Procyanidins improve some disrupted glucose homoeostatic situations: an analysis of doses and treatments according to different animal models

Comparisons of procyanidins with different low polymerization degrees on prevention of lipid metabolism in high-fat diet/streptozotocin-induced diabetic mice

Procyanidins, which are oligomerized flavan-3-ols with a polyphenolic structure, are bioactive substances that exhibit various biological effects. However, the relationship between the degree of polymerization (DP) of procyanidins and their bioactivities remains largely unknown. In this study, the preventive effects of procyanidins with different DP (EC, PB2 and PC1) on glucose improvement and liver lipid deposition were investigated using a high-fat diet/streptozotocin-induced diabetes mouse model. The results demonstrated that all the procyanidins with different DP effectively reduced fasting blood glucose and glucose/insulin tolerance, decreased the lipid profile (total cholesterol, triglyceride, and low-density lipoprotein cholesterol content) in serum and liver tissue as well as the liver oil red staining, indicating the improvement of glucose metabolism, insulin sensitivity and hepatic lipid deposition in diabetic mice. Furthermore, the procyanidins down-regulated expression of glucose regulated 78-kDa protein (GRP78) and C/EBP homologous protein (CHOP), indicating a regulation role of endoplasmic reticulum (ER) stress. The inhibition of ER stress by tauroursodeoxycholic acid (TUDCA) treatment abolished the effects of procyanidins with different DP in PA-induced HepG2 cells, confirming that procyanidins alleviate liver hyperlipidemia through the modulation of ER stress. Molecular docking results showed that EC and PB2 could better bind GRP78 and CHOP. Collectively, our study reveals that the structure of procyanidins, particularly DP, is not directly correlated with the improvement of blood glucose and lipid deposition, while highlighting the important role of ER stress in the bioactivities of procyanidins.

Two Prenylated Chalcones, 4-Hydroxyderricin, and Xanthoangelol Prevent Postprandial Hyperglycemia by Promoting GLUT4 Translocation via the LKB1/AMPK Signaling Pathway in Skeletal Muscle Cells

SCOPE

Stimulation of glucose uptake in the skeletal muscle is crucial for the prevention of postprandial hyperglycemia. Insulin and certain polyphenols enhance glucose uptake through the translocation of glucose transporter 4 (GLUT4) in the skeletal muscle. The previous study reports that prenylated chalcones, 4-hydroxyderricin (4-HD), and xanthoangelol (XAG) promote glucose uptake and GLUT4 translocation in L6 myotubes, but their underlying molecular mechanism remains unclear. This study investigates the mechanism in L6 myotubes and confirms antihyperglycemia by 4-HD and XAG.

METHODS AND RESULTS

In L6 myotubes, 4-HD and XAG promote glucose uptake and GLUT4 translocation through the activation of adenosine monophosphate-activated protein kinase (AMPK) and liver kinase B1 (LKB1) signaling pathway without activating phosphoinositide 3-kinase (PI3K)/protein kinase B (Akt) and Janus kinases (JAKs)/signal transducers and activators of transcriptions (STATs) pathways. Moreover, Compound C, an AMPK-specific inhibitor, as well as siRNA targeting AMPK and LKB1 completely canceled 4-HD and XAG-increased glucose uptake. Consistently, oral administration of 4-HD and XAG to male ICR mice suppresses acute hyperglycemia in an oral glucose tolerance test.

CONCLUSION

In conclusion, LKB1/AMPK pathway and subsequent GLUT4 translocation in skeletal muscle cells are involved in Ashitaba chalcone-suppressed acute hyperglycemia.

Polyphenol Composition and Antioxidant Activity of Japonica Rice Cultivars and Intake Status

Japonica rice is produced mainly in northeast China, Japan, and the Korean Peninsula. Polyphenols and flavonoids are the main antioxidants in japonica rice. This study reported the polyphenol content and antioxidant activity of nine brown and white japonica rice cultivars. The total phenolic and flavonoid contents of brown rice were in the ranges of 241.98-296.76 GAE mg/100 g, and 225.30-276.80 RE mg/100 g, respectively. These values were significantly higher than that of white rice by 118.98-206.06% and 135.0-217%, respectively. The bound fraction from phenolics and flavonoids contributed 41.1-63.6% and 62.22-78.19% of the total phenolic and flavonoid content in brown rice, respectively, while these ranges were 55.5-73.5% and 46.07-66.83% in white rice, respectively. p-Hydroxybenzonic acid was the predominant phenolic acid in japonica rice. All four antioxidant capacities of brown rice (DPPH, ABTS, OH, FRAP) were higher by up to 1.68-2.85 times than those of white rice. The PZ21 (Yanfeng 47) japonica rice variety has outstanding antioxidant capacity based on the weights of each antioxidant index. According to the differences of functional substances among varieties, it can provide guidance for consumers and theoretical basis for the production of healthy food.

Procyanidins and its metabolites by gut microbiome improves insulin resistance in gestational diabetes mellitus mice model via regulating NF-κB and NLRP3 inflammasome pathway

Gestational Diabetes Mellitus (GDM) has an effect on the health of pregnant women and fetuses. Procyanidins (PA) is a flavonoid with anti-diabetic activity, but its effects and mechanisms on GDM have not been defined. Herein, we studied further the functions and mechanisms of PA on insulin resistance (IR) in GDM mice, as well as on postpartum and offspring mice. GDM mice model was built by feeding a high-fat-high-sucrose diet, and PA intervention (27.8 mg/kg/d) was performed from 4 weeks before pregnancy to delivery. Intestinal flora deficient (IFD) mice model was established by broad spectrum antibiotics. PA decreased the gestational weight gain, and the levels of fasting blood glucose, insulin, homeostasis model of assessment for IR index, yet increased the levels of HOMA for insulin sensitivity index. Interestingly, in IFD mice the effect of PA on improving IR was significantly weakened. PA inhibited inflammation by decreasing the levels of IL-6, TNF-α, IL-17 and CRP, which also been blocked in the IFD mice. Moreover, PA improved glycometabolism and reduced the secretion of inflammatory factors and hepatic inflammation infiltration of mice at 4 weeks postpartum, but had no significant effect on offspring mice. Mechanistically, PA treatment suppressed the nuclear factor-κB (NF-κB) p65 nuclear translocation and nucleotide-binding domain like receptor protein 3 (NLRP3) inflammasome activation. In vitro studies, 4-hydroxyphenylacetic acid and 3-(4-hydroxyphenyl) propionic acid, main intestinal flora metabolites of PA restrained NF-κB/NLRP3 activation. In conclusions, PA improved IR via NF-κB/NLRP3 pathway in GDM and postpartum mice, which partly through its metabolites by gut microbiome.

Diabetes diminishes a typical metabolite of litchi pericarp oligomeric procyanidins (LPOPC) in urine mediated by imbalanced gut microbiota

Animal studies and clinical trials have shown that dietary polyphenols and polyphenol-rich foods can reduce the risk of type 2 diabetes (T2D) and its complications, but how diabetes regulates the metabolism of polyphenol has not been fully elucidated. This study investigated the effects of diabetes on litchi pericarp oligomeric procyanidin (LPOPC) dynamic metabolism and its major static metabolites in urine. First, a high-fat and streptozotocin (STZ)-induced diabetic Sprague Dawley (SD) rat model was established. In the diabetic rat model, elevated fasting blood glucose, severely impaired glucose tolerance test, and increased reactive oxygen species (ROS) levels in serum and the liver were observed. Subsequently, 200 mg per kg body weight of LPOPC was administrated to control and diabetic SD rats, and the gastrointestinal tract was collected at 0.5 h, 1 h, 3 h, and 6 h. The results showed that the retention time of LPOPC was not changed in our diabetic rat model. However, the gut microbiota were significantly altered, with elevated Proteobacteria and Verrucomicrobia abundance in diabetic rats and decreased short chain fatty acid (SCFA)-producing bacteria. Interestingly, after one dose of 300 mg per kg body weight LPOPC, the total antioxidant capacity of urine in diabetic rats significantly decreased. We then tested the static metabolites of LPOPC, demonstrating that epicatechin had not changed in urine in diabetic rats, but that shikimic acid was significantly reduced in urine in diabetic rats. The changes in shikimic acid may be due to the alteration of gut microbiota and elevated ROS levels in serum.

Analysis of Commercial Proanthocyanidins. Part 6: Sulfitation of Flavan-3-Ols Catechin and Epicatechin, and Procyanidin B-3

Proanthocyanidins (PACs) are natural plant-derived polymers consisting of flavan-3-ol monomers. Quebracho (Schinopsis lorentzii and balansae) heartwood and mimosa (Acacia mearnsii) bark extracts are the major industrial sources of PACs. These commercial extracts are often sulfited to reduce their viscosity and increase their solubility in water. The chemical process of sulfitation is still poorly understood regarding stereochemical influences during the reaction and during the cleavage of the interflavanyl bond of oligomers. To gain a better understanding of sulfitation, two diastereomeric flavan-3-ol monomers were sulfited under industrial conditions, and procyanidin B-3 (catechin-4α→8-catechin) were sulfited to investigate interflavanyl bond cleavage with sulfitation at C-4. Treatment of diastereomeric flavan-3-ols 2R,3S-catechin and 2R,3R-epicatechin with NaHSO3 at 100 °C in aqueous medium afforded the enantiomeric (1R,2S)- and (1S,2R)-1-(3,4-dihydroxyphenyl)-2-hydroxy-3-(2,4,6-trihydroxyphenyl)propane-1-sulfonic acid, respectively. Utilizing computational NMR PD4 calculations it was determined that the direction of stereoselective nucleophilic attack is controlled by the C-3 configuration of the flavan-3-ols catechin and epicatechin. Sulfitation of the catechin-4α→8-catechin dimer 7 (procyanidin B-3) under the same conditions led to the cleavage of the interflavanyl bond yielding the C-4 sulfonic acid substituted catechin momomer. From the heterocyclic ring coupling constants it was determined that nucleophilic attack occurs from the β-face of the dimer leading to the 2,3-trans-3,4-cis isomer as product.

Effects of Dietary Blueberry (Vaccinium ashei Reade) Leaves on Mildly Postprandial Hypertriglyceridemia

Prevention of postprandial hypertriglyceridemia is an important consideration for reducing the risk of developing cardiovascular disease. While blueberry fruits have been reported to ameliorate lipid metabolism in humans, there are only few research reports on the effects of blueberry leaves (BL). Here, we investigated the efficacy of BL on postprandial hyperlipidemia in subjects with high fasting triacylglycerol (TG) concentrations. Randomized, double-blind, cross-over design study was conducted. The subjects consumed a BL containing beverage or a placebo beverage before a fat-enriched test meal. Blood samples were collected prior to and 1, 2, 3, 4, and 5 hours after consuming the test beverage. The postprandial serum TG and remnant-like particle cholesterol (RLP-C) concentrations were significantly lower in the BL beverage compared with those in the placebo beverage. Additionally, BL was more effective in subjects with high fasting ghrelin with gastric emptying function. In current study, fasting ghrelin correlated with the increase in postprandial serum TG, suggesting that BL ameliorates hypertriglyceridemia through delayed gastric emptying. In conclusion, this pilot study suggests that BL may be useful as an early dietary therapy for treating postprandial hyperlipidemia.

Long-Lasting Effects of GSPE on Ileal GLP-1R Gene Expression Are Associated with a Hypomethylation of the GLP-1R Promoter in Female Wistar Rats

Flavonoids have been shown to modulate GLP-1 in obesity. GLP-1 induces some of its effects through the intestinal GLP-1 receptor (GLP-1R), though no data exist on how flavonoids affect this receptor. Here, we examine how a dose of grape seed proanthocyanidin extract (GSPE) with anti-obesity activity affects intestinal GLP-1R and analyze whether epigenetics play a role in the long-lasting effects of GSPE. We found that 10-day GSPE administration prior to the cafeteria diet upregulated GLP-1R mRNA in the ileum 17 weeks after the GSPE treatment. This was associated with a hypomethylation of the GLP-1R promoter near the region where the SP1 transcription factor binds. In the colon, the cafeteria diet upregulated GLP-1R without showing any GSPE effect. In conclusion, we have identified long-lasting GSPE effects on GLP-1R gene expression in the ileum that are partly mediated by hypomethylation at the gene promoter and may affect the SP1 binding factor.

Grape Seed Proanthocyanidins Target the Enteroendocrine System in Cafeteria-Diet-Fed Rats

SCOPE

The effects on the enteroendocrine system of three different grape seed proanthocyanidin extract (GSPE) treatments are analyzed in rats on a cafeteria diet for 17 weeks.

METHODS AND RESULTS

GSPE is administered in a corrective manner (15 last days of the cafeteria diet) at two doses, 100 and 500 mg GSPE per kg bw. A third, longer treatment in which GSPE (500 mg kg^-1 bw) is administered daily every other week during the 17 weeks of the cafeteria diet is also tested. Most GSPE treatments lead to ghrelin accumulation in the stomach, limited CCK secretion in the duodenum, and increased GLP-1 and PYY mRNA in colon. GSPE also increases cecal hypertrophy and reduces butyrate content. When the treatment is administered daily every other week during 17 weeks, there is also an increase in colon size. These effects are accompanied by a reduced food intake at the end of the experiment when GSPE is administered at 500 mg GSPE kg^-1 during the last 15 days, but not on the other treatments, despite an observed reduction in body weight in the longer treatment.

CONCLUSION

GSPE modulates the enteroendocrine system in models in which it also reduces food intake or body weight.

Effects of phytochemicals against diabetes

Diabetes mellitus, a chronic metabolic disease, characterized by elevated levels of blood glucose and insufficiency in production and action of insulin is the seventh leading cause of death worldwide. Numerous studies have shown that diabetes mellitus is associated with increased formation of free radicals and decrease in antioxidant potential. In the patients with diabetes mellitus, the levels of antioxidant parameters are found to decrease, hence in many studies phytochemicals which can exert antioxidant and free radical scavenging activities, are suggested to improve the insulin sensitivity. Several phytoactive compounds such as flavonoids, lignans, prophenylphenols, are also found to combat the complications of diabetes. This chapter mainly focuses on the relationship between diabetes mellitus and preventive roles of various phytochemicals on diabetes via their antioxidant properties.

Etiology of Metabolic Syndrome and Dietary Intervention

The growing prevalence of metabolic syndrome (MetS) in the U.S. and even worldwide is becoming a serious health problem and economic burden. MetS has become a crucial risk factor for the development of type 2 diabetes mellitus (T2D) and cardiovascular diseases (CVD). The rising rates of CVD and diabetes, which are the two leading causes of death, simultaneously exist. To prevent the progression of MetS to diabetes and CVD, we have to understand how MetS occurs and how it progresses. Too many causative factors interact with each other, making the investigation and treatment of metabolic syndrome a very complex issue. Recently, a number of studies were conducted to investigate mechanisms and interventions of MetS, from different aspects. In this review, the proposed and demonstrated mechanisms of MetS pathogenesis are discussed and summarized. More importantly, different interventions are discussed, so that health practitioners can have a better understanding of the most recent research progress and have available references for their daily practice.

Proanthocyanidins and hydrolysable tannins: occurrence, dietary intake and pharmacological effects

Tannins are a heterogeneous group of high MW, water-soluble, polyphenolic compounds, naturally present in cereals, leguminous seeds and, predominantly, in many fruits and vegetables, where they provide protection against a wide range of biotic and abiotic stressors. Tannins exert several pharmacological effects, including antioxidant and free radical scavenging activity as well as antimicrobial, anti-cancer, anti-nutritional and cardio-protective properties. They also seem to exert beneficial effects on metabolic disorders and prevent the onset of several oxidative stress-related diseases. Although the bioavailability and pharmacokinetic data for these phytochemicals are still sparse, gut absorption of these compounds seems to be inversely correlated with the degree of polymerization. Further studies are mandatory to better clarify how these molecules and their metabolites are able to cross the intestinal barrier in order to exert their biological properties. This review summarizes the current literature on tannins, focusing on the main, recently proposed mechanisms of action that underlie their pharmacological and disease-prevention properties, as well as their bioavailability, safety and toxicology.

LINKED ARTICLES

This article is part of a themed section on Principles of Pharmacological Research of Nutraceuticals. To view the other articles in this section visit http://onlinelibrary.wiley.com/doi/10.1111/bph.v174.11/issuetoc.

Attenuated mTOR Signaling and Enhanced Glucose Homeostasis by Dietary Supplementation with Lotus Seedpod Oligomeric Procyanidins in Streptozotocin (STZ)-Induced Diabetic Mice

This study investigated the protective role of lotus seedpod oligomeric procyanidins (LSOPC) and synbiotics (Bifidobacterium Bb-12 and xylo-oligosaccharide) against high fat and streptozotocin (STZ)-induced diabetes. Administration of LSOPC or synbiotics had no effect on blood glucose in normal mice. Treatments with LSOPC for 12 weeks markedly reduced blood glucose, FFA, endotoxin, and GHbA1c and improved glucose homeostasis, lipid metabolism, and insulin levels. In addition, administration of LSOPC significantly reversed the increase of mTOR and p66^Shc in liver, skeletal muscle, and white adipose tissue (WAT). LSOPC significantly increased glucose uptake and glycolysis in liver, skeletal muscle, and WAT while improving heat generation in brown adipose tissue (BAT) and inhibiting gluconeogenesis and lipogenesis in liver. Furthermore, synbiotics strengthened the improving effect of LSOPC. These findings demonstrated that LSOPC and synbiotics may regulate glucose disposal in peripheral target tissues through the p66^Shc-mTOR signaling pathway.

Factors influencing antioxidant compounds in rice

Epidemiological and clinical studies suggest that the additive/synergistic effects of several bioactive compounds are responsible for the health benefits of rice. Among the leading contenders are phenolic acids, flavonoids, anthocyanins, proanthocyanidins, tocotrienols, tocopherols, λ-oryzanol, and phytic acid, which all possess strong antioxidant activities in vitro. In this review, data related to health effects of rice antioxidants using cultured cells, rodents and humans models are first summarized. The evidence is strong that consumption of rice tocotrienols translates into improved health outcomes. Current research, however, does not strongly support the health-promoting effects of rice tocopherols and phenolic acids. The crucial limitations in studies using rice flavonoids, anthocyanins, proanthocyanidins, λ-oryzanol and phytic acid appear to be the appropriateness of the substance tested (i.e., purity), and the scarcity of animal and human interventions. In a second part, rice antioxidants are reviewed with an emphasis on their composition and contents. Taking into account the bioavailability of these compounds, it is evident that a number of factors affect the antioxidant composition of rice, making it difficult to estimate dietary intake. Before harvest, factors including soil type, atmospheric CO₂, chemical inputs, temperature, and degree of ripening are important. After harvest, rice is subjected to processing methods that include drying, parboiling, storage, irradiation, milling, stabilization, soaking, germination, fermentation, boiling, steaming, roasting, baking, and extrusion. Quantitative knowledge about the effects of these processes is summarized in this review. Surprisingly, a high level of agreement was found among study results, which could be useful in manipulating the growing and processing techniques of rice grains to facilitate efficient and safe consumption of antioxidant compounds.

Acutely administered grape-seed proanthocyanidin extract acts as a satiating agent

Grape-seed proanthocyanidins' role as stimulators of active GLP-1 in rats suggests that they could be effective as satiating agents. Wistar rats were used to study the effects of proanthocyanidins on food intake with different doses, administration times and proanthocyanidin extract compositions. A dose of 423 mg of phenolics per kg body weight (BW) of grape-seed proanthocyanidin extract (GSPE) was necessary to decrease the 12-hour cumulative food intake by 18.7 ± 3.4%. Proanthocyanidins were effective when delivered directly into the gastrointestinal tract one hour before, or simultaneously at the start of the feeding period. Proanthocyanidins without galloyl forms, such as those from cocoa extract, were not as effective as grape-seed derived forms. GSPE increased the portal levels of active GLP-1 and total ghrelin and decreased the CCK levels, simultaneously with a decrease in gastric emptying. In conclusion, grape-seed proanthocyanidins could be useful as a satiating agent under the conditions defined in this study.

Procyanidin Promotes Translocation of Glucose Transporter 4 in Muscle of Mice through Activation of Insulin and AMPK Signaling Pathways

Procyanidins are the oligomeric or polymeric forms of epicatechin and catechin. In this study, we isolated and purified dimer to tetramer procyanidins from black soybean seed coat and investigated the anti-hyperglycemic effects by focusing on glucose transporter 4 (GLUT4) translocation and the underlying molecular mechanism in skeletal muscle of mice. The anti-hyperglycemic effects of procyanidins were also compared with those of monomer (-)-epicatechin (EC) and major anthocyanin, cyanidin-3-O-β-glucoside (C3G). To investigate GLUT4 translocation and its related signaling pathways, ICR mice were orally given procyanidins, EC and C3G in water at 10 μg/kg body weight. The mice were sacrificed 60 min after the dose of polyphenols, and soleus muscle was extracted from the hind legs. The results showed that trimeric and tetrameric procyanidins activated both insulin- and AMPK-signaling pathways to induce GLUT4 translocation in muscle of ICR mice. We confirmed that procyanidins suppressed acute hyperglycemia with an oral glucose tolerance test in a dose-dependent manner. Of these beneficial effects, cinnamtannin A2, one of the tetramers, was the most effective. In conclusion, procyanidins, especially cinnamtannin A2, significantly ameliorate postprandial hyperglycemia at least in part by promoting GLUT4 translocation to the plasma membrane by activating both insulin- and AMPK-signaling pathways.

Antioxidant effects of proanthocyanidin-rich natural extracts from grape seed and cupuassu on gastrointestinal mucosa

BACKGROUND

The gastrointestinal tract (GI) is constantly exposed to reactive species released by the GI tract itself, and those present in food and beverages. Phenolic compounds may help in protecting the GI tract against damage produced by the reactive species. In this paper we have analyzed the effects of a grape seed proanthocyanidin extract (GSPE) on reactive oxygen species (ROS) production in two different intestinal cell types: the absorptive cell line Caco-2 and the enteroendocrine cell line STC-1.

RESULTS

We show that GSPE prevents tert-butylhydroperoxide-induced oxidative stress in both cell lines, and that the effects are dose and time dependent. We have also analyzed whether GSPE has any in vivo effect, and found that 25 mg kg(-1) body weight cannot counteract the increase in intestinal ROS induced by the cafeteria diet. However, an acute (1 h) treatment of 1 g GSPE kg(-1) body weight reduced ROS in fasted animals and also decreased ROS induction by food. These effects were found only after a short-term treatment. Furthermore, we have compared the in vitro GSPE effects with those of another proanthocyanidin-rich extract from cupuassu seeds, though it has compounds with different structures. Cupuassu extract also shows antioxidant effects in both cell types, which suggests different mechanisms from those of GSPE.

CONCLUSION

Natural proanthocyanidin-rich extracts have an antioxidant effect in the GI tract, acting on absorptive cells and enterohormone-secreting cells, although the effects depend on the dose and period of treatment. © 2015 Society of Chemical Industry.

Dietary proanthocyanidins modulate BMAL1 acetylation, Nampt expression and NAD levels in rat liver

Metabolism follows circadian rhythms, which are driven by peripheral clocks. Clock genes in the liver are entrained by daytime meals and food components. Proanthocyanidins (PAs), the most abundant flavonoids in the human diet, modulate lipid and glucose metabolism. The aim of this study was to determine whether PAs could adjust the clock system in the liver. Male Wistar rats were orally gavaged with 250 mg grape seed proanthocyanidin extract (GSPE)/kg body weight at zeitgeber time (ZT) 0 (light turned on), at ZT12 (light turned off), or before a 6 hour jet-lag and sacrificed at different times. The 24 hour rhythm of clock-core and clock-controlled gene expression indicated that nicotinamide phosphoribosyltransferase (Nampt) was the most sensitive gene to GSPE. However, Nampt was repressed or overexpressed after GSPE administration at ZT0 or ZT12, respectively. NAD levels, which are controlled by Nampt and also exhibit circadian rhythm, decreased or increased according to Nampt expression. Moreover, the ratio of acetylated Bmal1, that directly drives Nampt expression, only increased when GSPE was administered at ZT12. Therefore, GSPE modulated the clock system in the liver, suggesting that PAs can regulate lipid and glucose metabolism by adjusting the circadian rhythm in the liver.

The cardiovascular benefits of dark chocolate

Dark chocolate contains many biologically active components, such as catechins, procyanidins and theobromine from cocoa, together with added sucrose and lipids. All of these can directly or indirectly affect the cardiovascular system by multiple mechanisms. Intervention studies on healthy and metabolically-dysfunctional volunteers have suggested that cocoa improves blood pressure, platelet aggregation and endothelial function. The effect of chocolate is more convoluted since the sucrose and lipid may transiently and negatively impact on endothelial function, partly through insulin signalling and nitric oxide bioavailability. However, few studies have attempted to dissect out the role of the individual components and have not explored their possible interactions. For intervention studies, the situation is complex since suitable placebos are often not available, and some benefits may only be observed in individuals showing mild metabolic dysfunction. For chocolate, the effects of some of the components, such as sugar and epicatechin on FMD, may oppose each other, or alternatively in some cases may act together, such as theobromine and epicatechin. Although clearly cocoa provides some cardiovascular benefits according to many human intervention studies, the exact components, their interactions and molecular mechanisms are still under debate.

A grape seed extract increases active glucagon-like peptide-1 levels after an oral glucose load in rats

We have previously reported that procyanidins, a class of flavonoids, improve glycemia and exert an incretin-like effect, which was linked to their proven inhibitory effect on the dipeptidyl-peptidase 4 (DPP4) activity. However, their actual effect on incretin levels has not been reported yet. Therefore, in the present study we have evaluated whether a grape seed extract enriched in procyanidins (GSPE) modulates plasma incretin levels and attempted to determine the mechanisms involved. An acute GSPE treatment in healthy Wistar female rats prior to an oral glucose load induced an increase in plasma active glucagon-like peptide-1 (GLP-1), which was accompanied by an increase in the plasma insulin/glucose ratio and a simultaneous decrease in glucose levels. In agreement with our previous studies, the intestinal DPP4 activity was inhibited by the GSPE treatment. We have also assayed in vitro whether this inhibition occurs in inner intestinal tissues close to GLP-1-producing cells, such as the endothelium of the capillaries. We have found that the main compounds absorbed by intestinal CaCo-2 cells after an acute treatment with GSPE are catechin, epicatechin, B2 dimer and gallic acid, and that they inhibit the DPP4 activity in endothelial HUVEC cells in an additive way. Moreover, an increase in plasma total GLP-1 levels was found, suggesting an increase in GLP-1 secretion. In conclusion, our results show that GSPE improves glycemia through its action on GLP-1 secretion and on the inhibition of the inner intestinal DPP4 activity, leading to an increase in active GLP-1 levels, which, in turn, may affect the insulin release.

Roles of proanthocyanidin rich extracts in obesity

Obesity is a multifactorial disorder involving an abnormal or excessive amount of body fat.

Effect of single oral dose of proanthocyanidin on postprandial hyperglycemia in healthy rats: A comparative study with sitagliptin

Background:

Many of flavonoid rich natural products found to have a significant influence on postprandial hyperglycemia, a major risk factor for diabetic complications. Enhancement of insulinotropic gut hormones by inhibition of dipeptidyl peptidase-IV (DPP-IV) are among the newest strategies for treatments of Type 2 diabetes which thought to be the underlying action through which flavonoid can reduce postprandial hyperglycemia.

Aim:

This study aim was designed to investigate the potential role of standardized grape seed proanthocyanidin in controlling postprandial hyperglycemia by enhancing the regulatory incretin effect of gut hormones in response to oral and intraperitoneal (I.P) glucose load in healthy rats.

Materials and Methods:

Five groups of animals each of six rats were used in this study, which was conducted in March 2013. Groups (II and V) treated with single oral dose of proanthocyanidin (50 mg/kg), Group III received single oral dose of sitagliptin (40 mg/kg) and Groups (I and IV) treated with vehicle serve as control groups. All treatments were given 30 min before oral or I.P glucose load. Blood glucose was estimated over 2 h duration at (0, 30, 60, 90, and 120) min from glucose load.

Result:

Both proanthocyanidin and sitagliptin significantly improve hyperglycemia induced by oral glucose load relative to control. While non-significant changes were achieved by proanthocyanidin after I.P glucose challenge compared to untreated control group.

Conclusion:

The result of this study indicated that proanthocyanidin may possess an enhancement of incretin effect of gut peptides, which could be responsible for some of its action on glucose homeostasis. This finding may provide an opportunity for further pharmacological studies using more specific models to clarify the possible action of proanthocyanidin as a natural DPP-IV inhibitor.

Oligomeric cocoa procyanidins possess enhanced bioactivity compared to monomeric and polymeric cocoa procyanidins for preventing the development of obesity, insulin resistance, and impaired glucose tolerance during high-fat feeding

There is interest in the potential of cocoa flavanols, including monomers and procyanidins, to prevent obesity and type-2 diabetes. Fermentation and processing of cocoa beans influence the qualitative and quantitative profiles of individual cocoa constituents. Little is known regarding how different cocoa flavanols contribute to inhibition of obesity and type-2 diabetes. The objective of this study was to compare the impacts of long-term dietary exposure to cocoa flavanol monomers, oligomers, and polymers on the effects of high-fat feeding. Mice were fed a high-fat diet supplemented with either a cocoa flavanol extract or a flavanol fraction enriched with monomeric, oligomeric, or polymeric procyanidins for 12 weeks. The oligomer-rich fraction proved to be most effective in preventing weight gain, fat mass, impaired glucose tolerance, and insulin resistance in this model. This is the first long-term feeding study to examine the relative activities of cocoa constituents on diet-induced obesity and insulin resistance.

Grape-seed procyanidins prevent the cafeteria-diet-induced decrease of glucagon-like peptide-1 production

Grape-seed procyanidin extract (GSPE) has been reported to improve insulin resistance in cafeteria rats. Because glucagon-like peptide-1 (GLP-1) is involved in glucose homeostasis, the preventive effects of GSPE on GLP-1 production, secretion, and elimination were evaluated in a model of diet-induced insulin resistance. Rats were fed a cafeteria diet for 12 weeks, and 25 mg of GSPE/kg of body weight was administered concomitantly. Vehicle-treated cafeteria-fed rats and chow-fed rats were used as controls. The cafeteria diet decreased active GLP-1 plasma levels, which is attributed to a decreased intestinal GLP-1 production, linked to reduced colonic enteroendocrine cell populations. Such effects were prevented by GSPE. In the same context, GSPE avoided the decrease on intestinal dipeptidyl-peptidase 4 (DPP4) activity and modulated the gene expression of GLP-1 and its receptor in the hypothalamus. In conclusion, the preventive treatment with GSPE abrogates the effects of the cafeteria diet on intestinal GLP-1 production and DPP4 activity.

Grape-seed procyanidins modulate cellular membrane potential and nutrient-induced GLP-1 secretion in STC-1 cells

Grape-seed procyanidin extracts (GSPE) modulate glucose homeostasis, and it was suggested that GSPE may achieve this by enhancing the secretion of incretin hormones such as glucagon-like peptide-1 (GLP-1). Therefore, the aim of the present study is to examine in detail the effects of GSPE on intestinal endocrine cells (STC-1). GSPE was found to modulate plasma membrane potential in enteroendocrine cells, inducing depolarization at low concentrations (0.05 mg/l) and hyperpolarization at high concentrations (50 mg/l), and surprisingly this was also accompanied by suppressed GLP-1 secretion. Furthermore, how GSPE affects STC-1 cells under nutrient-stimulated conditions (i.e., glucose, linoleic acid, and l-proline) was also explored, and we found that the higher GSPE concentration was effective in limiting membrane depolarization and reducing GLP-1 secretion. Next, it was also examined whether GSPE affected mitochondrial membrane potential, and it was found that this too is altered by GSPE; however, this does not appear to explain the observed effects on plasma membrane potential and GLP-1 secretion. In conclusion, our results show that grape-seed procyanidins modulate cellular membrane potential and nutrient-induced enteroendocrine hormone secretion in STC-1 cells.

Gallic acid is an active component for the anticarcinogenic action of grape seed procyanidins in pancreatic cancer cells

The aim of the present work was to evaluate the effects of a grape seed procyanidin extract (GSPE) on proliferation and apoptosis in the pancreatic adenocarcinoma cell line MIA PaCa-2 and identify the components of the extract with higher activity. The effects of the extract were analyzed on the proliferation and apoptosis processes in MIA PaCa-2 cells, as well as in the levels of the apoptosis markers Bcl-2 and Bax, the mitochondrial membrane potential, and reactive oxygen species levels. Finally, the components of the extract with higher effects were elucidated using enriched fractions of the extract and pure compounds. The results showed that GSPE inhibits cell proliferation and increases apoptosis in MIA PaCa-2 cells, which is primarily mediated by the downregulation of the antiapoptotic protein Bcl-2 and the depolarization of the mitochondrial membrane. GSPE also reduced the formation of reactive oxygen species. The component of the extract that possesses the highest antiproliferative and proapoptotic activity was gallic acid. In conclusion, GSPE acts as anticarcinogenic in MIA PaCa-2 cells, with gallic acid as the major single active constituent of the extract.

Grape Seed Procyanidin Extract Improves Insulin Production but Enhances Bax Protein Expression in Cafeteria-Treated Male Rats

In a previous study, the administration of a grape seed procyanidin extract (GSPE) in female Wistar rats improved insulin resistance, reduced insulin production, and modulated apoptosis biomarkers in the pancreas. Considering that pharmacokinetic and pharmacodynamic parameters in females are different from these parameters in males, the aim of the present study was to evaluate the effects of GSPE on male Wistar cafeteria-induced obese rats. The results have confirmed that the cafeteria model is a robust model mimicking a prediabetic state, as these rats display insulin resistance, increased insulin synthesis and secretion, and increased apoptosis in the pancreas. In addition, GSPE treatment (25 mg/kg of GSPE for 21 days) in male rats improves insulin resistance and counteracts the cafeteria-induced effects on insulin synthesis. However, the administration of the extract enhances the cafeteria-induced increase in Bax protein levels, suggesting increased apoptosis. This result contradicts previous results from cafeteria-fed female rats, in which GSPE seemed to counteract the increased apoptosis induced by the cafeteria diet.

Flavanol metabolites distribute in visceral adipose depots after a long-term intake of grape seed proanthocyanidin extract in rats

A considerable number of epidemiological investigations and intervention studies have supported an association between the intake of flavanol- and proanthocyanidin-containing foods and a decreased risk of metabolic diseases. Nonetheless, less is know about the capacity of tissues to accumulate flavanols and/or their metabolites. The main objective of the present study was to determine (n 20) plasma bioavailability and disposition in the liver, muscle, brown adipose tissue (BAT) and white adipose tissues (mesenteric and perirenal) in rats after a long-term consumption of three doses of grape seed phenolic extract (5, 25 and 50 mg/kg body weight) for 21 d in order to determine whether there is a dose–response relationship. Glucuronidated conjugates (total glucuronidated conjugates: C5mg/kg 1·9; C25mg/kg 6·4; C50mg/kg 27·7 μmol/l plasma) followed by methyl glucuronidated conjugates (total methyl glucuronidated conjugates: C5mg/kg 1·98; C25mg/kg 4·48; C50mg/kg 12·5 μmol/l plasma) were the main flavanol metabolites quantified in plasma, also detecting a dimer in its free form (C25mg/kg 0·74; C50mg/kg 0·79 μmol/l plasma). Each of the studied organs has a particular behaviour of accumulation and response to the assayed grape seed extract doses, with an exponential bioavailability–dose relationship in BAT, in which flavanols could play an important role in the reduction or prevention of obesity, modulating the functionality of that tissue.

Procyanidins target mesenteric adipose tissue in Wistar lean rats and subcutaneous adipose tissue in Zucker obese rat

Visceral and subcutaneous adipose depots have different metabolic roles that may be involved in the development of obesity-related pathologies. Procyanidins have beneficial effects on insulin resistance, and they target adipose tissue. We analyse whether procyanidins exert different effects, depending on the adipose tissue depot, and whether these effects show a relation to the amount of phenolic compound in the tissue. We studied the effects of a grape seed procyanidin extract (GSPE) treatment at the transcriptional level on genes expressed differentially between mesenteric and subcutaneous adipose tissue depots and genes previously shown to be targets of procyanidins. Procyanidins target mesenteric adipose tissue in Wistar lean rats but subcutaneous adipose tissue in Zucker obese rats. Non-modified structures also accumulated, preferentially in the same respective tissues that were responsive to GSPE. Thus, procyanidins target and accumulate differently in mesenteric and subcutaneous adipose tissue depots, depending on the metabolic condition of the animal model.

Procyanidins modulate microRNA expression in pancreatic islets

Procyanidins modulate glucose metabolism, partly due to its effects on pancreas. Given the role of microRNAs (miRNAs) in the regulation of diabetes and the fact that flavonoids modulate miRNAs in other tissues, we hypothesized that procyanidins might target miRNAs in the pancreas. We investigated the miRNA expression profile in pancreatic islets isolated from rats treated with a daily dose of grape seed procyanidin extract (GSPE) (25 mg/kg of body weight) for 45 days. The miRWalk database identified putative target genes of these miRNAs. We found that GSPE altered significantly the expression of miR-1249, miR-483, miR-30c-1*, and miR-3544. In silico prediction studies suggested that ion transport and response to glucose are among the regulated pathways. As a conclusion, this is the first study showing that procyanidins can also exert their bioactivity on pancreatic islets by modifying the miRNA expression pattern.

Grape seed-derived procyanidins decrease dipeptidyl-peptidase 4 activity and expression

Dipeptidyl-peptidase 4 (DPP4) inhibitors are among the newest treatments against type 2 diabetes. Since some flavonoids modulate DPP4 activity, we evaluated whether grape seed-derived procyanidins (GSPEs), which are antihyperglycemic, modulate DPP4 activity and/or expression. In vitro inhibition assays showed that GSPEs inhibit pure DPP4. Chronic GSPE treatments in intestinal human cells (Caco-2) showed a decrease of DPP4 activity and gene expression. GSPE was also assayed in vivo. Intestinal but not plasmatic DPP4 activity and gene expression were decreased by GSPE in healthy and diet-induced obese animals. Healthy rats also showed glycemia improvement after oral glucose consumption but not after an intraperitoneal glucose challenge. In genetically obese rats, only DPP4 gene expression was down-regulated. Thus, procyanidin inhibition of intestinal DPP4 activity, either directly and/or via gene expression down-regulation, could be responsible for some of their effects in glucose homeostasis.