Standardized Mixed-Meal Tolerance and Arginine Stimulation Tests Provide Reproducible and Complementary Measures of β-Cell Function: Results From the Foundation for the National Institutes of Health Biomarkers Consortium Investigative Series

Myths and methodologies: Assessing glycaemic control and associated regulatory mechanisms in human physiology research

Accurate measurements of glycaemic control and the underpinning regulatory mechanisms are vital in human physiology research. Glycaemic control is the maintenance of blood glucose concentrations within optimal levels and is governed by physiological variables including insulin sensitivity, glucose tolerance and β-cell function. These can be measured with a plethora of methods, all with their own benefits and limitations. Deciding on the best method to use is challenging and depends on the specific research question(s). This review therefore discusses the theory and procedure, validity and reliability and any special considerations of a range common methods used to measure glycaemic control, insulin sensitivity, glucose tolerance and β-cell function. Methods reviewed include glycosylated haemoglobin, continuous glucose monitors, the oral glucose tolerance test, mixed meal tolerance test, hyperinsulinaemic euglycaemic clamp, hyperglycaemic clamp, intravenous glucose tolerance test and indices derived from both fasting concentrations and the oral glucose tolerance test. This review aims to help direct understanding, assessment and decisions regarding which method to use based on specific physiology-related research questions.

Elevations in plasma glucagon are associated with reduced insulin clearance after ingestion of a mixed-macronutrient meal in people with and without type 2 diabetes

AIMS/HYPOTHESIS

The temporal suppression of insulin clearance after glucose ingestion is a key determinant of glucose tolerance for people without type 2 diabetes. Whether similar adaptations are observed after the ingestion of a mixed-macronutrient meal is unclear.

METHODS

In a secondary analysis of data derived from two randomised, controlled trials, we studied the temporal responses of insulin clearance after the ingestion of a standardised breakfast meal consisting of cereal and milk in lean normoglycaemic individuals (n=12; Lean-NGT), normoglycaemic individuals with central obesity (n=11; Obese-NGT) and in people with type 2 diabetes (n=19). Pre-hepatic insulin secretion rates were determined by the deconvolution of C-peptide, and insulin clearance was calculated using a single-pool model. Insulin sensitivity was measured by an oral minimal model.

RESULTS

There were divergent time course changes in insulin clearance between groups. In the Lean-NGT group, there was an immediate post-meal increase in insulin clearance compared with pre-meal values (p<0.05), whereas insulin clearance remained stable at baseline values in Obese-NGT or declined slightly in the type 2 diabetes group (p<0.05). The mean AUC for insulin clearance during the test was ~40% lower in the Obese-NGT (1.3 ± 0.4 l min-1 m-2) and type 2 diabetes (1.4 ± 0.7 l min-1 m-2) groups compared with Lean-NGT (1.9 ± 0.5 l min-1 m-2; p<0.01), with no difference between the Obese-NGT and type 2 diabetes groups. HOMA-IR and glucagon AUC emerged as predictors of insulin clearance AUC, independent of BMI, age or insulin sensitivity (adjusted R2=0.670). Individuals with increased glucagon AUC had a 40% reduction in insulin clearance AUC (~ -0.75 l min-1 m-2; p<0.001).

CONCLUSIONS/INTERPRETATION

The ingestion of a mixed-macronutrient meal augments differing temporal profiles in insulin clearance among individuals without type 2 diabetes, which is associated with HOMA-IR and the secretion of glucagon. Further research investigating the role of hepatic glucagon signalling in postprandial insulin kinetics is warranted.

TRIAL REGISTRATION

ISRCTN17563146 and ISRCTN95281775.

A mixed meal tolerance test predicts onset of type 2 diabetes in Southwestern Indigenous adults

BACKGROUND/OBJECTIVE

To identify predictors of incident type 2 diabetes using a mixed meal tolerance test (MMTT).

METHODS

Adult Indigenous Americans without diabetes (n = 501) from a longitudinal cohort underwent at baseline a 4-h MMTT, measures of body composition, an oral glucose tolerance test, an intravenous glucose tolerance test for acute insulin response (AIR), and a hyperinsulinemic-euglycemic clamp for insulin action (M). Plasma glucose responses from the MMTT were quantified by the total and incremental area under the curve (AUC/iAUC).

RESULTS

At follow-up (median time 9.6 [inter-quartile range: 5.6-13.5] years), 169 participants were diagnosed with diabetes. Unadjusted Cox proportional hazards models, glucose AUC180-min (HR: 1.98, 95% CI: 1.67, 2.34, p < 0.0001), AUC240-min (HR: 1.93, 95% CI: 1.62, 2.31, p < 0.0001), and iAUC180-min (HR: 1.43, 95% CI: 1.20, 1.71, p < 0.0001) were associated with an increased risk of diabetes. After adjustment for covariates (age, sex, body fat percentage, M, AIR, Indigenous American heritage) in three subsequent models, AUC180-min (HR: 1.44, 95% CI: 1.10, 1.88, p = 0.007) and AUC240-min (HR: 1.41, 95% CI: 1.09, 1.84, p < 0.01) remained associated with increased risk of diabetes.

CONCLUSIONS

Glucose responses to a mixed meal predicted the development of type 2 diabetes. This indicates that a mixed nutritional challenge provides important information on disease risk.

CLINICAL TRIAL REGISTRY

ClinicalTrials.gov identifier : NCT00340132, NCT00339482.

Prediction of personalised postprandial glycaemic response in type 1 diabetes mellitus

Objectives

Patients with type 1 diabetes (T1D) face unique challenges in glycaemic control due to the complexity and uniqueness of the dietary structure in China, especially in terms of postprandial glycaemic response (PPGR). This study aimed to establish a personalized model for predicting PPGR in patients with T1D.

Materials and methods

Data provided by the First People's Hospital of Yunnan Province, 13 patients with T1D, were recruited and provided with an intervention for at least two weeks. All patients were asked to wear a continuous glucose monitoring (CGM) device under free-living conditions during the study period. To tackle the challenge of incomplete data from wearable devices for CGM measurements, the GAIN method was used in this paper to achieve a more rational interpolation process. In this study, patients' PPGRs were calculated, and a LightGBM prediction model was constructed based on a Bayesian hyperparameter optimisation algorithm and a random search algorithm, which integrated glucose measurement, insulin dose, dietary nutrient content, blood measurement and anthropometry as inputs.

Results

The experimental outcomes revealed that the PPGR prediction model presented in this paper demonstrated superior accuracy (R=0.63) compared to both the carbohydrate content only model (R=0.14) and the baseline model emulating the standard of care for insulin administration (R=0.43). In addition, the interpretation of the model using the SHAP method showed that blood glucose levels at meals and blood glucose trends 30 minutes before meals were the most important features of the model.

Conclusion

The proposed model offers a heightened precision in predicting PPGR in patients with T1D, so it can better guide the diet plan and insulin intake dose of patients with T1D.

Comparison of an oral mixed meal plus arginine and intravenous glucose, GLP-1 plus arginine to unmask residual islet function in longstanding type 1 diabetes

Residual beta cells are present in most patients with longstanding type 1 diabetes but it is unknown whether these beta cells react normally to different stimuli. Moreover a defect in proinsulin conversion and abnormal alpha cell response are also part of the islet dysfunction. A three-phase [euglycemia, hyperglycemia, and hyperglycemia + glucagon-like peptide 1 (GLP-1)] clamp was performed in patients with longstanding type 1 diabetes. Intravenous arginine boluses were administered at the end of each phase. On another day, a mixed meal stimulation test with a subsequent intravenous arginine bolus was performed. C-peptide was detectable in a subgroup of subjects at baseline (2/15) or only after stimulation (3/15). When detectable, C-peptide increased 2.9-fold [95% CI: 1.2-7.1] during the hyperglycemia phase and 14.1-fold [95% CI: 3.1-65.2] during the hyperglycemia + GLP-1 phase, and 22.3-fold [95% CI: 5.6-89.1] during hyperglycemia + GLP-1 + arginine phase when compared with baseline. The same subset of patients with a C-peptide response were identified during the mixed meal stimulation test as during the clamp. There was an inhibition of glucagon secretion (0.72-fold, [95% CI: 0.63-0.84]) during the glucose clamp irrespective of the presence of detectable beta cell function. Proinsulin was only present in a subset of subjects with detectable C-peptide (3/15) and proinsulin mimicked the C-peptide response to the different stimuli when detectable. Residual beta cells in longstanding type 1 diabetes respond adequately to different stimuli and could be of clinical benefit.NEW & NOTEWORTHY If beta cell function is detectable, the beta cells react relatively normal to the different stimuli except for the first phase response to intravenous glucose. An oral mixed meal followed by an intravenous arginine bolus can identify residual beta cell function/mass as well as the more commonly used glucose potentiated arginine-induced insulin secretion during a hyperglycemic clamp.

Estimating insulin sensitivity and β-cell function from the oral glucose tolerance test: validation of a new insulin sensitivity and secretion (ISS) model

Efficient and accurate methods to estimate insulin sensitivity (SI) and β-cell function (BCF) are of great importance for studying the pathogenesis and treatment effectiveness of type 2 diabetes (T2D). Existing methods range in sensitivity, input data, and technical requirements. Oral glucose tolerance tests (OGTTs) are preferred because they are simpler and more physiological than intravenous methods. However, current analytical methods for OGTT-derived SI and BCF also range in complexity; the oral minimal models require mathematical expertise for deconvolution and fitting differential equations, and simple algebraic surrogate indices (e.g., Matsuda index, insulinogenic index) may produce unphysiological values. We developed a new insulin secretion and sensitivity (ISS) model for clinical research that provides precise and accurate estimates of SI and BCF from a standard OGTT, focusing on effectiveness, ease of implementation, and pragmatism. This model was developed by fitting a pair of differential equations to glucose and insulin without need of deconvolution or C-peptide data. This model is derived from a published model for longitudinal simulation of T2D progression that represents glucose-insulin homeostasis, including postchallenge suppression of hepatic glucose production and first- and second-phase insulin secretion. The ISS model was evaluated in three diverse cohorts across the lifespan. The new model had a strong correlation with gold-standard estimates from intravenous glucose tolerance tests and insulin clamps. The ISS model has broad applicability among diverse populations because it balances performance, fidelity, and complexity to provide a reliable phenotype of T2D risk.NEW & NOTEWORTHY The pathogenesis of type 2 diabetes (T2D) is determined by a balance between insulin sensitivity (SI) and β-cell function (BCF), which can be determined by gold standard direct measurements or estimated by fitting differential equation models to oral glucose tolerance tests (OGTTs). We propose and validate a new differential equation model that is simpler to use than current models and requires less data while maintaining good correlation and agreement with gold standards. Matlab and Python code is freely available.

Early Metabolic Measures Predict Long-term Insulin Independence in Recipients of Total Pancreatectomy and Islet Autotransplantation

Background

Although diabetes after total pancreatectomy and islet autotransplantation (TP-IAT) is one of the biggest concerns for TP-IAT recipients and physicians, reliable prediction of post-TP-IAT glycemic control remains unestablished. This study was conducted to identify early predictors of insulin independence and goal glycemic control by hemoglobin A1c (HbA1c) ≤ 6.5% after TP-IAT.

Methods

In this single-center, retrospective study, patients who underwent TP-IAT (n = 227) were reviewed for simple metabolic markers or surrogate indices of β-cell function obtained 3 mo after TP-IAT as part of standard clinical testing. Long-term metabolic success was defined as (1) insulin independence and (2) HbA1c ≤ 6.5% 1, 3, and 5 y after TP-IAT. Single- and multivariate modeling used 3-mo markers to predict successful outcomes.

Results

Of the 227 recipients, median age 31 y, 30% male, 1 y after TP-IAT insulin independence, and HbA1c ≤ 6.5% were present in 39.6% and 72.5%, respectively. In single-predictor analyses, most of the metabolic markers successfully discriminated between those attaining and not attaining metabolic goals. Using the best model selected by random forests analysis, we accurately predicted 1-y insulin independence and goal HbA1c control in 77.3% and 86.4% of the patients, respectively. A simpler "clinically feasible" model using only transplanted islet dose and BETA-2 score allowed easier prediction at a small accuracy loss (74.1% and 82.9%, respectively).

Conclusions

Metabolic testing measures performed 3 mo after TP-IAT were highly associated with later diabetes outcomes and provided a reliable prediction model, giving valuable prognostic insight early after TP-IAT and help to identify recipients who require early intervention.

Evaluating Glycemic Control Efficacy and Safety of the Oral Small Molecule Glucagon-Like Peptide 1 Receptor Agonist Danuglipron in Type 2 Diabetes Patients: A Systemic Review and Meta-Analysis

Introduction

Diabetes Mellitus (DM) is a significant global health concern, with Type 2 DM (T2DM) being highly prevalent. Glucagon-Like Peptide 1 receptor agonists (GLP-1RA), such as Danuglipron, offer potential benefits in T2DM management. This meta-analysis examines the safety and efficacy of Danuglipron, focusing on adverse outcomes and glycemic parameters.

Methods

A systematic search was conducted in PubMed, Scopus, and Cochrane Library for RCTs involving Danuglipron till August 2023, following PRISMA guidelines. The Cochrane risk-of-bias tool was used for quality assessment. Adverse outcomes (diarrhea, nausea, vomiting, headache, decreased appetite, dyspepsia, dizziness) and glycemic parameters like changes in HbA1C, fasting plasma glucose (FPG), and body weight were analyzed.

Results

Four RCTs published from 2021 to 2023 were included. Both doses of Danuglipron were associated with diarrhea (RR=2.66, 90% CI: 1.32 to 5.35, p=0.02), nausea (RR=5.5, 90% CI: 3.4 to 8.88, p<0.00001), and vomiting (RR=5.98, 90% CI: 2.93 to 12.23, p=0.0001). The 120mg dose showed decreased appetite (RR=3.46, 90% CI: 1.57 to 7.62, p=0.01), dyspepsia (RR=4.04, 90% CI: 1.93 to 8.43, p=0.002), and dizziness (RR=5.08, 90% CI: 1.45 to 17.82, p=0.03). Reductions in HbA1C (SMD -1.09, 90% CI -1.39 to -0.8, p < 0.00001), FPG (SMD -1.10, 90% CI -1.46 to -0.75, p < 0.00001), and body weight (SMD -1.08, 90% CI -1.42 to -0.74, p < 0.00001) were observed for both doses.

Conclusion

Danuglipron demonstrates potential for glycemic control and weight reduction in T2DM. Adverse outcomes include diarrhea, nausea, vomiting, and decreased appetite, with dose-related effects. Clinicians must weigh benefits against side effects when considering Danuglipron for T2DM management.

Dysregulation of early gene response to a mixed meal in skeletal muscle in obesity and type 2 diabetes

Obesity- and type 2 diabetes mellitus-induced changes in the expression of protein-coding genes in human skeletal muscle were extensively examined at baseline (after an overnight fast). We aimed to compare the early transcriptomic response to a typical single meal in skeletal muscle of metabolically healthy subjects and obese individuals without and with type 2 diabetes. Transcriptomic response (RNA-seq) to a mixed meal (nutritional drink, ∼25 kJ/kg of body mass) was examined in the vastus lateralis muscle (1 h after a meal) in 7 healthy subjects and 14 obese individuals without or with type 2 diabetes. In all obese individuals, the transcriptome response to a meal was dysregulated (suppressed and altered) and associated with different biological processes compared with healthy control. To search for potential transcription factors regulating transcriptomic response to a meal, the enrichment of transcription factor-binding sites in individual promoters of the human skeletal muscle was examined. In obese individuals, the transcriptomic response is associated with a different set of transcription factors than that in healthy subjects. In conclusion, metabolic disorders are associated with a defect in the regulation of mixed meal/insulin-mediated gene expression-insulin resistance in terms of gene expression. Importantly, this dysregulation occurs in obese individuals without type 2 diabetes, i.e., at the first stage of the development of metabolic disorders.NEW & NOTEWORTHY In skeletal muscle of metabolically healthy subjects, a typical single meal normalized to body mass induces activation of various transcription factors, expression of numerous receptor tyrosine kinases associated with the insulin signaling cascade, and transcription regulators. In skeletal muscle of obese individuals without and with type 2 diabetes, this signaling network is poorly regulated at the transcriptional level, indicating dysregulation of the early gene response to a mixed meal.

Estimating Insulin Sensitivity and Beta-Cell Function from the Oral Glucose Tolerance Test: Validation of a new Insulin Sensitivity and Secretion (ISS) Model

Efficient and accurate methods to estimate insulin sensitivity (SI) and beta-cell function (BCF) are of great importance for studying the pathogenesis and treatment effectiveness of type 2 diabetes. Many methods exist, ranging in input data and technical requirements. Oral glucose tolerance tests (OGTTs) are preferred because they are simpler and more physiological. However, current analytical methods for OGTT-derived SI and BCF also range in complexity; the oral minimal models require mathematical expertise for deconvolution and fitting differential equations, and simple algebraic models (e.g., Matsuda index, insulinogenic index) may produce unphysiological values. We developed a new ISS (Insulin Secretion and Sensitivity) model for clinical research that provides precise and accurate estimates of SI and BCF from a standard OGTT, focusing on effectiveness, ease of implementation, and pragmatism. The model was developed by fitting a pair of differential equations to glucose and insulin without need of deconvolution or C-peptide data. The model is derived from a published model for longitudinal simulation of T2D progression that represents glucose-insulin homeostasis, including post-challenge suppression of hepatic glucose production and first- and second-phase insulin secretion. The ISS model was evaluated in three diverse cohorts including individuals at high risk of prediabetes (adult women with a wide range of BMI and adolescents with obesity). The new model had strong correlation with gold-standard estimates from intravenous glucose tolerance tests and hyperinsulinemic-euglycemic clamp. The ISS model has broad clinical applicability among diverse populations because it balances performance, fidelity, and complexity to provide a reliable phenotype of T2D risk.

Intermittent fasting plus early time-restricted eating versus calorie restriction and standard care in adults at risk of type 2 diabetes: a randomized controlled trial

Intermittent fasting appears an equivalent alternative to calorie restriction (CR) to improve health in humans. However, few trials have considered applying meal timing during the 'fasting' day, which may be a limitation. We developed a novel intermittent fasting plus early time-restricted eating (iTRE) approach. Adults (N = 209, 58 ± 10 years, 34.8 ± 4.7 kg m-2) at increased risk of developing type 2 diabetes were randomized to one of three groups (2:2:1): iTRE (30% energy requirements between 0800 and 1200 hours and followed by a 20-h fasting period on three nonconsecutive days per week, and ad libitum eating on other days); CR (70% of energy requirements daily, without time prescription); or standard care (weight loss booklet). This open-label, parallel group, three-arm randomized controlled trial provided nutritional support to participants in the iTRE and CR arms for 6 months, with an additional 12-month follow-up. The primary outcome was change in glucose area under the curve in response to a mixed-meal tolerance test at month 6 in iTRE versus CR. Glucose tolerance was improved to a greater extent in iTRE compared with CR (-10.10 (95% confidence interval -14.08, -6.11) versus -3.57 (95% confidence interval -7.72, 0.57) mg dl-1 min-1; P = 0.03) at month 6, but these differences were lost at month 18. Adverse events were transient and generally mild. Reports of fatigue were higher in iTRE versus CR and standard care, whereas reports of constipation and headache were higher in iTRE and CR versus standard care. In conclusion, incorporating advice for meal timing with prolonged fasting led to greater improvements in postprandial glucose metabolism in adults at increased risk of developing type 2 diabetes. ClinicalTrials.gov identifier NCT03689608 .

Reproducibility and determinants of the metabolic responses during a mixed-meal tolerance test

OBJECTIVE

The aim of this study was to assess the reproducibility and physiological determinants of mixed-meal tolerance tests (MMTTs) on glucose and insulin responses.

METHODS

While inpatients on a weight-maintaining diet, 894 individuals (574 with normal and 267 with impaired glucose regulation and 53 with type 2 diabetes [T2D]) underwent 9-hour MMTTs (breakfast and lunch; 30% weight-maintaining diet each; 40% carbohydrate, 40% fat, and 20% protein). Total/incremental areas under the curve (AUC/iAUC) were calculated from MMTT plasma glucose/insulin concentrations. Acute insulin response (AIR) was quantified by intravenous glucose tolerance test and insulin action (M) via hyperinsulinemic-euglycemic clamp. A subset had repeat MMTTs (median follow-up = 1.4 years).

RESULTS

In individuals without T2D, for breakfast-versus-lunch reproducibility of glucose, AUCs were moderate (intraclass correlation coefficients [ICCs]: 0.44-0.61), and iAUCs were poor (ICCs < 0.15). For repeated MMTTs, reproducibility of AUC/iAUCs was low (ICCs: 0.11-0.36). For insulin, AUC reproducibility was high (ICCs > 0.70), and iAUCs were moderate (ICCs: 0.64-0.71). For repeated MMTTs, ICC AUC/iAUCs were 0.34 to 0.54. In those with T2D, ICC glucose AUC/iAUCs were >0.80 and >0.50, respectively, and for insulin were <0.40. For repeated MMTTs, ICC glucose/insulin AUC/iAUCs were moderate. Glucose AUCs associated with M/AIR (partial Rs < -0.25), and insulin AUCs negatively/positively associated with M/AIR (partial Rs = -0.51/0.24).

CONCLUSIONS

Reproducibility of glucose/insulin responses to MMTTs varied by subtraction of fasting values, glucose status, and time. Insulin secretion and action explained ~20% of MMTT responses. The substantial variability in MMTT response requires consideration in studies using MMTT outcomes.

Visceral fat correlates with insulin secretion and sensitivity independent of BMI and subcutaneous fat in Chinese with type 2 diabetes

AIM

Clinical heterogeneity exists in overall obesity and abdominal obesity in terms of insulin secretion and sensitivity. Further, the impact of visceral fat (VF) on the first- and second-phase insulin secretion (FPIS and SPIS) is controversial. We aim to investigate insulin secretion and sensitivity in Chinese patients with T2DM according to different BMI and VF levels.

METHODS

This study enrolled 300 participants. A dual bioelectrical impedance analyzer was used to assess the visceral and subcutaneous fat area (VFA and SFA). VF levels were categorized as normal or high, with the cutoff value of 100 cm². FPIS and SPIS were evaluated by arginine stimulation test and standardized steamed bread meal tolerance test, respectively. β-cell function (HOMA2-β), insulin resistance (HOMA2-IR), and Gutt's insulin sensitivity index (Gutt-ISI) were also calculated. Spearman's correlation analysis and multivariate linear regression analysis were adopted for statistical analysis.

RESULTS

Participants were categorized into four groups: normal weight-normal VF, normal weight-high VF, overweight/obese-normal VF and overweight/obese-high VF. Multivariate linear regression showed that both VFA and SFA were correlated with FPIS, HOMA2-IR and Gutt-ISI after controlling for gender and diabetes duration. After further adjustment for BMI and VFA, some associations of SFA with insulin secretion and sensitivity disappeared. After adjustment for gender, diabetes duration, BMI and SFA, VFA was positively correlated with FPIS, SPIS and HOMA2-IR. Subjects with overweight/obese-high VF were more likely to have higher FPIS, HOMA2-IR and lower Gutt-ISI (all p < 0.05).

CONCLUSION

VF affects both FPIS and SPIS, and worsens insulin sensitivity independent of BMI and subcutaneous fat in Chinese patients with T2DM.

CLINICAL TRIAL REGISTRATION

http://www.chictr.org.cn, identifier ChiCTR2200062884.

Differential contribution of alpha and beta cell dysfunction to impaired fasting glucose and impaired glucose tolerance

AIMS/HYPOTHESIS

People with isolated impaired fasting glucose (IFG) have normal beta cell function. We hypothesised that an increased glucose threshold for beta cell secretion explains IFG.

METHODS

We used graded glucose infusion to examine the relationship of insulin secretion rate (ISR) and glucagon secretion rate (GSR) with rising glucose. We studied 39 non-diabetic individuals (53 ± 2 years, BMI 30 ± 1 kg/m2), categorised by fasting glucose and glucose tolerance status. After an overnight fast, a variable insulin infusion was used to maintain glucose at ~4.44 mmol/l (07:00 to 08:30 hours). At 09:00 hours, graded glucose infusion commenced at 1 mg kg-1 min-1 and doubled every 60 min until 13:00 hours. GSR and ISR were calculated by nonparametric deconvolution from concentrations of glucagon and C-peptide, respectively.

RESULTS

The relationship of ISR with glucose was linear and the threshold for insulin secretion in isolated IFG did not differ from that in people with normal fasting glucose and normal glucose tolerance. GSR exhibited a single-exponential relationship with glucose that could be characterised by G50, the change in glucose necessary to suppress GSR by 50%. G50 was increased in IFG compared with normal fasting glucose regardless of the presence of impaired or normal glucose tolerance.

CONCLUSIONS/INTERPRETATION

These data show that, in non-diabetic humans, alpha cell dysfunction contributes to the pathogenesis of IFG independently of defects in insulin secretion. We also describe a new index that quantifies the suppression of glucagon secretion by glucose.

Prediction of subclinical atherosclerosis in low Framingham risk score individuals by using the metabolic syndrome criteria and insulin sensitivity index

Background

Subclinical atherosclerosis can be present in individuals with an optimal cardiovascular risk factor profile. Traditional risk scores such as the Framingham risk score do not adequately capture risk stratification in low-risk individuals. The aim of this study was to determine if markers of metabolic syndrome and insulin resistance can better stratify low-risk individuals.

Methods

A cross-sectional study of 101 healthy participants with a low Framingham risk score and no prior morbidities was performed to assess prevalence of subclinical atherosclerosis using computed tomography (CT) and ultrasound. Participants were compared between groups based on Metabolic Syndrome (MetS) and Insulin-Sensitivity Index (ISI-cal) scores.

Results

Twenty three individuals (23%) had subclinical atherosclerosis with elevated CT Agatston score ≥1. Presence of both insulin resistance (ISI-cal <9.23) and fulfillment of at least one metabolic syndrome criterion denoted high risk, resulting in significantly improved AUC (0.706 95%CI 0.588–0.822) over the Framingham risk score in predicting elevated CT Agatston score ≥1, with net reclassification index of 50.9 ± 23.7%. High-risk patients by the new classification also exhibited significantly increased carotid intima thickness.

Conclusions

The overlap of insulin resistance and presence of ≥1 criterion for metabolic syndrome may play an instrumental role in identifying traditionally low-risk individuals predisposed to future risk of atherosclerosis and its sequelae.

GLP-1 Receptor Blockade Reduces Stimulated Insulin Secretion in Fasted Subjects With Low Circulating GLP-1

CONTEXT

Glucagon-like peptide 1 (GLP-1), an insulinotropic peptide released into the circulation from intestinal enteroendocrine cells, is considered a hormonal mediator of insulin secretion. However, the physiological actions of circulating GLP-1 have been questioned because of the short half-life of the active peptide. Moreover, there is mounting evidence for localized, intra-islet mediation of GLP-1 receptor (GLP-1r) signaling including a role for islet dipeptidyl-peptidase 4 (DPP4).

OBJECTIVE

To determine whether GLP-1r signaling contributes to insulin secretion in the absence of enteral stimulation and increased plasma levels, and whether this is affected by DPP4.

METHODS

Single-site study conducted at an academic medical center of 20 nondiabetic subjects and 13 subjects with type 2 diabetes. This was a crossover study in which subjects received either a DPP4 inhibitor (DPP4i; sitagliptin) or placebo on 2 separate days. On each day they received a bolus of intravenous (IV) arginine during sequential 60-minute infusions of the GLP-1r blocker exendin[9-39] (Ex-9) and saline. The main outcome measures were arginine-stimulated secretion of C-Peptide (C-PArg) and insulin (InsArg).

RESULTS

Plasma GLP-1 remained at fasting levels throughout the experiments and IV arginine stimulated both α- and β-cell secretion in all subjects. Ex-9 infusion reduced C-PArg in both the diabetic and nondiabetic groups by ~14% (P < .03 for both groups). Sitagliptin lowered baseline glycemia but did not affect the primary measures of insulin secretion. However, a significant interaction between sitagliptin and Ex-9 suggested more GLP-1r activation with DPP4i treatment in subjects with diabetes.

CONCLUSION

GLP-1r activation contributes to β-cell secretion in diabetic and nondiabetic people during α-cell activation, but in the absence of increased circulating GLP-1. These results are compatible with regulation of β-cells by paracrine signals from α-cells. This process may be affected by DPP4 inhibition.

Fu Brick Tea Manages HFD/STZ-Induced Type 2 Diabetes by Regulating the Gut Microbiota and Activating the IRS1/PI3K/Akt Signaling Pathway

The antidiabetic effects of Fu brick tea aqueous extract (FTE) and its underlying molecular mechanism in type 2 diabetes mellitus (T2DM) mice were investigated. FTE treatment significantly relieved dyslipidemia, insulin resistance (IR), and hepatic oxidative stress caused by T2DM. FTE also ameliorated the T2DM-induced gut dysbiosis by decreasing the Firmicutes/Bacteroidota (F/B) ratio at the phylum level and promoting the proliferation of Bifidobacterium, Parabacteroides, and Roseburia at the genus level. Besides, FTE significantly improved colonic short-chain fatty acid levels of T2DM mice. Furthermore, the antidiabetic effects of FTE were proved to be mediated by the IRS1/PI3K/Akt and AMPK-mediated gluconeogenesis signaling pathways. Metabolomics analysis illustrated that FTE recovered the levels of 28 metabolites associated with T2DM to the levels of normal mice. Taken together, these findings suggest that FTE can alleviate T2DM by reshaping the gut microbiota, activating the IRS1/PI3K/Akt pathway, and regulating intestinal metabolites.

The β-cell glucose toxicity hypothesis: Attractive but difficult to prove

β cells in the hyperglycemic environment of diabetes have marked changes in phenotype and function that are largely reversible if glucose levels can be returned to normal. A leading hypothesis is that these changes are caused by the elevated glucose levels leading to the concept of glucose toxicity. Support for the glucose toxicity hypothesis is largely circumstantial, but little progress has been made in defining the responsible mechanisms. Then questions emerge that are difficult to answer. In the very earliest stages of diabetes development, there is a dramatic loss of glucose-induced first-phase insulin release (FPIR) with only trivial elevations of blood glucose levels. A related question is how impaired insulin action on target tissues such as liver, muscle and fat can cause increased insulin secretion. The existence of a sophisticated feedback mechanism between insulin secretion and insulin action on peripheral tissues driven by glucose has been postulated, but it has been difficult to measure increases in blood glucose levels that might have been expected. These complexities force us to challenge the simplicity of the glucose toxicity hypothesis and feedback mechanisms. It may turn out that glucose is somehow driving all of these changes, but we must develop new questions and experimental approaches to test the hypothesis.

Danuglipron (PF-06882961) in type 2 diabetes: a randomized, placebo-controlled, multiple ascending-dose phase 1 trial

Agonism of the glucagon-like peptide-1 receptor (GLP-1R) results in glycemic lowering and body weight loss and is a therapeutic strategy to treat type 2 diabetes (T2D) and obesity. We developed danuglipron (PF-06882961), an oral small-molecule GLP-1R agonist and found it had comparable efficacy to injectable peptidic GLP-1R agonists in a humanized mouse model. We then completed a placebo-controlled, randomized, double-blind, multiple ascending-dose phase 1 study ( NCT03538743 ), in which we enrolled 98 patients with T2D on background metformin and randomized them to receive multiple ascending doses of danuglipron or placebo for 28 d, across eight cohorts. The primary outcomes were assessment of adverse events (AEs), safety laboratory tests, vital signs and 12-lead electrocardiograms. Most AEs were mild, with nausea, dyspepsia and vomiting most commonly reported. There were no clinically meaningful AEs in laboratory values across groups. Heart rate generally increased with danuglipron treatment at day 28, but no heart-rate AEs were reported. Systolic blood pressure was slightly decreased and changes in diastolic blood pressure were similar with danuglipron treatment at day 28, compared with placebo. There were no clinically meaningful electrocardiogram findings. In this study in T2D, danuglipron was generally well tolerated, with a safety profile consistent with the mechanism of action of GLP-1R agonism.

Effects of mixed meal tolerance test on gastric emptying, glucose and lipid homeostasis in obese nonhuman primates

Meal ingestion elicits a variety of neuronal, physiological and hormonal responses that differ in healthy, obese or diabetic individuals. The mixed meal tolerance test (MMTT) is a well-established method to evaluate pancreatic β-cell reserve and glucose homeostasis in both preclinical and clinical research in response to calorically defined meal. Nonhuman primates (NHPs) are highly valuable for diabetic research as they can naturally develop type 2 diabetes mellitus (T2DM) in a way similar to the onset and progression of human T2DM. The purpose of this study was to investigate the reproducibility and effects of a MMTT containing acetaminophen on plasma glucose, insulin, C-peptide, incretin hormones, lipids, acetaminophen appearance (a surrogate marker for gastric emptying) in 16 conscious obese cynomolgus monkeys (Macaca fascicularis). Plasma insulin, C-peptide, TG, aGLP-1, tGIP, PYY and acetaminophen significantly increased after meal/acetaminophen administration. A subsequent study in 6 animals showed that the changes of plasma glucose, insulin, C-peptide, lipids and acetaminophen were reproducible. There were no significant differences in responses to the MMTT among the obese NHPs with (n = 11) or without (n = 5) hyperglycemia. Our results demonstrate that mixed meal administration induces significant secretion of several incretins which are critical for maintaining glucose homeostasis. In addition, the responses to the MMTTs are reproducible in NHPs, which is important when the MMTT is used for evaluating post-meal glucose homeostasis in research.

Acute and long-term disruption of glycometabolic control after SARS-CoV-2 infection

Patients with coronavirus disease 2019 (COVID-19) are reported to have a greater prevalence of hyperglycaemia. Cytokine release as a consequence of severe acute respiratory syndrome coronavirus 2 infection may precipitate the onset of metabolic alterations by affecting glucose homeostasis. Here we describe abnormalities in glycometabolic control, insulin resistance and beta cell function in patients with COVID-19 without any pre-existing history or diagnosis of diabetes, and document glycaemic abnormalities in recovered patients 2 months after onset of disease. In a cohort of 551 patients hospitalized for COVID-19 in Italy, we found that 46% of patients were hyperglycaemic, whereas 27% were normoglycaemic. Using clinical assays and continuous glucose monitoring in a subset of patients, we detected altered glycometabolic control, with insulin resistance and an abnormal cytokine profile, even in normoglycaemic patients. Glycaemic abnormalities can be detected for at least 2 months in patients who recovered from COVID-19. Our data demonstrate that COVID-19 is associated with aberrant glycometabolic control, which can persist even after recovery, suggesting that further investigation of metabolic abnormalities in the context of long COVID is warranted.

Impact of mixed meal tolerance test composition on measures of beta-cell function in type 2 diabetes

Background

Application of mixed meal tolerance tests (MMTT) to measure beta-cell function in long-term studies is limited by modification of the commercial products occurring over time. This study assessed the intra-individual reliability of MMTTs and compared the effects of liquid meals differing in macronutrient composition on the estimation of beta-cell function in type 2 diabetes (T2DM).

Methods

To test the reliability of MMTTs, 10 people with T2DM (age 58 ± 11 years, body mass index 30.0 ± 4.9 kg/m²) received Boost®high Protein 20 g protein three times. For comparing different meals, another 10 persons with T2DM (58 ± 5 years, 31.9 ± 5.3 kg/m²) ingested either Boost®high Protein 20 g protein or the isocaloric Boost®high Protein 15 g protein containing 35% less protein and 18% more carbohydrates. C-peptide, insulin and glucose release were assessed from the incremental area under the concentration time curve (iAUC) and the intra- and inter-individual variation of these parameters from the coefficients of variations (CV).

Results

Repetitive ingestion of one meal revealed intra-individual CVs for the iAUCs of C-peptide, insulin and glucose, which were at least 3-times lower than the inter-individual variation of these parameters (18.2%, 19.7% and 18.9% vs. 74.2%, 70.5% and 207.7%) indicating a good reliability. Ingestion of two different meals resulted in comparable intra-individual CVs of the iAUCs of C-peptide and insulin (16.9%, 20.5%).

Conclusion

MMTTs provide reliable estimation of beta-cell function in people with T2DM. Furthermore, moderate differences in the protein and carbohydrate contents in a standardized liquid meal do not result in relevant changes of C-peptide and insulin responses.

Trial registration: Clinicaltrials.gov, Identifier number: NCT01055093. Registered 22 January 2010 – Retrospectively registered, https://www.clinicaltrials.gov/ct2/show/study/NCT01055093

Post-Hoc Analysis of a Randomized, Double Blind, Prospective Study at the University of Chicago: Additional Standardizations of Trial Protocol are Needed to Evaluate the Effect of a CXCR1/2 Inhibitor in Islet Allotransplantation

A recent randomized, multicenter trial did not show benefit of a CXCR1/2 receptor inhibitor (Reparixin) when analysis included marginal islet mass (>3,000 IEQ/kg) for allotransplantation and when immunosuppression regimens were not standardized among participating centers. We present a post-hoc analysis of trial patients from our center at the University of Chicago who received an islet mass of over 5,000 IEQ/kg and a standardized immunosuppression regimen of anti-thymocyte globulin (ATG) for induction. Twelve islet allotransplantation (ITx) recipients were randomized (2:1) to receive Reparixin (N = 8) or placebo (N = 4) in accordance with the multicenter trial protocol. Pancreas and donor characteristics did not differ between Reparixin and placebo groups. Five (62.5%) patients who received Reparixin, compared to none in the placebo group, achieved insulin independence after only one islet infusion and remained insulin-free for over 2 years (P = 0.08). Following the first ITx with ATG induction, distinct cytokine, chemokine, and miR-375 release profiles were observed for both the Reparixin and placebo groups. After excluding procedures with complications, islet engraftment on post-operative day 75 after a single transplant was higher in the Reparixin group (n = 7) than in the placebo (n = 3) group (P = 0.03) when islet graft function was measured by the ratio of the area under the curve (AUC) for c-peptide to glucose in mixed meal tolerance test (MMTT). Additionally, the rate of engraftment was higher when determined via BETA-2 score instead of MMTT (P = 0.01). Our analysis suggests that Reparixin may have improved outcomes compared to placebo when sufficient islet mass is transplanted and when standardized immunosuppression with ATG is used for induction. However, further studies are warranted. Investigation of Reparixin and other novel agents under more standardized and optimized conditions would help exclude confounding factors and allow for a more definitive evaluation of their role in improving outcomes in islet transplantation. Clinical trial reg. no. NCT01817959, clinicaltrials.gov.

The effects of ertugliflozin on β-cell function: Pooled analysis from four phase 3 randomized controlled studies

AIM

To identify potential predictors and mediators of changes in β-cell function in response to ertugliflozin treatment in people with type 2 diabetes mellitus (T2DM).

PARTICIPANTS AND METHODS

Data from patients with T2DM randomized to ertugliflozin (5 or 15 mg; observations from both doses were pooled) or placebo in four phase 3 clinical studies (clinicaltrials.gov: NCT01958671, NCT02226003, NCT02036515, NCT02099110) were pooled and analysed. Change from baseline in β-cell function at week 26 was assessed, and its potential predictors and mediators were analysed using linear and multiple regression analyses.

RESULTS

Compared with placebo, ertugliflozin improved β-cell function when assessed by mean percent change from baseline in homeostatic model assessment of β-cell function (HOMA-%β; ertugliflozin: 14.7%, 95% confidence interval [CI] 12.3, 17.1; placebo: -0.4%, 95% CI -3.4, 2.5], but not when assessed by change in C-peptide index following a mixed meal tolerance test. Change in HOMA-%β correlated with change from baseline in glycated haemoglobin (HbA1c) and treatment with ertugliflozin, and weakly with change from baseline in body weight. In the ertugliflozin group, change in HOMA-%β correlated with baseline fasting plasma glucose (FPG; r = 0.235, P < 0.001), baseline HbA1c (r = 0.138, P < 0.001), baseline homeostatic model assessment of insulin resistance (HOMA-IR; r = 0.162, P < 0.01), and baseline HOMA-%β (r = -0.321, P < 0.001) in linear regression analyses. Multiple regression analyses yielded similar results.

DISCUSSION

In people with T2DM, ertugliflozin treatment improved fasting β-cell function, but no effect on postprandial β-cell function was observed in this analysis. Improvement in HOMA-%β was predicted by high baseline FPG, HbA1c, HOMA-IR, and low baseline HOMA-%β, and mediated by ertugliflozin treatment, and improved HbA1c and body weight.

Population insulin sensitivity from sparsely sampled oral glucose tolerance tests

OBJECTIVE

This work aimed to estimate population-level insulin sensitivity (S_I) from 2-hour oral glucose tolerance tests (OGTT) with less than 7 samples.

RESEARCH DESIGN AND METHODS

The current methodology combines the OGTT mathematical model developed by Dalla Man et al., with nonlinear multilevel (NLML) statistical model to estimate population-level insulin sensitivity (S_I) from sparsely sampled datasets (3 or 4 samples per subject obtained in 120 min). To validate our novel methodology of population S_I estimation, we simulated 50 virtual subjects. We simulated 10 observations per subject over 240 minutes. After estimating their S_I using the OGTT model, the virtual subjects were split into two groups, subjects with S_I above the average and ones with below average. Subsequently, the simulated data were analyzed using statistical software and employing a t-test. The mean estimates of population S_I for the two groups of virtual subjects and their respective 95% CI were compared to the estimates obtained with our novel NLML group S_I estimates obtained using the 3 and 4 time points per subject. To further validate the performance of the novel NLML model, a set of 34 prediabetic and 30 diabetic subjects with T2D was used. As outlined above for the in-silico subjects, differences between the prediabetic and T2D subjects in regard to S_I was assessed using the classical two-stage approach (individual S_I estimation followed by statistical comparison of the two groups). The average estimates obtained with the classical two-stage approach were compared to the group estimated obtained with the NLML approach using 3 (0, 60, and 120 minutes) points per subject obtained in 120 minutes.

RESULTS

Unique and identifiable individual estimates of S_I were obtained for all virtual subjects. In comparison to the subjects with above average S_I (n=25), the subjects with simulated below average S_I (n=25) exhibited significantly lower insulin sensitivity (P<0.001). Our novel NLML population model confirmed these findings (4-point OGTT: P<0.001; 3-point OGTT: P<0.001). In a similar fashion to the one outlined for the virtual subjects, the median insulin sensitivities estimated with the classical two-stage approach were different between the prediabetic (n=34) and T2D subjects (n=32, P=0.004). Using 3 points per subject, our novel NLML model confirmed these findings (P<0.001).

CONCLUSIONS

The population estimates of S_I from OGTT data is an effective tool to assess population insulin sensitivity and assess differences that may not be possible when calculating individual S_I or when less than 7 samples are available.

Alterations in Enteroendocrine Hormones After Total Pancreatectomy With Islet Autotransplantation

OBJECTIVE

When total pancreatectomy with islet autotransplantation (TPIAT) is performed for chronic pancreatitis, the pancreas and most of the duodenum are removed, with Roux-en-Y reconstruction of the gastrointestinal tract. Enteroendocrine cells in the intestines and pancreas secrete hormones coordinating digestion and motility, but anatomic reconstruction alters transit of nutrients to these cells. We hypothesized that TPIAT leads to changes in enteroendocrine hormones.

METHODS

Glucagon-like peptide 1 (GLP-1), peptide YY (PYY), and pancreatic polypeptide (PP) were measured from mixed-meal tolerance tests of 34 clinical trial participants before and 18 months after TPIAT. Area under the curve of GLP-1 and PYY-stimulated responses were calculated by trapezoidal method, and the PP response was measured as the stimulated max minus baseline (ΔPP).

RESULTS

Area under the curve of GLP-1 and PYY increased significantly after TPIAT (GLP-1 average +553.1 pg/mL per minute, P = 0.004; PYY average +4647.9 pg/mL per minute, P = 0.02). ΔPP trended toward lower after TPIAT (average, -52.2 pg/mL, P = 0.06).

CONCLUSIONS

In this novel study of enteroendocrine hormones in TPIAT patients, stimulated levels of GLP-1 and PYY were significantly higher after versus before TPIAT. ΔPP was lower after TPIAT, but not significantly. These hormone changes have potential clinical implications that warrant further research.

Diabetes-associated genetic variation in TCF7L2 alters pulsatile insulin secretion in humans

BACKGROUNDMetabolic disorders such as type 2 diabetes have been associated with a decrease in insulin pulse frequency and amplitude. We hypothesized that the T allele at rs7903146 in TCF7L2, previously associated with β cell dysfunction, would be associated with changes in these insulin pulse characteristics.METHODSTwenty-nine nondiabetic subjects (age 46 ± 2, BMI 28 ± 1 kg/m2) participated in this study. Of these, 16 were homozygous for the C allele at rs7903146 and 13 were homozygous for the T allele. Deconvolution of peripheral C-peptide concentrations allowed the reconstruction of portal insulin secretion over time. These data were used for subsequent analyses. Pulse orderliness was assessed by approximate entropy (ApEn), and the dispersion of insulin pulses was measured by a frequency dispersion index (FDI) after a Fast Fourier Transform (FFT) of individual insulin secretion rates.RESULTSDuring fasting conditions, the CC genotype group exhibited decreased pulse disorderliness compared with the TT genotype group (1.10 ± 0.03 vs. 1.19 ± 0.04, P = 0.03). FDI decreased in response to hyperglycemia in the CC genotype group, perhaps reflecting less entrainment of insulin secretion during fasting.CONCLUSIONDiabetes-associated variation in TCF7L2 is associated with decreased orderliness and pulse dispersion, unchanged by hyperglycemia. Quantification of ApEn and FDI could represent novel markers of β cell health.FUNDINGThis work was funded by US NIH (DK78646, DK116231), University of Padova research grant CPDA145405, and Mayo Clinic General Clinical Research Center (UL1 TR000135).

Impact of acute-phase insulin secretion on glycemic variability in insulin-treated patients with type 2 diabetes

AIMS

The association between β-cell function and glycemic variability remains to be clarified in insulin-treated patients with type 2 diabetes. Therefore, the study sought to examine the association of various indices of β-cell function with glycemic variability in Chinese insulin-treated patients with type 2 diabetes.

METHODS

Glycemic variability was assessed by the coefficient of variation (CV) of glucose levels with the use of continuous glucose monitoring (CGM). Basal β-cell function was evaluated by fasting C-peptide (FCP) and the homeostasis model assessment 2 for β-cell function (HOMA2-%β). Postload β-cell function was measured by 2-hour C-peptide (2hCP) and the acute C-peptide response (ACPR) to arginine.

RESULTS

When a cutoff value of CV ≥ 36% was used to define unstable glucose, the multivariable-adjusted odds ratios for labile glycemic control were 0.34 (95% CI 0.18-0.64) for each 1 ng/mL increase in ACPR, 0.47 (95% CI 0.27-0.81) for each 1 ng/mL increase in FCP, 0.77 (95% CI 0.61-0.97) for each 1 ng/mL increase in 2hCP, and 1.00 (95% CI 0.98-1.01) for each 1% increase in HOMA2-%β. When we further adjusted for 2hCP and HOMA2-%β in the ACPR and FCP analyses, and adjusted for ACPR or FCP in the 2hCP analyses, only ACPR but not FCP or 2hPC remained to be a significant and inverse predictor for labile glycemic control.

CONCLUSIONS

ACPR evaluated by the arginine stimulation test may be superior to other commonly used β-cell function parameters to reflect glycemic fluctuation in insulin-treated patients with type 2 diabetes.

Human Physiology of Genetic Defects Causing Beta-cell Dysfunction

The last decade has revealed hundreds of genetic variants associated with type 2 diabetes, many especially with insulin secretion. However, the evidence for their single or combined effect on beta-cell function relies mostly on genetic association of the variants or genetic risk scores with simple traits, and few have been functionally fully characterized even in cell or animal models. Translating the measured traits into human physiology is not straightforward: none of the various indices for beta-cell function or insulin sensitivity recapitulates the dynamic interplay between glucose sensing, endogenous glucose production, insulin production and secretion, insulin clearance, insulin resistance-to name just a few factors. Because insulin sensitivity is a major determinant of physiological need of insulin, insulin secretion should be evaluated in parallel with insulin sensitivity. On the other hand, multiple physiological or pathogenic processes can either mask or unmask subtle defects in beta-cell function. Even in monogenic diabetes, a clearly pathogenic genetic variant can result in different phenotypic characteristics-or no phenotype at all. In this review, we evaluate the methods available for studying beta-cell function in humans, critically examine the evidence linking some identified variants to a specific beta-cell phenotype, and highlight areas requiring further study.

Clinical Utility of the Meal Tolerance Test in the Care of Patients with Type 2 Diabetes Mellitus

Objective The measurement of C-peptide immunoreactivity (CPR) is essential for evaluating the pancreatic β-cell function and selecting appropriate therapeutic agents in patients with diabetes mellitus. The meal tolerance test (MTT) is simple to administer physiological insulin-stimulating test. Previous studies have reported that several CPR-related indices are useful markers for predicting insulin requirement in type 2 diabetes. In the present study, we investigated the serum CPR response during the MTT in hospitalized patients with type 2 diabetes mellitus in order to clarify the clinical utility of the MTT. Methods We performed the MTT using a test meal with timed measurements of the serum CPR level based on the oral glucose tolerance test over 180 minutes and tested the correlation of various CPR-related indices and clinical factors in patients with type 2 diabetes mellitus. Patients The subjects were patients with type 2 diabetes mellitus who had been admitted to our hospital for diabetes management and education. The final study population consisted of 68 patients. Results The fasting CPR level was correlated with the 24-hour urinary CPR excretion and body mass index. The serum CPR level at 120 minutes in the MTT was strongly correlated with the area under the curve of CPR during the MTT. The patients who needed insulin therapy at 6 months after hospitalization showed a significant lower incremental CPR value from 0 to 120 minutes in the MTT than those who did not need insulin therapy. Conclusion The plasma C-peptide levels at 0 and 120 minutes in the MTT provide essential information for the clinical management of patients with type 2 diabetes mellitus.

Influence of Diabetogenic Factors on Fasting and Postprandial Glucose Levels in Patients with Type 2 Diabetes Mellitus

Background: This study evaluated the relative influence of insulin resistance (IR), first-phase insulin secretion (FPIS), second-phase insulin secretion (SPIS), and glucose effectiveness (GE) in determining the difference between fasting plasma glucose (FPG) and postprandial plasma glucose (PPG) (ΔPG), in a Chinese population with type 2 diabetes (T2D) mellitus. Methods: In total, we enrolled 1213 participants with T2D (479 women). IR, FPIS, SPIS, and GE were estimated by using equations we built previously. ΔPG was defined as FPG - PPG. Results: The relative contribution of the four diabetogenic factors (DFs) was analyzed by multiple linear regression, and GE was the greatest contributor in the ΔPG value (β = 0.171, P < 0.001), whereas IR had the least influence on ΔPG (β = -0.040, P = 0.439). DFs were analyzed by using binary logistic regression to ascertain if ΔPG ≥0 (high fasting plasma glucose, HFG). Three models were built: Model 0: SPIS, Model 1: SPIS + FPIS, and Model 2: Model 1 + GE. Model 2 had the most accurate predictive power; the equation for Model 2 is P = 1/(1 - e^-x), where x = -11.88 + 312.89 × (GE) -1.22 × log(SPIS) +1.63 × log(FPIS). In this equation, P refers to the risk of HFG. Conclusions: For Chinese patients, GE had the most profound effect in determining ΔPG, followed by FPIS, SPIS, and IR. The model suggested that participants with high FPIS, SPIS, and GE would have a high incidence of HFG.

Utility of arginine stimulation testing in preoperative assessment of children undergoing total pancreatectomy with islet autotransplantation

Metabolic outcomes after total pancreatectomy with islet autotransplantation (TPIAT) are influenced by the islet mass transplanted. Preclinical and clinical studies indicate that insulin and C-peptide levels measured after intravenous administration of the beta cell secretagogue arginine can be used to estimate the available islet mass. We sought to determine if preoperative arginine stimulation test (AST) results predicted transplanted islet mass and metabolic outcomes in pediatric patients undergoing TPIAT. We evaluated the association of preoperative C-peptide and insulin responses to AST with islet isolation metrics using linear regression, and with postoperative insulin independence using logistic regression. Twenty-six TPIAT patients underwent preoperative AST from 2015 to 2018. The acute C-peptide response to arginine (ACRarg) was correlated with isolated islet equivalents (IEQ; r = 0.59, P = 0.002) and islet number (IPN; r = 0.48, P = 0.013). The acute insulin response to arginine (AIRarg) was not significantly correlated with IEQ (r = 0.38, P = 0.095) or IPN (r = 0.41, P = 0.071). Neither ACRarg nor AIRarg was associated with insulin use at 6 months postoperatively. Preoperative C-peptide response to arginine correlates with islet mass available for transplant in pediatric TPIAT patients. AST represents an additional tool before autotransplant to provide counseling on likely islet mass and to inform quality improvements of islet isolation techniques.

Contribution of pancreatic α-cell function to insulin sensitivity and glycemic variability in patients with type 1 diabetes

AIMS/INTRODUCTION

To evaluate the contribution of pancreatic α-cell function to the dawn phenomenon, insulin sensitivity, hepatic glucose uptake and glycemic variability in patients with type 1 diabetes.

MATERIALS AND METHODS

In 40 patients with type 1 diabetes, arginine stimulation tests were carried out, and the area under the curve (AUC) of glucagon was measured using radioimmunoassays (AUCglc RIA ) and enzyme-linked immunosorbent assays (AUCglc ELISA ). The ratio of the insulin dose delivered by an artificial pancreas to maintain euglycemia between 04.00 and 08.00 hours or between 00.00 and 04.00 hours was measured as the dawn index. The glucose infusion rate and hepatic glucose uptake were measured using hyperinsulinemic euglycemic clamp and clamp oral glucose loading tests. Glycemic variability in 96 h was measured by continuous glucose monitoring.

RESULTS

The median dawn index (1.7, interquartile range 1.0-2.8) was not correlated with AUCglc RIA (R2  = 0.03, P = 0.39) or AUCglc ELISA (R2  = 0.04, P = 0.32). The median glucose infusion rate (7.3 mg/kg/min, interquartile range 6.4-9.2 mg/kg/min) was significantly correlated with AUCglc RIA (R2  = 0.20, P = 0.02) and AUCglc ELISA (R2  = 0.21, P = 0.02). The median hepatic glucose uptake (65.3%, interquartile range 40.0-87.3%) was not correlated with AUCglc RIA (R2  = 0.07, P = 0.26) or AUCglc ELISA (R2  = 0.26, P = 0.79). The standard deviation of glucose levels measured by continuous glucose monitoring was significantly correlated with AUCglc RIA (R2  = 0.11, P = 0.049), but not with AUCglc ELISA (R2  = 0.01, P = 0.75).

CONCLUSIONS

Pancreatic α-cell function contributed to insulin sensitivity in patients with type 1 diabetes.

Decreased VMAT2 in the pancreas of humans with type 2 diabetes mellitus measured in vivo by PET imaging

AIMS/HYPOTHESIS

The progressive loss of beta cell function is part of the natural history of type 2 diabetes. Autopsy studies suggest that this is, in part, due to loss of beta cell mass (BCM), but this has not been confirmed in vivo. Non-invasive methods to quantify BCM may contribute to a better understanding of type 2 diabetes pathophysiology and the development of therapeutic strategies. In humans, the localisation of vesicular monoamine transporter type 2 (VMAT2) in beta cells and pancreatic polypeptide cells, with minimal expression in other exocrine or endocrine pancreatic cells, has led to its development as a measure of BCM. We used the VMAT2 tracer [¹⁸F]fluoropropyl-(+)-dihydrotetrabenazine to quantify BCM in humans with impaired glucose tolerance (prediabetes) or type 2 diabetes, and in healthy obese volunteers (HOV).

METHODS

Dynamic positron emission tomography (PET) data were obtained for 4 h with metabolite-corrected arterial blood measurement in 16 HOV, five prediabetic and 17 type 2 diabetic participants. Eleven participants (six HOV and five with type 2 diabetes) underwent two abdominal PET/computed tomography (CT) scans for the assessment of test-retest variability. Standardised uptake value ratio (SUVR) was calculated in pancreatic subregions (head, body and tail), with the spleen as a reference region to determine non-specific tracer uptake at 3-4 h. The outcome measure SUVR minus 1 (SUVR-1) accounts for non-specific tracer uptake. Functional beta cell capacity was assessed by C-peptide release following standard (arginine stimulus test [AST]) and acute insulin response to the glucose-enhanced AST (AIRargMAX). Pearson correlation analysis was performed between the binding variables and the C-peptide AUC post-AST and post-AIRargMAX.

RESULTS

Absolute test-retest variability (aTRV) was ≤15% for all regions. Variability and overlap of SUVR-1 was measured in all groups; HOV and participants with prediabetes and with type 2 diabetes. SUVR-1 showed significant positive correlations with AIRargMAX (all groups) in all pancreas subregions (whole pancreas p = 0.009 and pancreas head p = 0.009; body p = 0.019 and tail p = 0.023). SUVR-1 inversely correlated with HbA_1c (all groups) in the whole pancreas (p = 0.033) and pancreas head (p = 0.008). SUVR-1 also inversely correlated with years since diagnosis of type 2 diabetes in the pancreas head (p = 0.049) and pancreas tail (p = 0.035).

CONCLUSIONS/INTERPRETATION

The observed correlations of VMAT2 density in the pancreas and pancreas regions with years since diagnosis of type 2 diabetes, glycaemic control and beta cell function suggest that loss of BCM contributes to deficient insulin secretion in humans with type 2 diabetes.

Mixed Meal and Intravenous L-Arginine Tests Both Stimulate Incretin Release Across Glucose Tolerance in Man: Lack of Correlation with β Cell Function

BACKGROUND

The aims of this study were to 1. define the responses of glucagon-like peptide-1 (GLP-1), glucose-dependent insulinotropic polypeptide (GIP), glucagon, and peptide YY (PYY) to an oral meal and to intravenous L-arginine; and 2. examine correlation of enteroendocrine hormones with insulin secretion. We hypothesized a relationship between circulating incretin concentrations and insulin secretion.

METHODS

Subjects with normal glucose tolerance (NGT, n = 23), prediabetes (PDM, n = 17), or with type 2 diabetes (T2DM, n = 22) were studied twice, following a mixed test meal (470 kCal) (mixed meal tolerance test [MMTT]) or intravenous L-arginine (arginine maximal stimulation test [AST], 5 g). GLP-1 (total and active), PYY, GIP, glucagon, and β cell function were measured before and following each stimulus.

RESULTS

Baseline enteroendocrine hormones differed across the glucose tolerance (GT) spectrum, T2DM generally >NGT and PDM. In response to MMTT, total and active GLP-1, GIP, glucagon, and PYY increased in all populations. The incremental area-under-the-curve (0-120 min) of analytes like total GLP-1 were often higher in T2DM compared with NGT and PDM (35-51%; P < 0.05). At baseline glucose, L-arginine increased total and active GLP-1 and glucagon concentrations in all GT populations (all P < 0.05). As expected, the MMTT and AST provoked differential glucose, insulin, and C-peptide responses across GT populations. Baseline or stimulated enteroendocrine hormone concentrations did not consistently correlate with either measure of β cell function.

CONCLUSIONS/INTERPRETATION

Both MMTT and AST resulted in insulin and enteroendocrine hormone responses across GT populations without consistent correlation between release of incretins and insulin, which is in line with other published research. If a defect is in the enteroendocrine/β cell axis, it is probably reduced response to rather than diminished secretion of enteroendocrine hormones.

Total pancreaticoduodenectomy with autologous islet transplantation 14 years after liver-contained composite visceral transplantation

Chronic pancreatitis (CP) is a severely disabling disorder with potential detrimental effects on quality of life, gut function, and glucose homeostasis. Disease progression often results in irreversible morphological and functional abnormalities with development of chronic pain, mechanical obstruction, and pancreatic insufficiency. Along with comprehensive medical management, the concept of total pancreatectomy and islet autotransplantation (TP-AIT) was introduced 40 years ago for patients with intractable pain and preserved beta-cell function. With anticipated technical difficulties, total excision of the inflamed-disfigured gland is expected to alleviate the incapacitating visceral pain and correct other associated abdominal pathology. With retrieval of sufficient islet-cell mass, the autologous transplant procedure has the potential to maintain an euglycemic state without exogenous insulin requirement. The reported herein case of CP-induced recalcitrant pain and foregut obstruction is exceptional because of the technical challenges in performing native pancreaticoduodenectomy in close proximity to the composite visceral allograft with complex vascular and gut reconstructions. Equally novel is transplanting the auto-islets in the liver-contained visceral allograft. Despite intravenous nutrition shortly after birth, liver transplantation at age 13, retransplantation with liver-contained visceral allograft at age 17 and TP-AIT at age 31, the 38-year-old recipient is currently pain free with full nutritional autonomy and normal glucose homeostasis.

Outpatient versus inpatient mixed meal tolerance and arginine stimulation testing yields comparable measures of variability for assessment of beta cell function

Standard practice to minimize variability in beta cell function (BCF) measurement is to test in inpatient (IP) settings. IP testing strains trial subjects, investigators, and budgets. Outpatient (OP) testing may be a solution although there are few reports on OP BCF testing variability. We compared variability metrics between OP and IP from a standardized mixed meal tolerance test (MMTT) and arginine stimulation test (AST) in two separate type 2 diabetes (T2DM) cohorts (OP, n = 20; IP n = 22) in test-retest design. MMTT variables included: insulin sensitivity (Si); beta cell responsivity (Φtot); and disposition index (DItot = Si* Φtot) following 470 kCal meal. AST variables included: acute insulin response to arginine (AIRarg) and during hyperglycemia (AIRargMAX).

Results

Baseline characteristics were well-matched. Between and within subject variance for each parameter across cohorts, and intraclass correlation coefficients (ICC-a measure of reproducibility) across parameters were generally comparable for OP to IP. Table summarizes the ICC results for each key parameter and cohort.

Test/Parameter	Outpatient (95% CI)	Inpatient (95% CI)
MMTT: Si	0.49(0,0.69)	0.28(0,0.60)
MMTT: Φtot	0.65(0.16,0.89)	0.81(0.44,0.93)
MMTT: DI	0.67(0,0.83)	0.36(0,0.69)
AST: AIR Arg	0.96(0.88,0.98)	0.84(0.59,0.94)
AST: AIR Arg Max	0.97(0.90,0.99)	0.95(0.86,0.97)
AST: ISR	0.93(0.77,0.97)	0.93(0.82,0.96)

In conclusion, the variability (reproducibility) of BCF measures from standardized MMTT and AST is comparable between OP and IP settings. These observations have significant implications for complexity and cost of metabolic studies.

Insulin Resistance, Hyperinsulinemia, and LH: Relative Roles in Peripubertal Obesity-Associated Hyperandrogenemia

CONTEXT

Peripubertal obesity is associated with variable hyperandrogenemia, but precise mechanisms remain unclear.

OBJECTIVE

To assess insulin resistance, hyperinsulinemia, and LH roles in peripubertal obesity-associated hyperandrogenemia.

DESIGN

Cross-sectional analysis.

SETTING

Academic clinical research unit.

PARTICIPANTS

Eleven obese (body mass index for age ≥95%) peripubertal girls.

INTERVENTION

Blood samples were taken during a mixed-meal tolerance test (1900 to 2100), overnight (2100 to 0700), while fasting (0700 to 0900), and during an 80 mU/m2/min hyperinsulinemic-euglycemic clamp (0900 to 1100).

MAIN OUTCOME MEASURES

The dependent variable was morning free testosterone level; independent variables were insulin sensitivity index (ISI), estimated 24-hour insulin, and estimated 24-hour LH levels.

RESULTS

All participants demonstrated insulin resistance and hyperinsulinemia. ISI, but not estimated 24-hour insulin level, correlated positively with morning free testosterone level when correcting for estimated 24-hour LH level and Tanner stage (rs = 0.68, P = 0.046). The correlation between estimated 24-hour LH and free testosterone levels approached significance after adjusting for estimated 24-hour insulin level and Tanner stage (rs = 0.63, P = 0.067). Estimated 24-hour insulin level did not correlate with free testosterone level after adjusting for estimated 24-hour LH level and Tanner stage (rs = 0.47, P = 0.20).

CONCLUSION

In insulin-resistant obese girls with hyperinsulinemia, free testosterone levels correlated positively with insulin sensitivity and, likely, circulating LH concentrations but not with circulating insulin levels. In the setting of relatively uniform hyperinsulinemia, variable steroidogenic-cell insulin sensitivity may correlate with metabolic insulin sensitivity and contribute to variable free testosterone concentrations.

[Correlation between fasting C-peptide and serum uric acid in patients with type 2 diabetes mellitus]

OBJECTIVE

To explore the relationship between fasting C-peptide (F-CP) and serum uric acid (SUA) in patients with type 2 diabetes mellitus (T2DM).

METHODS

A total of 347 hospitalized patients with T2DM were stratified according to F-CP level to analyze the impact of increased F-CP levels on SUA level and the incidence of hyperuricemia (HUA). The patients with an elevated SUA level (>420 µmol/L) and a normal SUA level (≤420 µmol/L) were compared for general data, fasting C-peptide and other clinical indexes. Pearson or Spearman correlation analysis was used to analyze the correlation of SUA level with F-CP levels and other parameters. The risk factors of elevated SUA were analyzed by binary logistic regression, multiple regression analysis and hierarchical interaction analysis. The ROC curve was used to analyze the independent risk factors of elevated SUA and determine the corresponding cut-off values.

RESULTS

Compared with those with a normal SUA level, patients with elevated SUA had higher body mass index (BMI), waist-to-hip ratio, F-CP, postprandial 2hC peptide (2hP-CP), triglyceride (TG), homocysteine (HCY), serum creatinine (SCr) level (P<0.05), and a greater percentage of drinking (44.8% vs 32.6%, P=0.006), but had significantly lowered levels of HbA1c, high-density lipoprotein (HDL), and estimated glomerular filtration rate (eGFR) (P<0.05). SUA was found to be positively correlated with F-CP, 2hP-CP, BMI, waist-to-hip ratio, diastolic blood pressure, TG, HCY, SCr, smoking and drinking (P<0.05), and was negatively correlated with gender, age, age of disease onset, HbA1c, HDL and eGFR (P<0.05). SUA level and the incidence of hyperuricemia increasea significantly with F-CP level (P<0.05). F-CP was identified as an independent risk factor for elevated SUA, and gender did not affect the relationship between F-CP and SUA. ROC curve analysis showed that a F-CP level >1.260 ng/mL was associated with a significantly increased risk of hyperuricemia in T2DM patients.

CONCLUSION

F-CP is closely related with SUA and may be an independent risk factor of elevated SUA in patients with T2DM.

[Correlation between fasting C-peptide and serum uric acid in patients with type 2 diabetes mellitus]

OBJECTIVE

To explore the relationship between fasting C-peptide (F-CP) and serum uric acid (SUA) in patients with type 2 diabetes mellitus (T2DM).

METHODS

A total of 347 hospitalized patients with T2DM were stratified according to F-CP level to analyze the impact of increased F-CP levels on SUA level and the incidence of hyperuricemia (HUA). The patients with an elevated SUA level (>420 µmol/L) and a normal SUA level (≤420 µmol/L) were compared for general data, fasting C-peptide and other clinical indexes. Pearson or Spearman correlation analysis was used to analyze the correlation of SUA level with F-CP levels and other parameters. The risk factors of elevated SUA were analyzed by binary logistic regression, multiple regression analysis and hierarchical interaction analysis. The ROC curve was used to analyze the independent risk factors of elevated SUA and determine the corresponding cut-off values.

RESULTS

Compared with those with a normal SUA level, patients with elevated SUA had higher body mass index (BMI), waist-to-hip ratio, F-CP, postprandial 2hC peptide (2hP-CP), triglyceride (TG), homocysteine (HCY), serum creatinine (SCr) level (P<0.05), and a greater percentage of drinking (44.8% vs 32.6%, P=0.006), but had significantly lowered levels of HbA1c, high-density lipoprotein (HDL), and estimated glomerular filtration rate (eGFR) (P<0.05). SUA was found to be positively correlated with F-CP, 2hP-CP, BMI, waist-to-hip ratio, diastolic blood pressure, TG, HCY, SCr, smoking and drinking (P<0.05), and was negatively correlated with gender, age, age of disease onset, HbA1c, HDL and eGFR (P<0.05). SUA level and the incidence of hyperuricemia increasea significantly with F-CP level (P<0.05). F-CP was identified as an independent risk factor for elevated SUA, and gender did not affect the relationship between F-CP and SUA. ROC curve analysis showed that a F-CP level >1.260 ng/mL was associated with a significantly increased risk of hyperuricemia in T2DM patients.

CONCLUSION

F-CP is closely related with SUA and may be an independent risk factor of elevated SUA in patients with T2DM.

Performance of individually measured vs population-based C-peptide kinetics to assess β-cell function in the presence and absence of acute insulin resistance

AIMS

To compare the performance of population-based kinetics with that of directly measured C-peptide kinetics when used to calculate β-cell responsivity indices, and to study people with and without acute insulin resistance to ensure that population-based kinetics apply to all conditions where β-cell function is measured.

METHODS

Somatostatin was used to inhibit endogenous insulin secretion in 56 people without diabetes. Subsequently, a C-peptide bolus was administered and the changing concentrations were used to calculate individual kinetic measures of C-peptide clearance. In addition, the participants were studied on 2 occasions in random order using an oral glucose tolerance test (OGTT). On one occasion, free fatty acid elevation, to cause insulin resistance, was achieved by infusion of Intralipid + heparin. The Disposition Index (DI) was then estimated by the oral minimal model using either population-based or individual C-peptide kinetics.

RESULTS

There were marked differences in the exchange variables (k ₁₂ and k ₂₁ ) of the model describing C-peptide kinetics, but smaller differences in the fractional clearance; that is, the irreversible loss from the accessible compartment (k ₀₁ ), obtained from population-based estimates compared with experimental measurement. Because it is predominantly influenced by k ₀₁ , DI estimated using individual kinetics correlated well with DI estimated using population-based kinetics.

CONCLUSIONS

These data support the use of population-based measures of C-peptide kinetics to estimate β-cell function during an OGTT.

Efficacy and pharmacokinetics of subcutaneous exendin (9-39) in patients with post-bariatric hypoglycaemia

AIM

To evaluate the efficacy, pharmacokinetic (PK) profile and tolerability of subcutaneous (s.c.). exendin 9-39 (Ex-9) injection in patients with post-bariatric hypoglycaemia (PBH).

METHODS

Nine women who had recurrent symptomatic hypoglycaemia after undergoing Roux-en-Y gastric bypass were enrolled in this 2-part, single-blind, single-ascending-dose study. In Part 1, a single participant underwent equimolar low-dose intravenous (i.v.) vs s.c. Ex-9 administration; in Part 2, 8 participants were administered single ascending doses of s.c. Ex-9 during an oral glucose tolerance test (OGTT). Glycaemic, hormonal, PK and symptomatic responses were compared with those obtained during the baseline OGTT.

RESULTS

Although an exposure-response relationship was observed, all doses effectively prevented hyperinsulinaemic hypoglycaemia and improved associated symptoms. On average, the postprandial glucose nadir was increased by 66%, peak insulin was reduced by 57%, and neuroglycopenic symptoms were reduced by 80%. All doses were well tolerated with no treatment-emergent adverse events observed.

CONCLUSIONS

Injection s.c. of Ex-9 appears to represent a safe, effective and targeted therapeutic approach for treatment of PBH. Further investigation involving multiple doses with chronic dosing is warranted.

Review of methods for measuring β-cell function: Design considerations from the Restoring Insulin Secretion (RISE) Consortium

The Restoring Insulin Secretion (RISE) study was initiated to evaluate interventions to slow or reverse the progression of β-cell failure in type 2 diabetes (T2D). To design the RISE study, we undertook an evaluation of methods for measurement of β-cell function and changes in β-cell function in response to interventions. In the present paper, we review approaches for measurement of β-cell function, focusing on methodologic and feasibility considerations. Methodologic considerations included: (1) the utility of each technique for evaluating key aspects of β-cell function (first- and second-phase insulin secretion, maximum insulin secretion, glucose sensitivity, incretin effects) and (2) tactics for incorporating a measurement of insulin sensitivity in order to adjust insulin secretion measures for insulin sensitivity appropriately. Of particular concern were the capacity to measure β-cell function accurately in those with poor function, as is seen in established T2D, and the capacity of each method for demonstrating treatment-induced changes in β-cell function. Feasibility considerations included: staff burden, including time and required methodological expertise; participant burden, including time and number of study visits; and ease of standardizing methods across a multicentre consortium. After this evaluation, we selected a 2-day measurement procedure, combining a 3-hour 75-g oral glucose tolerance test and a 2-stage hyperglycaemic clamp procedure, augmented with arginine.

Adding to the spectrum of insulin sensitive populations for mixed meal tolerance test glucose reliability assessment

As a measure of insulin sensitivity, the mixed meal tolerance test (MMTT) is a simple technique that can provide robust results. The assay consists of examining plasma glucose, insulin and C-peptide prior to and following the consumption of a test meal. While this procedure has been used in clinical research for several years, there is no set standard protocol, and only until recently has the reliability of this assay been thoroughly evaluated in prediabetes and type 2 diabetes subjects. Interestingly, the results from this recent study demonstrated stronger MMTT reliability for the prediabetes and diabetes cohorts compared to obese controls. This finding suggests that the obese control group may have more inherent variability in glucose response during a meal challenge likely due to compensatory influences typically observed in non-diabetic insulin-resistant subjects. Furthermore, this study raises the question whether the MMTT assay is reliable in a non-obese cohort. Therefore, to promote the standardization of this technique and contribute to the band of insulin sensitive populations, we employed the same methodology and test meal as the reference study to evaluate the MMTT reliability in healthy and overweight men. Indeed, the interclass coefficient revealed high glucose response repeatability during the MMTT in insulin-sensitive men. Overall, the MMTT is a reliable test across a range of insulin sensitivity including healthy men. However, we propose further investigation may be required to fully define the utility of this methodology in obese non-diabetic insulin-resistant populations.