Metabolic syndrome and endothelial dysfunction

Long-term cardiac rehabilitation and exercise training programs improve metabolic parameters in metabolic syndrome patients with and without coronary heart disease

BACKGROUND AND AIMS

The effectiveness of long-term cardiac rehabilitation and exercise training programs on metabolic parameters was evaluated in metabolic syndrome subjects with and without coronary heart disease (CHD).

METHODS AND RESULTS

Fifty-nine CHD and 81 non-coronary patients with metabolic syndrome (59+/-8 vs 56+/-9years) were identified retrospectively at entry into identical cardiac rehabilitation and exercise-training programs. Metabolic syndrome was defined using modified Adult Treatment Panel III criteria. Exercise training occurred approximately twice per week. Metabolic and exercise testing data were collected at baseline and after 12months during the course of the program. Mean duration of cardiac rehabilitation and exercise training programs was over one year in both coronary and non-coronary patients (366+/-111 vs 414+/-102days for CHD and non-coronary CHD cohorts respectively, p<0.01). Significant improvements in bodyweight, body mass index, blood lipids, triglyceride/HDL ratio and exercise tolerance were noted in both cohorts. At the end of follow-up, 31% of CHD and 20% of non-CHD subjects no longer possessed diagnostic criteria for metabolic syndrome (p<0.0001 and p<0.001 respectively).

CONCLUSIONS

A long-term cardiac rehabilitation program reduces metabolic syndrome prevalence in CHD patients and results in a similar improvement in risk factor control for metabolic syndrome patients without CHD.

Markers of endothelial activity are related to components of the metabolic syndrome, but not to circulating concentrations of the advanced glycation end-product Nɛ-carboxymethyl-lysine in healthy Swedish men

Endothelial function is considered important in the development of cardiovascular diseases and type 2 diabetes. Circulating advanced glycation end-products (AGEs) and dietary components have been shown to affect endothelial function in type 2 diabetics, but determinants of endothelial function in a non-diabetic population are more poorly investigated. Therefore, we investigated relationships between dietary habits, AGEs and endothelial activation in men with isolated metabolic disturbances. Circulating markers of endothelial activation (soluble forms of vascular cell adhesion molecule-1, intercellular adhesion molecule-1, E-selectin and von Willebrand factor) and plasma N epsilon-carboxymethyl-lysine (CML, the predominant AGE in human plasma) were analyzed in a cross-sectional study of 294 healthy men. Individuals completed a 7-day dietary record, and metabolic and inflammatory parameters were determined. NCEP/ATPIII-criteria were used to define the metabolic syndrome. Endothelial activation was higher in individuals with the metabolic syndrome, and was positively related to certain features of the syndrome (insulin, glucose, inflammation and obesity), but not to others (triacylglycerol and blood pressure). Dietary factors were related to endothelial activation, but CML was not. Multivariate analysis revealed energy and alcohol intake, along with insulin and markers of oxidative stress and inflammation, to be positive predictors of endothelial activation. In this cohort of otherwise healthy men, endothelial activation was increased in individuals with the full metabolic syndrome, but not in those with only some of the components of the metabolic syndrome. Insulin resistance, inflammation, oxidative stress, the dietary intake of energy and alcohol, but not plasma CML, predicted endothelial activation in these men.

The vascular effects of metabolic impairment clusters in subjects of different ethnicities

BACKGROUND

Although metabolic syndrome affects vascular function, the impact of individual impairments and their clustering is unclear.

OBJECTIVE

To assess the vascular impact of metabolic impairments before they reach treatment thresholds in different ethnic groups.

METHODS

Metabolic variables, inflammatory markers, endothelium dependent vasodilatation (EDV) and carotid intima media thickness (CIMT) were measured in population samples of 82 Caucasians and 78 matched Afro-Caribbeans with no vascular disease. Insulin resistance was assessed using homeostasis model assessment (HOMA-IR). EDV was measured as the change in the height of the inflection point of the digital volume pulse following intravenous infusion of 5 mcg/min of albuterol (DeltaRIDeltaLB). Regression models were used to investigate the independent effects of metabolic impairment clusters and their interaction with ethnicity on EDV and CIMT.

RESULTS

HOMA-IR (2.4-3.8, p < 0.0001), IL-6 levels (1.1-2.8 pg/mL, p = 0.02) and CIMT (0.71-0.83 mm, p = 0.009) increased whereas in DeltaRIBASELINE (77.6-72.9 percentage points, p < 0.0001) and DeltaRIDeltaLB (15.5-7.1 percentage points, p < 0.0001) decreased with the number of metabolic impairments present. DeltaRIDeltaLB decreased by 1.6 (95% CI 0.2-3.7) percentage points and CIMT increased by 0.06 (95% CI 0.02-0.10) mm for each metabolic impairment present after adjusting for age, gender, ethnicity and HOMA-IR. There were significant interactions between Afro-Caribbean ethnicity and metabolic impairments for IL-6 (p = 0.037) and DeltaRIDeltaLB (p = 0.002).

CONCLUSIONS

Clustering of metabolic impairments is associated with inflammatory activation, impaired EDV and increased CIMT even before reaching treatment thresholds for individual impairments. This effect was more marked in Afro-Caribbean subjects.

Dissociation between metabolic and vascular insulin resistance in aging

Physiological actions of insulin via activation of the phosphatidylinositol 3-kinase/Akt pathway in the endothelium serve to couple regulation of hemodynamic and metabolic homeostasis. Insulin resistance, endothelial dysfunction, and hypertension increase in prevalence with aging. We investigated the metabolic and endothelial actions of insulin in 24- vs. 3-mo Sprague-Dawley rats. With the use of the hyperinsulinemic euglycemic clamp, the rate of glucose infusion necessary to maintain equivalent plasma glucose (5.5 mmol/l) was similar in 24- vs. 3-mo rats, as was fasting glucose (5.2 +/- 0.33 vs. 4.4 +/- 0.37 mmol/l; mean +/- SE) and insulin (0.862 +/- 0.193 vs. 1.307 +/- 0.230 mg/l). Systolic blood pressure was higher in 24-mo rats (133 +/- 5 vs. 110 +/- 4 mmHg; P = 0.005). Endothelial nitric oxide (NO)-dependent relaxation to insulin was impaired in aortas of 24- vs. 3-mo rats (maximal response 8.9 +/- 4.3 vs. 34.9 +/- 3.9%; P = 0.002); N(G)-nitro-l-arginine methyl ester abolished insulin-mediated relaxation in 3- but not 24-mo rats. Endothelium NO-dependent (acetylcholine) and -independent (sodium nitroprusside) relaxation, as well as NADPH oxidase activity, were similar in 3- and 24-mo rats. Insulin increased aortic serine phosphorylation of Akt in 3-mo rats by 120% over 24-mo rats (P < 0.05) and serine phosphorylation of endothelial NO synthase (eNOS) in 3-mo rats by 380% over 24-mo rats (P < 0.05). Aortic expression of phosphorylated c-Jun NH(2)-terminal kinase-1 and serine phosphorylated insulin receptor substrate-1, known mediators of metabolic insulin resistance, was similar in 3- and 24-mo rats. Expression of caveolin-1, a regulator of eNOS activity and insulin signaling, was 55% lower in 24- than 3-mo rats (P = 0.002). In summary, impaired vasorelaxation to insulin in aging was independent of metabolic insulin sensitivity and associated with impaired insulin-mediated activation of the Akt/eNOS pathway, but intact activation of the acetylcholine-mediated Ca(2+)-calmodulin/eNOS pathway. Vascular insulin resistance in aging may add to the increased susceptibility of this population to vascular injury induced by traditional cardiovascular risk factors.

Increased blood pressure reactivity to dietary salt in patients with the metabolic syndrome

The metabolic syndrome is a predictor of type II diabetes mellitus and cardiovascular disease. The mechanisms of the increased blood pressure (BP) in patients with the metabolic syndrome are poorly understood. We investigated if salt-sensitivity is a characteristic of the metabolic syndrome. A total of 301 subjects (87 male subjects, 214 female subjects) of 41.5+/-0.7 years of age completed a salt sensitivity test, and were evaluated for the presence of metabolic syndrome. BP and 24-h sodium excretion were obtained under usual, high- and low-salt intakes. BP reactivity to salt was markedly increased in subjects with the metabolic syndrome; its magnitude was directly related to the severity of the syndrome. Reducing dietary salt from the average usual intake (8.2 g/day) to nearly 2.3 g/day lowered systolic blood pressure (SBP) by 8.7+/-1.3 mm Hg in subjects with four and five traits, 6.0+/-1.1 in those with three traits and failed to modify the BP of subjects with one or no traits of the syndrome (P < 0.0001). Salt restriction reduced the percentage of subjects with metabolic syndrome that were hypertensive (8.2 g/day of salt) from 23.8 to 8.2% (chi2: 23.6; P<0.0001). BP of non-hypertensive subjects with metabolic syndrome was also significantly reduced by salt restriction (7.1+/-1.5 and 4.2+/-1.1 mm Hg in those with four or five traits and three traits, respectively). In conclusion, the metabolic syndrome is a strong clinical predictor of salt sensitivity. The enhanced BP reactivity to dietary salt observed in subjects with the metabolic syndrome, may determine the increased BP levels commonly associated with the syndrome.

Intake and circulating concentrations of antioxidants in metabolic syndrome

Metabolic syndrome, which occurs commonly in populations around the world, has been associated with an increased risk for developing cardiovascular disease and diabetes. Oxidative stress, which has been implicated in the pathogenesis of cardiovascular disease and diabetes, is a common feature of metabolic syndrome. Limited evidence suggests that circulating concentrations of antioxidants are decreased among people with metabolic syndrome. The contributions of reduced consumption and increased utilization of antioxidants leading to increased oxidative stress are largely unknown. People with metabolic syndrome appear to be an attractive group for future research about possible therapeutic options of antioxidants in the medical management of this syndrome.

Early experimental obesity is associated with coronary endothelial dysfunction and oxidative stress

Obesity is independently associated with increased cardiovascular risk. However, since established obesity clusters with various cardiovascular risk factors, configuring the metabolic syndrome, the early effects of obesity on vascular function are still poorly understood. The current study was designed to evaluate the effect of early obesity on coronary endothelial function in a new animal model of swine obesity. As to method, juvenile domestic crossbred pigs were randomized to either high-fat/high-calorie diet (HF) or normal chow diet for 12 wk. Coronary microvascular permeability and abdominal wall fat were determined by using electron beam computerized tomography. Epicardial endothelial function and oxidative stress were measured in vitro. Systemic oxidative stress, renin-angiotensin activity, leptin levels, and parameters of insulin sensitivity were evaluated. As a result, HF pigs were characterized by abdominal obesity, hypertension, and elevated plasma lysophosphatidylcholine and leptin in the presence of increased insulin sensitivity. Coronary endothelium-dependent vasorelaxation was reduced in HF pigs and myocardial microvascular permeability increased compared with those values in normal pigs. Systemic redox status in HF pigs was similar to that in normal pigs, whereas the coronary endothelium demonstrated higher content of superoxide anions, nitrotyrosine, and NADPH-oxidase subunits, indicating increased tissue oxidative stress. In conclusion, the current study shows that early obesity is characterized by increased vascular oxidative stress and endothelial dysfunction in association with increased levels of leptin and before the development of insulin resistance and systemic oxidative stress. Vascular dysfunction is therefore an early manifestation of obesity and might contribute to the increased cardiovascular risk, independently of insulin resistance.

Brief overview of maternal triglycerides as a risk factor for pre-eclampsia

BACKGROUND

Features of the metabolic syndrome-maternal obesity, diabetes mellitus and chronic hypertension-are risk factors for pre-eclampsia.

OBJECTIVES

To determine the risk of pre-eclampsia in the presence of maternal hypertriglyceridemia, another major element of the metabolic syndrome.

SEARCH STRATEGY

Two investigators independently searched PubMed and Embase databases from 1980 to December 2004 for relevant studies. The terms preeclampsia, eclampsia, pregnancy-induced hypertension or toxemia were combined with dyslipidemia, hyperlipidemia, hypertriglyceridemia, lipids, cholesterol, triglycerides (TG) or lipoprotein.

SELECTION CRITERIA

We included case-control and cohort studies published in English that included at least 20 women with pre-eclampsia and that sampled serum or plasma TG at any time before, during or after pregnancy.

DATA COLLECTION AND ANALYSIS

Mean maternal TG concentrations were compared between cases and controls within each study. The odds ratio of pre-eclampsia was calculated by comparing the risk of pre-eclampsia among women in each higher TG concentration category with that in the lowest reference category.

MAIN RESULTS

A total of 19 case-control and 3 prospective cohort studies were included. In 14 studies, the mean TG concentration was significantly higher among pre-eclamptic cases than among unaffected controls; in seven other studies, there was a nonsignificant trend in the same direction. The risk of pre-eclampsia typically doubled with each increasing TG category. In the four studies that adjusted for potential confounders, such as maternal age, parity and body mass index, there was about a four-fold higher risk of pre-eclampsia in the highest relative to the lowest TG category.

AUTHOR'S CONCLUSIONS

There exists a consistent positive association between elevated maternal TG and the risk of pre-eclampsia. Given that maternal hypertriglyceridemia is a common feature of the metabolic syndrome, interventional studies are needed to determine whether pre-pregnancy weight reduction and dietary modification can lower the risk of pre-eclampsia.

Altered arachidonic acid metabolism impairs functional vasodilation in metabolic syndrome

These studies tested the hypothesis that in obese Zucker rats (OZRs), a model of metabolic syndrome, the impaired functional vasodilation is due to increased thromboxane receptor (TP)-mediated vasoconstriction and/or decreased prostacyclin-induced vasodilation. Spinotrapezius arcade arterioles from 12-wk-old lean (LZR) and OZR were chosen for microcirculatory observation. Arteriolar diameter (5 LZR and 6 OZR) was measured after 2 min of muscle stimulation in the absence or presence of 1 microM SQ-29548 (TP antagonist). Additionally, arteriolar diameter (6 for each group) was measured after application of iloprost (prostacyclin analog; 0.28, 2.8, and 28 microM), arachidonic acid (10 microM), and sodium nitroprusside (0.1, 1, and 10 microM) in the absence or presence of 1 microM SQ-29548. A 10 microM concentration of adenosine was used to induce a maximal dilation. Basal diameters were not different between LZRs and OZRs. Functional hyperemia and arachidonic acid-mediated vasodilations were significantly attenuated in OZR compared with LZR, and treatment with 1 microM SQ-29548 significantly enhanced the dilations in OZRs, although it had no effect in LZRs. Vasodilatory responses to iloprost and sodium nitroprusside (1 and 10 microM) were significantly reduced in OZR. Adenosine-mediated vasodilation was not different between groups. These results suggest that the impaired functional dilation in the OZR is due to an increased TP-mediated vasoconstriction and a decreased PGI2-induced vasodilation.