Asystole in 2 Pediatric Patients During Dexmedetomidine Infusion.

INTRODUCTION: Bradycardia is a known side effect of dexmedetomidine. Reports of sinus pauses or asystole, however, are rare. We present 2 cases of pediatric patients who developed asystole on a dexmedetomidine infusion. SUMMARY OF CASES: An 8-week-old male with RSV bronchiolitis and acute hypoxemic respiratory failure was started on dexmedetomidine for sedation at 0.2 mcg/kg/h with a maximum dose of 0.7mcg/kg/h. On Hospital day (HD) 4, on dexmedetomidine at 0.7 mcg/kg/h, he developed intermittent episodes of bradycardia with heart rates in the 60 s. Echocardiogram on HD 6 showed normal function. On HD 7, he began having periods of asystole lasting up to 6 seconds. Dexmedetomidine was discontinued, with the resolution of episodes of asystole after 6 hours. A 27-month-old male with a congenital left diaphragmatic hernia and pulmonary hypertension who had been weaned off sildenafil 6 months earlier underwent re-repair of left diaphragmatic hernia. Postoperatively he remained intubated and paralyzed. Dexmedetomidine was started at 0.3 mcg/kg/h for sedation, with a maximum dose of 1.2 mcg/kg/h. An echocardiogram on HD 3 showed good function with mild to moderate pulmonary hypertension. That evening, with dexmedetomidine at 1.1 mcg/kg/h, he developed a 15 second period of asystole requiring CPR. Dexmedetomidine was discontinued, and he was started on a midazolam infusion with no further episodes. DISCUSSION: Both cases occurred in patients without cardiac conduction defects or on negative chronotropic or sympatholytic medications that have been associated with dexmedetomidine-induced asystole. We hypothesize that both episodes of asystole were due to increased patient-related vagal tone exacerbated by dexmedetomidine.

Ventilation causes pulmonary vascular dilation and modulates the NOS and VEGF pathway on newborn rats with CDH.

BACKGROUND/PURPOSE: Congenital diaphragmatic hernia (CDH) is a defect that presents high mortality because of pulmonary hypoplasia and hypertension. Mechanical ventilation changes signaling pathways, such as nitric oxide and VEGF in the pulmonary arterioles. We investigated the production of NOS2 and NOS3 and expression of VEGF and its receptors after ventilation in rat fetuses with CDH. METHODS: CDH was induced by Nitrofen. The fetuses were divided into 6 groups: 1) control (C); 2) control ventilated (CV); 3) exposed to nitrofen (N-); 4) exposed to nitrofen ventilated (N-V), 5) CDH and 6) CDH ventilated (CDHV). Fetuses were harvested and ventilated. We assessed body weight (BW), total lung weight (TLW), TLW/BW ratio, the median pulmonary arteriolar wall thickness (MWT). We analyzed the expression of NOS2, NOS3, VEGF and its receptors by immunohistochemistry and Western blotting. RESULTS: BW, TLW, and TLW/BW ratio were greater on C than on N- and CDH (p<0.05). The MWT was higher in CDH than in CDHV (p<0.001). CDHV showed increased expression of NOS3 (p<0.05) and VEGFR1 (p<0.05), but decreased expression of NOS2 (p<0.05) and VEGFR2 (p<0.001) compared to CDH. CONCLUSION: Ventilation caused pulmonary vasodilation and changed the expression of NOS and VEGF receptors.

Increased pulmonary vascular expression of receptor for advanced glycation end products (RAGE) in experimental congenital diaphragmatic hernia.

AIM OF THE STUDY: Persistent pulmonary hypertension (PH) continues to be a major cause of high mortality in congenital diaphragmatic hernia (CDH). The receptor for advanced glycation end products (RAGE) is a member of the immunoglobulin protein family. Recently, RAGE has been implicated in mediating pulmonary arterial smooth muscle cell proliferation and vascular remodeling in experimental PH. RAGE has been reported to be highly upregulated in lung tissue of patients with severe PH. We designed this study to investigate the hypothesis that RAGE expression is increased in nitrofen-induced CDH. METHODS: Pregnant rats were exposed to nitrofen or vehicle on D9. Fetuses were sacrificed on D21 and divided into nitrofen (n=16) and control group (n=16). Quantitative real-time polymerase chain reaction, Western blotting, and confocal immunofluorescence were performed. MAIN RESULTS: Pulmonary RAGE gene expression levels were significantly increased in nitrofen-induced CDH compared to controls (p<0.003). Western blotting and confocal microscopy revealed increased pulmonary RAGE protein expression in CDH compared to controls. CONCLUSION: This study provides striking evidence of increased gene and protein expression of RAGE in the pulmonary vasculature of nitrofen-induced CDH, suggesting that increased expression of RAGE may play a role in the pathogenesis of PH in nitrofen-induced CDH.

Decreased apelin and apelin-receptor expression in the pulmonary vasculature of nitrofen-induced congenital diaphragmatic hernia.

BACKGROUND: The high morbidity and mortality in congenital diaphragmatic hernia (CDH) are attributed to severe pulmonary hypoplasia and persistent pulmonary hypertension (PH). PH is characterized by structural changes in pulmonary arteries, resulting in adventitial and medial thickness. These effects are triggered by abnormal apoptosis and proliferation of pulmonary vascular endothelial and smooth muscle cells (SMCs). Apelin (APLN), a target gene of bone morphogenic protein receptor 2 (BMPR2), is known to play an important and manifold role in regulating pulmonary homeostasis promoting endothelial cell (EC) survival, proliferation and migration. In addition to these autocrine effects of apelin, it displays a paracrine function attenuating the response of pulmonary SMCs to growth factors and promoting apoptosis. Apelin exerts its effect via its G-protein-coupled receptor (APLNR) and is solely expressed by pulmonary vascular EC, whereas APLNR is co-localized in pulmonary ECs and SMCs. Dysfunction of BMPR2 and downstream signalling have been shown to disturb the crucial balance of proliferation of SMCs contributing to the pathogenesis of human and experimentally induced PH. We designed this study to investigate the hypothesis that apelin and APLNR signalling are disrupted in the pulmonary vasculature of rats in nitrofen-induced CDH. METHODS: Pregnant rats were exposed to nitrofen or vehicle on D9 of gestation. Foetuses were sacrificed on D21 and divided into nitrofen and control group (n = 32). Pulmonary RNA was extracted and mRNA levels of APLN and APLNR were determined by quantitative real-time PCR. Protein expression of apelin and APLNR was investigated by western blotting. Confocal immunofluorescence double staining for apelin, APLNR and SMCs were performed. RESULTS: Relative mRNA level of APLN and APLNR were significantly decreased in the CDH group compared to control lungs. Western blotting and confocal microscopy confirmed the qRT-PCR results showing decreased pulmonary protein expression of apelin and APLNR in lungs of nitrofen-exposed foetuses compared to controls. CONCLUSION: This study provides striking evidence of markedly decreased gene and protein expression of apelin and its receptor APLNR in the pulmonary vasculature of nitrofen-induced CDH. The disruption of the apelin-APLNR signalling axis in the pulmonary vasculature may lead to extensive vascular remodelling and contribute to PPH in the nitrofen-induced CDH model.

Spatiotemporal alterations in Sprouty-2 expression and tyrosine phosphorylation in nitrofen-induced pulmonary hypoplasia.

BACKGROUND/PURPOSE: Pulmonary hypoplasia (PH) is a life-threatening condition of newborns presenting with congenital diaphragmatic hernia (CDH). Sprouty-2 functions as a key regulator of fibroblast growth factor receptor (FGFR) signalling in developing foetal lungs. It has been reported that FGFR-mediated alveolarization is disrupted in nitrofen-induced PH. Sprouty-2 knockouts show severe defects in lung morphogenesis similar to nitrofen-induced PH. Upon FGFR stimulation, Sprouty-2 is tyrosine-phosphorylated, which is essential for its physiological function during foetal lung development. We hypothesized that Sprouty-2 expression and tyrosine phosphorylation are altered in nitrofen-induced PH. METHODS: Time-pregnant rats received either nitrofen or vehicle on gestation day 9 (D9). Foetal lungs were dissected on D18 and D21. Pulmonary Sprouty-2 gene and protein expression levels were analyzed by qRT-PCR, Western blotting and immunohistochemical staining. RESULTS: Relative mRNA expression of Sprouty-2 was significantly decreased in hypoplastic lungs without CDH (0.1050±0.01 vs. 0.3125±0.01; P<.0001) and with CDH (0.1671±0.01 vs. 0.3125±0.01; P<.0001) compared to controls on D18. Protein levels of Sprouty-2 were markedly decreased in hypoplastic lungs on D18 with decreased tyrosine phosphorylation levels on D18 and D21 detected at the molecular weight of Sprouty-2 consistent with Sprouty-2 tyrosine phosphorylation. Sprouty-2 immunoreactivity was markedly decreased in hypoplastic lungs on D18 and D21. CONCLUSION: Spatiotemporal alterations in pulmonary Sprouty-2 expression and tyrosine phosphorylation during the late stages of foetal lung development may interfere with FGFR-mediated alveolarization in nitrofen-induced PH.

Downregulated bone morphogenetic protein signaling in nitrofen-induced congenital diaphragmatic hernia.

PURPOSE: Bone morphogenetic proteins (BMP) have been shown to play crucial roles in not only lung and heart development, but also in the pathogenesis of pulmonary vascular remodeling in pulmonary hypertension (PH). We therefore hypothesized that BMP signaling could be altered in nitrofen-induced congenital diaphragmatic hernia (CDH) and associated PH. METHODS: Pregnant rats were exposed to either 100 mg nitrofen or vehicle on embryonic day (E) 9.5. On E17 and E21, fetuses were delivered by cesarean section, killed and checked for left-sided CDH. The tissue was then harvested for pathobiological evaluation. RESULTS: In nitrofen-induced CDH, pulmonary expressions of BMP4, BMP receptor (BMPR) type 2 and Id1 decreased on E17 and E21. On E17, pulmonary gremlin-1 expression increased, while BMP7 decreased. In the lungs, Id1 expression was correlated to BMP4 and BMPR2 and inversely correlated to gremlin-1 expression. Myocardial expressions of BMPR2, BMPR1A, BMP7 and SERCA-2A decreased, while gremlin-1 and noggin expressions increased on E17. On E21, myocardial expressions of Id1 and SERCA-2A decreased, while gremlin-1 expression increased. Moreover, BMPR2 and BMPR1A expressions were correlated to SERCA-2A expression and inversely correlated to pro-apoptotic Bax/Bcl2 ratio within the myocardium. CONCLUSION: Downregulation of BMP signaling seems to contribute to pulmonary and myocardial anomalies observed in nitrofen-induced CDH.

Aberrant pulmonary lymphatic development in the nitrofen mouse model of congenital diaphragmatic hernia.

PURPOSE: Many infants develop a postsurgical chylothorax after diaphragmatic hernia repair. The pathogenesis remains elusive but may be owing to dysfunctional lymphatic development. This study characterizes pulmonary lymphatic development in the nitrofen mouse model of CDH. METHODS: CD1 pregnant mice were fed nitrofen/bisdiamine (N/B) or olive oil at E8.5. At E14.5 and E15.5, lung buds were categorized by phenotype: normal, N/B without CDH (N/B - CDH), or N/B with CDH (N/B+CDH). Anti-CD31 was used to localize all endothelial cells, while anti-LYVE-1 was used to identify lymphatic endothelial cells in lung buds using immunofluorescence. Differential protein expression of lymphatic-specific markers was analyzed. RESULTS: Lymphatic endothelial cells localized to the mesenchyme surrounding the airway epithelium at E15.5. CD31 and LYVE-1 colocalization identified lymphatic endothelial cells. LYVE-1 expression was upregulated in N/B+CDH lung buds in comparison to N/B - CDH and normal lung buds by immunofluorescence. Western blotting shows that VEGF-D, LYVE-1, Prox-1, and VEGFR-3 expression was upregulated in N/B+CDH lung buds in comparison to N/B - CDH or control lung buds at E14.5. CONCLUSIONS: Lung lymphatics are hyperplastic in N/B+CDH. Upregulation of lymphatic-specific genes suggests that lymphatic hyperplasia plays an important role in dysfunctional lung lymphatic development in the nitrofen mouse model of CDH.

Disruption of the bone morphogenetic protein receptor 2 pathway in nitrofen-induced congenital diaphragmatic hernia.

BACKGROUND/PURPOSE: Congenital diaphragmatic hernia (CDH) remains a major therapeutic challenge despite advances in neonatal resuscitation and intensive care. The high mortality and morbidity in CDH has been attributed to pulmonary hypoplasia and persistent pulmonary hypertension (PH). Bone morphogenetic protein receptor 2 (BMPR2) plays a key role in pulmonary vasculogenesis during the late stages of fetal lung development. BMPR2 is essential for control of endothelial and smooth muscle cell proliferation. Dysfunction of BMPR2 and downstream signaling have been shown to disturb the crucial balance of proliferation of smooth muscle cells contributing to the pathogenesis of human and experimental PH. We designed this study to investigate the hypothesis that BMPR2 signaling is disrupted in nitrofen-induced CDH. METHODS: Pregnant rats were treated with nitrofen or vehicle on gestational day 9 (D9). Fetuses were sacrificed on D21 and divided into CDH and control. Quantitative real-time polymerase chain reaction, Western blotting, and confocal-immunofluorescence were performed to determine pulmonary gene expression levels and protein expression of BMPR2 and related proteins. RESULTS: Pulmonary Bmpr2 gene expression levels were significantly decreased in nitrofen-induced CDH compared to controls. Western blotting and confocal microscopy revealed decreased pulmonary BMPR2 protein expression and increased activation of p38(MAPK) in CDH compared to controls. CONCLUSION: The observed disruption of the BMPR2 signaling pathway may lead to extensive vascular remodeling and contribute to PH in the nitrofen-induced CDH model. BMPR2 may therefore represent a potential target for the treatment of PH in CDH.

Decreased expression of GATA4 in the diaphragm of nitrofen-induced congenital diaphragmatic hernia.

BACKGROUND: The molecular mechanisms underlying the diaphragmatic defect in congenital diaphragmatic hernia (CDH) are still poorly understood. The transcription factor GATA4 is essential for normal development of the diaphragm. Recently, mutations in the GATA4 gene have been linked to human and rodent CDH. We hypothesized that diaphragmatic GATA4 expression is downregulated in the nitrofen CDH model. METHODS: Pregnant rats received Nitrofen or vehicle on day 9 of gestation (D9). Fetuses were sacrificed on D13, D18, or D21. Pleuroperitoneal folds (n=20) and fetal diaphragms (n=40) were (micro) dissected and divided into CDH group and controls. RNA and protein were extracted. GATA4 mRNA levels were determined by real-time PCR. Protein levels were determined by ELISA and Immunohistochemistry. RESULTS: mRNA levels and Protein levels were significantly decreased in the CDH group compared to controls on D13 (mRNA 15.96±6.99 vs. 38.10±5.01, p<0.05), D18 (mRNA 10.45±1.84 vs. 17.68±2.11, Protein 2.59±0.06 vs. 4.58±0.35 p<0.05) and D21 (mRNA 4.31±0.83 vs. 6.87±0.88, Protein 0.16±0.08 vs. 1.26±0.49, p<0.05). Immunoreactivity of GATA4 was markedly decreased in CDH-diaphragms on D13, D18, and D21. CONCLUSIONS: We provide evidence for the first time that diaphragmatic expression of GATA4 is downregulated in the nitrofen model, suggesting that decreased expression of GATA4 may impair diaphragmatic development in nitrofen-induced CDH.

Effect of nitrofen in the final stages of development of the diaphragm muscle in rats.

PURPOSE: To evaluate the expression of myosin in muscle fibers of the diaphragm in experimental congenital diaphragmatic hernia (CDH). METHODS: Fetuses of pregnant rats were divided into four groups: External Control (EC), composed of non-manipulated rats; Nitrofen, composed of pregnant rats that received 100 mg of nitrofen (2,4-dichloro-4'nitrodiphenyl ether) diluted in olive oil on gestational day (GD) 9.5, whose fetuses developed CDH (N+) or not (N-), and Olive Oil Placebo (OO), composed of pregnant rats that received the oil on the same GD. The fetuses were collected on GD 18.5, 19.5, 20.5 and 21.5 (term = 22 days). We obtained body weight (BW) and photographed the diaphragm area (DA), hernia area (HA) and subsequent calculated the HA/DA ratio in N+ group. Samples of Diaphragm muscle were processed for histological staining with H/E and immunohistochemistry (IHQ) for myosin. RESULTS: The fetuses of N- and N+ groups had decreased BW and DA compared to EC and OO groups (p < 0.001). HA was decreased on GD 18.5 compared to 21.5 (p < 0.001) and the HA/DA ratio showed no difference. IHQ showed decreased expression of myosin in nitrofen groups. CONCLUSION: CDH induced by nitrofen model contributes to the understanding of muscularization in the formation of the diaphragm where the myosin expression is decreased.

Increased trophoblastic apoptosis mediated by neutrophil gelatinase-associated lipocalin (NGAL) activation in the nitrofen model of congenital diaphragmatic hernia.

BACKGROUND: Retinoids play a key role in fetal lung development. It has been suggested that the maternal-fetal retinol transport is disrupted by trophoblastic apoptosis. The mechanism underlying nitrofen-induced apoptosis in placenta is not fully understood. Neutrophil gelatinase-associated lipocalin (NGAL) is expressed in the fetal part of the maternal-fetal interface. NGAL is part of the immune barrier and serves primarily as a transport protein transferring biologically hazardous molecules in a safe and controlled way. It has been shown that over-activation of NGAL induces apoptosis. We hypothesized that increased placental NGAL expression induces trophoblastic apoptosis in the nitrofen model of CDH. METHODS: Pregnant rats were exposed to either olive oil or nitrofen on day 9 of gestation (D9). Placenta harvested on D21 and divided into two groups: control and nitrofen with CDH. Immunohistochemistry was performed to evaluate trophoblasts (by cytokeratin expression), NGAL expression, and apoptotic trophoblastic cells (using TUNEL assay). Total RNA was extracted from each placenta and the relative mRNA expression levels of NGAL were analyzed using RT-PCR. RESULTS: Immunohistochemistry showed NGAL immunoreactivity both in control and CDH in the fetal part of the fetal-maternal interface of placenta. Markedly increased NGAL expression was detected in CDH group compared to controls. Relative mRNA expression levels of NGAL gene were significantly increased in the CDH group compared to control in the placenta (5.924 ± 0.93 vs. 1.895 ± 0.54, p < 0.001). Markedly increased numbers of apoptotic trophoblastic cells were seen in the maternal-fetal interface in the CDH group compared to controls. CONCLUSIONS: NGAL activation may lead to increased trophoblastic apoptosis in the maternal-fetal interface in the nitrofen model of CDH. These changes may therefore cause disturbance in maternal-fetal retinol transport affecting fetal lung morphogenesis.

Decreased pulmonary c-Cbl expression and tyrosine phosphorylation in the nitrofen-induced rat model of congenital diaphragmatic hernia.

PURPOSE: The high morbidity of newborn infants with congenital diaphragmatic hernia (CDH) is attributed to pulmonary hypoplasia (PH), which is characterized by a failure of alveolar development. The nitrofen-induced CDH model has been widely used to investigate the pathogenesis of PH in CDH. It has previously been shown that the fibroblast growth factor receptor (FGFR) pathway, which is essential for a proper lung development, is disrupted during late gestation of nitrofen-induced CDH. Casitas B-lineage lymphoma (c-Cbl) proteins are known regulators of signal transduction through FGFRs, indicating their important role during alveolarization in developing lungs. Furthermore, it has been demonstrated that tyrosine phosphorylation of c-Cbl proteins has a pivotal role for their physiological function and activity during fetal lung development. We designed this study to test the hypothesis that pulmonary c-Cbl expression and tyrosine phosphorylation status are decreased in the nitrofen-induced CDH model. METHODS: Timed-pregnant rats received either 100 mg nitrofen or vehicle on gestation day 9 (D9). Fetuses were harvested on D18 and D21, and lungs were divided into two groups: control and hypoplastic lungs with CDH (CDH(+)) (n = 10 at each time-point, respectively). Pulmonary gene expression levels of c-Cbl were analyzed by quantitative real-time polymerase chain reaction. Western blotting combined with densitometry analysis was used for semi-quantification of protein levels of pulmonary c-Cbl and tyrosine phosphorylation status. Confocal-immunofluorescence staining was performed to evaluate c-Cbl protein expression and distribution. RESULTS: Relative mRNA expression levels of pulmonary c-Cbl were significantly decreased in CDH(+) on D18 and D21 compared to controls. Western blotting showed markedly decreased protein levels of pulmonary c-Cbl and tyrosine phosphorylation status in CDH(+) on D18 and D21. Confocal-immunofluorescence analysis confirmed decreased c-Cbl expression in CDH(+) on D18 and D21 mainly in the distal alveolar epithelium compared to controls. CONCLUSION: Decreased pulmonary c-Cbl gene and protein expression accompanied by a decreased tyrosine phosphorylation status during the late stages of fetal lung development may result in reduced c-Cbl activity, and thus interfere with the FGFR-mediated alveolarization in the nitrofen-induced CDH model.

Effect of nitrofen in the final stages of development of the diaphragm muscle in rats / Efeito do nitrofen na fase final do desenvolvimento da musculatura do diafragma em ratos

PURPOSE: To evaluate the expression of myosin in muscle fibers of the diaphragm in experimental congenital diaphragmatic hernia (CDH). METHODS: Fetuses of pregnant rats were divided into four groups: External Control (EC), composed of non-manipulated rats; Nitrofen, composed of pregnant rats that received 100 mg of nitrofen (2,4-dichloro-4'nitrodiphenyl ether) diluted in olive oil on gestational day (GD) 9.5, whose fetuses developed CDH (N+) or not (N-), and Olive Oil Placebo (OO), composed of pregnant rats that received the oil on the same GD. The fetuses were collected on GD 18.5, 19.5, 20.5 and 21.5 (term = 22 days). We obtained body weight (BW) and photographed the diaphragm area (DA), hernia area (HA) and subsequent calculated the HA/DA ratio in N+ group. Samples of Diaphragm muscle were processed for histological staining with H/E and immunohistochemistry (IHQ) for myosin.} RESULTS: The fetuses of N- and N+ groups had decreased BW and DA compared to EC and OO groups (p <0.001). HA was decreased on GD 18.5 compared to 21.5 (p <0.001) and the HA/DA ratio showed no difference. IHQ showed decreased expression of myosin in nitrofen groups. CONCLUSION: CDH induced by nitrofen model contributes to the understanding of muscularization in the formation of the diaphragm where the myosin expression is decreased.

OBJETIVO: Avaliar a expressão da miosina na muscularização do diafragma na hérnia diafragmática congênita (CDH) experimental. MÉTODOS: Fetos de ratas foram divididos em quatro grupos: Controle Externo (EC), composto de ratas não manipuladas; Nitrofen, composto de ratas que receberam 100 mg de nitrofen (2,4-dicloro-4'nitrodifenil éter) diluído no azeite no dia de gestação (GD) 9.5, cujos fetos desenvolveram CDH (N+) ou não (N-) e Placebo óleo de oliva (OO), composto de ratas que ingeriram apenas óleo no mesmo GD. Os fetos foram coletados com 18,5, 19,5, 20,5 e 21,5 GD (termo = 22 dias). Foi obtido o peso corporal (BW) e tiradas fotografias da área do diafragma (DA), da hérnia (HA) e calculada a relação HA/DA no grupo N+. Amostras de diafragmas foram processadas histologicamente para coloração com H/E e imunohistoquímica. RESULTADOS: Os fetos dos grupos N- e N+ tiveram BW e DA diminuídos em relação aos grupos EC e OO (p<0.001). Só houve diferença na HA entre os GD 18.5 e 21.5 (p<0.001) e a relação HA/DA não mostrou diferença entre os grupos. A imunohistoquímica mostrou menor expressão de miosina nos grupos que receberam nitrofen. CONCLUSÃO: O modelo de CDH induzida por nitrofen contribui para entender a muscularização na formação do diafragma onde a expressão da miosina está diminuída.

Pax3 gene expression is not altered during diaphragmatic development in nitrofen-induced congenital diaphragmatic hernia.

BACKGROUND/PURPOSE: Malformations of the pleuroperitoneal folds (PPFs) have been identified as the origin of the diaphragmatic defect in congenital diaphragmatic hernia (CDH). Pax3, expressed in muscle precursor cells (MPCs), plays a key role in regulating myogenesis and muscularization in the fetal diaphragm. Pax3 mutant mice display absence of muscular diaphragm. However, the distribution of muscle precursor cells is reported to be normal in the PPF of the nitrofen-CDH model. We designed this study to investigate the hypothesis that Pax3 gene expression is unaltered in the PPF and developing diaphragm in the nitrofen-induced CDH model. METHODS: Pregnant rats were treated with nitrofen or vehicle on gestational day (D) 9 and sacrificed on D13, D18, and D21. Pleuroperitoneal folds (D13) and developing diaphragms (D18 and D21) were dissected, total RNA was extracted, and real-time quantitative polymerase chain reaction was performed to determine Pax3 messenger RNA levels. Confocal immunofluorescence microscopy was performed to evaluate protein expression/distribution of Pax3. RESULTS: Relative messenger RNA expression levels of Pax3 in PPFs and developing diaphragms were not significantly different in the nitrofen group compared with controls. Intensity of Pax3 immunofluorescence was also not altered in PPFs and developing diaphragms of the nitrofen group compared with controls. CONCLUSION: Pax3 gene expression is not altered in the PPFs and developing diaphragm of nitrofen-CDH model, suggesting that the diaphragmatic defect is not caused by disturbance of myogenesis and muscularization.

Prenatal retinoic acid improves lung vascularization and VEGF expression in CDH rat.

OBJECTIVE: We sought to investigate the effects of antenatal retinoic acid on the pulmonary vasculature and vascular endothelial growth factor (VEGF) and VEGF receptors (VEGFR) expression in a nitrofen-induced congenital diaphragmatic hernia (CDH) model. STUDY DESIGN: Rat fetuses were exposed to nitrofen at gestational day 9.5 and/or all-trans retinoic acid (ATRA) at gestational days 18.5-20.5. We assessed lung growth, airway, and vascular morphometry. VEGF, VEGFR1, and VEGFR2 expression was analyzed by Western blotting and immunohistochemistry. Continuous data were analyzed by analysis of variance and Kruskal-Wallis test. RESULTS: CDH decreased lung to body weight ratio, increased mean linear intercept and mean transection length/airspace, and decreased mean airspace cord length. ATRA did not affect lung growth or morphometry. CDH increased proportional medial wall thickness of arterioles while ATRA reduced it. ATRA recovered expression of VEGF and receptors, which were reduced in CDH. CONCLUSION: Retinoic acid and VEGF may provide pathways for preventing pulmonary hypertension in CDH.

Alterations of peroxisome proliferator-activated receptor γ and monocyte chemoattractant protein 1 gene expression in the nitrofen-induced hypoplastic lung.

BACKGROUND/PURPOSE: Peroxisome proliferator-activated receptor γ (PPARγ) plays a key role in normal lung development. Peroxisome proliferator-activated receptor γ messenger RNA (mRNA) is detectable at 18 days of gestation in fetal rat lungs, and levels peak just before birth. Peroxisome proliferator-activated receptor γ agonists are reported to stimulate lung development, whereas inhibition of PPARγ disrupts postnatal lung maturation. Monocyte chemoattractant protein 1 (MCP-1), which is inhibited by PPARγ, is reported to disrupt late lung morphogenesis. This study was designed to investigate the hypothesis that PPARγ expression is downregulated and that MCP-1 expression is upregulated during the late stages of lung development in nitrofen-induced hypoplastic lungs. METHODS: Pregnant rats were treated with nitrofen or vehicle on D9. RNA was extracted from fetal lungs (D18 and D21), and relative mRNA expression levels of PPARγ and MCP-1 were determined by reverse transcriptase-polymerase chain reaction. Immunohistochemistry was performed to evaluate protein expression/distribution of PPARγ and MCP-1. RESULTS: Relative mRNA expression levels of PPARγ were significantly downregulated in the nitrofen group compared with controls on D21, whereas MCP-1 levels were upregulated. Immunohistochemical study showed markedly decreased PPARγ and increased MCP-1 immunoreactivity in the nitrofen-induced hypoplastic lungs compared with controls on gestational day 21. CONCLUSION: Altered pulmonary gene expression of PPARγ and MCP-1 during late gestation may impair lung development and maturation, contributing to pulmonary hypoplasia in the nitrofen-induced congenital diaphragmatic hernia model.

ANG-1 TIE-2 and BMPR signalling defects are not seen in the nitrofen model of pulmonary hypertension and congenital diaphragmatic hernia.

BACKGROUND: Pulmonary hypertension (PH) is a lethal disease that is associated with characteristic histological abnormalities of the lung vasculature and defects of angiopoetin-1 (ANG-1), TIE-2 and bone morphogenetic protein receptor (BMPR)-related signalling. We hypothesized that if these signalling defects cause PH generically, they will be readily identifiable perinatally in congenital diaphragmatic hernia (CDH), where the typical pulmonary vascular changes are present before birth and are accompanied by PH after birth. METHODS: CDH (predominantly left-sided, LCDH) was created in Sprague-Dawley rat pups by e9.5 maternal nitrofen administration. Left lungs from normal and LCDH pups were compared at fetal and postnatal time points for ANG-1, TIE-2, phosphorylated-TIE-2, phosphorylated-SMAD1/5/8 and phosphorylated-ERK1/2 by immunoprecipitation and Western blotting of lung protein extracts and by immunohistochemistry on lung sections. RESULTS: In normal lung, pulmonary ANG-1 protein levels fall between fetal and postnatal life, while TIE-2 levels increase. Over the corresponding time period, LCDH lung retained normal expression of ANG-1, TIE-2, phosphorylated-TIE-2 and, downstream of BMPR, phosphorylated-SMAD1/5/8 and phosphorylated-p44/42. CONCLUSION: In PH and CDH defects of ANG-1/TIE-2/BMPR-related signalling are not essential for the lethal vasculopathy.

Antenatal imatinib treatment reduces pulmonary vascular remodeling in a rat model of congenital diaphragmatic hernia.

The pathophysiology of congenital diaphragmatic hernia (CDH) is constituted by pulmonary hypoplasia and pulmonary hypertension (PH). We previously reported successful treatment with imatinib of a patient with CDH. This study examines the effect of antenatal imatinib administration on the pulmonary vasculature in a rat model of CDH. Pregnant rats were given nitrofen to induce CDH. Controls were given olive oil. Half of the CDH fetuses and half of the controls were treated with imatinib antenatally E17-E21, rendering four groups: Control, Control+Imatinib, CDH, and CDH+Imatinib. Lung sections were obtained for morphometry and immunohistochemistry, and protein was purified for Western blot. Effects of nitrofen and imatinib on Ki-67, caspase-3, PDGF-B, and PDGF receptors were analyzed. Imatinib significantly reduced medial wall thickness in pulmonary arteries of rats with CDH. It also normalized lumen area and reduced the proportion of fully muscularized arteries. Imatinib also caused medial thinning in the control group. Cell proliferation was increased in CDH, and this proliferation was significantly reduced by imatinib. PDGF-B and PDGFR-ß were upregulated in CDH, and imatinib treatment resulted in a downregulation. PDGFR-α remained unchanged in CDH but was significantly downregulated by imatinib. Antenatal imatinib treatment reduces development of medial wall thickness and restores lumen area in pulmonary arteries in nitrofen-induced CDH. The mechanism is reduced cell proliferation. Imatinib is an interesting candidate for antenatal therapy for PH in CDH, but potential side effects need to be investigated and more specific targeting of PDGF signaling is needed.

Prenatal retinoic acid upregulates connexin 43 (Cx43) gene expression in pulmonary hypoplasia in the nitrofen-induced congenital diaphragmatic hernia rat model.

PURPOSE: Connexin 43 (Cx43), a major gap junction protein, is necessary for alveologenesis and plays an important role in the differentiation of type II to type I alveolar epithelial cells. Knockout mice of Cx43 display severe pulmonary hypoplasia (PH). Prenatal administration of retinoic acid (RA) is known to stimulate alveologenesis in nitrofen-induced PH. Recent studies revealed that retinoids upregulate Cx43 expression. We hypothesized that gene expression of Cx43 is downregulated during alveologenesis and that administration of RA upregulates Cx43 expression in the nitrofen-induced PH. METHODS: Pregnant rats were exposed to olive oil or nitrofen on day 9 (D9) of gestation. Retinoic acid was given intraperitoneally on D18, D19, and D20. Fetal lungs were harvested on D18 and D21 and divided into control, nitrofen, control+RA (D21), and nitrofen+RA (D21). The Cx43 expression levels were determined using reverse transcription polymerase chain reaction and immunohistochemistry. RESULTS: On D18 and D21, Cx43 relative messenger RNA expression levels were significantly downregulated in nitrofen compared with those in the control group. On D21, expression levels of Cx43 were significantly upregulated in nitrofen+RA and control+RA compared with those in nitrofen group. Immunohistochemical studies confirmed these results. CONCLUSION: Downregulation of Cx43 expression may interfere with normal alveologenesis. Upregulation of Cx43 pulmonary gene expression after RA treatment may promote lung growth by stimulating alveologenesis in nitrofen-induced PH.

Retinoic acid rescues deficient airway innervation and peristalsis of hypoplastic rat lung explants.

BACKGROUND: Bronchial peristalsis modulates lung growth and is deficient in hypoplastic nitrofen-exposed rat lung explants. Retinoic acid (RA) rescues lung hypoplasia. This study examines whether decreased bronchial innervation contributes to this developmental deficiency and if RA is able to recover bronchial innervation and motility. MATERIAL AND METHODS: After IRB approval, pregnant rats received either 100 mg nitrofen or vehicle on gestational day 9.5 (E9.5). Embryonic lung primordia harvested on E13 were cultured for 72 h and RA was added daily to the medium when appropriate. Lung growth was assessed by counting the number of terminal buds and measuring explant surface, total DNA and protein in control, control + RA, nitrofen and nitrofen + RA groups. Peristaltic contractions were recorded for 10 min under an inverted microscope. Lung explants stained for anti-protein gene product 9.5 (PGP 9.5) and smooth muscle α-actin were examined under a confocal microscope for depicting the specific relationship between neural and smooth muscle cells. PGP 9.5 and smooth muscle α-actin levels were quantified by Western blot analysis for assessing the neural and muscle cell expressions. Comparisons between groups were made with non-parametric tests. RESULTS: The number of terminal buds, the explants' surface and the DNA and protein contents were significantly decreased in nitrofen-exposed lungs in comparison with controls. In contrast, these measurements were normal in explants exposed to both nitrofen and RA. Bronchial peristalsis (contractions/min) was significantly decreased in nitrofen-exposed lungs in comparison with controls; in contrast, in nitrofen + RA lungs it was similar to controls. In all study groups, the airways were surrounded by smooth muscle and ensheathed in a plexus of nerve fibers containing ganglia. PGP 9.5 protein levels were decreased in nitrofen-exposed lungs, but they normalized when RA was added. No differences were found in α-actin protein levels. Explants exposed only to RA were similar to control. CONCLUSIONS: Lung growth, bronchial innervation and peristalsis are decreased in nitrofen-exposed lung explants and are rescued by RA. If deficient airway innervation contributing to dysmotility and pulmonary hypoplasia can be pharmacologically rescued, new relatively simple prenatal interventions could be envisioned.