Effect of sugars on artemisinin production in Artemisia annua L.: transcription and metabolite measurements

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.

Establishment of feijoa (Acca sellowiana) callus and cell suspension cultures and identification of arctigenin - a high value bioactive compound

Feijoa (Acca sellowiana (O. Berg.) Burret), also known as pineapple guava, is a member of the Myrtaceae family and is well known for its fruit. Chemical profiling of the different tissues of the feijoa plant has shown that they generate an array of useful bioactive compounds which have health benefits such as significant antioxidant activities. In this study, an in vitro culture system has been developed, which could be explored to extract high-value bioactive compounds from feijoa. Feijoa tissue culture was initiated by the induction of callus from floral buds. Sections of floral buds were plated on MS medium supplemented with 2,4-D and BAP at 2.0mg/L and 0.2mg/L concentrations, respectively. Cell suspension cultures of feijoa were established using a liquid MS medium with different concentrations of 2,4-D and BAP and cultured on a rotary shaker. The growth of the cell suspension was evaluated with different parameters such as different carbohydrate sources, concentration of MS media, and inoculum density. When the cell suspensions were treated with different concentrations of MeJA at different time points, phytochemicals UPLC - QTOF MS analysis identified extractables of interest. The main compounds identified were secondary metabolites (flavonoids and flavonoid-glucosides) and plant hormones. These compounds are of interest for their potential use in therapeutics or skin and personal care products. This report investigates essential methodology parameters for establishing cell suspension cultures from feijoa floral buds, which could be used to generate in vitro biomass to produce high-value bioactive compounds. This is the first study reporting the identification of arctigenin from feijoa, a high-value compound whose pharmaceutical properties, including anti-tumour, anti-inflammatory and anti-colitis effects, have been widely reported. The ability of feijoa cell cultures to produce such high-value bioactive compounds is extremely promising for its use in pharmaceuticals, cosmeceuticals and nutraceuticals applications.

In Vitro Evaluation of Biological and Anticancer Activities Exhibited by Five Varieties of Vitis vinifera L

Vitis vinifera commonly known as grapevine is one of the most important fruit crops worldwide. Its cultivation started more than 7000 years ago in the Near East, and over the millennia was followed by the development of thousands of cultivars that were further selected and characterized for specific purposes. Its important pharmacological value and its richness in phytoconstituents were the triggers to perform this project. Seven extracts were prepared from five different V. vinifera varieties (V. vinifera 'Black Pearl' (BP), V. vinifera 'Red Glob' (RG), V. vinifera 'Crimson' (CR), V. vinifera 'Beitamouni' (BE) and V. vinifera 'Superior' (SU)) by separating the pulp from the seeds, followed by methanolic extraction. The phytochemical analysis showed that red colored grapes (RE, BP and CR), the seeds from V. vinifera 'Black Pearl' and V. vinifera 'Red Globe' contain higher amounts of primary and secondary metabolites such as polyphenols, anthocyanins and reducing sugars. In addition to their richness in phytoconstituents, these varieties/seeds possess an important antioxidant activity. The results of the cell viability assays showed that the red varieties have a potential anticancer activity against Capan-2 pancreatic cancer and MDA-MB231(TNBC) breast cancer cell lines, with the greatest promise when combined with the seeds.

Plant secondary metabolic responses to global climate change: A meta-analysis in medicinal and aromatic plants

Plant secondary metabolites (SMs) play crucial roles in plant-environment interactions and contribute greatly to human health. Global climate changes are expected to dramatically affect plant secondary metabolism, yet a systematic understanding of such influences is still lacking. Here, we employed medicinal and aromatic plants (MAAPs) as model plant taxa and performed a meta-analysis from 360 publications using 1828 paired observations to assess the responses of different SMs levels and the accompanying plant traits to elevated carbon dioxide (eCO₂ ), elevated temperature (eT), elevated nitrogen deposition (eN) and decreased precipitation (dP). The overall results showed that phenolic and terpenoid levels generally respond positively to eCO₂ but negatively to eN, while the total alkaloid concentration was increased remarkably by eN. By contrast, dP promotes the levels of all SMs, while eT exclusively exerts a positive influence on the levels of phenolic compounds. Further analysis highlighted the dependence of SM responses on different moderators such as plant functional types, climate change levels or exposure durations, mean annual temperature and mean annual precipitation. Moreover, plant phenolic and terpenoid responses to climate changes could be attributed to the variations of C/N ratio and total soluble sugar levels, while the trade-off supposition contributed to SM responses to climate changes other than eCO₂ . Taken together, our results predicted the distinctive SM responses to diverse climate changes in MAAPs and allowed us to define potential moderators responsible for these variations. Further, linking SM responses to C-N metabolism and growth-defence balance provided biological understandings in terms of plant secondary metabolic regulation.

Comparative transcriptome analysis provides insights into steviol glycoside synthesis in stevia (Stevia rebaudiana Bertoni) leaves under nitrogen deficiency

Transcriptome analysis revealed the potential mechanism of nitrogen regulating steviol glycosides synthesis via shifting of leaf carbon metabolic flux or inducing certain transcription factors. Nitrogen (N) plays key regulatory roles in both stevia (Stevia rebaudiana) growth and the synthesis of its functional metabolite steviol glycosides (SGs), but the mechanism by which this nutrient regulates SGs synthesis remains to be elucidated. To address this question, a pot experiment was performed in a greenhouse where stevia plants fertilized with N (the control as CK plants) and compared with plants without the supply of N. Physiological and biochemical analyses were conducted to test the growth and metabolic responses of plants to N regimes. Our results showed that N deficiency significantly inhibited plant growth and leaf photosynthesis, while increased leaf SGs contents in stevia (49.97, 46.64 and 84.80% respectively for rebaudioside A, stevioside, and rebaudioside C), which may be partly due to "concentration effect". Then, transcriptome analysis was conducted to understand the underlying mechanisms. A total of 535 differentially expressed genes were identified, and carbon metabolism-related events were highlighted by Gene Ontology and Kyoto Encyclopedia of Genes and Genomes. Many of these genes were significantly upregulated by N-deficiency, including those involved in "phenylpropanoid biosynthesis", "flavonoid biosynthesis" and "starch and sucrose metabolism". Our study also analyzed the expression patterns of SGs synthesis-related genes under two N regimes and the potential transcription factors linking N nutrition and SG metabolism. N-deficiency may promote SGs synthesis by changing the carbon metabolism flux or inducing certain transcription factors. Our results provide deeper insight into the relationship between N nutrition and SGs synthesis in stevia plants.

Enhancing artemisinin content in and delivery from Artemisia annua: a review of alternative, classical, and transgenic approaches

This review analyses the most recent scientific research conducted for the purpose of enhancing artemisinin production. It may help to devise better artemisinin enhancement strategies, so that its production becomes cost effective and becomes available to masses. Malaria is a major threat to world population, particularly in South-East Asia and Africa, due to dearth of effective anti-malarial compounds, emergence of quinine resistant malarial strains, and lack of advanced healthcare facilities. Artemisinin, a sesquiterpene lactone obtained from Artemisia annua L., is the most potent drug against malaria and used in the formulation of artemisinin combination therapies (ACTs). Artemisinin is also effective against various types of cancers, many other microbes including viruses, parasites and bacteria. However, this specialty metabolite and its derivatives generally occur in low amounts in the source plant leading to its production scarcity. Considering the importance of this drug, researchers have been working worldwide to develop novel strategies to augment its production both in vivo and in vitro. Due to complex chemical structure, its chemical synthesis is quite expensive, so researchers need to devise synthetic protocols that are economically viable and also work on increasing the in-planta production of artemisinin by using various strategies like use of phytohormones, stress signals, bioinoculants, breeding and transgenic approaches. The focus of this review is to discuss these artemisinin enhancement strategies, understand mechanisms modulating its biosynthesis, and evaluate if roots play any role in artemisinin production. Furthermore, we also have a critical analysis of various assays used for artemisinin measurement. This may help to develop better artemisinin enhancement strategies which lead to decreased price of ACTs and increased profit to farmers.

TiO2 nanoparticles and salinity stress in relation to artemisinin production and ADS and DBR2 expression in Artemisia absinthium L

Artemisia absinthium L. is an important herb that is widely cultivated in different parts of the world for its medicinal properties. The present study evaluated the effects of four concentrations of nanoparticles treatment (0, 10, 20 and 30 mg L-1) and NaCl salinity stress (0, 50, 100 and 150 mM NaCl) and their interactions with respect to the expression of two key genes, i.e. DBR2 and ADS, in the biosynthesis pathway of artemisinin in A. absinthium. Total RNA was extracted and a relative gene expression analysis was carried out using Real-Time PCR. The amount of artemisinin was also determined by HPLC. All the experiments were performed as factorial in a completely randomized design in three replications. The results revealed that salinity stress and nanoparticles treatment and their interaction affected the expressions of these genes significantly. The highest levels of ADS gene expression were observed in the 30 mg L-1 nanoparticles-treated plants in the presence of 150 mM salinity stress and the lowest levels in the 10 mg L-1 nanoparticles-treated plants under 50 mM salinity stress. The maximum DBR2 gene expression was recorded in the 10 mg L-1 nanoparticles-treated plants in the absence of salinity stress and the minimum expression in the 100 mM salinity-stressed plants in the absence of nanoparticles treatment. Moreover, the smallest amounts of artemisinin were observed in the 150 mM salinity-stressed plants in the absence of nanoparticles and the highest amounts in the 30 mg L-1 nanoparticles-treated plants. The maximum amounts of artemisinin and ADS gene expression were reported from the plants in the same nanoparticles treatment and salinity stress conditions. In this regard, the amount of artemisinin was decreased by half in the plants containing the highest DBR2 gene expression. Meanwhile, no significant correlation was observed between these gene expressions and the artemisinin amount in the other nanoparticles-treated plants under different levels of salinity stress. The biosynthetic pathway of secondary metabolites appears to be very complex and dose not directly dependent on these gene expressions.

Reducing Sugar, Total Phenolic Content, and Antioxidant Potential of Nepalese Plants

The aim of the present study was to investigate the reducing sugar, total phenolic content, and in vitro antioxidant activity of 70% (v/v) ethanolic extract of seven medicinal plants grown in Nepal. The reducing sugar content and total phenolic content were determined by 3,5-dinitrosalicylic acid (DNSA) and the Folin–Ciocalteu method, respectively. The in vitro antioxidant activity was evaluated using the 2,2-diphenyl-1-picrylhydrazyl (DPPH) assay. The reducing sugar content of the studied plant samples ranged from 6.89 ± 2.44 to 674.13 ± 2.43 mg GE/g dry extract weight and the total phenolic content ranged from 14.87 ± 0.41 to 281.71 ± 1.47 mg GAE/g dry extract weight. The reducing sugar and total phenolic content were found highest in Ficus glaberrima. Antioxidant activity was found highest in Melastoma malabathricum (IC₅₀value = 6.27 μg/mL), followed by F. glaberrima (IC₅₀value = 11.7 μg/mL). A positive and significant correlation was found between (i) total phenolic content and reducing sugar content and (ii) total phenolic content and antioxidant activity. The present study is the first study for the analysis of reducing sugar content of selected plants and for the scientific exploration of F. glaberrima. The present result suggests that the various parts of these studied plants could be assumed as a rich source of biologically active compounds and considered beneficial for the food and pharmaceutical industries.

An oxidatively stressful situation: a case of Artemisia annua L

Artemisinin (ART) is an antimalarial compound that possesses a variety of novel biological activities. Due to the low abundance of ART in natural sources, agricultural supply has been erratic, and prices are highly volatile. While heterologous biosynthesis and semi-synthesis are advantageous in certain aspects, these approaches remained disadvantageous in terms of productivity and cost-effectiveness. Therefore, further improvement in ART production calls for approaches that should supplement the agricultural production gap, while reducing production costs and stabilising supply. The present review offers a discussion on the elicitation of plants and/or in vitro cultures as an economically feasible yield enhancement strategy to address the global problem of access to affordable ART. Deemed critical for the manipulation of biosynthetic potential, the mechanism of ART biosynthesis is reviewed. It includes a discussion on the current biotechnological solutions to ART production, focusing on semi-synthesis and elicitation. A brief commentary on the possible aspects that influence elicitation efficiency and how oxidative stress modulates ART synthesis is also presented. Based on the critical analysis of current literature, a hypothesis is put forward to explain the possible involvement of enzymes in assisting the final non-enzymatic transformation step leading to ART formation. This review highlights the critical factors limiting the success of elicitor-induced modulation of ART metabolism, that will help inform strategies for future improvement of ART production. Additionally, new avenues for future research based on the proposed hypothesis will lead to exciting perspectives in this research area and continue to enhance our understanding of this intricate metabolic process.

Glucose: Sweet or bitter effects in plants-a review on current and future perspective

Sugars are metabolic substrates playing a part in modulating various processes in plants during different phases of development. Thus, modulating the sugar metabolism can have intense effects on the plant metabolism. Glucose is a soluble sugar, found throughout the plant kingdom. Apart from being a universal carbon source, glucose also operates as a signaling molecule modulating various metabolic processes in plants. From germination to senescence, wide range of processes in plants is regulated by glucose. The effect of glucose is found to be concentration dependent. Photosynthesis and its related attributes, respiration and nitrogen metabolism are influenced by glucose application. Endogenous content of glucose increases upon exposure of plant to various abiotic stresses and also when glucose is supplied exogenously. Glucose accumulation alleviates the damaging effects of stress by enhancing production of antioxidants and compounds similar to that of photosynthetic CO₂ fixation which act as an osmoticum by maintaining osmotic pressure inside the cell, pH homeostasis regulator and reduce membrane permeability during stress. Glucose interaction with various phytohormones has also been discussed in this review.

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

Effects of different doses of cadmium on secondary metabolites and gene expression in Artemisia annua L

This study aims to elucidate the underlying molecular mechanisms of artemisinin accumulation induced by Cd. The effects of different Cd concentrations (0, 20, 60, and 120 μmol/L) on the biosynthesis of Artemisia annua L. were examined. Intermediate and end products were quantified by HPLC-ESI-MS/MS analysis. The expression of key biosynthesis enzymes was also determined by qRT-PCR. The results showed that the application of treatment with 60 and 120 μmol/L Cd for 3 days significantly improved the biosynthesis of artemisinic acid, arteannuin B, and artemisinin. The concentrations of artemisinic acid, arteannuin B, and artemisinin in the 120 μmol/L Cd-treated group were 2.26, 102.08, and 33.63 times higher than those in the control group, respectively. The concentrations of arteannuin B and artemisinin in 60 μmol/L Cd-treated leaves were 61.10 and 26.40 times higher than those in the control group, respectively. The relative expression levels of HMGR, FPS, ADS, CYP71AV1, DBR2, ALDH1, and DXR were up-regulated in the 120 μmol/L Cd-treated group because of increased contents of artemisinic metabolites after 3 days of treatment. Hence, appropriate doses of Cd can increase the concentrations of artemisinic metabolites at a certain time point by up-regulating the relative expression levels of key enzyme genes involved in artemisinin biosynthesis.

Cellular engineering of Artemisia annua and Artemisia dubia with the rol ABC genes for enhanced production of potent anti-malarial drug artemisinin

BACKGROUND

Malaria is causing more than half of a million deaths and 214 million clinical cases annually. Despite tremendous efforts for the control of malaria, the global morbidity and mortality have not been significantly changed in the last 50 years. Artemisinin, extracted from the medicinal plant Artemisia sp. is an effective anti-malarial drug. In 2015, elucidation of the effectiveness of artemisinin as a potent anti-malarial drug was acknowledged with a Nobel prize. Owing to the tight market and low yield of artemisinin, an economical way to increase its production is to increase its content in Artemisia sp. through different biotechnological approaches including genetic transformation.

METHODS

Artemisia annua and Artemisia dubia were transformed with rol ABC genes through Agrobacterium tumefacienes and Agrobacterium rhizogenes methods. The artemisinin content was analysed and compared between transformed and untransformed plants with the help of LC-MS/MS. Expression of key genes [Cytochrome P450 (CYP71AV1), aldehyde dehydrogenase 1 (ALDH1), amorpha-4, 11 diene synthase (ADS)] in the biosynthetic pathway of artemisinin and gene for trichome development and sesquiterpenoid biosynthetic (TFAR1) were measured using Quantitative real time PCR (qRT-PCR). Trichome density was analysed using confocal microscope.

RESULTS

Artemisinin content was significantly increased in transformed material of both Artemisia species when compared to un-transformed plants. The artemisinin content within leaves of transformed lines was increased by a factor of nine, indicating that the plant is capable of synthesizing much higher amounts than has been achieved so far through traditional breeding. Expression of all artemisinin biosynthesis genes was significantly increased, although variation between the genes was observed. CYP71AV1 and ALDH1 expression levels were higher than that of ADS. Levels of the TFAR1 expression were also increased in all transgenic lines. Trichome density was also significantly increased in the leaves of transformed plants, but no trichomes were found in control roots or transformed roots. The detection of significantly raised levels of expression of the genes involved in artemisinin biosynthesis in transformed roots correlated with the production of significant amounts of artemisinin in these tissues. This suggests that synthesis is occurring in tissues other than the trichomes, which contradicts previous theories.

CONCLUSION

Transformation of Artemisia sp. with rol ABC genes can lead to the increased production of artemisinin, which will help to meet the increasing demand of artemisinin because of its diverse pharmacological and anti-malarial importance.

Molecular Farming in Artemisia annua, a Promising Approach to Improve Anti-malarial Drug Production

Malaria is a parasite infection affecting millions of people worldwide. Even though progress has been made in prevention and treatment of the disease; an estimated 214 million cases of malaria occurred in 2015, resulting in 438,000 estimated deaths; most of them occurring in Africa among children under the age of five. This article aims to review the epidemiology, future risk factors and current treatments of malaria, with particular focus on the promising potential of molecular farming that uses metabolic engineering in plants as an effective anti-malarial solution. Malaria represents an example of how a health problem may, on one hand, influence the proper development of a country, due to its burden of the disease. On the other hand, it constitutes an opportunity for lucrative business of diverse stakeholders. In contrast, plant biofarming is proposed here as a sustainable, promising, alternative for the production, not only of natural herbal repellents for malaria prevention but also for the production of sustainable anti-malarial drugs, like artemisinin (AN), used for primary parasite infection treatments. AN, a sesquiterpene lactone, is a natural anti-malarial compound that can be found in Artemisia annua. However, the low concentration of AN in the plant makes this molecule relatively expensive and difficult to produce in order to meet the current worldwide demand of Artemisinin Combination Therapies (ACTs), especially for economically disadvantaged people in developing countries. The biosynthetic pathway of AN, a process that takes place only in glandular secretory trichomes of A. annua, is relatively well elucidated. Significant efforts have been made using plant genetic engineering to increase production of this compound. These include diverse genetic manipulation approaches, such as studies on diverse transcription factors which have been shown to regulate the AN genetic pathway and other biological processes. Results look promising; however, further efforts should be addressed toward optimization of the most cost-effective biofarming approaches for synthesis and production of medicines against the malaria parasite.

Updates on artemisinin: an insight to mode of actions and strategies for enhanced global production

Application of traditional Chinese drug, artemisinin, originally derived from Artemisia annua L., in malaria therapy has now been globally accepted. Artemisinin and its derivatives, with their established safety records, form the first line of malaria treatment via artemisinin combination therapies (ACTs). In addition to its antimalarial effects, artemisinin has recently been evaluated in terms of its antitumour, antibacterial, antiviral, antileishmanial, antischistosomiatic, herbicidal and other properties. However, low levels of artemisinin in plants have emerged various conventional, transgenic and nontransgenic approaches for enhanced production of the drug. According to WHO (2014), approximately 3.2 billion people are at risk of this disease. However, unfortunately, artemisinin availability is still facing its short supply. To fulfil artemisinin's global demand, no single method alone is reliable, and there is a need to collectively use conventional and advanced approaches for its higher production. Further, it is the unique structure of artemisinin that makes it a potential drug not only against malaria but to other diseases as well. Execution of its action through multiple mechanisms is probably the reason behind its wide spectrum of action. Unfortunately, due to clues for developing artemisinin resistance in malaria parasites, it has become desirable to explore all possible modes of action of artemisinin so that new generation antimalarial drugs can be developed in future. The present review provides a comprehensive updates on artemisinin modes of action and strategies for enhanced artemisinin production at global level.

Artemisinin production by plant hairy root cultures in gas- and liquid-phase bioreactors

Alternative biotechnological protocol for large-scale artemisinin production was established. It featured enhanced growth and artemisinin production by cultivation of hairy roots in nutrient mist bioreactor (NMB) coupled with novel cultivation strategies. Artemisinin is used for the treatment of cerebral malaria. Presently, its main source is from seasonal plant Artemisia annua. This study featured investigation of growth and artemisinin production by A. annua hairy roots (induced by Agrobacterium rhizogenes-mediated genetic transformation of explants) in three bioreactor configurations-bubble column reactor, NMB and modified NMB particularly to establish their suitability for commercial production. It was observed that cultivation of hairy roots in a non-stirred bubble column reactor exhibited a biomass accumulation of 5.68 g/l only while batch cultivation in a custom-made NMB exhibited a higher biomass concentration of 8.52 g/l but relatively lower artemisinin accumulation of 0.22 mg/g was observed in this reactor. A mixture of submerged liquid-phase growth (for 5 days) followed by gas-phase cultivation in nutrient mist reactor operation strategy (for next 15 days) was adopted for hairy root cultivation in this investigation. Reasonably, high (23.02 g/l) final dry weight along with the artemisinin accumulation (1.12 mg/g, equivalent to 25.78 mg/l artemisinin) was obtained in this bioreactor, which is the highest reported artemisinin yield in the gas-phase NMB cultivation.

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.

The effect of roots and media constituents on trichomes and artemisinin production in Artemisia annua L

KEY MESSAGE : Rooting of Artemisia annua increases trichome size on leaves and helps drive the final steps of the biosynthesis of the sesquiterpene antimalarial drug, artemisinin. Artemisia annua produces the antimalarial drug, artemisinin (AN), which is synthesized and stored in glandular trichomes (GLTs). In vitro-grown A. annua shoots produce more AN when they form roots. This may be a function not of the roots, but rather media components such as the phytohormones, α-naphthaleneacetic acid (NAA) and 6-benzylaminopurine (BAP), or salts and sucrose used to maintain either rooted or unrooted shoot cultures. We investigated how three main media components altered artemisinic metabolite production, pathway gene transcripts, and GLT formation in both mature and developing leaves in rooted and unrooted cultures. Although transcript levels of AN biosynthetic genes were not altered, AN levels were significantly different, and there were major differences in both artemisinic metabolite levels and trichomes in mature versus developing leaves. For example, NAA induced higher AN production in rooted shoots, but only in mature leaves. In developing leaves, BAP increased GLT density on the leaf surface. When both phytohormones were present, GLTs were larger on young developing leaves, but smaller on mature leaves. Furthermore, although other media components increased GLT density, their size decreased on young leaves, but there was no effect on mature leaves. Roots also appeared to drive conversion of artemisinic precursors towards end products. These results suggest that, while the presence of roots affects AN and trichome production, phytohormones and other media constituents used for in vitro culture of A. annua also exert an influence.

Over-expression of HMG-CoA reductase and amorpha-4,11-diene synthase genes in Artemisia annua L. and its influence on artemisinin content

Artemisinin, an endoperoxide sesquiterpene lactone, is a novel antimalarial natural product isolated from Artemisia annua L. plants. The low concentrations (0.01-1.1%) of this compound in A. annua L. plants is, however, a major constraint for commercialization of artemisinin-based combination therapies (ACTs) recommended by WHO for treating malaria caused by multidrug-resistant P. falciparum sp. In this context, in vivo yield improvement programs were undertaken by us. In the present study, HMG-Co A reductase gene (hmgr) from Catharanthus roseus (L) G. Don and amorpha-4,11-diene synthase (ads) gene from A. annua L. were over-expressed in A. annua L. plants to study their effects on artemisinin yields. The transgenic lines developed from putative transgenic regenerants were evaluated for integration and copy number of the transgenes using hptII gene probe, as it was a part of the expression cassette. The transgenic lines showed positive bands of hptII gene on Southern blots confirming the integration of transgenes. Some of the transgenic lines had single copy of the transgenes, while others had multiple copies. The expressions of hmgr and ads at the transcriptional level were also confirmed in each transgenic line employing RT-PCR assays. The HPLC analyses showed that the artemisinin contents were significantly increased in these transgenics. One of the transgenic lines, TR4, was found to contain 7.65-fold higher (1.73 mg/gDW) artemisinin than the non-transgenic plant (W). The increased artemisinin levels were found to be correlated with HMG-Co A reductase and amorpha-4,11-diene synthase enzymatic activities in the biochemical analyses.

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.

β-Cyclodextrins enhance artemisinin production in Artemisia annua suspension cell cultures

Artemisinin is a sesquiterpene antimalarial compound produced, though at low levels (0.1-1% dry weight), in Artemisia annua in which it accumulates in the glandular trichomes of the plant. Due to its antimalarial properties and short supply, efforts are being made to improve our understanding of artemisinin biosynthesis and its production. Native β-cyclodextrins, as well as the chemically modified heptakis(2,6-di-O-methyl)-β-cyclodextrin (DIMEB) and 2-hydroxypropyl-β-cyclodextrins, were added to the culture medium of A. annua suspension cultures, and their effects on artemisinin production were analysed. The effects of a joint cyclodextrin and methyl jasmonate treatment were also investigated. Fifty millimolar DIMEB, as well as a combination of 50 mM DIMEB and 100 μM methyl jasmonate, was highly effective in increasing the artemisinin levels in the culture medium. The observed artemisinin level (27 μmol g(-1) dry weight) was about 300-fold higher than that observed in untreated suspensions. The influence of β-cyclodextrins and methyl jasmonate on the expression of artemisinin biosynthetic genes was also investigated.

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.