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      Dietary Anthocyanins and Insulin Resistance: When Food Becomes a Medicine

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          Abstract

          Insulin resistance is an abnormal physiological state that occurs when insulin from pancreatic β-cells is unable to trigger a signal transduction pathway in target organs such as the liver, muscles and adipose tissues. The loss of insulin sensitivity is generally associated with persistent hyperglycemia (diabetes), hyperinsulinemia, fatty acids and/or lipid dysregulation which are often prevalent under obesity conditions. Hence, insulin sensitizers are one class of drugs currently employed to treat diabetes and associated metabolic disorders. A number of natural products that act through multiple mechanisms have also been identified to enhance insulin sensitivity in target organs. One group of such compounds that gained interest in recent years are the dietary anthocyanins. Data from their in vitro, in vivo and clinical studies are scrutinized in this communication to show their potential health benefit through ameliorating insulin resistance. Specific mechanism of action ranging from targeting specific signal transduction receptors/enzymes to the general antioxidant and anti-inflammatory mechanisms of insulin resistance are presented.

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          Most cited references123

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          Retinol-binding protein 4 and insulin resistance in lean, obese, and diabetic subjects.

          Insulin resistance has a causal role in type 2 diabetes. Serum levels of retinol-binding protein 4 (RBP4), a protein secreted by adipocytes, are increased in insulin-resistant states. Experiments in mice suggest that elevated RBP4 levels cause insulin resistance. We sought to determine whether serum RBP4 levels correlate with insulin resistance and change after an intervention that improves insulin sensitivity. We also determined whether elevated serum RBP4 levels are associated with reduced expression of glucose transporter 4 (GLUT4) in adipocytes, an early pathological feature of insulin resistance. We measured serum RBP4, insulin resistance, and components of the metabolic syndrome in three groups of subjects. Measurements were repeated after exercise training in one group. GLUT4 protein was measured in isolated adipocytes. Serum RBP4 levels correlated with the magnitude of insulin resistance in subjects with obesity, impaired glucose tolerance, or type 2 diabetes and in nonobese, nondiabetic subjects with a strong family history of type 2 diabetes. Elevated serum RBP4 was associated with components of the metabolic syndrome, including increased body-mass index, waist-to-hip ratio, serum triglyceride levels, and systolic blood pressure and decreased high-density lipoprotein cholesterol levels. Exercise training was associated with a reduction in serum RBP4 levels only in subjects in whom insulin resistance improved. Adipocyte GLUT4 protein and serum RBP4 levels were inversely correlated. RBP4 is an adipocyte-secreted molecule that is elevated in the serum before the development of frank diabetes and appears to identify insulin resistance and associated cardiovascular risk factors in subjects with varied clinical presentations. These findings provide a rationale for antidiabetic therapies aimed at lowering serum RBP4 levels. Copyright 2006 Massachusetts Medical Society.
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            Metabolic syndrome and insulin resistance: underlying causes and modification by exercise training.

            Metabolic syndrome (MS) is a collection of cardiometabolic risk factors that includes obesity, insulin resistance, hypertension, and dyslipidemia. Although there has been significant debate regarding the criteria and concept of the syndrome, this clustering of risk factors is unequivocally linked to an increased risk of developing type 2 diabetes and cardiovascular disease. Regardless of the true definition, based on current population estimates, nearly 100 million have MS. It is often characterized by insulin resistance, which some have suggested is a major underpinning link between physical inactivity and MS. The purpose of this review is to: (i) provide an overview of the history, causes and clinical aspects of MS, (ii) review the molecular mechanisms of insulin action and the causes of insulin resistance, and (iii) discuss the epidemiological and intervention data on the effects of exercise on MS and insulin sensitivity.
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              Insulin resistance differentially affects the PI 3-kinase- and MAP kinase-mediated signaling in human muscle.

              The broad nature of insulin resistant glucose metabolism in skeletal muscle of patients with type 2 diabetes suggests a defect in the proximal part of the insulin signaling network. We sought to identify the pathways compromised in insulin resistance and to test the effect of moderate exercise on whole-body and cellular insulin action. We conducted euglycemic clamps and muscle biopsies on type 2 diabetic patients, obese nondiabetics and lean controls, with and without a single bout of exercise. Insulin stimulation of the phosphatidylinositol 3-kinase (PI 3-kinase) pathway, as measured by phosphorylation of the insulin receptor and IRS-1 and by IRS protein association with p85 and with PI 3-kinase, was dramatically reduced in obese nondiabetics and virtually absent in type 2 diabetic patients. Insulin stimulation of the MAP kinase pathway was normal in obese and diabetic subjects. Insulin stimulation of glucose-disposal correlated with association of p85 with IRS-1. Exercise 24 hours before the euglycemic clamp increased phosphorylation of insulin receptor and IRS-1 in obese and diabetic subjects but did not increase glucose uptake or PI 3-kinase association with IRS-1 upon insulin stimulation. Thus, insulin resistance differentially affects the PI 3-kinase and MAP kinase signaling pathways, and insulin-stimulated IRS-1-association with PI 3-kinase defines a key step in insulin resistance.
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                Author and article information

                Journal
                Nutrients
                Nutrients
                nutrients
                Nutrients
                MDPI
                2072-6643
                12 October 2017
                October 2017
                : 9
                : 10
                : 1111
                Affiliations
                [1 ]G.B. Pant Institute of Himalayan Environment and Development, Kosi Katarmal, Almora, Uttarakhand 263643, India; tarungbpihed@ 123456gmail.com
                [2 ]Applied Biotechnology Research Center, Baqiyatallah University of Medical Sciences, Tehran P.O. Box 19395-5487, Iran; Nabavisf@ 123456gmail.com (S.F.N.); Nabavi208@ 123456gmail.com (S.M.N.)
                [3 ]Pharmacognosy Research Laboratories & Herbal Analysis Services UK, University of Greenwich, Central Avenue, Charham-Maritime, Kent ME4 4TB, UK
                Author notes
                [* ]Correspondence: s.habtemariam@ 123456herbalanalysis.co.uk ; Tel.: +44-208-331-8302 or +44-208-331-8424
                Article
                nutrients-09-01111
                10.3390/nu9101111
                5691727
                29023424
                b03da31d-9e42-414c-8884-9deaf9ebf5f8
                © 2017 by the authors.

                Licensee MDPI, Basel, Switzerland. This article is an open access article distributed under the terms and conditions of the Creative Commons Attribution (CC BY) license ( http://creativecommons.org/licenses/by/4.0/).

                History
                : 04 September 2017
                : 10 October 2017
                Categories
                Review

                Nutrition & Dietetics
                dietary anthocyanins,insulin resistance,diabetes,obesity
                Nutrition & Dietetics
                dietary anthocyanins, insulin resistance, diabetes, obesity

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