Vascular superoxide production by NAD(P)H oxidase: association with endothelial dysfunction and clinical risk factors

Resveratrol supplementation gender independently improves endothelial reactivity and suppresses superoxide production in healthy rats

PURPOSE

Resveratrol, a polyphenolic compound mainly abundant in red wines, has beneficial cardiovascular effects on various pathological conditions. However, at present, the effect of resveratrol on health promotion remains unclear. Therefore, in this study, we assessed whether long-term resveratrol supplementation changes endothelial function, vascular contractility, nitric oxide and superoxide production in healthy male and female rats.

METHODS

Wistar rats were treated with resveratrol (50 mg/l) in their drinking water for 3 weeks. We investigated relaxation to acetylcholine (10(-9)-10(-4) M) and contractions to phenylephrine (10(-9)-3 x 10(-4) M) and angiotensin II (10(-10)-10(-5) M) in either endothelium-intact or denuded aortae from control and resveratrol-treated male and female rats. Aortic superoxide production capacity was measured in response to provocation by angiotensin II and NAD(P)H. Plasma nitrite/nitrate levels and superoxide dismutase (SOD) activity were also evaluated.

RESULTS

Resveratrol supplementation gender independently increased relaxation to acetylcholine and decreased contractions to phenylephrine and angiotensin II in endothelium-intact aortic rings, but not in endothelium-denuded arteries, from healthy male and female rats. This was associated with increased plasma nitrite/nitrate levels. Furthermore, resveratrol caused a refractoriness to angiotensin II and NAD(P)H-induced provocation in superoxide production.

CONCLUSION

Our results suggest that resveratrol supplementation gender independently could improve the capacity of endothelial function and suppression of oxidative stress under physiological conditions. Resveratrol ingestion indicates a potential for cardiovascular health promotion.

Dihydrochalcones: Implication in resistance to oxidative stress and bioactivities against advanced glycation end-products and vasoconstriction

Flavonoids are a group of polyphenol compounds with known antioxidant activities. Among them, dihydrochalcones are mainly found in apple leaves (Malus domestica). Glycosylated dihydrochalcones were previously found in large amounts in leaves of two genotypes of Malus with contrasting resistance to fire blight, a bacterial disease caused by Erwinia amylovora. In the present study we demonstrate that soluble polyphenol patterns comprised phloridzin alone or in combination with two additional dihydrochalcones, identified as sieboldin and trilobatin. Presence of sieboldin in young leaves correlated well with a high 1,1-diphenyl-2-picrylhydrazyl (DPPH) free radical scavenging activity. Moreover, these leaves displayed enhanced tolerance to paraquat, a photooxidative-stress generating herbicide. Interestingly, phloridzin had a high activity in the oxygen radical absorbance capacity (ORAC) assay, but its presence alone in leaves did not correlate with tolerance to paraquat. In order to further characterise the activity of these compounds, we tested their ability to prevent oxidative-dependent formation of advanced glycation end-products (AGEs) and phenylephrine-induced contraction of isolated rat mesenteric arteries. The antioxidant capacity of sieboldin was clearly demonstrated by showing that this compound (i) prevented vasoconstriction and (ii) inhibited AGEs formation. Both assays provided interesting information concerning a potential use of sieboldin as a therapeutic. Hence, our results strongly argue for a bioactivity of dihydrochalcones as functional antioxidants in the resistance of Malus leaves to oxidative stress. In addition, we demonstrate for the first time that sieboldin is a powerful multipotent antioxidant, effective in preventing physiopathological processes. Further work should aim at demonstrating the potential use of this compound as a therapeutic in treating free radical-involving diseases.

Molecular mechanisms underlying PGF2alpha-induced hypertrophy of vascular smooth muscle cells

The present review focuses primarily on the studies we made in recent years to improve the understanding of the molecular mechanisms of PGF2alpha-induced hypertrophy of Vascular Smooth Muscle Cells (VSMC). In this review, we will summarize the recent findings in the context of the PGF2alpha signaling pathway in three parts: PGF2alpha binding to its receptor, transactivation of EGF receptor, two independent signaling transduction pathways increasing the expression of NOX1 gene.

Targeting the redox regulation of SERCA in vascular physiology and disease

The sarco/endoplasmic reticulum calcium ATPase (SERCA) is essential for the control of intracellular free Ca(2+) levels. Although the importance for this enzyme in cardiac myocytes is well recognized, it is only recently that SERCA has been identified as an important effector of nitric oxide (NO) action in vascular cells. NO can stimulate the uptake of cytosolic Ca(2+) via SERCA by adducting glutathione to the reactive cysteine-674. Mutation of this single amino acid prevents the stimulation of Ca(2+) uptake by NO, as well as its ability to inhibit smooth muscle cell functions including migration. NO function is impaired in a variety of cardiovascular diseases, including diabetes, hypercholesterolemia, and atherosclerosis, which are all associated with SERCA dysfunction caused by the increased oxidants in these diseases. Targeting the oxidant sources in vascular diseases to prevent SERCA from being oxidized and/or increasing the expression of SERCA may improve vascular disease development.

Eotaxin increases monolayer permeability of human coronary artery endothelial cells

OBJECTIVE

The objective of this study was to determine the effects and molecular mechanisms of eotaxin, a newly discovered chemokine (CCL11), on endothelial permeability in the human coronary artery endothelial cells (HCAECs).

METHODS AND RESULTS

Cells were treated with eotaxin, and the monolayer permeability was studied by using a costar transwell system with a Texas Red-labeled dextran tracer. Eotaxin significantly increased monolayer permeability in a concentration-dependent manner. In addition, eotaxin treatment significantly decreased the mRNA and protein levels of endothelial junction molecules including zonula occludens-1 (ZO-1), occludin, and claudin-1 in a concentration-dependent manner as determined by real-time RT-PCR and Western blot analysis, respectively. Increased oxidative stress was observed in eotaxin-treated HCAECs by analysis of cellular glutathione levels. Furthermore, eotaxin treatment substantially activated the phosphorylation of MAPK p38. HCAECs expressed CCR3. Consequently, antioxidants (ginkgolide B and MnTBAP), specific p38 inhibitor SB203580, and anti-CCR3 antibody effectively blocked the eotaxin-induced permeability increase in HCAECs. Eotaxin also increased the phosphorylation of Stat3 and nuclear translocation of NF-kappaB in HCAECs.

CONCLUSIONS

Eotaxin increases vascular permeability through CCR3, the downregulation of tight junction proteins, increase of oxidative stress, and activation of MAPK p38, Stat3, and NF-kB pathways in HCAECs.

Docosahexaenoic acid down-regulates endothelial Nox 4 through a sPLA2 signalling pathway

We investigated the anti-inflammatory and antioxidant activities of docosahexaenoic acid (DHA) by evaluating its modulation of the two enzymes most involved in vascular inflammation, i.e. endothelial secreted phospholipase A(2) (sPLA(2)) and NADPH oxidase 4 (Nox) 4. Exposure of human aortic endothelial cells (HAECs) to DHA led to its preferential incorporation into outer leaflet phospholipids. Pre-treatment with DHA abolished HAECs stimulation induced by A23187 and Ang II, whereas the effects on IL-1beta treatment were less pronounced. Group V sPLA(2) RNA was similarly modulated by DHA supplementation. In addition, DHA decreased Nox 4 expression and activity; this effect was associated with reduced production of reactive oxygen species. Further, the use of specific inhibitors allowed demonstrating that group V sPLA(2) is involved in the down-regulation of Nox 4 expression and activity by DHA. This interplay is mediated by ERK and PKC.

Reactive Oxygen Species–Mediated Signal Transduction in the Endothelium

The endothelium is an important component of vascular homeostasis that is a target for injury in the setting of vascular disease. One means of promoting a maladaptive endothelial cell phenotype such as that seen in atherosclerosis is excess oxidative stress. Although this term once was almost exclusively used to describe low-density lipoprotein (LDL) and lipid oxidation in the vasculature, we now understand that the intracellular oxidant milieu is an important modulator of vascular cell function. Indeed, considerable data indicate that reactive oxygen species (ROS) are an important means of cellular signaling, although the precise mechanisms whereby ROS accomplish this are still under investigation. In this review, the data linking ROS to kinase activation and cell signaling in the endothelium is discussed, with a particular emphasis on the roles of protein thiol modification.

Accelerated atherosclerosis in inflammatory rheumatic diseases

Over recent years it has become clear that patients with inflammatory rheumatic diseases are at increased risk of developing atherosclerosis. The exact causes for this are probably related in part to a general adverse effect of inflammation on atherogenesis, and in part to immune mechanisms specific to individual rheumatic diseases. This review discusses proposed mechanisms of accelerated atherosclerosis, including abnormal lipid and lipoprotein profiles, oxidative stress, enhanced apoptosis, thrombophilia, immune complexes, and increased mononuclear cell infiltration of atherosclerotic lesions, and local generation of cytokines.

Nitric oxide, NAD(P)H oxidase, and atherosclerosis

The endothelial cell layer plays a major role in the development and progression of atherosclerosis. Endothelial NO synthase (eNOS) produces nitric oxide (NO) from L-arginine. NO can rapidly react with reactive oxygen species to form peroxynitrite. This reduces NO availability, impairs vasodilatation, and mediates proinflammatory and prothrombotic processes such as leukocyte adhesion and platelet aggregation. In the vessel wall, specific NAD(P)H oxidase complexes are major sources of reactive oxygen species. These NAD(P)H oxidases can transfer electrons across membranes to oxygen and generate superoxide anions. The short-lived superoxide anion rapidly dismutates to hydrogen peroxide, which can further increase the production of reactive oxygen species. This can lead to uncoupling of eNOS switching enzymatic activity from NO to superoxide production. This review describes the structure and regulation of different NAD(P)H oxidase complexes. We will also focus on NO/superoxide anion balance as modulated by hemodynamic forces, vasoconstrictors, and oxidized low-density lipoprotein. We will then summarize the recent advances defining the role of nitric oxide and NAD(P)H oxidase-derived reactive oxygen species in the development and progression of atherosclerosis. In conclusion, novel mechanisms affecting the vascular NO/superoxide anion balance will allow the development of therapeutic strategies in the treatment of cardiovascular diseases.

Protective effects of kaempferol against endothelial damage by an improvement in nitric oxide production and a decrease in asymmetric dimethylarginine level

Previous investigations have shown that asymmetric dimethylarginine (ADMA) inhibits nitric oxide (NO) synthases (NOS) and that ADMA is a risk factor for endothelial dysfunction. The objective of this study was to investigate the protective effect of kaempferol, a naturally occurring flavonoid antioxidant agent, against endothelial damage and the mechanisms involved. The experiments were performed in aorta and plasma from C57BL/6J control and apolipoprotein E-deficient (ApoE(-/-)) mice treated or not with kaempferol (50 or 100mg/kg, intragastrically) for 4 weeks, and in human umbilical vein endothelial cells (HUVECs) pretreated or not with kaempferol (1, 3 or 10 microM) for 1h and exposed to lysophosphatidylcholine (LPC) (10 microg/mL) for 24h. Kaempferol treatment improved endothelium-dependent vasorelaxation, increased the maximal relaxation value, and decreased the half-maximum effective concentration concomitantly with an increase in nitric oxide plasma concentration, a decrease in ADMA and malondialdehyde (MDA) plasma concentrations, and increase in the expression of aortic endothelial NOS (eNOS) as well as dimethylarginine dimethylaminohydrolase II (DDAH II) in ApoE(-/-) mice. In addition, LPC caused a reduction in NO production, an increase in ADMA concentration concomitantly with a decreased expression of eNOS and DDAH II in HUVECs, and the effect of LPC was abolished by kaempferol. Treatment with kaempferol also significantly decreased reactive oxygen species production in mice aorta and in HUVECs. The present results suggest that the protective effect of kaempferol against endothelial damage may be associated with an improvement in NO production and a decrease in ADMA level.

Oxidative stress and cardiovascular disease: novel tools give (free) radical insight

Cardiovascular disease is the most common cause of mortality in the Western world and accounts for up to a third of all deaths worldwide. Cardiovascular disease is multifactorial and involves complex interplay between lifestyle (diet, smoking, exercise, ethanol consumption) and fixed (genotype, age, menopausal status, gender) causative factors. The initiating step in cardiovascular disease is endothelial damage, which exposes these cells and the underlying cell layers to a deleterious inflammatory process which ultimately leads to the formation of atherosclerotic lesions. Intrinsic to lesion formation is cellular oxidative stress, due to the production of damaging free radicals (reactive oxygen and nitrogen species) by many cell types including endothelial cells, vascular smooth muscle cells and monocytes/macrophages. Exogenous factors such as smoking and the existence of other disease states such as diabetes also contribute to oxidative stress and are strong risk factors for cardiovascular disease. In this review we describe this role of free radicals in atherosclerosis and discuss the mechanisms and cellular systems by which these radicals are produced. We also highlight recent technological advances which have added to the vascular biologist's armoury and which promise to provide new insight into the role of reactive oxygen species in cardiovascular disease.

Suppressing NADPH oxidase-dependent oxidative stress in the vasculature with nitric oxide donors

1. Reactive oxygen species produced in the vasculature, including superoxide anion, contribute to the pathogenesis of cardiovascular disease states, such as atherosclerosis. A critical source of superoxide is vascular NADPH oxidase and upregulation of this enzyme brings about the oxidative stress underlying atherosclerosis. Excessive superoxide in arteries directly inactivates endothelium-derived nitric oxide (NO), compromising its vasoprotective effects. 2. Given that a reduction in NO bioavailability is key in the pathophysiology of atherosclerosis, replacement of NO by exogenously administered NO donors may restore the deficit in NO during disease. Although the organic nitrate family of NO donors is often the first choice for the acute management of symptoms of atherosclerosis and angina pectoris, most of the compounds in this class are unsuitable for long-term therapy because they cause oxidative stress by activation and upregulation of vascular NADPH oxidase and induce tolerance to subsequent nitrate treatment and endogenous NO. These problems of nitrates have not only limited their therapeutic exploitation, but have also stifled interest in newer-generation NO donors. 3. Recent evidence indicates that, in stark contrast with the organic nitrates, the newer-age diazeniumdiolate NONOate class of NO donors suppress vascular NADPH oxidase-dependent superoxide production and are less likely to induce tolerance, making them more suitable for suppression of oxidative stress in atherosclerosis. 4. Here, it is hypothesized that NONOates provide a novel means of suppressing NADPH oxidase-dependent oxidative stress to restore vascular NO levels to prevent, and even reverse, atherosclerosis.

Antioxidants attenuate hyperglycaemia-mediated brain endothelial cell dysfunction and blood-brain barrier hyperpermeability

AIMS

Hyperglycaemia (HG), in stroke patients, is associated with worse neurological outcome by compromising endothelial cell function and the blood-brain barrier (BBB) integrity. We have studied the contribution of HG-mediated generation of oxidative stress to these pathologies and examined whether antioxidants as well as normalization of glucose levels following hyperglycaemic insult reverse these phenomena.

METHODS

Human brain microvascular endothelial cell (HBMEC) and human astrocyte co-cultures were used to simulate the human BBB. The integrity of the BBB was measured by transendothelial electrical resistance using STX electrodes and an EVOM resistance meter, while enzyme activities were measured by specific spectrophotometric assays.

RESULTS

After 5 days of hyperglycaemic insult, there was a significant increase in BBB permeability that was reversed by glucose normalization. Co-treatment of cells with HG and a number of antioxidants including vitamin C, free radical scavengers and antioxidant enzymes including catalase and superoxide dismutase mimetics attenuated the detrimental effects of HG. Inhibition of p38 mitogen-activated protein kinase (p38MAPK) and protein kinase C but not phosphoinositide 3 kinase (PI3 kinase) also reversed HG-induced BBB hyperpermeability. In HBMEC, HG enhanced pro-oxidant (NAD(P)H oxidase) enzyme activity and expression that were normalized by reverting to normoglycaemia.

CONCLUSIONS

HG impairs brain microvascular endothelial function through involvements of oxidative stress and several signal transduction pathways.

Chronic production of peroxynitrite in the vascular wall impairs vasorelaxation function in SHR/NDmcr-cp rats, an animal model of metabolic syndrome

We have previously reported that peroxynitrite is involved in dysfunction of nitric oxide (NO)-mediated vasorelaxation in SHR/NDmcr-cp rats (SHR-cp), which display typical symptoms of metabolic syndrome. This study investigated whether peroxynitrite is actually generated in the vascular wall with angiotensin II-induced NADPH-oxidase activation, thus contributing to the dysfunction. In isolated mesenteric arteries of male 18-week-old SHR-cp, relaxations in response to acetylcholine and sodium nitroprusside were impaired compared with that in Wistar-Kyoto rats. This impaired relaxation was not restored by treatment with apocynin, an NADPH-oxidase inhibitor. Protein expression of endothelial NO synthase increased while that of soluble guanylyl cyclase (sGC) decreased in the artery. We observed increased production of superoxide anions and peroxynitrite from the artery and their inhibition by apocynin, and also increased contents of nitrotyrosine, a biomarker of peroxynitrite, in mesenteric arteries and angiotensin II in aortas. Long-term (8 weeks) administration of telmisartan, an angiotensin II type 1-receptor antagonist, prevented the impaired vasorelaxation, decreased sGC expression and increased nitrotyrosine content in mesenteric arteries. These findings suggest that in the vascular wall of SHR-cp, peroxynitrite is continually produced by the reaction of NO with NADPH oxidase-derived superoxide via angiotensin II and gradually denatures sGC protein, leading to vasorelaxation dysfunction.

NADPH oxidase-dependent signaling in endothelial cells: role in physiology and pathophysiology

Reactive oxygen species (ROS) including superoxide (O(2)(.-)) and hydrogen peroxide (H(2)O(2)) are produced endogenously in response to cytokines, growth factors; G-protein coupled receptors, and shear stress in endothelial cells (ECs). ROS function as signaling molecules to mediate various biological responses such as gene expression, cell proliferation, migration, angiogenesis, apoptosis, and senescence in ECs. Signal transduction activated by ROS, "oxidant signaling," has received intense investigation. Excess amount of ROS contribute to various pathophysiologies, including endothelial dysfunction, atherosclerosis, hypertension, diabetes, and acute respiratory distress syndrome (ARDS). The major source of ROS in EC is a NADPH oxidase. The prototype phagaocytic NADPH oxidase is composed of membrane-bound gp91phox and p22hox, as well as cytosolic subunits such as p47(phox), p67(phox) and small GTPase Rac. In ECs, in addition to all the components of phagocytic NADPH oxidases, homologues of gp91(phox) (Nox2) including Nox1, Nox4, and Nox5 are expressed. The aim of this review is to provide an overview of the emerging area of ROS derived from NADPH oxidase and oxidant signaling in ECs linked to physiological and pathophysiological functions. Understanding these mechanisms may provide insight into the NADPH oxidase and oxidant signaling components as potential therapeutic targets.

Association of plasma asymmetrical dimethylarginine (ADMA) with elevated vascular superoxide production and endothelial nitric oxide synthase uncoupling: implications for endothelial function in human atherosclerosis

BACKGROUND

Asymmetrical dimethylarginine (ADMA), an endogenous inhibitor of endothelial nitric oxide synthase (eNOS), is considered to be a risk factor for atherosclerosis. However, the mechanisms relating ADMA with vascular function have been evaluated in vitro and in animal models, but its effect in human vasculature is unclear.

AIMS

We examined the impact of serum ADMA on endothelial nitric oxide (NO) bioavailability and vascular superoxide radical (O2-) production in patients with advanced atherosclerosis.

METHODS AND RESULTS

Paired samples of saphenous veins (SVs) and internal mammary arteries (IMAs) were collected from 201 patients undergoing coronary bypass surgery, and serum ADMA was measured pre-operatively. The vasomotor responses of SV segments to acetylcholine (ACh) and bradykinin (Bk) were evaluated ex vivo. Vascular O2- was measured in paired SV and IMA by lucigenin-enhanced chemiluminescence. The l-NAME-inhibitable as well as the NADPH-stimulated vascular O2- generation was also determined by chemiluminescence. High serum ADMA levels were associated with decreased vasorelaxation of SV to ACh (P < 0.05) and Bk (P < 0.05). Similarly, high serum ADMA was associated with higher total O2- production in both SVs and IMAs (P < 0.05) and greater L-NAME-inhibitable vascular O2- (P < 0.05). However, serum ADMA was not associated with NADPH-stimulated vascular O2-. In multivariable linear regression, serum ADMA was independently associated with vascular O2- in both SVs [beta (SE): 0.987 (0.412), P = 0.019] and IMAs [beta (SE): 1.905 (0.541), P = 0.001]. Asymmetrical dimethylarginine was also independently associated with maximum vasorelaxation in response to both ACh [beta (SE): 14.252 (3.976), P = 0.001] and Bk [beta (SE): 9.564 (3.762), P = 0.013].

CONCLUSION

This is the first study that demonstrates an association between ADMA and important measures of vascular function, such as vascular O2- production and NO bioavailability directly in human vessels. Although serum ADMA has no effect on NADPH-stimulated superoxide in intact vessels, it is associated with greater eNOS uncoupling in the human vascular endothelium of patients with coronary artery disease.

Role of TNF-alpha in vascular dysfunction

Healthy vascular function is primarily regulated by several factors including EDRF (endothelium-dependent relaxing factor), EDCF (endothelium-dependent contracting factor) and EDHF (endothelium-dependent hyperpolarizing factor). Vascular dysfunction or injury induced by aging, smoking, inflammation, trauma, hyperlipidaemia and hyperglycaemia are among a myriad of risk factors that may contribute to the pathogenesis of many cardiovascular diseases, such as hypertension, diabetes and atherosclerosis. However, the exact mechanisms underlying the impaired vascular activity remain unresolved and there is no current scientific consensus. Accumulating evidence suggests that the inflammatory cytokine TNF (tumour necrosis factor)-α plays a pivotal role in the disruption of macrovascular and microvascular circulation both in vivo and in vitro. AGEs (advanced glycation end-products)/RAGE (receptor for AGEs), LOX-1 [lectin-like oxidized low-density lipoprotein receptor-1) and NF-κB (nuclear factor κB) signalling play key roles in TNF-α expression through an increase in circulating and/or local vascular TNF-α production. The increase in TNF-α expression induces the production of ROS (reactive oxygen species), resulting in endothelial dysfunction in many pathophysiological conditions. Lipid metabolism, dietary supplements and physical activity affect TNF-α expression. The interaction between TNF-α and stem cells is also important in terms of vascular repair or regeneration. Careful scrutiny of these factors may help elucidate the mechanisms that induce vascular dysfunction. The focus of the present review is to summarize recent evidence showing the role of TNF-α in vascular dysfunction in cardiovascular disease. We believe these findings may prompt new directions for targeting inflammation in future therapies.

Endothelial function and oxidative stress in cardiovascular diseases

The vascular endothelium is involved in the release of various vasodilators, including nitric oxide (NO), prostacyclin and endothelium-derived hyperpolarizing factor, as well as vasoconstrictors. NO plays an important role in the regulation of vascular tone, inhibition of platelet aggregation, and suppression of smooth muscle cell proliferation. Endothelial dysfunction is the initial step in the pathogenesis of atherosclerosis. Cardiovascular diseases are associated with endothelial dysfunction. It is well known that the grade of endothelial function is a predictor of cardiovascular outcomes. Oxidative stress plays an important role in the pathogenesis and development of cardiovascular diseases. Several mechanisms contribute to impairment of endothelial function. An imbalance of reduced production of NO or increased production of reactive oxygen species, mainly superoxide, may promote endothelial dysfunction. One mechanism by which endothelium-dependent vasodilation is impaired is an increase in oxidative stress that inactivates NO. This review focuses on recent findings and interaction between endothelial function and oxidative stress in cardiovascular diseases.

Role of nitrosative stress in the pathogenesis of diabetic vascular dysfunction

Here we overview the role of reactive nitrogen species (nitrosative stress) and associated pathways in the pathogenesis of diabetic vascular complications. Increased extracellular glucose concentration, a principal feature of diabetes mellitus, induces a dysregulation of reactive oxygen and nitrogen generating pathways. These processes lead to a loss of the vascular endothelium to produce biologically active nitric oxide (NO), which impairs vascular relaxations. Mitochondria play a crucial role in this process: endothelial cells placed in increase extracellular glucose respond with a marked increase in mitochondrial superoxide formation. Superoxide, when combining with NO generated by the endothelial cells (produced by the endothelial isoform of NO synthase), leads to the formation of peroxynitrite, a cytotoxic oxidant. Reactive oxygen and nitrogen species trigger endothelial cell dysfunction through a multitude of mechanisms including substrate depletion and uncoupling of endothelial isoform of NO synthase. Another pathomechanism involves DNA strand breakage and activation of the nuclear enzyme poly(ADP-ribose) polymerase (PARP). PARP-mediated poly(ADP-ribosyl)ation and inhibition of glyceraldehyde-3-phosphate dehydrogenase importantly contributes to the development of diabetic vascular complications: it induces activation of multiple pathways of injury including activation of nuclear factor kappa B, activation of protein kinase C and generation of intracellular advanced glycation end products. Reactive species generation and PARP play key roles in the pathogenesis of 'glucose memory' and in the development of injury in endothelial cells exposed to alternating high/low glucose concentrations.

Role of nitrosative stress in the pathogenesis of diabetic vascular dysfunction

Here we overview the role of reactive nitrogen species (nitrosative stress) and associated pathways in the pathogenesis of diabetic vascular complications. Increased extracellular glucose concentration, a principal feature of diabetes mellitus, induces a dysregulation of reactive oxygen and nitrogen generating pathways. These processes lead to a loss of the vascular endothelium to produce biologically active nitric oxide (NO), which impairs vascular relaxations. Mitochondria play a crucial role in this process: endothelial cells placed in increase extracellular glucose respond with a marked increase in mitochondrial superoxide formation. Superoxide, when combining with NO generated by the endothelial cells (produced by the endothelial isoform of NO synthase), leads to the formation of peroxynitrite, a cytotoxic oxidant. Reactive oxygen and nitrogen species trigger endothelial cell dysfunction through a multitude of mechanisms including substrate depletion and uncoupling of endothelial isoform of NO synthase. Another pathomechanism involves DNA strand breakage and activation of the nuclear enzyme poly(ADP-ribose) polymerase (PARP). PARP-mediated poly(ADP-ribosyl)ation and inhibition of glyceraldehyde-3-phosphate dehydrogenase importantly contributes to the development of diabetic vascular complications: it induces activation of multiple pathways of injury including activation of nuclear factor kappa B, activation of protein kinase C and generation of intracellular advanced glycation end products. Reactive species generation and PARP play key roles in the pathogenesis of 'glucose memory' and in the development of injury in endothelial cells exposed to alternating high/low glucose concentrations.

Relation of preoperative radial artery flow-mediated dilatation to nitric oxide bioavailability in radial artery grafts used in off-pump coronary artery bypass grafting

The radial artery is prone to vasospasm after coronary bypass surgery, and endothelial dysfunction is likely to be a key factor. We investigated whether endothelial dysfunction in radial artery conduits is present, and can be identified, preoperatively using a simple noninvasive ultrasound test of radial artery endothelial response, flow-mediated dilatation (FMD). The study population consisted of 126 patients scheduled for coronary artery bypass grafting. The afternoon before operation, patients had noninvasive ultrasound assessment of endothelial function in the left radial artery by FMD, which measures change in arterial size after an increase in flow-an endothelial-dependent response. Surplus graft segments were obtained at operation and nitric oxide bioavailability within the vessels determined from ex vivo responses to acetylcholine. Preoperative FMD in the radial artery was associated with vasorelaxations to acetylcholine in radial artery grafts (p<0.001 for both dose-response curves and maximum relaxations), although there was weak borderline association between FMD and vasorelaxations of saphenous vein grafts (p=0.07 for dose-response curves and p<0.05 for maximum relaxations). In multivariate analysis including cardiac risk factors, FMD was a predictor of vasorelaxations of radial artery grafts (beta=0.020, SE=0.009, p=0.030), independent of classic risk factors for atherosclerosis. In conclusion, there is significant interindividual variation in the endothelial function of vessels used for coronary artery bypass surgery, particularly the radial artery. These differences are present and can be identified preoperatively by FMD.

The influence of rich-in-cholesterol diet and fluoride ions contained in potable water upon the concentration of malondialdehyde and the activity of selected antioxidative enzymes in rabbit liver

Two experiments have been carried out, each on 18 (male) rabbits of the New Zealand breed. In each of them, animals were divided into three groups of six: control group, cholesterol group (CH), and cholesterol + fluoride group (CH+F). Experimental hypercholesterolemia has been induced in the animals with the diet enriched with 0.5 and 2 g% of cholesterol/100 g of fodder/24 h. The rabbits from CH+F groups have also been administered fluoride ions contained in drinking water (3 mg F(-)/kg of body mass/24 h). The influence of fluoride ions upon the concentrations of malondialdehyde (MDA) and activity of antioxidative enzymes, superoxide dismutase (SOD), mitochondrial enzyme (MnSOD), cytoplasmatic enzyme (ZnCuSOD), and glutathione peroxidase (GPX), has been examined in liver of rabbits. An increase (in comparison with cholesterol groups) in the concentration of MDA in both (CH+F) groups in rabbit liver has been noted. Moreover, a decrease (statistically significant) of SOD and MnSOD has been found in cholesterol groups, as well as in groups (CH+F) in comparison with control group. Furthermore, a decrease in the activity of SOD under the influence of F(-) together with increased activity of MnSOD (statistically significant in comparison with cholesterol groups) have been observed. The activity of ZnCuSOD increased in statistically significant manner in (CH) groups vs control group and decreased (statistically significantly in relation to cholesterol groups) under the influence of F(-).

Effect of endothelium-specific insulin resistance on endothelial function in vivo

OBJECTIVE

Insulin resistance is an independent risk factor for the development of cardiovascular atherosclerosis. A key step in the development of atherosclerosis is endothelial dysfunction, manifest by a reduction in bioactivity of nitric oxide (NO). Insulin resistance is associated with endothelial dysfunction; however, the mechanistic relationship between these abnormalities and the role of impaired endothelial insulin signaling versus global insulin resistance remains unclear.

RESEARCH DESIGN AND METHODS

To examine the effects of insulin resistance specific to the endothelium, we generated a transgenic mouse with endothelium-targeted overexpression of a dominant-negative mutant human insulin receptor (ESMIRO). This receptor has a mutation (Ala-Thr(1134)) in its tyrosine kinase domain that disrupts insulin signaling. Humans with the Thr(1134) mutation are insulin resistant. We performed metabolic and vascular characterization of this model.

RESULTS

ESMIRO mice had preserved glucose homeostasis and were normotensive. They had significant endothelial dysfunction as evidenced by blunted aortic vasorelaxant responses to acetylcholine (ACh) and calcium ionophore. Furthermore, the vascular action of insulin was lost in ESMIRO mice, and insulin-induced endothelial NO synthase (eNOS) phosphorylation was blunted. Despite this phenotype, ESMIRO mice demonstrate similar levels of eNOS mRNA and protein expression to wild type. ACh-induced relaxation was normalized by the superoxide dismutase mimetic, Mn(III)tetrakis(1-methyl-4-pyridyl) porphyrin pentachloride. Endothelial cells of ESMIRO mice showed increased superoxide generation and increased mRNA expression of the NADPH oxidase isoforms Nox2 and Nox4.

CONCLUSIONS

Selective endothelial insulin resistance is sufficient to induce a reduction in NO bioavailability and endothelial dysfunction that is secondary to increased generation of reactive oxygen species. This arises independent of a significant metabolic phenotype.

NADPH oxidase has a directional response to shear stress

Vessel regions with predilection to atherosclerosis have negative wall shear stress due to flow reversal. The flow reversal causes the production of superoxides (O(2)(-)), which scavenge nitric oxide (NO), leading to a decrease in NO bioavailability and endothelial dysfunction. Here, we implicate NADPH oxidase as the primary source of O(2)(-) during full flow reversal. Nitrite production and the degree of vasodilation were measured in 46 porcine common femoral arteries in an ex vivo system. Nitrite production and vasodilation were determined before and after the inhibition of NADPH oxidase, xanthine oxidase, or mitochondrial oxidase. NADPH oxidase inhibition with gp91ds-tat or apocynin restored nitrite production and vasodilation during reverse flow. Xanthine oxidase inhibition increased nitrite production at the highest flow rate, whereas mitochondrial oxidase inhibition had no effect. These findings suggest that the NADPH oxidase system can respond to directional changes of flow and is activated to generate O(2)(-) during reverse flow in a dose-dependent fashion. These findings have important clinical implications for oxidative balance and NO bioavailability in regions of flow reversal in a normal and compromised cardiovascular system.

Endothelial dysfunction in African-Americans

The journey of atherosclerosis begins with endothelial dysfunction and culminates into its most fearful destination producing ischemia, myocardial infarction and death. The excess cardiovascular disease morbidity and mortality in African-Americans is one of the major public health problems. In this review, we discuss vascular endothelial dysfunction as a key element for excess cardiovascular disease burden in this target population. It can be logical window of future atherosclerotic outcomes, and further efforts should be made to detect it at the earliest in African American individuals even if they are appearing healthy as the therapeutic interventions if instituted early, might prevent the subsequent cardiac events.

Nitric oxide and endothelial cellular senescence

Cellular senescence is characterized by permanent exit from the cell cycle and the appearance of distinct morphological and functional changes associated with an impairment of cellular homeostasis. Many studies support the occurrence of vascular endothelial cell senescence in vivo, and the senescent phenotype of endothelial cells can be transformed from anti-atherosclerotic to pro-atherosclerotic. Thus, endothelial cell senescence promotes endothelial dysfunction and may contribute to the pathogenesis of age-associated vascular disorders. Emerging evidence suggests that increasing nitric oxide (NO) bioavailability or endothelial NO synthase (eNOS) activity activates telomerase and delays endothelial cell senescence. In this review, we discuss the potential mechanisms underlying the ability of NO to prevent endothelial cell senescence and describe the possible changes in the NO-mediated anti-senescence effect under pathophysiological conditions, including oxidative stress and hyperglycemia. Further understanding of the mechanisms underlying the anti-senescence effect of NO in endothelial cells will provide insights into the potential of eNOS-based anti-senescence therapy for age-associated vascular disorders.

The molecular sources of reactive oxygen species in hypertension

In both animal models and humans, increased blood pressure has been associated with oxidative stress in the vasculature, i.e. an excessive endothelial production of reactive oxygen species (ROS), which may be both a cause and an effect of hypertension. In addition to NADPH oxidase, the best characterized source of ROS, several other enzymes may contribute to ROS generation, including nitric oxide synthase, lipoxygenases, cyclo-oxygenases, xanthine oxidase and cytochrome P450 enzymes. It has been suggested that also mitochondria could be considered a major source of ROS: in situations of metabolic perturbation, increased mitochondrial ROS generation might trigger endothelial dysfunction, possibly contributing to the development of hypertension. However, the use of antioxidants in the clinical setting induced only limited effects on human hypertension or cardiovascular endpoints. More clinical studies are needed to fully elucidate this so called "oxidative paradox" of hypertension.

Relation of the Glu298Asp polymorphism of the nitric oxide synthase gene to hypertension and serum cholesterol in Japanese workers

OBJECTIVE

To assess whether the Glu298Asp polymorphism of the endothelial nitric oxide synthase (eNOS) gene possibly mediates the relation of blood pressure and serum cholesterol.

METHOD

Regular health examination in 2003 of 1,694 Japanese workers from the Shimane Prefecture, Japan.

RESULTS

The frequencies of the Glu/Glu, Glu/Asp, and Asp/Asp genotypes were 85.9%, 13.4%, and 0.7%, respectively. After adjustment for age, sex, BMI, and lifestyle (drinking, smoking, exercise and stress), the odds ratio (OR) of hypertension associated with high (> or = 220 mg/dl or under treatment) total cholesterol was 2.08 (95% Confidence Interval (CI) 1.02-4.24) among carriers of the eNOS 298Asp allele versus 1.18 (95% CI 0.89-1.55, p for interaction=0.50) among non-carriers. Similarly, the ORs of hypertension associated with counseling-need (120-139 mg/dl) and high (> or = 140 mg/dl) levels of LDL cholesterol among carriers of the eNOS 298Asp allele were significantly higher than those among non-carriers, at 2.65 (95% CI 1.16-6.01) versus 1.03 (95% CI 0.77-1.39, p for interaction=0.01), and 2.80 (95% CI 1.33-5.89) versus 0.95 (95% CI 0.71-1.26, p for interaction=0.04), respectively.

CONCLUSION

These results indicate that the eNOS 298Asp allele, which is weakly associated with hypertension, may increase the risk of hypertension when associated with high serum lipid levels.

The AP-1 site is essential for the promoter activity of NOX1/NADPH oxidase, a vascular superoxide-producing enzyme: Possible involvement of the ERK1/2-JunB pathway

NADPH oxidase is a major source of the superoxide produced in cardiovascular tissues. The expression of NOX1, a catalytic subunit of NADPH oxidase, is induced by various vasoactive factors, including angiotensin II, prostaglandin (PG) F(2alpha), and platelet-derived growth factor (PDGF). It was reported previously that the inducible expression of NOX1 is governed by the activating transcription factor-1 (ATF-1)-myocyte enhancer factor 2B (MEF2B) cascade downstream of phosphoinositide 3 (PI3) kinase. It was also reported that extracellular signal-regulated kinase (ERK) 1/2 is involved in the expression of NOX1. To further clarify the factors involved in NOX1 induction downstream of ERK1/2, the promoter region of the NOX1 gene was analyzed. A consensus activator protein-1 (AP-1) site was found at -98/-92 in the 5'-flanking region of the rat NOX1 gene. The introduction of mutations at this site abolished PGF(2alpha)-induced transcriptional activation in a luciferase assay. Electrophoresis mobility shift assays demonstrated that PGF(2alpha) and PDGF augmented the binding of JunB to this sequence. PD98059, an inhibitor of MAPK/ERK kinase, suppressed the expression of JunB induced by PGF(2alpha) or PDGF. These results suggest that the ERK1/2-JunB pathway is a key regulator of the inducible expression of the NOX1 gene in vascular smooth muscle cells.

GCH1 haplotype determines vascular and plasma biopterin availability in coronary artery disease effects on vascular superoxide production and endothelial function

OBJECTIVES

This study sought to determine the effects of endogenous tetrahydrobiopterin (BH4) bioavailability on endothelial nitric oxide synthase (eNOS) coupling, nitric oxide (NO) bioavailability, and vascular superoxide production in patients with coronary artery disease (CAD).

BACKGROUND

GTP-cyclohydrolase I, encoded by the GCH1 gene, is the rate-limiting enzyme in the biosynthesis of BH4, an eNOS cofactor important for maintaining enzymatic coupling. We examined the associations between haplotypes of the GCH1 gene, GCH1 expression and biopterin levels, and the effects on endothelial function and vascular superoxide production.

METHODS

Blood samples and segments of internal mammary arteries and saphenous veins were obtained from patients with CAD undergoing coronary artery bypass grafting (n = 347). The GCH1 haplotypes were defined by 3 polymorphisms: rs8007267G

RESULTS

Haplotype frequencies were OO 70.6%, XO 27.4%, and XX 2.0%. The X haplotype was associated with significantly lower vascular GCH1 messenger ribonucleic acid expression and substantial reductions in both plasma and vascular BH4 levels. In X haplotype carriers both vascular superoxide and L-NAME-inhibitable superoxide were significantly increased, and were associated with reduced vasorelaxations to acetylcholine.

CONCLUSIONS

GCH1 gene expression, modulated by a particular GCH1 haplotype, is a major determinant of BH4 bioavailability both in plasma and in the vascular wall in patients with CAD. Genetic variation in GCH1 underlies important differences in endogenous BH4 availability and is a determinant of eNOS coupling, vascular redox state, and endothelial function in human vascular disease.

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Key Words

• tetrahydrobiopterin
• endothelial nitric oxide synthase
• gtp-cyclohydrolase i
• superoxide
• haplotype
• atherosclerosis

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MESH Headings

• Aged
• Biopterins/analogs & derivatives
• Biopterins/biosynthesis
• Biopterins/blood
• Coronary Artery Disease/genetics
• Coronary Artery Disease/metabolism
• Endothelium, Vascular/metabolism
• Female
• GTP Cyclohydrolase/genetics
• Genetic Variation
• Haplotypes
• Humans
• Male
• Mammary Arteries/metabolism
• Multivariate Analysis
• Nitric Oxide/metabolism
• Nitric Oxide Synthase Type III/metabolism
• Saphenous Vein/metabolism
• Superoxides/metabolism

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Grants

• R01 NS058870-01A1 NINDS NIH HHS
• FS/03/105/16340 British Heart Foundation
• R01 NS058870 NINDS NIH HHS
• RG/02/006 British Heart Foundation
• RG/07/003/23133 British Heart Foundation

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Affiliation(s)

Charalambos Antoniades Department of Cardiovascular Medicine, John Radcliffe Hospital, University of Oxford, Oxford, United Kingdom
Cheerag Shirodaria Department of Cardiovascular Medicine, John Radcliffe Hospital, University of Oxford, Oxford, United Kingdom
Tim Van Assche Department of Cardiovascular Medicine, John Radcliffe Hospital, University of Oxford, Oxford, United Kingdom
Colin Cunnington Department of Cardiovascular Medicine, John Radcliffe Hospital, University of Oxford, Oxford, United Kingdom
Irmgard Tegeder Neural Plasticity Research Group, Department of Anesthesia and Critical Care, Massachusetts General Hospital and Harvard Medical School, Boston, Massachusetts Pharmazentrum Frankfurt/ZAFES, Institute for Clinical Pharmacology, Johann Wolfgang Goethe University, Frankfurt am Main, Germany
Jörn Lötsch Pharmazentrum Frankfurt/ZAFES, Institute for Clinical Pharmacology, Johann Wolfgang Goethe University, Frankfurt am Main, Germany
Tomasz J. Guzik Department of Cardiovascular Medicine, John Radcliffe Hospital, University of Oxford, Oxford, United Kingdom Departments of Medicine and Pharmacology, Jagiellonian University, Cracow, Poland
Paul Leeson Department of Cardiovascular Medicine, John Radcliffe Hospital, University of Oxford, Oxford, United Kingdom
Jonathan Diesch Department of Cardiovascular Medicine, John Radcliffe Hospital, University of Oxford, Oxford, United Kingdom
Dimitris Tousoulis Athens University Medical School, 1st Cardiology Department, Hippokration Hospital, Athens, Greece
Christodoulos Stefanadis Athens University Medical School, 1st Cardiology Department, Hippokration Hospital, Athens, Greece
Michael Costigan
Clifford J. Woolf Neural Plasticity Research Group, Department of Anesthesia and Critical Care, Massachusetts General Hospital and Harvard Medical School, Boston, Massachusetts
Nicholas J. Alp Department of Cardiovascular Medicine, John Radcliffe Hospital, University of Oxford, Oxford, United Kingdom
Keith M. Channon Department of Cardiovascular Medicine, John Radcliffe Hospital, University of Oxford, Oxford, United Kingdom

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The role of inflammatory cytokines in endothelial dysfunction

Clinical and experimental data support a link between endothelial dysfunction and inflammation. Inflammatory cytokines are important protagonists in formation of atherosclerotic plaque, eliciting effects throughout the atherosclerotic vessel. Importantly, the development of atherosclerotic lesions, regardless of the risk factor, e.g., diabetes, hypertension, obesity, is characterized by disruption in normal function of the endothelial cells. Endothelial cells, which line the internal lumen of the vasculature, are part of a complex system that regulates vasodilation and vasoconstriction, growth of vascular smooth muscle cells, inflammation, and hemostasis, maintaining a proper blood supply to tissues and regulating inflammation and coagulation. Current concepts suggest that the earliest event in atherogenesis is endothelial dysfunction, manifested by deficiencies in the production of nitric oxide (NO) and prostacyclin. The focus of this review is to summarize recent evidence showing the effects of inflammation on vascular dysfunction in ischemic-heart disease, which may prompt new directions for targeting inflammation in future therapies.

CD4+ T lymphocytes mediate hypercholesterolemia-induced endothelial dysfunction via a NAD(P)H oxidase-dependent mechanism

Although hypercholesterolemia is known to impair endothelium-dependent vasodilation (EDV) long before the appearance of atherosclerotic plaques, it remains unclear whether the immune mechanisms that have been implicated in atherogenesis also contribute to the early oxidative stress and endothelial cell dysfunction elicited by hypercholesterolemia. EDV (wire myography), superoxide generation (cytochrome c reduction), and NAD(P)H oxidase mRNA expression were monitored in aortic rings from wild-type (WT) and mutant mice placed on either a normal diet or a cholesterol-enriched diet (HC) for 2 wk. WT mice on HC exhibited impaired EDV, enhanced superoxide generation, and increased expression of NAD(P)H oxidase subunit Nox-2 mRNA. The impaired EDV and increased superoxide generation induced by HC were significantly blunted in severe combined immunodeficient (SCID) mice and CD4+ T lymphocyte-deficient mice. These responses were also attenuated in HC mice genetically deficient in IFN-γ; however, adoptive transfer of WT-HC CD4+ T lymphocytes to IFN-γ-deficient recipients restored HC-induced responses. The HC-induced impaired EDV and oxidative stress were also attenuated in HC mice genetically deficient in Nox-2 (gp91 phox−/−) and in WT→gp91 phox−/−-HC chimeras. HC-induced gp91 phox mRNA expression was significantly blunted in mice deficient in CD4+ T cells or IFN-γ and was restored with adoptive transfer of WT-HC CD4+ T cells to IFN-γ-deficient recipients. These findings implicate the immune system in the early endothelial cell dysfunction associated with hypercholesterolemia and are consistent with a mechanism of impaired EDV that is mediated by CD4+ T cells and IFN-γ, acting through the generation of superoxide from vascular NAD(P)H oxidase.

Nitric oxide, tetrahydrobiopterin, oxidative stress, and endothelial dysfunction in hypertension

Endothelial dysfunction in the setting of cardiovascular risk factors such as hypercholesterolemia, diabetes mellitus, chronic smoking, as well hypertension, is, at least in part, dependent of the production of reactive oxygen species (ROS) and the subsequent decrease in vascular bioavailability of nitric oxide (NO). ROS-producing enzymes involved in increased oxidative stress within vascular tissue include NADPH oxidase, xanthine oxidase, and mitochondrial superoxide producing enzymes. Superoxide produced by the NADPH oxidase may react with NO, thereby stimulating the production of the NO/superoxide reaction product peroxynitrite. Peroxynitrite in turn has been shown to uncouple eNOS, therefore switching an antiatherosclerotic NO producing enzyme to an enzyme that may accelerate the atherosclerotic process by producing superoxide. Increased oxidative stress in the vasculature, however, is not restricted to the endothelium and also occurs within the smooth muscle cell layer. Increased superoxide production has important consequences with respect to signaling by the soluble guanylate cyclase and the cGMP-dependent kinase I, which activity and expression is regulated in a redox-sensitive fashion. The present review will summarize current concepts concerning eNOS uncoupling, with special focus on the role of tetrahydrobiopterin in mediating eNOS uncoupling.

Asymmetric dimethylarginine may be a missing link between cardiovascular disease and chronic kidney disease

Decreased nitric oxide (NO) production and/or impaired NO bioavailability may occur in patients with chronic kidney disease (CKD), and could contribute to the elevation of blood pressure, cardiovascular disease (CVD) and the progression of renal injury in these patients. However, the underlying molecular mechanisms for reduced NO action in patients with CKD remains to be elucidated. Asymmetric dimethylarginine (ADMA) is a naturally occurring L-arginine analogue found in plasma and various types of tissues, acting as an endogenous NO synthase inhibitor in vivo. Further, plasma level of ADMA is elevated in patients with CKD and found to be a strong biomarker or predictor for future cardiovascular events. In addition, plasma level of ADMA could predict the progression of renal injury in these patients as well. These findings suggest that elevation of ADMA may be a missing link between CVD and CKD. In this review, we discuss the molecular mechanisms for the elevation of ADMA and its pathophysiological role for CVD in high-risk patients, especially focusing on patients with CKD.

Plasma Total Antioxidant Activity in Comparison with Plasma NO and VEGF Levels in Patients with Metabolic Syndrome

Introduction

The aim of our study was to estimate plasma antioxidant activity as well as plasma nitric oxide (NO) and vascular endothelial growth factor levels in patients with metabolic syndrome compared with healthy participants.

Material and Methods

Fifty patients (24 women and 26 men, mean age 55.9 ± 11.8 years) with metabolic syndrome were compared with 25 healthy participants (12 women and 13 men, mean age 54.2 ± 12.8 years). Plasma total antioxidant activity and plasma levels of NO and VEGF were determined in all participants.

Results

In the patients with metabolic syndrome, plasma total antioxidant activity, nitric oxide, and vascular endothelial growth factor were significantly lower ( P < .001) than that observed in healthy participants (3.2 ± 1.6 vs 6.4 ± 2.1 mM/L), (6.3 ± 2.2 vs 9.8 ± 2.7 μM/L), and 71.0 ± 16.9 vs 137.5 ± 12.6 pg/mL), respectively.

Conclusions

Decreased plasma total antioxidant activity, NO, and VEGF levels in patients with metabolic syndrome reflect significant endothelial dysfunction. This suggests that oxidation–reduction balance disorders might play an important role in this process

NOX enzymes and diabetic complications

Several molecular mechanisms have been identified that mediate the tissue-damaging effects of hyperglycemia. These are increased flux through the polyol and hexosamine pathways, increased formation of advanced glycation end products, activation of protein kinase C, and augmented generation of reactive oxygen species (ROS). Increased production of ROS not only causes cellular damage but also activates the signal transduction cascade that activates specific target genes. Based on recent experimental data, it is now accepted that increased NADPH oxidase activity in tissues vulnerable to hyperglycemia takes place downstream of the advanced glycation end products and protein kinase C pathways, two of the primary mechanisms involved in the pathogenesis of diabetic complications. Thus, compounds that suppress NADPH oxidase activity may offer therapeutic benefits to ameliorate diabetic complications, highlighting the significance of NADPH oxidase as a new therapeutic target.

Exogenous hydrogen sulfide inhibits superoxide formation, NOX-1 expression and Rac1 activity in human vascular smooth muscle cells

The activity of NADPH oxidase (NOX) is blocked by nitric oxide (NO). Hydrogen sulfide (H(2)S) is also produced by blood vessels. It is reasonable to suggest that H(2)S may have similar actions to NO on NOX. In order to test this hypothesis, the effect of sodium hydrosulfide (NaHS) on O(2)(-) formation, the expression of NOX-1 (a catalytic subunit of NOX) and Rac(1) activity (essential for full NOX activity) in isolated vascular smooth muscle cells (hVSMCs) was investigated. hVSMCs were incubated with the thromboxane A(2) analogue U46619 +/- NaHS for 1 or 16 h, and O(2)(-) formation, NOX-1 expression and Rac(1) activity were assessed. The possible interaction between H(2)S and NO was also studied by using an NO synthase inhibitor, L-NAME, and an NO donor, DETA-NONOate. The role of K(ATP) channels was studied by using glibenclamide. NaHS inhibited O(2)(-) formation following incubation of 1 h (IC(50), 30 nM) and 16 h (IC(50), 20 nM), blocked NOX-1 expression and inhibited Rac(1) activity. These inhibitory effects of NaHS were mediated by the cAMP-protein-kinase-A axis. Exogenous H(2)S prevents NOX-driven intravascular oxidative stress through an a priori inhibition of Rac(1) and downregulation of NOX-1 protein expression, an effect mediated by activation of the adenylylcyclase-cAMP-protein-kinase-G system by H(2)S.

Role of oxidative stress and nitric oxide in atherothrombosis

During the last decade basic and clinical research has highlighted the central role of reactive oxygen species (ROS) in cardiovascular disease. Enhanced production or attenuated degradation of ROS leads to oxidative stress, a process that affects endothelial and vascular function, and contributes to vascular disease. Nitric oxide (NO), a product of the normal endothelium, is a principal determinant of normal endothelial and vascular function. In states of inflammation, NO production by the vasculature increases considerably and, in conjunction with other ROS, contributes to oxidative stress. This review examines the role of oxidative stress and NO in mechanisms of endothelial and vascular dysfunction with an emphasis on atherothrombosis.

Baroreflex sensitivity and oxidative stress in the LDL receptor knockout mice

This study aims at observing the effect of low-density lipoprotein (LDL) receptor deficiency in cholesterol blood levels, baroreflex sensitivity (BRS), nitric oxide (NO) bioavailability, and oxidative stress. The lack of LDL receptors in mice significantly increased the cholesterol blood levels (179+/-35 vs. 109+/-13mg/dL) in the knockout (KO) mice compared to control. There was no difference in basal mean arterial pressure and heart rate between the groups. However, in KO mice the BRS was significantly attenuated and the antioxidant enzyme activities, measured in erythrocytes and heart, were significantly decreased. On the other hand, the oxidative damage measured by chemiluminescence and carbonyls was increased, while total plasma nitrate levels were lower in KO mice, indicating a decrease in NO availability. In conclusion, these results indicate that the lack of LDL receptor increased cholesterol blood levels, induced oxidative stress and decreased BRS.

Comparative effects of dietary supplementation with red grape juice and vitamin E on production of superoxide by circulating neutrophil NADPH oxidase in hemodialysis patients

BACKGROUND

Atherosclerotic cardiovascular disease is the most common cause of death among hemodialysis patients; it has been attributed to increased oxidative stress, dyslipidemia, malnutrition, and chronic inflammation. Activation of neutrophils is a well-recognized feature in dialysis patients, and superoxide-anion production by neutrophil NADPH oxidase may contribute significantly to oxidative stress.

OBJECTIVE

The aim of the study was to compare the effects of dietary supplementation with concentrated red grape juice (RGJ), a source of polyphenols, and vitamin E on neutrophil NADPH oxidase activity and other cardiovascular risk factors in hemodialysis patients.

DESIGN

Thirty-two patients undergoing hemodialysis were recruited and randomly assigned to groups to receive dietary supplementation with RGJ, vitamin E, or both or a control condition without supplementation or placebo. Blood was obtained at baseline and on days 7 and 14 of treatment.

RESULTS

RGJ consumption but not vitamin E consumption reduced plasma concentrations of total cholesterol and apolipoprotein B and increased those of HDL cholesterol. Both RGJ and vitamin E reduced plasma concentrations of oxidized LDL and ex vivo neutrophil NADPH oxidase activity. These effects were intensified when the supplements were used in combination; in that case, reductions in the inflammatory biomarkers intercellular adhesion molecule 1 and monocyte chemoattractant protein 1 also were observed.

CONCLUSIONS

Regular ingestion of concentrated RGJ by hemodialysis patients reduces neutrophil NADPH-oxidase activity and plasma concentrations of oxidized LDL and inflammatory biomarkers to a greater extent than does that of vitamin E. This effect of RGJ consumption may favor a reduction in cardiovascular risk.

Pathophysiology, diagnosis and prognostic implications of endothelial dysfunction

Endothelial dysfunction (ED) in the setting of cardiovascular risk factors such as hypercholesterolemia, hypertension, diabetes mellitus, chronic smoking as well as in patients with heart failure has been shown to be at least in part dependent on the production of reactive oxygen species (ROS) such as superoxide and the subsequent decrease in vascular bioavailability of nitric oxide (NO). Methods to quantify endothelial dysfunction include forearm plethysmography, flow-dependent dilation of the brachial artery, finger-pulse plethysmography, pulse curve analysis, and quantitative coronary angiography after intracoronary administration of the endothelium-dependent vasodilator acetylcholine. Superoxide sources include the NADPH oxidase, xanthine oxidase, and mitochondria. Superoxide produced by the NADPH oxidase may react with NO released by the endothelial nitric oxide synthase (eNOS) thereby generating peroxynitrite (ONOO-), leading to eNOS uncoupling and therefore eNOS-mediated superoxide production. The present review will discuss current concepts of how to assess endothelial function, prognostic implications of ED, mechanisms underlying ED with focus on oxidative stress and circulating biomarkers, which have been proposed to indicate endothelial dysfunction and/or damage, respectively.

Accelerated endothelial dysfunction in mild prediabetic insulin resistance: the early role of reactive oxygen species

Insulin resistance is well established as an independent risk factor for the development of type 2 diabetes and cardiovascular atherosclerosis. Most studies have examined atherogenesis in models of severe insulin resistance or diabetes. However, by the time of diagnosis, individuals with type 2 diabetes already demonstrate a significant atheroma burden. Furthermore, recent studies suggest that, even in adolescence, insulin resistance is a progressive disorder that increases cardiovascular risk. In the present report, we studied early mechanisms of reduction in the bioavailability of the antiatheroscerotic molecule nitric oxide (NO) in very mild insulin resistance. Mice with haploinsufficiency for the insulin receptor (IRKO) are a model of mild insulin resistance with preserved glycemic control. We previously demonstrated that 2-mo-old (Young) IRKO mice have preserved vasorelaxation responses to ACh. This remained the case at 4 mo of age. However, by 6 mo, despite no significant deterioration in glucose homeostasis (Adult), IRKO mice had marked blunting of ACh-mediated vasorelaxation [IRKO maximum contraction response (E(max)) 66 +/- 5% vs. wild type 87 +/- 4%, P < 0.01]. Despite the endothelial dysfunction demonstrated, aortic endothelial nitric oxide synthase (eNOS) mRNA levels were similar in Adult IRKO and wild-type mice, and, interestingly, aortic eNOS protein levels were increased, suggesting a compensatory upregulation in the IRKO. We then examined the potential role of reactive oxygen species in mediating early endothelial dysfunction. The superoxide dismutase mimetic Mn(III)tetrakis(1-methyl-4-pyridyl) porphyrin pentachloride (MnTMPyP) restored ACh relaxation responses in the Adult IRKO (E(max) to ACh with MnTMPyP 85 +/- 5%). Dihydroethidium fluorescence of aortas and isolated coronary microvascular endothelial cells confirmed a substantial increase in endothelium-derived reactive oxygen species in IRKO mice. These data demonstrate that mild insulin resistance is a potent substrate for accelerated endothelial dysfunction and support a role for endothelial cell superoxide production as a mechanism underlying the early reduction in NO bioavailability.

Synthetic smooth muscle cell phenotype is associated with increased nicotinamide adenine dinucleotide phosphate oxidase activity: effect on collagen secretion

OBJECTIVE

Smooth muscle cells (SMCs) from prosthetic vascular grafts secrete higher levels of collagen than aortic SMCs under basal conditions and during incubation with oxidized low-density lipoprotein. We postulated that reactive oxygen species (ROS) contributed to the observed difference. The objective of this study was to assess the effect of ROS on collagen secretion by aortic and graft SMCs and explore the mechanism involved.

METHODS

SMCs isolated from canine aorta or Dacron thoracoabdominal grafts were incubated with 6-anilinoquinoline-5,8-quinone (LY83583), an agent that induces superoxide production. Type I collagen in the conditioned medium was measured by enzyme-linked immunosorbent assay, and superoxide anion production was measured by lucigenin assay.

RESULTS

LY83583 stimulated a rapid increase in collagen production by graft SMCs that paralleled the LY83583-induced increase in superoxide production. The increase in both collagen and superoxide was greater in graft SMCs than aortic SMCs. Collagen and superoxide production were inhibited by superoxide scavengers. Nicotinamide adenine dinucleotide phosphate (NADPH) induced significantly more superoxide production by graft SMCs than aortic SMCs, suggesting that the NADPH oxidase system was more active in graft SMCs. NADPH oxidase inhibitors blocked the superoxide and collagen production induced by LY83583.

CONCLUSION

In SMCs, the synthetic phenotype is associated with increased NADPH oxidase activity and elevated superoxide production in response to an oxidative stress. Superoxide, in turn, leads to increased collagen production.

CLINICAL RELEVANCE

The inflammatory process after prosthetic vascular graft implantation causes oxidative stress that can stimulate collagen production by graft SMCs, contributing to the progression of intimal hyperplasia. The exaggerated response of graft SMCs to oxidative stress offers a potential target for therapeutic interventions.