Effects of Oral and Transdermal Estrogen Replacement Therapy on Markers of Coagulation, Fibrinolysis, Inflammation and Serum Lipids and Lipoproteins in Postmenopausal Women

We compared the effects of oral estradiol (2 mg), transdermal estradiol (50 g), and placebo on measures of coagulation, fibrinolysis, inflammation and serum lipids and lipoproteins in 27 postmenopausal women at baseline and after 2 and 12 weeks of treatment. Oral and transdermal estradiol induced similar increases in serum free estradiol concentrations. Oral therapy increased the plasma concentrations of factor VII antigen (FVIIag) and activated factor VII (FVIIa), and the plasma concentration of the prothrombin activation marker prothrombin fragment 1+2 (F1+2). Oral but not transdermal estradiol therapy significantly lowered plasma plasminogen activator inhibitor-1 (PAI-1) antigen and tissue-type plasminogen activator (tPA) antigen concentrations and PAI-1 activity, and increased D-dimer concentrations, suggesting increased fibrinolysis. The concentration of soluble Eselectin decreased and serum C-reactive protein (CRP) increased significantly in the oral but not in the transdermal or placebo groups. In the oral but not in the transdermal or placebo estradiol groups low-density-lipoprotein (LDL) cholesterol, apolipoprotein B and lipoprotein (a) concentrations decreased while high-density-lipoprotein (HDL) cholesterol, apolipoprotein AI and apolipoprotein AII concentrations increased significantly. LDL particle size remained unchanged. In summary, oral estradiol increased markers of fibrinolytic activity, decreased serum soluble E-selectin levels and induced potentially antiatherogenic changes in lipids and lipoproteins. In contrast to these beneficial effects, oral estradiol changed markers of coagulation towards hypercoagulability, and increased serum CRP concentrations. Transdermal estradiol or placebo had no effects on any of these parameters. These data demonstrate that oral estradiol does not have uniformly beneficial effects on cardiovascular risk markers and that the oral route of estradiol administration rather than the circulating free estradiol concentration is critical for any changes to be observed.

Improved control of blood pressure and albuminuria among patients with type-2 diabetes in Finnish open care

Risk of cardiovascular events within the diabetic population has decreased and survival increased with patients living longer and thus facing the development of end-stage renal disease (ESRD). This calls for good care of patient with diabetes with a focus on hypertension. Patient data were collected from 42 Finnish primary care centres. Each was asked to enrol 10-12 consecutive patients with type-2 diabetes between March 2011 and August 2012. Along with the office blood pressure measurements and laboratory tests, the presence of albuminuria was measured and glomerular filtration rate estimated (eGFR). The 2013 ESH criteria for diabetic hypertensive patients (<140/85 mmHg) was reached by 39% of all 625 study patients and 38% of the pharmacologically treated 520 patients. The absence of detectable albumin in urine was significantly associated with the control of systolic blood pressure and achievement of treatment goals. Beta blockers were the most common antihypertensive agents and patients treated with them had lower eGFR compared to those not treated with these agents. The blood pressure of patients was not in full concordance with the present guideline recommendations. However, satisfactory improvement in blood pressure control, reduction of albuminuria and hence ESRD prevention was achieved.

High prevalence of chronic kidney disease in Finnish patients with type 2 diabetes treated in primary care

OBJECTIVE

To examine the prevalence of chronic kidney disease (CKD) and related cardiovascular morbidity in a cross-sectional population in patients with type 2 diabetes (T2D) treated in a primary care setting in Finland.

RESEARCH DESIGN AND METHODS

Data were collected and recorded from 42 primary care centres, which recruited 629 patients diagnosed with type 2 diabetes (T2D) to this non-interventional study. Data including patient characteristics, kidney function and albuminuria, blood pressure, HbA1c, lipid and lipoprotein levels, and diabetes duration as well as current medication was collected in each patient.

RESULTS

In the final study population of 625 patients, the mean age was 67 years (range 29-92 years), BMI 32.8 kg/m(2) (95% CI 32-33), blood pressure 142/80 mmHg (140-143/80-81) and HbA1c 7.1% (7.0-7.2) (53.8 mmol/mol, 53-55) and the median duration of diabetes was 9.2 years ranging from newly diagnosed to 43 years. History of dyslipidemia had in 73.3% of patients, 27.8% had cardiovascular disease and 82.7% had hypertension. The primary endpoint, prevalence of CKD of any grade (1-5) or albuminuria, was 68.6%. Regarding declined renal function, 16.2% of patients had an estimated glomerular filtration rate (eGFR) <60 ml/min/1.72 m(2), classifying as CKD 3-5. Only one patient was within CKD5. Regarding renal damage, albuminuria was present in 24.3% of patients, with microalbuminuria in 17.1% and macroalbuminuria in 7.2%, respectively. Combining the patients with CKD 3-5 and/or the presence of albuminuria, 34.7% seemed to suffer from significant CKD. The proportion of patients with albuminuria increased with a decrease in glomerular filtration rate. Historically, diabetic nephropathy had been diagnosed in 24.3% of the patients.

CONCLUSIONS

Nearly 70% of patients with T2D treated in primary care in Finland have some sign of CKD and nearly half of all T2D patients have a significant CKD. However, only half of the latter had it diagnosed and documented in their patient charts, thus highlighting the importance of performing routine screening of nephropathy by measuring both albuminuria and eGFR in patients with T2D. Prevention of this complication with active therapy for risk factors, such as hypertension and dyslipidemia is warranted.

The activation of hepatic and muscle polyamine catabolism improves glucose homeostasis

The mitochondrial biogenesis and energy expenditure regulator, PGC-1α, has been previously reported to be induced in the white adipose tissue (WAT) and liver of mice overexpressing spermidine/spermine N (1)-acetyltransferase (SSAT). The activation of PGC-1α in these mouse lines leads to increased number of mitochondria, improved glucose homeostasis, reduced WAT mass and elevated basal metabolic rate. The constant activation of polyamine catabolism produces a futile cycle that greatly reduces the ATP pools and induces 5'-AMP-activated protein kinase (AMPK), which in turn activates PGC-1α in WAT. In this study, we have investigated the effects of activated polyamine catabolism on the glucose and energy metabolisms when targeted to specific tissues. For that we used a mouse line overexpressing SSAT under the endogenous SSAT promoter, an inducible SSAT overexpressing mouse model using the metallothionein I promoter (MT-SSAT), and a mouse model with WAT-specific SSAT overexpression (aP2-SSAT). The results demonstrated that WAT-specific SSAT overexpression was sufficient to increase the number of mitochondria, reduce WAT mass and protect the mice from high-fat diet-induced obesity. However, the improvement in the glucose homeostasis is achieved only when polyamine catabolism is enhanced at the same time in the liver and skeletal muscle. Our results suggest that the tissue-specific targeting of activated polyamine catabolism may reveal new possibilities for the development of drugs boosting mitochondrial metabolism and eventually for treatment of obesity and type 2 diabetes.

Fasting plasma glucose variability as a marker of nocturnal hypoglycemia in diabetes: evidence from the PREDICTIVE study

The relationship between fasting glucose (FG) variability and nocturnal hypoglycemia was assessed using longitudinal data from PREDICTIVE, the large-scale observational study of insulin detemir. An HbA(1c)-corrected correlation was found between these endpoints, suggesting FG variability can serve as a useful marker for this risk in clinical practice.

Switching from NPH insulin to once-daily insulin detemir in basal-bolus-treated patients with diabetes mellitus: data from the European cohort of the PREDICTIVE study

BACKGROUND

The PREDICTIVE study is a multinational observational study designed to follow up patients with diabetes who started insulin detemir (IDet) in routine care. Recruitment started in June 2004 and is ongoing in some countries.

METHODS

We report 12-week follow-up data for patients with type 1 (T1D) or type 2 diabetes (T2D) in the European cohort who, as part of basal-bolus therapy, switched from once- (qd) or twice-daily (bid) neutral protamine Hagedorn insulin (NPH) to qd IDet. End-points - evaluated from patients' records and diaries - were incidence of serious adverse drug reactions, glycaemic parameters, hypoglycaemia and weight change.

RESULTS

A total of 3637 patients were included, n = 1500 T1D [mean age 40.9 years, body mass index (BMI) 25.0 kg/m(2), glycosylated haemoglobin (HbA(1c)) 7.9%] and n = 2137 T2D (mean age 60.5 years, BMI 31.9 kg/m(2), HbA(1c) 8.0%). IDet was well tolerated. Lower overall, major and nocturnal rates of hypoglycaemia were observed in T1D and T2D patients switching from NPH to IDet (overall, T1D: 38.2-18.56 episodes/patient year, p < 0.001; T2D: 13.8-3.3 [corrected] episodes/patient year, p < 0.001). Switching from bid NPH to qd IDet resulted in significant 12-week reductions in HbA(1c) (T1D: -0.40%; T2D: -0.56%; both p < 0.001). Switching from qd NPH to qd IDet, resulted in HbA(1c) reductions of: T1D -0.52%; T2D -0.56%; both p < 0.001. Fasting blood glucose levels were also significantly reduced in patients with T1D or T2D. Overall mean weight changes were: T1D: 0.0 kg, T2D: -0.2 kg after 12 weeks.

CONCLUSION

In routine care, patients with T1D or T2D may be switched from NPH to IDet qd as part of a basal-bolus regimen.

Enhanced polyamine catabolism alters homeostatic control of white adipose tissue mass, energy expenditure, and glucose metabolism

Peroxisome proliferator-activated receptor gamma coactivator 1 alpha (PGC-1 alpha) is an attractive candidate gene for type 2 diabetes, as genes of the oxidative phosphorylation (OXPHOS) pathway are coordinatively downregulated by reduced expression of PGC-1 alpha in skeletal muscle and adipose tissue of patients with type 2 diabetes. Here we demonstrate that transgenic mice with activated polyamine catabolism due to overexpression of spermidine/spermine N(1)-acetyltransferase (SSAT) had reduced white adipose tissue (WAT) mass, high basal metabolic rate, improved glucose tolerance, high insulin sensitivity, and enhanced expression of the OXPHOS genes, coordinated by increased levels of PGC-1 alpha and 5'-AMP-activated protein kinase (AMPK) in WAT. As accelerated polyamine flux caused by SSAT overexpression depleted the ATP pool in adipocytes of SSAT mice and N(1),N(11)-diethylnorspermine-treated wild-type fetal fibroblasts, we propose that low ATP levels lead to the induction of AMPK, which in turn activates PGC-1 alpha in WAT of SSAT mice. Our hypothesis is supported by the finding that the phenotype of SSAT mice was reversed when the accelerated polyamine flux was reduced by the inhibition of polyamine biosynthesis in WAT. The involvement of polyamine catabolism in the regulation of energy and glucose metabolism may offer a novel target for drug development for obesity and type 2 diabetes.

The effect of moderate exercise training on skeletal muscle myosin heavy chain distribution in chronic heart failure

BACKGROUND

The myosin heavy chain (MHC) is altered in chronic heart failure (CHF), but the effect of exercise on MHC expression in CHF patients is not understood. The aim of the present study was to show the effect of aerobic exercise on MHC distribution in patients with CHF.

METHODS

Patients (n=17) with stable NYHA class I-III CHF were randomised into training and control groups. For a period of three months, the training group cycled on an ergometric cycle 3 times a week for 30 min, the control group continued as they did previously. Both a baseline and a final 3 month graded maximal exercise test and exercise endurance test with constant submaximal work load were performed. Muscle samples, obtained from vastus lateralis muscle at baseline and after 3 months from the 8 patients in the training group and the 9 in the control group, were analysed for MHC distribution using SDS-polyacrylamide gel electrophoresis.

RESULTS

Baseline MHC distributions were similar in both groups and training did not alter the MHC distribution. Exercise duration, at constant submaximal work load, improved from 14.9+/-7.1 to 26.9+/-9.6 min (p<0.01 for the change between the groups). Training did not improve peak oxygen consumption.

CONCLUSION

No correlation between the change in exercise capacity and MHC distribution appeared despite the significant improvement of exercise duration.

Activation of the hexosamine pathway causes oxidative stress and abnormal embryo gene expression: involvement in diabetic teratogenesis

BACKGROUND

Oxidative stress is critical to the teratogenic effects of diabetic pregnancy, yet the specific biochemical pathways responsible for oxidative stress have not been fully elucidated. The hexosamine pathway is activated in many tissues during diabetes and could contribute to oxidative stress by inhibiting the pentose shunt pathway, thereby diminishing production of the cellular antioxidant, reduced glutathione (GSH).

METHODS

To test the hypothesis that activation of the hexosamine pathway might contribute to the teratogenic effects of diabetic pregnancy, pregnant mice were injected with glucose, to induce hyperglycemia, or glucosamine, to directly activate the hexosamine pathway. Embryo tissue fragments were also cultured in physiological glucose, high glucose, or physiological glucose plus glucosamine, to test effects on oxidative stress and embryo gene expression.

RESULTS

Glucosamine increased hexosamine synthesis and inhibited pentose shunt activity. There was a trend for transient hyperglycemia to have the same effects, but they did not reach statistical significance. However, both glucose and glucosamine significantly decreased GSH, and increased oxidative stress, as indicated by 2',7'-dichloro-dihydrofluorescein fluorescence. Glucose and glucosamine inhibited expression of Pax-3, a gene required for neural tube closure both in vivo and in vitro, and increased neural tube defects (NTDs) in vivo; these effects were prevented by GSH ethyl ester. High glucose and glucosamine inhibited Pax-3 expression by embryo culture, but culture in glutamine-free media to block the hexosamine pathway prevented the inhibition of Pax-3 expression by high glucose.

CONCLUSIONS

Activation of the hexosamine pathway causes oxidative stress through depletion of GSH and consequent disruption of embryo gene expression. Activation of this pathway may contribute to diabetic teratogenesis.

Effects of rosiglitazone on gene expression in subcutaneous adipose tissue in highly active antiretroviral therapy-associated lipodystrophy

Highly active antiretroviral therapy (HAART) has improved the prognosis of human immunodeficiency virus (HIV)-infected patients but is associated with severe adverse events, such as lipodystrophy and insulin resistance. Rosiglitazone did not increase subcutaneous fat in patients with HAART-associated lipodystrophy (HAL) in a randomized, double-blind, placebo-controlled trial, although it attenuated insulin resistance and decreased liver fat content. The aim of this study was to examine effects of rosiglitazone on gene expression in subcutaneous adipose tissue in 30 patients with HAL. The mRNA concentrations in subcutaneous adipose tissue were measured using real-time PCR. Twenty-four-week treatment with rosiglitazone (8 mg/day) compared with placebo significantly increased the expression of adiponectin, peroxisome proliferator-activated receptor-gamma (PPARgamma), and PPARgamma coactivator 1 and decreased IL-6 expression. Expression of other genes involved in lipogenesis, fatty acid metabolism, or glucose transport, such as acyl-CoA synthase, adipocyte lipid-binding protein, CD45, fatty acid transport protein-1 and -4, GLUT1, GLUT4, keratinocyte lipid-binding protein, lipoprotein lipase, PPARdelta, and sterol regulatory element-binding protein-1c, remained unchanged. Rosiglitazone also significantly increased serum adiponectin concentration. The change in serum adiponectin concentration was inversely correlated with the change in fasting serum insulin concentration and liver fat content. In conclusion, rosiglitazone induced significant changes in gene expression in subcutaneous adipose tissue and ameliorated insulin resistance in patients with HAL. Increased expression of adiponectin might have mediated most of the favorable insulin-sensitizing effects of rosiglitazone in these patients.

Expression of adipogenic transcription factors, peroxisome proliferator-activated receptor gamma co-activator 1, IL-6 and CD45 in subcutaneous adipose tissue in lipodystrophy associated with highly active antiretroviral therapy

OBJECTIVE

To determine the expressions of multiple genes in the subcutaneous adipose tissue of HIV-positive, highly active antiretroviral therapy (HAART)-treated patients with and without lipodystrophy.

DESIGN AND METHODS

Real-time polymerase chain reaction was used to measure gene expressions in this cross-sectional study.

RESULTS

The messenger RNA concentrations of adipose transcription factors (peroxisome proliferator-activated receptor (PPAR) gamma and delta and sterol regulatory element binding protein 1c) were all significantly lower in the lipodystrophic than the non-lipodystrophic group. The mRNA concentration of PPAR-gamma co-activator 1 (PGC-1), which regulates mitochondrial biogenesis, was lower in the lipodystrophic than the non-lipodystrophic group. The mRNA expression of lipoprotein lipase, acyl coenzyme A synthase and glucose transport protein 4 were significantly lower in the lipodystrophic than the non-lipodystrophic group, but the mRNA concentrations of fatty acid transport and binding proteins were similar in both groups. The mRNA concentrations of IL-6 and CD45 (a common leukocyte marker) were significantly higher in the lipodystrophic than the non-lipodystrophic group.

CONCLUSION

Multiple alterations characterize gene expression in the subcutaneous adipose tissue of patients with HAART-associated lipodystrophy compared with HIV-positive, HAART-treated patients without lipodystrophy. The low expression of transcription factors inhibits adipocyte differentiation. The low expression of PGC-1 may contribute to mitochondrial defects. In addition, IL-6 and CD45 expressions are increased, the latter implying an excessive number of cells of leukocyte origin in lipodystrophic adipose tissue. Mitochondrial injury and an excess of proinflammatory cytokines may lead to increased apoptosis. All these changes may contribute to the loss of subcutaneous fat in HAART-associated lipodystrophy.

Elevated fasting insulin concentrations associate with impaired insulin signaling in skeletal muscle of healthy subjects independent of obesity

BACKGROUND

Insulin signaling is impaired in the skeletal muscle of obese subjects but whether defects in skeletal muscle insulin signaling also characterize insulin resistance of non-obese individuals is unknown. The detection of insulin signaling defects in muscle biopsies is hampered by the variation of the contaminating non-muscle elements such as blood, connective tissue, fat, and blood vessel structures. Freeze-drying and macroscopic purification of the muscle fibers prior to the analysis might offer a possibility to minimize the analytical variation due to these contaminants.

METHODS

In the present study we first determined whether insulin signaling could be reliably assessed in freeze-dried muscle specimens, which are free of non-muscle contaminants, and then applied this method to the study of insulin signaling in weight-matched insulin-sensitive and insulin-resistant non-diabetic men.

RESULTS

In rat muscle, increases in tyrosine phosphorylation of insulin receptor (IR) and activity of the insulin receptor substrate-1 (IRS-1)-associated phosphatidylinositol (PI) 3-kinase activity by insulin were similar or higher in freeze-dried and purified muscle than wet muscle. Prior to freeze-drying and purification, biopsies of human vastus lateralis muscle contained between 1% and 40% non-muscle contaminants (11+/-3%, mean+/-SEM, n=19). In freeze-dried biopsies of human vastus lateralis muscle taken before and after 30 min of hyperinsulinemia (serum free insulin 61+/-1 mU/l) in 13 non-diabetic men, insulin increased IR tyrosine phosphorylation 1.4-fold (p<0.05) and IRS-1-associated PI 3-kinase activity 1.7-fold (p<0.005). Insulin-stimulated PI 3-kinase activity was significantly inversely correlated with the fasting serum insulin concentration (r=-0.57, p<0.05). When divided according to the median fasting serum insulin concentration, the men with high fasting insulin [HI, n=7, age 44+/-3 years, body mass index (BMI) 25+/-1 kg/m(2)] as compared to the men with low fasting insulin [LI, n=6, age 45+/-3 years (NS), BMI 24+/-1 kg/m(2) (NS)] had lower rates of whole-body glucose uptake (3.4+/-0.4 vs 5.5+/-0.3 mg/kg min, p<0.005), higher fasting plasma glucose concentrations (5.9+/-0.2 vs 5.2+/-0.1 mmol/l, p<0.05), higher fasting serum triglycerides (1.4+/-0.2 vs 0.9+/-0.1 mmol/l, p<0.05) and lower high-density lipoprotein (HDL) cholesterol concentrations (1.3+/-0.1 vs 1.7+/-0.1 mmol/l, p<0.05). Insulin-stimulated IR tyrosine phosphorylation (p<0.05) and IRS-1-associated PI 3-kinase activity (p<0.05) were significantly lower in the HI than the LI group.

CONCLUSIONS

Taken together these data demonstrate that early insulin signaling events can be reliably assessed in freeze-dried human skeletal muscle, and that in vivo insulin resistance and its accompanying features are associated with defects in early insulin signaling events in human skeletal muscle independent of body weight.

Intramyocellular lipid is associated with resistance to in vivo insulin actions on glucose uptake, antilipolysis, and early insulin signaling pathways in human skeletal muscle

To examine whether and how intramyocellular lipid (IMCL) content contributes to interindividual variation in insulin action, we studied 20 healthy men with no family history of type 2 diabetes. IMCL was measured as the resonance of intramyocellular CH(2) protons in lipids/resonance of CH(3) protons of total creatine (IMCL/Cr(T)), using proton magnetic resonance spectroscopy in vastus lateralis muscle. Whole-body insulin sensitivity was measured using a 120-min euglycemic-hyperinsulinemic (insulin infusion rate 40 mU/m(2). min) clamp. Muscle biopsies of the vastus lateralis muscle were taken before and 30 min after initiation of the insulin infusion to assess insulin signaling. The subjects were divided into groups with high IMCL (HiIMCL; 9.5 +/- 0.9 IMCL/Cr(T), n = 10) and low IMCL (LoIMCL; 3.0 +/- 0.5 IMCL/Cr(T), n = 10), the cut point being median IMCL (6.1 IMCL/Cr(T)). The groups were comparable with respect to age (43 +/- 3 vs. 40 +/- 3 years, NS, HiIMCL versus LoIMCL), BMI (26 +/- 1 vs. 26 +/- 1 kg/m(2), NS), and maximal oxygen consumption (33 +/- 2 vs. 36 +/- 3 ml. kg(-1). min(-1), NS). Whole-body insulin-stimulated glucose uptake was lower in the HiIMCL group (3.0 +/- 0.4 mg. kg(-1). min(-1)) than the LoIMCL group (5.1 +/- 0.5 mg. kg(-1). min(-1), P < 0.05). Serum free fatty acid concentrations were comparable basally, but during hyperinsulinemia, they were 35% higher in the HiIMCL group than the LoIMCL group (P < 0.01). Study of insulin signaling indicated that insulin-induced tyrosine phosphorylation of the insulin receptor (IR) was blunted in HiIMCL compared with LoIMCL (57 vs. 142% above basal, P < 0.05), while protein expression of the IR was unaltered. IR substrate-1-associated phosphatidylinositol (PI) 3-kinase activation by insulin was also lower in the HiIMCL group than in the LoIMCL group (49 +/- 23 vs. 84 +/- 27% above basal, P < 0.05 between HiIMCL and LoIMCL). In conclusion, IMCL accumulation is associated with whole-body insulin resistance and with defective insulin signaling in skeletal muscle independent of body weight and physical fitness.

Effects of oral and transdermal estrogen replacement therapy on markers of coagulation, fibrinolysis, inflammation and serum lipids and lipoproteins in postmenopausal women

We compared the effects of oral estradiol (2 mg), transdermal estradiol (50 microg), and placebo on measures of coagulation, fibrinolysis, inflammation and serum lipids and lipoproteins in 27 postmenopausal women at baseline and after 2 and 12 weeks of treatment. Oral and transdermal estradiol induced similar increases in serum free estradiol concentrations. Oral therapy increased the plasma concentrations of factor VII antigen (FVIIag) and activated factor VII (FVIIa), and the plasma concentration of the prothrombin activation marker prothrombin fragment 1+2 (F1+2). Oral but not transdermal estradiol therapy significantly lowered plasma plasminogen activator inhibitor-1 (PAI-1) antigen and tissue-type plasminogen activator (tPA) antigen concentrations and PAI-1 activity, and increased D-dimer concentrations, suggesting increased fibrinolysis. The concentration of soluble E-selectin decreased and serum C-reactive protein (CRP) increased significantly in the oral but not in the transdermal or placebo groups. In the oral but not in the transdermal or placebo estradiol groups low-density-lipoprotein (LDL) cholesterol, apolipoprotein B and lipoprotein (a) concentrations decreased while high-density-lipoprotein (HDL) cholesterol, apolipoprotein AI and apolipoprotein All concentrations increased significantly. LDL particle size remained unchanged. In summary, oral estradiol increased markers of fibrinolytic activity, decreased serum soluble E-selectin levels and induced potentially antiatherogenic changes in lipids and lipoproteins. In contrast to these beneficial effects, oral estradiol changed markers of coagulation towards hypercoagulability, and increased serum CRP concentrations. Transdermal estradiol or placebo had no effects on any of these parameters. These data demonstrate that oral estradiol does not have uniformly beneficial effects on cardiovascular risk markers and that the oral route of estradiol administration rather than the circulating free estradiol concentration is critical for any changes to be observed.

Effect of estrogen replacement therapy on insulin sensitivity of glucose metabolism and preresistance and resistance vessel function in healthy postmenopausal women

In the present study, we hypothesized that estradiol, via its ability to vasodilate in an endothelium-dependent manner, might enhance vascular effects of insulin. Basal and insulin-stimulated peripheral blood flow and resistance, arterial stiffness, and glucose metabolism were determined in 27 healthy postmenopausal women before and after 12 weeks of treatment with either transdermal or oral estradiol or corresponding placebo preparations. Whole body insulin sensitivity was determined using the euglycemic insulin clamp technique (rate of continuous insulin infusion 1 mU/kg.min), forearm blood flow with a strain-gauge plethysmography, and arterial stiffness using pulse wave analysis. Estradiol therapy increased basal peripheral blood flow (1.5 +/- 0.1 vs. 1.9 +/- 0.1 mL/dL.min, 0 vs. 12 weeks; P: < 0.01), decreased peripheral vascular resistance (65 +/- 3 vs. 52 +/- 3 mm Hg/mL/dL.min, respectively; P: < 0.01), and diastolic blood pressure (78 +/- 2 vs. 75 +/- 2 mm Hg, respectively; P: < 0.05) but had no effect on large artery stiffness. Infusion of insulin did not acutely alter peripheral blood flow but diminished large artery stiffness significantly both before and after the 12-week period of estradiol therapy. No measure of acute insulin action (glucose metabolism, blood flow, or large artery stiffness) was altered by estradiol or placebo treatment. These data demonstrate that insulin and estradiol have distinct hemodynamic effects. Physiological doses of estradiol increase peripheral blood flow but have no effects on large artery stiffness, whereas physiological concentrations of insulin acutely decrease stiffness without changing peripheral blood flow. Putative vasculoprotection by estradiol is, thus, not mediated via alterations in arterial stiffness or insulin sensitivity.

Differential effects of oral and transdermal estrogen replacement therapy on endothelial function in postmenopausal women

BACKGROUND

We determined whether the vascular effects of estradiol depend on the route of administration by comparing the effects of oral estradiol and transdermal placebo, transdermal estradiol and oral placebo, and transdermal placebo and oral placebo on in vivo endothelial function in 27 postmenopausal women.

METHODS AND RESULTS

Endothelial function was assessed from blood flow responses to intrabrachial artery infusions of endothelium-dependent (7.5 and 15 microgram/min acetylcholine) and endothelium-independent (3 and 10 microgram/min of sodium nitroprusside) vasodilators at 0, 2, and 12 weeks. In the oral estradiol group, the increase in flow above basal during infusion of the low dose of acetylcholine at 0, 2, and 12 weeks averaged 6.0+/-0.8, 6.9+/-0.8, and 11.3+/-1.2 (P<0.01 versus 0 and 2 weeks) mL. dL(-1). min(-1) at 0, 2, and 12 weeks. The percentage increases versus 0 weeks averaged 21+/-14% at 2 and 120+/-34% at 12 weeks. During the high-dose acetylcholine infusion, the increase in flow above basal averaged 8.6+/-1.3, 10.2+/-1.5, and 15.1+/-1.8 (P<0.05 versus 0 weeks) mL. dL(-1). min(-1), respectively. The percentage increases versus 0 weeks averaged 22+/-10% at 2 weeks and 119+/-46% at 12 weeks. In the oral estradiol group, endothelium-independent vasodilatation also improved significantly, but less markedly than endothelium-dependent responses. In the transdermal and placebo groups, all vascular responses remained unchanged. Oral but not transdermal estradiol also induced significant decreases in LDL cholesterol and Lp(a) concentrations and an increase in HDL cholesterol within 2 weeks.

CONCLUSIONS

We conclude that oral but not transdermal estradiol induces potentially antiatherogenic changes in in vivo endothelium-dependent vasodilatation and lipid concentrations.

Autoantibodies against oxidized LDL and endothelium-dependent vasodilation in insulin-dependent diabetes mellitus

We determined whether autoantibodies against oxidized LDL are increased in patients with IDDM, and if so, whether they are associated with endothelial dysfunction in vivo. Autoantibodies against oxidized LDL (ratio of antibodies against oxidized vs. native LDL, oxLDLab) were determined in 38 patients with IDDM (HbA(1c) 8.4+/-0.2%), who were clinically free of macrovascular disease, and 33 healthy normolipidemic subjects (HbA(1c) 5.1+/-0.1%, P<0.001 vs. IDDM). The groups had comparable serum total-, LDL- (2. 9+/-0.1 vs. 2.8+/-0.1 mmol/l, IDDM vs. controls), and HDL-cholesterol concentrations. OxLDLab were 1.5-fold higher in the IDDM patients (1.8+/-0.1) than in the normal subjects (1.2+/-0.1, P<0.001). OxLDLab were correlated with age in normal subjects, but not with age, duration of disease, LDL-cholesterol, HbA(1c) or degree of microvascular complications in patients with IDDM. To determine whether oxLDLab are associated with endothelial dysfunction in vivo, blood flow responses to intrabrachial infusions of acetylcholine, sodium nitroprusside and L-NMMA were determined in 23 of the patients with IDDM (age 33+/-1 years, body mass index 24. 3+/-0.6 kg/m(2), HbA(1c) 8.5+/-0.3%) and in the 33 matched normal males. OxLDLab were 41% increased in IDDM (1.7+/-0.2 vs. 1.2+/-0.1, P<0.01). Within the group of IDDM patients, HbA(1c) but not oxLDLab or LDL-cholesterol, was inversely correlated with the forearm blood flow response to acetylcholine (r=-0.51, P<0.02), an endothelium-dependent vasodilator, but not to sodium nitroprusside (r=0.06, NS). These data demonstrate that oxLDLab concentrations are increased in patients with IDDM, but show that chronic hyperglycemia rather than oxLDLab, is associated with impaired endothelium-dependent vasodilation in these patients.

Activation of the hexosamine pathway by glucosamine in vivo induces insulin resistance of early postreceptor insulin signaling events in skeletal muscle

To explore potential cellular mechanisms by which activation of the hexosamine pathway induces insulin resistance, we have evaluated insulin signaling in conscious fasted rats infused for 2-6 h with saline, insulin (18 mU x kg(-1) x min(-1)), or insulin and glucosamine (30 micromol x kg(-1) x min(-1)) under euglycemic conditions. Glucosamine infusion increased muscle UDP-N-acetylglucosamine concentrations 3.9- and 4.3-fold over saline- or insulin-infused animals, respectively (P < 0.001). Glucosamine induced significant insulin resistance to glucose uptake both at the level of the whole body and in rectus abdominis muscle, and it blunted the insulin-induced increase in muscle glycogen content. At a cellular level, these metabolic effects were paralleled by inhibition of postreceptor insulin signaling critical for glucose transport and glycogen storage, including a 45% reduction in insulin-stimulated insulin receptor substrate (IRS)-1 tyrosine phosphorylation (P = 0.02), a 44% decrease in IRS-1 association with the p85 regulatory subunit of phosphatidylinositol (PI) 3-kinase (P = 0.03), a 34% reduction in IRS-1-associated PI 3-kinase activity (P = 0.03), and a 51% reduction in insulin-stimulated glycogen synthase activity (P = 0.03). These alterations in postreceptor insulin signaling were time-dependent and paralleled closely the progressive inhibition of systemic glucose disposal from 2 to 6 h of glucosamine infusion. We also demonstrated that glucosamine infusion results in O-linked N-acetylglucosamine modification of IRS-1 and IRS-2. These data indicate that activation of the hexosamine pathway may directly modulate early postreceptor insulin signal transduction, perhaps via posttranslation modification of IRS proteins, and thus contribute to the insulin resistance induced by chronic hyperglycemia.

Glutamine: fructose-6-phosphate amidotransferase activity and gene expression are regulated in a tissue-specific fashion in pregnant rats

We examined whether regulation of glutamine: fructose-6-phosphate amidotransferase (GFA), the rate-limiting enzyme of the hexosamine pathway, is tissue specific and if so whether such regulation occurs at the level of gene expression. We compared GFA activity and expression and levels of UDP-hexosamines and UDP-hexoses between insulin-sensitive (liver and muscle) tissues and a glucose-sensitive (placenta) tissue from 19 day pregnant streptozotocin diabetic and non-diabetic rats. In pregnant non-diabetic rats GFA activities averaged (1521+/-75 pmol/mg protein x min) in the placenta, 895+/-74 in the liver and 81+/-11 in muscle (p<0.001 between each tissue). In the diabetic rats, GFA activities were approximately 50% decreased both in the liver (340+/-42 pmol/mg protein x min, p<0.05 vs control rats) and in skeletal muscle (46+/-3, p<0.05) compared to control rats. In the placenta, GFA activities were identical between diabetic (1519+/-112 pmol/mg protein x min) and non-diabetic (1521+/-75) animals. In the liver, the reduction in GFA activity could be attributed to a significant decrease in GFA mRNA concentrations, while GFA mRNA concentrations were similar in the placenta between diabetic and non-diabetic animals. UDP-N-acetylglucosamine (UDP-GlcNAc), the end product of the hexosamine pathway, was significantly reduced in the liver and in skeletal muscle but similar in the placenta between diabetic and non-diabetic rats. In summary, GFA activity and expression and the concentration of UDP-GlcNAc are decreased in the liver but unaltered in the placenta, although GFA activity is almost 2-fold higher in this tissue than in the liver. These data provide the first evidence for tissue specific regulation of GFA and for its regulation at the level of gene expression.

Allosteric regulation of glycogen synthase and hexokinase by glucosamine-6-phosphate during glucosamine-induced insulin resistance in skeletal muscle and heart

Glucosamine infusion induces insulin resistance in vivo, but the effect of glucosamine on intracellular metabolites of the hexosamine pathway, especially glucosamine-6-phosphate (GlcN6P) is unknown. Because of the structural similarity of glucose-6-phosphate (G-6-P) and GlcN6P, we hypothesized that accumulation of this metabolite might alter the activities of enzymes such as glycogen synthase and hexokinase. We infused glucosamine (30 micromol x kg(-1) x min(-1)) to induce insulin resistance in rats during a euglycemic-hyperinsulinemic clamp. Glucosamine induced whole-body insulin resistance, which was apparent after 90 min and continued progressively for 360 min. Despite inducing severe whole-body insulin resistance and decrease in glycogen synthase fractional activity in rectus abdominis muscle (69+/-3 vs. 83+/-1%, P<0.01) and heart (7+/-1 vs. 32+/-4%, P<0.001), glucosamine did not change the glycogen content in rectus and even increased it in the heart (209+/-13 vs. 117+/-9 mmol/kg dry wt, P<0.001). Glucosamine increased tissue concentrations of UDP-GlcNAc 4.4- and 4.6-fold in rectus abdominis and heart, respectively. However, GlcN6P concentrations increased 500- and 700-fold in glucosamine-infused animals in rectus abdominis (590+/-80 vs. 1.2+/-0.1 micromol/kg wet wt, P<0.001) and heart (7,703+/-993 vs. 11.2+/-2.3 micromol/kg wet wt, P<0.001). To assess the possible significance of GlcN6P accumulation, we measured the effect of GlcN6P on glycogen synthase and hexokinase activity in vitro. At the GlcN6P concentrations measured in rectus abdominis and heart in vivo, glycogen synthase was activated by 21 and 542%, while similar concentrations inhibited hexokinase activity by 5 and 46%, respectively. This study demonstrates that infusion of glucosamine during a euglycemic-hyperinsulinemic clamp results in marked accumulation of intracellular GlcN6P. The GlcN6P concentrations in the heart and rectus abdominis muscle reach levels sufficient to cause allosteric activation of glycogen synthase and inhibition of hexokinase.

Insulin and glucosamine infusions increase O-linked N-acetyl-glucosamine in skeletal muscle proteins in vivo

O-linked N-acetylglucosamine (O-GlcNAc) is an abundant posttranslational modification of serine/threonine residues of nuclear and cytoplasmic proteins. We determined whether insulin or coinfusion of glucosamine (GlcN) with insulin alters O-GlcNAc of skeletal muscle proteins. Three groups of conscious fasted rats received 6-hour infusions of either saline (BAS), insulin 18 mU/kg.min and saline (INS), or insulin and GlcN 30 micromol/kg.min (GLCN) during maintenance of normoglycemia. At 6 hours, the concentrations of muscle UDP-GlcNAc, UDP-N-acetylgalactosamine (UDP-GalNAc), UDP-glucose (UDP-Glc), UDP-galactose (UDP-Gal), glycogen, and N and O-linked GlcNAc (galactosyltransferase labeling followed by beta elimination) were measured in freeze-clamped abdominis muscle. Insulin increased whole-body glucose uptake from 49 +/- 5 to 239 +/- 8 micromol/kg.min (P < .001) and glycogen in abdominis muscle from 138 +/- 11 to 370 +/- 26 mmol/kg dry weight (P < .001). Insulin increased the amount of cytosolic N - and O-linked GlcNAc by 56% from 362 +/- 30 to 564 +/- 45 dpm/microg protein . 100 min (P < .02), and O-GlcNAc from 221 +/- 16 to 339 +/- 27 dpm/microg . 100 min (P < .02). Glycogen content was positively correlated with the amount of total (r = .90, P < .005) and O-linked GlcNAc in insulin-infused animals. Coinfusion of GlcN with insulin increased muscle UDP-GlcNAc about fourfold (100 +/- 6 nmol/g) compared with insulin (27 +/- 1, P < .001) or saline (25 +/- 1, P < .001) infusion. GlcN also decreased glucose uptake over 6 hours by 30% to 168 +/- 8 micromol/kg . min (P < .001 for GLCN v INS) and muscle glycogen to 292 +/- 24 mmol/kg dry weight (P < .05 for GLCN v INS). Both total (635 +/- 60 dpm/microg . 100 min, P < .002) and O-linked GlcNAc (375 +/- 36 dpm/microg . 100 min, P < .002) in the cytosol were significantly higher in GLCN rats (635 +/- 60 dpm/microg) versus BAS rats (P < .002). As in INS rats, muscle glycogen and O-GlcNAc were positively correlated in GLCN rats (r = .54, P < .05). Variation in total and O-linked GlcNAc in GLCN rats was due both to GlcN (P < .02) and to variation in the glycogen content (P < .005).

Incorporation of [3-3H]glucose and 2-[1-14C]deoxyglucose into glycogen in heart and skeletal muscle in vivo: implications for the quantitation of tissue glucose uptake

2-deoxyglucose has been widely used to quantitate tissue glucose uptake in vivo, assuming that 2-deoxyglucose is transported and phosphorylated but not further metabolized. We examined the validity of this assumption by infusing [3-3H]glucose and 2-[1-14C]deoxyglucose in a similar primed continuous fashion to chronically catheterized, freely moving rats during normoglycemic hyperinsulinemic conditions. The rates of 2-deoxyglucose uptake were determined from the accumulation of 2-[1-14C]deoxyglucose-6-phosphate and 2-[1-14C]deoxyglucose-6-phosphate combined with the rate of the incorporation of 2-[1-14C]deoxyglucose into glycogen in rectus abdominis muscle and the heart. When the rates of glycogen synthesis during the 2-h hyperinsulinemic period from the two tracers were compared in rectus abdominis muscle, the rate of glycogen synthesis was twofold higher when measured with [3-3H]glucose (337 +/- 14 micromol x kg(-1) x min(-1)) than when measured with 2-[1-14C]deoxyglucose (166 +/- 10 micromol x kg(-1) x min(-1), P < 0.001). In the heart, the rate of glycogen synthesis was twofold higher when measured with 2-[1-14C]deoxyglucose (141 +/- 20 micromol x kg(-1) x min(-1)) than when measured with [3-3H]glucose (72 +/- 15 micromol x kg(-1) x min(-1), P < 0.001). The rate of 2-deoxyglucose uptake was 29% underestimated in rectus abdominis muscle, when counts found in glycogen were not included in glucose uptake calculations (398 +/- 25 vs. 564 +/- 25 micromol x kg(-1) x min(-1), P < 0.001). In the heart, glucose uptake was underestimated by 7% if glycogen counts were not taken into account (1,786 +/- 278 vs. 1,926 +/- 291 micromol x kg(-1) dry x min(-1), P < 0.05). The fraction of [3-3H]glucose incorporated into glycogen of total glucose metabolism (calculated from 2-deoxyglucose conversion to 2-deoxyglucose-6-phosphate and glycogen) was 0.6 (337/564) in rectus abdominis muscle and 0.037 (72/1,926) in the heart. We conclude that 2-deoxyglucose is incorporated into glycogen in the heart and in skeletal muscle in vivo under normoglycemic hyperinsulinemic conditions in the rat. Failure to consider the incorporation of 2-deoxyglucose into glycogen will underestimate the rate of tissue glucose uptake. To avoid such problems, the amount of 2-deoxyglucose incorporated into glycogen should be quantitated in subsequent studies.

Activation of the hexosamine pathway by glucosamine in vivo induces insulin resistance in multiple insulin sensitive tissues

We determined the effect of infusion of glucosamine (GlcN), which bypasses the rate limiting reaction in the hexosamine pathway, on insulin-stimulated rates of glucose uptake and glycogen synthesis in vivo in rat tissues varying with respect to their glutamine:fructose-6-phosphate amidotransferase (GFA) activity. Three groups of conscious fasted rats received 6-h infusions of either saline (BAS), insulin (18 mU/kg x min) and saline (INS), or insulin and GlcN (30 micromol/ kg x min, GLCN). [3-(3)H]glucose was infused to trace whole body glucose kinetics and glycogen synthesis, and rates of tissue glucose uptake were determined using a bolus injection of [1-(14)C]2-deoxyglucose at 315 min. GlcN decreased insulin-stimulated glucose uptake (315-360 min) by 49% (P < 0.001) at the level of the whole body, and by 31-53% (P < 0.05 or less) in the heart, epididymal fat, submandibular gland and in soleus, abdominis and gastrocnemius muscles. GlcN completely abolished glycogen synthesis in the liver. GlcN decreased insulin-stimulated glucose uptake similarly in the submandibular gland (1.3 +/- 0.2 vs. 2.0 +/- 0.3 nmol/mg protein x min, GLCN vs. INS, P < 0.05) and gastrocnemius muscle (1.4 +/- 0.3 vs. 3.1 +/- 0.5 nmol/mg protein x min), although the activity of the hexosamine pathway, as judged from basal GFA activity, was 10-fold higher in the submandibular gland (286 +/- 35 pmol/mg protein x min) than in gastrocnemius muscle (27 +/- 3 pmol/mg protein x min, P < 0.001). These data raise the possibility that overactivity of the hexosamine pathway may contribute to glucose toxicity not only in skeletal muscle but also in other insulin sensitive tissues. They also imply that the magnitude of insulin resistance induced between tissues is determined by factors other than GFA.

Hyperreactivity to nitrovasodilators in forearm vasculature is related to autonomic dysfunction in insulin-dependent diabetes mellitus

BACKGROUND

The link between diabetes and vascular disease is poorly understood. Data regarding endothelial function in vivo in patients with insulin-dependent diabetes mellitus (IDDM) have been inconsistent with in vitro studies demonstrating hyperglycemia-induced impairments in endothelium-dependent vasodilation.

METHODS AND RESULTS

We determined whether alterations in neural control of the vascular tone might contribute to blood flow responses to intrabrachial infusions of acetylcholine (ACh), sodium nitroprusside (SNP), and L-N-monomethyl-arginine (L-NMMA) in 22 men with IDDM (12 with normoalbuminuria. HbA1c = 8.6 +/- 0.3%; 10 with macroalbuminuria, HbA1c = 8.6 +/- 0.3%) and 11 matched normal men. Autonomic function was assessed from reflex vasoconstriction to cold, the blood pressure response to standing and hand grip, and heart rate variation, including spectral analysis, during controlled breathing, and the Valsalva maneuver. IDDM with macroalbuminuria exhibited hyperresponsiveness to both ACh and SNP compared with the patients with normoalbuminuria or normal subjects. Reflex sympathetic vasoconstriction to cold was severely impaired in the IDDM patients with macroalbuminuria (-19 +/- 6%) compared with normoalbuminuric patients (-39 +/- 5%, P < .05) and normal subjects (-54 +/- 7%, P < .001). The macroalbuminuric patients also had evidence of autonomic dysfunction during controlled and deep breathing tests and during the Valsalva maneuver. Within the group of IDDM patients, neither the urinary albumin excretion rate nor other parameters such as HbA1c or serum cholesterol correlated with forearm blood flow during the vasoactive drug infusions. There were, however, significant inverse correlations between several measures of both sympathetic and parasympathetic autonomic functions and vascular hyperresponsiveness to SNP and ACh. For example, the Valsalva ratio was inversely correlated with the increase in blood flow in response to infusion of 3 (r = -.74, P < .001) and 10 (r = -.73, P < .001) micrograms/min SNP and 7.5 (r = -.73, P < .001) and 15 (r = -.75, P < .001) micrograms/min ACh.

CONCLUSIONS

These data are consistent with idea that altered neurotransmission is an important determinant of vascular reactivity of diabetic blood vessels to nitrovasodilators in vivo.

UDP-N-acetylglucosamine transferase and glutamine: fructose 6-phosphate amidotransferase activities in insulin-sensitive tissues

Glutamine:fructose 6-phosphate amidotransferase (GFA) is rate-limiting for hexosamine biosynthesis, while a UDP-GlcNAc beta-N-acetylglucosaminyltransferase (O-GlcNAc transferase) catalyses final O-linked attachment of GlcNAc to serine and threonine residues on intracellular proteins. Increased activity of the hexosamine pathway is a putative mediator of glucose-induced insulin resistance but the mechanisms are unclear. We determined whether O-GlcNAc transferase is found in insulin-sensitive tissues and compared its activity to that of GFA in rat tissues. We also determined whether non-insulin-dependent diabetes mellitus (NIDDM) or acute hyperinsulinaemia alters O-GlcNAc transferase activity in human skeletal muscle. O-GlcNAc transferase was measured using 3H-UDP-GlcNAc and a synthetic cationic peptide substrate containing serine and threonine residues, and GFA was determined by measuring a fluorescent derivative of GlcN6P by HPLC. O-GlcNAc transferase activities were 2-4 fold higher in skeletal muscles and the heart than in the liver, which had the lowest activity, while GFA activity was 14-36-fold higher in submandibular gland and 5-18 fold higher in the liver than in skeletal muscles or the heart. In patients with NIDDM (n = 11), basal O-GlcNAc transferase in skeletal muscle averaged 3.8 +/- 0.3 nmol/mg.min, which was not different from that in normal subjects (3.3 +/- 0.4 nmol/mg.min). A 180-min intravenous insulin infusion (40 mU/m2.min) did not change muscle O-GlcNAc transferase activity in either group. We conclude that O-GlcNAc transferase is widely distributed in insulin-sensitive tissues in the rat and is also found in human skeletal muscle. These findings suggest the possibility that O-linked glycosylation of intracellular proteins is involved in mediating glucose toxicity. O-GlcNAc transferase does not, however, appear to be regulated by either NIDDM or acute hyperinsulinaemia, suggesting that mass action effects determine the extent of O-linked glycosylation under hyperglycaemic conditions.

Physical fitness and endothelial function (nitric oxide synthesis) are independent determinants of insulin-stimulated blood flow in normal subjects

Insulin induces vasodilation via stimulation of nitric oxide (NO) synthesis. This action of insulin exhibits considerable interindividual variation. We determined whether the response of blood flow to endothelium-dependent vasoactive agents correlates with that to insulin or whether other factors, such as physical fitness, limb muscularity, or vasodilatory capacity, better explain variations in insulin-stimulated blood flow. Direct measurements of the forearm blood flow response to three 2-h sequential doses of insulin (1, 2, and 5 mU/ kg.min), endothelium-dependent (acetylcholine and NG-monomethyl-L-arginine) and endothelium-independent (sodium nitroprusside) vasoactive agents, and ischemia (reactive hyperemic forearm blood flow) were performed in 22 normal subjects (age, 24 +/- 1 yr; body mass index, 22.2 +/- 0.6 kg/m2; maximal aerobic power, 40 +/- 2 mL/kg.min). The highest insulin dose increased blood flow by 111 +/- 17%. The fraction of basal blood flow inhibited by NG-monomethyl-L-arginine (NO synthesis-dependent flow) varied from 6-47%. Maximal aerobic power (r = 0.52; P < 0.02), the percentage of forearm muscle (r = 0.50; P < 0.02), and the NO synthesis-dependent flow (r = 0.42; P < 0.05), but not reactive hyperemic, acetylcholine-stimulated, or sodium nitroprusside-stimulated flow, were significantly correlated with insulin-stimulated (5 mU/kg.min) blood flow. In multiple linear regression analysis, 52% of the variation (multiple R = 0.72; P < 0.001) in insulin-stimulated blood flow was explained by NO synthesis-dependent flow (P < 0.005) and the percentage of forearm muscle (P < 0.005). We conclude that endothelial function (NO synthesis-dependent basal blood flow) and forearm muscularity are independent determinants of insulin-stimulated blood flow.

Dissociation between insulin sensitivity of glucose uptake and endothelial function in normal subjects

Insulin increases limb blood flow in a time- and dose-dependent manner. This effect can be blocked by inhibiting nitric oxide synthesis. These data raise the possibility that insulin resistance is associated with endothelial dysfunction. To examine whether endothelial function and insulin sensitivity are interrelated we quantitated in vivo insulin-stimulated rates of whole body and forearm glucose uptake at a physiological insulin concentration (euglycaemic hyperinsulinaemic clamp, 1 mU.kg-1.min-1 insulin infusion for 2 h) and on another occasion, in vivo endothelial function (blood flow response to intrabrachial infusions of sodium nitroprusside, acetylcholine, and N-monomethyl-L-arginine) in 30 normal male subjects. Subjects were divided into an insulin-resistant (IR) and an insulin-sensitive (IS) group based on the median rate of whole body glucose uptake (31 +/- 2 vs 48 +/- 1 mumol.kg-1.min-1, p < 0.001). The IR and IS groups were matched for age, but the IR group had a slightly higher body mass index, percentage of body fat and blood pressure compared to the IS group. The IR group also had diminished insulin-stimulated glucose extraction (p < 0.05) compared to the IS group, while basal and insulin-stimulated forearm blood flow rates were identical. There was no difference between the IR and IS groups in the forearm blood flow response to endothelium-dependent (acetylcholine and N-monomethyl-L-arginine) or -independent (sodium nitroprusside) vasoactive drugs. In conclusion, the ability of insulin to stimulate glucose uptake at physiological insulin concentrations and endothelium-dependent vasodilatation are distinct phenomena and do not necessarily coexist.

Chronic hyperglycemia impairs endothelial function and insulin sensitivity via different mechanisms in insulin-dependent diabetes mellitus

BACKGROUND

We explored whether chronic hyperglycemia is associated with defects in endothelium-dependent vasodilatation in vivo and whether defects in the hemodynamic effects of insulin explain insulin resistance.

METHODS AND RESULTS

Vasodilator responses to brachial artery infusions of acetylcholine, sodium nitroprusside, and NG-monomethyl-L-arginine and, on another occasion, in vivo insulin sensitivity (euglycemic insulin clamp combined with the forearm catheterization technique) were determined in 18 patients with insulin-dependent diabetes mellitus (IDDM) and 9 normal subjects. At identical glucose and insulin levels, insulin stimulation of whole-body and forearm glucose uptake was 57% reduced in the IDDM patients compared with normal subjects (P < .001). The defect in forearm glucose uptake was attributable to a defect in glucose extraction (glucose AV difference, 1.1 +/- 0.2 versus 1.9 +/- 0.2 mmol/L, P < .001, IDDM versus normal subjects), not blood flow. Within the group of IDDM patients, hemoglobin A1c was inversely correlated with forearm blood flow during administration of acetylcholine (r = -.50, P < .02) but not sodium nitroprusside (r = .07). The ratio of endothelium-dependent to endothelium-independent blood flow was approximately 40% lower in patients with poor glycemic control than in normal subjects or patients with good or moderate glycemic control.

CONCLUSIONS

We conclude that chronic hyperglycemia is associated with impaired endothelium-dependent vasodilatation in vivo and with a glucose extraction defect during insulin stimulation. These data imply that chronic hyperglycemia impairs vascular function and insulin action via distinct mechanisms. The defect in endothelium-dependent vasodilatation could contribute to the increased cardiovascular risk in diabetes.

Increased glutamine:fructose-6-phosphate amidotransferase activity in skeletal muscle of patients with NIDDM

Overactivity of the hexosamine pathway mediates glucose-induced insulin resistance in rat adipocytes. Glutamine:fructose-6-phosphate amidotransferase (GFA) is the rate-limiting enzyme of this pathway. We determined GFA activity in human skeletal muscle biopsies and rates of insulin-stimulated whole-body, oxidative, and nonoxidative glucose disposal using the euglycemic insulin clamp technique combined with indirect calorimetry (insulin infusion rate (1.5 mU x kg-1 x min-1)) in 12 male patients with NIDDM (age 54 +/- 2 years, BMI 27.5 +/- 0.9 kg/m2, fasting plasma glucose 8.5 +/- 0.6 mmol/l) and 9 matched normal men. GFA activity was detectable in human skeletal muscles and completely inhibited by uridine-5'-diphospho-N-acetylglucosamine (UDP-GlcNAc) in all subjects. GFA activity was 46% increased in the NIDDM patients compared with the normal subjects (9.5 +/- 1.3 vs. 6.5 +/- 1.2 pmol, P < 0.05). Whole-body glucose uptake was 58% decreased in patients with NIDDM (20 +/- 3 micromol x kg body wt-1 x min-1) compared with normal subjects (47 +/- 4 micromol x kg body wt-1 x min-1, P < 0.001). This decrease was attributable to decreases in both glucose oxidation (9 +/- 1 vs. 15 +/- 1 micromol x kg-1 x min-1, NIDDM patients vs. control subjects, P < 0.002) and nonoxidative glucose disposal (11 +/- 2 vs. 31 +/- 4 micromol x kg-1 x min-1, P < 0.001). In patients with NIDDM, both HbA1c (r= 0.51, P < 0.05) and BMI (r= -0.57, P < 0.05) correlated with whole-body glucose uptake. HbA1c but not BMI or insulin sensitivity was correlated with basal GFA activity (r = -0.57,P < 0.01) in NIDDM patients and control subjects. We conclude that GFA is found in human skeletal muscle and that all this activity is sensitive to feedback inhibition by UDP-GlcNAc. Chronic hyperglycemia is associated with an increase in skeletal muscle GFA activity, suggesting that increased activity of the hexosamine pathway may contribute to glucose toxicity and insulin resistance in humans.

Insulin resistance in type I diabetes mellitus: a major role for reduced glucose extraction

We determined whether insulin resistance in Type I diabetes is caused by a defect in glucose extraction or blood flow and whether it is the rate of glucose metabolism rather than insulin that increases blood flow in these patients. To make this determination, 9 Type I diabetic patients (age 33 +/- 3 yr, body mass index 24 +/- 1 kg/m2, HbA1c 8.3 +/- 0.1%) and 10 matched normal subjects were first studied under normoglycemic hyperinsulinemic conditions. The diabetic patients were then restudied under similar conditions, but now whole body glucose uptake was normalized by glucose mass-action (glucose 8.7 +/- 0.6 mmol/L). During normoglycemia, rates of whole body (46 +/- 2 vs. 66 +/- 3 mumol/kg.min, P < 0.001) and forearm (47 +/- 9 vs. 78 +/- 7 mumol/kg forearm.min, P < 0.05) glucose uptake were decreased in the diabetic patients, because of a 32% decrease in the glucose AV-difference (1.5 +/- 0.2 vs. 2.2 +/- 0.2 mmol/L, P < 0.05). Forearm blood flow was similar in the diabetic patients (3.6 +/- 0.7 mL/dl.min) and normal subjects (3.7 +/- 0.3 mL/dL.min). During matched rates of whole body glucose uptake (68 +/- 1 vs. 66 +/- 3 mumol/kg.min, normoglycemic study in controls vs. hyperglycemic study in the diabetic patients), the glucose AV-difference across the forearm was 64% higher than during normoglycemia (2.4 +/- 0.3 vs. 1.5 +/- 0.2 mmol/L, P < 0.05). Forearm blood flow (3.6 +/- 0.4 mL/dL.min) under conditions of matched glucose flux was similar to that during the normoglycemic study. We conclude that a defect in glucose extraction rather than blood flow characterizes insulin resistance in uncomplicated Type I diabetes. The signal for the flow increase is insulin and not the rate of glucose metabolism.

Role of prostaglandins in mediating alterations in glucose metabolism during acute endotoxemia in the rat

We determined the role of prostanoids in mediating alterations in glucose metabolism during lipopolysaccharide (LPS)-induced (1 mg/kg; LD10) acute endotoxemia in chronically catheterized awake rats. Basal glucose turnover (Rt, infusion of [5-3H]glucose), in vivo insulin action on overall glucose utilization under normoglycemic conditions (euglycemic clamp), whole body glycolysis, and muscle glycogen synthesis were determined in four groups of rats. These groups received 1) LPS (LPS rats, n = 6); 2) saline (control rats, n = 6); 3) indomethacin and LPS (INDO and LPS rats, n = 6); or 4) saline and indomethacin (INDO control rats, n = 6). In the fasted rats, LPS induced hyperthermia, hypotension, and hyperglycemia. These changes were associated with glycogen depletion in both skeletal muscle and liver and with increased Rt. During hyperinsulinemia, whole body glucose disposal was decreased by 37% due to decreased muscle glycogen synthesis and glycogen synthase activity whereas the rate of whole body glycolysis was normal. INDO abolished hyperthermia, hypotension, and hyperglycemia but did not improve whole body insulin sensitivity, muscle glycogen synthesis, or glycogen synthase activity. These data indicate that prostanoids mediate hypotension, transient fasting hyperglycemia, and fever during LPS-induced acute endotoxemia. They do not, however, explain insulin resistance under these conditions.

Occurrence and biological properties of a common genetic variant of luteinizing hormone

We have characterized the frequency and selected biological properties of a variant form of LH caused by two point mutations in the gene of the LH beta-subunit. Detection of the LH variant (or polymorphism) is based on aberrant immunoreactivity; it is not detected by a monoclonal antibody (Mab) recognizing a specific epitope in the LH alpha/beta-dimer (assay 1), but an assay using two LH beta-specific Mab recognizes this LH form normally (assay 2). Hence, the ratio of LH measured by assays 1 and 2 is 1.18-2.10 (range of mean +/- 2 SD) in wild-type subjects, 0.54-0.98 in heterozygotes, and below 0.15 in homozygotes with regard to the mutant LH beta allele. Analysis of sera from 249 healthy male and female subjects of Finnish origin revealed a frequency of 24.1% heterozygotes and 3.6% homozygotes for the mutation, with similar proportions in each sex. The ratio of in vitro bioactivity to immunoreactivity (assay 2) of the variant LH was significantly (P < 0.01) increased (2.9 +/- 0.1; n = 11) compared to that of wild-type LH (2.2 +/- 0.1; n = 13). No difference was observed in LH pulsatility, measured from blood samples collected at 5-min intervals for 5 h, between three male and three female subjects homozygous for the LH variant and three matched male and three female controls with wild-type LH. Likewise, the responses of LH immunoreactivity (assay 2) to GnRH stimulation were similar with both types of LH. The half-time of the variant LH in rat circulation from both sexes was significantly shorter than that of LH from control subjects (males, 25.5 +/- 3.8 vs. 48.3 +/- 2.7 min, respectively; P < 0.01; n = 3). Upon isoelectric focusing of peripheral serum samples, the isoform distribution of the variant LH was similar to that of wild-type LH. In conclusion, the LH variant discovered by us appears to occur with high frequency in the Finnish population (28% homo- or heterozygotes). It has increased in vitro bioactivity and a decreased half-time in vivo. These differences are compatible with a putative extra carbohydrate chain in the LH beta-chain, as one of the two mutations introduces an extra glycosylation signal. The subjects homozygous for the LH polymorphism are apparently healthy. However, the altered bioactivity and in vivo kinetics of the LH variant may induce subtle changes in LH action, either predisposing the affected individuals to or protecting them from disease conditions related to LH action.

Mechanisms of insulin resistance during acute endotoxemia

We characterized the mechanisms underlying acute endotoxin-induced alterations in glucose metabolism and determined the extent to which catecholamines mediate these changes. Acute endotoxemia was induced in chronically catheterized awake rats by a bolus injection of lipopolysaccharide (LPS; 1 mg/kg; LD10). Basal glucose turnover (Rt; infusion of [5-3H]glucose), in vivo insulin action on overall glucose utilization (euglycemic clamp), glycolysis, and glycogen synthesis were determined in four groups of rats. These groups received 1) LPS (LPS rats; n = 6), 2) saline (control rats; n = 6), 3) LPS and alpha beta-blockade (alpha beta-blockade and LPS rats; n = 9), or 4) saline and alpha beta-blockade (alpha beta-blockade control rats; n = 9). In the basal state, LPS induced hypotension and transient hyperglycemia. These changes were associated with glycogen depletion in both skeletal muscle and liver, and increased Rt. During hyperinsulinemia, whole body glucose disposal was 37% decreased (105 vs. 166 mumol/kg.min; P < 0.01). This whole body insulin resistance was characterized by decreased glycogen synthesis and glycogen synthase activity, but not by altered whole body glycolysis. alpha beta-Blockade abolished transient hyperglycemia, increased Rt, and accelerated basal liver glycogen depletion (45 vs. 105 mmol/kg dry, LPS and alpha beta-blockade rats vs. LPS rats; P < 0.05), but inhibited muscle glycogenolysis. alpha beta-Blockade did not reverse the insulin resistance induced by endotoxin. These data suggest that catecholamines counteract the LPS-induced increase in basal glucose turnover and stimulate muscle glycogenolysis during acute endotoxemia. These effects might explain the better preservation of hepatic glycogen in the absence than in the presence of alpha beta-blockade and serve as a defense mechanism against hypoglycemia. Catecholamines do not seem to be the immediate causes of insulin resistance during acute endotoxemia.

Ethanol stimulates glycogenolysis in livers from fed rats

To determine the reason for the lack of a hypoglycemic effect of ethanol in the fed state, the effect of ethanol on glucose turnover, liver glycogenolysis, and glucose metabolites was determined. Chronically catheterized awake and freely moving fed rats received either ethanol (blood ethanol, 37 +/- 10 mmol/liter, n = 11) or saline (n = 13) intravenously for 4 hr. Glucose turnover was determined using a primed continuous infusion of [3-3H]glucose. The liver was freeze clamped at 4 hr for glycogen and metabolite measurements. Plasma glucose (5.8 +/- 0.3 mmol/liter vs 6.3 +/- 0.2 mmol/liter at 4 hr, ethanol versus saline) and the rate of glucose turnover (61 +/- 9 vs 58 +/- 8 moles/kg.min) were similar during the ethanol and saline infusions. Plasma lactate was significantly higher in the ethanol (1.32 +/- 0.05 mmol/liter) than in the saline (0.86 +/- 0.06 mmol/liter, P less than 0.001) study. Concentrations of gluconeogenic intermediates in the liver (glucose 6-phosphate, fructose 6-phosphate, glucose 1-phosphate, and pyruvate) were all significantly and -30% lower in ethanol-infused than in saline-infused rats. The liver citrate content was similar in ethanol-infused than in saline-infused rats. The liver citrate content was similar in ethanol (0.38 +/- 0.03 mmol/liter) and saline (0.37 +/- 0.04 mmol/liter) studies. Liver glycogen was 75% lower in the ethanol-infused (61 +/- 9 mmol/kg dry wt) than the saline (242 +/- 27 mmol/kg dry wt, P less than 0.001)-infused rats. These data demonstrate that in fed rats given ethanol, glucose turnover is maintained constant by accelerated glycogenolysis. Thus, inhibition of gluconeogenesis by ethanol does not lower hepatic glucose production unless compensatory glycogenolysis can be prevented.

Mechanisms of hepatic and peripheral insulin resistance during acute infections in humans

To examine mechanisms of insulin resistance, nine patients (age 33 +/- 4 yr, body mass index 22 +/- 1 kg/m2) with acute bacterial or viral infections and in six matched normal subjects were studied. Endogenous glucose appearance (Ra), glucose disappearance (Rd), and recycling, the percentage of plasma lactate originating from plasma glucose, total glucose oxidation, and whole body and forearm muscle Rd were measured after an overnight fast in the basal state and during physiological hyperinsulinemia (serum insulin approximately 215 pmol/L). Basally Ra, Rd, glucose recycling, and oxidation were similar in both groups. During hyperinsulinemia, insulin stimulated plasma Rd approximately 35% less (17.6 +/- 1.3 vs. 26.8 +/- 3.6 mumol/kg.min, P less than 0.01, patients vs. normal subjects), and inhibited endogenous Ra less in the patients (from 13.3 +/- 0.8 to 5.3 +/- 0.8 mumol/kg.min) than in the normal subjects (from 12.8 +/- 1.0 to 2.1 +/- 1.2 mumol/kg.min, P less than 0.01). The decrease in whole body Rd was largely explained by a approximately 75% reduction in muscle Rd (5.6 +/- 1.5 vs. 20.8 +/- 3.3 mumol/kg muscle.min, P less than 0.01, patients vs. normal subjects). The defect in Rd was confined to nonoxidative (4.8 +/- 1.1 vs. 11.0 +/- 3.0 mumol/kg.min, P less than 0.01, patients vs. normal subjects) but not to oxidative glucose metabolism. The percentage of plasma lactate derived from plasma glucose during hyperinsulinemia averaged 63 +/- 6% in the patients and 79 +/- 5% in the normal subjects, indicating that glycogenolysis did not excessively dilute glycolytic carbons in the patients. We conclude that during natural infections in humans, abnormal glucose metabolism is confined to the insulin-stimulated state and involves a marked defect in muscle glucose uptake and glycogen synthesis, as well as a less marked hepatic defect.

Measurement of lactate formation from glucose using [6-3H]- and [6-14C]glucose in humans

To assess the validity of determining the origin of plasma lactate from the ratio of lactate and glucose specific activities (SA) during infusion of labeled glucose, normal subjects received infusions of [6-3H]- and [6-14C]glucose for 4 h after a 12 h fast, and, on another day, cold glucose labeled with both tracers during 4-6 h of hyperinsulinemia (approximately 650 microU/ml). Basally, less lactate was derived from plasma glucose when measured with [6-3H]glucose (27 +/- 2%) than with [6-14C]glucose (40 +/- 2%, P less than 0.001). Insulin did not increase the percent of lactate derived from plasma glucose when measured with [6-3H]glucose (29 +/- 2%) but did increase when measured with [6-14C]glucose (60 +/- 4%). The arterialized blood (A) [3H]lactate SA was 30-40% higher (P less than 0.01) than deep venous blood (V) [3H]lactate SA, whereas A and V [14C]lactate SA were similar. During conversion of alanine to lactate with glutamic-pyruvic transaminase (GPT) and lactate dehydrogenase (LDH) in vitro, 32 +/- 2% of 3H in [3-3H]alanine was found in water and 68 +/- 2% in lactate. During infusion of [6-3H]- and [6-14C]glucose, the ratio of [14C]alanine to lactate SA (0.88 +/- 0.05) was less than the ratio of [3H]alanine to lactate SA (0.31 +/- 0.03, P less than 0.001). In conclusion 1) loss of 3H relative to 14C from position 6 in glucose occurs during lactate formation in extrahepatic tissues possibly due to the GPT reaction (alanine conversion to pyruvate), and 2) even under supraphysiologic hyperinsulinemic conditions not all of plasma lactate originates from plasma glucose.

No evidence for isotope discrimination of tritiated glucose tracers in measurements of glucose turnover rates in man

Under non-steady-state conditions, glucose turnover rates determined with tritiated glucose tracers are often underestimated. To examine whether isotope discrimination or a tracer contaminant can contribute to this, we compared the turnover rates of unlabelled and tritiated glucose under isotopic steady-state conditions. The turnover rates were measured in 20 healthy subjects at two insulin concentrations (79 +/- 3 mU.l-1 and 704 +/- 62 mU.l-1). Euglycaemia was maintained by infusing unlabelled glucose mixed with (3(3)H)- or (6(3)H)-glucose. In both studies, the isotopically determined glucose disposal rate was virtually identical to the exogenous glucose infusion rate (low insulin 7.66 +/- 0.48 vs 7.58 +/- 0.44 mg.kg-1.min-1, high insulin 13.36 +/- 0.74 vs 13.55 +/- 0.98 mg.kg-1.min-1). The individual values were correlated in both the low (r = 0.85, p less than 0.001) and high dose insulin (r = 0.81, p less than 0.001) studies. Tritiated glucose specific activities were also compared in arterialized and deep venous blood across forearm tissues during the high-dose insulin infusion. Glucose specific activities were similar in arterialized and deep venous blood when analysed with HPLC and conventional methods. In summary: (1) Under isotopic steady-state conditions the turnover rates of unlabelled and labelled glucoses are similar. (2) Unlabelled and labelled glucose are handled identically across forearm tissues. (3) We found no tracer impurity in our tritiated glucose preparations. We conclude that (3(3)H)- and (6(3)H)-glucose tracers can be used to reliably measure glucose turnover rates in man.

Carbodiimide as a tissue fixative in histamine immunohistochemistry and its application in developmental neurobiology

The object of this study was to develop an immunohistochemical method that could be used to study neuronal histamine, especially in nerve fibers and terminals where most previous methods have not been applicable. Three new antisera were produced in rabbits against conjugated histamine, and the fixative used in conjugation, 1-ethyl-3(3-diamethylaminopropyl)-carbodiimide (EDCDI), was used in tissue fixation and compared to paraformaldehyde. Specificity of the antisera was established with dot-blot tests on nitrocellulose, with blocking controls and affinity-purified antibodies. EDCDI appeared to be superior to paraformaldehyde as a fixative, and histamine-immunoreactive nerve cells were visualized in developing rat brain during late fetal development from embryonal day 12. By the second postnatal week, the distribution of histamine-immunoreactive neurons in rat brain had reached the adult pattern and immunoreactive nerve fibers were seen in many areas. Posterior hypothalamic neurons from newborn rat in vitro showed strong immunoreactivity for histamine and developed long varicose fibers, which covered the culture dish by the end of the fourth week in vitro. Fixation with EDCDI also allowed detection of histamine in gastric enterochromaffin-like cells and mast cells in rat. The results suggest that the histamine-containing neuron system in rat brain develops during the late fetal and early postnatal periods, and that immunoreactive neurons develop long fibers both in vivo and in vitro.