NADPH oxidases in the vasculature: Molecular features, roles in disease and pharmacological inhibition

Reactive oxygen species and vascular biology: implications in human hypertension

Increased vascular production of reactive oxygen species (ROS; termed oxidative stress) has been implicated in various chronic diseases, including hypertension. Oxidative stress is both a cause and a consequence of hypertension. Although oxidative injury may not be the sole etiology, it amplifies blood pressure elevation in the presence of other pro-hypertensive factors. Oxidative stress is a multisystem phenomenon in hypertension and involves the heart, kidneys, nervous system, vessels and possibly the immune system. Compelling experimental and clinical evidence indicates the importance of the vasculature in the pathophysiology of hypertension and as such much emphasis has been placed on the (patho)biology of ROS in the vascular system. A major source for cardiovascular, renal and neural ROS is a family of non-phagocytic nicotinamide adenine dinucleotide phosphate (NADPH) oxidases (Nox), including the prototypic Nox2 homolog-based NADPH oxidase, as well as other Noxes, such as Nox1 and Nox4. Nox-derived ROS is important in regulating endothelial function and vascular tone. Oxidative stress is implicated in endothelial dysfunction, inflammation, hypertrophy, apoptosis, migration, fibrosis, angiogenesis and rarefaction, important processes involved in vascular remodeling in hypertension. Despite a plethora of data implicating oxidative stress as a causative factor in experimental hypertension, findings in human hypertension are less conclusive. This review highlights the importance of ROS in vascular biology and focuses on the potential role of oxidative stress in human hypertension.

The anti-platelet effects of apocynin in mice are not mediated by inhibition of NADPH oxidase activity

Apocynin, or a (myelo)peroxidase-derived product thereof, is a powerful inhibitor of nicotinamide adenine dinucleotide phosphate (NADPH) oxidase. Apocynin has also been shown to prevent aggregation of platelets in response to agonists such as collagen and thrombin. The aims of this study were to establish whether NADPH oxidase activity is required for aggregation of murine platelets to collagen and other agonists and whether the anti-aggregatory effects of apocynin are due to an inhibitory action against this enzyme. Washed platelets were isolated from male C57BL6 (wild-type), Nox2-deficient (Nox2(-/y )), and p47phox-deficient (p47phox(-/-)) mice for assessment of aggregation and NADPH oxidase subunit (Nox2, p47phox) expression. Collagen and U46619 elicited aggregation of murine platelets, and these responses were inhibited by apocynin at concentrations ≥100 μM. By contrast, aggregations to a direct protein kinase C activator, phorbol-12,13-dibutyrate, were insensitive to apocynin. Immunoblotting of platelet protein homogenates from wild-type mice with anti-Nox2 or p47phox antibodies revealed strong bands at 58 and 50 kDa, respectively. While expression of these immunoreactive bands was greatly diminished in platelets from Nox2(-/y ) and p47phox(-/-) mice, collagen still elicited aggregations that were similar to those observed in platelets from wild-types. Moreover, apocynin was an equally effective inhibitor of aggregation in platelets from all three mouse strains. In conclusion, these data suggest that NADPH oxidase-derived reactive oxygen species play no role in the aggregation response of washed murine platelets to collagen. Thus, our observation that apocynin is a powerful inhibitor of platelet aggregation raises further questions about the selectivity of this drug as an NADPH oxidase inhibitor.

Nox isoforms in vascular pathophysiology: insights from transgenic and knockout mouse models

Elevated reactive oxygen species (ROS) formation in the vascular wall is a key feature of cardiovascular diseases and a likely contributor to oxidative stress, endothelial dysfunction and vascular inflammation. The NADPH oxidases are a family of ROS generating enzymes, of which four members (Nox1, Nox2, Nox4 and Nox5) are expressed in blood vessels. Numerous studies have demonstrated that expression and activity of at least two isoforms of NADPH oxidase - Nox1 and Nox2 - are up-regulated in animal models of hypertension, diabetes and atherosclerosis. However, these observations are merely suggestive of a role for NADPH oxidases in vessel pathology and by no means establish cause and effect. Furthermore, questions surrounding the specificity of current pharmacological inhibitors of NADPH oxidase mean that findings obtained with these compounds must be viewed with caution. Here, we review the literature on studies utilising genetically-modified mouse strains to investigate the roles of NADPH oxidases in experimental models of vascular disease. While several studies on transgenic over-expressing or knockout mice support roles for Nox1- and/or Nox2-containing oxidases as sources of excessive vascular ROS production and causes of endothelial dysfunction in hypertension, atherosclerosis and diabetes, there are still no published reports on the effects of genetic modification of Nox4 or Nox5 in vascular or indeed any other contexts. Further understanding of the roles of specific isoforms of NADPH oxidase in vascular (patho)physiology should provide direction for future programs aimed at developing selective inhibitors of these enzymes as novel therapeutics in cardiovascular disease.

A review of endothelial dysfunction in diabetes: a focus on the contribution of a dysfunctional eNOS

Although the etiology of vascular dysfunction in diabetes has been extensively investigated in both humans as well as animal models of human diabetes, the relative importance of the cellular pathways involved is still not fully understood. In this review, we focus on reviewing the literature that provides insights into how an acute exposure to hyperglycemia results in a dysregulation of endothelial nitric oxide synthase function, the subsequent downstream effects of endothelial nitric oxide synthase dysregulation, and the development of endothelial dysfunction.

Mechanisms contributing to cerebral infarct size after stroke: gender, reperfusion, T lymphocytes, and Nox2-derived superoxide

Cerebral infarct volume is typically smaller in premenopausal females than in age-matched males after ischemic stroke, but the underlying mechanisms are poorly understood. In this study we provide evidence in mice that this gender difference only occurs when the ischemic brain is reperfused. The limited tissue salvage achieved by reperfusion in male mice is associated with increased expression of proinflammatory proteins, including cyclooxygenase-2 (Cox-2), Nox2, and vascular cell adhesion molecule-1 (VCAM-1), and infiltration of Nox2-containing T lymphocytes into the infarcted brain, whereas such changes are minimal in female mice after ischemia-reperfusion (I-R). Infarct volume after I-R was no greater at 72 h than at 24 h in either gender. Infarct development was Nox2 dependent in male but not in female mice, and Nox2 within the infarct was predominantly localized in T lymphocytes. Stroke resulted in an approximately 15-fold increase in Nox2-dependent superoxide production by circulating, but not spleen-derived, T lymphocytes in male mice, and this was approximately sevenfold greater than in female mice. These circulating immune cells may thus represent a major and previously unrecognized source of superoxide in the acutely ischemic and reperfused brain of males (and potentially in postmenopausal females). Our findings provide novel insights into mechanisms that could be therapeutically targeted in acute ischemic stroke patients who receive thrombolysis therapy to induce cerebral reperfusion.

Endothelial activation and circulating markers of endothelial activation in kidney disease

The recognition of a central role for the endothelium in the development of kidney disease or the development of vascular lesions in patients with established renal dysfunction has led to the emergence of methods to test different aspects of endothelium function, including in endothelium injury and repair. Endothelial-cell activation is associated with the shedding of components of the glycocalyx, adhesion molecules and endothelial microparticles into the circulation. This process may eventually result in the detachment of endothelial cells and recruitment of circulating myeloid and progenitor cells that are involved in vascular remodeling and repair. Circulating markers of endothelium activation may therefore represent novel markers of vessel wall injury. This Review describes the biology of these circulating markers of vessel wall injury, the methodologies used to measure them, and their possible relevance to patients with kidney disease.

Transcriptional regulation of NADPH oxidase isoforms, Nox1 and Nox4, by nuclear factor-kappaB in human aortic smooth muscle cells

Inflammation-induced changes in the activity and expression of NADPH oxidases (Nox) play a key role in atherogenesis. The molecular mechanisms of Nox regulation are scantily elucidated. Since nuclear factor-kappaB (NF-kappaB) controls the expression of many genes associated to inflammation-related diseases, in this study we have investigated the role of NF-kappaB signaling in the regulation of Nox1 and Nox4 transcription in human aortic smooth muscle cells (SMCs). Cultured cells were exposed to tumor necrosis factor-alpha (TNFalpha), a potent inducer of both Nox and NF-kappaB, up to 24h. Lucigenin-enhanced chemiluminescence and dichlorofluorescein assays, real-time polymerase chain reaction, and Western blot analysis showed that inhibition of NF-kappaB pathway reduced significantly the TNFalpha-dependent up-regulation of Nox-derived reactive oxygen species production, Nox1 and Nox4 expression. In silico analysis indicated the existence of typical NF-kappaB elements in the promoters of Nox1 and Nox4. Transient overexpression of p65/NF-kappaB significantly increased the promoter activities of both isoforms. Physical interaction of p65/NF-kappaB proteins with the predicted sites was demonstrated by chromatin immunoprecipitation assay. These findings demonstrate that NF-kappaB is an essential regulator of Nox1- and Nox4-containing NADPH oxidase in SMCs. Elucidation of the complex relationships between NF-kappaB and Nox enzymes may lead to a novel pharmacological strategy to reduce both inflammation and oxidative stress in atherosclerosis and its associated complications.

The NADPH oxidase subunit NOX4 is a new target gene of the hypoxia-inducible factor-1

NADPH oxidases generate reactive oxygen species (ROS). We studied the role of NOX4 under hypoxia. Hypoxia enhanced NOX4 expression in lung smooth-muscle cells and lung tissue due to HIF-1α binding and activation of the NOX4 promoter. HIF-1α–dependent NOX4 induction restored ROS levels after hypoxia and induced proliferation by hypoxia. The following citations were not referenced in the reference list or the reference/citation is not styled correctly: Kietzmann et al., 1999.

NADPH oxidases are important sources of reactive oxygen species (ROS), possibly contributing to various disorders associated with enhanced proliferation. NOX4 appears to be involved in vascular signaling and may contribute to the response to hypoxia. However, the exact mechanisms controlling NOX4 levels under hypoxia are not resolved. We found that hypoxia rapidly enhanced NOX4 mRNA and protein levels in pulmonary artery smooth-muscle cells (PASMCs) as well as in pulmonary vessels from mice exposed to hypoxia. This response was dependent on the hypoxia-inducible transcription factor HIF-1α because overexpression of HIF-1α increased NOX4 expression, whereas HIF-1α depletion prevented this response. Mutation of a putative hypoxia-responsive element in the NOX4 promoter abolished hypoxic and HIF-1α–induced activation of the NOX4 promoter. Chromatin immunoprecipitation confirmed HIF-1α binding to the NOX4 gene. Induction of NOX4 by HIF-1α contributed to maintain ROS levels after hypoxia and hypoxia-induced proliferation of PASMCs. These findings show that NOX4 is a new target gene of HIF-1α involved in the response to hypoxia. Together with our previous findings that NOX4 mediates HIF-1α induction under normoxia, these data suggest an important role of the signaling axis between NOX4 and HIF-1α in various cardiovascular disorders under hypoxic and also nonhypoxic conditions.

Vascular dysfunction in cerebrovascular disease: mechanisms and therapeutic intervention

The endothelium plays a crucial role in the control of vascular homoeostasis through maintaining the synthesis of the vasoprotective molecule NO* (nitric oxide). Endothelial dysfunction of cerebral blood vessels, manifested as diminished NO* bioavailability, is a common feature of several vascular-related diseases, including hypertension, hypercholesterolaemia, stroke, subarachnoid haemorrhage and Alzheimer's disease. Over the past several years an enormous amount of research has been devoted to understanding the mechanisms underlying endothelial dysfunction. As such, it has become apparent that, although the diseases associated with impaired NO* function are diverse, the underlying causes are similar. For example, compelling evidence indicates that oxidative stress might be an important mechanism of diminished NO* signalling in diverse models of cardiovascular 'high-risk' states and cerebrovascular disease. Although there are several sources of vascular ROS (reactive oxygen species), the enzyme NADPH oxidase is emerging as a strong candidate for the excessive ROS production that is thought to lead to vascular oxidative stress. The purpose of the present review is to outline some of the mechanisms thought to contribute to endothelial dysfunction in the cerebral vasculature during disease. More specifically, we will highlight current evidence for the involvement of ROS, inflammation, the RhoA/Rho-kinase pathway and amyloid beta-peptides. In addition, we will discuss currently available therapies for improving endothelial function and highlight future therapeutic strategies.

NADPH oxidase and cardiac failure

Increases in oxidative stress in the heart play an important role in mediating hypertrophy, apoptosis, fibrosis, mitochondrial dysfunction, and the consequent development of heart failure. Although it has been widely believed that electron leakage from the mitochondrial electron transport chain is the primary source of oxidative stress in the failing heart, increasing lines of evidence suggest that enzymes which produce reactive oxygen species may also contribute to it. NADPH oxidases are transmembrane enzymes dedicated to producing superoxide (O(2)(-)) by transferring an electron from NAD(P)H to molecular oxygen. Nox4 is a major NADPH oxidase isoform expressed in the heart. Nox4 is localized primarily at mitochondria in cardiac myocytes, and upregulation of Nox4 hypertrophic stimuli enhances O(2)(-) production, apoptosis, and mitochondrial dysfunction, thereby playing an important role in mediating cardiac dysfunction. Since Nox4 could be a key molecule mediating oxidative stress and pathological hypertrophy, it may serve as an important target of heart failure treatment. In this review, the importance of NADPH oxidases as sources of increased oxidative stress in the failing heart and the role of Nox4 in mediating growth and death of cardiac myocytes are discussed.

NADPH oxidases: functions and pathologies in the vasculature

Reactive oxygen species are ubiquitous signaling molecules in biological systems. Four members of the NADPH oxidase (Nox) enzyme family are important sources of reactive oxygen species in the vasculature: Nox1, Nox2, Nox4, and Nox5. Signaling cascades triggered by stresses, hormones, vasoactive agents, and cytokines control the expression and activity of these enzymes and of their regulatory subunits, among which p22phox, p47phox, Noxa1, and p67phox are present in blood vessels. Vascular Nox enzymes are also regulated by Rac, ClC-3, Poldip2, and protein disulfide isomerase. Multiple Nox subtypes, simultaneously present in different subcellular compartments, produce specific amounts of superoxide, some of which is rapidly converted to hydrogen peroxide. The identity and location of these reactive oxygen species, and of the enzymes that degrade them, determine their downstream signaling pathways. Nox enzymes participate in a broad array of cellular functions, including differentiation, fibrosis, growth, proliferation, apoptosis, cytoskeletal regulation, migration, and contraction. They are involved in vascular pathologies such as hypertension, restenosis, inflammation, atherosclerosis, and diabetes. As our understanding of the regulation of these oxidases progresses, so will our ability to alter their functions and associated pathologies.

Translating the oxidative stress hypothesis into the clinic: NOX versus NOS

Cardiovascular diseases remain the leading cause of death in industrialised nations. Since the pathomechanisms of most cardiovascular diseases are not understood, the majority of therapeutic approaches are symptom-orientated. Knowing the molecular mechanism of disease would enable more targeted therapies. One postulated underlying mechanism of cardiovascular diseases is oxidative stress, i.e. the increased occurrence of reactive oxygen species such as superoxide. Oxidative stress leads to a dysfunction of vascular endothelium-dependent protective mechanisms. There is growing evidence that this scenario also involves impaired nitric oxide (NO)-cyclic GMP signalling. Out of a number of enzyme families that can produce reactive oxygen species, NADPH oxidases stand out, as they are the only enzymes whose sole purpose is to produce reactive oxygen species. This review focuses on the clinically validated targets of oxidative stress, NO synthase (NOS) and the NO receptor, soluble guanylate cyclase as well as the source of ROS, e.g. NADPH oxidases. We place recent knowledge in the function and regulation of these enzyme families into clinical perspective. For a comprehensive overview of the biology and pharmacology of oxidative stress and possible other sources and targets, we refer to other literature overviews.

Direct evidence of a role for Nox2 in superoxide production, reduced nitric oxide bioavailability, and early atherosclerotic plaque formation in ApoE-/- mice

The Nox family NADPH oxidases are reactive oxygen species (ROS)-generating enzymes that are strongly implicated in atherogenesis. However, no studies have examined which Nox isoform(s) are involved. Here we investigated the role of the Nox2-containing NADPH oxidase in atherogenesis in apolipoprotein E-null (ApoE(-/-)) mice. Wild-type (C57Bl6/J), ApoE(-/-), and Nox2(-/y)/ApoE(-/-) mice were maintained on a high-fat (21%) diet from 5 wk of age until they were 12 or 19 wk old. Mice were euthanized and their aortas removed for measurement of Nox2 expression (Western blot analysis and immunohistochemistry), ROS production (L012-enhanced chemiluminescence), nitric oxide (NO) bioavailability (contractions to N(omega)-nitro-L-arginine), and atherosclerotic plaque development along the aorta and in the aortic sinus. Nox2 expression was upregulated in the aortic endothelium of ApoE(-/-) mice before the appearance of lesions, and this was associated with elevated ROS levels. Within developing plaques, macrophages were also a prominent source of Nox2. The absence of Nox2 in Nox2(-/y)/ApoE(-/-) double-knockout mice had minimal effects on plasma lipids or lesion development in the aortic sinus in animals up to 19 wk of age. However, an en face examination of the aorta from the arch to the iliac bifurcation revealed a 50% reduction in lesion area in Nox2(-/y)/ApoE(-/-) versus ApoE(-/-) mice, and this was associated with a marked decrease in aortic ROS production and an increased NO bioavailability. In conclusion, this is the first demonstration of a role for Nox2-NADPH oxidase in vascular ROS production, reduced NO bioavailability, and early lesion development in ApoE(-/-) mice, highlighting this Nox isoform as a potential target for future therapies for atherosclerosis.

Dynamin 2 and c-Abl are novel regulators of hyperoxia-mediated NADPH oxidase activation and reactive oxygen species production in caveolin-enriched microdomains of the endothelium

Reactive oxygen species (ROS) generation, particularly by the endothelial NADPH oxidase family of proteins, plays a major role in the pathophysiology associated with lung inflammation, ischemia/reperfusion injury, sepsis, hyperoxia, and ventilator-associated lung injury. We examined potential regulators of ROS production and discovered that hyperoxia treatment of human pulmonary artery endothelial cells induced recruitment of the vesicular regulator, dynamin 2, the non-receptor tyrosine kinase, c-Abl, and the NADPH oxidase subunit, p47(phox), to caveolin-enriched microdomains (CEMs). Silencing caveolin-1 (which blocks CEM formation) and/or c-Abl expression with small interference RNA inhibited hyperoxia-mediated tyrosine phosphorylation and association of dynamin 2 with p47(phox) and ROS production. In addition, treatment of human pulmonary artery endothelial cells with dynamin 2 small interfering RNA or the dynamin GTPase inhibitor, Dynasore, attenuated hyperoxia-mediated ROS production and p47(phox) recruitment to CEMs. Using purified recombinant proteins, we observed that c-Abl tyrosine-phosphorylated dynamin 2, and this phosphorylation increased p47(phox)/dynamin 2 association (change in the dissociation constant (K(d)) from 85.8 to 6.9 nm). Furthermore, exposure of mice to hyperoxia increased ROS production, c-Abl activation, dynamin 2 association with p47(phox), and pulmonary leak, events that were attenuated in the caveolin-1 knock-out mouse confirming a role for CEMs in ROS generation. These results suggest that hyperoxia induces c-Abl-mediated dynamin 2 phosphorylation required for recruitment of p47(phox) to CEMs and subsequent ROS production in lung endothelium.

Insulin resistance, lipotoxicity and endothelial dysfunction

The number of people with the insulin-resistant conditions of type 2 diabetes mellitus (T2DM) and obesity has reached epidemic proportions worldwide. Eighty percent of people with T2DM will die from the complications of cardiovascular atherosclerosis. Insulin resistance is characterised by endothelial dysfunction, which is a pivotal step in the initiation/progression of atherosclerosis. A hallmark of endothelial dysfunction is an unfavourable imbalance between the bioavailability of the antiatherosclerotic signalling molecule nitric oxide (NO) and proatherosclerotic reactive oxygen species. In this review we discuss the mechanisms linking insulin resistance to endothelial dysfunction, with a particular emphasis on a potential role for a toxic effect of free fatty acids on endothelial cell homeostasis.

Nox5 and the regulation of cellular function

The NADPH oxidase (Nox) family of enzymes is comprised of seven members, Noxes 1-5 and the Duoxes 1 and 2. Nox5 was the last of the conventional Nox enzymes to be identified, and in comparison to its siblings, much less is known about its molecular regulation and even less regarding its functional significance. The loss of Nox5 from rodent genomes has contributed significantly to this deficit in knowledge, but recent discoveries have narrowed the gap. There are many differences between Nox5 and the other Nox isoforms including alternative splicing, transcriptional regulation, enzymatic control mechanisms, tissue distribution, and intracellular trafficking. The goal of this review is to outline recent advances in our knowledge of the genetic regulation, the molecular mechanisms governing its activity, and the functional significance of Nox5 in human physiology and pathophysiology.

NADPH oxidases: molecular understanding finally reaching the clinical level?

NADPH oxidases (Nox) have been the subject of very intensive research over the past several years, which has led to in-depth understanding of the function of these enzymes in health and disease. Discovery of novel Nox enzymes and identification of a very wide range of tissue expression has increased our understanding of how NADPH oxidases may regulate so many distinct cellular functions and how the dysfunction of these enzymes may lead to disease. The present Forum issue summarizes the most novel aspects of NADPH oxidase biology, focusing on linking the molecular basis of NADPH oxidase function, compartmentalization, and differential expression patterns to diseases such as those of the pulmonary system, inflammation, central nervous system disorders, endothelial and vascular dysfunction, as well as disorders involving angiogenesis and stem cell and endothelial progenitor cell functions. Establishing these links may be the first step for future therapeutic use of NADPH oxidase inhibitors, which are discussed at length within this Forum issue.

Small-molecule NOX inhibitors: ROS-generating NADPH oxidases as therapeutic targets

NOX NADPH oxidases are electron-transporting membrane enzymes whose primary function is the generation of reactive oxygen species (ROS). ROS produced by NOX enzymes show a variety of biologic functions, such as microbial killing, blood pressure regulation, and otoconia formation. Strong evidence suggests that NOX enzymes are major contributors to oxidative damage in pathologic conditions. Blocking the undesirable actions of NOX enzymes, therefore, is a therapeutic strategy for treating oxidative stress-related pathologies, such as ischemia/reperfusion tissue injury, and neurodegenerative and metabolic diseases. Most currently available NOX inhibitors have low selectivity, potency, and bioavailability, precluding a pharmacologic demonstration of NOX as therapeutic targets in vivo. This review has two main purposes. First, we describe a systematic approach that we believe should be followed in the search for truly selective NOX inhibitors. Second, we present a critical review of small-molecule NOX inhibitors described over the last two decades, including recently published patents from the pharmaceutical industry. Structures, activities, and in vitro/in vivo specificity of these NOX inhibitors are discussed. We conclude that NOX inhibition is a pertinent and promising novel pharmacologic concept, but that major efforts will be necessary to develop specific NOX inhibitors suited for clinical application.

Exploiting cGMP-based therapies for the prevention of left ventricular hypertrophy: NO* and beyond

Left ventricular hypertrophy (LVH), an increased left ventricular (LV) mass, is common to many cardiovascular disorders, initially developing as an adaptive response to maintain myocardial function. In the longer term, this LV remodelling becomes maladaptive, with progressive decline in LV contractility and diastolic function. Indeed LVH is recognised as an important blood-pressure independent predictor of cardiovascular morbidity and mortality. The clinical efficacy of current treatments for LVH is reduced, however, by their tendency to slow disease progression rather than induce its reversal, and thus the development of new therapies for LVH is paramount. The signalling molecule cyclic guanosine-3',5'-monophosphate (cGMP), well-recognised for its role in regulating vascular tone, is now being increasingly identified as an important anti-hypertrophic mediator. This review is focused on the various means by which cGMP can be stimulated in the heart, such as via the natriuretic peptides, to exert anti-hypertrophic actions. In particular we address the limitations of traditional nitric oxide (NO*) donors in the face of the potential therapeutic advantages offered by novel alternatives; NO* siblings, ligands of the cGMP-generating enzymes, soluble (sGC) and particulate guanylyl cyclases (pGC), and phosphodiesterase inhibitors. Further impact of cGMP within the cardiovascular system is also discussed with a view to representing cGMP-based therapies as innovative pharmacotherapy, alone or concurrent with standard care, for the management of LVH.

NADPH oxidases and reactive oxygen species at different stages of chronic hypoxia-induced pulmonary hypertension in newborn piglets

Recently, we reported that reactive oxygen species (ROS) generated by NADPH oxidase (NOX) contribute to aberrant responses in pulmonary resistance arteries (PRAs) of piglets exposed to 3 days of hypoxia (Am J Physiol Lung Cell Mol Physiol 295: L881-L888, 2008). An objective of the present study was to determine whether NOX-derived ROS also contribute to altered PRA responses at a more advanced stage of pulmonary hypertension, after 10 days of hypoxia. We further wished to advance knowledge about the specific NOX and antioxidant enzymes that are altered at early and later stages of pulmonary hypertension. Piglets were raised in room air (control) or hypoxia for 3 or 10 days. Using a cannulated artery technique, we found that treatments with agents that inhibit NOX (apocynin) or remove ROS [an SOD mimetic (M40403) + polyethylene glycol-catalase] diminished responses to ACh in PRAs from piglets exposed to 10 days of hypoxia. Western blot analysis showed an increase in expression of NOX1 and the membrane fraction of p67phox. Expression of NOX4, SOD2, and catalase were unchanged, whereas expression of SOD1 was reduced, in arteries from piglets raised in hypoxia for 3 or 10 days. Markers of oxidant stress, F(2)-isoprostanes, measured by gas chromatography-mass spectrometry, were increased in PRAs from piglets raised in hypoxia for 3 days, but not 10 days. We conclude that ROS derived from some, but not all, NOX family members, as well as alterations in the antioxidant enzyme SOD1, contribute to aberrant PRA responses at an early and a more progressive stage of chronic hypoxia-induced pulmonary hypertension in newborn piglets.

Endothelial cells negatively modulate reactive oxygen species generation in vascular smooth muscle cells: role of thioredoxin

In intact vessels, endothelial cells (ECs) and vascular smooth muscle cells (VSMCs) act as an integrated system, possibly through reactive oxygen species (ROS). Using a coculture system we tested whether ECs modulate VSMC redox status by regulating activity of NAD(P)H oxidase and antioxidants. VSMC production of O(2)(*-), H(2)O(2), and NO was assessed using fluoroprobes and amplex-red. NAD(P)H oxidase subunit expression and oxidase activity were determined by Western blotting and chemiluminescence, respectively. Expression of thioredoxin, SOD, growth signaling pathways (PCNA, p21cip1, CDK4, ERK1/2, p38MAPK) was evaluated by immunoblotting. Thioredoxin activity was assessed by the insulin disulfide reduction assay. In cocultured conditions, VSMC ROS production was reduced by approximately 50% without changes in NAD(P)H oxidase expression/activity versus monoculture (P<0.05). This was associated with decreased cell growth (P<0.05). Expression of Cu/Zn SOD and thioredoxin was increased in coculture versus monoculture VSMCs (P<0.01). Pretreatment of ECs with L-NAME (NOS inhibitor), NS-398 (Cox2 inhibitor), and HET0016 (20-HETE inhibitor) did not influence VSMC ROS formation, whereas CDNB, thioredoxin reductase inhibitor, abolished ROS modulating effects of ECs. These findings indicate that in a coculture system recapitulating intact vessels, ECs negatively regulate ROS production in VSMCs through thioredoxin upregulation. Functionally this is associated with growth inhibition. The modulatory actions of ECs are independent of NOS/NO, Cox2, and HETE and do not involve NAD(P)H oxidase. Our data identify novel mechanisms whereby ECs protect against VSMC oxidative stress, a process that may be important in maintaining vascular integrity.

Androgens induce oxidative stress and radiation resistance in prostate cancer cells though NADPH oxidase

Androgen deprivation therapy (ADT) facilitates the response of prostate cancer (PC) to radiation. Androgens have been shown to induce elevated basal levels of reactive oxygen species (ROS) in PC, leading to adaptation to radiation-induced cytotoxic oxidative stress. Here, we show that androgens increase the expression of p22^phox and gp91^phox subunits of NADPH oxidase (NOX) and ROS production by NOX2 and NOX4 in PC. Pre-radiation treatment of 22Rv1 human PC cells with NOX inhibitors sensitize the cells to radiation similarly to ADT, suggesting that their future usage may spare the need for adjuvant ADT in PC patients undergoing radiation.

Estrous cycle-dependent neurovascular dysfunction induced by angiotensin II in the mouse neocortex

Female mice are protected from the cerebrovascular dysfunction induced by angiotensin II (Ang II), an effect attributed to estrogen. We examined whether such cerebrovascular protection from Ang II is related to the estrous cycle. Cerebral blood flow was monitored by laser-Doppler flowmetry in anesthetized (urethane-chloralose) C57BL/6 female mice equipped with a cranial window. The phase of the estrous cycle was determined by vaginal smear cytology and plasma estrogen measurement. Ang II (0.25 microg/kg per minute, IV, 30 to 45 minutes) elevated arterial pressure (15 to 20 mm Hg) equally across the estrous cycle. However, in proestrus and estrus, phases in which estrogen is relatively high, Ang II did not impair the increase in the cerebral blood flow induced by neural activity or by endothelium-dependent vasodilators (P>0.05 from vehicle). In contrast, in diestrus (lower estrogen), Ang II induced a marked cerebrovascular dysfunction comparable to that of male mice. For example, the cerebral blood flow responses to whisker stimulation and to the endothelium-dependent vasodilator acetylcholine were attenuated by 41+/-12% and 49+/-12%, respectively (P<0.05; n=6 per group). The protection from the cerebrovascular effects of Ang II in proestrus was abolished by the estrogen receptor inhibitor ICI182,780. Ang II also increased production of free radicals in cerebral blood vessels in diestrus (+116+/-13%; P<0.05) but not in proestrus and estrus (P>0.05 from control). Topical treatment with ICI182,780 reestablished Ang II-induced oxidative stress in proestrus (P>0.05 from diestrus). We conclude that the protection from the neurovascular dysfunction induced by acute administration of Ang II in females depends on the estrous cycle and may underlie the increased propensity to cerebrovascular damage associated with low estrogen states.

NADPH oxidase isoform selective regulation of endothelial cell proliferation and survival

Proliferation and apoptosis of endothelial cells are crucial angiogenic processes that contribute to carcinogenesis and tumor progression. Emerging evidence implicates the regulation of proliferation and apoptosis by reactive oxygen species (ROS) such as superoxide and hydrogen peroxide (H(2)O(2)). In the present study, we investigated the roles of the ROS-generating Nox4- and Nox2-containing reduced nicotinamide adenine dinucleotide phosphate (NADPH) oxidases in proliferation of human endothelial cells by examining the impact of these enzyme systems on (1) specific proliferative and tumorigenic kinases, extracellular regulated kinase1/2 (ERK1/2) and Akt, (2) cytoskeletal organization, and (3) the mechanisms that influence cellular apoptosis. ROS production and the expression of NADPH oxidase subunit Nox4, but not Nox2, were markedly higher in proliferating than in quiescent endothelial cells. Addition of the H(2)O(2) scavenger catalase or downregulation of Nox4 protein with specific siRNA reduced ROS levels, cell proliferation, and ERK1/2 phosphorylation but had no effect on either cell morphology or caspase 3/7 activity. Although downregulation of Nox2 protein with siRNA also reduced ROS production and cell proliferation, it caused an increase in caspase 3/7 activity, reduced Akt phosphorylation, and caused cytoskeletal disorganization. Therefore, in endothelial cells, Nox4-derived H(2)O(2) activates ERK1/2 to promote proliferation, whereas Nox2-containing NADPH oxidase maintains the cytoskeleton and prevents apoptosis to support cell survival. Our study provides a new understanding of the molecular mechanisms that underpin endothelial cell survival and a rationale for the combined suppression of Nox4- and Nox2-containing NADPH oxidases for unwanted angiogenesis in cancer.

Nox2-containing NADPH oxidase and xanthine oxidase are sources of superoxide in mouse trachea

1. Superoxide anion plays an important role in host defence against invading pathogens and in the inflammation that arises in lungs. The aim of the present study was to elucidate whether the two key candidate superoxide-producing enzymes in mammalian cells, namely Nox2-containing NADPH oxidase and xanthine oxidase, are responsible for superoxide production in mouse trachea. 2. Superoxide production by isolated trachea, as measured by L-012-dependent chemiluminescence, was markedly reduced by superoxide dismutase (300 U/mL) and the xanthine oxidase inhibitor allopurinol (100 micromol/L). Tracheas from Nox2(-/-) mice had significantly lower levels (~60%) of superoxide than control mice. 3. These novel findings suggest that superoxide production by mouse trachea is attributed to both Nox2-containing NADPH oxidase and xanthine oxidase.