Neuroprotection of rhubarb extract against cerebral ischaemia-reperfusion injury via the gut-brain axis pathway

BACKGROUND

The gut-brain axis (GBA) plays a central role in cerebral ischaemia-reperfusion injury (CIRI). Rhubarb, known for its purgative properties, has demonstrated protective effects against CIRI. However, it remains unclear whether this protective effect is achieved through the regulation of the GBA.

AIM

This study aims to investigate the mechanism by which rhubarb extract improves CIRI by modulating the GBA pathway.

METHODS

We identified the active components of rhubarb extract using LC-MS/MS. The model of middle cerebral artery occlusion (MCAO) was established to evaluate the effect of rhubarb extract. We conducted 16S rDNA sequencing and untargeted metabolomics to analyze intestinal contents. Additionally, we employed HE staining, TUNEL staining, western blot, and ELISA to assess intestinal barrier integrity. We measured the levels of inflammatory cytokines in serum via ELISA. We also examined blood-brain barrier (BBB) integrity using Evans blue (EB) penetration, transmission electron microscopy (TEM), western blot, and ELISA. Neurological function scores and TTC staining were utilized to evaluate neurological outcomes.

RESULTS

We identified twenty-six active components in rhubarb. Rhubarb extract enhanced α-diversity, reduced the abundance of Enterobacteriaceae, and partially rectified metabolic disorders in CIRI rats. It also ameliorated pathological changes, increased the expressions of ZO-1, Occludin, and Claudin 1 in the colon, and reduced levels of LPS and d-lac in serum. Furthermore, it lowered the levels of IL-1β, IL-6, IL-10, IL-17, and TNF-α in serum. Rhubarb extract mitigated BBB dysfunction, as evidenced by reduced EB penetration and improved hippocampal microstructure. It upregulated the expressions of ZO-1, Occludin, Claudin 1, while downregulating the expressions of TLR4, MyD88, and NF-κB. Similarly, rhubarb extract decreased the levels of IL-1β, IL-6, and TNF-α in the hippocampus. Ultimately, it reduced neurological function scores and cerebral infarct volume.

CONCLUSION

Rhubarb effectively treats CIRI, potentially by inhibiting harmful bacteria, correcting metabolic disorders, repairing intestinal barrier function, alleviating BBB dysfunction, and ultimately improving neurological outcomes.

Herb pair of Rhubarb-Astragalus mitigates renal interstitial fibrosis through downregulation of autophagy via p38-MAPK/TGF-β1 and p38-MAPK/smad2/3 pathways

BACKGROUND

Chronic kidney disease (CKD) has a high incidence and poor prognosis; however, no effective treatment is currently available. Our previous study found that the improvement effect of the herb pair of Rhubarb-Astragalus on CKD is likely related to the inhibition of the TGF-β1/p38-MAPK pathway. In the present study, a p38-MAPK inhibitor was used to further investigate the inhibitory effect of Rhubarb-Astragalus on the TGF-β1/p38-MAPK pathway and its relationship with autophagy.

METHODS

A rat model of unilateral ureteral obstruction (UUO) was established, and a subgroup of rats was administered Rhubarb-Astragalus. Renal function and renal interstitial fibrosis (RIF) were assessed 21 d after UUO induction. In vitro, HK-2 cells were treated with TGF-β1 and a subset of cells were treated with Rhubarb-Astragalus or p38-MAPK inhibitor. Western blotting, immunohistochemistry, and qRT-PCR analyses were used to detect the relevant protein and mRNA levels. Transmission electron microscopy was used to observe autophagosomes.

RESULTS

Rhubarb-Astragalus treatment markedly decreased the elevated levels of blood urea nitrogen, serum creatinine, and urinary N-acetyl-β-D-glucosaminidase; attenuated renal damage and RIF induced by UUO; and reduced the number of autophagosomes and lysosomes in UUO-induced renal tissues. Additionally, Rhubarb-Astragalus reduced the protein and mRNA levels of α-SMA, collagen I, LC3, Atg3, TGF-β1, p38-MAPK, smad2/3, and TAK1 in renal tissues of UUO rats. Rhubarb-Astragalus also reduced protein and mRNA levels of these indicators in vitro. Importantly, the effect of the p38-MAPK inhibitor was similar to that of Rhubarb-Astragalus.

CONCLUSIONS

Rhubarb-Astragalus improves CKD possibly by downregulating autophagy via the p38-MAPK/TGF-β1 and p38-MAPK/smad2/3 pathways.

Topical rhubarb charcoal-crosslinked chitosan/silk fibroin sponge scaffold for the repair of diabetic ulcers improves hepatic lipid deposition in db/db mice via the AMPK signalling pathway

BACKGROUND

Type 2 diabetes mellitus (T2DM) is closely linked to metabolic syndrome, characterised by insulin resistance, hyperglycaemia, abnormal lipid metabolism, and chronic inflammation. Diabetic ulcers (DUs) comprise consequential complications that arise as a result of T2DM. To investigate, db/db mice were used for the disease model. The findings demonstrated that a scaffold made from a combination of rhubarb charcoal-crosslinked chitosan and silk fibroin, designated as RCS/SF, was able to improve the healing process of diabetic wounds in db/db mice. However, previous studies have primarily concentrated on investigating the impacts of the RSC/SF scaffold on wound healing only, while its influence on the entire body has not been fully elucidated.

MATERIAL AND METHODS

The silk fibroin/chitosan sponge scaffold containing rhubarb charcoal was fabricated in the present study using a freeze-drying approach. Subsequently, an incision with a diameter of 8 mm was made on the dorsal skin of the mice, and the RCS/SF scaffold was applied directly to the wound for 14 days. Subsequently, the impact of RCS/SF scaffold therapy on hepatic lipid metabolism was assessed through analysis of serum and liver biochemistry, histopathology, quantitative real-time PCR (qRT-PCR), immunohistochemistry, and Western blotting.

RESULTS

The use of the RCS/SF scaffold led to an enhancement in the conditions associated with serum glucolipid metabolism in db/db mice. An assessment of hepatic histopathology further confirmed this enhancement. Additionally, the qRT-PCR analysis revealed that treatment with RCS/SF scaffold resulted in the downregulation of genes associated with fatty acid synthesis, fatty acid uptake, triglyceride (TG) synthesis, gluconeogenesis, and inflammatory factors. Moreover, the beneficial effect of the RCS/SF scaffold on oxidative stress was shown by assessing antioxidant enzymes and lipid peroxidation. Additionally, the network pharmacology analysis verified that the adenosine monophosphate-activated protein kinase (AMPK) signalling pathway had a vital function in mitigating non-alcoholic fatty liver disease (NAFLD) by utilizing R. officinale. The measurement of AMPK, sterol regulatory element binding protein 1 (SREBP1), fatty acid synthase (FASN), and acetyl CoA carboxylase (ACC) gene and protein expression provided support for this discovery. Furthermore, the molecular docking investigations revealed a robust affinity between the active components of rhubarb and the downstream targets of AMPK (SREBP1 and FASN).

CONCLUSION

By regulating the AMPK signalling pathway, the RCS/SF scaffold applied topically effectively mitigated hepatic lipid accumulation, decreased inflammation, and attenuated oxidative stress. The present study, therefore, emphasises the crucial role of the topical RCS/SF scaffold in regulating hepatic lipid metabolism, thereby confirming the concept of "external and internal reshaping".

Rhubarb: A novel model plant to study the conundrum of calcium oxalate synthesis

The study investigated calcium oxalate (CaOx) crystal composition, accumulation, synthesis, and degradation in five rhubarb species from the North-Western Indian Himalayas. Techniques like optical and scanning electron microscopy (SEM), SEM-energy-dispersive X-ray spectroscopy (SEM-EDS), inductively coupled plasma-optical emission spectrometry (ICP-OES), X-ray diffraction spectroscopy (XRD), and real-time (qRT-PCR) expression analysis of strategic genes were used to understand the processes of oxalate synthesis and precipitation. Results showed crystals tend to accumulate around vascular bundles in all species, irrespective of size, indicating a consistent pattern. Crystal synthesis and accumulation were stress-driven, linked to substrate composition, and in planta soluble oxalate and calcium levels, paralleling oxalate precursors. Based on their availability, CaOx crystals precipitated heavy metals mostly associated with its weddellite form. Crystal content correlated positively with mRNA levels of calcium/oxalate/ascorbate-related and stress-responsive genes, and negatively with oxalate oxidation/decarboxylation genes. CaOx crystals were suggested as potential biominerals for addressing heavy metal stress in agriculture.

Transcriptome profiles of yellowish-white and fuchsia colored flowers in the Rheum palmatum complex reveal genes related to color polymorphism

Flower color variation is ubiquitous in many plant species, and several studies have been conducted to elucidate the underlying molecular mechanism. There are two flower color variants (yellowish-white and fuchsia) in the Rheum palmatum complex, however, few studies have investigated this phenomenon. Here, we used transcriptome sequencing of the two color variants to shed light on the molecular and biochemical basis for these color morphs. Comparison of the two transcriptomes identified 9641 differentially expressed unigenes (DEGs), including 6477 up-regulated and 3163 down-regulated genes. Functional analyses indicated that several DEGs were related to the anthocyanin biosynthesis pathway, and the expression profiles of these DEGs were coincident with the qRT-PCR validation results, indicating that expression levels of structural genes have a profound effect on the color variation in the R. palmatum complex. Our results suggested that the interaction of transcription factors (MYB, bHLH and WRKY) also regulated the anthocyanin biosynthesis in the R. palmatum complex. Estimation of selection pressures using the dN/dS ratio showed that 1106 pairs of orthologous genes have undergone positive selection. Of these positively selected genes, 21 were involved in the anthocyanin biosynthetic pathway, indicating that they may encode the proteins for structural alteration and affect flower color in the R. palmatum complex.

Apoptotic effects of rhein through the mitochondrial pathways, two death receptor pathways, and reducing autophagy in human liver L02 cells

Rhein (4,5-dihydroxyanthraquinone-2-carboxylic acid) is a major component of many medicinal herbs such as Rheum palmatum L. and Polygonum multiflorum. Despite being widely used, intoxication cases associated with rhein-containing herbs are often reported. Currently, there are no available reports addressing the effects of rhein on apoptosis in human liver L02 cells. Thus, the aim of this study is to determine the cytotoxic effects and the underlying mechanism of rhein on human normal liver L02 cells. In the present study, the methyl thiazolyl tetrazolium assay demonstrated that rhein decreased the viability of L02 cells in dose-dependent and time-dependent ways. Rhein was found to trigger apoptosis in L02 cells as shown by Annexin V-fluoresceine isothiocyanate (FITC) apoptosis detection kit and cell mitochondrial membrane potential (MMP) assay, with nuclear morphological changes demonstrated by Hoechst 33258 staining. Detection of intracellular superoxide dismutase activity, lipid oxidation (malondialdehyde) content, and reactive oxygen species (ROS) levels showed that apoptosis was associated with oxidative stress. Moreover, it was observed that the mechanism implicated in rhein-induced apoptosis was presumably via the death receptor pathway and the mitochondrial pathway, as illustrated by upregulation of TNF-α, TNFR1, TRADD, and cleaved caspase-3, and downregulation of procaspase-8, and it is suggested that rhein may increase hepatocyte apoptosis by activating the increase of TNF-α level. Meanwhile, rhein upregulates the expression of Bax and downregulates the expression of procaspase-9 and -3, and it is suggested that the mitochondrial pathway is activated and rhein-induced apoptosis may be involved. In addition, we also want to explore whether rhein-induced apoptosis is related to the autophagic changes induced by rhein. The results showed that rhein treatment increased P62 and decreased LC3-II and beclin-1, which means that autophagy was weakened. The results of our studies indicated that rhein induced caspase-dependent apoptosis via both the Fas death pathway and the mitochondrial pathway by generating ROS, and meanwhile the autophagy tended to weaken.

Effects of different nitrogen fertilizer levels on growth and active compounds of rhubarb from Qinghai plateau

BACKGROUND

Rheum tanguticum Maxim. ex Balf is one of the plants generically known as rhubarb, a culinary vegetable that has long been used as a herbal remedy both in China and Europe. Increasing demand for rhubarb has triggered the overexploitation of Rh. tanguticum. Cultivation is therefore necessary for quality control and protection of wild resources. Nitrogen fertilizer plays an important role in cultivation. This study aimed to explore how nitrogen fertilizer affects the growth and quality of rhubarb on the Qinghai-Tibetan plateau.

RESULTS

Nitrogen fertilizer promoted growth but had no significant influence on the active compounds of Rh. tanguticum. Generally, the N2 (150 kg ha^-1 ) and N3 (225 kg ha^-1 ) levels showed the most improved growth indexes, with no significant differences between them. The growth index and the amounts of eight of the nine studied active compounds in Rh. tanguticum increased from each year to the next and differed among growth stages. The contents of the active compounds were higher at the green stage and lower at the growth stage, which was opposite to the seasonal trends in root dry matter ratio. Gallic acid levels decreased with the growth of the plant.

CONCLUSION

The N2 level (150 kg ha^-1 ) was the recommended nitrogen fertilizer level in this study. It was revealed that seasonal changes rather than nitrogen fertilizer influenced active compounds in the root of Rh. tanguticum. © 2018 Society of Chemical Industry.

Investigation of species and environmental effects on rhubarb roots metabolome using 1H NMR combined with high performance thin layer chromatography

INTRODUCTION

The pharmacological activities of medicinal plants are reported to be due to a wide range of metabolites, therein, the concentrations of which are greatly affected by many genetic and/or environmental factors. In this context, a metabolomics approach has been applied to reveal these relationships. The investigation of such complex networks that involve the correlation between multiple biotic and abiotic factors and the metabolome, requires the input of information acquired by more than one analytical platform. Thus, development of new metabolomics techniques or hyphenations is continuously needed.

OBJECTIVES

Feasibility of high performance thin-layer chromatography (HPTLC) were investigated as a supplementary tool for medicinal plants metabolomics supporting ¹H nuclear magnetic resonance (¹H NMR) spectroscopy.

METHOD

The overall metabolic difference of plant material collected from two species (Rheum palmatum and Rheum tanguticum) in different geographical locations and altitudes were analyzed by ¹H NMR- and HPTLC-based metabolic profiling. Both NMR and HPTLC data were submitted to multivariate data analysis including principal component analysis and orthogonal partial least square analysis.

RESULTS

The NMR and HPTLC profiles showed that while chemical variations of rhubarb are in some degree affected by all the factors tested in this study, the most influential factor was altitude of growth. The metabolites responsible for altitude differentiation were chrysophanol, emodin and sennoside A, whereas aloe emodin, catechin, and rhein were the key species-specific markers.

CONCLUSION

These results demonstrated the potential of HTPLC as a supporting tool for metabolomics due to its high profiling capacity of targeted metabolic groups and preparative capability.

The pharmacokinetic screening of multiple components of the Nao Mai Tong formula in rat plasma by liquid chromatography tandem mass spectrometry combined with pattern recognition method and its application to comparative pharmacokinetics

The Nao Mai Tong formula (NMT) is composed of Rhubarb, Ginseng, Ligusticum wallichii and Pueraria in a ratio of 3:3:2:2 (w/w) and is a well-known traditional Chinese prescription that has been clinically employed for treating ischemia cerebrovascular disease. The goal of this study was to investigate the pharmacokinetics of multiple components (chryohol-8-O-β-D-glucoyroide, physcion-8-O-β-D-glucopyranoside, aloe-emodin, rhein, emodin, chrysophanol, ginsenoside Rg₁, ginsenoside Rb₁, ginsenoside Rb_3, ginsenoside Rc, senkyunolide I, ligustilide puerarin, daidzein, 3'-methoxy puerarin) after the oral administration of the NMT formula in rats. A rapid and sensitive UHPLC-Quadrupole-Orbitrap-MS with a sequential positive and negative ionization mode was developed to determine the 15 absorbed ingredients. After extraction from blood, the analytes and internal standards were subjected to ultra-high performance liquid chromatography with Agela Venusil MPC₁₈ (2.1mm×100mm, 3μm, Agela, USA). The mobile phase consisted of methanol and ammonium acetate (3mmolL^-1) under gradient elution conditions. This validated method was successfully applied to a comparative pharmacokinetic study of fifteen components in rat plasma after oral administration of the NMT formula or single herb extracts to normal and stroke-afflicted rats. A principal component analysis (PCA) was utilized to evaluate the differences in the pharmacokinetic behavior (time-course) of the absorbed components of NMT, and the absorbed components were assigned to 3 separate clusters. A comparison of the body dynamics of each group indicated that cluster B (ginsenoside Rg₁, ginsenoside Rb₁, ginsenoside Rb_3, ginsenoside Rc) might be the most important constituents controlling the pharmacological effects of NMT. The comparative pharmacokinetic study showed that the different groups had different pharmacokinetic characteristics. The pharmacokinetics-based UHPLC Quadrupole-Orbitrap-MS using a full-scan mode combined with a pattern recognition approach can provide a reliable and suitable means of screening and identifying potentially bioactive components that contribute to the pharmacological effects of Traditional Chinese Medicine (TCM).

Crude extract of Rheum palmatum L inhibits migration and invasion of LS1034 human colon cancer cells acts through the inhibition of matrix metalloproteinase-2/-9 by MAPK signaling

Crude extract of Rheum palmatum L. (CERP) has been used to treat different diseases in the Chinese population for decades. In this study, we investigated the anti-metastasis effects of CERP on LS1034 human colorectal cancer cells in vitro and examined potential mechanisms of its effects. CERP significantly inhibited cell migration and invasion of LS1034 cells. We also found that CERP inhibited protein levels of matrix metalloproteinases-2 (MMP-2) and matrix metalloproteinases-9 (MMP-9), and cytosolic NF-kB p65, RHO A, ROCK 1. Furthermore, we found CERP inhibited protein levels of GRB2, SOS1, MKK7, FAK, Rho A, ROCK 1, VEGF, PKC, AKT, phosphor-AKT (Thr308), Cyclin D, iNOS, COX2, NF-kB p65, p-ERK1/2, p-JNK1/2, p-p38, p-c-jun, MMP-2, MMP-9, MMP-1, MMP-7, MMP-10, UPA and increased the protein level of Ras in LS1034 cells. In conclusion, our results suggest that CERP may be used as a novel anti-metastasis agent for the treatment of human colon cancer cells.

[Metabolomics analysis revealing multiple compounds changed in rhubarb after processing]

Untargeted metabolomics analysis of rhubarb and stewed rhubarb samples shows that the determined samples clearly clustered in to two groups, indicating that the processing procedures caused changes in the composition and/or content of components in rhubarb. Ten components were identified by UHPLC-Q-TOF-MS/MS and references, which intensity declined in rhubarb after processing. Targeted metabolomics analysis of rhubarb and stewed rhubarb samples indicated that aloe-emodin, rhein, emodin and physcion were detected with lower intensity in stewed rhubarb samples than in rhubarb samples. Metabolomics analysis of rhubarb and stewed rhubarb indicated the various components of rhubarb changed after processing.

[Biotransformation of podophyllotoxin by cell suspension culture and root culture of Rheum palmatum]

OBJECTIVE

To study the biotransformation of podophyllotoxin by the cell suspension culture and root culture systems of Rheum palmatum.

METHOD

Using plant tissue culture technology and HPLC techniques to isolate products. The structures were elucidated by spectroscopic means.

RESULT

Cell suspension culture of R. palmatum could convert podophyllotoxin to produce picropodophyllotoxin with the yield of 73.8%, while root culture of R. palmatum could convert podophyllotoxin to produce epipodophyllotoxin and apopodophyllotoxin.

CONCLUSION

Podophyllotoxin did not affect the pH value of the media used in tissue cultures. Both cell suspension culture and root culture of R. palmatum can convert podophyllotoxin.

[Abiotic elicitation of the explant culture of Rheum palmatum L. by heavy metals]

Elicitation-produced stress activates the defensive reactions of the plant or plant explant, which result, among others, in a change in the transcription of the genes coding the enzymes influencing biosynthesis of secondary metabolites. The present paper investigated the effect of ions of heavy metals in concentrations od 1; 10, and 100 microM on the production of anthracene derivatives by the explant culture of Rheum palmatum L. cultivated on Murashige-Skoog medium with an addition of 10 mg.l(-1) of alpha-naphthylacetic acid. The periods of application of elicitation were 6; 24; 48, and 168 hours. It follows from the results that the applied abiotic elicitation positively influenced the production mainly in suspension culture. The maximal increase in the content of anthracene derivatives versus the control by 66% was observed after 48-hour action of 10 microM concentration of cadmium chloride. Aluminium chloride produced the largest increase in the production after 6-hour application of a 100 microM concentration, when in comparison with the control culture the production was stimulated by 60%.

[Effect of abiotic elicitation and calcium ions on production of explant cultures of Rheum palmatum L]

Elicitation is based on signal (elicitor)-induced expression of genes, which subsequently results in increased synthesis of secondary metabolities in plants and in vitro cultures. Elicitors do not usually influence gene activity directly but by means of transmitters of the signal, which include primarily calcium ions. The paper examined the effect of four concentrations of calcium ions on the production of anthracene derivatives by means of the callus and suspension cultures of Rheum palmatum L. (Polygonaceae), which was elicited by an abiotic elicitor--a 20 microM solution of lead dichloride. The culture was cultivated on a Murashige-Skoog medium with an addition of 10 mg.l-1 of alpha-naphthylacetic acid. It follows from the results that the maximal content of anthracene derivatives, determined by the photometric determination according to PhBs 4, was demonstrated in the suspension culture after 24-hr administration of the elicitor and a 10 mM calcium chloride solution. In comparison with the control and elicited groups, the production was stimulated by 44% and 17%, respectively. After an addition of calcium ions to the elicited callus culture, no positive influence on the production was observed.

[Effect of jasminic acid on production of anthracene derivatives in cultures of Rheum palmatum L]

The process of elicitation makes use of the capacity of plants and plant cells cultivated in vitro to react to various stress stimuli by a number of protective reactions leading to increased accumulation of secondary metabolites. The endogenic signal substances of plant protective reactions include jasminic acid, which in the case of exogenous application also acts as an elicitor. The paper examined the effect of four concentrations of jasminic acid on the production of anthracene derivatives by a three-year-old tissue culture, which was derived from the roots of a two-year-old intact plant Rheum palmatum L. (Polygonaceae). The culture was cultivated on Murashige-Skoog medium with an addition of 10 mg.l-1 of alpha-naphthylacetic acid. The results show that the optimal effect of jasminic acid on the production of callus culture was manifested after a 12-hour application of the strongest concentration of 5 mM, and on the production of suspension culture after a 48-hour application of a concentration of 0.05 mM, when the photometric determination according to PhBs 4 demonstrated the maximal content of anthracene derivatives (1.26%) and the production was stimulated by 109% in comparison with the control.

Aromatic and pyrone polyketides synthesized by a stilbene synthase from Rheum tataricum

A cDNA encoding a stilbene synthase, RtSTS, was isolated from the rhizomes of Tatar rhubarb, Rheum tataricum L. (Polygonaceae), a medicinal plant containing stilbenes and other polyketides. Recombinant RtSTS was expressed in E. coli and assayed with acetyl-coenzyme A (CoA), n-butyryl-CoA, isovaleryl-CoA, n-hexanoyl-CoA, cinnamoyl-CoA and p-coumaroyl-CoA as primers of polyketide synthesis. RtSTS synthesized resveratrol and a trace amount of naringenin chalcone from p-coumaroyl-CoA, supporting the enzyme's identification as a resveratrol-type stilbene synthase (EC 2.3.1.95). Bis-noryangonin and p-coumaroyl triacetic acid lactone (CTAL)-type pyrones were observed in minor amounts in the reaction with p-coumaroyl-CoA and as major products with cinnamoyl CoA. As well, such pyrones, and not aromatic polyketides, were identified as the only products in assays with aliphatic and benzoyl CoA esters. Acetonyl-4-hydroxy-2-pyrone, a pyrone synthesized from acetyl-CoA, was identified as a new product of a stilbene synthase. Using Northern blot analysis, RtSTS transcript was found to be highly expressed in R. tataricum rhizomes, with low transcript levels also present in young leaves. This expression pattern correlated with the occurrence of resveratrol, which was detected in higher amounts in R. tataricum rhizomes compared with leaves and petioles using HPLC. Few stilbene synthases have been found in plants, and the identification of RtSTS provides additional sequence and catalytic information with which to study the evolution of plant polyketide synthases.

The phytochemical lindleyin, isolated from Rhei rhizoma, mediates hormonal effects through estrogen receptors

Some plant compounds or herb mixtures are popular alternatives to conventional therapies and contain organic compounds that bind to some nuclear receptors, such as the estrogen receptor (ER), to exert various biological effects. We studied the effect of various herbal extracts on ERalpha and ERbeta isoforms. One herbal extract, Rhei rhizoma (rhubarb), acts as an agonist to both ERalpha and ERbeta. The phytochemical lindleyin, a major component of rhubarb, might contribute to this estrogenic activity through ERalpha and ERbeta. 4-Hydroxytamoxifen, an ER antagonist, completely reversed the estrogenic activity of lindleyin. Lindleyin binds to ERalpha in vitro, as demonstrated using a fluorescent polarization assay. The in vivo effect of rhubarb extract was studied using a vitellogenin assay system in the freshwater fish, Japanese medaka (Oryzias latipes). There were marked increases in serum vitellogenin levels in male medaka exposed to rhubarb extract. We conclude that lindleyin, a component of some herbal medicines, is a novel phytoestrogen and might trigger many of the biological responses evoked by the physiological estrogens.

[Effect of salicylic acid on production of anthracene derivatives in a culture of Rheum palmatum L. in vitro]

Elicitation is a method making use of protective mechanisms of plants to increase the production of secondary metabolites in plants and cultures in vitro. Salicylic acid acts in plants as an inducer of the expression of protective proteins and it can be thus included into biotic elicitors. That is why the present paper examined the effects of five concentrations of salicylic acid on the production of anthracene derivatives by a three-year and a nine-year old culture derived from the root of the intact plant Rheum palmatum L. The culture was cultivated on Murashige-Skoog medium with an addition of 10 mg.l-1 of alpha-naphthylacetic acid. It follows from the results that increase in production after elicitation is higher in the three-year old culture than in the nine-year old one and elicitation of suspension culture is more successful than elicitation of callus culture. The maximal content of anthracene derivatives (1.418%), detected by a photometric essay according to PhBS 4, was demonstrated after a 48-hour action of 1 mM aqueous solution of salicylic acid, when production was increased by 101% in comparison with the control.

[Effect of chitosan on the production of anthracene derivatives in tissue culture of Rheum palmatum L]

Explant cultures have been, besides other things, used for elicitation, which is an economically advantageous method making use of protective mechanism of plants to increase the production of secondary metabolites. The present study investigated the effect of 6, 12, 24, 48, 72, and 168 hours lasting action of four concentrations of the biotic elicitor chitosan on the production of anthracene derivatives by the callus and suspension culture of Rheum palmatum L. The culture was cultivated on a Murashige-Skoog medium with an addition of 10 mg.l-1 of alpha-naphthylacetic acid. A positive effect on the production was exerted in particular by elication of the suspension culture. The maximal content of anthracene derivatives (1.181%), found by photometric determination according to PhBs 4, as demonstrated after 24-hour action of a chitosan solution of a concentration of 1 mg/30 ml of the medium. In contrast to the suspension culture, the production of anthracene derivatives in the callus culture was influenced by elicitation only in the minimal way.

Benzalacetone synthase. A novel polyketide synthase that plays a crucial role in the biosynthesis of phenylbutanones in Rheum palmatum

Benzalacetone synthase (BSA) is a novel plant-specific polyketide synthase that catalyzes a one step decarboxylative condensation of 4-coumaroyl-CoA with malonyl-CoA to produce the C6-C4 skeleton of phenylbutanoids in higher plants. A cDNA encoding BAS was for the first time cloned and sequenced from rhubarb (Rheum palmatum), a medicinal plant rich in phenylbutanoids including pharmaceutically important phenylbutanone glucoside, lindleyin. The cDNA encoded a 42-kDa protein that shares 60-75% amino-acid sequence identity with other members of the CHS-superfamily enzymes. Interestingly, R. palmatum BAS lacks the active-site Phe215 residue (numbering in CHS) which has been proposed to help orient substrates and intermediates during the sequential condensation of 4-coumaroyl-CoA with malonyl-CoA in CHS. On the other hand, the catalytic cysteine-histidine dyad (Cys164-His303) in CHS is well conserved in BAS. A recombinant enzyme expressed in Escherichia coli efficiently afforded benzalacetone as a single product from 4-coumaroyl-CoA and malonyl-CoA. Further, in contrast with CHS that showed broad substrate specificity toward aliphatic CoA esters, BAS did not accept hexanoyl-CoA, isobutyryl-CoA, isovaleryl-CoA, and acetyl-CoA as a substrate. Finally, besides the phenylbutanones in rhubarb, BAS has been proposed to play a crucial role for the construction of the C6-C4 moiety of a variety of natural products such as medicinally important gingerols in ginger plant.

[Effect of the biotic elicitor, Candida utilis, on the production of anthracene derivatives in a tissue culture of Rheum palmatum L]

The paper studied the effect of the homogenate of Candida utilis on the production of anthracene derivatives by the callus and suspension culture of Rheum palmatum L. of different age and origin. The culture was cultivated on a Murashige-Skoog medium with an addition of 10 mg.l-1 of alpha-naphthylacetic acid. A positive effect on the production was caused mainly by the elicitation of the suspension culture. The maximal content of anthracene derivatives (1.346%), found by photometric determination according to PhBs 4, was demonstrated after 6-hour action of the homogenate of Candida utilis of a concentration of 0.143 mg/30 ml of the medium in an eight-year old culture derived from the root of the intact plant Rheum palmatum. A one-year-old culture derived from the root of the intact and germinating plant reacted to elicitation more sensitively as there was an increase in production up to 228% in comparison with the control. However, the content of anthracene derivatives was lower than in the eight-year-old culture. In contrast to the suspension culture, the production of anthracene derivatives in the callus culture was influenced by elicitation only in the minimal extent.

[Production of anthracene derivatives in elicited tissue cultures of Rheum palmatum L]

With a few exceptions, the characteristic problem of cultivation of plant explants in in vitro cultures is a low production of secondary metabolites by these cultures. One of the methods, which can achieve an increase in the production of natural substances in in vitro cultures, is elicitation of cell cultures. The effect of the biotic elicitor Pseudomonas aeruginosa in the form of a homogenate and an aqueous suspension of dead cells on the production of anthracene derivatives by the tissue culture of Rheum palmatum L. of different age and origin was examined. The culture was cultivated on a Murashige-Skoog medium with an addition of 10 mg.l-1 of alpha-naphthylacetic acid. The maximal content of anthracene derivatives found by photometric determination according to PhBs 4 was demonstrated in an eight years old culture (1.027%) after six hour elicitation with an aqueous suspension of dead cells of Pseudomonas aeruginosa (1.7 mg of dry matter/1 ml of solution). The culture newly derived from the root of the intact plant Rheum palmatum L. responded to elicitation more sensitively than the culture derived from the seed; nevertheless the content of anthracene derivatives was lower than in the eight years old culture.