Potentialities of Artemisia annua for malaria therapy

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Vipin K. Sharma

Vipin K. Sharma

Malaria is a major disease in developing countries, causing every year 1-2 million deaths1,2. Malaria disease is caused by protozoa parasites Plasmodium species . The parasite is transmitted by the female Anopheles mosquito, and transits through the liver and the blood of the mammalian host.

The symptoms occur at the erythrocytic stage. There is a high concern with deaths of children due to severe malaria. Its syndromes are cerebral malaria and severe anemia, both due to acidosis, which lead to death within 24 hours after hospital admission. Unfortunately there has been a spread of resistant strains of the parasite to the actual therapeutics (especially chloroquine), in numerous regions such as South America, Africa and South-East Asia3 A large number of collaborations are trying to develop a vaccine against malaria, as stated by the NIAID report4. These researches target either the blood stage or the liver stage of the parasite5. As far as chemotherapy is concerned, the search goes on for (1) synthetic analogues of quinine and chloroquine, (2) artemisinin analogues, (3) febrifugin analogues, (4) inhibitors of fatty acid synthesis or of membrane synthesis (inhibitors of choline uptake), (5) proteases inhibitors6,7.

Artimisinin is obtained from Artemisia (Artemisia annua L.,Asteraceae) , known in united states as sweet annnie or annual wormwood, that is an annual herb native to Asia most probably China, where it is known as quinghao. The plant has become naturalized in many countries as argentina, Bulgaria, France, Hungary, Romania, Italy, Spain, The United States and Yougosalavia8,9,10. Essential oils and artemisinin were assumed to be associated with secretory cells based on the association of mono- and sesquiterpenes with well-defined secretory structures11.  Leaves had 89% of the total artemisinin in the plant with the uppermost foliar portion of the plant (top 1/3 of growth at maturity) containing almost double that of the lower leaves6. Upto 35% of the mature leaf surface is covered with capitate glands which contain most of the monoterpenes and virtually all of the sesquiterpene lactones. Essential oils from A. annua are similarly distributed, with 36% of the total from the upper third of the foliage, 47% from the middle third, and 17% from the lower third, with only trace amounts in the main stem side shoots, and roots12. Wild harvesting of A. annua has the disadvantages of sparse distribution, low artemisinin content and unstable yields, which increase the production and processing cost. Usually, only artemisinin content over 0.6% has commercial value.

The extraction and purification technology of artemisinin using the hexane method was described by de Vries and Dien (1996)13. Recovering artemisinin from A. annua by high-pressure extraction with CO2 at 60-85 bar and 20-50oC, is a new technique. The recovery comprises: (a) grinding the above ground parts of the plant to powder; (b) subjecting this to high-pressure extraction with CO2 for recovery of artemisinin; (c) isolating artemisinin from the purified extract mixture; and (d) preparing, from artemisinin, a solution for use in preparation of liquid dosage forms. CIMAP has recently developed a new variety of A. annua "Jeevanraksha" containing high levels of artemisinin.

Pharmacodynamic/Pharmacokinetic effect of Artimisinin and its congeners:

 The artemisinins (term used collectively for artemisinin and its derivatives) compounds are potent and rapidly acting anti-malarials against Plasmodium falciparum and P. vivax, including multi-drug-resistant strains14. There is less information on the effect against the two other human malaria parasites, P. malariae and P. ovale, but they are likely to be effective against them as well. Artemisinin derivatives, dihydroartemisinin, arteether, artemether, artelinic acid and artesunate, are about five times as potent; this outweighs the added cost of derivation, and they are therefore cheaper per treatment course.

Artemisinin is a sesquiterpene lactone peroxide compound. Structure activity studies carried out indicated that the presence of the peroxide bridge correlates with, and is essential for, the antimalarial activity. Artemether is the methyl ether derivative of artemisinin, the antimalarial principal extracted from A. annua. Artemisinins rapidly kill the asexual blood stages of the parasites, which are responsible for the disease manifestations (blood schizonticidal activity), they have some effect on the gametocytes (the stage, which is infective to mosquitoes ingesting a blood-meal from an infected person), but have no effect on the hypnozoites, which lodge in the liver and can cause relapses in vivax and ovale malaria15. Biochemical studies suggest that its antimalarial effect involves lysosomal trapping of the drug in the intra-erythrocytic parasite, followed by binding to toxic haemin that is produced in the course of haemoglobin digestion. This binding prevents the polymerization of haemin to non-toxic malaria pigment1.

Pharmacokinetically, the artemisinins are characterized by fast absorption, large distribution volumes and short half-lives. They penetrate the blood-brain barrier, and accumulate in erythrocytes. The mechanism of action is different from that of other anti-malarial medicines and probably related to the release of free radicals, when the peroxide bridge bursts, which happens when the compounds encounter high concentrations of heme, a breakdown product of hemoglobin produced by malaria parasites living in red blood cells. The free radicals rapidly kill the malaria parasites, and the selectivity of their toxicity is probably related to the fact that they only reach high concentrations in the human body in parasitized red blood cells. The action of artemisinins is more rapid than that of other known antimalarials. It has been estimated that treatment with artemisinins reduces the parasite biomass by a factor of approximately 10 for each 36-48 hour asexual cycle of the parasite and by a factor of 106- 108 over a 3-day course of treatment.

Combinational therapy:

Because of the very short half-life, it is believed that, similar to quinine, the artemisinins are unlikely to be affected by the emergence of drug resistance. However, resistance can be elicited in animal models. Also, studies in Yunnan , where artemisinins have been used on a large scale, indicate some reduction of the parasite susceptibility, a trend which is worrying, although it has not yet been translated to lower clinical efficacy, as far as is known16. Coartem (artemether–lumefantrine) is a highly effective and well tolerated anti-malarial that achieves cure rates of up to 95%, even in areas of multi-drug resistance. It is indicated for the treatment of falciparum malaria, the most dangerous form of malaria.

Owing to the limited amount of research carried out on the artemisinins and concern that their unregulated use could lead to parasite resistance, WHO has until recently recommended that artemisinins should be used only in areas with multidrug-resistant falciparum malaria. In reality, however, as a result of market pressure they are already widely available, especially in the private sector, in most malaria-endemic countries. In this situation, their uncontrolled use could lead to the appearance of parasite-resistant strains without bringing much benefit to the most vulnerable populations. The disadvantage of these drugs, which is probably related to their short half-life, is that they must be given for at least 5 days for acceptable cure rates to be achieved. For this reason, which is a serious hindrance to compliance, and to reduce the risk of resistance, artemisinins should always be given in combination when used as part of malaria control in endemic countries. Numerous trials have shown that cure rates close or equal to 100% can be attained by giving the well tolerated combination of an artemisinin drug with mefloquine for 3 days. Combinations with other drugs also seem to be effective, but have not yet been studied so widely17.

WHO and UNICEF have called for tenders of co-blistered combinations of the following products for which there are not yet pre-qualified manufacturers: 1) artesunate plus amodiaquine; 2) artesunate plus sulfadoxine/pyrimethamine; 3) artesunate plus mefloquine; and 4) amodiaquine plus sulfadoxine/pyrimethamine1. Trials are now taking place to investigate the efficacy and safety of a combination of artesunate and sulfadoxine/pyrimethamine. A fixed combination of artemether with lumefantrine has already been registered, although the company has yet to develop a pricing strategy. Alternative options for combination with artemisinin derivatives include pyronaridine, chlorproguanil/dapsone and atovaquone/ proguanil, although atovaquone/proguanil is still too expensive for endemic countries. If an artemisinin drug with sulfadoxine/ pyrimethamine combination proves safe and effective, it can be recommended as routine first-line treatment in most countries where chloroquine resistance is a problem. Given that sulfadoxine/ pyrimethamine resistance already exists, the useful life of this combination would perhaps be limited, and research on the alternatives mentioned above has high priority. If one of these combinations proves safe and effective, it should be introduced as a replacement for artesunate plus sulfadoxine/pyrimethamine. The replacement would probably have a longer useful life, because there is as yet very little reported resistance to the components. In addition, pyronaridine as well as chlorproguanil/dapsone are better matched kinetically to artesunate than is sulfadoxine/pyrimethamine. The precondition for such combinations being effective is their correct use. Their large-scale distribution in package form, for example, a blister-pack where the two components are kept together, would improve compliance. A fixed combination formulation would be even better, but this will still take years to develop. The use of artemisinin drug combinations must be undertaken in a responsible way by public health services that can ensure that health staff is trained in their use. In addition, the drugs should not be available without the required information supplied in a locally appropriate form. Correct drug treatment requires diagnosis to be more specific than is currently the case in most places, and the drugs should be free or affordable to the patient populations, so that poverty does not become a cause of underdosing. Finally, the introduction of such combinations should be accompanied by monitoring of their impact on mortality and incidence of severe disease.

Side effects:

Despite neurotoxicity in animal studies at doses that far exceed those used for the treatment of malaria in humans; serious side-effects in humans have not been encountered. Side effects of artemesinin treatments at normal to high therapeutic doses appear to be rare and mostly involve gastro-intestinal reactions such as dizziness and fatigue, anorexia, nausea, vomiting, abdominal pain, palpitations, myalgia, sleep disorders, arthralgia, headache, rash, and diarrhea (with or without intestinal cramping). In a large study in Thailand comparing high-dose artemesinin derivatives (artemether and artesunate) alone versus in combination with mefloquine, the incidence of adverse effects with the artemesinin compounds was reported to be 34% for loss of appetite, 16% for nausea, 15% for dizziness, and 11% for vomiting18. Mefloquine greatly increased the incidence of side effects, doubling the rate. In a clinical trial comparing artesunate injection with chloroquine and with the combination of quinine and resorcin, no adverse effects of artesunate were reported, while dizziness was a common complaint with the drug therapies.

Parasite resistance

There is no convincing evidence yet of clinically relevant, stable, parasite resistance having developed to artesunate, or to the other artemisinins. It is interesting to note that resistance to artemisinins in humans has not been observed till date even in areas on the thai-Myanmar where artemisinins with mefloquine have been first line therapy for the past 7 years 19, 20. The short elimination half-life of the artemisinins and their gametocidal effect probably protect against development of resistance21. Use of artemisinin combination therapy is even being advocated in SubSaharan Africa to delay development  of drug resistance22. Recent studies suggest that SERCA, a calcium pump in the endoplasmic reticulum may be associated with artemisinin resistance22,23. Malaria parasites can develop resistance to artemisisnin and resistance can be produced by mutation of SERCA23.Resistant strains of fresh P. falciparum have been established although not sustained in vitro.

Use in pregnancy

Artemether-lumefantrine is contraindicated in: pregnant and lactating women (Safety of its use in pregnancy has not yet been established.), persons with known hypersensitivity to either of the components, persons with severe malaria1. Artemisinins are not recommended for use in the first trimester of pregnancy, unless they are of life-saving importance for the mother. According to WHO, they can be given in the second and third trimester, if no suitable alternate is available24. In view of the serious health implications of malaria in pregnancy, artemisinin and related compounds should not be withheld from pregnant women in areas where these drugs are indicated. For the management of uncomplicated malaria in pregnancy, artemisinin and its derivatives can be used in the second and third trimester, but their use in the first trimester is not recommended. For the treatment of severe malaria in the first trimester, the advantages of artemisinin drugs over quinine, especially the lower risk of hypoglycaemia, must be weighed against the fact that there is still limited documentation on pregnancy outcomes following their use. The inadequacy of current knowledge on the use of these drugs during pregnancy should be understood by care providers, and if possible, all pregnancies exposed to these drugs should be monitored. Reports of all clinical outcomes, both successful and adverse events should be made to regulatory authorities.

Toxicology

Well-documented clinical uses of Artemisinin and derivatives have shown few insignificant side effects. However, intra-muscular rats' brainstem studies have shown that intramuscular arteether at 25-mg/Kg/day resulted in rats' brainstem pathology with damage to the auditory nuclei. Parenteral artemether in the treatment of cerebral malaria in Gambien children shows a prolonged recovery from coma and post-treatment convulsions than the same treatment with quinine. Also in Vietnamese adults, a prolonged recovery was noted, but no increased in mortality or neurological behaviour afterwards1. Others are transient heart block, transient decrease in blood neutrophills and brief episodes of fever. In experimental animals severe neurotoxic effects have been induced by the administration of very high, prolonged doses, but there is no definitive evidence of neurotoxicity in humans. In rodents and other experimental animals, foetal resorption has been observed, when these drugs have been given in relatively low doses after the sixth day of gestation, and in some species malformations have been observed after exposure in early pregnancy24.

Conclusion:

The main constituent of Quinghao, artemisinin is highly active against plasmodium in erythrocytic cycle of the parasite. Due to peroxide linkage which is solely responsible for the mechanism till now, it is associated with activity against resistance strains of the parasite. Semi synthetic derivatives of it e.g. artemether, arteether can also solve the problem of cost of therapy and formulation fabrication.Also, it is with potential along with other antimalarial agents. Furthermore; Artemisia annua or “Sweet Wormwood” derivatives may be front line therapy of malaria and will be available at progressively low cost.

References:

  1. World Health Organization. (2005). World Malaria Report.
  2. Maitland, K., Bejon, P., Newton , C.R.J.C., Maitland, K., Bejon, P. and Newton , C.R.J.C. (2003). Malaria. Curr Opin Infect Dis. 16:389-395.
  3. Basco, L.K., Ndounga, M., Keundjian, A. and Ringwald, P.(2002). Molecular epidemiology of malaria in cameroon . IX. Characteristics of recrudescent and persistent Plasmodium falciparum infections after chloroquine or amodiaquine treatment in children. Am. J. Trop. Med. Hyg. 66:117-123.
  4. James, S. and Miller, L.(2001). Malaria Vaccine Development: Status report, NIAID.

    5. Woster, P.M.(2003). New Therapies for Malaria in Ann. Reports Med. Chem. Doherty, A.M.(eds.). Vol. 38, Academic Press, New York.203-211.

  5. Charles, D.J., Simon, J.E., Wood, K.V. and Heinstein, P.(1990). Germplasm variation in artemisinin content of Artemisia annua using an alternate method of artemisinin analysis from crude plant extracts. J. Agr. Food Chem. 39:991-994.
  6. Egan, T.J. (2004). Haemozoin Formation as a Target for the Rational Design of New Antimalarials  Drug Design Reviews-Online. 1:3-110 (18).
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  9. Klayman, D.L. (1993).Artemisia annua: From weed to respectable antimalarial plant. In: Kinghom, A.D. and Balandrin, M.F. (eds.), Human Medicinal Agents from Plants. Am. Chem. Soc. Symp. Series. Washington , DC .
  10. Ferreira, J.F.S., Laughlin, J.C., Delabays, N., Magalhães, P.M., de Magalhães, P.M. (2005).Cultivation and genetics of Artemisia annua L. for increased production of the antimalarial artemisinin. Plant Genetic Res.3: 206-229.
  11. Stephen, O. D. and Rex, N. P. (1993). Development and Fine Structure of the Glandular Trichomes of Artemisia annua L. Int J Plant Sci. 1(54):107-118.
  12. De Vries, P.J. and Dien, T.K.(1996). Clinical Pharmacology and Therapeutic Potential of Artemisinin and its derivatives in the treatment of malaria. Drugs.52:818-836.
  13. Maitland, K., Makanga, M. and  Williams, T.N. (2004) Falciparum malaria: current therapeutic challenges. Curr Opin Infect Dis. 17: 405-412.
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  15. Stephen, O. D. and Rex, N. P. (1993). Development and Fine Structure of the Glandular Trichomes of Artemisia annua L. Int J Plant Sci. 1(54):107-118.
  16. P, D’ Alessandro, U. (2004). Is amodiaquine failing in Rawanda? Efficacy of amodiaquine alone and combined with artesunate in children with uncomplicated malaria. Trop Med Int Health. 9(10):109-8.
  17. Zhang ZX, Li CZ, Huang GZ, Yang YM, Zhou S, Sun XD, Li L.(2002).Assessment of therapeutic efficacy of chloroquine against falciparum malaria in an outbreak area in Xishuangbanna, Yunnan. Zhongguo Ji Sheng Chong Xue Yu Ji Sheng Chong Bing Za Zhi. 20(2):94-107.
  18. Wongsrichanalai, C., Pickard, A.L., Wernsdorfer, W.H. and Meshnick, S.R. (2002). Epidemiology of drug-resistant malaria. Lancet  infectious Dis.2:209-218.
  19. Cooper, R.A. and Carucci, D.J. (2004). Proteomic Approaches to Studying Drug Targets and Resistance in PlasmodiumProteomic Approaches to Studying Drug Targets and Resistance in Plasmodium. Current Drug Targets-Infect. Disorders.4( 1):41-51(11).
  20. Warell, D.A.(2002). Treatment and Prevention of Malaria. In.Warell, Giles, H.M.,(eds). Essential Materiology. 4th ed. London . Hodder Arnold.270-311.
  21. Eckstein-Ludwig, U., Webb, R., Van Goethem, I., East, J., Lee, A., Kimura, M., O’Neill, P., Bray, P., Ward, S. and Krishna , S. (2003).  Artemisinins target the SERCA of Plasmodium falciparum. Nature. 424 (6951): 957-61.
  22. Uhelmann, A., Cameron, A., Ecksein-Ludwig, U., Fichbarg, J., Iservich, P., Zuniga, F., East, M., Lee, A., Brady, L., Haynes, r. and Krishna, S.(2005). A single amino acid residue may determine the sensivity of SER’CAs to artemisinins.Nat Struct Mol Bio. 12(7):628-9.
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About Authors:

Vipin K. Sharma

Vipin K. Sharma
He has done his M.Pharm.(Pharmaceutics) form the Department of Pharmaceutical Sciences, Dibrugarh University, Dibrugarh (Assam). He has publications in national and international journals of well repute. He is also pursuing Ph.D from the same department under the supervision of Dr.A.Bhattacharya, Head of the Depatment.
For Correspondence

A. Bhattacharya
Department of Pharmaceutical Sciences, Dibrugarh University, Dibrugarh (Assam-786004, India)