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Diabetes predisposes patients to peripheral artery disease (PAD). Muscle microvasculature plays a critical role in maintaining muscle function and health by delivering oxygen, nutrients and hormones to myocytes. Insulin dilates precapillary arterioles to increase muscle perfusion. To define the impact of ischemia to muscle microvascular perfusion and microvascular response to insulin, adult male rats were subject to hind limb ischemic surgery. Total hind limb blood flow was determined using laser Doppler blood flowmetry and muscle microvascular blood volume (MBV) measured using contrast-enhanced ultrasound in both the ischemic (left) and control (right) hind limb. Ischemic to control limb (I/C) ratios were calculated. Hyperinsulinemic euglycemia clamps were performed to determine microvascular responses to insulin. Hind limb ischemic surgery decreased total limb blood flow by ∼70% immediately, from a pre-surgical I/C ratio of 1.10 ± 0.07 to 0.34 ± 0.06. The I/C ratios then progressively increased to 0.45 ± 0.08, 0.54 ± 0.06, 0.67 ± 0.11, and 0.74± 0.11 on postsurgical day 3, 7, 14 and 21 respectively. Similarly, ischemic surgery decreased MBV promptly from a pre-surgical I/C ratio of 1.01 ± 0.04 to 0.39 ± 0.06. MBV I/C ratios completely recovered on day 3 (1.11 ± 0.09) and remained stable afterwards. Insulin induced similar increases in muscle MBV in both legs before surgery (I/C ratio 1.14 ± 0.16) but the increase was much less in ischemic leg on day 3 (I/C ratio 0.63 ± 0.15). Microvascular insulin responses fully recovered on day 7 (I/C ratio 0.97± 0.25). We conclude that hind limb ischemia is associated with decreased total blood flow, muscle microvascular perfusion as well as microvascular responses to insulin. While the recovery in muscle microvascular perfusion precedes that of total limb blood flow, recovery in muscle microvascular response to insulin is delayed. These changes may contribute to muscle injury in patients with diabetes and the muscle microvasculature is potentially a therapeutic target for PAD. Disclosure N. Wang: None. Z. Liu: None. Funding American Diabetes Association (1-17-ICTS-059 to Z.L.); National Institutes of Health (R01DK102359)

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)

Ice propagation is an essential step when freezing happens on hydrated surfaces. In this work, we choose polyelectrolyte brushes (PB), whose hydration ability can be controlled by simply exchanging the counterions, to demonstrate the distinct ice propagation mechanism on differently hydrated surfaces.

The Auger decay for the many-electron Xe+ (4 p 3 / 2 − 1 ) state is studied in detail, using multistep approaches. It is found that the single Auger decay channels are primarily Coster–Kronig processes, which is in accord with other theoretical and experimental results. The double and triple Auger decays result primarily from cascade processes, i.e., the sequential two-step and three-step Auger decay, and as such, the contributions from direct processes can be neglected. Level-to-level rates for single, double, and triple decays are obtained, based on which comprehensive Auger electron spectra and ion yields are obtained. Our decay paths and Auger electron spectra are in agreement with the experimental analysis [Hikosaka et al., Phys. Rev. A 76 (2007) 032708], and our ion yield ratios (Xe2+: Xe3+: Xe4+ = 4.6 : 87.0 : 8.4) are also in line with their values (5.0 : 86.0 : 9.0). However, with respect to the ion yield ratios, a discrepancy still remains among the experimental and theoretical results. Taking into account the complexity of Xe’s electronic structure, further, more detailed experiments are still required.

Curcumin, a yellow-orange substance that is extracted from the spice turmeric (Curcuma longa, Zinziberaceae), has been attributed with a wide range of pharmacological activities for the prevention and treatment of several disease conditions such as arthritis, hypertension, diabetes, Alzheimer's, antibacterial and cancer to name a few. However, its potential for use as an orally delivered medicinal product is hindered by its poor solubility and bioavailability. The low oral bioavailability of curcumin is caused by several factors including low aqueous solubility, poor intestinal permeability, unstable at alkaline pH and rapid metabolism. To improve curcumin's poor oral bioavailability, different formulation strategies such as incorporation into nanoparticles, liposomes, micelles, micro/nano-emulsions and solid dispersions as well as co-administration with piperine have been investigated in both animal models as well as human supplementation studies. In this review, novel formulations of curcumin for oral delivery that were developed in recent years are reviewed and discussed.

An in situ Ti2AlNb-reinforced Ti–45Al–5Nb–0.3 W-based intermetallic composite was prepared using 2 vol. % Nb powder and TiAl pre-alloy powder. The microstructure evolution and elevated-temperature mechanical properties of the Ti2AlNb/TiAl composite were investigated. The results show that during the hot isostatic pressing (HIP) process, Nb diffused into the TiAl matrix, and formed Nb-rich particles in which an Nb-rich-region and the coarse rod-like Ti2AlNb phase existed. After hot extrusion, the Nb-rich particles elongated along the direction of extrusion. Further, the mean diameter of the Ti2AlNb phase regions decreased, and the Ti2AlNb content increased. After heat treatment at 1280 °C for 1 h, the rod-like Ti2AlNb phase regions in the extruded specimen transformed into needle-like and fine lath-like structures, and the proportion of Ti2AlNb in the Nb-rich-regions increased. The extruded Ti2AlNb/TiAl specimen shows a high tensile elongation (TE), and the heat-treated specimen shows a high yield strength (YS) and ultimate tensile strength (UTS) at the test temperatures of 750 °C–900 °C. In particular, the extruded specimen shows excellent strength–ductility product (UTS × TE) values of 38.8 GPa% and 46.9 GPa% at 800 °C and 850 °C, respectively. The high toughness of TiAl intermetallic composites was because of the fibrous tough Nb-rich-regions that contained the fine Ti2AlNb phase.

Background Obesity is associated with impaired immunity and chronic, low-grade inflammation, but little is known about the immune system's response to bariatric surgery–induced weight loss. Objectives To determine whether circulating immunoglobulins and acute-phase reactant levels are altered after bariatric surgery. Setting University Hospital, China. Methods Fifty-eight patients with obesity were recruited from the Second Xiangya Hospital of Central South University; 48 underwent laparoscopic sleeve gastrectomy and 10 underwent traditional medical therapy. Results During the 12-month follow-up, bariatric surgery showed pronounced effects on weight loss and glucose and lipid metabolism. Circulating concentrations of hypersensitive C-reactive protein, and complement components 3 and 4 decreased significantly. Compared with the presurgery level, the immunoglobulin A, immunoglobulin M, and immunoglobulin G levels increased significantly at 2 and 6 months postsurgery. Compared with the whole group, the same results were observed after surgery in the circulating concentrations of complement components 3 and 4 and hypersensitive C-reactive protein in patients with class I obesity. However, the immunoglobulin G concentration increased at 6 and 12 months postsurgery, immunoglobulin A increased at 12 months postsurgery, and no postsurgery changes in immunoglobulin M were found in patients with class I obesity. No significant changes were noted in patients who underwent traditional medical therapy. We also found a correlation between decreased complement factor levels and improved insulin sensitivity. Conclusions In addition to reducing weight and controlling diabetes and dyslipidemia, bariatric surgery is also effective for improving the immune function of patients with obesity.

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.

Newer classes of medications have been proven useful in glycemic control in type 2 diabetes (T2D), but many do not appear capable to slow down the progressive loss of ß-cell function, or to improve population-level glycemic control. Positive energy balance, e.g. surplus energy intake over expenditure, is at the core for developing metabolic syndrome and T2D. Currently available glycemic control drugs come to the market based on their 1-2 years risk-benefit profiles, but most of them do not correct positive energy balance and lose efficacy in the long-term. This denouement is destined by a positive energy balance of T2D. There is continuous endeavor/investment in new drugs for T2D. In this review, we compared the effects of commonly used oral hypoglycemic agents on energy balance and discussed several novel therapeutic targets/approaches for T2D that could potentially correct positive energy balance: changing the composition of intestinal host-microbiota to alleviate excess caloric consumption, controlling chylomicron uptake into intestinal lacteals to reduce excessive caloric intake, and activating pyruvate kinase M2 (PKM2) to ameliorate glucose metabolism and increase energy expenditure. We further reviewed how nicotine affects body weight and ameliorates positive energy balance, and ways to encourage people to adopt a more healthy lifestyle by exercising more and/or decreasing caloric intake. These potential targets/approaches may hopefully correct positive energy balance, delay disease progression, reverse some pathophysiological changes, and eventually prevent and/or cure the disease. Drug development strategies applying new insights into T2D process and therapeutic index to correct positive energy balance need to be seriously considered.

Aims To investigate the prevalence of adult-onset autoimmune diabetes (ADM) and predisposition to autoimmune diseases by quantifying serum organ-specific autoantibodies in people with phenotype of type 2 diabetes (T2D). Materials and methods We included a nationally representative sample of 46 239 adults aged ≥20 years from 14 provinces, of whom 4671 had diabetes, plus 1000 control subjects with normal glucose tolerance (NGT). Participants were screened centrally for autoantibodies to glutamic acid decarboxylase (GAD), islet antigen 2 (IA2) and zinc transporter isoform-8 (Znt8) and were defined as having ADM where positive for these antibodies. We then assayed thyroid peroxidase (TPO), tissue transglutaminase (tTG) and 21-hydroxylase (21-OH) autoantibodies in randomly selected participants with ADM and in age-matched, sex-matched and non-ADM controls with T2D plus controls with NGT. Results Post-normalization, the standardized prevalence rate of ADM was 6.0% (95% confidence interval [CI] 5.3-6.8) in initially non-insulin-requiring participants with ADM, corresponding to six million adults in China, in whom adjusted antibody positivity was: TPO autoantibodies 16.3% (95% CI 10.8-21.8), tTG autoantibodies 2.1% (95% CI 0.0-4.2), and 21-OH autoantibodies 1.8% (95% CI -0.2 to 3.8). Those participants with ADM who were GAD autoantibody-positive had high risk of TPO autoantibody positivity (odds ratio [OR] 2.39, P = 0.0031) and tTG autoantibody positivity (OR 6.98, P = 0.027), while those positive for IA2 autoantibodies had a high risk of tTG autoantibody positivity (OR 19.05, P = 0.001). Conclusions A proportion of people with phenotype of T2D in China have ADM, with diabetes-associated autoantibodies, and may be at risk of developing other organ-specific autoimmune diseases; therefore, it may be clinically relevant to consider screening such Chinese populations.

Obesity is associated with metabolic and microvascular insulin resistance. The latter is characterized by impaired insulin-mediated microvascular recruitment. GLP-1 engenders vasodilation in addition to its glycemic actions. At physiological concentrations, GLP-1 acutely recruits skeletal and cardiac muscle microvasculature in healthy humans and this action is preserved in the insulin resistant rodents. To examine whether GLP-1 recruits microvasculature and improves insulin’s action in obese humans, 15 obese adults (age 27 ± 2.2, BMI 33.7 ± 1.2) were studied thrice at random order after an overnight fast. Subjects received an intravenous infusion of GLP-1 (1.2 pmol/kg/min) for 150 mins or an intravenous infusion of either normal saline or GLP-1 (1.2 pmol/kg/min) for 150 mins with a euglycemic insulin clamp (1 mU/kg/min) superimposed over the last 120 mins. Skeletal and cardiac muscle microvascular blood volume (MBV), flow velocity (MFV) and blood flow (MBF) were determined at 0, 30 and 150 min. Steady-state glucose infusion rate (GIR) was calculated. Insulin infusion alone did not change MBV or MBF 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 (p We conclude that in obese humans with microvascular insulin resistance GLP-1's vasodilatory actions are preserved in both skeletal and cardiac muscle microvasculature. This may contribute to improving metabolic responses to insulin and decreasing cardiovascular morbidity and mortality associated with obesity and diabetes. Disclosure N. Wang: None. A. Tan: None. L. Jahn: None. L. Hartline: None. K.W. Aylor: None. E. Barrett: None. Z. Liu: None.

Obesity and diabetes are associated with inflammation, endothelial dysfunction and insulin resistance in the muscle microvasculature. Inflammation-induced microvascular insulin resistance is an early event and plays a causative role in the development of metabolic insulin resistance in diet-induced obesity., Endothelial dysfunction and vascular insulin resistance usually coexist and chronic inflammation engenders both. In the present study, we investigate the temporal relationship between vascular insulin resistance and metabolic insulin resistance. We assessed insulin responses in all arterial segments, including aorta, distal saphenous artery and the microvasculature, as well as the metabolic insulin responses in muscle in rats fed on a high-fat diet (HFD) for various durations ranging from 3 days to 4 weeks with or without sodium salicylate treatment. Compared with controls, HFD feeding significantly blunted insulin-mediated Akt (protein kinase B) and eNOS [endothelial nitric oxide (NO) synthase] phosphorylation in aorta in 1 week, blunted vasodilatory response in small resistance vessel in 4 weeks and microvascular recruitment in as early as 3 days. Insulin-stimulated whole body glucose disposal did not begin to progressively decrease until after 1 week. Salicylate treatment fully inhibited vascular inflammation, prevented microvascular insulin resistance and significantly improved muscle metabolic responses to insulin. We conclude that microvascular insulin resistance is an early event in diet-induced obesity and insulin resistance and inflammation plays an essential role in this process. Our data suggest microvascular insulin resistance contributes to the development of metabolic insulin resistance in muscle and muscle microvasculature is a potential therapeutic target in the prevention and treatment of diabetes and its related complications.

Insulin enhances the compliance of conduit arteries, relaxes resistance arterioles to increase tissue blood flow, and dilates precapillary arterioles to expand muscle microvascular blood volume. These actions are impaired in the insulin resistant states. Exercise ameliorates endothelial dysfunction and improves insulin responses in insulin resistant patients, but the precise underlying mechanisms remain unclear. The microvasculature critically regulates insulin action in muscle by modulating insulin delivery to the capillaries nurturing the myocytes and trans-endothelial insulin transport. Recent data suggest that exercise may exert its insulin-sensitizing effect via recruiting muscle microvasculature to increase insulin delivery to and action in muscle. The current review focuses on how the interplay among exercise, insulin action, and the vasculature contributes to exercise-mediated insulin sensitization in muscle.

Context The most common modality used to address acute inflammation is cryotherapy. Whereas pain decreases with cryotherapy, evidence that changes occur in perfusion of skeletal muscle is limited. We do not know whether ice attenuates the increases in perfusion associated with acute inflammation. Objective To examine the effects of repeated applications of ice bags on perfusion of the gastrocnemius muscle after an eccentric exercise protocol. Design Controlled laboratory study. Setting Laboratory. Patients or Other Participants Eighteen healthy participants (3 men, 15 women; age = 22.2 ± 2.2 years, height = 166.0 ± 11.9 cm, mass = 69.4 ± 25.0 kg). Intervention(s) To induce eccentric muscle damage, participants performed 100 unilateral heel-lowering exercises off a step to the beat of a metronome. A randomized intervention (cryotherapy, sham, control) was applied to the exercised lower extremity immediately after the protocol and again at 10, 24, and 34 hours after the protocol. Main Outcome Measure(s) Baseline perfusion measurements (blood volume, blood flow, and blood flow velocity) were taken using contrast-enhanced ultrasound of the exercised leg. Perfusion was reassessed after the first intervention and 48 hours after the protocol as percentage change scores. Pain was measured with a visual analog scale at baseline and at 10, 24, 34, and 48 hours after the protocol. Separate repeated-measures analyses of variance were used to assess each dependent variable. Results We found no interactions among interventions for microvascular perfusion. Blood volume and blood flow, however, increased in all conditions at 48 hours after exercise (P < .001), and blood flow velocity decreased postintervention from baseline (P = .041). We found a time-by-intervention interaction for pain (P = .009). Visual analog scale scores were lower for the cryotherapy group than for the control group at 34 and 48 hours after exercise. Conclusions Whereas eccentric muscle damage resulted in increased blood flow, ice did not decrease muscle perfusion 48 hours after exercise. Therefore, ice does not seem to decrease muscle perfusion when blood flow is elevated, as it would be during inflammation.

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It has been debated for several years as to whether the antidiabetic drug pioglitazone increases the risk for bladder cancer. A series of recent large population studies yielded conflicting results. To investigate why the observational studies yielded conflicting results, we conducted stratified analyses to analyze the potential confounders behind these discordant outcomes. A total of 2,764,731 participants from observational (OB) studies and 9,999 from randomized control trials (RCTs) were identified for these analyses. The stratified analysis revealed that the study type, adjustment for age/sex, treatment duration, cumulative dose, agents used in a control group, mean period of follow-up and study population region might contribute to the discordant outcomes. In terms of population regions, pioglitazone increased the risk for bladder cancer could be found in European population, and patients who undergo treatment with pioglitazone for longer durations (>12 months) or are administrated a larger cumulative dose (>28,000 mg) might require more attention, and the long-term effects (≥3.6 years) of pioglitazone needs be monitored more carefully.

BACKGROUND Latent autoimmune diabetes in adults (LADA) exhibits significant clinical heterogeneity, but the underlying causes remain unclear. The aim of this study was to investigate whether age of onset of LADA contributes to the observed clinical heterogeneity by comparing the clinical, metabolic, and immunogenetic characteristics between elderly and young LADA patients. METHODS The cross-sectional study included a total of 579 patients with LADA which was further divided into elderly LADA (E-LADA) group (n = 135, age of onset ≥60 years) and young LADA (Y-LADA) group (n = 444, age of onset

Angiotensin II receptors regulate muscle microvascular recruitment and the delivery of nutrients, oxygen, and insulin to muscle. Although angiotensin type 1 receptor antagonism increases muscle microvascular perfusion and insulin action, angiotensin type 2 receptor blockade markedly restricts muscle microvascular blood volume and decreases muscle delivery of insulin. To examine the effects of direct type 2 receptor stimulation using Compound 21 (C21) on microvascular perfusion, insulin delivery and action, and tissue oxygenation in muscle, overnight-fasted adult male rats were infused with C21 systemically. C21 potently increased microvascular blood volume without altering microvascular flow velocity or blood pressure, resulting in a net increase in microvascular blood flow in muscle. This was associated with a substantial increase in muscle interstitial oxygen saturation and insulin delivery into the skeletal and cardiac muscle. These effects were neutralized by coinfusion of the type 2 receptor antagonist or nitric oxide synthase inhibitor. Superimposing C21 infusion on insulin infusion increased insulin-mediated whole body glucose disposal by 50%. C21 significantly relaxed the preconstricted distal saphenous artery ex vivo. We have concluded that direct type 2 receptor stimulation markedly increases muscle microvascular perfusion through nitric oxide biosynthesis and enhances insulin delivery and action in muscle. These findings provide a physiologic mechanistic insight into type 2 receptor modulation of insulin action and suggest that type 2 receptor agonists might have therapeutic potential in the management of diabetes and its associated complications.

Uniaxial forging (UAF) and multiaxial forging (MAF) were conducted on a Ti-45Al-7Nb-0.3W (at. %) alloy produced by powder metallurgy (PM) technique, and the deformed microstructures and deformation mechanism were investigated by scanning electron microscopy (SEM) and transmission electron microscopy (TEM). Results show that the near-gamma microstructure (NG) transformed into a fine and uniform duplex microstructure (DP) after MAF, and the mean grain size of the multiaxial forged alloy was 5 μm. The microstructure of the uniaxial forged alloy was inhomogeneous and anisotropy, while the microstructure of multiaxial forged alloy was very uniform and a higher amount of the β phase was distributed at the grain boundaries. During forging, deformation induced microstructure changes include dislocation movements, mechanical twinning, layer decomposition and dynamic recrystallization (DRX). The DRX occurred repeatedly and more severely during MAF than UAF process. Correspondingly, the multiaxial forged TiAl alloy exhibited excellent high temperature mechanical properties compared to the uniaxial forged alloy. At a temperature of 750 °C, the yield strength, ultimate tensile strength and elongation of the multiaxial forged alloy were 623 MPa, 697 MPa and 4.5%, respectively. It was noteworthy that the multiaxial forged alloy achieved highly plastic deformation and the elongation reached 173% at 900 °C with a strain rate of 1 × 10−3 s−1.

We have previously shown that insulin plays an important role in the nutrient-induced insulin resistance. In this study, we tested the hypothesis that chronic exposure to excess long-acting insulin (glargine) can cause typical type 2 diabetes mellitus (T2DM) in normal mice fed on a chow diet. C57BL/6 mice were treated with glargine once a day for 8 weeks, followed by evaluations of food intake, body weight, blood levels of glucose, insulin, lipids, and cytokines, insulin signaling, histology of pancreas, ectopic fat accumulation, oxidative stress level, and cholesterol content in mitochondria in tissues. Cholesterol content in mitochondria and its association with oxidative stress in cultured hepatocytes and β-cells were also examined. Results show that chronic exposure to glargine caused insulin resistance, hyperinsulinemia, and relative insulin deficiency (T2DM). Treatment with excess glargine led to loss of pancreatic islets, ectopic fat accumulation in liver, oxidative stress in liver and pancreas, and increased cholesterol content in mitochondria of liver and pancreas. Prolonged exposure of cultured primary hepatocytes and HIT-TI5 β-cells to insulin induced oxidative stress in a cholesterol synthesis-dependent manner. Together, our results show that chronic exposure to excess insulin can induce typical T2DM in normal mice fed on a chow diet.

Key points • Ranolazine, an anti-anginal compound, improves glycaemic control in clinical trials and increases myocardial perfusion via a direct vasodilatatory effect on coronary arteries. • Skeletal muscle microvasculature controls the delivery of nutrient and hormones into muscle and their exchanges between plasma and muscle interstitium by providing microvascular exchange surface area. • In this study we examined whether ranolazine improves glycaemic control via exerting vasodilatatory action on the pre-capillary arterioles to recruit muscle microvasculature. • We demonstrate that ranolazine potently recruits muscle microvasculature, which expands microvascular endothelial surface area in muscle and results in increased muscle delivery and action of insulin. • The results help us better understand the physiological mechanism by which ranolazine improves glycaemic control and its potential as an insulin-sensitizing agent. Abstract Ranolazine, an anti-anginal compound, has been shown to significantly improve glycaemic control in large-scale clinical trials, and short-term ranolazine treatment is associated with an improvement in myocardial blood flow. As microvascular perfusion plays critical roles in insulin delivery and action, we aimed to determine if ranolazine could improve muscle microvascular blood flow, thereby increasing muscle insulin delivery and glucose use. Overnight-fasted, anaesthetized Sprague-Dawley rats were used to determine the effects of ranolazine on microvascular recruitment using contrast-enhanced ultrasound, insulin action with euglycaemic hyperinsulinaemic clamp, and muscle insulin uptake using 125I-insulin. Ranolazine's effects on endothelial nitric oxide synthase (eNOS) phosphorylation, cAMP generation and endothelial insulin uptake were determined in cultured endothelial cells. Ranolazine-induced myographical changes in tension were determined in isolated distal saphenous artery. Ranolazine at therapeutically effective dose significantly recruited muscle microvasculature by increasing muscle microvascular blood volume (∼2-fold, P < 0.05) and increased insulin-mediated whole body glucose disposal (∼30%, P= 0.02). These were associated with an increased insulin delivery into the muscle (P < 0.04). In cultured endothelial cells, ranolazine increased eNOS phosphorylation and cAMP production without affecting endothelial insulin uptake. In ex vivo studies, ranolazine exerted a potent vasodilatatory effect on phenylephrine pre-constricted arterial rings, which was partially abolished by endothelium denudement. In conclusion, ranolazine treatment vasodilatates pre-capillary arterioles and increases microvascular perfusion, which are partially mediated by endothelium, leading to expanded microvascular endothelial surface area available for nutrient and hormone exchanges and resulting in increased muscle delivery and action of insulin. Whether these actions contribute to improved glycaemic control in patients with insulin resistance warrants further investigation.

Insulin delivery and transendothelial insulin transport are two discrete steps that limit muscle insulin action. Angiotensin II type 1 receptor (AT1R) blockade recruits microvasculature and increases glucose use in muscle. Increased muscle microvascular perfusion is associated with increased muscle delivery and action of insulin. To examine the effect of acute AT1R blockade on muscle insulin uptake and action, rats were studied after an overnight fast to examine the effects of losartan on muscle insulin uptake ( protocol 1), microvascular perfusion ( protocol 2), and insulin's microvascular and metabolic actions in the state of insulin resistance ( protocol 3). Endothelial cell insulin uptake was assessed, using125I-insulin as tracer. Systemic lipid infusion was used to induce insulin resistance. Losartan significantly increased muscle insulin uptake (∼60%, P < 0.03), which was associated with a two- to threefold increase in muscle microvascular blood volume (MBV; P = 0.002) and flow (MBF; P = 0.002). Losartan ± angiotensin II had no effect on insulin internalization in cultured endothelial cells. Lipid infusion abolished insulin-mediated increases in muscle MBV and MBF and lowered insulin-stimulated whole body glucose disposal ( P = 0.0001), which were reversed by losartan administration. Inhibition of nitric oxide synthase abolished losartan-induced muscle insulin uptake and reversal of lipid-induced metabolic insulin resistance. We conclude that AT1R blockade increases muscle insulin uptake mainly via microvascular recruitment and rescues insulin's metabolic action in the insulin-resistant state. This may contribute to the clinical findings of decreased cardiovascular events and new onset of diabetes in patients receiving AT1R blockers.

Vascular endothelium is an important insulin target and plays a pivotal role in the development of metabolic insulin resistance provoked by the Western lifestyle. It acts as a “first-responder” to environmental stimuli such as nutrients, cytokines, chemokines and physical activity and regulates insulin delivery to muscle and adipose tissue and thereby affecting insulin-mediated glucose disposal by these tissues. In addition, it also regulates the delivery of insulin and other appetite regulating signals from peripheral tissues to the central nervous system thus influencing the activity of nuclei that regulate hepatic glucose production, adipose tissue lipolysis and lipogenesis, as well as food consumption. Resistance to insulin’s vascular actions therefore broadly impacts tissue function and contribute to metabolic dysregulation. Moreover, vascular insulin resistance negatively impacts vascular health by affecting blood pressure regulation, vessel wall inflammation and atherogenesis thereby contributing to the burden of vascular disease seen with diabetes and metabolic syndrome. In the current review, we examined the evidence that supports the general concept of vascular endothelium as a target of insulin action and discussed the biochemical and physiological consequences of vascular insulin resistance.

Adult non–insulin requiring diabetes includes latent autoimmune diabetes of adults (LADA), distinguished from type 2 diabetes by the presence of islet autoantibodies. LADA China determined the characteristics of Chinese LADA. This nationwide, multicenter, clinic-based cross-sectional study was conducted in 46 university-affiliated hospitals in 25 Chinese cities. All 4,880 ketosis-free diabetic patients (6 months, aged ≥30 years) had GAD antibody (GADA) and HLA-DQ genotype measured centrally with clinical data collected locally. GADA-positive subjects were classified as LADA. Of the patients, 5.9% were GADA positive with LADA. LADA showed a north-south gradient. Compared with GADA-negative type 2 diabetes, LADA patients were leaner, with lower fasting C-peptide and less metabolic syndrome. Patients with high GADA titers are phenotypically different from those with low GADA titers, while only a higher HDL distinguished the latter from those with type 2 diabetes. HLA diabetes–susceptible haplotypes were more frequent in LADA, even in those with low-titer GADA. HLA diabetes-protective haplotypes were less frequent in LADA. Our study implicates universal immunogenetic effects, with some ethnic differences, in adult-onset autoimmune diabetes. Autoantibody positivity and titer could be important for LADA risk stratification and accurate therapeutic choice in clinical practice.

Insulin action on hippocampus improves cognitive function, and obesity and type 2 diabetes are associated with decreased cognitive function. Cerebral microvasculature plays a critical role in maintaining cerebral vitality and function by supplying nutrients, oxygen, and hormones such as insulin to cerebral parenchyma, including hippocampus. In skeletal muscle, insulin actively regulates microvascular opening and closure, and this action is impaired in the insulin-resistant states. To examine insulin’s action on hippocampal microvasculature and parenchyma and the impact of diet-induced obesity, we determined cognitive function and microvascular insulin responses, parenchyma insulin responses, and capillary density in the hippocampus in 2- and 8-mo-old rats on chow diet and 8-mo-old rats on a long-term high-fat diet (6 mo). Insulin infusion increased hippocampal microvascular perfusion in rats on chow diet by ~80–90%. High-fat diet feeding completely abolished insulin-mediated microvascular responses and protein kinase B phosphorylation but did not alter the capillary density in the hippocampus. This was associated with a significantly decreased cognitive function assessed using both the two-trial spontaneous alternation behavior test and the novel object recognition test. As the microvasculature provides the needed endothelial surface area for delivery of nutrients, oxygen, and insulin to hippocampal parenchyma, we conclude that hippocampal microvascular insulin resistance may play a critical role in the development of cognitive impairment seen in obesity and diabetes. Our results suggest that improvement in hippocampal microvascular insulin sensitivity might help improve or reverse cognitive function in the insulin-resistant states.

This work is the first to show that the ion specificity in tuning HIN on ionic surfaces follows the Hofmeister series., Heterogeneous ice nucleation (HIN) on ionic surfaces is ubiquitous in a wide range of atmospheric aerosols and at biological interfaces. Despite its great importance in cirrus cloud formation and cryopreservation of cells, organs, and tissues, it remains unclear whether the ion-specific effect on ice nucleation exists. Benefiting from the fact that ions at the polyelectrolyte brush (PB)/water interface can be reversibly exchanged, we report the effect of ions on HIN on the PB surface, and we discover that the distinct efficiency of ions in tuning HIN follows the Hofmeister series. Moreover, a large HIN temperature window of up to 7.8°C is demonstrated. By establishing a correlation between the fraction of ice-like water molecules and the kinetics of structural transformation from liquid- to ice-like water molecules at the PB/water interface with different counterions, we show that our molecular dynamics simulation analysis is consistent with the experimental observation of the ion-specific effect on HIN.

Muscle microvasculature critically regulates endothelial exchange surface area to facilitate transendothelial delivery of insulin, nutrients, and oxygen to myocytes. Insulin resistance blunts insulin-mediated microvascular recruitment and decreases muscle capillary density; both contribute to lower microvascular blood volume. Glucagon-like peptide 1 (GLP-1) and its analogs are able to dilate blood vessels and stimulate endothelial cell proliferation. In this study, we aim to determine the effects of sustained stimulation of the GLP-1 receptors on insulin-mediated capillary recruitment and metabolic insulin responses, small arterial endothelial function, and muscle capillary density. Rats were fed a high-fat diet (HFD) for 4 wk with or without simultaneous administration of liraglutide and subjected to a euglycemic hyperinsulinemic clamp for 120 min after an overnight fast. Insulin-mediated muscle microvascular recruitment and muscle oxygenation were determined before and during insulin infusion. Muscle capillary density was determined and distal saphenous artery used for determination of endothelial function and insulin-mediated vasodilation. HFD induced muscle microvascular insulin resistance and small arterial vessel endothelial dysfunction and decreased muscle capillary density. Simultaneous treatment of HFD-fed rats with liraglutide prevented all of these changes and improved insulin-stimulated glucose disposal. These were associated with a significantly increased AMPK phosphorylation and the expressions of VEGF and its receptors. We conclude that GLP-1 receptor agonists may exert their salutary glycemic effect via improving microvascular insulin sensitivity and muscle capillary density during the development of insulin resistance, and early use of GLP-1 receptor agonists may attenuate metabolic insulin resistance as well as prevent cardiovascular complications of diabetes.

Prediabetes is a heterogeneous term that encompasses different origins of insulin resistance and insulin secretion that contribute to distinct patterns of hyperglycemia. In fact, prediabetes is an umbrella term that characterizes individuals at high risk for developing type 2 diabetes (T2D) and/or cardiovascular disease (CVD). Based on current definitions there are at least 3 distinct phenotypes of prediabetes: impaired fasting glucose (IFG), impaired glucose tolerant (IGT), or the combination of both (IFG + IGT). Each phenotype is clinically relevant as they are uniquely recognized as having different levels of risk for progressing to T2D and CVD. Herein, we discuss the underlying pathophysiology that characterizes IFG, IGT and the combination, as well as examine how some of these phenotypes appear resistant to traditional exercise interventions. We propose that substrate metabolism differences between the prediabetes phenotypes may be a unifying mechanism that explains the inter-subject variation in response to exercise seen across obese, metabolic syndrome, pre-diabetic and T2D patients in the current literature. Ultimately, a better understanding of the pathophysiologic mechanisms that govern disturbances responsible for fasting vs. postprandial hyperglycemia and the combination of both is important for designing optimal and personalized exercise treatment strategies that treat and prevent hyperglycemia and CVD risk.

Angiotensin II type 1 receptor (AT(1)R) tone restricts muscle microvascular blood volume (MBV) and decreases muscle insulin delivery and glucose use.The objective of the study was to examine whether acute AT(1)R blockade alters microvascular perfusion in skeletal and cardiac muscle in humans.The study was conducted at the General Clinical Research Center at the University of Virginia.Eight overnight-fasted healthy young adults were studied thrice in random order. In study 1, each subject received candesartan (32 mg) orally at time 0. In study 2, each subject received placebo at time 0 and a 1 mU/min · kg euglycemic insulin clamp from time 240 to 360 min. In study 3, each subject received candesartan (32 mg) orally at time 0 and insulin infusion from 240 to 360 min. Forearm skeletal and cardiac muscle MBV, microvascular flow velocity, and microvascular blood flow (MBF) were determined at baseline and at 240 and 360 min.Candesartan treatment acutely recruited microvasculature in both skeletal and cardiac muscle by significantly increasing MBV (P0.03 and P = 0.02, respectively) and MBF (P0.03 for both) without altering microvascular flow velocity. Insulin infusion significantly increased cardiac MBV (P = 0.02) and MBF (P0.02). Superimposing insulin infusion 4 h after candesartan ingestion did not further recruit microvasculature. Insulin-mediated whole-body glucose disposal did not differ with or without candesartan pretreatment.Acute AT(1)R blockade with candesartan recruits skeletal as well as cardiac muscle microvasculature in healthy humans without altering insulin-mediated whole-body glucose disposal. This may contribute to the observed improvement in the cardiovascular outcomes in patients receiving prolonged treatment with AT(1)R blockers.

The study's purpose was to examine how the microvascularity of the gastrocnemius changed after a cryotherapy intervention based on subcutaneous tissue thickness. A secondary purpose was to compare intramuscular temperature change to subcutaneous tissue thickness.This was a single-blinded crossover study; each subject received both conditions (cryotherapy or sham). Subjects had baseline measurements of blood flow, blood volume, and intramuscular temperature recorded at 1 cm into the muscle belly of the medial gastrocnemius. The randomized condition was applied for 10, 25, 40, or 60 min, depending on subcutaneous tissue thickness. Immediate posttreatment microvascular measures were taken. After a designated rewarming period, again based on subcutaneous tissue thickness, measurements were retaken. At least 48 h separated the two conditions.There were significant condition × time interactions for blood flow (P = 0.01), blood volume (P = 0.022), and intramuscular temperature (P0.001). For blood flow and volume, the cryotherapy condition maintained baseline levels, whereas the sham condition increased immediately after treatment and rewarming. For intramuscular temperature, the cryotherapy condition caused a decrease in intramuscular temperature from baseline compared with no change in the sham condition from baseline. Intramuscular temperature change was significantly correlated to subcutaneous tissue thickness (r = 0.49, P = 0.05).Cryotherapy did not decrease blood flow and blood volume from resting levels, although the intramuscular temperature decreased. An intramuscular change of 7°C-9°C may not be cold enough to cause local vasoconstriction.

p38 MAPK has been strongly implicated in the development of atherosclerosis, but its role in cholesterol ester accumulation in macrophages and formation of foam cells, an early step in the development of atherosclerosis, has not been investigated. We addressed this issue and made some brand new observations. First, elevated intracellular cholesterol level induced by the exposure to LDL-activated p38 MAPK and activation of p38 MAPK with anisomycin increased the ratio of cholesterol esters over free cholesterol, whereas inhibition of p38 MAPK with SB203580 or siRNA reduced the LDL loading-induced intracellular accumulation of free cholesterol and cholesterol esters in macrophages. Second, exposure to LDL cholesterol inhibited autophagy in macrophages, and inhibition of autophagy with 3-methyladenine increased intracellular accumulation of cholesterol (free cholesterol and cholesterol esters), whereas activation of autophagy with rapamycin decreased intracellular accumulation of free cholesterol and cholesterol esters induced by the exposure to LDL cholesterol. Third, LDL cholesterol loading-induced inhibition of autophagy was prevented by blockade of p38 MAPK with SB203580 or siRNA. Neutral cholesterol ester hydrolase was co-localized with autophagosomes. Finally, LDL cholesterol loading and p38 activation suppressed expression of the key autophagy gene, ulk1, in macrophages. Together, our results provide brand new insight about cholesterol ester accumulation in macrophages and foam cell formation.

OBJECTIVE Angiotensin (ANG) II interacts with insulin-signaling pathways to regulate insulin sensitivity. The type 1 (AT1R) and type 2 (AT2R) receptors reciprocally regulate basal perfusion of muscle microvasculature. Unopposed AT2R activity increases muscle microvascular blood volume (MBV) and glucose extraction, whereas unopposed AT1R activity decreases both. The current study examined whether ANG II receptors modulate muscle insulin delivery and sensitivity. RESEARCH DESIGN AND METHODS Overnight-fasted rats were studied. In protocol 1, rats received a 2-h infusion of saline, insulin (3 mU/kg/min), insulin plus PD123319 (AT2R blocker), or insulin plus losartan (AT1R blocker, intravenously). Muscle MBV, microvascular flow velocity, and microvascular blood flow (MBF) were determined. In protocol 2, rats received 125I-insulin with or without PD123319, and muscle insulin uptake was determined. RESULTS Insulin significantly increased muscle MBV and MBF. AT2R blockade abolished insulin-mediated increases in muscle MBV and MBF and decreased insulin-stimulated glucose disposal by ~30%. In contrast, losartan plus insulin increased muscle MBV by two- to threefold without further increasing insulin-stimulated glucose disposal. Plasma nitric oxide increased by >50% with insulin and insulin plus losartan but not with insulin plus PD123319. PD123319 markedly decreased muscle insulin uptake and insulin-stimulated Akt phosphorylation. CONCLUSIONS We conclude that both AT1Rs and AT2Rs regulate insulin’s microvascular and metabolic action in muscle. Although AT1R activity restrains muscle metabolic responses to insulin via decreased microvascular recruitment and insulin delivery, AT2R activity is required for normal microvascular responses to insulin. Thus, pharmacologic manipulation aimed at increasing the AT2R-to-AT1R activity ratio may afford the potential to improve muscle insulin sensitivity and glucose metabolism.

The main goal of this review is to provide more specific and effective targets for prevention and treatment of insulin resistance and associated atherosclerosis. Modern technologies and medicine have vastly improved human health and prolonged the average life span of humans primarily by eliminating various premature deaths and infectious diseases. The modern technologies have also provided us abundant food and convenient transportation tools such as cars. As a result, more people are becoming overfed and sedentary. People are generally ingesting more calories than their bodies' need, leading to the so-called "positive energy imbalance", which is inseparable from the development of insulin resistance and its associated atherosclerosis. A direct consequence of insulin resistance is hyperinsulinemia. The current general view is that insulin is not functional properly in the presence of insulin resistance. Thus, the role of insulin itself in the development of insulin resistance and associated atherosclerosis has not been recognized. We have recently observed that the basal level of insulin signaling is increased in the presence of insulin resistance and hyperinsulinemia. In this review, we will explain how the increased basal insulin signaling contributes to the development of insulin resistance and associated atherosclerosis. We will first explain how insulin causes insulin resistance through two arbitrary stages (before and after the presence of obvious insulin resistance), and, then, explain how the excess exposure to insulin and the relative insulin insufficiency contributes to the atherosclerotic diseases. We propose that blockade of the excess insulin signaling is a viable approach to prevent and/or reverse insulin resistance and its associated atherosclerosis.

Resveratrol, a polyphenol found in many plants, has antioxidant and anti-inflammatory actions. It also improves endothelial function and may be cardioprotective. Tumor necrosis factor-α (TNFα) causes oxidative stress and microvascular endothelial dysfunction. Whether resveratrol affects microvascular function in vivo and, if so, whether inflammatory cytokines antagonize its microvascular action are not clear. In cultured bovine aortic endothelial cells (BAECs), reserveratrol (100 nM) increased the phosphorylation of protein kinase B (Akt), endothelial nitric oxide (NO) synthase (eNOS), and ERK1/2 within 15 min by more than twofold, and this effect lasted for at least 2 h. Treatment of BAECs with TNFα (10 ng/ml) significantly increased the NADPH oxidase activity and the production of hydrogen peroxide and superoxide. Pretreatment of cells with resveratrol (100 nM) prevented each of these. Injection (ip) of resveratrol in rats potently increased muscle microvascular blood volume (MBV; P = 0.007) and flow (MBF; P < 0.02) within 30 min, and this was sustained for at least 2 h. The phosphorylation of Akt in liver or muscle was unchanged. Superimposed systemic infusion of l-NAME (NOS inhibitor) completely abolished resveratrol-induced increases in MBV and MBF. Similarly, systemic infusion of TNFα prevented resveratrol-induced muscle microvascular recruitment. In conclusion, resveratrol activates eNOS and increases muscle microvascular recruitment via an NO-dependent mechanism. Despite the potent antioxidant effect of resveratrol, TNFα at concentrations that block insulin-mediated muscle microvascular recruitment completely neutralized resveratrol's microvascular action. Thus, chronic inflammation, as seen in type 2 diabetes, may limit resveratrol's vasodilatory actions on muscle microvasculature.

Type 2 diabetes is in essence a vascular disease and is frequently associated with hypertension, macrovascular events, and microvascular complications. Microvascular dysfunction, including impaired recruitment and capillary rarefaction, has been implicated in the pathogenesis of diabetic complications. Microvascular insulin resistance and renin-angiotensin system upregulation are present in diabetes, and each contributes to the development of hypertension and microvascular dysfunction. In the insulin-sensitive state, insulin increases microvascular perfusion by increasing endothelial nitric oxide production, but this effect is abolished by insulin resistance. Angiotensin II, acting via the type 1 receptors, induces inflammation and oxidative stress, leading to impaired insulin signaling, reduced nitric oxide availability, and vasoconstriction. Conversely, it acts on the type 2 receptors to cause vasodilatation. Because substrate and hormonal exchanges occur in the microvasculature, antihypertensive agents targeted to improve microvascular insulin sensitivity and function may have beneficial effects beyond their capacity to lower blood pressure in patients with diabetes.

Angiotensin II causes vasoconstriction via the type 1 receptor (AT 1 R) and vasodilatation through the type 2 receptor (AT 2 R). Both are expressed in muscle microvasculature, where substrate exchanges occur. Whether they modulate basal muscle microvascular perfusion and substrate metabolism is not known. We measured microvascular blood volume (MBV), a measure of microvascular surface area and perfusion, in rats during systemic infusion of angiotensin II at either 1 or 100 ng/kg per minute. Each caused a significant increase in muscle MBV. Likewise, administration of the AT 1 R blocker losartan increased muscle MBV by >3-fold ( P 2 R antagonist PD123319 significantly decreased muscle MBV by ≥80% ( P 2 R antagonism and inhibition of NO synthase each blocked the losartan-induced increase in muscle MBV and glucose uptake. In conclusion, angiotensin II acts on both AT 1 R and AT 2 R to regulate basal muscle microvascular perfusion. Basal AT 1 R tone restricts muscle MBV and glucose extraction, whereas basal AT 2 R activity increases muscle MBV and glucose uptake. Pharmacological manipulation of the balance of AT 1 R and AT 2 R activity affords the potential to improve glucose metabolism.

Autophagy is essential for maintaining both survival and health of cells. Autophagy is normally suppressed by amino acids and insulin. It is unclear what happens to the autophagy activity in the presence of insulin resistance and hyperinsulinemia. In this study, we examined the autophagy activity in the presence of insulin resistance and hyperinsulinemia and the associated mechanism. Insulin resistance and hyperinsulinemia were induced in mice by a high fat diet, followed by measurements of autophagy markers. Our results show that autophagy was suppressed in the livers of mice with insulin resistance and hyperinsulinemia. Transcript levels of some key autophagy genes were also suppressed in the presence of insulin resistance and hyperinsulinemia. Conversely, autophagy activity was increased in the livers of mice with streptozotocin-induced insulin deficiency. Levels of vps34, atg12, and gabarapl1 transcripts were elevated in the livers of mice with insulin deficiency. To study the mechanism, autophagy was induced by nutrient deprivation or glucagon in cultured hepatocytes in the presence or absence of insulin. Autophagy activity and transcript levels of vps34, atg12, and gabarapl1 genes were reduced by insulin. The effect of insulin was largely prevented by overexpression of the constitutive nuclear form of FoxO1. Importantly, autophagy of mitochondria (mitophagy) in cultured cells was suppressed by insulin in the presence of insulin resistance. Together, our results show that autophagy activity and expression of some key autophagy genes were suppressed in the presence of insulin resistance and hyperinsulinemia. Insulin suppression of autophagy involves FoxO1-mediated transcription of key autophagy genes.

Subjects with type 1 diabetes mellitus (T1DM) eventually develop insulin resistance and other features of T2DM such as cardiovascular disorders. The exact mechanism has been not been completely understood. In this study, we tested the hypothesis that excessive or inappropriate exposure to insulin is a primary mediator of insulin resistance in T1DM. We found that continuous exposure of mice with non-obese diabetes to insulin detemir, which is similar to some current conventional treatment of human T1DM, induced severe insulin resistance, whereas untreated hyperglycemia for the same amount of time (2 weeks) did not cause obvious insulin resistance. Insulin resistance was accompanied by decreased mitochondrial production as evaluated by mitochondrial DNA and levels of transcripts and proteins of mitochondrion-associated genes, increased ectopic fat accumulation in liver and skeletal muscle (gastrocnemius) evaluated by measurements of triglyceride content, and elevated oxidative stress detected by the GSH/GSSG ratio. Prolonged exposure of cultured hepatocytes to insulin induced significant insulin resistance, whereas the same length of exposure to a high level of glucose (33 mm) did not cause obvious insulin resistance. Furthermore, our results showed that prolonged exposure to insulin caused oxidative stress, and blockade of mitochondrion-derived oxidative stress by overexpression of manganese-superoxide dismutase prevented insulin resistance induced by the prolonged exposure to insulin. Together, our results show that excessive exposure to insulin is a primary inducer of insulin resistance in T1DM in mice.

Insulin recruits muscle microvasculature, which increases the endothelial exchange surface area to facilitate substrate delivery. Elevated plasma concentrations of free fatty acids (FFAs) cause insulin resistance.The aim of the study was to examine whether FFAs cause insulin resistance in human muscle microvasculature.The study was conducted at the General Clinical Research Center at the University of Virginia.Twenty-two healthy subjects were studied under two protocols designed to raise plasma insulin concentrations to postprandial levels using either an insulin infusion or a mixed meal challenge. Within each protocol, subjects were studied twice. In random order, they received a 5-h systemic infusion of either saline or Intralipid/heparin. Three hours into the infusion, baseline muscle microvascular blood volume (MBV), microvascular flow velocity, and microvascular blood flow (MBF) were measured. Each subject was then given either the mixed meal or a 1 mU/kg x min insulin clamp for 2 h. Microvascular parameters were again obtained 2 h after the meal or at the end of insulin infusion.Meal feeding and insulin infusion raised plasma insulin concentrations to approximately 200 pm, and each significantly increased muscle MBV (P = 0.03 and P0.01, respectively). MBF trended up after meal feeding (P = 0.08) and increased significantly after insulin infusion (P = 0.02). In the presence of Intralipid, neither the meal nor the insulin infusion increased muscle MBV and MBF.Compared to saline, lipid infusion raises plasma FFA concentrations and blocks the ability of insulin or meal to recruit muscle microvasculature. High plasma FFA concentrations may contribute to muscle insulin resistance and the microvascular complications of diabetes.

Insulin is the central regulator of metabolism and is necessary for storing energy as fat efficiently. Mitochondria are primary sites of energy consumption of most cells. Increased plasma insulin level and mitochondrial dysfunction are features of insulin resistance. The exact role of insulin in regulation of mitochondrial production and function remains unestablished. In this study, we observed that mitochondrial production in liver and skeletal muscle gastrocnemius was increased in mice with insulin deficiency (streptozotocin-induced type 1 diabetes). In contrast, prolonged exposure (24 h) of isolated hepatocytes to insulin decreased mitochondrial mass, mitochondrial DNA (mtDNA), intracellular ATP content, and cellular O2 consumption. Transcript levels of genes associated with mitochondrial production and β oxidation were decreased, whereas those of lipogenic genes were increased by the prolonged exposure to insulin. Insulin-induced changes in mtDNA, mitochondrial mass, intracellular ATP content, and transcripts of mitochondrion-associated genes were prevented by blockade of Akt activation with the phosphatidylinositol 3-kinase inhibitor LY294002. Conversely, levels of mtDNA, intracellular ATP content, and expression of mitochondrion-associated genes were decreased by overexpression of the constitutively active Akt. Finally, insulin suppression of mtDNA, ATP production, and expression of mitochondrion-related genes was largely prevented by inhibition of cyclic nucleotide phosphodiesterase with isobutylmethylxanthine. Together, our results show prolonged exposure of isolated hepatocytes to insulin suppresses mitochondrial production and function through the classical Akt-dependent insulin signaling pathway.

Evidence suggests that insulin delivery to skeletal muscle interstitium is the rate-limiting step in insulin-stimulated muscle glucose uptake and that this process is impaired by insulin resistance. In this review we examine the basis for the hypothesis that insulin acts on the vasculature at three discrete steps to enhance its own delivery to muscle: (1) relaxation of resistance vessels to increase total blood flow; (2) relaxation of pre-capillary arterioles to increase the microvascular exchange surface perfused within skeletal muscle (microvascular recruitment); and (3) the trans-endothelial transport (TET) of insulin. Insulin can relax resistance vessels and increase blood flow to skeletal muscle. However, there is controversy as to whether this occurs at physiological concentrations of, and exposure times to, insulin. The microvasculature is recruited more quickly and at lower insulin concentrations than are needed to increase total blood flow, a finding consistent with a physiological role for insulin in muscle insulin delivery. Microvascular recruitment is impaired by obesity, diabetes and nitric oxide synthase inhibitors. Insulin TET is a third potential site for regulating insulin delivery. This is underscored by the consistent finding that steady-state insulin concentrations in plasma are approximately twice those in muscle interstitium. Recent in vivo and in vitro findings suggest that insulin traverses the vascular endothelium via a trans-cellular, receptor-mediated pathway, and emerging data indicate that insulin acts on the endothelium to facilitate its own TET. Thus, muscle insulin delivery, which is rate-limiting for its metabolic action, is itself regulated by insulin at multiple steps. These findings highlight the need to further understand the role of the vascular actions of insulin in metabolic regulation.

Type 2 diabetes is associated with insulin resistance, endothelial dysfunction and accelerated atherosclerotic diseases. Though underlying mechanisms remain to be unraveled, p38 mitogen-activated protein kinase (MAPK) appears to play important roles in their pathogenesis. As a member of the MAPK family, it regulates the activities of many transcription factors and proteins/enzymes and thus has a wide-spectrum of biological effects. Patients with insulin resistance and/or type 2 diabetes have high levels of plasma free fatty acids, inflammatory cytokines, and/or glucose, and over-activation of the cardiovascular renin-angiotensin system, all are capable of activating p38 MAPK. p38 MAPK plays a central role in hepatic glucose and lipid metabolism, leading to increased hepatic glucose production and decreased hepatic lipogenesis. The roles of p38 MAPK in insulin-mediated glucose uptake in skeletal muscle and adipose tissue remain controversial. p38 MAPK also mediates inflammatory processes and cell apoptosis. Recent evidence suggests that p38 MAPK may be the key node linking cardiovascular insulin resistance, endothelial dysfunction and the pathogenesis of atherosclerotic diseases through its influences on monocytes/macrophages, vascular endothelial cells, and vascular smooth muscle cells in type 2 diabetes. In addition, p38 MAPK also contributes significantly to cardiac injury during ischemia-reperfusion.