Microvascular Insulin Resistance Research Articles

Microvascular insulin resistance with enhanced muscle glucose disposal in CD36 deficiency.

Microvascular dysfunction contributes to insulin resistance. CD36, a fatty acid transporter and modulator of insulin signalling, is abundant in microvascular endothelial cells. Humans carrying the minor allele (G) of CD36 coding variant rs3211938 have 50% reduced CD36 expression and show endothelial dysfunction. We aimed to determine whether G allele carriers have microvascular resistance to insulin and, if so, how this affects glucose disposal. Our multi-disciplinary approach included hyperinsulinaemic-euglycaemic clamps in Cd36-/- and wild-type mice, and in individuals with 50% CD36 deficiency, together with control counterparts, in addition to primary human-derived microvascular endothelial cells with/without CD36 depletion. Insulin clamps showed that Cd36-/- mice have enhanced insulin-stimulated glucose disposal but reduced vascular compliance and capillary perfusion. Intravital microscopy of the gastrocnemius showed unaltered transcapillary insulin flux. CD36-deficient humans had better insulin-stimulated glucose disposal but insulin-unresponsive microvascular blood volume (MBV). Human microvascular cells depleted of CD36 showed impaired insulin activation of Akt, endothelial NO synthase and NO generation. Thus, in CD36 deficiency, microvascular insulin resistance paradoxically associated with enhanced insulin sensitivity of glucose disposal. CD36 deficiency was previously shown to reduce muscle/heart fatty acid uptake, whereas here we showed that it reduced vascular compliance and the ability of insulin to increase MBV for optimising glucose and oxygen delivery. The muscle and heart respond to these energy challenges by transcriptional remodelling priming the tissue for insulin-stimulated glycolytic flux. Reduced oxygen delivery activating hypoxia-induced factors, endothelial release of growth factors or small intracellular vesicles might mediate this adaptation. Targeting NO bioavailability in CD36 deficiency could benefit the microvasculature and muscle/heart metabolism. Clinicaltrials.gov NCT03012386 DATA AVAILABILITY: The RNAseq data generated in this study have been deposited in the NCBI Gene Expression Omnibus ( www.ncbi.nlm.nih.gov/geo/ ) under accession code GSE235988 ( https://www.ncbi.nlm.nih.gov/geo/query/acc.cgi?acc=GSE235988 ).

Impaired microvascular insulin-dependent dilation in women with a history of gestational diabetes.

Women with a history of gestational diabetes mellitus (GDM) have a significantly greater lifetime risk of developing cardiovascular disease and type 2 diabetes compared with women who had an uncomplicated pregnancy (HC). Microvascular endothelial dysfunction, mediated via reduced nitric oxide (NO)-dependent dilation secondary to increases in oxidative stress, persists after pregnancy complicated by GDM. We examined whether this microvascular dysfunction reduces insulin-mediated vascular responses in women with a history of GDM. We assessed in vivo microvascular endothelium-dependent vasodilator function by measuring cutaneous vascular conductance responses to graded infusions of acetylcholine (10-10-10-1 M) and insulin (10-8-10-4 M) in control sites and sites treated with 15 mM l-NAME [NG-nitro-l-arginine methyl ester; NO-synthase (NOS) inhibitor] or 5 mM l-ascorbate. We also measured protein expression of total endothelial NOS (eNOS), insulin-mediated eNOS phosphorylation, and endothelial nitrotyrosine in isolated endothelial cells from GDM and HC. Women with a history of GDM had reduced acetylcholine (P < 0.001)- and insulin (P < 0.001)-mediated dilation, and the NO-dependent responses to both acetylcholine (P = 0.006) and insulin (P = 0.006) were reduced in GDM compared with HC. Insulin stimulation increased phosphorylated eNOS content in HC (P = 0.009) but had no effect in GDM (P = 0.306). Ascorbate treatment increased acetylcholine (P < 0.001)- and insulin (P < 0.001)-mediated dilation in GDM, and endothelial cell nitrotyrosine expression was higher in GDM compared with HC (P = 0.014). Women with a history of GDM have attenuated microvascular vasodilation responses to insulin, and this attenuation is mediated, in part, by reduced NO-dependent mechanisms. Our findings further implicate increased endothelial oxidative stress in this microvascular insulin resistance.NEW & NOTEWORTHY Women who have gestational diabetes during pregnancy are at a greater risk for cardiovascular disease and type 2 diabetes in the decade following pregnancy. The mechanisms mediating this increased risk are unclear. Herein, we demonstrate that insulin-dependent microvascular responses are reduced in women who had gestational diabetes, despite the remission of glucose intolerance. This reduced microvascular sensitivity to insulin may contribute to increased cardiovascular disease and type 2 diabetes risk in these women.

345-OR: Exercise and Liraglutide Synergistically Attenuate Vascular Inflammation and Enhance Metabolic Insulin Action in Diet-Induced Obesity

Endothelial oxidative stress and vascular inflammation induce microvascular insulin resistance which is an early event in diet-induced obesity and contributes to metabolic insulin resistance. To examine whether exercise and glucagon-like peptide 1 (GLP-1) receptor agonism, alone or in combination, modulate vascular and metabolic insulin actions during obesity development, we performed an euglycemic insulin clamp, in conjunction with contrast enhanced ultrasound, in adult male rats after 2 weeks of high-fat diet feeding with either access to running wheel (exercise), liraglutide (200 mg/kg subcutaneously twice daily), or the combination of both. Rats exhibited increased visceral adiposity and blunted microvascular responses (microvascular blood volume, flow velocity, and total flow) and metabolic insulin actions (glucose infusion rates). Exercise and liraglutide alone each improved muscle insulin sensitivity but their combination fully restored insulin-mediated glucose infusion rates. The combined exercise and liraglutide intervention enhanced insulin-mediated muscle microvascular perfusion, reduced perivascular macrophage accumulation and oxidative stress in the muscle, attenuated blood vessel inflammation and improved endothelial function, along with increased nucleus translocation of nuclear factor erythroid 2-related factor 2 (NRF2) and phosphorylation of AMP-activated protein kinase (AMPK) and nitric oxide synthase (eNOS) in endothelial cells. We conclude that exercise and liraglutide synergistically enhance the metabolic actions of insulin and reduce vascular oxidative stress and inflammation in the early stage of obesity development. Our data suggest that early combination use of exercise and GLP-1 receptor agonism might be an effective strategy in preventing microvascular and metabolic insulin resistance and associated complications during the development of obesity. Disclosure J.Liu: None. K.W.Aylor: None. Z.Liu: None. Funding National Institutes of Health (R01DK125330), (R01DK1124344 to Z.L.)

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.

Metformin's Impact on the Microvascular Response to Insulin.

Metformin improves insulin's action on whole-body glucose metabolism in various insulin-resistant populations. The detailed cellular mechanism(s) for its metabolic actions are multiple and still incompletely understood. Beyond metabolic actions, metformin also impacts microvascular function. However, the effects of metformin on microvascular function and microvascular insulin action specifically are poorly defined. In this mini-review, we summarize what is currently known about metformin's beneficial impact on both microvascular function and the microvascular response to insulin while highlighting methodologic issues in the literature that limit straightforward mechanistic understanding of these effects. We examine potential mechanisms for these effects based on pharmacologically dosed studies and propose that metformin may improve human microvascular insulin resistance by attenuating oxidative stress, inflammation, and endothelial dysfunction. Finally, we explore several important evidence gaps and discuss avenues for future investigation that may clarify whether metformin's ability to improve microvascular insulin sensitivity is linked to its positive impact on vascular outcomes.

Metformin prevents endothelial oxidative stress and microvascular insulin resistance during obesity development in male rats.

Insulin increases muscle microvascular perfusion, which contributes to its metabolic action in muscle, but this action is impaired in obesity. Metformin improves endothelial function beyond its glucose lowering effects. We aim to examine whether metformin could prevent microvascular insulin resistance and endothelial dysfunction during the development of obesity. Adult male rats were fed a high-fat diet (HFD) with or without simultaneous metformin administration for either 2 or 4 wk. Insulin's metabolic and microvascular actions were determined using a combined euglycemic-hyperinsulinemic clamp and contrast-enhanced ultrasound approach. Compared with chow-fed controls, HFD feeding increased body adiposity without excess body weight gain, and this was associated with a marked decrease in insulin-mediated whole body glucose disposal and abolishment of insulin-induced muscle microvascular recruitment. Simultaneous administration of metformin fully rescued insulin-induced muscle microvascular recruitment as early as 2 wk and normalized insulin-mediated whole body glucose disposal at week 4. The divergent responses between insulin's microvascular and metabolic actions seen at week 2 were accompanied with reduced endothelial oxidative stress and vascular inflammation, and improved endothelial function and vascular insulin signaling in metformin-treated rats. In conclusions, metformin could prevent the development of microvascular insulin resistance and endothelial dysfunction by alleviating endothelial oxidative stress and vascular inflammation during obesity development.NEW & NOTEWORTHY Muscle microvascular insulin action contributes to insulin-mediated glucose use. Microvascular insulin resistance is an early event in diet-induced obesity and is associated with vascular inflammation. Metformin effectively reduces endothelial oxidative stress, improves endothelial function, and prevents microvascular insulin resistance during obesity development. These may contribute to metformin's salutary diabetes prevention and cardiovascular protective actions.

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.

Skeletal muscle microvascular insulin resistance in type 2 diabetes is not improved by eight weeks of regular walking.

We aimed to examine whether individuals with type 2 diabetes (T2D) exhibit suppressed leg vascular conductance and skeletal muscle capillary perfusion in response to a hyperinsulinemic-euglycemic clamp and to test whether these two variables are positively correlated. Subsequently, we examined whether T2D-associated skeletal muscle microvascular insulin resistance, as well as overall vascular dysfunction, would be ameliorated by an 8-wk walking intervention (45 min at 60% of heart rate reserve, 5 sessions/week). We report that, relative to healthy subjects, overweight and obese individuals with T2D exhibit depressed insulin-stimulated increases in leg vascular conductance, skeletal muscle capillary perfusion, and Akt phosphorylation. Notably, we found that within individuals with T2D, those with lesser increases in leg vascular conductance in response to insulin exhibited the lowest increases in muscle capillary perfusion, suggesting that limited muscle capillary perfusion may be, in part, linked to the impaired ability of the upstream resistance vessels to dilate in response to insulin. Furthermore, we show that the 8-wk walking intervention, which did not evoke weight loss, was insufficient to ameliorate skeletal muscle microvascular insulin resistance in previously sedentary, overweight/obese subjects with T2D, despite high adherence and tolerance. However, the walking intervention did improve (P < 0.05) popliteal artery flow-mediated dilation (+4.52%) and reduced HbA1c (-0.75%). It is possible that physical activity interventions that are longer in duration, engage large muscle groups with recruitment of the maximum number of muscle fibers, and lead to a robust reduction in metabolic risk factors may be required to overhaul microvascular insulin resistance in T2D.NEW & NOTEWORTHY This report provides evidence that in sedentary subjects with type 2 diabetes diminished insulin-stimulated increases in leg vascular conductance and ensuing blunted capillary perfusion in skeletal muscle are not restorable by increased walking alone. More innovative physical activity interventions that ultimately result in a robust mitigation of metabolic risk factors may be vital for reestablishing skeletal muscle microvascular insulin sensitivity in type 2 diabetes.

1889-P: Light Exercise and Liraglutide Synergistically Improve Muscle Insulin Action in Diet-Induced Obesity

Insulin recruits muscle microvasculature which contributes to insulin’s metabolic action but is blunted in humans with obesity. Both exercise and glucagon-like peptide 1 (GLP-1) are potent enhancers of muscle microvascular perfusion and their actions are preserved in the insulin resistant states. To examine whether light exercise and GLP-1 receptor agonism modulate insulin’s microvascular and metabolic actions during the development of obesity, adult male rats were fed a high-fat diet (HFD) for 2 weeks with either free access to running wheel (light exercise), liraglutide (200 mcg/kg subcutaneously twice daily), or light exercise + liraglutide. Rats were then fasted overnight and received a euglycemic insulin clamp (3 mU/kg/min) for 120 min. Insulin-mediated muscle microvascular recruitment was measured using contrast-enhanced ultrasound. Rats on HFD alone (control) displayed marked microvascular insulin resistance. Light exercise increased basal plasma nitric oxide levels and fully rescued insulin’s microvascular action. Liraglutide similarly increased basal plasma NO contents but did not reverse microvascular insulin resistance. Both light exercise and liraglutide improved insulin-stimulated whole body glucose disposal in the first 30 min but did not significantly increase the steady-state glucose infusion rates. Combined light exercise and liraglutide treatment not only fully restored microvascular insulin responses but also significantly enhanced insulin-stimulated whole body glucose disposal (&amp;gt;50%, p&amp;lt;0.01). We conclude that light exercise and liraglutide differentially modulate microvascular insulin responses but synergistically enhance metabolic insulin actions during the development of obesity. Our findings provide a novel insight into the exercise and liraglutide interplay and support the early use of exercise and GLP-1 receptor agonism to correct microvascular and metabolic insulin resistance during the development of obesity. Disclosure J. Liu: None. K.W. Aylor: None. Z. Liu: None. Funding American Diabetes Association (1-17-ICTS-059 to Z.L.); National Institutes of Health (R01HL094722, R01DK102359)

1755-P: Insulin-Mediated Glucose Disposal and Muscle Microvascular Recruitment Are Mutual Predictors in Humans

Insulin recruits muscle microvasculature to enhance insulin and nutrient delivery. Insulin resistance (IR) blunts this microvascular action. While metabolic and microvascular IR usually coexist, and phenotypic traits which foretell metabolic IR are well established, those which predict microvascular IR are unknown. To test whether metabolic IR and its associated traits predict microvascular IR, we performed euglycemic insulin clamps (1 mU/kg/min) in healthy lean (n= 57), healthy obese (n=15) and lean type 1 diabetes subjects (T1D) (n=25), and tested parametric correlations and a multivariate model ANOVA. We measured insulin-mediated whole body glucose disposal (M-value) and insulin-induced changes in muscle microvascular blood volume (ΔMBV) by contrast-enhanced ultrasound. Predictor variables included body mass index (BMI), total body weight (WT), percent body fat (BF), lean body mass, blood pressure, maximal rate of oxygen consumption (VO2max), and plasma levels of LDL cholesterol (LDL-C), HDL cholesterol, triglycerides (TG), fasting insulin (INS) and free fatty acids. A total of 97 subjects were included (mean age 25.4±6.8, 47% women) in the analyses. Among all factors, only M-value (r=0.23, p=0.023) and VO2max (r=0.20, p=0.047) correlated with ΔMBV. Conversely, INS (r=-0.59, P≤0.001), BF (r=-0.54, p≤0.001), VO2max (r=0.5, p≤0.001), BMI (r=-0.40, p&amp;lt;0.001), WT (r=-0.33, p=0.001), LDL-C (r=-0.26, p=0.009), TG (r=-0.25, p=0.012), as well as ΔMBV correlated with M-value. While both ΔMBV (p=0.045) and TG (p=0.037) independently predicted M-value, only M-value independently predicted ΔMBV (p=0.045). In conclusion, both M-value and VO2max correlated with but only M-value independently predicted microvascular IR. This suggests that, while metabolic and microvascular IR are important predictors of one another, most phenotypic predictors of metabolic IR do not predict microvascular IR. Disclosure K. Love: None. L. Jahn: None. L. Hartline: None. E. Barrett: None. Z. Liu: None. Funding American Diabetes Association (1-17-ICST-059 to Z.L.); National Institutes of Health (1F32DK121431-01)

972-P: Liraglutide Attenuates Lipid-Induced Microvascular Insulin Resistance in Humans

Insulin recruits skeletal and cardiac muscle microvasculature to increase insulin and nutrient delivery, but this action is lost in insulin resistant states. Glucagon-like peptide 1 (GLP-1) improves microvascular perfusion in humans with obesity and the GLP-1 receptor agonist liraglutide attenuates muscle microvascular insulin resistance (IR) in rodents. To examine whether GLP-1 receptor agonism improves insulin’s microvascular actions in humans with acute IR, 18 healthy human subjects randomly received a systemic infusion of either saline or lipid emulsion (20%, 45 mL x 1 h and then 30 mL x 4 h) for 5 h or lipid emulsion for 5 h + liraglutide pre-treatment (0.6, 1.2, then 1.8 mg daily SC each x 2 days) with euglycemic insulin clamp (1 mU/kg/min) superimposed for the last 120 min. Skeletal and cardiac muscle microvascular blood volume (MBV), flow-mediated dilation (FMD), pulse wave velocity (PWV), and augmentation index (AI) were determined before and after insulin clamp. Compared with saline admission, insulin failed to increase MBV following lipid infusion in both skeletal (28.4 ± 14.1% vs. -1.3 ± 9.6% respectively, p=0.011) and cardiac (28.4 ± 14.1% vs. -1.3 ± 8.9%, p=0.027) muscle, consistent with acute IR induced by lipid infusion in both microvascular beds. Liraglutide pre-treatment improved insulin-mediated increases in MBV in the presence of lipid infusion in skeletal (8.9 ± 13.5%, p=0.117 vs. saline) and cardiac (12.6 ± 12.1%, p=0.101 vs. saline) muscle. There was no significant change in PWV, AI, or FMD amongst admissions. Glucose infusion rates were not significantly different amongst admissions (saline 6.02 ± 0.52, lipid 5.58 ± 0.62, vs. liraglutide + lipid 5.46 ± 0.46 mg/kg/min). In conclusion, liraglutide pretreatment effectively ameliorates lipid-induced skeletal and cardiac muscle microvascular IR in healthy humans. These data provide a mechanistic insight into the metabolic and cardiovascular benefits of GLP-1 receptor agonism seen in humans with obesity and type 2 diabetes. Disclosure K. Love: None. L. Jahn: None. L. Hartline: None. Z. Liu: None. Funding American Diabetes Association (1-17-ICST-059 to Z.L.); National Institutes of Health (1R01DK102359-01A1)

ADAM17 Cleaves the Insulin Receptor Ectodomain on Endothelial Cells and Induces Vascular Insulin Resistance

Despite efforts to reduce the incidence of type 2 diabetes (T2D) and its cardiovascular consequences, T2D‐associated cardiovascular mortality continues to rise in the US and worldwide. The presence of a pro‐inflammatory state and microvascular insulin resistance are hallmarks of T2D that contribute to cardiovascular disease. The former is associated with increased activity of ADAM17, an enzyme that cleaves the ectodomain of multiple transmembrane proteins, while the latter is characterized by decreased insulin‐induced vasodilatory responses. However, the specific mechanisms, including the potential role(s) of ADAM17, underlying vascular insulin resistance in T2D, remain unknown. We hypothesize that in T2D, increased expression and activation of ADAM17 sheds the insulin receptor ectodomain (IRα) from endothelial cells and thus impairs insulin‐induced vasodilation. We tested this hypothesis using isolated small visceral arteries from T2D and non‐T2D subjects undergoing bariatric surgery and cultured human endothelial cells. Results indicate that arteries from subjects with T2D exhibit increased ADAM17 expression, reduced presence of TIMP3 (the endogenous inhibitor of ADAM17), decreased extracellular IRα, and impaired insulin‐induced vasodilation in comparison with arteries from non‐T2D subjects (P&lt;0.05). In vitro, ADAM17 cleaved insulin receptor recombinant proteins at a specific extracellular site of the IRβ subunit (p&lt;0.05). Exposure of endothelial cells to the PKC activator, PMA, increased the shedding activity of ADAM17 (P&lt;0.05) and decreased the presence of IRα on cell surfaces occupied by ADAM17, as observed using super‐resolution microscopy. Moreover, pharmacological inhibition of ADAM17 with TAPI‐0 rescued PMA‐induced impairments in insulin signaling in endothelial cells and insulin‐stimulated vasodilation in human small visceral arteries (P&lt;0.05). Collectively, these findings suggest that ADAM17‐mediated shedding of IR ectodomains from the endothelial surface impairs insulin‐mediated vasodilation. Therefore, inhibition of ADAM17 sheddase activity should be considered a potential new therapeutic strategy to restore vascular insulin sensitivity in T2D.Support or Funding InformationResearch support: National Institutes of Health grants: R01 HL137769 (JP), R01 HL088105 (LM‐L).

Vasodilatory Actions of Glucagon-Like Peptide 1 Are Preserved in Skeletal and Cardiac Muscle Microvasculature but Not in Conduit Artery in Obese Humans With Vascular Insulin Resistance.

Obesity is associated with microvascular insulin resistance, which is characterized by impaired insulin-mediated microvascular recruitment. Glucagon-like peptide 1 (GLP-1) recruits skeletal and cardiac muscle microvasculature, and this action is preserved in insulin-resistant rodents. We aimed to examine whether GLP-1 recruits microvasculature and improves the action of insulin in obese humans. Fifteen obese adults received intravenous infusion of either saline or GLP-1 (1.2 pmol/kg/min) for 150 min with or without a euglycemic insulin clamp (1 mU/kg/min) superimposed over the last 120 min. Skeletal and cardiac muscle microvascular blood volume (MBV), flow velocity and blood flow, brachial artery diameter and blood flow, and pulse wave velocity (PWV) were determined. Insulin failed to change MBV or flow in either skeletal or cardiac muscle, confirming the presence of microvascular insulin resistance. GLP-1 infusion alone increased MBV by ∼30% and ∼40% in skeletal and cardiac muscle, respectively, with no change in flow velocity, leading to a significant increase in microvascular blood flow in both skeletal and cardiac muscle. Superimposition of insulin to GLP-1 infusion did not further increase MBV or flow in either skeletal or cardiac muscle but raised the steady-state glucose infusion rate by ∼20%. Insulin, GLP-1, and GLP-1 + insulin infusion did not alter brachial artery diameter and blood flow or PWV. The vasodilatory actions of GLP-1 are preserved in both skeletal and cardiac muscle microvasculature, which may contribute to improving metabolic insulin responses and cardiovascular outcomes. In obese humans with microvascular insulin resistance, GLP-1's vasodilatory actions are preserved in both skeletal and cardiac muscle microvasculature, which may contribute to improving metabolic insulin responses and cardiovascular outcomes.

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.

477-P: Inhibiting Myeloperoxidase (MPO) Prevents Onset and Reverses Established High-Fat Diet (HFD)-Induced Microvascular Insulin Resistance (IR)

HFD rapidly recruits neutrophils to insulin target tissues and induces microvascular IR. MPO is abundant in neutrophils, inhibits nitric oxide mediated vaso-relaxation, and associates with increased cardiovascular risk. AZD5904 (AstraZeneca) irreversibly inhibits MPO and is in clinical trials. MPO knockout, or chemical inhibition, improves glucose regulation in HFD-fed mice. Whether MPO affects muscle microvascular or metabolic IR in vivo is unknown. To test whether AZD5904 can prevent onset of HFD-induced vascular and metabolic IR, Sprague-Dawley rats were fed chow or a HFD (60% calories) for 2 weeks. HFD-fed rats received vehicle (n=8) or AZD5904 subcutaneously (n=10) via Alzet pump. Chow-fed rats (n=8) received vehicle alone. On day 15, we measured muscle microvascular perfusion in all rats by contrast-enhanced ultrasound, at 0, 60 and 120 minutes of a 2-hour euglycemic insulin clamp (3 mU/kg/minutes) and glucose disposal was determined. We next tested whether AZD5904 can reverse established vascular IR. Two groups of rats (n = 10, each) were fed the HFD for 2 weeks to induce vascular and metabolic IR, HFD was continued for 2 additional weeks while giving vehicle or AZD5904. Microvascular and metabolic insulin action was measured again using the insulin clamp. HFD for 2 weeks completely blocked insulin-mediated muscle capillary recruitment, decreased glucose utilization by 35%, and inhibited muscle Akt phosphorylation (P&amp;lt;0.05, for each measure). AZD5904 during HFD selectively and completely restored insulin-induced microvascular sensitivity (P&amp;lt;0.05). Furthermore, AZD5904 during the last 2 of 4 weeks of HFD feeding fully restored insulin-mediated microvascular perfusion (P&amp;lt;0.05) again without affecting glucose disposal. We conclude that inhibiting MPO selectively corrects vascular IR. This effect may connote a therapeutic potential for MPO inhibition in the prevention of vascular disease/dysfunction seen in IR humans. Disclosure E. Barrett: Research Support; Self; AstraZeneca. W. Chai: None. K.W. Aylor: None. L. Gan: Employee; Self; AstraZeneca. E. Michaëlsson: Employee; Self; AstraZeneca. Funding University of Virginia; AstraZeneca

Fat-Specific Protein 27 Regulation of Vascular Function in Human Obesity.

BackgroundPathophysiological mechanisms that connect obesity to cardiovascular disease are incompletely understood. FSP27 (Fat‐specific protein 27) is a lipid droplet‐associated protein that regulates lipolysis and insulin sensitivity in adipocytes. We unexpectedly discovered extensive FSP27 expression in human endothelial cells that is downregulated in association with visceral obesity. We sought to examine the functional role of FSP27 in the control of vascular phenotype.Methods and ResultsWe biopsied paired subcutaneous and visceral fat depots from 61 obese individuals (body mass index 44±8 kg/m2, age 48±4 years) during planned bariatric surgery. We characterized depot‐specific FSP27 expression in relation to adipose tissue microvascular insulin resistance, endothelial function and angiogenesis, and examined differential effects of FSP27 modification on vascular function. We observed markedly reduced vasodilator and angiogenic capacity of microvessels isolated from the visceral compared with subcutaneous adipose depots. Recombinant FSP27 and/or adenoviral FSP27 overexpression in human tissue increased endothelial nitric oxide synthase phosphorylation and nitric oxide production, and rescued vasomotor and angiogenic dysfunction (P<0.05), while siRNA‐mediated FSP27 knockdown had opposite effects. Mechanistically, we observed that FSP27 interacts with vascular endothelial growth factor‐A and exerts robust regulatory control over its expression. Lastly, in a subset of subjects followed longitudinally for 12±3 months after their bariatric surgery, 30% weight loss improved metabolic parameters and increased angiogenic capacity that correlated positively with increased FSP27 expression (r=0.79, P<0.05).ConclusionsOur data strongly support a key role and functional significance of FSP27 as a critical endogenous modulator of human microvascular function that has not been previously described. FSP27 may serve as a previously unrecognized regulator of arteriolar vasomotor capacity and angiogenesis which are pivotal in the pathogenesis of cardiometabolic diseases linked to obesity.

171-OR: Metformin Prevents Microvascular Insulin Resistance and Preserves Endothelial Function in High-Fat Diet-Fed Rats

Endothelial dysfunction and vascular insulin resistance coexist and both contribute to the development of type 2 diabetes mellitus (T2DM) and increased cardiovascular risks. Insulin relaxes precapillary arterioles to increase insulin delivery to and action in muscle via recruiting muscle microvasculature and this action is impaired in the insulin resistant states. Metformin is the first line therapy for T2DM and has been shown to improve endothelial function beyond its hypoglycemic effects. Here we aim to examine whether metformin could restore vascular insulin responses in the setting of insulin resistance induced by high fat diet (HFD) feeding via the modulation of endothelial function. Adult, male Sprague-Dawley rats were fed on HFD with or without metformin treatment for 2 weeks. A chow fed group served as control. After dietary intervention, rats were fasted overnight and received a euglycemic-hyperinsulinemic clamp for 120 min. Insulin-mediated muscle microvascular recruitment was assessed before and during insulin infusion using contrast-enhanced ultrasound. Distal saphenous artery was isolated and used for determination of endothelial function and vascular insulin responses. Compared with controls, HFD feeding abolished insulin-induced muscle microvascular recruitment in muscle, decreased insulin-mediated whole body glucose disposal and blunted the vasodilatory response to insulin in small resistance vessel. Metformin treatment significantly enhanced insulin’s microvascular action, effectively rescued small arteriole endothelial function, but did not improve insulin-stimulated whole body glucose disposal in HFD rats. We conclude that metformin could reverse microvascular insulin resistance and attenuate endothelial dysfunction induced by HFD feeding. There findings may provide a novel mechanistic insight into metformin’s cardiovascular protective effect in patients with diabetes. Disclosure J. Liu: None. W. Chai: None. L. Gong: None. K.W. Aylor: None. Z. Liu: None. Funding American Diabetes Association (1-17-ICTS-059 to Z.L.); National Institutes of Health (R01HL094722, R01DK102359)

ADAM17 Cleaves the Insulin Receptor α‐Subunit on Endothelial Cells and Induces Vascular Insulin Resistance in Type 2 Diabetes

Microvascular insulin resistance is a hallmark of type 2 diabetes (T2D) and an underlying event in the pathophysiology of endothelial dysfunction and cardiovascular disease. However, the molecular mechanisms by which T2D causes vascular insulin resistance remain largely unknown. Hyperglycemia and the proinflammatory state associated with T2D are characterized, in part, by an increased activity of ADAM17, an enzyme that cleaves the ectodomain of various transmembrane proteins. Here, we hypothesized that increased expression and activation of ADAM17 sheds the insulin receptor α‐subunit (IRα) from endothelial cells causing vascular insulin resistance in T2D. We tested this hypothesis in isolated resistance arteries from T2D and non‐T2D subjects undergoing bariatric surgery and in cultured human umbilical vein endothelial cells (HUVECs). Resistance arteries from T2D subjects exhibited increased ADAM17 expression, reduced presence of endothelial IRα as well as the endogenous ADAM17 inhibitor, TIMP3, and impaired insulin‐induced vasodilation, relative to arteries from non‐T2D subjects (P&lt;0.05). Exposure of HUVECs to high glucose (30mM, 24h) increased the expression and activity of ADAM17 (P&lt;0.05), led to increased shedding of IRα detected in the cell culture media supernatant (P&lt;0.05) and decreased IRα on cell surfaces as observed using super‐resolution microscopy. Moreover, pharmacological inhibition of ADAM17 led to reduced shedding of IRα and improved insulin signaling in cells exposed to high glucose or the ADAM17 activator, PMA (P&lt;0.05). Collectively, these findings suggest that T2D, and in particular hyperglycemia, leads to ADAM17 shedding of IRα from the endothelial surface and reduced insulin‐dependent vasodilation, all of which supports ADAM17 activity as a new therapeutic target to ameliorate vascular insulin resistance in T2D.Support or Funding InformationResearch support: National Institutes of Health grants: R01 HL137769 (JP), R01 HL088105 (LM‐L).This abstract is from the Experimental Biology 2019 Meeting. There is no full text article associated with this abstract published in The FASEB Journal.

Muscle Insulin Resistance and the Inflamed Microvasculature: Fire from Within

Insulin is a vascular hormone and regulates vascular tone and reactivity. Muscle is a major insulin target that is responsible for the majority of insulin-stimulated glucose use. Evidence confirms that muscle microvasculature is an important insulin action site and critically regulates insulin delivery to muscle and action on myocytes, thereby affecting insulin-mediated glucose disposal. Insulin via activation of its signaling cascade in the endothelial cells increases muscle microvascular perfusion, which leads to an expansion of the endothelial exchange surface area. Insulin’s microvascular actions closely couple with its metabolic actions in muscle and blockade of insulin-mediated microvascular perfusion reduces insulin-stimulated muscle glucose disposal. Type 2 diabetes is associated with chronic low-grade inflammation, which engenders both metabolic and microvascular insulin resistance through endocrine, autocrine and paracrine actions of multiple pro-inflammatory factors. Here, we review the crucial role of muscle microvasculature in the regulation of insulin action in muscle and how inflammation in the muscle microvasculature affects insulin’s microvascular actions as well as metabolic actions. We propose that microvascular insulin resistance induced by inflammation is an early event in the development of metabolic insulin resistance and eventually type 2 diabetes and its related cardiovascular complications, and thus is a potential therapeutic target for the prevention or treatment of obesity and diabetes.

Acute, local infusion of angiotensin II impairs microvascular and metabolic insulin sensitivity in skeletal muscle.

Angiotensin II (AngII) is a potent vasoconstrictor implicated in both hypertension and insulin resistance. Insulin dilates the vasculature in skeletal muscle to increase microvascular blood flow and enhance glucose disposal. In the present study, we investigated whether acute AngII infusion interferes with insulin's microvascular and metabolic actions in skeletal muscle. Adult, male Sprague-Dawley rats received a systemic infusion of either saline, AngII, insulin (hyperinsulinaemic euglycaemic clamp), or insulin (hyperinsulinaemic euglycaemic clamp) plus AngII. A final, separate group of rats received an acute local infusion of AngII into a single hindleg during systemic insulin (hyperinsulinaemic euglycaemic clamp) infusion. In all animals' systemic metabolic effects, central haemodynamics, femoral artery blood flow, microvascular blood flow, and skeletal muscle glucose uptake (isotopic glucose) were monitored. Systemic AngII infusion increased blood pressure, decreased heart rate, and markedly increased circulating glucose and insulin concentrations. Systemic infusion of AngII during hyperinsulinaemic euglycaemic clamp inhibited insulin-mediated suppression of hepatic glucose output and insulin-stimulated microvascular blood flow in skeletal muscle but did not alter insulin's effects on the femoral artery or muscle glucose uptake. Local AngII infusion did not alter blood pressure, heart rate, or circulating glucose and insulin. However, local AngII inhibited insulin-stimulated microvascular blood flow, and this was accompanied by reduced skeletal muscle glucose uptake. Acute infusion of AngII significantly alters basal haemodynamic and metabolic homeostasis in rats. Both local and systemic AngII infusion attenuated insulin's microvascular actions in skeletal muscle, but only local AngII infusion led to reduced insulin-stimulated muscle glucose uptake. While increased local, tissue production of AngII may be a factor that couples microvascular insulin resistance and hypertension, additional studies are needed to determine the molecular mechanisms responsible for these vascular defects.