Nitric oxide: an endogenous modulator of leukocyte adhesion

Exposure to shear stress alters endothelial adhesiveness. Role of nitric oxide

BACKGROUND

Shear stress increases the release of nitric oxide (NO) by endothelial cells (ECs). We and others have provided evidence that endothelium-derived NO inhibits monocyte adhesion to the vessel wall. We therefore hypothesized that previous exposure to shear stress would inhibit endothelial adhesiveness for monocytes by virtue of its effect to increase NO release.

METHODS AND RESULTS

Confluent monolayers of bovine aortic endothelial cells, human aortic endothelial cells, or human venous endothelial cells were exposed to laminar fluid flow. Culture media were collected for measurement of NO (by chemiluminescence) and the prostacyclin metabolite 6-keto-prostaglandin F1 alpha. NOx and 6-keto-prostaglandin F1 alpha accumulated in the conditioned medium during laminar fluid flow from 30 minutes to 24 hours in a time-dependent fashion. In another set of studies, ECs previously exposed to flow or to static conditions were washed with Hanks' buffer and exposed to THP-1 cells for 30 minutes. Adherent cells were counted by microscopy. Previous exposure to flow reduced endothelial adhesiveness for monocytes by 50% (P < .05). The effect of flow on endothelial adhesiveness occurred within 30 minutes. This effect was abrogated by nitro-L-arginine (an antagonist of NO synthesis), as well as by tetraethylammonium ion (an antagonist of the flow-activated potassium channel); the effects of these inhibitors were reversed by the NO donor SPM-5185. Although the cyclo-oxygenase inhibitor indomethacin totally inhibited the flow-induced production of prostacyclin by ECs, it minimally affected adherence of THP-1 cells. The early effect of flow on endothelial adhesiveness was not mediated by alterations in the expression of the endothelial adhesion molecules VCAM-1 or ICAM-1 as assessed by fluorescent activated cell sorting.

CONCLUSIONS

Shear stress alters endothelial adhesiveness for monocytes; at early time points, this effect is largely due to flow-stimulated release of NO and, to a lesser extent, prostacyclin. This effect of flow occurs within 30 minutes and is probably due to alterations in the signal transduction or activation state (rather than the expression) of endothelial adhesion molecules.

Effects of magnesium on nitric oxide synthase activity in endothelial cells

Pages C612<C618: A. B. Howard, R. W. Alexander, and W. R. Taylor. “Effects of magnesium on nitric oxide synthase activity in endothelial cells.” Page C614, legend to Fig. 1: the open bars refer to A-23187-stimulated cells and the solid bars refer to cells under basal conditions, not the reverse as published.

Effect of nitric oxide donors on neutrophil responses induced by immune complexes

The present study characterizes the effect of two nitric oxide (NO) donors, S-nitrosoglutathione (GSNO) and sodium nitroprusside (SNP), on the ability of neutrophils to perform different responses triggered by immune complexes (IC). Pretreatment of neutrophils with either GSNO or SNP exerted a biphasic action on antibody-dependent cellular cytotoxicity (ADCC) performed against erythrocytes (E) coated with IgG antibodies (IgG-E), depending on the amount of IgG employed. While with high amounts of antibodies ADCC was markedly inhibited, at low amounts of antibodies it was significantly increased. Both effects were prevented by haemoglobin, a NO scavenger. Moreover, these effects were reproduced by the cell-permeable analogue of cGMP, dibutyryl cGMP (Bt2cGMP). Other neutrophil functions triggered by IgG-E were also examined. It was found that NO donors did not affect either the phagocytosis of IgG-E or the emission of chemiluminescence (CL). Finally, neutrophil functions triggered by soluble IC (sIC) and precipitating IC (pIC) were analysed. It was observed that NO donors did not modify either cytotoxicity performed towards non-sensitized target cells or CL emission. The significance of these results is discussed.

Inhibition of neointimal proliferation in rabbits after vascular injury by a single treatment with a protein adduct of nitric oxide

Endothelium-derived relaxing factor is important for vascular homeostasis and possesses qualities that may modulate vascular injury, including vasodilation, platelet inhibition, and inhibition of smooth muscle proliferation. S-nitrososerum albumin is a naturally occurring adduct of nitric oxide (NO) with a prolonged biologic half-life and is a potent vasodilator and platelet inhibitor. Given the avidity of serum albumin for subendothelial matrix and the antiproliferative effects of NO, we investigated the effects of locally delivered S-nitroso-bovine serum albumin (S-NO-BSA) and a polythiolated form of bovine serum albumin (pS-BSA) modified to carry several S-nitrosothiol groups (pS-NO-BSA) on neointimal responses in an animal model of vascular injury. Locally delivered S-NO-BSA bound preferentially to denuded rabbit femoral vessels producing a 26-fold increase in local concentration compared with uninjured vessels (P = 0.029). pS-NO-BSA significantly reduced the intimal/medial ratio (P = 0.038) and did so in conjunction with elevations in platelet (P < 0.001) and vascular cGMP content (P < or = 0.001). pS-NO-BSA treatment also inhibited platelet deposition (P = 0.031) after denuding injury. Comparison of BSA, S-NO-BSA, pS-NO-BSA, and control revealed a dose-response relationship between the amount of displaceable NO delivered and the extent of inhibition of neointimal proliferation at 2 wk (P < or = 0.001). Local administration of a stable protein S-nitrosothiol inhibits intimal proliferation and platelet deposition after vascular arterial balloon injury. This strategy for the local delivery of a long-lived NO adduct has potential for preventing restenosis after angioplasty.

Effects of magnesium on nitric oxide synthase activity in endothelial cells

Pages C612<C618: A. B. Howard, R. W. Alexander, and W. R. Taylor. “Effects of magnesium on nitric oxide synthase activity in endothelial cells.” Page C614, legend to Fig. 1: the open bars refer to A-23187-stimulated cells and the solid bars refer to cells under basal conditions, not the reverse as published.

MRF4, Myf-5, and myogenin mRNAs in the adaptive responses of mature rat muscle

Pages C1045,C1052: J. Jacobs-El, M.-Y. Zhou, and B. Russell. “MRF4, Myf-5, and myogenin mRNAs in the adaptive responses of mature rat muscle.” Pages C1049 and C1051, Figs. 4 and 6 were inadvertently switched, although the legends as placed are correct. The correct Figs. 4 and 6 with their legends are as follows.

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Clinical biology of nitric oxide

Nitric oxide is a pluripotential molecule that acts as both an autocrine and paracrine mediator of homoeostasis, and derangement of its metabolism can be linked with many pathophysiological events. This review provides a broad overview of the basic and clinical scientific aspects of nitric oxide.

Pyocyanin from Pseudomonas aeruginosa inhibits prostacyclin release from endothelial cells

Pseudomonas aeruginosa pneumonia causes a vasculitis of small pulmonary arteries. While the fully developed lesion demonstrates vessel wall necrosis, the early lesion is remarkable for preservation of viable endothelium despite vessel wall invasion by bacteria. Pyocyanin, an exoproduct of P. aeruginosa, markedly inhibited prostacyclin production by pulmonary artery endothelial cells without causing cell lysis. Pyocyanin might after vascular homeostasis in the absence of cytolysis.

Peritoneal dialysis solutions reverse the hemodynamic effects of nitric oxide synthesis inhibitors

Nitric oxide (NO) synthesis is inhibited by a variety of L-arginine analogs including NG-nitro-L-arginine methyl ester (L-NAME) and NG NG-dimethylarginine (ADMA). ADMA is present in elevated concentrations in renal failure and potentially could alter microcirculatory hemodynamics during peritoneal dialysis (PD). This investigation utilized the techniques of intravital microscopy to quantitate the mesenteric arteriolar hemodynamic effects of PD solutions during NO synthesis inhibition. L-NAME (100 microns) produced maximum arteriolar vasoconstriction to 74% of baseline diameter (19.9 +/- 2.2 vs. 26.9 +/- 1.4 microns, P < 0.001, N = 10) and ADMA (100 microns) to 68% (20.5 +/- 2.5 vs. 30.1 +/- 2.0 microns, P < 0.01, N = 6). L-NAME decreased red blood cell velocity to 44% of baseline velocity (3.8 +/- 0.8 vs. 8.5 +/- 1.1 mm/second, P < 0.001) and ADMA to 52% (5.1 +/- 1.1 vs. 9.8 +/- 0.9 mm/second, P < 0.01, N = 6). Despite NO synthesis inhibition, standard PD solutions reversed these hemodynamic effects with both 1.5% and 4.25% Dianeal (Baxter) rapidly reversing the vasoconstriction and restoring blood flow back to baseline values. When Dianeal and L-NAME were simultaneously superfused, no L-NAME induced vasoconstriction occurred and Dianeal maintained vasodilatory properties despite L-NAME (P < 0.01, N = 5). This investigation reaffirms that basal levels of NO are important in maintaining normal hemodynamics in the mesenteric microcirculation. Reversal of the L-NAME induced arteriolar hemodynamic effects by Dianeal suggests that the endogenous NO synthesis inhibitor ADMA has no significant effects in the regulation of the mesenteric microvascular arteriolar hemodynamics during PD. Since these PD solutions remain vasoactive despite NO synthesis inhibition, this suggests that these PD solutions possess vasoactive properties primarily through a NO independent mechanism.

Exogenous nitric oxide elicits chemotaxis of neutrophils in vitro

Nitric oxide (NO) has been shown to be both an intercellular and intracellular messenger. We propose here that exogenous NO induces chemotactic locomotion of human neutrophils. Indeed, when human neutrophils were placed in a gradient of a nitric oxide donor (S-nitroso-N-acetylpenicillamine; SNAP), a directed locomotion was induced, as evidenced by experiments of chemotaxis under agarose. Degraded SNAP (i.e., SNAP solution which had previously released NO) did not induce directed locomotion. Moreover, oxyhemoglobin, a scavenger of free NO, suppressed the chemotactic effect of SNAP, whereas LY-83583, a soluble guanylate cyclase inhibitor, inhibited the SNAP-mediated chemotaxis in a dose-response manner. Other unrelated NO donors, SIN-1 and S-nitroso-cysteine--a natural S-nitroso-compound, also induced a directed locomotion of neutrophils. Taken together, these in vitro experiments indicate that exogenous NO could mediate the chemotaxis of neutrophils and thus suggest that NO could contribute to neutrophil recruitment in vivo.

Dietary antioxidants and cigarette smoke-induced biomolecular damage: a complex interaction

Epidemiologic evidence suggests that cigarette smoking is a major risk factor for chronic obstructive pulmonary diseases such as chronic bronchitis and emphysema, for carcinogenesis, and for cardiovascular disease. However, the precise mechanisms of these effects are incompletely understood. The gas phase of cigarette smoke contains abundant free radicals including nitric oxide. Hence, cigarette smoke may induce some of its damaging effects by free radical mechanisms. We report that exposure of plasma, a model for respiratory tract lining fluids, to gas-phase cigarette smoke causes depletion of antioxidants, including ascorbate, urate, ubiquinol-10, and alpha-tocopherol, and a variety of carotenoids, including beta-carotene. Gas-phase cigarette smoke induced some lipid peroxidation, as measured by cholesteryl linoleate hydroperoxide (18:2OOH) formation. Ascorbate was effective in preventing 18:2OOH formation. In contrast to the low concentrations of lipid hydroperoxides measured (< 1 mumol/L), protein carbonyl formation, a measure of protein modification, increased by approximately 400 mumol/L after nine puffs of cigarette smoke. Reduced glutathione inhibited protein carbonyl formation, whereas other plasma antioxidants, including ascorbate, were ineffective. alpha, beta-Unsaturated aldehydes (acrolein and crotonaldehyde) in cigarette smoke may react with protein -SH and -NH2 groups by a Michael addition reaction that results in a protein-bound aldehyde functional group. Gas-phase cigarette smoke is capable of converting tyrosine to 3-nitrotyrosine and dityrosine, indicating free radical mechanisms of protein damage by nitrogen oxides. Aldehydes and nitrogen oxides in cigarette smoke may be significant contributors to biomolecular damage, and endogenous antioxidants can attenuate some of these adverse effects.

Regulation of endothelial cell nitric oxide synthase mRNA expression by shear stress

Shear stress enhances expression of Ca(2+)-calmodulin-sensitive endothelial cell nitric oxide synthase (ecNOS) mRNA and protein in bovine aortic endothelial cells (BAEC). The present studies were performed to investigate mechanisms responsible for regulation of ecNOS mRNA expression by shear stress and to determine if this induction of ecNOS mRNA is accompanied by an enhanced nitric oxide (NO) production. Shear stresses of 15 dyn/cm2 for 3-24 h resulted in a two- to threefold increase of ecNOS mRNA content quantified by Northern analysis in BAEC. Shear stresses (1.2-15 dyn/cm2) for 3 h resulted in an induction of ecNOS mRNA in a dose-dependent manner. In human aortic endothelial cells, shear stresses of 15 dyn/cm2 for 3 h also resulted in ecNOS mRNA induction. In BAEC, this induction in ecNOS mRNA was prevented by coincubation with actinomycin D (10 micrograms/ml). The K+ channel antagonist tetraethylammonium chloride (3 mM) prevented increase in ecNOS mRNA in response to shear stress. The ecNOS promotor contains putative binding domains for AP-1 complexes, potentially responsive to activation of protein kinase C (PKC). However, selective PKC inhibitor calphostin C (100 nM) did not inhibit ecNOS induction by shear stress. Finally, production of nitrogen oxides under both basal conditions and in response to the calcium ionophore A-23187 (1 microM) by BAEC exposed to shear stress was increased approximately twofold compared with cells not exposed to shear stress. These data suggest that ecNOS mRNA expression is regulated by K+ channel opening, but not by activation of PKC, and that shear not only enhances ecNOS mRNA expression but increases capacity of endothelial cells to release NO.

Disparate effects of nitric oxide on lung ischemia-reperfusion injury

BACKGROUND

Inhaled nitric oxide (.NO) has been found to be a potent pulmonary vasodilator. We assessed whether .NO, through this function or others, could alleviate lung reperfusion injury.

METHODS

Rats underwent thoracotomy, with clamps used to create left lung ischemia. After 90 minutes of ischemia, clamps were released, permitting reperfusion for either 30 minutes or 4 hours. Additional animals received inhaled .NO via the ventilator to determine its effects on reperfusion injury.

RESULTS

Lung injury, measured by increased vascular permeability using iodine-125-labeled bovine serum albumin leakage, was significantly increased in ischemic-reperfused animals compared with time-matched shams not undergoing ischemia. Inhaled .NO delivered at the start of reperfusion worsened injury at 30 minutes but was protective at 4 hours. The increased injury could be avoided either by delaying .NO for 10 minutes or by treating the animals with superoxide dismutase before reperfusion. .NO reversed postischemic pulmonary hypoperfusion at 4 hours, as measured by labeled microspheres. Lung neutrophil content was significantly reduced at 4 hours in .NO-treated animals.

CONCLUSIONS

.NO is toxic early in reperfusion, due to its interaction with superoxide, but is protective at 4 hours of reperfusion, due to reversal of postischemic lung hypoperfusion and reduction of lung neutrophil sequestration.

Effect of L-arginine cardioplegia on recovery of neonatal lamb hearts after 2 hours of cold ischemia

BACKGROUND

Despite hypothermia and cardioplegia, myocardial ischemia followed by reperfusion results in both ventricular and endothelial dysfunction. The endothelial dysfunction is characterized by a reduced response to acetylcholine, which implies a reduced ability of the endothelium to release nitric oxide after hypothermic ischemia and reperfusion. We have previously demonstrated that infusion of the nitric oxide precursor L-arginine only during reperfusion after hypothermic ischemia significantly improves the recovery of ventricular function and results in an increased vasodilator response to the infusion of acetylcholine. In contrast, other investigators have found that nitric oxide has deleterious effects during postischemic reperfusion.

METHODS

In the current experiments we have further examined the role of endothelial production of nitric oxide by adding 10 mmol/L L-arginine to cardioplegia in isolated, blood-perfused neonatal lamb hearts having 2 hours of cold cardioplegic ischemia. In another group 10 mmol/L D-arginine, an inactive enantiomer of L-arginine, was added to the cardioplegia. Controls received only cardioplegia (dextrose-potassium).

RESULTS

At 30 minutes of reperfusion, the L-arginine group showed a significantly improved recovery in left ventricular systolic function (maximum developed pressure, developed pressure at a constant balloon volume [V10] resulting in an end-diastolic pressure of 10 mm Hg before ischemia, positive maximum dP/dt, and dP/dt at V10), diastolic function (negative maximum dP/dt and end-diastolic pressure at V10), coronary blood flow, endothelial function (assessed by the coronary vascular resistance response to acetylcholine), and myocardial oxygen consumption compared with the control group (p < 0.05). There were no significant differences in the recovery of any variables between the D-arginine and control groups.

CONCLUSIONS

These results suggest that provision of more substrate for the endothelial production of nitric oxide during ischemia has an important salutary effect on the recovery of postischemic myocardial and endothelial function and provide further evidence for an important role for the endothelial production of nitric oxide in the response to hypothermic ischemia and reperfusion in the neonatal lamb heart.

L-arginine reduces endothelial inflammation and myocardial stunning during ischemia/reperfusion

BACKGROUND

This study evaluated whether the nitric oxide precursor L-arginine could reduce ischemia/reperfusion injury by preventing leukocyte-endothelial interactions.

METHODS

Normothermic regional ischemia was induced in the open-chest working pig heart for 30 minutes followed by 90 minutes of reperfusion. A preischemic 10-minute intravenous infusion of 4 mg.kg-1.min-1 of L-arginine (n = 12) was compared with 12 control pigs. Nitric oxide release was measured from the coronary sinus using an amperometric probe. Left ventricular function, malonaldehyde, creatine kinase, myocardial oxygen extraction, and the soluble adhesion molecules (intracellular adhesion molecule-1, endothelial leukocyte adhesion molecule-1, and vascular cell adhesion molecule-1) were measured.

RESULTS

Nitric oxide release was significantly reduced from baseline throughout ischemia/reperfusion only in the control group. Systolic and diastolic function, and myocardial oxygen extraction were also significantly decreased during early reperfusion in the control compared with the L-arginine group. Peak creatine kinase release was not significantly different between groups. The incidence of ventricular fibrillation, malonaldehyde release, and soluble intracellular adhesion molecule-1, endothelial leukocyte adhesion molecule-1, and vascular cell adhesion molecule-1 were each significantly decreased during reperfusion in the L-arginine group.

CONCLUSIONS

L-Arginine reduced lipid peroxidation, plasma levels of soluble adhesion molecules, myocardial stunning, and arrhythmias. These results support an excessive endothelial injury/inflammatory response after regional ischemia/reperfusion that can be ameliorated through augmented nitric oxide.

Supplement of nitric oxide attenuates neutrophil-mediated reperfusion injury

BACKGROUND

Nitric oxide (NO) derived from the endothelial cell has been identified as a constitutive chemical mediator that regulates the function of the endothelial cell in association with neutrophil (PMN) adhesion and activation. However, its role in the pathogenesis of myocardial reperfusion injury is not clear.

METHODS AND RESULTS

Fifteen isolated rat hearts were perfused with modified Krebs-Henseleit solution and subjected to 20 minutes of global and normothermic ischemia. Then the hearts were reperfused for 45 minutes with different protocols: the control (C) group was reperfused without PMNs, the P group was reperfused with PMNs, and the N group was reperfused with PMNs and nitroprusside (10(-5) mol/L). The ozone chemiluminescence method was used for direct measurement of NO in the coronary effluent during reperfusion. NO in the coronary effluent in the C group decreased at reperfusion after normoxic perfusion, and this decrease in NO continued for the first 15 minutes of reperfusion. Percentage recovery of left ventricular developed pressure and coronary flow was significantly lower in the P group than that in the N group. Also, the N group had a significantly lesser Luminol-elicited chemiluminescence of the coronary effluent and ratio of PMN adherence to myocardial vasculature compared with the P group.

CONCLUSIONS

This study demonstrated directly the decrease in NO production during reperfusion and showed that supplement of NO with NO donor attenuated the injury in which PMNs were involved. The results suggest that NO plays a significant role in reperfusion injury and that supplement of NO during reperfusion appears to be useful to attenuate this injury.

Nitric oxide regulates the chemiluminescence from stimulated human neutrophils

Nitric oxide produced from L-arginine by a variety of cells, is a biologically active compound that can react with iron and thiols. The objective of this study was to investigate the effects of nitric oxide on the respiratory burst from human neutrophils. Treatment with nitroprusside increased the chemiluminescence from neutrophils stimulated with PMA or collagen, but not from cells stimulated with FMLP. Addition of L-arginine increased the chemiluminescence after stimulation with any of the three stimuli, while N omega-nitro-L-arginine methyl ester decreased it. Low doses of nitric oxide, either endogenously or exogenously produced, probably inhibited catalase or glutathione, leading to an increase in hydrogen peroxide available for chemiluminescence detection. This indicates that nitric oxide may reduce the protection against hydrogen peroxide in tissue and in invading catalase-positive bacteria.

Inhibition of nitric oxide biosynthesis promotes P-selectin expression in platelets. Role of protein kinase C

Inhibition of NO synthesis promotes P-selectin expression on endothelial cells; however, the precise mechanism is unclear. Because No has been shown to inhibit protein kinase C (PKC) activity, we examined the hypothesis that the NO synthase inhibitor NG-nitro-L-arginine methyl ester (L-NAME) stimulates P-selectin expression on platelets via PKC activation. Ten-minute incubation with either phorbol 12-myristate 13-acetate (PMA), thrombin, or L-NAME significantly increased P-selectin expression on platelets (as assessed by flow-cytometric analysis) and PKC activity of platelet membranes. Increased P-selectin expression induced by either PMA, thrombin, or L-NAME was significantly attenuated by the selective PKC inhibitor UCN-01 (7-hydroxystaurosporine). Furthermore, L-NAME-induced P-selectin expression was significantly attenuated by either L-arginine, 8-bromo-cGMP, or sodium nitroprusside (SNP). Interestingly, L-NAME further potentiated P-selectin upregulation by thrombin. L-NAME, thrombin, and PMA also significantly increased polymorphonuclear leukocyte adherence to the coronary artery endothelium, an effect that was significantly attenuated by the anti-P-selectin monoclonal antibody PB1.3 or by UCN-01, L-arginine, 8-bromo-cGMP or SNP but not by D-arginine or he nonblocking anti-P-selectin monoclonal antibody NBP1.6. These results indicate that inhibition of NO synthesis induces rapid P-selectin expression, which appears to be at least partially mediated by PKC activation in platelets. Similar effects and mechanisms of L-NAME on P-selectin function were also observed in endothelial cells, another site of P-selectin expression.

Immunohistochemical characterization of nitric oxide synthase activity in squamous cell carcinoma of the head and neck

This study was designed to investigate the presence of nitric oxide in human squamous cell carcinoma of the head and neck. We localized the activity of nitric oxide synthase in these tumors through immunohistochemical analysis using antibodies to L-citrulline (a byproduct of nitric oxide synthase), to inducible nitric oxide synthase, and to constitutive nitric oxide synthase. We found presence of inducible enzyme in squamous cells throughout these tumors, with the highest intensity staining occurring directly around keratin pearls. Our findings suggest that inducible nitric oxide synthase activity is present in squamous cell carcinomas of the head and neck, leading us to conclude that inducible nitric oxide synthase may play a significant role in tumor growth.

Angiotensin II-induced cardiac fibrosis in the rat is increased by chronic inhibition of nitric oxide synthase

These studies were performed to determine if the effects of angiotensin II infusion on the development of cardiac fibrosis could be modified by the chronic inhibition of nitric oxide synthase activity. NG-nitro-L-arginine-methyl ester (L-NAME) was administered to adult Wistar rats in drinking water (40 mg/kg per d). Although blood pressure was maintained at hypertensive levels after 2 wk, cardiac hypertrophy or fibrosis did not occur. Angiotensin II, given for 3 d at a dose which induced little or no blood pressure elevation and minimal if any fibrosis, caused significant fibrosis when given to a rat pretreated for 2 wk with L-NAME. This marked fibrosis did not occur if angiotensin II was given shortly after L-NAME treatment was begun or briefly after discontinuation of L-NAME. The fibrosis that occurred with combined treatment was characterized by increased immunodetectable fibronectin, the presence of inflammatory cells within interstitial and perivascular regions, and increased steady state mRNA levels for matrix genes and atrial natriuretic protein. The data indicated a regulatory role for nitric oxide in modulating the angiotensin II-induced cardiac fibrosis and suggest a potentially important autocrine or paracrine role for nitric oxide in fibroblast proliferation.

Aminoguanidine-provoked leukocyte adherence to rat mesenteric venules: role of constitutive nitric oxide synthase inhibition

1. The effects of aminoguanidine on neutrophil adherence to venules and on the diameter of arterioles in the mesenteric vascular bed of the pentobarbitone-anaesthetized rat have been compared with those of the nitric oxide synthase inhibitor, NG-nitro-L-arginine methyl ester (L-NAME). 2. Administration of L-NAME (1-10 mg kg-1, i.v.) caused a dose-dependent increase in leukocyte adherence and a reduction in leukocyte rolling velocity in postcapillary venules of the rat mesentery over 1 h. 3. Likewise, aminoguanidine (10-100 mg kg-1, i.v.) dose-dependently increased leukocyte adherence and decreased leukocyte rolling velocity over 1 h. 4. Both L-NAME and aminoguanidine caused a dose-dependent reduction in mesenteric arteriolar diameter and an increase in systemic arterial blood pressure. 5. The effects of aminoguanidine (50 mg kg-1, i.v.) on leukocyte adherence, arteriolar diameter and on blood pressure were significantly reversed by pretreatment with L-arginine (300 mg kg-1, i.v.). 6. These findings indicate that, like L-NAME, aminoguanidine can acutely promote leukocyte adherence to the mesenteric venular wall and reduce arteriolar diameter. Moreover, these acute effects were reversed by L-arginine, suggesting they are mediated through inhibition of constitutive NO synthase.

Effects of endothelin-1 and endothelin-A receptor antagonist on recovery after hypothermic cardioplegic ischemia in neonatal lamb hearts

BACKGROUND

Prior studies suggest an important role for coronary endothelium in ischemia/reperfusion (I/R) injury. Decreased endothelial release of the vasodilator nitric oxide occurs after I/R, but the role of the endothelium-derived vasoconstrictor endothelin-1 (ET-1) in I/R is unknown.

METHODS AND RESULTS

We measured plasma ET-1 concentrations by radioimmunoassay in isolated blood-perfused neonatal lamb hearts before and after 2 hours of 10 degrees C cardioplegic ischemia and examined the effects of ET-1 and the endothelin-A (ET-A) receptor antagonist BE-18257B on the postischemic recovery of isolated hearts. ET-1 levels in coronary sinus blood before ischemia and at 0 and 30 minutes of reperfusion in 8 control hearts were constant (2.2 +/- 1.2 fmol/L, 2.2 +/- 1.3 fmol/L, and 2.5 +/- 1.0 fmol/L, respectively). In group 2 (n = 6), 10 mumol/L of BE-18257B was given just before reperfusion. In group 3 (n = 8), 10 pmol/L ET-1 was given just before the start of reperfusion. At 30 minutes of reperfusion, the ET-A antagonist hearts had significantly greater recovery of LV systolic (positive dP/dt and dP/dt at V10) and diastolic function (negative dP/dt), coronary blood flow (CBF), and MVo2 compared with controls (P < .05). The ET-1 hearts showed significantly reduced recovery of LV systolic (positive maximum and volume-normalized dP/dt) and diastolic (negative maximum dP/dt) function, CBF, and myocardial oxygen consumption compared with controls (P < .05).

CONCLUSIONS

These results, combined with prior studies, suggest that I/R causes reduced production of endogenous vasodilators (eg, nitric oxide), leaving unopposed the vasoconstriction that is caused by the continued presence of ET-1. This imbalance may contribute to I/R injury. ET-A receptor antagonists may be useful therapeutic agents in reducing the injury that results from I/R.

Inhaled nitric oxide fails to confer the pulmonary protection provided by distal stimulation of the nitric oxide pathway at the level of cyclic guanosine monophosphate

It has been suggested that inhaled nitric oxide gas may be beneficial after lung transplantation, because endogenous levels of pulmonary nitric oxide decline rapidly after reperfusion. However theoretical concerns remain about the formation of highly toxic oxidants during the quenching of nitric oxide by superoxide. To determine whether distal stimulation of the nitric oxide-cyclic guanosine monophosphate pathway at the level of cyclic guanosine monophosphate might confer the beneficial vascular effects of nitric oxide without its potential toxicities, we studied an orthotopic rat left lung transplant model. In this model, hemodynamic and survival measurements can be obtained independent of the native right lung. Lungs were preserved for 6 hours at 4 degrees C in Euro-Collins solution alone (control, n = 6) or supplemented with the cyclic guanosine monophosphate analog, 8-(4-chlorophenylthio)-guanosine-3',5'-cyclic guanosine monophosphate (cGMP, n = 4). In additional experiments in which lungs were preserved with Euro-Collins solution alone, inhaled nitric oxide was administered during reperfusion (NO, n = 12). Thirty minutes after transplantation and ligation of the native right pulmonary artery, pulmonary vascular resistance, arterial oxygenation, graft neutrophil infiltration (myeloperoxidase activity), and recipient survival were evaluated. Cyclic guanosine monophosphate decreased pulmonary vascular resistance (1.1 +/- 0.2 vs 12.1 +/- 6.3 mm Hg/ml/min, p < 0.05), improved oxygen tension (369 +/- 56 vs 82.8 +/- 48 mm Hg, p < 0.05), reduced myeloperoxidase activity (1.7 +/- 0.3 vs 3.1 +/- 0.9 delta Abs 460 nm/min, p < 0.05), and improved recipient survival (100% vs 0%, p < 0.005) compared with Euro-Collins solution alone (control group). Animals receiving inhaled nitric oxide during reperfusion did not differ from control animals with respect to any of these parameters. These data suggest that distal stimulation of the nitric oxide-cyclic guanosine monophosphate pathway at the level of cyclic guanosine monophosphate has a protective effect that is not seen with inhaled nitric oxide in the immediate pulmonary reperfusion period.

Inducible nitric oxide synthase in inflammation

Inflammation, the reaction of vascularized tissue to local injury, not only limits the effects of injury; it may also be the underlying pathological process which initiates or sustains disease. In this paper, the evidence is reviewed for a role for nitric oxide (NO) as a chemical indicator of inflammation and inflammatory diseases.

Human endothelial cells bioactivate organic nitrates to nitric oxide: implications for the reinforcement of endothelial defence mechanisms

Although in therapeutic use for more than a century, the mode of cellular action of organic nitrates remains incompletely understood. Despite ample experimental evidence from animal studies to show that nitrates are metabolized to NO in the vascular smooth muscle, direct demonstration of such an activity in human vascular cells is still lacking. Moreover, the role of the endothelium in modulating the pharmacodynamic action of nitrates is far from clear. We therefore aimed to investigate whether or not human endothelial cells are capable of bioactivating these drugs to NO and whether the amounts generated are sufficient to elicit any biological effects. Using cultured human umbilical vein endothelial cells (HUVECs) as an established model system a combination of three different methods was used to address this issue: (1) quantification of NO formation upon endothelial nitrate metabolism using the oxyhaemoglobin technique; (2) evaluation of the second messenger response using radioimmunoassay for cGMP; and (3) assessment of mechanism and extent of potentiation of the anti-aggregatory effect of nitrates in the presence of endothelial cells as a relevant bioassay. We now show that superfusion of cultured human endothelial cells on microcarrier beads with either glyceryl trinitrate (GTN) or isosorbide dinitrate (ISDN; both at 0.1-100 mumol L-1) results in a concentration-dependent formation of NO. NO generation from isosorbide 5-mononitrate (IS-5-N) was below the detection limit. The amounts of NO produced (maximally 2.97 +/- 0.98 pmoles NO min-1 x mg protein with 100 mumol L-1 GTN; n = 8) were similar to those elicited upon challenge of the cells with 100 nM bradykinin. NO formation from either organic nitrate was accompanied, in a concentration-dependent and methylene blue-inhibitable manner, by stimulation of endothelial soluble guanylyl cyclase with consequent increases in the intracellular level of cGMP (maximally 32-fold over basal levels with ISDN), a significant portion of which was released into the extracellular space. Upon continuous 30 min superfusion or repeated application of high concentrations of GTN (100 mumol L-1) nitrate bioactivation to NO was subject to partial tachyphylaxis. Co-incubation of washed human platelets with HUVECs potentiated the anti-aggregatory action of nitrates in a cell number dependent and oxyhaemoglobin-sensitive manner and this effect, too, was accompanied by increases in intraplatelet cGMP levels. The potentiating effect was largely inhibited after blockade of sulfhydryl groups by pre-incubation of HUVECs with N-ethylmaleimide and completely abrogated after pretreatment of cells with the tissue fixative glutaraldehyde. These results demonstrate that human endothelial cells are capable of bioactivating organic nitrates to NO by an enzymatic, apparently thiol-sensitive pathway, in quantities sufficient to influence endothelial and platelet function. Besides the well known vasorelaxant action of organic nitrates, which is mainly due to their metabolism in the smooth muscle compartment, these drugs may therefore be endowed with a hitherto underestimated potential to directly influence endothelial functions via the NO/cGMP pathway. Through specific bioactivation in the endothelium itself organic nitrates can thus mimic and reinforce protective functions normally served by a functional endothelium such as the modulation of blood cell/vessel wall interactions and inhibition of cell proliferation.

Accelerated endothelial regeneration and intimal hyperplasia following a repeated denudation of rabbit carotid arteries: morphological and immunohistochemical studies

1. We compared endothelial regeneration and intimal thickening after endothelial denudation between normal and sclerotic carotid arteries (CA). Endothelial denudation of the right CA of rabbits formed intimal thickening covered with regenerated endothelial cells (EC) in 6 weeks, which was considered as the sclerosis model. Both CA were then denuded. Morphological and immunohistochemical studies using antibodies for proliferating cell nuclear antigen (PCNA), von Willebrand factor and macrophages were performed. 2. Regeneration of EC were observed 24 h after denudation on both CA, but completed earlier in the double-denuded right CA. The density of EC in both CA increased after regeneration and gradually decreased afterwards. 3. After a single denudation on the left CA, PCNA-positive cells clearly appeared in 24 h, markedly increased in 72 h both in the intima and media, then greatly decreased in 4 and 6 weeks. 4. After a double denudation of the right CA, enhancement of the intimal hyperplasia was observed. PCNA-positive cells markedly increased in 1 week and remained significantly increased in 6 weeks both in the intima and the media. 5. We concluded from these results that the repeated endothelial denudation caused more sustained proliferation of smooth muscle cells which led to an enhancement of the intimal hyperplasia.

The involvement of nitric oxide in a mouse model of adult respiratory distress syndrome

The release of free radicals and pro-inflammatory cytokines such as nitric oxide (NO) and tumor necrosis factor alpha (TNF alpha) is commonly observed in adult respiratory distress syndrome (ARDS) following infection or exposure to microbial products. The aim of this study was to scrutinize the involvement of NO in ARDS in a mouse model determined by the sequential exposure to lipopolysaccharide (LPS) and formyl-norleucyl-phenylalanine (FNLP). Nitrite measurements in bronchoalveolar lavage fluids (BALF) and sera demonstrated that exposure to microbial products elicits large amounts of NO in LPS/FNLP-challenged mice. This release was significantly inhibited by infusion with the inducible NO synthase antagonist, aminoguanidine (AG). Our results show that LPS/FNLP exposure induces lung damage as demonstrated by protein and lactate dehydrogenase (LDH) increases in BALF. Liver damage was also detected in LPS/FNLP-challenged mice with increases in serum ornithine-carbamoyltransferase (OCT) levels. LPS/FNLP infusion led to elevated levels of the cytokines interleukin-6 (IL-6) and tumor necrosis factor alpha (TNF alpha) in the sera. LPS/FNLP also led to neutrophil adhesion in the lung vasculature, as seen by increased levels of myeloperoxydase. Interestingly, inhibition of NO release in challenged mice led to an important increase in markers of tissue damage in the lungs and livers, but a decrease in neutrophil recruitment. Infusion of AG in LPS/FNLP-challenged mice led to a much increased level of sera TNF alpha. These data suggest that after exposure to microbial products, NO generated as a result of activation of the inducible NO synthase blocks the full expression of tissue damage in the lungs.

Urinary nitrate excretion is increased in patients with rheumatoid arthritis and reduced by prednisolone

OBJECTIVES

To determine daily production of nitric oxide (NO) measured as urinary nitrate excretion, and the effect of prednisolone in patients with rheumatoid arthritis (RA).

METHODS

Twenty four hour urinary nitrate was measured by gas chromatography in 10 patients with RA, before and two to four weeks after commencement of prednisolone 0.5 mg/kg body weight, and in 18 healthy controls.

RESULTS

Before the start of prednisolone treatment the urinary nitrate excretion in patients with RA was 2.7-fold greater (p < 0.001) than that in healthy volunteers. After prednisolone it decreased significantly, by 28%, at which time inflammatory activity (as indicated by C reactive protein, erythrocyte sedimentation rate, joint count, and early morning stiffness) was also reduced considerably. Despite this decrease, the urinary nitrate excretion in patients with RA remained twice that in the control group (p < 0.05).

CONCLUSIONS

Our data suggest that the endogenous production of NO is enhanced in patients with RA. Furthermore, the results indicate that, in parallel with suppression of inflammation, this increased NO synthesis could be reduced by prednisolone treatment.

The role of nitric oxide and other endothelium-derived vasoactive substances in vascular disease

Alteration in the release and action of endothelium-derived vasoactive factors is responsible for changes in vascular reactivity early in the course of vascular disease. These factors include nitric oxide, eicosanoids, endothelium-derived hyperpolarizing factor, endothelin, and angiotensin II. Because endothelial dysfunction occurs at early stages of disease, it may reflect physiological changes that, if allowed to become chronic, are responsible for changes in vascular structure and growth and adhesivity to platelets and leukocytes, ultimately leading to atherosclerosis and thrombosis. Each of the major risk factors predisposing to vascular disease are associated with endothelial cell dysfunction, suggesting a direct etiologic link between the effects of the risk factors on the endothelium and their propensity to accelerate vascular disease. Restoration or replacement of endothelium-derived factors such as nitric oxide and prostacyclin, which impede the progression of vascular disease, or preventing the action of mediators such as vasoconstrictor eicosanoids, angiotensin II, or endothelin, which accelerate the progression of vascular disease, has become a useful paradigm in the treatment and prevention of vascular disease. Thus, understanding the physiology of endothelium-derived vasoactive factors is a necessary part of every physician's education.

Pattern of cytokines and pharmacomodulation in sepsis induced by cecal ligation and puncture compared with that induced by endotoxin

The production of tumor necrosis factor alpha (TNF-alpha), interleukin-1 beta (IL-1 beta), and IL-6 and their pharmacomodulation were evaluated in a model of polymicrobial sepsis induced in mice by cecal ligation and puncture (CLP) and were compared with the effects of endotoxin (lipopolysaccharide [LPS]) treatment. LPS levels rose as early as 1 h after CLP and increased further after 2 and 21 h. TNF-alpha was detectable in serum, spleen, liver, and lungs during the first 4 h, with a peak 2 h after CLP. IL-1 beta was measurable in serum after 24 h, and levels increased significantly in spleen and liver 4 and 8 h after CLP. IL-6 levels increased significantly in serum throughout the first 16 h after CLP. These cytokines were detectable after LPS injection, with kinetics similar to those after CLP but at a significantly higher level. To cast more light on the differences between these two animal models of septic shock, we studied the effects of different reference drugs. Pretreatment with dexamethasone (DEX); ibuprofen (IBU), an inhibitor of cyclooxygenase; and NG-nitro-L-arginine, an inhibitor of nitric oxide synthase, significantly reduced survival, while chlorpromazine (CPZ) and TNF did not affect it. Only the antibiotics and pentoxifylline significantly increased survival in mice with CLP. However, CPZ and DEX protected the mice from LPS mortality. On inhibiting TNF-alpha with DEX, CPZ, or pentoxifylline, survival was reduced, unchanged, and increased, respectively, and on increasing TNF-alpha with IBU and TNF, survival was decreased or unchanged, respectively, suggesting that the modulation of this cytokine does not play a significant role in sepsis induced by CLP, unlike treatment with LPS. The negative effects of IBU and N(G)-nitro-L-arginine suggest a protective role by prostaglandins and nitric oxide in sepsis induced by CLP.

Cyclic strain upregulates nitric oxide synthase in cultured bovine aortic endothelial cells

In vivo, endothelial cells (EC) are subjected to hemodynamic forces which may influence the production of nitric oxide. This study was designed to examine the effect of cyclic strain on the expression of endothelial nitric oxide synthase (eNOS) in cultured bovine aortic EC. EC were grown on flexible membranes which were subjected to deformation at 60 cycles/min with -5 or -20 kPa of vacuum. This results in an average strain of 6 and 10%, respectively, which is transmitted to the attached cells. Northern blot analysis of total cytosolic RNA demonstrated an increase in eNOS gene expression with both strain regimens but the increase with 10% average strain was greater than that at 6%. Nuclear runoff transcription assays confirmed the induction of eNOS transcripts. Western blot analysis showed an increase in eNOS level after 24 h of cyclic 10% average strain compared with controls or 6% average strain. Immunohistochemical staining of EC for eNOS was increased in the high strain periphery (7-24% strain) of membranes deformed with -20 kPa vacuum. These results demonstrate that cyclic strain upregulates the expression of eNOS transcripts and protein levels in bovine aortic EC thus emphasizing the importance of hemodynamic forces in the regulation of eNOS in vivo.

Nitric oxide and its role in the cardiovascular system

Nitric oxide (NO) is a ubiquitous, naturally occurring molecule found in a variety of cell types and organ systems. In the cardiovascular system, NO is an important determinant of basal vascular tone, prevents platelet activation, limits leukocyte adhesion to the endothelium, and regulates myocardial contractility. NO may also play a role in the pathogenesis of common cardiovascular disorders, including hypotension accompanying shock states, essential hypertension, and atherosclerosis. In this review, we discuss the biochemistry of NO and focus on its biology and pathophysiology in the cardiovascular system.

Suppression of cytokine production in T helper type 2 cells by nitric oxide in comparison with T helper type 1 cells

We examined the effect of nitric oxide (NO) on cytokine production in T helper (Th) cell subsets, using murine splenic CD4+ T cells and two types of Th clones. Interferon-gamma-treated murine peritoneal exudate cells (IFN-PEC) suppressed DNA synthesis to 60% of the control level in CD4+ T cells stimulated with the anti-CD3 monoclonal antibody. The production of IL-2 and IL-4 in the CD4+ T cells decreased to 63.2% and 9.2%, respectively, of the control value by co-culture with IFN-PEC. The addition of NG-monomethyl-L-arginine (L-NMMA) partially recovered the suppression of DNA synthesis. In the presence of indomethacin, the suppression of DNA synthesis was partially inhibited and the reduction in the cytokine production caused by IFN-PEC was partially recovered. The simultaneous addition of NG-monomethyl-L-arginine (L-NMMA) and indomethacin completely inhibited not only the suppression of DNA synthesis but also the reduction in the cytokine production caused by IFN-PEC. Moreover, DNA synthesis in the Th2 clone was suppressed to a greater extent than that in the Th1 clone by co-culture with IFN-PEC. This suppression in the Th1 clone was inhibited by the addition of L-NMMA, whereas the DNA synthesis in the Th2 clone was not recovered by L-NMMA. In addition, sodium nitroprusside (SNP) suppressed IL-4 production in the Th2 clone but had no effect on IL-2 production in the Th1 clone. In the experiment of the co-culture with IFN-PEC, the inhibitory-effect of NO on T cell activation was not clarified by the influence of prostaglandins. However, in conclusion, cytokine production in Th2 cells may be more susceptible to NO than that in Th1 cells.

Involvement of superoxide and xanthine oxidase in neutrophil-independent rat gastric damage induced by NO donors

1. Nitric oxide (NO) and the superoxide anion can interact to form the cytotoxic moiety, peroxynitrite. The involvement and potential source of superoxide in the gastric mucosal damage induced by local infusion of NO donors, has now been investigated in the pentobarbitone-anaesthetized rat. 2. Local intra-arterial infusion of the NO donor, sodium nitroprusside (40 micrograms kg-1 min-1) for 10 min induced macroscopically apparent gastric mucosal injury. 3. This mucosal damage was dose-dependently reduced by prior administration of a systemically acting form of superoxide dismutase conjugated with polyethylene glycol (500-2000 iu kg-1, i.v.). 4. Likewise, the mucosal damage induced by nitroprusside was dose-dependently reduced by prior administration of the xanthine oxidase inhibitor, allopurinol (20-100 mg kg-1, i.p. or 100 mg kg-1, p.o.). 5. Pretreatment with allopurinol (100 mg kg-1, i.p.) also reduced the mucosal injury induced by local intra-arterial infusion of the nitrosothiol, S-nitroso-N-acetyl-penicillamine (40 micrograms kg-1 min-1), but not that induced by local infusion of endothelin-1 (5 pmol kg-1 min-1), indicating specificity of action. 6. Prior administration (4h) of rabbit anti-rat neutrophil serum (0.4 ml kg-1, i.p.), which reduced circulating neutrophils by 90%, did not significantly protect against mucosal injury induced by nitroprusside. 7. Intravenous administration of the platelet-activating factor receptor antagonists, WEB 2086 (1 mg kg-1) or BN 52021 (10 mg kg-1), or the thromboxane synthase inhibitor, OKY 15181 (25 mg kg-1), did not modify mucosal damage induced by nitroprusside, showing lack of involvement of these neutrophil-derived mediators. 8. These findings indicate the involvement of superoxide in the injurious actions of the NO donors, implicating a cytotoxic role of peroxynitrite. Xanthine oxidase, but not neutrophils, appears to be a source of the superoxide.

Cardioprotective effect of insulin-like growth factor I in myocardial ischemia followed by reperfusion

In the present study, the cardioprotective effects of insulin-like growth factor I (IGF-I) were examined in a murine model of myocardial ischemia reperfusion (i.e., 20 min + 24 hr). IGF-I (1-10 micrograms per rat) administered 1 hr prior to ischemia significantly attenuated myocardial injury (i.e., creatine kinase loss) compared to vehicle (P < 0.001). In addition, cardiac myeloperoxidase activity, an index of neutrophil accumulation, in the ischemic area was significantly attenuated by IGF-I (P < 0.001). This protective effect of IGF-I was not observed with des-(1-3)-IGF-I. Immunohistochemical analysis of ischemic-reperfused myocardial tissue demonstrated markedly increased DNA fragmentation due to programmed cell death (i.e., apoptosis) compared to nonischemic myocardium. Furthermore, IGF-I significantly attenuated the incidence of myocyte apoptosis after myocardial ischemia and reperfusion. Therefore, IGF-I appears to be an effective agent for preserving ischemic myocardium from reperfusion injury and protects via two different mechanisms--inhibition of polymorphonuclear leukocyte-induced cardiac necrosis and inhibition of reperfusion-induced apoptosis of cardiac myocytes.

Supplemental L-arginine during cardioplegic arrest and reperfusion avoids regional postischemic injury

Unenhanced hypothermic cardioplegia does not prevent postischemic endothelial and contractile dysfunction in hearts subjected to antecedent regional or global ischemia. This study tested the hypothesis that supplementing blood cardioplegic solution and reperfusion with the nitric oxide precursor L-arginine would preserve endothelial function, reduce infarct size, and reverse postcardioplegia regional contractile dysfunction by the L-arginine-nitric oxide pathway. In 23 anesthetized dogs, the left anterior descending coronary artery was ligated for 90 minutes, after which total bypass was established for surgical "revascularization." In 10 dogs, unsupplemented multidose hypothermic blood cardioplegic solution was administered for a total of 60 minutes of cardioplegic arrest. In eight dogs, L-arginine was given intravenously (4 mg/kg per minute) and in blood cardioplegic solution (10 mmol) during arrest. In five dogs, the nitric oxide synthesis blocker N omega-nitro-L-arginine (1 mmol) was used to block the L-arginine-nitric oxide pathway during cardioplegia and reperfusion. Infarct size (triphenyltetrazolium chloride) as percent of the area at risk was significantly reduced by L-arginine compared with blood cardioplegic solution (28.2% +/- 4.1% versus 40.5% +/- 3.5%) and was reversed by N omega-nitro-L-arginine to 68.9% +/- 3.0% (p < 0.05). Postischemic regional segmental work in millimeters of mercury per millimeter (sonomicrometry) was significantly better with L-arginine (92 +/- 15) versus blood cardioplegic solution (28 +/- 3) and N omega-nitro-L-arginine (26 +/- 6). Segmental diastolic stiffness was significantly lower with L-arginine (0.46 +/- 0.06) compared with blood cardioplegic solution (1.10 +/- 0.11) and was significantly greater with N omega-nitro-L-arginine (2.70 +/- 0.43). In ischemic-reperfused left anterior descending coronary arterial vascular rings, maximum relaxation responses to acetylcholine, the stimulator of endothelial nitric oxide, was depressed in the blood cardioplegic solution group (77% +/- 4%) and was significantly reversed by L-arginine (92% +/- 3%). Smooth muscle function was unaffected in all groups. We conclude that cardioplegic solution supplemented with L-arginine reduces infarct size, preserves postischemic systolic and diastolic regional function, and prevents arterial endothelial dysfunction via the L-arginine-nitric oxide pathway.

Role of nitric oxide in lung injury associated with experimental acute pancreatitis

This study evaluated the effect of varying the synthesis of nitric oxide with sodium nitroprusside or N-nitro-L-arginine methyl ester (L-NAME) in a pancreatitis-lung injury model. Rats (n = 45) were randomized to control or caerulein-induced pancreatitis groups, treated with saline, sodium nitroprusside (0.4 micrograms/kg) or L-NAME (10 mg/kg). Myeloperoxidase activity was used as a measure of neutrophil infiltration. Wet to dry (W:D) lung weight and bronchoalveolar lavage (BAL) protein concentrations were used to assess vascular leakage. Pancreatitis was shown to induce pulmonary neutrophil influx: mean(s.e.m.) myeloperoxidase activity 6.79(0.5) units/g in caerulein-treated animals versus 2.08(0.5) units/g in controls (P < 0.001). Animals with pancreatitis showed increased microvascular leakage compared with controls (mean(s.e.m.) W:D lung weight 7.01(0.5) versus 2.85(0.2), P < 0.001; BAL protein concentration 2539(222) versus 347(32) micrograms/ml, P < 0.001). Compared with the saline-treated pancreatitis group, these changes were reduced by sodium nitroprusside (mean(s.e.m.) myeloperoxidase activity to 2.5(0.4) units/g, P < 0.001; W:D lung weight to 3.8(0.37), P < 0.001; BAL protein concentration 1389(182) micrograms/ml, P < 0.05). L-NAME exacerbated the pancreatitis-induced pulmonary oedema (W:D lung weight increased to 11.96(0.6), P < 0.001), protein leakage (BAL protein concentration rose to 3707(309) micrograms/ml, P < 0.05) and neutrophil infiltration (myeloperoxidase activity increased to 9.01(0.3) units/g, P < 0.05). These data suggest that, in vivo, nitric oxide inhibits pancreatitis-induced lung injury, possibly in part by inhibiting pulmonary neutrophil influx.

Intestinal reperfusion up-regulates inducible nitric oxide synthase activity within the lung

BACKGROUND

This study examines the hypothesis that pulmonary inducible nitric oxide synthase (iNOS) activity is up-regulated during intestinal reperfusion and that inhibition of NO generation exacerbates pulmonary microvascular dysfunction.

METHODS

Sprague-Dawley rats underwent intestinal ischemia and reperfusion (IIR) or sham operation (SHAM). Pulmonary iNOS activity was measured by quantitating the conversion of L-arginine (L-Arg) to L-citrulline. Another set of animals undergoing IIR or SHAM received an inhibitor of NOS (NG-nitro-L-arginine methylester; L-NAME; 20 mg/kg intravenously), substrate for NO generation (L-Arg; 300 mg/kg intravenously), or vehicle (normal saline solution; 3 ml). Pulmonary microvascular dysfunction was then quantitated by measuring the extravasation of Evans blue dye (EBD) into the lung.

RESULTS

Inducible NOS activity was six times greater in the lungs of animals sustaining IIR when compared with SHAM (p = 0.0005). The concentration of EBD within the lungs of animals sustaining IIR was 30% greater than SHAM (p < 0.05). Inhibiting NOS with L-NAME significantly increased pulmonary EBD concentration of both IIR and SHAM groups when compared with normal saline solution-treated animals (p < 0.0001). Treatment with L-Arg prevented this IIR-induced increase in pulmonary dye extravasation.

CONCLUSIONS

These data suggest that pulmonary iNOS activity is up-regulated in animals sustaining IIR and that this may serve as a compensatory protective response to remote organ injury.

Impaired endothelial function in patients with nephrotic range proteinuria

Proteinuria is associated with increased cardiovascular morbidity and mortality. Release of nitric oxide by the endothelium has been advanced as an important defense mechanism against vessel-wall damage. In the present study we therefore tested the hypothesis that proteinuria is associated with a defect in nitric oxide-dependent vasodilation, by using venous occlusion plethysmography of the forearm in nine patients with nephrotic range proteinuria (> 3.5 g/24 hr) and normal renal function (creatinine 83.1 +/- 8.7 mumol/liter), eight patients with active glomerulonephritis but normal renal function (creatinine 81.2 +/- 5.4 mumol/liter) and low range proteinuria (< 1.0 g/24 hr), and ten healthy volunteers. We infused L-NMMA (2 mg/min) to inhibit basal nitric oxide production, serotonin (0.1, 0.3 and 1.0 ng/kg/min) as an endothelium-dependent vasodilator, and nitroprusside (1, 10, 30 and 100 ng/kg/min) as an endothelium-independent vasodilator into the brachial artery. Administration of L-NMMA decreased basal forearm vascular resistance (FVR) by 30 +/- 4% in the nephrotic subjects, 38 +/- 4% in the non-nephrotic patients and by 37 +/- 2% in the healthy controls (P = 0.15). Upon the highest dose of serotonin FVR decreased in nephrotic subjects by 40 +/- 5%, which was less than in non-nephrotic patients (56 +/- 3%; P < 0.05) or in healthy controls (55 +/- 3%; P < 0.05). The maximal decrease in FVR upon nitroprusside infusion was not different between the groups (respectively 84 +/- 2, 84 +/- 3 and 84 +/- 2%). The impaired serotonin-induced vasodilation could be attributed to a defect in nitric oxide production, since L-NMMA almost completely prevented serotonergic vasodilation.(ABSTRACT TRUNCATED AT 250 WORDS)

Enhancing and inhibitory effects of nitric oxide on superoxide anion generation in human polymorphonuclear leukocytes

1. The effects of sodium nitroprusside (SNP, a nitric oxide donor) and authentic nitric oxide (NO) on superoxide anion (O2-) generation were investigated in human polymorphonuclear leukocytes (PMNs). 2. Neither SNP (10 nM to 10 microM) nor NO (40 nM to 40 microM) alone induced O2- generation or change of intracellular Ca2+ concentration ([Ca2+]i) in human PMNs. 3. Pretreatment with SNP or NO at the concentrations used (SNP, 10 nM to 10 microM: NO, 40 nM to 40 microM) showed a biphasic concentration-dependent effect on O2- generation induced by f-methionyl-leucyl-phenylalanine (FMLP). Low concentrations of SNP (10 nM to 100 nM) and NO (400 nM) did not affect either basal cyclic GMP levels or cyclic GMP levels stimulated by FMLP, but enhanced FMLP-induced O2- generation and [Ca2+]i elevation. On the other hand, high concentrations of SNP (10 microM) and NO (40 microM) alone elevated cyclic GMP levels and inhibited FMLP-induced O2- generation and [Ca2+]i elevation. 4. 8-Bromo-cyclic GMP (8-Br-cyclic GMP) at concentrations ranging from 1 microM to 1 mM did not induce O2- generation on its own and had little effect on FMLP-induced O2- generation and [Ca2+]i elevation. 5. Addition of a high concentration of NO (40 microM) decreased authentic O2- formation by pyrogallol in a cell-free system, but a low concentration of NO (400 nM) had no effect on this. On the other hand, addition of SNP in the concentration-ranges used had no effect on authentic O2- formation by pyrogallol. 6. In this study, we have shown that SNP and NO have dual effects (enhancement and inhibition) on 02- generation induced by FMLP in human peripheral PMNs. The results suggest that the enhancement observed with SNP and NO at low concentrations is not mediated by activation of the guanylate cyclase-cyclic GMP pathway. The suppressive effect of SNP and NO at higher concentrations is mediated by the NO-induced O2--scavenging effect and activation of the guanylate cyclase-cyclic GMP pathway.

Molecular regulation of the bovine endothelial cell nitric oxide synthase by transforming growth factor-beta 1

The promoter region of the endothelial cell nitric oxide synthase (ecNOS) gene contains potential response elements for transforming growth factor-beta 1 (TGF beta 1). TGF beta 1 plays an important role in the pathogenesis of atherosclerosis, vascular hypertrophy, and angiogenesis. We therefore sought to determine whether TGF beta 1 might modulate ecNOS expression in bovine aortic endothelial cells (BAEC). TGF beta 1 increased ecNOS mRNA in a dose-dependent manner. TGF beta 1 also increased ecNOS protein content. The production of nitrogen oxides (NOx), assessed by chemiluminescence, and nitric oxide synthase activity, assessed by arginine/citrulline conversion were increased in TGF beta 1-treated cells. Transcriptional activity of the 5'-flanking promoter region of the ecNOS gene was increased by TGF beta 1, as assessed by transfection with promoter/luciferase constructs. Deletion analysis suggested that the TGF beta 1-response element was present between nucleotides -1269 and -935 from the first transcription start site, in which a putative nuclear factor-1 (NF-1) binding site existed. Gel shift assays showed that nuclear protein(s), immunologically similar to CCAAT transcription factor/NF-1, bound to the putative NF-1 binding site in a sequence-specific manner. Mutation of the putative NF-1 binding site in the promoter/luciferase construct significantly decreased the responsiveness to TGF beta 1. In conclusion, TGF beta 1 increases ecNOS expression associated with an increase in production of NO in BAEC. This response is probably mediated by transcriptional activation of the ecNOS gene promoter.

Myocardial and coronary endothelial protective effects of acetylcholine after myocardial ischaemia and reperfusion in rats: role of nitric oxide

1. Recent experiments suggest that acetylcholine (ACh) may exert myocardial protective effects during ischaemia (I) and reperfusion (R). The present study was designed (i) to assess whether ACh limits infarct size and protects coronary endothelial cells in a rat model of I and R, (ii) to evaluate the role of ATP-sensitive potassium (KATP) channels and nitric oxide (NO) in the beneficial effect of ACh (iii) to evaluate whether the protective effect of ACh also extends to coronary endothelial cells and (iv) to assess whether ACh contributes to the beneficial effect of preconditioning. 2. Anaesthetized rats were subjected to 20 min I (left coronary artery occlusion) and 2 h of R. Infarct size was assessed by triphenyltetrazolium (TTC) staining and expressed as a % of the area at risk (India ink injection). Vascular studies were performed on 1.5-2 mm coronary segments (internal diameter 250-300 micros) removed distal to the site of occlusion and mounted in wire myographs. 3. ACh limited infarct size (from 59 +/- 3 to 26 +/- 5%, P < 0.01), and this was prevented by atropine (46 +/- 7%; P < 0.05 vs ACh), but not by the inhibitor of KATP channels, glibenclamide (29 +/- 8%). The inhibitor of NO synthesis NG-nitro L-arginine did not affect infarct size (54 +/- 5%) but abolished the beneficial effect of ACh (59 +/- 8%; P < 0.05 vs ACh), whereas the NO donor 3-morpholinosydnonimine-N-ethylcarbamide (SIN-1 limited infarct size to the same extent as ACh (28 +/- 6%). Preconditioning also limited infarct size (5 +/- 2%, P< 0.01 vs control), and this was not affected by atropine (6 +/- 2%). I and R induced a significant decrease in the endothelium-dependent relaxations of isolated coronary arteries toACh (maximal response: sham: 58+/-4; I/R: 25+/-5%; P<0.01) and this dysfunction was prevented by prior in vivo treatment with ACh (55+/-7%; P<0.01 vs I/R) or (SIN-1 50+/-5%; P<0.05 vs I/R).4 Thus, in the rat model, ACh is able to stimulate potent endogenous protective mechanisms during I and R, which are evident both at the level of myocardial and coronary endothelial cells, and appear entirely mediated through the production of NO. Pharmacological stimulation of this endogenous protective mechanism may constitute a new approach in the treatment of acute myocaridal ischaemia.

Nitric oxide inhibits macrophage-colony stimulating factor gene transcription in vascular endothelial cells

Macrophage-colony stimulating factor (M-CSF) contributes to atherogenesis by regulating macrophage-derived foam cells in atherosclerotic lesions. Here we report that nitric oxide (NO) inhibits the expression of M-CSF in human vascular endothelial cells independent of guanylyl cyclase activation. The induction of M-CSF mRNA expression by either oxidized low density lipoprotein (ox-LDL) or tumor necrosis factor-alpha (TNF alpha) was attenuated by NO donors, S-nitrosoglutathione (GSNO), sodium nitroprusside (SNP), and 3-morpholinosydnonimine, but not by cGMP analogues, glutathione, or nitrite. Inhibition of endogenous NO production by N-monomethyl-L-arginine (L-NMA) also increased M-CSF expression in control and TNF alpha-stimulated cells. Nuclear run-on assays and transfection studies using M-CSF promoter constructs linked to chloramphenicol acetyltransferase reporter gene indicated that NO repressed M-CSF gene transcription through nuclear factor-kappa B (NF-kappa B). Electrophoretic mobility shift assays demonstrated that activation of NF-kappa B by L-NMA, ox-LDL, and TNF alpha was attenuated by GSNO and SNP, but not by glutathione or cGMP analogues. Since the induction of M-CSF expression depends upon NF-kappa B activation, the ability of NO to inhibit NF-kappa B activation and M-CSF expression may contribute to some of NO's antiatherogenic properties.

Additive effects of L-arginine infusion and leukocyte depletion on recovery after hypothermic ischemia in neonatal lamb hearts

Prior experiments on hypothermic ischemia/reperfusion have shown that (1) leukocytes have an important role in the injury resulting from hypothermic ischemia/reperfusion and (2) endothelial dysfunction with reduced release of nitric oxide occurs after hypothermic ischemia/reperfusion. L-Arginine is a nitric oxide precursor, and the effects of nitric oxide released from endothelial cells include vasorelaxation and inhibition of leukocyte adhesion to endothelium. The potential roles of an interaction between endothelial dysfunction and leukocyte-mediated injury were examined in neonatal hearts. Thirty-two isolated, blood-perfused neonatal lamb hearts were subjected to 2 hours of 10 degrees C cardioplegic ischemia. Group L-arginine received a 3 mmol/L dose of L-arginine during the first 20 minutes of reperfusion. In group leukocyte depletion, leukocytes were depleted (Sepacell filter) from the perfusate before reperfusion. In group L-arginine+leukocyte depletion, leukocytes were depleted and a 3 mmol/L dose of L-arginine was infused during early reperfusion. The control group had no intervention during reperfusion. At 30 minutes of reperfusion, left ventricular maximum developed pressure, positive maximum and negative maximum first derivative of left ventricular pressure (dP/dt), developed pressure at V10 (volume that produces a left ventricular endiastolic pressure of 10 mm Hg at baseline measurement), and dP/dt at V10 were measured. Coronary blood flow was continuously monitored and oxygen consumption was also measured to evaluate the metabolic recovery. In each heart, we also tested coronary vascular resistance response to the endothelium-dependent vasodilator acetylcholine 10(-7) mol/L and the endothelium-independent vasodilator trinitroglycerin 3 x 10(-5) mol/L to assess endothelial function. Results are given as mean percent recovery of baseline values +/- standard deviation. Group L-arginine+leukocyte depletion showed significantly greater recovery of left ventricular function than the other three groups, and groups L-arginine and leukocyte depletion also showed better recovery than the control group (positive maximum dP/dt: control group = 68.3% +/- 8.8%, group L-arginine = 88.8% +/- 3.8%, group L-arginine+leukocyte+leukocyte depletion = 100.6% +/- 8.7%, group leukocyte depletion = 79.3% +/- 8.1%; p < 0.05). Groups L-arginine and L-arginine+leukocyte depletion had higher postischemic coronary blood flow than other groups (control group = 133.0% +/- 31.6%, group L-arginine = 203.2% +/- 32.1%, group L-arginine+leukocyte depletion = 222.0% +/- 30.4%, group leukocyte depletion = 156.3% +/- 29.0%; p < 0.05).(ABSTRACT TRUNCATED AT 400 WORDS)

Augmentation of microvascular nitric oxide improves myocardial performance following global ischemia

Hearts exposed to global myocardial ischemia associated with cardiac surgery often suffer postischemic endothelial and contractile dysfunction related to antecedent regional or global ischemia. Our studies tested the hypothesis that supplementing blood cardioplegia and reperfusion with the nitric oxide (NO) precursor L-arginine or the NO donor SPM-5185 would preserve endothelial function, reduce infarct size, and reverse postcardioplegia regional contractile dysfunction or global dysfunction. In the first study involving 23 anesthetized dogs undergoing regional ischemia, supplementation of blood cardioplegia with L-arginine: (1) reduced infarct size; (2) improved postischemic regional segmental work and diastolic stiffness; (3) attenuated neutrophil accumulation in the area at risk; and (4) improved postischemic depressed coronary artery endothelial function. The NO synthase inhibitor N-nitro-L-arginine (L-NA) reversed these protective effects. In another experiment involving 18 anesthetized dogs undergoing normothermic global ischemia, hearts treated with blood cardioplegia supplemented with the NO donor SPM-5185 demonstrated better postischemic coronary artery endothelial function, lowered myeloperoxidase activity in the ischemic-reperfused myocardium, and significantly improved global ventricular function in the group receiving high-dose SPM-5185. We conclude that the inclusion of L-arginine or high-dose NO donor SPM-5185 in blood cardioplegia improves postischemic ventricular performance and endothelial function in ischemically injured hearts, possibly by inhibition of neutrophil-mediated damage via the L-arginine-NO pathway.

Nitric oxide decreases cytokine-induced endothelial activation. Nitric oxide selectively reduces endothelial expression of adhesion molecules and proinflammatory cytokines

To test the hypothesis that nitric oxide (NO) limits endothelial activation, we treated cytokine-stimulated human saphenous vein endothelial cells with several NO donors and assessed their effects on the inducible expression of vascular cell adhesion molecule-1 (VCAM-1). In a concentration-dependent manner, NO inhibited interleukin (IL)-1 alpha-stimulated VCAM-1 expression by 35-55% as determined by cell surface enzyme immunoassays and flow cytometry. This inhibition was paralleled by reduced monocyte adhesion to endothelial monolayers in nonstatic assays, was unaffected by cGMP analogues, and was quantitatively similar after stimulation by either IL-1 alpha, IL-1 beta, IL-4, tumor necrosis factor (TNF alpha), or bacterial lipopolysaccharide. NO also decreased the endothelial expression of other leukocyte adhesion molecules (E-selectin and to a lesser extent, intercellular adhesion molecule-1) and secretable cytokines (IL-6 and IL-8). Inhibition of endogenous NO production by L-N-monomethyl-arginine also induced the expression of VCAM-1, but did not augment cytokine-induced VCAM-1 expression. Nuclear run-on assays, transfection studies using various VCAM-1 promoter reporter gene constructs, and electrophoretic mobility shift assays indicated that NO represses VCAM-1 gene transcription, in part, by inhibiting NF-kappa B. We propose that NO's ability to limit endothelial activation and inhibit monocyte adhesion may contribute to some of its antiatherogenic and antiinflammatory properties within the vessel wall.