Biosynthesis of sterols and ecdysteroids in Ajuga hairy roots

Control Phytophagous Nematodes By Engineering Phytosterol Dealkylation Caenorhabditis elegans as a Model

Plant-parasitic nematodes ingest and convert host phytosterols via dealkylation to cholesterol for both structural and hormonal requirements. The insect 24-dehydrocholesterol reductase (DHCR24) was shown in vitro as a committed enzyme in the dealkylation via chemical blocking. However, an increased brood size and ovulation rate, instead compromised development, were observed in the engineered nematode Caenorhabditis elegans where the DHCR24 gene was knocked down, indicating the relationship between DHCR24 and dealkylation and their function in nematodes remains illusive. In this study, a defect in C. elegans DHCR24 causes impaired growth of the nematode with sitosterol (a major component of phytosterols) as a sole sterol source. Plant sterols with rationally designed structure (null substrates for dealkylation) can't be converted to cholesterol in wild-type worms, and their development was completely halted. This study underpins the essential function of DHCR24 in nematodes and would be beneficial for the development of novel nematocidal strategies.

Sustainable Production of Ajuga Bioactive Metabolites Using Cell Culture Technologies: A Review

The genus Ajuga (Lamiaceae) is rich in medicinally important species with biological activities ranging from anti-inflammatory, antitumor, neuroprotective, and antidiabetic to antibacterial, antiviral, cytotoxic, and insecticidal effects. Every species contains a unique and complex mixture of bioactive metabolites-phytoecdysteroids (PEs), iridoid glycosides, withanolides, neo-clerodane terpenoids, flavonoids, phenolics, and other chemicals with high therapeutic potential. Phytoecdysteroids, the main compounds of interest, are natural anabolic and adaptogenic agents that are widely used as components of dietary supplements. Wild plants remain the main source of Ajuga bioactive metabolites, particularly PEs, which leads to frequent overexploitation of their natural resources. Cell culture biotechnologies offer a sustainable approach to the production of vegetative biomass and individual phytochemicals specific for Ajuga genus. Cell cultures developed from eight Ajuga taxa were capable of producing PEs, a variety of phenolics and flavonoids, anthocyanins, volatile compounds, phenyletanoid glycosides, iridoids, and fatty acids, and demonstrated antioxidant, antimicrobial, and anti-inflammatory activities. The most abundant PEs in the cell cultures was 20-hydroxyecdysone, followed by turkesterone and cyasterone. The PE content in the cell cultures was comparable or higher than in wild or greenhouse plants, in vitro-grown shoots, and root cultures. Elicitation with methyl jasmonate (50-125 µM) or mevalonate and induced mutagenesis were the most effective strategies that stimulated cell culture biosynthetic capacity. This review summarizes the current progress in cell culture application for the production of pharmacologically important Ajuga metabolites, discusses various approaches to improve the compound yield, and highlights the potential directions for future interventions.

Balance of Δ5-and Δ7-sterols and stanols in halophytes in connection with salinity tolerance

Sterols (STs) have a key role in regulating the fluidity and permeability of membranes in plants (phytosterols) that have wide structural diversity. We studied the effect of structural STs diversity on salt tolerance in halophytes. Specifically, we used gas chromatography-mass spectrometry (GC-MS), including two-dimensional gas chromatography-mass spectrometry (GCxGC-MS), to assess the STs composition in leaves of 21 species of wild-growing halophytes from four families (Asteraceae, Chenopodiaceae, Plumbaginaceae, Tamaricaceae) and three ecological groups (Euhalophytes (Eu), recretophytes (Re), salt excluders (Ex)). Fifteen molecular species of STs from three main groups, Δ⁵-, Δ⁷-and Δ⁰- STs (stanols), were detected. Plants of the genus Artemisia were characterized by a high content of stigmasterol (30-49% of the total STs), while β-sitosterol was the major compound in two Limonium spp., where it comprised 84-92% of the total STs. Species of Chenopodiaceae were able to accumulate both Δ⁵-and Δ⁷-STs and stanols. The content of the predominant Δ⁵-STs decreased in the order Ex → Re → Eu. Molecular species with a saturated steroid nucleus were identified in Eu and Re, suggesting their special salt-accumulating and salt-releasing functions. The structural analogues of stigmasterol, having a double bond C-22, were stigmasta-7,22-dien-3β-ol (spinasterol) and stigmast-22-en-3β-ol (Δ^7--sitosterol). The ratio of Δ⁵-stigmasterol/Δ⁵-β-sitosterol increased in Ex plants, and spinasterol/Δ^7--sitosterol and 22-stigmastenol/sitostanol increased in Eu plants. These data support the well-known role of stigmasterol and its isomers in plant responses to abiotic and biotic factors. The variability in STs types and their ratios suggested some involvement of the sterol membrane components in plant adaptation to growth conditions. The balance of Δ⁵-, Δ⁷-and stanols, as well as the accumulation of molecular analogues of stigmasterol, was suggested to be associated with salt tolerance of the plant species in this investigation.

20-Hydroxyecdysone, from Plant Extracts to Clinical Use: Therapeutic Potential for the Treatment of Neuromuscular, Cardio-Metabolic and Respiratory Diseases

There is growing interest in the pharmaceutical and medical applications of 20-hydroxyecdysone (20E), a polyhydroxylated steroid which naturally occurs in low but very significant amounts in invertebrates, where it has hormonal roles, and in certain plant species, where it is believed to contribute to the deterrence of invertebrate predators. Studies in vivo and in vitro have revealed beneficial effects in mammals: anabolic, hypolipidemic, anti-diabetic, anti-inflammatory, hepatoprotective, etc. The possible mode of action in mammals has been determined recently, with the main mechanism involving the activation of the Mas1 receptor, a key component of the renin-angiotensin system, which would explain many of the pleiotropic effects observed in the different animal models. Processes have been developed to produce large amounts of pharmaceutical grade 20E, and regulatory preclinical studies have assessed its lack of toxicity. The effects of 20E have been evaluated in early stage clinical trials in healthy volunteers and in patients for the treatment of neuromuscular, cardio-metabolic or respiratory diseases. The prospects and limitations of developing 20E as a drug are discussed, including the requirement for a better evaluation of its safety and pharmacological profile and for developing a production process compliant with pharmaceutical standards.

Chemical and pharmacological research on the plants from genus Ajuga

The genus

Ecdysteroids: production in plant in vitro cultures

Ecdysteroids are secondary metabolites, widely distributed in the animal and plant kingdoms. They have a wide range of pharmacological effects in vertebrates, including mammals, most of which are beneficial for humans. Therefore, they have become compounds of interest for the pharmaceutical industry due to their adaptogenic, anabolic, hypoglycaemic, hypocholesterolaemic and antimicrobial activities, which are still being researched. Nowadays, ecdysteroids are present as active ingredients in bodybuilding supplements. Because of their complex structures, their chemical synthesis seems unprofitable and impractical. Due to high content of ecdysteroids in many plants, they are primarily obtained by extraction of the plant material. Plant in vitro cultures provide an alternative source of these compounds, helping to avoid problems associated with field production-such as variable yield or dependence on environmental factors, as well as limited availability of natural resources. Plant cell and tissue cultures may be suggested as alternatives for the production of plant biomass rich in pharmaceutically active ecdysteroids. Moreover, the use of common biotechnological strategies, such as elicitation or precursor feeding, may further increase the yield and improve production of these compounds. In this paper, we describe general information about ecdysteroids: their structure, biosynthesis, distribution, role in plants, and we review recent studies on micropropagation of ecdysteroid-producing plants and cell cultures, and potential ability of ecdysteroids enhancement in in vitro cultures.

Ajuga Δ24-Sterol Reductase Catalyzes the Direct Reductive Conversion of 24-Methylenecholesterol to Campesterol

Dimunito/Dwarf1 (DWF1) is an oxidoreductase enzyme that is responsible for the conversion of C28- and C29-Δ(24(28))-olefinic sterols to 24-methyl- and 24-ethylcholesterols. Generally, the reaction proceeds in two steps via the Δ(24(25))intermediate. In this study, we characterized theArDWF1gene from an expression sequence tag library ofAjuga reptansvar.atropurpureahairy roots. The gene was functionally expressed in the yeast T21 strain. Thein vivoandin vitrostudy of the transformed yeast indicated that ArDWF1 catalyzes the conversion of 24-methylenecholesterol to campesterol. A labeling study followed by GC-MS analysis suggested that the reaction proceeded with retention of the C-25 hydrogen. The 25-H retention was established by the incubation of the enzyme with (23,23,25-(2)H3,28-(13)C)-24-methylenecholesterol, followed by(13)C NMR analysis of the resulting campesterol. Thus, it has been concluded that ArDWF1 directly reduces 24-methylenecholesterol to produce campesterol without passing through a Δ(24(25))intermediate. This is the first characterization of such a unique DWF1 enzyme. For comparison purposes,Oryza sativa DWF1(OsDWF1) was similarly expressed in yeast. Anin vivoassay of OsDWF1 supported the generally accepted two-step mechanism because the C-25 hydrogen of 24-methylenecholesterol was eliminated during its conversion to 24-methylcholesterol. As expected, the 24-methylcholesterol produced by OsDWF1 was a mixture of campesterol and dihydrobrassicasterol. Furthermore, the 24-methylcholesterol contained in theAjugahairy roots was determined to be solely campesterol through its analysis using chiral GC-MS. Therefore, ArDWF1 has another unique property in that only campesterol is formed by the direct reduction catalyzed by the enzyme.

Phytoecdysteroids and flavonoid glycosides among Chilean and commercial sources of Chenopodium quinoa: variation and correlation to physico-chemical characteristics

BACKGROUND

Little is known about varietal differences in the content of bioactive phytoecdysteroids (PE) and flavonoid glycosides (FG) from quinoa (Chenopodium quinoa Willd.). The aim of this study was to determine the variation in PE and FG content among 17 distinct quinoa sources and identify correlations to genotypic (highland vs. lowland) and physico-chemical characteristics (seed color, 100-seed weight, protein content, oil content).

RESULTS

PE and FG concentrations exhibited over four-fold differences across quinoa sources, ranging from 138 ± 11 µg g(-1) to 570 ± 124 µg g(-1) total PE content and 192 ± 24 µg g(-1) to 804 ± 91 µg g(-1) total FG content. Mean FG content was significantly higher in highland Chilean varieties (583.6 ± 148.9 µg g(-1)) versus lowland varieties (228.2 ± 63.1 µg g(-1)) grown under the same environmental conditions (P = 0.0046; t-test). Meanwhile, PE content was positively and significantly correlated with oil content across all quinoa sources (r = 0.707, P = 0.002; Pearson correlation).

CONCLUSION

FG content may be genotypically regulated in quinoa. PE content may be increased via enhancement of oil content. These findings may open new avenues for the improvement and development of quinoa as a functional food.

20-hydroxyecdysone accumulation and regulation in Ajuga lobata D. Don suspension culture

Suspension culture of Ajuga lobata D. Don cells provides a method of synthesis of the phytoecdysteroid 20-hydroxyecdysone (20E) which can regulate the molting process of larvae. We characterized the culture conditions to optimize 20E production. Growth of A. lobata D. Don cells fits the logistic equation curve with a growth cycle of 19 days. Medium conductivity was negatively correlated with dry cell weight and 20E accumulation, thus could be used to determine the optimal time for cell harvest. Continuous subculture reduced 20E synthesis, but supplementing medium with 20E precursors mevalonic (MVA), α-Pinene, and nitric oxide (NO) can significantly promote cell growth and influence 20E accumulation. Combination of α-Pinene, MVA, and SNP significantly elevated 20E accumulation, thus may synergistically enhance 20E synthesis in A. lobata D. Don. The optimal concentrations of α-Pinene, MVA, and NO donor SNP in suspension culture were 50 μL L(-1), 10 mg L(-1), and 80 μmol L(-1).

Phytoecdysteroid C2-hydroxylase is microsomal in spinach, Spinacia oleracea L

An enzyme involved in the biosynthesis of phytoecdysteroids, the C2-hydroxylase, has been investigated in spinach, Spinacia oleracea. This enzyme is microsomal and its K(m) has been determined using 2-deoxy-20-hydroxyecdysone as substrate (K(m)=3.72 microM). It is much more efficient with 2-deoxy-20-hydroxyecdysone than with 2-deoxyecdysone and, conversely, the C20-hydroxylase is more active on 2-deoxyecdysone than on ecdysone. These data support the conclusion that C20-hydroxylation precedes C2-hydroxylation. The C2-hydroxylase is inhibited by high concentrations of 20E. Substrate specificity and subcellular localization of C2-hydroxylase differ between plants and insects, and these data, as well as those previously reported on other biosynthetic steps, show the great difference between plant and insect ecdysteroid biosynthetic pathways and suggest an independent origin for the pathways in both kingdoms.

Ecdysteroids in spinach (Spinacia oleracea L.): biosynthesis, transport and regulation of levels

Many plant species produce phytoecdysteroids (PEs: i.e. analogues of insect steroid hormones). There is increasing evidence that PEs are used as a chemical defence by plants against non-adapted insects and nematodes. PEs are good candidates for the development of an environmentally safe approach to crop protection. Most crop species do not accumulate PEs. However, many arguments support the idea that most, if not all, plant species have the genetic ability to produce PEs, but the biosynthetic pathway is not active. A better understanding of the PE biosynthetic pathway and its regulation is consequently necessary. Spinach is one of the very few crop plants which produce large amounts of PEs, of which 20-hydroxyecdysone is the major component. Labeling experiments with radiolabeled precursor (mevalonic acid), putative ecdysteroid intermediates and 20-hydroxyecdysone itself have allowed investigation of PE biosynthesis and transport during spinach development. Biosynthesis takes place in older leaf sets ("sources"), but not in the young developing ones, which in contrast accumulate (acting as "sinks") the PEs produced by the older leaves. PEs are thus continuously redistributed within the developing plant, as its leaf set number increases. The biosynthetic pathway has been analyzed using excised leaves and various labeled precursors, and a preferential sequence of the last steps has been established. Although they do not produce PEs, apical leaf sets are nevertheless able to perform several putative terminal steps of PE biosynthesis. The regulatory mechanisms of PE synthesis appear to involve a direct negative feedback of 20-hydroxyecdysone (the major PE in spinach) on its own synthesis; thus, a sustained synthesis in older leaves requires that they can export the PE they produce.

Metabolic conversion of 24-methyl-Delta25-cholesterol to 24-methylcholesterol in higher plants

Feeding of chemically synthesized [27-13C]codisterol ([27-13C]2), [27-13C]24-epicodisterol ([27-13C]3), [23,24-2H2]codisterol ([23,24-2H2]2), and [26,27-2H6]24-methyldesmosterol ([26,27-2H6]8) to Oryza sativa cell cultures, followed by MS and NMR analysis of the biosynthesized dihydrobrassicasterol (9)/campesterol (10), revealed that both (24R)- and (24S)-epimers of 24-methyl-Delta25-cholesterol (2/3) were converted to 9 and 10 via the common intermediate 24-methyldesmosterol (8).

Structure elucidation of cyasterone stereoisomers isolated from Cyathula officinalis

Chemical investigation of ecdysteroidal constituents of the roots and stems of Cyathula officinalis led to the isolation of two cyasterone stereoisomers, 2 and 3, together with the known cyasterone 1. The structures of compounds 2 and 3 were determined to be 28-epi-cyasterone and 25-epi-28-epi-cyasterone, respectively, by means of spectroscopic analysis. X-Ray structures of 1 and 2 confirmed the 24S,25S,28R configuration for 1 and 24S,25S,28S for 2.

Acute and chronic toxicological studies of Ajuga iva in experimental animals

Ajuga iva (L.) Schreber (AI), is widely used in the Moroccan pharmacopoeia as a panacea (cure-all), and specifically for gastrointestinal disorders and diabetes, and as an anthelmintic. No toxicological investigations have been carried out on this plant. We have previously observed that single oral doses (2-14 g/kg) of a lyophilised aqueous extract of AI (AI-extract) in mice or daily oral administration of 10 mg/kg of AI-extract in rats for 2 weeks did not result in any adverse effects. We have now evaluated AI-extract for its behavioural and pharmaco-toxicological effects after acute and chronic administration by the oral and intraperitoneal routes in rats and mice. No toxicity was observed in mice after single oral doses of as high as 14 g/kg of the AI-extract. However, single intraperitoneal injections of the AI-extract (1500-5500 mg/kg BW) produced a dose-dependent increase in adverse effects in the general behaviour and the mortality rate; the LD50 of acute intraperitoneal dose was 3.6 g/kg. In chronic toxicological studies in rats, the AI-extract (administered orally at daily doses of 100, 300 and 600 mg/kg for 3 months), did not cause any changes in haematological and biochemical parameters, with the exception of a transient rise in platelet counts and a short-term decrease in serum glucose levels. Histopathological examination of the brain, liver and the kidneys at the end of the study (3 months) showed normal architecture suggesting no morphological disturbances.

Biosynthesis of 2,3-epoxybrassinosteroids in seedlings of Secale cereale

Two new brassinosteroids, (22R,23R,24S)-22,23-dihydroxy-24-methyl-5alpha-cholest-2-en-6-one (secasterol) and (22R,23R,24S)-22,23-dihydroxy-2alpha,3alpha-epoxy-24-methyl-5alpha-cholest-6-one (2,3-diepisecasterone) have been identified together with a known 2,3-epoxybrassinosteroid, secasterone, in seedlings of Secale cereale. Deuterated secasterol, teasterone, and typhasterol, upon administration to rye seedlings, were incorporated into secasterone and 2,3-diepisecasterone, indicating a biosynthetic route via teasterone/typhasterol to secasterol to 2,3-epoxybrassinosteroids.

Hypoglycaemic effect of the lyophilised aqueous extract of Ajuga iva in normal and streptozotocin diabetic rats

The purpose of this study was to examine the hypoglycaemic effect of the lyophilised aqueous extract of the whole plant of Ajuga iva (L.) Schreber (Labiatae) in normal and streptozotocin-induced diabetic rats. Single and repeated oral administration of the extract of Ajuga iva L (AI) at a dose of 10 mg/kg produced a slight and significant decrease in plasma glucose levels in normal rats 6 h after administration and after 3 weeks of treatment. AI reduced plasma glucose levels of streptozotocin diabetic rats from 337+/-9.3 to 102.2+/-17.7 mg/dl after 6 h of oral administration (P<0.001). Repeated oral administration of AI to streptozotocin diabetic rats significantly decreased the plasma glucose levels after 1 week of treatment (112+/-14.4 mg/dl at 1 week vs 337+/-9.3 mg/dl at the baseline values, (P<0.001). It continuously decreased thereafter and showed a rapid normalisation after 1 week of AI treatment. It is concluded that these results demonstrated that the water extract of the whole plant of AI possess a strong hypoglycaemic effect in diabetic rats, and support therefore, its traditional use in diabetes mellitus control.

Analysis of steroidal lipids by gas and liquid chromatography

This article describes the most commonly used procedures and recent laboratory methodologies using gas and liquid chromatography developed for separation and quantitation of non-saponifiable steroidal lipids from clinical (human) studies, edible fats and oils or fatty foods.

Phytoecdysteroids: biological aspects

Phytoecdysteroids are a family of about 200 plant steroids related in structure to the invertebrate steroid hormone 20-hydroxyecdysone. Typically, they are C27, C28 or C29 compounds possessing a 14alpha-hydroxy-7-en-6-one chromophore and A/B-cis ring fusion (5beta-H). In the present review, the distribution, biosynthesis, biological significance and potential applications of phytoecdysteroids are summarised.