9 results
Search Results
Now showing 1 - 9 of 9
Publication Open Access The threat of antimalarial drug resistance(2016) Borimas Hanboonkunupakarn; White, Nicholas J.; Mahidol University. Faculty of Tropical Medicine. Department of Clinical Tropical MedicineThe battle between man and malaria has continued for thousands of years. Antimalarial drugs are essential weapons to fight the disease, but their efficacy is threatened by drug resistance which continues to emerge creating a major obstacle to malaria control and jeopardizing renewed hopes for elimination. As 2016 is the first year under WHO Global Technical Strategy for Malaria 2016–2030, it is a good time to ponder the progress of both sides and plan for the future.Publication Open Access Protein-based signatures of functional evolution in Plasmodium falciparum(2011-09-14) Gardner, Kate B.; Sinha, Ipsita; Bustamante, Leyla Y.; Day, Nicholas P.J.; White, Nicholas J.; Woodrow, Charles J.; Woodrow, Charles J.; Mahidol University. Faculty of Tropical Medicine. Wellcome Trust Mahidol University-Oxford Tropical Medicine Research Unit (MORU).fixed differences within the hominid malaria clade indicating near complete release from purifying selection (dN/dS ratio at residues non-aligning across genus: 0.64, dN/dS ratio at residues identical across genus: 0.03). Regions of low conservation also... mutations associated with laboratory-selected drug resistance, such as those in PfATPase4 selected by spiroindolone, were similarly restricted while mutations in another calcium ATPase (PfSERCA, a gene proposed to mediate artemisinin resistance) that reachPublication Open Access Population genetic analysis of Plasmodium falciparum parasites using a customized Illumina GoldenGate genotyping assay.(2011) Campino, Susana; Auburn, Sarah; Kivinen, Katja; Zongo, Issaka; Ouedraogo, Jean-Bosco; Mangano, Valentina; Djimde, Abdoulaye; Doumbo, Ogobara K.; Kiara, Steven M.; Nzila, Alexis; Borrmann, Steffen; Marsh, Kevin; Michon, Pascal; Mueller, Ivo; Siba, Peter; Jiang, Hongying; Su, Xin-Zhuan; Chanaki Amaratunga; Socheat, Duong; Fairhurst, Rick M.; Mallika Imwong; มัลลิกา อิ่มวงศ์; Anderson, Timothy; Nosten, Francois; White, Nicholas J.; Gwilliam, Rhian; Deloukas, Panos; MacInnis, Bronwyn; Newbold, Christopher I.; Rockett, Kirk; Clark, Taane G.; Kwiatkowski, Dominic P.; Campino, Susana; Fitzgerald, J. Ross; Mahidol University. Faculty of Tropical Medicine. Mahidol-Oxford University Research Unit.; Mahidol University. Faculty of Tropical Medicine. Department of Clinical Tropical Medicine.; Mahidol University. Faculty of Tropical Medicine. Department of Molecular Tropical Medicine and Genetics.The diversity in the Plasmodium falciparum genome can be used to explore parasite population dynamics, with practical applications to malaria control. The ability to identify the geographic origin and trace the migratory patterns of parasites with clinically important phenotypes such as drug resistance is particularly relevant. With increasing single-nucleotide polymorphism (SNP) discovery from ongoing Plasmodium genome sequencing projects, a demand for high SNP and sample throughput genotyping platforms for large-scale population genetic studies is required. Low parasitaemias and multiple clone infections present a number of challenges to genotyping P. falciparum. We addressed some of these issues using a custom 384-SNP Illumina GoldenGate assay on P. falciparum DNA from laboratory clones (long-term cultured adapted parasite clones), short-term cultured parasite isolates and clinical (non-cultured isolates) samples from East and West Africa, Southeast Asia and Oceania. Eighty percent of the SNPs (n = 306) produced reliable genotype calls on samples containing as little as 2 ng of total genomic DNA and on whole genome amplified DNA. Analysis of artificial mixtures of laboratory clones demonstrated high genotype calling specificity and moderate sensitivity to call minor frequency alleles. Clear resolution of geographically distinct populations was demonstrated using Principal Components Analysis (PCA), and global patterns of population genetic diversity were consistent with previous reports. These results validate the utility of the platform in performing population genetic studies of P. falciparum.Publication Open Access Rationale for recommending a lower dose of primaquine as a Plasmodium falciparum gametocytocide in populations where G6PD deficiency is common(2012) White, Nicholas J; Guo Qiao, Li; Qi, Gao; Luzzatto, Lucio; Mahidol University. Faculty of Tropical Medicine. Tropical Medicine Research UnitIn areas of low malaria transmission, it is currently recommended that a single dose of primaquine (0.75 mg base/kg; 45 mg adult dose) be added to artemisinin combination treatment (ACT) in acute falciparum malaria to block malaria transmission. Review of studies of transmission-blocking activity based on the infectivity of patients or volunteers to anopheline mosquitoes, and of haemolytic toxicity in glucose 6-dehydrogenase (G6PD) deficient subjects, suggests that a lower primaquine dose (0.25 mg base/kg) would be safer and equally effective. This lower dose could be deployed together with ACTs without G6PD testing wherever use of a specific gametocytocide is indicated.Publication Open Access Assessment of the pharmacokinetics and dynamics of two combination regimens of fosmidomycin-clindamycin in patients with acute uncomplicated falciparum malaria(2008-10-31) Ronnatrai Ruangweerayut; รณไตร เรืองวีรยุทธ; Sornchai Looareesuwan; ศรชัย หลูอารีย์สุวรรณ; Hutchinson, David; Anurak Chauemung; Vick Banmairuroi; Kesara Na-Bangchang; Kesara Na-Bangchang; Mahidol University. Faculty of Tropical Diseases. Hospital for Tropical DiseasesBACKGROUND: This study investigated the pharmacokinetics of fosmidomycin when given in combination with clindamycin at two dosage regimens in patients with acute uncomplicated falciparum malaria. METHODS: A total of 70 patients with acute uncomplicated Plasmodium falciparum malaria who fulfilled the enrolment criteria were recruited in the pharmacokinetic study. Patients were treated with two different dosage regimens of fosmidomycin in combination with clindamycin as follows:Group I: fosmidomycin (900 mg) and clindamycin (300 mg) every 6 hours for 3 days (n = 25); and Group II: fosmidomycin (1,800 mg) and clindamycin (600 mg) every 12 hours for 3 days (n = 54). RESULTS: Both regimens were well tolerated with no serious adverse events. The 28-day cure rates for Group I and Group II were 91.3 and 89.7%, respectively. Steady-state plasma concentrations of fosmidomycin and clindamycin were attained at about 24 hr after the first dose. The pharmacokinetics of both fosmidomycin and clindamycin analysed by model-independent and model-dependent approaches were generally in broad agreement. There were marked differences in the pharmacokinetic profiles of fosmidomycin and clindamycin when given as two different combination regimens. In general, most of the dose-dependent pharmacokinetic parameters (model-independent C(max): 3.74 vs 2.41 microg/ml; C(max-ss): 2.80 vs 2.08 microg/ml; C(max-min-ss): 2.03 vs 0.71 microg/ml; AUC: 23.31 vs 10.63 microg.hr/ml (median values) were significantly higher in patients who received the high dose regimen (Group II). However, C(min-ss) was lower in this group (0.80 vs 1.37 microg/ml), resulting in significantly higher fluctuations in the plasma concentrations of both fosmidomycin and clindamycin following multiple dosing (110.0 vs 41.9%). Other pharmacokinetic parameters, notably total clearance (CL/F), apparent volume of distribution (V/F, V(z)/F) and elimination half-life (t(1/2z), t(1/2e)) were also significantly different between the two dosage regimens. In addition, the dose-dependent pharmacokinetics of both fosmidomycin and clindamycin tended to be lower in patients with recrudescence responses in both groups. CONCLUSION: The findings may suggest that dosing frequency and duration have a significant impact on outcome. The combination of fosmidomycin (900 mg) and clindamycin (300-600 mg) administered every six hours for a minimum of five days would constitute the lowest dose regimen with the shortest duration of treatment and which could result in a cure rate greater than 95%.Publication Open Access Elimination of Plasmodium falciparum in an area of multi‑drug resistance(2015) Lwin, Khin Maung; Mallika Imwong; Preyanan Suangkanarat; Atthanee Jeeyapant; Benchawan Vihokhern; Klanarong Wongsaen; Georges Snounou; Lilly Keereecharoen; White, Nicholas J; Francois Nosten; Mahidol University. Faculty of Tropical Medicine. Mahidol-Oxford Tropical Medicine Research UnitBackground: Resistance to the artemisinin derivatives in Plasmodium falciparum has emerged in Cambodia and is now spreading throughout South-East Asia. The rapid elimination of P. falciparum seems to be the only viable option to avoid a public health disaster but this is difficult because even in low transmission settings many residents have asymptomatic parasitaemias. Methods: In response to a large number of malaria cases reported in three remote villages on the Thai-Myanmar border where malaria is endemic and the disease is seasonal, surveys were conducted using an ultra-sensitive qPCR assay (LOD 22 parasites per mL). In one of the villages where it was feasible, mass anti-malarial drug administration was proposed to the population as a potential solution, and this was adopted. Results: In the three villages 204/356 (57.3 %), 212/385 (55.1 %) and 195/286 (68.2 %) of the resident populations were positive by qPCR (approximately one-third P. falciparum and two-thirds P. vivax). Of those positive for P. falciparum 62 % carried single point mutations in the P. falciparum kelch protein (a marker of artemisinin resistance). In one of the villages 217 of 674 inhabitants received at least one dose of dihydroartemisinin-piperaquine chemoprevention in June 2012, 155 (71.4 %) received two consecutive months, and 98 (45.2 %) received three treatment doses. The chemoprevention was generally well tolerated. The sub-microscopic reservoir of P. falciparum malaria was eliminated during the six-month follow-up period (prevalence fell from 7 to 0 %); P. vivax malaria persisted (prevalence fell from 35 to 8 %). From June to October 2012 (rainy season) the number of clinical episodes of P. falciparum was six times lower (46), than during the same period in the previous year (290). Conclusion: Mass drug administration with dihydroartemisinin-piperaquine may be an effective strategy to eliminate P. falciparum rapidly where multi-drug resistance is present.Publication Open Access Long-term storage limits PCR-based analyses of malaria parasites in archival dried blood spots(2012-10) Hwang, Joyce; Juthamas Jaroensuk; Leimanis, Mara L.; Russell, Bruce; McGready, Rose; Day, Nicholas; Snounou, George; Nosten, Francois; Mallika Imwong; มัลลิกา อิ่มวงศ์; Snounou, George; Mahidol University. Faculty of Tropical Medicine. Department of Molecular Tropical Medicine and GeneticsBACKGROUND: Blood samples collected in epidemiological and clinical investigations and then stored, often at room temperature, as blood spots dried on a filter paper have become one of the most popular source of material for further molecular analyses of malaria parasites. The dried blood spots are often archived so that they can be used for further retrospective investigations of parasite prevalence, or as new genetic markers come to the fore. However, the suitability of the template obtained from dried blood spots that have been stored for long periods for DNA amplification is not known. METHODS: DNA from 267 archived blood spots collected over a period of 12 years from persons with microscopically confirmed Plasmodium falciparum infection was purified by one of two methods, Chelex and Qiagen columns. These templates were subjected to highly sensitive nested PCR amplification targeting three parasite loci that differ in length and/or copy number. RESULTS: When a 1.6 kb fragment of the parasites' small subunit ribosomal RNA was targeted (primary amplification), the efficiency of P. falciparum detection decreased in samples archived for more than six years, reaching very low levels for those stored for more than 10 years. Positive amplification was generally obtained more often with Qiagen-extracted templates. P. falciparum could be detected in 32 of the 40 negative Qiagen-extracted templates when a microsatellite of about 180 bp was targeted. The remaining eight samples gave a positive amplification when a small region of 238 bp of the higher copy number (20 to 200) mitochondrial genome was targeted. CONCLUSIONS: The average length of DNA fragments that can be recovered from dried blood spots decreases with storage time. Recovery of the DNA is somewhat improved, especially in older samples, by the use of a commercial DNA purification column, but targets larger than 1.5 kb are unlikely to be present 10 years after the initial blood collection, when the average length of the DNA fragments present is likely to be around a few hundred bp. In conclusion, the utility of archived dried blood spots for molecular analyses decreases with storage time.Publication Open Access Population pharmacokinetics of Artemether and dihydroartemisinin in pregnant women with uncomplicated Plasmodium falciparum malaria in Uganda.(2012-08-22) Tarning, Joel; Kloprogge, Frank; Piola, Patrice; Dhorda, Mehul; Muwanga, Sulaiman; Turyakira, Eleanor; Nitra Nuengchamnong; นิทรา เนื่องจำนงค์; Nosten, François; Day, Nicholas P.J.; White, Nicholas J.; Guerin, Philippe J.; Lindegardh, Niklas; Tarning, Joel; Mahidol University. Faculty of Tropical Medicine. Mahidol-Oxford Tropical Medicine Research Unit.BACKGROUND: Malaria in pregnancy increases the risk of maternal anemia, abortion and low birth weight. Approximately 85.3 million pregnancies occur annually in areas with Plasmodium falciparum transmission. Pregnancy has been reported to alter the pharmacokinetic properties of many anti-malarial drugs. Reduced drug exposure increases the risk of treatment failure. The objective of this study was to evaluate the population pharmacokinetic properties of artemether and its active metabolite dihydroartemisinin in pregnant women with uncomplicated P. falciparum malaria in Uganda. METHODS: Twenty-one women with uncomplicated P. falciparum malaria in the second and third trimesters of pregnancy received the fixed oral combination of 80 mg artemether and 480 mg lumefantrine twice daily for three days. Artemether and dihydroartemisinin plasma concentrations after the last dose administration were quantified using liquid chromatography coupled to tandem mass-spectroscopy. A simultaneous drug-metabolite population pharmacokinetic model for artemether and dihydroartemisinin was developed taking into account different disposition, absorption, error and covariate models. A separate modeling approach and a non-compartmental analysis (NCA) were also performed to enable a comparison with literature values and different modeling strategies. RESULTS: The treatment was well tolerated and there were no cases of recurrent malaria. A flexible absorption model with sequential zero-order and transit-compartment absorption followed by a simultaneous one-compartment disposition model for both artemether and dihydroartemisinin provided the best fit to the data. Artemether and dihydroartemisinin exposure was lower than that reported in non-pregnant populations. An approximately four-fold higher apparent volume of distribution for dihydroartemisinin was obtained by non-compartmental analysis and separate modeling compared to that from simultaneous modeling of the drug and metabolite. This highlights a potential pitfall when analyzing drug/metabolite data with traditional approaches. CONCLUSION: The population pharmacokinetic properties of artemether and dihydroartemisinin, in pregnant women with uncomplicated P. falciparum malaria in Uganda, were described satisfactorily by a simultaneous drug-metabolite model without covariates. Concentrations of artemether and its metabolite dihydroartemisinin were relatively low in pregnancy compared to literature data. However, this should be interpreted with caution considered the limited literature available. Further studies in larger series are urgently needed for this vulnerable group.Publication Open Access Biochemical and functional characterization of Plasmodium falciparum DNA polymerase δ(2016) Jitlada Vasuvat; Atcha Montree; Sangduen Moonsom; Ubolsree Leartsakulpanich; Songsak Petmitr; Federico Focher; Wright, George E.; Porntip Chavalitshewinkoon‑Petmitr; Mahidol University. Faculty of Tropical Medicine. Department of ProtozoologyBackground: Emergence of drug-resistant Plasmodium falciparum has created an urgent need for new drug targets. DNA polymerase δ is an essential enzyme required for chromosomal DNA replication and repair, and therefore may be a potential target for anti-malarial drug development. However, little is known of the characteristics and function of this P. falciparum enzyme. Methods: The coding sequences of DNA polymerase δ catalytic subunit (PfPolδ-cat), DNA polymerase δ small subunit (PfPolδS) and proliferating cell nuclear antigen (PfPCNA) from chloroquine- and pyrimethamine-resistant P. falciparum strain K1 were amplified, cloned into an expression vector and expressed in Escherichia coli. The recombinant proteins were analysed by SDS-PAGE and identified by LC–MS/MS. PfPolδ-cat was biochemically characterized. The roles of PfPolδS and PfPCNA in PfPolδ-cat function were investigated. In addition, inhibitory effects of 11 compounds were tested on PfPolδ-cat activity and on in vitro parasite growth using SYBR Green I assay. Results: The purified recombinant protein PfPolδ-cat, PfPolδS and PfPCNA showed on SDS-PAGE the expected size of 143, 57 and 34 kDa, respectively. Predicted amino acid sequence of the PfPolδ-cat and PfPolδS had 59.2 and 24.7 % similarity respectively to that of the human counterpart. The PfPolδ-cat possessed both DNA polymerase and 3′–5′ exonuclease activities. It used both Mg2+ and Mn2+ as cofactors and was inhibited by high KCl salt (>200 mM). PfPolδS stimulated PfPolδ-cat activity threefolds and up to fourfolds when PfPCNA was included in the assay. Only two compounds were potent inhibitors of PfPolδ-cat, namely, butylphenyl-dGTP (BuPdGTP; IC50 of 38 μM) and 7-acetoxypentyl-( 3, 4 dichlorobenzyl) guanine (7-acetoxypentyl-DCBG; IC50 of 55 μM). The latter compound showed higher inhibition on parasite growth (IC50 of 4.1 μM). Conclusions: Recombinant PfPolδ-cat, PfPolδS and PfPCNA were successfully expressed and purified. PfPolS and PfPCNA increased DNA polymerase activity of PfPolδ-cat. The high sensitivity of PfPolδ to BuPdGTP can be used to differentiate parasite enzyme from mammalian and human counterparts. Interestingly, 7-acetoxypentyl-DCBG showed inhibitory effects on both enzyme activity and parasite growth. Thus, 7-acetoxypentyl-DCBG is a potential candidate for future development of a new class of anti-malarial agents targeting parasite replicative DNA polymerase.