Pharmacology and mechanism of action
Artemisinin (qinghaosu) is an antimalarial compound first isolated in pure form in 1972 by Chinese scientists from the herb qinghao (Artemisia annua). This herb (worm wood) has been used in Chinese traditional medicine to control fever for over 2000 years
[1]. Artemisinin is a compound with a peculiar structure, low toxicity and high efficacy even in severe chloroquine resistant P. falciparum malaria. Unlike current antimalarial drugs which have a nitrogen-containing heterocylic ring system, it is a sesquiterpene lactone with an endoperoxide linkage. The endoperoxide linkage is essential for the antimalarial activity of the drug. Artemisinin has been shown to be a potent schizontocidal drug both in vitro and in experimental animal models, but it has no practical effect against the exoerythrocytic tissue phase, the sporozoites and the gametocytes
[2].
The mechanism of action of artemisinin is not clearly understood. The drug selectively concentrates in parasitized cells by reacting with the intraparasitic hemin (hemozoin). In vitro this reaction appears to generate toxic organic free radicals causing damage to parasite membranes
[2-4]. The derivatives of artemisinin are more potent than the parent drug and have apparently a similar mechanism of action
[1,2].
Indications
A sesquiterpene peroxide derived from A. annua, chiefly used in the form of artemether, the methyl ester synthesized from dihydroartemisinin, or artesunate, the water-soluble hemisuccinate. Formulated for administration by the oral, intramuscular or intrarectal routes; artesunate can also be given intravenously.
Artemisinin and its derivatives are valuable drugs for the management of malaria. They should not be used unnecessarily or with incomplete dosage regimens. They are indicated only in areas where multidrug resistant P. falciparum malaria is prevalent
[5].
Side effects
Artemisinin and its derivatives are exceptionally safe drugs. Millions of people have taken them and serious side effects have yet to be reported. The most commonly reported side effects include mild and transient gastrointestinal problems (such as nausea, vomiting, abdominal pain and diarrhoea), headache, and dizziness particularly after oral administration. Transient first degree heart block and bradycardia were reported in a few individuals, who received artesunate or artemether at the standard doses. Brief episodes of drug-induced fever have also been observed in a few studies
[6,5]. After rectal administration the patients may experience tenesmus, abdominal pain and diarrhoea. A transient dose-related decrease in circulating reticulocytes has been reported following high doses of artesunate above 4 mg/kg for 3 days. All values returned to pre-treatment values within 14 days
[6,5]. Neurotoxicity has been observed in animal studies but has never been documented in man
[7].
Contraindications
There are no known contraindications. However, artemisinin and its derivatives should only be used when other antimalarial drugs do not work.
Preparations
Artemether
• Paluther® (Rhône-Poulenc Rorer). Solution for injection 80 mg/ml.
• Artenam® (Dragon Pharmaceuticals Ltd, Wales UK). Solution for injection 100 mg/ml.
Several other preparations containing artemisinin derivatives are manufactured in China and Vietnam. The availability of these preparations is presently uncertain.
Pharmaceutical Applications
The genus Artemisia of the family Asteraceae is comprised of more than 500 species which are found all over the world. Many members of the genus are used in various traditional therapies including East Asian medicine and Ayurveda. Some important species which have been studied for their various therapeutic potentials are A. asiatica for inflammation, infection, and ulcerogenic disorders; A. annua for fevers specially malaria; A. afra for cough, cold, headache, dyspepsia, colic, diabetes, and kidney disorders; A. judaica for gastrointestinal disorders; A. tripartite for sore throat, tonsillitis, cold, headache, and wounds; A. vulgaris as analgesic, anti-inflammatory, and antispasmodic; and A. verlotorum for hypertension (Bora and Sharma 2011).
Artemisinin is the major bioactive compound, which is rich in mono- and sesquiterpenes, and is a new class of potential antimalarial drug used throughout the globe. The combination therapies of artemisinin are considered to be the best treatment for Plasmodium falciparum malaria (He et al. 2009). Apart from antimalarial activity, the oil has antibacterial and antifungal (Bilia et al. 2014), immunosuppressive, anti-inflammatory, antioxidant (Cavar et al. 2012), and antiviral (Alesaeidi and Miraj 2016) activities. A. annua has also been studied against diabetes, heart diseases, arthritis, eczema, and cancer.
In vitro and in vivo studies on artemisinin have given good evidence of its anticancer activity. The mechanism of action of its antineoplastic activity has also been exhaustively studied and reviewed. Artemisinin is described to induce oxidative stress and nitric oxide production; cause DNA damage and repair; induce apoptosis, autophagy, and necrosis; and inhibit angiogenesis and mitogen-activated protein kinases (MAPK) pathway, metastatic pathway, etc. (Efferth 2017). Phase I and II clinical trials for the molecule have also been done; but hepatotoxicity caused by artemisinin combination therapy is a limitation as of now. The anticancer activity of artemisinin has been studied in breast cancer, in lung cancer, and in prostate carcinoma (Lai and Singh 2006; Sun et al. 2014; Michaelsen et al. 2015).
Drugs for treatment of malaria
Artemisinin is the drug for the treatment of malaria with the most excellent efficacy, being a kind of sesquiterpene lactone containing peroxide group extracted from the traditional Chinese medicine Artemisia annua. It is characterized with high efficiency, rapid efficacy, clearing summer-heat, clearing deficiency heat, protozoa-killing effect and low toxicity. Currently, the efficacy of the artemisinin-based combination therapy (ACT) for the treatment of malaria worldwide has reached over 90%. ACT has been already widely applied to the treatment of malaria in many countries around the world.
It has a strong and rapid killing effect on the erythrocytic stage of plasmodium, being able to rapidly control the clinical seizures and symptoms. Meanwhile, it also has prominent efficacy in the treatment of chicken coccidiosis, Mycoplasma Suis, toxoplasmosis, weakness and fever, damp heat jaundice, tertian malaria, falciparum malaria, cerebral malaria and chloroquine malaria.
Artemisinin was first successfully developed by Chinese scientists, being effective monomer originated from the folk malaria-treatment herbs Artemisia annua. China is one of the major resource countries for the growth of such plants. The demands for research and development originated from the Vietnam War in 1960s when Malaria parasites had been resistant to special drug chloroquine at that time. In Vietnam War, many soldiers are not killed in the war, but instead died of malaria.
Because of the presence of artemisinin resistance in the border areas of Cambodia and Thailand, the World Health Organization advocates the use of combinations rather than monomeric formulation. In this environment, the world's first artemisinin-based compound antimalarial drug-compound artemether has been successfully developed in China. However, due to the lack of attention on the importance of intellectual property of Chinese pharmaceutical companies, currently in the world, only Novartis Company has the authority of foreign selling of artemether compound that has been recognized by the World Health Organization. The Novartis Company has offered the drug to the WHO at the cost price, wining the wide acclaim from international community. However, in this trade war, China can only play a role of major drug producing countries.
Chemical properties
It appears as colorless needle crystal with a melting point being156-157 °C. It is easily soluble in chloroform, acetone, ethyl acetate and benzene, being soluble in methanol, ethanol and insoluble in water.
Uses
Artemisia annua is used as antimalarial drugs. Clinical application has shown that artemisinin and its derivatives have special effects on treating the malaria and falciparum malaria, especially artemisinin which has stronger killing effect on Plasmodium falciparum intracellular phorozoon than other artemisinin drugs, characterized by high efficiency, rapid efficacy, low toxicity and no cross-resistance with chloroquine, etc. It can be not only used for treatment, but also for emergency treatment. It is applicable to a variety of malaria such as falciparum malaria, vivax malaria, anti-chloroquine malaria and cerebral malaria, including dangerous type.
The most notable drug is dihydroartemisinin and its tablets. This drug has its antimalarial effect be 10 times as strong as artemisinin with the recurrence rate of only 1.95%, thus having been rated as China's top ten scientific and technological achievements in 1992. Artemisinin and its derivatives not only are excellent antimalarial drugs, but also have potentially attractive prospect in the treatment of other diseases. Animal experiments have found that artemisinin treatment of Clonorchis sinensis can achieve a rate of pest control being up to 100%; treatment of animal schistosomiasis can achieve a pest control rate of 33.8-99.3%. Application of artemisinin treatment of discoid lupus erythematosus can achieve a total effective rate of 90%. Its efficacy in the treatment of dengue fever is significantly better than morphine biguanide and other western medicines. Immunologists have also found that artemisinin can significantly improve the lymphocyte transformation rate and enhance the immune function of antibodies. People haven’t found toxic effect of this product on the heart, liver and kidney. People haven’t observed any significant side effects in clinical practice.
Production method
It can be extracted from the leaves of Artemisia annua L. (Compositae). In addition to artemisinin, China also produces both artemether and sodium artemisinin.
References
1. Luo XD, Shen CC (1987). The chemistry, pharmacology and clinical applications of qinghaosu (artemisinin) and its derivatives. Med Res Rev, 7, 29–52.
2. Klayman DL (1985). Qinghaosu (artemisinin): an antimalarial drug from China. Science, 228, 1049–1055.
3. Zhang F, Gosser Jr. DK, Meshnick SR (1992). Hemin-catalyzed decomposition of artemisinin (qinghaosu). Biochem Pharmacol, 43, 1805–1809.
4. Meshnick SR, Yang YZ, Lima V, Kuypers F, Kamchonwongpaisan S, Yuthavong Y (1993). Irondependent free radical generation from the antimalarial artemisinin (qinghaosu). Antimicrob Agents Chemother, 37, 1108–1114.
5. The role of artemisinin and its derivatives in the current treatment of malaria (1994–1995). Report of an informal consultation convened by WHO, 27–29 September, 1993. (Geneva: World Health Organization).
6. Hien TT, White NJ (1993). Qinghaosu. Lancet, 341, 603–608.
7. Brewer TG, Grate SJ, Peggins JO, Weina PJ, Petras JM, Levine BS, Heiffer MH, Schuster BG (1994). Fatal neurotoxicity of arteether and artemether. Am J Trop Med Hyg, 51, 251–259.
Description
Artemisinin is an antimalarial agent with anticancer activity. It is an iron(II) oxide-reactive endoperoxide that generates reactive oxygen species (ROS) upon cleavage of its endoperoxide bridge. It reduces the growth of various
P. falciparum strains
in vitro (IC
50s = 3.98-20.36 nM) and reduces parasitemia in mice infected with
P. falciparum with a curative dose (CD
50) value of 140 mg/kg. It also reduces
P. berghei infection in mice (ED
50 = 5.6 mg/kg per day). Artemisinin (100-400 μM) induces cell cycle arrest in the G
0/G
1 phase and apoptosis and inhibits growth of SK-N-AS, BE(2)-C, SK-N-DZ, and SHEP1 neuroblastoma cells in a time- and concentration-dependent manner. It also suppresses BE(2)-C cell colony formation in a soft agar assay and reduces tumor growth in a BE(2)-C mouse xenograft model. Formulations containing artemisinin have been used in combination therapies for the treatment of malaria.
Description
Artemisinin, a sesquiterpene isolated from a traditional Chinese remedy (quinghao), is
useful in the treatment of Fafciparum malaria, including infections caused by chloroquine
resistant strains. It is reported to clear parasitemia quicker than i.v. quinine, and is
effective in cerebral malaria.
Chemical Properties
Crystalline Solid
Physical properties
Appearance: colorless needles or white crystalline powder. Solubility: practically
insoluble in water, very soluble in dichloromethane, freely soluble in acetone and
ethyl acetate, and soluble in glacial acetic acid, methanol, and ethanol. Melting
point: 150–153?°C. Specific optical rotation: +75 to +78°.
Originator
Ping Hau Sau Res. Group (China)
History
The discovery of artemisinin dramatically changes the landscape to combat malaria
and leads to a paradigm shift in antimalarial drug development.
However, the discovery of artemisinin is the first stage; the development of artemisinin derivatives and their compound preparations is another important stage.
Based on artemisinin, scientists obtained artemisinin ether derivatives by semisynthetic method. After screening of antimalarial activity, artemether was found. To
further improve the solubility of artemisinin derivatives, artesunate was also found.
The discovery of artesunate makes artemisinin and its derivatives much easier to
promote, and more convenient dosage forms to treat malaria enriched the clinic
application of artemisinin and its derivatives .
Uses
An antimalarial agent that inhibits VEGF expression and NOS2.
Uses
Active antimalarial constituent of the tradional Chinese medicinal herb Artemisia annua L., Compositae, which has been known for almost 2000 years as Qinghao. Antimalarial
Uses
Artemisinin inhibits angiogenesis by down-regulating HIF-1α and VEGF expression in mouse embryonic stem cells. Artemisinin crosses the blood-brain barrier and is an inhibitor of human NOS2 (iNOS).
Definition
ChEBI: A sesquiterpene lactone obtained from sweet wormwood, Artemisia annua, which is used as an antimalarial for the treatment of multi-drug resistant strains of falciparum malaria.
Indications
Clinically, artemisinin is mainly used to treat malaria symptoms, malignant cerebral
malaria, uncomplicated malaria, and severe malaria. Combined with different antimalarial can delay and prevent resistance of malaria parasites. In additional, artemisinin can also be used for systemic lupus erythematosus or discoid lupus
erythematosus. Currently, artemisinin derivatives and their compound preparations
are widely used in clinic.
Antimicrobial activity
Artemisinins are active against the erythrocytic and gametocyte
stages of chloroquine-sensitive and chloroquine-resistant
strains of P. falciparum and other malaria parasites. Two anomers
of artemether are produced on synthesis, α-artemether
and β-artemether, of which the latter has higher antimalarial
activity. Activity against the protozoa Tox. gondii and
Leishmania major and the helminth Schistosoma mansoni has
been demonstrated in experimental models.
Acquired resistance
Resistance caused, for example, by changes in the plasmodial
endoplasmic reticulum ATPase has been shown in experimental
models. There have been clinical reports of reduced
susceptibility to treatment with artesunate in Cambodia.
General Description
The artemisinin series are the newest of the antimalarialdrugs and are structurally unique when comparedwith the compounds previously and currently used. Theparent compound, artemisinin, is a natural product extractedfrom the dry leaves of Artemisia Annua (sweetwormwood). The plant has to be grown each year fromseed because mature plants may lack the active drug. The growing conditions are critical to maximize artemisininyield. Thus far, the best yields have been obtained fromplants grown in North Vietnam, Chongqing province inChina, and Tanzania.
Pharmaceutical Applications
Artemisinin (qinghaosu), a compound derived from a plant used in traditional Chinese medicine, Artemisia annua, has been used extensively in East Asia and Africa for the treatment of malaria. This drug, and derivatives that have higher intrinsic antimalarial activity (artesunate, artemether and arteether), have replaced quinine as a treatment of falciparum malaria in many countries, normally in combination with other antimalarials. A semisynthetic derivative, artemisone, which has higher efficacy than artesunate and lower toxicity potential, is in development. Artemisinin and its derivatives also show broad antiprotozoal, anthelmintic and antiviral activities.
The novel structure, containing an endoperoxide bridge, has stimulated the development of semisynthetic and synthetic dioxane, trioxane and tetroxane compounds with activity against Plasmodium spp. and Schistosoma spp. Some of these synthetic trioxalanes are now in clinical development with Medicines for Malaria Venture and other organizations.
Biological Activity
Antimalarial agent; interacts with heme to produce carbon-centred free radicals, causes protein alkylation and damages parasite microorganelles and membranes. Also selectively inhibits the P-type ATPase (PfATP6) of Plasmodium falciparum (K i ~ 150 nM). Displays antiangiogenic effects in mouse embryonic stem cell-derived embryoid bodies.
Biochem/physiol Actions
Artemisinin (Qinghaosu), a sesquiterpene lactone, is a highly active anti-malarial (falciparum malaria) drug. Artemisinin is also an anthelmintic (parasitic worm) effective against the blood fluke, schistosomiasis.
Pharmacology
The mechanism of artemisinins is not known, but the most widely accepted theory
is that they are first activated through cleavage after reacting with haem and iron(II)
oxide, which results in the generation of free radicals that in turn damage susceptible proteins, resulting in the death of the parasite .
Artemisinin and its derivatives also show a good antitumor effect , which is
mainly via (1) apoptosis, ferroptosis, or necrosis; (2) anti-angiogenesis; (3) oxidative stress; (4) tumor suppressor genes; and (5) protein targeting. In addition, artemisinin can exhibit antiarrhythmic, anti-fibrotic, and immunomodulating effects.
Pharmacokinetics
Oral absorption: Incomplete
C
max 500 mg oral: 0.4 mg/L after 1.8 h
Plasma half-life (dihydroartemisinin): 40–60 min
Volume of distribution: c. 0.25 L/kg
Plasma protein binding (artemether): 77%
Artemisinins are concentrated by erythrocytes and are rapidly
hydrolyzed to dihydroartemisinin. They are hydroxylated by cytochromes
2B6, 2C19 and 3A4; the derivatives induce this metabolism.
After injection, peak plasma concentrations are reached
within 1–3 h, when levels of dihydroartemisinin are included.
The elimination half-life of intravenous artesunate is <30 min;
artemether appears to have a much longer half-life (4–11 h).
Clinical Use
Malaria (including cerebral malaria), in combination with other antimalarials.
Side effects
A few toxic effects in addition to drug-induced fever and a
reversible decrease in reticulocyte counts have been reported.
High-dose studies in animal models show neurotoxicity and
reproducible dose-related neuropathic lesions; dihydroartemisinin
is a toxic metabolite but the precise causes of neurotoxicity
are not clear. Embryotoxicity of artemisinin and
derivatives has been reported in rodent and primate models,
probably due to depletion of erythroblasts.
Safety Profile
Moderately toxic by ingestion,intramuscular, and intraperitoneal routes. When heated todecomposition it emits acrid smoke and fumes.
Synthesis
Quinghaosu, octahydro-3,6,9-trimethyl-3,12-epoxy-12Hpyrano-(4,3-di)-1,2-benzodioxepin-10-(3H)-one (37.1.1.57), is isolated from the plant
Artemisia annua. It also has been made synthetically.
