Sildenafil therapy for bronchopulmonary dysplasia: not quite yet

Continuous intravenous sildenafil as an early treatment in neonates with congenital diaphragmatic hernia

BACKGROUND

Pulmonary hypertension (PH) is an important contributor of morbidity and mortality in infants with congenital diaphragmatic hernia (CDH). Treatment options are limited, but sildenafil might improve oxygenation and PH in neonates with CDH.

OBJECTIVE

Aim of this study is to assess effects of intravenous sildenafil on oxygenation and PH in neonates with CDH.

METHODS

A retrospective chart review was performed in all neonates with CDH born in our institution between September 2012 and December 2014. Indication for sildenafil was an OI > 15, PH > 2/3 systemic pressure, or a difference in pre- and postductal oxygen saturation (≥8%). A sildenafil bolus was administered followed by a maintenance infusion of 1.6 mg/kg/d. Primary outcome was improved oxygenation after starting sildenafil. Patients were compared according to improvement in oxygenation (responder vs non-responder).

RESULTS

A total of 26 of 44 neonates were treated with intravenous sildenafil and in all sildenafil were initiated within the first 24 h of life (median age 3.1 h). Improved oxygenation was observed in 11 infants (42.3%). Among the 15 non-responders (57.6%) ECMO was started in 13 and two infants died without ECMO. Vasopressor support increased significantly during the first hours after commencing sildenafil in responders and non-responders. Echocardiographic indices demonstrated an effect on pulmonary arterial pressure within the first 24 h after starting sildenafil.

CONCLUSIONS

Treatment of neonates with intravenous sildenafil during the first day of life was associated with acute improvement in oxygenation in more than 40% of patients. However, a significant increase in vasopressor support was observed.

Role of the Nrf2/HO-1 axis in bronchopulmonary dysplasia and hyperoxic lung injuries

Bronchopulmonary dysplasia (BPD) is a chronic illness that usually originates in preterm newborns. Generally, BPD is a consequence of respiratory distress syndrome (RDS) which, in turn, comes from the early arrest of lung development and the lack of pulmonary surfactant. The need of oxygen therapy to overcome premature newborns' compromised respiratory function generates an increasing amount of reactive oxygen species (ROS), the onset of sustained oxidative stress (OS) status, and inflammation in the pulmonary alveoli deputies to respiratory exchanges. BPD is a severe and potentially life-threatening disorder that in the most serious cases, can open the way to neurodevelopmental delay. More importantly, there is no adequate intervention to hamper or treat BPD. This perspective article seeks to review the most recent and relevant literature describing the very early stages of BPD and hyperoxic lung injuries focussing on nuclear factor erythroid derived 2 (Nrf2)/heme oxygenase-1 (HO-1) axis. Indeed, Nrf2/HO1 activation in response to OS induced lung injury in preterm concurs to the induction of certain number of antioxidant, anti-inflammatory, and detoxification pathways that seem to be more powerful than the activation of one single antioxidant gene. These elicited protective effects are able to counteract/mitigate all multifaceted aspects of the disease and may support novel approaches for the management of BPD.

Considerations in the management of hypoxemic respiratory failure and persistent pulmonary hypertension in term and late preterm neonates

Recent advances in our understanding of neonatal pulmonary circulation and the underlying pathophysiology of hypoxemic respiratory failure (HRF)/persistent pulmonary hypertension of the newborn (PPHN) have resulted in more effective management strategies. Results from animal studies demonstrate that low alveolar oxygen tension (PAO2) causes hypoxic pulmonary vasoconstriction, whereas an increase in oxygen tension to normoxic levels (preductal arterial partial pressure of oxygen (PaO2) between 60 and 80 mm Hg and/or preductal peripheral capillary oxygen saturation between 90% and 97%) results in effective pulmonary vasodilation. Hyperoxia (preductal PaO2 >80 mm Hg) does not cause further pulmonary vasodilation, and oxygen toxicity may occur when high concentrations of inspired oxygen are used. It is therefore important to avoid both hypoxemia and hyperoxemia in the management of PPHN. In addition to oxygen supplementation, therapeutic strategies used to manage HRF/PPHN in term and late preterm neonates may include lung recruitment with optimal mean airway pressure and surfactant, inhaled and intravenous vasodilators and 'inodilators'. Clinical evidence suggests that administration of surfactant or inhaled nitric oxide (iNO) therapy at a lower acuity of illness can decrease the risk of extracorporeal membrane oxygenation/death, progression of HRF and duration of hospital stay. Milrinone may be beneficial as an inodilator and may have specific benefits following prolonged exposure to iNO plus oxygen owing to inhibition of phosphodiesterase (PDE)-3A. Additionally, sildenafil, and, in selected cases, hydrocortisone may be appropriate options after hyperoxia and oxidative stress owing to their effects on PDE-5 activity and expression. Continued investigation into these and other interventions is needed to optimize treatment and improve outcomes.

Sildenafil attenuates vaso-obliteration and neovascularization in a mouse model of retinopathy of prematurity

PURPOSE

We sought to determine the effect of sildenafil on retinal vascular changes in a mouse model of oxygen-induced retinopathy (OIR).

METHODS

Vascular defects in OIR mice were quantified by measuring vaso-obliteration at postnatal days 12 and 17 (P12 and P17) and neovascularization at P17 to compare sildenafil-treated to dextrose-treated OIR mice. Retinal HIF1α protein expression was quantified by Western blotting and normalized to that of β-actin. Right ventricular hypertrophy was measured by Fulton's index as a surrogate for hyperoxia-induced pulmonary hypertension.

RESULTS

At P12, OIR mice treated with sildenafil demonstrated a 24% reduction in vaso-obliteration (P < 0.05), whereas at P17, treated animals showed a 50% reduction in neovascularization (P < 0.05) compared to dextrose-treated controls. Sildenafil-treated OIR mice had stabilization of retinal HIF1α at P12, immediately after hyperoxia. At P17, sildenafil-treated OIR mice had decreased HIF1α relative to untreated mice. OIR mice developed right ventricle hypertrophy that was significant compared to that in room air controls, which was abrogated by sildenafil.

CONCLUSIONS

Sildenafil treatment significantly decreased retinal vaso-obliteration and neovascularization in a mouse OIR model. These effects are likely due to sildenafil-induced HIF1α stabilization during hyperoxia exposure. Furthermore, we confirm disease overlap by showing that OIR mice also develop hyperoxia-induced right ventricular hypertrophy, which is prevented by sildenafil. This study is a first step toward delineating a potential therapeutic role for sildenafil in OIR and further suggests that there may be common pathophysiologic mechanisms underlying hyperoxia-induced retinal and pulmonary vascular disease.

Disrupted pulmonary artery cyclic guanosine monophosphate signaling in mice with hyperoxia-induced pulmonary hypertension

Pulmonary hypertension (PH) occurs in 25 to 35% of premature infants with significant bronchopulmonary dysplasia (BPD). Neonatal mice exposed to 14 days of hyperoxia develop BPD-like lung injury and PH. To determinne the impact of hyperoxia on pulmonary artery (PA) cyclic guanosine monophosphate (cGMP) signaling in a murine model of lung injury and PH, neonatal C57BL/6 mice were placed in room air, 75% O2 for 14 days (chronic hyperoxia [CH]) or 75% O2 for 24 hours, followed by 13 days of room air (acute hyperoxia with recovery [AHR]) with or without sildenafil. At 14 days, mean alveolar area, PA medial wall thickness (MWT), right ventricular hypertrophy (RVH), and vessel density were assessed. PA protein was analyzed for cGMP, soluble guanylate cyclase, and PDE5 activity. CH and AHR mice had RVH, but only CH mice had increased alveolar area and MWT and decreased vessel density. In CH and AHR PAs, soluble guanylate cyclase activity was decreased, and PDE5 activity was increased. In CH mice, sildenafil attenuated MWT and RVH but did not improve mean alveolar area or vessel density. In CH and AHR PAs, sildenafil decreased PDE5 activity and increased cGMP. Our results indicate that prolonged hyperoxia leads to lung injury, PH, RVH, and disrupted PA cGMP signaling. Furthermore, 24 hours of hyperoxia causes RVH and disrupted PA cGMP signaling that persists for 13 days. Sildenafil reduced RVH and restored vascular cGMP signaling but did not attenuate lung injury. Thus, hyperoxia can rapidly disrupt PA cGMP signaling in vivo with sustained effects, and concurrent sildenafil therapy can be protective.

Pulmonary hypertension in bronchopulmonary dysplasia: clinical findings, cardiovascular anomalies and outcomes

OBJECTIVE

Pulmonary hypertension (PH) worsens the prognosis of bronchopulmonary dysplasia (BPD). The following items have not been fully established for PH in BPD: clinical characterization, incidence of cardiovascular anomalies (CVAs), response to PH treatment, and outcome.

STUDY DESIGN

A review of clinical records, computed tomography (CT) images and catheterization data of 36 patients with PH-BPD referred to our PH Unit (March 2006 to December 2011) was performed. Twenty-nine patients without major congenital heart defects and with complete follow-up data were included.

RESULTS

The diagnosis of PH was made at a median age of 4.5 months (IQR 2.4-7.8), with an echocardiography estimated median right ventricular pressure/systemic pressure ratio of 70% (IQR 60-80%). CT scanning was performed in 21 patients and catheterization in 14 patients. CVAs were found in 19 patients (65.5%): aortopulmonary collaterals (n = 9), pulmonary vein stenosis (n = 7), ASD (n = 4), and PDA (n = 9). Hemodynamic data: PVRI 4.3 UW m(2) (2.7-7); PVRI/SVRI 0.44 (0.32-0.8); and transpulmonary gradient 28 mmHg (19-40). At a median follow-up of 35 months (IQR 21-91), 6 patients had undergone shunts closure, 22 received specific PH drugs, 3 spontaneously improved of their PH, and 8 (26%) had died.

CONCLUSION

PH in BPD is not always a transient condition; it can be diagnosed at later stages and can have a protracted course. The incidence of associated CVAs is high. Prompt diagnosis, detection, and treatment of CVAs, and specific drug therapy can improve the outcome in these patients, although the mortality rate remains high.

Oral clonidine in the management of acquired opioid dependency

Clonidine is a nonnarcotic analgesic historically used as a nasal decongestant and more recently established as an antihypertensive agent in adults. Because of its sedative properties with few adverse effects, clonidine has also been reported to be an effective pharmacologic agent for the treatment of neonatal abstinence syndrome (NAS). The use of oral clonidine as a primary or secondary agent in the treatment of NAS has been found to reduce hospitalization and duration of treatment in this population.

Pulmonary hypertension in bronchopulmonary dysplasia

Pulmonary hypertension (PH) is a common complication of neonatal respiratory diseases, including bronchopulmonary dysplasia (BPD), and recent studies have increased awareness that PH worsens the clinical course, morbidity and mortality of BPD. Recent evidence indicates that up to 18% of all extremely low-birth-weight infants will develop some degree of PH during their hospitalization, and the incidence rises to 25-40% of the infants with established BPD. Risk factors are not yet well understood, but new evidence shows that fetal growth restriction is a significant predictor of PH. Echocardiography remains the primary method for evaluation of BPD-associated PH, and the development of standardized screening timelines and techniques for identification of infants with BPD-associated PH remains an important ongoing topic of investigation. The use of pulmonary vasodilator medications, such as nitric oxide, sildenafil, and others, in the BPD population is steadily growing, but additional studies are needed regarding their long-term safety and efficacy.

The pulmonary circulation in neonatal respiratory failure

The pulmonary circulation rapidly adapts at birth to establish lungs as the site of gas exchange. Abnormal transition at birth and/or parenchymal lung disease can result in neonatal hypoxemic respiratory failure. This article reviews the functional changes in pulmonary hemodynamics and structural changes in pulmonary vasculature secondary to (1) normal and abnormal transition at birth, and (2) diseases associated with neonatal hypoxemic respiratory failure. Various management strategies to correct respiratory failure are also discussed.