Anti-malarial market and policy surveys in sub-Saharan Africa

Background

Malaria microscopy and rapid diagnostic tests are insensitive for very low-density parasitaemia. This insensitivity may lead to missed asymptomatic sub-microscopic parasitaemia, a potential reservoir for infection. Similarly, mixed infections and interactions between Plasmodium species may be missed. The objectives were first to develop a rapid and sensitive PCR-based diagnostic method to detect low parasitaemia and mixed infections, and then to investigate the epidemiological importance of sub-microscopic and mixed infections in Rattanakiri Province, Cambodia.

Methods

A new malaria diagnostic method, using restriction fragment length polymorphism analysis of the cytochrome b genes of the four human Plasmodium species and denaturing high performance liquid chromatography, has been developed. The results of this RFLP-dHPLC method have been compared to 1) traditional nested PCR amplification of the 18S rRNA gene, 2) sequencing of the amplified fragments of the cytochrome b gene and 3) microscopy. Blood spots on filter paper and Giemsa-stained blood thick smears collected in 2001 from 1,356 inhabitants of eight villages of Rattanakiri Province have been analysed by the RFLP-dHPLC method and microscopy to assess the prevalence of sub-microscopic and mixed infections.

Results

The sensitivity and specificity of the new RFLP-dHPLC was similar to that of the other molecular methods. The RFLP-dHPLC method was more sensitive and specific than microscopy, particularly for detecting low-level parasitaemia and mixed infections. In Rattanakiri Province, the prevalences of Plasmodium falciparum and Plasmodium vivax were approximately two-fold and three-fold higher, respectively, by RFLP-dHPLC (59% and 15%, respectively) than by microscopy (28% and 5%, respectively). In addition, Plasmodium ovale and Plasmodium malariae were never detected by microscopy, while they were detected by RFLP-dHPLC, in 11.2% and 1.3% of the blood samples, respectively. Moreover, the proportion of mixed infections detected by RFLP-dHPLC was higher (23%) than with microscopy (8%).

Conclusions

The rapid and sensitive molecular diagnosis method developed here could be considered for mass screening and ACT treatment of inhabitants of low-endemicity areas of Southeast Asia.     

Anti-malarial market and policy surveys in sub-Saharan Africa

At a recent meeting (Sept 18, 2009) in which reasons for the limited access to artemisinin-based combination therapy (ACT) in sub-Saharan Africa were discussed, policy and market surveys on anti-malarial drug availability and accessibility in Burundi and Sierra Leone were presented in a highly interactive brainstorming session among key stakeholders across private, public, and not-for-profit sectors. The surveys, the conduct of which directly involved the national malaria control programme managers of the two countries, provides the groundwork for evidence-based policy implementation. The results of the surveys could be extrapolated to other countries with similar socio-demographic and malaria profiles. The meeting resulted in recommendations on key actions to be taken at the global, national, and community level for better ACT accessibility.At the global level, both public and private sectors have actions to take to strengthen policies that lead to the replacement of loose blister packs with fixed-dose ACT products, develop strategies to ban inappropriate anti-malarials and regulate those bans, and facilitate technology and knowledge transfer to scale up production of fixed-dose ACT products, which should be readily available and affordable to those patients who are in the greatest need of these medicines.At the national level, policies that regulate the anti-malarial medicines market should be enacted and enforced. The public sector, including funding donors, should participate in ensuring that the private sector is engaged in the ACT implementation process. Research similar to the surveys discussed is important for other countries to develop and evaluate the right incentives at a local level.At the community level, community outreach and education about appropriate preventive and treatment measures must continue and be strengthened, with service delivery systems developed within both public and private sectors, among other measures, to decrease access to ineffective and inappropriate anti-malarial medicines.What was clear during the meeting is that continuing commitment, strengthened interaction and transparency among various stakeholders, with focus on communities, national governments, and evidence-based policy and action are the only way to sustainably address the control of malaria, a disease which continues to have a significant health and socio-economic impact worldwide, particularly in sub-Saharan Africa.Details on the methodology employed in carrying out the studies discussed at this meeting, as well as more detailed results, data analysis and discussion of the studies are soon to be published.     

Interaction of LL-37 with model membrane systems of different complexity: influence of the lipid matrix

As the main difference between bacterial and mammalian cell membranes is their net charge, the focal point of consideration in many model membrane experiments with antimicrobial peptides is lipid headgroup charge. We studied the interaction of the human multifunctional peptide LL-37 with single phospholipid monolayers, bilayers, and bilayers composed of binary mixtures of the four phospholipid species predominantly used in model membrane experiments (phosphatidylcholine, phosphatidylethanolamine, phosphatidylglycerol, and phosphatidylserine). We found that 1), the effects on single lipid monolayers are not comparable to those on the corresponding bilayers; 2), there are four different effects of LL-37 on bilayers of the four lipids; 3), the preference of LL-37 for the specific lipids is roughly inversely related to chain packing density; and 4), in the binary lipid mixtures, one lipid—and not necessarily the charged one—generally governs the mode of lipid/peptide interaction. Thus, our results show that lipid net charge is not the decisive factor determining the membrane-perturbing mechanism of LL-37, but only one of several parameters, among them packing density, the ability to form intermolecular H-bonds, and lipid molecular shape, which emphasizes how profoundly the choice of the model system can influence the outcome of a study of lipid/peptide interaction.     

Composition dependence of vesicle morphology and mixing properties in a bacterial model membrane system

We have determined the mixing properties and lamellar organization of bacterial membrane mimetics composed of 1-palmitoyl-2-oleoyl-phosphatidylethanolamine (POPE) and -phosphatidylglycerol (POPG) at various molar ratios applying differential scanning calorimetry, small and wide-angle X-ray scattering, as well as optical phase contrast microscopy. Combining the experimental thermodynamic data with a simulation of the liquidus and solidus lines, we were able to construct a phase diagram. Using this approach, we find that the lipids mix in all phases non-ideally in the thermodynamic sense. As expected, pure POPE assembles into multilamellar and pure POPG into unilamellar vesicles, respectively, which are stable within the studied temperature range. In contrast, mixtures of the two components form oligolamellar vesicles consisting of about three to five bilayers. The layers within these oligolamellar liposomes are positionally correlated within the gel phase, but become uncorrelated within the fluid phase exhibiting freely fluctuating bilayers, while the vesicles as a whole remain intact and do not break up into unilamellar forms. X-ray, as well as DSC data, respectively, reveal a miscibility gap due to a lateral phase segregation at POPG concentrations above about 70 mol%, similar to previously reported data on mixtures composed of disaturated PEs and PGs. Hence, the existence of a region of immiscibility is a general feature of PE/PG mixtures and the mixing properties are dominated by PE/PG headgroup interactions, but are largely independent of the composition of the hydrocarbon chains. This is in accordance with a recent theoretical prediction.     

Serum-free transfection of CHO-cells with tailor-made unilamellar vesicles

At present, a number of transfection techniques are available to introduce foreign DNA into cells, but still minimal intrusion or interference with normal cell physiology, low toxicity, reproducibility, cost efficiency and successful creation of stable transfectants are highly desirable properties for improved transfection techniques. For all previous transfection experiments done in our labs, using serum-free cultivated host cell lines, an efficiency value of ∼0.1% for selection of stable cell lines has not been exceeded, consequently we developed and improved a transfection system based on defined liposomes, so-called large unilamellar vesicles, consisting of different lipid compositions to facilitate clone selection and increase the probability for creation of recombinant high-production clones. DNA and DOTAP/DOPE or CHEMS/DOPE interact by electrostatic means forming so-called lipoplexes (Even-Chen and Barenholz 2000) and the lipofection efficiency of those lipoplexes has been determined via confocal microscopy. In addition, the expression of the EGFP was determined by FACS to investigate transient as well as stable transfection and the transfection efficiency of a selection of different commercially available transfection reagents and kits has been compared to our tailor-made liposomes.     

Abundance and night-time habitat use patterns of Ponto-Caspian gobiid species (Pisces, Gobiidae) in the littoral zone of the River Danube, Hungary

We examined the abundance and meso‐habitat use of gobiid species during both day and night along 43 stretches (500‐m long) of the littoral zone at five locations of the Middle Danube, Hungary, in spring and in summer 2004. Electro‐fishing catch per unit effort sampling revealed significantly higher relative densities at night than during the day. Gobiids occupied all the available habitats encountered during sampling. Habitat‐abundance relationships from night‐time samples revealed that the two most abundant species, round goby Neogobius melanostomus and bighead goby Neogobius kessleri, were found in highest relative density along gravel beach and artificial rip‐rap habitats; these species were in relatively low density in sandy areas. Monkey goby Neogobius fluviatilis was more abundant in natural shorelines than in rip‐rap habitats and dispersed more consistently between sandy and gravel beaches. Tubenose goby Proterorhinus marmoratus demonstrated great plasticity in meso‐habitat use. In conclusion, Ponto‐Caspian gobies occurred rather consistently along the Hungarian section of the Danube, occupying all available habitats examined. Abundance‐habitat relations suggest plasticity in meso‐habitat use but partial segregation between species. Further studies are required at multiple spatial scales to assess how micro‐ and meso‐habitat use varies with fluctuating population densities.     

Oxidized phospholipids in minimally modified low density lipoprotein induce apoptotic signaling via activation of acid sphingomyelinase in arterial smooth muscle cells

Oxidized phospholipids, including 1-palmitoyl-2-glutaroyl-sn-glycero-3-phosphocholine (PGPC) and 1-palmitoyl-2-(5-oxovaleroyl)-sn-glycero-3-phosphocholine (POVPC), typically present in minimally modified low density lipoprotein, have been found in atherosclerotic lesions. These compounds are gaining increasing importance as inducers of different cellular responses (inflammation, proliferation, or cell death). It was the aim of this study to understand their impact on intracellular signal transduction pathways that are responsible for these biological effects. We found that in arterial smooth muscle cells, PGPC and POVPC activated sphingomyelinases, in particular the acid isoform, which is known to participate in the very early phase of apoptotic stress responses. In addition, mitogen-activated protein kinases, which are involved in induction of stress response and apoptosis were phosphorylated (activated). Finally, activation of caspase 3 was observed, showing that stimulation of smooth muscle cells with POVPC and PGPC is associated with apoptosis. Stimulation of all these enzymes by the oxidized phospholipids almost perfectly matched their activation by minimally modified LDL. Consequently, these phospholipids seem to be responsible for the effect of this particle on cell signaling. Survival and proliferation pathways including NF-kappa B or AKT kinase were not induced by POVPC and PGPC. Experiments with a specific inhibitor of acid sphingomyelinase named NB6 showed that this enzyme plays a central role in mediating the apoptotic effects of the oxidized lipids. Thus, we conclude that modified phospholipids induce signaling cascades via activation of acid sphingomyelinase finally leading to apoptosis of smooth muscle cells, which is a detrimental process in the development of atherosclerosis.     

How lipids influence the mode of action of membrane-active peptides

The human, multifunctional peptide LL-37 causes membrane disruption by distinctly different mechanisms strongly dependent on the nature of the membrane lipid composition, varying not only with lipid headgroup charge but also with hydrocarbon chain length. Specifically, LL-37 induces a peptide-associated quasi-interdigitated phase in negatively charged phosphatidylglycerol (PG) model membranes, where the hydrocarbon chains are shielded from water by the peptide. In turn, LL-37 leads to a disintegration of the lamellar organization of zwitterionic dipalmitoyl-phosphatidylcholine (DPPC) into disk-like micelles. Interestingly, interdigitation was also observed for the longer-chain C18 and C20 PCs. This dual behavior of LL-37 can be attributed to a balance between electrostatic interactions reflected in different penetration depths of the peptide and hydrocarbon chain length. Thus, our observations indicate that there is a tight coupling between the peptide properties and those of the lipid bilayer, which needs to be considered in studies of lipid/peptide interaction. Very similar effects were also observed for melittin and the frog skin peptide PGLa. Therefore, we propose a phase diagram showing different lipid/peptide arrangements as a function of hydrocarbon chain length and LL-37 concentration and suggest that this phase diagram is generally applicable to membrane-active peptides localized parallel to the membrane surface.     

How lipids influence the mode of action of membrane-active peptides

The human, multifunctional peptide LL-37 causes membrane disruption by distinctly different mechanisms strongly dependent on the nature of the membrane lipid composition, varying not only with lipid headgroup charge but also with hydrocarbon chain length. Specifically, LL-37 induces a peptide-associated quasi-interdigitated phase in negatively charged phosphatidylglycerol (PG) model membranes, where the hydrocarbon chains are shielded from water by the peptide. In turn, LL-37 leads to a disintegration of the lamellar organization of zwitterionic dipalmitoyl-phosphatidylcholine (DPPC) into disk-like micelles. Interestingly, interdigitation was also observed for the longer-chain C18 and C20 PCs. This dual behavior of LL-37 can be attributed to a balance between electrostatic interactions reflected in different penetration depths of the peptide and hydrocarbon chain length. Thus, our observations indicate that there is a tight coupling between the peptide properties and those of the lipid bilayer, which needs to be considered in studies of lipid/peptide interaction. Very similar effects were also observed for melittin and the frog skin peptide PGLa. Therefore, we propose a phase diagram showing different lipid/peptide arrangements as a function of hydrocarbon chain length and LL-37 concentration and suggest that this phase diagram is generally applicable to membrane-active peptides localized parallel to the membrane surface.