Attenuation of ductus arteriosus intimal thickening in preterm sheep twins compared with singletons

Morbidity and mortality of twins and triplets compared to singleton infants delivered between 26-34 weeks gestation in the United States

OBJECTIVE

To describe in-hospital morbidities and mortality among twins and triplets delivered at ≥26 to ≤34 weeks gestational age (GA) while controlling for prematurity and growth restriction.

STUDY DESIGN

Retrospective analysis of inborn infants discharged from a neonatal intensive care unit (NICU) managed by the Pediatrix Medical Group between 2010 and 2018.

RESULT

Among 247 437 infants included, 27.4% were multiples. Adjusted for GA and other factors typically known prior to delivery, in-hospital morbidities varied by plurality and generally were more common in singletons. The odds of death prior to discharge were less for twins at 0.74 (95% CI: 0.67-0.83) and triplets at 0.69 (95% CI: 0.51-0.92) compared to singletons.

CONCLUSION

Singletons experience greater morbidity and mortality compared to twins and triplets born ≥26 weeks to ≤34 weeks GA, except PDA requiring procedural intervention, ROP requiring treatment, and longer length of stay.

Predictors of a non-response to prophylactic indomethacin for patent ductus arteriosus in preterm infants

BACKGROUND

Preterm infants are recommended for prophylactic indomethacin (PIND) to promote closure of patent ductus arteriosus (PDA) and reduce morbidity and mortality. This study investigated the predictive factors of a non-response to PIND for PDA in preterm-birth infants.

METHODS

Consecutive preterm-birth infants (gestational age: < 28 weeks) who received PIND between 2009 and 2019 were retrospectively enrolled. Seventy-six eligible participants were classified as PIND responders (N = 42) or non-responders (N = 34). Information on potential confounders in maternal obstetric and perinatal data were collected from medical records. Multiple logistic regression analysis was carried out to identify the prognostic factors of a PIND response in preterm-birth infants.

RESULTS

The prevalence of intrauterine infection and multiple births was significantly different between responders and non-responders to PIND (intrauterine infection: 2 [4.8%] vs. 8 [23.5%], P = 0.036; twins: 3 [7.1%] vs. 9 [ 26.5%], P = 0.029, respectively). In multivariate logistic regression analysis after adjustment for multiple births, intrauterine infection was a significant and independent predictive factor of a non-response to PIND (odds ratio [OR] 5.54, 95% confidence interval [CI] 1.05-29.2, P = 0.044). A remarkable association was also noted for multiple births with a non-response to PIND (OR 4.22, 95% CI 0.99-17.8, P = 0.050).

CONCLUSIONS

Intrauterine infection and multiple births were identified as potential risk factors of a non-response to PIND for PDA in preterm infants.

Ductus Arteriosus of Extremely Preterm Twins is More Resistant to Cyclooxygenase Inhibitors Than Those of Singletons

Symptomatic patent ductus arteriosus (sPDA) is common among preterm infants, and can lead to several complications. This is particularly true for extremely preterm infants, as closure of the ductus arteriosus using cyclooxygenase inhibitors is often difficult. A recent study using a preterm sheep model showed that intimal thickening-required for anatomical closure of the ductus arteriosus-is less developed in twins than in singletons. Therefore, this study primarily aimed to prove that the ductus arteriosus of extremely preterm twins is more resistant to cyclooxygenase inhibitors than those of extremely preterm singletons. Its secondary aim was to assess whether the resistance against cyclooxygenase inhibitors differed according to chorionicity. In this retrospective case-control study, medical records of 162 extremely preterm infants (gestational age < 28 weeks) were reviewed, and the treatment course of sPDA was subsequently compared between singletons (n = 131) and twins (n = 31). The median indomethacin doses for sPDA and the necessity for surgical ligation were significantly higher in twins than in singletons (5 vs 2 [p < 0.001] and 42% vs 21% [p = 0.018], respectively). No significant differences in sPDA treatment, including the number of indomethacin doses and the necessity for surgical ligation, were observed between monochorionic diamniotic and dichorionic diamniotic twins. This study confirms that the ductus arteriosus of extremely preterm twins is more resistant to cyclooxygenase inhibitors than those of singletons. However, there was no significant difference in sPDA treatment by chorionicity.

[A new therapeutic target for patent ductus arteriosus]

The ductus arteriosus (DA) maintains the fetal circulation by connecting the aorta and pulmonary arteries. Patent ductus arteriosus (PDA) occurs in >70% extremely-low-birth-weight infants. Patients with PDA exhibit circulatory failure, which is caused by left-to-right shunt. The DA immediately contracts after birth in response to the elevation of blood oxygen tension and to the decline in circulating prostaglandin E₂ (PGE₂). Cyclooxygenase inhibitors targeting smooth muscle cell (SMC) contraction represent only pharmacological treatment for PDA. However, it is important for DA anatomical closure that intimal thickening (IT) is appropriately formed between SMC layer and endothelial cells (EC). IT begins to form before the second-trimester and becomes prominent toward the end of third-trimester as an increase in placenta-derived PGE₂. Immature DAs frequently fail to be close due to poorly formed IT. IT consists of extracellular matrices (ECM) and migrated DA-SMCs from the tunica media. A glycoprotein fibulin-1 is expressed in developing cardiovascular system and binds to multiple ECMs. We found that PGE₂ increased fibulin-1 via EP4 in DA-SMCs, and Fbln1-deficient mice exhibited PDA with poor IT formation. Although EP4 is a Gs-coupled GPCR, fibulin-1 was secreted from DA-SMCs through the phospholipase C-protein kinase C-non-canonical NFκB signaling pathway. Fibulin-1 bound to DA-EC-derived versican which is a binding partner of hyaluronan, which promoted directional DA-SMC migration toward ECs and contributed to IT formation in the DA. Fibulin-1 upregulation by the activation of specific downstream pathway of EP4 may serve a new pharmacological strategy for PDA.

Extracellular matrix-mediated remodeling and mechanotransduction in large vessels during development and disease

The vascular extracellular matrix (ECM) is synthesized and secreted during embryogenesis and facilitates the growth and remodeling of large vessels. Proper interactions between the ECM and vascular cells are pivotal for building the vasculature required for postnatal dynamic circulation. The ECM serves as a structural component by maintaining the integrity of the vessel wall while also regulating intercellular signaling, which involves cytokines and growth factors. The major ECM component in large vessels is elastic fibers, which include elastin and microfibrils. Elastin is predominantly synthesized by vascular smooth muscle cells (SMCs) and uses microfibrils as a scaffold to lay down and assemble cross-linked elastin. The absence of elastin causes developmental defects that result in the subendothelial proliferation of SMCs and inward remodeling of the vessel wall. Notably, elastic fiber formation is attenuated in the ductus arteriosus and umbilical arteries. These two vessels function during embryogenesis and close after birth via cellular proliferation, migration, and matrix accumulation. In dynamic postnatal mechano-environments, the elastic fibers in large vessels also serve an essential role in proper signal transduction as a component of elastin-contractile units. Disrupted mechanotransduction in SMCs leads to pathological conditions such as aortic aneurysms that exhibit outward remodeling. This review discusses the importance of the ECM-mainly the elastic fiber matrix-in large vessels during developmental remodeling and under pathological conditions. By dissecting the role of the ECM in large vessels, we aim to provide insights into the role of ECM-mediated signal transduction that can provide a basis for seeking new targets for intervention in vascular diseases.

Molecular Mechanisms Underlying Remodeling of Ductus Arteriosus: Looking beyond the Prostaglandin Pathway

The ductus arteriosus (DA) is a physiologic vessel crucial for fetal circulation. As a major regulating factor, the prostaglandin pathway has long been the target for DA patency maintenance or closure. However, the adverse effect of prostaglandins and their inhibitors has been a major unsolved clinical problem. Furthermore, a significant portion of patients with patent DA fail to respond to cyclooxygenase inhibitors that target the prostaglandin pathway. These unresponsive medical patients ultimately require surgical intervention and highlight the importance of exploring pathways independent from this well-recognized prostaglandin pathway. The clinical limitations of prostaglandin-targeting therapeutics prompted us to investigate molecules beyond the prostaglandin pathway. Thus, this article introduces molecules independent from the prostaglandin pathway based on their correlating mechanisms contributing to vascular remodeling. These molecules may serve as potential targets for future DA patency clinical management.

Fibulin-1 Integrates Subendothelial Extracellular Matrices and Contributes to Anatomical Closure of the Ductus Arteriosus

OBJECTIVE

The ductus arteriosus (DA) is a fetal artery connecting the aorta and pulmonary arteries. Progressive matrix remodeling, that is, intimal thickening (IT), occurs in the subendothelial region of DA to bring anatomic DA closure. IT is comprised of multiple ECMs (extracellular matrices) and migrated smooth muscle cells (SMCs). Because glycoprotein fibulin-1 binds to multiple ECMs and regulates morphogenesis during development, we investigated the role of fibulin-1 in DA closure. Approach and Results: Fibulin-1-deficient (Fbln1^-/-) mice exhibited patent DA with hypoplastic IT. An unbiased transcriptome analysis revealed that EP4 (prostaglandin E receptor 4) stimulation markedly increased fibulin-1 in DA-SMCs via phospholipase C-NFκB (nuclear factor κB) signaling pathways. Fluorescence-activated cell sorting (FACS) analysis demonstrated that fibulin-1 binding protein versican was derived from DA-endothelial cells (ECs). We examined the effect of fibulin-1 on directional migration toward ECs in association with versican by using cocultured DA-SMCs and ECs. EP4 stimulation promoted directional DA-SMC migration toward ECs, which was attenuated by either silencing fibulin-1 or versican. Immunofluorescence demonstrated that fibulin-1 and versican V0/V1 were coexpressed at the IT of wild-type DA, whereas 30% of versican-deleted mice lacking a hyaluronan binding site displayed patent DA. Fibulin-1 expression was attenuated in the EP4-deficient mouse (Ptger4^-/-) DA, which exhibits patent DA with hypoplastic IT, and fibulin-1 protein administration restored IT formation. In human DA, fibulin-1 and versican were abundantly expressed in SMCs and ECs, respectively.

CONCLUSIONS

Fibulin-1 contributes to DA closure by forming an environment favoring directional SMC migration toward the subendothelial region, at least, in part, in combination with EC-derived versican and its binding partner hyaluronan.