H2O2 but not O2- elevated by oxidized LDL enhances human aortic smooth muscle cell proliferation

Pterostilbene Attenuates Experimental Atherosclerosis through Restoring Catalase-Mediated Redox Balance in Vascular Smooth Muscle Cells

Atherosclerosis, the major risk of cardiovascular events, is a chronic vascular inflammatory disease. Pterostilbene is a naturally occurring dimethylated analogue of resveratrol and has recently been demonstrated to be beneficial against cardiovascular diseases. However, the underlying mechanisms of pterostilbene on atherosclerosis remain elusive. Experimental atherosclerosis was induced by a high-fat diet (HFD) in apolipoprotein E knockout (ApoE^-/-) mice. Pterostilbene was administered intragastrically for 16 weeks. We found that pterostilbene significantly attenuated thoracic and abdominal atherosclerotic plaque formation in HFD-fed ApoE^-/-mice, accompanied by modulated lipid profiles and reduced production of proinflammatory cytokines (including IL-6, IFN-γ, and TNF-α). In addition, pterostilbene restored vascular redox balance in thoracic and abdominal aorta, evidenced by enhanced catalase (CAT) expression and activities, and decreased malondialdehyde and H₂O₂ production. Notably, pterostilbene specifically induced CAT expression and activities in the vascular smooth muscle cells (VSMCs) of thoracic and abdominal aorta. In vitro, pterostilbene markedly promoted the expression and activity of CAT and decreased ox-low-density lipoprotein (LDL)-mediated VSMC proliferation and intracellular H₂O₂ production, which was abolished by CAT siRNA knockdown or inhibition. Pterostilbene-induced CAT expression was associated with inhibition of Akt, PRAS40, and GSK-3β signaling activation and upregulation of PTEN. Our data clearly demonstrated that pterostilbene exerted an antiatherosclerotic effect by inducing CAT and modulating the VSMC function.

Altered Redox Balance in the Development of Chronic Hypoxia-induced Pulmonary Hypertension

Normally, the pulmonary circulation is maintained in a low-pressure, low-resistance state with little resting tone. Pulmonary arteries are thin-walled and rely heavily on pulmonary arterial distension and recruitment for reducing pulmonary vascular resistance when cardiac output is elevated. Under pathophysiological conditions, however, active vasoconstriction and vascular remodeling lead to enhanced pulmonary vascular resistance and subsequent pulmonary hypertension (PH). Chronic hypoxia is a critical pathological factor associated with the development of PH resulting from airway obstruction (COPD, sleep apnea), diffusion impairment (interstitial lung disease), developmental lung abnormalities, or high altitude exposure (World Health Organization [WHO]; Group III). The rise in pulmonary vascular resistance increases right heart afterload causing right ventricular hypertrophy that can ultimately lead to right heart failure in patients with chronic lung disease. PH is typically characterized by diminished paracrine release of vasodilators, antimitogenic factors, and antithrombotic factors (e.g., nitric oxide and protacyclin) and enhanced production of vasoconstrictors and mitogenic factors (e.g., reactive oxygen species and endothelin-1) from the endothelium and lung parenchyma. In addition, phenotypic changes to pulmonary arterial smooth muscle cells (PASMC), including alterations in Ca²⁺ homeostasis, Ca²⁺ sensitivity, and activation of transcription factors are thought to play prominent roles in the development of both vasoconstrictor and arterial remodeling components of hypoxia-associated PH. These changes in PASMC function are briefly reviewed in Sect. 1 and the influence of altered reactive oxygen species homeostasis on PASMC function discussed in Sects. 2-4.

NADPH oxidase activation contributes to native low-density lipoprotein-induced proliferation of human aortic smooth muscle cells

Elevated plasma concentration of native low-density lipoprotein (nLDL) is associated with vascular smooth muscle cell (VSMC) activation and cardiovascular disease. We investigated the mechanisms of superoxide generation and its contribution to pathophysiological cell proliferation in response to nLDL stimulation. Lucigenin-induced chemiluminescence was used to measure nLDL-induced superoxide production in human aortic smooth muscle cells (hAoSMCs). Superoxide production was increased by nicotinamide adenine dinucleotide phosphate (NADPH) and decreased by NADPH oxidase inhibitors in nLDL-stimulated hAoSMC and hAoSMC homogenates, as well as in prepared membrane fractions. Extracellular signal-regulated kinase 1/2 (Erk1/2), protein kinase C-θ (PKCθ) and protein kinase C-β (PKCβ) were phosphorylated and maximally activated within 3 min of nLDL stimulation. Phosphorylated Erk1/2 mitogen-activated protein kinase, PKCθ and PKCβ stimulated interactions between p47phox and p22phox; these interactions were prevented by MEK and PKC inhibitors (PD98059 and calphostin C, respectively). These inhibitors decreased nLDL-dependent superoxide production and blocked translocation of p47phox to the membrane, as shown by epifluorescence imaging and cellular fractionation experiments. Proliferation assays showed that a small interfering RNA against p47phox, as well as superoxide scavenger and NADPH oxidase inhibitors, blocked nLDL-induced hAoSMC proliferation. The nLDL stimulation in deendothelialized aortic rings from C57BL/6J mice increased dihydroethidine fluorescence and induced p47phox translocation that was blocked by PD98059 or calphostin C. Isolated aortic SMCs from p47phox^−/− mice (mAoSMCs) did not respond to nLDL stimulation. Furthermore, NADPH oxidase 1 (Nox1) was responsible for superoxide generation and cell proliferation in nLDL-stimulated hAoSMCs. These data demonstrated that NADPH oxidase activation contributed to cell proliferation in nLDL-stimulated hAoSMCs.

Sex-based differential regulation of oxidative stress in the vasculature by nitric oxide

Background

Nitric oxide (^•NO) is more effective at inhibiting neointimal hyperplasia following arterial injury in male versus female rodents, though the etiology is unclear. Given that superoxide (O₂^•−) regulates cellular proliferation, and ^•NO regulates superoxide dismutase-1 (SOD-1) in the vasculature, we hypothesized that ^•NO differentially regulates SOD-1 based on sex.

Materials and methods

Male and female vascular smooth muscle cells (VSMC) were harvested from the aortae of Sprague-Dawley rats. O₂^•− levels were quantified by electron paramagnetic resonance (EPR) and HPLC. sod-1 gene expression was assayed by qPCR. SOD-1, SOD-2, and catalase protein levels were detected by Western blot. SOD-1 activity was measured via colorimetric assay. The rat carotid artery injury model was performed on Sprague-Dawley rats ±^•NO treatment and SOD-1 protein levels were examined by Western blot.

Results

In vitro, male VSMC have higher O₂^•− levels and lower SOD − 1 activity at baseline compared to female VSMC (P < 0.05). ^•NO decreased O₂^•− levels and increased SOD − 1 activity in male (P<0.05) but not female VSMC. ^•NO also increased sod− 1 gene expression and SOD − 1 protein levels in male (P<0.05) but not female VSMC. In vivo, SOD-1 levels were 3.7-fold higher in female versus male carotid arteries at baseline. After injury, SOD-1 levels decreased in both sexes, but ^•NO increased SOD-1 levels 3-fold above controls in males, but returned to baseline in females.

Conclusions

Our results provide evidence that regulation of the redox environment at baseline and following exposure to ^•NO is sex-dependent in the vasculature. These data suggest that sex-based differential redox regulation may be one mechanism by which ^•NO is more effective at inhibiting neointimal hyperplasia in male versus female rodents.

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The baseline redox environment in the vascular is sex-dependent.

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Nitric oxide differentially affects the vascular redox environment between the sexes.

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Nitric oxide decreases superoxide (O₂^.) levels, by increasing SOD-1 activity, sod1 gene expression and SOD-1 protein levels in male vascular smooth muscle cells, but not in females.

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Sex-based differential redox regulation may be one mechanism by which is more effective at inhibiting neointimal hyperplasia in male versus female rodents.

Nitric oxide inhibits neointimal hyperplasia following vascular injury via differential, cell-specific modulation of SOD-1 in the arterial wall

Superoxide (O2(•-)) promotes neointimal hyperplasia following arterial injury. Conversely, nitric oxide ((•)NO) inhibits neointimal hyperplasia through various cell-specific mechanisms, including redox regulation. What remains unclear is whether (•)NO exerts cell-specific regulation of the vascular redox environment following arterial injury to inhibit neointimal hyperplasia. Therefore, the aim of the present study was to assess whether (•)NO exerts cell-specific, differential modulation of O2(•-) levels throughout the arterial wall, establish the mechanism of such modulation, and determine if it regulates (•)NO-dependent inhibition of neointimal hyperplasia. In vivo, (•)NO increased superoxide dismutase-1 (SOD-1) levels following carotid artery balloon injury in a rat model. In vitro, (•)NO increased SOD-1 levels in vascular smooth muscle cells (VSMC), but had no effect on SOD-1 in endothelial cells or adventitial fibroblasts. This SOD-1 increase was associated with an increase in sod1 gene expression, increase in SOD-1 activity, and decrease in O2(•-) levels. Lastly, to determine the role of SOD-1 in (•)NO-mediated inhibition of neointimal hyperplasia, we performed the femoral artery wire injury model in wild type and SOD-1 knockout (KO) mice, with and without (•)NO. Interestingly, (•)NO inhibited neointimal hyperplasia only in wild type mice, with no effect in SOD-1 KO mice. In conclusion, these data show the cell-specific modulation of O2(•-) by (•)NO through regulation of SOD-1 in the vasculature, highlighting its importance on the inhibition of neointimal hyperplasia. These results also shed light into the mechanism of (•)NO-dependent redox balance, and suggest a novel VSMC redox target to prevent neointimal hyperplasia.

Improvements of atherosclerosis and hepatic oxidative stress are independent of exercise intensity in LDLr(-/-) mice

BACKGROUND

Cardiovascular diseases are the main causes of death in the Western world and are manifested by atherosclerosis. Depending on its intensity, regular aerobic exercise may be either beneficial or harmful to the atherosclerosis process.

AIM

The aim of this study was to verify the effects of aerobic exercise training of different intensities on the profile of atherosclerotic lesions and serum lipid, and in the hepatic oxidative balance of low-density lipoprotein receptor-deficient (LDLr(-/-)) mice previously developed with atherosclerosis.

METHODS

All animals were submitted to a three-month high-fat and high-cholesterol diet regime. The animals were then randomly divided into no exercise (G1, n=9), low-intensity aerobic exercise (G2, n=10, 8 weeks of treadmill running, 30 min/day(-1) at 8-10 m/min(-1)) and moderate-intensity aerobic exercise (G3, n=10, 8 weeks of treadmill running, 30 min/day(-1) at 10-16 m/min(-1)) groups. Serum total cholesterol (TC), high-density lipoprotein cholesterol (HDL-C) and triglycerides (TG), and oxidative damage (protein carbonyls and lipid hydroperoxides) were measured. The activity of catalase (CAT), superoxide dismutase (SOD) and glutathione peroxidase (GPx) in the liver tissue was assessed.

RESULTS

G2 (0.015 ± 0.005cm(2)) and G3 (0.014 ± 0.001cm(2)) presented lower aortic fat deposition than G1 (0.039 ± 0.005cm(2)). G2 and G3 exhibited higher HDL-C, TG and CAT activity, but lower lipid peroxidation and carbonyl protein than G1. SOD values were higher in G3 than G2 and G1, and GPx was higher in G2 than in G3 and G1.

CONCLUSIONS

Our protocols of low- and moderate-intensity aerobic exercise training (30 min daily for 8 weeks) induced similar benefits in LDLr(-/-) mice with atherosclerosis.

Biochemistry, physiology, and pathophysiology of NADPH oxidases in the cardiovascular system

The NADPH oxidase (Nox) enzymes are critical mediators of cardiovascular physiology and pathophysiology. These proteins are expressed in virtually all cardiovascular cells, and regulate such diverse functions as differentiation, proliferation, apoptosis, senescence, inflammatory responses and oxygen sensing. They target a number of important signaling molecules, including kinases, phosphatases, transcription factors, ion channels, and proteins that regulate the cytoskeleton. Nox enzymes have been implicated in many different cardiovascular pathologies: atherosclerosis, hypertension, cardiac hypertrophy and remodeling, angiogenesis and collateral formation, stroke, and heart failure. In this review, we discuss in detail the biochemistry of Nox enzymes expressed in the cardiovascular system (Nox1, 2, 4, and 5), their roles in cardiovascular cell biology, and their contributions to disease development.

Effect of irreversibly glycated LDL in human vascular smooth muscle cells: lipid loading, oxidative and inflammatory stress

The major complication of diabetes is accelerated atherosclerosis, the progression of which entails complex interactions between the modified low-density lipoproteins (LDL) and the cells of the arterial wall. Advanced glycation end product-modified-LDL (AGE-LDL) that occurs at high rate in diabetes contributes to diabetic atherosclerosis, but the underlying mechanisms are not fully understood. The aim of this study was to assess the direct effect of AGE-LDL on human vascular smooth muscle cells (hSMC) dysfunction. Cultured hSMC incubated (24 hrs) with human AGE-LDL, native LDL (nLDL) or oxidized LDL (oxLDL) were subjected to: (i) quantification of the expression of the receptors for modified LDL and AGE proteins (LRP1, CD36, RAGE) and estimation of lipid loading, (ii) determination of NADPH oxidase activity and reactive oxygen species (ROS) production and (iii) evaluation of the expression of monocyte chemoattractant protein-1 (MCP-1). The results show that exposure of hSMC to AGE-LDL (compared to nLDL) induced: (a) increased NADPH oxidase activity (30%) and ROS production (28%) by up-regulation of NOX1, NOX4, p22phox and p67phox expression, (b) accumulation of intracellular cholesteryl esters, (c) enhanced gene expression of LRP1 (160%) and CD36 (35%), and protein expression of LRP1, CD36 and RAGE, (d) increased MCP-1 gene expression (160%) and protein secretion (300%) and (e) augmented cell proliferation (30%). In conclusion, AGE-LDL activates hSMC (increasing CD36, LRP1, RAGE), inducing a pro-oxidant state (activation of NADPHox), lipid accumulation and a pro-inflammatory state (expression of MCP-1). These results may partly explain the contribution of AGE-LDL and hSMC to the accelerated atherosclerosis in diabetes.

Protandim attenuates intimal hyperplasia in human saphenous veins cultured ex vivo via a catalase-dependent pathway

Human saphenous veins (HSVs) are widely used for bypass grafts despite their relatively low long-term patency. To evaluate the role of reactive oxygen species (ROS) signaling in intima hyperplasia (IH), an early stage pathology of vein-graft disease, and to explore the potential therapeutic effects of up-regulating endogenous antioxidant enzymes, we studied segments of HSV cultured ex vivo in an established ex vivo model of HSV IH. Results showed that HSV cultured ex vivo exhibit an ~3-fold increase in proliferation and ~3.6-fold increase in intimal area relative to freshly isolated HSV. Treatment of HSV during culture with Protandim, a nutritional supplement known to activate Nrf2 and increase the expression of antioxidant enzymes in several in vitro and in vivo models, blocks IH and reduces cellular proliferation to that of freshly isolated HSV. Protandim treatment increased the activity of SOD, HO-1, and catalase 3-, 7-, and 12-fold, respectively, and decreased the levels of superoxide (O(2)(•-)) and the lipid peroxidation product 4-HNE. Blocking catalase activity by cotreating with 3-amino-1,2,4-triazole abrogated the protective effect of Protandim on IH and proliferation. In conclusion, these results suggest that ROS-sensitive signaling mediates the observed IH in cultured HSV and that up-regulation of endogenous antioxidant enzymes can have a protective effect.

A influência da intensidade do exercício físico aeróbio no processo aterosclerótico

A aterosclerose é um processo inflamatório crônico e degenerativo que acomete os vasos, sendo caracterizada pelo acúmulo de lipídeos no espaço subendotelial da íntima, acúmulo de células inflamatórias e elementos fibrosos. A oxidação de LDL-c parece ser o principal evento para o início da aterosclerose. O exercício físico aeróbio melhora os sistemas de defesa orgânicos contra aterosclerose, diminuindo o estresse oxidativo e aumentando a síntese de enzimas antioxidantes; aumento da vasodilatação via óxido nítrico (NO) e óxido nítrico sintase endotelial (eNOS) e diminuição da inflamação sistêmica com produção de citocinas pró-inflamatórias e aumento de fatores anti-inflamatórios. Porém, de maneira aguda, o exercício aeróbio de alta intensidade aumenta o risco de desenvolvimento de eventos cardiovasculares e, de forma crônica, pode atuar negativa ou positivamente na prevenção do processo aterosclerótico.

Erythropoietin increases expression and function of vascular copper- and zinc-containing superoxide dismutase

Previous studies have shown that treatment with erythropoietin (EPO) exerts vascular protective effects. The exact mechanisms responsible for these effects are not completely understood. In the present study, we hypothesized that EPO stimulates expression and activity of copper- and zinc-containing superoxide dismutase (SOD1), thus protecting vascular tissue from oxidative stress induced by excessive concentrations of superoxide anions. EPO treatment of wild-type mice for 2 weeks (1000 U/kg, SC, biweekly) significantly increased aortic expression of SOD1. This effect resulted in a significant reduction of superoxide anion concentrations in aorta of treated mice. The ability of EPO to reduce vascular production of superoxide anions was abolished in SOD1-deficient mice. In a mouse model of wire-induced injury of the common carotid artery, treatment of wild-type mice with EPO prevented pathological remodeling, whereas the vascular effect of EPO was absent in SOD1-deficient mice. Our findings demonstrate that treatment with EPO increases vascular expression of SOD1. This effect appears to be an important molecular mechanism underlying vascular protection by EPO.

NADPH oxidases: functions and pathologies in the vasculature

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

Hemoglobin conjugated with a Band 3 N-terminus derived peptide as an oxygen carrier

A peptide composed of 9 amino acids, 7 residues from N-terminus of human erythrocytic Band 3 protein (AcMEELQDD) followed by cysteine and glutamic acids, was conjugated to hemoglobin (Hb) serving as an allosteric effector for oxygen release. The activated polyethylene glycol (PEG), maleimide-PEG-N-hydroxysuccinimidyl, was used to crosslink Hb with the peptide. The putative conjugation site on Hb for effective enhancement of oxygen release was characterized as Lys-beta95 by liquid chromatography-tandem mass spectrometry. In addition, the conjugated peptide causes a rightward shift of the oxygen dissociation curve as compared to that of its parent Hb when the degree of oxygen saturation is higher than 50%. Furthermore, this conjugated peptide remains effective on lowering Hb's oxygen affinity after Hb polymerization by another PEG crosslinker. The allosteric properties of the peptide-conjugated Hb may provide a new aspect of Hb-based oxygen carriers.

Distinct roles of Nox1 and Nox4 in basal and angiotensin II-stimulated superoxide and hydrogen peroxide production

NADPH oxidases are major sources of superoxide (O2*-) and hydrogen peroxide (H2O2) in vascular cells. Production of these reactive oxygen species (ROS) is essential for cell proliferation and differentiation, while ROS overproduction has been implicated in hypertension and atherosclerosis. It is known that the heme-containing catalytic subunits Nox1 and Nox4 are responsible for oxygen reduction in vascular smooth muscle cells from large arteries. However, the exact mechanism of ROS production by NADPH oxidases is not completely understood. We hypothesized that Nox1 and Nox4 play distinct roles in basal and angiotensin II (AngII)-stimulated production of O2*- and H2O2. Nox1 and Nox4 expression in rat aortic smooth muscle cells (RASMCs) was selectively reduced by treatment with siNox4 or antisense Nox1 adenovirus. Production of O2*- and H2O2 in intact RASMCs was analyzed by dihydroethidium and Amplex Red assay. Activity of NADPH oxidases was measured by NADPH-dependent O2*- and H2O2 production using electron spin resonance (ESR) and 1-hydroxy-3-carboxypyrrolidine (CPH) in the membrane fraction in the absence of cytosolic superoxide dismutase. It was found that production of O2*- by quiescent RASMC NADPH oxidases was five times less than H2O2 production. Stimulation of cells with AngII led to a 2-fold increase of O2*- production by NADPH oxidases, with a small 15 to 30% increase in H2O2 formation. Depletion of Nox4 in RASMCs led to diminished basal H2O2 production, but did not affect O2*- or H2O2 production stimulated by AngII. In contrast, depletion of Nox1 in RASMCs inhibited production of O2*- and AngII-stimulated H2O2 in the membrane fraction and intact cells. Our data suggest that Nox4 produces mainly H2O2, while Nox1 generates mostly O2*- that is later converted to H2O2. Therefore, Nox4 is responsible for basal H2O2 production, while O2*- production in nonstimulated and AngII-stimulated cells depends on Nox1. The difference in the products generated by Nox1 and Nox4 may help to explain the distinct roles of these NADPH oxidases in cell signaling. These findings also provide important insight into the origin of H2O2 in vascular cells, and may partially account for the limited pharmacological effect of antioxidant treatments with O2*- scavengers that do not affect H2O2.

NOX enzymes as novel targets for drug development

The members of the NOX/DUOX family of NADPH oxidases mediate such physiologic functions as host defense, cell signaling, and thyroid hormone biosynthesis through the generation of reactive oxygen species (ROS), including superoxide anion and hydrogen peroxide. Moreover, ROS are involved in a broad range of fundamental biochemical and cellular processes, and data accumulated in recent years indicate that the NOX enzymes comprise one of the most important biological sources of ROS. Given the high biochemical reactivity of ROS, it is not surprising that they have been implicated in a wide variety of pathologies and diseases. Prominent among the settings that feature ROS-mediated tissue injury are disorders associated with inflammation, aging, and progressive degenerative changes in cells and organ systems, and it appears that essentially no organ system is exempt. Among the disorders currently believed to be mediated at least in part by NOX-derived ROS are hypertension, aortic aneurysm, myocardial infarction (and other ischemia-reperfusion disorders), pulmonary fibrosis and hypertension, amyotropic lateral sclerosis, Alzheimer's disease, Parkinson's disease, ischemic stroke, diabetic nephropathy, and renal cell carcinoma. Several small-molecule and peptide inhibitors of the NOX enzymes have been useful in experimental studies, but issues of specificity, potency, and toxicity militate against any of the existing published compounds as candidates for drug development. Given the broad array of disease targets documented in recent work, the time is here for vigorous efforts to develop clinically useful inhibitors of the NOX enzymes. As most (though not all) NOX-related diseases appear to be mediated by a single member of the NOX family, agents with isoform specificity will be preferred, although broadly active NOX inhibitors may prove to be useful in some settings.