Residual malaria transmission: Magnitude and drivers of persistent Plasmodium infections despite high coverage of control interventions in Burkina Faso, West Africa.

This study collected baseline data on malaria vectors to characterize the drivers and the factors of persistent malaria transmission in two villages in the western part of Burkina Faso. Mosquitoes were collected in each village using the Human landing catch and pyrethrum spray catch and identified using the morphological keys. Molecular analyses were performed for the identification of An. gambiae complex species, the detection of Plasmodium infection and kdr-995F mutation. Anopheles mosquito larvae were also collected in the same villages, reared to adult's stage for the WHO tube and cone tests performing. The physical integrity of the LLINs already used by people in each village was assessed using the proportional hole index (pHI). An. gambiae s.l. was the main malaria vector accounting for 79.82% (5560/6965) of all collected mosquitoes. The biting pattern of An. gambiae s.l. was almost constant during the survey with an early aggressiveness before 8 p.m. and later biting activity after 6 a.m. The EIR varied from 0.13 to 2.55 infected bites per human per night (average: 1.03 infected bites per human per night). An. gambiae s.l. populations were full susceptible to Chlorpyrifos-methyl (0.4%) and Malathion (5%) with high kdr-995F mutation frequencies (>0.8). The physical integrity assessment showed high proportion of good nets in Santidougou compared to those collected in Kimidougou. This study highlighted a persistence of malaria transmission despite the intense use of vector control tools as LLINs and IRS by correlating mosquito biting time and human behavior. It provided a baseline guide for the monitoring of the residual malaria transmission in sub-Saharan Africa and encouraging the development of new alternative strategies to support the current malaria control tools.

Impedimetric nano-collision Escherichia coli analysis based on Silver-Gold bimetallic nanoparticles.

An impedimetric detection of E. coli was developed using chemically synthesised bimetallic Ag-Au (1:2) nanoparticles (NPs). The UV-visible spectra of the NPs had absorption bands at 470 and 580 nm for Ag NPs and Au NPs, respectively. In the presence of E. coli, a negative potential shift and a blue shift was observed in the voltammograms and spectra respectively. The complex formed had an oxidation potential at + 0.95 V. Technique choice was based on sensitivity comparison of Differential pulse voltammetry, cyclic voltammetry and impedance spectroscopy in 0.1 M PBS with Impedance being the best choice. Optimum sensing conditions of the NPs-E. coli complex for NPs concentration, incubation period, method modulation amplitude and applied potential were 5 mM, 20 min, 10 mV and + 0.5 V, respectively. The sensor's linearity range, lower limits of detection and quantification were found to be 101-107, 1.88 × 101, 2.34 × 102 cells/mL, respectively. The sensor's applicability was validated by repeatability, stability and selectivity studies showing minimum changes in signal. Potential usage of the sensor in real samples was demonstrated by standard addition analysis of sea and River water samples as well as recovery of spiked water and fruit juices with acceptable % RSD < 2%.

Using nylon strips to dispense mosquito attractants for sampling the malaria vector Anopheles gambiae s.s.

Synthetic versions of human derived kairomones can be used as baits when trapping host seeking mosquitoes. The effectiveness of these lures depends not only on their attractiveness to the mosquitoes but also on the medium from which they are dispensed. We report on the development and evaluation of nylon strips as a method of dispensing odorants attractive to the malaria vector, Anopheles gambiae s.s. (Giles). When a synthetic blend of attractants was dispensed using this method, significantly more mosquitoes were trapped than when two previous methods, open glass vials or low density polyethylene sachets were used. We conclude that the nylon strips are suitable for dispensing odorants in mosquito trapping operations and can be adopted for use in rural and remote areas. The nylon material required is cheap and widely available and the strips can be prepared without specialized equipment or electricity.

Safety, tolerance, and pharmacokinetic studies of OPT-80 in healthy volunteers following single and multiple oral doses.

Current therapies for Clostridium difficile infection (CDI) are encumbered by treatment failures and recurrences. Due to its high in vitro activity against C. difficile but low activity against the typical intestinal flora, minimal absorption, and durable cure in the hamster model of C. difficile infection, OPT-80 was considered for clinical development as a therapy for CDI. This trial consisted of two phases. Four single oral doses of OPT-80 (100, 200, 300, and 450 mg) were administered in a crossover manner to 16 healthy volunteers in a double-blind, placebo-controlled phase 1A study; a 1- to 2-week washout interval separated the treatments. In the double-blind phase 1B study, 24 healthy subjects were randomized to receive OPT-80 (150, 300, or 450 mg) or placebo for 10 days. In both studies, OPT-80's safety and tolerability were evaluated and the concentrations of OPT-80 and its primary metabolite (OP-1118) in plasma and feces were determined. OPT-80 levels in the urine were also analyzed for the phase 1A study. In both the single-dose and the multiple-dose studies, OPT-80 was well tolerated by all subjects in all dose groups. Maximal plasma concentrations were near or below the limit of quantification (5 ng/ml) across the dose range; urine concentrations were below the detection limit. The fecal total recovery of OPT-80 plus its major metabolite, OP-1118, approximated 100%. The tolerability, high fecal concentration, and low systemic exposure data from these studies support the further clinical development of OPT-80 as an oral therapy for CDI.

Cost-sharing strategies combining targeted public subsidies with private-sector delivery achieve high bednet coverage and reduced malaria transmission in Kilombero Valley, southern Tanzania.

BACKGROUND: Cost-sharing schemes incorporating modest targeted subsidies have promoted insecticide-treated nets (ITNs) for malaria prevention in the Kilombero Valley, southern Tanzania, since 1996. Here we evaluate resulting changes in bednet coverage and malaria transmission. METHODS: Bednets were sold through local agents at fixed prices representing a 34% subsidy relative to full delivery cost. A further targeted subsidy of 15% was provided to vulnerable groups through discount vouchers delivered through antenatal clinics and regular immunizations. Continuous entomological surveys (2,376 trap nights) were conducted from October 2001 to September 2003 in 25 randomly-selected population clusters of a demographic surveillance system which monitored net coverage. RESULTS: Mean net usage of 75% (11,982/16,086) across all age groups was achieved but now-obsolete technologies available at the time resulted in low insecticide treatment rates. Malaria transmission remained intense but was substantially reduced: Compared with an exceptionally high historical mean EIR of 1481, even non-users of nets were protected (EIR [fold reduction] = 349 infectious bites per person per year [x4]), while the average resident (244 [x6]), users of typical nets (210 [x7]) and users of insecticidal nets (105 [x14]) enjoyed increasing benefits. CONCLUSION: Despite low net treatment levels, community-level protection was equivalent to the personal protection of an ITN. Greater gains for net users and non-users are predicted if more expensive long-lasting ITN technologies can be similarly promoted with correspondingly augmented subsidies. Cost sharing strategies represent an important option for national programmes lacking adequate financing to fully subsidize comprehensive ITN coverage.

A slow release formulation of insulin as a treatment for osteoarthritis.

OBJECTIVE: To examine the potential of insulin, in a sustained delivery system, as a treatment for arthritis. DESIGN: The effect of insulin on matrix synthesis, matrix breakdown, and nitric oxide production in primary cartilage explants was examined. The activity of insulin on diseased cartilage from Dunkin Hartley guinea pigs, diabetic mice, and osteoarthritic patients was measured. The specificity of insulin stimulation was compared to that of IGF-I using osteoblasts and fibroblasts. Finally, the stability of insulin in a biologically relevant system was tested, and a slow-release formulation of insulin was developed and characterized. RESULTS: In articular cartilage explants, insulin stimulated proteoglycan (PG) synthesis, inhibited PG release and nitric oxide production, and overcame the detrimental effects of interleukin 1 (IL-1). The mechanism whereby insulin decreased matrix breakdown was through inhibition of aggrecanase activity. Insulin was active on cartilage at concentrations at which insulin does not cross-react with insulin-like growth factor I (IGF-I) receptors nor stimulate proliferation of other cells types. The response of cartilage to insulin did not diminish with age or disease. Insulin stimulated matrix synthesis in osteoarthritic cartilage and local treatment with insulin overcame endogenous suppression of matrix synthesis in diabetic cartilage. Poly-lactic-coglycolic acid (PLGA) was found to be an effective carrier for delivery of insulin, and PLGA-Insulin was active on articular cartilage in vitro and in vivo. CONCLUSIONS: As the incidence of arthritis increases with the aging population, an effective therapy to induce repair of cartilage is needed. Based on its biological activities, insulin appears to be an attractive protein therapeutic candidate. Maximum insulin effectiveness may require a sustained delivery system.

Effect of size and charge on the passive diffusion of peptides across Caco-2 cell monolayers via the paracellular pathway.

PURPOSE: To evaluate the effect of size and charge on the permeation characteristics of peptides across the intestinal mucosa. METHODS: The lipophilicities of neutral, positively and negatively charged capped amino acids (Asn, Lys, Asp), tripeptides (Ac-Gly-X-Ala-NH2; X = Asn, Lys, Asp) and hexapeptides (Ac-Trp-Ala-Gly-Gly-X-Ala-NH2; X = Asn, Lys, Asp) were estimated using an immobilized artificial membrane. The diffusion coefficients used to calculate the molecular radii were measured by NMR. The transport characteristics of the model peptides were determined across Caco-2 cell monolayers. RESULTS: When model compounds having the same charge were compared, permeation was highly size-dependent (capped amino acids > tripeptides > hexapeptides), suggesting transport predominantly via the paracellular route. For example, the flux of the negatively charged Asp amino acid (Papp = 10.04 +/- 0.43 x 10(-8) cm/s) was 3 times greater than that observed for the Asp-containing hexapeptide (Papp = 3.19 +/- 0.27 x 10(-8) cm/s). When model compounds of the same size were compared, permeation across the cell monolayer was charge-dependent (negative < positive < or = neutral). For example, the neutral, Asn-containing tripeptide (Papp = 25.79 +/- 4.86 x 10(-8) cm/s) was substantially more able to permeate the Caco-2 cell monolayer than the negatively charged Asp-containing tripeptide (Papp = 7.95 +/- 1.03 x 10(-8) cm/s) and the positively charged Lys-containing tripeptide (Papp = 9.86 +/- 0.18 x 10(-8) cm/s). The permeability of the cell monolayer to peptides became less sensitive to net charge as the size of the peptides increased. CONCLUSIONS: A positive net charge of hydrophilic peptides enhances their permeation across the intestinal mucosa via the paracellular pathway. With increasing molecular size, molecular sieving of the epithelial barrier dominates the transport of peptides, and the effect of the net charge becomes less significant.

Effect of restricted conformational flexibility on the permeation of model hexapeptides across Caco-2 cell monolayers.

PURPOSE: To determine how restricted conformational flexibility of hexapeptides influences their cellular permeation characteristics. METHODS: Linear (Ac-Trp-Ala-Gly-Gly-X-Ala-NH2; X = Asp, Asn, Lys) and cyclic (cyclo[Trp-Ala-Gly-Gly-X-Ala]; X = Asp, Asn, Lys) hexapeptides were synthesized, and their transport characteristics were assessed using the Caco-2 cell culture model. The lipophilicities of the hexapeptides were determined using an immobilized artificial membrane. Diffusion coefficients used to calculate molecular radii were determined by NMR. Two-dimensional NMR spectroscopy, circular dichroism, and molecular dynamic simulations were used to elucidate the most favorable solution structure of the cyclic Asp-containing peptide. RESULTS: The cyclic hexapeptides used in this study were 2-3 times more able to permeate (e.g., Papp = 9.3 +/- 0.3 x 10(-8) cm/sec, X = Asp) the Caco-2 cell monolayer than were their linear analogs (e.g., Papp = 3.2 +/- 0.3 x 10(-8) cm/sec, X = Asp). In contrast to the linear hexapeptides, the flux of the cyclic hexapeptides was independent of charge. The cyclic hexapeptides were shown to be more lipophilic than the linear hexapeptides as determined by their retention times on an immobilized phospholipid column. Determination of molecular radii by two different techniques suggests little or no difference in size between the linear and cyclic hexapeptides. Spectroscopic data indicate that the Asp-containing linear hexapeptide exists in a dynamic equilibrium between random coil and beta-turn structures while the cyclic Asp-containing hexapeptide exists in a well-defined compact amphophilic structure containing two beta-turns. CONCLUSIONS: Cyclization of the linear hexapeptides increased their lipophilicities. The increased permeation characteristics of the cyclic hexapeptides as compared to their linear analogs appears to be due to an increase in their flux via the transcellular route because of these increased lipophilicities. Structural analyses of the cyclic Asp-containing hexapeptide suggest that its well-defined solution structure and, specifically the existence of two beta-turns, explain its greater lipophilicity.

Esterase-sensitive cyclic prodrugs of peptides: evaluation of an acyloxyalkoxy promoiety in a model hexapeptide.

PURPOSE: To evaluate a cyclic acyloxyalkoxycarbamate prodrug of a model hexapeptide (H-Trp-Ala-Gly-Gly-Asp-Ala-OH) as a novel approach to enhance the membrane permeation of the peptide and stabilize it to metabolism. METHODS: Conversion to the linear hexapeptide was studied at 37 degrees C in aqueous buffered solutions and in various biological milieus having measurable esterase activities. Transport and metabolism characteristics were assessed using the Caco-2 cell culture model. RESULTS: In buffered solutions the cyclic prodrug degraded chemically to the linear hexapeptide in stoichiometric amounts. Maximum stability was observed between pH 3-4. In 90% human plasma (t1/2 = 100 +/- 4 min) and in homogenates of the rat intestinal mucosa (t1/2 = 136 +/- 4 min) and rat liver (t1/2 = 65 +/- 3 min), the cyclic prodrug disappeared faster than in buffered solution, pH 7.4 (t1/2 = 206 +/- 11 min). Pretreatment of these media with paraoxon significantly decreased the degradation rate of the prodrug. When applied to the apical side of Caco-2 cell monolayers, the cyclic prodrug (t1/2 = 282 +/- 25 min) was significantly more stable than the hexapeptide (t1/2 = 14 min) and at least 76-fold more able to permeate (Papp = 1.30 +/- 0.15 x 10(-7) cm/s) than the parent peptide (Papp < or = 0.17 x 10(-8) cm/s). CONCLUSIONS: Preparation of a cyclic peptide using an acyloxyalkoxy promoiety reduced the lability of the peptide to peptidase metabolism and substantially increased its permeation through biological membranes. In various biological media the parent peptide was released from the prodrug by an apparent esterase-catalyzed reaction, sensitive to paraoxon inhibition.