Impaired Nitric Oxide Signaling Research Articles

Arginase II Inhibitory Activity of Phenolic Compounds from Saururus chinensis

Pukyoung National University, Busan 608-737, KoreaReceived April 1, 2012, Accepted May 26, 2012Key Words : Saururus chinensis , Saururaceae, Lignan, ArginaseThe endothelium plays a central role in overall vascularhomeostasis by regulating vasoreactivity, platelet activation,leukocyte adhesion, and smooth muscle cell proliferationand migration. Endothelial nitric oxide (NO), an importantvasoprotective molecule, is a major modulator of theseeffects, and impaired NO signaling associated with endo-thelial function is considered as an early marker of theatherogenic process.

Role of neural NO synthase (nNOS) uncoupling in the dysfunctional nitrergic vasorelaxation of penile arteries from insulin-resistant obese Zucker rats.

ObjectiveErectile dysfunction (ED) is considered as an early sign of vascular disease due to its high prevalence in patients with cardiovascular risk factors. Endothelial and neural dysfunction involving nitric oxide (NO) are usually implicated in the pathophysiology of the diabetic ED, but the underlying mechanisms are unclear. The present study assessed the role of oxidative stress in the dysfunctional neural vasodilator responses of penile arteries in the obese Zucker rat (OZR), an experimental model of metabolic syndrome/prediabetes.Methods and ResultsElectrical field stimulation (EFS) under non-adrenergic non-cholinergic (NANC) conditions evoked relaxations that were significantly reduced in penile arteries of OZR compared with those of lean Zucker rats (LZR). Blockade of NO synthase (NOS) inhibited neural relaxations in both LZR and OZR, while saturating concentrations of the NOS substrate L-arginine reversed the inhibition and restored relaxations in OZR to levels in arteries from LZR. nNOS expression was unchanged in arteries from OZR compared to LZR and nNOS selective inhibition decreased the EFS relaxations in LZR but not in OZR, while endothelium removal did not alter these responses in either strain. Superoxide anion production and nitro-tyrosine immunostaining were elevated in the erectile tissue from OZR. Treatment with the NADPH oxidase inhibitor apocynin or acute incubation with the NOS cofactor tetrahydrobiopterin (BH4) restored neural relaxations in OZR to levels in control arteries, while inhibition of the enzyme of BH4 synthesis GTP-cyclohydrolase (GCH) reduced neural relaxations in arteries from LZR but not OZR. The NO donor SNAP induced decreases in intracellular calcium that were impaired in arteries from OZR compared to controls.ConclusionsThe present study demonstrates nitrergic dysfunction and impaired neural NO signalling due to oxidative stress and nNOS uncoupling in penile arteries under conditions of insulin resistance. This dysfunction likely contributes to the metabolic syndrome-associated ED, along with the endothelial dysfunction also involving altered NO signalling.

Immunohistochemical evidence for impaired nitric oxide signaling of the locus coeruleus in bipolar disorder

Nitric oxide (NO) is an important messenger in brain signaling and influences the balance of monoaminergic and glutamatergic neurotransmission. Alterations of NO signaling are thought to play a crucial role in the pathophysiology of mood disorders. The locus coeruleus (LC) comprises the largest group of norepinephrine containing neurons in the mammalian brain. These norepinephrinergic LC neurons are able to generate NO. Immunohistochemical staining of neuronal nitric oxide synthase (nNOS)-immunoreactive (ir) neurons was performed in the LC of the brains of 10 patients with bipolar I disorder (BD), 8 patients with major depressive disorder (MDD) and 16 control cases (C). Analysis of variance (ANOVA) revealed significant differences between the groups, and post hoc tests indicated a lower nNOS-ir neuron number in bipolar patients than in controls (left −34%, right −17%). The total number of Nissl-stained LC neurons showed no changes between major depressive disorder patients, bipolar patients and controls. In the mood disorder patients, illness duration correlated negatively with nNOS-ir neuronal number (r=−0.74, p=0.002). A reduced relative amount of NO in the LC of bipolar patients is likely a result of a compensation for increased glutamatergic activity. The current data on nNOS suggest a dysregulation of the nitrergic system in bipolar disorder. Future studies may clarify the potential role of glial cells in the context of the described nNOS deficit.

Soluble Guanylate Cyclase as an Emerging Therapeutic Target in Cardiopulmonary Disease

Soluble guanylate cyclase (sGC), a key enzyme of the nitric oxide (NO) signaling pathway, is attracting rapidly growing interest as a therapeutic target in cardiopulmonary disease, with several sGC agonists currently in clinical development. On binding of NO to a prosthetic heme group on sGC, the enzyme catalyzes synthesis of the second messenger cGMP, which produces vasorelaxation and inhibits smooth muscle proliferation, leukocyte recruitment, and platelet aggregation through a number of downstream mechanisms.1,2 Impaired NO and cGMP signaling has been implicated in the pathogenesis of cardiovascular disease, including systemic arterial and pulmonary hypertension (PH), coronary artery disease, peripheral vascular disease (including erectile dysfunction), and atherosclerosis.1,3,–,5 Organic nitrates that target the NO signaling pathway have been used to treat cardiovascular disease for >150 years. More recently, gaseous NO administered by inhalation has been approved for the treatment of persistent PH of the newborn.3,6 These agents nonetheless have several important limitations. Cardiovascular disease is associated with resistance to NO and organic nitrates.7 This may be due to the oxidative stress–induced alteration of the redox state of the prosthetic heme on sGC (from ferrous to ferric) that weakens the binding of heme to the enzyme and renders sGC unresponsive to NO.1,8 Furthermore, the long-term efficacy of organic nitrates is limited by the development of tolerance.9 Nitric oxide may also have numerous cytotoxic effects, mostly attributed to the reactive oxidant peroxynitrite (formed from the diffusion-controlled reaction of NO with superoxide).3,10 Peroxynitrite interacts with proteins and lipids, altering cellular signaling, disrupting mitochondrial function, and damaging DNA, which can eventually culminate in cellular dysfunction and/or death.3 Because the beneficial effects of NO appear to be …

Cellular Senescence, Vascular Disease, and Aging

> You must remember this, > > A kiss is just a kiss, > > A sigh is just a sigh, > > The fundamental things apply, > > As time goes by. “As Time Goes By,” by Herman Hupfeld, Casablanca (1942)1 The increasing prevalence of older-age people in our society represents the culmination of centuries of medical, scientific, and social endeavors. At least in Western society, now relatively freed from pestilence, abject poverty, gross malnutrition, and polluted water and food sources, an increasing proportion of the population can expect to make it to old age. However, although US age-adjusted death rates from cardiovascular disease, coronary heart disease, and stroke continue to fall, a disproportionate number of people who reach old age (≈80% of people aged ≥80 years) suffer from these diseases.1a In this 2-part review, we consider important pathobiological changes that occur with aging in the cardiovascular system, exploring promising areas of recent scientific progress and novel insights that may be translatable into targeted clinical strategies to help to alleviate the excess morbidity and mortality imposed by cardiovascular disease in the elderly. In this second installment, we focus specifically on vascular disease states of the elderly, including systolic hypertension, vascular calcification, and dementia, and we review relevant basic and clinical discoveries that further elucidate these conditions. ### The Elderly Vascular Phenotype Aging is associated with various changes in the vascular system at differing structural and functional levels. At the macroscopic level, an increase in arterial lumen size and arterial wall thickening, mainly of the intima, are observed.2 In addition, increased vascular calcification and a generalized stiffening of the arterial tree lead to increased arterial wave reflectance, increased systolic blood pressure, decreased diastolic blood pressure, and a widened pulse pressure. An interesting aspect of vascular biology in which significant inroads have been made is our understanding of pulse wave velocity, which …

Biomarkers of Oxidative Stress in Heart Failure

Oxidative stress is the relative excess of reactive oxygen species (ROS) versus endogenous defense mechanisms. Abundant evidence has demonstrated the role of ROS, along with reactive nitrogen species (RNS), in the pathophysiology of cardiovascular disease, including heart failure. Many biomarkers of oxidative stress have been studied as surrogates of oxidative damage. Recently, markers of impaired nitric oxide signaling have also been identified. Many biomarkers have been associated with prognosis and mortality, and some may even be modified by therapy. However, the clinical utility is limited by less than optimal standardization techniques and the lack of sufficient large-sized, multimarker prospective trials.

Role of Aging Versus the Loss of Estrogens in the Reduction in Vascular Function in Female Rats

Although aging is known to lead to increased vascular stiffness, the role of estrogens in the prevention of age-related changes in the vasculature remains to be elucidated. To address this, we measured vascular function in the thoracic aorta in adult and old ovariectomized (ovx) rats with and without immediate 17beta-estradiol (E2) replacement. In addition, aortic mRNA and protein were analyzed for proteins known to be involved in vasorelaxation. Aging in combination with the loss of estrogens led to decreased vasorelaxation in response to acetylcholine and sodium nitroprusside, indicating either smooth muscle dysfunction and/or increased fibrosis. Loss of estrogens led to increased vascular tension in response to phenylephrine, which could be partially restored by E2 replacement. Levels of endothelial nitric oxide synthase and inducible nitric oxide synthase did not differ among the groups, nor did total nitrite plus nitrate levels. Old ovx exhibited decreased expression of both the alpha and beta-subunits of soluble guanylyl cyclase (sGC) and had impaired nitric oxide signaling in the vascular smooth muscle. Immediate E2 replacement in the aged ovx prevented both the impairment in vasorelaxation, and the decreased sGC receptor expression and abnormal sGC signaling within the vascular smooth muscle.

Coronary microvascular dysfunction in the setting of chronic ischemia is independent of arginase activity

Background Chronic myocardial ischemia induces endothelial dysfunction in the coronary microcirculation resulting in impaired nitric oxide signaling. This dysfunction has wide-ranging effects including impaired tissue perfusion and is implicated in impairment of the angiogenic process in settings of endothelial dysfunction. We hypothesized chronic myocardial ischemia results in increased activity of Arginase I, diminishing bioavailability of l-arginine, the substrate for endothelial nitric oxide production. Methods Chronic myocardial ischemia was induced for 7-weeks in 6 Yucatan miniswine utilizing an ameroid constrictor placed around the left circumflex coronary artery. Ischemic and non-ischemic tissue was harvested at the 7-week time point. Expression of Arginase I, eNOS, and phospho-eNOS was assessed utilizing Western blotting. Arginase activity was measured. Immunofluorescent staining assessed expression of Arginase I between ischemic and non-ischemic microvessels. Coronary microvascular relaxation studies were performed. Results Arginase I expression, activity, and staining was similar between ischemic and non-ischemic territories. Significant impairments in coronary microvascular relaxation were observed in microvessels from the ischemic territory in response to endothelial-dependent agents but remained similar between territories in response to endothelial independent agents. Regression analysis between arginase activity and degree of microvascular vasorelaxation demonstrated no significant correlation. Conclusions Coronary microvascular dysfunction in the setting of chronic myocardial ischemia occurs independently of Arginase I activity and expression. Alternative therapeutic strategies focusing away from arginine may be need for the treatment of this dysfunction.

NO-dependent blood pressure regulation in RGS2-deficient mice

The regulator of G protein signaling (RGS) 2, a GTPase-activating protein, is activated via the nitric oxide (NO)-cGMP pathway and thereby may influence blood pressure regulation. To test that notion, we measured mean arterial blood pressure (MAP) and heart rate (HR) with telemetry in N(omega)-nitro-l-arginine methyl ester (l-NAME, 5 mg l-NAME/10 ml tap water)-treated RGS2-deficient (RGS2(-/-)) and RGS2-sufficient (RGS2(+/+)) mice and assessed autonomic function. Without l-NAME, RGS2(-/-) mice showed during day and night a similar increase of MAP compared with controls. l-NAME treatment increased MAP in both strains. nNOS is involved in this l-NAME-dependent blood pressure increase, since 7-nitroindazole increased MAP by 8 and 9 mmHg (P < 0.05) in both strains. The l-NAME-induced MAP increase of 14-15 mmHg during night was similar in both strains. However, the l-NAME-induced MAP increase during the day was smaller in RGS2(-/-) than in RGS2(+/+) (11 +/- 1 vs. 17 +/- 2 mmHg; P < 0.05). Urinary norepinephrine and epinephrine excretion was higher in RGS2(-/-) than in RGS2(+/+) mice. The MAP decrease after prazosin was more pronounced in l-NAME-RGS2(-/-). HR variability parameters [root mean square of successive differences (RMSSD), low-frequency (LF) power, and high-frequency (HF) power] and baroreflex sensitivity were increased in RGS2(-/-). Atropine and atropine plus metoprolol markedly reduced RMSSD, LF, and HF. Our data suggest an interaction between RGS2 and the NO-cGMP pathway. The blunted l-NAME response in RGS2(-/-) during the day suggests impaired NO signaling. The MAP increases during the active phase in RGS2(-/-) mice may be related to central sympathetic activation and increased vascular adrenergic responsiveness.

Even Flow

The appreciation that biomechanical forces induce signaling responses that regulate vascular tone and inflammatory responses has had a paradigm-shifting effect on our understanding of vascular biology. Endothelial cells are constantly exposed to rheologically imposed forces that vary due to vascular anatomic features and hemodynamic parameters, and of course shear fluctuates cyclically during the cardiac cycle. Simple laminar flow and high shear forces elicit a cellular response characterized by quiescence and alignment of endothelial cells in the direction of fluid flow, whereas disturbed flow and low shear forces induce an inflammatory procoagulant phenotype. These cellular effects are mediated through well-defined signaling pathways and gene expression responses. The cellular sensors or receptors for shear forces are incompletely characterized, but detection of stress seems to depend on the transmission of forces to points of cell–matrix and cell–cell attachment and requires specific conformational activation of integrins.1 From a pathophysiological perspective, disturbed laminar flow has been linked to inflammatory responses that initiate atheroma formation and elicit plaque instability. It is also generally accepted that flow is required for some aspects of vascular remodeling during vascular development and in adult angiogenic responses; however, specific roles for flow in vascular developmental programs have been incompletely characterized. See page 1817 Two recent reports, including one published in this issue of Arteriosclerosis, Thrombosis, and …

Impaired NO signaling in small pulmonary arteries of chronically hypoxic newborn piglets.

We performed studies to determine whether chronic hypoxia impairs nitric oxide (NO) signaling in resistance level pulmonary arteries (PAs) of newborn piglets. Piglets were maintained in room air (control) or hypoxia (11% O(2)) for either 3 (shorter exposure) or 10 (longer exposure) days. Responses of PAs to a nonselective NO synthase (NOS) antagonist, N(omega)-nitro-L-arginine methylester (L-NAME), a NOS-2-selective antagonist, aminoguanidine, and 7-nitroindazole, a NOS-1-selective antagonist, were measured. Levels of NOS isoforms and of two proteins involved in NOS signaling, heat shock protein (HSP) 90 and caveolin-1, were assessed in PA homogenates. PAs from all groups constricted to L-NAME but not to aminoguanidine or 7-nitroindazole. The magnitude of constriction to L-NAME was similar for PAs from control and hypoxic piglets of the shorter exposure period but was diminished for PAs from hypoxic compared with control piglets of the longer exposure period. NOS-3, HSP90, and caveolin-1 levels were similar in hypoxic and control PAs. These findings indicate that NOS-3, but not-NOS 2 or NOS-1, is involved with basal NO production in PAs from both control and hypoxic piglets. After 10 days of hypoxia, NO function is impaired in PAs despite preserved levels of NOS-3, HSP90, and caveolin-1. The development of NOS-3 dysfunction in resistance level PAs may contribute to the progression of chronic hypoxia-induced pulmonary hypertension in newborn piglets.