Gallotannin biosynthesis: two new galloyltransferases from Rhus typhina leaves preferentially acylating hexa- and heptagalloylglucoses

A chromosome-scale genome of Rhus chinensis Mill. provides new insights into plant-insect interaction and gallotannins biosynthesis

Rhus chinensis Mill., an economically valuable Anacardiaceae species, is parasitized by the galling aphid Schlechtendalia chinensis, resulting in the formation of the Chinese gallnut (CG). Here, we report a chromosomal-level genome assembly of R. chinensis, with a total size of 389.40 Mb and scaffold N50 of 23.02 Mb. Comparative genomic and transcriptome analysis revealed that the enhanced structure of CG and nutritional metabolism contribute to improving the adaptability of R. chinensis to S. chinensis by supporting CG and galling aphid growth. CG was observed to be abundant in hydrolysable tannins (HT), particularly gallotannin and its isomers. Tandem repeat clusters of dehydroquinate dehydratase/shikimate dehydrogenase (DQD/SDH) and serine carboxypeptidase-like (SCPL) and their homologs involved in HT production were determined as specific to HT-rich species. The functional differentiation of DQD/SDH tandem duplicate genes and the significant contraction in the phenylalanine ammonia-lyase (PAL) gene family contributed to the accumulation of gallic acid and HT while minimizing the production of shikimic acid, flavonoids, and condensed tannins in CG. Furthermore, we identified one UDP glucosyltransferase (UGT84A), three carboxylesterase (CXE), and six SCPL genes from conserved tandem repeat clusters that are involved in gallotannin biosynthesis and hydrolysis in CG. We then constructed a regulatory network of these genes based on co-expression and transcription factor motif analysis. Our findings provide a genomic resource for the exploration of the underlying mechanisms of plant-galling insect interaction and highlight the importance of the functional divergence of tandem duplicate genes in the accumulation of secondary metabolites.

Rhus coriaria L. (Sumac), a Versatile and Resourceful Food Spice with Cornucopia of Polyphenols

In recent years, utilization of Rhus coriaria L. (sumac) is upgrading not only in their culinary use and human nutrition, but also in the pharmaceutical industry, food industry and veterinary practices. This is driven by accumulating evidence that support the ethnobotanical use of this plant; in particular, advanced knowledge of the content of nutritional, medicinal and techno-functional bioactive ingredients. Herein, we discuss polyphenolic compounds as the main bioactive ingredients in Rhus coriaria L., which contribute mainly to the significance and utility of this spice. Most of the antioxidant potential and therapeutic roles of sumac are increasingly attributed to its constituent tannins, flavonoids, and phenolic acids. Hydroxyphenyl pyranoanthocyanins and other anthocynins are responsible for the highly desired red pigments accounting for the strong pigmentation capacity and colorant ability of sumac. Certain polyphenols and the essential oil components are responsible for the peculiar flavor and antimicrobial activity of sumac. Tannin-rich sumac extracts and isolates are known to enhance the food quality and the oxidative stability of animal products such as meat and milk. In conclusion, polyphenol-rich sumac extracts and its bioactive ingredients could be exploited towards developing novel food products which do not only address the current consumers' interests regarding organoleptic and nutritional value of food, but also meet the growing need for 'clean label' as well as value addition with respect to antioxidant capacity, disease prevention, and health promotion in humans.

Effects of Rhus coriaria L. hydroalcoholic extract on the lipid and antioxidant profile in high fat diet-induced hepatic steatosis in rats

Oxidative stress is related to increased fat deposition in the liver, known as hepatic steatosis. The present study is an evaluation of the anti-oxidative and antihyperlipidemic effects of the hydroalcoholic extract of Rhus coriaria L. (HARE) in rats on a high-fat diet (HFD). Twenty male Wistar rats were divided into four groups: control, HFD, HFD + HARE 50 mg/kg/day, and HFD + HARE 250 mg/kg/day for 12 weeks. Animals were weighed weekly and treated with the HARE extract for 12 weeks by gavage. Subsequently, the histopathological changes, oxidative markers, and lipid profile were evaluated. Statistical analysis was performed using the one-way analysis of variance (ANOVA) for multiple comparisons. First, the active ingredients of the extract were determined by HPLC. Then, the levels in the serum lipid profile (TG, cholesterol, HDL, and LDL) in rats fed with the HFD + HARE were analyzed where a significant reduction was observed. The HFD proved to increase the activity of the liver enzymes, the serum lipid levels, and the malondialdehyde (MDA) level. The ferric-reducing antioxidant activity power (FRAP), catalase (CAT), and superoxide dismutase (SOD) catalytic activity were reduced in the liver homogenate of HFD rats compared to the controls. Additionally, the aforementioned liver enzymes activities were reduced in response to HARE. Evaluation of oxidative stress determined a reduction in the MDA level while a raised FRAP was confirmed. In accordance with the present results, histopathological observations have also demonstrated that HARE ameliorated grade-1 hepatic steatosis induced by HFD. Taken together, the findings of this study introduce HARE as a future potential therapeutic agent in treating hepatic steatosis and reducing oxidative damages of an HFD in the liver.

Characterization of Secondary Metabolites in Flowers of Sanguisorba officinalis L. by HPLC-DAD-MSn and GC/MS

The investigations reported here focus on an in-depth characterization of the secondary metabolite profile of Sanguisorba officinalis flowers. For this purpose, fresh flowers were extracted with MeOH/H₂ O and EtOH/H₂ O and the resulting crude extracts fractionated using CH₂ Cl₂ , AcOEt, and BuOH. Individual compounds were characterized by high performance liquid chromatography and gas chromatography coupled with mass spectrometric detection (HPLC-DAD-MSⁿ and GC/MS). MeOH/H₂ O extraction and LC/MSⁿ investigations revealed the occurrence of flavonoid glycosides (quercetin, kaempferol), ellagitannin glycosides and four anthocyanins. Among the latter, two components, i. e., cyanidin-malonyl-glucose and cyanidin-galloyl-hexose, have not been reported for S. officinalis so far. Furthermore, phenylethylamine was characterized for the first time in Sanguisorba by pH value dependent extraction with CH₂ Cl₂ . In addition, AcOEt and BuOH extracts were analyzed by GC/MS both prior to and after acid hydrolysis of secondary metabolites. For this purpose, the extracts were treated with 1 n HCl solution (105 °C, 1 h) and derivatized with BSTFA. Analyses revealed the occurrence of several classes of phenolic compounds, such as gallic acid, hydroxybenzoic acid, hydroxycinnamic acid and ellagic acid derivatives. Additionally, the most prominent ursane-type triterpenoid (ziyu-glycoside I) from Sanguisorba and its corresponding aglycone isomers were detected and assigned based on their characteristic fragmentation patterns.

Simultaneous determination of the pharmacokinetics of A-type EGCG and ECG dimers in mice plasma and its metabolites by UPLC-QTOF-MS

A-type epigallocatechin-3-gallate (EGCG) and epicatechin-3-O-gallate (ECG) dimers have multiply biological activities. In this study, the pharmacokinetics of them were investigated in mice after a single dose intravenous administration, and the metabolites in mice plasma and urine were investigated by ultra-performance liquid chromatography-Quadrupole-time of flight mass spectrometer (UPLC-QTOF-MS). Our results showed that the half-life (t_1/2) of A-type EGCG and ECG dimers were 116.37 min and 33.04 min, respectively, and the maximal concentration in plasma was 32.81 μg/mL and 55.59 μg/mL, respectively. It was found that two dimers were firstly experienced by quinone methide (QM) fission to form the EGCG and ECG analogue, and the phase II metabolites were generated subsequently. The main metabolites in plasma and urine were glucuronidation and sulphation derivatives. In addition, small molecule weight of phenolic acids were detected in urine.

Anti-quorum sensing activity, toxicity in zebrafish (Danio rerio) embryos and phytochemical characterization of Trapa natans leaf extracts

ETHNOPHARMACOLOGICAL RELEVANCE

Trapa natans L. (water chestnut or water caltrop) is a widespread aquatic plant, which has been cultivated for food and traditional medicine since ancient times. Pharmacological studies showed that water chestnut exhibits the wide range of biological activities, such as antimicrobial, antioxidative, analgesic, anti-inflammatory, as well as antiulcer.

AIM OF THE STUDY

Evaluation of anti-virulence potential and toxicity of T. natans methanol (TnM), acetone (TnA) and ethyl acetate (TnEA) leaf extracts.

MATERIALS AND METHODS

The anti-quorum sensing activity of Tn extracts was addressed by measuring their effects on biofilm formation, swarming motility and pyocyanin and elastase production in Pseudomonas aeruginosa. Specific P. aeruginosa biosensors were used to identify which of the signaling pathways were affected. The lethal and developmental toxicity of extracts were addressed in vivo using the zebrafish (Danio rerio) model system. The phenolic composition of T. natans leafs extracts was analyzed by a linear ion trap-OrbiTrap hybrid mass spectrometer (LTQ OrbiTrapMS) and UHPLC system configured with a diode array detector (DAD) hyphenated with the triple quadrupole mass spectrometer.

RESULTS

Subinhibitory concentrations of Tn leaf extracts (0.2 MIC) inhibited pyocyanin and elastase production up to 50% and 60%, respectively, and reduced swarming zones, comparing to non-treated P. aeruginosa. TnA inhibited biofilm formation by 15%, TnM showed a stimulatory effect on biofilm formation up to 20%, while TnEA showed no effect. The bioactive concentrations of TnM and TnA were not toxic in the zebrafish model system. Twenty-two phenolic compounds were tentatively identified in TnM, where thirteen of them were identified in T. natans for the first time. Tn extracts, as well as their major components, ellagic and ferulic acids, demonstrated the ability to interfere with P. aeruginosa Las and PQS signaling pathways.

CONCLUSIONS

This study demonstrates anti-virulence potential of Tn leaf extracts against medically important pathogen P. aeruginosa and confirms the ethnopharmacological application of this plant against microbial infections.

The role of acyl-glucose in anthocyanin modifications

Higher plants can produce a wide variety of anthocyanin molecules through modification of the six common anthocyanin aglycons that they present. Thus, hydrophilic anthocyanin molecules can be formed and stabilized by glycosylation and acylation. Two types of glycosyltransferase (GT) and acyltransferase (AT) have been identified, namely cytoplasmic GT and AT and vacuolar GT and AT. Cytoplasmic GT and AT utilize UDP-sugar and acyl-CoA as donor molecules, respectively, whereas both vacuolar GT and AT use acyl-glucoses as donor molecules. In carnation plants, vacuolar GT uses aromatic acyl-glucoses as the glucose donor in vivo; independently, vacuolar AT uses malylglucose, an aliphatic acyl-glucose, as the acyl-donor. In delphinium and Arabidopsis, p-hydroxybenzoylglucose and sinapoylglucose are used in vivo as bi-functional donor molecules by vacuolar GT and AT, respectively. The evolution of these enzymes has allowed delphinium and Arabidopsis to utilize unique donor molecules for production of highly modified anthocyanins.

Plant polyphenols: chemical properties, biological activities, and synthesis

Eating five servings of fruits and vegetables per day! This is what is highly recommended and heavily advertised nowadays to the general public to stay fit and healthy! Drinking green tea on a regular basis, eating chocolate from time to time, as well as savoring a couple of glasses of red wine per day have been claimed to increase life expectancy even further! Why? The answer is in fact still under scientific scrutiny, but a particular class of compounds naturally occurring in fruits and vegetables is considered to be crucial for the expression of such human health benefits: the polyphenols! What are these plant products really? What are their physicochemical properties? How do they express their biological activity? Are they really valuable for disease prevention? Can they be used to develop new pharmaceutical drugs? What recent progress has been made toward their preparation by organic synthesis? This Review gives answers from a chemical perspective, summarizes the state of the art, and highlights the most significant advances in the field of polyphenol research.

Ecophysiological evaluation of the potential invasiveness of Rhus typhina in its non-native habitats

Rhus typhina L. (staghorn sumac) is a clonal woody species that is considered potentially invasive in its non-native habitats. It is slow growing as seedlings, but grows fast once established. Its growth in the early stages is limited by many abiotic factors, including light intensity. To evaluate its potential of becoming invasive in areas it has been introduced into, we conducted a field experiment to investigate the effects of light intensity on the physiology and growth of R. typhina. Two-month-old R. typhina seedlings were examined under five light levels, that is, 100% full sunlight (unlimited light), moderate stress (50% or 25% of full sunlight) and severe stress (10% or 5% of full sunlight), for 60 days in Hunshandak Sandland, China. Net photosynthetic rate (PN) was reduced significantly under severe light stress, but PN of the moderately stressed seedlings was unaffected. Light stress also led to a reduction in saturated light intensity of the moderately stressed seedlings by 20% and of the severely stressed seedlings by 40%, although the light saturation points were as high as 800 and 600 micromol m(-2) s(-1) for the moderately and severely stressed seedlings, respectively. Under severe light stress, the maximum quantum yield of Photosystem II (Fv/Fm) decreased significantly, but the minimal fluorescence yield (F0) increased compared to that of the control plants. The number of newly produced leaves and the stem height, however, decreased as the light intensity became lower. Root length and leaf area decreased, whereas specific leaf area significantly increased as light became increasingly lower. Biomass production was significantly reduced by light stress, but the allocation pattern was unaffected. Our results demonstrated that R. typhina seedlings can survive low light and grow well in other light conditions. The physiology and growth of R. typhina will likely enable it to acclimate to varying light conditions in Hunshandak Sandland, where R. typhina has been widely cultivated for sand stabilization and other purposes. Because of its ability to tolerate low light and to compete aggressively for light resource once established, that is, becoming invasive, we urge caution when it comes to introducing R. typhina into its non-native habitats, despite its many ecological benefits.

Anti-cancer, anti-diabetic and other pharmacologic and biological activities of penta-galloyl-glucose

1, 2, 3, 4, 6-penta-O-galloyl-beta-D-glucose (PGG) is a polyphenolic compound highly enriched in a number of medicinal herbals. Several in vitro and a handful of in vivo studies have shown that PGG exhibits multiple biological activities which implicate a great potential for PGG in the therapy and prevention of several major diseases including cancer and diabetes. Chemically and functionally, PGG appears to be distinct from its constituent gallic acid or tea polyphenols. For anti-cancer activity, three published in vivo preclinical cancer model studies with PGG support promising efficacy to selectively inhibit malignancy without host toxicity. Potential mechanisms include anti-angiogenesis; anti-proliferative actions through inhibition of DNA replicative synthesis, S-phase arrest, and G(1) arrest; induction of apoptosis; anti-inflammation; and anti-oxidation. Putative molecular targets include p53, Stat3, Cox-2, VEGFR1, AP-1, SP-1, Nrf-2, and MMP-9. For anti-diabetic activity, PGG and analogues appear to improve glucose uptake. However, very little is known about the absorption, pharmacokinetics, and metabolism of PGG, or its toxicity profile. The lack of a large quantity of highly pure PGG has been a bottleneck limiting in vivo validation of cancer preventive and therapeutic efficacies in clinically relevant models.

Induction of salivary polypeptides associated with parotid hypertrophy by gallotannins administered topically into the mouse mouth

Isoproterenol-induced salivary polypeptides (IISP), a group of proline-rich proteins synthesized by mouse parotids, have been considered as markers for isoproterenol-induced parotid hypertrophy. Rodents fed diets containing high-tannin cereals (sorghum), also develop parotid hypertrophy. To test whether tannins are directly involved in provoking sialotrophic growth, we studied the effect of intraperitoneal and topical oral administrations of tannic acid (TA) on the induction of IISP polypeptides in endogamic mice (A/Snell). TA was characterized by HPLC chromatography and spectral analysis and shown to be composed solely of gallotannins, a complex family of glucose and gallic acid esters. IISP polypeptides were monitored in saliva by SDS-polyacrylamide gel electrophoresis during 36 h after ending TA stimulation. Single daily intraperitoneal administrations of TA for 3 consecutive days (0.033 mg/g bw/day), at variance of parallel administrations of isoproterenol (0.042 mg/g bw/day) failed to induce IISP polypeptides. However, repeated topical applications of TA into the mouse mouths (1.21 mg/g bw divided into three equal doses given at 4-h intervals within a single day) resulted in unequivocal induction of IISP polypeptides. That response was clearly intensified by increasing the stimulation frequency to eight equivalent doses given at 1.5-h intervals within a single day (corresponding to 3.23 mg/g bw) and even further by repeating this protocol for 3 days. Under these productive schemes of stimulations by TA, electrophoretic fractionation of parotid homogenates showed new polypeptide bands migrating in parallel to salivary IISP. These results suggest that topically administered gallotannins are effective inducers of trophic growth in mouse parotids.

Biodegradation of gallotannins and ellagitannins

Nowadays, many researches have been made on gallotannin biodegradation and have gained great success in further utilization. Some of industrial applications of these findings are in the production of tannase, the biotransformation of tannic acid to gallic acid or pyrogallol and detannification of food and fodder. Although ellagitannins have the typical C-C bound which is more difficult to be degraded than gallotannins, concerted efforts are still in progress to improve ellagitannin degradation and utilization. Currently, more attention is mainly focused on intestinal microflora biodegradation of tannins especially ellagitannins which can contribute to the definition of their bioavailability for both human beings and ruminants. Also there have been endeavours to utilize the tannin-degrading activity of different fungi for ellagitannin-rich biomass, which will facilitate application of tannin-degrading enzymes in strategies for improving industrial and livestock production. Due to the complicated structures of complex tannins and condensed tannins, the biodegradation of them is much more difficult and there are fewer researches on them. Therefore, the researches on the mechanisms of gallotannin and ellagitannin biodegradation can result in the overall understanding to the biodegradation of complex tannins and condensed tannins. Biodegradation of tannins is in an incipient stage and further studies have to be carried out to exploit the potential of various tannins for largescale applications in food, fodder, medicine and tannery effluent treatment.

Enzymology of gallotannin and ellagitannin biosynthesis

Gallotannins and ellagitannins, the two subclasses of hydrolyzable tannins, are derivatives of 1,2,3,4,6-penta-O-galloyl-beta-D-glucopyranose. Enzyme studies with extracts from oak leaves (Quercus robur, syn. Quercus pedunculata; Quercus rubra) and from staghorn sumac (Rhus typhina) revealed that this pivotal intermediate is synthesized from beta-glucogallin (1-O-galloyl-beta-D-glucopyranose) by a series of strictly position-specific galloylation steps, affording so-called 'simple' gallotannins, i.e., mono- to pentagallyoylglucose esters. Besides its role as starter molecule, beta-glucogallin was also recognized as the principal energy-rich acyl donor required in these transformations. Subsequent pathways to 'complex' gallotannins have recently been elucidated by the isolation of five different enzymes from sumac leaves that were purified to apparent homogeneity. They catalyzed the beta-glucogallin-dependent galloylation of pentagallyoylglucose to a variety of hexa- and heptagalloylglucoses, plus several not yet characterized higher substituted analogous galloylglucoses. With respect to the biosynthesis of ellagitannins, postulates that had been formulated already decades ago were proven by the purification of a new laccase-like phenol oxidase from leaves of fringe cups (Tellima grandiflora) that regio- and stereospecifically oxidized pentagallyoylglucose to the monomeric ellagitannin, tellimagrandin II. This compound was further oxidized by a similar but different laccase-like oxidase to yield a dimeric ellagitannin, cornusiin E.

Ellagitannin biosynthesis: laccase-catalyzed dimerization of tellimagrandin II to cornusiin E in Tellima grandiflora

An enzyme has been purified from leaves of the weed Tellima grandiflora (fringe cups, Saxifragaceae) that catalyzed the O2-dependent oxidation of the monomeric ellagitannin, tellimagrandin II, to a dimeric derivative, cornusiin E. The apparently homogeneous enzyme preparation had a Mr of ca. 160,000 (with four subunits of Mr 40,000), a pH-optimum and an isoelectric point at pH 5.2, and was most stable at pH 4.3. Inhibition studies revealed that this new enzyme, for which the systematic name 'tellimagrandin II: O2 oxidoreductase' is proposed, is a member of the laccase (EC 1.10.3.2) family of phenol oxidases. The properties of this enzyme differed from that of a related laccase that catalyzed the transition of 1,2,3,4,6-pentagalloylglucopyranose to tellimagrandin II, the preceding step in the biosynthetic route to cornusin E.

Biosynthesis of the dimeric ellagitannin, cornusiin E, in Tellima grandiflora

First evidence for the in vitro synthesis of a dimeric ellagitannin has been obtained with cell-free extracts from the weed Tellima grandiflora (fringe cups, Saxifragaceae). Partially purified enzyme preparations from leaves of this plant catalyzed the oxidation of 1,2,3,4,6-pentagalloyl-beta-D-glucose to the monomeric ellagitannin, tellimagrandin II, followed by oxidative coupling of two units of this intermediate to yield a dimeric derivative. Chemical degradation, MALDI-TOF mass spectrometry, 1H and 13C nuclear magnetic resonance, and CD spectroscopy were employed to identify this enzyme reaction product as cornusiin E which is characterized by a (S)-valoneoyl bridge between glucose-positions 2, 4' and 6'. This result was supported by comparison with data obtained for cornusiin E that had been isolated from leaves of intact T. grandiflora plants. No indication for the earlier proposed existence of rugosin D (an isomer with a 1,4',6'-bound valoneoyl unit) in T. grandiflora has been obtained in this investigation.

Oxidation of pentagalloylglucose to the ellagitannin, tellimagrandin II, by a phenol oxidase from Tellima grandiflora leaves

A new enzyme has been isolated from leaves of the weed Tellima grandiflora (fringe cups, Saxifragaceae) that catalyzed the O(2)-dependent oxidation of 1,2,3,4,6-penta-O-galloyl-beta-D-glucopyranose to tellimagrandin II, the first intermediate in the (4)C(1)-glucose derived series of ellagitannins. CD-spectra revealed that the 4,6-O-HHDP-residue of the in vitro product had the (S)-stereoconfiguration characteristic of tellimagrandin II from natural sources. The enzyme, for which a M(r) of ca. 60,000 was determined, was purified to apparent homogeneity. It had a pH-optimum at pH 5.0, an isoelectric point at pH 6.3 and was most stable at pH 4.2. Inhibition studies suggested that this new enzyme, for which the systematic name 'pentagalloylglucose: O(2) oxidoreductase' is proposed, belongs to the vast group of laccase-type phenol oxidases (EC 1.10.3.2).