Hypoxia and hyperoxia potentiate PAF receptor-mediated effects in newborn ovine pulmonary arterial smooth muscle cells: significance in oxygen therapy of PPHN

Abstract

Platelet‐activating factor (PAF) acting via its receptor (PAFR) is implicated in the pathogenesis of persistent pulmonary hypertension of the newborn (PPHN). Effects of long‐term oxygen therapy on newborn lung are not well understood; therefore, we studied the effect of oxygen tension on ovine newborn pulmonary artery smooth muscle cells (NBPASMC). Our global hypothesis is that PPHN results from failure of newborn lamb pulmonary system to downregulate PAFR activity or to upregulate vasodilatory cyclic nucleotides (Cnucs) activity. NBPASMC from newborns 6–12 days old were studied in vitro at three different oxygen tensions (pO 2, [Torr]: hypoxia, <40; normoxia, 80–100; and hyperoxia, >100 Torr often clinically imposed upon newborns with PPHN). PAFR‐ and Cnucs mediated effects were determined. PAFR and PKA Cα mRNA expression as well as prostacyclin, thromboxane, cAMP production, and DNA synthesis was studied to assess PAFR‐mediated hypertrophy and/or hyperplasia. Hypoxia and hyperoxia increased specific PAFR binding. PAF treatment during hyperoxia increased PAFR gene, but decreased PKA‐Cα gene expression. Hypoxia and hyperoxia increased NBPASMC proliferation via PAFR signaling. Baseline prostacyclin level was ninefold greater than in fetal PASMC, whereas baseline thromboxane was sevenfold less suggesting greater postnatal cyclooxygenase activity in NBPASMC. PAF decreased, while forskolin and 8‐Br‐cAMP increased cAMP production. Decrease of PAFR effects by Cnucs indicates that normal newborn PA physiology favors vasodilator pathways to minimize PAF‐induced hypertrophy or hyperplasia. We speculate that failure of newborn lung to anchor downregulation of vasoconstrictors with upregulation of vasodilators leads to PPHN.

In Vitro Consequences of Electronic-Cigarette Flavoring Exposure on the Immature Lung

“…Primary pulmonary artery smooth muscle cell (PASMC) cultures were prepared from intrapulmonary arteries collected from healthy 125 (gestational) day fetal, 2 day newborn lambs, and adult ewes as previously published [44]. Numerous publications support our use of this large animal model, as ovine pulmonary development and physiology parallel human, while cellular metabolism and signaling in isolated tissue and cell lines correlate with findings in human disease [44,45,46,47,48,49,50,51,52,53]. For toxicity studies, cells were maintained in Dulbecco’s Modified Eagle Medium (DMEM) with 10% fetal bovine serum (FBS), 2 mM l-glutamine and 100 units/mL penicillin, 100 mg/mL streptomycin (P/S) under standard cell culture conditions (37 °C with 5% CO 2 ).…”

Oxidative Stress and Respiratory Diseases in Preterm Newborns

“…Furthermore, hyperoxia has been shown to cause mitochondrial dysregulation and genetic reprogramming in the right ventricles of premature rats and stimulate PASMC proliferation in newborn sheep [73,74]. These two mechanisms increase vascular hypertrophy and dysfunction, which are essential for the initiation and maintenance of PPHN.…”

“…Current therapeutic strategies are based on the restoration of all these mechanisms that are altered by oxidative stress, such as the administration of inhaled nitric oxide, sildenafil, bosentan, milrinone, and prostaglandins, which act as vasodilators, in addition to glucocorticoids, which play a role in reducing inflammation. Among commonly used drugs, sildenafil has been shown to reestablish vascular cGMP signaling and reduce right ventricular hypertrophy in a mouse model of hyperoxia-induced PPHN [74].…”

Persistent Pulmonary Hypertension of the Newborn: Pathophysiological Mechanisms and Novel Therapeutic Approaches

“…Exposure to hyperoxia disrupts the normal crosstalk between PAFR-mediated and cAMP/PKA-mediated axes, resulting in increased PASMCs' proliferation. This culminates in vascular hypertrophy and dysfunction, critical for the onset and maintenance of PPHN (117).…”