Structurally diverse stilbenes from Gnetum parvifolium and their anti-neuroinflammatory activities

Phytochemical investigation on the aerial parts of Gnetum parvifolium led to the isolation of 15 new and eight known structurally diverse stilbenes. The isolated compounds comprised (E)- or (Z)-stilbene (1-6, 15-20), dihydrostilbene (21), phenylbenzofuran (7, 8, 22), benzylated stilbene (9-11), benzylated stilbene dimer (12), and nitrogen-containing stilbene (13a, 13b, 14) types. The structures of the new compounds (1-12, 13a, 13b, 14) were established through spectroscopic analyses and experimental and calculated ECD data. Compound 12 is the first stilbene dimer connected through a benzyl group. In the anti-neuroinflammatory activity assay, compounds 4, 5, 9-11, 13b, and 16-21 displayed significant inhibitory effects against LPS-induced NO release in BV-2 microglial cells, with IC50 values of 0.35-16.1 μM. Compound 10 had the most potent activity (IC50 = 0.35 μM), and the further research indicated that it could decrease the mRNA levels of iNOS, IL-1β, IL-6, and TNF-α in a dose-dependent manner.

Oligostilbenes from the leaves of Gnetum latifolium and their biological potential to inhibit neuroinflammation

Oligostilbenes are polyphenol oligomers derived from resveratrol and are commonly produced by members of the Gnetaceae family, and many researchers have focused on their anti-inflammatory activities. The EtOAc fraction of a Gnetum latifolium extract showed inhibitory activity against neuroinflammation induced by the transfection of Aβ_1-42 into microglial BV-2 cells. The bioassay-guided isolation of the 70% EtOH extract of this plant resulted in three previously undescribed resveratrol oligostilbenes and ten known stilbene derivatives. The structures of the isolated compounds were established based on extensive NMR spectroscopic analysis. The absolute configurations of the three undescribed compounds were confirmed by comparison with available compounds with known stereochemistry and by ECD calculations and molecular modelling. Latifoliols A and B are the first reported oligostilbenes with a bridged 3-oxabicyclo[3.3.0]octane moiety, and latifoliol C was formed by the condensation of gnemontanin G with oxyresveratrol. Moreover, the hypothetical biogenetic pathway of latifoliols A, B and C was proposed. The potential anti-inflammatory activities of the thirteen isolated compounds were tested by measuring their effect on the secreted NO concentrations induced by transfection with plasmids expressing the Aβ_1-42 gene in the BV-2 cell line. Interestingly, cis- and trans-shegansu B and latifolol, whose structures contained double bonds, strongly inhibited NO secretion in BV-2 cells, supporting the double binding effect of the stilbene derivative on inhibitory activity.

Proteome-Level Analysis of Metabolism- and Stress-Related Proteins during Seed Dormancy and Germination in Gnetum parvifolium

Gnetum parvifolium is a rich source of materials for traditional medicines, food, and oil, but little is known about the mechanism underlying its seed dormancy and germination. In this study, we analyzed the proteome-level changes in its seeds during germination using isobaric tags for relative and absolute quantitation. In total, 1,040 differentially expressed proteins were identified, and cluster analysis revealed the distinct time points during which signal transduction and oxidation-reduction activity changed. Gene Ontology analysis showed that "carbohydrate metabolic process" and "response to oxidative stress" were the main enriched terms. Proteins associated with starch degradation and antioxidant enzymes were important for dormancy-release, while proteins associated with energy metabolism and protein synthesis were up-regulated during germination. Moreover, protein-interaction networks were mainly associated with heat-shock proteins. Furthermore, in accord with changes in the energy metabolism- and antioxidant-related proteins, indole-3-acetic acid, Peroxidase, and soluble sugar content increased, and the starch content decreased in almost all six stages of dormancy and germination analyzed (S1-S6). The activity of superoxide dismutase, abscisic acid, and malondialdehyde content increased in the dormancy stages (S1-S3) and then decreased in the germination stages (S4-S6). Our results provide new insights into G. parvifolium seed dormancy and germination at the proteome and physiological levels, with implications for improving seed propagation.

A new stilbenoid compound from the lianas of Gnetum microcarpum

A new stilbene, malaysianol E (1), together with five known stilbenes namely gnetol (2), gnetucleistol C (3), gnetucleistol D (4), resveratrol (5) and E-viniferin (6) were successfully discovered from the acetone extract of the lianas of Gnetum microcapum. The structures of these stilbenes were determined on the basis of spectroscopic (1D and 2D NMR) and MS evidence. This paper describes the structural elucidation of the new compound, malaysianol E. The chemotaxonomic significance of this compound is briefly discussed.

Unambiguous Determination of the Absolute Configuration of Dimeric Stilbene Glucosides from the Rhizomes of Gnetum africanum

Dimeric stilbene glucosides 1-3 [two diastereomers of (-)-gnemonoside A (1a and 1b), (-)-gnemonoside C (2), and (-)-gnemonoside D (3)] as well as a mixture of the two enantiomers of gnetin C (4) were isolated from the rhizomes of Gnetum africanum. The two enantiomers of gnetin C, (+)-4 and (-)-4, were obtained from the aglycones of 1a and 1b, respectively. The configurations of these stilbenoids were investigated by NMR and vibrational circular dichroism (VCD) experiments. The absolute configurations of (-)-1a, (-)-2, (-)-3, and (-)-4 were established as 7aS,8aS by VCD spectroscopy in combination with density functional theory calculations. The antiamyloidogenic activity of the isolated stilbenes was also evaluated versus beta-amyloid fibrils. The four glucosides of gnetin C (1a, 1b, 2, and 3) were found to be the most active compounds, with inhibition percentages of 56, 56, 58, and 54 at 10 μM, respectively.

Highly potent oligostilbene sbLOX-1 inhibitor from Gnetum macrostachyum

Isolated oligostilbenes from G. macrostachyum exhibited sbLOX-1 inhibitory activity with IC50 values ranging from 0.14-11.91 microM. Of these oligostilbenoids, 12 (IC50 0.14 +/- 0.01 microM), 10 (IC50 0.33 +/- 0.11 microM), 11 (IC50 0.49 +/- 0.05 microM) and 7 (IC50 1.03 +/- 0.43 microM) were more active than nordihydroguaiaretic acid (NDGA) (P < 0.05) which was the positive control. The enzyme kinetic analysis revealed that 7 and 11 inhibited sbLOX-1 noncompetitively with Ki values of 11.2 and 71.4 nM. Compound 10 inhibited sbLOX-1 through mixed-competitive mechanisms (Ki = 13.8 nM and Ki' 56.7 nM). Moreover, 12 was an uncompetitive inhibitor with a Ki value of 0.8 nM. The inhibitory activity of oligostilbenes did not result from the antioxidant property, as demonstrated by DPPH and 13-HPOD scavenging assays. These compounds also showed ferric reducing capabilities, but had no effect in a Fe(3+)-bound sbLOX-1 model, as indicated by UV spectrophotometric and CD spectroscopic studies.

Pharmacokinetics and safety of resveratrol derivatives in humans after oral administration of melinjo (Gnetum gnemon L.) seed extract powder

Fruits and seeds of melinjo (Gnetum gnemon L.) are resveratrol derivative-rich materials. Pharmacokinetics of resveratrol derivatives in healthy volunteers after oral administration of 1000 mg of melinjo seed extract (MSE) powder were assessed and compared with those after oral dosing of trans-resveratrol (tRV) powder containing 4.8 mg of tRV only, equivalent to the content in 1000 mg MSE powder. Plasma tRV concentrations with enzymatic hydrolysis were maintained over 24 h, with a tmax of 12 h and a mean residence time (MRT) of 14 h, 5 and 2 times higher than those for tRV powder intake, respectively. Gnetin C, a resveratrol dimer, with hydrolysis was maintained in plasma for >96 h with a 36 h MRT. With repeated doses once daily for 28 days, plasma tRV and gnetin C concentrations with hydrolysis were in good agreement with the theoretical curves. MSE powder was well tolerated up to the oral dosing of 5000 mg with no serious adverse events.

trans-Resveratrol in Gnetum gnemon protects against oxidative-stress-induced endothelial senescence

Gnetum gnemon is an arboreal dioecious plant that is cultivated in Indonesia. The seeds of this species mainly contain dimeric stilbenoid compounds [gnetin C (1), gnemonoside A (2), and gnemonoside D (3)] along with trans-resveratrol (4). trans-Resveratrol has been reported to have antiaging, anticancer, and antidiabetic effects, as well as being a calorie restriction mimetic. SIRT1 exerts a protective effect against vascular senescence. In this study, the effects of these four main stilbenoid derivatives of a G. gnemon seed endosperm ethanolic extract on endothelial senescence were investigated. In streptozotocin-induced diabetic mice, administration of the G. gnemon ethanolic extract increased SIRT1 and decreased endothelial senescence. The concentration of 1 in blood plasma was 6-fold higher than 4 in these mice. Next, the in vitro effects of the four main stilbenoid derivatives of G. gnemon seeds were investigated. Senescent human umbilical vein endothelial cells were induced by hydrogen peroxide. Endothelial senescence was inhibited by 4, which increased the expression of endothelial nitric oxide synthase and SIRT1, whereas 1-3 had no effect. These results indicated that the ethanolic extract of G. gnemon seeds inhibits endothelial senescence, suggesting that 4 plays a critical role in the prevention of endothelial senescence.

Inhibitory activity of plant stilbenoids against nitric oxide production by lipopolysaccharide-activated microglia

Microglia-driven inflammatory processes are thought to play an important role in ageing and several neurological disorders. Since consumption of a diet rich in polyphenols has been associated with anti-inflammatory and neuroprotective effects, we studied the effects of twenty-five stilbenoids isolated from Milicia excelsa, Morus alba, Gnetum africanum, and Vitis vinifera. These compounds were tested at 5 and 10 µM on BV-2 microglial cells stimulated with bacterial lipopolysaccharide. Ten stilbenoids reduced lipopolysaccharide-induced nitric oxide production at 5 and/or 10 µM. Two tetramers, E-vitisin A and E-vitisin B, were the most effective molecules. Moreover, they attenuated the expression of the inducible NO synthase protein and gene.

Piper nigrum, Piper betle and Gnetum gnemon--natural food sources with anti-quorum sensing properties

Various parts of Piper nigrum, Piper betle and Gnetum gnemon are used as food sources by Malaysians. The purpose of this study is to examine the anti-quorum sensing (anti-QS) properties of P. nigrum, P. betle and G. gnemon extracts. The hexane, chloroform and methanol extracts of these plants were assessed in bioassays involving Pseudomonas aeruginosa PA01, Escherichia coli [pSB401], E. coli [pSB1075] and Chromobacterium violaceum CV026. It was found that the extracts of these three plants have anti-QS ability. Interestingly, the hexane, chloroform and methanol extracts from P. betle showed the most potent anti-QS activity as judged by the bioassays. Since there is a variety of plants that serve as food sources in Malaysia that have yet to be tested for anti-QS activity, future work should focus on identification of these plants and isolation of the anti-QS compounds.

A new resveratrol trimer derivative from Gnetum brunonianum

A new resveratrol trimer derivative, named as gnetubrunol A (1), together with five known stilbene derivatives, shegansu B (2), resveratrol (3), isorhapontigenin (4), gnetifolin E (5), and isorhapontigenin-11-O-β-d-glucopyranoside (6) were isolated from the lianas of Gnetum brunonianum Griff. Their structures were elucidated on the basis of spectral analysis (UV, IR, MS, (1)H NMR, (13)C NMR, and 2D NMR). The anti-inflammatory activities of 1, 5, and 6 have also been assayed.

Alkaloids from the Chinese vine Gnetum montanum

During a high-throughput screening campaign of a prefractionated natural product library, fractions from the Chinese vine Gnetum montanum showed in vitro activity against Pseudomonas aeruginosa wild-type strain, PAO1. UV-directed isolation of the organic extract from the vine leaves resulted in the purification of the new natural products N-methyllaudanosolinium trifluoroacetate (1), 3'-hydroxy-N,N-dimethylcoclaurinium trifluoroacetate (2), 1,9,10-trihydroxy-2-methoxy-6-methylaporphinium trifluoroacetate (3), and 6a,7-didehydro-1,9,10-trihydroxy-2-methoxy-6-methylaporphinium trifluoroacetate (4). Compound 4 is described here for the first time, and this is the first report of compounds 1-3 as natural products. Compounds 1-3 were found to racemize over time. Starting from commercially available (+)-boldine, through a series of semisynthetic reactions, a mechanism for the racemization of the isolated compounds is proposed. The known natural products (-)-latifolian A (5) and magnocurarine (6) were also isolated during these studies. The antibacterial activity was explained by the presence of 5, which displayed an IC50 value of 9.8 μM (MIC = 35 μM).

Stilbenoids from the melinjo (Gnetum gnemon L.) fruit modulate cytokine production in murine Peyer's patch cells ex vivo

Melinjo fruit ( Gnetum gnemon L.) has been used as a food in Southeast Asia. To investigate if this fruit has regulatory actions on ileal immune responses, we measured T-helper (Th) cytokine production, i.e., interleukin-2 (IL-2), IL-4, IL-5, and interferon-gamma (IFN- γ), in cultured Peyer's patch (PP) cells from mice orally treated with a methanol extract of melinjo fruit. Oral administration of the 50 % ethanol extract at 100 mg/kg/day significantly enhanced the production of the Th1 cytokines IL-2 and IFN- γ irrespective of concanavalin-A stimulation, whereas the production of the Th2 cytokines IL-4 and IL-5 was not affected. We also isolated seven active constituents accompanied with two new stilbenoids from the ethylacetate fraction of the extracts. The structure of the new stilbene glucosides gnemonoside L (5) and gnemonoside M (7) was determined by 1D and 2D NMR and MS analyses. Five known stilbenoids were identified as resveratrol (1), isorhapontigenin (2), gnemonoside D (4), gnetins C (3) and E (6). Among these tested compounds, only new stilbenoid 7 strongly enhanced Th1 cytokine production in cultured PP cells at 10 mg/kg/day. These results indicated that this melinjo extract and its active constituent 7 potentiated T-cell-dependent immune responses in the ileal mucosa.

[Synthesis and HIV-1 inhibitory activity of natural products isolated from Gnetum parvifolium and their analogues]

Resveratrol, isorhapontigenin and pinosylvin, isolated from Gnetum parvifolium, and their analogues have been synthesized and tested for their inhibitory activity of HIV-1. Natural product 12a and analogues (12d, 12e, 12g) display significant inhibitory activity of HIV-1 replication. Among them, compound 12d (trans-3, 4, 5, 4'-tetrahydroxystilbene) exhibits the most potent anti-HIV-1 activity with an IC50 value of 1.84 micromol x L(-1).

In vitro anti-influenza viral activities of stilbenoids from the lianas of Gnetum pendulum

The anti-influenza viral activities of six stilbenoids from the lianas of Gnetum pendulum C. Y. Cheng were evaluated with two different assays, neuraminidase (NA) activity assay and cytopathic effect (CPE) reduction assay. The NA assay results showed that all six stilbenoids exerted an NA inhibitory effect, while the CPE assay indicated that among them, isorhapontigenin (2), gnetupendin B (3), shegansu B (4), and gnetin D 6) exhibit significant in vitro anti-influenza viral activity in MDCK cells, with IC(50) values from 0.67 to 11.99 µg/mL in comparison to the positive controls oseltamivir acid and ribavirin whose IC(50) values were 0.040 and 5.54 µg/mL, respectively.

Gneyulins A and B, stilbene trimers, and noidesols A and B, dihydroflavonol-C-glucosides, from the bark of Gnetum gnemonoides

Gneyulins A (1) and B (2), two new stilbene trimers consisting of oxyresveratrol constituent units, and noidesols A (3) and B (4), two new dihydroflavonol-C-glucosides, were isolated from the bark of Gnetum gnemonoides. The structures and configurations of 1-4 were elucidated on the basis of 2D NMR correlations and X-ray analysis. Gneyulins A (1) and B (2) showed inhibition of Na(+)-glucose transporters (SGLT-1 and SGLT-2).

Stilbenoids isolated from the seeds of Melinjo (Gnetum gnemon L.) and their biological activity

A 50% EtOH extract of the dried endosperms of melinjo (Gnetum gnemon L.) was purified by a combination of column chromatography, including highly porous polymer, octadecylated silica (ODS), hydroxypropylated dextran (LH-20), and silica gel, resulting in the isolation of a new stilbenoid 1, named gnetin L, along with five previously identified stilbenoids 2-6 (gnetin C, gnemonosides A, C, and D, and resveratrol). All of these stilbenoids showed 1,1-diphenyl-2-picrylhydrazyl (DPPH) radical scavenging activity similar to that of ascorbic acid and dl-alpha-tocopherol. With the exception of gnemonoside A (3), these stilbenoids showed moderate antimicrobial activity. Inhibition of lipase from porcine pancreas was recognized in four stilbenoids excluding gnemonoside A (3) and resveratrol (6). Gnetin C (2), gnemonoside C (4), and gnemonoside D (5) inhibited the hydrolysis of starch by alpha-amylase from porcine pancreas. An EtOH extract containing these stilbenoids also showed DPPH radical scavenging effect, lipase and alpha-amylase inhibition activity, and antimicrobial activity against food microorganisms and enterobacteria. The present study indicates that melinjo and extracts containing these constituents are useful as health supplements.

Two new components from Gnetum pendulum

Two new compounds, 3-O-(13-hydroxy-9Z,11E,15E-octadecatrienoyl) cycloeucalenol (1) and 24'-hydroxy-tetracosyl ferulate (2), together with one known compound, tetracosyl ferulate (3), were isolated from the dried stems of Gnetum pendulum. The two new compounds were structurally elucidated by spectroscopic and chemical methods.

Isolation and biomimetic synthesis of anti-inflammatory stilbenolignans from Gnetum cleistostachyum

One new stilbenolignan, gnetucleistol F (1), and four known stilbenolignans, gnetofuran A (2), lehmbachol D (3), gnetifolin F (4) and gnetumontanin C (5) were isolated from the lianas of Gnetum cleistostachyum C. Y. CHENG (Gnetaceae). Their structures and relative configurations were determined by means of spectroscopic evidence. Compounds 1, 2, 3 and 4 were synthesized for the first time on the basis of their biogenetic pathway, and their possible biomimetical synthetic mechanisms were discussed. The pharmacological activities of all stilbenolignans have been tested. Among them, 1, 2, 3, 4 and 5 showed moderate inhibitory activities on TNF-alpha and 1 also showed potent inhibitory activity on malondialdehyde.

Bioactive stilbene dimers from Gnetum cleistostachyum

Two new stilbene dimers, named bisisorhapontigenin A (1) and cis shegansu B (2), together with gnetuhainin P (3) and gnetulin (4), were isolated from the lianas of Gnetum cleistostachyum C. Y. Cheng. Their structures were elucidated by means of spectroscopic evidences, including UV, IR, MS, 1H NMR, 13C NMR, NOE and 2D NMR, respectively. The pharmacological activities of compounds 1, 2 and 3 also have been tested.

Latifolians A and B, novel JNK3 kinase inhibitors from the Papua New Guinean plant Gnetum latifolium

As part of our search for natural products active against the JNK3 kinase, two novel, charged benzylisoquinolines, latifolian A (1) and latifolian B (2), were isolated from the stem bark of the Papua New Guinean vine Gnetum latifolium. The planar structures were determined through detailed 2D NMR analysis. The relative configurations were assigned after examination of the ROESY data and through detailed molecular modeling studies.

Stilbene derivatives from Gnetum cleistostachyum

Three new stilbene derivatives, named gnetucleistol A (1), B (2) and C (3), together with four known compounds, gnetifolin A (4), p-hydroxycinnamic acid (5), piceatannol (6) and resveratrol (7), were isolated from Gnetum cleistostachyum C.Y. Cheng (Gnetaceae). Their structures were elucidated on the basis of spectroscopic evidence (EI-MS, UV, IR, NOE, 1H, 13C and 2D NMR).

Preparation on Oligostilbenes of Isorhapontigenin by Oxidative Coupling Reaction

Four new compounds 1-4 were obtained from an oxidative coupling reaction of (E)-isorhapontigenin using FeCl(3) as oxidant. Their structures and stereochemistry were determined on the basis of spectroscopic evidence [UV, IR, MS, (1)H-, (13)C-NMR, NOE and 2D NMR], and their possible formation mechanisms were also discussed, respectively.

Stilbenoids from the lianas of Gnetum pendulum

The first new isorhapontigenin dimer glucoside gnetupendin D (1) and a stilbene dimer coupled by a resveratrol and an oxyresveratrol with a cis-dihydrobenzofuran were obtained from the lianas of Gnetum pendulum C. Y. Cheng (Gnetaceae), along with nine known compounds. Their structures and stereochemistry were elucidated by chemical and spectral evidence, especially 2D NMR spectroscopic techniques. Pharmacological activities on anti-inflammation have been tested.

Phenolic constituents of Gnetum klossii

Four new phenolic derivatives, gnetofurans A-C (1-3) and dihydropinosylvindiol (4), were isolated from a methanol-soluble extract of the stems of Gnetum klossii, together with nine known compounds [gnetifolin F (5), isorhapontigenin, gnetulin, gnetins E and C, latifolol, gnetol, (-)-epsilon-viniferin, and trans-resveratrol]. The structures of the new compounds were determined by spectral data analysis.

Gnetol as a potent tyrosinase inhibitor from genus Gnetum

Gnetol (2,3',5',6-tetrahydroxy-trans-stilbene), a naturally occurring compound particularly found in the genus Gnetum, had a strong inhibitory effect on murine tyrosinase activity. Gnetol (IC50, 4.5 microM) was stronger than kojic acid (IC50, 139 microM) as a standard inhibitor for murine tyrosinase activity. Moreover, gnetol significantly suppressed, melanin biosynthesis in murine B16 melanoma cells.

Stilbene derivatives from Gnetum gnemon Linn

Four stilbene derivatives, gnemonols K and L (resveratrol trimers), M (isorhapontigenin dimer), and gnemonoside K (glucoside of resveratrol trimer) together with eleven known stilbenoids and a lignan were isolated from the acetone, methanol and 70% methanol soluble parts of the root of Gnetum gnemon (Gnetaceae). The structures of the isolates were determined by spectral analysis. The antioxidant activity of the stilbenoids on lipid peroxide inhibition and super oxide scavenging activity were also investigated.

Three new trimeric stilbenes from Gnetum gnemon

Three stilbene trimers (gnemonols D, E, F) were isolated from the root of Gnetum gnemon. The structures were determined by spectroscopic analysis. In addition, the antioxidant activity of the compounds on lipid peroxide inhibition and super oxide scavenging activity were also investigated.

Stilbenoids from the stem of Gnetum latifolium (Gnetaceae)

An acetone extract of the stem of Gnetum latifolium Blume afforded the stilbene trimer (latifolol) together with five known stilbenoids (gnetin E, gnetin D, gnetin C, (-)epsilon -viniferin and resveratrol). Their structures were elucidated on the basis of spectral evidence, in particular by using 2D NMR methods.

[Effect of stilbene polymer (Gn-3) on experimental liver injuries in mice]

AIM

To study the protective effect of Gn-3 (a stilbene polymer isolated from Gnetum parvifolium) against liver injury induced by CCl4, N-acetyl-p-aminophenol (APAP) and Bacillus Calmette-Guerin (BCG) plus bacterial lipopolysaccharide (LPS) in mice.

METHODS

The experimental model of liver injury were induced by 0.1% CCl4 i.p. (10 mL.kg-1.d-1 for 3d), APAP i.p. (150 mg.kg-1) or BCG (5 mg) plus LPS (7.5 micrograms) in mice. The levels of ALT in serum, MDA and GSH in liver tissues were detected. The histopathologic changes were observed by light microscope.

RESULTS

Gn-3 was shown to markedly reduce the elevated serum ALT levels, liver tissue MDA and improve the histopathological changes in all the three experimental liver injury models. No effect of Gn-3 was observed on the liver GSH level in liver injury mice.

CONCLUSION

Gn-3 was found to inhibit the development of liver injury caused by CCl4, APAP, or BCG plus LPS. This means that Gn-3 has liver protective effects.