Attenuated cyclooxygenase-2 expression contributes to patent ductus arteriosus in preterm mice

Complementary mRNA expression of enzymes producing nitric oxide and prostaglandin in ductus arteriosus with respect to their role in maintaining patency

mRNA expression of molecules related to the activity of nitric oxide or prostaglandin E2, the critical regulators maintaining the ductus arteriosus patency, was examined in rat ductus arteriosus at preterm (days 18.5 and 19.5 of pregnancy) and near term (days 20.5 and 21.5). The endothelial nitric oxide synthase mRNA level increased transiently at preterm and then decreased at near term. The cyclooxygenase 2 mRNA increased gradually from near-term to the term complementary to the reduced endothelial nitric oxide synthase mRNA. These results suggest that the role shift between nitric oxide and prostaglandin E2 in maintaining ductus arteriosus patency at preterm and near term may be due to complementary expression changes of endothelial nitric oxide synthase and cyclooxygenase 2 at the transcriptional level.

Intravenous acetaminophen (at 15 mg/kg/dose every 6 hours) in critically ill preterm neonates with patent ductus arteriosus: A prospective study

WHAT IS KNOWN AND OBJECTIVES

Acetaminophen has been increasingly used in treating patent ductus arteriosus (PDA) in preterm neonates. Variations were observed in the dosing regimen of acetaminophen across the studies. There is hardly any data available for a relatively higher dose of intravenous acetaminophen (15 mg/kg/dose every 6 hours) in the preterm population. We present here the results of a prospective study with this dose of intravenous acetaminophen for treating PDA in critically ill preterm neonates.

METHODS

Preterm neonates (≤37 weeks of gestational age) with haemodynamically significant PDA were enrolled. Intravenous acetaminophen at 15 mg/kg/dose every 6 hours was administered. Echocardiographic monitoring, liver and renal function tests were carried out. Standard definitions were adhered for defining acute kidney injury (AKI) and hepatotoxicity.

RESULTS

Fifty-five neonates were recruited. Following the first dose, less than half had their serum acetaminophen concentrations in the therapeutic range. Extreme preterm neonates were less likely to have a sustained therapeutic acetaminophen concentration after the first dose. Following multiple doses and at steady state, 97.2% and 98.8% respectively were in the therapeutic range. Forty-three (78.2%) neonates had successful closure of the ductus arteriosus of which 22 were extreme preterm, 17 were very preterm and 4 were late preterm neonates; and considering their birthweights, 21 were extremely low, 16 were very low and 6 were low birthweight categories. Ten neonates had elevated alanine aminotransferase levels with three in the low-to-moderate risk of hepatotoxicity category. Eight neonates had altered renal function tests indicating AKI.

WHAT IS NEW AND CONCLUSION

Intravenous acetaminophen at 15 mg/kg/dose every 6 hours was efficacious in 78.2% of the preterm neonates with PDA. We observed a lower incidence of hepatotoxicity, and AKI in the study population. No association was observed between the serum acetaminophen concentrations and PDA closure.

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.

[Establishment of the patent ductus arteriosus model in preterm rats]

OBJECTIVE

To establish the patent ductus arteriosus model in preterm rats using the improved natural development method.

METHODS

In the light of the flaws of the natural development method in establishing the patent ductus arteriosus model, the experimental technology was modified to avoid the influence of fixation, dehydration, and section method on blood vessel diameter. Cesarean section was performed for a Wistar rat pregnant for 19 days, and 8 neonatal rats were obtained. After they were sacrificed by dislocation, they were embedded as a whole to avoid dehydration, and the microsection and horizontal section were made. After hematoxylin and eosin staining, a microscope was used to measure the inner diameters of the ductus arteriosus, the main pulmonary artery, and the descending aorta.

RESULTS

After the cesarean section for the rat pregnant for 19 days, patent ductus arteriosus occurred in all the 8 neonatal rats. The measurements of the inner diameters of blood vessels were as follows: the long diameter and short diameter of the descending aorta were 354±106 and 182±140 μm, respectively; the short diameter of the ductus arteriosus was 155±122 μm, and its area was 36,847±42,582 μm(2); the long axis and short axis of the main pulmonary artery were 589±150 and 174±170 μm, respectively.

CONCLUSIONS

The improved natural development method can help to successfully establish the patent ductus arteriosus model in preterm rats.

Isoprostanes as physiological mediators of transition to newborn life: novel mechanisms regulating patency of the term and preterm ductus arteriosus

BACKGROUND

Increased oxygen tension at birth regulates physiologic events that are essential to postnatal survival, but the accompanying oxidative stress may also generate isoprostanes. We hypothesized that isoprostanes regulate ductus arteriosus (DA) function during postnatal vascular transition.

METHODS

Isoprostanes were measured by gas chromatography-mass spectrometry. DA tone was assessed by pressure myography. Gene expression was measured by quantitative PCR.

RESULTS

Oxygen exposure was associated with increased 8-iso-prostaglandin (PG)F2α in newborn mouse lungs. Both 8-iso-PGE2 and 8-iso-PGF2α induced concentration-dependent constriction of the isolated term DA, which was reversed by the thromboxane A2 (TxA2) receptor antagonist SQ29548. SQ29548 pretreatment unmasked an isoprostane-induced DA dilation mediated by the EP4 PG receptor. Exposure of the preterm DA to 8-iso-PGE2 caused unexpected DA relaxation that was reversed by EP4 antagonism. In contrast, exposure to 8-iso-PGF2α caused preterm DA constriction via TxA2 receptor activation. Further investigation revealed the predominance of the TxA2 receptor at term, whereas the EP4 receptor was expressed and functionally active from mid-gestation onward.

CONCLUSION

This study identifies a novel physiological role for isoprostanes during postnatal vascular transition and provide evidence that oxidative stress may act on membrane lipids to produce vasoactive mediators that stimulate physiological DA closure at birth or induce pathological patency of the preterm DA.

Genetics of patent ductus arteriosus susceptibility and treatment

The ductus arteriosus is a vital fetal structure designed to close shortly after birth. Although many physiologic and pharmacologic investigations have characterized the closure of this structure, genetic studies of persistent patency of the ductus arteriosus (patent ductus arteriosus, PDA) are relatively recent. Progress in the identification of specific genes associated with PDA is well behind that of many adult-onset diseases because of several reasons ranging from the lack of large biorepositories for this unique population to the belief that any genetic contribution to PDA is minimal. Viewing the PDA as a complex, developmentally influenced disease with both genetic and environmental risk factors has resulted in initial successes in some genetic studies. We will introduce several genetic approaches, which have been or are currently being applied to the study of PDA, that have been successful in identifying polymorphisms associated with adult diseases. Genetic investigations of PDA will be discussed with respect to heritability, in general, and to specific risk genes. Several animal models that have been used to study PDA-related genes will also be presented. Further advances in discovering genetic variation causing PDA will drive the more rational use of current therapies, and may help identify currently unknown targets for future therapeutic manipulation.

Evidence-based use of indomethacin and ibuprofen in the neonatal intensive care unit

Indomethacin and ibuprofen are potent inhibitors of prostaglandin synthesis. Neonates have been exposed to these compounds for more than 3 decades. Indomethacin is commonly used to prevent intraventricular hemorrhage (IVH), and both drugs are prescribed for the treatment or prevention of patent ductus arteriosus (PDA). This review examines the basis for indomethacin and ibuprofen use in the neonatal intensive care population. Despite the call for restrained use of each drug, the most immature infants are likely to need pharmacologic approaches to reduce high-grade IVH, avoid the need for PDA ligation, and preserve the opportunity for an optimal outcome.

Current Perspectives on Pathobiology of the Ductus Arteriosus

The ductus arteriosus (DA) shunts blood away from the lungs during fetal life, but at birth this shunt is no longer needed and the vessel rapidly constricts. Postnatal persistence of the DA, patent ductus arteriosus (PDA), is predominantly a detrimental condition for preterm infants but is simultaneously a condition required to maintain systemic blood flow for infants born with certain severe congenital heart defects. Although PDA in preterm infants is associated with significant morbidities, there is controversy regarding whether PDA is truly causative. Despite advances in our understanding of the pathobiology of PDA, the optimal treatment strategy for PDA in preterm infants is unclear. Here we review recent studies that have continued to elucidate the fundamental mechanisms of DA development and pathogenesis.

International Union of Basic and Clinical Pharmacology. LXXXIII: classification of prostanoid receptors, updating 15 years of progress

It is now more than 15 years since the molecular structures of the major prostanoid receptors were elucidated. Since then, substantial progress has been achieved with respect to distribution and function, signal transduction mechanisms, and the design of agonists and antagonists (http://www.iuphar-db.org/DATABASE/FamilyIntroductionForward?familyId=58). This review systematically details these advances. More recent developments in prostanoid receptor research are included. The DP(2) receptor, also termed CRTH2, has little structural resemblance to DP(1) and other receptors described in the original prostanoid receptor classification. DP(2) receptors are more closely related to chemoattractant receptors. Prostanoid receptors have also been found to heterodimerize with other prostanoid receptor subtypes and nonprostanoids. This may extend signal transduction pathways and create new ligand recognition sites: prostacyclin/thromboxane A(2) heterodimeric receptors for 8-epi-prostaglandin E(2), wild-type/alternative (alt4) heterodimers for the prostaglandin FP receptor for bimatoprost and the prostamides. It is anticipated that the 15 years of research progress described herein will lead to novel therapeutic entities.

Contractile effects of 15-E2t-isoprostane and 15-F2t-isoprostane on chicken embryo ductus arteriosus

Isoprostanes (IsoPs) are prostaglandin (PG)-like compounds produced nonenzymatically by free radical-catalyzed peroxidation of arachidonate. Cyclooxygenase-derived PGs play a major role in ductus arteriosus (DA) homeostasis but the putative role of IsoPs has not been studied so far. We investigated, using wire myography, the vasoactive effects of 15-E(2t)-IsoP and 15-F(2t)-IsoP in the chicken embryo DA, pulmonary artery (PA) and femoral artery (FA). 15-E(2t)-IsoP and 15-F(2t)-IsoP contracted DA, PA, and FA rings in a concentration-dependent manner. 15-E(2t)-IsoP was equally efficacious (mean±SE E(max)=1.25±0.06 mN/mm) as and more potent (-log of molar concentration producing 50% of E(max)=pEC(50)=7.00±0.04) than the thromboxane-prostanoid (TP) receptor agonist U46619 (E(max)=1.49±0.11 mN/mm; pEC(50)=6.48±0.05) in contracting chicken DA (pulmonary side). 15-F(2t)-IsoP was less potent (pEC(50)=5.74±0.11) and less efficacious (E(max)=0.96±0.11) than U46619. Concentration-dependent contractions to 15-E(2t)-IsoP and U46619 in DA rings were competitively inhibited by the TP receptor antagonist SQ29548 (0.1 μM to 10 μM) with no decrease in the E(max) values. SQ29548 also inhibited concentration-dependent contraction to 15-F(2t)-IsoP but this inhibition was associated with a decrease in E(max). Pre-incubation of DA rings with 15-F(2t)-IsoP inhibited responses to U46619 and, in vessels contracted with U46619 (1 μM), 15-F(2t)-IsoP (>1 μM) evoked a relaxant response. Enzyme immunoassay did not show a measurable release of 15-F(2t)-IsoP by DA rings. In conclusion, 15-E(2t)-IsoP is a potent and efficacious constrictor of chicken DA, acting through TP receptors. In contrast, 15-F(2t)-IsoP is probably acting as a partial agonist at TP receptors. We speculate that IsoPs play a role in the control of chicken DA tone and could participate in its closure.

Intrauterine inflammation as a risk factor for persistent ductus arteriosus patency after cyclooxygenase inhibition in extremely low birth weight infants

OBJECTIVES

To test the hypothesis that intrauterine inflammation increases prostaglandin production and may be a risk factor for persistent ductus arteriosus after therapy with indomethacin, a nonselective cyclooxygenase inhibitor.

STUDY DESIGN

Indomethacin therapy was started after confirming ductus arteriosus within 24 hours after birth in extremely low birth weight infants. After one cycle of therapy, infants with closed ductus were classified as responders, and those with patent ductus were classified as nonresponders. Multiple logistic regression analysis was used to determine important perinatal factors associated with persistent ductus arteriosus. Immunohistochemistry with cyclooxygenase antibodies and radioimmunoassay by 6-keto prostaglandin F(1α) kit were used to determine the relationship between intrauterine inflammation and ductal patency.

RESULTS

Forty-one infants were responders, and 37 infants were nonresponders. Responders were frequently small for gestational age; nonresponders frequently had lower gestational age, respiratory distress syndrome, and intrauterine inflammation. By multiple logistic regression analysis, respiratory distress syndrome and intrauterine inflammation were more frequent in nonresponders. Cyclooxygenase-1 expression in the umbilical arteries and plasma 6-keto prostaglandin F(1α) levels were higher in nonresponders.

CONCLUSIONS

Respiratory distress syndrome and intrauterine inflammation were independent risk factors for persistent ductus arteriosus after indomethacin therapy in extremely low-birth weight infants. Intrauterine inflammation may have a negative influence on ductus arteriosus closure via increased cyclooxygenase-1 activity.

Distinct roles for basal and induced COX-2 in podocyte injury

Transgenic mice that overexpress cyclooxygenase-2 (COX-2) selectively in podocytes are more susceptible to glomerular injury by adriamycin and puromycin (PAN). To investigate the potential roles of COX-2 metabolites, we studied mice with selective deletion of prostanoid receptors and generated conditionally immortalized podocyte lines from mice with either COX-2 deletion or overexpression. Podocytes that overexpressed COX-2 were virtually indistinguishable from wild-type podocytes but were significantly more sensitive to PAN-induced injury, produced more prostaglandin E(2) and thromboxane B(2), and had greater expression of prostaglandin E(2) receptor subtype 4 (EP(4)) and thromboxane receptor (TP). Treatment of COX-2-overexpressing podocytes with a TP antagonist reduced apoptosis, but treatment with an EP(4) antagonist did not. In contrast, podocytes from COX-2-knockout mice exhibited increased apoptosis, markedly decreased cell adhesion, and prominent stress fibers. In vivo, selective deletion of podocyte EP(4) did not alter the increased sensitivity to adriamycin-induced injury observed in mice overexpressing podocyte COX-2. In contrast, genetic deletion of TP in these mice prevented adriamycin-induced injury, with attenuated albuminuria and foot process effacement. These results suggest that basal COX-2 may be important for podocyte survival, but overexpression of podocyte COX-2 increases susceptibility to podocyte injury, which is mediated, in part, by activation of the thromboxane receptor.

Genetic contribution to patent ductus arteriosus in the premature newborn

BACKGROUND

The most common congenital heart disease in the newborn population, patent ductus arteriosus, accounts for significant morbidity in preterm newborns. In addition to prematurity and environmental factors, we hypothesized that genetic factors play a significant role in this condition.

OBJECTIVE

The objective of this study was to quantify the contribution of genetic factors to the variance in liability for patent ductus arteriosus in premature newborns.

PATIENTS AND METHODS

A retrospective study (1991-2006) from 2 centers was performed by using zygosity data from premature twins born at < or =36 weeks' gestational age and surviving beyond 36 weeks' postmenstrual age. Patent ductus arteriosus was diagnosed by echocardiography at each center. Mixed-effects logistic regression was used to assess the effect of specific covariates. Latent variable probit modeling was then performed to estimate the heritability of patent ductus arteriosus, and mixed-effects probit modeling was used to quantify the genetic component.

RESULTS

We obtained data from 333 dizygotic twin pairs and 99 monozygotic twin pairs from 2 centers (Yale University and University of Connecticut). Data on chorioamnionitis, antenatal steroids, gestational age, body weight, gender, respiratory distress syndrome, patent ductus arteriosus, necrotizing enterocolitis, oxygen supplementation, and bronchopulmonary dysplasia were comparable between monozygotic and dizygotic twins. We found that gestational age, respiratory distress syndrome, and institution were significant covariates for patent ductus arteriosus. After controlling for specific covariates, genetic factors or the shared environment accounted for 76.1% of the variance in liability for patent ductus arteriosus.

CONCLUSIONS

Preterm patent ductus arteriosus is highly familial (contributed to by genetic and environmental factors), with the effect being mainly environmental, after controlling for known confounders.

Regulation of the fetal mouse ductus arteriosus is dependent on interaction of nitric oxide and COX enzymes in the ductal wall

Nitric oxide (NO) and cyclooxygenase (COX)-derived prostaglandins are critical regulators of the fetal ductus arteriosus. To examine the interaction of these pathways within the ductus wall, the ductus arteriosus of term and preterm fetal mice was evaluated by pressurized myography. The isolated preterm ductus was more sensitive to NOS inhibition than at term. Sequential NOS and COX inhibition caused 36% constriction of the preterm ductus regardless of drug order. In contrast, constriction of the term ductus was dependent on the sequence of inhibition; NOS inhibition prior to COX inhibition produced greater constriction than when inhibitors were given in reverse order (36+/-6% versus 23+/-5%). Selective COX-1 or COX-2 inhibition prior to N(G)-nitro-l-arginine methyl ester (l-NAME) induced the expected degree of constriction. However, NOS inhibition followed by selective COX-2 inhibition caused unexpected ductal dilation. These findings are consistent with NO-induced activation of COX in the ductus arteriosus wall and the production of a COX-2-derived constrictor prostanoid that contributes to the balance of vasoactive forces that maintain fetal ductus arteriosus tone.