Myricetin, quercetin and catechin-gallate inhibit glucose uptake in isolated rat adipocytes

Pathogenic obesity and nutraceuticals

Over a decade of intense research in the field of obesity has led to the knowledge that chronic, excessive adipose tissue expansion leads to an increase in the risk for CVD, type 2 diabetes mellitus and cancer. This is primarily thought to stem from the low-grade, systemic inflammatory response syndrome that characterises adipose tissue in obesity, and this itself is thought to arise from the complex interplay of factors including metabolic endotoxaemia, increased plasma NEFA, hypertrophic adipocytes and localised hypoxia. Plasma concentrations of vitamins and antioxidants are lower in obese individuals than in the non-obese, which is hypothesised to negatively affect the development of inflammation and disease in obesity. This paper provides a review of the current literature investigating the potential of nutraceuticals to ameliorate the development of oxidative stress and inflammation in obesity, thereby limiting the onset of obesity complications. Research has found nutraceuticals able to positively modulate the activity of adipocyte cell lines and further positive effects have been found in other aspects of pathogenic obesity. While their ability to affect weight loss is still controversial, it is clear that they have a great potential to reverse the development of overweight and obesity-related comorbidities; this, however, still requires much research especially that utilising well-structured randomised controlled trials.

Preventing bone loss and weight gain with combinations of vitamin D and phytochemicals

Vitamin D and certain natural compounds have been shown to regulate both lipid metabolism and bone formation. Treatments that prevent or reverse age-related increase in bone marrow adiposity could both increase new bone formation and inhibit bone destruction. We tested the hypothesis that dietary supplementation with combinations of vitamin D and phytochemicals inhibits bone loss and decreases adiposity to a greater extent than control or vitamin D-alone diets. Aged ovariectomized female rats (12 months old, n=50, initial body weight=240 g) were given control (AIN-93M diet), vitamin D (2,400 IU/kg), or vitamin D plus resveratrol (16, 80, or 400 mg/kg of diet [low, medium, and high dose, respectively]), quercetin (80, 400, or 2,000 mg/kg of diet), and genistein (64, 256, or 1,040 mg/kg of diet) for 8 weeks. The high-dose treatment (vitamin D+400 mg/kg resveratrol+2,000 mg/kg quercetin+1,040 mg/kg genistein) reduced body weight gain (P<.05) and the fat pad weights (P<.05). This treatment also increased the serum concentration of insulin-like growth factor-1 (P<.05) and the bone mineral content of the femur. Micro-computed tomography and histomorphometric analyses indicated that the high-dose treatment prevented loss of trabecular bone (P<.05) and reduced marrow adipocytes (P<.001) and osteoclasts (P<.05) compared with the control and vitamin D alone (P<.05). We conclude that aged ovariectomized female rats supplemented with vitamin D combined with genistein, quercetin, and resveratrol had improved bone mineral density and reduced body weight gain and a significant decrease in bone marrow adipocytes. The synergistic effects of a combination of phytochemicals with vitamin D may be effective in reducing bone loss and weight gain after menopause.

SEAWEED EXTRACTS AS A POTENTIAL TOOL FOR THE ATTENUATION OF OXIDATIVE DAMAGE IN OBESITY-RELATED PATHOLOGIES1

Recent studies suggest that seaweed extracts are a significant source of bioactive compounds comparable to the dietary phytochemicals such as onion and tea extracts. The exploration of natural antioxidants that attenuate oxidative damage is important for developing strategies to treat obesity-related pathologies. The objective of this study was to screen the effects of seaweed extracts of 49 species on adipocyte differentiation and reactive oxygen species (ROS) production during the adipogenesis in 3T3-L1 adipocytes, and to investigate their total phenol contents and 2,2-diphenyl-1-picrylhydrazyl (DPPH) radical scavenging activities. Our results show that high total phenol contents were observed in the extracts of Ecklonia cava (see Table 1 for taxonomic authors) (681.1 ± 16.0 μg gallic acid equivalents [GAE] · g^-1 ), Dictyopteris undulata (641.3 ± 70.7 μg GAE · g^-1 ), and Laurencia intermedia (560.9 ± 48.1 μg GAE · g^-1 ). In addition, DPPH radical scavenging activities were markedly higher in Sargassum macrocarpum (60.2%), Polysiphonia morrowii (55.0%), and Ishige okamurae (52.9%) than those of other seaweed extracts (P < 0.05). Moreover, treatment with several seaweed extracts including D. undulata, Sargassum micracanthum, Chondrus ocellatus, Gelidium amansii, Gracilaria verrucosa, and Grateloupia lanceolata significantly inhibited adipocyte differentiation and ROS production during differentiation of 3T3-L1 preadipocytes. Furthermore, the production of ROS was positively correlated with lipid accumulation (R²  = 0.8149). According to these preliminary results, some of the seaweed extracts can inhibit ROS generation, which may protect against oxidative stress that is linked to obesity. Further studies are required to determine the molecular mechanism between the verified seaweeds and ROS, and the resulting effects on obesity. [Table: see text].

Identification of the metabolites of the antioxidant flavonoid 7-mono-O-(β-hydroxyethyl)-rutoside in mice

The clinical use of the anticancer drug doxorubicin is limited by severe cardiotoxicity. In mice, the semisynthetic antioxidant flavonoid 7-mono-O-(β-hydroxyethyl)-rutoside (monoHER) has been successfully used as a protector against doxorubicin-induced cardiotoxicity. However, most monoHER has already been cleared from the body at the time that doxorubicin concentrations are still high. This result suggests that not only the parent compound monoHER itself but also monoHER metabolites could be responsible for the observed cardioprotective effects in mice. Therefore, in the present study, we investigated the metabolism of monoHER in mice. Mice were administered 500 mg/kg monoHER intraperitoneally. At different time points after monoHER administration, bile was collected and analyzed for the presence of monoHER metabolites. The formed metabolites were identified by liquid chromatography-diode array detection-time of flight-mass spectrometry. Thirteen different metabolites were identified. The observed routes of monoHER metabolism are methylation, glucuronidation, oxidation of its hydroxyethyl group, GSH conjugation, and hydrolysis of its disaccharide. In line with other flavonoids, methylated monoHER and the monoHER glucosides are expected to have relatively high cellular uptake and low clearance from the body. Therefore, these metabolites might contribute to the observed protection of monoHER against doxorubicin-induced cardiotoxicity.

Quercetin-iron chelates are transported via glucose transporters

Flavonoids are well-known antioxidants and free radical scavengers. Their metal-binding activity suggests that they could be effective protective agents in pathological conditions caused by both extracellular and intracellular oxidative stress linked to metal overload. Quercetin is both a permeant ligand via glucose transport proteins (GLUTs) and a high-affinity inhibitor of GLUT-mediated glucose transport. Chelatable "free iron" at micromolar concentrations in body fluids is a catalyst of hydroxyl radical (OH(•)) production from hydrogen peroxide. A number of flavonoids, e.g., quercetin, luteolin, chrysin, and 3,6-dihydroxyflavone, have been demonstrated to chelate intracellular iron and suppress OH(•) radical production in Madin Darby canine kidney cells. The most effective chelation comes from the flavonone B ring catechol found in both quercetin and luteolin. We show here that quercetin concentrations of <1μM can facilitate chelatable iron shuttling via GLUT1 in either direction across the cell membrane. These siderophoric effects are inhibited by raised quercetin concentrations (>1μM) or GLUT inhibitors, e.g., phloretin or cytochalasin B, and iron efflux is enhanced by impermeant extracellular iron chelators, either desferrioxamine or rutin. This iron shuttling property of quercetin might be usefully harnessed in chelotherapy of iron-overload conditions.

The effect of acute pre-exercise dark chocolate consumption on plasma antioxidant status, oxidative stress and immunoendocrine responses to prolonged exercise

PURPOSE

Acute antioxidant supplementation may modulate oxidative stress and some immune perturbations that typically occur following prolonged exercise. The aims of the present study were to examine the effects of acutely consuming dark chocolate (high polyphenol content) on plasma antioxidant capacity, markers of oxidative stress and immunoendocrine responses to prolonged exercise.

METHODS

Fourteen healthy men cycled for 2.5 h at ~60% maximal oxygen uptake 2 h after consuming 100 g dark chocolate (DC), an isomacronutrient control bar (CC) or neither (BL) in a randomised-counterbalanced design.

RESULTS

DC enhanced pre-exercise antioxidant status (P = 0.003) and reduced by trend (P = 0.088) 1 h post-exercise plasma free [F₂-isoprostane] compared with CC (also, [F₂-isoprostane] increased post-exercise in CC and BL but not DC trials). Plasma insulin concentration was significantly higher pre-exercise (P = 0.012) and 1 h post-exercise (P = 0.026) in the DC compared with the CC trial. There was a better maintenance of plasma glucose concentration on the DC trial (2-way ANOVA trial × time interaction P = 0.001), which decreased post-exercise in all trials but was significantly higher 1 h post-exercise (P = 0.039) in the DC trial. There were no between trial differences in the temporal responses (trial × time interactions all P > 0.05) of hypothalamic-pituitary-adrenal axis stress hormones, plasma interleukin-6, the magnitude of leukocytosis and neutrophilia and changes in neutrophil function.

CONCLUSION

Acute DC consumption may affect insulin, glucose, antioxidant status and oxidative stress responses, but has minimal effects on immunoendocrine responses, to prolonged exercise.

Beneficial effects of Undaria pinnatifida ethanol extract on diet-induced-insulin resistance in C57BL/6J mice

This study was performed to evaluate the beneficial effect of Undaria pinnatifida ethanol extract (UEFx) on insulin resistance in diet-induced obese mice. A high-fat diet was supplemented with the UEFx at 0.69% (wt/wt) dose, which contains an equivalent amount of 0.02% fucoxanthin (wt/wt), or with Fx at 0.02% (wt/wt) dose in diet. After 9 weeks, both UEFx supplement significantly lowered the amount of visceral fat, the size of adipocyte, the fasting blood glucose concentration, the plasma insulin and the insulin resistance index similar to pure as shown by Fx supplement, compared to the high-fat (HF) control group. Blood glucose level was negatively correlated with hepatic glucokinase activity (r = -0.533, p < 0.05), whereas positively correlated with hepatic gluconeogenic enzyme activities (r = 0.463, p < 0.05 for glucose-6-phosphatase; r = 0.457, p < 0.05 for phosphoenolpyruvate carboxykinase). Ratio of hepatic glucokinase/glucose-6-phosphatase and glycogen content were significantly elevated by the UEFx and Fx supplements. Supplementation of the UEFx as well as Fx seemed to stimulate the β-oxidation activity and inhibit the phosphatidate phosphohydrolase activity resulting in a decrease in the hepatic lipid droplet accumulation. The results indicate that the UEFx can prevent insulin resistance and hepatic fat accumulation that is partly mediated by modulating the hepatic glucose and lipid homeostasis in the high fat-induced obese mice.

Effect of flavonoids on basal and insulin-stimulated 2-deoxyglucose uptake in adipocytes

SCOPE

The adipose tissue is a major site of insulin action and contributes substantially to energy homeostasis. Insulin increases the extraction of glucose from circulation into adipose tissue by recruiting the glucose transporter GLUT4 to the plasma membrane. It has been proposed that dietary flavonoids may interfere with glucose transport processes.

METHODS AND RESULTS

We have used murine 3T3-L1 adipocytes and isolated mature human adipocytes to assess the interaction of selected flavonoids with glucose uptake, both in the basal state and after insulin stimulation. Kinetic characterization of 2-deoxyglucose uptake in the basal state revealed in both cell types an apparent K(m) of around 8 mM with no change in affinity but a significant increase in maximal influx in the presence of insulin. A screening of representative flavonoids of different structural classes revealed the flavanone naringenin and the isoflavone daidzein to affect glucose transport significantly with half-maximal inhibition at concentrations of around 60-80 μM for basal and 70-110 μM for insulin-stimulated glucose uptake in both 3T3-L1 adipocytes and mature human adipocytes.

CONCLUSION

Considering attainable plasma concentrations of flavonoids in vivo, we assume that even under physiological conditions naringenin and daidzein could impair glucose removal from plasma, which may pose a risk to patients with diabetes mellitus.

Molecular dynamics simulation studies of GLUT4: substrate-free and substrate-induced dynamics and ATP-mediated glucose transport inhibition

Background

Glucose transporter 4 (GLUT4) is an insulin facilitated glucose transporter that plays an important role in maintaining blood glucose homeostasis. GLUT4 is sequestered into intracellular vesicles in unstimulated cells and translocated to the plasma membrane by various stimuli. Understanding the structural details of GLUT4 will provide insights into the mechanism of glucose transport and its regulation. To date, a crystal structure for GLUT4 is not available. However, earlier work from our laboratory proposed a well validated homology model for GLUT4 based on the experimental data available on GLUT1 and the crystal structure data obtained from the glycerol 3-phosphate transporter.

Methodology/Principal Findings

In the present study, the dynamic behavior of GLUT4 in a membrane environment was analyzed using three forms of GLUT4 (apo, substrate and ATP-substrate bound states). Apo form simulation analysis revealed an extracellular open conformation of GLUT4 in the membrane favoring easy exofacial binding of substrate. Simulation studies with the substrate bound form proposed a stable state of GLUT4 with glucose, which can be a substrate-occluded state of the transporter. Principal component analysis suggested a clockwise movement for the domains in the apo form, whereas ATP substrate-bound form induced an anti-clockwise rotation. Simulation studies suggested distinct conformational changes for the GLUT4 domains in the ATP substrate-bound form and favor a constricted behavior for the transport channel. Various inter-domain hydrogen bonds and switching of a salt-bridge network from E345-R350-E409 to E345-R169-E409 contributed to this ATP-mediated channel constriction favoring substrate occlusion and prevention of its release into cytoplasm. These data are consistent with the biochemical studies, suggesting an inhibitory role for ATP in GLUT-mediated glucose transport.

Conclusions/Significance

In the absence of a crystal structure for any glucose transporter, this study provides mechanistic details of the conformational changes in GLUT4 induced by substrate and its regulator.

Quercetin is equally or more effective than resveratrol in attenuating tumor necrosis factor-{alpha}-mediated inflammation and insulin resistance in primary human adipocytes

BACKGROUND

Quercetin and trans-resveratrol (trans-RSV) are plant polyphenols reported to reduce inflammation or insulin resistance associated with obesity. Recently, we showed that grape powder extract, which contains quercetin and trans-RSV, attenuates markers of inflammation in human adipocytes and macrophages and insulin resistance in human adipocytes. However, we do not know how quercetin and trans-RSV individually affected these outcomes.

OBJECTIVE

The aim of this study was to examine the extent to which quercetin and trans-RSV prevented inflammation or insulin resistance in primary cultures of human adipocytes treated with tumor necrosis factor-α (TNF-α)-an inflammatory cytokine elevated in the plasma and adipose tissue of obese, diabetic individuals.

DESIGN

Cultures of human adipocytes were pretreated with quercetin and trans-RSV followed by treatment with TNF-α. Subsequently, gene and protein markers of inflammation and insulin resistance were measured.

RESULTS

Quercetin, and to a lesser extent trans-RSV, attenuated the TNF-α-induced expression of inflammatory genes such as interleukin (IL)-6, IL-1β, IL-8, and monocyte chemoattractant protein-1 (MCP-1) and the secretion of IL-6, IL-8, and MCP-1. Quercetin attenuated TNF-α-mediated phosphorylation of extracellular signal-related kinase and c-Jun-NH₂ terminal kinase, whereas trans-RSV attenuated only c-Jun-NH₂ terminal kinase phosphorylation. Quercetin and trans-RSV attenuated TNF-α-mediated phosphorylation of c-Jun and degradation of inhibitory κB protein. Quercetin, but not trans-RSV, decreased TNF-α-induced nuclear factor-κB transcriptional activity. Quercetin and trans-RSV attenuated the TNF-α-mediated suppression of peroxisome proliferator-activated receptor γ (PPARγ) and PPARγ target genes and of PPARγ protein concentrations and transcriptional activity. Quercetin prevented the TNF-α-mediated serine phosphorylation of insulin receptor substrate-1 and protein tyrosine phosphatase-1B gene expression and the suppression of insulin-stimulated glucose uptake, whereas trans-RSV prevented only the TNF-α-mediated serine phosphorylation of insulin receptor substrate-1.

CONCLUSION

These data suggest that quercetin is equally or more effective than trans-RSV in attenuating TNF-α-mediated inflammation and insulin resistance in primary human adipocytes.

Bioactive food components and cancer-specific metabonomic profiles

Cancer cells possess unique metabolic signatures compared to normal cells, including shifts in aerobic glycolysis, glutaminolysis, and de novo biosynthesis of macromolecules. Targeting these changes with agents (drugs and dietary components) has been employed as strategies to reduce the complications associated with tumorigenesis. This paper highlights the ability of several food components to suppress tumor-specific metabolic pathways, including increased expression of glucose transporters, oncogenic tyrosine kinase, tumor-specific M2-type pyruvate kinase, and fatty acid synthase, and the detection of such effects using various metabonomic technologies, including liquid chromatography/mass spectrometry (LC/MS) and stable isotope-labeled MS. Stable isotope-mediated tracing technologies offer exciting opportunities for defining specific target(s) for food components. Exposures, especially during the early transition phase from normal to cancer, are critical for the translation of knowledge about food components into effective prevention strategies. Although appropriate dietary exposures needed to alter cellular metabolism remain inconsistent and/or ill-defined, validated metabonomic biomarkers for dietary components hold promise for establishing effective strategies for cancer prevention.

Flavonols and cardiovascular disease

Flavonols, and specially quercetin, are widely distributed in plants and are present in considerable amounts in fruits and vegetables. In addition to their anti-oxidant effect, flavonols interfere with a large number of biochemical signaling pathways and, therefore, physiological and pathological processes. There is solid evidence that, in vitro, quercetin and related flavonols exert endothelium-independent vasodilator effects, protective effect on nitric oxide and endothelial function under conditions of oxidative stress, platelet antiaggregant effects, inhibition of LDL oxidation, reduction of adhesion molecules and other inflammatory markers and prevention of neuronal oxidative and inflammatory damage. The metabolites of quercetin show partial protective effects on endothelial function and LDL oxidation. Quercetin produces undisputed antihypertensive and antiatherogenic effects, prevents endothelial dysfunction and protects the myocardium from ischemic damage. It has no clear effects on serum lipid profile and on insulin resistance. Human intervention trials with isolated flavonols demonstrate an antihypertensive effect. The meta-analysis of epidemiological studies show an inverse association between flavonol (together with flavone) intake and coronary heart disease and stroke. Therefore, although there is no solid proof yet, a substantial body of evidence suggests that quercetin may prevent the most common forms of cardiovascular disease contributing to the protective effects afforded by fruits and vegetables.

Role of (-)-epigallocatechin-3-gallate in cell viability, lipogenesis, and retinol-binding protein 4 expression in adipocytes

(-)-Epigallocatechin-3-gallate (EGCG), a bioactive compound of green tea, is known to combat obesity by reducing the viability and lipid accumulation of adipocytes. In this study, we evaluated the mechanism and clinical relevance on those actions of EGCG. We measured the viability of 3T3-L1 preadipocytes and adipocytes by the 3-(4, 5-dimethylthiazol-2yl)-2, 5-diphenyltetrazolium bromide assay. Lipid accumulation was measured by Oil Red O staining. Intracellular accumulation of reactive oxygen species (ROS) was determined using a flow cytometer. Cellular glucose uptake was determined with 2-deoxy-[(3)H]-glucose. The protein levels of peroxisome proliferator-activated receptor (PPAR)-γ and adiponectin in 3T3-L1 adipocytes, as well as the protein level and secretion of plasma retinol-binding protein (RBP4) in human adipocytes, were measured by western blot. EGCG at concentrations higher than 10 μM induced ROS generation and decreased the viability and lipid accumulation of adipocytes. It also decreased the expression of PPAR-γ and adiponectin. At concentrations readily achievable in human plasma via green tea intake (≤10 μM), EGCG inhibited cellular glucose uptake and enhanced the expression and secretion of RBP4 in adipocytes. Pharmacological doses of EGCG showed cytotoxic effects in preadipocytes and adipocytes. EGCG-mediated glucose uptake inhibition in adipocytes may be clinically relevant and is probably linked to the increase in the expression and secretion of RBP4. Because secreted RBP4 from adipocytes inhibits muscular glucose uptake and enhance hepatic glucose output, the systemic effect of EGCG associated with its effect on RBP4 secretion should be further determined, as it may negatively regulate whole-body insulin sensitivity, contrary to general belief.

Effects of a flavonol-rich diet on select cardiovascular parameters in a Golden Syrian hamster model

The concept that the consumption of a diet rich in flavonoids can be associated with a reduced risk for cardiovascular disease is becoming increasingly accepted. In the present study we investigated the effects of the following four diets on blood pressure and cholesterol ester levels in hypercholesterolemic Golden Syrian hamsters: a high-fat, high-cholesterol diet (HFHC); a HFHC with 2% cranberry concentrate powder (HFHC+CE); a HFHC with 0.1% rutin (HFHC+Rutin); and a HFHC with 30 mg/kg vitamin E (HFHC+Vit.E). Diets were fed for either 12 or 20 weeks. Over the experimental period, heart rate and blood pressure measurements increased in the animals fed HFHC and HFHC+Vit.E; in contrast, these measurements were not increased in the animals fed HFHC+CE and HFHC+Rutin. Mesenteric and total abdominal fat were significantly lower in the animals fed HFHC+Rutin than in animals fed the other three diets. Ratios of plasma high-density lipoprotein cholesterol (HDL-C) to very-low-density lipoprotein cholesterol and of plasma HDL-C to low-density lipoprotein cholesterol were significantly higher in animals consuming HFHC+Vit.E than in animals fed the other three diets. Aortic cholesteryl ester levels were significantly lower in animals fed HFHC+CE, HFHC+Rutin, and HFHC+Vit.E at 20 weeks than in the animals fed HFHC. Fasting blood glucose concentrations were significantly lower in animals fed HFHC+Rutin and HFHC+Vit.E, and glucose clearance rates improved in animals fed HFHC+Rutin compared to animals fed the other three diets. Results obtained from this study support the concept that the chronic consumption of a flavonoid-rich diet can be beneficial with respect to cardiovascular health.

Flavonoids: new roles for old molecules

Flavonoids are ubiquitous in the plant kingdom and have many diverse functions including defense, UV protection, auxin transport inhibition, allelopathy, and flower coloring. Interestingly, these compounds also have considerable biological activity in plant, animal and bacterial systems - such broad activity is accomplished by few compounds. Yet, for all the research over the last three decades, many of the cellular targets of these secondary metabolites are unknown. The many mutants available in model plant species such as Arabidopsis thaliana and Medicago truncatula are enabling the intricacies of the physiology of these compounds to be deduced. In the present review, we cover recent advances in flavonoid research, discuss deficiencies in our understanding of the physiological processes, and suggest approaches to identify the cellular targets of flavonoids.

Gallic acid induces GLUT4 translocation and glucose uptake activity in 3T3-L1 cells

GLUT4, a 12 transmembrane protein, plays a major role in insulin mediated glucose transport in muscle and adipocytes. For glucose transport, the GLUT4 protein needs to be translocated to the plasma membrane from the intracellular pool and it is possible that certain compounds may be able to enhance this process. In the present work, we have shown that gallic acid can increase GLUT4 translocation and glucose uptake activity in an Akt-independent but wortmannin-sensitive manner. Further analysis suggested the role of atypical protein kinase Czeta/lambda in gallic acid mediated GLUT4 translocation and glucose uptake.

Comparison of effects of green tea catechins on apicomplexan hexose transporters and mammalian orthologues

Here we have investigated the inhibitory properties of green tea catechins on the Plasmodium falciparum hexose transporter (PfHT), the Babesia bovis hexose transporter 1 (BboHT1) and the mammalian facilitative glucose transporters, GLUT1 and GLUT5, expressed in Xenopus laevis oocytes. (-)-Epicatechin-gallate (ECG) and (-)-epigallocatechin-gallate (EGCG) inhibited D-glucose transport by GLUT1 and PfHT, and D-fructose transport by GLUT5, with apparent K(i) values between 45 and 117 microM. BboHT1 was more potently inhibited by the ungallated catechins (-)-epicatechin (EC) and (-)-epigallocatechin (EGC), with apparent K(i) values of 108 and 168 microM, respectively. Site-directed mutagenesis experiments provided little further support for previously reported models of catechin binding to hexose transporters. Furthermore, P. falciparum growth inhibition by catechins was not affected by the external D-glucose concentration. Our results provide new data on the inhibitory action of catechins against sugar transporters but were unable to elucidate the antimalarial mechanism of action of these agents.

Mitochondria accumulate large amounts of quercetin: prevention of mitochondrial damage and release upon oxidation of the extramitochondrial fraction of the flavonoid

Quercetin uptake in Jurkat cells is extremely rapid and associated with a remarkable accumulation of the flavonoid, dependent on its binding to intracellular components. Cell-associated quercetin is biologically active, quantitatively consumed to promote survival in the presence of reactive species, such as peroxynitrite (ONOO(-)), or reduction of extracellular oxidants via activation of plasma membrane oxidoreductases. In alternative, quercetin is very slowly released upon post-incubation in drug-free medium, an event significantly accelerated by extracellular albumin. Quercetin uptake is also observed in isolated mitochondria, resulting in an enormous accumulation of the flavonoid, consumed under conditions associated with prevention of lipid peroxidation induced by ONOO(-). Interestingly, remarkable quercetin accumulation is also detected in the mitochondria isolated from quercetin-pre-loaded cells, and exposure to either ONOO(-) or extracellular oxidants caused the parallel loss of both the mitochondrial and cytosolic fractions of the flavonoid. In conclusion, Jurkat cells accumulate large amounts of quercetin and even larger amounts of the flavonoid further accumulate in their mitochondria. Intramitochondrial quercetin appears to be functional for prevention of mitochondrial damage as well as for redistribution to the cytosol, when the fraction of the flavonoid therein retained is progressively consumed either by cell-permeant oxidants or by activation of plasma membrane oxidoreductases.

Favorable glycemic response of type 2 diabetics to low-calorie cranberry juice

Fruit and vegetable intake is typically low for type 2 diabetics, possibly due to a perceived adverse effect on glycemic control. Cranberry juice (CBJ) may represent an attractive means for increasing fruit intake and simultaneously affording positive health benefits. This single cross-over design compared metabolic responses of type 2 diabetics (n= 12) to unsweetened low-calorie CBJ (LCCBJ; 19 Cal/240 mL), carbohydrate sweetened normal calorie CBJ (NCCBJ; 120 Cal/240 mL), isocaloric low-calorie sugar water control (LCC), and isocaloric normal calorie sugar water control (NCC) interventions. CBJ flavonols and anthocyanins, and proanthocyanidins were quantified with HPLC, LC-MS, and MALDI-TOF that includes an original characterization of several large oligomeric proanthocyanidins. Blood glucose peaked 30 min postingestion after NCCBJ and NCC at 13.3 +/- 0.5 and 12.8 +/- 0.9 (mmol/L), and these responses were significantly greater than the LCCBJ and LCC peaks of 8.1 +/- 0.5 and 8.7 +/- 0.5, respectively. Differences in glycemic response remained significant 60 min, but not 120 min postingestion. Plasma insulin values 60 min postingestion for NCCBJ and NCC interventions were 140 +/- 19 and 151 +/- 18 (pmol/L), respectively, and significantly greater than the LCCBJ and LCC values of 56 +/- 10 and 54 +/- 10; differences were not significant 120 min postingestion. Metabolic responses within the 2 high and 2 low-calorie beverages were virtually identical; however, exposure to potentially beneficial nutrients was greater with CBJ. Relative to conventionally sweetened preparation, LCCBJ provides a favorable metabolic response and should be useful for promoting increased fruit consumption among type 2 diabetics or others wishing to limit carbohydrate intake.

A catechin-rich beverage improves obesity and blood glucose control in patients with type 2 diabetes

We investigated the effects of continuous ingestion of a catechin-rich beverage in patients with type 2 diabetes who were not receiving insulin (Ins) therapy in a double-blind controlled study. The participants ingested green tea containing either 582.8 mg of catechins (catechin group; n = 23) or 96.3 mg of catechins (control group; n = 20) per day for 12 weeks. At week 12, the decrease in waist circumference was significantly greater in the catechin group than in the control group. Adiponectin, which is negatively correlated with visceral adiposity, increased significantly only in the catechin group. Although the increase in Ins at week 12 was significantly greater in the catechin group than in the control group, no apparent difference was noted between the two groups in glucose and hemoglobin A(1c). In patients treated with insulinotropic agents, the increase in Ins at week 12 was significantly greater in the catechin group than in the control group. This significant increase in Ins levels was observed only in the catechin group. In the catechin group receiving other treatments, Ins levels remained unchanged. In addition, in patients treated with insulinotropic agents, the decrease in hemoglobin A(1c) at week 12 was significantly greater in the catechin group than in the control group. These results suggest that a catechin-rich beverage might have several therapeutic uses: in the prevention of obesity; in the recovery of Ins-secretory ability; and, as a way to maintain low hemoglobin A(1c) levels in type 2 diabetic patients who do not yet require Ins therapy.

Bioactivity and structure of biophenols as mediators of chronic diseases

Biophenols and their associated activity have generated intense interest. Current topics of debate are their bioavailability and bioactivity. It is generally assumed that their plasma concentrations are insufficient to produce the health benefits previously attributed to their consumption. However, data on localized in vivo concentrations are not available and many questions remain unanswered. Potential mechanisms by which they may exert significant bioactivity are discussed together with structure activity relationships. Biophenols are highly reactive species and they can react with a range of other compounds. Products of their reaction when functioning as antioxidants are examined.

Inhibitory mechanisms of flavonoids on insulin-stimulated glucose uptake in MC3T3-G2/PA6 adipose cells

We assessed the effects of different classes of flavonoids on insulin-stimulated 2-deoxy-D-[1-(3)H]glucose uptake by mouse MC3T3-G2/PA6 cells differentiated into mature adipose cells. Among the flavonoids examined, the flavones, apigenin and luteolin, the flavonols, kaempferol, quercetin and fisetin, an isoflavone, genistein, a flavanonol, silybin, and the flavanols, (-)-epigallocatechin gallate (EGCG) and theaflavins, significantly inhibited insulin-stimulated glucose uptake. Key structural features of flavonoids for inhibition of insulin-stimulated glucose uptake are the B-ring 4'- or 3',4'-OH group and the C-ring C2-C3 double bond of the flavones and flavonols, the A-ring 5-OH of isoflavones, and the galloyl group of EGCG and theaflavins. Luteolin significantly inhibits insulin-stimulated phosphorylation of insulin receptor-beta subunit (IR-beta), and apigenin, kaempferol, quercetin and fisetin, also tended to inhibit the IR-beta phosphorylation. On the other hand, isoflavones, flavanols or flavanonols did not affect insulin-stimulated IR-beta phosphorylation. Apigenin, luteolin, kaempferol, quercetin and fisetin also appeared to inhibit insulin-stimulated activation of Akt, a pivotal downstream effector of phosphatidylinositol 3-kinase (PI3K), and suppressed insulin-dependent translocation of a glucose transporter, (GLUT)4, into the plasma membrane. Although genistein, silybin, EGCG and theaflavins had no effect on the insulin-stimulated activation of Akt, they blocked insulin-dependent GLUT4 translocation. These results provide novel insights into the modulation by flavonoids of insulin's actions, including glucose uptake in adipocytes.

Procyanidin effects on adipocyte-related pathologies

Procyanidins, a class of flavonoids, have clear and well-defined beneficial effects against several pathologies including cardiovascular heart disease. Now, studies in vivo are revealing the effects of procyanidins against obesity, where they prevent weight gain and adipose tissue mass increase, and against diabetes and insulin resistance, where they act as antihiperglycemic agents. Several mechanisms may be responsible for these effects. One of these, due to the key role of adipose tissue in the development of obesity and insulin resistance, is their effect on adipocytes. In this review we compile the studies that indicate a protective role for procyanidins in obesity and insulin resistance, focusing on their effects on the adipocyte, where procyanidins modify lipid synthesis, lipid degradation, glucose uptake, and adipose differentiation.

Human glycemic response and phenolic content of unsweetened cranberry juice

This cross-sectional study determined the phenolic composition of an over-the-counter cranberry juice (CBJ) with high-performance liquid chromatography and examined the effects of low- and normal-calorie CBJ formulations on the postprandial glycemic response in healthy humans. The CBJ used in this study contained seven phenolic acids, with 3- and 5-caffeoylquinic acid being the primary components, and 15 flavonol glycosides, with myricetin-3-galactoside and quercetin-3-galactoside being the most prevalent. CBJ proanthocyanidins consisted of three different tetramers and a heptamer, which were confirmed with matrix-assisted laser desorption ionization-time of flight-mass spectrometry analysis. Participants received one of the following six treatments: nothing (no water/beverage), water (480 mL), unsweetened low-calorie CBJ (38 Cal/480 mL), normal-calorie CBJ (280 Cal/480 mL), isocaloric normal calorie (high fructose corn syrup [HFCS]), or isocaloric low-calorie beverages. No significant differences in postprandial blood glucose or insulin were observed in the groups receiving nothing, water, or low-calorie treatments. In contrast, the ingestion of normal-calorie CBJ and normal-calorie control beverage resulted in significantly higher blood glucose concentrations 30 minutes postprandially, although the differences were no longer significant after 180 minutes. Plasma insulin of normal-calorie CBJ and control (HFCS) recipients was significantly higher 60 minutes postprandially, but not significantly different 120 minutes postprandially. CBJ ingestion did not affect heart rate or blood pressure. This study suggests that the consumption of a low-calorie CBJ rich in previously uncharacterized trimer and heptamer proanthocyanidins is associated with a favorable glycemic response and may be beneficial for persons with impaired glucose tolerance.

The association between dietary macronutrient intake and the prevalence of the metabolic syndrome

We examined the association of dietary carbohydrates, protein, fat (including fatty acid subtypes) and alcohol with the metabolic syndrome and its components, in a cross-sectional study of 1626 patients with at least one cardiovascular risk factor. Multivariate nutrient density substitution models were used to examine the associations between macronutrients (assessed by 24 h dietary recall) and the metabolic syndrome. These models express the effects of ‘substituting’ one macronutrient for another without altering total energy intake. Increases in carbohydrates offset by isoenergetic decreases in either fat or protein were associated with a decrease in the prevalence of the metabolic syndrome (OR 0·87 (95 % CI 0·81, 0·93), P < 0·0001; OR 0·70 (95 % CI 0·61, 0·79), P < 0·0001, per 5 % energy intake respectively). Increased intake of dietary fat at the expense of dietary protein was also associated with a decreased prevalence of the metabolic syndrome (OR 0·80 (95 % CI 0·70, 0·92), P = 0·002 per 5 % energy intake). There were no statistically significant differences between fatty acid subtypes (P>0·10). Consumption of up to one standard alcoholic drink per d was associated with a lower prevalence of the metabolic syndrome when compared with non-drinkers (OR 0·67 (95 % CI 0·50, 0·89), P = 0·006); however, these benefits were weakened with higher levels of alcohol intake (P = 0·10 for one to three drinks and P = 0·29 for >three drinks). Thus, a diet high in carbohydrates, low in fat and protein, with low-to-moderate alcohol intake, is associated with a reduced prevalence of the metabolic syndrome.

The anti-obesity effect of quercetin is mediated by the AMPK and MAPK signaling pathways

Quercetin is the most abundant flavonoid and is assumed to have protective roles against the pathogenesis of multiple diseases associated with oxidative stress. In the present study, we investigated the molecular mechanisms by which quercetin affects adipogenesis and apoptosis in 3T3-L1 cells. The exposure of 3T3-L1 preadipocytes to quercetin resulted in attenuated adipogenesis and decreased expression of adipogenesis-related factors and enzymes. Moreover, quercetin exposure up-regulated the levels of phosphorylated adenosine monophosphate-activated protein kinase (AMPK) and its substrate, acetyl-CoA carboxylase (ACC). Treatment of 3T3-L1 adipocytes with quercetin resulted in the induction of apoptosis and a concomitant decrease in ERK and JNK phosphorylation. Taken together, these data indicate that quercetin exerts anti-adipogenesis activity by activating the AMPK signal pathway in 3T3-L1 preadipocytes, while the quercetin-induced apoptosis of mature adipocytes was mediated by modulation of the ERK and JNK pathways, which play pivotal roles during apoptosis.

Enhanced inhibition of adipogenesis and induction of apoptosis in 3T3-L1 adipocytes with combinations of resveratrol and quercetin

Certain flavonoids have been shown to have specific effects on biochemical and metabolic functions of adipocytes. In this study, we investigated the effects of combinations of resveratrol and quercetin on adipogenesis and apoptosis in 3T3-L1 cells. In maturing preadipocytes resveratrol and quercetin at 25 microM individually suppressed intracellular lipid accumulation by 9.4+/-3.9% (p<0.01) and 15.9+/-2.5%, respectively, (p<0.001). The combination of resveratrol and quercetin at the same dose, however, decreased lipid accumulation by 68.6+/-0.7% (p<0.001). In addition, combinations of resveratrol and quercetin at 25 microM significantly decreased the expression of peroxisome proliferators-activated receptor gamma (PPAR gamma) and CCAAT/enhancer-binding protein (C/EBP)alpha, both of which act as key transcription factors. In mature adipocytes resveratrol and quercetin at 100 microM individually decreased viability by 18.1+/-0.6% (p<0.001) and 15.8+/-1% (p<0.001) and increased apoptosis (100 microM) by 120.5+/-8.3% (p<0.001) and 85.3+/-10% (p<0.001) at 48 h, respectively. Combinations of resveratrol and quercetin further decreased viability (73.5+/-0.9%, p<0.001) and increased apoptosis (310.3+/-9.6%, p<0.001) more than single compounds alone. The combination of resveratrol and quercetin at 100 muM increased release of cytochrome c from mitochondria to cytosol and decreased ERK 1/2 phosphorylation. Taken together, our data indicate that combinations of resveratrol and quercetin can exert potential anti-obesity effects by inhibiting differentiation of preadipocytes and inducing apoptosis of mature adipocytes.

Green tea modulates alpha(1)-adrenergic stimulated glucose transport in cultured rat cardiomyocytes

alpha1-Adrenergic stimulation triggers glucose transport in the heart through the translocation of glucose transporter (GLUT) 1 and GLUT4 to plasma membranes, mediated by protein kinase C (PKC) isoforms. Evidence is emerging that dietary polyphenolic compounds may act not only as antioxidants but also by modulating PKC-mediated signaling. This study evaluated the ability of a green tea extract (GTE) to modulate alpha1-adrenoceptor-mediated glucose transport in rat cardiomyocytes. GTE supplementation decreased phenylephrine (PhE)-stimulated glucose uptake and GLUT4 recruitment. PhE stimulation activated PKC alpha, beta, delta, and epsilon, while GTE supplementation decreased the translocation of beta and delta isoforms, but not alpha and epsilon, supporting the notion that GTE directly affects PKC activation and is a beta and delta isoform-selective PKC inhibitor. Due to reactive oxygen species (ROS) involvement in pathological heart alterations, the observation that GTE is able to both inhibit effects originated by some PKC isoforms and counteract ROS deleterious effects could be important in the prevention/counteraction of these diseases.

Flavonoid glycosides are not transported by the human Na+/glucose transporter when expressed in Xenopus laevis oocytes, but effectively inhibit electrogenic glucose uptake

There is controversy as to whether intestinal absorption of glycosylated flavonoids, and particularly quercetin glycosides, involves their uptake in intact form via the human sodium-coupled glucose transporter hSGLT1. We here describe studies using Xenopus oocytes that express hSGLT1 and the two-electrode voltage clamp technique to determine the transport characteristics of a variety of flavonoids carrying glucose residues at different positions as well as of their aglycones (altogether 27 compounds). Neither quercetin, luteolin, apigenin, naringenin, pelarginidin, daidzein, or genistein, nor any of their glycosylated derivatives generated significant transport currents. However, the inward current evoked by 1 mM of the hSGLT1 substrate alpha-methyl-D-glucopyranoside was potently reduced by the simultaneous application of not only various flavonoid glycosides but also by some aglycones. The inhibitory potency remained unchanged when the attached glucose was replaced by galactose, suggesting that these residues may bind to SGLT1. Kinetic analysis by Dixon plots revealed inhibition of competitive type with high affinities, particularly when the glucose was attached to the position 4' of the aromatic ring of the flavonoids. The affinities became lower when the glucose was attached to a different position. Unexpectedly, the aglycone form of luteolin also inhibited the transport competitively with high affinity. These data show that hSGLT1 does not transport any of the flavonoids and seems therefore not involved in their intestinal absorption. However, not only glycosylated but also a few nonglycosylated flavonoids show a structure-dependent capability for effective inhibition of SGLT1.

Epigallocatechin gallate suppresses expression of receptor activator of NF-κB ligand (RANKL) in Staphylococcus aureus infection in osteoblast-like NRG cells

Catechin, a constituent of tea, possesses various bioactivities. In particular, the most abundant catechin in tea is epigallocatechin gallate (EGCg), which has an anti-inflammatory effect. In the present study, the usability of EGCg for osteomyelitis treatment was examined. Osteomyelitis is a difficult disease to cure, partly due to bone lysis caused by infected osteoblasts. Since bone lysis is promoted by proinflammatory cytokines and the receptor activator of NF-κB ligand (RANKL), osteoblasts were infected with Staphylococcus aureus and the effect of EGCg on the production of cytokines was examined. It was found that the production of interleukin 6 and RANKL was suppressed in the osteoblasts treated with EGCg, which indicated an inflammation suppression effect of EGCg in osteomyelitis treatment.

Increased acylated plasma ghrelin, but improved lipid profiles 24-h after consumption of carob pulp preparation rich in dietary fibre and polyphenols

We have recently shown that a polyphenol-rich insoluble dietary fibre preparation from carob pulp (Ceratonia siliqua L; carob fibre) decreased postprandial acylated ghrelin, TAG and NEFA during an acute liquid meal challenge test. However, delayed effects of carob fibre consumption are unknown. Therefore, a randomized controlled crossover study in nineteen healthy volunteers consuming foods with or without 50 g carob fibre was conducted. On the subsequent day (day 2), glucose, TAG, total and acylated ghrelin as well as insulin, NEFA and leptin were assessed at baseline and at timed intervals for 300 min after ingestion of standardized bread. Consumption of carob fibre-enriched foods did not affect fasting concentrations of glucose, TAG, total ghrelin, NEFA, insulin and leptin. Fasting acylated ghrelin was increased on the day subsequent to carob fibre consumption compared with control (P = 0.046). After consumption of the standard bread on day 2, glucose response (P = 0.029) was increased, and TAG (P = 0.033) and NEFA (P < 0.001) responses were decreased compared with control. Postprandial responses of total and acylated ghrelin, insulin and leptin on day 2 were unaffected by carob fibre consumption the previous day. In conclusion, an increase in total and acylated plasma ghrelin accompanied by enhanced lipid metabolism after carob fibre consumption suggests higher lipid utilization and suppressed lipolysis on the day subsequent to carob fibre consumption. However, elevated glucose levels after carob fibre consumption need to be addressed in future studies.

Bis(quercetinato)oxovanadium IV Reverses Metabolic Changes in Streptozotocin-Induced Diabetic Mice

Organic vanadium compounds offer several advantages in the treatment of diabetes, yet they are impractical to use because of known side effects. In order to ameliorate the side effects of vanadium, we conjugated it with quercetin to form bis(quercetinato)oxovanadium IV (BQOV). This study evaluates the effect of BQOV treatment on carbohydrate metabolism and overall oxidative stress in streptozotocin-induced (STZ) diabetic mice. Administration of BQOV orally to diabetic mice for 3 weeks led to a reduction of blood glucose levels and the animals exhibited normal glucose tolerance at the end of the study period. The increase in glucose uptake by skeletal muscle and liver as well as the normalization of mRNA levels of G-6-Pase and glucokinase in the liver after BQOV treatment pointed to improvements in carbohydrate metabolism. The analysis of the antioxidant status of serum, liver and pancreas revealed reduced oxidative stress in BQOV-treated animals compared to untreated diabetic controls. Serum analyses for kidney and liver function showed that BQOV treatment provoked total protection of the kidney and partial protection of the liver from diabetogenic insults. The number of insulin-positive cells and the amount of pancreatic insulin in treated mice (1.2038 +/- 0.34 ng/mg tissue) did not account for pancreatic regeneration but suggested an insulin-mimetic action on the part of BQOV. Moreover, administration of BQOV for 3 weeks did not show any visible side-effects. This data indicate that BQOV is a safe and potent agent for diabetes treatment, because it is able to improve carbohydrate metabolism and to reduce overall oxidative stress.

Carob pulp preparation rich in insoluble dietary fibre and polyphenols increases plasma glucose and serum insulin responses in combination with a glucose load in humans

Dietary fibre consumption is associated with improved glucose homeostasis. In contrast, dietary polyphenols have been suggested to exert both beneficial and detrimental effects on glucose and insulin metabolism. Recently, we reported that a polyphenol-rich insoluble dietary fibre preparation from carob pulp (carob fibre) resulted in lower postprandial acylated ghrelin levels after a liquid meal challenge test compared with a control meal without supplementation. The effects may, however, differ when a different food matrix is used. Thus, we investigated the effects of carob fibre on glucose, insulin and ghrelin responses in healthy humans in combination with a glucose load. In a randomized single-blind cross-over study involving twenty healthy subjects (aged 22-62 years), plasma glucose, total and acylated ghrelin, and serum insulin were repeatedly assessed before and after the ingestion of 200 ml water with 50 g glucose and 0, 5, 10 or 20 g carob fibre over a period of 180 min. The intake of 5 and 10 g carob fibre increased the plasma glucose by 47 % and 64 % (P < 0.001), and serum insulin by 19.9 and 24.8 % (P < 0.001), compared with the control. Plasma acylated ghrelin concentrations did not change significantly after the consumption of carob-enriched glucose solution. Total ghrelin decreased only after 10 g carob fibre (P < 0.001) compared with control. In conclusion, we showed that polyphenol-rich carob fibre, administered within a water-glucose solution, increases postprandial glucose and insulin responses, suggesting a deterioration in glycaemic control.

Effect of dietary quercetin and sphingomyelin on intestinal nutrient absorption and animal growth

Research on cancer and other conditions has shown flavonoids and sphingolipids to be food components capable of exerting chemoprotective action. Nevertheless, little is known about their effects on healthy individuals and their potential usefulness as therapeutic agents. The present study examined the possible action of a dietary flavonoid, quercetin, and a sphingolipid, sphingomyelin, as functional foods in healthy animals. In particular, the effect on animal growth of supplementing a conventional diet with one or other of these substances (0·5% quercetin and 0·05% sphingomyelin) was considered. Possible action affecting intestinal physiology was also analysed by measuring the uptake of sugar and dipeptide, mediated by the Na+-dependent sugar transporter SGLT1 and the dipeptide Na+/H+ exchanger PEPT1 respectively, and the activity of related intestinal enzymes such as sucrase, maltase and aminopeptidase N. Both substances seemed to modify small intestinal activity in healthy mice, altering intestinal enzymatic activity and nutrient uptake. These effects observed in the small intestine did not impair normal development of the animals, as no differences in serum biochemical parameters or in organ and body weights were found. The findings should help in elucidating the mechanisms of action of these food components with a view to their possible use in the prevention of certain pathological conditions.

Inhibition of the intestinal glucose transporter GLUT2 by flavonoids

We tested whether the dominant intestinal sugar transporter GLUT2 was inhibited by intestinal luminal compounds that are inefficiently absorbed and naturally present in foods. Because of their abundance in fruits and vegetables, flavonoids were selected as model compounds. Robust inhibition of glucose and fructose transport by GLUT2 expressed in Xenopus laevis oocytes was produced by the flavonols myricetin, fisetin, the widely consumed flavonoid quercetin, and its glucoside precursor isoquercitrin [corrected]. IC50s for quercetin, myricetin, and isoquercitirin [corrected]were approximately 200- to 1000-fold less than glucose or fructose concentrations, and noncompetitive inhibition was observed. The two other major intestinal sugar transporters, GLUT5 and SGLT1, were unaffected by flavonoids. Sugar transport by GLUT2 overexpressed in pituitary cells and naturally present in Caco-2E intestinal cells was similarly inhibited by quercetin. GLUT2 was detected on the apical side of Caco-2E cells, indicating that GLUT2 was in the correct orientation to be inhibited by luminal compounds. Quercetin itself was not transported by the three major intestinal glucose transporters. Because the flavonoid quercetin, a food component with an excellent pharmacology safety profile, might act as a potent luminal inhibitor of sugar absorption independent of its own transport, flavonols show promise as new pharmacologic agents in the obesity epidemic.

Anti-diabetic properties of the Canadian lowbush blueberry Vaccinium angustifolium Ait

Incidence of type II diabetes is rapidly increasing worldwide. In order to identify complementary or alternative approaches to existing medications, we studied anti-diabetic properties of Vaccinium angustifolium Ait., a natural health product recommended for diabetes treatment in Canada. Ethanol extracts of root, stem, leaf, and fruit were tested at 12.5 microg/ml for anti-diabetic activity in peripheral tissues and pancreatic beta cells using a variety of cell-based bioassays. Specifically, we assessed: (1) deoxyglucose uptake in differentiated C2C12 muscle cells and 3T3-L1 adipocytes; (2) glucose-stimulated insulin secretion (GSIS) in beta TC-tet pancreatic beta cells; (3) beta cell proliferation in beta TC-tet cells; (4) lipid accumulation in differentiating 3T3-L1 cells; (5) protection against glucose toxicity in PC12 cells. Root, stem, and leaf extracts significantly enhanced glucose transport in C2C12 cells by 15-25% in presence and absence of insulin after 20 h of incubation; no enhancement resulted from a 1 h exposure. In 3T3 cells, only the root and stem extracts enhanced uptake, and this effect was greater after 1 h than after 20 h; uptake was increased by up to 75% in absence of insulin. GSIS was potentiated by a small amount in growth-arrested beta TC-tet cells incubated overnight with leaf or stem extract. However, fruit extracts were found to increase 3H-thymidine incorporation in replicating beta TC-tet cells by 2.8-fold. Lipid accumulation in differentiating 3T3-L1 cells was accelerated by root, stem, and leaf extracts by as much as 6.5-fold by the end of a 6-day period. Stem, leaf, and fruit extracts reduced apoptosis by 20-33% in PC12 cells exposed to elevated glucose for 96 h. These results demonstrate that V. angustifolium contains active principles with insulin-like and glitazone-like properties, while conferring protection against glucose toxicity. Enhancement of proliferation in beta cells may represent another potential anti-diabetic property. Extracts of the Canadian blueberry thus show promise for use as a complementary anti-diabetic therapy.

Flavonoids attenuate cardiovascular disease, inhibit phosphodiesterase, and modulate lipid homeostasis in adipose tissue and liver

Plant flavonoids are widely distributed polyphenolic compounds of the human diet. They consist of six major classes based on specific structural differences: flavonols, flavones, flavanones, catechins, anthocyanidins, and isoflavones. All of the major classes of flavonoids are comprised of three six-membered rings: an aromatic A-ring fused to a heterocyclic C-ring that is attached through a single carbon-carbon bond to an aromatic Bring. Population studies have shown that flavonoid intake is inversely correlated with mortality from cardiovascular disease, and numerous flavonoids of dietary significance have been shown to beneficially impact parameters associated with atherosclerosis, including lipoprotein oxidation, blood platelet aggregation, and vascular reactivity. Therapeutic effects of flavonoids on platelet aggregability and blood pressure have been attributed to competitive inhibition of cyclic nucleotide phosphodiesterase (PDE), an elevation in cAMP level, and subsequent activation of protein kinase A (cAMP-dependent protein kinase). In addition, flavonoids may induce neutral lipid hydrolysis from lipid stores through PDE inhibition in adipose tissue and liver. Indeed, the three-dimensional structure of many flavonoids is sterically and electrostatically compatible with the catalytic site of cAMP PDE3 and PDE4. Flavonoids have also been reported to suppress pathways of lipid biosynthesis and of very low-density lipoprotein production in cultured hepatocytes. Continued studies of the biochemical mechanisms underlying the biological effects of plant flavonoids may uncover new strategies for the treatment of cardiovascular disease, as well as associated conditions such as obesity, hepatic steatosis, and Type 2 diabetes.

A central role of eNOS in the protective effect of wine against metabolic syndrome

The positive health effects derived from moderate wine consumption are pleiotropic. They appear as improvements in cardiovascular risk factors such as plasma lipids, haemostatic mechanisms, endothelial function and antioxidant defences. The active principles would be ethanol and mainly polyphenols. Results from our and other laboratories support the unifying hypothesis that the improvements in risk factors after red wine consumption are mediated by endothelial nitric oxide synthase (eNOS). Many genes are involved, but the participation of eNOS would be a constant feature. The metabolic syndrome is a cluster of metabolic risk factors associated with high risk of cardiovascular disease (CVD). The National Cholesterol Education Programmmes Adult Treatment Panel III (NCEPATP III) clinical definition of the metabolic syndrome requires the presence of at least three risk factors, from among abdominal obesity, high plasma triacylglycerols, low plasma HDL, high blood pressure and high fasting plasma glucose. The molecular mechanisms responsible for the metabolic syndrome are not known. Since metabolic syndrome apparently affects 10-30% of the population in the world, research on its pathogenesis and control is needed. The recent finding that eNOS knockout mice present a cluster of cardiovascular risk factors comparable to those of the metabolic syndrome suggests that defects in eNOS function may cause human metabolic syndrome. These mice are hypertensive, insulin resistant and dyslipidemic. Further support for a pathogenic role of eNOS comes from the finding in humans that eNOS polymorphisms associate with insulin resistance and diabetes, with hypertension, with inflammatory and oxidative stress markers and with albuminuria. So, the data sustain the hypothesis that eNOS enhancement should reduce metabolic syndrome incidence and its consequences. Therefore red wine, since it enhances eNOS function, should be considered as a potential tool for the control of metabolic syndrome. This hypothesis is supported by epidemiological observations and needs experimental validation in human intervention studies.

Docking studies show that D-glucose and quercetin slide through the transporter GLUT1

On a three-dimensional templated model of GLUT1 (Protein Data Bank code 1SUK), a molecular recognition program, AUTODOCK 3, reveals nine hexose-binding clusters spanning the entire "hydrophilic" channel. Five of these cluster sites are within 3-5 A of 10 glucose transporter deficiency syndrome missense mutations. Another three sites are within 8 A of two other missense mutations. D-glucose binds to five sites in the external channel opening, with increasing affinity toward the pore center and then passes via a narrow channel into an internal vestibule containing four lower affinity sites. An external site, not adjacent to any mutation, also binding phloretin but recognizing neither D-fructose nor L-glucose, may be the main threading site for glucose uptake. Glucose exit from human erythrocytes is inhibited by quercetin (K(i) = 2.4 mum) but not anionic quercetin-semiquinone. Quercetin influx is retarded by extracellular D-glucose (50 mm) but not by phloretin and accelerated by intracellular D-glucose. Quercetin docking sites are absent from the external opening but fill the entire pore center. In the inner vestibule, Glu(254) and Lys(256) hydrogen-bond quercetin (K(i) approximately 10 microm) but not quercetin-semiquinone. Consistent with the kinetics, this site also binds D-glucose, so quercetin displacement by glucose could accelerate quercetin influx, whereas quercetin binding here will competitively inhibit glucose efflux. Beta-D-hexoses dock twice as frequently as their alpha-anomers to the 23 aromatic residues in the transport pathway, suggesting that endocyclic hexose hydrogens, as with maltosaccharides in maltoporins, form pi-bonds with aromatic rings and slide between sites instead of being translocated via a single alternating site.