Secreted phospholipase A2 hydrolyzes surfactant phospholipids and is crucial for the inflammatory cascade; preterm neonates are treated with exogenous surfactant, but the interaction between surfactant and phospholipase is unknown. We hypothesize that this interplay is complex and the enzyme plays a relevant role in neonates needing surfactant replacement. We aimed to: 1) identify phospholipases A2 isoforms expressed in preterm lung; 2) study the enzyme role on surfactant retreatment and function and the effect of exogenous surfactant on the enzyme system; and 3) verify whether phospholipase A2 is linked to respiratory outcomes. In bronchoalveolar lavages of preterm neonates, we measured enzyme activity (alone or with inhibitors), enzyme subtypes, surfactant protein-A, and inflammatory mediators. Surfactant function and phospholipid profile were also tested. Urea ratio was used to obtain epithelial lining fluid concentrations. Follow-up data were prospectively collected. Subtype-IIA is the main phospholipase isoform in preterm lung, although subtype-IB may be significantly expressed. Neonates needing surfactant retreatment have higher enzyme activity (P = 0.021) and inflammatory mediators (P always ≤ 0.001) and lower amounts of phospholipids (P always < 0.05). Enzyme activity was inversely correlated to surfactant adsorption (ρ = -0.6; P = 0.008; adjusted P = 0.009), total phospholipids (ρ = -0.475; P = 0.05), and phosphatidylcholine (ρ = -0.622; P = 0.017). Exogenous surfactant significantly reduced global phospholipase activity (P < 0.001) and subtype-IIA (P = 0.005) and increased dioleoylphosphatidylglycerol (P < 0.001) and surfactant adsorption (P < 0.001). Enzyme activity correlated with duration of ventilation (ρ = 0.679, P = 0.005; adjusted P = 0.04) and respiratory morbidity score at 12 mo postnatal age (τ-b = 0.349, P = 0.037; adjusted P = 0.043) but was not associated with mortality, bronchopulmonary dysplasia, or other long-term respiratory outcomes.
Keywords: RDS; lung injury; newborn infant; phospholipase A2; prematurity; surfactant.