Insulin-induced Microvascular Recruitment Research Articles

Multiscale and morphological analysis of microvascular patterns depicted in contrast-enhanced ultrasound images.

Purpose: Impaired insulin-induced microvascular recruitment in skeletal muscle contributes to insulin resistance in type 2 diabetic disease. Previously, quantification of microvascular recruitment at the capillary level has been performed with either the full image or manually selected region-of-interests. These subjective approaches are imprecise, time-consuming, and unsuitable for automated processes. Here, an automated multiscale image processing approach was performed by defining a vessel diameter threshold for an objective and reproducible analysis at the microvascular level. Approach: A population of C57BL/6J male mice fed standard chow and studied at age 13 to 16 weeks comprised the lean group and 24- to 31-week-old mice who received a high-fat diet were designated the obese group. A clinical ultrasound scanner (Acuson Sequoia 512) equipped with an 15L8-S linear array transducer was used in a nonlinear imaging mode for sensitive detection of an intravascular microbubble contrast agent. Results: By eliminating large vessels from the dynamic contrast-enhanced ultrasound (DCE-US) images (above in diameter), obesity-related changes in perfusion and morphology parameters were readily detected in the smaller vessels, which are known to have a greater impact on skeletal muscle glucose disposal. The results from the DCE-US images including all of the vessels were compared for three different-sized vessel groups, namely, vessels smaller than 300, 200, and in diameter. Conclusions: Our automated image processing provides objective and reproducible results by focusing on a particular size of vessel, thereby allowing for a selective evaluation of longitudinal changes in microvascular recruitment for a specific-sized vessel group between diseased and healthy microvascular networks.

Abstract P3011: Role of CD36 in Insulin Mediated Microvascular Vasodilation in African Americans

CD36 is a membrane protein involved in fatty acids uptake that is expressed in the endothelium, which has been associated with endothelial dysfunction in African Americans (AA). One in four AA is G-allele carriers for coding CD36 SNP rs3211938, which results in ~50% reduction in its expression. We reported that potentiating nitric oxide action (NO) with sildenafil restored endothelial dysfunction in conduit arteries in G-allele carriers. In this study, we tested the hypothesis that in G-allele carriers, sildenafil would improve insulin-induced microvascular recruitment (MBV) in response to fat infusion. We recruited 25 healthy AA (17 non-carriers [ages 34 ± 7.4] and eight G-allele carriers [42 ± 7.4 yrs]). Subjects underwent three visits: Visit 1: Saline infusion and hyperinsulinemic euglycemic clamp (HIE clamp). Visit 2: Lipid infusion and HIE clamp and Visit 3: Lipid infusion and HIE clamp after a four-week sildenafil treatment (60 mg/day). During each visit, the subjects underwent an assessment of MBV at baseline (bsl), after 3-hour insulin (Ins) infusion (40mu/m 2 /min) and after Ins and L-arginine (10mg/kg/min) for 30 min. infusion (Ins+L-arg). Ins+L-arg (saline day) increased the % change in MBV in both groups. However, this increase was less in carriers as compared to non-carriers (13.6±42.4 and 38.9±74.4), Fig. A. Intralipid (IL) infusion increased MBV but only in non-carriers, Fig. B . Treatment with sildenafil in the presence of IL infusion induced a decline in MBV in G-allele carriers Fig. C . In conclusion, healthy AAs with CD36 deficiency had a poor insulin-induced microvascular recruitment and appeared to be worsened by potentiating NO function with sildenafil.

Super-Resolution Ultrasound Imaging of Skeletal Muscle Microvascular Dysfunction in an Animal Model of Type 2 Diabetes.

To evaluate the use of super-resolution ultrasound (SR-US) imaging for quantifying microvascular changes in skeletal muscle using a mouse model of type 2 diabetes. Study groups were young, standard chow-fed male C57BL/6J mice (lean group) and high fat diet-fed older mice (obese group). After an overnight fast, dynamic contrast-enhanced US imaging was performed on the proximal hind limb adductor muscle group for 10 minutes at baseline and again at 1 and 2 hours during administration of a hyperinsulinemic-euglycemic clamp. Dynamic contrast-enhanced US images were collected on a clinical US scanner (Acuson Sequoia 512; Siemens Healthcare, Mountain View, CA) equipped with a 15L8 linear array transducer. Dynamic contrast-enhanced US images were processed with a spatiotemporal filter to remove tissue clutter. Individual microbubbles were localized and counted to create an SR-US image. A frame-by-frame analysis of the microbubble count was generated (ie, time-microbubble count curve [TMC]) to estimate tissue perfusion and microvascular blood flow. The conventional time-intensity curve (TIC) was also generated for comparison. In vivo SR-US imaging could delineate microvascular structures in the mouse hind limb. Compared with lean animals, insulin-induced microvascular recruitment was attenuated in the obese group. The SR-US-based TMC analysis revealed differences between lean and obese animal data for select microvascular parameters (P < .04), which was not true for TIC-based measurements. Whereas the TMC and TIC microvascular parameters yielded similar temporal trends, there was less variance associated with the TMC-derived values. Super-resolution US imaging is a new modality for measuring the microvascular properties of skeletal muscle and dysfunction from type 2 diabetes.

Inhibition of Myeloperoxidase and MPO Reverses Microvascular Insulin Resistance in High-Fat Diet (HFD)-Fed Rats

Chronic, low-level inflammation underlies much of the vascular and metabolic insulin resistance associated with HFD. Release of MPO by leukocytes may be an early contributor to the inflammatory process and endothelial dysfunction that accompanies HFD feeding. Plasma MPO concentrations are increased in both human obesity and diabetes and HFD-fed rats. However, the impact of MPO on microangiopathy and its relation to insulin resistance is unclear. We tested whether AZD5904 (a potent, irreversible inhibitor of MPO, AstraZeneca) improves endothelial function and vascular insulin responses in insulin resistant, adult male SD rats fed a HFD (60% calories from fat) for 2 weeks. HFD fed rats received vehicle (n=8) or AZD5904 (75 µmol/kg/day, n=10) via an Alzet Mini pump for 2 weeks. A 3rd group of rats (n=8, vehicle alone) were fed a chow diet for 2 weeks. After 2 weeks of HFD or control diet, rats were fasted overnight and received a 2-hour euglycemic insulin clamp (3 mU/kg/minutes). Hindleg muscle microvascular perfusion was assessed using contrast-enhanced ultrasound and insulin-stimulated steady-state whole body glucose disposal was determined. Insulin infusion increased muscle microvascular perfusion by 2-3 fold in chow fed rats (p&amp;lt;0.05). HFD feeding abolished insulin-induced microvascular recruitment in muscle, and decreased insulin-mediated glucose disposal by ∼45% (p&amp;lt;0.01). Simultaneous treatment with AZD5904 fully restored insulin-mediated muscle microvascular perfusion (p&amp;lt;0.05) in HFD rats, but did not improve insulin-stimulated glucose disposal in HFD-fed rats. We conclude that inhibition of MPO with AZD5904specifically reverses muscle microvascular insulin resistance in HFD rats. This implicates MPO as a significant contributor to HFD-induced endothelial inflammation and suggests a role for MPO inhibition to improve microvascular complications in patients with vascular insulin resistance. Disclosure E. Barrett: None. K.W. Aylor: None. W. Chai: None. L. Gan: Employee; Self; AstraZeneca.

Insulin-induced changes in skeletal muscle microvascular perfusion are dependent upon perivascular adipose tissue in women.

Aims/hypothesisObesity increases the risk of cardiovascular disease and type 2 diabetes, partly through reduced insulin-induced microvascular vasodilation, which causes impairment of glucose delivery and uptake. We studied whether perivascular adipose tissue (PVAT) controls insulin-induced vasodilation in human muscle, and whether altered properties of PVAT relate to reduced insulin-induced vasodilation in obesity.MethodsInsulin-induced microvascular recruitment was measured using contrast enhanced ultrasound (CEU), before and during a hyperinsulinaemic–euglycaemic clamp in 15 lean and 18 obese healthy women (18–55 years). Surgical skeletal muscle biopsies were taken on a separate day to study perivascular adipocyte size in histological slices, as well as to study ex vivo insulin-induced vasoreactivity in microvessels in the absence and presence of PVAT in the pressure myograph. Statistical mediation of the relation between BMI and microvascular recruitment by PVAT was studied in a mediation model.ResultsObese women showed impaired insulin-induced microvascular recruitment and lower metabolic insulin sensitivity compared with lean women. Microvascular recruitment was a mediator in the association between obesity and insulin sensitivity. Perivascular adipocyte size, determined in skeletal muscle biopsies, was larger in obese than in lean women, and statistically explained the difference in microvascular recruitment between obese and lean women. PVAT from lean women enhanced insulin-induced vasodilation in isolated skeletal muscle resistance arteries, while PVAT from obese women revealed insulin-induced vasoconstriction.Conclusions/interpretationPVAT from lean women enhances insulin-induced vasodilation and microvascular recruitment whereas PVAT from obese women does not. PVAT adipocyte size partly explains the difference in insulin-induced microvascular recruitment between lean and obese women.Electronic supplementary materialThe online version of this article (doi:10.1007/s00125-015-3606-8) contains peer-reviewed but unedited supplementary material, which is available to authorised users.

PS14 - 74. Microvascular insulin sensitivity in human skeletal muscle and skin are related and both are associated with metabolic insulin sensitivity

Insulin recruits microvascular vessels to increase the available surface area for exchange of insulin with the interstitium. Insulin-induced microvascular recruitment is perturbed in insulin resistance, and may even be the culprit of insulin resistance. As such, insulin-induced microvascular recruitment has received increasing attention. The study of the human microcirculation has however been hampered by a perceived lack of appropriate techniques. Skin microcirculation has been used as a model for the muscle microcirculation, even though the skin is an insulin sensitive organ, doubt remained whether skin microcirculation is indeed a good model for the muscle microcirculation. In recent years, Contrast Enhanced UltraSound (CEUS) emerged as a novel tool to study muscle microcirculation. In this study, we set out to clarify the relation between insulin-induced capillary recruitment in skin and microvascular recruitment in muscle.

Fitness Abrogates the Ability of Free Fatty Acids (FFA) to Inhibit Insulin's Microvascular Action

Insulin acutely (within 20 min) increases microvascular blood volume (MBV) within human forearm muscle as measured by contrast enhanced ultrasound (CEU). This serves to increase insulin delivery to muscle and facilitates insulin's metabolic action. This vascular effect of insulin is impaired by the insulin resistance that accompanies either chronic obesity or acute (within 2-4hr) increases in the circulating levels of FFA. Interestingly, and as yet unexplained, raising plasma FFA via infusion of Intralipid has less effect on insulin sensitivity in individuals who are highly trained. It is not known whether training affects the ability of FFA to inhibit insulin-induced microvascular recruitment. PURPOSE: The current study was undertaken to address whether the level of fitness (VO2 max) or adiposity (% body fat) predicted MBV and/or glucose infusion rate (GIR) during a euglycemic insulin clamp. METHODS: A group (n =11) of young (18-35), lean (BMI≤25), healthy subjects received Intralipid 20% + heparin for 5 hrs (3hr prior to and throughout a 2hr, 1mU/kg/min insulin clamp). MBV as measured by CEU was obtained continuously during the first 30 min of the clamp. Fitness level was assessed by conducting an exercise test (Bruce protocol) to obtain VO2 max in a subset (n=8) on a separate day. RESULTS: We found that VO2 max was a strong predictor of MBV (r = 0.74 p <0.05) the GIR likewise strongly correlated with MBV(r = 0.75, p= 0.01) supporting the hypothesis that insulin's vascular action is a significant contributor to its metabolic effects. We also observed the expected inverse relationship between VO2 max and % body fat (r = -0.79, p= 0.02). CONCLUSION: Fitness limits the ability of elevated FFA to block both insulin's vasodilatory and metabolic effects. The increased microvascular surface area in response to insulin seen in those with higher VO2 max can facilitate exchange of insulin and glucose with muscle interstitium thereby contributing to the higher GIR. In addition the lower body fat %, therefore greater % lean body mass, may also contribute to the higher GIR. Taken together these findings suggest that a more fit person is less likely to develop either vascular or metabolic insulin resistance in response to elevated circulation FFA. The mechanism for the protective effect of fitness is unclear. Supported by NIH Grant RO1 DK073759

Contrast-Enhanced Ultrasound Imaging of Insulin-Induced Microvascular Recruitment in Type 1 Diabetes

Type 1 diabetes mellitus (T1DM) patients relies exclusively on exogenous insulin to maintain safe blood glucose levels. It has been recently demonstrated that insulin promotes its own action by enhancing capillary recruitment which occurs 15–20 minutes before increase in glucose uptake. In this study, we examine insulin-induced capillary recruitment in T1DM patients with various levels of insulin sensitivity. Eleven hyperinsulinemic euglycemic clamps were performed on nine T1DM patients during which capillary recruitment was assessed at basal insulin concentration levels and at hyperphysiological levels 30 min after the start of the clamp using contrast-enhance ultrasound (CEU) imaging. A systematic procedure was developed to select regions of interest (ROI) in the sequences of ultrasound images, thus bypassing the subjectivity of a selection done “by hand”. The replenishment curves were then obtained and fitted with exponential curves which parameters provide measures of microvascular blood volume (MBV) and microvascular flow (MF). Higher basal MBV and MF were observed in high insulin sensitive subjects compared to low SI subjects. Hyperphysiological insulin concentrations induced by the clamp yielded opposite effects in low insulin sensitivity (SI) and high SI patients: capillary recruitment and derecruitment was observed respectively. It was hypothesized that insulin-induced capillary recruitment occurs at a subject-specific level of insulin concentration, and that this level is low (below basal) for sensitive patients and higher (above basal) for more resitant patients. Furthermore, diabetic microvascular complications significantly correlated with the effect of hyperphysiological insulin levels on the capillary recruitment/derecruitment in the two groups.