Metabolic Insulin Sensitivity Research Articles

Impact of Insulin-Induced Relative Hypoglycemia on Vascular Insulin Sensitivity and Central Hemodynamics in Prediabetes.

Relative hypoglycemia (RH) is linked to sympathetic responses that can alter vascular function in individuals with type 2 diabetes. However, less is known about the role of RH on hemodynamics or metabolic insulin sensitivity in prediabetes. Determine if RH alters peripheral endothelial function or central hemodynamics to a greater extent in those with prediabetes (PD) versus normoglycemia (NG). Seventy adults with obesity were classified using ADA criteria as PD (n=34 (28F); HbA1c=6.02±0.1%) or NG (n=36 (30F); HbA1c=5.4±0.0%). Brachial artery endothelial function, skeletal muscle capillary perfusion, and aortic waveforms were assessed at 0 and 120min of a euglycemic clamp (40 mU/m2/min, 90 mg/dl). Plasma nitrate/nitrite and endothelin-1 (ET-1) were measured as surrogates of nitric oxide-mediated vasodilation and vasoconstriction, respectively. RH was defined as the drop in glucose (%) from fasting to clamp steady state. There were no differences in age, weight, or VO2max between groups. PD had higher HbA1c (P<0.01) and a greater drop in glucose in response to insulin (14 vs. 8%; P=0.03). Further, heart rate (HR) increased in NG compared to PD (P<0.01), while forward wave (Pf) decreased in PD (P=0.04). Insulin also tended to reduce arterial stiffness (cfPWV) in NG versus PD (P=0.07), despite similar increases in pre-occlusion diameter (P=0.02), blood flow (P=0.02), and lower augmentation index (AIx75) (P≤0.05). Compared with NG, insulin-induced RH corresponded with a blunted rise in HR and drop in Pf during insulin infusion in adults with PD, independent of changes in peripheral endothelial function.

Insulin-induced vasoconstriction is prevalent in muscle microvasculature of otherwise healthy persons with type 1 diabetes.

Insulin's microvascular actions and their relationship to insulin's metabolic actions have not been well studied in adults with type 1 diabetes mellitus (T1DM). We compared the metabolic and selected micro- and macrovascular responses to insulin by healthy adult control (n = 16) and subjects with T1DM (n = 15) without clinical microvascular disease. We measured insulin's effect on 1) skeletal muscle microvascular perfusion using contrast-enhanced ultrasound (CEU), 2) arterial stiffness using carotid-femoral pulse-wave velocity (cfPWV) and radial artery pulse wave analysis (PWA), and 3) metabolic insulin sensitivity by the glucose infusion rate (GIR) during a 2-h, 1 mU/min/kg euglycemic-insulin clamp. Subjects with T1DM were metabolically insulin resistant (GIR = 5.2 ± 0.7 vs. 6.6 ± 0.6 mg/min/kg, P < 0.001). Insulin increased muscle microvascular blood volume and flow in control (P < 0.001, for each) but not in subjects with T1DM. Metabolic insulin sensitivity correlated with increases of muscle microvascular perfused volume (P < 0.05). Baseline measures of vascular stiffness did not differ between groups. However, during hyperinsulinemia, cfPWV was greater (P < 0.02) in the T1DM group and the backward pulse wave pressure declined with insulin only in controls (P < 0.03), both indices indicating that insulin-induced vascular relaxation in controls only. Subjects with T1DM have muscle microvascular insulin resistance that may precede clinical microvascular disease.NEW & NOTEWORTHY Using contrast ultrasound and measures of vascular stiffness, we compared vascular and metabolic responses to insulin in patients with type 1 diabetes with age-matched controls. The patients with type 1 diabetes demonstrated both vascular and metabolic insulin resistance with more than half of the patients with diabetes having a paradoxical vasoconstrictive vascular response to insulin.

Aortic waveform responses to insulin in late versus early chronotype with metabolic syndrome.

Late chronotype (LC) correlates with reduced metabolic insulin sensitivity and cardiovascular disease. It is unclear if insulin action on aortic waveforms and inflammation is altered in LC versus early chronotype (EC). Adults with metabolic syndrome (n = 39, MetS) were classified as either EC (Morning‐Eveningness Questionnaire [MEQ] = 63.5 ± 1.2) or LC (MEQ = 45.5 ± 1.3). A 120 min euglycemic clamp (40 mU/m2/min, 90 mg/dL) with indirect calorimetry was used to determine metabolic insulin sensitivity (glucose infusion rate [GIR]) and nonoxidative glucose disposal (NOGD). Aortic waveforms via applanation tonometry and inflammation by blood biochemistries were assessed at 0 and 120 min of the clamp. LC had higher fat‐free mass and lower VO2max, GIR, and NOGD (between groups, all p ≤ 0.05) than EC. Despite no difference in 0 min waveforms, both groups had insulin‐stimulated elevations in pulse pressure amplification with reduced AIx75 and augmentation pressure (AP; time effect, p ≤ 0.05). However, EC had decreased forward pressure (Pf; interaction effect, p = 0.007) with insulin versus rises in LC. Although LC had higher tumor necrosis factor‐α (TNF‐α; group effect, p ≤ 0.01) than EC, both LC and EC had insulin‐stimulated increases in TNF‐α and decreases in hs‐CRP (time effect, both p ≤ 0.01). Higher MEQ scores related to greater insulin‐stimulated reductions in AP (r = −0.42, p = 0.016) and Pf (r = −0.41, p = 0.02). VO2max correlated with insulin‐mediated reductions in AIx75 (r = −0.56, p < 0.01) and AP (r = −0.49, p < 0.01). NOGD related to decreased AP (r = −0.44, p = 0.03) and Pf (r = −0.43, p = 0.04) during insulin infusion. LC was depicted by blunted forward pressure waveform responses to insulin and higher TNF‐α in MetS. More work is needed to assess endothelial function across chronotypes.

Altered Aortic Waveform Responses To Insulin In Late Chronotype With Metabolic Syndrome

PURPOSE: Late chronotype (LC) is linked to insulin resistance & cardiovascular disease. However, it is unclear if insulin reduces aortic waveforms & inflammation in LC versus early chronotype (EC). METHODS: Using the Morning-Eveningness Questionnaire (MEQ), adults with metabolic syndrome (MetS; 54.9 ± 1.1y; VO2MAX 22.2 ± 0.7 ml/kg/min, 3.5 ± 0.1 ATP-III score) were classified as either LC (n = 19 (16F); MEQ = 45.5 ± 1.3) or EC (n = 20 (16F); MEQ = 63.5 ± 1.2). A 120 min euglycemic clamp (40 mU/m2/min, 90 mg/dl) with indirect calorimetry was used to determine metabolic insulin sensitivity (glucose infusion rate (GIR)) & non-oxidized glucose disposal (NOGD; GIR-total carbohydrate oxidation). Aortic waveforms via applanation tonometry were taken at 0 & 120-min of the clamp & included augmentation index (AIx75), augmentation pressure (AP), pulse pressure amplification (PPA), mean arterial pressure (MAP), as well as forward (Pf) & backward (Pb) pulse wave. Inflammation (ICAM, VCAM, hs-CRP, TNF-α, & MMP-7) was also assessed before and after the clamp. RESULTS: While age, fat mass, & ATP III score were similar between groups, LC had higher FFM (P = 0.04) and lower VO2MAX (P = 0.05), GIR (P < 0.01) and NOGD (P < 0.01) than EC. No difference in 0 min waveforms were noted. Nonetheless, LC had increases in Pf versus EC (∆:1.9 ± 1.1 vs. -2.3 ± 1.0 mmHg; P = 0.007) during insulin infusion, though reflection magnitude decreased similarly (∆: -6.0 ± 2.2 vs. -5.9 ± 2.3%; P = 0.02). Further, both LC and EC had elevated PPA (∆: 0.04 ± 0.02 vs. 0.05 ± 0.02 mmHg; P = 0.02) & reduced AP (∆: -2.0 ± 1.0 vs. -2.8 ± 1.1 mmHg; P = 0.02) in response to insulin, while only EC had lower AIx75 (P = 0.02). LC had increased TNF-α (P = 0.04) and decreased MMP-7 (P = 0.04) in response to insulin, and EC decreased in hs-CRP (P = 0.009), ICAM (P = 0.009), and VCAM (P = 0.09). VO2MAX correlated with insulin-mediated reductions in AIx75 (r = -0.56, P < 0.01) and AP (r = -0.49, P < 0.01), while NOGD related to decreased AP during insulin (r = -0.44, P = 0.03) and Pf (r = -0.43, P = 0.04). Insulin-mediated reductions in VCAM also correlated with lower MAP during the clamp (r = 0.41, P = 0.03). CONCLUSIONS: LC was depicted by altered aortic waveform and inflammatory responses to insulin in MetS. More work is needed to assess peripheral endothelial function in chronotype. Funding: NIH RO1-HL130296

Insulin infusion decreases medium-sized extracellular vesicles in adults with metabolic syndrome.

Elevated extracellular vesicles (EVs) are associated with glucose dysmetabolism. However, the effects of insulin on EVs and subsequent relationships with insulin sensitivity, substrate oxidation, and inflammation are unknown. We tested the hypothesis that insulin would lower EVs and relate to insulin action. Fifty-one sedentary adults (54.8 ± 1.0 yr; V̇o2peak : 22.1 ± 0.6 mL/kg/min) with metabolic syndrome (MetS) and obesity (36.4 ± 0.65 kg/m2) underwent a 2-h euglycemic-hyperinsulinemic clamp (5 mmol/L; 40 mU/m2/min). Count and size (medium: 200-624 nm; larger: 625-1,000 nm) for total particle count, endothelial- (CD105+), leukocyte- (CD45+), platelet- (CD41+), and tetraspanin- (TX+: CD9/CD81/CD63), as well as platelet endothelial cell adhesion molecule- (CD31+) derived EVs were determined before and following the clamp using Full Spectrum Profiling (FSPM). Size and MESF (molecules of equivalent soluble fluorochrome) data were generated using FCMPASS Software. Fat and carbohydrate oxidation, in addition to high-sensitivity c-reactive protein (hsCRP), were measured to understand insulin effects and associations between EVs, metabolic flexibility, and inflammation. Despite low metabolic insulin sensitivity (M-Value = 2.56 ± 0.17 mg/kg/min), insulin increased carbohydrate (P = 0.015) and decreased fat oxidation (P = 0.048) and hsCRP (P = 0.016) compared with fasting. Insulin also decreased total particle count (P < 0.001), attributable to decreased medium-sized CD105+ (P = 0.052) and CD45+ EVs (P < 0.001). Elevated fasting insulin was associated with reduced insulin-stimulated changes in all EVs phenotypes (P < 0.001). Interestingly, fasting EVs were associated with increased fasting carbohydrate oxidation (all P < 0.05). These findings suggest that insulin decreases medium-sized EVs in conjunction with metabolic flexibility under euglycemic conditions in adults with MetS. More research is needed to determine how therapies alter EV phenotype/size and consequent cardiometabolic risk.NEW & NOTEWORTHY This study is one of the first to investigate the effects of insulin on medium and larger extracellular vesicles (EVs) in relation to metabolic insulin sensitivity and fuel use in adults with metabolic syndrome. Our data suggest that insulin infusion decreases the concentration of total particle counts, mainly due to reductions in medium-sized EVs. Furthermore, EVs, predominantly medium-sized, are inversely associated with metabolic flexibility.

Human umbilical cord-derived mesenchymal stem cells alleviate insulin resistance in diet-induced obese mice via an interaction with splenocytes

BackgroundPrevious research has demonstrated that the spleen plays an important role in mesenchymal stem cell (MSC)-mediated alleviation of acute inflammation, as MSC infusion increases the spleen-derived anti-inflammatory cytokine interleukin 10 (IL-10) levels. However, studies on splenic involvement in MSC-induced protection against chronic inflammatory diseases are limited. Obesity is characterized by chronic low-grade inflammation, a key driver of insulin resistance. This study aims to evaluate the effects of MSCs on obesity-related insulin resistance and explore the underlying mechanism, particularly regarding splenic involvement.MethodsWe induced obesity in mice by feeding them high-fat diets for 20 weeks. Human umbilical cord-derived MSCs (UC-MSCs) were systemically infused into the obese mice once per week for 6 weeks. Systemic glucose metabolic homeostasis and insulin sensitivity in epididymal adipose tissue (EAT) were evaluated. Then, we conducted in vivo blockade of IL-10 during UC-MSC infusion by intraperitoneally administrating an IL-10-neutralizing antibody twice per week. We also investigated the therapeutic effects of UC-MSCs on obese mice after removal of the spleen by splenectomy.ResultsUC-MSC infusions improved systemic metabolic homeostasis and alleviated insulin resistance in EAT but elicited no change in weight. Despite rare engraftment of UC-MSCs in EAT, UC-MSC infusions attenuated insulin resistance in EAT by polarizing macrophages into the M2 phenotype, coupled with elevated serum IL-10 levels. In vivo blockade of IL-10 blunted the effects of UC-MSCs on obese mice. Furthermore, UC-MSCs overwhelmingly homed to the spleen, and the ability of UC-MSCs to elevate serum IL-10 levels and alleviate insulin resistance was impaired in the absence of the spleen. Further in vivo and in vitro studies revealed that UC-MSCs promoted the capacity of regulatory T cells (Treg cells) to produce IL-10 in the spleen.ConclusionsOur results demonstrated that UC-MSCs elevated serum IL-10 levels and subsequently promoted macrophage polarization, leading to alleviation of insulin resistance in EAT. The underlying mechanism was that UC-MSCs improved the capacity of Treg cells to produce IL-10 in the spleen. Our findings indicated that the spleen played a critical role in amplifying MSC-mediated immunomodulatory effects, which may contribute to maximizing MSC efficacy in clinical applications in the future.

Acute exercise decreases insulin-stimulated extracellular vesicles in conjunction with augmentation index in adults with obesity.

Extracellular vesicles (EVs) are often elevated in obesity and may modulate disease risk. Although acute exercise reduces fasting EVs in adults with obesity, no data exist on insulin-mediated EV responses. This study evaluated the effects of exercise on EV responses to insulin in relation to vascular function. Ten (5M/5F) sedentary adults with obesity (34.3±3.7kg/m2 ) completed an evening control and acute exercise condition (70% to expend 400kcal). Following an overnight fast, participants underwent a 2h euglycaemic-hyperinsulinaemic clamp (90mg/dl; 40mU/m2 /min) to determine metabolic insulin sensitivity (M-value), phenotypes of medium- to large-sized EVs, and aortic waveform measures. Endothelial (CD105+ , CD41- /CD31+ )-, leukocyte (CD45+ )-, platelet (CD41+ , CD41+ /31+ )- and tetraspanin (TX+ )-derived EVs, as well as platelet endothelial cell adhesion molecule (CD31+ ), were determined before and after the clamp using high resolution spectral flow cytometry. Although exercise did not alter fasting haemodynamics, it lowered the augmentation index (AIx75, P=0.024) and increased the M-value (P=0.042). Further, exercise decreased all fasting EVs (P<0.01) and decreased insulin-stimulated TX+ (P=0.060), CD31+ (P=0.060) and CD41- /31+ (P=0.045) compared to rest. Interestingly, greater insulin-stimulated decreases in CD41- /31+ were associated with reduced AIx75 during the clamp (r=0.62, P=0.059), while insulin-stimulated decreases in CD41+ (r=-0.68, P=0.031), CD41+ /31+ (r=-0.69, P=0.262), TX+ (r=-0.66, P=0.037) and CD31+ (r=-0.69, P=0.028) correlated with M-value following exercise. Thus, acute exercise may decrease fasting and insulin-stimulated medium- to large-size EVs in conjunction with improved M-value and AIx75. More research is needed to understand effects of exercise on EVs in the regulation of glucose homeostasis and vascular function. KEY POINTS: Extracellular vesicles (EVs) are increased in states of obesity and may play a role in altered insulin sensitivity and blood pressure; aerobic exercise decreases fasting EV concentrations the following day in adults with obesity. This study directly tested the effects of insulin on EVs and how a single bout of exercise impacts these responses. Together, these data highlight the positive effects of a single bout of exercise on fasting and insulin-stimulated EVs, with the latter relating to increased insulin sensitivity and decreased augmentation index. These results support future research identifying EVs as mechanistic factors in glucose regulation and vascular function as well as clinical use of exercise to reduce cardiovascular disease risk.

The association between serum adropin and carotid atherosclerosis in patients with type 2 diabetes mellitus: a cross\u2011sectional study

BackgroundAdropin, a newly‑identified energy homeostasis protein, has been implicated in the maintenance of metabolic homeostasis and insulin sensitivity. This study attempts to measure the association between serum adropin and carotid atherosclerosis in patients with type 2 diabetes mellitus (T2DM).MethodsThis cross‑sectional study was performed in 503 hospitalized patients with T2DM.Serum adropin level was measured by a sandwich enzyme-linked immunosorbent assay. The carotid atherosclerosis was assessed by color Doppler sonography. The association between adropin and carotid atherosclerotic plaque was tested by logistic regression model. The effect of adropin on carotid intimal-medial thickness (CIMT) was estimated using linear regression model.ResultsOverall, 280 (55.7%) patients had carotid atherosclerotic plaque. The risk of carotid atherosclerotic plaque decreased with the increment of serum adropin level (adjusted odds ratio [aOR], 0.90; 95%CI: 0.81–0.99) in patients with T2DM. Serum adropin (Standardized β = − 0.006, p = 0.028) was also independently protective factor for CIMT in patients with T2DM.ConclusionIn patients with T2DM, high serum adropin level was correlated with a decreased risk of carotid atherosclerosis in T2DM patients. Low circulating level of adropin may promote carotid atherosclerosis.

Metformin improves skeletal muscle microvascular insulin resistance in metabolic syndrome.

Microvascular insulin resistance is present in metabolic syndrome and may contribute to increased cardiovascular disease risk and the impaired metabolic response to insulin observed. Metformin improves metabolic insulin resistance in humans. Its effects on macro and microvascular insulin resistance have not been defined. Eleven subjects with nondiabetic metabolic syndrome were studied four times (before and after 12 wk of treatment with placebo or metformin) using a crossover design, with an 8-wk washout interval between treatments. On each occasion, we measured three indices of large artery function [pulse wave velocity (PWV), radial pulse wave separation analysis (PWSA), brachial artery endothelial function (flow-mediated dilation-FMD)] as well as muscle microvascular perfusion [contrast-enhanced ultrasound (CEU)] before and at 120 min into a 150 min, 1 mU/min/kg euglycemic insulin clamp. Metformin decreased body mass index (BMI), fat weight, and % body fat (P < 0.05, each), however, placebo had no effect. Metformin (not placebo) improved metabolic insulin sensitivity, (clamp glucose infusion rate, P < 0.01), PWV, and FMD after insulin were unaffected by metformin treatment. PWSA improved with insulin only after metformin P < 0.01). Insulin decreased muscle microvascular blood volume measured by contrast ultrasound both before and after placebo and before metformin (P < 0.02 for each) but not after metformin. Short-term metformin treatment improves both metabolic and muscle microvascular response to insulin. Metformin's effect on microvascular insulin responsiveness may contribute to its beneficial metabolic effects. Metformin did not improve aortic stiffness or brachial artery endothelial function, but enhanced radial pulse wave properties consistent with relaxation of smaller arterioles.NEW & NOTEWORTHY Metformin, a first-line treatment for type 2 diabetes, is often used in patients with insulin resistance and metabolic syndrome. Here, we provide the first evidence for metformin improving muscle microvascular insulin sensitivity in insulin-resistant humans. Simultaneously, metformin improved muscle glucose disposal, supporting a close relationship between insulin's microvascular and its metabolic actions in muscle. Whether enhanced microvascular insulin sensitivity contributes to metformin's ability to decrease microvascular complications in diabetes remains to be resolved.

Cyanidin-3-O-Glucoside Supplementation Ameliorates Metabolic Insulin Resistance via Restoration of Nitric Oxide-Mediated Endothelial Insulin Transport.

Anthocyanin cyanidin-3-O-glucoside (Cy3G) possesses a great potential in prevention of diabetes and its vascular complications while the underlying mechanisms are still far from clear. Accumulating evidence suggests that endothelial insulin transport plays a critical role in regulating metabolic insulin sensitivity. Whether Cy3G can modulate metabolic insulin resistance via regulating endothelial insulin transport is not reported yet. Palmitic acid (PA)-treated mouse aortic endothelial cells (MAECs) model and high-fat diet (HFD) fed mice model are used. Compared with HFD mice, Cy3G supplementation decrease exogenous insulin content in skeletal muscle and ameliorate metabolic insulin resistance. In culture, Cy3G can directly ameliorate PA-induced impairment on FITC-insulin uptake in MAECs. Mechanistically, Cy3G can effectively decrease inflammatory cytokines and toll-like receptor 4 (TLR4)/nuclear factor-kappa-B inhibitor alpha (IκBα) activation, and restore the attenuated Akt/eNOS signaling pathway. Blunted nitric oxide (NO) synthase with N-nitro-l-arginine methyl ester (L-NAME) can effectively abolish the protective role of Cy3G on endothelial insulin transport and insulin-stimulated glucose utilization in HFD-fed mice. These findings suggest that Cy3G supplementation can directly restore the attenuated nitic oxide-mediated endothelial insulin transport and thereby ameliorate metabolic insulin resistance. Our finding can provide a novel explanation for the anti-diabetic effects of Cy3G.

A Single Bout Of Exercise Decreases Fasting And Insulin-stimulated Extracellular Vesicles In Adults With Obesity

PURPOSE: Extracellular vesicle (EV) concentrations are elevated in states of insulin resistance and may modulate type 2 diabetes and cardiovascular risk. While recent work has suggested that acute exercise reduces fasting EV concentrations, whether exercise alters EV responses to insulin is unknown. METHODS: Ten sedentary adults (5F/5M, Age: 49.5 ± 2.4 yr; VO2max: 23.9 ± 1.8 kg/mg/min) with obesity (body fat: 41.7 ± 2.3 %) completed a control and acute exercise bout condition (70% VO2max to expend 400 kcals between 4-7 pm). After an overnight fast, participants underwent a 2-hr euglycemic-hyperinsulinemic clamp (90 mg/dl; 40 mU/m2/min) to determine metabolic insulin sensitivity (M-value) and EV concentrations. Endothelial (CD105+, CD41-/CD31+), leukocyte (CD45+), platelet (CD41+, CD41+/31+), and tetraspnain-derived EVs (TX+), as well as platelet endothelial cell adhesion molecule (CD31+) were detected in platelet poor plasma samples at 0 and 2-hr of the clamp using spectral flow cytometry. Statistical significance was accepted as P ≤ 0.05. RESULTS: Exercise decreased fasting CD41-/31+ (P = 0.05), CD45+ (P = 0.04), CD41+ (P < 0.001), CD41+/31+ (P = 0.001), CD31+ (P = 0.001), and TX+ (P < 0.001) compared to rest. In addition, exercise tended to promote a greater reduction in insulin-stimulated CD31+ and TX+ (both P = 0.06) and increased the M-value compared to rest (3.68 ± 0.69 vs 2.94 ± 0.49 mg/kg/min, P = 0.03). While there were no relations among rest EVs and M-value, fasting exercise concentrations of CD105+ (r = 0.89, P = 0.001), CD41-/CD31+ (r = 0.89, P = 0.001), CD45+ (r = 0.87, P = 0.001), CD41+ (r = 0.84, P < 0.01), CD41 + 31+ (r = 0.84, P < 0.01), CD31+ (r = 0.85, P < 0.01), and TX+ (r = 0.85, P < 0.01) were associated with exercise M-value. Interestingly, the increase in the M-value following exercise (delta) was associated with overall lower concentrations of CD41+ (r = -0.68, P = 0.03), CD31 (r = -0.69, P = 0.03), and TX+ (r = -0.66, P = 0.04) with insulin infusion (delta: 2-0 hr). CONCLUSION: A single bout of exercise decreases fasting and insulin-stimulated EVs in conjunction with metabolic insulin sensitivity. More research is needed to understand the effects of exercise on EVs in the regulation of glucose homeostasis. Funding: ACSM Foundation Doctoral Student Research Grant (EMH); UVA LaunchPad (UE, SKM); NIH RO1 HL130296 (SKM)

Effects of imatinib on vascular insulin sensitivity and free fatty acid transport in early weight gain.

Vascular endothelial dysfunction is an essential part of the pathophysiology of type 2 diabetes and its complications. In type 2 diabetes, endothelial dysfunction is characterized by reduced insulin signaling and increased transendothelial transport of fatty acids (FA). As the Abl kinase inhibitor imatinib was previously shown to reverse type 2 diabetes and to inhibit VEGF signaling via Abl kinases, we studied the effect of imatinib on vascular insulin sensitivity and fatty acid transport in vivo and in vitro. C57/BL6J mice were fed a chow diet or Western diet (WD), and received daily imatinib injections for two weeks. Insulin-mediated vasoreactivity of resistance arteries was studied using intravital microscopy, and metabolic insulin sensitivity using the hyperinsulinemic-euglycemic clamp. The effect of imatinib on triglyceride content in skeletal muscle and heart in vivo was also determined. In vitro, the effect of imatinib on fatty acid transport was studied in human umbilical vein endothelial cells (HUVECs) by evaluating the effect of imatinib on fluorescently labeled FA uptake both under basal and VEGF-B-stimulated conditions. Imatinib prevented the WD-induced weight gain in mice, independently from food intake. In line with this, imatinib enhanced insulin-mediated vasoreactivity of resistance arteries in the WD-fed mice. However, imatinib did not affect triglyceride content in muscle. In cultured endothelial cells, VEGF-B stimulation resulted in a time-dependent uptake of fatty acids in parallel with increased phosphorylation of the Abl kinase substrate Crk-like protein (CrkL) at Tyr207. Although imatinib effectively prevented VEGF-B-mediated Abl kinase activation, it had no effect on VEGF-B mediated endothelial FA uptake. Imatinib prevents weight gain and preserves insulin-mediated vasodilation in WD-fed mice, but does not affect endothelial FA transport despite inhibiting VEGF-B signaling. The beneficial effect of imatinib on insulin-mediated vasodilation may contribute to the anti-diabetic effects of imatinib.

199-OR: Insulin Infusion Decreases Extracellular Vesicles in Adults with Metabolic Syndrome

Elevated extracellular vesicles (EVs) are associated with glucose dysmetabolism. However, the direct effects of insulin on EVs and subsequent relationship with insulin sensitivity and substrate oxidation is unknown in adults with metabolic syndrome (MetS). Fifty sedentary adults (54.5 ± 1.0 yr; VO2peak: 22.3 ± 0.6 ml/kg/min) with MetS (36.3 ± 0.7 kg/m2; ATP III Criteria: 3.46 ± 1.0) underwent a 2-hr euglycemic-hyperinsulinemic clamp (90 mg/dl; 40 mU/m2/min) to determine EV responses to insulin and metabolic insulin sensitivity (M-Value). Endothelial (CD105+, CD41-/CD31+), leukocyte (CD45+), platelet (CD41+, CD41+/CD31+), and tetraspanin-derived EVs (TX+), as well as platelet endothelial cell adhesion molecule (CD31+) were detected in platelet poor plasma samples at 0 and 2-hr of the clamp using spectral flow cytometry. Fat (Fox) and carbohydrate oxidation (CHOox) were also measured (indirect calorimetry) to determine metabolic flexibility. Despite low metabolic insulin sensitivity (2.55 ± 0.2 mg/kg/min), insulin (82.9 ± 3.7 uU/ml) reduced Fox (delta, P=0.001) compared to fasting. Insulin also decreased CD105+ (P&amp;lt;0.01), CD41-/CD31+ (P=0.03), CD41+ (trend: P=0.06), TX+ (P&amp;lt;0.01), and CD31+ (P=0.03). Surprisingly, there were no correlations between EVs and metabolic insulin sensitivity. However, higher fasting insulin levels were related to lower insulin-stimulated changes in CD105+ (r=0.32, P=0.03), CD41-/CD31+ (r=0.33, P=0.05), and CD45+ (r=0.33, P=0.04). Further, fasting TX+ and CD41+ (r=0.33, P=0.05 and r=0.42, P&amp;lt;0.01) were related to fasting CHOox while CD105+ was inversely associated with fasting Fox (r=-0.33, P=0.03). Fasting TX+ (r=-0.42, P=0.01), CD31+ (r=-0.33, P=0.04), and CD41+ (r=-0.32, P=0.04) also correlated with CHOox metabolic flexibility. Insulin infusion decreases EVs in adults with MetS. Additional work investigating the role of EVs on substrate metabolism is warranted to elucidate mechanisms for type 2 diabetes risk. Disclosure E. Heiston: None. A. Ballantyne: None. N. Stewart: None. L. Musante: None. U. Erdbruegger: None. S. K. Malin: None. Funding National Institutes of Health (R01HL130296)

Insulin Action, Glucose Homeostasis and Free Fatty Acid Metabolism: Insights From a Novel Model.

Glucose and free fatty acids (FFA) are essential nutrients that are both partly regulated by insulin. Impaired insulin secretion and insulin resistance are hallmarks of aberrant glucose disposal, and type 2 diabetes (T2DM). In the current study, a novel model of FFA kinetics is proposed to estimate the role insulin action on FFA lipolysis and oxidation allowing estimation of adipose tissue insulin sensitivity (SIFFA ). Twenty-five normal volunteers were recruited for the current study. To participate, volunteers had to be less than 40 years of age and have a body mass index (BMI) < 30 kg/m2, and be free of medical comorbidity. The proposed model of FFA kinetics was used to analyze the data derived from the insulin-modified FSIGT. Mean fractional standard deviations of the parameter estimates were all less than 20%. Standardized residuals of the fit of the model to the FFA temporal data were randomly distributed, with only one estimated point lying outside the 2-standard deviation range, suggesting an acceptable fit of the model to the FFA data. The current study describes a novel one-compartment non-linear model of FFA kinetics during an FSIGT that provides an FFA metabolism insulin sensitivity parameter (SIFFA ). Furthermore, the models suggest a new role of glucose as the modulator of FFA disposal. Estimates of SIFFA confirmed previous findings that FFA metabolism is more sensitive to changes in insulin than glucose metabolism. Novel derived indices of insulin sensitivity of FFA (SIFFA ) were correlated with minimal model indices. These associations suggest a cooperative rather than competitive interplay between the two primary nutrients (glucose and FFA) and allude to the FFA acting as the buffer, such that glucose homeostasis is maintained.

Influence Of Type 2 Diabetes And Cardiovascular Disease Family History On Metabolic Syndrome Severity

BACKGROUND: Family history of cardiovascular disease (CVD) is considered a strong predictor of developing metabolic syndrome (MetS), in part through promoting endothelial dysfunction. In addition, a family history of type 2 diabetes (T2D) relates to lower metabolic insulin sensitivity and may compound their MetS risk severity. We examined in people with MetS if a family history of CVD and T2D (CVD+T2D) increases MetS risk severity compared to individuals with a family history of CVD only (CVD). METHODS: Twenty, middle-aged obese individuals with MetS (55.9 ± 6.5yrs; 32.5 ± 3.6kg/m2) were divided into CVD (n=9; 6F) or CVD+T2D (n=11; 9F). MetS was defined using the NCEP ATP III criteria. MetS severity Z-score was calculated from waist circumference, blood pressure, fasting blood glucose, triglycerides, and high-density lipoproteins. Metabolic insulin sensitivity (i.e. glucose infusion rate, GIR) was measured using a 2-hr hyperinsulinemic-euglycemic (40 mU/m2/min, 90 mg/dl) clamp. Insulin-stimulated brachial artery flow-mediated dilation (FMD) was also measured as the change from fasting to 2-hr during the clamp to assess endothelial function and gain tissue-specific insight into the origin of insulin action. RESULTS: There was no difference in anthropometrics between groups. There was also no statistical difference between CVD and CVD+T2D in MetS severity (2.62±1.12 vs. 1.65±0.56, P=0.42), GIR (2.35±0.55 mg/kg/min vs. 2.63±1.56 mg/kg/min, P=0.86), or insulin-stimulated FMD (0.33±1.57% vs. 1.68±1.19%, P=0.52). However, waist circumference was inversely correlated to GIR (r= -0.63, P=0.01). CONCLUSION: In adults with MetS, T2D family history does not exacerbate MetS severity in adults with CVD family history. However, waist circumference appears to be important for lowering metabolic insulin sensitivity. Thus, targeting abdominal fat may contribute to improved metabolic health independent of T2D and/or CVD family history. Funding was supported by the National Institutes of Health RO1-HL130296.

PREDIABETES PHENOTYPE DOES NOT EXACERBATE MICROVASCULAR INSULIN SENSITIVITY IN METABOLIC SYNDROME

Metabolic syndrome (MetS) and elevated glucose each promote microvascular dysfunction. Whether in combination these two conditions create increased dysfunction is not clear. Here, we tested whether glucose status worsens microvascular insulin sensitivity in MetS. Thirty-two sedentary, obese adults (54.2±1.2yrs; 35.9±1.3kg/m2; VO2max: 19.9±1.3ml/kg/min) with MetS (≥3 ATP III criteria) were classified as normal glucose tolerant (NGT, n=8; 6F), impaired fasting glucose (IFG; n=10; 7F) or IFG+IGT (n=14; 11F) according to ADA criteria using a 75g OGTT. Capillary perfusion (microvascular blood volume, MBV), filling rate (microvascular flow velocity, MFV) and blood flow (MBF=MBV*MFV) were assessed as the change before and after a 2hr euglycemic-hyperinsulinemic clamp (90mg/dl, 40mU/m2/min) using contrast enhanced ultrasound. Glucose infusion rate (GIR) was used to determine metabolic insulin sensitivity while carbohydrate oxidation (CHOox) was measured before and after the clamp to understand nutrient utilization. T-tests, repeated measures ANOVAs and correlations were used when appropriate. Significance was accepted as P≤0.05. There were no differences in age, BMI, VO2max or GIR (NGT: 2.26±0.48 vs. IFG: 2.66±0.46 vs. IFG+IGT: 1.91±0.37mg/kg/min, P=0.44) among groups. Insulin did not stimulate capillary perfusion (NGT: 0.16±0.19 vs. IFG: -0.02±0.14 vs. IFG+IGT: 0.08±0.12AI, P=0.40), filling rate (NGT: 0.006±0.005 vs. IFG: 0.003±0.004 vs. IFG+IGT: 0.004±0.004sec-1, P=0.11) or blood flow (NGT: 0.02±0.02 vs. IFG: 0.01±0.01 vs. IFG+IGT: 0.01±0.01AI/sec, P=0.21). CHOox was likewise unresponsive to insulin (P=0.34). Although age, BMI, fasting and 2hr glucose concentrations did not relate to insulin effects on microvascular function, fasting triglycerides was related to insulin-stimulated MBF (r=-0.39, P=0.03). Prediabetes phenotype does not worsen microvascular insulin sensitivity in adults with MetS. Future work is warranted to examine the effects of different therapies (lifestyle, medication) on microvascular function. Funding was supported by the National Institutes of Health RO1-HL130296.

Acupuncture or auricular electro-acupuncture as adjuncts to lifestyle interventions for weight management in PCOS: protocol for a randomised controlled feasibility study

BackgroundPolycystic ovary syndrome (PCOS) is a prevalent women’s health condition with reproductive, metabolic, and psychological manifestations. Weight loss can improve these symptoms and is a key goal; however, many women find this difficult to achieve. Acupuncture is a Chinese medical treatment that involves insertion of very fine metal needles into specific areas of the body and has been shown to be efficacious for weight loss in non-PCOS populations. However, few studies have been conducted in women with PCOS. A variant of acupuncture, auricular electro-acupuncture (AEA), may have beneficial effects on sympathetic tone, which is associated with insulin resistance, obesity and PCOS.MethodsThis prospective three-arm open label parallel randomised controlled trial will assess feasibility and acceptability of acupuncture and/or AEA for weight loss in women with PCOS. We will enrol 39 women from the community aged between 18 and 45 years, with physician diagnosis of PCOS according to the Rotterdam criteria: body mass index (BMI) between 25 and 40 kg/m2. Women will be randomly allocated to receive one of three treatments for 12 weeks duration: body electro-acupuncture + lifestyle interventions, AEA + lifestyle interventions, or lifestyle interventions alone. The lifestyle intervention in this study is telephone-based health coaching (between 4 and 13 phone calls, depending on individual need), provided by the Get Healthy Service. Primary outcomes of the study are feasibility and acceptability of trial methods as determined by recruitment and retention rates, adherence, acceptability, credibility, and safety. Secondary outcomes include anthropometric (body weight, BMI, waist and hip circumference), metabolic (glucose tolerance and insulin sensitivity obtained from a 2-h 75 g oral glucose tolerance test with area under the curve insulin calculated using the trapezoid rule), reproductive (androgen levels, menstrual cyclicity, clinical hyperandrogenism using the Ferriman-Gallwey scoring system), autonomic (heart rate variability, blood pressure), lifestyle (physical activity levels, diet quality, weight self-efficacy), quality of life, and psychological (depression and anxiety symptoms, internal health locus of control).DiscussionThis study addresses the feasibility and acceptability of novel interventions to treat overweight/obesity in PCOS. Study findings have the potential to generate a new understanding of the role of acupuncture and auricular acupuncture in weight management.Trial registrationAustralian New Zealand Clinical Trial Registry, 8/6/18 ACTRN12618000975291

Glucocorticoids affect metabolic but not muscle microvascular insulin sensitivity following high versus low salt intake.

BACKGROUNDSalt-sensitive hypertension is often accompanied by insulin resistance in obese individuals, but the underlying mechanisms are obscure. Microvascular function is known to affect both salt sensitivity of blood pressure and metabolic insulin sensitivity. We hypothesized that excessive salt intake increases blood pressure and decreases insulin-mediated glucose disposal, at least in part by impairing insulin-mediated muscle microvascular recruitment (IMMR).METHODSIn 20 lean and 20 abdominally obese individuals, we assessed mean arterial pressure (MAP; 24-hour ambulatory blood pressure measurements), insulin-mediated whole-body glucose disposal (M/I value; hyperinsulinemic-euglycemic clamp technique), IMMR (contrast-enhanced ultrasound), osmolyte and water balance, and excretion of mineralocorticoids, glucocorticoids, and amino and organic acids after a low- and high-salt diet during 7 days in a randomized, double-blind, crossover design.RESULTSOn a low-, as compared with a high-salt, intake, MAP was lower, M/I value was lower, and IMMR was greater in both lean and abdominally obese individuals. In addition, natural logarithm IMMR was inversely associated with MAP in lean participants on a low-salt diet only. On a high-salt diet, free water clearance decreased, and excretion of glucocorticoids and of amino acids involved in the urea cycle increased.CONCLUSIONOur findings imply that hemodynamic and metabolic changes resulting from alterations in salt intake are not necessarily associated. Moreover, they are consistent with the concept that a high-salt intake increases muscle glucose uptake as a response to high salt-induced, glucocorticoid-driven muscle catabolism to stimulate urea production and thereby renal water conservation.TRIAL REGISTRATIONClinicalTrials.gov, NCT02068781.

Inhibiting myeloperoxidase prevents onset and reverses established high-fat diet-induced microvascular insulin resistance.

A high-fat diet (HFD) can rapidly recruit neutrophils to insulin target tissues and within days induce microvascular insulin resistance (IR). Myeloperoxidase (MPO) is highly enriched in neutrophils, can inhibit nitric oxide-mediated vasorelaxation in vitro and is associated with increased cardiovascular disease risk. AZD5904 irreversibly inhibits MPO and in human clinical trials. MPO knockout, or chemical inhibition, blunts HFD-induced metabolic IR in mice. Whether MPO affects microvascular IR or muscle metabolic insulin sensitivity in vivo is unknown. We used contrast-enhanced ultrasound and the euglycemic insulin clamp to test whether inhibiting MPO could prevent the development or reverse established HFD-induced metabolic and/or microvascular IR in Sprague-Dawley rats. Two weeks of HFD feeding blocked insulin-mediated skeletal muscle capillary recruitment, inhibited glucose utilization, and insulin signaling to muscle. Continuous subcutaneous AZD5904 infusion during the 2 wk selectively blocked HFD's microvascular effect. Furthermore, AZD5904 infusion during the last 2 of 4 wk of HFD feeding restored microvascular insulin sensitivity but not metabolic IR. We conclude that inhibiting MPO selectively improves vascular IR. This selective microvascular effect may connote a therapeutic potential for MPO inhibition in the prevention of vascular disease/dysfunction seen in IR humans.

Abstract 569: Functional Benefits of Muscle PGC-1alpha in Aged Animals

Metabolic homeostasis requires a complex network of transcriptional programs. PGC-1 (peroxisome-proliferator-activated receptor-γ coactivator-1) alpha is a potent transcriptional coactivator that coordinates the activation of a large number of nuclear-encoded genes, which, in turn, regulate numerous metabolic processes. Exercise strongly induces muscle PGC-1alpha in both humans and rodents. Over-expression of PGC-1alpha in skeletal muscle activates mitochondrial oxidative metabolism, fast-to-slow fiber-type switching, and neovascularization, leading to markedly increased endurance. In light of these findings, PGC-1alpha has been proposed to protect from age-associated sarcopenia, bone loss, and whole-body metabolic dysfunction, although these findings have been controversial. We therefore comprehensively evaluated muscle and whole-body function and metabolism in 24 month-old transgenic mice that over-express PGC-1alpha in skeletal muscle. We find that the powerful effects of PGC-1alpha on promoting muscle oxidative capacity and protection from muscle fatigability persist in aged animals, although at the expense of muscle strength. However, skeletal muscle PGC-1alpha does not prevent bone loss and in fact accentuates it, nor does it have long-term benefit on whole-body metabolic composition or insulin sensitivity. Interestingly, we see protection from sarcopenia in male animals with over-expression of PGC-1alpha in skeletal muscle but not in female animals. In summary, muscle-specific expression of PGC-1alpha into old age has beneficial effects on muscle fatigability and may protect from sarcopenia in males, but does not improve whole-body metabolism and appears to worsen age-related trabecular bone loss.