Endothelial dysfunction: a marker of atherosclerotic risk

Left ventricular mass increases with deteriorating glucose tolerance, especially in women: independence of increased arterial stiffness or decreased flow-mediated dilation: the Hoorn study

OBJECTIVE

Type 2 diabetes and impaired glucose metabolism (IGM) are associated with an increased cardiovascular disease (CVD) risk. Increased left ventricular mass (LVM) is thought to increase CVD risk through several unfavorable cardiac changes. Type 2 diabetes and IGM are associated with increased LVM, but the underlying mechanism is unclear. We investigated the association between glucose tolerance status (GTS) and LVM and explored whether any such association could be mediated through increased arterial stiffness, impaired endothelial function, or the presence of atherosclerosis.

RESEARCH DESIGN AND METHODS

We used ultrasound to measure LVM, carotid and femoral stiffness, carotid-femoral transit time, and flow-mediated vasodilation (FMD) and tonometry to estimate compliance and augmentation index. The study population (n = 780) consisted of 287 individuals with normal glucose metabolism (NGM), 179 with IGM, and 314 with type 2 diabetes, and the mean age was 68.4 years.

RESULTS

In women, after adjusting for age, height, BMI, and mean arterial pressure, LVM increased significantly with deteriorating GTS (LVM 157 g in NGM, 155 g in IGM, and 169 g in type 2 diabetes; P for trend <0.018). Additional adjustment for arterial stiffness, FMD, or the presence of atherosclerosis did not materially alter the results, even though these variables were significantly associated with both GTS and LVM. Indexes of hyperglycemia/-insulinemia or insulin resistance explained at most 7% of the association between GTS and LVM. In men, no statistically significant associations were observed.

CONCLUSIONS

Our data expand the conceptual view of the pathogenesis of GTS-related changes in LVM because we show that the increase in LVM in women is independent of increased arterial stiffness, impaired FMD, or the presence of atherosclerosis. In addition, we show that this increase in LVM is only minimally explained by indexes of hyperglycemia/-insulinemia or insulin resistance. Our data may, in part, explain the increased CVD risk seen in women with deteriorating GTS.

Blunt Circulatory Response to Exercise in Coronary High-Risk Subjects Among Apparently Healthy Japanese

BACKGROUND

Endothelial dysfunction leads to atherosclerosis and the hypothesis of the present study was that the systemic circulatory response during exercise would be a manifestation of endothelial dysfunction.

METHODS AND RESULTS

The circulatory response to exercise of 1,214 apparently healthy people (946 men, mean age 51.2 +/- 10.3; 268 women, mean age 52.7 +/- 10.1) was investigated, as well as the number of coronary risk factors. Systemic vascular resistance (SVR) was calculated from heart rate, blood pressure and oxygen uptake at rest and at maximal exercise during a ramp protocol using a bicycle ergometer. SVRs at rest (1,751-2,001 (dynes.s.cm(-5)) in women and 1,528-1,564 in men) did not significantly differ among the groups by number of coronary risk factors. At maximal exercise, however, they were lower in the group with fewer risk factors; that is, among women 929 (dynes.s.cm (-5)) with no risk factor to 1,305 with 5 risk factors; among men 793 with 1 risk factor to 1,170 with 6 risk factors.

CONCLUSIONS

Those with more coronary risk factors showed a lower but lengthier reduction in SVR during exercise. This weak circulatory response to exercise is a manifestation of deteriorated circulatory function in coronary high-risk subjects.

The cardioprotective effects of statins

In addition to their lipid-modulating properties, statins have a large number of beneficial cardiovascular effects that have emerged over time and that were not anticipated during drug development. The lipid and nonlipid effects act in a concerted way to reduce the ischemic burden of the myocardium and to protect it against injury. By acting on the vessel wall, statins may prevent lesion initiation and repair injuries, enhance myocardial perfusion, slow lesion progression, and prevent coronary occlusion. They may also directly reduce myocardial damage, favor myocardial repair, and protect against immune injury. This review focuses on properties of statins that contribute to their cardioprotective effect. The first section includes information on modulation of vascular tone, endothelial permeability and function, inhibition of complement injury, curbing of foam cell formation, antioxidant and anti-inflammatory properties, and profibrinolytic and anticoagulant activities. The second section relates to reduction of myocardial necrosis, myocardial hypertrophy, blood pressure, and heart failure, as well as mobilization of endothelial progenitor cells for repair, angiogenic effects, and immunomodulation. In many instances, results of in vitro and animal studies have raised expectations and prompted studies in humans. Several clinical trials have confirmed these expectations and have strengthened the value of statins as valuable antiatherosclerotic and cardioprotective agents.

Clinical implications of thermal therapy in lifestyle-related diseases

Systemic thermal therapy, such as taking a warm-water bath and sauna, induces systemic vasodilation. It was found that repeated sauna therapy (60 degrees C for 15 min) improved hemodynamic parameters, clinical symptoms, cardiac function, and vascular endothelial function in patients with congestive heart failure. Vascular endothelial function is impaired in subjects with lifestyle-related diseases, such as hypertension, hyperlipidemia, diabetes mellitus, obesity, and smoking. Sauna therapy also improved endothelial dysfunction in these subjects, suggesting a preventive role for atherosclerosis. In animal experiments, sauna therapy increases mRNA and protein levels of endothelial nitric oxide synthase (eNOS) in aortas. In normal-weight patients with appetite loss, repeated sauna therapy increased plasma ghrelin concentrations and daily caloric intake and improved feeding behavior. In obese patients, the body weight and body fat significantly decreased after 2 weeks of sauna therapy without increase of plasma ghrelin concentrations. On the basis of these data, sauna therapy may be a promising therapy for patients with lifestyle-related diseases.

Circulating progenitor cells regenerate endothelium of vein graft atherosclerosis, which is diminished in ApoE-deficient mice

Previously we showed that a large number of endothelial cells in vein grafts undergo apoptosis or necrosis during the first few days followed by endothelial regeneration. In the present study, we investigated endothelial cell death and regeneration in vein grafts using transgenic mice carrying LacZ genes driven by an endothelial TIE2 promoter. When a vein fragment from TIE2-LacZ was isografted into the carotid artery of wild-type mice, the number of beta-gal+ cells were reduced at 3 days and disappeared completely by 4 weeks after grafting. Conversely, beta-gal+ cells were observed on the surface of vein segments donated by wild-type mice isografted into TIE2-LacZ mice at 1 week and reached confluence by 4 weeks, suggesting recipient origins of endothelial cells. Interestingly, beta-gal+ cells were evenly distributed on the surface of the whole vein segment grafted into TIE2-LacZ mice, indicating a contribution of circulating progenitor cells. When wild-type veins were grafted into a chimeric mouse carrying TIE2-LacZ genes in bone marrow cells, a proportion of cells displayed a beta-gal+ staining. Furthermore, the number of CD34+ and Flk+ progenitor cells in blood of apoE-deficient mice were significantly lower than those of wild-type controls, which coincided with diminished beta-gal+ endothelial cells on the surface of vein grafts in TIE2-LacZ/apoE-/- mice. Thus, we provide the first evidence that endothelial cells of vein grafts are derived from circulating progenitor cells, of which one-third are derived from bone marrow progenitor cells. Hyperlipidemia due to apoE deficiency results in a lower number of endothelial progenitors in blood and correlated with enhanced atherosclerosis. The full text of this article is available online at http://www.circresaha.org.

Cardiovascular risk in women with type 2 diabetes

Type 2 DM appears to eliminate the relative survival advantage experienced by premenopausal nondiabetic women compared with men with regard to CVD. The role of traditional cardiovascular risk factors, while important, cannot fully account for the disparate increase in CVD among women with type 2 DM compared with nondiabetic women. The interplay between type 2 DM and female hormones may prove important. Other less traditional risk factors such as endothelial dysfunction and impaired fibrinolysis may also play a role. Impairments in cardiovascular exercise performance in women with type 2 DM may provide insight in the future as representative of a pre-CVD state. Future research should focus on the specific causes of CVD in women with DM. In the meantime, it is important to aggressively treat modifiable risk factors in this population (Table 1). The impact of this health problem will continue to increase in our aging society, because a steadily increasing proportion of the population will be women; furthermore, an increasing percentage of these women will have diabetes if current trends continue.

Enhanced external counterpulsation for ischemic heart disease: what's behind the curtain?

Enhanced external counterpulsation (EECP) has been shown to reduce angina and to improve objective measures of myocardial ischemia in patients with refractory angina. Prospective clinical studies and large treatment registries suggest that a course of EECP is associated with prolongation of the time to exercise-induced ST-segment depression and resolution of myocardial perfusion defects, as well as with enhanced exercise tolerance and quality of life. With a growing knowledge base supporting the safety and beneficial clinical effects associated with EECP, this therapy can be considered a valuable treatment option, particularly in patients who have exhausted traditional revascularization methods and yet remain symptomatic despite optimal medical care. However, although the concept of external counterpulsation was introduced almost four decades ago, and despite growing evidence supporting the clinical benefit and safety of this therapeutic modality, little is firmly established regarding the mechanisms responsible for the beneficial effects associated with this technique. Suggested mechanisms contributing to the clinical benefit of EECP include improvement in endothelial function, promotion of coronary collateralization, enhancement of ventricular function, peripheral effects similar to those observed with regular physical exercise, and nonspecific placebo effects. This review summarizes the current evidence for a contribution of these mechanisms to the clinical benefit associated with EECP.

Enhanced external counterpulsation improves endothelial function in patients with symptomatic coronary artery disease

OBJECTIVES

The goal of this study was to examine the effect of enhanced external counterpulsation (EECP) on endothelial function.

BACKGROUND

Enhanced external counterpulsation improves symptoms and exercise tolerance in patients with symptomatic coronary artery disease (CAD). However, the exact mechanisms by which this technique exerts its clinical benefit are unclear.

METHODS

Reactive hyperemia-peripheral arterial tonometry (RH-PAT), a noninvasive method to assess peripheral endothelial function by measuring reactive hyperemic response in the finger, was performed in 23 patients with refractory angina undergoing a 35-h course of EECP. In each patient RH-PAT measurements were performed before and after the first, at midcourse, and the last EECP session. In addition, RH-PAT response was assessed one month after completion of EECP therapy; RH-PAT index, a measure of reactive hyperemia, was calculated as the ratio of the digital pulse volume during reactive hyperemia divided by that at rest.

RESULTS

Enhanced external counterpulsation led to symptomatic improvement (>/=1 Canadian Cardiovascular Society class) in 17 (74%) patients; EECP was associated with a significant immediate increase in average RH-PAT index after each treatment (p < 0.05). In addition, average RH-PAT index at one-month follow-up was significantly higher than that before EECP therapy (p < 0.05). When patients were divided by their clinical response, RH-PAT index at one-month follow-up increased only in those patients who experienced clinical benefit.

CONCLUSIONS

Enhanced external counterpulsation enhances peripheral endothelial function with beneficial effects persisting at one-month follow-up in patients with a positive clinical response. This suggests that improvement in endothelial function may contribute to the clinical benefit of EECP in patients with symptomatic CAD.

Interactions of Homocysteine, Nitric Oxide, Folate and Radicals in the Progressively Damaged Endothelium

The endothelium exerts fundamental control over vascular tone, and injury to the endothelium followed by dysfunction is an early key event preceding manifestation of vessel pathology. Both elevated plasma homocysteine and low folate status have been identified as major and independent risk factors for atherosclerosis and have stirred an enormous and still increasing interest. The damaging effects of hyperhomocysteinemia on endothelial function are, at least in part, reversible through folate supplementation. Because of the inverse relationship between plasma folate and homocysteine levels, however, it is difficult to discriminate between their respective effects. Endothelial dysfunction refers mainly to reduced bioavailability of nitric oxide (NO), which is involved in homocysteinemediated vascular damage. Accumulating evidence further suggests that radical oxygen species are fundamentally involved in hyperhomocysteinemia. NO production is determined by cofactors such as tetrahydrobiopterin, which is oxidized and depleted in conditions of oxidant stress by peroxynitrite. Deficiency of tetrahydrofolate contributes to uncoupling, turning the NO synthase into a superoxide radical-producing enzyme. It appears that progression of vascular disease is likely to determine the multiple interactions between homocysteine, NO, oxygen radicals and folate. Folate has only recently been found to exert direct anti-oxidative effects and contribute to restoration of impaired NO metabolism. Understanding of the complex interactions between homocysteine, radicals, NO and folate offers promising perspectives in the individual treatment of vascular disease. Thus, preventive and therapeutic strategies may require a more distinct approach and better discrimination of target groups for greatest possible efficacy.