Inhibitory actions of diphenyleneiodonium on endothelium-dependent vasodilatations in vitro and in vivo

N-Acetylcysteine and Safranal prevented the brain damage induced by hyperthyroidism in adult male rats

Background: Hyperthyroidism is associated with impairment in the neurotransmission and severe tissue damage in the brain. The present study explored the potential deleterious effects of experimentally-induced hyperthyroidism on the neurotransmitters, oxidative homeostasis, apoptosis and DNA fragmentation in cerebral cortex, thalamus & hypothalamus, and hippocampus in rats.Methods and Results: The ameliorative effects of N-acetylcysteine (NAC; 50 mg/kg, oral) and safranal (50 mg/kg, intraperitoneal) against hyperthyroidism (L-T4 500 µg/kg, subcutaneous) were investigated. All treatments continued daily over three weeks. Hyperthyroidism was manifested by significant elevations in serum fT3 and fT4 levels and a decline in serum TSH level and body weight. It was also characterized by significant elevations in the levels of dopamine, serotonin, and 5-hydroxyindole acetic acid, and monoamine oxidase activity to varying degrees in the brain regions examined and a significant reduction in norepinephrine in hippocampus only. Hyperthyroidism resulted in a significant oxidative stress in brain typified by elevations in malondialdehyde and nitric oxide content and reductions in glutathione level and SOD and catalase activities. This led to elevations in Caspases 9 and 3 and a reduction in Bcl2 resulting in DNA damage and confirmed by the histopathology of brain tissue. The administration of NAC or safranal with L-T4 prevented these deleterious effects by reducing the oxidative load and improving the brain antioxidant status.Conclusions: Hyperthyroidism disrupted the neurotransmitters in the brain which aggravated the oxidative stress and resulted in apoptosis. N-Acetylcysteine and safranal prevented these deleterious effects by enhancing the poor antioxidant milieu of the brain.

Mitochondrial angiotensin receptors in dopaminergic neurons. Role in cell protection and aging-related vulnerability to neurodegeneration

The renin–angiotensin system (RAS) was initially considered as a circulating humoral system controlling blood pressure, being kidney the key control organ. In addition to the ‘classical' humoral RAS, a second level in RAS, local or tissular RAS, has been identified in a variety of tissues, in which local RAS play a key role in degenerative and aging-related diseases. The local brain RAS plays a major role in brain function and neurodegeneration. It is normally assumed that the effects are mediated by the cell-surface-specific G-protein-coupled angiotensin type 1 and 2 receptors (AT1 and AT2). A combination of in vivo (rats, wild-type mice and knockout mice) and in vitro (primary mesencephalic cultures, dopaminergic neuron cell line cultures) experimental approaches (confocal microscopy, electron microscopy, laser capture microdissection, transfection of fluorescent-tagged receptors, treatments with fluorescent angiotensin, western blot, polymerase chain reaction, HPLC, mitochondrial respirometry and other functional assays) were used in the present study. We report the discovery of AT1 and AT2 receptors in brain mitochondria, particularly mitochondria of dopaminergic neurons. Activation of AT1 receptors in mitochondria regulates superoxide production, via Nox4, and increases respiration. Mitochondrial AT2 receptors are much more abundant and increase after treatment of cells with oxidative stress inducers, and produce, via nitric oxide, a decrease in mitochondrial respiration. Mitochondria from the nigral region of aged rats displayed altered expression of AT1 and AT2 receptors. AT2-mediated regulation of mitochondrial respiration represents an unrecognized primary line of defence against oxidative stress, which may be particularly important in neurons with increased levels of oxidative stress such as dopaminergic neurons. Altered expression of AT1 and AT2 receptors with aging may induce mitochondrial dysfunction, the main risk factor for neurodegeneration.

The NADPH oxidase inhibitor DPI can abolish hypoxia-induced apoptosis of human kidney proximal tubular epithelial cells through Bcl2 up-regulation via ERK activation without ROS reduction

AIMS

Ischemia/reperfusion injury (IRI), resulting from hypoxic damage within a graft, is the leading cause of cell death and graft rejection. In this study, we investigated whether a HIF-1α inhibitor or various antioxidants were able to prevent ischemic injury in a cellular model in which experimental hypoxia was induced using CoCl2.

MAIN METHODS

The ischemic injury induced in HK-2 cells by CoCl2 was validated by increased reactive oxygen species (ROS) production, reduced cell viability, and increased apoptosis at different times and doses. The preventative effects of various anti-oxidants on ischemic injury were evaluated using ROS levels, cell viability, and apoptosis. The MAPK phosphorylation status and Bcl2/Bax expression levels were evaluated after treatment with various antioxidants.

KEY FINDINGS

The increase in ROS induced by hypoxia was significantly inhibited by NAC and CAPE, but not by any other treatment. The reduction in cell viability induced by CoCl2 was significantly inhibited by NAC and DPI, but not by any other treatment. The apoptosis induced by CoCl2 was also significantly inhibited by NAC and DPI, but not by any other treatment. Moreover, NAC and DPI prevented CoCl2-induced apoptosis in HK-2 cells in a dose- and time-dependent manner. Treatment of CoCl2 and HK-2 cells treated with DPI, but not NAC, significantly induced ERK activation and Bcl2 expression. NAC and DPI treatment prevented the apoptosis of cells cultured under hypoxic conditions.

SIGNIFICANCE

Our results suggest that DPI should be investigated further as a novel protective agent that prevents kidney ischemia.

ATP modulates acute inflammation in vivo through dual oxidase 1-derived H2O2 production and NF-κB activation

Dual oxidase 1 (Duox1) is the NADPH oxidase responsible for the H2O2 gradient formed in tissues after injury to trigger the early recruitment of leukocytes. Little is known about the signals that modulate H2O2 release from DUOX1 and whether the H2O2 gradient can orchestrate the inflammatory response in vivo. In this study, we report on a dominant-negative form of zebrafish Duox1 that is able to inhibit endogenous Duox1 activity, H2O2 release and leukocyte recruitment after tissue injury, with none of the side effects associated with morpholino-mediated Duox1 knockdown. Using this specific tool, we found that ATP release following tissue injury activates purinergic P2Y receptors, and modulates Duox1 activity through phospholipase C (PLC) and intracellular calcium signaling in vivo. Furthermore, Duox1-derived H2O2 is able to trigger the NF-κB inflammatory signaling pathway. These data reveal that extracellular ATP acting as an early danger signal is responsible for the activation of Duox1 via a P2YR/PLC/Ca(2+) signaling pathway and the production of H2O2, which, in turn, is able to modulate in vivo not only the early recruitment of leukocytes to the wound but also the inflammatory response through activation of the NF-κB signaling pathway.

NO-β-catenin crosstalk modulates primitive streak formation prior to embryonic stem cell osteogenic differentiation

Nitric oxide (NO) has been shown to play a crucial role in bone formation in vivo. We sought to determine the temporal effect of NO on murine embryonic stem cells (ESCs) under culture conditions that promote osteogenesis. Expression profiles of NO pathway members and osteoblast-specific markers were analyzed using appropriate assays. We found that NO was supportive of osteogenesis specifically during an early phase of in vitro development (days 3-5). Furthermore, ESCs stably overexpressing the inducible NO synthase showed accelerated and enhanced osteogenesis in vitro and in bone explant cultures. To determine the role of NO in early lineage commitment, a stage in ESC differentiation equivalent to primitive streak formation in vivo, ESCs were transfected with a T-brachyury-GFP reporter. Expression levels of T-brachyury and one of its upstream regulators, β-catenin, the major effector in the canonical Wnt pathway, were responsive to NO levels in differentiating primitive streak-like cells. Our results indicate that NO may be involved in early differentiation through regulation of β-catenin and T-brachyury, controlling the specification of primitive-streak-like cells, which may continue through differentiation to later become osteoblasts.

TRPM7 activates m-calpain by stress-dependent stimulation of p38 MAPK and c-Jun N-terminal kinase

TRPM7 is a Ca(2)(+)-permeant and Mg(2)(+)-permeant ion channel in possession of its own kinase domain. In a previous study, we showed that overexpression of the channel-kinase in HEK-293 cells produced cell rounding and loss of adhesion, which was dependent on the Ca(2+)-dependent protease m-calpain. The TRPM7-elicited change in cell morphology was channel-dependent and occurred without any significant increase in cytosolic Ca(2+). Here we demonstrate that overexpression of TRPM7 increased levels of cellular reactive oxygen species (ROS) and nitric oxide, causing the activation of p38 mitogen-activated protein kinase (MAPK) and c-Jun N-terminal kinase (JNK). Application of inhibitors of p38 MAPK and JNK blocked TRPM7-induced cell rounding and activation of m-calpain, without affecting the phosphorylation state of the protease. Overexpression of TRPM7 increased intracellular Mg(2+); however, when the concentration of either external Ca(2+) or Mg(2+) was increased to favor the permeation of one divalent cation over the other, a similar increase in cell rounding and calpain activity was detected, indicating that TRPM7-mediated activation of m-calpain is not dependent on the nature of the divalent conducted by the channel. Application of inhibitors of nitric oxide synthase and mitochondrial-derived ROS reduced TRPM7-induced increases in nitric oxide and ROS production, blocked the change in cell morphology, and reduced cellular calpain activity. Collectively, our data reveal that excessive TRPM7 channel activity causes oxidative and nitrosative stresses, producing cell rounding mediated by p38 MAPK/JNK-dependent activation of m-calpain.

Extracellular matrix modifications at fertilization: regulation of dityrosine crosslinking by transamidation

Fertilization is accompanied by the construction of an extracellular matrix that protects the new zygote. In sea urchins, this structure is built from glycoproteins residing at the egg surface and in secretory vesicles at the egg cortex. Four enzymatic activities are required for the transformation of these proteins into the mechanically and chemically resilient fertilization envelope: proteolysis, transamidation, NADPH-dependent oxidation and peroxidation. Here, we identify the Strongylocentrotus purpuratus enzymes responsible for the formation of epsilon(gamma-glutamyl)lysine crosslinks (transamidation). We find that these two transglutaminases are activated by local acidification and act on specific substrates within the fertilization envelope (including ovoperoxidase, rendezvin and SFE9). Surprisingly, these enzymes also regulate dityrosine crosslinking both by direct conjugation of ovoperoxidase and by modulating hydrogen peroxide production. Together, these results emphasize how transglutaminases can coordinate the activities of other enzymes during extracellular matrix transmogrifications.

Nitric oxide (NO) increase at fertilization in sea urchin eggs upregulates fertilization envelope hardening

Previous studies indicate that the nitric oxide (NO) increase at fertilization in sea urchin eggs is Ca(2+)-dependent and attributed to the late Ca(2+) rise. However, its role in fertilization still remains unclear. Simultaneous measurements of the activation current, by a single electrode voltage clamp, and NO, using the NO indicator DAF-FM, showed that the NO increase occurred at the time of peak current (t(p)) which corresponds to peak [Ca(2+)](i), suggesting that NO is not related to any other ionic changes besides [Ca(2+)](i). We measured O(2) consumption by a polarographic method to examine whether NO regulated a respiratory burst for protection as reported in other biological systems. Our results suggested NO increased O(2) consumption. The fluorescence of reduced pyridine nucleotides, NAD(P)H was measured in controls and when the NO increase was eliminated by PTIO, a NO scavenger. Surprisingly, PTIO decreased the rate of the fluorescence change and the late phase of increase in NAD(P)H was eliminated. PTIO also suppressed the production of H(2)O(2) and caused weak and high fertilization envelope (FE). Our results suggest that NO increase upregulates NAD(P)H and H(2)O(2) production and consolidates FE hardening by H(2)O(2).

NADPH oxidase inhibitors: new antihypertensive agents?

NADPH oxidases have recently been shown to contribute to the pathogenesis of hypertension. The development of specific inhibitors of these enzymes has focused attention on their potential therapeutic use in hypertensive disease. Two of the most specific inhibitors, gp91ds-tat and apocynin, have been shown to decrease blood pressure in animal models of hypertension. Other inhibitors, including diphenylene iodonium, aminoethyl benzenesulfono fluoride, S17834, PR39, protein kinase C inhibitors, and VAS2870, have shown promise in vitro, but their in vivo specificity, pharmacokinetics, and effectiveness in hypertension remains to be determined. Of importance, the currently available antihypertensive agents angiotensin-converting enzyme inhibitors and angiotensin receptor blockers also effectively inhibit NADPH oxidase activation. Similarly, the cholesterol-lowering agents, statins, have been shown to attenuate NADPH oxidase activation. Although, antioxidants act to scavenge the reactive oxygen species produced by these enzymes, their effectiveness is limited. Targeting NADPH homologues may have a distinct advantage over current therapies because it would specifically prevent the pathophysiological formation of reactive oxygen species that contributes to hypertension.

Flow-induced cerebral vasodilatation in vivo involves activation of phosphatidylinositol-3 kinase, NADPH-oxidase, and nitric oxide synthase

Reactive oxygen species (ROS) such as superoxide (O2*-) and hydrogen peroxide (H2O2) are known cerebral vasodilators. A major source of vascular ROS is the flavin-containing enzyme nicotinamide adenine dinucleotide phosphate (NADPH)-oxidase. Activation of NADPH-oxidase leads to dilatation of the basilar artery in vivo via production of H2O2, but the endogenous stimuli for this unique vasodilator mechanism are unknown. Shear stress is known to activate both NADPH-oxidase and phosphatidylinositol-3 kinase (PI3-K) in cultured cells. Hence, this study used a cranial window preparation in anesthetized rats to investigate whether increased intraluminal blood flow could induce cerebral vasodilatation via the activation of NADPH-oxidase and/or PI3-K. Bilateral occlusion of the common carotid arteries to increase basilar artery blood flow caused reproducible, reversible vasodilatation. Topical treatment of the basilar artery with the NADPH-oxidase inhibitor diphenyleneiodonium (DPI) (0.5 and 5 micromol/L) inhibited flow-induced dilatation by up to 50% without affecting dilator responses to acetylcholine. Treatment with the H2O2 scavenger, catalase similarly attenuated flow-induced dilatation, suggesting a role for NADPH-oxidase-derived H2O2 in this response. The nitric oxide synthase inhibitor N(G)-nitro-L-arginine methyl ester (L-NAME) partially reduced flow-induced dilatation, and combined treatment with a ROS inhibitor (DPI or catalase) and L-NAME caused a greater reduction in flow-induced dilatation than that seen with any of these inhibitors alone. Flow-induced dilatation was also markedly inhibited by the PI3-K inhibitor, wortmannin. Increased O2*- production in the endothelium of the basilar artery during acute increases in blood flow was confirmed using dihydroethidium. Thus, flow-induced cerebral vasodilatation in vivo involves production of ROS and nitric oxide, and is dependent on PI3-K activation.

Reactive oxygen species and Udx1 during early sea urchin development

Sea urchin fertilization is marked by a massive conversion of molecular oxygen to hydrogen peroxide by a sea urchin dual oxidase, Udx1. This enzyme is essential for completing the physical block to polyspermy. Yet, its expression is maintained during development, as indicated by the presence of both Udx1 mRNA and Udx1 protein enriched at the surface of all non-mesenchymal blastomeres. When hydrogen peroxide synthesis by Udx1 is inhibited, either pharmacologically or by specific antibody injection, cleavage is delayed. Application of exogenous hydrogen peroxide, however, partially rescues a fraction of these defective embryos. We also report an unequal distribution of reactive oxygen species between sister blastomeres during early cleavage stages, suggesting a functional role for Udx1 in intracellular signaling.

Nitric oxide dynamics and endothelial dysfunction in type II model of genetic diabetes

Although diabetes is a major risk factor for vascular diseases, e.g., hypertension and atherosclerosis, mechanisms that underlie the "risky" aspects of diabetes remain obscure. The current study is intended to examine the notion that diabetic endothelial dysfunction stems from a heightened state of oxidative stress induced by an imbalance between vascular production and scavenging of reactive oxygen/nitrogen species. Goto-Kakizaki (GK) rats were used as a genetic animal model for non-obese type II diabetes. Nitric oxide (NO) bioavailability and O2- generation in aortic tissues of GK rats were assessed using the Griess reaction and a lucigenin-chemiluminescence-based technique, respectively. Organ chamber-based isometric tension studies revealed that aortas from GK rats had impaired relaxation responses to acetylcholine whereas a rightward shift in the dose-response curve was noticed in the endothelium-independent vasorelaxation exerted by the NO donor sodium nitroprusside. An enhancement in superoxide (O2-) production and a diminuation in NO bioavailability were evident in aortic tissues of GK diabetic rats. Immunoblotting and high-performance liquid chromatography (HPLC)-based techniques revealed, respectively, that the above inverse relationship between O2- and NO was associated with a marked increase in the protein expression of nitric oxide synthase (eNOS) and a decrease in the level of its cofactor tetrahydrobiopterin (BH4) in diabetic aortas. Endothelial denudation by rubbing or the addition of pharmacological inhibitors of eNOS (e.g. N(omega)-nitro-L-arginine methyl ester (L-NAME)), and NAD(P)H oxidase (e.g. diphenyleneiodonium, apocynin) strikingly reduced the diabetes-induced enhancement in vascular O2- production. Aortic contents of key markers of oxidative stress (isoprostane F2alpha III, protein-bound carbonyls, nitrosylated protein) in connection with the protein expression of superoxide generating enzyme NAD(P)H oxidase (e.g. p47phox, pg91phox), a major source of reactive oxygen species in vascular tissue, were elevated as a function of diabetes. In contrast, the process involves in the vascular inactivation of reactive oxygen species exemplified by the activity of CuZnSOD was reduced in this diseased state. Our studies suggest that diabetes produces a cascade of events involving production of reactive oxygen species from the NADPH oxidase leading to oxidation of BH4 and uncoupling of NOS. This promotes the oxidative inactivation of NO with subsequent formation of peroxynitrite. An alteration in the balance of these bioactive radicals in concert with a defect in the antioxidant defense counteracting mechanism may favor a heightened state of oxidative stress. This phenomenon could play a potentially important role in the pathogenesis of diabetic endothelial dysfunction.

The oxidative burst at fertilization is dependent upon activation of the dual oxidase Udx1

The sea urchin egg is a quiescent cell...until fertilization, when the egg is activated. The classic respiratory burst at fertilization is the result of prodigious hydrogen peroxide production, but the mechanism for this synthesis is not known. Here we quantitate the kinetics of hydrogen peroxide synthesis at a single-cell level using an imaging photon detector, showing that 60 nM hydrogen peroxide accumulates within the perivitelline space of each zygote. We find that the NADPH oxidation activity is enriched at the cell surface and is sensitive to a pharmacological inhibitor of NADPH oxidase enzymes. Finally, we show that a sea urchin dual oxidase homolog, Udx1, is responsible for generating the hydrogen peroxide necessary for the physical block to polyspermy. Phylogenetic analysis of the enzymatic modules in Udx1 suggests a potentially conserved role for the dual oxidase family in hydrogen peroxide production and regulation during fertilization.

Oxidative stress-associated vascular aging is independent of the protein kinase C/NAD(P)H oxidase pathway

Aging is an independent risk factor for the development of cardiovascular disease. Vascular aging is mainly characterized by endothelial dysfunction, which, in turn, is primarily attributable to increased superoxide (O(2)(*)(-)) formation with age. To date, the source of this age-associated increased O(2)(*)(-) production remains obscure. We investigated whether like in hyperglycemia or hypertension protein kinase C (PKC)-mediated activation of the NAD(P)H oxidase system is involved. Here we show that both PKC translocation, necessary for its activation, and expression of the cytosolic subunits of the NAD(P)H oxidase, p47(phox) and p67(phox), remain unchanged with age. Therefore, we suggest that oxidative stress-associated vascular aging mechanistically differs from endothelial dysfunction seen in the context of other cardiovascular risk factors, for which the PKC/NAD(P)H oxidase pathway has been shown responsible.

Role of NADPH oxidases in the control of vascular gene expression

All vascular cells, including endothelial cells and smooth muscle cells, express components of the leukocyte NADPH oxidase such as p22phox, p47phox, and Rac. Endothelial cells and fibroblasts also express the leukocyte NADPH oxidase subunit gp91phox/nox2, whereas in smooth muscle cells nox1 and nox4 are found. The different vascular NADPH oxidases represent important sources for the basal as well as the agonist-induced superoxide anion (O(2) .-) generation in the vasculature. In vascular smooth muscle cells, activation of the NADPH oxidases and the subsequent formation of O(2) .- has been demonstrated for various agents including angiotensin II, thrombin, lysophosphatidylcholine, and tumor necrosis factor alpha. By influencing the activity of p38 mitogen-activated protein kinase and AKT, NADPH oxidase-derived O(2) .- increases the expression of several pro-arteriosclerotic genes, such as monocyte chemoattractant protein-1, tissue factor, and vascular endothelial growth factor. Thus, the vascular NADPH oxidases play an important role in mediating the signal transduction cascade of pro-arteriosclerotic stimuli.

Reactive oxygen species as downstream mediators of angiogenic signaling by vascular endothelial growth factor receptor-2/KDR

Recent evidence shows the involvement of reactive oxygen species (ROS) in the mitogenic cascade initiated by the tyrosine kinase receptors of several growth factor peptides. We have asked whether also the vascular endothelial growth factor (VEGF) utilizes ROS as messenger intermediates downstream of the VEGF receptor-2 (VEGFR-2)/KDR receptor given that the proliferation of endothelial cells during neoangiogenesis is physiologically regulated by oxygen and likely by its derivative species. In porcine aortic endothelial cells stably expressing human KDR, receptor activation by VEGF is followed by a rapid increase in the intracellular generation of hydrogen peroxide as revealed by the peroxide-sensitive probe dichlorofluorescein diacetate. Genetic and pharmacological studies suggest that such oxidant burst requires as upstream events the activation of phosphatidylinositol 3-kinase and the small GTPase Rac-1 and is likely initiated by lipoxygenases. Interestingly, ROS generation in response to VEGF is not blocked but rather potentiated by endothelial nitric-oxide synthase inhibitors diphenyleneiodonium and N(G)methyl-l-arginine, ruling out the possibility of nitric oxide being the oxidant species here detected in VEGF-stimulated cells. Inhibition of KDR-dependent generation of ROS attenuates early signaling events including receptor autophosphorylation and binding to a phospholipase C-gamma-glutathione S-transferase fusion protein. Moreover, catalase, the lipoxygenase inhibitor nordihydroguaiaretic acid, the synthetic ROS scavenger EUK-134, and phosphatidylinositol 3-kinase inhibitor wortmannin all reduce ERK phosphorylation in response to VEGF, and antioxidants prevent VEGF-dependent mitogenesis. Finally, cell culture and stimulation in a nearly anoxic environment mimic the effect of ROS scavenger on receptor and ERK phosphorylation, reinforcing the idea that ROS are necessary components of the mitogenic signaling cascade initiated by KDR. These data identify ROS as a new class of intracellular angiogenic mediators and may represent a potential premise for new antioxidant-based antiangiogenic therapies.

Superoxide excess in hypertension and aging: a common cause of endothelial dysfunction

There is evidence in humans that hypertension and aging similarly impair endothelial function, although the mechanism remains unclear. Superoxide anion (O(2)(-)) is a major determinant of nitric oxide (NO) bioavailability and thus endothelial function. We sought to determine the relationship between endothelial function, O(2)(-), and age in normotensive Wistar-Kyoto (WKY) and stroke-prone spontaneously hypertensive rats (SHRSP). Aortic rings were removed from female WKY and SHRSP at 3 to 4 months (young) and 9 to 12 months (old). O(2)(-) generation by aortic rings was measured before and after removal of the endothelium or incubation with N(G) nitro-L-arginine methyl ester, diphenyleneiodonium, or apocynin. Levels of p22phox were studied with immunohistochemistry and used as a marker of NAD(P)H oxidase expression. NO bioavailability was significantly lower in old WKY compared with young WKY (P=0.0009) and in old SHRSP compared with young SHRSP (P=0.005). O(2)(-) generation was significantly greater in old WKY compared with young WKY (P=0.0001). Removal of the endothelium and N(G) nitro-L-arginine methyl ester treatment resulted in a significant reduction in O(2)(-) generation in old SHRSP (P=0.009 and 0.001, respectively). Diphenyleneiodonium significantly reduced O(2)(-) generation in 12-month WKY (P=0.008) and 12-month SHRSP (P=0.009). Apocynin attenuated O(2)(-) generation by older WKY (P=0.038) and SHRSP (P=0.028). p22phox was increased in older animals compared with young. We conclude that NO bioavailability decreases with age in female WKY and SHRSP. O(2)(-) generation increases with age in WKY and is higher in SHRSP and may contribute to the reduced NO by scavenging. NAD(P)H oxidase may contribute to the age-related increase in O(2)(-).

Hydrogen peroxide--an intracellular signal in the pulmonary circulation: involvement in hypoxic pulmonary vasoconstriction

Hypoxic pulmonary vasoconstriction (HPV) is a regulatory feature of the pulmonary circulation that ensures consistent matching of perfusion to ventilation in the normal lung. However, under pathophysiological conditions, HPV contributes to the elevated pulmonary arterial pressure inherent to numerous disease states. Consequently, control of HPV is an avenue of potential therapy for such conditions. This review discusses the role of hydrogen peroxide (H(2)O(2)) as an intracellular signal in the pulmonary circulation, concentrating on the potential involvement of H(2)O(2) in HPV and in the control of pulmonary arterial tone. Sites of hypoxic pulmonary arterial H(2)O(2) production include the mitochondrial electron transport chain, a microsomal electron transport chain containing an NADH oxidoreductase and alternatively, a membrane-bound NADPH oxidase. Each of these sources of H(2)O(2) and the effect of hypoxia on the production of reactive oxygen species are considered. The review also discusses the variance in vascular reactivity of H(2)O(2), which is described to elicit both pulmonary arterial vasoconstriction and dilatation at varying concentrations. The redox capabilities of H(2)O(2) are also considered. The relevance of all of these actions of H(2)O(2) are also assessed as potential pharmacological targets for the future development of therapy for lung diseases that are characterised by some degree of HPV and in the pathogenesis of pulmonary diseases in which reactive oxygen species are implicated.

Pharmacological effects of novel quinone compounds, 6-(fluorinated-phenyl)amino-5,8-quinolinediones, on inhibition of drug-induced relaxation of rat aorta and their putative action mechanism

Two 6-(fluorinated-phenyl)amino-5,8-quinolinedione derivatives, OQ21 and OQ1, were newly synthesized as potent inhibitors of endothelial-dependent vasorelaxation. The purpose of the present study was to investigate the effects of OQ21 and OQ1 on different types of vasorelaxation and to pursue their action mechanisms. For acetylcholine both compounds, at a low concentration (0.1 microM), reduced the maximal response with increase of EC(50) values. OQ21 is a novel quinone compound and showed a more potent and efficacious inhibitory effect on acetylcholine-induced relaxation of rat aorta than that of LY83583 (6-anilino-5,8-quinolinedione). Relatively high concentrations (1 microM) of OQ21 and OQ1 inhibited the sodium nitroprusside-induced relaxation of endothelium-denuded ring, producing rightward shifts of the curve for sodium nitroprusside without altering the maximal response. They also prevented acetylcholine and sodium nitroprusside-induced elevations of cyclic GMP. In addition, OQ21 and OQ1 (1 microM) significantly decreased (52-72%) the sensitivity of L-arginine-induced relaxation of precontracted endothelium-denuded aortic rings from lipopolysaccaride-treated (20 mg/kg, i.p.) rats. The inhibitory effect of OQ21 on endothelium-dependent vasodilation was enhanced by N(G)-nitro-L-arginine, which inhibits nitric oxide synthase (NOS) by binding the oxygenase domain of the enzyme, but not by diphenylendiodonium, which inhibits NOS by binding to the reductase domain of the enzyme. Treatment of blood vessels with OQ21 or OQ1 showed a significant increase in chemiluminescence output, which was prevented by adding superoxide dismutase, suggesting that superoxide generation is involved in the action mechanism for OQ21. Present results indicate that a novel naphthoquinone compound, OQ21, potently inhibits endothelial NOS, possibly by interacting with the reductase domain of the enzyme, which leads to induce superoxide formation. The new benzoquinone compounds, OQ21 and OQ1, inhibit not only endothelium-dependent vasorelaxation but also endothelium-independent relaxation induced by exogenous NO generated from a nitrovasodilator via the reduction of cyclic GMP. They also reduced L-arginine-induced vasorelaxation in endotoxin-treated rats, indicating their possession of inhibitory effect on inducible NOS.

Inhibition of the endothelial isoform of nitric oxide synthase impairs long-term memory formation in the chick

Previous studies with general inhibitors of nitric oxide synthase have yielded variable and contradictory results with respect to their effects on memory. This may have been due to differential effects of blocking the various isoforms of this enzyme. We show that day-old chicks trained on a single-trial passive-avoidance task suffered significant memory loss from approximately 40 min post-training following post-training intracranial administration of a potent inhibitor of eNOS. Administration of a specific nNOS or iNOS inhibitor at the same time had no effect on retention, although a role for either of these isoforms when administered at a different time after learning has yet to be fully investigated. The onset of memory loss following eNOS inhibition is the same as observed following general NOS inhibition, which suggests that amnestic effects observed in previous studies using nonspecific inhibitors may be attributable to blocking the function of eNOS. The findings indicate that eNOS may play a role in memory formation for this task, which is at least distinct from any role that may be played by nNOS.

Long-term vascular effects of Nomega-nitro-L-arginine methyl ester are not soley mediated by inhibition of endothelial nitric oxide synthesis in the rat mesenteric artery

Nomega-nitro-L-arginine methyl ester (L-NAME), one of the synthetic L-arginine analogues with inhibitory effects of nitric oxide (NO) synthesis, is now widely used to examine the role of NO in various organs. We and others demonstrated that long-term treatment with L-NAME causes hypertension and cardiovascular lesions (perivascular fibrosis and medial thickening), especially at microvascular levels. However, convincing evidence is still lacking that these long-term cardiovascular effects of L-NAME are solely mediated by the inhibition of the synthesis of endothelium-derived NO (EDNO). This study was thus designed to better understand the effects of long-term treatment with L-NAME with special reference to EDNO synthesis. Male Wister-Kyoto rats were orally administered L-NAME for 8 weeks. Blood pressure significantly increased at 3 days and 1 and 8 weeks of the treatment. Endothelium-dependent relaxations to acetylcholine (ACh) of the aorta were reduced 3 days after the treatment, recovered at 1 week, and again reduced at 8 weeks, whereas the relaxations of the small mesenteric artery were unaltered throughout the experimental periods. At 8 weeks, indomethacin-sensitive, endothelium-dependent contractions to ACh were noted. The relative contributions of NO and endothelium-derived hyperpolarizing factor also were unchanged. Citrulline assay demonstrated that substantial levels of constitutive NO synthase activity remained in the aorta during the experiments. The long-term treatment with L-NAME caused perivascular fibrosis and medial thickening, not only in the aorta but also in the mesenteric artery. These results suggest that mechanism(s) other than simple inhibition of EDNO synthesis is involved in the long-term cardiovascular effects of L-NAME in the rat mesenteric artery.

Endothelial dysfunction in hypertension

The endothelium modulates the tone of the underlying vascular smooth muscle by releasing relaxing factors, including prostacyclin, nitric oxide (NO), and endothelium-derived hyperpolarizing factor (EDHF). In most types of hypertension, endothelium-dependent relaxations are impaired because of a reduced production and/or action of endothelium-derived NO and EDHF. In essential hypertension, endothelium-dependent relaxations are reduced because of a concomitant release of vasoconstrictor prostanoids (endoperoxides and thromboxane A2). These prostanoids may be produced in the vascular smooth muscle rather than in the endothelium. The endothelial dysfunction observed in hypertension is likely to be a consequence rather than a cause of the disease, representing premature aging of the blood vessels due to the chronic exposure to the high blood pressure. The endothelial dysfunction can be improved by antihypertensive therapy, favoring the prevention of the occurrence of vascular complications in hypertension.

Dynamic changes in NADPH-diaphorase staining reflect activity of nitric oxide synthase: evidence for a dopaminergic regulation of striatal nitric oxide release

In fixed tissue, neuronal NADPH-diaphorase staining results from nitric oxide synthase (NOS) activity. Neuronal NOS only synthesizes nitric oxide once activated by the binding of Ca2+/calmodulin. We show here that neuronal NADPH-diaphorase staining is also dependent on Ca2+/calmodulin, implying that only activated NOS is detected. In addition, in bovine pulmonary endothelial cells, carbachol and bradykinin dramatically and rapidly increase the intensity of NADPH-diaphorase staining. Furthermore, administration of MK801, an NMDA antagonist, decreases neuronal NADPH-diaphorase staining. This suggests that the intensity of the NADPH-diaphorase staining is related to the level of enzyme activation at the moment of tissue fixation. The potential of exploiting this observation to detect cellular activation of NOS is illustrated by the observations that the intensity of NADPH-diaphorase staining in rat striatal neurones is decreased following systemic treatment with the D1-like dopamine receptor antagonist SCH23390, and increased by the D2-like antagonist eticlopride. These results therefore provide strong evidence that the NADPH-diaphorase reaction can be used to monitor NOS activity at a cellular level of resolution, and reveal a dopaminergic regulation of NOS activity in the striatum mediated by D1-like and D2-like dopamine receptors.

Inactivation and recovery of nitric oxide synthetic capability in cytokine-induced RAW 264.7 cells treated with "irreversible" NO synthase inhibitors

As measured at 100 microM extracellular arginine, aminoguanidine produced a time- and concentration-dependent inactivation of nitric oxide (NO) synthesis by cytokine-induced RAW cells. Inactivation obeyed first-order kinetics and occurred at a maximal rate of 0.22 min(-1) with a half-maximal inactivation rate observed at a concentration of 670 microM aminoguanidine (K(I) value). Inactivation of NO synthetic activity in the presence of N(G)-methyl-L-arginine similarly followed first-order kinetics with a maximal inactivation rate of 0.07 min(-1) and a K(I) value of 170 microM. Inactivation of NO synthetic activity in the presence of diphenyliodonium chloride occurred with a maximal inactivation rate of 0.24 min(-1) with a K(I) value of 14 microM. Diphenyliodonium chloride also produced a first-order rate of inactivation of cytokine-inducible nitric oxide synthase (iNOS) activity affinity purified from cytokine-induced RAW cells with a maximal inactivation rate of its cytochrome c reductase activity of 0.24 min(-1) with a K(I) value of 18 microM. Cytokine-induced RAW cells were treated with aminoguanidine, N(G)-methyl-L-arginine, and diphenyliodonium chloride at concentrations and for a time sufficient to completely inactivate NO synthesis by the cells and were allowed to recover in drug-free medium. Despite the presence of cycloheximide, NO synthetic rate recovered from 70 to 90% of its pretreatment activity over 4 h in cells exposed to either aminoguanidine or N(G)-methyl-L-arginine but did not recover from exposure to diphenyliodonium chloride. Analysis by sucrose density gradient centrifugation of the cytochrome c reductase and citrulline-forming activities in extracts of cells recovered from aminoguanidine treatment revealed that recovery was accompanied by a diminished population of iNOS monomers with an increased population of iNOS dimers. This observation is consistent with the hypothesis that for the mechanism-based inactivator aminoguanidine, functional dimers can be assembled from "drug-undamaged" monomers during the recovery period.

Endothelium-independent relaxation of aortic rings by the nitric oxide synthase inhibitor diphenyleneiodonium

1. The flavoprotein binder diphenyleneiodonium (DPI) is a potent, irreversible inhibitor of nitric oxide synthase (NOS), but produces only a transient pressor response following systemic administration to animals, despite evidence of persistent NOS inhibition. To characterize further the effects of DPI on vascular tone, isometric tension was recorded from rat isolated aortic rings mounted between steel wires in an organ bath. 2. The NOS inhibitor NG-nitro-L-arginine methyl ester (L-NAME, 1 mM) initiated an additional contraction of prostaglandin F2 alpha-preconstricted rings with endothelium which was sustained throughout the period of L-NAME exposure (+234 +/- 39% at 15 min). In contrast, addition of DPI (5 microM) to rings with endothelium produced a transient initial contraction (+111 +/- 27% at 2 min) followed by a more sustained relaxation (-27 +/- 19% at 15 min, P < 0.001 vs L-NAME). 3. The contraction to DPI was also observed in rings without endothelium, was abolished by L-NAME pretreatment, and was unaffected by the alpha-adrenoreceptor inhibitor prazosin. Relaxation in response to DPI was not inhibited by endothelium removal or by pretreatment with either L-NAME or with the ATP-sensitive potassium channel blocker glibenclamide. 4. The endothelium-independent relaxation to DPI was inhibited at 23 degrees C and its time course was delayed by pretreatment with the guanylate cyclase inhibitor methylene blue. 5. Thus, in addition to a transient initial contraction due to NOS inhibition, DPI produces an endothelium-independent, temperature-dependent relaxation which appears in part due to activation of guanylate cyclase. This relaxant effect of DPI may explain the transient nature of its pressor effect in vivo despite sustained NOS inhibition.

Lack of inhibition of glyceryl trinitrate by diphenyleneiodonium in bovine coronary artery

Recent studies indicate that diphenyleneiodonium is a potent inhibitor of glyceryl trinitrate-induced relaxation in rat aorta precontracted with phenylephrine. We have explored the generality of this action in bovine coronary artery precontracted with the thromboxane A2 mimetic, 9,11-dideoxy-11 alpha, 9 alpha-epoxy-methano-prostaglandin F2 alpha (U46619). Diphenyleneiodonium 0.3 microM was without effect (endothelium absent) or caused mild potentiation (0.3 microM or 10 microM; endothelium present) of the relaxant response to gylceryl trinitrate. Lack of inhibition was not due to U46619, since inhibition was still prominent in rat aorta precontracted with this agent. It is concluded that diphenyleneiodonium distinguishes between cellular mechanisms mediating vasodilator responses to glyceryl trinitrate in rat aorta and bovine coronary artery.

NMDA-mediated activation of the NO/cGMP pathway: characteristics and regulation in cultured neocortical neurones

The linkage of the N-methyl-D-aspartate (NMDA) subtype of L-glutamate receptor to the nitric oxide (NO)/3, 5'-cyclic guanosine monophosphate (cGMP) intracellular signalling system was investigated in murine neocortical cultures by examining the effects of NMDA antagonists, NO synthase inhibitors, and drugs targeting second messenger systems on NMDA-stimulated synthesis of cGMP. NMDA-stimulated synthesis of cGMP was time- and concentration-dependent, and inhibited by competitive (LY 274614, 100 mu M) and non-competitive NMDA antagonists (MK-801 30 mu M, 7-chlorokynurenate 100 mu M, and ifenprodil 100 mu M). NO synthase inhibitors (NG-nitro-L-arginine, KN-62, diphenyleneiodonium) and LY 83583, an inhibitor of guanylate cyclase, all inhibited NMDA-stimulated cGMP synthesis in a concentration-dependent manner, demonstrating its dependence on the two enzymes. Phorbol 12-myristyl 13-acetate (0.1 mu M), arachidonic acid (1 mu M), and thapsigargin (10 mu M) produced approximately 50% inhibition of NMDA-induced cGMP synthesis. These observations demonstrate that all domains of the NMDA receptor-complex and of NO synthase are active in neocortical neuronal cultures, and that the essential NO/cGMP signalling system has complex interactions with other second messengers.

Reversal of in vitro lipopolysaccharide-induced suppression of contraction in rat aorta by NG-nitro-arginine, diphenyleneiodonium and di-2-thienyliodonium

The effects of NG-nitro-L-arginine (L-NNA), D-NNA, diphenyleneiodonium and di-2-thienyliodonium on contraction were studied in endothelium-denuded rat aortic rings incubated for 4 h with lipopolysaccharide (10 mu g ml-1) or vehicle. Lipopolysaccharide reduced Emax and increased EC50 of the phenylephrine (10-9-10-5 M) curve. Addition of D-NNA (4, 6 x 10-4 M), L-NNA (1, 10 x 10-6 M) and diphenyleneiodonium (1, 3 x 10-7 M), but not di-2-thienyliodonium (10-7 M), increased Emax and reduced EC50 of the phenylephrine curve of lipopolysaccharide-incubated but not control rings. Therefore, D-NNA, L-NNA and diphenyleneiodonium, but not di-2-thienyliodonium, inhibit inducible NO synthase in vascular smooth muscles.

Vascular pharmacology of methylene blue in vitro and in vivo: a comparison with NG-nitro-L-arginine and diphenyleneiodonium

1. The vascular effects of the soluble guanylyl cyclase inhibitor, methylene blue as well as the nitric oxide (NO) synthase inhibitors, NG-nitro-L-arginine (L-NOARG) and diphenyleneiodonium (DPI) were studied in rat isolated aortic rings and conscious, unrestrained rats. 2. Acetylcholine (ACh) and sodium nitroprusside (SNP) caused concentration-dependent relaxation of preconstricted aortic rings. Both methylene blue (1 x 10(-5) M) and L-NOARG (3 x 10(-5) M) abolished ACh-induced relaxation; however, methylene blue but not L-NOARG shifted the concentration-response curve of SNP to the right. 3. In conscious rats, i.v. infusion of methylene blue (1.1 x 10(-5) mol kg-1 min-1), at a concentration which reduced the aortic tissue level of cyclic GMP by 50%, did not significantly alter mean arterial pressure (MAP) and heart rate (HR). In contrast, i.v. bolus injection of L-NOARG (1.5 x 10(-4) mol kg-1) markedly increased MAP and decreased HR. 4. Both ACh and SNP dose-dependently decreased MAP in conscious rats. Methylene blue did not alter the magnitude or duration of ACh- or SNP-induced depressor responses. L-NOARG, on the other hand, significantly though incompletely, reduced the magnitude and duration of the depressor response to ACh but not SNP. The depressor response to ACh or SNP was not altered by pretreatment with indomethacin (1.4 x 10(-5) mol kg-1) or capsaicin (3.3 x 10(-4) mol kg-1). 5. NG-nitro-L-arginine methyl ester (L-NAME) also caused dose-dependent increases in MAP in conscious rats. Both methylene blue and DPI (1 x 10-5 mol kg-1) selectively shifted the dose-pressor response curve of L-NAME to the right.6. These results suggest that: (1) the inhibition of endogenous NO biosynthesis does not necessarily lead to pressor response in vivo, (2) L-NOARG may not produce pressor response solely via the inhibition of endogenous endothelial NO biosynthesis, and (3) the depressor responses to ACh and SNP may not involve the release of NO or prostanoids or afferent nerve transmitters.