Gene transfer of NAD(P)H oxidase inhibitor to the vascular adventitia attenuates medial smooth muscle hypertrophy

Activation of NADPH oxidase 1 in tumour colon epithelial cells

In the plasma membrane fraction from Caco-2 human colon carcinoma cells, active Nox1 (NADPH oxidase 1) endogenously co-localizes with its regulatory components p22phox, NOXO1, NOXA1 and Rac1. NADPH-specific superoxide generating activity was reduced by 80% in the presence of either a flavoenzyme inhibitor DPI (diphenyleneiodonium) or NADP+. The plasma membranes from PMA-stimulated cells showed an increased amount of Rac1 (19.6 pmol/mg), as compared with the membranes from unstimulated Caco-2 cells (15.1 pmol/mg), but other components did not change before and after the stimulation by PMA. Spectrophotometric analysis found approx. 36 pmol of FAD and 43 pmol of haem per mg of membrane and the turnover of superoxide generation in a cell-free system consisting of the membrane and FAD was 10 mol/s per mol of haem. When the constitutively active form of Rac, Rac1(Q61L) or GTP-bound Rac1 was added exogenously to the membrane, O2−-producing activity was enhanced up to 1.5-fold above the basal level, but GDP-loaded Rac1 did not affect superoxide-generating kinetics. A fusion protein [NOXA1N–Rac1(Q61L)] between truncated NOXA1(1–211) and Rac1-(Q61L) exhibited a 6-fold increase of the basal Nox1 activity, but NOXO1N(1–292) [C-terminal truncated NOXO1(1–292)] alone showed little effect on the activity. The activated forms of Rac1 and NOXA1 are essentially involved in Nox1 activation and their interactions might be responsible for regulating the O2−-producing activity in Caco-2 cells.

Prevention of aortic fibrosis by N-acetyl-seryl-aspartyl-lysyl-proline in angiotensin II-induced hypertension

Fibrosis is an important component of large conduit artery disease in hypertension. The endogenous tetrapeptide N-acetyl-seryl-aspartyl-lysyl-proline (Ac-SDKP) has anti-inflammatory and antifibrotic effects in the heart and kidney. However, it is not known whether Ac-SDKP has an anti-inflammatory and antifibrotic effect on conduit arteries such as the aorta. We hypothesize that in ANG II-induced hypertension Ac-SDKP prevents aortic fibrosis and that this effect is associated with decreased protein kinase C (PKC) activation, leading to reduced oxidative stress and inflammation and a decrease in the profibrotic cytokine transforming growth factor-beta1 (TGF-beta1) and phosphorylation of its second messenger Smad2. To test this hypothesis we used rats with ANG II-induced hypertension and treated them with either vehicle or Ac-SDKP. In this hypertensive model we found an increased collagen deposition and collagen type I and III mRNA expression in the aorta. These changes were associated with increased PKC activation, oxidative stress, intercellular adhesion molecule (ICAM)-1 mRNA expression, and macrophage infiltration. TGF-beta1 expression and Smad2 phosphorylation also increased. Ac-SDKP prevented these effects without decreasing blood pressure or aortic hypertrophy. Ac-SDKP also enhanced expression of inhibitory Smad7. These data indicate that in ANG II-induced hypertension Ac-SDKP has an aortic antifibrotic effect. This effect may be due in part to inhibition of PKC activation, which in turn could reduce oxidative stress, ICAM-1 expression, and macrophage infiltration. Part of the effect of Ac-SDKP could also be due to reduced expression of the profibrotic cytokine TGF-beta1 and inhibition of Smad2 phosphorylation.

Regulation of smooth muscle by inducible nitric oxide synthase and NADPH oxidase in vascular proliferative diseases

Inflammation plays a critical role in promoting smooth muscle migration and proliferation during vascular diseases such as postangioplasty restenosis and atherosclerosis. Another common feature of many vascular diseases is the contribution of reactive oxygen (ROS) and reactive nitrogen (RNS) species to vascular injury. Primary sources of ROS and RNS in smooth muscle are several isoforms of NADPH oxidase (Nox) and the cytokine-regulated inducible nitric oxide (NO) synthase (iNOS). One important example of the interaction between NO and ROS is the reaction of NO with superoxide to yield peroxynitrite, which may contribute to the pathogenesis of hypertension. In this review, we discuss the literature that supports an alternate possibility: Nox-derived ROS modulate NO bioavailability by altering the expression of iNOS. We highlight data showing coexpression of iNOS and Nox in vascular smooth muscle demonstrating the functional consequences of iNOS and Nox during vascular injury. We describe the relevant literature demonstrating that the mitogen-activated protein kinases are important modulators of proinflammatory cytokine-dependent expression of iNOS. A central hypothesis discussed is that ROS-dependent regulation of the serine/threonine kinase protein kinase Cdelta is essential to understanding how Nox may regulate signaling pathways leading to iNOS expression. Overall, the integration of nonphagocytic NADPH oxidase with cytokine signaling in general and in vascular smooth muscle in particular is poorly understood and merits further investigation.

NADPH oxidase inhibitors: new antihypertensive agents?

NADPH oxidases have recently been shown to contribute to the pathogenesis of hypertension. The development of specific inhibitors of these enzymes has focused attention on their potential therapeutic use in hypertensive disease. Two of the most specific inhibitors, gp91ds-tat and apocynin, have been shown to decrease blood pressure in animal models of hypertension. Other inhibitors, including diphenylene iodonium, aminoethyl benzenesulfono fluoride, S17834, PR39, protein kinase C inhibitors, and VAS2870, have shown promise in vitro, but their in vivo specificity, pharmacokinetics, and effectiveness in hypertension remains to be determined. Of importance, the currently available antihypertensive agents angiotensin-converting enzyme inhibitors and angiotensin receptor blockers also effectively inhibit NADPH oxidase activation. Similarly, the cholesterol-lowering agents, statins, have been shown to attenuate NADPH oxidase activation. Although, antioxidants act to scavenge the reactive oxygen species produced by these enzymes, their effectiveness is limited. Targeting NADPH homologues may have a distinct advantage over current therapies because it would specifically prevent the pathophysiological formation of reactive oxygen species that contributes to hypertension.

Role of reactive oxygen species in chronic hypoxia-induced pulmonary hypertension and vascular remodeling

Pulmonary hypertension is a life-threatening disease process that affects adults and children. Pediatric patients with lung diseases that can be complicated by alveolar hypoxia, such as bronchopulmonary dysplasia (BPD), are at risk for developing pulmonary hypertension, which leads to right heart failure and greatly increases morbidity and mortality. We review the evidence that reactive oxygen species (ROS) are generated by pulmonary vascular wall cells in response to a hypoxic exposure, and that this response contributes to chronic hypoxic pulmonary hypertension. We summarize the accumulating data implicating NADPH oxidase as a major source of O2 responsible for vascular remodeling and hypertension. We also consider the effects of chronic hypoxia on the clearance of O2 by superoxide dismutases, specifically extracellular superoxide dismutase, which is highly expressed in the pulmonary artery. We review the role of the activated vascular adventitial fibroblast in the generation of ROS and in the pathogenesis of vascular remodeling, and provide a rationale to consider the role of the activated fibroblast and ROS in hypoxic pulmonary hypertension using a clinically relevant bovine model of neonatal chronic hypoxic pulmonary hypertension.

Activation of adventitial fibroblasts contributes to the early development of atherosclerosis: A novel hypothesis that complements the “Response-to-Injury Hypothesis” and the “Inflammation Hypothesis”

The role of the adventitia in vascular function and vascular lesion formation has been largely ignored. This article introduces the hypothesis that the activation of the adventitia, specifically the fibroblasts, contributes to the formation of intimal atherosclerotic lesions. The evidence for this hypothesis includes: (a) the early proliferative changes seen in fibroblasts found in the adventitia; (b) the increase and the alteration of extracellular matrix deposition in the adventitia; (c) fibroblast differentiation into myofibroblasts and migration into the intima; and (d) fibroblast synthesis and release of cytokines that have potent effects on neighboring smooth muscle and endothelial cells prior to intimal lesion formation. In conclusion, the activation of adventitial fibroblasts is a key regulator of vascular function and structure from the "outside-in" and contributes to the development of atherosclerotic lesions. The outer location of the adventitia makes it a suitable location for drug delivery and gene therapy aimed at preventing and treating atherosclerosis.

Role of the adventitia in pulmonary vascular remodeling

An increasing volume of experimental data indicates that the adventitial fibroblast, in both the pulmonary and systemic circulations, is a critical regulator of vascular wall function in health and disease. A rapidly emerging concept is that the vascular adventitia acts as biological processing center for the retrieval, integration, storage, and release of key regulators of vessel wall function. In response to stress or injury, resident adventitial cells can be activated and reprogrammed to exhibit different functional and structural behaviors. In fact, under certain conditions, the adventitial compartment may be considered the principal injury-sensing tissue of the vessel wall. In response to vascular stresses such as overdistension and hypoxia, the adventitial fibroblast is activated and undergoes phenotypic changes, which include proliferation, differentiation, upregulation of contractile and extracellular matrix proteins, and release of factors that directly affect medial smooth muscle cell tone and growth and that stimulate recruitment of inflammatory and progenitor cells to the vessel wall. Each of these changes in fibroblast phenotype modulates either directly or indirectly changes in overall vascular function and structure. The purpose of this review is to present the current evidence demonstrating that the adventitial fibroblast acts as a key regulator of pulmonary vascular function and structure from the "outside-in."

Nox2-containing NADPH oxidase and Akt activation play a key role in angiotensin II-induced cardiomyocyte hypertrophy

Angiotensin II (ANG II) has profound effects on the development and progression of pathological cardiac hypertrophy; however, the intracellular signaling mechanisms are not fully understood. In this study, we used genetic tools to test the hypothesis that increased formation of superoxide (O2−·) radicals from a Rac1-regulated Nox2-containing NADPH oxidase is a key upstream mediator of ANG II-induced activation of serine-threonine kinase Akt, and that this signaling cascade plays a crucial role in ANG II-dependent cardiomyocyte hypertrophy. ANG II caused a significant time-dependent increase in Rac1 activation and O2−· production in primary neonatal rat cardiomyocytes, and these responses were abolished by adenoviral (Ad)-mediated expression of a dominant-negative Rac1 (AdN17Rac1) or cytoplasmic Cu/ZnSOD (AdCu/ZnSOD). Moreover, both AdN17Rac1 and AdCu/ZnSOD significantly attenuated ANG II-stimulated increases in cardiomyocyte size. Quantitative real-time PCR analysis demonstrated that Nox2 is the homolog expressed at highest levels in primary neonatal cardiomyocytes, and small interference RNA (siRNA) directed against it selectively decreased Nox2 expression by >95% and abolished both ANG II-induced O2−· generation and cardiomyocyte hypertrophy. Finally, ANG II caused a time-dependent increase in Akt activity via activation of AT1 receptors, and this response was abolished by Ad-mediated expression of cytosolic human O2−· dismutase (AdCu/ZnSOD). Furthermore, pretreatment of cardiomyocytes with dominant-negative Akt (AdDNAkt) abolished ANG II-induced cellular hypertrophy. These findings suggest that O2−· generated by a Nox2-containing NADPH oxidase is a central mediator of ANG II-induced Akt activation and cardiomyocyte hypertrophy, and that dysregulation of this signaling cascade may play an important role in cardiac hypertrophy.

Adventitial delivery of dominant-negative p67phox attenuates neointimal hyperplasia of the rat carotid artery

Several essential components of NADPH oxidase, including p22phox, gp91phox (nox2) and its homologs nox1 and nox4, p47phox, p67phox, and rac1, are present in the vasculature. We previously reported that p67phox is essential for adventitial fibroblast NADPH oxidase O2- production. Thus we postulated that inhibition of adventitial p67phox activity would attenuate angioplasty-induced hyperplasia. To test this hypothesis, we treated the adventitia of carotid arteries with a control adenovirus (Ad-control), a virus expressing dominant-negative p67phox (Ad-p67dn), or a virus expressing a competitive peptide (gp91ds) targeting the p47phox-gp91phox interaction (Ad-gp91ds). Common carotid arteries (CCAs) from male Sprague-Dawley rats were transfected with Ad-control, Ad-p67dn, or Ad-gp91ds in pluronic gel. After 2 days, a 2-F (Fogarty) catheter was used to injure CCAs in vivo. After 14 days, CCAs were perfusion-fixed and analyzed. In 13 experiments, digital morphometry suggested a reduction of neointimal hyperplasia with Ad-p67dn compared with Ad-control; however, the reduction did not reach statistical significance (P = 0.058). In contrast, a significant reduction was achieved with Ad-gp91ds (P = 0.006). No changes in medial area or remodeling were observed with either treatment. Moreover, adventitial fibroblast proliferation in vitro was inhibited by Ad-gp91ds but not by Ad-p67dn, despite confirmation that Ad-p67dn inhibits NADPH oxidase in fibroblasts. These data appear to suggest that a multicomponent vascular NADPH oxidase plays a role in neointimal hyperplasia. However, inhibition of p47phox may be more effective than inhibition of p67phox at attenuating neointimal growth.

An osteopontin-NADPH oxidase signaling cascade promotes pro-matrix metalloproteinase 9 activation in aortic mesenchymal cells

Osteopontin (OPN) is a cytokine upregulated in diabetic vascular disease. To better understand its role in vascular remodeling, we assessed how OPN controls metalloproteinase (MMP) activation in aortic adventitial myofibroblasts (AMFs) and A7r5 vascular smooth muscle cells (VSMCs). By zymography, OPN and tumor necrosis factor (TNF)-alpha preferentially upregulate pro-matrix metalloproteinase 9 (pro-MMP9) activity. TNF-alpha upregulated pro-MMP9 in AMFs isolated from wild-type (OPN(+/+)) mice, but pro-MMP9 induction was abrogated in AMFs from OPN(-/-) mice. OPN treatment of VSMCs enhanced pro-MMP9 activity, and TNF-alpha induction of pro-MMP9 was inhibited by anti-OPN antibody and apocynin. Superoxide and the oxylipid product 8-isoprostaglandin F(2) alpha-isoprostane (8-IsoP) were increased by OPN treatment, and anti-OPN antibody suppressed 8-IsoP production. Like OPN and TNF-alpha, 8-IsoP preferentially activated pro-MMP9. Superoxide, 8-IsoP, and NADPH oxidase 2 (Nox2) subunits were reduced in OPN(-/-) AMFs. Treatment of A7r5 VSMCs with OPN upregulated NADPH oxidase subunit accumulation. OPN structure/function studies mapped these activities to the SVVYGLR heptapeptide motif in the thrombin-liberated human OPN N-terminal domain (SLAYGLR in mouse OPN). Treatment of aortic VSMCs with SVVYGLR upregulated pro-MMP9 activity and restored TNF-alpha activation of pro-MMP9 in OPN(-/-) AMFs. Injection of OPN-deficient OPN(+/-) mice with SVVYGLR peptide upregulated pro-MMP9 activity, 8-IsoP levels, and Nox2 protein levels in aorta and increased panmural superoxide production (dihydroethidium staining). At equivalent hyperglycemia and dyslipidemia, 8-IsoP levels and aortic pro-MMP9 were reduced with complete OPN deficiency in a model of diet-induced diabetes, achieved by comparing OPN(-/-)/LDLR(-/-) versus OPN(+/-)/LDLR(-/-) siblings. Thus, OPN provides a paracrine signal that augments vascular pro-MMP9 activity, mediated in part via superoxide generation and oxylipid formation.

NADPH oxidases in cardiovascular health and disease

Increased oxidative stress plays an important role in the pathophysiology of cardiovascular diseases such as hypertension, atherosclerosis, diabetes, cardiac hypertrophy, heart failure, and ischemia-reperfusion. Although several sources of reactive oxygen species (ROS) may be involved, a family of NADPH oxidases appears to be especially important for redox signaling and may be amenable to specific therapeutic targeting. These include the prototypic Nox2 isoform-based NADPH oxidase, which was first characterized in neutrophils, as well as other NADPH oxidases such as Nox1 and Nox4. These Nox isoforms are expressed in a cell- and tissue-specific fashion, are subject to independent activation and regulation, and may subserve distinct functions. This article reviews the potential roles of NADPH oxidases in both cardiovascular physiological processes (such as the regulation of vascular tone and oxygen sensing) and pathophysiological processes such as endothelial dysfunction, inflammation, hypertrophy, apoptosis, migration, angiogenesis, and vascular and cardiac remodeling. The complexity of regulation of NADPH oxidases in these conditions may provide the possibility of targeted therapeutic manipulation in a cell-, tissue- and/or pathway-specific manner at appropriate points in the disease process.

Regulation of NADPH oxidases: the role of Rac proteins

The role for reactive oxygen species (ROS) in cellular (patho)physiology, in particular in signal transduction, is increasingly recognized. The family of NADPH oxidases (NOXes) plays an important role in the production of ROS in response to receptor agonists such as growth factors or inflammatory cytokines that signal through the Rho-like small GTPases Rac1 or Rac2. The phagocyte oxidase (gp91phox/NOX2) is the best characterized family member, and its mode of activation is relatively well understood. Recent work has uncovered novel and increasingly complex modes of control of the NOX2-related proteins. Some of these, including NOX2, have been implicated in various aspects of (cardio)vascular disease, including vascular smooth muscle and endothelial cell hypertrophy and proliferation, inflammation, and atherosclerosis. This review focuses on the role of the Rac1 and Rac2 GTPases in the activation of the various NOX family members.

Targeting reactive oxygen species in hypertension

PURPOSE OF REVIEW

Hypertension is a major risk factor for vascular diseases such as stroke, myocardial infarction, and renal microvascular disease. The mechanism by which vascular disease develops is complex, and growing evidence suggests that an increase in reactive oxygen species during hypertension is a major contributing factor. NADPH oxidase, the primary source of reactive oxygen species in the cardiovascular system, is a strong candidate for the development of therapeutic agents to ameliorate hypertension and end-organ damage.

RECENT FINDINGS

Various scavengers and inhibitors of reactive oxygen species have been proposed for use in animal as well as human studies. While many of these agents are effective at lowering tissue reactive oxygen species levels, their specificity is a serious concern. Our laboratory has developed cell-permeant peptidic inhibitors targeting key interactions among the different NAD(P)H oxidase homologues. One of these inhibitors targeting nox2 and p47-phox interaction has proven useful in attenuating target neoplasia and hypertrophy.

SUMMARY

Strategies aimed at specifically inhibiting NAD(P)H oxidase have proven effective in attenuating cardiovascular oxidative stress. The development of new inhibitors targeting novel oxidase homologues appears to hold significant promise for clarifying the physiologic role of these homologues as well as for the development of new antioxidant therapies.

Point Mutations in the Proline-rich Region of p22 Are Dominant Inhibitors of Nox1- and Nox2-dependent Reactive Oxygen Generation

The integral membrane protein p22phox is an indispensable component of the superoxide-generating phagocyte NADPH oxidase, whose catalytic core is the membrane-associated gp91phox (also known as Nox2). p22phox associates with gp91phox and, through its proline-rich C terminus, provides a binding site for the tandem Src homology 3 domains of the activating subunit p47phox. Whereas p22phox is expressed ubiquitously, its participation in regulating the activity of other Nox enzymes is less clear. This study investigates the requirement of p22phox for Nox enzyme activity and explores the role of its proline-rich region (PRR) for regulating activity. Coexpression of specific Nox catalytic subunits (Nox1, Nox2, Nox3, Nox4, or Nox5) along with their corresponding regulatory subunits (NOXO1/NOXA1 for Nox1; p47phox/p67phox/Rac for Nox2; NOXO1 for Nox3; no subunits for Nox4 or Nox5) resulted in marked production of reactive oxygen. Small interfering RNAs decreased endogenous p22phox expression and inhibited reactive oxygen generation from Nox1, Nox2, Nox3, and Nox4 but not Nox5. Truncated forms of p22phox that disrupted the PRR-inhibited reactive oxygen generation from Nox1, Nox2, and Nox3 but not from Nox4 and Nox5. Similarly, p22phox (P156Q), a mutation that disrupts Src homology 3 binding by the PRR, potently inhibited reactive oxygen production from Nox1 and Nox2 but not from Nox4 and Nox5. Expression of p22phox (P156Q) inhibited NOXO1-stimulated Nox3 activity, but co-expression of NOXA1 overcame the inhibitory effect. The P157Q and P160Q mutations of p22phox showed selective inhibition of Nox2/p47phox/p67phox, and selectivity was specific for the organizing subunit (p47phox or NOXO1) rather than the Nox catalytic subunit. These studies stress the importance of p22phox for the function of Nox1, Nox2, Nox3, and Nox4, and emphasize the key role of the PRR for regulating Nox proteins whose activity is dependent upon p47phox or NOXO1.

Contribution of arachidonic acid metabolites derived via cytochrome P4504A to angiotensin II-induced neointimal growth

Angiotensin II and the arachidonic acid metabolite derived via cytochrome P450 20-hydroxyeicostetraenoic acid promote vasoconstriction and vascular smooth muscle cell (VSMC) proliferation. This study was conducted to determine if 20-hydroxyeicostetraenoic acid contributes to angiotensin II-induced neointimal formation in balloon-injured rat carotid artery. In anesthetized rats, the drugs were infused into the clamped segment of the injured right common carotid artery for 60 minutes. The drug solution and catheter were withdrawn, the common carotid artery was ligated, and blood flow was restored. Exposure of the injured artery to angiotensin II (200 nmol/L) or arachidonic acid (10 micromol/L) increased neointimal thickening at day 14 (intima/media ratio 0.71+/-0.14 with vehicle versus 1.65+/-0.10 with angiotensin II or 1.31+/-0.13 with arachidonic acid; P<0.05). Cytochrome P450 4A1 antisense, but not scrambled, oligodeoxynucleotide (100 nmol/L) reduced angiotensin II-induced or arachidonic acid-induced neointimal thickening (intima/media ratio 0.90+/-0.07 for angiotensin II and 0.95+/-0.06 for arachidonic acid). 20-hydroxyeicostetraenoic acid (0.5 micromol/L) also increased neointimal thickening of injured artery (intima/media ratio 1.15+/-0.03); this was not altered by cytochrome P450 4A1 antisense oligodeoxynucleotide. Angiotensin II, arachidonic acid, and 20-hydroxyeicostetraenoic acid also induced the expression of cytochrome P450 4A and increased the number of CD45-positive cells; the latter effect of angiotensin II and arachidonic acid, but not 20-hydroxyeicostetraenoic acid, was diminished by cytochrome P450 4A1 antisense oligodeoxynucleotide. These data suggest that arachidonic acid metabolites derived via cytochrome P450 4A, most likely 20-hydroxyeicostetraenoic acid, mediate angiotensin II-induced neointimal thickening in injured rat carotid artery.

Redox control of growth factor signaling: recent advances in cardiovascular medicine

Growth factors play vital roles in the regulation of various biologic processes, including those in cardiovascular and respiratory systems. Accumulating evidence suggests that reactive oxygen species mediate growth factor signal transduction. The discovery of reactive oxygen species production by angiotensin II in vascular smooth muscle cells via the activation of NAD(P)H oxidase promoted studies of redox control of growth factor signaling. In the past few years, there have been further advances in this field. In addition to established roles of reactive oxygen species in vascular smooth muscle growth, these species have been demonstrated to serve as second messengers for cardiac hypertrophy induced by angiotensin II. NAD(P)H oxidase also produces reactive oxygen species in response to endothelin-1 in vascular smooth muscle and cardiac muscle cells. These results suggest that inhibiting NAD(P)H oxidase might be a useful therapeutic strategy. In fact, adenovirus-mediated gene transfer appears to be an effective approach to prevent vascular hypertrophy in rodent models. Growth factors also induce survival signaling in cardiac and smooth muscle cells, and redox control may play a role in such events. It is likely that studies reporting the mechanisms of redox control of growth factor signaling will rapidly emerge in the next several years, and understanding of such regulation should help in the development of therapeutic strategies against heart and lung diseases.