Pathogenesis and Physiologic Mechanisms of Neonatal Pulmonary Hypertension: Preclinical Studies

Neonatal pulmonary hypertension (PH) is a devastating disorder of the pulmonary vasculature characterized by elevated pulmonary vascular resistance and mean pulmonary arterial pressure. Occurring predominantly because of maldevelopment or maladaptation of the pulmonary vasculature, PH in neonates is associated with suboptimal short-term and long-term outcomes because its pathobiology is unclear in most circumstances, and it responds poorly to conventional pulmonary vasodilators. Understanding the pathogenesis and pathophysiology of neonatal PH can lead to novel strategies and precise therapies. The review is designed to achieve this goal by summarizing pulmonary vascular development and the pathogenesis and pathophysiology of PH associated with maladaptation, bronchopulmonary dysplasia, and congenital diaphragmatic hernia based on evidence predominantly from preclinical studies. We also discuss the pros and cons of and provide future directions for preclinical studies in neonatal PH.

Development of a portable mini-generator to safely produce nitric oxide for the treatment of infants with pulmonary hypertension

OBJECTIVES

To test the safety of a novel miniaturized device that produces nitric oxide (NO) from air by pulsed electrical discharge, and to demonstrate that the generated NO can be used to vasodilate the pulmonary vasculature in rabbits with chemically-induced pulmonary hypertension.

STUDY DESIGN

A miniature NO (mini-NO) generator was tested for its ability to produce therapeutic levels (20-80 parts per million (ppm)) of NO, while removing potentially toxic gases and metal particles. We studied healthy 6-month-old New Zealand rabbits weighing 3.4 ± 0.4 kg (mean ± SD, n = 8). Pulmonary hypertension was induced by chemically increasing right ventricular systolic pressure to 28-30 mmHg. The mini-NO generator was placed near the endotracheal tube. Production of NO was triggered by a pediatric airway flowmeter during the first 0.5 s of inspiration.

RESULTS

In rabbits with acute pulmonary hypertension, the mini-NO generator produced sufficient NO to induce pulmonary vasodilation. Potentially toxic nitrogen dioxide (NO₂) and ozone (O₃) were removed by the Ca(OH)₂ scavenger. Metallic particles, released from the electrodes by the electric plasma, were removed by a 0.22 μm filter. While producing 40 ppm NO, the mini-NO generator was cooled by a flow of air (70 ml/min) and the external temperature of the housing did not exceed 31 °C.

CONCLUSIONS

The mini-NO generator safely produced therapeutic levels of NO from air. The mini-NO generator is an effective and economical approach to producing NO for treating neonatal pulmonary hypertension and will increase the accessibility and therapeutic uses of life-saving NO therapy worldwide.

2-AMINOETHYLDIPHENYLBORINATE MODIFIES THE PULMONARY CIRCULATION IN PULMONARY HYPERTENSIVE NEWBORN LAMBS WITH PARTIAL GESTATION AT HIGH ALTITUDE

Calcium signaling through store operated channels (SOC) is involved in hypoxic pulmonary hypertension. We determined whether a treatment with 2-aminoethyldiphenylborinate (2-APB), a compound with SOC blocker activity, reduces pulmonary hypertension and vascular remodeling. Twelve newborn lambs exposed to perinatal chronic hypoxia were studied, 6 of them received a 2-APB treatment and the other 6 received vehicle treatment, for 10 days in both cases. Throughout this period, we recorded cardiopulmonary variables and on day 11 we evaluated the response to an acute hypoxic challenge. Additionally, we assessed the vasoconstrictor and vasodilator function in isolated pulmonary arteries as well as their remodeling in lung slices. 2-APB reduced pulmonary arterial pressure at the third and tenth days, cardiac output between the fourth and eighth days, and pulmonary vascular resistance at the tenth day of treatment. The pulmonary vasoconstrictor response to acute hypoxia was reduced by the end of treatment. 2-APB also decreased maximal vasoconstrictor response to the thromboxane mimetic U46619 and endothelin-1 and increased maximal relaxation to 8-Br-cGMP. The maximal relaxation and potency to phosphodiesterase-5 and Rho-kinase inhibition with sildenafil and fasudil respectively, were also increased. Finally, 2-APB reduced the medial and adventitial layers' thickness, the expression of α-actin and the percentage of Ki67+ nuclei of small pulmonary arteries. Taken together, our results indicate that 2-APB reduces pulmonary hypertension, vasoconstrictor responses and pathological remodeling in pulmonary hypertensive lambs. We conclude that SOC targeting may be a useful strategy for the treatment of neonatal pulmonary hypertension, however, further testing of specific blockers is needed.