Substrate specificity in vivo and in vitro in the formation of stilbenes. Biosynthesis of rhaponticin

The Effect of External Treatment of Arabidopsis thaliana with Plant-Derived Stilbene Compounds on Plant Resistance to Abiotic Stresses

Stilbenes are a group of plant phenolic secondary metabolites, with trans-resveratrol (3,5,4'-trihydroxy-trans-stilbene) being recognized as the most prominent and studied member. Stilbenes have a great potential for use in agriculture and medicine, as they have significant activities against plant pathogens and have valuable beneficial effects on human health. In this study, we analyzed the effects of direct application of stilbenes, stilbene precursor, and stilbene-rich extract solutions to the plant foliar surface for increasing the resistance of Arabidopsis thaliana to various abiotic stresses (heat, cold, drought, and soil salinity). Exogenous treatment of A. thaliana with stilbenes (trans-resveratrol, piceid, and spruce bark extract) and phenolic precursor (p-coumaric acid or CA) during germination resulted in considerable growth retardation of A. thaliana plants: a strong delay in the root and stem length of 1-week-old seedlings (in 1.3-4.5 fold) and rosette diameter of 1-month-old plants (in 1.2-1.8 fold), while the 2-month-old treated plants were not significantly different in size from the control. Plant treatments with stilbenes and CA increased the resistance of A. thaliana to heat and, to a lesser extent, to soil salinity (only t-resveratrol and spruce extract) to drought (only CA), while cold resistance was not affected. Plant treatments with stilbenes and CA resulted in a significant increase in plant resistance and survival rates under heat, with plants showing 1.5-2.3 times higher survival rates compared to untreated plants. Thus, exogenous stilbenes and a CA are able to improve plant survival under certain abiotic stresses via specific activation of the genes involved in the biosynthesis of auxins, gibberellins, abscisic acid, and some stress-related genes. The present work provides new insights into the application of stilbenes to improve plant stress tolerance.

VqMAPK3/VqMAPK6, VqWRKY33, and VqNSTS3 constitute a regulatory node in enhancing resistance to powdery mildew in grapevine

Grapevine powdery mildew is caused by Erysiphe necator, which seriously harms grape production in the world. Stilbene synthase makes phytoalexins that contribute to the resistance of grapevine against powdery mildew. A novel VqNSTS3 was identified and cloned from Chinese wild Vitis quinquangularis accession Danfeng-2. The novel VqNSTS3 was transferred into susceptible 'Thompson Seedless' by Agrobacterium-mediated transformation. The transgenic plants showed resistance to the disease and activated other resistance-related genes. VqNSTS3 expression in grapevine is regulated by VqWRKY33, and which binds to TTGACC in the VqNSTS3 promoter. Furthermore, VqWRKY33 was phosphorylated by VqMAPK3/VqMAPK6 and thus led to enhanced signal transduction and increased VqNSTS3 expression. ProVqNSTS3::VqNSTS3-GFP of transgenic VqNSTS3 in Arabidopsis thaliana was observed to move to and wrap the pathogen's haustoria and block invasion by Golovinomyces cichoracearum. These results demonstrate that stilbene accumulation of novel VqNSTS3 of the Chinese wild Vitis quinquangularis accession Danfeng-2 prevented pathogen invasion and enhanced resistance to powdery mildew. Therefore, VqNSTS3 can be used in generating powdery mildew-resistant grapevines.

Protection and Mitigation by Resveratrol of DNA Damage Induced in Irradiated Human Lymphocytes In Vitro

The aim of this study was to examine the protective and/or mitigative properties of resveratrol (RSV) administered before or after irradiation of human lymphocytes in vitro. The isolated lymphocytes were incubated for 1 h with resveratrol, at doses of 0.1 (lowest), 0.5 (medium) or 1 (highest) mM/ml: 1 h before; immediately before; immediately after irradiation; and 1 h after irradiation with 0.5, 1 and 2 Gy. The degree of DNA damage was evaluated by Comet Assay. Treatment of human lymphocytes with resveratrol 1 h before or immediately after radiation exposure showed protection from radiation-induced DNA damage. However, 1 Gy irradiation + 1 mM/ml RSV, and 2 Gy irradiation + 0.5 and 1 mM/ml RSV 1 h before irradiation did not provide the same protection. Significant dose-dependent reduction of the level of DNA damage was observed after application of RSV immediately postirradiation or 1 h postirradiation. The reduction in DNA damage was the highest at the 0.1 dose of resveratrol. Our results lead to the conclusion that resveratrol may act both as a radioprotector as well as a radiomitigator. Resveratrol at the lowest (0.5 mM/ml) dose was more effective when combined with 0.5 and 1 Gy doses of radiation.

Potential Associations among Bioactive Molecules, Antioxidant Activity and Resveratrol Production in Vitis vinifera Fruits of North America

Grapes (Vitis vinifera L.) are rich in bioactive molecules contributing to health benefits. Consumption of grapes is linked to reduced incidence of cardiovascular diseases. Studies on table grape cultivars are limited although much attention in research was focused on the wine industry. Bioactive effects of grapes as anti-inflammatory, anticarcinogenic, cardioprotective, vasorelaxant, phytoestrogenic and neuroprotective have also been reported. For example, resveratrol is a natural food ingredient present in grapes, with high antioxidant potential. Here we conducted an exploratory study to investigate bioactive molecules, antioxidant activity and the association between constitutive stilbene synthase (STS) gene expression and the resveratrol biosynthesis in selected table grape varieties in North America. The phenolic compounds, fatty acid composition and antioxidant activity of four grape varieties were compared. Red Globe variety was rich in unsaturated fatty acids as well as phenolic compounds such as caffeic acid, quercetin and resveratrol. Meanwhile, the constitutive expression of grape stilbene synthase gene was higher in Flame and Autumn Royal where resveratrol content of these cultivars was relatively low compared to the Red Globe variety. This study shows the potential links in grape antioxidant activity and resveratrol production, but more studies are necessary to show the association.

Rhaponticin contained Rheum officinale root extract improved Postmenopause symptom of Ovariectomized Rat

Postmenopausal women have decreased levels of the hormone estrogen. Reduced estrogen levels will often involve many symptoms that reduced quality of life. This research aims to analyze the effects of Rheum officinale root extract on postmenopausal model rats. To this end, thirty rats underwent ovariectomy (OVX) surgery and six rats were operated without having their ovaries removed. The OVX was confirmed by body weight–uterus weight ratio and a vaginal swab. Six groups of the rats were performed: SHAM group and negative control groups are given vehicle; the positive control was assigned tamoxifen; and the extract has been given three doses 7, 35, and 175 mg/200 g BW, respectively, for 30 days. The calcium content of bone ash was measured using atomic absorption spectrophotometer. Blood pressure was evaluated using CODA^®, and the metabolites in the blood were assessed using gas chromatography–mass spectrometry (MS) and high-performance liquid chromatography. As a result, using ultra-performance liquid chromatography (UPLC)-MS, we found that the extract's major component was rhaponticin and its metabolites. The bone calcium levels increased with increasing doses of the extract. In the OVX group, the bone calcium content was decreased significantly 51.56% ± 8.9% g compared with the SHAM group 62.97% ±5.6% g, and the administration of Rheum extract could restore the calcium content of the bone to become 69.27% ± 3.8% g. From the above data, we concluded that Rheum root extracts contain astrigin, rhaponticin, rhapontigenin, and desoxyrhaponticin. Rheum root extract could improve calcium content and lipid profiles of OVX rats by stimulation osteoblastogenesis. Rheum root extracts could control the blood pressure of OVX rats by reducing lipid profiles.

Impact of Environmental Factors on Stilbene Biosynthesis

Stilbenes are a small family of polyphenolic secondary metabolites that can be found in several distantly related plant species. These compounds act as phytoalexins, playing a crucial role in plant defense against phytopathogens, as well as being involved in the adaptation of plants to abiotic environmental factors. Among stilbenes, trans-resveratrol is certainly the most popular and extensively studied for its health properties. In recent years, an increasing number of stilbene compounds were subjected to investigations concerning their bioactivity. This review presents the most updated knowledge of the stilbene biosynthetic pathway, also focusing on the role of several environmental factors in eliciting stilbenes biosynthesis. The effects of ultraviolet radiation, visible light, ultrasonication, mechanical stress, salt stress, drought, temperature, ozone, and biotic stress are reviewed in the context of enhancing stilbene biosynthesis, both in planta and in plant cell and organ cultures. This knowledge may shed some light on stilbene biological roles and represents a useful tool to increase the accumulation of these valuable compounds.

Solvation effect and binding of rhaponticin with iron: a spectroscopic and DFT/TDDFT study

In this article, both experimental and computational methods are employed to investigate the photophysics of rhaponticin (RH). The bathochromic shift was observed in absorption and fluorescence spectra with increasing solvent polarity, which implied that the charge transition of RH involved was π → π*. The results showed that RH possess strong intramolecular charge transfer (ICT), and the most important parameter to characterize the photophysical behavior of RH is the intermolecular hydrogen bonding ability of the solvent. The hydrogen bonding effect occurred at the localized electron-acceptor oxygen at the glycoside bond. Density functional theory (DFT) and time dependent density functional theory (TDDFT) were used to obtain the most stable structure, electronic excitation energy, dipole moments and charge distribution. The result was found to be 2.23 and 3.67 D in ground state and excited state respectively. Fluorescence quenching of RH owing to the photoinduced electron transfer (PET) is facilitated in alkaline media. The pK_a value of RH was 6.39, which defined RH as a highly efficient “off–on” switcher. The effect of different metal ions on the fluorescence spectra of RH was also investigated, and the fluorescence quenching of RH depended on the nature of ions. The best performance was accomplished for binding with the Fe³⁺ ion. The interactions of RH with the Fe³⁺ ion were studied by FT-IR and HPLC, and the binding parameter was calculated by the Stern–Volmer equation. The results obtained reveal the binding activity of RH can make this a candidate as a good source of new agents for thalassemic patients.

In this article, both experimental and computational methods are employed to investigate the photophysics of rhaponticin (RH).

Salicylic acid induces alterations in the methylation pattern of the VaSTS1, VaSTS2, and VaSTS10 genes in Vitis amurensis Rupr. cell cultures

Salicylic acid (SA) treatment selectively reduced the cytosine DNA methylation of stilbene synthase ( STS ) genes and stimulated resveratrol production in cell cultures of Vitis amurensis. The effect of salicylic acid (SA) on plant growth, flowering time, and fruit number is known to correlate with the level of DNA methylation, while the potential correlation between SA-induced changes in DNA methylation and biosynthesis of secondary metabolites has not been studied. Trans-resveratrol, a naturally occurring plant phenol, has been reported to exhibit a wide range of valuable biological and pharmacological properties. In this study, cell cultures of Vitis amurensis capable of producing t-resveratrol were used as a model system to study whether the SA-induced increase in t-resveratrol production is associated with changes in DNA methylation of stilbene synthase (STS) genes. T-resveratrol is synthesized via the phenylpropanoid pathway, in which STS genes are the key enzymes. Treatment of V. amurensis callus cultures with SA significantly increased t-resveratrol production and the expression of certain STS genes (e.g., VaSTS2 and VaSTS10). A marked decrease in the methylation of the VaSTS2 and VaSTS10 genes in response to SA was demonstrated using bisulfite sequencing, while no considerable changes were detected in the methylation of VaSTS1, a constitutively and highly expressed STS gene. The obtained results show that SA treatment selectively reduced cytosine methylation of VaSTS genes. The data suggest that selective DNA demethylation of particular STS genes could be necessary for the activation of t-resveratrol biosynthesis in response to SA. This finding provides an insight into the mechanism of SA action and biosynthesis of secondary metabolites in plant cells.

Involvement of DNA methylation in the regulation of STS10 gene expression in Vitis amurensis

DNA methylation is known to play an important role in various developmental processes and defense mechanisms in plants and other organisms. However, it is not known whether DNA methylation is implicated in the genetic regulation of plant secondary metabolism, including resveratrol biosynthesis. Resveratrol is a naturally occurring polyphenol that is present in grapes, peanuts, and other plant sources, and it exhibits a wide range of valuable biologically active properties. The transformation of the wild-growing grape Vitis amurensis with the oncogene rolB from Agrobacterium rhizogenes has been demonstrated to considerably increase resveratrol production. To investigate whether DNA methylation regulates resveratrol biosynthesis, we treated both rolB transgenic and empty vector control V. amurensis cell cultures with the DNA demethylation agent 5-azacytosine (azaC). The azaC treatment significantly increased stilbene synthase 10 gene (VaSTS10) expression and resveratrol content in the V. amurensis cell cultures. Using bisulfite sequencing, we examined the methylation status of VaSTS10 in cell cultures under normal conditions and after azaC treatment. Both the promoter and 3'-end of the protein coding region of the VaSTS10 gene were hypermethylated (54-67 %) in the control cell culture. The rolB transgenic cell culture had high levels of resveratrol and lower hypermethylation levels of the VaSTS10 gene (20-47 %). The azaC treatment resulted in reduction in the DNA methylation levels in the promoter and coding regions of the VaSTS10 gene in both cell cultures. These data suggest that the DNA methylation may be involved in the control of resveratrol biosynthesis via the regulation of STS genes expression.

A simple and rapid spectrofluorimetric method for determining the pharmacokinetics and metabolism of rhaponticin in rat plasma, feces and urine using a cerium probe

Rhaponticin (RH) demonstrates a variety of pharmacological activities, including antitumor, antithrombotic and antioxidant effects. It is essential to establish a simple, rapid and reliable analytical method for determining the pharmacokinetics of RH. A simple cerium ion (Ce(3+)) probe method was developed and validated to determine RH in rat plasma, feces and urine. The fluorescence intensities of the cerium ion (Ce(3+)) were quenched by addition of RH, along with a remarkable red shift. Spectral data revealed that fluorescence quenching of Ce(3+) by RH was due to the formation of a Ce(3+)-RH complex. Using to the Stern-Volmer equation, the binding parameters for interactions between Ce(3+) and RH were obtained. Based on these, a rapid and simple spectrofluorimetric method was developed to determine the metabolism and pharmacokinetics of RH using a Ce(3+) probe. The assay was linear over the concentration range of 0.11-9.52, 0.25-8.87 and 0.18-9.10 μM for plasma, feces and urine, respectively and RH recoveries were found to be 98.24 ± 0.8, 97.78 ± 1.2 and 97.54 ± 0.8% for plasma, feces and urine, respectively. The relative standard deviations were < 9.5%. The spectrofluorimetric method was simple and rapid for quantitative determination of RH and its metabolism, and was affordable for most laboratories because of the fluorescence spectroscopy and low equipment cost. These pharmacokinetic, bioavailability and metabolism studies of RH will provide helpful information for the development of suitable dosage forms and clinical references on rational administration.

Studies on the binding of rhaponticin with human serum albumin by molecular spectroscopy, modeling and equilibrium dialysis

Rhaponticin (RHA) possesses a variety of pharmacological activities including potent antitumor, antitumor-promoting, antithrombotic, antioxidant and vasorelaxant effects. In the solvation effect, RHA exhibited bathochromic shift in emission spectra with the increasing solvent polarity. The binding between RHA and HSA was investigated by molecular spectroscopy combining with modeling and equilibrium dialysis. Fluorescence data showed that the quenching of HSA by RHA was result of forming the complex of RHA-HSA. According to Stern-Volmer equation, the binding parameters between RHA and HSA were determined. The enthalpy change (ΔH) and entropy change (ΔS) were calculated to be -2.75kJmol(-1) and 1.58Jmol(-1)K(-1), indicating that the hydrogen bonds and hydrophobic interactions played a dominant role in the binding. The conformational investigation revealed the α-helical structure was decreased and the polypeptides of HSA were slightly folded upon the addition of RHA. The effect of common ions on the binding between RHA and HSA was also investigated. Furthermore, the result of warfarin displacement site indicated that RHA could bind to the site I of HSA, which was in agreement with the molecular modeling. When excitation wavelength was set at 260 or 355nm, RHA exhibited a fluorescence peak at 390nm, based on which, a simple and rapid fluorimetric method was developed and validated to determine RHA in the equilibrium dialysis. Calibration curves of RHA were linear over the concentration range of 1.1-15.0μM with the detection limits of 0.03μM. Examination of protein binding ability showed that RHA with 8.0μM concentrations in HSA achieved the percent of bound 82.3±2.5%.

Biosynthesis of the major tetrahydroxystilbenes in spruce, astringin and isorhapontin, proceeds via resveratrol and is enhanced by fungal infection

Stilbenes are dibenzyl polyphenolic compounds produced in several unrelated plant families that appear to protect against various biotic and abiotic stresses. Stilbene biosynthesis has been well described in economically important plants, such as grape (Vitis vinifera), peanut (Arachis hypogaea), and pine (Pinus species). However, very little is known about the biosynthesis and ecological role of stilbenes in spruce (Picea), an important gymnosperm tree genus in temperate and boreal forests. To investigate the biosynthesis of stilbenes in spruce, we identified two similar stilbene synthase (STS) genes in Norway spruce (Picea abies), PaSTS1 and PaSTS2, which had orthologs with high sequence identity in sitka (Picea sitchensis) and white (Picea glauca) spruce. Despite the conservation of STS sequences in these three spruce species, they differed substantially from angiosperm STSs. Several types of in vitro and in vivo assays revealed that the P. abies STSs catalyze the condensation of p-coumaroyl-coenzyme A and three molecules of malonyl-coenzyme A to yield the trihydroxystilbene resveratrol but do not directly form the dominant spruce stilbenes, which are tetrahydroxylated. However, in transgenic Norway spruce overexpressing PaSTS1, significantly higher amounts of the tetrahydroxystilbene glycosides, astringin and isorhapontin, were produced. This result suggests that the first step of stilbene biosynthesis in spruce is the formation of resveratrol, which is further modified by hydroxylation, O-methylation, and O-glucosylation to yield astringin and isorhapontin. Inoculating spruce with fungal mycelium increased STS transcript abundance and tetrahydroxystilbene glycoside production. Extracts from STS-overexpressing lines significantly inhibited fungal growth in vitro compared with extracts from control lines, suggesting that spruce stilbenes have a role in antifungal defense.

Treatment of menopausal symptoms by an extract from the roots of rhapontic rhubarb: the role of estrogen receptors

A dry extract from the roots of rhapontic rhubarb (extract Rheum rhaponticum (L.); ERr) has been commercially available in Germany for over two decades to treat menopausal symptoms. However, the molecular basis of its clinical effectiveness remains obscure. This article reviews the in vitro and in vivo data of its estrogenic actions, particularly those mediated by estrogen receptor-beta (ERbeta).

Effects of the special extract ERr 731 from Rheum rhaponticum on estrogen-regulated targets in the uterotrophy model of ovariectomized rats

A recent clinical study with a two-year application of the extract ERr 731 from Rheum rhaponticum demonstrated its efficacy and potentially suggested it safety regarding unwanted endometrial side effects. The aim of the present study is to provide experimental proof for the latter observation in a preclinical experimental animal model by assessing dose-dependent effects of ERr 731 - either alone or in combination with estradiol (E2) - on growth and proliferation in the uterus of ovariectomized (ovx) rats. ERr 731 was given in a dose corresponding to human therapeutic application and additionally in three pharmacologically relevant doses. In addition to uterine wet weight, this study examines the effects of ERr 731 on the uterine mRNA expression of the proliferation marker Ki67, proliferating cell nuclear antigen (PCNA), insulin-like growth factor-1 (IGF-1), type 1 IGF receptor (IGF-1R), the two estrogen receptor (ER) subtypes alpha and beta (ERalpha and ERbeta) and the estrogen-responsive gene complement C3 (C3). ERr 731 did neither stimulate an uterotrophic response in the uterotrophic assay with ovx rats nor stimulate or modulate the expression of genes associated with proliferation. In combination with E2, ERr 731 reduced the E2-induced uterine growth stimulation. These observations were further substantiated by the expression pattern of genes related to proliferation control, in view of the fact that the E2-induced elevation of Ki67 mRNA and PCNA protein levels in the uterus were counteracted by simultaneous treatment of the animals with ERr 731. In conclusion, the experimental findings presented here provide further evidence for the safety of ERr 731 towards unwanted uterine and endometrial proliferative events in response to ERr 731 and support observations from recent clinical trials.

Longevity nutrients resveratrol, wines and grapes

A mild-to-moderate wine drinking has been linked with reduced cardiovascular, cerebrovascular, and peripheral vascular risk as well as reduced risk due to cancer. The reduced risk of cardiovascular disease associated with wine drinking is popularly known as French Paradox. A large number of reports exist in the literature indicating that resveratrol present in wine is primarily responsible for the cardioprotection associated with wine. Recently, resveratrol was shown to extend life span in yeast through the activation of longevity gene SirT1, which is also responsible for the longevity mediated by calorie restriction. This review summarizes the reports available on the functional and molecular biological aspects of resveratrol, wine and grapes in potentiating the longevity genes.

Trans-resveratrol alone and hydroxystilbenes of rhubarb (Rheum rhaponticum L.) root reduce liver damage induced by chronic ethanol administration: a comparative study in mice

The hepatoprotective effects and pharmacokinetics of trans-resveratrol and hydroxystilbenes of the garden rhubarb (Rheum rhaponticum L., R. rhaponticum) root ethanol extract were studied. Ethanol was administered to male BALB/c mice for 35 days in an inhalation chamber. During this time vehicle, trans-resveratrol (20 mg/kg per day) or R. rhaponticum extract was intraperitoneally (i.p.) administered and mice were sacrificed for the collection of liver and blood. In an additional experiment, the level of parent compounds and metabolites was estimated in the blood after acute i.p. administration of trans-resveratrol or R. rhaponticum extract. The levels of hydroxystilbenes, their metabolites and fatty acid oxy-metabolites (oxylipins) were studied by LC-tandem DAD-MS/MS. Ethanol induced hepatotoxicity, as evidenced by histological changes and accumulation of oxylipins in the blood. Both trans-resveratrol and R. rhaponticum extract reduced the extent of these changes. The pharmacokinetics of trans-resveratrol was characterized by a rapid removal from the blood and metabolism to sulfates and glucuronides. After the administration of R. rhaponticum extract, in addition to trans-resveratrol glucoside and its metabolites, several other hydroxystilbenes were found. Inhibition of oxidation of polyunsaturated fatty acids is proposed as a basis of the hepatoprotective effect of both trans-resveratrol and R. rhaponticum extract.

Polyphenolic composition of roots and petioles of Rheum rhaponticum L

INTRODUCTION

Various species of the genus Rheum (Polygonaceae) are known for their high content of medicinally important hydroxyanthraquinones. However, little information is available concerning the polyphenolic composition of garden or dietary rhubarb Rheum rhaponticum L. (R. rhaponticum).

OBJECTIVE

Determination of further polyphenols in the roots and petioles of R. rhaponticum.

METHODOLOGY

The dried plant material was extracted with 10-fold excess (v/w) of methanol and subsequently diluted five times with methanol-water (1:1) and analysed by reversed-phase liquid chromatography using tandem UV-photodiode array and mass selective detection (RP-HPLC-UV-ESI/MS(2)). Polyphenols were identified using either HPLC-ESI/MS(2) data obtained for respective commercial standards or by comparison of a parent ion fragmentation picture with the respective MS(2 )spectrum from the literature.

RESULTS

The roots of R. rhaponticum were very rich in various hydroxystilbenes and contained four main substance groups--derivatives of trans-piceatannol, trans-resveratrol, trans-rhapontigenin and trans-deoxyrhapontigenin. Additionally, pterostilbene acetylglucosides and a number of hydroxyanthraquinones and their glycosides were identified in the root samples. The profile of polyphenols in the petioles of R. rhaponticum was similar to that of the roots but the content of individual substances was remarkably lower. The petioles of the R. rhaponticum additionally contained significant amounts of derivatives of flavonol quercetin, which is a good antioxidant.

CONCLUSION

The study has shown that roots of R. rhaponticum contain a wide variety of hydroxystilbenes and deserve further consideration as a source of medicinally interesting compounds.

Introducing N-glycans into natural products through a chemoenzymatic approach

The present study describes an efficient chemoenzymatic method for introducing a core N-glycan of glycoprotein origin into various lipophilic natural products. It was found that the endo-beta-N-acetylglucosaminidase from Arthrobactor protophormiae (Endo-A) had broad substrate specificity and can accommodate a wide range of glucose (Glc)- or N-acetylglucosamine (GlcNAc)-containing natural products as acceptors for transglycosylation, when an N-glycan oxazoline was used as a donor substrate. Using lithocholic acid as a model compound, we have shown that introduction of an N-glycan could be achieved by a two-step approach: chemical glycosylation to introduce a monosaccharide (Glc or GlcNAc) as a handle, and then Endo-A catalyzed transglycosylation to accomplish the site-specific N-glycan attachment. For those natural products that already carry terminal Glc or GlcNAc residues, direct enzymatic transglycosylation using sugar oxazoline as the donor substrate was achievable to introduce an N-glycan. It was also demonstrated that simultaneous double glycosylation could be fulfilled when the natural product contains two Glc residues. This chemoenzymatic method is concise, site-specific, and highly convergent. Because N-glycans of glycoprotein origin can serve as ligands for diverse lectins and cell-surface receptors, introduction of a defined N-glycan into biologically significant natural products may bestow novel properties onto these natural products for drug discovery and development.

Long-term toxicity studies in dogs support the safety of the special extract ERr 731 from the roots of Rheum rhaponticum

The special extract ERr 731 from the roots of rhapontic rhubarb has been regularly prescribed for women with menopausal symptoms since 1993. As its constituents belong to the class of natural hydroxystilbenes, concerns have been raised about possible health risks similar to those known for the estrogenic diethylstilbestrol. To demonstrate the safety of the medical use of ERr 731, the extract was tested in long-term toxicity studies in dogs. In two independent studies, male and female beagle dogs were treated with 100, 300 and 1000 mg ERr 731/kg body weight (bw)/day and observed for 4 and 13 weeks followed by recovery periods. A histopathological examination of a full set of organs of all animals was examined. In both studies, all animals survived the scheduled treatment and recovery periods. The administration of ERr 731 resulted in increased incidences of feces with white particles due to an incomplete absorption of the extract. In the 13-week study, a slight decrease in glucose levels was recorded in both sexes at 1000 mg/kg bw/day. All other clinical changes were marginal and not related to ERr 731. Importantly, there was no increase in weight of organs of the genital tract due to ERr 731 intake. Based on these results, the no-observed-adverse-effect-level is 1000 mg/kg bw/day. No pathological findings where detected following ERr 731 treatment demonstrating that the toxicological risk for women taking ERr 731 regularly is extremely low.

Phytoalexins from the Vitaceae: biosynthesis, phytoalexin gene expression in transgenic plants, antifungal activity, and metabolism

Resistance of plants to infection by phytopathogenic microorganisms is the result of multiple defense reactions comprising both constitutive and inducible barriers. In grapevine, the most frequently observed and best characterized defense mechanisms are the accumulation of phytoalexins and the synthesis of PR-proteins. Particular attention has been given here to stilbene phytoalexins produced by Vitaceae, specifically, their pathway of biosynthesis (including stilbene phytoalexin gene transfer experiments to other plants) and their biological activity together with fungal metabolism.

9,10-Dihydrophenanthrenes as phytoalexins of Orchidaceae. Biosynthetic studies in vitro and in vivo proving the route from L-phenylalanine to dihydro-m-coumaric acid, dihydrostilbene and dihydrophenanthrenes

Hydroxy derivatives of 9,10-dihydrophenanthrenes, orchinol and hircinol, were isolated from bulbs of Orchidaceae which had been induced to accumulate phytoalexins. Incorporation of radioactive precursors, L-phenylalanine and various hydroxycinnamic acids, has been investigated by feeding experiments in vivo. m-Coumaric acid and dihydro-m-coumaric acid were found to be efficiently incorporated into the dihydrophenanthrene derivatives. Dihydro-m-coumaric acid was not only converted into the dihydrophenanthrenes but was also formed from L-phenylalanine in the same tissue; it was thus proved to be an intermediate. The role of dihydro-m-coumaric acid was substantiated by studies in vitro. An active stilbene synthase was detected in enzyme preparations from induced orchid bulbs and assayed with different CoA esters. The enzyme, characterized on the basis of its substrate specificity, selectively converted dihydro-m-coumaroyl-CoA plus malonyl-CoA into 3,3',5-trihydroxybibenzyl. The role of 3,3',5-trihydroxybibenzyl as physiological intermediate was further corroborated by investigations with intact plants. Both its formation from phenylpropanoids and its conversion into orchinol was demonstrated. The data provided evidence for a biosynthetic sequence originating from L-phenylalanine and leading to 9,10-dihydrophenanthrenes via m-coumaric acid, dihydro-m-coumaric acid, and 3,3',5-trihydroxybibenzyl.

Cultured cells of Arachis hypogaea susceptible to induction of stilbene synthase (resveratrol-forming)

Callus cultures were established from cotyledons of Arachis hypogaea. The cultured cells were shown to produce stilbene synthase (resveratrol-forming) if the cells were irradiated with 254 nm UV light. The lag period after which the stilbene synthase activity appeared was similar for cultured cells and intact cotyledons.

Coordinate induction by UV light of stilbene synthase, phenylalanine ammonia-lyase and cinnamate 4-hydroxylase in leaves of vitaceae

A stilbene synthase catalyzing the formation of resveratrol from 4-hydroxycinnamoyl-CoA and malonyl-CoA was found in the leaves of several Vitaceae. This stilbene synthase and two other enzymes functioning on the route from phenylalanine to stilbenes were induced concurrently upon irradiation of the leaves with UV light. With leaves of Cissus antarctica, an increase of stilbene synthase activity, more than hundred-fold, was observed with a maximum appearing 15 h after the induction with UV light.