NADPH oxidase accounts for enhanced superoxide production and impaired endothelium-dependent smooth muscle relaxation in BKbeta1-/- mice

Pathological high intraocular pressure induces glial cell reactive proliferation contributing to neuroinflammation of the blood-retinal barrier via the NOX2/ET-1 axis-controlled ERK1/2 pathway

BACKGROUND

NADPH oxidase (NOX), a primary source of endothelial reactive oxygen species (ROS), is considered a key event in disrupting the integrity of the blood-retinal barrier. Abnormalities in neurovascular-coupled immune signaling herald the loss of ganglion cells in glaucoma. Persistent microglia-driven inflammation and cellular innate immune system dysregulation often lead to deteriorating retinal degeneration. However, the crosstalk between NOX and the retinal immune environment remains unresolved. Here, we investigate the interaction between oxidative stress and neuroinflammation in glaucoma by genetic defects of NOX2 or its regulation via gp91ds-tat.

METHODS

Ex vivo cultures of retinal explants from wildtype C57BL/6J and Nox2 -/- mice were subjected to normal and high hydrostatic pressure (Pressure 60 mmHg) for 24 h. In vivo, high intraocular pressure (H-IOP) was induced in C57BL/6J mice for two weeks. Both Pressure 60 mmHg retinas and H-IOP mice were treated with either gp91ds-tat (a NOX2-specific inhibitor). Proteomic analysis was performed on control, H-IOP, and treatment with gp91ds-tat retinas to identify differentially expressed proteins (DEPs). The study also evaluated various glaucoma phenotypes, including IOP, retinal ganglion cell (RGC) functionality, and optic nerve (ON) degeneration. The superoxide (O2-) levels assay, blood-retinal barrier degradation, gliosis, neuroinflammation, enzyme-linked immunosorbent assay (ELISA), western blotting, and quantitative PCR were performed in this study.

RESULTS

We found that NOX2-specific deletion or activity inhibition effectively attenuated retinal oxidative stress, immune dysregulation, the internal blood-retinal barrier (iBRB) injury, neurovascular unit (NVU) dysfunction, RGC loss, and ON axonal degeneration following H-IOP. Mechanistically, we unveiled for the first time that NOX2-dependent ROS-driven pro-inflammatory signaling, where NOX2/ROS induces endothelium-derived endothelin-1 (ET-1) overexpression, which activates the ERK1/2 signaling pathway and mediates the shift of microglia activation to a pro-inflammatory M1 phenotype, thereby triggering a neuroinflammatory outburst.

CONCLUSIONS

Collectively, we demonstrate for the first time that NOX2 deletion or gp91ds-tat inhibition attenuates iBRB injury and NVU dysfunction to rescue glaucomatous RGC loss and ON axon degeneration, which is associated with inhibition of the ET-1/ERK1/2-transduced shift of microglial cell activation toward a pro-inflammatory M1 phenotype, highlighting NOX2 as a potential target for novel neuroprotective therapies in glaucoma management.

Cardiovascular prevention in childhood: a consensus document of the Italian Society of Cardiology Working Group on Congenital Heart Disease and Cardiovascular Prevention in Paediatric Age

Cardiovascular diseases (CVD) may be manifested from a very early age. Genetic and environmental (epigenetic) factors interact to affect development and give rise to an abnormal phenotypical expression of genetic information, although not eliciting changes in the nucleotide sequence of DNA. It has been scientifically proven that increased oxidative stress (OS) caused by disease (overweight, obesity, diabetes), nutritional imbalances, unhealthy lifestyles (smoking, alcohol, substance abuse) in the mother during pregnancy may induce placental dysfunction, intrauterine growth restriction, prematurity, low birth weight, postnatal adiposity rebound, metabolic alterations and consequent onset of traditional cardiovascular risk factors. OS represents the cornerstone in the onset of atherosclerosis and manifestation of CVD following an extended asymptomatic period. OS activates platelets and monocytes eliciting the release of pro-inflammatory, pro-atherogenic and pro-oxidising substances resulting in endothelial dysfunction, decrease in flow-mediated arterial dilatation and increase in carotid intima-media thickness. The prevention of CVD is defined as primordial (aimed at preventing risk factors development), primary (aimed at early identification and treatment of risk factors), secondary (aimed at reducing risk of future events in patients who have already manifested a cardiovascular event), and tertiary (aimed at limiting the complex outcome of disease). Atherosclerosis prevention should be implemented as early as possible. Appropriate screening should be carried out to identify children at high risk who are apparently healthy and implement measures including dietary and lifestyle changes, addition of nutritional supplements and, lastly, pharmacological treatment if risk profiles fail to normalise. Reinstating endothelial function during the reversible stage of atherosclerosis is crucial.

Ca2+-Activated K+ Channels and the Regulation of the Uteroplacental Circulation

Adequate uteroplacental blood supply is essential for the development and growth of the placenta and fetus during pregnancy. Aberrant uteroplacental perfusion is associated with pregnancy complications such as preeclampsia, fetal growth restriction (FGR), and gestational diabetes. The regulation of uteroplacental blood flow is thus vital to the well-being of the mother and fetus. Ca²⁺-activated K⁺ (K_Ca) channels of small, intermediate, and large conductance participate in setting and regulating the resting membrane potential of vascular smooth muscle cells (VSMCs) and endothelial cells (ECs) and play a critical role in controlling vascular tone and blood pressure. K_Ca channels are important mediators of estrogen/pregnancy-induced adaptive changes in the uteroplacental circulation. Activation of the channels hyperpolarizes uteroplacental VSMCs/ECs, leading to attenuated vascular tone, blunted vasopressor responses, and increased uteroplacental blood flow. However, the regulation of uteroplacental vascular function by K_Ca channels is compromised in pregnancy complications. This review intends to provide a comprehensive overview of roles of K_Ca channels in the regulation of the uteroplacental circulation under physiological and pathophysiological conditions.

Mitochondrial DNA integrity and function are critical for endothelium-dependent vasodilation in rats with metabolic syndrome

Endothelial dysfunction in diabetes is generally attributed to oxidative stress, but this view is challenged by observations showing antioxidants do not eliminate diabetic vasculopathy. As an alternative to oxidative stress-induced dysfunction, we interrogated if impaired mitochondrial function in endothelial cells is central to endothelial dysfunction in the metabolic syndrome. We observed reduced coronary arteriolar vasodilation to the endothelium-dependent dilator, acetylcholine (Ach), in Zucker Obese Fatty rats (ZOF, 34 ± 15% [mean ± standard deviation] 10^-3 M) compared to Zucker Lean rats (ZLN, 98 ± 11%). This reduction in dilation occurred concomitantly with mitochondrial DNA (mtDNA) strand lesions and reduced mitochondrial complex activities in the endothelium of ZOF versus ZLN. To demonstrate endothelial dysfunction is linked to impaired mitochondrial function, administration of a cell-permeable, mitochondria-directed endonuclease (mt-tat-EndoIII), to repair oxidatively modified DNA in ZOF, restored mitochondrial function and vasodilation to Ach (94 ± 13%). Conversely, administration of a cell-permeable, mitochondria-directed exonuclease (mt-tat-ExoIII) produced mtDNA strand breaks in ZLN, reduced mitochondrial complex activities and vasodilation to Ach in ZLN (42 ± 16%). To demonstrate that mitochondrial function is central to endothelium-dependent vasodilation, we introduced (via electroporation) liver mitochondria (from ZLN) into the endothelium of a mesenteric vessel from ZOF and restored endothelium-dependent dilation to vasoactive intestinal peptide (VIP at 10^-5 M, 4 ± 3% vasodilation before mitochondrial transfer and 48 ± 36% after transfer). Finally, to demonstrate mitochondrial function is key to endothelium-dependent dilation, we administered oligomycin (mitochondrial ATP synthase inhibitor) and observed a reduction in endothelium-dependent dilation. We conclude that mitochondrial function is critical for endothelium-dependent vasodilation.

Elevated Intraocular Pressure Causes Abnormal Reactivity of Mouse Retinal Arterioles

Objective

Glaucoma is a leading cause of severe visual impairment and blindness. Although high intraocular pressure (IOP) is an established risk factor for the disease, the role of abnormal ocular vessel function in the pathophysiology of glaucoma gains more and more attention. We tested the hypothesis that elevated intraocular pressure (IOP) causes vascular dysfunction in the retina.

Methods

High IOP was induced in one group of mice by unilateral cauterization of three episcleral veins. The other group received sham surgery only. Two weeks later, retinal vascular preparations were studied by video microscopy in vitro. Reactive oxygen species (ROS) levels and expression of hypoxia markers and of prooxidant and antioxidant redox genes as well as of inflammatory cytokines were determined.

Results

Strikingly, responses of retinal arterioles to stepwise elevation of perfusion pressure were impaired in the high-IOP group. Moreover, vasodilation responses to the endothelium-dependent vasodilator, acetylcholine, were markedly reduced in mice with elevated IOP, while no differences were seen in response to the endothelium-independent nitric oxide donor, sodium nitroprusside. Remarkably, ROS levels were increased in the retinal ganglion cell layer including blood vessels. Expression of the NADPH oxidase isoform, NOX2, and of the inflammatory cytokine, TNF-α, was increased at the mRNA level in retinal explants. Expression of NOX2, but not of the hypoxic markers, HIF-1α and VEGF-A, was increased in the retinal ganglion cell layer and in retinal blood vessels at the protein level.

Conclusion

Our data provide first-time evidence that IOP elevation impairs autoregulation and induces endothelial dysfunction in mouse retinal arterioles. Oxidative stress and inflammation, but not hypoxia, appear to be involved in this process.

Endothelial GLP-1 (Glucagon-Like Peptide-1) Receptor Mediates Cardiovascular Protection by Liraglutide In Mice With Experimental Arterial Hypertension

Supplemental Digital Content is available in the text.

Cardiovascular outcome trials demonstrated that GLP-1 (glucagon-like peptide-1) analogs including liraglutide reduce the risk of cardiovascular events in type 2 diabetes mellitus. Whether GLP-1 analogs reduce the risk for atherosclerosis independent of glycemic control is challenging to elucidate as the GLP-1R (GLP-1 receptor) is expressed on different cell types, including endothelial and immune cells.

Apolipoprotein E Deficiency Causes Endothelial Dysfunction in the Mouse Retina

Objective

Atherogenic lipoproteins may impair vascular reactivity consecutively causing tissue damage in multiple organs via abnormal perfusion and excessive reactive oxygen species generation. We tested the hypothesis that chronic hypercholesterolemia causes endothelial dysfunction and cell loss in the retina.

Methods

Twelve-month-old apolipoprotein E-deficient (ApoE-/-) mice and age-matched wild-type controls were used in this study (n = 8 per genotype for each experiment). Intraocular pressure, blood pressure, and ocular perfusion pressure were determined. Retinal arteriole responses were studied in vitro, and reactive oxygen and nitrogen species were quantified in the retinal and optic nerve cryosections. The expression of the lectin-like oxidized low-density lipoprotein receptor-1 (LOX-1) and the NADPH oxidase isoforms, NOX1, NOX2, and NOX4, were determined in retinal cryosections by immunofluorescence microscopy. Pro- and antioxidant redox genes were quantified in retinal explants by PCR. Moreover, cell number in the retinal ganglion cell layer and axon number in the optic nerve was calculated.

Results

Responses to the endothelium-dependent vasodilator, acetylcholine, were markedly impaired in retinal arterioles of ApoE-/- mice (P < 0.01). LOX-1 (P = 0.0007) and NOX2 (P = 0.0027) expressions as well as levels of reactive oxygen species (P = 0.0022) were increased in blood vessels but not in other retinal structures. In contrast, reactive nitrogen species were barely detectable in both mouse genotypes. Messenger RNA for HIF-1α, VEGF-A, NOX1, and NOX2, but also for various antioxidant redox genes was elevated in the retina of ApoE-/- mice. Total cell number in the retinal ganglion cell layer did not differ between ApoE-/- and wild-type mice (P = 0.2171). Also, axon number in the optic nerve did not differ between ApoE-/- and wild-type mice (P = 0.6435).

Conclusion

Apolipoprotein E deficiency induces oxidative stress and endothelial dysfunction in retinal arterioles, which may trigger hypoxia in the retinal tissue. Oxidative stress in nonvascular retinal tissue appears to be prevented by the upregulation of antioxidant redox enzymes, resulting in neuron preservation.

Impaired Endothelium-Dependent Hyperpolarization Underlies Endothelial Dysfunction during Early Metabolic Challenge: Increased ROS Generation and Possible Interference with NO Function

Endothelial dysfunction is a hallmark of diabetic vasculopathies. Although hyperglycemia is believed to be the culprit causing endothelial damage, the mechanism underlying early endothelial insult in prediabetes remains obscure. We used a nonobese high-calorie (HC)-fed rat model with hyperinsulinemia, hypercholesterolemia, and delayed development of hyperglycemia to unravel this mechanism. Compared with aortic rings from control rats, HC-fed rat rings displayed attenuated acetylcholine-mediated relaxation. While sensitive to nitric oxide synthase (NOS) inhibition, aortic relaxation in HC-rat tissues was not affected by blocking the inward-rectifier potassium (Kir) channels using BaCl₂ Although Kir channel expression was reduced in HC-rat aorta, Kir expression, endothelium-dependent relaxation, and the BaCl₂-sensitive component improved in HC rats treated with atorvastatin to reduce serum cholesterol. Remarkably, HC tissues demonstrated increased reactive species (ROS) in smooth muscle cells, which was reversed in rats receiving atorvastatin. In vitro ROS reduction, with superoxide dismutase, improved endothelium-dependent relaxation in HC-rat tissues. Significantly, connexin-43 expression increased in HC aortic tissues, possibly allowing ROS movement into the endothelium and reduction of eNOS activity. In this context, gap junction blockade with 18-β-glycyrrhetinic acid reduced vascular tone in HC rat tissues but not in controls. This reduction was sensitive to NOS inhibition and SOD treatment, possibly as an outcome of reduced ROS influence, and emerged in BaCl₂-treated control tissues. In conclusion, our results suggest that early metabolic challenge leads to reduced Kir-mediated endothelium-dependent hyperpolarization, increased vascular ROS potentially impairing NO synthesis and highlight these channels as a possible target for early intervention with vascular dysfunction in metabolic disease. SIGNIFICANCE STATEMENT: The present study examines early endothelial dysfunction in metabolic disease. Our results suggest that reduced inward-rectifier potassium channel function underlies a defective endothelium-mediated relaxation possibly through alteration of nitric oxide synthase activity. This study provides a possible mechanism for the augmentation of relatively small changes in one endothelium-mediated relaxation pathway to affect overall endothelial response and highlights the potential role of inward-rectifier potassium channel function as a therapeutic target to treat vascular dysfunction early in the course of metabolic disease.

CD40L controls obesity-associated vascular inflammation, oxidative stress, and endothelial dysfunction in high fat diet-treated and db/db mice

Aims

CD40 ligand (CD40L) signaling controls vascular oxidative stress and related dysfunction in angiotensin-II-induced arterial hypertension by regulating vascular immune cell recruitment and platelet activation. Here we investigated the role of CD40L in experimental hyperlipidemia.

Methods and results

Male wild type and CD40L-/- mice (C57BL/6 background) were subjected to high fat diet for sixteen weeks. Weight, cholesterol, HDL, and LDL levels, endothelial function (isometric tension recording), oxidative stress (NADPH oxidase expression, dihydroethidium fluorescence) and inflammatory parameters (inducible nitric oxide synthase, interleukin-6 expression) were assessed. CD40L expression, weight, leptin and lipids were increased, and endothelial dysfunction, oxidative stress and inflammation were more pronounced in wild type mice on a high fat diet, all of which was almost normalized by CD40L deficiency. Similar results were obtained in diabetic db/db mice with CD40/TRAF6 inhibitor (6877002) therapy. In a small human study higher serum sCD40L levels and an inflammatory phenotype were detected in the blood and Aorta ascendens of obese patients (body mass index > 35) that underwent by-pass surgery.

Conclusion

CD40L controls obesity-associated vascular inflammation, oxidative stress and endothelial dysfunction in mice and potentially humans. Thus, CD40L represents a therapeutic target in lipid metabolic disorders which is a leading cause in cardiovascular disease.

Taking up the cudgels for the traditional reactive oxygen and nitrogen species detection assays and their use in the cardiovascular system

Reactive oxygen and nitrogen species (RONS such as H2O2, nitric oxide) confer redox regulation of essential cellular functions (e.g. differentiation, proliferation, migration, apoptosis), initiate and catalyze adaptive stress responses. In contrast, excessive formation of RONS caused by impaired break-down by cellular antioxidant systems and/or insufficient repair of the resulting oxidative damage of biomolecules may lead to appreciable impairment of cellular function and in the worst case to cell death, organ dysfunction and severe disease phenotypes of the entire organism. Therefore, the knowledge of the severity of oxidative stress and tissue specific localization is of great biological and clinical importance. However, at this level of investigation quantitative information may be enough. For the development of specific drugs, the cellular and subcellular localization of the sources of RONS or even the nature of the reactive species may be of great importance, and accordingly, more qualitative information is required. These two different philosophies currently compete with each other and their different needs (also reflected by different detection assays) often lead to controversial discussions within the redox research community. With the present review we want to shed some light on these different philosophies and needs (based on our personal views), but also to defend some of the traditional assays for the detection of RONS that work very well in our hands and to provide some guidelines how to use and interpret the results of these assays. We will also provide an overview on the "new assays" with a brief discussion on their strengths but also weaknesses and limitations.

Glucagon-like peptide-1 receptor signalling reduces microvascular thrombosis, nitro-oxidative stress and platelet activation in endotoxaemic mice

BACKGROUND AND PURPOSE

Excessive inflammation in sepsis causes microvascular thrombosis and thrombocytopenia associated with organ dysfunction and high mortality. The present studies aimed to investigate whether inhibition of dipeptidyl peptidase-4 (DPP-4) and supplementation with glucagon-like peptide-1 (GLP-1) receptor agonists improved endotoxaemia-associated microvascular thrombosis via immunomodulatory effects.

EXPERIMENTAL APPROACH

Endotoxaemia was induced in C57BL/6J mice by a single injection of LPS (17.5 mg kg^-1 for survival and 10 mg kg^-1 for all other studies). For survival studies, treatment was started 6 h after LPS injection. For all other studies, drugs were injected 48 h before LPS treatment.

KEY RESULTS

Mice treated with LPS alone showed severe thrombocytopenia, microvascular thrombosis in the pulmonary circulation (fluorescence imaging), increased LDH activity, endothelial dysfunction and increased markers of inflammation in aorta and whole blood (leukocyte-dependent oxidative burst, nitrosyl-iron haemoglobin, a marker of nitrosative stress, and expression of inducible NOS). Treatment with the DPP-4 inhibitor linagliptin or the GLP-1 receptor agonist liraglutide, as well as genetic deletion of DPP-4 (DPP4^-/- mice) improved all these parameters. In GLP-1 receptor-deficient mice, both linagliptin and liraglutide lost their beneficial effects and improvement of prognosis. Incubation of platelets and cultured monocytes (containing GLP-1 receptor protein) with GLP-1 receptor agonists inhibited the monocytic oxidative burst and platelet activation, with a GLP-1 receptor-dependent elevation of cAMP levels and PKA activation.

CONCLUSIONS AND IMPLICATIONS

GLP-1 receptor activation in platelets by linagliptin and liraglutide strongly attenuated endotoxaemia-induced microvascular thrombosis and mortality by a cAMP/PKA-dependent mechanism, preventing systemic inflammation, vascular dysfunction and end organ damage.

LINKED ARTICLES

This article is part of a themed section on Redox Biology and Oxidative Stress in Health and Disease. To view the other articles in this section visit http://onlinelibrary.wiley.com/doi/10.1111/bph.v174.12/issuetoc.

BK Channels in the Vascular System

Autoregulation of blood flow is essential for the preservation of organ function to ensure continuous supply of oxygen and essential nutrients and removal of metabolic waste. This is achieved by controlling the diameter of muscular arteries and arterioles that exhibit a myogenic response to changes in arterial blood pressure, nerve activity and tissue metabolism. Large-conductance voltage and Ca(2+)-dependent K(+) channels (BK channels), expressed exclusively in smooth muscle cells (SMCs) in the vascular wall of healthy arteries, play a critical role in regulating the myogenic response. Activation of BK channels by intracellular, local, and transient ryanodine receptor-mediated "Ca(2+) sparks," provides a hyperpolarizing influence on the SMC membrane potential thereby decreasing the activity of voltage-dependent Ca(2+) channels and limiting Ca(2+) influx to promote SMC relaxation and vasodilation. The BK channel α subunit, a large tetrameric protein with each monomer consisting of seven-transmembrane domains, a long intracellular C-terminal tail and an extracellular N-terminus, associates with the β1 and γ subunits in vascular SMCs. The BK channel is regulated by factors originating within the SMC or from the endothelium, perivascular nerves and circulating blood, that significantly alter channel gating properties, Ca(2+) sensitivity and expression of the α and/or β1 subunit. The BK channel thus serves as a central receiving dock that relays the effects of the changes in several such concomitant autocrine and paracrine factors and influences cardiovascular health. This chapter describes the primary mechanism of regulation of myogenic response by BK channels and the alterations to this mechanism wrought by different vasoactive mediators.

Molecular mechanisms of the crosstalk between mitochondria and NADPH oxidase through reactive oxygen species-studies in white blood cells and in animal models

AIMS

Oxidative stress is involved in the development of cardiovascular disease. There is a growing body of evidence for a crosstalk between different enzymatic sources of oxidative stress. With the present study, we sought to determine the underlying crosstalk mechanisms, the role of the mitochondrial permeability transition pore (mPTP), and its link to endothelial dysfunction.

RESULTS

NADPH oxidase (Nox) activation (oxidative burst and translocation of cytosolic Nox subunits) was observed in response to mitochondrial reactive oxygen species (mtROS) formation in human leukocytes. In vitro, mtROS-induced Nox activation was prevented by inhibitors of the mPTP, protein kinase C, tyrosine kinase cSrc, Nox itself, or an intracellular calcium chelator and was absent in leukocytes with p47phox deficiency (regulates Nox2) or with cyclophilin D deficiency (regulates mPTP). In contrast, the crosstalk in leukocytes was amplified by mitochondrial superoxide dismutase (type 2) (MnSOD(+/-)) deficiency. In vivo, increases in blood pressure, degree of endothelial dysfunction, endothelial nitric oxide synthase (eNOS) dysregulation/uncoupling (e.g., eNOS S-glutathionylation) or Nox activity, p47phox phosphorylation in response to angiotensin-II (AT-II) in vivo treatment, or the aging process were more pronounced in MnSOD(+/-) mice as compared with untreated controls and improved by mPTP inhibition by cyclophilin D deficiency or sanglifehrin A therapy.

INNOVATION

These results provide new mechanistic insights into what extent mtROS trigger Nox activation in phagocytes and cardiovascular tissue, leading to endothelial dysfunction.

CONCLUSIONS

Our data show that mtROS trigger the activation of phagocytic and cardiovascular NADPH oxidases, which may have fundamental implications for immune cell activation and development of AT-II-induced hypertension.

Current status of NADPH oxidase research in cardiovascular pharmacology

The implications of reactive oxygen species in cardiovascular disease have been known for some decades. Rationally, therapeutic antioxidant strategies combating oxidative stress have been developed, but the results of clinical trials have not been as good as expected. Therefore, to move forward in the design of new therapeutic strategies for cardiovascular disease based on prevention of production of reactive oxygen species, steps must be taken on two fronts, ie, comprehension of reduction-oxidation signaling pathways and the pathophysiologic roles of reactive oxygen species, and development of new, less toxic, and more selective nicotinamide adenine dinucleotide phosphate (NADPH) oxidase inhibitors, to clarify both the role of each NADPH oxidase isoform and their utility in clinical practice. In this review, we analyze the value of NADPH oxidase as a therapeutic target for cardiovascular disease and the old and new pharmacologic agents or strategies to prevent NADPH oxidase activity. Some inhibitors and different direct or indirect approaches are available. Regarding direct NADPH oxidase inhibition, the specificity of NADPH oxidase is the focus of current investigations, whereas the chemical structure-activity relationship studies of known inhibitors have provided pharmacophore models with which to search for new molecules. From a general point of view, small-molecule inhibitors are preferred because of their hydrosolubility and oral bioavailability. However, other possibilities are not closed, with peptide inhibitors or monoclonal antibodies against NADPH oxidase isoforms continuing to be under investigation as well as the ongoing search for naturally occurring compounds. Likewise, some different approaches include inhibition of assembly of the NADPH oxidase complex, subcellular translocation, post-transductional modifications, calcium entry/release, electron transfer, and genetic expression. High-throughput screens for any of these activities could provide new inhibitors. All this knowledge and the research presently underway will likely result in development of new drugs for inhibition of NADPH oxidase and application of therapeutic approaches based on their action, for the treatment of cardiovascular disease in the next few years.

Effects of telmisartan or amlodipine monotherapy versus telmisartan/amlodipine combination therapy on vascular dysfunction and oxidative stress in diabetic rats

Our previous studies identified potent antioxidant effects and improvement of vascular function by telmisartan therapy in experimental diabetes and nitrate tolerance. The present study compared the beneficial effects of single telmisartan or amlodipine versus telmisartan/amlodipine combination therapy (T+A) in streptozotocin (STZ)-induced type 1 diabetic rats. Male Wistar rats were injected once with STZ (60 mg/kg, i.v.) and 1 week later the drugs (telmisartan, amlodipine, or T+A) were administrated orally by a special diet (2.5-5 mg kg(-1) day(-1)) for another 7 weeks. We only observed a marginal beneficial on-top effect of T+A therapy over the single drug regimen that was most evident in the improvement of endothelial function (acetylcholine response) and less pronounced in the reduction of whole blood, vascular and cardiac oxidative stress (blood leukocyte oxidative burst, aortic dihydroethidine and 3-nitrotyrosine staining, as well as cardiac NADPH oxidase activity and uncoupling of endothelial nitric oxide synthase) in diabetic rats. These effects on oxidative stress parameters were paralleled by those on the expression pattern of NADPH oxidase and nitric oxide synthase isoforms. In addition, development of mild hypotension in the T+A-treated rats was observed. Reasons for this moderate synergistic effect of T+A therapy may be related to the potent beneficial effects of telmisartan alone and the fact that amlodipine and telmisartan share similar pathways to improve endothelial function. Moreover, hypotension in the T+A-treated rats could partially antagonize the beneficial additive effects by counter-regulatory mechanisms (e.g., activation of the renin-angiotensin-aldosterone system).

A process-based review of mouse models of pulmonary hypertension

Genetically modified mouse models have unparalleled power to determine the mechanisms behind different processes involved in the molecular and physiologic etiology of various classes of human pulmonary hypertension (PH). Processes known to be involved in PH for which there are extensive mouse models available include the following: (1) Regulation of vascular tone through secreted vasoactive factors; (2) regulation of vascular tone through potassium and calcium channels; (3) regulation of vascular remodeling through alteration in metabolic processes, either through alteration in substrate usage or through circulating factors; (4) spontaneous vascular remodeling either before or after development of elevated pulmonary pressures; and (5) models in which changes in tone and remodeling are primarily driven by inflammation. PH development in mice is of necessity faster and with different physiologic ramifications than found in human disease, and so mice make poor models of natural history of PH. However, transgenic mouse models are a perfect tool for studying the processes involved in pulmonary vascular function and disease, and can effectively be used to test interventions designed against particular molecular pathways and processes involved in disease.

Reduced atherosclerotic burden in subjects with genetically determined low oxidative stress

OBJECTIVE

NADPH oxidase, one of the most important enzymes producing reactive oxidant species, is suggested to play a role in experimental atherosclerosis, but its role in human atherosclerosis is still unclear. We hypothesized that a reduced activity of NADPH oxidase might be linked to a reduced atherosclerotic burden.

METHODS AND RESULTS

Thirty-one women carriers of hereditary deficiency of NOX2, the catalytic subunit of NADPH oxidase, were matched for sex and age with 31 controls and 31 obese women. Flow-mediated dilation and intima-media thickness, 2 surrogate markers of atherosclerosis, serum activity of NOX2, urinary isoprostanes, serum levels of nitrite/nitrate, and platelet production of isoprostanes and nitrite/nitrate were determined. Compared with controls (5.7±3.0% and 0.60±0.11 mm), carriers of NOX2 deficiency had higher flow-mediated dilation (9.2±5.0%; P<0.001) and lower intima-media thickness (0.50±0.11 mm; P=0.002), whereas obese women had lower flow-mediated dilation (3.2±2.1%; P=0.007) and higher intima-media thickness (0.71±0.15 mm; P<0.001). Compared with controls, carriers of NOX2 deficiency had lower urinary isoprostanes (132.6±87.3 versus 82.3±46.0 pg/mg creatinine; P=0.007) and serum NOX2 activity (24.9±19.3 versus 12.8±11.9 pg/mL; P=0.004) and higher serum nitrite/nitrate (23.8±7.6 versus 30.5±6.3 µmol/L; P<0.001), whereas obese women had higher urinary isoprostanes (132.6±87.3 versus 182.2±84.6 pg/mg creatinine; P=0.008) and serum NOX2 activity (24.9±19.3 versus 36.1±18.6 pg/mL; P=0.008) and lower serum nitrite/nitrate (23.8±7.6 versus 12.6±4.2 µmol/L; P<0.001). Flow-mediated dilation correlated with intima-media thickness (r=-0.433; P<0.001), serum NOX2 activity (r=-325; P<0.001), and urinary isoprostanes (r=-0.314; P=0.002). Ex vivo study showed that, compared with controls, platelets from carriers of NOX2 deficiency had lower isoprostanes (P<0.001) and higher nitrite/nitrate (P<0.001), whereas platelets from obese women had higher isoprostanes (P<0.001) and lower nitrite/nitrate (P=0.013).

CONCLUSIONS

The study shows reduced atherosclerotic burden in carriers of NOX2 deficiency, suggesting that oxidative stress generated by this enzymatic pathway is implicated in human atherosclerosis.

Weight loss is associated with improved endothelial dysfunction via NOX2-generated oxidative stress down-regulation in patients with the metabolic syndrome

The aim of this study was to assess whether adherence to a restricted-calorie, Mediterranean-type diet improves endothelial dysfunction and markers of oxidative stress in patients with metabolic syndrome. A moderately low-calorie (600 calories/day negative energy balance), low-fat, high-carbohydrate diet (<30% energy from fat, <10% from saturated fat and 55% from carbohydrate) was prescribed to 53 outpatients with the metabolic syndrome. Participants were divided into two groups according to body weight loss > or < 5% after 6 months. Group A (n = 23) showed a remarkable decrease in body weight (-6.8%), body-mass-index (-4.6%), waist circumference (-4.8%), HOMA-IR (-27.2%), plasma glucose, glycosylated haemoglobin, total and LDL-cholesterol, blood pressure, serum NOX2 (the catalytic core of NADPH oxidase) (-22.2%) and urinary8-isoprostanes (-39.0%) and an increase of serum NOx (Nitrite/Nitrate) (+116.8%) and adiponectine (+125.5%) as compared with those in group B (n = 30). A statistically significant increase in brachial artery flow-mediated dilatation was observed in group A (+24.7%; p < 0.001), while no changes were present in group B. Variations of flow-mediated dilatation were statistically and negatively correlated with changes of serum NOX2 levels (p = 0.04), body-mass-index (p < 0.01), waist circumference (0.01), glycosylated haemoglobin (p < 0.01), LDL-cholesterol (p < 0.01) and triglycerides (p < 0.05) and positively correlated with changes of serum NOx (p < 0.001) and adiponectin (p = 0.01). The results show that moderate weight loss is able to improve endothelial dysfunction in patients with the metabolic syndrome. The coexistent decrease of NOX2 activation suggests a role for oxidative stress in eliciting artery dysfunction.

Chronic therapy with isosorbide-5-mononitrate causes endothelial dysfunction, oxidative stress, and a marked increase in vascular endothelin-1 expression

AIMS

Isosorbide-5-mononitrate (ISMN) is one of the most frequently used compounds in the treatment of coronary artery disease predominantly in the USA. However, ISMN was reported to induce endothelial dysfunction, which was corrected by vitamin C pointing to a crucial role of reactive oxygen species (ROS) in causing this phenomenon. We sought to elucidate the mechanism how ISMN causes endothelial dysfunction and oxidative stress in vascular tissue.

METHODS AND RESULTS

Male Wistar rats (n= 69 in total) were treated with ISMN (75 mg/kg/day) or placebo for 7 days. Endothelin (ET) expression was determined by immunohistochemistry in aortic sections. Isosorbide-5-mononitrate infusion caused significant endothelial dysfunction but no tolerance to ISMN itself, whereas ROS formation and nicotinamide adenine dinucleotidephosphate (NADPH) oxidase activity in the aorta, heart, and whole blood were increased. Isosorbide-5-mononitrate up-regulated the expression of NADPH subunits and caused uncoupling of the endothelial nitric oxide synthase (eNOS) likely due to a down-regulation of the tetrahydrobiopterin-synthesizing enzyme GTP-cyclohydrolase-1 and to S-glutathionylation of eNOS. The adverse effects of ISMN were improved in gp91phox knockout mice and normalized by bosentan in vivo/ex vivo treatment and suppressed by apocynin. In addition, a strong increase in the expression of ET within the endothelial cell layer and the adventitia was observed.

CONCLUSION

Chronic treatment with ISMN causes endothelial dysfunction and oxidative stress, predominantly by an ET-dependent activation of the vascular and phagocytic NADPH oxidase activity and NOS uncoupling. These findings may explain at least in part results from a retrospective analysis indicating increased mortality in post-infarct patients in response to long-term treatment with mononitrates.

NOX2 up-regulation is associated with artery dysfunction in patients with peripheral artery disease

OBJECTIVE

Oxidative stress seems to play a role in impairing flow-mediated dilation (FMD) in patients with peripheral artery disease (PAD) but the underlying mechanism is still undefined. We evaluated whether NOX2, the catalytic core of NADPH oxidase, the most important producer of reactive oxidant species (ROS), is implicated in impairing FMD.

METHODS

We measured FMD, urinary isoprostanes, a marker of oxidative stress, nitric oxide generation by serum levels of nitrite/nitrate (NOx), and serum levels of soluble NOX2-derived peptide (sNOX2-dp), a marker of NOX2 activation, in 50 PAD patients and 50 controls. Also, we performed an interventional cross-over study to assess if propionyl-L-carnitine (PLC) (6g/day), vs. placebo, was able to affect FMD via an oxidative stress-mediated mechanism.

RESULTS

Compared to controls, patients with PAD had enhanced sNOX2-dp and isoprostanes and reduced NOx and FMD. Multiple linear regression analysis showed that FMD was independently associated with sNOX2-dp. After PLC infusion FMD increased while sNOX2-dp and isoprostanes significantly decreased; no changes were observed after placebo. In vitro study by incubating platelets or white cells with PLC demonstrated a significant inhibition of p47(phox) translocation on cellular surface and ROS generated by NOX2 activation.

CONCLUSION

This study suggests that in PAD patients ROS generated by NOX2 contribute to reduce FMD and that the administration of an antioxidant is able to improve arterial dilatation via NOX2 inhibition.

Chronic granulomatous disease

Chronic granulomatous disease (CGD) is a rare primary immunodeficiency due to an abnormal function of the nicotinamide adenine dinucleotide phosphate (NADPH) oxidase; NADPH oxidase is a key enzyme for the cellular "respiratory burst", the cellular process that converts molecular oxygen to the oxygen free-radical superoxide. As a consequence of NADPH oxidase defect, CGD patients suffer from recurrent life-threatening infections and from exceeding inflammatory responses leading to granulomas. This article analyzes clinical aspects of CGD. Furthermore, using the CGD model, we focused on the future perspective to reduce atherosclerosis and its complications.

Combating oxidative stress in vascular disease: NADPH oxidases as therapeutic targets

NADPH oxidases are a family of enzymes that generate reactive oxygen species (ROS). The NOX1 (NADPH oxidase 1) and NOX2 oxidases are the major sources of ROS in the artery wall in conditions such as hypertension, hypercholesterolaemia, diabetes and ageing, and so they are important contributors to the oxidative stress, endothelial dysfunction and vascular inflammation that underlies arterial remodelling and atherogenesis. In this Review, we advance the concept that compared to the use of conventional antioxidants, inhibiting NOX1 and NOX2 oxidases is a superior approach for combating oxidative stress. We briefly describe some common and emerging putative NADPH oxidase inhibitors. In addition, we highlight the crucial role of the NADPH oxidase regulatory subunit, p47phox, in the activity of vascular NOX1 and NOX2 oxidases, and suggest how a better understanding of its specific molecular interactions may enable the development of novel isoform-selective drugs to prevent or treat cardiovascular diseases.

Large-conductance Ca2+-activated K+ channel beta1-subunit knockout mice are not hypertensive

Large-conductance Ca2+-activated K+ (BK) channels are composed of pore-forming α-subunits and accessory β1-subunits that modulate Ca2+ sensitivity. BK channels regulate arterial myogenic tone and renal Na+ clearance/K+ reabsorption. Previous studies using indirect or short-term blood pressure measurements found that BK channel β1-subunit knockout (BK β1-KO) mice were hypertensive. We evaluated 24-h mean arterial pressure (MAP) and heart rate in BK β1-KO mice using radiotelemetry. BK β1-KO mice did not have a higher 24-h average MAP when compared with wild-type (WT) mice, although MAP was ∼10 mmHg higher at night. The dose-dependent peak declines in MAP by nifedipine were only slightly larger in BK β1-KO mice. In BK β1-KO mice, giving 1% NaCl to mice to drink for 7 days caused a transient (5 days) elevation of MAP (∼5 mmHg); MAP returned to pre-saline levels by day 6. BK β1-KO mesenteric arteries in vitro demonstrated diminished contractile responses to paxilline, increased reactivity to Bay K 8644 and norepinephrine (NE), and maintained relaxation to isoproterenol. Paxilline and Bay K 8644 did not constrict WT or BK β1-KO mesenteric veins (MV). BK β1-subunits are not expressed in MV. The results indicate that BK β1-KO mice are not hypertensive on normal or high-salt intake. BK channel deficiency increases arterial reactivity to NE and L-type Ca2+ channel function in vitro, but the L-type Ca2+ channel modulation of MAP is not altered in BK β1-KO mice. BK and L-type Ca(2+) channels do not modulate murine venous tone. It appears that selective loss of BK channel function in arteries only is not sufficient to cause sustained hypertension.

Reactive oxygen species cause endothelial dysfunction in chronic flow overload

Although elevation of shear stress increases production of vascular reactive oxygen species (ROS), the role of ROS in chronic flow overload (CFO) has not been well investigated. We hypothesize that CFO increases ROS production mediated in part by NADPH oxidase, which leads to endothelial dysfunction. In six swine, CFO in carotid arteries was induced by contralateral ligation for 1 wk. In an additional group, six swine received apocynin (NADPH oxidase blocker and anti-oxidant) treatment in conjunction with CFO for 1 wk. The blood flow in carotid arteries increased from 189.2 ± 25.3 ml/min (control) to 369.6 ± 61.9 ml/min (CFO), and the arterial diameter increased by 8.6%. The expressions of endothelial nitric oxide synthase (eNOS), p22/p47(phox), and NOX2/NOX4 were upregulated. ROS production increased threefold in response to CFO. The endothelium-dependent vasorelaxation was compromised in the CFO group. Treatment with apocynin significantly reduced ROS production in the vessel wall, preserved endothelial function, and inhibited expressions of p22/p47phox and NOX2/NOX4. Although the process of CFO remodeling to restore the wall shear stress has been thought of as a physiological response, the present data implicate NADPH oxidase-produced ROS and eNOS uncoupling in endothelial dysfunction at 1 wk of CFO.

Ancillary subunits associated with voltage-dependent K+ channels

Since the first discovery of Kvbeta-subunits more than 15 years ago, many more ancillary Kv channel subunits were characterized, for example, KChIPs, KCNEs, and BKbeta-subunits. The ancillary subunits are often integral parts of native Kv channels, which, therefore, are mostly multiprotein complexes composed of voltage-sensing and pore-forming Kvalpha-subunits and of ancillary or beta-subunits. Apparently, Kv channels need the ancillary subunits to fulfill their many different cell physiological roles. This is reflected by the large structural diversity observed with ancillary subunit structures. They range from proteins with transmembrane segments and extracellular domains to purely cytoplasmic proteins. Ancillary subunits modulate Kv channel gating but can also have a great impact on channel assembly, on channel trafficking to and from the cellular surface, and on targeting Kv channels to different cellular compartments. The importance of the role of accessory subunits is further emphasized by the number of mutations that are associated in both humans and animals with diseases like hypertension, epilepsy, arrhythmogenesis, periodic paralysis, and hypothyroidism. Interestingly, several ancillary subunits have in vitro enzymatic activity; for example, Kvbeta-subunits are oxidoreductases, or modulate enzymatic activity, i.e., KChIP3 modulates presenilin activity. Thus different modes of beta-subunit association and of functional impact on Kv channels can be delineated, making it difficult to extract common principles underlying Kvalpha- and beta-subunit interactions. We critically review present knowledge on the physiological role of ancillary Kv channel subunits and their effects on Kv channel properties.

Hydroethidine- and MitoSOX-derived red fluorescence is not a reliable indicator of intracellular superoxide formation: another inconvenient truth

Hydroethidine (HE; or dihydroethidium) is the most popular fluorogenic probe used for detecting intracellular superoxide radical anion. The reaction between superoxide and HE generates a highly specific red fluorescent product, 2-hydroxyethidium (2-OH-E(+)). In biological systems, another red fluorescent product, ethidium, is also formed, usually at a much higher concentration than 2-OH-E(+). In this article, we review the methods to selectively detect the superoxide-specific product (2-OH-E(+)) and the factors affecting its levels in cellular and biological systems. The most important conclusion of this review is that it is nearly impossible to assess the intracellular levels of the superoxide-specific product, 2-OH-E(+), using confocal microscopy or other fluorescence-based microscopic assays and that it is essential to measure by HPLC the intracellular HE and other oxidation products of HE, in addition to 2-OH-E(+), to fully understand the origin of red fluorescence. The chemical reactivity of mitochondria-targeted hydroethidine (Mito-HE, MitoSOX red) with superoxide is similar to the reactivity of HE with superoxide, and therefore, all of the limitations attributed to the HE assay are applicable to Mito-HE (or MitoSOX) as well.

Pentaerythritol tetranitrate improves angiotensin II-induced vascular dysfunction via induction of heme oxygenase-1

The organic nitrate pentaerythritol tetranitrate is devoid of nitrate tolerance, which has been attributed to the induction of the antioxidant enzyme heme oxygenase (HO)-1. With the present study, we tested whether chronic treatment with pentaerythritol tetranitrate can improve angiotensin II-induced vascular oxidative stress and dysfunction. In contrast to isosorbide-5 mononitrate (75 mg/kg per day for 7 days), treatment with pentaerythritol tetranitrate (15 mg/kg per day for 7 days) improved the impaired endothelial and smooth muscle function and normalized vascular and cardiac reactive oxygen species production (mitochondria, NADPH oxidase activity, and uncoupled endothelial NO synthase), as assessed by dihydroethidine staining, lucigenin-enhanced chemiluminescence, and quantification of dihydroethidine oxidation products in angiotensin II (1 mg/kg per day for 7 days)-treated rats. The antioxidant features of pentaerythritol tetranitrate were recapitulated in spontaneously hypertensive rats. In addition to an increase in HO-1 protein expression, pentaerythritol tetranitrate but not isosorbide-5 mononitrate normalized vascular reactive oxygen species formation and augmented aortic protein levels of the tetrahydrobiopterin-synthesizing enzymes GTP-cyclohydrolase I and dihydrofolate reductase in angiotensin II-treated rats, thereby preventing endothelial NO synthase uncoupling. Haploinsufficiency of HO-1 completely abolished the beneficial effects of pentaerythritol tetranitrate in angiotensin II-treated mice, whereas HO-1 induction by hemin (25 mg/kg) mimicked the effect of pentaerythritol tetranitrate. Improvement of vascular function in this particular model of arterial hypertension by pentaerythritol tetranitrate largely depends on the induction of the antioxidant enzyme HO-1 and identifies pentaerythritol tetranitrate, in contrast to isosorbide-5 mononitrate, as an organic nitrate able to improve rather than to worsen endothelial function.

Hereditary deficiency of gp91(phox) is associated with enhanced arterial dilatation: results of a multicenter study

BACKGROUND

NADPH oxidase is believed to modulate arterial tone, but its role in humans is still unclear. The objective of this study was to evaluate whether NADPH oxidase is involved in flow-mediated arterial dilation (FMD).

METHODS AND RESULTS

Twenty-five patients with hereditary deficiency of gp91(phox), the catalytic core of NADPH oxidase, (X-CGD), 25 healthy subjects, and 25 obese patients matched for sex and age were recruited. FMD, platelet gp91(phox), serum levels of nitrite and nitrate as markers of nitric oxide generation, oxidized low-density lipoprotein, and urinary excretion of isoprostanes as markers of oxidative stress were determined. Platelet gp91(phox) expression was downregulated in X-CGD patients (1.0+/-0.8 mean fluorescence; P<0.001) and upregulated in obese patients (4.1+/-2.2 mean fluorescence; P=0.01) compared with healthy subjects (2.9+/-1.7 mean fluorescence). Urinary excretion of isoprostanes was reduced in X-CGD patients (41.7+/-33.3 pg/mg creatinine; P=0.04) and increased in obese patients (154.4+/-91 pg/mg creatinine; P<0.001) compared with healthy subjects (69.5+/-52.4 pg/mg creatinine). Obese patients had higher serum oxidized low-density lipoprotein than healthy subjects (35.3+/-6.7 versus 24.8+/-9.8 U/L; P<0.001) and X-CGD patients (28.5+/-7.2 U/L; P<0.001). X-CGD patients had significantly higher FMD (14.7+/-5.9%) compared with healthy subjects (7.9+/-2.5%; P<0.001); obese patients had lower FMD (5.3+/-3.0%; P=0.028) compared with healthy subjects. Serum nitrite and nitrate levels were significantly higher in patients with X-CGD (36.0+/-10.8 micromol/L; P=0.016) and lower in obese patients (9.3+/-11.0 micromol/L; P=0.001) compared with healthy subjects (27.1+/-19.1 micromol/L). Serum nitrite and nitrate levels significantly correlated with FMD (R(s)=0.403, P<0.001) and platelet gp91(phox) (R(s)=-0.515, P<0.001). FMD inversely correlated with platelet gp91(phox) (R(s)=-0.502, P<0.001) and isoprostanes (R(s)=-0.513, P<0.001).

CONCLUSIONS

This study provides the first evidence that, in humans, gp91(phox) is implicated in the modulation of arterial tone.

Calcium-activated potassium channels and endothelial dysfunction: therapeutic options?

The three subtypes of calcium-activated potassium channels (K(Ca)) of large, intermediate and small conductance (BK(Ca), IK(Ca) and SK(Ca)) are present in the vascular wall. In healthy arteries, BK(Ca) channels are preferentially expressed in vascular smooth muscle cells, while IK(Ca) and SK(Ca) are preferentially located in endothelial cells. The activation of endothelial IK(Ca) and SK(Ca) contributes to nitric oxide (NO) generation and is required to elicit endothelium-dependent hyperpolarizations. In the latter responses, the hyperpolarization of the smooth muscle cells is evoked either via electrical coupling through myo-endothelial gap junctions or by potassium ions, which by accumulating in the intercellular space activate the inwardly rectifying potassium channel Kir2.1 and/or the Na(+)/K(+)-ATPase. Additionally, endothelium-derived factors such as cytochrome P450-derived epoxyeicosatrienoic acids and under some circumstances NO, prostacyclin, lipoxygenase products and hydrogen peroxide (H(2)O(2)) hyperpolarize and relax the underlying smooth muscle cells by activating BK(Ca). In contrast, cytochrome P450-derived 20-hydroxyeicosatetraenoic acid and various endothelium-derived contracting factors inhibit BK(Ca). Aging and cardiovascular diseases are associated with endothelial dysfunctions that can involve a decrease in NO bioavailability, alterations of EDHF-mediated responses and/or enhanced production of endothelium-derived contracting factors. Because potassium channels are involved in these endothelium-dependent responses, activation of endothelial and/or smooth muscle K(Ca) could prevent the occurrence of endothelial dysfunction. Therefore, direct activators of these potassium channels or compounds that regulate their activity or their expression may be of some therapeutic interest. Conversely, blockers of IK(Ca) may prevent restenosis and that of BK(Ca) channels sepsis-dependent hypotension.

Manganese superoxide dismutase and aldehyde dehydrogenase deficiency increase mitochondrial oxidative stress and aggravate age-dependent vascular dysfunction

AIMS

Imbalance between pro- and antioxidant species (e.g. during aging) plays a crucial role for vascular function and is associated with oxidative gene regulation and modification. Vascular aging is associated with progressive deterioration of vascular homeostasis leading to reduced relaxation, hypertrophy, and a higher risk of thrombotic events. These effects can be explained by a reduction in free bioavailable nitric oxide that is inactivated by an age-dependent increase in superoxide formation. In the present study, mitochondria as a source of reactive oxygen species (ROS) and the contribution of manganese superoxide dismutase (MnSOD, SOD-2) and aldehyde dehydrogenase (ALDH-2) were investigated.

METHODS AND RESULTS

Age-dependent effects on vascular function were determined in aortas of C57/Bl6 wild-type (WT), ALDH-2(-/-), MnSOD(+/+), and MnSOD(+/-) mice by isometric tension measurements in organ chambers. Mitochondrial ROS formation was measured by luminol (L-012)-enhanced chemiluminescence and 2-hydroxyethidium formation with an HPLC-based assay in isolated heart mitochondria. ROS-mediated mitochondrial DNA (mtDNA) damage was detected by a novel and modified version of the fluorescent-detection alkaline DNA unwinding (FADU) assay. Endothelial dysfunction was observed in aged C57/Bl6 WT mice in parallel to increased mitochondrial ROS formation and oxidative mtDNA damage. In contrast, middle-aged ALDH-2(-/-) mice showed a marked vascular dysfunction that was similar in old ALDH-2(-/-) mice suggesting that ALDH-2 exerts age-dependent vasoprotective effects. Aged MnSOD(+/-) mice showed the most pronounced phenotype such as severely impaired vasorelaxation, highest levels of mitochondrial ROS formation and mtDNA damage.

CONCLUSION

The correlation between mtROS formation and acetylcholine-dependent relaxation revealed that mitochondrial radical formation significantly contributes to age-dependent endothelial dysfunction.

Fluvastatin prevents glutamate-induced blood-brain-barrier disruption in vitro

Glutamate is an important excitatory amino acid in the central nervous system. Under pathological conditions glutamate levels dramatically increase. Aim of the present study was to examine whether the HMG-CoA inhibitor fluvastatin prevents glutamate-induced blood-brain-barrier (BBB) disruption. Measurements of transendothelial electrical resistance (TEER) were performed to analyze BBB integrity in an in vitro co-culture model of brain endothelial and glial cells. Myosin light chain (MLC) phosphorylation was detected by immunohistochemistry, or using the in-cell western technique. Intracellular Ca2+ and reactive oxygen species (ROS) levels were analyzed using the fluorescence dyes Ca-green or DCF. Glutamate induced a time- (1-3 h) and concentration- (0.25-1 mmol/l) dependent decrease of TEER values that was blocked by the NMDA-receptor antagonist MK801, the Ca2+ chelator BAPTA, the NAD(P)H-oxidase inhibitor apocynin and the MLC-kinase inhibitor ML-7. Furthermore we observed a concentration-dependent increase of intracellular Ca2+ and ROS after glutamate application. Glutamate caused an increase of MLC phosphorylation that was antagonized by apocynin, or BAPTA, indicating that Ca2+ and ROS signaling is involved in the activation of the contractile machinery. Fluvastatin (10-25 micromol/l) completely abolished the glutamate-induced barrier disruption and oxidative stress. The BBB-protecting effect of fluvastatin was completely lost if the cells were treated with the nitric oxide (NO) synthase inhibitor L-NMMA (300 micromol/l). In the present study we demonstrated that glutamate-induced BBB disruption involves Ca2+ signalling via NMDA receptors, which is followed by an increased ROS generation by the NAD(P)H-oxidase. This oxidative stress then activates the MLC kinase. Fluvastatin preserves barrier function in a NO-dependent way and reduces glutamate-induced oxidative stress.

Reactive oxygen species participate in acute renal vasoconstrictor responses induced by ETAand ETBreceptors

Reactive oxygen species (ROS) play important roles in renal vasoconstrictor responses to acute and chronic stimulation by angiotensin II and norepinephrine, as well as in long-term effects of endothelin-1 (ET-1). Little is known about participation of ROS in acute vasoconstriction produced by ET-1. We tested the influence of NAD(P)H oxidase inhibition by apocynin [4 mg·kg−1·min−1, infused into the renal artery (ira)] on ETAand ETBreceptor signaling in the renal microcirculation. Both receptors were stimulated by ET-1, ETAreceptors by ET-1 during ETBantagonist BQ-788, and ETBby ETBagonist sarafotoxin 6C. ET-1 (1.5 pmol injected ira) reduced renal blood flow (RBF) 17 ± 4%. Apocynin raised baseline RBF (+10 ± 1%, P < 0.001) and attenuated the ET-1 response to 10 ± 2%, i.e., 35 ± 9% inhibition ( P < 0.05). Apocynin reduced ETA-induced vasoconstriction by 42 ± 12% ( P < 0.05) and that of ETBstimulation by 50 ± 8% ( P < 0.001). During nitric oxide (NO) synthase inhibition ( Nω-nitro-l-arginine methyl ester), apocynin blunted ETA-mediated vasoconstriction by 60 ± 8% ( P < 0.01), whereas its effect on the ETBresponse (by 87 ± 8%, P < 0.001) was even larger without than with NO present ( P < 0.05). The cell-permeable superoxide dismutase mimetic tempol (5 mg·kg−1·min−1ira), which reduces O2−and may elevate H2O2, attenuated ET-1 responses similar to apocynin (by 38 ± 6%, P < 0.01). We conclude that ROS, O2−rather than H2O2, contribute substantially to acute renal vasoconstriction elicited by both ETAand ETBreceptors and to basal renal vasomotor tone in vivo. This physiological constrictor action of ROS does not depend on scavenging of NO. In contrast, scavenging of O2−by NO seems to be more important during ETBstimulation.

Oxidative stress-mediated arterial dysfunction in patients with metabolic syndrome: Effect of ascorbic acid

Arterial dysfunction is a hallmark of early atherosclerosis; however, its behavior in patients with metabolic syndrome (MS) is still unclear. We investigated the role of oxidative stress on ischemia-induced flow-mediated dilatation (FMD) in patients with MS. FMD and oxidative stress, as assessed by serum levels of 8-hydroxy-2-deoxy-2-deoxyguanosine (8-OHdG), were studied in 18 MS and 30 control subjects. Thereafter, in the 18 MS patients, FMD was assessed after iv infusion of 1 g vitamin C or placebo in a randomized, double-blind, crossover design; serial blood samples were taken in peripheral circulation before and after FMD to analyze 8-OHdG. Compared to controls, MS patients had higher 8-OHdG (p<0.001) and lower FMD (p<0.001); 8-OHdG and FMD were inversely correlated (R=-0.74; p<0.01). In MS patients, placebo administration did not change FMD, whereas vitamin C significantly enhanced it (p<0.001). After placebo, ischemia-induced FMD was associated with a significant increase in 8-OHdG (p<0.001), an effect that was counteracted by vitamin C. Vitamin C infusion was associated with an inverse correlation between the changes in FMD and oxidative stress (R=-0.67; p<0.01). The present study shows that arterial dilatation is impaired and that enhanced oxidative stress may play a key role in patients with MS.

Electron paramagnetic resonance (EPR) spin trapping of biological nitric oxide

Nitric oxide (NO) is a free radical species with multiple physiological functions. Because of low concentrations and short half-life of NO, its direct measurement in living tissues remains a difficult task. Electron paramagnetic resonance (EPR) spin trapping is probably one of the best suitable platforms for development of new methods for quantification of biological NO. The most reliable EPR-based approaches developed so far are based on the reaction of NO with various iron complexes, both intrinsic and exogenously applied. This review is focused on the current state and perspectives of EPR spin trapping for experimental and clinical NO biology.

Superoxide mediates acute renal vasoconstriction produced by angiotensin II and catecholamines by a mechanism independent of nitric oxide

NAD(P)H oxidases (NOX) and reactive oxygen species (ROS) are involved in vasoconstriction and vascular remodeling during hypertension produced by chronic angiotensin II (ANG II) infusion. These effects are thought to be mediated largely through superoxide anion (O2−) scavenging of nitric oxide (NO). Little is known about the role of ROS in acute vasoconstrictor responses to agonists. We investigated renal blood flow (RBF) reactivity to ANG II (4 ng), norepinephrine (NE, 20 ng), and α1-adrenergic agonist phenylephrine (PE, 200 ng) injected into the renal artery (ira) of anesthetized Sprague-Dawley rats. The NOX inhibitor apocynin (1–4 mg·kg−1·min−1 ira, 2 min) or the superoxide dismutase mimetic Tempol (1.5–5 mg·kg−1·min−1 ira, 2 min) rapidly increased resting RBF by 8 ± 1% ( P < 0.001) or 3 ± 1% ( P < 0.05), respectively. During NO synthase (NOS) inhibition ( Nω-nitro-l-arginine methyl ester, 25 mg/kg iv), the vasodilation tended to increase (apocynin 13 ± 4%, Tempol 10 ± 1%). During control conditions, both ANG II and NE reduced RBF by 24 ± 4%. Apocynin dose dependently reduced the constriction by up to 44% ( P < 0.05). Similarly, Tempol blocked the acute actions of ANG II and NE by up to 48–49% ( P < 0.05). In other animals, apocynin (4 mg·kg−1·min−1 ira) attenuated vasoconstriction to ANG II, NE, and PE by 46–62% ( P < 0.01). During NOS inhibition, apocynin reduced the reactivity to ANG II and NE by 60–72% ( P < 0.01), and Tempol reduced it by 58–66% ( P < 0.001). We conclude that NOX-derived ROS substantially contribute to basal RBF as well as to signaling of acute renal vasoconstrictor responses to ANG II, NE, and PE in normal rats. These effects are due to O2− rather than H2O2, occur rapidly, and are independent of scavenging of NO.