Vessel remodeling in the newborn: platelets fill the gap

Platelets and ductus arteriosus closure in neonates

Platelet plug formation is critically involved in murine ductus arteriosus closure and thrombocytopenia in preterm infants seems to negatively affect spontaneous and pharmacologically induced ductal closure. Furthermore, platelet dysfunction may contribute to ductal patency, especially in extremely immature infants. Neonatal platelets likely have multifaceted roles during ductal closure, such as secretion of several signaling molecules and facilitation of specific cell-cell interactions. The only available randomized-controlled trial on platelet transfusions in preterm infants with patent ductus arteriosus demonstrated that a liberal transfusion regimen did not promote ductal closure, but was associated with an increased rate of intraventricular hemorrhage. Herein, we discuss the available mechanistic evidence on the role of platelets in ductus arteriosus closure and their potential clinical implications in preterm infants. We further briefly outline future research directions aimed at a better understanding of platelet-endothelial interactions in neonatal health and disease.

Does Early Neonatal Thrombocytopenia Affect Ductal Therapeutic Response to Acetaminophen in Preterm Neonates?

OBJECTIVE

Perinatal thrombocytopenia has been shown to affect responsiveness to therapeutic ductal closure with cyclooxygenase (COX) inhibitors. This has not been studied in responsiveness to acetaminophen, which has less effect on platelet function. The objective of this study was to evaluate whether thrombocytopenia affects ductal responsiveness to acetaminophen.

STUDY DESIGN

This study was a retrospective review of preterm neonates <1,500 g. Echocardiograms were performed within the first week of life; if ductal status was found to be hemodynamically significant, infants were treated with acetaminophen.

RESULTS

We studied 254 infants. Fifty-seven of these (22%) had a hemodynamically significant patent ductus arteriosus (hsPDA) and were treated with acetaminophen. Forty (70%) of those treated responded with ductal closure after one to two courses of acetaminophen. Seventeen infants were considered nonresponsive, requiring the addition of ibuprofen and/or surgical ligation. Sixty seven of the 254 infants (26%) developed moderate thrombocytopenia (platelets <100,000) within the first 10 days of life, more within the hsPDA group (54 vs. 18% p < 0.001); however, no differences in platelet-related parameters were observed between those who did and did not respond to acetaminophen treatment when comparing infants with hsPDA. Twenty-six of the 67 thrombocytopenic infants were already thrombocytopenic prior to acetaminophen treatment, and 19 of these 26 (73%) with pretreatment thrombocytopenia responded to acetaminophen treatment-with the overall response rate of 70%.

CONCLUSIONS

This study is the first to document that, in contrast to the COX inhibitors, there is no association between early neonatal thrombocytopenia and ductal therapeutic responsiveness to acetaminophen.

KEY POINTS

· Perinatal thrombocytopenia affects ductal closure with COX inhibitors.. · In contrast to the COX inhibitors, acetaminophen responsiveness is not affected by thrombocytopenia.. · Acetaminophen can be recommended to close hsPDA in the presence of thrombocytopenia..

Current Controversy on Platelets and Patent Ductus Arteriosus Closure in Preterm Infants

Platelets are critically involved in murine patent ductus arteriosus (PDA) closure. To date, the clinical significance of these findings in human preterm infants with PDA is still controversial. We discuss the available study data on the role of platelets for PDA closure in preterm infants: Several mostly retrospective studies have yielded conflicting results on whether thrombocytopenia contributes to failed spontaneous ductal closure. The same applies to investigations on the role of thrombocytopenia as a risk factor for unsuccessful ductus arteriosus closure by pharmacological treatment with cyclooxygenase inhibitors. Nonetheless, recent meta-analyses have concluded that thrombocytopenia constitutes an independent risk factor for both failed spontaneous and pharmacological PDA closure in preterm infants. However, the available investigations differ in regard to patient characteristics, diagnostic strategies, and treatment protocols. Several studies suggest that impaired platelet function rather than platelet number is critically involved in failure of ductus arteriosus closure in the preterm infant. A recent randomized-controlled trial on platelet transfusions in preterm infants with PDA failed to show any benefit for liberal vs. restrictive transfusion thresholds on PDA closure rates. Importantly, liberal transfusions were associated with an increased rate of intraventricular hemorrhage, and thus should be avoided. In conclusion, the available evidence suggests that thrombocytopenia and platelet dysfunction contribute to failure of spontaneous and pharmacological PDA closure in preterm infants. However, these platelet effects on PDA seem to be of only moderate clinical significance. Furthermore, platelet transfusions in thrombocytopenic preterm infants in order to facilitate PDA closure appear to cause more harm than good.

Molecular and Mechanical Mechanisms Regulating Ductus Arteriosus Closure in Preterm Infants

Failure of ductus arteriosus closure after preterm birth is associated with significant morbidities. Ductal closure requires and is regulated by a complex interplay of molecular and mechanical mechanisms with underlying genetic factors. In utero patency of the ductus is maintained by low oxygen tension, high levels of prostaglandins, nitric oxide and carbon monoxide. After birth, ductal closure occurs first by functional closure, followed by anatomical remodeling. High oxygen tension and decreased prostaglandin levels mediated by numerous factors including potassium channels, endothelin-1, isoprostanes lead to the contraction of the ductus. Bradykinin and corticosteroids also induce ductal constriction by attenuating the sensitivity of the ductus to PGE2. Smooth muscle cells of the ductus can sense oxygen through a mitochondrial network by the role of Rho-kinase pathway which ends up with increased intracellular calcium levels and contraction of myosin light chains. Anatomical closure of the ductus is also complex with various mechanisms such as migration and proliferation of smooth muscle cells, extracellular matrix production, endothelial cell proliferation which mediate cushion formation with the interaction of blood cells. Regulation of vessel walls is affected by retinoic acid, TGF-β1, notch signaling, hyaluronan, fibronectin, chondroitin sulfate, elastin, and vascular endothelial cell growth factor (VEGF). Formation of the platelet plug facilitates luminal remodeling by the obstruction of the constricted ductal lumen. Vasa vasorum are more pronounced in the term ductus but are less active in the preterm ductus. More than 100 genes are effective in the prostaglandin pathway or in vascular smooth muscle development and structure may affect the patency of ductus. Hemodynamic changes after birth including fluid load and flow characteristics as well as shear forces within the ductus also stimulate closure. Current pharmacological treatment for the closure of a patent ductus is based on the blockage of the prostaglandin pathway mainly through COX or POX inhibition, albeit with some limitations and side effects. Further research for new agents aiming ductal closure should focus on a clear understanding of vascular biology of the ductus.

Plasma B-type natriuretic peptide cannot predict treatment response to ibuprofen in preterm infants with patent ductus arteriosus

Plasma B-type natriuretic peptide (BNP) is a useful marker for diagnosis of hemodynamically significant PDA (hsPDA) and serial BNP measurement is also valuable for monitoring treatment response. This retrospective study was performed to evaluate whether plasma BNP level can predict treatment response to ibuprofen in preterm infants born at <30 weeks of gestation with hsPDA. Plasma BNP was measured before (baseline) and 12 to 24 h after (post-treatment) completion of the first (IBU1) and second (IBU2) course of ibuprofen. We compared the BNP levels of responders (closed or insignificant PDA) with those of non-responders (hsPDA requiring further pharmacologic or surgical closure) to each course of ibuprofen. The treatment response rates for IBU1 (n = 92) and IBU2 (n = 19) were 74% and 26%, respectively. In IBU1, non-responders had lower gestational age and birth weight than responders (both, P = 0.004), while in IBU2, non-responders had lower birth weight (P = 0.014) and platelet counts (P = 0.005) than responders; however, baseline BNP levels did not differ significantly between responders and non-responders in either IBU1 (median 1,434 vs. 1,750 pg/mL) or IBU2 (415 vs. 596 pg/mL). Post-treatment BNP was a useful marker for monitoring treatment efficacy of IBU1 and IBU2 for hsPDA with a cut-off value of 331 pg/mL (P < 0.001) and 423 pg/mL(P < 0.010), respectively. We did not identify a cut-off baseline BNP level that could predict treatment response to ibuprofen in preterm infants with hsPDA.

The Thromboelastographic Profile at Birth in Very Preterm Newborns with Patent Ductus Arteriosus

BACKGROUND

The role of hemostasis in the closure of patent ductus arteriosus (PDA) in preterm infants is controversial.

OBJECTIVE

To assess thromboelastography (TEG) at birth in very-low-birth-weight (VLBW) infants affected by PDA.

METHODS

This was an ancillary study of a prospective observational study aimed at defining the TEG profile in healthy VLBW infants in the first month of life. In this analysis, we included neonates of <33 weeks' gestational age (GA) with PDA and compared TEG traces based on (1) spontaneous closure versus the need for pharmacological treatment and (2) treatment response. We collected blood samples in the 1st day of life to perform recalcified native-blood TEG (reaction time, maximum amplitude, and lysis at 30 min [Ly30)]), standard coagulation tests, and a full blood count.

RESULTS

We enrolled 151 infants with a PDA at the first echocardiogram; 111 experienced spontaneous PDA closure while 40 required treatment. Mean GA was 29.7 ± 1.7 and 27.6 ± 2.1 weeks, and birth weight was 1,158 ± 256 and 933 ± 263 g in the 2 groups, respectively (p < 0.001). The hemostatic profile was similar between groups. Median hematocrit (44.6 and 48.7%; p = 0.01) and platelet count (187 and 216 × 103/μL; p = 0.04) were lower in the treated group, although differences lost significance after controlling for GA and illness severity in the multivariate analysis. Responders to PDA treatment (n = 20) had a significantly lower median Ly30 than nonresponders (0 and 0.7%; p = 0.02).

CONCLUSION

TEG at birth does not predict spontaneous PDA closure in preterm newborns. Fibrinolysis is enhanced in nonresponders to PDA treatment; this observation warrants further investigation.

Platelet Counts and Patent Ductus Arteriosus in Preterm Infants: A Systematic Review and Meta-Analysis

BACKGROUND

Several cohort studies have shown an association between low platelet counts in the first day(s) of life and patent ductus arteriosus (PDA) in preterm infants. However, these results have not been confirmed by other studies.

OBJECTIVE

To perform a meta-analysis of all the studies addressing the relationship between platelet counts in the first day(s) of life and PDA in preterm infants.

METHODS

PubMed/MEDLINE and EMBASE were searched from their inception until December 2014. Results from 11 cohort studies involving 3,479 preterm infants (gestational age <32 weeks) were pooled using random-effects modeling.

RESULTS

Meta-analysis showed a significant positive association between PDA and platelet counts <150 × 10(9)/l [6 studies, risk ratio (RR) = 1.215, 95% CI: 1.027-1.436], between PDA and platelet counts <100 × 10(9)/l (5 studies, RR = 1.255, 95% CI: 1.034-1.525), and between significant PDA (SPDA) and platelet counts <100 × 10(9)/l (5 studies, RR = 1.254, 95% CI: 1.021-1.540). The association between SPDA and platelet counts <150 × 10(9)/l was not statistically significant (6 studies, RR = 1.289, 95% CI: 0.925-1.795). Pooled standard differences in mean platelet counts between infants with and without PDA/SPDA were not statistically different.

CONCLUSION

This meta-analysis reveals a marginal but significant association between low platelet counts in the first day(s) of life and PDA/SPDA in very preterm infants. This association needs to be confirmed in prospective studies.

Efficacy of paracetamol for the treatment of patent ductus arteriosus in preterm neonates

Inhibitors of the cyclo-oxygenase component of prostaglandin-H₂ synthetase, namely indomethacin and ibuprofen, are commonly used in the treatment of hemodynamically significant patent ductus arteriosus. These drugs are associated with serious adverse events, including gastrointestinal perforation, renal failure and bleeding. The role of paracetamol, an inhibitor of the peroxidase component of prostaglandin-H₂ synthetase, has been proposed for the treatment of patent ductus arteriosus. We report a series of 8 neonates (birth weight: 724 ± 173 g; gestational age: 26 ± 2 weeks) treated with paracetamol for a hemodynamically significant patent ductus arteriosus, because of contraindications to ibuprofen or indomethacin. Successful closure was achieved in 6 out of 8 babies (75%). Median ductal diameter was significantly reduced after treatment (from 1.2 mm, range 1.0-2.5 mm to 0.6 mm, range 0.0-2.5 mm, p = 0.038). No adverse or side effects were observed during treatment. On the basis of these results, paracetamol could be considered a promising and safe therapy for the treatment of patent ductus arteriosus in neonates.

Low platelet count is associated with ductus arteriosus patency in preterm newborns

BACKGROUND/AIM

To determine whether there is an association between platelet counts and patent ductus arteriosus (PDA) incidence and/or closure in preterm newborns.

STUDY DESIGN AND SUBJECTS

Premature infants with hemodynamically significant PDA (n=154) and a control group without PDA (n=207) who were hospitalized in the NICU were retrospectively evaluated. Platelet counts and other platelet indices including mean platelet volume (MPV) and platelet distribution width (PDW) of the infants in both groups during the first 3 days of life were recorded. Ibuprofen was started in infants with hemodynamically significant PDA and echocardiography was repeated 48 h thereafter to assess the closure of ductus.

RESULTS

Median gestational age and birth weight of the infants with PDA were 28 (range 26-29) weeks and 1060 (range 892-1250) g respectively. Platelet counts were significantly lower in the patient group than in the control group (p<0.001). Multivariate analysis including gestational age, presence of RDS, presence of thrombocytopenia and PDW showed that hemodynamically significant PDA was independently associated with platelet count <150,000 (OR=2.13, 95% CI 1.26-3.61; p=0.005), high PDW (>17) (OR=2.68, 95% CI 1.41-5.09; p=0.003) and the presence of RDS (OR=2.25, 95% CI 1.41-3.59; p=0.001). Baseline platelet counts of the infants in whom ductus closed or persisted after ibuprofen treatment were similar.

CONCLUSIONS

PDA was associated with low platelet count and high PDW but not with other platelet indices in preterm infants. We could not show an association between platelet counts and persistence or closure after medical treatment.

Prenatal cardiovascular shunts in amniotic vertebrates

During amniotic vertebrate development, the embryo and fetus employ a number of cardiovascular shunts. These shunts provide a right-to-left shunt of blood and are essential components of embryonic life ensuring proper blood circulation to developing organs and fetal gas exchanger, as well as bypassing the pulmonary circuit and the unventilated, fluid filled lungs. In this review we examine and compare the embryonic shunts available for fetal mammals and embryonic reptiles, including lizards, crocodilians, and birds. These groups have either a single ductus arteriosus (mammals) or paired ductus arteriosi that provide a right-to-left shunt of right ventricular output away from the unventilated lungs. The mammalian foramen ovale and the avian atrial foramina function as a right-to-left shunt of blood between the atria. The presence of atrial shunts in non-avian reptiles is unknown. Mammals have a venous shunt, the ductus venosus that diverts umbilical venous return away from the liver and towards the inferior vena cava and foramen ovale. Reptiles do not have a ductus venosus during the latter two thirds of development. While the fetal shunts are well characterized in numerous mammalian species, much less is known about the developmental physiology of the reptilian embryonic shunts. In the last years, the reactivity and the process of closure of the ductus arteriosus have been characterized in the chicken and the emu. In contrast, much less is known about embryonic shunts in the non-avian reptiles. It is possible that the single ventricle found in lizards, snakes, and turtles and the origin of the left aorta in the crocodilians play a significant role in the right-to-left embryonic shunt in these species.