Expression and function of phosphodiesterases in nitrofen-induced congenital diaphragmatic hernia in rats

Vascular reactivity is altered in the placentas of fetuses with congenital diaphragmatic hernia

INTRODUCTION

Infants with congenital diaphragmatic hernia (CDH) often develop pulmonary hypertension but frequently fail to respond to vasodilator therapy, for instance because of an altered pulmonary vasoreactivity. Investigating such alterations in vivo is impossible. We hypothesised that these alterations are also present in fetoplacental vessels, since both vasculatures are exposed to the same circulating factors (e.g. endothelin-1) and respond similarly to certain stimuli (e.g. hypoxia). As proof-of-concept, we compared fetoplacental vasoreactivity between healthy and CDH-affected placentas.

METHODS

Fetoplacental vascular function of healthy and antenatally diagnosed left-sided CDH fetuses was assessed by wire myography. Placental expression of enzymes and receptors involved in the altered vasoreactive pathways was measured using quantitative PCR.

RESULTS

CDH arteries (n = 6) constricted more strongly to thromboxane A2 agonist U46619 (p < 0.001) and dilated less to bradykinin (p = 0.01) and nitric oxide (NO)-donor sodium nitroprusside (p = 0.04) than healthy arteries (n = 8). Vasodilation to prostacyclin analogue iloprost and adenylate cyclase stimulator forskolin, and vasoconstriction to endothelin-1 were not different between both groups. Angiotensin II did not induce vasoconstriction. Phosphodiesterase inhibitors sildenafil and milrinone did not affect responses to sodium nitroprusside, forskolin, or U46619. The mRNA expression of guanylate cyclase 1 soluble subunit alpha 1 (p = 0.003) and protein kinase cyclic guanine monophosphate (cGMP)-dependent 1 (p = 0.02) were reduced in CDH versus healthy placentas.

DISCUSSION

The identified changes in the thromboxane and NO-cGMP pathways in the fetoplacental vasculature correspond with currently described alterations in the pulmonary vasculature in CDH. Therefore, fetoplacental arteries may provide an opportunity to predict pulmonary therapeutic responses in infants with CDH.

Combined Inhibition of Phosphodiesterase-5 and -9 in Experimental Heart Failure

BACKGROUND

Intracellular second messenger cyclic guanosine monophosphate (cGMP) mediates bioactivity of the natriuretic peptides and nitric oxide, and is key to circulatory homeostasis and protection against cardiovascular disease. Inhibition of cGMP-degrading phosphodiesterases (PDEs) PDE5 and PDE9 are emerging as pharmacological targets in heart failure (HF).

OBJECTIVES

The present study investigated dual enhancement of cGMP in experimental HF by combining inhibition of PDE-5 (P5-I) and PDE-9 (P9-I).

METHODS

Eight sheep with pacing-induced HF received on separate days intravenous P5-I (sildenafil), P9-I (PF-04749982), P5-I+P9-I, and vehicle control, in counterbalanced order.

RESULTS

Compared with control, separate P5-I and P9-I significantly increased circulating cGMP concentrations in association with reductions in mean arterial pressure (MAP), left atrial pressure (LAP), and pulmonary arterial pressure (PAP), with effects of P5-I on cGMP, MAP, and PAP greater than those of P9-I. Only P5-I decreased pulmonary vascular resistance. Combination P5-I+P9-I further reduced MAP, LAP, and PAP relative to inhibition of either phosphodiesterase alone. P9-I and, especially, P5-I elevated urinary cGMP levels relative to control. However, whereas inhibition of either enzyme increased urine creatinine excretion and clearance, only P9-I induced a significant diuresis and natriuresis. Combined P5-I+P9-I further elevated urine cGMP with concomitant increases in urine volume, sodium and creatinine excretion, and clearance similar to P9-I alone, despite the greater MAP reductions induced by combination treatment.

CONCLUSIONS

Combined P5-I+P9-I amalgamated the superior renal effects of P9-I and pulmonary effects of P5-1, while concurrently further reducing cardiac preload and afterload. These findings support combination P5-I+P9-I as a therapeutic strategy in HF.

Intra-Amniotic Sildenafil Treatment Promotes Lung Growth and Attenuates Vascular Remodeling in an Experimental Model of Congenital Diaphragmatic Hernia

BACKGROUND

Defective lung development resulting in lung hypoplasia and an attenuated and hypermuscularized pulmonary vasculature contributes to significant postnatal mortality in congenital diaphragmatic hernia (CDH). We hypothesize that deficient embryonic pulmonary blood flow contributes to defective lung development in CDH, which may therefore be ameliorated via enhancement of embryonic pulmonary blood flow.

METHODS

The mouse nitrofen model of CDH was utilized to measure embryonic pulmonary blood flow by in utero intracardiac injection of FITC-labeled tomato lectin and color-flow Doppler ultrasound. The effect of prenatal intra-amniotic treatment with sildenafil on survival, lung growth, and vascular morphology in the nitrofen model was determined.

RESULTS

Nitrofen-treated embryos exhibited decreased blood flow in the lung periphery compared to controls, and intra-amniotic sildenafil significantly improved embryonic pulmonary blood flow. Similar to nitrofen alone, pups delivered after nitrofen treatment and intra-amniotic injection of dextrose control exhibited respiratory distress and never survived beyond 6 h. Intra-amniotic sildenafil ameliorated respiratory distress in nitrofen-treated pups and improved postnatal survival to 82%. Following intra-amniotic sildenafil treatment at embryonic day (E)10.5, nitrofen-treated P0 lungs were larger with increased left lobe weight, reduced small pulmonary arterial wall muscularization, and increased airway branching complexity compared to controls. Intra-amniotic sildenafil treatment later at E15.5 also resulted in improved survival, lung growth, and attenuation of vascular remodeling in nitrofen-treated embryos.

CONCLUSIONS

Defective embryonic pulmonary blood flow may contribute to lung maldevelopment in CDH. Enhancement of embryonic pulmonary blood flow via intra-amniotic sildenafil results in lung growth and attenuation of pulmonary vascular remodeling and may have therapeutic potential for CDH.

Pulmonary hypertension secondary to congenital diaphragmatic hernia: factors and pathways involved in pulmonary vascular remodeling

Congenital diaphragmatic hernia (CDH) is a severe birth defect that is characterized by pulmonary hypoplasia and pulmonary hypertension (PHTN). PHTN secondary to CDH is a result of vascular remodeling, a structural alteration in the pulmonary vessel wall that occurs in the fetus. Factors involved in vascular remodeling have been reported in several studies, but their interactions remain unclear. To help understand PHTN pathophysiology and design novel preventative and treatment strategies, we have conducted a systematic review of the literature and comprehensively analyzed all factors and pathways involved in the pathogenesis of pulmonary vascular remodeling secondary to CDH in the nitrofen model. Moreover, we have linked the dysregulated factors with pathways involved in human CDH. Of the 358 full-text articles screened, 75 studies reported factors that play a critical role in vascular remodeling secondary to CDH. Overall, the impairment of epithelial homeostasis present in pulmonary hypoplasia results in altered signaling to endothelial cells, leading to endothelial dysfunction. This causes an impairment of the crosstalk between endothelial cells and pulmonary artery smooth muscle cells, resulting in increased smooth muscle cell proliferation, resistance to apoptosis, and vasoconstriction, which clinically translate into PHTN.

Pulmonary hypertension and the asphyxiated newborn

Persistent pulmonary hypertension of the newborn may occur with perinatal asphyxia, either because of direct effects of hypoxia/ischemia on pulmonary arterial function or indirectly because both are associated with meconium aspiration syndrome or perinatal sepsis/pneumonia. Therapies for persistent pulmonary hypertension of the newborn have the potential to affect cerebral function and cerebral perfusion in infants with hypoxic ischemic encephalopathy. Our literature review concludes that hyperventilation should be avoided, bicarbonate therapy is unproven, and hypoxia and hyperoxia should both be avoided. Nitric oxide improves pulmonary artery pressure and systemic perfusion. The effects of inotropic agents on cerebral perfusion or outcomes are uncertain.