The Anthocyanin Delphinidin 3-Rutinoside Stimulates Glucagon-Like Peptide-1 Secretion in Murine GLUTag Cell Line via the Ca2+/Calmodulin-Dependent Kinase II Pathway

Physiologic effects of the maqui berry (Aristotelia chilensis): a focus on metabolic homeostasis

The prevalence and socioeconomic impact of metabolic diseases is rapidly growing. The limited availability of effective and affordable treatments has fuelled interest in the therapeutic potential of natural compounds as they occur in selected food sources. These compounds might help to better manage the current problems of treatment availability, affordability, and adverse effects that, in combination, limit treatment duration and efficacy at present. Specifically, berries garnered interest given a strong epidemiological link between their consumption and improved metabolic functions, making the analysis of their phytochemical composition and the identification and characterization of biologically active ingredients an emerging area of research. In this regard, the present review focuses on the South American maqui berry Aristotelia chilensis, which has been extensively used by the indigenous Mapuche population for generations to treat a variety of disease conditions. An overview of the maqui plant composition precedes a review of pre-clinical and clinical studies that investigated the effects of maqui berries and their major components on metabolic homeostasis. The final part of the review highlights possible technologies to conserve maqui berry structural and functional integrity during passage through the small intestine, ultimately aiming to augment their systemic and luminal bioavailability and biological effects. The integration of the various aspects discussed herein can assist in the development of effective maqui-based therapies to benefit the growing population of metabolically compromised patients.

Physiological functions of poorly absorbed polyphenols via the glucagon-like peptide-1

Polyphenols are compounds of plant origin with several documented bioactivities related to health promotion. Some polyphenols are hard to be absorbed into the body due to their structural characteristics. This review focuses on the health beneficial effects of polyphenols mediated by intestinal hormones, particularly related to the systemic functions through the secretion of glucagon-like peptide-1 (GLP-1), an enteric hormone that stimulates postprandial insulin secretion. GLP-1 is secreted from L cells in the distal small intestine. Therefore, some poorly absorbed polyphenols are known to have the ability to act on the intestines and promote GLP-1 secretion. It has been reported that it not only reduces hyperglycemia but also prevents obesity by reduction of overeating and improves blood vessel function. This review discusses examples of health effects of polyphenols mediated by GLP-1 secretion.

The functions of Ca2+/calmodulin-dependent protein kinase II (CaMKII) in diabetes progression

The increase in blood glucose causes a myriad of pathways and molecular components to malfunction, leading to diabetes. Diabetes affects each organ differently by activating distinct pathways. It has an impact on the liver, pancreas, kidney (nephropathy), eyes (retinopathy), and nervous system (neuropathy). Understanding the effects of diabetes on each organ is the first step in developing a sustained treatment for the disease. Among the many cellular molecules impacted by diabetes is Ca²⁺/calmodulin-dependent protein kinase II (CaMKII), a complex Ca²⁺/calmodulin-activated serine/threonine-protein kinase. When intracellular [Ca²⁺] rises, it binds to calmodulin (CaM) to produce Ca²⁺/CaM, which activates CaMKIIs. This factor is involved in the pancreas, liver, heart, muscles, and various organs. Thus, Understanding CaMKII action in each organ is critical for gaining a complete picture of diabetic complications. Therefore, this review covers CaMKII's functions in many organs and how it affects and has been affected by diabetes.

Biodegradable Polymeric Nanoparticles Loaded with Flavonoids: A Promising Therapy for Inflammatory Bowel Disease

Inflammatory bowel disease (IBD) is a group of disorders that cause chronic non-specific inflammation in the gastrointestinal (GI) tract, primarily affecting the ileum and colon. The incidence of IBD has risen sharply in recent years. Despite continuous research efforts over the past decades, the aetiology of IBD is still not fully understood and only a limited number of drugs are available for its treatment. Flavonoids, a ubiquitous class of natural chemicals found in plants, have been widely used in the prevention and treatment of IBD. However, their therapeutic efficacy is unsatisfactory due to poor solubility, instability, rapid metabolism, and rapid systemic elimination. With the development of nanomedicine, nanocarriers can efficiently encapsulate various flavonoids and subsequently form nanoparticles (NPs), which greatly improves the stability and bioavailability of flavonoids. Recently, progress has also been made in the methodology of biodegradable polymers that can be used to fabricate NPs. As a result, NPs can significantly enhance the preventive or therapeutic effects of flavonoids on IBD. In this review, we aim to evaluate the therapeutic effect of flavonoid NPs on IBD. Furthermore, we discuss possible challenges and future perspectives.

Anthocyanin actions at the gastrointestinal tract: Relevance to their health benefits

Anthocyanins (AC) are flavonoids abundant in the human diet, which consumption has been associated to several health benefits, including the mitigation of cardiovascular disease, type 2 diabetes, non-alcoholic fatty liver disease, and neurological disorders. It is widely recognized that the gastrointestinal (GI) tract is not only central for food digestion but actively participates in the regulation of whole body physiology. Given that AC, and their metabolites reach high concentrations in the intestinal lumen after food consumption, their biological actions at the GI tract can in part explain their proposed local and systemic health benefits. In terms of mechanisms of action, AC have been found to: i) inhibit GI luminal enzymes that participate in the absorption of lipids and carbohydrates; ii) preserve intestinal barrier integrity and prevent endotoxemia, inflammation and oxidative stress; iii) sustain goblet cell number, immunological functions, and mucus production; iv) promote a healthy microbiota; v) be metabolized by the microbiota to AC metabolites which will be absorbed and have systemic effects; and vi) modulate the metabolism of GI-generated hormones. This review will summarize and discuss the latest information on AC actions at the GI tract and their relationship to overall health benefits.

Does anthocyanins consumption affect weight and body composition? A systematic review and meta-analysis of randomized controlled trials

Background and Aims

Anthocyanins (ACNs) are water-soluble plant pigments belong to flavonoids with beneficial effects on health and disease prevention. Some studies have examined the effect of ACNs on anthropometric and body composition indices, but the findings were inconsistent. This systematic review and meta-analysis aimed to investigate the effect of ACNs and sources rich in anthocyanins on body mass index (BMI), body weight (BW), waist circumference (WC), hip circumference (HC), waist-hip ratio (WHR), percentage of fat mass (PFM) and fat free mass (FFM).

Methods

PubMed, Web of Science, Scopus, and Google Scholar were searched with no limitation until May 2021 to find relevant randomized controlled clinical trials (RCT). The risk of bias was assessed utilizing Cochrane collaboration's tool. Weighted mean differences (WMD) and 95% confidence intervals (CIs) were obtained using a random effects model.

Results

A total of 31 RCTs (with 0.77-640 mg/day of ACNs supplementation for 28-90 days) with 1438 participants were included. No significant effect was found in BMI, WC, HC, WHR, PFM and FFM after ACNs consumption.

Conclusions

The results showed that ACNs did not significantly affect anthropometric and body composition parameters. Further high-quality RCTs are required to validate these findings.

Analysis of Floral Color Differences between Different Ecological Conditions of Clematis tangutica (Maxim.) Korsh

The Clematis tangutica (Maxim.) Korsh. is a wild flowering plant that is most widely distributed on the Qinghai-Tibet Plateau, with beautiful, brightly colored flowers and good ornamental properties and adaptability. In diverse natural environments, the blossom color of C. tangutica (Maxim.) Korsh. varies greatly, although it is unclear what causes this diversity. It was examined using UPLC-MS/MS and transcriptome sequencing for the investigation of various compounds, differentially expressed genes (DEGs), and flavonoid biosynthesis-related pathways in two flowers in two ecological settings. The results showed that a total of 992 metabolites were detected, of which 425 were differential metabolites, mainly flavonoid metabolites associated with its floral color. The most abundant flavonoids, flavonols and anthocyanin metabolites in the G type were cynaroside, isoquercitrin and peonidin-3-O-glucoside, respectively. Flavonoids that differed in multiplicity in G type and N type were rhoifolin, naringin, delphinidin-3-O-rutinoside, chrysoeriol and catechin. Rhoifolin and chrysoeriol, produced in flavone and flavonol biosynthesis, two flavonoid compounds of C. tangutica (Maxim.) Korsh. with the largest difference in floral composition in two ecological environments. In two ecological environments of flower color components, combined transcriptome and metabolome analyses revealed that BZ1-1 and FG3-1 are key genes for delphinidin-3-O-rutinoside in anthocyanin biosynthesis, and HCT-5 and FG3-3 are key genes for rhoifolin and naringin in flavonoid biosynthesis and flavone and flavonol. Key genes for chlorogenic acid in flavonoid biosynthesis include HCT-6, CHS-1 and IF7MAT-1. In summary, differences in flavonoids and their content are the main factors responsible for the differences in the floral color composition of C. tangutica (Maxim.) Korsh. in the two ecological environments, and are associated with differential expression of genes related to flavonoid synthesis.

Polyphenol-Rich Beverage Consumption Affecting Parameters of the Lipid Metabolism in Healthy Subjects

Polyphenols are a diverse and widely distributed class of secondary metabolites, which possess numerous beneficial properties including a modulation of glucose and lipid metabolism. This placebo-controlled human intervention study was performed to explore effects of polyphenol-rich beverage (PRB) uptake on lipid metabolism, as well as DNA integrity. In this case, 36 healthy men were randomly divided to consume either 750 mL of a PRB (containing 51% chokeberry, cranberry, and pomegranate) or a placebo drink daily for eight weeks. Only PRB consumption was found to decrease fat and protein intakes significantly compared to the preceding one-week washout period. During the intervention with PRB an increased fat-free mass was shown after four weeks, whereas a significant elevation in body weight and leptin was observed in placebo group. Blood lipids were not significantly altered after PRB consumption, while triglyceride levels increased after placebo drink intake. In platelets, a significant inhibition of phosphodiesterase (PDE) activity was observed, more pronounced in test group. Consuming the PRB decreased total DNA strand breaks in whole blood as well as H₂O₂-induced breaks in isolated lymphocytes. Overall, our study suggested beneficial effects on lipid metabolism by reduced energy intake, modulation of biomarkers such as PDE activity and improved DNA integrity associated with PRB consumption.

Research progress of anthocyanin prebiotic activity: A review

BACKGROUND

Anthocyanins are a kind of flavonoids and natural water-soluble pigments, which endow fruits, vegetables, and plants with multiple colors. They are important source of new products with prebiotic activity. However, there is no systematic review documenting prebiotic activity of anthocyanins and their structural analogues. This study aims to fill this gap in literature.

PURPOSE

The objective of this review is to summarize and evaluate the prebiotic activity of anthocyanin's, and discuss the physical and molecular modification methods to improve their biological activities.

STUDY DESIGN AND METHODS

In this review, the databases (PubMed, Google Scholar, Web of Science, Researchgate and Elsevier) were searched profoundly with keywords (anthocyanin's, prebiotics, probiotics, physical embedding and molecular modification).

RESULTS

A total of 34 articles were considered for reviewing. These studies approved that anthocyanins play an important role in promoting the proliferation of probiotics, inhibiting the growth of harmful bacteria and improving the intestinal environment. In addition, physical embedding and molecular modification have also been proved to be effective methods to improve the prebiotic activity of anthocyanins. Anthocyanins could promote the production of short chain fatty acids, accelerate self degradation and improve microbial related enzyme activities to promote the proliferation of probiotics. They inhibited the growth of harmful bacteria by inhibiting the expression of harmful bacteria genes, interfering with the role of metabolism related enzymes and affecting respiratory metabolism. They promoted the formation of a complete intestinal barrier and regulated the intestinal environment to keep the body healthy. Physical embedding, including microencapsulation and colloidal embedding, greatly improved the stability of anthocyanins. On the other hand, molecular modification, especially enzymatic modification, significantly improved the biological activities (antioxidant, prebiotic activity and so on) of anthocyanins.

CONCLUSION

All these research results displayed by this review indicate that anthocyanins are a useful tool for developing prebiotic products. The better activities of the new anthocyanins formed by embedding and modification may make them become more effective raw materials. Our review provides a scientific basis for the future research and application of anthocyanins.

Chemistry and Pharmacological Actions of Delphinidin, a Dietary Purple Pigment in Anthocyanidin and Anthocyanin Forms

Anthocyanins are naturally occurring water-soluble flavonoids abundantly present in fruits and vegetables. They are polymethoxyderivatives of 2-phenyl-benzopyrylium or flavylium salts. Delphinidin (Dp) is a purple-colored plant pigment, which occurs in a variety of berries, eggplant, roselle, and wine. It is found in a variety of glycosidic forms ranging from glucoside to arabinoside. Dp is highly active in its aglycone form, but the presence of a sugar moiety is vital for its bioavailability. Several animal and human clinical studies have shown that it exerts beneficial effects on gut microbiota. Dp exhibits a variety of useful biological activities by distinct and complex mechanisms. This manuscript highlights the basic characteristics, chemistry, biosynthesis, stability profiling, chemical synthesis, physicochemical parameters along with various analytical methods developed for extraction, isolation and characterization, diverse biological activities and granted patents to this lead anthocyanin molecule, Dp. This review aims to open pathways for further exploration and research investigation on the true potential of the naturally occurring purple pigment (Dp) in its anthocyanidin and anthocyanin forms beyond nutrition.

Hypoglycemic bioactivity of anthocyanins: A review on proposed targets and potential signaling pathways

Type 2 diabetes mellitus (T2DM) is a chronic metabolic disease with complicated interrelationships responsible for initiating its pathogenesis. Novel strategies for the treatment of this devastating disease have attracted increasing attention worldwide. Anthocyanins are bioactive compounds that are widely distributed in the plant kingdom, and multiple studies have elucidated their beneficial role in preventing and managing T2DM. This review summarizes and comments on the hypoglycemic actions of anthocyanins from the perspective of molecular mechanisms and different target-related signaling pathways in vitro, in vivo, and clinical trials. Anthocyanins can ameliorate T2DM by functioning as carbohydrate digestive enzyme inhibitors, facilitating glucose transporter 4 (GLUT4) translocation, suppressing the effectiveness of dipeptidyl peptidase IV (DPP-IV), promoting glucagon-like peptide-1 (GLP-1) secretion, inhibiting protein tyrosine phosphatase 1B (PTP1B) overexpression, and interacting with sodium-glucose co-transporter (SGLT) to delay glucose absorption in various organs and tissues. In summary, anthocyanin is a promising and practical small molecule that can hyperglycemic symptoms and accompanying complications suffered by patients with diabetes. However, rational and potent doses for daily intake and clinical studies are required in the future.

Cucurbitane-type triterpenoids from the vines of Momordica charantia and their anti-inflammatory, cytotoxic, and antidiabetic activity

Phytochemical investigation of the ethanol extract from wild Momordica charantia vines has resulted in isolation of seven cucurbitane-type triterpenoids, including six undescribed compounds, kuguaovins H‒M, and the known compound, momordicoside K. The structures of the isolated compounds were elucidated on the basis of spectroscopic analyses, including 1D and 2D NMR, and MS experiments. The chemical structure of momordicoside K was determined for the first time by X-ray crystallographic analysis and its absolute configuration assigned. The cytotoxicity against four human tumor cell lines and anti-inflammatory activities on LPS-stimulated RAW264.7 macrophages were evaluated. Of the isolates, kaguaovin L exhibited potential cytotoxicity against MCF-7, HEp-2, Hep-G2, and WiDr cancer cell lines and showed moderate anti-NO production activity. In addition, kuguaovins H and J also showed the stimulatory effect of GLP-1 secretion on the murine intestinal secretin tumor cell line (STC-1).

A Novel Pathway of Flavonoids Protecting against Inflammatory Bowel Disease: Modulating Enteroendocrine System

Inflammatory bowel disease (IBD) is a comprehensive term for chronic or relapsing inflammatory diseases occurring in the intestinal tract, generally including Crohn's disease (CD) and ulcerative colitis (UC). Presently, the pathogenesis of IBD is unknown, yet multiple factors have been reported to be related with the development of IBD. Flavonoids are phytochemicals with biological activity, which are ubiquitously distributed in edible plants, such as fruits and vegetables. Recent studies have demonstrated impressively that flavonoids have anti-IBD effects through multiple mechanisms. These include anti-inflammatory and antioxidant actions; the preservation of the epithelial barrier integrity, the intestinal immunomodulatory property, and the shaping microbiota composition and function. In addition, a few studies have shown the impact of flavonoids on enterohormones release; nonetheless, there is hardly any work showing the link between flavonoids, enterohormones release and IBD. So far, the interaction between flavonoids, enterohormones and IBD is elucidated for the first time in this review. Furthermore, the inference can be drawn that flavonoids may protect against IBD through modulating enterohormones, such as glucagon-like peptide 1 (GLP-1), GLP-2, dipeptidyl peptidase-4 inhibitors (DPP-4 inhibitors), ghrelin and cholecystokinin (CCK). In conclusion, this manuscript explores a possible mechanism of flavonoids protecting against IBD.

Acylated anthocyanins: A review on their bioavailability and effects on postprandial carbohydrate metabolism and inflammation

Anthocyanins, the natural red and purple colorants of berries, fruits, vegetables, and tubers, improve carbohydrate metabolism and decrease the risk factors of metabolic disorders, but their industrial use is limited by their chemical instability. Acylation of the glycosyl moieties of anthocyanins, however, changes the chemical properties of anthocyanins and provides enhanced stability. Thus, acylated anthocyanins are more usable as natural colorants and bioactive components of innovative functional foods. Acylated anthocyanins are common in pigmented vegetables and tubers, the consumption of which has the potential to increase the intake of health-promoting anthocyanins as part of the daily diet. For the first time, this review presents the current findings on bioavailability, absorption, metabolism, and health effects of acylated anthocyanins with comparison to more extensively investigated nonacylated anthocyanins. The structural differences between nonacylated and acylated anthocyanins lead to enhanced color stability, altered absorption, bioavailability, in vivo stability, and colonic degradation. The impact of phenolic metabolites and their potential health effects regardless of the low bioavailability of the parent anthocyanins as such is discussed. Here, purple-fleshed potatoes are presented as a globally available, eco-friendly model food rich in acylated anthocyanins, which further highlights the industrial possibilities and nutritional relevance of acylated anthocyanins. This work supports the academic community and industry in food research and development by reviewing the current literature and highlighting gaps of knowledge.

The Role of Anthocyanins in Drug Discovery: Recent Developments

Natural compounds have always played a key role in drug discovery. Anthocyanins are secondary metabolites belonging to the flavonoids family responsible for the purple, blue, and red colour of many vegetables and fruits. These phytochemicals have attracted the interest of researchers for their important implications in human health and for their use as natural colorants. Many in vitro and in vivo studies demonstrated the potential effects of anthocyanins and anthocyanins-rich foods in the prevention and/or treatment of diabetes, cancer, and cardiovascular and neurodegenerative diseases. This review reports the recent literature data and focuses on the potential role of anthocyanins in drug discovery. Their biological activity, analysis of structure-activity relationships, bioavailability, metabolism, and future prospects of their uses are critically described.

Slow digestion-oriented dietary strategy to sustain the secretion of GLP-1 for improved glucose homeostasis

Dysregulated glucose metabolism is associated with many chronic diseases such as obesity and type 2 diabetes mellitus (T2DM), and strategies to restore and maintain glucose homeostasis are essential to health. The incretin hormone of glucagon-like peptide-1 (GLP-1) is known to play a critical role in regulating glucose homeostasis and dietary nutrients are the primary stimuli to the release of intestinal GLP-1. However, the GLP-1 producing enteroendocrine L-cells are mainly distributed in the distal region of the gastrointestinal tract where there are almost no nutrients to stimulate the secretion of GLP-1 under normal situations. Thus, a dietary strategy to sustain the release of GLP-1 was proposed, and the slow digestion property and dipeptidyl peptidase IV (DPP-IV) inhibitory activity of food components, approaches to reduce the rate of food digestion, and mechanisms to sustain the release of GLP-1 were reviewed. A slow digestion-oriented dietary approach through encapsulation of nutrients, incorporation of viscous dietary fibers, and enzyme inhibitors of phytochemicals in a designed whole food matrix will be implemented to efficiently reduce the digestion rate of food nutrients, potentiate their distal deposition and a sustained secretion of GLP-1, which will be beneficial to improved glucose homeostasis and health.

Improvement of Glucose Tolerance by Food Factors Having Glucagon-Like Peptide-1 Releasing Activity

Glucagon-like peptide-1 (GLP-1) is a gastrointestinal hormone released from enteroendocrine L cells in response to meal ingestion. GLP-1 receptor agonists and GLP-1 enhancers have been clinically employed to treat diabetes owing to their glucose-dependent insulin-releasing activity. The release of GLP-1 is primarily stimulated by macronutrients such as glucose and fatty acids, which are nutritionally indispensable; however, excessive intake of sugar and fat is responsible for the development of obesity and diabetes. Therefore, GLP-1 releasing food factors, such as dietary peptides and non-nutrients, are deemed desirable for improving glucose tolerance. Human and animal studies have revealed that dietary proteins/peptides have a potent effect on stimulating GLP-1 secretion. Studies in enteroendocrine cell models have shown that dietary peptides, amino acids, and phytochemicals, such as quercetin, can directly stimulate GLP-1 secretion. In our animal experiments, these food factors improved glucose metabolism and increased GLP-1 secretion. Furthermore, some dietary peptides not only stimulated GLP-1 secretion but also reduced plasma peptidase activity, which is responsible for GLP-1 inactivation. Herein, we review the relationship between GLP-1 and food factors, especially dietary peptides and flavonoids. Accordingly, utilization of food factors with GLP-1-releasing/enhancing activity is a promising strategy for preventing and treating obesity and diabetes.

Effects of Anthocyanins on Vascular Health

Cardiovascular disorders are leading mortality causes worldwide, often with a latent evolution. Vascular health depends on endothelial function, arterial stiffness, and the presence of atherosclerotic plaques. Preventive medicine deserves special attention, focusing on modifiable cardiovascular risk factors, including diet. A diet rich in fruits and vegetables has well-known health benefits, especially due to its polyphenolic components. Anthocyanins, water-soluble flavonoid species, responsible for the red-blue color in plants and commonly found in berries, exert favorable effects on the endothelial function, oxidative stress, inhibit COX-1, and COX-2 enzymes, exert antiatherogenic, antihypertensive, antiglycation, antithrombotic, and anti-inflammatory activity, ameliorate dyslipidemia and arterial stiffness. The present review aims to give a current overview of the mechanisms involved in the vascular protective effect of anthocyanins from the human diet, considering epidemiological data, in vitro and in vivo preclinical research, clinical observational, retrospective, intervention and randomized studies, dietary and biomarker studies, and discussing preventive benefits of anthocyanins and future research directions.

Aqueous Blackcurrant Extract Improves Insulin Sensitivity and Secretion and Modulates the Gut Microbiome in Non-Obese Type 2 Diabetic Rats

This study was undertaken to determine whether aqueous blackcurrant extracts (BC) improve glucose metabolism and gut microbiomes in non-obese type 2 diabetic animals fed a high-fat diet and to identify the mechanism involved. Partially pancreatectomized male Sprague–Dawley rats were provided a high-fat diet containing 0% (control), 0.2% (L-BC; low dosage), 0.6% (M-BC; medium dosage), and 1.8% (H-BC; high dosage) blackcurrant extracts; 0.2% metformin (positive-C); plus 1.8%, 1.6%, 1.2%, 0%, and 1.6% dextrin, specifically indigestible dextrin, daily for 8 weeks. Daily blackcurrant extract intakes were equivalent to 100, 300, and 900 mg/kg body weight (bw). After a 2 g glucose or maltose/kg bw challenge, serum glucose and insulin concentrations during peak and final states were obviously lower in the M-BC and H-BC groups than in the control group (p < 0.05). Intraperitoneal insulin tolerance testing showed that M-BC and H-BC improved insulin resistance. Hepatic triglyceride deposition, TNF-α expression, and malondialdehyde contents were lower in the M-BC and H-BC groups than in the control group. Improvements in insulin resistance in the M-BC and H-BC groups were associated with reduced inflammation and oxidative stress (p < 0.05). Hyperglycemic clamp testing showed that insulin secretion capacity increased in the acute phase (2 to 10 min) in the M-BC and H-BC groups and that insulin sensitivity in the hyperglycemic state was greater in these groups than in the control group (p < 0.05). Pancreatic β-cell mass was greater in the M-BC, H-BC, and positive-C groups than in the control group. Furthermore, β-cell proliferation appeared to be elevated and apoptosis was suppressed in these three groups (p < 0.05). Serum propionate and butyrate concentrations were higher in the M-BC and H-BC groups than in the control group. BC dose-dependently increased α-diversity of the gut microbiota and predicted the enhancement of oxidative phosphorylation-related microbiome genes and downregulation of carbohydrate digestion and absorption-related genes, as determined by PICRUSt2 analysis. In conclusion, BC enhanced insulin sensitivity and glucose-stimulated insulin secretion, which improved glucose homeostasis, and these improvements were associated with an incremental increase of the α-diversity of gut microbiota and suppressed inflammation and oxidative stress.

Acute Consumption of Blueberries and Short-Term Blueberry Supplementation Improve Glucose Management and Insulin Levels in Sedentary Subjects

BACKGROUND

Blueberries are polyphenol-rich fruits with antioxidant and anti-inflammatory properties. Polyphenols from berries act by blocking digestive enzymes, reshaping gastrointestinal microbiota, and affecting the release of gastrointestinal hormones to regulate insulin dynamics and glucose management. However, most studies use fruit extracts instead of fresh fruit. We aimed to evaluate postprandial glucose management and antioxidant capacity of fresh blueberries consumed acutely or as a six-day supplementation in 10 sedentary subjects.

METHODS

To evaluate the effect of acute blueberry intake, 150 g of blueberries were consumed together with 150 g of white bread by the subject and blood samples were collected at 0, 30, 60, 90 and 120 min to measure glucose, insulin, and plasma antioxidant capacity. To evaluate supplementation, 150 g of blueberries were provided daily for six days and sample collection was performed at day 7.

RESULTS

Acute consumption of blueberries decreased postprandial glucose area under the curve (AUC) and increased insulin levels at 15 min timepoint. Supplementation did not affect glucose levels but decreased insulin levels at 120 min. No changes in antioxidant capacity were observed.

CONCLUSIONS

Consumption of fresh blueberries improves postprandial glucose management presumably due to actions on the gastrointestinal tract, while supplementation improves insulin sensitivity, probably due antioxidant and anti-inflammatory effects.

Going "Green" in the Prevention and Management of Atherothrombotic Diseases: The Role of Dietary Polyphenols

During the 20th century processed and ready-to-eat foods became routinely consumed resulting in a sharp rise of fat, salt, and sugar intake in people's diets. Currently, the global incidence of obesity, raised blood lipids, hypertension, and diabetes in an increasingly aged population contributes to the rise of atherothrombotic events and cardiovascular diseases (CVD) mortality. Drug-based therapies are valuable strategies to tackle and help manage the socio-economic impact of atherothrombotic disorders though not without adverse side effects. The inclusion of fresh fruits and vegetables rich in flavonoids to human diets, as recommended by WHO offers a valuable nutritional strategy, alternative to drug-based therapies, to be explored in the prevention and management of atherothrombotic diseases at early stages. Though polyphenols are mostly associated to color and taste in foods, food flavonoids are emerging as modulators of cholesterol biosynthesis, appetite and food intake, blood pressure, platelet function, clot formation, and anti-inflammatory signaling, supporting the health-promoting effects of polyphenol-rich diets in mitigating the impact of risk factors in atherothrombotic disorders and CVD events. Here we overview the current knowledge on the effect of polyphenols particularly of flavonoid intake on the atherothrombotic risk factors and discuss the caveats and challenges involved with current experimental cell-based designs.

(-)-Epicatechin and Anthocyanins Modulate GLP-1 Metabolism: Evidence from C57BL/6J Mice and GLUTag Cells

BACKGROUND

Generated in intestinal L cells through cleavage of proglucagon (Gcg), glucagon-like peptide 1 (GLP-1) is secreted and rapidly inactivated by dipeptidyl peptidase IV (DPP-IV). GLP-1 regulates insulin secretion and overall glucose homeostasis. The capacity of dietary bioactives to increase GLP-1 circulating levels, and therefore increase insulin secretion and glucose metabolism, has gained significant interest of late.

OBJECTIVES

We evaluated the effects of (-)-epicatechin (EC) and different anthocyanins (ACs) and AC metabolites on GLP-1 metabolism in mice and on GLUTag cells.

METHODS

We fed 6-week-old C57BL/6J male mice a control diet or a control diet supplemented with either 40 mg AC or 20 mg EC/kg body weight for 14 weeks (AC) or 15 weeks (EC). Intestinal mRNA levels of Gcg and Dpp-iv were measured. In vitro, GLUTag cells were incubated in the presence or absence of different ACs, the AC metabolite protocatechuic acid (PCA), and EC. GLP-1 secretion and the main pathways involved in its release were assessed.

RESULTS

Long-term supplementation with EC or AC increased mouse GLP-1 plasma concentrations (55% and 98%, respectively; P < 0.05). In mice, 1) EC and AC increased Gcg mRNA levels in the ileum (91%) and colon (41%), respectively (P < 0.05); and 2) AC lowered ileum Dpp-iv mRNA levels (35%), while EC decreased plasma DPP-IV activity (15%; P < 0.05). In GLUTag cells, 1) cyanidin, delphinidin, PCA, and EC increased GLP-1 secretion (53%, 33%, 53%, and 68%, respectively; P < 0.05); and 2) cyanidin, delphinidin, EC, and PCA increased cyclin adenosine monophosphate levels (25-50%; P < 0.05) and activated protein kinase A (PKA; 100%, 50%, 80%, and 86%, respectively; P < 0.05).

CONCLUSIONS

In mice, EC and ACs regulated different steps in GLP-1 regulation, leading to increased plasma GLP-1. Cyanidin, delphinidin, PCA, and EC promoted GLP-1 secretion from GLUTag cells by activating the PKA-dependent pathway. These findings support the beneficial actions of these flavonoids in sustaining intestinal and glucose homeostasis through the modulation of the GLP-1 metabolism.

The Emerging Role of Polyphenols in the Management of Type 2 Diabetes

Type 2 diabetes (T2D) is a fast-increasing health problem globally, and it results from insulin resistance and pancreatic β-cell dysfunction. The gastrointestinal (GI) tract is recognized as one of the major regulatory organs of glucose homeostasis that involves multiple gut hormones and microbiota. Notably, the incretin hormone glucagon-like peptide-1 (GLP-1) secreted from enteroendocrine L-cells plays a pivotal role in maintaining glucose homeostasis via eliciting pleiotropic effects, which are largely mediated via its receptor. Thus, targeting the GLP-1 signaling system is a highly attractive therapeutic strategy to treatment T2D. Polyphenols, the secondary metabolites from plants, have drawn considerable attention because of their numerous health benefits, including potential anti-diabetic effects. Although the major targets and locations for the polyphenolic compounds to exert the anti-diabetic action are still unclear, the first organ that is exposed to these compounds is the GI tract in which polyphenols could modulate enzymes and hormones. Indeed, emerging evidence has shown that polyphenols can stimulate GLP-1 secretion, indicating that these natural compounds might exert metabolic action at least partially mediated by GLP-1. This review provides an overview of nutritional regulation of GLP-1 secretion and summarizes recent studies on the roles of polyphenols in GLP-1 secretion and degradation as it relates to metabolic homeostasis. In addition, the effects of polyphenols on microbiota and microbial metabolites that could indirectly modulate GLP-1 secretion are also discussed.

Anthocyanin Bioactivity in Obesity and Diabetes: The Essential Role of Glucose Transporters in the Gut and Periphery

Obesity and type-2 diabetes trends continue to worsen in the United States. Dietary anthocyanins (typically provided by berries and other fruits) are reported to have protective effects against both conditions using a variety of experimental research models including animal and human feeding studies. This review highlights studies that explore the biochemical pathways in both tissue and rodent models which could explain clinical improvements noted with anthocyanin consumption. First, the primary mode of intestinal absorption of anthocyanins is through both sGLT1 and GLUT2 glucose transporters. Stronger binding affinities may allow anthocyanins to be more inhibitive to glucose absorption compared to the reverse, where GLUT2 expression may also be affected. Genetic or chemical inhibition of sGLT1 or GLUT2 demonstrate their essential function in anthocyanin absorption across the enterocyte, where the former interacts with a greater variety of anthocyanins but the latter is the major transporter for specific anthocyanin-glycosides. Once absorbed, anthocyanins positively modulate GLUT4 density and function in both skeletal muscle and adipose tissues via the upregulation of AMPK and restoration of insulin sensitivity. Antioxidant properties and phosphodiesterase inhibition by anthocyanins promote both mitochondrial function and density which could be novel targets for dietary management of obesity and its complications.

Postprandial Effect of Yogurt Enriched with Anthocyanins from Riceberry Rice on Glycemic Response and Antioxidant Capacity in Healthy Adults

The pigment of riceberry rice has been reported to contain anthocyanins which act as a free radical scavenger and inhibitor of carbohydrate digestive enzymes. Since the probiotic yogurt incorporated with the pigment of riceberry rice extract was previously developed, the present study was aimed to investigate the acute effect of riceberry rice yogurt consumption on postprandial glycemic response, antioxidant capacity, and subjective ratings in healthy adults. In a cross-over design, 19 healthy participants were randomized to consume 350 g of yogurt supplemented with 0.25% (w/w) riceberry rice extract or the control yogurt. Postprandial plasma glucose, antioxidant status, and subjective ratings were measured at fasting and intervals (0–3 h) after ingestion of yogurt. The primary outcome was glycemic response; the secondary outcomes were plasma antioxidant capacity. In comparison to the yogurt control, riceberry rice yogurt reduced plasma glucose concentration after 30 min of consumption. The incremental area under the curve (iAUC) was significantly lower after riceberry rice yogurt load than after the control yogurt load. The consumption of riceberry yogurt caused an acute increase in plasma ferric reducing ability of plasma (FRAP), Trolox equivalent antioxidant capacity (TEAC), and oxygen radical absorbance capacity (ORAC) from the baseline values after 60 min of 0.25 ± 0.06 mM FeSO₄, 253.7 ± 35.5 mM Trolox equivalents, and 166.8 ± 28.9 mM Trolox equivalents, respectively. Furthermore, the iAUCs for FRAP, TEAC, ORAC, and protein thiol were higher in riceberry yogurt consumption compared with the control yogurt (1.6-, 1.6-, 2.9-, and 1.9-fold, respectively). A decrease in iAUC for plasma malondialdehyde (MDA) concentration was also observed in the riceberry yogurt group. However, consumption of riceberry rice yogurt and control yogurt showed similar subjective rating scores of hunger, desire to eat, fullness, and satiety. In conclusion, acute consumption of riceberry rice yogurt suppressed postprandial glucose level and improved plasma antioxidant capacity in healthy volunteers.

Dietary Cyanidin-3-Glucoside Attenuates High-Fat-Diet-Induced Body-Weight Gain and Impairment of Glucose Tolerance in Mice via Effects on the Hepatic Hormone FGF21

BACKGROUND

Dietary polyphenols including anthocyanins target multiple organs.

OBJECTIVE

We aimed to assess the involvement of glucagon-like peptide 1 (GLP-1), leptin, insulin and fibroblast growth factor 21 (FGF21) in mediating metabolic beneficial effects of purified anthocyanin cyanidin-3-glucoside (Cy3G).

METHODS

Intestinal proglucagon gene (Gcg; encoding GLP-1) and liver Fgf21 expression were assessed in 6-wk-old male C57BL-6J mice fed a low-fat-diet (LFD; 10% of energy from fat), alone or with 1.6 mg Cy3G/L in drinking water for 3 wk [experiment (Exp.) 1; n = 5/group]. Similar mice were fed the LFD or a high-fat diet (HFD; 60% energy from fat) with or without Cy3G for 20 wk. Half of the mice administered Cy3G also received 4 broad-spectrum antibiotics (ABs) in drinking water between weeks 11 and 14, for a total of 6 groups (n = 8/group). Metabolic tolerance tests were conducted between weeks 2 and 16. Relevant hormone gene expression and plasma hormone concentrations were assessed mainly at the end of 20 wk (Exp. 2).

RESULTS

In Exp. 1, Cy3G administration increased ileal but not colonic Gcg level by 2-fold (P < 0.05). In Exp. 2, Cy3G attenuated HFD-induced body-weight gain (20.3% at week 16), and improved glucose tolerance (26.5% at week 15) but not insulin tolerance. Although Cy3G had no effect on glucose tolerance in LFD mice, LFD/Cy3G/AB mice showed better glucose tolerance than LFD/Cy3G mice (23%). In contrast, HFD/Cy3G/AB mice showed worse glucose tolerance compared with HFD/Cy3G mice (15%). Beneficial effects of Cy3G in HFD mice were not associated with changes in plasma leptin, insulin or GLP-1 concentrations. However, Cy3G increased hepatic Fgf21 expression in mice in Exp. 1 by 4-fold and attenuated Fgf21 overexpression in HFD mice (Exp. 2, 22%), associated with increased expression of genes that encode FGFR1 and β-klotho (>3-fold, P < 0.05).

CONCLUSIONS

Dietary Cy3G may reduce body weight and exert metabolic homeostatic effects in mice via changes in hepatic FGF21.

The role of anthocyanins as antidiabetic agents: from molecular mechanisms to in vivo and human studies

Diabetes mellitus is a chronic metabolic disease characterized by high blood glucose concentration. Nowadays, type 2 diabetes or insulin resistant diabetes is the most common diabetes, mainly due to unhealthy lifestyle. Healthy habits like appropriate nutritional approaches or the consumption of certain natural products or food supplements have been suggested as non-pharmacological strategies for the treatment and prevention of type 2 diabetes. Some of the main bioactive compounds from plant foods are polyphenols, important mainly for their antioxidant capacity in oxidative stress conditions and ageing. Anthocyanins are polyphenols of the flavonoid group, which act as pigments in plants, especially in fruits such as berries. A search of in vitro, in vivo and human studies in relation with antidiabetic properties of anthocyanins has been performed in different electronic databases. Results of this review demonstrate that these compounds have the ability to inhibit different enzymes as well as to influence gene expression and metabolic pathways of glucose, such as AMPK, being able to modulate diabetes and other associated disorders, as hyperlipidaemia, overweight, obesity and cardiovascular diseases. Additionally, human interventional studies have shown that high doses of anthocyanins have potential in the prevention or treatment of type 2 diabetes; nevertheless, anthocyanins used in these studies should be standardized and quantified in order to make general conclusions about its use and to claim benefits for the human population.

Flavone Hispidulin Stimulates Glucagon-Like Peptide-1 Secretion and Ameliorates Hyperglycemia in Streptozotocin-Induced Diabetic Mice

SCOPE

Loss of functional β-cell mass is central for the deterioration of glycemic control in diabetes. The incretin hormone glucagon-like peptide-1 (GLP-1) plays a critical role in maintaining glycemic homeostasis via potentiating glucose-stimulated insulin secretion and promoting β-cell mass. Agents that can directly promote GLP-1 secretion, thereby increasing insulin secretion and preserving β-cell mass, hold great potential for the treatment of T2D.

METHODS AND RESULTS

GluTag L-cells, INS832/13 cells, and mouse ileum crypts and islets are cultured for examining the effects of flavone hispidulin on GLP-1 and insulin secretion. Mouse livers and isolated hepatocytes are used for gluconeogenesis. Streptozotocin-induced diabetic mice are treated with hispidulin (20 mg kg^-1 day^-1 , oral gavage) for 6 weeks to evaluate its anti-diabetic potential. Hispidulin stimulates GLP-1 secretion from the L-cell line, ileum crypts, and in vivo. This hispidulin action is mediated via activation of cyclic adenosine monophosphate/protein kinase A signaling. Hispidulin significantly improves glycemic control in diabetic mice, concomitant with improved insulin release, and β-cell survival. Additionally, hispidulin decreases hepatic pyruvate carboxylase expression in diabetic mice and suppresses gluconeogenesis in hepatocytes. Furthermore, hispidulin stimulates insulin secretion from β-cells.

CONCLUSION

These findings suggest that Hispidulin may be a novel dual-action anti-diabetic compound via stimulating GLP-1 secretion and suppressing hepatic glucose production.

Black soybean seed coat polyphenols promote nitric oxide production in the aorta through glucagon-like peptide-1 secretion from the intestinal cells

Black soybean seed coat polyphenols were reported to possess various bioregulatory functions. However, the effects of black soybean seed coat polyphenols on vascular functions are unknown. Vascular dysfunction caused by aging and vascular stiffness is associated with a risk of cardiovascular disease (CVD), and a reduction in nitric oxide (NO) levels can trigger the onset of CVD. In the present study, we investigated the effect of polyphenol-rich black soybean seed coat extract (BE) on vascular functions and the underlying mechanisms involved. The oral administration of BE at 50 mg per kg body weight to Wistar rats increased NO levels as determined by eNOS phosphorylation. The administration of BE also increased GLP-1 and cAMP levels. Furthermore, the effects of BE were inhibited in the presence of a GLP-1 receptor antagonist. This suggests that GLP-1 is strongly involved in the underlying mechanism of NO production in vivo. In conclusion, BE contributes to the improvement of vascular functions by promoting NO production. Regarding the putative underlying mechanism, GLP-1 secreted from intestinal cells by the polyphenols in BE activates eNOS in vascular endothelial cells.

The Potential of Hibiscus sabdariffa Linn in Inducing Glucagon-Like Peptide-1 via SGLT-1 and GLPR in DM Rats

Background

Glucagon-like peptide 1 (GLP-1) hormone is an incretin hormone that is secreted in the ileum and plays a role in the pancreas to increase insulin secretion, stimulate proliferation, and prevent pancreatic β-cell apoptosis. Currently, diabetes mellitus (DM) treatment based on GLP-1 work is being developed, for instance, from herbal plants such as Hibiscus sabdariffa Linn (H. sabdariffa). Therefore, this study aims to determine the potential of H. sabdariffa in GLP-1 secretion in the ileum and its action in pancreatic β-cells. In addition, this study also aims to determine the active ingredients of H. sabdariffa (Hib) that interact with sodium-glucose cotransporter-1 (SGLT-1) so that it can increase GLP-1 secretion in the ileum and interact with GLP-1 receptors (GLP-1R) in the pancreas.

Method

This experimental study used 24 experimental animals of Sprague-Dawley type (aged 8-10 weeks, weight 200-250 g) that were divided into 6 groups, namely, (i) normal (C), (ii) normal-Hib 200 (C-Hib200), (iii) normal-Hib 500 (C-Hib500), (iv) DM (C-DM), (v) DM-Hib200, and (vi) DM-Hib500. H. sabdariffa extract was given orally once a day for 5 weeks. Testing of GLP-1 levels in the ileum and pancreatic tissue was performed by enzyme-linked immunosorbent assay. The prediction of the interaction mechanism of the active substance H. sabdariffa against GLP-1 was done using molecular docking.

Results

There was a decrease in GLP-1 levels in the ileum of DM rats (p < 0.05). However, DM rats administered H. sabdariffa 500 mg/kg BW had GLP-1 levels that were the same as in normal rats (p > 0.05). This is due to active ingredients such as leucosin, which binds to SGLT-1. Administration of 500 mg/kg BW H. sabdariffa in DM rats resulted in GLP-1 levels in the pancreas that were the same as in normal rats (p > 0.05). In addition, the active ingredient of H. sabdariffa, delphinidin, binds to GLPR in the pancreas.

Conclusion

The active ingredient of H. sabdariffa can increase GLP-1 secretion in the ileum and can interact with G protein-linked receptors in the pancreas.

The Gastrointestinal Tract as Prime Site for Cardiometabolic Protection by Dietary Polyphenols

Substantial evidence from nutritional epidemiology links polyphenol-rich diets with reduced incidence of chronic disorders; however, biological mechanisms underlying polyphenol-disease relations remain enigmatic. Emerging evidence is beginning to unmask the contribution of the gastrointestinal tract on whole-body energy homeostasis, suggesting that the intestine may be a prime target for intervention and a fundamental site for the metabolic actions of polyphenols. During their transit through the gastrointestinal tract, polyphenols may activate enteric nutrient sensors ensuing appropriate responses from other peripheral organs to regulate metabolic homeostasis. Furthermore, polyphenols can modulate the absorption of glucose, attenuating exaggerated hormonal responses and metabolic imbalances. Polyphenols that escape absorption are metabolized by the gut microbiota and the resulting catabolites may act locally, activating nuclear receptors that control enteric functions such as intestinal permeability. Finally, polyphenols modulate gut microbial ecology, which can have profound effects on cardiometabolic health.

The Multifunctional Benefits of Naturally Occurring Delphinidin and Its Glycosides

Delphinidin (Del) and its glycosides are water-soluble pigments, belonging to a subgroup of flavonoids. They are health-promoting candidates for pharmaceutical and nutraceutical uses, as indicated by exhibiting antioxidation, anti-inflammation, antimicroorganism, antidiabetes, antiobesity, cardiovascular protection, neuroprotection, and anticancer properties. Glycosylation modification of Del is associated with increased stability and reduced biological activity. Del and its glycosides can be the alternative inhibitors of CBRs, ERα/β, EGFR, BCRP, and SGLT-1, and virtual docking indicates that the sugar moiety may not effectively interact with the active sites of the targets. Structure-based characteristics confer the multifunctional properties of Del and its glycosides. Because of their health-promoting effects, Del and its glycosides are promising and have been developed as potential pharmaceuticals. However, more investigation on the underlying mechanisms of Del and its glycosides in mediating cellular processes with high specificity are still needed. The research progression of Del and its glycosides over the last 10 years is comprehensively reviewed in this article.

Bioassay-guided fractionation and identification of antidiabetic compounds from the rind of Punica Granatum Var. nana

This study aimed to evaluate the antidiabetic potential of the rind of Punica granatum var. nana. Acute oral toxicity test revealed the safety profile of its ethanolic extract. The extract was administered at 200 mg/kg b.wt to streptozotocin-induced diabetic rats. Serum diagnostic markers of diabetes (insulin, glucose and glycated hemoglobin), inflammatory mediators (tumor necrosis factor-α, interleukin-6, and nitric oxide), and oxidative stress (total antioxidant capacity and reduced glutathione and malondialdehyde) were assayed. The ethanolic extract was further fractionated and assessed for the aforementioned bioactivities at two different doses (100 and 200 mg/kg b.wt). The results revealed that the ethyl acetate fraction of rind exhibited the highest activities. Using different chromatographic techniques, four compounds were isolated and identified as rutin, gallic acid, nictoflorin, and tulipanin. In conclusion: The ethyl acetate fraction of the rind of Punica granatum var. nana may provide a potential therapeutic approach for hyperglycemia.

Avoiding holiday seasonal weight gain with nutrient-supported intermittent energy restriction: a pilot study

This pilot randomised controlled study evaluated the effects of a nutrient-supported intermittent energy restriction nutrition programme to prevent weight gain in healthy overweight adults during the 6-week winter holiday period between Thanksgiving and New Year. For 52 d, twenty-two overweight adults (mean age 41·0 years, BMI 27·3 kg/m²) were assigned to either the nutrition programme (n 10; two fasting days of 730 kcal/d (3050 kJ/d) of balanced shake and dietary supplements to support weight management efforts, followed by 5 d of habitual diet) or a control group (n 12; habitual diet). A significant weight loss from baseline (pre-holiday 10 d before Thanksgiving) to day 52 (post-holiday 3 January) was observed in the nutrition programme (75·0 (sd 9·8) v. 76·3 (sd 9·8) kg; P < 0·05). Body weight did not significantly change in the control group and there was no between-group difference. Increases from baseline in fasting insulin (42·9 %; P = 0·0256), updated homoeostasis model assessment (HOMA2) (43 %; P = 0·025), LDL-cholesterol (8·4 %; P = 0·0426) and total cholesterol (7·1 %; P = 0·0154) levels were also reported in the control group. In the nutrition programme group, baseline HDL-cholesterol and TAG levels measured after two fasting days increased (13 %; P = 0·0245) and decreased (22·8 %; P = 0·0416), respectively. There was no significant change in HOMA2. Between-group differences in changes in insulin levels (P = 0·0227), total cholesterol:HDL-cholesterol ratio (P = 0·0419) and HOMA2 (P = 0·0210) were significant. Overall compliance rate was 98 % and no severe adverse events were reported. These preliminary findings suggest that this intermittent energy restriction intervention might support weight management efforts and help promote metabolic health during the winter holiday season.

Role of intestinal microecology in the regulation of energy metabolism by dietary polyphenols and their metabolites

Background

Polyphenols are a class of plant secondary metabolites with a variety of physiological functions. Polyphenols and their intestinal metabolites could greatly affect host energy metabolism via multiple mechanisms.

Objective

The objective of this review was to elaborate the role of intestinal microecology in the regulatory effects of dietary polyphenols and their metabolites on energy metabolism.

Methods

In this review, we illustrated the potential mechanisms of energy metabolism regulated by the crosstalk between polyphenols and intestinal microecology including intestinal microbiota, intestinal epithelial cells, and mucosal immune system.

Results

Polyphenols can selectively regulate the growth of susceptible microorganisms (eg. reducing the ratio of Firmicutes to Bacteroides, promoting the growth of beneficial bacteria and inhibiting pathogenic bacteria) as well as alter bacterial enzyme activity. Moreover, polyphenols can influence the absorption and secretion of intestinal epithelial cells, and alter the intestinal mucosal immune system.

Conclusion

The intestinal microecology play a crucial role for the regulation of energy metabolism by dietary polyphenols.

Blackcurrant Extract Ameliorates Hyperglycemia in Type 2 Diabetic Mice in Association with Increased Basal Secretion of Glucagon-Like Peptide-1 and Activation of AMP-Activated Protein Kinase

Blackcurrants are berries that contain high levels of anthocyanins, particularly delphinidin 3-rutinoside (D3R). Several studies have reported that the consumption of blackcurrant extract (BCE) lowers blood glucose levels and ameliorates glucose tolerance, but the mechanism underlying this effect remains unclear. Glucagon-like peptide-1 (GLP-1) and AMP-activated protein kinase (AMPK) are considered one of the most significant molecular targets for the prevention and treatment of type 2 diabetes. In this study, we showed that dietary BCE significantly reduced blood glucose concentration and improved glucose tolerance in type 2 diabetic mice (KK-A^y). The basal GLP-1 concentration in plasma was significantly increased in the BCE group accompanied by upregulation of prohormone convertase 1/3 (PC1/3), the enzyme that processes intestinal proglucagon. Moreover, the level of phospho-AMPKα protein in skeletal muscle was significantly increased in the BCE group, and this was increase accompanied by significant upregulation of glucose transporter 4 (Glut4) proteins in the plasma membrane of BCE group. In conclusion, dietary BCE significantly reduced blood glucose concentration and improved glucose tolerance in association with increased basal GLP-1 concentration in plasma, upregulation of PC1/3 expression, and translocation of Glut4 to the plasma membrane of skeletal muscle in type 2 diabetic mice; furthermore, these effects were accompanied by activation of AMPK. Our findings demonstrated that D3R-rich BCE may help prevent diabetes and allow the dosages of diabetes drugs to be reduced.

α7 Nicotinic Acetylcholine Receptor Regulates the Function and Viability of L Cells

Enteroendocrine L cells secrete the incretin hormone glucagon-like peptide-1 (GLP-1), and they also express the α7 nicotinic acetylcholine receptor (α7nAChR), which may regulate GLP-1 secretion. Here, GTS-21, a selective α7nAChR agonist, was used to examine the effect of α7nAChR activation in L-cell lines, mouse intestinal primary cell cultures, and C57BL/6 mice. GTS-21 stimulated GLP-1 secretion in vitro, and this effect was attenuated by an α7nAChR antagonist or by α7nAChR-specific small interfering RNA. Under in vitro cell culture conditions of glucotoxicity, GTS-21 restored GLP-1 secretion and improved L-cell viability while also acting in vivo to raise levels of circulating GLP-1 in mice. To assess potential signaling mechanisms underlying these actions of GTS-21, we first monitored Ca2+, cAMP, and phosphatidylinositol 3-kinase (PI3K) activity. As expected for a GLP-1 secretagogue promoting Ca2+ influx through α7nAChR cation channels, [Ca2+]i increased in response to GTS-21, but [cAMP]i was unchanged. Surprisingly, pharmacological inhibition of growth factor signaling pathways revealed that GTS-21 also acts on the PI3K-protein kinase B-mammalian target of rapamycin pathway to promote L-cell viability. Moreover, the Ca2+ chelator BAPTA-AM counteracted GTS-21‒stimulated PI3K activity, thereby indicating unexpected crosstalk of L-cell Ca2+ and growth factor signaling pathways. Collectively, these data demonstrate that α7nAChR activation enhances GLP-1 secretion by increasing levels of cytosolic Ca2+ while also revealing Ca2+- and PI3K-dependent processes of α7nAChR activation that promote L-cell survival.

Cyanidin and delphinidin modulate inflammation and altered redox signaling improving insulin resistance in high fat-fed mice

Consumption of diets high in fat and/or fructose content promotes tissue inflammation, oxidative stress, and insulin resistance, activating signals (e.g. NF-κB/JNK) that downregulate the insulin cascade. Current evidence supports the concept that select flavonoids can mitigate obesity and type 2 diabetes (T2D). This work investigated if supplementation with the anthocyanidins (AC) cyanidin and delphinidin could attenuate the adverse consequences of consuming a high fat diet (HFD) in mice. Consumption of an AC-rich blend mitigated HFD-induced obesity, dyslipidemia and insulin resistance (impaired responses to insulin and glucose). HFD-fed mice were characterized by increased liver lipid deposition and inflammation, which were also attenuated upon AC supplementation. HFD caused liver oxidative stress showing an increased expression of NADPH oxidases, generators of superoxide and H2O2, and high levels of oxidized lipid-protein adducts. This was associated with the activation of the redox sensitive signals IKK/NF-κB and JNK1/2, and increased expression of the NF-κB-regulated PTP1B phosphatase, all known inhibitors of the insulin pathway. In agreement with an improved insulin sensitivity, AC supplementation inhibited oxidative stress, NF-κB and JNK activation, and PTP1B overexpression. Thus, cyanidin and delphinidin consumption either through diet or by supplementation could be a positive strategy to control the adverse effects of Western style diets, including overweight, obesity, and T2D. Modulation of inflammation, oxidative stress, and NF-κB/JNK activation emerge as relevant targets of AC beneficial actions.

Curcumin as a functional food-derived factor: degradation products, metabolites, bioactivity, and future perspectives

Curcumin is a polyphenol found in turmeric (Curcuma longa), used as a spice, in food coloring, and as a traditional herbal medicine. It has been shown that curcumin has health benefits such as antioxidant, anti-inflammatory, and anticancer properties, improvement of brain function, and control of obesity and diabetes. However, native curcumin easily degrades and has low oral bioavailability, and a recent report has expressed doubt about curcumin's various effects. To overcome its low bioavailability, various curcumin formulations with enhanced bioavailability are currently being developed. This review discusses the chemistry, metabolism, and absorption of curcumin, to which various reported health benefits have been ascribed, as well as curcumin's degradation products and metabolites and their possible functions. Moreover, the research trend towards the obesity- and diabetes-preventing/suppressing aspects of curcumin and the latest case studies on highly water-dispersible and bioavailable curcumin formulations will be discussed. We summarize the challenges concerning research on curcumin's health benefits as follows: clarifying the relationship between curcumin's health benefits and the formation of curcumin-derived oxidation and degradation products and metabolites, determining whether curcumin itself or other components in turmeric are responsible for its effects, and conducting further human trials in which multiple research groups employ the same samples and conditions. High-bioavailability formulations would be useful in such future studies.

Epicatechin potentiation of glucose-stimulated insulin secretion in INS-1 cells is not dependent on its antioxidant activity

Epicatechin (EC) is a monomeric flavan-3-ol. We have previously demonstrated that glucose-intolerant rats fed flavan-3-ols exhibit improved pancreatic islet function corresponding with an increase in circulating EC-derived metabolites. Thus, we speculate that EC may act as a cellular signaling molecule in vivo to modulate insulin secretion. In this study we further examined the effects of different concentrations of EC on H2O2 or hyperglycemia-induced ROS production, as well as on saturated fatty acid (SFA)-impaired glucose-stimulated insulin secretion (GSIS) in INS-1 cell line in vitro. We showed that EC at a high concentration (30 μmol/L), but not a low concentration (0.3 μmol/L), significantly decreased H2O2 or hyperglycemia-induced ROS production in INS-1 cells. However, EC (0.3 μmol/L) significantly enhanced SFA-impaired GSIS in INS-1 cells. Addition of KN-93, a CaMKII inhibitor, blocked the effect of EC on insulin secretion and decreased CaMKII phosphorylation. Addition of GW1100, a GPR40 antagonist, significantly attenuated EC-enhanced GSIS, but only marginally affected CaMKII phosphorylation. These results demonstrate that EC at a physiological concentration promotes GSIS in SFA-impaired β-cells via activation of the CaMKII pathway and is consistent with its function as a GPR40 ligand. The findings support a role for EC as a cellular signaling molecule in vivo and further delineate the signaling pathways of EC in β-cells.

Flavonoid-rich extract of Chromolaena odorata modulate circulating GLP-1 in Wistar rats: computational evaluation of TGR5 involvement

Chromolaena odorata is a major bio-resource in folkloric treatment of diabetes. In the present study, its anti-diabetic component and underlying mechanism were investigated. A library containing 140 phytocompounds previously characterized from C. odorata was generated and docked (Autodock Vina) into homology models of dipeptidyl peptidase (DPP)-4, Takeda-G-protein-receptor-5 (TGR5), glucagon-like peptide 1 (GLP1) receptor, renal sodium dependent glucose transporter (SGLUT)-1/2 and nucleotide-binding oligomerization domain (NOD) proteins 1&2. GLP-1 gene (RT-PCR) modulation and its release (EIA) by C. odorata were confirmed in vivo. From the docking result above, TGR5 was identified as a major target for two key C. odorata flavonoids (5,7-dihydroxy-6-4-dimethoxyflavanone and homoesperetin-7-rutinoside); sodium taurocholate and C. odorata powder included into the diet of the animals both raised the intestinal GLP-1 expression versus control (p < 0.05); When treated with flavonoid-rich extract of C. odorata (CoF) or malvidin, circulating GLP-1 increased by 130.7% in malvidin-treated subjects (0 vs. 45 min). CoF treatment also resulted in 128.5 and 275% increase for 10 and 30 mg/kg b.w., respectively.

CONCLUSIONS

The results of this study support that C. odorata flavonoids may modulate the expression of GLP-1 and its release via TGR5. This finding may underscore its anti-diabetic potency.

Canagliflozin potentiates GLP-1 secretion and lowers the peak of GIP secretion in rats fed a high-fat high-sucrose diet

The glucose-induced secretion of incretins, including glucagon-like peptide-1 (GLP-1) and glucose-dependent insulinotropic polypeptide (GIP), is dependent on luminal glucose levels and transport of glucose via the sodium-glucose transporter 1 (SGLT1) in the small intestine. Because GLP-1 and GIP function in decreasing and increasing the body weight, respectively, we aimed to analyze the effect of transient inhibition of SGLT1 by canagliflozin on incretin secretion in an obese rat model. Male Sprague-Dawley rats were maintained on a high-fat high-sucrose diet for 6-7 weeks, and plasma GLP-1 and GIP levels were measured during an oral glucose tolerance test (OGTT). In addition, GLP-1 secretion was examined in a murine GLP-1 producing enteroendocrine cell line, GLUTag. Concomitant administration of 10 mg/kg canagliflozin with glucose loading suppressed glucose excursion, increased total GLP-1 levels, and reduced total GIP levels in systemic circulation, as revealed in the OGTT. Total and active GLP-1 levels were increased in portal blood, whereas total and active GIP levels tended to be decreased 15 min after the administration of canagliflozin with glucose. Canagliflozin (at 0.1-30 μM) did not directly affect release of GLP-1 in vitro. These results suggest that the oral administration of canagliflozin suppresses GIP secretion via the inhibition of SGLT1 in the upper part of the intestine and enhances GLP-1 secretion by increasing the glucose delivery to the lower part of the small intestine in an obese rodent model.

Contribution of anthocyanin-rich foods in obesity control through gut microbiota interactions

Obesity is characterized by low-grade inflammation and a number of metabolic disorders. Distal gut microbes' content (microbiota) is not yet fully understood but evidence shows that it is influenced by internal and external factors that modulate its composition and function. The evidence that gut microbiota composition can differ between healthy and obese individuals, as well as for those who maintain specific dietary habits, has led to the study of this environmental factor as a key link between the pathophysiology of obesity and gut microbiota. Data obtained about the role of anthocyanins (ACNs) in microbiota may lead to different strategies to manipulate bacterial populations and promote health. Anthocyanins have been identified as modulators of gut microbiota that contribute to obesity control and these bioactive compounds should be considered to have a prebiotic action. This review addresses the relevance of knowledge about the influence of anthocyanins-rich food consumption on microbiota, and their health-promoting potential in the pathophysiology of obesity. © 2017 BioFactors, 43(4):507-516, 2017.

Delphinidin 3-rutinoside-rich blackcurrant extract ameliorates glucose tolerance by increasing the release of glucagon-like peptide-1 secretion

Glucagon‐like peptide‐1 (GLP‐1) is an incretin that is secreted from enteroendocrine L‐cells. Dietary factor‐stimulation of endogenous GLP‐1 is a promising strategy for increasing the action of GLP‐1. Recent studies have shown that berries rich in anthocyanins improve insulin sensitivity and reduce the risk of type 2 diabetes. Our previous study found that the anthocyanin delphinidin 3‐rutinoside (D3R) significantly increases GLP‐1 secretion in GLUTag cells (enteroendocrine L cell line). Blackcurrants are berries that contain high levels of anthocyanins, particularly D3R. Pre‐administered blackcurrant extract (BCE) 5 mg/kg body weight (1 mg D3R/kg) significantly ameliorated glucose tolerance after intraperitoneal glucose injection in rats by stimulating the secretion of GLP‐1 and subsequently inducing insulin secretion. D3R did not break down significantly in the gastrointestinal tract for at least 45−60 min after BCE was administered, suggesting that BCE‐induced GLP‐1 secretion is mainly mediated by D3R and not its degradation products. These findings demonstrate the novel biological function of D3R‐rich BCE as a GLP‐1 secretagogue. An increase in endogenous GLP‐1 secretion induced by BCE may help to reduce the dosages of diabetic medicines and prevent diabetes.

Delphinidin Reduces Glucose Uptake in Mice Jejunal Tissue and Human Intestinal Cells Lines through FFA1/GPR40

Anthocyanins are pigments with antihyperglycemic properties, and they are potential candidates for developing functional foods for the therapy or prevention of Diabetes mellitus type 2 (DM2). The mechanism of these beneficial effects of anthocyanins are, however, hard to explain, given their very low bioavailability due to poor intestinal absorption. We propose that free fatty acid receptor 1 (FFA1, also named GPR40), is involved in an inhibitory effect of the anthocyanidin delphinidin over intestinal glucose absorption. We show the direct effects of delphinidin on the intestine using jejunum samples from RF/J mice, and the human intestinal cell lines HT-29, Caco-2, and NCM460. By the use of specific pharmacological antagonists, we determined that delphinidin inhibits glucose absorption in both mouse jejunum and a human enterocytic cell line in a FFA1-dependent manner. Delphinidin also affects the function of sodium-glucose cotransporter 1 (SGLT1). Intracellular signaling after FFA1 activation involved cAMP increase and cytosolic Ca²⁺ oscillations originated from intracellular Ca²⁺ stores and were followed by store-operated Ca²⁺ entry. Taken together, our results suggest a new GPR-40 mediated local mechanism of action for delphinidin over intestinal cells that may in part explain its antidiabetic effect. These findings are promising for the search for new prevention and pharmacological treatment strategies for DM2 management.

Curcumin improves glucose tolerance via stimulation of glucagon-like peptide-1 secretion

SCOPE

Glucagon-like peptide-1 (GLP-1) is a type of incretin secreted from enteroendocrine L-cells. Our previous studies demonstrated that curcumin (a yellow pigment of turmeric) significantly increases the secretion of GLP-1 in enteroendocrine L cell line (GLUTag cells). However, it is not clear whether its action in vivo directly enhances GLP-1 secretion, which then leads to a reduction in blood glucose levels via the stimulation of insulin secretion. In addition, the molecular target of curcumin-induced GLP-1 secretion has not been clarified.

METHODS AND RESULTS

Glucose tolerance was significantly improved in rats after pre-administered curcumin (1.5 mg/kg) followed by intraperitoneal glucose injections via the stimulation of GLP-1 secretion and the induction of insulin secretion. In GLUTag cells, curcumin-induced GLP-1 secretion was associated with G protein-coupled receptor (GPR) 40/120. Furthermore, the glucose-lowering effect induced by curcumin was significantly reduced after the administration of a GPR40/120 antagonist in rats.

CONCLUSION

These findings demonstrate the biological function of curcumin as a GLP-1 secretagogue and the possible molecular target that mediates GLP-1 secretion. Increases in the secretion of endogenous GLP-1 induced by curcumin may allow the dosages of other diabetic medicines to be reduced and aid in the prevention of diabetes.