Gastric inhibitory polypeptide: the neglected incretin revisited

Incretin-based therapies for the management of cardiometabolic disease in the clinic: Past, present, and future

Among newer classes of drugs for type 2 diabetes mellitus (T2DM), glucagon-like peptide 1 receptor agonists (GLP-1 RAs) are incretin-based agents that lower both blood sugar levels and promote weight loss. They do so by activating pancreatic GLP-1 receptors (GLP-1R) to promote glucose-dependent insulin release and inhibit glucagon secretion. They also act on receptors in the brain and gastrointestinal tract to suppress appetite, slow gastric emptying, and delay glucose absorption. Phase 3 clinical trials have shown that GLP-1 RAs improve cardiovascular outcomes in the setting of T2DM or overweight/obesity in people who have, or are at high risk of having atherosclerotic cardiovascular disease. This is largely driven by reductions in ischemic events, although emerging evidence also supports benefits in other cardiovascular conditions, such as heart failure with preserved ejection fraction. The success of GLP-1 RAs has also seen the evolution of other incretin therapies. Tirzepatide has emerged as a dual glucose-dependent insulinotropic polypeptide (GIP)/GLP-1 RA, with more striking effects on glycemic control and weight reduction than those achieved by isolated GLP-1R agonism alone. This consists of lowering glycated hemoglobin levels by more than 2% and weight loss exceeding 15% from baseline. Here, we review the pharmacological properties of GLP-1 RAs and tirzepatide and discuss their clinical effectiveness for T2DM and overweight/obesity, including their ability to reduce adverse cardiovascular outcomes. We also delve into the mechanistic basis for these cardioprotective effects and consider the next steps in implementing existing and future incretin-based therapies for the broader management of cardiometabolic disease.

Glucagon-Like Peptide-1 (GLP-1) during Ramadan: Narrative Review of the Published Literature

Ramadan fasting, a religious practice observed by Muslims worldwide, involves abstaining from eating, drinking, smoking, and using oral medications from dawn to dusk during the ninth lunar month. Studies have demonstrated that fasting during Ramadan has been shown to increase HDL cholesterol, leptin, adiponectin, and insulin sensitivity, as well as lower several hemostatic risk factors for cardiovascular diseases. Additionally, it may result in a drop in blood sugar levels, especially in diabetics who are also on blood sugar-lowering medicine. Hypoglycemia, characterized by low blood sugar levels, could also result from fasting during Ramadan. The GLP-1 (glucagon-like peptide-1) hormone plays a significant role in regulating glucose metabolism and insulin secretion, and Ramadan fasting can affect its production and release in the gut. Research contributes to our understanding of the utilization of GL-1 medications during Ramadan among patients, broadening therapy alternatives and offering insightful information for well-informed decision-making. Therefore, this narrative review aims to explore the current evidence that studies the safety and efficacy of GLP-1 agonists during Ramadan for nondiabetic and diabetic patients to ensure healthy fasting during Ramadan.

Glucagon-like peptide-1/glucose-dependent insulinotropic polypeptide receptor co-agonists for cardioprotection, type 2 diabetes and obesity: a review of mechanisms and clinical data

PURPOSE OF REVIEW

Glucagon-like peptide-1 receptor agonists (GLP-1RAs) are approved for the management of type 2 diabetes (T2D) and obesity, and some are recommended for cardiorenal risk reduction in T2D. To enhance the benefits with GLP-RA mono-agonist therapy, GLP-1/glucose-dependent insulinotropic polypeptide (GIP) receptor co-agonists are in development to capitalize on the synergism of GLP-1 and GIP agonism. We review the mechanisms of action and clinical data for GLP-1/GIP receptor co-agonists in T2D and obesity and their potential role in cardiovascular protection.

RECENT FINDINGS

Tirzepatide, a first-in-class unimolecular GLP-1/GIP receptor co-agonist, is approved for T2D and is awaiting approval for obesity management. Phase 3 trials in T2D cohorts revealed significant reductions in glycemia and body weight and superiority compared with GLP-1R mono-agonism with semaglutide. Tirzepatide has demonstrated significant body weight reductions in individuals with obesity but not diabetes. It enhances lipid metabolism, reduces blood pressure, and lowers liver fat content. Pooled phase 2/3 data showed cardiovascular safety in T2D while a post hoc analysis suggested tirzepatide slows the decline of kidney function in T2D.

SUMMARY

GLP-1/GIP receptor co-agonists are a novel addition to the diabetes and obesity armamentarium. The cardiorenal-metabolic benefits position them as promising multiprong tools for metabolically complex individuals with chronic vascular complications.

Impact of TOTUM-63, a fibre and polyphenol rich plant-based composition, on gut and pancreatic hormone secretion in diet-induced obese mice

BACKGROUND AND AIMS

TOTUM-63, a fibre and polyphenol rich plant-based composition, has been demonstrated to significantly improve body weight and glucose homeostasis in animal models of obesity. Our study aimed at exploring whether the mechanisms include modulation of gut (glucose-dependent insulinotropic peptide (GIP), glucagon-like petide-1 (GLP-1), cholecystokinin (CCK), peptide YY (PYY)) and pancreatic (insulin, glucagon) hormones, all important regulators of glucose control, appetite and body weight.

METHODS AND RESULTS

Male C57BL/6JRJ mice were assigned to either standard chow (CON), high fat diet (HF, 60% energy from fat) or HF-TOTUM-63 (HF diet 60% supplemented with TOTUM-63 2.7%) for 10 weeks. In vivo glucose homeostasis (oral glucose tolerance test (OGTT), intraperitoneal pyruvate tolerance test (ipPTT)), glucose-induced portal vein hormone concentration, gut hormone gene expression and protein content as well as enteroendocrine cell contents were assessed at the end of the dietary intervention. The present study evidenced that TOTUM-63 reduced food intake, limited weight gain and improved glucose and pyruvate tolerance of HF-fed animals. This was associated with an increase in PYY content in the colon, an altered pattern of PYY secretion between fasted and glucose-stimulated states, and with a significant improvement in the portal vein concentration of GLP-1, insulin and glucagon, but not GIP and CCK, in response to glucose stimulation.

CONCLUSION

Overall, these data suggest that TOTUM-63 might have a specific impact on gut L-cells and on the expression and secretion of GLP-1 and PYY incretins, potentially contributing to the reduced food intake, body weight gain and improved glucose homeostasis.

Peptides in the regulation of glucagon secretion

Glucose homeostasis is maintained by the glucoregulatory hormones, glucagon, insulin and somatostatin, secreted from the islets of Langerhans. Glucagon is the body's most important anti-hypoglycemic hormone, mobilizing glucose from glycogen stores in the liver in response to fasting, thus maintaining plasma glucose levels within healthy limits. Glucagon secretion is regulated by both circulating nutrients, hormones and neuronal inputs. Hormones that may regulate glucagon secretion include locally produced insulin and somatostatin, but also urocortin-3, amylin and pancreatic polypeptide, and from outside the pancreas glucagon-like peptide-1 and 2, peptide tyrosine tyrosine and oxyntomodulin, glucose-dependent insulinotropic polypeptide, neurotensin and ghrelin, as well as the hypothalamic hormones arginine-vasopressin and oxytocin, and calcitonin from the thyroid. Each of these hormones have distinct effects, ranging from regulating blood glucose, to regulating appetite, stomach emptying rate and intestinal motility, which makes them interesting targets for treating metabolic diseases. Awareness regarding the potential effects of the hormones on glucagon secretion is important since secretory abnormalities could manifest as hyperglycemia or even lethal hypoglycemia. Here, we review the effects of each individual hormone on glucagon secretion, their interplay, and how treatments aimed at modulating the plasma levels of these hormones may also influence glucagon secretion and glycemic control.

Roles of Alkaloids from Medicinal Plants in the Management of Diabetes Mellitus

Medicinal plants play a fundamental part in health sectors via the management of different infectious diseases because of their wide plenitude wellspring of bioactive phytochemicals. Research activities on them have got attention throughout the world in the present days in search of low-cost and safe compounds for the management of diabetes. This is the literature-based analysis of alkaloids from medicinal plants in preventive or treatment approaches to diabetes. The most abundant and diversified group of secondary metabolites, i.e., alkaloids, show antidiabetic activity through the inhibition of enzymes (α-amylase, α-glucosidase, aldose reductase, dipeptidyl peptidase-IV, and protein tyrosine phosphatase-1B); inhibition of advanced glycation end products; increment of insulin secretion and its sensitivity; enhancement of glucose uptake; and their antioxidant ability. The study is useful for the examination of dynamic alkaloids for the advancement of a new medication for mankind.

An overview of alogliptin + pioglitazone for the treatment of type 2 diabetes

INTRODUCTION

Type 2 diabetes (T2D) is a progressive condition, and sequential additions of therapy are usually required to maintain glycemic control. The options for glucose lowering therapies have increased considerably in recent years. Fixed-dose combinations such as alogliptin with pioglitazone provide a convenient choice which can improve medication adherence.

AREAS COVERED

The authors performed a literature search to identify publications describing the efficacy and safety of alogliptin and pioglitazone when used separately and in combinations.

EXPERT OPINION

Pioglitazone activates peroxisome proliferator-activated receptor-gamma which improves insulin sensitivity and helps to preserve β-cell function with a durable improvement in glycemic control. Pioglitazone can retard the progression of atherosclerosis and reduce cardiovascular events, but it is associated with adverse events including weight gain, fluid retention, and increased risk of fractures. Alogliptin improves glycemic control and appears neutral in terms of cardiovascular events. It does not appear to increase the adverse events associated with pioglitazone and use of the combination may permit the use of lower doses of pioglitazone with reduced adverse effects. There are no cardiovascular outcome studies with the combination but the cardiovascular benefits of pioglitazone and additional glucose lowering effects of alogliptin provide a useful combination with convenient once daily dosing.

The evolving story of incretins (GIP and GLP-1) in metabolic and cardiovascular disease: A pathophysiological update

The incretin hormones glucose-dependent insulinotropic polypeptide (GIP) and glucagon-like peptide-1 (GLP-1) have their main physiological role in augmenting insulin secretion after their nutrient-induced secretion from the gut. A functioning entero-insular (gut-endocrine pancreas) axis is essential for the maintenance of a normal glucose tolerance. This is exemplified by the incretin effect (greater insulin secretory response to oral as compared to "isoglycaemic" intravenous glucose administration due to the secretion and action of incretin hormones). GIP and GLP-1 have additive effects on insulin secretion. Local production of GIP and/or GLP-1 in islet α-cells (instead of enteroendocrine K and L cells) has been observed, and its significance is still unclear. GLP-1 suppresses, and GIP increases glucagon secretion, both in a glucose-dependent manner. GIP plays a greater physiological role as an incretin. In type 2-diabetic patients, the incretin effect is reduced despite more or less normal secretion of GIP and GLP-1. While insulinotropic effects of GLP-1 are only slightly impaired in type 2 diabetes, GIP has lost much of its acute insulinotropic activity in type 2 diabetes, for largely unknown reasons. Besides their role in glucose homoeostasis, the incretin hormones GIP and GLP-1 have additional biological functions: GLP-1 at pharmacological concentrations reduces appetite, food intake, and-in the long run-body weight, and a similar role is evolving for GIP, at least in animal studies. Human studies, however, do not confirm these findings. GIP, but not GLP-1 increases triglyceride storage in white adipose tissue not only through stimulating insulin secretion, but also by interacting with regional blood vessels and GIP receptors. GIP, and to a lesser degree GLP-1, play a role in bone remodelling. GLP-1, but not GIP slows gastric emptying, which reduces post-meal glycaemic increments. For both GIP and GLP-1, beneficial effects on cardiovascular complications and neurodegenerative central nervous system (CNS) disorders have been observed, pointing to therapeutic potential over and above improving diabetes complications. The recent finding that GIP/GLP-1 receptor co-agonists like tirzepatide have superior efficacy compared to selective GLP-1 receptor agonists with respect to glycaemic control as well as body weight has renewed interest in GIP, which previously was thought to be without any therapeutic potential. One focus of this research is into the long-term interaction of GIP and GLP-1 receptor signalling. A GLP-1 receptor antagonist (exendin [9-39]) and, more recently, a GIP receptor agonist (GIP [3-30] NH₂ ) and, hopefully, longer-acting GIP receptor agonists for human use will be helpful tools to shed light on the open questions. A detailed knowledge of incretin physiology and pathophysiology will be a prerequisite for designing more effective incretin-based diabetes drugs.

Probiotic and resveratrol normalize GLP-1 levels and oxidative stress in the intestine of diabetic rats

Background

Recently, the use of incretins has been considered as a therapeutic target for diabetes. One of the important incretins in the improvement of diabetes is glucagon-like peptide (GLP-1), which is secreted by the gut and reduces the apoptosis of pancreatic β-cells and improves insulin sensitivity. In this experiment we determined the effects of resveratrol and probiotics on insulin resistance, oxidative stress, and GLP-1 in type 2 diabetes (T2D) rats.

Methods

In this study, 40 male Wistar male rats were divided into 5 groups: 1. Control group, 2. T2D, 3. T2D treated with probiotics, 4. T2D treated with resveratrol, 5. T2D group treated with probiotics and resveratrol. After four weeks, the intestine were removed for histopathological analysis, biochemical tests, and oxidative stress markers.

Results

Probiotics and resveratrol significantly decreased (p < 0.001) glucose and insulin resistance, and increased (p < 0.001) GLP1 and total antioxidant capacity compared to the diabetic group. Treatment with probiotics and resveratrol also returned intestinal histological changes in diabetic rats to normal.

Conclusion

Resveratrol and probiotics appear to be effective in controlling T2D by increasing GLP-1 levels and reducing oxidative stress.

Beneficial Effects of Vitamin K Status on Glycemic Regulation and Diabetes Mellitus: A Mini-Review

Type 2 diabetes mellitus is a chronic disease that is characterized by hyperglycemia, insulin resistance, and dysfunctional insulin secretion. Glycemic control remains a crucial contributor to the progression of type 2 diabetes mellitus as well as the prevention or delay in the onset of diabetes-related complications. Vitamin K is a fat-soluble vitamin that plays an important role in the regulation of the glycemic status. Supplementation of vitamin K may reduce the risk of diabetes mellitus and improve insulin sensitivity. This mini-review summarizes the recent insights into the beneficial effects of vitamin K and its possible mechanism of action on insulin sensitivity and glycemic status, thereby suppressing the progression of diabetes mellitus.

Effects of Agave Fructans, Inulin, and Starch on Metabolic Syndrome Aspects in Healthy Wistar Rats

Healthy Wistar rats were supplemented during 20 weeks with commercial inulin (I) and Agave tequilana fructans (CAT), experimental fructans from A. tequilana (EAT) and A. salmiana (AS) mature stems, rice starch 10% (RS), and standard feed for rodents (C). Feed intake was kept steady, but with I, body weight and abdominal adipose tissue (6.01 g) decreased at the end. Glucose (mg/dL) (C, 120.52; I, 110.69; CAT, 105.75; EAT, 115.48; AS, 101.63; and RS, 121.82), total cholesterol (C, 89.89; I, 64.48; CAT, 68.04; EAT, 68.74; AS, 68.04; and RS, 82), and triglycerides (C, 84.03; I, 59.52; CAT, 68.56; EAT, 59.08; AS, 75.27; and RS, 81.8) kept being normal and without differences between fructans. At the end, there was a significant increase in lactic acid bacteria when the I and AS groups were compared to the C group (C, 9.18; I, 10.64; CAT, 10.34; EAT, 10.36; AS, 10.49; and RS, 9.62 log 10 CFU/g of feces). In addition, with fructans, there was an accelerated process in feces emptiness, Lieberkühn crypts kept their morphology, and there was an increment of goblet cells.

Glucose-Dependent Insulinotropic Polypeptide Is a Pancreatic Polypeptide Secretagogue in Humans

BACKGROUND

Glucose-dependent insulinotropic polypeptide (GIP) has been suggested to stimulate the secretion of pancreatic polypeptide (PP), an islet hormone thought to regulate gut motility, appetite, and glycemia.

OBJECTIVE

To determine whether human GIP1-42 (hGIP) stimulates PP secretion.

METHOD

As glycemia modulates the secretion of PP, we measured plasma PP concentrations from 2 studies in healthy men (n = 10) and in patients with type 2 diabetes (T2D) (n = 12), where hGIP1-42 had been administered intravenously during fasting glycemia, hyperglycemia (12 mmol/L), and insulin-induced hypoglycemia (targets: 2.5 mmol/L [healthy]; 3.5 mmol/L [T2D]). Porcine GIP1-42 (pGIP) was also infused intra-arterially in isolated porcine pancreata (n = 4).

RESULTS

Mean fasting plasma glucose concentrations were approximately 5 mmol/L (healthy) and approximately 8 mmol/L (T2D). At fasting glycemia, PP concentrations were higher during intravenous hGIP1-42 infusion compared with saline in healthy men (mean [standard error of the mean, SEM], net incremental areas under the curves (iAUCs)[0-30min], 403 [116] vs -6 [57] pmol/L × min; P = 0.004) and in patients with T2D (905 [177] vs -96 [86] pmol/L × min; P = 0.009). During hyperglycemic clamping, mean [SEM] PP concentrations were significantly higher during hGIP1-42 infusion compared with saline in patients with T2D (771 [160] vs -183 [117] pmol/L × min; P = 0.001), but not in healthy individuals (-8 [86] vs -57 [53] pmol/L × min; P = 0.69). When plasma glucose levels were declining in response to exogenous insulin, mean [SEM] PP concentrations were higher during hGIP1-42 infusion compared with saline in healthy individuals (294 [88] vs -82 [53] pmol/L × min; P = 0.0025), but not significantly higher in patients with T2D (586 [314] vs -120 [53]; P = 0.070). At target hypoglycemia, PP levels surged in both groups during both hGIP1-42 and saline infusions. In isolated pancreata, pGIP1-42 increased mean [SEM] PP output in the pancreatic venous effluent (baseline vs infusion, 24[5] vs 79 [16] pmol/min x min; P = 0.044).

CONCLUSION

GIP1-42 increases plasma PP secretion in healthy individuals, patients with T2D, and isolated porcine pancreata. Hyperglycemia blunts the stimulatory effect of hGIP1-42 in healthy individuals, but not in patients with T2D.

The early history of GIP 1969-2000: From enterogastrone to major metabolic hormone

This paper describes the early history of Gastric Inhibitory Polypeptide, better referred to simply as GIP, from its isolation by purification from a crude preparation of CCK-PZ (cholecystokinin/pancreozymin) to its recognition as a key play in the pathogenesis of obesity and other metabolic disorders far removed from the enterogastrone properties by which it was originally identified. Augmentation of glucose mediated insulin release, the incretin effect, was discovered soon after GIP was first isolated and only much later was its important role in the pathogenesis of obesity, through mechanism other than its insulin secretion, appreciated. Immunoassay - the method by which the concentration of GIP was measured in plasma until quite recently - was found to be flawed and to depend upon which specific epitope of the hormone an assay detected. This was especially true if it was an amino-acid sequence specific to porcine rather than human GIP. A further confounder was the discovery that much of the GIP measured by immunoassay was its biological antagonist produced by cleavage of its two N-terminal amino-acids in the circulation by the same dipeptidyl-peptidase as de-activates GLP-1. Potential use of synthetic agonistic and antagonistic GIP analogues in therapeutics was barely alluded to before year 2000.

The early history of GIP 1969-2000: From enterogastrone to major metabolic hormone

This paper describes the early history of Gastric Inhibitory Polypeptide, better referred to simply as GIP, from its isolation by purification from a crude preparation of CCK-PZ (cholecystokinin/pancreozymin) to its recognition as a key player in the pathogenesis of obesity and other metabolic disorders far removed from the enterogastrone properties by which it was originally identified. Augmentation of glucose mediated insulin release, the incretin effect, was discovered soon after GIP was first isolated and only much later was its important role in the pathogenesis of obesity, through mechanism other than insulin secretion, appreciated. Immunoassay - the only method by which the concentration of GIP was measured in plasma until quite recently - was found to be flawed and to depend upon which specific epitope of the hormone an assay detected. This was especially true if it was an amino-acid sequence specific to porcine rather than human GIP. A further confounder was the discovery that much of the GIP measured by immunoassay was its biological antagonist produced by cleavage of its two N-terminal amino-acids in the circulation by the same dipeptidyl-peptidase as de-activates GLP-1. Potential use of synthetic agonistic and antagonistic GIP analogues in therapeutics was barely alluded to before year 2000.

Role of Peptide Hormones in the Adaptation to Altered Dietary Protein Intake

Dietary protein profoundly influences organismal traits ultimately affecting healthspan. While intracellular signalling downstream of altered amino acid supply is undoubtedly important, peptide hormones have emerged as critical factors determining systemic responses to variations in protein intake. Here the regulation and role of certain peptides hormones in such responses to altered dietary protein intake is reviewed.

The Role of DPP-4 Inhibitors in the Treatment Algorithm of Type 2 Diabetes Mellitus: When to Select, What to Expect

Type 2 diabetes mellitus is a growing global public health problem, the prevalence of which is projected to increase in the succeeding decades. It is potentially associated with many complications, affecting multiple organs and causing a huge burden to the society. Due to its multi-factorial pathophysiology, its treatment is varied and based upon a multitude of pharmacologic agents aiming to tackle the many aspects of the disease pathophysiology (increasing insulin availability [either through direct insulin administration or through agents that promote insulin secretion], improving sensitivity to insulin, delaying the delivery and absorption of carbohydrates from the gastrointestinal tract, or increasing urinary glucose excretion). DPP-4 (dipeptidyl peptidase-4) inhibitors (or “gliptins”) represent a class of oral anti-hyperglycemic agents that inhibit the enzyme DPP-4, thus augmenting the biological activity of the “incretin” hormones (glucagon-like peptide-1 [GLP-1] and glucose-dependent insulinotropic polypeptide [GIP]) and restoring many of the pathophysiological problems of diabetes. They have already been used over more than a decade in the treatment of the disease. The current manuscript will review the mechanism of action, therapeutic utility, and the role of DPP-4 inhibitors for the treatment of type 2 diabetes mellitus.

Menaquinone-4 Amplified Glucose-Stimulated Insulin Secretion in Isolated Mouse Pancreatic Islets and INS-1 Rat Insulinoma Cells

Vitamin K2 is indispensable for blood coagulation and bone metabolism. Menaquinone-4 (MK-4) is the predominant homolog of vitamin K2, which is present in large amounts in the pancreas, although its function is unclear. Meanwhile, β-cell dysfunction following insulin secretion has been found to decrease in patients with type 2 diabetes mellitus. To elucidate the physiological function of MK-4 in pancreatic β-cells, we studied the effects of MK-4 treatment on isolated mouse pancreatic islets and rat INS-1 cells. Glucose-stimulated insulin secretion significantly increased in isolated islets and INS-1 cells treated with MK-4. It was further clarified that MK-4 enhanced cAMP levels, accompanied by the regulation of the exchange protein directly activated by the cAMP 2 (Epac2)-dependent pathway but not the protein kinase A (PKA)-dependent pathway. A novel function of MK-4 on glucose-stimulated insulin secretion was found, suggesting that MK-4 might act as a potent amplifier of the incretin effect. This study therefore presents a novel potential therapeutic approach for impaired insulinotropic effects.

Glucose Appearance Rate Rather than the Blood Glucose Concentrations Explains Differences in Postprandial Insulin Responses between Wholemeal Rye and Refined Wheat Breads-Results from A Cross-Over Meal Study

SCOPE

Ingestion of rye bread leads to lower postprandial plasma insulin concentrations than wheat bread ingestion, but most often not too different glucose profiles. The mechanism behind this discrepancy is still largely unknown. This study investigates whether glucose kinetics may explain the observed discrepancy.

METHODS AND RESULTS

Nine healthy men participated in a crossover study, eating 50 g of available carbohydrates as either refined wheat (WB) or traditional wholemeal rye bread (WMR) during d-[6,6-² H₂ ]glucose infusion. Labeled glucose enrichment is measured by an HPLC-TOF-MS method. The calculated rate of glucose appearance (RaE) is significantly lower after ingestion of WMR during the initial 15 min postprandial period. Additionally, the 0-90 min RaE area under the curve (AUC) is significantly lower after ingestion of WMR, as is plasma gastric inhibitory polypeptide (GIP) at 60 and 90 min. Postprandial glycemic responses do not differ between the breads. Postprandial insulin is lower after ingestion of WMR at 45 and 60 min, as is the 0-90 min AUC.

CONCLUSION

Ingestion of WMR elicits a lower rate of glucose appearance into the bloodstream compared with WB. This may explain the lower insulin response observed after rye bread ingestion, commonly known as the rye factor.

Effect of coffee or coffee components on gut microbiome and short-chain fatty acids in a mouse model of metabolic syndrome

We previously showed that male Tsumura Suzuki obese diabetes (TSOD) mice, a spontaneous mouse model of metabolic syndrome, manifested gut dysbiosis and subsequent disruption of the type and quantity of plasma short-chain fatty acids (SCFAs), and daily coffee intake prevented nonalcoholic steatohepatitis in this mouse model. Here, we present a preliminary study on whether coffee and its major components, caffeine and chlorogenic acid, would affect the gut dysbiosis and the disrupted plasma SCFA profile of TSOD mice, which could lead to improvement in the liver pathology of these mice. Three mice per group were used. Daily intake of coffee or its components for 16 wk prevented liver lobular inflammation without improving obesity in TSOD mice. Coffee and its components did not repair the altered levels of Gram-positive and Gram-negative bacteria and an increased abundance of Firmicutes in TSOD mice but rather caused additional changes in bacteria in six genera. However, caffeine and chlorogenic acid partially improved the disrupted plasma SCFA profile in TSOD mice, although coffee had no effects. Whether these alterations in the gut microbiome and the plasma SCFA profile might affect the liver pathology of TSOD mice may deserve further investigation.

Enteroendocrine K and L cells in healthy and type 2 diabetic individuals

AIMS/HYPOTHESIS

Enteroendocrine K and L cells are pivotal in regulating appetite and glucose homeostasis. Knowledge of their distribution in humans is sparse and it is unknown whether alterations occur in type 2 diabetes. We aimed to evaluate the distribution of enteroendocrine K and L cells and relevant prohormone-processing enzymes (using immunohistochemical staining), and to evaluate the mRNA expression of the corresponding genes along the entire intestinal tract in individuals with type 2 diabetes and healthy participants.

METHODS

In this cross-sectional study, 12 individuals with type 2 diabetes and 12 age- and BMI-matched healthy individuals underwent upper and lower double-balloon enteroscopy with mucosal biopsy retrieval from approximately every 30 cm of the small intestine and from seven specific anatomical locations in the large intestine.

RESULTS

Significantly different densities for cells positive for chromogranin A (CgA), glucagon-like peptide-1, glucose-dependent insulinotropic polypeptide, peptide YY, prohormone convertase (PC) 1/3 and PC2 were observed along the intestinal tract. The expression of CHGA did not vary along the intestinal tract, but the mRNA expression of GCG, GIP, PYY, PCSK1 and PCSK2 differed along the intestinal tract. Lower counts of CgA-positive and PC1/3-positive cells, respectively, were observed in the small intestine of individuals with type 2 diabetes compared with healthy participants. In individuals with type 2 diabetes compared with healthy participants, the expression of GCG and PYY was greater in the colon, while the expression of GIP and PCSK1 was greater in the small intestine and colon, and the expression of PCSK2 was greater in the small intestine.

CONCLUSIONS/INTERPRETATION

Our findings provide a detailed description of the distribution of enteroendocrine K and L cells and the expression of their products in the human intestinal tract and demonstrate significant differences between individuals with type 2 diabetes and healthy participants.

TRIAL REGISTRATION

NCT03044860.

Mechanisms of weight loss and improved metabolism following bariatric surgery

Bariatric surgery is increasingly recognized as one of the most effective interventions to help patients achieve significant and sustained weight loss, as well as improved metabolic and overall health. Unfortunately, the cellular and physiological mechanisms by which bariatric surgery achieves weight loss have not been fully elucidated, yet are critical to understanding the central role of the intestinal tract in whole-body metabolism and to developing novel strategies for the treatment of obesity. In this review, we provide an overview of potential mechanisms contributing to weight loss, including effects on regulation of energy balance and both central and peripheral nervous system regulation of appetite and metabolism. Moreover, we highlight the importance of the gastrointestinal tract, including alterations in bile acid physiology, secretion of intestinally derived hormones, and the microbiome, as a potent mediator of improved metabolism in postbariatric patients.

Generation of a highly diverse panel of antagonistic chicken monoclonal antibodies against the GIP receptor

Raising functional antibodies against G protein-coupled receptors (GPCRs) is challenging due to their low density expression, instability in the absence of the cell membrane's lipid bilayer and frequently short extracellular domains that can serve as antigens. In addition, a particular therapeutic concept may require an antibody to not just bind the receptor, but also act as a functional receptor agonist or antagonist. Antagonizing the glucose-dependent insulinotropic polypeptide (GIP) receptor may open up new therapeutic modalities in the treatment of diabetes and obesity. As such, a panel of monoclonal antagonistic antibodies would be a useful tool for in vitro and in vivo proof of concept studies. The receptor is highly conserved between rodents and humans, which has contributed to previous mouse and rat immunization campaigns generating very few usable antibodies. Switching the immunization host to chicken, which is phylogenetically distant from mammals, enabled the generation of a large and diverse panel of monoclonal antibodies containing 172 unique sequences. Three-quarters of all chicken-derived antibodies were functional antagonists, exhibited high-affinities to the receptor extracellular domain and sampled a broad epitope repertoire. For difficult targets, including GPCRs such as GIPR, chickens are emerging as valuable immunization hosts for therapeutic antibody discovery.

Diabetes: Rationale for Dipeptidyl Peptidase 4 Inhibitors: A New Class of Oral Agents for the Treatment of Type 2 Diabetes Mellitus

Objective:

To review advances in understanding the pathophysiologic basis of type 2 diabetes mellitus and the pharmacology and mechanism of action of dipeptidyl peptidase 4 (DPP-4) inhibition in correcting the underlying defects in glycemic control.

Data Sources:

Articles were identified through MEDLINE for the period 1966 through November 2006. Abstracts and presentations from the American Diabetes Association Scientific Sessions and the European Association for the Study of Diabetes (2002–2006) were also searched for scientific reports on DPP-4 inhibitors.

Study Selection And Data Extraction:

Abstracts, original clinical and preclinical research reports, and review articles published in the English language were identified for review. Literature discussing glucose regulation, incretin hormones, type 2 diabetes pathophysiology, and DPP-4 inhibition were evaluated and selected based on consideration of their support for the proof of concept, mechanistic and in vivo findings, and timeliness.

Data Synthesis:

The search for new and effective therapies for type 2 diabetes has led to the identification of a novel therapeutic target, the incretin hormones, which play a role in mediating glucose homeostasis via effects on glucagon and insulin secretion from pancreatic islet α- and β-cells, respectively. The incretins' glucagon-like peptide-1 and glucose-dependent insulinotropic polypeptide are rapidly inactivated by the enzyme DPP-4. DPP-4 inhibitor agents act by blocking the active site of DPP-4, thereby preventing inactivation of and prolonging the duration of action of incretins, which in turn helps to correct the defective insulin and glucagon secretion that marks type 2 diabetes. Clinical studies to date indicate that DPP-4 inhibitors effectively stimulate insulin secretion, suppress glucagon release, and improve glucose control in patients with type 2 diabetes. These agents are well tolerated and have a low incidence of adverse effects.

Conclusions:

The DPP-4 inhibitors are novel agents for the treatment of type 2 diabetes. Compounds under development in this new class of oral antidiabetic drugs may be free of the limitations of current therapies.

Comparative Analysis of Binding Kinetics and Thermodynamics of Dipeptidyl Peptidase-4 Inhibitors and Their Relationship to Structure

The binding kinetics and thermodynamics of dipeptidyl peptidase (DPP)-4 inhibitors (gliptins) were investigated using surface plasmon resonance and isothermal titration calorimetry. Binding of gliptins to DPP-4 is a rapid electrostatically driven process. Off-rates were generally slow partly because of reversible covalent bond formation by some gliptins, and partly because of strong and extensive interactions. Binding of all gliptins is enthalpy-dominated due to strong ionic interactions and strong solvent-shielded hydrogen bonds. Using a congeneric series of molecules which represented the intermediates in the lead optimization program of linagliptin, the onset of slow binding kinetics and development of the thermodynamic repertoire were analyzed in the context of incremental changes of the chemical structures. All compounds rapidly associated, and therefore the optimization of affinity and residence time is highly correlated. The major contributor to the increasing free energy of binding was a strong increase of binding enthalpy, whereas entropic contributions remained low and constant despite significant addition of lipophilicity.

Successful weight loss maintenance includes long-term increased meal responses of GLP-1 and PYY3-36

OBJECTIVE

The hormones glucagon-like peptide 1 (GLP-1), peptide YY3-36 (PYY3-36), ghrelin, glucose-dependent insulinotropic polypeptide (GIP) and glucagon have all been implicated in the pathogenesis of obesity. However, it is unknown whether they exhibit adaptive changes with respect to postprandial secretion to a sustained weight loss.

DESIGN

The study was designed as a longitudinal prospective intervention study with data obtained at baseline, after 8 weeks of weight loss and 1 year after weight loss.

METHODS

Twenty healthy obese individuals obtained a 13% weight loss by adhering to an 8-week very low-calorie diet (800kcal/day). After weight loss, participants entered a 52-week weight maintenance protocol. Plasma levels of GLP-1, PYY3-36, ghrelin, GIP and glucagon during a 600-kcal meal were measured before weight loss, after weight loss and after 1 year of weight maintenance. Area under the curve (AUC) was calculated as total AUC (tAUC) and incremental AUC (iAUC).

RESULTS

Weight loss was successfully maintained for 52 weeks. iAUC for GLP-1 increased by 44% after weight loss (P<0.04) and increased to 72% at week 52 (P=0.0001). iAUC for PYY3-36 increased by 74% after weight loss (P<0.0001) and by 36% at week 52 (P=0.02). tAUC for ghrelin increased by 23% after weight loss (P<0.0001), but at week 52, the increase was reduced to 16% compared with before weight loss (P=0.005). iAUC for GIP increased by 36% after weight loss (P=0.001), but returned to before weight loss levels at week 52. Glucagon levels were unaffected by weight loss.

CONCLUSIONS

Meal responses of GLP-1 and PYY3-36 remained increased 1 year after weight maintenance, whereas ghrelin and GIP reverted toward before-weight loss values. Thus, an increase in appetite inhibitory mechanisms and a partly decrease in appetite-stimulating mechanisms appear to contribute to successful long-term weight loss maintenance.

The incretin effect in healthy individuals and those with type 2 diabetes: physiology, pathophysiology, and response to therapeutic interventions

The incretin effect describes the phenomenon whereby oral glucose elicits higher insulin secretory responses than does intravenous glucose, despite inducing similar levels of glycaemia, in healthy individuals. This effect, which is uniformly defective in patients with type 2 diabetes, is mediated by the gut-derived incretin hormones glucose-dependent insulinotropic polypeptide (GIP) and glucagon-like peptide-1 (GLP-1). The importance of the incretin effect for the maintenance of glucose homoeostasis is clearly established, and incretin-based therapies are among the most promising new therapies for type 2 diabetes. However, despite the effectiveness of these therapies in many patients, the idea that they restore the incretin effect is a common misconception. In type 2 diabetes, the endocrine pancreas remains responsive to GLP-1 but is no longer responsive to GIP, which is the most likely reason for a reduced or absent incretin effect. Incretin-based drugs, including GLP-1 receptor agonists and dipeptidyl peptidase 4 (DPP-4) inhibitors, stimulate GLP-1 receptors and thus augment insulin secretion in response to both oral and intravenous glucose stimulation, thereby abolishing any potential difference in the responses to these stimuli. These drugs therefore do not restore the defective incretin effect in patients. By contrast, some bariatric surgical procedures enhance GLP-1 responses and also restore the incretin effect in obese individuals with type 2 diabetes. Thus, not all biological actions elicited by the stimulation of GLP-1 receptors lead to quantitative changes to the incretin effect.

Short-term outcomes of laparoscopic single anastomosis gastric bypass (LSAGB) for the treatment of type 2 diabetes in lower BMI (<30 kg/m(2)) patients

BACKGROUND

Bariatric surgery is an efficient procedure for remission of type 2 diabetes (T2DM) in morbid obesity. However, in Asian countries, mean body mass index (BMI) of T2DM patients is about 25 kg/m(2). Various data on patients undergoing gastric bypass surgery showed that control of T2DM after surgery occurs rapidly and somewhat independent to weight loss. We hypothesized that in non-obese patients with T2DM, the glycemic control would be achieved as a consequence of gastric bypass surgery.

METHODS

From September 2009, the 172 patients have had laparoscopic single anastomosis gastric bypass (LSAGB) surgery. Among them, 107 patients have been followed up more than 1 year. We analyzed the dataset of these patients. Values related to diabetes were measured before and 1, 2, and 3 years after the surgery.

RESULTS

The mean BMI decreased during the first year after the surgery but plateaued after that. The mean glycosylated hemoglobin level decreased continuously. The mean fasting and postglucose loading plasma glucose level also decreased.

CONCLUSION

After LSAGB surgery in non-obese T2DM patients, the control of T2DM was possible safely and effectively. However, longer follow-up with matched control group is essential.

Functional GIP receptors play a major role in islet compensatory response to high fat feeding in mice

BACKGROUND

Consumption of high fat diet and insulin resistance induce significant changes in pancreatic islet morphology and function essential for maintenance of normal glucose homeostasis. We have used incretin receptor null mice to evaluate the role of gastric inhibitory polypeptide (GIP) in this adaptive response.

METHODS

C57BL/6 and GIPRKO mice were fed high fat diet for 45 weeks from weaning. Changes of pancreatic islet morphology were assessed by immunohistochemistry. Body fat, glucose, insulin, glucagon, glucagon-like peptide 1 (GLP-1) and GIP were assessed by routine assays.

RESULTS

Compared with normal diet controls, high fat fed C57BL/6 mice exhibited increased body fat, hyperinsulinaemia and insulin resistance, associated with decreased pancreatic glucagon, unchanged pancreatic GLP-1 and marked increases of insulin, islet number, islet size and both beta- and alpha-cell areas. Beta cell proliferation and apoptosis were increased under high fat feeding, but the overall effect favoured enhanced beta cell mass. A broadly similar pattern of change was observed in high fat fed GIPRKO mice but islet compensation was severely impaired in every respect. The inability to enhance beta cell proliferation was associated with the depletion of pancreatic GLP-1 and lack of hyperinsulinaemic response, resulting in non-fasting hyperglycaemia. GIP and GLP-1 were expressed in islets of all groups of mice but high fat fed GIPRKO mice displayed decreased numbers of GLP-1 containing alpha cells plus non-functional enhancement of pancreatic GIP content.

GENERAL SIGNIFICANCE

These data suggest that GIP released from islet alpha-cells and intestinal K-cells plays an important role in islet adaptations to high fat feeding.

Effects of High Glucose Levels and Glycated Serum on GIP Responsiveness in the Pancreatic Beta Cell Line HIT-T15

Glucose-dependent insulinotropic peptide (GIP) is an incretin hormone produced in the gastrointestinal tract that stimulates glucose dependent insulin secretion. Impaired incretin response has been documented in diabetic patients and was mainly related to the inability of the pancreatic beta cells to secrete insulin in response to GIP. Advanced Glycation End Products (AGEs) have been shown to play an important role in pancreatic beta cell dysfunction. The aim of this study is to investigate whether the exposure to AGEs can induce GIP resistance in the pancreatic beta cell line HIT-T15. Cells were cultured for 5 days in low (CTR) or high glucose (HG) concentration in the presence of AGEs (GS) to evaluate the expression of GIP receptor (GIPR), the intracellular signaling activated by GIP, and secretion of insulin in response to GIP. The results showed that incubation with GS alone altered intracellular GIP signaling and decreased insulin secretion as compared to CTR. GS in combination with HG reduced the expression of GIPR and PI3K and abrogated GIP-induced AKT phosphorylation and GIP-stimulated insulin secretion. In conclusion, we showed that treatment with GS is associated with the loss of the insulinotropic effect of GIP in hyperglycemic conditions.

Incretins and the intensivist: what are they and what does an intensivist need to know about them?

Hyperglycaemia occurs frequently in the critically ill, even in those patients without a history of diabetes. The mechanisms underlying hyperglycaemia in this group are complex and incompletely defined. In health, the gastrointestinal tract is an important modulator of postprandial glycaemic excursions and both the rate of gastric emptying and the so-called incretin hormones, glucagon-like peptide-1 and glucose-dependent insulinotropic polypeptide, are pivotal determinants of postprandial glycaemia. Incretin-based therapies (that is, glucagon-like peptide- 1 agonists and dipeptidyl-peptidase-4 inhibitors) have recently been incorporated into standard algorithms for the management of hyperglycaemia in ambulant patients with type 2 diabetes and, inevitably, an increasing number of patients who were receiving these classes of drugs prior to their acute illness will present to ICUs. This paper summarises current knowledge of the incretin effect as well as the incretin-based therapies that are available for the management of type 2 diabetes, and provides suggestions for the potential relevance of these agents in the management of dysglycaemia in the critically ill, particularly to normalise elevated blood glucose levels.

Cytokines and Hormones That Contribute to the Positive Association between Fat and Bone

The positive association between body weight and bone density has been established in numerous laboratory and clinical studies. Apart from the direct effect of soft tissue mass on bone through skeletal loading, a number of cytokines and hormones contribute to the positive association between adipose and bone tissue, acting either locally in sites where cells of the two tissues are adjacent to each other or systemically through the circulation. The current review describes the effects of such local and systemic factors on bone physiology. One class of factors are the adipocyte-secreted peptides (adipokines), which affect bone turnover through a combination of direct effects in bone cells and indirect mechanisms mediated by the central nervous system. Another source of hormones that contribute to the coupling between fat and bone tissue are beta cells of the pancreas. Insulin, amylin, and preptin are co-secreted from pancreatic beta cells in response to increased glucose levels after feeding, and are also found in high circulating levels in obesity. A number of peptide hormones secreted from the gastrointestinal tract in response to feeding affect both fat and bone cells and thus can also act as mediators of the association between the two tissues. The current review focuses on results of laboratory studies investigating possible mechanism involved in the positive association between fat mass and bone mass.

Incretin levels 1 month after laparoscopic single anastomosis gastric bypass surgery in non-morbid obese type 2 diabetes patients

PURPOSE

Bariatric surgery is an efficient procedure for the remission of type 2 diabetes (T2DM) from morbid obesity. However, in Asian countries, the mean body mass index (BMI) of T2DM patients is about 25 kg/m(2). Various data on patients undergoing gastric bypass surgery suggest that the control of T2DM after surgery occurs rapidly. We hypothesized that even in nonobese patients with T2DM, the levels of incretin and insulin changed along with the improvement of T2DM as a consequence of the gastric bypass.

MATERIALS AND METHODS

From March to December 2011, 12 nonobese patients (mean BMI; 26.2 kg/m(2)) with poorly-controlled [mean glycated hemoglobin (HbA1C); 9.5%] diabetes underwent gastric bypass surgery. Values related to diabetes, including incretin [gastric inhibitory peptide (GIP) and glucagon-like peptide-1 (GLP-1)] levels were measured before and 1 month after surgery. All values were measured in response to a 75 g oral glucose tolerance test (OGTT).

RESULTS

On average, the BMI decreased by 2.1 ± 0.7 kg/m(2). Mean HbA1C level decreased by 1.6 ± 2%. Oral glucose-stimulated insulin levels increased and GLP-1 levels also increased significantly. Oral glucose-stimulated GIP levels decreased sharply.

CONCLUSION

Soon after gastric bypass in nonobese T2DM patients, control of T2DM is achieved. The incretin release after oral glucose is improved. This could be a consequence of changes of the enteroinsular axis, particularly in the incretins.

Glucose metabolism in critically ill patients: are incretins an important player?

Critical illness afflicts millions of people worldwide and is associated with a high risk of organ failure and death or an adverse outcome with persistent physical or cognitive deficits. Spontaneous hyperglycemia is common in critically ill patients and is associated with an adverse outcome compared to normoglycemia. Insulin is used for treating hyperglycemia in the critically ill patients but may be complicated by hypoglycemia, which is difficult to detect in these patients and which may lead to serious neurological sequelae and death. The incretin hormone, glucagon-like peptide (GLP) 1, stimulates insulin secretion and inhibits glucagon release both in healthy individuals and in patients with type 2 diabetes (T2DM). Compared to insulin, GLP-1 appears to be associated with a lower risk of severe hypoglycemia, probably because the magnitude of its insulinotropic action is dependent on blood glucose (BG). This is taken advantage of in the treatment of patients with T2DM, for whom GLP-1 analogs have been introduced during the recent years. Infusion of GLP-1 also lowers the BG level in critically ill patients without causing severe hypoglycemia. The T2DM and critical illness share similar characteristics and are, among other things, both characterized by different grades of systemic inflammation and insulin resistance. The GLP-1 might be a potential new treatment target in critically ill patients with stress-induced hyperglycemia.

Dysglycaemia in the critically ill - significance and management

Hyperglycaemia frequently occurs in the critically ill, in patients with diabetes, as well as those who were previously glucose-tolerant. The terminology 'stress hyperglycaemia' reflects the pathogenesis of the latter group, which may comprise up to 40% of critically ill patients. For comparable glucose concentrations during acute illness outcomes in stress hyperglycaemia appear to be worse than those in patients with type 2 diabetes. While several studies have evaluated the optimum glycaemic range in the critically ill, their interpretation in relation to clinical recommendations is somewhat limited, at least in part because patients with stress hyperglycaemia and known diabetes were grouped together, and the optimum glycaemic range was regarded as static, rather than dynamic, phenomenon. In addition to hyperglycaemia, there is increasing evidence that hypoglycaemia and glycaemic variability influence outcomes in the critically ill adversely. These three categories of disordered glucose metabolism can be referred to as dysglycaemia. While stress hyperglycaemia is most frequently managed by administration of short-acting insulin, guided by simple algorithms, this does not treat all dysglycaemic categories; rather the use of insulin increases the risk of hypoglycaemia and may exacerbate variability. The pathogenesis of stress hyperglycaemia is complex, but hyperglucagonaemia, relative insulin deficiency and insulin resistance appear to be important. Accordingly, novel agents that have a pathophysiological rationale and treat hyperglycaemia, but do not cause hypoglycaemia and limit glycaemic variability, are appealing. The potential use of glucagon-like peptide-1 (or its agonists) and dipeptyl-peptidase-4 inhibitors is reviewed.

Structural and pharmacological characterization of novel potent and selective monoclonal antibody antagonists of glucose-dependent insulinotropic polypeptide receptor

Glucose-dependent insulinotropic polypeptide (GIP) is an endogenous hormonal factor (incretin) that, upon binding to its receptor (GIPr; a class B G-protein-coupled receptor), stimulates insulin secretion by beta cells in the pancreas. There has been a lack of potent inhibitors of the GIPr with prolonged in vivo exposure to support studies on GIP biology. Here we describe the generation of an antagonizing antibody to the GIPr, using phage and ribosome display libraries. Gipg013 is a specific competitive antagonist with equally high potencies to mouse, rat, dog, and human GIP receptors with a K_i of 7 nm for the human GIPr. Gipg013 antagonizes the GIP receptor and inhibits GIP-induced insulin secretion in vitro and in vivo. A crystal structure of Gipg013 Fab in complex with the human GIPr extracellular domain (ECD) shows that the antibody binds through a series of hydrogen bonds from the complementarity-determining regions of Gipg013 Fab to the N-terminal α-helix of GIPr ECD as well as to residues around its highly conserved glucagon receptor subfamily recognition fold. The antibody epitope overlaps with the GIP binding site on the GIPr ECD, ensuring competitive antagonism of the receptor. This well characterized antagonizing antibody to the GIPr will be useful as a tool to further understand the biological roles of GIP.

Acute peripheral administration of synthetic human GLP-1 (7-36 amide) decreases circulating IL-6 in obese patients with type 2 diabetes mellitus: a potential role for GLP-1 in modulation of the diabetic pro-inflammatory state?

BACKGROUND

To explore the effects of acute administration of GLP-1 and GIP on circulating levels of key adipocyte-derived hormones and gut-brain peptides with established roles in energy and appetite regulation, modulation of insulin sensitivity and inflammation.

METHODS

Six obese male patients with diet-treated type 2 diabetes (T2DM) and 6 healthy lean subjects were studied. The protocol included 4 experiments for each participant that were carried out in randomised order and comprised: GLP-1 infusion at a rate of 1 pmol/kg/min for 4h, GIP at a rate of 2 pmol/kg/min, GLP-1+GIP and placebo infusion. Plasma leptin, adiponectin, IL-6, insulin, ghrelin and obestatin were measured at baseline, 15, 60, 120, 180 and 240 min following the start of infusion.

RESULTS

Patients with T2DM had higher baseline IL-6 compared with healthy [day of placebo infusion: T2DM IL-6 mean (SEM) 1.3 (0.3) pg/ml vs 0.3 (0.1)pg/ml, p=0.003]. GLP-1 infusion in T2DM was associated with a significant reduction in circulating IL-6 [baseline IL-6 1.2 pg/ml vs IL-6=0.7 at 120 min, p=0.0001; vs IL-6=0.8 at 180 min, p=0.001]. There was no significant change in leptin, adiponectin, ghrelin or obestatin compared to baseline on all 4 experimental days in both groups.

CONCLUSION

Short-term infusion of supraphysiological concentrations of GLP-1 in T2DM results in suppression of IL-6, a key inflammatory mediator strongly linked to development of obesity and T2DM-related insulin resistance. It remains to be confirmed whether GLP-1-based diabetes therapies can impact favourably on cardiovascular outcomes.

Menin and GIP are inversely regulated by food intake and diet via PI3/AKT signaling in the proximal duodenum

Background and Aims:

Ingestion of food stimulates the secretion of incretin peptides glucose-dependent insulinotropic polypeptide (GIP) and glucagon-like peptide 1 to ensure the proper absorption and storage of nutrients. Menin is the 67 kDa protein product of the MEN1 gene recently reported to have a role in metabolism. In this study, we will determine the regulation of menin in the proximal duodenum by food intake and diet in correlation with GIP levels in the proximal duodenum of mice after an 18 h fast followed by 4 and 7 h refeeding and 3 months of high-fat diet.

Methods:

A dual luciferase assay was used to determine GIP promoter activity and ELISA was used to measure the levels of GIP after inhibition of menin through small interfering RNA (siRNA) and exposure to MAPK and AKT inhibitors. Colocalization of menin and GIP were determined by immunofluorescence.

Results:

Menin and GIP expression are regulated by fasting, refeeding and diet in the proximal duodenum. Overexpression of menin in STC-1 cells significantly inhibited GIP mRNA and promoter activity, whereas menin siRNA upregulated GIP levels. Inhibition of GIP expression by the PI3/AKT inhibitor, LY294002, was abrogated in STC-1 cells with reduced menin levels, whereas the MAPK inhibitor, UO126, inhibited the expression of GIP independent of menin. Exposure of STC-1 cells to GIP reduced menin expression in a dose-dependent manner via PI3K-AKT signaling.

Conclusion:

Feeding and diet regulates the expression of menin, which inversely correlates with GIP levels in the proximal duodenum. In vitro assays indicate that menin is a negative regulator of GIP via inhibition of PI3K-AKT signaling. We show menin colocalizing with GIP in K cells of the proximal gut and hypothesize that downregulation of menin may serve as a mechanism by which GIP is regulated in response to food intake and diet.

Comparison of Bariatric Surgical Procedures for Diabetes Remission: Efficacy and Mechanisms

Bariatric surgery induces a mean weight loss of 15-30% of initial body weight (depending on the procedure), as well as a 45-95% rate of diabetes remission. Procedures that induce greater weight loss are associated with higher rates of diabetes remission. Improvements in glucose homeostasis after bariatric surgery are likely mediated by a combination of caloric restriction (followed by weight loss) and the effects of altered gut anatomy on the secretion of glucoregulatory gut hormones.

Identification of novel human dipeptidyl peptidase-IV inhibitors of natural origin (Part II): in silico prediction in antidiabetic extracts

BACKGROUND

Natural extracts play an important role in traditional medicines for the treatment of diabetes mellitus and are also an essential resource for new drug discovery. Dipeptidyl peptidase IV (DPP-IV) inhibitors are potential candidates for the treatment of type 2 diabetes mellitus, and the effectiveness of certain antidiabetic extracts of natural origin could be, at least partially, explained by the inhibition of DPP-IV.

METHODOLOGY/PRINCIPAL FINDINGS

Using an initial set of 29,779 natural products that are annotated with their natural source and an experimentally validated virtual screening procedure previously developed in our lab (Guasch et al.; 2012) [1], we have predicted 12 potential DPP-IV inhibitors from 12 different plant extracts that are known to have antidiabetic activity. Seven of these molecules are identical or similar to molecules with described antidiabetic activity (although their role as DPP-IV inhibitors has not been suggested as an explanation for their bioactivity). Therefore, it is plausible that these 12 molecules could be responsible, at least in part, for the antidiabetic activity of these extracts through their inhibitory effect on DPP-IV. In addition, we also identified as potential DPP-IV inhibitors 6 molecules from 6 different plants with no described antidiabetic activity but that share the same genus as plants with known antidiabetic properties. Moreover, none of the 18 molecules that we predicted as DPP-IV inhibitors exhibits chemical similarity with a group of 2,342 known DPP-IV inhibitors.

CONCLUSIONS/SIGNIFICANCE

Our study identified 18 potential DPP-IV inhibitors in 18 different plant extracts (12 of these plants have known antidiabetic properties, whereas, for the remaining 6, antidiabetic activity has been reported for other plant species from the same genus). Moreover, none of the 18 molecules exhibits chemical similarity with a large group of known DPP-IV inhibitors.

Identification of novel human dipeptidyl peptidase-IV inhibitors of natural origin (part I): virtual screening and activity assays

Background

There has been great interest in determining whether natural products show biological activity toward protein targets of pharmacological relevance. One target of particular interest is DPP-IV whose most important substrates are incretins that, among other beneficial effects, stimulates insulin biosynthesis and secretion. Incretins have very short half-lives because of their rapid degradation by DPP-IV and, therefore, inhibiting this enzyme improves glucose homeostasis. As a result, DPP-IV inhibitors are of considerable interest to the pharmaceutical industry. The main goals of this study were (a) to develop a virtual screening process to identify potential DPP-IV inhibitors of natural origin; (b) to evaluate the reliability of our virtual-screening protocol by experimentally testing the in vitro activity of selected natural-product hits; and (c) to use the most active hit for predicting derivatives with higher binding affinities for the DPP-IV binding site.

Methodology/Principal Findings

We predicted that 446 out of the 89,165 molecules present in the natural products subset of the ZINC database would inhibit DPP-IV with good ADMET properties. Notably, when these 446 molecules were merged with 2,342 known DPP-IV inhibitors and the resulting set was classified into 50 clusters according to chemical similarity, there were 12 clusters that contained only natural products for which no DPP-IV inhibitory activity has been previously reported. Nine molecules from 7 of these 12 clusters were then selected for in vitro activity testing and 7 out of the 9 molecules were shown to inhibit DPP-IV (where the remaining two molecules could not be solubilized, preventing the evaluation of their DPP-IV inhibitory activity). Then, the hit with the highest activity was used as a lead compound in the prediction of more potent derivatives.

Conclusions/Significance

We have demonstrated that our virtual-screening protocol was successful in identifying novel lead compounds for developing more potent DPP-IV inhibitors.

The effect of oral glucose tolerance test on serum osteocalcin and bone turnover markers in young adults

Osteocalcin (OC) is an osteoblast-derived protein implicated in the regulation of glucose tolerance and energy metabolism. This endocrine function has been suggested to be exerted via its undercarboxylated form, which has been shown to induce expression of adiponectin, insulin, and islet cell proliferation in mice. Furthermore, insulin has recently been shown to regulate the biological activity of OC in bone. Our aim was to explore the association between glucose and bone metabolism by evaluating the effect of a standard 75 g oral glucose tolerance test (OGTT) on serum OC, carboxylated OC (cOC) and bone-turnover markers (BTMs) C terminal telopeptide (βCTX-I) and N terminal propeptide (PINP) of type I collagen and tartrate-resistant acid phosphatase 5b (TRACP5b). Serum samples collected at 0 and at 120 min were analyzed in a cohort of normoglycemic young adults (n = 23, mean age 23.6 years). During OGTT a significant decrease was observed in all BTMs (P < 0.001 for all variables). The median decreases from 0 to 120 min for OC, cOC, βCTX-I, PINP, and TRACP5b were -32.1% (-37.9 to -19.6), -34.4% (-39.8 to -22.2), -61.4% (-68.5 to -53.0), -26.8% (-33.2 to -19.2), and -44.5% (-48.3 to -40.2), respectively. A strong association between the changes in OC and cOC was observed (r = 0.83, P < 0.001). The decrease in PINP was associated with changes in OC, whereas the changes in βCTX-I and TRACP5b were not associated with decreases in OC or cOC. The observed OGTT-induced changes in bone-derived proteins were partially independent of each other and potentially mediated by different mechanisms.

The pharmacological landscape and therapeutic potential of serine hydrolases

Serine hydrolases perform crucial roles in many biological processes, and several of these enzymes are targets of approved drugs for indications such as type 2 diabetes, Alzheimer's disease and infectious diseases. Despite this, most of the human serine hydrolases (of which there are more than 200) remain poorly characterized with respect to their physiological substrates and functions, and the vast majority lack selective, in vivo-active inhibitors. Here, we review the current state of pharmacology for mammalian serine hydrolases, including marketed drugs, compounds that are under clinical investigation and selective inhibitors emerging from academic probe development efforts. We also highlight recent methodological advances that have accelerated the rate of inhibitor discovery and optimization for serine hydrolases, which we anticipate will aid in their biological characterization and, in some cases, therapeutic validation.

The emerging role of the intestine in metabolic diseases

The intestine is an important metabolic organ that has gained attention in recent years for the newly identified role that it plays in the pathophysiology of various metabolic diseases including obesity, insulin resistance and diabetes. Recent insights regarding the role of enteroendocrine hormones, such as GIP, GLP-1, and PYY in metabolic diseases, as well as the emerging role of the gut microbial community and gastric bypass bariatric surgeries in modulating metabolic function and dysfunction have sparked a wave of interest in understanding the mechanisms involved, in an effort to identify new therapeutics and novel regulators of metabolism. This review summarizes the current evidence that the gastrointestinal tract has a key role in the development of obesity, inflammation, insulin resistance and diabetes and discusses the possible players that can be targeted for therapeutic intervention.

GIP and bariatric surgery

Bariatric surgery is the most effective modality of achieving weight loss as well as the most effective treatment for type 2 diabetes mellitus (T2DM). Glucose-dependent insulinotropic polypeptide (GIP) is an incretin and is implicated in the pathogenesis of obesity and T2DM. Its role in weight loss and resolution of T2DM after bariatric surgery is very controversial. We have made an attempt to review the physiology of GIP and its role in weight loss and resolution of T2DM after bariatric surgery. We searched PubMed and included all relevant original articles (both human and animal) in the review. Whereas most human studies have shown a decrease in GIP post-malabsorptive bariatric surgery, the role of GIP in bariatric surgery done in animal experiments remains inconclusive.

Glucose-dependent insulinotropic polypeptide receptor knockout mice are impaired in learning, synaptic plasticity, and neurogenesis

Glucose-dependent insulinotropic polypeptide (GIP) is a key incretin hormone, released from intestine after a meal, producing a glucose-dependent insulin secretion. The GIP receptor (GIPR) is expressed on pyramidal neurons in the cortex and hippocampus, and GIP is synthesized in a subset of neurons in the brain. However, the role of the GIPR in neuronal signaling is not clear. In this study, we used a mouse strain with GIPR gene deletion (GIPR KO) to elucidate the role of the GIPR in neuronal communication and brain function. Compared with C57BL/6 control mice, GIPR KO mice displayed higher locomotor activity in an open-field task. Impairment of recognition and spatial learning and memory of GIPR KO mice were found in the object recognition task and a spatial water maze task, respectively. In an object location task, no impairment was found. GIPR KO mice also showed impaired synaptic plasticity in paired-pulse facilitation and a block of long-term potentiation in area CA1 of the hippocampus. Moreover, a large decrease in the number of neuronal progenitor cells was found in the dentate gyrus of transgenic mice, although the numbers of young neurons was not changed. Together the results suggest that GIP receptors play an important role in cognition, neurotransmission, and cell proliferation.

The small intestine of the adult New Hampshire chicken: an immunohistochemical study

The presence and distribution of glucose-dependent insulinotropic polypeptide or gastric inhibitory polypeptide (GIP), gastric-releasing peptide (GRP) and glucagon immunoreactivity were studied in the small intestine of the New Hampshire chicken using immunohistochemistry. This is the first report of the presence of GIP-immunoreactive (ir) cells in avian small intestine. GIP, GRP and glucagon immunoreactivity was localized in the epithelium of the villi and crypts of the duodenum, jejunum and ileum. In particular, both in the duodenum and in the jejunum immunoreactive endocrine cells to GIP, GRP and glucagon were observed. In the ileum, we noticed GIP-ir and glucagon-ir cells. GRP-ir was found in nerve fibres of all three segments of the small intestine. The distribution of these bioactive agents in the intestinal tract of the chicken suggests that GIP and glucagon may play a role in the enteropancreatic axis in which intestinal peptides modulate pancreas secretion.