Therapies that enhance pulmonary vascular NO-signaling in the neonate

Nitric oxide regulation of fetal and newborn lung development and function

In the developing lung, nitric oxide (NO) and cyclic guanosine monophosphate (cGMP) signaling are essential in regulating lung formation and vascular tone. Animal studies have linked many anatomical and pathophysiological features of newborn lung disease to abnormalities in the NO/cGMP signaling system. They have demonstrated that driving this system with agonists and antagonists alleviates many of them. This research has spurred the rapid clinical development, testing, and application of several NO/cGMP-targeting therapies with the hope of treating and potentially preventing significant pediatric lung diseases. However, there are instances when the therapeutic effectiveness of these agents is limited. Studies indicate that injury-induced disruption of several critical components within the signaling system may hinder the promise of some of these therapies. Recent research has identified basic mechanisms that suppress NO/cGMP signaling in the injured newborn lung. They have also pinpointed biomarkers that offer insight into the activation of these pathogenic mechanisms and their influence on the NO/cGMP signaling system's integrity in vivo. Together, these will guide the development of new therapies to protect NO/cGMP signaling and safeguard newborn lung development and function. This review summarizes the important role of the NO/cGMP signaling system in regulating pulmonary development and function and our evolving understanding of how it is disrupted by newborn lung injury.

Successful Weaning From Veno-Venous Extracorporeal Membrane Oxygenation (VV-ECMO) After Initiation of Inhaled Epoprostenol in a Neonate With Refractory Persistent Pulmonary Hypertension of the Newborn (PPHN)

Despite improvements in the medical management of persistent pulmonary hypertension of the newborn (PPHN), a significant number of patients persist with inadequate gas exchange and are treated with extracorporeal membrane oxygenation (ECMO). Prolonged time to weaning ECMO can increase mortality risk. Therefore, multiple therapies are utilized for pulmonary hypertension treatment, including pharmacotherapy with pulmonary vasodilators, to improve the prognosis of these critical patients. We report a case of a 37 2/7-week neonate with severe PPHN refractory to triple pulmonary vasodilator therapy (inhaled nitric oxide (iNO), sildenafil, and milrinone) and required veno-venous (VV)-ECMO support to improve oxygenation. Our patient was successfully weaned from ECMO after the addition of inhaled epoprostenol (iEPO) therapy. This report indicates that inhaled prostacyclin therapy effectively helps refractory PPHN patients off extracorporeal life support (ECLS) and should be considered a valuable treatment.

Worsened short-term clinical outcomes in a cohort of patients with iNO-unresponsive PPHN: a case for improving iNO responsiveness

OBJECTIVES

To identify distinguishing characteristics of neonates with persistent pulmonary hypertension of the newborn (PPHN) unresponsive to inhaled nitric oxide (iNO) and evaluate the use of milrinone in this cohort.

STUDY DESIGN

Retrospective chart review of 99 neonates with PPHN treated with iNO over a five-year period at a quaternary neonatal intensive care unit.

RESULTS

Neonates with iNO-unresponsive PPHN had an increased number of ventilator days (10 vs 7 days, p = 0.02), greater length of hospital stay (30 vs 22 days, p = 0.02), and increased risk of death or ECMO than iNO-responsive neonates (p = 0.03). Inhaled NO non-responders treated with milrinone had improved oxygenation (p < 0.03) and no change in systemic hemodynamics.

CONCLUSION

Neonates with iNO-unresponsive PPHN had worse clinical outcomes than iNO responders. Milrinone may be a safe and effective adjuvant therapy, although large-scale studies are lacking. Identifying early predictors of iNO response and novel strategies to enhance iNO responsiveness should be prioritized.

Nitric Oxide-cGMP Pathway Modulation in an Experimental Model of Hypoxic Pulmonary Hypertension

Manipulation of nitric oxide (NO) may enable control of progression and treatment of pulmonary hypertension (PH). Several approaches may modulate the NO-cGMP pathway in vivo. Here, we investigate the effectiveness of 3 modulatory sites: (i) the amount of l-arginine; (ii) the size of plasma NO stores that stimulate soluble guanylate cyclase; (iii) the conversion of cGMP into inactive 5′-GMP, with respect to hypoxia, to test the effectiveness of the treatments with respect to hypoxia-induced PH. Male rats (n = 80; 10/group) maintained in normoxic (21% O₂) or hypoxic chambers (10% O₂) for 14 days were subdivided in 4 sub-groups: placebo, l-arginine (20 mg/ml), the NO donor molsidomine (15 mg/kg in drinking water), and phoshodiesterase-5 inhibitor sildenafil (1.4 mg/kg in 0.3 ml saline, i.p.). Hypoxia depressed homeostasis and increased erythropoiesis, heart and right ventricle hypertrophy, myocardial fibrosis and apoptosis inducing pulmonary remodeling. Stimulating anyone of the 3 mechanisms that enhance the NO-cGMP pathway helped rescuing the functional and morphological changes in the cardiopulmonary system leading to improvement, sometimes normalization, of the pressures. None of the treatments affected the observed parameters in normoxia. Thus, the 3 modulatory sites are essentially similar in enhancing the NO-cGMP pathway, thereby attenuating the hypoxia-related effects that lead to pulmonary hypertension.

Preserved activity of soluble guanylate cyclase (sGC) in iliac artery from middle-aged rats: Role of sGC modulators

Vascular aging leads to structural and functional changes. Iliac arteries (IA) provide blood flow to lower urinary tract and pelvic ischemia has been reported as an important factor for bladder remodeling and overactivity. Dysfunction of the nitric oxide (NO)-cyclic guanosine monophosphate pathway (cGMP) is one factor involved in the development of lower urinary tract (LUT) disorders. Therefore, we hypothesized that ageing-associated LUT disorders is a consequence of lower cGMP productions due to an oxidation of soluble guanylate cylase (sGC) that results in local ischemia. In the present study IA from middle-aged and young rats were isolated and the levels of NO, reactive oxygen species (ROS), the gene expression of the enzymes involved in the NO-pathway and concentration-response curves to the soluble guanylate (sGC) stimulator (BAY 41-2272), sGC activator (BAY 58-2667), tadalafil, acetylcholine (ACh) and sodium nitroprusside (SNP) were determined. In IA from middle-aged rats the gene expression for endothelial nitric oxide synthase and the ROS were lower and higher, respectively than the young group. The relaxations induced by ACh and SNP were significantly lower in IA from middle-aged rats. In IA from middle-aged rats the mRNA expression of PDE5 was 55% higher, accompanied by lower relaxation induced by tadalafil. On the other hand, the gene expression for sGCα1 were similar in IA from both groups. Both BAY 41-2272 and BAY 58-2667 produced concentration-dependent relaxations in IA from both groups, however, the latter was 9-times more potent than BAY 41-2272 and produced similar relaxations in IA in both middle-aged and young groups. Yet, the sGC oxidant, ODQ increased the relaxation and the cGMP levels induced by BAY 58-2667. On the other hand, in tissues stimulated with SNP, tadalafil and BAY-2272, the intracellular levels of cGMP were lower in IA from middle-aged than young rats. In conclusion, our results clearly showed that the relaxations induced by the endothelium-dependent and -independent agents, by the PDE5 inhibitor and by sGC stimulator were impaired in IA from aged rats, while that induced by sGC activator was preserved. It suggests that sGC activator may be advantageous in treating ischemia-related functional changes in the lower urinary tract organs in situations where the NO levels are reduced.

Life-threatening PPHN refractory to nitric oxide: proposal for a rational therapeutic algorithm

Persistent pulmonary hypertension of the neonate (PPHN) refractory to inhaled nitric oxide still represents a frequent clinical challenge with negative outcomes in neonatal critical care. Several pulmonary vasodilators have become available thanks to improved understanding of pulmonary hypertension pathobiology. These drugs are commonly used in adults and there are numerous case series and small studies describing their potential usefulness in neonates, as well. New vasodilators act on different pathways, some of them can have additive effects and all have different pharmacology features. This information has never been summarized so far and no comprehensive pathobiology-driven algorithm is available to guide the treatment of refractory PPHN.Conclusion: We offer a rational clinical algorithm to guide the treatment of refractory PPHN based on expert advice and the more recent pathobiology and pharmacology knowledge. What is Known: • Refractory PPHN occurs in 30-40% of iNO-treated neonates and represents a significant clinical problem. Several pulmonary vasodilators have become available thanks to a better understanding of pulmonary hypertension pathobiology. What is New: • Available vasodilators have different pharmacology, mechanisms of action and may provide additive effect. We provide a rational clinical algorithm to guide the treatment of refractory PPHN based on expert advice and the more recent pathobiology and pharmacology knowledge.