Secretory phospholipases A2 stimulate mucus secretion, induce airway inflammation, and produce secretory hyperresponsiveness to neutrophil elastase in ferret trachea
Secretory phospholipases A2 (sPLA2) are increased in the bronchoalveolar lavage fluid of patients with asthma and acute respiratory distress syndrome. Intratracheal sPLA2 instillation induces acute lung injury in the rat and guinea pig. We hypothesized that sPLA2 would stimulate mucus secretion in vitro and that intratracheal sPLA2 exposure would induce mucus hypersecretion and airway inflammation in the ferret trachea in vivo. In vitro, porcine pancreatic sPLA2 at a concentration of 0.5 or 5 U/ml significantly increased mucous glycoconjugate (MG) secretion from the excised ferret trachea. P-bromophenacylbromide (a sPLA2 inhibitor), quercetin (a lipoxygenase inhibitor), or MK-886 (a 5-lipoxygenase inhibitor), each at 10−4 M, significantly reduced sPLA2-induced MG secretion. sPLA2-stimulated MG secretion was decreased in Ca2+-free medium. In vivo, ferrets were intubated for 30 min once per day for 3 days using an ETT coated with 20 units of porcine pancreatic sPLA2 mixed in water-soluble jelly. Constitutive MG secretion increased 1 day after sPLA2 exposure and returned to control 5 days later. Human neutrophil elastase (HNE) at 10−8 M increased MG secretion in the sPLA2-exposed trachea compared with that in the control trachea, but methacholine at 10−7 M did not. sPLA2-induced secretory hyperresponsiveness continued for at least 5 days after sPLA2 exposure ended. sPLA2 increased tracheal inflammation, MG secretion, and secretory hyperresponsiveness to HNE probably through enzymatic action rather than by activation of its receptor.