Current strategies and perspectives for correcting endothelial dysfunction in atherosclerosis

Disturbed Flow-Induced Endothelial Proatherogenic Signaling Via Regulating Post-Translational Modifications and Epigenetic Events

SIGNIFICANCE

Hemodynamic shear stress, the frictional force exerted onto the vascular endothelial cell (EC) surface, influences vascular EC functions. Atherosclerotic plaque formation in the endothelium is known to be site specific: disturbed blood flow (d-flow) formed at the lesser curvature of the aortic arch and branch points promotes plaque formation, and steady laminar flow (s-flow) at the greater curvature is atheroprotective.

RECENT ADVANCES

Post-translational modifications (PTMs), including phosphorylation and SUMOylation, and epigenetic events, including DNA methylation and histone modifications, provide a new perspective on the pathogenesis of atherosclerosis, elucidating how gene expression is altered by d-flow. Activation of PKCζ and p90RSK, SUMOylation of ERK5 and p53, and DNA hypermethylation are uniquely induced by d-flow, but not by s-flow.

CRITICAL ISSUES

Extensive cross talk has been observed among the phosphorylation, SUMOylation, acetylation, and methylation PTMs, as well as among epigenetic events along the cascade of d-flow-induced signaling, from the top (mechanosensory systems) to the bottom (epigenetic events). In addition, PKCζ activation plays a role in regulating SUMOylation-related enzymes of PIAS4, p90RSK activation plays a role in regulating SUMOylation-related enzymes of Sentrin/SUMO-specific protease (SENP)2, and DNA methyltransferase SUMOylation may play a role in d-flow signaling.

FUTURE DIRECTIONS

Although possible contributions of DNA events such as histone modification and the epigenetic and cytosolic events of PTMs in d-flow signaling have become clearer, determining the interplay of each PTM and epigenetic event will provide a new paradigm to elucidate the difference between d-flow and s-flow and lead to novel therapeutic interventions to inhibit plaque formation. Antioxid. Redox Signal. 25, 435-450.

Tetrahydrobiopterin in cardiovascular health and disease

Tetrahydrobiopterin (BH4) functions as a cofactor for several important enzyme systems, and considerable evidence implicates BH4 as a key regulator of endothelial nitric oxide synthase (eNOS) in the setting of cardiovascular health and disease. BH4 bioavailability is determined by a balance of enzymatic de novo synthesis and recycling, versus degradation in the setting of oxidative stress. Augmenting vascular BH4 levels by pharmacological supplementation has been shown in experimental studies to enhance NO bioavailability. However, it has become more apparent that the role of BH4 in other enzymatic pathways, including other NOS isoforms and the aromatic amino acid hydroxylases, may have a bearing on important aspects of vascular homeostasis, inflammation, and cardiac function. This article reviews the role of BH4 in cardiovascular development and homeostasis, as well as in pathophysiological processes such as endothelial and vascular dysfunction, atherosclerosis, inflammation, and cardiac hypertrophy. We discuss the therapeutic potential of BH4 in cardiovascular disease states and attempt to address how this modulator of intracellular NO-redox balance may ultimately provide a powerful new treatment for many cardiovascular diseases.

Catheter-based renal sympathetic denervation improves central hemodynamics and arterial stiffness: a pilot study

Renal sympathetic denervation (RDN) is a novel treatment strategy for patients with resistant arterial hypertension. Recently, the Symplicity trials demonstrated significant peripheral blood pressure (BP) reduction. The present study aimed at measuring central aortic pressures and arterial stiffness as better predictors for cardiovascular risk in patients undergoing RDN. RDN was performed in 21 patients (systolic peripheral BP ≥150 mm Hg) with an Ardian/Medtronic (Mountain View, CA) ablation system. Data were recorded with an Arteriograph. After 6 months, peripheral systolic BP was reduced by 6.1% (P<.05) while central systolic pressure was reduced by 7.0% (P<.05). Subgroup analysis showed that in responders, peripheral systolic BP was reduced by 16.1% (P<.01) while central systolic pressure was reduced by 18.3% (P<.01). Arterial stiffness improved significantly. Aortic augmentation index (AIx) improved by 9.5% (P<.05). In responders, AIx improved by 19.2% (P<.02). Pulse wave velocity (PWV) was high at baseline (10.8 m/s) and improved by 10.4% (P<.05). In responders, PWV improved by 13.7% (P<.05). Multivariate analysis showed that short-term effects on PWV were BP-related, whereas during follow-up, improvement of PWV becomes BP-unrelated. RDN improves peripheral and central blood pressure as well as arterial stiffness and, thus, may improve cardiovascular outcome.

Effect of bis (maltolato) oxovanadium (BMOV) in uric acid and sodium arsenite-induced vascular endothelial dysfunction in rats

The study has been designed to investigate the effect of BMOV, a protein tyrosine phosphatase (PTPase) inhibitor in uric acid and sodium arsenite-induced vascular endothelial dysfunction (VED). Uric acid (150 mg kg(-)(1) day(-)(1), i.p., 3 weeks) and sodium arsenite (1.5 mg kg(-)(1) day(-)(1), i.p., 2 weeks) were administered to produce VED in rats. VED was assessed by employing isolated aortic ring preparation, electron microscopy of thoracic aorta and estimating serum concentration of nitrite/nitrate. Further, serum thiobarbituric acid reactive substances (TBARS) and aortic production of superoxide anion were estimated to assess oxidative stress. Uric acid and sodium arsenite were noted to produce VED by attenuating acetylcholine-induced endothelium dependent relaxation, impairing the integrity of vascular endothelial lining, decreasing serum nitrite/nitrate concentration and increasing serum TBARS and aortic superoxide anion generation which were significantly attenuated by BMOV (0.2 mg ml(-)(1) day(-)(1) in drinking water) or atorvastatin (30 mg kg(-)(1) day(-)(1)p.o., a standard agent). However, these ameliorative effects of BMOV have been prevented by N-omega-nitro-L-arginine methyl ester (L-NAME) (25 mg kg(-)(1) day(-)(1), i.p.), an inhibitor of NOS and glibenclamide (5 mg kg(-)(1) day(-)(1), i.p.), a blocker of ATP-sensitive K(+) channel. It may be concluded that BMOV-induced inhibition of PTPase may activate eNOS by opening of ATP-sensitive K(+) channels and consequently decrease oxidative stress to prevent uric acid and sodium arsenite-induced vascular endothelial dysfunction.

Protection of endothelial function: targets for nutritional and pharmacological interventions

The vascular endothelium synthesizes and releases a spectrum of vasoactive substances and therefore plays a fundamental role in the basal and dynamic regulation of the circulation. Nitric oxide (NO)-originally described as endothelium-derived relaxing factor-is released from endothelial cells in response to shear stress produced by blood flow, and in response to activation of a variety of receptors. After diffusion from endothelial to vascular smooth muscle cells, NO increases intracellular cyclic guanosine-monophosphate concentrations by activation of the enzyme guanylate cyclase leading to relaxation of the smooth muscle cells. NO has also antithrombogenic, antiproliferative, leukocyte-adhesion inhibiting effects, and influences myocardial contractility. Endothelium-derived NO-mediated vascular relaxation is impaired in spontaneously hypertensive animals. NO decomposition by free oxygen radicals is a major mechanism of impaired NO bioavailability. The resulting imbalance of endothelium-derived relaxing and contracting substances disturbs the normal function of the vascular endothelium. Endothelin acts as the natural counterpart to endothelium-derived NO. Besides its arterial blood pressure rising effect in humans, endothelin-1 induces vascular and myocardial hypertrophy, which are independent risk factors for cardiovascular morbidity and mortality. Current therapeutic strategies concentrate mainly on lowering low-density lipoprotein cholesterol and an impressive reduction in the risk for cardiovascular morbidity and mortality has been achieved. Inflammatory mechanisms play an important role in vascular disease and inflammatory plasma markers correlate with prognosis. The production of reactive oxygen species under pathological conditions may represent an important inflammatory trigger. Novel therapeutic strategies specifically targeting inflammation thus bear great potential for the prevention and treatment of atherosclerotic vascular disease. In this context, the vascular actions of flavanol-rich cocoa, particularly with regard to enhanced NO synthesis and endothelial function observed in humans following consumption, warrants further attention. This review discusses pharmacological and dietary intervention.

Endogenous estrogens increase postischemic hyperemia in the skin microcirculation

Estrogens have been recognized as a major regulator of vascular tone and structure, particularly in the skin. The objective of this study was to investigate the effects of endogenous estrogens on the skin microcirculation. Skin blood flow was measured at the forearm at rest and during postischemic hyperemia using laser Doppler flowmetry in 32 healthy women (mean age 34.5 +/- 3.9 years) involved in an in-vitro fertilization program. Women were treated for 10 to 12 days with gonadotropin-releasing hormone agonist (total dose 40.3 +/- 3.3 mg) and human menopausal gonadotropin (1942 +/- 801 IE) or follicle-stimulating hormone (2544 +/- 1071 IE) according to individual estrogen levels. Plasma estrogen levels increased from 132 +/- 90 pmol/L (36 +/- 25 pg/mL) to 8471 +/- 4386 pmol/L (2308 +/- 1195 pg/mL) during treatment (P < 0.0001). Maximal hyperemic blood flow increased from 353 +/- 81% before treatment to 516 +/- 144% after hormonal stimulation (P < 0.0001), whereas basal skin flow was not altered. This study shows that endogenous estrogens enhance the postischemic hyperemic response of the skin microcirculation.

Platelet hyperactivity in clinical depression and the beneficial effect of antidepressant drug treatment: how strong is the evidence?

OBJECTIVE

Platelet hyperactivity is thought to contribute to the increased coronary artery disease (CAD) risk in depression. This study reviewed the evidence for hyperactive platelets and for effects of antidepressant drug treatment on platelet 'stickiness' in clinical depression.

METHOD

By means of PubMed electronic library search, 34 studies in English were identified (1983-2003) and critically reviewed.

RESULTS

In depression, flow cytometry studies allowing detection of subtle platelet activation states consistently found at least one platelet activation marker to be increased, while the bulk of platelet aggregation studies did not suggest increased platelet aggregability. Platelets seem to be more activated in depressed patients with CAD than in depressed individuals without CAD. The selective serotonin reuptake inhibitors normalized platelet hyperactivity in four studies.

CONCLUSION

Data on platelet activity in depression are inconclusive. To resolve this issue and its clinical implications, studies in larger sample sizes controlling for confounders of platelet functioning and prospectively designed are needed.

Statins in atherosclerosis: lipid-lowering agents with antioxidant capabilities

Low-density lipoprotein (LDL) cholesterol is an established risk factor for coronary heart disease (CHD). In the presence of oxidative stress LDL particles can become oxidized to form a lipoprotein species that is particularly atherogenic. Indeed, oxidized LDL (oxLDL) is pro-inflammatory, it can cause endothelial dysfunction and it readily accumulates within the arterial wall. Several factors may influence the susceptibility of LDL to oxidation, including its size and composition, and the presence of endogenous antioxidant compounds, such as alpha-tocopherol. Individuals with type 2 diabetes or the metabolic syndrome have high levels of oxidative stress and consequently are at an increased risk for cardiovascular events. Reducing oxidative stress has been proposed as a potential approach to prevent CHD and antioxidant vitamins have been employed with encouraging results in experimental models of atherosclerosis. However, clinical trials have not demonstrated consistent beneficial effects of antioxidants on cardiovascular outcomes. Statins (3-hydroxy-3-methylglutaryl coenzyme A reductase inhibitors) are the first-line choice for lowering total and LDL cholesterol levels and they have been proven to reduce the risk of CHD. Recent data suggest that these compounds, in addition to their lipid-lowering ability, can also reduce the production of reactive oxygen species and increase the resistance of LDL to oxidation. It may be that the ability of statins to limit the oxidation of LDL contributes to their effectiveness at preventing atherosclerotic disease.

ETA receptors mediate vasoconstriction of large conduit arteries during reduced flow in humans

Vascular tone is regulated by endothelium-derived vasodilating and constricting substances, mainly nitric oxide and endothelin (ET)-1. These 2 mediators, which antagonize the actions of each other, are released in response to shear-stress produced by blood flow. The aim of this study was to delineate the contribution of endogenous ET-1 on vascular tone of a large conduit artery during reduced and hyperemic flow. Radial artery diameter was continuously measured with a high-resolution ultrasonic echo-tracking device in 8 healthy subjects. After establishing stable baseline conditions, a wrist cuff was inflated to suprasystolic pressure for 5 minutes. In another 5 subjects, measurements were obtained during intraarterial infusion of saline or an ETA receptor antagonist (BQ-123, 1 nmol/min) in a dosage not affecting basal radial diameter. Wrist occlusion caused a progressive vasoconstriction of the radial artery (P = 0.0001). Vasoconstriction of the radial artery during wrist occlusion was significantly attenuated by ETA receptor antagonism (-2.7% +/- 0.6% versus -6.8% +/- 0.6% during saline, P = 0.007). Flow-mediated vasodilation was not influenced by BQ-123 (7.5% +/- 0.8% versus 7.8% +/- 1.1%, P = NS). This study demonstrates active vasoconstriction of large conduit arteries during conditions of reduced blood flow via ETA receptoractivation. This may play an important role in disease states with reduced systemic or local blood flow and indicates the therapeutic potential of ETA receptor antagonism.

Aspirin protects endothelial cells from oxidant damage via the nitric oxide-cGMP pathway

OBJECTIVE

Aspirin is known to exert cytoprotection by presently unidentified mechanisms. This study investigates the involvement of nitric oxide (NO) in antioxidant cellular protection induced by aspirin.

METHODS AND RESULTS

A 24-hour incubation with hydrogen peroxide markedly reduced viability of cultured endothelial cells. Preincubation with aspirin (3 to 30 micromol/L) protected endothelial cells from hydrogen peroxide-mediated toxicity and increased viability in a concentration-dependent fashion by up to 95% of control. This effect was specific in that other nonsteroidal anti-inflammatory drugs, such as salicylate or indomethacin, did not alter hydrogen peroxide toxicity. Aspirin-induced endothelial protection was abrogated in the presence of the NO scavenger PTIO (30 micromol/L) and the inhibitor of soluble guanylyl cyclase ODQ (1 micromol/L). Moreover, the l-arginine antagonist L-NMMA (25 micromol/L), but not its D-enantiomer, led to complete inhibition of aspirin-dependent cytoprotection. Correspondingly, aspirin enhanced NO synthase activity (citrulline formation) and intracellular cyclic GMP accumulation in endothelial cells. Protein expression of endothelial NO synthase remained unaffected in the presence of aspirin.

CONCLUSIONS

Our data suggest that endothelial NO synthase is a site of action of aspirin and that the NO/cyclic GMP system assumes a crucial function in mediating the cytoprotective action of aspirin.

Chronic high pressure potentiates the antiproliferative effect and abolishes contractile phenotypic changes caused by endothelial cells in cocultured smooth muscle cells

High in vitro pressures have been reported to alter smooth muscle cell (SMC) and endothelial cell (EC) phenotype, while endothelial cells (ECs) can influence the proliferation, phenotype, and contractile features of smooth muscle cells (SMC) in coculture systems. However, little is known about the in vitro effects of pressure on EC/SMC cocultures. We therefore sought to compare SMC proliferation in independent and EC coculture under ambient and high pressure, and identify changes in the contractile phenotype of SMCs by measuring levels of the L-type Ca(2+) channel a(1) subunit (dihydropyridine-DHP receptor) which is critical for Ca(2+) transients, differentiation and contractility in SMC.

METHODS

Rat aortic SMCs in independent culture (SMC/0) and coculture with ECs (SMC/EC) were maintained in 5% CO(2) under either atmospheric or high pressure (130 mmHg). SMC were counted at 0, 1, 3, and 5 days and compared to initial cell counts of day 0 before the exposure to experimental conditions. DHP receptor levels were quantitated by Western blotting (three similar studies).

RESULTS

ECs suppressed SMC proliferation on day 1 of coculture in both atmospheric and high pressure (20% inhibition vs independent culture, P < or = 0.05). By day 3, cocultured SMC under atmospheric pressure displayed no EC-mediated inhibition, and at day 5, atmospheric cocultured SMCs revealed statistically significant enhanced proliferation as compared with SMCs in independent cultures. However, cocultured SMCs exposed to 130 mmHg pressure displayed sustained sensitivity to EC growth inhibition at both days 3 and 5 of the experiment. Coculture decreased SMC DHP-receptor levels under atmospheric pressure. However, this effect was abolished in cocultures exposed to high pressure.

CONCLUSIONS

High pressure substantially alters the regulatory influence of EC on SMC proliferation and contractile potential. This pressure/coculture model should increase our understanding of cellular interaction in hypertensive vasculopathy.