Antidiabetic Activity and Potential Mechanism of Amentoflavone in Diabetic Mice

Aim: To investigate the anti-diabetic activity of amentoflavone (AME) in diabetic mice, and to explore the potential mechanisms. Methods: Diabetic mice induced by high fat diet and streptozotocin were administered with amentoflavone for 8 weeks. Biochemical indexes were tested to evaluate its anti-diabetic effect. Hepatic steatosis, the histopathology change of the pancreas was evaluated. The activity of glucose metabolic enzymes, the expression of Akt and pAkt, and the glucose transporter type 4 (GLUT4) immunoreactivity were detected. Results: AME decreased the level of glucose, total cholesterol (TC), triglyceride (TG), low density lipoprotein cholesterol (LDL-C) and glucagon, and increased the levels of high density lipoprotein cholesterol (HDL-C) and insulin. Additionally, AME increased the activity of glucokinase (GCK), phosphofructokinase-1 (PFK-1), and pyruvate kinase (PK), and inhibited the activity of glycogen synthase kinase-3 (GSK-3), phosphoenolpyruvate carboxykinase (PEPCK), and glucose-6-phosphatase (G-6-Pase). Mechanistically, AME increased superoxide dismutase (SOD), decreased malondialdehyde (MDA), activation of several key signaling molecules including pAkt (Ser473), and increased the translocation to the sedimenting membranes of GLUT4 in skeletal muscle tissue. Conclusions: AME exerted anti-diabetic effects by regulating glucose and lipid metabolism, perhaps via anti-oxidant effects and activating the PI3K/Akt pathway. Our study provided novel insight into the role and underlying mechanisms of AME in diabetes.

Postprandial levels of GLP-1, GIP and glucagon after 2 years of weight loss with a Paleolithic diet: a randomised controlled trial in healthy obese women

Objective To investigate how weight loss by different diets impacts postprandial levels of glucagon-like peptide 1 (GLP-1), glucose-dependent insulinotropic polypeptide (GIP) and glucagon. Methods In this single-centre, parallel group 2-year trial, 70 healthy postmenopausal obese women were randomised to the Paleolithic diet or a healthy control diet based on Nordic Nutrition Recommendations. Both diets were without calorie restriction. The primary outcome was the change in fat mass. Here, secondary analyses on GLP-1, GIP and glucagon measured during an OGTT are described. Results In the Paleolithic diet group, mean weight loss compared to baseline was 11% at 6 months and 10% at 24 months. In the control diet group, mean weight loss was 6% after 6 and 24 months (P = 0.0001 and P = 0.049 for the comparison between groups at 6 and 24 months respectively). Compared to baseline, the mean incremental area under the curve (iAUC) for GLP-1 increased by 34 and 45% after 6 and 24 months in the Paleolithic diet group and increased by 59% after 24 months in the control diet group. The mean iAUC for GIP increased only in the Paleolithic diet group. The area under the curve (AUC) for glucagon increased during the first 6 months in both groups. The fasting glucagon increase correlated with the β-hydroxybutyrate increase. Conclusions Weight loss caused an increase in postprandial GLP-1 levels and a further rise occurred during weight maintenance. Postprandial GIP levels increased only after the Paleolithic diet. Reduced postprandial glucagon suppression may be caused by a catabolic state.

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.

Intranasal glucagon acutely increases energy expenditure without inducing hyperglycaemia in overweight/obese adults

AIM

To assess the acute effects of 0.7 mg intranasal glucagon (ING) vs intranasal placebo (INP) on food intake and resting energy expenditure (REE).

METHODS

A single-blind, crossover study was conducted in 19 overweight/obese adults (15 men, 4 women). REE was assessed by indirect calorimetry over 90 minutes, after which appetite was assessed using a visual analogue scale, and ad libitum caloric intake was assessed. Plasma samples were obtained at baseline and at 15-minute intervals post-treatment up to 90 minutes.

RESULTS

ING increased total REE (INP 61.5 ± 1.2 kcal vs ING 69.4 ± 1.2 kcal; P = 0.027). There were no between-treatment differences in blood glucose, food intake and appetite. There were no adverse effects.

CONCLUSION

ING acutely increases REE without increasing plasma glucose. Longer term studies with multiple daily dosing will establish whether this affects body weight.

Dynamic changes in insulin and glucagon during disease progression in rhesus monkeys with obesity-related type 2 diabetes mellitus

AIMS

To investigate the progression of obesity-related type 2 diabetes mellitus (T2DM) in rhesus monkeys, especially dynamic changes in insulin and glucagon.

MATERIALS AND METHODS

We followed a cohort of 52 rhesus monkeys for 7 years throughout the progression of obesity-related T2DM. Intravenous glucose tolerance tests were performed every 6 months to evaluate dynamic changes in glucose, insulin and glucagon levels.

RESULTS

Obesity in rhesus monkeys increased the overall mortality and T2DM morbidity. During the progression of T2DM, glucagon remained consistently elevated, while insulin initially increased in compensation but then dropped to below normal levels when the monkeys developed overt T2DM. After a glucose challenge, both the first and second phases of insulin secretion increased during the early stage of T2DM; in later stages the first phase was delayed and the second phase was diminished.

CONCLUSION

Our findings showed that, beside the decreased insulin level, hyperglucagonaemia also plays an important role in the development of T2DM.

Phosphorylation of Forkhead Protein FoxO1 at S253 Regulates Glucose Homeostasis in Mice

The transcription factor forkhead box O1 (FoxO1) is a key mediator in the insulin signaling pathway and controls multiple physiological functions, including hepatic glucose production (HGP) and pancreatic β-cell function. We previously demonstrated that S256 in human FOXO1 (FOXO1-S256), equivalent to S253 in mouse FoxO1 (FoxO1-S253), is a key phosphorylation site mediating the effect of insulin as a target of protein kinase B on suppression of FOXO1 activity and expression of target genes responsible for gluconeogenesis. Here, we investigated the role of FoxO1-S253 phosphorylation in control of glucose homeostasis in vivo by generating global FoxO1-S253A/A knockin mice, in which FoxO1-S253 alleles were replaced with alanine (A substitution) blocking FoxO1-S253 phosphorylation. FoxO1-S253A/A mice displayed mild increases in feeding blood glucose and insulin levels but decreases in fasting blood glucose and glucagon concentrations, as well as a reduction in the ratio of pancreatic α-cells/β-cells per islet. FoxO1-S253A/A mice exhibited a slight increase in energy expenditure but barely altered food intake and glucose uptake among tissues. Further analyses revealed that FoxO1-S253A/A enhances FoxO1 nuclear localization and promotes the effect of glucagon on HGP. We conclude that dephosphorylation of S253 in FoxO1 may reflect a molecular basis of pancreatic plasticity during the development of insulin resistance.

Separate and Combined Glucometabolic Effects of Endogenous Glucose-Dependent Insulinotropic Polypeptide and Glucagon-like Peptide 1 in Healthy Individuals

The incretin hormones glucose-dependent insulinotropic polypeptide (GIP) and glucagon-like peptide 1 (GLP-1) are secreted postprandially and contribute importantly to postprandial glucose tolerance. In this study, we assessed the individual and combined contributions of endogenous GIP and GLP-1 to the postprandial changes in glucose and glucoregulatory hormones using the novel GIP receptor antagonist GIP(3-30)NH₂ and the well-established GLP-1 receptor antagonist exendin(9-39)NH₂ During 4-h oral glucose tolerance tests (75 g) combined with an ad libitum meal test, 18 healthy men received on four separate days in randomized, double-blinded order intravenous infusions of A) GIP(3-30)NH₂ (800 pmol/kg/min) plus exendin(9-39)NH₂ (0-20 min: 1,000 pmol/kg/min; 20-240 min: 450 pmol/kg/min), B) GIP(3-30)NH₂, C) exendin(9-39)NH₂, and D) saline, respectively. Glucose excursions were significantly higher during A than during B, C, and D, while glucose excursions during B were higher than during C and D. Insulin secretion (assessed by C-peptide/glucose ratio) was reduced by 37 ± 16% (A), 30 ± 17% (B), and 8.6 ± 16% (C) compared with D (mean ± SD). A and C resulted in higher glucagon levels and faster gastric emptying. In conclusion, endogenous GIP affects postprandial plasma glucose excursions and insulin secretion more than endogenous GLP-1, but the hormones contribute additively to postprandial glucose regulation in healthy individuals.

Inappropriate glucagon and GLP-1 secretion in individuals with long-standing type 1 diabetes: effects of residual C-peptide

AIMS/HYPOTHESIS

Recent studies have demonstrated that residual beta cells may be present in some people with long-standing type 1 diabetes, but little is known about the potential impact of this finding on alpha cell function and incretin levels. This study aimed to evaluate whether insulin microsecretion could modulate glucagon and glucagon-like peptide-1 (GLP-1) responses to a mixed meal tolerance test (MMTT).

METHODS

Adults with type 1 diabetes onset after the age of 15 years (n = 29) underwent a liquid MMTT after an overnight fast. Insulin microsecretion was defined when peak C-peptide levels were >30 pmol/l using an ultrasensitive assay. Four individuals with recent-onset type 1 diabetes were included as controls. Glucagon and GLP-1 responses were analysed according to C-peptide patterns.

RESULTS

We found comparable peak values, Δ_0-max levels and AUCs of glucagon and GLP-1 responses in C-peptide-positive participants (n = 9) and C-peptide-negative participants (n = 16) with long-standing diabetes and in participants with recent-onset diabetes (n = 4). Mean glucagon levels, however, differed (p = 0.01). Mean GLP-1 responses were significantly lower according to C-peptide positivity (p < 0.001, ANOVA). Interestingly, GLP-1 levels correlated to glucagon values in C-peptide-positive participants with long-standing diabetes (Pearson's r = 0.915, p = 0.004) and in participants with recent-onset diabetes (p < 0.001) but not in C-peptide-negative participants.

CONCLUSIONS/INTERPRETATION

The glucagon response to an MMTT in people with long-standing type 1 diabetes is not reduced by the presence of residual beta cells. The reduction of GLP-1 responses according to residual C-peptide levels suggests specific regulatory pathways.

Symptomatic and Radiological Response to 177Lu-DOTATATE for the Treatment of Functioning Pancreatic Neuroendocrine Tumors

PURPOSE

Peptide receptor radionuclide therapy (PRRT) with the radiolabeled somatostatin analogue [Lutetium-177-DOTA0-Tyr3]octreotate (177Lu-DOTATATE) is widely applied for inoperable metastatic small intestinal and nonfunctioning pancreatic neuroendocrine tumors (pNETs). The aim of this study is to describe the safety and efficacy of the treatment of functioning pNETs.

METHODS

Patients were treated with up to four cycles of 177Lu-DOTATATE with an intended dose of 7.4 Gbq per cycle. Radiological (Response Evaluation Criteria in Solid Tumors 1.1), symptomatic, and biochemical response were analyzed retrospectively for all patients with a functioning pNET (insulinoma, gastrinoma, VIPoma, and glucagonoma) treated with 177Lu-DOTATATE. Quality of life (QOL) was assessed with the European Organization for Research and Treatment of Cancer Quality of Life Questionnaire-Core Module questionnaire.

RESULTS

Thirty-four patients with a metastatic functioning pNET (European Neuroendocrine Tumor Society grade 1 or 2) were included: 14 insulinomas, 5 VIPomas, 7 gastrinomas, and 8 glucagonomas. Subacute hematological toxicity, grade 3 or 4 occurred in 4 patients (12%) and a hormonal crisis in 3 patients (9%). PRRT resulted in partial or complete response in 59% of patients and the disease control rate was 78% in patients with baseline progression. 71% of patients with uncontrolled symptoms had a reduction of symptoms and a more than 80% decrease of circulating hormone levels was measured during follow-up. After PRRT, median progression-free survival was 18.1 months (interquartile range: 3.3 to 35.7) with a concurrent increase in QOL.

CONCLUSION

Treatment with 177Lu-DOTATATE is a safe and effective therapy resulting in radiological, symptomatic and biochemical response in a high percentage of patients with metastatic functioning pNETs. Hormonal crises occur relatively frequent and preventive therapy should be considered before and/or during PRRT.

Mechanisms of early glucose regulation disturbance after out-of-hospital cardiopulmonary resuscitation: An explorative prospective study

Background

Hyperglycemia is common and associated with increased mortality after out-of-hospital cardiac arrest (OHCA) and return of spontaneous circulation (ROSC). Mechanisms behind ultra-acute hyperglycemia are not well known. We performed an explorative study to describe the changes in glucose metabolism mediators during the prehospital postresuscitation phase.

Methods

We included patients who were successfully resuscitated from out-of-hospital cardiac arrest in two physician-staffed units. Insulin, glucagon, and glucagon-like peptide 1 (GLP-1) were measured in prehospital and hospital admission samples. Additionally, interleukin-6 (IL-6), cortisol, and HbA1c were measured at hospital admission.

Results

Thirty patients participated in the study. Of those, 28 cases (71% without diabetes) had sufficient data for analysis. The median time interval between prehospital samples and hospital admission samples was 96 minutes (IQR 85–119). At the time of ROSC, the patients were hyperglycemic (11.2 mmol/l, IQR 8.8–15.7), with insulin and glucagon concentrations varying considerably, although mostly corresponding to fasting levels (10.1 mU/l, IQR 4.2–25.2 and 141 ng/l, IQR 105–240, respectively). GLP-1 increased 2- to 8-fold with elevation of IL-6. The median glucose change from prehospital to hospital admission was -2.2 mmol/l (IQR -3.6 to -0.2). No significant correlations between the change in plasma glucose levels and the changes in insulin (r = 0.30, p = 0.13), glucagon (r = 0.29, p = 0.17), or GLP-1 levels (r = 0.32, p = 0.15) or with IL-6 (r = (-0.07), p = 0.75), cortisol (r = 0.13, p = 0.52) or HbA1c levels (r = 0.34, p = 0.08) were observed. However, in patients who did not receive exogenous epinephrine during resuscitation, changes in blood glucose correlated with changes in insulin (r = 0.59, p = 0.04) and glucagon (r = 0.65, p = 0.05) levels, demonstrating that lowering glucose values was associated with a simultaneous lowering of insulin and glucagon levels.

Conclusions

Hyperglycemia is common immediately after OHCA and cardiopulmonary resuscitation. No clear hormonal mechanisms were observed to be linked to changes in glucose levels during the postresuscitation phase in the whole cohort. However, in patients without exogenous epinephrine treatment, the correlations between glycemic and hormonal changes were more obvious. These results call for future studies examining the mechanisms of postresuscitation hyperglycemia and the metabolic effects of the global ischemic insult and medical treatment.

Impaired glucagon secretion in patients with fulminant type 1 diabetes mellitus

PURPOSE

Fulminant type 1 diabetes mellitus (FT1DM), characterized by rapid and almost complete destruction of pancreatic β-cells, is a newly identified subtype of type 1 diabetes mellitus. Although, the pathophysiology of this condition remains still unclear, histological evidence suggests that not only β-cells but also α-cells of pancreatic islets are reduced in number in FT1DM. However, the ability of glucagon secretion in patients with this condition has remained largely uncharacterized. We therefore examined glucagon secretion in patients with FT1DM and compared that with patients with other types of diabetes mellitus.

METHODS

Fasting glucagon levels as well as glucagon secretion induced by intravenous administration of arginine were measured in hospitalized 83 patients with diabetes mellitus, including 4 with FT1DM, 18 with type 1 diabetes mellitus (T1DM), 40 with type 2 diabetes mellitus (T2DM), 5 with slowly progressive insulin-dependent diabetes mellitus (SPIDDM), and 16 with pancreatic diabetes mellitus (PDM).

RESULTS

The area under the curve for serum glucagon levels after arginine infusion in FT1DM patients was significantly smaller than that in T1DM, T2DM, or SPIDDM patients but was similar to that in PDM patients. The fasting serum glucagon level of FT1DM patients was lower than that of T1DM or T2DM patients but did not significantly differ from that of SPIDDM or PDM patients.

CONCLUSIONS

These results suggest that glucagon secretion is impaired in patients with FT1DM.

Association of glucagon-to-insulin ratio and nonalcoholic fatty liver disease in patients with type 2 diabetes mellitus

OBJECTIVE

The aim of this study is to investigate the association between glucagon-to-insulin ratio and the presence of nonalcoholic fatty liver disease on ultrasonography in participants with type 2 diabetes mellitus.

RESEARCH DESIGN AND METHODS

This cross-sectional study was performed with data obtained from 172 participants with type 2 diabetes mellitus admitted to a University hospital of Korea. Participants were assessed for serum fasting and postprandial serum glucagon-to-insulin ratio and divided into tertiles. Nonalcoholic fatty liver disease was defined as ultrasonographically detected fatty liver.

RESULTS

Prevalence of nonalcoholic fatty liver disease was significantly decreased across tertile of fasting and postprandial glucagon-to-insulin ratio ( p = 0.009 for trend, p = 0.001 for trend, respectively). Lower glucagon-to-insulin ratio was significantly associated with the presence of nonalcoholic fatty liver disease even after adjustment for potential confounding variables [fasting glucagon-to-insulin ratio: odds ratio (95% confidence interval), 2.68 (1.08-6.86)], postprandial glucagon-to-insulin ratio: [2.72 (1.03-7.35)]. The participants in the lowest tertile of fasting glucagon-to-insulin ratio had higher body mass index, visceral fat thickness, subcutaneous fat thickness, homeostasis model assessment-insulin resistance and shorter duration of diabetes mellitus.

CONCLUSION

This study suggests that lower glucagon relative insulin may be independently associated with nonalcoholic fatty liver disease in participants with type 2 diabetes.

Gut Hormone Responses to Mixed Meal Test in New-Onset Prediabetes/Diabetes After Acute Pancreatitis

The study was aimed to investigate gut hormone responses to mixed meal test in individuals with new-onset prediabetes or diabetes after acute pancreatitis (cases) compared with healthy controls, and the effect of body fat parameters. A total of 29 cases and 29 age- and sex-matched healthy controls were recruited. All participants were given standard mixed meal drink and blood samples were collected to measure dipeptidyl peptidase IV, gastric inhibitory peptide, glucagon like peptide-1, insulin, oxyntomodulin, and peptide YY. Body fat parameters were measured using magnetic resonance imaging. Repeated measures and linear regression analyses were conducted in unadjusted and adjusted models. Gastric inhibitory peptide levels were significantly higher whereas oxyntomodulin levels were significantly lower in cases compared with controls in both the unadjusted (p<0.001 and p<0.001, respectively) and adjusted (p<0.001 and p<0.001, respectively) models. In cases, liver fat % contributed up to 13.4% (vs. 2.9% in controls) to variance in circulating levels of gastric inhibitory peptide whereas body mass index - up to 20.8% (vs. 9.9% in controls) in circulating levels of oxyntomodulin. New-onset prediabetes/diabetes after acute pancreatitis is characterised by increased levels of gastric inhibitory peptide and decreased levels of oxyntomodulin. Further, liver fat % and body mass index appear to be the body fat parameters that contribute most significantly to gastric inhibitory peptide and oxyntomodulin levels, respectively.

Glucagon Levels During Short-Term SGLT2 Inhibition Are Largely Regulated by Glucose Changes in Patients With Type 2 Diabetes

CONTEXT

The mechanism mediating sodium glucose cotransporter-2 (SGLT2) inhibitor-associated increase in glucagon levels is unknown.

OBJECTIVE

To assess short-term effects on glucagon, other hormones, and energy substrates after SGLT2 inhibition and whether such effects are secondary to glucose lowering. The impact of adding a dipeptidyl peptidase-4 inhibitor was addressed.

DESIGN, SETTING, AND PATIENTS

A phase 4, single-center, randomized, three-treatment crossover, open-label study including 15 patients with type 2 diabetes treated with metformin.

INTERVENTIONS

Patients received a single-dose of dapagliflozin 10 mg accompanied by the following in randomized order: isoglycemic clamp (experiment DG); saline infusion (experiment D); or saxagliptin 5 mg plus saline infusion (experiment DS). Directly after 5-hour infusions, a 2-hour oral glucose tolerance test (OGTT) was performed.

RESULTS

Glucose and insulin levels were stable in experiment DG and decreased in experiment D [P for difference (Pdiff) < 0.001]. Glucagon-to-insulin ratio (Pdiff < 0.001), and levels of glucagon (Pdiff < 0.01), nonesterified fatty acids (Pdiff < 0.01), glycerol (Pdiff < 0.01), and β-OH-butyrate (Pdiff < 0.05) were lower in DG vs D. In multivariate analysis, change in glucose level was the main predictor of change in glucagon level. In DS, glucagon and active GLP-1 levels were higher than in D, but glucose and insulin levels did not differ. During OGTT, glucose levels rose less and glucagon levels fell more in DS vs D.

CONCLUSION

The degree of glucose lowering markedly contributed to regulation of glucagon and insulin secretion and to lipid mobilization during short-term SGLT2 inhibition.

Dysregulated plasma glucagon levels in Japanese young adult type 1 diabetes patients

Currently, the clinical dynamics of glucagon need to be revised based on previous data obtained from conventional glucagon radioimmunoassays. In the present study, we evaluated plasma glucagon levels in type 1 diabetes patients using a newly-developed sandwich enzyme-linked immunosorbent assay, and its association with clinical parameters and markers of diabetes complications were statistically assessed. The plasma glucagon level in 77 Japanese type 1 diabetes patients was 28.1 ± 17.7 pg/mL, and comparable with that reported previously for type 2 diabetes patients. However, the values were widely spread and did not correlate with plasma glucose values. Additionally, the average glucagon levels in patients in a hypoglycemic state (glucose level <80 mg/dL) did not increase (21.7 ± 12.2 pg/mL). The average glucagon level of patients experiencing hypoglycemia unawareness was significantly lower. Plasma glucagon levels evaluated using the new enzyme-linked immunosorbent assay were dysregulated in type 1 diabetes patients in respect to plasma glucose levels, suggesting dysregulation of secretion.

Hyperpolarized [1-13 C] pyruvate as a possible diagnostic tool in liver disease

Introduction of hyperpolarized magnetic resonance in preclinical studies and lately translation to patients provides new detailed in vivo information of metabolic flux in organs. Hyperpolarized magnetic resonance based on 13 C enriched pyruvate is performed without ionizing radiation and allows quantification of the pyruvate conversion products: alanine, lactate and bicarbonate in real time. Thus, this methodology has a promising potential for in vivo monitoring of energetic alterations in hepatic diseases. Using 13 C pyruvate, we investigated the metabolism in the porcine liver before and after intravenous injection of glucose. The overall mean lactate to pyruvate ratio increased significantly after the injection of glucose whereas the bicarbonate to pyruvate ratio was unaffected, representative of the levels of pyruvate entering the tricarboxylic acid cycle. Similarly, alanine to pyruvate ratio did not change. The increased lactate to pyruvate ratio over time showed an exponential correlation with insulin, glucagon and free fatty acids. Together, these data, obtained by hyperpolarized 13 C magnetic resonance spectroscopy and by blood sampling, indicate a hepatic metabolic shift in glucose utilization following a glucose challenge. Our findings demonstrate the capacity of hyperpolarized 13 C magnetic resonance spectroscopy for quantifying hepatic substrate metabolism in accordance with well-known physiological processes. When combined with concentration of blood insulin, glucagon and free fatty acids in the blood, the results indicate the potential of hyperpolarized magnetic resonance spectroscopy as a future clinical method for quantification of hepatic substrate metabolism.

Insulin regulates GLUT4 in the ventromedial hypothalamus to restore the sympathoadrenal response to hypoglycemia in diabetic rats

It is proposed that the impaired counterregulatory response (CRR) to hypoglycemia in insulin-deficient diabetes may be due to chronic brain insulin deficiency. To test this hypothesis, streptozotocin-induced diabetic Sprague-Dawley rats were infused with insulin (3 mU/day) or artificial cerebrospinal fluid (aCSF) bilaterally into the ventromedial hypothalamus (VMH) for 2 wk and compared with nondiabetic rats. Rats underwent hyperinsulinemic (50 mU·kg^-1·min^-1)-hypoglycemic (~45 mg/dl) clamps. Diabetic rats demonstrated an impaired CRR to hypoglycemia, noted by a high glucose infusion rate and blunted epinephrine and glucagon responses. The defective sympathoadrenal response was restored by chronic infusion of insulin into the VMH. Diabetic rats had decreased VMH Akt phosphorylation and decreased VMH glucose transporter 4 (GLUT4) content, which was also restored by chronic infusion of insulin into the VMH. Separate experiments in nondiabetic rats in which GLUT4 translocation into the VMH was inhibited with an infusion of indinavir were notable for an impaired CRR to hypoglycemia, indicated by increased glucose infusion rate and diminished epinephrine and glucagon responses. Results suggest that, in this model of diabetes, VMH insulin deficiency impairs the sympathoadrenal response to hypoglycemia and that chronic infusion of insulin into the VMH is sufficient to normalize the sympathoadrenal response to hypoglycemia via restoration of GLUT4 expression in the VMH.

Contribution of systemic inflammation to permanence of KATP-induced neonatal diabetes in mice

Gain-of-function (GOF) mutations in the ATP-sensitive potassium (K_ATP) channels cause neonatal diabetes. Despite the well-established genetic root of the disease, pathways modulating disease severity and treatment effectiveness remain poorly understood. Patient phenotypes can vary from severe diabetes to remission, even in individuals with the same mutation and within the same family, suggesting that subtle modifiers can influence disease outcome. We have tested the underlying mechanism of transient vs. permanent neonatal diabetes in K_ATP-GOF mice treated for 14 days with glibenclamide. Some K_ATP-GOF mice show remission of diabetes and enhanced insulin sensitivity long after diabetes treatment has ended, while others maintain severe insulin-resistance. However, insulin sensitivity is not different between the two groups before or during diabetes induction, suggesting that improved sensitivity is a consequence, rather than the cause of, remission, implicating other factors modulating glucose early in diabetes progression. Leptin, glucagon, insulin, and glucagon-like peptide-1 are not different between remitters and nonremitters. However, liver glucose production is significantly reduced before transgene induction in remitter, relative to nonremitter and nontreated, mice. Surprisingly, while subsequent remitter animals exhibited normal serum cytokines, nonremitter mice showed increased cytokines, which paralleled the divergence in blood glucose. Together, these results suggest that systemic inflammation may play a role in the remitting versus non-remitting outcome. Supporting this conclusion, treatment with the anti-inflammatory meloxicam significantly increased the fraction of remitting animals. Beyond neonatal diabetes, the potential for inflammation and glucose production to exacerbate other forms of diabetes from a compensated state to a glucotoxic state should be considered.

Glucagon revisited: Coordinated actions on the liver and kidney

Glucagon secretion is stimulated by a low plasma glucose concentration. By activating glycogenolysis and gluconeogenesis in the liver, glucagon contributes to maintain a normal glycemia. Glucagon secretion is also stimulated by the intake of proteins, and glucagon contributes to amino acid metabolism and nitrogen excretion. Amino acids are used for gluconeogenesis and ureagenesis, two metabolic pathways that are closely associated. Intriguingly, cyclic AMP, the second messenger of glucagon action in the liver, is released into the bloodstream becoming an extracellular messenger. These effects depend not only on glucagon itself but on the actual glucagon/insulin ratio because insulin counteracts glucagon action on the liver. This review revisits the role of glucagon in nitrogen metabolism and in disposal of nitrogen wastes. This role involves coordinated actions of glucagon on the liver and kidney. Glucagon influences the transport of fluid and solutes in the distal tubule and collecting duct, and extracellular cAMP influences proximal tubule reabsorption. These combined effects increase the fractional excretion of urea, sodium, potassium and phosphates. Moreover, the simultaneous actions of glucagon and extracellular cAMP are responsible, at least in part, for the protein-induced rise in glomerular filtration rate that contributes to a more efficient excretion of protein-derived end products.

Characterization of the endocannabinoid system in subcutaneous adipose tissue in periparturient dairy cows and its association to metabolic profiles

Adipose tissue (AT) plays a major role in metabolic adaptations in postpartum (PP) dairy cows. The endocannabinoid (eCB) system is a key regulator of metabolism and energy homeostasis; however, information about this system in ruminants is scarce. Therefore, this work aimed to assess the eCB system in subcutaneous AT, and to determine its relation to the metabolic profile in peripartum cows. Biopsies of AT were performed at 14 d prepartum, and 4 and 30 d PP from 18 multiparous peripartum cows. Cows were categorized retrospectively according to those with high body weight (BW) loss (HWL, 8.5 ± 1.7% BW loss) or low body weight loss (LWL, 2.9 ± 2.5% BW loss) during the first month PP. The HWL had higher plasma non-esterified fatty acids and a lower insulin/glucagon ratio PP than did LWL. Two-fold elevated AT levels of the main eCBs, N-arachidonoylethanolamine (AEA) and 2-arachidonoylglycerol (2-AG), were found 4 d PP compared with prepartum in HWL, but not in LWL cows. AT levels of the eCB-like molecules oleoylethanolamide, palmitoylethanolamide, and of arachidonic acid were elevated PP compared with prepartum in all cows. The abundance of monoglyceride lipase (MGLL), the 2-AG degrading enzyme, was lower in HWL vs. LWL AT PP. The relative gene expression of the cannabinoid receptors CNR1 and CNR2 in AT tended to be higher in HWL vs. LWL PP. Proteomic analysis of AT showed an enrichment of the inflammatory pathways’ acute phase signaling and complement system in HWL vs. LWL cows PP. In summary, eCB levels in AT were elevated at the onset of lactation as part of the metabolic adaptations in PP dairy cows. Furthermore, activating the eCB system in AT is most likely associated with a metabolic response of greater BW loss, lipolysis, and AT inflammation in PP dairy cows.

Role of biomarker tests for diagnosis of neuroendocrine tumours

Neuroendocrine tumours (NETs) are neoplasms that arise from neuroendocrine cells. Neuroendocrine cells and their tumours can secrete a wide range of amines and polypeptide hormones into the systemic circulation. This feature has triggered widespread investigation into circulating biomarkers for the diagnosis of NETs as well as for the prediction of the biological behaviour of tumour cells. Classic examples of circulating biomarkers for gastroenteropancreatic NETs include chromogranin A, neuron-specific enolase and pancreatic polypeptide as well as hormones that elicit clinical syndromes, such as serotonin and its metabolites, insulin, glucagon and gastrin. Biomarker metrics of general markers for diagnosing all gastroenteropancreatic NET subtypes are limited, but specific hormonal measurements can be of diagnostic value in select cases. In the past decade, methods for detecting circulating transcripts and tumour cells have been developed to improve the diagnosis of patients with NETs. Concurrently, modern scanning techniques and superior radiotracers for functional imaging have markedly expanded the options for clinicians dealing with NETs. Here, we review the latest research on biomarkers in the NET field to provide clinicians with a comprehensive overview of relevant diagnostic biomarkers that can be implemented in dedicated situations.

Water intake keeps type 2 diabetes away? Focus on copeptin

INTRODUCTION

In both diabetic subjects and animal models high levels of vasopressin (AVP) have beendetected. The relationship between AVP and glucose metabolism is mediated through several direct andindirect effects and most of them are still unknown.

METHODS

We have reviewed 100 manuscripts retrieved from Cochrane Library, Embase and Pubmeddatabases in order to highlight a possible relationship between copeptin and type 2 diabetes and to provideinsights on the molecular mechanism that could explain this association.

RESULTS AND CONCLUSIONS

AVP potentiates CRH action at pituitary level resulting in an increased ACTH secretion and in turn in an increased cortisol secretion that escapes the negative feedback loop. Further, AVP regulates insulin and glucagon secretion through V1b receptor and promotes hepatic glycogenolysis and gluconeogenesis through V1a receptor. In addition to worsen glucose metabolism, AVP has been reported to have a role in the pathogenesis of diabetic complications such as cardiovascular diseases, kidney and ocular complications. Due to the very low concentration of AVP in the blood, the small size and poor stability, the assay of AVP is very difficult to perform. Thus, copeptin, the stable C-terminal portion of the prepro-vasopressin peptide has been identified as an easier assay to be measured and that mirrors AVP activity. Although there are promising evidence that copeptin could be involved in the pathogenesis of type 2 diabetes, further studies need to demonstrate the importance of copeptin as clinical marker to predict glucose metabolism derangements.

Zinc Supplementation Does Not Affect Glucagon Response to Intravenous Glucose and Insulin Infusion in Patients with Well-Controlled Type 2 Diabetes

Glucagon dysregulation is an essential component in the pathophysiology of type 2 diabetes. Studies in vitro and in animal models have shown that zinc co-secreted with insulin suppresses glucagon secretion. Zinc supplementation improves blood glucose control in patients with type 2 diabetes, although there is little information about how zinc supplementation may affect glucagon secretion. The objective of this study was to evaluate the effect of 1-year zinc supplementation on fasting plasma glucagon concentration and in response to intravenous glucose and insulin infusion in patients with type 2 diabetes. A cross-sectional study was performed after 1-year of intervention with 30 mg/day zinc supplementation or a placebo on 28 patients with type 2 diabetes. Demographic, anthropometric, and biochemical parameters were determined. Fasting plasma glucagon and in response to intravenous glucose and insulin infusion were evaluated. Patients of both placebo and supplemented groups presented a well control of diabetes, with mean values of fasting blood glucose and glycated hemoglobin within the therapeutic goals established by ADA. No significant differences were observed in plasma glucagon concentration, glucagon/glucose ratio or glucagon/insulin ratio fasting, after glucose or after insulin infusions between placebo and supplemented groups. No significant effects of glucose or insulin infusions were observed on plasma glucagon concentration. One-year zinc supplementation did not affect fasting plasma glucagon nor response to intravenous glucose or insulin infusion in well-controlled type 2 diabetes patients with an adequate zinc status.

Hypercalcemia in Glucagon Cell Hyperplasia and Neoplasia (Mahvash Syndrome): A New Association

CONTEXT

Hyperglucagonemia in the absence of glucagonomas is rare. Biallelic-inactivating mutations in the glucagon receptor gene (GCGR) cause glucagon cell hyperplasia and neoplasia (GCHN), also termed Mahvash syndrome. Here, we report the first case to our knowledge of GCHN presenting with hypercalcemia and demonstrate a unique relationship between calcium and α-cell hyperplasia.

CASE DESCRIPTION

A 47-year-old man presented with severe PTH-independent hypercalcemia, 13.95 mg/dL (3.48 mmol/L). Imaging and extensive pathology tests yielded no conclusive cause. Glucagon levels >300 times the upper limit of normal were discovered. Subtotal pancreatectomy identified α-cell hyperplasia and neoplasia with metastatic disease in lymph nodes. Genomic analysis confirmed a homozygous missense variant in GCGR (Asp63Asn). This is a previously described pathologic variant and has a known association with GCHN.

CONCLUSIONS

Inactivating mutations of the glucagon receptor gene lead to nonfunctional hyperglucagonemia and are associated with GCHN. Homozygous or compound heterozygous GCGR mutations are associated with α-cell hyperplasia, a known precursor to pancreatic neuroendocrine tumors that can metastasize. Hypercalcemia is an unreported consequence of GCHN with an unclear mechanism.

Changes in metabolism but not myocellular signaling by training with CHO-restriction in endurance athletes

Carbohydrate (CHO) restricted training has been shown to increase the acute training response, whereas less is known about the acute effects after repeated CHO restricted training. On two occasions, the acute responses to CHO restriction were examined in endurance athletes. Study 1 examined cellular signaling and metabolic responses after seven training-days including CHO manipulation (n = 16). The protocol consisted of 1 h high-intensity cycling, followed by 7 h recovery, and 2 h of moderate-intensity exercise (120SS). Athletes were randomly assigned to low (LCHO: 80 g) or high (HCHO: 415 g) CHO during recovery and the 120SS. Study 2 examined unaccustomed exposure to the same training protocol (n = 12). In Study 1, muscle biopsies were obtained at rest and 1 h after 120SS, and blood samples drawn during the 120SS. In Study 2, substrate oxidation and plasma glucagon were determined. In Study 1, plasma insulin and proinsulin C-peptide were higher during the 120SS in HCHO compared to LCHO (insulin: 0 min: +37%; 60 min: +135%; 120 min: +357%, P = 0.05; proinsulin C-peptide: 0 min: +32%; 60 min: +52%; 120 min: +79%, P = 0.02), whereas plasma cholesterol was higher in LCHO (+15-17%, P = 0.03). Myocellular signaling did not differ between groups. p-AMPK and p-ACC were increased after 120SS (+35%, P = 0.03; +59%, P = 0.0004, respectively), with no alterations in p-p38, p-53, or p-CREB. In Study 2, glucagon and fat oxidation were higher in LCHO compared to HCHO during the 120SS (+26-40%, P = 0.03; +44-76%, P = 0.01 respectively). In conclusion, the clear respiratory and hematological effects of CHO restricted training were not translated into superior myocellular signaling after accustomization to CHO restriction.

Associations of serum glucagon levels with glycemic variability in type 1 diabetes with different disease durations

PURPOSE

Glucagon has been recognized as a pivotal factor implicated in the pathophysiology ofdiabetes. The purpose of this study is to investigate the dynamic secretion levels of serum glucagon (GLA) in patients with type 1 diabetes mellitus (T1DM) with different courses of disease, and to analyze its correlation with blood glucose fluctuation.

METHODS

This observational study included 55 T1DM patients and divided into 3 groups according to the courses of disease. Group 1(the disease duration <1 year), Group 2(1≤the disease durations≤5), 3(the disease durations >5 years). All patients underwent a 100g standard steamed buns meal test,measuring the levels of serum glucose, glucagon, insulin, C-peptide in different points of time, and 48 of the total patients used continuous glucose monitoring system (CGMS) to monitor blood glucose.

RESULTS

The fasting glucagon level in Group 1 was significantly higher than it in Group 2. Furthermore, the GLA1h, the GLA3h and the AUCGLA0-3h in Group 1 were greatly larger than those in Group 3. Referring to glycemic variability, the LBGI, AUC of hypoglycemia, the percentage of hypoglycemia time andthe times of nocturnal hypoglycemia in Group 1 were significantly lower than those in Group 3. Moreover,the fasting glucagon level was the independent factors to SD and MAGE. The AUCGLA0-3h were negatively correlated with MODD, LBGI, GRADE-hypo and AUC of nocturnal hypoglycemia.

CONCLUSIONS

It is concluded that glucagon secretory function impairs with duration of type 1 diabetes extended and correlates to glycemic fluctuation, especially hypoglycemia.

Effects on the glucagon response to hypoglycaemia during DPP-4 inhibition in elderly subjects with type 2 diabetes: A randomized, placebo-controlled study

AIMS

Maintainance of glucagon response to hypoglycaemia is important as a safeguard against hypoglycaemia during glucose-lowering therapy in type 2 diabetes. During recent years, DPP-4 (dipeptidyl peptidase-4) inhibition has become more commonly used in elderly patients. However, whether DPP-4 inhibition affects the glucagon response to hypoglycaemia in the elderly is not known and was the aim of this study.

METHODS

In a single-centre, double-blind, randomized, placebo-controlled crossover study, 28 subjects with metformin-treated type 2 diabetes (17 male, 11 female; mean age, 74 years [range 65-86]; mean HbA1c, 51.5 mmol/mol [6.9%]) received sitagliptin (100 mg once daily) as add-on therapy or placebo for 4 weeks with a 4-week washout period in between. After each treatment period, the subjects underwent a standard breakfast test, followed by a 2-step hyperinsulinaemic hypoglycaemic clamp (target 3.5 and 3.0 mmol/L), followed by lunch.

RESULTS

Glucagon levels after breakfast and lunch, and the glucagon response at 3.5 mmol/L, were lower after sitagliptin than after placebo. However, the glucagon response to hypoglycaemia at 3.1 mmol/L did not differ significantly between the two. Similarly, the noradrenaline, adrenaline and cortisol responses were lower with sitagliptin than with placebo at 3.5 mmol/L, but not at 3.1 mmol/L glucose. Responses in pancreatic polypeptide did not differ between the two.

CONCLUSIONS

Elderly subjects with metformin-treated type 2 diabetes have lower glucagon levels at 3.5 mmol/L glucose, but maintain the glucagon response to hypoglycaemia at 3.1 mmol/L during DPP-4 inhibition, which safeguards against hypoglycaemia and may contribute to decreasing the risk of hypoglycaemia by DPP-4 inhibition in this age group.

Effects of acute NEFA manipulation on incretin-induced insulin secretion in participants with and without type 2 diabetes

AIMS/HYPOTHESIS

Incretin effect-the potentiation of glucose-stimulated insulin release induced by the oral vs the i.v. route-is impaired in dysglycaemic states. Despite evidence from human islet studies that NEFA interfere with incretin function, little information is available about the effect in humans. We tested the impact of acute bidirectional NEFA manipulation on the incretin effect in humans.

METHODS

Thirteen individuals with type 2 diabetes and ten non-diabetic volunteers had a 3 h OGTT, and, a week later, an i.v. isoglycaemic glucose infusion (ISO; OGTT matched). Both pairs of studies were repeated during an exogenous lipid infusion in the non-diabetic volunteers, and following acipimox administration (to inhibit lipolysis) in people with diabetes. Mathematical modelling of insulin secretion dynamics assessed total insulin secretion (TIS), beta cell glucose sensitivity (β-GS), glucose-induced potentiation (P_GLU) and incretin-induced potentiation (P_INCR); the oral glucose sensitivity index was used to estimate insulin sensitivity.

RESULTS

Lipid infusion increased TIS (from 61 [interquartile range 26] to 78 [31] nmol/m² on OGTT and from 29 nmol/m² [26] to 57 nmol/m² [30] on ISO) and induced insulin resistance. P_INCR decreased from 1.6 [1.1] to 1.3 [0.1] (p < 0.05). β-GS, P_GLU and glucagon, glucagon-like peptide 1 (GLP-1) and gastric inhibitory polypeptide (GIP) responses were unaffected. Acipimox (lowering NEFA by ~55%) reduced plasma glucose and TIS and enhanced insulin sensitivity, but did not change β-GS, P_INCR, P_GLU or glucagon, GLP-1 or GIP responses. As the per cent difference, incretin effect was decreased in non-diabetic participants and unchanged in those with diabetes.

CONCLUSIONS/INTERPRETATION

Raising NEFA selectively impairs incretin effect and insulin sensitivity in non-diabetic individuals, while acute NEFA reduction lowers plasma glucose and enhances insulin sensitivity in people with diabetes but does not correct the impaired incretin-induced potentiation.

A long-acting FGF21 alleviates hepatic steatosis and inflammation in a mouse model of non-alcoholic steatohepatitis partly through an FGF21-adiponectin-IL17A pathway

BACKGROUND AND PURPOSE

Non-alcoholic steatohepatitis (NASH) is the most severe form of non-alcoholic fatty liver disease and is a serious public health problem around the world. There are currently no approved treatments for NASH. FGF21 has recently emerged as a promising drug candidate for metabolic diseases. However, the disadvantages of FGF21 as a clinically useful medicine include its short plasma half-life and poor drug-like properties. Here, we have explored the effects of PsTag600-FGF21, an engineered long-acting FGF21 fusion protein, in mice with NASH and describe some of the underlying mechanisms.

EXPERIMENTAL APPROACH

A long-acting FGF21 was prepared by genetic fusion with a 600 residues polypeptide (PsTag600). We used a choline-deficient high-fat diet-induced model of NASH in mice. The effects on body weight, insulin sensitivity, inflammation and levels of hormones and metabolites were studied first. We further investigated whether PsTag600-FGF21 attenuated inflammation through the Th17-IL17A axis and the associated mechanisms.

KEY RESULTS

PsTag600-FGF21 dose-dependently reduced body weight, blood glucose, and insulin and lipid levels and reversed hepatic steatosis. PsTag600-FGF21 enhanced fatty acid activation and mitochondrial β-oxidation in the liver. The profound reduction in hepatic inflammation in NASH mice following PsTag600-FGF21 was associated with inhibition of IL17A expression in Th17 cells. Furthermore, PsTag600-FGF21 depended on adiponectin to exert its suppression of Th17 cell differentiation and IL17A expression.

CONCLUSIONS AND IMPLICATIONS

Our data have uncovered some of the mechanisms by which PsTag600-FGF21 suppresses hepatic inflammation and further suggest that PsTag600-FGF21 could be an effective approach in NASH treatment.

Effect of gender on the acute effects of whey protein ingestion on energy intake, appetite, gastric emptying and gut hormone responses in healthy young adults

BACKGROUND/OBJECTIVES

Protein supplements, usually drinks rich in whey protein, are used widely for weight loss purposes in overweight adults. Information comparing the effects of whey protein on appetite and energy intake in men and women is limited. The objective was to compare the acute effects of whey-protein intake on energy intake, appetite, gastric emptying and gut hormones in healthy young men and women.

SUBJECTS/METHODS

Gastric emptying (3D-ultrasonography), blood glucose and plasma insulin, glucagon, ghrelin, cholecystokinin (CCK), gastric inhibitory polypeptide (GIP) and glucagon-like peptide-1 (GLP-1) concentrations (0-180 min), appetite (visual analogue scales), and ad libitum energy intake from a buffet meal (180-210 min) were determined after ingestion of 30 g (120 kcal) or 70 g (280 kcal) whey protein, or a flavoured-water control drink (~2 kcal) in 8 healthy young men (25 ± 2 y, 72 ± 3 kg, 23 ± 1 kg/m²) and 8 women (23 ± 1 y, 64 ± 2 kg, 24 ± 0.4 kg/m²).

RESULTS

There was a protein-load effect on gastric emptying, blood glucose, plasma insulin, glucagon, ghrelin, CCK, GIP and GLP-1 concentrations, and perceptions of hunger, desire to eat and prospective food consumption (P < 0.05). Ad libitum energy intake (average decrease of 206 ± 39 kcal (15 ± 2%) for men and of 46 ± 54 kcal (0 ± 26%) for women for the mean of the intakes after the 30 and 70 g whey-protein loads) and hunger were suppressed more by whey-protein ingestion in men than women (P = 0.046). There was no difference in suppression of energy intake between the 30 and 70 g protein loads (P = 0.75, interaction effect P = 0.19). Consequently, total energy intake (protein drink plus buffet meal) increased more compared to control in women than men (P = 0.010). The drinks emptied more slowly, and plasma glucagon, CCK and GLP-1 increased less after the protein drinks, in women than men (P < 0.05).

CONCLUSION

The acute effects of whey protein ingestion on appetite, energy intake, gastric emptying and gut hormone responses are influenced by gender in healthy young adults.

Gastric Plication and Sleeve Gastrectomy in an Experimental Model of Obesity: New Insights into Weight Loss, Intake and Metabolic Results

AIM

Laparoscopic gastric plication (LGP) is a bariatric surgical technique based on the anatomical principles of laparoscopic sleeve gastrectomy (LSG), but its effects on the metabolic profile are still uncertain. The aim of our study is to compare the changes in weight, metabolic parameters and gastric histology following intervention by gastric plication (GP) and sleeve gastrectomy (SG) in an experimental model of obesity.

METHODS

To conduct the study, 32 8-week-old male Sprague-Dawley rats (Charles River®) were fattened by means of a cafeteria diet and randomly assigned to the following experimental groups: group 1: GP (n = 12); group 2: SG (n = 12) and group 3: sham (n = 8).

RESULTS

Unlike the SG group, the GP group attained the weight of the sham group at the end of the experiment (week 16). The GP group continued to eat more cafeteria diet than the SG group. In addition, the SG group achieved better glycaemic control than the GP group. Significantly higher plasma ghrelin levels were observed at week 16 in the GP group than in the SG group (2.29 ± 0.5 vs 1.07 ± 0.4, p < 0.05), which also occurred for the glucagon plasmatic levels (62.71 ± 36.2 vs 24.63 ± 9.3, p < 0.05).

CONCLUSIONS

GP is not as effective as SG and cannot be considered a metabolic surgery due to observed hormonal variations. The animals subjected to a GP continued to have a high appetite for the cafeteria diet unlike the animals submitted to an SG. Hormonal mechanisms possibly related to glucagon and ghrelin may be involved in this metabolic response.

Noradrenergic Activity in the Human Brain: A Mechanism Supporting the Defense Against Hypoglycemia

CONTEXT

Hypoglycemia, one of the major factors limiting optimal glycemic control in insulin-treated patients with diabetes, elicits a brain response to restore normoglycemia by activating counterregulation. Animal data indicate that local release of norepinephrine (NE) in the hypothalamus is important for triggering hypoglycemia-induced counterregulatory (CR) hormonal responses.

OBJECTIVE

To examine the potential role of brain noradrenergic (NA) activation in humans during hypoglycemia.

DESIGN

A hyperinsulinemic-hypoglycemic clamp was performed in conjunction with positron emission tomographic imaging.

PARTICIPANTS

Nine lean healthy volunteers were studied during the hyperinsulinemic-hypoglycemic clamp.

DESIGN

Participants received intravenous injections of (S,S)-[11C]O-methylreboxetine ([11C]MRB), a highly selective NE transporter (NET) ligand, at baseline and during hypoglycemia.

RESULTS

Hypoglycemia increased plasma epinephrine, glucagon, cortisol, and growth hormone and decreased [11C]MRB binding potential (BPND) by 24% ± 12% in the raphe nucleus (P < 0.01). In contrast, changes in [11C]MRB BPND in the hypothalamus positively correlated with increments in epinephrine and glucagon levels and negatively correlated with glucose infusion rate (all P < 0.05). Furthermore, in rat hypothalamus studies, hypoglycemia induced NET translocation from the cytosol to the plasma membrane.

CONCLUSIONS

Insulin-induced hypoglycemia initiated a complex brain NA response in humans. Raphe nuclei, a region involved in regulating autonomic output, motor activity, and hunger, had increased NA activity, whereas the hypothalamus showed a NET-binding pattern that was associated with the individual's CR response magnitude. These findings suggest that NA output most likely is important for modulating brain responses to hypoglycemia in humans.

EJE PRIZE 2018: A gut feeling about glucagon

Hyperglucagonaemia (in the fasting as well as in the postprandial state) is considered a core pathophysiological component of diabetes and is found to contribute substantially to the hyperglycaemic state of diabetes. Hyperglucagonaemia is usually viewed upon as a consequence of pancreatic alpha cell insensitivity to the glucagon-suppressive effects of glucose and insulin. Since we observed that the well-known hyperglucagonaemic response to oral glucose in patients with type 2 diabetes is exchanged by normal suppression of plasma glucagon levels following isoglycaemic intravenous glucose administration in these patients, we have been focusing on the gut and gut-derived factors as potential mediators of diabetic hyperglucagonaemia. In a series of clinical experiments, we have elucidated the role of gut-derived factors in diabetic hyperglucagonaemia and shown that glucose-dependent insulinotropic polypeptide promotes hyperglucagonaemia and that glucagon, hitherto considered a pancreas-specific hormone, may also be secreted from extrapancreatic tissues - most likely from proglucagon-producing enteroendocrine cells. Furthermore, our observation that fasting hyperglucagonaemia is unrelated to the diabetic state, but strongly correlates with obesity, liver fat content and circulating amino acids, has made us question the common 'pancreacentric' and 'glucocentric' understanding of hyperglucagonaemia and led to the hypothesis that steatosis-induced hepatic glucagon resistance (and reduced amino acid turnover) and compensatory glucagon secretion mediated by increased circulating amino acids constitute a complete endocrine feedback system: the liver-alpha cell axis. This article summarises the physiological regulation of glucagon secretion in humans and considers new findings suggesting that the liver and the gut play key roles in determining fasting and postabsorptive circulating glucagon levels.

Endogenous Glucose Production and Hormonal Changes in Response to Canagliflozin and Liraglutide Combination Therapy

The decrement in plasma glucose concentration with SGLT2 inhibitors (SGLT2i) is blunted by a rise in endogenous glucose production (EGP). We investigated the ability of incretin treatment to offset the EGP increase. Subjects with type 2 diabetes (n = 36) were randomized to 1) canagliflozin (CANA), 2) liraglutide (LIRA), or 3) CANA plus LIRA (CANA/LIRA). EGP was measured with [3-³H]glucose with or without drugs for 360 min. In the pretreatment studies, EGP was comparable and decreased (2.2 ± 0.1 to 1.7 ± 0.2 mg/kg ⋅ min) during a 300- to 360-min period (P < 0.01). The decrement in EGP was attenuated with CANA (2.1 ± 0.1 to 1.9 ± 0.1 mg/kg ⋅ min) and CANA/LIRA (2.2 ± 0.1 to 2.0 ± 0.1 mg/kg ⋅ min), whereas with LIRA it was the same (2.4 ± 0.2 to 1.8 ± 0.2 mg/kg ⋅ min) (all P < 0.05 vs. baseline). After CANA, the fasting plasma insulin concentration decreased (18 ± 2 to 12 ± 2 μU/mL, P < 0.05), while it remained unchanged in LIRA (18 ± 2 vs. 16 ± 2 μU/mL) and CANA/LIRA (17 ± 1 vs. 15 ± 2 μU/mL). Mean plasma glucagon did not change during the pretreatment studies from 0 to 360 min, while it increased with CANA (69 ± 3 to 78 ± 2 pg/mL, P < 0.05), decreased with LIRA (93 ± 6 to 80 ± 6 pg/mL, P < 0.05), and did not change in CANA/LIRA. LIRA prevented the insulin decline and blocked the glucagon rise observed with CANA but did not inhibit the increase in EGP. Factors other than insulin and glucagon contribute to the stimulation of EGP after CANA-induced glucosuria.

Dendrobium Officinale Kimura et Migo Ameliorates Insulin Resistance in Rats with Diabetic Nephropathy

BACKGROUND Emerging evidence suggests the potential of Dendrobium officinale Kimura et Migo (DO) in treating the complications of diabetes mellitus (DM). We evaluated the therapeutic potential of DO in treating diabetic nephropathy (DN) by preventing insulin resistance. MATERIAL AND METHODS A DN model was established. Mean glomerular volume of rats was estimated by the method of Weibel-Gomez. Reverse transcription quantitative polymerase chain reaction (RT-qPCR) was used to determine the expression of mRNAs and we used Western blot assay to determine the expression of proteins. The levels of fasting insulin (FINS) and glucagon (GLU) were measured and we assessed the levels of high-sensitivity C-reactive protein (hs-CRP), tumor necrosis factor-a (TNF-a), and interleukin-6 (IL-6) using the enzyme-linked immunosorbent assay (ELISA). RESULTS Compared with the Normal rats, the levels of urinary glucose, albuminuria, Scr, albuminuria/Scr and BUN, and the expression levels of CaN, TLR-2, TLR-4, MyD88, hs-CRP, TNF-a, and IL-6, the level of FINS, GLU, and HOMAIR were increased in DN, DO 1.0, DO 2.0, and DMBG groups. Compared with the DN rats, in DO 1.0, DO 2.0, and DMBG groups the glomerular volume was smaller, the levels of urinary glucose, albuminuria, Scr, albuminuria/Scr, and BUN, the expression levels of CaN, TLR-2, TLR-4, MyD88, hs-CRP, TNF-a, and IL-6, the level of FINS, GLU, and HOMA-IR were decreased. CONCLUSIONS We found that DO prevents insulin resistance in rats with DN. This may be associated with reduction of TLRs and inflammatory response, which should be further verified by loss of DO effects on DN after treatment of inhibitors of TLRs.

The effects of add-on exenatide to insulin on glycemic variability and hypoglycemia in patients with type 1 diabetes mellitus

OBJECTIVE

To investigate the effect of add-on exenatide to insulin on glycemic excursion and the counter-regulatory hormone in response to hypoglycemia in patients with type 1 diabetes mellitus (T1DM).

METHODS

30 patients with T1DM were recruited and randomly assigned to exenatide + insulin-treated group (group 1, n = 15) or insulin-only-treated group (group 2, n = 15) for 4 weeks. All patients had continuous glucose monitor system (CGMS) applied at before (week-0) and after (week-4) treatment to evaluate the glycemic variability. All patients had an arginine-stimulated test at before and after treatment. Six patients from each group also had hypoglycemic clamp test to assess counter-regulatory hormone level.

RESULTS

Patients in the exenatide group had significant reductions in body weight, body mass index (BMI), total insulin dose, bolus insulin dose, fructosamine, and glycemic excursion after 4 weeks' treatment. Compared with patients in group 2, the mean amplitude of glycemic excursion (MAGE) and coefficient of variation (CV) of exenatide group decreased significantly. Similarly, a significant decrease of glucagon (GLC) in the arginine-stimulated test was found in group 1. No significant changes of GLC, growth hormone (GH), cortisol (COR), epinephrine (E), and norepinephrine (NE) were found in both groups during hypoglycemia clamp test. However, patients who had residual islet function in group 1 showed an upward trend of basic C-peptide (C-P) and GLC during the hypoglycemia period.

CONCLUSION

Although exenatide could inhibit glucagon secretion during euglycemia or hyperglycemia in patients with T1DM, it has no effect on GLC and counter-regulatory hormones during hypoglycemia clamp in patients with no functional residual islet test.

Personalizing physical exercise in a computational model of fuel homeostasis

The beneficial effects of physical activity for the prevention and management of several chronic diseases are widely recognized. Mathematical modeling of the effects of physical exercise in body metabolism and in particular its influence on the control of glucose homeostasis is of primary importance in the development of eHealth monitoring devices for a personalized medicine. Nonetheless, to date only a few mathematical models have been aiming at this specific purpose. We have developed a whole-body computational model of the effects on metabolic homeostasis of a bout of physical exercise. Built upon an existing model, it allows to detail better both subjects' characteristics and physical exercise, thus determining to a greater extent the dynamics of the hormones and the metabolites considered.

Effects of Intragastric Administration of Tryptophan on the Blood Glucose Response to a Nutrient Drink and Energy Intake, in Lean and Obese Men

Tryptophan stimulates plasma cholecystokinin and pyloric pressures, both of which slow gastric emptying. Gastric emptying regulates postprandial blood glucose. Tryptophan has been reported to decrease energy intake. We investigated the effects of intragastric tryptophan on the glycaemic response to, and gastric emptying of, a mixed-nutrient drink, and subsequent energy intake. Lean and obese participants (n = 16 each) received intragastric infusions of 1.5 g ("Trp-1.5g") or 3.0 g ("Trp-3.0g") tryptophan, or control, and 15 min later consumed a mixed-nutrient drink (56 g carbohydrates). Gastric emptying (¹³C-acetate breath-test), blood glucose, plasma C-peptide, glucagon, cholecystokinin and tryptophan concentrations were measured (t = 0-60 min). Energy intake was assessed between t = 60-90 min. In lean individuals, Trp-3.0g, but not Trp-1.5g, slowed gastric emptying, reduced C-peptide_AUC and increased glucagon_AUC (all P < 0.05), but did not significantly decrease the blood glucose response to the drink, stimulate cholecystokinin or reduce mean energy intake, compared with control. In obese individuals, Trp-3.0g, but not Trp-1.5g, tended to slow gastric emptying (P = 0.091), did not affect C-peptide_AUC, increased glucagon_AUC (P < 0.001) and lowered blood glucose at t = 30 min (P < 0.05), and did not affect cholecystokinin or mean energy intake. In obese individuals, intragastrically administered tryptophan may reduce postprandial blood glucose by slowing gastric emptying; the lack of effect on mean energy intake requires further investigation.

A novel role of the corticotrophin-releasing hormone regulating peptide, teneurin C-terminal associated peptide 1, on glucose uptake into the brain

Teneurin C-terminal associated peptide (TCAP) is an ancient paracrine signalling agent that evolved via lateral gene transfer from prokaryotes into an early metazoan ancestor. Although it bears structural similarity to corticotrophin-releasing hormone (CRH), it inhibits the in vivo actions of CRH. The TCAPs are highly expressed in neurones, where they induce rapid cytoskeletal rearrangement and are neuroprotective. Because these processes are highly energy-dependent, this suggests that TCAP has the potential to regulate glucose uptake because glucose is the primary energy substrate in brain, and neurones require a steady supply to meet the high metabolic demands of neuronal communication. Therefore, the objective of the present study was to assess the effect of TCAP-mediated glucose uptake in the brain and in neuronal cell models. TCAP-mediated ¹⁸ F-deoxyglucose (FDG) uptake into brain tissue was assessed in male wild-type Wistar rats by functional positron emission tomography. TCAP-1 increased FDG uptake by over 40% into cortical regions of the brain, demonstrating that TCAP-1 can significantly enhance glucose supply. Importantly, a single nanomolar injection of TCAP-1 increased brain glucose after 3 days and decreased blood glucose after 1 week. This is corroborated by a decreased serum concentration of insulin and an increased serum concentration of glucagon. In immortalised hypothalamic neurones, TCAP-1 increased ATP production and enhanced glucose uptake by increasing glucose transporter recruitment to the plasma membrane likely via AKT and mitogen-activated protein kinase/ERK phosphorylation events. Taken together, these data demonstrate that TCAP-1 increases glucose metabolism in neurones, and may represent a peptide signalling agent that regulated glucose uptake before insulin and related peptides.

Deficient Glucagon Response to Hypoglycemia During a Mixed Meal in Total Pancreatectomy/Islet Autotransplantation Recipients

CONTEXT

Total pancreatectomy and intrahepatic islet autotransplantation (TP/IAT) is performed to alleviate severe abdominal pain, avoid narcotic use, maintain islet function, and avoid diabetes in patients with chronic pancreatitis. However, many TP/IAT recipients complain of postprandial hypoglycemia.

OBJECTIVE

This study was designed to discover the mechanisms of this problem.

DESIGN

Participants consumed a triple-isotope mixed meal.

SETTING

This study was performed in a hospital research unit.

PARTICIPANTS

We studied 10 TP/IAT recipients and 10 age- and body mass index-matched control subjects. Seven of 10 recipients had a history of postprandial hypoglycemia.

INTERVENTIONS

Participants were given a [1-13C]-labeled mixed meal and two tracer infusions ([6,6-2H2]- and [6-3H]-glucose).

MAIN OUTCOME MEASURES

Glucose kinetics and concentrations of regulatory hormones were determined.

RESULTS

Immediately after the meal, peak glucose was elevated in recipients compared with control subjects [266 ± 20 mg/dL (14.8 ± 1.1 mmol/L) vs 185 ± 13 mg/dL (10.3 ± 0.7 mmol/L); P = 0.01]. However, mean Δ glucose for TP/IAT recipients between minutes 240 and 360 postprandially was significantly lower than for control subjects (P < 0.05); six of the seven recipients with a history of hypoglycemia experienced abnormally low postprandial Δ glucose. Δ Glucagon remained unchanged (minutes 240 to 360; P = 0.58) in TP/IAT recipients despite abnormal decreases in postprandial glucose. Radioisotopic studies revealed that meal appearance, glucose disappearance, and endogenous glucose production in TP/IAT recipients were not different from control subjects.

CONCLUSION

Initially high glucose levels followed by hypoglycemia with an absent glucagon response is a mechanistic sequence that contributes to postprandial hypoglycemia after TP/IAT.

Impact of C-Peptide Status on the Response of Glucagon and Endogenous Glucose Production to Induced Hypoglycemia in T1DM

CONTEXT

Complete loss of β-cell function in patients with type 1 diabetes mellitus (T1DM) may lead to an increased risk of severe hypoglycemia.

OBJECTIVE

We aimed to determine the impact of C-peptide status on glucagon response and endogenous glucose production (EGP) during hypoglycemia in patients with T1DM.

DESIGN AND SETTING

We conducted an open, comparative trial.

PATIENTS

Ten C-peptide positive (C-pos) and 11 matched C-peptide negative (C-neg) patients with T1DM were enrolled.

INTERVENTION

Plasma glucose was normalized over the night fast, and after a steady-state (baseline) plateau all patients underwent a hyperinsulinemic, stepwise hypoglycemic clamp with glucose plateaus of 5.5, 3.5, and 2.5 mmol/L and a recovery phase of 4.0 mmol/L. Blood glucagon was measured with a specific and highly sensitive glucagon assay. EGP was determined with a stable isotope tracer technique.

MAIN OUTCOME MEASURE

Impact of C-peptide status on glucagon response and EGP during hypoglycemia.

RESULTS

Glucagon concentrations were significantly lower in C-pos and C-neg patients than previously reported. At baseline, C-pos patients had higher glucagon concentrations than C-neg patients (8.39 ± 4.6 vs 4.19 ± 2.4 pmol/L, P = 0.016, mean ± standard deviation) but comparable EGP rates (2.13 ± 0.2 vs 2.04 ± 0.3 mg/kg/min, P < 0.391). In both groups, insulin suppressed glucagon levels, but hypoglycemia revealed significantly higher glucagon concentrations in C-pos than in C-neg patients. EGP was significantly higher in C-pos patients at hypoglycemia (2.5 mmol/L) compared with C-neg patients.

CONCLUSIONS

Glucagon concentrations and EGP during hypoglycemia were more pronounced in C-pos than in C-neg patients, which indicates that preserved β-cell function may contribute to counterregulation during hypoglycemia in patients with T1DM.

In Uncontrolled Diabetes, Hyperglucagonemia and Ketosis Result From Deficient Leptin Action in the Parabrachial Nucleus

Growing evidence implicates neurons that project from the lateral parabrachial nucleus (LPBN) to the hypothalamic ventromedial nucleus (VMN) in a neurocircuit that drives counterregulatory responses to hypoglycemia, including increased glucagon secretion. Among LPBN neurons in this circuit is a subset that expresses cholecystokinin (LPBNCCK neurons) and is tonically inhibited by leptin. Because uncontrolled diabetes is associated with both leptin deficiency and hyperglucagonemia, and because intracerebroventricular (ICV) leptin administration reverses both hyperglycemia and hyperglucagonemia in this setting, we hypothesized that deficient leptin inhibition of LPBNCCK neurons drives activation of this LPBN→VMN circuit and thereby results in hyperglucagonemia. Here, we report that although bilateral microinjection of leptin into the LPBN does not ameliorate hyperglycemia in rats with streptozotocin-induced diabetes mellitus (STZ-DM), it does attenuate the associated hyperglucagonemia and ketosis. To determine if LPBN leptin signaling is required for the antidiabetic effect of ICV leptin in STZ-DM, we studied mice in which the leptin receptor was selectively deleted from LPBNCCK neurons. Our findings show that although leptin signaling in these neurons is not required for the potent antidiabetic effect of ICV leptin, it is required for leptin-mediated suppression of diabetic hyperglucagonemia. Taken together, these findings suggest that leptin-mediated effects in animals with uncontrolled diabetes occur through actions involving multiple brain areas, including the LPBN, where leptin acts specifically to inhibit glucagon secretion and associated ketosis.

Evidence of a liver-alpha cell axis in humans: hepatic insulin resistance attenuates relationship between fasting plasma glucagon and glucagonotropic amino acids

AIMS/HYPOTHESIS

The secretion of glucagon is controlled by blood glucose and inappropriate secretion of glucagon contributes to hyperglycaemia in diabetes. Besides its role in glucose regulation, glucagon regulates amino acid metabolism in hepatocytes by increasing ureagenesis. Disruption of this mechanism causes hyperaminoacidaemia, which in turn increases glucagon secretion. We hypothesised that hepatic insulin resistance (secondary to hepatic steatosis) via defective glucagon signalling/glucagon resistance would lead to impaired ureagenesis and, hence, increased plasma concentrations of glucagonotropic amino acids and, subsequently, glucagon.

METHODS

To examine the association between glucagon and amino acids, and to explore whether this relationship was modified by hepatic insulin resistance, we studied a well-characterised cohort of 1408 individuals with normal and impaired glucose regulation. In this cohort, we have previously reported insulin resistance to be accompanied by increased plasma concentrations of glucagon. We now measure plasma levels of amino acids in the same cohort. HOMA-IR was calculated as a marker of hepatic insulin resistance.

RESULTS

Fasting levels of glucagonotropic amino acids and glucagon were significantly and inversely associated in linear regression models (persisting after adjustment for age, sex and BMI). Increasing levels of hepatic, but not peripheral insulin resistance (p > 0.166) attenuated the association between glucagon and circulating levels of alanine, glutamine and tyrosine, and was significantly associated with hyperaminoacidaemia and hyperglucagonaemia. A doubling of the calculated glucagon-alanine index was significantly associated with a 30% increase in hepatic insulin resistance, a 7% increase in plasma alanine aminotransferase levels, and a 14% increase in plasma γ-glutamyltransferase levels.

CONCLUSIONS/INTERPRETATION

This cross-sectional study supports the existence of a liver-alpha cell axis in humans: glucagon regulates plasma levels of amino acids, which in turn feedback to regulate the secretion of glucagon. With hepatic insulin resistance, reflecting hepatic steatosis, the feedback cycle is disrupted, leading to hyperaminoacidaemia and hyperglucagonaemia. The glucagon-alanine index is suggested as a relevant marker for hepatic glucagon signalling.

Pramlintide but Not Liraglutide Suppresses Meal-Stimulated Glucagon Responses in Type 1 Diabetes

CONTEXT

Postprandial hyperglycemia remains a challenge in type 1 diabetes (T1D) due, in part, to dysregulated increases in plasma glucagon levels after meals.

OBJECTIVE

This study was undertaken to examine whether 3 to 4 weeks of therapy with pramlintide or liraglutide might help to blunt postprandial hyperglycemia in T1D by suppressing plasma glucagon responses to mixed-meal feedings.

DESIGN

Two parallel studies were conducted in which participants underwent mixed-meal tolerance tests (MMTTs) without premeal bolus insulin administration before and after 3 to 4 weeks of treatment with either pramlintide (8 participants aged 20 ± 3 years, hemoglobin A1c 6.9 ± 0.5%) or liraglutide (10 participants aged 22 ± 3 years, hemoglobin A1c 7.6 ± 0.9%).

RESULTS

Compared with pretreatment responses to the MMTT, treatment with pramlintide reduced the peak increment in glucagon from 32 ± 16 to 23 ± 12 pg/mL (P < 0.02). In addition, the incremental area under the plasma glucagon curve from 0 to 120 minutes dropped from 1988 ± 590 to 737 ± 577 pg/mL/min (P < 0.001), which was accompanied by a similar reduction in the meal-stimulated increase in the plasma glucose curve from 11,963 ± 1424 mg/dL/min pretreatment vs 2493 ± 1854 mg/dL/min after treatment (P < 0.01). In contrast, treatment with liraglutide had no effect on plasma glucagon and glucose responses during the MMTT.

CONCLUSIONS

Adjunctive treatment with pramlintide may provide an effective means to blunt postmeal hyperglycemia in T1D by suppressing dysregulated plasma glucagon responses. In contrast, plasma glucose and glucagon responses were unchanged after 3 to 4 weeks of treatment with liraglutide.

Patterns of Plasma Glucagon Dynamics Do Not Match Metabolic Phenotypes in Young Women

CONTEXT

The role of hyperglucagonemia in type 2 diabetes is still debated.

OBJECTIVE

We analyzed glucagon dynamics during oral glucose tolerance tests (oGTTs) in young women with one out of three metabolic phenotypes: healthy control (normoglycemic after a normoglycemic pregnancy), normoglycemic high-risk (normoglycemic after a pregnancy complicated by gestational diabetes), and prediabetes/screening-diagnosed type 2 diabetes. We asked if glucagon patterns were homogeneous within the metabolic phenotypes.

DESIGN AND SETTING

Five-point oGTT, sandwich enzyme-linked immunosorbent assay for glucagon, and functional data analysis with unsupervised clustering.

PARTICIPANTS

Cross-sectional analysis of 285 women from the monocenter observational study Prediction, Prevention, and Subclassification of gestational and type 2 Diabetes, recruited between November 2011 and May 2016.

RESULTS

We found four patterns of glucagon dynamics that did not match the metabolic phenotypes. Elevated fasting glucagon and delayed glucagon suppression was overrepresented with prediabetes/diabetes, but this was only detected in 21% of this group. It also occurred in 8% of the control group.

CONCLUSIONS

We conclude that hyperglucagonemia may contribute to type 2 diabetes in a subgroup of affected individuals but that it is not a sine qua non for the disease. This should be considered in future pathophysiological studies and when testing pharmacotherapies addressing glucagon signaling.

Effects of three major amino acids found in Japanese broth on glucose metabolism and gastric emptying

OBJECTIVES

To our knowledge, the effect of the broth of dried kelp and dried bonito, dashi, on glucose metabolism and digestion has rarely been studied. Based on the component analysis of three actual broths served in traditional restaurants, a chemically synthesized broth with three free amino acids (histidine, glutamate, aspartate) and salt was prepared to investigate their effect on glucose metabolism, glucose-dependent insulinotropic polypeptide (GIP), and glucagon-like peptide 1 (GLP-1) secretion, and digestion.

METHODS

In study 1, seven healthy individuals were enrolled in a four-period crossover study. Participants drank or ate hot water, synthesized broth, hot water with rice, and synthesized broth with rice. Plasma glucose, serum insulin, plasma glucagon, plasma GIP, and plasma GLP-1 were measured at baseline and after ingestion. In study 2, 6 of the 7 individuals ingested rice steamed with 13C-labeled sodium acetate with hot water or synthesized broth to estimate gastric emptying by the 13C-labeled acetate breath test in a two-period crossover trial.

RESULTS

Ingesting water or synthesized broth alone elicited no change in plasma glucose or serum insulin levels. Ingesting synthesized broth with rice resulted in a rapid rise in plasma glucose and GLP-1 (P = 0.01 and 0.02, respectively) in an early postprandial phase compared with that by ingesting water with rice, but the area under the curve of those showed no significant differences. Ingesting synthesized broth with rice resulted in a significantly higher gastric emptying coefficient than that after rice with water (P = 0.03).

CONCLUSIONS

Three amino acids and sodium chloride corresponding to those found in actual broth promoted gastric emptying and led to a rapid response of plasma glucose. Our findings suggest that ingestion of the broth of dried kelp and dried bonito may improve gastric motility.

Dose-Dependent Effects of Randomized Intraduodenal Whey-Protein Loads on Glucose, Gut Hormone, and Amino Acid Concentrations in Healthy Older and Younger Men

Protein-rich supplements are used widely for the prevention and management of malnutrition in older people. We have reported that healthy older, compared to younger, adults have less suppression of energy intake by whey-protein-effects on appetite-related hormones are unknown. The objective was to determine the effects of intraduodenally administered whey-protein on glucose, gut hormone, and amino acid concentrations, and their relation to subsequent ad libitum energy intake at a buffet meal, in healthy older and younger men. Hydrolyzed whey-protein (30 kcal, 90 kcal, and 180 kcal) and a saline control (~0 kcal) were infused intraduodenally for 60 min in 10 younger (19-29 years, 73 ± 2 kg, 22 ± 1 kg/m²) and 10 older (68-81 years, 79 ± 2 kg, 26 ± 1 kg/m²) healthy men in a randomized, double-blind fashion. Plasma insulin, glucagon, gastric inhibitory peptide (GIP), glucagon-like peptide-1 (GLP-1), peptide tyrosine-tyrosine (PYY), and amino acid concentrations, but not blood glucose, increased, while ghrelin decreased during the whey-protein infusions. Plasma GIP concentrations were greater in older than younger men. Energy intake correlated positively with plasma ghrelin and negatively with insulin, glucagon, GIP, GLP-1, PYY, and amino acids concentrations (p < 0.05). In conclusion, intraduodenal whey-protein infusions resulted in increased GIP and comparable ghrelin, insulin, glucagon, GIP, GLP-1, PYY, and amino acid responses in healthy older and younger men, which correlated to subsequent energy intake.

Bidirectional Relationship between Gastric Emptying and Plasma Glucose Control in Normoglycemic Individuals and Diabetic Patients

Gastric emptying and glycemic control pathways are closely interrelated processes. Gastric chyme is transferred into the duodenum with velocities depending on its solid or liquid state, as well as on its caloric and nutritional composition. Once nutrients enter the intestine, the secretion of incretins (hormonal products of intestinal cells) is stimulated. Among incretins, glucagon-like peptide-1 (GLP-1) has multiple glycemic-regulatory effects that include delayed gastric emptying, thus triggering a feedback loop lowering postprandial serum glucose levels. Glycemic values also influence gastric emptying; hyperglycemia slows it down, and hypoglycemia accelerates it, both limiting glycemic fluctuations. Disordered gastric emptying in diabetes mellitus is understood today as a complex pathophysiological condition, with both irreversible and reversible components and high intra- and interindividual variability of time span and clinical features. While limited delays may be useful for reducing postprandial hyperglycemias, severely hindered gastric emptying may be associated with higher glycemic variability and worsened long-term glycemic control. Therapeutic approaches for both gastric emptying and glycemic control include dietary modifications of meal structure or content and drugs acting as GLP-1 receptor agonists. In the foreseeable future, we will probably witness a wider range of dietary interventions and more incretin-based medications used for restoring both gastric emptying and glycemic levels to nearly physiological levels.

Impaired Insulin Action Is Associated With Increased Glucagon Concentrations in Nondiabetic Humans

CONTEXT

Abnormal glucagon concentrations contribute to hyperglycemia, but the mechanisms of α-cell dysfunction in prediabetes are unclear.

OBJECTIVE

We sought to determine the relative contributions of insulin secretion and action to α-cell dysfunction in nondiabetic participants across the spectrum of glucose tolerance.

DESIGN

This was a cross-sectional study. A subset of participants (n = 120) was studied in the presence and absence of free fatty acid (FFA) elevation, achieved by infusion of Intralipid (Baxter Healthcare, Deerfield, IL) plus heparin, to cause insulin resistance.

SETTING

An inpatient clinical research unit at an academic medical center.

PARTICIPANTS

A total of 310 nondiabetic persons participated in this study.

INTERVENTIONS

Participants underwent a seven-sample oral glucose tolerance test. Subsequently, 120 participants were studied on two occasions. On one day, infusion of Intralipid plus heparin raised FFA. On the other day, participants received glycerol as a control.

MAIN OUTCOME MEASURE(S)

We examined the relationship of glucagon concentration with indices of insulin action after adjusting for the effects of age, sex, and weight. Subsequently, we sought to determine whether an acute decrease in insulin action, produced by FFA elevation, altered glucagon concentrations in nondiabetic participants.

RESULTS

Fasting glucagon concentrations correlated positively with fasting insulin and C-peptide concentrations and inversely with insulin action. Fasting glucagon was not associated with any index of β-cell function in response to an oral challenge. As expected, FFA elevation decreased insulin action and also raised glucagon concentrations.

CONCLUSIONS

In nondiabetic participants, glucagon secretion was altered by changes in insulin action.

Effect of Age on Blood Glucose and Plasma Insulin, Glucagon, Ghrelin, CCK, GIP, and GLP-1 Responses to Whey Protein Ingestion

Protein-rich supplements are used widely to prevent and manage undernutrition in older people. We have previously shown that healthy older, compared to younger, adults have less suppression of energy intake by whey protein-although the effects of age on appetite-related gut hormones are largely unknown. The aim of this study was to determine and compare the acute effects of whey protein loads on blood glucose and plasma gut hormone concentrations in older and younger adults. Sixteen healthy older (eight men, eight women; mean ± SEM: age: 72 ± 1 years; body mass index: 25 ± 1 kg/m²) and 16 younger (eight men, eight women; 24 ± 1 years; 23 ± 0.4 kg/m²) adults were studied on three occasions in which they ingested 30 g (120 kcal) or 70 g (280 kcal) whey protein, or a flavored-water control drink (~2 kcal). At regular intervals over 180 min, blood glucose and plasma insulin, glucagon, ghrelin, cholecystokinin (CCK), gastric inhibitory peptide (GIP), and glucagon-like peptide-1 (GLP-1) concentrations were measured. Plasma ghrelin was dose-dependently suppressed and insulin, glucagon, CCK, GIP, and GLP-1 concentrations were dose-dependently increased by the whey protein ingestion, while blood glucose concentrations were comparable during all study days. The stimulation of plasma CCK and GIP concentrations was greater in older than younger adults. In conclusion, orally ingested whey protein resulted in load-dependent gut hormone responses, which were greater for plasma CCK and GIP in older compared to younger adults.