Rapid diagnostic tests for malaria: past, present and future

Prompt and accurate diagnosis of malaria is part of an effective disease management (1) , because if not treated malaria can quickly become life-threatening, whereas false positives increase treatment costs and drug-induced resistance, giving a wrong idea of therapeutic efficacy. Since the symptoms of malaria are nonspecific, the observation of clinical features alone might not be enough and should be confirmed with a parasitological analysis. Microscopic examination of Giemsa-stained thin and/or thick blood smears remains the conventional approach for diagnosis (2). The sensitivity of this relatively inexpensive method is excellent, allowing the detection of as few as 5 parasites per µL of blood, and permitting also the determination of the infecting species and of the developmental stage of circulating parasites. In addition, smears provide a permanent record for quality assessment of the diagnosis. However, microscopy requires considerable expertise learned through extended training, the procedure is labor-intensive and time-consuming, and the variability in stains and in techniques used to collect and process blood affects slide interpretation (3). Finally, routine clinical microscopy cannot reliably detect very low parasitemias (<5 parasites/µL) or sequestered parasites, and mixed infections are often missed, especially when Plasmodium malariae and Plasmodium ovale are present, as their densities are often low relative to Plasmodium falciparum

Polyamidoamine nanoparticles as nanocarriers for the drug delivery to malaria parasite stages in the mosquito vector

Malaria is arguably one of the main medical concerns worldwide because of the numbers of people affected, the severity of the disease and the complexity of the life cycle of its causative agent, the protist Plasmodium spp. With the advent of nanoscience, renewed hopes have appeared of finally obtaining the long sought-after magic bullet against malaria in the form of a nanovector for the targeted delivery of antimalarial compounds exclusively to Plasmodium-infected cells, thus increasing drug efficacy and minimizing the induction of resistance to newly developed therapeutic agents. Polyamidoamine-derived nanovectors combine into a single chemical structure drug encapsulating capacity, antimalarial activity, low unspecific toxicity, specific targeting to Plasmodium, optimal in vivo activity and affordable synthesis cost. After having shown their efficacy in targeting drugs to intraerythrocytic parasites, now polyamidoamines face the challenge of spearheading a new generation of nanocarriers aiming at the malaria parasite stages in the mosquito vector

Heparin: New life for an old drug

© 2017 Future Medicine Ltd. Heparin is one of the oldest drugs, which nevertheless remains in widespread clinical use as an inhibitor of blood coagulation. The history of its identification a century ago unfolded amid one of the most fascinating scientific controversies turning around the distribution of credit for its discovery. The composition, purification and structure-function relationship of this naturally occurring glycosaminoglycan regarding its classical role as anticoagulant will be dealt with before proceeding to discuss its therapeutic potential in, among other, inflammatory and infectious disease, cancer treatment, cystic fibrosis and Alzheimer's disease. The first bibliographic reference hit using the words 'nanomedicine' and 'heparin' is as recent as 2008. Since then, nanomedical applications of heparin have experienced an exponential growth that will be discussed in detail, with particular emphasis on its antimalarial activity. Some of the most intriguing potential applications of heparin nanomedicines will be exposed, such as those contemplating the delivery of drugs to the mosquito stages of malaria parasites

Nanotribology Results Show that DNA Forms a Mechanically Resistant 2D Network in Metaphase Chromatin Plates

AbstractIn a previous study, we found that metaphase chromosomes are formed by thin plates, and here we have applied atomic force microscopy (AFM) and friction force measurements at the nanoscale (nanotribology) to analyze the properties of these planar structures in aqueous media at room temperature. Our results show that high concentrations of NaCl and EDTA and extensive digestion with protease and nuclease enzymes cause plate denaturation. Nanotribology studies show that native plates under structuring conditions (5 mM Mg2+) have a relatively high friction coefficient (μ ≈ 0.3), which is markedly reduced when high concentrations of NaCl or EDTA are added (μ ≈ 0.1). This lubricant effect can be interpreted considering the electrostatic repulsion between DNA phosphate groups and the AFM tip. Protease digestion increases the friction coefficient (μ ≈ 0.5), but the highest friction is observed when DNA is cleaved by micrococcal nuclease (μ ≈ 0.9), indicating that DNA is the main structural element of plates. Whereas nuclease-digested plates are irreversibly damaged after the friction measurement, native plates can absorb kinetic energy from the AFM tip without suffering any damage. These results suggest that plates are formed by a flexible and mechanically resistant two-dimensional network which allows the safe storage of DNA during mitosis

Marine organism sulfated polysaccharides exhibiting significant antimalarial activity and inhibition of red blood cell invasion by Plasmodium

The antimalarial activity of heparin, against which there are no resistances known, has not been therapeutically exploited due to its potent anticoagulating activity. Here, we have explored the antiplasmodial capacity of heparin-like sulfated polysaccharides from the sea cucumbers Ludwigothurea grisea and Isostichopus badionotus, from the red alga Botryocladia occidentalis, and from the marine sponge Desmapsamma anchorata. In vitro experiments demonstrated for most compounds significant inhibition of Plasmodium falciparum growth at low-anticoagulant concentrations. This activity was found to operate through inhibition of erythrocyte invasion by Plasmodium, likely mediated by a coating of the parasite similar to that observed for heparin. In vivo four-day suppressive tests showed that several of the sulfated polysaccharides improved the survival of Plasmodium yoelii-infected mice. In one animal treated with I. badionotus fucan parasitemia was reduced from 10.4% to undetectable levels, and Western blot analysis revealed the presence of antibodies against P. yoelii antigens in its plasma. The retarded invasion mediated by sulfated polysaccharides, and the ensuing prolonged exposure of Plasmodium to the immune system, can be explored for the design of new therapeutic approaches against malaria where heparin-related polysaccharides of low anticoagulating activity could play a dual role as drugs and as potentiators of immune responses

An immunoPEGliposome for targeted antimalarial combination therapy at the nanoscale

Combination therapies, where two drugs acting through different mechanisms are administered simultaneously, are one of the most efficient approaches currently used to treat malaria infections. However, the different pharmacokinetic profiles often exhibited by the combined drugs tend to decrease treatment efficacy as the compounds are usually eliminated from the circulation at different rates. To circumvent this obstacle, we have engineered an immunoliposomal nanovector encapsulating hydrophilic and lipophilic compounds in its lumen and lipid bilayer, respectively. The antimalarial domiphen bromide has been encapsulated in the liposome membrane with good efficiency, although its high IC50 of ca. 1 µM for living parasites complicates its use as immunoliposomal therapy due to erythrocyte agglutination. The conjugation of antibodies against glycophorin A targeted the nanocarriers to Plasmodium-infected red blood cells and to gametocytes, the sole malaria parasite stage responsible for the transmission from the human to the mosquito vector. The antimalarials pyronaridine and atovaquone, which block the development of gametocytes, have been co-encapsulated in glycophorin A-targeted immunoliposomes. The co-immunoliposomized drugs have activities significantly higher than their free forms when tested in in vitro Plasmodium falciparum cultures: Pyronaridine and atovaquone concentrations that, when encapsulated in immunoliposomes, resulted in a 50% inhibition of parasite growth had no effect on the viability of the pathogen when used as free drugs

Repurposing Heparin as Antimalarial: Evaluation of Multiple Modifications Toward In Vivo Application

Heparin is a promising antimalarial drug due to its activity in inhibiting Plasmodium invasion of red blood cells and to the lack of resistance evolution by the parasite against it, but its potent anticoagulant activity is preventing the advance of heparin along the clinical pipeline. We have determined, in in vitro Plasmodium falciparum cultures, the antimalarial activity of heparin-derived structures of different origins and sizes, to obtain formulations having a good balance of in vitro safety (neither cytotoxic nor hemolytic), low anticoagulant activity (≤23 IU/mL according to activated partial thromboplastin time assays), and not too low antimalarial activity (IC50 at least around 100 µg/mL). This led to the selection of five chemically modified heparins according to the parameters explored, i.e., chain length, sulfation degree and position, and glycol-split, and whose in vivo toxicity indicated their safety for mice up to an intravenous dose of 320 mg/kg. The in vivo antimalarial activity of the selected formulations was poor as a consequence of their short blood half-life. The covalent crosslinking of heparin onto the surface of polyethylene glycol-containing liposomes did not affect its antimalarial activity in vitro and provided higher initial plasma concentrations, although it did not increase mean circulation time. Finding a suitable nanocarrier to impart long blood residence times to the modified heparins described here will be the next step toward new heparin-based antimalarial strategies

Immunoliposome-mediated drug delivery to Plasmodium-infected and non-infected red blood cells as a dual therapeutic/prophylactic antimalarial stragegy

One of the most important factors behind resistance evolution in malaria is the failure to deliver sufficiently high amounts of drugs to early stages of Plasmodium-infected red blood cells (pRBCs). Despite having been considered for decades as a promising approach, the delivery of antimalarials encapsulated in immunoliposomes targeted to pRBCs has not progressed towards clinical applications, whereas in vitro assays rarely reach drug efficacy improvements above 10-fold. Here we show that encapsulation efficiencies reaching N96% are achieved for the weak basic drugs chloroquine (CQ) and primaquine using the pH gradient loading method in liposomes containing neutral saturated phospholipids. Targeting antibodies are best conjugated through their primary amino groups, adjusting chemical crosslinker concentration to retain significant antigen recognition. Antigens from non-parasitized RBCs have also been considered as targets for the delivery to the cell of drugs not affecting the erythrocytic metabolism. Using this strategy, we have achieved unprecedented complete nanocarrier targeting to early intraerythrocytic stages of the malaria parasite for which there is a lack of specific extracellular molecular tags. Immunoliposomes studded with monoclonal antibodies raised against the erythrocyte surface protein glycophorin A were capable of targeting 100% RBCs and pRBCs at the low concentration of 0.5 μM total lipid in the culture, with N95% of added liposomes retained on cell surfaces. When exposed for only 15 min to Plasmodium falciparum in vitro cultures of early stages, free CQ had no significant effect on the viability of the parasite up to 200 nM, whereas immunoliposomal 50 nM CQ completely arrested its growth. In vivo assays in mice showed that immunoliposomes cleared the pathogen below detectable levels at a CQ dose of 0.5 mg/kg, whereas free CQ administered at 1.75 mg/kgwas, atmost, 40-fold less efficient. Our data suggest that this significant improvement is in part due to a prophylactic effect of CQ found by the pathogen in its host cell right at the very moment of invasion