Artemisinin and sesquiterpene precursors in dead and green leaves of Artemisia annua L. crops

This paper analyses the accumulation and concentrations of the antimalarial artemisinin in green and dead leaves of Artemisia annua crops in two field experiments. Concentration differences were analysed as being determined by (a) the total production of artemisinin plus its upstream precursors dihydroartemisinic acid, dihydroartemisinic aldehyde, artemisinic aldehyde and artemisinic alcohol and (b) the conversion of precursors towards artemisinin. Concentrations of the total of artemisinin plus its precursors were higher in green leaves than in dead leaves in the younger crop stages, but were comparable at the final harvests. In every crop stage, the conversion of precursors to artemisinin was more advanced in dead leaves than in green leaves. This resulted in the molar concentrations of artemisinin being higher in dead leaves than in green leaves at the final harvests. The molar quantity of dihydroartemisinic acid, the last enzymatically produced precursor, was higher than that of artemisinin in green leaves, but only 19 - 27% of that of artemisinin in dead leaves. Dead leaves were very important for the final artemisinin yield. They constituted on average 34% of the total leaf dry matter and 47% of the total artemisinin yield at the final harvests. The possibility to convert a larger part of dihydroartemisinic acid into artemisinin during post-harvest handling is discussed.     

Seasonal variation of artemisinin and its biosynthetic precursors in plants of Artemisia annua of different geographical origin: proof for the existence of chemotypes

The time course of the levels of artemisinin, its biosynthetic precursors and the biosynthetically related sesquiterpenes was monitored during a vegetation period of Artemisia annua plants of different geographical origin. Considerable differences in contents of artemisinin and its direct precursors artemisinic acid and dihydroartemisinic acid were found between these A. annua's. For the first time the A. annua plants of different geographical origin were found to belong to different chemotypes. A chemotype with a high artemisinin level was found to have also a high dihydroartemisinic acid level but a relatively low artemisinic acid level. Reversibly, a chemotype with low levels of artemisinin and dihydroartemisinic acid contained a high artemisinic acid level. Artemisinic acid is considered to be the direct precursor of dihydroartemisinic acid in the biosynthetic pathway of artemisinin. The observed accumulation of artemisinic acid in one of the A. annua chemotypes may indicate the presence of a rate-limiting step in the biosynthetic pathway of artemisinin. The enzymatic reduction of artemisinic acid into dihydroartemisinic acid is probably a "bottle neck" in the biosynthetic pathway of artemisinin in varieties with high artemisinic acid and consequentially low artemisinin levels. After a night-frost period, the level of artemisinin was increased, in the Vietnamese A. annua plants, while the dihydroartemisinic acid level was decreased. This phenomenon is in accordance with our hypothesis that stress triggers the conversion of dihydroartemisinic acid to artemisinin. It is suggested that the presence of high levels of dihydroartemisinic acid may be an adaptation to stress conditions (e.g., night-frost), during which relatively high levels of 1O2 are formed. Dihydroartemisinic acid gives the plant protection by reacting with these reactive oxygen species yielding artemisinin as stable end-product.     

HMG-CoA还原酶和FPP合酶基因拷贝数对紫穗槐-4,11-二烯酵母工程菌产量的影响

从青蒿中克隆了紫穗槐-4,11-二烯合酶基因(ADS)，从酿酒酵母中克隆了HMG-CoA还原酶(HMGR)催化结构域和FPP合酶(FPPS)基因。构建含ADS基因的酿酒酵母表达载体pYeDP60/G/AS，将其转入酿酒酵母，获得能产生紫穗槐-4,11-二烯的酵母工程菌，以朱栾倍半萜为参照，产量为10 μg·L^-1。另外构建了含HMGR和FPPS基因的酵母表达载体pGBT9/A/HMG/G/FPP，将该载体和pYeDP60/G/AS共转入酿酒酵母，得到第二个能产生紫穗槐-4,11-二烯的酵母工程菌，产量为23.6 mg·L^-1，结果表明增加HMG-CoA还原酶和FPP合酶基因的拷贝数能显著增加酵母工程菌的紫穗槐-4,11-二烯产量。     

Trichome dynamics and artemisinin accumulation during development and senescence of Artemisia annua leaves

Artemisinin is a sesquiterpene lactone endoperoxide and an important antimalarial drug produced in Artemisia annua. To unravel the diverse processes determining artemisinin yield in A. annua crops, artemisinin accumulation during the development of individual leaves was studied in two field experiments. During the life cycle of a leaf, artemisinin was always present. Quantities were low at leaf appearance and increased steadily. In leaves studied until after senescence, maximum quantities and concentrations were achieved after the leaf had turned brown. The total quantity of possible artemisinin precursors per leaf (dihydroartemisinic acid and other upstream precursors) was highest early in the leaf cycle when the leaf was still expanding. Dihydroartemisinic acid was more abundant than the other compounds and its quantity declined during leaf development whereas that of artemisinin increased. Dihydroartemisinic acid was not converted directly into artemisinin, because on a per leaf basis the decline in molar quantity of precursors in the earliest formed leaves was not compensated for by a simultaneous increase in artemisinin. Our results suggest that a (putative) intermediate such as dihydroartemisinic acid hydroperoxide temporarily may have accumulated in considerable quantities. The number of mature, capitate trichomes on the adaxial leaf side increased after leaf appearance until the end of leaf expansion, and then decreased, probably due to collapse of trichomes. Artemisinin production thus (also) occurred when trichomes were collapsing. Later formed leaves achieved higher concentrations of artemisinin than earlier formed leaves, because of a higher trichome density and a higher capacity per trichome.     

青蒿素生物合成的研究进展

青蒿素是上世纪70年代初中国科学家从药用植物黄花蒿(Artemisia annua L.)中分离得到的、含有过氧基团的新型倍半萜内酯抗疟药物。笔者综述了近年来青蒿素生物合成机理的研究进展,从青蒿素的前体如青蒿乙素和青蒿酸到青蒿素的合成,讨论了青蒿素生物合成的基本途径;从参与青蒿素合成的关键酶组成和功能,探讨了合成路线的主要构成,并介绍了青蒿素合成代谢调控的基因工程手段,为青蒿素的生物技术开发提供参考。     

Isolation of a high artemisinic acid containing plant of Artemisia annua

A plant of Artemisia annua containing high amounts of artemisinic acid (0.8%) was isolated. the combined concentration of the sesquiterpene artemisinin, and its intermediates artemisinic acid and artemisinin-b in this plant was 1.35%. the plant has been cloned by micropropagation in tissue culture.     

The presence of amorpha-4, 11-diene synthase, a key enzyme in artemisinin production in ten Artemisia species

BACKGROUND AND THE PURPOSE OF THE STUDY: Artemisinin is one of the most effective medicine against malaria, which is produced naturally by Artemisia annua in low yield. It is produced in a metabolic pathway, in which several genes and gene products are involved. One of the key genes in this pathway is am1, which encodes amorpha-4, 11-diene synthase (ADS), a key enzyme in artemisinin biosynthesis pathway. The aim of this study was to determine the presence of this gene in ten Artemisia species in order to increase the yield of production of Artemisinin. METHODS: The experiments were carried out using PCR. Specific primers were designed based on the published am1 gene sequence obtained from A. annua (NCBI, accession number AF327527). RESULTS: The amplification of this gene by the specific primers was considered as a positive sign for the potentiality of artemisinin production. Since the entire am1 gene was not amplified in any of the 10 species used, four parts of the gene, essential in ADS enzyme function, corresponding to a) pair site of Arg10-Pro12 in the first 100 amino acids, b) aspartate rich motif (DDXXD), c) active site final lid and d) active site including farnesyl diphosphate (FDP) ionization sites and catalytic site in the ADS enzyme, were investigated. MAJOR CONCLUSION: The sequence corresponding to ADS active site was amplified only in A. annua, A. aucheri and A. chamaemelifolia. The negative results obtained with other species could be due to some sequence alteration, such as point mutations or INDELs. We propose A. aucheri and A. chamaemelifolia as two potential candidate species for further characterization, breeding and transferring am1 gene for artemisinin overproduction.     

不同产地的青蒿药用成分含量研究

目的：研究不同产地的青蒿药用成分的含量。方法：从全国各地采集22批青蒿药材,通过高效液相色谱法测定药材中的青蒿酸、青蒿乙素、青蒿素和东莨菪内酯的含量,并以所测含量为指标,进行相关分析和聚类分析。结果：相关分析和聚类分析均显示,不同产地的青蒿中上述4种成分含量差异较大,各自聚为一类。结论：青蒿活性成分的积累与产地有一定的相关性。     

抗疟植物黄花蒿中青蒿酸的绝对构型研究

从中国东北部产黄花蒿中分离得到主成分青蒿酸（１）．通过分析青蒿酸对溴苯酰甲酯的Ｘ－衍射结晶学数据，确定了青蒿酸的绝对构型．另外，从同植物中还分离得到少量青蒿素（２），以及青蒿乙素（３），谷甾醇和豆甾醇．     

Production of Artemisinin and Related Sesquiterpenes in Japanese Artemisia annua During a Vegetation Period

Seeds of ARTEMISIA ANNUA L. originating from a wild population in Japan were cultivated in the garden planters of our Institute in 1995, and the seasonal and positional variations in content of artemisinin, artemisinic acid, arteannuin B and artemisitene, were measured. The content of artemisinic acid in leaves was high [max. 1.0% (dry wt basis)], as compared with other cultivars previously reported. This is the first report on a Japanese strain of ARTEMISIA ANNUA.     

青蒿素生物合成研究进展

青蒿素是目前治疗疟疾的特效药。该文通过对青蒿植物组织培养、青蒿素生物合成中生理生态因子的影响、青蒿素生物合成场所研究、青蒿素生物合成路线、青蒿素生物合成酶及基因调控等进行介绍，综述青蒿素生物合成的最新研究进展，并对其研究方向进行了展望。     

Artemisinin, Related Sesquiterpenes, and Essential Oil in Artemisia annua During a Vegetation Period in Vietnam

The active principle of ARTEMISIA ANNUA L., artemisinin, is currently being developed to a registered antimalarial drug. For production purposes, plants with a high artemisinin content are required. We followed the development of the artemisinin content and of the biosynthetically related sesquiterpenes artemisinic acid, arteannuin B, and artemisitene in A. ANNUA plants, during a vegetation period in Vietnam, where this species is indigenous. In addition, the essential oil content and composition were studied. Samples of leaves, buds, flowers, or post-bloom flowers and fruits were taken at different stages: vegetative (5, 6, and 8 months old), at mass formation of buds (9 months), at full bloom (10 months), and post-bloom (10S months). The highest artemisinin content (0.86% dry wt) was present in the leaves of 5 months-old plants. At this stage also the highest leaf yield was found. Subsequently, the artemisinin content gradually dropped. At the age of 5 months the highest artemisinic acid and arteannuin B contents, 0.16 and 0.08% dry wt, respectively, were found as well. Artemisitene was present at all stages of development, ranging from 0.002 to 0.09% dry wt. With 1.9% v/w, the essential oil content was maximal just before flowering and was composed of 55% monoterpenes and 45% sesquiterpenes. At all other stages (0.4 - 1.0% v/w oil) this ratio was ca. 30%/70%. The main components of the oil were camphor and germacrene-D.     

HPLC-UV-ELSD法同时测定青蒿中青蒿素、青蒿乙素和青蒿酸的含量

用HPLC-UV-ELSD法同时测定青蒿药材中青蒿素、青蒿乙素和青蒿酸的含量。采用Nucleodur C₁₈色谱柱(250 mm×4.6 mm，5 μm ID)；以乙腈-0.1%乙酸水(50∶50)为流动相；紫外检测波长209 nm,蒸发光散射检测器漂移管温度50 ℃。结果显示，青蒿素、青蒿乙素和青蒿酸能够达到很好分离。它们的线性范围分别为0.52～2.6 μg， r=0.999 4(n=5)； 0.022～4.4 μg， r=0.999 9(n=5)； 0.203～8.12 μg，r=0.999 8(n=5)。平均回收率分别为99.45%(RSD=2.3%， n=6)；102.37%(RSD=1.7%， n=6)；101.10%(RSD=0.79%， n=6)。本法简单、准确、快速，可同时测定青蒿药材中青蒿素、青蒿乙素和青蒿酸的含量。     

Seasonal variations of Artemisinin and its biosynthetic precursors in tetraploid Artemisia annua plants compared with the diploid wild-type

Using colchicine we induced tetraploidy in Artemisia annua L. plants. During a vegetation period we monitored the time course of the levels of artemisinin, its direct precursors, the biosynthetically related sesquiterpenes and the essential oil content in the diploid (wild-type) and tetraploid A. annua plants. The averaged artemisinin level in tetraploids was 38% higher than that of the wild-type as measured over the whole vegetation period. In contrast, the averaged essential oil content of the tetraploids over this period was 32% lower. This might suggest a reciprocal correlation between artemisinin (sesquiterpenes) and the essential oil content (monoterpenes). The averaged biomass of the leaves of the tetraploid plants was lower compared to the wild-type plants. Therefore, the artemisinin yield per m2 tetraploids was decreased by 25%. Although the tetraploid plants were smaller than the wild-type plants, certain individual organs like the leaves were considerably larger, and seeds obtained by cross pollination between tetraploid A. annua plants had a spectacular size. In principle, tetraploid A. annua can be a useful starting material for a breeding program in order to obtain larger and faster growing plants, which produce higher levels of artemisinin.     

Review of the use of artemisinin and its derivatives in the treatment of malaria

This article reviews the development of the artemisinins used in the treatment of drug-resistant Plasmodium falciparum malaria. The story starts in China with Artemisia annua L., a plant that was traditionally used as an antipyretic. The activity of Annual wormwood can be explained by the presence of the active substance artemisinin. Soon, artemether, artemotil, artenimol, artesunate and sodium artesunate, derivatives of artemisinin, have been developed. Each has its own physical and pharmaceutical properties, dosage and dosage forms. Other aspects, such as the general guidelines for use, safety during pregnancy and the perspectives of artemisinin compounds, are being discussed.     

黄花蒿发根的液体培养及青蒿素合成的动态特征研究

目的:探讨黄花蒿发根生长及青蒿素生物合成的动态特征,建立高效、稳定的黄花蒿发根液体培养体系。方法:测定不同培养基以及MS培养基中不同营养元素对黄花蒿发根生物量和青蒿素含量的影响。结果:筛选出优化的黄花蒿发根液体培养基,获得拟合的黄花蒿发根生长和青蒿素合成的Logistic方程。结论:在优化的MS培养基中黄花蒿发根生长迅速且能稳定合成青蒿素,为工业化大规模生产青蒿素提供了可能。     

Searching for artemisinin production improvement in plants and microorganisms

The endoperoxide sesquiterpene lactone artemisinin which is isolated from the plant Artemisia annua, and its semi-synthetic derivatives, are potent, novel, antimalarial drugs. They are effective against multidrug-resistant Plasmodium strains and have become essential components of the so-called Artemisinin-based Combination Therapy, that is recommended by the World Health Organization as the treatment of choice for malaria tropica. Moreover, artemisinin and its derivatives show additional anti-parasite, antitumor, and anti-viral properties. The plants, however, are very poor resources for the drug, as the content of artemisinin is low (from 0,1 to 1,5 % of dried leaves) and dependent on seasonal and somatic variations as well as the infestation of bacteria, fungi and insects. A chemical synthesis of the compound is complex and uneconomic. Therefore, artemisinin is in short supply and remains unaffordable for most people in malaria-endemic countries. Thus, many researchers have focused on enhancing the production of artemisinin, first, through traditional breeding and in in vitro plant tissue cultures and, then, by heterologous expression systems (a semi-synthetic approach) with the use of genetically-modified or transgenic microbes. In this review, we summarize the progress made in the production of artemisinin by the biotechnological approach.