Artemisia annua, also known as sweet wormwood, sweet annie, sweet sagewort, annual mugwort or annual wormwood, is a common type of wormwood native to temperate Asia, but naturalized in many countries including scattered parts of North America.

The chemical compound artemisinin, which is isolated from A. annua, is a medication used to treat malaria due to Plasmodium falciparum, the deadliest species of malarial parasite. Discovery of artemisinin and its antimalarial properties made the Chinese scientist Tu Youyou recipient of the 2011 Lasker Prize and 2015 Nobel Prize in Physiology or Medicine.

Description

Artemisia annua belongs to the plant family of Asteraceae and is an annual short-day plant. Its stem is erect and brownish or violet-brown. The plant itself is hairless and naturally grows from 30 to 100 cm tall, although in cultivation plants can reach a height of 200 cm. The leaves of A. annua have a length of 3–5 cm and are divided by deep cuts into two or three small leaflets. The intensive aromatic scent of the leaves is characteristic. The artemisinin content in dried leaves is in between 0% and 1.5%. New hybrids of A. annua developed in Switzerland can reach a leaf artemisinin content of up to 2%. The small flowers have a diameter of 2–2.5 mm and are arranged in loose panicles. Their color is greenish-yellow. The seeds are brown achenes with a diameter of only 0.6–0.8 mm. Their thousand-kernel weight (TKW) averages around 0.03 g (in comparison, wheat has a TKW of approximately 45 g). The scent of the essential oil is fresh, herbaceous-camphorous, slightly spicy.

Agricultural practice

thumb|upright|Artemisia annua

thumb|Seeds

The growing period of A. annua from seeding through to harvest is 190–240 days, depending on the climate and altitude of the production area. The plant is harvested at the beginning of flowering when the artemisinin content is highest.

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!Growth Phases

A. annua is best sown in rows to facilitate the removal of weeds, which has to be done mechanically or manually because herbicides are typically not used. It is recommended to sow 1.4 – 2 seeds per square meter. Phosphate on the other hand is required during the blooming stages. Phosphate fertilization can lead to a higher artemisinin content in the leaves. The application of salicylic acid to the leaves shortly before harvesting the plant also can raise its artemisinin content. Besides few viral diseases, A. annua has no major diseases that need to be controlled.

The harvest of the plant is best done when plants reach peak artemisinin, which may be in the state of flower budding, for early-flowering cultivars. However, for late flowering cultivars that were reported to reach peak artemisinin in early September in the United States, the harvest will happen about a month before the flowering stage when plants produce more artemisinin in leaves. This peak artemisinin in early September was observed for Brazilian, Chinese, and Swiss clones in West Virginia. Drying the plants before extraction will significantly increase artemisinin as dihydroartemisinic acid and artemisinic acid seem to be converted into artemisinin. The whole plant is harvested and cut into branches which are dried in the sun or an oven. Some report that drying artemisia plants at 45 °C for 24h increased artemisinin and maintained leaf antioxidant capacity. The dry branches are shaken or beaten to separate the leaves from the stem. The leaves are then packed into fabric bags and shipped for further processing.

The first isolation of artemisinin from the herb occurred from a military project known as Project 523, following the study of traditional medicine pharmacopoeias performed by Tu Youyou and other researchers within the project. A. annua contains diverse phytochemicals, including polyphenols such as coumarins, flavones, flavonols, and phenolic acids which have unknown biological properties in vivo. Other phytochemicals include 38 sesquiterpenes.

Malaria treatment

Research to develop antimalarial drugs led to the discovery of artemisinin in the 1970s by the Chinese scientist Tu Youyou, who shared the 2015 Nobel Prize in Physiology or Medicine. An improved extract was obtained by using a low-temperature ether-based extraction method, further showing the artemisinin derivative artemether to be an effective antimalarial drug. Research has found that artemisinin is not soluble in water and the concentrations in these infusions are considered insufficient to treat malaria. A 2012 review stated that artemisinin-based remedies are the most effective drugs for the treatment of malaria. A 2013 review suggested that although A. annua may not cause hepatotoxicity, haematotoxicity, or hyperlipidemia, it should be used cautiously during pregnancy owing to a potential risk of embryotoxicity at a high dose.

The WHO has approved riamet (Coartem), a combination of lumefantrine (120 mg) and artemether (an artemisinin derivative extracted with ether, 20 mg) in repeat treatments over two days, producing efficacy of up to 98% against malaria. Malaria is caused by apicomplexans, primarily Plasmodium falciparum, which largely reside in red blood cells and contain iron-rich heme-groups (in the form of hemozoin). In 2015, artemisinin was shown to bind to a large number of cell targets, indicating its potential for diverse effects.

Artemisinin resistance

Despite global efforts in combating malaria, it remains a large burden for the population, particularly in tropical and subtropical regions. Emergence of artemisinin resistance has been identified in Cambodia and the border of Thailand. Resistance will likely spread to other endemic areas across the world.

Traditional medicine

In traditional Chinese medicine (TCM), A. annua is prepared with water to treat fever.

References

  • Distribution of artemisinin in Artemisia annua
  • Project to improve artemesinin yield at the University of York (UK)
  • Data sheet about Artemisia annua from Purdue University