Intima media thickness of carotid arteries is reduced in heterozygous carriers of the Gly972Arg variant in the insulin receptor substrate-1 gene

Endothelial Dysfunction in Type 2 Diabetes Mellitus

Endothelial dysfunction is an imbalance in the production of vasodilator factors and when this balance is disrupted, it predisposes the vasculature towards pro-thrombotic and pro-atherogenic effects. This results in vasoconstriction, leukocyte adherence, platelet activation, mitogenesis, pro-oxidation, impaired coagulation and nitric oxide production, vascular inflammation, atherosclerosis and thrombosis. Endothelial dysfunction is focussed as it is a potential contributor to the pathogenesis of vascular disease in diabetes mellitus. Under physiological conditions, there is a balanced release of endothelial-derived relaxing and contracting factors, but this delicate balance is altered in diabetes mellitus and atherosclerosis, thereby contributing to further progression of vascular and end-organ damage. This review focuses on endothelial dysfunction in atherosclerosis, insulin resistance, metabolic syndrome, oxidative stress associated with diabetes mellitus, markers and genetics that are implicated in endothelial dysfunction.

Are plasma VEGF and its soluble receptor sFlt-1 atherogenic risk factors? Cross-sectional data from the SAPHIR study

AIMS

Vascular endothelial growth factor (VEGF) is a potent hypoxia-regulated angiogenic factor. Its soluble receptor soluble (s)Flt-1 binds VEGF with high affinity inhibiting the angiogenic function of VEGF. The role of circulating VEGF in atherosclerosis is unclear.

METHODS AND RESULTS

In 909 healthy subjects (511 male, 398 female) from the Salzburg Atherosclerosis Prevention Program in Subjects at High Individual Risk (SAPHIR) we determined fasting plasma VEGF and sFlt-1 concentration, cardiovascular risk factors and carotid atherosclerosis. VEGF levels were lower and sFlt-1 levels higher in men than in women. VEGF and sFlt-1 showed a positive correlation. In the entire population VEGF correlated positively with age, BMI, insulin resistance, white blood cell and platelet count, C-reactive protein (CRP) and carotid intima media thickness (IMT). After adjustment for age, VEGF showed a weak positive correlation with BMI, liver enzymes, CRP and platelet count in males. In females VEGF correlated negatively with LDL-cholesterol and positively with insulin resistance and platelet count. After adjustment for age, no significant correlation with carotid atherosclerosis could be detected.

CONCLUSION

Plasma VEGF and sFlt-1 are only weakly correlated with cardiovascular risk factors, suggesting that circulating VEGF levels do have only a minor impact on the development of atherosclerosis.

Comparison of different definitions of the metabolic syndrome

BACKGROUND

The International Diabetes Federation (IDF) published a new definition of the metabolic syndrome (MetS). For this definition we compared frequency, concordance, clinical and laboratory stigmata and carotid atherosclerosis with those of the established definitions by the National Cholesterol Education Program (NCEP) and World Health Organization (WHO).

MATERIALS AND METHODS

A total of 1518 subjects (943 men, 575 women) from the Salzburg Atherosclerosis Prevention Program in Subjects at High Individual Risk (SAPHIR), free of clinical atherosclerosis, were included in this study. To estimate insulin sensitivity two methods, i.e. homeostasis model assessment of insulin resistance (HOMA-IR) and the short insulin tolerance test, were employed. Carotid intima media thickness (IMT) and plaque extent were quantified for all subjects using high-resolution ultrasound.

RESULTS

Prevalence of the MetS was 18.7% for men and 16.2% for women for the WHO definition, 18.9% and 17.0%, respectively, for the NCEP definition, and 25.8% and 19.5%, respectively, for the IDF definition. Concordance was lower between the definitions of WHO and IDF (< 50%) than between NCEP and IDF (> 67%). Compared to subjects identified by NCEP definition, subjects identified in excess by IDF (3.1-11.7%) showed less insulin resistance and lower IMT and plaque extent indistinguishable from MetS-free subjects.

CONCLUSIONS

Our data suggest that the IDF definition includes subjects as MetS sufferers above these detected by NCEP or WHO, who exhibit considerably less insulin resistance and carotid atherosclerosis blurring the distinction between health and disease.

An association between a common variant (G972R) in the IRS-1 gene and sex hormone levels in post-menopausal breast cancer survivors

Insulin receptor substrate-1 (IRS-1) is a key downstream signaling molecule common to both the insulin and IGF signaling pathways that can interact with the estrogen pathway to regulate breast cell growth. We investigated whether a putative functional variant for IRS-1 (G972R) influences circulating levels of sex hormones, sex hormone binding globulin (SHBG), C-peptide, and insulin-like growth factor 1 (IGF-1) levels among post-menopausal African-American and non-Hispanic white breast cancer patients enrolled in the Health, Eating, Activity, and Lifestyle (HEAL) Study. Circulating levels of sex hormones and growth factors can influence breast cancer recurrence and survival. Serum estrone, estradiol, testosterone, SHBG, IGF-1 and C-peptide were measured in 468 patients at 30+ months post diagnosis. Non-protein bound hormone levels (free estradiol, free testosterone) were calculated. In African-American patients, the IRS-1 variant was associated with increased serum levels of estrone (p = 0.02), free estradiol (p = 0.04), total testosterone (p = 0.04), free testosterone (p = 0.006) and decreased levels of sex hormone-binding globulin (p = 0.02). No association was present for white patients. Our findings provide suggestive evidence that IRS-1 G972R variant may be associated with circulating levels of sex hormones and SHBG in African American breast cancer survivors.

Prediction of cardiovascular morbidity and mortality: comparison of the internal carotid artery resistive index with the common carotid artery intima-media thickness

BACKGROUND AND PURPOSE

The intima-media thickness (IMT) of the common carotid artery (CCA) is well correlated with the degree of arteriosclerosis and is a predictor of cardiovascular morbidity and mortality. The (hemodynamic) resistive index (RI) of the internal carotid artery (ICA) correlates with the degree of arteriosclerosis just as well as IMT. The aim of the study was to compare the predictive values of RI and IMT with regard to cardiovascular morbidity and mortality.

METHODS

A total of 146 patients with cardiovascular risk factors or established arteriosclerosis were included. Duplex sonography of the CCA and ICA was performed, and the IMT and RI were measured in both vessels. During follow-up for a median of 36 months, the occurrence of cardiovascular events (myocardial infarction, stroke, or cardiovascular death) was assessed.

RESULTS

Thirty-nine cardiovascular events occurred in 28 patients (19.2%). The relative risk for a cardiovascular event per increase of the IMT by 1 SD (0.16 mm) was 1.53 (95% CI, 1.07 to 2.18) and 1.91 (95% CI, 1.34 to 2.73) for RI ICA (0.08). The event rate in patients with IMT <0.79 mm (mean) and RI ICA <0.66 (mean) was 11.8% and 12.7% compared with 25.6% (P=0.03) and 25.0% (P=0.06) in patients with IMT > or =0.79 mm and RI ICA > or =0.66, respectively. Log rank analysis showed a continuous increase in the risk of cardiovascular event with increasing range of the IMT (P=0.029) and RI ICA (P<0.001).

CONCLUSIONS

The RI ICA is a predictor of cardiovascular mortality and morbidity, at least comparable to the well-established IMT.

Plasma adiponectin levels and sonographic phenotypes of subclinical carotid artery atherosclerosis: data from the SAPHIR Study

BACKGROUND AND PURPOSE

Adipose tissue produces and secretes a number of bioactive molecules, conceptualized as adipocytokines. Adiponectin has been identified as one of the adipocytokines, and hypoadiponectinemia was demonstrated in patients with obesity, diabetes mellitus, and coronary artery disease. Whether decreased adiponectin levels are cause or consequence is an important issue in the discussion on the association between adiponectin and atherosclerosis. In the present study, we investigated the association of plasma adiponectin levels with sonographic phenotypes of subclinical atherosclerosis, which may represent different stages of disease as well as common and distinct determinants.

METHODS

A total of 1515 middle-aged healthy white subjects (940 males and 575 females) were included. Common carotid artery intima-media thickness (CIMT) and presence of atherosclerotic plaques were assessed by B-mode ultrasound.

RESULTS

After adjustment for established risk factors, per 1 microg/mL decrease in adiponectin CIMT increased on the average by 3.48 microm in males (95% CI, 1.23 to 5.73 microm) and by 2.39 microm in females (95% CI, 0.50 to 4.27 microm). After dichotomizing adiponectin levels at the median and adjustment for established risk factors, the mean difference of CIMT between subjects with low and high adiponectin levels was 20.42 microm in men (95% CI, 6.80 to 34.04; P=0.003) and 20.75 microm in women (95% CI, 1.08 to 40.42; P=0.039). No significant relationship was found between adiponectin levels and presence of atherosclerotic plaques.

CONCLUSIONS

Our results demonstrate an independent negative association of adiponectin levels and CIMT, whereas no relationship with presence of atherosclerotic plaques was found, thus suggesting hypoadiponectinemia as a risk factor in the development of early atherosclerosis.

The Metabolic Syndrome Is a Stronger Risk Factor for Early Carotid Atherosclerosis in Women Than in Men

Background and Purpose— The metabolic syndrome (MetS) is associated with an increased risk for subsequent development of type 2 diabetes mellitus, cardiovascular disease, and stroke. Type 2 diabetes increases the risk of stroke and coronary heart disease in women to a greater extent than in men, and thus the question arises whether there are sex differences in the association of early atherosclerosis and MetS.

Methods— 1588 middle-aged Austrian subjects (1001 males, 587 females) were included in the present study. MetS was defined by the criteria of the National Cholesterol Education Program Adult Treatment Panel III. Early atherosclerosis was assessed by intima-media thickness (IMT) and extent of plaques (B-score) of the carotid arteries.

Results— B-score and carotid artery IMT parameters were significantly higher in subjects with the MetS. After adjustment for established risk factors, the difference in B-score remained significant only in women. Computed common carotid artery IMT values using general linear model equations with age, body mass index, and low-density lipoprotein cholesterol as covariates displayed the highest values for men with MetS (811.8±9.5 μm). Women with MetS (797.6±15 μm) and men without the syndrome (788.8±5 μm) showed similar IMTs, whereas women without the MetS presented significantly lower values (735.6±7 μm). Among the subcomponents of the MetS, high-density lipoprotein cholesterol showed the strongest impact on IMT in men, whereas blood glucose ranked first in women.

Conclusions— The effect of MetS on early atherosclerosis is more pronounced in females. The impact of the components of MetS on carotid IMT differs between men and women.

Increased insulin receptor substrate 1 serine phosphorylation and stress-activated protein kinase/c-Jun N-terminal kinase activation associated with vascular insulin resistance in spontaneously hypertensive rats

Insulin resistance is associated with cardiovascular disease. Impaired insulin receptor substrate (IRS)-mediated signal transduction is a major contributor to insulin resistance. Recently, IRS-1 phosphorylation at serine 307 by stress-activated protein kinase/c-Jun N-terminal kinase (SAPK/JNK) has been highlighted as a molecular event that causes insulin resistance. We investigated IRS-1-mediated insulin signaling, IRS-1 phosphorylation at serine 307, and SAPK/JNK activation status in the aorta of spontaneously hypertensive rats (SHR) by immunoprecipitation and immunoblotting. Insulin-stimulated tyrosine phosphorylation of insulin receptor and IRS-1 in SHR was decreased to 55% (P<0.01) and 40% (P<0.01) of the levels in Wistar-Kyoto rats (WKY), respectively. Insulin-stimulated IRS-1-associated phosphatidylinositol 3-kinase activation in SHR was reduced to 28% of the level in WKY (P<0.0001). Immunoblot analysis revealed that phosphorylated IRS-1 at serine 307 in SHR was increased to 261% (P<0.001) of the level in WKY. Phosphorylated (activated) SAPK/JNK in SHR was increased to 223% of the level in WKY (P<0.01). Serine-phosphorylated IRS-1 that was immunoprecipitated from the aorta of SHR was capable of inhibiting in vitro tyrosine phosphorylation by recombinant insulin receptor compared with WKY-derived IRS-1. These findings demonstrate that insulin resistance in the aorta of SHR was associated with elevated IRS-1 phosphorylation at serine 307 and increased SAPK/JNK activation. The present study suggests that increased SAPK/JNK activation may play an important role in the pathogenesis of vascular insulin resistance via inhibitory serine phosphorylation of IRS-1.