Adam Harvey

Oxidative Stress and Human Hypertension: Vascular Mechanisms, Biomarkers, and Novel Therapies

Hypertension is a major cardiovascular risk factor. Of the many processes involved in the pathophysiology of hypertension, vascular damage due to oxidative stress (excess bioavailability of reactive oxygen species [ROS]) is particularly important. Physiologically, ROS regulate vascular function through redox-sensitive signalling pathways. In hypertension, oxidative stress promotes endothelial dysfunction, vascular remodelling, and inflammation, leading to vascular damage. Vascular ROS are derived primarily by nicotinamide adenine dinucleotide phosphate oxidases, which are prime targets for therapeutic development. Although experimental evidence indicates a causative role for oxidative stress in hypertension, human data are less convincing. This might relate, in part, to suboptimal methods to accurately assess the redox state. Herein we review current knowledge on oxidative stress in vascular pathobiology and implications in human hypertension. We also discuss biomarkers to assess the redox state in the clinic, highlight novel strategies to inhibit ROS production, and summarize how lifestyle modifications promote vascular health by reducing oxidative stress.

Vascular biology of ageing-Implications in hypertension.

Ageing is associated with functional, structural and mechanical changes in arteries that closely resemble the vascular alterations in hypertension. Characteristic features of large and small arteries that occur with ageing and during the development of hypertension include endothelial dysfunction, vascular remodelling, inflammation, calcification and increased stiffness. Arterial changes in young hypertensive patients mimic those in old normotensive individuals. Hypertension accelerates and augments age-related vascular remodelling and dysfunction, and ageing may impact on the severity of vascular damage in hypertension, indicating close interactions between biological ageing and blood pressure elevation. Molecular and cellular mechanisms underlying vascular alterations in ageing and hypertension are common and include aberrant signal transduction, oxidative stress and activation of pro-inflammatory and pro-fibrotic transcription factors. Strategies to suppress age-associated vascular changes could ameliorate vascular damage associated with hypertension. An overview on the vascular biology of ageing and hypertension is presented and novel molecular mechanisms contributing to these processes are discussed. The complex interaction between biological ageing and blood pressure elevation on the vasculature is highlighted. This article is part of a Special Issue entitled: CV Ageing.

Vascular Fibrosis in Aging and Hypertension: Molecular Mechanisms and Clinical Implications

Aging is the primary risk factor underlying hypertension and incident cardiovascular disease. With aging, the vasculature undergoes structural and functional changes characterized by endothelial dysfunction, wall thickening, reduced distensibility, and arterial stiffening. Vascular stiffness results from fibrosis and extracellular matrix (ECM) remodelling, processes that are associated with aging and are amplified by hypertension. Some recently characterized molecular mechanisms underlying these processes include increased expression and activation of matrix metalloproteinases, activation of transforming growth factor-β1/SMAD signalling, upregulation of galectin-3, and activation of proinflammatory and profibrotic signalling pathways. These events can be induced by vasoactive agents, such as angiotensin II, endothelin-1, and aldosterone, which are increased in the vasculature during aging and hypertension. Complex interplay between the “aging process” and prohypertensive factors results in accelerated vascular remodelling and fibrosis and increased arterial stiffness, which is typically observed in hypertension. Because the vascular phenotype in a young hypertensive individual resembles that of an elderly otherwise healthy individual, the notion of “early” or “premature” vascular aging is now often used to describe hypertension-associated vascular disease. We review the vascular phenotype in aging and hypertension, focusing on arterial stiffness and vascular remodelling. We also highlight the clinical implications of these processes and discuss some novel molecular mechanisms of fibrosis and ECM reorganization.

Redox signaling, Nox5 and vascular remodeling in hypertension

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.

Nicotinamide Adenine Dinucleotide Phosphate Oxidase-Mediated Redox Signaling and Vascular Remodeling by 16α-Hydroxyestrone in Human Pulmonary Artery Cells: Implications in Pulmonary Arterial Hypertension.

Estrogen and oxidative stress have been implicated in pulmonary arterial hypertension (PAH). Mechanisms linking these systems are elusive. We hypothesized that estrogen metabolite, 16&agr;-hydroxyestrone (16&agr;OHE1), stimulates nicotinamide adenine dinucleotide phosphate oxidase (Nox)–induced reactive oxygen species (ROS) generation and proliferative responses in human pulmonary artery smooth muscle cells (hPASMCs) and that in PAH aberrant growth signaling promotes vascular remodeling. The pathophysiological significance of estrogen–Nox–dependent processes was studied in female Nox1−/− and Nox4−/− mice with PAH. PASMCs from control subjects (control hPASMCs) and PAH patients (PAH-hPASMCs) were exposed to estrogen and 16&agr;OHE1 in the presence/absence of inhibitors of Nox, cytochrome P450 1B1, and estrogen receptors. Estrogen, through estrogen receptor-&agr;, increased Nox-derived ROS and redox-sensitive growth in hPASMCs, with greater effects in PAH-hPASMCs versus control hPASMCs. Estrogen effects were inhibited by cytochrome P450 1B1 blockade. 16&agr;OHE1 stimulated transient ROS production in hPASMCs, with sustained responses in PAH-hPASMCs. Basal expression of Nox1/Nox4 was potentiated in PAH-hPASMCs. In hPASMCs, 16&agr;OHE1 increased Nox1 expression, stimulated irreversible oxidation of protein tyrosine phosphatases, decreased nuclear factor erythroid–related factor 2 activity and expression of nuclear factor erythroid–related factor 2–regulated antioxidant genes, and promoted proliferation. This was further amplified in PAH-hPASMCs. Nox1−/− but not Nox4−/− mice were protected against PAH and vascular remodeling. Our findings demonstrate that in PAH-hPASMCs, 16&agr;OHE1 stimulates redox-sensitive cell growth primarily through Nox1. Supporting this, in vivo studies exhibited protection against pulmonary hypertension and remodeling in Nox1−/− mice. This study provides new insights through Nox1/ROS and nuclear factor erythroid–related factor 2 whereby 16&agr;OHE1 influences hPASMC function, which when upregulated may contribute to vascular injury in PAH, particularly important in women.

Serotonin signaling through the 5-HT1B receptor and NADPH oxidase 1 in pulmonary arterial hypertension

Objective— Serotonin can induce human pulmonary artery smooth muscle cell (hPASMC) proliferation through reactive oxygen species (ROS), influencing the development of pulmonary arterial hypertension (PAH). We hypothesize that in PASMCs, serotonin induces oxidative stress through NADPH-oxidase–derived ROS generation and reduced Nrf-2 (nuclear factor [erythroid-derived 2]-like 2) antioxidant systems, promoting vascular injury. Approach and Results— HPASMCs from controls and PAH patients, and PASMCs from Nox1−/− mice, were stimulated with serotonin in the absence/presence of inhibitors of Src kinase, the 5-HT1B receptor, and NADPH oxidase 1 (Nox1). Markers of fibrosis were also determined. The pathophysiological significance of our findings was examined in vivo in serotonin transporter overexpressing female mice, a model of pulmonary hypertension. We confirmed thatserotonin increased superoxide and hydrogen peroxide production in these cells. For the first time, we show that serotonin increased oxidized protein tyrosine phosphatases and hyperoxidized peroxiredoxin and decreased Nrf-2 and catalase activity in hPASMCs. ROS generation was exaggerated and dependent on cellular Src-related kinase, 5-HT1B receptor, and the serotonin transporter in human pulmonary artery smooth muscle cells from PAH subjects. Proliferation and extracellular matrix remodeling were exaggerated in human pulmonary artery smooth muscle cells from PAH subjects and dependent on 5-HT1B receptor signaling and Nox1, confirmed in PASMCs from Nox1−/− mice. In serotonin transporter overexpressing mice, SB216641, a 5-HT1B receptor antagonist, prevented development of pulmonary hypertension in a ROS-dependent manner. Conclusions— Serotonin can induce cellular Src-related kinase–regulated Nox1-induced ROS and Nrf-2 dysregulation, contributing to increased post-translational oxidative modification of proteins and activation of redox-sensitive signaling pathways in hPASMCs, associated with mitogenic responses. 5-HT1B receptors contribute to experimental pulmonary hypertension by inducing lung ROS production. Our results suggest that 5-HT1B receptor–dependent cellular Src-related kinase-Nox1-pathways contribute to vascular remodeling in PAH.

Internal Pudental Artery Dysfunction in Diabetes Mellitus Is Mediated by NOX1-Derived ROS-, Nrf2-, and Rho Kinase–Dependent Mechanisms

Oxidative stress plays an important role in diabetes mellitus (DM)–associated vascular injury. DM is an important risk factor for erectile dysfunction. Functional and structural changes in internal pudendal arteries (IPA) can lead to erectile dysfunction. We hypothesized that downregulation of nuclear factor E2–related factor 2 (Nrf2), consequent to increased nicotinamide adenine dinucleotide phosphate oxidase 1 (NOX1)-derived reactive oxygen species (ROS), impairs IPA function in DM. IPA and vascular smooth muscle cells from C57BL/6 (control) and NOX1 knockout mice were used. DM was induced by streptozotocin in C57BL/6 mice. Functional properties of IPA were assessed using a myograph, protein expression and peroxiredoxin oxidation by Western blot, RNA expression by polymerase chain reaction, carbonylation by oxyblot assay, ROS generation by lucigenin, nitrotyrosine, and amplex red, and Rho kinase activity and nuclear accumulation of Nrf2 by ELISA. IPA from diabetic mice displayed increased contractions to phenylephrine (control 138.5±9.5 versus DM 191.8±15.5). ROS scavenger, Nrf2 activator, NOX1 and Rho kinase inhibitors normalized vascular function. High glucose increased ROS generation in IPA vascular smooth muscle cell. This effect was abrogated by Nrf2 activation and not observed in NOX1 knockout vascular smooth muscle cell. High glucose also increased levels of nitrotyrosine, protein oxidation/carbonylation, and Rho kinase activity, but reduced Nrf2 activity and expression of Nrf2-regulated genes (catalase [25.6±0.05%], heme oxygenase-1 [21±0.1%], and NAD(P)H:quinone oxidoreductase 1 [22±0.1%]) and hydrogen peroxide levels. These effects were not observed in vascular smooth muscle cell from NOX1 knockout mice. In these cells, high glucose increased hydrogen peroxide levels. In conclusion, Rho kinase activation, via NOX1-derived ROS and downregulation of Nrf2 system, impairs IPA function in DM. These data suggest that Nrf2 is vasoprotective in DM-associated erectile dysfunction.

Vascular dysfunction and fibrosis in stroke-prone spontaneously hypertensive rats: The aldosterone-mineralocorticoid receptor-Nox1 axis

Aims: We questioned whether aldosterone and oxidative stress play a role in vascular damage in severe hypertension and investigated the role of Nox1 in this process. Materials and methods: We studied mesenteric arteries, aortas and vascular smooth muscle cells (VSMC) from WKY and SHRSP rats. Vascular effects of eplerenone or canrenoic acid (CA) (mineralocorticoid receptor (MR) blockers), ML171 (Nox1 inhibitor) and EHT1864 (Rac1/2 inhibitor) were assessed. Nox1‐knockout mice were also studied. Vessels and VSMCs were probed for Noxs, reactive oxygen species (ROS) and pro‐fibrotic/inflammatory signaling. Key findings: Blood pressure and plasma levels of aldosterone and galectin‐3 were increased in SHRSP versus WKY. Acetylcholine‐induced vasorelaxation was decreased (61% vs 115%) and phenylephrine‐induced contraction increased in SHRSP versus WKY (Emax 132.8% vs 96.9%, p < 0.05). Eplerenone, ML171 and EHT1864 attenuated hypercontractility in SHRSP. Vascular expression of collagen, fibronectin, TGF&bgr;, MCP‐1, RANTES, MMP2, MMP9 and p66Shc was increased in SHRSP versus WKY. These changes were associated with increased ROS generation, 3‐nitrotyrosine expression and Nox1 upregulation. Activation of vascular p66Shc and increased expression of Nox1 and collagen I were prevented by CA in SHRSP. Nox1 expression was increased in aldosterone‐stimulated WKY VSMCs, an effect that was amplified in SHRSP VSMCs (5.2vs9.9 fold‐increase). ML171 prevented aldosterone‐induced VSMC Nox1‐ROS production. Aldosterone increased vascular expression of fibronectin and PAI‐1 in wild‐type mice but not in Nox1‐knockout mice. Significance: Our findings suggest that aldosterone, which is increased in SHRSP, induces vascular damage through MR‐Nox1‐p66Shc‐mediated processes that modulate pro‐fibrotic and pro‐inflammatory signaling pathways.

Small vessels, dementia and chronic diseases - molecular mechanisms and pathophysiology

Cerebral small vessel disease (SVD) is a major contributor to stroke, cognitive impairment and dementia with limited therapeutic interventions. There is a critical need to provide mechanistic insight and improve translation between pre-clinical research and the clinic. A 2-day workshop was held which brought together experts from several disciplines in cerebrovascular disease, dementia and cardiovascular biology, to highlight current advances in these fields, explore synergies and scope for development. These proceedings provide a summary of key talks at the workshop with a particular focus on animal models of cerebral vascular disease and dementia, mechanisms and approaches to improve translation. The outcomes of discussion groups on related themes to identify the gaps in knowledge and requirements to advance knowledge are summarized.

Progenitor Cells, Bone Marrow-Derived Fibrocytes and Endothelial-to-Mesenchymal Transition: New Players in Vascular Fibrosis.

See related article, pp 461–468 Tissue fibrosis, defined as an excessive accumulation of extracellular matrix (ECM) components leading to the destruction of organ architecture and impaired function, affects virtually every tissue and organ in the body, including the arteries. Vascular fibrosis of small and large arteries contributes to arterial remodeling, important in the development and complications of hypertension.1 Fibrogenesis is an active process that involves accumulation of structural proteins (collagen and fibronectin) and adhesion proteins (laminin and fibronectin), expression of adhesion molecules and integrins, and remodeling of the ECM.2 Healthy arteries are surrounded by perivascular adventitial tissue comprising collagens I and III in the intima, media, and adventitia, with collagen types I, III, IV, and V in the endothelial and vascular smooth muscle cell basement membranes.3 These fibrillar proteins maintain vascular integrity and normal vascular tone and function. In hypertension, accumulation of collagen and fibronectin and ECM reorganization lead to increased stiffness of the vessel wall.4 Initially, these processes are adaptive and reversible and may compensate for higher blood pressures, but with time and progressive increases in blood pressure, this becomes maladaptive and decompensated, leading to arterial stiffness that contributes to hypertension-associated target organ damage. These events have been demonstrated in many experimental models of hypertension and in hypertensive patients and have been attributed to activation of ERK1/2, p38mitogen-activated protein kinase, transforming growth factor-β, SMAD pathways, oxidative stress, and dysregulation of matrix metalloproteinases.2 Decreased activation of matrix metalloproteinases and increased activity of tissue inhibitors of metalloproteinase leads to reduced collagen turnover and consequent accumulation, with thickening and remodeling of the vascular wall. Vascular fibrosis is a dynamic and active phenomenon, where a proinflammatory, oxidative milieu, triggered by prohypertensive stimuli, lays the foundation for fibrosis and activation of ECM-producing cells. Until recently the process seemed fairly …