Out of the four species of malarial parasites, Plasmodium falciparum, is most deadly. Nearly one million people die, every year, from P. falciparum infections. When the parasite enters red blood cells, it ingests their haemoglobin and deposits it in a digestive vacuole. Here, hemoglobin is broken down to heme and peptides. While peptides are useful to the pathogen, the heme, which is toxic to the pathogen, is converted to nontoxic hemazoin, a crystalline polymer. Chloroquine, used to treat falciparum malaria, interferes with this by binding to the byproducts of hemoglobin breakdown. The toxic byproducts, thus, kill the pathogen.
Though chloroquine diphosphate is commonly used as treatment, in blood, chloroquine takes uncharged and positively charged forms and only the latter can enter the digestive vacuole of the pathogen. So, most of the chloroquine in blood has no effect on the pathogen.
Moreover, some of these parasites have mutated and are now able to clear chloroquine from their food vacuole, giving rise to a dangerous, drug–resistant form of falciparum malaria. Scientists have been trying to deliver the drug in a form that can pass the barrier of the pathogen’s digestive vacuole.
Researchers from the Chandigarh College of Pharmacy, the Maharaja Ranjit Singh Punjab Technical University and the University of Delhi collaborated to overcome the problem. They knew that dextran, a form of branched polysaccharides, crosses the barrier of the vacuole. Dextran is taken up by the parasites as a nutrient from the external medium.
The scientists also knew that dextran of up to 40000 Daltons molecular weight is not harmful to normal erythrocyte functions. They hypothesised that if they make a drug-carrying nanoparticle with dextran, perhaps, it would cross the membranes of the red blood cells and the vacuole, through the duct that connects the parasite to the outside for entry of nutritional molecules. So they made dextran nanoparticles loaded with chloroquine phosphate using a solvent diffusion method.
The dextran nanoparticles that were about 7 nanometers, when loaded with chloroquine, became about 60 nanometers, well below the size that can pass through to the vacuole.
With more than 80 percent encapsulation efficiency, nearly half the weight of the nanoparticle was due to chloroquine phosphate. The nanosuspension was quite stable.
Perhaps due to the positive charge of chloroquine, the nanoparticles had a negative zeta potential, keeping them away from each other in the suspension, explain the researchers.
The researchers determined that most of the drug is in its amorphous form in the polymeric matrix. This was encouraging because it improves bioavailability.
Using dialysis, they found that the drug is released from the matrix quickly, initially, due to diffusion and, then, it slows down and releases the drug slowly over eight hours, instead of just two hours, as in the case of chloroquine solution.
By labelling the drug with a dye, the researchers could detect that it can indeed reach the food vacuole of the falciparum parasite.
They found that the nanoparticles are effective against both the resistant variety as well as against falciparum that is sensitive to chloroquine. However, the resistant variety needed a higher concentration of the drug.
The nanoparticle did not lead to hemolysis of the red blood cells and, therefore, is safe, say the researchers.
“Though the results are very promising, it will take many animal experiments and clinical trials before the drug formulation is available for clinical practice,” says Jitender Madan, the leader of the team. Besides his students, in the Chandigarh College of Pharmacy Ashish Baldi from the Maharaja Ranjit Singh Punjab Technical University, and Ramesh Chandra from the University of Delhi, collaborated in the research.