Artemisinins target the SERCA of Plasmodium falciparum

QSAR modeling, docking and ADMET studies for exploration of potential anti-malarial compounds against Plasmodium falciparum

Development of resistance in the Plasmodium falciparum to Artemisinin, the most effective anti-malarial compound, threatens malaria elimination tactics. To gain more efficacious Artemisinin derivatives, QSAR modeling and docking was performed. In the present study, 2D-QSAR model and molecular docking were used to evaluate the Artemisinin compounds and to reveal their binding modes and structural basis of inhibitory activity. Moreover, ADMET-related descriptors have been calculated to predict the pharmacokinetic properties of the effective compounds. The correlation expressed as coefficient of determination (r²) and prediction accuracy expressed in the form of cross-validated r² (q²) of QSAR model are found 0.9687 and 0.9586, respectively. Total 239 descriptors have been included in the study as independent variables. The four chemical descriptors, namely radius of gyration, mominertia Z, SssNH count and SK Average have been found to be well correlated with anti-malarial activities. The model was statistically robust and has good predictive power which could be employed for virtual screening of proposed anti-malarial compounds. QSAR and docking results revealed that studied compounds exhibit good anti-malarial activities and binding affinities. The outcomes could be useful for the design and development of the potent inhibitors which after optimization can be potential therapeutics for malaria.

Amodiaquine resistance in Plasmodium berghei is associated with PbCRT His95Pro mutation, loss of chloroquine, artemisinin and primaquine sensitivity, and high transcript levels of key transporters

Background: The human malaria parasite Plasmodium falciparum has evolved complex drug evasion mechanisms to all available antimalarials. To date, the combination of amodiaquine-artesunate is among the drug of choice for treatment of uncomplicated malaria. In this combination, a short acting, artesunate is partnered with long acting, amodiaquine for which resistance may emerge rapidly especially in high transmission settings. Here, we used a rodent malaria parasite Plasmodium berghei ANKA as a surrogate of P. falciparum to investigate the mechanisms of amodiaquine resistance. Methods: We used serial technique to select amodiaquine resistance by submitting the parasites to continuous amodiaquine pressure. We then employed the 4-Day Suppressive Test to monitor emergence of resistance and determine the cross-resistance profiles. Finally, we genotyped the resistant parasite by PCR amplification, sequencing and relative quantitation of mRNA transcript of targeted genes. Results: Submission of P. berghei ANKA to amodiaquine pressure yielded resistant parasite within thirty-six passages. The effective dosage that reduced 90% of parasitaemia (ED90) of sensitive line and resistant line were 4.29mg/kg and 19.13mg/kg, respectively. After freezing at -80ºC for one month, the resistant parasite remained stable with an ED90 of 18.22mg/kg. Amodiaquine resistant parasites are also resistant to chloroquine (6fold), artemether (10fold), primaquine (5fold), piperaquine (2fold) and lumefantrine (3fold). Sequence analysis of Plasmodium berghei chloroquine resistant transporter revealed His95Pro mutation. No variation was identified in Plasmodium berghei multidrug resistance gene-1 (Pbmdr1), Plasmodium berghei deubiquitinating enzyme-1 or Plasmodium berghei Kelch13 domain nucleotide sequences. Amodiaquine resistance is also accompanied by high mRNA transcripts of key transporters; Pbmdr1, V-type/H+ pumping pyrophosphatase-2 and sodium hydrogen ion exchanger-1 and Ca2+/H+ antiporter. Conclusions: Selection of amodiaquine resistance yielded stable “multidrug-resistant’’ parasites and thus may be used to study common resistance mechanisms associated with other antimalarial drugs. Genome wide studies may elucidate other functionally important genes controlling AQ resistance in P. berghei.

Molecular markers of anti-malarial drug resistance in Central, West and East African children with severe malaria

Background

The Plasmodium falciparum multidrug resistance 1 (PfMDR1), P. falciparum Ca²⁺-ATPase (PfATP6) and Kelch-13 propeller domain (PfK13) loci are molecular markers of parasite susceptibility to anti-malarial drugs. Their frequency distributions were determined in the isolates collected from children with severe malaria originating from three African countries.

Methods

Samples from 287 children with severe malaria [(Gabon: n = 114); (Ghana: n = 89); (Kenya: n = 84)] were genotyped for pfmdr1, pfatp6 and pfk13 loci by DNA sequencing and assessing pfmdr1 copy number variation (CNV) by real-time PCR.

Results

Pfmdr1-N86Y mutation was detected in 48, 10 and 10% in Lambaréné, Kumasi and Kisumu, respectively. At codon 184, the prevalence of the mutation was 73% in Lambaréné, 63% in Kumasi and 49% Kisumu. The S1034C and N1042D variants were absent at all three sites, while the frequency of the D1246Y mutation was 1, 3 and 13% in Lambaréné, Kumasi and Kisumu, respectively. Isolates with two pfmdr1 gene copy number predominantly harboured the N86Y wild-type allele and were mostly found in Kumasi (10%) (P < 0.0001). Among the main pfmdr1 haplotypes (NFD, NYD and YFD), NYD was associated with highest parasitaemia (P = 0.04). At the pfatp6 locus, H243Y and A623E mutations were observed at very low frequency at all three sites. The prevalence of the pfatp6 E431K variant was 6, 18 and 17% in Lambaréné, Kumasi and Kisumu, respectively. The L263E and S769N mutations were absent in all isolates. The pfk13 variants associated with artemisinin resistance in Southeast Asia were not observed. Eleven novel substitutions in the pfk13 locus occurring at low frequency were observed.

Conclusions

Artemisinins are still highly efficacious in large malaria-endemic regions though declining efficacy has occurred in Southeast Asia. The return of chloroquine-sensitive strains following the removal of drug pressure is observed. However, selection of wild-type alleles in the multidrug-resistance gene and the increased gene copy number is associated with reduced lumefantrine sensitivity. This study indicates a need to constantly monitor drug resistance to artemisinin in field isolates from malaria-endemic countries.

Molecular surveillance of Plasmodium falciparum drug resistance in the Republic of Congo: four and nine years after the introduction of artemisinin-based combination therapy

BACKGROUND

Resistance to anti-malarial drugs hinders efforts on malaria elimination and eradication. Following the global spread of chloroquine-resistant parasites, the Republic of Congo adopted artemisinin-based combination therapy (ACT) in 2006 as a first-line treatment for uncomplicated malaria. To assess the impacts after implementation of ACT, a molecular surveillance for anti-malarial drug resistance was conducted in Congo 4 and 9 years after the introduction of ACT.

METHODS

Blood samples of 431 febrile children aged 1-10 years were utilized from two previous studies conducted in 2010 (N = 311) and 2015 (N = 120). All samples were screened for malaria parasites using nested PCR. Direct sequencing was used to determine the frequency distribution of genetic variants in the anti-malarial drug-resistant Plasmodium falciparum genes (Pfcrt, Pfmdr1, Pfatp6, Pfk13) in malaria-positive isolates.

RESULTS

One-hundred and nineteen (N = 70 from 2010 and N = 49 from 2015) samples were positive for P. falciparum. A relative decrease in the proportion of chloroquine-resistant haplotype (CVIET) from 100% in 2005, 1 year before the introduction and implementation of ACT in 2006, to 98% in 2010 to 71% in 2015 was observed. Regarding the multidrug transporter gene, a considerable reduction in the frequency of the mutations N86Y (from 73 to 27%) and D1246Y (from 22 to 0%) was observed. However, the prevalence of the Y184F mutation remained stable (49% in 2010 compared to 54% in 2015). Isolates carrying the Pfatp6 H243Y was 25% in 2010 and this frequency was reduced to null in 2015. None of the parasites harboured the Pfk13 mutations associated with prolonged artemisinin clearance in Southeast Asia. Nevertheless, 13 new Pfk13 variants are reported among the investigated isolates.

CONCLUSION

The implementation of ACT has led to the decline in prevalence of chloroquine-resistant parasites in the Republic of Congo. However, the constant prevalence of the PfMDR1 Y184F mutation, associated with lumefantrine susceptibility, indicate a selective drug pressure still exists. Taken together, this study could serve as the basis for epidemiological studies monitoring the distribution of molecular markers of artemisinin resistance in the Republic of Congo.

Biodegradable Polymeric Nanocapsules Prevent Cardiotoxicity of Anti-Trypanosomal Lychnopholide

Chagas disease is a neglected parasitic disease caused by the protozoan Trypanosoma cruzi. New antitrypanosomal options are desirable to prevent complications, including a high rate of cardiomyopathy. Recently, a natural substance, lychnopholide, has shown therapeutic potential, especially when encapsulated in biodegradable polymeric nanocapsules. However, little is known regarding possible adverse effects of lychnopholide. Here we show that repeated-dose intravenous administration of free lychnopholide (2.0 mg/kg/day) for 20 days caused cardiopathy and mortality in healthy C57BL/6 mice. Echocardiography revealed concentric left ventricular hypertrophy with preserved ejection fraction, diastolic dysfunction and chamber dilatation at end-stage. Single cardiomyocytes presented altered contractility and Ca²⁺ handling, with spontaneous Ca²⁺ waves in diastole. Acute in vitro lychnopholide application on cardiomyocytes from healthy mice also induced Ca²⁺ handling alterations with abnormal RyR2-mediated diastolic Ca²⁺ release. Strikingly, the encapsulation of lychnopholide prevented the cardiac alterations induced in vivo by the free form repeated doses. Nanocapsules alone had no adverse cardiac effects. Altogether, our data establish lychnopholide presented in nanocapsule form more firmly as a promising new drug candidate to cure Chagas disease with minimal cardiotoxicity. Our study also highlights the potential of nanotechnology not only to improve the efficacy of a drug but also to protect against its adverse effects.

Determination of glutathione redox potential and pH value in subcellular compartments of malaria parasites

The malaria parasite Plasmodium falciparum is exposed to multiple sources of oxidative challenge during its complex life cycle in the Anopheles vector and its human host. In order to further elucidate redox-based parasite host cell interactions and mechanisms of drug action, we targeted the genetically encoded glutathione redox sensor roGFP2 coupled to human glutaredoxin 1 (roGFP2-hGrx1) as well as the ratiometric pH sensor pHluorin to the apicoplast and the mitochondrion of P. falciparum. Using live cell imaging, this allowed for the first time the determination of the pH values of the apicoplast (7.12±0.40) and mitochondrion (7.37±0.09) in the intraerythrocytic asexual stages of the parasite. Based on the roGFP2-hGrx1 signals, glutathione-dependent redox potentials of -267mV and -328mV, respectively, were obtained. Employing these novel tools, initial studies on the effects of redox-active agents and clinically employed antimalarial drugs were carried out on both organelles.

Unlocking Nanocarriers for the Programmed Release of Antimalarial Drugs

A programmable release system with wide range of release profiles of the antimalarial artemisone (ART) from fibrous nanocarriers (NFN) is presented. This is achieved following a new paradigm of using ART-loaded NFN in infusion system of hydrophobic drug eluting nanocarriers, adapted to clinical applications. Very importantly, under these conditions ART did not degrade as it was observed in solution.

In silico approaches and chemical space of anti-P-type ATPase compounds for discovering new antituberculous drugs

Tuberculosis (TB) is one of the most important public health problems around the world. The emergence of multi-drug-resistant (MDR) and extensively drug-resistant (XDR) Mycobacterium tuberculosis strains has driven the finding of alternative anti-TB targets. In this context, P-type ATPases are interesting therapeutic targets due to their key role in ion homeostasis across the plasma membrane and the mycobacterial survival inside macrophages. In this review, in silico and experimental strategies used for the rational design of new anti-TB drugs are presented; in addition, the chemical space distribution based on the structure and molecular properties of compounds with anti-TB and anti-P-type ATPase activity is discussed. The chemical space distribution compared to public compound libraries demonstrates that natural product libraries are a source of novel chemical scaffolds with potential anti-P-type ATPase activity. Furthermore, compounds that experimentally display anti-P-type ATPase activity belong to a chemical space of molecular properties comparable to that occupied by those approved for oral use, suggesting that these kinds of molecules have a good pharmacokinetic profile (drug-like) for evaluation as potential anti-TB drugs.

Design, in silico and in vitro evaluation of curcumin analogues against Plasmodium falciparum

The polyphenolic compound curcumin has been reported for its antimalarial properties in various scientific studies. Plasmodium falciparum ATP6, the parasite orthologue of mammalian sarcoplasmic Ca²⁺ ATPase (SERCA) has been identified as a key molecular target of both artemisinin and curcumin. The work was thereby undertaken to study the anti-malarial properties of two different series of curcumin analogues based on their docking interactions with PfATP6 and correlating the results with their anti-malarial activity. The compounds were designed retaining similar functional groups as that of the parent curcumin nucleus while incorporating changes in the carbon chain length, unsaturated groups and the number of ketone groups. The compounds (1E, 4E)-1,5-bis(4-methylphenyl)penta-1,4-dien-3-one (CD-9), (1E, 4E)-1,5-bis(4-methoxyphenyl)penta-1,4-dien-3-one (CD-8) and (E)-1,3-bis(4-hydroxylphenyl)prop-2-en-1-one (CD-1) showed IC₅₀ values of 1.642 μM, 1.764 μM and 2.59 μM in 3D7 strain and 3.039 μM, 7.40 μM and 11.3 μM in RKL-2 strain respectively. Detailed structure-activity relationship studies of the compounds showed that CD-9 and CD-8 had a common hydrophobic interaction with the residue Leu268 of the PfATP6 protein and has been postulated through our study to be the reason for their antimalarial activity as seen after corroborating the results with the in vitro study. The study provided valuable insight about the ligand-protein interaction of the various functional groups of curcumin and its analogues against the PfATP6 protein and their importance in imparting antimalarial action.

SC83288 is a clinical development candidate for the treatment of severe malaria

Severe malaria is a life-threatening complication of an infection with the protozoan parasite Plasmodium falciparum, which requires immediate treatment. Safety and efficacy concerns with currently used drugs accentuate the need for new chemotherapeutic options against severe malaria. Here we describe a medicinal chemistry program starting from amicarbalide that led to two compounds with optimized pharmacological and antiparasitic properties. SC81458 and the clinical development candidate, SC83288, are fast-acting compounds that can cure a P. falciparum infection in a humanized NOD/SCID mouse model system. Detailed preclinical pharmacokinetic and toxicological studies reveal no observable drawbacks. Ultra-deep sequencing of resistant parasites identifies the sarco/endoplasmic reticulum Ca2+ transporting PfATP6 as a putative determinant of resistance to SC81458 and SC83288. Features, such as fast parasite killing, good safety margin, a potentially novel mode of action and a distinct chemotype support the clinical development of SC83288, as an intravenous application for the treatment of severe malaria.

Target identification with quantitative activity based protein profiling (ABPP)

As many small bioactive molecules fulfill their functions through interacting with protein targets, the identification of such targets is crucial in understanding their mechanisms of action (MOA) and side effects. With technological advancements in target identification, it has become possible to accurately and comprehensively study the MOA and side effects of small molecules. While small molecules with therapeutic potential were derived solely from nature in the past, the remodeling and synthesis of such molecules have now been made possible. Presently, while some small molecules have seen successful application as drugs, the majority remain undeveloped, requiring further understanding of their MOA and side effects to fully tap into their potential. Given the typical promiscuity of many small molecules and the complexity of the cellular proteome, a high-flux and high-accuracy method is necessary. While affinity chromatography approaches combined with MS have had successes in target identification, limitations associated with nonspecific results remain. To overcome these complications, quantitative chemical proteomics approaches have been developed including metabolic labeling, chemical labeling, and label-free methods. These new approaches are adopted in conjunction with activity-based protein profiling (ABPP), allowing for a rapid process and accurate results. This review will briefly introduce the principles involved in ABPP, then summarize current advances in quantitative chemical proteomics approaches as well as illustrate with examples how ABPP coupled with quantitative chemical proteomics has been used to detect the targets of drugs and other bioactive small molecules including natural products.

Artemisinins Target GABAA Receptor Signaling and Impair α Cell Identity

Type 1 diabetes is characterized by the destruction of pancreatic β cells, and generating new insulin-producing cells from other cell types is a major aim of regenerative medicine. One promising approach is transdifferentiation of developmentally related pancreatic cell types, including glucagon-producing α cells. In a genetic model, loss of the master regulatory transcription factor Arx is sufficient to induce the conversion of α cells to functional β-like cells. Here, we identify artemisinins as small molecules that functionally repress Arx by causing its translocation to the cytoplasm. We show that the protein gephyrin is the mammalian target of these antimalarial drugs and that the mechanism of action of these molecules depends on the enhancement of GABA_A receptor signaling. Our results in zebrafish, rodents, and primary human pancreatic islets identify gephyrin as a druggable target for the regeneration of pancreatic β cell mass from α cells.

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Artemisinins inhibit ARX function and impair α cell identity

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Compounds act by stabilizing gephyrin, thus enhancing GABA_A receptor signaling

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Artemisinins increase β cell mass in zebrafish and rodent models

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Functional and transcriptional data indicate a conserved phenotype in human islets

Pharmacokinetics of the Antischistosomal Lead Ozonide OZ418 in Uninfected Mice Determined by Liquid Chromatography-Tandem Mass Spectrometry

One of the major neglected tropical diseases, schistosomiasis, is currently treated and controlled with a single drug, praziquantel. The quest for an alternative drug is fueled by the lack of activity of praziquantel against juvenile Schistosoma worms and the fear of emerging resistance. The synthetic ozonide OZ418 has shown high activity against Schistosoma mansoni, S. haematobium, and S. japonicum in vivo, but its drug disposition remains unknown. To bridge this gap, our study determined the basic pharmacokinetic (PK) parameters of a single oral dose (400 mg/kg of body weight) of OZ418 in uninfected mice. First, a simple liquid chromatography-tandem mass spectrometry (LC-MS/MS) method to quantify OZ418 concentrations in mouse plasma was successfully developed and validated according to U.S. FDA guidelines. This method proved to be selective, accurate (93 to 103%), precise (5 to 16%), and devoid of significant matrix effects (90 to 102%) and provided excellent recovery (101 to 102%). A median peak concentration of 190 (range, 185 to 231) μg/ml was reached at 2 h (2 to 3 h) posttreatment. A naive pooled noncompartmental PK analysis estimated a mean area under the plasma concentration-versus-time curve (AUC) of 9,303 μg h/ml (7,039.2 to 11,908.5 μg h/ml) and a half-life of 38.7 h (20 to 64.6 h). Thus, the OZ418 level in plasma remained well above its in vitro 50% inhibitory concentrations (IC₅₀s) of 27.4 μg/ml (adult S. mansoni worms at 72 h) for at least 75 h. Consistently, OZ418 degraded little in plasma at 37°C (<20% in 121 h) and weakly inhibited cytochrome P450 (CYP450) metabolism (IC₅₀ of 37 to 144 μM). Our results provide a first insight into the disposition of OZ418, paving the way for further studies of its biological fate and effect.

Artemisinin and its derivatives in treating protozoan infections beyond malaria

Parasitic protozoan diseases continue to rank among the world's greatest global health problems, which are also common among poor populations. Currently available drugs for treatment present drawbacks, urging the need for more effective, safer, and cheaper drugs. Artemisinin (ART) and its derivatives are some of the most important classes of antimalarial agents originally derived from Artemisia annua L. However, besides the outstanding antimalarial and antischistosomal activities, ART and its derivatives also possess activities against other parasitic protozoa. In this paper we review the activities of ART and its derivatives against protozoan parasites in vitro and in vivo, including Leishmania spp., Trypanosoma spp., Toxoplasma gondii, Neospora caninum, Eimeria tenella, Acanthamoeba castellanii, Naegleria fowleri, Cryptosporidium parvum, Giardia lamblia, and Babesia spp. We conclude that ART and its derivatives may be good alternatives for treating other non-malarial protozoan infections in developing countries, although more studies are necessary before they can be applied clinically.

The Fascinating Effects of Baicalein on Cancer: A Review

Cancer is one of the leading causes of death worldwide and a major global health problem. In recent decades, the rates of both mortality and morbidity of cancer have rapidly increased for a variety of reasons. Despite treatment options, there are serious side effects associated with chemotherapy drugs and multiple forms of drug resistance that significantly reduce their effects. There is an accumulating amount of evidence on the pharmacological activities of baicalein (e.g., anti-inflammatory, antioxidant, antiviral, and antitumor effects). Furthermore, there has been great progress in elucidating the target mechanisms and signaling pathways of baicalein's anti-cancer potential. The anti-tumor functions of baicalein are mainly due to its capacities to inhibit complexes of cyclins to regulate the cell cycle, to scavenge oxidative radicals, to attenuate mitogen activated protein kinase (MAPK), protein kinase B (Akt) or mammalian target of rapamycin (mTOR) activities, to induce apoptosis by activating caspase-9/-3 and to inhibit tumorinvasion and metastasis by reducing the expression of matrix metalloproteinase-2/-9 (MMP-2/-9). In this review, we focused on the relevant biological mechanisms of baicalein involved in inhibiting various cancers, such as bladder cancer, breast cancer, and ovarian cancer. Moreover, we also summarized the specific mechanisms by which baicalein inhibited the growth of various tumors in vivo. Taken together, baicalein may be developed as a potential, novel anticancer drug to treat tumors.

Organism-like formation of Schistosoma hemozoin and its function suggest a mechanism for anti-malarial action of artemisinin

The current theories of antimalarial mechanism of artemisinin are inadequate to fully explain the observed effects. In our study, “organism-like” formation of Schistosoma hemozoin granules by attaching to and utilizing erythrocytes to form new ones was observed. This indicates that heme iron is transferred from erythrocytes to hemozoin granules during their formation. However, as a disposal product of heme detoxification, these granules are not completely expelled from the Schistosoma gut, but decomposed again between microvilli in the posterior portion of the gut to transfer iron to eggs. Based on the function of iron transport supported by our observation of the unique process of Schistosoma hemozoin formation, here we propose a new viewpoint of antimalarial mechanism of artemisinin, which emphasizes the final outcome, i.e., interference of iron utilization in parasites by artemisinin, instead of focusing on the mode of interaction between artemisinin and heme or hemozoin. This suggests that artemisinin and its endoperoxides derivatives likely hit the Achilles’ heel of hemozoin-producing and iron-dependent organisms.

Clinical and non-clinical safety of artemisinin derivatives in pregnancy

Malaria in pregnancy is a clinically wasting infectious disease, where drug therapy has to be promptly initiated. Currently, the treatment of this infection depends on the use of artemisinin derivatives. The World Health Organization does not recommend the use of these drugs in the first trimester of pregnancy due to non-clinical findings that have shown embryolethality and teratogenic effects. Nevertheless, until now, this toxicity has not been proved in humans. Artemisinin derivatives mechanisms of embryotoxicity are related to depletion of circulating embryonic primitive erythroblasts. Species differences in this sensitive period for toxicity and the presence of malaria infection, which could reduce drug distribution to the fetus, are significant to the risk assessment of artemisinin derivatives treatment to pregnant women. In this review we aimed to assess the results of non-clinical and clinical studies with artemisinin derivatives, their mechanisms of embryotoxicity and discuss the safety of their use during pregnancy.

Mechanism of artemisinin resistance for malaria PfATP6 L263 mutations and discovering potential antimalarials: An integrated computational approach

Artemisinin resistance in Plasmodium falciparum threatens global efforts in the elimination or eradication of malaria. Several studies have associated mutations in the PfATP6 gene in conjunction with artemisinin resistance, but the underlying molecular mechanism of the resistance remains unexplored. Associated mutations act as a biomarker to measure the artemisinin efficacy. In the proposed work, we have analyzed the binding affinity and efficacy between PfATP6 and artemisinin in the presence of L263D, L263E and L263K mutations. Furthermore, we performed virtual screening to identify potential compounds to inhibit the PfATP6 mutant proteins. In this study, we observed that artemisinin binding affinity with PfATP6 gets affected by L263D, L263E and L263K mutations. This in silico elucidation of artemisinin resistance enhanced the identification of novel compounds (CID: 10595058 and 10625452) which showed good binding affinity and efficacy with L263D, L263E and L263K mutant proteins in molecular docking and molecular dynamics simulations studies. Owing to the high propensity of the parasite to drug resistance the need for new antimalarial drugs will persist until the malarial parasites are eventually eradicated. The two compounds identified in this study can be tested in in vitro and in vivo experiments as possible candidates for the designing of new potential antimalarial drugs.

Immune suppressive properties of artemisinin family drugs

Artemisinin and its derivatives are the first-line antimalarial drugs, and have saved millions of lives across the globe, especially in developing world. The discovery of artemisinin by Youyou Tu was awarded the 2015 Nobel Prize in Physiology or Medicine. In addition to treating malaria, accumulating evidences suggest that artemisinin and its derivatives also possess potent anti-inflammatory and immunoregulatory properties. We recently showed that artesunate, an artemisinin analog, dramatically ameliorated autoimmune arthritis by selectively diminishing germinal center B cells. Herein, we review the immunosuppressive properties of artemisinin family drugs and the potential underlying mechanisms.

Artemisinin-based antimalarial research: application of biotechnology to the production of artemisinin, its mode of action, and the mechanism of resistance of Plasmodium parasites

Malaria is a worldwide disease caused by Plasmodium parasites. A sesquiterpene endoperoxide artemisinin isolated from Artemisia annua was discovered and has been accepted for its use in artemisinin-based combinatorial therapies, as the most effective current antimalarial treatment. However, the quantity of this compound produced from the A. annua plant is very low, and the availability of artemisinin is insufficient to treat all infected patients. In addition, the emergence of artemisinin-resistant Plasmodium has been reported recently. Several techniques have been applied to enhance artemisinin availability, and studies related to its mode of action and the mechanism of resistance of malaria-causing parasites are ongoing. In this review, we summarize the application of modern technologies to improve the production of artemisinin, including our ongoing research on artemisinin biosynthetic genes in other Artemisia species. The current understanding of the mode of action of artemisinin as well as the mechanism of resistance against this compound in Plasmodium parasites is also presented. Finally, the current situation of malaria infection and the future direction of antimalarial drug development are discussed.

Understanding malarial toxins

Recognized since antiquity, malaria is one of the most infamous and widespread infectious diseases in humans and, although the death rate during the last century has been diminishing, it still accounts for more than a half million deaths annually. It is caused by the Plasmodium parasite and typical symptoms include fever, shivering, headache, diaphoresis and nausea, all resulting from an excessive inflammatory response induced by malarial toxins released into the victim's bloodstream. These toxins are hemozoin and glycosylphosphatidylinositols. The former is the final product of the parasite's detoxification of haeme, a by-product of haemoglobin catabolism, while the latter anchor proteins to the Plasmodium cell surface or occur as free molecules. Currently, only two groups of antimalarial toxin drugs exist on the market, quinolines and artemisinins. As we describe, they both target biosynthesis of hemozoin. Other substances, currently in various phases of clinical trials, are directed towards biosynthesis of glycosylphosphatidylinositol, formation of hemozoin, or attenuation of the inflammatory response of the patient. Among the innovative approaches to alleviating the effects of malarial toxins, is the development of antimalarial toxin vaccines. In this review the most important lessons learned from the use of treatments directed against the action of malarial toxins in antimalarial therapy are emphasized and the most relevant and promising directions for future research in obtaining novel antimalarial agents acting on malarial toxins are discussed.

Ion Regulation in the Malaria Parasite

Some hours after invading the erythrocytes of its human host, the malaria parasite Plasmodium falciparum induces an increase in the permeability of the erythrocyte membrane to monovalent ions. The resulting net influx of Na(+) and net efflux of K(+), down their respective concentration gradients, converts the erythrocyte cytosol from an initially high-K(+), low-Na(+) solution to a high-Na(+), low-K(+) solution. The intraerythrocytic parasite itself exerts tight control over its internal Na(+), K(+), Cl(-), and Ca(2+) concentrations and its intracellular pH through the combined actions of a range of membrane transport proteins. The molecular mechanisms underpinning ion regulation in the parasite are receiving increasing attention, not least because PfATP4, a P-type ATPase postulated to be involved in Na(+) regulation, has emerged as a potential antimalarial drug target, susceptible to inhibition by a wide range of chemically unrelated compounds.

Artemisinin Action and Resistance in Plasmodium falciparum

The worldwide use of artemisinin-based combination therapies (ACTs) has contributed in recent years to a substantial reduction in deaths resulting from Plasmodium falciparum malaria. Resistance to artemisinins, however, has emerged in Southeast Asia. Clinically, resistance is defined as a slower rate of parasite clearance in patients treated with an artemisinin derivative or an ACT. These slow clearance rates associate with enhanced survival rates of ring-stage parasites briefly exposed in vitro to dihydroartemisinin. We describe recent progress made in defining the molecular basis of artemisinin resistance, which has identified a primary role for the P. falciparum K13 protein. Using K13 mutations as molecular markers, epidemiological studies are now tracking the emergence and spread of artemisinin resistance. Mechanistic studies suggest potential ways to overcome resistance.

Dihydroartemisinin, an Anti-Malaria Drug, Suppresses Estrogen Deficiency-Induced Osteoporosis, Osteoclast Formation, and RANKL-Induced Signaling Pathways

Osteoporosis is an osteolytic disease that features enhanced osteoclast formation and bone resorption. Identification of agents that can inhibit osteoclast formation and function is important for the treatment of osteoporosis. Dihydroartemisinin is a natural compound used to treat malaria but its role in osteoporosis is not known. Here, we found that dihydroartemisinin can suppress RANKL-induced osteoclastogenesis and bone resorption in a dose-dependent manner. Dihydroartemisinin inhibited the expression of osteoclast marker genes such as cathepsin K, calcitonin receptor, and tartrate-resistant acid phosphatase (TRAcP). Furthermore, dihydroartemisinin inhibited RANKL-induced NF-κB and NFAT activity. In addition, using an in vivo ovariectomized mouse model, we show that dihydroartemisinin is able to reverse the bone loss caused by ovariectomy. Together, this study shows that dihydroartemisinin attenuates bone loss in ovariectomized mice through inhibiting RANKL-induced osteoclast formation and function. This indicates that dihydroartemisinin, the first physiology or medicine nobel prize discovery of China, is a potential treatment option against osteolytic bone disease. © 2015 American Society for Bone and Mineral Research.

Antiparasitic peptides

: The most important parasitic diseases, malaria, leishmaniasis, trypanosomiasis, and schistosomiasis, are a great burden to mankind, threatening the life of millions of people worldwide and mostly affecting the poorest. Because drug resistance is increasing and vaccines are rarely available, novel chemotherapeutic compounds are necessary in order to treat these devastating diseases. Insects serve as vectors of many human parasitic diseases and have been shown to express a huge variety of antimicrobial peptides (AMPs). Therefore, research activity on insect-derived AMPs has been increasing in the last 40 years. This chapter summarizes the current state of research on the possible role of AMPs as potential chemotherapeutic compounds against human parasitic diseases. As a representative antimicrobial peptide with antiparasitic activity, the structure of insect defensin A is shown [PDB accession code: 1ICA]. The molecule is surrounded by schematic representations of the human pathogenic parasites Plasmodium, Leishmania and Trypanosoma.

Examining Plasmodium falciparum and P. vivax clearance subsequent to antimalarial drug treatment in the Myanmar-China border area based on quantitative real-time polymerase chain reaction

BACKGROUND

Recent emergence of artemisinin-resistant P. falciparum has posed a serious hindrance to the elimination of malaria in the Greater Mekong Subregion. Parasite clearance time, a measure of change in peripheral parasitaemia in a sequence of samples taken after treatment, can be used to reflect the susceptibility of parasites or the efficiency of antimalarials. The association of genetic polymorphisms and artemisinin resistance has been documented. This study aims to examine clearance time of P. falciparum and P. vivax parasitemia as well as putative gene mutations associated with residual or recurred parasitemia in Myanmar.

METHODS

A total of 63 P. falciparum and 130 P. vivax samples collected from two internally-displaced populations and one surrounding village were examined for parasitemia changes. At least four samples were taken from each patient, at the first day of diagnosis up to 3 months following the initial treatment. The amount of parasite gene copy number was estimated using quantitative real-time PCR based on a species-specific region of the 18S rRNA gene. For samples that showed residual or recurred parasitemia after treatment, microsatellites were used to identify the 'post-treatment' parasite genotype and compared such with the 'pre-treatment' genotype. Mutations in genes pfcrt, pfmdr1, pfatp6, pfmrp1 and pfK13 that are potentially associated with ACT resistance were examined to identify if mutation is a factor for residual or persistent parasitemia.

RESULTS

Over 30% of the P. falciprium infections showed delayed clearance of parasitemia after 2-3 days of treatment and 9.5% showed recurred parasitemia. Mutations in codon 876 of the pfmrp1 corroborated significance association with slow clearance time. However, no association was observed in the variation in pfmdr1 gene copy number as well as mutations of various codonsinpfatp6, pfcrt, and pfK13 with clearance time. For P. vivax, over 95% of the infections indicated cleared parasitemia at days 2-3 of treatment. Four samples were found to be re-infected with new parasite strains based on microsatellite genotypes after initial treatment.

CONCLUSION

The appearance of P.falciparum infected samples showing delayed clearance or recurred parasitemia after treatment raises concerns on current treatment and ACT drug resistance.

Profiling of Multiple Targets of Artemisinin Activated by Hemin in Cancer Cell Proteome

The antimalarial drug artemisinin is found to have diverse biological activities ranging from anti-inflammatory to anticancer properties; however, as of today, the cellular targets and mechanism of action of this important compound have remained elusive. Here, we report the global protein target profiling of artemisinin in the HeLa cancer cell proteome using a chemical proteomics approach. In the presence of hemin, multiple proteins were targeted by artemisinin probe through covalent modification. Further studies revealed that reducing of hemin to heme by protein thiols was essential for endoperoxide activation and subsequent protein alkylation. Artemisinin may exert its synergistic therapeutic anticancer effects via modulation of a variety of cellular pathways through acting on multiple targets.

The molecular and cellular action properties of artemisinins: what has yeast told us?

Artemisinin (ART) or Qinghaosu is a natural compound possessing superior anti-malarial activity. Although intensive studies have been done in the medicinal chemistry field to understand the structure-effect relationship, the biological actions of artemisinin are poorly understood and controversial. Due to the current lack of a genetic amiable model to address this question, and an accidental finding made more than a decade ago during our initial exploratory efforts that yeast Saccharomyces cerevisiae can be inhibited by artemisinin, we have since been using the baker's yeast as a model to probe the molecular and cellular properties of artemisinin and its derivatives (ARTs) in living cells. ARTs were found to possess potent and specific anti-mitochondrial properties and, to a lesser extent, the ability to generate a relatively general oxidative damage. The anti-mitochondrial effects of artemisinin were later confirmed with purified mitochondria from malaria parasites. Inside some cells heme appears to be a primary reducing agent and reduction of ARTs by heme can induce a relatively nonspecific cellular damage. The molecular basis of the anti-mitochondrial properties of ARTs remains not well elucidated yet. We propose that the anti-mitochondrial and heme-mediated ROS-generating properties constitute two cellcidal actions of ARTs. This review summarizes what we have learned from yeast about the basic biological properties of ARTs, as well as some key unanswered questions. We believe yeast could serve as a window through which to peek at some of the biological action secrets of ARTs that might be difficult for us to learn otherwise.

Ca(2+) monitoring in Plasmodium falciparum using the yellow cameleon-Nano biosensor

Calcium (Ca(2+))-mediated signaling is a conserved mechanism in eukaryotes, including the human malaria parasite, Plasmodium falciparum. Due to its small size (<10 μm) measurement of intracellular Ca(2+) in Plasmodium is technically challenging, and thus Ca(2+) regulation in this human pathogen is not well understood. Here we analyze Ca(2+) homeostasis via a new approach using transgenic P. falciparum expressing the Ca(2+) sensor yellow cameleon (YC)-Nano. We found that cytosolic Ca(2+) concentration is maintained at low levels only during the intraerythrocytic trophozoite stage (30 nM), and is increased in the other blood stages (>300 nM). We determined that the mammalian SERCA inhibitor thapsigargin and antimalarial dihydroartemisinin did not perturb SERCA activity. The change of the cytosolic Ca(2+) level in P. falciparum was additionally detectable by flow cytometry. Thus, we propose that the developed YC-Nano-based system is useful to study Ca(2+) signaling in P. falciparum and is applicable for drug screening.

The Golgi Apparatus: Panel Point of Cytosolic Ca(2+) Regulation

The Golgi apparatus (GA), an intermediate organelle of the cell inner membrane system, plays a key role in protein glycosylation and secretion. In recent years, this organelle has been found to act as a vital intracellular Ca(2+) store because different Ca (2+) regulators, such as the inositol-1,4,5-triphosphate receptor, sarco/endoplasmic reticulum Ca(2+) -ATPase and secretory pathway Ca 2+ -ATPase, were demonstrated to localize on their membrane. The mechanisms involved in Ca(2+) release and uptake in the GA have now been established.Here, based on careful backward looking on compartments and patterns in GA Ca (2+) regulation, we review neurological diseases related to GA calcium remodeling and propose a modified cytosolic Ca(2+) adjustment model, in which GA acts as part of the panel point.

Identification and Functional Characterization of Sesquiterpene Synthases from Xanthium strumarium

Xanthium strumarium synthesizes various pharmacologically active sesquiterpenes. The molecular characterization of sesquiterpene biosynthesis in X. strumarium has not been reported so far. In this study, the cDNAs coding for three sesquiterpene synthases (designated as XsTPS1, XsTPS2 and XsTPS3) were isolated using the X. strumarium transcriptome that we recently constructed. XsTPS1, XsTPS2 and XsTPS3 were revealed to have primary activities forming germacrene D, guaia-4,6-diene and germacrene A, respectively, by either ectopic expression in yeast cells or purified recombinant protein-based in vitro assays. Quantitative real-time PCRs and metabolite analysis for the different plant parts showed that the transcript abundance of XsTPS1-XsTPS3 is consistent with the accumulation pattern of their enzymatic products, supporting their biochemical functions in vivo. In particular, we discovered that none of the XsTPS2 product, guaia-4,6-diene, can be detected in one of the X. strumarium cultivars used in this study (it was named the Hubei-cultivar), in which a natural deletion of two A bases in the XsTPS2 cDNA disrupts its activity, which further confirmed the proposed biochemical role of XsTPS2 in X. strumarium in vivo.

Artemisinin activity-based probes identify multiple molecular targets within the asexual stage of the malaria parasites Plasmodium falciparum 3D7

The artemisinin (ART)-based antimalarials have contributed significantly to reducing global malaria deaths over the past decade, but we still do not know how they kill parasites. To gain greater insight into the potential mechanisms of ART drug action, we developed a suite of ART activity-based protein profiling probes to identify parasite protein drug targets in situ. Probes were designed to retain biological activity and alkylate the molecular target(s) of Plasmodium falciparum 3D7 parasites in situ. Proteins tagged with the ART probe can then be isolated using click chemistry before identification by liquid chromatography-MS/MS. Using these probes, we define an ART proteome that shows alkylated targets in the glycolytic, hemoglobin degradation, antioxidant defense, and protein synthesis pathways, processes essential for parasite survival. This work reveals the pleiotropic nature of the biological functions targeted by this important class of antimalarial drugs.

Assessment of in vivo antimalarial activity of arteether and garlic oil combination therapy

The study evaluates in vivo antimalarial activity of arteether and garlic pearl oil combination in Plasmodium berghei-infected mouse model of malaria. 72 h (Day 3) post infection, at 2–4% parasitemia, mice were treated with single dose intramuscular injection of α-β arteether, at 750 μg, in combination with three 100 μL oral doses of garlic pearl oil on Day 3, Day 4 and Day 5. Following the treatment, 100% protection and survival of mice were observed. Inhibition of parasitemia in combination treated animals and protection during recrudescence interval of α-β arteether monotherapy was observed in Giemsa-stained blood smears. In addition, a striking increase in anti-parasite antibody IgG contributing protective immunity during the recrudescence phase was observed. These results correlate with western blot analysis, where sera from the recrudescence stage and later period of arteether and garlic oil combination treated animals found to interact with several parasite specific proteins as compared to controls. The present approach shows that arteether and garlic pearl oil combination provides complete protection in P. berghei-infected mice. Thus, for the first time, garlic pearl oil appears to be an ideal antimalarial candidate in artemisinin combination therapy.

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Garlic pearl oil enhanced antimalarial activity of α-β arteether.

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Garlic pearl oil and α-β arteether combination effectively evaded recrudescence.

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Garlic pearl oil and α-β arteether combination may elicit immunomodulatory effect.

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This combination therapy resulted in a striking increase in anti-parasite antibody.

Quantitative proteomic analyses of Schistosoma japonicum in response to artesunate

Artesunate (ART) has high prophylactic efficacy against Schistosoma japonicum infections and has been used to treat and prevent schistosomiasis in China since 1995. However, the molecular mechanism of ART's effects on S. japonicum remains unclear. Herein, we applied isobaric tagging reagents for relative and absolute quantification analyses coupled with two-dimensional liquid chromatography and tandem mass spectrometry to investigate the effect of ART on the proteome of S. japonicum in susceptible mice. 4529 proteins were quantified on the basis of 21,825 unique peptides. Comparative proteomic analyses revealed that 145, 228 and 185 proteins were significantly differentially expressed after ART treatment in schistosomula, juvenile and adult worms, respectively. Ninety proteins were differentially expressed between each two treatment groups in response to ART treatment: 67 proteins were associated with S. japonicum development/aging and 23 were specifically associated with ART treatment. Quantitative real-time PCR of selected genes verified the proteomic data. Gene ontology annotation and Kyoto encyclopedia of genes and genomes pathway mapping analysis showed that the majority of differentially expressed proteins were involved in stress/defense/detoxification, signal transduction, carbohydrate metabolism, amino acid metabolism, transcription/translation, and protein synthesis/assembly/degradation. Thirty-four of the proteins differentially expressed under ART treatment encoded hypothetical, uncharacterized proteins with unknown functions. This study obtained the first comprehensive protein expression profile of S. japonicum in response to ART, and provides a basis for a better understanding of the molecular mechanisms of ART effects on S. japonicum.

Updates on artemisinin: an insight to mode of actions and strategies for enhanced global production

Application of traditional Chinese drug, artemisinin, originally derived from Artemisia annua L., in malaria therapy has now been globally accepted. Artemisinin and its derivatives, with their established safety records, form the first line of malaria treatment via artemisinin combination therapies (ACTs). In addition to its antimalarial effects, artemisinin has recently been evaluated in terms of its antitumour, antibacterial, antiviral, antileishmanial, antischistosomiatic, herbicidal and other properties. However, low levels of artemisinin in plants have emerged various conventional, transgenic and nontransgenic approaches for enhanced production of the drug. According to WHO (2014), approximately 3.2 billion people are at risk of this disease. However, unfortunately, artemisinin availability is still facing its short supply. To fulfil artemisinin's global demand, no single method alone is reliable, and there is a need to collectively use conventional and advanced approaches for its higher production. Further, it is the unique structure of artemisinin that makes it a potential drug not only against malaria but to other diseases as well. Execution of its action through multiple mechanisms is probably the reason behind its wide spectrum of action. Unfortunately, due to clues for developing artemisinin resistance in malaria parasites, it has become desirable to explore all possible modes of action of artemisinin so that new generation antimalarial drugs can be developed in future. The present review provides a comprehensive updates on artemisinin modes of action and strategies for enhanced artemisinin production at global level.

Haem-activated promiscuous targeting of artemisinin in Plasmodium falciparum

The mechanism of action of artemisinin and its derivatives, the most potent of the anti-malarial drugs, is not completely understood. Here we present an unbiased chemical proteomics analysis to directly explore this mechanism in Plasmodium falciparum. We use an alkyne-tagged artemisinin analogue coupled with biotin to identify 124 artemisinin covalent binding protein targets, many of which are involved in the essential biological processes of the parasite. Such a broad targeting spectrum disrupts the biochemical landscape of the parasite and causes its death. Furthermore, using alkyne-tagged artemisinin coupled with a fluorescent dye to monitor protein binding, we show that haem, rather than free ferrous iron, is predominantly responsible for artemisinin activation. The haem derives primarily from the parasite's haem biosynthesis pathway at the early ring stage and from haemoglobin digestion at the latter stages. Our results support a unifying model to explain the action and specificity of artemisinin in parasite killing.

The mechanism of action of artemisinin, an antimalarial drug, is not well understood. Here, the authors use a labelled artemisinin analogue to show that the drug is mainly activated by haem and then binds covalently to over 120 proteins in the malaria parasite, affecting many of its cellular processes.