Impact of Extended Duration of Artesunate Treatment on Parasitological Outcome in a Cytocidal Murine Malaria Model

Hemozoin-induced IFN-γ production mediates innate immune protection against sporozoite infection

Hemozoin is a crystal synthesized by Plasmodium parasites during hemoglobin digestion in the erythrocytic stage. The hemozoin released when the parasites egress from the red blood cell, which is complexed with parasite DNA, is cleared from the circulation by circulating and tissue-resident monocytes and macrophages, respectively. Recently, we reported that intravenous administration of purified hemozoin complexed with Plasmodium berghei DNA (HzPbDNA) resulted in an innate immune response that blocked liver stage development of sporozoites that was dose-dependent and time-limited. Here, we further characterize the organismal, cellular, and molecular events associated with this protective innate response in the liver and report that a large proportion of the IV administered HzPbDNA localized to F4/80+ cells in the liver and that the rapid and strong protection against liver-stage development waned quickly such that by 1 week post-HzPbDNA treatment animals were fully susceptible to infection. RNAseq of the liver after IV administration of HzPbDNA demonstrated that the rapid and robust induction of genes associated with the acute phase response, innate immune activation, cellular recruitment, and IFN-γ signaling observed at day 1 was largely absent at day 7. RNAseq analysis implicated NK cells as the major cellular source of IFN-γ. In vivo cell depletion and IFN-γ neutralization experiments supported the hypothesis that tissue-resident macrophages and NK cells are major contributors to the protective response and the NK cell-derived IFN-γ is key to induction of the mechanisms that block sporozoite development in the liver. These findings advance our understanding of the innate immune responses that prevent liver stage malaria infection.

Application of machine learning in a rodent malaria model for rapid, accurate, and consistent parasite counts

Rodent malaria models serve as important preclinical antimalarial and vaccine testing tools. Evaluating treatment outcomes in these models often requires manually counting parasite-infected red blood cells (iRBCs), a time-consuming process, which can be inconsistent between individuals and labs. We have developed an easy-to-use machine learning (ML)-based software, Malaria Screener R, to expedite and standardize such studies by automating the counting of Plasmodium iRBCs in rodents. This software can process Giemsa-stained blood smear images captured by any camera-equipped microscope. It features an intuitive graphical user interface that facilitates image processing and visualization of the results. The software has been developed as a desktop application that processes images on standard Windows and Mac OS computers. A previous ML model created by the authors designed to count P. falciparum -infected human RBCs did not perform well counting Plasmodium -infected mouse RBCs. We leveraged that model by loading the pre-trained weights and training the algorithm with newly collected data to target P. yoelii and P. berghei mouse iRBCs. This new model reliably measured both P. yoelii and P. berghei parasitemia (R 2 = 0.9916). Additional rounds of training data to incorporate variances due to length of Giemsa staining, microscopes etc, have produced a generalizable model, meeting WHO Competency Level 1 for the sub-category of parasite counting using independent microscopes. Reliable, automated analyses of blood-stage parasitemia will facilitate rapid and consistent evaluation of novel vaccines and antimalarials across labs in an easily accessible in vivo malaria model.

Plasmodium berghei Purified Hemozoin Associated with DNA Strongly Inhibits P. berghei Liver-Stage Development in BALB/c Mice after Intravenous Inoculation

In the acidic lysosome-like digestive vacuole, Plasmodium parasites crystallize heme from hemoglobin into hemozoin, or malaria pigment. Upon release of progeny merozoites, the residual hemozoin is phagocytized by macrophages principally in the liver and spleen where the heme crystals can persist for months to years, as heme oxygenase does not readily degrade the crystal. Previous studies demonstrated hemozoin modulation of monocytes and macrophages. Hemozoin modulates immune function activity of monocytes/macrophages. Here, we used purified/washed hemozoin (W-Hz) isolated from murine Plasmodium berghei infections and intravenously (i.v.) injected it back into naive mice. We characterized the modulating effect of W-Hz on liver-stage replication. Purified washed hemozoin decreases P. berghei liver levels both at 1 week and 1 month after i.v. injection in a dose and time dependent fashion. The injected hemozoin fully protected in nine out of 10 mice given a 50 sporozoite inoculum, and in 10 out of 10 mice against 2,000 sporozoites when they were infected an hour or a day after hemozoin inoculation. DNase treatment at the hemozoin reversed the observed liver load reduction. The liver load reduction was similar in mature B- and T-cell-deficient RAG-1 knockout (KO) mice suggesting an innate immune protection mechanism. This work indicates a role for residual hemozoin in down modulation of Plasmodium liver stages.

Artemisinin resistance and malaria elimination: Where are we now?

The emergence of artemisinin resistance is a major obstacle to the global malaria eradication/elimination programs. Artemisinin is a very fast-acting antimalarial drug and is the most important drug in the treatment of severe and uncomplicated malaria. For the treatment of acute uncomplicated falciparum malaria, artemisinin derivatives are combined with long half-life partner drugs and widely used as artemisinin-based combination therapies (ACTs). Some ACTs have shown decreased efficacy in the Southeast Asian region. Fortunately, artemisinin has an excellent safety profile and resistant infections can still be treated successfully by modifying the ACT. This review describes the pharmacological properties of ACTs, mechanisms of artemisinin resistance and the potential changes needed in the treatment regimens to overcome resistance. The suggested ACT modifications are extension of the duration of the ACT course, alternating use of different ACT regimens, and addition of another antimalarial drug to the standard ACTs (Triple-ACT). Furthermore, a malaria vaccine (e.g., RTS,S vaccine) could be added to mass drug administration (MDA) campaigns to enhance the treatment efficacy and to prevent further artemisinin resistance development. This review concludes that artemisinin remains the most important antimalarial drug, despite the development of drug-resistant falciparum malaria.

Lactic Acid Supplementation Increases Quantity and Quality of Gametocytes in Plasmodium falciparum Culture

Malaria infection by Plasmodium falciparum continues to afflict millions of people worldwide, with transmission being dependent upon mosquito ingestion of the parasite gametocyte stage. These sexually committed stages develop from the asexual stages, yet the factors behind this transition are not completely understood. Here, we found that lactic acid increases gametocyte quantity and quality in P. falciparum culture. Low-passage-number NF54 parasites exposed to 8.2 mM lactic acid for various times were monitored using blood film gametocyte counts and RNA analysis throughout 2 weeks of gametocyte development in vitro for a total of 5 biological cohorts. We found that daily continuous medium exchange and 8.2 mM lactic acid supplementation increased gametocytemia approximately 2- to 6-fold relative to controls after 5 days. In membrane feeding mosquito infection experiments, we found that gametocytes continuously exposed to 8.2 mM lactic acid supplementations were more infectious to Anopheles stephensi mosquitoes, essentially doubling prevalence of infected midguts and oocyst density. Supplementation on days 9 to 16 did not increase the quantity of gametocytes but did increase quality, as measured by oocyst density, by 2.4-fold. Lactic acid did not impact asexual growth, as measured by blood film counts and luciferase quantification, as well as radioactive hypoxanthine incorporation assays. These data indicate a novel role for lactic acid in sexual development of the parasite.

Experimentally Engineered Mutations in a Ubiquitin Hydrolase, UBP-1, Modulate In Vivo Susceptibility to Artemisinin and Chloroquine in Plasmodium berghei

As resistance to artemisinins (current frontline drugs in malaria treatment) emerges in Southeast Asia, there is an urgent need to identify the genetic determinants and understand the molecular mechanisms underpinning such resistance. Such insights could lead to prospective interventions to contain resistance and prevent the eventual spread to other regions where malaria is endemic. Reduced susceptibility to artemisinin in Southeast Asia has been primarily linked to mutations in the Plasmodium falciparum Kelch-13 gene, which is currently widely recognized as a molecular marker of artemisinin resistance.

As resistance to artemisinins (current frontline drugs in malaria treatment) emerges in Southeast Asia, there is an urgent need to identify the genetic determinants and understand the molecular mechanisms underpinning such resistance. Such insights could lead to prospective interventions to contain resistance and prevent the eventual spread to other regions where malaria is endemic. Reduced susceptibility to artemisinin in Southeast Asia has been primarily linked to mutations in the Plasmodium falciparum Kelch-13 gene, which is currently widely recognized as a molecular marker of artemisinin resistance. However, two mutations in a ubiquitin hydrolase, UBP-1, have been previously associated with reduced artemisinin susceptibility in a rodent model of malaria, and some cases of UBP-1 mutation variants associated with artemisinin treatment failure have been reported in Africa and SEA. In this study, we employed CRISPR-Cas9 genome editing and preemptive drug pressures to test these artemisinin susceptibility-associated mutations in UBP-1 in Plasmodium berghei sensitive lines in vivo. Using these approaches, we show that the V2721F UBP-1 mutation results in reduced artemisinin susceptibility, while the V2752F mutation results in resistance to chloroquine (CQ) and moderately impacts tolerance to artemisinins. Genetic reversal of the V2752F mutation restored chloroquine sensitivity in these mutant lines, whereas simultaneous introduction of both mutations could not be achieved and appears to be lethal. Interestingly, these mutations carry a detrimental growth defect, which would possibly explain their lack of expansion in natural infection settings. Our work provides independent experimental evidence on the role of UBP-1 in modulating parasite responses to artemisinin and chloroquine under in vivo conditions.

Increase hemoglobin level in severe malarial anemia while controlling parasitemia: A mathematical model

Macrophage migration inhibitory factor (MIF) is a pleiotropic cytokine produced by immune cells; it can play a protective or deleterious role in response to pathogens. The intracellular malaria parasite secretes a similar protein, PMIF. The present paper is concerned with severe malarial anemia (SMA), where MIF suppresses the recruitment of red blood cells (RBCs) from the spleen and the bone marrow. This suppression results in a decrease of the hemoglobin (H_b) in the blood to a dangerous level. Indeed, SMA is responsible for the majority of death-related malaria cases. Artesunate is the first line of treatment of SMA; it accelerates the death of infected RBCs (iRBCs), thereby decreasing parasitemia. However, artesunate does not increase the level of H_b, and, in some cases, post-artesunate hemolytic anemia requires blood transfusion. In order to avoid this situation, we explore combining artesunate with another drug so that the H_b level is increased to healthy levels while parasitemia is still controlled. In this paper we show, by a mathematical model, that increasing the H_b levels while controlling parasitemia in malarial anemia can be done with the experimental drug Epoxyazadiradione (Epoxy) in combination with artesunate. Epoxy acts as MIF inhibitor and thus has the potential to increase the H_b level. Simulations of the model show that the two drugs compliment each other: while artesunate is primarily responsible for decreasing parasitemia, Epoxy is primarily responsible for increasing the hemoglobin level.

Artemisinin and its derivatives prevent Helicobacter pylori-induced gastric carcinogenesis via inhibition of NF-κB signaling

BACKGROUND

Gastric cancer has a high morbidity and is a leading cause of cancer-related mortality worldwide. Helicobacter pylori (H. pylori) infection is commonly found in the early stage of gastric cancer pathogenesis, which induces chronic gastritis. Artemisinin (ART) and its derivatives (ARTS, artesunate and DHA, dihydroartemisinin), a new class of potent antimalarials, have been reported to exert both preventive and anti-gastric cancer effects. However, the underlying mechanisms of the chemopreventive effects of ART and its derivatives in H. pylori infection induced-gastric cancer are not fully elucidated.

PURPOSE

We investigated the effects of H. pylori infection in gastric cancer; and the preventive mechanisms of ART, ARTS and DHA.

METHODS

The H. pylori growth was determined by the broth macro-dilution method, and its adhesion to gastric cancer cells was evaluated by using the urease assay. The protein and mRNA levels, reactive oxygen species (ROS) production, as well as the production of inflammatory cytokines were evaluated by Western blot, real-time PCR, flow cytometry and ELISA, respectively. Moreover, an in vivo MNU (N-methyl-N-nitroso-urea) and H. pylori-induced gastric adenocarcinoma mouse model was established for the investigation of the cancer preventive effects of ART and its derivaties, and the underlying mechanisms of action.

RESULTS

ART, DHA and ARTS inhibited the growth of H. pylori and gastric cancer cells,suppressed H. pylori adhesion to the gastric cancer cells, and reduced the H. pylori-enhanced ROS production. Moreover, ART, DHA and ARTS significantly reduced tumor incidence, number of tumor nodules and tumor size in the mouse model. Among these three compounds, DHA exerted the most potent chemopreventive effect. Mechanistic studies showed that ART and its derivatives potently inhibited the NF-κB activation.

CONCLUSION

ART, DHA and ARTS have potent preventive effects in H. pylori-induced gastric carcinogenesis. These effects are, at least in part, attributed to the inhibition of NF-κB signaling pathway. Our findings provide a molecular justification of using ART and its derivatives for the prevention and treatment of gastric cancer.

Efficacy and resistance of different artemisinin-based combination therapies: a systematic review and network meta-analysis

BACKGROUND

Malaria parasites have developed resistance to most of the known antimalarial drugs in clinical practice, with reports of artemisinin resistance emerging in South East Asia (SEA). We sort to find the status of artemisinin resistance and efficacy of different modalities of the current artemisinin-based combination therapies (ACTs).

METHODS

We carried out a systematic search in 11 electronic databases to identify in vivo studies published between 2001 and 2017 that reported artemisinin resistance. This was then followed by A network meta-analysis to compare the efficacy of different ACTs. Quality assessment was performed using the Cochrane Risk of Bias (ROB) tool for randomized controlled trials and National Institute of Health (NIH) tool for cross-sectional studies. The study protocol was registered in PROSPERO under number CRD42018087574.

RESULTS

With 8400 studies initially identified, 82 were eligible for qualitative and quantitative analysis. Artemisinin resistance was only reported in South East Asia. K13 mutation C580Y was the most abundant mutation associated with resistance having an abundance of 63.1% among all K13 mutations reported. Although the overall network meta-analysis had shown good performance of dihydroartemisinin piperaquine in the early years, a subgroup analysis of the recent years revealed a poor performance of the drug in relation to recrudescence, clinical failure and parasitological failure especially in the artemisinin resistant regions.

CONCLUSION

With report of high resistance and treatment failure against the leading artemisinin combination therapy in South East Asia, it is imperative that a new drug or a formulation is developed before further spread of resistance.

In vivo compartmental kinetics of Plasmodium falciparum histidine-rich protein II in the blood of humans and in BALB/c mice infected with a transgenic Plasmodium berghei parasite expressing histidine-rich protein II

Background

The Plasmodium falciparum histidine-rich protein II (PfHRP2) is a common biomarker used in malaria rapid diagnostic tests (RDTs), but can persist in the blood for up to 40 days following curative treatment. The persistence of PfHRP2 presents a false positive limitation to diagnostic interpretation. However, the in vivo dynamics and compartmentalization underlying PfHRP2 persistence have not been fully characterized in the plasma and erythrocyte (RBC) fraction of the whole blood.

Methods

The kinetics and persistence of PfHRP2 in the plasma and RBC fractions of the whole blood were investigated post-treatment in human clinical samples and samples isolated from BALB/c mice infected with a novel transgenic Plasmodium berghei parasite engineered to express PfHRP2 (PbPfHRP2).

Results

PfHRP2 levels in human RBCs were consistently 20–40 times greater than plasma levels, even post-parasite clearance. PfHRP2 positive, DNA negative, once-infected RBCs were identified in patients that comprised 0.1–1% of total RBCs for 6 and 12 days post-treatment, even post-atovaquone–proguanil regimens. Transgenic PbPfHRP2 parasites in BALB/c mice produced and exported tgPfHRP2 to the RBC cytosol similar to P. falciparum. As in humans, tgPfHRP2 levels were found to be approximately 20-fold higher within the RBC fraction than the plasma post-treatment. RBC localized tgPfHRP2 persisted longer than tgPfHRP2 in the plasma after curative treatment. tgPfHRP2 positive, but DNA negative once-infected RBCs were also detected in mouse peripheral blood for 7–9 days after curative treatment.

Conclusions

The data suggest that persistence of PfHRP2 is due to slower clearance of protein from the RBC fraction of the whole blood. This appears to be a result of the presence PfHRP2 in previously infected, pitted cells, as opposed to PfHRP2 binding naïve RBCs in circulation post-treatment. The results thus confirm that the extended duration of RDT positivity after parasite clearance is likely due to pitted, once-infected RBCs that remain positive for PfHRP2.

Electronic supplementary material

The online version of this article (10.1186/s12936-019-2712-3) contains supplementary material, which is available to authorized users.

Superior Pyronaridine Single-Dose Pharmacodynamics Compared to Artesunate, Chloroquine, and Amodiaquine in a Murine Malaria Luciferase Model

Many previous in vitro and in vivo preclinical malaria drug studies have relied on low-parasite-number drug inhibition numerically compared to the untreated controls. In contrast, human malaria drug studies measure the high-parasite-density killing near 100 million/ml. Here we compared the in vivo single-dose pharmacodynamic properties of artesunate and the 4-aminoquinolines pyronaridine, chloroquine, and amodiaquine in a Plasmodium berghei ANKA-green fluorescent protein GFP-luciferase-based murine malaria blood-stage model. Pyronaridine exhibited dose-dependent killing, achieving parasite reductions near 5 to 6 logs at 48 h, with complete cure at 10 mg/kg of body weight compared to artesunate, which exhibited a 48-h dose-dependent killing with a 2-log drop at the noncurative 250-mg/kg dose. Chloroquine, which was noncurative, and amodiaquine, which was partially curative, had nearly the same initial dose-independent killing, with a lag phase of minimal parasite reduction at all doses between 6 and 24 h, followed by a 2.5-log reduction at 48 h. In experiments with drug-treated, washed infected blood transfer to naive mice, chloroquine and amodiaquine showed fewer viable parasites at the 24-h transfer than at the 8-h transfer, measured by a prolonged return to parasitemia, despite a similar parasite log reduction at these time points, in contrast to the correlation of the parasite log reduction to viable parasites with artesunate and pyronaridine. Artesunate in combination with pyronaridine exhibited an initial parasite reduction similar to that achieved with pyronaridine, while with chloroquine or amodiaquine, the reduction was similar to that achieved with artesunate. Single-oral-dose pyronaridine was much more potent in vivo than artesunate, chloroquine, and amodiaquine during the initial decline in parasites and cure.

A cryptic cycle in haematopoietic niches promotes initiation of malaria transmission and evasion of chemotherapy

Blood stage human malaria parasites may exploit erythropoietic tissue niches and colonise erythroid progenitors; however, the precise influence of the erythropoietic environment on fundamental parasite biology remains unknown. Here we use quantitative approaches to enumerate Plasmodium infected erythropoietic precursor cells using an in vivo rodent model of Plasmodium berghei. We show that parasitised early reticulocytes (ER) in the major sites of haematopoiesis establish a cryptic asexual cycle. Moreover, this cycle is characterised by early preferential commitment to gametocytogenesis, which occurs in sufficient numbers to generate almost all of the initial population of circulating, mature gametocytes. In addition, we show that P. berghei is less sensitive to artemisinin in splenic ER than in blood, which suggests that haematopoietic tissues may enable origins of recrudescent infection and emerging resistance to antimalarials. Continuous propagation in these sites may also provide a mechanism for continuous transmission and infection in malaria endemic regions.