Endothelial Regulation of Vascular Tone and Growth

The endothelium regulates vascular tone by releasing factors involved in relaxation and contraction, in coagulation and thrombus formation, and in growth inhibition and stimulation. Endothelium-dependent relaxations are elicited by transmitters, hormones, platelet substances, and the coagulation system, and by physical stimuli such as the shear stress from circulating blood. They are mediated by the endothelium-derived relaxing factor, recently identified as nitric oxide, which causes vasodilation and platelet deactivation. Other proposed endothelium- derived relaxing factors include a hyperpolarizing factor, lipooxygenase products, and the cytochrome P450 pathway. Endothelium-derived contracting factors are produced by the cyclooxygenase pathway and by endothelial cells, which produce the peptide endothelin-1, a potent vasoconstrictor that under normal conditions circulates at low levels. The endothelium produces both growth inhibitors— normally dominant—and growth stimuli. Denuded or dysfunctional endothelium leads to a proliferative response and intimal hyperplasia in the vessel wall; moreover, platelets adhere to the site and release potent growth factors. Endothelial dysfunction has numerous causes: Aging is associated with increased formation of contracting factor and decreased relaxing factor; denudation, such as by coronary angioplasty, impairs the capacities of regenerated endothelial cells; oxidized low-density lipoproteins and hypercholesterolemia interfere with nitric oxide production; hypertension morphologically and functionally alters the endothelium; and atherosclerosis markedly attenuates some endothelium- dependent relaxations. For patients with coronary bypass grafts, differences in endotheliumderived vasoactive factors between the internal mammary artery and the saphenous vein may be important determinants of graft function, with the mammary artery having more pronounced relaxations than the saphenous vein and thus a higher patency rate. Am J Hypertens 1993;6:283S-293

Clinical impact of repolarization changes in supine versus upright body position

Background: The impact of postural changes on various electrocardiography (ECG) characteristics has only been assessed in a few small studies. This large prospective trial was conducted to confirm or refute preliminary data and add important results with immediate impact on daily clinical practice. Methods: ECGs in supine and upright position from 1028 patients were analyzed. Evaluation was made according to changes in T-wave vector and direction, ST-segment deviation, heart rate, QT interval and QTc interval was performed. Findings were correlated with the medical history of patients. Results: Positional change from supine to upright resulted in a significantly increased heart rate (8.05 ± 7.71 bpm) and a significantly increased QTc interval after Bazetts (18 ± 23.45 ms) and Fridericas (8.84 ± 17.30) formula. In the upright position significantly more T-waves turned negative (14.7%) than positive (5.7%). ST elevation was recorded in only 0.4% and ST depression in not more than 0.2% of all patients. Conclusions: The majority of the patients do not show significant morphological changes in their ECG by changing the body position from supine to upright. Changes of QTc time instead, are significant and the interval might be overestimated in upright. Therefore assessment of the QTc interval should strictly be done in a supine position

PDGF-CC induces tissue factor expression: role of PDGF receptor α/β

Tissue factor (TF) is the principal trigger of the coagulation cascade and involved in arterial thrombus formation. Platelet-derived growth factor CC (PDGF-CC) is a recently discovered member of the PDGF family released upon platelet activation. This study assesses the impact of PDGF-CC on TF expression in human cells. PDGF-CC concentration-dependently induced TF expression by 2.5-fold in THP-1 cells, by 2.0-fold in human peripheral blood monocytes, by 1.4-fold in vascular smooth muscle cells, and by 2.6-fold in microvascular endothelial cells, but did not affect TF expression in aortic endothelial cells. A similar pattern was observed with PDGF-BB. In contrast, PDGF-AA did not alter TF expression in THP-1 cells. TF whole cell activity was induced following stimulation with PDGF-BB and PDGF-CC in THP-1 cells. Real-time polymerase chain reaction revealed that PDGF-CC induced TF mRNA. PDGF-CC transiently activated p42/44 MAP kinase [extracellular signal-regulated kinase (ERK)], while phosphorylation of the MAP kinases c-Jun NH2-terminal kinase (JNK) and p38 remained unaffected. PD98059, a specific inhibitor of ERK phosphorylation, but not the p38 inhibitor SB203580 or the JNK inhibitor SP600125 prevented PDGF-CC induced TF expression in a concentration-dependent manner. The effect of PDGF-CC was antagonized by both PDGF receptor α and PDGF receptor β neutralizing antibodies; in contrast, PDGF-BB was only inhibited by PDGF receptor β blocking antibody. PDGF receptor α and PDGF receptor β inhibition prevented PDGF-CC-induced ERK phosphorylation. PDGF-CC induces TF expression via activation of α/β receptor heterodimers and an ERK-dependent signal transduction pathwa

Guggulsterone, an anti-inflammatory phytosterol, inhibits tissue factor and arterial thrombosis

Background: The phytosterol guggulsterone is a potent anti-inflammatory mediator with less side effects than classic steroids. This study assesses the impact of guggulsterone on tissue factor (TF) expression and thrombus formation. Methods and results: Guggulsterone inhibited TNF-α-induced endothelial TF protein expression and surface activity in a concentration-dependent manner; in contrast, dexamethasone did not affect TNF-α-induced TF expression. Guggulsterone enhanced endothelial tissue factor pathway inhibitor and impaired plasminogen activator inhibitor-1 as well as vascular cell adhesion molecule-1 protein. Real-time polymerase chain reaction revealed that guggulsterone inhibited TNF-α-induced TF mRNA expression; moreover, it impaired activation of the MAP kinases JNK and p38, while that of ERK remained unaffected. In vivo, guggulsterone inhibited TF activity and photochemical injury induced thrombotic occlusion of mouse carotid artery. Guggulsterone also inhibited TF expression, proliferation, and migration of vascular smooth muscle cells in a concentration-dependent manner. Conclusions: Guggulsterone inhibits TF expression in vascular cells as well as thrombus formation in vivo; moreover, it impairs vascular smooth muscle cell activation. Hence, this phytosterol offers novel therapeutic options, in particular in inflammatory diseases associated with an increased risk of thrombosi

Amphetamines induce tissue factor and impair tissue factor pathway inhibitor: role of dopamine receptor type 4

Aims Amphetamine intake is associated with acute vascular syndromes. Since these events are caused by arterial thrombosis and this in turn is triggered by tissue factor (TF), this study examines whether amphetamines regulate TF in human endothelial cells. Methods and results Amphetamine (10−7-10−4 mol/L) enhanced thrombin- and tumour necrosis factor (TNF)-α-induced as well as basal TF expression (P = 0.029, 0.0003, and 0.003 at maximal concentration), and TNF-α-induced plasminogen activator inhibitor (PAI)-1 expression (P = 0.003), whereas tissue factor pathway inhibitor expression was impaired (P = 0.008). Similarly, 3,4-methylenedioxymethamphetamine (10−7-10−4 mol/L) enhanced TF expression (P = 0.046). These effects were paralleled by an increased TF activity (P = 0.002); moreover, clotting time of human plasma was accelerated by supernatant from amphetamine-treated cells (P = 0.03). Amphetamine enhanced TF mRNA expression via phosphorylation of the mitogen-activated protein kinases (MAPKs) extracellular signal-regulated kinase (ERK) and p38 (P = 0.03 and 0.033), but not c-Jun NH2-terminal kinase (JNK; P = 0.81). The effect of amphetamine on TF expression was abrogated by the dopamine D4 receptor antagonists L-745,870 and L-750,667, but not D2 or D3 receptor antagonists; furthermore, L-745,870 blunted the amphetamine-induced activation of ERK and p38, but not JNK. Conclusion Amphetamines induce endothelial TF expression via stimulation of dopamine D4 receptor and activation of the MAPKs p38 and ERK. These effects occur at clinically relevant amphetamine concentrations and may account for the increased incidence of acute vascular syndromes after amphetamine consumptio

17β-Estradiol inhibits proliferation and migration of human vascular smooth muscle cells: similar effects in cells from postmenopausal females and in males

Objectives: Cardiovascular disease is rare in premenopausal women, but increases after the menopause when hormone replacement therapy reduces coronary events. Vascular smooth muscle cell (SMC) proliferation and migration occur in atherosclerosis, restenosis and venous graft disease. We studied the effects of 17β-estradiol on SMC proliferation and migration. Methods: SMC were cultured from saphenous veins of postmenopausal women and age-matched men. Cell growth was determined by 3H-thymidine incorporation and cell counting. Migration of SMC was assessed in 4-well chambers. SMC were seeded in one corner and PDGF-BB in filter paper glued onto the opposite wall. Results: PDGF-BB (5 ng/ml for 24 h) similarly stimulated 3H-thymidine incorporation in female (511 ± 57%; n = 8) and male (528 ± 62%; n = 12) SMC. This was reduced by 17β-estradiol (10−8-10−6 M; female 313 ± 52%; male 337 ± 54%; P < 0.05). PDGF-BB increased the number of SMC (P < 0.0001 at 10 days) obtained from females (153 ± 3%; n = 5) and males (150 ± 4%; n = 5), which was inhibited by 17 β-estradiol (10−6 M; female 134 ± 7%; male 128 ± 5%; P < 0.05). Similar results were obtained with basic fibroblast growth factor. In contrast to 17β-estradiol, another steroid (dexamethasone) had no effects on 3H-thymidine incorporation in these cells stimulated with PDGF-BB. PDGF-BB (0.01-1 ng) stimulated SMC migration (P < 0.05) which was inhibited by 17β-estradiol (10−10-10−6 M; n = 5; P < 0.005). Conclusion: 17β-Estradiol inhibits growth-factor-induced SMC proliferation and migration regardless of gender. These effects of 17β-estradiol may contribute to its cardiovascular protective properties in postmenopausal women during replacement therap

Rapamycin promotes arterial thrombosis in vivo: implications for everolimus and zotarolimus eluting stents

Aims Drug-eluting stents (DES) may be associated with an increased risk for stent thrombosis when compared with bare-metal stents. In endothelial cells, rapamycin induces tissue factor (TF) by inhibiting the mammalian target of rapamycin (mTOR). However, the effect of mTOR inhibition on TF activity and thrombus formation in vivo has not yet been studied. Moreover, it is unclear whether second-generation DES substances everolimus and zotarolimus have an effect on endothelial TF expression. Methods and results In a mouse carotid artery photochemical injury model, rapamycin (182 ± 27.5 µg/L) decreased time to thrombotic occlusion by 40%, increased TF activity, and abrogated p70S6K phosphorylation when compared with controls. In vitro, rapamycin, everolimus, and zotarolimus (each 10−7 mol/l) enhanced TNF-α-induced TF expression by 2.2-, 1.7-, and 2.4-fold, respectively, which was paralleled by an increase in TF surface activity. Similar to rapamycin, everolimus and zotarolimus abrogated TNF-α-induced p70S6K phosphorylation under these conditions. Conclusion Rapamycin increases TF activity and promotes arterial thrombosis in vivo at concentrations relevant in patients undergoing DES implantation; this effect may increase the thrombogenicity of DES. Since everolimus and zotarolimus augment endothelial TF expression and activity in vitro in a similar manner as rapamycin, these findings may also be relevant for second generation DE

Lack of protective role of HDL-C in patients with coronary artery disease undergoing elective coronary artery bypass grafting

Aims Primary prevention studies have confirmed that high-density lipoprotein cholesterol (HDL-C) levels are strongly associated with reduced cardiovascular events. However, recent evidence suggests that HDL-C functionality may be impaired under certain conditions. In the present study, we hypothesize that HDL-C may lose their protective role in the secondary prevention of coronary artery disease (CAD). Methods and results A consecutive series of 1548 patients undergoing isolated first-time elective CABG at one institution between 2004 and 2009 was studied. According to the ATPIII criteria, pre-operative HDL-C values were used to identify patients with high (Group A) vs. low HDL-C (Group B). To eliminate biased estimates, a propensity score model was built and two cohorts of 1:1 optimally matched patients were obtained. Cumulative survival and major adverse cardiovascular events (MACE) were analysed by means of Kaplan-Meier method. Cox proportional-hazards regression models were used to identify independent predictors of MACE and death. Propensity matching identified two cohorts of 502 patients each. At a median follow-up time of 32 months, there were 44 out of 502 (8.8%) deaths in Group A and 36 out of 502 deaths in Group B (7.2%, HR 1.19; P = 0.42). MACE occurred in 165 out of 502 (32.9%) in Group A and 120 out of 502 (23.9%) in Group B (P = 0.04). Regression analysis showed that pre-operative HDL-C levels were not associated with reduced but rather increased MACE occurrence during follow-up (HR 1.43, P = 0.11). Conclusion Higher HDL-C levels are not associated with reduced risk of vascular events in CAD patients undergoing CABG. Our findings may support efforts to improve HDL-C functionality instead of increasing their level

A randomized placebo-controlled study on the effect of nifedipine on coronary endothelial function and plaque formation in patients with coronary artery disease: the ENCORE II study

Aims Endothelial dysfunction and plaque formation are features of atherosclerosis. Inhibition of L-type calcium channels or HMG-CoA pathway improves endothelial function and reduces plaque size. Thus, we investigated in stable coronary artery disease (CAD) the effects of a calcium antagonist on coronary endothelial function and plaque size. Methods and results In 454 patients undergoing PCI, acetylcholine (10−6 to 10−4 M) was infused in a coronary segment without significant CAD. Changes in coronary diameter were measured and an intravascular ultrasound examination (IVUS) was performed. On top of statin therapy, patients were randomized in a double-blind fashion to placebo or nifedipine GITS 30-60 mg/day and followed for 18-24 months. Blood pressure was lower on nifedipine than on placebo by 5.8/2.1 mmHg (P < 0.001) as was total and LDL cholesterol (4.8 mg/dL; P = 0.495), while HDL was higher (3.6 mg/dL; P = 0.026). In the most constricting segment, nifedipine reduced vasoconstriction to acetylcholine (14.0% vs. placebo 7.7%; P < 0.0088). The percentage change in plaque volume with nifedipine and placebo, respectively, was 1.0 and 1.9%, ns. Conclusion The ENCORE II trial demonstrates in a multi-centre setting that calcium channel blockade with nifedipine for up to 2 years improves coronary endothelial function on top of statin treatment, but did not show an effect of nifedipine on plaque volum