Antimalarial Agent Artemisinin Research Articles

Design, synthesis, and study of a mycobactin-artemisinin conjugate that has selective and potent activity against tuberculosis and malaria.

Although the antimalarial agent artemisinin itself is not active against tuberculosis, conjugation to a mycobacterial-specific siderophore (microbial iron chelator) analogue induces significant and selective antituberculosis activity, including activity against multi- and extensively drug-resistant strains of Mycobacterium tuberculosis. The conjugate also retains potent antimalarial activity. Physicochemical and whole-cell studies indicated that ferric-to-ferrous reduction of the iron complex of the conjugate initiates the expected bactericidal Fenton-type radical chemistry on the artemisinin component. Thus, this "Trojan horse" approach demonstrates that new pathogen-selective therapeutic agents in which the iron component of the delivery vehicle also participates in triggering the antibiotic activity can be generated. The result is that one appropriate conjugate has potent and selective activity against two of the most deadly diseases in the world.

Artemisinin, an anti-malarial agent, inhibits rat cardiac hypertrophy via inhibition of NF-κB signaling

The nuclear factor (NF)-κB signaling pathway is an important intracellular mediator of cardiac hypertrophy. Recent studies have indicated that the anti-malarial agent artemisinin has the ability to inhibit NF-κB activation. We hypothesized that artemisinin would suppress cardiac hypertrophy by inhibiting NF-κB signal pathways. We tested this hypothesis using primary cultured rat cardiac myocytes and well-established rat models of cardiac hypertrophy. Artemisinin blocked angiotensin II-induced cardiac hypertrophy in vitro in a concentration-dependent manner. Furthermore, artemisinin protected against rat cardiac hypertrophy induced by transaortic constriction (TAC), as assessed by heart weight/body weight and lung weight/body weight ratios, echocardiographic parameters, and gene expression of hypertrophic markers. Electrophoretic mobility shift assays revealed increased NF-κB binding activity in cardiac nuclear extracts of banded rats that was prevented by artemisinin treatment. Banded rats treated with oral artemisinin, compared with untreated rats, showed significantly decreased the levels of IL-6, TNF-α and MCP-1 mRNA expression and increased protein levels of IκB-α, which forms a cytoplasmic inactive complex with the p65-p50 heterodimeric complex. The effect of artemisinin on cardiac hypertrophy was blocked after IκB-α was silenced by transfection of cardiomyocytes with IκB-α siRNA. Our results indicate that artemisinin inhibits cardiomyocyte growth by interfering with NF-κB signaling.

The anti-malaria agent artesunate inhibits expression of vascular endothelial growth factor and hypoxia-inducible factor-1α in human rheumatoid arthritis fibroblast-like synoviocyte

Increasing evidence indicates that the anti-malarial agent artemisinin and its derivatives may exert anti-angiogenic effect. In the present study, we explored the effect of artesunate, a artemisinin derivative, on TNFα- and hypoxia-induced expression of hypoxia inducible factor-1α (HIF-1α) and secretion of vascular endothelial growth factor (VEGF) and inteleukin-8 (IL-8) in human rheumatoid arthritis fibroblast-like synoviocytes (RA FLS), and further investigated the signal mechanism by which this compound modulates HIF-1α, VEGF and IL-8 expression. RA FLS obtained from patients with active rheumatoid arthritis were pretreated with artesunate, and then stimulated with TNFα and hypoxia. Production of VEGF and IL-8 was measured by ELISA. Nuclear location of HIF-1α was measured by confocal fluorescence microscopy. HIF-1α and other signal transduction proteins expression was measured by Western blot. Artesunate decreased the secretion of VEGF and IL-8 from TNFα- or hypoxia-stimulated RA FLS in a dose-dependent manner. Artesunate also inhibited TNFα- or hypoxia-induced nuclear expression and translocation of HIF-1α. We also showed that artesunate prevented Akt phosphorylation, but did not find evidence that phosphorylation of p38 and ERK was affected. TNFα- or hypoxia-induced secretion of VEGF and IL-8 and expression of HIF-1α were hampered by treatment with the PI3 kinase inhibitor LY294002, suggesting that inhibition of PI3 kinase/Akt activation might inhibit VEGF and IL-8 secretion and HIF-1α expression induced by TNFα or hypoxia. Our results suggest that artesunate inhibits angiogenic factor expression in RA FLS, and provide novel evidence that, as a low-cost agent, artesunate may have therapeutic potential for RA.

Tehranolide, A sesquiterpene lactone with an endoperoxide group that probably has the same effect as the antimalarial agent Artemisinin

The malaria situation is aggravated by the appearance of strains of Plasmodium falciparum resistant to antimalarial drugs as well as by the resistance of vector Anopheles mosquitoes to DDT and other insecticides. Nearly 300–500 million people are infected by malaria and the incidence of this disease is dramatically increasing, since many strains of Plasmodium falciparum, the parasite responsible for the majority of fatal malaria infections, have become resistant to chloroquine and other traditional antimalarial drugs. Fortunately, these strains are still susceptible to the artemisinin derivatives. All of the artemisinin compounds contain stable endoperoxide bridges. The extract of the aerial parts of A. diffusa collected in the Province of Khorassan (Iran) afforded, in addition to several eudesmanolides, a new type of sesquiterpene lactone (Tehranolide) with an endoperoxide group. Previously, we reported antimalarial effect of extract of A. diffusa against P. berghei. Since the endoperoxide group is an essential requirement for the antimalarial activity of artemisinin, we have presumed the antimalarial properties of the crude extract are attributed to Tehranolide. We report here the in vivo laboratory evaluation of anti-malarial effects of Tehranolide, was done on P. berghei infected NMRI mice. The antimalarial effects of Tehranolide in 27mg/ml concentration (high dose) were injected s.c. every day for 12 days after infection in malaria mice. Three groups of mice (n=5) were investigated for antimalarial efficacy, the degree of parasitaemia, assessment of pathology including body weight, physiological activities, hepatomegaly and splenomegaly. Parasitaemia was measured every other day by counting Geimsa-stained blood smears which were taken from end tail cutting.

Modern Approaches in the Search for New Lead Antiparasitic Compounds from Higher Plants

Higher plants represent a rich source of new molecules with pharmacological properties, which are lead compounds for the development of new drugs. During the last decades, the renewed interest in investigating natural products has led to the introduction of several important drugs, such as the anticancer drugs vinblastine and taxol, or the antimalarial agent artemisinin. Success in natural products research is conditioned by careful plant selection, based on various criteria such as chemotaxonomic data, information from traditional medicine, field observation, or even random collection. One main strategy in the isolation of new lead compounds consists of so-called bioactivity-guided isolation, in which pharmacological or biological assays are used to target the isolation of bioactive compounds. One major drawback of this strategy is the frequent isolation of known metabolites. Therefore, metabolite profiling using hyphenated techniques such as LC/UV, LC/MS and more recently LC/NMR rapidly provides plenty of structural information, leading to a partial or a complete on-line de novo structure determination of the natural products of interest. The combination of metabolite profiling and LC/bioassays gives the possibility to distinguish between already known bioactive compounds and new molecules directly in crude plant extracts (dereplication). Thus, the tedious isolation of compounds of low interest can be avoided and a targeted isolation of new bioactive products. Some examples of rapid localization of bioactive compounds, based on post-chromatographic bioautographic testing of LC/NMR microfractions and subsequent on-line identification will be illustrated in this review. Possibilities and limitations of LC/UV/NMR/MS and LC/bioassay as well as future developments expected in this field will be discussed.

Anti-malarial agent artesunate inhibits TNF- -induced production of proinflammatory cytokines via inhibition of NF- B and PI3 kinase/Akt signal pathway in human rheumatoid arthritis fibroblast-like synoviocytes

Recent studies indicate that the anti-malarial agent artemisinin and its derivatives may exert an anti-inflammatory effect. In this study, we explored the effect of artesunate, an artemisinin derivative, on tumour necrosis factor (TNF)-alpha-induced production of interleukins, IL-1beta, IL-6 and IL-8, in human rheumatoid arthritis (RA) fibroblast-like synoviocytes (FLS), and further investigated the signal mechanism by which this compound modulates those cytokines' production. RA FLS obtained from patients with active RA were stimulated with TNF-alpha and incubated with artesunate, and IL-1beta, IL-6 and IL-8 production was measured by ELISA. DNA-binding activity and nuclear translocation of nuclear factor kappa B (NF-kappaB) were measured by a sensitive multi-well colourimetric assay and confocal fluorescence microscopy, respectively. Signal transduction proteins expression was measured by western blot. Artesunate decreased the secretion of IL-1beta, IL-6 and IL-8 from TNF-alpha-stimulated RA FLS in a dose-dependent manner. Artesunate also prevented TNF-alpha-induced nuclear NF-kappaB translocation, DNA-binding activity and gene transcriptional activity, as well as phosphorylation and degradation of IkappaBalpha, but phosphorylation of p38 mitogen-activated protein kinase, extracellular signal-regulated kinase and c-Jun N-terminal kinase were unaffected. The production of IL-1beta, IL-6 and IL-8 induced by TNF-alpha was decreased by pyrrolidine dithiocarbamate (PDTC), a chemical inhibitor of NF-kappaB. These observations suggest that artesunate inhibits production of IL-1beta, IL-6 and IL-8 through inhibition of NF-kappaB signalling pathway. We also showed that artesunate prevented Akt phosphorylation. TNF-alpha-induced production of IL-1beta, IL-6 and IL-8 was hampered by treatment with the phosphatidylinositol 3 (PI3) kinase inhibitor LY294002, suggesting that inhibition of Akt activation might inhibit IL-1beta, IL-6 and IL-8 production induced by TNF-alpha. Our results indicate that artesunate exerts an anti-inflammatory effect in RA FLS and provide the evidence that artesunate may have therapeutic potential for RA.

Investigation of Medicinal Plants for the Treatment of Neglected Diseases

Higher plants represent a rich source of new molecules with pharmacological properties, which could become lead compounds for the development of new drug products. During the last decades, the renewed interest in investigating natural substances has led to the introduction of several important drugs, such as the anticancer substances vinblastine, vincristine, taxol and camptothecine derivatives, or the antimalarial agent artemisinin. Despite recent scientific and technological advances, parasitic diseases continue to affect millions of people in both tropical and subtropical zones of the world. On the other hand the drugs used for the treatment of most parasitic diseases are extremely limited. In this field, natural products constitute a reservoir of new molecules with potential therapeutic interest. An outline is presented here of some important results obtained by the Laboratory of Pharmacognosy and Phytochemistry of the University of Geneva on plants used to treat some of the neglected diseases. The strategy employed for the study of these plants is outlined, covering all aspects from the selection of plant material to the isolation of the active substances. Different bioactivities have been investigated such as the search for new molluscicidal and larvicidal agents. Results are also included for antileishimanial and antimalarial compounds.

Reply to Comments on “Highly Antimalaria‐Active Artemisinin Derivatives: Biological Activity Does Not Correlate with Chemical Reactivity”

In light of the discussion on C10‐substituted derivatives of the antimalarial agent artemisinin in the preceding correspondence article which relates to his earlier work, R. K. Haynes reiterates here that there is no correlation between the ability of artemisinins to react with heme‐ or non‐heme‐FeII and their antimalarial activity.

A circular dichroism and structural study of the inclusion complex artemisinin-β-cyclodextrin

The inclusion complex between the powerful antimalarial agent Artemisinin and β-cyclodextrin has been studied by means of Circular Dichroism and elucidated by Density Functional Theory calculations on the isolated molecule combined to a statistical Monte Carlo search of the most stable geometry of the complex. The results evidence a host–guest structure in full agreement with the almost unaffected functionality of the drug, which is found to experience a significant hydrophilic environment when complexed.

Search for New Lead Compounds from Higher Plants

Higher plants represent a rich source of new molecules with pharmacological properties, which are lead compounds for the development of new drugs. During the last decades, the renewed interest in investigating natural products has led to the advent of several important drugs, such as the anticancer substances vinblastine, vincristine and taxol, or the antimalarial agent artemisinin. Success in natural products reasearch is conditioned by a careful plant selection, based on various criteria such as chemotaxonomic data, information from traditional medicine, field observations or even random collection. One main strategy in the isolation of new leads consists of the so-called bioactivity-guided isolation, in which pharmacological or biological assays are used to target the isolation of bioactive compounds. One major drawback of this strategy is the frequent isolation of known metabolites. Therefore, hyphenated techniques (LC-UV/DAD, LC-MS, LC-NMR) have been developed, in order to detect as early as possible potential original structures. These compounds can then be tested in various bioassays. Using a combination of hyphenated techniques and bioactivity-guided isolation procedures, a series of new diterpenoic antifungal quinones have been isolated from the African tree, Bobgunnia madagascariensis (Leguminosae) and recently patented for their strong activity and for their potential use in the treatment of systemic mycoses.

Interaction of Antimalarial Agent Artemisinin with Cyclodextrins

To obtain an effective solution of the poorly water soluble antimalarial agent artemisinin, the use of several kinds of cyclodextrins (CDs) as solubilizers was examined. The following CDs were used in this study: α-CD, β-CD, γ-CD as parent CDs, 2-hydroxypropyl-β-CD (HP-β-CD), sulfobutyl ether β-CD (SBE7-β-CD), heptakis (2,6-di-O-methyl)-β-CD (DM-β-CD), 2,3,6-partially methylated-β-CD (PM-β-CD) as modified CDs, and glucosyl-β-CD (G1-β-CD), and maltosyl-β-CD (G2-β-CD) as branched CDs. The solubility curves of artemisinin with CDs can all be classified as type AL. The apparent stability constants for artemisinin-parent CD complexes increased in the order of α- < γ- ≤ β-CD. The constants for artemisinin-β-CD derivative (and β-CD) complexes increased in the order of G2-β-CD ≅ G1-β-CD cong; PM-β-CD ≅ β-CD < HP-β-CD < SBE7-β-CD < DM-β-CD. These results suggest that the addition of CDs enables the solubilization of artemisinin.

First Determination of the Standard Potential for the Dissociative Reduction of the Antimalarial Agent Artemisinin

The reduction of the known antimalarial agent Artemisinin (ART) has been studied in N,N-dimethylformamide (DMF) by cyclic voltammetry and other electrochemical techniques. ART undergoes an irreversible, dissociative reduction with an anodic peak potential (Ep) that varies with scan rate and is −1.68 V vs SCE at 1 V/s. Direct electrochemical reduction of ART is subject to a large activation overpotential, and thus the Ep's do not provide an accurate value of the standard reduction potential (E°diss(ART)) required for the determination of the free energy of electron transfer from possible biological electron donors (ΔG°ET = F(E°D•+/D − E°diss(ART))). Using careful heterogeneous electrochemical methods with convolution analysis, the standard potential of the dissociative reduction of ART (E°diss(ART)) has been determined for the first time to be −0.89 V versus SCE in DMF. This value is ca. 0.8 V more positive than the irreversible direct reduction observed using cyclic voltammetric measurements. In addition, the value E°diss(ART) allows the estimation of the O−O bond dissociation energy. The thermochemical values determined are important to understanding ART's biological activity and investigating its potential for undergoing electron-transfer-initiated processes with biological donors.

Patent Evaluation: Artemisinin Analogues as Potential Antimalarial Agents

SummarySummaryNovelty: A process for synthesizing polyoxa heterocyles and, in particular, the antimalarial agent artemisinin and its analogues is disclosed. A new family of artemisinin analogues is disclosed.Biology: In vitro IC50 data for selected tricyclic artemisinin analogues in drug-resistant strains of P. falciparum are presented. For example, t-butylteperether has IC50 values of 0.41 and 0.53 mg/ml against W-2 and D-6 clones, respectively.Chemistry: The total synthesis by diastereo-selective silyation is described.

Reversed-Phase High-Performance Liquid Chromatographic Determination of Artemisitene in Artemisinin

Abstract A new, simple and selective reversed-phase HPLC assay is developed for the determination of the clinically undesirable artemisitene in the antimalarial agent artemisinin (qinghaosu). It involves the use of an internal standard (santonin) and the determination time is less than 5 minutes. Detection was accomplished using a UV detector set at 216 nm and limits were as low as 15ng for a 10μl injection. Being simple and selective this method is particularly useful for the routine analysis of artemisinin to check its purity. In addition, the method can be used for preparative scale purification of these compounds. It has been applied for the evaluation of crystalline samples of artemisinin without prior preparation.

Conversion of Artemisinin (Qinghaosu) toIso-Artemisitene and to 9-Epi-Artemisinin1

The antimalarial agent artemisinin has been converted to two new compounds, ISO-artemisitene and 9- EPI-artemisinin.