Late-gestation tracheal occlusion in the fetal lamb causes rapid lung growth with type II cell preservation

Surfactant Therapy in Congenital Diaphragmatic Hernia and Fetoscopic Endoluminal Tracheal Occlusion

INTRODUCTION

Congenital diaphragmatic hernia (CDH) is a complex pathology with severe pulmonary morbidity. Administration of surfactant in CDH is controversial, and the advent of fetoscopic endoluminal tracheal occlusion (FETO) has added further complexity. While FETO has been shown to improve survival outcomes, there are risks of prematurity and potential surfactant deficiency. We aim to evaluate the characteristics and outcomes of surfactant administration for CDH infants and elucidate potential benefits or risks in this unique population.

METHODS

A single-center retrospective cohort review of patients with unilateral CDH from September 2015 to July 2022 was performed. Demographics, prognostic perinatal imaging features, and outcomes were collected. Patients were stratified by surfactant administration and history of FETO. Data were analyzed with descriptive statistics, two-sample t-tests, chi-squared analyses, and logistic regression.

RESULTS

Of 105 included patients, 19 (18%) underwent FETO and 25 (24%) received surfactant. Overall, surfactant recipients were born at earlier gestational ages and lower birthweights regardless of FETO history. Surfactant recipients possessed significantly worse prenatal prognostic features such as observed to expected total fetal lung volume, observed to expected lung to head ratio, and percent liver herniation. In CDH patients without FETO history, surfactant recipients demonstrated worse outcomes than nonrecipients. This association is notably absent in the FETO population, where surfactant recipients have more favorable survival and comparable outcomes. When controlling for defect severity or surfactant usage, as a proxy for respiratory status, surfactant recipients that underwent FETO trended toward improved survival and decreased ECMO use.

CONCLUSIONS

Surfactant administration is not associated with increased morbidity and mortality and may be beneficial in CDH patients that have undergone FETO.

The effect of tracheal occlusion in congenital diaphragmatic hernia in the nitrofen rat lung explant model

PURPOSE

Here, we establish a tracheal occlusion (TO) model with rat lung explants in nitrofen-induced pulmonary hypoplasia in the congenital diaphragmatic hernia (CDH).

METHODS

We extracted lungs from rats on an embryonic day 18. We mimicked TO in the lung explants by tying the trachea. We assessed lung weight, morphometry, and abundance of Ki-67, Active caspase-3, and Prosurfactant Protein C (proSP-C) with immunofluorescence.

RESULTS

Lung weight was higher in TO + than TO - on day 1. Abundance of Ki-67 was higher in TO + than TO - (0.15 vs. 0.32, p = 0.009 for day 1, 0.07 vs. 0.17, p = 0.004 for day 2, 0.07 vs. 0.12, p = 0.044 for day 3), and Active caspase-3 was higher in TO + than TO - on day 2 and day 3 (0.04 vs. 0.03 p = 0.669 for day 1, 0.03 vs. 0.13 p < 0.001 for day 2, 0.04 vs. 0.17 p = 0.008 for day3). However, proSP-C protein abundance was lower in TO + than TO - (67.9 vs. 59.1 p = 0.033 for day 1, 73.5 vs. 51.6 p = 0.038 for day 2, 83.1 vs. 56.4 p = 0.009 for day 3).

CONCLUSIONS

The TO model in lung explants mimics the outcomes of current surgical models of TO and further studies can reveal the cellular and molecular effects of TO in CDH lungs.

The Cellular and Molecular Effects of Fetoscopic Endoluminal Tracheal Occlusion in Congenital Diaphragmatic Hernia

Congenital diaphragmatic hernia (CDH) is a complex disease associated with pulmonary hypoplasia and pulmonary hypertension. Great strides have been made in our ability to care for CDH patients, specifically in the prenatal improvement of lung volume and morphology with fetoscopic endoluminal tracheal occlusion (FETO). While the anatomic effects of FETO have been described in-depth, the changes it induces at the cellular and molecular level remain a budding area of CDH research. This review will delve into the cellular and molecular effects of FETO in the developing lung, emphasize areas in which further research may improve our understanding of CDH, and highlight opportunities to optimize the FETO procedure for improved postnatal outcomes.

In vivo evidence by magnetic resonance volumetry of a gestational age dependent response to tracheal occlusion for congenital diaphragmatic hernia

OBJECTIVE

We aimed to assess in vivo changes in lung and liver volumes in fetuses with isolated congenital diaphragmatic hernia, either expectantly managed or treated in utero.

METHOD

This is a secondary analysis of prospectively collected data at two fetal therapy centers. We used archived magnetic resonance images of fetuses taken ≥7 days apart, creating paired observations in 20 expectantly managed cases, 41 with a second magnetic resonance prior to balloon reversal and 64 after balloon removal. We measured observed to expected total fetal lung volume (O/E TFLV) and liver-to-thoracic volume ratio. We calculated changes in volume as compared with the initial measurement and its rate as a function of gestational age (GA) at occlusion.

RESULTS

The liver-to-thoracic volume ratio did not change in either group. In expectantly managed fetuses, O/E TFLV did not increase with gestation. In fetuses undergoing tracheal occlusion, the measured increase in volume was 2.6 times larger with balloon in place as compared with that after its removal. GA at tracheal occlusion was an independent predictor of the O/E TFLV. The net rate seems to initially increase and plateau at a maximum of 1.5% per week by 35 to 45 days after occlusion.

CONCLUSIONS

Tracheal occlusion induces a net increase in volume, its magnitude essentially dependent on the GA at occlusion.

New and/or improved aspects of fetal surgery

Open fetal surgery through a wide hysterotomy is no longer a real option for prenatal intervention, but a minimally invasive approach has emerged as treatment for a small number of indications. Endoscopic ablation of placental vessels is the preferred treatment for severe twin-to-twin transfusion syndrome and it may be the only chance to salvage the most severe forms of congenital diaphragmatic hernia. Several other indications are currently under review and may become justified in the future, provided that diagnostic accuracy and patient selection become more accurate. Before invasive fetal intervention becomes widely accepted, however, we need to better define outcome. It is no longer acceptable to express results in terms of survival at birth. Survival at discharge and long-term morbidity must be considered as well.

Antenatal fetal VEGF therapy to promote pulmonary maturation in a preterm rabbit model

AIM

To assess the effects of fetal tracheal administration of VEGF on pulmonary maturation in a preterm rabbit model.

METHODS

On day 26 (term=31days), fetal rabbits received recombinant rat VEGF (30microg in 70microL normal saline) or placebo (normal saline 70microL) intratracheally, with or without subsequent tracheal occlusion. Non-operated littermates served as internal controls. Fetuses were harvested on day 28 for morphometric study of the lungs or for mechanical ventilation and measurement of lung mechanics. In total, 96 fetuses from 42 does were used, 47 for ventilation and 49 for morphometry.

RESULTS

In fetuses receiving intratracheal VEGF, an increase in immunoreactivity for Flk-1 was observed throughout the lung parenchyma. Tracheal occlusion (TO) adversely affected pulmonary mechanics as compared to un-occluded controls. That effect is partly reversed by intratracheal VEGF. Intratracheal injection of VEGF without tracheal occlusion improves lung mechanics but no more than what was observed in placebo injected controls.

CONCLUSION

Antenatal intratracheal VEGF administration was associated with an increase in Flk-1 immunoreactivity. It also improves lung mechanics, however more so when the trachea is occluded. Without TO, the effects were comparable to placebo controls.

Increased distension stimulates distal capillary growth as well as expression of specific angiogenesis genes in fetal mouse lungs

Tracheal occlusion (TO) performed surgically in utero near the end of gestation causes a rapid increase in the distension of future airspaces, resulting in accelerated lung development. The authors hypothesize that TO stimulates microvascular growth concomitant with a rapid increase in the expression of genes implicated in angiogenesis. Mouse fetuses underwent in utero surgery (TO or sham-TO surgery) at 16.5 days of gestation, whereupon development was allowed to continue for a further 1 or 24 hours. Microvascular changes were assessed by immunohistochemical staining of fetal lung sections for platelet endothelial cell adhesion molecule-1. Levels of vascular endothelial growth factor-A (VEGF-A; isoforms 120, 164 and 188), VEGF receptors 1 and 2 (VEGFR-1 and -2), angiopoietins 1 and 2, and Tie2 mRNAs were determined by quantitative real-time polymerase chain reaction (PCR). The authors observed more intercapillary interconnection, less isolated capillaries, and a more extended capillary network inside septa of lungs that underwent 24 h of TO versus sham-TO. Moreover, the authors observed a significant increase in mRNA levels of VEGF 188 and VEGFR-1 as early as 1 hour following TO and of VEGFR-1 and angiopoietin 1 after 24 hours. Together, these results suggest that surgically applied stretching quickly enhances the expression of specific angiogenesis and vessel maintenance genes, which seems to result in the maturation and organization of a more extensive and complex capillary network.

Fetal lung-to-head ratio in the prediction of survival in severe left-sided diaphragmatic hernia treated by fetal endoscopic tracheal occlusion (FETO)

OBJECTIVE

The objective of the study was to investigate the value of fetal lung area to head circumference ratio in the prediction of the postnatal outcome in left-sided congenital diaphragmatic hernia treated by fetoscopic endoluminal tracheal occlusion.

STUDY DESIGN

The lung area to head circumference ratio was measured before fetoscopic endoluminal tracheal occlusion in 28 fetuses with congenital diaphragmatic hernia at 25 to 29 weeks. Regression analysis was used to investigate the effect on survival of lung area to head circumference ratio, gestation at fetoscopic endoluminal tracheal occlusion, gestation at delivery, preterm amniorrhexis following fetoscopic endoluminal tracheal occlusion, and prenatal removal of the balloon.

RESULTS

The median lung area to head circumference ratio prior to fetoscopic endoluminal tracheal occlusion was 0.7 (range 0.5 to 0.9). The median gestation at delivery was 34 (range 27 to 39) weeks, and there were 16 survivors (57%). Only lung area to head circumference ratio provided significant prediction of survival, which increased from 17% for lung area to head circumference ratio of 0.4 to 0.5 to 62% for lung area to head circumference ratio of 0.6 to 0.7 and 78% for lung area to head circumference ratio of 0.8 to 0.9.

CONCLUSION

In congenital diaphragmatic hernia treated by fetoscopic endoluminal tracheal occlusion, postnatal survival can be predicted by the lung area to head circumference ratio measured prior to the procedure.

Tracheal occlusion in fetal rats alters expression of mesenchymal nuclear transcription factors without affecting surfactant protein expression

BACKGROUND/PURPOSE

Mesenchymal nuclear transcription factors (MNTF) are involved in lung development and maturation and regulate surfactant protein (SP) expression. Prolonged (>2 weeks) fetal tracheal occlusion (TO) has been shown to accelerate lung growth and inhibit pulmonary surfactant synthesis. The effects of TO on SP expression and MNTF, however, have not been formally assessed. The objectives of this study were to evaluate the effects of short-term (3 days) TO on normal lung growth and protein expression of pulmonary MNTF involved in SP synthesis.

METHODS

At E19 (term, 22 days), 2 fetuses per time-dated Sprague-Dawley rats underwent either TO (n = 23) or a sham (n = 22) operation. Lungs were harvested 72 hours post surgery. Pulmonary SP-A; SP-B; SP-C messenger RNA (mRNA) expression; and SP-A and SP-B, Hoxb5, thyroid transcription factor 1, and retinoic X receptor-alpha protein expression were analyzed.

RESULTS

Lung weight was significantly increased by TO (TO 0.32 +/- 0.02g vs SHAM 0.14 +/- 0.01 g; P < .001), resulting in 123% increase of the lung-to-body-weight ratio. No difference of SP-A-mRNA (177 +/- 4.3 TO vs 169 +/- 4.4 SHAM; P = .25), SP-B-mRNA (87.7 +/- 0.2 TO vs 87.4 +/- 0.02 SHAM; P = .33), and SP-C-mRNA (186.5 +/- 3.2 TO vs 183.2 +/- 2.7 SHAM; P = .45) expression was found. Surfactant protein A (175.6 +/- 25.3 TO vs 192.5 +/- 19.8 SHAM; P = .59) and SP-B (163.4 +/- 5.2 TO vs 166.8 +/- 9.3 SHAM; P = .75) protein expression were similar in both groups; however, Hoxb5 (70.3 +/- 18.9 TO vs 130.6 +/- 5.1 SHAM; P = .02) and thyroid transcription factor 1 (102.6 +/- 19 TO vs 181.1 +/- 6.3 SHAM; P = .007) expression were significantly decreased. Retinoic X receptor-alpha expression tended to be increased by TO (171.9 +/- 6.0 TO vs 155.4 +/- 6.7 SHAM; P = .06).

CONCLUSIONS

Short-term TO late in gestation induces rapid lung growth. Surfactant protein-mRNA and protein expression are not significantly altered. Thyroid transcription factor 1 and Hoxb5 are down-regulated by TO, suggesting that duration and timing of occlusion are important in balancing the effects of TO on lung growth vs lung maturation.

Mechanical stretch induces fetal type II cell differentiation via an epidermal growth factor receptor-extracellular-regulated protein kinase signaling pathway

Mechanical forces are important for fetal alveolar epithelial cell differentiation. However, the signal transduction pathways regulating this process remain largely unknown. Based on the importance of the extracellular-regulated protein kinase (ERK) pathway in cell differentiation, we hypothesized that this cascade mediates stretch-induced fetal type II cell differentiation. We demonstrate that ERK1/2 was maximally activated (> 3-fold) after 15 min of cyclic stretch. Blockage of the ERK pathway with U0126 (a selective MEK1/2 inhibitor) significantly decreased stretch-inducible surfactant protein-C (SP-C) mRNA expression. We examined upstream activators of ERK1/2 and found that stretch induced phosphorylation of Raf-1 and activation of Ras. Moreover, GW5074, a selective c-Raf-1 inhibitor, decreased stretch-inducible SP-C mRNA accumulation. Mechanical stretch also stimulated epidermal growth factor receptor (EGFR) phosphorylation. Finally, blockage of the EGFR, either with tyrphostin AG1478 or neutralizing antibody, decreased stretch-inducible SP-C mRNA expression. We conclude that stretch, at least in part, induces differentiation of fetal epithelial cells via EGFR activation of the ERK pathway. These results suggest that EGFR may be a mechanosensor during fetal lung development. These findings may have significant implications for the design of strategies to accelerate lung maturation.

Tracheal occlusion stimulates cell cycle progression and type I cell differentiation in lungs of fetal rats

Fetal tracheal occlusion (TO) has been reported to stimulate lung growth but decreases number and maturation of type II cells, effects that vary with gestational age and duration of TO. We examined effects of a novel method of TO (unipolar microcautery to seal the trachea) produced at 19.5-20 days (d) of gestation in fetal rats; fetuses were delivered at term, 22 d. Controls were sham operated and unoperated littermates. TO increased wet lung weight but not dry lung weight or lung DNA and protein. To evaluate further the effects of TO, we examined the cell cycle regulators, cyclins D1 and A, in fetal lungs. Cyclin D1 increased with TO (P < 0.005). TO also increased expression of the type I epithelial cell marker RTI40 (mRNA and protein). TO decreased mRNA for surfactant proteins (SP)-A and -C but did not affect protein levels of SP-A and -B and of RTII70, a type II epithelial cell marker. We conclude that TO by microcautery, even of short duration, has diverse pulmonary effects including stimulating increased levels of cyclin D1 with probable cell cycle progression, type I cell differentiation, and possibly inhibiting type II cell function.

In vivo tracheal occlusion in fetal mice induces rapid lung development without affecting surfactant protein C expression

Fetal tracheal occlusion (TO) reverses lung hypoplasia by inducing rapid lung growth. Although increases in lung size accompanied by increased numbers of alveoli and capillaries have been reported, effects of TO on lung development have not been formally assessed. In the present study, the objective was to verify our prediction that the main effect of TO would be to accelerate fetal lung development. We have developed and characterized a new fetal mouse model of TO to best realize this goal. At embryonic day 16.5, pregnant CD1 mice were operated under general anesthesia. One fetus per dam was selected to undergo surgical TO with a surgical clip or a sham operation. The fetuses were delivered 24 or 36 h postsurgery. The maturation of lung parenchyma, evaluated by counting the generations of alveolar saccules from the terminal bronchiole to the pleura, was significantly accelerated in the TO group with a complexity of the gas exchange region comparable with postnatal days 1 and 3 after 24 or 36 h of TO. Cellular proliferation and apoptosis peaks, assessed by immunohistochemistry directed against PCNA and the active form of caspase-3, were significantly increased 24 h after surgery in the TO group compared with the sham group. However, in situ hybridization showed no significant difference in the density of type II pneumocytes expressing surfactant protein C mRNA. Our results show that brief TO during late gestation in fetal mice induces accelerated lung development with minimal effects on surfactant protein C mRNA expression.

Temporary tracheal occlusion in fetal sheep with lung hypoplasia does not improve postnatal lung function

Prolonged fetal tracheal occlusion (TO) accelerates lung growth but leads to loss of alveolar epithelial type II (AE2) cells. In contrast, temporary TO leads to recovery of AE2 cells and their ability to produce surfactant. The aim of this study was to determine the effects of temporary TO in fetal sheep with lung hypoplasia on postnatal lung function, structure, and surfactant protein mRNA expression. Diaphragmatic hernia (DH) was created in 22 fetal sheep at 65 days of gestation. TO was performed between 110 days of gestation and full term (DH/TO, n = 7) and between 110 and 130 days of gestation (DH/TO+R, n = 6). Sham-operated fetuses (n = 11) served as controls. Lambs were delivered at approximately 139 days of gestation, and blood gas tensions were monitored over a 2-h resuscitation period. Temporary TO increased growth of the hypoplastic lung and restored surfactant protein mRNA expression and AE2 cell density but did not improve respiratory function above that of animals that underwent prolonged TO; DH/TO and DH/TO+R lambs were hypoxic and hypercapnic compared with Sham animals. Lung compliance remained low in DH/TO+R lambs, most likely as a consequence of the persistent increase in alveolar wall thickness in these animals.

Congenital diaphragmatic hernia

Congenital diaphragmatic hernia occurs in approximately 1 in every 2500 live births and is associated with a reported mortality of almost 35% in live-born patients and a higher mortality when in utero deaths are counted. Ventilator-induced lung injury, pulmonary hypoplasia, and other associated anomalies account for the high death rate. Numerous adjunctive measures have been used to treat these patients. Inhaled vasodilators (nitric oxide), intravenous vasodilators, and fetal therapy have no proven benefit. While animal models of congenital diaphragmatic hernia are surfactant deficient, controversy remains over the use of surfactant in infants. There has been no clinical trial showing any clear benefit with the use of exogenous surfactant in these patients. Similarly, prenatal corticosteroids show some improvements in animal models, but again, there is a complete absence of supportive data to show benefit in humans. Mechanical ventilator strategies that limit ventilator-induced lung injury by avoiding hyperventilation and lung over inflation are the strategies currently in use that have been associated with improved survival. Long-term follow-up of these patients is quite important since gastroesophageal reflux, developmental delay, chronic lung disease, and chest wall deformity are all seen with increased frequency in these children.

Effect of lung fluid composition on type II cellular activity after tracheal occlusion in the fetal lamb

BACKGROUND/PURPOSE

Fetal tracheal occlusion (TO) causes accelerated lung growth. However, prolonged TO is associated with a decline in the type II cell number. Type II cell function after TO is unclear. Herein, the authors examine type II cell function after TO and the role of tracheal fluid.

METHODS

Fetal lambs (term, 145 days) underwent TO at 122 days. Tracheal pressure was recorded daily. In one group of animals (TF; n = 6), lung fluid was aspirated, measured, and reinfused daily. In their respective twins, NS group, lung fluid was replaced milliliter per milliliter with normal saline (NS; n = 6). At death near term, lung weight was obtained, and tissues were processed for stereologic volumetry. Type II cells were quantitated using antisurfactant protein B immunohistochemistry. Surfactant protein B-mRNA expression was studied by Northern analysis. Wilcoxon signed rank test and single factor analysis of variance (ANOVA) were used for statistical analysis (P<.05 was significant).

RESULTS

In both experimental groups, intratracheal pressure rose from 1.9+/-1.0 torr to 3.7 to 4.8 torr by day 1, and remained constant thereafter. Lung fluid volume increased from 11.9+/-4.2 on day 0 to 36.8+/-8.0 mL/kg in TF, and to 28.4+/-9.3 mL/kg in NS by day 1 (P<.05). At death, lung weight/body weight ratio was higher in TF (5.45% +/- 0.91%) than in NS (4.40% +/- 0. 67%) or control (3.83%+/-0.58%; P<.05). Type II numerical density was substantially reduced after TO: 57.7+/-12.8 x 10(6)/mL (TF) and 45.0 +/-25.9 x 10(6)/mL (NS), versus 82.3+/-13.6 x 10(6)/mL in controls. Ultrastructurally, remaining type II cells in TF were enlarged and engorged with lamellar bodies; in NS, they were smaller and contained fewer lamellar bodies. Surfactant protein B mRNA expression was significantly decreased in NS, but not in TF, compared with controls.

CONCLUSIONS

Type II cell function as well as overall lung growth are stimulated by TO. Lung growth after TO is therefore not unavoidably detrimental to type II cells. After isobaric saline exchange of lung fluid, type II cell function is severely inhibited, confirming the role of tracheal fluid composition in type II stimulating type II cell function.