Insulin-stimulated Whole-body Glucose Disposal Research Articles

Triterpenoid CDDO-EA inhibits lipopolysaccharide-induced inflammatory responses in skeletal muscle cells through suppression of NF-κB.

Chronic inflammation is a major contributor to the development of obesity-induced insulin resistance, which then can lead to the development of type 2 diabetes (T2D). Skeletal muscle plays a pivotal role in insulin-stimulated whole-body glucose disposal. Therefore, dysregulation of glucose metabolism by inflammation in skeletal muscle can adversely affect skeletal muscle insulin sensitivity and contribute to the pathogenesis of T2D. The mechanism underlying insulin resistance is not well known; however, macrophages are important initiators in the development of the chronic inflammatory state leading to insulin resistance. Skeletal muscle consists of resident macrophages which can be activated by lipopolysaccharide (LPS). These activated macrophages affect myocytes via a paracrine action of pro-inflammatory mediators resulting in secretion of myokines that contribute to inflammation and ultimately skeletal muscle insulin resistance. Therefore, knowing that synthetic triterpenoid 2-cyano-3,12-dioxooleana-1,9(11)-dien-28-oic acids (CDDOs) can attenuate macrophage pro-inflammatory responses in chronic disorders, such as cancer and obesity, and that macrophage pro-inflammatory responses can modulate skeletal muscle inflammation, we first examined whether CDDO-ethyl amide (CDDO-EA) inhibited chemokine and cytokine production in macrophages since this had not been reported for CDDO-EA. CDDO-EA blocked LPS-induced tumor necrosis factor-alpha (TNF-α), monocyte chemotactic protein-1 (MCP-1), interleukine-1beta (IL-1β), and interleukine-6 (IL-6) production in RAW 264.7 mouse and THP-1 human macrophages. Although many studies show that CDDOs have anti-inflammatory properties in several tissues and cells, little is known about the anti-inflammatory effects of CDDOs on skeletal muscle. We hypothesized that CDDO-EA protects skeletal muscle from LPS-induced inflammation by blocking nuclear factor kappa B (NF-κB) signaling. Our studies demonstrate that CDDO-EA prevented LPS-induced TNF-α and MCP-1 gene expression by inhibiting the NF-κB signaling pathway in L6-GLUT4myc rat myotubes. Our findings suggest that CDDO-EA suppresses LPS-induced inflammation in macrophages and myocytes and that CDDO-EA is a promising compound as a therapeutic agent for protecting skeletal muscle from inflammation.

Improving skeletal muscle insulin sensitivity via beta2 -agonist administration: a promising strategy to counteract metabolic disease and muscle loss.

Improving skeletal muscle insulin sensitivity via beta2 -agonist administration: a promising strategy to counteract metabolic disease and muscle loss.

Muscle hypertrophic effect of inhaled beta2 -agonist is associated with augmented insulin-stimulated whole-body glucose disposal in young men.

Rodent studies highlight enhancement of glucose tolerance and insulin sensitivity as potential clinically relevant effects of chronic beta2‐agonist treatment. However, the doses administered to rodents are not comparable with the therapeutic doses used for humans. Thus, we investigated the physiological effects of prolonged beta2‐agonist treatment at inhaled doses resembling those used in respiratory diseases on insulin‐stimulated whole‐body glucose disposal and putative mechanisms in skeletal muscle and adipose tissue of healthy men. Utilizing a randomized placebo‐controlled parallel‐group design, we assigned 21 healthy men to 4 weeks daily inhalation of terbutaline (TER; 4 mg × day−1, n = 13) or placebo (PLA, n = 8). Before and after treatments, we assessed subjects’ whole‐body insulin‐stimulated glucose disposal and body composition, and collected vastus lateralis muscle and abdominal adipose tissue biopsies. Glucose infusion rate increased by 27% (95% CI: 80 to 238 mg × min−1, P = 0.001) in TER, whereas no significant changes occurred in PLA (95% CI: −37 to 195 mg × min−1, P = 0.154). GLUT4 content in muscle or adipose tissue did not change, nor did hexokinase II content or markers of mitochondrial volume in muscle. Change in lean mass was associated with change in glucose infusion rate in TER (r = 0.59, P = 0.03). Beta2‐agonist treatment in close‐to‐therapeutic doses may augment whole‐body insulin‐stimulated glucose disposal in healthy young men and part of the change is likely to be explained by muscle hypertrophy. These findings highlight the therapeutic potential of beta2‐agonists for improving insulin sensitivity.Key points While studies in rodents have highlighted beta2‐agonists as a means to augment insulin sensitivity, these studies utilized beta2‐agonists at doses inapplicable to humans.Herein we show that a 4‐week treatment period with daily therapeutic inhalation of beta2‐agonist increases insulin‐stimulated whole‐body glucose disposal in young healthy lean men.This effect was associated with an increase of lean mass but not with changes in GLUT4 and hexokinase II or basal glycogen content in skeletal muscle nor GLUT4 content in abdominal adipose tissue.These findings suggest that the enhanced insulin‐stimulated whole‐body glucose disposal induced by a period of beta2‐agonist treatment in humans, at least in part, is attributed to muscle hypertrophy.Our observations extend findings in rodents and highlight the therapeutic potential of beta2‐agonists to enhance the capacity for glucose disposal and whole‐body insulin sensitivity, providing important knowledge with potential application in insulin resistance.

Heterogeneity in insulin-stimulated glucose uptake among different muscle groups in healthy lean people and people with obesity

It has been proposed that muscle fibre type composition and perfusion are key determinants of insulin-stimulated muscle glucose uptake, and alterations in muscle fibre type composition and perfusion contribute to muscle, and consequently whole-body, insulin resistance in people with obesity. The goal of the study was to evaluate the relationships among muscle fibre type composition, perfusion and insulin-stimulated glucose uptake rates in healthy, lean people and people with obesity. We measured insulin-stimulated whole-body glucose disposal and glucose uptake and perfusion rates in five major muscle groups (erector spinae, obliques, rectus abdominis, hamstrings, quadriceps) in 15 healthy lean people and 37 people with obesity by using the hyperinsulinaemic-euglycaemic clamp procedure in conjunction with [2H]glucose tracer infusion (to assess whole-body glucose disposal) and positron emission tomography after injections of [15O]H2O (to assess muscle perfusion) and [18F]fluorodeoxyglucose (to assess muscle glucose uptake). A biopsy from the vastus lateralis was obtained to assess fibre type composition. We found: (1) a twofold difference in glucose uptake rates among muscles in both the lean and obese groups (rectus abdominis: 67 [51, 78] and 32 [21, 55] μmol kg-1min-1 in the lean and obese groups, respectively; erector spinae: 134 [103, 160] and 66 [24, 129] μmol kg-1min-1, respectively; median [IQR]) that was unrelated to perfusion or fibre type composition (assessed in the vastus only); (2) the impairment in insulin action in the obese compared with the lean group was not different among muscle groups; and (3) insulin-stimulated whole-body glucose disposal expressed per kg fat-free mass was linearly related with muscle glucose uptake rate (r2 = 0.65, p < 0.05). Obesity-associated insulin resistance is generalised across all major muscles, and is not caused by alterations in muscle fibre type composition or perfusion. In addition, insulin-stimulated whole-body glucose disposal relative to fat-free mass provides a reliable index of muscle glucose uptake rate.

2031-P: Obesity and Insulin Resistance Alter the Biodistribution of Whole Body Insulin-Stimulated Glucose Disposal

Insulin-stimulated whole-body (WB) glucose disposal (GD) is thought to occur predominately in skeletal muscle (SM). Studies in animals suggest adipose tissue (AT) could also be an important site of GD, especially in people with obesity and insulin resistance. The interrelationship between adiposity, insulin sensitivity, and organ-specific insulin-stimulated GD is not known. We evaluated WB, SM, and AT insulin-stimulated GD by using the hyperinsulinemic-euglycemic clamp procedure together with [6,6-2H2]glucose infusion and 18F-deoxyglucose positron emission tomography in healthy lean people (n=13, age: 39±12 yrs, BMI: 23±2 kg/m2; body fat: 31±7%, mean±SD) and 27 people with obesity, who were then characterized as insulin sensitive (OIS, n=9, age: 48±10 yrs, body fat: 45±10%) or insulin resistant (OIR, n=9, age: 40±10 yrs, body fat: 48±4%) based on the top and bottom tertile values for WB insulin-stimulated GD. WB insulin-stimulated GD was 60% lower in the OIR (1,636±283 µmol/min) than both the OIS and Lean groups (P&amp;lt;0.01), without a difference between the OIS and Lean groups (4,188±758 and 3,855±1115 µmol/min). Total GD in subcutaneous AT was lower in the OIR than the OIS group (392±134 vs. 663±224 µmol/min) and greater in the OIS than the Lean (305±97 µmol/min, P&amp;lt;0.01) group. However, the contribution of AT to WB GD was greater in the OIR than the OIS and Lean groups (24±6%, 16±5%, and 9±4% of WB GD, P&amp;lt;0.01). GD rate in four major muscle groups (erector spinae, obliques, hamstrings, quadriceps) was 75% lower in the OIR (median [IQR]: 29 [23-35] µmol/kg muscle/min) than the OIS and the Lean groups (P&amp;lt;0.01), without a difference between the OIS and Lean groups (115 [89-139] and 102 [90-127] µmol/kg muscle/min). We conclude that: 1) a decrease in insulin-stimulated SM GD is responsible for the decrease in WB insulin-stimulated GD in the OIR group and 2) AT is a more important site of insulin-stimulated GD in people with obesity, particularly those with insulin resistance, than lean people. Disclosure H. Koh: None. S. van Vliet: None. R. Laforest: None. R. Gropler: None. S. Klein: Advisory Panel; Self; Danone Nutricia, Merck &amp; Co., Inc. Research Support; Self; Johnson &amp; Johnson, Pfizer Inc. Stock/Shareholder; Self; Aspire Bariatrics. B. Mittendorfer: None. Funding American Diabetes Association (1-18-ICTS-119 to B.M.); National Institutes of Health (DK115400, DK56341, DK020579, UL1TR000448)

Reduction in Global Myocardial Glucose Metabolism in Subjects With 1-Hour Postload Hyperglycemia and Impaired Glucose Tolerance.

Impaired insulin-stimulated myocardial glucose uptake has occurred in patients with type 2 diabetes with or without coronary artery disease. Whether cardiac insulin resistance is present remains uncertain in subjects at risk for type 2 diabetes, such as individuals with impaired glucose tolerance (IGT) or those with normal glucose tolerance (NGT) and 1-h postload glucose ≥155 mg/dL during an oral glucose tolerance test (NGT 1-h high). This issue was examined in this study. The myocardial metabolic rate of glucose (MRGlu) was measured by using dynamic 18F-fluorodeoxyglucose positron emission tomography combined with a euglycemic-hyperinsulinemic clamp in 30 volunteers without coronary artery disease. Three groups were studied: 1) those with 1-h postload glucose <155 mg/dL (NGT 1-h low) (n = 10), 2) those with NGT 1-h high (n = 10), 3) and those with IGT (n = 10). After adjusting for age, sex, and BMI, both subjects with NGT 1-h high (23.7 ± 6.4 mmol/min/100 mg; P = 0.024) and those with IGT (16.4 ± 6.0 mmol/min/100 mg; P < 0.0001) exhibited a significant reduction in global myocardial MRGlu; this value was 32.8 ± 9.7 mmol/min/100 mg in subjects with NGT 1-h low. Univariate correlations showed that MRGlu was positively correlated with insulin-stimulated whole-body glucose disposal (r = 0.441; P = 0.019) and negatively correlated with 1-h (r = -0.422; P = 0.025) and 2-h (r = -0.374; P = 0.05) postload glucose levels, but not with fasting glucose. This study shows that myocardial insulin resistance is an early defect that is already detectable in individuals with dysglycemic conditions associated with an increased risk of type 2 diabetes, such as IGT and NGT 1-h high.

Correlates of Insulin-Stimulated Glucose Disposal in Recent-Onset Type 1 and Type 2 Diabetes.

Not only type 2 diabetes (T2D), but also type 1 diabetes (T1D), can be associated with insulin resistance, as assessed using insulin-stimulated whole-body glucose disposal (M-value). We hypothesized that different factors would affect the M-value at the onset of T1D and T2D. We examined 132 patients with T1D or T2D matched for sex, age, and body mass index with a known diabetes duration of <12 months. Multivariable linear regression analyses were applied to test the associations between glycemic control, blood lipid levels, adiponectin, and proinflammatory immune mediators and the M-value, obtained from the hyperinsulinemic-euglycemic clamp. Despite comparable age, body mass index, and near-normoglycemic control, the mean M-value was lower in those with T2D than in those with T1D. Patients with T1D had a lower waist/hip ratio and serum triglycerides but higher serum adiponectin than patients with T2D. However, the circulating proinflammatory markers were not different. Even with adjustments for glucose-lowering treatments, the fasting blood glucose correlated negatively with the M-value in both groups. However, gamma-glutamyl transferase-independently of any treatments-correlated negatively only in T2D. In contrast, serum adiponectin correlated positively with the M-values. Fasting glycemia correlated with insulin-stimulated glucose disposal in both diabetes types. However, altered liver and adipose tissue function were associated with insulin-stimulated glucose disposal only in T2D, underpinning the specific differences between these diabetes types.

Skeletal muscle inflammation and insulin resistance in obesity.

Obesity is associated with chronic inflammation, which contributes to insulin resistance and type 2 diabetes mellitus. Under normal conditions, skeletal muscle is responsible for the majority of insulin-stimulated whole-body glucose disposal; thus, dysregulation of skeletal muscle metabolism can strongly influence whole-body glucose homeostasis and insulin sensitivity. Increasing evidence suggests that inflammation occurs in skeletal muscle in obesity and is mainly manifested by increased immune cell infiltration and proinflammatory activation in intermyocellular and perimuscular adipose tissue. By secreting proinflammatory molecules, immune cells may induce myocyte inflammation, adversely regulate myocyte metabolism, and contribute to insulin resistance via paracrine effects. Increased influx of fatty acids and inflammatory molecules from other tissues, particularly visceral adipose tissue, can also induce muscle inflammation and negatively regulate myocyte metabolism, leading to insulin resistance.

Preoperative carbohydrate supplementation attenuates post-surgery insulin resistance via reduced inflammatory inhibition of the insulin-mediated restraint on muscle pyruvate dehydrogenase kinase 4 expression

We hypothesized that the so far poorly understood improvement in postoperative insulin sensitivity, when surgery is preceded by a carbohydrate (CHO) drink, occurs via attenuation of skeletal muscle inflammatory responses to surgery, improved insulin signaling and attenuated expression of muscle pyruvate dehydrogenase kinase (PDK) 4. Vastus lateralis muscle biopsies, collected before and after major abdominal surgery and during postoperative hyperinsulinaemic-euglycaemic clamping from 16 pigs randomized to either 200 ml of a CHO-supplemented drink 2 h before surgery (CHO, 25 g; n = 8), or preoperative overnight fasting (fasted; n = 8), were analyzed by fast qRT-PCR and IR-Western blotting. During clamping, expression of IKKβ, SOCS3 and the ratio of phosphorylated/total JNK2 proteins were lower in the CHO group than in the fasted group (-1.0 vs. 2.9-fold, P < 0.001; -0.6 vs. 3.2-fold, P < 0.01; and -0.5 vs. 1.1-fold, P < 0.02, respectively). Furthermore, the ratio of Ser(307)-phosphorylated (inhibition)/total IRS1 protein was reduced only in the CHO group (-2.4 fold, P < 0.02), whereas FOXO1 phosphorylation (inactivation), which correlated negatively with PDK4 mRNA (r(2) = 0.275, P < 0.05), was lower in the CHO group than in the fasted group (-1.1-fold, P > 0.05 vs. -2.3-fold, P = 0.05). Post-surgery, PDK4 mRNA increased ∼20-fold (P < 0.01) in both groups, but was reversed to a greater extent by insulin in the CHO group (-40.5 vs. -22.7-fold, P < 0.05), resulting in 5-fold lower PDK4 protein levels, which correlated negatively with insulin-stimulated whole-body glucose disposal rates (r(2) = -0.265, P < 0.05). Preoperative carbohydrate supplementation was found to ameliorate postoperative insulin sensitivity by reducing muscle inflammatory responses and improved insulin inhibition of FOXO1-mediated PDK4 mRNA and protein expression after surgery.

Single-dose carbohydrate treatment in the immediate preoperative phase diminishes development of postoperative peripheral insulin resistance

Preoperative oral carbohydrate (CHO) treatment is known to reduce postoperative insulin resistance, but the necessity of a preoperative evening dose is uncertain. We investigated the effect of single-dose CHO treatment two hours before surgery on postoperative insulin sensitivity. Thirty two pigs (∼ 30 kg) were randomized to 4 groups (n = 8) followed by D-[6,6-(2)H2] glucose infusion and hyperinsulinemic-euglycemic step clamping. Two groups received a morning drink of 25 g carbohydrate (CHO/surgery and CHO/control). Animals in the other two groups were fasted overnight (fasting/surgery and fasting/control). Counter-regulatory hormones, free fatty acids (FFA) and liver and muscle glycogen content were measured serially. Glucose infusion rates needed to maintain euglycemia were higher after CHO/surgery than fasting/surgery during low (8.54 ± 0.82 vs. 6.15 ± 0.27 mg/kg/min, P < 0.05), medium (17.26 ± 1.08 vs. 14.02 ± 0.56 mg/kg/min, P < 0.02) and high insulin clamping (19.83 ± 0.95 vs. 17.16 ± 0.58 mg/kg/min, P < 0.05). The control groups exhibited identical insulin sensitivity. Compared to their respective controls, insulin-stimulated whole-body glucose disposal was significantly reduced after fasting/surgery (-41%, P < 0.001), but not after CHO/surgery (-16%, P = 0.180). CHO reduced FFA perioperatively (P < 0.05) and during the clamp procedures (P < 0.02), but did not affect hepatic insulin sensitivity, liver and muscle glycogen content or counter-regulatory hormone profiles. A strong negative correlation between peripheral insulin sensitivity and mean cortisol levels was seen in fasted (R = -0.692, P = 0.003), but not in CHO loaded pigs. Single-dose preoperative CHO treatment is sufficient to reduce postoperative insulin resistance, possibly due to the antilipolytic effects and antagonist properties of preoperative hyperinsulinemia on the suppressant actions of cortisol on carbohydrate oxidation.

The peroxisome proliferator-activated receptor alpha agonist fenofibrate has no effect on insulin sensitivity compared to atorvastatin in type 2 diabetes mellitus; a randomised, double-blind controlled trial

AimsAssess insulin sensitivity after treatment with a selective PPAR-alpha agonist compared to an HMG CoA reductase inhibitor in human subjects with type 2 diabetes mellitus. MethodsThirteen subjects with Type 2 diabetes mellitus were studied in a double-blind crossover design with 4-week placebo run-in and washout and 12-week treatment periods, randomised to micronised fenofibrate 267mg or atorvastatin 10mg daily followed by the alternate drug in the second period. Insulin resistance was measured using the isoglycaemic hyperinsulinaemic clamp method with isotope dilution. ResultsWeight, physical activity and other medications did not change. Total cholesterol (mean +/− standard error) was 4.60+/−0.21 versus 3.9+/−0.22mmol/L after fenofibrate and atorvastatin respectively, p<0.05. LDL was 2.70+/−0.19 versus 1.95+/−0.23mmol/L, p<0.05 and triglyceride 1.64+/−0.23 versus 1.84+/−0.26mmol/L, p<0.05. Insulin-stimulated whole-body glucose disposal (35.4+/−3.1 versus 33.2+/−3.0μmol/kg/min) and nadir endogenous glucose production (6.2+/−1.4 versus 7.0+/−1.1μmol/kg/min) revealed no significant differences in effects of the treatments. ConclusionsIn human subjects with Type 2 diabetes mellitus there were characteristic differences in lipid profile changes but no difference in insulin sensitivity after treatment with micronised fenofibrate compared to atorvastatin. This study finds no evidence of increased insulin sensitivity using this selective PPAR-alpha agonist over a commonly used statin at these doses.

Pioglitazone improves glucose metabolism and modulates skeletal muscle TIMP-3–TACE dyad in type 2 diabetes mellitus: a randomised, double-blind, placebo-controlled, mechanistic study

Pioglitazone (PIO) is a peroxisome proliferator-activated receptor (PPAR)γ agonist insulin-sensitiser with anti-inflammatory and anti-atherosclerotic effects. Our objective was to evaluate the effect of low-dose PIO (15 mg/day) on glucose metabolism and inflammatory state in obese individuals with type 2 diabetes. A randomised, double-blind, placebo-controlled, mechanistic trial was conducted on 29 patients with type 2 diabetes treated with metformin and/or sulfonylurea. They were randomised to receive PIO or placebo (PLC) for 6 months, in a 1:1 ratio. Participants were allocated to interventions by central office. All study participants, investigators and personnel performing measurements were blinded to group assignment. At baseline and after 6 months patients underwent: (1) OGTT; (2) muscle biopsy to evaluate expression of TNF-α, tissue inhibitor of metalloproteases 3 (TIMP-3) levels, TNF-α converting enzyme (TACE) expression and enzymatic activity; (3) euglycaemic-hyperinsulinaemic clamp; (4) measurement of plasma high-sensitivity C-reactive protein (hsCRP), plasminogen activator inhibitor type-1 (PAI-1), TNF-α, IL-6, monocyte chemotactic protein-1 (MCP-1), adiponectin and fractalkine (FRK). The interventions were PIO 15 mg/day vs placebo and the main outcomes measured were absolute changes in whole-body insulin sensitivity, insulin secretion and inflammatory state. Fifteen participants were randomized to receive PIO and 14 participants were randomized to receive PLC. Eleven participants completed the study in the PIO group and nine participants completed the study in the PLC group and were analysed. Fasting plasma glucose and HbA1c decreased modestly (p < 0.05) after PIO and did not change after PLC. M/I (insulin-stimulated whole-body glucose disposal), adipose tissue insulin resistance (IR) index, insulin secretion/IR (disposition) index and insulinogenic index improved significantly after PIO, but not after PLC. Circulating MCP-1, IL-6, FRK, hsCRP and PAI-1 levels decreased in PIO- as compared with PLC-treated patients, while TNF-α did not change. TNF-α protein expression and TACE enzymatic activity in muscle were significantly reduced by PIO but not PLC. Adiponectin levels increased significantly after PIO as compared with PLC treatment. Given that the mean TACE enzymatic activity level at baseline in the PIO group was 0.29 ± 0.07 (fluorescence units [FU]), and at end of study decreased to 0.05 vs 0.14 in the PLC group, the power to reject the null hypothesis that the population means of the PIO and PLC groups are equal after 6 months is greater than 0.80. Given that M/I was 2.41 ± 0.35 μmol kg(-1) min(-1) (pmol/l)(-1) at baseline and increased by 0.55 in the PIO and 0.17 in the PLC groups, the power to reject the null hypothesis that the population means of the PIO and PLC groups are equal after 6 months is greater than 0.85. The type I error probability associated with this test of this null hypothesis is 0.05. No serious adverse events occurred in either group. Low-dose PIO (15 mg/day) improves glycaemic control, beta cell function and inflammatory state in obese patients with type 2 diabetes. Clinical.Trial.gov NCT01223196. This study was funded by TAKEDA.

Globular Adiponectin Enhances Muscle Insulin Action via Microvascular Recruitment and Increased Insulin Delivery

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. To examine whether adiponectin modulates muscle microvascular recruitment thus insulin delivery and action in vivo. 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. Globular adiponectin increases muscle insulin uptake by recruiting muscle microvasculature, which contributes to its insulin-sensitizing action.

Free Fatty Acids Induce Insulin Resistance in Both Cardiac and Skeletal Muscle Microvasculature in Humans

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 (P < 0.0001 for both) and skeletal (P = 0.008 and < 0.03, 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.

Angiotensin II Enhances Insulin-Stimulated Whole-Body Glucose Disposal but Impairs Insulin-Induced Capillary Recruitment in Healthy Volunteers

Angiotensin II (AngII) increases insulin-mediated glucose uptake in healthy individuals. The underlying mechanisms are undefined. AngII may increase glucose uptake through a direct effect on muscle cell insulin signaling or through increasing insulin delivery to muscle cells through effects on the microvasculature. Our objective was to determine whether AngII increases insulin-mediated glucose uptake through effects on insulin-induced capillary recruitment. We examined the effects of AngII on hyperinsulinemia-induced capillary density by measuring skin capillary density, capillary recruitment, and capillary density during venous congestion in 18 healthy subjects in the basal state, during systemic hyperinsulinemia, and during hyperinsulinemia with coinfusion of AngII or phenylephrine (pressor control). In addition, whole-body glucose uptake and blood pressure were measured. Capillaroscopy data of 13 subjects were available for analysis. Compared with the basal state, hyperinsulinemia increased baseline capillary density (51.5+/-9.0 vs. 55.2+/-10.8 n/mm2, P<0.01), capillary recruitment (67.8+/-6.8 vs. 70.6+/-7.5 n/mm2, P<0.05), and capillary density during venous congestion (78.5+/-12.0 vs. 80.3+/-12.0 n/mm2, P<0.01). Infusion of AngII, but not phenylephrine, reduced insulin-induced capillary recruitment (69.3+/-8.6 vs. 65.2+/-8.0 n/mm2, P<0.05) and capillary density during venous congestion (79.7+/-15.3 vs. 73.9+/-12.1, P<0.05) while enhancing glucose uptake [2.40+/-0.7 vs. 2.68+/-0.6 (mg/kg.min per pmol/l)x100, P<0.01)] (n=18). AngII increases insulin-mediated glucose uptake in healthy individuals. This increase was probably not related to increases in microvascular perfusion because infusion of AngII during hyperinsulinemia reduced insulin-mediated skin capillary recruitment. Additional studies are needed to investigate whether AngII directly affects insulin delivery through increasing insulin transport across the microvasculature.

The Role of Peroxisome Proliferator-Activated Receptor γ Coactivator-1 β in the Pathogenesis of Fructose-Induced Insulin Resistance

Peroxisome proliferator-activated receptor gamma coactivator-1 beta (PGC-1beta) is known to be a transcriptional coactivator for SREBP-1, the master regulator of hepatic lipogenesis. Here, we evaluated the role of PGC-1beta in the pathogenesis of fructose-induced insulin resistance by using an antisense oligonucletoide (ASO) to knockdown PGC-1beta in liver and adipose tissue. PGC-1beta ASO improved the metabolic phenotype induced by fructose feeding by reducing expression of SREBP-1 and downstream lipogenic genes in liver. PGC-1beta ASO also reversed hepatic insulin resistance induced by fructose in both basal and insulin-stimulated states. Furthermore, PGC-1beta ASO increased insulin-stimulated whole-body glucose disposal due to a threefold increase in glucose uptake in white adipose tissue. These data support an important role for PGC-1beta in the pathogenesis of fructose-induced insulin resistance and suggest that PGC-1beta inhibition may be a therapeutic target for treatment of NAFLD, hypertriglyceridemia, and insulin resistance associated with increased de novo lipogenesis.

Targeting Foxo1 in Mice Using Antisense Oligonucleotide Improves Hepatic and Peripheral Insulin Action

Fasting hyperglycemia, a prominent finding in diabetes, is primarily due to increased gluconeogenesis. The transcription factor Foxo1 links insulin signaling to decreased transcription of PEPCK and glucose-6-phosphatase (G6Pase) and provides a possible therapeutic target in insulin-resistant states. Synthetic, optimized antisense oligonucleotides (ASOs) specifically inhibit Foxo1 expression. Here we show the effect of such therapy on insulin resistance in mice with diet-induced obesity (DIO). Reducing Foxo1 mRNA expression with ASO therapy in mouse hepatocytes decreased levels of Foxo1 protein and mRNA expression of PEPCK by 48 +/- 4% and G6Pase by 64 +/- 3%. In mice with DIO and insulin resistance, Foxo1 ASO therapy lowered plasma glucose concentration and the rate of basal endogenous glucose production. In addition, Foxo1 ASO therapy lowered both hepatic triglyceride and diacylglycerol content and improved hepatic insulin sensitivity. Foxo1 ASO also improved adipocyte insulin action. At a tissue-specific level, this manifested as improved insulin-mediated 2-deoxyglucose uptake and suppression of lipolysis. On a whole-body level, the result was improved glucose tolerance after an intraperitoneal glucose load and increased insulin-stimulated whole-body glucose disposal during a hyperinsulinemic-euglycemic clamp. In conclusion, Foxo1 ASO therapy improved both hepatic insulin and peripheral insulin action. Foxo1 is a potential therapeutic target for improving insulin resistance.

Postoperative parenteral nutrition while proactively minimizing insulin resistance

Objective We compared the metabolic effects of postoperative total parenteral nutrition (TPN) and hypocaloric glucose after treatment with oral carbohydrates preoperatively and epidural anesthesia to proactively minimize postoperative insulin resistance. Methods Thirteen patients undergoing colorectal resections were given oral carbohydrates preoperatively and epidural anesthesia and randomized to TPN or hypocaloric glucose during and after surgery. Insulin sensitivity (hyperinsulinemic clamp [0.8 mU · kg −1 · min −1], normoglycemic clamps [4.5 mM]), and glucose kinetics (6,6 2H 2- d-glucose), were studied before and on postoperative day 3. Indirect calorimetry was performed and nitrogen excretion in urine was measured. Values are presented as mean ± standard deviation. Analysis of variance, planned comparison, and Bonferroni’s correction were used for statistical analysis. Results Three days after surgery insulin-stimulated whole-body glucose disposal decreased by 24 ± 11% versus 28 ± 23% in patients receiving TPN and hypocaloric glucose, respectively ( P < 0.05 for both, not significant between groups). Endogenous glucose production during insulin stimulation was increased only in the glucose group after surgery ( P < 0.05 versus before). After surgery, insulin-stimulated glucose oxidation was higher after treatment with TPN, whereas fat oxidation was lower ( P < 0.05 for both versus glucose treatment). Fat oxidation increased in the glucose group at basal after surgery ( P < 0.05 versus before). Nitrogen balance was less negative after treatment with TPN ( P < 0.01). Conclusions Treatment with TPN does not seem to improve postoperative peripheral insulin sensitivity in patients with minor insulin resistance after pretreatment with preoperative carbohydrates and perioperative epidural anesthesia. Hypocaloric nutrition results in changes in substrate utilization and nitrogen balance resembling starvation, whereas TPN attenuates these changes.

Increased energy expenditure, decreased adiposity, and tissue-specific insulin sensitivity in protein-tyrosine phosphatase 1B-deficient mice.

Protein-tyrosine phosphatase 1B (PTP-1B) is a major protein-tyrosine phosphatase that has been implicated in the regulation of insulin action, as well as in other signal transduction pathways. To investigate the role of PTP-1B in vivo, we generated homozygotic PTP-1B-null mice by targeted gene disruption. PTP-1B-deficient mice have remarkably low adiposity and are protected from diet-induced obesity. Decreased adiposity is due to a marked reduction in fat cell mass without a decrease in adipocyte number. Leanness in PTP-1B-deficient mice is accompanied by increased basal metabolic rate and total energy expenditure, without marked alteration of uncoupling protein mRNA expression. In addition, insulin-stimulated whole-body glucose disposal is enhanced significantly in PTP-1B-deficient animals, as shown by hyperinsulinemic-euglycemic clamp studies. Remarkably, increased insulin sensitivity in PTP-1B-deficient mice is tissue specific, as insulin-stimulated glucose uptake is elevated in skeletal muscle, whereas adipose tissue is unaffected. Our results identify PTP-1B as a major regulator of energy balance, insulin sensitivity, and body fat stores in vivo.

Transgenic Overexpression of Hexokinase II in Skeletal Muscle Does Not Increase Glucose Disposal in Wild-type or Glut1-overexpressing Mice

Glut1 transgenic mice were bred with transgenic mice that overexpress hexokinase II in skeletal muscle in order to determine whether whole-body glucose disposal could be further augmented in mice overexpressing glucose transporters. Overexpression of hexokinase alone in skeletal muscle had no effect on glucose transport or metabolism in isolated muscles, nor did it alter blood glucose levels or the rate of whole-body glucose disposal. Expression of the hexokinase transgene in the context of the Glut1 transgenic background did not alter glucose transport in isolated muscles but did cause additional increases in steady-state glucose 6-phosphate (3.2-fold) and glycogen (7.5-fold) levels compared with muscles that overexpress the Glut1 transporter alone. Surprisingly, however, these increases were not accompanied by a change in basal or insulin-stimulated whole-body glucose disposal in the doubly transgenic mice compared with Glut1 transgenic mice, probably due to an inhibition of de novo glycogen synthesis as a result of the high levels of steady-state glycogen in the muscles of doubly transgenic mice (430 micromol/g versus 10 micromol/g in wild-type mice). We conclude that the hexokinase gene may not be a good target for therapies designed to counteract insulin resistance or hyperglycemia.