The oral minimal model method

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

Assessment of insulin secretion is key to diagnose postprandial hyperinsulinemic hypoglycemia (PHH), an increasingly recognized complication following bariatric surgery. To this end, the Oral C-peptide Minimal Model (OCMM) can be used. This usually requires fixing C-peptide (CP) kinetics to the ones derived from the Van Cauter population model (VCPM), which has never been validated in PHH individuals. The objective of this work was to test the validity of the OCMM coupled with the VCPM in PHH subjects and propose a method to overcome the observed limitations. Two cohorts of adults with PHH after gastric bypass (GB) underwent either a 75 g oral glucose (9F/3M; age=42±9 y; BMI=28.3±6.9 kg/m²) or a 60 g mixed-meal (7F/3M; age = 43 ± 11 y; BMI=27.5±4.2 kg/m²) tolerance test. The OCMM was identified on CP concentration data with CP kinetics fixed to VCPM (VC approach). In both groups, the VC approach underestimated CP-peak and overestimated CP-tail suggesting CP kinetics predicted by VCPM to be inaccurate in this population. Thus, the OCMM was identified using CP kinetics estimated from the data (DB approach) using a Bayesian Maximum a Posteriori estimator. CP data were well predicted in all the subjects using the DB approach, highlighting a significantly faster CP kinetics in patients with PHH compared to the one predicted by VCPM. Finally, a simulation study was used to validate the proposed approach. The present findings question the applicability of the VCPM in patients with PHH after GB and call for CP bolus experiments to develop a reliable CP kinetic model in this population.

Dipeptidyl-Peptidase-IV Inhibitors, Imigliptin and Alogliptin, Improve Beta-Cell Function in Type 2 Diabetes

OBJECTS

Imigliptin is a novel dipeptidyl peptidase-4 inhibitor. In the present study, we aimed to evaluate the effects of imigliptin and alogliptin on insulin resistance and beta-cell function in Chinese patients with type-2 diabetes mellitus (T2DM).

METHODS

A total of 37 Chinese T2DM patients were randomized to receive 25 mg imigliptin, 50 mg imigliptin, placebo, and 25 mg alogliptin (positive drug) for 13 days. Oral glucose tolerance tests were conducted at baseline and on day 13, followed by the oral minimal model (OMM).

RESULTS

Imigliptin or alogliptin treatment, compared with their baseline or placebo, was associated with higher beta-cell function parameters (φ_s and φ_tot) and lower glucose area under the curve (AUC) and postprandial glucose levels. The changes in the AUC for the glucose appearance rate between 0 and 120 min also showed a decrease in imigliptin or alogliptin groups. However, the insulin resistance parameter, fasting glucose, was not changed. For the homeostatic model assessment (HOMA-β and HOMA-IR) parameters or secretory units of islets in transplantation index (SUIT), no statistically significant changes were found both within treatments and between treatments.

CONCLUSIONS

After 13 days of treatment, imigliptin and alogliptin could decrease glycemic levels by improving beta-cell function. By comparing OMM with HOMA or SUIT results, glucose stimulation might be more sensitive for detecting changes in beta-cell function.

Assessment of individual and standardized glucagon kinetics in healthy humans

Impaired glucose tolerance arises out of impaired postprandial insulin secretion and delayed suppression of glucagon. These defects occur early and independently in the pathogenesis of prediabetes. Quantification of the contribution of α-cell dysfunction to glucose tolerance has been lacking because knowledge of glucagon kinetics in humans is limited. Therefore, in a series of experiments examining the interaction of glucagon suppression with insulin secretion we studied 51 nondiabetic subjects (age = 54 ± 13 yr, BMI = 28 ± 4 kg/m²). Glucose was infused to mimic the systemic appearance of an oral challenge. Somatostatin was used to inhibit endogenous hormone secretion. 120 min after the start of the experiment, glucagon was infused at 0.65 ng/kg/min. The rise in glucagon concentrations was used to estimate its kinetic parameters [volume of distribution (V_d), half-life (t_1/2), and clearance rate (CL)]. A single-exponential model provided the best fit for the data, and individualized kinetic parameters were estimated: V_d = 8.2 ± 2.7 L, t_1/2 = 4 ± 1.1 min, CL = 1.4 ± 0.33 L/min. Stepwise linear regression was used to correlate V_d with BMI and sex (R²_adj = 0.44), whereas CL similarly correlated with lean body mass or BSA (both R² = 0.28). This enabled the development of a population-based model using anthropometric characteristics to predict V_d and CL. These data demonstrate that it is feasible to derive glucagon kinetic parameters from anthropometric characteristics, thereby enabling quantitation of the rate of glucagon appearance in the systemic circulation in large populations.NEW & NOTEWORTHY State-of-the-art measurement of insulin secretion in humans is accomplished by deconvolution of peripheral C-peptide concentrations using population-derived parameters of C-peptide kinetics. In contrast, knowledge of the kinetic parameters of glucagon in humans is lacking so that measurement of glucagon secretion to date is largely qualitative. This series of experiments enabled measurement of glucagon kinetics in 51 subjects, and subsequently, stepwise linear regression was used to correlate these parameters with anthropometric characteristics. This enabled the development of a population-based model using anthropometric characteristics to predict the volume of distribution and the rate of clearance. This is a necessary first step in the development of a model to quantitate of glucagon secretion and action (and its contribution to glucose tolerance) in large populations.

Mathematical Modeling for the Physiological and Clinical Investigation of Glucose Homeostasis and Diabetes

Mathematical modeling in the field of glucose metabolism has a longstanding tradition. The use of models is motivated by several reasons. Models have been used for calculating parameters of physiological interest from experimental data indirectly, to provide an unambiguous quantitative representation of pathophysiological mechanisms, to determine indices of clinical usefulness from simple experimental tests. With the growing societal impact of type 2 diabetes, which involves the disturbance of the glucose homeostasis system, development and use of models in this area have increased. Following the approaches of physiological and clinical investigation, the focus of the models has spanned from representations of whole body processes to those of cells, i.e., from in vivo to in vitro research. Model-based approaches for linking in vivo to in vitro research have been proposed, as well as multiscale models merging the two areas. The success and impact of models has been variable. Two kinds of models have received remarkable interest: those widely used in clinical applications, e.g., for the assessment of insulin sensitivity and β-cell function and some models representing specific aspects of the glucose homeostasis system, which have become iconic for their efficacy in describing clearly and compactly key physiological processes, such as insulin secretion from the pancreatic β cells. Models are inevitably simplified and approximate representations of a physiological system. Key to their success is an appropriate balance between adherence to reality, comprehensibility, interpretative value and practical usefulness. This has been achieved with a variety of approaches. Although many models concerning the glucose homeostasis system have been proposed, research in this area still needs to address numerous issues and tackle new opportunities. The mathematical representation of the glucose homeostasis processes is only partial, also because some mechanisms are still only partially understood. For in vitro research, mathematical models still need to develop their potential. This review illustrates the problems, approaches and contribution of mathematical modeling to the physiological and clinical investigation of glucose homeostasis and diabetes, focusing on the most relevant and stimulating models.

Visual food cues decrease blood glucose and glucoregulatory hormones following an oral glucose tolerance test in normal-weight and obese men

Previous experiments of our group have demonstrated that preprandial processing of food cues attenuates postprandial blood glucose excursions. Here we systematically re-evaluated the glucose-lowering effect of visual food cues by submitting 40 healthy fasted men (20 normal-weight men, mean age 24.8 ± 3.7 years, BMI 21.9 ± 0.3 kg/m²; 20 obese men, 26.8 ± 4.2 years, 34.3 ± 1.3 kg/m²) to an oral glucose tolerance test (OGTT) following exposure to pictures of high-calorie food items versus neutral items. OGTT-related changes in blood concentrations of glucose and relevant glucoregulatory hormones including GLP-1 were assessed and analyzed according to the oral minimal model. Independent of body weight, food-cue compared to neutral stimulus presentation reduced postprandial concentrations of glucose (p = 0.041), insulin (p = 0.026) and C-peptide (p = 0.007); accordingly, oral minimal model analyses yielded a food-cue induced decrease of dynamic-phase insulin secretion (p = 0.036). We also observed a trend towards lower GLP-1 levels directly after food cue stimulation in both body weight groups (p = 0.057), as well as a trend towards decreased heart rate (p = 0.093) and significantly decreased diastolic blood pressure (p = 0.019). While we did not detect indicators of an early rise in insulin levels in terms of a 'cephalic phase insulin response', our findings support the assumption that preprandial processing of food cues exerts marked effect on postprandial glucose regulation, with possible contributions of changes in GLP-1. The mechanisms linking food cue exposure and glucoregulatory improvements should be investigated in greater detail, to potentially open new treatment options for metabolic dysfunctions.

Good agreement between hyperinsulinemic-euglycemic clamp and 2 hours oral minimal model assessed insulin sensitivity in adolescents

BACKGROUND/OBJECTIVE

Rates of dysglycemia are increasing in youth, secondary to obesity and decreased insulin sensitivity (IS) in puberty. The oral minimal model (OMM) has been developed in order to measure IS using an easy oral glucose load, such as an oral glucose tolerance test (OGTT), instead of an hyperinsulinemic-euglycemic clamp (HE-clamp), a more invasive and time-consuming procedure. However, this model, following a standard 2 hour- OGTT has never been validated in youth, a population known for a different physiologic response to OGTT than adults. Thus, we compared IS measurements obtained from OMM following a 2-hour OGTT to HE-clamp and isotope tracer-assessed tissue IS in adolescents. We also compared the liver/muscle-specific IS from HE-clamp with other liver/muscle-specific IS surrogates following an OGTT previously validated in adults.

METHODS

Secondary analysis of a cross-sectional study. Adolescent girls with (n = 26) and without (n = 7) polycystic ovary syndrome (PCOS) (14.6 ± 1.7 years; BMI percentile 23.3%-98.2%) underwent a 2-hour 75 g OGTT and a 4-phase HE-clamp. OMM IS (Si), dynamic Si (Si^d ) and other OGTT-derived muscle and liver IS indices were correlated with HE-clamp tissue-specific IS.

RESULTS

OMM Si and Si^d correlated with HE-clamp-measured peripheral IS (r = 0.64, P <.0001 and r = 0.73; P <.0001, respectively) and the correlation coefficient trended higher than the Matsuda index (r = 0.59; P =.003). The other tissue-specific indices were poorly correlated with their HE-clamp measurements.

CONCLUSION

In adolescent girls, the 2-hour OMM provided the best estimate of peripheral IS. Additional surrogates for hepatic IS are needed for youth.

A Reduced Incretin Effect Mediated by the rs7903146 Variant in the TCF7L2 Gene Is an Early Marker of β-Cell Dysfunction in Obese Youth

OBJECTIVE

The risk genotype for the common variant rs7903146 of the transcription factor 7-like-2 (TCF7L2) gene has been found to affect the incretin response in healthy and obese adults; however, whether a similar functional defect is also present in obese adolescents remains unexplored. Herein, we examined the functional effect of the rs7903146 variant in the TCF7L2 gene on the incretin effect and determined its translational metabolic manifestation by performing deep phenotyping of the incretin system, β-cell function relative to insulin sensitivity, the gastrointestinal-induced glucose disposal (GIGD) in obese youth with normal and impaired glucose tolerance.

RESEARCH DESIGN AND METHODS

Thirty-nine obese adolescents without diabetes (median age 15 [25th, 75th percentile 14, 18] years; BMI 37 [33, 43] kg/m²) were genotyped for the rs7903146 variant of TCF7L2 and underwent a 3-h oral glucose tolerance test (OGTT) followed by an isoglycemic intravenous glucose infusion (iso-intravenous glucose tolerance test [IVGTT]) to match the plasma glucose concentrations during the OGTT and a hyperglycemic clamp with arginine stimulation. The incretin effect was measured as 100 * (AUC-SR_OGTT - AUC-SR_iso-IVGTT) / AUC-SR_OGTT, where AUC-SR = area under the curve of C-peptide secretion rate. Participants were grouped into tertiles according to the percentage incretin effect (high, moderate, and low) to describe their metabolic phenotype.

RESULTS

The presence of T risk allele for TCF7L2 was associated with a markedly reduced incretin effect compared with the wild-type genotype (0.3% [-7.2, 14] vs. 37.8% [12.5, 52.4], P < 0.002). When the cohort was stratified by incretin effect, the high, moderate, and low incretin effect groups did not differ with respect to anthropometric features, while the low incretin effect group exhibited higher 1-h glucose (P = 0.015) and a reduced disposition index, insulin sensitivity, and insulin clearance compared with the high incretin effect group. GIGD was reduced in the low incretin effect group (P = 0.001). The three groups did not differ with respect to intravenous glucose-induced insulin secretion and arginine response during the hyperglycemic clamp.

CONCLUSIONS

A reduced incretin effect and its association with the TCF7L2 variant rs7903146 identify an early metabolic phenotype in obese youth without diabetes, featuring a higher plasma glucose peak at 1 h; lower insulin secretion, sensitivity, and clearance; and GIGD.

Type 2 diabetes: one disease, many pathways

Diabetes is a chronic, progressive disease that calls for longitudinal data and analysis. We introduce a longitudinal mathematical model that is capable of representing the metabolic state of an individual at any point in time during their progression from normal glucose tolerance to type 2 diabetes (T2D) over a period of years. As an application of the model, we account for the diversity of pathways typically followed, focusing on two extreme alternatives, one that goes through impaired fasting glucose (IFG) first and one that goes through impaired glucose tolerance (IGT) first. These two pathways are widely recognized to stem from distinct metabolic abnormalities in hepatic glucose production and peripheral glucose uptake, respectively. We confirm this but go beyond to show that IFG and IGT lie on a continuum ranging from high hepatic insulin resistance and low peripheral insulin resistance to low hepatic resistance and high peripheral resistance. We show that IFG generally incurs IGT and IGT generally incurs IFG on the way to T2D, highlighting the difference between innate and acquired defects and the need to assess patients early to determine their underlying primary impairment and appropriately target therapy. We also consider other mechanisms, showing that IFG can result from impaired insulin secretion, that non-insulin-dependent glucose uptake can also mediate or interact with these pathways, and that impaired incretin signaling can accelerate T2D progression. We consider whether hyperinsulinemia can cause insulin resistance in addition to being a response to it and suggest that this is a minor effect.

Linearization of the Disposition Index equation allows evaluation of secretion-sensitivity coupling slopes

AIMS

The Disposition Index (DI) is widely used in clinical studies of β-cell function. However, direct physiologic interpretation of the DI value and the inverse exponential slope relating insulin secretion and insulin sensitivity terms is difficult. We evaluated a linearization of the relationship that allows separate evaluation of the DI term and the slope.

METHODS

Insulin secretion and sensitivity indices were derived from standardized oral glucose tolerance testing, including commonly used terms and model-derived terms. The population included participants with normoglycemia, dysglycemia or Type 2 diabetes. Logarithmic transformation of the DI equation to linearize the secretion-sensitivity relationship was performed, and the resulting secretion-sensitivity relationships were evaluated using standard linear regression methods.

RESULTS

Simple logarithmic transformation linearized the secretion-sensitivity relationships available from a variety of OGTT-derived metrics. In normoglycemic subjects the slopes approximated -1 in insulin-basedsecretion-sensitivity pairs, and approximated -0.6 in C-peptide based secretion-sensitivity pairs. Group differences in DI terms were observed as expected. These analyses also revealed differing secretion-sensitivity slopes, with IGT and T2D demonstrating progressively impaired coupling.

CONCLUSIONS

Linearization of the secretion-sensitivity relationship provides simplified interpretation of the DI value and allows simple analysis and meaningful interpretation of the secretion-sensitivity slope. This linear relationship is amenable to standard statistical evaluations for comparisons of insulin secretion responses and of secretion-sensitivity coupling across groups.

Circulating Retinol-Binding Protein 4 Is Inversely Associated With Pancreatic β-Cell Function Across the Spectrum of Glycemia

OBJECTIVE

The aim of this study was to examine the association of circulating retinol-binding protein 4 (RBP4) levels with β-cell function across the spectrum of glucose tolerance from normal to overt type 2 diabetes.

RESEARCH DESIGN AND METHODS

A total of 291 subjects aged 35-60 years with normal glucose tolerance (NGT), newly diagnosed impaired fasting glucose or glucose tolerance (IFG/IGT), or type 2 diabetes were screened by a standard 2-h oral glucose tolerance test (OGTT) with the use of traditional measures to evaluate β-cell function. From these participants, 74 subjects were recruited for an oral minimal model test, and β-cell function was assessed with model-derived indices. Circulating RBP4 levels were measured by a commercially available ELISA kit.

RESULTS

Circulating RBP4 levels were significantly and inversely correlated with β-cell function indicated by the Stumvoll first-phase and second-phase insulin secretion indices, but not with HOMA of β-cell function, calculated from the 2-h OGTT in 291 subjects across the spectrum of glycemia. The inverse association was also observed in subjects involved in the oral minimal model test with β-cell function assessed by both direct measures and model-derived measures, after adjustment for potential confounders. Moreover, RBP4 emerged as an independent factor of the disposition index-total insulin secretion.

CONCLUSIONS

Circulating RBP4 levels are inversely and independently correlated with β-cell function across the spectrum of glycemia, providing another possible explanation of the linkage between RBP4 and the pathogenesis of type 2 diabetes.

Theoretical Modeling of Oral Glucose Tolerance Tests Guides the Interpretation of the Impact of Perinatal Cadmium Exposure on the Offspring's Glucose Homeostasis

Oral glucose tolerance tests, in which the concentration of glucose is monitored in the circulation over 2 h after ingesting a bolus, probe diabetic or pre-diabetic conditions. The resulting glucose curves inform about glucose turnover, insulin production and sensitivity, and other parameters. However, extracting the relevant parameters from a single complex curve is not straightforward. We propose a simple modeling method recapitulating the most salient features of the role of insulin-secreting pancreatic β-cells and insulin sensitive tissues. This method implements four ordinary differential equations with ten parameters describing the time-dependence of glucose concentration, its removal rate, and the circulating and stored insulin concentrations. From the initial parameter set adjusted to a reference condition, fitting is done by minimizing a weighted least-square residual. In doing so, the sensitivity of β-cells to glucose was identified as the most likely impacted function at weaning for the progeny of rats that were lightly exposed to cadmium in the perigestational period. Later in life, after young rats received non-contaminated carbohydrate enriched food, differences are more subtle, but modeling agrees with long-lasting perturbation of glucose homeostasis.

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).

Dual glucagon-like peptide-1 receptor/glucagon receptor agonist SAR425899 improves beta-cell function in type 2 diabetes

AIM

To evaluate the change in insulin sensitivity, β-cell function and glucose absorption after 28 days of treatment with high and low doses of SAR425899, a novel dual glucagon-like peptide-1 receptor/glucagon receptor agonist, versus placebo.

MATERIALS AND METHODS

Thirty-six overweight to obese subjects with type 2 diabetes were randomized to receive daily subcutaneous administrations of low-dose SAR425899 (0.03, 0.06 and 0.09 mg) and high-dose SAR425899 (0.06, 0.12 and 0.18 mg) or placebo for 28 days; dose escalation occurred after days 7 and 14. Mixed meal tolerance tests were conducted before treatment (day -1) and on days 1 and 28. Oral glucose and C-peptide minimal models were used to quantify metabolic indices of insulin sensitivity, β-cell responsiveness and glucose absorption.

RESULTS

With low-dose SAR425899, high-dose SAR425899 and placebo, β-cell function from day -1 to day 28 increased by 163%, 95% and 23%, respectively. The change in area under the curve for the rate of meal glucose appearance between 0 and 120 minutes was -32%, -20% and 8%, respectively.

CONCLUSIONS

After 28 days of treatment, SAR425899 improved postprandial glucose control by significantly enhancing β-cell function and slowing glucose absorption rate.

The Use of a Smart Bolus Calculator Informed by Real-time Insulin Sensitivity Assessments Reduces Postprandial Hypoglycemia Following an Aerobic Exercise Session in Individuals With Type 1 Diabetes

OBJECTIVE

Insulin dosing in type 1 diabetes (T1D) is oftentimes complicated by fluctuating insulin requirements driven by metabolic and psychobehavioral factors impacting individuals' insulin sensitivity (IS). In this context, smart bolus calculators that automatically tailor prandial insulin dosing to the metabolic state of a person can improve glucose management in T1D.

RESEARCH DESIGN AND METHODS

Fifteen adults with T1D using continuous glucose monitors (CGMs) and insulin pumps completed two 24-h admissions in a hotel setting. During the admissions, participants engaged in an early afternoon 45-min aerobic exercise session, after which they received a standardized dinner meal. The dinner bolus was computed using a standard bolus calculator or smart bolus calculator informed by real-time IS estimates. Glucose control was assessed in the 4 h following dinner using CGMs and was compared between the two admissions.

RESULTS

The IS-informed bolus calculator allowed for a reduction in postprandial hypoglycemia as quantified by the low blood glucose index (2.02 vs. 3.31, P = 0.006) and percent time <70 mg/dL (8.48% vs. 15.18%, P = 0.049), without increasing hyperglycemia (high blood glucose index: 3.13 vs. 2.09, P = 0.075; percent time >180 mg/dL: 13.24% vs. 10.42%, P = 0.5; percent time >250 mg/dL: 2.08% vs. 1.19%, P = 0.317). In addition, the number of hypoglycemia rescue treatments was reduced from 12 to 7 with the use of the system.

CONCLUSIONS

The study shows that the proposed IS-informed bolus calculator is safe and feasible in adults with T1D, appropriately reducing postprandial hypoglycemia following an exercise-induced IS increase.

Fasting glucagon concentrations are associated with longitudinal decline of β-cell function in non-diabetic humans

PURPOSE

Abnormal glucagon concentrations are a feature of prediabetes but it is uncertain if α-cell dysfunction contributes to a longitudinal decline in β-cell function. We therefore sought to determine if a decline in β-cell function is associated with a higher nadir glucagon in the postprandial period or with higher fasting glucagon.

METHODS

This was a longitudinal study in which 73 non-diabetic subjects were studied on 2 occasions 6.6 ± 0.3 years apart using a 2-hour, 7-sample oral glucose tolerance test. Disposition Index (DI) was calculated using the oral minimal model applied to the measurements of glucose, insulin, C-peptide concentrations during the studies. We subsequently examined the relationship of glucagon concentrations at baseline with change in DI (used as a measure of β-cell function) after adjusting for changes in weight and the baseline value of DI.

RESULTS

After adjusting for covariates, nadir postprandial glucagon concentrations were not associated with changes in β-cell function as quantified by DI. On the other hand, fasting glucagon concentrations during the baseline study were inversely correlated with longitudinal changes in DI.

CONCLUSIONS

Defects in α-cell function, manifest as elevated fasting glucagon, are associated with a subsequent decline in β-cell function. It remains to be ascertained if abnormal α-cell function contributes directly to loss of β-cell secretory capacity in the pathogenesis of type 2 diabetes.

When does diabetes start? Early detection and intervention in type2 diabetes mellitus

Type 2 diabetes mellitus (DM2) is a progressive disease whose pathophysiological changes occur several years before its detection. An approach based on the pathophysiological development of DM2 and its complications emphasises the importance of early and intensive intervention, not only to prevent beta-cell dysfunction but also to act on the potential associated cardiovascular risk factors before reaching the blood glucose thresholds currently set for diagnosing DM2. In the field of recently diagnosed DM2, the VERIFY study has shown that early treatment combined with metformin-vildagliptin provides relevant improvements in long-term glycaemic control and can positively affect the disease's progression.

Metabolic and Genetic Determinants of Glucose Shape After Oral Challenge in Obese Youths: A Longitudinal Study

CONTEXT

The time-to-glucose-peak following the oral glucose tolerance test (OGTT) is a highly reproducible marker for diabetes risk. In obese youths, we lack evidence for the mechanisms underlying the effects of the TCF7L2 rs7903146 variant on glucose peak.

METHODS

We analyzed the metabolic phenotype and the genotype for the TCF7L2 rs7903146 in 630 obese youths with normal (NGT) and impaired (IGT) glucose tolerance. Participants underwent a 3-hour, 9-point OGTT to estimate, using the oral minimal model, the disposition index (DI), the static (φstatic) and dynamic (φdynamic) components β-cell responsiveness and insulin sensitivity (SI). In a subgroup (n = 241) longitudinally followed for 2 years, we estimated the effect of time-to-glucose-peak on glucose tolerance change.

RESULTS

Participants were grouped into early (<30 minutes) and late (≥30 minutes) glucose peakers. A delayed glucose peak was featured by a decline in φstatic (P < .001) in the absence of a difference in φdynamic. The prevalence of T-risk allele for TCF7L2 rs7903146 variant significantly increased in the late peak group. A lower DI was correlated with higher glucose concentration at 1 and 2 hours, whereas SI was inversely associated with 1-hour glucose. Glucose peak <30 minutes was protective toward worsening of glucose tolerance overtime (odds ratio 0.35 [0.15-0.82]; P = .015), with no subjects progressing to NGT or persisting IGT, in contrast to the 40% of progressor in those with late glucose peak.

CONCLUSION

The prevalence of T-risk allele for the TCF7L2 rs7903146 prevailed in the late time-to-glucose peak group, which in turn is associated with impaired β-cell responsiveness to glucose (φ), thereby predisposing to prediabetes and diabetes in obese youths.

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.

A Modular Safety System for an Insulin Dose Recommender: A Feasibility Study

BACKGROUND

Delivering insulin in type 1 diabetes is a challenging, and potentially risky, activity; hence the importance of including safety measures as part of any insulin dosing or recommender system. This work presents and clinically evaluates a modular safety system that is part of an intelligent insulin dose recommender platform developed within the EU-funded PEPPER project.

METHODS

The proposed safety system is composed of four modules which use a novel glucose forecasting algorithm. These modules are predictive glucose alerts and alarms; a predictive low-glucose basal insulin suspension module; an advanced rescue carbohydrate recommender for resolving hypoglycemia; and a personalized safety constraint applied to insulin recommendations. The technical feasibility of the proposed safety system was evaluated in a pilot study including eight adult subjects with type 1 diabetes on multiple daily injections over a duration of six weeks. Glycemic control and safety system functioning were compared between the two-weeks run-in period and the end point at eight weeks. A standard insulin bolus calculator was employed to recommend insulin doses.

RESULTS

Overall, glycemic control improved over the evaluated period. In particular, percentage time in the hypoglycemia range (<3.0 mmol/l) significantly decreased from 0.82% (0.05-4.79) at run-in to 0.33% (0.00-0.93) at endpoint (P = .02). This was associated with a significant increase in percentage time in target range (3.9-10.0 mmol/l) from 52.8% (38.3-61.5) to 61.3% (47.5-71.7) (P = .03). There was also a reduction in number of carbohydrate recommendations.

CONCLUSION

A safety system for an insulin dose recommender has been proven to be a viable solution to reduce the number of adverse events associated to glucose control in type 1 diabetes.

Association between allelic variants in the glucagon-like peptide 1 and cholecystokinin receptor genes with gastric emptying and glucose tolerance

BACKGROUND

Nutrient-mediated release of cholecystokinin and glucagon-like peptide-1 (GLP-1) regulates gastric emptying (GE) via duodenogastric feedback mechanisms; GLP-1 also regulates postprandial insulin secretion. Some patients with functional upper gastrointestinal symptoms have impaired glucose tolerance during enteral dextrose infusion. Our hypothesis was that variants in CCK, GLP-1, and TCF7L2 (transcription factor 7-like 2 locus), which is associated with greatest genetic risk for development of type 2 diabetes mellitus, are associated with GE and independently with glucose tolerance. Our aims were to evaluate the associations between these GE, glucose tolerance, and these single nucleotide polymorphisms (SNPs).

METHODS

Genetic variants, scintigraphic GE of solids, plasma glucose, insulin, and GLP-1 during enteral dextrose infusion (75gm over 2 hours) were measured. GE and enteral dextrose infusion were, respectively, evaluated in 44 (27 controls and 17 patients with functional dyspepsia or nausea) and 42 (28 controls, 14 patients) participants; of these, 51 participants consented to assessment of SNPs. Four functional SNPs were studied: rs6923761 and rs1042044 at GLP-1 receptor, rs7903146 (TCF7L2), and rs1800857 (CCK receptor).

KEY RESULTS

Gastric emptying was normal in 38, rapid in 4, and delayed in two participants; 38 had normal, and four had impaired glucose tolerance. The T allele at rs7903146 (TCF7L2) was non-significantly associated (P = .14) with faster GE. The associations between SNPs and demographic variables, GE t_half , glucose tolerance and plasma GLP1 levels were not significant.

CONCLUSIONS & INFERENCES

There is a trend toward an association between faster GE and the diabetes-associated allele at rs7903146 in TCF7L2. However, these SNPs were not associated with plasma glucose or GLP1 concentrations during enteral dextrose infusion.

Continuous Glucose Monitors and Activity Trackers to Inform Insulin Dosing in Type 1 Diabetes: The University of Virginia Contribution

Objective: Suboptimal insulin dosing in type 1 diabetes (T1D) is frequently associated with time-varying insulin requirements driven by various psycho-behavioral and physiological factors influencing insulin sensitivity (IS). Among these, physical activity has been widely recognized as a trigger of altered IS both during and following the exercise effort, but limited indication is available for the management of structured and (even more) unstructured activity in T1D. In this work, we present two methods to inform insulin dosing with biosignals from wearable sensors to improve glycemic control in individuals with T1D. Research Design and Methods: Continuous glucose monitors (CGM) and activity trackers are leveraged by the methods. The first method uses CGM records to estimate IS in real time and adjust the insulin dose according to a person’s insulin needs; the second method uses step count data to inform the bolus calculation with the residual glucose-lowering effects of recently performed (structured or unstructured) physical activity. The methods were tested in silico within the University of Virginia/Padova T1D Simulator. A standard bolus calculator and the proposed “smart” systems were deployed in the control of one meal in presence of increased/decreased IS (Study 1) and following a 1-hour exercise bout (Study 2). Postprandial glycemic control was assessed in terms of time spent in different glycemic ranges and low/high blood glucose indices (LBGI/HBGI), and compared between the dosing strategies. Results: In Study 1, the CGM-informed system allowed to reduce exposure to hypoglycemia in presence of increased IS (percent time < 70 mg/dL: 6.1% versus 9.9%; LBGI: 1.9 versus 3.2) and exposure to hyperglycemia in presence of decreased IS (percent time > 180 mg/dL: 14.6% versus 18.3%; HBGI: 3.0 versus 3.9), tending toward optimal control. In Study 2, the step count-informed system allowed to reduce hypoglycemia (percent time < 70 mg/dL: 3.9% versus 13.4%; LBGI: 1.7 versus 3.2) at the cost of a minor increase in exposure to hyperglycemia (percent time > 180 mg/dL: 11.9% versus 7.5%; HBGI: 2.4 versus 1.5). Conclusions: We presented and validated in silico two methods for the smart dosing of prandial insulin in T1D. If seen within an ensemble, the two algorithms provide alternatives to individuals with T1D for improving insulin dosing accommodating a large variety of treatment options. Future work will be devoted to test the safety and efficacy of the methods in free-living conditions.

Hypoglycemia Prevention via Personalized Glucose-Insulin Models Identified in Free-Living Conditions

BACKGROUND

The objective of this research is to show the effectiveness of individualized hypoglycemia predictive alerts (IHPAs) based on patient-tailored glucose-insulin models (PTMs) for different subjects. Interpatient variability calls for PTMs that have been identified from data collected in free-living conditions during a one-month trial.

METHODS

A new impulse-response (IR) identification technique has been applied to free-living data in order to identify PTMs that are able to predict the future glucose trends and prevent hypoglycemia events. Impulse response has been applied to seven patients with type 1 diabetes (T1D) of the University of Amsterdam Medical Centre. Individualized hypoglycemia predictive alert has been designed for each patient thanks to the good prediction capabilities of PTMs.

RESULTS

The PTMs performance is evaluated in terms of index of fitting (FIT), coefficient of determination, and Pearson's correlation coefficient with a population FIT of 63.74%. The IHPAs are evaluated on seven patients with T1D with the aim of predicting in advance (between 45 and 10 minutes) the unavoidable hypoglycemia events; these systems show better performance in terms of sensitivity, precision, and accuracy with respect to previously published results.

CONCLUSION

The proposed work shows the successful results obtained applying the IR to an entire set of patients, participants of a one-month trial. Individualized hypoglycemia predictive alerts are evaluated in terms of hypoglycemia prevention: the use of a PTM allows to detect 84.67% of the hypoglycemia events occurred during a one-month trial on average with less than 0.4% of false alarms. The promising prediction capabilities of PTMs can be a key ingredient for new generations of individualized model predictive control for artificial pancreas.

Impaired insulin signaling in unaffected siblings and patients with first-episode psychosis

Patients with psychotic disorders are at high risk for type 2 diabetes mellitus, and there is increasing evidence that patients display glucose metabolism abnormalities before significant antipsychotic medication exposure. In the present study, we examined insulin action by quantifying insulin sensitivity in first-episode psychosis (FEP) patients and unaffected siblings, compared to healthy individuals, using a physiological-based model and comprehensive assessment battery. Twenty-two unaffected siblings, 18 FEP patients, and 15 healthy unrelated controls were evaluated using a 2-h oral glucose tolerance test (OGTT), with 7 samples of plasma glucose and serum insulin concentration measurements. Insulin sensitivity was quantified using the oral minimal model method. Lipid, leptin, free fatty acids, and inflammatory marker levels were also measured. Anthropometric, nutrient, and activity assessments were conducted; total body composition and fat distribution were determined using whole-body dual-energy X-ray absorptiometry. Insulin sensitivity significantly differed among groups (F = 6.01 and 0.004), with patients and siblings showing lower insulin sensitivity, compared to controls (P = 0.006 and 0.002, respectively). Body mass index, visceral adipose tissue area (cm²), lipids, leptin, free fatty acids, inflammatory markers, and activity ratings were not significantly different among groups. There was a significant difference in nutrient intake with lower total kilocalories/kilogram body weight in patients, compared to siblings and controls. Overall, the findings suggest that familial abnormal glucose metabolism or a primary insulin signaling pathway abnormality is related to risk for psychosis, independent of disease expression and treatment effects. Future studies should examine underlying biological mechanisms of insulin signaling abnormalities in psychotic disorders.

A novel natural tracer method to measure complex carbohydrate metabolism

While the triple tracer isotope dilution method has enabled accurate estimation of carbohydrate turnover after a mixed meal, use of the simple carbohydrate glucose as the carbohydrate source limits its translational applicability to everyday meals that typically contain complex carbohydrates. Hence, utilizing the natural enrichment of [¹³C]polysaccharide in commercially available grains, we devised a novel tracer method to measure postprandial complex carbohydrate turnover and indices of insulin action and β-cell function and compared the parameters to those obtained after a simple carbohydrate containing mixed meal. We studied healthy volunteers after either rice (n = 8) or sorghum (n = 8) and glucose (n = 16) containing mixed meals and modified the triple tracer technique to calculate carbohydrate turnover. All meals were matched for calories and macronutrient composition. Rates of meal glucose appearance (2,658 ± 736 vs. 4,487 ± 909 μM·kg^-1·2 h^-1), endogenous glucose production (-835 ± 283 vs. -1,123 ± 323 μM·kg^-1·2 h^-1) and glucose disappearance (1,829 ± 807 vs. 3,606 ± 839 μM·kg^-1·2 h^-1) differed (P < 0.01) between complex and simple carbohydrate containing meals, respectively. Interestingly, there were significant increase in indices of insulin sensitivity (32.5 ± 3.5 vs. 25.6 ± 3.2 10^-5 (dl·kg^-1·min^-2)/pM, P = 0.006) and β-cell responsivity (disposition index: 1,817 ± 234 vs. 1,236 ± 159 10^-14 (dl·kg^-1·min^-2)/pM, P < 0.005) with complex than simple carbohydrate meals. We present a novel triple tracer approach to estimate postprandial turnover of complex carbohydrate containing mixed meals. We also report higher insulin sensitivity and β-cell responsivity with complex than with simple carbohydrates in mixed meals of identical calorie and macronutrient compositions in healthy adults.

Blood glucose regulation in type 1 diabetic patients: an adaptive parametric compensation control-based approach

Here, a direct adaptive control strategy with parametric compensation is adopted for an uncertain non‐linear model representing blood glucose regulation in type 1 diabetes mellitus patients. The uncertain parameters of the model are updated by appropriate design of adaptation laws using the Lyapunov method. The closed‐loop response of the plasma glucose concentration as well as external insulin infusion rate is analysed for a wide range of variation of the model parameters through extensive simulation studies. The result indicates that the proposed adaptive control scheme avoids severe hypoglycaemia and gives satisfactory performance under parametric uncertainty highlighting its ability to address the issue of inter‐patient variability.

Fructose Consumption Contributes to Hyperinsulinemia in Adolescents With Obesity Through a GLP-1-Mediated Mechanism

CONTEXT

The consumption of high-fructose beverages is associated with a higher risk for obesity and diabetes. Fructose can stimulate glucagon-like peptide 1 (GLP-1) secretion in lean adults, in the absence of any anorexic effect.

OBJECTIVE

We hypothesized that the ingestion of glucose and fructose may differentially stimulate GLP-1 and insulin response in lean adolescents and adolescents with obesity.

DESIGN

We studied 14 lean adolescents [four females; 15.9 ± 1.6 years of age; body mass index (BMI), 21.8 ± 2.2 kg/m2] and 23 adolescents with obesity (five females; 15.1 ± 1.6 years of age; BMI, 34.5 ± 4.6 kg/m2). Participants underwent a baseline oral glucose tolerance test to determine their glucose tolerance and estimate insulin sensitivity and β-cell function [oral disposition index (oDIcpep)]. Eligible subjects received, in a double-blind, crossover design, 75 g of glucose or fructose. Plasma was obtained every 10 minutes for 60 minutes for the measures of glucose, insulin, and GLP-1 (radioimmunoassay) and glucose-dependent insulinotropic polypeptide (GIP; ELISA). Incremental glucose and hormone levels were compared between lean individuals and those with obesity by a linear mixed model. The relationship between GLP-1 increment and oDIcpep was evaluated by regression analysis.

RESULTS

Following the fructose challenge, plasma glucose excursions were similar in both groups, yet the adolescents with obesity exhibited a greater insulin (P < 0.001) and GLP-1 (P < 0.001) increase than did their lean peers. Changes in GIP were similar in both groups. After glucose ingestion, the GLP-1 response (P < 0.001) was higher in the lean group. The GLP-1 increment during 60 minutes from fructose drink was correlated with a lower oDIcpep (r2 = 0.22, P = 0.009).

CONCLUSION

Fructose, but not glucose, ingestion elicits a higher GLP-1 and insulin response in adolescents with obesity than in lean adolescents. Fructose consumption may contribute to the hyperinsulinemic phenotype of adolescent obesity through a GLP-1-mediated mechanism.

Ethnic distinctions in the pathophysiology of type 2 diabetes: a focus on black African-Caribbean populations

Type 2 diabetes (T2D) is a global public health priority, particularly for populations of black African-Caribbean ethnicity, who suffer disproportionately high rates of the disease. While the mechanisms underlying the development of T2D are well documented, there is growing evidence describing distinctions among black African-Caribbean populations. In the present paper, we review the evidence describing the impact of black African-Caribbean ethnicity on T2D pathophysiology. Ethnic differences were first recognised through evidence that metabolic syndrome diagnostic criteria fail to detect T2D risk in black populations due to less central obesity and dyslipidaemia. Subsequently more detailed investigations have recognised other mechanistic differences, particularly lower visceral and hepatic fat accumulation and a distinctly hyperinsulinaemic response to glucose stimulation. While epidemiological studies have reported exaggerated insulin resistance in black populations, more detailed and direct measures of insulin sensitivity have provided evidence that insulin sensitivity is not markedly different to other ethnic groups and does not explain the hyperinsulinaemia that is exhibited. These findings lead us to hypothesise that ectopic fat does not play a pivotal role in driving insulin resistance in black populations. Furthermore, we hypothesise that hyperinsulinaemia is driven by lower rates of hepatic insulin clearance rather than heightened insulin resistance and is a primary defect rather than occurring in compensation for insulin resistance. These hypotheses are being investigated in our ongoing South London Diabetes and Ethnicity Phenotyping study, which will enable a more detailed understanding of ethnic distinctions in the pathophysiology of T2D between men of black African and white European ethnicity.

Improved quantification of muscle insulin sensitivity using oral glucose tolerance test data: the MISI Calculator

The Muscle Insulin Sensitivity Index (MISI) has been developed to estimate muscle-specific insulin sensitivity based on oral glucose tolerance test (OGTT) data. To date, the score has been implemented with considerable variation in literature and initial positive evaluations were not reproduced in subsequent studies. In this study, we investigate the computation of MISI on oral OGTT data with differing sampling schedules and aim to standardise and improve its calculation. Seven time point OGTT data for 2631 individuals from the Maastricht Study and seven time point OGTT data combined with a hyperinsulinemic-euglycaemic clamp for 71 individuals from the PRESERVE Study were used to evaluate the performance of MISI. MISI was computed on subsets of OGTT data representing four and five time point sampling schedules to determine minimal requirements for accurate computation of the score. A modified MISI computed on cubic splines of the measured data, resulting in improved identification of glucose peak and nadir, was compared with the original method yielding an increased correlation (ρ = 0.576) with the clamp measurement of peripheral insulin sensitivity as compared to the original method (ρ = 0.513). Finally, a standalone MISI calculator was developed allowing for a standardised method of calculation using both the original and improved methods.

Mixed-meal tolerance test to assess residual beta-cell secretion: Beyond the area-under-curve of plasma C-peptide concentration

AIMS

Residual beta-cell secretion in type 1 diabetes is commonly assessed by area-under-curve of plasma C-peptide concentration (AUCCpep ) following mixed-meal tolerance test (MMTT). We aimed to investigate alternative measures of beta-cell responsiveness.

METHODS

We analyzed data from 32 youth (age 7 to 17 years) undergoing MMTT within 6 months of type 1 diabetes diagnosis. We related AUCCpep with (a) validated mechanistic index of postprandial beta-cell responsiveness MI accounting for glucose level during MMTT, and (b) pragmatic marker calculated as baseline plasma C-peptide concentration corrected for baseline plasma glucose concentration.

RESULTS

Postprandial responsiveness MI was correlated with age and BMI SDS (Rs = 0.66 and 0.44, P < 0.01 and P < 0.05) and was more correlated with glycated hemoglobin than AUCCpep (Rs = 0.79, P = 0.04). The pragmatic marker was highly correlated with AUCCpep (Rs = 0.94, P < 0.01).

CONCLUSIONS

Postprandial responsiveness MI may be more relevant to glucose control than AUCCpep . Baseline C-peptide corrected for baseline glucose appears to be a suitable surrogate of AUCCpep if MMTT is not performed.

Assessment of pulsatile insulin secretion derived from peripheral plasma C-peptide concentrations by nonparametric stochastic deconvolution

The characteristics of pulsatile insulin secretion are important determinants of type 2 diabetes pathophysiology, but they are understudied due to the difficulties in measuring pulsatile insulin secretion noninvasively. Deconvolution of either peripheral C-peptide or insulin concentrations offers an appealing alternative to hepatic vein catheterization. However, to do so, there are a series of methodological challenges to overcome. C-peptide has a relatively long half-life and accumulates in the circulation. On the other hand, peripheral insulin concentrations reflect relatively fast clearance and hepatic extraction as it leaves the portal circulation to enter the systemic circulation. We propose a method based on nonparametric stochastic deconvolution of C-peptide concentrations, using individually determined C-peptide kinetics, to overcome these limitations. The use of C-peptide (instead of insulin) concentrations allows estimation of portal (and not post-hepatic) insulin pulses, whereas nonparametric stochastic deconvolution allows evaluation of pulsatile signals without any a priori assumptions of pulse shape and occurrence. The only assumption required is the degree of smoothness of the (unknown) secretion rate. We tested this method first on simulated data and then on 29 nondiabetic subjects studied during euglycemia and hyperglycemia and compared our estimates with the profiles obtained from hepatic vein insulin concentrations. This method produced satisfactory results both in the ability to fit the data and in providing reliable estimates of pulsatile secretion, in agreement with hepatic vein measurements. In conclusion, the proposed method enables reliable and noninvasive measurement of pulsatile insulin secretion. Future studies will be needed to validate this method in people with type 2 diabetes.

Elevated insulin levels following 7 days of increased sedentary time are due to lower hepatic extraction and not higher insulin secretion

Higher insulin following sedentary behavior may be due to increased insulin secretion (IS), decreased hepatic insulin extraction (HIE), or a combination of both. Ten healthy adults completed glucose tolerance tests following 7 days of normal activity and 7 days of increased sitting. There were no differences in IS; however, HIE at 120 min after ingestion (85.4% ± 7.2% vs. 74.6% ± 6.6%, p < 0.05) and the area under the curve (73.6% ± 9.4% vs. 67.5% ± 11.3%, p < 0.05) were reduced following 7 days of increased sedentary time.

Contribution of endogenous glucagon-like peptide-1 to changes in glucose metabolism and islet function in people with type 2 diabetes four weeks after Roux-en-Y gastric bypass (RYGB)

Glucagon-Like Peptide-1 (GLP-1) is an insulin secretagogue which is elevated after Roux-en-Y Gastric Bypass (RYGB). However, its contribution to glucose metabolism after RYGB remains uncertain.

AIMS

We tested the hypothesis that GLP-1 lowers postprandial glucose concentrations and improves β-cell function after RYGB.

MATERIALS AND METHODS

To address these questions we used a labeled mixed meal to assess glucose metabolism and islet function in 12 obese subjects with type 2 diabetes studied before and four weeks after RYGB. During the post-RYGB study subjects were randomly assigned to receive an infusion of either saline or Exendin-9,39 a competitive antagonist of GLP-1 at its receptor. Exendin-9,39 was infused at 300 pmol/kg/min for 6 h. All subjects underwent RYGB for medically-complicated obesity.

RESULTS

Exendin-9,39 resulted in increased integrated incremental postprandial glucose concentrations (181 ± 154 vs. 582 ± 129 mmol per 6 h, p = 0.02). In contrast, this was unchanged in the presence of saline (275 ± 88 vs. 315 ± 66 mmol per 6 h, p = 0.56) after RYGB. Exendin-9,39 also impaired β-cell responsivity to glucose but did not alter Disposition Index (DI).

CONCLUSIONS

These data indicate that the elevated GLP-1 concentrations that occur early after RYGB improve postprandial glucose tolerance by enhancing postprandial insulin secretion.

Brief communication: β-cell function influences dopamine receptor availability

We aim to identify physiologic regulators of dopamine (DA) signaling in obesity but previously did not find a compelling relationship with insulin sensitivity measured by oral-minimal model (OMM) and DA subtype 2 and 3 receptor (D2/3R) binding potential (BPND). Reduced disposition index (DI), a β-cell function metric that can also be calculated by OMM, was shown to predict a negative reward behavior that occurs in states of lower endogenous DA. We hypothesized that reduced DI would occur with higher D2/3R BPND, reflecting lower endogenous DA. Participants completed PET scanning, with a displaceable radioligand to measure D2/3R BPND, and a 5-hour oral glucose tolerance test to measure DI by OMM. We studied 26 age-similar females without (n = 8) and with obesity (n = 18) (22 vs 39 kg/m2). Reduced DI predicted increased striatal D2/3R BPND independent of BMI. By accounting for β-cell function, we were able to determine that the state of insulin and glucose metabolism is pertinent to striatal D2/3R BPND in obesity. Clinical Trial Registration Number: NCT00802204.

Intranasal oxytocin fails to acutely improve glucose metabolism in obese men

The hypothalamic neuropeptide oxytocin not only modulates psychosocial function, but also contributes to metabolic regulation. We have recently shown that intranasal oxytocin acutely improves beta-cell responsivity and glucose tolerance in normal-weight men. In the present experiment, we investigated the acute glucoregulatory impact of oxytocin in obese men with impaired insulin sensitivity. Fifteen obese healthy men with an average body mass index of 35 kg/m² and an average body fat content of 33% received a single intranasal dose (24 IU) of oxytocin before undergoing an oral glucose tolerance test. Results were analysed according to the oral minimal model and compared with our findings in normal-weight participants. In contrast to the results in normal-weight subjects, oxytocin did not blunt postprandial glucose and insulin excursions in obese men, and moreover failed to enhance beta-cell responsivity and glucose tolerance. These results indicate that pronounced obesity may be associated with a certain degree of resistance to the glucoregulatory impact of exogenous oxytocin, and underlines the need for further investigations into the potential of oxytocin to improve glucose homeostasis in the clinical context.

Time-Restricted Feeding Improves Glucose Tolerance in Rats, but Only When in Line With the Circadian Timing System

Epidemiological studies indicate that shift-workers have an increased risk of type 2 diabetes mellitus (T2DM). Glucose tolerance and insulin sensitivity both are dependent on the circadian timing system (i.e., the time-of-day) and fasting duration, in rodents as well as humans. Therefore, question is whether manipulation of the circadian timing system, for example by changing the timing of feeding and fasting, is a potential preventive treatment for T2DM. Time-restricted feeding (TRF) is well-known to have profound effects on various metabolic measures, including glucose metabolism. However, experiments that directly measure the effects of TRF on glucose tolerance and/or insulin sensitivity at different time points throughout the 24 h cycle are lacking. Here we show, in rats, that TRF in line with the circadian timing system (i.e., feeding during the active phase) improves glucose tolerance during intravenous glucose tolerance tests (ivGTT) in the active phase, as lower insulin levels were observed with similar levels of glucose clearance. However, this was not the case during the inactive phase in which more insulin was released but only a slightly faster glucose clearance was observed. Contrasting, TRF out of sync with the circadian timing system (i.e., feeding during the inactive phase) worsened glucose tolerance, although only marginally, likely because of adaptation to the 4 week TRF regimen. Our results show that TRF can improve glucose metabolism, but strict adherence to the time-restricted feeding period is necessary, as outside the regular eating hours glucose tolerance is worsened.

A Systematic Review of Beta Cell Function in Adults of Black African Ethnicity

BACKGROUND

Understanding ethnic differences in beta cell function has important implications for preventative and therapeutic strategies in populations at high risk of type 2 diabetes (T2D). The existing literature, largely drawn from work in children and adolescents, suggests that beta cell function in black African (BA) populations is upregulated when compared to white Europeans (WE).

METHODS

A systematic literature search was undertaken in June 2018 to identify comparative studies of beta cell function between adults (>age 18 years) of indigenous/diasporic BA and WE ethnicity. All categories of glucose tolerance and all methodologies of assessing beta cell function in vivo were included.

RESULTS

41 studies were identified for inclusion into a qualitative synthesis. The majority were studies in African American populations (n = 30) with normal glucose tolerance (NGT)/nondiabetes (n = 25), using intravenous glucose stimulation techniques (n = 27). There were fewer studies in populations defined as only impaired fasting glucose/impaired glucose tolerance (IFG/IGT) (n = 3) or only T2D (n = 3). Although BA broadly exhibited greater peripheral insulin responses than WE, the relatively small number of studies which measured C-peptide to differentiate between beta cell insulin secretion and hepatic insulin extraction (n = 14) had highly variable findings. In exclusively IGT or T2D cohorts, beta cell insulin secretion was found to be lower in BA compared to WE.

CONCLUSIONS

There is inconsistent evidence for upregulated beta cell function in BA adults, and they may in fact exhibit greater deficits in insulin secretory function as glucose intolerance develops.

Increased Rates of Meal Absorption Do Not Explain Elevated 1-Hour Glucose in Subjects With Normal Glucose Tolerance

Context

In subjects with normal fasting glucose (NFG) and normal glucose tolerance (NGT), glucose concentrations >155 mg/dL 1 hour after 75 g of oral glucose predict increased risk of progression to diabetes. Recently, it has been suggested that the mechanism underlying this abnormality is increased gut absorption of glucose.

Objective

We sought to determine the rate of systemic appearance of meal-derived glucose in subjects classified by their 1-hour glucose after a 75-g oral glucose challenge.

Design

This was a cross-sectional study. Participating subjects underwent a 75-g oral glucose challenge and a labeled mixed meal test.

Setting

An inpatient clinical research unit at an academic medical center.

Participants

Thirty-six subjects with NFG/NGT participated in this study.

Interventions

Subjects underwent an oral glucose tolerance test. Subsequently, they underwent a labeled mixed meal to measure fasting and postprandial glucose metabolism.

Main Outcome Measures

We examined β-cell function and the rate of meal appearance (Meal R_a) in NFG/NGT subjects. Subsequently, we examined the relationship of peak postchallenge glucose with Meal R_a and indices of β-cell function.

Results

Peak glucose concentrations correlated inversely with β-cell function. No relationship of Meal R_a with peak postchallenge glucose concentrations was observed.

Conclusion

In subjects with NFG/NGT, elevated 1-hour peak postchallenge glucose concentrations reflect impaired β-cell function rather than increased systemic meal appearance.

Differential effects of the circadian system and circadian misalignment on insulin sensitivity and insulin secretion in humans

Glucose tolerance is lower at night and higher in the morning. Shift workers, who often eat at night and experience circadian misalignment (i.e. misalignment between the central circadian pacemaker and the environmental/behavioural cycles), have an increased risk of type 2 diabetes. To determine the separate and relative impacts of the circadian system, behavioural/environmental cycles, and their interaction (i.e. circadian misalignment) on insulin sensitivity and β-cell function, the oral minimal model was used to quantitatively assess the major determinants of glucose control in 14 healthy adults using a randomized, cross-over design with two 8-day laboratory protocols. Both protocols involved 3 baseline inpatient days with habitual sleep/wake cycles, followed by 4 inpatient days with the same nocturnal bedtime (circadian alignment) or with 12-hour inverted behavioural/environmental cycles (circadian misalignment). The data showed that circadian phase and circadian misalignment affect glucose tolerance through different mechanisms. While the circadian system reduces glucose tolerance in the biological evening compared to the biological morning mainly by decreasing both dynamic and static β-cell responsivity, circadian misalignment reduced glucose tolerance mainly by lowering insulin sensitivity, not by affecting β-cell function.

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.

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.

What Can Diabetes-Associated Genetic Variation in TCF7L2 Teach Us About the Pathogenesis of Type 2 Diabetes?

Type 2 diabetes mellitus (T2DM) is a polygenic metabolic disorder characterized by hyperglycemia occurring as a result of impaired insulin secretion and/or insulin resistance. Among the various genetic factors associated with T2DM, a common genetic variant within the transcription factor 7-like 2 locus (TCF7L2) confers the greatest genetic risk for development of the disease. However, the mechanism(s) by which TCF7L2 predisposes to diabetes remain uncertain. Here we review the current literature pertaining to the potential mechanisms by which TCF7L2 confers risk of T2DM, using genetic variation as a probe to understand the pathogenesis of the disease.

A Hepatocyte FOXN3-α Cell Glucagon Axis Regulates Fasting Glucose

The common genetic variation at rs8004664 in the FOXN3 gene is independently and significantly associated with fasting blood glucose, but not insulin, in non-diabetic humans. Recently, we reported that primary hepatocytes from rs8004664 hyperglycemia risk allele carriers have increased FOXN3 transcript and protein levels and liver-limited overexpression of human FOXN3, a transcriptional repressor that had not been implicated in metabolic regulation previously, increases fasting blood glucose in zebrafish. Here, we find that injection of glucagon into mice and adult zebrafish decreases liver Foxn3 protein and transcript levels. Zebrafish foxn3 loss-of-function mutants have decreased fasting blood glucose, blood glucagon, liver gluconeogenic gene expression, and α cell mass. Conversely, liver-limited overexpression of foxn3 increases α cell mass. Supporting these genetic findings in model organisms, non-diabetic rs8004664 risk allele carriers have decreased suppression of glucagon during oral glucose tolerance testing. By reciprocally regulating each other, liver FOXN3 and glucagon control fasting glucose.

Actions of metformin and statins on lipid and glucose metabolism and possible benefit of combination therapy

Patients with diabetes type 2 have an increased risk for cardiovascular disease and commonly use combination therapy consisting of the anti-diabetic drug metformin and a cholesterol-lowering statin. However, both drugs act on glucose and lipid metabolism which could lead to adverse effects when used in combination as compared to monotherapy. In this review, the proposed molecular mechanisms of action of statin and metformin therapy in patients with diabetes and dyslipidemia are critically assessed, and a hypothesis for mechanisms underlying interactions between these drugs in combination therapy is developed.

Methods for Measuring Risk for Type 2 Diabetes in Youth: the Oral Glucose Tolerance Test (OGTT)

PURPOSE OF REVIEW

The oral glucose tolerance test (OGTT) is used both in clinical practice and research to assess glucose tolerance. In addition, the OGTT is utilized for surrogate measures of insulin sensitivity and the insulin response to enteral glucose and has been widely applied in the evaluation of β-cell dysfunction in obesity, prediabetes, and type 2 diabetes. Here we review the use of the OGTT and the OGTT-derived indices for measurement of risk markers for type 2 diabetes in youth.

RECENT FINDINGS

Advantages of using the OGTT for measures of diabetes risk include its accessibility and the incorporation of physiological contributions of the gut-pancreas axis in the measures of insulin response to glucose. Mathematical modeling expands the potential gains from the OGTT in physiology and clinical research. Disadvantages include individual differences in the rate of glucose absorption that modify insulin responses, imperfect control of the glycemic stimulus, and poor intraindividual reproducibility. Available research suggests the OGTT provides valuable information about the development of impaired glycemic control and β-cell function in obese youth along the spectrum of glucose tolerance.

In vivo and in silico dynamics of the development of Metabolic Syndrome

The Metabolic Syndrome (MetS) is a complex, multifactorial disorder that develops slowly over time presenting itself with large differences among MetS patients. We applied a systems biology approach to describe and predict the onset and progressive development of MetS, in a study that combined in vivo and in silico models. A new data-driven, physiological model (MINGLeD: Model INtegrating Glucose and Lipid Dynamics) was developed, describing glucose, lipid and cholesterol metabolism. Since classic kinetic models cannot describe slowly progressing disorders, a simulation method (ADAPT) was used to describe longitudinal dynamics and to predict metabolic concentrations and fluxes. This approach yielded a novel model that can describe long-term MetS development and progression. This model was integrated with longitudinal in vivo data that was obtained from male APOE*3-Leiden.CETP mice fed a high-fat, high-cholesterol diet for three months and that developed MetS as reflected by classical symptoms including obesity and glucose intolerance. Two distinct subgroups were identified: those who developed dyslipidemia, and those who did not. The combination of MINGLeD with ADAPT could correctly predict both phenotypes, without making any prior assumptions about changes in kinetic rates or metabolic regulation. Modeling and flux trajectory analysis revealed that differences in liver fluxes and dietary cholesterol absorption could explain this occurrence of the two different phenotypes. In individual mice with dyslipidemia dietary cholesterol absorption and hepatic turnover of metabolites, including lipid fluxes, were higher compared to those without dyslipidemia. Predicted differences were also observed in gene expression data, and consistent with the emergence of insulin resistance and hepatic steatosis, two well-known MetS co-morbidities. Whereas MINGLeD specifically models the metabolic derangements underlying MetS, the simulation method ADAPT is generic and can be applied to other diseases where dynamic modeling and longitudinal data are available.

Measurement of postprandial glucose fluxes in response to acute and chronic endurance exercise in healthy humans

The effect of endurance exercise on enhancing insulin sensitivity and glucose flux has been well established with techniques such as the hyperinsulinemic clamp. Although informative, such techniques do not emulate the physiological postprandial state, and it remains unclear how exercise improves postprandial glycaemia. Accordingly, combining mixed-meal tolerance testing and the triple-stable isotope glucose tracer approach, glucose fluxes [rates of meal glucose appearance (Ra), disposal (Rd), and endogenous glucose production (EGP)] were determined following acute endurance exercise (1 h cycling; ~70% V̇o_2max) and 4 wk of endurance training (cycling 5 days/wk). Training was associated with a modest increase in V̇o_2max (~7%, P < 0.001). Postprandial glucose and insulin responses were reduced to the same extent following acute and chronic training. Interestingly, this was not accompanied by changes to rates of meal Ra, Rd, or degree of EGP suppression. Glucose clearance (Rd relative to prevailing glucose) was, however, enhanced with acute and chronic exercise. Furthermore, the duration of EGP suppression was shorter with acute and chronic exercise, with EGP returning toward fasting levels more rapidly than pretraining conditions. These findings suggest that endurance exercise influences the efficiency of the glucoregulatory system, where pretraining rates of glucose disposal and production were achieved at lower glucose and insulin levels. Notably, there was no influence of chronic training over and above that of a single exercise bout, providing further evidence that glucoregulatory benefits of endurance exercise are largely attributed to the residual effects of the last exercise bout.

Prospective evaluation of insulin and incretin dynamics in obese adults with and without diabetes for 2 years after Roux-en-Y gastric bypass

AIMS/HYPOTHESIS

In this prospective case-control study we tested the hypothesis that, while long-term improvements in insulin sensitivity (S_I) accompanying weight loss after Roux-en-Y gastric bypass (RYGB) would be similar in obese individuals with and without type 2 diabetes mellitus, stimulated-islet-cell insulin responses would differ, increasing (recovering) in those with diabetes but decreasing in those without. We investigated whether these changes would occur in conjunction with favourable alterations in meal-related gut hormone secretion and insulin processing.

METHODS

Forty participants with type 2 diabetes and 22 participants without diabetes from the Longitudinal Assessment of Bariatric Surgery (LABS-2) study were enrolled in a separate, longitudinal cohort (LABS-3 Diabetes) to examine the mechanisms of postsurgical diabetes improvement. Study procedures included measures of S_I, islet secretory response and gastrointestinal hormone secretion after both intravenous glucose (frequently-sampled IVGTT [FSIVGTT]) and a mixed meal (MM) prior to and up to 24 months after RYGB.

RESULTS

Postoperatively, weight loss and S_I-_FSIVGTT improvement was similar in both groups, whereas the acute insulin response to glucose (AIRglu) decreased in the non-diabetic participants and increased in the participants with type 2 diabetes. The resulting disposition indices (DI_FSIVGTT) increased by three- to ninefold in both groups. In contrast, during the MM, total insulin responsiveness did not significantly change in either group despite durable increases of up to eightfold in postprandial glucagon-like peptide 1 levels, and S_I-MM and DI_MM increased only in the diabetes group. Peak postprandial glucagon levels increased in both groups.

CONCLUSIONS/INTERPRETATION

For up to 2 years following RYGB, obese participants without diabetes showed improvements in DI that approach population norms. Those with type 2 diabetes recovered islet-cell insulin secretion response yet continued to manifest abnormal insulin processing, with DI values that remained well below population norms. These data suggest that, rather than waiting for lifestyle or medical failure, RYGB is ideally considered before, or as soon as possible after, onset of type 2 diabetes.

TRIAL REGISTRATION

ClinicalTrials.gov NCT00433810.

Increase in hepatic and decrease in peripheral insulin clearance characterize abnormal temporal patterns of serum insulin in diabetic subjects

Insulin plays a central role in glucose homeostasis, and impairment of insulin action causes glucose intolerance and leads to type 2 diabetes mellitus (T2DM). A decrease in the transient peak and sustained increase of circulating insulin following an infusion of glucose accompany T2DM pathogenesis. However, the mechanism underlying this abnormal temporal pattern of circulating insulin concentration remains unknown. Here we show that changes in opposite direction of hepatic and peripheral insulin clearance characterize this abnormal temporal pattern of circulating insulin concentration observed in T2DM. We developed a mathematical model using a hyperglycemic and hyperinsulinemic-euglycemic clamp in 111 subjects, including healthy normoglycemic and diabetic subjects. The hepatic and peripheral insulin clearance significantly increase and decrease, respectively, from healthy to borderline type and T2DM. The increased hepatic insulin clearance reduces the amplitude of circulating insulin concentration, whereas the decreased peripheral insulin clearance changes the temporal patterns of circulating insulin concentration from transient to sustained. These results provide further insight into the pathogenesis of T2DM, and thus may contribute to develop better treatment of this condition.

Type 2 diabetes mellitus (T2DM) is one of the fastest growing public health problems, characterized by chronic hyperglycemia with the failure of glucose homeostasis. Evaluating alteration in biological functions regulating circulating glucose concentration is complicated due to the mutual relation between circulating glucose and insulin. A team led by Wataru Ogawa at Kobe University designed clinical experiments for breaking such feedback relations, and a team led by Shinya Kuroda at University of Tokyo developed mathematical models for specifically quantifying the functions from the clinical data. The estimated model parameters revealed the significant increase in hepatic and decrease in peripheral insulin clearance, which occur before and after insulin delivery into systemic circulation, respectively, from healthy to T2DM subjects. Model analysis suggested these insulin clearances centrally regulate the dynamics of circulating insulin concentration in the glucose-insulin regulatory system.