Hyperinsulinemic-euglycemic Clamp Research Articles

Intermittent fasting for systemic triglyceride metabolic reprogramming (IFAST): Design and methods of a prospective, randomized, controlled trial

BackgroundCaloric restriction prolongs lifespan in model organisms and improves metrics of aging-related diseases in humans, but daily compliance is challenging. Intermittent fasting improves metrics of lipid and glucose metabolism in the setting of weight loss but whether these metrics are improved independent of weight loss is not known. MethodsWe seek to address this gap with IFAST, a single-center, three-arm, prospective, randomized, controlled clinical trial. Eligible study participants are adults with no chronic medical conditions beyond prediabetes or overweight but who are at high risk for type 2 diabetes mellitus (T2D), defined as having a history of gestational diabetes or a first-degree relative with T2D. Participants will be randomized in a 1:2:2 schema to either a control group, a fasting group, or a fasting/weight maintenance group. The fasting groups will complete a 24-h fast one day per week for 12 weeks. The key mechanistic endpoint is change in triglyceride composition (defined by carbon content and degree of saturation) as measured by longitudinal metabolomics. The key safety endpoint is percent change from baseline in bone volume fraction (BV/TV; high-resolution peripheral quantitative CT) at the radius in the fasting group. Secondary endpoints include measures of insulin sensitivity (hyperinsulinemic-euglycemic clamp), clinical lipid profiling, systemic inflammation markers, hunger assessment, bone density, and bone microarchitecture with high-resolution peripheral quantitative CT. ConclusionIFAST will investigate intrinsic metabolic benefits of intermittent fasting beyond weight loss. Trial registrationClinicalTrials.gov ID NCT05722873.

Effect of Weight Loss on Skeletal Muscle Bioactive Lipids in People with Obesity and Type 2 Diabetes.

Muscle sn-1,2-diacylglycerol (DAG) and C18:0 ceramide accumulation in sarcolemmal and mitochondrial compartments have been proposed to regulate muscle insulin sensitivity. Here, we evaluated whether weight loss-induced improvements in insulin sensitivity were associated with changes in muscle sn-1,2-DAG and ceramide content in people with obesity and type 2 diabetes. We measured skeletal muscle insulin sensitivity, assessed by using the hyperinsulinemic-euglycemic clamp procedure in conjunction with stable isotopically labeled glucose tracer infusion, and skeletal muscle sn-1,2-DAG and ceramide contents by using liquid chromatography-tandem mass spectrometry after subcellular fractionation and DAG isomer separation in 14 adults with obesity and type 2 diabetes before and after marked (18.6 ± 2.1%) weight loss. Whole-body insulin sensitivity doubled after weight loss. Sarcolemmal sn-1,2-DAG and C18:0 ceramide contents after weight loss were not different than values before weight loss. In contrast, mitochondrial/ER C18:0 ceramide content decreased by ∼20% after weight loss (from 2.16 ± 0.08 to 1.71 ± 0.13 nmol/g, P<0.005). These results suggest a decrease in muscle mitochondrial/ER C18:0 ceramide content could contribute to the beneficial effect of weight loss on skeletal muscle insulin sensitivity.

Impaired insulin sensitivity measured by estimated glucose disposal rate is associated with decreased myocardial mechano-energetic efficiency in non-diabetic individuals

Background and aimsImpaired myocardial mechano-energetic efficiency (MEE) has been associated with cardiac insulin resistance measured by dynamic positron emission tomography (PET) with 18F-fluorodeoxyglucose (18F-FDG) combined with euglycemic–hyperinsulinemic clamp. Estimate glucose disposal rate (eGDR) index has a good correlation with whole-body insulin sensitivity. It remains unsettled whether eGDR index is a suitable proxy of cardiac insulin sensitivity as well as its association with myocardial MEE. The aims of this study were: 1) to compare eGDR index with HOMA-IR, QUICKI and FIRI indexes for association with myocardial glucose metabolic rate (MrGlu); and 2) to determine the association of eGDR index with myocardial MEE. MethodsWe evaluated MrGlu using PET with 18F-FDG combined with euglycemic–hyperinsulinemic clamp in 50 individuals without history of coronary heart disease. Myocardial MEE per gram of left ventricular mass (MEEi) was measured in 1181 subjects by echocardiography. eGDR (mg kg-1/min) was calculated as: 21.158 - (0.09 × waist circumference in cm) - (3.407 × hypertension, 1 = yes 0 = no) - (0.551 × HbA1c%). ResultseGDR index was more strongly associated with myocardial MrGlu than HOMA-IR, QUICKI, and FIRI indexes (r = -0.662, r = -0.492, r = 0.570, and r = -0.492, respectively). Individuals in the lower tertiles of eGDR exhibited a significant reduction of MEEi as compared to those in the highest tertile (P < 0.001). In a stepwise multivariate linear regression analysis eGDR index was the major determinant of MEEi independently of well-established cardio-metabolic risk factors. ConclusionsThese data suggest that the eGDR index may be a useful marker to identifying individuals at high cardiovascular risk.

Insulin sensitivity and skeletal muscle mitochondrial respiration in Black and White women with obesity.

Non-Hispanic black women (BW) have a greater risk of type 2 diabetes (T2D) and insulin resistance (IR) compared to non-Hispanic white women (WW). The mechanisms leading to these differences are not understood, and it is unclear whether synergistic effects of race and obesity impact disease risk. To understand the interaction of race and weight, hepatic and peripheral IR were compared in WW and BW with and without obesity. Hepatic and peripheral IR was measured by a labeled, hyperinsulinemic-euglycemic clamp in BW (n=32) and WW (n=32) with and without obesity. Measurements of body composition, cardiorespiratory fitness, and skeletal muscle (SM) respiration were completed. Data were analyzed by mixed model ANOVA. Subjects with obesity had greater hepatic and peripheral IR and lower SM respiration (P<0.001). Despite 14% greater insulin (P=0.066), BW tended to have lower peripheral glucose disposal (Rd; P=0.062), which was driven by women without obesity (P=0.002). BW had significantly lower glucose production (P=0.005), hepatic IR (P=0.024), and maximal coupled and uncoupled respiration (P<0.001) than WW. Maximal coupled and uncoupled SM mitochondrial respiration was strongly correlated with peripheral and hepatic IR (P<0.01). While BW without obesity had lower Rd than WW, race and obesity did not synergistically impact peripheral IR. Paradoxically, WW with obesity had greater hepatic IR compared to BW. Relationships between SM respiration and IR persisted across a range of body weight. These data provide support for therapies in BW, like exercise, that improve SM mitochondrial respiration to reduce IR and T2D risk.

Serum proteomic profiling of physical activity reveals CD300LG as a novel exerkine with a potential causal link to glucose homeostasis

Background:Physical activity has been associated with preventing the development of type 2 diabetes and atherosclerotic cardiovascular disease. However, our understanding of the precise molecular mechanisms underlying these effects remains incomplete and good biomarkers to objectively assess physical activity are lacking.Methods:We analyzed 3072 serum proteins in 26 men, normal weight or overweight, undergoing 12 weeks of a combined strength and endurance exercise intervention. We estimated insulin sensitivity with hyperinsulinemic euglycemic clamp, maximum oxygen uptake, muscle strength, and used MRI/MRS to evaluate body composition and organ fat depots. Muscle and subcutaneous adipose tissue biopsies were used for mRNA sequencing. Additional association analyses were performed in samples from up to 47,747 individuals in the UK Biobank, as well as using two-sample Mendelian randomization and mice models.Results:Following 12 weeks of exercise intervention, we observed significant changes in 283 serum proteins. Notably, 66 of these proteins were elevated in overweight men and positively associated with liver fat before the exercise regimen, but were normalized after exercise. Furthermore, for 19.7 and 12.1% of the exercise-responsive proteins, corresponding changes in mRNA expression levels in muscle and fat, respectively, were shown. The protein CD300LG displayed consistent alterations in blood, muscle, and fat. Serum CD300LG exhibited positive associations with insulin sensitivity, and to angiogenesis-related gene expression in both muscle and fat. Furthermore, serum CD300LG was positively associated with physical activity and negatively associated with glucose levels in the UK Biobank. In this sample, the association between serum CD300LG and physical activity was significantly stronger in men than in women. Mendelian randomization analysis suggested potential causal relationships between levels of serum CD300LG and fasting glucose, 2 hr glucose after an oral glucose tolerance test, and HbA1c. Additionally, Cd300lg responded to exercise in a mouse model, and we observed signs of impaired glucose tolerance in male, but not female, Cd300lg knockout mice.Conclusions:Our study identified several novel proteins in serum whose levels change in response to prolonged exercise and were significantly associated with body composition, liver fat, and glucose homeostasis. Serum CD300LG increased with physical activity and is a potential causal link to improved glucose levels. CD300LG may be a promising exercise biomarker and a therapeutic target in type 2 diabetes.Funding:South-Eastern Norway Regional Health Authority, Simon Fougners Fund, Diabetesforbundet, Johan Selmer Kvanes’ legat til forskning og bekjempelse av sukkersyke. The UK Biobank resource reference 53641. Australian National Health and Medical Research Council Investigator Grant (APP2017942). Australian Research Council Discovery Early Career Award (DE220101226). Research Council of Norway (Project grant: 325640 and Mobility grant: 287198). The Medical Student Research Program at the University of Oslo. Novo Nordisk Fonden Excellence Emerging Grant in Endocrinology and Metabolism 2023 (NNF23OC0082123).Clinical trial number:clinicaltrials.gov: NCT01803568.

The role of myocardial blood volume in the pathophysiology of angina with non-obstructed coronary arteries: The MICORDIS study

BackgroundAngina with Non-Obstructed Coronary Arteries (ANOCA) involves abnormal vasomotor responses. While reduced coronary flow is an established contributor to myocardial hypoxia, myocardial blood volume (MBV) independently regulates myocardial oxygen uptake but its role in ANOCA remains unclear. ObjectivesWe hypothesized that reduced MBV contributes to ANOCA, and associates with insulin resistance in ANOCA. MethodsMBV in ANOCA patients was compared to age- and sex-matched healthy controls. ANOCA patients underwent coronary angiography with invasive coronary function testing (CFT) to identify vasospasm and coronary microvascular dysfunction. In all subjects MBV was quantified at baseline, during hyperinsulinemia and during dobutamine-induced stress using myocardial contrast echocardiography (MCE). The hyperinsulinemic-euglycemic clamp was used to assess insulin resistance. ResultsTwenty-eight ANOCA patients (21% men, 56.8 ± 8.6 years) and 28 healthy controls (21% men, 56.5 ± 7.0 years) were included. During CFT 11% of patients showed epicardial vasospasm, 39% microvascular vasospasm, 25% coronary microvascular dysfunction, and 11% of patients had a negative CFT. ANOCA patients had significant lower insulin-sensitivity (p < 0.01). During MCE, ANOCA patients showed a significantly lower MBV at baseline (0.388 vs 0.438 mL/mL, p = 0.04), during hyperinsulinemia (0.395 vs 0.447 mL/mL, p = 0.02), and during dobutamine-induced stress (0.401 vs 0.476 mL/mL, p = 0.030). ConclusionsIn ANOCA patients MBV is diminished at baseline, during hyperinsulinemia and dobutamine-induced stress in the absence of differences in microvascular recruitment. These findings support the presence of capillary rarefaction in ANOCA patients. ANOCA patients showed metabolic insulin resistance, but insulin did not acutely alter myocardial perfusion.

A Mathematical Model-Derived Disposition Index Without Insulin Validated in Youth with Obesity.

The gold standard clamp measurements for insulin sensitivity (cSI), β-cell function (cBCF) and disposition index (cDI = cSI*cBCF), are not practical in large-scale studies. We sought to: 1) validate a mathematical model-derived DI from oral glucose tolerance tests (OGTT) with insulin (mDI) and without (mDI-woI) against cDI and oral disposition index (oDI) evaluate the ability of the novel indices to detect prediabetes and type 2 diabetes. We carried out a secondary analysis of previously reported cross-sectional observational studies. The Insulin Sensitivity and Secretion mathematical model for glucose-insulin dynamics was applied to five-point and three-point OGTTs synchronized with hyperinsulinemic-euglycemic and hyperglycemic clamps from 130 youth with obesity (68 NGT, 33 IGT, 29 T2D). Model-derived DI correlated well with clamp DI (R = 0.76 (logged)). Between NGT and IGT, mDI and mDI-woI decreased more than oDI and cDI, (60 and 59% vs 29 and 27%), and by receiver operating characteristic (ROC) analysis were superior at detecting IGT than oDI and cDI (AUC 0.88, 0.87 vs 0.68, 0.65), as was mean glucose (AUC 0.87). mDI-woI is better than oDI or the labor-intensive cDI for detecting dysglycemia in obese youth. Bypassing insulin measurements with mDI-woI from the OGTT provides a cost-effective approach for large-scale epidemiological studies of dysglycemia in youth.

Hepatic Insulin Resistance Increases Risk of Gallstone Disease in Indigenous Americans in the Southwestern United States.

Animal models indicate that hepatic insulin resistance (IR) promotes cholesterol gallstone disease (GSD). We sought to determine whether hepatic and whole-body IR is associated with incident GSD. At baseline, 450 Southwestern Indigenous American adults without GSD were included. Participants had a 2-step hyperinsulinemic-euglycemic clamp with glucose tracer at submaximal and maximal insulin stimulation (240 and 2,400 pmol/m 2 /min) for whole-body IR (M-low and M-high) and hepatic glucose production (HGP) before and during submaximal insulin infusion (HGP-basal and HGP-insulin). Incident GSD was identified during follow-up visits conducted at ∼2-year intervals. The associations of HGP (basal, insulin, and % suppression), M-low, and M-high with risk of GSD were assessed by Cox regression models adjusted for age, sex, body fat (%), glucose, and insulin. Sixty participants (13%) developed GSD (median follow-up: 11.6 years). Participants who developed GSD were of similar age and whole-body IR as those who did not ( P 's > 0.07) but were more likely to be female; have higher body fat, higher HGP-basal, and HGP-insulin; and lower % suppression of HGP ( P 's < 0.02). In separate adjusted models, higher HGP-insulin and lower % suppression of HGP were associated with increased risk for GSD (hazard ratio [HR] per SD: HR 1.38, 95% CI 1.12-1.69, P = 0.002; HR 1.41, 95% CI 1.16-1.72, P = 0.0007). HGP-basal, M-low, and M-high were not associated with GSD in adjusted models ( P 's > 0.22). Resistance to insulin suppression of HGP increases risk for GSD. Hepatic IR is a link between GSD and other conditions of the metabolic syndrome.

Acute Sympathetic Blockade Improves Insulin-Mediated Microvascular Blood Flow in the Forearm of Adult Human Subjects With Obesity.

Obesity is associated with resistance to the metabolic (glucose uptake) and vascular (nitric-oxide mediated dilation and microvascular recruitment) actions of insulin. These vascular effects contribute to insulin sensitivity by increasing tissue delivery of glucose. Studies by us and others suggest that sympathetic activation contributes to insulin resistance to glucose uptake. Here we tested the hypothesis that sympathetic activation contributes to impaired insulin-mediated vasodilation in adult subjects with obesity. In a randomized crossover study, we used a euglycemic hyperinsulinemic clamp in 12 subjects with obesity to induce forearm arterial vasodilation (forearm blood flow) and microvascular recruitment (contrast-enhanced ultrasonography) during an intrabrachial infusion of saline (control) or phentolamine (sympathetic blockade). Insulin increased forearm blood flow on both study days (from 2.21±1.22 to 4.89±4.21 mL/100 mL per min, P=0.003 and from 2.42±0.89 to 7.19±3.35 mL/100 mL per min, P=0.002 for the intact and blocked day, respectively). Sympathetic blockade with phentolamine resulted in a significantly greater increase in microvascular flow velocity (∆microvascular flow velocity: 0.23±0.65 versus 2.51±3.01 arbitrary intensity units (AIU/s) for saline and phentolamine respectively, P=0.005), microvascular blood volume (∆microvascular blood volume: 1.69±2.45 versus 3.76±2.93 AIU, respectively, P=0.05), and microvascular blood flow (∆microvascular blood flow: 0.28±0.653 versus 2.51±3.01 AIU2/s, respectively, P=0.0161). To evaluate if this effect was not due to nonspecific vasodilation, we replicated the study in 6 subjects with obesity comparing intrabrachial infusion of phentolamine to sodium nitroprusside. At doses that produced similar increases in forearm blood flow, insulin-induced changes in microvascular flow velocity were greater during phentolamine than sodium nitroprusside (%microvascular flow velocity=58% versus 29%, respectively, P=0.031). We conclude that sympathetic activation impairs insulin-mediated microvascular recruitment in adult subjects with obesity.

The undervalued league of insulin resistance testing: uncovering their importance.

Type 2 diabetes, obesity, and several other metabolic diseases are all largely attributed to the problem known as insulin resistance. Diagnosing insulin resistance promptly and accurately is essential for adequately managing and intervening in metabolic disorders. Several diagnostic methods have been developed to assess insulin resistance. However, each method has advantages and disadvantages. The most precise test is the hyperinsulinemic-euglycemic clamp, which examines the direct impact of insulin on glucose uptake by tissues. However, it is primarily utilized in research due to its complexity and intrusiveness. Homeostatic Model Assessment of Insulin Resistance (HOMA-IR) and the Quantitative Insulin Sensitivity Check Index (QUICKI) are the second most used Insulin resistance tests in the clinical setup. These tests are based on measuring the fasting glucose and insulin levels. The Oral Glucose Tolerance Test (OGTT), Insulin tolerance test, and the Matsuda Index are further diagnostic procedures that shed light on insulin sensitivity. The improved techniques, such as the insulin suppression test and the minimal model analysis, provide substitutes for unique clinical circumstances. Additionally, including extra measurements with these tests, like waist circumference, lipid profiles, and inflammatory markers, can improve the evaluation of insulin resistance. In summary, identifying insulin resistance is essential for the early detection and treatment of various metabolic illnesses. To make educated judgments and improve patient care, healthcare workers should be aware of thedifferent available diagnostic tests and how they are used in each situation. Insulin resistance detection and monitoring will require further study to improve current diagnostic approaches and create novel, less invasive techniques.

An E115A Missense Variant in CERS2 Is Associated With Increased Sleeping Energy Expenditure and Hepatic Insulin Resistance in American Indians.

Genetic determinants of inter-individual differences in energy expenditure (EE) are largely unknown. Sphingolipids, such as ceramides, have been implicated in the regulation of human EE via mitochondrial uncoupling. In this study, we investigated whether genetic variants within enzymes involved in sphingolipid synthesis and degradation affect EE and insulin-related traits in a cohort of American Indians informative for 24-hour EE and glucose disposal rates during a hyperinsulinemic-euglycemic clamp. Association analysis of 10,084 genetic variants within 28 genes involved in sphingolipid pathways identified a missense variant (rs267738, A>C, E115A) in exon 4 of CERS2 that was associated with higher sleeping EE (+116 kcal/day) and increased rates of endogenous glucose production during basal (+5%) and insulin-stimulated (+43%) conditions, both indicators of hepatic insulin resistance. The rs267738 variant did not affect ceramide synthesis in HepG2 cells but resulted in a 30% decrease in basal mitochondrial respiration. In conclusion, we provide evidence that the CERS2 rs267738 missense variant may influence hepatic glucose production and post-absorptive sleeping metabolic rate.

Resting energy expenditure in women with polycystic ovary syndrome.

Is resting energy expenditure (REE) altered in women with polycystic ovary syndrome (PCOS)? Women with PCOS have a reduction in REE, when corrected for fat-free mass, independent of PCOS clinical phenotypes and BMI categories. Obesity is an important issue in women with PCOS, in terms of frequency and pathophysiological implications. It has been hypothesized that obesity may be favoured by alterations in REE, but the studies have been limited and conflicting. This case-control study was a comparison of 266 women with PCOS and 51 healthy controls, recruited in the Verona 3P study from 2010 to 2021. Women with PCOS diagnosed by the Rotterdam criteria, with normal thyroid function and no interfering medications, were referred to the outpatient clinic of a tertiary care centre of endocrinology and metabolism for a measurement of REE. Healthy controls were recruited in the same period and submitted to the same procedure. In all subjects, REE was measured by indirect calorimetry and serum androgens were measured by LC-MS/MS. In women with PCOS, insulin sensitivity was assessed using the hyperinsulinemic-euglycemic clamp. REE was similar in women with PCOS and controls. However, REE corrected for fat-free mass (REE/FFM) was significantly lower in women with PCOS than in controls (31.8 ± 4.0 vs 35.4 ± 3.9kcal/kgFFM·day, P < 0.001). REE/FFM did not differ between normal-weight, overweight, or obese women with PCOS, and each of these subgroups showed lower REE/FFM values than controls. Reduced REE/FFM values were found in each phenotype of the syndrome. In multiple regression analysis, REE/FFM was independently associated with age and PCOS status, but not with fat mass. In PCOS women, REE/FFM was independently and directly associated with ovarian follicle number. Limitations of the study are the cross-sectional design, which limits the causal inference of the results, and the unavailability of precise information about lifestyle factors, which may be potential confounders. Further prospective studies are needed to establish the importance of this phenomenon in contributing to the weight excess of PCOS. A reduction of REE could potentially favour weight gain in women with PCOS and possibly contribute to the altered metabolic profile typical of this condition, even counteracting the therapeutic strategies aimed to reduce excess body fat in these women. Nevertheless, the presence of this abnormality in both obese/overweight and normal-weight patients suggests that other factors must play a role in this phenomenon. This work was supported by academic grants to PM from the University of Verona (FUR 2010-2022). All authors declare no conflict of interest. N/A.

Greater molecular potential for glucose metabolism in adipose tissue and skeletal muscle of women compared with men.

Women typically have less muscle mass and more fat mass than men, while at the same time possessing similar or even greater whole-body insulin sensitivity. Our study aimed to investigate the molecular factors in primarily adipose tissue, but also in skeletal muscle, contributing to this sex difference. In healthy, moderately active premenopausal women and men with normal weight (28 ± 5 and 23 ± 3 years old; BMI 22.2 ± 1.9 and 23.7 ± 1.7) and in healthy, recreationally active women and men with overweight (32.2 ± 6 and 31.0 ± 5 years old; BMI 29.8 ± 4.3 & 30.9 ± 3.7) matched at age, BMI, and fitness level, we assessed insulin sensitivity and glucose tolerance with a hyperinsulinemic-euglycemic clamp or oral glucose tolerance test and studied subcutaneous adipose tissue and skeletal muscle samples with western blotting. Additionally, we traced glucose-stimulated glucose disposal in adipose tissues of female and male C57BL/6J littermate mice aged 16 weeks and measured glucose metabolic proteins. Our findings revealed greater protein expression related to glucose disposal in the subcutaneous adipose tissue (AKT2, insulin receptor, glucose transport 4) and skeletal muscle (hexokinase II, pyruvate dehydrogenase) in women compared to matched men with normal weight and with overweight. This increased protein capacity for glucose uptake extended to white adipose tissues of mice accompanied with ~2-fold greater glucose uptake compared to male mice. Furthermore, even in the obese state, women displayed better glucose tolerance than matched men, despite having 46% body fat and 20 kg less lean mass. In conclusion, our findings suggest that the superior potential for glucose disposal in female subcutaneous adipose tissue and skeletal muscle, driven by greater expression of various glucose metabolic proteins, compensates for their lower muscle mass. This likely explains women's superior glucose tolerance and tissue insulin sensitivity compared to men.

Postprandial fatty acid-binding protein4 is associated with muscle insulin resistance.

Fatty acid-binding protein4 (FABP4) has been reported to act as a hepatic insulin resistance factor. We previously reported that fasting FABP4 was correlated with insulin resistance measurements derived from the glucose clamp, and another study reported that postprandial FABP4 levels were decreased in healthy volunteers but were not reported (or known) in participants with type 2 diabetes. We have limited knowledge about the direct effect of FABP4 on muscle cells. We investigated the postprandial FABP4 levels in participants with type 2 diabetes, and the basic mechanism of muscle insulin resistance and FABP4. We performed a meal tolerance test and hyperinsulinaemic-euglycaemic clamp in 22 participants with type 2 diabetes and 26 participants without diabetes. We measured fasting and postprandial serum FABP4. We cultured mouse C2C12 muscle cells, and investigated the effect of FABP4 on glucose uptake. We analysed insulin signalling by western blot and insulin binding assay. The postprandial FABP4 level in participants with type 2 diabetes was higher than that in participants without diabetes. Participants without diabetes had lower postprandial FABP4 than fasting except for one participant, whereas one-third of participants with type 2 diabetes had higher postprandial FABP4 than fasting. Postprandial FABP4 was correlated with the muscle insulin resistance M/I value from a glucose clamp in participants without diabetes (r=-0.42, p<0.05). The increase in FABP4 after a meal correlated with the muscle insulin resistance M/I value (r=-0.44, p<0.05) and the difference between fasting and postprandial glucagon in participants with type 2 diabetes (r=0.36, p<0.05). FABP4 alone appears to increase glucose uptake, and the combination of FABP4 and insulin decreases glucose uptake when compared with insulin alone. FABP4 inhibits insulin signalling of muscle cells through decreases in phosphorylation of insulin receptor substrate1 and Akt. The physiological concentration of FABP4 did not inhibit insulin binding to muscle cells. These results suggested that the postprandial FABP4 level is associated with insulin resistance, and FABP4 may suppress insulin signals.

Sleep Duration Alters Overfeeding-mediated Reduction in Insulin Sensitivity.

Weight gain and sleep restriction both reduce insulin sensitivity. However, it is not known if sleep duration alters glucose metabolism in response to overfeeding. To examine the effect of sleep duration on overfeeding-mediated alterations in carbohydrate metabolism and insulin sensitivity. Retrospective exploratory analysis of a longitudinal overfeeding study in healthy participants (n = 28, age: 26.9 ± 5.5 years, body mass index: 25.74 ± 2.45 kg/m2). After providing baseline study measures, participants were overfed 40% above weight maintenance calorie requirements for 8 weeks. Insulin sensitivity was determined by a 2-step hyperinsulinemic-euglycemic clamp. Baseline habitual sleep duration was estimated by accelerometry, and sleep groups were created based on median sleep duration (5.2 hours/night). Overfeeding led to an average body weight gain of 7.3 ± .4 kg. Habitual sleep duration did not alter overfeeding-mediated body weight gain, fat gain, and fat distribution (all P > .15). Compared to participants with more sleep, fasting insulin (P = .01) and homeostatic model assessment for insulin resistance (P = .02) increased while fasting glucose remained unchanged (P = .68) with overfeeding in participants with shorter sleep duration. Glucose infusion rate during high insulin dose was reduced with overfeeding in participants with short sleep duration but not in participants with more sleep (P < .01). Overfeeding mediated weight gain reduced liver, adipose, and whole-body insulin sensitivity prominently in individuals with short sleep duration but not in individuals with longer sleep duration. This suggests that promoting adequate sleep during short periods of overeating may prevent detrimental effects on glucose metabolism.

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 testand 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.

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

Background/ObjectiveTo identify predictors of incident type 2 diabetes using a mixed meal tolerance test (MMTT).MethodsAdult 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).ResultsAt 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.ConclusionsGlucose 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 RegistryClinicalTrials.gov identifier : NCT00340132, NCT00339482

Assessment of Cardiometabolic Risk Factors and Insulin Sensitivity by Hyperinsulinemic-Euglycemic Clamp in Resistance to Thyroid Hormone β Syndrome.

Background: Resistance to thyroid hormone beta (RTHβ) is a rare disease resulting from mutations in the THRB gene, characterized by reduced T3 action in tissues with high thyroid hormone receptor β expression. Thyroid hormones regulate body composition and metabolism in general, and increased or decreased hormone levels are associated with insulin resistance. This study evaluated the presence of cardiometabolic risk factors and insulin sensitivity in patients with RTHβ. Methods: In all, 16 patients, 8 adults (52.3 ± 16.3 years of age) and 8 children (10.9 ± 3.9 years of age), were compared to 28 control individuals matched for age, sex, and body mass index (BMI). Anthropometry evaluation and blood samples were collected for glycemia, lipids, insulin, interleukin-6 (IL-6), tumor necrosis factor-alpha (TNF-α), leptin, adiponectin, ultrasensitive C-reactive protein (CRPus), free thyroxine, total triiodothyronine, thyrotropin, and anti-thyroid peroxidase measurements. Body composition was assessed using dual-emission X-ray absorptiometry and bioimpedance. Insulin sensitivity was evaluated in adult patients and controls using the hyperinsulinemic-euglycemic clamp (HEC), whereas homeostasis model assessment of insulin resistance (HOMA-IR) was calculated in all individuals studied. Results: Patients and controls presented similar weight, BMI, abdominal perimeter, and total fat body mass. Patients with RTHβ demonstrated higher total cholesterol (TC), p = 0.04, and low-density lipoprotein cholesterol (LDL-C), p = 0.03, but no alteration was observed in other parameters associated with metabolic risk, such as leptin, TNF-α, and CRPus. Two adult patients met the criteria for metabolic syndrome. There was no evidence of insulin resistance assessed by HEC or HOMA-IR. Elevated IL-6 levels were observed in patients with RTHβ. Conclusion: Using HEC as the gold standard method, no evidence of reduced insulin sensitivity in skeletal muscle was documented in RTHβ adult patients; however, higher levels of TC and LDL-C were observed in these patients, which suggest the need for active monitoring of this abnormality to minimize cardiometabolic risk. In addition, we demonstrated, for the first time, that the increase in IL-6 levels in patients with RTHβ is probably secondary to metabolic causes as they have normal levels of TNF-α and CRPus, which may contribute to an increase in cardiovascular risk. A larger number of patients must be studied to confirm these results.

Intermuscular adipose tissue accumulation is associated with higher tissue sodium in healthy individuals.

High tissue sodium accumulation and intermuscular adipose tissue (IMAT) are associated with aging, type 2 diabetes, and chronic kidney disease. In this study, we aim to investigate whether high lower-extremity tissue sodium accumulation relates to IMAT quantity and whether systemic inflammatory mediators and adipocytokines contribute to such association. Tissue sodium content and IMAT accumulation (percentage of IMAT area to muscle area) were measured in 83 healthy individuals using sodium imaging (23Na-MRI) and proton (1H-MRI) imaging of the calf. Insulin sensitivity was assessed by glucose disposal rate (GDR) measured with the hyperinsulinemic-euglycemic clamp. Median (interquartile range) muscle and skin sodium contents were 16.6 (14.9, 19.0) and 12.6 (10.9, 16.7) mmol/L, respectively. Median IMAT was 3.69 (2.80, 5.37) %. In models adjusted for age, sex, BMI, GDR, adiponectin, and high-sensitivity C-reactive protein, increasing tissue sodium content was significantly associated with higher IMAT quantity (p = 0.018 and 0.032 for muscle and skin tissue sodium, respectively). In subgroup analysis stratified by sex, skin sodium was significantly associated with IMAT only among men. In interaction analysis, the association between skin sodium and IMAT was greater with increasing levels of high-sensitivity C-reactive protein and interleukin-6 (p for interaction = 0.022 and 0.006, respectively). Leg muscle and skin sodium are associated with IMAT quantity among healthy individuals. The relationship between skin sodium and IMAT may be mediated by systemic inflammation.

Insulin Resistance and Its Detection

Abstract Insulin resistance is a characteristic of adiposity, metabolic disorders, and several heart disorders, and it correlates to the diabetic state. As a result, determining insulin responsiveness in animals and humans is critical for an observational study, fundamental medical and preclinical research, and therapeutic application. Directly and indirectly, approaches of varied intricacy are now employed for this purpose. Several approaches use constant glucose and insulin analysis while others use dynamic testing. Every approach has its own set of pros and cons. As a result, the best strategy to utilize and choose is determined by the nature of the current research. The sources of primary data for evaluating insulin sensitivity in vivo that has been developed were rather complicated. The hyperinsulinemic-euglycemic glucose clamps and insulin-suppressing tests assess insulin-dependent sugar consumption in constant circumstances which need effort and time. The indirect technique depends on a basic pattern recognition of regularly selected intravenously glucose tolerance testing, which is significantly less complicated. Furthermore, basic substitute measures for insulin sensitiveness/resistances are known, which are calculated from blood insulin and glucose levels in fasted (stable conditions) or just after taking sugar by mouth (dynamics). Thus, quantifiable control index of insulin sensitiveness, in an instance, has now been thoroughly verified against the gold standard of glucose clamping. Quantifiable glycemic control check indicator’s quantitative insulin-sensitivity check index an easy, reformable methodology for measuring reforms in insulin sensitivities as a result of therapeutic protocols and the onset of diabetics. Researchers address the benefits, limitations, and correct implementation of established in vivo insulin sensitivity/resistance testing in this Frontier article.