Interleukin-6 enhances insulin secretion by increasing glucagon-like peptide-1 secretion from L cells and alpha cells

Stimulation of incretin secreting cells

The incretin hormones glucose-dependent insulinotropic polypeptide (GIP) and glucagon like peptide-1 (GLP-1) are secreted from enteroendocrine cells in the gut and regulate physiological and homeostatic functions related to glucose control, metabolism and food intake. This review provides a systematic summary of the molecular mechanisms underlying secretion from incretin cells, and an understanding of how they sense and interact with lumen and vascular factors and the enteric nervous system through transporters and G-protein coupled receptors (GPCRs) present on their surface to ultimately culminate in hormone release. Some of the molecules described below such as sodium coupled glucose transporter 1 (SGLT1), G-protein coupled receptor (GPR) 119 and GPR40 are targets of novel therapeutics designed to enhance endogenous gut hormone release. Synthetic ligands at these receptors aimed at treating obesity and type 2 diabetes are currently under investigation.

Do glucagonomas always produce glucagon?

Pancreatic islet α-cell tumours that overexpress proglucagon are typically associated with the glucagonoma syndrome, a rare disease entity characterised by necrolytic migratory erythema, impaired glucose tolerance, thromboembolic complications and psychiatric disturbances. Paraneoplastic phenomena associated with enteric overexpression of proglucagon-derived peptides are less well recognized and include gastrointestinal dysfunction and hyperinsulinaemic hypoglycaemia. The diverse clinical manifestations associated with glucagon-expressing tumours can be explained, in part, by the repertoire of tumorally secreted peptides liberated through differential post-translational processing of tumour-derived proglucagon. Proglucagon-expressing tumours may be divided into two broad biochemical subtypes defined by either secretion of glucagon or GLP-1, GLP-2 and the glucagon-containing peptides, glicentin and oxyntomodulin, due to an islet α-cell or enteroendocrine L-cell pattern of proglucagon processing, respectively. In the current review we provide an updated overview of the clinical presentation of proglucagon-expressing tumours in relation to known physiological actions of proglucagon-derived peptides and suggest that detailed biochemical characterisation of the peptide repertoire secreted from these tumours may provide new opportunities for diagnosis and clinical management.

Oxidative and endoplasmic reticulum stress in β-cell dysfunction in diabetes

The inability of pancreatic β-cells to make sufficient insulin to control blood sugar is a central feature of the aetiology of most forms of diabetes. In this review we focus on the deleterious effects of oxidative stress and endoplasmic reticulum (ER) stress on β-cell insulin biosynthesis and secretion and on inflammatory signalling and apoptosis with a particular emphasis on type 2 diabetes (T2D). We argue that oxidative stress and ER stress are closely entwined phenomena fundamentally involved in β-cell dysfunction by direct effects on insulin biosynthesis and due to consequences of the ER stress-induced unfolded protein response. We summarise evidence that, although these phenomenon can be driven by intrinsic β-cell defects in rare forms of diabetes, in T2D β-cell stress is driven by a range of local environmental factors including increased drivers of insulin biosynthesis, glucolipotoxicity and inflammatory cytokines. We describe our recent findings that a range of inflammatory cytokines contribute to β-cell stress in diabetes and our discovery that interleukin 22 protects β-cells from oxidative stress regardless of the environmental triggers and can correct much of diabetes pathophysiology in animal models. Finally we summarise evidence that β-cell dysfunction is reversible in T2D and discuss therapeutic opportunities for relieving oxidative and ER stress and restoring glycaemic control.

Activation of Transmembrane Bile Acid Receptor TGR5 Modulates Pancreatic Islet α Cells to Promote Glucose Homeostasis

The physiological role of the TGR5 receptor in the pancreas is not fully understood. We previously showed that activation of TGR5 in pancreatic β cells by bile acids induces insulin secretion. Glucagon released from pancreatic α cells and glucagon-like peptide 1 (GLP-1) released from intestinal L cells regulate insulin secretion. Both glucagon and GLP-1 are derived from alternate splicing of a common precursor, proglucagon by PC2 and PC1, respectively. We investigated whether TGR5 activation in pancreatic α cells enhances hyperglycemia-induced PC1 expression thereby releasing GLP-1, which in turn increases β cell mass and function in a paracrine manner. TGR5 activation augmented a hyperglycemia-induced switch from glucagon to GLP-1 synthesis in human and mouse islet α cells by GS/cAMP/PKA/cAMP-response element-binding protein-dependent activation of PC1. Furthermore, TGR5-induced GLP-1 release from α cells was via an Epac-mediated PKA-independent mechanism. Administration of the TGR5 agonist, INT-777, to db/db mice attenuated the increase in body weight and improved glucose tolerance and insulin sensitivity. INT-777 augmented PC1 expression in α cells and stimulated GLP-1 release from islets of db/db mice compared with control. INT-777 also increased pancreatic β cell proliferation and insulin synthesis. The effect of TGR5-mediated GLP-1 from α cells on insulin release from islets could be blocked by GLP-1 receptor antagonist. These results suggest that TGR5 activation mediates cross-talk between α and β cells by switching from glucagon to GLP-1 to restore β cell mass and function under hyperglycemic conditions. Thus, INT-777-mediated TGR5 activation could be leveraged as a novel way to treat type 2 diabetes mellitus.

Physiological Roles of Adipokines, Hepatokines, and Myokines in Ruminants

Since the discovery of leptin secreted from adipocytes, specialized tissues and cells have been found that secrete the several peptides (or cytokines) that are characterized to negatively and positively regulate the metabolic process. Different types of adipokines, hepatokines, and myokines, which act as cytokines, are secreted from adipose, liver, and muscle tissue, respectively, and have been identified and examined for their physiological roles in humans and disease in animal models. Recently, various studies of these cytokines have been conducted in ruminants, including dairy cattle, beef cattle, sheep, and goat. Interestingly, a few cytokines from these tissues in ruminants play an important role in the post-parturition, lactation, and fattening (marbling) periods. Thus, understanding these hormones is important for improving nutritional management in dairy cows and beef cattle. However, to our knowledge, there have been no reviews of the characteristics of these cytokines in beef and dairy products in ruminants. In particular, lipid and glucose metabolism in adipose tissue, liver tissue, and muscle tissue are very important for energy storage, production, and synthesis, which are regulated by these cytokines in ruminant production. In this review, we summarize the physiological roles of adipokines, hepatokines, and myokines in ruminants. This discussion provides a foundation for understanding the role of cytokines in animal production of ruminants.

Incretins

Glucose-dependent insulinotropic polypeptide (GIP) and glucagon-like peptide-1 (GLP-1) are the known incretin hormones in humans, released predominantly from the enteroendocrine K and L cells within the gut. Their secretion is regulated by a complex of integrated mechanisms involving direct contact for the activation of different chemo-sensors on the brush boarder of K and L cells and several indirect neuro-immuno-hormonal loops. The biological actions of GIP and GLP-1 are fundamental determinants of islet function and blood glucose homeostasis in health and type 2 diabetes. Moreover, there is increasing recognition that GIP and GLP-1 also exert pleiotropic extra-glycaemic actions, which may represent therapeutic targets for human diseases. In this review, we summarise current knowledge of the biology of incretin hormones in health and metabolic disorders and highlight the therapeutic potential of incretin hormones in metabolic regulation.

Does Glucagon-like Peptide-1 Ameliorate Oxidative Stress in Diabetes? Evidence Based on Experimental and Clinical Studies

Glucagon-like peptide-1 (GLP-1) has shown to influence the oxidative stress status in a number of in vitro, in vivo and clinical studies. Well-known effects of GLP-1 including better glycemic control, decreased food intake, increased insulin release and increased insulin sensitivity may indirectly contribute to this phenomenon, but glucose-independent effects on ROS level, production and antioxidant capacity have been suggested to also play a role. The potential 'antioxidant' activity of GLP-1 along with other proposed glucose-independent modes of action related to ameliorating redox imbalance remains a controversial topic but could hold a therapeutic potential against micro- and macrovascular diabetic complications. This review discusses the presently available knowledge from experimental and clinical studies on the effects of GLP-1 on oxidative stress in diabetes and diabetes-related complications.

Evolving function and potential of pancreatic alpha cells

The alpha cells that co-occupy the islets in association with beta cells have been long recognized as the source of glucagon, a hyperglycemia-producing and diabetogenic hormone. Although the mechanisms that control the functions of alpha cells, glucagon secretion, and the role of glucagon in diabetes have remained somewhat enigmatic over the fifty years since their discovery, seminal findings during the past few years have moved alpha cells into the spotlight of scientific discovery. These findings obtained largely from studies in mice are: Alpha cells have the capacity to trans-differentiate into insulin-producing beta cells. Alpha cells contain a GLP-1 generating system that produces GLP-1 locally for paracrine actions within the islets that likely promotes beta cell growth and survival and maintains beta cell mass. Impairment of glucagon signaling both prevents the occurrence of diabetes in conditions of the near absence of insulin and expands alpha cell mass. Alpha cells appear to serve as helper cells or guardians of beta cells to ensure their health and well-being. Of potential relevance to the possibility of promoting the transformation of alpha to beta cells is the observation that impairment of glucagon signaling leads to a marked increase in alpha cell mass in the islets. Such alpha cell hyperplasia provides an increased supply of alpha cells for their transdifferentiation into new beta cells. In this review we discuss these recent discoveries from the perspective of their potential relevance to the treatment of diabetes.

Heterogeneity of glucagonomas due to differential processing of proglucagon-derived peptides

Pancreatic neuroendocrine tumours (pNETs) secreting proglucagon are associated with phenotypic heterogeneity. Here, we describe two patients with pNETs and varied clinical phenotypes due to differential processing and secretion of proglucagon-derived peptides (PGDPs). Case 1, a 57-year-old woman presented with necrolytic migratory erythema, anorexia, constipation and hyperinsulinaemic hypoglycaemia. She was found to have a grade 1 pNET, small bowel mucosal thickening and hyperglucagonaemia. Somatostatin analogue (SSA) therapy improved appetite, abolished hypoglycaemia and improved the rash. Case 2, a 48-year-old male presented with diabetes mellitus, diarrhoea, weight loss, nausea, vomiting and perineal rash due to a grade 1 metastatic pNET and hyperglucagonaemia. In both cases, plasma levels of all measured PGDPs were elevated and attenuated following SSA therapy. In case 1, there was increased production of intact glucagon-like peptide 1 (GLP-1) and GLP-2, similar to that of the enteroendocrine L cell. In case 2, pancreatic glucagon was elevated due to a pancreatic α-cell-like proglucagon processing profile. In summary, we describe two patients with pNETs and heterogeneous clinical phenotypes due to differential processing and secretion of PGDPs. This is the first description of a patient with symptomatic hyperinsulinaemic hypoglycaemia and marked gastrointestinal dysfunction due to, in part, a proglucagon-expressing pNET.

Cholecystokinin expression in the β-cell leads to increased β-cell area in aged mice and protects from streptozotocin-induced diabetes and apoptosis

Cholecystokinin (CCK) is a peptide hormone produced in the gut and brain with beneficial effects on digestion, satiety, and insulin secretion. CCK is also expressed in pancreatic β-cells, but only in models of obesity and insulin resistance. Whole body deletion of CCK in obese mice leads to reduced β-cell mass expansion and increased apoptosis. We hypothesized that islet-derived CCK is important in protection from β-cell apoptosis. To determine the specific role of β-cell-derived CCK in β-cell mass dynamics, we generated a transgenic mouse that expresses CCK in the β-cell in the lean state (MIP-CCK). Although this transgene contains the human growth hormone minigene, we saw no expression of human growth hormone protein in transgenic islets. We examined the ability of MIP-CCK mice to maintain β-cell mass when subjected to apoptotic stress, with advanced age, and after streptozotocin treatment. Aged MIP-CCK mice have increased β-cell area. MIP-CCK mice are resistant to streptozotocin-induced diabetes and exhibit reduced β-cell apoptosis. Directed CCK overexpression in cultured β-cells also protects from cytokine-induced apoptosis. We have identified an important new paracrine/autocrine effect of CCK in protection of β-cells from apoptotic stress. Understanding the role of β-cell CCK adds to the emerging knowledge of classic gut peptides in intraislet signaling. CCK receptor agonists are being investigated as therapeutics for obesity and diabetes. While these agonists clearly have beneficial effects on body weight and insulin sensitivity in peripheral tissues, they may also directly protect β-cells from apoptosis.

ADAM17 controls IL-6 signaling by cleavage of the murine IL-6Rα from the cell surface of leukocytes during inflammatory responses

The cytokine IL-6 is part of a regulatory signaling network that controls immune responses. IL-6 binds either to the membrane-bound IL-6 receptor-α (classic signaling) or to the soluble IL-6 receptor-α (trans-signaling) to initiate signal transduction via gp130 activation. Because classic and trans-signaling of IL-6 fulfill different tasks during immune responses, controlled shedding of the membrane-bound IL-6 receptor-α from the surface of immune cells can be considered a central regulator of IL-6 function. The results from cell culture-based experiments have implicated both a disintegrin and metalloprotease 10 and a disintegrin and metalloprotease 17 in IL-6 receptor-α shedding. However, the nature of the protease mediating IL-6 receptor-α release in vivo is not yet known. We used hypomorphic a disintegrin and metalloprotease 17 mice and conditional a disintegrin and metalloprotease 10 knock-out mice to identify the natural protease of the murine IL-6 receptor-α. Circulating homeostatic soluble IL-6 receptor-α levels are not dependent on a disintegrin and metalloprotease 10 or 17 activity. However, during Listeria monocytogenes infection, IL-6 receptor-α cleavage by the α-secretase a disintegrin and metalloprotease 17 is rapidly induced from the surface of different leukocyte populations. In contrast, CD4-Cre-driven a disintegrin and metalloprotease 10 deletion in T cells did not influence IL-6 receptor-α shedding from these cells after L. monocytogenes infection. A disintegrin and metalloprotease 17 was also required for IL-6 receptor-α ectodomain cleavage and release during endotoxemia. These results demonstrate a novel physiologic role for a disintegrin and metalloprotease 17 in regulating murine IL-6 signals during inflammatory processes.

Skeletal muscle as an endocrine organ: PGC-1α, myokines and exercise

An active lifestyle is crucial to maintain health into old age; inversely, sedentariness has been linked to an elevated risk for many chronic diseases. The discovery of myokines, hormones produced by skeletal muscle tissue, suggests the possibility that these might be molecular mediators of the whole body effects of exercise originating from contracting muscle fibers. Even though less is known about the sedentary state, the lack of contraction-induced myokines or the production of a distinct set of hormones in the inactive muscle could likewise contribute to pathological consequences in this context. In this review, we try to summarize the most recent developments in the study of muscle as an endocrine organ and speculate about the potential impact on our understanding of exercise and sedentary physiology, respectively. This article is part of a Special Issue entitled "Muscle Bone Interactions".

Chronic Exposure to TNFα Impairs Secretion of Glucagon-Like Peptide-1

Obesity is associated with systemic inflammation and elevated levels of TNFα, leading to impaired glucose tolerance. In humans, obesity is also associated with reduced nutrient-stimulated secretion of the intestinal incretin hormone, glucagon-like peptide-1 (GLP-1). We hypothesized that TNFα plays a direct role in the impairment of GLP-1 secretion from the enteroendocrine L-cell and that blocking TNFα can restore both GLP-1 secretion and glucose homeostasis. Expression of the TNFα receptor subytpe-1 was detected in the human NCI-H716 and murine GLUTag L-cell models and in mouse ileal sections. Although TNFα acutely increased GLP-1 release from NCI-H716 cells (P < .05-.001), preincubation with TNFα for 24 hours reduced proglucagon mRNA (P < .05) and GLP-1 cellular (P < .05) levels without affecting cell viability. Furthermore, both NCI-H716 and GLUTag cells pretreated with TNFα for 24 hours no longer responded to known GLP-1 secretagogues, an effect that was reversed by coincubation with the Nuclear Factor Kappa B inhibitor, 5-aminosalicylic acid, in the NCI-H716 cells. Mice given a high-fat diet (HFD) for 12 weeks developed impaired glucose tolerance, hyperinsulinemia, and increased TNFα mRNA expression in fat and ileal tissue. Hyperglycemia and hyperinsulinemia were reduced in HFD mice treated with the anti-TNFα biological, etanercept, for 2 weeks. In primary intestinal cultures from these animals, HFD control mice had impaired GLP-1 secretion, and this was not observed in the HFD etanercept-derived cultures (P < .05). In conclusion, chronic exposure to TNFα directly impairs GLP-1 secretion at the level of the intestinal L-cell, an effect that is reversed by anti-TNFα therapy in association with improved glucose tolerance.

Lipolytic and thermogenic depletion of adipose tissue in cancer cachexia

Although muscle wasting is the obvious manifestation of cancer cachexia that impacts on patient quality of life, the loss of lipid reserves and metabolic imbalance in adipose tissue also contribute to the devastating impact of cachexia. Depletion of fat depots in cancer patients is more pronounced than loss of muscle and often precedes, or even occurs in the absence of, reduced lean body mass. Rapid mobilisation of triglycerides stored within adipocytes to supply the body with fatty acids in periods of high-energy demand is normally mediated through a well-defined process of lipolysis involving the lipases ATGL, HSL and MGL. Studies into how these lipases contribute to fat loss in cancer cachexia have revealed the prominent role for ATGL in initiating lipolysis during adipose tissue atrophy, together with links between tumour-derived factors and the signalling pathways that control lipid flux within fat cells. The recent findings of increased thermogenesis in brown fat during cancer cachexia indicate that metabolically active adipose tissue contributes to the imbalance in energy homeostasis involved in catabolic wasting. Such energetically futile use of fatty acids liberated from adipose tissue to generate heat represents a maladaptive response in conjunction with anorexia experienced by cancer patients. As IL-6 release by tumours provokes lipolysis and activates the thermogenic programme in brown fat, this review explores the overlap in dysregulated metabolic processes due to inflammatory mediators in cancer cachexia and other disease states characterised by elevated cytokines such as obesity and diabetes.

Exercise-mediated IL-6 signaling occurs independent of inflammation and is amplified by training in mouse adipose tissue

The purpose of this investigation was to determine whether exercise-induced increases in adipose tissue interleukin 6 (IL-6) signaling occurred as part of a larger proinflammatory response to exercise and whether the induction of IL-6 signaling with acute exercise was altered in trained mice in parallel with changes in the IL-6 receptor complex. Sedentary and trained C57BL/6J mice were challenged with an acute bout of exercise. Adipose tissue and plasma were collected immediately and 4 h afterward and analyzed for changes in indices of IL-6 signaling, circulating IL-6, markers of adipose tissue inflammation, and expression/content of IL-6 receptor and glycoprotein 130 (gp130). In untrained mice, IL-6 mRNA increased immediately after exercise, and increases in indices of IL-6 signaling were increased 4 h after exercise in epididymal, but not inguinal adipose tissue. This occurred independent of increases in plasma IL-6 and alterations in markers of inflammation. When compared with untrained mice, in trained mice, acute exercise induced the expression of gp130 and IL-6 receptor alpha (IL-6Rα), and training increased the protein content of these. Acute exercise induced the expression, and training increased the protein content, of glycoprotein 130 and IL-6Rα and was associated with a more rapid increase in markers of IL-6 signaling in epididymal adipose tissue from trained compared with untrained mice. The ability of exogenous IL-6 to increase phosphorylation of STAT3 was similar between groups. Our findings demonstrate that acute exercise increases IL-6 signaling in a depot-dependent manner, likely through an autocrine/paracrine mechanism. This response is initiated more rapidly after exercise in trained mice, potentially as a result of increases in IL-6Rα and gp130.

Acute effects of different degrees of ultra-endurance exercise on systemic inflammatory responses

BACKGROUND

Intense physical stress might promote inflammatory responses, whereas a regular physical exercise has positive influence. Little is known on the acute metabolic and inflammatory responses to different levels of strenuous exercise in trained athletes.

AIM

To compare the short-term effect of two different ultra-endurance competitions on the inflammatory profile in male triathletes.

METHODS

We studied 14 Ironman (IR) and 13 Half Ironman (HIR) before and after their own specific race. We assessed body composition and measured blood cells, lipids, iron metabolism and plasma levels of some acute-phase cytokines and inflammatory markers.

RESULTS

After the race, IR showed reduced total body water and fat-free mass, not related with the duration of exercise, and increased white cells and platelets; high-density lipoprotein levels also increased. IR, but not HIR, showed reduced iron levels, increased ferritin and transferrin, reduced % saturated transferrin. HIR showed higher basal interleukin (IL)-6, tumour necrosis factor (TNF)-α, IL-10, IL-1β than IR; however, the post-performance rise was greater in IR. Irisin increased only in HIR and osteocalcin decreased in IR. In the whole study group, delta of white blood cells was directly related with delta of monocyte chemoattractant protein 1, and Δ ferritin was inversely related with Δosteocalcin.

CONCLUSIONS

A single ultra-endurance competition induces an inflammatory response depending on the duration of physical effort, with increased acute-phase cytokines, and an altered iron metabolism. Irisin, whose biological meaning is still uncertain, seems to be associated with acute variations of some metabolic parameters.

High intensity interval training improves liver and adipose tissue insulin sensitivity

Objective

Endurance exercise training reduces insulin resistance, adipose tissue inflammation and non-alcoholic fatty liver disease (NAFLD), an effect often associated with modest weight loss. Recent studies have indicated that high-intensity interval training (HIIT) lowers blood glucose in individuals with type 2 diabetes independently of weight loss; however, the organs affected and mechanisms mediating the glucose lowering effects are not known. Intense exercise increases phosphorylation and inhibition of acetyl-CoA carboxylase (ACC) by AMP-activated protein kinase (AMPK) in muscle, adipose tissue and liver. AMPK and ACC are key enzymes regulating fatty acid metabolism, liver fat content, adipose tissue inflammation and insulin sensitivity but the importance of this pathway in regulating insulin sensitivity with HIIT is unknown.

Methods

In the current study, the effects of 6 weeks of HIIT were examined using obese mice with serine–alanine knock-in mutations on the AMPK phosphorylation sites of ACC1 and ACC2 (AccDKI) or wild-type (WT) controls.

Results

HIIT lowered blood glucose and increased exercise capacity, food intake, basal activity levels, carbohydrate oxidation and liver and adipose tissue insulin sensitivity in HFD-fed WT and AccDKI mice. These changes occurred independently of weight loss or reductions in adiposity, inflammation and liver lipid content.

Conclusions

These data indicate that HIIT lowers blood glucose levels by improving adipose and liver insulin sensitivity independently of changes in adiposity, adipose tissue inflammation, liver lipid content or AMPK phosphorylation of ACC.

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High-intensity interval training (HIIT) improves exercise capacity and whole-body glucose homeostasis.

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HIIT enhances liver and adipose tissue insulin sensitivity independent of body weight and adiposity.

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HIIT does not change adipose tissue cell size, macrophage infiltration, inflammation and liver lipid content.

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HIIT exercise training improves insulin sensitivity independently of the AMPK-ACC signaling pathway.

Muscle-Derived IL-6 Is Not Regulated by IL-1 during Exercise. A Double Blind, Placebo-Controlled, Randomized Crossover Study

Exercise increases muscle derived Interleukin–6 (IL–6) leading to insulin secretion via glucagon-like peptide–1. IL–1 antagonism improves glycemia and decreases systemic inflammation including IL–6 in patients with type 2 diabetes. However, it is not known whether physiological, exercise-induced muscle-derived IL–6 is also regulated by the IL–1 system. Therefore we conducted a double blind, crossover study in 17 healthy male subjects randomized to receive either the IL–1 receptor antagonist IL-1Ra (anakinra) or placebo prior to an acute treadmill exercise. Muscle activity led to a 2–3 fold increase in serum IL–6 concentrations but anakinra had no effect on this exercise-induced IL–6. Furthermore, the IL–1 responsive inflammatory markers CRP, cortisol and MCP–1 remained largely unaffected by exercise and anakinra. We conclude that the beneficial effect of muscle-induced IL–6 is not meaningfully affected by IL–1 antagonism.

Targeting Inflammation Through a Physical Active Lifestyle and Pharmaceuticals for the Treatment of Type 2 Diabetes

Evidence exists that interleukin (IL)-1β is involved in pancreatic β-cell damage, whereas TNF-α appears to be a key molecule in peripheral insulin resistance. Although increased plasma levels of IL-6 are seen in individuals with type 2 diabetes, mechanistic studies suggest that moderate acute elevations in IL-6, as provoked by exercise, exert anti-inflammatory effects by an inhibition of TNF-α and by stimulating IL-1 receptor antagonist (ra), thereby limiting IL-1β signaling. A number of medical treatments have anti-inflammatory effects. IL-1 antagonists have been tested in clinical studies and appear very promising. Also, there is a potential for anti-TNF-α strategies and salsalate has been shown to improve insulin sensitivity in clinical trials. Furthermore, the anti-inflammatory potential of statins, antagonists of the renin-angiotensin system, and glucose-lowering agents are discussed. While waiting for the outcome of long-term clinical pharmacological trials, it should be emphasized that physical activity represents a natural strong anti-inflammatory intervention with little or no side effects.

Skeletal Muscle to Pancreatic β-Cell Cross-talk: The Effect of Humoral Mediators Liberated by Muscle Contraction and Acute Exercise on β-Cell Apoptosis

CONTEXT

Mechanisms explaining exercise-induced β-cell health are unknown.

OBJECTIVE

This study aimed to define the role of muscle contraction and acute exercise-derived soluble humoral mediators on β-cell health.

DESIGN

In vitro models were used.

SETTING

University.

PARTICIPANTS

Healthy subjects.

INTERVENTION(S)

Conditioned media (CM) were collected from human skeletal muscle (HSkM) cells treated with or without electrical pulse stimulation (EPS). Antecubital and femoral venous blood serum were collected before and after an exercise bout. CM and sera with or without IL-6 neutralization were used to incubate insulin-producing INS-1 cells and rat islets for 24 h in the presence or absence of proinflammatory cytokines (IL-1β+IFN-γ).

MAIN OUTCOME MEASURE(S)

INS-1 and islet apoptosis and accumulated insulin secretion.

RESULTS

IL-1β+IFN-γ increased INS-1 and islet apoptosis and decreased insulin secretion. EPS-treated HSkM cell CM did not affect these variables. Exercise-conditioned antecubital but not femoral sera prevented IL-1β+IFN-γ-induced INS-1 and islet apoptosis. Femoral sera reduced insulin secretion under normal and proinflammatory conditions in INS-1 but not islet cells. EPS increased HSkM cell IL-6 secretion and exercise increased circulating IL-6 levels in antecubital and femoral serum. IL-6 neutralization demonstrated that muscle-derived IL-6 prevents INS-1 and islet apoptosis in the absence of IL-1β+IFN-γ, but augments apoptosis under proinflammatory conditions, and that muscle-derived IL-6 supports islet insulin secretion in the absence of IL-1β+IFN-γ.

CONCLUSIONS

Unidentified circulating humoral mediators released during exercise prevent proinflammatory cytokine-induced β-cell apoptosis. Muscle-derived mediators released during exercise suppress β-cell insulin secretion. Furthermore, muscle-derived IL-6 seems to prevent β-cell apoptosis under normal conditions but contributes to β-cell apoptosis under proinflammatory conditions.

Stress signaling between organs in metazoa

Many organisms have developed a robust ability to adapt and survive in the face of environmental perturbations that threaten the integrity of their genome, proteome, or metabolome. Studies in multiple model organisms have shown that, in general, when exposed to stress, cells activate a complex prosurvival signaling network that includes immune and DNA damage response genes, chaperones, antioxidant enzymes, structural proteins, metabolic enzymes, and noncoding RNAs. The manner of activation runs the gamut from transcriptional induction of genes to increased stability of transcripts to posttranslational modification of important biosynthetic proteins within the stressed tissue. Superimposed on these largely autonomous effects are nonautonomous responses in which the stressed tissue secretes peptides and other factors that stimulate tissues in different organs to embark on processes that ultimately help the organism as a whole cope with stress. This review focuses on the mechanisms by which tissues in one organ adapt to environmental challenges by regulating stress responses in tissues of different organs.

Human skeletal myotubes display a cell-autonomous circadian clock implicated in basal myokine secretion

OBJECTIVE

Circadian clocks are functional in all light-sensitive organisms, allowing an adaptation to the external world in anticipation of daily environmental changes. In view of the potential role of the skeletal muscle clock in the regulation of glucose metabolism, we aimed to characterize circadian rhythms in primary human skeletal myotubes and investigate their roles in myokine secretion.

METHODS

We established a system for long-term bioluminescence recording in differentiated human myotubes, employing lentivector gene delivery of the Bmal1-luciferase and Per2-luciferase core clock reporters. Furthermore, we disrupted the circadian clock in skeletal muscle cells by transfecting siRNA targeting CLOCK. Next, we assessed the basal secretion of a large panel of myokines in a circadian manner in the presence or absence of a functional clock.

RESULTS

Bioluminescence reporter assays revealed that human skeletal myotubes, synchronized in vitro, exhibit a self-sustained circadian rhythm, which was further confirmed by endogenous core clock transcript expression. Moreover, we demonstrate that the basal secretion of IL-6, IL-8 and MCP-1 by synchronized skeletal myotubes has a circadian profile. Importantly, the secretion of IL-6 and several additional myokines was strongly downregulated upon siClock-mediated clock disruption.

CONCLUSIONS

Our study provides for the first time evidence that primary human skeletal myotubes possess a high-amplitude cell-autonomous circadian clock, which could be attenuated. Furthermore, this oscillator plays an important role in the regulation of basal myokine secretion by skeletal myotubes.

Effects of aerobic exercise with or without metformin on plasma incretins in type 2 diabetes

OBJECTIVE

Despite positive effects of incretins on insulin secretion, little is known about the effect of exercise on these hormones. Metformin can affect incretin concentrations and is prescribed to a large proportion of people with diabetes. We, therefore, examined the effects of aerobic exercise and/or metformin on incretin hormones.

METHODS

Ten participants with type 2 diabetes were recruited for this randomized crossover study. Metformin or placebo was given for 28 days, followed by the alternate treatment for 28 days. On the last 2 days of each condition, participants were assessed during a non-exercise day and a subsequent exercise day. Aerobic exercise took place in the morning and blood samples were taken in the subsequent hours (before and after lunch).

RESULTS

Aerobic exercise did not increase total plasma glucagon-like peptide-1 (GLP-1) or glucose-dependent insulinotropic polypeptide (GIP) in the pre- or post-lunch periods (all p>0.1). GLP-1 was higher in the pre-lunch (p=0.016) and post-lunch (p=0.018) periods of the metformin conditions compared with the placebo. Total plasma GIP was higher in the pre-lunch period (p=0.05), but not in the post-lunch period (p=0.95), with metformin compared with placebo.

CONCLUSIONS

In contrast to our hypothesis, aerobic exercise did not acutely increase total GLP-1 and GIP levels in patients with type 2 diabetes. Metformin, independent of exercise, significantly increased total plasma GLP-1 and GIP concentrations in these patients.

Pharmacology and physiology of gastrointestinal enteroendocrine cells

Gastrointestinal (GI) polypeptides are secreted from enteroendocrine cells (EECs). Recent technical advances and the identification of endogenous and synthetic ligands have enabled exploration of the pharmacology and physiology of EECs. Enteroendocrine signaling pathways stimulating hormone secretion involve multiple nutrient transporters and G protein-coupled receptors (GPCRs), which are activated simultaneously under prevailing nutrient conditions in the intestine following a meal. The majority of studies investigate hormone secretion from EECs in response to single ligands and although the mechanisms behind how individual signaling pathways generate a hormonal output have been well characterized, our understanding of how these signaling pathways converge to generate a single hormone secretory response is still in its infancy. However, a picture is beginning to emerge of how nutrients and full, partial, or allosteric GPCR ligands differentially regulate the enteroendocrine system and its interaction with the enteric and central nervous system. So far, activation of multiple pathways underlies drug discovery efforts to harness the therapeutic potential of the enteroendocrine system to mimic the phenotypic changes observed in patients who have undergone Roux-en-Y gastric surgery. Typically obese patients exhibit ∼30% weight loss and greater than 80% of obese diabetics show remission of diabetes. Targeting combinations of enteroendocrine signaling pathways that work synergistically may manifest with significant, differentiated EEC secretory efficacy. Furthermore, allosteric modulators with their increased selectivity, self-limiting activity, and structural novelty may translate into more promising enteroendocrine drugs. Together with the potential to bias enteroendocrine GPCR signaling and/or to activate multiple divergent signaling pathways highlights the considerable range of therapeutic possibilities available. Here, we review the pharmacology and physiology of the EEC system.

Anti-diabetic effects of shubat in type 2 diabetic rats induced by combination of high-glucose-fat diet and low-dose streptozotocin

ETHNOPHARMACOLOGICAL RELEVANCE

Shubat, probiotic fermented camel milk, has been used both as a drink with ethnic flavor and a medicine among Kazakh population for diabetic patients. Kazakh people have lower diabetic prevalence and impaired fasting glucose (IFG) than do other ethnic groups living in Xinjiang China, which might be related to the beneficial properties of shubat. We therefore prepared shubat in laboratory and tested anti-diabetic activity and evaluated its possible hypolipidemic and renoprotective effects in type 2 diabetic rats.

MATERIALS AND METHODS

Type 2 diabetic rats were induced by an administration of high-glucose-fat diet for 6 weeks and an intraperitoneal injection of streptozotocin (STZ, 30mg/kg). Diabetic rats were divided randomly into four groups and treated for 28 days with sitagliptin (30mg/kg) or shubat (6.97×10(6) lactic acid bacteria+2.20×10(4) yeasts) CFU/mL, (6.97×10(7) lactic acid bacteria+2.20×10(5) yeasts) CFU/mL and (6.97×10(8) lactic acid bacteria+2.20×10(6) yeasts) CFU/mL. In addition, a normal control group and a diabetic control group were used for comparison. All drugs were given orally once daily 10mL/kg for 4 weeks. Fasting blood glucose (FBG) and body weight (BW) were measured before treatment and every week thereafter. Total cholesterol (TC), triglycerides (TG), low-density lipoprotein cholesterol (LDL-c), high density lipoprotein cholesterol (HDL-c), serum creatinine (SCr), blood urea nitrogen (BUN), C-peptide, glycated hemoglobin (HbAlc), glucagon-like peptide-1 (GLP-1) levels and pancreas tissue sections were tested after 4 weeks.

RESULTS

Shubat demonstrated positive hypoglycemic activity on FBG, HbAlc, C-peptide and GLP-1 levels, high dose shubat decreased FBG (P<0.01) and HbAlc (P<0.05), increased C-peptide (P<0.05) and GLP-1 (P<0.01), decreased serum TC, TG, LDL-c (P<0.05), increased HDL-c (P<0.01), and improved the reduction of body weight as well as decreased SCr and BUN levels (P<0.01) compared to diabetic controls. Histological analysis showed shubat protected the function of islets of type 2 diabetic rats.

CONCLUSION

The results of this study indicate that shubat has significant hypoglycemic potential in T2D rats and may modulate lipid metabolism and protect renal function in the type 2 diabetic condition, which might be related to various probiotics acting through promoting the release of GLP-1 and improving the function of β-cells.

GLP-1R Agonists Modulate Enteric Immune Responses Through the Intestinal Intraepithelial Lymphocyte GLP-1R

Obesity and diabetes are characterized by increased inflammation reflecting disordered control of innate immunity. We reveal a local intestinal intraepithelial lymphocyte (IEL)-GLP-1 receptor (GLP-1R) signaling network that controls mucosal immune responses. Glp1r expression was enriched in intestinal IEL preparations and copurified with markers of Tαβ and Tγδ IELs, the two main subsets of intestinal IELs. Exendin-4 increased cAMP accumulation in purified IELs and reduced the production of cytokines from activated IELs but not from splenocytes ex vivo. These actions were mimicked by forskolin, absent in IELs from Glp1r(-/-) mice, and attenuated by the GLP-1R agonist exendin (9-39) consistent with a GLP-1R-dependent mechanism of action. Furthermore, Glp1r(-/-) mice exhibited dysregulated intestinal gene expression, an abnormal representation of microbial species in feces, and enhanced sensitivity to intestinal injury following administration of dextran sodium sulfate. Bone marrow transplantation using wild-type C57BL/6 donors normalized expression of multiple genes regulating immune function and epithelial integrity in Glp1r(-/-) recipient mice, whereas acute exendin-4 administration robustly induced the expression of genes encoding cytokines and chemokines in normal and injured intestine. Taken together, these findings define a local enteroendocrine-IEL axis linking energy availability, host microbial responses, and mucosal integrity to the control of innate immunity.

Gut-brain connection: The neuroprotective effects of the anti-diabetic drug liraglutide

Long-acting glucagon-like peptide-1 (GLP-1) analogues marketed for type 2 diabetes (T2D) treatment have been showing positive and protective effects in several different tissues, including pancreas, heart or even brain. This gut secreted hormone plays a potent insulinotropic activity and an important role in maintaining glucose homeostasis. Furthermore, growing evidences suggest the occurrence of several commonalities between T2D and neurodegenerative diseases, insulin resistance being pointed as a main cause for cognitive decline and increased risk to develop dementia. In this regard, it has also been suggested that stimulation of brain insulin signaling may have a protective role against cognitive deficits. As GLP-1 receptors (GLP-1R) are expressed throughout the central nervous system and GLP-1 may cross the blood-brain-barrier, an emerging hypothesis suggests that they may be promising therapeutic targets against brain dysfunctional insulin signaling-related pathologies. Importantly, GLP-1 actions depend not only on the direct effect mediated by its receptor activation, but also on the gut-brain axis involving an exchange of signals between both tissues via the vagal nerve, thereby regulating numerous physiological functions (e.g., energy homeostasis, glucose-dependent insulin secretion, as well as appetite and weight control). Amongst the incretin/GLP-1 mimetics class of anti-T2D drugs with an increasingly described neuroprotective potential, the already marketed liraglutide emerged as a GLP-1R agonist highly resistant to dipeptidyl peptidase-4 degradation (thereby having an increased half-life) and whose systemic GLP-1R activity is comparable to that of native GLP-1. Importantly, several preclinical studies showed anti-apoptotic, anti-inflammatory, anti-oxidant and neuroprotective effects of liraglutide against T2D, stroke and Alzheimer disease (AD), whereas several clinical trials, demonstrated some surprising benefits of liraglutide on weight loss, microglia inhibition, behavior and cognition, and in AD biomarkers. Herein, we discuss the GLP-1 action through the gut-brain axis, the hormone’s regulation of some autonomic functions and liraglutide’s neuroprotective potential.

Blood pressure-lowering effects of incretin-based diabetes therapies

Glucagon-like peptide-1 receptor (GLP-1) agonists and dipeptidyl-peptidase-4 (DPP-4) inhibitors are therapies that are used to treat hyperglycemia in patients with type 2 diabetes mellitus. Although both of these medication types primarily lower prandial and fasting blood glucose levels by enhanced GLP-1 receptor signalling, they have distinct mechanisms of action. Whereas DPP-4 inhibitors boost patient levels of endogenously produced GLP-1 (and glucose-dependent insulinotropic peptide) by preventing its metabolism by DPP-4 enzymatic activity, GLP-1 receptor agonists are either synthetic analogues of human GLP-1 or exendin-4 based molecules. They are tailored to resist hydrolysis by DPP-4 activity and to provide longer durability in the circulation compared with native GLP-1. Several roles for incretin-based diabetes therapies beyond the endocrine pancreas and their glycemic-lowering properties have now been described, including attenuation of cardiac myocyte injury and reduction in post-ischemic infarction size after cardiovascular insult. Favourable outcomes have also been observed on systolic blood pressure reduction, postprandial intestinal lipoprotein metabolism, endothelial cell function, modulation of innate immune-mediated inflammation and surrogate markers of renal function. As hypertension is an independent risk factor for premature death in patients with type 2 diabetes, potential favourable extrapancreatic actions, particularly within the heart, blood vessels and kidney, for this drug class are of considerable clinical interest. Herein, we highlight and provide critical appraisal of the clinical data supporting the antihypertensive effects of GLP-1 receptor agonists and DPP-4 inhibitors and link possible mechanisms of action to clinical outcomes reported for this drug class.

Physiology of proglucagon peptides: role of glucagon and GLP-1 in health and disease

The preproglucagon gene (Gcg) is expressed by specific enteroendocrine cells (L-cells) of the intestinal mucosa, pancreatic islet α-cells, and a discrete set of neurons within the nucleus of the solitary tract. Gcg encodes multiple peptides including glucagon, glucagon-like peptide-1, glucagon-like peptide-2, oxyntomodulin, and glicentin. Of these, glucagon and GLP-1 have received the most attention because of important roles in glucose metabolism, involvement in diabetes and other disorders, and application to therapeutics. The generally accepted model is that GLP-1 improves glucose homeostasis indirectly via stimulation of nutrient-induced insulin release and by reducing glucagon secretion. Yet the body of literature surrounding GLP-1 physiology reveals an incompletely understood and complex system that includes peripheral and central GLP-1 actions to regulate energy and glucose homeostasis. On the other hand, glucagon is established principally as a counterregulatory hormone, increasing in response to physiological challenges that threaten adequate blood glucose levels and driving glucose production to restore euglycemia. However, there also exists a potential role for glucagon in regulating energy expenditure that has recently been suggested in pharmacological studies. It is also becoming apparent that there is cross-talk between the proglucagon derived-peptides, e.g., GLP-1 inhibits glucagon secretion, and some additive or synergistic pharmacological interaction between GLP-1 and glucagon, e.g., dual glucagon/GLP-1 agonists cause more weight loss than single agonists. In this review, we discuss the physiological functions of both glucagon and GLP-1 by comparing and contrasting how these peptides function, variably in concert and opposition, to regulate glucose and energy homeostasis.

The regulatory roles of NADPH oxidase, intra- and extra-cellular HSP70 in pancreatic islet function, dysfunction and diabetes

The 70 kDa heat-shock protein (HSP70) family is important for a dynamic range of cellular processes that include protection against cell stress, modulation of cell signalling, gene expression, protein synthesis, protein folding and inflammation. Within this family, the inducible 72 kDa and the cognate 73 kDa forms are found at the highest level. HSP70 has dual functions depending on location. For example, intracellular HSP70 (iHSP70) is anti-inflammatory whereas extracellular HSP70 (eHSP70) has a pro-inflammatory function, resulting in local and systemic inflammation. We have recently identified a divergence in the levels of eHSP70 and iHSP70 in subjects with diabetes compared with healthy subjects and also reported that eHSP70 was correlated with insulin resistance and pancreatic β-cell dysfunction/death. In the present review, we describe possible mechanisms by which HSP70 participates in cell function/dysfunction, including the activation of NADPH oxidase isoforms leading to oxidative stress, focusing on the possible role of HSPs and signalling in pancreatic islet α- and β-cell physiological function in health and Type 2 diabetes mellitus.

Islet α cells and glucagon--critical regulators of energy homeostasis

Glucagon is secreted from islet α cells and controls blood levels of glucose in the fasting state. Impaired glucagon secretion predisposes some patients with type 1 diabetes mellitus (T1DM) to hypoglycaemia; whereas hyperglycaemia in patients with T1DM or type 2 diabetes mellitus (T2DM) is often associated with hyperglucagonaemia. Hence, therapeutic strategies to safely achieve euglycaemia in patients with diabetes mellitus now encompass bihormonal approaches to simultaneously deliver insulin and glucagon (in patients with T1DM) or reduce excess glucagon action (in patients with T1DM or T2DM). Glucagon also reduces food intake and increases energy expenditure through central and peripheral mechanisms, which suggests that activation of signalling through the glucagon receptor might be useful for controlling body weight. Here, we review new data that is relevant to understanding α-cell biology and glucagon action in the brain, liver, adipose tissue and heart, with attention to normal physiology, as well as conditions associated with dysregulated glucagon action. The feasibility and safety of current and emerging glucagon-based therapies that encompass both gain-of-function and loss-of-function approaches for the treatment of T1DM, T2DM and obesity is discussed in addition to developments, challenges and critical gaps in our knowledge that require additional investigation.

Glucagon-Like Peptide-1 Regulates Cholecystokinin Production in β-Cells to Protect From Apoptosis

Cholecystokinin (CCK) is a classic gut hormone that is also expressed in the pancreatic islet, where it is highly up-regulated with obesity. Loss of CCK results in increased β-cell apoptosis in obese mice. Similarly, islet α-cells produce increased amounts of another gut peptide, glucagon-like peptide 1 (GLP-1), in response to cytokine and nutrient stimulation. GLP-1 also protects β-cells from apoptosis via cAMP-mediated mechanisms. Therefore, we hypothesized that the activation of islet-derived CCK and GLP-1 may be linked. We show here that both human and mouse islets secrete active GLP-1 as a function of body mass index/obesity. Furthermore, GLP-1 can rapidly stimulate β-cell CCK production and secretion through direct targeting by the cAMP-modulated transcription factor, cAMP response element binding protein (CREB). We find that cAMP-mediated signaling is required for Cck expression, but CCK regulation by cAMP does not require stimulatory levels of glucose or insulin secretion. We also show that CREB directly targets the Cck promoter in islets from obese (Leptin(ob/ob)) mice. Finally, we demonstrate that the ability of GLP-1 to protect β-cells from cytokine-induced apoptosis is partially dependent on CCK receptor signaling. Taken together, our work suggests that in obesity, active GLP-1 produced in the islet stimulates CCK production and secretion in a paracrine manner via cAMP and CREB. This intraislet incretin loop may be one mechanism whereby GLP-1 protects β-cells from apoptosis.

Glucocorticoids decrease the production of glucagon-like peptide-1 at the transcriptional level in intestinal L-cells

Glucocorticoids are widely used as anti-inflammatory or immunosuppressive drugs, but often induce hyperglycemia as a side effect. Glucagon-like peptide-1 (GLP-1) is secreted from intestinal L cells and plays crucial roles in maintaining glucose homeostasis. However, the direct effects of glucocorticoids on the GLP-1 production pathway in L cells remain unclear. We investigated the effects of glucocorticoids on GLP-1 production in vitro and in vivo. In L cell lines, glucocorticoids decreased GLP-1 release and expression of the precursor, proglucagon, at protein and mRNA levels, which were inhibited by mifepristone. The administration of dexamethasone or budesonide to mice significantly decreased the mRNA expression of proglucagon in the ileum and partially decreased glucose-stimulated GLP-1 secretion. Compound A, a dissociated glucocorticoid receptor modulator, did not affect the expression of proglucagon in vitro. These results suggested that glucocorticoids directly reduced GLP-1 production at the transcriptional level in L cells through a glucocorticoid receptor dimerization-dependent mechanism.

Combined supplementation of carbohydrate, alanine, and proline is effective in maintaining blood glucose and increasing endurance performance during long-term exercise in mice

Carbohydrate supplementation is extremely important during prolonged exercise because it maintains blood glucose levels during later stages of exercise. In this study, we examined whether maintaining blood glucose levels by carbohydrate supplementation could be enhanced during long-term exercise by combining this supplementation with alanine and proline, which are gluconeogenic amino acids, and whether such a combination would affect exercise endurance performance. Male C57BL/6J mice were orally administered either maltodextrin (1.25 g/kg) or maltodextrin (1.0 g/kg) with alanine (0.225 g/kg) and proline (0.025 g/kg) 15 min before running for 170 min. Combined supplementation of maltodextrin, alanine, and proline induced higher blood glucose levels than isocaloric maltodextrin alone during the late exercise phase (100-170 min). The hepatic glycogen content of mice administered maltodextrin, alanine, and proline was higher than that of mice ingesting maltodextrin alone 60 min after beginning exercise, but the glycogen content of the gastrocnemius muscle showed no difference. We conducted a treadmill running test to determine the effect of alanine and proline on endurance performance. The test showed that running time to exhaustion of mice that were supplemented with maltodextrin (2.0 g/kg) was longer than that of mice that were supplemented with water alone. Maltodextrin supplementation (1.0 g/kg) with alanine (0.9 g/kg) and proline (0.1 g/kg) further increased running time to exhaustion compared to maltodextrin alone (2.0 g/kg). These results indicate that combined supplementation of carbohydrate, alanine, and proline is effective for maintaining blood glucose and hepatic glycogen levels and increasing endurance performance during long-term exercise in mice.

The insulinotrophic effect of insulin-like peptide 5 in vitro and in vivo

We report that INSL5 increases glucose-dependent insulin secretion in vitro and in vivo, and the intestinal L-cell line GLUTag expresses RXFP4 and responds to INSL5 stimulation by secreting GLP-1.

The effects of a TGR5 agonist and a dipeptidyl peptidase IV inhibitor on dextran sulfate sodium-induced colitis in mice

BACKGROUND AND AIM

Luminal nutrients stimulate enteroendocrine L cells to release gut hormones, including intestinotrophic glucagon-like peptide-2 (GLP-2). Because L cells express the bile acid receptor TGR5 and dipeptidyl peptidase-IV (DPPIV) rapidly degrades GLPs, we hypothesized that luminal TGR5 activation may attenuate intestinal injury via GLP-2 release, which is enhanced by DPPIV inhibition.

METHODS

Intestinal injury was induced in mice by administration of dextran sulfate sodium (DSS) in drinking water (free access to water containing 5% DSS for 7 days). The selective TGR5 agonist betulinic acid (BTA) and the DPPIV inhibitor sitagliptin phosphate monohydrate (STG) were administered orally for 7 days. Male C57BL/6 mice (6-7 weeks old) were divided into five groups: normal control group, disease control group, BTA low group (drinking water containing 15 mg/L BTA), BTA high group (50 mg/L BTA), and BTA high + STG (3 mg/kg, i.g.) group.

RESULTS

The selective TGR5 agonist BTA dose-dependently suppressed disease activity index and mRNA expression of the pro-inflammatory cytokines interleukin (IL)-1β, IL-6, and tumor necrosis factor-α in the colon. Nevertheless, STG administration had little additive effect on BTA-induced protection. Fibroblast activation protein mRNA expression, but not expression of other DPP family members, was increased in the colon of DSS-treated mice with increased mucosal DPPIV. Co-administration of the selective GLP-2 antagonist GLP-2 (3-33) reversed the effect of BTA.

CONCLUSION

The selective TGR5 agonist BTA ameliorated DSS-induced colitis in mice via the GLP-2 pathway with no effect of DPPIV inhibition, suggesting that other DPP enzymatic activity is involved in GLP-2 degradation.

Gut chemosensing mechanisms

The enteroendocrine system is the primary sensor of ingested nutrients and is responsible for secreting an array of gut hormones, which modulate multiple physiological responses including gastrointestinal motility and secretion, glucose homeostasis, and appetite. This Review provides an up-to-date synopsis of the molecular mechanisms underlying enteroendocrine nutrient sensing and highlights our current understanding of the neuro-hormonal regulation of gut hormone secretion, including the interaction between the enteroendocrine system and the enteric nervous system. It is hoped that a deeper understanding of how these systems collectively regulate postprandial physiology will further facilitate the development of novel therapeutic strategies.

Mosapride citrate increases postprandial glucagon-like peptide-1, insulin, and gene expression of sweet taste receptors

BACKGROUND AND AIM

Mosapride citrate-a prokinetic agent-improves hemoglobin A1c levels in diabetic patients; however, the underlying mechanism is unclear. We aimed to clarify this mechanism.

METHODS

Preprandial and postprandial (90 min after a meal) blood was obtained from 12 healthy men, and serum insulin and plasma active glucagon-like peptide-1 concentrations were measured. Measurements were also taken after the administration of 5 mg of mosapride citrate three times per day after every meal for 14 days. In addition, C57BL/6 mice were permitted free access to water containing 0.04 % domperidone (D group) or 0.02 % mosapride citrate (M group) for 2 weeks (four mice per group). T1r2 (taste receptor, type 1, member 2), T1r3, and Gnat3 (guanine nucleotide-binding protein, alpha transducing 3) mRNA expression levels of the stomach, duodenum, and proximal and mid-jejunum were evaluated.

RESULTS

In human subjects, postprandial plasma active glucagon-like peptide-1 and serum insulin concentrations after administration of mosapride citrate were significantly higher than those pre-administration (4.8 ± 2.2 pmol/L, 45.6 ± 41.6 μIU/mL, and 3.7 ± 1.2 pmol/L, 34.1 ± 28.4 μIU/mL, respectively). The mouse expression levels of T1r2 and Gnat3 in the proximal jejunum and mid-jejunum in the M group (4.1 ± 1.8-fold, 3.1 ± 1.6-fold, and 4.6 ± 0.8-fold, 3.1 ± 0.9-fold increases, respectively), were significantly higher than those of the control group.

CONCLUSIONS

The administration of mosapride citrate for 2 weeks enhanced postprandial plasma active glucagon-like peptide-1 and serum insulin concentration and increased the expression of sweet taste receptors in the upper intestine.

Versatile functions for IL-6 in metabolism and cancer

Owing to its abundance in inflammatory settings, interleukin IL-6 is frequently viewed as a proinflammatory cytokine, with functions that parallel those of tumor necrosis factor (TNF) and IL-1β in the context of inflammation. However, accumulating evidence points to a broader role for IL-6 in a variety of (patho)physiological conditions, including functions related to the resolution of inflammation. We review recent findings on the complex biological functions governed by IL-6 signaling, focusing on its role in inflammation-associated cancer and metabolic disorders such as obesity and type 2 diabetes mellitus (T2DM). We propose that the anti-inflammatory functions of IL-6 may extend to multiple settings and cell types, and suggest that these dimensions should be incorporated in therapeutic approaches to these diseases. Finally, we outline important areas of inquiry towards understanding this pleiotropic cytokine.

Ghrelin augments the expressions and secretions of proinflammatory adipokines, VEGF120 and MCP-1, in differentiated 3T3-L1 adipocytes

Ghrelin is a physiological-active peptide with growth hormone-releasing activity, orexigenic activity, etc. In addition, the recent study has also suggested that ghrelin possesses the pathophysiological abilities related with type 2 diabetes. However, the ghrelin-direct-effects implicated in type 2 diabetes on peripheral tissues have been still unclear, whereas its actions on the central nervous system (CNS) appear to induce the development of diabetes. Thus, to assess its peripheral effects correlated with diabetes, we investigated the regulatory mechanisms about adipokines, which play a central role in inducing peripheral insulin resistance, secreted from mature 3T3-L1 adipocytes stimulated with ghrelin in vitro . The stimulation with 50 nmol/L ghrelin for 24 h resulted in the significant 1.9-fold increase on vascular endothelial growth factor-120 (VEGF(120)) releases (p < 0.01) and the 1.7-fold on monocyte chemoattractant protein-1 (MCP-1) (p < 0.01) from 3T3-L1 adipocytes, respectively, while ghrelin failed to enhance tumor necrosis factor-α (TNF-α), interleukin-1β (IL-1β), IL-6, IL-10 and adiponectin secretions. In addition, Akt phosphorylation on Ser473 and c-Jun NH2 -terminal protein kinase (JNK) phosphorylation on Thr183/Tyr185 were markedly enhanced 1.4-fold (p < 0.01) and 1.6-fold (p < 0.01) in the ghrelin-stimulated adipocytes, respectively. Furthermore, the treatment with LY294002 (50 μmol/L) and Wortmannin (10nmol/L), inhibitors of phosphatidylinositol 3-kinase (PI3K), significantly decreased the amplified VEGF(120) secretion by 29% (p < 0.01) and 28% (p < 0.01) relative to the cells stimulated by ghrelin alone, respectively, whereas these inhibitors had no effects on increased MCP-1 release. On the other hand, JNK inhibitor SP600125 (10 μmol/L) clearly reduced the increased MCP-1, but not VEGF(120), release by 35% relative to the only ghrelin-stimulated cells (p < 0.01). In conclusion, ghrelin can enhance the secretions of proinflammatory adipokines, VEGF(120) and MCP-1, but fails to affect IL-10 and adiponectin which are considered to be anti-inflammatory adipokines. Moreover, this augmented VEGF(120) release is invited through the activation of PI3K pathways and the MCP-1 is through JNK pathways. Consequently, our results strongly suggest that ghrelin can induce the development of diabetes via its direct-action in peripheral tissues as well as via in CNS.

Effects of Roux-en-Y gastric bypass on fasting and postprandial inflammation-related parameters in obese subjects with normal glucose tolerance and in obese subjects with type 2 diabetes

BACKGROUND

Obesity is characterized by low grade inflammation and an altered secretion of inflammatory cytokines from the adipose tissue. Weight loss has shown to reduce inflammation; however, changes in cytokine profiles during massive weight loss are not well described. The present study explored the hypothesis that Roux-en-Y gastric bypass (RYGB) reduces circulating levels of pro-inflammatory cytokines, while increasing anti-inflammatory cytokines in obese subjects with type 2 diabetes (T2D) and in obese normal glucose tolerant (NGT) subjects.

METHODS

Thirteen obese subjects with T2D [weight; 129 ± 14 kg, glycated hemoglobin (HbA1c); 7.0 ± 0.9%, body mass index (BMI); 43.2 ± 5.3 kg/m(2), mean ± SD] and twelve matched obese NGT subjects [weight; 127 ± 15 kg, HbA1c; 5.5 ± 0.4%, BMI; 41.5 ± 4.8 kg/m(2), mean ± SD] were examined before, one week, three months, and one year after surgery. Interleukin (IL)-6, leptin, adiponectin, IL-8, transforming growth factor beta (TGF-β), and the incretin hormone glucagon-like peptide-1 (GLP-1) were measured in the fasting state and during a liquid meal. Insulin resistance was evaluated by HOMA-IR.

RESULTS

Weight loss did not differ between the two groups. Before surgery, HbA1c was higher and HOMA-IR lower in T2D patients, however, converged to the values of NGT subjects one year after surgery. Circulating cytokine concentrations did not differ between the two groups at any time point. One week after surgery, circulating IL-6 and IL-8 were increased, while adiponectin and leptin were reduced compared with pre-surgical concentrations. Three months after surgery, IL-8 was increased, leptin was reduced, and no change was observed for IL-6, TGF-β, and adiponectin. One year after surgery, concentrations of IL-6, TGF-β, and leptin were significantly reduced compared to before surgery, while adiponectin was significantly increased.

CONCLUSIONS

One year after RYGB, fasting concentrations of IL-6 and leptin were reduced, while no changes were observed in IL-8. TGF-β was decreased and adiponectin increased in both T2D and NGT obese subjects. This study is the first to examine IL-8 and TGF-β in obese subject after RYGB. Resolution of inflammation could offer a potential explanation for the health improvement associated with major weight loss after bariatric surgery.

TRIAL REGISTRATION

http://www.clinicaltrials.gov (NCT01579981).

The time has come to test the beta cell preserving effects of exercise in patients with new onset type 1 diabetes

Type 1 diabetes is characterised by immune-mediated destruction of insulin-producing beta cells. Significant beta cell function is usually present at the time of diagnosis with type 1 diabetes, and preservation of this function has important clinical benefits. The last 30 years have seen a number of largely unsuccessful trials for beta cell preservation, some of which have been of therapies that have potential for significant harm. There is a need to explore new, more tolerable approaches to preserving beta cell function that can be implemented on a large clinical scale. Here we review the evidence for physical exercise as a therapy for the preservation of beta cell function in patients with newly diagnosed type 1 diabetes. We highlight possible mechanisms by which exercise could preserve beta cell function and then present evidence from other models of diabetes that demonstrate that exercise preserves beta cell function. We conclude by proposing that there is now a need for studies to explore whether exercise can preserve beta cell in patients newly diagnosed with type 1 diabetes.

Insulin resistance pathogenesis in metabolic obesity

In this review we discuss the molecular mechanisms of insulin resistance concomitant with metabolic inflammation. We also analyze the world results of experimental and clinical studies which aimed at identifying the molecular targets for the development of new prevention and treatment of insulin resistance.

Interleukin-6 amplifies glucagon secretion: coordinated control via the brain and pancreas

Inappropriate glucagon secretion contributes to hyperglycemia in inflammatory disease. Previous work implicates the proinflammatory cytokine interleukin-6 (IL-6) in glucagon secretion. IL-6-KO mice have a blunted glucagon response to lipopolysaccharide (LPS) that is restored by intravenous replacement of IL-6. Given that IL-6 has previously been demonstrated to have a transcriptional (i.e., slow) effect on glucagon secretion from islets, we hypothesized that the rapid increase in glucagon following LPS occurred by a faster mechanism, such as by action within the brain. Using chronically catheterized conscious mice, we have demonstrated that central IL-6 stimulates glucagon secretion uniquely in the presence of an accompanying stressor (hypoglycemia or LPS). Contrary to our hypothesis, however, we found that IL-6 amplifies glucagon secretion in two ways; IL-6 not only stimulates glucagon secretion via the brain but also by direct action on islets. Interestingly, IL-6 augments glucagon secretion from both sites only in the presence of an accompanying stressor (such as epinephrine). Given that both adrenergic tone and plasma IL-6 are elevated in multiple inflammatory diseases, the interactions of the IL-6 and catecholaminergic signaling pathways in regulating GCG secretion may contribute to our present understanding of these diseases.