Tracheal ligation and mechanical ventilation do not improve the antioxidant enzyme status in the lamb model of congenital diaphragmatic hernia

Antenatal vitamin A decreases ventilation-induced lung injury in the lamb model of congenital diaphragmatic hernia

OBJECTIVE

Infants with congenital diaphragmatic hernia (CDH) are susceptible to ventilation-induced lung injury. Vitamin A may protect the lung from injury during ventilation. The authors investigated the effects of antenatal vitamin A on ventilation-induced lung injury in CDH lambs using lung myeloperoxidase (MPO) activity as an indicator of lung injury.

METHODS

Left-sided diaphragmatic defects were created in 10 lambs at 79-81 days' gestation. Six CDH lambs had right jugular venous catheters inserted at 120 days' gestation and were given vitamin A until 135 days' gestation. Four CDH lambs were not treated. Twin littermates (n = 3) served as controls. All lambs were delivered at 136-139 days of gestation and ventilated for 2 hours. Lambs were sacrificed following ventilation and samples of left lung were snap frozen. MPO was extracted from lung tissue and MPO activity was assayed.

RESULTS

CDH lambs treated with antenatal vitamin A demonstrated significantly lower MPO activity than untreated CDH lambs (0.0477 +/- 0.0150 vs. 0.1106 +/- 0.0230 units/mg protein, p < 0.05).

CONCLUSION

This is the first study to look at the effect of vitamin A on lung injury in CDH. In the lamb model of CDH, antenatal vitamin A decreases ventilation-induced lung injury.

Up-regulation of fetal rat lung parathyroid hormone-related protein gene regulatory network down-regulates the Sonic Hedgehog/Wnt/betacatenin gene regulatory network

Lung development depends on endodermal Sonic Hedgehog (Shh) signaling to mesodermal Wingless/int/beta catenin (Wnt/betacatenin), followed by parathyroid hormone-related protein (PTHrP) signaling from endoderm to mesoderm. Fluid distension of fetal rat lung explants up-regulates PTHrP signaling and down-regulates Shh/Wnt/betacatenin signaling, marked by decreases in Patched, Gli, Frizzled, and Dishevelled, inducing fibroblast triglyceride uptake, type II cell saturated phosphatidylcholine, and surfactant protein-B expression. Bumetanide, which inhibits fluid distension, blocked down-regulation of the Shh/Wnt/betacatenin pathway and up-regulation of the PTHrP pathway, whereas PTHrP (1-34, 5 x 10(-7) M) treatment overcame bumetanide inhibition, and the PTHrP receptor antagonist PTHrP (7-34) amide (5 x 10(-6) M) mimicked bumetanide, indicating that PTHrP signaling mediates fluid distension-induced alveolar differentiation. Fetal rat lung explant automaturation was characterized by decreased Wnt/betacatenin signaling and increased PTHrP/PTHrP receptor signaling, up-regulating fibroblast-specific adipocyte differentiation related protein (ADRP) and peroxisome proliferator-activated receptor gamma. Wnt/betacatenin agonists (LiCl or SB415268) maintained Shh/Wnt/betacatenin signaling, blocking spontaneous up-regulation of the PTHrP pathway, whereas PTHrP or cAMP down-regulated Shh/Wnt/betacatenin signaling and stimulated PTHrP signaling for fibroblast and type II cell differentiation. This is the first evidence that alveolar fluid distension is an organizing principle for PTHrP signaling down-regulation of the Shh/Wnt/betacatenin pathway.

Can maternal vitamin e supplementation prevent lung hypoplasia in the nitrofen-induced rat model of congenital diaphragmatic hernia?

Recent studies suggest a role for antioxidants in the prevention of pulmonary hypoplasia associated with congenital diaphragmatic hernia (CDH). We studied the effects of vitamin E in the nitrofen-rat model of CDH. After an initial fast, timed-pregnant Sprague-Dawley rats were gavage-fed nitrofen at gestational day 11 (term is 22 d). On the same day, one group was given a s.c. injection of vitamin E in alcohol; a second group was given an injection of alcohol alone. A third group received no treatment (control). Fetuses were delivered on day 21, and static pressure-volume curves were measured by immersion. Lungs were analyzed for total DNA and protein content by standard methods. A total of 203 fetuses were studied. Of 151 nitrofen-exposed fetuses, 77% had CDH; 92% of these were right-sided. CDH was present in 82% of vehicle-treated fetuses and 71% of vitamin E-treated fetuses (p=0.17). Nitrofen-exposed fetuses not only were smaller than control fetuses but also had disproportionately smaller lungs and poorer lung function, even when CDH was absent; however, lung function was worse when CDH was present. Vitamin E treatment did not improve either lung growth or function, although there was a trend toward less CDH. We have shown, for the first time, that the lung hypoplasia seen in nitrofen-exposed rat fetuses is associated with a dramatic reduction in static lung function, even when CDH is not present. Finally, our findings support the notion that lung hypoplasia in the nitrofen-rat model is independent of CDH formation.

Myeloperoxidase activity as a lung injury marker in the lamb model of congenital diaphragmatic hernia

PURPOSE

The antioxidant system is the primary intracellular defense system of the lung against oxygen toxicity (neutrophil sequestration). The CDH lamb model antioxidant system is deficient. It is hypothesized that pulmonary neutrophil sequestration may play a part in the acute lung injury of CDH patients. Myeloperoxidase (MPO) is a major constituent of neutrophil cytoplasmic granules and its activity therefore is a direct measure of neutrophil presence and an indirect indicator of lung injury.

METHODS

Eight lambs had left-sided diaphragmatic hernias surgically created at 80 days' gestation and were delivered by cesarean section at 140 to 145 days. Eight littermate lambs served as controls. Lambs were either killed before ventilation or were ventilated conventionally for 4 hours with 100% O(2) and then killed. The lungs were dissected en bloc and snap frozen. The samples were homogenized, sonicated, freeze-thawed, and separated by density centrifugation. Supernatants were analyzed for myeloperoxidase (MPO) activity by spectrophotometry with o-dianisidine dihydrochloride and hydrogen peroxide at 460 nm. The MPO activity was normalized to the protein content of the supernatant and expressed as units of MPO activity per milligram of protein.

RESULTS

There was significantly more MPO activity in the CDH-ventilated lungs than controls similarly ventilated (3,203 +/- 665 versus 1,220 +/- 194, P =.001). There was no difference in MPO activity between the CDH and control lungs (318 +/- 57 v 348 +/- 61; P =.5). There was no difference between right and left lungs in any group.

CONCLUSION

Ventilation and hyperoxia leads to neutrophil accumulation in lung tissue, which is most pronounced in the CDH lung tissue. This is a further clue to the pathophysiology of iatrogenic lung injury in CDH. The myeloperoxidase assay may now be used to evaluate antenatal or postnatal antioxidant therapies for iatrogenic lung injury in CDH.

Requirements for fetal surgery: the diaphragmatic hernia model

Fetal surgery for congenital diaphragmatic hernia and other fetal conditions can only be considered if (1) the morbidity of antenatal intervention is acceptable, (2) the diagnosis of the condition can be made accurately, (3) the condition can be differentiated from other, non-surgical anomalies. In addition, (4) the natural evolution of the disease, if left untreated, should be predictable, and the condition should be lethal or severely debilitating, (5) there should not exist adequate postnatal treatment, and (6) the proposed in utero operation should be technically feasible. Open fetal surgery has proven too invasive to be justified for the treatment of diaphragmatic hernia, and progress in postnatal therapy (including ECMO) has dramatically improved the neonatal outcome in all but a severe subgroup of patients. Recently, advances in endoscopic fetal surgery (which appears to be less stressful for the fetus and the gravid uterus) and a new approach to accelerate fetal lung growth and maturation have renewed the feasibility of in utero intervention for diaphragmatic hernia.