Plasmodium falciparum strain GC-03 exhibits hyper-gametocytogenesis in partially hemoglobin depleted red blood cells

Investigation of factors affecting the production of P. falciparum gametocytes in an Indian isolate

The fundamental requirement of every gametocytocidal drug screening assay is the sufficient numbers of healthy and viable gametocytes. The number of in vitro gametocytes grossly depends on the genetic capacity of parasites to produce gametocytes and on various environmental factors that are not precisely elucidated. In the present study, we tested multiple environmental factors that are reported, hypothesized, or predicted to influence gametocyte numbers. We observed that hypoxanthine and the use of freshly drawn human blood significantly enhance gametocytemia (p < 0.05) in vitro. However, other tested factors did not significantly affect gametocytemia. The addition of N-acetyl glucosamine to the culture enriched the gametocytes but d-sorbitol (5% v/v) in amounts and duration of incubation tested was unable to do so without negatively affecting the maturity and health of the gametocytes. Although the in vitro gametocyte production depends on the genetic capability of the parasite strain tested, various environmental factors also control the ability of the strain to produce gametocytes up to a certain extent. This is the first study testing the role of various environmental factors that might affect the gametocyte development in a gametocyte producing strain. The results presented herein will help in the optimization of gametocyte production procedures for various gametocytocidal drug screening assays.

Targeting Human Transmission Biology for Malaria Elimination

Malaria remains one of the leading causes of death worldwide, despite decades of public health efforts. The recent commitment by many endemic countries to eliminate malaria marks a shift away from programs aimed at controlling disease burden towards one that emphasizes reducing transmission of the most virulent human malaria parasite, Plasmodium falciparum. Gametocytes, the only developmental stage of malaria parasites able to infect mosquitoes, have remained understudied, as they occur in low numbers, do not cause disease, and are difficult to detect in vivo by conventional methods. Here, we review the transmission biology of P. falciparum gametocytes, featuring important recent discoveries of genes affecting parasite commitment to gametocyte formation, microvesicles enabling parasites to communicate with each other, and the anatomical site where immature gametocytes develop. We propose potential parasite targets for future intervention and highlight remaining knowledge gaps.

Whole-cell in vitro screening for gametocytocidal compounds

The discovery of new chemical starting points with the ability to inhibit Plasmodium falciparum sexual stages, and therefore block the disease transmission, is urgently required. These will form the basis for the development of new therapeutic combinations for the treatment and elimination of malaria and the ultimate goal of global eradication. Recent screening of large chemical libraries against the parasite asexual stages has resulted in the public availability of focused subsets of known antimalarial actives, which represent an excellent starting point for the identification of new gametocytocidal compounds. New stage-specific methodologies aimed at increasing the throughput for assessing compound activity against in vitro cultured gametocytes have recently been published. This article discusses the challenges of assay-oriented large-scale gametocyte culturing and reviews the state-of-the art in gametocytocidal assay development and outcomes.

Comparison and Optimization of Different Methods for the In Vitro Production of Plasmodium falciparum Gametocytes

The generation of sexually committed parasites (gametocytogenesis) is poorly understood in malaria. If the mechanisms regulating this process were elucidated, new opportunities for blocking malaria transmission could be revealed. Here we compare several methods described previously for the in vitro production of Plasmodium falciparum gametocytes. Our approach relies on the combination of several factors that we demonstrated as impacting on or being critical to gametocytogenesis. An improved method has been developed for the in vitro production of P. falciparum gametocytes as the first step toward obtaining adequate numbers of pure gametocytes for in vitro studies, such as, for example, the identification of transmission blocking drugs.

Chloroquine resistance-conferring mutations in pfcrt give rise to a chloroquine-associated H+ leak from the malaria parasite's digestive vacuole

Chloroquine resistance in the malaria parasite Plasmodium falciparum is conferred by mutations in the P. falciparum chloroquine resistance transporter (PfCRT). PfCRT localizes to the membrane of the parasite's internal digestive vacuole, an acidic organelle in which chloroquine accumulates to high concentrations and exerts its toxic effect. Mutations in PfCRT are thought to reduce chloroquine accumulation in this organelle. How they do so is the subject of ongoing debate. Recently we have shown that in the presence of chloroquine there is an increased leak of H+ from the digestive vacuole in chloroquine-resistant but not chloroquine-sensitive parasites. Here, using transfectant parasite strains of a single genetic background and differing only in their pfcrt allele, we show that chloroquine resistance-conferring PfCRT mutations are responsible for this chloroquine-associated H+ leak. This is consistent with the hypothesis that the chloroquine resistance-conferring forms of PfCRT mediate the efflux of chloroquine, in association with H+, from the malaria parasite's digestive vacuole.