Modeling and Remodeling of the Lung in Neonatal Chronic Lung Disease

Addressing the long-term risks of administering antenatal steroids

INTRODUCTION

A single course of antenatal steroid (ANS) therapy is standard of care for women at risk of preterm birth, reducing the risk of neonatal respiratory distress syndrome, neonatal morbidity, and mortality. An unresolved challenge relates to the potential risk of adverse long-term effects, and how these risks might be balanced with therapeutic benefit.

AREAS COVERED

We outline key concepts in glucocorticoid signaling, pharmacokinetics/pharmacodynamics, and clinical use before presenting data on the potential long-term harms of ANS therapy.

EXPERT OPINION

Our assessment is that: i) Currently used, high dose ANS regimens can induce multi-system changes in the fetus that alter growth and development, potentially increasing long-term disease risk; and ii) relative risks likely increase proportionally to the magnitude and duration of steroid exposure, in late preterm and term ANS use, and in off-target treatments. A single course of ANS therapy to at risk women between 24- and 34-weeks' gestation is well justified. Efforts should be made to improve dosing and patient selection. At periviable gestations, the high immediate risk of serious disease or death justifies modest long-term risks. At late preterm and term gestations, where steroids do not provide notable survival or health benefits, supporting routine ANS use is more difficult.

Characterization of the fetal blood transcriptome and proteome in maternal anti-fetal rejection: evidence of a distinct and novel type of human fetal systemic inflammatory response

BACKGROUND

The human fetus is able to mount a systemic inflammatory response when exposed to microorganisms. This stereotypic response has been termed the 'fetal inflammatory response syndrome' (FIRS), defined as an elevation of fetal plasma interleukin-6 (IL-6). FIRS is frequently observed in patients whose preterm deliveries are associated with intra-amniotic infection, acute inflammatory lesions of the placenta, and a high rate of neonatal morbidity. Recently, a novel form of fetal systemic inflammation, characterized by an elevation of fetal plasma CXCL10, has been identified in patients with placental lesions consistent with 'maternal anti-fetal rejection'. These lesions include chronic chorioamnionitis, plasma cell deciduitis, and villitis of unknown etiology. In addition, positivity for human leukocyte antigen (HLA) panel-reactive antibodies (PRA) in maternal sera can also be used to increase the index of suspicion for maternal anti-fetal rejection. The purpose of this study was to determine (i) the frequency of pathologic lesions consistent with maternal anti-fetal rejection in term and spontaneous preterm births; (ii) the fetal serum concentration of CXCL10 in patients with and without evidence of maternal anti-fetal rejection; and (iii) the fetal blood transcriptome and proteome in cases with a fetal inflammatory response associated with maternal anti-fetal rejection.

METHOD OF STUDY

Maternal and fetal sera were obtained from normal term (n = 150) and spontaneous preterm births (n = 150). A fetal inflammatory response associated with maternal anti-fetal rejection was diagnosed when the patients met two or more of the following criteria: (i) presence of chronic placental inflammation; (ii) ≥80% of maternal HLA class I PRA positivity; and (iii) fetal serum CXCL10 concentration >75th percentile. Maternal HLA PRA was analyzed by flow cytometry. The concentrations of fetal CXCL10 and IL-6 were determined by ELISA. Transcriptome analysis was undertaken after the extraction of total RNA from white blood cells with a whole-genome DASL assay. Proteomic analysis of fetal serum was conducted by two-dimensional difference gel electrophoresis. Differential gene expression was considered significant when there was a P < 0.01 and a fold-change >1.5.

RESULTS

(i) The frequency of placental lesions consistent with maternal anti-fetal rejection was higher in patients with preterm deliveries than in those with term deliveries (56% versus 32%; P < 0.001); (ii) patients with spontaneous preterm births had a higher rate of maternal HLA PRA class I positivity than those who delivered at term (50% versus 32%; P = 0.002); (iii) fetuses born to mothers with positive maternal HLA PRA results had a higher median serum CXCL10 concentration than those with negative HLA PRA results (P < 0.001); (iv) the median serum CXCL10 concentration (but not IL-6) was higher in fetuses with placental lesions associated with maternal anti-fetal rejection than those without such lesions (P < 0.001); (v) a whole-genome DASL assay of fetal blood RNA demonstrated differential expression of 128 genes between fetuses with and without lesions associated with maternal anti-fetal rejection; and (vi) comparison of the fetal serum proteome demonstrated 20 proteins whose abundance differed between fetuses with and without lesions associated with maternal anti-fetal rejection.

CONCLUSION

We describe a systemic inflammatory response in human fetuses born to mothers with evidence of maternal anti-fetal rejection. The transcriptome and proteome of this novel type of fetal inflammatory response were different from that of FIRS type I (which is associated with acute infection/inflammation).

The physiological determinants of sudden infant death syndrome

It is well-established that environmental and biological risk factors contribute to Sudden Infant Death Syndrome (SIDS). There is also growing consensus that SIDS requires the intersection of multiple risk factors that result in the failure of an infant to overcome cardio-respiratory challenges. Thus, the critical next steps in understanding SIDS are to unravel the physiological determinants that actually cause the sudden death, to synthesize how these determinants are affected by the known risk factors, and to develop novel ideas for SIDS prevention. In this review, we will examine current and emerging perspectives related to cardio-respiratory dysfunctions in SIDS. Specifically, we will review: (1) the role of the preBötzinger complex (preBötC) as a multi-functional network that is critically involved in the failure to adequately respond to hypoxic and hypercapnic challenges; (2) the potential involvement of the preBötC in the gender and age distributions that are characteristic for SIDS; (3) the link between SIDS and prematurity; and (4) the potential relationship between SIDS, auditory function, and central chemosensitivity. Each section underscores the importance of marrying the epidemiological and pathological data to experimental data in order to understand the physiological determinants of this syndrome. We hope that a better understanding will lead to novel ways to reduce the risk to succumb to SIDS.

Risk factors for bronchopulmonary dysplasia in five Portuguese neonatal intensive care units

The pathogenesis of bronchopulmonary dysplasia (BPD) is clearly multifactorial. Specific pathogenic risk factors are prematurity, respiratory distress, oxygen supplementation, mechanical ventilation (MV), inflammation, patent ductus arteriosus (PDA), etc.

AIM

To evaluate BPD prevalence and to identify risk factors for BPD in five Portuguese Neonatal Intensive Care Units in order to develop better practices the management of these newborns.

MATERIAL AND METHODS

256 very low birth weight infants with gestational age (GA) <30 weeks and/or birthweight (BW) <1250 g admitted in five Portuguese NICUs, between 2004 and 2006 were studied. A protocol was filled in based on clinical information registered in the hospital charts. BPD was defined as oxygen dependency at 36 weeks of postconceptional age.

RESULTS

BPD prevalence was 12.9% (33/256). BPD risk decreased 46% per GA week and of 39% per 100g BW. BPD risk was significantly higher among newborns with low BW (adj OR= 0.73, 95% CI=0.57- 0.95), severe hyaline membrane disease (adj OR= 9.85, 95% CI=1.05-92.35), and those with sepsis (adj OR=6.22, 95% CI=1.68-23.02), those with longer duration on ventilatory support (42 vs 3 days, respectively in BPD and no BPD patients, p <0.001) and longer duration of FiO2>0.30 (85 vs 5 days, respectively in BPD and no BPD patients, p <0.001).

COMMENTS

The most relevant risk factors were low birth weight, severe hyaline membrane disease, duration of respiratory support and oxygen therapy, and nosocomial sepsis. The implementation of potentially better practices to reduce lung injury in neonates must be addressed to improve practices to decrease these risk factors.

Relationship between endotracheal tube leakage and under-reading of tidal volume in neonatal ventilators

AIM

Protective ventilation in neonates requires careful volume monitoring to prevent ventilator-induced lung injury caused by baro/volutrauma and hence chronic lung disease. This study investigated the effect of endotracheal tube (ET) leakage on the displayed tidal volume using an in vitro model.

METHODS

A neonatal lung model was ventilated via a 3 mm ET using three ventilators [Babylog 8000 (BL), Leoni (LE) and Stephanie (ST)]. Tidal volume was measured by each ventilator at the Y-piece and by a pneumotach (CO(2)SMO(+)) in the model. ET leaks were simulated by open tubes of different lengths. PIP (20 cmH(2)O) and PEEP (5 cmH(2)O) were kept constant, and the respiratory rate (RR) was varied between 20/min and 70/min (Ti:Te = 1:1).

RESULTS

Tidal volume displayed by a ventilator decreased independently of RR with increasing leakage up to 21% (BL), 30% (LE) and 33% (ST). However, the volume delivered to the lung was nearly constant. The displayed leakage varied between 0 and 78% and was dependent on RR and leakage resistance. There were distinct differences between the three ventilators in the relationship between displayed leakage and volume error. Accepting a volume error <10% for RR between 20 and 70/min, ET leakage of up to 20% for BL, 12% for LE, but only <5% for ST, was acceptable.

CONCLUSION

Tidal volume underestimation arising from ET leakage depends on ventilator pressures, timing parameters and ventilator-specific algorithms for signal processing. Therefore, neonatologists should be aware of these issues to prevent lung over-inflation when adjusting target volume in the presence of ET leakage.

Retinol combined with retinoic acid increases retinol uptake and esterification in the lungs of young adult rats when delivered by the intramuscular as well as oral routes

The lungs require an adequate supply of vitamin A for normal embryonic development, postnatal maturation, and maintenance and repair during adult life. We have previously shown that a nutrient-metabolite combination of vitamin A admixed with a small proportion (10%) of retinoic acid (RA), referred to as VARA, acts synergistically to increase lung retinyl ester (RE) concentration in neonatal rats. A series of studies was designed to test whether VARA increases RE in adult lungs, and whether VARA is more effective than vitamin A when given by the i.m. route. Orally administered VARA increased RE in the lungs of vitamin A-marginal adult rats more than either vitamin A or RA alone (P < 0.05). In vitamin A-deficient young adult rats, lung RE was increased by VARA when administered by the i.m. route. When a tracer of (3)H-retinol was added to the placebo (oil), vitamin A, and VARA doses, total (3)H and (3)H-RE increased in the lungs more with VARA than vitamin A alone, for oral and i.m. dosing. Nevertheless, when VARA and vitamin A were given by the oral route, they were more effective in increasing RE in the liver. Plasma retinol was increased similarly in vitamin A-deficient rats after administration of VARA and vitamin A, by either the oral or the i.m. route. Overall, VARA can increase retinol uptake and esterification in adult lungs when delivered intramuscularly as well as orally.

Cell type-specific effect of hypoxia and platelet-derived growth factor-BB on extracellular matrix turnover and its consequences for lung remodeling

Hypoxia is associated with extracellular matrix remodeling in several inflammatory lung diseases, such as fibrosis, chronic obstructive pulmonary disease, and asthma. In a human cell culture model, we assessed whether extracellular matrix modification by hypoxia and platelet-derived growth factor (PDGF) involves the action of matrix metalloproteinases (MMPs) and thereby affects cell proliferation. Expression of MMP and its activity were assessed by zymography and enzyme-linked immunosorbent assay in human lung fibroblasts and pulmonary vascular smooth muscle cells (VSMCs), and synthesis of soluble collagen type I was assessed by enzyme-linked immunosorbent assay. In both cell types, hypoxia up-regulated the expression of MMP-1, -2, and -9 precursors without subsequent activation. MMP-13 was increased by hypoxia only in fibroblasts. PDGF-BB inhibited the synthesis and secretion of all hypoxia-dependent MMP via Erk1/2 mitogen-activated protein (MAP) kinase activation. Hypoxia and PDGF-BB induced synthesis of soluble collagen type I via Erk1/2 and p38 MAP kinase. Hypoxia-induced cell proliferation was blocked by antibodies to PDGF-BB or by inhibition of Erk1/2 but not by the inhibition of MMP or p38 MAP kinase in fibroblasts. In VSMCs, hypoxia-induced proliferation involved Erk1/2 and p38 MAP kinases and was further increased by fibroblast-conditioned medium or soluble collagen type I via Erk1/2. In conclusion, hypoxia controls tissue remodeling and proliferation in a cell type-specific manner. Furthermore, fibroblasts may affect proliferation of VSMC indirectly by inducing the synthesis of soluble collagen type I.

Lung disease and brain development

With the technical progress made in fetal and neonatal intensive care, perinatal mortality has decreased by 25% over the last decade and has expanded the surviving premature population. Prematurity drastically changes the environment of the developing organism. Striking evidence from a number of disciplines has focused attention on the interplay between the developing organism and the circumstances in which it finds itself. The environmental event during a sensitive period in development, induces injury and/or biological adaptations that lead to altered differentiation of tissues. The organism can express specific adaptive responses to its environment which include short-term changes in physiology as well as long-term adjustments. This review addresses these short-term as well as longer-term changes occurring in lung and brain tissue and illustrates how these changes can be studied using advanced imaging techniques such as magnetic resonance imaging