Grape seed-derived procyanidins have an antihyperglycemic effect in streptozotocin-induced diabetic rats and insulinomimetic activity in insulin-sensitive cell lines

Ficus deltoidea: A Potential Alternative Medicine for Diabetes Mellitus

Ficus deltoidea from the Moraceae family has been scientifically proven to reduce hyperglycemia at different prandial states. In this study, we evaluate the mechanisms that underlie antihyperglycemic action of Ficus deltoidea. The results had shown that hot aqueous extract of Ficus deltoidea stimulated insulin secretion significantly with the highest magnitude of stimulation was 7.31-fold (P < 0.001). The insulin secretory actions of the hot aqueous extract involved K⁺  _ATP channel-dependent and K⁺  _ATP-channel-independent pathway. The extract also has the ability to induce the usage of intracellular Ca²⁺ to trigger insulin release. The ethanolic and methanolic extracts enhanced basal and insulin-mediated glucose uptake into adipocytes cells. The extracts possess either insulin-mimetic or insulin-sensitizing property or combination of both properties during enhancing glucose uptake into such cells. Meanwhile, the hot aqueous and methanolic extracts augmented basal and insulin-stimulated adiponectin secretion from adipocytes cells. From this study, it is suggested that Ficus deltoidea has the potential to be developed as future oral antidiabetic agent.

Cacao liquor procyanidin extract improves glucose tolerance by enhancing GLUT4 translocation and glucose uptake in skeletal muscle

Hyperglycaemia and insulin resistance are associated with the increased risk of the metabolic syndrome and other severe health problems. The insulin-sensitive GLUT4 regulates glucose homoeostasis in skeletal muscle and adipose tissue. In this study, we investigated whether cacao liquor procyanidin (CLPr) extract, which contains epicatechin, catechin and other procyanidins, improves glucose tolerance by promoting GLUT4 translocation and enhances glucose uptake in muscle cells. Our results demonstrated that CLPr increased glucose uptake in a dose-dependent manner and promoted GLUT4 translocation to the plasma membrane of L6 myotubes. Oral administration of a single dose of CLPr suppressed the hyperglycaemic response after carbohydrate ingestion, which was accompanied by enhanced GLUT4 translocation in ICR mice. These effects of CLPr were independent of α-glucosidase inhibition in the small intestine. CLPr also promoted GLUT4 translocation in skeletal muscle of C57BL/6 mice fed a CLPr-supplemented diet for 7 d. These results indicate that CLPr is a beneficial food material for improvement of glucose tolerance by promoting GLUT4 translocation to the plasma membrane of skeletal muscle.

Low doses of grape seed procyanidins reduce adiposity and improve the plasma lipid profile in hamsters

OBJECTIVE

Procyanidins are polyphenolic compounds with beneficial effects on health in relation to cardiovascular disease and metabolic syndrome. In this study, we evaluated the potential beneficial effects of low doses of a grape seed procyanidin extract (GSPE) on body weight and fat deposition.

DESIGN

Four groups of hamsters were fed either a standard diet (STD) or a high-fat diet (HFD) for 30 days and supplemented with either GSPE at 25 mg per kg of body weight per day (STD-GSPE and HFD-GSPE groups) or vehicle (STD and HFD groups) during the last 15 days of the study.

RESULTS

A significant decrease in body weight gain was observed in both GSPE-treated animals at the end of the experiment. GSPE treatment significantly reduced the adiposity index and the weight of all the white adipose tissue depots studied (retroperitoneal (RWAT), mesenteric (MWAT), epididymal (EWAT) and inguinal (IWAT)) in both GSPE-treated groups. GSPE administration reversed the increase in plasma phospholipids induced by the HFD feeding. In the RWAT, GSPE treatment increased the mRNA expression of genes related to β-oxidation and the glycerolipid/free fatty acid (GL/FFA) cycle, mainly in HFD-GSPE animals. In the MWAT, the effects of GSPE at the transcriptional level were not as evident as in the RWAT. Moreover, GSPE treatment induced heparin-releasable lipoprotein lipase activity in the RWAT and MWAT depots. The alterations in the lipid metabolic pathways induced by GSPE were accompanied by lower FFA levels in the plasma and decreased lipid and triglyceride accumulation in the MWAT.

CONCLUSION

The use of GSPE at low doses protects against fat accumulation and improves the plasma lipid profile in hamsters. We suggest that GSPE exerts these effects in part through the activation of both β-oxidation and the GL/FFA cycle, mainly in the RWAT.

Procyanidins modify insulinemia by affecting insulin production and degradation

Previous studies from our research group have suggested that procyanidins modify glycemia and insulinemia. The aim of this work was to evaluate the effects of procyanidins on β-cell functionality in a nonpathological system. Four groups of healthy rats were studied. The animals were given daily acute doses of grape seed procyanidin extract (GSPE) for different time periods and at different daily amounts. A β-cell line (INS-1E) was treated with 25 mg GSPE/L for 24 h to identify possible mechanisms of action for the procyanidins. In vivo experiments showed that different doses of GSPE affected insulinemia in different ways by modifying β-cell functionality and/or insulin degradation. The islets isolated from rats that were treated with 25 mg GSPE/kg of body weight for 45 days exhibited a limited response to glucose stimulation. In addition, insulin gene expression, insulin synthesis and expression of genes related to insulin secretion were all down-regulated. In vitro studies revealed that GSPE decreased the ability of β-cells to secrete insulin in response to glucose. GSPE increased glucose uptake in β-cells under high-glucose conditions but impaired glucose-induced mitochondrial hyperpolarization, decreased adenosine triphosphate (ATP) synthesis and altered cellular membrane potentials. GSPE also modified Glut2, glucokinase and Ucp2 gene expression as well as altered the expression of hepatic insulin-degrading enzyme (Ide), thereby altering insulin degradation. At some doses, procyanidins changed β-cell functionality by modifying insulin synthesis, secretion and degradation under nonpathological conditions. Membrane potentials and Ide provide putative targets for procyanidins to induce these effects.

Proanthocyanidins: Oligomeric Structures with Unique Biochemical Properties and Great Therapeutic Promise

Proanthocyanidins represent a unique class of oligomeric and polymeric secondary metabolites found ubiquitously and in considerable amounts in plants and some algae. These substances exhibit a range of rather surprising physical and chemical properties which, once applied to living organisms, are translated into a multitude of biological activities. The latter include antioxidant properties, cancer chemoprevention, anti-inflammatory and anti-diabetic effects as well as some exceptional, yet highly interesting activities, such as anti-nutritional and antimicrobial activity. Despite the wide range of activities and possible medical/agricultural applications of proanthocyanidins, many questions still remain, including issues related to bioavailability, metabolism and the precise biochemical, extra- and intracellular targets and mode(s) of action of these highly potent materials. Among the various physical and chemical interactions of such substances, strong binding to proteins appears to form the basis of many of their biological activities. Once easy-to-use synthetic methods to produce appropriate quantities of pure proanthocyanidins are available, it will be possible to identify the prime biological targets of these oligomers, study oligomer-protein interactions in more detail and develop possible practical applications in medicine and agriculture.

Foods for the prevention of diabetes: how do they work?

With the diabetes epidemic reaching menacing proportions worldwide, there is an urgent need for the development of cost-efficient prevention strategies to be effective at the population level. Great potential in this direction lies in properly designed, large-scale dietary interventions. The macronutrient composition and the caloric content of our diet are major determinants of glucose homeostasis and there is a continuously growing list of foods, nutrients or individual compounds that have been associated with an increased or reduced incidence of diabetes mellitus. These include fat, carbohydrates, fibre, alcohol, polyphenols and other micronutrients or individual dietary compounds, which have been shown to either promote or prevent a progression towards a (pre-)diabetic state. This review aims to briefly summarize relevant epidemiological data linking foods to diabetes and to provide insights into the mechanisms through which these effects are mediated. These include improvement of insulin sensitivity or promotion of insulin resistance, regulation of inflammatory pathways, regulation of glucose transport and tissue glucose uptake, aggravation or attenuation of postprandial glycaemia/insulinaemia, interactions with hormonal responses and β-cell-dependent mechanisms.

Vitis vinifera L. grape skin extract activates the insulin-signalling cascade and reduces hyperglycaemia in alloxan-induced diabetic mice

Objectives

This study examined the effect of Vitis vinifera grape skin extract (ACH09) on hyperglycaemia and the insulin-signalling cascade in alloxan-treated mice.

Methods

Glycaemia, serum insulin and Western blot analysis of insulin cascade proteins were evaluated in the gastrocnemius muscles of four groups of adult mice: control, ACH09 (200 mg/kg per day, p.o.), alloxan (300 mg/kg, i.p.) and alloxan + ACH09. Insulin secretion in isolated pancreatic islets was also studied.

Key findings

Glycaemia values in the alloxan + ACH09 and ACH09 groups were significantly lower than in the alloxan-treated and control groups, respectively. Increased insulin resistance (HOMA index) was observed in the alloxan-treated group but not in the alloxan + ACH09 group. Insulin receptor content and Akt phosphorylation were significantly greater in the alloxan + ACH09 group compared with the alloxan-treated group. The glucose transporter (GLUT-4) content was reduced in alloxan-treated mice compared with the control group, while alloxan + ACH09 and ACH09-treated mice showed a significant increase in GLUT-4 content. ACH09 treatment did not change glucose-induced insulin secretion in isolated pancreatic islets.

Conclusions

The results suggest that ACH09 has hypoglycaemic and antihyperglycaemic effects that are independent of an increase in insulin release but are probably dependent on an increase in insulin sensitivity resulting from an activation of the insulin-signalling cascade in skeletal muscle.

The effects of corni fructus extract and its fractions against α-glucosidase inhibitory activities in vitro and sucrose tolerance in normal rats

Corni fructus (Cornus officinalis Sieb. et Zucc.) is a traditional medicine exerting multifaceted protective effects against diabetes and its complications. In this study, to further identify the physiological effects of corni fructus against diabetes and its complications, we investigated α-glucosidase inhibitory activities in vitro and employed the sucrose tolerance test as an indicator of the control of the postprandial blood glucose level. In vitro assays showed that corni fructus extract has a higher inhibitory activity than its major components. Then, corni fructus extract was fractionated again to screen the fractions showing a strong inhibitory activity against α-glucosidase. Of the tested fractions, five showed a rate of α-glucosidase inhibition of over 80%. Next, the four abundant fractions were evaluated their IC(50) values, as well as the inhibition mode in vitro and plasma glucose level after sucrose loading in normal Wistar rats. As a result, the IC(50) values of these fractions were between 1.1-2.1 μg/ml. Among the four fractions, three showed mixed inhibition, while one (Fr. 4-9) showed the competition-independent inhibition of α-glucosidase. In addition, Fr. 4S-1 significantly inhibited the rise in the plasma glucose levels at a dose of 20 mg/kg body weight after sucrose loading. These results indicate that Fr. 4S-1 from corni fructus has a potential to control postprandial hyperglycemia by α-glucosidase inhibition.

Grape seed extract supplementation prevents high-fructose diet-induced insulin resistance in rats by improving insulin and adiponectin signalling pathways

Recent evidence strongly supports the contention that grape seed extract (GSE) improves hyperglycaemia and hyperinsulinaemia in high-fructose-fed rats. To explore the underlying molecular mechanisms of action, we examined the effects of GSE on the expression of muscle proteins related to the insulin signalling pathway and of mRNA for genes involved in the adiponectin signalling pathway. Compared with rats fed on a normal diet, high-fructose-fed rats developed pathological changes, including insulin resistance, hyperinsulinaemia, hypertriacylglycerolaemia, a low level of plasma adiponectin and a high level of plasma fructosamine. These disorders were effectively attenuated in high-fructose-fed rats supplemented with GSE. A high-fructose diet causes insulin resistance by significantly reducing the protein expression of insulin receptor, insulin receptor substrate-1, Akt and GLUT4, and the mRNA expression of adiponectin, adiponectin receptor R1 (AdipoR1) and AMP-activated protein kinase (AMPK)-α in the skeletal muscle. Supplementation of GSE enhanced the expression of insulin signalling pathway-related proteins, including Akt and GLUT4. GSE also increased the mRNA expression of adiponectin, AdipoR1 and AMPK-α. In addition, GSE increased the mRNA levels of glycogen synthase and suppressed the mRNA expression of glycogen synthase kinase-3-α, causing an increase in glycogen accumulation in the skeletal muscle. These results suggest that GSE ameliorates the defective insulin and adiponectin signalling pathways in the skeletal muscle, resulting in improved insulin resistance in fructose-fed rats.

Dietary supplementation of grape skin extract improves glycemia and inflammation in diet-induced obese mice fed a Western high fat diet

Dietary antioxidants may provide a cost-effective strategy to promote health in obesity by targeting oxidative stress and inflammation. We recently found that the antioxidant-rich grape skin extract (GSE) also exerts a novel anti-hyperglycemic activity. This study investigated whether 3-month GSE supplementation can improve oxidative stress, inflammation, and hyperglycemia associated with a Western diet-induced obesity. Young diet-induced obese (DIO) mice were randomly divided to three treatment groups (n = 12): a standard diet (S group), a Western high fat diet (W group), and the Western diet plus GSE (2.4 g GSE/kg diet, WGSE group). By week 12, DIO mice in the WGSE group gained significantly more weight (24.6 g) than the W (20.2 g) and S groups (11.2 g); the high fat diet groups gained 80% more weight than the standard diet group. Eight of 12 mice in the W group, compared to only 1 of 12 mice in the WGSE group, had fasting blood glucose levels above 140 mg/dL. Mice in the WGSE group also had 21% lower fasting blood glucose and 17.1% lower C-reactive protein levels than mice in the W group (P < 0.05). However, the GSE supplementation did not affect oxidative stress in diet-induced obesity as determined by plasma oxygen radical absorbance capacity, glutathione peroxidase, and liver lipid peroxidation. Collectively, the results indicated a beneficial role of GSE supplementation for improving glycemic control and inflammation in diet-induced obesity.

Resveratrol ameliorates early diabetic nephropathy associated with suppression of augmented TGF-β/smad and ERK1/2 signaling in streptozotocin-induced diabetic rats

Diabetic nephropathy (DN) is the major cause of end-stage renal disease. The early changes in DN are characterized by an increased in kidney size, glomerular volume, and kidney function, followed by the accumulation of glomerular extracellular matrix, increased urinary albumin excretion (UAE), glomerular sclerosis, and tubular fibrosis. Resveratrol (RSV) has been shown to ameliorate hyperglycemia and hyperlipidemia in streptozotocin-induced diabetic rats. In the present study, we examined the beneficial effects of RSV on DN and explored the possible mechanism of RSV action. Male Sprague-Dawley rats were injected with streptozotocin at 65mg/kg body weight. The induction of diabetes mellitus (DM) was confirmed by a fasting plasma glucose level ≥300mg/dL and symptoms of polyphagia and polydipsia. The DM rats were treated with or without RSV at 0.75mg/kg body weight 3 times a day for 8 weeks. Animals were sacrificed and kidney histology was examined by microscopy. Urinary albumin excretion, glomerular hypertrophy and expressions of fibronectin, collagen IV, and TGF-β in the glomeruli were alleviated in RSV-treated DM rats, but not in untreated DM rats. In addition, RSV treatment reduced the thickness of the glomerular basement membrane (GBM) to the original thickness and increased nephrin expressions to normal levels in DM rats. Moreover, RSV inhibited phosphorylation of smad2, smad3 and ERK1/2 in diabetic rat kidneys. This is the first report showing that RSV alleviates early glomerulosclerosis in DN through TGF-β/smad and ERK1/2 inhibition. In addition, podocyte injuries of diabetic kidneys are lessened by RSV.

Vaccinium arctostaphylos, a common herbal medicine in Iran: molecular and biochemical study of its antidiabetic effects on alloxan-diabetic Wistar rats

AIM OF THE STUDY

The purpose of this study was to define antidiabetic effects of fruit of Vaccinium arctostaphylos L. (Ericaceae) which is traditionally used in Iran for improving of health status of diabetic patients.

MATERIALS AND METHODS

Firstly, we examined the effect of ethanolic extract of Vaccinium arctostaphylos fruit on postprandial blood glucose (PBG) after 1, 3, 5, 8, and 24h following a single dose administration of the extract to alloxan-diabetic male Wistar rats. Also oral glucose tolerance test was carried out. Secondly, PBG was measured at the end of 1, 2 and 3 weeks following 3 weeks daily administration of the extract. At the end of treatment period the pancreatic INS and cardiac GLUT-4 mRNA expression and also the changes in the plasma lipid profiles and antioxidant enzymes activities were assessed. Finally, we examined the inhibitory activity of the extract against rat intestinal α-glucosidase.

RESULTS

The obtained results showed mild acute (18%) and also significant chronic (35%) decrease in the PBG, significant reduction in triglyceride (47%) and notable rising of the erythrocyte superoxide dismutase (57%), glutathione peroxidase (35%) and catalase (19%) activities due to treatment with the extract. Also we observed increased expression of GLUT-4 and INS genes in plant extract treated Wistar rats. Furthermore, in vitro studies displayed 47% and 56% inhibitory effects of the extract on activity of intestinal maltase and sucrase enzymes, respectively.

CONCLUSIONS

Findings of this study allow us to establish scientifically Vaccinium arctostaphylos fruit as a potent antidiabetic agent with antihyperglycemic, antioxidant and triglyceride lowering effects.

Organic grape juice intake improves functional capillary density and postocclusive reactive hyperemia in triathletes

OBJECTIVE

The aim of this study was to evaluate the effect of organic grape juice intake on biochemical variables and microcirculatory parameters in triathlon athletes.

INTRODUCTION

The physiological stress that is imposed by a strenuous sport, such as a triathlon, together with an insufficient amount of antioxidants in the diet may cause oxidative imbalance and endothelial dysfunction.

METHODS

Ten adult male triathletes participated in this study. A venous blood sample was drawn before (baseline) and after 20 days of organic grape juice intake (300 ml/day). Serum insulin, plasma glucose and uric acid levels, the total content of polyphenols, and the erythrocyte superoxide dismutase activity were determined. The functional microcirculatory parameters (the functional capillary density, red blood cell velocity at baseline and peak levels, and time required to reach the peak red blood cell velocity during postocclusive reactive hyperemia after a one-min arterial occlusion) were evaluated using nailfold videocapillaroscopy.

RESULTS

Compared with baseline levels, the peak levels of serum insulin ( p = 0.02), plasma uric acid ( p = 0.04), the functional capillary density ( p = 0.003), and the red blood cell velocity (p < 0.001) increased, whereas the plasma glucose level (p,0.001), erythrocyte superoxide dismutase activity ( p = 0.04), and time required to reach red blood cell velocity during postocclusive reactive hyperemia ( p = 0.04) decreased after organic grape juice intake.

CONCLUSION

Our data showed that organic grape juice intake improved glucose homeostasis, antioxidant capacity, and microvascular function, which may be due to its high concentration of polyphenols. These results indicate that organic grape juice has a positive effect in endurance athletes.

Biomedical effects of grape products

Accumulating evidence suggests that consumption of grapes and grape products can positively influence risk factors associated with cardiovascular health, cancer, neurodegenerative disease, and age-related cognitive decline. These effects are often attributed to the antioxidant activity and function of flavonoid compounds found in grapes as well as other actions such as increasing nitric oxide production. The well-established health effects of grapes on cardiovascular disease risk, mainly on endothelial function, LDL oxidation, progression of atherosclerosis, and reduction in oxidative stress, have been clearly identified. Emerging research has also demonstrated that grapes have beneficial effects on other chronic-degenerative diseases such as cancer, Alzheimer's disease, age-related cognitive decline, and diabetes. Further beneficial effects of grapes on oral health, immune function, and antiviral activity have also been reported. This review examines the published evidence on the human health benefits associated with grapes and grape products, with animal and cell studies included for areas in which human research is either limited or unavailable.

Effect of pycnogenol on glucose transport in mature 3T3-L1 adipocytes

Pycnogenol, a procyanidins-enriched extract of Pinus maritima bark, possesses antidiabetic properties, which improves the altered parameters of glucose metabolism that are associated with type 2 diabetes mellitus (T2DM). Since the insulin-stimulated antidiabetic activities of natural bioactive compounds are mediated by GLUT4 via the phosphatidylinositol-3-kinase (PI3K) and/or p38 mitogen activated protein kinase (p38-MAPK) pathway, the effects of pycnogenol were examined on the molecular mechanism of glucose uptake by the glucose transport system. 3T3-L1 adipocytes were treated with various concentrations of pycnogenol, and glucose uptake was examined using a non-radioisotope enzymatic assay and by molecular events associated with the glucose transport system using semi-quantitative reverse transcription-polymerase chain reaction (RT-PCR). The results show that pycnogenol increased glucose uptake in fully differentiated 3T3-L1 adipocytes and increased the relative abundance of both GLUT4 and Akt mRNAs through the PI3K pathway in a dose dependent manner. Furthermore, pycnogenol restored the PI3K antagonist-induced inhibition of glucose uptake in the presence of wartmannin, an inhibitor of the PI3K. Overall, these results indicate that pycnogenol may stimulate glucose uptake via the PI3K dependent tyrosine kinase pathways involving Akt. Further the results suggest that pycnogenol might be useful in maintaining blood glucose control.

Effects of dietary consumption of cranberry powder on metabolic parameters in growing rats fed high fructose diets

The effect of dietary consumption of a cranberry powder (CP) containing increased amounts of procyanidins and other phytochemicals on metabolic parameters associated with metabolic syndrome was investigated in growing rats fed a high fructose diet. Dietary treatments were control (starch based), high fructose (HF), and HF containing either 3.3, 6.6, or 33 g CP/kg diet. Fasting plasma glucose and triglycerides tended to be higher with HF feeding and were reduced by feeding CP. The area under curve following an oral glucose tolerance test was 35-50% higher in animals fed HF diet vs. control and was decreased to control levels by the low or medium but not high CP diet. Feeding CP tended to lower fasting plasma insulin. Homeostatic models of insulin resistance (HOMA-IR) and β-cell function (HOMA-BCF) were lowest in animals fed low or medium CP diets (p < 0.05). Rats fed the control starch diet had slightly higher food intake, final body weight, and abdominal fat compared to animals fed other diets. Kidney weight was higher in HF group and feeding CP decreased kidney weight to normal levels. In the fed state, plasma triglyceride was increased with HF diet, whereas insulin was lower in animals fed HF diet. Overall, inclusion of CP in the diet was effective in modulating some aspects of metabolic parameters associated with metabolic syndrome and the medium level of CP in the diet produced a better response than the lower and higher CP levels.

Protective effects of grape seed proanthocyanidin extracts on cerebral cortex of streptozotocin-induced diabetic rats through modulating AGEs/RAGE/NF-kappaB pathway

Diabetic encephalopathy is a severe complication in patients with long-term hyperglycemia. Oxidative stress is thought to be closely implicated in this disorder, so in this study, we examined whether grape seed proanthocyanidin extract (GSPE), a naturally occurring antioxidant derived from grape seeds, could reduce the injuries in the cerebral cortex of diabetic rats by modulating advanced glycation end products (AGEs)/the receptor for AGEs (RAGE)/nuclear factor-kappa B p65 (NF-kappaB p65) pathway, which is crucial in oxidative stress. Body weight and serum AGEs were tested; cerebral cortexes were isolated for morphological observations and the pyramidal cell layers were immunohistochemically stained for the detection of RAGE, NF-kappaB p65, intercellular adhesion molecule-1 (ICAM-1) and vascular cell adhesion molecule-1 (VCAM-1) as well. For RAGE and NF-kappaB p65, quantitative reverse transcriptase coupled to polymerase chain reaction (RT-PCR) was employed for determination of mRNA levels, and western blot was used to detect protein expression. Our results showed that long term hyperglycemia in diabetic rats caused the degeneration of neurons and the up-regulation of serum AGEs, and also the up-regulation of RAGE, NF-kappaB p65, VCAM-1 and ICAM-1 in the brain. We found that GSPE treatment improved the pathological changes of diabetic rats by modulating the AGEs/RAGE/NF-kappaB p65 pathway. This study enables us to further understand the key role that the AGEs/RAGE/NF-kappaB pathway plays in the pathogenesis of diabetic encephalopathy, and confirms that GSPE might be a therapeutical means to the prevention and treatment of this disorder.

The effect of grape seed extracts on serum paraoxonase activities in streptozotocin-induced diabetic rats

Procyanidins, a group of flavonoids, are oligomeric forms of catechins that are abundant in red wine, grapes, cocoa, and apples. Paraoxonase acts as an antioxidant enzyme and protects low-density lipoprotein-cholesterol against oxidation. In our study we aimed to evaluate the effects of grape seed extract (GSE) on paraoxonase activities in streptozotocin-induced diabetic rats. Our study included four groups of rats: Group I (n = 8), control; Group II (n = 10), GSE-supplemented; Group III (n = 6), streptozotocin-induced diabetic; and Group IV (n = 7), GSE-supplemented diabetic rats. Serum paraoxonase activities were determined with a spectrophotometric method. Paraoxonase activities in Group III were significantly lower than in the other three groups (P < .001, P < .001, and P = .005 for Groups I, II, and IV, respectively), and Group IV showed increased paraoxonase activities compared to Group III (P = .005). This is the first study to show an association between paraoxonase status and GSE supplementation and demonstrated that GSE increased paraoxonase activities. This beneficial effect of GSE was more obvious in the diabetic group, which was more prone to atherosclerotic events compared to the healthy population.

Evaluation of alpha-glucosidase, alpha-amylase and protein glycation inhibitory activities of edible plants

The present study was to investigate in vitro alpha-glucosidase, pancreatic alpha-amylase and protein glycation inhibitory activities of nine edible plants. The results indicated that total phenolics, flavonoids, and condensed tannins of nine edible plants showed marked variations, ranging from 12.2 to 80.1 mg gallic acid equivalent/g extract, 2.34 to 13.65 mg quercetin equivalent/g extract, and 97.2 to 460.1 mg catechin equivalent/g extract, respectively. Our findings showed that grape seed, Cat's whiskers and Sweetleaf extract were the most effective pancreatic alpha-amylase, intestinal maltase, and sucrase inhibitor with IC(50) values of 0.29 +/- 0.01 mg/ml, 0.97 +/- 0.10 mg/ml and 0.86 +/- 0.01 mg/ml, respectively. All extracts (1 mg/ml) markedly inhibited the glycation of bovine serum albumin in fructose-mediated non-enzyme glycation by 50-30% at week 1. It was found that Pennywort maintained the high percentage inhibition among those of the extracts during the 4 weeks of experiment. These edible plants may be used for controlling blood glucose level and prevention of the development of type 2 diabetes.

Grape seed proanthocyanidins attenuate vascular smooth muscle cell proliferation via blocking phosphatidylinositol 3-kinase-dependent signaling pathways

The excess generation of reactive oxygen species (ROS) play important role in the development and progression of diabetes and related vascular complications. Therefore, blocking the production of ROS will be able to improve hyperglycemia-induced vascular dysfunction. The objective of this study was to determine whether a novel IH636 grape seed proanthocyanidins (GSPs) could protect against hyperproliferation of cultured rat vascular smooth muscle cells (VSMCs) induced by high glucose (HG) and determine the related molecular mechanisms. Our data demonstrated that GSPs markedly inhibited rat VSMCs proliferation as well as ROS generation and NAPDH oxidase activity induced by HG treatment. Further studies revealed that HG treatment resulted in phosphorylation and membrane translocation of Rac1, p47phox, and p67phox subunits leading to NADPH oxidase activation. GSPs treatment remarkably disrupted the phosphorylation and membrane translocation of Rac1, p47phox, and p67phox subunits. More importantly, our data further revealed that GSPs significantly disrupted HG-induced activation of ERK1/2, JNK1/2, and PI3K/AKT/GSK3beta as well as NF-kappaB signalings, which were dependent on reactive oxygen species (ROS) generation and Rac1 activation. In addition, our results also demonstrated that HG-induced cell proliferation and excess ROS production was dependent on the activation of PI3 kinase subunit p110alpha. Collectively, these results suggest that HG-induced VSMC growth was attenuated by grape seed proanthocyanidin (GSPs) treatment through blocking PI3 kinase-dependent signaling pathway, indicating that GSPs may be useful in retarding intimal hyperplasia and restenosis in diabetic vessels.

Impact of dietary polyphenols on carbohydrate metabolism

Polyphenols, including flavonoids, phenolic acids, proanthocyanidins and resveratrol, are a large and heterogeneous group of phytochemicals in plant-based foods, such as tea, coffee, wine, cocoa, cereal grains, soy, fruits and berries. Growing evidence indicates that various dietary polyphenols may influence carbohydrate metabolism at many levels. In animal models and a limited number of human studies carried out so far, polyphenols and foods or beverages rich in polyphenols have attenuated postprandial glycemic responses and fasting hyperglycemia, and improved acute insulin secretion and insulin sensitivity. The possible mechanisms include inhibition of carbohydrate digestion and glucose absorption in the intestine, stimulation of insulin secretion from the pancreatic β–cells, modulation of glucose release from the liver, activation of insulin receptors and glucose uptake in the insulin-sensitive tissues, and modulation of intracellular signalling pathways and gene expression. The positive effects of polyphenols on glucose homeostasis observed in a large number of in vitro and animal models are supported by epidemiological evidence on polyphenol-rich diets. To confirm the implications of polyphenol consumption for prevention of insulin resistance, metabolic syndrome and eventually type 2 diabetes, human trials with well-defined diets, controlled study designs and clinically relevant end-points together with holistic approaches e.g., systems biology profiling technologies are needed.

Resveratrol ameliorates vasculopathy in STZ-induced diabetic rats: role of AGE-RAGE signalling

BACKGROUND

Resveratrol (RSV) has been shown to ameliorate hyperglycaemia and hyperlipidaemia in streptozotocin-induced diabetic rats. In the present study, we examined the beneficial effects of RSV on diabetes mellitus (DM)-induced vasculopathy and explored its possible mechanism.

METHODS

Male Sprague-Dawley rats were injected with streptozotocin at 65 mg/kg body weight The induction of DM was confirmed by a fasting plasma glucose level > or = 300 mg/dL and symptoms of polyphagia and polydipsia. The DM rats were treated with or without RSV at 0.75 mg/kg body weight three times a day for 4-8 weeks. Animals were sacrificed and vessel wall histology was examined by microscopy. The vascular smooth muscle cell activation was assessed by the medial thickness, collagen deposition, and the expressions receptor for advanced glycation end product, NF-kappaB, proliferation cell nuclear antigen, and the levels of Erk1/2 phosphorylation.

RESULTS

In RSV-treated DM rats, the vascular wall thickening, collagen deposition/cross-linking, and vascular permeability were all alleviated compared with that of the untreated DM rats. The vascular smooth muscle cell of the RSV-treated rats was characterized with less proliferation, lower NF-kappaB, and Erk1/2 activation, decreased proliferation cell nuclear antigen and receptor for advanced glycation end product expression. Moreover, the plasma fructosamine was significantly reduced in RSV-treated DM rats.

CONCLUSIONS

RSV alleviated DM-induced vasculopathy through attenuation of advanced glycation end product-receptor for advanced glycation end product-NF-kappaB signalling pathway.

Prevention of colon carcinogenesis by apple juice in vivo: impact of juice constituents and obesity

It is estimated that 75-85% of all chronic diseases are linked to lifestyle-related and environmental factors. The development of colon cancer is positively associated with obesity and inversely associated with the intake of dietary fibre, fruit and vegetable. Apple juice is the most widely consumed fruit beverage in Germany. It contains a specific spectrum of polyphenols and other components that may reduce the risk of colon cancer. Epidemiologic studies suggest an inverse correlation between apple consumption and colon cancer risk, although the mechanisms for these observations are not clear. The present review summarizes the preventive potential of apple juices and different apple constituents on biomarkers related to colon carcinogenesis with special focus on the in vivo evidence and the cancer promoting condition of obesity. However, under the cancer promoting condition of obesity, apple juice did not show cancer-preventive bioactivity. In our experiments a cancer-preventive bioactivity of apple juice is lacking in rats under the cancer-promoting condition of obesity. To further investigate, whether this lack of efficacy observed in obese rats might be representative for obese individuals human intervention studies on high risk groups such as obese or diabetic individuals are of interest and will be conducted.

Tannins: current knowledge of food sources, intake, bioavailability and biological effects

Tannins are a unique group of phenolic metabolites with molecular weights between 500 and 30 000 Da, which are widely distributed in almost all plant foods and beverages. Proanthocyanidins and hydrolysable tannins are the two major groups of these bioactive compounds, but complex tannins containing structural elements of both groups and specific tannins in marine brown algae have also been described. Most literature data on food tannins refer only to oligomeric compounds that are extracted with aqueous-organic solvents, but a significant number of non-extractable tannins are usually not mentioned in the literature. The biological effects of tannins usually depend on their grade of polymerisation and solubility. Highly polymerised tannins exhibit low bioaccessibility in the small intestine and low fermentability by colonic microflora. This review summarises a new approach to analysis of extractable and non-extractable tannins, major food sources, and effects of storage and processing on tannin content and bioavailability. Biological properties such as antioxidant, antimicrobial and antiviral effects are also described. In addition, the role of tannins in diabetes mellitus has been discussed.

Bioavailability of procyanidin dimers and trimers and matrix food effects in in vitro and in vivo models

Among procyanidins (PC), monomers, such as catechin and epicatechin, have been widely studied, whereas dimer and trimer oligomers have received much less attention, despite their abundance in our diet. Recent studies have showed that as dimers and trimers could be important in determining the biological effects of procyanidin-rich food, understanding their bioavailability and metabolism is fundamental. The purpose of the present work is to study the stability of PC under digestion conditions, the metabolism and the bioavailability by using a combination of in vitro and in vivo models. Simultaneously, the matrix effect of a carbohydrate-rich food on the digestibility and bioavailability of PC is investigated. The results show a high level of stability of PC under gastric and duodenal digestion conditions. However, the pharmacokinetic study revealed limited absorption. Free forms of dimers and trimers have been detected in rat plasma, reaching the maximum concentration 1 h after oral intake of a grape seed extract.

The potential of cinnamon to reduce blood glucose levels in patients with type 2 diabetes and insulin resistance

AIM

Cinnamon has a long history as an antidiabetic spice, but trials involving cinnamon supplementation have produced contrasting results. The aim of this review was to examine the results of randomized controlled clinical trials of cinnamon and evaluate the therapeutic potential amongst patients with diabetes and insulin-resistant patients, particularly the ability to reduce blood glucose levels and inhibit protein glycation.

METHODS

A systematic electronic literature search using the medical subject headings 'cinnamon' and 'blood glucose' was carried out to include randomized, placebo-controlled in vivo clinical trials using Cinnamomum verum or Cinnamomum cassia conducted between January 2003 and July 2008.

RESULTS

Five type 2 diabetic and three non-diabetic studies (total N = 311) were eligible. Two of the diabetic studies illustrated significant fasting blood glucose (FBG) reductions of 18-29% and 10.3% (p < 0.05), supported by one non-diabetic trial reporting an 8.4% FBG reduction (p < 0.01) vs. placebo, and another illustrating significant reductions in glucose response using oral glucose tolerance tests (p < 0.05). Three diabetic studies reported no significant results.

CONCLUSIONS

Whilst definitive conclusions cannot be drawn regarding the use of cinnamon as an antidiabetic therapy, it does possess antihyperglycaemic properties and potential to reduce postprandial blood glucose levels. Further research is required to confirm a possible correlation between baseline FBG and blood glucose reduction and to assess the potential to reduce pathogenic diabetic complications with cinnamon supplementation.

Type 2 diabetes and glycemic response to grapes or grape products

Type 2 diabetes affects approximately 7% of the population in the United States and is characterized by decreased disposal of glucose in peripheral tissues due to insulin resistance and overproduction of glucose by the liver, defects in pancreatic beta-cell function, and decreased beta-cell mass. Obesity, decreased physical exercise, and consumption of foods with a high glycemic index (GI) and load are major predisposing factors in the development of type 2 diabetes. The GI is used to evaluate the rise in blood glucose levels in response to food. The GI provides an indication of the quality of carbohydrate in a food. The glycemic load (GL) is used to provide information about the quantity of carbohydrates in a food and the insulin demand. Individuals with diabetes are advised to maintain a diet of low-GL foods, because low-GL diets improve diabetes symptoms. Grapes have a mean GI and GL in the low range. Little research has been performed with grapes and/or grape products to determine the glycemic response either alone or with a meal. Grapes and other fruits contain numerous polyphenols, including the stilbene resveratrol, the flavanol quercetin, catechins, and anthocyanins that have shown potential for reducing hyperglycemia, improving beta-cell function, and protecting against beta-cell loss. Therefore, with a low mean GI and GL, grapes or grape products may provide health benefits to type 2 diabetics.

Grapes and cardiovascular disease

Epidemiological studies suggest that consumption of wine, grape products, and other foods containing polyphenols is associated with decreased risk for cardiovascular disease. The benefits of wine consumption appear to be greater than other alcoholic beverages. Experimental studies indicate that grape polyphenols could reduce atherosclerosis by a number of mechanisms, including inhibition of oxidation of LDL and other favorable effects on cellular redox state, improvement of endothelial function, lowering blood pressure, inhibition of platelet aggregation, reducing inflammation, and activating novel proteins that prevent cell senescence, e.g. Sirtuin 1. Translational studies in humans support these beneficial effects. More clinical studies are needed to confirm these effects and formulate dietary guidelines. The available data, however, strongly support the recommendation that a diet rich in fruits and vegetables, including grapes, can decrease the risk for cardiovascular disease.