Ellagitannins of Davidia involucrata. I. Structure of Davicratinic Acid A and Effects of Davidia Tannins on Drug-Resistant Bacteria and Human Oral Squamous Cell Carcinomas

Metabolome profiling of stratified seeds provides insight into the regulation of dormancy in Davidia involucrata

Dove tree (Davidia involucrata), a tertiary vestige species, is well-adapted to cool conditions. Dormancy in D. involucrata seed lasts for an extremely long period of time, typically between 3 and 4 years, and this characteristic makes the species an excellent model for studying the mechanisms of seed dormancy. The molecular mechanisms governing germination control in D. involucrata are still unknown. Seed stratification have been reported to enhance germination in recalcitrant seeds. We performed a widely targeted metabolome profiling to identify metabolites and associated pathways in D. involucrata seeds from six different moist sand stratification durations (0-30 months) using the ultra-high-performance liquid chromatography-Q Exactive Orbitrap-Mass spectrometry. There was an increasing germination rate with prolonged stratification durations (12-30 months). Furthermore, we detected 10,008 metabolites in the stratified seeds. We also detected 48 differentially accumulated metabolites (DAMs) between all stratification periods in the seeds, with 10 highly conserved metabolites. Most of the differentially accumulated metabolites between unstratified and stratified seeds were enriched in purine metabolism, pyrimidine metabolism, flavone and flavonol biosynthesis, phenylpropanoid biosynthesis, and arginine biosynthesis pathways. Key phytohormones, abscisic acid, indole-3 acetic acid, and sinapic acid were differentially accumulated in the seeds and are predicted to regulate dormancy in D. involucrata. We have provided extensive metabolic information useful for future works on dove tree germination study.

The Potential of Flavonoids and Tannins from Medicinal Plants as Anticancer Agents

The tendency of using herbs extracts or natural compounds extracted from herbs for preventing or treating different illnesses, including cancer, continues to be an alternative to drug use. Many studies of plant compounds aimed at finding substances with selective cytotoxicity on abnormal cells. Phenolic compounds, as important secondary metabolites from plants, are one of them. In this review, the recent literature data from the past five years about anticancer/antitumor effect of flavonoids and tannins extracted from medicinal plants are surveyed. The cytostatic/antitumor effects of the individual compounds extracted from plants and/or of the plants' polyphenolic extracts are considered, in order to point out the most significant constituents or plants with anticancer potential. The most important results concerning these compounds and their derivatives in cancer prevention and treatment, the importance of their chemical structure, their mechanism of action in vitro and in vivo, and some bioavailability aspects are discussed.

Two new C-glycosidic ellagitannins and accompanying tannins from Lawsonia inermis leaves and their cytotoxic effects

Investigation on tannins having antitumor properties led to the isolation of two new C-glycosidic ellagitannins (1 and 2) along with seven known ellagitannins (3-9) and a related polyphenolic constituent (10) from Lawsonia inermis leaves. Our intensive HRESIMS, 1D and 2D NMR, and ECD spectroscopic studies of new tannins have shown that one (1) has a monomer structure of C-glycosidic tannin, and the other (2) has a dimeric structure of 2,3-O-hexahydroxydiphenoyl glucopyranose and a C-glycosidic tannin. Among the known compounds, one (3) is a C-glycosidic tannin that was isolated first of all from nature, five were C-glycosidic tannins, vescalagin (4), 1-O-methylvescalagin (5), castalagin (6), stachyurin (7), and casuarinin (8), and one was an O-glycosidic ellagitannin, tellimagrandin II (9). The remaining phenolic constituent from the leaves was identified as valoneic acid dilactone (10). The ellagitannins 1, and 3-9 demonstrated noticeable cytotoxicity on human oral squamous cell carcinoma cell lines (HSC-2, HSC-4, and Ca9-22), and lower effects on human oral normal cells (HGF, HPC, and HPLF). Tellimagrandin II (9) had the highest tumor-specific cytotoxicity, and also cleaved poly (ADP-ribose) polymerase 1 in HSC-2 cells. These findings showed that L. inermis ellagitannins may be a candidate for the production of anti-oral cancer materials.

Antimicrobial Capacity of Plant Polyphenols against Gram-positive Bacteria: A Comprehensive Review

BACKGROUND

Multi-drug-resistant bacteria such as Methicillin-Resistant Staphylococcus aureus (MRSA) disseminate rapidly amongst patients in healthcare facilities and suppose an increasingly important cause of community-associated infections and associated mortality. The development of effective therapeutic options against resistant bacteria is a public health priority. Plant polyphenols are structurally diverse compounds that have been used for centuries for medicinal purposes, including infections treatment and possess, not only antimicrobial activity, but also antioxidant, anti-inflammatory and anticancer activities among others. Based on the existing evidence on the polyphenols' antibacterial capacity, polyphenols may be postulated as an alternative or complementary therapy for infectious diseases.

OBJECTIVE

To review the antimicrobial activity of plant polyphenols against Gram-positive bacteria, especially against S. aureus and its resistant strains. Determine the main bacterial molecular targets of polyphenols and their potential mechanism of action.

METHODOLOGY

The most relevant reports on plant polyphenols' antibacterial activity and their putative molecular targets were studied. We also performed virtual screening of thousand different polyphenols against proteins involved in the peptidoglycan biosynthesis to find potential valuable bioactive compounds. The bibliographic information used in this review was obtained from MEDLINE via PubMed.

RESULTS

Several polyphenols: phenolic acids, flavonoids (especially flavonols), tannins, lignans, stilbenes and combinations of these in botanical mixtures, have exhibited significant antibacterial activity against resistant and non-resistant Gram-positive bacteria at low μg/mL range MIC values. Their mechanism of action is quite diverse, targeting cell wall, lipid membrane, membrane receptors and ion channels, bacteria metabolites and biofilm formation. Synergic effects were also demonstrated for some combinations of polyphenols and antibiotics.

CONCLUSION

Plant polyphenols mean a promising source of antibacterial agents, either alone or in combination with existing antibiotics, for the development of new antibiotic therapies.

Antitumor Effects of Trimethylellagic Acid Isolated From Sanguisorba officinalis L. on Colorectal Cancer via Angiogenesis Inhibition and Apoptosis Induction

Previous studies have demonstrated that tannin could inhibit the proliferation and angiogenesis of cancer cells. However, the mechanism(s) associated with its antitumor effect remains unclear. Here, we investigated the effects of 3,3',4'-trimethylellagic acid (TMEA), a tannin compound isolated from Sanguisorba officinalis L., on the proliferation, angiogenesis, and apoptosis in cancer cells, as well as the underlying mechanism(s) related to its antitumor activity. TMEA was isolated from Sanguisorba officinalis L. by silica gel column chromatography. Molecular docking was carried out to assess active pocket binding between TMEA and vascular endothelial growth factor receptor 2 (VEGFR2). The antiangiogenic effect of TMEA on the migration and tube formation was detected in HUVECs by wound healing and tube formation assays, respectively. The antitumor effects of TMEA on the cell proliferation were determined in HepG2, A549, and SW620 cells by MTS assay in vitro and on the tumor growth of SW620 xenografts bearing in nude mice in vivo. The mRNA expression of Bcl-2, Bax, caspase-3, VEGF, PI3K, and mTOR were measured by qRT-PCR and protein expression of Bcl-2, Bax, caspase-3, VEGF, PI3K, and mTOR by Western blotting, and the protein expression of Bcl-2, Bax, caspase-3 and CD31 were detected by immunohistochemical analysis in vivo, respectively. The results showed that TMEA combined with VEGFR2 in the functional pockets of Asn223A, Gly922A, and Leu840A and inhibited the proliferation, migration, tube formation, and expression of VEGF and its downstream signaling mediators in HUVECs. TMEA also significantly inhibited the proliferation of HepG2, A549, and SW620 cancer cells in vitro, and suppressed the growth of SW620 tumors in vivo. Moreover, TMEA upregulated the expression of proapoptotic factors Bax and caspase-3 and downregulated the expression of antiapoptotic factors CD31 and Bcl-2 in cancer cells and/or tumor tissues. The data indicate that TMEA executes its anticancer activity by inducing apoptosis and inhibiting angiogenesis in cancer cells in vitro and tumor growth in vivo. The underlying anticancer mechanism is associated with the apoptotic and VEGF/PI3K/AKT/mTOR pathways.

Characterization of the complete chloroplast genome of Davidia involucrata Baill. (Nysssaceae), an endangered species endemic to China

Davidia involucrata Baill. is a kind of tertiary paleotropical plant floristic relic species unique to China. This rare plant is disappearing due to poor adaptability and serious poaching. We first assembled the complete chloroplast (cp) genome of Davidia involucrata Baill. by Illumina paired-end reads data. The whole genome was 169,085 bp, consisting of a pair of inverted repeats of 169,379 bp, large single copy region and a small single copy region (96,712 and 67,667 bp in length, respectively). The cp genome contained 90 genes, including 64 protein-coding genes, 22 trRNA genes and 4 rRNA genes. The overall GC content of the whole genome was 38.04%. A neighbor-joining phylogenetic analysis demonstrated a close relationship between Davidia involucrata Baill. and Nyssa yunnanensis.

Structures, NMR Spectroscopic Features, and Cytotoxic Properties of Oligomeric Hellinoyl (m-GO-m-GOG)-Type Ellagitannins from the Galls of Tamarix aphylla

Ellagitannin oligomers are large molecules habitually showing complex NMR spectra that are sometimes misinterpreted and lead to incorrect structures. Understanding the NMR spectroscopic features of a group of ellagitannins would overcome these inadequacies. In this study, investigation of the galls of Tamarix aphylla led to the isolation of three new ellagitannin oligomers, phyllagallins T1 (1), T2 (2), and Q1 (3), a known monomer nilotinin M4 (4), four known dimers, nilotinins D7 (5) and D8 (6), hirtellin B (7), and tamarixinin A (8), and a simple phenolic, dehydrotrigallic acid (9). 1D and 2D NMR, HRESI-TOFMS, and ECD experiments show that compounds 1-8 are hellinoyl-type ellagitannins. The NMR spectroscopic features of this type of ellagitannins and the reasons for the abnormal upfield shifts of glucose anomeric proton and hellinoyl moiety proton signals are established considering the experimental results as well as quantum chemical calculation on a simple hellinoyl-type monomer, phyllagallin M2. Based on these results, the NMR assignments reported previously by a different research group for bracteatinin T₁ and hirtellin T₃ are revised. A cytotoxicity study against human oral squamous cell carcinoma cell lines (Ca9-22, HSC-2, and HSC-4) and human mesenchymal normal oral cells (HGF, HPC, and HPLF) showed cytotoxic effects with tumor-specificity higher than 5.2, 3.0, 1.6, and 2.0 for compounds 5, 2, 9, and 3, respectively.

Transcriptomic Responses of Dove Tree (Davidia involucrata Baill.) to Heat Stress at the Seedling Stage

The dove tree (Davidia involucrata Baill.), a tertiary relic species, is adapted to cool climates. With the progression of global warming, high-temperature stress has become the primary environmental factor restricting geographic distribution, ex situ conservation, and landscape application for D. involucrata resources. However, the detailed molecular events underlying D. involucrata responses to heat stress are poorly understood. Here, we conducted RNA-Seq-based gene expression profiling in D. involucrata seedlings during the time course of a 42 °C heat treatment (0, 1, 6, and 12 h). After de novo assembly, we obtained 138,923 unigenes, of which 69,743 were annotated in public databases. Furthermore, 19,532, 20,497 and 27,716 differentially expressed genes (DEGs) were identified after 1 h (HS1), 6 h (HS6), and 12 h (HS12) of heat treatment in comparison to 0 h (HS0), respectively. Based on a KEGG enrichment analysis, the two pathways “protein processing in endoplasmic reticulum” and “plant hormone signal transduction” are hypothesized to play vital roles during heat response in D. involucrata, and their potential interactions during heat stress are also discussed. In addition, 32 genes encoding putative heat shock transcription factors (Hsfs) were found to be associated with the response of D. involucrata to heat stress. Finally, the expression patterns of eight heat-responsive genes derived from qRT-PCR were in agreement with their transcript level alterations, as determined by a transcriptome analysis. Taken together, our transcriptomic data provide the first comprehensive transcriptional profile affected by heat stress in D. involucrata, which will facilitate further studies on the improvement of heat tolerance in this rare and endangered species.

Elaeocarpusin Inhibits Mast Cell-Mediated Allergic Inflammation

Mast cells are major effector cells for allergic responses that act by releasing inflammatory mediators, such as histamine and pro-inflammatory cytokines. Accordingly, different strategies have been pursued to develop anti-allergic and anti-inflammatory candidates by regulating the function of mast cells. The purpose of this study was to determine the effectiveness of elaeocarpusin (EL) on mast cell-mediated allergic inflammation. We isolated EL from Elaeocarpus sylvestris L. (Elaeocarpaceae), which is known to possess anti-inflammatory properties. For this study, various sources of mast cells and mouse anaphylaxis models were used. EL suppressed the induction of markers for mast cell degranulation, such as histamine and β-hexosaminidase, by reducing intracellular calcium levels. Expression of pro-inflammatory cytokines, such as tumor necrosis factor-α and IL-4, was significantly decreased in activated mast cells by EL. This inhibitory effect was related to inhibition of the phosphorylation of Fyn, Lyn, Syk, and Akt, and the nuclear translocation of nuclear factor-κB. To confirm the effect of EL in vivo, immunoglobulin E-mediated passive cutaneous anaphylaxis (PCA) and ovalbumin-induced active systemic anaphylaxis (ASA) models were induced. EL reduced the PCA reaction in a dose dependent manner. In addition, EL attenuated ASA reactions such as hypothemia, histamine release, and IgE production. Our results suggest that EL is a potential therapeutic candidate for allergic inflammatory diseases that acts via the inhibition of mast cell degranulation and expression of proinflammatory cytokines.

Telomerase Inhibitors from Natural Products and Their Anticancer Potential

Telomeres and telomerase are nowadays exploring traits on targets for anticancer therapy. Telomerase is a unique reverse transcriptase enzyme, considered as a primary factor in almost all cancer cells, which is mainly responsible to regulate the telomere length. Hence, telomerase ensures the indefinite cell proliferation during malignancy—a hallmark of cancer—and this distinctive feature has provided telomerase as the preferred target for drug development in cancer therapy. Deactivation of telomerase and telomere destabilization by natural products provides an opening to succeed new targets for cancer therapy. This review aims to provide a fundamental knowledge for research on telomere, working regulation of telomerase and its various binding proteins to inhibit the telomere/telomerase complex. In addition, the review summarizes the inhibitors of the enzyme catalytic subunit and RNA component, natural products that target telomeres, and suppression of transcriptional and post-transcriptional levels. This extensive understanding of telomerase biology will provide indispensable information for enhancing the efficiency of rational anti-cancer drug design.

Structures and Antibacterial Properties of Isorugosins H-J, Oligomeric Ellagitannins from Liquidambar formosana with Characteristic Bridging Groups between Sugar Moieties

Three new ellagitannin oligomers, isorugosins H (1), I (2), and J (3), together with 11 known hydrolyzable tannins were isolated from an aqueous acetone extract of the fresh leaves of Liquidambar formosana. Their chemical structures were elucidated based on spectroscopic data and chemical conversion into known hydrolyzable tannins. The bridging mode of the valoneoyl groups between their sugar moieties has been identified only in this plant species. Additionally, the effects of the isorugosins isolated from this species on drug-resistant bacteria were evaluated and showed that isorugosin A (4) exhibited the most potent antibacterial activity against methicillin-resistant Staphylococcus aureus (MRSA). The isorugosins also had a suppressing effect on pigment formation in Pseudomonas aeruginosa. The isorugosin-protein complexes were analyzed using size-exclusion chromatography and polyacrylamide gel electrophoresis to clarify the relationship of their antibacterial properties with their protein interaction potency as hydrolyzable tannins. The results suggested that the antibacterial properties of hydrolyzable tannins are not simply a result of their binding activity to proteins, but are due to other factors such as the accessibility of polyphenolic acyl groups to bacterial membranes.