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

Natural Products and Diabetes: (-)-Epicatechin and Mechanisms Involved in the Regulation of Insulin Sensitivity

Type 2 diabetes (T2D) is a disease that occurs when cells do not respond normally to insulin, a condition called insulin resistance, which leads to high blood glucose levels. Although it can be treated pharmacologically, dietary habits beyond carbohydrate restriction can be highly relevant in the management of T2D. Emerging evidence supports the possibility that natural products (NPs) could contribute to managing blood glucose or counteract the undesirable effects of hyperglycemia and insulin resistance. This chapter summarizes the relevant preclinical evidence involving the flavonoid (-)-epicatechin (EC) in the optimization of glucose homeostasis, reducing insulin resistance and/or diabetes-associated disorders. Major effects of EC are observed on (i) intestinal functions, including digestive enzymes, glucose transporters, microbiota, and intestinal permeability, and (ii) redox homeostasis, including oxidative stress and inflammation. There is still a need for further clinical studies to confirm the in vitro and rodent data, allowing recommendations for EC, particularly in prediabetic and T2D patients. The collection of similar data and the lack of clinical evidence for EC is also applicable to other NPs.

Effects of epicatechin on cardiovascular function in middle-aged diet-induced obese rat models of metabolic syndrome

The current study aimed to investigate the cardiovascular effects of epicatechin, a flavonoid found in green tea and cocoa, in attenuating complications associated with metabolic syndrome in diet-induced obese rats. Male Wistar-Kyoto (WKY) rats aged 16 weeks were fed either standard rat chow or given a high-fat-high-carbohydrate (HFHC) diet for 20 weeks. Epicatechin treatment (5 mg/kg/d) was administered to a subset of WKY rats commencing at week 8 of the 20 week HFHC feeding period. Body weights, food, water and energy intakes, blood pressure, heart rate and glucose tolerance were measured throughout the treatment period. Oxidative stress and inflammatory markers, lipid levels, cardiac collagen deposition, cardiac electrical function, aortic and mesenteric vessel reactivity were examined after the treatment. Twenty weeks of HFHC feeding in WKY rats resulted in the development of metabolic syndrome indicated by the presence of abdominal obesity, dyslipidaemia, glucose intolerance and increased blood pressure. Epicatechin treatment was found to enhance the oxidative stress status in HFHC groups through an increase in serum nitric oxide levels and a decrease in 8-isoprostane concentrations. Furthermore, WKY-HFHC rats displayed a decrease in IL-6 levels. The lipid profiles in HFHC groups showed improvement, with a decrease in LDL-cholesterol and TAG and an increase in HDL-cholesterol levels observed in WKY-HFHC rats. However, epicatechin was not effective in preventing weight gain, glucose intolerance or hypertension in HFHC fed rats. Overall, the results of this study suggest that epicatechin has the potential to improve the underlying mechanisms associated with metabolic syndrome in obese rats.

Synergistic Effect of a Flavonoid-Rich Cocoa-Carob Blend and Metformin in Preserving Pancreatic Beta Cells in Zucker Diabetic Fatty Rats

The loss of functional beta-cell mass in diabetes is directly linked to the development of diabetic complications. Although dietary flavonoids have demonstrated antidiabetic properties, their potential effects on pancreatic beta-cell preservation and their synergistic benefits with antidiabetic drugs remain underexplored. We have developed a potential functional food enriched in flavonoids by combining cocoa powder and carob flour (CCB), which has shown antidiabetic effects. Here, we investigated the ability of the CCB, alone or in combination with metformin, to preserve pancreatic beta cells in an established diabetic context and their potential synergistic effect. Zucker diabetic fatty rats (ZDF) were fed a CCB-rich diet or a control diet, with or without metformin, for 12 weeks. Markers of pancreatic oxidative stress and inflammation, as well as relative beta-cell mass and beta-cell apoptosis, were analyzed. Results demonstrated that CCB feeding counteracted pancreatic oxidative stress by enhancing the antioxidant defense and reducing reactive oxygen species. Moreover, the CCB suppressed islet inflammation by preventing macrophage infiltration into islets and overproduction of pro-inflammatory cytokines, along with the inactivation of nuclear factor kappa B (NFκB). As a result, the CCB supplementation prevented beta-cell apoptosis and the loss of beta cells in ZDF diabetic animals. The observed additive effect when combining the CCB with metformin underscores its potential as an adjuvant therapy to delay the progression of type 2 diabetes.

Urinary Metabolomics Study on the Protective Role of Cocoa in Zucker Diabetic Rats via 1H-NMR-Based Approach

Cocoa constitutes one of the richest sources of dietary flavonoids with demonstrated anti-diabetic potential. However, the metabolic impact of cocoa intake in a diabetic context remains unexplored. In this study, metabolomics tools have been used to investigate the potential metabolic changes induced by cocoa in type 2 diabetes (T2D). To this end, male Zucker diabetic fatty rats were fed on standard (ZDF) or 10% cocoa-rich diet (ZDF-C) from week 10 to 20 of life. Cocoa supplementation clearly decreased serum glucose levels, improved glucose metabolism and produced significant changes in the urine metabolome of ZDF animals. Fourteen differential urinary metabolites were identified, with eight of them significantly modified by cocoa. An analysis of pathways revealed that butanoate metabolism and the synthesis and degradation of branched-chain amino acids and ketone bodies are involved in the beneficial impact of cocoa on diabetes. Moreover, correlation analysis indicated major associations between some of these urine metabolites (mainly valine, leucine, and isoleucine) and body weight, glycemia, insulin sensitivity, and glycated hemoglobin levels. Overall, this untargeted metabolomics approach provides a clear metabolic fingerprint associated to chronic cocoa intake that can be used as a marker for the improvement of glucose homeostasis in a diabetic context.

Nutrition in the management of type 2 diabetes mellitus: review

Type 2 diabetes mellitus (T2DM) is the most prevalent disease and becoming a serious public health threat worldwide. In recent years, numerous effective T2DM intervention regimens have been developed, with promising results. However, these regimens are not usually economically available, and they are not well tolerated due to treatment-related toxicities. The focus nowadays is to identify new effective therapeutic agents, with relatively low cost and low toxicity, which can be used regularly to control a progression of T2DM in the prediabetic population. Accordingly, there has been growing attention in herbal remedies that can be presented into the general population with the tiniest side effects and the maximal preventive outcome. This article reviews recent publications in experimental models of T2DM not revised before, and supporting the potential use of nutraceuticals and phytochemicals through different mechanisms with promising results in the context of T2DM.

Optimum biscuit from Musa sapientum L. and Vigna unguiculata L. composite flour: effect on pancreatic histology, biochemical and hematological parameters of diabetic rats

This study investigated the effect of consumption of an optimum biscuit from composite flour of Musa sapientum L. ('banana cochon') and Vigna unguiculata L. (cowpea) on the pancreatic histology, biochemical and hematological parameters of streptozotocin-induced diabetic Wistar rats. The optimum biscuit was evaluated for its chemical properties and glycaemic index. The weekly fasting blood glucose level, food intake and weight of the rats were recorded. The effect of 28 days' consumption of different percentages of optimum biscuit with/without Metformin was also evaluated on the pancreatic histology, biochemical and hematological parameters of rats. Results showed that, the optimum biscuit is rich in minerals (potassium, magnesium and calcium), dietary fibre (9.4%) and is a low glycaemic index product (50.91%). Also, the optimum biscuit significantly lowered/maintained the blood glucose level of diabetic rats even though the weekly weights of the rats were reduced while food intake increased. Nonetheless, the hematological parameters of the treated diabetic rats were significantly (P < 0.05) improved when compared to the untreated diabetic rats groups. With the exception of total serum protein, other biochemical parameters such as serum creatinine, urea, alanine aminotransferase, alkaline phosphatase, aspartate aminotransferase and bilirubin in the treated diabetic groups were significantly (P < 0.05) reduced or closer to those of non-diabetic rats. The serum cholesterol, triglyceride, low-density lipoprotein levels were significantly (p < 0.05) reduced while the HDL level significantly increased in treated diabetic groups. Histological examination of the pancreas showed that treatment of diabetic groups with optimum biscuit was able to slow down the destruction (protection) of beta-cells. Thus, optimum biscuit could be used to improve the health status during the management and prevention of complications in diabetic patients.

Benefits of Polyphenols and Methylxanthines from Cocoa Beans on Dietary Metabolic Disorders

Theobroma cacao L. is an ancestral cultivated plant which has been consumed by various populations throughout history. Cocoa beans are the basic material occurring in the most consumed product in the world, namely chocolate. Their composition includes polyphenols, methylxanthines, lipids and other compounds that may vary qualitatively and quantitatively according to criteria such as variety or culture area. Polyphenols and methylxanthines are known as being responsible for many health benefits, particularly by preventing cardiovascular and neurodegenerative diseases. Recent studies emphasized their positive role in dietary metabolic disorders, such as diabetes and weight gain. After a brief presentation of cocoa bean, this review provides an overview of recent research activities highlighting promising strategies which modulated and prevented gastro-intestinal metabolism dysfunctions.

Proanthocyanidins and Where to Find Them: A Meta-Analytic Approach to Investigate Their Chemistry, Biosynthesis, Distribution, and Effect on Human Health

Proanthocyanidins (PACs) are a class of polyphenolic compounds that are attracting considerable interest in the nutraceutical field due to their potential health benefits. However, knowledge about the chemistry, biosynthesis, and distribution of PACs is limited. This review summarizes the main chemical characteristics and biosynthetic pathways and the main analytical methods aimed at their identification and quantification in raw plant matrices. Furthermore, meta-analytic approaches were used to identify the main plant sources in which PACs were contained and to investigate their potential effect on human health. In particular, a cluster analysis identified PACs in 35 different plant families and 60 different plant parts normally consumed in the human diet. On the other hand, a literature search, coupled with forest plot analyses, highlighted how PACs can be actively involved in both local and systemic effects. Finally, the potential mechanisms of action through which PACs may impact human health were investigated, focusing on their systemic hypoglycemic and lipid-lowering effects and their local anti-inflammatory actions on the intestinal epithelium. Overall, this review may be considered a complete report in which chemical, biosynthetic, ecological, and pharmacological aspects of PACs are discussed.

Dietary Flavonoids and Insulin Signaling in Diabetes and Obesity

Type 2 diabetes (T2D) and obesity are relevant worldwide chronic diseases. A common complication in both pathologies is the dysregulation of the insulin-signaling pathway that is crucial to maintain an accurate glucose homeostasis. Flavonoids are naturally occurring phenolic compounds abundant in fruits, vegetables and seeds. Rising evidence supports a role for the flavonoids against T2D and obesity, and at present, these compounds are considered as important potential chemopreventive agents. This review summarizes in vitro and in vivo studies providing data related to the effects of flavonoids and flavonoid-rich foods on the modulation of the insulin route during T2D and obesity. Notably, few human studies have evaluated the regulatory effect of these phenolic compounds at molecular level on the insulin pathway. In this context, it is also important to note that the mechanism of action for the flavonoids is not fully characterized and that a proper dosage to obtain a beneficial effect on health has not been defined yet. Further investigations will contribute to solve all these critical challenges and will enable the use of flavonoids to prevent, delay or support the treatment of T2D and obesity.

Significantly hypoglycemic effect of a novel functional bread rich in mulberry bark and improving the related functions of liver, pancreas, and kidney, on T2D mice

To develop a novel functional food with lowering blood glucose for diabetics, the mixed bread containing mulberry branch bark powder (MBBP) was used for the oral administration of the type 2 diabetic (T2D) mice induced by streptozocin (STZ), high-fat and high-sugar diet for 7 weeks. 5%, 10%, and 15% MBBP bread diets had a significatively positive influence on the biochemical indicators, histological examination, and immunohistochemistry observations in T2D mice. The 15% MBBP-rich bread diet evidently retarded loss weight of T2D mice, and decreased in FBG by about 55% and in glycosylated hemoglobin (HbA1c) levels by about 30%. Its glucose tolerance and serum insulin levels were very close to normal level. The abnormal lipid metabolism and insulin-related index of T2D mice in both the 10% and 15% MBBP bread diet groups were partly reversed. The Western blotting results showed that the expression levels of key proteins in PI3K/AKT signaling pathway were decreased and expression levels of immunoproteins PPARγ, TNF-α, P65, and IL6 were increased. In general, oral MBBP bread diets effectively restored some functions and repaired damage to the pancreas, liver, and kidney in T2D mice. Therefore, MBBP is potential to develop into a novel functional food additive with significantly hypoglycemic effect.

Cocoa ameliorates renal injury in Zucker diabetic fatty rats by preventing oxidative stress, apoptosis and inactivation of autophagy

Redox balance, autophagy and apoptosis are main processes involved in the development of diabetic nephropathy. Epidemiological and animal studies suggest that cocoa might reduce the risk of diabetic complications. However, the molecular mechanisms responsible for these potential preventive activities and whether cocoa exerts beneficial effects on dysregulated signalling pathways involved in cellular antioxidant defence, autophagy and apoptosis in the diabetic kidney remain largely unknown. Therefore, this work investigated the effect of a cocoa-rich diet on the mentioned processes in the renal cortex of Zucker Diabetic Fatty (ZDF) rats. Male ZDF rats were fed either a control or cocoa-rich diet (10%), and Zucker lean animals received the control diet (10-20 weeks-of-life). ZDF rats fed with cocoa decreased body weight and glucose and insulin levels, and improved renal function. Cocoa intake further prevented the enhanced renal cortical oxidative stress in diabetic rats by regulating the antioxidant defence system and close-related proteins to cytoprotection and cell response; thus, cocoa diminished oxidative markers (reactive oxygen species and carbonyl groups) and NADPH-oxidase-4 levels, and restored key enzymatic antioxidant activities (superoxide dismutase and catalase), nuclear-erythroid-2-related factor-2, and ERK-MAPK levels, as well as sirtuin-1/5'-AMP-activated-protein kinase signalling. Moreover, in ZDF rats cocoa-rich diet contributed to alleviation of the renal cortical injury through autophagy activation (p62 upregulation, and downregulation of beclin-1 and LC3), and inhibition of apoptosis (Bcl-xL stimulation and suppression of Bax and caspases-9 and -3). These findings provide the first in vivo evidence on the molecular mechanisms of cocoa to circumvent renal cortical damage that involve improvement of antioxidant competences, stimulation of autophagy and suppression of apoptosis in ZDF rats.

Salvianolic Acid A Ameliorates Early-Stage Atherosclerosis Development by Inhibiting NLRP3 Inflammasome Activation in Zucker Diabetic Fatty Rats

Salvianolic acid A (SAA), an important bioactive polyphenolic acid found in Salvia miltiorrhiza Bunge, may be used for treating metabolic disorders due to its anti-inflammatory activity. Since chronic inflammation plays an important role in type 2 diabetes mellitus (T2DM) complicated with atherosclerosis (AS), SAA may have beneficial effects on AS. Here, we evaluated the effects of SAA on metabolic disorders in male Zucker diabetic fatty (ZDF) rats induced by a high-fat diet and Vitamin D3 injections. Compared with the model group, the SAA high dosage (1 mg/kg) group exhibited decreased hemoglobin A1C levels but unchanged blood glucose levels. The disrupted lipid profiles were ameliorated by SAA, with significantly decreased levels of blood cholesterol, LDL-C and triglyceride. The protective effects of SAA against early AS were further confirmed by histopathological examination of aortic tissues. In addition, we observed that SAA decreased serum hs-CRP levels and suppressed the activation of NLRP3 inflammasome and NF-κB signaling in aortic tissues of ZDF rats. Collectively, our results demonstrate the potential of SAA to alleviate AS and T2DM in ZDF rats as a result of its anti-inflammatory effects.

Cacao extract enriched in polyphenols prevents endocrine-metabolic disturbances in a rat model of prediabetes triggered by a sucrose rich diet

ETHNOPHARMACOLOGICAL RELEVANCE

Cocoa extracts rich in polyphenols are used as potential agent for treating diabetes. Cocoa polyphenols have been proved to ameliorate important hallmarks of type-2 diabetes (T2D). They can regulate glucose levels by increasing insulin secretion, promoting β-cell proliferation and a reduction of insulin resistance. In addition, epidemiological evidence indicates that consumption of flavonoid decreases the incidence of T2D.

AIM OF THE STUDY

T2D is preceded by a prediabetic state in which the endocrine-metabolic changes described in T2D are already present. Since epidemiological evidence indicates that consumption of flavonoid decreases its incidence, we evaluated possible preventive effects of polyphenol-enriched cocoa extract on a model of prediabetes induced by sucrose.

MATERIALS AND METHODS

We determined circulating parameters and insulin sensitivity indexes, liver protein carbonyl groups and reduced glutathione, liver mRNA expression levels of lipogenic enzymes, expression of different pro-inflammatory mediators, fructokinase activity and liver glycogen content. For that, radioimmunoassay, real-time polymerase chain reaction, Western blot, spectrophotometry, and immunohistochemistry were used.

RESULTS

We demonstrated that sucrose administration triggered hypertriglyceridemia, insulin-resistance, and liver increased oxidative stress and inflammation markers compared to control rats. Additionally, we found an increase in glycogen deposit, fructokinase activity, and lipogenic genes expression (SREBP-1c, FAS and GPAT) together with a decrease in P-Akt and P-eNOS protein content (P < 0.05). Sucrose-induced insulin resistance, hepatic carbohydrate and lipid dysmetabolism, oxidative stress, and inflammation were effectively disrupted by polyphenol-enriched cocoa extract (PECE) co-administration (P < 0.05).

CONCLUSION

Dietary administration of cocoa flavanols may be an effective and complementary tool for preventing or reverting T2D at an early stage of its development (prediabetes).

Peptides from walnut (Juglans mandshurica Maxim.) protect hepatic HepG2 cells from high glucose-induced insulin resistance and oxidative stress

Schematic of the mechanism underlying the protection of hepatic HepG2 cells against high glucose-induced insulin resistance and oxidative stress by walnut-derived peptides.

Antidiabetic Effects of Soluble Dietary Fiber from Steam Explosion-Modified Black Soybean Hull in Low-Dose Streptozotocin-Induced Type 2 Diabetic Mouses

This paper studies the antidiabetic effects of soluble dietary fiber (SDF) from steam explosion-modified black soybean hull in low-dose streptozotocin- (STZ-) induced type 2 diabetic mouses. Male C57/BL6 mouses were divided into 4 groups: control (nondiabetic, no SDF intake), model (diabetes only), metformin (metformin: 100 mg/kg body weight), and SDF (SDF: 600 mg/kg body weight). Four weeks post-SDF treatment, treatment of SDF decreased the weight gain of diabetic mouses, normalised the blood glucose level, and reduced the serum cholesterol, serum insulin, leptin, glucagon-like peptide, total cholesterol, triglyceride, low-density lipoprotein cholesterol, arteriosclerosis index, aspartate aminotransferase activity, and malondialdehyde. It also increased high-density lipoprotein cholesterol, adiponectin, glycopeptide peroxidase, superoxide dismutase activity and repaired the pancreatic injury of the diabetic mouses. Our research results show that SDF has the potential for use in type 2 diabetes treatment.

Gynura divaricata ameliorates hepatic insulin resistance by modulating insulin signalling, maintaining glycolipid homeostasis and reducing inflammation in type 2 diabetic mice

Diabetes mellitus, one of the fastest growing epidemics worldwide, has become a serious health problem in modern society. Gynura divaricata (GD), an edible medicinal plant, has been shown to have hypoglycaemic effects. The molecular mechanisms by which GD improves hepatic insulin resistance (IR) in mice with type 2 diabetes (T2D) remain largely unknown. The aerial parts of GD were prepared in a lyophilized powder, which was added into the diet of T2D mice for 4 weeks. GD could result in an obvious decrease in fasting blood glucose and insulin levels in T2D mice. Meanwhile, the underlying mechanisms involved in the insulin-signalling pathway, glucose metabolism, lipid metabolism and inflammatory reaction in the liver tissue were also investigated by western blot, which indicated that GD further ameliorated hepatic IR by activating the PI3K/p-AKT pathway, decreasing the levels of hepatic phosphoenolpyruvate carboxykinase and glucose-6-phosphatase and increasing the levels of glucokinase and peroxisome proliferator-activated receptor-γ in the livers of T2D mice. GD has the potential to alleviate both hyperglycaemia and hepatic IR in T2D mice. Therefore, GD might be a promising functional food or medicine for T2D treatment.

Role of Theobromine in Cocoa's Metabolic Properties in Healthy Rats

Cocoa is rich in polyphenols and methylxanthines, and it has been reported that its consumption, among other properties, has beneficial effects on metabolism. This study aimed to investigate the role of theobromine in cocoa's metabolic properties in healthy rats. In addition to morphometric measurements, biochemical markers of lipids and glucose metabolism and gene expression of molecules related to immune cells in adipose and hepatic tissues were assessed after 7 or 18 days of diet. Additionally, a metabolomic analysis was carried out at day 7. This study revealed the presence of six discriminant metabolites in plasma due to the diets. Moreover, the results showed that theobromine is the main responsible factor for cocoa's effects on body weight gain as well as on lipid and glucose metabolism. The effects on body weight and lipids appeared as early as after 7 days of diet, whereas those affecting glucose metabolism required a longer intervention.

A 6-week supplementation with grape pomace to subjects at cardiometabolic risk ameliorates insulin sensitivity, without affecting other metabolic syndrome markers

Grape polyphenols have shown a promising role in the modulation of metabolic syndrome (MetS), mostly in animal models. However, clinical studies are scarce and they usually only consider a fraction of polyphenols, ignoring the non-extractable polyphenols (high molecular weight compounds or associated with macromolecules such as dietary fibre). This study aimed at evaluating the effect of grape pomace, rich in both extractable and non-extractable polyphenols, on markers of MetS. Fifty subjects (22 women) aged 20-65 with at least two MetS factors were randomly assigned to the product (daily dose of 8 g of dried grape pomace) or to the control group in a 6 week crossover design with a 4 week wash-out. Samples were collected at the beginning and at the end of both periods; half of the participants were subjected to an oral glucose tolerance test at the beginning and the end of the supplementation period. Grape pomace supplementation significantly improved fasting insulinaemia (p < 0.01), without affecting other cardiometabolic risk parameters. A tendency towards an improvement in postprandial insulinaemia was observed, particularly in those subjects with higher fasting insulin levels. Therefore, supplementation with grape pomace may be a strategy for improving insulin sensitivity in subjects at high cardiometabolic risk.

(-)-Epicatechin in the control of glucose homeostasis: Involvement of redox-regulated mechanisms

Emerging evidence supports a beneficial action of the flavan-3-ol (-)-epicatechin (EC) on insulin sensitivity and potential impact on the development/progression of type 2 diabetes (T2D). In humans, supplementation with EC-rich foods, extracts, and pure EC improves insulin sensitivity and glucose tolerance in normal weight, overweight, obese and T2D individuals. These effects of EC are also observed in rodent models of diet-induced obesity and T2D. The events involved in the development of insulin resistance and T2D are multiple and interrelated. EC has been shown to inhibit inflammation, oxidative and endoplasmic reticulum stress, to modulate mitochondrial biogenesis and function, and to regulate events in the gastrointestinal tract and the pancreas that impact glucose homeostasis. A downregulation of oxidant production, particularly through direct inhibition or suppression of NADPH oxidase expression, and of redox sensitive signals (NF-κB, JNK1/2) that inhibit the insulin pathway, appear to be central to the beneficial actions of EC on insulin sensitivity. Overall, EC seems to have a positive role in the regulation of glucose homeostasis, however definitive answers on its importance for the management of T2D will depend on further clinical and mechanistic studies.

Galangin and Pinocembrin from Propolis Ameliorate Insulin Resistance in HepG2 Cells via Regulating Akt/mTOR Signaling

Insulin resistance has a critical role in type 2 diabetes. The aim of this study was to investigate the effect of pinobanksin, galangin, chrysin, and pinocembrin from propolis on insulin resistance. Our study shows that galangin and pinocembrin can ameliorate insulin resistance; on the contrary, pinobanksin and chrysin are ineffective. Galangin and pinocembrin treatments substantially increase glucose consumption and glycogen content by enhancing the activities of hexokinase and pyruvate kinase. Galangin treatment with 80 μM increased hexokinase and pyruvate kinase activities by 21.94% and 29.12%, respectively. Moreover, we hypothesize that galangin and pinocembrin may have a synergistic effect on the improvement of insulin resistance via Akt/mTOR signaling pathway, through distinctly upregulating the phosphorylation of IR, Akt, and GSK3β and remarkably downregulating the phosphorylation of IRS. Most notably, this is the first study to our knowledge to investigate pinocembrin about the alleviation of insulin resistance. Our results provide compelling evidence for the depth development of propolis products to ameliorate insulin resistance.

Protective effects of (-)-epicatechin and the colonic metabolite 3,4-dihydroxyphenylacetic acid against glucotoxicity-induced insulin signalling blockade and altered glucose uptake and production in renal tubular NRK-52E cells

Glucotoxicity (high levels of glucose) is a major cause in the pathogenesis of diabetes. Evidences indicate that (-)-epicatechin (EC) and colonic metabolites derived from flavonoid intake could possess antidiabetic effects, but the mechanisms for their preventive activities related to glucose homeostasis and insulin signalling in the kidney remain largely unknown. This work is aimed to investigate the effect of EC and main colonic phenolic acids derived from flavonoid intake, i.e. 2,3-dihydroxybenzoic-acid, 3,4-dihydroxyphenylacetic-acid (DHPAA) and 3-hydroxyphenylpropionic-acid, on insulin signalling, and glucose production and uptake in renal tubular proximal NRK-52E cells treated with high glucose. Pre-treatment with EC or DHPAA prevented the decreased tyrosine-phosphorylated and total levels of IR caused by high glucose. EC and DHPAA pre-treatment also avoided the inactivation of the PI3K/AKT pathway and AMPK, and the elevation of PEPCK levels induced by high glucose. Additionally, EC and DHPAA pre-treatment alleviated the altered glucose uptake and production caused by high glucose, although this protective effect was abrogated when AKT and AMPK were inhibited. These results suggest EC and DHPAA prevent or delay a potential dysfunction of NRK-52E cells treated with high glucose through the attenuation of the insulin signalling blockade and the modulation of glucose homeostasis via AKT and AMPK.

Antidiabetic Effects of the Auricularia auricular Polysaccharides Simulated Hydrolysates in Experimental Type-2 Diabetic Rats

A model of type-2 diabetes mellitus (T2DM) using high-fat diet and low-dose STZ was established to assess the antidiabetic effects of Auricularia auricular polysaccharides simulated hydrolysates (AAPHs) obtained from the dried fruiting body of A. auricular. AAPHs were administered intragastrically (i.g.) at the dose of 0.15 g/kg b. W. to diabetic Wistar rats for 4 weeks. Results show that AAPHs was demonstrated to exhibit significant diminution in T-CHO and LDL-C levels (P < 0.05 or P < 0.01) compared to the diabetic control group. In addition, the secretion level of GLP-1 were different with the diabetes model group from 0 to 30 min, and had a tendency to alleviate weight loss. The current study suggests that AAPHs might be incorporated as a supplement in diabetic agents or combined with other health-care foods.

(-)-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.

Effects of Cocoa Antioxidants in Type 2 Diabetes Mellitus

Type 2 Diabetes mellitus (T2D) is the most common form of diabetes and one of the most common chronic diseases. Control of hyperglycaemia by hypoglycaemic drugs is insufficient in for patients and nutritional approaches are currently being explored. Natural dietary compounds such as flavonoids, abundant in fruits and vegetables, have received broad attention because of their potential capacity to act as anti-diabetic agents. Especially cocoa flavonoids have been proved to ameliorate important hallmarks of T2D. In this review, an update of the most relevant reports published during the last decade in cell culture, animal models and human studies is presented. Most results support an anti-diabetic effect of cocoa flavonoids by enhancing insulin secretion, improving insulin sensitivity in peripheral tissues, exerting a lipid-lowering effect and preventing the oxidative and inflammatory damages associated to the disease. While it could be suggested that daily consumption of flavanols from cocoa or dark chocolate would constitute a potential preventive tool useful for the nutritional management of T2D, this recommendation should be cautious since most of commercially available soluble cocoa products or chocolates contain low amount of flavanols and are rich in sugar and calories that may aggravate glycaemic control in T2D patients.

Protective effects of tea, red wine and cocoa in diabetes. Evidences from human studies

Prevention of diabetes through the diet has recently received an increasing interest, and polyphenolic compounds, such as flavanols, have become important potential chemopreventive natural agents due to their proved benefits on health, with low toxicity and cost. Tea, red wine and cocoa are good sources of flavanols and these highly consumed foods might contribute to prevent diabetes. In this regard, there is increasing evidence for a protective effect of tea, red wine and cocoa consumption against this disorder. This review summarizes the available epidemiological and interventional human studies providing evidence for and against this effect. Overall observational data suggest a benefit, but results are still equivocal and likely confounded by lifestyle and background dietary factors. The weight of data indicate favourable effects on diabetes risk factors for tea, red wine and cocoa intake, and a number of plausible mechanisms have been elucidated in human studies. However, despite the growing evidence it remains uncertain whether tea, red wine and cocoa consumption should be recommended to the general population or to patients as a strategy to reduce the risk of diabetes.

Gut Microbiota in a Rat Oral Sensitization Model: Effect of a Cocoa-Enriched Diet

Increasing evidence is emerging suggesting a relation between dietary compounds, microbiota, and the susceptibility to allergic diseases, particularly food allergy. Cocoa, a source of antioxidant polyphenols, has shown effects on gut microbiota and the ability to promote tolerance in an oral sensitization model. Taking these facts into consideration, the aim of the present study was to establish the influence of an oral sensitization model, both alone and together with a cocoa-enriched diet, on gut microbiota. Lewis rats were orally sensitized and fed with either a standard or 10% cocoa diet. Faecal microbiota was analysed through metagenomics study. Intestinal IgA concentration was also determined. Oral sensitization produced few changes in intestinal microbiota, but in those rats fed a cocoa diet significant modifications appeared. Decreased bacteria from the Firmicutes and Proteobacteria phyla and a higher percentage of bacteria belonging to the Tenericutes and Cyanobacteria phyla were observed. In conclusion, a cocoa diet is able to modify the microbiota bacterial pattern in orally sensitized animals. As cocoa inhibits the synthesis of specific antibodies and also intestinal IgA, those changes in microbiota pattern, particularly those of the Proteobacteria phylum, might be partially responsible for the tolerogenic effect of cocoa.

Loss of Native Flavanols during Fermentation and Roasting Does Not Necessarily Reduce Digestive Enzyme-Inhibiting Bioactivities of Cocoa

Polyphenol profiles and in vitro digestive enzyme inhibitory activities were compared between cocoa extracts from unfermented beans (UB), fermented beans (FB), unfermented liquor (UL), and fermented liquor (FL). Total polyphenols, total flavanols, and individual flavanols were significantly different between UB/FB and UL/FL. All extracts effectively inhibited α-glucosidase (lowest IC50 = 90.0 μg/mL, UL) and moderately inhibited α-amylase (lowest IC50 = 183 μg/mL, FL) and lipase (lowest IC25 = 65.5 μg/mL, FB). Our data suggest that fermentation does not reduce α-glucosidase inhibition, while roasting may enhance inhibition. For α-amylase, both fermentation and roasting improved inhibition. Finally, for lipase, both fermentation and roasting attenuated inhibition. Conclusive correlations between inhibition and mDP, total polyphenol, and flavanol contents were not found. Our data suggest that enzyme inhibition activities of cocoa are not uniformly reduced by polyphenol/flavanol losses during fermentation and roasting. This paradigm-challenging finding suggests other cocoa constituents, potentially formed during processing, contribute to digestive enzyme inhibition.

Mechanisms by which cocoa flavanols improve metabolic syndrome and related disorders

Dietary administration of cocoa flavanols may be an effective complementary strategy for alleviation or prevention of metabolic syndrome, particularly glucose intolerance. The complex flavanol composition of cocoa provides the ability to interact with a variety of molecules, thus allowing numerous opportunities to ameliorate metabolic diseases. These interactions likely occur primarily in the gastrointestinal tract, where native cocoa flavanol concentration is high. Flavanols may antagonize digestive enzymes and glucose transporters, causing a reduction in glucose excursion, which helps patients with metabolic disorders maintain glucose homeostasis. Unabsorbed flavanols, and ones that undergo enterohepatic recycling, will proceed to the colon where they can exert prebiotic effects on the gut microbiota. Interactions with the gut microbiota may improve gut barrier function, resulting in attenuated endotoxin absorption. Cocoa may also positively influence insulin signaling, possibly by relieving insulin-signaling pathways from oxidative stress and inflammation and/or via a heightened incretin response. The purpose of this review is to explore the mechanisms that underlie these outcomes, critically review the current body of literature related to those mechanisms, explore the implications of these mechanisms for therapeutic utility, and identify emerging or needed areas of research that could advance our understanding of the mechanisms of action and therapeutic potential of cocoa flavanols.

α-Glucosidase inhibitory activities of phenolic acid amides with l-amino acid moiety

Phenolic acid amides with a l-amino acid moiety showed excellent inhibitory activity on α-glucosidase.