Inhaled nitric oxide increases endothelin-1 levels: a potential cause of rebound pulmonary hypertension

Inhaled NO at a crossroads in cardiac surgery: current need to improve mechanistic understanding, clinical trial design and scientific evidence

Inhaled nitric oxide (NO) has been used in pediatric and adult perioperative cardiac intensive care for over three decades. NO is a cellular signaling molecule that induces smooth muscle relaxation in the mammalian vasculature. Inhaled NO has the unique ability to exert its vasodilatory effects in the pulmonary vasculature without any hypotensive side-effects in the systemic circulation. In patients undergoing cardiac surgery, NO has been reported in numerous studies to exert beneficial effects on acutely lowering pulmonary artery pressure and reversing right ventricular dysfunction and/or failure. Yet, various investigations failed to demonstrate significant differences in long-term clinical outcomes. The authors, serving as an advisory board of international experts in the field of inhaled NO within pediatric and adult cardiac surgery, will discuss how the existing scientific evidence can be further improved. We will summarize the basic mechanisms underlying the clinical applications of inhaled NO and how this translates into the mandate for inhaled NO in cardiac surgery. We will move on to the popular use of inhaled NO and will talk about the evidence base of the use of this selective pulmonary vasodilator. This review will elucidate what kind of clinical and biological barriers and gaps in knowledge need to be solved and how this has impacted in the development of clinical trials. The authors will elaborate on how the optimization of inhaled NO therapy, the development of biomarkers to identify the target population and the definition of response can improve the design of future large clinical trials. We will explain why it is mandatory to gain an international consensus for the state of the art of NO therapy far beyond this expert advisory board by including the different major players in the field, such as the different medical societies and the pharma industry to improve our understanding of the real-life effects of inhaled NO in large scale observational studies. The design for future innovative randomized controlled trials on inhaled NO therapy in cardiac surgery, adequately powered and based on enhanced biological phenotyping, will be crucial to eventually provide scientific evidence of its clinical efficacy beyond its beneficial hemodynamic properties.

Pulmonary hypertension associated with cardiopulmonary bypass and cardiac surgery

BACKGROUND AND AIM

Pulmonary hypertension (PH) is frequently associated with cardiovascular surgery and is a common complication that has been observed after surgery utilizing cardiopulmonary bypass (CPB). The purpose of this review is to explain the characteristics of PH, the mechanisms of PH induced by cardiac surgery and CPB, treatments for postoperative PH, and future directions in treating PH induced by cardiac surgery and CPB using up-to-date findings.

METHODS

The PubMed database was utilized to find published articles.

RESULTS

There are many mechanisms that contribute to PH after cardiac surgery and CPB which involve pulmonary vasomotor dysfunction, cyclooxygenase, the thromboxane A2 and prostacyclin pathway, the nitric oxide pathway, inflammation, and oxidative stress. Furthermore, there are several effective treatments for postoperative PH within different types of cardiac surgery.

CONCLUSIONS

By possessing a deep understanding of the mechanisms that contribute to PH after cardiac surgery and CPB, researchers can develop treatments for clinicians to use which target the mechanisms of PH and ultimately reduce and/or eliminate postoperative PH. Additionally, learning about the most up-to-date studies regarding treatments can allow clinicians to choose the best treatments for patients who are undergoing cardiac surgery and CPB.

Novel use of riociguat in infants with severe pulmonary arterial hypertension unable to wean from inhaled nitric oxide

INTRODUCTION

Riociguat, an oral soluble guanylate cyclase stimulator, has been approved for use in adults with pulmonary arterial hypertension (PAH) and chronic thromboembolic pulmonary hypertension. However, there is limited data on its therapeutic use in children.

CASE PRESENTATION

We report the case of two infants with severe suprasystemic pulmonary hypertension who were successfully treated with riociguat after failure to wean off inhaled nitric oxide (iNO) despite combination PAH therapy. Case 1 is a 6-month-old term male with TBX4 deletion who presented with severe hypoxemic respiratory failure and severe PAH immediately after birth. Initial cardiac catheterization showed PVRi 15.5 WU*m2. Marked hypoxemia and PAH persisted despite aggressive therapy with sildenafil, bosentan, intravenous treprostinil, and milrinone. The infant required high doses of inhaled nitric oxide (60 ppm) and manifested significant post-ductal hypoxemia and hemodynamic instability with any attempt at weaning. After discontinuation of sildenafil, initiation, and very slow uptitration of riociguat, the patient was able to maintain hemodynamic stability and wean from nitric oxide over 6 weeks with persistently severe but not worsened pulmonary hypertension. Case 2 is a 4-month-old term male with compound heterozygous SLC25A26 mutation and severe pulmonary hypertension. Initial cardiac catheterization showed PVRi 28.2 WU*m2. After uptitration of sildenafil, bosentan, and IV treprostinil, serial echocardiograms continued to demonstrate near-systemic pulmonary hypertension. He failed multiple attempts to wean off typical doses of iNO (10-20 ppm) over the following weeks with tachypnea, hypoxemia, and worsening pulmonary hypertension on echocardiogram despite continued aggressive combination targeted therapy. After a 24-h sildenafil washout, he was initiated and uptitrated on riociguat with concomitant, successful wean of nitric oxide over one week that was well tolerated. No serious adverse effects in the titration period were observed.

CONCLUSION

Riociguat may be considered as an adjuvant therapeutic agent in selected children with severe PAH who are poorly responsive to sildenafil therapy and unable to wean from iNO.

The effects of extended nitric oxide release on responses of the human non-pregnant myometrium to endothelin-1 or vasopressin

BACKGROUND

Uterotonic mediators: endothelin-1 (ET-1), arginine vasopressin (AVP), and nitric oxide (NO) play important roles in the regulation of uterine contractility. We hypothesize that NO affects both ET-1 or AVP. Therefore, this study investigated the involvement of extended exogenous NO release in the regulation of responses of the human non-pregnant myometrium to ET-1 and AVP.

METHODS

Specimens were obtained from 10 premenopausal women, undergoing hysterectomy for benign gynecological disorders. Responses of the myometrial strips to ET-1 or AVP in the absence and presence of an exogenous NO donor (diethylenetriamine; DETA/NO; 10-4 mol/L) were recorded under isometric conditions. To inhibit endogenous NO, a competitive inhibitor of NO synthase, L-NG-nitroarginine (L-NNA) was added to the organ bath.

RESULTS

ET-1 enhanced the spontaneous contractile activity of the myometrium more powerfully (p < 0.01) than AVP. Preincubation with exogenous NO weakened ET-1- or AVP-induced increases in this contractile activity (p < 0.05). However, unexpected results were obtained after preincubation with L-NNA and with DETA/NO then added. Both ET-1 and AVP induced augmented contractile effects in almost all concentrations compared with the responses to these peptides alone or after NOS synthase inhibition (both p < 0.01).

CONCLUSIONS

This study demonstrated for the first time that extended incubation with a NO donor influences the uterine muscle response evoked by ET-1 and AVP. Both endogenous and exogenous NO is involved in the control of the uterine responses to ET-1 or AVP of non-pregnant myometrium. Furthermore, both peptides stimulate increased uterine contractility when the local imbalance between the constrictive and relaxing mediators takes place.

In Vitro Consequences of Electronic-Cigarette Flavoring Exposure on the Immature Lung

Background: The developing lung is uniquely susceptible and may be at increased risk of injury with exposure to e-cigarette constituents. We hypothesize that cellular toxicity and airway and vascular responses with exposure to flavored refill solutions may be altered in the immature lung. Methods: Fetal, neonatal, and adult ovine pulmonary artery smooth muscle cells (PASMC) were exposed to popular flavored nicotine-free e-cigarette refill solutions (menthol, strawberry, tobacco, and vanilla) and unflavored solvents: propylene glycol (PG) or vegetable glycerin (VG). Viability was assessed by lactate dehydrogenase assay. Brochodilation and vasoreactivity were determined on isolated ovine bronchial rings (BR) and pulmonary arteries (PA). Results: Neither PG or VG impacted viability of immature or adult cells; however, exposure to menthol and strawberry flavored solutions increased cell death. Neonatal cells were uniquely susceptible to menthol flavoring-induced toxicity, and all four flavorings demonstrated lower lethal doses (LD50) in immature PASMC. Exposure to flavored solutions induced bronchodilation of neonatal BR, while only menthol induced airway relaxation in adults. In contrast, PG/VG and flavored solutions did not impact vasoreactivity with the exception of menthol-induced relaxation of adult PAs. Conclusion: The immature lung is uniquely susceptible to cellular toxicity and altered airway responses with exposure to common flavored e-cigarette solutions.

Sildenafil for Pulmonary Hypertension in the Early Postoperative Period After Mitral Valve Surgery

OBJECTIVES

The phosphodiesterase-5 inhibitor sildenafil was developed for the treatment of pulmonary hypertension. The authors investigated the efficacy and safety of sildenafil in the early postoperative period after mitral valve surgery in patients with pulmonary hypertension.

DESIGN

A double-blind, placebo-controlled randomized trial was performed.

SETTING

The trial was performed in a single tertiary referral center.

PARTICIPANTS

Fifty consecutive patients who experienced pulmonary hypertension and underwent mitral valve surgery.

INTERVENTIONS

Patients were randomly assigned to the following 2 groups: 25 patients received 20 mg sildenafil every 8 hours, and the remaining 25 patients received placebo during the same period. Hemodynamic parameters were studied by using a pulmonary artery catheter at baseline and every 6 hours up to 36 hours.

RESULTS

Patients who received sildenafil showed a decrease in mean pulmonary pressure, from 32 ± 7 mmHg at baseline to 26 ± 3 mmHg after 36 hours, whereas no change was seen in patients who received placebo (mean pulmonary pressure 34 ± 6 mmHg at baseline and 35 ± 5 mmHg after 36 h) (p < 0.001). No significant changes in systemic hemodynamic and oxygenation were observed. Patients who received sildenafil compared with those who received placebo had a median mechanical lung ventilation time of 16 (10-31) hours versus 19 (13-41) hours (p = 0.431), intensive care unit stay of 74 (44-106) hours versus 91 (66-141) hours (p = 0.410), and a total hospitalization stay of 7 (5-10) days versus 11 (7-15) days (p = 0.009).

CONCLUSIONS

The immediate postoperative administration of sildenafil after mitral valve surgery is safe. Sildenafil demonstrates a favorable decreasing effect on pulmonary vascular pressure without systemic hypotension and ventilation-perfusion mismatch.

Nitric Oxide and Other Novel Therapies for Pulmonary Hypertension

Pulmonary hypertension is an uncommon, yet devastating, syndrome with a complex underlying pathobiology. Hypoxia, inflammation, and increased shear stress appear to be the primary pathogenic events; however, mechanisms by which these processes lead to pulmonary hypertension remain incompletely understood. The ultimate increase in pulmonary vascular resistance is attributed to remodelling of the walls of resistance vessels, which can lead to encroachment on and reduction of the vascular lumen. The number of blood vessels per unit of cross-sectional area in the hypertensive lung is also reduced, which can contribute to increased vascular resistance. Regardless of its etiology, endothelial dysfunction underlies pulmonary hypertension, one manifestation of which is the attenuated production of bioactive nitric oxide. Nitric oxide administration can exert beneficial effects at various stages of the disease. Here we review the known pathobiology of pulmonary hypertension, with a principal focus on endothelial nitric oxide, and also summarize the data on nitric oxide replacement therapy and other novel therapies that relate to nitric oxide as one approach to treatment.

Inhaled nitric oxide decreases pulmonary endothelial nitric oxide synthase expression and activity in normal newborn rat lungs

Inhaled nitric oxide (iNO) is commonly used in the treatment of very ill pre-term newborns. Previous studies showed that exogenous NO could affect endothelial NO synthase (eNOS) activity and expression in vascular endothelial cell cultures or adult rat models, but this has never been fully described in newborn rat lungs. We therefore aimed to assess the effects of iNO on eNOS expression and activity in newborn rats.

Rat pups, post-natal day (P) 0 to P7, and their dams were placed in a chamber containing NO at 5 ppm (iNO-5 ppm group) or 20 ppm (iNO-20 ppm group), or in room air (control group). Rat pups were sacrificed at P7 and P14 for evaluation of lung eNOS expression and activity.

At P7, eNOS protein expression in total lung lysates, in bronchial and arterial sections, was significantly decreased in the iNO-20 ppm versus control group. At P14, eNOS expression was comparable among all three groups. The amounts of eNOS mRNA significantly differed at P7 between the iNO-20 ppm and control groups. NOS activity decreased in the iNO-20 ppm group at P7 and returned to normal levels at P14. There was an imbalance between superoxide dismutase and NOS activities in the iNO-20 ppm group at P7.

Inhalation of NO at 20 ppm early after birth decreases eNOS gene transcription, protein expression and enzyme activity. This decrease might account for the rebound phenomenon observed in patients treated with iNO.

Inhaled NO decreases endogenous NO synthesis and favours rebound pulmonary hypertension after inhaled NO withdrawalhttp://ow.ly/WNDq2

Iloprost for children with pulmonary hypertension after surgery to correct congenital heart disease

Congenital heart disease (CHD) can cause pulmonary hypertension (PH) in children, and surgery to correct CHD may be complicated by postoperative pulmonary hypertensive crises (PHC). Clinical data regarding the use of inhaled iloprost to treat children with PH are scarce. Our aim was to determine the efficacy and safety of iloprost in children with PH following surgery to correct CHD. This was a randomized, placebo-controlled study of 22 children (median age 7 months) undergoing surgery to achieve biventricular repair. The combined clinical endpoint was a decrease of more than 20% in the ratio of systolic pulmonary arterial pressure to systolic arterial pressure or pulmonary resistance to systemic resistance, with no PHC or death. Patients were randomized to receive low-dose iloprost (30 ng/kg/min), high-dose iloprost (50 ng/kg/min), or placebo, for 10 min every 2 hr in the first 48 hr after surgery. PHC were experienced by two patients who received placebo and one patient treated with high-dose iloprost. The combined clinical endpoint was reached by six patients administered low-dose iloprost (P = 0.005) and four administered high-dose iloprost (P = 0.077), compared with none in the placebo group. Patients treated with iloprost showed a significant reduction from baseline in mean pulmonary vascular resistance index (-2.2 Wood units, P < 0.05), whereas patients who received placebo showed no significant change. This study supports the use of iloprost to treat children with PH following surgery to correct CHD.

No redistribution of lung blood flow by inhaled nitric oxide in endotoxemic piglets pretreated with an endothelin receptor antagonist

Inhaled nitric oxide (INO) improves ventilation-perfusion matching and alleviates pulmonary hypertension in patients with acute respiratory distress syndrome. However, outcome has not yet been shown to improve, and nonresponse is common. A better understanding of the mechanisms by which INO acts may guide in improving treatment with INO in patients with severe respiratory failure. We hypothesized that INO may act not only by vasodilation in ventilated lung regions, but also by causing vasoconstriction via endothelin (ET-1) in atelectatic, nonventilated lung regions. This was studied in 30 anesthetized, mechanically ventilated piglets. The fall in oxygenation and rise in pulmonary artery pressure during a sepsislike condition (infusion of endotoxin) were blunted by INO 40 ppm. Endotoxin infusion increased serum ET-1, and INO almost doubled the ratio between mRNA expression of endothelin receptor A (mediating vasoconstriction) and B (mediating vasodilation and clearance of ET-1) (ET-A/ET-B) in atelectatic lung regions. INO caused a shift in blood flow away from atelectatic lung regions in the endotoxemic piglets, but not during ET receptor antagonism. We conclude that INO in short-term experiments, in addition to causing selective pulmonary vasodilation in ventilated lung regions, increases the ET-A/ET-B mRNA expression ratio in lung tissue. This might augment the vasoconstriction in atelectatic lung regions, enhancing the redistribution of pulmonary blood flow to ventilated lung regions which are reached by INO. Such vasoconstriction may be an important additional factor explaining the effect of INO.

Pharmacologic management of perioperative pulmonary hypertension

Perioperative pulmonary hypertension can originate from an established disease or acutely develop within the surgical setting. Patients with increased pulmonary vascular resistance are consequently at greater risk for complications. Despite the various specific therapies available, the ideal therapeutic approach in this patient population is not currently clear. This article describes the basic principles of perioperative pulmonary hypertension and reviews the different classes of agents used to promote pulmonary vasodilation in the surgical setting.

Reducing variation in the use of inhaled nitric oxide

BACKGROUND AND OBJECTIVE

Decreasing practice variation and following clinical guidelines improve patient outcomes and reduce costs. Inhaled nitric oxide (iNO) is an effective but expensive treatment of pulmonary hypertension and right heart failure in patients with congenital or acquired heart disease. Our objective was to implement standardized initiation and weaning guidelines for iNO usage in the cardiothoracic ICU (CTICU) to reduce variation in use while maintaining quality patient care.

METHODS

All CTICU patients who received iNO from January 2011 to December 2012 were retrospectively reviewed. Standardized iNO initiation and weaning guidelines were implemented in January 2012. Variables before and after guideline implementation were compared.

RESULTS

From January to December 2011, there were 36 separate iNO events (6% of CTICU admissions; n = 547). Mean ± SD iNO usage per event was 159 ± 177 hours (median: 63 hours; range: 27-661 hours). From January to December 2012, there were 47 separate iNO events (8% of CTICU admissions; n = 554). Mean iNO usage per event was 125 ± 134 hours (median: 72 hours; range: 2-557 hours). Initiation guideline compliance improved from 83% to 86% (P = .9); weaning guideline compliance improved from 17% to 79% (P < .001). Although mean iNO usage per event decreased, there was no significant reduction in utilization of iNO (P = .09).

CONCLUSIONS

Implementation of standardized iNO initiation and weaning guidelines in the CTICU was successful in reducing practice variation supported by increasing guideline compliance. However, decreasing practice variation did not significantly reduce iNO utilization and does not necessarily reduce cost.

Oxygenation and plasma endothelin-1 concentrations in healthy horses recovering from isoflurane anaesthesia administered with or without pulse-delivered inhaled nitric oxide

OBJECTIVE

To assess oxygenation, ventilation-perfusion (V/Q) matching and plasma endothelin (ET-1) concentrations in healthy horses recovering from isoflurane anaesthesia administered with or without pulse-delivered inhaled nitric oxide (iNO).

STUDY DESIGN

Prospective experimental trial.

ANIMALS

Healthy adult Standardbred horses.

METHODS

Horses were anaesthetized with isoflurane in oxygen and placed in lateral recumbency. Six control (C group) horses were anaesthetized without iNO delivery and six horses received pulse-delivered iNO (NO group). After 2.5 hours of anaesthesia isoflurane and iNO were abruptly discontinued, inhaled oxygen was reduced from 100% to approximately 30%, and the horses were moved to the recovery stall. At intervals during a 30-minute period following the discontinuation of anaesthesia, arterial and mixed venous blood gas values, shunt fraction (Qs/Qt), plasma ET-1 concentration, pulse rate and respiratory rate were measured or calculated. Repeated measures anova and a Bonferroni post hoc test was used to analyze data with significance set at p < 0.05.

RESULTS

At all time points in the recovery period, NO horses maintained better arterial oxygenation (oxygen partial pressure: NO 13.2 ± 2.7-11.1 ± 2.7 versus C 6.7 ± 1.1-7.1 ± 1.1 kPa) and better V/Q matching (Qs/Qt NO 0.23 ± 0.05-0.14 ± 0.06 versus C 0.48 ± 0.03-0.32 ± 0.08%) than C horses. Mixed venous oxygenation was higher in NO for 25 minutes following the discontinuation of anaesthesia (NO 6.3 ± 0.2-4.5 ± 0.07 versus C 4.7 ± 0.6-3.7 ± 0.3 kPa). In both groups of horses arterial oxygenation remained fairly stable; venous oxygenation declined over this time period in the NO group but still remained higher than venous oxygen in the C group. ET-1 concentrations were higher at most time points in C than NO. Changes in other parameters were either minor or absent.

CONCLUSIONS AND CLINICAL RELEVANCE

Delivery of iNO to healthy horses during anaesthesia results in better arterial and venous oxygenation and V/Q matching (as determined by lower Qs/Qt) and lower ET-1 concentrations throughout a 30-minute anaesthetic recovery period.

Review of inhaled nitric oxide in the pediatric cardiac surgery setting

Surgical intervention for congenital heart disease (CHD) can be complicated by pulmonary hypertension (PH), which increases morbidity, mortality, and medical burden. Consequently, postoperative management of PH is an important clinical consideration to improve outcomes. Inhaled nitric oxide (iNO) is a widely accepted standard of care for PH and has been studied in the context of cardiac surgery for CHD. However, large randomized, double-blind, placebo-controlled, multicenter clinical trials in pediatric patients are limited. This review will provide an overview of the clinical studies in this setting and will discuss general treatment considerations to facilitate a better understanding of the clinical use of iNO for PH after pediatric cardiac surgery.

Congenital diaphragmatic hernia: endothelin-1, pulmonary hypertension, and disease severity

RATIONALE

Endothelin-1 (ET1) is dysregulated in pulmonary hypertension (PH). It may be important in the pathobiology of congenital diaphragmatic hernia (CDH).

OBJECTIVES

We hypothesized that ET1 levels in the first month would be higher in infants with CDH who subsequently expired or were discharged on oxygen (poor outcome). We further hypothesized that ET1 levels would be associated with concurrent severity of PH.

METHODS

We sampled plasma at 24 to 48 hours, and 1, 2, and 4 weeks of age in 40 prospectively enrolled newborns with CDH. We performed echocardiograms to estimate pulmonary artery pressure at less than 48 hours of age and weekly to 4 weeks. PH was classified in relationship to systemic blood pressure (SBP): less than 2/3 SBP, 2/3 SBP-systemic is related to pressure, or systemic-to-suprasystemic pressure.

MEASUREMENTS AND MAIN RESULTS

ET1 levels at 1 and 2 weeks were higher in infants with poor outcome compared with infants discharged on room air (median and interquartile range: 27.2 [22.6, 33.7] vs. 19.1 [16.1, 29.5] pg/ml, P = 0.03; and 24.9 [17.6, 39.5] vs. 17.4 [13.7, 21.8] pg/ml, P = 0.01 at 1 and 2 weeks, respectively). Severity of PH was significantly associated with increasing ET1 levels at 2 weeks (16.1 [13.7, 21.8], 21.0 [17.4, 31.1], and 23.6 [21.9, 39.5] pg/ml for increasing PH class, P = 0.03). Increasing severity of PH was also associated with poor outcome at that time (P = 0.001).

CONCLUSIONS

Infants with CDH and poor outcome have higher plasma ET1 levels and severity of PH than infants discharged on room air. Severity of PH is associated with ET1 levels.

Pulmonary vasodilator testing and use of calcium channel blockers in pulmonary arterial hypertension

Pulmonary arterial hypertension (PAH) encompasses a number of diseases responsible for a specific set of hemodynamic findings during right heart catheterization. During initial workup, pulmonary vasodilator testing is performed. A positive acute pulmonary vasodilator test predicts better survival and response to calcium channel blocker (CCB) therapy. There is lack of consensus on the preferred agent for determining acute pulmonary vasoreactivity. The ACCP guidelines and the 4(th) World Symposium on Pulmonary Hypertension support the use of intravenous epoprostenol or nitric oxide (NO) as the preferred agents for pulmonary vasodilator testing. A decrease in the mean pulmonary artery pressure by at least 10 mmHg to reach an absolute value of 40 mmHg or less without a decrease in cardiac output is currently considered a positive pulmonary vasodilator test. A positive test by the current recommended criteria is observed in about 10-15% of patients with idiopathic PAH. Approximately half of these patients will experience long-term benefits with CCBs. A positive test may select patients with an earlier or less aggressive form of disease, which may carry a better prognosis. A positive vasodilator test is observed very infrequently in patients with pulmonary arterial hypertension other than idiopathic PAH or anorexigen associated PAH. This article reviews the literature regarding pulmonary vasodilator testing and use of CCB therapy in patients with PAH, while identifying the gaps in knowledge concerning this diagnostic procedure.

Use of sildenafil to facilitate weaning from inhaled nitric oxide in children with pulmonary hypertension following surgery for congenital heart disease

Pulmonary hypertension frequently complicates the postoperative management of patients after congenital cardiac surgery. Inhaled nitric oxide is an effective treatment option, but rebound pulmonary hypertension can occur upon its withdrawal. Sildenafil may facilitate its withdrawal by restoring cyclic guanosine monophosphate availability via phosphodiesterase-5 inhibition. The purpose of this study was to evaluate the use of sildenafil in facilitating weaning from inhaled nitric oxide after congenital cardiac surgery in patients who had previously failed weaning, and to compare the effects of sildenafil on pulmonary and systemic hemodynamics. Children who received sildenafil after cardiovascular surgery during a 23-month period at Riley Hospital for Children were identified. Medical records were retrospectively reviewed to determine sildenafil and nitric oxide dosing, pulmonary and systemic blood pressures, and adverse effects. Oral sildenafil was administered to 7 children who had failed attempts at inhaled nitric oxide weaning. Inhaled nitric oxide was weaned from 29.8+/-5.9 ppm prior to sildenafil initiation to 12.2+/-3.4 ppm (mean +/- SE; P= .024) in the 24 hours after sildenafil. Mean pulmonary artery and systemic arterial pressure were unchanged from baseline when measured 1 hour after sildenafil dosing (mean pulmonary artery pressure, 29+/-1 to 27+/-0.7 mm Hg, P= .066; mean systemic arterial pressure, 56+/-1.2 to 54+/-1.2 mm Hg, P= .202). Sildenafil may facilitate withdrawal of inhaled nitric oxide and prevent rebound pulmonary hypertension in patients previously failing inhaled nitric oxide weaning attempts.

Hsp72 induces inflammation and regulates cytokine production in airway epithelium through a TLR4- and NF-kappaB-dependent mechanism

Heat shock proteins are generally regarded as intracellular proteins acting as molecular chaperones; however, Hsp72 is also detected in the extracellular compartment. Hsp72 has been identified in the bronchoalveolar lavage fluid (BALF) of patients with acute lung injury. To address whether Hsp72 directly activated airway epithelium, human bronchial epithelial cells (16HBE14o-) were treated with recombinant Hsp72. Hsp72 induced a dose-dependent increase in IL-8 expression, which was inhibited by the NF-kappaB inhibitor parthenolide. Hsp72 induced activation of NF-kappaB, as evidenced by NF-kappaB trans-activation and by p65 RelA and p50 NF-kappaB1 binding to DNA. Endotoxin contamination of the Hsp72 preparation was not responsible for these effects. Next, BALB/c mice were challenged with a single intratracheal inhalation of Hsp72 and killed 4 h later. Hsp72 induced significant up-regulation of KC, TNF-alpha, neutrophil recruitment, and myeloperoxidase in the BALF. A similar challenge with Hsp72 in TLR4 mutant mice did not stimulate the inflammatory response, stressing the importance of TLR4 in Hsp72-mediated lung inflammation. Last, cultured mouse tracheal epithelial cells (MTEC) from BALB/c and TLR4 mutant and wild-type mice were treated ex vivo with Hsp72. Hsp72 induced a significant increase in KC expression from BALB/c and wild-type MTEC in an NF-kappaB-dependent manner; however, TLR4 mutant MTEC had minimal cytokine release. Taken together, these data suggest that Hsp72 is released and biologically active in the BALF and can regulate airway epithelial cell cytokine expression in a TLR4 and NF-kappaB-dependent mechanism.

MAPK pathway mediates EGR-1-HSP70-dependent cigarette smoke-induced chemokine production

Cigarette smoking, a major risk factor for chronic obstructive pulmonary disease, can cause airway inflammation, airway narrowing, and loss of elasticity, leading to chronic airflow limitation. In this report, we sought to define the signaling pathways activated by smoke and to identify molecules responsible for cigarette smoke-induced inflammation. We applied cigarette smoke water extract (CSE) to primary human lung fibroblasts and found that CSE significantly increased CXC chemokine IL-8 production. Meanwhile, 70-kDa heat shock protein (HSP70) was also induced by CSE in a dose- and time-dependent manner. CSE treatment stimulated HSP70 secretion by primary fibroblasts, which augmented IL-8 production. This was further confirmed by exogenously added recombinant HSP70. Using HSP70 small interfering RNA, we confirmed that CSE-induced chemokine production was dependent on heat shock protein expression. Further investigation showed that CSE could also stimulate early growth response-1 (EGR-1) in an ERK-dependent manner and that the expression of HSP70 was EGR-1 dependent. In view of these findings, we hypothesize that the MAPK-EGR-1-HSP70 pathway regulates the cigarette smoke-induced inflammatory process.

fMLP induces Hsp27 expression, attenuates NF-kappaB activation, and confers intestinal epithelial cell protection

Sustained expression of cytoprotective intestinal epithelial heat shock proteins (Hsps), particularly Hsp27, depends on stimuli derived from bacterial flora. In this study, we examined the role of the bacterial chemotactic peptide fMLP in stimulating colonic epithelial Hsp expression at concentrations encountered in a physiological milieu. Treatment of the polarized human intestinal epithelial cell line Caco2bbe with physiological concentrations of fMLP (10-100 nM) induced expression of Hsp27, but not Hsp72, in a time- and concentration-dependent manner. Induction of Hsp27 by fMLP was specific since the fMLP analogs MRP and MLP were not effective. Hsp27 induction by fMLP was blocked by the fMLP-receptor antagonist BOC-FLFLF and was blocked when the dipeptide transporter PepT1, an entry pathway for fMLP, was silenced. fMLP activated both the p38 and ERK1/2 MAP kinase pathways in Caco2bbe cells, but not the SAPK/JNK pathway. The p38 inhibitor SB203580, but not the MEK-1 inhibitor PD98059, blocked Hsp27 induction by fMLP. fMLP treatment inhibited actin depolymerization and decreased transepithelial resistance caused by the oxidant monochloramine, and this inhibition was reversed by silencing Hsp27 expression. fMLP pretreatment also inhibited activation of proinflammatory transcription factor NF-kappaB by TNF-alpha in Caco2bbe cells, reducing induction of NF-kappaB target genes by TNF-alpha both in human intestinal biopsies and Caco2bbe cells. In conclusion, fMLP may contribute to the maintenance of intestinal homeostasis by mediating physiological expression of Hsp27, enhancing cellular protection, and negatively regulating the inflammatory response.

Role of heat shock protein 70 in hepatic ischemia-reperfusion injury in mice

It is well established that liver ischemia-reperfusion induces the expression of heat shock protein (HSP) 70. However, the biological function of HSP70 in this injury is unclear. In this study, we sought to determine the role of HSP70 in hepatic ischemia-reperfusion injury in mice. Male mice were subjected to 90 min of partial hepatic ischemia followed by up to 8 h of reperfusion. HSP70 was rapidly upregulated after reperfusion. To explore the function of HSP70, sodium arsenite (8 mg/kg iv) was injected before surgery. We found that this dose induced HSP70 expression within 6 h of treatment. Induction of HSP70 with arsenite resulted in a >50% reduction in liver injury as determined by serum transaminases and histology. In addition, arsenite similarly reduced liver neutrophil recruitment and liver nuclear factor-kappaB activation, and attenuated serum levels of tumor necrosis factor-alpha and macrophage inflammatory protein-2, but increased levels of interleukin (IL)-6. In HSP70 knockout mice, arsenite did not protect against liver injury but did reduce liver neutrophil accumulation. Arsenite-induced reductions in neutrophil accumulation in HSP70 knockout mice were found to be mediated by IL-6. To determine whether extracellular HSP70 contributed to the injury, recombinant HSP70 was injected before surgery. Intravenous injection of 10 microg of recombinant HSP70 had no effect on liver injury after ischemia-reperfusion. The data suggest that intracellular HSP70 is directly hepatoprotective during ischemia-reperfusion injury and that extracellular HSP70 is not a significant contributor to the injury response in this model. Targeted induction of HSP70 may represent a potential therapeutic option for postischemic liver injury.

HSP70 induction by ING proteins sensitizes cells to tumor necrosis factor alpha receptor-mediated apoptosis

ING proteins affect apoptosis, growth, and DNA repair by transducing stress signals such as DNA damage, binding histones, and subsequently regulating chromatin structure and p53 activity. p53 target genes, including the p21 cyclin-dependent kinase inhibitor and Bax, an inducer of apoptosis, are regulated by ING proteins. To identify additional targets downstream of p33ING1 and p32ING2, cDNA microarrays were performed on phenotypically normal human primary fibroblasts. The 0.36% of genes affected by ING proteins in primary fibroblasts were distinct from targets seen in established cells and included the HSP70 heat shock gene, whose promoter was specifically induced >10-fold. ING1-induced expression of HSP70 shifted cells from survival to a death pathway in response to tumor necrosis factor alpha (TNF-alpha), and p33ING1b protein showed synergy with TNF-alpha in inducing apoptosis, which correlated with reduced NF-kappaB-dependent transcription. These findings are consistent with previous reports that HSP70 promotes TNF-alpha-mediated apoptosis by binding I-kappaBeta kinase gamma and impairing NF-kappaB survival signaling. Induction of HSP70 required the amino terminus of ING1b but not the plant homeodomain region that was recently identified as a histone binding domain. Regulation of HSP70 gene expression by the ING tumor suppressors provides a novel link between the INGs and the stress-regulated NF-kappaB survival pathway important in hypoxia and angiogenesis.

Oxidative and nitrosative stress in pediatric pulmonary hypertension: roles of endothelin-1 and nitric oxide

An increasing number of studies implicate oxidative stress in the development of endothelial dysfunction and the pathogenesis of cardiovascular disease. Further, this oxidative stress has been shown to be associated with alterations in both the endothelin-1 (ET-1) and nitric oxide (NO) signaling pathways such that bioavailable NO is decreased and ET-1 signaling is potentiated. However, recent data, from our groups and others, have shown that oxidative stress, ET-1, and NO are co-regulated in a complex fashion that appears to be dependent on the cellular levels of each species. Thus, when ROS levels are transiently elevated, NO signaling is potentiated through transcriptional, post-transcriptional, and post-translational mechanisms. However, in pediatric pulmonary hypertensive disorders, when reactive oxygen species (ROS) increases are sustained by ET-1 mediated activation of smooth muscle cell ET(A) subtype receptors, NOS gene expression and NO signaling are reduced. Further, increases in oxidative stress can stimulate both the expression of the ET-1 gene and the secretion of the ET-1 peptide. Finally, the addition of exogenous NO, and increasingly utilized therapy for pulmonary hypertension, can also lead to increases ROS generation via the activation of ROS generating enzymes and through the induction of mitochondrial dysfunction. Thus, this manuscript will review the available data regarding the interaction of oxidative and nitrosative stress, endothelial dysfunction, and its role in the pathophysiology of pediatric pulmonary hypertension. In addition, we will suggest avenues of both basic and clinical research that will be important to develop novel pulmonary hypertension treatment and prevention strategies, and resolve some of the remaining clinical issues regarding the use of NO augmentation.

Iloprost inhalation solution for the treatment of pulmonary arterial hypertension

Pulmonary arterial hypertension (PAH) is a condition that is characterised by increased pulmonary arterial pressure and vascular resistance that can lead to right ventricular failure and death. A variety of disturbances in pulmonary vascular endothelial and smooth muscle function are present in PAH, including reduced production of vasodilator and antiproliferative substances, such as nitric oxide and prostacyclin, and an overproduction of mitogens, such as endothelin. As a result of these observations, therapies have been developed for PAH that specifically target these pathogenic processes, including prostacyclin analogues and endothelin receptor antagonists. This article reviews iloprost inhalation solution, the most recently approved form of prostacyclin therapy that is delivered directly to the lungs by inhalation.

Heat intolerance: does gene transcription contribute?

During exertion in the heat, heat-intolerant (HI) subjects have a physiological disability in metabolic heat dissipation. The HI state is either permanent or temporary, depending on whether it stems from transient predisposing factors or inherent thermoregulatory dysfunction. In this investigation, we studied protein levels of heat shock protein (HSP) 70 and HSP72, HSP90, bcl-2xL, glutathione S-transferase-p, heat shock factor-1, TATA-binding protein-associated factor, and NF-κB transcripts using Western blot and quantitative RT-PCR, respectively, in lymphocytes of HI and tolerant (T) male volunteers of similar anthropometric features. Measurements were made from blood drawn before, during the heat tolerance test (3.5 mph, 40°C, 40% relative humidity, 2 h), and 1 h after recovery at 24°C. Rectal and skin temperatures, as well as heart rate, were continuously recorded. Of 58 subjects, 7 were identified as HI, with a significantly higher physiological strain index than in the T group (6.3 ± 0.9 vs. 3.8 ± 0.6, P < 0.001). The responsiveness of the vasculature to thermal stimuli was decreased in the HI group, as indicated by rectal temperature minus skin temperature. The HSP72 level in the HI group dropped during the recovery session ( P < 0.01), whereas that of the T group continued to rise. A significantly increased expression of the transcription factors in the T subjects and significantly decreased expression in the HI group ( P < 0.009, 0.013, and 0.005 for heat shock factor-1, NF-κB, and TATA-binding protein-associated factor, respectively) points to impaired transcriptional processes in the HI group. Our data suggest that transcriptional malfunction and sluggishness of the vasculature to thermal stimuli are predisposing factors in the HI group.

Persistent pulmonary hypertension of the newborn: not a honeymoon anymore

Persistent pulmonary hypertension of the newborn is a disorder of transition to extrauterine life, in which the newly born baby cannot decrease the high pulmonary vascular resistance and low pulmonary blood flow, characteristic of the fetus, to that of a low pulmonary vascular resistance and high pulmonary blood flow necessary for postnatal survival. The syndrome primarily affects the neonate 34 weeks postmenstrual age and greater. The article will summarize the latest understanding of the pathophysiology and review innovations in management strategies that have greatly decreased mortality and morbidity since the advent of neonatal intensive care units.

Gene transfer with inducible nitric oxide synthase decreases production of urea by arginase in pulmonary arterial endothelial cells

Nitric oxide (NO) is a vasodilator produced from L-arginine (L-Arg) by NO synthase (NOS). Gene therapy for hypertensive disorders has been proposed using the inducible isoform of NOS (iNOS). L-Arg also can be metabolized to urea and L-ornithine (L-Orn) by arginase, and L-Orn can be metabolized to proline and/or polyamines, which are vital for cellular proliferation. To determine the effect of iNOS gene transfer on arginase, we transfected bovine pulmonary arterial endothelial cells (bPAEC) with an adenoviral vector containing the gene for iNOS (AdiNOS). As expected, NO production in AdiNOS bPAEC was substantially greater than in control bPAEC. Although urea production was significantly less in the AdiNOS bPAEC than in the control bPAEC, despite similar levels of arginase I protein, AdiNOS transfection of bPAEC had no effect on the uptake of L-Arg. Inhibiting NO production with Nomega-nitro-L-arginine methyl ester increased urea production, and inhibiting urea production with L-valine increased nitrite production, in AdiNOS bPAEC. The addition of L-Arg to the medium increased urea production by AdiNOS bPAEC in a concentration-dependent manner. Thus, in these iNOS-transfected bPAEC, the transfected iNOS and native arginase compete for a common intracellular pool of L-Arg. This competition for substrate resulted in impaired proliferation in the AdiNOS-transfected bPAEC. These findings suggest that the use of iNOS gene therapy for pulmonary hypertensive disorders may not only be beneficial through NO-mediated pulmonary vasodilation but also may decrease vascular remodeling by limiting L-Orn production by native arginase.

Heat shock-mediated regulation of MKP-1

Heat shock modulates cellular proinflammatory responses, and we have been interested in elucidating the mechanisms that govern this modulation. The dual specific phosphatase, MAP kinase phosphatase-1 (MKP-1), is an important modulator of cellular inflammatory responses, and we recently reported that heat shock increases expression of MKP-1. Herein we sought to elucidate the mechanisms by which heat shock modulates MKP-1 gene expression. Subjecting RAW264.7 macrophages to heat shock increased MKP-1 gene expression in a time-dependent manner. Transfection with a wild-type murine MKP-1 promoter luciferase reporter plasmid demonstrated that heat shock activates the MKP-1 promoter. When the reporter plasmid was transfected into heat shock factor-1 (HSF-1)-null fibroblasts, the MKP-1 promoter was activated in response to heat shock in a manner similar to that of wild-type fibroblasts with intact HSF-1. Site-directed mutagenesis of two potential heat shock elements in the MKP-1 promoter demonstrated that both sites are required for basal promoter activity. mRNA stability assays demonstrated that heat shock increased MKP-1 mRNA stability compared with cells maintained at 37 degrees C. Inhibition of p38 MAP kinase activity inhibited heat shock-mediated expression of MKP-1. These data demonstrate that heat shock regulates MKP-1 gene expression at both the transcriptional and posttranscriptional levels. Transcriptional mechanisms are HSF-1 independent but are dependent on putative heat shock elements in the MKP-1 promoter. Posttranscriptional mechanisms involve increased stability of MKP-1 mRNA that is partially dependent on p38 MAP kinase activity. These data demonstrate another potential mechanism by which heat shock can modulate inflammation-related signal transduction.

Pathophysiologic mechanisms of persistent pulmonary hypertension of the newborn

Persistent pulmonary hypertension of the newborn (PPHN), among the most rapidly progressive and potentially fatal of vasculopathies, is a disorder of vascular transition from fetal to neonatal circulation, manifesting as hypoxemic respiratory failure. PPHN represents a common pathway of vascular injury activated by numerous perinatal stresses: hypoxia, hypoglycemia, cold stress, sepsis, and direct lung injury. As with other multifactorial diseases, a single inciting event may be augmented by multiple concurrent/subsequent phenomena that result in differing courses of disease progression. I review the various mechanisms of vascular injury involved in neonatal pulmonary hypertension: endothelial dysfunction, inflammation, hypoxia, and mechanical strain, in the context of downstream effects on pulmonary vascular endothelial-myocyte interactions and myocyte phenotypic plasticity.

Lack of alteration of endogenous nitric oxide pathway during prolonged nitric oxide inhalation in intensive care unit patients

OBJECTIVE

To compare hemodynamic and gasometric variables and the plasma concentrations of nitric oxide metabolites (cyclic guanosine monophosphate and nitrate and nitrite), endothelin-1, and renin-angiotensin metabolites before and after the start of nitric oxide inhalation, after prolonged nitric oxide inhalation, and before and after nitric oxide withdrawal.

DESIGN

Prospective study.

SETTING

Surgical intensive care unit, university hospital.

SUBJECTS

Patients with acute lung injury and right ventricular failure.

INTERVENTIONS

Nitric oxide inhalation (10-12 ppm) during a median of 2.9 days (12 hrs to 6.5 days).

MEASUREMENTS AND MAIN RESULTS

The pulmonary vasodilator effects of inhaled nitric oxide improved arterial oxygenation in patients with acute lung injury (p < .05) and reduced right atrial pressure in patients with right ventricular dysfunction (p < .01). These beneficial effects lasted the whole period of prolonged inhaled nitric oxide therapy up to 6.5 days. However, when inhaled nitric oxide was withdrawn, pulmonary vasodilator effects rapidly disappeared, and Pao2/Fio2 ratio markedly deteriorated in all studied patients to return to pre-inhaled nitric oxide levels. Changes in plasma cyclic guanosine monophosphate and nitrate and nitrite paralleled those of pulmonary vasodilatory effects. An immediate increase in plasma cyclic guanosine monophosphate with a slightly delayed increase in plasma nitrate and nitrite was observed at inhaled nitric oxide start with no attenuation during the prolonged inhaled nitric oxide therapy. A marked decrease toward pre-inhaled nitric oxide levels was seen within hours of inhaled nitric oxide withdrawal. In addition, no alteration of plasma endothelin-1 or renin-angiotensin mediators was observed during or after inhaled nitric oxide therapy.

CONCLUSIONS

Our study showed a lack of attenuation in the beneficial effects of inhaled nitric oxide and a lack of alteration of endogenous nitric oxide, endothelin-1, and renin-angiotensin pathways during prolonged nitric oxide inhalation.

The Effect of a Combination of Inhaled Nitric Oxide and an EndothelinA-Receptor Antagonist onHemodynamic Dysfunction in Experimental AcutePulmonary Thromboembolism

Although either inhaled nitric oxide (NO) or endothelinA receptor antagonist has been tried in the treatment of various forms of pulmonary hypertension, the effects of combination therapy have not been reported. We evaluated the effects of inhaled NO alone or a combination of inhaled NO and ZD2574 (an endothelinA receptor antagonist) in an experimental canine acute pulmonary thromboembolism model. Forty parts per million of inhaled NO alone, or a combination of inhaled NO and 10 mg/kg of ZD2574 was administered 1 hour after embolization with an autologous blood clot. We compared the hemodynamic and gas exchange parameters between the two treatment groups. Two treatment regimens decreased mean pulmonary arterial pressure and pulmonary vascular resistance and attenuated decrease in cardiac output. Moreover, systemic arterial hypotension or worsening of hypoxemia did not occur in either of the treatment groups. In the combined group, more favorable hemodynamic outcomes were maintained than in the inhaled NO alone group. And hemodynamic deterioration shown after NO withdrawal was attenuated in the combined group. These findings suggest that when inhaled NO is concomitantly administered with an ETA receptor antagonist, more favorable hemodynamic outcomes can be expected during and after NO inhalation in acute pulmonary thromboembolism.

Sequestration of TRAF2 into stress granules interrupts tumor necrosis factor signaling under stress conditions

The cellular stress response (SR) is a phylogenetically conserved protection mechanism that involves inhibition of protein synthesis through recruitment of translation factors such as eIF4G into insoluble stress granules (SGs) and blockade of proinflammatory responses by interruption of the signaling pathway from tumor necrosis factor alpha (TNF-alpha) to nuclear factor-kappaB (NF-kappaB) activation. However, the link between these two physiological phenomena has not been clearly elucidated. Here we report that eIF4GI, which is a scaffold protein interacting with many translation factors, interacts with TRAF2, a signaling molecule that plays a key role in activation of NF-kappaB through TNF-alpha. These two proteins colocalize in SGs during cellular exposure to stress conditions. Moreover, TRAF2 is absent from TNFR1 complexes under stress conditions even after TNF-alpha treatment. This suggests that stressed cells lower their biological activities by sequestration of translation factors and TRAF2 into SGs through a protein-protein interaction.

Severe paediatric pulmonary hypertension: new management strategies

Pulmonary hypertension is a significant complication in many paediatric disease states. This article discusses current understanding of pulmonary hypertension and includes definition, diagnosis, and management. A description of the latest advances in targeted pharmacological therapy in children is also provided as well as impact on morbidity and mortality.

Sildenafil citrate alleviates pulmonary hypertension after hypoxia and reoxygenation with cardiopulmonary bypass

BACKGROUND

Sudden reoxygenation of hypoxic neonates undergoing cardiac operation exacerbates the systemic inflammatory response to cardiopulmonary bypass secondary to reoxygenation injury, worsening cardiopulmonary dysfunction. Reports suggest sildenafil decreases pulmonary hypertension and may affect myocardial function. Sildenafil's efficacy for treating postbypass cardiopulmonary dysfunction remains unknown.

STUDY DESIGN

Fourteen neonatal piglets (5 to 7 kg) underwent 90 minutes of hypoxia, 60 minutes of reoxygenation with cardiopulmonary bypass, and 120 minutes of recovery. Six animals received 50 mg oral sildenafil and eight received saline at hypoxia. Data are presented as mean +/- SD.

RESULTS

Sildenafil prevented the high pulmonary vascular resistance observed in controls (controls baseline 81 +/- 37 dynes. s/cm(5) versus recovery 230 +/- 93 dynes. s/cm(5), p = 0.004; sildenafil baseline 38 +/- 17 dynes. s/cm(5) versus recovery 101 +/- 60 dynes. s/cm(5), p = 0.003). Despite lower pulmonary vascular resistance after sildenafil, arterial endothelin-1 (ET-1) was increased in both groups (control baseline 1.3 +/- 0.5 pg/mL versus recovery 4.5 +/- 3.7 pg/mL, p = 0.01; sildenafil baseline 1.3 +/- 0.3 pg/mL versus recovery 9.8 +/- 4.9 pg/mL, p = 0.003). Intravenous nitric oxide (NO) levels were preserved after sildenafil treatment (sildenafil baseline 340 +/- 77 nM versus recovery 394 +/- 85 nM). IV NO levels in controls were decreased when compared with baseline (control baseline 364 +/- 83 nM versus recovery 257 +/- 97 nM, p = 0.028). Although levels of exhaled NO decreased in both groups, the sildenafil-treated animals had higher levels of exhaled NO when compared with controls at the end of recovery (0.6 +/- 0.4 parts per billion versus 1.8 +/- 0.9 parts per billion, respectively, p = 0.029).

CONCLUSIONS

Sildenafil alleviated pulmonary hypertension after reoxygenation with cardiopulmonary bypass. Despite increased ET-1 levels, pulmonary vascular resistance was lower with sildenafil treatment, suggesting sildenafil's effect on the pulmonary vasculature is capable of countering vasoconstriction by ET-1. Further study into the role of sildenafil in perioperative therapy and its interactions with ET-1 are warranted.

Evidence for a role of heat shock factor 1 in inhibition of NF-κB pathway during heat shock response-mediated lung protection

Heat shock transcription factor (HSF)-1 is recognized as a central component of the heat shock response, which protects against various harmful conditions. However, the mechanisms underlying the protection and the role of HSF-1 in these mechanisms have not yet been clearly elucidated. Using HSF-1 knockout mice ( Hsf1−/−), we examined whether heat shock response-mediated lung protection involved an inhibition of the proinflammatory pathway via an interaction between HSF-1 and NF-κB, in response to cadmium insult. The HSF-1-dependent protective effect against intranasal instillation of cadmium (10 and 100 μg/mouse) was demonstrated by the higher protein content (1.2- and 1.4-fold), macrophage (1.6- and 1.9-fold), and neutrophil (2.6- and 1.8-fold) number in bronchoalveolar fluids, higher lung wet-to-dry weight ratio, and more severe lung damage evaluated by histopathology in Hsf1−/−compared with wild-type animals. These responses were associated with higher granulocyte/macrophage colony-stimulating factor (GM-CSF; 1.7-fold) but not TNF-α concentrations in bronchoalveolar fluids of Hsf1−/−mice compared with those of wild-type animals, indicating that HSF-1 behaved as a repressor of specific cytokine production in our model. To further investigate the mechanism of GM-CSF repression, we analyzed the NF-κB activity and IκB stability. The DNA binding NF-κB activity, in particular p50 homodimer activity, was higher in Hsf1−/−mice than in wild-type mice after cadmium exposure. These results provide a first line of evidence that mechanisms of lung protection depending on HSF-1 involve specific cytokine repression via inhibition of NF-κB activation in vivo.

Effects of exercise on gene expression in human peripheral blood mononuclear cells

Exercise leads to increases in circulating levels of peripheral blood mononuclear cells (PBMCs) and to a simultaneous, seemingly paradoxical increase in both pro- and anti-inflammatory mediators. Whether this is paralleled by changes in gene expression within the circulating population of PBMCs is not fully understood. Fifteen healthy men (18–30 yr old) performed 30 min of constant work rate cycle ergometry (∼80% peak O2 uptake). Blood samples were obtained preexercise (Pre), end-exercise (End-Ex), and 60 min into recovery (Recovery), and gene expression was measured using microarray analysis (Affymetrix GeneChips). Significant differential gene expression was defined with a posterior probability of differential expression of 0.99 and a Bayesian P value of 0.005. Significant changes were observed from Pre to End-Ex in 311 genes, from End-Ex to Recovery in 552 genes, and from Pre to Recovery in 293 genes. Pre to End-Ex upregulation of PBMC genes related to stress and inflammation [e.g., heat shock protein 70 (3.70-fold) and dual-specificity phosphatase-1 (4.45-fold)] was followed by a return of these genes to baseline by Recovery. The gene for interleukin-1 receptor antagonist (an anti-inflammatory mediator) increased between End-Ex and Recovery (1.52-fold). Chemokine genes associated with inflammatory diseases [macrophage inflammatory protein-1α (1.84-fold) and -1β (2.88-fold), and regulation-on-activation, normal T cell expressed and secreted (1.34-fold)] were upregulated but returned to baseline by Recovery. Exercise also upregulated growth and repair genes such as epiregulin (3.50-fold), platelet-derived growth factor (1.55-fold), and hypoxia-inducible factor-I (2.40-fold). A single bout of heavy exercise substantially alters PBMC gene expression characterized in many cases by a brisk activation and deactivation of genes associated with stress, inflammation, and tissue repair.

Endothelin-A receptor blockade and inhaled nitric oxide in a porcine model of meconium aspiration syndrome

Acute neonatal pulmonary hypertension is associated with increased activation of the endogenous endothelin pathway. We investigated the role of selective endothelin-A receptor blockade using i.v. BQ-123 in a piglet model of meconium aspiration syndrome. Meconium aspiration was induced in 18 anesthetized piglets. Six controls received no further intervention. Six piglets received 1 mg/kg BQ-123 at 120 min, with the addition of 20 ppm inhaled nitric oxide at 240 min. Six commenced nitric oxide therapy at 120 min, and were given i.v. BQ-123 at 240 min. The total study duration was 360 min. Meconium aspiration resulted in acute pulmonary hypertension and elevated endothelin-1 levels in all animals. There were no changes in pulmonary hemodynamics or endothelin-1 levels beyond 120 min in controls. In the group receiving BQ-123 first, this agent alone reduced the pulmonary artery pressure and pulmonary vascular resistance, and the subsequent addition of inhaled nitric oxide further reduced pulmonary artery pressure. In the group first receiving nitric oxide alone, this reduced the pulmonary artery pressure, and the addition of BQ-123 resulted in a fall in pulmonary vascular resistance. Endothelin-1 levels increased with both agents. BQ-123 was found to be a highly effective pulmonary vasodilator and augmented the effects of nitric oxide in this model of acute pulmonary hypertension.

Factors contributing to successful discontinuation from inhaled nitric oxide therapy in pediatric patients after congenital cardiac surgery

OBJECTIVE

To investigate variables that contribute to successful discontinuation from inhaled nitric oxide (iNO) therapy in children after surgical repair of congenital heart disease.

DESIGN

Analysis of retrospectively collected data.

SETTING

The pediatric intensive care unit of a university hospital.

PATIENTS

A total of 65 pediatric patients receiving iNO therapy for the purpose of pulmonary circulation control after cardiac surgery.

INTERVENTIONS

None.

MEASUREMENTS AND MAIN RESULTS

Patients were classified into two groups: those successfully weaned from iNO therapy on the initial attempt (group A, n = 45) and those for whom the initial attempt at weaning failed (group B, n = 20). Variables including intraoperative findings, postoperative hemodynamic and ventilatory variables, medication profiles, and dose and duration of iNO therapy were compared between groups. Using a multivariate logistic regression model, iNO therapy of >72 hrs (odds ratio, 5.6) and NO dose at discontinuation of <2 ppm (odds ratio, 4.1) were found to be significantly associated with successful weaning. Those results could be emphasized in a subgroup of left-to-right shunt cardiac anomaly.

CONCLUSIONS

Longer continuation (>72 hrs) and lower final concentration (<2 ppm) represent factors contributing to successful discontinuation of iNO therapy in pediatric patients after cardiac surgery, specifically for children with left-to-right shunt correction.

Inhaled nitric oxide results in deteriorating hemodynamics when administered during cardiopulmonary bypass in neonatal swine

OBJECTIVE

To evaluate if inhaled nitric oxide (iNO) has a lung-protective effect when it is delivered during the ischemic phase of neonatal cardiopulmonary bypass (CPB).

DESIGN

Prospective, randomized, controlled study.

SETTING

Surgical research laboratory in a university hospital.

SUBJECTS

Thirty-five neonatal swine.

INTERVENTIONS

One-week-old swine (2.1-3.4 kg) were exposed to cool, low-flow CPB bypass designed to mimic the bypass used during neonatal congenital heart repair. Animals were randomized to four groups: a) CPB without exposure to iNO (n = 9); b) iNO delivery only during CPB with discontinuation of iNO at the start of reperfusion (n = 7); c) iNO delivery both during CPB and during the 90-min post-CPB observation period (n = 7); and d) iNO delivery only after separation from CPB (n = 7). Each animal was placed on nonpulsatile CPB and cooled to a nasopharyngeal temperature of 18 degrees C (64 degrees F). Low-flow CPB (35 mL.kg(-1).min(-1)) was instituted for 90 mins. The blood flow then was returned to 100 mL.kg(-1).min(-1), and the animals were warmed to 36 degrees C (96.8 degrees F) before separation from CPB. Animals were followed 90 mins post-CPB. Lung tissue was harvested and evaluated for myeloperoxidase activity, wet/dry weight, and lung pathology. Five animals underwent sham protocol, receiving instrumentation but not exposure to CPB or iNO.

MEASUREMENTS AND MAIN RESULTS

We measured pulmonary vascular resistance, right ventricular output, and pulmonary artery pressure in all animals at 30, 60, and 90 mins following separation from CPB. Study animals that received iNO during the ischemic period of CPB were not protected against CPB-induced lung injury. Those animals treated with iNO both during and after CPB trended worse than those receiving iNO only after CPB. Inhaled nitric oxide delivered only after separation from CPB improved the hemodynamic variables compared with all other groups. Differences in lung wet/dry weight, myeloperoxidase, and pathology were not significantly different among groups.

CONCLUSIONS

The delivery of iNO during the ischemic period of CPB does not protect against CPB-induced lung injury in a neonatal piglet CPB model. Delivery of iNO during this phase of CPB may, in fact, worsen the post-CPB hemodynamic condition. Inhaled nitric oxide should be used with caution during periods of low pulmonary blood flow CPB. Inhaled nitric oxide remains effective for reducing pulmonary vascular resistance after CPB.

Phosphodiesterase inhibitors for persistent pulmonary hypertension of the newborn: a review

Persistent pulmonary hypertension of the newborn (PPHN) is a complex syndrome with multiple causes, with an incidence of 0.43-6.8/1,000 live births and a mortality of 10-20%. Survivors have high morbidity in the forms of neurodevelopmental and audiological impairment, cognitive delays, hearing loss, and a high rate of rehospitalization. The optimal approach to the management of PPHN remains controversial. Inhaled nitric oxide (iNO) is currently regarded as the gold standard therapy, but with as many as 30% of cases failing to respond, has not proven to be the single magic bullet. Given the complex pathophysiology of the disease, any such magic bullet is unlikely. A number of recent studies have suggested a role for specific phosphodiesterase (PDE) inhibitors in the management of PPHN. Sildenafil, a specific PDE5 inhibitor, appears the most promising of such agents. We aim to review the current status and limitations of iNO and the potential of PDE inhibitors in the management of PPHN. The reasons why caution is warranted before specific PDE5 inhibitors like sildenafil are labelled as potential magic bullets for PPHN will be discussed. The need for randomized-controlled trials to determine the safety, efficacy, and long-term outcome following treatment with sildenafil in PPHN is emphasized.

Acute hemodynamic effects and home therapy using a novel pulsed nasal nitric oxide delivery system in children and young adults with pulmonary hypertension

In 26 patients, we evaluated a novel pulsed nasal delivery system for nitric oxide (NO) that, in the short term, was as effective as continuous delivery for decreasing pulmonary artery pressure and pulmonary vascular resistance. In 2 patients, NO delivered in the home using this pulsing system was well tolerated for up to 2 years. The long-term safety, efficacy, and acceptability of NO delivered in the home remains to be studied.

Regulation of nitric oxide consumption by hypoxic red blood cells

The homeostasis of nitric oxide (NO) is attained through a balance between its production and consumption. Shifts in NO bioavailability have been linked to a variety of diseases. Although the regulation of NO production has been well documented, its consumption is largely thought to be unregulated. Here, we have demonstrated that under hypoxic conditions, NO accelerates its own consumption by increasing its entry into RBCs. When RBCs were exposed to NO (1:400 NO/heme ratio) under hypoxic conditions to form HbFe(II)NO, the consumption rate of NO increased significantly. This increase in NO consumption converted the bioactivity of serotonin from a vasodilator to a vasoconstrictor in isolated coronary arterioles. We identified HbFe(II)NO as a potential mediator of accelerated NO consumption. Accelerated NO consumption by HbFe(II)NO-bearing RBCs may contribute to hypoxic pulmonary vasoconstriction and the rebound effect seen on termination of NO inhalation therapy. Furthermore, accelerated NO consumption may exacerbate ischemia-mediated vasospasm and nitrate tolerance. Finally, this phenomenon may be an evolved mechanism to stabilize the vasculature in sepsis.