The Discovery Of Artemisinin

Qing Hao is a herb commonly used in China with a long history of use as an antipyretic to treat the alternate chill and fever symptoms of malaria and other "heat syndromes" in the traditional Chinese medical system. The name Qing Hao first appeared in a silk book excavated from the tomb at Mawangdui belonging to the Han dynasty; it was entitled "Wu Shi Er Bin Fang" (Prescriptions for Fifty-two ailments) and dated from as early as 168 BC, and described the use of Qing Hao for the treatment of haemorrhoids. In 340 AD, Qing Hao was recorded for the first time as a treatment for fevers in a medical book, "Zhou Hou Bei Ji Fang" (Handbook of Prescriptions for Emergency Treatment). In this work, the author, Ge Hong, recommended that, to reduce fevers one should soak a handful of Qing Hao in one sheng (approx. 1 L) of water, strain the liquor and drink it all. Li Shi-Zhen, the author of the famous materia medica "Ben Cao Gang Mu" (1596 AD), based on the former medical text records and his own experience, stated that malaria with chills and fever could be treated with Qing Hao (Klayman, 1985 and references therein). Qing Hao has been recommended for use alone or with other herbs for malaria as well as for other conditions (see below).

Qing Hao is the aerial part of Artemisia annua L. of the family Asteraceae (formerly Compositae), and it is now officially listed in the Chinese pharmacopoeia (Anon. 1992). In the early literature, Qing Hao referred to two species, A. annua and A. apiacea but nowadays Qing Hao is usually taken to be A. annua.

In 1967, the Chinese government began a systematic examination of plant species used in TCM in order to discover new drugs, especially for malaria. The many plants tested included Qing Hao, but no activity was seen when hot-water extracts of this herb were tested in mice infected with the rodent malaria parasite Plasmodium berghei. However, when cold ether extracts of Qing Hao were tested, encouraging activity was observed (Klayman, 1985).

Since then, Chinese researchers in many institutions have devoted considerable resources to investigate the active components responsible for the anti-malarial activities of the crude drug Qing Hao and this has resulted in the discovery of the active compound, Qinghaosu, which means "a principle from Qing Hao" and which was also referred to as arteannuin and artemisinine; today, the accepted western name is artemisinin (since the compound is a terpene, not an alkaloid as the suffixine implies). Artemisinin was first isolated and identified in 1972 as a novel compound with its chemical structure representing a new type of sesquiterpene lactone with an unusual endoperoxide moiety (see chapter 12).

Following intensive investigations into the pharmacology, pharmacokinetics and toxicology of artemisinin and its natural and synthetic derivatives, artemisinin was found to have a rapid schizonticidal action (i.e. it kills the forms of malaria parasites infecting red blood cells), with low toxicity (see chapter 13). Of particular significance was its remarkably potent therapeutic effect against malaria caused by drug-resistant Plasmodium falciparum. In clinical studies with 2099 patients infected with Plasmodium vivax or P. falciparum, artemisinin showed very good therapeutic efficacy in almost all patients without obvious side effects (Anon. 1979). Moreover, artemisinin was also found to be effective in the treatment of chloroquine resistant falciparum malaria and its often fatal complication, cerebral malaria (see chapter 14).

The discovery of a new potent antimalarial from a TCM herb was so significant that it attracted great attention from the World Health Organsation and a number of research establishments around the world. Although artemisinin has been syn-thesised by a few research groups in several countries, the high cost made synthetic artemisinin an uneconomic choice for large-scale production of the drug so that it is extracted from its natural source (see chapter 12). Consequently, many taxonomy-orientated scientists started screening dozens of other Artemisia species in an attempt to find new source plant for artemisinin but Artemisia annua remains the only species that is known to produce artemisinin.

Several hundred years ahead of modern medicine, practitioners of TCM recorded the presence of a biological clock in human body, the diagnosis of diabetes, the function of hormones, described the circulation of the blood and the application of inoculation (Temple 1986). The discovery of artemisinin from a TCM herb is an excellent example of the contribution that TCM may make to modern medical science.

Traditional Chinese Medicine

Traditional Chinese Medicine

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