Sildenafil stimulates and dexamethasone inhibits pulmonary vascular development in congenital diaphragmatic hernia rat lungs

Congenital diaphragmatic hernia: phosphodiesterase-5 and Arginase inhibitors prevent pulmonary vascular hypoplasia in rat lungs

BACKGROUND

Severe pulmonary hypoplasia related to congenital diaphragmatic hernia (CDH) continues to be a potentially fatal condition despite advanced postnatal management strategies.

OBJECTIVE

To evaluate the effect of the antenatal sildenafil and 2(S)-amino-6-boronohexanoic acid (ABH-Arginase inhibitor) on lung volume, pulmonary vascular development, and nitric oxide (NO) synthesis in a Nitrofen-induced CDH rat model.

METHODS

Nitrofen-induced CDH rat model was used. Nitrofen was administrated on embryonic day(E) 9,5. At E14, five intervention groups were treated separately: Nitrofen, Nitrofen+Sildenafil, Nitrofen+ABH, Nitrofen+Sildenafil+ABH and Control. At term, offspring's lungs were weighed, some paraffin-embedded for histology, others snap-frozen to analyze eNOS, Arginase I-II expression, and activity.

RESULTS

In CDH-bearing offsprings, ABH or Sildenafil+ABH preserved the total lung/body-weight index (p < 0.001), preventing pulmonary vascular smooth muscle cell hyperproliferation and improving lung morphometry. Sildenafil+ABH increased 1.7-fold the lung nitrite levels (p < 0.01) without changes in eNOS expression. Sildenafil and ABH improved the number of pulmonary vessels.

CONCLUSION

These results suggest that in this CDH rat model, the basal activity of Arginase participates in the lung volume and, together with phosphodiesterase-5, regulates NOS activity in the term fetal lung. The combined treatment (Sildenafil+ABH) could revert some of the pulmonary features in CDH by improving the local NO synthesis and preventing smooth muscle cell hyperproliferation.

IMPACT

This study presents Arginase inhibition as a new therapeutic target and the importance of the combined antenatal treatment to improve pulmonary vascular development in a congenital diaphragmatic hernia (CDH) rat model. This study shows that the action of an Arginase inhibitor (ABH) enhances the effects already described for sildenafil in this model. These results reinforce the importance of prenatal treatments' synergy in recovering the hypoplastic lung in the Nitrofen-induced CDH rat model.

Sildenafil during the 2nd and 3rd Trimester of Pregnancy: Trials and Tribulations

Sildenafil, a phosphodiesterase 5 inhibitor with a vasodilatory and anti-remodeling effect, has been investigated concerning various conditions during pregnancy. Per indication, we herein review the rationale and the most relevant experimental and clinical studies, including systematic reviews and meta-analyses, when available. Indications for using sildenafil during the second and third trimester of pregnancy include maternal pulmonary hypertension, preeclampsia, preterm labor, fetal growth restriction, oligohydramnios, fetal distress, and congenital diaphragmatic hernia. For most indications, the rationale for administering prenatal sildenafil is based on limited, equivocal data from in vitro studies and rodent disease models. Clinical studies report mild maternal side effects and suggest good fetal tolerance and safety depending on the underlying pathology.

Pharmacokinetics and pharmacodynamics of sildenafil in fetal lambs on extracorporeal support

BACKGROUND

Maternal transplacental administration of sildenafil is being considered for a variety of fetal conditions. Clinical translation also requires evaluation of fetal safety in a higher species, such as the fetal lamb. Experiments with the pregnant ewe are curtailed by minimal transplacental transfer as well as limited access to the fetus. The EXTra-uterine Environment for Neonatal Development (EXTEND) model renders the isolated fetal lamb readily accessible and allows for direct fetal administration of sildenafil.

METHODS

Five fetal lambs were placed on extracorporeal support in the EXTEND device and received continuous intravenous (IV) sildenafil (0.3-0.5-0.7 mg/kg/24hr) for a duration of one to seven days. Plasma sildenafil concentrations were sampled at regular intervals to establish the pharmacokinetic profile using population pharmacokinetic modeling. Serial Doppler ultrasound examination, continuous non-invasive hemodynamic monitoring and blood gas analysis were done to evaluate the pharmacodynamic effects and fetal response.

FINDINGS

The target concentration range (47-500 ng/mL) was attained with all doses. Sildenafil induced an immediate and temporary reduction of pulmonary vascular resistance, mean arterial pressure and circuit flow, without change in fetal lactate levels and acid-base status. The duration of the systemic effects increased with the dose.

INTERPRETATION

Immediate temporary pulmonary vascular and systemic hemodynamic changes induced by sildenafil were biochemically well tolerated by fetal lambs on extracorporeal support, with the 0.5 mg/kg/24 h dose balancing rapid attainment of target concentrations with short-lived systemic effects.

RESEARCH IN CONTEXT

None.

SEARCH STRATEGY BEFORE UNDERTAKING THE STUDY

A literature review was conducted searching online databases (Medline, Embase and Cochrane), using search terms: fetal OR prenatal OR antenatal AND sildenafil, without time-limit and excluding human studies. Where relevant, investigators were contacted in order to avoid duplication of work.

EVIDENCE BEFORE THIS STUDY

Prenatal therapy with sildenafil, a phosphodiesterase-5 inhibitor with vasodilatory and anti-remodeling effects on vascular smooth muscle cells, has been considered for a variety of fetal conditions. One multicenter clinical trial investigating the benefit of sildenafil in severe intrauterine growth restriction (the STRIDER-trial) was halted early due to excess mortality in the sildenafil-exposed arm at one treatment site. Such findings demonstrate the importance of extensive preclinical safety assessment in relevant animal models. Transplacentally administered sildenafil leads to decreased pulmonary arterial muscularization, preventing or reducing the occurrence of pulmonary hypertension in rat and rabbit fetuses with diaphragmatic hernia (DH). Validation of these results in a higher and relevant animal model, e.g. fetal lambs, is the next step to advance clinical translation. We recently demonstrated that, in contrast to humans, transplacental transfer of sildenafil in sheep is minimal, precluding the in vivo study of fetal effects at target concentrations using the conventional pregnant ewe model.

ADDED VALUE OF THIS STUDY

We therefore used the extracorporeal support model for fetal lambs, referred to as the EXTra-uterine Environment for Neonatal Development (EXTEND) system, bypassing placental and maternal metabolism, to investigate at what dose the target concentrations are reached, and what the fetal hemodynamic impact and response are. Fetal hemodynamic and metabolic tolerance to sildenafil are a crucial missing element on the road to clinical translation. This is therefore the first study investigating the pharmacokinetics, hemodynamic and biochemical effects of clinical-range concentrations of sildenafil in fetal lambs, free from placental and maternal interference.

IMPLICATIONS OF ALL THE AVAILABLE EVIDENCE

We demonstrated self-limiting pulmonary vasodilation, a decrease of both systemic arterial pressures and circuit flows, induced by clinical range concentrations of sildenafil, without the development of fetal acidosis. This paves the way for further investigation of prenatal sildenafil in fetal lambs on extracorporeal support. A dose of 0.5 mg/kg/24 h offered the best trade-off between rapid achievement of target concentrations and shortest duration of systemic effects. This is also the first study using the EXTEND as a model for pharmacotherapy during pregnancy.

Honeymoon Period in Newborn Rats With CDH Is Associated With Changes in the VEGF Signaling Pathway

Background: Patients with congenital diaphragmatic hernia (CDH) have a short postnatal period of ventilatory stability called the honeymoon period, after which changes in pulmonary vascular reactivity result in pulmonary hypertension. However, the mechanisms involved are still unknown. The aim of this study was to evaluate mechanical ventilation's effect in the honeymoon period on VEGF, VEGFR-1/2 and eNOS expression on experimental CDH in rats. Materials and Methods: Neonates whose mothers were not exposed to nitrofen formed the control groups (C) and neonates with left-sided defects formed the CDH groups (CDH). Both were subdivided into non-ventilated and ventilated for 30, 60, and 90 min (n = 7 each). The left lungs (n = 4) were evaluated by immunohistochemistry of the pulmonary vasculature (media wall thickness), VEGF, VEGFR-1/2 and eNOS. Western blotting (n = 3) was performed to quantify the expression of VEGF, VEGFR-1/2 and eNOS. Results: CDH had lower biometric parameters than C. Regarding the pulmonary vasculature, C showed a reduction in media wall thickness with ventilation, while CDH presented reduction with 30 min and an increase with the progression of the ventilatory time (honeymoon period). CDH and C groups showed different patterns of VEGF, VEGFR-1/2 and eNOS expressions. The receptors and eNOS findings were significant by immunohistochemistry but not by western blotting, while VEGF was significant by western blotting but not by immunohistochemistry. Conclusion: VEGF, its receptors and eNOS were altered in CDH after mechanical ventilation. These results suggest that the VEGF-NO pathway plays an important role in the honeymoon period of experimental CDH.

Emerging antenatal therapies for congenital diaphragmatic hernia-induced pulmonary hypertension in preclinical models

Congenital diaphragmatic hernia (CDH)-related deaths are the largest contributor to in-hospital neonatal deaths in children with congenital malformations. Morbidity and mortality in CDH are directly related to the development of pulmonary hypertension (PH). Current treatment consists of supportive measures. To date, no pharmacotherapy has been shown to effectively reverse the hallmark finding of pulmonary vascular remodeling that is associated with pulmonary hypertension in CDH (CDH-PH). As such, there is a great need for novel therapies to effectively manage CDH-PH. Our review aims to evaluate emerging therapies, and specifically focuses on those that are still under investigation and not approved for clinical use by the Food and Drug Administration. Therapies were categorized into antenatal pharmacotherapies or antenatal regenerative therapies and assessed on their method of administration, safety profile, the effect on pulmonary vascular pathophysiology, and overall efficacy. In general, emerging antenatal pharmaceutical and regenerative treatments primarily aim to alleviate pulmonary vascular remodeling by restoring normal function and levels of key regulatory factors involved in pulmonary vascular development and/or in promoting angiogenesis. Overall, while these emerging therapies show great promise for the management of CDH-PH, most require further assessment of safety and efficacy in preclinical models before translation into the clinical setting. IMPACT: Emerging antenatal therapies for congenital diaphragmatic hernia-induced pulmonary hypertension (CDH-PH) show promise to effectively mitigate vascular remodeling in preclinical models. Further investigation is needed in preclinical and human studies to evaluate safety and efficacy prior to translation into the clinical arena. This review offers a comprehensive and up-to-date summary of emerging therapies currently under investigation in experimental animal models. There is no cure for CDH-PH. This review explores emerging therapeutic options for the treatment of CDH-PH and evaluates their impact on key molecular pathways and clinical markers of disease to determine efficacy in the preclinical stage.

Vitamin D improves pulmonary function in a rat model for congenital diaphragmatic hernia

A congenital diaphragmatic hernia (CDH) is an anomaly caused by defects in the diaphragm; the resulting limited thorax cavity in turn restricts lung growth (pulmonary hypoplasia). This condition is related to pulmonary hypertension. Despite advances in neonatal CDH therapy, the mortality for severe pulmonary hypoplasia remains high. Therefore, it is essential to establish prenatal therapeutic interventions. Vitamin D was reported to have beneficial effects on adult pulmonary hypertension. This study aims to evaluate the efficacy of prenatal vitamin D administration for CDH. First, serum 25-hydroxyvitamin D [25(OH)D] levels in umbilical cord blood were evaluated among CDH newborns. Second, Sprague Dawley rat CDH models were exposed to nitrofen on embryo day 9 (E9). Randomly selected rats in the nitrofen-treated group were infused with calcitriol from E9 to E21. Samples from CDH pups diagnosed after birth were used for lung weight measurements, blood gas analysis, and immunohistochemical analysis. Third, microarray analysis was performed to examine the effect of vitamin D on gene expression profiles in CDH pulmonary arterial tissues. Serum 25(OH)D levels in the umbilical cord blood of newborns who did not survive were significantly lower than those who were successfully discharged. Prenatal vitamin D showed no significant effect on CDH incidence or lung weight but attenuated alveolarization and pulmonary artery remodeling accompanied the improved blood gas parameters. Vitamin D inhibited several gene expression pathways in the pulmonary arteries of CDH rats. Our results suggest that prenatal vitamin D administration attenuates pulmonary vascular remodeling by influencing several gene pathways in CDH.

Antenatal sildenafil treatment improves neonatal pulmonary hemodynamics and gas exchange in lambs with diaphragmatic hernia

OBJECTIVES

Infants with congenital diaphragmatic hernia (CDH) are predisposed to pulmonary hypertension after birth, owing to lung hypoplasia that impairs fetal pulmonary vascular development. Antenatal sildenafil treatment attenuates abnormal pulmonary vascular and alveolar development in rabbit and rodent CDH models, but whether this translates to functional improvements after birth remains unknown. We aimed to evaluate the effect of antenatal sildenafil on neonatal pulmonary hemodynamics and lung function in lambs with diaphragmatic hernia (DH).

METHODS

DH was surgically induced at approximately 80 days' gestation in 16 lamb fetuses (term in lambs is approximately 147 days). From 105 days' gestation, ewes received either sildenafil (0.21 mg/kg/h intravenously) or saline infusion until delivery (n = 8 fetuses in each group). At approximately 138 days' gestation, all lambs were instrumented and then delivered via Cesarean section. The lambs were ventilated for 120 min with continuous recording of physiological (pulmonary and carotid artery blood flow and pressure; cerebral oxygenation) and ventilatory parameters, and regular assessment of arterial blood gas tensions. Only lambs that survived until delivery and with a confirmed diaphragmatic defect at postmortem examination were included in the analysis; these comprised six DH-sildenafil lambs and six DH-saline control lambs.

RESULTS

Lung-to-body-weight ratio (0.016 ± 0.001 vs 0.013 ± 0.001; P = 0.06) and dynamic lung compliance (0.8 ± 0.2 vs 0.7 ± 0.2 mL/cmH₂ O; P = 0.72) were similar in DH-sildenafil lambs and controls. Pulmonary vascular resistance decreased following lung aeration to a greater degree in DH-sildenafil lambs, and was 4-fold lower by 120 min after cord clamping than in controls (0.6 ± 0.1 vs 2.2 ± 0.6 mmHg/(mL/min); P = 0.002). Pulmonary arterial pressure was also lower (46 ± 2 vs 59 ± 2 mmHg; P = 0.048) and pulmonary blood flow higher (25 ± 3 vs 8 ± 2 mL/min/kg; P = 0.02) in DH-sildenafil than in DH-saline lambs at 120 min. Throughout the 120-min ventilation period, the partial pressure of arterial carbon dioxide tended to be lower in DH-sildenafil lambs than in controls (63 ± 8 vs 87 ± 8 mmHg; P = 0.057), and there was no significant difference in partial pressure of arterial oxygen between the two groups.

CONCLUSIONS

Sustained maternal antenatal sildenafil infusion reduced pulmonary arterial pressure and increased pulmonary blood flow in DH lambs for the first 120 min after birth. These findings of improved pulmonary vascular function are consistent with improved pulmonary vascular structure seen in two previous animal models. The data support the rationale for a clinical trial investigating the effect of antenatal sildenafil in reducing the risk of neonatal pulmonary hypertension in infants with CDH. Copyright © 2019 ISUOG. Published by John Wiley & Sons Ltd.

Effects of Simvastatin on Fetal Cardiac Impairment in the Diaphragmatic Experimental Hernia Model

BACKGROUND

Statins and sildenafil have been shown to exert beneficial effects in cardiac injury. We hypothesized that antenatal maternal administration of simvastatin and/or sildenafil might also promote benefits in cardiac remodeling of congenital diaphragmatic hernia (CDH). Therefore, we performed micro-CT image analysis and histology of the heart after antennal treatment in experimental nitrofen-induced CDH.

METHODS

At 9.5 days post conception (dpc), pregnant rats were exposed to nitrofen. At 16 and 20 dpc fetuses were treated with simvastatin and/or sildenafil. At 21 dpc postmortem micro-CT and autopsy were performed.

RESULTS

All nitrofen-treated fetuses had a lower birth weight compared to controls; in the simvastatin-treated group, a significant improvement in CDH was noted. Impairment of the lung and liver was also noted in CDH. Compared to controls, CDH rats showed lower ventricular mass, with greater left ventricular thickness; simvastatin decreased the ventricular mass and improved wall thickness. CDH rats exhibited myocardial hypotrophy, severe vascular depression in the left ventricle, and intense interstitial edema compared to controls and nitrofen-exposed animals without CDH. In CDH, the cardiac morphology appeared deformed with left ventricular wall verticalization. Simvastatin improved cardiac myocyte appearance and heart morphology.

CONCLUSION

The potential to treat CDH with antenatal simvastatin may improve the management of this malformation.

Treatment of rat congenital diaphragmatic hernia with sildenafil and NS-304, selexipag's active compound, at the pseudoglandular stage improves lung vasculature

Patients with congenital diaphragmatic hernia (CDH) often suffer from severe pulmonary hypertension, and the choice of current vasodilator therapy is mostly based on trial and error. Because pulmonary vascular abnormalities are already present early during development, we performed a study to modulate these pulmonary vascular changes at an early stage during gestation. Pregnant Sprague-Dawley rats were treated with nitrofen at day 9.5 of gestation (E9.5) to induce CDH in the offspring, and subsequently, the phosphodiesterase-5 inhibitor sildenafil and/or the novel prostaglandin-I receptor agonist selexipag (active compound NS-304) were administered from E17.5 until E20.5. The clinical relevant start of the treatment corresponds to week 20 of gestation in humans, when CDH is usually detected by ultrasound. CDH pups showed increased density of air saccules that was reverted after the use of only sildenafil. The pulmonary vascular wall was thickened, and right ventricular hypertrophy was present in the CDH group and improved both after single treatment with sildenafil or selexipag, whereas the combination therapy with both compounds did not have additive value. In conclusion, antenatal treatment with sildenafil improved airway morphogenesis and pulmonary vascular development, whereas selexipag only acted positively on pulmonary vascular development. The combination of both compounds did not act synergistically, probably because of a decreased efficiency of both compounds caused by cytochrome- P450 3A4 interaction and induction. These new insights create important possibilities for future treatment of pulmonary vascular abnormalities in CDH patients already in the antenatal period of life.

Current and future antenatal management of isolated congenital diaphragmatic hernia

Congenital diaphragmatic hernia is surgically correctable, yet the poor lung development determines mortality and morbidity. In isolated cases the outcome may be predicted prenatally by medical imaging. Cases with a poor prognosis could be treated before birth. However, prenatal modulation of lung development remains experimental. Fetoscopic endoluminal tracheal occlusion triggers lung growth and is currently being evaluated in a global clinical trial. Prenatal transplacental sildenafil administration may in due course be a therapeutic approach, reducing the occurrence of persistent pulmonary hypertension, either alone or in combination with fetal surgery.

Congenital diaphragmatic hernias: from genes to mechanisms to therapies

Congenital diaphragmatic hernias (CDHs) and structural anomalies of the diaphragm are a common class of congenital birth defects that are associated with significant morbidity and mortality due to associated pulmonary hypoplasia, pulmonary hypertension and heart failure. In ∼30% of CDH patients, genomic analyses have identified a range of genetic defects, including chromosomal anomalies, copy number variants and sequence variants. The affected genes identified in CDH patients include transcription factors, such as GATA4, ZFPM2, NR2F2 and WT1, and signaling pathway components, including members of the retinoic acid pathway. Mutations in these genes affect diaphragm development and can have pleiotropic effects on pulmonary and cardiac development. New therapies, including fetal endoscopic tracheal occlusion and prenatal transplacental fetal treatments, aim to normalize lung development and pulmonary vascular tone to prevent and treat lung hypoplasia and pulmonary hypertension, respectively. Studies of the association between particular genetic mutations and clinical outcomes should allow us to better understand the origin of this birth defect and to improve our ability to predict and identify patients most likely to benefit from specialized treatment strategies.

Fetal imaging and therapy for CDH-Current status

In congenital diaphragmatic hernia (CDH), herniation of the abdominal organs into the fetal chest causes pulmonary hypoplasia and pulmonary hypertension, the main causes of neonatal mortality. As antenatal ultrasound screening improves, the risk of postnatal death can now be better predicted, allowing for the identification of fetuses that might most benefit from a prenatal intervention. Fetoscopic tracheal occlusion is being evaluated in a large international randomized controlled trial. We present the antenatal imaging approaches that can help identify fetuses that might benefit from antenatal therapy, and review the evolution of fetal surgery for CDH to date.

Clinically relevant timing of antenatal sildenafil treatment reduces pulmonary vascular remodeling in congenital diaphragmatic hernia

Patients with congenital diaphragmatic hernia (CDH) suffer from severe pulmonary hypertension attributable to altered development of the pulmonary vasculature, which is often resistant to vasodilator therapy. Present treatment starts postnatally even though significant differences in the pulmonary vasculature are already present early during pregnancy. We examined the effects of prenatal treatment with the phosphodiesterase-5 inhibitor sildenafil on pulmonary vascular development in experimental CDH starting at a clinically relevant time. The well-established, nitrofen-induced CDH rodent model was treated daily with 100 mg/kg sildenafil from day 17.5 until day 20.5 of gestation (E17.5–20.5). Importantly, this timing perfectly corresponds to the developmental stage of the lung at 20 wk of human gestation, when CDH is detectable by 2D-ultrasonography and/or MRI. At E21.5 pups were delivered by caesarean section and euthanized by lethal injection of pentobarbital. The lungs were isolated and subsequently analyzed using immunostaining, real-time PCR, and volume measurements. Prenatal treatment with sildenafil improved lung morphology and attenuated vascular remodeling with reduced muscularization of the smaller vessels. Pulmonary vascular volume was not affected by sildenafil treatment. We show that prenatal treatment with sildenafil within a clinically relevant period improves pulmonary vascular development in an experimental CDH model. This may have important implications for the management of this disease and related pulmonary vascular diseases in human.

Improved pulmonary function in the nitrofen model of congenital diaphragmatic hernia following prenatal maternal dexamethasone and/or sildenafil

BACKGROUND

Pulmonary hypoplasia and hypertension is a leading cause of morbidity and mortality in congenital diaphragmatic hernia (CDH). The etiologic insult occurs early in gestation highlighting the potential of prenatal interventions. We evaluated prenatal pharmacologic therapies in the nitrofen CDH model.

METHODS

Olive oil or nitrofen were administered alone or with dexamethasone (DM), sildenafil, or DM+sildenafil to pregnant rats. Newborn pups were assessed for lung function, structure and pulmonary artery (PA) flow and resistance.

RESULTS

Prenatal DM treatment of CDH pups increased alveolar volume density (Vva), decreased interalveloar septal thickness, increased tidal volumes and improved ventilation without improving oxygenation or PA resistance. Sildenafil decreased PA resistance and improved oxygenation without improving ventilation or resulting in significant histologic changes. DM+sildenafil decreased PA resistance, improved oxygenation and ventilation while increasing Vva and decreasing interalveolar septal and pulmonary arteriole medial wall thickness. Lung and body weights were decreased in pups treated with DM and/or sildenafil.

CONCLUSION

Prenatal DM or sildenafil treatment increased pulmonary compliance and decreased pulmonary vascular resistance respectively, and was associated with improved neonatal gas exchange but had a detrimental effect on lung and fetal growth. This study highlights the potential of individual and combined prenatal pharmacologic therapies for CDH management.