Impact of Enhancing Fetal Lung Vascular and Alveolar Development by Slow-release Novel Synthetic Prostacyclin Agonist for Treatment of Fetal Lung Hypoplasia

Background: Lung hypoplasia and persistent pulmonary hypertension associated with critical pathologies, such as congenital diaphragmatic hernia (CDH), is the major cause of mortality in the neonates. Although prostaglandins pathway is known to play a pivotal role in the lung development, effectiveness of postnatal treatment by prostaglandin agonists was reported to be suboptimal. We hypothesized that prenatal treatment by ONO-1301SR, slow-release form of a novel synthetic prostacyclin agonist with thromboxane inhibitory activity, might promote development of lungs having hypoplasia in the fetal period. Methods: On embryonic day (E) 9.5, nitrofen was given to pregnant Sprague-Dawley rats to produce a CDH-relating lung hypoplasia model, while normal rats (n=4) received vehicle only. At the same day, either ONO-1301SR or placebo was randomly given to the nitrofen-treated rats (placebo; n=7, ONO; n=5). On E21.5, the normal fetuses, and the fetuses having CDH were analyzed. Results: Prenatal ONO-1301SR administration had no influence on incidence of nitrofen-induced CDH. One-seventh of maternal blood concentration of ONO-1301 was transferred to fetal blood at E21.5, warranting efficient placental permeability of this molecule. Prostacyclin receptor was expressed in pulmonary arterial smooth muscle cells in the fetus. Lung-to-body weight ratio (%) in the ONO group (1.88±0.07) was greater than that in the placebo group (1.60±0.04, p<0.01). Histologically, medial wall thickness in the ONO group was two-third thinner than that in the placebo group (p<0.01). In addition, the number of Ttf-1-positive cells and capillary density were 1.5 times or more greater in the ONO group than that in the placebo group (p<0.05), associated with a greater expression of VEGF and SDF-1 in the ONO group, suggesting enhanced development of the alveolar and capillary network. Conclusions: Prenatal ONO-1301SR administration promoted efficient development of hypoplastic lungs associated with CDH in the nitrofen-induced rat model, indicating potential of this treatment for pathologies having lung hypoplasia.