Inter-individual variation in the metabolic activation of the antimalarial biguanides

The aryl-biguanides proguanil and chlorproguanil were developed as part of a collaborative programme between ICI and the Liverpool School of Tropical Medicine during the 1940s. The compounds were characterized by their absence of host toxicity. However, the rapid development of parasite resistance to the actions of these drugs and the development of the 4-aminoquinoline, chloroquine, severely limited their use. The subsequent widespread development of parasite resistance to chloroquine, together with the observations that the magnitude of dihydrofolate reductase inhibitor resistance (the site of action of the biguanides) developed to pyrimethamine is not directly correlated with biguanide resistance(1,2). has resulted in renewed interest in these drugs. In particular, proguanil is now the drug of choice for malaria prophylaxis, in combination with chloroquine; used in combination with a suitable sulphonamide, it may be of value in malaria therapy.

Genetic diversity of Plasmodium falciparum parasites from Kenya is not affected by antifolate drug selection

The genotypes of merozoite surface protein-1, merozoite surface protein-2 and glutamine rich protein are frequently used to distinguish recrudescence from reinfection when parasitaemia reappears after antimalarial drug treatment. However, none of the previous reports has clearly assessed the change of genetic diversity following drug treatment. In the present study, we have assessed the impact of pyrimethamine/sulfadoxine and chlorproguanil/dapsone on the genetic diversity of isolates and the multiplicity of infection in patient isolates from Kilifi, Kenya. We have analysed the length polymorphism of merozoite surface protein-1, merozoite surface protein-2 and glutamine rich protein and the data clearly show that treatment with pyrimethamine/sulfadoxine and chlorproguanil/dapsone did not change the multiplicity of infection found in patients, in contrast to the selection that these drugs exert on the genes encoded by the target enzymes. In addition, we report that children of less than 2 years tend to have fewer numbers of clones per isolate when compared with older children. Overall, this study shows that the selection for genes that confer drug resistance is not a factor in reducing the genetic diversity of parasite clones in a patient.

Chlorproguanil-dapsone versus sulfadoxine-pyrimethamine for sequential episodes of uncomplicated falciparum malaria in Kenya and Malawi: a randomised clinical trial

BACKGROUND

Chlorproguanil-dapsone exerts lower resistance pressure on Plasmodium falciparum than does sulfadoxine-pyrimethamine, but is rapidly eliminated. We aimed to find out whether chlorproguanil-dapsone results in a higher retreatment rate for malaria than sulfadoxine-pyrimethamine.

METHODS

In a randomised trial of paediatric outpatients with uncomplicated falciparum malaria, patients received either chlorproguanil-dapsone or sulfadoxine-pyrimethamine and were followed up for up to 1 year. Sites were in Kenya (n=410) and Malawi (n=500). We used per-protocol analysis to assess the primary outcome of annual malaria incidence.

FINDINGS

Drop-outs were 117 of 410 (28.5%) in Kenya, and 342 of 500 (68.4%) in Malawi. Follow-up was for a median of 338 days (IQR 128-360) and 342 days (152-359) in Kilifi (chlorproguanil-dapsone and sulfadoxine-pyrimethamine, respectively), and for 120 days (33-281) and 84 days (26-224) in Blantyre. Mean annual malaria incidence was 2.5 versus 2.1 in Kenya (relative risk 1.16, 95% CI 0.98-1.37), and 2.2 versus 2.8 in Malawi (0.77, 0.63-0.94). 4.3% versus 12.8%, and 5.4% versus 20.1%, of patients were withdrawn for treatment failure in Kenya and Malawi, respectively. In Kenya haemoglobin concentration of 50 g/L or less caused exit in 6.9% of chlorproguanil-dapsone patients and 1.5% of sulfadoxine-pyrimethamine patients, but most anaemia occurred before re-treatment. In Malawi only one patient exited because of anaemia.

INTERPRETATION

Despite the rapid elimination of chlorproguanil-dapsone, children treated with this drug did not have a higher incidence of malaria episodes than those treated with sulfadoxine-pyrimethamine. Treatment failure was more common with sulfadoxine-pyrimethamine. Cause of anaemia in Kenya was probably not adverse reaction to chlorproguanil-dapsone, but this observation requires further study.

Pharmacokinetics of phenytoin following intravenous and intramuscular administration of fosphenytoin and phenytoin sodium in the rabbit

The purpose of this study was to evaluate and compare plasma phenytoin concentration versus time profiles following intravenous (i.v.) and intramuscular (i.m.) administration of fosphenytoin sodium with those obtained following administration of standard phenytoin sodium injection in the rabbit. Twenty-four adult New Zealand White rabbits (2.1 +/- 0.4 kg) were anaesthetized with sodium pentobarbitone (30 mg/kg) followed by i.v. or i.m. administration of a single 10 mg/kg phenytoin sodium or fosphenytoin sodium equivalents. Blood samples (1.5 ml) were obtained from a femoral artery cannula predose and at 1, 3, 5, 7, 10, 15, 20, 30, 45, 60, 90, 120, 180, 240 and 300 min after drug administration. Plasma was separated by centrifugation (1000 g; 5 min) and fosphenytoin, total and free plasma phenytoin concentrations were measured using high performance liquid chromatography (HPLC). Following i.v. administration of fosphenytoin sodium plasma phenytoin concentrations were similar to those obtained following i.v. administration of an equivalent dose of phenytoin sodium. Mean peak plasma phenytoin concentrations (Cmax) was 158% higher (P = 0.0277) following i.m. administration of fosphenytoin sodium compared to i.m. administration of phenytoin sodium. The mean area under the plasma total and free phenytoin concentration-time curve from time zero to 120 min (AUC(0-120)) following i.m. administration was also significantly higher (P = 0.0277) in fosphenytoin treated rabbits compared to the phenytoin group. However, there was no significant difference in AUC(0-180) between fosphenytoin and phenytoin-treated rabbits following i.v. administration. There was also no significant difference in the mean times to achieve peak plasma phenytoin concentrations (Tmax) between fosphenytoin and phenytoin-treated rabbits following i.m. administration. Mean plasma albumin concentrations were comparable in both groups of animals. Fosphenytoin was rapidly converted to phenytoin both after i.v. and i.m. administration, with plasma fosphenytoin concentrations declining rapidly to undetectable levels within 10 min following administration via either route. These results confirm the rapid and complete hydrolysis of fosphenytoin to phenytoin in vivo, and the potential of the i.m. route for administration of fosphenytoin delivering phenytoin in clinical settings where i.v. administration may not be feasible.

Pyrimethamine-sulfadoxine resistance in Plasmodium falciparum: what next?

Chemotherapy remains the only practicable tool to control falciparum malaria in sub-Saharan Africa, where >90% of the world's burden of malaria mortality and morbidity occurs. Resistance is rapidly eroding the efficacy of chloroquine, and the combination pyrimethamine-sulfadoxine is the most commonly chosen alternative. Resistant populations of Plasmodium falciparum were selected extremely rapidly in Southeast Asia and South America. If this happens in sub-Saharan Africa, it will be a public health disaster because no inexpensive alternative is currently available. This article reviews the molecular mechanisms of this resistance and discusses how to extend the therapeutic life of antifolate drugs.

The Genetic Regulation of Fucosylated and Sialylated Antigens on Developing Myeloid Cells

The first part of this article reviews the stages of normal development of haemopoietic cells committed to the myeloid lineage, properties of leukaemic cell lines that are arrested at specific maturation stages along the granulocytic pathway, the structures of carbohydrate antigenic markers that appear on myeloid cell surfaces, with especial reference to sialyl-Le(x) (NeuAcalpha2-3Galbeta1-4[Fucalpha1-3]GlcNAc), and the role of this antigen on mature granulocytes as a ligand for selectin molecules. The families of fucosyl- and sialyltransferase genes encoding enzymes responsible for the biosynthesis of sialyl-Le(x), and the pathways leading to the formation of this antigen, and more complex related structures, are described. The second part of the article outlines the work carried out in the authors' laboratory with leukaemic cell lines in an attempt to ascertain the biochemical and genetic basis of the lowering of sialyl-Le(x) expression that occurs at intermediate stages of normal haemopoietic development. Analysis of enzyme levels and mRNA expression of the fucosyl- and sialyltransferase genes has led to the conclusion that depletion of substrate resulting from high levels of enzyme activity from co-expressed genes FUT4 and ST6Gal1 probably accounts for the dip in expression of sialyl-Le(x), rather than a change in the level of expression of FUT7, the gene in myeloid cells encoding the enzyme ultimately responsible for the synthesis of sialyl-Le(x). The possible significance of this change in relation to normal cell maturation is discussed.

Unravelling the biochemical basis of blood group ABO and Lewis antigenic specificity

The ABO blood-group polymorphism is still the most clinically important system in blood transfusion practice. The groups were discovered in 1900 and the genes at the ABO locus were cloned nearly a century later in 1990. To enable this goal to be reached intensive studies were carried out in the intervening years on the serology, genetics, inheritance and biochemistry of the antigens belonging to this system. This article describes biochemical genetic investigations on ABO and the related Lewis antigens starting from the time in the 1940s when serological and classical genetical studies had established the immunological basis and mode of inheritance of the antigens but practically nothing was known about their chemical structure. Essential steps were the definition of H as the product of a genetic system Hh independent of ABO, and the establishment of the precursor-product relationship of H to A and B antigens. Indirect methods gave first indications that the specificity of antigens resided in carbohydrate and revealed the immunodominant sugars in the antigenic structures. Subsequently chemical fragmentation procedures enabled the complete determinant structures to be established. Degradation experiments with glycosidases revealed how loss of one specificity by the removal of a single sugar unit exposed a new specificity and suggested that biosynthesis proceeded by a reversal of this process whereby the oligosaccharide structures were built up by the sequential addition of sugar units. Hence, the primary blood-group gene products were predicted to be glycosyltransferase enzymes that added the last sugar to complete the determinant structures. Identification of these enzymes gave new genetic markers and eventually purification of the blood-group A-gene encoded N-acetylgalactosaminyltransferase gave a probe for cloning the ABO locus. Blood-group ABO genotyping by DNA methods has now become a practical possibility.

Molecular evidence of greater selective pressure for drug resistance exerted by the long-acting antifolate Pyrimethamine/Sulfadoxine compared with the shorter-acting chlorproguanil/dapsone on Kenyan Plasmodium falciparum

Pyrimethamine (PM) plus sulfadoxine (SD) is the last remaining affordable drug for treating uncomplicated malaria in Africa. The selective pressure exerted by the slowly eliminated combination PM/SD was compared with that exerted by the more rapidly eliminated combination chlorproguanil/dapsone (CPG/Dap) on Kenyan Plasmodium falciparum. Point mutations were analyzed in dihydrofolate reductase and dihydropteroate synthase and in the genetic diversity of 3 genes in isolates collected before and after CPG/Dap and PM/SD treatments. PM/SD was associated strongly with the disappearance of fully drug-sensitive parasites and with a significant increase in the prevalence of resistant parasites in subsequent parasitemias. However, this was not a characteristic of treatment with CPG/Dap. Moreover, most of the patients who returned with recrudescent infections were in the PM/SD-treated group. The data predict a longer useful therapeutic life for CPG/Dap than for PM/SD, and, thus, CPG/Dap is a preferable alternative for treatment of chloroquine-resistant falciparum malaria in sub-Saharan Africa.

Towards an understanding of the mechanism of pyrimethamine-sulfadoxine resistance in Plasmodium falciparum: genotyping of dihydrofolate reductase and dihydropteroate synthase of Kenyan parasites

The antifolate combination of pyrimethamine (PM) and sulfadoxine (SD) is the last affordable drug combination available for wide-scale treatment of falciparum malaria in Africa. Wherever this combination has been used, drug-resistant parasites have been selected rapidly. A study of PM-SD effectiveness carried out between 1997 and 1999 at Kilifi on the Kenyan coast has shown the emergence of RI and RII resistance to PM-SD (residual parasitemia 7 days after treatment) in 39 out of 240 (16.25%) patients. To understand the mechanism that underlies resistance to PM-SD, we have analyzed the dihydrofolate reductase (DHFR) and dihydropteroate synthase (DHPS) genotypes of 81 patients. Fifty-one samples were obtained, before treatment, from patients who remained parasite free for at least 7 days after treatment. For a further 20 patients, samples were obtained before treatment and again when they returned to the clinic with parasites 7 days after PM-SD treatment. Ten additional isolates were obtained from patients who were parasitemic 7 days after treatment but who were not sampled before treatment. More than 65% of the isolates (30 of 46) in the initial group had wild-type or double mutant DHFR alleles, and all but 7 of the 47 (85%) had wild-type DHPS alleles. In the paired (before and after treatment) samples, the predominant combinations of DHFR and DHPS alleles before treatment were of triple mutant DHFR and double mutant DHPS (41% [7 of 17]) and of double mutant DHFR and double mutant DHPS (29% [5 of 17]). All except one of the posttreatment isolates had triple mutations in DHFR, and most of these were "pure" triple mutants. In these isolates, the combination of a triple mutant DHFR and wild-type DHPS was detected in 6 of 29 cases (20.7%), the combination of a triple mutant DHFR and a single mutant (A437G) DHPS was detected in 4 of 29 cases (13.8%), and the combination of a triple mutant DHFR and a double mutant (A437G, L540E) DHPS was detected in 16 of 29 cases (55.2%). These results demonstrate that the triply mutated allele of DHFR with or without mutant DHPS alleles is associated with RI and RII resistance to PM-SD. The prevalence of the triple mutant DHFR-double mutant DHPS combination may be an operationally useful marker for predicting the effectiveness of PM-SD as a new malaria treatment.

The changing in vitro susceptibility pattern to pyrimethamine/sulfadoxine in Plasmodium falciparum field isolates from Kilifi, Kenya

Two clinical trials that used Falcidin (Cosmos Ltd., Nairobi, Kenya), the antifolate combination of pyrimethamine/sulfadoxine (PM/SD), as treatment for non-severe falciparum malaria in children at Kilifi, Kenya in 1987-1988 and 1993-1995 have presented an opportunity to assess in vitro the susceptibility trend of Plasmodium falciparum to PM and SD over time on the Kenya coast. The first set of isolates was collected prior to the introduction of PM/SD into the Kenya Medical Research Institute/Wellcome Trust Research unit while the second set was taken soon after PM/SD was introduced in the study area as the first-line treatment drug for uncomplicated falciparum malaria. In the first trial, 69 isolates collected before and after treatment of malaria with PM/SD were tested directly in the field for susceptibility to PM and SD using the standard in vitro micro-test technique, with minimal levels of folate. In the second trial, 97 isolates similarly collected were adapted to culture, and tested as described elsewhere. In both studies, PM and SD susceptibility tests were done separately. There was a highly significant decrease (P < 0.01) in the in vitro sensitivity of P. falciparum isolates to PM and SD between the two trials. In the first trial, the isolates were either sensitive to both PM and SD or resistant to PM and sensitive to SD. During the second trial, isolates were either resistant to PM and sensitive to SD or resistant to both drugs. These results are important in estimating the useful therapeutic life (UTL) of PM/SD in this area and in identifying alternative antifolate drugs.

Studies on anti-folate antimalarials in east Africa

Chlorproguanil-dapsone (CD) appears to be a promising anti-folate combination (Amukoye et al., 1997) to substitute for pyrimethamine-sulfadoxine (PS), which has a long half-life and against which there is resistance in several Plasmodium falciparum populations including the highly endemic lowland area near Muheza, Tanzania (Trigg et al., 1997).

The antimalarial triazine WR99210 and the prodrug PS-15: folate reversal of in vitro activity against Plasmodium falciparum and a non-antifolate mode of action of the prodrug

We have studied the reversal of activity against Plasmodium falciparum of WR99210, a triazine antimalarial drug, and of the pro-drug PS-15 by folic acid (FA) and folinic acid (FNA). Folic acid and FNA inhibit the growth of P. falciparum in vitro at concentrations > 10(-4.5) and 10(-3.5) mol/L, respectively. The activity of pyrimethamine against Kenyan strains M24 and K39 is reduced 10-12-fold by 10(-5) mol/L of FA, and virtually eliminated by 10(-5) mol/L of FNA. Folates do not antagonise the action of WR99210 against Kenyan strains, and only partially antagonize the action of WR99210 action against the Southeast Asian strains V1/S and W282. Similarly, FA and FNA exerted weak or no antagonism of the action of PS-15. The inability of folates to antagonize the action of WR99210 can be explained in terms of high drug-enzyme affinity, but this does not account for the inability of FA and FNA to antagonize PS-15. These results suggest that action of PS-15 against P. falciparum is primarily due to a non-folate mechanism.

Changing home treatment of childhood fevers by training shop keepers in rural Kenya

BACKGROUND

Malaria control in Africa relies primarily on early effective treatment for clinical disease, but most early treatments for fever occur through self-medication with shop-bought drugs. Lack of information to community members on over-the-counter drug use has led to widespread ineffective treatment of fevers, increased risks of drug toxicity and accelerating drug resistance. We examined the feasibility and measured the likely impact of training shop keepers in rural Africa on community drug use.

METHODS

In a rural area of coastal Kenya, we implemented a shop keeper training programme in 23 shops serving a population of approximately 3500, based on formative research within the community. We evaluated the training by measuring changes in the proportions of drug sales where an adequate amount of chloroquine was purchased and in the percentage of home-treated childhood fevers given an adequate amount of chloroquine. The programme was assessed qualitatively in the community following the shop keeper training.

RESULTS

The percentage of drug sales for children with fever which included an antimalarial drug rose from 34.3% (95% CI 28.9%-40.1%) before the training to a minimum of 79.3% (95% CI 71.8%-85.3%) after the training. The percentage of antimalarial drug sales where an adequate amount of drug was purchased rose from 31.8% (95% CI 26.6%-37.6%) to a minimum of 82.9% (95% CI 76.3%-87.3%). The percentage of childhood fevers where an adequate dose of chloroquine was given to the child rose from 3.7% (95% CI 1.2%-9.7%) before the training to a minimum of 65.2% (95% CI 57.7%-72.0%) afterwards, which represents an increase in the appropriate use of over-the-counter chloroquine by at least 62% (95% CI 53.7%-69.3%). Shop keepers and community members were strongly supportive of the aims and outcome of the programme.

CONCLUSIONS

The large shifts in behaviour observed indicate that the approach of training shop keepers as a channel for information to the community is both feasible and likely to have a significant impact. Whilst some of the impact seen may be attributable to research effects in a relatively small scale pilot study, the magnitude of the changes support further investigation into this approach as a potentially important new strategy in malaria control.

Prevalence of anaemia in patients attending an outpatient clinic in western Rift Valley in Kenya during a low malaria season

OBJECTIVE

To assess the prevalence of anaemia in outpatients attending a rural health clinic in an area of seasonal malaria, during the low transmission season.

METHODS

Haemoglobin estimation and blood slide examination for malaria parasites were performed on 280 consecutive patients attending outpatient curative services at Entasopia Health Centre, Kajiado District, Kenya, between April-May 1996. Anaemia was defined according to World Health Organisation guidelines for age, sex and pregnancy status.

RESULTS

In all groups except adult males, more than half of the patients tested had haemoglobin values below the lower reference limits, suggesting that anaemia is widely present in this population even during the low malaria season. Only 5% of patients were positive for Plasmodium falciparum malaria. Peripheral blood film examination suggested iron deficiency as the major cause of anaemia.

CONCLUSIONS

Further studies to define the underlying causes of anaemia and to develop community strategies to prevent anaemia are required. The association between fever and anaemia and the use of pallor to diagnose anaemia, are discussed.

Expression of human alpha-l-fucosyltransferase gene homologs in monkey kidney COS cells and modification of potential fucosyltransferase acceptor substrates by an endogenous glycosidase

Previous investigations on the monkey kidney COS cell line demonstrated the weak expression of fucosylated cell surface antigens and presence of endogenous fucosyltransferase activities in cell extracts. RT-PCR analyses have now revealed expression of five homologs of human fucosyltransferase genes, FUT1, FUT4, FUT5, FUT7, and FUT8, in COS cell mRNA. The enzyme in COS cell extracts acting on unsialylated Type 2 structures is closely similar in its properties to the alpha1,3-fucosyltransferase encoded by human FUT4 gene and does not resemble the product of the FUT5 gene. Although FUT1 is expressed in the COS cell mRNA, it has not been possible to demonstrate alpha1,2-fucosyltransferase activity in cell extracts but the presence of Le(y) and blood-group A antigenic determinants on the cell surface imply the formation of H-precursor structures at some stage. The most strongly expressed fucosyltransferase in the COS cells is the alpha1,6-enzyme transferring fucose to the innermost N -acetylglucosamine unit in N -glycan chains; this enzyme is similar in its properties to the product of the human FUT8 gene. The enzymes resembling the human FUT4 and FUT8 gene products both had pH optima of 7.0 and were resistant to 10 mM NEM. The incorporation of fucose into asialo-fetuin was optimal at 5.5 and was inhibited by 10 mM NEM. This result initially suggested the presence of a third fucosyltransferase expressed in the COS cells but we have now shown that triantennary N- glycans with terminal nonreducing galactose units, similar to those present in asialo-fetuin, are modified by a weak endogenous beta-galactosidase in the COS cell extracts and thereby rendered suitable substrates for the alpha1,6-fucosyltransferase.

Antiprotozoal properties of 16,17-dihydrobrachycalyxolide from Vernonia brachycalyx

Extracts of the leaves from Vernonia brachycalyx showed in vitro activity against Plasmodium falciparum and promastigotes of Leishmania major. The germacrane dilactone 16,17-dihydrobrachycalyxolide (1) which was previously isolated from the aerial parts of the plant was shown to be the major antiplasmodial principle. An X-ray crystallographic analysis established the absolute configuration and some signals in the NMR spectra were reassigned. 16,17-Dihydrobrachycalyxolide (1) elicited a strong antiplasmodial and antileishmanial activity but also a high toxicity against human lymphocytes.

Differential binding of human blood group Sd(a+) and Sd(a-) Tamm-Horsfall glycoproteins with Dolichos biflorus and Vicia villosa-B4 agglutinins

The binding patterns of human blood group Sd(a+) and Sd(a-) Tamm-Horsfall glycoproteins (THGPs) with respect to four GalNAc specific agglutinins were studied by quantitative precipitin assay (QPA) and enzyme linked lectinosorbent assay (ELLSA). Of the native and asialo Sd(a+) and Sd(a-) THGP tested by QPA and ELLSA, only native and asialo Sd(a+) bound well with Dolichos biflorus (DBA) and Vicia villosa-B4 (VVA-B4), while Sd(a-) THGP reacted poorly with these two lectins. Neither Sd(a+) nor Sd(a-) THGPs reacted with two other GalNAc alpha-anomer specific lectins: Codium fragile subspecies tomentosoides and Artocarpus integrifolia. Furthermore, the binding of asialo Sd(a+)THGP-VVA-B4 and native Sd(a+)THGP-DBA through GalNAc beta--> was confirmed by inhibition assay. These results demonstrate that DBA and VVA-B4 are useful reagents to differentiate between Sd(a+) and Sd(a-) THGP.

Kenyan Plasmodium falciparum field isolates: correlation between pyrimethamine and chlorcycloguanil activity in vitro and point mutations in the dihydrofolate reductase domain

Sixty-nine Kenyan Plasmodium falciparum field isolates were tested in vitro against pyrimethamine (PM), chlorcycloguanil (CCG), sulfadoxine (SD), and dapsone (DDS), and their dihydrofolate reductase (DHFR) genotypes were determined. The in vitro data show that CCG is more potent than PM and that DDS is more potent than SD. DHFR genotype is correlated with PM and CCG drug response. Isolates can be classified into three distinct groups based on their 50% inhibitory concentrations (IC50s) for PM and CCG (P < 0.01) and their DHFR genotypes. The first group consists of wild-type isolates with mean PM and CCG IC50s of 3.71 +/- 6.94 and 0.24 +/- 0.21 nM, respectively. The second group includes parasites which all have mutations at codon 108 alone or also at codons 51 or 59 and represents one homogeneous group for which 25- and 6-fold increases in PM and CCG IC50s, respectively, are observed. Parasites with mutations at codons 108, 51, and 59 (triple mutants) form a third distinct group for which nine- and eightfold increases in IC50s, respectively, of PM and CCG compared to the second group are observed. Surprisingly, there is a significant decrease (P < 0.01) of SD and DDS susceptibility in these triple mutants. Our data show that more than 92% of Kenyan field isolates have undergone at least one point mutation associated with a decrease in PM activity. These findings are of great concern because they may indicate imminent PM-SD failure, and there is no affordable antimalarial drug to replace PM-SD (Fansidar).

The efficacy of antifolate antimalarial combinations in Africa: a predictive model based on pharmacodynamic and pharmacokinetic analyses

At present, effective treatment for non-severe malaria is the most important malaria control strategy in Africa. Pyrimethamine-sulfadoxine (PSD) is rapidly becoming the first-line treatment in areas of chloroquine resistance, although the parasite chemoresistance factors that dispose towards clinical failure with PSD are still unclear. Here, Bill Watkins and colleagues analyse the relationship between the pharmacokinetic properties of two treatment combinations (PSD and chlorproguanil-dapsone) in vivo and the respective in vitro isobolograms for parasites with specific drug-resistance patterns. From this relationship, they develop a hypothesis that may explain clinical drug failure and differential efficacy between treatments. The deductions can be tested in field studies to validate or refute the model.

Mutations in Plasmodium falciparum dihydrofolate reductase and dihydropteroate synthase and epidemiologic patterns of pyrimethamine-sulfadoxine use and resistance

To assess the relationship between mutations in Plasmodium falciparum dihydrofolate reductase (DHFR) and dihydropteroate synthase (DHPS) and clinical pyrimethamine-sulfadoxine resistance, polymerase chain reaction surveys and analyses for new mutations were conducted in four countries with increasing levels of pyrimethamine-sulfadoxine resistance: Mali, Kenya, Malawi, and Bolivia. Prevalence of mutations at DHFR codon 108 and a new mutation at DHPS 540 correlated with increased pyrimethamine-sulfadoxine resistance (P < .05). Mutations at DHFR 51, DHFR 59, and DHPS 437 correlated with resistance without achieving statistical significance. Mutations at DHFR 164 and DHPS 581 were common in Bolivia, where pyrimethamine-sulfadoxine resistance is widespread, but absent in African sites. Two new DHFR mutations, a point mutation at codon 50 and an insert at codon 30, were found only in Bolivia. DHFR and DHPS mutations occur in a progressive, stepwise fashion. Identification of specific sets of mutations causing in vivo drug failure may lead to the development of molecular surveillance methods for pyrimethamine-sulfadoxine resistance.

Resistance to antifolates in Plasmodium falciparum monitored by sequence analysis of dihydropteroate synthetase and dihydrofolate reductase alleles in a large number of field samples of diverse origins

Resistance of Plasmodium falciparum to antifolate chemotherapy is a significant problem where combinations such as Fansidar (pyrimethamine-sulfadoxine; PYR-SDX) are used in the treatment of chloroquine-resistant malaria. Antifolate resistance has been associated with variant sequences of dihydrofolate reductase (DHFR) and dihydropteroate synthetase (DHPS), the targets of PYR and SDX respectively. However, while the nature and distribution of mutations in the dhfr gene are well established, this is not yet the case for dhps. We have thus examined by DNA sequence analysis 141 field samples from several geographical regions with differing Fansidar usage (West and East Africa, the Middle East and Viet Nam) to establish a database of the frequency and repertoire of dhps mutations, which were found in 60% of the samples. We have also simultaneously determined from all samples their dhfr sequences, to better understand the relationship of both types of mutation to Fansidar resistance. Whilst the distribution of mutations was quite different across the regions surveyed, it broadly mirrored our understanding of relative Fansidar usage. In samples taken from individual patients before and after drug treatment, we found an association between the more highly mutated forms of dhps and/or dhfr and parasites that were not cleared by antifolate therapy. We also report a novel mutation in a Pakistani sample at position 16 of DHFR (A16S) that is combined with the familiar C59R mutation, but is wild-type at position 108. This is the first observation in a field sample of a mutant dhfr allele where the 108 codon is unchanged.

Chlorproguanil-dapsone: effective treatment for uncomplicated falciparum malaria

Pyrimethamine-sulfadoxine, the first choice for uncomplicated falciparum malaria in Africa, exerts strong selection pressure for resistance because of its slow elimination. It is likely that resistance will emerge rapidly, and there is no widely affordable replacement. Chlorproguanil-dapsone is cheap, rapidly eliminated, more potent than pyrimethamine-sulfadoxine, and could be introduced in the near future to delay the onset of antifolate resistance and as "salvage therapy" for pyrimethamine-sulfadoxine failure. A total of 448 children were randomly allocated (double blind) to either a single dose of pyrimethamine-sulfadoxine or to one of two chlorproguanil-dapsone regimens: a single dose or three doses at 24-h intervals. Reinfections are clinically indistinguishable from recrudescence and are more likely after treatment with rapidly eliminated drugs; we measured the incidence of parasitemia in 205 initially aparasitemic children to allow comparison with the three treatment groups. The patients and a community surveillance group were followed up for 28 days. At the study end point, 31.2% (95% confidence interval, 24.9-38.0) of the community surveillance group subjects were parasitemic, compared with subjects in the treatment groups, whose rates of parasitemia were 40.8% (32.9-49.0; relative risk [RR], 1.31 [0.99-1.73]) after triple-dose chlorproguanil-dapsone, 19.7% (13.5-27.2; RR, 0.63 [0.43-0.93]) after pyrimethamine-sulfadoxine, and 65.6% (57.5-73.0; RR, 2.10 [1.66-2.65]) after single-dose chlorproguanil-dapsone. Pyrimethamine-sulfadoxine and triple-dose chlorproguanil-dapsone were effective treatments. Pyrimethamine-sulfadoxine provided chemoprophylaxis during follow-up because of its slow elimination. Triple-dose chlorproguanil-dapsone should now be developed in an attempt to reduce the rate of emergence of antifolate resistance in Africa and for affordable salvage therapy in cases of pyrimethamine-sulfadoxine failure.

Independent regulation of Fuc-TIV and Fuc-TVII genes leading to modulation of cell surface antigen expression in developing myeloid cells

Fucosylated antigen expression, fucosyltransferase activities and expression of Fuc-TIV and Fuc-TVII genes have been measured in the human leukemic cell lines KG1a, arrested at the undifferentiated myeloblast stage of maturation and KG1, arrested at the myeloblast and early promyelocytic stage. The results are compared with those we earlier found for the later promyelocytic cell line HL-60 and the myelocyte form into which HL-60 cells can be induced to differentiate. These leukemic cell lines, and the differentiated HL-60 cells, are believed to correspond to four successive stages of myeloid maturation in the bone marrow. Fuc-TVII mRNA was strongly expressed in the myeloblastic KG1a cells but expression was less in KG1 and HL-60 cells. In contrast to the sharp fall in Fuc-TIV expression observed on differentiation of HL-60 cells, the expression of Fuc-TIV mRNA showed a progressive increase from KG1a to HL-60 cells; thus the peak of expression of this gene was at the HL-60 promyelocyte stage. This peak correlated with an increase in fucosyltransferase activity with nonsialylated acceptors and the transitory downregulation of cell surface sialyl-Le(x) expression and upregulation of Le(x), VIM-2 and Le(y) expression. The variations in levels of expression of the fucosylated antigens on the surface of the developing myeloid cells therefore correlate with variations in mRNA expression arising from the independent regulation of Fuc-TIV and Fuc-TVII genes.

Three different endogenous alpha-L-fucosyltransferases expressed in COS cells

The monkey kidney COS cell line is frequently used for the transient expression of cloned human fucosyltransferase cDNAs in the belief that negligible endogenous expression of fucosyltransferase genes occurs in these cells. In the course of transfection experiments we observed weak cell surface expression of sialyl-Lex and weak fucosyltransferase activity in extracts of control untransfected cells. Since these activities could complicate interpretation of the results with the transfected genes, a more detailed examination was undertaken that has now revealed expression of three different fucosyltransferases in the cells. One enzyme, which utilises N-acetyllactosamine as substrate, has a pH optimum of 7.0, is resistant to heat inactivation, and has been tentatively identified as an alpha1,3-fucosyltransferase. A second enzyme which acts on asialo-fetuin has a pH optimum of 5.5 and is rapidly inactivated by heat; the acceptor sugar and positional linkage of the transferred fucose are not yet established. A third enzyme that utilises asialo-agalacto-fetuin as acceptor is provisionally identified as an alpha1,6-fucosyltransferase.

The disposition of intramuscular artemether in children with cerebral malaria; a preliminary study

The disposition of intramuscular artemether (AM) was studied in 26 Kenyan children with cerebral malaria. Antimalarial activity determined by bioassay was compared with total plasma AM plus dihydroartemisinin (DHA) determined by high power liquid chromatography (HPLC). Therapeutic levels were achieved in most subjects (21/26) within 1 h of receiving intramuscular AM (3.2 mg/kg), with close correlation between bioassay and HPLC measurements (r = 0.706). However, there was marked inter-individual variation, antimalarial activity was undetectable in 5 subjects ('non-absorbers'), and plasma concentrations were lower in subject with respiratory distress. The 50% parasite clearance time was significantly longer in non-absorbers (mean = 13.1 h, SD = 10.8 vs. mean = 7.8 h, SD = 5.5; P = 0.013). We conclude that the bioavailability of intramuscular AM in children with severe malaria may be highly variable, particularly in the presence of respiratory distress, and may be associated with an inadequate therapeutic response.

Poor efficacy of antimalarial biguanide-dapsone combinations in the treatment of acute, uncomplicated, falciparum malaria in Thailand

Combinations of dapsone with proguanil or chlorproguanil have proved effective in the treatment of chloroquine-resistant falciparum malaria in Africa and for prophylaxis in Asia. These combinations have not been used for treatment in areas with multi-drug-resistant parasites such as in Thailand. Combinations of dapsone (approximately 4 mg/kg) plus ether proguanil (approximately 8 mg/kg; DP regimen; N = 10) or chlorproguanil (approximately 1.4 mg/kg; DC regimen; N = 16) were given once a day for 3 days to adult Thai patients with acute, uncomplicated, falciparum malaria. The two regimens were well tolerated and had no side-effects, but the cure rates, assessed at 28-day follow-up, were only 10% for DP (60% with RI response and 30% with RII) and 14% for DC (29% with RI response and 57% with RII). The mean (S.D.) fever-clearance times in those patients who were cured (S) or whose infections recrudesced (RI response) were 103 (56) h for those given DP and 90 (42) h for 6 those given DC. The corresponding parasite-clearance times were 83 (46) for DP and 53 (21) h for DC. In-vitro susceptibility testing of isolates obtained both before treatment and at recrudescence demonstrated marked resistance to cycloguanil, dapsone, chloroquine and mefloquine. The results demonstrate that short-course treatment with dapsone plus either proguanil or chlorproguanil is ineffective for the treatment of falciparum malaria in Thailand.

Antimalarial activity in crude extracts of Malawian medicinal plants

Aqueous and organic fractions from Cassia abbreviata, Senna petersiana (both Caesalpiniaceae) and Azanza garckeana (Malvaceae) were tested for in-vitro antimalarial activity against the multi-drug-resistant, Vietnam-Smith strain of Plasmodium falciparum; VI/S. Both roots and leaves from these Malawian medicinal plants were investigated. High activity, with a median inhibitory concentration < 3 micrograms/ml, was seen in the organic fractions of C. abbreviata and S. petersiana, the two species most commonly cited by traditional healers in an ethnobotanical investigation of Malawian antimalarials. Extracts of A. garckeana showed weaker activity. Biologically active compounds have thus been detected within species of the family Caesalpiniaceae. Ethnobotanical investigation appears to be useful in identifying plants with antimalarial activity.

Binding properties of a blood group Le(a+) active sialoglycoprotein, purified from human ovarian cyst, with applied lectins

Studies on the structures and binding properties of the glycoproteins, purified from human ovarian cyst fluids, will aid the understanding of the carbohydrate alterations occurring during the biosynthesis of blood group antigens and neoplasm formation. These glycoproteins can also serve as important biological materials to study blood group A, B, H, Le(a), Le(b), Le(x), Le(y), T and Tn determinants, precursor type I and II sequences and cold agglutinin I and i epitopes. In this study, the binding property of a cyst glycoprotein from a human blood group Le(a+) nonsecretor individual, that contains an unusually high amount (18%) of sialic acid (HOC 350) was characterized by quantitative precipitin assay with a panel of lectins exhibiting a broad range of carbohydrate-binding specificities. Native HOC 350 reacted well only with three out of nineteen lectins tested. It precipitated about 80% of Ricinus communis (RCA1), 50% of Triticum vulgaris (WGA) and 37% of Bauhinia purpurea aba (BPA) agglutinins, respectively. However, its asialo product had dramatically enhanced reactivity and reacted well with many I/II (Gal beta1 --> 3/4GcNAc), T(Gal beta1 --> 3GalNAc) and Tn(GaNIAc alphaI --> Ser/Thr) active lectins. It bound best to Jacalin, BPA, and abrin-a and completely precipitated all the lectins added. Asialo-HOC 350 also reacted strongly with Wistaria floribunda, Abrus precatorius agglutinin, ricin and RCA1 and precipitated over 75% of the lectin nitrogen added, and moderately with Arachis hypogaea, Maclura pomifera, WGA, Vicia viosa-B4, Codium fragile tomentosoides and Ulex europaeus-II. But native HOC 350 and its asialo product reacted not at all or poorly with Dolichos biflorus, Helix pomatia, Lotus tetra-gonolobus, Ulex europaeus-I, Lens culinaris lectins and Con A. The lectin-glycoform interactions through bioactive sugars were confirmed by precipitin inhibition assay. Mapping the precipitation profiles of the interactions have led to the conclusion that HOC 350 contains a large number of receptors for I/II, T, and Tn active lectins. But in the untreated (or native) substance, most of these determinants are masked by sialic acids.

A malariometric survey in Turkana District, Kenya: chemosensitivity in vivo of Plasmodium falciparum infections and identity of the vector

We have carried out a limited survey in vivo of the efficacy of chloroquine (n = 39) and pyrimethamine-sulfadoxine (n = 29) as treatments for falciparum malaria in Kaling, Turkana District, northern Kenya. Both treatments were effective, achieving clinical cure (> 75% reduction in parasitaemia on day 2 with clinical improvement, and negative blood slide on day 7) in both children and adults. A limited entomological survey suggested that the main malaria vector in this area was Anopheles arabiensis.

Interaction of a human blood group Sd(a-) Tamm-Horsfall glycoprotein with applied lectins

Unlike the human blood group Sd(a+) Tamm-Horsfall glycoprotein (THGP), the Sd(a-) one lacks terminal GalNAcbeta1--> residues at the nonreducing ends. The binding properties of this glycoprotein and its asialo product with lectins were characterized by quantitative precipitin (QPA) and precipitin inhibition assays. Among 20 lectins tested by QPA, both native and asialo Sd(a-) THGP reacted best with Abrus precatorius and Ricinus communis and completely precipitated the lectin added. They also precipitated well Wistaria floribunda (WFA), Glycine max (SBA), Bauhinia purpurea alba, abrin-a and ricin, all of which recognize the Galbeta1--> 4GlcNAcbeta1--> sequence, although at different strength. The lectin-glycan interactions were inhibited by Galbeta1--> 4GlcNAc and Galbeta1--> 4Glc. When the precipitability of Sd(a-) THGP was compared with that of the Sd(a+) phenotype, the native Sd(a-) THGP exhibited a 40% lesser affinity for WFA, SBA, WGA and mistletoe lectin-I (ML-I). Mapping the precipitation and inhibition profiles of the present study and the results of THGP Sd(a+), it is concluded that Sd(a-) THGP showed a strongly diminished affinity for GalNAcbeta1--> active lectins (SBA and WFA) than the Sd(a+) phenotype.

Measurement of physiological concentrations of dapsone and its monoacetyl metabolite: a miniaturised assay for liquid or filter paper-absorbed samples

A modification of existing HPLC assay methods is described for the measurement of dapsone and monoacetyldapsone in 50-microliter samples of plasma and whole blood. This method, in particular the use of small sample volumes dried onto filter paper strips, is applicable to multi-sample clinical and pharmacokinetic studies in children with malaria, who are often anaemic, and where sample volume must be kept to a minimum. Basified samples were extracted into 5 ml of ethyl acetate-tert.-butylmethyl ether (1:1, v/v), chromatographed on a mu BondapaK C18, 10-micron column with water-acetonitrile-glacial acetic acid (81:17.5:5, v/v) containing 2 g/l l-octanesulphonic acid as the mobile phase and detected at 274 nm.

Cutaneous hypersensitivity reactions to thiacetazone, HIV infection and thiacetazone concentrations in plasma

We have studied the relationship between the plasma concentration-time profile of thiacetazone over the 24 h between doses [AUC(0.24h)] and the incidence of cutaneous reactions among HIV-infected patients with tuberculosis in Kenya. Cutaneous reactions due to thiacetazone occurred in 4/14 [28.6%] HIV+ve patients compared with 3/47 [6.4%] HIV-ve patients [RR = 4.48, 95% CI-1.1 to 17.7], and all resolved on alternative therapy. Among the HIV+ve patients, those with cutaneous reactions had higher AUC(0.24h) values, although the difference was not significant. These results do not exclude pharmacokinetic change as being at least partly responsible for cutaneous reactions to TCZ in HIV+ve patients, and do not refute an immunological basis for the reaction. With regard to the operational use of TCZ in Africa, there is no indication that a modification of the dose will reduce the frequency of drug reactions.

Potent antimalarial activity of the alkaloid nitidine, isolated from a Kenyan herbal remedy

Bioassay-guided fractionation of extracts of Toddalia asiatica, a plant used by the Pokot tribe of Kenya to treat fevers, has yielded the alkaloid nitidine as the major antimalarial component. Fractions containing nitidine have in vitro 50% inhibitory concentrations against Plasmodium falciparum in the range of 9 to 108 ng/ml for a range of chloroquine-susceptible and -resistant strains. The results show a lack of cross-resistance between chloroquine and nitidine.

Purification, properties and possible gene assignment of an alpha 1,3-fucosyltransferase expressed in human liver

alpha 1,3-Fucosyltransferase solubilized from human liver has been purified 40,000-fold to apparent homogeneity by a multistage process involving cation exchange chromatography on CM-Sephadex, hydrophobic interaction chromatography on Phenyl Sepharose, affinity chromatography on GDP-hexanolamine Sepharose and HPLC gel exclusion chromatography. The final step gave a major protein peak that co-chromatographed with alpha 1,3-fucosyltransferase activity and had a specific activity of approximately 5-6 mumol min-1 mg-1 and an M(r) approximately 44,000 deduced from SDS-PAGE and HPLC analysis. The purified enzyme readily utilized Gal beta 1-4GlcNAc, NeuAc alpha 2-3Gal beta 1-4GlcNAc and Fuc alpha 1-2Gal beta 1-4GlcNAc, with a preference for sialylated and fucosylated Type 2 acceptors. Fuc alpha 1-2Gal beta 1-4Glc and the Type 1 compound Gal beta 1-3GlcNAc were very poor acceptors and no incorporation was observed with NeuAc alpha 2-6Gal beta 1-4GlcNAc. A polyclonal antibody raised against the liver preparation reacted with the homologous enzyme and also with the blood group Lewis gene-associated alpha 1,3/1,4-fucosyltransferase purified from the human A431 epidermoid carcinoma cell line. No cross reactivity was found with alpha 1,3-fucosyltransferase(s) isolated from myeloid cells. Examination by Northern blot analysis of mRNA from normal liver and from the HepG2 cell line, together with a comparison of the specificity pattern of the purified enzyme with that reported for the enzyme expressed in mammalian cells transfected with the Fuc-TVI cDNA, suggests a provisional identification of Fuc-TVI as the major alpha 1,3-fucosyltransferase gene expressed in human liver.