An extended minimal model of OGTT: estimation of α- and ß-cell dysfunction, insulin resistance, and the incretin effect.

Loss of insulin sensitivity, α- and ß-cell dysfunction, and impairment in incretin effect have all been implicated in the pathophysiology of type 2 diabetes (T2D). Parsimonious mathematical models are useful in quantifying parameters related to the pathophysiology of T2D. Here, we extend the minimum model developed to describe the glucose-insulin-glucagon dynamics in the isoglycemic intravenous glucose infusion (IIGI) experiment to the oral glucose tolerance test (OGTT). The extended model describes glucose and hormone dynamics in OGTT including the contribution of the incretin hormones, glucose-dependent insulinotropic polypeptide (GIP), and glucagon-like peptide-1 (GLP-1), to insulin secretion. A new function describing glucose arrival from the gut is introduced. The model is fitted to OGTT data from eight individuals with T2D and eight weight-matched controls (CS) without diabetes to obtain parameters related to insulin sensitivity, ß- and α-cell function. The parameters, i.e., measures of insulin sensitivity, a1, suppression of glucagon secretion, k1, magnitude of glucagon secretion, γ2, and incretin-dependent insulin secretion, γ3, were found to be different between CS and T2D with P values < 0.002, <0.017, <0.009, <0.004, respectively. A new rubric for estimating the incretin effect directly from modeling the OGTT is presented. The average incretin effect correlated well with the experimentally determined incretin effect with a Spearman rank test correlation coefficient of 0.67 (P < 0.012). The average incretin effect was found to be different between CS and T2D (P < 0.032). The developed model is shown to be effective in quantifying the factors relevant to T2D pathophysiology.NEW & NOTEWORTHY A new extended model of oral glucose tolerance test (OGTT) has been developed that includes glucagon dynamics and incretin contribution to insulin secretion. The model allows the estimation of parameters related to α- and ß-cell dysfunction, insulin sensitivity, and incretin action. A new function describing the influx of glucose from the gut has been introduced. A new rubric for estimating the incretin effect directly from the OGTT experiment has been developed. The effect of glucose dose was also investigated.

Assessment of the incretin effect in healthy subjects: concordance between clamp and OGTT methods.

The incretin effect describes the insulin response to nutrient ingestion that exceeds the response to glycemia per se. It is mediated by gastrointestinal factors and is necessary to maintain postprandial glucose homeostasis. The incretin effect results in a more than twofold increase of the insulin response to a meal in healthy people and two different techniques have been used in the past to measure its magnitude. Most studies employ an OGTT on 1 day, followed by a matching glucose infusion on a separate day. Another study design employs a hyperglycemic glucose clamp that is maintained after oral ingestion of glucose. Both protocols allow quantification of the incretin effect by comparing the insulin response to an identical glycemic stimulus. Here we performed a within-subject comparison of both techniques to quantify the incretin effect and suggest different calculation methods to interpret the results derived from the clamp experiment in a cohort of healthy young adults (n = 10, age 33 ± 4 yr). All subjects participated on four different study days: 1) OGTT, 2) isoglycemic glucose infusion (Iso-IV), 3) hyperglycemic clamp with oral glucose ingestion (clamp-OGTT), and 4) hyperglycemic clamp (clamp). With the classic OGTT/Iso-IV method, the insulin response to glucose ingestion increased more than twofold and was 60 ± 6% and 49 ± 5% for insulin and c-peptide. Different estimates of the incretin effect based on the clamp method ranged from 58% to 79% for insulin and 38% to 61% for c-peptide, both significantly higher than values derived from the OGTT/isoglycemic infusion method. However, when the effect of continuous hyperglycemia on insulin secretion was accounted for, using extrapolation from early time points of the clamp, good agreement was noted between the two methods. Based on these results, both techniques seem to be equally suited to measure the incretin effect and should be employed according to the scientific questions, experimental contingencies, and investigator experience.NEW & NOTEWORTHY This proof-of-concept study shows that the incretin effect can be reliably assessed by two different methods with similar quantitative results. A single-day hyperglycemic clamp with oral glucose ingestion allows the determination of the incretin effect with fewer study days and less day-to-day variability.

Glucose metabolism, gut-brain hormones, and acromegaly treatment: an explorative single centre descriptive analysis.

PURPOSE: Active acromegaly is associated with impaired glucose metabolism, which improves upon treatment. Treatment options include surgery, medical therapy with somatostatin analogues (SSA) and Pegvisomant (PEG), and irradiation. The objective of the study was to describe the differential effect of various treatment regimens on the secretion of glucose, insulin, glucagon, glucagon-like peptide-1 (GLP-1), and glucose-dependent insulinotropic polypeptide (GIP) in patients with acromegaly. METHODS: 23 surgically treated, non-diabetic patients with acromegaly and 12 healthy controls underwent an oral glucose tolerance test (OGTT) and subsequently isoglycaemic intravenous glucose infusion on a separate day. Baseline hormone concentrations, time-to-peak and area under the curve (AUC) on the OGTT-day and incretin effect were compared according to treatment regimens. RESULTS: The patients treated with SSA (N = 15) had impaired GIP-response (AUC, P = 0.001), and numerical impairment of all other hormone responses (P > 0.3). Patients co-treated with PEG (SSA + PEG, N = 4) had increased secretion of insulin and glucagon compared to patients only treated with SSA (SSA ÷ PEG, N = 11) (insulinAUC mean ± SEM, SSA + PEG 49 ± 8.3 nmol/l*min vs SSA ÷ PEG 25 ± 3.4, P = 0.007; glucagonAUC, SSA + PEG 823 ± 194 pmol/l*min vs SSA ÷ PEG 332 ± 69, P = 0.009). GIP secretion remained significantly impaired, whereas GLP-1 secretion was numerically increased with PEG (SSA + PEG 3088 ± 366 pmol/l*min vs SSA ÷ PEG 2401 ± 239, P = 0.3). No difference was found in patients treated with/without radiotherapy nor substituted or not with hydrocortisone. CONCLUSION: SSA impaired the insulin, glucagon, and incretin hormone secretions. Co-treatment with PEG seemed to counteract the somatostatinergic inhibition of the glucagon and insulin response to OGTT. We speculate that PEG may exert its action through GH-receptors on pancreatic δ-cells. Clinical trial registration NCT02005978.

Beta cell function, incretin hormones, and incretin effect in obese children and adolescents with prediabetes.

BACKGROUND: Defects of incretin hormones and incretin effect may be underlying mechanisms of abnormal glucose metabolism in youth. OBJECTIVE: To assess incretin hormone dynamics during an oral glucose tolerance test (OGTT) and incretin effect in obese children with prediabetes in comparison with those with normal glucose tolerance (NGT). METHODS: Overweight and obese children were enrolled and classified according to OGTT results as NGT and prediabetes. Insulin sensitivity, insulin secretion, incretin hormone concentrations during OGTT; and incretin effect derived from OGTT and intravenous glucose tolerance test were determined and compared between NGT and prediabetes groups. RESULTS: Sixty-three patients (43 NGT and 20 prediabetes) were enrolled. Their median (interquartile range) age was 12.5 (11.1, 13.8) years. Peak glucagon-like peptide-1 (GLP-1) was demonstrated at 30 min during OGTT and was higher in the prediabetes group (49.2 [35.6, 63.6] versus 36.5 [27.6, 44.2] pmol/L, p = 0.009). However, incremental areas under the curves (iAUCs) of GLP-1 and glucose-dependent insulinotropic polypeptide (GIP) were not different between the two groups. There was no difference in incretin effect between NGT and prediabetes (NGT: 66.5% [60.2%, 77.5%] vs. prediabetes: 70.0% [61.5%, 75.0%], p = 0.645). Incretin effect had positive correlations with iAUCs of both GLP-1 and GIP (GLP-1: r = 0.40, p = 0.004 and GIP: r = 0.37, p = 0.009). CONCLUSIONS: Comparing between obese children with prediabetes and NGT, there were no differences in overall incretin hormone changes during OGTT and incretin effect. Incretin effect was positively correlated with iAUCs of GLP-1 and GIP.

Effects of prebiotics on postprandial GLP-1, GLP-2 and glucose regulation in patients with type 2 diabetes: A randomised, double-blind, placebo-controlled crossover trial.

AIMS: We aimed to investigate the effect of prebiotic inulin-type fructans (ITF) versus a control supplement on postprandial levels of glucagon-like peptide-1 and -2 (GLP-1 and -2), glucose and insulin in people with type 2 diabetes. METHODS: Adult men and women with type 2 diabetes were randomised in a double-blind, placebo-controlled crossover study. The study participants received 16 g/d ITF and 16 g/d control supplement (maltodextrin) for 6 weeks each in two phases separated by a 4-week washout. A standardised mixed-meal test was performed before and after each intake period. The primary end point was changes in the GLP-1 response, and secondary end points were GLP-2, glucose and insulin responses. Data were analysed using mixed-model analysis. RESULTS: A total of 29 participants were included in the study. Differences between and within the two treatments in estimated area under the curves were not significant. Yet, the predicted means for meal-induced GLP-1 response in plasma showed a 4.8% decline after the prebiotic treatment and an 8.6% increase after the control treatment (difference in changes between the treatments, p < 0.001). Fasting or postprandial glucose, insulin or GLP-2 levels were not changed. CONCLUSIONS: Our findings do not support that ITF improve incretin responses or glucose regulations in this population. Clinicaltrials.gov (NCT02569684).

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

AIMS/HYPOTHESIS: Incretin effect-the potentiation of glucose-stimulated insulin release induced by the oral vs the i.v. route-is impaired in dysglycaemic states. Despite evidence from human islet studies that NEFA interfere with incretin function, little information is available about the effect in humans. We tested the impact of acute bidirectional NEFA manipulation on the incretin effect in humans. METHODS: Thirteen individuals with type 2 diabetes and ten non-diabetic volunteers had a 3 h OGTT, and, a week later, an i.v. isoglycaemic glucose infusion (ISO; OGTT matched). Both pairs of studies were repeated during an exogenous lipid infusion in the non-diabetic volunteers, and following acipimox administration (to inhibit lipolysis) in people with diabetes. Mathematical modelling of insulin secretion dynamics assessed total insulin secretion (TIS), beta cell glucose sensitivity (ß-GS), glucose-induced potentiation (PGLU) and incretin-induced potentiation (PINCR); the oral glucose sensitivity index was used to estimate insulin sensitivity. RESULTS: Lipid infusion increased TIS (from 61 [interquartile range 26] to 78 [31] nmol/m2 on OGTT and from 29 nmol/m2 [26] to 57 nmol/m2 [30] on ISO) and induced insulin resistance. PINCR decreased from 1.6 [1.1] to 1.3 [0.1] (p < 0.05). ß-GS, PGLU and glucagon, glucagon-like peptide 1 (GLP-1) and gastric inhibitory polypeptide (GIP) responses were unaffected. Acipimox (lowering NEFA by ~55%) reduced plasma glucose and TIS and enhanced insulin sensitivity, but did not change ß-GS, PINCR, PGLU or glucagon, GLP-1 or GIP responses. As the per cent difference, incretin effect was decreased in non-diabetic participants and unchanged in those with diabetes. CONCLUSIONS/INTERPRETATION: Raising NEFA selectively impairs incretin effect and insulin sensitivity in non-diabetic individuals, while acute NEFA reduction lowers plasma glucose and enhances insulin sensitivity in people with diabetes but does not correct the impaired incretin-induced potentiation.

Women with prior gestational diabetes mellitus and prediabetes are characterised by a decreased incretin effect.

AIMS/HYPOTHESIS: We investigated whether a reduced incretin effect, as observed in patients with type 2 diabetes, can be detected in high-risk individuals, such as women with prior gestational diabetes mellitus (pGDM). METHODS: In this cross-sectional study, 102 women without diabetes with pGDM and 15 control participants without pGDM and with normal glucose tolerance (NGT) underwent a 4 h 75 g OGTT and an isoglycaemic i.v. glucose infusion (IIGI). Women with pGDM were classified as having NGT or prediabetes (impaired fasting glucose and/or impaired glucose tolerance). Insulin sensitivity was assessed using the Matsuda index and HOMA2-IR and the incretin effect was calculated from insulin responses during the study (100% × [AUCinsulin,OGTT - AUCinsulin,IIGI]/AUCinsulin,OGTT). RESULTS: Sixty-three of the 102 women with pGDM (62%) had prediabetes (median [interquartile range]: age, 38.3 [6.5] years; BMI, 32.1 [5.8] kg/m2) and 39 women (38%) had NGT (age, 39.5 [5.6] years; BMI, 31.0 [6.7] kg/m2). Control participants (n = 15) were not significantly different from the pGDM group with regards to age (39.2 [7.4] years) and BMI (28.8 [9.2] kg/m2). Compared with women with NGT and control participants, women with prediabetes had lower insulin sensitivity, as measured by the Matsuda index (3.0 [2.4] vs 5.0 [2.6] vs 1.5 [1.8], respectively; p < 0.001). The incretin effect was 55.3% [27.8], 73.8% [19.0] and 76.7% [24.6] in women with prediabetes, women with normal glucose tolerance and control participants, respectively (p < 0.01). CONCLUSION/INTERPRETATION: Prediabetes was highly prevalent in women with pGDM, and alterations in the incretin effect were detected in this group before the development of type 2 diabetes. TRIAL REGISTRATION: clinicaltrialsregister.eu 2012-001371-37-DK.

Lactoferrin potentially facilitates glucose regulation and enhances the incretin effect.

Lactoferrin (Lf) is known for its physiologically pleiotropic properties. In this study, we investigated whether Lf affects glycemic regulation, including glucose absorption from the small intestine. Bovine Lf (bLf, 100 mg/kg body mass) was administered to rats by intraperitoneal injection before intravenous (intravenous glucose tolerance test, IVGTT) or oral glucose administration (oral glucose tolerance test, OGTT). With IVGTT, bLf pretreatment had no significant effect on plasma levels of glucose or insulin. With OGTT, the bLf treatment group tended to show lower plasma levels of glucose than the control group at and after the 15 min peak, and decreased levels of plasma glucose at 180 min. The change in plasma levels of insulin from 0 to 30 min was higher in the bLf treatment group than in the control group. Total plasma glucose-dependent insulinotropic polypeptide (GIP) was lowered at 60 min by the bLf treatment, while an immediate increase in total plasma glucagon-like peptide-1 (GLP-1) was observed within the bLf group undergoing OGTT. In addition, bLf was associated with an increase in the amount of glucose absorbed into the everted jejunum sac. These results suggest that Lf could suppress hyperglycemia, accompanied by elevated plasma levels of insulin via transiently accelerating GLP-1 secretion, and that Lf even enhances glucose absorption from the small intestine.

GLP-1 response to sequential mixed meals: influence of insulin resistance.

Previous work has shown that potentiation of insulin release is impaired in non-diabetic insulin resistance; we tested the hypothesis that this defect may be related to altered glucagon-like peptide-1 (GLP-1) release. On consecutive days, 82 non-diabetic individuals, classified as insulin sensitive (IS, n=41) or insulin resistant (IR, n=41) by the euglycaemic clamp, were given two sequential mixed meals with standard (75 g, LCD) or double (150 g, HCD) carbohydrate content. Plasma glucose, insulin, C-peptide, non-esterified fatty acids (NEFA) and GLP-1 concentrations were measured; ß-cell function (glucose sensitivity and potentiation) was resolved by mathematical modelling. Fasting GLP-1 levels were higher in IR than IS (by 15%, P=0.006), and reciprocally related to insulin sensitivity after adjustment for sex, age, fat mass, fasting glucose or insulin concentrations. Mean postprandial GLP-1 responses were tightly correlated with fasting GLP-1, were higher for the second than the first meal, and higher in IR than IS subjects but only with LCD. In contrast, incremental GLP-1 responses were higher during (i) the second than the first meal, (ii) on HCD than LCD, and (iii) significantly smaller in IR than IS independently of meal and load. Potentiation of insulin release was markedly reduced in IR vs IS across meal and carbohydrate loading. In the whole dataset, incremental GLP-1 was directly related to potentiation, and both were inversely related to mean NEFA concentrations. We conclude that (a) raised GLP-1 tone may be inherently linked with a reduced GLP-1 response and (b) defective post-meal GLP-1 response may be one mechanism for impaired potentiation of insulin release in insulin resistance.

Impaired beta cell sensitivity to incretins in type 2 diabetes is insufficiently compensated by higher incretin response.

BACKGROUND AND AIMS: The incretin effect is impaired in type 2 diabetes (T2D), but the underlying mechanisms are only partially understood. We investigated the relationships between the time course of the incretin effect and that of glucose-dependent insulinotropic polypeptide (GIP) and glucagon-like peptide-1 (GLP-1) during oral glucose tolerance tests (OGTTs), thereby estimating incretin sensitivity of the beta cell, and its associated factors. METHODS AND RESULTS: Eight patients with T2D and eight matched subjects with normal glucose tolerance (NGT) received 25, 75, and 125 g OGTTs and corresponding isoglycemic glucose infusions (IIGI). The time course of the incretin effect, representing potentiation of insulin secretion by incretins (PINCR), was determined by mathematical modelling as the time-dependent fold increase in insulin secretion during OGTT compared to IIGI. The time course of PINCR was correlated with that of both GIP and GLP-1 in each subject (median r = 0.67 in NGT and 0.45 in T2D). We calculated an individual beta cell sensitivity to incretins (SINCR) using a weighted average of GIP and GLP-1 (pooled incretin concentration, PIC), as the slope of the relationship between PINCR and PIC. SINCR was reduced in T2D (p < 0.01). In the whole group, mean PIC, GIP and GLP-1 concentrations during the OGTT were inversely correlated with SINCR, but T2D had lower PIC, GIP and GLP-1 levels at the same SINCR (p < 0.05). CONCLUSION: Relative incretin insensitivity is partly compensated for by higher incretin secretory responses. However, T2D shows both impairment in incretin sensitivity and abnormal compensation by incretin secretion.

Increased Incretin But Not Insulin Response after Oral versus Intravenous Branched Chain Amino Acids.

BACKGROUND/AIMS: Branched chain amino acids (BCAAs) are known to exert an insulinotropic effect. Whether this effect is mediated by incretins (glucagon like peptide 1 [GLP-1] or glucose-dependent insulinotropic peptide [GIP]) is not known. The aim of this study was to show whether an equivalent dose of BCAA elicits a greater insulin and incretin response when administered orally than intravenously (IV). METHODS: Eighteen healthy, male subjects participated in 3 tests: IV application of BCAA solution, oral ingestion of BCAA and placebo in an equivalent dose (30.7 ± 1.1 g). Glucose, insulin, C-peptide, glucagon, GLP-1, GIP, valine, leucine and isoleucine concentrations were measured. RESULTS: Rise in serum BCAA was achieved in both BCAA tests, with incremental areas under the curve (iAUC) being 2.1 times greater for IV BCAA compared with those of the oral BCAA test (p < 0.0001). Oral and IV BCAA induced comparable insulin response greater than placebo (240 min insulin iAUC: oral 3,411 ± 577 vs. IV 2,361 ± 384 vs. placebo 961.2 ± 175 pmol/L, p = 0.0006). Oral BCAA induced higher GLP-1 (p < 0.0001) and GIP response (p < 0.0001) compared with the IV or placebo. Glucose levels declined significantly (p < 0.001) in the same pattern during both BCAA tests with no change in the placebo group. CONCLUSIONS: An equivalent dose of BCAA elicited a comparable insulin and greater incretin response when administered orally and not when administered through IV. We conclude that insulinotropic effects of BCAA are partially incretin dependent.

The incretin effect in obese adolescents with and without type 2 diabetes: impaired or intact?

The incretin effect reflects the actions of enteral stimuli to promote prandial insulin secretion. Impairment of this measure has been proposed as an early marker of ß-cell dysfunction and described in T2D, IGT, and even obesity without IGT. We sought to determine the effects of obesity and diabetes on the incretin effect in young subjects with short exposures to metabolic abnormalities and a few other confounding medical conditions. Subjects with T2D (n = 10; 18.0 ± 0.4 yr) or NGT, either obese (n = 11; 17.7 ± 0.4 yr) or lean (n = 8; 26.5 ± 2.3 yr), had OGTT and iso-iv. The incretin effect was calculated as the difference in insulin secretion during these tests and was decreased ∼50% in both the NGT-Ob and T2D subjects relative to the NGT-Ln group. The T2D group had impaired glucose tolerance and insulin secretion during the OGTT, whereas the lean and obese NGT subjects had comparable glucose excursions and ß-cell function. During the iso-iv test, the NGT-Ob subjects had significantly greater insulin secretion than the NGT-Ln and T2D groups. These findings demonstrate that in young subjects with early, well-controlled T2D the incretin effect is reduced, similar to what has been described in diabetic adults. The lower incretin effect calculated for the obese subjects with NGT is driven by a disproportionately greater insulin response to iv glucose and does not affect postprandial glucose regulation. These findings confirm that the incretin effect is an early marker of impaired insulin secretion in persons with abnormal glucose tolerance but suggest that in obese subjects with NGT the incretin effect calculation can be confounded by exaggerated insulin secretion to iv glucose.

Diabetic and nondiabetic patients with nonalcoholic fatty liver disease have an impaired incretin effect and fasting hyperglucagonaemia.

OBJECTIVE: We evaluated whether patients with histologically verified nonalcoholic fatty liver disease (NAFLD) have an impaired incretin effect and hyperglucagonaemia. METHODS: Four groups matched for age, sex and body mass index were studied: (i) 10 patients with normal glucose tolerance and NAFLD; (ii) 10 patients with type 2 diabetes and NAFLD; (iii) eight patients with type 2 diabetes and no liver disease; and (iv) 10 controls. All participants underwent a 50-g oral glucose tolerance test (OGTT) and an isoglycaemic intravenous glucose infusion (IIGI). We determined the incretin effect by relating the beta cell secretory responses during the OGTT and IIGI. Data are presented as medians (interquartile range), and the groups were compared by using the Kruskal-Wallis test. RESULTS: Controls exhibited a higher incretin effect [55% (43-73%)] compared with the remaining three groups (P < 0.001): 39% (44-71%) in the nondiabetic NAFLD patients, 20% (-5-50%) in NAFLD patients with type 2 diabetes, and 2% (-8-6%) in patients with type 2 diabetes and no liver disease. We found fasting hyperglucagonaemia in NAFLD patients with [7.5 pmol L(-1) (6.8-15 pmol L(-1))] and without diabetes [7.5 pmol L(-1) (5.0-8.0 pmol L(-1))]. Fasting glucagon levels were lower but similar in patients with type 2 diabetes and no liver disease [4.5 pmol L(-1) (3.0-6.0 pmol L(-1))] and controls [3.4 pmol L(-1) (1.8-6.0 pmol L(-1) )]. All groups had similar glucagon-like peptide-1 and glucose-dependent insulinotropic polypeptide responses. CONCLUSIONS: Patients with NAFLD have a reduced incretin effect and fasting hyperglucagonaemia, with the latter occurring independently of glucose (in)tolerance.

Impaired incretin effect is an early sign of glucose dysmetabolism in nondiabetic patients with psoriasis.

BACKGROUND: Patients with psoriasis have an increased risk of type 2 diabetes. The gastrointestinal system plays a major role in normal glucose metabolism, and in healthy individuals, postprandial insulin secretion is largely mediated by the gut incretin hormones. This potentiation is termed the incretin effect and is reduced in type 2 diabetes. The impact of psoriasis on gastrointestinal factors involved in glucose metabolism has not previously been examined. OBJECTIVE: To investigate whether the incretin effect, gastrointestinal-mediated glucose disposal (GIGD) and/or secretion of glucagon and gut incretin hormones are impaired in normal glucose-tolerant patients with psoriasis. METHODS: Oral glucose tolerance tests and intravenous isoglycaemic glucose infusions were performed in 12 patients with moderate-to-severe psoriasis and 12 healthy matched control subjects. RESULTS: In patients with psoriasis, the incretin effect (39% vs. 57%, P = 0.02) and GIGD (53% vs. 61%, P = 0.04) were significantly reduced compared to control subjects. In addition, patients were glucose intolerant and showed exaggerated glucose-dependent insulinotropic polypeptide responses. CONCLUSION: These novel findings support the notion that psoriasis is a prediabetic condition and suggest that gastrointestinal-related mechanisms are involved in the increased susceptibility to type 2 diabetes in patients with psoriasis.

The Potential Mechanism of Remission in Type 2 Diabetes Mellitus After Vertical Sleeve Gastrectomy.

In recent years, there has been a gradual increase in the prevalence of obesity and type 2 diabetes mellitus (T2DM), with bariatric surgery remaining the most effective treatment strategy for these conditions. Vertical sleeve gastrectomy (VSG) has emerged as the most popular surgical procedure for bariatric/metabolic surgeries, effectively promoting weight loss and improving or curing T2DM. The alterations in the gastrointestinal tract following VSG may improve insulin secretion and resistance by increasing incretin secretion (especially GLP-1), modifying the gut microbiota composition, and through mechanisms dependent on weight loss. This review focuses on the potential mechanisms through which the enhanced action of incretin and metabolic changes in the digestive system after VSG may contribute to the remission of T2DM.

Rectal sensitivity correlated with gastrointestinal-mediated glucose disposal, but not the incretin effect.

OBJECTIVE: The mechanisms behind the diminished incretin effect in type 2 diabetes are uncertain, but impaired vagal transmission has been suggested. We aimed to investigate the association between the incretin effect and autonomic neuropathy, and the degree of dysglycaemia and duration of diabetes. DESIGN AND METHODS: For a cross-sectional study, we included participants with either longstanding type 2 diabetes, recent onset, untreated diabetes and controls without diabetes matched for age, sex and body mass index. Autonomic nerve function was assessed with cardiovascular reflex tests, heart rate variability and sudomotor function. Visceral afferent nerves in the gut were tested performing rapid rectal balloon distention. An oral glucose tolerance test and an intravenous isoglycaemic glucose infusion were performed to calculate the incretin effect and gastrointestinal-mediated glucose disposal (GIGD). RESULTS: Sixty-five participants were recruited. Participants with diabetes had rectal hyposensitivity for earliest sensation (3.7 ± 1.1 kPa in longstanding, 4.0 ± 1.3 in early), compared to controls (3.0 ± 0.9 kPa), p = .005. Rectal hyposensitivity for earliest sensation was not associated with the incretin effect (rho = -0.204, p = .106), but an association was found with GIGD (rho -0.341, p = .005). Incretin effect and GIGD were correlated with all glucose values, HbA1c and duration of diabetes. CONCLUSIONS: Rectal hyposensitivity was uncovered in both longstanding and early type 2 diabetes, and was not associated with the incretin effect, but with GIGD, implying a potential link between visceral neuropathy and gastrointestinal handling of glucose. Both the incretin effect and GIGD were associated with the degree of dysglycaemia and the duration of diabetes. PREVIOUSLY PUBLISHED: Some of the data have previously been published and presented as a poster on the American Diabetes Association 83rd Scientific Sessions: Meling et al; 1658-P: Rectal Hyposensitivity, a Potential Marker of Enteric Autonomic Nerve Dysfunction, Is Significantly Associated with Gastrointestinally Mediated Glucose Disposal in Persons with Type 2 Diabetes. Diabetes 20 June 2023; 72 (Supplement_1): 1658-P. https://doi.org/10.2337/db23-1658-P.

Predicting Type 2 Diabetes Metabolic Phenotypes Using Continuous Glucose Monitoring and a Machine Learning Framework.

Type 2 diabetes (T2D) and prediabetes are classically defined by the level of fasting glucose or surrogates such as hemoglobin HbA1c. This classification does not take into account the heterogeneity in the pathophysiology of glucose dysregulation, the identification of which could inform targeted approaches to diabetes treatment and prevention and/or predict clinical outcomes. We performed gold-standard metabolic tests in a cohort of individuals with early glucose dysregulation and quantified four distinct metabolic subphenotypes known to contribute to glucose dysregulation and T2D: muscle insulin resistance, ß-cell dysfunction, impaired incretin action, and hepatic insulin resistance. We revealed substantial inter-individual heterogeneity, with 34% of individuals exhibiting dominance or co-dominance in muscle and/or liver IR, and 40% exhibiting dominance or co-dominance in ß-cell and/or incretin deficiency. Further, with a frequently-sampled oral glucose tolerance test (OGTT), we developed a novel machine learning framework to predict metabolic subphenotypes using features from the dynamic patterns of the glucose time-series ("shape of the glucose curve"). The glucose time-series features identified insulin resistance, ß-cell deficiency, and incretin defect with auROCs of 95%, 89%, and 88%, respectively. These figures are superior to currently-used estimates. The prediction of muscle insulin resistance and ß-cell deficiency were validated using an independent cohort. We then tested the ability of glucose curves generated by a continuous glucose monitor (CGM) worn during at-home OGTTs to predict insulin resistance and ß-cell deficiency, yielding auROC of 88% and 84%, respectively. We thus demonstrate that the prediabetic state is characterized by metabolic heterogeneity, which can be defined by the shape of the glucose curve during standardized OGTT, performed in a clinical research unit or at-home setting using CGM. The use of at-home CGM to identify muscle insulin resistance and ß-cell deficiency constitutes a practical and scalable method by which to risk stratify individuals with early glucose dysregulation and inform targeted treatment to prevent T2D.

The incretin effect in type 2 diabetes in a Sub-Saharan African population.

AIM: Type 2 diabetes is increasing in Sub-Saharan Africa, but the pathophysiology in this population is poorly investigated. In Western populations, the incretin effect is reduced in type 2 diabetes, leading to lowered insulin secretion. The aim of this study was to investigate the incretin effect in a group of Sub-Saharan Africans with type 2 diabetes. METHODS: Twenty adults diagnosed with type 2 diabetes, based on either an oral glucose tolerance test (n = 10) or on glycated hemoglobin A1c (n = 10), and 10 non-diabetic controls were included in an interventional study in Tanzania. We investigated the incretin effect as the difference between the plasma insulin area under the curve during an oral glucose tolerance test and that obtained during an intravenous glucose infusion. Differences between diabetes groups were analyzed by Kruskal-Wallis one-way analysis of variance. RESULTS: The incretin effect did not differ between groups (p = 0.45), and there was no difference in plasma concentrations of the incretin hormones during the OGTT. CONCLUSION: A reduced incretin effect appears not to contribute to hyperglycemia in type 2 diabetes in this Tanzanian population. More research is needed to explain the diabetes phenotype often seen in Sub-Saharan Africa. TRIAL REGISTRATION: Clinicaltrials.gov: NCT03106480 , date of registration: 04/10/2017.

Impact of Lycium barbarum polysaccharide on the expression of glucagon-like peptide 1 in vitro and in vivo.

Several studies showed the efficacy of Lycium barbarum polysaccharide (LBP) in diabetic animals and patients with type 2 diabetes mellitus (T2DM). However, the mechanism of LBP in alleviating T2DM based on glucagon-like peptide 1 (GLP1) has not been suitably elucidated. GLP1 is an important peptide that plays a role in blood glucose homeostasis. Inhibition of sodium/glucose cotransporter 1 (SGLT1) can result in a net increase in GLP1 release. We found that LBP could reduce SGLT1 expression. Thus, the effects of LBP on the first- and second-phase secretion of GLP1 were systematically assessed in vitro using STC1 cells and in vivo using diabetic KKAy mice. LBP could induce the first-phase secretion of GLP1 by stimulating calcium ion influx in vitro and by inhibiting alpha-glucosidase activity in vivo. Regulation of Gcg gene expression by modulating the Wnt/ß-catenin and cAMP/Epac pathways, as well as inhibition of alpha-glucosidase activity, was responsible for the second-phase secretion of GLP1. LBP could stimulate GLP1 secretion; however, dipeptidyl peptidase 4 (DPP4) activated by LBP might offset the second-phase secretion of GLP1. Thus, we suggest considering the simultaneous use of LBP and a DPP4 inhibitor to stimulate slow, continuous GLP1 secretion. Further studies are warranted for in-depth mechanistic information.

Exendin-4 affects calcium signalling predominantly during activation and activity of beta cell networks in acute mouse pancreas tissue slices.

Tight control of beta cell stimulus-secretion coupling is crucial for maintaining homeostasis of energy-rich nutrients. While glucose serves as a primary regulator of this process, incretins augment beta cell function, partly by enhancing cytosolic [Ca2+] dynamics. However, the details of how precisely they affect beta cell recruitment during activation, their active time, and functional connectivity during plateau activity, and how they influence beta cell deactivation remain to be described. Performing functional multicellular Ca2+ imaging in acute mouse pancreas tissue slices enabled us to systematically assess the effects of the GLP-1 receptor agonist exendin-4 (Ex-4) simultaneously in many coupled beta cells with high resolution. In otherwise substimulatory glucose, Ex-4 was able to recruit approximately a quarter of beta cells into an active state. Costimulation with Ex-4 and stimulatory glucose shortened the activation delays and accelerated beta cell activation dynamics. More specifically, active time increased faster, and the time required to reach half-maximal activation was effectively halved in the presence of Ex-4. Moreover, the active time and regularity of [Ca2+]IC oscillations increased, especially during the first part of beta cell response. In contrast, subsequent addition of Ex-4 to already active cells did not significantly enhance beta cell activity. Network analyses further confirmed increased connectivity during activation and activity in the presence of Ex-4, with hub cell roles remaining rather stable in both control experiments and experiments with Ex-4. Interestingly, Ex-4 demonstrated a biphasic effect on deactivation, slightly prolonging beta cell activity at physiological concentrations and shortening deactivation delays at supraphysiological concentrations. In sum, costimulation by Ex-4 and glucose increases [Ca2+]IC during beta cell activation and activity, indicating that the effect of incretins may, to an important extent, be explained by enhanced [Ca2+]IC signals. During deactivation, previous incretin stimulation does not critically prolong cellular activity, which corroborates their low risk of hypoglycemia.