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

Literature-Based Discovery to Elucidate the Biological Links between Resistant Hypertension and COVID-19

Multiple studies have reported new or exacerbated persistent or resistant hypertension in patients previously infected with COVID-19. We used literature-based discovery to identify and prioritize multi-scalar explanatory biology that relates resistant hypertension to COVID-19. Cross-domain text mining of 33+ million PubMed articles within a comprehensive knowledge graph was performed using SemNet 2.0. Unsupervised rank aggregation determined which concepts were most relevant utilizing the normalized HeteSim score. A series of simulations identified concepts directly related to COVID-19 and resistant hypertension or connected via one of three renin-angiotensin-aldosterone system hub nodes (mineralocorticoid receptor, epithelial sodium channel, angiotensin I receptor). The top-ranking concepts relating COVID-19 to resistant hypertension included: cGMP-dependent protein kinase II, MAP3K1, haspin, ral guanine nucleotide exchange factor, N-(3-Oxododecanoyl)-L-homoserine lactone, aspartic endopeptidases, metabotropic glutamate receptors, choline-phosphate cytidylyltransferase, protein tyrosine phosphatase, tat genes, MAP3K10, uridine kinase, dicer enzyme, CMD1B, USP17L2, FLNA, exportin 5, somatotropin releasing hormone, beta-melanocyte stimulating hormone, pegylated leptin, beta-lipoprotein, corticotropin, growth hormone-releasing peptide 2, pro-opiomelanocortin, alpha-melanocyte stimulating hormone, prolactin, thyroid hormone, poly-beta-hydroxybutyrate depolymerase, CR 1392, BCR-ABL fusion gene, high density lipoprotein sphingomyelin, pregnancy-associated murine protein 1, recQ4 helicase, immunoglobulin heavy chain variable domain, aglycotransferrin, host cell factor C1, ATP6V0D1, imipramine demethylase, TRIM40, H3C2 gene, COL1A1+COL1A2 gene, QARS gene, VPS54, TPM2, MPST, EXOSC2, ribosomal protein S10, TAP-144, gonadotropins, human gonadotropin releasing hormone 1, beta-lipotropin, octreotide, salmon calcitonin, des-n-octanoyl ghrelin, liraglutide, gastrins. Concepts were mapped to six physiological themes: altered endocrine function, 23.1%; inflammation or cytokine storm, 21.3%; lipid metabolism and atherosclerosis, 17.6%; sympathetic input to blood pressure regulation, 16.7%; altered entry of COVID-19 virus, 14.8%; and unknown, 6.5%.

The Enigmatic Vascular NOX: From Artifact to Double Agent of Change: Arthur C. Corcoran Memorial Lecture - 2019

NOXs (NADPH oxidases) comprise a family of proteins whose primary function is the production of reactive oxygen species, namely, superoxide anion and hydrogen peroxide. The prototype first being discovered and characterized in neutrophils, multiple NOXs are now known to be broadly expressed in cell and organ systems and whose phylogeny spans countless life forms beginning with prokaryotes. This long-enduring evolutionary conservation underscores the importance of fundamental NOX functions. This review chronicles a personal perspective of the field beginning with the discovery of NOXs in the vasculature and the advances achieved through the years as to our understanding of their mechanisms of action and role in oxidative stress and disease. Furthermore, applications of isoform-selective inhibitors to dissect the role of NOX isozymes in vascular biology, focusing on inflammation, pulmonary hypertension, and aging are described.

The Role of Oxidative Stress in Cardiac Disease: From Physiological Response to Injury Factor

Reactive oxygen species (ROS) are highly reactive chemical species containing oxygen, controlled by both enzymatic and nonenzymatic antioxidant defense systems. In the heart, ROS play an important role in cell homeostasis, by modulating cell proliferation, differentiation, and excitation-contraction coupling. Oxidative stress occurs when ROS production exceeds the buffering capacity of the antioxidant defense systems, leading to cellular and molecular abnormalities, ultimately resulting in cardiac dysfunction. In this review, we will discuss the physiological sources of ROS in the heart, the mechanisms of oxidative stress-related myocardial injury, and the implications of experimental studies and clinical trials with antioxidant therapies in cardiovascular diseases.

Distinct Redox Signalling following Macrophage Activation Influences Profibrotic Activity

Aims

To date, the ROS-generating capacities of macrophages in different activation states have not been thoroughly compared. This study is aimed at determining the nature and levels of ROS generated following stimulation with common activators of M1 and M2 macrophages and investigating the potential for this to impact fibrosis.

Results

Human primary and THP-1 macrophages were treated with IFN-γ+LPS or IL-4-activating stimuli, and mRNA expression of established M1 (CXCL11, CCR7, IL-1β) and M2 (MRC-1, CCL18, CCL22) markers was used to confirm activation. Superoxide generation was assessed by L-012-enhanced chemiluminescence and was increased in both M(IFN-γ+LPS) and M(IL-4) macrophages, as compared to unpolarised macrophages (MΦ). This signal was attenuated with NOX2 siRNA. Increased expression of the p47phox and p67phox subunits of the NOX2 oxidase complex was evident in M(IFN-γ+LPS) and M(IL-4) macrophages, respectively. Amplex Red and DCF fluorescence assays detected increased hydrogen peroxide generation following stimulation with IL-4, but not IFN-γ+LPS. Coculture with human aortic adventitial fibroblasts revealed that M(IL-4), but not M(IFN-γ+LPS), enhanced fibroblast collagen 1 protein expression. Macrophage pretreatment with the hydrogen peroxide scavenger, PEG-catalase, attenuated this effect.

Conclusion

We show that superoxide generation is not only enhanced with stimuli associated with M1 macrophage activation but also with the M2 stimulus IL-4. Macrophages activated with IL-4 also exhibited enhanced hydrogen peroxide generation which in turn increased aortic fibroblast collagen production. Thus, M2 macrophage-derived ROS is identified as a potentially important contributor to aortic fibrosis.

Redox-Sensitive Innate Immune Pathways During Macrophage Activation in Type 1 Diabetes

SIGNIFICANCE

Type 1 diabetes (T1D) is an autoimmune disease resulting in β-cell destruction mediated by islet-infiltrating leukocytes. The role of oxidative stress in human and murine models of T1D is highly significant as these noxious molecules contribute to diabetic complications and β-cell lysis, but their direct impact on dysregulated autoimmune responses is highly understudied. Pro-inflammatory macrophages play a vital role in the initiation and effector phases of T1D by producing free radicals and pro-inflammatory cytokines to facilitate β-cell destruction and to present antigen to autoreactive T cells. Recent Advances: Redox modulation of macrophage functions may play critical roles in autoimmunity. These include enhancing pro-inflammatory innate immune signaling pathways in response to environmental triggers, enforcing an M1 macrophage differentiation program, controlling antigen processing, and altering peptide recognition by oxidative post-translational modification. Therefore, an oxidative environment may act on multiple macrophage functions to orchestrate T1D pathogenesis.

CRITICAL ISSUES

Mechanisms involved in the initiation of T1D remain unclear, making preventive and early therapeutics difficult to develop. Although many of these advances in the redox regulation of macrophages are in their infancy, they provide insight into how oxidative stress aids in the precipitating event of autoimmune activation.

FUTURE DIRECTIONS

Future studies should be aimed at mechanistically determining which redox-regulated macrophage functions are pertinent in T1D pathogenesis, as well as at investigating potential targetable therapeutics to halt and/or dampen innate immune activation in T1D.

Microvascular NADPH oxidase in health and disease

The systemic and cerebral microcirculation contribute critically to regulation of local and global blood flow and perfusion pressure. Microvascular dysfunction, commonly seen in numerous cardiovascular pathologies, is associated with alterations in the oxidative environment including potentiated production of reactive oxygen species (ROS) and subsequent activation of redox signaling pathways. NADPH oxidases (Noxs) are a primary source of ROS in the vascular system and play a central role in cardiovascular health and disease. In this review, we focus on the roles of Noxs in ROS generation in resistance arterioles and capillaries, and summarize their contributions to microvascular physiology and pathophysiology in both systemic and cerebral microcirculation. In light of the accumulating evidence that Noxs are pivotal players in vascular dysfunction of resistance arterioles, selectively targeting Nox isozymes could emerge as a novel and effective therapeutic strategy for preventing and treating microvascular diseases.

Roles of Cells from the Arterial Vessel Wall in Atherosclerosis

Atherosclerosis has been identified as a chronic inflammatory disease of the arterial vessel wall. Accumulating evidence indicates that different cells from the tunica intima, media, adventitia, and perivascular adipose tissue not only comprise the intact and normal arterial vessel wall but also participate all in the inflammatory response of atherosclerosis via multiple intricate pathways. For instance, endothelial dysfunction has historically been considered to be the initiator of the development of atherosclerosis. The migration and proliferation of smooth muscle cells also play a pivotal role in the progression of atherosclerosis. Additionally, the fibroblasts from the adventitia and adipocytes from perivascular adipose tissue have received considerable attention given their special functions that contribute to atherosclerosis. In addition, numerous types of cytokines produced by different cells from the arterial vessel wall, including endothelium-derived relaxing factors, endothelium-derived contracting factors, tumor necrosis factors, interleukin, adhesion molecules, interferon, and adventitium-derived relaxing factors, have been implicated in atherosclerosis. Herein, we summarize the possible roles of different cells from the entire arterial vessel wall in the pathogenesis of atherosclerosis.

Hydrogen Peroxide as a Paracrine Vascular Mediator: Regulation and Signaling Leading to Dysfunction

Numerous studies have demonstrated the ability of a variety of vascular cells, including endothelial cells, smooth muscle cells, and fibroblasts, to produce reactive oxygen species (ROS). Until recently, major emphasis was placed on the production of superoxide anion (O2–) in the vasculature as a result of its ability to directly attenuate the biological activity of endothelium-derived nitric oxide (NO). The short half-life and radius of diffusion of O2– drastically limit the role of this ROS as an important paracrine hormone in vascular biology. On the contrary, in recent years, the O2– metabolite hydrogen peroxide (H2O2) has increasingly been viewed as an important cellular signaling agent in its own right, capable of modulating both contractile and growth-promoting pathways with more far-reaching effects. In this review, we will assess the vascular production of H2O2, its regulation by endogenous scavenger systems, and its ability to activate a variety of vascular signaling pathways, thereby leading to vascular contraction and growth. This discussion will include the ability of H2O2 to (i) Initiate calcium flux as well as (ii) stimulate pathways leading to sensitization of contractile elements to calcium. The latter involves a variety of protein kinases that have also been strongly implicated in vascular hypertrophy. Previous Intensive study has emphasized the ability of NADPH oxidase-derived O2– and H2O2 to activate these pathways in cultured smooth muscle cells. However, growing evidence indicates a considerably more complex array of unique oxidase systems in the endothelium, media, and adventitia that appear to participate in these deleterious effects in a sequential and temporal manner. Taken together, these findings seem consistent with a paracrine effect of H2O2 across the vascular wall.

NADPH oxidases and vascular remodeling in cardiovascular diseases

Reactive oxygen species (ROS) are key signaling molecules that regulate vascular function and structure in physiological conditions. A misbalance between the production and detoxification of ROS increases oxidative stress that is involved in the vascular remodeling associated with cardiovascular diseases such as hypertension by affecting inflammation, hypertrophy, migration, growth/apoptosis and extracellular matrix protein turnover. The major and more specific source of ROS in the cardiovascular system is the NADPH oxidase (NOX) family of enzymes composed of seven members (NOX1-5, DUOX 1/2). Vascular cells express several NOXs being NOX-1 and NOX-4 the most abundant NOXs present in vascular smooth muscle cells. This review focuses on specific aspects of NOX-1 and NOX-4 isoforms including information on regulation, function and their role in vascular remodeling. In order to obtain a more integrated view about the role of the different NOX isoforms in different types of vascular remodeling, we discuss the available literature not only on hypertension but also in atherosclerosis, restenosis and aortic dilation.

Carotid extramedial thickness is associated with local arterial stiffness in children

OBJECTIVES

Experimental evidence suggests that structural changes to the arterial adventitia may be a key vascular determinant of early arterial stiffening, although this has not been directly studied. Accordingly, we hypothesized that in young children, in whom this relationship would not be altered by atheroma, carotid extramedial thickness (EMT), a measure that incorporates the thickness of the arterial adventitia, perivascular tissues and the internal jugular venous wall, would be associated with localized arterial stiffness of the same arterial region.

METHODS

We studied 248 healthy prepubescent children (aged 8 years). Carotid diameter and carotid EMT were measured by high-resolution ultrasound. Carotid blood pressure was derived from brachial blood pressure and carotid tonometry. Three measures of localized arterial stiffness (β stiffness index, distensibility coefficient and incremental modulus of elasticity) were calculated for the common carotid artery. Results were adjusted for heart rate and DBP, two important hemodynamic determinants of arterial stiffness.

RESULTS

Carotid EMT was associated with all three measures of arterial stiffness (β stiffness index: standardized β = 0.121, P = 0.03; distensibility coefficient: standardized β = -0.121, P = 0.05; incremental modulus of elasticity: standardized β = 0.140, P = 0.02). These associations remained significant after adjustment for potential confounders such as sex, height, waist circumference, BMI and body surface area.

CONCLUSION

Carotid EMT is associated with the stiffness of the same arterial segment in children, suggesting that the arterial adventitia may be involved in early changes in arterial stiffness during childhood.

Evolution of NADPH Oxidase Inhibitors: Selectivity and Mechanisms for Target Engagement

SIGNIFICANCE

Oxidative stress, an excess of reactive oxygen species (ROS) production versus consumption, may be involved in the pathogenesis of different diseases. The only known enzymes solely dedicated to ROS generation are nicotinamide adenine dinucleotide phosphate (NADPH) oxidases with their catalytic subunits (NOX). After the clinical failure of most antioxidant trials, NOX inhibitors are the most promising therapeutic option for diseases associated with oxidative stress.

RECENT ADVANCES

Historical NADPH oxidase inhibitors, apocynin and diphenylene iodonium, are un-specific and not isoform selective. Novel NOX inhibitors stemming from rational drug discovery approaches, for example, GKT137831, ML171, and VAS2870, show improved specificity for NADPH oxidases and moderate NOX isoform selectivity. Along with NOX2 docking sequence (NOX2ds)-tat, a peptide-based inhibitor, the use of these novel small molecules in animal models has provided preliminary in vivo evidence for a pathophysiological role of specific NOX isoforms.

CRITICAL ISSUES

Here, we discuss whether novel NOX inhibitors enable reliable validation of NOX isoforms' pathological roles and whether this knowledge supports translation into pharmacological applications. Modern NOX inhibitors have increased the evidence for pathophysiological roles of NADPH oxidases. However, in comparison to knockout mouse models, NOX inhibitors have limited isoform selectivity. Thus, their use does not enable clear statements on the involvement of individual NOX isoforms in a given disease.

FUTURE DIRECTIONS

The development of isoform-selective NOX inhibitors and biologicals will enable reliable validation of specific NOX isoforms in disease models other than the mouse. Finally, GKT137831, the first NOX inhibitor in clinical development, is poised to provide proof of principle for the clinical potential of NOX inhibition.

Adventitial gene transfer of catalase attenuates angiotensin II-induced vascular remodeling

Vascular adventitia and adventitia-derived reactive oxygen species (ROS) contribute to vascular remodeling following vascular injury. A previous ex vivo study in adventitial fibroblasts showed that catalase, one of most important anti-oxide enzymes, was downregulated by angiotensin II (AngII). The aim of the present study was to investigate whether adventitial gene transfer of catalase affects AngII-induced vascular remodeling in vivo. Adenoviruses co-expressing catalase and enhanced green fluorescent protein (eGFP) or expressing eGFP only were applied to the adventitial surface of common carotid arteries of Sprague-Dawley rats. Alzet minipumps administering AngII (0.75 mg/kg/day) were then implanted subcutaneously for 14 days. Systolic blood pressure and biological parameters of vascular remodeling were measured in each group. Adventitial fibroblasts were cultured and p38 mitogen-activated protein kinase (MAPK) phosphorylation was measured using western blot analysis. The results showed that adventitial gene transfer of catalase had no effect on AngII-induced systolic blood pressure elevation. However, catalase adenovirus transfection significantly inhibited AngII-induced media hypertrophy compared with that of the control virus (P<0.05). In addition, catalase transfection significantly attenuated AngII-induced ROS generation, macrophage infiltration, collagen deposition and adventitial α-smooth muscle actin expression. Furthermore, catalase transfection significantly inhibited the AngII-induced increase in p38MAPK phosphorylation. In conclusion, the results of the present study demonstrated that adventitial gene transfer of catalase significantly attenuated AngII-induced vascular remodeling in rats via inhibition of adventitial p38MAPK phosphorylation.

Opposing changes in thoracic and abdominal aortic biomechanical properties in rodent models of vascular calcification and hypertension

This study investigated the effects of hypertension on regional aortic biomechanical and structural properties in three rat models of vascular calcification: the hypertensive Lewis polycystic kidney (LPK; n = 13) model of chronic kidney disease, spontaneously hypertensive rats (SHRs; n = 12), and calcification in normotensive Lewis rats induced by vitamin D3 and nicotine (VDN; n = 8). Lewis and Wistar-Kyoto rats were controls. Thoracic and abdominal aortic stiffness parameters were assessed by tensile testing. In models where aortic stiffness differences compared with controls existed in both thoracic and abdominal segments, an additional cohort was quantified by histology for thoracic and abdominal aortic elastin, collagen, and calcification. LPK and VDN animals had higher thoracic breaking strain than control animals ( P < 0.01 and P < 0.05, respectively) and lower energy absorption within the tensile curve of the abdominal aorta ( P < 0.05). SHRs had a lower abdominal breaking stress than Wistar-Kyoto rats. LPK and VDN rats had more elastic lamellae fractures than control rats ( P < 0.001), which were associated with calcium deposition (thoracic R = 0.37, P = 0.048; abdominal: R = 0.40, P = 0.046). LPK rats had higher nuclear density than control rats ( P < 0.01), which was also evident in the thoracic but not abdominal aorta of VDN rats ( P < 0.01). In LPK and VDN rats, but not in control rats, media thickness and cross-sectional area were at least 1.5-fold greater in thoracic than abdominal regions. The calcification models chronic kidney disease and induced calcification in normotension caused differences in regional aortic stiffness not seen in a genetic form of hypertension. Detrimental abdominal aortic remodeling but lower stiffness in the thoracic aorta with disease indicates possible compensatory mechanisms in the proximal aorta.

The quest for selective nox inhibitors and therapeutics: challenges, triumphs and pitfalls

SIGNIFICANCE

Numerous studies in animal models and human subjects corroborate that elevated levels of reactive oxygen species (ROS) play a pivotal role in the progression of multiple diseases. As a major source of ROS in many organ systems, the NADPH oxidase (Nox) has become a prime target for therapeutic development.

RECENT ADVANCES

In recent years, intense efforts have been dedicated to the development of pan- and isoform-specific Nox inhibitors as opposed to antioxidants that proved ineffective in clinical trials. Over the past decade, an array of compounds has been proposed in an attempt to fill this void.

CRITICAL ISSUES

Although many of these compounds have proven effective as Nox enzyme family inhibitors, isoform specificity has posed a formidable challenge to the scientific community. This review surveys the most prominent Nox inhibitors, and discusses potential isoform specificity, known mechanisms of action, and shortcomings. Some of these inhibitors hold substantial promise as targeted therapeutics.

FUTURE DIRECTIONS

Increased insight into the mechanisms of action and regulation of this family of enzymes as well as atomic structures of key Nox subunits are expected to give way to a broader spectrum of more potent, efficacious, and specific molecules. These lead molecules will assuredly serve as a basis for drug development aimed at treating a wide array of diseases associated with increased Nox activity.

Thrombospondin-1 activation of signal-regulatory protein-α stimulates reactive oxygen species production and promotes renal ischemia reperfusion injury

Ischemia reperfusion injury (IRI) causes tissue and organ injury, in part, through alterations in tissue blood flow and the production of reactive oxygen species. The cell surface receptor signal-regulatory protein-α (SIRP-α) is expressed on inflammatory cells and suppresses phagocytosis, but the function of SIRP-α in IRI has not been determined. We reported previously that the matricellular protein thrombospondin-1 is upregulated in IRI. Here, we report a novel interaction between thrombospondin-1 and SIRP-α on nonphagocytic cells. In cell-free experiments, thrombospondin-1 bound SIRP-α. In vascular smooth muscle cells and renal tubular epithelial cells, treatment with thrombospondin-1 led to phosphorylation of SIRP-α and downstream activation of Src homology domain 2-containing phosphatase-1. Thrombospondin-1 also stimulated phosphorylation of p47(phox) (an organizer subunit for nicotinamide adenine dinucleotide phosphate (NADPH) oxidase 1/2) and increased production of superoxide, both of which were abrogated by knockdown or antibody blockade of SIRP-α. In rodent aortic rings, treatment with thrombospondin-1 increased the production of superoxide and inhibited nitric oxide-mediated vasodilation in a SIRP-α-dependent manner. Renal IRI upregulated the thrombospondin-1-SIRP-α signaling axis and was associated with increased superoxide production and cell death. A SIRP-α antibody that blocks thrombospondin-1 activation of SIRP-α mitigated the effects of renal IRI, increasing blood flow, suppressing production of reactive oxygen species, and preserving cellular architecture. A role for CD47 in SIRP-α activation in these pathways is also described. Overall, these results suggest that thrombospondin-1 binding to SIRP-α on nonphagocytic cells activates NADPH oxidase, limits vasodilation, and promotes renal IRI.

Regulation of cellular communication by signaling microdomains in the blood vessel wall

It has become increasingly clear that the accumulation of proteins in specific regions of the plasma membrane can facilitate cellular communication. These regions, termed signaling microdomains, are found throughout the blood vessel wall where cellular communication, both within and between cell types, must be tightly regulated to maintain proper vascular function. We will define a cellular signaling microdomain and apply this definition to the plethora of means by which cellular communication has been hypothesized to occur in the blood vessel wall. To that end, we make a case for three broad areas of cellular communication where signaling microdomains could play an important role: 1) paracrine release of free radicals and gaseous molecules such as nitric oxide and reactive oxygen species; 2) role of ion channels including gap junctions and potassium channels, especially those associated with the endothelium-derived hyperpolarization mediated signaling, and lastly, 3) mechanism of exocytosis that has considerable oversight by signaling microdomains, especially those associated with the release of von Willebrand factor. When summed, we believe that it is clear that the organization and regulation of signaling microdomains is an essential component to vessel wall function.

A quinazoline-derivative compound with PARP inhibitory effect suppresses hypertension-induced vascular alterations in spontaneously hypertensive rats

AIMS

Oxidative stress and neurohumoral factors play important role in the development of hypertension-induced vascular remodeling, likely by disregulating kinase cascades and transcription factors. Oxidative stress activates poly(ADP-ribose)-polymerase (PARP-1), which promotes inflammation and cell death. We assumed that inhibition of PARP-1 reduces the hypertension-induced adverse vascular changes. This hypothesis was tested in spontaneously hypertensive rats (SHR).

METHODS AND RESULTS

Ten-week-old male SHRs and wild-type rats received or not 5mg/kg/day L-2286 (a water-soluble PARP-inhibitor) for 32 weeks, then morphological and functional parameters were determined in their aortas. L-2286 did not affect the blood pressure in any of the animal groups measured with tail-cuff method. Arterial stiffness index increased in untreated SHRs compared to untreated Wistar rats, which was attenuated by L-2286 treatment. Electron and light microscopy of aortas showed prominent collagen deposition, elevation of oxidative stress markers and increased PARP activity in SHR, which were attenuated by PARP-inhibition. L-2286 treatment decreased also the hypertension-activated mitochondrial cell death pathway, characterized by the nuclear translocation of AIF. Hypertension activated all three branches of MAP-kinases. L-2286 attenuated these changes by inducing the expression of MAPK phosphatase-1 and by activating the cytoprotective PI-3-kinase/Akt pathway. Hypertension activated nuclear factor-kappaB, which was prevented by PARP-inhibition via activating its nuclear export.

CONCLUSION

PARP-inhibition has significant vasoprotective effects against hypertension-induced vascular remodeling. Therefore, PARP-1 can be a novel therapeutic drug target for preventing hypertension-induced vascular remodeling in a group of patients, in whom lowering the blood pressure to optimal range is harmful or causes intolerable side effects.

Activation of angiotensin II type 1 receptor-associated protein exerts an inhibitory effect on vascular hypertrophy and oxidative stress in angiotensin II-mediated hypertension

AIMS

Activation of tissue angiotensin II (Ang II) type 1 receptor (AT1R) plays an important role in the development of vascular remodelling. We have shown that the AT1R-associated protein (ATRAP/Agtrap), a specific binding protein of AT1R, functions as an endogenous inhibitor to prevent pathological activation of the tissue renin-angiotensin system. In this study, we investigated the effects of ATRAP on Ang II-induced vascular remodelling.

METHODS AND RESULTS

Transgenic (Tg) mice with a pattern of aortic vascular-dominant overexpression of ATRAP were obtained, and Ang II or vehicle was continuously infused into Tg and wild-type (Wt) mice via an osmotic minipump for 14 days. Although blood pressure of Ang II-infused Tg mice was comparable with that of Ang II-infused Wt mice, the Ang II-mediated development of aortic vascular hypertrophy was partially inhibited in Tg mice compared with Wt mice. In addition, Ang II-mediated up-regulation of vascular Nox4 and p22(phox), NADPH oxidase components, and 4-HNE, a marker of reactive oxygen species (ROS) generation, was significantly suppressed in Tg mice, with a concomitant inhibition of activation of aortic vascular p38MAPK and JNK by Ang II. This protection afforded by vascular ATRAP against Ang II-induced activation of NADPH oxidase is supported by in vitro experimental data using adenoviral transfer of recombinant ATRAP.

CONCLUSION

These results indicate that activation of aortic vascular ATRAP partially inhibits the Nox4/p22(phox)-ROS-p38MAPK/JNK pathway and pathological aortic hypertrophy provoked by Ang II-mediated hypertension, thereby suggesting ATRAP as a novel receptor-binding modulator of vascular pathophysiology.

The adventitia: Essential role in pulmonary vascular remodeling

A rapidly emerging concept is that the vascular adventitia acts as a biological processing center for the retrieval, integration, storage, and release of key regulators of vessel wall function. It is the most complex compartment of the vessel wall and comprises a variety of cells including fibroblasts, immunomodulatory cells, resident progenitor cells, vasa vasorum endothelial cells, and adrenergic nerves. In response to vascular stress or injury, resident adventitial cells are often the first to be activated and reprogrammed to then influence tone and structure of the vessel wall. Experimental data indicate that the adventitial fibroblast, the most abundant cellular constituent of adventitia, is a critical regulator of vascular wall function. In response to vascular stresses such as overdistension, hypoxia, or infection, the adventitial fibroblast is activated and undergoes phenotypic changes that include proliferation, differentiation, and production of extracellular matrix proteins and adhesion molecules, release of reactive oxygen species, chemokines, cytokines, growth factors, and metalloproteinases that, collectively, affect medial smooth muscle cell tone and growth directly and that stimulate recruitment and retention of circulating inflammatory and progenitor cells to the vessel wall. Resident dendritic cells also participate in "sensing" vascular stress and actively communicate with fibroblasts and progenitor cells to simulate repair processes that involve expansion of the vasa vasorum, which acts as a conduit for further delivery of inflammatory/progenitor cells. This review presents the current evidence demonstrating that the adventitia acts as a key regulator of pulmonary vascular wall function and structure from the "outside in."

Strategies Aimed at Nox4 Oxidase Inhibition Employing Peptides from Nox4 B-Loop and C-Terminus and p22 (phox) N-Terminus: An Elusive Target

Although NADPH oxidase 4 (Nox4) is the most abundant Nox isoform in systemic vascular endothelial and smooth muscle cells, its function in the vascular tissue is not entirely known. The literature describes a pathophysiological role for Nox4 in cardiovascular disease; however, some studies have reported that it has a protective role. To date, specific Nox4 inhibitors are not available; hence, the development of a pharmacologic tool to assess Nox4's pathophysiological role garners intense interest. In this study, we selected peptides corresponding to regions in the Nox4 oxidase complex critical to holoenzyme activity and postulated their utility as specific competitive inhibitors. Previous studies in our laboratory yielded selective inhibition of Nox2 using this strategy. We postulated that peptides mimicking the Nox4 B-loop and C-terminus and regions on p22^phox inhibit Nox4 activity. To test our hypothesis, the inhibitory activity of Nox4 B-loop and C-terminal peptides as well as N-terminal p22^phox peptides was assessed in a reconstituted Nox4 system. Our findings demonstrate that Nox4 inhibition is not achieved by preincubation with this comprehensive array of peptides derived from previously identified active regions. These findings suggest that Nox4 exists in a tightly assembled and active conformation which, unlike other Noxes, cannot be disrupted by conventional means.

Aquaporin 1, Nox1, and Ask1 mediate oxidant-induced smooth muscle cell hypertrophy

AIMS

Reactive oxygen species (ROS)-mediated intracellular signalling is well described in the vasculature, yet the precise roles of ROS in paracrine signalling are not known. Studies implicate interstitial ROS hydrogen peroxide (H(2)O(2)) in vascular disease, and plasma H(2)O(2) levels in the micromolar range are detectable in animal models and humans with hypertension. Recently, H(2)O(2) was shown to cross biological membranes of non-vascular cells via aquaporin (Aqp) water channels. Previous findings suggest that H(2)O(2) activates NADPH oxidase (Nox) enzymes in vascular cells and apoptosis signal-regulating kinase 1 (Ask1) in non-vascular cells. We hypothesized that extracellular H(2)O(2) induces smooth muscle cell (SMC) hypertrophy by a mechanism involving Aqp1, Nox1, and Ask1.

METHODS AND RESULTS

Treatment of rat aortic SMCs (rASMC) with exogenous H(2)O(2) resulted in a concentration-dependent increase in Nox-derived superoxide (O(2)(•-)), determined by L-012 chemiluminescence, cytochrome c and electron paramagnetic resonance. Nox1 was verified as the source of O(2)(·-) by siRNA. Aqp1 siRNA attenuated H(2)O(2) cellular entry and H(2)O(2)-induced O(2)(•-) production. H(2)O(2) treatment increased Ask1 activation and induced rASMC hypertrophy in a Nox1-dependent mechanism. Adenoviral-dominant-negative Ask1 attenuated H(2)O(2)-induced rASMC hypertrophy and adenoviral overexpression of Ask1 augmented it.

CONCLUSION

Our results demonstrate for the first time that extracellular H(2)O(2), at pathophysiological concentrations, stimulates rASMC Nox1-derived O(2)(•-), subsequent Ask1 activation and SMC hypertrophy. The data demonstrate a novel pathway by which H(2)O(2) enters vascular cells via aquaporins and activates Nox, leading to hypertrophy, and provide multiple novel targets for combinatorial therapeutics development targeting hypertrophy and vascular disease.

Phosphorylation of Smooth Muscle 22α Facilitates Angiotensin II–Induced ROS Production Via Activation of the PKCδ-P47 phox Axis Through Release of PKCδ and Actin Dynamics and Is Associated With Hypertrophy and Hyperplasia of Vascular Smooth Muscle Cells In Vitro and In Vivo

Rationale:

We have demonstrated that smooth muscle (SM) 22α inhibits cell proliferation via blocking Ras-ERK1/2 signaling in vascular smooth muscle cells (VSMCs) and in injured arteries. The recent study indicates that SM22α disruption can independently promote arterial inflammation through activation of reactive oxygen species (ROS)-mediated NF-κB pathways. However, the mechanisms by which SM22α controls ROS production have not been characterized.

Objective:

To investigate how SM22α disruption promotes ROS production and to characterize the underlying mechanisms.

Methods and Results:

ROS level was measured by dihydroethidium staining for superoxide and TBA assay for malondialdehyde, respectively. We showed that downregulation and phosphorylation of SM22α were associated with angiotensin (Ang) II–induced increase in ROS production in VSMCs of rats and human. Ang II induced the phosphorylation of SM22α at Serine 181 in an Ang II type 1 receptor–PKCδ pathway–dependent manner. Phosphorylated SM22α activated the protein kinase C (PKC)δ-p47 phox axis via 2 distinct pathways: (1) disassociation of PKCδ from SM22α, and in turn binding to p47 phox , in the early stage of Ang II stimulation; and (2) acceleration of SM22α degradation through ubiquitin-proteasome, enhancing PKCδ membrane translocation via induction of actin cytoskeletal dynamics in later oxidative stress. Inhibition of SM22α phosphorylation abolished the Ang II–activated PKCδ-p47 phox axis and inhibited the hypertrophy and hyperplasia of VSMCs in vitro and in vivo, accompanied with reduction of ROS generation.

Conclusions:

These findings indicate that the disruption of SM22α plays pivotal roles in vascular oxidative stress. PKCδ-mediated SM22α phosphorylation is a novel link between actin cytoskeletal remodeling and oxidative stress and may be a potential target for the development of new therapeutics for cardiovascular diseases.

The 1027th target candidate in stroke: Will NADPH oxidase hold up?

As recently reviewed, 1026 neuroprotective drug candidates in stroke research have all failed on their road towards validation and clinical translation, reasons being quality issues in preclinical research and publication bias. Quality control guidelines for preclinical stroke studies have now been established. However, sufficient understanding of the underlying mechanisms of neuronal death after stroke that could be possibly translated into new therapies is lacking. One exception is the hypothesis that cellular death is mediated by oxidative stress. Oxidative stress is defined as an excess of reactive oxygen species (ROS) derived from different possible enzymatic sources. Among these, NADPH oxidases (NOX1-5) stand out as they represent the only known enzyme family that has no other function than to produce ROS. Based on data from different NOX knockout mouse models in ischemic stroke, the most relevant isoform appears to be NOX4. Here we discuss the state-of-the-art of this target with respect to stroke and open questions that need to be addressed on the path towards clinical translation.

NADPH oxidase inhibitors: a decade of discovery from Nox2ds to HTS

NADPH oxidases (Nox) are established as major sources of reactive oxygen species (ROS). Over the past two decades, Nox-derived ROS have emerged as pivotal in the development of myriad diseases involving oxidative stress. In contrast, Nox are also involved in signaling mechanisms necessary for normal cell function. The study of these enzymes in physiological and pathophysiological conditions is made considerably more complex by the discovery of 7 isoforms: Nox1 through 5 as well as Duox1 and 2, each with its own specific cytosolic components, regulatory control mechanisms, subcellular localization and/or tissue distribution. A clear understanding of the role individual isoforms play in a given system is hindered by the lack of isoform-specific inhibitors. In animal models, knockdown or knockout methodologies are providing definitive answers to perplexing questions of the complex interplay of multiple Nox isoforms in cell and tissue signaling. However, the complex structures and interactions of these heteromeric isozymes predict pleiotropic actions of the Nox subunits and thus suppression of these proteins is almost certain to have untoward effects. Thus, as both therapies and pharmacological tools, molecule-based inhibitors continue to prove extremely useful and rational in design. Unfortunately, many of the available inhibitors have proven non-specific, falling into the category of scavengers or inhibitors of more than one source of ROS. Here, we will review some of the efforts that have been undertaken to develop specific inhibitors of NADPH oxidase over the past decade, from the peptidic inhibitor Nox2ds-tat to more recent small molecule inhibitors that have emerged from high-throughput screening campaigns.

Carotid extra-medial thickness in childhood: early life effects on the arterial adventitia

OBJECTIVE

Structural modification of the arterial adventitia may be an early event in atherosclerosis. Carotid extra-medial thickness is a new measure of arterial adventitial thickness. We examined the association of cardiovascular risk factors with extra-medial thickness, in childhood.

METHODS

Carotid extra-medial thickness was assessed by high-resolution ultrasound in 389 non-diabetic children aged 8-years. A non-fasting blood sample was collected from 314 participants. Associations of gender, age, lipoproteins, blood pressure, BMI z-score, waist:height ratio and parental history of early vascular disease, with extra-medial thickness were examined.

RESULTS

Carotid extra-medial thickness was lower in girls (r=-.163, P=.001) and directly associated with systolic (r=.128, P=.009), diastolic blood pressure (r=.130, P=.009), and height (r=.170, P=.0006). These associations remained after adjustment for carotid intima-media thickness. In multivariable analysis including carotid intima-media thickness, only gender and height were significantly associated with carotid extra-medial thickness. In gender-stratified analysis, the strongest associations with extra-medial thickness were BMI z-score (r=.181, P=.01), height (r=.210, P=.003) and diastolic blood pressure (r=.167, P=.02) for boys; and systolic blood pressure (r=.153, P=.03) and parental history of premature cardiovascular disease (r=.139, P=.05) for girls. The association of BMI z-score with extra-medial thickness differed by gender (P-interaction=.04).

CONCLUSIONS

Carotid extra-medial thickness is independently associated with gender and height in childhood. Extra-medial thickness may provide important information concerning early arterial health, particularly related to the arterial adventitia.

Differential roles of NADPH oxidases in vascular physiology and pathophysiology

Reactive oxygen species (ROS) are produced by all vascular cells and regulate the major physiological functions of the vasculature. Production and removal of ROS are tightly controlled and occur in discrete subcellular locations, allowing for specific, compartmentalized signaling. Among the many sources of ROS in the vessel wall, NADPH oxidases are implicated in physiological functions such as control of vasomotor tone, regulation of extracellular matrix and phenotypic modulation of vascular smooth muscle cells. They are involved in the response to injury, whether as an oxygen sensor during hypoxia, as a regulator of protein processing, as an angiogenic stimulus, or as a mechanism of wound healing. These enzymes have also been linked to processes leading to disease development, including migration, proliferation, hypertrophy, apoptosis and autophagy. As a result, NADPH oxidases participate in atherogenesis, systemic and pulmonary hypertension and diabetic vascular disease. The role of ROS in each of these processes and diseases is complex, and a more full understanding of the sources, targets, cell-specific responses and counterbalancing mechanisms is critical for the rational development of future therapeutics.

NADPH oxidase-dependent and -independent mechanisms of reported inhibitors of reactive oxygen generation

NADPH oxidase isoform-2 (NOX2) generates reactive oxygen species (ROS) that contribute to neurodegenerative and cardiovascular pathologies. However, validation of NOX2 as a pharmacotherapeutic target has been hampered by a lack of mechanistically-defined inhibitors. Using cellular and biochemical assays, we explored previously reported inhibitors of ROS production (perhexiline, suramin, VAS2870 and two Shionogi patent compounds) as direct NOX2 inhibitors. All but suramin, which presumably lacks cell penetrance, inhibit cellular ROS production. However, only perhexiline and suramin inhibit biochemical NOX2 activity. Indeed, our data suggest that NOX2 inhibition by perhexiline may contribute significantly to its demonstrated cardioprotective effects. Inhibition of protein kinase CβII explains the cellular activity of the Shionogi compounds, whereas VAS2870 inhibits by an as-yet unidentified mechanism unrelated to direct NOX2 function or subunit assembly. These data delineate the mechanisms of action of these compounds and highlight their strengths and limitations for use in future target validation studies.

Oxidases and peroxidases in cardiovascular and lung disease: new concepts in reactive oxygen species signaling

Reactive oxygen species (ROS) are involved in numerous physiological and pathophysiological responses. Increasing evidence implicates ROS as signaling molecules involved in the propagation of cellular pathways. The NADPH oxidase (Nox) family of enzymes is a major source of ROS in the cell and has been related to the progression of many diseases and even environmental toxicity. The complexity of this family's effects on cellular processes stems from the fact that there are seven members, each with unique tissue distribution, cellular localization, and expression. Nox proteins also differ in activation mechanisms and the major ROS detected as their product. To add to this complexity, mounting evidence suggests that other cellular oxidases or their products may be involved in Nox regulation. The overall redox and metabolic status of the cell, specifically the mitochondria, also has implications on ROS signaling. Signaling of such molecules as electrophilic fatty acids has an impact on many redox-sensitive pathologies and thus, as anti-inflammatory molecules, contributes to the complexity of ROS regulation. This review is based on the proceedings of a recent international Oxidase Signaling Symposium at the University of Pittsburgh's Vascular Medicine Institute and Department of Pharmacology and Chemical Biology and encompasses further interaction and discussion among the presenters.

ETA and ETB receptors are expressed in vascular adventitial fibroblasts

The adventitia has been recognized to play important roles in vascular oxidative stress, remodeling, and contraction. We recently demonstrated that adventitial fibroblasts are able to express endothelin (ET)-1 in response to ANG II. However, it is unclear whether ET-1 receptors are expressed in the adventitia. We therefore investigated the expression and roles of both ET(A) and ET(B) receptors in collagen synthesis and ET-1 clearance in adventitial fibroblasts. Adventitial fibroblasts were isolated and cultured from the mouse thoracic aorta by the explant method. Cultured cells were treated with ANG II (100 nmol/l) or ET-1 (10 pM) in the presence or absence of the ANG II type 1 receptor antagonist losartan (100 μM), the ET-1 receptor antagonists BQ-123 (ET(A) receptor, 1 μM) and BQ-788 (ET(B) receptor, 1 μM), and the ET(B) receptor agonist sarafotoxin 6C (100 nM). ET-1 peptide levels were determined by ELISA, whereas ET(A), ET(B), and collagen levels were determined by Western blot analysis. ANG II increased ET-1 peptide levels in a time-dependent manner. ANG II increased ET(A) and ET(B) receptor protein levels as well as collagen in a similar fashion. ANG II-induced collagen was reduced while in the presence of BQ-123, suggesting a role for the ET(A) receptor in the regulation of the extracellular matrix. ANG II treatment in the presence of BQ-788 significantly increased ET-1 peptide levels. Conversely, the ET(B) receptor agonist sarafotoxin 6C significantly decreased ET-1 peptide levels. These data implicate a role for the ET(B) receptor in the clearance of the ET-1 peptide. In conclusion, both ET(A) and ET(B) receptors are expressed in adventitial fibroblasts, which paves the ground for the biological significance of adventitial ET-1. The ET(A) receptor subtype mediates collagen I expression, whereas the ET(B) receptor subtype may play a protective role through increasing the clearance of the ET-1 peptide.

Adventitia-derived hydrogen peroxide impairs relaxation of the rat carotid artery via smooth muscle cell p38 mitogen-activated protein kinase

The role of adventitia-derived reactive oxygen species (ROS) in vascular disease and impaired vascular relaxation is not clear. Based on robust adventitial ROS generation and effects on MAPK involvement in vascular dysfunction, we hypothesized that adventitia-derived ROS hydrogen peroxide (H(2)O(2)) impairs vascular relaxation through activation of medial smooth muscle p38 MAPK. By using a novel in vivo model, the adventitial surface of rat carotid arteries was bathed in situ for 90 min with vehicle, angiotensin II (AngII; 500 nM), AngII+H(2)O(2)-scavenger catalase (3,000 U/ml), AngII+p38 MAPK inhibitor SB203580 (10 μM), or AngII+superoxide dismutase (SOD; 150 U/ml). After these in vivo treatments, ex vivo tone measurements on isolated vessels revealed that periadventitial application of AngII impaired both acetylcholine-induced (endothelium-dependent) and sodium nitroprusside-induced (endothelium-independent) relaxations. In vivo coincubation with catalase or SB203580 significantly improved, but SOD exacerbated AngII-induced impairment of in vitro endothelium-dependent and -independent vascular relaxations. Western blots of vascular media, separated from the adventitia, demonstrated increased medial p38 MAPK activation and decreased medial phosphatase SHP-2 activity in AngII-treated vessels. These effects were reversed by in vivo periadventitial addition of catalase. These findings provide the first evidence that adventitia-derived H(2)O(2) participates in vascular dysfunction through p38 MAPK activation and SHP-2 inhibition.

Nox2 B-loop peptide, Nox2ds, specifically inhibits the NADPH oxidase Nox2

In recent years, reactive oxygen species (ROS) derived from the vascular isoforms of NADPH oxidase, Nox1, Nox2, and Nox4, have been implicated in many cardiovascular pathologies. As a result, the selective inhibition of these isoforms is an area of intense current investigation. In this study, we postulated that Nox2ds, a peptidic inhibitor that mimics a sequence in the cytosolic B-loop of Nox2, would inhibit ROS production by the Nox2-, but not the Nox1- and Nox4-oxidase systems. To test our hypothesis, the inhibitory activity of Nox2ds was assessed in cell-free assays using reconstituted systems expressing the Nox2-, canonical or hybrid Nox1-, or Nox4-oxidase. Our findings demonstrate that Nox2ds, but not its scrambled control, potently inhibited superoxide (O(2)(•-)) production in the Nox2 cell-free system, as assessed by the cytochrome c assay. Electron paramagnetic resonance confirmed that Nox2ds inhibits O(2)(•-) production by Nox2 oxidase. In contrast, Nox2ds did not inhibit ROS production by either Nox1- or Nox4-oxidase. These findings demonstrate that Nox2ds is a selective inhibitor of Nox2-oxidase and support its utility to elucidate the role of Nox2 in organ pathophysiology and its potential as a therapeutic agent.

The vascular adventitia: its role in the arterial injury response

The belief that the adventitia serves only a structural purpose has changed over the last decade. Studies have begun to elucidate the role the adventitia plays in the arterial response to injury. The adventitial fibroblast plays an integral part in the development of neointimal hyperplasia. Adiponectin, an adipokine produced from periadventitial adipose tissue, exhibits numerous vasoprotective properties. Stem cells arise, in part, from the adventitia, and stem cell recruitment into the adventitia from the vasa vasorum has been shown to be important in the development of neointimal hyperplasia. The exact role the vasa vasorum plays in neointimal growth is poorly understood and different studies endorse conflicting viewpoints. Thus, understanding the nuances of adventitial pathophysiology will allow us to better appreciate the mechanisms behind the pathology of neointimal hyperplasia. This review will summarize recent findings on the active role the adventitia plays toward the development of neointimal hyperplasia.

Renal protective effects of N-acetyl-Ser-Asp-Lys-Pro in deoxycorticosterone acetate-salt hypertensive mice

BACKGROUND

Hypertension-induced renal injury is characterized by inflammation, fibrosis and proteinuria. Previous studies have demonstrated that N-acetyl-Ser-Asp-Lys-Pro (Ac-SDKP) inhibits renal damage following diabetes mellitus and antiglomerular basement membrane nephritis. However, its effects on low-renin hypertensive nephropathy are not known. Thus, we hypothesized that Ac-SDKP has renal protective effects on deoxycorticosterone acetate (DOCA)-salt hypertensive mice, decreasing inflammatory cell infiltration, matrix deposition and albuminuria.

METHOD

We uninephrectomized 16-week-old C57BL/6J mice and treated them with either placebo, DCOA (10 mg/10 g body weight subcutaneous) and 1% sodium chloride with 0.2% potassium chloride in drinking water (DOCA-salt) or DOCA-salt with Ac-SDKP (800 μg/kg per day) for 12 weeks. We measured blood pressure, urine albumin, glomerular matrix, renal collagen content, monocyte/macrophage infiltration and glomerular nephrin expression.

RESULTS

Treatment with DOCA-salt significantly increased blood pressure (P < 0.01), which remained unaltered by Ac-SDKP. Ac-SDKP decreased DOCA-salt-induced renal collagen deposition, glomerular matrix expansion and monocyte/macrophage infiltration. Moreover, DOCA-salt-induced increase in albuminuria was normalized by Ac-SDKP (controls, 10.8 ± 1.7; DOCA-salt, 41 ± 5; DOCA-salt + Ac-SDKP, 13 ± 3 μg/10 g body weight per 24 h; P < 0.001, DOCA-salt vs. DOCA-salt + Ac-SDKP). Loss of nephrin reportedly causes excess urinary protein excretion; therefore, we determined whether Ac-SDKP inhibits proteinuria by restoring nephrin expression in the glomerulus of hypertensive mice. DOCA-salt significantly downregulated glomerular nephrin expression (controls, 37 ± 8; DOCA-salt, 10 ± 1.5% of glomerular area; P < 0.01), which was partially reversed by Ac-SDKP (23 ± 4.0% of glomerular area; P = 0.065, DOCA-salt vs. DOCA-salt + Ac-SDKP).

CONCLUSION

We concluded that Ac-SDKP prevents hypertension-induced inflammatory cell infiltration, collagen deposition, nephrin downregulation and albuminuria, which could lead to renoprotection in hypertensive mice.

Fibroblast activation in vascular inflammation

Vascular inflammation is implicated in both local and systemic inflammatory conditions. Endothelial activation and leukocyte extravasation are key events in vascular inflammation. Lately, the role of the stromal microenvironment as a source of proinflammatory stimuli has become increasingly appreciated. Stromal fibroblasts produce cytokines, growth factors and proteases that trigger and maintain acute and chronic inflammatory conditions. Fibroblasts have been associated with connective tissue pathologies such as scar formation and fibrosis, but recent research has also connected them with vascular dysfunctions. Fibroblasts are able to modulate endothelial cell functions in a paracrine manner, including proinflammatory activation and promotion of angiogenesis. They are also able to activate and attract leukocytes. Stromal fibroblasts can thus cause a proinflammatory switch in endothelial cells, and promote leukocyte infiltration into tissues. New insights in the role of adventitial fibroblasts have further strengthened the link between stromal fibroblasts and proinflammatory vascular functions. This review focuses on the role of fibroblasts in inducing and maintaining vascular inflammation, and describes recent findings and concepts in the field, along with examples of pathologic implications.

Tachycardia of atrial myocytes induces collagen expression in atrial fibroblasts through transforming growth factor β1

AIMS

We investigated the molecular mechanism of rapid-depolarization-induced atrial fibrosis.

METHODS AND RESULTS

We used a direct atrial myocyte-fibroblast contact co-culture and a fibroblast-specific transforming growth factor β1 (TGF-β1), connective tissue growth factor (CTGF) and procollagen type I α-1 (COL1A1) luciferase reporter system to investigate the possible molecular mechanism of rapid-depolarization-induced atrial fibrosis. Mouse atrial fibroblasts were first transfected with promoter-luciferase reporters, and then co-cultured with HL-1 atrial myocytes. Rapid depolarization of atrial myocytes by rapid electrical field stimulation induced increased TGF-β1, CTGF and COL1A1 promoter activities in the co-cultured atrial fibroblasts (2.4 ± 0.3-fold increase, P= 0.008 for TGF-β1; 2.9 ± 0.4-fold increase, P< 0.001 for CTGF; and 2.1 ± 0.2-fold increase, P= 0.008 for COL1A1). Rapid depolarization of atrial myocytes increased paracrine secretion of angiotensin II (Ang II) and reactive oxygen species in the co-culture medium. Rapid electrical field stimulation-induced ROS generation in atrial myocytes was attenuated by the membrane NADPH oxidase inhibitor, apocynin. Atrial myocyte-induced expression of TGF-β1, CTGF and COL1A1 in atrial fibroblasts was attenuated by co-treatment with the Ang II receptor blocker, losartan, and apocynin. Atrial myocyte-induced COL1A1 expression in atrial fibroblasts was attenuated by anti-TGF-β1 antibody and RNA interference knockdown of the TGF-β1 receptor.

CONCLUSION

We first demonstrated that tachycardia of atrial myocytes induced paracrine secretion of Ang II and reactive oxygen species, which in turn induced expression of CTGF and procollagen in co-cultured atrial fibroblasts through increasing TGF-β1 expression. The results may imply that use of an Ang II receptor blocker, in combination with an anti-oxidant, blocks rapid-depolarization-induced atrial fibrosis.

Superoxide anion and hydrogen peroxide-induced signaling and damage in angiotensin II and aldosterone action

The formation of reactive oxygen species (ROS) can be induced by xenobiotic substances, such as redox cycling molecules, but also by endogenous substances such as hormones and cytokines. Recent research shows the importance of ROS in cellular signaling. Here, the signaling pathways of the two blood pressure-regulating hormones angiotensin II and aldosterone are presented, focusing on both their physiological effects and the change of signaling owing to the action of increased concentrations or prolonged exposure. When present in high concentrations, both angiotensin II and aldosterone, as various other endogenous substances, activate NADPH oxidase, which produces superoxide. In this review the generation of superoxide anions and hydrogen peroxide in cells stimulated with angiotensin II or aldosterone, as well as the subsequently induced signaling processes and DNA damage is discussed.

New perspectives on vascular wall signaling: role of perivascular adipocytes and fibroblasts

This communication represents personal perspectives of recent development in the newly evolved areas in vascular signaling mechanisms at the anatomical level of vascular walls from outside in, that is, from perivascular adventitial side to effectuate the control of vascular reactivity. Since half a century ago, the focus of interest in vascular biology has been confined primarily to the study of the excitation-contraction coupling of vascular smooth muscle (VSM) as well as neuroeffector mechanisms. During the past 3 decades, considerable advancement in the understanding of vascular signaling has been made via the discovery of endothelium-derived relaxation factors (EDRF), endothelium-derived hyperpolarizing factors (EDHF) and endothelium-derived contracting factors (EDCF). The discovery of nitric oxide (NO) as a major cellular messenger has also helped open up another huge area of research in oxidative stress and vascular diseases. In the past decade, concepts on vascular wall signaling have been extended from vascular endothelial cells and then translated to the other seemingly inert cellular components, such as perivascular adipocytes and adventitial fibroblasts. Growing body of evidences show that these cellularities contribute to both functional as well as structural integrity in vasculature with significant pathophysiological implications.

Genetic deletion of apolipoprotein A-I increases airway hyperresponsiveness, inflammation, and collagen deposition in the lung

The relationship between high-density lipoprotein and pulmonary function is unclear. To determine mechanistic relationships we investigated the effects of genetic deletion of apolipoprotein A-I (apoA-I) on plasma lipids, paraoxonase (PON1), pro-inflammatory HDL (p-HDL), vasodilatation, airway hyperresponsiveness and pulmonary oxidative stress, and inflammation. ApoA-I null (apoA-I(-/-)) mice had reduced total and HDL cholesterol but increased pro-inflammatory HDL compared with C57BL/6J mice. Although PON1 protein was increased in apoA-I(-/-) mice, PON1 activity was decreased. ApoA-I deficiency did not alter vasodilatation of facialis arteries, but it did alter relaxation responses of pulmonary arteries. Central airway resistance was unaltered. However, airway resistance mediated by tissue dampening and elastance were increased in apoA-I(-/-) mice, a finding also confirmed by positive end-expiratory pressure (PEEP) studies. Inflammatory cells, collagen deposition, 3-nitrotyrosine, and 4-hydroxy-2-nonenal were increased in apoA-I(-/-) lungs but not oxidized phospholipids. Colocalization of 4-hydroxy-2-nonenal with transforming growth factor beta-1 (TGFbeta-1 was increased in apoA-I(-/-) lungs. Xanthine oxidase, myeloperoxidase and endothelial nitric oxide synthase were increased in apoA-I(-/-) lungs. Dichlorodihydrofluorescein-detectable oxidants were increased in bronchoalveolar lavage fluid (BALF) in apoA-I(-/-) mice. In contrast, BALF nitrite+nitrate levels were decreased in apoA-I(-/-) mice. These data demonstrate that apoA-I plays important roles in limiting pulmonary inflammation and oxidative stress, which if not prevented, will decrease pulmonary artery vasodilatation and increase airway hyperresponsiveness.

Adventitial fibroblasts in vascular structure and function: the role of oxidative stress and beyondThis review is one of a selection of papers published in a Special Issue on Oxidative Stress in Health and Disease

The vascular adventitia, defined as the area between the external elastic lamina and the outermost edge of the blood vessel, is composed primarily of fibroblasts and for years was thought to be merely a passive structural support for the blood vessel. Consequently, studies pertaining to the role of the adventitia in regulating vascular function have been far outnumbered by those regarding the vascular endothelium. However, recent work has begun to reveal the dynamic properties of the adventitia. It was therefore the aim of this review to provide an overview of the existing knowledge demonstrating the role of the adventitia in regulating vessel structure and function. The main topics covered in this review include the cellular composition of the adventitia and the role of the adventitia in vascular oxidative stress, vasomotor responses, extracellular matrix protein expression, growth factor expression, and endothelin-1 (ET-1) expression. Recent evidence suggests that the adventitia is a major producer of vascular reactive oxygen species. It displays a distinct response to injury, hypoxia, and pulmonary hypertension, mediating vascular remodelling, repair, and extracellular matrix deposition. It may also play a role in regulating vascular tone. More recently, it has been reported that adventitial fibroblasts can produce ET-1 after Ang II treatment. Additionally, emerging evidence suggests that the adventitia may be a potent source of vasoactive hormones such as growth factors and ET-1, which may regulate vascular structure and function via autocrine or paracrine signalling mechanisms. Despite these findings, many important questions regarding the role of the vascular adventitia remain unanswered, suggesting the need for further research to determine its exact function in health and disease.

Lack of glutathione peroxidase 1 accelerates cardiac-specific hypertrophy and dysfunction in angiotensin II hypertension

Glutathione peroxidase 1 (Gpx1) plays an important role in cellular defense by converting hydrogen peroxide and organic hydroperoxides to nonreactive products, and Gpx1(-/-) mice, which are characterized by reduced tissue glutathione peroxidase activity, are known to exhibit enhanced oxidative stress. Peroxides participate in tissue injury, as well as the hypertrophy of cultured cells, yet the role of Gpx1 to prevent end organ damage in cardiovascular tissue is not clear. We postulated that Gpx1 deletion would potentiate both aortic and cardiac hypertrophy, as well as mean arterial blood pressure, in response to angiotensin II (AngII). Our results show that short-term AngII markedly increased left ventricular mass, myocyte cross-sectional area, and interventricular septum thickness and decreased shortening fraction in Gpx1(-/-) mice as compared with wild-type animals. On the other hand, AngII resulted in a similar increase in mean arterial blood pressure in wild-type and Gpx1(-/-) mice. Collagen deposition increased in response to AngII, but no differences were found between strains. Vascular hypertrophy increased to the same extent in Gpx1(-/-) and wild-type mice. Collectively, our results indicate that Gpx1 deficiency accelerates cardiac hypertrophy and dysfunction but has no effect on vascular hypertrophy and mean arterial blood pressure and suggest a major role for Gpx1 in cardiac dysfunction in AngII-dependent hypertension.

NOX and inflammation in the vascular adventitia

Vascular inflammation has traditionally been thought to be initiated at the luminal surface and progress through the media toward the adventitial layer. In recent years, however, evidence has emerged suggesting that the vascular adventitia is activated early in a variety of cardiovascular diseases and that it plays an important role in the initiation and progression of vascular inflammation. Adventitial fibroblasts have been shown to produce substantial amounts of NAD(P)H oxidase-derived reactive oxygen species (ROS) in response to vascular injury. Additionally, inflammatory cytokines, lipids, and various hormones, implicated in fibroblast proliferation and migration, lead to recruitment of inflammatory cells to the adventitial layer and impairment of endothelium-dependent relaxation. Early in the development of vascular disease, there is clear evidence for progression toward a denser vasa vasorum which delivers oxygen and nutrients to an increasingly hypoxic and nutrient-deficient media. This expanded vascularization appears to provide enhanced delivery of inflammatory cells to the adventitia and outer media. Combined adventitial fibroblast and inflammatory cell-derived ROS therefore are expected to synergize their local effect on adventitial parenchymal cells, leading to further cytokine release and a feed-forward propagation of adventitial ROS production. In fact, data from our laboratory and others suggest a broader paracrine positive feedback role for adventitia-derived ROS in medial smooth muscle cell hypertrophy and neointimal hyperplasia. A likely candidate responsible for the adventitia-derived paracrine signaling across the vessel wall is the superoxide anion metabolite hydrogen peroxide, which is highly stable, cell permeant, and capable of activating downstream signaling mechanisms in smooth muscle cells, leading to phenotypic modulation of smooth muscle cells. This review addresses the role of adventitial NAD(P)H oxidase-derived ROS from a nontraditional, perivascular vantage of promoting vascular inflammation and will discuss how ROS derived from adventitial NAD(P)H oxidases may be a catalyst for vascular remodeling and dysfunction.

Flavonoids from Inula britannica L. inhibit injury-induced neointimal formation by suppressing oxidative-stress generation

AIM OF THE STUDY

We aimed to investigate whether and how the total flavonoid extracts (TFE) from Inula britannica L. block neointimal hyperplasia induced by balloon injury in rats.

MATERIALS AND METHODS

Rats were administered orally TFE doses of 12.5, 25 and 50 mg/kg/d by gastric gavage from 3 days before balloon injury to 14 days after the injury. The ratio of intima (I) to media (M) thickness (I/M) in carotid arteries was examined by morphological analyses. The MDA content and SOD activity in plasma were measured. The O(2)(-) production in vascular tissues was detected in situ. The expression of p47(phox) in carotid arteries was analyzed by Western blot analysis and immunohistochemistry.

RESULTS

The rats treated with TFE 50 mg/kg/d showed a reduction in neointimal hyperplasia, and the ratio of I/M of balloon injured-carotid arteries was significantly reduced by over 70% after TFE treatment, compared with the injured group. The inhibitory effect of TFE on neointimal hyperplasia was almost consistent with that of atorvastatin, a positive control. The plasma SOD activity was obviously increased by TFE treatment (P<0.01), while plasma MDA production was markedly decreased by TFE treatment (P<0.05). On day 14 after balloon injury, the carotid arteries showed an increase in O(2)(-) production that was most evident in the neointimal and medial layer of the vessel. Thus, TFE significantly inhibited injury-induced O(2)(-) production and p47(phox) expression in carotid arteries.

CONCLUSION

Our results suggest that TFE inhibit the neointimal hyperplasia after balloon injury, at least partly, by suppressing oxidative-stress generation.

Cyclic stretch, reactive oxygen species, and vascular remodeling

Blood vessels respond to changes in mechanical load from circulating blood in the form of shear stress and mechanical strain as the result of heart propulsions by changes in intracellular signaling leading to changes in vascular tone, production of vasoactive molecules, and changes in vascular permeability, gene regulation, and vascular remodeling. In addition to hemodynamic forces, microvasculature in the lung is also exposed to stretch resulting from respiratory cycles during autonomous breathing or mechanical ventilation. Among various cell signaling pathways induced by mechanical forces and reported to date, a role of reactive oxygen species (ROS) produced by vascular cells receives increasing attention. ROS play an essential role in signal transduction and physiologic regulation of vascular function. However, in the settings of chronic hypertension, inflammation, or acute injury, ROS may trigger signaling events that further exacerbate smooth muscle hypercontractility and vascular remodeling associated with hypertension and endothelial barrier dysfunction associated with acute lung injury and pulmonary edema. These conditions are also characterized by altered patterns of mechanical stimulation experienced by vasculature. This review will discuss signaling pathways regulated by ROS and mechanical stretch in the pulmonary and systemic vasculature and will summarize functional interactions between cyclic stretch- and ROS-induced signaling in mechanochemical regulation of vascular structure and function.

Redox control of renal function and hypertension

Loss of redox homeostasis and formation of excessive free radicals play an important role in the pathogenesis of kidney disease and hypertension. Free radicals such as reactive oxygen species (ROS) are necessary in physiologic processes. However, loss of redox homeostasis contributes to proinflammatory and profibrotic pathways in the kidney, which in turn lead to reduced vascular compliance and proteinuria. The kidney is susceptible to the influence of various extracellular and intracellular cues, including the renin-angiotensin-aldosterone system (RAAS), hyperglycemia, lipid peroxidation, inflammatory cytokines, and growth factors. Redox control of kidney function is a dynamic process with reversible pro- and anti-free radical processes. The imbalance of redox homeostasis within the kidney is integral in hypertension and the progression of kidney disease. An emerging paradigm exists for renal redox contribution to hypertension.