Maintenance Of Vascular Homeostasis Research Articles

Controlling angiogenesis by two unique TGF-β type I receptor signaling pathways.

Genetic studies in mice and humans have revealed a pivotal function for transforming growth factor-beta (TGF-β) in vascular development and maintenance of vascular homeostasis. Mice deficient for various TGF-β signaling components develop an embryonic lethality due to vascular defects. In patients, mutations in TGF-β receptors have been linked to vascular dysplasia like Hereditary Hemorrhagic Telangiectasia (HHT) and pulmonary arterial hypertension (PAH). Besides indirect effects by regulating the expression of angiogenic regulators, TGF-β also has potent direct effects on endothelial cell growth and migration, and we have proposed that TGF-β regulates the activation state of the endothelium via two opposing type I receptor/Smad pathways, activin receptor-like kinase (ALK)1 and ALK5. TGF-β is also critical for the differentiation of mural precursors into pericytes and smooth muscle cells. Furthermore, defective paracrine TGF-β signaling between endothelial and neighboring mural cells may be responsible for a leaky vessel phenotype that is characteristic of HHT. In this review, we discuss our current understanding of the TGF-β signaling pathway and its regulation of endothelial and vascular smooth muscle cell function.

CGMP and PKGI are required for vascular BMP signaling

Background Maintenance of vascular homeostasis depends on phenotypic switching of vascular smooth muscle cells (VSMCs) during development, vascular injury repair, and disease. In healthy blood vessels, VSMCs exhibit a differentiated, ‘contractile’ phenotype, but in diseased vascular tissue or after vascular injury, they de-differentiate into a ‘synthetic’ state, characterized by decreased smooth muscle (SM)-specific gene expression and increased proliferation and motility [1].

Widespread distribution of HLA-DR-expressing cells in macroscopically undiseased intima of the human aorta: A possible role in surveillance and maintenance of vascular homeostasis

The architectonics and cell composition of the human large arteries are not sufficiently understood. The present study is the first to undertake an analysis of the distribution and quantities of HLA-DR-expressing cells in grossly undiseased human intima using immunohistochemical and immunofluorescent analysis, complemented by the advantages of confocal microscopy. The study revealed a widespread distribution of HLA-DR-expressing cells throughout the intimal space where the cells were integrated into continuous networks via long cell processes. Numbers of HLA-DR+ cells were found to be significantly larger in the middle third of the intima than in the superficial and deep intimal portions. We speculate that a widespread distribution of HLA-DR-expressing cells in the intima of normal human aorta might play a role in the surveillance and maintenance of vascular homeostasis.

The role of nuclear endothelial nitric oxide synthase in the endothelial and prostate microenvironments.

This review is based on novel observations from our laboratory on the nuclear translocation and functional role of endothelial nitric oxide synthase (eNOS) in endothelial and prostate cancer (PCa) epithelial cells. Nitric oxide (NO), the product of eNOS, is a free radical involved in the physiology and pathophysiology of living organisms and in a variety of biological processes including the maintenance of vascular homeostasis. Of relevance in this context is the role that estrogens play in the apoptotic process and the migration of endothelial cells through the regulation of target genes such as eNOS itself. It has been shown that both estrogen and NO signaling, mediated respectively by the estrogen receptors (ERs) and eNOS, can strongly counteract endothelial senescence through a common effector, the catalytic subunit of human telomerase. Therefore, this protein has been identified as a key molecule in the aging process which, intriguingly, is considered the only risk factor in the development of PCa and one of the major determinants of cardiovascular diseases. Indeed, in both these contexts we have defined a molecular mechanism involving activation of eNOS and hypoxia-inducible factors in association with ERβ that characterizes the most aggressive form of PCa or influences endothelial cell differentiation. Altogether these data led us to postulate that activation of eNOS is a crucial requirement for the delaying of endothelial senescence as well as for the acquisition of androgen-independence and for tumor progression in the prostate microenvironment.

Dysregulation of angiogenesis-related microRNAs in endothelial progenitor cells from patients with coronary artery disease

Endothelial progenitor cells (EPCs) play an important role in vascular repair and maintenance of vascular homeostasis through re-endothelialization and neovascularization. Cardiovascular risk factors that contribute to coronary artery disease (CAD) have been shown to negatively impact EPCs, although the mechanisms are poorly understood. MicroRNAs (miRNAs) which negatively regulate gene expression at the post-transcriptional level have been shown to impact endothelial cell (EC) angiogenic actions, but little is known about their role in modulating EPC function. In this study we first investigated if EPCs expressed EC specific, angiogenesis-related miRNAs; then determined whether the expression of these miRNAs was altered in EPCs from CAD patients as compared with healthy controls. Furthermore, we examined if atorvastatin, known to increase circulating EPC numbers, had any effect on EPC miRNA expression. We found EPCs produced miR-126, miR-130a, miR-221, miR-222 and miR-92a which have thus far been identified as the most important angiogenic miRNAs. Dysregulation of these miRNAs was detected in EPCs from CAD patients and atorvastatin treatment selectively impacted miRNA expression in EPCs. Our data provide evidence that angiogenic miRNAs might play an important role in the control of EPC function, and that their dysregulation might contribute to EPC dysfunction in patients suffering from coronary artery disease. These findings might lead to the development of novel therapeutic modalities for the prevention and treatment of CAD.

THE S1P1 AGONIST AUY954 ACTIVATES ENOS VIA AKT-MEDIATED PATHWAY: 1D.02

Objective: In the mammalian cardiovascular system, nitric oxide (NO) plays a pivotal role in the maintenance of vascular homeostasis. The endothelial isoform (eNOS) is a key determinant of blood pressure or other fundamental response in the vascular wall. Sphingosin-1-phosphate (S1P) is a bioactive sphingolipid which regulates diverse physiological processes by serving as ligand to G-protein coupled S1P receptors and recently identified as eNOS activator, whereas the S1P1 receptor play a key role. A newly developed mono-selective S1P1 modulator – AUY954 – should be investigated in this study on its potential to active eNOS. Methods: Human umbicial vein endothelial cells (HUVEC) were used. S1P receptor mRNA was detected via RT-PCR. Phosphorylation of eNOS was detected by Western Blot technique. Akt phosphorylation was measured using Luminex™ technology. The production of NO was measured in DAF2-DA labeled cells. Results: AUY954 [0.1 – 10 μmol/L] led to a significant and dose-dependent increase in NO liberation in HUVEC detected by fluorescence increase in DAF2-DA labelled cells. This effect could be blocked by L-NAME [100 μmol/L], an inhibitor of NO synthases. AUY954 significantly increase Ser1177 phosphorylation time- and dose-dependently. S1P1 and S1P3 receptor are the most prominent S1P receptors in HUVECs and only a weak expression of S1P2 was detectable. So, we next investigated a specific, non-selective inhibitor of S1P1/3 receptor, VPC23019 which significantly block the AUY954-induced NO liberation. Cay10444, a selective S1P3 antagonist doesn't have any effect. This indicates a S1P1 specific effect. Furthermore, AUY954 is able to stimulate Akt phosphorylation in a significant and time-dependent manner. The co-stimulation of AUY954 with a specific Akt inhibitor blocked the NO production in DAF2-DA labeled HUVECs. Conclusions: Here, we showed that the selective S1P1 receptor agonist AUY954 is a very potent activator of endothelial NO synthase via a Akt-mediated process which results in increased NO liberation of human endothelial cells. Therefore, eNOS/NO activation by AUY954 might play a role in cardiovascular response by promoting endothelial cell survival, proliferation and migration.

Number of circulating endothelial progenitor cells as a marker of vascular endothelial function for type 2 diabetes

Vascular endothelial dysfunction is an early marker of atherosclerosis seen in type 2 diabetes (T2DM). Circulating endothelial progenitor cell (EPC) is involved in the neovasculogenesis and maintenance of vascular homeostasis, whose impairment may have an important role in the pathogenesis of diabetic vasculopathy. This study was performed to investigate the relationship between vascular endothelial function and circulating EPC number in T2DM. A total of 46 newly diagnosed T2DM patients (DM group) and 51 healthy subjects (NG group) were recruited. Metformin was administered to all patients for 16 weeks. Endothelial function was assessed by flow-mediated brachial artery dilatation (FMD). EPC was defined by CD45( low)/CD34(+)/VEGFR2(+) and quantified by flow cytometry. The EPC number in the DM group was significantly lower than that in the NG group (p < 0.001), and improved markedly after treatment (p < 0.001). The results of FMD were consistent with EPC variations among the three groups (p < 0.001). In multivariate regression analysis, the EPC number was an independent risk factor for FMD at baseline (p < 0.05). The absolute changes of EPC number showed significant correlation with the changes of FMD before and after treatment (r = 0.63, p < 0.001). This study demonstrated that the circulating EPC number was related to endothelial function and could be considered as a surrogate biological marker of endothelial function for T2DM.

The Effect of Graft-Versus-Host Disease on Skin Endothelial and Epithelial Cell Chimerism in Stem-Cell Transplant Recipients

Recent evidence indicates that bone marrow-derived cells contribute to endothelial and epithelial cell renewal in recipients of an allogeneic stem-cell transplantation (SCT). Controversy remains on the biological significance of these donor-derived cells. This study investigated the occurrence of endothelial and epithelial cell chimerism in relation to the conditioning regimen, time interval after SCT, and development of acute and chronic graft-versus-host disease (GVHD). Fifty-five skin biopsy samples from 35 female patients transplanted with a male donor were screened for donor-derived endothelial and epithelial cells using in situ hybridization for Y chromosomes in combination with immunohistochemical cell-marking techniques. Endothelial cell chimerism was found in 25% of the biopsies and increased in time after SCT. Its appearance was increased in patients with acute GVHD more than 2 weeks before biopsy. Epithelial cell chimerism was found in 85% of the biopsies. Appearance of epithelial cell chimerism was not correlated with the time interval after SCT or with tissue damage caused by GVHD. From these results, we conclude that donor-derived endothelial cell chimerism results from repair of damaged endothelium and maintenance of vascular homeostasis. In contrast, epithelial cell chimerism follows a more uniform pattern of engraftment, not influenced by tissue damage.

Non-Invasive Diagnostic Tools for Investigating Endothelial Dysfunction

The endothelium is not merely a barrier but it plays a key role in the maintenance of vascular homeostasis. A dysfunctional endothelium is an early marker of the development of atherosclerotic changes and can also contribute to cardiovascular events. Vascular reactivity tests represent the most widely used methods in the clinical assessment of endothelial function and in the last two decades, several methodologies were developed to study it non invasively in the peripheral macrocirculation (conduit arteries) and microcirculation (resistance arteries and arterioles). This review will centre on the most relevant available non-invasive techniques in the research on endothelial function, their advantages and limitations. Flow mediated dilation (FMD) of the brachial artery by ultrasounds is the most widely used vascular test to assess endothelium-dependent vasodilation. Other approaches include measurement of microcirculatory reactive hyperaemia by forearm venous pletysmography or digital pulse amplitude tonometry, response to beta2 agonist by applanation tonometry or digital photoplethysmography and several test by skin laser doppler. It appears that FMD is the most reproducible test when an appropriate and accurate methodology is applied. Recently, post-ischemic vasodilation in the cavernous arteries was also suggested to study endothelial function in patients with erectile dysfunction. Systemic markers proposed as measures of NO biology, inflammatory cytokines, adhesion molecules, or markers of endothelial damage and repair have only a very limited role as a result of biological and assay availability and variability, these factors currently have a limited role in the assessment of individual patients. The optimal methodology for investigating the multifaceted aspects of endothelial dysfunction is still under debate. Therefore, no available test to assess endothelial function has sufficient sensitivity and specificity to be used yet in clinical practice. Only the growing concordant results from different reproducible and reliable non-invasive methods exploring endothelial function with different stimuli will support and strengthen experimental findings, thus providing conclusive answers in this area of research.

Angiotensin converting enzyme-2 confers endothelial protection and attenuates atherosclerosis

The endothelium plays a central role in the maintenance of vascular homeostasis. One of the main effectors of endothelial dysfunction is ANG II, and pharmacological approaches to limit ANG II bioactivity remain the cornerstone of cardiovascular therapeutics. Angiotensin converting enzyme-2 (ACE2) has been identified as a critical negative modulator of ANG II bioactivity, counterbalancing the effects of ACE in determining net tissue ANG II levels; however, the role of ACE2 in the vasculature remains unknown. In the present study, we hypothesized that ACE2 is a novel target to limit endothelial dysfunction and atherosclerosis. To this aim, we performed in vitro gain and loss of function experiments in endothelial cells and evaluated in vivo angiogenesis and atherosclerosis in apolipoprotein E-knockout mice treated with AdACE2. ACE2-deficient mice exhibited impaired endothelium-dependent relaxation. Overexpression of ACE2 in human endothelial cells stimulated endothelial cell migration and tube formation, and limited monocyte and cellular adhesion molecule expression; effects that were reversed in ACE2 gene silenced and endothelial cells isolated from ACE2-deficient animals. ACE2 attenuated ANG II-induced reactive oxygen species production in part through decreasing the expression of p22phox. The effects of ACE2 on endothelial activation were attenuated by pharmacological blockade of ANG-(1-7) with A779. ACE2 promoted capillary formation and neovessel maturation in vivo and reduced atherosclerosis in apolipoprotein E-knockout mice These data indicate that ACE2, in an ANG-(1-7)-dependent fashion, functions to improve endothelial homeostasis via a mechanism that may involve attenuation of NADPHox-induced reactive oxygen species production. ACE2-based treatment approaches may be a novel approach to limit aberrant vascular responses and atherothrombosis.

Implicaciones del óxido nítrico y otras moléculas con potencial redox en el glaucoma primario de ángulo abierto

Nitric oxide (NO) and other molecules with redox potential are involved in cell signalling, including endothelial-dependent relaxation and the maintenance of vascular homeostasis. We investigated the availability of NO and the formation of reactive oxygen species (ROS) in the aqueous humour and its relationship to the pathogenic mechanisms of primary open-angle glaucoma (POAG). We analysed biochemically aqueous humour samples from patients having anterior segment surgery that were divided into two separate groups: 1) patients having a Watson's trabeculectomy because of worsening of the glaucoma evolution (GG; n=60), and 2) a comparative group of individuals having phacoemulsification for non-complicated cataracts (CG; n=60). Enzymatic-colorimetric methods were used to analyse the NO concentration, the lipid peroxidation by-product malondialdehyde (MDA) and the total antioxidant status (TAS). Statistical analysis was carried out in the two groups by means of the SPSS 15.0 programme. A significant increase in both the NO concentration (p<0.05) and MDA levels (p<0.05), and a significant decrease of the TAS (p<0.05) were detected in the GG versus the CG samples. Changes in NO availability and the concomitance of oxidative stress in the aqueous humour of the POAG patients may be useful markers for identifying those at risk of glaucoma progression and visual loss.

Abstract 916: Klotho-protein Regulates Transient Receptor Potential Canonical-1-mediated Ca(2+)-influx In Endothelial Cells And Prevents Cell Death And Disruption Of Endothelial Integrity Induced By Ca(2+)-overload

Introduction Klotho-deficient mice have extensive vascular calcification. However, the mechanism involved has not been elucidated. We analyzed the endothelial cells of Klotho-deficient mice (Klotho-ECs) and found a novel functional role for the Klotho-protein in the maintenance of vascular homeostasis. Methods and Results Primary-cultured endothelial cells from the aorta of wild-type- (WT) and Klotho- deficient mice were loaded with fura-2 and stimulated with VEGF. In WT-ECs, intracellular Ca(2+) concentration ([Ca(2+)]i) elevated to the peak level, and it decreased to the basal level in +5 minutes. Whereas, in Klotho-ECs, after similar peak level to WT-ECs, the elevation of [Ca(2+)]i was sustained at ~35% of the peak level for more than 10 minutes. In Ca(2+) free medium, this sustained elevation was abolished. Immunostaining revealed that, in Klotho-ECs, VEGF-induced co-internalization of the Ca(2+) channel; TRPC-1, with VEGF-receptor-2 (VEGFR-2) was abolished, thereby, at 30 minutes after VEGF-stimulation, expression levels of TRPC-1 in the plasmamembrane was 2.2-fold higher than in WT-ECs. Klotho-protein constitutively bound to VEGFR-2 and TRPC-1, strengthened their association, and promoted their co-internalization. VEGF-induced activation of Rac-1 and reorganization of F-actin, which are involved in internalization, were impaired in Klotho-ECs, and restored by the replacement of Klotho-protein. VEGF-induced phosphorylation of VEGFR-2 and its downstream signaling molecules, including Src, Akt, PLCγ, and Caveolin1, was attenuated. As the biological consequence of sustained increase in [Ca(2+)]i, activation of calpain and caspase-3 followed by apoptosis was promoted in Klotho-ECs in vivo and vitro. Also, expression of VE-cadherin in the plasmamembrane was reduced and intimal hyperpermeability was observed in the aorta of Klotho-deficient mice, which presumably lead to exudation of the Ca(2+)/phosphor -rich serum into the vessel walls, followed by extensive vascular calcification. Conclusion Thus, Klotho-protein regulates ligand-induced Ca(2+) influx and subsequent biological functions involved in vascular calcification.

Abstract 1041: Endovascular Injury Affects Adipocytokine Profile Of The Periadventitial Adipose Tissue

Background: Adipose tissue secretes not only proinflammatory cytokines but also anti-inflammatory cytokines such as adiponectin. Arteries are surrounded by abundant periadventitial fat tissues, which have been suggested to play a role in maintenance of vascular homeostasis. Here, we investigated whether endovascular injury affects the profile of adipocytokines expressed by perivascular adipose tissue (PAT). Methods and Results: First, the femoral artery of C57BL/6 mice was overstretched by insertion of a large wire. Real-time PCR analysis revealed that wire injury markedly down-regulated adiponectin expression (0.64±0.09 fold, p&lt;0.01) and up-regulated expression of proinflammatory cytokines, TNF alpha, IL-6, PAI-1, and MCP-1 (p&lt;0.01) 1 day after overstretch within PAT. Neutrophils and macrophages accumulated in the adventitia surrounding the injury site at 1 day after the injury. Inflammation was associated temporally with the expression of mRNAs encoding inflammatory adipocytokines. Second, the iliac artery of Wistar rats was dilated percutaneously with a balloon for 1 minute. There were up-regulation of proinflammatory cytokines and down-regulation of adiponectin 1 and 3days after endovascular injury within PAT (p&lt;0.05). Third, abdominal aortas removed from Wistar rat with PAT were dilated with a balloon PTCA catheter for 1 minute ex vivo. After stretching, aortas with PAT were cultured for 6 hours, and we observed increased synthesis of proinflammatory cytokines and decreased synthesis of adiponectin within PAT (p&lt;0.05). Fourth, the stimulation of TNF alpha, which markedly increased in injured arteries, caused significant down-regulation of adiponectin expression and up-regulation of IL-6, PAI-1, and MCP-1 in 3T3L1-derived adipocytes (p&lt;0.01). Conclusions: Angioplasty may induce the changes of perivascular cytokines expression. The accumulation of neutrophils and macrophages at PAT in injured arteries and/or increased proinflammatory expression of injured vascular arteries may reflect these proinflammatory activities of PAT. Increased proinflammatory cytokines and decreased anti-inflammatory cytokine adiponectin in PAT possibly may have a role in vascular remodeling following PTCA-mediated vascular injury.

Mechanisms Underlying the Cardiovascular Effects of COX-Inhibition: Benefits and Risks

Selective inhibitors of cyclooxygenase-2 (COX-2) were designed to minimize gastrointestinal complications of traditional non-steroidal anti-inflammatory drugs (NSAIDs) attributed to the suppression of COX-1-derived prostanoids. Selective COX-2 inhibitors (coxibs) are effective anti-inflammatory and analgesic drugs. However, recently it has become apparent that some coxibs increase the risk of serious cardiovascular events, including myocardial infarction and stroke. This has led to the withdrawal of rofecoxib from markets and has raised the concern about an inherent atherothrombotic risk of this class of drugs. This question should be carefully analyzed in the light of the current knowledge on COX-2 functions in the cardiovascular system. COX-2 is regarded as an inducible enzyme involved in the pathophysiology of inflammation and pain. In the cardiovascular system, COX-2 has also been associated with pro-inflammatory/pro-atherogenic stages, due to its up-regulation in monocyte-derived macrophages present in atherosclerotic lesions. However, experimental and clinical studies suggest that COX-2 is "constitutively" expressed in some tissues, among them in the vascular endothelium, where COX-2-derived prostanoids, especially prostacyclin (PGI(2)), contribute in the maintenance of vascular homeostasis and integrity. This review provides an updated overview on the functions of COX-2 in the cardiovascular system addressing key issues that could help to understand why chronic COX-2 inhibition may have undesirable effects in patients at cardiovascular risk.

Diabetes mellitus as a prothrombotic condition

Diabetes mellitus (DM) is characterized by fasting hyperglycaemia and a high risk of atherothrombotic disorders affecting the coronary, cerebral and peripheral arterial trees. The risk of myocardial infarction (MI) is 3-5 fold higher in Type 2 DM and a DM subject with no history of MI has the same risk as a non-DM subject with a past history of MI. In total around 70% of deaths are vascular with poorer outcomes to both acute events and cardiological interventions. It was proposed that clustering of vascular risk factors (hyperinsulinaemia, dysglycaemia, dyslipidaemia and hypertension) around insulin resistance (IR) accounted for the increase in risk with Type 2 DM. The importance of this became apparent with the recognition that risk clustering occurs in normoglycaemic and impaired glucose tolerance (IGT) subjects with IR, in total around 25% of the population in addition to long-standing Type 1 subjects with renal disease. Evidence indicates that thrombotic risk clustering also occurs in association with IR, suppression of fibrinolysis due to elevated concentrations of the fibrinolytic inhibitor, plasminogen activator inhibitor-1 (PAI-1) is invariable with IR and there is evidence that this is regulated by the effects of triglyceride on the PAI-1 gene promoter. Other studies indicated that prothrombotic risk (coagulation factors VII, XII and fibrinogen) also associates with the IR syndrome. The development of endothelial cell dysfunction with suppression of nitric oxide and prostacyclin synthesis, combined with platelet resistance to the anti-aggregatory effects of these hormones leads to loss of control over platelet activation. In addition, hyperglycaemia and glycation have marked effects on fibrin structure function, generating a clot which has a denser structure, resistant to fibrinolysis. The combination of increased circulating coagulation zymogens, inhibition of fibrinolysis, changes in fibrin structure/function and alterations in platelet reactivity creates a thrombotic risk clustering which underpins the development of cardiovascular disease.

Peroxisome Proliferator-Activated Receptor-&amp;#947; in Vascular Biology

Peroxisome proliferator-activated receptor-gamma (PPAR-gamma) belongs to a family of ligand-activated nuclear receptor and transcription factors. The essential roles of PPAR-gamma in controlling metabolic processes have been underscored by the successful use of PPAR-gamma agonists thiazolidinediones to treat insulin resistance, a central feature of metabolic syndrome. PPAR-gamma is also expressed in the vascular tissues including endothelial cells (ECs), smooth muscle cells (SMCs) and macrophages. Increasing evidence suggests that PPAR-gamma is implicated both in the maintenance of vascular homeostasis and in the pathogenesis of a number of vascular conditions such as atherosclerosis, hypertension and restenosis. As an important regulator of vascular biology, PPAR-gamma may represent a potential therapeutic target for these metabolic vascular disorders. This review will focus on the recent advances related to the biological functions of PPAR-gamma in various vascular processes as well as the significances of the pharmacological activators/modulators of this metabolic nuclear receptor in vascular disorders.

Activation of endothelial nitric oxide synthase by dietary isoflavones: Role of NO in Nrf2-mediated antioxidant gene expression

The endothelium plays a key role in the maintenance of vascular homeostasis, and increased oxidative stress in vascular disease leads to reduced nitric oxide bioavailability and impaired endothelium-dependent relaxation of resistance vessels. Although epidemiological evidence suggests that diets containing high amounts of natural antioxidants afford protection against coronary heart disease (CHD), antioxidant supplementation trials have largely reported only marginal health benefits. There is controversy concerning the cardiovascular benefits of prolonged estrogen/progestin or soy isoflavone therapy for postmenopausal women and patients with an increased risk of CHD. Research on the potential health benefits of soy isoflavones and other polyphenols contained in red wine, green and black tea and dark chocolate developed rapidly during the 1990's, and recent clinical trials and studies in animal models and cultured endothelial cells provide important and novel insights into the mechanisms by which dietary polyphenols afford protection against oxidative stress. In this review, we highlight that NO and reactive oxygen radicals may mediate dietary polyphenol induced activation of Nrf2, which in turn triggers antioxidant response element (ARE) driven transcription of phase II detoxifying and antioxidant defense enzymes in vascular cells.

Gene and Stem Cell Therapy in the Treatment of Erectile Dysfunction and Pulmonary Hypertension; Potential Treatments for the Common Problem of Endothelial Dysfunction

The endothelium has an important regulatory role in the maintenance of vascular homeostasis, vascular tone, blood flow, and in preserving a non-thrombogenic blood-tissue interface. Injury to the vascular wall with subsequent endothelial dysfunction alters these important regulatory functions leading to a state of abnormal endothelial function. In this paper, we review the pathophysiology of endothelial dysfunction and how this disorder is common to the development of erectile dysfunction and of pulmonary arterial hypertension. Current medical therapies for these two disorders are discussed followed by a review of the preclinical studies involving currently available strategies for gene and stem cell therapy and their potential for the clinical treatment of these two disorders of endothelial dysfunction.

Nitric Oxide and Malondialdehyde in Human Hypertension

Nitric oxide (NO), a multifunctional effector molecule that plays a central role in the maintenance of vascular homeostasis, regulates vascular tone and inhibits platelet and leukocyte adhesion to endothelial cells. NO status is related to the endothelial function. Patients with hypertension have lower levels of NO, increased free radical production, higher oxidative stress, augmented platelet aggregation, and a change in the arachidonic acid cascade metabolism, all leading to the acceleration of the atherosclerotic process. The study subjects included a group of 21 normotensive healthy subjects (8 males and 13 females) with a mean age of 39.2 +/- 1.8 years and a body mass index of 27.9 kg/m, and another group of 42 patients (19 males and 23 females) with untreated essential hypertension with a mean age of 47.6 +/- 1.7 years and a body mass index of 28.3 kg/m. Serum levels and urinary excretion of NO determined as combined nitrate/nitrite (NOx) and serum malondialdehyde (MDA) concentrations were measured in the 2 groups of subjects. The serum levels and 24-hour urinary excretion of NOx were significantly higher and the renal clearance of NO was lower in the normotensive group than in the hypertensive patients, indicating decreased NO status in hypertension. There was a negative correlation between serum NO levels and mean arterial pressure, suggesting that a decrease in NO availability is related to increase in blood pressure. Serum concentrations of MDA were higher in the hypertensive patients as compared with the normotensive individuals, suggesting increased oxidative stress in hypertensive patients. These results are in agreement with previous studies showing decreased NO and increased oxidative stress in hypertension. In conclusion, patients with essential hypertension as compared with normotensive individuals have lower NO status, which may contribute to the endothelial dysfunction in hypertension. Increased serum malondialdehyde in hypertensives suggests an association between increased oxidative stress with higher blood pressure.

Preconditioning with low concentration NO attenuates subsequent NO-induced apoptosis in vascular smooth muscle cells via HO-1-dependent mitochondrial death pathway

Nitric oxide (NO) signaling pathways are important in both the maintenance of vascular homeostasis and disease progression. Overproduction of NO has been associated with ischemia/reperfusion (I/R) injury. Growing evidences suggest that NO preconditioning has cytoprotective effects against I/R injury. However, the mechanism with which NO mediates these effects remains to be elucidated. The purpose of this study was to examine the mechanism of how NO preconditioning inhibits subsequent NO-induced apoptosis in vascular smooth muscle cells (VSMC), specifically focusing on heme oxygenase-1 (HO-1). According to our data, sodium nitroprusside (SNP) increased HO-1 expression in a concentration dependent manner. Preconditioning with low concentration SNP (0.3mM) inhibited subsequent high concentration SNP (1.5mM)-induced apoptosis, and this effect was reversed by the HO-1 inhibitor SnPP. Low concentration SNP-mediated protection involved p38 kinase inactivation and increased Bcl-2 expression. Furthermore, mitochondrial membrane potential was concomitantly increased with decreased expressions of Bax, Apaf-1, and activity of caspase-3, which was reversed by SnPP treatment. Our results show that low concentration SNP preconditioning suppresses subsequent high concentration SNP-induced apoptosis by inhibiting p38 kinase and mitochondrial death pathway via HO-1-dependent mechanisms in VSMC.