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At least 19 recordsLinked to original sources
PubMed2004

Effects of benzyl ether type dendrons as hole-harvesting antennas, and shielding for the neutralization of stilbene core radical cations with chloride ion during two-photon ionization of stilbene dendrimers having stilbene core and benzyl ether type dendrons.

The two-photon ionization (TPI) process (308 and 266 nm) of stilbene dendrimers having a stilbene core and benzyl ether type dendrons has been investigated in an acetonitrile and 1,2-dichloroethane mixture (3:1) in order to elucidate the dendrimer effects. The quantum yield of the formation of stilbene core radical cation during the 308-nm TPI was independent of the dendron generation of the dendrimers, whereas a generation dependence of the quantum yield of the radical cation was observed during the 266-nm TPI, where both the stilbene core and benzyl ether type dendron were ionized, suggesting that the subsequent hole transfer occurs from the dendron to the stilbene core, and that the dendron acts as a hole-harvesting antenna. The neutralization rate of the stilbene core radical cation with the chloride ion, generated from the dissociative electron capture by 1,2-dichloroethane, decreased with the increase in the dendrimer generation, suggesting that the dendron is an effective shield of the stilbene core radical cation against the chloride ion.

Journal Article↗
PubMed2000

Metabolic activation of the proestrogens trans-stilbene and trans-stilbene oxide by rat liver microsomes.

A liver microsome-mediated activation of the proestrogens trans-stilbene and trans-stilbene oxide was found in this study. trans-Stilbene and trans-stilbene oxide were negative in estrogen reporter assay using estrogen-responsive human breast cancer cell line MCF-7 and growth assay in rat pituitary tumor cell line MtT/E-2. However, these compounds exhibited estrogenic activity after incubation with liver microsomes of 3-methylcholanthrene-treated rats in the presence of NADPH. In contrast, cis-stilbene and cis-stilbene oxide did not show estrogenic activity after such incubation. When trans-stilbene was incubated with the liver microsomes of 3-methylcholanthrene-treated rats in the presence of NADPH, two metabolites were detected by HPLC. They were identified unequivocally as trans-4-hydroxystilbene and trans-4, 4'-dihydroxystilbene by mass and UV spectral comparison with authentic samples. The oxidase activity of the liver microsomes toward trans-stilbene was inhibited by SKF 525-A and alpha -naphthoflavone. Minor activity was observed when liver microsomes of untreated or phenobarbital-treated rats were used instead of those from 3-methylcholanthrene-treated rats. trans-4-Hydroxystilbene and trans-4,4'-dihydroxystilbene exhibited significant estrogenic activities. These results suggest that the estrogenic activities of trans-stilbene and trans-stilbene oxide were due to formation of hydroxylated metabolites.

Animals↗
PubMed1997

Induction of hepatic heme oxygenase and changes in cytochrome P-450s in response to oxidative stress produced by stilbenes and stilbene oxides in rats.

Both trans- and cis-stilbene oxide (TSO and CSO) markedly induced heme oxygenase-1 (HO-1) at the transcriptional level in rat liver. HO-1 induction by TSO and CSO was preceded by glutathione (GSH) depletion in the liver. Pretreatment of rats with buthionine sulfoximine (BSO), an inhibitor of GSH biosynthesis, enhanced GSH depletion evoked by either TSO or CSO and augmented the increase in HO-1 mRNA. In contrast, pretreatment with perfluorodecanoic acid (PFDA), which reduced hepatic GSH S-transferase activity, prevented TSO- and CSO-mediated GSH depletion and abolished HO-1 induction. In addition, TSO and CSO enhanced c-jun but not c-fos mRNA, which is in parallel with the HO-1 mRNA change. These findings indicate that the oxidative stress evoked by GSH depletion after the treatment of rats with stilbene oxides could stimulate both HO-1 and c-jun gene expression. Pretreatment with either BSO or PFDA also affected the induction of CYP2B1/2 mRNA and apoprotein by TSO or CSO, suggesting that not only the change of heme pool size but also some other unknown factor or factors may be involved in the regulation of the CYP2B1/2 and HO-1 gene expression. cis-Stilbene (CS), a parent compound of CSO, also induced HO-1 mRNA, together with hepatic GSH depletion, but trans-stilbene (TS) failed to elevate HO-1 mRNA under the experimental conditions. In addition, CS increased CYP2B1/2 mRNA, whereas TS did not. These results suggest that CS could be rapidly oxidized by cytochrome P-450 (P-450) to CSO, leading to GSH depletion in the liver. Such differences in the hepatic metabolic pathways of CS and TS are attributable to the differential effects on HO and P-450 induction by these compounds. Like other phenobarbital-type P-450 inducers, TSO and CSO also induced CYP2C6 and 3A2 apoproteins in rat liver. Stilbene oxide reduced CYP2E1 mRNA and apoproteins for CYP2E1 and 2C11. All of these findings indicate that stilbene compounds have unique effects on hepatic HO-1 and P-450 regulation in rats.

Animals↗
PubMed2003

Isolation and characterization of a stilbene-degrading strain of Pseudomonas fluorescens, and production of antioxidant compounds by stilbene metabolism.

In this study, we consider the use of hydrocarbon-degrading bacteria that degrade trans-stilbene as a novel approach for synthesizing potentially bioactive hydroxylated stilbenes. A trans-stilbene-degrading bacterium, MN2, was isolated from activated sludge through enrichment culture, and identified as Pseudomonas fluorescens using conventional techniques. Degradation of trans-stilbene by this strain yielded two metabolites that had significant antioxidant activity.

Antioxidants↗
PubMed2005

Excited-state behavior of trans and cis isomers of stilbene and stiff stilbene: a TD-DFT study.

The first part of the isomerization path on the two lowest excited states of trans and cis isomers of stilbene and stiff stilbene is investigated by means of TD-PBE0 calculations in the gas phase and in heptane solution. Solvent effects are taken into account by the PCM model. The excited-state optimized structures and the computed absorption and emission frequencies are in good agreement with the available experimental results. In all of the examined compounds, the isomerization process before barrier crossing occurs on the HOMO --> LUMO bright state, whereas the role played by other single-excitation states appears negligible. The relative energy barriers on the isomerization paths are consistent with the experimental excited-state lifetimes, suggesting a unifying picture of the isomerization process in stilbene-like molecules.

Models, Chemical↗
PubMed2005

Importance of properties of the lowest and higher singlet excited states on the resonant two-photon ionization of stilbene and substituted stilbenes using two-color two-lasers.

Radical cations of trans-stilbene and substituted trans-stilbenes (stilbenes and the radical cations denote Sand S(*+), respectively) were generated from the resonant two-photon ionization (TPI) in acetonitrile with irradiation of one-laser (266- or 355-nm laser) and with simultaneous irradiation of two-color two-lasers (266- and 532-nm or 355- and 532-nm lasers) with the pulse width of 5 ns each. The formation yields of S(*+), the TPI efficiency, depended on the properties of S in the lowest and higher singlet excited state (S(S(1)) and S(S(n))), generated from one-photon excitation with 266- or 355-nm laser and from two-photon excitation with simultaneous irradiation of 266- and 532-nm or 355- and 532-nm lasers, respectively. The TPI efficiency using two-color two-lasers increased compared with that using one-laser. It is confirmed that the TPI proceeds through two-step two-photon excitation with the S(0) --> S(1) --> S(n)() transition. In addition to the electronic character of S(S(0)) which depends on the substituent of S, oxidation potential, and molar absorption coefficient of the S(0) --> S(1) absorption as well-known important factors for the TPI efficiency, it is shown that properties of S(S(1)) and S(S(n)) such as lifetimes, electronic characters of S(S(1)) and S(S(n)), molar absorption coefficient of the S(1) --> S(n) absorption, and ionization rate from S(S(n)) are also important.

Journal Article↗
PubMed2005

Expression of transgenic stilbene synthases in wheat causes the accumulation of unknown stilbene derivatives with antifungal activity.

The expression of foreign phytoalexins in a new host is thought to increase fungal resistance, since host-specific pathogens have not experienced selection for detoxifying or metabolising the novel antifungal compounds. Two resveratrol synthase genes vst1 and vst2 from grapevine (Vitis vinifera L.) and the pinosylvin synthase gene pss from pine (Pinus sylvestris L.) were stably transformed into bread wheat. The expression of the target genes is regulated by stress-inducible grapevine promoters. The vst1 and vst2 promoters were functional in wheat and retained their expression profiles described for grapevine. ALL vst and pss transgenic lines accumulated stilbene derivatives upon induction by UV light. The detected stilbenes showed a remarkable similarity to resveratrol and pinosylvin, however were found to be more hydrophilic than resveratrol and pinosylvin. Upon inoculation with the biotrophic pathogen Puccinia recondita f.sp. tritici several vst expressing wheat lines showed a significant reduction of disease symptoms (19 +/- 9% to 27 +/- 8%) compared to wild-type plants. The reduction of disease symptoms was even more obvious after inoculation with the facultative biotrophic pathogen Septoria nodorum Berk. and ranged from 42 +/- 13% to 71 +/- 4%. None of the four tested pss expressing lines showed a reduction in disease incidence.

Acyltransferases↗
PubMed2001

Stilbene compounds and stilbene synthase expression during ripening, wilting, and UV treatment in grape cv. Corvina.

The content of selected phenolic compounds including resveratrol (trans-3,5,4'-trihydroxystilbene) and its cis-isomer and glucosides (piceides) were monitored in grape (Vitis vinifera L. cv. Corvina) berry skin during ripening in the vineyard and in response to the post-harvest drying process (wilting). Four wilting conditions were compared (traditional, mixed, low-temperature, and high-temperature) to verify the eliciting effect of drying on resveratrol production. During fruit ripening the cis-piceid was the major stilbene found in berry skins, and a weak accumulation of stilbene synthase (STS) mRNA was observed, whereas UV-light irradiation greatly stimulated STS transcript of unripe berries. A time-course experiment showed the highest STS mRNA accumulation and resveratrol content (34 microg/g fresh weight at 58 days) occurring in berry skins in a mixed wilting process.

Acyltransferases↗
PubMed1995

Reaction mechanisms of homodimeric plant polyketide synthase (stilbenes and chalcone synthase). A single active site for the condensing reaction is sufficient for synthesis of stilbenes, chalcones, and 6'-deoxychalcones.

Stilbene (STS) and chalcone (CHS) synthases are homodimeric, related plant-specific polyketide synthases. Both perform a sequential condensation of three acetate units to a starter residue to form a tetraketide intermediate that is folded to the ring systems specific to the different products. Protein cross-linking and site-directed mutagenesis identified a subunit contact site in position 158, close to the active site (Cys169). This suggested that the active site pockets may be neighboring, possibly alternating in the condensing reactions rather than acting independently. This was investigated by coexpression of active site mutants with differently mutated, inactive proteins. With both STS and CHS, the heterodimers synthesized the end products, indicating that each subunit performed all three condensations. In co-action with a monomeric reductase, CHS also synthesizes 6'-deoxychalcone, but with the chalcone as second product when using plant preparations. The two enzymes expressed as single species in Escherichia coli synthesized both products, and both were also obtained with a CHS heterodimer containing a single active site. The results showed that 6'-deoxychalcone synthesis required no other plant factor and that the formation of two products may be an intrinsic property of the interaction between dimeric CHS and monomeric reductase.

Acyltransferases↗
PubMed2003

Synthesis, photochemistry and photophysics of stilbene-derivatized fullerenes.

The photochemistry and photophysics of two sets of stilbene-derivatized fullerene isomers, in which stilbene is covalently linked to C60, are described. Synthesis and characterization of cis- and trans-stilbene substituted methanofullerenes 1 and 2, and cis- and trans-stilbene substituted fulleropyrrolidines 7 and 8 are described. While UV irradiation of the stilbene-substituted ketal precursors to 1 and 2 lacking the fullerene moiety afforded a photostationary state with 90:10 cis:trans ratio, similar to that of other model stilbene systems, direct and fluorenone-sensitized irradiation of 1 and 2 led to complete conversion to the trans isomer 2, as determined by HPLC analysis. The same results were obtained using cis-trans isomers 7 and 8, namely, the photostationary state on excitation below 350 nm is essentially 100% trans. No isomerisation in either system was obtained on excitation above 400 nm, where all the light is absorbed by the fullerene moiety. By analogy to previous studies of quenching of stilbene excited states, these results suggest that both singlet and triplet excited states of the trans-stilbene moiety in 2 and 8 are being quenched by intramolecular energy transfer to the attached C60, while the much shorter lived cis-stilbene excited states are not similarly quenched. Fluorescence studies on compound 8 support this hypothesis, since the characteristic fluorescence emission of trans-stilbene and trans-stilbene derivatives is not observed in the case of adduct 8. Because of the well established fact that trans-stilbene S1 states are longer lived than the S1 states of the corresponding cis isomers, rapid intramolecular singlet-singlet energy transfer to the appended C60 moiety, ket approximately 10(12) s(-1), is able to compete effectively with radiative and radiationless deactivation of the trans-stilbene S1 states in 2 and 8, but not in the corresponding cis isomers 1 and 7.

Energy Transfer↗
PubMed2006

Biosynthesis of plant-specific stilbene polyketides in metabolically engineered Escherichia coli.

BACKGROUND: Phenylpropanoids are the precursors to a range of important plant metabolites such as the cell wall constituent lignin and the secondary metabolites belonging to the flavonoid/stilbene class of compounds. The latter class of plant natural products has been shown to function in a wide range of biological activities. During the last few years an increasing number of health benefits have been associated with these compounds. In particular, they demonstrate potent antioxidant activity and the ability to selectively inhibit certain tyrosine kinases. Biosynthesis of many medicinally important plant secondary metabolites, including stilbenes, is frequently not very well understood and under tight spatial and temporal control, limiting their availability from plant sources. As an alternative, we sought to develop an approach for the biosynthesis of diverse stilbenes by engineered recombinant microbial cells. RESULTS: A pathway for stilbene biosynthesis was constructed in Escherichia coli with 4-coumaroyl CoA ligase 1 4CL1) from Arabidopsis thaliana and stilbene synthase (STS) cloned from Arachis hypogaea. E. coli cultures expressing these enzymes together converted the phenylpropionic acid precursor 4-coumaric acid, added to the growth medium, to the stilbene resveratrol (>100 mg/L). Caffeic acid, added in the same way, resulted in the production of the expected dihydroxylated stilbene, piceatannol (>10 mg/L). Ferulic acid, however, was not converted to the expected stilbene product, isorhapontigenin. Substitution of 4CL1 with a homologous enzyme, 4CL4, with a preference for ferulic acid over 4-coumaric acid, had no effect on the conversion of ferulic acid. Accumulation of tri- and tetraketide lactones from ferulic acid, regardless of the CoA-ligase expressed in E. coli, suggests that STS cannot properly accommodate and fold the tetraketide intermediate to the corresponding stilbene structure. CONCLUSION: Phenylpropionic acids, such as 4-coumaric acid and caffeic acid, can be efficiently converted to stilbene compounds by recombinant E. coli cells expressing plant biosynthetic genes. Optimization of precursor conversion and cyclization of the bulky ferulic acid precursor by host metabolic engineering and protein engineering may afford the synthesis of even more structurally diverse stilbene compounds.

Acyltransferases↗
PubMed2002

Density functional studies of the ground- and excited-state potential-energy curves of stilbene cis-trans isomerization.

Using spin-unrestricted density functional theory (the VWN Becke-Perdew potential), including broken-symmetry and spin-projection methods, we have obtained the potential-energy curves as a function of the central torsional angle of stilbene in the ground (S0), the first excited triplet (T1), the first excited singlet (S1), and the doubly excited singlet (S2) states. The thermal trans-->cis isomerization of stilbene passes through a diradical broken-symmetry electronic structure around the twisted conformation (90 degrees central torsional angle) in the ground state. Our calculations support the proposed triplet mechanism for sensitized cis [symbol: see text] trans photoisomerization and the nonadiabatic singlet mechanism proposed by Orlandi and Siebrand. On the T1 potential-energy curve, the rotation of the C=C bond for both trans- and cis-stilbene will lead stilbene to the twisted conformation, from which the twisted stilbene will decay to the ground-state surface that is nearly isoenergetic with the T1 surface and has diradical electronic structure in the twisted region. On the S1 potential-energy curve, the energy increases in the direction from trans- to the twisted stilbene, and crosses with the neutral doubly excited S2 potential-energy curve, which has a minimum at the twisted structure and is lower in energy than the zwitterionic doubly excited state. The twisted stilbene around the energy minimum of the neutral doubly excited S2-state will decay onto the ground-state surface from where the rotation of the C=C bond leads the twisted stilbene to either the trans or cis configuration and the isomerization of stilbene is then completed. Similar studies have also been performed on a stilbene derivative with a substituent group, NHCOCH3.

Journal Article↗
PubMed1991

Coordinate- and elicitor-dependent expression of stilbene synthase and phenylalanine ammonia-lyase genes in Vitis cv. Optima.

The mechanisms controlling the induction of stilbene synthase and phenylalanine ammonia-lyase (PAL), two putative key regulatory enzymes of the biosynthetic pathway to stilbene phytoalexins, have been investigated. The induction was studied in cell suspension cultures of grape (Vitis cv. Optima) by treatment with fungal cell wall. Several independent cDNA clones for PAL and stilbene synthase were isolated from a cDNA library of fungal cell wall-induced grape cells and identified by sequence analysis. The stilbene synthase cDNA sequence of pSV21 predicted a protein of 392 amino acids and Mr 42,791, similar in size to that observed experimentally for immunodetected stilbene synthase. The cDNA sequences of pSV21 and pSV25 differed in 76 bp in the coding region. The sequences of grape stilbene synthase cDNAs exhibited significant homology to the sequence reported for the peanut stilbene synthase cDNA. Both PAL and stilbene synthase mRNA, measured by RNA blot hybridizations, were induced within 1 h of addition of fungal cell wall preparations to the cell cultures, rose to a maximum by the sixth hour, then declined slowly over the next 20 h. The activities of PAL and stilbene synthase were also induced in parallel, but reached their maximum at different times after fungal cell wall addition to the cell cultures. The induction patterns of stilbene synthase and PAL in grape and peanut are discussed.

Acyltransferases↗
PubMed2003

Role of viticultural factors on stilbene concentrations of grapes and wine.

Stilbenes are phenolics that can be found in different grapevine organs, such as berries, leaves, canes and roots. Stilbenes act as antifungal compounds since they are synthesized by the plant in response to pathogen attack. Other abiotic elicitors, such as ultraviolet rays and heavy metals, can trigger stilbene production. Many stilbenic compounds have been detected in grapes and wine (resveratrol, piceid, viniferins, astringin, etc.). The latest stilbene to be analyzed is piceatannol (or astringinin). Stilbene synthesis in grapes depends on different viticultural factors such as the grape variety, the environment and cultural practices. Concerning grape variety, red berry-grapes have higher stilbene levels than white berry-grapes. With regard to climate, preliminary results suggest a positive correlation between vineyard elevation and stilbene grape concentrations. Quality-oriented cultural practices produce grapes with high levels of stilbenes.

Agriculture↗
PubMed2000

Effects of naturally occurring stilbene glucosides from medicinal plants and wine, on tumour growth and lung metastasis in Lewis lung carcinoma-bearing mice.

Stilbene glucosides are naturally occurring phytoalexins, found in a variety of medicinal plants. Among the stilbene derivatives, resveratrol 3-O-D-glucoside (piceid) is found in grapes and wine. We studied the effects of stilbene glucosides isolated from medicinal plants and grapes on tumour growth and lung metastasis in mice bearing highly metastatic Lewis lung carcinoma (LLC) tumours. We also studied the inhibitory effects of stilbene glucosides on differentiation of human umbilical vein endothelial cells (HUVECs) to form a capillary network. Tumour growth in the right hind paw and lung metastasis were inhibited by oral administration of the stilbene glucosides, piceid and 2,3,5,4'-tetrahydroxystilbene-2-O-D-glucoside for 33 consecutive days, in LLC-bearing mice. As the number of CD8+ and NK1.1+ T cells in the spleen was not affected, the inhibitory effects of these stilbene glucosides on tumour growth and lung metastasis could not be explained by natural killer or cytotoxic T lymphocyte activation. Piceid inhibited the DNA synthesis in LLC cells at a concentration of 1000 microM, but not at lower concentrations (10-100 microM). 2,3,5,4'-Tetra-hydroxystilbene-2-O-D-glucoside also inhibited DNA synthesis in LLC cells (IC50 81 microM). In addition, both stilbene glucosides inhibited the formation of capillary-like tube networks (angiogenesis) of HUVECs at concentrations of 100 to 1000 microM. We suggest that the antitumour and antimetastatic activity of the stilbene glucosides, piceid and 2,3,5,4'-tetrahydroxystilbene-2-O-D-glucoside, might be due to the inhibition of DNA synthesis in LLC cells and angiogenesis of HUVECs.

Animals↗