Effect of epidermal growth factor on pulmonary hypoplasia in experimental diaphragmatic hernia

Fetal hypoplastic lungs have multilineage inflammation that is reversed by amniotic fluid stem cell extracellular vesicle treatment

Antenatal administration of extracellular vesicles from amniotic fluid stem cells (AFSC-EVs) reverses features of pulmonary hypoplasia in models of congenital diaphragmatic hernia (CDH). However, it remains unknown which lung cellular compartments and biological pathways are affected by AFSC-EV therapy. Herein, we conducted single-nucleus RNA sequencing (snRNA-seq) on rat fetal CDH lungs treated with vehicle or AFSC-EVs. We identified that intra-amniotically injected AFSC-EVs reach the fetal lung in rats with CDH, where they promote lung branching morphogenesis and epithelial cell differentiation. Moreover, snRNA-seq revealed that rat fetal CDH lungs have a multilineage inflammatory signature with macrophage enrichment, which is reversed by AFSC-EV treatment. Macrophage enrichment in CDH fetal rat lungs was confirmed by immunofluorescence, flow cytometry, and inhibition studies with GW2580. Moreover, we validated macrophage enrichment in human fetal CDH lung autopsy samples. Together, this study advances knowledge on the pathogenesis of pulmonary hypoplasia and further evidence on the value of an EV-based therapy for CDH fetuses.

The Effect of Transplacental Administration of Glucagon-Like Peptide-1 on Fetal Lung Development in the Rabbit Model of Congenital Diaphragmatic Hernia

Objective: Glucagon-like peptide-1 (GLP-1) increases surfactant protein expression in type 2 pneumocytes. Herein, we determine if transplacental GLP-1 treatment accelerates lung growth in the fetal rabbit model of congenital diaphragmatic hernia (DH). Methods: Time-mated does had an induction of DH on day 23 followed by daily GLP-1 or placebo injection until term. At that time, the does were weighed, fetal blood was obtained for GLP-1 assay, and the lungs were dissected. Fetal outcome measures were lung-to-body-weight ratio (LBWR), morphometry, and Ki67 and surfactant protein B (SPB) expression. Results: Maternal weight loss in the GLP-1 group was 7.1%. Fetal survival was lower in GLP-1 fetuses compared to placebo controls (27/85, 32% vs. 35/57, 61%; p < 0.05). Fetal GLP-1 levels were increased 3.6-fold. The LBWR of GLP-1 DH fetuses fell within the range of DH placebo fetuses (1.166 ± 0.207% vs. 1.312 ± 0.418%), being significantly lower than that of placebo-exposed unoperated fetuses (2.280 ± 0.522%; p < 0.001). GLP-1 did not improve airway morphometry. GLP-1 DH lungs had a reduced adventitial and medial thickness within the range of controls, and lesser muscularization of vessels measuring 30-60 µm. There were no differences in Ki67 and SPB expression. Conclusion: GLP-1 at this dosage improves peripheric pulmonary vessel morphology in intra-acinar vessels with no effect on airway morphometry but with significant maternal and fetal side effects. Thus, it is an unlikely medical strategy.

Medical interventions to reverse pulmonary hypoplasia in the animal model of congenital diaphragmatic hernia: A systematic review

We aimed to systematically review all published pre-clinical research on prenatal medical treatment of pulmonary hypoplasia in congenital diaphragmatic hernia (CDH). Background The neonatal mortality due to isolated CDH remains high. Whether fetal endoscopic tracheal occlusion (FETO) reduces mortality is still to be demonstrated. Therefore more potent preferentially medical therapy would be welcomed. Methods We searched MEDLINE (Pubmed), Embase and the Web of Science including all studies from the earliest date (1951) to December 2013. Article quality was assessed using the modified CAMRADES checklist. Inclusion criteria were those animal studies addressing prenatal medical interventions and principal variables were confirmation of a diaphragmatic defect, lung to body weight ratio (LBWR), formal airway morphometry or DNA/protein content. Results In total 983 articles were identified. Following abstract review, 96 articles were assessed by two authors in agreement with a third for eligibility. Of these, 43 were included in the final analysis. The median number of study quality checklist items (maximum 10) scored was 4 (IQ range: 2-5). Thirty (69.8%) of studies were in the nitrofen rat. The majority were treated with vitamins or glucocorticoids. Single studies reported some improvement in lung morphology with alternative therapies. It was impossible to identify a pattern in animal model selection or creation, mode, time point or duration of treatment and readouts. Only one study reported a sample size calculation. Conclusion Comparison in pre-clinical studies in CDH is challenging due to methodological variation. Agreed standardized methods need to be applied in future investigation of new medical therapies.

Epimorphin expression in a rat model of pulmonary hypoplasia associated with congenital diaphragmatic hernia

PURPOSE

The pathogenesis of pulmonary hypoplasia associated with congenital diaphragmatic hernia (CDH) remains unclear. Interactions between the epithelium and surrounding mesenchyme play an important role in normal lung morphogenesis. Epimorphin, a stromal protein, plays a role in epithelial morphogenesis and lung branching, both of which are involved in pulmonary hypoplasia. In this study, we aimed to examine the relationship between epimorphin and pulmonary hypoplasia associated with CDH in an animal model.

METHODS

Time-pregnant rats were exposed to nitrofen or vehicle on gestational day 9 (D9). Fetuses were harvested on D16 and D20, and were divided into control, hypoplastic lungs with CDH (CDH+), and hypoplastic lungs without CDH (CDH-). Both lungs of each fetus were removed and subjected to morphometric and molecular biologic analyses. Lung-to-body weight ratios were calculated. Pulmonary RNA was extracted, and relative mRNA level of epimorphin was determined by quantitative real-time PCR (qRT-PCR). Protein expression of epimorphin was investigated by Western blotting.

RESULTS

In groups D16 and D20, lung-to-body weight ratios in subgroups CDH+ were significantly lower than those of controls and CDH-. The relative mRNA expression levels of epimorphin were significantly increased in both lungs in subgroup CDH+ compared with controls and CDH- on D16. Pulmonary epimorphin gene expression levels were significantly decreased in CDH+ group on D20 compared to controls. Western blotting confirmed the qRT-PCR results showing decreased pulmonary epimorphin protein expression in CDH+ hypoplastic lungs compared to controls on D20.

CONCLUSION

Our study shows that there is an association between the epimorphin expression and pulmonary hypoplasia associated with CDH. Although the cause-effect relationship is far from being established, epimorphin-related mechanisms have a more critical role in early (D16) developmental stage.

Is there a role for antioxidants in prevention of pulmonary hypoplasia in nitrofen-induced rat model of congenital diaphragmatic hernia?

BACKGROUND/PURPOSE

Many studies suggest a role for antioxidants in the prevention of lung hypoplasia in nitrofen-induced rat models with congenital diaphragmatic hernia (CDH). This study investigates the oxidative status and the histological outcome of prenatal administration of vitamins E and C with synergistic effect, and effect of N-acetylcysteine (NAC) to improve lung maturation of nitrofen-induced rats.

METHODS

CDH was induced by maternal administration of a single oral dose of nitrofen on day 9.5 of gestation, and the Sprague-Dawley rats were randomly divided into five groups: nitrofen (N), nitrofen + vitamin C (NC), nitrofen + vitamin E (NE), nitrofen + vitamin C + vitamin E (NCE) and nitrofen + NAC (NNAC). A control group in which only vehicle was administered was included. Cesarean section was performed on day 21. Body weight (BW) and total lung weight (LW) of all fetuses with CDH were recorded; lung histological evaluation was performed, and protein content of lungs, determination of thiobarbituric acid reactive substances, and the protein carbonyls in tissue samples were determined.

RESULTS

A total of 133 rat fetuses with CDH were investigated. The body weight and the lung weight of fetuses of all groups that were exposed to nitrofen were significantly decreased than of the control group (P < 0.05). The animals exposed to nitrofen with different antioxidants showed increased protein levels in lung tissue. However, in the NCE and the NNAC groups, protein levels were significantly increased than in the others. Malondialdehyde levels significantly decreased in the NCE and the NNAC groups when compared with the NC and the NE groups. In addition, the NCE and NNAC groups decreased protein oxidation to control levels, and no significant difference was observed between control and these two antioxidants groups. The N, NC, NE and NNAC groups showed minimal improvement in lung histology; the NCE groups showed the most improvement in lung histology when compared with the other nitrofen plus antioxidant groups.

CONCLUSION

Prenatal administration of NAC and vitamin E in combination with vitamin C represented the best effects to avoid oxidative damage and protein content of the lungs in rat pups with CDH at birth.

Albumin as an adjunct to tracheal occlusion in fetal rats with congenital diaphragmatic hernia: a placebo-controlled study

OBJECTIVE

We sought to investigate effects of intratracheal albumin injection prior to tracheal occlusion (TO) on lung proliferation in fetal rats with nitrofen-induced congenital diaphragmatic hernia.

STUDY DESIGN

On embryonic day 19, nitrofen-exposed fetuses underwent TO, TO and 50 microL of either intratracheal albumin 20% or saline, or remained untouched. Main outcome at embryonic day 21.5 was expression of the proliferation marker Ki-67. Secondary outcomes were lung-to-bodyweight ratio (LBWR), tropoelastin expression, density and spatial distribution of elastin, pulmonary/alveolar morphometry, and fetal survival.

RESULTS

TO increased Ki-67 messenger RNA and LBWR. Albumin further increased LBWR and density of Ki-67-positive cells but also fetal mortality. TO with or without adjuncts induced elastin deposits at the tips of arising secondary crests, increased air space size, and decreased septal thickness.

CONCLUSION

TO had effects on lung proliferation and advanced the morphologic appearance. Addition of albumin increased density of proliferating cells and LBWR, yet at the expense of additional fetal loss.

The effect of fetal tracheal occlusion on lung tissue mechanics and tissue composition

Fetal tracheal occlusion (TO) is currently used to treat severe cases of congenital diaphragmatic hernia (DH). Clinical and experimental studies suggest an improved postnatal outcome, but lung tissue mechanics after TO have not been studied. We determined the effect of TO on mechanical impedance and lung tissue components in a rabbit model for DH. At 23 days of gestation (term = 31 days) either a sham thoracotomy or a diaphragmatic defect was induced. DH fetuses were randomly assigned to undergo 5 days later TO. Fetuses were delivered by term cesarean section to determine lung to body weight ratio (LBWR), dynamic lung mechanics and lung impedance. Airway resistance (R(aw)), elastance (H(L)), tissue damping (G(L)) and hysteresivity (G(L)/H(L)) were calculated from impedance data. Collagen I and III and elastin were quantified histologically. LBWR was significantly increased by TO compared to DH (P < 0.001) and resistance and compliance of the respiratory system (R(rs), C(rs)) were improved as well. TO resulted in a significant decrease of R(aw) comparable to observations in sham-fetuses, without effect on lung tissue mechanics H(L), G(L) and hysteresivity. This coincides with a significant decrease of collagen I, III and elastin in comparison to DH fetuses. In this first report on lung tissue mechanics in a rabbit model of DH, TO had a substantial effect on tissue morphology yet this was not mirrored in lung mechanics. We conclude that the effect of TO on lung mechanics without in utero reversal of occlusion, is dominated by airway remodeling.

Effect of antenatal tetrandrine administration on endothelin-1 and epidermal growth factor levels in the lungs of rats with experimental diaphragmatic hernia

PURPOSE

The aim of this study was to evaluate the effect of the traditional Chinese medicine tetrandrine (Tet) and to determine its possible mechanism on expression of endothelin-1 (ET-1) and epidermal growth factor (EGF) in the lung of a rat model of nitrofen-induced congenital diaphragmatic hernia (CDH).

METHODS

A single oral dose (115 mg/kg) of nitrofen on day 9.5 of pregnancy was maternally administered to induce CDH. Pregnant rats were divided into 4 groups on day 18.5: control (n = 5), CDH (n = 5), CDH+dexamethasone (Dex) (n = 5), and CDH+Tet (n = 5). All fetuses were delivered by cesarean delivery on day 21.5. Accordingly, there were 4 groups of fetuses: control (n = 38), CDH (n = 25), CDH+Dex (n = 21), and CDH+Tet (n = 22). Lung tissue weight (LW) and body weight (BW) of each fetus were recorded, lung histologic evaluations and ET-1 and EGF immunohistochemistry staining were performed, and image analysis was performed after lung processing.

RESULTS

Five female rats in the control group produced 38 fetuses without CDH. CDH was observed in 68 of the 128 rat fetuses (53.1%) among the other 3 groups. The LW/BW ratio of the CDH group was significantly lower than those of the Dex and EGF groups (P < .05). The lungs of fetuses with CDH showed marked abnormal structure such as pulmonary hypoplasia and vascular remodeling, in contrast to improved pulmonary structure in lungs of fetuses in the CDH+Dex and CDH+Tet groups. Statistical differences in morphologic parameters (radial alveolar counts, percentage of alveoli, percentage of medial wall thickness, and vascular volume) were found (P < .05). The immunoreactivity of EGF and ET-1 in the CDH group was markedly stronger than that in the control, CDH+Dex, and CDH+Tet groups (P < .01). In addition, EGF and ET-1 expression in the CDH+Dex and CDH+Tet groups was stronger than that in the control group (P < .05). There was no difference in lung EGF and ET-1 immunoreactivity between CDH+Dex and CDH+Tet groups (P > .05).

CONCLUSION

Antenatal treatment with Tet may improve lung growth and vascular remodeling, and its mechanism seems to be involved in decreasing EGF and ET-1 expression. Tet administered maternally may be a hopeful new therapeutic option in the treatment of CDH and may be effective in helping to avoid the side effects of Dex.

Lung tissue mechanics predict lung hypoplasia in a rabbit model for congenital diaphragmatic hernia

Several animal models have been proposed to study the pathophysiology of congenital diaphragmatic hernia (CDH). Surgical induction of CDH in fetal rabbits during the pseudoglandular phase has been shown to induce severe pulmonary hypoplasia, but functional studies in this model are scarce. We aimed to measure neonatal pulmonary impedance and related it to the severity of lung hypoplasia. CDH was surgically created in rabbits at 23 days of gestation. Following cesarean delivery at term (31 days) pups were subjected to measurement of total lung capacity (TLC), lung to body weight ratio (LBWR) and lung impedance by forced oscillation technique (FOT). Airway resistance (R(aw)), tissue elastance (H(L)), tissue damping (G(L)), and hysteresivity (eta) (G(L)/H(L)) were calculated from impedance data. Twelve CDH fetuses and 15 controls were available for final analysis. LBWR and TLC were significantly lower in the CDH group compared to gestational and age matched controls (P<0.001). R(aw), H(L), and G(L) were significantly increased in CCDH fetuses. eta and H(L) best reflected lung hypoplasia (LBWR) (r(2) = 0.42 and 0.43; P=0.001), indicating a dominant contribution of lung tissue mechanics to CDH-induced lung hypoplasia. We successfully introduced lung impedance measurement by FOT in neonatal rabbits. Following surgical induction of CDH in the pseudoglandular phase, they have, next to morphological evidence of pulmonary hypoplasia, changes in lung mechanics. Our results for lung tissue mechanics support the concept of delayed pulmonary tissue modeling. We propose to employ functional studies in future experiments when evaluating prenatal interventions aimed at reversing pulmonary hypoplasia.

Nitrofen suppresses cell proliferation and promotes mitochondria-mediated apoptosis in type II pneumocytes

AIM

To characterize the molecular mechanisms of nitrofen-induced pulmonary hypoplasia.

METHODS

After administration of nitrofen to cultured type II A549 pneumocytes, cell proliferation and DNA synthesis were investigated by 3-(4,5- dimethylthiazol-2-yl)-2,5-diphenyl tetrazolium bromide colorimetry, colony formation assay, flow cytometry and [3H]-thymidine incorporation assay. Apoptosis was measured by terminal transferase-mediated dUTP nick-end-labeling, acridine orange-ethidium bromide staining and flow cytometry. Expression of proliferating cell nuclear antigen (PCNA) and apoptosis-related genes was assayed by immunofluorescence, RT-PCR and Western blot.

RESULTS

Nitrofen inhibited the cell proliferation of A549 cells in a dose- and time-dependent manner, accompanied by downregulation of PCNA. As a result, the DNA synthesis of nitrofentreated A549 cells decreased, while cell cycle was arrested at G0/G1 phase. Moreover, nitrofen induced apoptosis of A549 cells, which was not abolished by Z-Val-Ala- Asp(OCH3)- fluoromethylketone. In addition, nitrofen decreased the expression of Bcl-x( L), but not of Bcl-2, Bax, and Bak, resulting in a loss of mitochondrial membrane potential and the nuclear translocation of apoptosis-inducing factor (AIF). Meanwhile, nitrofen strongly activated the p38 mitogen-activated protein kinase (p38-MAPK). Pretreatment of cells with SB203580 (5 micromol/L) blocked nitrofen-induced phosphorylation of p38-MAPK and abolished nitrofen-induced AIF translocation and apoptosis in A549 cells.

CONCLUSION

Nitrofen suppresses the proliferation of cultured type II pneumocytes accompanied by the downregulation of PCNA, and induces mitochondria-mediated apoptosis involving the activation of p38-MAPK.

Ghrelin expression in human and rat fetal lungs and the effect of ghrelin administration in nitrofen-induced congenital diaphragmatic hernia

Ghrelin is a strong physiologic growth hormone secretagogue that exhibits endocrine and non-endocrine actions. In this study, ghrelin expression in humans and rats was evaluated throughout development of normal and hypoplastic lungs associated with congenital diaphragmatic hernia (CDH). Additionally, the effect of antenatal treatment with ghrelin in the nitrofen-induced CDH rat model was tested. In normal lungs, ghrelin was expressed in the primitive epithelium at early stages of development and decreased in levels of expression with gestational age. In hypoplastic lungs ghrelin was overexpressed in both human and rat CDH fetuses when compared with controls. Exogenous administration of ghrelin to nitrofen-treated dams led to an attenuation of pulmonary hypoplasia of CDH pups. Furthermore, the growth hormone, secretagogue receptor (GHSR1a), could not be amplified from human or rat fetal lungs by RT-PCR. In conclusion, of all the lungs studied so far, the fetal lung is one of the first to express ghrelin during development and might be considered a new source of circulating fetal ghrelin. Overexpression of ghrelin in hypoplastic lungs and the effect of exogenous administration of ghrelin to nitrofen-treated dams strongly suggest a role for ghrelin in mechanisms involved in attenuation of fetal lung hypoplasia, most likely through a GHSR1a-independent pathway.

Growth factors in lung development

Organized and coordinated lung development follows transcriptional regulation of a complex set of cell-cell and cell-matrix interactions resulting in a blood-gas interface ready for physiologic gas exchange at birth. Transcription factors, growth factors, and various other signaling molecules regulate epithelial-mesenchymal interactions by paracrine and autocrine mechanisms. Transcriptional control at the earliest stages of lung development results in cell differentiation and cell commitment in the primitive lung bud, in essence setting up a framework for pattern formation and branching morphogenesis. Branching morphogenesis results in the formation of the conductive airway system, which is critical for alveolization. Lung development is influenced at all stages by spatial and temporal distribution of various signaling molecules and their receptors and also by the positive and negative control of signaling by paracrine, autocrine, and endocrine mechanisms. Lung bud formation, cell differentiation, and its interaction with the splanchnic mesoderm are regulated by HNF-3beta, Shh, Nkx2.1, HNF-3/Forkhead homolog-8 (HFH-8), Gli, and GATA transcription factors. HNF-3beta regulates Nkx2.1, a transcription factor critical to the formation of distal pulmonary structures. Nkx2.1 regulates surfactant protein genes that are important for the development of alveolar stability at birth. Shh, produced by the foregut endoderm, regulates lung morphogenesis signaling through Gli genes expressed in the mesenchyme. FGF10, produced by the mesoderm, regulates branching morphogenesis via its receptors on the lung epithelium. Alveolization and formation of the capillary network are influenced by various factors that include PDGF, vascular endothelial growth factor (VEGF), and retinoic acid. Epithelial-endothelial interactions during lung development are important in establishing a functional blood-gas interface. The effects of various growth factors on lung development have been demonstrated by gain- or loss-of-function studies in null mutant and transgenic mice models. Understanding the role of growth factors and various other signaling molecules and their cellular interactions in lung development will provide us with new insights into the pathogenesis of bronchopulmonary dysplasia and disorders of lung morphogenesis.