Identification of intermediates and enzymes involved in the early steps of artemisinin biosynthesis in Artemisia annua

An important group of antimalarial drugs consists of the endoperoxide sesquiterpene lactone artemisinin and its derivatives. Only little is known about the biosynthesis of artemisinin in Artemisia annua L., particularly about the early enzymatic steps between amorpha-4,11-diene and dihydroartemisinic acid. Analyses of the terpenoids from A. annua leaves and gland secretory cells revealed the presence of the oxygenated amorpha-4,11-diene derivatives artemisinic alcohol, dihydroartemisinic alcohol, artemisinic aldehyde, dihydroartemisinic aldehyde and dihydroartemisinic acid. We also demonstrated the presence of a number of biosynthetic enzymes such as the amorpha-4,11-diene synthase and the--so far unknown--amorpha-4,11-diene hydroxylase as well as artemisinic alcohol and dihydroartemisinic aldehyde dehydrogenase activities in both leaves and glandular trichomes. From these results, we hypothesise that the early steps in artemisinin biosynthesis involve amorpha-4,11-diene hydroxylation to artemisinic alcohol, followed by oxidation to artemisinic aldehyde, reduction of the C11-C13 double bond to dihydroartemisinic aldehyde and oxidation to dihydroartemisinic acid.     

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.     

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.     

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.     

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.     

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。     

Artemisinin,a novel antimalarial drug: biochemical and molecular approaches for enhanced production

Artemisinin, a sesquiterpene lactone containing an endoperoxide bridge, has been isolated from the aerial parts of Artemisia annua L. plants. It is effective against both drug-resistant and cerebral malaria-causing strains of Plasmodium falciparum. The relatively low yield (0.01-0.8 %) of artemisinin in A. annua is a serious limitation to the commercialization of the drug. Therefore, the enhanced production of artemisinin either in cell/tissue culture or in the whole plant of A. annua is highly desirable. It can be achieved by a better understanding of the biochemical pathway leading to the synthesis of artemisinin and its regulation by both exogenous and endogenous factors. Furthermore, genetic engineering tools can be employed to overexpress gene(s) coding for enzyme(s) associated with the rate limiting step(s) of artemisinin biosynthesis or to inhibit the enzyme(s) of other pathway competing for its precursors. These aspects which may be employed to enhance the yield of artemisinin both in vitro and in vivo are discussed in this review.     

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。     

HPLC-UV-ELSD联用测定黄花蒿叶片中青蒿素及相关倍半萜的含量

目的HPLC-UV-ELSD联用建立黄花蒿叶片中青蒿素及其生合成相关倍半萜的含量测定方法。方法采用Venusil XBP-C18色谱柱(200 mm×4.6 mm,5μm),流动相:乙腈-水梯度洗脱,检测波长:203 nm,流速:1.0 mL.min-1,ELSD载气压力:0.35 MPa,喷嘴温度:35℃,漂移管温度:60℃,检测器:UV-ELSD联用,测定黄花蒿叶片中青蒿素、青蒿素B、3α-羟基-1-去氧青蒿素含量。同一色谱柱条件下流动相改为乙腈-水-甲酸(体积比为60.00∶40.00∶0.08),检测波长:215 nm,流速:1.0 mL.min-1,检测器:UV检测器,测定黄花蒿叶片中青蒿酸含量。结果4种倍半萜在各自的线性范围内线性关系良好(r≥0.9990),RSD<3%,平均加样回收率分别为98.5%(RSD=2.3%)、96.5%(RSD=1.8%)、97.5%(RSD=3.6%)、95.4%(RSD=2.5%)。结论该方法可作为黄花蒿中青蒿素及其生合成相关倍半萜的含量测定方法。     

Effect of plant density on the yields of artemisinin and essential oil in Artemisia annua cropped under low input cost management in North-Central India

A field experiment was conducted on Artemisia annua L. during the winter-summer season of 1995-96 at Lucknow, located at 26.5 degrees N, 80.5 degrees E and 120 m above mean sea level, representing a semiarid-subtropical climate with hot summer and fairly cool winters to study the effect of varying plant densities on the yields of essential oil and artemisinin under the conditions of no interculture and fertilizer applications. Results showed that A. annua at the population density of 2.22 x 10(5) plants ha(-1) yielded 7.4 kg of artemisinin and 91 kg of essential oil. It was also observed that at the same oil yield level, the yield of artemisinin increased by 1.5-, 2-, and 2.5-fold when the plant densities increased by about 2-, 4-, and 8-fold. Correspondingly, the suppression of weeds occurred by about 33, 133, and 333%, respectively. The plant architecture and canopy structure produced in high density A. annua plots presumably favoured the synthesis and accumulation of artemisinin resulting in artemisinin-rich, mature plants. It is recommended that, under subtropical agroclimatic conditions of north Indian plains, the A. annua should be cultivated at very high plant densities such as 2.22 x 10(5) plants ha(-1) forgetting high artemisinin yields.     

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.     

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．     

The genetics of artemisinin content in Artemisia annua L. and the breeding of high yielding cultivars.

Artemisinin, the endoperoxide sesquiterpene lactone produced by the Chinese medicinal herb Artemisia annua, is very difficult to synthesise. Moreover, its production by mean of cell, tissue or organ cultures is very low. Presently, only its extraction from cultivated plants is viable. A large variation in artemisinin content has been observed in the leaves of plants from different origins. The genetic basis of this variation has been assessed and evidence for a quantitative inheritance of the artemisinin concentration presented. Additive genetic components were predominant, resulting in a high narrow-sense heritability estimate. Thus, goods results can be expected from mass selection for the breeding of lines of Artemisia annua rich in artemisinin. Yet, dominance variance is also present in the total genetic variability, indicating that crosses between selected genotypes should generate progenies with particularly high artemisinin content. As a matter of fact, selection and crossing, in wild populations, of genotypes with high artemisinin concentration resulted in hybrid lines containing up to 1.4 % artemisinin (on dry leaves basis).     

An approach to the inheritance of the sesquiterpene chemotypes within Petasites hybridus

Sesquiterpene esters are the active principle in the medicinal plant Petasites hybridus. Two chemotypes, the petasin chemotype and the furanopetasin chemotype, are known, but only the first one is suitable for pharmaceutical purposes. Experimental crossings were performed within and between plants of both chemotypes to study the genetic basis of the occurrence of these sesquiterpenes. The chemotype was determined by TLC in extracts of a small piece of rhizome in the parent plants and the progenies. A model including the combined action of two genes is proposed to explain the inheritance of the chemotypes where the furanopetasin chemotype is under recessive genetic control.     

低温诱导青蒿素生物合成

目的:研究低温处理对青蒿素及其他萜类合成通路的影响。方法:以4℃为胁迫条件,利用高效液相色谱法测定青蒿素含量;硫酸钛沉淀法和N,N-二甲基-对-亚硝基苯胺漂白测定法分别检测黄花蒿叶片过氧化氢(H2O2)和单线态氧(1O2)含量;紫外分光光度法检测过氧化氢酶(CAT)活性;实时荧光定量PCR技术定量分析青蒿素合成途径及竞争途径关键酶基因的表达。结果:4℃处理4h后黄花蒿叶片中1O2和H2O2含量升高,并伴随青蒿素含量和CAT活性逐步提高,4、24和48h后青蒿素含量分别提高20%、65%和80%;4℃处理24h后,青蒿素合成相关基因[3-羟基-3-甲基戊二酰辅酶A还原酶基因(HMGR)、法呢基焦磷酸合酶基因(FPS)、紫穗槐二烯合酶基因(ADS)、细胞色素P450单加氧酶基因(CYP71AV1)、细胞色素P450氧化还原酶基因(CPR)、青蒿醛Δ11(13)双键还原酶基因(DBR2)]的表达普遍上调,其中ADS的表达提高16倍;而青蒿素合成竞争途径的β-石竹烯合酶基因(CS)表达则下调近20倍。结论:低温刺激可能通过产生高浓度活性氧(ROS)促进青蒿素合成前体转化、上调青蒿素合成相关基因表达并抑制竞争途径基因表达等途径促进青蒿素合成。     

Agrobacterium rhizogenes-mediated transformation of Artemisia annua: production of transgenic plants

Transgenic hairy roots were induced in the leaves of Artemisia annua by treatment with the LBA 9402 strain of Agrobacterium rhizogenes. The axenic hairy root cultures were found to produce the sesquiterpenes artemisinic acid and arteannuin B. The hairy root cultures were observed to spontaneously regenerate into plantlets on solid hormone-free MS medium. The regenerated plants had phenotypic characteristics typical to the transformed plants. Among the plants of the age of one month in culture, the transgenic plant was bigger (2.643 g/plant) than the normal (0.856 g/plant). Both these kinds of in vitro plants carried sesquiterpenes-artemisinic acid and arteannuin B.     

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。