Mechanisms of action of the congenital diaphragmatic hernia-inducing teratogen nitrofen

Abstract

Congenital diaphragmatic hernia (CDH) is a developmental anomaly that results in significant mortality and morbidity. The underlying etiology is poorly understood. Insights will arise from an understanding of the mechanisms by which the teratogen nitrofen induces CDH in rodent models. In this study, we use in vitro cell assays in conjunction with whole animal rodent studies to test hypotheses regarding nitrofen's mechanism of action. The first component examined the interaction of nitrofen with various aspects of the retinoid signaling pathway including uptake proteins, binding proteins, receptors, conversion, and degradation enzymes. The second component examined the interactions of nitrofen and vitamins A, C, and E to test the hypothesis that nitrofen was functioning as an antioxidant to interfere with retinoid signaling. Third, we performed a series of experiments examining the interaction of nitrofen and thyroid signaling. Collectively, the data suggest that the primary aspect of retinoid signaling affected by nitrofen is via inhibition of the rate-limiting enzymes controlling retinoic acid synthesis. Retinoid signaling perturbations do not appear to involve oxidative effects of nitrofen. Any substantial roles of nitrofen-induced perturbations of thyroid hormone signaling or receptor function are not supported. retinoid signaling CONGENITAL DIAPHRAGMATIC HERNIA (CDH) is a serious developmental abnormality that occurs in ϳ1 in 2,500 live births (41). The most commonly observed type of this anomaly is the Bochdalek hernia, characterized by incomplete formation of the posterolateral diaphragm and the invasion of the thoracic cavity by abdominal viscera. The ensuing abnormal fetal breathing movements and physical constraints on the developing lungs and heart contribute to pulmonary and left ventricular hypoplasia and pulmonary hypertension (20,35,37). Despite improved treatment strategies, CDH continues to have significant morbidity and mortality (50,69). Insights into the pathogenesis of the diaphragm defect have arisen from teratogenic, dietary, and genetic rodent models of Bochdalek CDH in conjunction with examination of human postmortem tissue (17). Specifically, the initial diaphragmatic defect appears to occur early (before week 5) during the embryogenesis of the amuscular component of the primordial diaphragm, the pleuroperitoneal fold. Much less is known about the etiology of CDH. However, considering the partial similarities between the pathologies observed in the teratogenic nitrofen-induced rat model and infants with CDH (1, 19, 40), the possibility that a common underlying etiology exists has received consideration. There have been a number of hypotheses put forth to explain the teratogenic effects of nitrofen. The retinoid hypothesis suggests that abnormalities in retinoid signaling, or regulation of the retinoid pathway, lead to the development of the primary diaphragm defect and potentially to direct effects on lung development (reviewed in Ref. 33). Other studies have suggested that nitrofen alte...

Congenital Diaphragmatic Hernia: Comparison of Animal Models and Relevance to the Human Situation

“…In vitro experiments have demonstrated that several agents (including nitrofen) responsible for the induction of diaphragmatic hernias, inhibit RALDH2 activity [71,72] . Others have proposed that nitrofen interferes with the uptake of retinol by lung cells.…”

Targeted array comparative genomic hybridisation (array CGH) identifies genomic imbalances associated with isolated congenital diaphragmatic hernia (CDH)

“…A number of candidate genes are involved in the retinoic acid pathway (Montedonico et al, 2008;Klaassens et al, 2009). Previous research using animal models has demonstrated that environmental factors including a vitamin A-deficient (VAD) diet or exposure to teratogenic agents, particularly nitrofen, can disrupt the retinoid signalling pathway resulting in CDH (Wilson et al, 1953;Thebaud et al, 1999;Babiuk et al, 2004;Oshiro et al, 2005;Nakazawa et al, 2007a,b;Noble et al, 2007;Clugston et al, 2010). Further evidence of the involvement of this pathway comes from knockout or mutant mouse models in which genes involved in retinoid signalling are shown to cause CDH when silenced, including compound null retinoic acid receptor (RAR) mutants which were shown to have a spectrum of VAD-like defects including diaphragm defects (Lohnes et al, , 1995Mendelsohn et al, 1994).…”

Retinoid Pathway and Congenital Diaphragmatic Hernia: Hypothesis from the Analysis of Chromosomal Abnormalities

“…The primordial diaphragm development arises from four different structures: septum transversum, pleuroperitoneal folds, dorsal mesentery and elements from the thoracic body wall [5,6] . Several theories have been proposed to explain primary embryologic events leading to CDH, including failure of closure of the pleuroperitoneal canals, defective myoblast formation or abnormal phrenic nerve innervation [7][8][9] . In animal models, CDH arises from a malformation of the amuscular mesenchymal substratum of the pleuroperitoneal folds before pleuroperitoneal canal closure [10,11] .…”

“…The development of the diaphragm strongly depends on the role of proteins associated with the metabolism and binding of retinoids [47,48] . The nitrofen rat model has particularly highlighted the importance of retinoic acid (RA) in the diaphragm development, but this model has also provided limited insights into understanding the genetic basis of CDH [9] . Retinoids play a central role in many biological processes, particularly during embryogenesis and lung development [49][50][51][52][53] .…”