Search

Ibuprofen-induced ductus closure improves pulmonary mechanics and increases alveolar surface area in premature baboons compared with baboons with a persistent patent ductus arteriosus (PDA). Ibuprofen-treatment has no effect on the expression of genes that regulate pulmonary inflammation but does increase the expression of alpha-ENaC (the transepithelial sodium channel that is critical for alveolar water clearance). Although ligation eliminates the PDA, it does not improve pulmonary mechanics or increase alveolar surface area. We used preterm baboons (delivered at 67% of term gestation and ventilated for 14 days) to study whether the lack of beneficial effects, following PDA ligation, might be due to alterations in pulmonary gene expression. We found no differences in Ventilation or Oxygenation Indices between animals that were ligated (n=7) on day of life 6 and those that had a persistent PDA (n=12) during the entire 14 days study. In contrast with no intervention, PDA ligation produced a significant increase in the expression of genes involved with pulmonary inflammation (COX-2, TNF-alpha, and CD14), and a significant decrease in alpha-ENaC sodium channel expression. We speculate that these changes may decrease the rate of alveolar fluid clearance and contribute to the lack of improvement in pulmonary mechanics after PDA ligation.

Ibuprofen is an effective pharmacological intervention for closure of a patent ductus arteriosus in preterm infants, and is an alternative to surgical ligation; however it is not certain whether ibuprofen treatment is associated with adverse effects on the brain. Therefore, this study examined neuropathological outcomes of ibuprofen therapy for a patent ductus arteriosus. Fetal baboons were delivered at 125-days of gestation (dg, term ~185dg) by caesarean section, given surfactant and ventilated for 14-days with positive pressure ventilation. Baboons were randomly allocated to receive either ibuprofen (PPV + ibuprofen, n=8) or no therapy (PPV, n=5). Animals were euthanased on day 14 and brains assessed for cerebral growth, development and neuropathology. Body and brain weights, the total volume of the brain and the surface folding index (measure of brain growth) were not different (p>0.05) between PPV + ibuprofen-treated and PPV animals. There was no difference (p>0.05) in the number of myelin basic protein-immunoreactive oligodendrocytes, glial fibrillary acid protein-immunoreactive astrocytes or Iba1-immunoreactive macrophages/microglia in the forebrain. No overt cerebellar alterations were observed in either group. Ibuprofen treatment for patent ductus arteriosus closure in the preterm baboon neonate is not associated with any increased risk of neuropathology or alterations to brain growth and development.

Premature newborn baboons [125 d (67%) gestation], exposed to a moderate-size patent ductus arteriosus (PDA) [pulmonary-to-systemic blood-flow-ratio (Qp/Qs) = 1.8] for 14 d, have impaired pulmonary function and arrested alveolar development and surface area when compared with age matched fetuses (140 d gestation). Pharmacologic closure of the PDA reduces the detrimental effects of preterm delivery on pulmonary function and surface area. We used preterm baboons (delivered at 125 d gestation and ventilated for 14 d) to study the effects of surgical PDA ligation on pulmonary function and alveolar surface area. After ligation (on day of life 6), ligated animals had lower Qp/Qs ratios [Qp/Qs (ligated, n = 10) = 1.00 +/- 0.04; (nonligated, n = 12) = 2.05 +/- 0.17; mean +/- SD] and higher systemic blood pressures than nonligated control animals. Ventilation and oxygenation indices did not differ between the groups, during either the pre- or postoperative periods. Alveolar surface area measurements were made by digital image analysis and compared with measurements made from fetal lungs at 125 d (n = 6) and 140 d (n = 7) gestation. PDA ligation failed to improve the postnatal arrest in alveolar surface area. In contrast with pharmacologic closure of the PDA, surgical closure failed to improve either pulmonary function or alveolar surface area in baboons with a moderate PDA shunt.

Retinoids regulate elastin synthesis by alveolar myofibroblasts and affect angiogenesis pathways, both of which are processes critical for alveolar development. Retinoids accelerate alveolarization in rodents and are now used therapeutically in premature infants at risk of bronchopulmonary dysplasia (BPD). This study examined the effects of retinoid supplementation on alveolar elastin expression and deposition and angiogenesis-related signaling in a primate model of BPD. Premature baboons delivered at 125 d of gestation after maternal steroid treatment were given surfactant and ventilated with minimal supplemental oxygen for 14 d with (n = 5) and without (n = 5) supplemental vitamin A (5000 U/kg/d) and compared with 140-d unventilated controls. Ventilatory efficiency index (VEI) and oxygenation index (OI) were not statistically different between ventilated treatment groups. Expression of vascular endothelial growth factor A (VEGF-A), fms-related tyrosine kinase 1 (Flt-1), and tyrosine kinase with immunoglobulin-like and EGF-like domains 1 (TIE-1) was repressed by premature delivery and mechanical ventilation and was not altered by retinoid supplementation. Retinoid supplementation did not enhance alveolar angiogenesis. Elastin expression was repressed by premature delivery and extended ventilation, and retinoid supplementation increased elastin expression specifically in alveolar myofibroblasts within alveolar walls. These results suggest that the small decrease in mortality among premature infants receiving retinoid supplementation may not be mediated through enhanced alveolar development.

Bronchopulmonary dysplasia, or chronic lung disease (CLD), of premature infants involves injury from hyperoxia and mechanical ventilation to an immature lung. We examined surfactant and nitric oxide (NO), which are developmentally deficient in premature infants, in the baboon model of developing CLD. Fetuses were delivered at 125 d gestation and were managed for 14 d with ventilation and oxygen prn without (controls) or with inhaled NO at 5 ppm. Compared with term infants, premature control infants had reduced maximal lung volume, decreased tissue content of surfactant proteins SP-A, -B, and -C, abnormal lavage surfactant as assessed by pulsating bubble surfactometer, and a low concentration of SP-B/phospholipid. NO treatment significantly increased maximal lung volume and tissue SP-A and SP-C, reduced recovery of lavage surfactant by 33%, decreased the total protein:phospholipid ratio of surfactant by 50%, and had no effect on phospholipid composition or SP content except for SP-C (50%). In both treatment groups, levels of SP-B and SP-C in surfactant were negatively correlated with STmin, with a 5-fold greater SP efficiency for NO versus control animals. By contrast, lung volume and compliance were not correlated with surfactant function. We conclude that surfactant is often dysfunctional in developing CLD secondary to SP-B deficiency. NO treatment improves the apparent ability of hydrophobic SP to promote low surface tension, perhaps secondary to less protein inactivation of surfactant, and improves lung volume by a process unrelated to surfactant function.

Early adrenal insufficiency is associated with cardiopulmonary dysfunction in immature infants. Isolated cortisol levels and ACTH stimulation testing may not adequately show ontogeny of postnatal cortisol secretion nor identify at risk infants. Our objectives were 1) to determine postnatal urinary cortisol excretion rate (UCER) from birth to 14 d in immature baboons and 2) to evaluate the relation between UCER and cardiac performance. UCER was assessed via 6-h blocked urine collections from birth to 336 h of age in twenty-one 125-d gestation (term = 185 d) baboons. Urinary cortisol was measured by RIA. Cardiopulmonary parameters were averaged over the same time periods as urine collection. Serial two-dimensional echocardiograms were performed. After 24-h age, a subgroup (n = 8) received up to four doses (0.5-1.0 mg/kg each) of hydrocortisone for refractory hypotension. UCER significantly increased from 0 to 6 h through 66 to 72 h age for non-cortisol-treated infants. Significantly reduced UCER patterns between birth and 24 h were found for animals subsequently requiring cortisol treatment. Cortisol-treated infants had lower mean blood pressure, worse metabolic acidosis, increased fluid needs, and impaired left ventricular function between 12 and 48 h of age. No group differences were found in gas exchange or ventilator support. We conclude that adrenal cortisol secretion significantly improves over the initial 72 h of life in the 125-d immature baboon. Failure to increase UCER after 12-24 h of life correlated with poor cardiovascular function that improved with hydrocortisone therapy. Adrenal hypofunction in the immature baboon is similar to the very preterm human and could serve as a model for future postnatal investigations.

Transient neonatal hyperglycemia (HG) has been reported in up to 80% of extremely preterm human infants. We hypothesize that severe HG is associated with increased morbidity and mortality in preterm baboons. Sixty-six baboons born at 67% of gestation were studied. HG was defined as serum glucose level ≥150 mg/dl during the first week of life. Animals were stratified into two groups: severe HG (≥8 events) and nonsevere HG (

Cerebral white-matter (WM) abnormalities on magnetic resonance imaging (MRI) correlate with neurodevelopmental disability in infants born prematurely.Quantitative histological measures of WM and ventricular volumes correlated with qualitative MRI scores of WM volume loss and ventriculomegaly. Diffuse astrocytosis was associated with signal abnormality on T(2)-weighted imaging and higher apparent diffusion coefficient in WM. Loss of oligodendrocytes was associated with lower relative anisotropy characterized by higher radial diffusivity values. The relationship between histopathology and MRI abnormalities was more pronounced in animals in the 28 d model, equivalent to the term human infant.MRI reflects microstructural and anatomical abnormalities that are characteristic of WM injury in the preterm brain, and these changes are more evident on MRI at term-equivalent postmenstrual age.We assessed the histopathological correlates of MRI abnormalities in a baboon model of premature birth. Baboons were delivered at 125 d of gestation (dg, term ~185 dg) and maintained in an animal intensive care unit for 14 (n = 26) or 28 d (n = 17). Gestational control animals were delivered at 140 dg (n = 9) or 153 dg (n = 4). Cerebral WM in fixed brains was evaluated using MRI, diffusion tensor imaging (DTI), and histopathology.

Three independent risk factors (immature gestation, absence of antenatal glucocorticoid exposure, and presence of the rs2817399(A) allele of the gene TFAP2B) are associated with patent ductus arteriosus (PDAs) that fail to close during prostaglandin inhibition. We hypothesized that these three factors may affect a common set of genes that increase the risk of persistent PDA after birth. We studied baboon ductus from term, preterm, and glucocorticoid-treated preterm fetuses and found that both immature gestation and absence of antenatal glucocorticoid exposure decreased RNA expression of calcium- and potassium-channel genes involved in oxygen-induced constriction, and phosphodiesterase genes (that modulate cAMP/cGMP signaling). Ductus obtained from second trimester human pregnancies were genotyped for TFAP2B polymorphisms. When present, the rs2817399(A) allele also was associated with decreased expression of calcium- and potassium-channel genes. In contrast, alleles of two other TFAP2B polymorphisms, rs2817419(G) and rs2635727(T), which are not related to the incidence of PDA after birth, had no effect on RNA expression. In conclusion, three calcium- and potassium-channel genes (CACNA1G/ alpha1G, CACNB 2/CaL-beta2, and KCNA2/ Kv1.2) were similarly affected by each of the PDA risk factors. We speculate that these channels may play a significant role in closing the preterm ductus during prostaglandin inhibition and may be potential targets for future pharmacologic manipulations.

Compared with the full-term ductus arteriosus, the premature ductus is less likely to constrict when exposed to postnatal oxygen concentrations. We used isolated fetal sheep ductus arteriosus (pretreated with inhibitors of prostaglandin and nitric oxide production) to determine whether changes in K+ - and CaL-channel activity could account for the developmental differences in oxygen-induced tension. In the mature ductus, KV-channels appear to be the only K+-channels that oppose ductus tension. Oxygen concentrations between (2% and 15%) inhibit KV-channel activity, which increases the CaL-channel-mediated increase in tension. Low oxygen concentrations have a direct inhibitory effect on CaL-channel activity in the immature ductus; this is not the case in the mature ductus. In the immature ductus, three different K+-channel activities (KV, KCa, and KATP) oppose ductus tension and contribute to its decreased tone. Oxygen inhibits the activities of all three K+ -channels. The inhibitory effects of the three K+-channel activities decline with advancing gestation. The decline in K+ -channel activity is not due to decreased K+ -channel expression. Super-physiologic oxygen concentrations (or=30% O2) constrict the ductus by using calcium-dependent pathways that are independent of K+- and CaL-channel activities. Super-physiologic oxygen concentrations eliminate the difference in tensions between the two age groups.

A patent ductus arteriosus (PDA) alters pulmonary mechanics and regional blood flow in the preterm infant. Its significance with respect to brain injury and brain development are unclear. We evaluated the effects of surgical ductal ligation on the preterm baboon brain. Baboons were delivered at 125 d of gestation (dg, term approximately 185 dg) and ventilated for 14 d (n = 12). The PDA was ligated 6 d after delivery (n = 7) or left untreated (n = 5). Animals were euthanized at 139 dg and brains compared histologically with gestational control fetuses (n = 7) at 140 dg. Brain and body weights were reduced (p < 0.05) in both groups of ventilated preterm animals; however, the brain to body weight ratio was increased (p < 0.01) in ligated, but not unligated newborns compared with gestational controls. No overt lesions were observed in either premature newborn group. Astrocyte density in the neocortex and hippocampus were greatest in the unligated newborns (p < 0.01). Myelination and oligodendrocytes were reduced (p < 0.05) in both premature newborn groups. The brain growth and development index was reduced, and the damage index was increased in prematurely delivered baboons. Surgical ligation of the PDA does not increase the incidence of brain injury and may be beneficial if the PDA is contributing to persistent pulmonary and hemodynamic instability.

Inhaled nitric oxide (iNO) enhances ventilation in very preterm infants, but the effects on the brain remain uncertain. We evaluated the impact of iNO on brain growth and cerebral injury in a premature baboon model. Baboons were delivered at 125 d of gestation (term 185 d of gestation) and ventilated for 14 d with either positive pressure ventilation (PPV) (n = 7) or PPV + iNO (n = 8). Brains were assessed histologically for parameters of development and injury. Compared with gestational controls (n = 7), brain and body weights were reduced but brain-to-body weight ratios were increased in all prematurely delivered (PD) animals; the surface folding index (SFI), was reduced in PPV but not PPV + iNO animals. Compared with controls, the brain damage index was increased (p < 0.05) in both cohorts of PD animals. There was no difference between ventilatory regimens, however, in 25% of animals with iNO therapy, there were organized hematomas in the subarachnoid space. Overall, iNO did not alter the extent of brain damage but did result in the presence of hematomas. These results do not confirm any protective or major injurious effect of nitric oxide therapy on the developing brain.

Inflammatory processes play a crucial role in the pathogenesis of atherosclerosis and other vascular disorders. We hypothesized that ischemia of the ductus arteriosus might initiate an active inflammatory response that could play a role in ductus remodeling and permanent closure. To test this hypothesis, we studied effects of postnatal ductus construction on inflammatory processes and remodeling in late-gestation fetal and newborn baboons, and preterm newborn baboons. After postnatal ductus constriction, the expression of several genes known to be essential for atherosclerotic remodeling [vascular cell adhesion molecule (VCAM)-1, E-selectin, IL-8, macrophage colony stimulating factor-1, CD154, interferon-gamma, IL-6, and tumor necrosis factor-alpha] was increased in the ductus wall. We were unable to detect intercellular adhesion molecule (ICAM)-1, ICAM-2, P-selectin, monocyte chemoattractant protein-1, or IL-1 by either real-time PCR or immunohistochemistry. VCAM-1, which is newly expressed by luminal cells of the closed ductus, is an important ligand for the mononuclear cell adhesion receptor VLA4. After postnatal constriction, VLA4+ monocytes/macrophages (CD68+ and CD14+) and, to a lesser extent, T-lymphocytes adhered to the ductus wall. Neutrophils and platelets were not observed. The extent of postnatal neointimal remodeling (both endothelial cell layering and subendothelial space thickening) was associated with the degree of mononuclear cell adhesion. Similarly, the extent of vasa vasorum ingrowth correlated with the invasion of CD68+ cells, from the adventitia into the muscle media. Based on these data, we conclude that the inflammatory response following postnatal ductus constriction may be as necessary for ductus remodeling as it is for atherosclerotic remodeling.

RANDOMIZED, MULTICENTER TRIAL OF INHALED NITRIC OXIDE AND HIGH FREQUENCY OSCILLATORY VENTILATION IN SEVERE PERSISTENT PULMONARY HYPERTENSION OF THE NEWBORN (PPHN). • 1315