Antibacterial mouthwash alters gut microbiome, reducing nutrient absorption and fat accumulation in Western diet-fed mice

Prolonged use of antibacterial mouthwash is linked to an increased risk of systemic disease. We aimed to investigate if disturbing the oral microbiota would impact the lower gut microbiome with functional effects in diet-induced obesity. Mice were exposed to oral chlorhexidine and fed a Western diet (WD). Food intake and weight gain were monitored, and metabolic function, blood pressure, and microbiota were analyzed. Chlorhexidine reduced the number of viable bacteria in the mouth and lowered species richness in the gut but with proportional enrichment of some bacteria linked to metabolic pathways. In mice fed a Western diet, chlorhexidine reduced weight gain, body fat, steatosis, and plasma insulin without changing caloric intake, while increasing colon triglycerides and proteins, suggesting reduced absorption of these nutrients. The mechanisms behind these effects as well as the link between the oral microbiome and small intestinal function need to be pinpointed. While the short-term effects of chlorhexidine in this model appear beneficial, potential long-term disruptions in the oral and gut microbiota and possible malabsorption should be considered.

NO-ferroheme is a signaling entity in the vasculature

Despite wide appreciation of the biological role of nitric oxide (NO) synthase (NOS) signaling, questions remain about the chemical nature of NOS-derived bioactivity. Here we show that NO-like bioactivity can be efficiently transduced by mobile NO-ferroheme species, which can transfer between proteins, partition into a hydrophobic phase and directly activate the sGC-cGMP-PKG pathway without intermediacy of free NO. The NO-ferroheme species (with or without a protein carrier) efficiently relax isolated blood vessels and induce hypotension in rodents, which is greatly potentiated after the blockade of NOS activity. While free NO-induced relaxations are abolished by an NO scavenger and in the presence of red blood cells or blood plasma, a model compound, NO-ferroheme-myoglobin preserves its vasoactivity suggesting the physiological relevance of NO-ferroheme species. We conclude that NO-ferroheme behaves as a signaling entity in the vasculature.

Red blood cells from endothelial nitric oxide synthase-deficient mice induce vascular dysfunction involving oxidative stress and endothelial arginase I

BACKGROUND & AIMS

Nitric oxide bioactivity (NO) from endothelial NO synthase (eNOS) importantly contributes to the maintenance of vascular homeostasis, and reduced eNOS activity has been associated with cardiovascular disease. Emerging evidence suggests interaction(s) between red blood cells (RBCs) and the endothelium in vascular control; however, the specific role of RBC eNOS is less clear. We aimed to investigate the hypothesis that a lack of RBC eNOS induces endothelial dysfunction.

METHODS & RESULTS

RBCs from global eNOS knockout (KO) and wildtype (WT) mice were co-incubated ex vivo overnight with healthy mouse aortic rings, followed by functional and mechanistic analyses of endothelium-dependent and independent relaxations. RBCs from eNOS KO mice induced endothelial dysfunction and vascular oxidative stress, whereas WT RBC did not. No differences were observed for endothelium-independent relaxations. This eNOS KO RBC-induced endothelial dysfunctional phenotype was prevented by concomitant co-incubation with reactive oxygen species scavenger (TEMPOL), arginase inhibitor (nor-NOHA), NO donor (detaNONOate) and NADPH oxidase 4 (NOX4) inhibitor. Moreover, vessels from endothelial cell-specific arginase 1 KO mice were resistant to eNOS KO-RBC-induced endothelial dysfunction. Finally, in mice aortae co-incubated with RBCs from women with preeclampsia, we observed a significant reduction in endothelial function compared to when using RBCs from healthy pregnant women or from women with uncomplicated gestational hypertension.

CONCLUSIONS

RBCs from mice lacking eNOS, and patients with preeclampsia, induce endothelial dysfunction in adjacent blood vessels. Thus, RBC-derived NO bioactivity acts to prevent induction of vascular oxidative stress occurring via RBC NOX4-derived ROS in a vascular arginase-dependent manner. Our data highlight the intrinsic protective role of RBC-derived NO bioactivity in preventing the damaging potential of RBCs. This provides novel insight into the functional relationship between RBCs and the vasculature in health and cardiovascular disease, including preeclampsia.

Hemoglobin β93 Cysteine Is Not Required for Export of Nitric Oxide Bioactivity From the Red Blood Cell

BACKGROUND

Nitrosation of a conserved cysteine residue at position 93 in the hemoglobin β chain (β93C) to form S-nitroso (SNO) hemoglobin (Hb) is claimed to be essential for export of nitric oxide (NO) bioactivity by the red blood cell (RBC) to mediate hypoxic vasodilation and cardioprotection.

METHODS

To test this hypothesis, we used RBCs from mice in which the β93 cysteine had been replaced with alanine (β93A) in a number of ex vivo and in vivo models suitable for studying export of NO bioactivity.

RESULTS

In an ex vivo model of cardiac ischemia/reperfusion injury, perfusion of a mouse heart with control RBCs (β93C) pretreated with an arginase inhibitor to facilitate export of RBC NO bioactivity improved cardiac recovery after ischemia/reperfusion injury, and the response was similar with β93A RBCs. Next, when human platelets were coincubated with RBCs and then deoxygenated in the presence of nitrite, export of NO bioactivity was detected as inhibition of ADP-induced platelet activation. This effect was the same in β93C and β93A RBCs. Moreover, vascular reactivity was tested in rodent aortas in the presence of RBCs pretreated with S-nitrosocysteine or with hemolysates or purified Hb treated with authentic NO to form nitrosyl(FeII)-Hb, the proposed precursor of SNO-Hb. SNO-RBCs or NO-treated Hb induced vasorelaxation, with no differences between β93C and β93A RBCs. Finally, hypoxic microvascular vasodilation was studied in vivo with a murine dorsal skin-fold window model. Exposure to acute systemic hypoxia caused vasodilatation, and the response was similar in β93C and β93A mice.

CONCLUSIONS

RBCs clearly have the fascinating ability to export NO bioactivity, but this occurs independently of SNO formation at the β93 cysteine of Hb.

The NO-heme signaling hypothesis

While the biological role of nitric oxide (NO) synthase (NOS) is appreciated, several fundamental aspects of the NOS/NO-related signaling pathway(s) remain incompletely understood. Canonically, the NOS-derived NO diffuses through the (inter)cellular milieu to bind the prosthetic ferro(Fe²⁺)-heme group of the soluble guanylyl cyclase (sGC). The formation of ternary NO-ferroheme-sGC complex results in the enzyme activation and accelerated production of the second messenger, cyclic GMP. This paper argues that cells dynamically generate mobile/exchangeable NO-ferroheme species, which activate sGC and regulate the function of some other biomolecules. In contrast to free NO, the mobile NO-ferroheme may ensure safe, efficient and coordinated delivery of the signal within and between cells. The NO-heme signaling may contribute to a number of NOS/NO-related phenomena (e.g. nitrite bioactivity, selective protein S-(N-)nitrosation, endothelium and erythrocyte-dependent vasodilation, some neural and immune NOS functions) and predicts new NO-related discoveries, diagnostics and therapeutics.

Glycyrrhetinic acid reverses the lipopolysaccharide-induced hypocontractility to noradrenaline in rat aorta: implications to septic shock

Septic shock and associated vascular hyporeactivity to vasoconstrictor agonists remain a major problem of critical care medicine. Here we report that glycyrrhetinic acid (GA), the active component of licorice, effectively restores vascular contractility in the model of lipopolysaccharide (LPS)-treated rat aorta. GA was as effective as the NO synthase inhibitor N(G)-nitroarginine methylester. GA did not affect the vascular NO levels (measured by EPR spin trapping) and relaxations to L-arginine in LPS-treated rings as well as relaxation to S-nitroso-N-acetylpenicillamine in control rings. Thus, GA may represent an interesting alternative to NO synthase inhibitors in sepsis-associated vascular dysfunction.

Heparin-polynitroxides: synthesis and preliminary evaluation as cardiovascular EPR/MR imaging probes and extracellular space-targeted antioxidants

We report here the synthesis of heparin-polynitroxide derivatives (HPNs) in which nitroxide moieties are linked either to uronic acid or glycosamine residues of the heparin macromolecule. HPNs have low anticoagulant activity, possess superoxide scavenging properties, bind to the vascular endothelium/extra-cellular matrix and can be detected by EPR and MRI techniques. As the vascular wall-targeted redox-active paramagnetic compounds, HPNs may have both diagnostic (molecular MRI) and therapeutic (ecSOD mimics) applications.

α1AMP-activated protein kinase preserves endothelial function during chronic angiotensin II treatment by limiting Nox2 upregulation

OBJECTIVE

Besides its well-described metabolic effects, vascular AMP-activated protein kinase (AMPK) can activate endothelial NO synthase, promotes angiogenesis, and limits endothelial cell apoptosis. The current study was designed to study the effects of α1AMPK deletion during vascular disease in vivo.

METHODS AND RESULTS

Chronic angiotensin II infusion at low subpressor doses caused a mild endothelial dysfunction that was significantly aggravated in α1AMPK-knockout mice. Unexpectedly, this endothelial dysfunction was not associated with decreased NO content, because NO levels measured by serum nitrite or electron paramagnetic resonance were even increased. However, because of parallel superoxide production, NO was consumed under production of peroxynitrite in angiotensin II-treated α1AMPK-knockout mice, associated with NADPH oxidase activation and Nox2 upregulation. As Nox2 is also a component of phagocyte NADPH oxidases, we found a vascular upregulation of several proinflammatory markers, including inducible NO synthase, vascular cell adhesion molecule-1, and cyclooxygenase-2. Cotreatment with the NADPH oxidase inhibitor apocynin was able to prevent vascular inflammation and also partially restored endothelial function in α1AMPK-knockout mice.

CONCLUSIONS

Our data indicate that in vivo α1AMPK deletion leads to Nox2 upregulation, resulting in endothelial dysfunction and vascular inflammation. This implicates basal AMPK activity as a protective, redox-regulating element in vascular homeostasis.

Cyclooxygenase 2-selective and nonselective nonsteroidal anti-inflammatory drugs induce oxidative stress by up-regulating vascular NADPH oxidases

Cyclooxygenase 2-selective inhibitors (coxibs) and nonselective nonsteroidal anti-inflammatory drugs (NSAIDs) are associated with an increase in cardiovascular events. The current study was designed to test the effect of coxibs and nonselective NSAIDs on vascular superoxide and nitric oxide (NO) production. mRNA expression of endothelial NO synthase (eNOS) and of the vascular NADPH oxidases was studied in spontaneously hypertensive rats (SHR) and in human endothelial cells. The expression of Nox1, Nox2, Nox4, and p22phox was increased markedly by the nonselective NSAIDs diclofenac or naproxen and moderately by rofecoxib or celecoxib in the aorta and heart of SHR. The up-regulation of NADPH oxidases by NSAIDs was associated with increased superoxide content in aorta and heart, which could be prevented by the NADPH oxidase inhibitor apocynin. NSAIDs reduced plasma nitrite and diminished the phosphorylation of vasodilator-stimulated phosphoprotein. This demonstrates a reduction in vascular NO production. Aortas from diclofenac-treated SHR showed an enhanced protein nitrotyrosine accumulation, indicative of vascular peroxynitrite formation. Peroxynitrite can uncouple oxygen reduction from NO synthesis in eNOS. Accordingly, the eNOS inhibitor N(G)-nitro-L-arginine methyl ester reduced superoxide content in aortas of NSAID-treated animals, demonstrating eNOS uncoupling under those conditions. Also in human endothelial cells, NSAIDs increased Nox2 expression and diminished production of bioactive NO. In healthy volunteers, NSAID treatment reduced nitroglycerin-induced, NO-mediated vasodilatation of the brachial artery. These results indicate that NSAIDs may increase cardiovascular risk by inducing oxidative stress in the vasculature, with nonselective NSAIDs being even more critical than coxibs in this respect.

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.

Deficiency of Glutathione Peroxidase-1 Accelerates the Progression of Atherosclerosis in Apolipoprotein E-Deficient Mice

BACKGROUND

We have recently demonstrated that activity of red blood cell glutathione peroxidase-1 is inversely associated with the risk of cardiovascular events in patients with coronary artery disease. The present study analyzed the effect of glutathione peroxidase-1 deficiency on atherogenesis in the apolipoprotein E-deficient mouse.

METHODS AND RESULTS

Female apolipoprotein E-deficient mice with and without glutathione peroxidase-1 deficiency were placed on a Western-type diet for another 6, 12, or 24 weeks. After 24 weeks on Western-type diet, double-knockout mice (GPx-1(-/-)ApoE(-/-)) developed significantly more atherosclerosis than control apolipoprotein E-deficient mice. Moreover, glutathione peroxidase-1 deficiency led to modified atherosclerotic lesions with increased cellularity. Functional experiments revealed that glutathione peroxidase-1 deficiency leads to increased reactive oxygen species concentration in the aortic wall as well as increased overall oxidative stress. Peritoneal macrophages from double-knockout mice showed increased in vitro proliferation in response to macrophage-colony-stimulating factor. Also, we found lower levels of bioactive nitric oxide as well as increased tyrosine nitration as a marker of peroxynitrite production.

CONCLUSIONS

Deficiency of an antioxidative enzyme accelerates and modifies atherosclerotic lesion progression in apolipoprotein E-deficient mice.

Gp91phox-containing NAD(P)H oxidase increases superoxide formation by doxorubicin and NADPH

Doxorubicin is a highly effective antineoplastic drug associated with a dose-dependent cardiotoxicity that may result in irreversible cardiomyopathy and heart failure. Gene variants of the superoxide-generating enzyme NAD(P)H oxidase have recently been associated with this phenotype. We investigated the mechanism of this association using lucigenin-enhanced chemiluminescence, spectrophotometry, electrochemical sensor, and electron paramagnetic resonance spectroscopy. Superoxide production was measured in female wild-type and NAD(P)H oxidase-deficient (gp91phox knockout) mice. The magnitude of the increase in superoxide production on the addition of doxorubicin was much higher in hearts of wild-type mice than in enzyme-deficient mice. An increase in superoxide production was observed also on the addition of the NADPH cytochrome P450 reductase. However, doxorubicin reacted with NADPH producing superoxide even in the absence of any enzymatic activity. Taken together, gp91phox-containing NAD(P)H oxidase and NADPH cytochrome P450 reductase can enhance superoxide production caused by the chemical interaction of doxorubicin and NADPH. These findings are in agreement with the recently reported reduced cardiotoxicity following doxorubicin treatment in gp91phox knockout mice and with associations between NAD(P)H oxidase gene variants and sensitivity to doxorubicin.

Number of nitrate groups determines reactivity and potency of organic nitrates: a proof of concept study in ALDH-2-/- mice

BACKGROUND AND PURPOSE

Mitochondrial aldehyde dehydrogenase (ALDH-2) has been shown to provide a pathway for bioactivation of organic nitrates and to be prone to desensitization in response to highly potent, but not to less potent, nitrates. We therefore sought to support the hypothesis that bioactivation by ALDH-2 critically depends on the number of nitrate groups within the nitrovasodilator.

EXPERIMENTAL APPROACH

Nitrates with one (PEMN), two (PEDN; GDN), three (PETriN; glyceryl trinitrate, GTN) and four (pentaerithrityl tetranitrate, PETN) nitrate groups were investigated. Vasodilatory potency was measured in isometric tension studies using isolated aortic segments of wild type (WT) and ALDH-2-/- mice. Activity of the cGMP-dependent kinase-I (reflected by levels of phosphorylated VAsodilator Stimulated Phosphoprotein, P-VASP) was quantified by Western blot analysis, mitochondrial dehydrogenase activity by HPLC. Following incubation of isolated mitochondria with PETN, PETriN-chromophore and PEDN, metabolites were quantified using chemiluminescence nitrogen detection and mass spectrometry.

KEY RESULTS

Compared to WT, vasorelaxation in response to PETN, PETriN and GTN was attenuated about 10fold in ALDH-2-/- mice, identical to WT vessels preincubated with inhibitors of ALDH-2. Reduced vasodilator potency correlated with reduced P-VASP formation and diminished biotransformation of the tetranitrate- and trinitrate-compounds. None of these findings were observed for PEDN, GDN and PEMN.

CONCLUSIONS AND IMPLICATIONS

Our results support the crucial role of ALDH-2 in bioactivating highly reactive nitrates like GTN, PETN and PETriN. ALDH-2-mediated relaxation by organic nitrates therefore depends mainly on the number of nitrate groups. Less potent nitrates like PEDN, GDN and PEMN are apparently biotransformed by other pathways.

Nebivolol inhibits superoxide formation by NADPH oxidase and endothelial dysfunction in angiotensin II-treated rats

Nebivolol is a beta(1)-receptor antagonist with vasodilator and antioxidant properties. Because the vascular NADPH oxidase is an important superoxide source, we studied the effect of nebivolol on endothelial function and NADPH oxidase activity and expression in the well-characterized model of angiotensin II-induced hypertension. Angiotensin II infusion (1 mg/kg per day for 7 days) caused endothelial dysfunction in male Wistar rats and increased vascular superoxide as detected by lucigenin-derived chemiluminescence, as well as dihydroethidine staining. Vascular NADPH oxidase activity, as well as expression at the mRNA and protein level, were markedly upregulated, as well as NOS III uncoupled, as evidenced by NO synthase III inhibitor experiments and dihydroethidine staining and by markedly decreased hemoglobin-NO concentrations. Treatment with the beta-receptor blocker nebivolol but not metoprolol (10 mg/kg per day for each drug) normalized endothelial function, reduced superoxide formation, increased NO bioavailability, and inhibited upregulation of the activity and expression of the vascular NADPH oxidase, as well as membrane association of NADPH oxidase subunits (Rac1 and p67(phox)). In addition, NOS III uncoupling was prevented. In vitro treatment with nebivolol but not atenolol or metoprolol induced a dissociation of p67(phox) and Rac1, as well as an inhibition of NADPH oxidase activity assessed in heart membranes from angiotensin II-infused animals, as well as in homogenates of Nox1 and cytosolic subunit-transfected and phorbol ester-stimulated HEK293 cells. These findings indicate that nebivolol interferes with the assembly of NADPH oxidase. Thus, inhibitory effects of this beta-blocker on vascular NADPH oxidase may explain, at least in part, its beneficial effect on endothelial function in angiotensin II-induced hypertension.

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

OBJECTIVE

Nitric oxide (NO)-induced vasorelaxation involves activation of large conductance Ca2+-activated K+ channels (BK). A regulatory BKbeta1 subunit confers Ca2+, voltage, and NO/cGMP sensitivity to the BK channel. We investigated whether endothelial function and NO/cGMP signaling is affected by a deletion of the beta1-subunit.

METHODS AND RESULTS

Vascular superoxide in BKbeta1-/- was measured using the fluorescent dye hydroethidine and lucigenin-enhanced chemiluminescence. Vascular NO formation was analyzed using electron paramagnetic resonance (EPR), expression of NADPH oxidase subunits, the endothelial NO synthase (eNOS), the soluble guanylyl cyclase (sGC), as well as the activity and expression of the cyclic GMP-dependent kinase I (cGK-I) were assessed by Western blotting technique. eNOS, sGC, cGK-I expression and acetylcholine-induced NO production were unaltered in Bkbeta1-/- animals, whereas endothelial function was impaired and the activity of the cGK-I was reduced. Vascular O2- and expression of the NADPH oxidase subunits p67phox and Nox1 were increased. Endothelial dysfunction was normalized by the NADPH oxidase inhibitor apocynin. Potassium chloride- and iberiotoxin-induced depolarization mimicked the effect of BKbeta1-deletion by increasing vascular O2- in an NADPH-dependent fashion.

CONCLUSIONS

The deletion of BKbeta1 causes endothelial dysfunction by increasing O2- formation via increasing activity and expression of the vascular NADPH oxidase.

Dinitrosyl-iron triggers apoptosis in Jurkat cells despite overexpression of Bcl-2

Cells expressing the cytokine-inducible NO synthase are known to trigger apoptosis in neighboring cells. Paramagnetic dinitrosyl nonheme iron complexes (DNIC) were found in tumor tissue about 40 years ago; however, the role of these NO(+)-bearing species is not completely understood. In the human Jurkat leukemia cell line, the application of the model complex DNIC-thiosulfate (50-200 microM) induced apoptosis (defined by phosphatidylserine externalization) in a concentration- and time-dependent manner. In Jurkat cells, the pan-caspase inhibitor, zVADfmk (50 microM), and/or stable transfection of antiapoptotic protein, Bcl-2, was unable to afford protection against DNIC-induced apoptosis. The membrane-impermeable metal chelator, N-methyl-D-glucamine dithiocarbamate (MGD; 200 microM), in the presence of DNIC significantly increased apoptosis, but had no effect on its own. Electron paramagnetic resonance studies showed that MGD led to rapid transformation of the extracellular DNIC into the stable impermeable NO-Fe-MGD complex and to a burst-type release of nitrosonium (NO(+)) equivalents in the extracellular space. These results suggest that in Jurkat cells, DNIC-thiosulfate induces Bcl-2- and caspase-independent apoptosis, which is probably secondary to local nitrosative stress at the cell surface. We hypothesize that the local release of nonheme Fe-NO species by activated macrophages may play a role in the killing of malignant cells that have high Bcl-2 levels.

Mechanisms underlying dysfunction of carotid arteries in genetically hyperlipidemic rabbits

In the present study we compared the vascular reactivity and integrity of the nitric oxide (NO)-cyclic 3',5'-guanosine monophopsphate (cGMP) pathway in carotid arteries of hyper- and normolipidemic rabbits. Vasodilation to acetylcholine, nitroglycerin, and sodium nitroprusside was desensitized in hyperlipidemia, but the nitroprusside-induced relaxation was normalized by an NO synthase inhibitor in endothelium-intact and -denuded vessels. Hyperlipidemic carotid arteries exhibited increased basal NO (detected by EPR spin-trapping) and reactive oxygen species formation (detected by chemiluminescence), whereas acetylcholine-induced NO formation was nearly abolished. Hyperlipidemia increased NADPH-dependent superoxide formation in carotid membranes, and carotid cryosections stained with the fluorescent dye dihydroethidium revealed increased endothelial and medial reactive oxygen species formation. Hyperlipidemia elicited macrophage invasion into the carotid wall, as detected by a dot-immunoblot. The basal activity of cGMP-dependent proteinkinase, the nitroprusside-stimulated activity of soluble guanylyl cyclase, and its protein expression were decreased by hyperlipidemia. The cGMP phosphodiesterase activity was marginally increased by hyperlipidemia, such that the ratio of cGMP-forming vs. -degrading capacity was decreased by 2-fold. Hyperlipidemia triggers infiltration of macrophages into the carotid wall and endothelial as well as smooth muscle superoxide formation. Consequently, relaxation of the carotid arteries are impaired due to smooth muscle and endothelial dysfunction.

Mechanisms of Increased Vascular Superoxide Production in an Experimental Model of Idiopathic Dilated Cardiomyopathy

Objective— In the present study, we sought to identify mechanisms underlying increased oxidative stress in vascular tissue in an experimental animal model of chronic congestive heart failure (CHF).

Methods and Results— Superoxide and nitric oxide (NO) was measured in vessels from cardiomyopathic hamsters (CHF hamsters) and golden Syrian hamsters. We also determined expression of endothelial nitric oxide synthase (NOSIII), the soluble guanylyl cyclase, the cGMP-dependent kinase, and the NADPH oxidase. To analyze the contribution of the renin-angiotensin system to oxidative stress, CHF hamsters were treated with the angiotensin-converting enzyme inhibitor captopril for 200 days (120 mg · kg −1 · d −1 ). CHF led to increased superoxide production by NOSIII and the NADPH oxidase. Decreased NO production in CHF was associated with a decrease in the expression of NOSIII and an inhibition of NO downstream signaling in the aorta. NOSIII expression was increased within the left ventricle. Captopril treatment normalized NOSIII expression in vessels and the myocardium, reduced superoxide levels, and prevented NOSIII uncoupling. Accordingly, endothelial function, NO production, and downstream signaling were improved in CHF vessels.

Conclusions— Oxidative stress in CHF is mediated by NADPH oxidase and an uncoupled NOSIII secondary to an activation of the renin-angiotensin system leading to impaired NO downstream signaling.

Nomega-hydroxy-L-arginine homologues and hydroxylamine as nitric oxide-dependent vasorelaxant agents

Endothelium-independent relaxant activities of N(omega)-hydroxy-L-arginine (L-NOHA) homologues and hydroxylamine, a possible intermediate in nitric oxide (NO) formation, were examined in rat aortic rings. Addition of one -CH(2)- group to the -(CH(2))(x)- chain between the alpha-amino acid and the hydroxyguanidine group (x=4) almost abolished-while deletion of one or two -CH(2)- (x=1 or 2) enhanced-the relaxant activity of L-NOHA homologues. N(omega)-hydroxy-nor-L-arginine- (x=2) and hydroxylamine-induced relaxations were blunted by a NO scavenger and by inhibitors of the guanylyl cyclase pathway, but not by NO synthase or cytochrome P(450) inhibitors (except 7-ethoxyresorufin). However, aortic NO formation was detected (using electron paramagnetic resonance) in the presence of concentrations of these compounds higher than those producing relaxation. These findings support the view that endothelium-independent vasorelaxations induced by both L-NOHA homologues with a required chain length x</=3 and hydroxylamine are mediated by NO-dependent activation of guanylyl cyclase, through a 7-ethoxyresorufin-inhibited mechanism.

Differential effects of diabetes on the expression of the gp91phox homologues nox1 and nox4

The nox2-dependent NADPH oxidase was shown to be a major superoxide source in vascular disease, including diabetes. Smooth muscle cells of large arteries lack the phagocytic gp91phox subunit of the enzyme; however, two homologues have been identified in these cells, nox1 and nox4. It remained to be established whether also increases in protein levels of the nonphagocytic NADPH oxidase contribute to increased superoxide formation in diabetic vessels. To investigate changes in the expression of these homologues, we measured their expression in aortic vessels of type I diabetic rats. Eight weeks after streptozotocin treatment, we found a doubling in nox1 protein expression, while the expression of nox4 remained unchanged. This was associated with a significant increase in the NADPH oxidase activity in membrane fractions of diabetic heart and aortic tissue. Furthermore, we observed a decreased sensitivity of diabetic vessels to acetylcholine and nitroglycerin and a decrease in both acetylcholine-stimulated NO production and phosphorylation of VASP, despite an increase in endothelial NO synthase (NOSIII) expression. In addition, xanthine oxidase activity was markedly increased in plasma and 100,000 g supernatant of cardiac tissue of diabetic rats, while myocardial mitochondrial superoxide formation was only weakly enhanced. We conclude that in addition to phagocytic NADPH oxidase, also nonphagocytic, vascular NADPH oxidase subunit nox1, uncoupled NOSIII, and plasma xanthine oxidase contribute to endothelial dysfunction in the setting of diabetes mellitus.

Endothelium- and nitric oxide-dependent vasorelaxing activities of gamma-butyrobetaine esters: possible link to the antiischemic activities of mildronate

Mildronate [3-(2,2,2-trimethylhydrazine) propionate (THP)] is an antiischemic drug acting mainly via inhibition of fatty acid beta-oxidation. Some effects of the drug cannot be explained by the latter mechanism. We tested the eventual nitric oxide (NO) dependence of the mildronate action. Mildronate, gamma-butyrobetaine (GBB) and GBB methyl ester induced transient increases in nitric oxide (NO) concentrations in rat blood and myocardium. In vitro, these compounds neither modified the activities of purified neuronal and endothelial recombinant nitric oxide synthases (NOSs) nor were able to interact with their active site. GBB induced vasodilatation at high concentrations only (EC50 = 5 x 10(-5) M) while mildronate alone displayed no vasodilating effect although it enhanced the GBB vasodilating activity. GBB methyl and ethyl esters were found more potent vasodilators (EC50 = 2.5 x 10(-6) M). Pretreatment of aortic rings with NOS inhibitor Nomega-nitro-L-arginine methyl ester (L-NAME) abolished vasodilating effects of the compounds. A hypothesis explaining NO and endothelium-dependent effects of mildronate and its analogues is proposed.

Role of the adventitia in the cyclic GMP-mediated relaxant effect of N-hydroxy-L-arginine in rat aorta

N(omega)-hydroxy-L-arginine (L-NOHA), the stable intermediate of the nitric oxide synthase (NOS)-catalyzed reaction, can induce NO/cyclic GMP-dependent relaxation in the rat aorta, in an endothelium- and NOS-independent manner. In this study, the role of the adventitia in the endothelium-independent effect of L-NOHA was investigated. Despite a decrease in norepinephrine (NE)-induced precontraction, adventitia removal in the rat aorta did not markedly alter the relaxant effect of forskolin, S-nitroso-N-acetylpenicillamine or glyceryl trinitrate. In contrast, both inhibition of NE-induced contraction and relaxation of NE-precontracted rings produced by L-NOHA were diminished in the absence of adventitia. Moreover, exposure to L-NOHA significantly enhanced the cyclic GMP level in the media of the aorta with, but not without adventitia. These findings demonstrate the role of the adventitia in the L-NOHA-induced decrease in tone and increase in cyclic GMP in the endothelium-denuded rat aorta. They suggest that NO or an NO-related compound formed from L-NOHA in the adventitia may produce paracrine effects.

Molecular mechanisms underlying the role of nitric oxide in the cardiovascular system

In the cardiovascular system, nitric oxide (NO) is involved in the short and long-term regulation of haemodynamics, and in a number of their pathological alterations. Investigation into the biochemistry of NO-synthase isoforms has confirmed that they also all produce superoxide anion (O(*)). The free radical NO can interact with many targets on which novel information has been recently obtained. The major results of these interactions are not only the well known activation of guanylyl cyclase, but also the formation of potentially cytotoxic peroxynitrite (ONOO(-)), and the formation of S-nitrosothiols and non-haem iron-dinitrosyl dithiolate complexes. Tissue O(2), O(*), low molecular weight thiols and transition metals (especially FeII) play a pivotal role in directing NO towards targets responsible for biological effects, or storage or release from these stores. In addition, circulating forms of NO have been proposed with S-nitrosation of blood proteins. All these mechanisms provide potential pharmacological targets for future therapeutic strategies.

Detection of superoxide and peroxynitrite in model systems and mitochondria by the luminol analogue L-012

In the present study we investigated the specificity and sensitivity of the chemiluminescence (CL) dye and luminol analogue 8-amino-5-chloro-7-phenylpyrido[3,4-d]pyridazine-1,4-(2H,3H) dione (L-012) to detect reactive oxygen species (ROS) such as superoxide, peroxynitrite and hydrogen peroxide in cell free systems as well as in isolated mitochondria. The results obtained by L-012 were compared with other CL substances such as luminol, lucigenin, coelenterazine and the fluorescence dye dihydroethidine. The results indicate that the L-012-derived chemiluminescence induced by superoxide from hypoxanthine/xanthine oxidase (HX/XO) or by 3-morpholino sydnonimine (SIN-1)-derived peroxynitrite largely depends on the incubation time. Irrespective of the experimental conditions, L-012-derived CL in response to HX/XO and SIN-1 was 10-100 fold higher than with other CL dyes tested. In a cell-free system, authentic peroxynitrite yielded a higher L-012-enhanced CL signal than authentic superoxide and the superoxide-induced signal in cell-free as well as isolated mitochondria increased in the presence of equimolar concentrations of nitrogen monoxide (NO). The superoxide signal/background ratio detected by L-012-enhanced CL in isolated mitochondria with blocked respiration was 7 fold higher than that obtained by the superoxide sensitive fluorescence dye dihydroethidine. We conclude that L-012-derived CL may provide a sensitive and reliable tool to detect superoxide and peroxynitrite formation in mitochondrial suspensions.

Oxidative stress and mitochondrial aldehyde dehydrogenase activity: a comparison of pentaerythritol tetranitrate with other organic nitrates

Mitochondrial aldehyde dehydrogenase (ALDH-2) was recently identified to be essential for the bioactivation of glyceryl trinitrate (GTN). Here we assessed whether other organic nitrates are bioactivated by a similar mechanism. The ALDH-2 inhibitor benomyl reduced the vasodilator potency, but not the efficacy, of GTN, pentaerythritol tetranitrate (PETN), and pentaerythritol trinitrate in phenylephrine-constricted rat aorta, whereas vasodilator responses to isosorbide dinitrate, isosorbide-5-mononitrate, pentaerythritol dinitrate, pentaerythritol mononitrate, and the endothelium-dependent vasodilator acetylcholine were not affected. Likewise, benomyl decreased GTN- and PETN-elicited phosphorylation of the cGMP-activated protein kinase substrate vasodilator-stimulated phosphoprotein (VASP) but not that elicited by other nitrates. The vasodilator potency of organic nitrates correlated with their potency to inhibit ALDH-2 dehydrogenase activity in mitochondria from rat heart and increase mitochondrial superoxide formation, as detected by chemiluminescence. In contrast, mitochondrial ALDH-2 esterase activity was not affected by PETN and its metabolites, whereas it was inhibited by benomyl, GTN applied in vitro and in vivo, and some sulfhydryl oxidants. The bioactivation-related metabolism of GTN to glyceryl-1,2-dinitrate by isolated RAW macrophages was reduced by the ALDH-2 inhibitors benomyl and daidzin, as well as by GTN at concentrations >1 microM. We conclude that mitochondrial ALDH-2, specifically its esterase activity, is required for the bioactivation of the organic nitrates with high vasodilator potency, such as GTN and PETN, but not for the less potent nitrates. It is interesting that ALDH-2 esterase activity was inhibited by GTN only, not by the other nitrates tested. This difference might explain why GTN elicits mitochondrial superoxide formation and nitrate tolerance with the highest potency.

Measurement of NAD(P)H oxidase-derived superoxide with the luminol analogue L-012

In the present study we sought to determine the ability of the chemiluminescence dye 8-amino-5-chloro-7-phenylpyridol[3,4-d]pyridazine-1,4-(2H,3H)dione sodium salt (L-012) to detect superoxide in different biological systems. In human whole blood or isolated leukocytes, the sensitivity of the luminol analogue L-012 to detect superoxide was higher as compared with luminol, lucigenin, coelenterazine, and the fluorescence dye dihydroethidine. In isolated leukocytes as well as aortic rings from control (New Zealand White) and hyperlipidemic (Watanabe heritable hyperlipidemic) rabbits, L-012-enhanced chemiluminescence was successful in detecting differences in superoxide formation under basal conditions and on stimulation with the direct activator of protein kinase C, phorbol 12,13-dibutyrate (PDBu). The effects of PDBu were abrogated by gliotoxin and inhibitors of protein kinase C such as chelerythrine, identifying NAD(P)H oxidase as the significant superoxide source. Experiments using electron paramagnetic resonance and the spin trap 5-diethoxyphosphoryl-5-methyl-1-pyrroline-N-oxide revealed that in contrast to lucigenin, L-012 is not subject to redox cycling. These findings indicate that L-012-enhanced chemiluminescence represents a sensitive and reliable probe to detect superoxide in whole blood, inflammatory cells, and vascular tissue.

Does nitric oxide mediate the vasodilator activity of nitroglycerin?

Nitroglycerin (glyceryl trinitrate, GTN) relaxes blood vessels primarily via activation of the soluble guanylyl cyclase (sGC)/cGMP/cGMP-dependent protein kinase (cGK-I) pathway. Although the precise mechanism of sGC activation by GTN in the vascular wall is unknown, the mediatory role of nitric oxide (NO) has been postulated. We tested the GTN/NO hypothesis in different types of isolated rat and rabbit blood vessels using two novel approaches: (1) EPR spin trapping using colloid Fe(DETC)2 and (2) analysis of cGK-I-dependent phosphorylation of the vasodilator-stimulated phosphoprotein at Ser239 (P-VASP). For comparison, another organic nitrate, isosorbide dinitrate (ISDN), and endothelium-dependent vasodilator, calcium ionophore A23187, were tested. We found a marked discrepancy between GTN's strong vasoactivity (vasodilation and augmentation of P-VASP) and its poor NO donor properties. In aortas precontracted with phenylephrine, GTN, ISDN, and A23187 induced nearly full relaxations (>80%) and doubling of vascular P-VASP content at concentrations of 100 nmol/L, 100 micromol/L, and 1 micromol/L, respectively. GTN applied in vasorelaxant concentrations (10 to 1000 nmol/L) did not significantly increase the basal vascular NO production, in contrast to ISDN and A23187. The absence of GTN-derived NO was confirmed in rabbit vena cava and renal artery. A significant increase in vascular NO formation was observed only at suprapharmacological GTN concentrations (>10 micromol/L). The concentration dependency of NO formation from GTN was comparable to that of ISDN, although the latter exhibits 100-folds lower vasorelaxant potency. We conclude that GTN activates the sGC/cGMP/cGK-I pathway and induces vasorelaxation without intermediacy of the free radical NO. The full text of this article is available online at http://www.circresaha.org.

Nebivolol prevents vascular NOS III uncoupling in experimental hyperlipidemia and inhibits NADPH oxidase activity in inflammatory cells

OBJECTIVE

Nebivolol, in contrast to other selective beta1-adrenergic receptor antagonists like atenolol, improves endothelial function in patients with oxidative stress within vascular tissue. With the present studies we sought to determine whether beta receptor blockade with nebivolol may improve endothelial function in hyperlipidemia and whether this is attributable to reductions in vascular oxidative stress.

METHODS AND RESULTS

Watanabe heritable hyperlipidemic rabbits (WHHL) were treated with nebivolol (10 mg/kg per day for 8 weeks). New Zealand white rabbits (NZWR) served as controls. Nebivolol improved endothelial function, reduced vascular superoxide and vascular macrophage infiltration, and prevented NO synthase uncoupling in WHHL. Nebivolol treatment did not modify the expression of sGC or cGK-I but improved cGK-I activity (assessed by the phosphorylation state of the VAsodilator Stimulated Phosphoprotein at serine239, P-VASP). NAD(P)H oxidase activity in whole blood and isolated neutrophils was dose-dependently inhibited by nebivolol, whereas atenolol, metoprolol, and carvedilol were markedly less effective.

CONCLUSIONS

Nebivolol therapy effectively prevents NO synthase III uncoupling and prevents activation of the neutrophil NAD(P)H oxidase and infiltration of inflammatory cells. These novel antioxidative stress actions of this compound may explain partly the beneficial effects on endothelial function in patients with enhanced vascular oxidative stress.

Detection of superoxide in vascular tissue

During the past decade, it has become apparent that reactive oxygen species play a critical role in the genesis of many vascular diseases. The superoxide anion is among the most important of these, not only because of its rapid reaction with NO but also because it serves as a progenitor for many other reactive oxygen species. Although there are many approaches to detecting and quantifying superoxide in chemical systems, its detection in intact tissues is more difficult. The validity of the most popular and frequently used assay for this purpose, lucigenin-enhanced chemiluminescence, has been recently questioned. It has been suggested that lucigenin itself, especially at high concentrations (>50 micromol/L), may act as a source for superoxide via redox cycling. Lower lucigenin concentrations (5 micromol/L) do not participate in redox cycling to an important extent in intact tissues and, therefore, provide an accurate assessment of the rate of superoxide production in such samples. Other useful assays for superoxide include those using the fluorescent dye dihydroethidine, 2-methyl-6-phenyl-3,7-dihydroimidazo(1,2-alpha)pyrazin-3-one (CLA), and 2-(p-hydroxybenzyl)-6-(p-hydroxyphenyl) 8-benzylimidazo[1,2-alpha]pyrazin-3-one (coelenterazine). The chemiluminescent compound 5-amino-2,3-dihydroxy-1,4-phthalayineidone (luminol) may also be used to detect various reactive oxygen species and may be made specific for various oxidants, such as hydrogen peroxide, superoxide, and peroxynitrite, by altering the experimental conditions. Although each of these methods may be associated with potential artifacts, the use of > or =2 different techniques that yield similar results provides a reliable approach for the study of reactive oxygen species in intact vascular tissues.

Nitric oxide transport and storage in the cardiovascular system

Despite short halflife in biological fluids, nitric oxide (NO) can produce remote or long lasting effect in the cardiovascular system. Long distance transport or local storage of NO might explain these effects. In blood, recent findings suggest that in addition to being a major consumption pathway, interaction of NO with hemoglobin may permit O(2)-governed transport of NO (as S-nitrosohemoglobin) to tissues in which NO may be released together with O(2), via transnitrosation of a transport protein. In blood vessels, two different putative NO stores have been characterized. The first is the photosensitive store, formed from endothelium-derived NO. The mechanism of NO release from this store in the body (in absence of light) and its physiological relevance are unknown. The second store is generated in conditions of high tissue NO levels, as a consequence of the inducible NO synthase activity or in various stress conditions. This NO store involves formation of protein-bound dinitrosyl iron complexes or S-nitrosated proteins, or both. Low molecular weight thiols can displace NO from these stores and probably transfer it to target membrane protein(s) such as K(+) channels, via transnitrosation reactions. These stores may be involved in defence mechanisms against inflammation or stress. Thus, NO transport and storage mechanisms may be implicated in a variety of NO effects. The mechanisms of their formation and of NO release and their physiologic and pathophysiologic relevance deserve further investigations.

Effects of angiotensin II infusion on the expression and function of NAD(P)H oxidase and components of nitric oxide/cGMP signaling

Angiotensin II infusion causes endothelial dysfunction by increasing NAD(P)H oxidase-mediated vascular superoxide production. However, it remains to be elucidated how in vivo angiotensin II treatment may alter the expression of the gp91(phox) isoforms and the endothelial nitric oxide synthase (NOS III) and subsequent signaling events and whether, in addition to the NAD(P)H oxidase, NOS III contributes to vascular superoxide formation. We therefore studied the influence of in vivo angiotensin II treatment (7 days) in rats on endothelial function and on the expression of the NAD(P)H oxidase subunits p22(phox), nox1, nox4, and gp91(phox) and NOS III. Further analysis included the expression of NO-downstream targets, the soluble guanylyl cyclase (sGC), the cGMP-dependent protein kinase I (cGK-I), and the expression and phosphorylation of the vasodilator-stimulated phosphoprotein (VASP) at Ser239 (P-VASP). Angiotensin II caused endothelial dysfunction and increased vascular superoxide. Likewise, we found an increase in vascular protein kinase C (PKC) activity, in the expression of nox1 (6- to 7-fold), gp91(phox) (3-fold), p22(phox) (3-fold), NOS III mRNA, and protein. NOS-inhibition with N(G)-nitro-L-arginine decreased superoxide in vessels from angiotensin II-treated animals, compatible with NOS-uncoupling. Vascular NO assessed with electron paramagnetic resonance was markedly reduced. Likewise, a decrease in sGC-expression and P-VASP levels was found. In vivo PKC-inhibition with chelerythrine reduced angiotensin II-induced superoxide production and markedly inhibited upregulation of NAD(P)H oxidase subunits. We therefore conclude that angiotensin II-induced increases in the activity and the expression of NAD(P)H oxidase are at least in part PKC-dependent. NADPH oxidase-induced superoxide production may trigger NOS III uncoupling, leading to impaired NO/cGMP signaling and to endothelial dysfunction in this animal model. The full text of this article is available at http://www.circresaha.org.

Low molecular mass dinitrosyl nonheme-iron complexes up-regulate noradrenaline release in the rat tail artery

BACKGROUND

Dinitrosyl nonheme-iron complexes can appear in cells and tissues overproducing nitric oxide. It is believed that due to their chemical nature these species may be implicated in certain pathophysiological events. We studied the possible role of low molecular mass dinitrosyl iron complexes in the control of noradrenaline release in electrically stimulated rat tail artery.

RESULTS

A model complex, dinitrosyl-iron-thiosulfate (at 1-10 microM) produced a concentration-dependent enhancement of electrical field stimulated [3H]noradrenaline release (up to 2 fold). At the same time, dinitrosyl-iron-thiosulfate inhibited neurogenic vasoconstriction, consistent with its nitric oxide donor properties. A specific inhibitor of cyclic GMP dependent protein kinase, Rp-8pCPT-cGMPS, partially inhibited the effect of dinitrosyl-iron-thiosulfate on neurogenic vasoconstriction, but not on [3H]noradrenaline release. Another model complex, dinitrosyl-iron-cysteine (at 3 microM) elicited similar responses as dinitrosyl-iron-thiosulfate. Conventional NO and NO+ donors such as sodium nitroprusside, S-nitroso-L-cysteine or S-nitroso-glutathione (at 10 microM) had no effect on [3H]noradrenaline release, though they potently decreased electrically-induced vasoconstriction. The "false complex", iron(II)-thiosulfate showed no activity.

CONCLUSIONS

Low molecular mass iron dinitrosyl complexes can up-regulate the stimulation-evoked release of vascular [3H]noradrenaline, apparently independently of their NO donor properties. This finding may have important implications in inflammatory tissues.

Novel activation of non-selective cationic channels by dinitrosyl iron-thiosulfate in PC12 cells

Low molecular mass dinitrosyl iron complexes (DNICs) are nitrosating agents and it is known that the dinitrosyl iron moiety can be transferred to proteins. The aim of the present study was to determine if the formation of protein-bound dinitrosyl iron can modulate ionic channel activity. In PC12 cells, dinitrosyl iron-thiosulfate (50 microM) caused irreversible activation of a depolarizing inward current (IDNIC). IDNIC was partially inhibited by the metal chelator diethyldithiocarbamate (DETC, 1 mM), but not by the reducing/denitrosylating agent dithiothreitol (DTT, 5 mM). The activation of IDNIC was not reproduced by application of nitric oxide (NO., 100 microM), S-nitrocysteine (200 microM) or ferrous iron-thiosulfate (50 microM), and was not prevented by the irreversible guanylyl cyclase inhibitor 1H-[1,2,4]oxadiazolo-[4, 3-a]quinoxalin-1-one (ODQ, 1 microM). Similarly, intracellular perfusion of dinitrosyl iron-thiosulfate (100 microM) did not result in activation of IDNIC. Ion replacement experiments show that the DETC-sensitive component of IDNIC is a non-selective cationic current. In accordance, IDNIC was blocked by antagonists of receptor-operated calcium entry, gadolinium (25 microM) and SK&F 96365 (25 microM). Single-channel measurements from outside-out patches reveal that the DETC-sensitive component of IDNIC is an inward current carried by a cationic channel having a conductance of 50 pS. The present observations suggest that the formation of ion channel-bound dinitrosyl iron represents another mechanism of regulation of ion channel activity by NO.-related species, which may be particularly important in pathophysiological processes where NO. is overproduced.

Adventitia-derived nitric oxide in rat aortas exposed to endotoxin: cell origin and functional consequences

The role of adventitial cells in bacterial lipopolysaccharide (LPS)-induced vascular nitric oxide (NO) overproduction has been largely ignored. In rat aortas exposed to LPS in vitro or in vivo, it was found that adventitia contained the major part of NO synthase (NOS)-2 protein (Western blot and immunohistochemistry) and generated the largest amount of NO (electron paramagnetic resonance spin trapping). NOS-2 immunoreactive cells were mainly resident macrophages at an early stage (5 h, in vitro or in vivo) and fibroblasts at a later stage (20 h, in vitro). Adventitial NOS-2 activity largely accounted for 1) the relaxing effect of L-arginine in rings exposed to LPS in vivo, 2) generation of an "NO store" revealed by N-acetylcysteine-induced relaxation, and 3) formation of protein-bound dinitrosyl iron complexes in the medial layer of aortic rings exposed to LPS in vitro. In conclusion, the adventitia is a powerful source of NO triggered by LPS in the rat aorta. This novel source of NO has an important impact on smooth muscle function and might be implicated in various inflammatory diseases.

Spin trapping of vascular nitric oxide using colloid Fe(II)-diethyldithiocarbamate

Currently available EPR spin-trapping techniques are not sensitive enough for quantification of basal vascular nitric oxide (NO) production from isolated vessels. Here we demonstrate that this goal can be achieved by the use of colloid Fe(DETC)(2). Rabbit aortic or venous strips incubated with 250 microM colloid Fe(DETC)(2) exhibited a linear increase in tissue-associated NO-Fe(DETC)(2) EPR signal during 1 h. Removal of endothelium or addition of 3 mM N(G)-nitro-l-arginine methyl ester (L-NAME) inhibited the signal. The basal NO production was estimated as 5.9 +/- 0.5 and 8.3 +/- 2.1 pmol/min/cm(2) in thoracic aorta and vena cava, respectively. Adding sodium nitrite (10 microM) or xanthine/xanthine oxidase in the incubation medium did not modify the intensity of the basal NO-Fe(DETC)(2) EPR signal. Reducing agents were not required with this method and superoxide dismutase activity was unchanged by the Fe(DETC)(2) complex. We conclude that colloid Fe(DETC)(2) may be a useful tool for direct detection of low amounts of NO in vascular tissue.

Inducible NO synthase activity in blood vessels and heart: new insight into cell origin and consequences

Induction of the inducible form of nitric oxide synthase (iNOS) in the vascular and cardiac tissue by several inflammatory stimuli may result in the production of large amounts of nitric oxide (NO) for a sustained period. Recent data obtained in the rat aorta in which iNOS was induced by lipopolysaccharide (LPS) have demonstrated that adventitial cells represent the main site of NO production. Adventitial-derived NO can exert an immediate down-regulatory effect on smooth muscle contraction (via activation of the cyclic GMP pathway) but may also initiate longer lasting effects through the formation of NO stores within the medial layer. One candidate for such NO stores are dinitrosyl non-heme iron complexes. Low molecular weight thiols interact with preformed NO stores and promote vasorelaxation by a cyclic GMP-independent mechanism involving the activation of potassium channels. In the heart, the induction of iNOS is involved in delayed protection against ischemia-reperfusion-induced functional damages. Recent data obtained with monophosphoryl lipid A, a non-toxin derivative of LPS, strongly suggest that iNOS-derived NO in the rat heart does not act as an immediate mediator of the cardioprotection but rather as a trigger of long-term protective mechanisms. Thus, the present data reveal the important role of adventitial cells as a site of iNOS expression and activity in intact blood vessels. The induction of adaptive mechanisms in the heart and the formation of releasable NO stores in blood vessels are examples of long-term consequences of iNOS induction. These new information are relevant for a better understanding of the circumstances in which NO overproduction by iNOS may play either a beneficial or deleterious role in these tissues.

Triggering role of nitric oxide in the delayed protective effect of monophosphoryl lipid A in rat heart

1. The main objective of the present study was to further evaluate the role of nitric oxide (NO) in delayed cardiac protection against ischaemia-reperfusion injury induced by monophosphoryl lipid A (MLA). 2. For this purpose, rats were administered with either 0.5 or 2.5 mg kg(-1) MLA (i.p.). Eight or 24 h later, in vivo NO production in the heart was analysed by electron paramagnetic resonance (EPR) spin trapping technique. In parallel experiments, hearts were removed and perfused according to Langendorff. Functional ventricular parameters and incidence of ventricular fibrillation (VF) were determined after 30 min global ischaemic insult (37 degrees C) followed by 30 min reperfusion. Vascular reactivity of aortic rings was also assessed. 3. Hearts from rats pretreated with 2.5 mg kg(-1) MLA for 24 h (but not those from rats treated with 0.5 mg kg(-1) MLA for 8 and 24 h, or with 2.5 mg kg(-1) MLA for 8 h) exhibited preservation of ventricular function (LVDP, +/-dP/dtmax) and a reduced incidence of VF (25% vs 87.5% in vehicle control) during reperfusion. At the cardioprotective dose of 2.5 mg kg(-1) (for 8 or 24 h), MLA did not produce alterations of the contractile response of aortic rings to noradrenaline. 4. An increased formation of NO was detected in hearts removed from rats pretreated with 2.5 mg kg(-1) MLA for 8 h, but not in those from rats treated for 24 h (or with 0.5 mg kg(-1) MLA). 5. Pretreatment of the animals with the inhibitors of inducible NO-synthase, aminoguanidine (2x300 mg kg(-1)) or L-N6-(1-Iminoethyl)-lysine (L-NIL, 10 mg kg(-1)) abolished both MLA (2. 5 mg kg(-1))-induced rise of NO production (observed 8 h after MLA) and cardioprotection (observed 24 h after MLA). However MLA-induced cardioprotection was not attenuated when the hearts were perfused with aminoguanidine (150 microM) for 30 min before the ischaemic insult. 6. Altogether, the present data suggest that NO acts as a trigger rather then a direct mediator of the delayed cardioprotective effect of MLA in rat heart.

Dinitrosyl iron complexes with thiol-containing ligands and S-nitroso-D,L-penicillamine as inductors of heat shock protein synthesis in H35 hepatoma cells

The concentration-dependent effect of various nitric oxide donors on synthesis of different heat shock proteins was evaluated in Reuber H35 hepatoma cells and their heat shock protein-inducing ability was compared with the effect of a heat shock. A 6 h incubation of H35 cells with the dimeric (diamagnetic) form of dinitrosyl iron complex with glutathione or N-acetyl-L-cysteine activated synthesis of various heat shock proteins, heat shock protein 28, 32, 60, 70, 90 and 100. Synthesis of these proteins was evaluated by [35S]methionine and [35S]cysteine labelling with subsequent separation of proteins by polyacrylamide gel electrophoresis. The dinitrosyl iron complex with glutathione appeared to be the most efficient inductor of heat shock protein synthesis and initiated the synthesis of heat shock protein 28 even more efficiently than a 30 min heating of cells. In the same experiments, S-nitroso-D,L-penicillamine exerted a considerably lesser effect on the synthesis of heat shock proteins. It was suggested that the active moiety of dinitrosyl iron complexes as inductors of heat shock protein synthesis is represented by their Fe+(NO+)2 groups which move to thiol groups of the proteins participating in the initiation of heat shock protein synthesis.

Induction of nitric oxide synthase and dual effects of nitric oxide and cyclooxygenase products in regulation of arterial contraction in human septic shock

BACKGROUND

The role of endogenous nitric oxide (NO) and cyclooxygenase metabolites was investigated in contractile responses of small omental arteries from patients with hyperdynamic septic shock.

METHODS AND RESULTS

Expression of inducible NO synthase (immunostaining) and a high but variable level of NO production (NO spin trapping) was detected in arteries from patients with septic shock. In these vessels, ex vivo contractile responses to the thromboxane A2 analogue U46619 and to low concentrations of norepinephrine (NE) (up to 10 micromol/L) were not significantly different from controls. However, higher concentrations of NE caused pronounced fading of contraction in septic but not in nonseptic arteries. Exposure to either the NO synthase inhibitor NG-nitro-L-arginine methyl ester or the cyclooxygenase inhibitor indomethacin had no effect in control vessels. However, both inhibitors increased the response to the contractile effects of the 2 agonists only in patients with septic shock. In contrast to NG-nitro-L-arginine methyl ester, which decreased the threshold concentration of the fading effect of NE, indomethacin abolished this effect in arteries from septic patients.

CONCLUSIONS

These results provide direct evidence for the induction of NO synthase in small arteries from patients with septic shock. They suggest that in these arteries, increased production of NO, in conjunction with vasodilatory cyclooxygenase metabolites, contributes to counteract hyperreactivity to agonists and decreases the cyclooxygenase product-mediated pronounced fading of contraction caused by a high concentration of NE.

The inducible nitric oxide synthase in vascular and cardiac tissue

Expression of the inducible form of nitric oxide synthase (iNOS) has been reported in a variety of cardiovascular diseases. The resulting high output nitric oxide (NO) formation, besides the level of iNOS expression, depends also on the expression of the metabolic pathways providing the enzyme with substrate and cofactor. NO may trigger short and long term effects which are either beneficial or deleterious, depending on the molecular targets with which it interacts. These interactions are governed by local factors (like the redox state). In the cardiovascular system, the major targets involve not only guanylyl cyclase, but also other haem proteins, protein thiols, iron-non-haem complexes, and superoxide anion (forming peroxynitrite). The latter has several intracellular targets and may be cytotoxic, despite the existence of endogenous defence mechanisms. These interactions may either trigger NO effects or represent releasable NO stores, able to buffer NO and prolong its effects in blood vessels and in the heart. Besides selectively inhibiting iNOS, a number of other therapeutic strategies are conceivable to alleviate deleterious effects of excessive NO formation, including peroxynitrite (ONOO-) scavenging and inhibition of metabolic pathways triggered by ONOO-. When available, these approaches might have the advantage to preserve beneficial effects of iNOS induction. Counteracting vascular hyper-responsiveness to endogenous vasoconstrictor agonists in septic shock, or inducing cardiac protection against ischaemia-reperfusion injury are examples of such beneficial effects of iNOS induction.

Role of adventitial nitric oxide in vascular hyporeactivity induced by lipopolysaccharide in rat aorta

This study was designed to elucidate the role of the adventitia in NO-mediated vascular effects of lipopolysaccharide (LPS). After incubation of rat aorta with LPS, the adventitia generated 3.5 times more nitrite plus nitrate than a corresponding segment of media. Control media covered by adventitia from LPS-treated aortic rings exhibited a 4 fold elevated level of cyclic GMP. Medial layers from LPS-treated aortic rings (like LPS-treated adventitia-intact rings) exhibited a decrease in sensitivity to noradrenaline (NA) that was reversed by 1H-(1,2,4)oxadiazolo(4,3-a)quinoxalin-1-one (1 microM) or N omega-nitro-L-arginine methylester (0.3 mM). However, in contrast to LPS-treated adventitia-intact rings, medial layers showed no reduction in maximal contraction to NA and virtually no relaxation to L-arginine. These data indicate that in blood vessels exposed to LPS, the adventitia is a more powerful source of NO than the media. The adventitia-derived NO can reach soluble guanylyl cyclase in the medial layer and contribute greatly to vascular hyporeactivity and L-arginine-induced relaxation observed in blood vessels exposed to LPS.

Nitric oxide-related cyclic GMP-independent relaxing effect of N-acetylcysteine in lipopolysaccharide-treated rat aorta

1. We have recently demonstrated the formation of protein-bound dinitrosyl-iron complexes (DNIC) in rat aortic rings exposed to lipopolysaccharide (LPS) and shown that N-acetylcysteine (NAC) can promote vasorelaxation in these arteries, possibly via the release of nitric oxide (NO) as low molecular weight DNIC from these storage sites. The aim of the present study was to investigate further the mechanism of the relaxation induced by NAC in LPS-treated vessels. 2. In rings incubated with LPS (10 microg ml(-1) for 18 h) and precontracted with noradrenaline (NA, 3 microM) plus N(omega)-nitro-L-arginine methylester (L-NAME, 3 mM), the relaxation evoked by NAC (0.1 to 10 mM) was abolished by 1H-[1,2,4]oxadiazolo[4,3-a]quinoxalin-1-one (ODQ, 1 microM, a selective inhibitor of soluble guanylyl cyclase) but not affected by Rp-8-bromoguanosine 3'5'-cyclic monophosphorothioate (Rp-8BrcGMPS, 60 microM a selective inhibitor of cyclic GMP-dependent protein kinase). Tetrabutylammonium (TBA, 3 mM, as a non selective K+ channels blocker) or elevated concentration of external KCl (25 or 50 mM) significantly attenuated the NAC-induced relaxation. Selective K+ channels blockers (10 microM glibenclamide, 0.1 microM charybdotoxin, 0.5 microM apamin or 3 mM 4-aminopyridine) did not affect the NAC-induced relaxation. The relaxing effect of NAC (10 mM) was not associated with an elevation of guanosine 3':5' cyclic monophosphate (cyclic GMP) in LPS-treated rings. 3. In aortic rings precontracted with NA (0.1 microM), low molecular weight DNIC (with thiosulphate as ligand, 1 nM to 10 microM) evoked a concentration-dependent relaxation which was antagonized by ODQ (1 microM) and Rp-8BrcGMPS (150 microM) but not significantly affected by TBA (3 mM) or by the use of KCl (50 mM) as preconstricting agent. The relaxation produced by DNIC (0.1 microM) was associated with an 11 fold increase in aortic cyclic GMP content, which was completely abolished by ODQ (1 microM). 4. Taken together with our previous data, the main finding of the present study is that the vascular relaxation induced by NAC in LPS-treated aorta, although probably related to NO through an interaction via preformed NO stores, was not mediated by activation of the cyclic GMP pathway. It may involve the activation of TBA-sensitive K+ channels. The differences in the mechanism of relaxation induced by NAC and by exogenous DNIC suggest that the generation of low molecular weight DNIC from protein-bound species does not play a major role in the NAC-induced relaxation observed in LPS-treated rat aorta. In addition, it is suggested that ODQ may display other properties than the inhibition of soluble guanylyl cyclase.

Induction of nitric oxide production by polyosides from the cell walls of Streptococcus mutans OMZ 175, a gram-positive bacterium, in the rat aorta

The cardiovascular dysfunctions associated with septic shock induced by gram-negative or gram-positive bacteria (gram-positive or gram-negative septic shock) are comparable. In gram-negative septic shock, lipopolysaccharide (LPS) induces nitric oxide (NO) synthase, which contributes to the vascular hypotension and hyporeactivity to vasoconstrictors. The role of NO in gram-positive septic shock and the nature of the bacterial wall components responsible for the vascular effects of gram-positive bacteria are not well known. This study investigated the vascular effects of cell wall serotype polyosides, rhamnose glucose polymers (RGPs), from Streptococcus mutans, in comparison with lipoteichoic acid (LTA) from Staphylococcus aureus, on the induction of NO synthase activity in the rat aorta. We show that 10 microg of both RGPs and LTA per ml induced hyporeactivity to noradrenaline, L-arginine-induced relaxation, increases of 2.2- and 7.8-fold, respectively, of cyclic GMP production, and increases of 7- and 12-fold in nitrite release. All of these effects appeared after several hours of incubation and were inhibited by N(omega)-nitro-L-arginine methyl ester (L-NAME), an inhibitor of NO synthase. Electron paramagnetic resonance spin trapping experiments demonstrated directly that RGPs and LTA induced NO overproduction (four- to eightfold, respectively) in rat aortic rings; this production was inhibited by L-NAME and prevented by dexamethasone. These results demonstrate directly the induction of NO production in vascular tissue by LTA and show that another, chemically different component of gram-positive bacteria can also have these properties. This result suggests that different components of the gram-positive bacterial wall could be implicated in the genesis of cardiovascular dysfunctions observed in gram-positive septic shock.