A prospective longitudinal study was conducted for one year in these sites to examine the relationship between specific in vitro immune responses and susceptibility to clinical malaria. Clinical protection was related to high proliferative responses (merozoite surface antigen-1 [MSA-1] and MSA-2 peptides) as well as to elevated antibody levels (schizont extract, MSA-2, and rhoptry-associated protein-1 [RAP-1] peptides) in the village of Dienga, Gabon. Higher response rates of interferon-gamma but lower response rates of tumor necrosis factor-alpha to four and six peptides, respectively, were observed in Dienga than in Pouma that were independent of the older age of the Gabonese children. Age accounted only for the higher prevalence rate in Dienga of the antibody responders to the peptide from Pf155/ring-infected erythrocyte surface antigen (RESA). Our results support the inclusion of epitopes from MSA-1, MSA-2, RAP-1, and Pf155/RESA antigens in a subunit vaccine against malaria, but show that a longitudinal clinical, parasitologic, and immunologic study conducted according to identical criteria in two separate areas may lead to contrasting observations, demonstrating the geographic limitation of the interpretation of such results.

Adolescent↗
PubMed1999

Molecular epidemiology of malaria in Yaounde, Cameroon IV. Evolution of pyrimethamine resistance between 1994 and 1998.

Pyrimethamine, in combination with sulfadoxine, is currently one of the major alternative drugs used for the treatment of chloroquine-resistant Plasmodium falciparum malaria infections in Africa. The mechanism of pyrimethamine resistance has been strongly associated with a single, key point mutation in the dihydrofolate reductase-thymidylate synthase gene, resulting in the substitution of the wild-type allele Ser-108 by either Asn-108 or Thr-108. The pyrimethamine-resistant phenotype and/or genotype were determined in 273 Cameroonian clinical isolates obtained in Yaounde by in vitro assays and polymerase chain reaction-restriction fragment length polymorphism over a 5-year period. The in vitro assays showed that 42% (18 of 43) and 63% (69 of 110) of the isolates obtained in 1994-1995 and 1997-1998, respectively, were resistant to pyrimethamine (50% inhibitory concentration [IC50] > 100 nM). The polymerase chain reaction showed that 43% (55 of 127) and 59% (50 of 85) of the isolates in 1994-1995 and 1997-1998, respectively, had the mutant Asn-108 allele. The pyrimethamine-resistant genotype (Asn-108) corresponded with the pyrimethamine-resistant phenotype (IC50 > or = 100 nM) in a large majority (> 95%) of the isolates. The results of our study suggest an increasing prevalence of pyrimethamine resistance in Yaounde. Our study further suggests that pyrimethamine resistance can be monitored by a technique that can be adopted by malaria research centers in Africa.

Adolescent↗
PubMed1999

Molecular epidemiology of malaria in Yaounde, Cameroon V. analysis of the omega repetitive region of the plasmodium falciparum CG2 gene and chloroquine resistance.

A novel Plasmodium falciparum gene, denoted cg2 gene, has been recently discovered, and a distinct genotype, characterized by 12 point mutations and 3 size polymorphisms, has been shown to be associated with chloroquine resistance in laboratory-adapted parasite strains. One of the polymorphic regions, denoted the omega region, consists of 16 tandem repeat units in chloroquine-resistant strains, while the chloroquine-sensitive strains have either < or = 15 or > or = 17 repeat units. In this study, the in vivo and in vitro responses were compared with the number of repeat units in the omega region of the cg2 gene for 75 Cameroonian isolates determined either by DNA sequencing or agarose gel electrophoresis. The 16-repeat units that characterize the resistant strains were found in 10 chloroquine-sensitive isolates (50% inhibitory concentration [IC50] < 100 nM) and 30 chloroquine-resistant isolates (IC50 > or = 100 nM). Thirty-five isolates (28 chloroquine-sensitive isolates and 7 chloroquine-resistant isolates) displayed < or = 15 or > or = 17 repeat units. Of the 18 patients responding with treatment failure, 15 were infected with parasites carrying 16 repeat units. Twenty-eight patients (11 with isolates carrying 16 repeat units and 17 with isolates carrying < or = 15 or > or = 17 repeat units) showed an adequate clinical response. The sensitivity, specificity, and predictive value were 81% (83%), 74% (61%), and 75% (58%), respectively compared with in vitro (or in vivo) responses. Neither the level of IC50 nor the key P. falciparum multidrug resistance gene 1 (pfmdr 1) allele at position 86 was associated with the number of omega repeat units. Although in vitro and in vivo resistance to chloroquine was statistically associated with the presence of 16 repeat units in the omega region (P < 0.05), the number of omega repeat units did not adequately discriminate patients infected with chloroquine-resistant parasites from those infected with chloroquine-sensitive parasites. Further studies on the cg2 gene are needed to determine whether cg2 gene is a reliable genetic marker for chloroquine resistance.

Adolescent↗
PubMed1999

Relationships between malaria prevalence and malaria-related morbidity in school children from two villages in central Africa.

To investigate the relationship between parasite prevalence and malaria-related morbidity, we carried out a comparative study among cohorts of school children from two villages, Dienga, Gabon, and Pouma, Cameroon, both located in malaria-endemic areas. Seven to 17 year-old children attending primary schools were similarly followed-up at each site to evaluate the frequency of malaria attacks. Follow-up involved daily temperature recording (and blood smears in the case of fever) and preparation of blood smears every two weeks. In Pouma, 186 children were followed-up for six months. In Dienga, 228 children were followed-up for nine months. The mean prevalence rate of Plasmodium falciparum infections (as assessed by the blood smears) was twice as high in Pouma compared with Dienga (45.2% versus 26.8%; P < 0.0001), whereas the monthly malaria attack rate (as assessed by the daily surveillance) was twice as high in Dienga compared with Pouma (21.5% versus 41.4%; P = 0.003). The possible implication of several parameters that may differ between the two areas, such as the malaria transmission level, the economical and social status of the inhabitants, the characteristics of infecting parasite strains, and the genetic background of the population, is discussed.

Adolescent↗
PubMed1999

Comparison of in vivo and in vitro tests of resistance in patients treated with chloroquine in Yaoundé, Cameroon.

The usefulness of an isotopic in vitro assay in the field was evaluated by comparing its results with the therapeutic response determined by the simplified WHO in vivo test in symptomatic Cameroonian patients treated with chloroquine. Of the 117 enrolled patients, 102 (87%) completed the 14-day follow-up, and 95 isolates obtained from these patients (46 children, 49 adults) yielded an interpretable in vitro test. A total of 57 of 95 patients (60%; 28 children and 29 adults) had an adequate clinical response with negative smears (n = 46) or with an asymptomatic parasitaemia (n = 11) on day 7 and/or day 14. The geometric mean 50% inhibitory concentration of the isolates obtained from these patients was 63.3 nmol/l. Late and early treatment failure was observed in 29 (30.5%) and 9 (9.5%) patients, respectively. The geometric mean 50% inhibitory concentrations of the corresponding isolates were 173 nmol/l and 302 nmol/l. Among the patients responding with late and early treatment failure, five isolates and one isolate, respectively, yielded a discordant result (in vivo resistance and in vitro sensitivity). The sensitivity, specificity, and predictive value of the in vitro test to detect chloroquine-sensitive cases was 67%, 84% and 86%, respectively. There was moderate concordance between the in vitro and in vivo tests (kappa value = 0.48). The in vitro assay agrees relatively well with the therapeutic response and excludes several host factors that influence the results of the in vivo test. However, in view of some discordant results, the in vitro test cannot substitute for in vivo data on therapeutic efficacy. The only reliable definition of "resistance" in malaria parasites is based on clinical and parasitological response in symptomatic patients, and the in vivo test provides the standard method to determine drug sensitivity or resistance as well as to guide national drug policies.

Adolescent↗
PubMed1999

[Comparative study of artemether and quinine in severe Plasmodium falciparum malaria in adults and older children in Cameroon].

From June 1993 to June 1994, a study was carried out to compare artemether and quinine for management of severe falciparum malaria in adults and adolescents in Cameroon. Artemether was administered intramuscularly at a dose of 3.6 mg/kg on the first day and 1.6 mg/kg for the following 4 days. Quinine was administered intravenously at a dose of 1.6 mg/kg for the first 4 hours and 8 mg every 8 hours for the next 3 days. The files of 84 of the 95 patients recruited were validated for inclusion in the final study. There were 40 patients in the artemether group and 44 in the quinine group. The two groups were comparable with regard to all factors at the time of inclusion. Findings showed that artemether was more effective than quinine with regard to total clearance of parasitemia, 90 p. 100 clearance, and fever control and that it was as effective with regard to 50 p. 100 clearance and recovery of consciousness. In view of its good performance and of the simplicity of its administration by intramuscular injection, artemether would appear to be an excellent alternative for treatment of severe malaria and cerebral malaria in areas with poor medical facilities.

Adolescent↗
PubMed1999

[Variability of in vitro activity of proguanil and cycloguanil on erythrocyte stages of Plasmodium falciparum as a function of culture conditions].

The in vitro activity of proguanil, cycloguanil (active metabolite of proguanil), pyrimethamine, and chloroquine was determined for 14 isolates of Plasmodium falciparum and the chloroquine-resistant W2 clone. In vitro assays were performed by using different types of RPMI 1640 culture medium and incubation period. The use of the standard RPMI medium or RPMI medium containing low concentrations of folate and para-aminobenzoic acid increases the 50% inhibitory concentrations of cycloguanil and pyrimethamine, as compared with the use of folate- and para-aminobenzoic acid-free RPMI medium. The concentrations of folate and para-aminobenzoic acid did not affect the in vitro activity of proguanil and chloroquine. However, prolongation of the incubation period from 42 to 66 hours decreased the 50% inhibitory concentrations of all test compounds. The weak antagonism in vitro between chloroquine and proguanil or cycloguanil does not seem to have any repercussion on the in vivo efficacy of chloroquine-proguanil combination.

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PubMed1998

Heterogeneity in the circumsporozoite protein gene of Plasmodium malariae isolates from sub-Saharan Africa.

Polymorphism of the circumsporozoite protein (CSP) of Plasmodium malariae was characterized by comparing gene sequences of twelve field isolates obtained in Yaoundé, Cameroon, Central Africa, and one clinical isolate originating from Côte d'Ivoire, West Africa. The length of the CSP gene ranged from 1266 to 1302 bp. The size polymorphism was due to variation in the number of tandem repeat units. All P. malariae isolates displayed a highly conserved 5' non-repeat region. Seven non-synonymous and two synonymous nucleotide variations were observed in the 3' non-repeat region. In the deduced amino acid sequence the repetitive sequences consisted of a varying number of major (Asn Ala Ala Gly (NAAG); range between 42 and 46 units) and minor (Asn Asp Ala Gly (NDAG) or Asn Asp Gln Gly (NDEG); n = six or seven units) tetrapeptide units. None of the isolates had an identical sequence at nucleotide level. These findings suggest that polymorphism in CSP is essentially limited to the tandem repeat domain.

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