Insulin and the vasculature

The genetic causal relationship between type 2 diabetes, glycemic traits and venous thromboembolism, deep vein thrombosis, pulmonary embolism: a two-sample Mendelian randomization study

OBJECTIVE

To investigate the genetic underpinnings of the association between type 2 diabetes (T2D), glycemic indicators such as fasting glucose (FG), fasting insulin (FI), and glycated hemoglobin (GH), and venous thromboembolism (VTE), encompassing deep vein thrombosis (DVT) and pulmonary embolism (PE), thereby contributing novel insights to the scholarly discourse within this domain.

METHODS

Genome-wide association study (GWAS) summary data pertaining to exposures (T2D, FG, FI, GH) and outcomes (VTE, DVT, PE) were acquired from the IEU Open GWAS database, encompassing participants of European descent, including both male and female individuals. Two-sample Mendelian randomization (MR) analyses were conducted utilizing the TwoSampleMR and MRPRESSO packages within the R programming environment. The primary analytical approach employed was the random-effects inverse variance weighted (IVW) method. Heterogeneity was assessed via Cochran's Q statistic for MR-IVW and Rucker's Q statistic for MR-Egger. Horizontal pleiotropy was evaluated using the intercept test of MR Egger and MR pleiotropy residual sum and outlier (MR-PRESSO) analysis, with the latter also employed for outlier detection. Additionally, a "Leave one out" analysis was conducted to ascertain the influence of individual single nucleotide polymorphisms (SNPs) on MR results.

RESULTS

The random-effects IVW analysis revealed a negative genetic causal association between T2D) and VTE (P = 0.008, Odds Ratio [OR] 95% confidence interval [CI] = 0.896 [0.827-0.972]), as well as between FG and VTE (P = 0.002, OR 95% CI = 0.655 [0.503-0.853]), GH and VTE (P = 0.010, OR 95% CI = 0.604 [0.412-0.884]), and GH and DVT (P = 0.002, OR 95% CI = 0.413 [0.235-0.725]). Conversely, the random-effects IVW analysis did not detect a genetic causal relationship between FI and VTE (P > 0.05), nor between T2D, FG, or FI and DVT (P > 0.05), or between T2D, FG, FI, or GH and PE (P > 0.05). Both the Cochran's Q statistic for MR-IVW and Rucker's Q statistic for MR-Egger indicated no significant heterogeneity (P > 0.05). Moreover, the intercept tests of MR Egger and MR-PRESSO suggested the absence of horizontal pleiotropy (P > 0.05). MR-PRESSO analysis identified no outliers, while the "Leave one out" analysis underscored that the MR analysis was not influenced by any single SNP.

CONCLUSION

Our investigation revealed that T2D, FG, and GH exhibit negative genetic causal relationships with VTE at the genetic level, while GH demonstrates a negative genetic causal relationship with DVT at the genetic level. These findings furnish genetic-level evidence warranting further examination of VTE, DVT, and PE, thereby making a contribution to the advancement of related research domains.

Skipping breakfast does not accelerate the hyperglycemia-induced endothelial dysfunction but reduces blood flow of the brachial artery in young men

PURPOSE

Postprandial hyperglycemia is assumed to have a negative impact on flow-mediated dilation (FMD), an index of endothelial function, and blood flow of the peripheral conduit arteries. This study aimed to determine whether the enhancement of postprandial hyperglycemia by skipping breakfast accelerates endothelial dysfunction and reduces the blood flow in the brachial artery in young men.

METHODS

Using a randomized cross-over design, ten healthy men completed two trials: with and without breakfast (Eating and Fasting trials, respectively). Venous blood sampling and brachial FMD tests were conducted before, 30, 60, 90, and 120 min after a 75-g oral glucose tolerance test (OGTT).

RESULTS

Skipping breakfast boosted post-OGTT glucose levels than having breakfast (P = 0.01). The magnitude of the decrease in FMD via OGTT did not vary between trials (main effect of trial P = 0.55). Although brachial blood flow tended to decrease after OGTT in both trials (interaction and main effect of time P = 0.61 and P = 0.054, respectively), the decrease in blood flow following OGTT was greater in the Fasting trial than in the Eating trial (main effect of trial, mean difference =  - 15.8 mL/min [95%CI =  - 25.6 to - 6.0 mL/min], P < 0.01).

CONCLUSION

Skipping breakfast did not enhance the magnitude of the decrease in FMD following glucose loading, but did accelerate hyperglycemia-induced reduction in brachial blood flow. Current findings suggest that even missing one breakfast has negative impacts on the blood flow regulation of the peripheral conduit arteries in young men who habitually eat breakfast.

Relationship Between the Lipid Accumulation Product Index and Arterial Stiffness in the Chinese Population With Hypertension: A Report From the China H-Type Hypertension Registry Study

Background

Lipid accumulation product (LAP) index, as a new index to predict cardiovascular disease (CVD), has attracted the attention of many researchers. The relation of the LAP index with brachial-ankle pulse wave velocity (baPWV) has been evaluated in several previous studies and yielded inconsistent results. This study aimed to investigate the association between the LAP index and arterial stiffness in the Chinese population with hypertension.

Methods

We conducted a cross-sectional analysis in 4,926 Chinese population with hypertension (aged 64.42 ± 9.44 years). The LAP index was developed from population-based frequency plots of adult waist circumferences and circulating triglyceride concentrations according to men and women. Arterial stiffness was determined by measuring baPWV.

Results

The multivariate linear regression analyses showed that the LAP index was independently and positively associated with baPWV [beta coefficients (β), 24.10 cm/s; 95% CI: 5.72, 42.49 cm/s]. Consistently, the multivariate logistic regression analyses showed a positive association between the LAP index risk of elevated baPWV (>75th percentile) [odds ratio (OR), 1.19; 95% CI 1.01, 1.41]. A restricted cubic spline showed that a significant linear association existed between the LAP index and baPWV. In different subgroups of diastolic blood pressure (DBP), there is interaction between the LAP index and baPWV (DBP <90, 90–99, ≥100 mm Hg; p-interaction = 0.006).

Conclusion

LAP is significantly positively associated with baPWV and elevated baPWV in Chinese hypertensive adults and especially among participants with DBP ≤ 99 mm Hg.

Insulin: The Friend and the Foe in the Development of Type 2 Diabetes Mellitus

Insulin, a hormone produced by pancreatic β-cells, has a primary function of maintaining glucose homeostasis. Deficiencies in β-cell insulin secretion result in the development of type 1 and type 2 diabetes, metabolic disorders characterized by high levels of blood glucose. Type 2 diabetes mellitus (T2DM) is characterized by the presence of peripheral insulin resistance in tissues such as skeletal muscle, adipose tissue and liver and develops when β-cells fail to compensate for the peripheral insulin resistance. Insulin resistance triggers a rise in insulin demand and leads to β-cell compensation by increasing both β-cell mass and insulin secretion and leads to the development of hyperinsulinemia. In a vicious cycle, hyperinsulinemia exacerbates the metabolic dysregulations that lead to β-cell failure and the development of T2DM. Insulin and IGF-1 signaling pathways play critical roles in maintaining the differentiated phenotype of β-cells. The autocrine actions of secreted insulin on β-cells is still controversial; work by us and others has shown positive and negative actions by insulin on β-cells. We discuss findings that support the concept of an autocrine action of secreted insulin on β-cells. The hypothesis of whether, during the development of T2DM, secreted insulin initially acts as a friend and contributes to β-cell compensation and then, at a later stage, becomes a foe and contributes to β-cell decompensation will be discussed.

Alteration of Pressure-Induced Vasodilation in Aging and Diabetes, a Neuro-Vascular Damage

Skin is constantly subjected to pressure at different levels. Pressure-induced vasodilation (PIV) is one of the response mechanisms to low pressure that maintains the homeostasis of the skin. PIV results from the interaction of primary afferent nerves and vascular endothelium of skin vessels. Thanks to this cutaneous neuro-vascular interaction, the cutaneous blood flow increase allows the maintenance of an optimal level of oxygenation and minimizes the lack of vascularization of the skin tissue under low pressure. It seems to be associated with the cutaneous protection mechanisms to prevent pressure ulcers. In some contexts, where microangiopathy and neuropathy can occur, such as aging and diabetes, PIV is impaired, leading to a dramatic early decrease in local skin blood flow when low pressure is applied. In aging, PIV alteration is due to endothelial dysfunction, essentially from an alteration of the nitric oxide pathway. In the inflamm-aging context, oxidative stress increases leading to endothelial cell and nerve damages. An age-related sensory neuropathy will exacerbate the alteration of PIV during the aging process. In diabetes, non-controlled hyperglycaemia leads to an increase in several pathological biochemical pathways that involve oxidative stress and can affect PIV. Sorbinil, alagebrium and alpha-lipoic acid are able individually to restore PIV through a possible oxidative stress reduction. Candesartan, an angiotensin II type 1 receptor blocker, is also able to restore PIV and prevent pressure ulcer formation. The possibility of preventing pressure ulcer associated to diabetes and/or aging with the restoration of PIV seems to be a promising research path.

Five-year weight changes associate with blood pressure alterations independent of changes in serum insulin

OBJECTIVE

In overweight-related hypertension, the effect of weight changes on blood pressure (BP) is believed to be mediated by insulin. To test this hypothesis, we studied 5-year changes in weight, BP, and insulin in a general population of Danish adults (n = 3443; mean age 45.7 ± 7.6 years).

METHODS

We assessed the glucose-insulin metabolism by a standard oral glucose tolerance test. We divided the antihypertensive and antidiabetic medication-free participants into three groups: weight loss (n = 515), weight stable (n = 1778), and weight gain (n = 1150).

RESULTS

Losing on average 6.5 kg body weight, the weight loss group experienced a 28.2% reduction [(95% confidence interval [CI] -31 to -25); P < 0.001] in fasting insulin and a 23.9% reduction [(95% CI -28 to -19); P < 0.001] in 2-h insulin. Gaining on average 6.4 kg, the weight gain group experienced a 12.5% increase [(95% CI 9 to 16); P < 0.001] in fasting insulin and 32.8% increase [(95% CI 28 to 38); P < 0.001] in 2-h insulin. Using linear regression adjusting for differences in sex, age, family history of hypertension, baseline BMI, SBP and DBP, lifestyle risk factors, and their 5-year changes, weight loss was associated with a decrease in SBP of -1.8 mmHg (95% CI -2.8 to -0.7), whereas weight gain with an increase in SBP of 1.9 mmHg (95% CI 1.2 to 2.6), both with P less than 0.001. Adding fasting insulin, 2-h insulin, Δfasting insulin, and Δ2-h insulin only marginally attenuated the association, and furthermore, none of the insulin variables was significantly associated with SBP or DBP (P ≥ 0.08). The results for changes in DBP were similar to SBP.

CONCLUSION

Five-year weight changes associate with BP alterations independent of the insulin changes.

Differential associations of oral glucose tolerance test-derived measures of insulin sensitivity and pancreatic β-cell function with coronary artery calcification and microalbuminuria in type 2 diabetes

OBJECTIVE We evaluated relationships of oral glucose tolerance testing (OGTT)-derived measures of insulin sensitivity and pancreatic β-cell function with indices of diabetes complications in a cross-sectional study of patients with type 2 diabetes who are free of overt cardiovascular or renal disease. RESEARCH DESIGN AND METHODS A subset of participants from the Penn Diabetes Heart Study (n = 672; mean age 59 ± 8 years; 67% male; 60% Caucasian) underwent a standard 2-h, 75-g OGTT. Insulin sensitivity was estimated using the Matsuda Insulin Sensitivity Index (ISI), and β-cell function was estimated using the Insulinogenic Index. Multivariable modeling was used to analyze associations between quartiles of each index with coronary artery calcification (CAC) and microalbuminuria. RESULTS The Insulinogenic Index and Matsuda ISI had distinct associations with cardiometabolic risk factors. The top quartile of the Matsuda ISI had a negative association with CAC that remained significant after adjusting for traditional cardiovascular risk factors (Tobit ratio -0.78 [95% CI -1.51 to -0.05]; P = 0.035), but the Insulinogenic Index was not associated with CAC. Conversely, the highest quartile of the Insulinogenic Index, but not the Matsuda ISI, was associated with lower odds of microalbuminuria (OR 0.52 [95% CI 0.30-0.91]; P = 0.022); however, this association was attenuated in models that included duration of diabetes. CONCLUSIONS Lower β-cell function is associated with microalbuminuria, a microvascular complication, while impaired insulin sensitivity is associated with higher CAC, a predictor of macrovascular complications. Despite these pathophysiological insights, the Matsuda ISI and Insulinogenic Index are unlikely to be translated into clinical use in type 2 diabetes beyond established clinical variables, such as obesity or duration of diabetes.

Insulin resistance correlates with the arterial stiffness before glucose intolerance

OBJECTIVE

The elevated plasma glucose level and/or insulin resistance in diabetes or impaired glucose tolerance play important roles in the pathogenesis of arterial stiffness. The present study investigated whether insulin resistance correlated with arterial stiffness before the development of glucose intolerance.

METHODS

We conducted a cross-sectional analysis in 872 young to middle-age individuals with normal glucose tolerance (aged 36.2±8.5 years, BMI 24.6±3.1 kg/m2 [mean±SD]). The homeostasis model assessment (HOMA) index was used as a quantitative assessment of the fasting insulin resistance (FIR), and the plasma insulin level after glucose loading was adopted as an index of the post-challenge insulin resistance (PIR). The Matsuda index [ISI (composite)] was used as a measurement of the insulin sensitivity. The arterial stiffness assessed by the brachial-ankle pulse wave velocity (baPWV) was adopted to quantify its independent associations with insulin resistance.

RESULTS

The univariate linear regression analysis indicated that the fasting plasma glucose level (FPG, β = 68.2; 95% CI 40.9, 95.6; p<0.001), post-challenge plasma glucose level (PPG, β = 25.3; 95% CI 15.6, 35.0; p<0.001), FIR (β = 24.5; 95% CI 14.1, 35.0; p<0.001), PIR (β=1.30; 95% CI 0.87, 1.73; p<0.001) and ISI (composite) (β = -3.55; 95% CI -5.02, -2.07; p<0.001) were all significantly correlated with the baPWV. After adjustment for sex, age, BMI, heart rate, smoking, systolic blood pressure, total cholesterol, LDL-cholesterol and family history of diabetes, the multivariate linear regression analysis demonstrated that the PIR (model 1, β = 0.39, p=0.038; model 2, β = 0.39, p=0.035; model 3, β = 0.39, p=0.035) was an independent contributor to the baPWV, while the FIR, FPG, PPG and ISI (composite) failed to show any significant contribution.

CONCLUSION

The insulin resistance correlated with the arterial stiffness before glucose intolerance.

The effects of postprandial glucose and insulin levels on postprandial endothelial function in subjects with normal glucose tolerance

BACKGROUND

Previous studies have demonstrated that postprandial hyperglycemia attenuates brachial artery flow-mediated dilation (FMD) in prediabetic patients, in diabetic patients, and even in normal subjects. We have previously reported that postprandial hyperinsulinemia also attenuates FMD. In the present study we evaluated the relationship between different degrees of postprandial attenuation of FMD induced by postprandial hyperglycemia and hyperinsulinemia and differences in ingested carbohydrate content in non-diabetic individuals.

METHODS

Thirty-seven healthy subjects with no family history of diabetes were divided into 3 groups: a 75-g oral glucose loading group (OG group) (n = 14), a test meal group (TM group) (n = 12; 400 kcal, carbohydrate content 40.7 g), and a control group (n = 11). The FMD was measured at preload (FMD0) and at 60 minutes (FMD60) and 120 (FMD120) minutes after loading. Plasma glucose (PG) and immunoreactive insulin (IRI) levels were determined at preload (PG0, IRI0) and at 30 (PG30, IRI30), 60 (PG60, IRI60), and 120 (PG120, IRI120) minutes after loading.

RESULT

Percentage decreases from FMD0 to FMD60 were significantly greater in the TM group (-21.19% ± 17.90%; P < 0.001) and the OG group (-17.59% ± 26.64%) than in the control group (6.46% ± 9.17%; P < 0.01), whereas no significant difference was observed between the TM and OG groups. In contrast, the percentage decrease from FMD0 to FMD120 was significantly greater in the OG group (-18.91% ± 16.58%) than in the control group (6.78% ± 11.43%; P < 0.001) or the TM group (5.22% ± 37.22%; P < 0.05), but no significant difference was observed between the control and TM groups. The FMD60 was significantly correlated with HOMA-IR (r = -0.389; P < 0.05). In contrast, FMD120 was significantly correlated with IRI60 (r = -0.462; P < 0.05) and the AUC of IRI (r = -0.468; P < 0.05). Furthermore, the percentage change from FMD0 to FMD120 was significantly correlated with the CV of PG (r = 0.404; P < 0.05), IRI60 (r = 0.401; p < 0.05) and the AUC of IRI (r = 0.427; P < 0.05). No significant correlation was observed between any other FMDs and glucose metabolic variables.

CONCLUSION

Differences in the attenuation of postprandial FMD induced by different postprandial insulin levels may occur a long time postprandially but not shortly after a meal.

Low insulin level is associated with aortic stiffness

Recent studies have demonstrated that hyperinsulinemia is a risk factor for cardiovascular disease. The aim of this study was to evaluate the relationship between serum insulin level and the cardio-ankle vascular index (CAVI), which was developed as a marker of arterial stiffness. We performed a cross-sectional study of 260 consecutive and nondiabetic subjects with clinical suspicion of coronary heart disease. We measured CAVI in all subjects. A standard 75-g oral glucose tolerance test was performed, and plasma glucose and serum insulin levels were measured in venous blood collected at 0, 30, 60 and 120 min after the test. Statistical analyses were conducted for four subgroups according to the insulin area under the concentration time curve (InsAUC). Mean CAVI and InsAUC were 8.7 and 109.5 μIUml(-1)h(-1), respectively. Unadjusted analysis demonstrated that the InsAUC quartiles were significantly associated with CAVI (P<0.0001), and the lowest InsAUC quartile (P=0.001) had a lower glucose AUC. Analysis of covariance demonstrated that the lowest InsAUC quartile had the highest CAVI, and, after adjusting for several coronary risk factors, the highest InsAUC quartile had a higher CAVI than the second and third InsAUC quartiles (P<0.0001). In conclusion, the lowest InsAUC quartile was related to CAVI, although the lowest InsAUC quartile maintained glucose homeostasis in this study population. Both hyperinsulinemia and low insulin level are independently associated with CAVI.

Metabolic syndrome and mitochondrial function: molecular replacement and antioxidant supplements to prevent membrane peroxidation and restore mitochondrial function

Metabolic syndrome consists of a cluster of metabolic conditions, such as hypertriglyceridemia, hyper-low-density lipoproteins, hypo-high-density lipoproteins, insulin resistance, abnormal glucose tolerance and hypertension, that-in combination with genetic susceptibility and abdominal obesity-are risk factors for type 2 diabetes, vascular inflammation, atherosclerosis, and renal, liver and heart disease. One of the defects in metabolic syndrome and its associated diseases is excess cellular oxidative stress (mediated by reactive oxygen and nitrogen species, ROS/RNS) and oxidative damage to mitochondrial components, resulting in reduced efficiency of the electron transport chain. Recent evidence indicates that reduced mitochondrial function caused by ROS/RNS membrane oxidation is related to fatigue, a common complaint of MS patients. Lipid replacement therapy (LRT) administered as a nutritional supplement with antioxidants can prevent excess oxidative membrane damage, restore mitochondrial and other cellular membrane functions and reduce fatigue. Recent clinical trials have shown the benefit of LRT plus antioxidants in restoring mitochondrial electron transport function and reducing moderate to severe chronic fatigue. Thus LRT plus antioxidant supplements should be considered for metabolic syndrome patients who suffer to various degrees from fatigue.

Effect of dietary chromium on resistance artery function and nitric oxide signaling in the sucrose-fed spontaneously hypertensive rat

BACKGROUND

Consumption of high-glycemic index foods contributes to the development of hypertension in some patients. Likewise, in spontaneously hypertensive rats (SHR), high sucrose promotes a secondary rise in systolic blood pressure (SBP). Chromium (III) (Cr(3+)) prevents sucrose-induced hypertension, but leaves the basal hypertension that characterizes SHR intact.

METHODS

Since hypertension entails increased peripheral resistance, we compared effects of Cr(3+) on resistance arteries from SHR fed low-glycemic (starch) versus high-glycemic (sucrose) index diets. Subgroups of SHR also received Cr(3+). Structure, stiffness, and vasodilation of mesenteric resistance arteries were studied using pressurized myography.

RESULTS

Sucrose increased SBP in SHR and, exclusively in sucrose-fed SHR, Cr(3+) reduced SBP and augmented acetylcholine or nitroprusside-dependent vasodilation. Neither sucrose nor Cr(3+) affected artery structure or stiffness. Since Cr(3+) enhanced vasodilation, we assessed endothelial NO synthase (eNOS), guanylate cyclase, cGMP-dependent protein kinase (PKG-1alpha and 1beta), and PKG activity by immunoblotting. Sucrose reduced eNOS, PKG-1beta, and PKG activity. Cr(3+) prevented the effects of sucrose on NO signaling.

CONCLUSION

In hypertension exacerbated by high-glycemic index diet, Cr(3+) reduces SBP. The BP-lowering effect of Cr(3+), selectively on sucrose-induced but not basal hypertension in SHR, involves at least in part, improving vasodilatory function vis-à-vis restoration of NO signaling in resistance arteries.

Postprandial endothelial dysfunction: role of glucose, lipids and insulin

Endothelium plays a key role in the regulation of vascular tone and development of atherosclerosis. Endothelial function is impaired early in patients with risk factors and endothelial dysfunction is a strong and independent predictor of cardiovascular events. Because in normal subjects blood concentrations of glucose, lipids and insulin are increased after each meals, and postprandial changes last a long time after the meals, these changes might be of importance in the process of atherosclerosis initiation and development. Experimental and human studies have shown that a transient increase of blood concentrations of glucose, triglycerides and fatty acids, and insulin are able to depress endothelium-dependent vasodilation in healthy subjects and that hyperglycemia, hypertriglyceridemia and hyperinsulinemia are generator of reactive oxygen species at the origin of a cascade of pathophysiological events resulting in the activation of nuclear factor-kappaB. Nuclear factor-kappaB is an ubiquitous transcription factor controlling the expression of numerous genes and is involved in immunity, inflammation, regulation of cell proliferation and growth and apoptosis. These mechanisms may be involved in the development of atherosclerosis in normal subjects when food intake is chronically modified towards glucids and lipids with cumulative effects both on depression of endothelium dependent dilation and oxidative stress.

Impaired coronary blood flow in patients with metabolic syndrome: documented by Thrombolysis in Myocardial Infarction (TIMI) frame count method

BACKGROUND

Endothelium plays an important role in regulating coronary vascular tone. In addition, several of cardiovascular risk factors that are associated metabolic syndrome have been reported to be associated with endothelial dysfunction. In the present study we aimed to evaluate the coronary blood flow in patients with metabolic syndrome by means of the Thrombolysis in Myocardial Infarction (TIMI) frame count.

METHOD

Forty-two patients with metabolic syndrome (group I) and 42 control subjects without metabolic syndrome (group II) were included in the study. All subjects had angiographically proven normal coronary arteries. Diagnosis of metabolic syndrome was based on the National Cholesterol Education Program Adult Treatment Panel III (NCEP ATP III) guidelines published in 2001. Coronary flow rates of all subjects were documented by TIMI frame count method.

RESULTS

TIMI frame counts for each of the major epicardial coronary arteries were found to be significantly higher in patients with metabolic syndrome compared with control subjects (corrected TIMI frame count for left anterior descending coronary artery: 35 +/- 7 vs 25 +/- 7, respectively; left circumflex coronary artery: 32 +/- 9 vs 25 +/- 7, respectively; right coronary artery: 31 +/- 9 vs 24 +/- 5, respectively; P < .001 for all). Statistically significant independent relationships were found between TIMI frame count and body mass index (R(2) = 0.480, P = .009), waist circumference (R2 = 0.551, P = .001), and triglyceride level (R2 = 0.434, P = .036).

CONCLUSION

We have shown for the first time that patients with metabolic syndrome and angiographically normal coronary arteries have higher TIMI frame counts for all 3 coronary vessels, indicating impaired coronary blood flow, compared to control subjects without metabolic syndrome.

Food and red wine do not exert acute effects on vascular reactivity

Experimental hyperglycemia and hyperinsulinemia have been shown to affect vascular reactivity. Chronic red wine consumption is associated with less cardiovascular mortality. Whether ingestion of a natural meal and red wine causes acute changes in vascular homeostasis is poorly understood. The aim of the current study was to clarify whether meal ingestion, with and without red wine, exert acute effects on vascular reactivity in healthy humans. We studied vascular reactivity and forearm nitrite balance in 10 healthy subjects under 3 different circumstances: (1) fasting; (2) after ingestion of a standard natural meal (1,050 kcal); and (3) after the same meal enriched with a glass of red wine. We measured forearm blood flow (FBF) by strain-gauge plethismography during intrabrachial, graded infusion of acetylcholine (ACh), sodium nitroprusside (NP), and norepinephrine (NE). We also measured the forearm balance of nitrite before and during ACh infusion. Despite significant increases in plasma glucose and insulin concentrations, the vasodilatory response to Ach and NP after meal ingestion was not different from the fasting response. Similarly, the vasoconstrictory response to NE was similar postprandially and during fasting. Addition of red wine did not modify the response to any of the vasoactive agents. Finally, the forearm nitrite production during Ach infusion was not different in the 3 experimental settings. Food intake, whether associated or not with red wine, does not affect vascular reactivity in normal human subjects.

Interactive relation of insulin and gender to cardiovascular reactivity in healthy young adults

High levels of insulin may promote hypertension pathogenesis, in part, via enhanced sympathetic nervous system (SNS) activity. This study examined potential interactive relations of fasting insulin levels, gender, and race to cardiovascular reactivity-a correlate of SNS activation. Hemodynamic responses to 4 laboratory challenges were determined by impedance cardiography in 64 healthy young adults (ages 18-26; 48% male; 50% White, 50% African American). Also examined were lipoprotein lipids, central and total adiposity, self-reported dietary factors, and physical activity. High-insulin (>10.2 mU/ml) men showed greater total peripheral resistance and longer pre-ejection period responses than low-insulin ( pound 10.2 mU/ml) men. High-insulin women displayed greater cardiac index responses than high-insulin men. High insulin levels were related to greater percentage body fat, dietary carbohydrate and fat intake, lower high-density lipoprotein (HDL) cholesterol (in men), higher total cholesterol (in women), and a trend toward higher triglycerides. Cardiovascular reactivity findings were unchanged after statistical adjustment for total and HDL cholesterol, triglycerides, percentage body fat, dietary carbohydrates, and fat. The Gender x Insulin (continuous scores) interaction accounted for 7% and 9% of the variance in cardiac index and total peripheral resistance responses, respectively. These results indicate that high insulin levels are associated with greater vascular reactivity in young men and cardiac reactivity in young women. Enhanced cardiovascular reactivity may constitute a biobehavioral dimension of the metabolic syndrome.

Peripheral adiposity exhibits an independent dominant antiatherogenic effect in elderly women

BACKGROUND

Although several lines of evidence point to an atherogenic role of central fat mass (CFM), few data are available to address the specific role played by peripheral fat mass (PFM).

METHODS AND RESULTS

This study was a cross-sectional analysis of 1356 women aged 60 to 85 years. Study variables were physical measures, CFM and PFM measured by DEXA, aortic calcification (AC) graded on lateral radiographs, lipid and glucose metabolites, blood pressure, and information on lifestyle factors and coronary disease. Peripheral fat mass showed independent negative correlation with both atherogenic metabolic risk factors and AC (P<0.001). The most severe insulin resistance-dyslipidemic syndrome and AC (score 5.10+/-0.76) was found in women with high central fat percentage (CF%, 21.7+/-0.2%) and low peripheral fat percentage (PF%, 18.3+/-0.2%, n=48). The least severe AC (score 2.45+/-0.31) was found in obese women with high CF% (21.6+/-0.1%) and high PF% (27.3+/-0.14%, n=112). The insulin resistance-dyslipidemic syndrome was also less severe compared with those with the same CF% but low PF%. The most favorable metabolic profile characterized women with low CF% (11.56+/-0.16%) and high PF% (26.86+/-0.33%, n=44). In women with a history of myocardial infarct (18.41+/-0.55%, n=45), CF% was significantly higher compared with women with no manifest coronary disease (16.48+/-0.12%, n=1210) without differences in PF%.

CONCLUSIONS

In elderly women, localization of fat mass is apparently more important for atherosclerosis than obesity per se; although CFM is associated with atherogenic tendencies, PFM seems to exhibit an independent dominant antiatherogenic effect.

Oral insulin supplementation attenuates atherosclerosis progression in apolipoprotein E-deficient mice

OBJECTIVE

The role of insulin in atherosclerosis progression in diabetes is uncertain. We examined the effects of oral insulin supplementation on atherogenesis in apolipoprotein E-deficient (E(0)) mice.

METHODS AND RESULTS

One-month-old male E(0) mice were orally supplemented with human insulin (0.1, 0.5, and 1 U/mL) or placebo for 3 months. At the end of the study, serum and macrophage oxidative stress and atherosclerosis progression were studied. Insulin reduced lesion size by 22% to 37% (P<0.05) in all study groups. Lipid peroxides serum levels were 18% lower (P<0.01), and serum paraoxonase activity was 30% higher (P<0.01) in mice supplemented with 1.0 U/mL insulin compared with controls. Insulin reduced mouse peritoneal macrophage (MPM) lipid peroxides content and superoxide anion release by up to 44% and 62%, respectively (P<0.01). In addition, oral insulin reduced MPM cholesterol content and cholesterol biosynthesis by up to 36% and 53%, respectively (P<0.01). In vitro incubation of E(0) mice MPM with increasing insulin concentrations (0 to 100 micro U/mL) resulted in a dose-dependent reduction of cholesterol synthesis by up to 66% (P<0.05).

CONCLUSIONS

In E(0) mice, oral insulin supplementation attenuates the atherosclerotic process. This may be attributable to insulin-mediated reduction of oxidative stress in serum and macrophages as well as reduction in macrophage cholesterol content.

Homeostasis model assessment of insulin resistance in relation to the incidence of cardiovascular disease: the San Antonio Heart Study

OBJECTIVE

The prospective association between insulin levels and risk of cardiovascular disease (CVD) is controversial. The objective of the present study was to investigate the relationship of the homeostasis model assessment of insulin resistance (HOMA-IR), as well as insulin levels, with risk of nonfatal and fatal CVD over the 8-year follow-up of the San Antonio Heart Study.

RESEARCH DESIGN AND METHODS

Between 1984 and 1988, randomly selected Mexican-American and non-Hispanic white residents of San Antonio participated in baseline examinations that included fasting blood samples for glucose, insulin, and lipids, a glucose tolerance test, anthropometric measurements, and a lifestyle questionnaire. Between 1991 and 1996, 2,569 subjects who were free of diabetes at baseline were reexamined using the same protocol.

RESULTS

Over the follow-up period, 187 subjects experienced an incident cardiovascular event (heart attack, stroke, heart surgery, angina, or CVD death). Logistic regression analysis indicated that risk of a CVD event increased across quintiles of HOMA-IR after adjustment for age, sex, and ethnicity (P for trend <0.0001; quintile 5 vs. quintile 1, odds ratio [OR] 2.52, 95% CI 1.46-4.36). Additional adjustment for LDL, triglyceride, HDL, systolic blood pressure, smoking, alcohol consumption, exercise, and waist circumference only modestly reduced the magnitude of these associations (P for trend 0.02; quintile 5 vs. quintile 1, OR 1.94, 95% CI 1.05-3.59). Furthermore, there were no significant interactions between HOMA-IR and ethnicity, sex, hypertension, dyslipidemia, glucose tolerance (impaired glucose tolerance versus normal glucose tolerance), or obesity. The magnitude and direction of the relationship between insulin concentration and incident CVD were similar.

CONCLUSIONS

We found a significant association between HOMA-IR and risk of CVD after adjustment for multiple covariates. The topic remains controversial, however, and additional studies are required, particularly among women and minority populations.

Insulin causes endothelial dysfunction in humans: sites and mechanisms

BACKGROUND

Insulin resistance is often accompanied by hyperinsulinemia and may predispose to atherosclerosis. Endothelium plays a central role in atherogenesis. The in vivo effects of hyperinsulinemia on endothelial function of large conduit arteries are unknown.

METHODS AND RESULTS

Twenty-five healthy subjects were enrolled for study. In study A (n=9), subjects underwent both a time-control saline study and a euglycemic low-dose insulin (insulin approximately 110 pmol/L) clamp for 6 hours. Study B (n=5) was identical to study A except that the euglycemic clamp was performed at high physiological insulin concentrations (approximately 440 pmol/L). In study C (n=7), subjects underwent two 4-hour euglycemic insulin (approximately 110 pmol/L) clamps with and without the concomitant infusion of an antioxidant (vitamin C). In study D (n=4), two saline time-control studies were performed with and without the concomitant infusion of vitamin C. In all studies, both at baseline and throughout the experimental period, endothelium-dependent (flow-mediated) and endothelium-independent (nitroglycerin-induced) vasodilation was assessed in femoral and brachial arteries by echo Doppler. Both low (study A) and high physiological (study B) hyperinsulinemia abolished endothelium-dependent vasodilation, whereas endothelium-independent vasodilation was unaffected. Vitamin C fully restored insulin-impaired endothelial function without affecting endothelium-independent vasodilation (study C). Vitamin C had no effects on endothelium-dependent or endothelium-independent vasodilation during saline control studies (study D).

CONCLUSIONS

Modest hyperinsulinemia, mimicking fasting hyperinsulinemia of insulin-resistant states, abrogates endothelium-dependent vasodilation in large conduit arteries, probably by increasing oxidant stress. These data may provide a novel pathophysiological basis to the epidemiological link between hyperinsulinemia/insulin-resistance and atherosclerosis in humans.

Obesity, body fat distribution, and ambulatory blood pressure in children and adolescents

Obesity is a common disease with an ever-increasing prevalence and usually with late-onset consequences. If acquired during childhood, it tracks into adult life to some extent, and since the relationship between obesity and hypertension is well established in adults, obese children appear to be at particularly high risk of becoming hypertensive adults. In the authors' study, obese children seemed to have significantly higher casual and ambulatory blood pressure than nonobese children, except for nighttime diastolic blood pressure. The health effects of obesity may depend on the anatomic distribution of body fat, which in turn may be a better indicator of endocrinologic imbalance, environmental stress, or genetic factors than is fatness per se. Subjects with a higher waist-to-hip ratio or a larger waist, as an estimate of central obesity, tend to have higher blood pressure values even during childhood. Prevention of the onset of obesity in early life may be important to reducing the risk of coronary heart disease in later life.

The metabolic syndrome and related cardiovascular risk

The metabolic syndrome is a complex association of several risk factors including insulin resistance, dyslipidemia, and essential hypertension. Insulin resistance has been associated with sympathetic activation and endothelial dysfunction, which are the main mechanisms involved in the pathophysiology of hypertension and its related cardiovascular risk. According to the Sixth Report of the Joint National Committee, and guidelines of the World Health Organization/International Society of Hypertension, the presence of multiple risk markers suggests that both hypertension and risk factors should be aggressively managed in order to obtain a better outcome. Primary prevention of obesity at different levels--individual, familial, and social-- starting early in childhood has proven to be cost effective, and will be mandatory to reduce the world epidemic of obesity and its severe consequences.