Insulin sensitivity depends on the route of glucose administration

GLP-1 enhances β-cell response to protein ingestion and bariatric surgery amplifies it

OBJECTIVE

The glycemic-independent actions of glucagon-like peptide-1 (GLP-1) in the prandial state in humans are unknown. We examined the contribution of GLP-1 to β-cell secretory response (primary endpoint) and glucose metabolism during protein ingestion under basal glycemia, as well as whether these responses are affected by rerouted gut after gastric bypass (GB) or sleeve gastrectomy (SG).

METHODS

Insulin secretion rate (ISR) and glucose fluxes during a 50-g oral protein load were compared among 10 nondiabetic individuals with GB, 9 with SG, and 7 non-operated controls (CN), with and without intravenous infusion of exendin(9-39) (Ex-9), a GLP-1 receptor (GLP-1R) antagonist.

RESULTS

Blocking GLP-1R increased glucose before and after protein ingestion and decreased β-cell sensitivity to glucose in the first 30 min of protein ingestion in all three groups (p < 0.05). Reduction in the premeal ISR by Ex-9 infusion was only observed in CN, whereas diminished prandial ISR3h by GLP-1R blockade was only observed in GB and SG (p < 0.05 for interaction). GLP-1R blockade enhanced post-protein insulin action in GB and SG, but not in CN, and exaggerated endogenous glucose production only GB (p < 0.05 for interaction).

CONCLUSIONS

These findings are consistent with both pancreatic and extra-pancreatic roles for GLP-1 during protein ingestion in humans that are exaggerated by bariatric surgery.

The Impact of Type 2 Diabetes Mellitus on Non-Surgical Periodontal Treatment: A Non-Randomized Clinical Trial

Background/Objectives: Periodontitis (P), a chronic inflammatory condition that affects the supportive tissues around the teeth, is three to four times more prevalent in individuals with diabetes mellitus (DM), with a direct correlation between its severity and the levels of glycosylated hemoglobin (HbA1c). This study aimed to evaluate the periodontal clinical parameters following non-surgical periodontal treatment (NSPT) in P patients with or without type 2 DM. Methods: Forty patients with P were divided into two groups: Group DM/P and Group P. All the patients were assessed at baseline and at 90 and 180 days after receiving NSPT. The parameters evaluated included the HbA1c level, plaque index (PI), probing pocket depth (PPD), clinical attachment level (CAL), and bleeding on probing (BoP). A statistical analysis was performed with a significance level set at α = 5%. Results: There were significant differences in the HbA1c levels between the DM/P and P groups at baseline, 90, and 180 days, as expected. Importantly, the HbA1c levels did not change after NSPT. Group P showed a significant reduction in both the PI and the BoP values at 90 and 180 days (p < 0.05). In contrast, Group DM/P demonstrated a significant increase in the percentage of sites with a PPD ≥ 5 mm at 180 days (p < 0.05). Additionally, Group P exhibited an increase in sites with a PPD ≤ 4 mm and a decrease in sites with a PPD ≥ 5 mm at both 90 and 180 days (p < 0.05). Conclusions: Our findings suggest that DM may compromise the effectiveness of NSPT, potentially hindering favorable outcomes during the follow-up period.

GLP-1 enhances beta-cell response to protein ingestion and bariatric surgery amplifies it

OBJECTIVE

Protein ingestion stimulates β-cell secretion and alters glucose flux. Enhanced action of glucagon-like peptide 1 (GLP-1) and increased plasma glucose excursion contribute to prandial hyperinsulinemia after gastric bypass surgery (GB) and sleeve gastrectomy (SG). We examined the contribution of endogenous GLP-1 to glucose kinetics and β-cell response to protein ingestion under basal glucose concentrations in humans, and whether these responses are affected by rerouted gut after GB or SG.

DESIGN

Glucose fluxes, insulin secretion rate (ISR), and incretin responses to a 50-gram oral protein load were compared between 10 non-diabetic individuals with GB, 9 matched subjects with SG and 7 non-operated controls (CN) with and without intravenous infusion of exendin-(9- 39) [Ex-9), a specific GLP-1 receptor (GLP-1R) antagonist.

RESULTS

Blocking GLP-1R increased the plasma glucose concentration before and after protein ingestion in all 3 groups (p<0.05) and decreased β-cell sensitivity to glucose in the first 30 minutes of protein ingestion (p<0.05). Reduction in the prandial ISR3h by Ex-9 infusion, however, only was observed in GB and SG (p<0.05 for interaction) and not in controls. Also, GLP-1R blockade increased post-protein insulin action in GB and SG, but not CN (p=0.09 for interaction). Endogenous glucose production (EGP) during the first 60 minutes after protein ingestion was increased in all 3 groups but EGP3h only was accentuated in GB by Ex-9 infusion (p<0.05 for interaction).

CONCLUSION

These findings are consistent with both a pancreatic and extrapancreatic role for GLP-1 during protein ingestion in humans, and GLP-1 actions are exaggerated by bariatric surgery.

Endogenous glucagon-like peptide 1 diminishes prandial glucose counterregulatory response to hypoglycemia after gastric bypass surgery

We have previously shown that prandial endogenous glucose production (EGP) during insulin-induced hypoglycemia is smaller in non-diabetic subjects with gastric bypass (GB), where prandial glucagon-like peptide 1 (GLP-1) concentrations are 5-10 times higher than those in non-operated controls. Here, we sought to determine the effect of endogenous GLP-1 on prandial counterregulatory response to hypoglycemia after GB. Glucose fluxes, and islet-cell and gut hormone responses before and after mixed-meal ingestion were compared during a hyperinsulinemic hypoglycemic (~3.2 mmol/l) clamp with and without a GLP-1 receptor (GLP-1R) antagonist exendin-(9-39) (Ex-9) in non-diabetic subjects with prior GB compared to matched subjects with SG and non-surgical controls. In this setting, GLP-1R blockade had no effect on insulin secretion or insulin action, whereas prandial glucagon was enhanced in all 3 groups. Ex-9 infusion raised prandial EGP response to hypoglycemia in every GB subject but had no consistent effects on EGP among subjects with SG or non-operated controls (P < 0.05 for interaction). These results indicate that impaired post-meal glucose counterregulatory response to hypoglycemia after GB is partly mediated by endogenous GLP-1, highlighting a novel mechanism of action of GLP-1R antagonists for the treatment of prandial hypoglycemia in this population.

Differential effect of gastric bypass versus sleeve gastrectomy on insulinotropic action of endogenous incretins

OBJECTIVE

Prandial hyperinsulinemia after Roux-en-Y gastric bypass surgery (GB), and to lesser degree after sleeve gastrectomy (SG), has been attributed to rapid glucose flux from the gut and increased insulinotropic gut hormones. However, β-cell sensitivity to exogenous incretin is reduced after GB. This study examines the effect of GB versus SG on prandial glycemia and β-cell response to increasing concentrations of endogenous incretins.

METHODS

Glucose kinetics, insulin secretion rate (ISR), and incretin responses to 50-g oral glucose ingestion were compared between ten nondiabetic participants with GB versus nine matched individuals with SG and seven nonoperated normal glucose tolerant control individuals (CN) with and without administration of 200 mg of sitagliptin.

RESULTS

Fasting glucose and hormonal levels were similar among three groups. Increasing plasma concentrations of endogenous incretins by two- to three-fold diminished prandial glycemia and increased β-cell secretion in all three groups (p < 0.05), but insulin secretion per insulin sensitivity (i.e., disposition index) was increased only in GB (p < 0.05 for interaction). However, plot of the slope of ISR (from premeal to peak values) versus plasma glucagon-like peptide-1 concentration was smaller after GB compared with SG and CN.

CONCLUSIONS

After GB, increasing incretin activity augments prandial β-cell response whereas the β-cell sensitivity to increasing plasma concentrations of endogenous incretin is diminished.

Effects of different doses of exercise and diet-induced weight loss on beta-cell function in type 2 diabetes (DOSE-EX): a randomized clinical trial

Diet-induced weight loss is associated with improved beta-cell function in people with type 2 diabetes (T2D) with remaining secretory capacity. It is unknown if adding exercise to diet-induced weight loss improves beta-cell function and if exercise volume is important for improving beta-cell function in this context. Here, we carried out a four-armed randomized trial with a total of 82 persons (35% females, mean age (s.d.) of 58.2 years (9.8)) with newly diagnosed T2D (<7 years). Participants were randomly allocated to standard care (n = 20), calorie restriction (25% energy reduction; n = 21), calorie restriction and exercise three times per week (n = 20), or calorie restriction and exercise six times per week (n = 21) for 16 weeks. The primary outcome was beta-cell function as indicated by the late-phase disposition index (insulin secretion multiplied by insulin sensitivity) at steady-state hyperglycemia during a hyperglycemic clamp. Secondary outcomes included glucose-stimulated insulin secretion and sensitivity as well as the disposition, insulin sensitivity, and secretion indices derived from a liquid mixed meal tolerance test. We show that the late-phase disposition index during the clamp increases more in all three intervention groups than in standard care (diet control group, 58%; 95% confidence interval (CI), 16 to 116; moderate exercise dose group, 105%; 95% CI, 49 to 182; high exercise dose group, 137%; 95% CI, 73 to 225) and follows a linear dose-response relationship (P > 0.001 for trend). We report three serious adverse events (two in the control group and one in the diet control group), as well as adverse events in two participants in the diet control group, and five participants each in the moderate and high exercise dose groups. Overall, adding an exercise intervention to diet-induced weight loss improves glucose-stimulated beta-cell function in people with newly diagnosed T2D in an exercise dose-dependent manner (NCT03769883).

Counter-regulatory responses to postprandial hypoglycaemia in patients with post-bariatric hypoglycaemia vs surgical and non-surgical control individuals

AIMS/HYPOTHESIS

Post-bariatric hypoglycaemia is an increasingly recognised complication of bariatric surgery, manifesting particularly after Roux-en-Y gastric bypass. While hyperinsulinaemia is an established pathophysiological feature, the role of counter-regulation remains unclear. We aimed to assess counter-regulatory hormones and glucose fluxes during insulin-induced postprandial hypoglycaemia in patients with post-bariatric hypoglycaemia after Roux-en-Y gastric bypass vs surgical and non-surgical control individuals.

METHODS

In this case-control study, 32 adults belonging to four groups with comparable age, sex and BMI (patients with post-bariatric hypoglycaemia, Roux-en-Y gastric bypass, sleeve gastrectomy and non-surgical control individuals) underwent a postprandial hypoglycaemic clamp in our clinical research unit to reach the glycaemic target of 2.5 mmol/l 150-170 min after ingesting 15 g of glucose. Glucose fluxes were assessed during the postprandial and hypoglycaemic period using a dual-tracer approach. The primary outcome was the incremental AUC of glucagon during hypoglycaemia. Catecholamines, cortisol, growth hormone, pancreatic polypeptide and endogenous glucose production were also analysed during hypoglycaemia.

RESULTS

The rate of glucose appearance after oral administration, as well as the rates of total glucose appearance and glucose disappearance, were higher in both Roux-en-Y gastric bypass groups vs the non-surgical control group in the early postprandial period (all p<0.05). During hypoglycaemia, glucagon exposure was significantly lower in all surgical groups vs the non-surgical control group (all p<0.01). Pancreatic polypeptide levels were significantly lower in patients with post-bariatric hypoglycaemia vs the non-surgical control group (median [IQR]: 24.7 [10.9, 38.7] pmol/l vs 238.7 [186.3, 288.9] pmol/l) (p=0.005). Other hormonal responses to hypoglycaemia and endogenous glucose production did not significantly differ between the groups.

CONCLUSIONS/INTERPRETATION

The glucagon response to insulin-induced postprandial hypoglycaemia is lower in post-bariatric surgery individuals compared with non-surgical control individuals, irrespective of the surgical modality. No significant differences were found between patients with post-bariatric hypoglycaemia and surgical control individuals, suggesting that impaired counter-regulation is not a root cause of post-bariatric hypoglycaemia.

TRIAL REGISTRATION

ClinicalTrials.gov NCT04334161.

Insulinotropic effect of endogenous incretins is greater after gastric bypass than sleeve gastrectomy despite diminished beta-cell sensitivity to plasma incretins

BACKGROUND/AIMS

Prandial hyperinsulinemia after Roux-en Y gastric bypass surgery (GB), and to lesser degree after sleeve gastrectomy (SG), has been attributed to rapid glucose flux from the gut and increased insulinotropic gut hormones. However, β-cell sensitivity to exogenous incretin is markedly reduced after GB. This study examines the effect of GB versus SG on prandial glycemia and β-cell response to increasing concentrations of endogenous incretins.

METHODS

Glucose kinetics, insulin secretion rate (ISR), and incretin responses to 50-gram oral glucose ingestion were compared between 10 non-diabetic subjects with GB versus 9 matched individuals with SG and 7 non-operated normal glucose tolerant controls (CN) on two days with and without administration of 200 mg sitagliptin.

RESULTS

Fasting glucose and hormonal levels were similar among 3 groups. Increasing plasma concentrations of endogenous incretins by 2-3-fold diminished post-OGTT glycemia and increased β-cell secretion in all 3 groups (p<0.05), but insulin secretion per insulin sensitivity (i.e., disposition index) was increased only in GB (p<0.05 for interaction). As a result, sitagliptin administration led to hypoglycemia in 3 of 10 GB. Yet, plot of the slope of ISR versus the increase in endogenous incretin concentration was smaller after GB compared to both SG and CN.

CONCLUSION

Augmented glycemic-induced β-cell response caused by enhanced incretin activity is unique to GB and not shared with SG. However, the β-cell sensitivity to increasing concentrations of endogenous incretin is smaller after bariatric surgery, particularly after GB, compared to non-operated controls, indicating a long-term adaptation of gut-pancreas axis after these procedures.

HIGHLIGHTS

What is known?: Glycemic effects of gastric bypass (GB) and sleeve gastrectomy (SG) is attributed to rapid nutrient flux and enhanced insulinotropic effects of gut hormones but β-cell sensitivity to exogenous GLP-1 or GIP is diminished after GB. What the present findings add?: Post-OGTT β-cell sensitivity to enhanced endogenous incretins by DPP4i is markedly reduced in bariatric subjects versus non-operated controls, and yet insulin secretory response (disposition index) is increased leading to hypoglycemia in GB and not SG. Significance?: Blunted sensitivity to GLP-1 may represent β-cell adaptation to massive elevation in GLP-1 secretion following bariatric surgery to protect against hypoglycemia.The differential effect of enhanced concentrations of incretins on post-OGTT insulin response (disposition index) among GB versus SG highlights a distinct adaptive process among the two procedures.Augmented insulinotropic effects of gut hormones on postprandial insulin secretory response after GB despite a reduced beta-cell sensitivity to plasma concentrations of GLP-1 makes a case for non-hormonal mechanisms of GLP-1 action after GB.Better understanding of long-term effects of bariatric surgery on gut-pancreas axis activity is critical in development of GLP-1-based strategies to address glucose abnormalities (both hyperglycemia and hypoglycemia) in these settings.

A modelling approach to hepatic glucose production estimation

Stable isotopes are currently used to measure glucose fluxes responsible for observed glucose concentrations, providing information on hepatic and peripheral insulin sensitivity. The determination of glucose turnover, along with fasting and postprandial glucose concentrations, is relevant for inferring insulin sensitivity levels. At equilibrium (e.g. during the fasting state) the rate of glucose entering the circulation equals its rate of disappearance from the circulation. If under these conditions tracer is infused at a constant rate and Specific Activity (SA) or Tracer to Tracee (TTR) ratio is computed, the Rate of Appearance (RA) equals the Rate of Disappearance (RD) and equals the ratio between infusion rate and TTR or SA. In the post-prandial situation or during perturbation studies, however, estimation of RA and RD becomes more complex because they are not necessarily equal and, furthermore, may vary over time due to gastric emptying, glucose absorption, appearance of ingested or infused glucose, variations of EGP and glucose disappearance. Up to now, the most commonly used approach to compute RA, RD and EGP has been the single-pool model by Steele. Several authors, however, report pitfalls in the use of this method, such as "paradoxical" increase in EGP immediately after meal ingestion and "negative" rates of EGP. Different attempts have been made to reduce the impact of these errors, but the same problems are still encountered. In the present work a completely different approach is proposed, where cold and labeled [6, 6-2H2] glucose observations are simultaneously fitted and where both RD and EGP are represented by simple but reasonable functions. As an example, this approach is applied to an intra-venous experiment, where cold glucose is infused at variable rates to reproduce a desired glycaemic time-course. The goal of the present work is to show that appropriate, if simple, modelling of the whole infusion procedure together with the underlying physiological system allows robust estimation of EGP with single-tracer administration, without the artefacts produced by the Steele method.

The effect of trimethylamine N-oxide on the metabolism of visceral white adipose tissue in spontaneously hypertensive rat

Strong links have been reported among trimethylamine N-oxide (TMAO), visceral white adipose tissue (vWAT), and cardiometabolic diseases. However, the effects of TMAO on vWAT in hypertension remained incompletely explored. The impact of a chronic 22-week-long treatment with 1 g/L TMAO on vWAT, and its transcriptional and metabolic changes in spontaneously hypertensive rats (SHRs) were evaluated by serum cytokine measurements, histological analysis, fatty acid determinations, and co-expression network analyses. TMAO increased the serum interleukin-6 levels and insulin secretion in SHRs. The adipocyte size was diminished in the SHR 1 g/L TMAO group. In addition, one kind of monounsaturated fatty acids (cis-15-tetracosenoate) and four kinds of polyunsaturated fatty acids (cis-11,14,17-eicosatrienoic acid, docosatetraenoate, docosapentaenoate n-3, and docosapentaenoate n-6) were elevated by TMAO treatment. Three co-expression modules significantly related to TMAO treatment were identified and pathway enrichment analyses indicated that phagosome, lysosome, fatty acid metabolism, valine, leucine, and isoleucine degradation and metabolic pathways were the most significantly altered biological pathways. This study shed new light on the metabolic roles of TMAO on the vWAT of SHRs. TMAO regulated the metabolic status of vWAT, including reduced lipogenesis and an improved specific fatty acid composition. The mechanisms underlying these effects likely involve phagosome and lysosome pathways. 

Altered Insulin Clearance after Gastric Bypass and Sleeve Gastrectomy in the Fasting and Prandial Conditions

Background: The liver has the capacity to regulate glucose metabolism by altering the insulin clearance rate (ICR). The decreased fasting insulin concentrations and enhanced prandial hyperinsulinemia after Roux-en-Y gastric-bypass (GB) surgery and sleeve gastrectomy (SG) are well documented. Here, we investigated the effect of GB or SG on insulin kinetics in the fasting and fed states. Method: ICR was measured (i) during a mixed-meal test (MMT) in obese non-diabetic GB (n = 9) and SG (n = 7) subjects and (ii) during a MMT combined with a hyperinsulinemic hypoglycemic clamp in the same GB and SG subjects. Five BMI-matched and non-diabetic subjects served as age-matched non-operated controls (CN). Results: The enhanced ICR during the fasting state after GB and SC compared with CN (p < 0.05) was mainly attributed to augmented hepatic insulin clearance rather than non-liver organs. The dose-response slope of the total insulin extraction rate (InsExt) of exogenous insulin per circulatory insulin value was greater in the GB and SG subjects than in the CN subjects, despite the similar peripheral insulin sensitivity among the three groups. Compared to the SG or the CN subjects, the GB subjects had greater prandial insulin secretion (ISR), independent of glycemic levels. The larger post-meal ISR following GB compared with SG was associated with a greater InsExt until it reached a plateau, leading to a similar reduction in meal-induced ICR among the GB and SG subjects. Conclusions: GB and SG alter ICR in the presence or absence of meal stimulus. Further, altered ICR after bariatric surgery results from changes in hepatic insulin clearance and not from a change in peripheral insulin sensitivity.

Prandial hepatic glucose production during hypoglycemia is altered after gastric bypass surgery and sleeve gastrectomy

AIMS/HYPOTHESIS

Roux-en Y gastric bypass surgery (GB) and sleeve gastrectomy (SG) alter prandial glucose metabolism, producing lower nadir glucose values and predisposing susceptible individuals to prandial hypoglycemia. The glycemic phenotype of GB or SG is associated with prandial hyperinsulinemia and hyperglucagonemia along with an increased influx of ingested glucose. Following insulin-induced hypoglycemia, glucagon is the most important stimulus for hepatic glucose production (HGP). It is unclear whether prandial hyperglucagonemia after GB or SG changes HGP under hyperinsulinemic hypoglycemia conditions. This study examined the hypothesis that prandial glucose production is reduced after GB and SG during hypoglycemia.

METHODS

Glucose kinetics and islet-cell and gut hormone secretion during hyperinsulinemic (120 mU.m^-2.min^-1) hypoglycemic clamp (~3.2 mM) were measured before and after mixed meal ingestion in 9 non-diabetic subjects with GB, 7 with SG, and 5 matched non-operated controls (CN).

RESULTS

Systemic appearance of ingested glucose was faster in GB compared to SG, and in SG compared to CN (p < 0.05). Subjects with GB and SG had greater plasma glucagon levels after eating (AUC_Glucagon) compared to CN (p < 0.05). But prandial HGP response during insulin-induced hypoglycemia (AUC_HGP) was smaller and shorter in duration in surgical groups (p < 0.05). In the absence of meal stimuli, however, glucose counterregulatory response to hypoglycemia was comparable among the 3 groups during hyperinsulinemic clamp.

CONCLUSION

After bariatric surgery, prandial glucose counterregulatory response to hypoglycemia is impaired. Considering post-meal hyperglucagonemia after GB or SG the blunted HGP response suggests a lower sensitivity of liver to glucagon that can predispose to hypoglycemia in this population.

Evidence of a Gastro-Duodenal Effect on Adipose Tissue and Brain Metabolism, Potentially Mediated by Gut-Liver Inflammation: A Study with Positron Emission Tomography and Oral 18FDG in Mice

Interventions affecting gastrointestinal (GI) physiology suggest that the GI tract plays an important role in modulating the uptake of ingested glucose by body tissues. We aimed at validating the use of positron emission tomography (PET) with oral 18FDG administration in mice, and to examine GI effects on glucose metabolism in adipose tissues, brain, heart, muscle, and liver, and interfering actions of oral lipid co-administration. We performed sequential whole-body PET studies in 3 groups of 10 mice, receiving i.p. glucose and 18FDG or oral glucose and 18FDG ± lipids, to measure tissue glucose uptake (GU) and GI transit, and compute the absorption lumped constant (LCa) as ratio of oral 18FDG-to-glucose incremental blood levels. GI and liver histology and circulating hormones were tested to generate explanatory hypothesis. Median LCa was 1.18, constant over time and not significantly affected by lipid co-ingestion. Compared to the i.p. route, the oral route (GI effect) resulted in lower GU rates in adipose tissues and brain, and a greater steatohepatitis score (+17%, p = 0.03). Lipid co-administration accelerated GI transit, in relation to the suppression in GIP, GLP1, glucagon, PP, and PYY (GI motility regulators), abolishing GI effects on subcutaneous fat GU. Duodenal crypt size, gastric wall 18FDG uptake, and macro-vesicular steatosis were inversely related to adipose tissue GU, and positively associated with liver GU. We conclude that 18FDG-PET is a suitable tool to examine the role of the GI tract on glucose transit, absorption, and bio-distribution. The GI effect consists in the suppression of glucose metabolism selectively in organs responsible for energy intake and storage, and is blunted by lipid ingestion. Modulation of gut and liver inflammation, as reflected by high GU, may be involved in the acute signalling of the energy status.

Insulin clearance and incretin hormones following oral and "isoglycemic" intravenous glucose in type 2 diabetes patients under different antidiabetic treatments

It has not been elucidated whether incretins affect insulin clearance in type 2 diabetes (T2D). We aimed exploring possible associations between insulin clearance and endogenously secreted or exogenously administered incretins in T2D patients. Twenty T2D patients were studied (16 males/4 females, 59 ± 2 years (mean ± standard error), BMI = 31 ± 1 kg/m2, HbA1c = 7.0 ± 0.1%). Patients were treated with metformin, sitagliptin, metformin/sitagliptin combination, and placebo (randomized order). On each treatment period, oral and isoglycemic intravenous glucose infusion tests were performed (OGTT, IIGI, respectively). We also studied twelve T2D patients (9 males/3 females, 61 ± 3 years, BMI = 30 ± 1 kg/m2, HbA1c = 7.3 ± 0.4%) that underwent infusion of GLP-1(7-36)-amide, GIP, GLP-1/GIP combination, and placebo. Plasma glucose, insulin, C-peptide, and incretins were measured. Insulin clearance was assessed as insulin secretion to insulin concentration ratio. In the first study, we found OGTT/IIGI insulin clearance ratio weakly inversely related to OGTT/IIGI total GIP and intact GLP-1 (R2 = 0.13, p < 0.02). However, insulin clearance showed some differences between sitagliptin and metformin treatment (p < 0.02). In the second study we found no difference in insulin clearance following GLP-1 and/or GIP infusion (p > 0.5). Thus, our data suggest that in T2D there are no relevant incretin effects on insulin clearance. Conversely, different antidiabetic treatments may determine insulin clearance variations.

Insulin Clearance in Obesity and Type 2 Diabetes

Plasma insulin clearance is an important determinant of plasma insulin concentration. In this review, we provide an overview of the factors that regulate insulin removal from plasma and discuss the interrelationships among plasma insulin clearance, excess adiposity, insulin sensitivity, and type 2 diabetes (T2D). We conclude with the perspective that the commonly observed lower insulin clearance rate in people with obesity, compared with lean people, is not a compensatory response to insulin resistance but occurs because insulin sensitivity and insulin clearance are mechanistically, directly linked. Furthermore, insulin clearance decreases postprandially because of the marked increase in insulin delivery to tissues that clear insulin. The commonly observed high postprandial insulin clearance in people with obesity and T2D likely results from the relatively low insulin secretion rate, not an impaired adaptation of tissues that clear insulin.

Twenty-four hour assessments of substrate oxidation reveal differences in metabolic flexibility in type 2 diabetes that are improved with aerobic training

AIMS/HYPOTHESIS

The aim of this study was to assess metabolic flexibility (MetFlex) in participants with type 2 diabetes within the physiologically relevant conditions of sleeping, the post-absorptive (fasting) state and during meals using 24 h whole-room indirect calorimetry (WRIC) and to determine the impact of aerobic training on these novel features of MetFlex.

METHODS

Normal-weight, active healthy individuals (active; n = 9), obese individuals without type 2 diabetes (ND; n = 9) and obese individuals with type 2 diabetes (n = 23) completed baseline metabolic assessments. The type 2 diabetes group underwent a 10 week supervised aerobic training intervention and repeated the metabolic assessments. MetFlex was assessed by indirect calorimetry in response to insulin infusion and during a 24 h period in a whole-room indirect calorimeter. Indices of MetFlex evaluated by WRIC included mean RQ and RQ kinetic responses after ingesting a standard high-carbohydrate breakfast (RQ_BF) and sleep RQ (RQ_sleep). Muscle mitochondrial energetics were assessed in the vastus lateralis muscle in vivo and ex vivo using ³¹P-magnetic resonance spectroscopy and high-resolution respirometry, respectively.

RESULTS

The three groups had significantly different RQ_sleep values (active 0.823 ± 0.04, ND 0.860 ± 0.01, type 2 diabetes 0.842 ± 0.03; p < 0.05). The active group had significantly faster RQ_BF and more stable RQ_sleep responses than the ND and type 2 diabetes groups, as demonstrated by steeper and flatter slopes, respectively. Following the training intervention, the type 2 diabetes group displayed significantly increased RQ_BF slope. Several indices of RQ kinetics had significant associations with in vivo and ex vivo muscle mitochondrial capacities.

CONCLUSIONS/INTERPRETATION

Twenty-four hour WRIC revealed that physiological RQ responses exemplify differences in MetFlex across a spectrum of metabolic health and correlated with skeletal muscle mitochondrial energetics. Defects in certain features of MetFlex were improved with aerobic training, emphasising the need to assess multiple aspects of MetFlex and disentangle insulin resistance from MetFlex in type 2 diabetes.

TRIAL REGISTRATION

ClinicalTrials.gov NCT01911104.

FUNDING

This study was funded by the ADA (grant no. 7-13-JF-53).

Small intestinal metabolism is central to whole-body insulin resistance

OBJECTIVE

To assess the role of jejunum in insulin resistance in humans and in experimental animals.

DESIGN

Twenty-four subjects undergoing biliopancreatic diversion (BPD) or Roux-en-Y gastric bypass (RYGB) were enrolled. Insulin sensitivity was measured at baseline and at 1 week after surgery using oral glucose minimal model.We excluded the jejunum from intestinal continuity in pigs and created a jejunal loop with its vascular and nerve supply intact accessible from two cutaneous stomas, and reconnected the bowel with an end-to-end anastomosis. Glucose stable isotopes were given in the stomach or in the jejunal loop.In vitro studies using primary porcine and human hepatocytes or myoblasts tested the effects of plasma on gluconeogenesis or glucose uptake and insulin signalling.

RESULTS

Whole-body insulin sensitivity (S_I∙10⁴: 0.54±0.12 before vs 0.82±0.11 after BPD, p=0.024 and 0.41±0.09 before vs 0.65±0.09/pM/min after RYGB, p=not significant) and Glucose Disposition Index increased only after BPD. In pigs, insulin sensitivity was significantly lower when glucose was administered in the jejunal loop than in the stomach (glucose rate of disappearance (R_d) area under the curve (AUC)/insulin AUC∙10: 1.82±0.31 vs 2.96±0.33 mmol/pM/min, p=0.0017).Metabolomics showed a similar pattern before surgery and during jejunal-loop stimulation, pointing to a higher expression of gluconeogenetic substrates, a metabolic signature of impaired insulin sensitivity.A greater hepatocyte phosphoenolpyruvate-carboxykinase and glucose-6-phosphatase gene expression was elicited with plasma from porcine jejunal loop or before surgery compared with plasma from jejunectomy in pigs or jejunal bypass in humans.Stimulation of myoblasts with plasma from porcine jejunal loop or before surgery reduced glucose uptake, Ser473-Akt phosphorylation and GLUT4 expression compared with plasma obtained during gastric glucose administration after jejunectomy in pigs or after jejunal bypass in humans.

CONCLUSION

Proximal gut plays a crucial role in controlling insulin sensitivity through a distinctive metabolic signature involving hepatic gluconeogenesis and muscle insulin resistance. Bypassing the jejunum is beneficial in terms of insulin-mediated glucose disposal in obesity.

TRIAL REGISTRATION NUMBER

NCT03111953.

The role of the liver in the modulation of glucose and insulin in non alcoholic fatty liver disease and type 2 diabetes

In this review we have discussed how the liver plays a central role in the regulation of glucose metabolism and in insulin clearance. Both non-alcoholic fatty liver disease (NAFLD) and diabetes (T2D) are characterized by high plasma insulin concentrations, hepatic insulin resistance, high hepatic glucose production (HGP), in particular gluconeogenesis (GNG), that are increased proportionally to fasting hyperglycemia, while postprandial hyperglycemia is due to impaired suppression of HGP by insulin, and reduced hepatic glycogen storage. The liver acts also as a modulator of peripheral insulin since most of insulin secreted by the pancreas is cleared by the liver during the first pass. Hepatokines and hepatic lipids can act in either autocrine or paracrine way and can be responsible of the changes in insulin sensitivity and alterations in glucose metabolism.

Glucose Homeostasis, Fetal Growth and Gestational Diabetes Mellitus in Pregnancy after Bariatric Surgery: A Scoping Review

BACKGROUND

Pregnancies in women with a history of bariatric surgery are becoming increasingly prevalent. Surgically induced metabolic changes benefit mother and child, but can also lead to some adverse pregnancy outcomes. Knowledge about glucose homeostasis in these pregnancies could elucidate some of the mechanisms behind these outcomes. This review focusses on glucose homeostasis and birth weight.

METHODS

We considered papers dealing with glucose homeostasis, gestational diabetes mellitus (GDM) and/or small-for-gestational age infants (SGA) in pregnancies with a history of sleeve gastrectomy (SG) or Roux-en-y gastric bypass (RYGB).

RESULTS

Since an OGTT is unreliable to diagnose GDM in a pregnancy after bariatric surgery, the true incidence of GDM is unknown. Alternative screening strategies are needed. Furthermore, these pregnancies are marked by frequent hypoglycemic events as well as wide and rapid glycemic excursions, an issue that is very likely underreported. There is a lack of uniformity in reporting key outcomes and a large variation in study design and control population.

CONCLUSION

Alteration of glucose homeostasis in a pregnancy after bariatric surgery should be further studied using unequivocal definition of key concepts. Glycemic control may prove to be a modifiable risk factor for adverse pregnancy outcomes such as the delivery of an SGA baby.

Exercise-Induced Improvements in Postprandial Glucose Response Are Blunted by Pre-Exercise Hyperglycemia: A Randomized Crossover Trial in Healthy Individuals

BACKGROUND

Exercise improves glycemic control but the magnitude, and in some cases, the direction of this effect is variable. Ambient hyperglycemia has been implicated in this exercise response heterogeneity. The current study investigated whether pre-exercise hyperglycemia directly impacts the effect of exercise on glycemic control.

METHODS

Twelve healthy normal glucose-tolerant males completed four trials in a randomized, crossover design. Each trial consisted of 24-h pre-intervention monitoring, a 7-h intervention, and 24-h post-intervention monitoring. Glycemic control was measured throughout the study by continuous glucose monitoring. The four interventions were no exercise (CON) or 45 min of cycling exercise (70%HRmax) preceded by 3.5 h of either normoglycemia (NG-Ex), steady-state hyperglycemia induced by constant glucose infusion (HG-Ex) or fluctuating glycemia induced by repeated glucose bolus infusions (FG-Ex).

RESULTS

Physical activity and diet were similar between trials, and energy expenditure during exercise was matched between exercise trials (all P > 0.05). Mean glucose during the 3.5 h ± infusion period was higher in HG-Ex (mean ± SEM; 7.2 ± 0.4 mmol/L) and FG-Ex (7.3 ± 0.3 mmol/L) compared to CON (4.8 ± 0.2 mmol/L) and NG-Ex (5.0 ± 0.2 mmol/L) trials (P < 0.01). Glycemic variability was greatest in FG-Ex (P < 0.01). Following the interventions, the postprandial glucose response (iAUC) was reduced by exercise in NG-Ex compared to CON (321.1 ± 38.6 vs. 445.5 ± 49.7 mmol/L.8h, P < 0.05, d=0.81). This benefit was blunted when exercise was preceded by steady-state (HG-Ex, 425.3 ± 45.7 mmol/L.8h) and fluctuating (FG-Ex, 465.5 ± 39.3 mmol/L.8h) hyperglycemia (both P > 0.05 vs. CON).

CONCLUSION

Pre-exercise hyperglycemia blunted the glucoregulatory benefits of acute exercise upon postprandial glucose response, suggesting that exposure to hyperglycemia contributes to exercise response heterogeneity.

CLINICAL TRIAL REGISTRATION

ClinicalTrials.gov, identifier NCT03284216.