Effects of a grapeseed procyanidin extract (GSPE) on insulin resistance

Rhythm and ROS: Hepatic Chronotherapeutic Features of Grape Seed Proanthocyanidin Extract Treatment in Cafeteria Diet-Fed Rats

Polyphenols play a key role in the modulation of circadian rhythms, while the cafeteria diet (CAF) is able to perturb the hepatic biological rhythm and induce important ROS production. Consequently, we aimed to elucidate whether grape seed proanthocyanidin extract (GSPE) administration recovers the CAF-induced hepatic antioxidant (AOX) misalignment and characterize the chronotherapeutic properties of GSPE. For this purpose, Fischer 344 rats were fed a standard diet (STD) or a CAF and concomitantly treated with GSPE at two time-points (ZT0 vs. ZT12). Animals were euthanized every 6 h and the diurnal rhythms of hepatic ROS-related biomarkers, hepatic metabolites, and AOX gene expression were examined. Interestingly, GSPE treatment was able to recover the diurnal rhythm lost due to the CAF. Moreover, GSPE treatment also increased the acrophase of Sod1, as well as bringing the peak closer to that of the STD group. GSPE also corrected some hepatic metabolites altered by the CAF. Importantly, the differences observed at ZT0 vs. ZT12 due to the time of GSPE administration highlight a chronotherapeutic profile on the proanthocyanin effect. Finally, GSPE could also reduce diet-induced hepatic oxidative stress not only by its ROS-scavenging properties but also by retraining the circadian rhythm of AOX enzymes.

Metabolism disturbance by light/dark cycle switching depends on the rat health status: the role of grape seed flavanols

Changes in light/dark cycles and obesogenic diets are related to the disruption of circadian rhythms and metabolic disorders. Grape seed flavanols have shown beneficial effects on metabolic diseases and, recently, a circadian system modulation has been suggested to mediate their health-enhancing properties. Therefore, the aim of this study was to evaluate the grape seed (poly)phenol extract (GSPE) effects in healthy and obese rats after a light/dark cycle disruption. Forty-eight rats were fed a standard (STD) or cafeteria (CAF) diet for 6 weeks under STD conditions of a light/dark cycle (12 h light per day, L12). Then, animals were switched to a long (18 h light per day, L18) or short (6 h light per day, L6) photoperiod and administered a vehicle (VH) or GSPE (25 mg kg-1) for 1 week. The results showed changes in serum lipids and insulin and metabolomic profiles dependent on the photoperiod and animal health status. GSPE administration improved serum parameters and increased the Nampt gene expression in CAF rats and modified the metabolomic profile in a photoperiod-dependent manner. Metabolic effects of light/dark disturbance depend on the health status of the rats, with diet-induced CAF-induced obese rats being more affected. Grape seed flavanols improve the metabolic status in a photoperiod-dependent manner and their effects on the circadian system suggest that part of their metabolic effects could be mediated by their action on biological rhythms.

GSPE Pre-Treatment Exerts Long-Lasting Preventive Effects against Aging-Induced Changes in the Colonic Enterohormone Profile of Female Rats

The impact that healthy aging can have on society has raised great interest in understanding aging mechanisms. However, the effects this biological process may have on the gastrointestinal tract (GIT) have not yet been fully described. Results in relation to changes observed in the enteroendocrine system along the GIT are controversial. Grape seed proanthocyanidin extracts (GSPE) have been shown to protect against several pathologies associated with aging. Based on previous results, we hypothesized that a GSPE pre-treatment could prevent the aging processes that affect the enteroendocrine system. To test this hypothesis, we treated 21-month-old female rats with GSPE for 10 days. Eleven weeks after the treatment, we analyzed the effects of GSPE by comparing these aged animals with young animals. Aging induced a greater endocrine response to stimulation in the upper GIT segments (cholecystokinin (CCK) and glucagon-like peptide-1 (GLP-1)), a decrease in the mRNA abundance of GLP-1, peptide YY (PYY) and chromogranin A (ChgA) in the colon, and an increase in colonic butyrate. GSPE-treated rats were protected against a decrease in enterohormone expression in the colon. This effect is not directly related to the abundance of microbiome or short-chain fatty acids (SCFA) at this location. GSPE may therefore be effective in preventing a decrease in the colonic abundance of enterohormone expression induced by aging.

Differential effects of a cafeteria diet and GSPE preventive treatments on the enterohormone secretions of aged vs. young female rats

Grape seed derived procyanidins (GSPE) have been shown to effectively prevent intestinal disarrangements induced by a cafeteria diet in young rats. However, little is known about the effects of procyanidins and cafeteria diet on enterohormone secretion in aged rats, as the ageing processes modify these effects. To study these effects in aged rats, we subjected 21-month-old and young 2-month-old female rats to two sub-chronic preventive GSPE treatments. After three months of cafeteria diet administration, we analysed the basal and stimulated secretion and mRNA expression of CCK, PYY and GLP-1, caecal SCFA and intestinal sizes. We found that the effects of a cafeteria diet on the basal duodenal CCK secretion are age dependent. GLP-1 in the ileum was not modified regardless of the rat's age, and GSPE preventive effects differed in the two age groups. GSPE pre-treatment reduced GLP-1, PYY and ChgA in mRNA in aged ileum tissue, while the cafeteria diet increased these in aged colon. The GSPE treatments only modified low-abundance SCFAs. The cafeteria diet in aged rats increases the caecum size differently from that in young rats and GSPE pre-treatment prevents this increase. Therefore, ageing modifies nutrient sensing, and the cafeteria diet acts mainly on the duodenum and colon, while procyanidins have a larger effect on the ileum.

The effects of grape seed proanthocyanidins in cafeteria diet-induced obese Fischer 344 rats are influenced by faecal microbiota in a photoperiod dependent manner

Polyphenols are of high interest due to their beneficial health effects, including anti-obesity properties. The gut microbiota may play an important role in polyphenol-mediated effects as these bacteria are significantly involved in the metabolism of polyphenols. Moreover, seasonal rhythms have been demonstrated to influence both the gut microbiota composition and polyphenol bioavailability. Thus, the goal of this study was to evaluate the impact of photoperiods and microbiota on polyphenol functionality in an obesogenic context. Towards this aim, cafeteria diet-fed Fischer 344 rats were housed under three different photoperiod conditions (L6: 6 h of light, L12: 12 h of light and L18: 18 h of light) for 9 weeks. During the last 4 weeks of the experiment, rats were daily administered with an oral dose of a grape seed proanthocyanidin extract (GSPE) (25 mg per kg body weight). Additionally, rats treated with GSPE and an antibiotic cocktail (ABX) in their drinking water were included for a better understanding of the gut microbiota role in GSPE functionality. Vehicle and non-ABX treated rats were included as controls. GSPE decreased body weight gain and fat depots only under L18 conditions. Interestingly, the gut microbiota composition was strongly altered in this photoperiod. GSPE + ABX-treated rats gained significantly less body weight compared to the rats of the rest of the treatments under L18 conditions. These results suggest that GSPE functionality is modulated by the gut microbiota in a photoperiod dependent manner. These novel findings corroborate seasonal rhythms as key factors that must be taken into account when investigating the effects of polyphenols in the treatment or prevention of chronic diseases.

Time-of-day dependent effect of proanthocyanidins on adipose tissue metabolism in rats with diet-induced obesity

BACKGROUND

Grape-seed proanthocyanidin extract (GSPE) improve white adipose tissue (WAT) expansion during diet-induced obesity. However, because adipose metabolism is synchronized by circadian rhythms, it is plausible to speculate that the bioactivity of dietary proanthocyanidins could be influenced by the time-of-day in which they are consumed. Therefore, the aim of the present study was to determine the interaction between zeitgeber time (ZT) and GSPE consumption on the functionality of WAT in rats with diet-induced obesity.

METHODS

Male Wistar rats were fed a cafeteria diet for 9 weeks. After 5 weeks, the animals were supplemented with 25 mg GSPE/kg for 4 weeks at the beginning of the light/rest phase (ZT0) or of the dark/active phase (ZT12). Body fat content was determined by nuclear magnetic resonance and histological analyses were performed in the epididymal (EWAT) and inguinal (IWAT) fat depots to determine adipocyte size and number. In addition, the expression of genes related to adipose metabolism and circadian clock function were analyzed by qPCR.

RESULTS

GSPE consumption at ZT0 was associated with a potential antidiabetic effect without affecting adiposity and energy intake and downregulating the gene expression of inflammatory markers in EWAT. In contrast, GSPE consumption at ZT12 improved adipose tissue expansion decreasing adipocyte size in IWAT. In accordance with this adipogenic activity, the expression of genes involved in fatty acid metabolism were downregulated at ZT12 in IWAT. In turn, GSPE consumption at ZT12, but not at ZT0, repressed the expression of the clock gene Cry1 in IWAT.

CONCLUSIONS

The interaction between ZT and GSPE consumption influenced the metabolic response of WAT in a tissue-specific manner. Understanding the impact of circadian clock on adipose metabolism and how this is regulated by polyphenols will provide new insights for the management of obesity.

Time-of-Day Circadian Modulation of Grape-Seed Procyanidin Extract (GSPE) in Hepatic Mitochondrial Dynamics in Cafeteria-Diet-Induced Obese Rats

Major susceptibility to alterations in liver function (e.g., hepatic steatosis) in a prone environment due to circadian misalignments represents a common consequence of recent sociobiological behavior (i.e., food excess and sleep deprivation). Natural compounds and, more concisely, polyphenols have been shown as an interesting tool for fighting against metabolic syndrome and related consequences. Furthermore, mitochondria have been identified as an important target for mediation of the health effects of these compounds. Additionally, mitochondrial function and dynamics are strongly regulated in a circadian way. Thus, we wondered whether some of the beneficial effects of grape-seed procyanidin extract (GSPE) on metabolic syndrome could be mediated by a circadian modulation of mitochondrial homeostasis. For this purpose, rats were subjected to “standard”, “cafeteria” and “cafeteria diet + GSPE” treatments (n = 4/group) for 9 weeks (the last 4 weeks, GSPE/vehicle) of treatment, administering the extract/vehicle at diurnal or nocturnal times (ZT0 or ZT12). For circadian assessment, one hour after turning the light on (ZT1), animals were sacrificed every 6 h (ZT1, ZT7, ZT13 and ZT19). Interestingly, GSPE was able to restore the rhythm on clock hepatic genes (Bmal1, Per2, Cry1, Rorα), as this correction was more evident in nocturnal treatment. Additionally, during nocturnal treatment, an increase in hepatic fusion genes and a decrease in fission genes were observed. Regarding mitochondrial complex activity, there was a strong effect of cafeteria diet at nearly all ZTs, and GSPE was able to restore activity at discrete ZTs, mainly in the diurnal treatment (ZT0). Furthermore, a differential behavior was observed in tricarboxylic acid (TCA) metabolites between GSPE diurnal and nocturnal administration times. Therefore, GSPE may serve as a nutritional preventive strategy in the recovery of hepatic-related metabolic disease by modulating mitochondrial dynamics, which is concomitant to the restoration of the hepatic circadian machinery.

Grape seed proanthocyanidins reduced the overweight of C57BL/6J mice through modulating adipose thermogenesis and gut microbiota

Activating the thermogenic function of adipocytes is an attractive therapeutic strategy against obesity and its associated metabolic complications. Proanthocyanidins are a class of polyphenols which are widely found in plants and daily foods. This aim of this study is to investigate the modulatory effects of grape seed proanthocyanidin extract (GSPE) on brown adipose tissue (BAT) activity, browning of white adipose tissue (WAT) and microbiome regulation in high-fat diet (HFD)-fed mice and its associated molecular mechanism. An 8-week administration of GSPE at 200 mg per kg bw in mice significantly reduced their final body weight, antagonized their HFD-induced insulin resistance and elevated their levels of adiponectin and leptin, respectively (p < 0.05). GSPE significantly increased the expression levels of thermogenic marker UCP1 in BAT and elevated the expression of a key transcription factor of browning, PRDM16, and thermogenic markers UCP1 and PGC-1α in inguinal white adipose tissue (iWAT). The high doses of GSPE also increased the levels of acetic acid, propionic acid and butyric acid in the colon of HFD-fed mice (p < 0.05). Furthermore, GSPE normalized the colonic Firmicutes/Bacteroidetes ratios, reversed the relative abundance of Weissella, Faecalibaculum, Bacteroides, Akkermansia and Ruminococcus 1 induced by HFD, and improved the structural diversity of the gut microbiota in C57BL/6J mice.

Changes in arterial blood pressure caused by long-term administration of grape seed proanthocyanidins in rats with established hypertension

The development of hypertension (HTN) in cafeteria (CAF) diet-fed rats was demonstrated to be attenuated after grape seed proanthocyanidin extract (GSPE) administration. However, the long-term antihypertensive effect of GSPE in animals with established HTN has not been investigated. Thus, the aim of this study was to evaluate if GSPE shows a blood pressure-lowering effect in hypertensive rats after its administration for 3 weeks. Wistar rats were fed a standard or CAF diet for 12 weeks, and during the last 3 weeks, animals were administered vehicle, captopril or a low dose of GSPE (25 mg per kg body weight, bw). Both systolic and diastolic blood pressure (SBP and DBP) were monitored weekly. The liver reduced glutathione (GSH) levels, plasma angiotensin converting enzyme activity and endothelial gene expression of eNOS, KLF-2, Sirt-1, NOX4 and ET-1 were studied at the end-point. The results demonstrated that 3 weeks of CAF diet administration with 25 mg per kg bw GSPE significantly reduced SBP and DBP in hypertensive rats. GSPE induced the upregulation of Sirt-1 gene expression and downregulated the vasoconstrictor ET-1, suggesting the vasoprotective effect of GSPE and increased the antioxidant GSH activity. The administration of 25 mg per kg bw GSPE for 3 weeks significantly reduced BP in CAF diet fed animals with established HTN.

Glucagon Shows Higher Sensitivity than Insulin to Grapeseed Proanthocyanidin Extract (GSPE) Treatment in Cafeteria-Fed Rats

The endocrine pancreas plays a key role in metabolism. Procyanidins (GSPE) targets β-cells and glucagon-like peptide-1 (GLP-1)-producing cells; however, there is no information on the effects of GSPE on glucagon. We performed GSPE preventive treatments administered to Wistar rats before or at the same time as they were fed a cafeteria diet during 12 or 17 weeks. We then measured the pancreatic function and GLP-1 production. We found that glucagonemia remains modified by GSPE pre-treatment several weeks after the treatment has finished. The animals showed a higher GLP-1 response to glucose stimulation, together with a trend towards a higher GLP-1 receptor expression in the pancreas. When the GSPE treatment was administered every second week, the endocrine pancreas behaved differently. We show here that glucagon is a more sensitive parameter than insulin to GSPE treatments, with a secretion that is highly linked to GLP-1 ileal functionality and dependent on the type of treatment.

Efficient Chemical Synthesis of (Epi)catechin Glucuronides: Brain-Targeted Metabolites for Treatment of Alzheimer's Disease and Other Neurological Disorders

Grape seed extract (GSE) is rich in flavonoids and has been recognized to possess human health benefits. Our group and others have demonstrated that GSE is able to attenuate the development of Alzheimer's disease (AD). Moreover, our results have disclosed that the anti-Alzheimer's benefits are not directly/solely related to the dietary flavonoids themselves, but rather to their metabolites, particularly to the glucuronidated ones. To facilitate the understanding of regioisomer/stereoisomer-specific biological effects of (epi)catechin glucuronides, we here describe a concise chemical synthesis of authentic standards of catechin and epicatechin metabolites 3-12. The synthesis of glucuronides 9 and 12 is described here for the first time. The key reactions employed in the synthesis of the novel glucuronides 9 and 12 include the regioselective methylation of the 4'-hydroxyl group of (epi)catechin (≤1.0/99.0%; 3'-OMe/4'-OMe) and the regioselective deprotection of the tert-butyldimethylsilyl (TBS) group at position 5 (yielding up to 79%) over the others (3, 7 and 3' or 4').

Ion mobility-mass spectrometry for the separation and analysis of procyanidins

Procyanidins are polymeric flavan-3-ones occurring in many plants with antioxidant and other beneficial bioactivities. They are composed of catechin and epicatechin monomeric units connected by single carbon-carbon B-type linkages or A-type linkages containing both carbon-carbon and carbon-oxygen-carbon bonds. Their polymeric structure makes analysis of procyanidin mixtures always difficult. Evaluation of procyanidins according to degree of polymerization (DP) using high-performance liquid chromatography (HPLC) is time-consuming and at best has resolved polymeric families up to DP-17. To expedite studies of procyanidins, the utility of positive ion electrospray ion mobility-mass spectrometry (IM-MS) was investigated for the rapid separation and characterization of procyanidins in mixtures. Applying IM-MS to analyse structurally defined standards containing up to five subunits, procyanidins could be resolved in less than 6 ms not only by degree of polymerization but also by linkage type. A-type procyanidins could be resolved from B-type and both could be at least partially resolved from mixed-type procyanidins of the same DP. IM-MS separated higher order procyanidins with DP of at least 24 from extracts of cranberry. As DP increased, the abundances of multiply-charged procyanidins also increased. During IM-MS of ions of similar m/z, the ion drift times decreased inversely with increasing charge state. Therefore, IM-MS was shown to separate mixtures of procyanidins containing at least 24 interconnected subunits in less than 16 ms, not only according to DP, but also according to linkage type between subunits and charge state.

The roles of gut microbiota and circadian rhythm in the cardiovascular protective effects of polyphenols

Polyphenols are secondary metabolites of plants that have been widely studied for their health benefits as antioxidants. In the last decade, several clinical trials and epidemiological studies have shown that long‐term consumption of polyphenol‐rich diet protects against chronic diseases such as cancers and cardiovascular diseases. Current cardiovascular studies have also suggested an important role of gut microbiota and circadian rhythm in the pathogenesis metabolic and cardiovascular diseases. It is known that polyphenols can modulate the composition of core gut microbiota and interact with circadian clocks. In this article, we summarize recent findings, review the molecular mechanisms and the potential of polyphenols as dietary supplements for regulating gut microbiota and circadian rhythms, and discuss future research directions.

Linked Articles

This article is part of a themed section on The Pharmacology of Nutraceuticals. To view the other articles in this section visit http://onlinelibrary.wiley.com/doi/10.1111/bph.v177.6/issuetoc

Grape Seeds Proanthocyanidins: An Overview of In Vivo Bioactivity in Animal Models

Over the last decade, proanthocyanidins (PACs) are attracting attention not only from the food industry but also from public health organizations due to their health benefits. It is well-known that grapes are a good source of PACs and for that reason, the industry is also focused on grape by-products identification and bioactivity evaluation. Grape seeds extract (GSPE) is a rich source of PACs, mainly composed of monomeric catechin and epicatechin, gallic acid and polymeric and oligomeric proanthocyanidins. Thus, this review encompasses the state-of-art structure and the most recent evidence about the impact of GSPE on chronic diseases, with a focus on oxidative stress, inflammation and metabolic syndrome (MeS)-related disorders such as obesity, diabetes and cardiovascular risk disease in vivo to offer new perspectives in the field that allow further research. Despite the controversial results, is undeniable that PACs from grape seeds are highly antioxidants, thus, the capacity of GSPE to improve oxidative stress might mediate the inflammation process and the progress of MeS-related pathologies. However, further well-design animal studies with standardized dosages and GSPE composition are necessary to shed light into the cause-effect relationship in a more accurate way to later allow a deeper study of the effect of GSPE in humans.

A high-throughput chemical-genetics screen in murine adipocytes identifies insulin-regulatory pathways

Pathways linking activation of the insulin receptor to downstream targets of insulin have traditionally been studied using a candidate gene approach. To elucidate additional pathways regulating insulin activity, we performed a forward chemical-genetics screen based on translocation of a glucose transporter 4 (Glut4) reporter expressed in murine 3T3-L1 adipocytes. To identify compounds with known targets, we screened drug-repurposing and natural product libraries. We identified, confirmed, and validated 64 activators and 65 inhibitors that acutely increase or rapidly decrease cell-surface Glut4 in adipocytes stimulated with submaximal insulin concentrations. These agents were grouped by target, chemical class, and mechanism of action. All groups contained multiple hits from a single drug class, and several comprised multiple structurally unrelated hits for a single target. Targets include the β-adrenergic and adenosine receptors. Agonists of these receptors increased and inverse agonists/antagonists decreased cell-surface Glut4 independently of insulin. Additional activators include insulin sensitizers (thiazolidinediones), insulin mimetics, dis-inhibitors (the mTORC1 inhibitor rapamycin), cardiotonic steroids (the Na⁺/K⁺-ATPase inhibitor ouabain), and corticosteroids (dexamethasone). Inhibitors include heterocyclic amines (tricyclic antidepressants) and 21 natural product supplements and herbal extracts. Mechanisms of action include effects on Glut4 trafficking, signal transduction, inhibition of protein synthesis, and dissipation of proton gradients. Two pathways that acutely regulate Glut4 translocation were discovered: de novo protein synthesis and endocytic acidification. The mechanism of action of additional classes of activators (tanshinones, dalbergiones, and coumarins) and inhibitors (flavonoids and resveratrol) remains to be determined. These tools are among the most sensitive, responsive, and reproducible insulin-activity assays described to date.

Grape seed procyanidin extract inhibits adipogenesis and stimulates lipolysis of porcine adipocytes in vitro

The objective of this article was to evaluate in vitro effect of grape seed procyanidin extract (GSPE) on differentiation, proliferation, and lipolysis of porcine adipocytes, providing a molecular basis for the use of GSPE in pig fat regulation. Primary preadipocytes isolated from subcutaneous adipose tissue of pigs were used as the in vitro cell model. Treatment of GSPE repressed preadipocyte differentiation, as evidenced by reduced lipid accumulation, decreased mRNA expressions of peroxisome proliferator-activated receptor gamma (PPARγ) and fatty acid-binding protein 4 (FABP4), as well as enhanced expressions of preadipocyte factor-1. Activity of glycerol-3-phosphate dehydrogenase (GPDH), one of the most important enzymes in the pathway for triacylglycerol biosynthesis, was also decreased. Furthermore, GSPE could suppress preadipocyte proliferation by inducing G0/G1 cell cycle arrest and cell apoptosis. In porcine mature adipocytes, treatment with GSPE attenuated lipid content and GPDH activity, and the release of both free fatty acid and glycerol were enhanced; mRNA expressions of key lipolytic transcription factors, including hormone-sensitive lipase (HSL) and adipose triglyceride lipase (ATGL), were elevated in GSPE-treated adipocytes. In summary, our results suggest GSPE inhibits porcine preadipocyte differentiation and proliferation and stimulates lipolysis of mature adipocytes, thus providing novel insights for further exploring the use of GSPE as a fat accumulation inhibitor.

Bio-Based Compounds from Grape Seeds: A Biorefinery Approach

Food and agricultural waste represents a growing problem with negative effects on the economy, environment, and human health. Winemaking produces byproducts with high added value, which can be used for new productions in several application fields. From the perspective of biorefinery and circular economy, grape seeds could be exploited by extracting bioactive compounds with high added value before using biomass for energy purposes. The markets concerned are, in addition to the food, cosmetics, and pharmaceuticals sectors, which use bioactive compounds, the sector of biopolymeric materials and of energy for the production of biohydrogen and biomethane. Generally, bioactive components should be investigated through an integrated and multidisciplinary study approach based on emerging analytical techniques; in this context, attention is addressed towards green and sustainable procedures; an update of extraction techniques, innovative technologies, and chemometrics are described. Nowadays, processes so far tested on a pilot scale for grape waste are developed to enhance the extraction yields. Here, a picture of the Italian experience applied to the byproducts of the wine industry is given.

Extract Enriched in Flavan-3-ols and Mainly Procyanidin Dimers Improves Metabolic Alterations in a Mouse Model of Obesity-Related Disorders Partially via Estrogen Receptor Alpha

Red wine polyphenol extracts improve cardiovascular and metabolic disorders linked to obesity. Their vascular protection is mediated by the activation of the alpha isoform of the estrogen receptor (ERα). In the present study, we explored the effects of a grape seed extract (GSE) enriched in the flavan-3-ols procyanidin dimers on obesity-related cardiovascular and metabolic disorders; with a particular interest in the role/contribution of ERα. Ovariectomized wild type or ERα knockout (KO) mice were fed with standard or western diet, supplemented or not with GSE, for 12 weeks. Their body weight was monitored throughout the study, and an echocardiography was performed at the end of the treatment. Blood and tissues were collected for biochemical and functional analysis, including nitric oxide and oxidative stress measurement. Vascular reactivity and liver mitochondrial complexes activity were also analyzed. In western diet-fed mice, GSE reduced adiposity, plasma triglycerides, and oxidative stress in the heart, liver, adipose and skeletal tissues; but did not improve the vascular dysfunction. In western diet-fed mice, ERα deletion prevented or reduced the beneficial effects of GSE on plasma triglycerides and visceral adiposity. ERα deletion also prevented/reduced the anti-oxidant effect of GSE in the liver, but did not affect its capacity to reduce oxidative stress in the heart and adipose tissue. In conclusion, dietary supplementation of GSE attenuated features of metabolic syndrome partially through ERα-dependent mechanisms. This report highlights the therapeutic potential of polyphenols, and especially extract enriched in procyanidin dimers, against the metabolic disorders associated with excessive energy intake.

Chrysanthemum indicum L. ethanol extract reduces high-fat diet-induced obesity in mice

The present study was undertaken to investigate the mechanism behind the anti-obesity effect of the 50% ethanol extract of Chrysanthemum indicum L. flowers (CIEE) in a mouse model of high-fat diet (HFD)-induced obesity. Male C57BL/6J mice (six mice in each group) were administered CIEE (8, 40 and 200 mg/kg) for 6 weeks while being fed with a HFD. Garcinia cambogia (GC) was used as the positive control and was administered in the same manner as CIEE. Results demonstrated that oral administration of CIEE significantly reduced body weight, epididymal white adipose tissue (EWAT), liver weight and serum levels of total cholesterol and triglyceride (P<0.05). In addition, CIEE reduced serum leptin and increased adiponectin levels. CIEE significantly downregulated peroxisome proliferator-activated receptor γ (PPARγ), CCAAT/enhancer-binding protein-α and fatty acid synthase expression levels in EWAT, and upregulated the protein expression of PPARα in liver tissue of HFD-fed obese mice (P<0.05). These results suggested that Chrysanthemum indicum L. flowers may be a potentially effective therapeutic agent for obesity and its associated complications.

Dietary Flavonoids in the Prevention of T2D: An Overview

Type 2 diabetes (T2D) is a progressive metabolic disease that is increasing in prevalence globally. It is well established that insulin resistance (IR) and a progressive decline in functional β-cell mass are hallmarks of developing T2D. Obesity is a leading pathogenic factor for developing IR. Constant IR will progress to T2D when β-cells are unable to secret adequate amounts of insulin to compensate for decreased insulin sensitivity. Recently, a considerable amount of research has been devoted to identifying naturally occurring anti-diabetic compounds that are abundant in certain types of foods. Flavonoids are a group of polyphenols that have drawn great interest for their various health benefits. Results from many clinical and animal studies demonstrate that dietary intake of flavonoids might be helpful in preventing T2D, although cellular and molecular mechanisms underlying these effects are still not completely understood. This review discusses our current understanding of the pathophysiology of T2D and highlights the potential anti-diabetic effects of flavonoids and mechanisms of their actions.

(-)-Epicatechin and its metabolites prevent palmitate-induced NADPH oxidase upregulation, oxidative stress and insulin resistance in HepG2 cells

While diets rich in fruit and vegetables can decrease the risk for type 2 diabetes (T2D), diets rich in fat and carbohydrates can increase it. The flavanol-3-ol (-)-epicatechin (EC) can improve insulin sensitivity both in humans and animal models of T2D. NADPH oxidases and oxidative stress can contribute to the development of insulin resistance. This study investigated the capacity of EC and EC metabolites (ECM) to downregulate NADPH oxidases and oxidative stress, and its association to an improvement of insulin sensitivity. This was studied in in vivo (high fat-fed mice) and in vitro (HepG2 cells) conditions of hepatic lipid overload. EC decreased NOX3/NOX4 liver expression and mitigated oxidative stress in high fat-fed mice. In HepG2 cells, incubation with palmitate increased: i) lipid deposition, ii) NOX3/NOX4 expression, iii) NADPH oxidase activity, and iv) oxidative stress; promoting v) the activation of redox-sensitive kinases (JNK and IKK), and vi) impaired insulin responses. Physiological concentrations of EC and ECM, and NADPH oxidase inhibitors (apocynin, VAS2870) prevented all those deleterious effects of palmitate. The obtained results points to NADPH oxidases as an important target in the capacity of EC to improve insulin sensitivity in conditions of liver lipid overload, as those associated with Western-style diets.

Effects of an Intermittent Grape-Seed Proanthocyanidin (GSPE) Treatment on a Cafeteria Diet Obesogenic Challenge in Rats

Obesity is highly associated with the pathologies included in the concept of the Metabolic Syndrome. Grape-seed proanthocyanins (GSPE) have showed very positive effects against all these metabolic disruptions; however, there is, as yet, no consensus about their effectiveness against an obesogenic challenge, such as a cafeteria diet. We determined the effectiveness of a dose of 500 mg GSPE/kg b.w. (body weight) against the obesogenic effects of a 17-week cafeteria diet, administered as a sub-chronic treatment, 10–15 days before, intermittently and at the end of the diet, in Wistar rats. Body weight, adiposity, indirect calorimetry and plasma parameters were analyzed. GSPE pre-treatment showed a long-lasting effect on body weight and adiposity that was maintained for seven weeks after the last dose. A corrective treatment was administered for the last two weeks of the cafeteria diet intervention; however, it did not effectively correct any of the parameters assessed. The most effective treatment was an intermittent GSPE dosage, administered every second week during the cafeteria diet. This limited body weight gain, adiposity and most lipotoxic effects. Our results support the administration of this GSPE dose, keeping an intermittent interval between dosages longer than every second week, to improve obesogenic disruptions produced by a cafeteria diet.

Morphometric and histopathological evaluation of the effect of grape seed proanthocyanidin on alveolar bone loss in experimental diabetes and periodontitis

OBJECTIVE

Grape seed proanthocyanidine extract (GSPE) is a strong antioxidant derived from the grape seeds (Vitis vinifera, Terral J.F.) and has a polyphenolic structure with a wide range of biological activity. The aim of the present study was to evaluate the effects of GSPE on alveolar bone loss and histopathological changes in rats with diabetes mellitus and ligature-induced periodontitis.

MATERIAL AND METHODS

Forty rats were divided into 6 study groups. Control (C, 6 rats) group, periodontitis (P, 6 rats) group, diabetes (D, 6 rats) group, diabetes and periodontitis (D+P, 6 rats) group, diabetes, periodontitis and 100 mg/kg/day GSPE (GSPE-100, 8 rats), and diabetes, periodontitis and 200 mg/kg/day GSPE (GSPE-200, 8 rats) group. Diabetes mellitus was induced by intraperitoneal injection of a single dose of streptozotocin (60 mg/kg). Periodontitis was induced via ligation method. Silk ligatures were placed at the mandibular right first molars. GSPE was administered by oral gavage. After 30 days, all rats were killed. Alveolar bone loss was measured morphometrically via a stereomicroscope. For histopathological analyses, Alizarin red staining, and matrix metalloproteinase (MMP)-8, vascular endothelial growth factor and hypoxia inducible factor (HIF)-1α immunohistochemistry were performed. Tartrate-resistant acid phosphatase-positive osteoclast cells and relative total inflammatory cells were also determined.

RESULTS

The highest alveolar bone loss was observed in the D+P group (P < .05). GSP-200 group decreased alveolar bone loss (P < .05). The D+P group had the highest osteoclast counts, but the difference was not significant compared to the P, GSPE-100 and GSPE-200 groups (P > .05). The inflammation in the D+P group was also higher than the other groups (P < .05). The osteoblast numbers increased in the GSPE-100 and GSPE-200 groups compared to the P and D+P groups (P < .05). MMP-8 and HIF-1α levels were highest in the D+P group and GSPE significantly decreased these levels (P < .05).

CONCLUSION

Within the limits of this animal study, it can be suggested that GSPE administration may decrease periodontal inflammation and alveolar bone loss via decreasing MMP-8 and HIF-1α levels and increase osteoblastic activity in diabetic rats with experimental periodontitis.

Chrysanthemum indicum Inhibits Adipogenesis and Activates the AMPK Pathway in High-Fat-Diet-Induced Obese Mice

Chrysanthemum indicum (CI) is widely distributed in China and many parts of the tropical world, and has been reported to have antibacterial, antiviral, anti-oxidant and immunomodulatory effects, but no information is available on its effects on high fat diet (HFD)-induced obesity. This was undertaken to investigate the mechanism responsible for the effect of ethyl acetate fraction of CI (CIEA) on adipogenesis, in vitro and in vivo models of obesity. In the in vitro study, differentiating 3T3-L1 cells were treated with media to initiate differentiation (MDI) in the presence or absence of CIEA with different concentrations, and in the in vivo study, C57BL/6 mice were fed with HFD and administered CIEA daily for six weeks. Garcinia cambogia (GC) was used as the positive control, and was administered in the same manner as CIEA. Results showed CIEA reduced HFD-induced body weight gain, epididymal white adipose tissue (eWAT), and liver weight. In addition, CIEA significantly decreased serum lipid profiles, including total cholesterol (TC), triglyceride (TG) and low density lipoprotein cholesterol (LDLc) and increased high density lipoprotein cholesterol (HDLc) levels. Furthermore, CIEA also reduced leptin levels and increased adiponectin levels in serum, and significantly decreased peroxisome proliferator-activated receptor [Formula: see text] (PPAR[Formula: see text]) and CCAAT/enhancer-binding protein (C/EPBs) levels, but increased PPAR[Formula: see text] level and the phosphorylation of AMP-activated protein kinase (AMPK) in eWATs and in the liver tissues of HFD fed obese mice. Taken together, these results indicate CIEA might be beneficial for preventing obesity.

Procyanidins: a comprehensive review encompassing structure elucidation via mass spectrometry

Procyanidins are polyphenols abundant in dietary fruits, vegetables, nuts, legumes, and grains with a variety of chemopreventive biological effects. Rapid structure determination of these compounds is needed, notably for the more complex polymeric procyanidins. We review the recent developments in the structure elucidation of procyanidins with a focus on mass spectrometric approaches, especially liquid chromatography-tandem mass spectrometry (LC-MS/MS) and matrix-assisted laser desorption ionization (MALDI) MS/MS.

(-)-Epicatechin and the Colonic 2,3-Dihydroxybenzoic Acid Metabolite Regulate Glucose Uptake, Glucose Production, and Improve Insulin Signaling in Renal NRK-52E Cells

SCOPE

(-)-Epicatechin (EC) and main colonic phenolic acids derived from flavonoid intake, such as 2,3-dihydroxybenzoic acid (DHBA), 3,4-dihydroxyphenylacetic acid (DHPAA), 3-hydroxyphenylpropionic acid (HPPA), and vanillic acid (VA), have been suggested to exert beneficial effects in diabetes, although the mechanism for their actions remains unknown. In this study, the modulation of glucose homeostasis and insulin signaling by the mentioned compounds on renal proximal tubular NRK-52E cells is investigated.

METHODS AND RESULTS

Levels of the glucose transporters SGLT-2 and GLUT-2, as well as glucose uptake, glucose production, and key proteins of the insulin pathways, namely insulin receptor (IR), insulin receptor substrate-1 (IRS-1), and PI3K/AKT pathway are analyzed. EC (5-20 μm) and DHBA (20 μm) reduced both renal glucose uptake and production. Interestingly, EC and DHBA did not modify the levels of SGLT-2 and GLUT-2, and modulated the expression of phosphoenolpyruvate carboxykinase via AKT leading to a diminished glucose production. EC and DHBA also enhanced the tyrosine phosphorylation and total IR and IRS-1 levels, and activated the PI3K/AKT pathway in NRK-52E cells.

CONCLUSION

EC and DHBA regulate the renal glucose homeostasis by modulating both glucose uptake and production, and strengthen the insulin signaling by activating key proteins of that pathway in NRK-52E cells.

Phytochemical Constituents, Health Benefits, and Industrial Applications of Grape Seeds: A Mini-Review

Grapes are one of the most widely grown fruits and have been used for winemaking since the ancient Greek and Roman civilizations. Grape seeds are rich in proanthocyanidins which have been shown to possess potent free radical scavenging activity. Grape seeds are a complex matrix containing 40% fiber, 16% oil, 11% proteins, and 7% complex phenols such as tannins. Grape seeds are rich sources of flavonoids and contain monomers, dimers, trimers, oligomers, and polymers. The monomeric compounds includes (+)-catechins, (−)-epicatechin, and (−)-epicatechin-3-O-gallate. Studies have reported that grape seeds exhibit a broad spectrum of pharmacological properties against oxidative stress. Their potential health benefits include protection against oxidative damage, and anti-diabetic, anti-cholesterol, and anti-platelet functions. Recognition of such health benefits of proanthocyanidins has led to the use of grape seeds as a dietary supplement by the consumers. This paper summarizes the studies of the phytochemical compounds, pharmacological properties, and industrial applications of grape seeds.

Cyanidin-3-rutinoside increases glucose uptake by activating the PI3K/Akt pathway in 3T3-L1 adipocytes

In this study, the effect of cyanidin-3-rutinoside (C3R) on glucose uptake by 3T3-L1 adipocytes was studied. C3R significantly increased glucose uptake, which was associated with enhanced plasma membrane glucose transporter type 4 (PM-GLUT4) expression in 3T3-L1 adipocytes. The potentiating effect of C3R on glucose uptake and PM-GLUT4 expression was related to enhanced phosphorylation of insulin receptor substrate 1 (IRS-1) and Akt, as well as augmented activation of phosphatidylinositol-3-kinase (PI3K) in the insulin signaling pathway. C3R induced glucose uptake was inhibited only by the PI3K inhibitor, but not by an AMPK inhibitor in 3T3-L1 adipocytes. Therefore, C3R likely up-regulates glucose uptake and PM-GLUT4 expression in 3T3-L1 adipocytes by activating the PI3K/Akt pathways.

Grape seed proanthocyanidin supplementation reduces adipocyte size and increases adipocyte number in obese rats

Objectives:

White adipose tissue (WAT) expands through hypertrophy (increased adipocyte size) and/or hyperplasia (increased adipocyte number). Hypertrophy has been associated with insulin resistance and dyslipidemia independently of body composition and fat distribution. In contrast, hyperplasia protects against metabolic alterations. Proanthocyanidins, which are the most abundant flavonoids in the human diet, improve metabolic disturbances associated with diet-induced obesity without reducing body weight or adiposity. The aim of this study was to determine whether grape seed proanthocyanidin extract (GSPE) can modulate WAT expandability. Because GSPE also contains gallic acid, we also studied the capacity of gallic acid to remodel WAT.

Design:

Male Wistar rats were fed a standard chow diet (n=6) or a cafeteria diet (CAF) for 11 weeks. After 8 weeks, the CAF-fed animals were supplemented with 25 mg GSPE/kg body weight (n=6), 7 mg gallic acid/kg body weight (n=6) or the vehicle (n=6) for 3 weeks. Histological analyses were performed in the retroperitoneal (rWAT) and inguinal (iWAT) WAT to determine adipocyte size and number. Specific markers for adipogenesis and WAT functionality were analysed in rWAT using quantitative RT-PCR.

Results:

GSPE or gallic acid supplementation did not reduce weight gain or reverse and adiposity. However, GSPE reduced adipocyte size significantly in rWAT and moderately in iWAT and tripled the adipocyte number in rWAT. Gallic acid slightly reduced adipocyte size in rWAT and iWAT and doubled the adipocyte number in both WATs. In accordance with this adipogenic activity, Pref-1 and PPARγ tended to be overexpressed in rWAT of rats supplemented with GSPE. Moreover, GSPE supplementation increased Plin1 and Fabp4 expression and restored adiponectin expression completely, indicating a better functionality of visceral WAT.

Conclusions:

GSPE supplementation has anti-hypertrophic and hyperplasic activities in rats with established obesity, mainly in visceral WAT inducing a healthier expansion of WAT to match the surplus energy provided by the cafeteria diet.

A lipidomic study on the regulation of inflammation and oxidative stress targeted by marine ω-3 PUFA and polyphenols in high-fat high-sucrose diets

The ability of polyphenols to ameliorate potential oxidative damage of ω-3 PUFAs when they are consumed together and then, to enhance their potentially individual effects on metabolic health is discussed through the modulation of fatty acids profiling and the production of lipid mediators. For that, the effects of the combined consumption of fish oils and grape seed procyanidins on the inflammatory response and redox unbalance triggered by high-fat high-sucrose (HFHS) diets were studied in an animal model of Wistar rats. A standard diet was used as control. Results suggested that fish oils produced a replacement of ω-6 by ω-3 PUFAs in membranes and tissues, and consequently they improved inflammatory and oxidative stress parameters: favored the activity of 12/15-lipoxygenases on ω-3 PUFAs, enhanced glutathione peroxidases activity, modulated proinflammatory lipid mediators synthesis through the cyclooxygenase (COX) pathways and down-regulated the synthesis de novo of ARA leaded by Δ5 desaturase. Although polyphenols exerted an antioxidative and antiinflammatory effect in the standard diet, they were less effective to reduce inflammation in the HFHS dietary model. Contrary to the effect observed in the standard diet, polyphenols up-regulated COX pathways toward ω-6 proinflammatory eicosanoids as PGE₂ and 11-HETE and decreased the detoxification of ω-3 hydroperoxides in the HFHS diet. As a result, additive effects between fish oils and polyphenols were found in the standard diet in terms of reducing inflammation and oxidative stress. However, in the HFHS diets, fish oils seem to be the one responsible for the positive effects found in the combined group.

High-molecular-weight cocoa procyanidins possess enhanced insulin-enhancing and insulin mimetic activities in human primary skeletal muscle cells compared to smaller procyanidins

Dysregulation of glucose metabolism is a primary hallmark of metabolic disease (i.e., diabetes, obesity, etc.). Complementary nonpharmaceutical strategies are needed to prevent and/or ameliorate dysregulation of glucose metabolism and prevent progression from normoglycemia to prediabetes and type 2 diabetes across the lifespan. Cocoa compounds, particularly the procyanidins, have shown promise for improving insulin sensitivity and blood glucose homeostasis. However, the molecular mechanisms by which cocoa procyanidins exert these functions remain poorly understood. Furthermore, cocoa procyanidins exhibit size diversity, and evidence suggests that procyanidin bioactivity and size may be related. Here, we show that a procyanidin-rich cocoa extract elicits an antidiabetic effect by stimulating glycogen synthesis and glucose uptake, independent of insulin. Cocoa procyanidins did not appear to act via stimulation of AMPK or CaMKII activities. Additionally, in the presence of insulin, glycogen synthesis and AKT phosphorylation were affected. These mechanisms of action are most pronounced in response to oligomeric and polymeric procyanidins. These results demonstrate (1) specific mechanisms by which cocoa procyanidins improve glucose utilization in skeletal muscle and (2) that larger procyanidins appear to possess enhanced activities. These mechanistic insights suggest specific strategies and biological contexts that may be exploited to maximize the antidiabetic benefits of cocoa procyanidins.

The combined action of omega-3 polyunsaturated fatty acids and grape proanthocyanidins on a rat model of diet-induced metabolic alterations

It has been suggested that food components such as ω-3 polyunsaturated fatty acids (ω-3 PUFAs) and (poly)phenols counteract diet-induced metabolic alterations by common or complementary mechanisms. To examine the effects of a combination of ω-3 PUFAs and (poly)phenols on such alterations, adult Wistar-Kyoto rats were fed an obesogenic high-fat high-sucrose diet supplemented, or not, for 24 weeks with: eicosapentaenoic acid (EPA)/docosahexaenoic acid (DHA) 1 : 1 (16.6 g kg(-1) feed); proanthocyanidin-rich grape seed extract (GSE, 0.8 g kg(-1) feed); or EPA/DHA 1 : 1 + GSE. Body weight, feed intake, and plasma glucose were evaluated every 6 weeks, while adipose tissue weight, insulin, glucagon, ghrelin, leptin, adiponectin, cholesterol, and triglycerides were evaluated at the end of the experiment. ω-3 PUFAs reduced plasma leptin and cholesterol levels, but did not modify diet-induced perigonadal fat or plasma insulin levels; while GSE increased plasma triglyceride levels. The combined action of ω-3 PUFAs and the proanthocyanidins reduced plasma insulin and leptin, as well as partially prevented perigonadal fat accumulation. While separate supplementation with ω-3 PUFAs or grape proanthocyanidins may not counteract all the key metabolic changes induced by a high-energy-dense diet, the combination of both supplements reverts altered insulin, leptin and triglyceride levels to normal.

Anti-inflammatory effects of grape seed procyanidin B2 on a diabetic pancreas

The prevalence of type 2 diabetes mellitus (T2DM) has increased considerably in recent years, highlighting the importance of developing new therapeutic strategies. Insulin-resistance and gradual dysfunction of pancreatic islets are the mainstay in the progression of T2DM. Therefore, preserving the function of the pancreas may lead to new prospective approaches. Our previous studies suggested that grape seed procyanidin B2 (GSPB2), a natural polyphenol product, exhibited protective effects on diabetic vasculopathy. However, effects of GSPB2 on a diabetic pancreas remain unknown. In this study, we provided strong evidence that GSPB2 exerted protective effects on a diabetic pancreas. GSPB2 attenuated the elevated body weights, food intake and advanced glycation end-product (AGE) levels in db/db mice (p < 0.05), though it had no significant effect on glucose levels. The increased islet sizes, insulin levels, as well as HOMA-IR were also improved by GSPB2 treatment in db/db mice (p < 0.05). Milk fat globule epidermal growth factor-8 (MFG-E8), an estimated target of GSPB2 in our previous studies, was up-regulated in pancreatic tissues whereas GSPB2 treatment down-regulated the protein level (p < 0.05). Since MFG-E8 is highly involved in inflammation, we further investigate pro-inflammatory cytokines interleukin-1β (IL-1β) and NLRP3 levels. We found that levels of IL-1β and NLRP3 increased in a diabetic pancreas while GSPB2 treatment notably attenuated these alterations (p < 0.05). In conclusion, our results suggest that inflammation is involved in the damage of a diabetic pancreas and GSPB2 provides protective effects at least in part through anti-inflammation.

Effects of dietary Corinthian currants (Vitis vinifera L., var. Apyrena) on atherosclerosis and plasma phenolic compounds during prolonged hypercholesterolemia in New Zealand White rabbits

Corinthian currants are a rich source of phenolic compounds, which are known to exert beneficial effects on cardiovascular disease. The hypothesis tested is whether dietary supplementation with currants attenuates atherosclerosis and affects plasma phenolics during prolonged hypercholesterolemia in rabbits. Thirty New Zealand White rabbits were fed one of four diets (normal and supplemented with 10% currants, with 0.5% cholesterol, and with 0.5% cholesterol plus 10% currants) for eight weeks. Plasma lipids, glucose and hepatic enzymes were determined. Individual phenolic compounds were identified and quantified in plasma during the dietary intervention. At the end of the study, histological examinations of aorta and liver were performed. The high-cholesterol diet resulted in hypercholesterolemia and oxidative stress, increased aspartate aminotransferase (AST) activity and induced aortic and hepatic lesion formation. Corinthian currant supplementation attenuated atherosclerotic lesions, maintained AST within the normal range and reduced oxidative stress without affecting glucose concentrations. The p-OH-benzoic and p-OH-phenylacetic acids predominated at high concentrations in plasma and remained almost constant during the study in the group that received the normal rabbit chow and the groups given food with added cholesterol either alone or supplemented with currants. Currant supplementation to the normal diet resulted in the reduced absorption of phenolic compounds, as revealed by the measurement of their plasma metabolites, suggesting a regulatory mechanism at the gut level under normal conditions.

Grapes (Vitis vinifera) as a Potential Candidate for the Therapy of the Metabolic Syndrome

Metabolic syndrome is associated with several disorders, including hypertension, diabetes, hyperlipidemia as well as cardiovascular diseases and stroke. Plant-derived polyphenols, compounds found in numerous plant species, play an important role as potential treatments for components of metabolic syndrome. Studies have provided evidence for protective effects of various polyphenol-rich foods against metabolic syndrome. Fruits, vegetables, cereals, nuts, and berries are rich in polyphenolic compounds. Grapes (Vitis vinifera), especially grape seeds, stand out as rich sources of polyphenol potent antioxidants and have been reported helpful for inhibiting the risk factors involved in the metabolic syndrome such as hyperlipidemia, hyperglycemia, and hypertension. There are also many studies about gastroprotective, hepatoprotective, and anti-obesity effects of grape polyphenolic compounds especially proanthocyanidins in the literature. The present study investigates the protective effects of grape seeds in metabolic syndrome. The results of this study show that grape polyphenols have significant effects on the level of blood glucose, lipid profile, blood pressure, as well as beneficial activities in liver and heart with various mechanisms. In addition, the pharmacokinetics of grape polyphenols is discussed. More detailed mechanistic investigations and phytochemical studies for finding the exact bioactive component(s) and molecular signaling pathways are suggested.

Interdependence of nutrient metabolism and the circadian clock system: Importance for metabolic health

BACKGROUND

While additional research is needed, a number of large epidemiological studies show an association between circadian disruption and metabolic disorders. Specifically, obesity, insulin resistance, cardiovascular disease, and other signs of metabolic syndrome all have been linked to circadian disruption in humans. Studies in other species support this association and generally reveal that feeding that is not in phase with the external light/dark cycle, as often occurs with night or rotating shift workers, is disadvantageous in terms of energy balance. As food is a strong driver of circadian rhythms in the periphery, understanding how nutrient metabolism drives clocks across the body is important for dissecting out why circadian misalignment may produce such metabolic effects. A number of circadian clock proteins as well as their accessory proteins (such as nuclear receptors) are highly sensitive to nutrient metabolism. Macronutrients and micronutrients can function as zeitgebers for the clock in a tissue-specific way and can thus impair synchrony between clocks across the body, or potentially restore synchrony in the case of circadian misalignment. Circadian nuclear receptors are particularly sensitive to nutrient metabolism and can alter tissue-specific rhythms in response to changes in the diet. Finally, SNPs in human clock genes appear to be correlated with diet-specific responses and along with chronotype eventually may provide valuable information from a clinical perspective on how to use diet and nutrition to treat metabolic disorders.

SCOPE OF REVIEW

This article presents a background of the circadian clock components and their interrelated metabolic and transcriptional feedback loops, followed by a review of some recent studies in humans and rodents that address the effects of nutrient metabolism on the circadian clock and vice versa. We focus on studies in which results suggest that nutrients provide an opportunity to restore or, alternatively, can destroy synchrony between peripheral clocks and the central pacemaker in the brain as well as between peripheral clocks themselves. In addition, we review several studies looking at clock gene SNPs in humans and the metabolic phenotypes or tendencies associated with particular clock gene mutations.

MAJOR CONCLUSIONS

Targeted use of specific nutrients based on chronotype has the potential for immense clinical utility in the future. Macronutrients and micronutrients have the ability to function as zeitgebers for the clock by activating or modulating specific clock proteins or accessory proteins (such as nuclear receptors). Circadian clock control by nutrients can be tissue-specific. With a better understanding of the mechanisms that support nutrient-induced circadian control in specific tissues, human chronotype and SNP information might eventually be used to tailor nutritional regimens for metabolic disease treatment and thus be an important part of personalized medicine's future.

Grape powder attenuates the negative effects of GLP-1 receptor antagonism by exendin-3 (9–39) in a normoglycemic mouse model

Acute oral administration of grape powder attenuates the hyperglycemic effects of GLP-1 receptor antagonism in rats.

Grape seed proanthocyanidin extracts prevent high glucose-induced endothelia dysfunction via PKC and NF-κB inhibition

In our study, it has been detected in vivo and in vitro that GSPE reversed high glucose-induced the increase of ICAM-1 and VCAM-1. It is shown that by western blotting detection, GSPE significantly inhibited the activation of NF-κB induced by high glucose while there was significant decrease of the expression of PKC with GSPE intervention. By adding the NF-κB blocker PDTC and the PKC inhibitor peptide 19–31(10−6 M), no significant difference was found in the levels of VCAM-1 and ICAM-1 among GSPE group, the PKC inhibitor peptide 19–31-added GSPE group and the PDTC-added GSPE group. So the conclusion could be drawn that PKC inhibition must be involved in GSPE decreasing the level of ICAM-1 and VCAM-1.We proved for the first time that GSPE prevented high glucose-induced the increase of ICAM-1 and VCAM-1 by PKC and NF-κB inhibition. These findings show a novel mechanism of the action GSPE preventing endothelial dysfunction, which may have clinical application values.

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.

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.

Cocoa-rich diet ameliorates hepatic insulin resistance by modulating insulin signaling and glucose homeostasis in Zucker diabetic fatty rats

Insulin resistance is the primary characteristic of type 2 diabetes and results from insulin signaling defects. Cocoa has been shown to exert anti-diabetic effects by lowering glucose levels. However, the molecular mechanisms responsible for this preventive activity and whether cocoa exerts potential beneficial effects on the insulin signaling pathway in the liver remain largely unknown. Thus, in this study, the potential anti-diabetic properties of cocoa on glucose homeostasis and insulin signaling were evaluated in type 2 diabetic Zucker diabetic fatty (ZDF) rats. Male ZDF rats were fed a control or cocoa-rich diet (10%), and Zucker lean animals received the control diet. ZDF rats supplemented with cocoa (ZDF-Co) showed a significant decrease in body weight gain, glucose and insulin levels, as well as an improved glucose tolerance and insulin resistance. Cocoa-rich diet further ameliorated the hepatic insulin resistance by abolishing the increased serine-phosphorylated levels of the insulin receptor substrate 1 and preventing the inactivation of the glycogen synthase kinase 3/glycogen synthase pathway in the liver of cocoa-fed ZDF rats. The anti-hyperglycemic effect of cocoa appeared to be at least mediated through the decreased levels of hepatic phosphoenolpyruvate carboxykinase and increased values of glucokinase and glucose transporter 2 in the liver of ZDF-Co rats. Moreover, cocoa-rich diet suppressed c-Jun N-terminal kinase and p38 activation caused by insulin resistance. These findings suggest that cocoa has the potential to alleviate both hyperglycemia and hepatic insulin resistance in type 2 diabetic ZDF rats.