Metabolic and endocrine responses to a standard mixed meal. A physiologic study

A prospective study on glucagon responses to oral glucose and mixed meal and 7-year change in fasting glucose

INTRODUCTION

The role of insufficient glucagon suppression after an oral load in the development of type 2 diabetes mellitus is unclear. The aim of this study was to examine the association between glucagon responses at baseline and fasting glucose levels 7 years later.

METHODS

Data of the Hoorn Meal Study were used, an observational cohort study among 121 persons without diabetes with a mean age of 61.1 ± 6.7 years and 50% being female. The glucagon response to an oral glucose tolerance test and mixed meal test was expressed as early and late incremental area under the curve. The association with change in fasting glucose levels at follow-up was assessed by linear regression analysis.

RESULTS

The early glucagon response following the mixed meal test was associated with an increase in fasting glucose levels of 0.18 mmol/L (95%-CI: 0.04-0.31, P = 0.01), per unit increase in the incremental area under the curve of glucagon, adjusted for confounders. No significant associations were observed for the late response after the mixed meal test or oral glucose tolerance test.

CONCLUSIONS

Within a population without diabetes, relative lack of glucagon suppression early after a meal was associated with increased glucose levels over time, suggesting a role of insufficient glucagon suppression in the deterioration of glycaemic control.

Exploring the insulin secretory properties of the PGD2-GPR44/DP2 axis in vitro and in a randomized phase-1 trial of type 2 diabetes patients

Aims/Hypothesis

GPR44 (DP2, PTGDR2, CRTh2) is the receptor for the pro-inflammatory mediator prostaglandin D₂ (PGD₂) and it is enriched in human islets. In rodent islets, PGD₂ is produced in response to glucose, suggesting that the PGD₂-GPR44/DP2 axis may play a role in human islet function during hyperglycemia. Consequently, the aim of this work was to elucidate the insulinotropic role of GPR44 antagonism in vitro in human beta-cells and in type 2 diabetes (T2DM) patients.

Methods

We determined the drive on PGD₂ secretion by glucose and IL-1beta, as well as, the impact on insulin secretion by pharmacological GPR44/DP2 antagonism (AZD1981) in human islets and beta-cells in vitro. To test if metabolic control would be improved by antagonizing a hyperglycemia-driven increased PGD₂ tone, we performed a proof-of-mechanism study in 20 T2DM patients (average 54 years, HbA1c 9.4%, BMI 31.6 kg/m²). The randomized, double-blind, placebo-controlled cross-over study consisted of two three-day treatment periods (AZD1981 or placebo) separated by a three-day wash-out period. Mixed meal tolerance test (MMTT) and intravenous graded glucose infusion (GGI) was performed at start and end of each treatment period. Assessment of AZD1981 pharmacokinetics, glucose, insulin, C-peptide, glucagon, GLP-1, and PGD₂ pathway biomarkers were performed.

Results

We found (1) that PGD₂ is produced in human islet in response to high glucose or IL-1beta, but likely by stellate cells rather than endocrine cells; (2) that PGD₂ suppresses both glucose and GLP-1 induced insulin secretion in vitro; and (3) that the GPR44/DP2 antagonist (AZD1981) in human beta-cells normalizes insulin secretion. However, AZD1981 had no impact on neither glucose nor incretin dependent insulin secretion in humans (GGI AUC _{C-peptide 1-2h} and MMTT AUC _{Glucose 0-4h} LS mean ratios vs placebo of 0.94 (80% CI of 0.90–0.98, p = 0.12) and 0.99 (90% CI of 0.94–1.05, p = 0.45), despite reaching the expected antagonist exposure.

Conclusion/Interpretation

Pharmacological inhibition of the PGD₂-GPR44/DP2 axis has no major impact on the modulation of acute insulin secretion in T2DM patients.

Trial registration

ClinicalTrials.gov NCT02367066.

Nonsuppressed Glucagon After Glucose Challenge as a Potential Predictor for Glucose Tolerance

Glucagon levels are classically suppressed after glucose challenge. It is still not clear as to whether a lack of suppression contributes to hyperglycemia and thus to the development of diabetes. We investigated the association of postchallenge change in glucagon during oral glucose tolerance tests (OGTTs), hypothesizing that higher postchallenge glucagon levels are observed in subjects with impaired glucose tolerance (IGT). Glucagon levels were measured during OGTT in a total of 4,194 individuals without diabetes in three large European cohorts. Longitudinal changes in glucagon suppression were investigated in 50 participants undergoing a lifestyle intervention. Only 66-79% of participants showed suppression of glucagon at 120 min (fold change glucagon_120/0 <1) during OGTT, whereas 21-34% presented with increasing glucagon levels (fold change glucagon_120/0 ≥1). Participants with nonsuppressed glucagon₁₂₀ had a lower risk of IGT in all cohorts (odds ratio 0.44-0.53, P < 0.01). They were also leaner and more insulin sensitive and had lower liver fat contents. In the longitudinal study, an increase of fold change glucagon_120/0 was associated with an improvement in insulin sensitivity (P = 0.003). We characterize nonsuppressed glucagon₁₂₀ during the OGTT. Lower glucagon suppression after oral glucose administration is associated with a metabolically healthier phenotype, suggesting that it is not an adverse phenomenon.

Spontaneous Hypoglycemia After Islet Autotransplantation for Chronic Pancreatitis

CONTEXT

Spontaneous hypoglycemia has been reported in patients after total pancreatectomy (TP) and islet autotransplantation (IAT) with maintained insulin independence. Details surrounding these events have not been well described.

OBJECTIVE

The objective of the study was to determine the frequency and characteristics of spontaneous hypoglycemia in patients undergoing TP-IAT and/or to ascertain predictive or protective factors of its development.

DESIGN

This was an observational cohort study in 40 patients who underwent TP-IAT from August 2008 to May 2014, with a median follow-up of 34 months.

SETTING

The study was conducted at a single institution (Cleveland Clinic).

PATIENTS

Patients included recipients of TP-IAT.

INTERVENTION

The intervention included small, frequent meals in those patients who developed spontaneous hypoglycemia.

MAIN OUTCOME MEASURES

Incidence of spontaneous hypoglycemia development, characteristics of the patients developing hypoglycemia, and their response to small, frequent meals were measured.

RESULTS

Six of 12 patients, who maintained insulin independence, developed spontaneous hypoglycemia. The episodes could be fasting, postprandial, and/or exercise associated, with the frequency ranging from two to three times daily to once every 1-2 weeks. All patients experienced at least one episode that required external assistance, glucagon administration, and/or emergent medical attention. Patients who developed hypoglycemia had a lower median age and tended to have a lower median islet equivalent/kg body weight but a higher median total islet equivalent, body mass index, and homeostatic model assessment for insulin resistance score. All patients who received small, frequent meal intervention had improvement in severity and/or frequency of the hypoglycemic episodes.

CONCLUSIONS

Spontaneous hypoglycemia is prevalent after TP-IAT. Although the underlying pathophysiology responsible for these hypoglycemia events remains to be elucidated, small, frequent meal intervention is helpful in ameliorating this condition.

Effects of meal composition on postprandial incretin, glucose and insulin responses after surgical and medical weight loss

Background

Meal tolerance tests are frequently used to study dynamic incretin and insulin responses in the postprandial state; however, the optimal meal that is best tolerated and suited for hormonal response following surgical and medical weight loss has yet to be determined.

Objective

To evaluate the tolerability and effectiveness of different test meals in inducing detectable changes in markers of glucose metabolism in individuals who have undergone a weight loss intervention.

Methods

Six individuals who underwent surgical or medical weight loss (two Roux‐en‐Y gastric bypass, two sleeve gastrectomy and two medical weight loss) each completed three meal tolerance tests using liquid‐mixed, solid‐mixed and high‐fat test meals. The tolerability of each test meal, as determined by the total amount consumed and palatability, as well as fasting and meal‐stimulated glucagon‐like peptide, glucose‐dependent insulinotropic polypeptide, insulin and glucose were measured.

Results

Among the six individuals, the liquid‐mixed meal was better and more uniformly tolerated with a median meal completion rate of 99%. Among the four bariatric surgical patients, liquid‐mixed meal stimulated on average a higher glucagon‐like peptide (percent difference: 83.7, 89), insulin secretion (percent difference: 155.1, 158.7) and glucose‐dependent insulinotropic polypeptide (percent difference: 113.5, 34.3) compared with solid‐mixed and high‐fat meals.

Conclusions

The liquid‐mixed meal was better tolerated with higher incretin and insulin response compared with the high‐fat and solid‐mixed meals and is best suited for the evaluation of stimulated glucose homeostasis.

Influence of protein intake on renal hemodynamics and plasma hormone concentrations in normal subjects

Glomerular filtration rate (GFR) by clearance of inulin and creatinine and effective renal plasma flow (ERPF) by para-aminohippurate clearance was investigated in 8 normal volunteers on low protein (LP) and high protein (HP) diet for 6 days in the basal state and after a mixed protein-rich test meal. Plasma immunoreactive insulin (IRI), glucagon (IRG) and growth hormone (IRHGH) were followed before and after the test meal. GFR was higher on HP than on LP diet and increased within one hour after the test meal. ERPF also increased significantly after the meal on LP diet. IRI increased maximally at 60 min after the test meal and then declined gradually. IRG increased after a latency period of 90 min and IRHGH consistently did not change. Since the increase in GFR was significant already one hour after the test meal, i.e. before IRG was changed, we conclude that glucagon is not a mediator of the protein-induced increased in GFR. Neither insulin nor growth hormone appeared to be involved.

Carbohydrate, fat, and protein metabolism in muscle and in the whole body after mixed meal ingestion

The effect of ingesting a meal containing 3,275 kJ (47.3% carbohydrate, two-thirds of which was in the form of simple sugars, 39.4% fat, and 13.2% protein) on the oxidation of carbohydrate fat and protein (or amino acids) was assessed by indirect calorimetry and measurement of the rate of excretion of nitrogenous end products in urine and changes in the plasma urea concentration. Simultaneously, an assessment was made of substrate metabolism in forearm muscle by measuring forearm blood flow and concentration of metabolites in arterialized and deep venous blood. The mean resting energy expenditure during the first four hours after food ingestion was 15% higher than in the preprandial period (P less than .01). The extra energy dissipated during this time is equivalent to 5.3% of the energy provided in the meal. Carbohydrate oxidation increased by 111% (P less than .01), protein oxidation increased by 40% (P less than .05), and fat oxidation decreased by 21% (P less than .05). The concentration of glucose and amino acids and their uptake by muscle increased after food ingestion, while the reverse occurred with nonesterified fatty acids (NEFA). In the early postprandial period there was a marked suppression in the uptake of NEFA by muscle and a tendency toward decreased rather than increased release of glycolytic products (lactate + pyruvate + alanine), despite an up to sevenfold increase in the uptake of glucose. Fructose, which accounted for about 30% of the carbohydrate in the diet, was not taken up by muscle to any significant extent. It is estimated that during the first four hours after the meal muscle accounted for the uptake of 20% to 25% of the carbohydrate provided in the meal. This was associated with a small and nonsignificant change in the oxygen uptake by muscle. The data suggest that: (1) the increased uptake of glucose by muscle in the postprandial period does not necessarily increase the release of glycolytic products or increase the activity of the glucose-alanine and Cori cycles between muscle and liver; (2) triglyceride may become a more important energy source for muscle than circulating NEFA, especially in the early postprandial period; (3) muscle is not a major site of dietary-induced thermogenesis (zero to four hours); and (4) it is likely that nonmuscular tissues took up more carbohydrate (including fructose) than skeletal muscle during the first four hours after ingestion of this meal (even if it is assumed that as little as 50% of the dietary carbohydrate had been absorbed by four hours).

Reflex insulin response associated to food intake in human subjects

The occurrence of a reflex insulin discharge at the beginning of a meal, and its possible influence on intake were studied in 7 normal weight humans. Each subject was tested twice under three standard meal conditions. The evolutions of insulinemia and glycemia were recorded over an 84 min observation period, starting 2 min before food presentation. Blood was drawn continuously from an antecubital vein, and collected in 1-min samples for the first 30 min, and then in 3-min samples. The average glycemia curve was stable until some 18-20 min after meal onset. By contrast, a significant rise in plasma insulin appeared as early as the 4th min after meal onset and it is hypothesized to be preabsorptive, of cephalic and/or gastric origin. However, inter-test variations were large even in the same person. Schematically, three types of early insulin responses were observed: high and/or sustained rise, moderate and/or short increase, moderate decrease in plasma insulin. The shape of the early insulin response was not related to any meal characteristic. The potential biological and behavioral significance of the early insulin release is discussed.

Substrate, hormone, and temperature responses in males and females to a common breakfast

To evaluate the response to a mixed meal we studied oral temperature, metabolite, and hormonal responses to a common American breakfast containing 11 kcal/kg body weight (carbohydrate 43%, fat 42%, and protein 15%) in 12 normal volunteers (6 males and 6 females). There was a significant rise in oral temperature during the postcibal period. This change in oral temperature did not depend upon food consumption in males but was meal-dependent in females. Food ingestion caused increases in the peripheral circulating concentrations of glucose, lactate, pyruvate, and amino acids and reciprocal decreases in the concentrations of free fatty acids, glycerol, and urea nitrogen. Acetoacetate and beta-hydroxybutyrate decreased during the postcibal period but the changes were not statistically significant. Although peripheral venous serum insulin and plasma glucagon concentrations were indistinguishable between the sexes, males had higher concentrations of plasma triglycerides, plasma amino acids, and serum urea nitrogen. Peripheral venous plasma somatostatin and secretin remained unchanged, but pancreatic polypeptide hormone showed a large biphasic response to the meal. After breakfast the blood glucose concentration tended to be greater in males than in females and this difference was significant at 60 and 120 min postcibal. Furthermore, every female had a 120 min postcibal glucose concentration that was lower than her basal fasting glucose concentration. This suggests that postcibal glucose concentrations should be related to gender in making the diagnosis of carbohydrate intolerance or reactive hypoglycemia.