Proinsulin associates with poor β-cell function, glucose-dependent insulinotropic peptide, and insulin resistance in persistent type 2 diabetes after Roux-en-Y gastric bypass in humans

Insulin resistance levels predicted metabolic improvement and weight loss after metabolic surgery in Chinese patients with type 2 diabetes

BACKGROUND

The causes for failure of metabolic improvement and inadequate weight loss after metabolic surgery (MS) in Chinese patients with type 2 diabetes (T2D) have not been fully elucidated. The effect of insulin resistance (IR) on the outcome of T2D, hypertension, hyperlipidemia, and obesity after MS in Chinese patients with T2D and a body mass index (BMI) of 25-32.5 kg/m2 warrants further study.

OBJECTIVES

Patients with T2D and a BMI of 25-32.5 kg/m2 who underwent MS between July 2019 and June 2021 were included.

SETTING

University hospital, China.

METHODS

IR levels were evaluated with the glucose disposal rate (GDR). Improvement of T2D, hypertension, and hyperlipidemia was assessed with the composite triple endpoint (CTEP), and weight loss was assessed with the percent of total weight loss (%TWL). Partial correlation analysis, binary logistic regression analysis, multiple linear regression analysis, receiver operating characteristic curve (ROC) analysis, and subgroup analysis were used to analyze the relationship between the CTEP, %TWL at 1 year postoperative, and GDR preoperative.

RESULTS

This study analyzed the data of 51 patients with T2D and a BMI of 25-32.5 kg/m2 (30 men and 21 women) with a mean preoperative GDR of 3.72 ± 1.48 mg/kg/min. Partial correlation coefficients between CTEP, %TWL, and GDR were .303 (P = .041) and .449 (P = .001), respectively. The preoperative GDR was significantly positively correlated with CTEP (OR = 1.610, P = .024) and %TWL (β = 1.38, P = .003). The preoperative GDR predicted cutoff values of 4.36 and 5.35 mg/kg/min for CTEP attainment and %TWL ≥ 20%, respectively.

CONCLUSION

IR levels predicted metabolic improvement and weight loss 1 year after MS in Chinese patients with T2D and a BMI of 25-32.5 kg/m2.

Glucagon-like peptide-1 effect on β-cell function varies according to diabetes remission status after Roux-en-Y gastric bypass

AIMS

The contribution of endogenous glucagon-like peptide (GLP)-1 to β-cell function after Roux-en-Y gastric bypass surgery (RYGB) is well established in normoglycaemic individuals, but not in those with postoperative hyperglycaemia. We, therefore, studied the effect of GLP-1 on β-cell function in individuals with varying degrees of type 2 diabetes mellitus (T2D) control after RYGB.

MATERIALS AND METHODS

Glucose, insulin secretion rates, β-cell glucose sensitivity and glucagon were measured during an oral glucose tolerance test before (saline only) and at 3, 12 and 24 months after RYGB with and without infusion of the GLP-1 receptor blocker exendin9-39 (EX9). The cohort was retrospectively classified based on T2D remission (REM) status at the latest study time point: REM (n = 5), persistent T2D (n = 8), or impaired glucose tolerance (n = 16).

RESULTS

EX9 blunted the increase in β-cell glucose sensitivity at 3 months (-44.1%, p < .001) and 12 months (-43.3%, p < .001), but not at 24 months (-12.4%, p = .243). EX9 enhanced postprandial glucagon concentrations by 62.0% at 3 months (p = .008), 46.5% at 12 months (p = .055), and 30.4% at 24 months (p = .017). EX9 counterintuitively decreased glucose concentrations at 3 months in the entire cohort (p < .001) but had no effect on glycaemia at 12 and 24 months in persistent T2D and impaired glucose tolerance; it minimally worsened glycaemia in REM at 12 months.

CONCLUSIONS

GLP-1 blockade reversed the improvement in β-cell function observed after RYGB, but this effect varied temporally and by REM status. GLP-1 blockade transiently and minimally worsened glycaemia only in REM, and lowered postprandial glucose values at 3 months, regardless of REM status.

Sleeve Gastrectomy and Roux-En-Y Gastric Bypass. Two Sculptors of the Pancreatic Islet

Several surgical procedures are performed for the treatment of obesity. A main outcome of these procedures is the improvement of type 2 diabetes mellitus. Trying to explain this, gastrointestinal hormone levels and their effect on organs involved in carbohydrate metabolism, such as liver, gut, muscle or fat, have been studied intensively after bariatric surgery. These effects on endocrine-cell populations in the pancreas have been less well studied. We gathered the existing data on these pancreatic-cell populations after the two most common types of bariatric surgery, the sleeve gastrectomy (SG) and the roux-en-Y gastric bypass (RYGB), with the aim to explain the pathophysiological mechanisms underlying these surgeries and to improve their outcome.

Preintervention Clinical Determinants and Measured β-Cell Function As Predictors of Type 2 Diabetes Remission After Roux-en-Y Gastric Bypass Surgery

BACKGROUND

Bariatric surgery results in improved glycemic control in individuals with type 2 diabetes. Single and clusters of clinical determinants have been identified as presurgery predictors of postsurgery diabetes remission. Our goal was to assess whether the addition of measured preoperative β-cell function would improve established clinical models of prediction of diabetes remission.

RESEARCH DESIGN AND METHODS

Presurgery clinical characteristics, metabolic markers, and β-cell function after oral and intravenous (IV) glucose challenges were assessed in 73 individuals with severe obesity and type 2 diabetes and again 1 year after gastric bypass surgery. Single and multivariate analyses were conducted with preoperative variables to determine the best predictive models of remission.

RESULTS

Presurgery β-cell glucose sensitivity, a surrogate of β-cell function, was negatively correlated with known diabetes duration, HbA1c, insulin use, and the diabetes remission scores DiaRem and advanced (Ad)-DiaRem (all P < 0.001). Measured β-cell function after oral glucose was 1.6-fold greater than after the IV glucose challenge and more strongly correlated with preoperative clinical and metabolic characteristics. The addition of preoperative β-cell function to clinical models containing well-defined diabetes remission scores did not improve the model's ability to predict diabetes remission after Roux-en-Y gastric bypass.

CONCLUSIONS

The addition of measured β-cell function does not add predictive value to defined clinical models of diabetes remission 1 year after surgical weight loss.

Dual GIP and GLP-1 Receptor Agonist Tirzepatide Improves Beta-cell Function and Insulin Sensitivity in Type 2 Diabetes

CONTEXT

Novel dual glucose-dependent insulinotropic polypeptide (GIP) and glucagon-like peptide-1 (GLP-1) receptor agonist (RA) tirzepatide demonstrated substantially greater glucose control and weight loss (WL) compared with selective GLP-1RA dulaglutide.

OBJECTIVE

Explore mechanisms of glucose control by tirzepatide.

DESIGN

Post hoc analyses of fasting biomarkers and multiple linear regression analysis.

SETTING

Forty-seven sites in 4 countries.

PATIENTS OR OTHER PARTICIPANTS

Three hundred and sixteen subjects with type 2 diabetes.

INTERVENTIONS

Tirzepatide (1, 5, 10, 15 mg), dulaglutide (1.5 mg), placebo.

MAIN OUTCOME MEASURES

Analyze biomarkers of beta-cell function and insulin resistance (IR) and evaluate WL contributions to IR improvements at 26 weeks.

RESULTS

Homeostatic model assessment (HOMA) 2-B significantly increased with dulaglutide and tirzepatide 5, 10, and 15 mg compared with placebo (P ≤ .02). Proinsulin/insulin and proinsulin/C-peptide ratios significantly decreased with tirzepatide 10 and 15 mg compared with placebo and dulaglutide (P ≤ .007). Tirzepatide 10 and 15 mg significantly decreased fasting insulin (P ≤ .033) and tirzepatide 10 mg significantly decreased HOMA2-IR (P = .004) compared with placebo and dulaglutide. Markers of improved insulin sensitivity (IS) adiponectin, IGFBP-1, and IGFBP-2 significantly increased by 1 or more doses of tirzepatide (P < .05). To determine whether improvements in IR were directly attributable to WL, multiple linear regression analysis with potential confounding variables age, sex, metformin, triglycerides, and glycated hemoglobin A1c was conducted. WL significantly (P ≤ .028) explained only 13% and 21% of improvement in HOMA2-IR with tirzepatide 10 and 15 mg, respectively.

CONCLUSIONS

Tirzepatide improved markers of IS and beta-cell function to a greater extent than dulaglutide. IS effects of tirzepatide were only partly attributable to WL, suggesting dual receptor agonism confers distinct mechanisms of glycemic control.

Distinct secretion pattern of serum proinsulin in different types of diabetes

Background

Latent autoimmune diabetes in adults (LADA) is characterized by autoimmunity, late-onset and intermediate beta-cell deprivation rate between type 2 diabetes mellitus (T2DM) and type 1 diabetes mellitus (T1DM). Herein, we investigated proinsulin (PI) secretion patterns and the endoplasmic reticulum (ER) dysfunction biomarker, PI-to-C-peptide (PI:CP) ratio, to elucidate beta-cell intrinsic pathogenesis mechanisms in different types of diabetes.

Methods

Total serum fasting PI (FPI) were measured in adult-onset and newly-diagnosed diabetes patients, including 60 T1DM, 60 LADA and 60 T2DM. Thirty of each type underwent mixed meal tolerance tests (MMTTs), and hence 120 min postprandial PI (PPI) were detected. PI:CP ratio = PI (pmol/L) ÷ CP (pmol/L) × 100%. PI-related measurements among types of diabetes were compared. Correlation between PI-related measurements and beta-cell autoimmunity were analyzed. The possibility of discriminating LADA from T1DM and T2DM with PI-related measurements were tested.

Results

FPI and PPI were significantly higher in LADA than T1DM (P<0.001 for both comparisons), but lower than those in T2DM (P<0.001 and P=0.026, respectively). Fasting PI:CP ratio was significantly higher in T1DM than both LADA and T2DM (median 3.25% vs. 2.13% and 2.32%, P=0.011 and P=0.017, respectively). In LADA, positive autoantibody numbers increased by both fasting and postprandial PI:CP ratio (P=0.007 and P=0.034, respectively). Areas under receiver operation characteristic curves (AUC_ROC) of FPI and PPI for discriminating LADA from adult-onset T1DM were 0.751 (P<0.001) and 0.838 (P<0.001), respectively. Between LADA and T2DM, AUC_ROC of FPI and PPI were 0.685 (P<0.001) and 0.741 (P=0.001), respectively.

Conclusions

In the development of autoimmune diabetes, interplays between ER stress and beta-cell autoimmunity are potentially responsible for severer beta-cell destruction. PI-related measurements could help in differentiating LADA from adult-onset T1DM and T2DM.