Model-Based Assessment of C-Peptide Secretion and Kinetics in Post Gastric Bypass Individuals Experiencing Postprandial Hyperinsulinemic Hypoglycemia

Unraveling, contributing factors to the severity of postprandial hypoglycemia after gastric bypass surgery

BACKGROUND

Despite the increasing prevalence of postbariatric hypoglycemia (PBH), a late metabolic complication of bariatric surgery, our understanding of its diverse manifestations remains incomplete.

OBJECTIVES

To contrast parameters of glucose-insulin homeostasis in 2 distinct phenotypes of PBH (mild versus moderate hypoglycemia) based on nadir plasma glucose.

SETTING

University Hospital (Bern, Switzerland).

METHODS

Twenty-five subjects with PBH following gastric bypass surgery (age, 41 ± 12 years; body mass index, 28.1 ± 6.1kg/m²) received 75g of glucose with frequent blood sampling for glucose, insulin, C-peptide, and glucagon-like peptide 1 (GLP)-1. Based on nadir plasma glucose (</≥50mg/dL), subjects were grouped into level 1 (L1) and level 2 (L2) PBH groups. Beta-cell function (BCF), GLP-1 exposure (λ), beta-cell sensitivity to GLP-1 (π), potentiation of insulin secretion by GLP-1 (PI), first-pass hepatic insulin extraction (HE), insulin sensitivity (SI), and rate of glucose appearance (Ra) were calculated using an oral model of GLP-1 action coupled with the oral minimal model.

RESULTS

Nadir glucose was 43.3 ± 6.0mg/dL (mean ± standard deviation) and 60.1 ± 9.1mg/dL in L2- and L1-PBH, respectively. Insulin exposure was significantly higher in L2 versus L1 (P = .004). Mathematical modeling revealed higher BCF in L2 versus L1 (34.3 versus 18.8 10^-9∗min^-1; P = .003). Despite an increased GLP-1 exposure in L2 compared to L1 PBH (50.7 versus 31.9pmol∗L^-1∗min∗10²; P = .021), no significant difference in PI was observed (P = .204). No significant differences were observed for HE, Ra, and SI.

CONCLUSIONS

Our results suggest that higher insulin exposure in PBH patients with lower postprandial nadir glucose values mainly relate to a higher responsiveness to glucose, rather than GLP-1.

Study protocol for a randomised, double-blind, placebo-controlled crossover trial assessing the impact of the SGLT2 inhibitor empagliflozin on postprandial hypoglycaemia after gastric bypass

INTRODUCTION

Postprandial hypoglycaemia after gastric bypass surgery (also known as postbariatric hypoglycaemia or PBH) is an increasingly encountered clinical problem. PBH is characterised by meal-induced rapid spikes and consequent falls in glycaemia, resulting in both hypoglycaemia burden and high glycaemic variability. Despite its frequency, there is currently no approved pharmacotherapy. The purpose of this investigation is to evaluate efficacy and safety of empagliflozin 25 mg, a sodium-glucose cotransporter 2-inhibitor, to reduce glucose excursions and hypoglycaemia burden in patients with PBH after gastric bypass surgery.

METHODS AND ANALYSIS

In a prospective, single-centre, randomised, double-blind, placebo-controlled, crossover trial, we plan to enrol 22 adults (≥18 years) with PBH after Roux-en-Y gastric bypass surgery (plasma or sensor glucose <3.0 mmol/L). Eligible patients will be randomised to receive empagliflozin 25 mg and placebo once daily, each for 20 days, in random order. Study periods will be separated by a 2-6 weeks wash-out period. The primary efficacy outcome will be the amplitude of plasma glucose excursion (peak to nadir) during a mixed meal tolerance test. Results will be presented as paired-differences±SD plus 95% CIs with p values and hypothesis testing for primary and secondary outcomes according to intention-to-treat. Secondary outcomes include continuous glucose monitoring-based outcomes, further metabolic measures and safety.

ETHICS AND DISSEMINATION

The DEEP-EMPA trial (original protocol title: Randomized, double-blind, placebo-controlled crossover trialassessing the impact of the SGLT2 inhibitor empagliflozin onpostprandial hypoglycaemia after gastric bypass) was approved by the Bern Ethics Committee (ID 2021-01187) and Swissmedic (Ref. Number: 102663190) in October and November 2021, respectively. First results are expected in the first quarter of 2023 and will be disseminated via peer-reviewed publications and presented at national and international conferences. The acronym DEEP was derived from an overarching project title (DEciphering the Enigma of Postprandial Hyperinsulinaemic Hypoglycaemia after Bariatric Surgery), the term EMPA stands for the drug empagliflozin.

TRIAL REGISTRATION NUMBER

NCT05057819.

Inferring Insulin Secretion Rate from Sparse Patient Glucose and Insulin Measures

The insulin secretion rate (ISR) contains information that can provide a personal, quantitative understanding of endocrine function. If the ISR can be reliably inferred from measurements, it could be used for understanding and clinically diagnosing problems with the glucose regulation system. Objective: This study aims to develop a model-based method for inferring a parametrization of the ISR and related physiological information among people with different glycemic conditions in a robust manner. The developed algorithm is applicable for both dense or sparsely sampled plasma glucose/insulin measurements, where sparseness is defined in terms of sampling time with respect to the fastest time scale of the dynamics. Methods: An algorithm for parametrizing and validating a functional form of the ISR for different compartmental models with unknown but estimable ISR function and absorption/decay rates describing the dynamics of insulin accumulation was developed. The method and modeling applies equally to c-peptide secretion rate (CSR) when c-peptide is measured. Accuracy of fit is reliant on reconstruction error of the measured trajectories, and when c-peptide is measured the relationship between CSR and ISR. The algorithm was applied to data from 17 subjects with normal glucose regulatory systems and 9 subjects with cystic fibrosis related diabetes (CFRD) in which glucose, insulin and c-peptide were measured in course of oral glucose tolerance tests (OGTT). Results: This model-based algorithm inferred parametrization of the ISR and CSR functional with relatively low reconstruction error for 12 of 17 control and 7 of 9 CFRD subjects. We demonstrate that when there are suspect measurements points, the validity of excluding them may be interrogated with this method. Significance: A new estimation method is available to infer the ISR and CSR functional profile along with plasma insulin and c-peptide absorption rates from sparse measurements of insulin, c-peptide, and plasma glucose concentrations. We propose a method to interrogate and exclude potentially erroneous OGTT measurement points based on reconstruction errors.

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.