Recent developments in the pathophysiology and treatment of persistent pulmonary hypertension of the newborn

Evaluation of Morbidities and Complications of Neonatal İntensive Care Unit Patients with Respiratory Disorders at Different Gestational Ages

OBJECTIVE

Respiratory distress presented within the first few days of life is life-threatening and common problem in the neonatal period. The aim of this study is to estimate (1) the incidence of respiratory diseases in newborns and related mortality; (2) the relationship between acute neonatal respiratory disorders rates and gestational age, birth weight, and gender; and (3) the incidence of complications associated with respiratory disturbances.

STUDY DESIGN

Only inborn patients with gestational age between 23^0/7 and 41^6/7 weeks having respiratory distress were included in the study. The data were collected from the medical records and gestational age was based on the menstrual dating.

RESULTS

There were 8,474 live births between January 1, 2013, and June 30, 2013, in our hospital. A total of 1,367 newborns were hospitalized and oxygen therapy was applied in 903 of them because of respiratory distress. An acute respiratory disorder was found to be in 10.6% (903/8,474) among all live births. Mortality was 0.76% (66/8,474). The incidence of respiratory distress syndrome was 2.8% (n = 242). The occurrence of transient tachypnea of newborn was 3.1% (n = 270). Meconium aspiration syndrome, pneumonia, congenital diaphragmatic hernia, and pulmonary maladaptation and primary persistent pulmonary hypertension rates were 0.1, 0.7, 2.2, and 0%, respectively. Overall, 553 (61%) of the 903 newborns having respiratory diseases had complications. The occurrence of necrotizing enterocolitis, patent ductus arteriosus, bronchopulmonary dysplasia, intraventricular hemorrhage and air leak was 6.8, 19.8, 4.7, 24.9, and 5%, respectively.

CONCLUSION

This study offers an epidemiological perspective for respiratory disorders from a single-center level-III neonatal intensive care unit. Although number of births, premature newborns, extremely low birth weight/very low birth weight infants, and complicated pregnancies increase in years, decreasing rates of mortality and complications are very promising. As perinatal and neonatal cares are getting better in every day, we think that more promising results can be achieved over the coming years.

KEY POINTS

· Respiratory distress in the newborn is life-threatening.. · Pulmonary or extrapulmonary diseases may be underlying cause.. · More promising results can be achieved over the coming years with advanced care..

Repurposing of the PDE5 Inhibitor Sildenafil for the Treatment of Persistent Pulmonary Hypertension in Neonates

Nitric oxide (NO), an important endogenous signaling molecule released from vascular endothelial cells and nerves, activates the enzyme soluble guanylate cyclase to catalyze the production of cyclic guanosine monophosphate (cGMP) from guanosine triphosphate. cGMP, in turn, activates protein kinase G to phosphorylate a range of effector proteins in smooth muscle cells that reduce intracellular Ca²⁺ levels to inhibit both contractility and proliferation. The enzyme phosphodiesterase type 5 (PDE5) curtails the actions of cGMP by hydrolyzing it into inactive 5'-GMP. Small molecule PDE5 inhibitors (PDE5is), such as sildenafil, prolong the availability of cGMP and therefore, enhance NO-mediated signaling. PDE5is are the first-line treatment for erectile dysfunction but are also now approved for the treatment of pulmonary arterial hypertension (PAH) in adults. Persistent pulmonary hypertension in neonates (PPHN) is currently treated with inhaled NO, but this is an expensive option and around 1/3 of newborns are unresponsive, resulting in the need for alternative approaches. Here the development, chemistry and pharmacology of PDE5is, the use of sildenafil for erectile dysfunction and PAH, are summarized and then current evidence for the utility of further repurposing of sildenafil, as a treatment for PPHN, is critically reviewed.

Clinical and echocardiography predictors of response to inhaled nitric oxide in hypoxemic term and near-term neonates

Approximately 40% of hypoxemic term/near-term neonates are nonresponders to inhaled nitric oxide (iNO). Phenotypic characterization of patients less likely to respond may improve diagnostic precision and therapeutic decisions. We conducted a retrospective cohort study of neonates born ≥35 weeks gestation with hypoxemia who received iNO in the first 72 h of life and classified them into responders and nonresponders according to changes in the fraction of inspired oxygen, saturations and/or arterial partial pressure of oxygen after 1 h of administration. Comprehensive targeted neonatal echocardiography (TnECHO) data were collected when performed up to 6 h prior or 24 h after iNO initiation. Descriptive statistics, univariate analysis, and binary logistic regression were used to compare the groups. There were 183 patients included (63% responders) and TnECHO was performed in 54 infants. The presence of lung disease, and particularly meconium aspiration syndrome (p = .004), was associated with nonresponse to iNO. Nonresponders were characterized by a higher need for rescue high-frequency ventilation (p < .001), longer duration of mechanical ventilation (p < .001), and need for oxygen support (p = .003). Pulmonary hypertension documented on TnECHO was present in 96.3% of the patients but there was no difference in frequency or severity of pulmonary hypertension, or rates of low cardiac output between the groups. Moderate-to-severe right ventricular systolic dysfunction (p > .05) and lower left ventricular strain (p < .05) were more likely in the nonresponder group. In summary, response to iNO is influenced by lung disease, choice of ventilation strategy, and perhaps underlying cardiovascular physiology. Prospective pre- and post-iNO echocardiography data may provide novel physiologic insights.

Vasodilator effects of dehydroepiandrosterone (DHEA) on fetal pulmonary circulation: An experimental study in pregnant sheep

Persistent pulmonary hypertension (PPHN) remains a severe complication of the transition to extra-uterine life with significant morbidity and mortality in the newborns. Dehydroepiandrosterone (DHEA) represents a new pharmacological agent with vascular effects, including improvement of PPHN in several animal models. We hypothesized that DHEA could decrease pulmonary vascular resistance (PVR) in the pulmonary circulation of fetal sheep. We studied the effect of intravenous infusion of DHEA in fetal lambs using chronically instrumented sheep at 128 days of gestation. PVR was computed before and after intravenous infusion of increasing doses of DHEA. We assessed pre-treatment by L-nitroarginine, an inhibitor of NO production. Blood gases and doses of DHEA were measured in both sheep and fetus before/after DHEA infusion. Intravenous infusion of DHEA had a vasodilator effect with a significant decrease in PVR (respectively -11%, -14% and -36% after infusion of 6, 12 and 24 mg DHEA, p<0.01) without damaging effects on systemic circulation or on blood gases. The inhibitory effect of pre-treatment with L-nitroarginine resulted in a significant increase in PVR. We demonstrated a potent vasodilator effect of DHEA on fetal pulmonary circulation without deleterious effects. DHEA might represent a new treatment for PPHN.

Lung size and liver herniation predict need for extracorporeal membrane oxygenation but not pulmonary hypertension in isolated congenital diaphragmatic hernia: systematic review and meta-analysis

OBJECTIVES

To identify antenatal predictors of persistent pulmonary hypertension (PPH) and the need for extracorporeal membrane oxygenation (ECMO) in fetuses with congenital diaphragmatic hernia (CDH).

METHODS

We performed a systematic literature review on antenatal diagnostic tests in fetuses with isolated CDH. The primary outcomes assessed were PPH within 28 days of age and the need for ECMO. Quality of studies was assessed with the QUADAS-2 tool. Meta-analysis was performed when at least three studies reported on the same test. Sensitivity analysis was performed according to prenatal management of CDH (tracheal occlusion vs expectant management).

RESULTS

Thirty-eight studies met the inclusion criteria. Fifteen reported on the incidence of PPH only, 19 on the need for ECMO only and four reported on both outcomes. The general quality of the studies was moderate; most studies were retrospective (61%) and single-center series (92%). One study included only fetuses undergoing tracheal occlusion, 22 included only fetuses managed expectantly in utero and 15 included both populations. We could not identify antenatal predictors of PPH. The need for ECMO was predicted by parameters indicative of lung size: lung-to-head ratio (LHR) (relative risk (RR) for LHR < 1, 1.65 (95% CI, 1.27-2.14)) and observed/expected LHR (standardized mean difference (SMD), -0.70 (95% CI, -0.98 to -0.42)) measured by ultrasound and observed/expected total lung volume (SMD, -1.00 (95% CI, -1.52 to -0.48)) measured by magnetic resonance imaging. Liver herniation was also associated with an increased risk of need for ECMO (RR, 3.04 (95% CI, 2.23-4.14)). These results were confirmed by a sensitivity analysis of studies that included only expectantly managed cases. Data on vascular assessment for the prediction of PPH could not be pooled as most of the parameters were evaluated in a single series or in different series by the same principal investigator.

CONCLUSIONS

In fetuses with CDH, lung size and liver herniation predict the need for ECMO, however a predictor for PPH is still lacking. Further studies aimed at diagnosing impaired vascular development in utero should therefore be undertaken. Copyright © 2016 ISUOG. Published by John Wiley & Sons Ltd.

Administration of Inhaled Pulmonary Vasodilators to the Mechanically Ventilated Neonatal Patient

Pulmonary hypertension is a life-threatening condition that affects people of all ages that can occur as an idiopathic disorder at birth or as part of a variety of cardiovascular and infectious disorders. It is commonly treated with inhaled pulmonary vasodilators such as nitric oxide and less frequently using formulations and analogs of prostacyclin. To minimize systemic effects and preserve pulmonary vasodilation, vasodilators are often administered directly into the airway. Nitric oxide is the only USA Food and Drug Administration-approved inhaled pulmonary vasodilator that can be used during mechanical ventilation. Over the past two decades, interest has grown in the use of aerosolized prostacyclin and prostacyclin analogs for the treatment of pulmonary hypertension during mechanical ventilation. Clinicians who administer inhaled prostacyclin may not have a clear understanding of its risks because of the lack of data from large clinical trials examining safety and efficacy; moreover, its safe use remains poorly documented. The off-label use of drugs is legitimate, but prescribers must recognize the potential complications and liability in doing so. This manuscript aims to address potential problems related to the aerosol administration of pulmonary vasodilators in the mechanically ventilated neonatal patient.

Unique aspects of the developing lung circulation: structural development and regulation of vasomotor tone

This review summarizes our current knowledge on lung vasculogenesis and angiogenesis during normal lung development and the regulation of fetal and postnatal pulmonary vascular tone. In comparison to that of the adult, the pulmonary circulation of the fetus and newborn displays many unique characteristics. Moreover, altered development of pulmonary vasculature plays a more prominent role in compromised pulmonary vasoreactivity than in the adult. Clinically, a better understanding of the developmental changes in pulmonary vasculature and vasomotor tone and the mechanisms that are disrupted in disease states can lead to the development of new therapies for lung diseases characterized by impaired alveolar structure and pulmonary hypertension.

Clinical hypoxic-ischemic encephalopathy score of the Iberoamerican Society of Neonatology (Siben): A new proposal for diagnosis and management

Summary Hypoxic ischemic encephalopathy is a major complication of perinatal asphyxia, with high morbidity, mortality and neurologic sequelae as cerebral palsy, mostly in poor or developing countries. The difficulty in the diagnosis and management of newborns in these countries is astonishing, thus resulting in unreliable data on this pathology and bad outcomes regarding mortality and incidence of neurologic sequelae. The objective of this article is to present a new clinical diagnostic score to be started in the delivery room and to guide the therapeutic approach, in order to improve these results.

An international survey on persistent pulmonary hypertension of the newborn: A need for an evidence-based management

OBJECTIVE

To assess the current practice preferences in diagnosis and management of persistent hypertension of the newborn (PPHN) of neonatologists or pediatricians with expertise in neonatal care.

STUDY DESIGN

Investigators identified potential participants worldwide through a literature search. They were emailed the URL of an online 25-item questionnaire through the web survey site SurveyMonkey®. Additional respondents were also acquired through a professional online discussion group. The survey was conducted during July - September 2015.

RESULTS

Overall, there were 200 respondents from 51 different countries. Of these, the average 2014 mortality rate of the 90 respondents who completed this section of the questionnaire was 8.3% (interquartile range (IQR): 0-20.3). Echocardiography together with pre-to-post ductal oxygen pulse oximetry (SpO2) gradient was the most common PPHN diagnostic method. The most frequent first-line pulmonary vasodilator was inhaled nitric oxide (155/199, 77.9%). Oral sildenafil was most commonly used as second-line adjunctive therapy by 46.3% (81/175). Dopamine (139/198, 70.2%) was chosen to be the initial inotropic agent and normal saline (191/199, 96.0%) was the preferred initial fluid resuscitation for hypotension. Sedation and analgesia were routinely used for PPHN treatment. Twenty-one percent (42/199) of respondents also used muscle relaxants to control respiratory distress. The most commonly used targets for partial pressure of oxygen, partial pressure of carbon dioxide, SpO2 and hemoglobin were 71-80 mmHg (60/197, 30.4%), 36-45 mmHg (100/199, 50.2%), 91-95% (111/199, 55.8%), and 13-15 gm/dL (156/196, 79.6%), respectively.

CONCLUSIONS

This survey shows that the management of PPHN varies widely around the world. The major PPHN diagnostic method is echocardiography together with bedside SpO2 monitoring. The study numbers show the main differences are between developed and developing countries. Further studies exploring evidence-based principles of diagnosis and management in PPHN are warranted.

Pediatric Pulmonary Hypertension: Guidelines From the American Heart Association and American Thoracic Society

Pulmonary hypertension is associated with diverse cardiac, pulmonary, and systemic diseases in neonates, infants, and older children and contributes to significant morbidity and mortality. However, current approaches to caring for pediatric patients with pulmonary hypertension have been limited by the lack of consensus guidelines from experts in the field. In a joint effort from the American Heart Association and American Thoracic Society, a panel of experienced clinicians and clinician-scientists was assembled to review the current literature and to make recommendations on the diagnosis, evaluation, and treatment of pediatric pulmonary hypertension. This publication presents the results of extensive literature reviews, discussions, and formal scoring of recommendations for the care of children with pulmonary hypertension.

Effect of persistent pulmonary hypertension on brain oxygenation in asphyxiated term newborns treated with hypothermia

OBJECTIVE

To better understand the impact of persistent pulmonary hypertension (PPHN) on brain oxygenation in term asphyxiated newborns treated with hypothermia.

METHODS

The regional cerebral oxygenation saturation (rSO2) measured by near-infrared spectroscopy was compared to pre/post-ductal oxygen saturation and mean arterial blood pressure in three term asphyxiated newborns with documented PPHN during their first 4 days of life while they were being treated with hypothermia.

RESULTS

The cerebral oxygen saturation remained relatively stable when oxygen saturation was more than 92% and when there was no difference between pre- and post-ductal oxygen saturations. Episodes of desaturations with a difference between pre- and post-ductal saturations, as well as episodes of hypotension, caused a significant decrease in rSO2 in these newborns.

CONCLUSION

This case series demonstrates that PPHN has a profound impact on brain oxygenation in term asphyxiated newborns treated with hypothermia during the first days of life after birth. PPHN may represent an additional risk factor for brain injury in these newborns during the first days of life.

Persistent pulmonary hypertension of the newborn

Persistent pulmonary hypertension of the newborn (PPHN) is characterized by elevated pulmonary vascular resistance resulting in right-to-left shunting of blood and hypoxemia. PPHN is often secondary to parenchymal lung disease (such as meconium aspiration syndrome, pneumonia or respiratory distress syndrome) or lung hypoplasia (with congenital diaphragmatic hernia or oligohydramnios) but can also be idiopathic. The diagnosis of PPHN is based on clinical evidence of labile hypoxemia often associated with differential cyanosis. The diagnosis is confirmed by the echocardiographic demonstration of - (a) right-to-left or bidirectional shunt at the ductus or foramen ovale and/or, (b) flattening or leftward deviation of the interventricular septum and/or, (c) tricuspid regurgitation, and finally (d) absence of structural heart disease. Management strategies include optimal oxygenation, avoiding respiratory and metabolic acidosis, blood pressure stabilization, sedation and pulmonary vasodilator therapy. Failure of these measures would lead to consideration of extracorporeal membrane oxygenation (ECMO); however decreased need for this rescue therapy has been documented with advances in medical management. While trends also note improved survival, long-term neurodevelopmental disabilities such as deafness and learning disabilities remain a concern in many infants with severe PPHN. Funded by: 1R01HD072929-0 (SL).

The Robyn Barst Memorial Lecture: Differences between the fetal, newborn, and adult pulmonary circulations: relevance for age-specific therapies (2013 Grover Conference series)

Pulmonary arterial hypertension (PAH) contributes to poor outcomes in diverse diseases in newborns, infants, and children. Many aspects of pediatric PAH parallel the pathophysiology and disease courses observed in adult patients; however, critical maturational differences exist that contribute to distinct outcomes and therapeutic responses in children. In comparison with adult PAH, disruption of lung vascular growth and development, or angiogenesis, plays an especially prominent role in the pathobiology of pediatric PAH. In children, abnormalities of lung vascular development have consequences well beyond the adverse hemodynamic effects of PAH alone. The developing endothelium also plays critical roles in development of the distal airspace, establishing lung surface area for gas exchange and maintenance of lung structure throughout postnatal life through angiocrine signaling. Impaired functional and structural adaptations of the pulmonary circulation during the transition from fetal to postnatal life contribute significantly to poor outcomes in such disorders as persistent pulmonary hypertension of the newborn, congenital diaphragmatic hernia, bronchopulmonary dysplasia, Down syndrome, and forms of congenital heart disease. In addition, several studies support the hypothesis that early perinatal events that alter lung vascular growth or function may set the stage for increased susceptibility to PAH in adult patients ("fetal programming"). Thus, insights into basic mechanisms underlying unique features of the developing pulmonary circulation, especially as related to preservation of endothelial survival and function, may provide unique therapeutic windows and distinct strategies to improve short- and long-term outcomes of children with PAH.

Vasopressin improves hemodynamic status in infants with congenital diaphragmatic hernia

OBJECTIVE

To assess the ability of vasopressin to stabilize hemodynamics in infants with systemic hypotension secondary to congenital diaphragmatic hernia (CDH).

STUDY DESIGN

A retrospective chart review was performed to identify 13 patients with CDH treated with vasopressin for refractory hypotension to assess the effect of vasopressin on pulmonary and systemic hemodynamics and gas exchange in this setting. Data collected included demographics, respiratory support, inotropic agents, pulmonary and systemic hemodynamics, urine output, and serum and urine sodium levels during vasopressin therapy.

RESULTS

Vasopressin therapy increased mean arterial pressure and decreased pulmonary/systemic pressure ratio, heart rate, and fraction of inspired oxygen. In 6 of 13 patients, extracorporeal membrane oxygenation therapy was no longer indicated after treatment with vasopressin. Improvement in left ventricular function and oxygenation index after vasopressin initiation was associated with a decreased need for extracorporeal membrane oxygenation therapy. Prolonged vasopressin treatment was associated with hyponatremia, increased urine output, and increased urine sodium.

CONCLUSIONS

Vasopressin stabilized systemic hemodynamics without adverse effects on pulmonary hemodynamics in a subset of infants with CDH. Our results suggest a potential role for vasopressin therapy in patients with CDH with catecholamine-resistant refractory hypotension.

Pathophysiology of persistent pulmonary hypertension of the newborn: impact of the perinatal environment

The main cause of pulmonary hypertension in newborn babies results from the failure of the pulmonary circulation to dilate at birth, termed 'persistent pulmonary hypertension of the newborn' (PPHN). This syndrome is characterized by sustained elevation of pulmonary vascular resistance, causing extrapulmonary right-to-left shunting of blood across the ductus arteriosus and foramen ovale and severe hypoxaemia. It can also lead to life-threatening circulatory failure. There are many controversial and unresolved issues regarding the pathophysiology of PPHN, and these are discussed. PPHN is generally associated with factors such as congenital diaphragmatic hernia, birth asphyxia, sepsis, meconium aspiration and respiratory distress syndrome. However, the perinatal environment-exposure to nicotine and certain medications, maternal obesity and diabetes, epigenetics, painful stimuli and birth by Caesarean section-may also affect the maladaptation of the lung circulation at birth. In infants with PPHN, it is important to optimize circulatory function. Suggested management strategies for PPHN include: avoidance of environmental factors that worsen PPHN (e.g. noxious stimuli, lung overdistension); adequate lung recruitment and alveolar ventilation; inhaled nitric oxide (or sildenafil, if inhaled nitric oxide is not available); haemodynamic assessment; appropriate fluid and cardiovascular resuscitation and inotropic and vasoactive agents.

Intrauterine inflammation alters cardiopulmonary and cerebral haemodynamics at birth in preterm lambs

Intrauterine inflammation is associated with preterm birth and poor long-term cardiopulmonary outcomes. We aimed to determine the effect of intrauterine inflammation on the cardiopulmonary and cerebral haemodynamic transition at birth, and the response to subsequent haemodynamic challenge. Fetal instrumentation was performed at ∼112 days gestation (term is 147 days) for measurement of cardiopulmonary and cerebral haemodynamics. At 118 days, inflammation was induced by intra-amniotic administration of lipopolysaccharide (LPS; n = 7); controls (n = 5) received intra-amniotic saline. At 125 days lambs were delivered and mechanically ventilated. Arterial blood gases, pulmonary and systemic arterial blood pressures and flows were measured during the perinatal period. At 10 min a haemodynamic challenge was administered by increasing positive end-expiratory pressure. During the first 10 min after birth, LPS-exposed lambs had higher pulmonary vascular resistance and lower pulmonary blood flow and left ventricular output than controls. Carotid arterial blood flow was higher in LPS-exposed lambs than controls between 3 and 7 min after delivery, and cerebral oxygen delivery was higher at 5 min. During the haemodynamic challenge, pulmonary blood flow and left ventricular output were reduced in controls but not in LPS-exposed lambs; a transient reduction in brachiocephalic arterial pressure occurred in LPS-exposed lambs but not in controls. Intrauterine inflammation altered the cardiopulmonary and cerebral haemodynamic transition at birth and reduced the cardiopulmonary response to a haemodynamic challenge after birth. The transient reduction in brachiocephalic arterial pressure suggests intrauterine inflammation may alter cerebrovascular control following an increase in positive end-expiratory pressure.

Risk factors for persistent pulmonary hypertension of the newborn

In utero, pulmonary blood flow is closely circumscribed and oxygenation and ventilation occur via the placental circulation. Within the first few breaths of air-breathing life, the perinatal pulmonary circulation undergoes a dramatic transition as pulmonary blood flow increases 10-fold and the pulmonary arterial blood pressure decreases by 50% within 24 hours of birth. With the loss of the placental circulation, the increase in pulmonary flow enables oxygen to enter the bloodstream. The physiologic mechanisms that account for the remarkable transition of the pulmonary circulation include establishment of an air-liquid interface, rhythmic distention of the lung, an increase in shear stress and elaboration of nitric oxide from the pulmonary endothelium. If the perinatal pulmonary circulation does not dilate, blood is shunted away from the lungs at the level of the patent foramen ovale and the ductus arteriosus leading to the profound and unremitting hypoxemia that characterizes persistent pulmonary hypertension of the newborn (PPHN), a syndrome without either optimally effective preventative or treatment strategies. Despite significant advances in treatment, PPHN remains a major cause of morbidity and mortality in neonatal centers across the globe. While there is information surrounding factors that might increase the risk of PPHN, knowledge remains incomplete. Cesarean section delivery, high maternal body mass index, maternal use of aspirin, nonsteroidal anti-inflammatory agents and maternal diabetes mellitus are among the factors associated with an increased risk for PPHN. Recent data suggest that maternal use of serotonin reuptake inhibitors might represent another important risk factor for PPHN.

Hypoxia-inducible factor-1α regulates KCNMB1 expression in human pulmonary artery smooth muscle cells

Previously, we observed that hypoxia increases the expression of the β1-subunit (KCNMB1) of the calcium-sensitive potassium channel (BK(Ca)). Herein, we elucidate the mechanism whereby hypoxia increases KCNMB1 expression in human pulmonary artery smooth muscle cells (hPASMC). In response to hypoxia, the expression of both the transcription factor hypoxia-inducible factor 1-α (HIF-1α) and KCNMB1 are increased. Knockdown of HIF-1α using a shRNA plasmid blocked the hypoxic induction of KCNMB1 expression. Chromatin immunoprecipitation (ChIP) demonstrated HIF-1α binding to three discrete regions of the human KCNMB1 promoter known to contain hypoxia response elements (HREs). A KCNMB1 promoter reporter assay combined with site-directed mutagenesis identified two adjacent HREs located between -3,540 bp and -3,311 bp that are essential for the hypoxic induction of KCNMB1 promoter activity. Furthermore, additional ChIP assays demonstrated recruitment of the HIF-1α transcriptional coactivator, p300, to this same promoter region. Treatment of hPASMC with the histone deacetylase inhibitor, trichostatin, prolonged the increase in KCNMB1 observed with hypoxia, suggesting that alterations in chromatin remodeling function to limit the hypoxic induction of KCNMB1. Finally, KCNMB1 knockdown potentiated the hypoxia-induced increase in cytosolic calcium in hPASMC, highlighting the contribution of the β1-subunit in modulating vascular SMC tone in response to acute hypoxia. In conclusion, HIF-1α increases KCNMB1 expression in response to hypoxia in hPASMC by binding to two HREs located at -3,540 to -3,311 of the KCNMB1 promoter. We speculate that selective modulation of KCNMB1 expression may serve as a novel therapeutic approach to address diseases characterized by an increase in vascular tone.

Cinaciguat, a soluble guanylate cyclase activator, augments cGMP after oxidative stress and causes pulmonary vasodilation in neonatal pulmonary hypertension

Although inhaled NO (iNO) therapy is often effective in treating infants with persistent pulmonary hypertension of the newborn (PPHN), up to 40% of patients fail to respond, which may be partly due to abnormal expression and function of soluble guanylate cyclase (sGC). To determine whether altered sGC expression or activity due to oxidized sGC contributes to high pulmonary vascular resistance (PVR) and poor NO responsiveness, we studied the effects of cinaciguat (BAY 58-2667), an sGC activator, on pulmonary artery smooth muscle cells (PASMC) from normal fetal sheep and sheep exposed to chronic intrauterine pulmonary hypertension (i.e., PPHN). We found increased sGC α(1)- and β(1)-subunit protein expression but lower basal cGMP levels in PPHN PASMC compared with normal PASMC. To determine the effects of cinaciguat and NO after sGC oxidation in vitro, we measured cGMP production by normal and PPHN PASMC treated with cinaciguat and the NO donor, sodium nitroprusside (SNP), before and after exposure to 1H-[1,2,4]oxadiazolo[4,3-a]quinoxalin-1-one (ODQ, an sGC oxidizer), hyperoxia (fraction of inspired oxygen 0.50), or hydrogen peroxide (H(2)O(2)). After treatment with ODQ, SNP-induced cGMP generation was markedly reduced but the effects of cinaciguat were increased by 14- and 64-fold in PPHN fetal PASMC, respectively (P < 0.01 vs. controls). Hyperoxia or H(2)O(2) enhanced cGMP production by cinaciguat but not SNP in PASMC. To determine the hemodynamic effects of cinaciguat in vivo, we compared serial responses to cinaciguat and ACh in fetal lambs after ductus arteriosus ligation. In contrast with the impaired vasodilator response to ACh, cinaciguat-induced pulmonary vasodilation was significantly increased. After birth, cinaciguat caused a significantly greater fall in PVR than either 100% oxygen, iNO, or ACh. We conclude that cinaciguat causes more potent pulmonary vasodilation than iNO in experimental PPHN. We speculate that increased NO-insensitive sGC may contribute to the pathogenesis of PPHN, and cinaciguat may provide a novel treatment of severe pulmonary hypertension.

Persistent pulmonary hypertension results in reduced tetralinoleoyl-cardiolipin and mitochondrial complex II + III during the development of right ventricular hypertrophy in the neonatal pig heart

Persistent pulmonary hypertension of the newborn (PPHN) results in right ventricular (RV) hypertrophy followed by right heart failure and an associated mitochondrial dysfunction. The phospholipid cardiolipin plays a key role in maintaining mitochondrial respiratory and cardiac function via modulation of the activities of enzymes involved in oxidative phosphorylation. In this study, changes in cardiolipin and cardiolipin metabolism were investigated during the development of right heart failure. Newborn piglets (<24 h old) were exposed to a hypoxic (10% O(2)) environment for 3 days, resulting in the induction of PPHN. Two sets of control piglets were used: 1) newborn or 2) exposed to a normoxic (21% O(2)) environment for 3 days. Cardiolipin biosynthetic and remodeling enzymes, mitochondrial complex II + III activity, incorporation of [1-(14)C]linoleoyl-CoA into cardiolipin precursors, and the tetralinoleoyl-cardiolipin pool size were determined in both the RV and left ventricle (LV). PPHN resulted in an increased heart-to-body weight ratio, RV-to-LV plus septum weight ratio, and expression of brain naturetic peptide in RV. In addition, PPHN reduced cardiolipin biosynthesis and remodeling in the RV and LV, which resulted in decreased tetralinoleoyl-cardiolipin levels and reduced complex II + III activity and protein levels of mitochondrial complexes II, III, and IV in the RV. This is the first study to examine the pattern of cardiolipin metabolism during the early development of both the RV and LV of the newborn piglet and to demonstrate that PPHN-induced alterations in cardiolipin biosynthetic and remodeling enzymes contribute to reduced tetralinoleoyl-cardiolipin and mitochondrial respiratory chain function during the development of RV hypertrophy. These defects in cardiolipin may play an important role in the rapid development of RV dysfunction and right heart failure in PPHN.

Effects of environmental tobacco smoke on the pulmonary circulation in the ovine fetus

OBJECTIVE

Epidemiologic studies have highlighted an association between maternal smoking and persistent pulmonary hypertension of the newborn infant. However, the impact of exposure to tobacco smoke on the perinatal pulmonary circulation is currently unknown. The purpose of this study was to assess the pulmonary vascular effects of environmental tobacco smoke in the fetus.

STUDY DESIGN

We performed surgery on 16 fetal lambs and placed catheters in the main pulmonary artery, aorta, and left atrium to measure pressures. An ultrasonic blood flow transducer was placed around the left pulmonary artery to measure blood flow. The ewes were exposed to tobacco smoke for 2 hours. In another set of experiments, the pulmonary vascular response to increased fetal O(2) tension has been assessed after 2 hours of tobacco smoke inhalation or not (control group).

RESULTS

Exposure to tobacco smoke decreased pulmonary blood flow by 30% and elevated pulmonary vascular resistance by 40%. The vasodilator response to increased O(2) tension was blunted after smoke inhalation compared with control animals. Smoke inhalation was associated with a decrease in fetal PaO(2) and SaO(2).

CONCLUSION

Exposure to environmental tobacco smoke in pregnant ewes impairs both basal tone and vascular reactivity of the fetal lung.

A consensus approach to the classification of pediatric pulmonary hypertensive vascular disease: Report from the PVRI Pediatric Taskforce, Panama 2011

Current classifications of pulmonary hypertension have contributed a great deal to our understanding of pulmonary vascular disease, facilitated drug trials, and improved our understanding of congenital heart disease in adult survivors. However, these classifications are not applicable readily to pediatric disease. The classification system that we propose is based firmly in clinical practice. The specific aims of this new system are to improve diagnostic strategies, to promote appropriate clinical investigation, to improve our understanding of disease pathogenesis, physiology and epidemiology, and to guide the development of human disease models in laboratory and animal studies. It should be also an educational resource. We emphasize the concepts of perinatal maladaptation, maldevelopment and pulmonary hypoplasia as causative factors in pediatric pulmonary hypertension. We highlight the importance of genetic, chromosomal and multiple congenital malformation syndromes in the presentation of pediatric pulmonary hypertension. We divide pediatric pulmonary hypertensive vascular disease into 10 broad categories.

Cinaciguat, a soluble guanylate cyclase activator, causes potent and sustained pulmonary vasodilation in the ovine fetus

Impaired nitric oxide-cGMP signaling contributes to severe pulmonary hypertension after birth, which may in part be due to decreased soluble guanylate cyclase (sGC) activity. Cinaciguat (BAY 58-2667) is a novel sGC activator that causes vasodilation, even in the presence of oxidized heme or heme-free sGC, but its hemodynamic effects have not been studied in the perinatal lung. We performed surgery on eight fetal (126 +/- 2 days gestation) lambs (full term = 147 days) and placed catheters in the main pulmonary artery, aorta, and left atrium to measure pressures. An ultrasonic flow transducer was placed on the left pulmonary artery to measure blood flow, and a catheter was placed in the left pulmonary artery for drug infusion. Cinaciguat (0.1-100 microg over 10 min) caused dose-related increases in pulmonary blood flow greater than fourfold above baseline and reduced pulmonary vascular resistance by 80%. Treatment with 1H-[1,2,4]oxadiazolo[4,3-a]quinoxalin-1-one (ODQ), an sGC-oxidizing inhibitor, enhanced cinaciguat-induced pulmonary vasodilation by >120%. The pulmonary vasodilator effect of cinaciguat was prolonged, decreasing pulmonary vascular resistance for >1.5 h after brief infusion. In vitro stimulation of ovine fetal pulmonary artery smooth muscle cells with cinaciguat after ODQ treatment resulted in a 14-fold increase in cGMP compared with non-ODQ-treated cells. We conclude that cinaciguat causes potent and sustained fetal pulmonary vasodilation that is augmented in the presence of oxidized sGC and speculate that cinaciguat may have therapeutic potential for severe neonatal pulmonary hypertension.

Inhaled nitric oxide in the term newborn

Inhaled nitric oxide is a selective pulmonary vasodilator that serves integral diagnostic and therapeutic roles in the clinical management of near-term and term newborns with hypoxemic respiratory failure and pulmonary hypertension. Its proper use and potential limitations in current clinical practice are reviewed.

Neonatal pulmonary hypertension treated with inhaled nitric oxide and high-frequency ventilation

Term and near-term infants with pulmonary hypertension are frequently treated with inhaled nitric oxide. This therapy can be delivered with high-frequency ventilation, but there has been limited study of the relative effectiveness of high-frequency jet ventilation and high-frequency oscillatory ventilation.

OBJECTIVE

To compare short-term clinical outcomes of neonates with pulmonary hypertension treated with inhaled nitric oxide plus either high-frequency jet ventilation or high-frequency oscillatory ventilation.

STUDY DESIGN

Study infants met the following criteria: >or=35 weeks gestation, respiratory failure with pulmonary hypertension, no congenital malformations and treatment in the first week of life with inhaled nitric oxide plus either high-frequency jet ventilation (n=22) or high-frequency oscillatory ventilation (n=43). Data were collected from medical records.

RESULT

The jet ventilation and oscillatory ventilation groups were similar in terms of gestational age, but the jet ventilation group had less severe respiratory illness (that is, lower oxygenation index) just prior to initiation of the combination of nitric oxide and high-frequency ventilation. The jet ventilation group spent more hours on inhaled nitric oxide (71.4 versus 40.8; P=0.004) but was less likely to require extracorporeal membrane oxygenation (2(9%) versus 19(44%); P=0.004). No difference was found in the ages at which oxygen and high-frequency ventilation were discontinued.

CONCLUSION

Term and near-term neonates with pulmonary hypertension who require nitric oxide have similar short-term outcomes regardless of whether nitric oxide is delivered by high-frequency jet ventilation or high-frequency oscillatory ventilation.

Pulmonary circulatory effects of norepinephrine in newborn infants with persistent pulmonary hypertension

OBJECTIVE

To evaluate the respiratory and the pulmonary circulatory effects of norepinephrine in newborn infants with persistent pulmonary hypertension (PPHN)-induced cardiac dysfunction.

STUDY DESIGN

Inclusion criteria were: 1) Newborn infants >35 weeks gestational age; 2) PPHN treated with inhaled nitric oxide; and 3) symptoms of circulatory failure despite adequate fluid resuscitation. Lung function and pulmonary hemodynamic variables assessed with Doppler echocardiography were recorded prospectively before and after starting norepinephrine.

RESULTS

Eighteen newborns were included (gestational age: 37 +/- 3 weeks; birth weight: 2800 +/- 700 g). After starting norepinephrine, systemic pressure and left ventricular output increased respectively from 33 +/- 4 mm Hg to 49 +/- 4 mm Hg and from 172 +/- 79 mL/kg/min to 209+/-90 mL/kg/min (P < .05). Although the mechanical ventilatory variables have not been changed, the post-ductal transcutaneous arterial oxygen saturation increased from 89% +/- 1% to 95% +/- 4%, whereas the oxygen need decreased from 51% +/- 24% to 41% +/- 20% (P < .05). The pulmonary/systemic pressure ratio decreased from 0.98 +/- 0.1 to 0.87 +/- 0.1 (P < .05). Mean left pulmonary artery blood flow velocity increased by 20% (P < .05).

CONCLUSION

Norepinephrine may improve lung function in newborn infants with PPHN through a decrease in pulmonary/systemic artery pressure ratio and improved cardiac performance.

Fasudil inhibits the myogenic response in the fetal pulmonary circulation

In addition to high pulmonary vascular resistance (PVR) and low pulmonary blood flow, the fetal pulmonary circulation is characterized by mechanisms that oppose vasodilation. Past work suggests that high myogenic tone contributes to high PVR and may contribute to autoregulation of blood flow in the fetal lung. Rho-kinase (ROCK) can mediate the myogenic response in the adult systemic circulation, but whether high ROCK activity contributes to the myogenic response and modulates time-dependent vasodilation in the developing lung circulation are unknown. We studied the effects of fasudil, a ROCK inhibitor, on the hemodynamic response during acute compression of the ductus arteriosus (DA) in chronically prepared, late-gestation fetal sheep. Acute DA compression simultaneously induces two opposing responses: 1) blood flow-induced vasodilation through increased shear stress that is mediated by NO release and 2) stretch-induced vasoconstriction (i.e., the myogenic response). The myogenic response was assessed during acute DA compression after treatment with N(omega)-nitro-L-arginine, an inhibitor of nitric oxide synthase, to block flow-induced vasodilation and unmask the myogenic response. Intrapulmonary fasudil infusion (100 microg over 10 min) did not enhance flow-induced vasodilation during brief DA compression but reduced the myogenic response by 90% (P<0.05). During prolonged DA compression, fasudil prevented the time-dependent decline in left pulmonary artery blood flow at 2 h (183+/-29 vs. 110+/-11 ml/min with and without fasudil, respectively; P<0.001). We conclude that high ROCK activity opposes pulmonary vasodilation in utero and that the myogenic response maintains high PVR in the normal fetal lung through ROCK activation.

Effects of sildenafil on the fetal growth of guinea pigs and their ability to survive induced intrapartum asphyxia

OBJECTIVE

Our goal was to determine whether sildenafil increased fetal weight and favored fetal tolerance to induced asphyxia at birth in guinea pigs.

STUDY DESIGN

Twenty guinea pigs were randomly allocated to placebo (n = 10) or sildenafil 50 microg/kg (n = 5) or 500 microg/kg (n = 5), starting from day 35 of gestation to delivery. Fetuses were delivered by cesarean section. Fetal asphyxia was induced by clamping the umbilical cord at birth for 5 minutes.

RESULTS

Sildenafil protected the pups against induced asphyxia at birth in a dose-dependent manner (eg, partial pressure (tension) of carbon dioxide levels were 75.9 +/- 19.3, 66.9 +/- 18.8, and 54.8 +/- 13.0 in the control and low- and high-dose sildenafil groups, respectively). The high-dose sildenafil group of piglets gained 1.5 times more body weight.

CONCLUSION

In guinea pigs, low doses of sildenafil administered from day 35 to the end of gestation favored fetal tolerability to induced intrapartum asphyxia. High doses of sildenafil increased fetal weight.

Intravenous tezosentan improves gas exchange and hemodynamics in acute lung injury secondary to meconium aspiration

OBJECTIVE

Meconium aspiration induces acute lung injury (ALI) and subsequent pulmonary arterial hypertension (PAH) which may lead to right ventricular failure. Increase of endothelin-1, thromboxane-A, and phosphodiesterases are discussed molecular mechanisms. We investigated the intrapulmonary and hemodynamic effects of the intravenous dual endothelin A and B receptor blocker tezosentan and inhalational iloprost in a model of ALI due to meconium aspiration.

DESIGN

Animal study.

SETTING

University-affiliated research laboratory.

SUBJECTS

White farm pigs.

INTERVENTIONS

Acute lung injury was induced in 24 pigs by instillation of meconium. Animals were randomly assigned to four groups to receive either intravenous tezosentan, inhalational iloprost, or combined tezosentan and iloprost, or to serve as controls.

MEASUREMENTS AND RESULTS

After meconium aspiration-induced lung injury each treatment increased oxyhemoglobin saturations (TEZO: 88 +/- 6% (p = 0.02), ILO: 85 +/- 13% (p = 0.05), TEZO-ILO: 89 +/- 6% (p = 0.02), control: 70 +/- 18%). TEZO but not ILO significantly decreased pulmonary arterial pressure and pulmonary vascular resistance (both p < 0.01). ILO alone decreased intrapulmonary shunt blood flow (p < 0.01). Compared with control, TEZO-ILO yielded the highest arterial partial pressure of oxygen (70 +/- 6 torr vs.49 +/- 9 torr, p = 0.04), although it decreased arterial blood pressure (change from 71 +/- 13 mmHg to 62 +/- 12 mmHg vs.85 +/- 14 mmHg to 80 +/- 11 mmHg (p = 0.01).

CONCLUSIONS

Intravenous TEZO improves pulmonary gas exchange and hemodynamics in experimental acute lung injury secondary to meconium aspiration. Inhaled ILO improves gas exchange only, thereby reducing intrapulmonary shunt blood flow. Combination of TEZO and ILO marginally improves pulmonary gas exchange at the disadvantage of pulmonary selectivity.

ABCA3 deficiency presenting as persistent pulmonary hypertension of the newborn

A newborn with persistent pulmonary hypertension (PH) unresponsive to conventional therapies was found to be homozygous for a mutation in the gene encoding adenosine triphosphate binding cassette protein, member A3 (ABCA3). Most causes of PH respond to lung recruitment, inhaled nitric oxide, and hemodynamic support. When PH is prolonged and does not respond to standard therapies, genetic causes of surfactant abnormalities should be considered in the differential diagnosis.

Inhaled nitric oxide treatment inhibits neuronal injury after meconium aspiration in piglets

BACKGROUND

Meconium aspiration-induced hypertensive lung injury is frequently associated with neuronal damage. Inhaled nitric oxide (iNO) is widely used in the treatment of pulmonary hypertension, but its effects on the brain are poorly known.

AIMS

The aim of this study was to determine the effects of iNO treatment on the neuronal tissue after meconium aspiration.

STUDY DESIGN

71 anesthetized, catheterized and ventilated newborn piglets were studied for 6 h. Thirty-five piglets were instilled with a bolus of human meconium intratracheally and 36 piglets with saline instillation served as controls. Nineteen meconium piglets and 17 control piglets were continuously treated with 20 ppm of iNO, started at 30 min after the insult. The extent of neuronal injury was analysed histologically, and the levels of brain tissue lipid peroxidation products, reduced glutathione (GSH), myeloperoxidase activity and oxidized DNA were analysed as indicators of oxidative stress.

RESULTS

iNO treatment diminished the pulmonary hypertensive response caused by meconium aspiration, but did not change systemic or carotid hemodynamics. NO administration was associated with reduced neuronal injury and diminished amount of oxidized DNA in the hippocampus of the meconium piglets. Further, iNO treatment was associated with decreased level of GSH in the cortex, but no change in lipid peroxidation production or myeloperoxidase activity was detected in any of the studied brain areas.

CONCLUSIONS

Our results suggest that iNO treatment may inhibit DNA oxidation and neuronal injury in the hippocampus, associated with newborn meconium aspiration.

Persistent pulmonary hypertension of the newborn: pathogenesis, etiology, and management

Persistent pulmonary hypertension of the newborn (PPHN) is characterized by severe hypoxemia shortly after birth, absence of cyanotic congenital heart disease, marked pulmonary hypertension, and vasoreactivity with extrapulmonary right-to-left shunting of blood across the ductus arteriosus and/or foramen ovale. In utero, a number of factors determine the normally high vascular resistance in the fetal pulmonary circulation, which results in a higher pulmonary compared with systemic vascular pressure. However, abnormal conditions may arise antenatally, during, or soon after birth resulting in the failure of the pulmonary vascular resistance to normally decrease as the circulation evolves from a fetal to a postnatal state. This results in cyanosis due to right-to-left shunting of blood across normally existing cardiovascular channels (foramen ovale or ductus arteriosus) secondary to high pulmonary versus systemic pressure. The diagnosis is made by characteristic lability in oxygenation of the infant, echocardiographic evidence of increased pulmonary pressure, with demonstrable shunts across the ductus arteriosus or foramen ovale, and the absence of cyanotic heart disease lesions. Management of the disease includes treatment of underlying causes, sedation and analgesia, maintenance of adequate systemic blood pressure, and ventilator and pharmacologic measures to increase pulmonary vasodilatation, decrease pulmonary vascular resistance, increase blood and tissue oxygenation, and normalize blood pH. Inhaled nitric oxide has been one of the latest measures to successfully treat PPHN and significantly reduce the need for extracorporeal membrane oxygenation.

Recent advances in the pathogenesis and treatment of persistent pulmonary hypertension of the newborn

Persistent pulmonary hypertension of the newborn (PPHN) is a clinical syndrome characterized by failure of the lung circulation to achieve or sustain the normal drop in pulmonary vascular resistance (PVR) at birth. Past laboratory studies identified the important role of nitric oxide (NO)-cGMP signaling in the regulation of the perinatal lung circulation, leading to the development and application of inhaled NO therapy for PPHN. Although inhaled NO therapy has improved the clinical course and outcomes of many infants, pulmonary hypertension can be refractory to inhaled NO, suggesting the need for additional approaches to severe PPHN. To develop novel therapeutic strategies for PPHN, ongoing studies continue to explore basic mechanisms underlying the pathobiology of PPHN in experimental models, including strategies to enhance NO-cGMP signaling. Recent studies have demonstrated that impaired vascular endothelial growth factor (VEGF) signaling may contribute to the pathogenesis of PPHN. Lung VEGF expression is markedly decreased in an experimental model of PPHN in sheep; inhibition of VEGF mimics the structural and functional abnormalities of PPHN, and VEGF treatment improves pulmonary hypertension through upregulation of NO production. Other studies have shown that enhanced NO-cGMP activity through the use of cGMP-specific phosphodiesterase inhibitors (sildenafil), soluble guanylate cyclase activators (BAY 41-2272), superoxide scavengers (superoxide dismutase), and rho-kinase inhibitors (fasudil) can lead to potent and sustained pulmonary vasodilation in experimental PPHN. Overall, these laboratory studies suggest novel pharmacologic strategies for the treatment of refractory PPHN.

Chronic intrauterine pulmonary hypertension increases capacitative calcium entry in fetal pulmonary artery smooth muscle cells

Oxygen causes perinatal pulmonary dilatation. Although fetal pulmonary artery smooth muscle cells (PA SMC) normally respond to an acute increase in oxygen (O2) tension with a decrease in cytosolic calcium ([Ca2+]i), an acute increase in O2 tension has no net effect on [Ca(2+)](i) in PA SMC derived from lambs with chronic intrauterine pulmonary hypertension (PHTN). The present experimental series tests the hypothesis that an acute increase in O2 tension decreases capacitative calcium entry (CCE) in normal, but not hypertensive, fetal PA SMC. PA SMC were isolated from late-gestation fetal lambs after either ligation of the ductus arteriosus (PHTN) or sham (control) operation at 127 days gestation. PA SMC were isolated from the distal PA (>or=4th generation) and maintained under hypoxic conditions ( approximately 25 Torr) in primary culture. After fura 2 loading, apparent [Ca2+]i in PA SMC was determined as the ratio of 340- to 380-nm fluorescence intensity. Under both hypoxic and normoxic conditions, cyclopiazonic acid (CPA) increased [Ca2+]i more in PHTN than in control PA SMC. CCE was determined in PA SMC under hypoxic and normoxic conditions, after superfusion with zero extracellular Ca2+ and intracellular store depletion with CPA, followed by superfusion with Ca2+-containing solution, in the presence of the voltage-operated calcium channel blockade. CCE was increased in PHTN compared with control PA SMC under conditions of both acute and sustained normoxia. Transient receptor potential channel gene expression was greater in control compared with PHTN PA SMC. PHTN may compromise perinatal pulmonary vasodilation, in part, by modulating PA SMC CCE.

Vascular endothelium summary statement V: Pulmonary hypertension and acute lung injury: public health implications

Although relatively rare, pulmonary hypertension can be devastating for those individuals who are affected and has significant societal implications. The 2003 WHO classification separates PAH (idiopathic, specific disease linked) from pulmonary hypertension related to lung disease, thromboembolic disease, and pulmonary venous hypertension. Another form of pulmonary hypertension, persistent pulmonary hypertension (PPHN), occurs in the newborn. In general, PPHN is thought to be responsible for approximately 10% of admissions to neonatal intensive care units and can be a complicating factor in 5 of 1000 live births. Acute lung injury (ALI) and the acute respiratory distress syndrome (ARDS) are complex disorders that pose a significant threat to critically ill patients. They are usually related to direct lung injury or indirect injury from sepsis, trauma, and other disorders. Although these pulmonary disorders reflect distinct pathophysiologic mechanisms, current evidence strongly suggests that a common denominator underlying many of the established molecular and cellular elements is endothelial cell activation and dysfunction. This summary statement briefly summarizes the state of the science and suggests future avenues of public health research.

Interaction of KATP channels and endothelin-1 in lambs with persistent pulmonary hypertension of the newborn

Persistent pulmonary hypertension of the newborn is a life-threatening condition in which half of infants fail to respond to inhaled nitric oxide. Development of new therapeutic pathways is crucial. The adenosine triphosphate (ATP)-sensitive potassium channels (K(ATP)) may be important in this condition. Concentration-response curves to the K(ATP) channel opener (SR47063) were performed in isolated pulmonary arterial rings from normal newborn lambs (n = 8) and pulmonary hypertensive lambs (n = 7) induced by intrauterine ductus arteriosus ligation. The effect of endothelin (ET) receptor antagonists was analyzed. Expression in the lung of the subunit Kir 6.1 of the K(ATP) channel and of ET were analyzed using Western blot and immunohistochemistry. Relaxation to SR47063 was increased in ligated animals compared with the control group. Endothelium removal enhanced this response in ligated animals (p < 0.01). The inhibitory effect of the endothelium was reversed by the Endothelin-A receptor (ET-A) antagonist BQ 123 (p < 0.01). Kir 6.1 expression was not different between groups and that of endothelin-1 (ET-1) was increased threefold in ligated animals (p = 0.007). In pulmonary hypertensive lambs, vasodilation to K(ATP) channel openers was enhanced compared with controls and further potentiated by ET-A blockade. These data might lead to new therapeutic strategies in infants with pulmonary hypertension.

DOSE RESPONSE OF INTRAVENOUS SILDENAFIL ON SYSTEMIC AND REGIONAL HEMODYNAMICS IN HYPOXIC NEONATAL PIGLETS

In neonates with acute pulmonary hypertension (PHT), the dose-response effect of sildenafil citrate, a selective phosphodiesterase-5 inhibitor that can alleviate PHT, has not been detailedly examined. We tested the hypothesis that the treatment of hypoxia-induced acute PHT with sildenafil would dose-dependently reduce the elevated pulmonary and systemic arterial pressures (PAP and SAP, respectively) with no effect on the oxygenation in newborn animals. We also examined the regional hemodynamic responses. Using a randomized controlled design, piglets (age range, 1-3 days; weight range, 1.5-2.1 kg) were anesthetized and acutely instrumented to measure cardiac index, left common carotid, superior mesenteric and left renal arterial flow indexes, SAP, and PAP. After stabilization, hypoxia was induced with fractional inspired oxygen concentration at 0.15 and, subsequently, piglets were randomized to receive i.v. sildenafil at 0.06, 0.2, or 2.0 mg/kg per hour or normal saline (controls) for 90 min (n = 6 each). Within 30 min of hypoxia (PaO2, 31 +/- 5 mmHg), the piglets developed PHT (PAP, 33 +/- 5 vs. 26 +/- 4 mmHg at baseline; P < 0.05. Sildenafil dose-dependently reduced the hypoxia-induced PHT (PAP at 90 min: 33 +/- 6, 29 +/- 6, and 26 +/- 6 mmHg of 0.06, 0.2, and 2.0 mg/kg per hour, respectively, vs. 44 +/- 8 mmHg of controls; P < 0.05. Sildenafil at 2.0 mg/kg per hour had the greatest decrease in SAP (P < 0.05) with no significant change at 0.06 and 0.2 mg/kg per hour. Pulmonary selectivity (PAP:SAP ratio) was best in the group treated with 0.2 mg/kg per hour dosage of sildenafil (P < 0.05). There were no differences in cardiac index and regional flow indexes between groups. Although hypoxia decreased oxygen delivery and increased oxygen extraction with no significant effect on oxygen consumption, the administration of sildenafil did not affect the oxygen metabolism (vs. controls). In neonatal piglets, i.v. sildenafil dose-dependently alleviates the hypoxia-induced acute PHT, with the best pulmonary selectivity at 0.2 mg/kg per hour, and shows no significant effect on regional circulation and oxygen metabolism.

pH and nitric oxide synthase activity and expression in bovine aortic endothelial cells

AIM

Nitric oxide (NO) plays an important role in the transition from intrauterine to extrauterine life. If this transition fails, a condition called persistent pulmonary hypertension of the neonate (PPHN) may develop. The current treatment modalities for this disease include induction of alkalosis by hyperventilation or alkali infusion, inhaled nitric oxide (iNO) and extracorporeal membrane oxygenation. There is evidence from animal studies that the elevated pH, not the low pCO2 is responsible for the resultant pulmonary vasodilatation. In this study, we examined the effect of pH on the activity and expression of endothelial nitric oxide synthase (eNOS) in cultured bovine aortic endothelial cells (BAEC) as a possible explanation for the pH dependent drop in pulmonary vascular resistance.

METHODS

BAEC were exposed to a pH gradient of 7.1-7.6 for 4 h (short-term) and 16 h (long-term). Standard Western blotting technique was used to detect expression of eNOS. Activity was measured by an indirect assay using bovine aortic smooth muscle cells (BASM) as reporter cells and measuring cGMP levels as a marker of NO production. The cells were exposed to the pH gradient for a total of 4 h and measurement were made at 30, 60 and 90 min, and 2, 3 and 4 hours.

RESULTS

eNOS activity and expression remained unchanged during the four and sixteen hours of exposure.

CONCLUSION

In this in vitro experiment, we could not demonstrate an alkalosis-induced increase in eNOS activity and expression. The clinically observed pH dependent vasodilatation does not appear to be directly mediated through the induction of eNOS.

Effect of intravenous sildenafil on pulmonary hemodynamics and gas exchange in the presence and absence of acute lung injury in piglets

Sildenafil is becoming increasingly popular for the treatment of pulmonary hypertension. However, there are potential concerns regarding its effects on oxygenation and systemic hemodynamics that could theoretically reduce its utility in the neonatal population. We performed a prospective cumulative dose-response study of increasing doses of i.v. sildenafil (0.4, 1, and 3 mg/kg) on hemodynamics and oxygenation in 32 anesthetized piglets, of which 17 had meconium-induced pulmonary hypertension and lung injury, and 15 did not. Sildenafil caused a reduction in mean pulmonary artery pressure and pulmonary vascular resistance (PVR) at all doses, in non-lung-injured animals. There was no difference in pulmonary hemodynamics between doses. Oxygenation index [OI = mean airway pressure (cm H2O) * FiO2 * 100/PaO2 (mm Hg)] did not reach critical levels at any dose. In lung-injured animals, sildenafil also reduced mean pulmonary artery pressure and PVR by 30%. Again, this effect was achieved at the lowest dose, without subsequent changes at higher doses. However, in lung-injured animals, sildenafil produced a dose-related increase in oxygenation index. Sildenafil reduced the systemic vascular resistance (SVR) at the lowest dose in lung-injured animals, but this occurred only at higher doses in non-lung-injured animals. In conclusion, sildenafil is a potent pulmonary vasodilator. However, it should be administered with caution in the presence of lung injury because of a dose-related increase in oxygenation index and concomitant systemic vasodilatation.

Inhaled nitric oxide in term and preterm infants

Nitric oxide (NO) is a gas that has potent vasodilator properties. It can be administered via inhalation in situations where NO production is impaired and results in vasodilatation of the pulmonary capillaries. In term infants, the administration of inhaled NO, at a dose of 20 parts per million, may reduce the need for extracorporeal membrane oxygenation by reducing pulmonary vascular resistance and improving oxygenation. Inhaled NO is an approved therapy in term babies with severe hypoxemic respiratory failure. In premature infants, inhaled NO may increase bleeding time and decrease platelet aggregation resulting in an increased risk for intraventricular hemorrhage. Early administration of inhaled NO may also potentially decrease the risk for developing chronic lung disease in premature infants. However, since studies show conflicting results, inhaled NO should only be used in premature neonates following investigational review board approved protocols.

Chronic intrauterine pulmonary hypertension selectively modifies pulmonary artery smooth muscle cell gene expression

Pulmonary artery smooth muscle cell (PASMC) relaxation at birth results from an increase in cytosolic cGMP, cGMP-dependent and kinase-mediated activation of the Ca2+-sensitive K+channel (KCa), and closure of voltage-operated Ca2+channels (VOCC). How chronic intrauterine pulmonary hypertension compromises perinatal pulmonary vasodilation remains unknown. We tested the hypothesis that chronic intrauterine pulmonary hypertension selectively modifies gene expression to mitigate perinatal pulmonary vasodilation mediated by the cGMP kinase-KCa-VOCC pathway. PASMC were isolated from late-gestation fetal lambs that had undergone either ligation of the ductus arteriosus (hypertensive) or sham operation (control) at 127 days of gestation and were maintained under either hypoxic (∼25 Torr) or normoxic (∼120 Torr) conditions in primary culture. We studied mRNA levels for cGMP kinase Iα (PKG-1α), the α-chain of VOCC (Cav1.2), and the α-subunit of the KCachannel. Compared with control PASMC, hypertensive PASMC had decreased VOCC, KCa, and PKG-1α expression. In response to sustained normoxia, expression of VOCC and KCachannel decreased and expression of PKG-1α increased. In contrast, sustained normoxia had no effect on PKG-1α levels and an attenuated effect on VOCC and KCachannel expression in hypertensive PASMC. Protein expression of PKG-1α was consistent with the mRNA data. We conclude that chronic intrauterine pulmonary hypertension decreases PKG expression and mitigates the genetic effects of sustained normoxia on pulmonary vasodilation, because gene expression remains compromised even after sustained exposure to normoxia.

Tezosentan decreases pulmonary artery pressure and improves survival rate in an animal model of meconium aspiration

Acute pulmonary arterial hypertension in acute lung injury aggravates the clinical course and complicates treatment. Increased release and turnover of endogenous endothelin-1 is known to be a major determinant in the pathophysiology of pulmonary arterial hypertension of various etiologies. We tested whether intravenous tezosentan, a dual endothelin receptor antagonist, reduced pulmonary artery pressure in a pig model of acute lung injury induced by meconium aspiration. Acute pulmonary arterial hypertension was induced in 12 anesthetized and instrumented pigs by instillation of human pooled meconium in a 20% solution. Hemodynamic and gas exchange parameters were recorded every 30 min. Six animals received tezosentan 5 mg/kg after 0 and 90 min; six animals served as controls. Tezosentan led to a decrease of mean pulmonary artery pressure (PAP) from 33.4 +/- 4.0 mm Hg to 24.7 +/- 2.1 mm Hg and pulmonary vascular resistance (PVR) from 7.8 +/- 1.4 mm Hg.L(-1).min.m2 to 5.2 +/- 0.7 mm Hg.L(-1).min.m2. All animals treated with tezosentan survived, whereas in the control group four out of six animals died. Tezosentan improved survival and decreased pulmonary artery pressure in a porcine model of acute pulmonary arterial hypertension after meconium aspiration. Tezosentan has the potential for effective pharmacological treatment of pulmonary arterial hypertension following acute lung injury.

Inhaled nitric oxide therapy in children

Inhaled nitric oxide therapy improves oxygenation and reduces the need for treatment with extracorporeal membrane oxygenation in term newborns with hypoxaemic respiratory failure and persistent pulmonary hypertension. In this review, we summarise the current status of iNO therapy in the newborn and the potential role of iNO in other paediatric populations.