Artemisia Drug Use

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Artemisia annua and research into Malaria therapy

279Artemisia annui

Artemisia annua

Artemisia annua is a vigorous weedy monocarpic species native to the Far East, (especially China), and now naturalised in many warm temperate to tropical areas including southern Europe and the Americas. It has long been used by the Chinese for treatment of fevers and especially malaria, and research over the last few decades has shown it to contain an active compound artemisinin, which is effective against drug resistant forms of the main malaria parasite Plasmodium falciparum.

Artemisinin has been shown to be a sesquiterpene lactone which contains a previously unknown endoperoxide bridge. Several similar chemical compounds are also present in the plant which may be potential starting points for other antimalarial drugs. These substances occur in glandular trichomes located on the leaves and flower heads of the plant.

Artemisinin is a complex molecule which is difficult to synthesise and at present the only way of providing sufficient material for drug use is to grow the plant as a field scale crop. Many different clones of the plant have developed across a range of climatic conditions and habitats, and they vary in the stimuli needed for flower induction and in their content of artemisinin or other active compounds. Published work suggests that they also differ in the stage at which peak artemisinin content occurs, ie either before or during flowering.

Artemisia annua is a rapid converter, typically growing from a tiny seed to about two metres and seeding within a single growing season, in an “annual” type of habit. The plant is actually monocarpic and dies after seeding, but in my experience its growth can easily be extended over winter (under protection) by means of cuttings taking before senescence or by preventing it from flowering. (One clone in the Plant Heritage/NCCPG Artemisia Collection has now been vegetatively maintained for over 12 years from an original seeding.)

UK Field Trials of A. annua

Hitherto the plant has been grown on a field scale in warmer parts of the temperate world, but recently there have been field trials of selected varieties in the UK. Cropping methods employed overseas have involved growing the plant from seed and taking a single crop. In this method the major cost of production is the establishment of the seedbed and seedling maintenance until the crop closes over. It may be possible to devise an alternative cultural regime which allows cropping to be extended over more than one growing season. Thus if a winter hardy strain or hybrid can be found which allows a useful crop to be taken before (or at an early stage of flowering) such that the plant survives to regrow during the following season, it may be possible to optimise production over several years. It may be necessary to hybridise strains to achieve this aim.

282field trials rescaled

A. annua field trials

The Artemisia Collection has been collaborating in a development project coordinated by the National Institute of Agricultural Botany (NIAB), to improve yields by selective breeding and improved cultivation techniques. Recent plant breeding work by NIAB (2009) has more than doubled the artemisinin content of high yielding varieties by developing a strain with over 2% artemisinin (in dry matter content).

Most Artemisia species are perennial in habit and many are more vigorous and reliably hardy in the UK than A.annua. A possible alternative approach may therefore be to explore the possibility of transferring suitable genes into another species. The National Collection of Artemisia holds several hundred different species, cultivars and strains from which initial selections could be made.

Dr J D Twibell
Plant Heritage/NCCPG Artemisia Collection

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