Pterostilbene production by microorganisms expressing resveratrol O-methyltransferase

Pterostilbene (3,5-dimethoxy-4′-hydroxyl-trans-stilbene)—a derivative of resveratrol—is a natural dietary compound and the primary antioxidant component in berries. Pterostilbene has significant advantages over resveratrol in bioavailability, half-life in the body, cellular uptake, oral absorption and metabolic stability. Here, we expressed the resveratrol O-methyltransferase (ROMT) gene (VvROMT) from grape (Vitis vinifera) in Escherichia coli and Saccharomyces cerevisiae and confirmed its specific ability to catalyze the production of pterostilbene from resveratrol. By co-expressing an additional two genes from the resveratrol biosynthetic pathway—4-coumarate CoA-ligase (4CL) and stilbene synthase (STS)—a large amount of pterostilbene was produced, with a trace amount of pinostilbene detected. To understand the molecular basis of the catalytic activity, four key amino acid residues were identified in a 3D-model of VvROMT and mutagenized and assayed for augmented catalytic activity. Our results demonstrate the potential utility of the engineered microorganisms for pterostilbene production and provide protein engineering targets that will hopefully lead to increased activity of the ROMT enzyme.     

Anti-proliferative effect of pterostilbene on rat hepatoma cells in culture

Pterostilbene, a methoxylated analogue of resveratrol, is a natural compound primarily found in blueberries and several types of grapes. However, little is known about the effect of pterostilbene on the proliferation of hepatoma cells and its modes of actions. This study was undertaken to characterize its ability to suppress the proliferation of hepatoma AH109A cells and the possible mechanism(s) involved. Pterostilbene showed a significant and dose-dependent effect on the anti-proliferative activity against AH109A cells. Pterostilbene exerted little or no effect on the proliferation of rat L6 myoblasts and rat skin fibroblasts. Pterostilbene-loaded rat sera could significantly inhibit the proliferation of AH109A cells, which suggests that pterostilbene could be absorbed through gastrointestinal tract and retain its anti-proliferative activity. Pterostilbene arrested the cell cycle of AH109A cells at G0/G1 phase and reduced the protein expression of cyclin-dependent kinase 4 and cyclin-dependent kinase 6 dose-dependently. We also found that pterostilbene could significantly increase the intracellular peroxide level of AH109A cells, which may be involved in its anti-proliferative activity.     

Scavenging of hydroxyl radical by resveratrol and related natural stilbenes after hydrogen peroxide attack on DNA

Resveratrol (3,5,4′-trihydroxystilbene) is of interest due to its role in prevention and therapy of degenerative diseases as cancer and aging. However, depending on its concentration and cell type studied, resveratrol activity appears conflicting. It exerts antioxidant action, as a scavenger of free radicals and as promoter of antioxidant enzyme activity, but resveratrol acts also as a pro-oxidant. Here we present experimental and theoretical studies for resveratrol and two methoxy-derivatives found in plants, pterostilbene and 3,5,4′-trimethoxystilbene. We show that both methoxy-derivatives induce less DNA damage than resveratrol. The protective effects of the three molecules against oxidative DNA damage induced by hydrogen peroxide treatment were analyzed on mammalian cells in vitro. Our data show for the first time that methoxylated derivatives of resveratrol are very efficient in reducing DNA damage: using the same concentration of the three molecules we obtain a relative reduction of 85.5% (pterostilbene), 43.7% (trimethoxystilbene) and 21.1% (resveratrol). Analysis of the crystal structures of pterostilbene and 3,5,4′-trimethoxystilbene, compared to resveratrol, show fewer intermolecular interactions and a lack of planarity, due to packing forces, which is confirmed by density functional theory (DFT) calculations. We also describe the results of DFT calculations (including water solvent effects) in which the three stilbene species scavenge the hydroxyl radical (associated with the H₂O₂ insult).     

Pterostilbene-induced tumor cytotoxicity: a lysosomal membrane permeabilization-dependent mechanism

The phenolic phytoalexin resveratrol is well known for its health-promoting and anticancer properties. Its potential benefits are, however, limited due to its low bioavailability. Pterostilbene, a natural dimethoxylated analog of resveratrol, presents higher anticancer activity than resveratrol. The mechanisms by which this polyphenol acts against cancer cells are, however, unclear. Here, we show that pterostilbene effectively inhibits cancer cell growth and stimulates apoptosis and autophagosome accumulation in cancer cells of various origins. However, these mechanisms are not determinant in cell demise. Pterostilbene promotes cancer cell death via a mechanism involving lysosomal membrane permeabilization. Different grades of susceptibility were observed among the different cancer cells depending on their lysosomal heat shock protein 70 (HSP70) content, a known stabilizer of lysosomal membranes. A375 melanoma and A549 lung cancer cells with low levels of HSP70 showed high susceptibility to pterostilbene, whereas HT29 colon and MCF7 breast cancer cells with higher levels of HSP70 were more resistant. Inhibition of HSP70 expression increased susceptibility of HT29 colon and MCF7 breast cancer cells to pterostilbene. Our data indicate that lysosomal membrane permeabilization is the main cell death pathway triggered by pterostilbene.     

A stress-inducible resveratrol O-methyltransferase involved in the biosynthesis of pterostilbene in grapevine

Stilbenes are considered the most important phytoalexin group in grapevine (Vitis vinifera) and they are known to contribute to the protection against various pathogens. The main stilbenes in grapevine are resveratrol and its derivatives and, among these, pterostilbene has recently attracted much attention due both to its antifungal and pharmacological properties. Indeed, pterostilbene is 5 to 10 times more fungitoxic than resveratrol in vitro and recent studies have shown that pterostilbene exhibits anticancer, hypolipidemic, and antidiabetic properties. A candidate gene approach was used to identify a grapevine resveratrol O-methyltransferase (ROMT) cDNA and the activity of the corresponding protein was characterized after expression in Escherichia coli. Transient coexpression of ROMT and grapevine stilbene synthase in tobacco (Nicotiana benthamiana) using the agroinfiltration technique resulted in the accumulation of pterostilbene in tobacco tissues. Taken together, these results showed that ROMT was able to catalyze the biosynthesis of pterostilbene from resveratrol both in vitro and in planta. ROMT gene expression in grapevine leaves was induced by different stresses, including downy mildew (Plasmopara viticola) infection, ultraviolet light, and AlCl(3) treatment.     

In planta production of the highly potent resveratrol analogue pterostilbene via stilbene synthase and O-methyltransferase co-expression

Resveratrol and related stilbenes are thought to play important roles in defence responses in several plant species and have also generated considerable interest as nutraceuticals owing to their diverse health-promoting properties. Pterostilbene, a 3,5-dimethylether derivative of resveratrol, possesses properties similar to its parent compound and, additionally, exhibits significantly higher fungicidal activity in vitro and superior pharmacokinetic properties in vivo. Recombinant enzyme studies carried out using a previously characterized O-methyltransferase sequence from Sorghum bicolor (SbOMT3) demonstrated its ability to catalyse the A ring-specific 3,5-bis-O-methylation of resveratrol, yielding pterostilbene. A binary vector was constructed for the constitutive co-expression of SbOMT3 with a stilbene synthase sequence from peanut (AhSTS3) and used for the generation of stably transformed tobacco and Arabidopsis plants, resulting in the accumulation of pterostilbene in both species. A reduced floral pigmentation phenotype observed in multiple tobacco transformants was further investigated by reversed-phase HPLC analysis, revealing substantial decreases in both dihydroquercetin-derived flavonoids and phenylpropanoid-conjugated polyamines in pterostilbene-producing SbOMT3/AhSTS3 events. These results demonstrate the potential utility of this strategy for the generation of pterostilbene-producing crops and also underscore the need for the development of additional approaches for minimizing concomitant reductions in key phenylpropanoid-derived metabolites.     

Pterostilbene effectively inhibits influenza A virus infection by promoting the type I interferon production

With the prevalence of novel strains and drug-resistant influenza viruses, there is an urgent need to develop effective and low-toxicity anti-influenza therapeutics. Regulation of the type I interferon antiviral response is considered an attractive therapeutic strategy for viral infection. Pterostilbene, a 3,5-dimethoxy analog of resveratrol, is known for its remarkable pharmacological activity. Here, we found that pterostilbene effectively inhibited influenza A virus infection and mainly affected the late stages of viral replication. A mechanistic study showed that the antiviral activity of pterostilbene might promote the induction of antiviral type I interferon and expression of its downstream interferon-stimulated genes during viral infection. The same effect of pterostilbene was also observed in the condition of polyinosinic-polycytidylic acid (poly I:C) transfection. Further study showed that pterostilbene interacted with influenza non-structural 1 (NS1) protein, inhibited ubiquitination mediated degradation of RIG-I and activated the downstream antiviral pathway, orchestrating an antiviral state against influenza virus in the cell. Taken together, pterostilbene could be a promising anti-influenza agent for future antiviral drug exploitation and compounds with similar structures may provide new options for the development of novel inhibitors against influenza A virus (IAV).     

Design, synthesis, biological evaluation and docking studies of pterostilbene analogs inside PPARalpha

Pterostilbene, a naturally occurring analog of resveratrol, has previously shown PPARalpha activation in H4IIEC3 cells and was found to decrease cholesterol levels in animals. In this study, analogs of pterostilbene were synthesized and their ability to activate PPARalpha was investigated. Among analogs that was synthesized (E)-4-(3,5-dimethoxystyryl)phenyl dihydrogen phosphate showed activity higher than pterostilbene and control drug ciprofibrate. Docking of the stilbenes inside PPARalpha showed the presence of important hydrogen bond interactions for PPARalpha activation.     

Pterostilbene,a dimethylated analog of resveratrol,promotes energy metabolism in obese rats

Pterostilbene (trans-3,5-dimethoxy-4-hydroxystilbene) is a dimethylated analog of resveratrol and has been reported to exert various pharmacological effects. In this study, we evaluated the effect of pterostilbene on the pathogenesis of obesity and energy metabolism in obese rats.Pterostilbene significantly activates silent mating type information regulation 2 homolog-1 and peroxisome proliferator-activated receptor-alpha in vitro. At 4 weeks a 0.5% pterostilbene diet markedly suppressed the abdominal white adipose tissue (WAT) accumulation in obese rats. The oxygen consumption and energy expenditure were significantly higher in the pterostilbene group, and pterostilbene increased the fat metabolism rather than the carbohydrate metabolism in obese rats. The mRNA level of uncoupling protein, a thermogenic regulator, was increased and the mRNA levels of fatty acid synthase and leptin, which are involved in lipogenesis and fat storage, were markedly decreased in WAT after the pterostilbene feeding. These results suggest that pterostilbene prevents WAT accumulation through the enhancement of energy metabolism and partly the suppression of lipogenesis in obese OLETF rats.     

Production of highly bioactive resveratrol analogues pterostilbene and piceatannol in metabolically engineered grapevine cell cultures

Grapevine stilbenes, particularly trans‐resveratrol, have a demonstrated pharmacological activity. Other natural stilbenes derived from resveratrol such as pterostilbene or piceatannol, display higher oral bioavailability and bioactivity than the parent compound, but are far less abundant in natural sources. Thus, to efficiently obtain these bioactive resveratrol derivatives, there is a need to develop new bioproduction systems. Grapevine cell cultures are able to produce large amounts of easily recoverable extracellular resveratrol when elicited with methylated cyclodextrins and methyl jasmonate. We devised this system as an interesting starting point of a metabolic engineering‐based strategy to produce resveratrol derivatives using resveratrol‐converting enzymes. Constitutive expression of either Vitis vinifera resveratrol O‐methyltransferase (VvROMT) or human cytochrome P450 hydroxylase 1B1 (HsCYP1B1) led to pterostilbene or piceatannol, respectively, after the engineered cell cultures were treated with the aforementioned elicitors. Functionality of both gene products was first assessed in planta by Nicotiana benthamiana agroinfiltration assays, in which tobacco cells transiently expressed stilbene synthase and VvROMT or HsCYP1B1. Grapevine cell cultures transformed with VvROMT produced pterostilbene, which was detected in both intra‐ and extracellular compartments, at a level of micrograms per litre. Grapevine cell cultures transformed with HsCYP1B1 produced about 20 mg/L culture of piceatannol, displaying a sevenfold increase in relation to wild‐type cultures, and reaching an extracellular distribution of up to 45% of total production. The results obtained demonstrate the feasibility of this novel system for the bioproduction of natural and more bioactive resveratrol derivatives and suggest new ways for the improvement of production yields.     

Pterostilbene and 3'-hydroxypterostilbene are effective apoptosis-inducing agents in MDR and BCR-ABL-expressing leukemia cells

Pterostilbene and 3,5-hydroxypterostilbene are the natural 3,5-dimethoxy analogs of trans-resveratrol and piceatannol, two compounds which can induce apoptosis in tumor cells. In previous studies we demonstrated the importance of a 3,5-dimethoxy motif in conferring pro-apoptotic activity to stilbene based compounds so we now wanted to evaluate the ability of pterostilbene and 3,5-hydroxypterostilbene in inducing apoptosis in sensitive and resistant leukemia cells. When tested in sensitive cell lines, HL60 and HUT78, 3'-hydroxypterostilbene was 50-97 times more potent than trans-resveratrol in inducing apoptosis, while pterostilbene appeared barely active. However, both compounds, but not trans-resveratrol and piceatannol, were able to induce apoptosis in the two Fas-ligand resistant lymphoma cell lines, HUT78B1 and HUT78B3, and the multi drug-resistant leukemia cell lines HL60-R and K562-ADR (a Bcr-Abl-expressing cell line resistant to imatinib mesylate). Of note, pterostilbene-induced apoptosis was not inhibited by the pancaspase-inhibitor Z-VAD-fmk, suggesting that this compound acts through a caspase-independent pathway. On the contrary, 3'-hydroxypterostilbene seemed to trigger apoptosis through the intrinsic apoptotic pathway: indeed, it caused a marked disruption of the mitochondrial membrane potential delta psi and its apoptotic effects were inhibited by Z-VAD-fmk and the caspase-9-inhibitor Z-LEHD-fmk. Moreover, pterostilbene and 3'-hydroxypterostilbene, when used at concentrations that elicit significant apoptotic effects in tumor cell lines, did not show any cytotoxicity in normal hemopoietic stem cells. In conclusion, our data show that pterostilbene and particularly 3'-hydroxypterostilbene are interesting antitumor natural compounds that may be useful in the treatment of resistant hematological malignancies, including imatinib, non-responsive neoplasms.     

Effect of resveratrol on high glucose-induced stress in human leukemia K562 cells

Hyperglycemia, a symptom of diabetes mellitus, induces hyperosmotic responses, including apoptosis, in vascular endothelial cells and leukocytes. Hyperosmotic shock elicits a stress response in mammalian cells, often leading to apoptotic cell death. In a previous report, we showed that hyperosmotic shock induced apoptosis in various mammalian cells. Importantly, apoptotic biochemical changes (i.e., caspase-3 activation and DNA fragmentation) were blocked by antioxidant pretreatment during hyperosmotic shock-induced cell death. In the present study, we report that resveratrol, a phytoalexin present in grapes with known antioxidant and anti-inflammatory properties, attenuates high glucose-induced apoptotic changes, including c-Jun N-terminal kinase (JNK) activation and caspase-3 activation in human leukemia K562 cells. Experiments with the cell permeable dye, 2',7'-dichlorofluorescein diacetate (DCF-DA), an indicator of reactive oxygen species (ROS) generation, revealed that high glucose treatment directly increased intracellular oxidative stress, which was attenuated by resveratrol. In addition, high glucose-treated K562 cells displayed a lower degree of attachment to collagen, the major component of vessel wall subendothelium. In contrast, cells pretreated with resveratrol followed by high glucose exhibited higher affinity for collagen. The results of this report collectively imply the involvement of oxidative stress in high glucose-induced apoptosis and alterations in attachment ability. Moreover, resveratrol blocks these events by virtue of its antioxidant property.     

Influence of calcium on the subcellular distribution of protein kinase C in human neutrophils. Extraction conditions determine partitioning of histone-phosphorylating activity and immunoreactivity between cytosol and particulate fractions

Activation of the neutrophil respiratory burst is thought to involve a translocation and activation of protein kinase C. We report that the presence of Ca2+ during the disruption of unstimulated human neutrophils and cytoplasts resulted in an increase in protein kinase C activity (histone phosphorylation) and immunoreactive protein kinase C species in the particulate (membrane) fraction and a reduction in such activities in the cytosol. This Ca2+-induced translocation of activity was concentration-dependent and occurred at physiologically relevant concentrations of Ca2+ (30-500 nM). The Ca2+-induced membrane association of protein kinase C could be reversed by removal of Ca2+. These findings indicate that the Ca2+ concentration of the extraction buffer can determine the subcellular distribution of protein kinase C in disrupted cells and suggest that the observed location of this enzyme activity in cell fractions may not necessarily reflect the localization in intact cells. These results also raise the possibility that the distribution of protein kinase C between cytosol and membrane is a dynamic equilibrium controlled by levels of free Ca2+. Thus, Ca2+ might regulate distribution as well as activation of protein kinase C.     

Characterization of human neutrophil ecto-protein kinase activity released by kinase substrates.

Although most studies of protein phosphorylation have focused on intracellular protein kinases, evidence for protein kinase activity on the surface of several types of cells has been described. Evidence was recently provided for the existence of ecto-protein kinase activity on the surface of human neutrophils. Evidence for three distinct ecto-protein kinase activities was detected, one that phosphorylates endogenous surface proteins, one that phosphorylates exogenous substrates in a cAMP-independent manner and is released in the presence of substrate, and a low level of activity of one that phosphorylates exogenous Kemptide in a cAMP-dependent manner. To begin to elucidate its role in neutrophil function, we have characterized several properties of the releasable ecto-protein kinase activity on human neutrophils. This enzyme activity was inhibited by impermeant stilbene disulfonic acids, which are known to alter neutrophil function, as well as by impermeant sulfhydryl reactive agents. Enzyme activity was detectable at physiologic concentrations of Mg2+, but was higher in the presence of Mn2+. Protein kinase activity was strongly inhibited by heparin, whereas trifluoperazine, cAMP, and cGMP had little effect on kinase activity. Protein kinase activity was selectively removed from the cell surface by incubation with the ecto-kinase substrates casein and phosvitin, but the enzyme was not released by phosphatidylinositol-specific phospholipase C. Repeated exposure of neutrophils to substrate depleted ecto-protein kinase activity from the cell surface, but activity was rapidly restored by incubation in buffer lacking substrate. The released protein kinase had a Km for ATP of approximately 0.5 microM and a pH maximum between 7.0 and 7.5. At least four ecto-protein kinase substrates were detected in serum; vitronectin was identified as one of these substrates by immunoprecipitation studies. Although the exact role of ecto-protein kinase activity in neutrophil function remains undefined, the identification of vitronectin as a serum substrate suggests that it interacts with a physiologically important substrate.     

Effects of pterostilbene in brown adipose tissue from obese rats

In recent years, much attention has been paid by the scientific community to phenolic compounds as active biomolecules naturally present in foods. Pterostilbene is a resveratrol dimethylether derivative which shows higher bioavailability. The aim of the present study was to analyze the effect of pterostilbene on brown adipose tissue thermogenic markers in a model of genetic obesity, which shows reduced thermogenesis. The experiment was conducted with 30 Zucker (fa/fa) rats that were distributed in three experimental groups: control and two groups orally administered with pterostilbene at 15 and 30 mg/kg body weight/day for 6 weeks. Gene expression of uncoupling protein 1 (Ucp1), peroxisome proliferator-activated receptor γ co-activator 1 α (Pgc-1α), carnitine palmitoyl transferase 1b (Cpt1b), peroxisome proliferator-activated receptor α (Pparα), nuclear respiratory factor 1 (Nfr1), and cyclooxygenase-2 (Cox-2); protein expression of PPARα, PGC-1α, p38 mitogen-activated protein kinase (p38 MAPK), UCP1 and glucose transporter (GLUT4); and enzyme activity of CPT 1b and citrate synthase (CS) were assessed in interscapular brown adipose tissue. With the exception of Pgc-1α expression, all these parameters were significantly increased by pterostilbene administration. These results show for the first time that pterostilbene increases thermogenic and oxidative capacity of brown adipose tissue in obese rats. Whether these effects effectively contribute to the antiobesity properties of these compound needs further research.     

Resveratrol downregulates Akt/GSK and ERK signalling pathways in OVCAR-3 ovarian cancer cells

Phytochemicals constitute a heterogeneous group of substances with an evident role in human health. Their properties on cancer initiation, promotion and progression are well documented. Particular attention is now devoted to better understand the molecular basis of their anticancer action. In the present work, we studied the effect of resveratrol on the ovarian cancer cell line OVCAR-3 by a proteomic approach. Our findings demonstrate that resveratrol down-regulates the protein cyclin D1 and, in a concentration dependent manner, the phosphorylation levels of protein kinase B (Akt) and glycogen synthase kinase-3β (GSK-3β). The dephosphorylation of these kinases could be responsible for the decreased cyclin D1 levels observed after treatment. We also showed that resveratrol reduces phosphorylation levels of the extracellular signal-regulated kinase (ERK) 1/2. Chemical inhibitors of phosphatidylinositol 3-kinase (PI3K) and ERK both increased the in vitro therapeutic efficacy of resveratrol. Moreover, resveratrol had an inhibitory effect on the AKT phosphorylation in cultured cells derived from the ascites of ovarian cancer patients and in a panel of human cancer cell lines. Thus, resveratrol shows antitumor activity in human ovarian cancer cell lines targeting signalling pathway involved in cell proliferation and drug-resistance.     

Chondroitin-4-sulphate reduced oxidative injury in caerulein-induced pancreatitis in mice: the involvement of NF-kappaB translocation and apoptosis activation

Activation of nuclear factor kappaB (NF-kappaB) and caspases may greatly amplify inflammation and cell damage in addition to that directly exerted by free radicals. Since reactive oxygen species (ROS) are involved in acute pancreatitis, we studied whether the administration of chondroitin-4-sulphate (C4S), in addition to its antioxidant activity, was able to modulate NF-kappaB and caspase activation in an experimental model of caerulein-induced acute pancreatitis in mice. Hyperstimulating doses of caerulein (50 microg/ kg), five injections per mouse given at hourly intervals produced the following: high serum lipase and amylase activity; lipid peroxidation, evaluated by 8-isoprostane concentrations; loss of antioxidant defenses such as glutathione reductase (GR) activity; NF-kappaB activation and loss of cytoplasmic IkappaBalpha protein; increases in tumor necrosis factor-alpha (TNF-alpha), interleukin-6 (IL-6), caspase-3, and caspase-7 gene expression and their related protein; accumulation and activation of neutrophils in the damaged tissue, evaluated by elastase (ELA) determination; and pancreatic injury, evaluated by histologic analysis. Pretreatment of mice with different doses of C4S, given 1 hr before caerulein injections and 1 and 2 hrs after the last caerulein injection, reduced lipid peroxidation, inhibited NF-kappaB translocation and cytoplasmic IkappaBalpha protein loss, decreased TNF-alpha, IL-6, and caspase gene expression and their related protein levels, limited endogenous antioxidant depletion, and reduced tissue neutrophils accumulation and tissue damage. Since molecules with antioxidant activity can block NF-kappaB and apoptosis activation, we suggest that C4S administration is able to block NF-kappaB and caspase activation by reducing the oxidative burst.