In vitro susceptibility of Indian Plasmodium falciparum isolates to different antimalarial drugs & antibiotics

Transforming the CRISPR/dCas9-based gene regulation technique into a forward screening tool in Plasmodium falciparum

It is a significant challenge to assess the functions of many uncharacterized genes in human malaria parasites. Here, we present a genetic screening tool to assess the contribution of essential genes from Plasmodium falciparum by the conditional CRISPR-/deadCas9-based interference and activation (i/a) systems. We screened both CRISPRi and CRISPRa sets, consisting of nine parasite lines per set targeting nine genes via their respective gRNAs. By conducting amplicon sequencing of gRNA loci, we identified the contribution of each targeted gene to parasite fitness upon drug (artemisinin, chloroquine) and stress (starvation, heat shock) treatment. The screening was highly reproducible, and the screening libraries were easily generated by transfection of mixed plasmids expressing different gRNAs. We demonstrated that this screening is straightforward, robust, and can provide a fast and efficient tool to study essential genes that have long presented a bottleneck in assessing their functions using existing genetic tools.

A patatin-like phospholipase is important for mitochondrial function in malaria parasites

Plasmodium parasites rely on a functional electron transport chain (ETC) within their mitochondrion for proliferation, and compounds targeting mitochondrial functions are validated antimalarials. Here, we localize Plasmodium falciparum patatin-like phospholipase 2 (PfPNPLA2, PF3D7_1358000) to the mitochondrion and reveal that disruption of the PfPNPLA2 gene impairs asexual replication. PfPNPLA2-null parasites are hypersensitive to proguanil and inhibitors of the mitochondrial ETC, including atovaquone. In addition, PfPNPLA2-deficient parasites show reduced mitochondrial respiration and reduced mitochondrial membrane potential, indicating that disruption of PfPNPLA2 leads to a defect in the parasite ETC. Lipidomic analysis of the mitochondrial phospholipid cardiolipin (CL) reveals that loss of PfPNPLA2 is associated with a moderate shift toward shorter-chained and more saturated CL species, implying a contribution of PfPNPLA2 to CL remodeling. PfPNPLA2-deficient parasites display profound defects in gametocytogenesis, underlining the importance of a functional mitochondrial ETC during both the asexual and sexual development of the parasite. IMPORTANCE For their proliferation within red blood cells, malaria parasites depend on a functional electron transport chain (ETC) within their mitochondrion, which is the target of several antimalarial drugs. Here, we have used gene disruption to identify a patatin-like phospholipase, PfPNPLA2, as important for parasite replication and mitochondrial function in Plasmodium falciparum. Parasites lacking PfPNPLA2 show defects in their ETC and become hypersensitive to mitochondrion-targeting drugs. Furthermore, PfPNPLA2-deficient parasites show differences in the composition of their cardiolipins, a unique class of phospholipids with key roles in mitochondrial functions. Finally, we demonstrate that parasites devoid of PfPNPLA2 have a defect in gametocyte maturation, underlining the importance of a functional ETC for parasite transmission to the mosquito vector.

Suitability of methods for Plasmodium falciparum cultivation in atmospheric air

BACKGROUND

One of the most controversial factors about malaria parasite culture is the gaseous composition used. The most commonly used one consists of a mixture poor in O₂ and rich in CO₂.

OBJECTIVES

The present study aimed to share standard methods from our research group simplifying Plasmodium falciparum cultures by employing atmospheric air (ATM) and reusable glass bottles under agitation.

METHODS

Here, it was compared the parasite viability, free oxygen in media, and drug sensitivity between different strains and isolates maintained for long periods under ATM or classic conditions.

FINDINGS

The oxygen concentration in media under ATM was slightly superior to that observed in human blood and the media under the classic gaseous mixture. However, ATM or the use of glass bottles did not affect parasitic proliferation after several years of culture. Noticeably, the introduction of ATM altered reversibly the efficacy of several antimalarials. This influence was different between the strains and isolate.

CONCLUSIONS

ATM conditions and shaken flasks could be used as a standard method condition for culture manutention since they do not differ greatly from classical 5% O₂ gas mixtures in terms of parasite proliferation and do not impose non-reversible changes to P. falciparum physiology.

Targeted Amplicon Deep Sequencing for Monitoring Antimalarial Resistance Markers in Western Kenya

Molecular surveillance of Plasmodium falciparum parasites is important to track emerging and new mutations and trends in established mutations and should serve as an early warning system for antimalarial resistance. Dried blood spots were obtained from a Plasmodium falciparum malaria survey in school children conducted across eight counties in western Kenya in 2019. Real-time PCR identified 500 P. falciparum-positive samples that were amplified at five drug resistance loci for targeted amplicon deep sequencing (TADS). The absence of important kelch 13 mutations was similar to previous findings in Kenya pre-2019, and low-frequency mutations were observed in codons 569 and 578. The chloroquine resistance transporter gene codons 76 and 145 were wild type, indicating that the parasites were chloroquine and piperaquine sensitive, respectively. The multidrug resistance gene 1 haplotypes based on codons 86, 184, and 199 were predominantly present in mixed infections with haplotypes NYT and NFT, driven by the absence of chloroquine pressure and the use of lumefantrine, respectively. The sulfadoxine-pyrimethamine resistance profile was a “superresistant” combination of triple mutations in both Pfdhfr (51I 59R 108N) and Pfdhps (436H 437G 540E), rendering sulfadoxine-pyrimethamine ineffective. TADS highlighted the low-frequency variants, allowing the early identification of new mutations, Pfmdr1 codon 199S and Pfdhfr codon 85I and emerging 164L mutations. The added value of TADS is its accuracy in identifying mixed-genotype infections and for high-throughput monitoring of antimalarial resistance markers.

Semimechanistic Pharmacokinetic and Pharmacodynamic Modeling of Piperaquine in a Volunteer Infection Study with Plasmodium falciparum Blood-Stage Malaria

Dihydroartemisinin-piperaquine is a recommended first-line artemisinin combination therapy for Plasmodium falciparum malaria. Piperaquine is also under consideration for other antimalarial combination therapies. The aim of this study was to develop a pharmacokinetic-pharmacodynamic model that might be useful when optimizing the use of piperaquine in new antimalarial combination therapies. The pharmacokinetic-pharmacodynamic model was developed using data from a previously reported dose-ranging study where 24 healthy volunteers were inoculated with 1,800 blood-stage Plasmodium falciparum parasites. All volunteers received a single oral dose of piperaquine (960 mg, 640 mg, or 480 mg) on day 7 or day 8 after parasite inoculation in separate cohorts. Parasite densities were measured by quantitative PCR (qPCR), and piperaquine levels were measured in plasma samples. We used nonlinear mixed-effect modeling to characterize the pharmacokinetic properties of piperaquine and the parasite dynamics associated with piperaquine exposure. The pharmacokinetics of piperaquine was described by a three-compartment disposition model. A semimechanistic parasite dynamics model was developed to explain the maturation of parasites, sequestration of mature parasites, synchronicity of infections, and multiplication of parasites, as seen in natural clinical infections with P. falciparum malaria. Piperaquine-associated parasite killing was estimated using a maximum effect (E _max) function. Treatment simulations (i.e., 3-day oral dosing of dihydroartemisinin-piperaquine) indicated that to be able to combat multidrug-resistant infections, an ideal additional drug in a new antimalarial triple-combination therapy should have a parasite reduction ratio of ≥10² per life cycle (38.8 h) with a duration of action of ≥2 weeks. The semimechanistic pharmacokinetic-pharmacodynamic model described here offers the potential to be a valuable tool for assessing and optimizing current and new antimalarial drug combination therapies containing piperaquine and the impact of these therapies on killing multidrug-resistant infections. (This study has been registered in the Australian and New Zealand Clinical Trials Registry under no. ANZCTRN12613000565741.).

Rapid and quantitative antimalarial drug efficacy testing via the magneto-optical detection of hemozoin

Emergence of resistant Plasmodium species makes drug efficacy testing a crucial part of malaria control. Here we describe a novel assay for sensitive, fast and simple drug screening via the magneto-optical detection of hemozoin, a natural biomarker formed during the hemoglobin metabolism of Plasmodium species. By quantifying hemozoin production over the intraerythrocytic cycle, we reveal that hemozoin formation is already initiated by ~ 6–12 h old ring-stage parasites. We demonstrate that the new assay is capable of drug efficacy testing with incubation times as short as 6–10 h, using synchronized P. falciparum 3D7 cultures incubated with chloroquine, piperaquine and dihydroartemisinin. The determined 50% inhibitory concentrations agree well with values established by standard assays requiring significantly longer testing time. Accordingly, we conclude that magneto-optical hemozoin detection provides a practical approach for the quick assessment of drug effect with short incubation times, which may also facilitate stage-specific assessment of drug inhibitory effects.