Effects of variations in duodenal glucose load on glycaemic, insulin, and incretin responses in type 2 diabetes

Gastric emptying in newly diagnosed, treatment-naïve Han Chinese with type 2 diabetes and the impact of 4-week insulin pump therapy

AIM

To evaluate gastric emptying (GE) and the glycaemic response to a 75-g oral glucose load in newly diagnosed, treatment-naïve Han Chinese with type 2 diabetes (T2D) before insulin pump therapy, after 4 weeks of insulin pump therapy, and 12-15 months after insulin pump therapy.

MATERIALS AND METHODS

Twenty participants with T2D (baseline glycated haemoglobin [± SD] 10.7% [± 1.2%] 93 [± 10] mmol/mol) ingested a 75-g glucose drink containing 150 mg 13C-acetate, to determine the gastric half-emptying time, and underwent assessment of plasma glucose and serum insulin, C-peptide and glucagon-like peptide-1 (GLP-1) over 180 min before and after 4 weeks of insulin pump therapy (discontinued for 48 h before re-assessment). Data were compared to those in 19 healthy participants matched for sex and age. After 12-15 months, GE was re-measured in 14 of the T2D participants.

RESULTS

At baseline, participants with T2D exhibited substantially augmented fasting and post-glucose glycaemia, diminished insulin secretion, and more rapid GE (p < 0.05 each), but comparable GLP-1, compared to healthy participants. Following insulin pump therapy, insulin secretion increased, GLP-1 secretion was attenuated, fasting and post-glucose glycaemia were lower, and GE was slowed (p < 0.05 each). The slowing of GE in T2D participants was sustained over 12-15 months of follow-up.

CONCLUSIONS

In newly diagnosed Han Chinese with T2D, GE is often accelerated despite poor glycaemic control and is slowed by short-term insulin pump therapy. The effect on GE is maintained for at least 12 months.

Disparities in the Glycemic and Incretin Responses to Intraduodenal Glucose Infusion Between Healthy Young Men and Women

CONTEXT

Premenopausal women are at a lower risk of type 2 diabetes (T2D) compared to men, but the underlying mechanism(s) remain elusive. The secretion of the incretin hormones, glucose-dependent insulinotropic polypeptide (GIP) and glucagon-like peptide-1 (GLP-1), from the small intestine is a major determinant of glucose homeostasis and may be influenced by sex.

OBJECTIVES

This study compared blood glucose and plasma insulin and incretin responses to intraduodenal glucose infusions in healthy young males and females.

DESIGN

In Study 1, 9 women and 20 men received an intraduodenal glucose infusion at 2 kcal/min for 60 minutes. In Study 2, 10 women and 26 men received an intraduodenal glucose at 3 kcal/min for 60 minutes. Venous blood was sampled every 15 minutes for measurements of blood glucose and plasma insulin, GLP-1 and GIP.

RESULTS

In response to intraduodenal glucose at 2 kcal/min, the incremental area under the curve between t = 0-60 minutes (iAUC0-60min) for blood glucose and plasma GIP did not differ between the 2 groups. However, iAUC0-60min for plasma GLP-1 (P = 0.016) and insulin (P = 0.011) were ∼2-fold higher in women than men. In response to intraduodenal glucose at 3 kcal/min, iAUC0-60min for blood glucose, plasma GIP, and insulin did not differ between women and men, but GLP-1 iAUC0-60min was 2.5-fold higher in women (P = 0.012).

CONCLUSION

Healthy young women exhibit comparable GIP but a markedly greater GLP-1 response to intraduodenal glucose than men. This disparity warrants further investigations to delineate the underlying mechanisms and may be of relevance to the reduced risk of diabetes in premenopausal women when compared to men.

Cooked rice- and wheat-based food structure influenced digestion kinetics and glycemic response in growing pigs

BACKGROUND

How starch-based food structure can impact the rate and extent of digestion in the small intestine and resulting glycemic response is not properly understood. One possible explanation is that food structure influences gastric digestion, which subsequently determines digestion kinetics in the small intestine and glucose absorption. However, this possibility has not been investigated in detail.

OBJECTIVES

Using growing pigs as a digestion model for adult humans, this study aimed to investigate how physical structure of starch-rich foods impacts small intestinal digestion and glycemic response.

METHODS

Male growing pigs (21.7 ± 1.8 kg, Large White × Landrace) were fed one of six cooked diets (250-g starch equivalent) with varying initial structures (rice grain, semolina porridge, wheat or rice couscous, or wheat or rice noodle). The glycemic response, small intestinal content particle size and hydrolyzed starch content, ileal starch digestibility, and portal vein plasma glucose were measured. Glycemic response was measured as plasma glucose collected from an in-dwelling jugular vein catheter for up to 390 min postprandial. Portal vein blood samples and small intestinal content were measured after sedation and euthanasia of the pigs at 30, 60, 120, or 240 min postprandial. Data were analyzed with a mixed-model ANOVA.

RESULTS

The plasma glucose Δmax_overall and iAUC_overall for couscous and porridge diets (smaller-sized diets) were higher than intact grain and noodle diets (larger-sized diets); 29.0 ± 3.2 vs. 21.7 ± 2.6 mg/dL and 5659 ± 727 vs. 2704 ± 521 mg/dL.min, for the smaller- and larger-sized diets, respectively (p < 0.05). Ileal starch digestibility was not significantly different between diets (p ≥ 0.05). The iAUC_overall was inversely related to the starch gastric emptying half-time of the diets (r = -0.90, p = 0.015).

CONCLUSIONS

Starch-based food structure affected the glycemic response and starch digestion kinetics in the small intestine of growing pigs.

The efficacy of GLP-1RAs for the management of postprandial hypoglycemia following bariatric surgery: a systematic review

OBJECTIVE

Postprandial hyperinsulinemic hypoglycemia with neuroglycopenia is an increasingly recognized complication of Roux-en-Y gastric bypass and gastric sleeve surgery that may detrimentally affect patient quality of life. One likely causal factor is glucagon-like peptide-1 (GLP-1), which has an exaggerated rise following ingestion of carbohydrates after bariatric surgery. This paper sought to assess the role of GLP-1 receptor agonists (GLP-1RAs) in managing postprandial hypoglycemia following bariatric surgery.

METHODS

MEDLINE, Embase, Cochrane Central Register of Controlled Trials (CENTRAL), ClinicalTrials.gov, and Scopus were systematically and critically appraised for all peer-reviewed publications that suitably fulfilled the inclusion criteria established a priori. This systematic review was developed according to the Preferred Reporting Items for Systematic Review and Meta-Analyses Protocols (PRISMA-P). It followed methods outlined in the Cochrane Handbook for Systematic Reviews of Interventions and is registered with PROSPERO (International Prospective Register of Systematic Reviews; identifier CRD420212716429).

RESULTS AND CONCLUSIONS

Postprandial hyperinsulinemic hypoglycemia remains a notoriously difficult to manage metabolic complication of bariatric surgery. This first, to the authors' knowledge, systematic review presents evidence suggesting that use of GLP-1RAs does not lead to an increase of hypoglycemic episodes, and, although this approach may appear counterintuitive, the findings suggest that GLP-1RAs could reduce the number of postprandial hypoglycemic episodes and improve glycemic variability.

Relationships of Glucose, GLP-1, and Insulin Secretion With Gastric Emptying After a 75-g Glucose Load in Type 2 Diabetes

CONTEXT

The relationships of gastric emptying (GE) with the glycemic response at 120 minutes, glucagon-like peptide-1 (GLP-1), and insulin secretion following a glucose load in type 2 diabetes (T2D) are uncertain.

OBJECTIVE

We evaluated the relationship of plasma glucose, GLP-1, and insulin secretion with GE of a 75-g oral glucose load in T2D.

DESIGN

Single-center, cross-sectional, post hoc analysis.

SETTING

Institutional research center.

PARTICIPANTS

43 individuals with T2D age 65.6 ± 1.1 years, hemoglobin A1c 7.2 ± 1.0%, median duration of diabetes 5 years managed by diet and/or metformin.

INTERVENTION

Participants consumed the glucose drink radiolabeled with 99mTc-phytate colloid following an overnight fast. GE (scintigraphy), plasma glucose, GLP-1, insulin, and C-peptide were measured between 0 and 180 minutes.

MAIN OUTCOME MEASURES

The relationships of the plasma glucose at 120 minutes, plasma GLP-1, and insulin secretion (calculated by Δinsulin0-30/ Δglucose0-30 and ΔC-peptide0-30/Δglucose0-30) with the rate of GE (scintigraphy) were evaluated.

RESULTS

There were positive relationships of plasma glucose at 30 minutes (r = 0.56, P < 0.001), 60 minutes (r = 0.57, P < 0.001), and 120 minutes (r = 0.51, P < 0.001) but not at 180 minutes (r = 0.13, P = 0.38), with GE. The 120-minute plasma glucose and GE correlated weakly in multiple regression models adjusting for age, GLP-1, and insulin secretion (P = 0.04 and P = 0.06, respectively). There was no relationship of plasma GLP-1 with GE. Multiple linear regression analysis indicated that there was no significant effect of GE on insulin secretion.

CONCLUSION

In T2D, while insulin secretion is the dominant determinant of the 120-minute plasma glucose, GE also correlates. Given the relevance to interpreting the results of an oral glucose tolerance test, this relationship should be evaluated further. There appears to be no direct effect of GE on either GLP-1 or insulin secretion.

A systematic review of whey protein supplementation effects on human glycemic control: A mechanistic insight

BACKGROUND/AIMS

Some studies showed that dietary factors such as whey protein (WP) are effective on glycemic regulation. Due to the current controversy about WP effects and mechanisms of its action on glycemic control, we conducted this systematic review to shed light on the subject.

METHODS

Web of Science, Medline (Pubmed), and Scopus online databases were searched from 2012 up to February 2022 using the following keywords: "whey protein" and "glycemic control"/"glycemia"/"glucose"/"insulin". The search included original English articles, human clinical trials with WP supplementation and measurement of glucose or insulin as an outcome, studies on healthy individuals/patients with diabetes mellitus (DM)/impaired fasting glucose (IFG).

RESULTS

Title/abstract of 1991 studies were reviewed. After excluding studies due to inappropriate full title and duplication, and exercising inclusion criteria, 58 studies were reviewed in detail. Ample evidence showed that WP decreased postprandial glucose incremental area under the curve (iAUC) and increased iAUCs of insulin and incretin hormones. WP affects glycemic control mainly through stimulating insulin and incretins secretion, slowing gastric emptying, and appetite suppression.

CONCLUSION

Although most of the recent evidence showed beneficial effects of WP supplementation on glycemic response, further long-term clinical trials are required which assess the long-term impact of WP supplementation and its exact mechanisms.

Effects of intraduodenal infusion of lauric acid and L-tryptophan, alone and combined, on glucoregulatory hormones, gastric emptying and glycaemia in healthy men

BACKGROUND AND AIM

In healthy men, intraduodenal administration of the fatty acid, lauric acid ('C12') and the amino acid, L-tryptophan ('TRP'), at loads that individually do not affect energy intake, reduce energy intake substantially when combined. C12 and TRP may also stimulate cholecystokinin and glucagon-like peptide-1 (GLP-1), which both slow gastric emptying, a key determinant of postprandial blood glucose. Accordingly, combination of C12 and TRP has the potential to reduce post-meal glycaemia more than either nutrient alone.

METHODS

Twelve healthy, lean men (age (mean ± SD): 28 ± 7 years) received, on 4 separate occasions, 45-min intraduodenal infusions of C12 (0.3 kcal/min), TRP (0.1 kcal/min), C12 + TRP (0.4 kcal/min), or 0.9% saline (control), in a randomised, double-blind fashion. 30 min after commencement of the infusion a mixed-nutrient drink was consumed and gastric emptying measured (¹³C breath-test) for 3 h. Blood samples were obtained at baseline, in response to treatments alone, and for 2 h post-drink for measurements of plasma glucose, cholecystokinin, GLP-1, C-peptide, insulin and glucagon. 'Early' (first 30 min) and 'overall' glycaemic and hormone responses were evaluated.

RESULTS

C12 + TRP and C12 delayed the rise in, but did not affect the overall glycaemic response to the drink, compared with control and TRP (all P < 0.05). C12 + TRP slowed gastric emptying compared with control and TRP (both P < 0.005), and C12 non-significantly slowed gastric emptying compared with control (P = 0.090). C12 + TRP and C12 delayed the rise in C-peptide and insulin, and also stimulated CCK and glucagon, compared with control and TRP (all P < 0.05). Only C12 + TRP stimulated early and overall GLP-1 compared with control (P < 0.05).

CONCLUSIONS

In healthy men, C12 + TRP and C12, in the loads administered, had comparable effects to delay the rise in glucose following a nutrient drink, probably primarily by slowing of gastric emptying, as a result of CCK and GLP-1 stimulation, while TRP had no effect.

Plasma GLP-1 Response to Oral and Intraduodenal Nutrients in Health and Type 2 Diabetes-Impact on Gastric Emptying

CONTEXT

Both gastric emptying and the secretion of glucagon-like peptide-1 (GLP-1) are major determinants of postprandial glycemia in health and type 2 diabetes (T2D). GLP-1 secretion after a meal is dependent on the entry of nutrients into the small intestine, which, in turn, slows gastric emptying.

OBJECTIVE

To define the relationship between gastric emptying and the GLP-1 response to both oral and small intestinal nutrients in subjects with and without T2D.

METHODS

We evaluated: (i) the relationship between gastric emptying (breath test) and postprandial GLP-1 levels after a mashed potato meal in 73 individuals with T2D; (ii) inter-individual variations in GLP-1 response to (a) intraduodenal glucose (4 kcal/min) during euglycemia and hyperglycemia in 11 healthy and 12 T2D, subjects, (b) intraduodenal fat (2 kcal/min) in 15 T2D subjects, and (c) intraduodenal protein (3 kcal/min) in 10 healthy subjects; and (iii) the relationship between gastric emptying (breath test) of 75 g oral glucose and the GLP-1 response to intraduodenal glucose (4 kcal/min) in 21 subjects (9 healthy, 12 T2D).

RESULTS

The GLP-1 response to the mashed potato meal was unrelated to the gastric half-emptying time (T50). The GLP-1 responses to intraduodenal glucose, fat, and protein varied substantially between individuals, but intra-individual variation to glucose was modest. The T50 of oral glucose was related directly to the GLP-1 response to intraduodenal glucose (r = 0.65, P = 0.002).

CONCLUSION

In a given individual, gastric emptying is not a determinant of the postprandial GLP-1 response. However, the intrinsic gastric emptying rate is determined in part by the responsiveness of GLP-1 to intestinal nutrients.

Comparative Effects of the Branched-Chain Amino Acids, Leucine, Isoleucine and Valine, on Gastric Emptying, Plasma Glucose, C-Peptide and Glucagon in Healthy Men

(1) Background: Whey protein lowers postprandial blood glucose in health and type 2 diabetes, by stimulating insulin and incretin hormone secretion and slowing gastric emptying. The branched-chain amino acids, leucine, isoleucine and valine, abundant in whey, may mediate the glucoregulatory effects of whey. We investigated the comparative effects of intragastric administration of leucine, isoleucine and valine on the plasma glucose, C-peptide and glucagon responses to and gastric emptying of a mixed-nutrient drink in healthy men. (2) Methods: 15 healthy men (27 ± 3 y) received, on four separate occasions, in double-blind, randomised fashion, either 10 g of leucine, 10 g of isoleucine, 10 g of valine or control, intragastrically, 30 min before a mixed-nutrient drink. Plasma glucose, C-peptide and glucagon concentrations were measured before, and for 2 h following, the drink. Gastric emptying of the drink was quantified using ¹³C-acetate breath-testing. (3) Results: Amino acids alone did not affect plasma glucose or C-peptide, while isoleucine and valine, but not leucine, stimulated glucagon (p < 0.05), compared with control. After the drink, isoleucine and leucine reduced peak plasma glucose compared with both control and valine (all p < 0.05). Neither amino acid affected early (t = 0–30 min) postprandial C-peptide or glucagon. While there was no effect on overall gastric emptying, plasma glucose at t = 30 min correlated with early gastric emptying (p < 0.05). (4) Conclusion: In healthy individuals, leucine and isoleucine lower postprandial blood glucose, at least in part by slowing gastric emptying, while valine does not appear to have an effect, possibly due to glucagon stimulation.

Effect of the glucagon-like peptide-1 analogue liraglutide versus placebo treatment on circulating proglucagon-derived peptides that mediate improvements in body weight, insulin secretion and action: A randomized controlled trial

AIM

To examine how circulating glucagon-like peptide-1 (GLP-1) concentrations during liraglutide treatment relate to its therapeutic actions on glucose and weight, and to study the effects of liraglutide on other proglucagon-derived peptides (PGDPs), including endogenous GLP-1, glucagon-like peptide-2, glucagon, oxyntomodulin, glicentin and major proglucagon fragment, which also regulate metabolic and weight control.

MATERIALS AND METHODS

Adults who were overweight/obese (body mass index 27-40 kg/m² ) with prediabetes were randomized to liraglutide (1.8 mg/day) versus placebo for 14 weeks. We used specific assays to measure exogenous (liraglutide, GLP-1 agonist [GLP-1A]) and endogenous (GLP-1E) GLP-1, alongside five other PGDP concentrations during a mixed meal tolerance test (MMTT) completed at baseline and at week 14 (liraglutide, n = 16; placebo, n = 19). Glucose during MMTT, steady-state plasma glucose (SSPG) concentration for insulin resistance and insulin secretion rate (ISR) were previously measured. MMTT area-under-the-curve (AUC) was calculated for ISR, glucose and levels of PGDPs.

RESULTS

Participants on liraglutide versus placebo had significantly (P ≤ .004) decreased weight (mean -3.6%, 95% CI [-5.2% to -2.1%]), SSPG (-32% [-43% to -22%]) and glucose AUC (-7.0% [-11.5% to -2.5%]) and increased ISR AUC (30% [16% to 44%]). GLP-1A AUC at study end was significantly (P ≤ .04) linearly associated with % decrease in weight (r = -0.54) and SSPG (r = -0.59) and increase in ISR AUC (r = 0.51) in the liraglutide group. Treatment with liraglutide significantly (P ≤ .005) increased exogenous GLP-1A AUC (median 310 vs. 262 pg/mL × 8 hours at baseline but decreased endogenous GLP-1E AUC [13.1 vs. 24.2 pmol/L × 8 hours at baseline]), as well as the five other PGDPs. Decreases in the PGDPs processed in the intestines are independent of weight loss, indicating a probable direct effect of GLP-1 receptor agonists to decrease their endogenous production in contrast to weight loss-dependent changes in glucagon and major proglucagon fragment that are processed in pancreatic alpha cells.

CONCLUSIONS

Circulating GLP-1A concentrations, reflecting liraglutide levels, predict improvement in weight, insulin action and secretion in a linear manner. Importantly, liraglutide also downregulates other PGDPs, normalization of the levels of which may provide additional metabolic and weight loss benefits in the future.

Enteroendocrine Hormone Secretion and Metabolic Control: Importance of the Region of the Gut Stimulation

It is now widely appreciated that gastrointestinal function is central to the regulation of metabolic homeostasis. Following meal ingestion, the delivery of nutrients from the stomach into the small intestine (i.e., gastric emptying) is tightly controlled to optimise their subsequent digestion and absorption. The complex interaction of intraluminal nutrients (and other bioactive compounds, such as bile acids) with the small and large intestine induces the release of an array of gastrointestinal hormones from specialised enteroendocrine cells (EECs) distributed in various regions of the gut, which in turn to regulate gastric emptying, appetite and postprandial glucose metabolism. Stimulation of gastrointestinal hormone secretion, therefore, represents a promising strategy for the management of metabolic disorders, particularly obesity and type 2 diabetes mellitus (T2DM). That EECs are distributed distinctively between the proximal and distal gut suggests that the region of the gut exposed to intraluminal stimuli is of major relevance to the secretion profile of gastrointestinal hormones and associated metabolic responses. This review discusses the process of intestinal digestion and absorption and their impacts on the release of gastrointestinal hormones and the regulation of postprandial metabolism, with an emphasis on the differences between the proximal and distal gut, and implications for the management of obesity and T2DM.

A Physiologically-Based Quantitative Systems Pharmacology Model of the Incretin Hormones GLP-1 and GIP and the DPP4 Inhibitor Sitagliptin

Incretin hormones glucagon‐like peptide‐1 (GLP‐1) and glucose‐dependent insulinotropic polypeptide (GIP) play a major role in regulation of postprandial glucose and the development of type 2 diabetes mellitus. The incretins are rapidly metabolized, primarily by the enzyme dipeptidyl‐peptidase 4 (DPP4), and the neutral endopeptidase (NEP), although the exact metabolization pathways are unknown. We developed a physiologically‐based (PB) quantitative systems pharmacology model of GLP‐1 and GIP and their metabolites that describes the secretion of the incretins in response to intraduodenal glucose infusions and their degradation by DPP4 and NEP. The model describes the observed data and suggests that NEP significantly contributes to the metabolization of GLP‐1, and the traditional assays for the total GLP‐1 and GIP forms measure yet unknown entities produced by NEP. We further extended the model with a PB pharmacokinetics/pharmacodynamics model of the DPP4 inhibitor sitagliptin that allows predictions of the effects of this medication class on incretin concentrations.

Exenatide once weekly slows gastric emptying of solids and liquids in healthy, overweight people at steady-state concentrations

AIMS

To evaluate the effects of 8 weeks' administration of exenatide (EXE) once weekly on gastric emptying of solids and liquids (using the "gold standard" technique, scintigraphy), glucose absorption and postprandial glycaemia in healthy people.

MATERIAL AND METHODS

A total of 32 healthy participants were randomized to receive either EXE once weekly (2 mg/wk subcutaneously; six men, 10 women, mean age 59.9 ± 0.9 years, mean body mass index [BMI] 29.6 ± 0.6 kg/m² ) or matching placebo (PBO; six men, 10 women, mean age 60.6 ± 1.2 years, mean BMI 29.5 ± 1.0 kg/m² ) for 8 weeks. Gastric emptying, nausea (visual analogue scale), and plasma glucose, insulin, C-peptide and glucagon were measured for 120 min after a solid/liquid meal, comprising 100 g ground beef (radiolabelled with 20 MBq ^99m Tc-sulphur colloid) and 150 mL 10% glucose (radiolabelled with 7 MBq ⁶⁷ Ga-EDTA), and containing 5 g 3-O-methyl-glucose (3-OMG) as a marker of glucose absorption, at baseline and after 8 weeks' treatment.

RESULTS

The study treatments were well tolerated. Scores for nausea were consistently low, with no difference between the EXE once weekly and PBO groups. EXE once weekly slowed gastric emptying of solids (area under the curve [AUC]_0-120min : P < 0.05) and liquids (AUC_0-120min : P = 0.01) substantially, and attenuated glucose absorption (3-OMG incremental AUC [iAUC]_0-30min : P = 0.001) and the postprandial rise in plasma glucose (iAUC_0-30min : P = 0.008). Plasma glucagon at 2 h was reduced by EXE once weekly (P = 0.001). The magnitude of the reduction in plasma glucose at t = 30 min from baseline to 8 weeks with EXE once weekly was related inversely to the 50% emptying time of the glucose drink (r = -0.55, P = 0.03).

CONCLUSIONS

In healthy participants, 8 weeks' administration of the "long-acting" glucagon-like peptide-1 receptor agonist EXE, slowed gastric emptying of solids and liquids substantially, with consequent reductions in glucose absorption and postprandial glycaemia.

Baroreflex function and postprandial hypotension in older adults

PURPOSE

Postprandial hypotension (PPH) is a common but poorly understood etiology for fainting in older adults. One potential mechanism is age-related baroreflex dysfunction. We examined baroreflex function in older adults with PPH and without PPH (noPPH) during a standardized meal test.

METHODS

57 adults (age ≥ 65; 24 PPH, 33 noPPH, mean age 77.9 ± 0.9 years, 54% female) were recruited and had meal tests performed. The baroreflex effectiveness index (BEI, %) and baroreflex sensitivity (BRS, ms/mm Hg) were calculated using the sequence method.

RESULTS

Baseline BEI (22 ± 2 versus 23 ± 2 percent, t = - 0.411, p = 0.682) and BRS (14.1 ± 2.4 versus 13.8 ± 2.5 ms/mm of Hg, t = - 0.084, p = 0.933) were similar in PPH and noPPH subjects. During the meal test PPH subjects showed significantly lower BEI as compared to noPPH subjects (time × PPH, F = 2.791, p = 0.042), while there was no difference in the postprandial change in BRS (time, F = 0.618, p = 0.605).

CONCLUSION

Patients with PPH demonstrated an acute postprandial decrease in baroreflex effectiveness during meal testing as compared with normal subjects, suggesting a potential contributing mechanism for this condition.

Effects of sitagliptin on gastric emptying of, and the glycaemic and blood pressure responses to, a carbohydrate meal in type 2 diabetes

AIMS

To determine the effects of the dipeptidyl peptidase-4 inhibitor, sitagliptin, on gastric emptying (GE) of a high-carbohydrate meal and associated glycaemic and blood pressure (BP) responses in type 2 diabetes mellitus (T2DM).

MATERIALS AND METHODS

Fourteen patients with T2DM (nine men, five women; age 67.8 ± 1.5 years; body mass index 31.2 ± 0.9 kg/m² ; T2DM duration: 4.2 ± 0.9 years; glycated haemoglobin: 46 ± 1.8 mmol/mol [6.4% ± 0.2%]), managed by diet and/or metformin, underwent concurrent measurements of GE, BP and plasma glucose for 240 minutes after ingestion of a radiolabelled mashed potato meal after receiving sitagliptin (100 mg) or placebo in randomized, double-blind, crossover fashion on 2 consecutive days.

RESULTS

Sitagliptin reduced postprandial plasma glucose (P < .005) without affecting GE (P = .88). The magnitude of the glucose-lowering effect (change in incremental area under the curve^{0-240 min} from placebo to sitagliptin) was related to GE (kcal/min) on placebo (r = 0.68, P = .008) There was a comparable fall in systolic BP (P = .80) following the meal, with no difference between the 2 days.

CONCLUSIONS

In T2DM, while sitagliptin has no effect on either GE or postprandial BP, its ability to lower postprandial glucose are dependent on the basal rate of GE.

Alterations of Gastric Emptying Features Following Laparoscopic Sleeve Gastrectomy in Chinese Patients with Obesity: a Self-Controlled Observational Study

BACKGROUND

Laparoscopic sleeve gastrectomy (LSG) has become an increasingly popular metabolic surgical procedure. Alteration in motor gastric function is a fundamental feature following LSG but still remains controversial.

PURPOSE

To determine the gastric emptying time 3 month after LSG, correlations between gastric emptying time and body weight, weight loss, and glycemia levels, alongside determining predictive factors of weight loss at the 3-month follow-up.

MATERIALS AND METHODS

Twenty-one patients were recruited in this study. Gastric emptying time was measured using a standard solid-phase gastric emptying scan at both baseline and 3 months after LSG. Paired sample t tests and a general linear model with repeated measures were applied to investigate the alterations in major parameters after surgery. Univariate analyses were performed to evaluate the factors predicting weight loss at the 3-month follow-up.

RESULTS

Compared with baseline levels, gastric emptying time, body weight, and HbA_1c levels decreased significantly at 3 months after LSG (P < 0.001). Significant positive correlations were detected between HbA_1c levels and gastric emptying time at baseline (P = 0.03). Significant positive correlations were detected between HbA_1c levels at baseline and change in gastric emptying time (P = 0.03). Univariate logistic regression revealed a lower baseline BMI level to be independently associated with %EWL (P < 0.001).

CONCLUSIONS

The rate of gastric emptying increased following LSG. Patients with a higher risk of type 2 diabetes at baseline had longer gastric emptying times prior to treatment and significantly shortened emptying times following surgery.

Mechanism of Glucagon-Like Peptide 1 Improvements in Type 2 Diabetes Mellitus and Obesity

PURPOSE OF REVIEW

The purpose of this review is to emphasize the pivotal role of glucagon-like peptide 1 (GLP-1) in tackling the parallel epidemics of obesity and type 2 diabetes (T2DM).

RECENT FINDINGS

GLP-1-based therapies and in particular GLP-1 receptor agonists (GLP-1 RA) have proven to be effective in lowering blood glucose and decreasing weight. GLP-1 RA not only mitigate these significant medical burdens but also result in weight loss and weight loss independent factors that decrease cardiovascular disease (CVD) and microvascular complications of T2DM, such as diabetic nephropathy. GLP-1-based therapies are critical for a patient-centered approach in choosing appropriate pharmacotherapy for T2DM and obesity while also taking into consideration comorbidities, such as cardiovascular and chronic kidney diseases.

Effects of lixisenatide on postprandial blood pressure, gastric emptying and glycaemia in healthy people and people with type 2 diabetes

AIM

To evaluate the effects of the prandial glucagon-like peptide-1 receptor agonist lixisenatide on gastric emptying and blood pressure (BP) and superior mesenteric artery (SMA) blood flow, and the glycaemic responses to a 75-g oral glucose load in healthy people and those with type 2 diabetes (T2DM).

MATERIALS AND METHODS

Fifteen healthy participants (nine men, six women; mean ± SEM age 67.2 ± 2.3 years) and 15 participants with T2DM (nine men, six women; mean ± SEM age 61.9 ± 2.3 years) underwent measurement of gastric emptying, BP, SMA flow and plasma glucose 180 minutes after a radiolabelled 75-g glucose drink on two separate days. All participants received lixisenatide (10 μg subcutaneously) or placebo in a randomized, double-blind, crossover fashion 30 minutes before the glucose drink.

RESULTS

Lixisenatide slowed gastric emptying (retention at 120 minutes, P < 0.01), attenuated the rise in SMA flow (P < 0.01) and markedly attenuated the decrease in systolic BP (area under the curve [AUC] 0-120 minutes, P < 0.001) compared to placebo in healthy participants and those with T2DM. Plasma glucose (incremental AUC 0-120 minutes) was greater in participants with T2DM (P < 0.005) than in healthy participants, and lower after lixisenatide in both groups (P < 0.001).

CONCLUSIONS

In healthy participants and those with T2DM, the marked slowing of gastric emptying of glucose induced by lixisenatide was associated with attenuation of the increments in glycaemia and SMA flow and decrease in systolic BP. Accordingly, lixisenatide may be useful in the management of postprandial hypotension.

Hypoglycaemia and gastric emptying

Hypoglycaemia is arguably the most important complication of insulin therapy in type 1 and type 2 diabetes. Counter-regulation of hypoglycaemia is dependent on autonomic function and frequent hypoglycaemia may lead to reductions in both autonomic warning signals and the catecholamine response, the so-called "impaired awareness of hypoglycaemia". It is now appreciated that gastric emptying is a major determinant of the glycaemic response to carbohydrate-containing meals in both health and diabetes, that disordered (especially delayed) gastric emptying occurs frequently in diabetes, and that acute hypoglycaemia accelerates gastric emptying substantially. However, the potential relevance of gastric emptying to the predisposition to, and counter-regulation of, hypoglycaemia has received little attention. In insulin-treated patients, the rate of gastric emptying influences the timing of the postprandial insulin requirement, and gastroparesis is likely to predispose to postprandial hypoglycaemia. Conversely, the marked acceleration of gastric emptying induced by hypoglycaemia probably represents an important counter-regulatory response to increase the rate of carbohydrate absorption. This review summarizes the current knowledge of the inter-relationships between hypoglycaemia and gastric emptying, with a focus on clinical implications.

Continuous feeding of a combined high-fat and high-sucrose diet, rather than an individual high-fat or high-sucrose diet, rapidly enhances the glucagon-like peptide-1 secretory response to meal ingestion in diet-induced obese rats

OBJECTIVES

Glucagon-like peptide-1 (GLP-1) is secreted by enteroendocrine L-cells in response to nutrient ingestion. To date, GLP-1 secretion in diet-induced obesity is not well characterized. We aimed to examine GLP-1 secretion in response to meal ingestion during the progression of diet-induced obesity and determinewhether a combined high-fat and high-sucrose (HFS) diet, an individual high-fat (HiFat), or a high-sucrose (HiSuc) diet affect adaptive changes in the postprandial GLP-1 response.

METHODS

Rats were fed a control, HiFat diet (30% weight), HiSuc diet (40% weight), or HFS (30% fat and 40% sucrose) diet for 5 wk. Meal tolerance tests were conducted to determine postprandial glucose, insulin, and GLP-1 responses to standard (control) diet ingestion every 2 wk.

RESULTS

After 5 wk, body weight gain of the HiFat (232.3 ± 7.8 g; P = 0.021) and HFS groups (228.0 ± 7.8; P = 0.039), but not the HiSuc group (220.3 ± 7.9; P = 0.244), were significantly higher than that of the control group (200.7 ± 5.4 g). In meal tolerance tests after 2 wk, GLP-1 concentration was significantly elevated in the HFS group only (17.2 ± 2.6 pM; P < 0.001) in response to meal ingestions, but the HiFat group (16.6 ± 3.7 pM; P = 0.156) had a similar response as the HFS group. After 4 wk, GLP-1 concentrations were similarly elevated at 15min in the HFS (14.1 ± 4.4; P = 0.010), HiFat (13.2 ± 2.0; P < 0.001), and HiSuc (13.0 ± 3.3; P = 0.016) groups, but the HFS (9.8 ± 1.0; P = 0.019) and HiFat (8.3 ± 1.5; P = 0.010) groups also had significant elevation at 30min.

CONCLUSIONS

These results demonstrate that the continuous ingestion of excessive fat and sucrose rapidly enhances the GLP-1 secretory response to luminal nutrients, and the HiFat diet may have a potent effect compared with the HiSuc diet on GLP-1 secretory responses. The increment of postprandial GLP-1 and insulinsecretion may have a role in normalizing postprandial glycaemia and slowing the establishment of glucose intolerance.

Implication of neurohormonal-coupled mechanisms of gastric emptying and pancreatic secretory function in diabetic gastroparesis

Recently, diabetic gastroparesis (DGP) has received much attention as its prevalence is increasing in a dramatic fashion and management of patients with DGP represents a challenge in the clinical practice due to the limited therapeutic options. DGP highlights an interrelationship between the gastric emptying and pancreatic secretory function that regulate a wide range of digestive and metabolic functions, respectively. It well documented that both gastric emptying and pancreatic secretion are under delicate control by multiple neurohormonal mechanisms including extrinsic parasympathetic pathways and gastrointestinal (GI) hormones. Interestingly, the latter released in response to various determinants that related to the rate and quality of gastric emptying. Others and we have provided strong evidence that the central autonomic nuclei send a dual output (excitatory and inhibitory) to the stomach and the pancreas in response to a variety of hormonal signals from the abdominal viscera. Most of these hormones released upon gastric emptying to provide feedback, and control this process and simultaneously regulate pancreatic secretion and postprandial glycemia. These findings emphasize an important link between gastric emptying and pancreatic secretion and its role in maintaining homeostatic processes within the GI tract. The present review deals with the neurohormonal-coupled mechanisms of gastric emptying and pancreatic secretory function that implicated in DGP and this provides new insights in our understanding of the pathophysiology of DGP. This also enhances the process of identifying potential therapeutic targets to treat DGP and limit the complications of current management practices.

What Has Bariatric Surgery Taught Us About the Role of the Upper Gastrointestinal Tract in the Regulation of Postprandial Glucose Metabolism?

The interaction between the upper gastrointestinal tract and the endocrine system is important in the regulation of metabolism and of weight. The gastrointestinal tract has a heterogeneous cellular content and comprises a variety of cells that elaborate paracrine and endocrine mediators that collectively form the entero-endocrine system. The advent of therapy that utilizes these pathways as well as the association of bariatric surgery with diabetes remission has (re-)kindled interest in the role of the gastrointestinal tract in glucose homeostasis. In this review, we will use the changes wrought by bariatric surgery to provide insights into the various gut-pancreas interactions that maintain weight, regulate satiety, and limit glucose excursions after meal ingestion.

Appetite, Glycemia, and Entero-Insular Hormone Responses Differ Between Oral, Gastric-Remnant, and Duodenal Administration of a Mixed-Meal Test After Roux-en-Y Gastric Bypass

OBJECTIVE

To examine the effect of different feeding routes on appetite and metabolic responses after Roux-en-Y gastric bypass (RYGB).

RESEARCH DESIGN AND METHODS

A standard liquid meal was administered either orally, into the gastric remnant, or intraduodenally 6 months after RYGB. Changes in plasma glucose, insulin, glucagon-like peptide 1 (GLP-1), glucose-dependent insulinotropic peptide (GIP), peptide YY (PYY), and appetite were measured pre- and postprandially.

RESULTS

Postprandial GLP-1 and PYY responses were similar, whereas glucose, insulin, and GIP levels differed markedly after oral versus intraduodenal feeding. Intraduodenal feeding prompted an intermediate appetite response (i.e., between oral and intragastric). For postprandial glucose, insulin, and GIP levels, the intraduodenal route was more similar to the intragastric than the oral route. Intragastric administration did not evoke changes in appetite, glucose, or insulin; however, it slightly increased GLP-1 and PYY and moderately increased GIP.

CONCLUSIONS

Appetite and metabolic responses after RYGB depend on the route by which nutrients enter the gastrointestinal tract.

Obstacles to Translating Genotype-Phenotype Correlates in Metabolic Disease

Type 2 diabetes mellitus is a polygenic disease with a variable phenotype. Many genetic associations have been described; however, understanding their underlying pathophysiological role in Type 2 diabetes mellitus is important for development of future therapeutic targets. Here, we review the physiological mechanisms of diabetes-associated variants that affect glycemia.

Effects of small intestinal glucose on glycaemia, insulinaemia and incretin hormone release are load-dependent in obese subjects

BACKGROUND/OBJECTIVES

Studies concerning the glycaemic response to oral glucose, or meals in obesity have usually failed to account for gastric emptying. It has been suggested that the incretin effect may be diminished in obesity as a result of a reduction in glucagon-like peptide-1 (GLP-1) secretion. We sought to determine the effect of two different rates of intraduodenal glucose infusions on glycaemic, insulinaemic and incretin hormone responses in lean and obese subjects and compare the effects of oral and intraduodenal glucose in obese subjects.

SUBJECTS/METHODS

Eleven obese subjects (age 37.5±4.1 years, body mass index (BMI) 35.7±1.4 kg m^-2) and 12 controls (age 34.7±4.0 years, BMI 23.9±0.7 kg m^-2) received intraduodenal infusions of glucose at 1 or 3 kcal min^-1, or saline for 60 min (t=0-60 min), followed by intraduodenal saline (t=60-120 min). In obese subjects, an oral glucose tolerance test was performed. Blood glucose, serum insulin, plasma total GLP-1 and total gastric inhibitory polypeptide (GIP) were measured.

RESULTS

In both the groups (P<0.001), the incremental areas under the curve (iAUC)_0-60 min for glucose was greater with the 3 kcal min^-1 than the 1 kcal min^-1 infusion; the iAUC_0-120 min for glucose during 3 kcal min^-1 was greater (P<0.05), in the obese. Insulin responses to 1 kcal min^-1 and, particularly, 3 kcal min^-1 were greater (P<0.001) in the obese. Stimulation of GLP-1 and GIP were greater (P<0.001) in response to 3 kcal min^-1, compared with 1 kcal min^-1 and saline, without any difference between the groups. In the obese, glycaemic, insulinaemic and GIP, but not GLP-1, responses to oral and intraduodenal glucose were related (P<0.05).

CONCLUSIONS

The rate of duodenal glucose delivery is a major determinant of glycaemia, insulinaemia and incretin hormone release in obese subjects. Obesity is not apparently associated with impaired GLP-1 secretion.

Ghrelin, CCK, GLP-1, and PYY(3-36): Secretory Controls and Physiological Roles in Eating and Glycemia in Health, Obesity, and After RYGB

The efficacy of Roux-en-Y gastric-bypass (RYGB) and other bariatric surgeries in the management of obesity and type 2 diabetes mellitus and novel developments in gastrointestinal (GI) endocrinology have renewed interest in the roles of GI hormones in the control of eating, meal-related glycemia, and obesity. Here we review the nutrient-sensing mechanisms that control the secretion of four of these hormones, ghrelin, cholecystokinin (CCK), glucagon-like peptide-1 (GLP-1), and peptide tyrosine tyrosine [PYY(3-36)], and their contributions to the controls of GI motor function, food intake, and meal-related increases in glycemia in healthy-weight and obese persons, as well as in RYGB patients. Their physiological roles as classical endocrine and as locally acting signals are discussed. Gastric emptying, the detection of specific digestive products by small intestinal enteroendocrine cells, and synergistic interactions among different GI loci all contribute to the secretion of ghrelin, CCK, GLP-1, and PYY(3-36). While CCK has been fully established as an endogenous endocrine control of eating in healthy-weight persons, the roles of all four hormones in eating in obese persons and following RYGB are uncertain. Similarly, only GLP-1 clearly contributes to the endocrine control of meal-related glycemia. It is likely that local signaling is involved in these hormones' actions, but methods to determine the physiological status of local signaling effects are lacking. Further research and fresh approaches are required to better understand ghrelin, CCK, GLP-1, and PYY(3-36) physiology; their roles in obesity and bariatric surgery; and their therapeutic potentials.

Small Intestinal Glucose Delivery Affects the Lowering of Blood Glucose by Acute Vildagliptin in Type 2 Diabetes

CONTEXT

The rate of gastric emptying is an important determinant of glucose-dependent insulinotropic polypeptide (GIP) and glucagon-like peptide-1 (GLP-1) secretion and may influence the magnitude of glucose lowering by dipeptidyl peptidase-4 (DPP-4) inhibitors.

OBJECTIVE

To evaluate the effects of the DPP-4 inhibitor, vildagliptin (VILD), during intraduodenal (ID) glucose infusion at 2 different rates within the physiological range of gastric emptying, in type 2 diabetes.

PARTICIPANTS AND DESIGN

A total of 16 diet-controlled type 2 diabetic patients were studied on 4 separate days in double-blind, randomized, fashion. On each day, either 5-mg VILD or placebo (PLBO) was given 60 minutes before a 120-minute ID glucose infusion at 2 or 4 kcal/min (ID2 or ID4). Plasma glucose and hormones were measured frequently.

RESULTS

Plasma glucose, insulin, C-peptide, glucagon, total GIP, and total and intact GLP-1 concentrations were higher during ID4 than ID2 (P < .01 for each). Compared with PLBO, VILD was associated with higher intact GLP-1, insulin, and C-peptide and lower glucose and total GIP and GLP-1 (P < .01 for each), without affecting glucagon. There were significant interactions between the rate of ID glucose and VILD treatment on plasma glucose, intact and total GLP-1, and GIP (P < .05 for each) but not insulin, C-peptide, or glucagon. The reduction in glucose and the increment in intact GLP-1 after VILD vs PLBO were 3.3- and 3.8-fold greater, respectively, during ID4 compared with ID2.

CONCLUSIONS/INTERPRETATION

These observations warrant further study to clarify whether type 2 diabetic patients with relatively more rapid gastric emptying have greater glucose lowering during treatment with DPP-4 inhibitors.

Regional specificity of the gut-incretin response to small intestinal glucose infusion in healthy older subjects

The importance of the region, as opposed to the length, of small intestine exposed to glucose in determining the secretion of the incretin hormones glucagon-like peptide-1 (GLP-1) and glucose-dependent insulinotropic polypeptide (GIP) remains unclear. We sought to compare the glycemic, insulinemic and incretin responses to glucose administered to the proximal (12-60cm beyond the pylorus), or more distal (>70cm beyond the pylorus) small intestine, or both. 10 healthy subjects (9M,1F; aged 70.3±1.4years) underwent infusion of glucose via a catheter into the proximal (glucose proximally; GP), or distal (glucose distally; GD) small intestine, or both (GPD), on three separate days in a randomised fashion. Blood glucose, serum insulin and plasma GLP-1, GIP and CCK responses were assessed. The iAUC for blood glucose was greater in response to GPD than GP (P<0.05), with no difference between GD and GP. GP was associated with minimal GLP-1 response (P=0.05), but substantial increases in GIP, CCK and insulin (P<0.001 for all). GPD and GD both stimulated GLP-1, GIP, CCK and insulin (P<0.001 for all). Compared to GP, GPD induced greater GLP-1, GIP and CCK responses (P<0.05 for all). Compared with GPD, GD was associated with greater GLP-1 (P<0.05), but reduced GIP and CCK (P<0.05 for both), responses. We conclude that exposure of glucose to the distal small intestine appears necessary for substantial GLP-1 secretion, while exposure of both the proximal and distal small intestine result in substantial secretion of GIP.

Inter-regulation of gastric emptying and incretin hormone secretion: implications for postprandial glycemic control

The GI tract is central to the regulation of postprandial glycemia, with the rate of gastric emptying and the secretion of the incretin hormones, glucose-dependent insulinotropic polypeptide and glucagon-like peptide-1, being key determinants. Gastric emptying exhibits a large interindividual variation; the latter not only accounts for differences in postprandial glycemia but also determines postprandial incretin profiles. Accordingly, the rate of gastric emptying may affect the glucose-lowering efficacy of dipeptidyl peptidase-4 inhibitors. In contrast, glucagon-like peptide-1 receptor agonists lower postprandial glycemia predominantly by their action to slow gastric emptying. This review discusses the inter-relationship between gastric emptying and the incretin axis in the context of changes in blood glucose, with an emphasis on the relevant clinical implications.

Mechanisms of surgical control of type 2 diabetes: GLP-1 is the key factor-Maybe

Bariatric surgery is the most effective treatment for obesity and diabetes. The 2 most commonly performed weight-loss procedures, Roux-en-Y gastric bypass (RYGB) and sleeve gastrectomy, improve glycemic control in patients with type 2 diabetes independent of weight loss. One of the early hypotheses raised to explain the immediate antidiabetic effect of RYGB was that rapid delivery of nutrients from the stomach pouch into the distal small intestine enhances enteroinsular signaling to promote insulin signaling. Given the tenfold increase in postmeal glucagon-like peptide-1 (GLP-1) response compared to unchanged integrated levels of postprandial glucose-dependent insulinotropic peptide after RYGB, enhanced meal-induced insulin secretion after this procedure was thought to be the result of elevated glucose and GLP-1 levels. In this contribution to the larger point-counterpoint debate about the role of GLP-1 after bariatric surgery, most of the focus will be on RYGB.

Roles of the Gut in Glucose Homeostasis

The gastrointestinal tract plays a major role in the regulation of postprandial glucose profiles. Gastric emptying is a highly regulated process, which normally ensures a limited and fairly constant delivery of nutrients and glucose to the proximal gut. The subsequent digestion and absorption of nutrients are associated with the release of a set of hormones that feeds back to regulate subsequent gastric emptying and regulates the release of insulin, resulting in downregulation of hepatic glucose production and deposition of glucose in insulin-sensitive tissues. These remarkable mechanisms normally keep postprandial glucose excursions low, regardless of the load of glucose ingested. When the regulation of emptying is perturbed (e.g., pyloroplasty, gastric sleeve or gastric bypass operation), postprandial glycemia may reach high levels, sometimes followed by profound hypoglycemia. This article discusses the underlying mechanisms.

Incretins

Glucose-dependent insulinotropic polypeptide (GIP) and glucagon-like peptide-1 (GLP-1) are the known incretin hormones in humans, released predominantly from the enteroendocrine K and L cells within the gut. Their secretion is regulated by a complex of integrated mechanisms involving direct contact for the activation of different chemo-sensors on the brush boarder of K and L cells and several indirect neuro-immuno-hormonal loops. The biological actions of GIP and GLP-1 are fundamental determinants of islet function and blood glucose homeostasis in health and type 2 diabetes. Moreover, there is increasing recognition that GIP and GLP-1 also exert pleiotropic extra-glycaemic actions, which may represent therapeutic targets for human diseases. In this review, we summarise current knowledge of the biology of incretin hormones in health and metabolic disorders and highlight the therapeutic potential of incretin hormones in metabolic regulation.

Novel insights into the effects of diabetes on gastric motility

Recent data from the Diabetes Control and Complications Trial/Epidemiology of Diabetic Interventions and Complications cohort indicate that the disease burden of gastroparesis in diabetes remains high, consistent with the outcome of cross-sectional studies in type 1 and 2 diabetes. An improved understanding of the pathogenesis of diabetic gastroparesis at the cellular level has emerged in the last decade, particularly as a result of initiatives such as the National Institute of Health funded Gastroparesis Clinical Research Consortium in the US. Management of diabetic gastroparesis involves dietary and psychological support, attention to glycaemic control, and the use of prokinetic agents. Given that the relationship between upper gastrointestinal symptoms and the rate of gastric emptying is weak, therapies targeted specifically at symptoms, such as nausea or pain, are important. The relationship between gastric emptying and postprandial glycaemia is complex and inter-dependent. Short-acting glucagon-like peptide-1 agonists, that slow gastric emptying, can be used to reduce postprandial glycaemic excursions and, in combination with basal insulin, result in substantial reductions in glycated haemoglobin in type 2 patients.

Effects of sitagliptin on blood pressure and heart rate in response to intraduodenal glucose infusion in patients with Type 2 diabetes: a potential role for glucose-dependent insulinotropic polypeptide?

AIMS

To evaluate the effects of the dipeptidyl peptidase-4 inhibitor sitagliptin on blood pressure and heart rate, measured during a previously reported study, in which the effects of sitagliptin during intraduodenal glucose infusion at the rate of 2 kcal/min on glucose homeostasis were examined in patients with Type 2 diabetes.

METHODS

A total of 10 people with Type 2 diabetes were studied on two different days, 30 min after oral ingestion of sitagliptin (100 mg) or placebo. Intraduodenal glucose was infused at 2 kcal/min (60 g over 120 min), and blood pressure, heart rate, plasma glucagon-like peptide-1 and glucose-dependent insulinotropic polypeptide (total and intact), glucose, insulin and glucagon responses were evaluated.

RESULTS

In response to intraduodenal glucose infusion, heart rate (treatment effect: P = 0.001) and serum insulin concentration (treatment × time interaction: P = 0.041) were higher after sitagliptin treatment than placebo, without a significant difference in blood pressure, plasma glucagon or glucose. During intraduodenal glucose infusion, there was a substantial increase in plasma total glucose-dependent insulinotropic polypeptide on both days (time effect: P < 0.001), but not in total glucagon-like peptide-1. After sitagliptin, plasma intact glucagon-like peptide-1 concentration increased slightly (treatment × time interaction: P = 0.044) and glucose-dependent insulinotropic polypeptide concentration increased substantially (treatment × time interaction: P = 0.003).The heart rate response to intraduodenal glucose was related directly to plasma intact glucose-dependent insulinotropic polypeptide concentrations (r = 0.75, P = 0.008).

CONCLUSIONS

Sitagliptin increased the heart rate response to intraduodenal glucose infusion at 2 kcal/min in people with Type 2 diabetes, which was associated with augmentation of plasma intact glucose-dependent insulinotropic polypeptide concentrations. These observations warrant further clarification of a potential role for glucose-dependent insulinotropic polypeptide in the control of the 'gut-heart' axis.

Gastric emptying and glycaemia in health and diabetes mellitus

The rate of gastric emptying is a critical determinant of postprandial glycaemia and, accordingly, is fundamental to maintaining blood glucose homeostasis. Disordered gastric emptying occurs frequently in patients with longstanding type 1 diabetes mellitus and type 2 diabetes mellitus (T2DM). A complex bidirectional relationship exists between gastric emptying and glycaemia--gastric emptying accounts for ∼35% of the variance in peak postprandial blood glucose concentrations in healthy individuals and in patients with diabetes mellitus, and the rate of emptying is itself modulated by acute changes in glycaemia. Clinical implementation of incretin-based therapies for the management of T2DM, which diminish postprandial glycaemia, in part by slowing gastric emptying, is widespread. Other therapies for patients with T2DM, which specifically target gastric emptying include pramlintide and dietary-based treatment approaches. A weak association exists between upper gastrointestinal symptoms and the rate of gastric emptying. In patients with severe diabetic gastroparesis, pathological changes are highly variable and are characterized by loss of interstitial cells of Cajal and an immune infiltrate. Management options for patients with symptomatic gastroparesis remain limited in their efficacy, which probably reflects the heterogeneous nature of the underlying pathophysiology.

Multiple Factors Related to the Secretion of Glucagon-Like Peptide-1

The glucagon-like peptide-1 is secreted by intestinal L cells in response to nutrient ingestion. It regulates the secretion and sensitivity of insulin while suppressing glucagon secretion and decreasing postprandial glucose levels. It also improves beta-cell proliferation and prevents beta-cell apoptosis induced by cytotoxic agents. Additionally, glucagon-like peptide-1 delays gastric emptying and suppresses appetite. The impaired secretion of glucagon-like peptide-1 has negative influence on diabetes, hyperlipidemia, and insulin resistance related diseases. Thus, glucagon-like peptide-1-based therapies (glucagon-like peptide-1 receptor agonists and dipeptidyl peptidase-4 inhibitors) are now well accepted in the management of type 2 diabetes. The levels of glucagon-like peptide-1 are influenced by multiple factors including a variety of nutrients. The component of a meal acts as potent stimulants of glucagon-like peptide-1 secretion. The levels of its secretion change with the intake of different nutrients. Some drugs also have influence on GLP-1 secretion. Bariatric surgery may improve metabolism through the action on GLP-1 levels. In recent years, there has been a great interest in developing effective methods to regulate glucagon-like peptide-1 secretion. This review summarizes the literature on glucagon-like peptide-1 and related factors affecting its levels.

Influence of gastric emptying on the control of postprandial glycemia: physiology and therapeutic implications

The maintenance of glucose homeostasis is complex and involves, besides the secretion and action of insulin and glucagon, a hormonal and neural mechanism, regulating the rate of gastric emptying. This mechanism depends on extrinsic and intrinsic factors. Glucagon-like peptide-1 secretion regulates the speed of gastric emptying, contributing to the control of postprandial glycemia. The pharmacodynamic characteristics of various agents of this class can explain the effects more relevant in fasting or postprandial glucose, and can thus guide the individualized treatment, according to the clinical and pathophysiological features of each patient.

Gastrointestinal hormones and polycystic ovary syndrome

Polycystic ovary syndrome (PCOS) is an endocrine disease of women in reproductive age. It is characterized by anovulation and hyperandrogenism. Most often patients with PCOS have metabolic abnormalities such as dyslipidemia, insulin resistance, and glucose intolerance. It is not surprising that obesity is high prevalent in PCOS. Over 60 % of PCOS women are obese or overweight. Modulation of appetite and energy intake is essential to maintain energy balance and body weight. The gastrointestinal tract, where nutrients are digested and absorbed, plays a central role in energy homeostasis. The signals from the gastrointestinal tract arise from the stomach (ghrelin release), proximal small intestine (CCK release), and distal small intestine (GLP-1 and PYY) in response to food. These hormones are recognized as "appetite regulatory hormones." Weight loss is the key in the treatments of obese/overweight patients with PCOS. However, current non-pharmacologic management of body weight is hard to achieve. This review highlighted the gastrointestinal hormones, and discussed the potential strategies aimed at modifying hormones for treatment in PCOS.

Measurement of gastric emptying in diabetes

There has been a substantial evolution of concepts related to disordered gastric emptying in diabetes. While the traditional focus has hitherto related to the pathophysiology and management of upper gastrointestinal symptoms associated with gastroparesis, it is now apparent that the rate of gastric emptying is central to the regulation of postprandial glycemia. This recognition has stimulated the development of dietary and pharmacologic approaches to optimize glycemic control, at least in part, by slowing gastric emptying. With the increased clinical interest in this area, it has proved necessary to expand the traditional indications for gastric emptying studies, and consider the relative strengths and limitations of available techniques. Scintigraphy remains the 'gold standard' for the measurement of gastric emptying, however, there is a lack of standardization of the technique, and the optimal test meal for the evaluation of gastrointestinal symptoms may be discordant from that which is optimal to assess impaired glycemic control. The stable isotope breath test provides an alternative to scintigraphy and can be performed in an office-based setting. The effect of glucagon-like peptide-1 (GLP-1) and its agonists to reduce postprandial glycemia is dependent on the baseline rate of gastric emptying, as well as the magnitude of slowing. Because the effect of exogenous GLP-1 to slow gastric emptying is subject to tachyphylaxis with sustained receptor exposure, 'short acting' or 'prandial' GLP-1 agonists primarily target postprandial glycemia through slowing of gastric emptying, while 'long acting' or 'non-prandial' agents lower fasting glucose primarily through insulinotropic and glucagonostatic mechanisms. Accordingly, the indications for the therapeutic use of these different agents are likely to vary according to baseline gastric emptying rate and glycemic profiles.

Impact of gastric emptying to the glycemic and insulinemic responses to a 75-g oral glucose load in older subjects with normal and impaired glucose tolerance

The majority of studies relating to the oral glucose tolerance test (OGTT) have not taken gastric emptying (GE), which exhibits a substantial inter-individual variation, into account. We sought to evaluate the impact of GE, on the glycemic and insulinemic responses to a 75-g oral glucose load in older subjects with normal and impaired glucose tolerance. Eighty-seven healthy 'older' subjects (47F, 40M; age 71.0 ± 0.5 year) were given a drink comprising of 75-g glucose and 150 mg C(13)-acetate made up to 300 mL with water on a single occasion. Exhaled breath was obtained for analysis of (13)CO2 and calculation of the 50% GE time (T50). Blood glucose, serum insulin and plasma glucagon-like peptide-1 (GLP-1) and glucose-dependent insulinotropic peptide (GIP) were measured, and the insulin sensitivity index (ISI), and the disposition index (DI), were calculated. Thirty-one subjects had normal glucose tolerance (NGT) and 46 had impaired glucose tolerance (IGT). Blood glucose at t = 60 min and t = 120 min were related inversely to ISI (P < 0.001) and DI P < 0.001). The rise in blood glucose at t = 60 min was related inversely to the T50 in all subjects (P < 0.01), and those with IGT (P < 0.001), but not NGT. There were no significant relationships between the blood glucose at t = 120 min with the T50, but in both groups the change in blood glucose from baseline at t = 180 min was related (NGT: P < 0.001; IGT: P < 0.001) to the T50. We conclude that in NGT and IGT, the effect of GE on both the 'early' and 'late' glycemic responses to a 75-g oral glucose load is complementary to that of insulin sensitivity.

Cystic fibrosis related diabetes--a new perspective on the optimal management of postprandial glycemia

As the average life expectancy of patients with cystic fibrosis (CF) improves, the long term co-morbidities assume increasing importance. CF related diabetes (CFRD) has adverse effects on both nutrition and pulmonary function, and is associated with increased mortality. Abnormalities of glucose metabolism in CF represent a continuum; however the predominant abnormality is postprandial, not pre-prandial, glycemia. Insulin is currently recommended as the treatment of choice for CFRD, but its use is associated with a number of limitations, including hypoglycemia. Both the rate of gastric emptying and the consequent release of the 'incretin' hormones, glucose-dependent insulinotropic polypeptide (GIP) and glucagon-like-peptide-1 (GLP-1), from the gut are important determinants of overall glycemic control, particularly postprandial glycemia. Both are abnormal in conditions associated with exocrine pancreatic insufficiency. Incretin based therapies that have the capacity to slow gastric emptying and/or modulate the release of 'incretin' hormones, are now used widely in type 2 diabetes (T2D). This paper explores the determinants of glycemic control in CF, with a particular focus on the roles of gastric emptying and 'incretin' hormones, providing a rationale for the use of therapies that delay gastric emptying, including incretin mimetics, to minimize postprandial glycemia and improve nutritional status.

Small intestinal glucose exposure determines the magnitude of the incretin effect in health and type 2 diabetes

The potential influence of gastric emptying on the "incretin effect," mediated by glucose-dependent insulinotropic polypeptide (GIP) and glucagon-like peptide-1 (GLP-1), is unknown. The objectives of this study were to determine the effects of intraduodenal (ID) glucose infusions at 2 (ID2) and 4 (ID4) kcal/min (equating to two rates of gastric emptying within the physiological range) on the size of the incretin effect, gastrointestinal glucose disposal (GIGD), plasma GIP, GLP-1, and glucagon secretion in health and type 2 diabetes. We studied 10 male BMI-matched controls and 11 male type 2 patients managed by diet or metformin only. In both groups, GIP, GLP-1, and the magnitude of incretin effect were greater with ID4 than ID2, as was GIGD; plasma glucagon was suppressed by ID2, but not ID4. There was no difference in the incretin effect between the two groups. Based on these data, we conclude that the rate of small intestinal glucose exposure (i.e., glucose load) is a major determinant of the comparative secretion of GIP and GLP-1, as well as the magnitude of the incretin effect and GIGD in health and type 2 diabetes.

Pancreatic enzyme supplementation improves the incretin hormone response and attenuates postprandial glycemia in adolescents with cystic fibrosis: a randomized crossover trial

CONTEXT

Cystic fibrosis-related diabetes is characterized by postprandial, rather than fasting, hyperglycemia. Gastric emptying and the release of the incretin hormones [glucagon-like peptide-1 (GLP-1) and glucose dependent insulinotropic polypeptide (GIP)] are central to postprandial glycemic control. Lipolysis is required for fat to slow gastric emptying and stimulate incretin release.

OBJECTIVE

We aimed to determine the effect of pancreatic enzyme replacement therapy (PERT) on postprandial glycemia in adolescents with cystic fibrosis (CF).

DESIGN

This was a double-blinded randomized crossover trial. Subjects consumed a high-fat pancake, with either PERT (50 000 IU lipase) or placebo. Gastric emptying was measured by a breath test and blood sampled frequently for plasma blood glucose, insulin, glucagon, GLP-1, and GIP. Data were also compared with seven healthy subjects.

PARTICIPANTS

Fourteen adolescents (13.1 ± 2.7 y) with pancreatic-insufficient CF and seven healthy age-matched controls participated in the study.

MAIN OUTCOME MEASURE

Postprandial hyperglycemia was measured as peak glucose and area under the curve for blood glucose at 240 minutes.

RESULTS

CF subjects had postprandial hyperglycemia compared with controls (area under the curve, P < .0001). PERT reduced postprandial hyperglycemia (P = .0002), slowed gastric emptying (P = .003), and normalized GLP-1 and GIP secretion (P < .001 for each) when compared with placebo, without affecting insulin.

CONCLUSION

In young people with pancreatic insufficient CF, PERT markedly attenuates postprandial hyperglycemia by slowing gastric emptying and augmenting incretin hormone secretion.

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

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

The incretin effect in Korean subjects with normal glucose tolerance or type 2 diabetes

BACKGROUND

The incretin effect is known to be decreased in type 2 diabetes. However, there are limited data on the incretin effect in non-Caucasian subjects. Because Asian patients with type 2 diabetes are characterized by decreased insulin secretion, this study set out to examine the incretin effect in Korean subjects with normal glucose tolerance (NGT) or type 2 diabetes.

METHODS

We performed 75-g oral glucose tolerance tests (OGTTs) and corresponding isoglycaemic intravenous glucose infusion (IIGI) studies in Korean subjects with NGT (n = 14) or type 2 diabetes (n = 16). The incretin effect was calculated based on the incremental area under the curves (iAUCs) of the plasma levels of insulin, C-peptide or insulin secretion rate (ISR). The plasma levels of total glucagon-like peptide-1 (GLP-1) and glucose-dependent insulinotropic polypeptide (GIP) were measured by ELISA.

RESULTS

The incretin effect was not different between the subjects with NGT and type 2 diabetes (43 ± 6% vs 47 ± 4%, P = 0·575 by insulin; 29 ± 7% vs 38 ± 4%, P = 0·253 by C-peptide; 28 ± 7% vs 35 ± 5%, P = 0·372 by ISR, respectively). However, the gastrointestinally mediated glucose disposal (GIGD) was markedly decreased in type 2 diabetes (28·5 ± 4·2% vs 59·0 ± 4·3%, P < 0·001). The plasma levels of the total GLP-1 and GIP during the OGTTs were comparable between the two groups.

CONCLUSION

In Koreans, the secretion of GLP-1 or GIP during OGTTs and the incretin effect were comparable between subjects with NGT and type 2 diabetes, whereas the GIGD was significantly decreased in patients with type 2 diabetes.