Pulmonary secretory phospholipase A2 in infants with respiratory distress syndrome stimulates in vitro neutrophil migration.

BACKGROUND: The massive pulmonary neutrophil influx in respiratory distress syndrome (RDS) in preterm infants has been ascribed to the effect of leukotriene B(4) (LTB(4)). OBJECTIVES: To investigate whether secretory phospholipase A(2) (sPLA(2)), the rate-limiting enzyme in LTB(4) production, is present in lungs of RDS infants and stimulates neutrophil migration. METHODS: sPLA(2) was measured in tracheal aspirates from 15 preterm infants with RDS. The effect of aspirates on cord blood neutrophil migration was first measured, and the contribution of sPLA(2) was assessed by addition of its endogenous inhibitor Clara cell protein (CC16) or absorption of sPLA(2) from the aspirates. The role of intracellular signal transduction activation and LTB(4) formation in sPLA(2)-induced neutrophil migration was determined using purified sPLA(2), several inhibitors of signal transduction, a LTB(4) synthesis inhibitor and a LTB(4) receptor antagonist. RESULTS: All aspirates contained sPLA(2), which significantly stimulated neutrophil migration. Addition of CC16 or absorption of sPLA(2) abolished the stimulatory effect. All inhibitors significantly reduced sPLA(2)-induced neutrophil migration. CONCLUSIONS: sPLA(2) is present in tracheal aspirates of preterm infants with RDS. Human recombinant sPLA(2) and pancreatic type sPLA(2) stimulate in vitro cord blood neutrophil migration via activation of intracellular signal transduction pathways, LTB(4) production and receptor binding. We speculate that sPLA(2) contributes to pulmonary neutrophil influx in RDS. Further studies are needed to determine the potential of sPLA(2) inhibition as a treatment for RDS.

Cord blood Clara cell protein CC16 predicts the development of bronchopulmonary dysplasia.

Clara cell protein (CC16) is an anti-inflammatory protein and a biomarker of pulmonary epithelial cells and alveolocapillary membrane injury in adults. We investigated whether low cord blood concentrations of CC16 are associated with the development of respiratory distress syndrome (RDS) and bronchopulmonary dysplasia (BPD) in preterm infants and the relationship between CC16 and its pro-inflammatory counterpart, the secretory phospholipase A(2) (sPLA(2)) enzyme. CC16 concentration, sPLA(2) activity and IL-6 concentration were measured in cord blood plasma from 79 preterm infants (25 controls, 37 infants who developed RDS and 17 infants who developed BPD). After adjustment for gestational age and Apgar score at 5 min, the CC16 concentration was lower in BPD infants than in preterm controls (p<0.01). sPLA(2) activity was similar in all groups and the IL-6 concentrations were increased in both RDS and BPD infants (p<0.01 and p<0.05, respectively, vs. controls). We conclude that low cord blood CC16 concentrations in preterm infants independently predict the development of BPD. Low CC16 levels may reflect early lung injury, which contributes to the severity of RDS and progress towards BPD. Future studies are needed to assess whether the early administration of recombinant human CC16 in preterm infants with low cord blood CC16 prevents the development of BPD.

Meconium is a source of pro-inflammatory substances and can induce cytokine production in cultured A549 epithelial cells.

Inflammation plays an important role in the pathogenesis of meconium aspiration syndrome, and pneumonitis is one of the major characteristics. We have previously shown that meconium has chemotactic properties because of the presence of IL-8. We hypothesize that IL-8 and other proinflammatory substances in meconium may amplify inflammation in meconium aspiration syndrome, inducing endogenous cytokine production by lung epithelial cells. We measured proinflammatory substances in first-pass meconium from healthy newborns and evaluated the effect of sterile meconium on cytokine production in cultured A549 alveolar epithelial cells in vitro. IL-1beta, IL-6, IL-8, and tumor necrosis factor-alpha were measured by ELISA, and heme was measured spectrophotometrically. After incubation of meconium samples with A549 cells, cytokine concentrations in the supernatant were measured. Meconium samples contained variable amounts of IL-1beta, IL-6, IL-8, tumor necrosis factor-alpha, and heme. On stimulation of A549 cells with meconium, the IL-8 concentration in the culture supernatant significantly increased above baseline measurements, whereas tumor necrosis factor-alpha showed a variable pattern and IL-1beta or IL-6 remained unchanged. There was no quantitative relationship between the concentration of the measured cytokines and heme in meconium and cytokine release by the A549 cells after meconium exposure. Meconium contains proinflammatory substances. All samples induced IL-8 release and some induced tumor necrosis factor-alpha release in cultured A549 epithelial cells. We speculate that proinflammatory substances in meconium can induce lung inflammation in meconium aspiration syndrome in two ways: directly via cytokines and heme present in meconium and indirectly by inducing cytokine release by the epithelial lung cells.