Recent advances in artemisinin production through heterologous expression

Developing the E. coli platform for efficient production of UMP-derived chemicals

5-Methyluridine (5-MU) is a prominent intermediate for industrial synthesis of several antiviral-drugs, however, its availability over the past decades has overwhelmingly relied on chemical and enzymatic strategies. Here, we have realized efficient production of 5-MU in E. coli, for the first time, via a designer artificial pathway consisting of a two-enzyme cascade (UMP 5-methylase and phosphatase). More importantly, we have engineered the E. coli cell factory to boost 5-MU production by systematic evaluation of multiple strategies, and as a proof of concept, we have further developed an antibiotic-free fermentation strategy to realize 5-MU production (10.71 g/L) in E. coli MB229 (a ΔthyA strain). Remarkably, we have also established a versatile and robust platform with exploitation of the engineered E. coli for efficient production of diversified UMP-derived chemicals. This study paves the way for future engineering of E. coli as a synthetic biology platform for acceleratively accessing UMP-derived chemical diversities.

Comparison of phytochemical properties and expressional profiling of artemisinin synthesis-related genes in various Artemisia species

The Artemisia genus belongs to the Asteraceae family and is used in the treatment of many different diseases such as hepatitis and cancer. So far, around 500 species of Artemisia have been found in different regions of the world. Artemisinin is one of the medicinal compounds found in Artemisia species. Hence, this medical feature encourages researchers to pay attention to various species of this genus to discover more genetic and phytochemical information. In the present study, five species of Artemisia including A. fragrans, A. annua, A. biennis, A. scoparia, and A. absinthium were compared to each other in terms of the artemisinin content and other phytochemical components. Moreover, the relative expression profiles of eight genes related to the accumulation and synthesis of artemisinin [including 4FPSF, DBR2, HMGR1, HMGR2, WIRKY, ADS, DXS, and SQS] were determined in investigated species. The result of high-performance liquid chromatography (HPLC) analysis showed that the content of artemisinin in various species was in the order of A. fragrans > A. annua > A. biennis > A. scoparia > A. absinthium. Based on the gas chromatography-mass spectrometry (GC-MS) analysis, 34, 26, 26, 24, and 20 phytochemical compounds were identified for A. scoparia, A. biennis, A. fragrans, A. absinthum, and A. annua species, respectively. Moreover, camphor (38.86%), β-thujone (68.42%), spathulenol (48.33%), β-farnesene (48.16%), and camphor (29.04%) were identified as the considerable compounds A. fragrans, A. absinthium, A. scoparia, A. biennis, and A. annua species, respectively. Considering the relative expression of the targeted genes, A. scoparia revealed higher expression for the 4FPSF gene. The highest relative expression of the DBR2, WIRKY, and SQS genes was found in A. absinthium species. Moreover, A. annua showed the highest expression of the ADS and DXS genes than the other species. In conclusion, our findings revealed that various species of Artemisia have interesting breeding potential for further investigation of different aspects such as medicinal properties and molecular studies.

Assessment of Artemisinin Contents in Selected Artemisia Species from Tajikistan (Central Asia)

Background: Central Asia is the center of origin and diversification of the Artemisia genus. The genus Artemisia is known to possess a rich phytochemical diversity. Artemisinin is the shining example of a phytochemical isolated from Artemisia annua, which is widely used in the treatment of malaria. There is great interest in the discovery of alternative sources of artemisinin in other Artemisia species. Methods: The hexane extracts of Artemisia plants were prepared with ultrasound-assisted extraction procedures. Silica gel was used as an adsorbent for the purification of Artemisia annua extract. High-performance liquid chromatography with ultraviolet detection was performed for the quantification of underivatized artemisinin from hexane extracts of plants. Results: Artemisinin was found in seven Artemisia species collected from Tajikistan. Content of artemisinin ranged between 0.07% and 0.45% based on dry mass of Artemisia species samples. Conclusions: The artemisinin contents were observed in seven Artemisia species. A. vachanica was found to be a novel plant source of artemisinin. Purification of A. annua hexane extract using silica gel as adsorbent resulted in enrichment of artemisinin.

Biotechnological approaches for artemisinin production in Artemisia

Abstract

Artemisinin and its analogues are naturally occurring most effective antimalarial secondary metabolites. These compounds also possess activity against various types of cancer cells, schistosomiasis, and some viral diseases. Artemisinin and its derivatives (A&D) are found in very low amounts in the only natural source i.e. Artemisia plant. To meet the global needs, plant sources have been exploited for the enhanced production of these natural products because their chemical synthesis is not profitable. The generally adopted approaches include non-transgenic (tissue and cell cultures) and transgenic together with the cell, tissue, and whole transgenic plant cultures. The genes targeted for the overproduction of A&D include the biosynthetic pathway genes, trichome development genes and rol genes, etc. Artemisinin is naturally produced in trichomes of leaves. At the same time, transgenic hairy roots are considered a good source to harvest artemisinin. However, the absence of trichomes in hairy roots suggests that artemisinin biosynthesis is not limited to trichomes. Moreover, the expression of the gene involved in trichome development and sesquiterpenoid biosynthesis (TFAR1) in transgenic and non-transgenic roots provokes researchers to look for new insight of artemisinin biosynthesis. Here we discuss and review precisely the various biotechnological approaches for the enhanced biosynthesis of A&D.

Graphical Abstract

Synthetic Strategies for Peroxide Ring Construction in Artemisinin

The present review summarizes publications on the artemisinin peroxide fragment synthesis from 1983 to 2016. The data are classified according to the structures of a precursor used in the key peroxidation step of artemisinin peroxide cycle synthesis. The first part of the review comprises the construction of artemisinin peroxide fragment in total syntheses, in which peroxide artemisinin ring resulted from reactions of unsaturated keto derivatives with singlet oxygen or ozone. In the second part, the methods of artemisinin synthesis based on transformations of dihydroartemisinic acid are highlighted.

Use of Model-Based Nutrient Feeding for Improved Production of Artemisinin by Hairy Roots of Artemisia Annua in a Modified Stirred Tank Bioreactor

Artemisinin has been indicated to be a potent drug for the cure of malaria. Batch growth and artemisinin production kinetics of hairy root cultures of Artemisia annua were studied under shake flask conditions which resulted in accumulation of 12.49 g/L biomass and 0.27 mg/g artemisinin. Using the kinetic data, a mathematical model was identified to understand and optimize the system behavior. The developed model was then extrapolated to design nutrient feeding strategies during fed-batch cultivation for enhanced production of artemisinin. In one of the fed-batch cultivation, sucrose (37 g/L) feeding was done at a constant feed rate of 0.1 L/day during 10-15 days, which led to improved artemisinin accumulation of 0.77 mg/g. The second strategy of fed-batch hairy root cultivation involved maintenance of pseudo-steady state sucrose concentration (20.8 g/L) during 10-15 days which resulted in artemisinin accumulation of 0.99 mg/g. Fed-batch cultivation (with the maintenance of pseudo-steady state of substrate) of Artemisia annua hairy roots was, thereafter, implemented in bioreactor cultivation, which featured artemisinin accumulation of 1.0 mg/g artemisinin in 16 days of cultivation. This is the highest reported artemisinin yield by hairy root cultivation in a bioreactor.

Affordable and rapid HPTLC method for the simultaneous analysis of artemisinin and its metabolite artemisinic acid in Artemisia annua L

Artemisinin (AN) and artemisinic acid (AA), valuable phyto-pharmaceutical molecules, are well known anti-malarials, but their activities against diseases like cancer, schistosomiasis, HIV, hepatitis-B and leishmaniasis are also being reported. For the simultaneous estimation of AN and AA in the callus and leaf extracts of A. annua L. plants, we embarked upon a simple, rapid, selective, reliable and fairly economical high performance thin layer chromatography (HPTLC) method. Experimental conditions such as band size, chamber saturation time, migration of solvent front and slit width were critically studied and the optimum conditions were selected. The separations were achieved using toluene-ethyl acetate, 9:1 (v/v) as mobile phase on pre-coated silica gel plates, G 60F254 . Good resolution was achieved with Rf values of 0.35 ± 0.02 and 0.26 ± 0.02 at 536 nm for AN and 626 nm for AA, respectively, in absorption-reflectance mode. The method displayed a linear relationship with r(2) value 0.992 and 0.994 for AN and AA, respectively, in the concentration range of 300-1500 ng for AN and 200-1000 ng for AA. The method was validated for specificity by obtaining in-situ UV overlay spectra and sensitivity by estimating limit of detection (30 ng for AN and 15 ng for AA) and limit of quantitation (80 ng for AN and 45 ng for AA) values. The accuracy was checked by the recovery studies conducted at three different levels with the known concentrations and the average percentage recovery was 101.99% for AN and 103.84% for AA. The precision was analyzed by interday and intraday precision and was 1.09 and 1.00% RSD for AN and 1.22 and 6.05% RSD for AA. The analysis of statistical data substantiates that this HPTLC method can be used for the simultaneous estimation of AN and AA in biological samples.

Peltate glandular trichomes of Colquhounia seguinii harbor new defensive clerodane diterpenoids

Glandular trichomes produce a wide variety of secondary metabolites that are considered as major defensive chemicals against herbivore attack. The morphology and secondary metabolites of the peltate glandular trichomes of a lianoid Labiatae, Colquhounia seguinii Vaniot, were investigated. Three new clerodane diterpenoids, seguiniilactones A-C (1-3), were identified through precise trichome collection with laser microdissection, metabolic analysis with ultra performance liquid chromatography-tandem mass spectrometer, target compound isolation with classical phytochemical techniques, structure elucidation with spectroscopic methods. All compounds showed significant antifeedant activity against a generalist plant-feeding insect Spodoptera exigua. Seguiniilactone A (1) was approximately 17-fold more potent than the commercial neem oil. α-Substituted α,β-unsaturated γ-lactone functionality was found to be crucial for strong antifeedant activity of this class of compounds. Quantitative results indicated that the levels of these compounds in the peltate glandular trichomes and leaves were sufficiently high to deter the feeding by generalist insects. Moderate antifungal activity was observed for seguiniilactone C (3) against six predominant fungal species isolated from the diseased leaves of C. seguinii, while seguiniilactones A and B were generally inactive. These findings suggested that seguiniilactones A-C might be specialized secondary metabolites in peltate glandular trichomes for the plant defense against insect herbivores and pathogens.

An enzymatic platform for the synthesis of isoprenoid precursors

The isoprenoid family of compounds is estimated to contain ∼65,000 unique structures including medicines, fragrances, and biofuels. Due to their structural complexity, many isoprenoids can only be obtained by extraction from natural sources, an inherently risky and costly process. Consequently, the biotechnology industry is attempting to genetically engineer microorganisms that can produce isoprenoid-based drugs and fuels on a commercial scale. Isoprenoid backbones are constructed from two, five-carbon building blocks, isopentenyl 5-pyrophosphate and dimethylallyl 5-pyrophosphate, which are end-products of either the mevalonate or non-mevalonate pathways. By linking the HMG-CoA reductase pathway (which produces mevalonate) to the mevalonate pathway, these building block can be synthesized enzymatically from acetate, ATP, NAD(P)H and CoA. Here, the enzymes in these pathways are used to produce pathway intermediates and end-products in single-pot reactions and in remarkably high yield, ∼85%. A strategy for the regio-specific incorporation of isotopes into isoprenoid backbones is developed and used to synthesize a series of isotopomers of diphosphomevalonate, the immediate end-product of the mevalonate pathway. The enzymatic system is shown to be robust and capable of producing quantities of product in aqueous solutions that meet or exceed the highest levels achieved using genetically engineered organisms in high-density fermentation.

Overexpression of membrane proteins from higher eukaryotes in yeasts

Heterologous expression and characterisation of the membrane proteins of higher eukaryotes is of paramount interest in fundamental and applied research. Due to the rather simple and well-established methods for their genetic modification and cultivation, yeast cells are attractive host systems for recombinant protein production. This review provides an overview on the remarkable progress, and discusses pitfalls, in applying various yeast host strains for high-level expression of eukaryotic membrane proteins. In contrast to the cell lines of higher eukaryotes, yeasts permit efficient library screening methods. Modified yeasts are used as high-throughput screening tools for heterologous membrane protein functions or as benchmark for analysing drug-target relationships, e.g., by using yeasts as sensors. Furthermore, yeasts are powerful hosts for revealing interactions stabilising and/or activating membrane proteins. We also discuss the stress responses of yeasts upon heterologous expression of membrane proteins. Through co-expression of chaperones and/or optimising yeast cultivation and expression strategies, yield-optimised hosts have been created for membrane protein crystallography or efficient whole-cell production of fine chemicals.

Effects of overexpression of AaWRKY1 on artemisinin biosynthesis in transgenic Artemisia annua plants

The effective anti-malarial medicine artemisinin is costly because of the low content in Artemisia annua. Genetic engineering of A. annua is one of the most promising approaches to improve the yield of artemisinin. In this work, the transcription factor AaWRKY1, which is thought to be involved in the regulation of artemisinin biosynthesis, was cloned from A. annua var. Chongqing and overexpressed using the CaMV35S promoter or the trichome-specific CYP71AV1 promoter in stably transformed A. annua plants. The transcript level of AaWRKY1 was increased more than one hundred times under the CaMV35S promoter and about 40 times under the CYP71AV1 promoter. The overexpressed AaWRKY1 activated the transcription of CYP71AV1 and moreover the trichome-specific overexpression of AaWRKY1 improved the transcription of CYP71AV1 much more effectively than the constitutive overexpression of AaWRKY1, i.e. up to 33 times as compared to the wild-type plant. However the transcription levels of FDS, ADS, and DBR2 did not change significantly in transgenic plants. The significantly up-regulated CYP71AV1 promoted artemisinin biosynthesis, i.e. up to about 1.8 times as compared to the wild-type plant. It is demonstrated that trichome-specific overexpression of AaWRKY1 can significantly activate the transcription of CYP71AV1 and the up-regulated CYP71AV1 promotes artemisinin biosynthesis.

Transgenic approach to increase artemisinin content in Artemisia annua L

Artemisinin, the endoperoxide sesquiterpene lactone, is an effective antimalarial drug isolated from the Chinese medicinal plant Artemisia annua L. Due to its effectiveness against multi-drug-resistant cerebral malaria, it becomes the essential components of the artemisinin-based combination therapies which are recommended by the World Health Organization as the preferred choice for malaria tropica treatments. To date, plant A. annua is still the main commercial source of artemisinin. Although semi-synthesis of artemisinin via artemisinic acid in yeast is feasible at present, another promising approach to reduce the price of artemisinin is using plant metabolic engineering to obtain a higher content of artemisinin in transgenic plants. In the past years, an Agrobacterium-mediated transformation system of A. annua has been established by which a number of genes related to artemisinin biosynthesis have been successfully transferred into A. annua plants. In this review, the progress on increasing artemisinin content in A. annua by transgenic approach and its future prospect are summarized and discussed.

Potential ecological roles of artemisinin produced by Artemisia annua L

Artemisia annua L. (annual wormwood, Asteraceae) and its secondary metabolite artemisinin, a unique sesquiterpene lactone with an endoperoxide bridge, has gained much attention due to its antimalarial properties. Artemisinin has a complex structure that requires a significant amount of energy for the plant to synthesize. So, what are the benefits to A. annua of producing this unique compound, and what is the ecological role of artemisinin? This review addresses these questions, discussing evidence of the potential utility of artemisinin in protecting the plant from insects and other herbivores, as well as pathogens and competing plant species. Abiotic factors affecting the artemisinin production, as well as mechanisms of artemisinin release to the surroundings also are discussed, and new data are provided on the toxicity of artemisinin towards soil and aquatic organisms. The antifungal and antibacterial effects reported are not very pronounced. Several studies have reported that extracts of A. annua have insecticidal effects, though few studies have proven that artemisinin could be the single compound responsible for the observed effects. However, the pathogen(s) or insect(s) that may have provided the selection pressure for the evolution of artemisinin synthesis may not have been represented in the research thus far conducted. The relatively high level of phytotoxicity of artemisinin in soil indicates that plant/plant allelopathy could be a beneficial function of artemisinin to the producing plant. The release routes of artemisinin (movement from roots and wash off from leaf surfaces) from A. annua to the soil support the rationale for allelopathy.

Bioengineering of plant (tri)terpenoids: from metabolic engineering of plants to synthetic biology in vivo and in vitro

Terpenoids constitute a large and diverse class of natural products that serve many functions in nature. Most of the tens of thousands of the discovered terpenoids are synthesized by plants, where they function as primary metabolites involved in growth and development, or as secondary metabolites that optimize the interaction between the plant and its environment. Several plant terpenoids are economically important molecules that serve many applications as pharmaceuticals, pesticides, etc. Major challenges for the commercialization of plant-derived terpenoids include their low production levels in planta and the continuous demand of industry for novel molecules with new or superior biological activities. Here, we highlight several synthetic biology methods to enhance and diversify the production of plant terpenoids, with a foresight towards triterpenoid engineering, the least engineered class of bioactive terpenoids. Increased or cheaper production of valuable triterpenoids may be obtained by 'classic' metabolic engineering of plants or by heterologous production of the compounds in other plants or microbes. Novel triterpenoid structures can be generated through combinatorial biosynthesis or directed enzyme evolution approaches. In its ultimate form, synthetic biology may lead to the production of large amounts of plant triterpenoids in in vitro systems or custom-designed artificial biological systems.

Plant community characteristics and their responses to environmental factors in the water level fluctuation zone of the three gorges reservoir in China

The annual water level regulating of the Three Gorges Reservoir prolonged the submerged duration (from 2 to 8 months) and resulted in the reversal of natural flood rhythms (winter submerged). These changes might alter plant community characteristics in the water level fluctuation zone (WLFZ). The aim of this study was to determine the plant community characteristics in the WLFZ and their responses to the environmental factors (i.e., annual hydrological regulation, topographic characteristics, soil physical properties and soil nutrients). The height, coverage, frequency and biomass of each plant species and the soil properties at each elevation zone (150, 155, 160, 165 and 170 m) were measured from March to September in 2010. Univariate two-factor analysis and redundancy analysis (RDA) were used to analyze the spatial and temporal variations of the community characteristics and identify the key environmental factors influencing vegetation. We found that 93.2 % of the species analysed were terrestrial vascular plants. Annual herbs made up the highest percentage of life forms at each altitude. The differences in the species number per square metre, the Shannon-Wiener diversity index and the biomass of vegetation demonstrated statistical significance with respect to sampling time but not elevation. The most dominant species at altitudes of 150, 155, 160, 165 and 170 m were Cynodon dactylon, Cyperus rotundus, Digitaria sanguinalis, Setaria viridis and Daucus carota, respectively. The concentrations of soil nutrients appeared to be the lowest at an altitude of 150 m, although the differences with respect to elevation were not significant. The results of the RDA indicated that the key factors that influenced the species composition of vegetation were elevation, slope, pH and the concentration of soil available phosphorus.

Dried whole plant Artemisia annua as an antimalarial therapy

Drugs are primary weapons for reducing malaria in human populations. However emergence of resistant parasites has repeatedly curtailed the lifespan of each drug that is developed and deployed. Currently the most effective anti-malarial is artemisinin, which is extracted from the leaves of Artemisia annua. Due to poor pharmacokinetic properties and prudent efforts to curtail resistance to monotherapies, artemisinin is prescribed only in combination with other anti-malarials composing an Artemisinin Combination Therapy (ACT). Low yield in the plant, and the added cost of secondary anti-malarials in the ACT, make artemisinin costly for the developing world. As an alternative, we compared the efficacy of oral delivery of the dried leaves of whole plant (WP) A. annua to a comparable dose of pure artemisinin in a rodent malaria model (Plasmodium chabaudi). We found that a single dose of WP (containing 24 mg/kg artemisinin) reduces parasitemia more effectively than a comparable dose of purified drug. This increased efficacy may result from a documented 40-fold increase in the bioavailability of artemisinin in the blood of mice fed the whole plant, in comparison to those administered synthetic drug. Synergistic benefits may derive from the presence of other anti-malarial compounds in A. annua. If shown to be clinically efficacious, well-tolerated, and compatible with the public health imperative of forestalling evolution of drug resistance, inexpensive, locally grown and processed A. annua might prove to be an effective addition to the global effort to reduce malaria morbidity and mortality.

An internal deletion in MTH1 enables growth on glucose of pyruvate-decarboxylase negative, non-fermentative Saccharomyces cerevisiae

Background

Pyruvate-decarboxylase negative (Pdc^-) strains of Saccharomyces cerevisiae combine the robustness and high glycolytic capacity of this yeast with the absence of alcoholic fermentation. This makes Pdc^-S. cerevisiae an interesting platform for efficient conversion of glucose towards pyruvate-derived products without formation of ethanol as a by-product. However, Pdc^- strains cannot grow on high glucose concentrations and require C₂-compounds (ethanol or acetate) for growth under conditions with low glucose concentrations, which hitherto has limited application in industry.

Results

Genetic analysis of a Pdc^- strain previously evolved to overcome these deficiencies revealed a 225bp in-frame internal deletion in MTH1, encoding a transcriptional regulator involved in glucose sensing. This internal deletion contains a phosphorylation site required for degradation, thereby hypothetically resulting in increased stability of the protein. Reverse engineering of this alternative MTH1 allele into a non-evolved Pdc^- strain enabled growth on 20 g l^-1 glucose and 0.3% (v/v) ethanol at a maximum specific growth rate (0.24 h^-1) similar to that of the evolved Pdc^- strain (0.23 h^-1). Furthermore, the reverse engineered Pdc^- strain grew on glucose as sole carbon source, albeit at a lower specific growth rate (0.10 h^-1) than the evolved strain (0.20 h^-1). The observation that overexpression of the wild-type MTH1 allele also restored growth of Pdc^-S. cerevisiae on glucose is consistent with the hypothesis that the internal deletion results in decreased degradation of Mth1. Reduced degradation of Mth1 has been shown to result in deregulation of hexose transport. In Pdc^- strains, reduced glucose uptake may prevent intracellular accumulation of pyruvate and/or redox problems, while release of glucose repression due to the MTH1 internal deletion may contribute to alleviation of the C₂-compound auxotrophy.

Conclusions

In this study we have discovered and characterised a mutation in MTH1 enabling Pdc^- strains to grow on glucose as the sole carbon source. This successful example of reverse engineering not only increases the understanding of the glucose tolerance of evolved Pdc^-S. cerevisiae, but also allows introduction of this portable genetic element into various industrial yeast strains, thereby simplifying metabolic engineering strategies.

Antimalarial Effects of Iranian Flora Artemisia sieberi on Plasmodium berghei In Vivo in Mice and Phytochemistry Analysis of Its Herbal Extracts

The aim of this study is pharmacochemistry of Iranian flora Artemisia sieberi and its antimalarial effects on Plasmodium berghei in vivo. This is the first application of A. sieberi for treatment of murine malaria. A. sieberi were collected at flowering stage from the Khorassan and Semnan provinces of Iran; the aerial parts were air-dried at room temperature and then powdered. The powder was macerated in methanol, filtered with Bokhner hopper and solvent was separated in rotary evaporator. Total herbal extract was subsequently processed for ether and chloroform extracts preparation. The toxicity of herbal extract was assessed on naive NMRI mice with high, average and low doses; then pathophysiological signs were assessed. Finally, the antimalarial efficacy was investigated on two groups of Plasmodium berghei infected mice. Percentage of parasitaemia and pathophysiology were also evaluated. The results of this assessment showed no toxicity even by high concentration of herbal extract. A significant reduction in percentage of parasitaemia was observed; no alterations of hepatosplenomegaly and body weight were indicated in study group. A. sieberi extracts showed antimalarial effects against murine malaria with some efficacies on reducing pathophysiology. However, there is requirement to find the major component of this herbal extract by further studies.

Monitoring of artemisinin, dihydroartemisinin, and artemether in environmental matrices using high-performance liquid chromatography-tandem mass spectrometry (LC-MS/MS)

The area cultivated with Artemisia annua for the extraction of the antimalarial compound artemisinin is increasing, but the environmental impact of this cultivation has not yet been studied. A sensitive and robust method using liquid chromatography-tandem mass spectrometry (LC-MS/MS) was developed for the determination of artemisinin in soil. Dihydroartemisinin and artemether were included in the method, and performance on analytical columns of both traditional C(18) phenyl-hexyl and porous shell particles-based Kinetex types was characterized. The versatility of the method was demonstrated on surface water and groundwater samples and plant extracts. The limit of detection was 55, 30 (25 ng/g soil), and 4 ng/mL for dihydroartemisinin, artemisinin, and artemether, respectively. Method performance was demonstrated using naturally contaminated soil samples from A. annua fields in Kenya. The highest observed concentrations were above EC(10) for lettuce growth. Monitoring of artemisinin in soil with A. annua crop production seems necessary to further understand the impact in the environment.

Arsenic-induced changes in morphological, physiological, and biochemical attributes and artemisinin biosynthesis in Artemisia annua, an antimalarial plant

Present study is the first to explore physiological, biochemical and molecular changes in the medicinal plant Artemisia annua under arsenic (As) stress. A. annua grown hydroponically in a nutrient solution was spiked with increasing doses of As (0, 1,500, 3,000 and 4,500 μg l(-1)) for 7 days. Plants accumulated As in a dose dependent manner with bioconcentration factor 13.4 and translocation factor 0.97. While a similar trend of As accumulation was observed under soil culture experiments, the transfer factor went up to 2.1, depicting high efficiency of As translocation from roots to shoots by A. annua. Plants raised in 0-3,000 μg l(-1) As containing nutrient solution registered increase in root length, biomass, and carotenoid contents without any visual toxicity symptoms. A dose dependent increase in the activities of enzymes such as superoxide dismutase, ascorbate peroxidase, glutathione reductase and guaiacol peroxidase followed by a gradual decline at higher concentrations suggested their role in alleviating oxidative stress. Significant increase in the levels of thiols, GSH, and pcs gene transcript up to 3,000 μg l(-1) As attested their roles in As detoxification. Enhanced artemisinin production (an antimalarial compound) under As stress and upregulation of the transcripts (measured by RT-PCR) of the genes HMGR, FDS, ADS, and CYP71AV1 involved in artemisinin biosynthesis reaffirmed induction of artemisinin biosynthesis in A. annua under As stress. The results of the present study vividly suggested that A. annua has considerable As tolerance, and thus can be successfully cultivated in As contaminated fields.

Isolation and characterization of culturable endophytic actinobacteria associated with Artemisia annua L

Endophytic actinobacteria isolated from Artemisia annua were characterized and evaluated for their bioactivities. A total of 228 isolates representing at least 19 different genera of actinobacteria were obtained and several of them seemed to be novel taxa. An evaluation of antimicrobial activity showed that more isolates possessed activity towards plant pathogens than activity against other pathogenic bacteria or yeasts. High frequencies of PCR amplification were obtained for type I polyketide synthases (PKS-I, 21.1%), type II polyketide synthases (PKS-II, 45.2%) and nonribosomal peptide synthetases (NRPS, 32.5%). The results of herbicidal activity screening indicated that 19 out of 117 samples of fermentation broths completely inhibited the germination of Echinochloa crusgalli. This study indicated that endophytic actinobacteria associated with A. annua are abundant and have potentially beneficial and diverse bioactivities which should be pursued for their biotechnical promise.

Artemisinin production in Artemisia annua: studies in planta and results of a novel delivery method for treating malaria and other neglected diseases

Artemisia annua L. produces the sesquiterpene lactone, artemisinin, a potent antimalarial drug that is also effective in treating other parasitic diseases, some viral infections and various neoplasms. Artemisinin is also an allelopathic herbicide that can inhibit the growth of other plants. Unfortunately, the compound is in short supply and thus, studies on its production in the plant are of interest as are low cost methods for drug delivery. Here we review our recent studies on artemisinin production in A. annua during development of the plant as it moves from the vegetative to reproductive stage (flower budding and full flower formation), in response to sugars, and in concert with the production of the ROS, hydrogen peroxide. We also provide new data from animal experiments that measured the potential of using the dried plant directly as a therapeutic. Together these results provide a synopsis of a more global view of regulation of artemisinin biosynthesis in A. annua than previously available. We further suggest an alternative low cost method of drug delivery to treat malaria and other neglected tropical diseases.

Trichomes + roots + ROS = artemisinin: regulating artemisinin biosynthesis in Artemisia annua L

Artemisinin is a highly effective sesquiterpene lactone therapeutic produced in the plant, Artemisia annua. Despite its efficacy against malaria and many other infectious diseases and neoplasms, the drug is in short supply mainly because the plant produces low levels of the compound. This review updates the current understanding of artemisinin biosynthesis with a special focus on the emerging knowledge of how biosynthesis of the compound is regulated in planta.

Dissection of the phytohormonal regulation of trichome formation and biosynthesis of the antimalarial compound artemisinin in Artemisia annua plants

• Biosynthesis of the sesquiterpene lactone and potent antimalarial drug artemisinin occurs in glandular trichomes of Artemisia annua plants and is subjected to a strict network of developmental and other regulatory cues. • The effects of three hormones, jasmonate, gibberellin and cytokinin, were studied at the structural and molecular levels in two different A. annua chemotypes by microscopic analysis of gland development, and by targeted metabolite and transcript profiling. Furthermore, a genome-wide cDNA-amplified fragment length polymorphism (AFLP)-based transcriptome profiling was carried out of jasmonate-elicited leaves at different developmental stages. • Although cytokinin and gibberellin positively affected at least one aspect of gland formation, these two hormones did not stimulate artemisinin biosynthesis. Only jasmonate simultaneously promoted gland formation and coordinated transcriptional activation of biosynthetic gene expression, which ultimately led to increased sesquiterpenoid accumulation with chemotype-dependent effects on the distinct pathway branches. Transcriptome profiling revealed a trichome-specific fatty acyl- coenzyme A reductase, trichome-specific fatty acyl-CoA reductase 1 (TFAR1), the expression of which correlates with trichome development and sesquiterpenoid biosynthesis. • TFAR1 is potentially involved in cuticular wax formation during glandular trichome expansion in leaves and flowers of A. annua plants. Analysis of phytohormone-modulated transcriptional regulons provides clues to dissect the concerted regulation of metabolism and development of plant trichomes.

Methods and options for the heterologous production of complex natural products

This review will detail the motivations, experimental approaches, and growing list of successful cases associated with the heterologous production of complex natural products.

Pitfalls in new artemisinin-containing antimalarial drug development

Artemisinin combination therapy (ACT) paves the way for new opportunities to eliminate malaria in the tropics. However, the huge increase of ACT consumption raises major concerns about their availability over the next few years. At the same time a decrease in their efficacy has already been reported. Alongside the deployment of multifocal control programs, the process ranging from artemisia crop production to accreditation of new ACT combinations urgently needs to be strengthened to supply sufficient quantities of high-quality drugs. New suppliers will have the opportunity to enter this market to develop new formulations, and bioequivalence studies are required to validate these new formulations. It is thus crucial for national malaria control teams to be able to better scrutinize the dossier of these new formulations.

Reproductive development modulates gene expression and metabolite levels with possible feedback inhibition of artemisinin in Artemisia annua

The relationship between the transition to budding and flowering in Artemisia annua and the production of the antimalarial sesquiterpene, artemisinin (AN), the dynamics of artemisinic metabolite changes, AN-related transcriptional changes, and plant and trichome developmental changes were measured. Maximum production of AN occurs during full flower stage within floral tissues, but that changes in the leafy bracts and nonbolt leaves as the plant shifts from budding to full flower. Expression levels of early pathway genes known to be involved in isopentenyl diphosphate and farnesyl diphosphate biosynthesis leading to AN were not immediately positively correlated with either AN or its precursors. However, we found that the later AN pathway genes, amorpha-4,11-diene synthase (ADS) and the cytochrome P450, CYP71AV1 (CYP), were more highly correlated with AN's immediate precursor, dihydroartemisinic acid, within all leaf tissues tested. In addition, leaf trichome formation throughout the developmental phases of the plant also appears to be more complex than originally thought. Trichome changes correlated closely with the levels of AN but not its precursors. Differences were observed in trichome densities that are dependent both on developmental stage (vegetative, budding, and flowering) and on position (upper and lower leaf tissue). AN levels declined significantly as plants matured, as did ADS and CYP transcripts. Spraying leaves with AN or artemisinic acid inhibited CYP transcription; artemisinic acid also inhibited ADS transcription. These data allow us to present a novel model for the differential control of AN biosynthesis as it relates to developmental stage and trichome maturation and collapse.

Biological actions of artemisinin: insights from medicinal chemistry studies

Artemisinins have become essential antimalarial drugs for increasingly widespread drug-resistant malaria strains. Although tremendous efforts have been devoted to decipher how this class of molecules works, their exact antimalarial mechanism is still an enigma. Several hypotheses have been proposed to explain their actions, including alkylation of heme by carbon-centered free radicals, interference with proteins such as the sarcoplasmic/endoplasmic calcium ATPase (SERCA), as well as damaging of normal mitochondrial functions. Besides artemisinins, other endoperoxides with various backbones have also been synthesized, some of which showed comparable or even higher antimalarial effects. It is noteworthy that among these artemisinin derivatives, some enantiomers displayed similar in vitro malaria killing efficacy. In this article, the proposed mechanisms of action of artemisinins are reviewed in light of medicinal chemistry findings characterized by efficacy-structure studies, with the hope of gaining more insight into how these potent drugs work.

In Vivo Antimalarial Effects of Iranian Flora Artemisia khorassanica against Plasmodium berghei and Pharmacochemistry of its Natural Components

BACKGROUND

The aim of this study was to evaluate the antimalarial effects of Iranian flora Artemisia khorassanica against Plasmodium bergheiin vivo and pharmacochemistry of its natural components.

METHODS

The aerial parts of Iranian flora A. khorasanica were collected at flowering stage from Khorassan Province, northeastern Iran in 2008. They were air-dried at room temperature; powder was macerated in methanol and the extract defatted in refrigerator, filtered, diluted with water, then eluted with n-hexane and finally non-polar components were identified through Gas Chromatography and Mass Spectroscopy (GC-MS). Toxicity of herbal extracts was assessed on naïve NMRI mice, and its anti-malarial efficacy was investigated on infected Plasmodium berghei animals. This is the first application on A. khorssanica extract for treatment of murine malaria. The significance of differences was determined by Analysis of Variances (ANOVA) and Student's t-test using Graph Pad Prism Software.

RESULTS

The herbal extract was successfully tested in vivo for its anti-plasmodial activity through artemisin composition, which is widely used as a standard malaria treatment.

CONCLUSION

Although, this study confirmed less anti-malarial effects of A. khorssanica against murine malaria in vivo, however there are some evidences on reducing pathophysiology by this medication. In complementary assay, major components were detected by GC-MS analysis in herbal extract including chrysanthenone (7.8%), palmitic acid (7.4%) and cis-thujone (5.8%). The most retention indices of the component are given as n-eicosane, palmitic acid and n-octadecane.

DMSO triggers the generation of ROS leading to an increase in artemisinin and dihydroartemisinic acid in Artemisia annua shoot cultures

The antimalarial sesquiterpene, artemisinin, is in short supply; demand is not being met, and the role of artemisinin in the plant is not well established. Prior work showed that addition of dimethyl sulfoxide (DMSO) to seedlings increased artemisinin in their shoots and this study further investigated that serendipitous observation. When in vitro-cultured Artemisia annua rooted shoots were fed different amounts of DMSO (0-2.0% v/v), artemisinin levels doubled and showed biphasic optima at 0.25 and 2.0% DMSO. Both artemisinin and its precursor, dihydroartemisinic acid, increased with the former continuing 7 days after DMSO treatment. There was no stimulation of artemisinin production in DMSO-treated unrooted shoots. The first gene in the artemisinin biosynthetic pathway, amorphadiene synthase, showed no increase in transcript level in response to DMSO compared to controls. In contrast, the second gene in the pathway, CYP71AV1, did respond to DMSO but at a level of transcripts inverse to artemisinin levels. When rooted shoots were stained for the reactive oxygen species (ROS), H2O2, ROS increased with increasing DMSO concentration; unrooted shoots produced no ROS in response to DMSO. Both the increases in DMSO-induced ROS response and corresponding artemisinin levels were inhibited by addition of vitamin C. Together these data show that at least in response to DMSO, artemisinin production and ROS increase and that when ROS is reduced, so also is artemisinin suggesting that ROS may play a role in artemisinin production in A. annua.

TrichOME: a comparative omics database for plant trichomes

Plant secretory trichomes have a unique capacity for chemical synthesis and secretion and have been described as biofactories for the production of natural products. However, until recently, most trichome-specific metabolic pathways and genes involved in various trichome developmental stages have remained unknown. Furthermore, only a very limited amount of plant trichome genomics information is available in scattered databases. We present an integrated "omics" database, TrichOME, to facilitate the study of plant trichomes. The database hosts a large volume of functional omics data, including expressed sequence tag/unigene sequences, microarray hybridizations from both trichome and control tissues, mass spectrometry-based trichome metabolite profiles, and trichome-related genes curated from published literature. The expressed sequence tag/unigene sequences have been annotated based upon sequence similarity with popular databases (e.g. Gene Ontology, Kyoto Encyclopedia of Genes and Genomes, and Transporter Classification Database). The unigenes, metabolites, curated genes, and probe sets have been mapped against each other to enable comparative analysis. The database also integrates bioinformatics tools with a focus on the mining of trichome-specific genes in unigenes and microarray-based gene expression profiles. TrichOME is a valuable and unique resource for plant trichome research, since the genes and metabolites expressed in trichomes are often underrepresented in regular non-tissue-targeted cDNA libraries. TrichOME is freely available at http://www.planttrichome.org/.

IspG enzyme activity in the deoxyxylulose phosphate pathway: roles of the iron-sulfur cluster

IspG is a [4Fe-4S] cluster-containing protein, and the [4Fe-4S](+) species is proposed to be the catalytically relevant species. However, attempts reported in the literature failed to detect the [4Fe-4S](+) species. In this study, using a potent reduction system, we have successfully detected the [4Fe-4S](+) species with X-band EPR spectroscopy. In addition, we have improved the Escherichia coli IspG activity to 550 nmol min(-1) mg(-1), which is approximately 20-fold greater than that of the NADPH-Fpr-FldA system in the literature.

Novel approaches and achievements in biosynthesis of functional isoprenoids in Escherichia coli

Isoprenoids, also referred to as terpenes, are the most diverse class of natural products appearing in a variety of natural sources, specifically in higher plants, and have a wide range of biological functions. This review describes novel or recent approaches and achievements in pathway engineering of Escherichia coli towards efficient biosynthesis of functional isoprenoids, specifically carotenoids and sesquiterpene, following description of "regularity and simplicity" in the biosynthesis of isoprenoid basic structures. The introduction of heterologous mevalonate pathway-based genes into E. coli has been shown to improve the productivity of carotenoids or sesquiterpenes that are synthesized from farnesyl diphosphate. This achievement also enables relevant researchers to efficiently analyze an isolated gene candidate for a terpene synthase (terpene cyclase).

Perspectives and limits of engineering the isoprenoid metabolism in heterologous hosts

Terpenoids belong to the largest class of natural compounds and are produced in all living organisms. The isoprenoid skeleton is based on assembling of C5 building blocks, but the biosynthesis of a great variety of terpenoids ranging from monoterpenoids to polyterpenoids is not fully understood today. Terpenoids play a fundamental role in human nutrition, cosmetics, and medicine. In the past 10 years, many metabolic engineering efforts have been undertaken in plants but also in microorganisms to improve the production of various terpenoids like artemisinin and paclitaxel. Recently, inverse metabolic engineering and combinatorial biosynthesis as main strategies in synthetic biology have been applied to produce high-cost natural products like artemisinin and paclitaxel in heterologous microorganisms. This review describes the recent progresses made in metabolic engineering of the terpenoid pathway with particular focus on fundamental aspects of host selection, vector design, and system biotechnology.