Serum saturated fatty acids containing triacylglycerols are better markers of insulin resistance than total serum triacylglycerol concentrations.

AIMS/HYPOTHESIS: The weak relationship between insulin resistance and total serum triacylglycerols (TGs) could be in part due to heterogeneity of TG molecules and their distribution within different lipoproteins. We determined concentrations of individual TGs and the fatty acid composition of serum and major lipoprotein particles and analysed how changes in different TGs and fatty acid composition are related to features of insulin resistance and abdominal obesity. METHODS: We performed lipidomic analyses of all major lipoprotein fractions using two analytical platforms in 16 individuals, who exhibited a broad range of insulin sensitivity. RESULTS: We identified 45 different TGs in serum. Serum TGs containing saturated and monounsaturated fatty acids were positively, while TGs containing essential linoleic acid (18:2 n-6) were negatively correlated with HOMA-IR. Specific serum TGs that correlated positively with HOMA-IR were also significantly positively related to HOMA-IR when measured in very-low-density lipoproteins (VLDLs), intermediate-density lipoproteins (IDLs) and LDL, but not in HDL subfraction 2 (HDL(2)) or 3 (HDL(3)). Analyses of proportions of esterified fatty acids within lipoproteins revealed that palmitic acid (16:0) was positively related to HOMA-IR when measured in VLDL, IDL and LDL, but not in HDL(2) or HDL(3). Monounsaturated palmitoleic (16:1 n-7) and oleic (18:1 n-9) acids were positively related to HOMA-IR when measured in HDL(2) and HDL(3), but not in VLDL, IDL or LDL. Linoleic acid was negatively related to HOMA-IR in all lipoproteins. CONCLUSIONS/INTERPRETATION: Serum concentrations of specific TGs, such as TG(16:0/16:0/18:1) or TG(16:0/18:1/18:0), may be more precise markers of insulin resistance than total serum TG concentrations.

A common variant in PNPLA3, which encodes adiponutrin, is associated with liver fat content in humans.

AIMS/HYPOTHESIS: It has recently been suggested that the rs738409 G allele in PNPLA3, which encodes adiponutrin, is strongly associated with increased liver fat content in three different ethnic groups. The aims of the present study were as follows: (1) to try to replicate these findings in European individuals with quantitative measures of hepatic fat content; (2) to study whether the polymorphism influences hepatic and adipose tissue insulin sensitivity; and (3) to investigate whether PNPLA3 expression is altered in the human fatty liver. METHODS: We genotyped 291 Finnish individuals in whom liver fat had been measured using proton magnetic resonance spectroscopy. Hepatic PNPLA3 expression was measured in 32 participants. Hepatic and adipose tissue insulin sensitivities were measured using a euglycaemic-hyperinsulinaemic (insulin infusion 0.3 mU kg(-1) min(-1)) clamp technique combined with infusion of [3-(3)H]glucose in 109 participants. RESULTS: The rs738409 G allele in PNPLA3 was associated with increased quantitative measures of liver fat content (p = 0.011) and serum aspartate aminotransferase concentrations (p = 0.002) independently of age, sex and BMI. Fasting serum insulin and hepatic and adipose tissue insulin sensitivity were related to liver fat content independently of genotype status. PNPLA3 mRNA expression in the liver was positively related to obesity (r = 0.62, p < 0.0001) and to liver fat content (r = 0.58, p = 0.025) in participants who were not morbidly obese (BMI < 40 kg/m(2)). CONCLUSIONS/INTERPRETATION: A common variant in PNPLA3 increases the risk of hepatic steatosis in humans.

Acute suppression of VLDL1 secretion rate by insulin is associated with hepatic fat content and insulin resistance.

AIMS/HYPOTHESIS: Overproduction of VLDL(1) seems to be the central pathophysiological feature of the dyslipidaemia associated with type 2 diabetes. We explored the relationship between liver fat and suppression of VLDL(1) production by insulin in participants with a broad range of liver fat content. METHODS: A multicompartmental model was used to determine the kinetic parameters of apolipoprotein B and TG in VLDL(1) and VLDL(2) after a bolus of [(2)H(3)]leucine and [(2)H(5)]glycerol during a hyperinsulinaemic-euglycaemic clamp in 20 male participants: eight with type 2 diabetes and 12 control volunteers. The participants were divided into two groups with low or high liver fat. All participants with diabetes were in the high liver-fat group. RESULTS: The results showed a rapid drop in VLDL(1)-apolipoprotein B and -triacylglycerol secretion in participants with low liver fat during the insulin infusion. In contrast, participants with high liver fat showed no significant change in VLDL(1) secretion. The VLDL(1) suppression following insulin infusion correlated with the suppression of NEFA, and the ability of insulin to suppress the plasma NEFA was impaired in participants with high liver fat. A novel finding was an inverse response between VLDL(1) and VLDL(2) secretion in participants with low liver fat: VLDL(1) secretion decreased acutely after insulin infusion whereas VLDL(2) secretion increased. CONCLUSIONS/INTERPRETATION: Insulin downregulates VLDL(1) secretion and increases VLDL(2) secretion in participants with low liver fat but fails to suppress VLDL(1) secretion in participants with high liver fat, resulting in overproduction of VLDL(1). Thus, liver fat is associated with lack of VLDL(1) suppression in response to insulin.

Increased expression of the macrophage markers and of 11beta-HSD-1 in subcutaneous adipose tissue, but not in cultured monocyte-derived macrophages, is associated with liver fat in human obesity.

OBJECTIVE: To determine whether increased expression of macrophage markers and of inflammatory markers in subcutaneous adipose tissue is associated with liver fat in human obesity. We also determined whether expression of TNF (gene encoding TNF-alpha), HSD11B1 (gene encoding 11beta-HSD-1) and RETN (gene encoding resistin) in cultured monocyte-derived macrophages differs between obese/overweight and non-obese subjects. DESIGN: Cross-sectional comparison of obese/overweight and non-obese subjects with respect to adipose tissue gene expression, gene expression in monocyte-derived macrophages, liver fat content and in vivo insulin sensitivity. SUBJECTS: Adipose tissue gene expression, gene expression in monocyte-derived macrophages, liver fat content and in vivo insulin sensitivity: 10 healthy non-obese (24.2+/-1.0 kg/m(2)) and 10 healthy obese/overweight (33.1+/-1.7 kg/m(2)) women. Gene expression in monocyte-derived macrophages: seven healthy non-obese (22.1+/-0.7 kg/m(2)) and seven healthy obese/overweight (36.9+/-2.2 kg/m(2)) women. MEASUREMENTS: Adipose tissue biopsies and blood samples for isolation of peripheral mononuclear cells were taken after an overnight fast. Liver fat content was measured using magnetic resonance proton spectroscopy. Whole body insulin sensitivity was measured using the hyperinsulinemic euglycemic clamp technique. Expression levels of TNF, HSD11B1, RETN and the macrophage markers CD68 and ITGAM were determined by real-time PCR. RESULTS: In adipose tissue, expression of HSD11B1, ITGAM and CD68 was significantly increased in the obese/overweight as compared to the non-obese group. Expression of all these genes was closely positively correlated with liver fat content and inversely correlated with whole body insulin sensitivity. The associations between expression of CD68, ITGAM and HSD11B1 and liver fat were independent of obesity. There were no differences in TNF, HSD11B1, RETN or CD68 gene expression basally or after stimulation with lipopolysaccharide in monocyte-derived macrophages between obese/overweight and non-obese subjects. CONCLUSION: Accumulation of fat in the liver is associated with increased adipose tissue inflammation independent of obesity.

Overproduction of large VLDL particles is driven by increased liver fat content in man.

AIMS/HYPOTHESIS: We determined whether hepatic fat content and plasma adiponectin concentration regulate VLDL(1) production. METHODS: A multicompartment model was used to simultaneously determine the kinetic parameters of triglycerides (TGs) and apolipoprotein B (ApoB) in VLDL(1) and VLDL(2) after a bolus of [(2)H(3)]leucine and [(2)H(5)]glycerol in ten men with type 2 diabetes and in 18 non-diabetic men. Liver fat content was determined by proton spectroscopy and intra-abdominal fat content by MRI. RESULTS: Univariate regression analysis showed that liver fat content, intra-abdominal fat volume, plasma glucose, insulin and HOMA-IR (homeostasis model assessment of insulin resistance) correlated with VLDL(1) TG and ApoB production. However, only liver fat and plasma glucose were significant in multiple regression models, emphasising the critical role of substrate fluxes and lipid availability in the liver as the driving force for overproduction of VLDL(1) in subjects with type 2 diabetes. Despite negative correlations with fasting TG levels, liver fat content, and VLDL(1) TG and ApoB pool sizes, adiponectin was not linked to VLDL(1) TG or ApoB production and thus was not a predictor of VLDL(1) production. However, adiponectin correlated negatively with the removal rates of VLDL(1) TG and ApoB. CONCLUSIONS/INTERPRETATION: We propose that the metabolic effect of insulin resistance, partly mediated by depressed plasma adiponectin levels, increases fatty acid flux from adipose tissue to the liver and induces the accumulation of fat in the liver. Elevated plasma glucose can further increase hepatic fat content through multiple pathways, resulting in overproduction of VLDL(1) particles and leading to the characteristic dyslipidaemia associated with type 2 diabetes.

Acute in vivo effects of insulin on gene expression in adipose tissue in insulin-resistant and insulin-sensitive subjects.

AIMS/HYPOTHESIS: We determined the response of selected genes to in vivo insulin in adipose tissue in 21 non-diabetic women. MATERIALS AND METHODS: The women were divided into insulin-sensitive and -resistant groups based on their median whole-body insulin sensitivity (8.7+/-0.4 vs 4.2+/-0.3 mg kg(-1) min(-1) for insulin-sensitive vs -resistant group). Subcutaneous adipose tissue biopsies were obtained before and after 3 and 6 h of i.v. maintained euglycaemic hyperinsulinaemia. Adipose tissue mRNA concentrations of facilitated glucose transporter, member 1 (SLC2A1, previously known as GLUT1), facilitated glucose transporter, member 4 (SLC2A4, previously known as GLUT4), peroxisome proliferator-activated receptor gamma ( PPARG), peroxisome proliferator-activated receptor gamma co-activator 1alpha (PPARGC1A), 11beta-hydroxysteroid dehydrogenase-1 (HSD11B1), TNF, adiponectin (ADIPOQ), IL6 and the macrophage marker CD68 were measured using real-time PCR. RESULTS: Basal expression of 'insulin-sensitivity genes' SLC2A4 and ADIPOQ was lower while that of 'insulin-resistance genes', HSD11B1 and IL6 was significantly higher in the insulin-resistant than in the insulin-sensitive group. Insulin significantly increased expression of 'insulin-sensitivity genes' SLC2A4, PPARG, PPARGC1A and ADIPOQ in the insulin-sensitive group, while only expression of PPARG and PPARGC1A was increased in the insulin-resistant group. The expression of 'insulin-resistance genes' HSD11B1 and IL6 was increased by insulin in the insulin-resistant group, but insulin failed to increase HSD11B1 expression in the insulin-sensitive group. At 6 h, expression of HSD11B1, TNF and IL6 was significantly higher in the insulin-resistant than in the insulin-sensitive group. IL6 expression increased significantly more in response to insulin in the insulin-resistant than in the insulin-sensitive group. CD68 was overexpressed in the insulin-resistant as compared with the insulin-sensitive group at both 0 and 6 h. CONCLUSIONS/INTERPRETATION: These data suggest that genes adversely affecting insulin sensitivity hyperrespond to insulin, while genes enhancing insulin sensitivity hyporespond to insulin in insulin-resistant human adipose tissue in vivo.

Increased augmentation of central blood pressure is associated with increases in carotid intima-media thickness in type 2 diabetic patients.

AIMS/HYPOTHESIS: Type 2 diabetes is associated with a two- to seven-fold increase in cardiovascular morbidity and mortality. The aim of this study was to determine the relationships between intima-media thickness (IMT), an established marker of atherosclerosis, large artery function and other determinants of cardiovascular risk in type 2 diabetic patients. METHODS: We studied 228 type 2 diabetic patients (75 women, aged 62+/-2 years [mean+/-SEM]). Carotid IMT was bilaterally measured using ultrasound technology. Applanation tonometry and pulse wave analysis were used to measure aortic systolic and diastolic blood pressures, central pressure augmentation (AG) and the augmentation index (AIx), a measure of systemic arterial stiffness. Conventional cardiovascular risk factors (lipids, HbA(1)c, smoking and diabetes duration) were also assessed. RESULTS: Women had higher AG and AIx (p<0.0001), despite comparable systolic BP and heart rate in women and men. In women, AG (r=0.39, p<0.001), age (r=0.32, p<0.01), brachial systolic BP (r=0.34, p<0.01) and aortic systolic BP (r=0.34, p<0.01) correlated with IMT. In men, age (r=0.41, p<0.001), diabetes duration (r=0.25, p<0.01), AG (r=0.22, p<0.01), aortic systolic BP (r=0.21, p<0.01), brachial systolic BP (r=0.21, p<0.01) and body weight (r=0.16, p<0.05) correlated with IMT. In multiple linear regression analyses, AG and aortic systolic BP, but not brachial systolic BP, were age-independent determinants of IMT in men and women. In all patients, increased AG (adjusted for sex, age and heart rate) correlated with longer duration of diabetes, urinary albumin excretion and IMT. CONCLUSIONS/INTERPRETATION: Measures of central systolic pressure correlate with carotid IMT, independently of age and other risk markers.

The fatty liver and insulin resistance.

Obesity is not necessary to observe insulin resistance in humans since severe insulin resistance also characterizes patients lacking subcutaneous fat such as those with HAART (highly-active antiretroviral therapy) - associated lipodystrophy. Both the obese and the lipodystrophic patients have, however, an increase in the amount of fat hidden in the liver. Liver fat content can be non-invasively accurately quantified by proton magnetic resonance spectroscopy. It is closely correlated with fasting insulin and direct measures of hepatic insulin sensitivity while the amount of subcutaneous adipose tissue is not. The causes of interindividual variation in liver fat content independent of obesity are largely unknown but could involve differences in signals from adipose tissue such as in the amount of adiponectin produced and differences in fat intake. Adiponectin deficiency characterizes both lipodystrophic and obese insulin resistant individuals, and serum levels correlate with liver fat content. Liver fat content can be decreased by weight loss. In addition, treatment of both lipodystrophic and type 2 diabetic patients with PPARgamma agonists but not metformin decreases liver fat and increases adiponectin levels. Markers of liver fat such as serum alanine aminotransferase activity have been shown to predict type 2 diabetes in several studies independent of obesity. The fatty liver thus may help to explain why some but not all obese individuals are insulin resistant and why even lean individuals may be insulin resistant, and thereby at risk of developing type 2 diabetes and cardiovascular disease.

Women and men have similar amounts of liver and intra-abdominal fat, despite more subcutaneous fat in women: implications for sex differences in markers of cardiovascular risk.

AIMS/HYPOTHESIS: Fat accumulation in the liver has been shown to be closely correlated with hepatic insulin resistance and features of insulin resistance, also independently of body weight. It remains to be established how fat in the liver correlates with that in other depots, and whether any association differs between men and women. METHODS: Liver fat (assessed using proton spectroscopy), intra-abdominal and subcutaneous fat (measured using magnetic resonance imaging) and markers of insulin resistance, including serum adiponectin, were determined in 132 non-diabetic subjects: 66 men (age 41+/-1 years) and 66 women (age 42+/-1 years). RESULTS: Although the women had almost twice as much subcutaneous fat as the men (5045+/-207 vs 2610+/-144 cm3, p<0.0001), amounts of intra-abdominal fat (1305+/-80 vs 1552+/-111 cm3, NS) and liver fat (6.7+/-0.8 vs 8.9+/-1.2%, NS) were similar. In this study, no sex differences were observed with respect to serum insulin, adiponectin, triglyceride and HDL cholesterol concentrations. Of all measures of body composition, liver fat was best correlated with serum insulin (r=0.58, p<0.001), with no difference observed between men and women. Serum adiponectin was inversely correlated with liver fat content (r=-0.21, p<0.05). Multiple linear regression analysis revealed that intra-abdominal fat was significantly associated with liver fat, independently of serum adiponectin and subcutaneous fat. Liver fat, but not intra-abdominal fat, significantly explained the variation in serum insulin concentrations. CONCLUSIONS/INTERPRETATION: Intra-abdominal fat is independently associated with liver fat, whereas subcutaneous fat is not. Liver fat, but not intra-abdominal fat, is independently associated with serum insulin. Men and women with similar amounts of intra-abdominal and liver fat do not exhibit sex differences in markers of insulin resistance (serum insulin, triglycerides, HDL cholesterol and adiponectin).

Low-grade inflammation, endothelial activation and carotid intima-media thickness in type 2 diabetes.

OBJECTIVES: The objective of this study was to assess the relationship between inflammation, endothelial activation and incipient atherosclerosis in type 2 diabetes. DESIGN: Cross-sectional study. Setting and subjects. We studied 239 type 2 diabetic patients [71 with clinical cardiovascular disease (CVD)] and 78 healthy control subjects, aged 50-75 in a single research centre. METHODS: Carotid intima-media thickness (IMT) was determined by ultrasound. Circulating intracellular adhesion molecule-1, vascular cell adhesion molecule-1, E-selectin, ultra-sensitive C-reactive protein, human serum amyloid A, interleukin-6, monocyte colony-stimulating factor, secretory nonpancreatic phospholipase A(2) type IIA, glucose, HbA1c, and lipid/lipoprotein variables were measured. RESULTS: Carotid IMT was significantly thicker in diabetic patients than healthy controls across the whole age range. IMT was also thicker in diabetic patients with, than without, CVD, but this difference disappeared after controlling for confounding factors. Concentrations of the inflammatory and endothelial markers except IL-6 were significantly higher in the diabetic patients than in healthy controls, but comparable in diabetic patients with and without CVD. The main determinants of IMT in the diabetic patients were blood pressure, age and diabetes duration. CONCLUSIONS: Low-grade inflammation and endothelial activation are increased in diabetic patients but do not associate with IMT or clinical CVD. The inflammatory reaction seems to be rather a feature of the metabolic syndrome than a direct determinant of atherosclerosis.

Comparison of in vivo effects of nitroglycerin and insulin on the aortic pressure waveform.

BACKGROUND: Individuals whose platelets are resistant to the antiaggregatory effects of insulin in vitro are also resistant to the antiaggregatory effects of nitroglycerin (GTN). We have previously shown that insulin acutely diminishes central wave reflection in large arteries and that this action of insulin is blunted in insulin-resistant subjects. However, as yet, no studies have compared the haemodynamic effects of insulin and GTN on large arterial function in the same group of subjects. The aim of this study was to determine whether resistance to the haemodynamic effects of insulin is a defect specific to insulin or whether individuals resistant to the vascular actions of insulin are also resistant to GTN. DESIGN AND RESULTS: Dose-response characteristics of insulin and GTN on the aortic waveform were determined using applanation tonometry and pulse wave analysis (PWA) in seven healthy men (age 26 +/- 1 year, BMI 25 +/- 2 kg m(-2)). Three doses of sublingual GTN (500 microg for 1, 3 or 5 min) and insulin (0.5, 1 or 2 mU kg(-1) min(-1) for 120 min) were administered on three separate occasions. Both agents dose-dependently decreased central pulse pressure and the augmentation index (AIx) without changing brachial artery blood pressure. We next compared responses to insulin (2 mU kg(-1) min(-1) for 120 min) and sublingual GTN (500 microg for 5 min) in 20 nondiabetic subjects (age 50 +/- 2 year, BMI 21.0-36.3 kg m(-2)). Again, both agents significantly decreased AIx. Although the vascular effects of insulin and GTN vascular were positively correlated [Spearman's r=0.92 (95% confidence interval 0.81-0.97), P<0.0001], the time-course for the action GTN was faster than that of insulin. Brachial systolic blood pressure remained unchanged during the insulin infusion (122 +/- 3 vs. 121 +/- 3 mmHg, 0 vs. 120 min) but aortic systolic blood pressure decreased significantly by 30 min (111 +/- 3 vs. 107 +/- 3 mmHg, 0 vs. 30 min, P<0.01). Similarly, GTN decreased aortic systolic blood pressure from 119 +/- 4 to maximally 112 +/- 3 mmHg (P<0.001) without significantly decreasing systolic blood pressure in the brachial artery. CONCLUSIONS: The effects of insulin and GTN on large arterial haemodynamics are dose-dependent and significantly correlated. The exact mechanisms and sites of action of insulin and GTN in subjects with insulin resistance remain to be established.

Insulin therapy improves insulin actions on glucose metabolism and aortic wave reflection in type 2 diabetic patients.

BACKGROUND: Normal insulin action in vivo involves a decrease in aortic systolic blood pressure as a result of an insulin-induced decrease in the amplitude of the second systolic (reflected) pressure wave. This action of insulin and insulin action on glucose metabolism is impaired in insulin-resistant and type 2 diabetic subjects. We determined whether 6 months of insulin therapy affects insulin actions on glucose metabolism and vascular function. MATERIALS AND METHODS: Thirteen type 2 diabetic patients (age 53 +/- 2 years, body mass index 30.8 +/- 1.2 kg m(-2), HbA1C 8.8 +/- 0.2%) were studied before and after insulin therapy. Central aortic pressure waveforms were reconstructed from those recorded in the periphery using applanation tonometry every 30 min. This allowed determination of augmentation, i.e. the pressure difference between the second and first systolic pressure peaks and the augmentation index (AgI, augmentation divided by pulse pressure). The measurements were performed basally and during euglycaemic hyperinsulinaemic conditions. RESULTS: Insulin therapy increased whole body glucose disposal by 35% from 5.1 +/- 0.7 to 6.8 +/- 0.6 mg kg ffm(-1) min(-1) (P<0.001 for 0 vs. 60 months). 6 months of insulin therapy decreased basal AgI from 26.2 +/- 1.8 to 22.7 +/- 2.3% (P<0.05). The change in AgI by insulin infusion was similar before and after insulin therapy at all time points. Peripheral blood flow, heart rate and blood pressures remained unchanged. CONCLUSIONS: Insulin therapy improves insulin action on glucose metabolism and decreases basal AgI. These data support the idea that insulin therapy has beneficial effects on vascular function.

Obesity is associated with impaired platelet-inhibitory effect of acetylsalicylic acid in nondiabetic subjects.

OBJECTIVE: Platelet aggregation responses to acetylsalicylic acid (ASA) show considerable interindividual variation, the causes of which are largely unknown. We determined whether variation in insulin action is associated with that of ASA on platelets. SUBJECTS: In all, 10 nonobese (age 50+/-3 y, BMI 25+/-1 kg/m(2)) and 11 obese (age 52+/-2 y, BMI 32+/-1 kg/m(2)) subjects. MEASUREMENTS: Insulin sensitivity of glucose uptake was determined by the euglycemic insulin clamp technique. Platelet aggregation responses to four doses of arachidonic acid (AA) and adenosine diphosphate (ADP) were assessed in platelet-rich plasma before and 1 h after ingestion of 50 mg ASA using Born's turbidometric aggregometer. RESULTS: Whole-body insulin sensitivity (M-value 0-180 min) was 36% lower in the obese (4.5+/-0.6) than the nonobese (7.1+/-0.6 mg/kg min, P<0.01) group. Before ASA, all doses of AA induced complete aggregation. After ASA ingestion, ASA inhibited maximal aggregation more in the nonobese than the obese group at AA concentrations of 0.75, 1 and 1.5 mmol/l (P=0.016 for ANOVA). ADP-induced aggregation at high doses (2 and 3 micromol/l) was also less inhibited in the obese group. In vivo insulin sensitivity (r=-0.68, P<0.001 for 1 mmol/l AA) and BMI (r=0.58, P<0.01 for 1 mmol/l AA) were closely correlated with residual aggregation after ASA administration. CONCLUSION: These data demonstrate that obese insulin-resistant subjects have a blunted response to platelet-inhibitory effect of ASA. If this blunted effect is of a single dose of ASA preserved in continuous use, it could contribute to the increased risk of atherothrombosis in insulin-resistant individuals.

Low HDL cholesterol concentration is associated with increased intima-media thickness independent of arterial stiffness in healthy subjects from families with low HDL cholesterol.

BACKGROUND: Low high-density lipoprotein cholesterol (HDL-C) is associated with increased risk for developing coronary artery disease. Cardiovascular disease is characterized by increased intima-media thickness (IMT) and arterial stiffness, but the effect of low HDL on these measurements has not been reported. MATERIALS AND METHODS: We studied 18 apparently healthy subjects from families with low HDL-C and 18 control subjects, which were pair-matched to maximize statistical power. Intima-media thickness was assessed using ultrasound examination of the carotid arteries. Arterial stiffness was measured using applanation tonometry on the radial artery and pulse-wave analysis to obtain central aortic pulse-pressure waveform, from which the augmentation index, a measure of global large artery stiffness, was calculated. RESULTS: Low HDL subjects (age 41 +/- 3 years, BMI 26.6 +/- 1.0 kg m(-2) had significantly lower HDL-C than the control subjects (age 41 +/- 3 years, BMI 26.5 +/- 1.0 kg m-2; 1.00 +/- 0.05 vs. 1.49 +/- 0.09 mmol L-1, low HDL vs. control subjects, P < 0.0001). Subjects with low HDL-C had significantly thicker mean IMTs than the control subjects (0.77 +/- 0.03 vs. 0.70 +/- 0.02 mm, low HDL vs. control subjects, P < 0.01). The maximal (0.99 +/- 0.04 vs. 0.89 +/- 0.03 mm, P < 0.01), far wall (0.76 +/- 0.04 vs. 0.69 +/- 0.02 mm, P < 0.05) and carotid bulb (1.11 +/- 0.06 vs. 0.97 +/- 0.04 mm) IMTs were also significantly increased, whereas the mean common carotid and the internal artery IMT were not. The age-related increase in mean IMT was more pronounced in the low HDL subjects than the control subjects (P < 0.01 for difference between elevations of age vs. IMT slopes). There were no differences in central pressure augmentation, the augmentation index, peripheral or central blood pressures between the groups. CONCLUSIONS: A low HDL-C concentration is associated with thickening of carotid IMT independent of other risk factors in healthy affected members of low HDL families.

Resistance to acute insulin induced decreases in large artery stiffness accompanies the insulin resistance syndrome.

Arterial stiffness has recently been recognized as an important cardiovascular risk marker. Physiological concentrations of insulin diminish wave reflection in the aorta in vivo. This decreases central blood pressure augmentation and augmentation divided by pulse pressure [the augmentation index (AgI)], a measure of arterial stiffness. In the present study, we examined whether a defect in this action of insulin is a feature of insulin resistance and how it relates to other acute actions of insulin, including stimulation of glucose uptake, peripheral blood flow, and autonomic control of heart rate variation. These actions of insulin were quantitated in 50 healthy men (age, 34 +/- 2 yr; body mass index, 27 +/- 1 kg/m2) during 2 sequential insulin infusions, each lasting 120 min (1 and 2 mU/kg x min). Insulin decreased AgI significantly within 30 min, whereas significant increases in peripheral blood flow and normalized low frequency power of heart rate variation, a measure of sympathetic control of heart rate variation, were observed at 150 and 210 min. A blunted decrease in the AgI was significantly associated with a low rate of insulin-stimulated glucose uptake, but not with the other actions of insulin. Insulin action of the AgI was correlated with body mass index and the waist to hip ratio independently of basal AgI, age, and low density lipoprotein cholesterol. We conclude that physiological concentrations of insulin diminish large artery stiffness within 30 min in nondiabetic men. This action precedes insulin action on peripheral vasodilation, heart rate, and autonomic control of heart rate variation. It is correlated with insulin stimulation of glucose uptake and is blunted by known causes of insulin resistance, including overall and abdominal obesity. Resistance of large arteries to insulin-induced decrease in their stiffness is therefore another facet of insulin resistance that could contribute to the association between insulin resistance and cardiovascular disease.

Insulin sensitivity regulates autonomic control of heart rate variation independent of body weight in normal subjects.

It is unclear whether insulin sensitivity independent of body weight regulates control of heart rate variation (HRV) by the autonomic nervous system. Insulin action on whole-body glucose uptake (M-value) and heart rate variability were measured in 21 normal men. The subjects were divided into 2 groups [normally insulin sensitive (IS, 8.0 +/- 0.4 mg/kg.min) and less insulin sensitive (IR, 5.1 +/- 0.3 mg/kg.min)] based on their median M-value (6.2 mg/kg x min). Spectral power analysis of heart rate variability was performed in the basal state and every 30 min during the insulin infusion. The IS and IR groups were comparable, with respect to age (27 +/- 2 vs. 26 +/- 2 yr), body mass index (22 +/- 1 vs. 23 +/- 1 kg/m(2)), body fat (13 +/- 1 vs. 13 +/- 1%), systolic (121 +/- 16 vs. 117 +/- 14 mm Hg) and diastolic (74 +/- 11 vs. 73 +/- 11 mm Hg) blood pressures, and fasting plasma glucose (5.4 +/- 0.1 vs. 5.5 +/- 0.1 mmol/L) concentrations. Fasting plasma insulin was significantly higher in the IR (30 +/- 4 pmol/L) than in the IS (17 +/- 3 pmol/L, P < 0.05) group. In the IS group, insulin significantly increased the normalized low-frequency (LFn) component, a measure of predominantly sympathetic nervous system activity, from 36 +/- 5 to 48 +/- 4 normalized units (nu; 0 vs. 30-120 min, P < 0.001); whereas the normalized high-frequency (HFn) component, a measure of vagal control of HRV, decreased from 66 +/- 9 to 48 +/- 5 nu (P < 0.001). No changes were observed in either the normalized LF component [35 +/- 5 vs. 36 +/- 2 nu, not significant (NS)] or the normalized HF component (52 +/- 6 vs. 51 +/- 4 nu, NS) in the IR group. The ratio LF/HF, a measure of sympathovagal balance, increased significantly in the IS group (0.92 +/- 0.04 vs. 1.01 +/- 0.04, P < 0.01) but remained unchanged in the IR group (0.91 +/- 0.04 vs. 0.92 +/- 0.03, NS). Heart rate and systolic and diastolic blood pressures remained unchanged during the insulin infusion in both groups. We conclude that insulin acutely shifts sympathovagal control of HRV toward sympathetic dominance in insulin-sensitive, but not in resistant, subjects. These data suggest that sympathetic overactivity is not a consequence of hyperinsulinemia.

Vascular actions of insulin in obesity.

An increased prevalence and incidence of cardiovascular disease is the most important clinical consequence of abdominal obesity. Although defects in glucose handling in skeletal muscle have been extensively investigated, they have failed to clarify why insulin resistance is linked to vascular disease. Non-classic actions of insulin such as those on haemodynamics, nerve function and haemostasis and on lipoprotein metabolism would appear of greater interest in this respect. It is now clear that obese individuals exhibit resistance to some of the non-classic effects of insulin. These include resistance to insulin action on large vessel compliance, nitric oxide-dependent stimulation of vasodilation in resistance vessels, activation of the sympathetic nervous system by insulin but not other stimuli, platelet anti-aggregation and suppression of hepatic very low density lipoprotein production. The exact cause(s) of resistance to these non-classic insulin actions are unclear but their understanding would seem important to understand the links between obesity and cardiovascular disease.

Hepatic fat content and insulin action on free fatty acids and glucose metabolism rather than insulin absorption are associated with insulin requirements during insulin therapy in type 2 diabetic patients.

To determine causes of interindividual variation in insulin requirements, we recruited 20 type 2 diabetic patients with stable glucose control and insulin doses for >1 year on combination therapy with bedtime NPH insulin and metformin. Insulin absorption (increase in free and total insulin over 8 h after a subcutaneous dose of regular insulin) and actions of intravenous (6-h 0.3 mU x kg(-1) x min(-1) euglycemic insulin clamp combined with [3-3H]glucose) and subcutaneous (glucose infusion rate required to maintain isoglycemia and suppression of free fatty acids [FFAs]) insulin, liver fat content (proton spectroscopy), visceral fat (magnetic resonance imaging), weight, and body composition were determined. We found the following variation in parameters: insulin dose range 10-176 U (mean 42 U, fold variation 17.6x) or 0.13-1.39 U/kg (0.44 U/kg, 10.7x), absorbed insulin 10.6x, action of subcutaneous insulin to suppress FFAs 7.5 x and to stimulate glucose metabolism (M value) 11.5x, body weight 67-127 kg (91 kg, 1.9x), liver fat 2-28% (12%, 14x), and visceral fat 179-2,053 ml (1,114 ml, 11.5x). The amount of insulin absorbed, measured as either free or total insulin, was significantly correlated with its ability to suppress FFAs and stimulate glucose metabolism but not with the insulin dose per se. The actions of absorbed insulin were, on the other hand, significantly correlated with the daily insulin dose (r = 0.70 for action on FFAs, P < 0.001, and r = -0.61 for M value, P < 0.005). Actions of subcutaneous and intravenous insulin to suppress FFAs were significantly correlated (r = 0.82, P < 0.001, R2 = 67%). Of the measures of adiposity, the percent hepatic fat was the parameter best correlated with the daily insulin dose (r = 0.76, P < 0.001). The percent hepatic fat was also significantly correlated with the ability of intravenous insulin to suppress endogenous glucose production (r = 0.72, P < 0.005). We conclude that the major reason for interindividual variation in insulin requirements in type 2 diabetes is the variation in insulin action. Variation in hepatic fat content may influence insulin requirements via an effect on the sensitivity of endogenous glucose production to insulin.

Insulin-induced decrease in large artery stiffness is impaired in uncomplicated type 1 diabetes mellitus.

Normal insulin action in vivo involves a decrease in stiffness of large arteries (a decrease in aortic pressure augmentation). We determined whether the ability of insulin to decrease arterial stiffness is altered in uncomplicated type 1 diabetes. Nine type 1 diabetic men (age 28+/-2 years, body mass index 24+/-1 kg/m(2)) and 9 matched normal men were studied under normoglycemic hyperinsulinemic (sequential 2-hour insulin infusions of 1 [step 1] and 2 [step 2] mU x kg(-1) x min(-1)) conditions. Central aortic pressure waveforms were synthesized from those recorded in periphery with applanation tonometry on the radial artery and a validated reverse transfer function to construct the central aortic pressure wave every 30 minutes. This allowed the determination of aortic augmentation (the pressure difference between the first and the second systolic peaks) and the augmentation index (augmentation divided by pulse pressure), as the measure of stiffness of large arteries. Whole-body glucose uptake was 44% (step 1) and 37% (step 2) lower (P<0.001) in the diabetic patients than in the normal subjects. At baseline, before the insulin infusion, augmentation averaged 0+/-1 and 2+/-1 mm Hg (NS) and the augmentation index was -1.5+/-4.5% and 4.0+/-3.7% (NS) in the normal and diabetic subjects, respectively. After 1 hour of hyperinsulinemia, the augmentation index had decreased significantly (P<0.01) to -9.5+/-4.8% in the normal subjects but remained at 4.4+/-4.2% in the diabetic patients. A significant decrease was not observed in the diabetic patients until 150 minutes (-1.2+/-4.1%, P<0.05 versus baseline). Whole-body glucose uptake was significantly inversely correlated with the change in the augmentation index during step 1 (r=-0.61, P<0.01). Insulin resistance in type 1 diabetes involves a defect in the ability of insulin to decrease central aortic pressure. This defect could predispose these patients to premature stiffening of large arteries.

Insulin therapy improves endothelial function in type 2 diabetes.

A total of 75 in vivo endothelial function tests (intrabrachial artery infusions of endothelium-dependent [acetylcholine] and -independent [sodium nitroprusside] vasoactive agents) were performed in 18 type 2 diabetic patients (aged 58+/-2 years, body mass index 28.5+/-0.6 kg/m(2), and fasting plasma glucose 229+/-11 mg/dL) and 27 matched normal subjects. These tests were performed before and 6 months after combination therapy with insulin and metformin and before and 6 months after metformin therapy only. Before insulin therapy, blood flow responses to acetylcholine (15 microg/min) were significantly blunted in type 2 diabetic patients (7.5+/-0.7 mL x dL(-1) x min(-1)) compared with normal subjects (11.6+/-0.9 mL x dL(-1) x min(-1), P<0.01). During insulin therapy, the acetylcholine response increased by 44% to 10.8+/-1.6 mL x dL(-1) x min(-1) (P<0.05). Insulin therapy also significantly increased the blood flow responses to both low and high doses of sodium nitroprusside. We conclude that insulin therapy improves endothelium-dependent and -independent vasodilatation. These data support the idea that insulin therapy has beneficial rather than harmful effects on vascular function.