Inhaled nitric oxide inhibits human platelet aggregation, P-selectin expression, and fibrinogen binding in vitro and in vivo

A new nitrate derivative of piperazine: its influence on platelet activity

Nitric oxide (NO) is a potent vasodilator and inhibitor of platelet activation. Its donors, organic nitrates, are still a main group of drugs administered in ischaemic heart disease. The aim of this study was to investigate the effect of a new NO-donor analogue, 1-(3-piperidinepropionyl)-4-(2-nitrooxy-3-piperidinepropyl) piperazine trihydrochloride (NO-P), on platelet activity. Its influence on the main mechanisms of human platelet activation (adhesion, shape change, secretion and aggregation) was evaluated with the use of a pharmacological model produced on the basis of known platelet activation measuring methods and our computer program. Our experiments revealed that the new NO derivative of piperazine favourably influences platelet activity, and decreases adhesion (spontaneous and induced by ADP) and aggregation. NO-P shows the same direction of action as nitroglycerin (used as a model compound), and is even stronger in the case of ADP-induced and collagen-induced aggregation. These findings broaden the possibility of using NO-P in cardiovascular diseases. Furthermore, our computer program, used to evaluate kinetic parameters of platelet aggregation, shape change, and the adhesion measuring method, provides a simple and accessible experimental model. This model can be useful in in-vitro screening studies, estimating the influence of new compounds (potential drugs) on platelet activity.

Prolonged exposure to inhaled nitric oxide does not affect haemostasis in piglets

OBJECTIVE

To examine possible adverse effects on haemostasis from prolonged exposure to inhaled nitric oxide (iNO).

DESIGN AND SETTING

Blinded, randomised, experimental animal study in a university animal laboratory.

INTERVENTIONS

Anaesthetised and intubated piglets received central venous, arterial, and transabdominal urinary catheters. Twelve piglets were studied with triggered pressure support ventilation breathing with an air-oxygen mixture for 30 h with nitric oxide (NO), 40 parts per million (ppm) (n = 6) or without NO gas (n = 6) added. The tests of platelet function were assessed in a separate 1-h experiment in which 12 additional animals were blindly randomised to receive intravenous acetylsalicylic acid (ASA) (n = 7) or placebo (n = 5).

MEASUREMENTS AND RESULTS

All 12 animals were clinically stable during the study period of 30 h. Haemostasis was assessed in terms of bleeding time and platelet function by Adeplat-S, reflecting platelet adhesion. Prothrombin fragment 1 + 2, fibrin D-dimer, tissue plasminogen activator and prothrombin complex were measured to investigate whether inhaled NO (iNO) had any effects on thrombin formation, fibrin formation, fibrinolysis or coagulation. All parameters including bleeding time and Adeplat-S were unaffected by iNO. ASA significantly increased bleeding time, but did not affect Adeplat-S. Nitrate in plasma and NOx (nitrate and nitrite) in urine increased significantly in pigs receiving iNO compared with controls.

CONCLUSIONS

Prolonged exposure to iNO at 40[Symbol: see text]ppm did not affect bleeding time or coagulation parameters in healthy piglets. The findings do not support the hypothesis that iNO increases the risk of bleeding in humans.

Effect of nitric oxide on oxygenation and mortality in acute lung injury: systematic review and meta-analysis

OBJECTIVE

To review the literature on the use of inhaled nitric oxide to treat acute lung injury/acute respiratory distress syndrome (ALI/ARDS) and to summarise the effects of nitric oxide, compared with placebo or usual care without nitric oxide, in adults and children with ALI or ARDS.

DESIGN

Systematic review and meta-analysis.

DATA SOURCES

Medline, CINAHL, Embase, and CENTRAL (to October 2006), proceedings from four conferences, and additional information from authors of 10 trials.

REVIEW METHODS

Two reviewers independently selected parallel group randomised controlled trials comparing nitric oxide with control and extracted data related to study methods, clinical and physiological outcomes, and adverse events.

MAIN OUTCOME MEASURES

Mortality, duration of ventilation, oxygenation, pulmonary arterial pressure, adverse events.

RESULTS

12 trials randomly assigning 1237 patients met inclusion criteria. Overall methodological quality was good. Using random effects models, we found no significant effect of nitric oxide on hospital mortality (risk ratio 1.10, 95% confidence interval 0.94 to 1.30), duration of ventilation, or ventilator-free days. On day one of treatment, nitric oxide increased the ratio of partial pressure of oxygen to fraction of inspired oxygen (PaO2/FiO2 ratio) (13%, 4% to 23%) and decreased the oxygenation index (14%, 2% to 25%). Some evidence suggested that improvements in oxygenation persisted until day four. There was no effect on mean pulmonary arterial pressure. Patients receiving nitric oxide had an increased risk of developing renal dysfunction (1.50, 1.11 to 2.02).

CONCLUSIONS

Nitric oxide is associated with limited improvement in oxygenation in patients with ALI or ARDS but confers no mortality benefit and may cause harm. We do not recommend its routine use in these severely ill patients.

Adrenomedullin 2 antagonist infusion to rats during midgestation causes fetoplacental growth restriction through apoptosis

Adrenomedullin 2 (ADM2) is a recently discovered member of the calcitonin/calcitonin gene-related peptide family with an exon-intron structure similar to that of ADM. The mRNA of ADM2 is expressed in several tissues, including uterus and ovary. The present study was designed to assess the effects of ADM2 antagonist (ADM2(17-47)) infusion to pregnant rats on fetal and placental growth. On Day 15 of gestation, rats were implanted s.c. with osmotic minipumps delivering 50 and 200 mug per rat per day of ADM2(17-47) and were killed on Gestational Day 18. In ADM2(17-47)-treated rats, placental weights were significantly inhibited in a dose-related manner, with an 11% reduction in the group of rats receiving 200 microg/day, whereas the fetal weights were reduced by 17% without significant differences between the two doses. 2 In ADM2(17-47)-infused rats, increased apoptosis was demonstrated in the labyrinth and junctional zones of rat placenta by the TUNEL method compared with the control animals. Western blot analysis demonstrated that in ADM2(17-47)-treated rats Bcl-2, mitochondrial cytochrome c, and active caspase-9 and caspase-3 were significantly increased compared with the controls. No significant treatment-associated changes were observed in Bax, Bid, p53, and caspase-8 and caspase-10 proteins in the treated placentas. In addition, infusion of ADM2(17-47) caused a significant decline in the transcripts of nitric oxide synthase 3 (NOS3) and NOS2. These findings show that ADM2(17-47) infusion in rats during midpregnancy cause fetoplacental growth restriction through the activation of mitochondrial apoptotic pathways. This study demonstrates for the first time (to our knowledge) a potential role for ADM2 in placental functions during pregnancy.

Extrapulmonary effects of inhaled nitric oxide: role of reversible S-nitrosylation of erythrocytic hemoglobin

Early applications of inhaled nitric oxide (iNO), typically in the treatment of diseases marked by acute pulmonary hypertension, were met by great enthusiasm regarding the purported specificity of iNO: vasodilation by iNO was specific to the lung (without a change in systemic vascular resistance), and within the lung, NO activity was said to be confined spatially and temporally by Hb within the vascular lumen. Underlying these claims were classical views of NO as a short-lived paracrine hormone that acts largely through the heme groups of soluble guanylate cyclase, and whose potential activity is terminated on encountering the hemes of red blood cell (RBC) Hb. These classical views are yielding to a broader paradigm, in which NO-related signaling is achieved through redox-related NO adducts that endow NO synthase products with the ability to act at a distance in space and time from NO synthase itself. Evidence supporting the biological importance of such stable NO adducts is probably strongest for S-nitrosothiols (SNOs), in which NO binds to critical cysteine residues in proteins or peptides. The circulating RBC is a major SNO reservoir, and RBC Hb releases SNO-related bioactivity peripherally on O2 desaturation. These new paradigms describing NO transport also provide a plausible mechanistic understanding of the increasingly recognized peripheral effects of inhaled NO. An explanation for the peripheral actions of inhaled NO is discussed here, and the rationale and results of attempts to exploit the "NO delivery" function of the RBC are reviewed.

[Thrombocytopathy and blood complications in uremia]

Bleeding diathesis and thrombotic tendencies are characteristic findings in patients with end-stage renal disease. The pathogenesis of uremic bleeding tendency is related to multiple dysfunctions of the platelets. The platelet numbers may be reduced slightly, while platelet turnover is increased. The reduced adhesion of platelets to the vascular subendothelial wall is due to reduction of GPIb and altered conformational changes of GPIIb/IIIa receptors. Alterations of platelet adhesion and aggregation are caused by uremic toxins, increased platelet production of NO, PGI(2), calcium and cAMP as well as renal anemia. Correction of uremic bleeding is caused by treatment of renal anemia with recombinant human erythropoietin or darbepoetin alpha, adequate dialysis, desmopressin, cryoprecipitate, tranexamic acid, or conjugated estrogens. Thrombotic complications in uremia are caused by increased platelet aggregation and hypercoagulability. Erythrocyte-platelet-aggregates, leukocyte-platelet-aggregates and platelet microparticles are found in higher percentage in uremic patients as compared to healthy individuals. The increased expression of platelet phosphatidylserine initiates phagocytosis and coagulation. Therapy with antiplatelet drugs does not reduce vascular access thrombosis but increases bleeding complications in endstage renal disease patients. Heparin-induced thrombocytopenia (HIT type II) may develop in 0-12 % of hemodialysis patients. HIT antibody positive uremic patients mostly develop only mild thrombocytopenia and only very few thrombotic complications. Substitution of heparin by hirudin, danaparoid or regional citrate anticoagulation should be decided based on each single case.

Combined administration of nitric oxide gas and iloprost during cardiopulmonary bypass reduces platelet dysfunction: a pilot clinical study

BACKGROUND

Thrombocytopenia and platelet dysfunction are major mechanisms of cardiopulmonary bypass-induced postoperative hemorrhage. This study evaluated the effects of low amounts of nitric oxide, iloprost (prostacyclin analog), and their combination administered directly into the oxygenator on platelet function, platelet-leukocyte interactions, and postoperative blood loss in patients undergoing coronary artery bypass grafting.

METHODS

Blood samples from 41 patients randomized to the control, nitric oxide (20 ppm), iloprost (2 ng x kg -1 x min -1 ), or nitric oxide plus iloprost groups were collected during cardiopulmonary bypass. Platelets and leukocytes were enumerated. Platelet membrane glycoprotein Ib and glycoprotein IIb/IIIa, P-selectin, platelet-derived microparticles, leukocyte CD11b/CD18 (Mac-1), and platelet-leukocyte aggregate were quantified by means of flow cytometry. Collagen and thrombin receptor-activating peptide-induced platelet aggregation in whole blood was analyzed by means of aggregometry.

RESULTS

Both nitric oxide or iloprost attenuated cardiopulmonary bypass-induced thrombocytopenia, reduction of glycoprotein Ib and glycoprotein IIb levels, translocation of P-selectin, microparticle formation, Mac-1 upregulation, and suppression of collagen-induced aggregation. Nitric oxide plus iloprost was significantly more effective in preventing thrombocytopenia, microparticle formation, and P-selectin translocation. Moreover, this treatment preserved thrombin receptor-activating peptide-induced aggregation, which was not rescued by single treatments. Both nitric oxide and nitric oxide plus iloprost attenuated postoperative blood loss.

CONCLUSIONS

Nitric oxide plus iloprost reduced the deleterious effects of cardiopulmonary bypass, such as thrombocytopenia, platelet activation, platelet-leukocyte aggregate formation, and suppression of platelet aggregative responses. The reduced postoperative bleeding observed with this treatment suggests that this is a new and clinically feasible therapeutic option for patients subjected to cardiopulmonary bypass.

Nitric oxide and blood: a review

Nitric oxide (NO) was identified as a physiological mediator of vascular tone in 1987. NO produced by endothelial cells causes vasodilatation and also inhibits platelet aggregation and leucocyte adhesion. Red cells metabolize NO to nitrate but may possibly carry and release, or even produce, NO in hypoxic conditions. NO physiology may have important implications for transfusion medicine, ranging from adverse effects of haemoglobin substitutes to preservation of stored platelets and to detrimental effects of stored red cells.

Measuring platelet aggregation to estimate small intestinal ischemia-reperfusion injury

BACKGROUND

The success of intestinal transplantation is affected by the extreme susceptibility of the small bowel to ischemia-reperfusion (I/R) injury. Currently, there is no quick, convenient method to estimate the extent of small bowel I/R injury. Although histological evaluation is reliable and accurate, it takes too long to allow favorable intervention in I/R injury. I/R causes the production of arachidonic acid products, oxygen free radicals, cytokines, and nitric oxide, which affect platelet function.

OBJECTIVE

This study determined whether measuring platelet aggregation is useful for evaluating small bowel I/R injury.

METHODS

Eighteen mongrel dogs were divided into three groups. In group A both the superior mesenteric artery (SMA) and vein (SMV) were occluded for 120 min. In group B the SMA was occluded for 60 min. Group C underwent a sham operation. Platelet aggregation was measured using a whole blood aggregometer (WBA analyzer), which readily handles small samples. Histological examination was performed. The correlation between platelet aggregation and histology was analyzed.

RESULTS

Platelet aggregation was similar in all groups before reperfusion. After reperfusion, platelet aggregation was significantly lower in group A than in groups B and C (P < 0.05), and mucosal damage was most severe in group A (P < 0.05). After 1 and 3 h of reperfusion, there was a significant negative correlation between platelet aggregation and histological damage.

CONCLUSIONS

Measuring platelet aggregation is rapid, easy, and useful for evaluating small bowel I/R injury.

Nitric oxide-releasing hydrophobic polymers: preparation, characterization, and potential biomedical applications

The synthetic methods used recently in this laboratory to prepare a variety of novel nitric oxide (NO)-releasing hydrophobic polymers are reviewed. Nitric oxide is a well known inhibitor of platelet adhesion and activation. Thus, such NO release polymers have potential applications as thromboresistant coatings for a large number of blood-contacting biomedical devices (e.g., in vivo sensors, arteriovenous grafts, stents, catheters, extracorporeal circuits). The approaches taken to prepare NO releasing poly(vinyl chloride) (PVC), silicone rubber (SR), polymethacrylate (PM), and polyurethane (PU) materials are grouped into three categories: (1) dispersion/doping of discrete diazeniumdiolated molecules within the polymeric films; (2) chemical derivatization of polymeric filler microparticles (e.g., silicon dioxide, titanium dioxide) to possess NO release chemistry and then their dispersion within the hydrophobic polymers; and (3) covalent attachment of NO release moieties to polymer backbones. Specific chemical examples of each of these approaches are summarized and the advantages and disadvantages of each are discussed. Other related work in the field of NO release polymers is also cited. It is further shown that several of the NO-releasing polymeric materials already prepared exhibit the expected improved thromboresistivity when tested in vivo using appropriate animal models.

Propofol Improves Skin Flap Survival in a Rat Model

Accumulation of neutrophils in a random pattern skin flap has been demonstrated to contribute to the necrosis of distal flap tissue. This study proposes that administration of propofol anesthesia can effectively reduce neutrophil activity and enhance skin flap survival. The study was a randomized controlled trial using male Sprague-Dawley rats as subjects. For flap survival studies, a 3- by 12-cm, dorsal, cranial-based, random pattern skin flap was elevated and reapproximated. Flaps were examined for viability 10 days postsurgery. To assess neutrophil activity, flap biopsies were taken 12, 24, or 48 hours postsurgery from distal, middle, and proximal flap regions, and myeloperoxidase enzyme content was analyzed. Animals were randomly assigned to 1 of 4 groups: group 1, ketamine anesthesia (controls); group 2, propofol anesthesia; group 3, ketamine anesthesia plus 10% lipid emulsion (propofol vehicle); group 4, ketamine anesthesia without flap elevation (nonoperated controls for myeloperoxidase study). Flap survival was significantly improved in the propofol group compared with both the ketamine and vehicle control groups (P <0.01). Increased flap viability was correlated with a reduction in myeloperoxidase content in the propofol group compared with control operated animals, with minor variations observed in the different flap regions and time points tested. This study indicates that the use of propofol can potentially improve skin flap survival. The beneficial effects may be attributed to a reduction in neutrophil activity within the flap.

Successful surgical management of a neonate with a saddle pulmonary embolus

A female neonate presented with evidence of a massive ventilation-perfusion mismatch. She was subsequently found to have a saddle pulmonary embolus. The infant successfully underwent surgical pulmonary embolectomy.

Synthesis and Selective Cyclooxygenase-2 Inhibitory Activity of a Series of Novel, Nitric Oxide Donor-Containing Pyrazoles

The synthesis of a series of novel pyrazoles containing a nitrate (ONO(2)) moiety as a nitric oxide (NO)-donor functionality is reported. Their COX-1 and COX-2 inhibitory activities in human whole blood are profiled. Our data demonstrate that pyrazole ring substituents play an important role in COX-2 selective inhibition, such that a cycloalkyl pyrazole (6b) was found to be a potent and selective COX-2 inhibitor. Other modifications at the 3 position of the central pyrazole ring (17b, 23b, 26b-I) enhanced COX-2 inhibitory potency. Among the pyrazoles synthesized, the oxime (23b) was identified as the most potent COX-2 selective inhibitor. Accordingly, 23b was profiled pharmacologically in the rat after oral administration and shown to possess potent antiinflammatory activity in the carrageenan-induced air-pouch model and less gastric toxicity than a standard COX-2 inhibitor when administered with background aspirin treatment. We suggest that the enhanced gastric tolerance of an NO-donor COX-2 selective inhibitor has the potential to augment the clinical profile of this drug class.

Supplemental nitric oxide and its effect on myocardial injury and function in patients undergoing cardiac surgery with extracorporeal circulation

BACKGROUND

Cardiopulmonary bypass induces a systemic inflammatory response that may contribute to clinical morbidity. Gaseous nitric oxide at relatively low concentrations may elicit peripheral anti-inflammatory effects in addition to a reduction of pulmonary resistances. We examined the effects of 20 ppm of inhaled nitric oxide administered for 8 hours during and after cardiopulmonary bypass.

METHODS AND RESULTS

Twenty-nine consecutive patients undergoing aortic valve replacement combined with aortocoronary bypass were randomly allocated to either 20 ppm of inhaled nitric oxide (n = 14) or no additional inhalatory treatment (n = 15). Blood samples for total creatine kinase, creatine kinase MB fraction, and troponin I measurements were collected at 4, 12, 24, and 48 hours postsurgery. In addition, we collected perioperative blood samples for measurements of circulating nitric oxide by-products and brain natriuretic peptide. Soluble P-selectin was analyzed in blood samples withdrawn from the coronary sinus before and after aortic clamping. The area under the curve of creatine kinase MB fraction (P =.03), total creatine kinase (P =.04), and troponin I (P =.04) levels were significantly decreased in the nitric oxide-treated patients. Moreover, in the same group we observed blunted P-selectin and brain natriuretic peptide release (P =.01 and P =.02, respectively). Nitric oxide inhalation consistently enhanced nitric oxide metabolite levels (P =.01).

CONCLUSIONS

Nitric oxide, when administered as a gas at low concentration, is able to blunt the release of markers of myocardial injury and to antagonize the left ventricular subclinical dysfunction during and immediately after cardiopulmonary bypass. The organ protection could be mediated, at least in part, by its anti-inflammatory properties.

Is there a place for inhaled nitric oxide in the therapy of acute pulmonary embolism?

Acute pulmonary embolism (PE) is a serious complication resulting from the migration of emboli to the lungs. Although deep venous thrombi are the most common source of emboli to the lungs, other important sources include air, amniotic fluid, fat and bone marrow. Regardless of the specific source of the emboli, very little progress has been made in the pharmacological management of this high mortality condition. Because the prognosis is linked to the degree of elevation of pulmonary vascular resistance, any therapeutic intervention to improve the hemodynamics would probably increase the low survival rate of this critical condition. Inhaled nitric oxide (iNO) has been widely tested and used in cases of pulmonary hypertension of different causes. In the last few years some authors have described beneficial effects of iNO in animal models of acute PE and in anecdotal cases of massive PE. The primary cause of death in massive PE that is caused by deep venous thrombi, gas or amniotic fluid, is acute right heart failure and circulatory shock. Increased pulmonary vascular resistance following acute PE is the cumulative result of mechanical obstruction of pulmonary vessels and pulmonary arteriolar constriction (attributable to a neurogenic reflex and to the release of vasoconstrictors). As such, the vasodilator effects of iNO could actively oppose the pulmonary hypertension following PE. This hypothesis is consistently supported by experimental studies in different animal models of PE, which demonstrated that iNO decreased (by 10 to 20%) the pulmonary artery pressure without improving pulmonary gas exchange. Although maximal vasodilatory effects are probably achieved by less than 5 parts per million iNO, which is a relatively low concentration, no dose-response study has been published so far. In addition to the animal studies, a few anecdotal reports in the literature suggest that iNO may improve the hemodynamics during acute PE. However, no prospective, controlled, randomized clinical trial addressing this issue has been conducted to date. Future investigations addressing the effects of iNO combined with other drugs such as vasoconstrictors and inhibitors of phosphodiesterase III or V, may increase the responsiveness to iNO in acute PE.

Inhaled nitric oxide for acute hypoxic respiratory failure in children and adults: a meta-analysis

We systematically reviewed randomized controlled trials examining inhaled nitric oxide (INO) for the treatment of acute respiratory distress syndrome or acute lung injury in children and adults. Qualitative assessments of identified trials were made, and metaanalyses were performed according to Cochrane methodology. Five randomized controlled trials (n = 535) met entry criteria. One study demonstrated significant improvement in oxygenation in the first 4 days of treatment, with no difference after this. There was no difference in ventilator-free days between treatment and placebo groups, and no specific dose of INO was more advantageous than any other. INO had no effect on mortality in trials without crossover of treatment failures to open-label INO (relative risk, 0.98; 95% confidence interval, 0.66-1.44). Other clinical indicators of effectiveness, such as duration of hospital and intensive care stay, were inconsistently reported. Lack of data prevented assessment of all outcomes. If further trials assessing INO in acute respiratory distress syndrome or acute lung injury are to proceed, they should be stratified for primary etiology, incorporate other modalities that may affect outcome, and evaluate clinically relevant outcomes before any benefit of INO can be excluded.

Inhaled NO inhibits platelet aggregation and elevates plasma but not intraplatelet cGMP in healthy human volunteers

Effects of inhaled nitric oxide (NO) on human platelet function are controversial. It is uncertain whether intraplatelet cGMP mediates the effect of inhaled NO on platelet function. We investigated the effect of 30 ppm inhaled NO on platelet aggregation and plasma and intraplatelet cGMP in 12 subjects. We performed platelet aggregation studies by using a photooptical aggregometer and five agonists (ADP, collagen, epinephrine, arachidonic acid, and ristocetin). During inhalation, the maximal extent of platelet aggregation decreased by 75% with epinephrine (P < 0.005), 56% with collagen (P < 0.005), and 20% with arachidonic acid (P < 0.05). Responses to ADP (8% P > 0.05) and ristocetin (5% P > 0.05) were unaffected. Platelet aggregation velocity decreased by 64% with collagen (P < 0.005), 60% with epinephrine (P < 0.05), 33% with arachidonic acid (P < 0.05), and 14% with ADP (P > 0.05). Plasma cGMP levels increased from 2.58 +/- 0.43 to 9.99 +/- 5.57 pmol/ml (P < 0.005), intraplatelet cGMP levels were unchanged (means +/- SD: 1.96 +/- 0.58 vs. 2.71 +/- 1.67 pmol/109 platelets; P > 0.05). Inhaled NO inhibits platelet aggregation via a cGMP independent mechanism.

Inhaled nitric oxide inhibits platelet-leukocyte interactions in patients with acute respiratory distress syndrome

INTRODUCTION

In addition to its effects on platelet function, recent studies suggest that inhaled nitric oxide (NO) also influences the function of circulating leukocytes. Therefore, the aim of this work was to investigate the formation of platelet-leukocyte aggregates (PLAs) and platelet and leukocyte cell surface receptor expression during NO therapy in patients with acute respiratory distress syndrome.

METHODS

In 16 patients responding to NO therapy with an improvement in oxygenation (NO group) and in four nonresponders (control), platelet P-selectin expression, platelet fibrinogen binding, the expression CD11a on leukocytes, and the formation of PLAs were investigated at 0, 60, 120, and 180 mins of therapy or at corresponding time points by means of flow cytometry. In addition, PLA was investigated in 30 healthy volunteers during NO inhalation, in five mechanically ventilated patients without acute respiratory distress syndrome and without NO inhalation, and during NO incubation in platelet-rich plasma of ten healthy volunteers in vitro.

RESULTS

NO therapy inhibited PLA formation at 60 (13% +/- 4% in the NO group vs. 19% +/- 7% in the control group, p <.01) and 120 mins (14% +/- 4% vs. 18% +/- 7%, p <.05) and slightly decreased CD11a expression at 60 mins (152 +/- 22 arbitrary units vs. 187 +/- 36 arbitrary units, p <.05). Furthermore, besides inhibiting platelet fibrinogen binding, NO also led to a significant inhibition of P-selectin expression at 120 (38% +/- 4% vs. 43% +/- 5%, p <.05) and 180 mins (34% +/- 5% vs. 43% +/- 6%, p <.01), demonstrating a significant correlation between changes in P-selectin expression and PLA formation. In contrast, PLA formation was not influenced by mechanical ventilation in patients without acute respiratory distress syndrome. These results were further supported by additional studies showing inhibition of PLA formation in healthy volunteers as well.

CONCLUSIONS

NO-dependent inhibition of PLA formation in patients with acute respiratory distress syndrome can be explained by the inhibition in platelet P-selectin expression. Thus, this study provides rational evidence of systemic antileukocytic and antiplatelet properties of NO therapy in the clinical setting.

Activation of calcium-dependent calmodulin by calcium(II)3(3,5-diisopropylsalicylate)6(H2O)6 decreases thrombin receptor activating peptide-induced P-selectin expression

We examined the influence of 3,5-diisopropylsalicylic acid (3,5-DIPS) and calcium(II)3 (3,5-diisopropylsalicylate)6 (H2 O)6 [Ca(II)3 (3,5-DIPS)6 ], a new activator of calcium-dependent calmodulin-triggered nitric oxide synthase, on thrombin-induced platelet P-selectin expression. Citrated whole blood samples were incubated with either ethanol vehicle, 3,5-DIPS, or Ca(II)3 (3,5-DIPS)6. These whole blood samples were also co-incubated with thrombin receptor activating peptide (TRAP) or adenosine diphosphate (ADP), to up-regulate P-selectin (CD62P) on platelets. Both TRAP and ADP up-regulated P-selectin on platelets compared with platelets in whole blood samples that were not incubated with either platelet activator. Co-incubation of whole blood samples with TRAP, ADP together with 3,5-DIPS, or Ca(II)3 (3,5-DIPS)6 revealed that Ca(II)3 (3,5-DIPS)6 caused a decrease in platelet P-selectin expression for TRAP, ADP, and no-activator co-incubated samples of whole blood. Incubation of platelets with 3,5-DIPS also caused a decrease in ADP-induced up-regulation of P-selectin but failed to affect TRAP or no-activator-treated platelets. Incubation of whole blood with Ca(II)3 (3,5-DIPS)6 induced some hemolysis. We found that hemolysis increases basal P-selectin expression on platelets. We therefore conclude that Ca(II)3 (3,5-DIPS)6 decreased not only basal, but also hemolysis-induced P-selectin expression on platelets. In contrast, incubation of haemolysed whole blood with SIN-1 (standard nitric oxide-releasing drug) had no effect on P-selectin expression. In summary, Ca(II)3 (3,5-DIPS)6, a new calmodulin-dependent nitric oxide synthase activator, decreases P-selectin expression of human platelets in response to thrombin receptor activation. Improved calcium-dependent calmodulin activators may become useful drugs for the treatment of disorders associated with platelet activation, and P-selectin may decrease expression due to hemolysis.

Inhaled nitric oxide for acute hypoxemic respiratory failure in children and adults

BACKGROUND

Acute hypoxemic respiratory failure affects all age groups and may result from a number of systemic diseases. It continues to be associated with high mortality and morbidity. Initial studies examining the effect of inhaled nitric oxide in respiratory failure demonstrated transient improvement in oxygenation but did not examine mortality or other significant morbidity outcomes.

OBJECTIVES

To systematically examine randomized controlled trials addressing the effect of inhaled nitric oxide, compared with placebo inhaled gas, on mortality and morbidity in patients with acute hypoxemic respiratory failure.

SEARCH STRATEGY

Randomized controlled trials were identified from electronic databases: The Cochrane Central Register of Controlled Trials (CENTRAL) (Issue 2, 2002;MEDLINE (January 1966-August 2002); EMBASE (1980-March 2001); CINAHL (1982-July 2002), as well as from bibliographies of retrieved articles. Relevant journals and conference proceedings were hand searched and authors published in this field were contacted for knowledge of unpublished ongoing trials.

SELECTION CRITERIA

Randomized controlled trials comparing inhaled nitric oxide with maximal conventional therapy and inhaled placebo, in either children or adults with acute hypoxemic respiratory failure.

DATA COLLECTION AND ANALYSIS

Qualitative assessment of each trial was made and analyses performed according to statistical methods in Review Manager MetaView 4.1. A sub-group analysis was performed to assess the impact of inhaled nitric oxide at varied doses.

MAIN RESULTS

Five randomized controlled trials were evaluated, assessing 535 patients with acute hypoxemic respiratory failure (Age range not provided). Lack of data prevented assessment of all outcomes. There was no significant difference of nitric oxide on mortality in trials without cross-over (RR 0.98, 95%CI 0.66,1.44). Published evidence from one study demonstrated nitric oxide to transiently improve oxygenation in the first 72 hours of treatment. Limited data demonstrated no significant difference in ventilator-free days between treatment and placebo groups, and no specific dose of nitric oxide was significantly advantageous over another. Other clinical indicators of effectiveness, such as duration of hospital and intensive care stay, were inconsistently reported. There were no significant complications directly attributable to this treatment.

REVIEWER'S CONCLUSIONS

Nitric oxide did not demonstrate any statistically significant effect on mortality and transiently improved oxygenation in patients with hypoxemic respiratory failure. Lack of data prevented assessment of other clinically relevant end points. If further trials comparing inhaled nitric oxide with an inhaled placebo are to proceed, they should be stratified for primary disease, assess the impact of other combined treatment modalities for respiratory failure, and must specifically evaluate clinically relevant outcomes, before any benefit of inhaled nitric oxide for respiratory failure can be excluded.

The effect of sildenafil on human vascular function, platelet activation, and myocardial ischemia

OBJECTIVE

We studied the effects of sildenafil, a phosphodiesterase 5 inhibitor, on coronary and peripheral vascular function, platelet activation, and myocardial ischemia.

BACKGROUND

Nitric oxide vasodilates and inhibits platelet activation by generating cyclic guanosine 5'-monophosphate, which is metabolized by phosphodiesterase type 5.

METHODS

The effect of oral sildenafil on resting coronary vascular tone, endothelium-dependent and -independent function and platelet activation was measured in 24 patients. An additional 24 patients with coronary artery disease (CAD) and ischemia during exercise, and 12 control subjects received either 100 mg of sildenafil, 10 mg of isosorbide dinitrate (ISDN) or placebo during exercise on three separate days in a randomized, double-blind manner. Flow-mediated dilation of the brachial artery was measured, and CAD patients underwent treadmill exercise testing.

RESULTS

Sildenafil (100 mg) vasodilated epicardial coronary arteries (+6.9 +/- 1.3%, p < 0.0001). Coronary epicardial and microvascular responses with acetylcholine and cold-pressor testing improved, with a greater enhancement in patients with CAD and endothelial dysfunction. Verapamil responses were unchanged. Both resting and adenosine diphosphate-stimulated platelet IIb/IIIa receptor activation was inhibited by sildenafil (p < 0.05). Brachial arteries dilated in response to sildenafil in controls. Peak flow-mediated dilation was similar, but the duration of hyperemia was prolonged after sildenafil administration (p < 0.001). Compared with placebo, ISDN improved myocardial ischemia during exercise (p < 0.05), whereas the effect of sildenafil was intermediate between the two.

CONCLUSIONS

Sildenafil dilates epicardial coronary arteries, improves endothelial dysfunction and inhibits platelet activation in patients with CAD. It has an intermediate effect on myocardial ischemia compared with ISDN and placebo.

Pulmonary arterial hypertension in congenital heart disease

Pulmonary arterial hypertension (PAH) is a recognized complication of congenital systemic to pulmonary arterial cardiac shunts. The prognosis of PAH in this situation is better than primary or other secondary forms of PAH. Our knowledge of the pathophysiology of PAH complicating congenital heart disease has evolved over the past decade. Despite differences in etiology and pathobiology, therapies that have proven successful for primary PAH may benefit this group of patients.

Inhaled nitric oxide: more than a selective pulmonary vasodilator

Because of its high diffusing capacity through the alveolar-blood barrier and its high selectivity for the pulmonary vasculature, inhaled nitric oxide (NO) has been recently shown to be a viable and efficient approach to restore pulmonary NO deficiency. The most relevant applications of inhaled NO are in infants with primary pulmonary hypertension or hypoxia. In these patients, inhaled NO improves gas exchange and ventilation-perfusion matching, reduces the length of hospitalization and is without severe detrimental effects. The use of inhaled NO has also been extended to adults with pulmonary hypertension and the acute respiratory distress syndrome. In addition, recent clinical evidence supported by data from animal models, shows beneficial extra-pulmonary effects of inhaled NO, including protection against myocardial ischaemia-reperfusion injury.

[Inhaled nitric oxide in the peroperative period and recovery]

OBJECTIVE

To analyse the current knowledge concerning use of inhaled NO (iNO) in anaesthesia and intensive care.

DATA SOURCE

References were obtained from Medline, recent review articles, the library of the department and personal files.

STUDY SELECTION

All categories of articles on this topic have been selected.

DATA EXTRACTION

Articles have been analysed for history, biochemistry, pharmacology, toxicity and clinical use of iNO.

DATA SYNTHESIS

Nitric oxide (NO) is a potent endothelium-dependent vasodilator. Because of its selective action on pulmonary circulation and the lack of effect on the systemic circulation due to its inactivation by haemoglobin, iNO has been presented as a new therapeutic agent in most diseases with pulmonary hypertension. During heart transplantation or surgical correction of congenital heart disease, iNO decreases pulmonary hypertension and improves altered right ventricular function. Studies included however small numbers of patients. Preliminary pharmacological studies demonstrated that iNO was able to decrease pulmonary hypertension and improve systemic oxygenation in adult respiratory distress syndrome. To date, none of the three multicentric studies performed was able to show any significant effect on duration of mechanical ventilation, morbidity or mortality. Finally, the sole demonstrated indication for iNO which remains is the persistent pulmonary hypertension of the newborn. Two multicentric studies have evidenced an improvement in systemic oxygenation and a reduced need for extracorporeal membrane oxygenation. In these two studies global mortality was however unchanged.

CONCLUSION

Persistent pulmonary hypertension is the sole demonstrated indication for iNO. Inhaled nitric oxide may be efficient in pulmonary hypertension, right ventricular dysfunction and severe hypoxemia. Inhaled nitric oxide must be considered as a rescue therapy or needs to be part of research protocols.

The effects of inhaled nitric oxide on the levels of cGMP plasma and lung tissue in a canine model of smoke inhalation injury

The effects of inhaled nitric oxide (NO) on pulmonary hypertension and their mechanisms were studied in a canine model of smoke inhalation injury. Twenty-one dogs were randomly divided into three groups: four dogs constituted the normal control group, eight dogs subjected to smoke inhalation followed by O(2) inhalation (FiO(2)=0.45) constituted the injury control group, and nine dogs inhaling a mixture of O(2) and 45ppm nitric oxide after smoke exposure served as the treatment group. The levels of cyclic guanosine monophosphate (cGMP) in arterial plasma of the treatment group were higher than that of the control group at 5, 8, and 12h after smoke exposure, while the levels of cGMP in lung tissue were also significantly higher compared with that of the control group (P<0.01). The levels of cGMP of injury control group were decreased significantly compared with normal controls (P<0.05). Pulmonary vasoconstriction following smoke inhalation was significantly attenuated by inhalation of NO (P<0.05), which exerted no apparent effect on the systemic circulation (P>0.05). Inhalation of NO may lower pulmonary hypertension induced by smoke inhalation injury in dogs. The selective effect of NO on pulmonary circulation may be attributed to an increase in level of cGMP in smooth muscle cells of the lung tissue after inhalation of NO.

Nitric oxide and free stable nitroxyl radicals in the mechanism of biological action of the spin-labeled compounds

A comparison of more important physical, chemical and biological properties of the nitric oxide (NO) and free stable nitroxyl radicals (nitroxides) on the base of their structural similarity is made in the article. The active moiety in the nitroxide molecule represents a sterically hindered nitric oxide. The mechanisms of biological action of the nitroxides and especially of their derivatives with antitumor agents from the groups of nitrogen mustards, nitrosoureas, aziridines and triazenes (spin-labeled compounds) is explained through the biological activities of sterically hindered NO. Similarly to NO, nitroxides also can react with superoxide anion radical (O(2)(-)), they possess superoxide dismutase (SOD) mimetic action. While the interaction of NO with O(2)(-)yields very toxic peroxynitrite (ONOO(-)), its formation is strongly limited in the presence of a nitroxide. It is known that the nitrosourea antitumor drugs, like lomustine (CCNU) and carmustine (BCNU), showed high general toxicity, one of the reasons for that probability is the formation of NO, and subsequently of ONOO(-), during their metabolism. The biological investigations of the nitroxides showed their considerably lower general toxicity that could be explained with the SOD-mimetic action of the nitroxide present in their molecule.

Prevention of intimal hyperplasia with recombinant soluble P-selectin glycoprotein ligand-immunoglobulin in the porcine coronary artery balloon injury model

OBJECTIVES

The role of P-selectin in the process of restenosis was evaluated using a recombinant immunoglobulin (Ig) chimera form of its ligand, soluble P-selectin glycoprotein ligand-Ig (rPSGL-Ig), as a competitive inhibitor for the natural ligand on leukocytes.

BACKGROUND

Inflammation and coagulation activation after vascular injury may be an important factor in the development of restenosis. P-selectin has been shown to mediate leukocyte-endothelium and leukocyte-platelet interaction. These interactions are mediated through binding of P-selectin to P-selectin glycoprotein ligand-1 (PSGL-1) located on the surface of leukocytes.

METHODS

Balloon injury was induced in the left anterior descending and right coronary arteries of 16 pigs at a balloon/artery diameter ratio of 1.5:1. Either rPSGL-Ig (1 mg/kg) or saline was randomly administered 15 min before balloon injury as an intravenous bolus. Four weeks after injury, morphometric analysis, immunohistochemistry and histological evaluation were performed on injured arterial segments.

RESULTS

Increased luminal area was found in the rPSGL-Ig group compared with the placebo group (1.63 +/- 0.57 mm2 vs. 1.26 +/- 0.32 mm2, p = 0.044) owing to significantly reduced neointimal hyperplasia (cross-sectional area, 0.46 +/- 0.45 mm2 vs. 0.13 +/- 0.11 mm2, p = 0.013). Immunohistochemistry and histological evaluation showed a significant decrease in the presence of tumor necrosis factor-alpha, interleukin-1 beta, and infiltration of macrophages in the injured vessel segments in the rPSGL-Ig group.

CONCLUSIONS

P-selectin antagonism using rPSGL-Ig decreases neointimal hyperplasia following balloon injury, by inhibiting the inflammatory and thrombotic responses at the site of balloon injury, which appears to play a pivotal role in the pathogenesis of restenosis.

Etomidate and thiopental inhibit platelet function in patients undergoing infrainguinal vascular surgery

BACKGROUND

Postoperative platelet hyperaggregability following general anesthesia has been reported in patients undergoing major vascular surgery. In contrast, since anesthetic agents inhibited platelet function both in vitro and in vivo, an increased risk for postoperative bleedings due to prolonged platelet dysfunction has been discussed. Nevertheless, data describing platelet-affecting properties of induction agents such as etomidate and thiopental in patients undergoing major vascular surgery are lacking.

METHODS

Platelet function was determined at 0, 2, 20, and 200 microg/ml thiopental and at 0, 0.2, 2, 20 microg/ml etomidate in vitro in blood samples drawn from 16 patients suffering from severe occlusive arterial disease. In addition, 30 patients undergoing vascular surgery were investigated before (PRE) and after anesthesia induction (T0) either with etomidate (ETO group, n=16) or thiopental (THIO group, n=14), and 2 h after the beginning of surgery (T2). Platelet function was determined according to platelet aggregation, in vitro bleeding time, and flow cytometric measurements.

RESULTS

In vitro, P-selectin expression was inhibited by etomidate at 2 and 20 microg/ml (-28% and -38%, respectively) and also by thiopental at 200 microg/ml (-27%). In patients undergoing vascular surgery, anesthesia induction in the ETO group resulted in a 31% prolongation of the in vitro bleeding time and an inhibition of ADP- and collagen-induced platelet aggregation (-30% and -17%, respectively) and of P-selectin expression (-25%) at T0. In the THIO group, only ADP-induced platelet aggregation was affected (-16%). At T2, all parameters had reached PRE level again in both groups. Furthermore, in comparison with the THIO group, operation time was significantly prolonged and transfusion volume was significantly increased in the ETO group. In addition, platelet count and hematocrit significantly decreased at T2, whereas levels of tPA, PAI-1, fibrinogen and antithrombin III and partial thromboplastin time remained unchanged in both groups during the study period.

CONCLUSIONS

In the present study, etomidate and, to a minor extent, thiopental offered significant platelet inhibitory properties. Anesthetic-induced platelet inhibition may lead to higher transfusion rates and prolonged operation times. Therefore, anesthetic-related platelet inhibitory properties should be considered when searching for the anesthetic agent of choice, especially in patients with compromised hemostasis and co-existing bleeding disorders.

Nitric oxide decreases coagulation protein function in rabbits as assessed by thromboelastography

Nitric oxide (NO) is administered via infusion of donors such as nitroglycerin or in inhaled form for treatment of ischemia and pulmonary hypertension, respectively. In rabbits, the NO donor, DETANONOate, decreases whole blood clotting function as assessed by thromboelastographic variables (R, reaction time; alpha, angle; and G, a measure of clot strength). I hypothesized that DETANONOate-derived NO would adversely affect coagulation protein and platelet function. Blood obtained from ear arteries of conscious rabbits (n = 8) anticoagulated with sodium citrate. The blood was then incubated with 0 or 10mM DETANONOate for 30 min. After incubation and recalcification, thromboelastography was performed for 60 min under four conditions: 1) 0mM DETANONOate, 2) 0mM DETANONOate with platelet inhibition with cytochalasin D, 3) 10mM DETANONOate, and 4) 10mM DETANONOate with platelet inhibition. DETANONOate significantly (P < 0.05) increased R and decreased alpha and G in samples with or without platelet inhibition, compared with samples not exposed to DETANONOate. Lastly, the percentage of total G (G(T)) attributable to platelet function (G(P)) was significantly more in the absence of DETANONOate (G(P) = 92.3% +/- 1.6%; mean +/- SD) than after exposure to DETANONOate (G(P) = 90.2% +/- 2.3%). DETANONOate-derived NO significantly decreased coagulation protein function and platelet function. Coagulation protein function may be similarly affected in clinical situations involving the administration of NO or NO donors.

Inhibition of human platelet aggregation by a novel S-nitrosothiol is abolished by haemoglobin and red blood cells in vitro: implications for anti-thrombotic therapy

1. S-Nitrosothiols are nitric oxide (NO) donor drugs that have been shown to inhibit platelet aggregation in platelet rich plasma (PRP) in vitro and to inhibit platelet activation in vivo. The aim of this study was to compare the platelet effects of a novel S-nitrosated glyco-amino acid, RIG200, with an established S-nitrosothiol, S-nitrosoglutathione (GSNO) in PRP, and to investigate the effects of cell-free haemoglobin and red blood cells on S-nitrosothiol-mediated inhibition of platelet aggregation. 2. The effects of GSNO and RIG200 in collagen (2.5 microg ml(-1))-induced platelet aggregation in PRP and whole blood were investigated in vitro. Both compounds were found to be powerful inhibitors of aggregation in PRP, and RIG200 was significantly more potent (IC(50)=2.0 microM for GSNO and 0.8 microM for RIG200; P=0.04). 3. Neither compound inhibited aggregation in whole blood, even at concentrations of 100 microM. Red blood cell concentrations as low as 1% of the haematocrit, and cell-free haemoglobin (> or = 2.5 microM), significantly reduced their inhibitory effects on platelets. 4. Experiments involving measurement of cyclic GMP levels, electrochemical detection of NO and electron paramagnetic resonance of haemoglobin in red blood cells, indicated that scavenging of NO generated from S-nitrosothiols by haemoglobin was responsible for the lack of effect of S-nitrosothiols on platelets in whole blood. 5. These studies suggest that scavenging of NO by haemoglobin in blood might limit the therapeutic application of S-nitrosothiols as anti-platelet agents.

Inhibition of agonist-induced p42 and p38 mitogen-activated protein kinase phosphorylation and CD40 ligand/P-selectin expression by cyclic nucleotide-regulated pathways in human platelets

Platelet activation and adhesion to endothelial cells and extracellular matrix proteins are crucial events in the development of arterial cardiovascular diseases. Platelet activation is initiated by stimulation of intracellular signaling cascades, including the p42 mitogen-activated protein kinase (MAPK) and p38 MAPK pathways, followed by major changes in the platelet cytoskeleton and expression and activation of platelet surface receptors, such as P-selectin (CD62P) and CD40 ligand (CD40L). Activated platelets directly bind to vascular endothelial cells via CD40L/CD40 interactions and induce inflammatory reactions that initiate or aggravate atherosclerotic lesions. The aim of this study was to investigate effects of two known platelet inhibitors-the cAMP-elevating prostaglandin E(1) (PG-E(1)) and the cGMP-elevating sodium nitroprusside (SNP)-on platelet p42 MAPK and p38 MAPK activation as well as on surface expression of CD62P and CD40L. MAPK activation was analyzed by Western blot experiments using phosphorylation-specific antibodies, and surface CD40L and CD62P expression was determined by flow cytometry analysis. PG-E(1) and SNP strongly inhibited p42 and p38 MAPK phosphorylation as well as CD40L and CD62P expression in response to thrombin, a thromboxane A(2) analog, and ADP. These data indicate that adenosine and guanosine 3',5'-cyclic monophosphate-dependent protein kinases not only inhibit platelet pathways leading to activation and aggregation, but also those resulting in enhanced surface expression of protein ligands involved in inflammation. Expression of CD40L and CD62P was found to be independent of MAPK activation, since it was not inhibited by specific MAPK inhibitors. Inhibition of platelet-induced inflammatory responses including CD62P- and CD40L-mediated interaction of platelets with leukocytes and endothelial cells, respectively, is suggested to be an important component of the long-term vasoprotective effects of cyclic nucleotide-elevating prostaglandins and NO donors.

17beta-estradiol corrects hemostasis in uremic rats by limiting vascular expression of nitric oxide synthases

Conjugated estrogens shorten the prolonged bleeding time in uremic patients and are similarly effective in a rat model of uremia. We have previously demonstrated that the shortening effect of a conjugated estrogen mixture or 17beta-estradiol on bleeding time was abolished by the nitric oxide (NO) precursor L-arginine, suggesting that the effect of these drugs on hemostasis in uremia might be mediated by changes in the NO synthetic pathway. The present study investigated the biochemical mechanism(s) by which conjugated estrogens limit the excessive formation of NO. 17beta-estradiol (0.6 mg/kg), given to rats made uremic by reduction of renal mass, significantly reduced bleeding time within 24 h and completely normalized plasma concentrations of the NO metabolites, nitrites and nitrates, and of NO synthase (NOS) catalytic activity, determined by NADPH-diaphorase staining in the thoracic aorta. Endothelial NOS (ecNOS) and inducible NOS (iNOS) immunoperoxidase staining in the endothelium of uremic aortas of untreated rats was significantly more intense than in control rats, while in uremic rats receiving 17beta-estradiol staining was comparable to controls. Thus 17beta-estradiol corrected the prolonged bleeding time of uremic rats and fully normalized the formation of NO by reducing the expression of ecNOS and iNOS in vascular endothelium. These results provide a possible biochemical explanation of the well-known effect of estrogens on primary hemostasis in uremia, in experimental animals and humans.

Inhaled nitric oxide does not enhance lipid peroxidation in patients with acute respiratory distress syndrome

OBJECTIVE

To investigate whether inhaled nitric oxide (NO) enhances pulmonary lipid peroxidation as indicated by arterial blood levels of malondialdehyde, hexanal, and pentanal in patients with acute respiratory distress syndrome (ARDS).

DESIGN

Prospective, nonrandomized, controlled trial.

SETTING

Surgical intensive care unit in a university hospital.

PATIENTS

Twenty-five patients with ARDS, as defined by the American-European Consensus Conference, and a PaO2/FIO2 < or = 170 mm Hg were enrolled in the study. Four healthy subjects were studied as controls.

INTERVENTIONS

On enrollment of the patients in the study, a dose-response test with increasing concentrations of inhaled NO (0, 2, 10, 40, 0 ppm) was performed. Patients who showed an increase of >20% in PaO2 were designated as responders and all others as nonresponders. In responders, this dose-response test was followed by 24 hrs of continuous treatment with inhaled NO at the best NO concentration determined during the dose-response test, whereas nonresponders received standard care. For healthy volunteers, the dose-response test took the form of spontaneous breathing of the same NO concentrations.

MEASUREMENTS AND MAIN RESULTS

Eighteen patients (72%) showed an increase of >20% in PaO2 during the dose-response test. This significant improvement in arterial oxygenation in responders led to a significant reduction in FIO2 (responders, 0.73 +/- 0.05 vs. nonresponders, 0.89 +/- 0.05) after 24 hrs of therapy. On enrollment, arterial blood concentrations of malondialdehyde, hexanal, and pentanal were significantly higher than those of healthy volunteers. In addition, arterial concentrations of hexanal and pentanal exceeded mixed venous levels two- to ten-fold. Inhalation of NO did not significantly alter these blood concentrations either during the dose response test or during 24 hrs of therapy.

CONCLUSIONS

In patients with ARDS, malondialdehyde, hexanal, and pentanal were significantly elevated, indicating lipid peroxidation. Lipid peroxidation was not further affected by inhalation of NO.

Inhaled NO reduces leukocyte-endothelial cell interactions and myocardial dysfunction in endotoxemic rats

Inhaled nitric oxide (NO) has been shown to have some protective effect in the peripheral distal inflamed vasculature. The objective of the study was to determine whether inhaled NO would reduce endotoxin-induced leukocyte activation and myocardial contractile dysfunction. Rats were treated with either saline or endotoxin (10 mg/kg iv) and then allowed to breathe (4 h) either air or air plus NO (10 ppm). In endotoxemic rats, mesenteric venular endothelium leukocyte firm adhesion increased compared with control rats (1.15 +/- 0.32 vs. 4.08 +/- 0.96 leukocytes/100 microm; P < 0.05). Inhaled NO significantly attenuated endotoxin-induced venular endothelium leukocyte adhesion (4.08 +/- 0.96 vs. 1.86 +/- 0.76 leukocytes/100 microm; P < 0.05) and FITC-conjugated anti-intercellular adhesion molecule-1 fluorescence intensity. Endotoxin-induced myocardial dysfunction and leukocyte content increases were reduced in inhaled NO-treated rats. These observations suggest that inhaled NO reduces the degree of cardiovascular dysfunction and inflammation in endotoxemic rats.

Inhaled nitric oxide modulates leukocyte kinetics in the mesenteric venules of endotoxemic rats

OBJECTIVE

to determine whether inhaled nitric oxide (NO) would alter leukocyte kinetics in the septic microvasculature.

DESIGN

Randomized, controlled trial.

SETTING

Experimental laboratory.

SUBJECTS

Male Sprague Dawley rats.

INTERVENTIONS

Rats were treated with either saline or endotoxin (10 mg/kg, iv) and then allowed to breathe either air or air plus NO (10 ppm).

MEASUREMENTS AND MAIN RESULTS

After a 4-hr period, rolling, firm adhesion, and emigration of leukocytes and endothelial dysfunction were monitored in mesenteric venules by using intravital videomicroscopy. Compared with controls, endotoxemic rats exhibited a profound influx in mesenteric venule rolling leukocytes (55+/-17 vs. 70+/-19 leukocytes/min; p < .05), associated with a reduction of leukocyte rolling velocity (83+/-14 vs. 34+/-3 microm/sec; p < .05). In endotoxemic rats, venular endothelium leukocyte firm adhesion (1.15+/-0.32 vs. 4.08+/-0.96 leukocytes/ 100 microm; p < .05) and emigration (0.84+/-0.47 vs. 4.23+/-1.2 leukocytes/100 microm; p < .05) increased compared with controls. Inhaled NO had no effect on leukocyte kinetics in control rats. Inhaled NO significantly attenuated endotoxin-induced venular endothelium leukocyte adhesion (4.08+/-0.96 vs. 1.86+/-0.76 leukocytes/100 microm; p < .05) and emigration (4.23+/-1.2 vs. 1.68+/-0.72 leukocytes/100 microm; p < .05). Compared with control rats, macromolecular (FITC-dextran) vascular leakage, expressed as the perivenular/intravenular fluorescence intensity ratio, increased in endotoxemic rats (0.56+/-0.02 vs. 0.81+/-0.05; p < .01). Endotoxin-induced macromolecular vascular leakage increases were partially prevented by inhaled NO (0.66+/-0.01 vs. 0.56+/-0.02; p < .05).

CONCLUSION

These observations suggest that inhaled NO reduces leukocyte adhesion and the degree of vascular permeability dysfunction in mesenteric venule of endotoxemic rats.

Monophosphoryl lipid A: a novel nitric oxide-mediated therapy to attenuate platelet thrombosis?

Nitric oxide (NO) is a potent inhibitor of platelet aggregation. However, the benefits of NO-based therapies can be confounded by concomitant hypotension. Monophosphoryl lipid A (MLA) is a nontoxic derivative of endotoxin that purportedly increases nitric oxide synthase (NOS) activity and, presumably, NO production, yet has a hemodynamically benign profile. Thus our aims were to determine whether (a) MLA attenuates in vivo platelet aggregation in damaged and stenotic canine coronary arteries by a NO-mediated mechanism but without reductions in arterial pressure; and (b) the platelet inhibitory effects are manifest in vitro. To address the first aim, anesthetized dogs underwent coronary injury + stenosis, resulting in cyclic variations in coronary blood flow (CFVs) caused by the formation/dislodgement of platelet-rich thrombi. In protocol I, dogs received MLA (100 microg/kg + 40 microg/kg/h) or vehicle beginning 15 min before stenosis. Protocol II was identical, except the NOS inhibitor aminoguanidine was coadministered with MLA/vehicle. Coronary patency was assessed throughout the initial 3 h after injury + stenosis. Infusion of MLA did not result in hypotension. However, in protocol I, the median nadir of the CFVs was higher (2.1 vs. 0.8 ml/min; p < 0.05), median duration of total thrombotic occlusion tended to be reduced (0 vs. 10.4 min; p = 0.1), and mean flow-time area, expressed as a percentage of baseline flow, was increased (53 +/- 9% vs. 33 +/- 3%; p < 0.05) in MLA-treated versus vehicle-treated dogs. In contrast, in protocol II, vessel patency was comparable in both groups. Finally, whole blood impedance aggregometry (protocol HI) revealed a significant reduction in the in vitro platelet aggregation in blood samples receiving exogenous MLA, which was blocked by coadministration of exogenous aminoguanidine. Thus MLA attenuates platelet-mediated thrombosis in both damaged and stenotic canine coronary arteries and in vitro, possibly by an NO-mediated mechanism, but without concomitant hypotension.

Effects of DETANONOate, a nitric oxide donor, on hemostasis in rabbits: an in vitro and in vivo thrombelastographic analysis

PURPOSE

The purpose of this study was to determine if whole blood thrombelastographic variables (reaction time, K, alpha, and maximum amplitude) would be adversely effected by exposure to the nitric oxide (NO) donor, DETANONOate, in vitro or after alveolar instillation in vivo.

MATERIALS AND METHODS

Conscious rabbits (n = 10) had blood sampled from ear arteries anticoagulated with sodium citrate. The blood was then incubated with 0, 1, 5, 10, or 20 mmol/L DETANONOate for 30 minutes. Arterial blood from anesthetized rabbits (n = 4) was obtained and anticoagulated before and 60 minutes after 1 mmol/L DETANONOate (2 mL/kg) was instilled into the right lung. After incubation, all samples were placed in a thrombelastograph and recalcified, with thrombelastographic variables measured for 45 minutes.

RESULTS

In vitro, 10 mmol/L DETANONOate significantly (P < .05) increased reaction time, K, and decreased alpha compared with values observed after incubation with 0, 1, and 5 mmol/L DETANONOate. Twenty mmol/L DETANONOate significantly (P < .05) increased reaction time, K, and decreased alpha and maximum amplitude values compared with all other concentrations. In vivo, DETANONOate administration did not significantly affect thrombelastographic variables.

CONCLUSION

DETANONOate significantly decreased hemostatic function in vitro in a dose-dependent fashion but did not significantly affect hemostatic function in vivo.

Antiplatelet effects of sodium nitroprusside in flowing human blood: studies under normoxic and hypoxic conditions

We explored the ability of sodium nitroprusside to modify adhesive and cohesive function of platelets in flowing blood, under normoxic and hypoxic conditions. Aliquots of both untreated and sodium nitroprusside-treated blood were prepared for studies of: (1) platelet aggregation in plasma; (2) erythrocyte deformability; (3) platelet interaction with damaged subendothelium, by using a well-defined perfusion system; and (4) blood gasometry in the perfused samples. Results showed that sodium nitroprusside-treated blood always showed a totally inhibited arachidonic acid-induced platelet aggregation in plasma, as well as significantly increased erythrocyte deformability (0.44+/-0.09 up to 0.66+/-0.05; p<0.05). However, treatment with sodium nitroprusside did not modify the pattern of platelet interaction with subendothelium (percentage of contact, adhesion, thrombus, and covered surface) with respect to untreated blood, under any of the shear rates used (300, 800, and 1800 seconds(-1)), although it significantly reduced the height of thrombi (9.8+/-0.4 vs. 8.3+/-0.4 microm; p<0.05). Hypoxic conditions did not have a noticeable effect in modifying antiplatelet effects of sodium nitroprusside. Additionally, the presence of sodium nitroprusside impaired the normal oxygenation of the blood during perfusion. pO2 in control untreated samples rose from 40.3+/-5.0 mm Hg perfusions to 100.4+/-12.5 mm Hg but remained at 66.3+/-6.3 mm Hg in sodium nitroprusside-treated blood (p<0.05). Our results did not show a significant effect of sodium nitroprusside in the modulation of platelet interaction with subendothelium. The marginal reduction in the thrombi height could be related to rheological interference of increased erythrocyte deformability.

Inhaled nitric oxide does not influence bleeding time or platelet function in healthy volunteers

BACKGROUND

Bleeding time has been reported to increase during gaseous nitric oxide (NO) inhalation in healthy volunteers and patients, and it has been speculated that inhaled NO inhibits platelet function. However, results have not been unanimous, and we have been unable to document any effects of inhaled NO on circulating platelets.

MATERIALS AND METHODS

We performed a double-blind, placebo controlled cross-over study in which healthy volunteers (n = 15) inhaled NO (30 ppm, 30 min) or control gas. Aspirin (640 mg x 1 orally) was used as positive control on the third occasion (n = 14). Bleeding time was measured, and platelet function was determined flow cytometrically by measuring the expression of P-selectin on circulating platelets and locally activated platelets in wound blood. Skin perfusion close to the site for bleeding time incisions was assessed by laser Doppler flowmetry.

RESULTS

Bleeding time was unaffected by NO, as there were slight increases during both NO and control inhalation (+20% and +14% respectively, P = 0.9). Similarly, NO inhalation had no effect on platelet P-selectin expression in either systemic or wound blood, or on skin perfusion. Aspirin pretreatment, on the other hand, prolonged bleeding time (P < 0.001) and decreased P-selectin expression of platelets in wound blood (P = 0.03).

CONCLUSIONS

This first placebo-controlled study indicates that inhaled NO does not influence either bleeding time, platelet activity or skin perfusion. Thus, it is unlikely that treatment of critically ill patients with inhaled NO will aggravate haemostatic disturbances, which has previously been feared, by influencing platelet function.

Chlamydia pneumoniae and anti-infective therapy: their role in the pathogenesis and treatment of coronary artery disease

Cardiovascular disease remains the most common cause of death in the United States; however, conventional cardiovascular risk factors fail to explain completely the pathogenesis of atherosclerosis and coronary artery disease. There has been recent interest in the association between Chlamydia pneumoniae and the risk of development or progression of atherosclerotic disease. This association has become evident through serologic, pathologic, and animal-based models and, more recently, through limited trials of antichlamydial antibiotics in humans. Whether C. pneumoniae is a causative agent or "innocent bystander" or whether antibiotic therapy has any role in the treatment of cardiovascular disease remains to be determined.

The effect of intravenously administered magnesium on platelet function in patients after cardiac surgery

After cardiac surgery, magnesium is often administered for prophylaxis and treatment of cardiac arrhythmias. Magnesium, however, inhibits platelet function in vitro and in healthy volunteers. We performed a randomized, blinded, and placebo-controlled study to investigate the effect of magnesium on platelet function in patients after cardiac surgery. We studied patients who underwent uneventful coronary revascularization with cardiopulmonary bypass on the first postoperative day. Before and after an infusion of either 5.4 mmol magnesium (n = 19) or saline (n = 20), platelet function was investigated by means of in vitro bleeding time, platelet aggregation, and flow-cytometric assays. In addition, to investigate platelet function in vitro, 1, 5, and 10 mM magnesium were added to platelet-rich plasma before and 24 h after surgery in 30 patients. Compared with the control group, magnesium prolonged the in vitro bleeding time (22%) and inhibited ADP- and collagen-induced platelet aggregation (13% and 17%), platelet P-selectin expression (18%), and the binding of fibrinogen to the platelet glycoprotein IIb/IIIa receptor (10%). Magnesium also led to significant dose-dependent inhibition of platelet aggregation (19%), P-selectin expression (14%), and fibrinogen binding (11%) before and after surgery in vitro. Although the antithrombotic effect of magnesium may be beneficial in patients after coronary revascularization, large-dose magnesium therapy should be carefully considered in patients with impaired platelet function and co-existing bleeding disorders.

IMPLICATIONS

In a randomized, blinded, placebo-controlled study of patients 24 h after coronary artery bypass grafting, IV administered magnesium inhibited platelet function in vitro and in vivo.

Nitric oxide metabolism and breakdown

The steady-state concentration and thus the biological effects of NO are critically determined not only by its rate of formation, but also by its rate of decomposition. Bioreactivity of NO at physiological concentrations may differ substantially from that suggested by in vitro experiments. The charge neutrality and its high diffusion capacity are hallmarks that characterize NO bioactivity. Reactive oxygen derived species are major determinants of NO breakdown. Biotransformation of NO and its related N-oxides occurs via different metabolic routes within the body. S-Nitrosothiols formed upon reaction of NO with redox-activated thiols represent an active storage pool for NO. The major oxidative metabolites represent nitrite and nitrate, the ratio of both is determined by the microenvironmental redox conditions. In humans, circulating nitrite represents an attractive estimate of regional endothelial NO formation, whereas nitrate, with some caution, appears useful in estimating overall nitrogen/NO turnover. Within the near future, more specific biochemical tools for diagnosis of reduced NO bioactivity will become available. Increasing knowledge on the complex metabolism of NO in vivo will lead to the development of new therapeutic strategies to enhance bioactivity of NO via modulation of its metabolism.