David A. D'Alessio

Evidence of Cosecretion of Islet Amyloid Polypeptide and Insulin by β-Cells

Islet amyloid polypeptide (IAPP) has been identified as the major constituent of the pancreatic amyloid of non-insulin-dependent diabetes mellitus (NIDDM) and is also present in normal β-cell secretory granules. To determine whether IAPP is a pancreatic secretory product, we measured the quantity of lAPP-like immunoreactivity (IAPP-LI), insulin, and glucagon released into 5 ml of incubation medium during a 2-h incubation of monolayer cultures (n = 5) of neonatal (3- to 5-day-old) Sprague-Dawley rat pancreases under three conditions: 1.67 mM glucose, 16.7 mM glucose, and 16.7 mM glucose plus 10 mM arginine and 0.1 mM isobutylmethylxanthine (IBMX). The quantity of IAPP-LI, insulin, and glucagon in the cell extract was also determined. Mean ± SE IAPP-LI in the incubation medium increased from 0.041 ± 0.003 pmol in 1.67 mM glucose to 0.168 ± 0.029 pmol in 16.7 mM glucose (P < 0.05) and 1.02 ± 0.06 pmol in 16.7 mM glucose plus arginine and IBMX (P < 0.05 vs. 1.67 or 16.7 mM glucose). Insulin secretion increased similarly from 4.34 ± 0.27 to 20.2 ± 0.6 pmol (P < 0.05) and then to 135 ± 5 pmol (P < 0.05 vs. 1.67 or 16.7 mM glucose). Glucagon release tended to decrease with the increase in glucose concentration (0.39 ± 0.01 vs. 0.33 ± 0.02 pmol, P < 0.1), whereas with the addition of arginine and IBMX to high glucose, glucagon release increased to 1.32 ± 0.03 pmol (P < 0.05 vs. 1.67 or 16.7 mM glucose). Thus, the molar proportion of IAPP-LI to insulin secreted in low glucose was ∼1% and did not differ significantly with stimulation (0.95 ± 0.08 vs. 0.84 ± 0.15 vs. 0.76 ± 0.05%). In contrast, there was no constant proportional relationship between the release of IAPP-LI and glucagon (10.6 ± 0.8 vs. 51.3 ± 8.7 vs. 77.5 ± 5.2%). After incubation in 1.67 mM glucose, the extracted cells contained 3.7 ± 0.2 pmol IAPP-LI, 944 ± 25 pmol insulin, and 28.2 ±1.5 pmol glucagon. After maximal stimulation, the fractional release of IAPP-LI was 26.7 ± 0.7% vs. 14.7 ± 0.6% of insulin and 4.4 ± 0.2% of glucagon. These data indicate that nondiabetic neonatal rat islet cultures contain IAPP-LI and release it after stimulation by glucose and nonglucose secretagogues. Furthermore, the data suggest that IAPP-LI is a product of the β-cell, which coreleases it with insulin in a molar ratio of ∼1.100.

Cloned mice have an obese phenotype not transmitted to their offspring.

Mammalian cloning using somatic cells has been accomplished successfully in several species, and its potential basic, clinical and therapeutic applications are being pursued on many fronts. Determining the long-term effects of cloning on offspring is crucial for consideration of future application of the technique. Although full-term development of animals cloned from adult somatic cells has been reported, problems in the resulting progeny indicate that the cloning procedure may not produce animals that are phenotypically identical to their cell donor. We used a mouse model to take advantage of its short generation time and lifespan. Here we report that the increased body weight of cloned B6C3F1 female mice reflects an increase of body fat in addition to a larger body size, and that these mice share many characteristics consistent with obesity. We also show that the obese phenotype is not transmitted to offspring generated by mating male and female cloned mice.

Hyperglycemia–related mortality in critically ill patients varies with admission diagnosis*

Objectives: Hyperglycemia during critical illness is common and is associated with increased mortality. Intensive insulin therapy has improved outcomes in some, but not all, intervention trials. It is unclear whether the benefits of treatment differ among specific patient populations. The purpose of the study was to determine the association between hyperglycemia and risk– adjusted mortality in critically ill patients and in separate groups stratified by admission diagnosis. A secondary purpose was to determine whether mortality risk from hyperglycemia varies with intensive care unit type, length of stay, or diagnosed diabetes. Design: Retrospective cohort study. Setting: One hundred seventy-three U.S. medical, surgical, and cardiac intensive care units. Patients: Two hundred fifty-nine thousand and forty admissions from October 2002 to September 2005; unadjusted mortality rate, 11.2%. Interventions: None. Measurements and Main Results: A two–level logistic regression model determined the relationship between glycemia and mortality. Age, diagnosis, comorbidities, and laboratory variables were used to calculate a predicted mortality rate, which was then analyzed with mean glucose to determine the association of hyperglycemia with hospital mortality. Hyperglycemia was associated with increased mortality independent of illness severity. Compared with normoglycemic individuals (70–110 mg/dL), adjusted odds of mortality (odds ratio, [95% confidence interval]) for mean glucose 111–145, 146–199, 200–300, and >300 mg/dL was 1.31 (1.26–1.36), 1.82 (1.74–1.90), 2.13 (2.03–2.25), and 2.85 (2.58–3.14), respectively. Furthermore, the adjusted odds of mortality related to hyperglycemia varied with admission diagnosis, demonstrating a clear association in some patients (acute myocardial infarction, arrhythmia, unstable angina, pulmonary embolism) and little or no association in others. Hyperglycemia was associated with increased mortality independent of intensive care unit type, length of stay, and diabetes. Conclusions: The association between hyperglycemia and mortality implicates hyperglycemia as a potentially harmful and correctable abnormality in critically ill patients. The finding that hyperglycemia–related risk varied with admission diagnosis suggests differences in the interaction between specific medical conditions and injury from hyperglycemia. The design and interpretation of future trials should consider the primary disease states of patients and the balance of medical conditions in the intensive care unit studied.

Central Control of Body Weight and Appetite

CONTEXT Energy balance is critical for survival and health, and control of food intake is an integral part of this process. This report reviews hormonal signals that influence food intake and their clinical applications. EVIDENCE ACQUISITION A relatively novel insight is that satiation signals that control meal size and adiposity signals that signify the amount of body fat are distinct and interact in the hypothalamus and elsewhere to control energy homeostasis. This review focuses upon recent literature addressing the integration of satiation and adiposity signals and therapeutic implications for treatment of obesity. EVIDENCE SYNTHESIS During meals, signals such as cholecystokinin arise primarily from the GI tract to cause satiation and meal termination; signals secreted in proportion to body fat such as insulin and leptin interact with satiation signals and provide effective regulation by dictating meal size to amounts that are appropriate for body fatness, or stored energy. Although satiation and adiposity signals are myriad and redundant and reduce food intake, there are few known orexigenic signals; thus, initiation of meals is not subject to the degree of homeostatic regulation that cessation of eating is. There are now drugs available that act through receptors for satiation factors and which cause weight loss, demonstrating that this system is amenable to manipulation for therapeutic goals. CONCLUSIONS Although progress on effective medical therapies for obesity has been relatively slow in coming, advances in understanding the central regulation of food intake may ultimately be turned into useful treatment options.

Glucagon-like peptide 1 enhances glucose tolerance both by stimulation of insulin release and by increasing insulin-independent glucose disposal.

Glucagon-like peptide 1 [7-36 amide] (GLP-1) has been shown to enhance insulin secretion in healthy and type II diabetic humans, and to increase glucose disposal in type I diabetic patients. To further define its action on glucose kinetics, we studied six healthy subjects who received either GLP-1 (45 pmol/kg per h) or 150 mM saline on two mornings during which a modified intravenous glucose tolerance test was performed. Plasma insulin and glucose levels were analyzed using Bergmans minimal model of glucose kinetics to derive indices of insulin sensitivity (SI) and glucose effectiveness at basal insulin (SG), the latter a measure of glucose disposition independent of changes in insulin. In addition, basal insulin concentrations, the acute insulin response to glucose (AIRg), plasma glucagon levels, and the glucose disappearance constant (Kg) were measured on the days that subjects received GLP-1 or saline. Compared with saline infusions, GLP-1 increased the mean Kg from 1.61 +/- 0.20 to 2.65 +/- 0.25%/min (P = 0.022). The enhanced glucose disappearance seen with GLP-1 was in part the result of its insulinotropic effect, as indicated by a rise in AIRg from 240 +/- 48 to 400 +/- 78 pM (P = 0.013). However, there was also an increase in SG from 1.77 +/- 0.11 to 2.65 +/- 0.33 x 10(-2).min-1 (P = 0.038), which was accounted for primarily by insulin-independent processes, viz glucose effectiveness in the absence of insulin. There was no significant effect of GLP-1 on SI or basal insulin, and glucagon levels were not different during the glucose tolerance tests with or without GLP-1. Thus, GLP-1 improves glucose tolerance both through its insulinotropic action and by increasing glucose effectiveness. These findings suggest that GLP-1 has direct effects on tissues involved in glucose disposition. Furthermore, this peptide may be useful for studying the process of insulin-independent glucose disposal, and pharmacologic analogues may be beneficial for treating patients with diabetes mellitus.

Arcuate Glucagon-Like Peptide 1 Receptors Regulate Glucose Homeostasis but Not Food Intake

OBJECTIVE—Glucagon-like peptide-1 (GLP-1) promotes glucose homeostasis through regulation of islet hormone secretion, as well as hepatic and gastric function. Because GLP-1 is also synthesized in the brain, where it regulates food intake, we hypothesized that the central GLP-1 system regulates glucose tolerance as well. RESEARCH DESIGN AND METHODS—We used glucose tolerance tests and hyperinsulinemic-euglycemic clamps to assess the role of the central GLP-1 system on glucose tolerance, insulin secretion, and hepatic and peripheral insulin sensitivity. Finally, in situ hybridization was used to examine colocalization of GLP-1 receptors with neuropeptide tyrosine and pro-opiomelanocortin neurons. RESULTS—We found that central, but not peripheral, administration of low doses of a GLP-1 receptor antagonist caused relative hyperglycemia during a glucose tolerance test, suggesting that activation of central GLP-1 receptors regulates key processes involved in the maintenance of glucose homeostasis. Central administration of GLP-1 augmented glucose-stimulated insulin secretion, and direct administration of GLP-1 into the arcuate, but not the paraventricular, nucleus of the hypothalamus reduced hepatic glucose production. Consistent with a role for GLP-1 receptors in the arcuate, GLP-1 receptor mRNA was found to be expressed in 68.1% of arcuate neurons that expressed pro-opiomelanocortin mRNA but was not significantly coexpressed with neuropeptide tyrosine. CONCLUSIONS—These data suggest that the arcuate GLP-1 receptors are a key component of the GLP-1 system for improving glucose homeostasis by regulating both insulin secretion and glucose production.

Ghrelin Suppresses Glucose-Stimulated Insulin Secretion and Deteriorates Glucose Tolerance in Healthy Humans

OBJECTIVE The orexigenic gut hormone ghrelin and its receptor are present in pancreatic islets. Although ghrelin reduces insulin secretion in rodents, its effect on insulin secretion in humans has not been established. The goal of this study was to test the hypothesis that circulating ghrelin suppresses glucose-stimulated insulin secretion in healthy subjects. RESEARCH DESIGN AND METHODS Ghrelin (0.3, 0.9 and 1.5 nmol/kg/h) or saline was infused for more than 65 min in 12 healthy patients (8 male/4 female) on 4 separate occasions in a counterbalanced fashion. An intravenous glucose tolerance test was performed during steady state plasma ghrelin levels. The acute insulin response to intravenous glucose (AIRg) was calculated from plasma insulin concentrations between 2 and 10 min after the glucose bolus. Intravenous glucose tolerance was measured as the glucose disappearance constant (Kg) from 10 to 30 min. RESULTS The three ghrelin infusions raised plasma total ghrelin concentrations to 4-, 15-, and 23-fold above the fasting level, respectively. Ghrelin infusion did not alter fasting plasma insulin or glucose, but compared with saline, the 0.3, 0.9, and 1.5 nmol/kg/h doses decreased AIRg (2,152 ± 448 vs. 1,478 ± 2,889, 1,419 ± 275, and 1,120 ± 174 pmol/l) and Kg (0.3 and 1.5 nmol/kg/h doses only) significantly (P < 0.05 for all). Ghrelin infusion raised plasma growth hormone and serum cortisol concentrations significantly (P < 0.001 for both), but had no effect on glucagon, epinephrine, or norepinephrine levels (P = 0.44, 0.74, and 0.48, respectively). CONCLUSIONS This is a robust proof-of-concept study showing that exogenous ghrelin reduces glucose-stimulated insulin secretion and glucose disappearance in healthy humans. Our findings raise the possibility that endogenous ghrelin has a role in physiologic insulin secretion, and that ghrelin antagonists could improve β-cell function.

Effects of Gastric Bypass and Gastric Banding on Glucose Kinetics and Gut Hormone Release

Background: Bariatric surgery markedly improves glucose homeostasis in patients with type 2 diabetes even before any significant weight loss is achieved. Procedures that involve bypassing the proximal small bowel, such as Roux‐en‐Y gastric bypass (RYGBP), are more efficient than gastric restriction procedures such as gastric banding (GB).

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.

Elimination of the action of glucagon-like peptide 1 causes an impairment of glucose tolerance after nutrient ingestion by healthy baboons.

Glucagon-like peptide 1 (GLP-1) is an insulinotropic hormone released after nutrient ingestion which is known to augment insulin secretion, inhibit glucagon release, and promote insulin-independent glucose disposition. To determine the overall effect of GLP-1 on glucose disposition after a meal we studied a group of healthy, conscious baboons before and after intragastric glucose administration during infusions of saline, and two treatments to eliminate the action of GLP-1: (a) exendin-[9-39] (Ex-9), a peptide receptor antagonist of GLP-1; or (b) an anti-GLP-1 mAb. Fasting concentrations of glucose were higher during infusion of Ex-9 than during saline (4.44 +/- 0.05 vs. 4.16 +/- 0.05 mM, P < 0.01), coincident with an elevation in the levels of circulating glucagon (96 +/- 10 vs. 59 +/- 3 ng/liter, P < 0.02). The postprandial glycemic excursions during administration of Ex-9 and mAb were greater than during the control studies (Ex-9 13.7 +/- 2.0 vs. saline 10.0 +/- 0.8 mM, P = 0.07; and mAb 13.6 +/- 1.2 vs. saline 10.6 +/- 0.9 mM, P = 0.044). The increments in insulin levels throughout the absorption of the glucose meal were not different for the experimental and control conditions, but the insulin response in the first 30 min after the glucose meal was diminished significantly during treatment with Ex-9 (Ex-9 761 +/- 139 vs. saline 1,089 +/- 166 pM, P = 0.044) and was delayed in three of the four animals given the neutralizing antibody (mAb 946 +/- 262 vs. saline 1,146 +/- 340 pM). Thus, elimination of the action of GLP-1 impaired the disposition of an intragastric glucose meal and this was at least partly attributable to diminished early insulin release. In addition to these postprandial effects, the concurrent elevation in fasting glucose and glucagon during GLP-1 antagonism suggests that GLP-1 may have a tonic inhibitory effect on glucagon output. These findings demonstrate the important role of GLP-1 in the assimilation of glucose absorbed from the gut.