Update in Pediatric Lung Disease 2009

A preterm pig model of lung immaturity and spontaneous infant respiratory distress syndrome

Respiratory distress syndrome (RDS) and bronchopulmonary dysplasia remain the leading causes of preterm infant morbidity, mortality, and lifelong disability. Research to improve outcomes requires translational large animal models for RDS. Preterm pigs delivered by caesarian section at gestation days (GD) 98, 100, 102, and 104 were provided 24 h of neonatal intensive care, monitoring (pulse oximetry, blood gases, serum biomarkers, radiography), and nutritional support, with or without intubation and mechanical ventilation (MV; pressure control ventilation with volume guarantee). Spontaneous development of RDS and mortality without MV are inversely related with GD at delivery and correspond with inadequacy of tidal volume and gas exchange. GD 98 and 100 pigs have consolidated lungs, immature alveolar architecture, and minimal surfactant protein-B expression, and MV is essential at GD 98. Although GD 102 pigs had some alveoli lined by pneumocytes and surfactant was released in response to MV, blood gases and radiography revealed limited recruitment 1-2 h after delivery, and mortality at 24 h was 66% (35/53) with supplemental oxygen provided by a mask and 69% (9/13) with bubble continuous positive airway pressure (8-9 cmH2O). The lungs at GD 104 had higher densities of thin-walled alveoli that secreted surfactant, and MV was not essential. Between GD 98 and 102, preterm pigs have ventilation inadequacies and risks of RDS that mimic those of preterm infants born during the saccular phase of lung development, are compatible with standards of neonatal intensive care, and are alternative to fetal nonhuman primates and lambs.

Prenatal inflammatory risk factors for development of bronchopulmonary dysplasia

BACKGROUND

Bronchopulmonary dysplasia (BPD) is a serious, chronic lung disease affecting preterm infants.

OBJECTIVE

To identify prenatal risk factors for BPD, focusing on inflammation.

METHODS

Observational cohort study including 106,339 preterm infants, live born before gestational week 37 + 0, from 1988 to 2009 in Sweden. A total of 2,115 infants were diagnosed with BPD, of which 1,393 were born extremely preterm, before gestational week 28 + 0. Information on risk factors was obtained from national health registers and included maternal chronic inflammatory diseases, pregnancy related diseases, and drugs related to treatment of inflammation or infection during pregnancy. Adjusted odds ratios (OR) were calculated in multivariable logistic regression models and are presented with 95% confidence intervals [95% CI].

RESULTS

Preeclampsia was the strongest risk factor for BPD [adjusted OR 2.04, 95% CI 1.83, 2.29]. For extremely preterm infants the adjusted OR was 1.33 [95% CI 1.08, 1.64]. Chorioamnionitis was associated with an increased risk of BPD, but only when including all infants in the analyses [OR 1.33, 95% CI 1.19, 1.48]. No apparent associations were found between maternal chronic inflammatory disease or use of anti-inflammatory drugs and the risk of BPD. Maternal diabetes mellitus, gestational diabetes and maternal use of antibiotics were associated with reduced risks of BPD.

CONCLUSION

Preeclampsia related disorders increased the risk and maternal diabetes mellitus and gestational diabetes reduced the risk for BPD. As angiogenic factors play a role in preeclampsia and diabetes our findings suggest that an impaired angiogenesis may contribute to BPD development.

IL-10 inhibits inflammatory cytokines released by fetal mouse lung fibroblasts exposed to mechanical stretch

BACKGROUND

Mechanical ventilation plays an important role in the pathogenesis of bronchopulmonary dysplasia. However, the molecular mechanisms by which excessive stretch induces lung inflammation are not well characterized.

OBJECTIVES

In this study, we investigated in vitro the contribution of lung mesenchymal cells to the inflammatory response mediated by mechanical stretch and the potential protective role of IL-10.

METHODS

Fetal mouse lung fibroblasts isolated during the saccular stage of lung development were exposed to 20% cyclic stretch to simulate mechanical injury. The phenotype of cultured fibroblasts was investigated by red oil O and alpha-smooth muscle actin (α-SMA) staining. Cell necrosis, apoptosis, and inflammation were analyzed by lactate dehydrogenase release, cleaved caspase-3 activation and release of cytokines and chemokines into the supernatant, respectively.

RESULTS

First, we characterized the phenotype of the cultured fibroblasts and found an absence of red oil O staining and 100% positive staining for α-SMA, indicating that cultured fibroblasts were myofibroblasts. Mechanical stretch increased necrosis and apoptosis by two- and three-fold, compared to unstretched samples. Incubation of monolayers with IL-10 prior to stretch did not affect necrosis but significantly decreased apoptosis. Mechanical stretch increased release of pro-inflammatory cytokines and chemokines IL-1β, MCP-1, RANTES, IL-6, KC and TNF-α into the supernatant by 1.5- to 2.5-fold, and administration of IL-10 before stretch blocked that release.

CONCLUSIONS

Our data demonstrate that lung interstitial cells may play a significant role in the inflammatory cascade triggered by mechanical stretch. IL-10 protects fetal fibroblasts from injury secondary to stretch. Pediatr. Pulmonol. 2011; 46:640-649. © 2011 Wiley-Liss, Inc.

Differential expression of MMP-2 and -9 and their inhibitors in fetal lung cells exposed to mechanical stretch: regulation by IL-10

STUDY OBJECTIVES

Abnormal remodeling of the extracellular matrix (ECM) has been implicated in the pathogenesis of bronchopulmonary dysplasia. However, the contribution of lung parenchymal cells to ECM remodeling after mechanical injury is not well defined. The objective of these studies was to investigate in vitro the release of MMP-2 and -9 and their respective inhibitors TIMP-2 and -1, and to explore potential regulation by IL-10.

DESIGN

Mouse fetal epithelial cells and fibroblasts isolated on E18-19 of gestation were exposed to 20% cyclic stretch to simulate lung injury. MMP-2 and MMP-9 activity were investigated by zymography and ELISA. TIMP-1 and TIMP-2 abundance were analyzed by Western blot.

RESULTS

We found that mechanical stretch increased MMP-2 and decreased TIMP-2 in fibroblasts, indicating that excessive stretch promotes MMP-2 activation, expressed as the MMP-2/TIMP-2 ratio. Incubation with IL-10 did not change MMP-2 activity. In contrast, mechanical stretch of epithelial cells decreased MMP-9 activity and the MMP-9/TIMP-1 ratio by 60-70%. When IL-10 was added, mechanical stretch increased the MMP-9/TIMP-1 ratio by 50%.

CONCLUSIONS

We conclude that mechanical stretch differentially affects MMP-2/9 and their inhibitors in fetal lung cells. IL-10 modulates MMP-9 activity through a combination of effects on MMP-9 and TIMP-1 levels.