Epidemiology of bronchopulmonary dysplasia

Risk Factors and Clinical Outcomes in Preterm Infants with Pulmonary Hypertension

BACKGROUND

Pulmonary hypertension (PH) is a significant cause of morbidity in preterm infants, but no screening guidelines exist. We sought to identify risk factors and clinical outcomes associated with PH in preterm infants to develop a PH risk score.

METHODS

Retrospective analysis of two separate populations of preterm infants (NICU cohort n = 230; Clinic registry n = 580).

RESULTS

8.3% of the NICU cohort had PH after 4 weeks of age, while 14.8% of the clinic registry had PH after 2 months of age. Lower birth weights and longer initial hospitalizations were associated with PH in both populations (p<0.001 for all tests). Using adjusted logistic regression, patent ductus arteriosus (PDA) requiring ligation was associated with PH in both the NICU cohort (OR: 3.19; p = 0.024) and the clinic registry (OR: 2.67; p<0.001). Risk factors (birth weight ≤780 grams, home supplemental oxygen use, and PDA ligation) identified in the clinic registry (training dataset) were validated in the NICU cohort with 0-1 factors present were associated with ≤1.5% probability of having PH, any 2 factors with a 25% probability, and all 3 factors with a 40% probability.

CONCLUSIONS

Lower birth weight, PDA ligation, and respiratory support were associated with PH in both populations. A PH risk score based on clinical indicators from the training dataset predicted PH in the validation set. This risk score could help focus resources to preterm infants at higher risk for PH. Further work is needed to determine whether earlier or more aggressive management of ductal lesions could alter PH outcomes.

Inhaled Vitamin D: A Novel Strategy to Enhance Neonatal Lung Maturation

INTRODUCTION

The physiologic vitamin D (VD), 1α,25(OH)₂D₃ (1,25D) is a local paracrine/autocrine effecter of fetal lung maturation. By stimulating alveolar type II cell and lipofibroblast proliferation and differentiation, parenterally administered 1,25D has been shown to enhance neonatal lung maturation; but due to the potential systemic side effects of the parenteral route, the translational value of these findings might be limited. To minimize the possibility of systemic toxicity, we examined the effects of VD on neonatal lung maturation, when delivered directly to lungs via nebulization.

METHODS

One-day-old rat pups were administered three different doses of 1,25D and its physiologic precursor 25(OH)D (25D), or the diluent, via nebulization daily for 14 days. Pups were sacrificed for lung, kidneys, and blood collection to determine markers of lung maturation, and serum 25D and calcium levels.

RESULTS

Compared to controls, nebulized 25D and 1,25D enhanced lung maturation as evidenced by the increased expression of markers of alveolar epithelial (SP-B, leptin receptor), mesenchymal (PPARγ, C/EBPα), and endothelial (VEGF, FLK-1) differentiation, surfactant phospholipid synthesis, and lung morphology without any significant increases in serum 25D and calcium levels.

CONCLUSIONS

Inhaled VD is a potentially safe and effective novel strategy to enhance neonatal lung maturation.

Neurally adjusted ventilatory assist (NAVA) in preterm newborn infants with respiratory distress syndrome-a randomized controlled trial

Neurally adjusted ventilatory assist (NAVA) improves patient-ventilator synchrony during invasive ventilation and leads to lower peak inspiratory pressures (PIP) and oxygen requirements. The aim of this trial was to compare NAVA with current standard ventilation in preterm infants in terms of the duration of invasive ventilation. Sixty infants born between 28 + 0 and 36 + 6 weeks of gestation and requiring invasive ventilation due to neonatal respiratory distress syndrome (RDS) were randomized to conventional ventilation or NAVA. The median durations of invasive ventilation were 34.7 h (quartiles 22.8-67.9 h) and 25.8 h (15.6-52.1 h) in the NAVA and control groups, respectively (P = 0.21). Lower PIPs were achieved with NAVA (P = 0.02), and the rapid reduction in PIP after changing the ventilation mode to NAVA made following the predetermined extubation criteria challenging. The other ventilatory and vital parameters did not differ between the groups. Frequent apneas and persistent pulmonary hypertension were conditions that limited the use of NAVA in 17 % of the patients randomized to the NAVA group. Similar cumulative doses of opiates were used in both groups (P = 0.71).

CONCLUSIONS

NAVA was a safe and feasible ventilation mode for the majority of preterm infants suffering from RDS, but the traditional extubation criteria were not clinically applicable during NAVA.

WHAT IS KNOWN

• NAVA improves patient-ventilator synchrony during invasive ventilation. • Lower airway pressures and oxygen requirements are achieved with NAVA during invasive ventilation in preterm infants by comparison with conventional ventilation. What is new: • Infants suffering from PPHN did not tolerate NAVA in the acute phase of their illness. • The traditional extubation criteria relying on inspiratory pressures and spontaneous breathing efforts were not clinically applicable during NAVA.

A three-dimensional human model of the fibroblast activation that accompanies bronchopulmonary dysplasia identifies Notch-mediated pathophysiology

Bronchopulmonary dysplasia (BPD) is a leading complication of premature birth and occurs primarily in infants delivered during the saccular stage of lung development. Histopathology shows decreased alveolarization and a pattern of fibroblast proliferation and differentiation to the myofibroblast phenotype. Little is known about the molecular pathways and cellular mechanisms that define BPD pathophysiology and progression. We have developed a novel three-dimensional human model of the fibroblast activation associated with BPD, and using this model we have identified the Notch pathway as a key driver of fibroblast activation and proliferation in response to changes in oxygen. Fetal lung fibroblasts were cultured on sodium alginate beads to generate lung organoids. After exposure to alternating hypoxia and hyperoxia, the organoids developed a phenotypic response characterized by increased α-smooth muscle actin (α-SMA) expression and other genes known to be upregulated in BPD and also demonstrated increased expression of downstream effectors of the Notch pathway. Inhibition of Notch with a γ-secretase inhibitor prevented the development of the pattern of cellular proliferation and α-SMA expression in our model. Analysis of human autopsy tissue from the lungs of infants who expired with BPD demonstrated evidence of Notch activation within fibrotic areas of the alveolar septae, suggesting that Notch may be a key driver of BPD pathophysiology.

IL-1β and Inflammasome Activity Link Inflammation to Abnormal Fetal Airway Development

Inflammation in the developing preterm lung leads to disrupted airway morphogenesis and chronic lung disease in human neonates. However, the molecular mechanisms linking inflammation and the pathways controlling airway morphogenesis remain unclear. In this article, we show that IL-1β released by activated fetal lung macrophages is the key inflammatory mediator that disrupts airway morphogenesis. In mouse lung explants, blocking IL-1β expression, posttranslational processing, and signaling protected the formation of new airways from the inhibitory effects ofEscherichia coliLPS. Consistent with a critical role for IL-1β, mice expressing a gain-of-functionNlrp3allele and subsequent overactive inflammasome activity displayed abnormal saccular-stage lung morphogenesis and died soon after birth. Although the early-stage fetal lung appeared capable of mounting an NF-κB-mediated immune response, airway formation became more sensitive to inflammation later in development. This period of susceptibility coincided with higher expression of multiple inflammasome components that could increase the ability to release bioactive IL-1β. Macrophages fromNlrp3gain-of-function mice also expressed higher levels of more mature cell surface markers, additionally linking inflammasome activation with macrophage maturation. These data identify developmental expression of the inflammasome and IL-1β release by fetal lung macrophages as key mechanisms and potential therapeutic targets for neonatal lung disease.

Reviewing the use of corticosteroids in bronchopulmonary dysplasia

OBJECTIVE

Review the risks and benefits of postnatal corticosteroid use for the treatment of bronchopulmonary dysplasia, considering that there is not a more effective therapy.

DATA SOURCES

The literature review was carried out in the BIREME database, using the terms "bronchopulmonary dysplasia and corticosteroid" in the LILACS, IBECS, MEDLINE, Cochrane Library, and SciELO databases, selecting the most relevant articles on the subject, with emphasis on recent literature published in the last five years.

SUMMARY OF THE DATA

In preterm infants, bronchopulmonary dysplasia is still a common problem and remains without a specific therapy, despite knowledge of the several risk factors. The treatment essentially consists of supportive measures, but in the past, corticosteroids were widely used, as they are the only medications that have an impact on disease progression. However, the emergence of cerebral palsy associated with the indiscriminate use of corticosteroids has prevented the prescription of this drug in the last 15 years. Since then, no new measures have been taken, and the incidence of the disease tended to increase during this period, creating the need for a review of corticosteroid use and, possibly, more restricted indications.

CONCLUSIONS

The association between risks and benefits of corticosteroid use in preterm infants needs to be considered due to the fact that some infant subpopulations may show more benefits than risks, such as those using mechanical ventilation with difficult weaning.

Common respiratory conditions of the newborn

KEY POINTS

Respiratory distress is a common presenting feature among newborn infants.Prompt investigation to ascertain the underlying diagnosis and appropriate subsequent management is important to improve outcomes.Many of the underlying causes of respiratory distress in a newborn are unique to this age group.A chest radiograph is crucial to assist in diagnosis of an underlying cause.

EDUCATIONAL AIMS

To inform readers of the common respiratory problems encountered in neonatology and the evidence-based management of these conditions.To enable readers to develop a framework for diagnosis of an infant with respiratory distress. The first hours and days of life are of crucial importance for the newborn infant as the infant adapts to the extra-uterine environment. The newborn infant is vulnerable to a range of respiratory diseases, many unique to this period of early life as the developing fluid-filled fetal lungs adapt to the extrauterine environment. The clinical signs of respiratory distress are important to recognise and further investigate, to identify the underlying cause. The epidemiology, diagnostic features and management of common neonatal respiratory conditions are covered in this review article aimed at all healthcare professionals who come into contact with newborn infants.

Prematurity and the burden of influenza and respiratory syncytial virus disease

BACKGROUND

Respiratory morbidity of former preterm infants and especially those with bronchopulmonary dysplasia (BPD) is high during infancy and early childhood.

DATA SOURCES

We performed a review based on a literature search including EMBASE, MEDLINE, and CINAHL databases to identify all relevant papers published in the English and German literature on influenza and respiratory syncytial virus infection associated with preterm infant, prematurity, and BPD between 1980 and 2014.

RESULTS

Recurrent respiratory symptoms remain common at preschool age, school age and even into young adulthood. Acute viral respiratory tract infections due to different pathogens cause significant morbidity and necessitate rehospitalizations during the first years of life. Influenza virus infection plays a minor role compared to respiratory syncytial virus (RSV) associated respiratory tract infection during infancy and early childhood. Nevertheless, particular morbidity to both viruses is high.

CONCLUSIONS

The particular burden of both viral diseases in preterm infants is dominated by RSV and its associated rehospitalizations during the first two years of life. Prophylactic measures include vaccination against influenza virus of family members and caregivers and active immunization starting at the age of 6 months, and monthly injections of palivizumab during the cold season to avoid severe RSV disease and its sequelae.

Respiratory Microbiome of New-Born Infants

The respiratory tract, once believed to be sterile, harbors diverse bacterial communities. The role of microorganisms within health and disease is slowly being unraveled. Evidence points to the neonatal period as a critical time for establishing stable bacterial communities and influencing immune responses important for long-term respiratory health. This review summarizes the evidence of early airway and lung bacterial colonization and the role the microbiome has on respiratory health in the short and long term. The challenges of neonatal respiratory microbiome studies and future research directions are also discussed.

What is the basis for a genetic approach in neonatal disorders?

Gene-environment interactions likely account for some degree of the variance in response rates that are clinically observed with antenatal corticosteroids, breast milk prophylaxis, surfactant administration, early recognition and treatment of sepsis, utility of non-invasive ventilation, and judicious exposure to supplemental oxygen. While these therapies and practice guidelines have significantly decreased overall neonatal mortality in the NICU, they have not made a marked impact on the frequency and severity of conditions such as bronchopulmonary dysplasia (BPD), necrotizing enterocolitis, and periventricular leukomalacia. One possible explanation is that genetic factors in the neonate modulate response to external intervention or preventative agents, culminating in variable levels of injury and different degrees of resolution and repair. Gene-environment explanations are supported by the observed heritability of BPD in twin studies, but they do not differentiate the interactions between neonate and offending toxin or pathogen, from interactions between neonate and intervention or therapeutic agent. Likely, both kinds of interactions are important in determining outcome.

Prenatal interventions to prevent bronchopulmonary dysplasia in animal models: a systematic review

OBJECTIVE

The objective of this study is to identify and systematically review in vivo animal studies on antenatal medical interventions to prevent bronchopulmonary dysplasia.

METHODS

An automated literature search was conducted using MEDLINE (Pubmed) and Embase including all studies using Medical Subject Headings (MeSH) and keywords following a step-by-step approach. All in vivo prenatal intervention studies in animal models mimicking key aspects of the pathophysiology of bronchopulmonary dysplasia were included. In view of relevance of the findings, an additional criterion was that outcomes at 48 h of life or beyond were available. The PRISMA statement concerning systemic reviews was applied and a quality checklist developed by the CAMARADES group was used.

RESULTS

In total, 518 abstracts were identified yet only eight studies were eligible for further analysis. Four studies involved administration of glucocorticoids, the other studies described therapy with epidermal growth factor, interleukin 1b, beta-naphthoflavone, or vitamin D. Outcomes were survival, pulmonary histology, lung function, and/or biochemical analysis.

CONCLUSIONS

Though many in vivo experimental studies in animal models for bronchopulmonary dysplasia have been done, only few have looked into the effect of prenatal interventions and measured outcomes after at least 48 h of life. Most involve the use of antenatal glucocorticoids, although still only four.

Risk of respiratory syncytial virus infection in preterm infants: reviewing the need for prevention

Premature infants are at substantial risk for a spectrum of morbidities that are gestational age dependent. Respiratory syncytial virus (RSV) infection is most common in the first two years of life with the highest burden in children aged <6 months. Preterm infants ≤35 weeks' gestation are handicapped by incomplete immunological and pulmonary maturation and immature premorbid lung function with the added risk of bronchopulmonary dysplasia. Superimposed RSV infection incites marked neutrophilic airway inflammation and innate immunological responses that further compromise normal airway modeling. This review addresses the epidemiology and burden of RSV disease, focusing on the preterm population. Risk factors that determine RSV-disease severity and hospitalization and the impact on healthcare resource utilization and potential long-term respiratory sequelae are discussed. The importance of disease prevention and the evidence-based rationale for prophylaxis with palivizumab is explored, while awaiting the development of a universal vaccine.

Correlation of radiographic thoracic area and oxygenation impairment in bronchopulmonary dysplasia

We hypothesized that radiographically-assessed hyperinflation in bronchopulmonary dysplasia (BPD) is related to the degree of oxygenation impairment. Our objective was to explore the relation of chest radiographic thoracic area (CRTA) with right-to-left shunt, right shift of the oxyhemoglobin dissociation curve and ventilation/perfusion ratio (VA/Q) in infants with BPD. Twenty-two infants born at median (IQR) gestation of 26 (24-28) weeks with BPD were prospectively studied at 39 (30-69) days. Inspired oxygen (FiO2) was varied to obtain transcutaneous oxygen saturation (SpO2) values between 85 and 96%. Shunt, shift and VA/Q were derived by plotting and analysing pairs of SpO2 and FiO2. CRTA was measured by free hand-tracing the perimeter of the thoracic area in anterio-posterior chest radiographs. Median (IQR) shunt was 8 (1-14)%, shift was 13 (11-19)kPa and VA/Q 0.42 (0.30-0.48). Median (IQR) CRTA/kg was 2495 (1962-2838)mm(2) and was significantly related to shift (r=0.674, p<0.001), VA/Q (r=-0.633, p<0.001), weight at study (r=-0.457, p=0.003) and day of life (r=-0.406, p=0.009), but not to shunt. CRTA in BPD is significantly related to oxygenation impairment as quantified by shift and VA/Q. CRTA can be used as a simple radiographic test to quantify BPD severity.

Transcriptome Analysis of the Preterm Rabbit Lung after Seven Days of Hyperoxic Exposure

The neonatal management of preterm born infants often results in damage to the developing lung and subsequent morbidity, referred to as bronchopulmonary dysplasia (BPD). Animal models may help in understanding the molecular processes involved in this condition and define therapeutic targets. Our goal was to identify molecular pathways using the earlier described preterm rabbit model of hyperoxia induced lung-injury. Transcriptome analysis by mRNA-sequencing was performed on lungs from preterm rabbit pups born at day 28 of gestation (term: 31 days) and kept in hyperoxia (95% O₂) for 7 days. Controls were preterm pups kept in normoxia. Transcriptomic data were analyzed using Array Studio and Ingenuity Pathway Analysis (IPA), in order to identify the central molecules responsible for the observed transcriptional changes. We detected 2217 significantly dysregulated transcripts following hyperoxia, of which 90% could be identified. Major pathophysiological dysregulations were found in inflammation, lung development, vascular development and reactive oxygen species (ROS) metabolism. To conclude, amongst the many dysregulated transcripts, major changes were found in the inflammatory, oxidative stress and lung developmental pathways. This information may be used for the generation of new treatment hypotheses for hyperoxia-induced lung injury and BPD.

Persistent pulmonary hypertension of the newborn: Advances in diagnosis and treatment

Persistent pulmonary hypertension of the newborn (PPHN) is a frequent cause for admission to the neonatal intensive care unit and is associated with mortality and variable morbidities. It is primarily a state of oxygenation failure representing a failure of the normal postnatal decline in pulmonary vascular resistance that may be associated with right ventricular dysfunction. Enhanced knowledge of the pathophysiologic contributors to this syndrome helps clinicians understand its phenotypic expression and facilitates more focused intensive care decision-making. The approach to treatment should be based on alleviation of the elevation in pulmonary vascular resistance and should include optimization of lung recruitment and judicious use of pulmonary vasodilators. When response to inhaled nitric oxide is suboptimal, the physiologic contributors to impaired oxygenation need further investigation. Targeted neonatal echocardiography provides novel physiologic insights; in particular, it may help assess the adequacy of right ventricular performance, the relative contribution of the fetal shunts and the magnitude of the overall impairment to cardiac output. This information may facilitate therapeutic next steps and whether adjunctive vasodilators or drugs to augment ventricular function are preferable. This article provides a comprehensive overview of the pathological contributors to PPHN, the physiologic constituents of its phenotypic expression, standard approach to therapeutic intervention, and the role of bedside echocardiography in enhancing the decision-making process.

Neonatal exposure to mild hyperoxia causes persistent increases in oxidative stress and immune cells in the lungs of mice without altering lung structure

Preterm infants often require supplemental oxygen due to lung immaturity, but hyperoxia can contribute to an increased risk of respiratory illness later in life. Our aim was to compare the effects of mild and moderate levels of neonatal hyperoxia on markers of pulmonary oxidative stress and inflammation and on lung architecture; both immediate and persistent effects were assessed. Neonatal mice (C57BL6/J) were raised in either room air (21% O2), mild (40% O2), or moderate (65% O2) hyperoxia from birth until postnatal day 7 (P7d). The mice were killed at either P7d (immediate effects) or lived in air until adulthood (P56d, persistent effects). We enumerated macrophages in lung tissue at P7d and immune cells in bronchoalveolar lavage fluid (BALF) at P56d. At P7d and P56d, we assessed pulmonary oxidative stress [heme oxygenase-1 (HO-1) and nitrotyrosine staining] and lung architecture. The data were interrogated for sex differences. At P7d, HO-1 gene expression was greater in the 65% O2 group than in the 21% O2 group. At P56d, the area of nitrotyrosine staining and number of immune cells were greater in the 40% O2 and 65% O2 groups relative to the 21% O2 group. Exposure to 65% O2, but not 40% O2, led to larger alveoli and lower tissue fraction in the short term and to persistently fewer bronchiolar-alveolar attachments. Exposure to 40% O2 or 65% O2 causes persistent increases in pulmonary oxidative stress and immune cells, suggesting chronic inflammation within the adult lung. Unlike 65% O2, 40% O2 does not affect lung architecture.

Permissive hypercapnia in extremely low birthweight infants (PHELBI): a randomised controlled multicentre trial

BACKGROUND

Tolerating higher partial pressure of carbon dioxide (pCO2) in mechanically ventilated, extremely low birthweight infants might reduce ventilator-induced lung injury and bronchopulmonary dysplasia. We aimed to test the hypothesis that higher target ranges for pCO2 decrease the rate of bronchopulmonary dysplasia or death.

METHODS

In this randomised multicentre trial, we recruited infants from 16 tertiary care perinatal centres in Germany with birthweight between 400 g and 1000 g and gestational age 23-28 weeks plus 6 days, who needed endotracheal intubation and mechanical ventilation within 24 h of birth. Infants were randomly assigned to either a high target or control group. The high target group aimed at pCO2 values of 55-65 mm Hg on postnatal days 1-3, 60-70 mm Hg on days 4-6, and 65-75 mm Hg on days 7-14, and the control target at pCO2 40-50 mmHg on days 1-3, 45-55 mm Hg on days 4-6, and 50-60 mm Hg on days 7-14. The primary outcome was death or moderate to severe bronchopulmonary dysplasia, defined as need for mechanical pressure support or supplemental oxygen at 36 weeks postmenstrual age. Cranial ultrasonograms were assessed centrally by a masked paediatric radiologist. This trial is registered with the ISRCTN registry, number ISRCTN56143743.

RESULTS

Between March 1, 2008, and July 31, 2012, we recruited 362 patients of whom three dropped out, leaving 179 patients in the high target and 180 in the control group. The trial was stopped after an interim analysis (n=359). The rate of bronchopulmonary dysplasia or death in the high target group (65/179 [36%]) did not differ significantly from the control group (54/180 [30%]; p=0·18). Mortality was 25 (14%) in the high target group and 19 (11%; p=0·32) in the control group, grade 3-4 intraventricular haemorrhage was 26 (15%) and 21 (12%; p=0·30), and the rate of severe retinopathy recorded was 20 (11%) and 26 (14%; p=0·36).

INTERPRETATION

Targeting a higher pCO2 did not decrease the rate of bronchopulmonary dysplasia or death in ventilated preterm infants. The rates of mortality, intraventricular haemorrhage, and retinopathy did not differ between groups. These results suggest that higher pCO2 targets than in the slightly hypercapnic control group do not confer increased benefits such as lung protection.

FUNDING

Deutsche Forschungsgemeinschaft.

Using Measurements of Shunt and Ventilation-to-Perfusion Ratio to Quantify the Severity of Bronchopulmonary Dysplasia

BACKGROUND

Classifying the severity of bronchopulmonary dysplasia (BPD) by continuous numerical variables would facilitate follow-up of disease progression and quantified analysis of disease determinants.

OBJECTIVES

To non-invasively measure oxygenation impairment in BPD by the degree of right-to-left shunt, right shift of the oxyhaemoglobin dissociation curve and ventilation/perfusion (VA/Q) inequality and to explore their relation with clinical parameters.

METHODS

Prospective cohort study of 24 infants with a median (interquartile range, IQR) gestation of 25 weeks (24-27) and a birth weight of 0.70 kg (0.63-0.93), studied at 36 days (30-66), at a postmenstrual age (PMA) of 33 weeks (29-36). Inspired oxygen (FIO2) was varied to obtain three to five transcutaneous oxygen saturation (SpO2) values between 85 and 96%. Values of shunt, shift and VA/Q were obtained by plotting the paired data of SpO2 against FIO2 for each infant using a unique program. Right-to-left shunt, right shift of the oxyhaemoglobin dissociation curve and VA/Q were measured in infants born <32 weeks PMA receiving oxygen at 28 days.

RESULTS

The median (IQR) shunt was 8% (0.3-16.5), shift 14.5 kPa (10.9-19.4) and VA/Q 0.40 (0.30-0.48). Shunt, shift and VA/Q were significantly related to gestational age (GA) at birth, PMA at study, weight at study and weight gain per week.

CONCLUSIONS

Severity of pulmonary oxygenation impairment in BPD can be quantified at the cot-side by non-invasive measurement of shunt, shift and VA/Q. Low GA at birth, low weight at birth and at the time of study and impaired weight gain are significantly associated with the severity of oxygen-exchange impairment in infants with BPD.

Oxygen, gastrin-releasing Peptide, and pediatric lung disease: life in the balance

Excessive oxygen (O2) can cause tissue injury, scarring, aging, and even death. Our laboratory is studying O2-sensing pulmonary neuroendocrine cells (PNECs) and the PNEC-derived product gastrin-releasing peptide (GRP). Reactive oxygen species (ROS) generated from exposure to hyperoxia, ozone, or ionizing radiation (RT) can induce PNEC degranulation and GRP secretion. PNEC degranulation is also induced by hypoxia, and effects of hypoxia are mediated by free radicals. We have determined that excessive GRP leads to lung injury with acute and chronic inflammation, leading to pulmonary fibrosis (PF), triggered via ROS exposure or by directly treating mice with exogenous GRP. In animal models, GRP-blockade abrogates lung injury, inflammation, and fibrosis. The optimal time frame for GRP-blockade and the key target cell types remain to be determined. The concept of GRP as a mediator of ROS-induced tissue damage represents a paradigm shift about how O2 can cause injury, inflammation, and fibrosis. The host PNEC response in vivo may depend on individual ROS sensing mechanisms and subsequent GRP secretion. Ongoing scientific and clinical investigations promise to further clarify the molecular pathways and clinical relevance of GRP in the pathogenesis of diverse pediatric lung diseases.

Potential contribution of type I alveolar epithelial cells to chronic neonatal lung disease

The alveolar surface is covered by large flat Type I cells (alveolar epithelial cells 1, AEC1). The normal physiological function of AEC1s involves gas exchange, based on their location in approximation to the capillary endothelium and their thinness, and in ion and water flux, as shown by the presence of solute active transport proteins, water channels, and impermeable tight junctions between cells. With the recent ability to produce relatively pure cultures of AEC1 cells, new functions have been described. These may be relevant to lung injury, repair, and the abnormal development that characterizes bronchopulmonary dysplasia (BPD). To hypothesize a potential role for AEC1 in the development of lung injury and abnormal repair/development in premature lungs, evidence is presented for their presence in the developing lung, how their source may not be the Type II cell (AEC2) as has been assumed for 40 years, and how the cell can be damaged by same type of stressors as those which lead to BPD. Recent work shows that the cells are part of the innate immune response, capable of producing pro-inflammatory mediators, which could contribute to the increase in inflammation seen in early BPD. One of the receptors found exclusively on AEC1 cells in the lung, called RAGE, may also have a role in increased inflammation and alveolar simplification. While the current evidence for AEC1 involvement in BPD is circumstantial and limited at present, the accumulating data supports several hypotheses and questions regarding potential differences in the behavior of AEC1 cells from newborn and premature lung compared with the adult lung.