High Doses of Exogenous Glucagon Stimulate Insulin Secretion and Reduce Insulin Clearance in Healthy Humans

Glucagon is generally defined as a counterregulatory hormone with a primary role to raise blood glucose concentrations by increasing endogenous glucose production (EGP) in response to hypoglycemia. However, glucagon has long been known to stimulate insulin release, and recent preclinical findings have supported a paracrine action of glucagon directly on islet β-cells that augments their secretion. In mice, the insulinotropic effect of glucagon is glucose dependent and not present during basal euglycemia. To test the hypothesis that the relative effects of glucagon on hepatic and islet function also vary with blood glucose, a group of healthy subjects received glucagon (100 ng/kg) during fasting glycemia or experimental hyperglycemia (∼150 mg/dL) on 2 separate days. During fasting euglycemia, administration of glucagon caused blood glucose to rise due to increased EGP, with a delayed increase of insulin secretion. When given during experimental hyperglycemia, glucagon caused a rapid, threefold increase in insulin secretion, as well as a more gradual increase in EGP. Under both conditions, insulin clearance was decreased in response to glucagon infusion. The insulinotropic action of glucagon, which is proportional to the degree of blood glucose elevation, suggests distinct physiologic roles in the fasting and prandial states.

ARTICLE HIGHLIGHTS

Effects of GLP-1 and GIP on Islet Function in Glucose-Intolerant, Pancreatic-Insufficient Cystic Fibrosis

Impaired insulin and incretin secretion underlie abnormal glucose tolerance (AGT) in pancreatic insufficient cystic fibrosis (PI-CF). Whether the incretin hormones glucagon-like peptide-1 (GLP-1) and glucose-dependent insulinotropic polypeptide (GIP) can enhance pancreatic islet function in cystic fibrosis (CF) is not known. We studied 32 adults with PI-CF and AGT randomized to receive either GLP-1 (n = 16) or GIP (n = 16) during glucose-potentiated arginine (GPA) testing of islet function on two occasions, with either incretin or placebo infused, in a randomized, double-blind, cross-over fashion. Another four adults with PI-CF and normal glucose tolerance (NGT) and four matched control participants without CF underwent similar assessment with GIP. In PI-CF with AGT, GLP-1 substantially augmented second-phase insulin secretion but without effect on the acute insulin response to GPA or the proinsulin secretory ratio (PISR), while GIP infusion did not enhance second-phase or GPA-induced insulin secretion but increased the PISR. GIP also did not enhance second-phase insulin in PI-CF with NGT but did so markedly in control participants without CF controls. These data indicate that GLP-1, but not GIP, augments glucose-dependent insulin secretion in PI-CF, supporting the likelihood that GLP-1 agonists could have therapeutic benefit in this population. Understanding loss of GIP's insulinotropic action in PI-CF may lead to novel insights into diabetes pathogenesis.

GLP-1 Receptor Blockade Reduces Stimulated Insulin Secretion in Fasted Subjects With Low Circulating GLP-1

CONTEXT

Glucagon-like peptide 1 (GLP-1), an insulinotropic peptide released into the circulation from intestinal enteroendocrine cells, is considered a hormonal mediator of insulin secretion. However, the physiological actions of circulating GLP-1 have been questioned because of the short half-life of the active peptide. Moreover, there is mounting evidence for localized, intra-islet mediation of GLP-1 receptor (GLP-1r) signaling including a role for islet dipeptidyl-peptidase 4 (DPP4).

OBJECTIVE

To determine whether GLP-1r signaling contributes to insulin secretion in the absence of enteral stimulation and increased plasma levels, and whether this is affected by DPP4.

METHODS

Single-site study conducted at an academic medical center of 20 nondiabetic subjects and 13 subjects with type 2 diabetes. This was a crossover study in which subjects received either a DPP4 inhibitor (DPP4i; sitagliptin) or placebo on 2 separate days. On each day they received a bolus of intravenous (IV) arginine during sequential 60-minute infusions of the GLP-1r blocker exendin[9-39] (Ex-9) and saline. The main outcome measures were arginine-stimulated secretion of C-Peptide (C-PArg) and insulin (InsArg).

RESULTS

Plasma GLP-1 remained at fasting levels throughout the experiments and IV arginine stimulated both α- and β-cell secretion in all subjects. Ex-9 infusion reduced C-PArg in both the diabetic and nondiabetic groups by ~14% (P < .03 for both groups). Sitagliptin lowered baseline glycemia but did not affect the primary measures of insulin secretion. However, a significant interaction between sitagliptin and Ex-9 suggested more GLP-1r activation with DPP4i treatment in subjects with diabetes.

CONCLUSION

GLP-1r activation contributes to β-cell secretion in diabetic and nondiabetic people during α-cell activation, but in the absence of increased circulating GLP-1. These results are compatible with regulation of β-cells by paracrine signals from α-cells. This process may be affected by DPP4 inhibition.

GIPR Is Predominantly Localized to Nonadipocyte Cell Types Within White Adipose Tissue

The incretin hormone glucose-dependent insulinotropic polypeptide (GIP) augments glucose-dependent insulin secretion through its receptor expressed on islet β-cells. GIP also acts on adipose tissue; yet paradoxically, both enhanced and reduced GIP receptor (GIPR) signaling reduce adipose tissue mass and attenuate weight gain in response to nutrient excess. Moreover, the precise cellular localization of GIPR expression within white adipose tissue (WAT) remains uncertain. We used mouse genetics to target Gipr expression within adipocytes. Surprisingly, targeting Cre expression to adipocytes using the adiponectin (Adipoq) promoter did not produce meaningful reduction of WAT Gipr expression in Adipoq-Cre:Giprflx/flx mice. In contrast, adenoviral expression of Cre under the control of the cytomegalovirus promoter, or transgenic expression of Cre using nonadipocyte-selective promoters (Ap2/Fabp4 and Ubc) markedly attenuated WAT Gipr expression. Analysis of single-nucleus RNA-sequencing, adipose tissue data sets localized Gipr/GIPR expression predominantly to pericytes and mesothelial cells rather than to adipocytes. Together, these observations reveal that adipocytes are not the major GIPR+ cell type within WAT-findings with mechanistic implications for understanding how GIP and GIP-based co-agonists control adipose tissue biology.

Interpreting Normetanephrines-the Significance of Clinical Context

Introduction: Pheochromocytoma ranges in presentation, but the diagnostic hallmarks are increased catecholamine secretion in patients with an adrenal mass. However, interpretation requires consideration of the clinical state.

Case: A 60-year-old man presented with 6 months of episodic flushing, night sweats, fatigue, back pain, and 20-pound weight loss. Vitals were notable for hypotension and mild tachycardia. He was thin with evidence of hyperpigmentation. Contrasted CT showed 15 cm heterogeneous masses of both adrenals and a rib lesion. Plasma normetanephrines were elevated on two separate measures (526 and 1,398 pg/mL, nl <=148). Plasma metanephrines were normal. Urine normetanephrines were increased 4-fold (2,165mcg/g Cr, n 108–524). Labs noted low DHEA-S (2 mcg/dL, n 38–313), high ACTH (204 pg/mL, n 6–50), random cortisol (5.2 mcg/dL, n 3.5–18.3), undetectable aldosterone, and high plasma renin activity (83 ng/mL/h, n 2.9–10.8). Cortisol peaked at 6.7 mcg/dL 1 hour after 250mcg of cosyntropin. MRI revealed over 15cm infiltrating masses arising from adrenals with modest flare on T2 imaging. Dotatate PET/CT showed mild uptake of bilateral adrenals and metastases to liver and bone. He was started on steroid replacement and doxazosin for presumed pheochromocytoma.

He was transferred to our facility where he remained hypotensive despite adequate glucocorticoid and mineralocorticoid replacement. Once stabilized, repeat plasma normetanephrines were insignificant (218 pg/mL, n 0–145) and chromogranin was normal (68 ng/mL, n<93). Biopsy of the rib lesion confirmed diffuse large B-cell lymphoma.

Discussion: Pheochromocytoma classically presents in the outpatient setting with palpitations, diaphoresis, pallor, and paroxysmal hypertension. Rarely, it results in hypertensive emergencies requiring hospitalization. In patients with catecholamine excess and an adrenal mass, pheochromocytoma is usually suspected. 3-fold or more increases of normetanephrines or metanephrines above upper cutoffs are rarely false-positives. However, this assumes clinical stability. Sympathoadrenal activation is a physiologic response to acute illness. Metanephrines in critically ill patients without pheochromocytoma approached those of pheochromocytoma in one study. Levels normalized upon recovery from illness, highlighting the importance of verifying biochemistries once the patient is stable. The degree of elevation in normetanephrines seen in this patient was a physiologic response to adrenal insufficiency and clinical instability. Pathology confirmed lymphoma rather than pheochromocytoma for which he was started on chemotherapy.

Conclusion: Elevated normetanephrines is an appropriate physiological response in the acutely ill. Careful consideration of the clinical picture in conjunction with biochemical data is critical.

Tirzepatide is an imbalanced and biased dual GIP and GLP-1 receptor agonist

Tirzepatide (LY3298176) is a dual GIP and GLP-1 receptor agonist under development for the treatment of type 2 diabetes mellitus (T2DM), obesity, and nonalcoholic steatohepatitis. Early phase trials in T2DM indicate that tirzepatide improves clinical outcomes beyond those achieved by a selective GLP-1 receptor agonist. Therefore, we hypothesized that the integrated potency and signaling properties of tirzepatide provide a unique pharmacological profile tailored for improving broad metabolic control. Here, we establish methodology for calculating occupancy of each receptor for clinically efficacious doses of the drug. This analysis reveals a greater degree of engagement of tirzepatide for the GIP receptor than the GLP-1 receptor, corroborating an imbalanced mechanism of action. Pharmacologically, signaling studies demonstrate that tirzepatide mimics the actions of native GIP at the GIP receptor but shows bias at the GLP-1 receptor to favor cAMP generation over β-arrestin recruitment, coincident with a weaker ability to drive GLP-1 receptor internalization compared with GLP-1. Experiments in primary islets reveal β-arrestin1 limits the insulin response to GLP-1, but not GIP or tirzepatide, suggesting that the biased agonism of tirzepatide enhances insulin secretion. Imbalance toward GIP receptor, combined with distinct signaling properties at the GLP-1 receptor, together may account for the promising efficacy of this investigational agent.

SAT-414 A Single Center Retrospective Analysis and Review of Endocrinopathies from Immune Checkpoint Inhibitors Between 2007 and 2017

Immune checkpoint inhibitors (ICI) specifically target and dysregulate immune tolerance. As a result of this immune activation, immune related adverse events (irAEs) are common. These can include endocrinopathies like immune hypophysitis (IH), primary adrenal insufficiency (PAI), autoimmune thyroid disease, Graves disease and type 1 Diabetes Mellitus (T1DM)[1]. The aim of this retrospective review was to describe the prevalence, timing, and clinical characteristics of ICI-related endocrinopathies at our institution. Methods: A retrospective chart review was conducted for all patients between January 01, 2007 and February 01, 2017 who met predefined clinical, biochemical and imaging criteria for endocrinopathies including IH, T1DM, autoimmune thyroid disease, Graves disease and PAI. Results: Among 690 patients who received ICPI during the study period, 91 unique patients with complete data developed endocrinopathies, for an overall prevalence of 13%. The study included 50 (55%) men and 41 (45%) women with a median age of 64 years (range 20-96 years). Grade 2 endocrinopathies were reported more commonly (n=49, 54%); grade 3/4 events were rare (15%). Among the ICIs, Nivolumab was the most common ICI noted for study patients (n=51, 56%). Autoimmune thyroid disease was the most common irAE in our study (n= 63, 9.1% overall prevalence). We also report 25 cases of IH (3.6%), 2 cases of PAI (0.3%) and 1 case of Graves disease (0.1%). Most patients with autoimmune thyroid disease developed subclinical hypothyroidism (n=26, 3.8%) and overt hyperthyroidism (n=21, 3.0%). We note a high median TSH of 67.3 µIU/mL; range- 20.6-111.0 in overt hypothyroidism compared to subclinical hypothyroidism (14.0 µIU/mL; range- 5.6-100 µIU/mL). Overall, median time to developing any endocrinopathy after initiating ICI was 13.7 weeks; range- 0.7-351.5 weeks. Among the subjects who developed IH, the median TSH was 0.37 µIU/mL (0.01 - 62.39 µIU/mL) with a free T4 of 0.74 ng/dL (0.25-1.86 ng/dL) and the median cortisol was 0.80 µg/dL (0.25-24.5 µg/dL). Amongst the IH group, 17 patients developed isolated secondary adrenal insufficiency and 8 patients developed combination of other hormone deficiencies with secondary AI including 6 with secondary hypothyroidism, 1 patient with hypogonadotropic hypogonadism and 1 with hypothyroidism and hypogonadism in addition to secondary AI. Despite development of irAEs, ICI therapy was continued in 59 pts (65%) who developed an endocrine irAE. Conclusions: In summary, this is one of the largest single institution retrospective studies on ICI related endocrinopathies. The majority of endocrinopathies were low grade, and most patients continued ICI treatment. Reference: Barroso-Sousa, Romualdo. Incidence of Endocrine Dysfunction Following the Use of Different Immune Checkpoint Inhibitor Regimens: A Systematic Review and Meta-analysis. JAMA, Sept 2017

SUN-LB124 Novel Elisa Assays Demonstrate Specificity of Islet and Intestinal Processing of Proglucagon

Circulating proglucagon peptides (PGP) are produced in islet α-cells, enteroendocrine L-cells. Release of PGP is thought to be tissue specific, e.g. α-cells make glucagon and L-cells make GLP-1 through predominant actions of proconvertases 2 and 1/3 (PC2 and PC1/3). However, this dichotomous model has recently been challenged. To address the contribution of the gut and pancreas to plasma PGP we developed 4 novel sandwich ELISA assays and applied them in studies with PGP stimulation from the islet (IV arginine) and intestine (meal). Monoclonal antibodies were raised in mice with genetic ablation of proglucagon transcription. Clones were screened and selected for affinity and specificity, and assays for glucagon, GLP-1, glicentin and oxyntomodulin developed. Eight healthy humans received 5 g arginine intravenously after a 12 hour fast and had blood sampled for 15 minutes; an additional 10 consumed a liquid mixed nutrient meal and prandial blood was taken for 180 minutes. None of the assays registered signal in plasma from proglucagon null mice, and specificity, background and cross-reactivity were acceptable in each. In response to IV arginine plasma glucagon increased 4-fold, and GLP-1 1.5-fold, with significant increases in 15-minute AUC; there was no significant change in either glicentin or oxyntomodulin. In response to meal ingestion there was no change in circulating glucagon, but oxyntomodulin, GLP-1 and glicentin increased 2, 3, and 4-fold respectively. These findings are generally compatible with PC1/3 dominant processing of PGP in the gut, but raise the possibility that α-cells produce both PC2 (glucagon) and PC1/3 (GLP-1) products.

The Effects of Bariatric Surgery on Islet Function, Insulin Secretion, and Glucose Control

Although bariatric surgery was developed primarily to treat morbid obesity, evidence from the earliest clinical observations to the most recent clinical trials consistently demonstrates that these procedures have substantial effects on glucose metabolism. A large base of research indicates that bariatric surgeries such as Roux-en-Y gastric bypass (RYGB), vertical sleeve gastrectomy (VSG), and biliopancreatic diversion (BPD) improve diabetes in most patients, with effects frequently evident prior to substantial weight reduction. There is now unequivocal evidence from randomized controlled trials that the efficacy of surgery is superior to intensive life-style/medical management. Despite advances in the clinical understanding and application of bariatric surgery, there remains only limited knowledge of the mechanisms by which these procedures confer such large changes to metabolic physiology. The improvement of insulin sensitivity that occurs with weight loss (e.g., the result of diet, illness, physical training) also accompanies bariatric surgery. However, there is evidence to support specific effects of surgery on insulin clearance, hepatic glucose production, and islet function. Understanding the mechanisms by which surgery affects these parameters of glucose regulation has the potential to identify new targets for therapeutic discovery. Studies to distinguish among bariatric surgeries on key parameters of glucose metabolism are limited but would be of considerable value to assist clinicians in selecting specific procedures and investigators in delineating the resulting physiology. This review is based on literature related to factors governing glucose metabolism and insulin secretion after the commonly used RYGB and VSG, and the less frequently used BPD and adjustable gastric banding.

Role of vagal activation in postprandial glucose metabolism after gastric bypass in individuals with and without hypoglycaemia

Patients who have undergone gastric bypass surgery (GB) have enhanced postprandial hyperinsulinaemia and a greater incretin effect is apparent. In the present study, we sought to determine the effect of vagal activation, a neural component of the enteroinsular axis, on postprandial glucose metabolism in patients with and without hypoglycaemia after GB. Seven patients with documented post-GB hypoglycaemia, seven asymptomatic patients without hypoglycaemia post-GB, and 10 weight-matched non-surgical controls with normal glucose tolerance were recruited. Blood glucose, and islet hormone and incretin secretion were compared during mixed meal tolerance tests (MMTs) with and without prior sham-feeding on two separate days. Sham feeding preceding the MMT caused a more rapid increase in prandial blood glucose levels but lowered overall glycaemia in all three groups (P < 0.05). Sham feeding had a similar effect to increase early (P < 0.05), but not overall, meal-induced insulin secretion in the three groups. Prandial glucagon concentrations were significantly greater in the GB groups, and sham feeding accentuated this response (P < 0.05). The effect of vagal activation on prandial glucose and islet-cell function is preserved in patients who have undergone GB, in those both with and without hypoglycaemia.

Beta-cell sensitivity to glucose is impaired after gastric bypass surgery

AIMS

Patients who have undergone Roux-en-Y gastric bypass surgery (GB) have exaggerated postprandial insulin secretion, which has been attributed to increased meal glucose appearance and enhanced incretin effect. Here, we sought to determine β-cell glucose sensitivity in the absence of meal stimulation and insulinotropic gut factors.

MATERIALS AND METHODS

A total of 12 non-diabetic subjects with prior GB, and 7 matched non-surgical control subjects with normal glucose tolerance were studied. Blood glucose and insulin secretion rates were measured during a graded glucose infusion at increasing and then decreasing rates. Insulin sensitivity (S_I ) and glucose effectiveness (S_G ) were determined by the minimal model.

RESULTS

GB subjects had S_I comparable to that of control subjects. GB subjects had relative hyperglycaemia during the highest dose of glucose infusion associated with significantly reduced β-cell glucose sensitivity throughout both step-up (GB: 34 ± 6, CN: 82 ± 9 pmol min^-1 mM^-1 L, P < .0001) and step-down (GB: 31 ± 6, CN: 74 ± 9 pmol min^-1 mM^-1 L, P < .0001) phases of the glucose infusion. GB subjects also had reduced S_G (GB: 0.04 ± 0.00, CN: 0.07 ± 0.01 min^-1 , P = .004).

CONCLUSION

In the absence of enteric stimuli, β-cell sensitivity to changes in glycaemia is blunted among individuals with GB, indicating a significant shift in a fundamental property of β-cell function several years after surgery.

β-Cell Function Over Time in Adolescents With New Type 2 Diabetes and Obese Adolescents Without Diabetes

PURPOSE

The progression of β-cell function in newly diagnosed adolescents with type 2 diabetes mellitus (T2DM) is not well documented. We hypothesized that at the time of diagnosis with T2DM, adolescents would have impaired β-cell function as demonstrated by the disposition index (calculated as: insulin secretion adjusted for insulin sensitivity), and this would be followed by a rapid decline of function despite standard medical management.

METHODS

Thirty-nine adolescents with recently diagnosed T2DM and 32 obese adolescent controls with normal glucose tolerance had acute insulin response to glucose, homeostatic model assessment of insulin resistance, and disposition index measured serially over 2 years.

RESULTS

In the adolescent T2DM group, fasting glucose increased over 2 years (p = .04), while DI was impaired at baseline and showed an overall relative decline of 25% per year. The mean Hemoglobin A_1c remained below 8% (64 mmol/mol). Differences were observed between the T2DM and control adolescents in the way DI changed over time (p = .02).

CONCLUSIONS

β-cell function in adolescents with recently diagnosed T2DM was impaired with no improvement of β-cell function over the 2 years of study despite stable Hemoglobin A_1c, body mass index markers of insulin sensitivity, and standard treatment of hyperglycemia.

Gastric bypass alters both glucose-dependent and glucose-independent regulation of islet hormone secretion

OBJECTIVE

Roux-en-Y gastric bypass surgery (GB) is characterized by accentuated but short-lived postprandial elevations of blood glucose and insulin. This profile has been attributed to effects of relative hyperglycemia to directly stimulate β-cells and an augmented incretin effect. An additional glucose-independent stimulation of insulin secretion in GB subjects was hypothesized.

METHODS

Fifteen subjects with prior GB, six matched obese non surgical controls, and seven lean individuals were recruited. Islet hormones were measured before and after meal ingestion during hyperinsulinemic hypoglycemic clamps to minimize the direct effects of glycemia and glucose-dependent gastrointestinal hormones on insulin secretion.

RESULTS

The GB subjects had less suppression of fasting β-cell secretion during the insulin clamp compared to controls. In addition, meal-induced insulin secretion increased in the GB subjects but not controls during fixed sub-basal glycemia. In contrast, the glucagon responses to hypoglycemia and meal ingestion were lower in the GB subjects than controls.

CONCLUSIONS

Among subjects with GB, the response of insulin and glucagon secretion to decreasing blood glucose is blunted, but meal-induced insulin secretion is stimulated even at fixed systemic sub-basal glycemia. These findings indicate that, following GB, islet hormone secretion is altered as a result of factors beyond circulatory glucose levels.

Effects of glucagon like peptide-1 to mediate glycemic effects of weight loss surgery

To date, weight loss surgeries are the most effective treatment for obesity and glycemic control in patients with type 2 diabetes. Roux-en-Y gastric bypass surgery (RYGB) and sleeve gastrectomy (SG), two widely used bariatric procedures for the treatment of obesity, induce diabetes remission independent of weight loss while glucose improvement after adjustable gastric banding (AGB) is proportional to the amount of weight loss. The immediate, weight-loss independent glycemic effect of gastric bypass has been attributed to postprandial hyperinsulinemia and an enhanced incretin effect. The rapid passage of nutrients into the intestine likely accounts for significantly enhanced glucagon like-peptide 1 (GLP-1) secretion, and postprandial hyperinsulinemia after GB is typically attributed to the combined effects of elevated glucose and GLP-1. For this review we focus on the beneficial effects of the three most commonly performed bariatric procedures, RYGB, SG, and AGB, on glucose metabolism and diabetes remission. Central to this discussion will be the extent to which the effects of surgery are mediated by GLP-1. Better understanding of these mechanisms could provide insight to development of novel therapeutic strategies for treatment of diabetes as well as refinement of surgical techniques.

GLP-1R responsiveness predicts individual gastric bypass efficacy on glucose tolerance in rats

Several bariatric operations are currently used to treat obesity and obesity-related comorbidities. These vary in efficacy, but most are more effective than current pharmaceutical treatments. Roux-en-Y gastric bypass (RYGB) produces substantial body weight (BW) loss and enhanced glucose tolerance, and is associated with increased secretion of the gut hormone glucagon-like peptide 1 (GLP-1). Given the success of GLP-1-based agents in lowering blood glucose levels and BW, we hypothesized that an individual sensitivity to GLP-1 receptor agonism could predict metabolic benefits of surgeries associated with increased GLP-1 secretion. One hundred ninety-seven high-fat diet-induced obese male Long-Evans rats were monitored for BW loss during exendin-4 (Ex4) administration. Stable populations of responders and nonresponders were identified based on Ex4-induced BW loss and GLP-1-induced improvements in glucose tolerance. Subpopulations of Ex4 extreme responders and nonresponders underwent RYGB surgery. After RYGB, responders and nonresponders showed similar BW loss compared with sham, but nonresponders retained impaired glucose tolerance. These data indicate that the GLP-1 response tests may predict some but not all of the improvements observed after RYGB. These findings present an opportunity to optimize the use of bariatric surgery based on an improved understanding of GLP-1 biology and suggest an opportunity for a more personalized therapeutic approach to the metabolic syndrome.

GLP-1R agonism enhances adjustable gastric banding in diet-induced obese rats

Bariatric procedures vary in efficacy, but overall are more effective than behavioral and pharmaceutical treatment. Roux-en-Y gastric bypass causes increased secretion of glucagon-like peptide 1 (GLP-1) and reduces body weight (BW) more than adjustable gastric banding (AGB), which does not trigger increased GLP-1 secretion. Since GLP-1-based drugs consistently reduce BW, we hypothesized that GLP-1 receptor (GLP-1R) agonists would augment the effects of AGB. Male Long-Evans rats with diet-induced obesity received AGB implantation or sham surgery. GLP-1R agonism, cannabinoid receptor-1 (CB1-R) antagonism, or vehicle was combined with inflation to evaluate interaction between AGB and pharmacological treatments. GLP1-R agonism reduced BW in both sham and AGB rats (left uninflated) compared with vehicle-treated animals. Subsequent band inflation was ineffective in vehicle-treated rats but enhanced weight loss stimulated by GLP1-R agonism. In contrast, there was no additional BW loss when CB1-R antagonism was given with AGB. We found band inflation to trigger neural activation in areas of the nucleus of the solitary tract known to be targeted by GLP-1R agonism, offering a potential mechanism for the interaction. These data show that GLP-1R agonism, but not CB1-R antagonism, improves weight loss achieved by AGB and suggest an opportunity to optimize bariatric surgery with adjunctive pharmacotherapy.

β-cell dysfunction in adolescents and adults with newly diagnosed type 2 diabetes mellitus

OBJECTIVE

To compare β-cell function in adolescents and adults with newly diagnosed type 2 diabetes (T2DM).

STUDY DESIGN

Thirty-nine adolescents with T2DM, 38 age- and weight-matched control subjects, and 19 adults with T2DM were studied. The adolescent subjects with diabetes were divided on the basis of whether they needed insulin to control their initial hyperglycemia. The primary outcome variable was the disposition index, computed from the acute insulin response to glucose corrected for insulin sensitivity (1/Homeostatic model assessment of insulin resistance).

RESULTS

The disposition index was significantly reduced in all 3 diabetic groups (control n=3360, adolescents with T2DM without insulin n=630, adolescents with T2DM with insulin n=120, adults with T2DM n=200; P<.001), and the adolescents with more severe hyperglycemia at diagnosis had lower disposition index than those with a more modest presentation (P<.05).

CONCLUSION

At the time of diagnosis, adolescents with T2DM have significant β-cell dysfunction, comparable with adults newly diagnosed with T2DM. Thus, severe β-cell impairment can develop within the first two decades of life and is likely to play a central role in the pathogenesis of T2DM in adolescents.

Weight-independent changes in blood glucose homeostasis after gastric bypass or vertical sleeve gastrectomy in rats

BACKGROUND & AIMS

Roux-en-Y gastric bypass (RYGB) and vertical sleeve gastrectomy (VSG) reduce weight and improve glucose metabolism in obese patients, although it is not clear if metabolic changes are independent of weight loss. We investigated alterations in glucose metabolism in rats following RYGB or VSG.

METHODS

Rats underwent RYGB or VSG and were compared to sham-operated rats fed ad lib or pair-fed to animals that received RYGB. Intraperitoneal glucose tolerance and insulin sensitivity tests were performed to assess glycemic function independent of incretin response. A hyperinsulinemic euglycemic clamp was used to compare tissue-specific changes in insulin sensitivity following each procedure. A mixed-meal tolerance test was used to assess the effect of each surgery on postprandial release of glucagon-like peptide 1 (GLP-1)(7-36) and glucose tolerance, and was also performed in rats given GLP-1 receptor antagonist exendin(9-39).

RESULTS

Following RYGB or VSG, glucose tolerance and insulin sensitivity improved in proportion to weight loss. Hepatic insulin sensitivity was significantly better in rats that received RYGB or VSG compared with rats fed ad lib or pair-fed, whereas glucose clearance was similar in all groups. During the mixed-meal tolerance test, plasma levels of GLP-1(7-36) and insulin were greatly and comparably increased in rats that received RYGB and VSG compared with those that were pair-fed or fed ad lib. Administration of a GLP-1 receptor antagonist prevented improvements in glucose and insulin responses after a meal among rats that received RYGB or VSG.

CONCLUSIONS

In obese rats, VSG is as effective as RYGB for increasing secretion of GLP-1 and insulin and improving hepatic sensitivity to insulin; these effects are independent of weight loss.

Impaired beta-cell sensitivity to glucose and maximal insulin secretory capacity in adolescents with type 2 diabetes

BACKGROUND

Adults with type 2 diabetes mellitus (T2DM) have broad impairments in beta-cell function, including severe attenuation of the first-phase insulin response to glucose, and reduced beta-cell mass. In adolescents with T2DM, there is some evidence that beta-cell dysfunction may be less severe. Our objective was to determine beta-cell sensitivity to glucose and maximal insulin secretory capacity (AIR(max)) in teenagers with T2DM.

METHODS

Fifteen adolescents with T2DM [11 F/4 M, age 18.4 +/- 0.3 yr, body mass index (BMI) 39.8 +/- 2.2 kg/m(2)] and 10 non-diabetic control subjects (7 F/3 M, age 17.4 +/- 0.5 yr, BMI 41.5 +/- 2.2 kg/m(2)) were studied. T2DM subjects had a mean duration of diabetes of 48.8 +/- 6.4 months, were treated with conventional therapies, and had good metabolic control [hemoglobin A1c (HbA1c) 6.7 +/- 1.2%]. Insulin and C-peptide were determined before and after a graded glucose infusion and after intravenous arginine at a whole blood glucose level of >or=22 mM.

RESULTS

The insulin response to increasing plasma glucose concentrations was blunted in the diabetic compared with control subjects (34.8 +/- 11.9 vs. 280.5 +/- 57.8 pmol/mmol; p < 0.0001), and AIR(max) was also significantly reduced in the diabetic group (1868 +/- 330 vs. 4445 +/- 606; p = 0.0005).

CONCLUSION

Even adolescents with well-controlled T2DM have severe impairments of insulin secretion. These data support beta-cell dysfunction as central in the pathogenesis of T2DM in young people, and indicate that these abnormalities can develop over a period of just several years.