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Endothelial dysfunction is common in patients with GH deficiency who are at increased risk for premature cardiovascular death. GH regulates vascular tone and reactivity in humans.Our objective was to explore the mechanisms underlying the GH's acute vascular effects. DESIGN AND STUDY SETTING: There were 10 healthy, lean and young, volunteers studied after an overnight fast. GH was infused systemically for 6 h at 0.06 microg/kg.min. Biopsy of the vastus lateralis muscle was done in seven subjects before and after GH infusion. Human aortic endothelial cells (HAECs) were incubated with GH in vitro.GH infusion increased plasma GH to 32.9 +/- 1.5 ng/ml and forearm blood flow by 66% (P0.001). GH infusion did not significantly change plasma IGF-I concentrations, muscle IGF-I mRNA expression, and muscle Akt phosphorylation, suggesting a lack of IGF-I action in muscle. Because it was reported that GH exerts an acute vascular effect via a nitric oxide (NO)-dependent mechanism, we performed additional in vitro experiments using HAECs. HAECs express abundant GH receptors. Incubating HAECs with GH at 30 ng/ml for 3 or 6 h did not alter endothelial NO synthase (eNOS) protein content but time dependently increased the phosphorylation and activity of eNOS, thus demonstrating a direct effect of GH on endothelial cells.GH exerts an acute vascular effect independent of both systemic and local IGF-I production, and this effect is likely via direct action on GH receptors and eNOS in the vascular endothelium.

Myocardial ischemia-reperfusion injury contributes significantly to morbidity and mortality in patients with diabetes. Insulin decreases myocardial infarct size in animals and the rate of apoptosis in cultured cells. Ischemia-reperfusion activates p38 mitogen-activated protein kinase (MAPK), which regulates cellular apoptosis. To examine whether p38 MAPK affects insulin's cardioprotection against ischemia-reperfusion injury, we studied overnight-fasted adult male rats by use of an in vivo rat model of myocardial ischemia-reperfusion. A euglycemic clamp (3 mU·min−1·kg−1) was begun either 10 min before ischemia (InsulinBI), 5 min before reperfusion (InsulinBR), or 30 min after the onset of reperfusion (InsulinAR), and continued until the end of the study. Compared with saline control, insulin decreased the infarct size in both InsulinBI ( P < 0.001) and InsulinBR ( P < 0.02) rats but not in InsulinAR rats. The ischemic area showed markedly increased phosphorylation of p38 MAPK compared with the nonischemic area in saline animals. Acute activation of p38 MAPK with anisomycin (2 mg/kg iv 10 min before ischemia) had no effect on infarct size in saline rats. However, it completely abolished insulin's protective effect in InsulinBI and InsulinBR rats. Activation of p38 MAPK by anisomycin was associated with marked and persistent elevation in IRS-1 serine phosphorylation. Treatment of animals with SB-239063, a potent and specific inhibitor of p38 MAPK, 10 min before reperfusion enabled insulin-mediated myocardial protection in InsulinAR rats. We conclude that insulin protects myocardium against ischemia-reperfusion injury when given prior to ischemia or reperfusion, and activation of p38 MAPK abolishes insulin's cardioprotective effect.

Epigallocatechin-3-gallate (EGCG), a main catechin of green tea, has been suggested to inhibit hepatic gluconeogenesis. However, the exact role and related mechanism have not been established. In this study, we examined the role of EGCG in hepatic gluconeogenesis at concentrations that are reachable by ingestion of pure EGCG or green tea, and are not toxic to hepatocytes. Our results show in isolated hepatocytes that EGCG at relatively low concentrations (

Plasma free fatty acids are elevated in patients with type 2 diabetes and contribute to the pathogenesis of insulin resistance and endothelial dysfunction. The p38 MAPK mediates stress, inflammation, and apoptosis. Whether free fatty acids induce apoptosis and/or activate nuclear factor-kappaB inflammatory pathway in human coronary artery endothelial cells (hCAECs) and, if so, whether this involves the p38 MAPK pathway is unknown. hCAECs (passages 4-6) were grown to 70% confluence and then incubated with palmitate at concentrations of 0-300 microm for 6-48 h. Palmitate at 100, 200, or 300 microm markedly increased apoptosis after 12 h of incubation. This apoptotic effect was time (P=0.008) and dose (P=0.006) dependent. Palmitate (100 microm for 24 h) induced a greater than 2-fold increase in apoptosis, which was accompanied with a 4-fold increase in p38 MAPK activity (P

Purpose – The purpose of this paper is to find out the anti‐smoking counselling frequency and its correlates in a sample of Chinese physicians.Design/methodology/approach – In this paper, 268 physicians in Baoding, a city near Beijing, filled out a questionnaire asking about their own smoking status, their anti‐smoking behaviors as well as their opinions on how to reduce cigarette smoking in China.Findings – The paper finds that 54 percent of the male and 8.4 percent of the female physicians were current cigarette smokers. When asked whether they had counselled their patients about cigarette smoking in the past year, 43.7 percent answered “always”; 38.1 percent “often”; 13.1 percent “sometimes”; 2.6 percent “occasionally”, and 2.6 percent said: “not much”. However, only 9.0 percent said that they were “very successful”. Physicians' anti‐smoking counselling practices were highly correlated with their own smoking status; whether they perceived their past anti‐smoking activities as successful; whether they t...

We have previously shown that skeletal muscle capillaries are rapidly recruited by physiological doses of insulin in both humans and animals. This facilitates glucose and insulin delivery to muscle, thus augmenting glucose uptake. In obese rats, both insulin-mediated microvascular recruitment and glucose uptake are diminished; however, this action of insulin has not been studied in obese humans. Here we used contrast ultrasound to measure microvascular blood volume (MBV) (an index of microvascular recruitment) in the forearm flexor muscles of lean and obese adults before and after a 120-min euglycemic-hyperinsulinemic (1 mU . min(-1) . kg(-1)) clamp. We also measured brachial artery flow, fasting lipid profile, and anthropomorphic variables. Fasting plasma glucose (5.4 +/- 0.1 vs. 5.1 +/- 0.1 mmol/l, P = 0.05), insulin (79 +/- 11 vs. 38 +/- 6 pmol/l, P = 0.003), and percent body fat (44 +/- 2 vs. 25 +/- 2%, P = 0.001) were higher in the obese than the lean adults. After 2 h of insulin infusion, whole-body glucose infusion rate was significantly lower in the obese versus lean group (19.3 +/- 3.2 and 37.4 +/- 2.6 mumol . min(-1) . kg(-1) respectively, P0.001). Compared with baseline, insulin increased MBV in the lean (18.7 +/- 3.3 to 25.0 +/- 4.1, P = 0.019) but not in the obese group (20.4 +/- 3.6 to 18.8 +/- 3.8, NS). Insulin increased brachial artery diameter and flow in the lean but not in the obese group. We observed a significant, negative correlation between DeltaMBV and BMI (R = -0.482, P = 0.027) in response to insulin. In conclusion, obesity eliminated the insulin-stimulated muscle microvascular recruitment and increased brachial artery blood flow seen in lean individuals.

For many decades, it has been recognized that insulin, growth hormone, glucocorticoids, insulin-like growth factor 1, thyroid hormones, and other hormones regulate body protein metabolism. It has been more recently recognized, but not understood, that humor factors present in states of acute and chronic inflammation could have a strong impact on protein turnover. Most recently, the role of amino acids, acting as signaling molecules, has become increasingly clarified. In aggregate, these factors (together with neuromuscular activity) determine the balance of body protein mass. We will review some of these data, particularly focusing on amino acids, insulin, and the growth hormone axis and their actions in muscle and how these relate to whole-body protein metabolism.

Amino acids are unique anabolic agents in that they nutritively signal to mRNA translation initiation and serve as substrates for protein synthesis in skeletal muscle. Glucocorticoid excess antagonizes the anabolic action of amino acids on protein synthesis in laboratory animals. To examine whether excessive glucocorticoids modulate mixed amino acid-signaled translation initiation in human skeletal muscle, we infused an amino acid mixture (10% Travasol) systemically to 16 young healthy male volunteers for 6 h in the absence ( n = 8) or presence ( n = 8) of glucocorticoid excess (dexamethasone 2 mg orally every 6 h for 3 days). Vastus lateralis muscles were biopsied before and after amino acid infusion, and the phosphorylation of eukaryotic initiation factor (eIF) 4E-binding protein 1 (4E-BP1), ribosomal protein S6 kinase (p70S6K), and eIF2α and the guanine nucleotide exchange activity of eIF2B were measured. Systemic infusion of mixed amino acids significantly stimulated the phosphorylation of 4E-BP1 ( P < 0.04) and p70S6K( P < 0.001) and the dephosphorylation of eIF2α ( P < 0.003) in the control group. Dexamethasone treatment did not alter the basal phosphorylation state of 4E-BP1, p70S6K, or eIF2α; however, it abrogated the stimulatory effect of amino acid infusion on the phosphorylation of 4E-BP1 ( P = 0.31) without affecting amino acid-induced phosphorylation of p70S6K( P = 0.002) or dephosphorylation of eIF2α ( P = 0.003). Neither amino acid nor dexamethasone treatment altered the guanine nucleotide exchange activity of eIF2B. We conclude that changes of amino acid concentrations within the physiological range stimulate mRNA translation by enhancing the binding of mRNA to the 43S preinitiation complex, and the activity of p70S6Kand glucocorticoid excess blocks the former action in vivo in human skeletal muscle.

Insulin stimulates muscle glucose disposal via both glycolysis and glycogen synthesis. Insulin activates glycogen synthase (GS) in skeletal muscle by phosphorylating PKB (or Akt), which in turn phosphorylates and inactivates glycogen synthase kinase 3 (GSK-3), with subsequent activation of GS. A rapamycin-sensitive pathway, most likely acting via ribosomal 70-kDa protein S6 kinase (p70S6K), has also been implicated in the regulation of GSK-3 and GS by insulin. Amino acids potently stimulate p70S6K, and recent studies on cultured muscle cells suggest that amino acids also inactivate GSK-3 and/or activate GS via activating p70S6K. To assess the physiological relevance of these findings to normal human physiology, we compared the effects of amino acids and insulin on whole body glucose disposal, p70S6K, and GSK-3 phosphorylation, and on the activity of GS in vivo in skeletal muscle of 24 healthy human volunteers. After an overnight fast, subjects received intravenously either a mixed amino acid solution (1.26 μmol·kg-1·min-1× 6 h, n = 9), a physiological dose of insulin (1 mU·kg-1·min-1euglycemic hyperinsulinemic clamp × 2 h, n = 6), or a pharmacological dose of insulin (20 mU·kg-1·min-1euglycemic hyperinsulinemic clamp × 2 h, n = 9). Whole body glucose disposal rates were assessed by calculating the steady-state glucose infusion rates, and vastus lateralis muscle was biopsied before and at the end of the infusion. Both amino acid infusion and physiological hyperinsulinemia enhanced p70S6Kphosphorylation without affecting GSK-3 phosphorylation, but only physiological hyperinsulinemia also increased whole body glucose disposal and GS activity. In contrast, a pharmacological dose of insulin significantly increased whole body glucose disposal, p70S6K, GSK-3 phosphorylation, and GS activity. We conclude that amino acids at physiological concentrations mediate p70S6Kbut, unlike insulin, do not regulate GSK-3 and GS phosphorylation/activity in human skeletal muscle.

In addition to functioning as the innermost barrier separating the blood from tissue interstitium, vascular endothelium actively regulates vessel functions by both secreting vasoactive factors and direct coupling to nearby smooth muscle. As arterial and arteriolar function varies depending on their size and location the role played by the endothelium differs accordingly. The conduit arteries mainly regulate arterial plasticity/compliance, the resistance arterioles blood pressure and total blood flow to tissues, the pre-capillary arterioles tissue perfusion and the capillaries exchanges of nutrients, oxygen and hormones between the plasma and tissue interstitium. Vascular endothelium has long been known to be insulin responsive. Endothelial cells express abundant insulin, insulin-like growth factor I (IGF-I) and the hybrid insulin/IGF-I receptors (1–3). At physiological concentrations, insulin binds and activates the insulin receptors exclusively. It exerts its biological actions mainly via two signaling pathways. One proceeds by activation of phosphatidylinositol 3-kinase (PI-3 kinase)/protein kinase B (PKB or Akt) pathway that leads to the phosphorylation of serine 1176 of the endothelial nitric oxide (NO) synthase (eNOS) to increase NO production (4; 5). NO is a potent vasodilator with important anti-atherosclerotic actions as well. Insulin also signals through the mitogen-activated protein kinase (MAPK) pathway to regulate cell proliferation and production of both the vasoconstrictor endothelin-1 and adhesion molecules (6–9). In the insulin sensitive state, insulin fine-tunes vascular functions via balancing its signals through these two signaling pathways to maintain endothelial health, arterial wall compliance, vascular tone and tissue perfusion. Diabetes causes significant morbidity and mortality to patients by accelerating atherosclerosis in large and medium arteries and injuring the microvasculature thus precipitating classical retinal, renal and neural complications. Mounting evidence has confirmed the central role of endothelial dysfunction, characterized by abnormal vascular reactivity, increased production of reactive oxygen species, decreased NO bioavailability, and altered barrier function, in the pathogenesis of both macro- and microvascular complications of diabetes. This is not surprising as diabetes is associated with a wide variety of metabolic/biochemical disturbances in many tissues and blood vessels play indispensible role in maintaining tissue function by delivering nutrients, oxygen and hormones and removing metabolic products. Thus, the endothelium is exposed to both environmental and endogenous stimuli such as nutrients, cytokines, chemokines, hypoxia and other factors. Endothelial dysfunction and endothelial insulin resistance co-exist in the state of insulin resistance including metabolic syndrome, obesity and diabetes. Almost all factors that cause metabolic insulin resistance also induce endothelial dysfunction and vascular insulin resistance. The term “vascular insulin resistance” can be misleading in that within endothelial cells resistance to insulin action is pathway selective (10–12). While insulin responses through the PI3-kinase/Akt/eNOS pathway are attenuated, its action via the MAPK pathway remains intact or even enhanced in the insulin resistant state. As a result, the net effect of insulin acting on the vasculature is increased production of adhesion molecules and ET-1 and decreased production/bioavailability of NO, tilting the balance towards pro-atherogenic and vasoconstrictive responses (11; 13–15). Markedly increased insulin concentrations which can accompany metabolic insulin resistance may contribute to this process by activating the IGF-I and/or insulin/IGF-I hybrid receptors. Combined, pathway selective insulin resistance and hyperinsulinema-driven MAPK signaling could handily explain why patients with diabetes have accelerated atherosclerosis and are prone to hypertension and tissue hypoxia (Figure). However, evidence supporting this selective insulin resistance mainly stemmed from in vitro cell culture studies and ex vivo studies using isolated blood vessels. Convincing in vivo evidence remains scant. Figure 1 The effects of insulin on the microvasculature have garnered much attention over the past decade. For insulin to exert its metabolic actions it has to be first delivered to tissue interstitium after it is secreted by the pancreatic β-cells. Vascular endothelium clearly plays a barrier role and actively with continuous endothelium like muscle, brain and adipose tissue. In the case of skeletal muscle, it is the muscle interstitial insulin concentrations, not the plasma insulin concentrations, that correlate closely with insulin’s metabolic action (16). Evidence from human, animal and cultured cell studies have repeatedly demonstrated that insulin itself actively regulates its own delivery to muscle insterstitium by dilating resistance vessels to increase total blood flow, relaxing pre-capillary arterioles to recruit microvasculature and increase endothelial exchange surface area (microvascular recruitment), and trans-endothelial transport of insulin from the plasma compartment to tissue interstitium (17; 18). When infused acutely, insulin increases muscle microvascular perfusion within 5–10 minutes and this action precedes and contributes (up to 40%) to insulin-stimulated glucose uptake in skeletal muscle (19; 20). This action is reduced in the presence of metabolic insulin resistance as seen in obese humans, healthy humans given lipid infusions to raise plasma free fatty acid levels as well as in animal models of insulin resistance (21–23). Overall, studies from the past two decades have convincingly shown that vascular endothelium is an insulin target and that vascular endothelial dysfunction and vascular insulin resistance play central roles in the pathogenesis of metabolic insulin resistance, organ damage/failure and cardiovascular complications of diabetes. These aggregate findings point to vascular endothelium as a very promising therapeutic target in the prevention and/or management of diabetes and insulin resistance. Reduced endothelial insulin resistance and improved endothelial function in the conduit arteries may reduce macrovascular atherosclerotic complications. In resistance arterioles it could improve blood pressure control. While in the microvasculature it could reduce/prevent microvascular complications and enhance tissue insulin action thus metabolic control. Currently available glycemic therapies, particularly exercise and insulin sensitization, have shown some salutary effects on endothelial function in patients with diabetes. However, only metformin has demonstrated a positive effect in reducing the clinical macrovascular endpoints in obese patients with T2DM (24). None of these therapeutic modalities target specifically the endothelium and the improved endothelial function associated with these therapies is likely secondary to improved glycemic control and perhaps some direct action on the endothelium. Several lines of evidence have shown that factors that in clinical studies improve insulin sensitivity and glycemic control, such as exercise, angiotensin II type 1 receptor blocker, and glucagon-like peptide 1, are able to increase microvascular recruitment and muscle delivery/action of insulin in experimental animals (25–27). Whether these effects remain in insulin resistant humans are under investigation. More studies are needed to better understand the mechanisms underlying endothelial insulin resistance and endothelial dysfunction in diabetes and other states of insulin resistance and their exact molecular and cellular roles in the pathogenesis of metabolic insulin resistance and diabetic vascular complications. Undoubtedly this will drive the development of endothelium targeted therapies for prevention of diabetes and the vascular injuries that accompany it and other insulin resistant states.

After confirming that adrenalectomy per se does not affect skeletal muscle protein synthesis rates, we examined whether endogenously produced glucocorticoids modulate the effect of physiological insulin concentrations on protein synthesis in overnight-fasted rats 4 days after either a bilateral adrenalectomy (ADX), ADX with dexamethasone treatment (ADX + DEX), or a sham operation (Sham; n = 6 each). Rats received a 3-h euglycemic insulin clamp (3 mU · min−1· kg−1). Rectus muscle protein synthesis was measured at the end of the clamp, and the phosphorylation states of protein kinase B (Akt), eukaryotic initiation factor 4E-binding protein 1 (4E-BP1), and ribosomal protein S6 kinase (p70S6K) were quantitated before and after the insulin clamp. The basal phosphorylation states of Akt, 4E-BP1, and p70S6Kwere similar between ADX and Sham rats. Insulin significantly enhanced the phosphorylation of Akt ( P < 0.03), 4E-BP1 ( P = 0.003), and p70S6K( P < 0.002) in ADX but not in Sham rats. Protein synthesis was significantly greater after insulin infusion in ADX than in Sham rats ( P = 0.01). Glucocorticoid replacement blunted the effect of insulin on Akt, 4E-BP1, and p70S6Kphosphorylation and protein synthesis. In conclusion, glucocorticoid deficiency enhances the insulin sensitivity of muscle protein synthesis, which is mediated by increased phosphorylation of translation initiation-regulatory proteins.

Adiponectin is an adipokine with anti-inflammatory and anti-diabetic properties. Hypoadiponectinaemia is closely associated with endothelial dysfunction and insulin resistance in obesity and diabetes. Insulin resistance is present in muscle microvasculature and this may contribute to decreased insulin delivery to, and action in, muscle. In this study we examined whether adiponectin ameliorates metabolic insulin resistance by affecting muscle microvascular recruitment. We demonstrated that a high-fat diet induces vascular adiponectin and insulin resistance but globular adiponectin administration can restore vascular insulin responses and improve insulin's metabolic action via an AMPK- and nitric oxide-dependent mechanism. This suggests that globular adiponectin might have a therapeutic potential for improving insulin resistance and preventing cardiovascular complications in patients with diabetes via modulation of microvascular insulin responses. Hypoadiponectinaemia is closely associated with endothelial dysfunction and insulin resistance, and microvasculature plays a critical role in the regulation of insulin action in muscle. Here we tested whether adiponectin replenishment could improve metabolic insulin sensitivity in male rats fed a high-fat diet (HFD) via the modulation of microvascular insulin responses. Male Sprague-Dawley rats were fed either a HFD or low-fat diet (LFD) for 4 weeks. Small resistance artery myograph changes in tension, muscle microvascular recruitment and metabolic response to insulin were determined. Compared with rats fed a LFD, HFD feeding abolished the vasodilatory actions of globular adiponectin (gAd) and insulin on pre-constricted distal saphenous arteries. Pretreatment with gAd improved insulin responses in arterioles isolated from HFD rats, which was blocked by AMP-activated protein kinase (AMPK) inhibition. Similarly, HFD abolished microvascular responses to either gAd or insulin and decreased insulin-stimulated glucose disposal by ∼60%. However, supplementing gAd fully rescued insulin's microvascular action and significantly improved the metabolic responses to insulin in HFD male rats and these actions were abolished by inhibition of either AMPK or nitric oxide production. We conclude that HFD induces vascular adiponectin and insulin resistance but gAd administration can restore vascular insulin responses and improve insulin's metabolic action via an AMPK- and nitric oxide-dependent mechanism in male rats.

The body's protein mass not only provides architectural support for cells but also serves vital roles in maintaining their function and survival. The whole body protein pool, as well as that of individual tissues, is determined by the balance between the processes of protein synthesis and degradation. These in turn are regulated by interactions among hormonal, nutritional, neural, inflammatory, and other influences. Prolonged changes in either the synthetic or degradative processes (or both) that cause protein wasting increase morbidity and mortality. The application of tracer kinetic methods, combined with measurements of the activity of components of the cellular signaling pathways involved in protein synthesis and degradation, affords new insights into the regulation of both protein synthesis and breakdown in vivo. These insights, including those from studies of insulin, insulin-like growth factor I, growth hormone, and amino acid-mediated regulation of muscle and whole body protein turnover, provide opportunities to develop and test therapeutic approaches with promise to minimize or prevent these adverse health consequences.

Background The role of serum 25-hydroxyvitamin D (25 (OH) D) in atherogenesis is unclear. We investigated whether the 25 (OH) D is independently associated with the carotid intima–media thickness (CIMT) and carotid plaques in normotensive and euglycemic postmenopausal women. Methods A total of 671 normotensive and euglycemic postmenopausal women (mean age, 58.8 years) were enrolled from the Changfeng Study. A standard interview, anthropometrics measurements and laboratory analyses were performed for each participant. Bilateral CIMTs were measured using ultrasonography, and the presence of carotid plaques was assessed. The serum 25 (OH) D was measured using electrochemiluminescence immunoassay. Results Serum 25 (OH) D was 43.6 ± 18.2 nmol/L in the postmenopausal women. Compared with subjects with 25 (OH) D in the first, second and third quartiles, subjects with 25 (OH) D in the fourth quartile had decreased CIMT and prevalence of carotid plaque (0.684 ± 0.009 mm vs 0.719 ± 0.009 mm, 0.708 ± 0.009 mm and 0.709 ± 0.009 mm; 10.8% vs 19.0%, 14.8% and 16.8%, respectively). After adjusting for conventional CVD risk factors, PTH, liver and renal function, postmenopausal women with 25 (OH) D in the fourth quartile still had lower CIMT than those in the first, second and third quartiles (p = 0.039) and the subjects in the fourth quartile had a 0.421-fold decreased risk of carotid plaques relative to those in the lowest quartile (95% confidence interval 0.209 to 0.848). Conclusions These results suggest serum 25 (OH) D is independently and inversely associated with carotid atherosclerosis in postmenopausal women with normal blood pressure and normal glucose tolerance.

Adiponectin exerts both vasodilatory and insulin-sensitizing actions and its levels are decreased in the insulin resistant humans and animals. The mechanisms underlying the adiponectin’s insulin-sensitizing effect have been extensively investigated but remain largely unclear. Muscle microvasculature critically regulates muscle insulin action by modulating insulin delivery to the microvessels nurturing the muscle cells and the trans-endothelial insulin transport. We have recently reported that adiponectin exerts its insulin-sensitizing effect via recruiting muscle microvasculature, expanding the endothelial surface area, and increasing insulin delivery to and thus action in muscle. The current review focuses on the microvascular connection between the adiponectin and insulin crosstalk.

Angiotensin-(1–7) [Ang-(1–7)], an endogenous ligand for the G protein–coupled receptor Mas , exerts both vasodilatory and insulin-sensitizing effects. In skeletal muscle, relaxation of precapillary arterioles recruits microvasculature and increases the endothelial surface area available for nutrient and hormone exchanges. To assess whether Ang-(1–7) recruits microvasculature and enhances insulin action in muscle, overnight-fasted adult rats received an intravenous infusion of Ang-(1–7) (0, 10, or 100 ng/kg per minute) for 150 minutes with or without a simultaneous infusion of the Mas inhibitor A-779 and a superimposition of a euglycemic insulin clamp (3 mU/kg per minute) from 30 to 150 minutes. Hind limb muscle microvascular blood volume, microvascular flow velocity, and microvascular blood flow were determined. Myographic changes in tension were measured on preconstricted distal saphenous artery. Ang-(1–7) dose-dependently relaxed the saphenous artery ( P P Mas inhibition. Systemic infusion of Ang-(1–7) rapidly increased muscle microvascular blood volume and microvascular blood flow ( P P P Mas recruits muscle microvasculature and enhances the metabolic action of insulin. These effects may contribute to the cardiovascular protective responses associated with Mas activation and explain the insulin-sensitizing action of Ang-(1–7).

Glucagon-like peptide 1 (GLP-1) acutely recruits muscle microvasculature, increases muscle delivery of insulin, and enhances muscle use of glucose, independent of its effect on insulin secretion. To examine whether GLP-1 modulates muscle microvascular and metabolic insulin responses in the setting of insulin resistance, we assessed muscle microvascular blood volume (MBV), flow velocity, and blood flow in control insulin-sensitive rats and rats made insulin-resistant acutely (systemic lipid infusion) or chronically (high-fat diet [HFD]) before and after a euglycemic-hyperinsulinemic clamp (3 mU/kg/min) with or without superimposed systemic GLP-1 infusion. Insulin significantly recruited muscle microvasculature and addition of GLP-1 further expanded muscle MBV and increased insulin-mediated glucose disposal. GLP-1 infusion potently recruited muscle microvasculature in the presence of either acute or chronic insulin resistance by increasing muscle MBV. This was associated with an increased muscle delivery of insulin and muscle interstitial oxygen saturation. Muscle insulin sensitivity was completely restored in the presence of systemic lipid infusion and significantly improved in rats fed an HFD. We conclude that GLP-1 infusion potently expands muscle microvascular surface area and improves insulin’s metabolic action in the insulin-resistant states. This may contribute to improved glycemic control seen in diabetic patients receiving incretin-based therapy.

Branched chain amino acids (BCAA) are particularly effective anabolic agents. Recent in vitro studies suggest that amino acids, particularly leucine, activate a signaling pathway that enhances messenger ribonucleic acid translation and protein synthesis. The physiological relevance of these findings to normal human physiology is uncertain. We examined the effects of BCAA on the phosphorylation of eukaryotic initiation factor 4E-binding protein 1 (eIF4E-BP1) and ribosomal protein S6 kinase (p70S6K) in skeletal muscle of seven healthy volunteers. We simultaneously examined whether BCAA affect urinary nitrogen excretion and forearm skeletal muscle protein turnover and whether the catabolic action of glucocorticoids could be mediated in part by inhibition of the action of BCAA on the protein synthetic apparatus.BCAA infusion decreased urinary nitrogen excretion (P < 0.02), whole body phenylalanine flux (P < 0.02), plasma phenylalanine concentration (P < 0.001), and improved forearm phenylalanine balance (P = 0.03). BCAA also increased the phosphorylation of both eIF4E-BP1 (P < 0.02) and p70S6K (P < 0.03), consistent with an action to activate the protein synthetic apparatus. Dexamethasone increased plasma phenylalanine concentration (P < 0.001), prevented the BCAA-induced anabolic shift in forearm protein balance, and inhibited their action on the phosphorylation of p70S6K. We conclude that in human skeletal muscle BCAA act directly as nutrient signals to activate messenger ribonucleic acid translation and potentiate protein synthesis. Glucocorticoids interfere with this action, and that may be part of the mechanism by which they promote net protein catabolism in muscle.

The ubiquitin-proteasome system is thought to play a major role in normal muscle protein turnover and to contribute to diabetes-induced protein wasting in skeletal muscle. However, its importance in cardiac muscle is not clear. We measured heart muscle mRNA for ubiquitin and for the C2 and C8 proteasomal subunits, the amount of free ubiquitin and the proteasome chymotrypsin-like proteolytic activity in control and diabetic rats. Results were compared to those in skeletal muscle (rectus). Heart ubiquitin, C2 and C8 subunit mRNA and proteolytic activity were significantly greater than in skeletal muscle (P

Muscle microvascular surface area determines substrate and hormonal exchanges between plasma and muscle interstitium. GLP-1 (glucagon-like peptide-1) regulates glucose-dependent insulin secretion and has numerous extrapancreatic effects, including a salutary vascular action. To examine whether GLP-1 recruits skeletal and cardiac muscle microvasculature in healthy humans, 26 overnight-fasted healthy adults received a systemic infusion of GLP-1 (1.2 pmol/kg of body mass per min) for 150 min. Skeletal and cardiac muscle MBV (microvascular blood volume), MFV (microvascular flow velocity) and MBF (microvascular blood flow) were determined at baseline and after 30 and 150 min. Brachial artery diameter and mean flow velocity were measured and total blood flow was calculated before and at the end of the GLP-1 infusion. GLP-1 infusion raised plasma GLP-1 concentrations to the postprandial levels and suppressed plasma glucagon concentrations with a transient increase in plasma insulin concentrations. Skeletal and cardiac muscle MBV and MBF increased significantly at both 30 and 150 min (P

Tetramethylpyrazine (TMP) is an active compound isolated from a Chinese herbal prescription that is widely used in traditional Chinese medicine for the treatment of inflammatory and cardiovascular diseases. We have previously reported that TMP acts as a potent antioxidant protecting endothelial cells against high glucose-induced damages. However, the molecular mechanism responsible for the antioxidant effect of TMP remains to be elucidated. In this study, we show that TMP increases nitric oxide production in endothelial cells and promotes endothelium-dependent relaxation in rate aortic rings. The antioxidant effect of TMP appears attributable to its ability to activate the mitochondrial biogenesis, as reflected in an up-regulation of complex III and amelioration of mitochondrial membrane potential. Furthermore, TMP is able to reverse high glucose-induced suppression of SIRT1 and the biogenesis-related factors, including PGC-1α, NRF1 and TFAM, suggesting a new molecular mechanism underlying the protective effect of TMP on the endothelium.

To develop standard in vitro chondrosarcoma models, we synthesized three hydrogels (i. e., PDMAAm, PNaAMPS and PMETAC) and investigated the influence of Young's modulus, swelling ratio and electric charges on the behavior of chondrosarcoma cells seeded on the hydrogels, including morphology, adhesion and aggregation. Results showed that the morphology of chondrosarcoma cells at 6h was dependent on the charges of hydrogels; cells present spindle-shaped and round-shaped morphology on negative charged and neutral hydrogel, respectively, while no cells spreaded on positive charged hydrogel. Chondrosarcoma cells formed aggregates on neutral PDMAAm after further culture. The hydrogels can be synthesized easily and has the characteristics of ease at use with defined components, which holds great potential for developing standard chondrosarcoma models in vitro.

PURPOSE:To examine the effects of exercise intensity on acute changes in endothelial function in lean and obese adults. METHODS:Sixteen lean (BMI 30, age 26 ± 6 yr) physically inactive adults were studied during 3 randomized admissions [control (C, no exercise), moderate-intensity exercise (M, @ lactate threshold (LT)) and high-intensity exercise (H, midway between LT and VO2peak) (30 min)]. Endothelial function was assessed by flow-mediated dilation (FMD) at baseline and 1, 2, and 4 h post-exercise. RESULTS:RM ANCOVA revealed significant main effects for group, time, and group x condition interaction (p

OBJECTIVES The purpose of this study was to assess microvascular perfusion immediately after eccentric exercise using contrast-enhanced sonography. METHODS An intravenous catheter was placed in the antecubital vein of the arm contralateral to the leg being tested for the delivery of microbubbles to 18 healthy volunteers (mean age ± SD, 22.2 ± 2.2 years; height, 166.0 ± 11.9 cm; weight, 69.4 ± 25.0 kg). Eccentric exercises were performed unilaterally in a randomized leg. Calf-lowering repetitions off a raised step were performed to the beat of a metronome over 3 seconds in the sequence of 50 repetitions, 5 minutes of rest, and 50 repetitions. Microvascular perfusion (blood volume, blood flow, and blood flow velocity) was measured before and immediately after exercise using replenishment kinetics. RESULTS Blood volume and flow both significantly increased after exercise (P < .001). Baseline measurements were 5.88 ± 1.33 dB and 2.34 ± 0.41 dB/s and increased to 12.20 ± 3.31 dB and 4.52 ± 1.05 dB/s, respectively. There was a significant decrease in blood flow velocity (P = .035) after exercise (0.38 ± 0.03 s(-1)) from baseline (0.41 ± 0.06 s(-1)). CONCLUSIONS Circulatory responses were altered after eccentric exercise, which may be due to the metabolic demand placed on the body. On the basis of this finding, eccentric exercise may be used as a model to assess the effect modalities have on the circulatory system after an elevated state of microvascular perfusion is reached.

Rationale: Adiponectin enhances insulin action and induces nitric oxide–dependent vasodilatation. Insulin delivery to muscle microcirculation and transendothelial transport are 2 discrete steps that limit insulin’s action. We have shown that expansion of muscle microvascular surface area increases muscle insulin delivery and action. Objective: To examine whether adiponectin modulates muscle microvascular recruitment thus insulin delivery and action in vivo. Methods and Results: Overnight fasted adult male rats were studied. We determined the effects of adiponectin on muscle microvascular recruitment, using contrast-enhanced ultrasound, on insulin-mediated microvascular recruitment and whole-body glucose disposal, using contrast-enhanced ultrasound and insulin clamp, and on muscle insulin clearance and uptake with 125 I-insulin. Globular adiponectin potently increased muscle microvascular blood volume without altering microvascular blood flow velocity, leading to a significantly increased microvascular blood flow. This was paralleled by a ≈30% to 40% increase in muscle insulin uptake and clearance, and ≈30% increase in insulin-stimulated whole-body glucose disposal. Inhibition of endothelial nitric oxide synthase abolished globular adiponectin-mediated muscle microvascular recruitment and insulin uptake. In cultured endothelial cells, globular adiponectin dose-dependently increased endothelial nitric oxide synthase phosphorylation but had no effect on endothelial cell internalization of insulin. Conclusions: Globular adiponectin increases muscle insulin uptake by recruiting muscle microvasculature, which contributes to its insulin-sensitizing action.

Context: Eccentric exercise increases local blood flow and volume as a result of increased metabolic demand. It is not known how eccentric exercise affects microvascular perfusion in the musculature of the opposite limb over this 48 hour period. Objective: To quantify microvascular perfusion immediately after eccentric exercise to the gastrocnemius in the opposite limb and over 48 hours following the exercise. Design: Descriptive laboratory study. Setting: Laboratory. Patients or Other Participants: Six healthy participants volunteered (1M, 5F; Age: 22.4 ± 2.1 years; Height: 165.2 ± 16.6 cm; Weight: 64.5 ± 25.1 Kg). Intervention(s): A unilateral, eccentric exercise was performed to a randomized leg. Each subject performed 100 calf-lowering repetitions in the sequence of 50 repetitions, 5 min rest and 50 repetitions. Main outcome measure: Micro vascular perfusion measurements (blood volume (dB), blood flow (dB/sec), and blood flow velocity (1/sec)) of the contralateral gastrocnemius were taken using contrast-enhanced ultrasound (CEU) at baseline, immediately after exercise, and 48 hours after exercise. Pain using a visual analog scale was also recorded baseline, 24, and 48 hours after exercise to determine the onset of delayed onset muscle soreness (DOMS). Results: There was a significant increase in blood volume immediately after exercise (9.77 ± 3.19 dB) from baseline (6.18 ± 2.05 dB) (p=.023). There was a significant increase in blood flow immediately after exercise (3.53 ± 0.86 dB/sec) from baseline (2.40 ± 0.69 dB/sec) (p=.010). There was no change in blood flow velocity (p=0.487). Blood flow (p=0.003) and volume (p=0.002) remained significantly higher at 48 hours from baseline, with no change in blood flow velocity (p=0.316). Pain significantly increased. Conclusion: Micro vascular perfusion increased immediately after exercise in the contralateral gastrocnemius. This increase was maintained following a single bout of eccentric exercise over a 48 hour period in the presence of DOMS.

Background In the China National Diabetes and Metabolic Disorders Study, age-standardised prevalence of total diabetes was 9·7%, accounting for 92·4 million adults, in China in 2010. Using clinical data and serum samples from this study, we aimed to investigate the prevalence of several organ-specific autoantibodies in patients with phenotypic type 2 diabetes. Methods This study included a nationally representative sample of 46 239 adults aged 20 years or older from 14 provinces and municipalities. After an overnight fast, participants had an oral glucose tolerance test. Previously diagnosed diabetes was self-reported. We randomly selected 4671 patients with diabetes and 1002 individuals with normal glucose tolerance as controls. Participants were screened centrally for glutamic acid decarboxylase autoantibodies (GAD-Ab), protein tyrosine phosphatase-like protein autoantibodies (IA2-Ab), and zinc transporter isoform 8 autoantibodies (ZnT8-Ab) using validated methods of the Islets Autoantibody Standardization Program 2012. We then assayed for thyroid peroxidase autoantibodies (TPO-Ab), tissue transglutaminase autoantibodies (tTG-Ab), and 21-hydroxylase autoantibodies (21-OH-Ab) in patients with islet autoantibody-positive diabetes (n=175), in randomly selected age-matched and sex-matched patients with islet autoantibody-negative diabetes (n=3052 for TPO-Ab, n=525 for tTG-Ab, and n=525 for 21-OH-Ab), and in individuals with normal glucose tolerance (n=954 for TPO-Ab, n=200 for tTG-Ab, and n=200 for 21-OH-Ab). We used multiple logistic regression analysis to determine the risk factor of each autoantibody. Ethics approval was granted by the Second Xiangya Hospital of Central South University, and all participants provided written informed consent. Findings After adjustment for age and sex using results from the national population census, the standardised prevalence of autoimmune diabetes was 6·0% in all patients with diabetes, which corresponded to about 6 million adults in China. In patients with diabetes, the adjusted antibody positivity was 3·6% for GAD-Ab, 1·2% for IA2-Ab, and 1·5% for ZnT8-Ab. In those with autoimmune diabetes, the adjusted antibody positivity was 16·3% for TPO-Ab, 2·1% for tTG-Ab, and 1·8% for 21-OH-Ab. In patients with islet autoantibody-negative diabetes, the adjusted positivity was 10·2% for TPO-Ab, 0·3% for tTG-Ab, and 0·5% for 21-OH-Ab. In Chinese adults with autoimmune diabetes, those positive for GAD-Ab had a high risk for TPO-Ab positivity (odds ratio 2·39, 95% CI 1·35–4·24; p=0·0031) and tTG-Ab positivity (6·983, 1·24–39·22; p=0·027), and those positive for IA2-Ab had a high risk for tTG-Ab positivity (19·05, 3·14–115·61; p=0·0010). Patients positive for TPO-Ab were at high risk of being positive for 21-OHAb (7·48, 1·44–38·74; p=0·016) and vice versa (7·21, 1·35–38·45; p=0·021). Of note, women had a high risk for TPO-Ab positivity compared with men (3·83, 2·20–6·68; p Interpretation Patients positive for islet autoantibodies have a high risk for other organ-specific autoimmune diseases. Screening of TPO-Ab and tTG-Ab in Chinese individuals with autoimmune diabetes should be considered a priority. Funding National Key Technology R&D Program (2012BAI02B04), the Grant of National Clinical Research Center for Metabolic Diseases (2013BAI09B12), the Program for Changjiang Scholars and Innovative Research Team in University (IRT1195), and the Key Project of Chinese Ministry of Education (113050A).

Glucagon-like peptide-1 (GLP-1) causes vasodilation and increases muscle glucose uptake independent of insulin. Recently, we have shown that GLP-1 recruits muscle microvasculature and increases muscle glucose use via a nitric oxide (NO)-dependent mechanism. Protein kinase A (PKA) is a major signaling intermediate downstream of GLP-1 receptors. To examine whether PKA mediates GLP-1's microvascular action in muscle, GLP-1 was infused to overnight-fasted male rats for 120 min in the presence or absence of H89, a PKA inhibitor. Hindleg muscle microvascular recruitment and glucose use were determined. GLP-1 infusion acutely increased muscle microvascular blood volume within 30 min without altering microvascular blood flow velocity or blood pressure. This effect persisted throughout the 120-min infusion period, leading to a significant increase in muscle microvascular blood flow. These changes were paralleled with an approximately twofold increase in plasma NO levels and hindleg glucose extraction. Systemic infusion of H89 completely blocked GLP-1-mediated muscle microvascular recruitment and increases in NO production and muscle glucose extraction. In cultured endothelial cells, GLP-1 acutely increased PKA activity and stimulated endothelial NO synthase phosphorylation at Ser1177and NO production. PKA inhibition abolished these effects. In ex vivo studies, perfusion of the distal saphenous artery with GLP-1 induced significant vasorelaxation that was also abolished by pretreatment of the vessels with PKA inhibitor H89. We conclude that GLP-1 recruits muscle microvasculature by expanding microvascular volume and increases glucose extraction in muscle via a PKA/NO-dependent pathway in the vascular endothelium. This may contribute to postprandial glycemic control and complication prevention in diabetes.

Resveratrol (RSV) has anti-inflammatory and anti-oxidant actions which may contribute to its cardiovascular protective effects. We examined whether RSV has any beneficial effects on pancreatic islets in db/db mice, an animal model of type 2 diabetes. The db/db and db/dm mice (non-diabetic control) were treated with (db-RSV) or without RSV (db-control) (20 mg/kg daily) for 12 weeks. After performing an intraperitoneal glucose tolerance test and insulin tolerance test, mice were sacrificed, the pancreas was weighed, pancreatic beta-cell mass was quantified by point count method, and the amount of islet fibrosis was determined. 8-Hydroxydeoxyguanosine (8-OHdG), an oxidative stress marker, was determined in 24 h urine and pancreatic islets. RSV treatment significantly improved glucose tolerance at 2 hrs in db/db mice (P = 0.036), but not in db/dm mice (P = 0.623). This was associated with a significant increase in both pancreas weight (P = 0.011) and beta-cell mass (P = 0.016). Islet fibrosis was much less in RSV-treated mice (P = 0.048). RSV treatment also decreased urinary 8-OHdG levels (P = 0.03) and the percentage of islet nuclei that were positive for 8-OHdG immunostaining (P = 0.019). We conclude that RSV treatment improves glucose tolerance, attenuates beta-cell loss, and reduces oxidative stress in type 2 diabetes. These findings suggest that RSV may have a therapeutic implication in the prevention and management of diabetes.

Effective mentorship is considered a prerequisite for success during medical training and an ensuing professional career in academic medicine. The Endocrine Society established sessions on mentorship at the Trainee Day during several annual meetings. These requests motivated a group of endocrinologists at the University of Virginia to assess prior literature on mentorship and collect opinions on the importance of the various characteristics of mentorship from endocrinologists, general faculty, and trainees. This information served as the basis for in-depth reflection and discussions on mentorship.The goal was to identify and prioritize the quintessential elements involved in mentorship and to reach practical conclusions that would be beneficial to academic endocrinologists.A multigenerational mentorship tree emphasizes that successful mentors can influence generations of mentees and that this represents a multiplier effect. The authors propose that trainees who are informed about the most important characteristics of an effective mentor can make better choices of a mentor. On the other hand, mentors can best define expectations when mentees know what to expect from a mentor, based on key characteristics.Similarities and differences in expectation about mentorship can be leveraged for better communication between mentor and mentee and for the development of stage-appropriate educational curricula on academic mentorship.

Rationale: Insulin delivery and transendothelial insulin transport are two discrete steps that limit muscle insulin action. Angiotensin II type 1 receptor (AT 1 R) blockade recruits microvasculature and increases glucose use in muscle. Increased muscle microvascular perfusion is associated with increased muscle delivery and action of insulin. Objective: To examine the effect of acute AT 1 R blockade on muscle insulin uptake and action in rats. Methods and Results: 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 using 125 I-insulin as tracer. Systemic lipid infusion was used to induce insulin resistance. Losartan significantly increased muscle insulin uptake (∼60%, p Conclusion: AT 1 R 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 AT 1 R blockers.

We addressed the link between excessive exposure to insulin and mitochondrion-derived oxidative stress in this study and found that prolonged exposure to insulin increased mitochondrial cholesterol in cultured hepatocytes and in mice and stimulated production of reactive oxygen species (ROS) and decreased the reduced glutathione to glutathione disulfide ratio in cultured hepatocytes. Exposure of isolated hepatic mitochondria to cholesterol alone promoted ROS emission. The oxidative stress induced by the prolonged exposure to insulin was prevented by inhibition of cholesterol synthesis with simvastatin. We further found that prolonged exposure to insulin decreased mitochondrial membrane potential and the increased ROS production came from mitochondrial respiration complex I. Finally, we observed that prolonged exposure to insulin decreased mitochondrial membrane fluidity in a cholesterol synthesis-dependent manner. Together our results demonstrate that excess exposure to insulin causes mitochondrion-derived oxidative stress through cholesterol synthesis in hepatocytes.

Glucagon-like peptide 1 (GLP-1) increases tissue glucose uptake and causes vasodilation independent of insulin. We examined the effect of GLP-1 on muscle microvasculature and glucose uptake. After confirming that GLP-1 potently stimulates nitric oxide (NO) synthase (NOS) phosphorylation in endothelial cells, overnight-fasted adult male rats received continuous GLP-1 infusion (30 pmol/kg/min) for 2 h plus or minus NOS inhibition. Muscle microvascular blood volume (MBV), microvascular blood flow velocity (MFV), and microvascular blood flow (MBF) were determined. Additional rats received GLP-1 or saline for 30 min and muscle insulin clearance/uptake was determined. GLP-1 infusion acutely increased muscle MBV (P < 0.04) within 30 min without altering MFV or femoral blood flow. This effect persisted throughout the 120-min infusion period, leading to a greater than twofold increase in muscle MBF (P < 0.02). These changes were paralleled with increases in plasma NO levels, muscle interstitial oxygen saturation, hind leg glucose extraction, and muscle insulin clearance/uptake. NOS inhibition blocked GLP-1–mediated increases in muscle MBV, glucose disposal, NO production, and muscle insulin clearance/uptake. In conclusion, GLP-1 acutely recruits microvasculature and increases basal glucose uptake in muscle via a NO-dependent mechanism. Thus, GLP-1 may afford potential to improve muscle insulin action by expanding microvascular endothelial surface area.

Insulin, at physiological concentrations, regulates the volume of microvasculature perfused within skeletal and cardiac muscle. It can also, by relaxing the larger resistance vessels, increase total muscle blood flow. Both of these effects require endothelial cell nitric oxide generation and smooth muscle cell relaxation, and each could increase delivery of insulin and nutrients to muscle. The capillary microvasculature possesses the greatest endothelial surface area of the body. Yet, whether insulin acts on the capillary endothelial cell is not known. Here, we review insulin's actions at each of three levels of the arterial vasculature as well as recent data suggesting that insulin can regulate a vesicular transport system within the endothelial cell. This latter action, if it occurs at the capillary level, could enhance insulin delivery to muscle interstitium and thereby complement insulin's actions on arteriolar endothelium to increase insulin delivery. We also review work that suggests that this action of insulin on vesicle transport depends on endothelial cell nitric oxide generation and that insulin's ability to regulate this vesicular transport system is impaired by inflammatory cytokines that provoke insulin resistance.

OBJECTIVE Insulin recruits muscle microvasculature, thereby increasing endothelial exchange surface area. Free fatty acids (FFAs) cause insulin resistance by activating inhibitor of κB kinase β. Elevating plasma FFAs impairs insulin’s microvascular and metabolic actions in vivo. Whether salsalate, an anti-inflammatory agent, prevents FFA-induced microvascular and/or metabolic insulin resistance in humans is unknown. RESEARCH DESIGN AND METHODS Eleven healthy, young adults were studied three times in random order. After an overnight fast, on two occasions each subject received a 5-h systemic infusion of Intralipid ± salsalate pretreatment (50 mg/kg/day for 4 days). On the third occasion, saline replaced Intralipid. A 1 mU/kg/min euglycemic insulin clamp was superimposed over the last 2-h of each study. Skeletal and cardiac muscle microvascular blood volume (MBV), microvascular flow velocity (MFV), and microvascular blood flow (MBF) were determined before and after insulin infusion. Whole body glucose disposal rates were calculated from glucose infusion rates. RESULTS Insulin significantly increased skeletal and cardiac muscle MBV and MBF without affecting MFV. Lipid infusion abolished insulin-mediated microvascular recruitment in both skeletal and cardiac muscle and lowered insulin-stimulated whole body glucose disposal (P < 0.001). Salsalate treatment rescued insulin’s actions to recruit muscle microvasculature and improved insulin-stimulated whole body glucose disposal in the presence of high plasma FFAs. CONCLUSIONS High plasma concentrations of FFAs cause both microvascular and metabolic insulin resistance, which can be prevented or attenuated by salsalate treatment. Our data suggest that treatments aimed at inhibition of inflammatory response might help alleviate vascular insulin resistance and improve metabolic control in patients with diabetes.

The primary player that induces insulin resistance has not been established. Here, we studied whether or not fat can cause insulin resistance in the presence of insulin deficiency. Our results showed that high-fat diet (HFD) induced insulin resistance in C57BL/6 (B6) mice. The HFD-induced insulin resistance was prevented largely by the streptozotocin (STZ)-induced moderate insulin deficiency. The STZ-induced insulin deficiency prevented the HFD-induced ectopic fat accumulation and oxidative stress in liver and gastrocnemius. The STZ-induced insulin deficiency prevented the HFD- or insulin-induced increase in hepatic expression of long-chain acyl-CoA synthetases (ACSL), which are necessary for fatty acid activation. HFD increased mitochondrial contents of long-chain acyl-CoAs, whereas it decreased mitochondrial ADP/ATP ratio, and these HFD-induced changes were prevented by the STZ-induced insulin deficiency. In cultured hepatocytes, we observed that expressions of ACSL1 and -5 were stimulated by insulin signaling. Results in cultured cells also showed that blunting insulin signaling by the PI3K inhibitor LY-294002 prevented fat accumulation, oxidative stress, and insulin resistance induced by the prolonged exposure to either insulin or oleate plus sera that normally contain insulin. Finally, knockdown of the insulin receptor prevented the oxidative stress and insulin resistance induced by the prolonged exposure to insulin or oleate plus sera. Together, our results show that insulin and insulin signaling are required for fat induction of insulin resistance in mice and cultured mouse hepatocytes.

The role of the IRE1α-X-box-binding protein 1 (XBP1) pathway in the insulin-mediated hepatic lipogenic program and associated mechanisms were investigated in this study. We observed that phosphorylation of IRE1α (an upstream activator of XBP1) and splicing (activation) of XBP1 were elevated in the liver of the C57BL/6 mice with insulin resistance/hyperinsulinemia induced by high-fat diet. Treatment of nonobese diabetic mice with insulin activated hepatic XBP1. In cultured primary mouse hepatocytes, prolonged exposure to insulin induced IRE1α phosphorylation and XBP1 splicing significantly in the presence of insulin resistance. Overexpression of the activated XBP1 elevated the promoter activities of the sterol regulatory element-binding protein (SREBP)-1c and fatty acid synthase (FAS) genes. Knockdown of either the IRE1α or XBP1 gene by small interfering RNA prevented the insulin-stimulated promoter activities of both SREBP-1 and FAS genes. In investigating the associated mechanisms, we found a direct interaction between XBP1 and SREBP-1 promoter detected by the chromatin immunoprecipitation assays. Furthermore, the XBP1-mediated stimulation of the FAS promoter was eliminated by knocking down the SREBP-1c gene (Srebf1). Finally, we observed that insulin activation of the IRE1α-XBP1 pathway was prevented by inhibition of mammalian target of rapamycin-dependent protein synthesis. In conclusion, our results show that the IRE1α-XBP1-mediated unfolded protein response pathway is an integrated part of the insulin-induced hepatic lipogenic program and functions at an increased basal level in the presence of insulin resistance and hyperinsulinemia. Besides, the insulin-mediated protein synthesis is tightly connected with the insulin-mediated lipogenic program.

OBJECTIVE - To determine the relationship between selected cytokines and diabetes in Chinese subjects. RESEARCH DESIGN AND METHODS - Adult patients with recent-onset type 1 diabetes (n = 53), latent autoimmune diabetes in adults (LADA) (n = 250), and type 2 diabetes (n= 285) from multiple centers were compared with normal subjects (n = 196). We centrally tested serum GAD antibodies (GADAs), interleukin-6 (IL-6), lipocalin 2 (LCN2), high-sensitivity C-reactive protein (hs-CRP), and adiponectin. RESULTS - After adjustment for age, sex, and BMI, all diabetes types had increased IL-6 and LCN2 (P < 0.01), and all four cytokines were increased in LADA (P < 0.01). In type 1 diabetes, adiponectin but not hs-CRP was increased (P < 0.01), whereas in type 2 diabetes, hs-CRP but not adiponectin was increased (P < 0.01). Adiponectin was correlated positively with GADA titer and negatively with hs-CRP (P < 0.01 for both). CONCLUSIONS - In China, inflammatory markers are increased in all three major types of diabetes, but probably for different reasons, even in autoimmune diabetes. © 2011 by the American Diabetes Association., link_to_OA_fulltext

It has previously been known that transcription of the PGC-1α gene can be either inhibited or stimulated by p38 MAP kinase (p38 MAPK). To determine whether p38 MAPK plays an inhibitory or stimulatory role in PGC-1α gene transcription, we further investigated the role of p38 MAPK in this study. Our results showed that the basal level of p38 MAPK phosphorylation was increased in gastrocnemius of mice under HFD and that p38 MAPK stimulated PGC-1α gene transcription in C2C12 myotubes. Our results also provided new mechanisms in myotubes that the p38 MAPK-induced PGC-1α gene transcription was mediated by CREB. In exploring the role of the Akt-dependent insulin signaling on PGC-1α gene transcription, we found that the basal Akt-dependent signaling was increased in gastrocnemius of mice under HFD. The p38 MAPK-induced PGC-1α gene transcription was prevented by insulin. Insulin suppression of PGC-1α gene transcription was neutralized by overexpression of the constitutively nuclear form of FoxO1. Finally, we located three insulin response elements (IREs) in the PGC-1α promoter, and mutations of these IREs abolish or blunt activity of the PGC-1α promoter. Together, our results show that transcription of the PGC-1α gene is balanced by different intracellular signaling pathways.

Insulin recruits microvasculature in both cardiac and skeletal muscle, which increases the endothelial exchange surface area. Plasma concentrations of free fatty acids (FFAs) are elevated in patients with diabetes, which impairs insulin-mediated skeletal muscle microvascular recruitment.The objective of the study was to examine whether elevated FFAs likewise cause insulin resistance in cardiac muscle microvasculature.The study was conducted at the General Clinical Research Center at the University of Virginia.Twenty-two healthy, young adults were studied twice in random order after an overnight fast. Each subject received a 5-h systemic infusion of either saline or Intralipid/heparin with a 1 mU/min · kg euglycemic insulin clamp superimposed for the last 2 h. Cardiac and forearm skeletal muscle microvascular blood volume (MBV) and flow velocity were measured and microvascular blood flow (MBF) calculated before and at the end of the insulin infusion.Insulin significantly increased MBV and MBF in both cardiac (P0.0001 for both) and skeletal (P = 0.008 and0.03, respectively) muscle. Microvascular flow velocity increased slightly but significantly in the skeletal (P = 0.04) but not in cardiac muscle. Lipid infusion lowered insulin-stimulated whole-body glucose disposal and abolished insulin-mediated increases in MBV and MBF in both cardiac and skeletal muscle. Whole-body insulin sensitivity predicted skeletal but not cardiac muscle microvascular responses to insulin. Insulin even decreased skeletal muscle MBV during lipid infusion in subjects who were moderately sensitive to insulin metabolically.In conclusion, high plasma concentrations of FFAs cause insulin resistance in cardiac as well as skeletal muscle microvasculature in healthy humans. This may contribute to the association of cardiac complications with metabolic insulin resistance in diabetes.

Since most of the current studies of thiazolidinediones (TZDs) are only focused on improving glycemic control, increasing insulin sensitivity, and regulating inflammatory states in Type 2 Diabetes, it is still controversial whether TZDs have direct, protective effects on pancreatic β-cells in autoimmune diabetes. Here, we show the protective effects of TZDs on mouse pancreatic β-cell line cells (NIT-1) impaired by exposure to inflammatory cytokines (IL-1β and IFN-γ) and explore the potential mechanisms for this. The apoptosis rate and caspase-3 activity were remarkably increased, and insulin secretion response to glucose was impaired severely by exposure to IL-1β/IFN-γ for 48 h compared to control cells, whereas apoptosis rate and caspase-3 activity were significantly decreased in cells with treatment of rosiglitazone (RGZ) or pioglitazone (PIG), and the capacity for insulin secretion response to glucose was recovered. TZDs protect pancreatic β-cells from cytokine-induced cytotoxicity through PPARγ activation. The protective effects of the TZDs on NIT-1 cells disappeared when PPARγ was blocked with PPARγ-siRNA interference or treatment with GW9662, the PPARγ antagonist. Additionally, the enhancement of PPARγ expression by treatment with TZDs inhibited the expression of caspase 3 in IL-1β/IFN-γ-induced NIT-cells. Also, the inhibition of caspase 3 expression by TZDs was blocked by co-treatment with GW9662 or infection with PPARγ-siRNA. Taken together, our data suggest that TZDs might serve to protect pancreatic β-cells directly from cytokine-induced cytotoxicity through a PPARγ-dependent pathway, and caspase-3 may play an important role in the mechanisms involved.

Background Fulminant type 1 diabetes mellitus (T1DM) is characterized by abrupt onset of hyperglycemia and rapid progression to ketoacidosis. This study aimed at examining the clinical and autoimmunity features of fulminant T1DM in Chinese. Methods A total of 24 patients with fulminant T1DM and 48 classical autoimmune T1DM patients with acute onset of ketoacidosis were recruited. Anthropometric and biochemical parameters were tested. Serum antibodies against glutamic acid decarboxylase 65, tyrosine phosphatase-2 and zinc transporter 8 were measured, and human leukocyte antigen-DQ haplotypes were determined. Peripheral glutamic acid decarboxylase 65-specific T-cell responses in some subjects were determined. Results Compared with autoimmune T1DM patients, patients with fulminant T1DM displayed more flu-like and gastrointestinal symptoms, and had significantly higher concentrations of plasma glucose, more severe ketoacidosis, very low levels of pancreatic β-cell reserve, but only slightly increased haemoglobin A1c levels. In some patients, the disease onset was associated with drug-related hypersensitivity, pregnancy, or positive serum IgM against viruses. Forty percent (8/20) had low titres of autoantibodies against at least one of the islet autoantigens tested. Three out of six patients had positive glutamic acid decarboxylase-reactive Th1 responses. The frequency of human leukocyte antigen -DQA1*0102-DQB1*0601 haplotype was significantly higher in patients with fulminant T1DM. Conclusions Fulminant T1DM is a distinct entity with unique clinical characteristics and may be mediated by multiple factors, including viral infection, pregnancy, and drug sensitivity syndrome, among others, in the presence of humoral and/or cellular autoimmunity and susceptible genetic background. Copyright © 2010 John Wiley & Sons, Ltd.

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.

A majority of subjects with insulin resistance and hyperinsulinemia can maintain their blood glucose levels normal for the whole life presumably through protein kinase B (Akt)-dependent insulin signaling. In this study, we found that the basal Akt phosphorylation level was increased in liver and gastrocnemius of mice under the high-fat diet (HFD). Levels of mitochondrial DNA and expression of some mitochondrion-associated genes were decreased by the HFD primarily in liver. Triglyceride content was increased in both liver and gastrocnemius by the HFD. Oxidative stress was induced by the HFD in both liver and gastrocnemius. Insulin sensitivity was decreased by the HFD. All of these changes were largely or completely reversed by treatment of animals with the phosphatidylinositol 3-kinase inhibitor LY-294002 during the time when animals usually do not eat. Consequently, the overall insulin sensitivity was increased by treatment with LY-294002. Together, our results indicate that increased basal Akt-dependent insulin signaling suppresses mitochondrial production, increases ectopic fat accumulation, induces oxidative stress, and desensitizes insulin signaling in subjects with insulin resistance and hyperinsulinemia.