Tracheomalacia in bronchopulmonary dysplasia: Trachealis hyper-relaxant responses to S-nitrosoglutathione in a hyperoxic murine model

Background: Bronchopulmonary dysplasia (BPD) with airway hyperreactivity is a long-term pulmonary complication of prematurity. The endogenous nonadrenergic, noncholinergic signaling molecule, S-nitrosoglutathione (GSNO) and its catabolism by GSNO reductase (GSNOR) modulate airway reactivity. Tracheomalacia is a major, underinvestigated complication of BPD. We studied trachealis, left main bronchus (LB), and intrapulmonary bronchiolar (IPB) relaxant responses to GSNO in a murine hyperoxic BPD model.

Methods: Wild-type (WT) or GSNOR knockout (KO) newborn mice were raised in 60% (BPD) or 21% (control) oxygen during the first 3 weeks of life. After room air recovery, adult trachealis, LB, and IPB smooth muscle relaxant responses to GSNO (after methacholine preconstriction) were studied using wire myographs. Studies were repeated after GSNOR Inhibitor (GSNORi) pretreatment and in KO mice.

Results: GSNO relaxed all airway preparations. GSNO relaxed WT BPD trachealis substantially more than WT controls (P < .05). Pharmacologic or genetic ablation of GSNOR abolished the exaggerated BPD tracheal relaxation to GSNO and also augmented BPD IPB relaxation to GSNO. LB ring contractility was not significantly different between groups or conditions. Additionally, GSNORi treatment induced relaxation of WT IPBs but not trachealis or LB.

Conclusion: GSNO dramatically relaxed the trachealis in our BPD model, an effect paradoxically reversed by loss of GSNOR. Conversely, GSNOR inhibition augmented IBP relaxation. These data suggest that GSNOR inhibition could benefit both the BPD trachealis and distal airways, restoring relaxant responses to those of room air controls. Because therapeutic options are limited in this high-risk population, future studies of GSNOR inhibition are needed.