Progressive Vascular Functional and Structural Damage in a Bronchopulmonary Dysplasia Model in Preterm Rabbits Exposed to Hyperoxia

Pathogenesis and Physiologic Mechanisms of Neonatal Pulmonary Hypertension: Preclinical Studies

Neonatal pulmonary hypertension (PH) is a devastating disorder of the pulmonary vasculature characterized by elevated pulmonary vascular resistance and mean pulmonary arterial pressure. Occurring predominantly because of maldevelopment or maladaptation of the pulmonary vasculature, PH in neonates is associated with suboptimal short-term and long-term outcomes because its pathobiology is unclear in most circumstances, and it responds poorly to conventional pulmonary vasodilators. Understanding the pathogenesis and pathophysiology of neonatal PH can lead to novel strategies and precise therapies. The review is designed to achieve this goal by summarizing pulmonary vascular development and the pathogenesis and pathophysiology of PH associated with maladaptation, bronchopulmonary dysplasia, and congenital diaphragmatic hernia based on evidence predominantly from preclinical studies. We also discuss the pros and cons of and provide future directions for preclinical studies in neonatal PH.

Long-term pulmonary and neurodevelopmental impairment in a fetal growth restriction rabbit model

Fetal growth restriction (FGR) remains one of the main obstetrical problems worldwide, with consequences beyond perinatal life. Animal models with developmental and structural similarities to the human are essential to understand FGR long-term consequences and design novel therapeutic strategies aimed at preventing or ameliorating them. Herein, we described the long-term consequences of FGR in pulmonary function, structure, and gene expression, and characterized neurodevelopmental sequelae up to preadolescence in a rabbit model. FGR was induced at gestational day 25 by surgically reducing placental blood supply in one uterine horn, leaving the contralateral horn as internal control. Neonatal rabbits born near term were assigned to foster care in mixed groups until postnatal day (PND) 21. At that time, one group underwent pulmonary biomechanical testing followed by lung morphometry and gene expression analysis. A second group underwent longitudinal neurobehavioral assessment until PND 60 followed by brain harvesting for multiregional oligodendrocyte and microglia quantification. FGR was associated with impaired pulmonary function and lung development at PND 21. FGR rabbits had higher respiratory resistance and altered parenchymal biomechanical properties in the lungs. FGR lungs presented thicker alveolar septal walls and reduced alveolar space. Furthermore, the airway smooth muscle content was increased, and the tunica media of the intra-acinar pulmonary arteries was thicker. In addition, FGR was associated with anxiety-like behavior, impaired memory and attention, and lower oligodendrocyte proportion in the frontal cortex and white matter. In conclusion, we documented and characterized the detrimental pulmonary function and structural changes after FGR, independent of prematurity, and beyond the neonatal period for the first time in the rabbit model, and describe the oligodendrocyte alteration in pre-adolescent rabbit brains. This characterization will allow researchers to develop and test therapies to treat FGR and prevent its sequelae.

Glutamine inhibits inflammation, oxidative stress, and apoptosis and ameliorates hyperoxic lung injury

Glutamine (Gln) is the most widely acting and abundant amino acid in the body and has anti-inflammatory properties, regulates body metabolism, and improves immune function. However, the mechanism of Gln's effect on hyperoxic lung injury in neonatal rats is unclear. Therefore, this work focused on examining Gln's function in lung injury of newborn rats mediated by hyperoxia and the underlying mechanism. We examined body mass and ratio of wet-to-dry lung tissue weights of neonatal rats. Hematoxylin and eosin (HE) staining was performed to examine histopathological alterations of lung tissues. In addition, enzyme-linked immunoassay (ELISA) was conducted to measure pro-inflammatory cytokine levels within bronchoalveolar lavage fluid (BALF). Apoptosis of lung tissues was observed using TUNEL assay. Western blotting was performed for detecting endoplasmic reticulum stress (ERS)-associated protein levels. The results showed that Gln promoted body weight gain, significantly reduced pathological damage and oxidative stress in lung tissue, and improved lung function in neonatal rats. Gln reduced pro-inflammatory cytokine release as well as inflammatory cell production in BALF and inhibited apoptosis in lung tissue cells. Furthermore, we found that Gln could downregulate ERS-associated protein levels (GRP78, Caspase-12, CHOP) and inhibit c-Jun N-terminal kinase (JNK) and inositol-requiring enzyme 1 alpha (IRE1α) phosphorylation. These results in an animal model of bronchopulmonary dysplasia (BPD) suggest that Gln may have a therapeutic effect on BPD by reducing lung inflammation, oxidative stress, and apoptosis and improving lung function; its mechanism of action may be related to the inhibition of the IRE1α/JNK pathway.

Time-resolved transcriptomic profiling of the developing rabbit's lungs: impact of premature birth and implications for modelling bronchopulmonary dysplasia

BACKGROUND

Premature birth, perinatal inflammation, and life-saving therapies such as postnatal oxygen and mechanical ventilation are strongly associated with the development of bronchopulmonary dysplasia (BPD); these risk factors, alone or combined, cause lung inflammation and alter programmed molecular patterns of normal lung development. The current knowledge on the molecular regulation of lung development mainly derives from mechanistic studies conducted in newborn rodents exposed to postnatal hyperoxia, which have been proven useful but have some limitations.

METHODS

Here, we used the rabbit model of BPD as a cost-effective alternative model that mirrors human lung development and, in addition, enables investigating the impact of premature birth per se on the pathophysiology of BPD without further perinatal insults (e.g., hyperoxia, LPS-induced inflammation). First, we characterized the rabbit's normal lung development along the distinct stages (i.e., pseudoglandular, canalicular, saccular, and alveolar phases) using histological, transcriptomic and proteomic analyses. Then, the impact of premature birth was investigated, comparing the sequential transcriptomic profiles of preterm rabbits obtained at different time intervals during their first week of postnatal life with those from age-matched term pups.

RESULTS

Histological findings showed stage-specific morphological features of the developing rabbit's lung and validated the selected time intervals for the transcriptomic profiling. Cell cycle and embryo development, oxidative phosphorylation, and WNT signaling, among others, showed high gene expression in the pseudoglandular phase. Autophagy, epithelial morphogenesis, response to transforming growth factor β, angiogenesis, epithelium/endothelial cells development, and epithelium/endothelial cells migration pathways appeared upregulated from the 28th day of gestation (early saccular phase), which represents the starting point of the premature rabbit model. Premature birth caused a significant dysregulation of the inflammatory response. TNF-responsive, NF-κB regulated genes were significantly upregulated at premature delivery and triggered downstream inflammatory pathways such as leukocyte activation and cytokine signaling, which persisted upregulated during the first week of life. Preterm birth also dysregulated relevant pathways for normal lung development, such as blood vessel morphogenesis and epithelial-mesenchymal transition.

CONCLUSION

These findings establish the 28-day gestation premature rabbit as a suitable model for mechanistic and pharmacological studies in the context of BPD.

Fetal Growth Restriction Impairs Lung Function and Neurodevelopment in an Early Preterm Rabbit Model

We previously reported the multi-system sequelae of fetal growth restriction, induced by placental underperfusion, in near-term born rabbits, in the immediate neonatal period and up to pre-adolescence. Herein, we describe the pulmonary and neurodevelopmental consequences of FGR in rabbits born preterm. We hypothesize that FGR has an additional detrimental effect on prematurity in both pulmonary function and neurodevelopment. FGR was induced at gestational day (GD) 25 by placental underperfusion, accomplished by partial uteroplacental vessel ligation in one uterine horn. Rabbits were delivered by cesarean section at GD 29, and placentas were harvested for histology. Neonates underwent neurobehavioral or pulmonary functional assessment at postnatal day 1, followed by brain or lung harvesting, respectively. The neurodevelopmental assessment included neurobehavioral testing and multiregional quantification of cell density and apoptosis in the brain. Lung assessment included functional testing, alveolar morphometry, and airway histology. FGR was associated with higher perinatal mortality, lower birth and placental weight, and a similar brain-to-body weight ratio compared to controls. Placental underperfusion decreased labyrinth and junction zone volumes in FGR placentas. FGR impaired pulmonary function, depicted by higher parenchymal resistance, damping, and elastance. Alveolar morphometry and airway smooth muscle content were comparable between groups. Neurobehavioral tests showed motoric and sensorial impairment in FGR rabbits. In FGR brains, cell density was globally reduced, with higher apoptosis in selected areas. In conclusion, in preterm-born rabbits, placental underperfusion leads to higher mortality, FGR, and impaired lung and brain development in early assessment. This study complements previous findings of placental, pulmonary, and neurodevelopmental impairment in near-term born rabbits in this model.

Placental vascular alterations are associated with early neurodevelopmental and pulmonary impairment in the rabbit fetal growth restriction model

Fetal growth restriction is one of the leading causes of perinatal mortality and morbidity and has consequences that extend well beyond the neonatal period. Current management relies on timely delivery rather than improving placental function. Several prenatal strategies have failed to show benefit in clinical trials after promising results in animal models. Most of these animal models have important developmental and structural differences compared to the human and/or are insufficiently characterized. We aimed to describe placental function and structure in an FGR rabbit model, and to characterize the early brain and lung developmental morbidity using a multimodal approach. FGR was induced in time-mated rabbits at gestational day 25 by partial uteroplacental vessel ligation in one horn. Umbilical artery Doppler was measured before caesarean delivery at gestational day 30, and placentas were harvested for computed microtomography and histology. Neonates underwent neurobehavioral or pulmonary functional assessment the day after delivery, followed by brain or lung harvesting, respectively. Neuropathological assessment included multiregional quantification of neuron density, apoptosis, astrogliosis, cellular proliferation, and oligodendrocyte progenitors. Brain region volumes and diffusion metrics were obtained from ex-vivo brain magnetic resonance imaging. Lung assessment included biomechanical tests and pulmonary histology. Fetal growth restriction was associated with labyrinth alterations in the placenta, driven by fetal capillary reduction, and overall reduced vessels volume. FGR caused altered neurobehavior paralleled by regional neuropathological deficits and reduced fractional anisotropy in the cortex, white matter, and hippocampus. In addition, FGR kittens presented functional alterations in the peripheral lung and structurally underdeveloped alveoli. In conclusion, in a uteroplacental insufficiency FGR rabbit model, placental vascular alterations coincide with neurodevelopmental and pulmonary disruption.

Daily Intraperitoneal Administration of Rosiglitazone Does Not Improve Lung Function or Alveolarization in Preterm Rabbits Exposed to Hyperoxia

Thiazolidinediones (TZDs) are potent PPARγ agonists that have been shown to attenuate alveolar simplification after prolonged hyperoxia in term rodent models of bronchopulmonary dysplasia. However, the pulmonary outcomes of postnatal TZDs have not been investigated in preterm animal models. Here, we first investigated the PPARγ selectivity, epithelial permeability, and lung tissue binding of three types of TZDs in vitro (rosiglitazone (RGZ), pioglitazone, and DRF-2546), followed by an in vivo study in preterm rabbits exposed to hyperoxia (95% oxygen) to investigate the pharmacokinetics and the pulmonary outcomes of daily RGZ administration. In addition, blood lipids and a comparative lung proteomics analysis were also performed on Day 7. All TZDs showed high epithelial permeability through Caco-2 monolayers and high plasma and lung tissue binding; however, RGZ showed the highest affinity for PPARγ. The pharmacokinetic profiling of RGZ (1 mg/kg) revealed an equivalent biodistribution after either intratracheal or intraperitoneal administration, with detectable levels in lungs and plasma after 24 h. However, daily RGZ doses of 1 mg/kg did not improve lung function in preterm rabbits exposed to hyperoxia, and daily 10 mg/kg doses were even associated with a significant lung function worsening, which could be partially explained by the upregulation of lung inflammation and lipid metabolism pathways revealed by the proteomic analysis. Notably, daily postnatal RGZ produced an aberrant modulation of serum lipids, particularly in rabbit pups treated with the 10 mg/kg dose. In conclusion, daily postnatal RGZ did not improve lung function and caused dyslipidemia in preterm rabbits exposed to hyperoxia.

Design-Based Stereology of the Lung in the Hyperoxic Preterm Rabbit Model of Bronchopulmonary Dysplasia

Bronchopulmonary dysplasia (BPD) is a complex condition frequently occurring in preterm newborns, and different animal models are currently used to mimic the pathophysiology of BPD. The comparability of animal models depends on the availability of quantitative data obtained by minimally biased methods. Therefore, the aim of this study was to provide the first design-based stereological analysis of the lungs in the hyperoxia-based model of BPD in the preterm rabbit. Rabbit pups were obtained on gestation day 28 (three days before term) by cesarean section and exposed to normoxic (21% O2, n = 8) or hyperoxic (95% O2, n = 8) conditions. After seven days of exposure, lung function testing was performed, and lungs were taken for stereological analysis. In addition, the ratio between pulmonary arterial acceleration and ejection time (PAAT/PAET) was measured. Inspiratory capacity and static compliance were reduced whereas tissue elastance and resistance were increased in hyperoxic animals compared with normoxic controls. Hyperoxic animals showed signs of pulmonary hypertension indicated by the decreased PAAT/PAET ratio. In hyperoxic animals, the number of alveoli and the alveolar surface area were reduced by one-third or by approximately 50% of control values, respectively. However, neither the mean linear intercept length nor the mean alveolar volume was significantly different between both groups. Hyperoxic pups had thickened alveolar septa and intra-alveolar accumulation of edema fluid and inflammatory cells. Nonparenchymal blood vessels had thickened walls, enlarged perivascular space, and smaller lumen in hyperoxic rabbits in comparison with normoxic ones. In conclusion, the findings are in line with the pathological features of human BPD. The stereological data may serve as a reference to compare this model with BPD models in other species or future therapeutic interventions.

Hyperoxia and Lungs: What We Have Learned From Animal Models

Although oxygen (O₂) is essential for aerobic life, it can also be an important source of cellular damage. Supra-physiological levels of O₂ determine toxicity due to exacerbated reactive oxygen species (ROS) production, impairing the homeostatic balance of several cellular processes. Furthermore, injured cells activate inflammation cascades, amplifying the tissue damage. The lung is the first (but not the only) organ affected by this condition. Critically ill patients are often exposed to several insults, such as mechanical ventilation, infections, hypo-perfusion, systemic inflammation, and drug toxicity. In this scenario, it is not easy to dissect the effect of oxygen toxicity. Translational investigations with animal models are essential to explore injuring stimuli in controlled experimental conditions, and are milestones in understanding pathological mechanisms and developing therapeutic strategies. Animal models can resemble what happens in critical care or anesthesia patients under mechanical ventilation and hyperoxia, but are also critical to explore the effect of O₂ on lung development and the role of hyperoxic damage on bronchopulmonary dysplasia. Here, we set out to review the hyperoxia effects on lung pathology, contributing to the field by describing and analyzing animal experimentation's main aspects and its implications on human lung diseases.

Aerosol drug delivery to spontaneously-breathing preterm neonates: lessons learned

Delivery of medications to preterm neonates receiving non-invasive ventilation (NIV) represents one of the most challenging scenarios for aerosol medicine. This challenge is highlighted by the undersized anatomy and the complex (patho)physiological characteristics of the lungs in such infants. Key physiological restraints include low lung volumes, low compliance, and irregular respiratory rates, which significantly reduce lung deposition. Such factors are inherent to premature birth and thus can be regarded to as the intrinsic factors that affect lung deposition. However, there are a number of extrinsic factors that also impact lung deposition: such factors include the choice of aerosol generator and its configuration within the ventilation circuit, the drug formulation, the aerosol particle size distribution, the choice of NIV type, and the patient interface between the delivery system and the patient. Together, these extrinsic factors provide an opportunity to optimize the lung deposition of therapeutic aerosols and, ultimately, the efficacy of the therapy.

In this review, we first provide a comprehensive characterization of both the intrinsic and extrinsic factors affecting lung deposition in premature infants, followed by a revision of the clinical attempts to deliver therapeutic aerosols to premature neonates during NIV, which are almost exclusively related to the non-invasive delivery of surfactant aerosols. In this review, we provide clues to the interpretation of existing experimental and clinical data on neonatal aerosol delivery and we also describe a frame of measurable variables and available tools, including in vitro and in vivo models, that should be considered when developing a drug for inhalation in this important but under-served patient population.

The Correlation Between Bronchopulmonary Dysplasia and Platelet Metabolism in Preterm Infants

Background: Platelets play an important role in the formation of pulmonary blood vessels, and thrombocytopenia is common in patients with pulmonary diseases. However, a few studies have reported on the role of platelets in bronchopulmonary dysplasia. Objective: The objective of the study was to explore the relationship between platelet metabolism and bronchopulmonary dysplasia in premature infants. Methods: A prospective case-control study was performed in a cohort of premature infants (born with a gestational age <32 weeks and a birth weight <1,500 g) from June 1, 2017 to June 1, 2018. Subjects were stratified into two groups according to the diagnostic of bronchopulmonary dysplasia: with bronchopulmonary dysplasia (BPD group) and without bronchopulmonary dysplasia (control group). Platelet count, circulating megakaryocyte count (MK), platelet-activating markers (CD62P and CD63), and thrombopoietin (TPO) were recorded and compared in two groups 28 days after birth; then serial thrombopoietin levels and concomitant platelet counts were measured in infants with BPD. Results: A total of 252 premature infants were included in this study. Forty-eight premature infants developed BPD, 48 premature infants without BPD in the control group who were matched against the study infants for gestational age, birth weight, and admission diagnosis at the age of postnatal day 28. Compared with the controls, infants with BPD had significantly lower peripheral platelet count [BPD vs. controls: 180.3 (24.2) × 10⁹/L vs. 345.6 (28.5) × 10⁹/L, p = 0.001]. Circulating MK count in the BPD group was significantly more abundant than that in the control group [BPD vs. controls: 30.7 (4.5)/ml vs. 13.3 (2.6)/ml, p = 0.025]. The level of CD62p, CD63, and TPO in BPD group was significantly higher than the control group [29.7 (3.1%) vs. 14.5 (2.5%), 15.4 (2.0%) vs. 5.8 (1.7%), 301.4 (25.9) pg/ml vs. 120.4 (14.2) pg/ml, all p < 0.05]. Furthermore, the concentration of TPO was negatively correlated with platelet count in BPD group with thrombocytopenia. Conclusions: Our findings suggest that platelet metabolism is involved in the development of BPD in preterm infants. The possible mechanism might be through increased platelet activation and promoted TPO production by feedback.

Combination of µCT and light microscopy for generation-specific stereological analysis of pulmonary arterial branches: a proof-of-concept study

Various lung diseases, including pulmonary hypertension, chronic obstructive pulmonary disease or bronchopulmonary dysplasia, are associated with structural and architectural alterations of the pulmonary vasculature. The light microscopic (LM) analysis of the blood vessels is limited by the fact that it is impossible to identify which generation of the arterial tree an arterial profile within a LM microscopic section belongs to. Therefore, we established a workflow that allows for the generation-specific quantitative (stereological) analysis of pulmonary blood vessels. A whole left rabbit lung was fixed by vascular perfusion, embedded in glycol methacrylate and imaged by micro-computed tomography (µCT). The lung was then exhaustively sectioned and 20 consecutive sections were collected every 100 µm to obtain a systematic uniform random sample of the whole lung. The digital processing involved segmentation of the arterial tree, generation analysis, registration of LM sections with the µCT data as well as registration of the segmentation and the LM images. The present study demonstrates that it is feasible to identify arterial profiles according to their generation based on a generation-specific color code. Stereological analysis for the first three arterial generations of the monopodial branching of the vasculature included volume fraction, total volume, lumen-to-wall ratio and wall thickness for each arterial generation. In conclusion, the correlative image analysis of µCT and LM-based datasets is an innovative method to assess the pulmonary vasculature quantitatively.

A semi-automated method for unbiased alveolar morphometry: Validation in a bronchopulmonary dysplasia model

Reproducible and unbiased methods to quantify alveolar structure are important for research on many lung diseases. However, manually estimating alveolar structure through stereology is time consuming and inter-observer variability is high. The objective of this work was to develop and validate a fast, reproducible and accurate (semi-)automatic alternative. A FIJI-macro was designed that automatically segments lung images to binary masks, and counts the number of test points falling on tissue and the number of intersections of the air-tissue interface with a set of test lines. Manual selection remains necessary for the recognition of non-parenchymal tissue and alveolar exudates. Volume density of alveolar septa (VVsep) and mean linear intercept of the airspaces (Lm) as measured by the macro were compared to theoretical values for 11 artificial test images and to manually counted values for 17 lungs slides using linear regression and Bland-Altman plots. Inter-observer agreement between 3 observers, measuring 8 lungs both manually and automatically, was assessed using intraclass correlation coefficients (ICC). VVsep and Lm measured by the macro closely approached theoretical values for artificial test images (R² of 0.9750 and 0.9573 and bias of 0.34% and 8.7%). The macro data in lungs were slightly higher for VVsep and slightly lower for Lm in comparison to manually counted values (R² of 0.8262 and 0.8288 and bias of -6.0% and 12.1%). Visually, semi-automatic segmentation was accurate. Most importantly, manually counted VVsep and Lm had only moderate to good inter-observer agreement (ICC 0.859 and 0.643), but agreements were excellent for semi-automatically counted values (ICC 0.956 and 0.900). This semi-automatic method provides accurate and highly reproducible alveolar morphometry results. Future efforts should focus on refining methods for automatic detection of non-parenchymal tissue or exudates, and for assessment of lung structure on 3D reconstructions of lungs scanned with microCT.

Simvastatin attenuates lung functional and vascular effects of hyperoxia in preterm rabbits

BACKGROUND

Bronchopulmonary dysplasia (BPD) remains a frequent complication following preterm birth, affecting respiratory health throughout life. Transcriptome analysis in a preterm rabbit model for BPD revealed dysregulation of key genes for inflammation, vascular growth and lung development in animals exposed to hyperoxia, which could be prevented by simvastatin.

METHODS

Preterm rabbits were randomized to either normoxia (21% O₂) or hyperoxia (95% O₂) and within each condition to treatment with 5 mg/kg simvastatin daily or control. Lung function, structure and mRNA-expression was assessed on day 7.

RESULTS

Simvastatin partially prevented the effect of hyperoxia on lung function, without altering alveolar structure or inflammation. A trend towards a less fibrotic phenotype was noted in simvastatin-treated pups, and airways were less muscularized. Most importantly, simvastatin completely prevented hyperoxia-induced arterial remodeling, in association with partial restoration of VEGFA and VEGF receptor 2 (VEGFR2) expression. Simvastatin however decreased survival in pups exposed to normoxia, but not to hyperoxia.

CONCLUSION

Repurposing of simvastatin could be an advantageous therapeutic strategy for bronchopulmonary dysplasia and other developmental lung diseases with pulmonary vascular disease. The increased mortality in the treated normoxia group however limits the translational value at this dose and administration route.

[Changes in serum human cartilage glycoprotein-39 and high-mobility group box 1 in preterm infants with bronchopulmonary dysplasia]

OBJECTIVE

To study the association of the dynamic changes of peripheral blood human cartilage glycoprotein-39 (YKL-40) and high-mobility group box 1 (HMGB1) with bronchopulmonary dysplasia (BPD) in preterm infants.

METHODS

Preterm infants, with a gestational age of 28-32 weeks and a birth weight of <1 500 g, who were admitted to the neonatal intensive care unit from July 2017 to August 2019 were prospectively selected and divided into a BPD group with 35 infants and a non-BPD group with 51 infants. ELISA was used to measure the serum concentrations of YKL-40 and HMGB1 in preterm infants on days 3, 7, and 14 after birth.

RESULTS

The BPD group had a significantly lower serum YKL-40 concentration and a significantly higher serum HMGB1 concentration than the non-BPD group on days 3, 7, and 14 (P<0.001). The serum concentrations of YKL-40 and HMGB1 on days 7 and 14 were significantly higher than those on day 3 in both groups (P<0.017). In the BPD group, HMGB1 concentration on day 14 was significantly higher than that on day 7 (P<0.017), while there was no significant change in YKL-40 concentration from day 7 to day 14 (P>0.017). In the non-BPD group, YKL-40 concentration on day 14 was significantly higher than that on day 7 (P<0.017), while there was no significant change in HMGB1 concentration from day 7 to day 14 (P>0.017).

CONCLUSIONS

There are significant differences in the levels of YKL-40 and HMGB1 in peripheral blood between the preterm infants with BPD and those without BPD on days 3, 7, and 14 after birth, suggesting that YKL-40 and HMGB1 might be associated with the development of BPD.

Intermittent CPAP limits hyperoxia-induced lung damage in a rabbit model of bronchopulmonary dysplasia

A significant proportion of preterm infants develop bronchopulmonary dysplasia (BPD) leading to poor lifelong respiratory health. Limited treatment options exist with continuous positive airway pressure (CPAP) ventilation being one of the few associated with diminished BPD. However, little is known about the effect of the distending pressure of CPAP on the developing lung exposed to hyperoxia. We aimed to identify the functional and structural effects of CPAP in a preterm hyperoxia rabbit model of BPD. Premature rabbit pups were randomized to normoxia, hyperoxia (≥95% O₂), or hyperoxia plus 4 h daily CPAP [fraction of inspired oxygen (Fi_O2) 0.95, 5 cmH₂O]. On day 7 postdelivery we performed invasive pressure-volume- and forced oscillation-based pulmonary function tests, before lung harvest for histological evaluation. Alveolar and vascular morphology, airway smooth muscle content, respiratory epithelium height, extracellular matrix components, and inflammatory cytokine expression were quantified. Hyperoxia-reared pups had restrictive lungs: alveolar walls were thickened, with the lung parenchymal tissue, collagen content, and airway smooth muscle content increased. In addition, peripheral pulmonary artery wall thickness was increased. CPAP increased alveolar recruitment and limited the structural effect of hyperoxia on the respiratory epithelium and pulmonary arteries. Additionally, CPAP improved lung function, mitigating hyperoxia-associated changes to respiratory system resistance, tissue damping, and tissue elastance. Hyperoxia disrupted functional and structural lung development. Daily intermittent CPAP limited hyperoxia-associated decreased lung function and attenuated structural changes to pulmonary arteries and respiratory epithelium while having no structural alveolar consequences. The mechanism by which CPAP has these beneficial effects needs further investigation.

Lipoxin A4 reduces hyperoxia-induced lung injury in neonatal rats through PINK1 signaling pathway

Bronchopulmonary dysplasia (BPD) is a common chronic lung disease in premature infants and is mainly caused by hyperoxia exposure and mechanical ventilation. Alveolar simplification, pulmonary vascular abnormalities and pulmonary inflammation are the main pathological changes in hyperoxic lung injury animals. Lipoxin A4 (LXA4) is an important endogenous lipid that can mediate the regression of inflammation and plays a role in acute lung injury and asthma. The purpose of this study was to evaluate the effects of LXA4 on inflammation and lung function in neonatal rats with hyperoxic lung injury and to explore the mechanism of the PINK1 pathway. After 85% oxygen exposure in newborn rats for 7 days, the BPD model was established. We found that LXA4 could significantly reduce cell and protein infiltration and oxidative stress in rat lungs, improve pulmonary function and alveolar simplification, and promote weight gain. LXA4 inhibited the expression of TNF-α, MCP-1 and IL-1β in serum and BALF from hyperoxic rats. Moreover, we found that LXA4 could reduce the expression of the PINK1 gene and down-regulate the expression of PINK1, Parkin, BNIP3L/Nix and the autophagic protein LC3B.These protective effects of LXA4 could be partially reversed by addition of BOC-2.Thus, we concluded that LXA4 can alleviate the airway inflammatory response, reduce the severity of lung injury and improve lung function in a hyperoxic rat model of BPD partly through the PINK1 signaling pathway.

Hyperoxia-induced lung structure-function relation, vessel rarefaction, and cardiac hypertrophy in an infant rat model

BACKGROUND

Hyperoxia-induced bronchopulmonary dysplasia (BPD) models are essential for better understanding and impacting on long-term pulmonary, cardiovascular, and neurological sequelae of this chronic disease. Only few experimental studies have systematically compared structural alterations with lung function measurements.

METHODS

In three separate and consecutive series, Sprague-Dawley infant rats were exposed from day of life (DOL) 1 to 19 to either room air (0.21; controls) or to fractions of inspired oxygen (FiO2) of 0.6, 0.8, and 1.0. Our primary outcome parameters were histopathologic analyses of heart, lungs, and respiratory system mechanics, assessed via image analysis tools and the forced oscillation technique, respectively.

RESULTS

Exposure to FiO2 of 0.8 and 1.0 resulted in significantly lower body weights and elevated coefficients of lung tissue damping (G) and elastance (H) when compared with controls. Hysteresivity (η) was lower due to a more pronounced increase of H when compared with G. A positive structure-function relation was demonstrated between H and the lung parenchymal content of α-smooth muscle actin (α-SMA) under hyperoxic conditions. Moreover, histology and morphometric analyses revealed alveolar simplification, fewer pulmonary arterioles, increased α-SMA content in pulmonary vessels, and right heart hypertrophy following hyperoxia. Also, in comparison to controls, hyperoxia resulted in significantly lower plasma levels of vascular endothelial growth factor (VEGF). Lastly, rats in hyperoxia showed hyperactive and a more explorative behaviour.

CONCLUSIONS

Our in vivo infant rat model mimics clinical key features of BPD. To the best of our knowledge, this is the first BPD rat model demonstrating an association between lung structure and function. Moreover, we provide additional evidence that infant rats subjected to hyperoxia develop rarefaction of pulmonary vessels, augmented vascular α-SMA, and adaptive cardiac hypertrophy. Thus, our model provides a clinically relevant tool to further investigate diseases related to O2 toxicity and to evaluate novel pharmacological treatment strategies.

Local pulmonary drug delivery in the preterm rabbit: feasibility and efficacy of daily intratracheal injections

Recent clinical trials in newborns have successfully used surfactant as a drug carrier for an active compound, to minimize systemic exposure. To investigate the translational potential of surfactant-compound mixtures and other local therapeutics, a relevant animal model is required in which intratracheal administration for maximal local deposition is technically possible and well tolerated. Preterm rabbit pups (born at 28 days of gestation) were exposed to either hyperoxia or normoxia and randomized to receive daily intratracheal surfactant, daily intratracheal saline, or no injections for 7 days. At day 7, the overall lung function and morphology were assessed. Efficacy in terms of distribution was assessed by micro-PET-CT on both day 0 and day 7. Lung function as well as parenchymal and vascular structure were altered by hyperoxia, thereby reproducing a phenotype reminiscent of bronchopulmonary dysplasia (BPD). Neither intratracheal surfactant nor saline affected the survival or the hyperoxia-induced BPD phenotype of the pups. Using PET-CT, we demonstrate that 82.5% of the injected radioactive tracer goes and remains in the lungs, with a decrease of only 4% after 150 min. Surfactant and saline can safely and effectively be administered in spontaneously breathing preterm rabbits. The described model and method enable researchers to evaluate intratracheal pharmacological interventions for the treatment of BPD.

Recent advances in the pathogenesis of BPD

Bronchopulmonary dysplasia (BPD) continues to be one of the most common complications of preterm birth and is characterized histopathologically by impaired lung alveolarization. Extremely preterm born infants remain at high risk for the development of BPD, highlighting a pressing need for continued efforts to understand the pathomechanisms at play in affected infants. This brief review summarizes recent progress in our understanding of the how the development of the newborn lung is stunted, highlighting recent reports on roles for growth factor signaling, oxidative stress, inflammation, the extracellular matrix and proteolysis, non-coding RNA, and fibroblast and epithelial cell plasticity. Additionally, some concerns about modeling BPD in experimental animals are reviewed, as are new developments in the in vitro modeling of pathophysiological processes relevant to impaired lung alveolarization in BPD.

Upregulation of Vascular Endothelial Growth Factor in Amniotic Fluid Stem Cells Enhances Their Potential to Attenuate Lung Injury in a Preterm Rabbit Model of Bronchopulmonary Dysplasia

BACKGROUND

Bronchopulmonary dysplasia (BPD) is a chronic lung disease that affects extremely preterm infants and remains - despite improvements in neonatal intensive care - a major cause of neonatal mortality and morbidity. Cell-therapeutic strategies employing mesenchymal stem cells (MSC) have been shown to modulate lung development in BPD models.

OBJECTIVE

Herein, we evaluate the potential of human amniotic fluid (hAF)-SC and hAF-SC with upregulated expression of vascular endothelial growth factor (VEGF) as cell-therapeutic agents for BPD.

METHODS

Preterm rabbit pups were raised in normoxia (21% O2) or hyperoxia (≥95% O2). Hyperoxia-exposed pups randomly received an intraperitoneal injection of fibroblasts, naïve hAF-SC, or hAF-SC-VEGF on postnatal day (PN) 0. On PN7, surviving pups were tested for pulmonary (forced oscillation technique) and vascular (pulmonary artery Doppler ultrasound) function, and lungs were processed for morphometric measurements of parenchymal and vascular structure and inflammation.

RESULTS

Intraperitoneal injection of cells resulted in homing to the lungs. The lungs of hyperoxia-exposed animals displayed parenchymal and vascular structural and functional damage reminiscent of BPD, which was significantly improved after treatment with hAF-SC-VEGF. Treating hyperoxia-exposed animals with naïve AF-SC attenuated only the lung inflammation and the vascular structural defect. Treatment with fibroblasts, which were used as a cellular control, did not lead to any improvements.

CONCLUSION

hAF-SC with upregulated VEGF expression display enhanced potential to prevent/reverse lung injury in preterm rabbits, whereas naïve hAF-SC only show a moderate therapeutic potential. These results point towards an added value of VEGF delivered by hAF-SC in the treatment of BPD.

Prevalence of Target Organ Damage in Chinese Hypertensive Children and Adolescents

Background: Subclinical target organ damage (TOD) has been common in hypertensive children, but there is limited data in the Chinese pediatric population. This study aimed to investigate the prevalence of subclinical TOD in the Chinese hypertensive children and adolescents. Methods: A cross-sectional study was performed in children and adolescents from four schools in Jinan, China between September 2012 and September 2014. The hypertensive status was confirmed based on elevated blood pressure across three different occasions. Those with hypertension were invited to participate in the evaluation of TOD (including heart, arteries, and kidney) and metabolic disorders. A total of 7,840 children and adolescents aged 6-17 years were recruited at baseline, of whom 373 were diagnosed as hypertensive after three separate visits, and 333 (89%) participated in evaluation of TOD. Results: Among 333 hypertensive children, 47.4% had elevated carotid intima-media thickness, 32.4% had left ventricular hypertrophy, 29.2% had dyslipidemia, 7.6% had liver dysfunction, and 4.1% had microalbuminuria. Cardiovascular damages were more prevalent in children aged 9-14 years than the other age groups (i.e., 6-8 and 15-17 years). Girls had higher proportion of microalbuminuria than boys (8.2 vs. 2.6%). No significant sex and age differences were observed for the prevalence of other TODs. Nearly all subclinical TODs were much more prevalent in hypertensive children who were overweight and obese than those with normal weight, except microalbuminuria. Conclusions: The subclinical TOD is prevalent in Chinese hypertensive children and adolescents. Effective measures should be taken to fight against subclinical TOD.

Spatial and temporal expression of SP-B and TGF-β1 in hyperoxia-induced neonatal rat lung injury

OBJECTIVE

Bronchopulmonary dysplasia (BPD) is a severe complication of extreme prematurity that can be caused by hyperoxia inhalation. SP-B and TGF-β have been reported to be implicated in the development of lung. This study aimed to reveal the spatial and temporal expression patterns of these two factors in an animal model of BPD.

METHODS

Newborn Sprague-Dawley (SD) rats were subjected to hyperoxia conditions to establish an animal model of BPD. The levels of SP-B, TGF-β, MDA and TAOC, as well as the activations of MAPK and PI3K/AKT pathways in lung tissues were monitored during newborn rats prolonged exposure to hyperoxia.

RESULTS

We found that hyperoxia exposure significantly induced body weight loss of SD rats. H&E staining for morphometric analyses revealed that hyperoxia arrested alveolar development or loss of alveoli, with fewer and dysmorphic capillaries. mRNA and protein levels of SP-B and TGF-β were high expressed in hyperoxic lung tissues. The concentrations of SP-B and TGF-β in bronchoalveolar lavage fluid were also increased. All these increases begin at the 3th day of hyperoxia exposure. MDA content was increased while TAOC content was decreased in response to hyperoxia. Furthermore, hyperoxia activated p38, and deactivated PI3K and AKT expression.

CONCLUSION

Our research demonstrated that SP-B and TGF-β1 were highly expressed in three levels: mRNA and protein levels in lung tissues, and the release of SP-B and TGF-β1 in bronchoalveolar lavage fluid, beginning at the 3th day of hyperoxia exposure.

Recent advances in our understanding of the mechanisms of late lung development and bronchopulmonary dysplasia

The objective of lung development is to generate an organ of gas exchange that provides both a thin gas diffusion barrier and a large gas diffusion surface area, which concomitantly generates a steep gas diffusion concentration gradient. As such, the lung is perfectly structured to undertake the function of gas exchange: a large number of small alveoli provide extensive surface area within the limited volume of the lung, and a delicate alveolo-capillary barrier brings circulating blood into close proximity to the inspired air. Efficient movement of inspired air and circulating blood through the conducting airways and conducting vessels, respectively, generates steep oxygen and carbon dioxide concentration gradients across the alveolo-capillary barrier, providing ideal conditions for effective diffusion of both gases during breathing. The development of the gas exchange apparatus of the lung occurs during the second phase of lung development-namely, late lung development-which includes the canalicular, saccular, and alveolar stages of lung development. It is during these stages of lung development that preterm-born infants are delivered, when the lung is not yet competent for effective gas exchange. These infants may develop bronchopulmonary dysplasia (BPD), a syndrome complicated by disturbances to the development of the alveoli and the pulmonary vasculature. It is the objective of this review to update the reader about recent developments that further our understanding of the mechanisms of lung alveolarization and vascularization and the pathogenesis of BPD and other neonatal lung diseases that feature lung hypoplasia.

Proteomic analysis of mitochondrial proteins in the guinea pig heart following long-term normobaric hyperoxia

Normobaric hyperoxia is applied for the treatment of a wide variety of diseases and clinical conditions related to ischemia or hypoxia, but it can increase the risk of tissue damage and its efficiency is controversial. In the present study, we analyzed cardiac mitochondrial proteome derived from guinea pigs after 60 h exposure to 100% molecular oxygen (NBO) or O₂ enriched with oxygen cation (NBO+). Two-dimensional gel electrophoresis followed by MALDI-TOF/TOF mass spectrometry identified twenty-two different proteins (among them ten nonmitochondrial) that were overexpressed in NBO and/or NBO+ group. Identified proteins were mainly involved in cellular energy metabolism (tricarboxylic acid cycle, oxidative phosphorylation, glycolysis), cardioprotection against stress, control of mitochondrial function, muscle contraction, and oxygen transport. These findings support the viewpoint that hyperoxia is associated with cellular stress and suggest complex adaptive responses which probably contribute to maintain or improve intracellular ATP levels and contractile function of cardiomyocytes. In addition, the results suggest that hyperoxia-induced cellular stress may be partially attenuated by utilization of NBO+ treatment.