Oxidative Stress and Vascular Damage in Hypertension: Role of Angiotensin II

Reactive oxygen species (ROS), including superoxide (*O2-), hydrogen peroxide (H2O2), and hydroxyl anion (OH-), and reactive nitrogen species, such as nitric oxide (NO) and peroxynitrite (ONOO-), are biologically important O2 derivatives that are increasingly recognized to be important in vascular biology through their oxidation/reduction (redox) potential. All vascular cell types (endothelial cells, vascular smooth muscle cells, and adventitial fibroblasts) produce ROS, primarily via cell membrane-associated NAD(P)H oxidase. Reactive oxygen species regulate vascular function by modulating cell growth, apoptosis/anoikis, migration, inflammation, secretion, and extracellular matrix protein production. An imbalance in redox state where pro-oxidants overwhelm anti-oxidant capacity results in oxidative stress. Oxidative stress and associated oxidative damage are mediators of vascular injury and inflammation in many cardiovascular diseases, including hypertension, hyperlipidemia, and diabetes. Increased generation of ROS has been demonstrated in experimental and human hypertension. Anti-oxidants and agents that interrupt NAD(P)H oxidase-driven *O2- production regress vascular remodeling, improve endothelial function, reduce inflammation, and decrease blood pressure in hypertensive models. This experimental evidence has evoked considerable interest because of the possibilities that therapies targeted against reactive oxygen intermediates, by decreasing generation of ROS and/or by increasing availability of antioxidants, may be useful in minimizing vascular injury and hypertensive end organ damage. The present chapter focuses on the importance of ROS in vascular biology and discusses the role of oxidative stress in vascular damage in hypertension.

Angiotensin II and vascular damage in hypertension: Role of oxidative stress and sympathetic activation

Signalling pathways activated by hydrogen peroxide in vascular smooth muscle

Over the past few years noninvasive and invasive techniques have allowed a better appreciation of vascular changes in hypertensive humans and experimental animals.1 Large arteries undergo outward hypertrophic remodeling and increased stiffness with aging,2–4 and in hypertension there may be an acceleration of this process leading to enhanced pulse pressure. A reduced aortic diameter in middle-aged hypertensive subjects may also play a role in increases in pulse pressure through increased specific impedance,5 contradicting the classic hypertensive aortic phenotype characterized by vascular wall degeneration and calcification and increased aortic diameter. In advanced hypertension, however, the elastic laminae undergo duplication and fragmentation, with increased deposition of collagen and fetal (EIIIA) fibronectin, contributing to increased stiffness. Classically the remodeling of small arteries in hypertension has been associated with increased media thickness, but recent studies have demonstrated that 2 types of remodeling are found, inward eutrophic or inward hypertrophic remodeling, depending on whether the media cross-sectional area is enlarged (true hypertrophy).6–9 Although eutrophic remodeling is usually found in essential (primary) hypertension in humans and spontaneously hypertensive rats (SHRs); in secondary hypertension such as in renovascular hypertension, primary aldosteronism, or in pheochromocytoma10; in hypertension associated with diabetes mellitus11,12; and in acromegaly,13 hypertrophic remodeling has been described. In mineralocorticoid hypertension in rodents14,15 and in salt-sensitive Dahl rats,16 in both of which the endothelin (ET) system is activated, remodeling of small arteries is also hypertrophic (see below). Thus, when the renin-angiotensin system is even mildly activated (primary hypertension and SHRs), remodeling is usually eutrophic. In salt-dependent hypertension, diabetes mellitus, and malignant hypertension, all conditions in which the ET system is activated, remodeling is hypertrophic.17 Hyperplasia of vascular smooth muscle cells (VSMCs) is found in small arteries of …

Reactive oxygen species (ROS) (eg, superoxide, peroxide, and hydroxyl radicals) and reactive nitrogen species (eg, peroxynitrite) are generated in both atherogenesis and advanced atherosclerosis,1 particularly by macrophages.2 ROS have many actions, including oxidative modification of LDL and oxidative damage of DNA. Although LDL is essential to deliver cholesterol to tissues, increased LDL cholesterol is associated with increased risk of cardiovascular disease. Oxidative modification of LDL promotes recruitment and retention of monocytes3 with formation of fatty streaks, the earliest lesions in atherosclerosis.4 Both macrophages and vascular smooth muscle cells (VSMCs) bind oxidized LDL via specific scavenger receptors,5 6 forming foam cells. Macrophage foam cells contain potent oxidant-generating systems that target lipids, including myeloperoxidase, nitric oxide (NO) synthase, and 15-lipoxygenase, allowing increased recognition and uptake by macrophages, creating a positive feedback loop. ROS also induce oxidative damage of DNA, including strand breaks and base and nucleotide modifications, particularly in sequences with high guanosine content.7 Oxidative modification induces a robust repair response, characterized by excision of modified bases and nucleotides. Double-stranded DNA breaks also activate DNA repair enzymes, including ATM (mutated in ataxia telangiectasia) and ATR (ATM-related kinase). Both ATM and ATR directly phosphorylate and activate specific checkpoint kinases, such as chk2 and hCDS1, with subsequent phosphorylation of the tumor suppressor gene p53. p53 is the commonest mutation in human cancer and …

Hypertrophy and hyperplasia of vascular smooth muscle cells are hallmarks of the common vascular disorders of atherosclerosis, restenosis, and hypertension and contribute to their long-term sequelae. Angiotensin II (Ang II) is a potent smooth muscle mitogen and hypertrophic agent. The importance of Ang II in the pathogenesis of vascular disease is reflected in the efficacy of angiotensin-converting enzyme inhibitors and Ang II receptor blockers in the treatment of atherosclerosis and hypertension. Despite the widespread use of these agents in clinical practice, our understanding of the mechanisms through which Ang II exerts its effects on the vasculature is not complete. The studies by Lassegue et al1 and Wang et al2 in this issue of Circulation Research go a long way in elucidating the molecular basis for the effects of Ang II on vascular smooth muscle cell growth. To fully appreciate the significance of the reported findings, one has to place them into historical perspective. The role of oxidative stress in the pathogenesis of the above-mentioned vascular disorders has been well recognized for some time.3 It has come to light that humoral factors, such as Ang II, platelet-derived growth factor, and thrombin, directly lead to oxidative stress in smooth muscle cells via the generation of reactive oxygen species (ROS), which are essential for their mitogenic and hypertrophic properties.4 5 6 7 With these findings in hand, investigators directed their efforts toward identifying the enzymatic source of growth …

Metabolism of oxygen by cells generates potentially deleterious reactive oxygen species, including superoxide anion radical, hydrogen peroxide, and hydroxyl radical. Under normal physiologic conditions the rate and magnitude of oxidant formation is balanced by the rate of oxidant elimination. However, an imbalance between prooxidants and antioxidants results in oxidative stress, which is the pathogenic outcome of the overproduction of oxidants that overwhelms the cellular antioxidant capacity. There is increasing evidence that an elevation of oxidative stress and associated oxidative damages are mediators of vascular injury in various cardiovascular pathologies, including hypertension, atherosclerosis, and ischemia-reperfusion. This review focuses on the vascular effects of reactive oxygen species and the role of oxidative stress in vascular damage in hypertension.

Oxidative stress, a state of excessive reactive oxidative species activity, is associated with vascular disease states such as hypertension. In this review, we discuss the recent advances in the field of reactive oxidative species-mediated vascular damage in hypertension. These include the identification of redox-sensitive tyrosine kinases, the characterization of enzymatic sources of superoxide production in human blood vessels, and their relationship with vascular damage in atherosclerosis and hypertension. Finally, recent developments in the search for strategies to attenuate vascular oxidative stress are reviewed.

The cellular metabolism of oxygen generates potentially deleterious reactive oxygen species, including superoxide anion, hydrogen peroxide and hydroxyl radical. Under normal physiologic conditions, the rate and magnitude of oxidant formation is balanced by the rate of oxidant elimination. However, an imbalance between pro-oxidants and antioxidants results in oxidative stress, which is the pathogenic outcome of the overproduction of oxidants that overwhelms the cellular antioxidant capacity. There is growing evidence that increased oxidative stress and associated oxidative damage are mediators of vascular injury in cardiovascular pathologies, including hypertension, atherosclerosis and ischemia–reperfusion. This development has evoked considerable interest because of the possibilities that therapies targeted against reactive oxygen intermediates by decreasing the generation of reactive oxygen species and/or by increasing availability of antioxidants may be useful in minimizing vascular injury. This review focuses on the vascular actions of reactive oxygen species, the role of oxidative stress in vascular damage in hypertension and the therapeutic potential of modulating oxygen radical bioavailability in hypertension. In particular, the following topics will be highlighted: chemistry and sources of reactive oxygen species, antioxidant defense mechanisms, signaling events mediated by reactive oxygen species, role of reactive oxygen species in hypertension and the putative therapeutic role of antioxidants in cardiovascular disease.

In this issue of Circulation Research , Gorlach et al1 present compelling evidence for conventional gp91 phox -containing NAD(P)H oxidase in the vascular endothelium and for the functional involvement of gp91 phox in endothelial cell NAD(P)H oxidase superoxide anion (O2–) production and aberrant endothelium-dependent relaxation. Many studies have implicated reactive oxygen species in the impairment of endothelium-dependent vascular responses.2 3 4 5 6 7 8 9 10 Since their initial discovery in the vasculature and the suggestion of their importance in the modulation of endothelium-derived relaxing factor nitric oxide (EDRF/NO) bioactivity, phagocyte-like NAD(P)H oxidases have been under intense study in 3 major vascular cell types.11 12 13 14 15 16 17 18 Griendling et al19 showed the presence of angiotensin II (Ang II)–activatable NAD(P)H oxidase in rat vascular smooth muscle, and Mohazzab-H and colleagues12 14 also made seminal discoveries of endothelial and smooth muscle isotypes in bovine arteries. Because of the juxtaposition of these important sources of O2− near the sites of release and action of EDRF/NO, most interest in vascular biology has concerned components in these 2 cell types. Additional studies have demonstrated molecular evidence for most NAD(P)H oxidase components in both cell types,13 15 16 20 whereas there has been scant evidence for gp91 phox in vascular smooth muscle, although a homologue, mox1, has been suggested to stand in for gp91 phox .21 In addition, my colleagues and I have shown that the vascular adventitia contains 4 phagocyte-like components, including gp91 phox ,9 10 18 and that rabbit adventitial fibroblasts contain an NAD(P)H oxidase functionally similar to the phagocyte oxidase.18 Recently, we screened a cDNA library prepared from these fibroblasts and obtained an 843-nucleotide base-pair coding region of neutrophil gp91 phox (amino acids 251 to …

Increased generation of reactive oxygen species (ROS) and altered Ca2+ handling cause vascular damage in hypertension. Mechanisms linking these systems are unclear, but TRPM2 (transient receptor potential melastatin 2) could be important because TRPM2 is a ROS sensor and a regulator of Ca2+ and Na+ transport. We hypothesized that TRPM2 is a point of cross-talk between redox and Ca2+ signaling in vascular smooth muscle cells (VSMC) and that in hypertension ROS mediated-TRPM2 activation increases [Ca2+]i through processes involving NCX (Na+/Ca2+ exchanger). VSMCs from hypertensive and normotensive individuals and isolated arteries from wild type and hypertensive mice (LinA3) were studied. Generation of superoxide anion and hydrogen peroxide (H2O2) was increased in hypertensive VSMCs, effects associated with activation of redox-sensitive PARP1 (poly [ADP-ribose] polymerase 1), a TRPM2 regulator. Ang II (angiotensin II) increased Ca2+ and Na+ influx with exaggerated responses in hypertension. These effects were attenuated by catalase-polyethylene glycol -catalase and TRPM2 inhibitors (2-APB, 8-Br-cADPR olaparib). TRPM2 siRNA decreased Ca2+ in hypertensive VSMCs. NCX inhibitors (Benzamil, KB-R7943, YM244769) normalized Ca2+ hyper-responsiveness and MLC20 phosphorylation in hypertensive VSMCs. In arteries from LinA3 mice, exaggerated agonist (U46619, Ang II, phenylephrine)-induced vasoconstriction was decreased by TRPM2 and NCX inhibitors. In conclusion, activation of ROS-dependent PARP1-regulated TRPM2 contributes to vascular Ca2+ and Na+ influx in part through NCX. We identify a novel pathway linking ROS to Ca2+ signaling through TRPM2/NCX in human VSMCs and suggest that oxidative stress-induced upregulation of this pathway may be a new player in hypertension-associated vascular dysfunction.

Purpose of reviewExtensive data indicate a role for reactive oxygen species (ROS) and redox signaling in vascular damage in hypertension. However, molecular mechanisms underlying these processes remain unclear, but oxidative post-translational modification of vascular proteins is critical. This review discusses how proteins are oxidatively modified and how redox signaling influences vascular smooth muscle cell growth and vascular remodeling in hypertension. We also highlight Nox5 as a novel vascular ROS-generating oxidase.Recent findingsOxidative stress in hypertension leads to oxidative imbalance that affects vascular cell function through redox signaling. Many Nox isoforms produce ROS in the vascular wall, and recent findings show that Nox5 may be important in humans. ROS regulate signaling by numerous processes including cysteine oxidative post-translational modification such as S-nitrosylation, S-glutathionylation and sulfydration. In vascular smooth muscle cells, this influences cellular responses to oxidative stimuli promoting changes from a contractile to a proliferative phenotype.SummaryIn hypertension, Nox-induced ROS production is increased, leading to perturbed redox signaling through oxidative modifications of vascular proteins. This influences mitogenic signaling and cell cycle regulation, leading to altered cell growth and vascular remodeling in hypertension.

Discovered and patented as an explosive by Alfred Nobel in the 1860s, nitroglycerin has been formulated for use in the treatment of symptomatic CAD for over 140 years. In fact, later in life, Nobel himself was prescribed the medication for angina, but refused to take it because of the associated side effect of headache. See page 1729 With glycerol trinitrate (GTN) as the prototype, nitrates represent one of the safest and most rapidly effective pharmacological means to reduce acute symptoms of myocardial ischemia attributable to obstructive coronary disease. This has led, over the years, to the development of long-acting oral and topical preparations. However, efficacy with chronic administration is more difficult to achieve because of the development of therapeutic resistance, generally occurring a few days after initiating treatment. This phenomenon known as nitrate tolerance has been the stimulus for intense investigation of the metabolic fate of nitroglycerin with the idea that modulation of its biotransformation could improve efficacy of chronic treatment. The mechanism of GTN-induced dilation is complex and was not identified until more than 100 years after its discovery. GTN is not a direct vasodilator, rather it must be converted to dinitrate products for vasoactivity. Biotransformation to the active metabolite nitric oxide (NO) occurs in parallel with the formation of glycerol-1,2-dinitrate and involves a dithiol-dependent process.1 It was not until recently that the principal enzyme responsible for biotransformation of GTN was identified. Chen et al1 showed that mitochondrial aldehyde dehydrogenase (ALDH-2) metabolizes GTN to glycerol-1,2-dinitrate and nitrite. This was confirmed by Sydow et al2 using mitochondrial-deficient cultured endothelial cells, although a cytosolic source of ALDH-2 has also been suggested.3 The mitochondrial enzyme converts nanomolar concentrations of GTN to active nitrodilator metabolites in vivo and in vitro, as shown by direct measurements coupled with the use …

The formation of vascular lesions is invariably associated with the accumulation of mesenchymal cells and their products in the intima, which either compromise the vessel lumen or contribute to retention of atherogenic molecules (reviewed in References 1 and 2).1,2⇓ As a result, pathological intimal hyperplasia is pivotal in the development of a wide range of clinical conditions, which are associated with increased cardiovascular morbidity and mortality. Nonetheless, the origin of intimal cells has remained a controversial issue in vascular biology and clinical cardiology. In addition to the expansion of preexisting intimal cells, the initial hypothesis argued for phenotypic modulation of medial smooth muscle cells (SMCs) from a contractile to a synthetic phenotype (dedifferentiation), resulting in their migration into the intima.3,4⇓ Several recent investigations, however, have shed new light on the mechanisms of arterial remodeling, coronary restenosis after transcatheter interventions, and vein graft changes after arterialization, which are accompanied by marked alterations in cellular composition of the affected vessel. Understanding how the vasculature alters its composition holds the key to discerning vascular responses under physiological and pathological conditions (Figure 1). In a recent issue of Circulation Research , Hu and colleagues5 join this quest, focusing on the origin of intimal cells during vein graft remodeling. In contrast to numerous observations after arterial injury, there are relatively few studies of vein graft remodeling under dyslipidemic conditions, making the analysis of vein grafts in apoE-deficient mice clearly relevant. In different types of transgenic animals, the authors demonstrated that intima of venous isografts appeared to contain SMC-like cells originating from both donor and recipient, with no apparent contribution of bone marrow-derived cells. These findings suggest vascular-bed dependent differences in the mechanisms of repair and remodeling. They also underscore the diverse cellular origin of intimal hyperplasia, which may originate from …

"Cre"ating New Tools for Smooth Muscle Analysis.