Artemisia L. (PROSEA)

Plant Resources of South-East Asia
Introduction

Protologue: Sp. pl. 2: 845 (1753); Gen. pl. ed. 5: 367 (1754).

Family: Compositae

Chromosome number: x= 8, 9;A. annua: 2n= 18,A. apiacea: 2n= 18,A. capillaris: 2n= 18, 36,A. vulgaris: 2n= 16, 18, 24, 54

Major species

Artemisia annua L., A. capillaris Thunb., A. vulgaris L.

Vernacular names

Mugwort, wormwood (En).

Origin and geographic distribution

Artemisia consists of approximately 200 species (some estimates are up to 400 species), most of which are native to dry grassland regions of Eurasia and North America. The regions of central and south-western Asia are particularly rich in species; the genus is thought to have originated here, and to have migrated to North America. Several species have been introduced in the Malesian area, usually as ornamentals; some have naturalized.

Uses

Artemisia is well known in phytotherapy all over the world. Numerous species are used in local medicine. The rediscovery in the 1970s of A. annua as remedy against malaria was spectacular. It had already been used for over 1000 years in China to treat malarial fever, but modern researchers became interested in its properties when the search for new antimalarial medicines started in response to the growing resistance of malaria-causing agents ( Plasmodium spp.) to the industrial antimalarial drugs currently in use. The active compound, artemisinin (or "quinghaosu" in China), a sesquiterpene lactone endoperoxide, may be administered in tablets or suppositories. A series of artemisinin derivatives has been semi-synthesized, often with improved pharmacological, pharmaceutical, technological or pharmacokinetic properties; some of them are also used clinically now. The methyl-ether derivative, artemether, and the ethyl-ether derivative artemotil (proposed INN name, previously β-arteether), which are better lipid soluble, are available for intra-muscular injection. The sodium salt of the hemisuccinate ester, also known as (sodium) artesunate is water soluble; it is administered orally or by intravenous injection.

Leaves and flowering tops of A. vulgaris are traditionally used to stimulate the appetite, as a sedative and as a vermifuge. However, the use of excessive doses over long periods may lead to digestive and urinary disorders. A gel containing A. vulgaris extract is considered a useful skin care product for dry and pruritic skin conditions. A. vulgaris (or a related species) is used in local medicine in India to treat rheumatism. Leaves are used in Chinese medicine as a remedy against haemorrhage and diarrhoea. In Vietnam, a decoction is prescribed to treat menorrhagia.

The buds of A. capillaris ("Artemisiae Capillaris Flos") have been used since antiquity in Chinese and Japanese medicine, mainly in the treatment of liver and related diseases, e.g. inflammation of the liver, jaundice and cholecystitis. The drug is also applied as cholagogue, anti-inflammatory drug, analgesic, antipyretic and diuretic.

A. absinthium L. is used in traditional medicine in several countries, e.g. in India to treat chronic fever, swellings and inflammation of the liver and as a tonic and stimulant. In Cuba it is applied to treat various diseases caused by parasites, whereas formerly in Europe it was used as a digestive, in the treatment of gastritis, against stomach cramps, stomach and intestinal atony, and as anthelmintic. Formerly it was an ingredient of a popular alcoholic drink in France, but its use in absinthe has been banned because of the suspected neurotoxicity of one of the chemical constituents, i.e. thujone. A. dracunculus L. and A. maritima L. are used as an aperient, stomachic, stimulant and febrifuge in India. The flowering heads of the latter and A. cina Berg ex Poljakov produce santonin, valued as an anthelmintic. In India, A. nilagirica (C.B. Clarke) Pampan. is considered an emmenagogue, anthelmintic, stomachic and febrifuge, and is also used to treat skin diseases and ulcers. A. scoparia Waldst. & Kit. is a source of scoparone, which exhibits significant hypotensive and tranquilizing activity.

A. vulgaris is sold as a vegetable on markets in Sarawak and Thailand.

Production and international trade

Artemisinin and its derivative artemether are produced commercially in several countries. Artemisinin is extracted industrially from cultivated A. annua in Vietnam, and pharmaceutical companies in China and France produce artemether industrially. Artemether is, for instance, marketed in ampules of 80 mg/ml in vegetable oil, to be administered by intra-muscular injection. Artemotil (proposed INN name, previously β-arteether) will be commercially available in 1 ml ampules containing 50 mg or 150 mg per ml sesame oil for intra-muscular injection in cases of severe Plasmodium falciparum malaria, as soon as marketing authorisation has been obtained in the Netherlands.

Properties

Extracts of A. annua show antimalarial activity, which can be attributed to the fraction containing sesquiterpene lactones (based on cadinane and closely related carbon frameworks). The most important active compound of A. annua against malaria from this fraction is the endoperoxide artemisinin, but some related compounds from A. annua and other Artemisia species also show some activity, e.g. arteannuin B and other peroxides such as artemisitene and arteinculton. However, artemisinin has significantly greater activity than the other peroxide compounds, having an EC₅₀of 0.01 μg/ml, compared with 1-10 μg/ml for the other compounds.

Artemisinic acid plays a pivotal role in the biosynthetic pathway of artemisinin. Artemisinic acid originates from mevalonic acid and farnesyldiphosphate, yielding a cadinane skeleton as a close precursor of this compound. The arteannuin B formed as a result of various processes, one being lactonization, is considered an intermediate in the bioconversion of artemisinic acid to artemisinin. Artemisinin is too complex to be synthesized on a large scale, and it is generally obtained by isolation from plant material. Leaves originating from the Washington (Virginia, United States) area and Europe contain 0.05-0.1% artemisinin (on dry-weight basis), while leaves originating from southern China and the northern provinces of Vietnam contain up to 1.3% artemisinin (on dry-weight basis). A liquid-liquid extraction technique, that allows the use of recovered solvents, has been developed for large-scale production of artemisinin.

Several analytical methods are in use to assay the biosynthetic precursors and metabolites of artemisinin. A simple TLC method is available for screening. HPLC with electrochemical detection, GC-MS and thermospray LC-MS allow very efficient detection of artemisinin and structurally related compounds.

Clinical tests in China, Cameroon, the Gambia, the Netherlands, Thailand, Vietnam, Zambia and other countries on volunteers and thousands of patients with severe and non-severe Plasmodium falciparum malaria indicated that artemisinin and its derivatives are safe and effective.

For instance β-dihydroartemisinin shows a rapid absorption and distribution, and depending on the dosis, blood levels peak in 1-2 hours, while the biological half-life lies between 1-2 hours too. Multiple dose treatment via the intra-muscular route with artemotil (β-arteether) attained a steady state level after 8-14 hours. The half-life varied between 35-45 hours. The artemisinin group of drugs is only valuable to treat cerebral or Plasmodium falciparum malaria.

Malaria is caused by a parasitic Plasmodium protozoan, which uses mosquitoes of the genus Anopheles as an intermediary host. When an infected mosquito bites a person, sporozoites enter the blood, but they disappear rapidly from the circulation to localize in the parenchymal cells of the liver in which they grow and segment to merozoites. This stage of the infection lasts for 5-16 days, depending on the Plasmodium species. On reaching maturity these merozoites are released from the liver cells and penetrate erythrocytes where further division and development takes place. When this process is complete, the erythrocytes burst open and the merozoites enter the blood stream. It is this periodic breaking of erythrocytes that causes the chill so characteristic of malaria. The fever following the chill is due to the liberated foreign protein and cell products. Some of the merozoites infect new blood corpuscles, while others develop into the sexual form, called gametes. The gametes can pass to a healthy mosquito when it bites a person suffering from malaria. The gametes conjugate in the mosquito, forming sporozoites, and the circle is complete.

Artemisinin acts as a so-called blood schizonticide on the asexual erythrocytic stage of the parasites. A critical step in the mechanism of action of artemisinin (and related drugs) seems a hemin-catalysed reduction of the peroxide moiety, resulting in more cytotoxic compounds, such as free radicals and reactive aldehydes that subsequently kill malarial parasites. Membrane damage, alkylation and oxidation of proteins, oxidation of fats, inhibition of the protein and nucleic acid synthesis have been found in these parasites, as well as interaction with cytochrome oxidase and with the glutamine transport system. The hemin-rich internal environment of the parasites in the erythrocyte is assumed to be responsible for the apparent selective toxicity of artemisinin towards these organisms. Artemisinin rapidly clears the blood from parasites (elimination and improvement of symptoms occur sooner than with chloroquine, and good results have also been obtained with patients who were no longer responsive to chloroquine), but it is inactive against liver stages of the parasite. Due to this spectrum, the drug should not be used as prophylactic; this also greatly reduces the risk that resistance will develop to this new class of antimalarials. Artemisinin and several derivatives have furthermore been found to kill early stages of gametocytes of Plasmodium falciparum too. This gametocidal effect may play a role in the interruption of malaria transmission. There are no reports of serious toxicity in humans. Toxicity to the myocardium in macaques after extreme high doses has been reported, while in a test on dogs the highest dose caused deaths. However, when the latter study was repeated under conditions of good laboratory practice, no mortality occurred, and the no toxic effect level was 3 mg/kg in dogs treated daily during 4 weeks with artemotil.

In addition to the antimalarial activity, some other biological activities of artemisinin (and related structures) and of other Artemisia -constituents have also been investigated, e.g. cytotoxicity to Ehrlich ascites tumour cells in vitro. All compounds (including artemisinin, artemether and sodium artesunate) showed cytotoxiticy, with IC₅₀values ranging from 12-30 μM. The variations in effect between the structurally strongly related compounds mostly correlated well with the theoretical capacity of radical formation and stabilization. Artemisinin, artemisinic acid, arteannuin B, a series of friedelane-type triterpenoids, and the flavonoid quercetagetin-6,7,3',4'-tetramethylether showed positive test results for in vitro cytotoxicity in a series of tumour cell lines (P-388 murine lymphocytic leukaemia, A-549 human lung carcinoma, MCF-7 human breast adenocarcinoma, HT-29 human colon adenocarcinoma and KB human nasopharynx carcinoma). Artemisinin and artesunate have been found effective against experimental schistosomiasis in mice and dogs.

Extracts of A. annua showed a strong inhibitory effect on tobacco mosaic virus; the inhibitory agents were identified as the sterols sitosterol and stigmasterol. The extracts also showed in vitro anticoccidial effect against Eimeria tenella , which causes a serious disease in poultry. Artemisinin has allelopathic activity, and inhibits seed germination, seedling growth and root induction of crops such as lettuce and beans.

An extract of 5 g dry powder of A. absinthium in 50 ml water, diluted 1:35, showed 90% growth inhibition of Plasmodium falciparum in a test in Cuba. An LD₅₀of 31 μg/ml was detected for the sesquiterpene lactone fraction. The test method available for the evaluation of crude extracts assesses the ability of the extract to inhibit [G-³H]-hypoxanthine uptake into Plasmodium falciparum .

A. vulgaris extracts show insecticidal, insect-repellent, antimutagenic and anthelmintic activities; reports on antimalarial activity are contradictory. The efficacy of a gel containing A. vulgaris (or a closely related species) extract has been studied in Japan on 56 patients having pruritic skin lesions. Excellent clinical improvement was obtained in 67% of the cases of pruritic dermatitis, in 56% of atopic dermatitis and 73% of senile xerosis; poor response was observed in 2 cases of contact dermatitis. No side effects were observed.

An aqueous extract of A. vulgaris markedly inhibited the growth of both gram-positive and gram-negative bacteria in vitro. It inhibited the growth of the cariogenic bacterium Streptococcus mutans considerably. The essential oil from fresh leaves tested at 5000 ppm against the storage fungus Aspergillus flavus showed 67% growth inhibition. The dehydromatricaria esters present in the plant showed some antifungal activity, but in general their biological activity is slight. Roots of A. vulgaris showed mild toxic activity against the oriental fruit fly. An extract of A. vulgaris (particularly of young leaves) inhibits germination and seedling growth of other plants, e.g. of lucerne; it showed some retarding effect on the growth of tea, but it increased the growth of the fungus Pythium myriotylum .

The essential oil from several species (e.g. A. annua , A. vulgaris ) is suitable for use in the perfume and cosmetics industry. The oil content of dried flowering parts of A. annua is approximately 0.6%. However, A. vulgaris normally has a low volatile oil content (0.03%), which accounts for its palatability and digestibility for animals as compared with other Artemisia species; the protein content is about 32% and the average in vitro digestibility 67%. A. vulgaris is, however, suspected of causing bladder cancer in cattle. The oil content can be much higher in certain types, e.g. in the Philippines where a yield of 0.3% from air-dried leaves has been reported. The volatile oil is yellowish-greenish with an intense and persistent fragrance. More than 70 compounds, mainly monoterpenes and sesquiterpenes have been identified structurally from the essential oil from flowering parts of A. vulgaris . The oil production is seasonally dependent and chemical composition is highly variable; 1,8-cineole, camphor, terpinen-4-ol, β-pinene, (+)- and (-)-borneol, myrcene and vulgarin are invariably present, but thujones (α- and γ-) are only present in traces or absent. A rather high concentration of thujones is present in oil from A. absinthium ; habitual use or large doses of absinthe beverages causes absinthism, characterized by neurotoxic symptoms such as restlessness, tremors and convulsions. Whether thujones are the sole cause of these symptoms remains an open question since absinthe formerly also contained cupric sulphate and indigo-based colorants. Almost 50 components were identified in leaves of A. vulgaris from Vietnam, the major ones being β-caryophyllene (24%) and β-cubebene (12%).

In A. capillaris it is the seed that contains most oil. In the essential oil of A. capillaris 25 terpenoids (e.g. β-pinene, limonene and γ-terpinene), 6 phenylacetylenes, 7 phenols and 15 fatty acids have been identified; capillen (a phenylacetylene) is the main component. The main components of drugs prepared from A. capillaris are scoparone (6,7-dimethoxycoumarin) and capillarisin. Several other flavonoids and the coumarin 6,7-dimethylesculetin have been identified in the active fraction of the methanol extract. An extract of A. capillaris inhibited bovine lens aldose aldehyde reductase and rabbit platelet aggregation; this may be of interest in the prevention of diabetes complications. Scoparone and scopoletin exhibited a potent inhibitory effect on rabbit platelet aggregation, and capillarisin did likewise on bovine lens aldose reductase. Scoparone and capillarisin have choleretic action. The flowers, as one of the ingredients in a herbal medicine, helped change the bile flow to almost normal level in α-naphthyl isothiocyanate-induced cholestasis in rats. In tests with mice, the buds and leaves of A. capillaris showed significant protective effect against liver lesions induced by carbon tetrachloride. The active principles were shown to be the flavones eupatolitin and arcapillin. An extract inhibited the adherence of Streptococcus mutans , a bacterium which causes dental caries, to teeth surfaces. Tests on isolated rat heart indicate that scoparone possesses anti-anginal action as a vasodilator. Furthermore, kinetic experiments using rabbit thoracic aorta showed that scoparone has a marked inhibitory effect on the contractions induced by norepinephrine (noradrenaline), 5-hydroxytryptamine, histamine and angiotensin II. Like nitroglycerin, scoparone appeared to be a competitive antagonist of norepinephrine.

Polymers of caffeoylquinic acids are the main polyphenolic components in A. capillaris ; caffeic acid can be produced by partial hydrolysis of these compounds. Extracts containing these "caffeetannins" and related compounds have protective action against liver damage. Species used as haemostatic generally also contain caffeetannins.

Extracts of A. capillaris have been found to be positive in the chromosomal aberration and micronucleus assays in mice. Leaf and stem extracts of A. capillaris showed pronounced nematicidal activity against Bursaphelenchus lignicolus . The phenylacetylenes capillen (1-phenyl-2,4-hexadiyne) and 2,4-pentadiynylbenzene (1-phenyl-2,4-pentadiyne) have been isolated from A. capillaris roots and buds; capillen inhibits the germination of seeds of, for instance, millet, cabbage and carrot, and both compounds have an antifeeding activity on cabbage butterfly ( Pieris rapae ) larvae, as do certain other minor constituents in growing buds such as capillarin, methyleugenol, ar-curcumene and bornyl acetate. A factor promoting root growth, capillarol, has also been isolated from the leaves; it increased root growth of rice by 80%. A. capillaris extracts showed antimicrobial action and were effective in suppressing the growth of food-poisoning bacteria, Lactobacillaceae and mycotoxigenic moulds. The flavonoid fraction has been patented for anti-acne treatment and the coumaric fraction for use as a hair stimulant.

The aerial parts of A. cina , which contain flavonoids (e.g. hispidulin, quercetin, rutin and caffeic acid), phenol acids and coumarins, and certain other Artemisia species indigenous in Russia showed anti-tumour activity in animal tests; these species may be useful in the treatment of Ehrlich carcinoma, breast adenocarcinoma, sarcoma and Walker carcinosarcoma. An aqueous extract of flowering parts of A. cina was found to be lethal to larvae of the mosquito Culex pipiens ; it had an EC₅₀value of 4 g/l 24 hours after treatment. At a dose of 40 ppm the extract is able to give a significant control of the root-knot nematode Meloidogyne incognita . Twenty components have been identified in A. cina oil including α-pinene, β-pinene, myrcene, camphene, β-ocimene, sabinene and limonene.

The large amounts of pollen produced by the wind-pollinated plants can cause allergic reactions in susceptible persons. Contact dermatitis caused by A. vulgaris has been reported.

Adulterations and substitutes

Synthetic antimalarials derived from quinine are widely used, as are related alkaloids from Cinchona spp. The search for new antimalarials in response to the growing resistance of malaria-causing agents to industrial drugs has not only resulted in interest in A. annua , but also in interest in certain other promising plant resources used in traditional medicine to treat malaria, e.g. Azadirachta indica A.H.L. Juss., Brucea javanica (L.) Merr., Cyclea barbata Miers and Dichroa febrifuga Lour.

Description

Erect or ascending aromatic annual or perennial herbs or subshrubs, usually densely hairy. Leaves alternate, usually divided or 1-3-pinnate; stipules absent. Flowering heads numerous and small, in spicate, racemose or paniculate inflorescences or sometimes solitary, usually nodding at anthesis, discoid, greenish or yellowish, rather few-flowered; involucre campanulate or subglobose to ovoid, with bracts imbricate in 1-3 series and scarious at margins, the outer bracts usually smaller; receptacle flat or conical to hemispherical, glabrous or pubescent. Flowers of two types, with 1 series of marginal pistillate ray flowers, and bisexual or functionally male tubular disk flowers in the centre of the head; pappus absent; corolla of ray flowers tubular and 2-3-fid, that of disk flowers tubular and 5-fid; stamens 5, inserted on the corolla, with distinct filaments and connate anthers forming a tube around the style, anthers often tipped with acute appendages; ovary inferior, 1-celled, style bifid and exserted in pistillate flowers and often dilated or penicillate in disk flowers. Fruit an obovoid or oblong, terete achene, rounded and with a disk at the apex, striate or 2-ribbed, glabrous or pubescent.

Growth and development

The life cycle of the Chinese-Vietnamese material of A. annua , under natural conditions, is completed within 10 months. Seeds germinate in January to March and fruits can be harvested in October-November. The harvest of plants for extraction of artemisinin takes place in July. Initially, growth is slow and seedlings reach a height of about 5 cm after one month and 25-30 cm after 3 months. Growth is much more rapid from the fourth month. The vegetative period lasts 6-8 months. By August, A. annua has become strongly branched, and flower buds become visible. The flowers do not secrete nectar and are wind pollinated; they produce pollen abundantly. The life-cycle of European-American material of A. annua is completed within 6 months. Germination takes place in May, while seeds can be harvested in November.

Chinese-Vietnamese material grown in Europe in the open cannnot be planted earlier than May-June because of night frost. In October one can observe elongation of stems and small branches as a prelude to flowering. Flowering is in general frustrated by early night frost and bad weather. Under green-house conditions seed can be produced.

A. annua is basically self-fertilizing, but considerable cross-pollination may occur. In some Artemisia species, the inner flowers in a flowering head are functionally male and do not set fruit (e.g. in A. capillaris ). This is also reported for A. annua , but in fact the inner flowers do produce seeds, but these are less viable and seedlings often die shortly after germinating.

Other botanical information

Artemisia is in desperate need of a thorough and complete taxonomical revision. Several closely related (or perhaps conspecific) species are often confused in eastern Asia, particularly in the group A. campestris L., A. capillaris Thunb. and A. scoparia Waldst. & Kit. of the section Dracunculus , and in the group of A. indica Willd. (synonym: A. princeps Pampan.), A. nilagirica (C.B. Clarke) Pampan. and A. vulgaris L. of the section Abrotanum . Consequently, the literature is often difficult to interpret, and information on A. vulgaris from eastern Asia probably often refers to other related species. In fact, some authors consider A. vulgaris to be a single very variable and widespread species, whereas many others consider it as a complex of up to about 100 closely related species.

A. annua , A. apiacea (both of the section Abrotanum ) and A. capillaris are sometimes confused. A. annua can be identified by its strongly branched panicle and small, subglobose heads. A. capillaris is a subshrub, the other two species are annuals.

A. annua material from European-American and Chinese-Vietnamese origin shows some clear differences. The European-American type has the ability to produce inflorescences 3-4 months after sowing, while the Chinese-Vietnamese type will not do so when planted in Europe in the open. In order to produce seed of the Chinese-Vietnamese type in Europe, one has to grow it under greenhouse conditions. Furthermore, the artemisinin content of the Chinese-Vietnamese type is ten-fold higher compared to the European-American type, also when raised under European conditions.

Ecology

Artemisia prefers full sunlight. It is often found in roadsides, waste places and fields. A. vulgaris is locally a noxious weed, e.g. in tea plantations.

In cultivation, A. annua demands fertile and moisture-retentive soils for optimal growth. It does not tolerate dry conditions or waterlogging, and it usually dies within 2-3 days of flooding. It tolerates neutral to slightly acid soils (pH no lower than 5), and is usually cultivated on rich sandy loams or alluvial soils.

Variation in acetylene content has been found in different ecotypes of A. capillaris ; the phenylacetylenes capillen and capillin were found to be the main constituents in the roots and leaves of plants growing along freshwater rivers, but were only found in the roots of plants growing in a saline environment.

Propagation and planting

A. annua is propagated by seed. In northern Vietnam, seeds are collected in November and sown in February-April or in July-August (southern Vietnam). One gram contains 20 000-22 000 seeds. Before sowing, seeds are soaked in warm water (45-50°C) for 2-3 hours or in a 0.1% gibberellin solution for 15-20 minutes. Under optimal soil moisture and temperature (20-25°C) conditions pretreated seeds start germinating 4-8 days after planting, untreated seeds 10-20 days after planting. The germination rate is usually 50-60% when fresh seed is sown, but drops to 2-3% after 6 months of storage. The usual rate for broadcasting seed in the field is 300-500 g per ha. About 40-50 days after sowing plants are thinned to 20-40 cm × 20-40 cm. Nowadays, seed is preferably sown in nurseries and when seedlings are 15-20 cm tall they are planted into the field at 20-40 cm × 20-40 cm. The latter method of propagation is preferred to direct seeding because it shortens the crop cycle by about 2 months and secures a better and more uniform stand.

Seedbeds are 1-1.2 m wide and 15-20 cm high and provided with a layer of fine-textured topsoil. The application of 5-10 t/ha of green manure or organic manure before planting is beneficial.

In vitro production of active compounds

Callus from A. annua seed has been initiated by transfer onto agar containing Murashige and Skoog basal salts with 5% sucrose, 0.1 mg/l kinetin and 1 mg/l 2,4-dichlorophenoxyacetic acid. The callus cultures were maintained at 25°C under constant illumination and subcultured every 4 weeks. After 3 subcultures, the calli were inoculated into liquid medium of the same ingredients (without agar) and maintained under the same conditions on a rotary shaker. The cell suspension culture was used for the isolation of constituents. The cell suspension cultures exhibited antimalarial activity in vitro, both in the n-hexane extract of the plant cell culture medium and in the chloroform extract of the cells. Trace amounts of artemisinin may account for the activity of the n-hexane fraction, but only the methoxylated flavonoids artemetin, chrysoplenetin, chrysoplenol-D and cirsilineol can account for the activity of the chloroform extract. However, the activity of these flavonoids is much lower than for artemisinin.

Husbandry

A. annua responds well to fertilization. N fertilizers are usually applied twice, each time 90-110 kg/ha, the first time about 2 months after direct sowing in the field or 2 weeks after transplanting from the nursery, the second time one month before harvesting. P and K fertilizer is sometimes also applied. However, the artemisinin content of the plants does not increase under these favourable growth conditions. In Vietnam, it has been reported that the artemisinin content of cultivated A. annua plants can be comparable to that in plants growing in the wild.

A. vulgaris has been intercropped successfully with poplar ( Populus sp.) in India. It responds well to the application of complete fertilizer (10 g/plant).

Diseases and pests

Several years of experience with trial plantations of A. annua in Vietnam did not reveal serious diseases or pests. Minor pests are ants carrying away seeds after sowing, crickets damaging seedlings, and caterpillars and aphids feeding on the crop.

Weedy Artemisia can serve as a host to pathogens and pests that can seriously affect crops. A. vulgaris , for instance is a host for cucumber mosaic virus, the worm Ostrinia nubilalis and the European corn borer. A. annua has been reported as a host of nematodes ( Meloidogyne spp.).

Harvesting

The highest leaf yield and the highest foliar artemisinin content in A. annua (up to 0.9%) are obtained when the crop is 5 months old. In Vietnam, the harvest is usually in August in the north and in November in the south. Harvesting should preferably be on dry, sunny days.

In Japan, tests with material of A. capillaris harvested on different dates showed considerable variation in activity of the drug and in the content of capillarisin and dimethylesculetin. In that country, the capillarisin and 6,7-dimethylesculetin contents reach maximum levels in leaves just before the appearence of flower buds (end of July), and one month later in the heads (end of August). The best time for harvesting is between the flower bud stage and early flowering, which is from late August to early September in Japan. The flavonoid content of A. cina is low during the vegetative period, increases during bud formation and flowering, and decreases again during fruiting.

Small quantities of A. vulgaris are usually collected all year round.

Yield

Yields of cultivated A. annua in Vietnam range between 25 and 45 t/ha of fresh material. Yields are generally lower in northern Vietnam than in southern Vietnam: 1.5-2.5 t/ha of dried cleaned material (0.5-0.9% artemisinin) in the north, 2-4 t/ha (0.3-0.6% artemisinin) in the south.

Handling after harvest

After harvesting, plants are usually sun-dried on brick or cement yards or on asphalt roads for 1-2 days. Broken parts of roots and stems are subsequently separated mechanically, and the remaining material is further dried to below 12% moisture content. Dried leaves of A. annua should be stored and packed in jute bags under air conditioning (low relative humidity). In experiments, where the relative moisture of the material varied between 4-16%, the artemisinin content was slightly affected over a period of one year. Material with a moisture content of 16% and stored in jute bags under air conditioning showed a decrease from 5.9-5.2% artemisinin only. Thus, if described storage conditions are maintained, there will be ample time to extract artemisinin before the next crop arrives, while extra electricity costs for air conditioning will be compensated by higher artemisinin extraction yields.

Moreover, there is advantage because of the fact that there is no pressure to extract the crop immediately. As highly volatile extraction solvents are used, chemical extraction can be carried out during the winter season in northern Vietnam and not during summer and autumn when high temperatures complicate cooling of these solvents.

Artemisinin has a low solubility in aqueous and oily solvents, thus causing problems for clinical application. The derivative sodium artesunate is readily water-soluble, and can be processed more easily to medicaments.

Genetic resources and breeding

Although A. capillaris has for centuries been considered useful as a medicinal plant in China and Japan, it has hardly been cultivated, and the crude drug has been largely derived from wild plants. A. apiacea occurs rather scattered and is poorly known. It has been reported that protection of A. cina is necessary in parts of Russia because of overcollecting for medicinal purposes. A. annua is increasingly being planted for artemisinin production (e.g. in Vietnam and China); in other regions (e.g. Java) it was already being planted for ornamental purposes. A. vulgaris is widespread and is not at risk of genetic erosion. There are no records of Artemisia species in germplasm banks, and there are no known breeding programmes.

Prospects

Interest in A. annua as an antimalaria crop is increasing enormously. Tests indicate that artemisinin and its derivatives have a rapid and effective action and low toxicity. To date, no resistance of Plasmodium against artemisinin and its active derivatives has been found. It is advisable to control the prescription strictly and not to use these compounds for preventive treatment (which is in any case not self-evident, given that the biological half-life of artemisinin is approximately 4 hours). The therapeutic indications should be provisionally the treatment of severe malaria or when resistance to other antimalarials is suspected. A. annua has great prospects in malaria control, and research should continue to optimize its utilization. Artemisinin yields are about 2 kg/ha and should be raised to at least 50 kg/ha to make a cheap antimalarial.

Several other Artemisia species have interesting medicinal properties and deserve more research. For instance, A. capillaris and A. vulgaris are of interest as an anti-inflammatory for treating skin complaints and for the prevention of dental caries, whereas the former species may be useful in the prevention of complications caused by diabetes and for its protective action against liver damage.

Literature

Bruneton, J., 1995. Pharmacognosy, phytochemistry, medicinal plants. Lavoisier Publishing, Paris, France. pp. 458-459, 506-508.
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Authors

Nguyen Tien Ban, Vu Xuan Phuong & Charles B. Lugt