Ronald I. Clyman

β1 And β3 integrins have different roles in the adhesion and migration of vascular smooth muscle cells on extracellular matrix

Extracellular matrix receptors on ductus arteriosus smooth muscle cells (SMC) must enable the cells to migrate through both interstitial and basement membrane matrices to form intimal mounds during postnatal ductus closure. We examined the role of beta 1 and beta 3 integrin receptors on SMC adhesion and migration. Using a new assay to measure cell migration, we found that lamb ductus arteriosus SMC attach to and migrate over surfaces coated with fibronectin (FN), laminin (LN), vitronectin (VN), and collagens I (I) and IV (IV). Blocking antibodies, specific to different integrin complexes, showed that SMC adhesion to FN, LN, I, and IV depended exclusively on functioning beta 1 integrins with little, if any, contribution by the alpha V beta 3 integrin; on the other hand, cell migration over these substrates depended to a large extent on the alpha V beta 3 receptor. Immunofluorescent staining demonstrated that during the early phase of SMC migration, the beta 1 integrins organized rapidly into focal plaques that, with time, gradually covered the cells basal surface; on the other hand, the beta 3 receptor remained concentrated at all times at the cells margins. Ligand affinity chromatography and immunoprecipitation techniques identified a unique series of beta 1 integrins binding to each matrix component: FN (alpha 5 beta 1, alpha 3 beta 1, alpha V beta 1), LN (alpha 1 beta 1, alpha 7 beta 1), VN (alpha V beta 1), I (alpha 1 beta 1, alpha 2 beta 1), and IV (alpha 1 beta 1). In contrast, the beta 3 integrin, alpha V beta 3, bound to all the substrates tested: FN, LN, VN, I, and IV. The results indicate that beta 1 and beta 3 integrins may play different roles in attachment and migration as SMC move through the vascular extracellular matrix to produce obliteration of the ductus arteriosus lumen.

Mechanisms Regulating the Ductus Arteriosus

A patent ductus arteriosus (PDA) results in increased pulmonary blood flow and redistribution of flow to other organs. Several co-morbidities (i.e., necrotizing enterocolitis, intracranial hemorrhage, pulmonary edema/hemorrhage, bronchopulmonary dysplasia, and retinopathy) are associated with the presence of a PDA, but whether or not a PDA is responsible for their development is still unclear. In this review, comparative physiology between the full term and preterm newborn and the barriers preventing the necessary cascade of events leading to permanent constriction of the PDA are reviewed.

Prophylactic Indomethacin Therapy for Patent Ductus Arteriosus in Very-Low-Birth-Weight Infants

We performed a double-blind, controlled study of prophylactic indomethacin therapy in 47 premature infants (less than 1700 g) who had subclinical patent ductus arteriosus. They received either indomethacin or placebo at a mean age of 2.9 days. Among the 25 infants weighing more than 1000 g, a hemodynamically important ductus shunt developed in only four of the 14 given placebo. The incidence of important shunts, the number of surgical ligations, and the duration of oxygen therapy were not appreciably different between the study groups. In contrast, among the 22 infants who weighed 1000 g or less, a major ductus shunt developed in 10 of the 12 given placebo. In the smaller infants indomethacin therapy was associated with a significantly lower incidence of major shunts, fewer surgical ligations, a decreased duration of oxygen therapy, and fewer days necessary to regain birth weight. We conclude that prophylactic indomethacin therapy in infants weighing under 1000 g prevents the later development of large ductus shunts and decreases morbidity.

Early Surgical Ligation Versus a Conservative Approach for Management of Patent Ductus Arteriosus That Fails to Close after Indomethacin Treatment

OBJECTIVE To examine whether a more conservative approach to treating patent ductus arteriosus (PDA) is associated with an increase or decrease in morbidity compared with an approach involving early PDA ligation. STUDY DESIGN In January 2005, we changed our approach to infants born at age<or=27 weeks gestation who failed indomethacin treatment. We changed from an early surgical approach, in which feedings were stopped and all PDAs were ligated (period 1: January 1999 to December 2004; n=216) to a more conservative approach in which feedings continued and PDAs were ligated only if cardiopulmonary compromise developed (period 2: January 2005 to August 2009; n=180). All infants in both periods received prophylactic indomethacin therapy. RESULTS The 2 periods had similar rates of perinatal/neonatal risk factors and indomethacin failure (24%), as well as ventilator management and feeding advance protocols. The conservative approach (period 2) was associated with decreased rates of duct ligation (72% vs 100%; P<.05). Even though infants subjected to this approach were exposed to larger PDA shunts for longer durations, the rates of bronchopulmonary dysplasia, sepsis, retinopathy of prematurity, neurologic injury, and death were similar to those in period 1. The overall rate of necrotizing enterocolitis was significantly lower in period 2 compared with period 1. CONCLUSIONS These findings support the need for new controlled, randomized trials to reexamine the benefits and risks of different approaches to PDA treatment.

Patent Ductus Arteriosus: Are Current Neonatal Treatment Options Better or Worse Than No Treatment at All?

Although a moderate-sized patent ductus arteriosus (PDA) needs to be closed by the time a child is 1-2 years old, there is great uncertainty about whether it needs to be closed during the neonatal period. Although 95% of neonatologists believe that a moderate-sized PDA should be closed if it persists in infants (born before 28 weeks) who still require mechanical ventilation, the number of neonatologists who treat a PDA when it occurs in infants who do not require mechanical ventilation varies widely. Both the high likelihood of spontaneous ductus closure and the absence of randomized controlled trials, specifically addressing the risks and benefits of neonatal ductus closure, add to the current uncertainty. New information suggests that early pharmacologic treatment has several important short-term benefits for the preterm newborn. By contrast, ductus ligation, while eliminating the detrimental effects of a PDA on lung development, may create its own set of morbidities that counteract many of the benefits derived from ductus closure.

Permanent Anatomic Closure of the Ductus Arteriosus in Newborn Baboons: The Roles of Postnatal Constriction, Hypoxia, and Gestation

Permanent closure of the ductus arteriosus require loss of cells from the muscle media and development of neointimal mounds, composed in part of proliferating endothelial cells. We hypothesized that postnatal ductus constriction produces hypoxia of the inner vessel wall; we also hypothesized that hypoxia might lead to cell death and the production of vascular endothelial cell growth factor (VEGF), a hypoxia-inducible growth factor that stimulates endothelial proliferation. We mapped the distribution of hypoxia in newborn baboons and correlated it with the appearance of cell death (TUNEL technique), VEGF expression, and endothelial proliferation (proliferating cell nuclear antigen expression). In the full-term baboon (n = 10), the ductus was functionally closed on Doppler examination by 24 h after delivery. Regions of the ductus where the lumen was most constricted were associated with moderate/intense hypoxia; VEGF expression was increased in the hypoxic muscle media, and luminal endothelial cells, adjacent to the hypoxic media, were proliferating. Cells in the most hypoxic regions of the ductus wall were undergoing DNA fragmentation. In contrast, regions of the ductus with mild degrees of hypoxia had no evidence of cell death, VEGF expression, or endothelial proliferation. Cell death and endothelial proliferation seemed to be limited to regions of the full-term ductus experiencing moderate/intense hypoxia. In the premature baboon (67% gestation) (n = 24), only 29% closed their ductus by Doppler examination before d 6. None of the premature baboons, including those with a closed ductus by Doppler, had evidence of moderate/intense hypoxia; also, there was no evidence of cell death, VEGF expression, endothelial proliferation, or neointima formation by d 6. Therefore, the premature ductus is resistant to developing hypoxia, even when its lumen is constricted; this may make it susceptible to later reopening.

Regulation of Ductus Arteriosus Patency by Nitric Oxide in Fetal Lambs: The Role of Gestation, Oxygen Tension, and Vasa Vasorum

We hypothesized that nitric oxide (NO) production by the fetal ductus arteriosus is limited because of low fetal PO2, but that at neonatal PO2, NO might be an important regulator of ductus arteriosus tone. We exposed isolated rings of fetal lamb ductus arteriosus to elevated PO2. L-NG-nitro-L-arginine methyl ester (L-NAME), an inhibitor of nitric oxide synthase (NOS), and methylene blue and 6-anilino-5,8-quinolinedione (LY83583), inhibitors of guanylate cyclase, produced constriction of the ductus arteriosus. When ductus arteriosus rings were exposed to low PO2, L-NAME had no effect, and methylene blue and LY83583 had only a small effect on ductus arteriosus tone. Sodium nitroprusside and calcium ionophore A23187 relaxed ductus arteriosus rings more than aortic rings, and relaxed ductus arteriosus rings from immature fetuses more than those from late gestation fetuses. In contrast, ductus arteriosus rings from both early and late gestation were equally sensitive to 8-bromo-cGMP. By both reverse transcriptase-polymerase chain reaction and immunohistochemistry, endothelial cell NOS and inducible calcium-independent NOS, but not nerve cell NOS, were detected in the ductus arteriosus. Inducible NOS was expressed only by endothelial cells lining the ductus arteriosus lumen; in contrast, endothelial cell NOS was expressed by both luminal and vasa vasorum endothelial cells. The role of inducible NOS in the ductus arteriosus is uncertain because the potency of a specific inducible NOS inhibitor in constricting the ductus arteriosus was negligible compared with that of an endothelial cell NOS inhibitor. We speculate that NO may be an important regulator of ductus arteriosus tone at high but not low PO2. The endothelial cell NOS isoform found in vasa vasorum may be an important source of NO because removal of ductus arteriosus luminal endothelium only partially blocks the effects of L-NAME, methylene blue, and LY83583.

Integrin receptors on aortic smooth muscle cells mediate adhesion to fibronectin, laminin, and collagen.

Extracellular matrix receptors on vascular smooth muscle cells help in anchoring the cells during contraction and in promoting cellular migration after vessel injury. We found that rat aortic smooth muscle cells attach to surfaces coated with fibronectin, laminin, and collagen types I and IV. Cell attachment to these substrates appears to be mediated by members of the beta 1 integrin family of extracellular matrix receptors. Antibodies to the beta 1 subunit not only demonstrated the presence of integrin complexes in focal adhesion plaques but also blocked cell adhesion to the different substrates. Ligand-affinity chromatography and sodium dodecyl sulfate-polyacrylamide gel electrophoresis isolated a series of receptor complexes that were recognized by antisera to beta 1 integrin receptors. Each of the receptors appeared to be a heterodimer in which one of several alpha subunits shared a common 120-kDa (nonreduced) beta 1 subunit protein. The rat aortic smooth muscle cells had one alpha subunit (150 kDa nonreduced, 140 kDa reduced) that bound exclusively to fibronectin. There was a second alpha subunit (150 kDa nonreduced, 160 kDa reduced) that bound exclusively to collagen type I. In addition, there was a third alpha subunit (185 kDa nonreduced, 200 kDa reduced) that was promiscuous and bound to collagen types I and IV as well as to laminin; the 185-kDa alpha subunit appeared to bind to collagen more efficiently than it did to laminin. Thus, smooth muscle cells express multiple integrin receptors with different ligand specificities that appear to mediate cell interactions with the extracellular matrix.

The Role of Patent Ductus Arteriosus Ligation in Bronchopulmonary Dysplasia: Reexamining a Randomized Controlled Trial

OBJECTIVE To reexamine data from a randomized controlled trial of prophylactic ductus ligation to determine whether ligation contributes directly to the development of bronchopulmonary dysplasia (BPD) in extremely low birth weight infants. STUDY DESIGN The control group underwent ligation only if they had development of a symptomatic patent ductus arteriosus (PDA). The Prophylactic Ligation group underwent ligation within 24 hours of birth regardless of the presence or absence of symptoms of a PDA. We hypothesized that the incidence of BPD would be higher in the prophylactic ligation group because more ligations were performed than in the control group. RESULTS Prophylactic ligation significantly increased the incidence of BPD (defined as a supplemental oxygen requirement at 36 weeks postmenstrual age) and the incidence of mechanical ventilation at 36 weeks. The groups were statistically similar in gestation, sex, race, fluid administration, intraventricular hemorrhage, pulmonary air leaks, and survival to 36 weeks. The lower incidence of BPD in the control group occurred despite the fact that the incidence of necrotizing enterocolitis (a known risk factor for BPD) was significantly elevated in the control group. Only infants who had previously undergone a PDA ligation had development of BPD in the control group. CONCLUSION Prophylactic ligation, while eliminating the PDA, increases the risk for BPD.

Ibuprofen and patent ductus arteriosus.

The ductus arteriosus connects the pulmonary artery to the descending aorta. During fetal life it diverts most of the combined ventricular output away from the lungs toward the placenta. In full-te...