Pulmonary hypertension impairs alveolarization and reduces lung growth in the ovine fetus

A comprehensive study on machine learning models combining with oversampling for bronchopulmonary dysplasia-associated pulmonary hypertension in very preterm infants

BACKGROUND

Bronchopulmonary dysplasia-associated pulmonary hypertension (BPD-PH) remains a devastating clinical complication seriously affecting the therapeutic outcome of preterm infants. Hence, early prevention and timely diagnosis prior to pathological change is the key to reducing morbidity and improving prognosis. Our primary objective is to utilize machine learning techniques to build predictive models that could accurately identify BPD infants at risk of developing PH.

METHODS

The data utilized in this study were collected from neonatology departments of four tertiary-level hospitals in China. To address the issue of imbalanced data, oversampling algorithms synthetic minority over-sampling technique (SMOTE) was applied to improve the model.

RESULTS

Seven hundred sixty one clinical records were collected in our study. Following data pre-processing and feature selection, 5 of the 46 features were used to build models, including duration of invasive respiratory support (day), the severity of BPD, ventilator-associated pneumonia, pulmonary hemorrhage, and early-onset PH. Four machine learning models were applied to predictive learning, and after comprehensive selection a model was ultimately selected. The model achieved 93.8% sensitivity, 85.0% accuracy, and 0.933 AUC. A score of the logistic regression formula greater than 0 was identified as a warning sign of BPD-PH.

CONCLUSIONS

We comprehensively compared different machine learning models and ultimately obtained a good prognosis model which was sufficient to support pediatric clinicians to make early diagnosis and formulate a better treatment plan for pediatric patients with BPD-PH.

Maternal hypertensive disorders and survival without major morbidities among extremely low gestation newborns

OBJECTIVE

Evaluate if odds of survival without major morbidity are higher among extremely low gestation neonates (ELGANs) born to mothers with chronic hypertension (cHTN) or hypertensive disorders of pregnancy (HDP) compared to ELGANs born to mothers without hypertension (HTN).

STUDY DESIGN

Retrospective study of prospectively collected data from the Eunice Kennedy Shriver National Institute of Child Health and Human Development Neonatal Research Network. Included children had a birthweight of 401-1000 g and/or gestational age of 220/7 to 286/7 wks. The primary outcome was survival to discharge without major morbidity. Multivariable regression models were used to compare outcomes among ELGANs born to women with cHTN, HDP, and no HTN.

RESULTS

Survival without morbidities for newborns of mothers with no HTN, cHTN and HDP (29.1%, 32.9%, 37.0% respectively) did not differ after adjustment.

CONCLUSION

After adjusting for contributing variables maternal HTN is not associated with improved survival free of morbidity among ELGANs.

TRIALS REGISTRATION

clinicaltrials.gov Identifier: NCT00063063 (generic database).

Impaired cell-cell communication and axon guidance because of pulmonary hypoperfusion during postnatal alveolar development

BACKGROUND

Pulmonary hypoperfusion is common in children with congenital heart diseases (CHDs) or pulmonary hypertension (PH) and causes adult pulmonary dysplasia. Systematic reviews have shown that some children with CHDs or PH have mitigated clinical outcomes with COVID-19. Understanding the effects of pulmonary hypoperfusion on postnatal alveolar development may aid in the development of methods to improve the pulmonary function of children with CHDs or PH and improve their care during the COVID-19 pandemic, which is characterized by cytokine storm and persistent inflammation.

METHODS AND RESULTS

We created a neonatal pulmonary hypoperfusion model through pulmonary artery banding (PAB) surgery at postnatal day 1 (P1). Alveolar dysplasia was confirmed by gross and histological examination at P21. Transcriptomic analysis of pulmonary tissues at P7(alveolar stage 2) and P14(alveolar stage 4) revealed that the postnatal alveolar development track had been changed due to pulmonary hypoperfusion. Under the condition of pulmonary hypoperfusion, the cell-cell communication and axon guidance, which both determine the final number of alveoli, were lost; instead, there was hyperactive cell cycle activity. The transcriptomic results were further confirmed by the examination of axon guidance and cell cycle markers. Because axon guidance controls inflammation and immune cell activation, the loss of axon guidance may explain the lack of severe COVID-19 cases among children with CHDs or PH accompanied by pulmonary hypoperfusion.

CONCLUSIONS

This study suggested that promoting cell-cell communication or supplementation with guidance molecules may treat pulmonary hypoperfusion-induced alveolar dysplasia, and that COVID-19 is less likely to cause a cytokine storm in children with CHD or PH accompanied by pulmonary hypoperfusion.

The newborn sheep translational model for pulmonary arterial hypertension of the neonate at high altitude

Chronic hypoxia during gestation induces greater occurrence of perinatal complications such as intrauterine growth restriction, fetal hypoxia, newborn asphyxia, and respiratory distress, among others. This condition may also cause a failure in the transition of the fetal to neonatal circulation, inducing pulmonary arterial hypertension of the neonate (PAHN), a syndrome that involves pulmonary vascular dysfunction, increased vasoconstrictor tone and pathological remodeling. As this syndrome has a relatively low prevalence in lowlands (~7 per 1000 live births) and very little is known about its prevalence and clinical evolution in highlands (above 2500 meters), our understanding is very limited. Therefore, studies on appropriate animal models have been crucial to comprehend the mechanisms underlying this pathology. Considering the strengths and weaknesses of any animal model of human disease is fundamental to achieve an effective and meaningful translation to clinical practice. The sheep model has been used to study the normal and abnormal cardiovascular development of the fetus and the neonate for almost a century. The aim of this review is to highlight the advances in our knowledge on the programming of cardiopulmonary function with the use of high-altitude newborn sheep as a translational model of PAHN.

Decreased Cyclic GMP-protein Kinase G signaling impairs Angiogenesis in a Lamb Model of Persistent Pulmonary Hypertension of Newborn

Impaired angiogenesis function of pulmonary artery endothelial cells (PAEC) contributes to persistent pulmonary hypertension of the newborn (PPHN). Decreased nitric oxide (NO) levels in PPHN lead to impaired mitochondrial biogenesis and angiogenesis in the lung; the mechanisms remain unclear. We hypothesized that decreased cGMP-Protein kinase G (PKG) signaling downstream of NO leads to decreased mitochondrial biogenesis and angiogenesis in PPHN. PPHN was induced by ductus arteriosus constriction from 128-136d gestation in fetal lambs. Controls were gestation matched lambs without ductal constriction. PAEC isolated from PPHN lambs were treated with soluble guanylyl cyclase activator, cinaciguat, PKG activator, 8-Br-cGMP or phosphodiesterase-V inhibitor, sildenafil. Lysates were immunoblotted for mitochondrial transcription factors and electron transport chain (ETC) complex proteins I-V. In vitro angiogenesis of PAEC was evaluated by tube formation and scratch recovery assays. cGMP levels were measured by enzyme immunoassay. Fetal lambs with ductal constriction were given sildenafil or control saline by continuous infusion in utero and lung histology, capillary counts, vessel density and right ventricular pressure were assessed at birth. PPHN PAEC showed decreased mitochondrial transcription factors, ETC proteins, and in vitro tube formation and cell migration; these were restored by cinaciguat, 8-Br-cGMP and sildenafil. Cinaciguat and sildenafil increased cGMP levels in PPHN PAEC. Radial alveolar and capillary counts and vessel density were lower and RV pressure and Fulton index higher in PPHN lungs; these were improved by in utero sildenafil infusion. cGMP-PKG signaling is a potential therapeutic target to restore decreased mitochondrial biogenesis and angiogenesis in PPHN.

AMP-Kinase Dysfunction Alters Notch Ligands to Impair Angiogenesis in Neonatal Pulmonary Hypertension

Decreased angiogenesis contributes to persistent pulmonary hypertension of the newborn (PPHN); mechanisms remain unclear. AMPK (5'AMP activated protein kinase) is a key regulator of cell metabolism. We investigated the hypothesis that a decrease in AMPK function leads to mitochondrial dysfunction and altered balance of notch ligands delta-like 4 (DLL4) and Jagged 1 (Jag1) to impair angiogenesis in PPHN. Studies were done in fetal lambs with PPHN induced by prenatal ductus arteriosus constriction and gestation-matched control lambs. PPHN lambs were treated with saline or AMPK agonist metformin. Angiogenesis was assessed in lungs with micro-computed tomography angiography and histology. AMPK function; expression of mitochondrial electron transport chain (ETC) complex proteins I-V, Dll4, and Jag1; mitochondrial number; and in vitro angiogenesis function were assessed in pulmonary artery endothelial cells (PAEC) from control and PPHN lambs. AMPK function was decreased in PPHN PAEC and lung sections. Expression of mitochondrial transcription factor, PGC-1α, ETC complex proteins I-V, and mitochondrial number were decreased in PPHN. In vitro angiogenesis of PAEC and capillary number and vessel volume fraction in the lung were decreased in PPHN. Expression of DLL4 was increased and Jag1 was decreased in PAEC from PPHN lambs. AMPK agonists A769662 and metformin increased the mitochondrial complex proteins and number, in vitro angiogenesis, and Jag1 levels and decreased DLL4 levels in PPHN PAEC. Infusion of metformin in vivo increased the vessel density in PPHN lungs. Decreased AMPK function contributes to impaired angiogenesis in PPHN by altered balance of notch ligands in PPHN.

Transcriptomic modifications in developmental cardiopulmonary adaptations to chronic hypoxia using a murine model of simulated high-altitude exposure

Mechanisms driving adaptive developmental responses to chronic high-altitude (HA) exposure are incompletely known. We developed a novel rat model mimicking the human condition of cardiopulmonary adaptation to HA starting at conception and spanning the in utero and postnatal timeframe. We assessed lung growth and cardiopulmonary structure and function and performed transcriptome analyses to identify mechanisms facilitating developmental adaptations to chronic hypoxia. To generate the model, breeding pairs of Sprague-Dawley rats were exposed to hypobaric hypoxia (equivalent to 9,000 ft elevation). Mating, pregnancy, and delivery occurred in hypoxic conditions. Six weeks postpartum, structural and functional data were collected in the offspring. RNA-Seq was performed on right ventricle (RV) and lung tissue. Age-matched breeding pairs and offspring under room air (RA) conditions served as controls. Hypoxic rats exhibited significantly lower body weights and higher hematocrit levels, alveolar volumes, pulmonary diffusion capacities, RV mass, and RV systolic pressure, as well as increased pulmonary artery remodeling. RNA-Seq analyses revealed multiple differentially expressed genes in lungs and RVs from hypoxic rats. Although there was considerable similarity between hypoxic lungs and RVs compared with RA controls, several upstream regulators unique to lung or RV were identified. We noted a pattern of immune downregulation and regulation patterns of immune and hormonal mediators similar to the genome from patients with pulmonary arterial hypertension. In summary, we developed a novel murine model of chronic hypoxia exposure that demonstrates functional and structural phenotypes similar to human adaptation. We identified transcriptomic alterations that suggest potential mechanisms for adaptation to chronic HA.

Phenotypes of Bronchopulmonary Dysplasia in Adults

Bronchopulmonary dysplasia (BPD), first described by Northway in 1967, is a process of neonatal lung injury that is most strongly associated with prematurity. The "old" form of the disease associated with the oxidative damage and volutrauma from perinatal mechanical ventilation has been increasingly supplanted by a "new" form resulting from interrupted growth of the lung at earlier stages of fetal development. Given the significant improvement in the survival of children with BPD since the 1980s, many more of these patients are living into adulthood and are being seen in adult pulmonary practices. In this review, we present three brief vignettes of patients from our practice to introduce three of the major patterns of disease seen in adult survivors of BPD, namely, asthma-like disease, obstructive lung disease, and pulmonary hypertension. Additional factors shown to affect the lives of adult BPD survivors are also discussed. Finally, we discuss insights into the process of transitioning these complex patients from pediatric to adult pulmonary practices. As survivors of BPD enter adulthood and continue to require specialty pulmonary care, awareness of the disease's varied manifestations and responses to treatment will become increasingly important.

Altered hypoxia-inducible factor-1α (HIF-1α) signaling contributes to impaired angiogenesis in fetal lambs with persistent pulmonary hypertension of the newborn (PPHN)

Previous studies in adult pulmonary hypertension reported that increased hypoxia-inducible factor-1α (HIF-1α) signaling contributes to pulmonary vascular remodeling. However, alterations in endothelial HIF-1α signaling and its contribution to impaired angiogenesis in persistent pulmonary hypertension of the newborn (PPHN) remain unclear. We investigated the hypothesis that HIF-1α levels are increased in lung endothelial cells in PPHN and contribute to impaired angiogenesis function. We examined HIF-1α expression and promoter activity in the isolated pulmonary artery endothelial cells (PAEC) from fetal lambs with or without PPHN induced by prenatal ductus arteriosus constriction. We measured the levels of HIF-1α downstream targets, vascular endothelial growth factor (VEGF) and glycolytic protein, hexokinase 2 (Hek-2) in PAEC from PPHN, and control lambs. We examined the effect of small interfering-RNA (siRNA) mediated knockdown of native HIF-1α on VEGF expression and in vitro angiogenesis function of PPHN-PAEC. HIF-1α protein levels were higher in the isolated PAEC from PPHN-lambs compared to controls. HIF-1α promoter activity and Hek-2 protein levels were higher in PPHN. VEGF protein levels and in vitro angiogenesis function were decreased in PAEC from PPHN lambs. HIF-1α silencing significantly increased the expression of VEGF and improved the angiogenesis function of PPHN PAEC. Aberrant HIF-1α signaling contributes to endothelial dysfunction and decreased angiogenesis in PPHN.

Dual ETA/ETB blockade with macitentan improves both vascular remodeling and angiogenesis in pulmonary arterial hypertension

Dysregulated metabolism and rarefaction of the capillary network play a critical role in pulmonary arterial hypertension (PAH) etiology. They are associated with a decrease in perfusion of the lungs, skeletal muscles, and right ventricle (RV). Previous studies suggested that endothelin-1 (ET-1) modulates both metabolism and angiogenesis. We hypothesized that dual ET_A/ET_B receptors blockade improves PAH by improving cell metabolism and promoting angiogenesis. Five weeks after disease induction, Sugen/hypoxic rats presented severe PAH with pulmonary artery (PA) remodeling, RV hypertrophy and capillary rarefaction in the lungs, RV, and skeletal muscles (microCT angiogram, lectin perfusion, CD31 staining). Two-week treatment with dual ET_A/ET_B receptors antagonist macitentan (30 mg/kg/d) significantly improved pulmonary hemodynamics, PA vascular remodeling, and RV function and hypertrophy compared to vehicle-treated animals (all P = 0.05). Moreover, macitentan markedly increased lung, RV and quadriceps perfusion, and microvascular density (all P = 0.05). In vitro, these effects were associated with increases in oxidative phosphorylation (oxPhox) and markedly reduced cell proliferation of PAH-PA smooth muscle cells (PASMCs) treated with macitentan without affecting apoptosis. While macitentan did not affect oxPhox, proliferation, and apoptosis of PAH-PA endothelial cells (PAECs), it significantly improved their angiogenic capacity (tube formation assay). Exposure of control PASMC and PAEC to ET-1 fully mimicked the PAH cells phenotype, thus confirming that ET-1 is implicated in both metabolism and angiogenesis abnormalities in PAH. Dual ET_A/ET_B receptor blockade improved the metabolic changes involved in PAH-PASMCs' proliferation and the angiogenic capacity of PAH-PAEC leading to an increased capillary density in lungs, RV, and skeletal muscles.

Nogo-B Receptor Modulates Pulmonary Artery Smooth Muscle Cell Function in Developing Lungs

Nogo-B and its receptor (NgBR) are involved in blood vessel growth in developing lungs, but their role in pulmonary artery smooth muscle cell (PASMC) growth is unknown. We hypothesized that NgBR regulates growth of PASMCs by modulating the function of endoplasmic reticulum (ER) and formation of reactive oxygen species (ROS). In utero constriction of the ductus arteriosus created pulmonary hypertension in fetal lambs (hypertensive fetal lamb [HTFL]). PASMCs isolated 8 days after surgery were assessed for the alteration of protein levels by immunoblots and ROS formation by dihydroethidium and Cell ROX deep red fluorescence. NgBR small interfering RNA and plasmid DNA were used to manipulate NgBR levels. Proliferation and wound healing were assessed by cell counts and scratch recovery assay, respectively. Acute ER stress was induced by tunicamycin. Differences of mitogen-activated protein kinase and Akt pathway activation in HTFL versus control PASMCs were evaluated. Results showed that HTFL PASMCs had decreased NgBR levels and increased proliferation, wound healing, ER stress, and ROS formation compared with controls. Knockdown of NgBR in control PASMCs generated a phenotype similar to HTFL, and overexpression in HTFL restored the defective phenotype to control. Decreased NgBR levels were associated with increased ROS formation in HTFL PASMCs. Subsequently, scavenging ROS decreased proliferation and wound healing. Mechanistically, ROS formation decreases NgBR expression, which induces ER stress. This leads to extracellular signal-regulated kinase pathway activation and PASMC phenotype alteration. Our data suggest that decreased NgBR expression in pulmonary hypertension of the newborn contributes to increased PASMC proliferation and oxidative stress, which lead to the pathogenesis of lung injury.

Altered vasoreactivity in neonatal rats with pulmonary hypertension associated with bronchopulmonary dysplasia: Implication of both eNOS phosphorylation and calcium signaling

Bronchopulmonary dysplasia (BPD) consists of an arrest of pulmonary vascular and alveolar growth, with persistent hypoplasia of the pulmonary microvasculature and alveolar simplification. In 25 to 40% of the cases, BPD is complicated by pulmonary hypertension (BPD-PH) that significantly increases the risk of morbidity. In vivo studies suggest that increased pulmonary vascular tone could contribute to late PH in BPD. Nevertheless, an alteration in vasoreactivity as well as the mechanisms involved remain to be confirmed. The purpose of this study was thus to assess changes in pulmonary vascular reactivity in a murine model of BPD-PH. Newborn Wistar rats were exposed to either room air (normoxia) or 90% O₂ (hyperoxia) for 14 days. Exposure to hyperoxia induced the well-known features of BPD-PH such as elevated right ventricular systolic pressure, right ventricular hypertrophy, pulmonary vascular remodeling and decreased pulmonary vascular density. Intrapulmonary arteries from hyperoxic pups showed decreased endothelium-dependent relaxation to acetylcholine without any alteration of relaxation to the NO-donor sodium nitroprusside. This functional alteration was associated with a decrease of lung eNOS phosphorylation at the Ser1177 activating site. In pups exposed to hyperoxia, serotonin and phenylephrine induced exacerbated contractile responses of intrapulmonary arteries as well as intracellular calcium response in pulmonary arterial smooth muscle cells (PASMC). Moreover, the amplitude of the store-operated Ca²⁺ entry (SOCE), induced by store depletion using a SERCA inhibitor, was significantly greater in PASMC from hyperoxic pups. Altogether, hyperoxia-induced BPD-PH alters the pulmonary arterial reactivity, with effects on both endothelial and smooth muscle functions. Reduced activating eNOS phosphorylation and enhanced Ca²⁺ signaling likely account for alterations of pulmonary arterial reactivity.

Consequences of a Maternal High-Fat Diet and Late Gestation Diabetes on the Developing Rat Lung

Rationale

Infants born to diabetic or obese mothers are at risk of respiratory distress and persistent pulmonary hypertension of the newborn (PPHN), conceivably through fuel-mediated pathogenic mechanisms. Prior research and preventative measures focus on controlling maternal hyperglycemia, but growing evidence suggests a role for additional circulating fuels including lipids. Little is known about the individual or additive effects of a maternal high-fat diet on fetal lung development.

Objective

The objective of this study was to determine the effects of a maternal high-fat diet, alone and alongside late-gestation diabetes, on lung alveologenesis and vasculogenesis, as well as to ascertain if consequences persist beyond the perinatal period.

Methods

A rat model was used to study lung development in offspring from control, diabetes-exposed, high-fat diet-exposed and combination-exposed pregnancies via morphometric, histologic (alveolarization and vasculogenesis) and physiologic (echocardiography, pulmonary function) analyses at birth and 3 weeks of age. Outcomes were interrogated for diet, diabetes and interaction effect using ANOVA with significance set at p≤0.05. Findings prompted additional mechanistic inquiry of key molecular pathways.

Results

Offspring exposed to maternal diabetes or high-fat diet, alone and in combination, had smaller lungs and larger hearts at birth. High-fat diet-exposed, but not diabetes-exposed offspring, had a higher perinatal death rate and echocardiographic evidence of PPHN at birth. Alveolar mean linear intercept, septal thickness, and airspace area (D₂) were not significantly different between the groups; however, markers of lung maturity were. Both diabetes-exposed and diet-exposed offspring expressed more T1α protein, a marker of type I cells. Diet-exposed newborn pups expressed less surfactant protein B and had fewer pulmonary vessels enumerated. Mechanistic inquiry revealed alterations in AKT activation, higher endothelin-1 expression, and an impaired Txnip/VEGF pathway that are important for vessel growth and migration. After 3 weeks, mortality remained highest and static lung compliance and hysteresis were lowest in combination-exposed offspring.

Conclusion

This study emphasizes the effects of a maternal high-fat diet, especially alongside late-gestation diabetes, on pulmonary vasculogenesis, demonstrates adverse consequences beyond the perinatal period and directs attention to mechanistic pathways of interest. Findings provide a foundation for additional investigation of preventative and therapeutic strategies aimed at decreasing pulmonary morbidity in at-risk infants.

Increased Lung Expression of Anti-Angiogenic Factors in Down Syndrome: Potential Role in Abnormal Lung Vascular Growth and the Risk for Pulmonary Hypertension

BACKGROUND AND AIMS

Infants with Down syndrome (DS) or Trisomy 21, are at high risk for developing pulmonary arterial hypertension (PAH), but mechanisms that increase susceptibility are poorly understood. Laboratory studies have shown that early disruption of angiogenesis during development impairs vascular and alveolar growth and causes PAH. Human chromosome 21 encodes known anti-angiogenic factors, including collagen18a1 (endostatin, ES), ß-amyloid peptide (BAP) and Down Syndrome Critical Region 1 (DSCR-1). Therefore, we hypothesized that fetal lungs from subjects with DS are characterized by early over-expression of anti-angiogenic factors and have abnormal lung vascular growth in utero.

METHODS

Human fetal lung tissue from DS and non-DS subjects were obtained from a biorepository. Quantitative reverse transcriptase PCR (qRT-PCR) was performed to assay 84 angiogenesis-associated genes and individual qRT-PCR was performed for ES, amyloid protein precursor (APP) and DSCR1. Western blot analysis (WBA) was used to assay lung ES, APP and DSCR-1 protein contents. Lung vessel density and wall thickness were determined by morphometric analysis.

RESULTS

The angiogenesis array identified up-regulation of three anti-angiogenic genes: COL18A1 (ES), COL4A3 (tumstatin) and TIMP3 (tissue inhibitor of metallopeptidase 3) in DS lungs. Single qRT-PCR and WBA showed striking elevations of ES and APP mRNA (p = 0.022 and p = 0.001) and protein (p = 0.040 and p = 0.002; respectively). Vessel density was reduced (p = 0.041) and vessel wall thickness was increased in DS lung tissue (p = 0.033) when compared to non-DS subjects.

CONCLUSIONS

We conclude that lung anti-angiogenic factors, including COL18A1 (ES), COL4A3, TIMP3 and APP are over-expressed and fetal lung vessel growth is decreased in subjects with DS. We speculate that increased fetal lung anti-angiogenic factor expression due to trisomy 21 impairs lung vascular growth and signaling, which impairs alveolarization and contributes to high risk for PAH during infancy.

Antenatal BAY 41-2272 reduces pulmonary hypertension in the rabbit model of congenital diaphragmatic hernia

Infants with congenital diaphragmatic hernia (CDH) fail to adapt at birth because of persistent pulmonary hypertension (PH), a condition characterized by excessive muscularization and abnormal vasoreactivity of pulmonary vessels. Activation of soluble guanylate cyclase by BAY 41-2272 prevents pulmonary vascular remodeling in neonatal rats with hypoxia-induced PH. By analogy, we hypothesized that prenatal administration of BAY 41-2272 would improve features of PH in the rabbit CDH model. Rabbit fetuses with surgically induced CDH at day 23 of gestation were randomized at day 28 for an intratracheal injection of BAY 41-2272 or vehicle. After term delivery (day 31), lung mechanics, right ventricular pressure, and serum NH2-terminal-pro-brain natriuretic peptide (NT-proBNP) levels were measured. After euthanasia, lungs were processed for biological or histological analyses. Compared with untouched fetuses, the surgical creation of CDH reduced the lung-to-body weight ratio, increased mean terminal bronchial density, and impaired lung mechanics. Typical characteristics of PH were found in the hypoplastic lungs, including increased right ventricular pressure, higher serum NT-proBNP levels, thickened adventitial and medial layers of pulmonary arteries, reduced capillary density, and lower levels of endothelial nitric oxide synthase. A single antenatal instillation of BAY 41-2272 reduced mean right ventricular pressure and medial thickness of small resistive arteries in CDH fetuses. Capillary density, endothelial cell proliferation, and transcripts of endothelial nitric oxide synthase increased, whereas airway morphometry, lung growth, and mechanics remained unchanged. These results suggest that pharmacological activation of soluble guanylate cyclase may provide a new approach to the prenatal treatment of PH associated with CDH.

Altered prostanoid metabolism contributes to impaired angiogenesis in persistent pulmonary hypertension in a fetal lamb model

BACKGROUND

Persistent pulmonary hypertension of the newborn (PPHN) is associated with decreased lung angiogenesis and impaired pulmonary vasodilatation at birth. Prostanoids are important modulators of vascular tone and angiogenesis. We hypothesized that altered levels of prostacyclin (PGI₂), a potent vasodilator, and thromboxane A₂ (TXA₂), a vasoconstrictor, contribute to impaired angiogenesis of pulmonary artery endothelial cells (PAEC) in PPHN.

METHODS

PAEC were isolated from fetal lambs with PPHN induced by prenatal ductus arteriosus constriction or from sham operated controls. Expression and activity of PGI₂ synthase (PGIS) and TXA₂ synthase (TXAS), expression of cyclooxygenases 1 and 2 (COX-1 and COX-2), and the role of PGIS/TXAS alterations in angiogenesis were investigated in PAEC from PPHN and control lambs.

RESULTS

PGIS protein and activity were decreased and PGIS protein tyrosine nitration was increased in PPHN PAEC. In contrast, TXAS protein and its stimulated activity were increased in PPHN PAEC. COX-1 and COX-2 proteins were decreased in PPHN PAEC. Addition of PGI₂ improved in vitro tube formation by PPHN PAEC, whereas indomethacin decreased tube formation by control PAEC. PGIS knockdown decreased the in vitro angiogenesis in control PAEC, whereas TXAS knockdown increased the in vitro angiogenesis in PPHN PAEC.

CONCLUSION

Reciprocal alterations in PGI₂ and TXA₂ may contribute to impaired angiogenesis in PPHN.

Chronic intrauterine pulmonary hypertension increases main pulmonary artery stiffness and adventitial remodeling in fetal sheep

Persistent pulmonary hypertension of the newborn (PPHN) is a clinical syndrome that is characterized by high pulmonary vascular resistance due to changes in lung vascular growth, structure, and tone. PPHN has been primarily considered as a disease of the small pulmonary arteries (PA), but proximal vascular stiffness has been shown to be an important predictor of morbidity and mortality in other diseases associated with pulmonary hypertension (PH). The objective of this study is to characterize main PA (MPA) stiffness in experimental PPHN and to determine the relationship of altered biomechanics of the MPA with changes in extracellular matrix (ECM) content and orientation of collagen and elastin fibers. MPAs were isolated from control and PPHN fetal sheep model and were tested by planar biaxial testing to measure stiffness in circumferential and axial vessel orientations. Test specimens were fixed for histological assessments of the vascular wall ECM constituents collagen and elastin. MPAs from PPHN sheep had increased mechanical stiffness (P < 0.05) and altered ECM remodeling compared with control MPA. A constitutive mathematical model and histology demonstrated that PPHN vessels have a smaller contribution of elastin and a greater role for collagen fiber engagement compared with the control arteries. We conclude that exposure to chronic hemodynamic stress in late-gestation fetal sheep increases proximal PA stiffness and alters ECM remodeling. We speculate that proximal PA stiffness further contributes to increased right ventricular impedance in experimental PPHN, which contributes to abnormal transition of the pulmonary circulation at birth.

Antenatal use of bosentan and/or sildenafil attenuates pulmonary features in rats with congenital diaphragmatic hernia

BACKGROUND

Lung hypoplasia, pulmonary persistent hypertension of the newborn and its morphological changes are the main features in congenital diaphragmatic hernia (CDH). This study was undertaken to investigate if antenatal use of sildenafil and/or bosentan attenuates vascular remodeling, promotes branching, and improves alveolarization in experimental nitrofeninduced CDH.

METHODS

Nitrofen (100 mg) was gavage-fed to pregnant rats at post conception day (PCD) 9 to induce CDH. The rats were randomized to 5 groups: 1) control; 2) nitrofen; 3) nitrofen+sildenafil 100 mg/kg per day at PCD 16-20; 4) nitrofen+bosentan 30 mg/kg per day, at PCD 16-20, and 5) nitrofen+bosentan+sildenafil, same doses and administration days. After cesarean delivery, the offsprings were sacrificed. The diaphragmatic defect and pulmonary hypoplasia were identified, and the lungs were dissected. Arterial wall thickness, bronchiolar density and alveolarization were assessed.

RESULTS

The offsprings with CDH were characterized by severe pulmonary hypoplasia (lung weight-to-body weight ratio: 0.0263 [95% confidence interval (CI) 0.0242-0.0278)] in the nitrofen group versus 0.0385 (95% CI 0.0355-0.0424) in the control group (P=0.0001). Pulmonary arterial wall thickness was decreased to 3.0 (95% CI 2.8-3.7) μm in the nitrofen+sildenafil group versus 5.0 (95% CI 4.1-4.9) μm in the nitrofen group (P=0.02). Terminal bronchioles increased to 13.7 (95% CI 10.7-15.2) μm in the nitrofen+bosentan group in contrast to 8.7 (95% CI 7.2-9.4) μm in the nitrofen group (P=0.002). More significant differences (P=0.0001) were seen in terminal bronchioles in the nitrofen+sildenafil+bosentan group than in the nitrofen group [14.0 (95% CI 12.5-15.4) μm versus 8.5 (95% CI 7.1-9.3) μm]. Pulmonary arterial wall thickness was also decreased in the former group.

CONCLUSIONS

In this rat model, antenatal treatment with sildenafil attenuates vascular remodeling. Bosentan promotes the development of terminal bronchioles in nitrofen-induced CDH.

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.

Prenatal programming of pulmonary hypertension induced by chronic hypoxia or ductal ligation in sheep

Pulmonary hypertension of the newborn is caused by a spectrum of functional and structural abnormalities of the cardiopulmonary circuit. The existence of multiple etiologies and an incomplete understanding of the mechanisms of disease progression have hindered the development of effective therapies. Animal models offer a means of gaining a better understanding of the fundamental basis of the disease. To that effect, a number of experimental animal models are being used to generate pulmonary hypertension in the fetus and newborn. In this review, we compare the mechanisms associated with pulmonary hypertension caused by two such models: in utero ligation of the ductus arteriosus and chronic perinatal hypoxia in sheep fetuses and newborns. In this manner, we make direct comparisons between ductal ligation and chronic hypoxia with respect to the associated mechanisms of disease, since multiple studies have been performed with both models in a single species. We present evidence that the mechanisms associated with pulmonary hypertension are dependent on the type of stress to which the fetus is subjected. Such an analysis allows for a more thorough evaluation of the disease etiology, which can help focus clinical treatments. The final part of the review provides a clinical appraisal of current treatment strategies and lays the foundation for developing individualized therapies that depend on the causative factors.

Endothelin-1 decreases endothelial PPARγ signaling and impairs angiogenesis after chronic intrauterine pulmonary hypertension

Increased endothelin-1 (ET-1) disrupts angiogenesis in persistent pulmonary hypertension of the newborn (PPHN), but pathogenic mechanisms are unclear. Peroxisome proliferator activated receptor γ (PPARγ) is decreased in adult pulmonary hypertension, but whether ET-1-PPARγ interactions impair endothelial cell function and angiogenesis in PPHN remains unknown. We hypothesized that increased PPHN pulmonary artery endothelial cell (PAEC) ET-1 production decreases PPARγ signaling and impairs tube formation in vitro. Proximal PAECs were harvested from fetal sheep after partial ligation of the ductus arteriosus in utero (PPHN) and controls. PPARγ and phospho-PPARγ protein were compared between normal and PPHN PAECs ± ET-1 and bosentan (ETA/ETB receptor blocker). Tube formation was assessed in response to PPARγ agonists ± ET-1, N-nitro-l-arginine (LNA) (NOS inhibitor), and PPARγ siRNA. Endothelial NO synthase (eNOS), phospho-eNOS, and NO production were measured after exposure to PPARγ agonists and PPARγ siRNA. At baseline, PPHN PAECs demonstrate decreased tube formation and PPARγ protein expression and activity. PPARγ agonists restored PPHN tube formation to normal. ET-1 decreased normal and PPHN PAEC tube formation, which was rescued by PPARγ agonists. ET-1 decreased PPARγ protein and activity, which was prevented by bosentan. PPARγ agonists increased eNOS protein and activity and NO production in normal and PPHN PAECs. LNA inhibited the effect of PPARγ agonists on tube formation. PPARγ siRNA decreased eNOS protein and tube formation in normal PAECs. We conclude that ET-1 decreases PPARγ signaling and contributes to PAEC dysfunction and impaired angiogenesis in PPHN. We speculate that therapies aimed at decreasing ET-1 production will restore PPARγ signaling, preserve endothelial function, and improve angiogenesis in PPHN.

Pulmonary vascular disease in bronchopulmonary dysplasia: pulmonary hypertension and beyond

PURPOSE OF REVIEW

Pulmonary hypertension contributes significantly to morbidity and mortality of chronic lung disease of infancy, or bronchopulmonary dysplasia (BPD). Advances in pulmonary vascular biology over the past few decades have led to new insights into the pathogenesis of BPD; however, many unique issues persist regarding our understanding of pulmonary vascular development and disease in preterm infants at risk for chronic lung disease.

RECENT FINDINGS

Recent studies have highlighted the important contribution of the developing pulmonary circulation to lung growth in the setting of preterm birth. These studies suggest that there is a spectrum of pulmonary vascular disease (PVD) in BPD rather than a simple question of whether or not pulmonary hypertension is present. Epidemiological studies underscore gaps in our understanding of PVD in the context of BPD, including universally accepted definitions, approaches to diagnosis and treatment, and patient outcomes. Unfortunately, therapeutic strategies for pulmonary hypertension in BPD are based on small observational studies with poorly defined endpoints and rely on results from older children and adult studies. Yet, unique characteristics of this population create other potential risks for the adoption of these strategies.

SUMMARY

Despite many recent advances, PVD remains an important contributor to poor outcomes in preterm infants with BPD. Substantial challenges persist, especially with regard to understanding mechanisms and the clinical approach to PVD. Future studies are needed to develop evidence-based definitions and clinical endpoints through which the pathophysiology can be investigated and potential therapeutic interventions evaluated.

Antenatal betamethasone improves postnatal transition in late preterm lambs with persistent pulmonary hypertension of the newborn

BACKGROUND

Persistent pulmonary hypertension of the newborn (PPHN) is associated with increased oxidative stress in pulmonary arteries (PAs). Betamethasone decreases the oxidative stress and improves antioxidant balance in PPHN. We investigated whether antenatal betamethasone improves pulmonary vasodilation and postnatal oxygenation in late preterm lambs with PPHN.

METHODS

PPHN was induced by constriction of fetal ductus arteriosus from 128 to 136 d gestation. Ewes were given two intramuscular doses of betamethasone or saline at 24 and 12 h before cesarean-section delivery at 136 d gestation, simulating late preterm birth. Newborn lambs were mechanically ventilated for 8 h with monitoring of blood gas and hemodynamic variables. Lungs were harvested postmortem to determine oxidative stress markers and in vitro responses of PAs.

RESULTS

Postnatal arterial partial pressure of oxygen and pH were higher and the oxygenation index and arterial partial pressure of carbon dioxide were lower in betamethasone-treated lambs. PA pressure was lower and systemic pressure higher in lambs treated with betamethasone. Betamethasone decreased the oxidative stress markers and increased endothelial nitric oxide synthase expression in ventilated PPHN lungs.

CONCLUSION

Antenatal betamethasone decreases oxidative stress and improves postnatal transition in late preterm lambs with PPHN. This study suggests a potential benefit for antenatal betamethasone in late preterm births.

Endothelin-1 impairs angiogenesis in vitro through Rho-kinase activation after chronic intrauterine pulmonary hypertension in fetal sheep

BACKGROUND

Endothelin-1 (ET-1) and Rho-kinase (ROCK) increase vascular tone in experimental persistent pulmonary hypertension of the newborn (PPHN). Whether ET-1 activates ROCK to decrease angiogenesis in the developing lung remains unknown.

METHODS

Proximal pulmonary artery endothelial cells (PAECs) were harvested from fetal sheep after partial ligation of the ductus arteriosus in utero (PPHN) and controls. Growth and tube formation were assessed after ET-1 treatment. The effect of ET-1 antagonism on tube formation was studied using ET-1 small interfering RNA (siRNA), ET-1 monoclonal antibodies (ET-1mAbs), BQ-123 (an ET(A) blocker), and bosentan (an ET(A)/ET(B) blocker). ET-1 gene and protein and ET(A)/ET(B) receptor protein expression were measured in normal and PPHN PAECs. ET-1-ROCK interactions were assessed by measuring ROCK activity after ET-1, ET-1 siRNA, and bosentan treatments, and tube formation with ET-1 and Y-27632 (ROCK inhibitor).

RESULTS

ET-1 did not affect growth but decreased tube formation in normal and PPHN PAECs. ET-1 protein and gene expression were increased and ET(B) receptor protein decreased in PPHN PAECs. ET-1 siRNA, ET-1mAbs, and bosentan, but not BQ-123, increased tube formation. ROCK activity was increased in PPHN PAECs and decreased with ET-1 siRNA and bosentan treatments. Y-27632 prevented the decrease in tube formation with ET-1.

CONCLUSION

ET-1 activation of ROCK impairs angiogenesis of fetal PAECs. Disruption of ET-1-ROCK interactions may increase vascular growth in PPHN.

Associated inflammation or increased flow-mediated shear stress, but not pressure alone, disrupts endothelial caveolin-1 in infants with pulmonary hypertension

Endothelial caveolin-1 loss is an important feature of pulmonary hypertension (PH); the rescue of caveolin-1 abrogates experimental PH. Recent studies in human PH suggest that the endothelial caveolin-1 loss is followed by an enhanced expression of caveolin-1 in smooth muscle cells (SMC) with subsequent neointima formation. In order to evaluate caveolin-1 expression in infants with PH, we examined the available clinical histories, hemodynamic data, and the expression of caveolin-1, PECAM-1, vWF, and smooth muscle α-actin in the lung biopsy/autopsy specimens obtained from infants with congenital heart disease (CHD, n = 8) and lung disease (n = 9). In CHD group, PH associated with increased pulmonary blood flow exhibited loss of endothelial caveolin-1 and PECAM-1 in pulmonary arteries; additional vWF loss was associated with enhanced expression of caveolin-1 in SMC. In the absence of PH, increased or decreased pulmonary blood flow did not disrupt endothelial caveolin-1, PECAM-1, or vWF; nor was there any enhanced expression of caveolin-1 in SMC. In Lung Disease + PH group, caveolin-1, PECAM-1, and vWF were well preserved in seven infants, and importantly, SMC in these arteries did not exhibit enhanced caveolin-1 expression. Two infants with associated inflammatory disease exhibited loss of endothelial caveolin-1 and PECAM-1; additional loss of vWF was accompanied by enhanced expression of caveolin-1 in SMC. Thus, associated flow-induced shear stress or inflammation, but not elevated pulmonary artery pressure alone, disrupts endothelial caveolin-1. Subsequent vWF loss, indicative of extensive endothelial damage is associated with enhanced expression of caveolin-1 in SMC, which may worsen the disease.

Associated inflammation or increased flow-mediated shear stress, but not pressure alone, disrupts endothelial caveolin-1 in infants with pulmonary hypertension

Endothelial caveolin-1 loss is an important feature of pulmonary hypertension (PH); the rescue of caveolin-1 abrogates experimental PH. Recent studies in human PH suggest that the endothelial caveolin-1 loss is followed by an enhanced expression of caveolin-1 in smooth muscle cells (SMC) with subsequent neointima formation. In order to evaluate caveolin-1 expression in infants with PH, we examined the available clinical histories, hemodynamic data, and the expression of caveolin-1, PECAM-1, vWF, and smooth muscle α-actin in the lung biopsy/autopsy specimens obtained from infants with congenital heart disease (CHD, n = 8) and lung disease (n = 9). In CHD group, PH associated with increased pulmonary blood flow exhibited loss of endothelial caveolin-1 and PECAM-1 in pulmonary arteries; additional vWF loss was associated with enhanced expression of caveolin-1 in SMC. In the absence of PH, increased or decreased pulmonary blood flow did not disrupt endothelial caveolin-1, PECAM-1, or vWF; nor was there any enhanced expression of caveolin-1 in SMC. In Lung Disease + PH group, caveolin-1, PECAM-1, and vWF were well preserved in seven infants, and importantly, SMC in these arteries did not exhibit enhanced caveolin-1 expression. Two infants with associated inflammatory disease exhibited loss of endothelial caveolin-1 and PECAM-1; additional loss of vWF was accompanied by enhanced expression of caveolin-1 in SMC. Thus, associated flow-induced shear stress or inflammation, but not elevated pulmonary artery pressure alone, disrupts endothelial caveolin-1. Subsequent vWF loss, indicative of extensive endothelial damage is associated with enhanced expression of caveolin-1 in SMC, which may worsen the disease.

Third trimester fetal pulmonary artery Doppler blood flow velocity characteristics following prenatal selective serotonin reuptake inhibitor (SSRI) exposure

BACKGROUND

There have been contradictory reports on the risks of persistent pulmonary hypertension (PPHN) in infants exposed to SSRIs in utero. However, there has been no assessment of fetal pulmonary arterial dynamics in such pregnancies. AIMS AND SUBJECTS: To measure fetal right pulmonary artery (RPA) variables using Doppler ultrasound at 36 weeks gestation in fetuses of mothers taking SSRI antidepressants (n=23) and in a control, normal pregnancy group (n=35).

OUTCOME MEASURES

At 36 weeks gestation, Doppler ultrasound estimates of Pulsatility Index (PI), Resistance Index (RI), vessel diameter, peak systolic velocity, mean velocity and volume flow were obtained from the fetal right pulmonary artery in a morning session (~0830), before the SSRI mothers took their daily drug dose and in an afternoon session (~1300). Venous blood was drawn at 5 time points across the day (~08:30AM, ~10:30AM, ~13:00PM, ~13:45PM, and ~15:00PM) from the SSRI treated mothers for measurement of plasma SSRI concentration using high performance liquid chromatography tandem mass spectrometry.

RESULTS

There were no differences in the RPA Doppler measures between the control and SSRI-exposed fetuses. However 8 of the 23 latter fetuses experience transient respiratory difficulties at birth and, in these RPA flow was significantly higher than in the SSR-exposed fetuses without respiratory problems. There were, however, no differences in RPA PI and RI between the 2 groups.

CONCLUSIONS

In SSRI-exposed infants with transient postnatal respiratory difficulties, fetal RPA flow in increased, likely due to partial constriction of the ductus arteriosus. However, this was not associated with PPHN.

Cross talk between NADPH oxidase and autophagy in pulmonary artery endothelial cells with intrauterine persistent pulmonary hypertension

Autophagy is a process for cells to degrade proteins or entire organelles to maintain a balance in the synthesis, degradation, and subsequent recycling of cellular products. Increased reactive oxygen species formation is known to induce autophagy. We previously reported that increased NADPH oxidase (NOX) activity in pulmonary artery endothelial cells (PAEC) from fetal lambs with persistent pulmonary hypertension (PPHN) contributes to impaired angiogenesis in PPHN-PAEC compared with normal PAEC. We hypothesized that increased NOX activity in PPHN-PAEC is associated with increased autophagy, which, in turn, contributes to impaired angiogenesis in PPHN-PAEC. In the present study, we detected increased autophagy in PPHN-PAEC as shown by increased ratio of the microtubule-associated protein 1 light chain (LC3)-II to LC3-I and increased percentage of green fluorescent protein-LC3 punctate positive cells. Inhibiting autophagy by 3-methyladenine, chloroquine, and beclin-1 knockdown in PPHN-PAEC has led to decreased autophagy and increased in vitro angiogenesis. Inhibition of autophagy also decreased the association between gp91(phox) and p47(phox), NOX activity, and superoxide generation. A nonspecific antioxidant N-acetylcysteine and a NOX inhibitor apocynin decreased autophagy in PPHN-PAEC. In conclusion, autophagy may contribute to impaired angiogenesis in PPHN-PAEC through increasing NOX activity. Our results suggest that, in PPHN-PAEC, a positive feedback relationship between autophagy and NOX activity may regulate angiogenesis.

Hypoxia and nitric oxide exposure promote apoptotic signaling in contractile pulmonary arterial smooth muscle but not in pulmonary epithelium

RATIONALE

Neonatal pulmonary hypertension is characterized by hypoxia, abnormal vascular remodeling, and impaired alveolarization. Nitric oxide (NO) regulates cell replication and activation of apoptosis. Our objective was to examine cell phenotype-specific effects of hypoxia and NO exposure on cumulative apoptotic signal in neonatal pulmonary epithelial cells and arterial smooth muscle.

DESIGN/METHODS

Primary cultured newborn porcine pulmonary arterial myocytes and epithelial cells were grown in normoxic (21% O2) or hypoxic conditions (10% O2). Myocyte phenotype was predetermined by serum-supplementation or -deprivation. Cells were exposed to sodium nitroprusside (10(-7) -10(-4)  M) or diluent for 3 days. Cell survival was estimated by MTT assay; BAX, Bcl-2, and cleaved caspase-3 by Western blot; cell cycle entry by laser scanning cytometry.

RESULTS

Hypoxic epithelial cells exhibited a small increase in anti-apoptotic Bcl2, and decrease in BAX. Cell survival and active caspase-3 were unchanged. Exposure to NO had no impact on epithelial apoptosis, but initiated necrosis. In contractile myocytes, pro-apoptotic BAX abundance and caspase-3 activation were increased by hypoxia, augmented by NO exposure promoting apoptosis. Hypoxia decreased BAX/Bcl-2 ratio and promoted survival of synthetic myocytes; NO increased apoptosis of normoxic synthetic myocytes, but decreased apoptosis of hypoxic synthetic myocytes.

CONCLUSION

The effect of NO on pulmonary apoptosis is phenotype-dependent. A cumulative apoptotic effect of hypoxia and NO in vitro exerted on contractile myocytes may lead to contraction of this subpopulation, while synthetic myocyte survival and proliferation is enhanced by hypoxia and NO. Epithelial survival is unaffected. We speculate that alveolar rarefaction reported after neonatal hypoxia may arise from growth arrest in the vascular rather than the epithelial compartment.

Intrauterine growth restriction decreases pulmonary alveolar and vessel growth and causes pulmonary artery endothelial cell dysfunction in vitro in fetal sheep

Intrauterine growth restriction (IUGR) increases the risk for bronchopulmonary dysplasia (BPD). Abnormal lung structure has been noted in animal models of IUGR, but whether IUGR adversely impacts fetal pulmonary vascular development and pulmonary artery endothelial cell (PAEC) function is unknown. We hypothesized that IUGR would decrease fetal pulmonary alveolarization, vascular growth, and in vitro PAEC function. Studies were performed in an established model of severe placental insufficiency and IUGR induced by exposing pregnant sheep to elevated temperatures. Alveolarization, quantified by radial alveolar counts, was decreased 20% (P < 0.005) in IUGR fetuses. Pulmonary vessel density was decreased 44% (P < 0.01) in IUGR fetuses. In vitro, insulin increased control PAEC migration, tube formation, and nitric oxide (NO) production. This response was absent in IUGR PAECs. VEGFA stimulated tube formation, and NO production also was absent. In control PAECs, insulin increased cell growth by 68% (P < 0.0001). Cell growth was reduced in IUGR PAECs by 29% at baseline (P < 0.01), and the response to insulin was attenuated (P < 0.005). Despite increased basal and insulin-stimulated Akt phosphorylation in IUGR PAECs, endothelial NO synthase (eNOS) protein expression as well as basal and insulin-stimulated eNOS phosphorylation were decreased in IUGR PAECs. Both VEGFA and VEGFR2 also were decreased in IUGR PAECs. We conclude that fetuses with IUGR are characterized by decreased alveolar and vascular growth and PAEC dysfunction in vitro. This may contribute to the increased risk for adverse respiratory outcomes and BPD in infants with IUGR.

Long-term exposure to high-altitude chronic hypoxia during gestation induces neonatal pulmonary hypertension at sea level

We determined whether postnatal pulmonary hypertension induced by 70% of pregnancy at high altitude (HA) persists once the offspring return to sea level and investigated pulmonary vascular mechanisms operating under these circumstances. Pregnant ewes were divided into two groups: conception, pregnancy, and delivery at low altitude (580 m, LLL) and conception at low altitude, pregnancy at HA (3,600 m) from 30% of gestation until delivery, and return to lowland (LHL). Pulmonary arterial pressure (PAP) was measured in vivo. Vascular reactivity and morphometry were assessed in small pulmonary arteries (SPA). Protein expression of vascular mediators was determined. LHL lambs had higher basal PAP and a greater increment in PAP after N^G-nitro-l-arginine methyl ester (20.9 ± 1.1 vs. 13.7 ± 0.5 mmHg; 39.9 ± 5.0 vs. 18.3 ± 1.3 mmHg, respectively). SPA from LHL had a greater maximal contraction to K⁺ (1.34 ± 0.05 vs. 1.16 ± 0.05 N/m), higher sensitivity to endothelin-1 and nitroprusside, and persistence of dilatation following blockade of soluble guanylate cyclase. The heart ratio of the right ventricle-to-left ventricle plus septum was higher in the LHL relative to LLL. The muscle area of SPA (29.3 ± 2.9 vs. 21.1 ± 1.7%) and the protein expression of endothelial nitric oxide synthase (1.7 ± 0.1 vs. 1.1 ± 0.2), phosphodiesterase (1.4 ± 0.1 vs. 0.7 ± 0.1), and Ca²⁺-activated K⁺ channel (0.76 ± 0.16 vs. 0.30 ± 0.01) were greater in LHL compared with LLL lambs. In contrast, LHL had decreased heme oxygenase-1 expression (0.82 ± 0.26 vs. 2.22 ± 0.44) and carbon monoxide production (all P < 0.05). Postnatal pulmonary hypertension induced by 70% of pregnancy at HA promotes cardiopulmonary remodeling that persists at sea level.

Partial pulmonary embolization disrupts alveolarization in fetal sheep

Background

Although bronchopulmonary dysplasia is closely associated with an arrest of alveolar development and pulmonary capillary dysplasia, it is unknown whether these two features are causally related. To investigate the relationship between pulmonary capillaries and alveolar formation, we partially embolized the pulmonary capillary bed.

Methods

Partial pulmonary embolization (PPE) was induced in chronically catheterized fetal sheep by injection of microspheres into the left pulmonary artery for 1 day (1d PPE; 115d gestational age; GA) or 5 days (5d PPE; 110-115d GA). Control fetuses received vehicle injections. Lung morphology, secondary septal crests, elastin, collagen, myofibroblast, PECAM1 and HIF1α abundance and localization were determined histologically. VEGF-A, Flk-1, PDGF-A and PDGF-Rα mRNA levels were measured using real-time PCR.

Results

At 130d GA (term ~147d), in embolized regions of the lung the percentage of lung occupied by tissue was increased from 29 ± 1% in controls to 35 ± 1% in 1d PPE and 44 ± 1% in 5d PPE fetuses (p < 0.001). Secondary septal crest density was reduced from 8 ± 0% in controls to 5 ± 0% in 1d PPE and 4 ± 0% in 5d PPE fetuses (p < 0.05), indicating impaired alveolar formation. The deposition of differentiated myofibroblasts (23 ± 1% vs 28 ± 1%; p < 0.001) and elastin fibres (3 ± 0% vs 4 ± 0%; p < 0.05) were also impaired in embolized lung regions of PPE fetuses compared to controls. PPE did not alter the deposition of collagen or PECAM1. At 116d GA in 5d PPE fetuses, markers of hypoxia indicated that a small and transient hypoxic event had occurred (hypoxia in 6.7 ± 1.4% of the tissue within embolized regions of 5d PPE fetuses at 116d compared to 0.8 ± 0.2% of tissue in control regions). There was no change in the proportion of tissue labelled with HIF1α. There was no change in mRNA levels of the angiogenic factors VEGF and Flk-1, although a small increase in PDGF-Rα expression at 116d GA, from 1.00 ± 0.12 in control fetuses to 1.61 ± 0.18 in 5d PPE fetuses may account for impaired differentiation of alveolar myofibroblasts and alveolar development.

Conclusions

PPE impairs alveolarization without adverse systemic effects and is a novel model for investigating the role of pulmonary capillaries and alveolar myofibroblasts in alveolar formation.

Impaired vascular endothelial growth factor signaling in the pathogenesis of neonatal pulmonary vascular disease

Abstract Of diverse growth factors that contribute to normal lung development, vascular endothelial growth factor (VEGF) plays an especially prominent role in the normal growth and development of the pulmonary circulation in the fetus and newborn. Strong experimental and clinical data support the role of impaired VEGF signaling in the pathogenesis of two major clinical disorders of the developing lung circulation: persistent pulmonary hypertension of the newborn (PPHN) and bronchopulmonary dysplasia (BPD). These disorders are each characterized by impaired vascular growth, structure and reactivity, which are at least partly due to endothelial cell dysfunction. This chapter will briefly discuss VEGF signaling during normal lung development and how disruption of VEGF signaling contribute to the pathogenesis of neonatal pulmonary vascular disease in these settings.

Advances in the diagnosis and management of persistent pulmonary hypertension of the newborn

Rapid evaluation of a neonate who is cyanotic and in respiratory distress is essential for achieving a good outcome. Persistent pulmonary hypertension of the newborn (PPHN) can be a primary cause or a contributing factor to respiratory failure, particularly in neonates born at 34 weeks or more of gestation. PPHN represents a failure of normal postnatal adaptation that occurs at birth in the pulmonary circulation. Rapid advances in therapy in recent years have led to a remarkable decrease in mortality for the affected infants. Infants who survive PPHN are at significant risk for long-term hearing and neurodevelopmental impairments, however. This review focuses on the diagnosis, recent advances in management, and recommendations for the long-term follow-up of infants who have PPHN.

Increased superoxide production contributes to the impaired angiogenesis of fetal pulmonary arteries with in utero pulmonary hypertension

Persistent pulmonary hypertension of newborn (PPHN) is associated with impaired pulmonary vasodilation at birth. Previous studies demonstrated that a decrease in angiogenesis contributes to this failure of postnatal adaptation. We investigated the hypothesis that oxidative stress from NADPH oxidase (Nox) contributes to impaired angiogenesis in PPHN. PPHN was induced in fetal lambs by ductus arteriosus ligation at 85% of term gestation. Pulmonary artery endothelial cells (PAEC) from fetal lambs with PPHN (HTFL-PAEC) or control lambs (NFL-PAEC) were compared for their angiogenic activities and superoxide production. HTFL-PAEC had decreased tube formation, cell proliferation, scratch recovery, and cell invasion and increased cell apoptosis. Superoxide (O(2)(-)) production, measured by dihydroethidium epifluorescence and HPLC, were increased in HTFL-PAEC compared with NFL-PAEC. The mRNA levels for Nox2, Rac1, p47(phox), and Nox4, protein levels of p67(phox) and Rac1, and NADPH oxidase activity were increased in HTFL-PAEC. NADPH oxidase inhibitor, apocynin (Apo), and antioxidant, N-acetyl-cysteine (NAC), improved angiogenic measures in HTFL-PAEC. Apo and NAC also reduced apoptosis in HTFL-PAEC. Our data suggest that PPHN is associated with increased O(2)(-) production from NADPH oxidase in PAEC. Increased oxidative stress from NADPH oxidase contributes to the impaired angiogenesis of PAEC in PPHN.

Treatment of pulmonary hypertension in children with chronic lung disease with newer oral therapies

Chronic lung disease (CLD) is often complicated by chronic pulmonary vascular changes and pulmonary hypertension (PH) in young children. Current therapies for severe PH in such patients, including oxygen, inhaled nitric oxide, and parenteral prostacyclin, are often suboptimal, cumbersome, and expensive. Recently, oral endothelin receptor blockers and phosphodiesterase-5 inhibitors have been used successfully to control and reverse pulmonary vascular disease in idiopathic PH, but the use and efficacy of these agents in pediatric CLD have not been previously reported. We report a series of six children with CLD and severe PH treated with bosentan (six of six) and sildenafil (four of six). Vascular reactivity was assessed by cardiac catheterization prior to and after 6 months of therapy. Serial echocardiography was also used to assess response. Patients have been treated for 2.1-2.9 years (mean, 2.53 years). Response to therapy has included improvement in oxygenation, symptoms, echocardiographic parameters, and hemodynamics by cardiac catheterization. Transiently elevated liver enzymes were noted associated with viral respiratory infections in two subjects; no other adverse effects were noted. Three patients with large cardiac right-to-left shunts prior to therapy had subsequent shunt reversal, two of whom underwent shunt closure later. Oral therapy with bosentan alone or in combination with sildenafil improves PH in patients with CLD over a period of 3-4 years.

Phasic hemodynamics and reverse blood flows in the aortic isthmus and pulmonary arteries of preterm lambs with pulmonary vascular dysfunction

Time-domain representations of the fetal aortopulmonary circulation were carried out in lamb fetuses to study hemodynamic consequences of congenital diaphragmatic hernia (CDH) and the effects of endothelin-receptor antagonist tezosentan (3 mg/45 min). From the isthmic aortic and left pulmonary artery (PA) flows (Q) and isthmic aortic, PA, and left auricle pressures (P) on day 135 in 10 controls and 7 CDH fetuses (28 ewes), discrete-triggered P and Q waveforms were modelized as Pt and Qt functions to obtain basic hemodynamic profiles, pulsatile waves [P, Q, and entry impedance (Ze)], and P and Q hysteresis loops. In the controls, blood propelling energy was accounted for by biventricular ejection flow waves (kinetic energy) with low Ze and by flow-driven pressure waves (potential energy) with low Ze. Weak fetal pulmonary perfusion was ensured by reflux (reverse flows) from PA branches to the ductus anteriosus and aortic isthmus as reverse flows. Endothelin-receptor antagonist blockade using tezosentan slightly increased the forward flow but largely increased diastolic backward flow with a diminished left auricle pre- and postloading. In CHD fetuses, the static component overrode phasic flows that were detrimental to reverse flows and the direction of the diastolic isthmic flow changed to forward during the diastole period. Decreased cardiac output, flattened pressure waves, and increased forward Ze promoted backward flow to the detriment of forward flow (especially during diastole). Additionally, the intrapulmonary arteriovenous shunting was ineffective. The slowing of cardiac output, the dampening of energetic pressure waves and pulsatility, and the heightening of phasic impedances contributed to the lowering of aortopulmonary blood flows. We speculate that reverse pulmonary flow is a physiological requirement to protect the fetal pulmonary circulation from the prominent right ventricular stream and to enhance blood flow to the fetal heart and brain.

Chronic intrauterine pulmonary hypertension increases endothelial cell Rho kinase activity and impairs angiogenesis in vitro

Persistent pulmonary hypertension of the newborn (PPHN) is characterized by endothelial dysfunction and decreased vascular growth. The role of Rho kinase activity in modulating endothelial function and regulating angiogenesis during normal lung development and in PPHN is unknown. We hypothesized that PPHN increases Rho kinase activity in fetal pulmonary artery endothelial cells (PAECs) and impairs angiogenesis in vitro. Proximal PAECs were harvested from fetal sheep with partial ligation of the ductus arteriosus in utero (PPHN) and age-matched controls. Rho kinase activity was measured by RhoA, Rho GTP, and phosphorylated MYPT-1 protein content. The effects of Rho kinase activity on angiogenesis, endothelial nitric oxide (NO) synthase (eNOS) protein expression, and NO production were determined in normal and PPHN PAECs. Angiogenesis was assessed by tube formation in vitro with/without Y-27632 (a Rho kinase inhibitor) and calpeptin (a Rho kinase activator) in the presence/absence of N-nitro-l-arginine (l-NA, an NOS inhibitor). RhoA, Rho GTP, and phosphorylated MYPT-1 protein were increased in PPHN PAECs. Tube formation was reduced 29% in PPHN PAECs (P < 0.001) and increased with Y-27632 treatment in normal and PPHN PAECs, with PPHN PAECs achieving levels similar to those of normal PAECs. l-NA inhibited the Y-27632-induced increase in tube formation in normal, but not PPHN, PAECs. Calpeptin reduced tube formation in normal and PPHN PAECs. eNOS expression was reduced 42% in PPHN PAECs (P < 0.01). Y-27632 increased eNOS protein and NO production in normal and PPHN PAECs. Calpeptin decreased eNOS protein only in normal PAECs but reduced NO production in normal and PPHN PAECs. We conclude that Rho kinase activity is increased in PPHN PAECs and impairs angiogenesis and downregulates eNOS protein and NO production in vitro.

Intrauterine pulmonary hypertension impairs angiogenesis in vitro: role of vascular endothelial growth factor nitric oxide signaling

RATIONALE

Mechanisms that impair angiogenesis in neonatal persistent pulmonary hypertension (PPHN) are poorly understood.

OBJECTIVES

To determine if PPHN alters fetal pulmonary artery endothelial cell (PAEC) phenotype and impairs growth and angiogenesis in vitro, and if altered vascular endothelial growth factor-nitric oxide (VEGF-NO) signaling contributes to this abnormal phenotype.

METHODS

Proximal PAECs were harvested from fetal sheep that had undergone partial ligation of the ductus arteriosus in utero (PPHN) and age-matched control animals. Growth and tube formation +/- VEGF and NO stimulation and inhibition were studied in normal and PPHN PAECs. Western blot analysis was performed for VEGF, VEGF receptor-2 (VEGF-R2), and endothelial NO synthase (eNOS) protein content. NO production with VEGF administration was measured in normal and PPHN PAECs.

MEASUREMENTS AND MAIN RESULTS

PPHN PAECs demonstrate decreased growth and tube formation in vitro. VEGF and eNOS protein expression were decreased in PPHN PAECs, whereas VEGF-R2 protein expression was not different. VEGF and NO increased PPHN PAEC growth and tube formation to values achieved in normal PAECs. VEGF inhibition decreased growth and tube formation in normal and PPHN PAECs. NOS inhibition decreased growth in normal and PPHN PAECs, but tube formation was only reduced in normal PAECs. NO reversed the inhibitory effects of VEGF-R2 inhibition on tube formation in normal and PPHN PAECs. VEGF increased NO production in normal and PPHN PAECs.

CONCLUSIONS

PPHN in utero causes sustained impairment of PAEC phenotype in vitro, with reduced PAEC growth and tube formation and down-regulation of VEGF and eNOS protein. VEGF and NO enhanced growth and tube formation of PPHN PAECs.

Pulmonary hypertension in congenital diaphragmatic hernia

Clinically significant pulmonary hypertension (PHTN) is a common finding in newborn infants with congenital diaphragmatic hernia (CDH) resulting in right to left shunting at pre- and postductal level, hypoxemia, and acute right heart failure in those most severely affected. Even in those without clinical manifestations of ductal shunting, cardiac echo studies would suggest that increased pulmonary vascular resistance and right ventricular pressures are almost a universal finding in this disease, and in some instances, may persist well into the postnatal period. The lung is small and structurally abnormal, and the pulmonary vascular bed is not only reduced in size, but responds abnormally to vasodilators. During the last 20 years, "gentle" ventilation, delayed surgery, and improved peri-operative care have made the greatest impact in decreasing mortality in this condition. Use of PGE1 should be considered early if there is hemodynamically significant PHTN, right ventricular dysfunction, and the patent ductus arteriosus (PDA) is becoming restrictive. In individual patients, inhaled nitric oxide (iNO) might be helpful, but the response to iNO should be confirmed using echocardiography. In patients who survive operation and leave the hospital, there are chronic causes of morbidity that need to be looked for and managed in a multi-disciplinary follow-up clinic.

Bronchopulmonary dysplasia: where have all the vessels gone? Roles of angiogenic growth factors in chronic lung disease

Bronchopulmonary dysplasia and emphysema are significant global health problems at the extreme stages of life. Both are characterized by arrested alveolar development or loss of alveoli, respectively. Both lack effective treatment strategies. Knowledge about the genetic control of branching morphogenesis in mammals derives from investigations of the respiratory system in Drosophila, but mechanisms that regulate alveolar development remain poorly understood. Even less is known about regulation of the growth and development of the pulmonary vasculature. Understanding how alveoli and the underlying capillary network develop, and how these mechanisms are disrupted in disease states, are critical for developing effective therapies for lung diseases characterized by impaired alveolar structure. Recent observations have challenged old notions that the development of the blood vessels in the lung passively follows that of the airways. Rather, increasing evidence suggests that lung blood vessels actively promote alveolar growth during development and contribute to the maintenance of alveolar structures throughout postnatal life. Our working hypothesis is that disruption of angiogenesis impairs alveolarization, and that preservation of vascular growth and endothelial survival promotes growth and sustains the architecture of the distal airspace. Furthermore, the explosion of interest in stem cell biology suggests potential roles for endothelial progenitor cells in the pathogenesis or treatment of lung vascular disease. In this Pulmonary Perspective, we review recent data on the importance of the lung circulation, specifically examining the relationship between dysmorphic vascular growth and impaired alveolarization, and speculate on how these new insights may lead to novel therapeutic strategies for bronchopulmonary dysplasia.

Pulmonary Arterial Hypertension

The first description of the circulation of blood through the lungs has been attributed to Ibn Nafis (1210–1288).1 The concept was rediscovered by Michael Servetus, a Spanish physician during the Renaissance (1511–1553) and recorded, oddly enough, in two pages of his religious treatise, Christianismi Restitutio (1553).2 The definitive exposition of the pulmonary circulation was made by William Harvey in DeMotu Cordis (1628).3 The first observation of the pulmonary capillaries was first reported by Marcellus Malpighi (1661).4 Heart catheterization in humans, driven by a desire to obtain the perfect mixed venous specimen and measure cardiac output, was first performed in 1929 by the German urologist Forssmann,5 using a ureteral catheter to access his own right atrium. Over a decade later, Cournand and Richards at Columbia University in New York subsequently used right heart catheterization to record pulmonary artery pressure (PAP) in patients with shock and secondary forms of pulmonary hypertension (PHT). For these accomplishments, which were inspired by an interest in the pulmonary circulation and PHT related to mitral stenosis, Forssmann, Cournand, and Richards received the Nobel Prize in 1956.