Expression of SP-C and Ki67 in lungs of preterm infants dying from respiratory distress syndrome

This study aimed at exploring the expression of Surfactant protein-C (SP-C) and Ki67 in autopsy lung tissues of premature infants dying from respiratory distress syndrome (RDS) who were exposed to mechanical ventilation and elevated oxygen concentrations. The possible influence of pulmonary surfactant (PS) on the expression of SP-C and Ki67 was also investigated. Thirty preterm infants were selected who were histologically and clinically diagnosed as RDS. Preterm infants with RDS were divided into 4 groups, according to the time of death: infants ventilated for 1–3 days, 4–8 days, 9–16 days and >6 days. Five premature infants died within 1 day after delivery for non- pulmonary reasons served as controls. The expression of SP-C and Ki67 in lungs was detected by immunohistochemistry. Compared with the control group, the expression of SP-C and Ki67 in RDS infants decreased significantly after 1–3 days of ventilation, but increased after 4 days and reached peak value after 9–16 days. No significant difference in the expression of SP-C and Ki67 was found between infants treated with PS and those without. Thus our results suggest SP-C and Ki67 may have participated in the pulmonary pathological process in ventilated/oxygen treated preterm infants with RDS, and exogenous surfactant had no effect on the expression of SP-C and Ki67 in the lungs of ventilated/oxygen treated preterm infants with RDS.Key words: respiratory distress syndrome, surfactant protein-C, Ki67, preterm.     

Postnatal triiodothyronine replacement and respiratory distress syndrome of the preterm infant

Improvements in the management of respiratory distress syndrome (RDS) include pre- and postnatal stimulation of pulmonary maturity, and triiodothyronine (T3) is believed to influence directly surfactant production. Its circulating levels are low in premature infants with RDS probably due to a low thyroxine T4-T3 hepatic conversion mechanism. While a state of hypotriiodothyroninemia exists at birth, we studied the influence of postnatal intravenous T3 administration on the course of RDS in preterm infants of less than 32 weeks' gestation. Fifty preterm infants with RDS were studied (mean gestational age 30.4 +/- 1.2 weeks and birth weight 1,180 +/- 220 g). They were at random assigned to treatment with 50 micrograms L-T3 (Thyrotardin) or to the control group. Mortality rate, peak oxygen concentrations, duration of artificial ventilation and development of major complications of RDS were the criteria to estimate the influence of T3 treatment on RDS. We failed to detect a statistically significant difference between the two groups in all of the mentioned criteria except for FiO2 concentrations required to maintain PaO2 between 50 and 60 mm Hg (p less than 0.05). These observations suggest a relative beneficial effect of T3 replacement on the course of RDS in preterm infants of less than 32 weeks of gestation.     

Respiratory distress syndrome in infants of Cardiff residents during 1965-75.

The incidence of respiratory distress syndrome (RDS) among singleton infants of Cardiff residents was greater during 1970-4 than in the preceding five years. This was consistent with changes in the distribution of gestational age and birth weight. Case fatality rates among infants with RDS fell only slightly during the period examined. Detailed examination of secular trends during 1965-75 suggested (a) that increased use of elective delivery without assessment of pulmonary maturity increases the risk of RDS, and (b) that innovations in the management of RDS during the early 1970s cannot be assumed to have had widespread impact on case fatality rates.     

Relation of amniotic fluid lecithin/sphingomyelin ratio and fetal asphyxia to respiratory distress syndrome in premature infants.

In a group of 81 prematurely delivered infants the amniotic fluid lecithin/sphingomyelin ratio was related to functional fetal lung maturity. Intrapartum fetal asphyxia occurred in 33% of the group. An association between fetal asphyxia and the development of respiratory distress syndrome (RDS) in the infant was observed. When pulmonary maturity was borderline according to the amniotic fluid assessment, intrapartum fetal asphyxia was associated with an increased risk for development of RDS in the infant.     

Association between the surfactant protein A (SP-A) gene locus and respiratory-distress syndrome in the Finnish population

Respiratory-distress syndrome (RDS) in the newborn is a major cause of neonatal mortality and morbidity. Although prematurity is the most-important risk factor for RDS, the syndrome does not develop in many premature infants. The main cause of RDS is a deficiency of pulmonary surfactant, which consists of phospholipids and specific proteins. The genes underlying susceptibility to RDS are insufficiently known. The candidate-gene approach was used to study the association between the surfactant protein A (SP-A) gene locus and RDS in the genetically homogeneous Finnish population. In the present study, 88 infants with RDS and 88 control infants that were matched for degree of prematurity, prenatal glucocorticoid therapy, and sex were analyzed for SP-A genotypes. We show that certain SP-A1 alleles (6A2 and 6A3) and an SP-A1/SP-A2 haplotype (6A2/1A0) were associated with RDS. The 6A2 allele was overrepresented and the 6A3 allele was underrepresented in infants with RDS. These associations were particularly strong among small premature infants born at gestational age <32 wk. In infants protected from RDS (those that had no RDS, despite extreme prematurity and lack of glucocorticoid therapy), compared with infants that had RDS develop despite having received glucocorticoid therapy, the frequencies of 6A2 (.22 vs.71), 6A3 (.72 vs.17), 6A2/1A0 (.17 vs.68), 6A3/1A1 (.39 vs.10), and 6A3/1A2 (.28 vs.06) in the two groups, respectively, were strikingly different. According to the results of conditional logistic-regression analysis, diseases associated with premature birth did not explain the association between the odds of a particular homozygous SP-A1 genotype (6A2/6A2 and 6A3/6A3) and RDS. In the population evaluated in the present study, SP-B intron 4 variant frequencies were low and had no detectable association with RDS. We conclude that the SP-A gene locus is an important determinant for predisposition to RDS in premature infants.     

Pressure oscillation delivery to the lung: Computer simulation of neonatal breathing parameters

Preterm newborn infants may develop respiratory distress syndrome (RDS) due to functional and structural immaturity. A lack of surfactant promotes collapse of alveolar regions and airways such that newborns with RDS are subject to increased inspiratory effort and non-homogeneous ventilation. Pressure oscillation has been incorporated into one form of RDS treatment; however, how far it reaches various parts of the lung is still questionable. Since in-vivo measurement is very difficult if not impossible, mathematical modeling may be used as one way of assessment. Whereas many models of the respiratory system have been developed for adults, the neonatal lung remains essentially ill-described in mathematical models. A mathematical model is developed, which represents the first few generations of the tracheo-bronchial tree and the 5 lobes that make up the premature ovine lung. The elements of the model are derived using the lumped parameter approach and formulated in Simulink? within the Matlab? environment. The respiratory parameters at the airway opening compare well with those measured from experiments. The model demonstrates the ability to predict pressures, flows and volumes in the alveolar regions of a premature ovine lung.     

Respiratory distress syndrome (RDS) in premature infants is underscored by the magnitude of Th1 cytokine polarization

Respiratory distress syndrome (RDS) is a common problem and the leading cause of death in premature infants (PI). The introduction of surfactant treatment for RDS management has lowered mortality and morbidity; nevertheless, some neonates do not improve and are at increased risk of pulmonary hemorrhage. Inflammation, not only local but also systemic, seems to play an important role in the pathogenesis of RDS. To determine whether cytokine patterns characterize RDS and its outcome, we measured type-1 (IL-2, TNF-α, IFN-γ, IL-6) and type-2 (IL-4, IL-5, IL-10, TGF-β1) serum cytokines of 47 PI with established RDS and a control group of 30 healthy, appropriate for gestational age, full-term neonates. Cord blood samples were obtained at the time of delivery from PI and controls. Venous blood samples were collected from PI who received surfactant treatment and/or developed pulmonary hemorrhage. Significantly elevated cord blood cytokine levels were observed in PI at time of delivery, compared to controls, except for IL-5 and TNF-α levels that were within control range. The type-1/type-2 cytokine ratio was significantly increased in PI vs controls. Neonates who developed pulmonary hemorrhage between 2 and 3 days of life and/or died, presented the strongest Th1 and type-1 cytokine polarization that was mainly due to increased IFN-γ and TNF-α, and decreased TGF-β1. The majority of these PI were female with very low gestational age. Overall, PI with RDS present a Th1/type-1 cytokine polarization, which persists irrespective of the treatment provided, and is amplified when complications appear. Th1 polarization is associated with poor prognosis.     

The role of arginine-vasopressin in the regulation of water metabolism in preterm infants in the first days of life

We studied the role of arginine-vasopressin (AVP) in the regulation of fluid homeostasis in preterm infants. Group 1 was fed orally, groups 2 and 3 received fluids parenterally, and group 3 developed respiratory distress syndrome (RDS) and had to be ventilated. The infants of group 3 were not able to excrete the administered fluid, gained weight and consecutively developed hyponatremia. 1-min Apgar scores as well as log FiO2 correlated significantly with urinary AVP excretion on day 1. We conclude that nonosmotic stimuli are involved in the release of AVP and therefore disturb fluid homeostasis in severely ill infants with RDS.     

Hypoxia-inducible factors HIF-1alpha and HIF-2alpha are decreased in an experimental model of severe respiratory distress syndrome in preterm lambs

Respiratory distress syndrome (RDS) secondary to preterm birth and surfactant deficiency is characterized by severe hypoxemia, lung injury, and impaired production of nitric oxide (NO) and vascular endothelial growth factor (VEGF). Since hypoxia-inducible factors (HIFs) mediate the effects of both NO and VEGF in part through regulation by prolyl-hydroxylase-containing domains (PHDs) in the presence of oxygen, we hypothesized that HIF-1alpha and -2alpha in the lung are decreased following severe RDS in preterm neonatal lambs. To test this hypothesis, fetal lambs were delivered at preterm gestation (115-day gestation, term = 145 days; n = 4) and mechanically ventilated for 4 h. Lambs developed respiratory failure characterized by severe hypoxemia despite treatment with mechanical ventilation with high inspired oxygen concentrations. Lung samples were compared with nonventilated control animals at preterm (115-day gestation; n = 3) and term gestation (142-day gestation; n = 3). We found that HIF-1alpha protein expression decreased (P < 0.05) and PHD-2 expression increased (P < 0.005) at birth in normal term animals before air breathing. Compared with age-matched controls, HIF-1alpha protein and HIF-2alpha protein expression decreased by 80% and 55%, respectively (P < 0.005 for each) in preterm lambs with RDS. Furthermore, VEGF mRNA was decreased by 40%, and PHD-2 protein expression doubled in RDS lambs. We conclude that pulmonary expression of HIF-1alpha, HIF-2alpha, and the downstream target of their regulation, VEGF mRNA, is impaired following RDS in neonatal lambs. We speculate that early disruption of HIF and VEGF expression after preterm birth and RDS may contribute to long-term abnormalities in lung growth, leading to bronchopulmonary dysplasia.     

Nasal potential difference to detect Na+ channel dysfunction in acute lung injury

Pulmonary fluid clearance is regulated by the active transport of Na(+) and Cl(-) through respiratory epithelial ion channels. Ion channel dysfunction contributes to the pathogenesis of various pulmonary fluid disorders including high-altitude pulmonary edema (HAPE) and neonatal respiratory distress syndrome (RDS). Nasal potential difference (NPD) measurement allows an in vivo investigation of the functionality of these channels. This technique has been used for the diagnosis of cystic fibrosis, the archetypal respiratory ion channel disorder, for over a quarter of a century. NPD measurements in HAPE and RDS suggest constitutive and acquired dysfunction of respiratory epithelial Na(+) channels. Acute lung injury (ALI) is characterized by pulmonary edema due to alveolar epithelial-interstitial-endothelial injury. NPD measurement may enable identification of critically ill ALI patients with a susceptible phenotype of dysfunctional respiratory Na(+) channels and allow targeted therapy toward Na(+) channel function.     

Is carbon monoxide-mediated cyclic guanosine monophosphate production responsible for low blood pressure in neonatal respiratory distress syndrome?

Infant respiratory distress syndrome (RDS) involves inflammatory processes, causing an increased expression of inducible heme oxygenase with subsequent production of carbon monoxide (CO). We hypothesized that increased production of CO during RDS might be responsible for increased plasma levels of vasodilatory cGMP and, consequently, low blood pressure observed in infants with RDS. Fifty-two infants (no-RDS, n = 21; RDS, n = 31), consecutively admitted to the neonatal intensive care unit (NICU) between January and October 2003 were included. Hemoglobin-bound carbon monoxide (COHb), plasma cGMP, plasma nitric oxide (NOx), and bilirubin were determined at 0-12, 48-72, and at 168 h postnatally, with simultaneous registration of arterial blood pressure. Infants with RDS had higher levels of cGMP and COHb compared with no-RDS infants (RDS vs. no-RDS: cGMP ranging from 76 to 101 vs. 58 to 82 nmol/l; COHb ranging from 1.2 to 1.4 vs. 0.9 to 1.0%). Highest values were reached at 48-72 h [RDS vs. no-RDS mean (SD): cGMP 100 (39) vs. 82 (25) nmol/l (P < 0.001); COHb 1.38 (0.46) vs. 0.91 (0.26)% (P < 0.0001)]. Arterial blood pressure was lower and more blood pressure support was needed in RDS infants at that point of time [RDS vs. no-RDS mean (SD): mean arterial blood pressure 33 (6) vs. 42 (5) mmHg (P < 0.05)]. NOx was not different between groups and did not vary with time. Multiple linear regression analysis showed a significant correlation between cGMP and COHb, suggesting a causal relationship. Mean arterial blood pressure appeared to be primarily correlated to cGMP levels (P < 0.001). We conclude that a CO-mediated increase in cGMP causes systemic vasodilation with a consequent lower blood pressure and increased need for blood pressure support in preterm infants with RDS.     

Respiratory distress syndrome: evaluation of genetic susceptibility and protection by transmission disequilibrium test

Based on epidemiological data and genetic association studies, neonatal respiratory distress syndrome (RDS) is a complex disease with a multigenic background. The genes coding for surfactant proteins (SP) A and B have been assigned as the most likely genes in the etiology of RDS. The major factor predisposing to RDS is prematurity, and thus the phenotype of a very premature newborn infant that does not develop the disease can be regarded as hypernormal. Altogether 107 father-mother-offspring trios were divided into two sets according to the proband's phenotype, to evaluate familial segregation of candidate gene polymorphisms by the transmission disequilibrium test. A set of 76 trios were analyzed for transmission disequilibrium from parents to affected offspring. Another set of 31 trios were studied for allele transmission from parents to hypernormal offspring born very prematurely before the gestational age of 32 weeks. SP-A1-A2 haplotype 6A(2)-1A(0) showed significant excess transmission to affected infants and SP-A1 allele 6A(2) decreased transmission to the hypernormals. The present family study provides strong support for a direct or indirect role of the SP-A alleles as genetic predisposers to RDS in premature infants. The inclusion of parent-hypernormal offspring trios in transmission disequilibrium test is a useful approach to test for genetic protection against a disease.     

Pulmonary surfactant layers accelerate O2 diffusion through the air-water interface

During respiration, it is accepted that oxygen diffuses passively from the lung alveolar spaces through the respiratory epithelium until reaching the pulmonary capillaries, where blood is oxygenated. It is also widely assumed that pulmonary surfactant, a lipid-protein complex secreted into alveolar spaces, has a main surface active function, essential to stabilize the air-liquid interface, reducing in this way the work of breathing. The results of the present work show that capillary water layers containing enough density of pulmonary surfactant membranes transport oxygen much faster than a pure water phase or a water layer saturated with purely lipidic membranes. Membranes reconstituted from whole pulmonary surfactant organic extract, containing all the lipids plus the hydrophobic surfactant proteins, permit also very rapid oxygen diffusion, substantially faster than achieved by membranes prepared from the surfactant lipid fraction depleted of proteins. A model is proposed suggesting that protein-promoted membrane networks formed by pulmonary surfactant might have important properties to facilitate oxygenation through the thin water layer covering the respiratory surface.     

Connexin 26 35delG does not represent a mutational hotspot

Recent evidence suggests that the susceptibility to respiratory distress syndrome (RDS) is partly explained by genetic variation in the surfactant proteins (SP) SP-A and SP-B. The present study was designed to evaluate the concordance difference method and candidate gene analysis, in parallel, for the investigation of genetic susceptibility to RDS. We studied 100 same-sex twin pairs with established RDS in at least one twin. The difference in RDS concordance rates between the monozygotic (MZ) and dizygotic (DZ) twin pairs as evidence of a genetic influence was evaluated, and the SP-A and SP-B genes were investigated for potential associations with the susceptibility to RDS. The concordance rates of RDS were 54 and 44% in the MZ and DZ pairs, respectively. The concordance difference of 10% was not significant [95% confidence interval (CI) -0.1 to +0.3, P=0.32], suggesting a low hereditary impact. However, the SP-B Ile131Thr polymorphism was associated with RDS. The threonine allele was associated with an increased risk of RDS [odds ratio (OR) 2.2, 95% CI 1.4-3.5, P=0.0014]. This was particularly apparent in first-born male infants (OR 6.2, 95% CI 2.4-16.3, P<0.001). The degree of prematurity (<32 weeks OR 2.0, 95% CI 1.1-3.7, P=0.021) and birth order (second-born OR 3.1, 95% CI 1.3-7.4, P=0.009) were the clinical variables affecting the risk of RDS. An association between the SP-B Ile131Thr polymorphism and RDS was found. The threonine allele was associated with the risk of RDS, particularly in the first-born twin infants. The concordance difference between MZ and DZ twin pairs underestimates the genetic impact on the risk of RDS. The traditional twin concordance study is insufficient to evaluate genetic predisposition to RDS or other diseases that are confounded by the birth order or multiple pregnancy in itself.     

Effects of glucose infusion on surfactant and glycogen regulation in fetal lamb lung

To investigate the increased incidence of respiratory distress syndrome (RDS) that occurs in infants of diabetic mothers (IDM) with poor maternal glucose homeostasis, we infused glucose intravenously at a rate of 14 +/- 2 (SD) mg.kg-1.min-1 into eight twin and four singleton chronically catheterized fetal lambs from 112 days (0.77) gestation onward. Twelve catheterized and seven uncatheterized fetuses served as controls, including the eight twins of the glucose-treated fetuses. Glucose infusion resulted in a twofold elevation in fetal serum glucose levels and a 2.2-fold elevation in fetal serum insulin levels. Before 113 days (0.9) gestation, pulmonary disaturated phosphatidylcholine (DSPC) content was 1.5-fold higher in the glucose-infused fetuses than in the controls. However, after 0.9 gestation, pulmonary DSPC content increased 2.2-fold in the controls but did not increase significantly in the glucose-infused fetuses. In addition, the DSPC content of lung lavage was 5.0-fold higher in the controls and lung stability to air inflation was 2.0-fold greater and to deflation was 2.2-fold greater than in the glucose-infused fetuses. Pulmonary adenosine 3',5'-cyclic monophosphate-dependent protein kinase activity was also 1.5-fold higher, and pulmonary protein kinase C activity was 1.3-fold higher in the controls than in the glucose-infused fetuses. In contrast, glucose infusion was associated with a 1.8-fold increase in pulmonary glycogen content and with increased activities of glycogen phosphorylase kinase and glycogen phosphorylase. We conclude that the effects of chronic glucose infusion on fetal lamb lung DSPC and lung stability are compatible with a predisposition of the fetus to develop RDS.(ABSTRACT TRUNCATED AT 250 WORDS)     

Chromosomal localization of three pulmonary surfactant protein genes in the mouse.

Pulmonary surfactant, a protein-phospholipid mixture, maintains surface tension at the lung epithelium/air interface preventing alveolar collapse during respiration. For mammals appropriate developmental production of surfactant is necessary for adaptation to the air breathing environment. Deficiency of pulmonary surfactant results in respiratory distress syndrome (RDS), a leading cause of death in premature infants. Recently, three lung-specific pulmonary surfactant proteins designated SP-A, SP-B, and SP-C have been described. Cloned sequences for the genes that encode each of these proteins have been partially characterized in humans and other species. Analysis of interspecific backcross mice has allowed us to map the chromosomal locations of these three genes in the mouse. The gene encoding SP-A (Sftp-1) and the gene encoding SP-C (Sftp-2) both map to mouse chromosome 14, although at separate locations, while the gene encoding SP-B (Sftp-3) maps to chromosome 6. The mouse map locations determined in this study for the Sftp genes are consistent with the locations of these genes on the human genetic map and the syntenic relationships between the human and the mouse genomes.     

Effect of position on the mechanical interaction between the rib cage and abdomen in preterm infants.

To determine the influence of body position on chest wall and pulmonary function, we studied the ventilatory, pulmonary mechanics, and thoracoabdominal motion profiles in 20 preterm infants recovering from respiratory disease who were positioned in both the supine and prone position. Thoracoabdominal motion was assessed from measurements of relative rib cage and abdominal movement and the calculated phase angle (an index of thoracoabdominal synchrony) of the rib and abdomen Lissajous figures. The ventilatory and pulmonary function profiles were assessed from simultaneous measurements of transpulmonary pressure, airflow, and tidal volume. The infants were studied in quiet sleep, and the order of positioning was randomized across patients. The results demonstrated no significant difference in ventilatory and pulmonary function measurements as a function of position. In contrast, there was a significant reduction (-49%) in the phase angle of the Lissajous figures and an increase (+66%) in rib cage motion in prone compared with the supine position. In addition, the degree of improvement in phase angle in the prone position was correlated to the severity of asynchrony in the supine position. We speculate that the improvement in thoracoabdominal synchrony in the prone position is related to alterations of chest wall mechanics and respiratory muscle tone mediated by a posturally related shift in the area of apposition of the diaphragm to the anterior inner rib cage wall and increase in passive tension of the muscles of the rib cage. This study suggests that the mechanical advantage associated with prone positioning may confer a useful alternative breathing pattern to the preterm infant in whom elevated respiratory work loads and respiratory musculoskeletal immaturity may predispose to respiratory failure.     

Effects of leukotriene inhibition on pulmonary morphology in rat pup lungs exposed to hyperoxia

Assisted ventilation is necessary for treating preterm infants with respiratory distress syndrome. Unfortunately, high and prolonged concentrations of oxygen associated with assisted ventilation often lead to pulmonary changes, such as hemorrhage and inflammation. The resulting chronic pulmonary condition is known as bronchopulmonary dysplasia. Pulmonary changes characteristic of this syndrome can be produced in rat pups exposed to high oxygen levels. We exposed 21-d-old rats to room air or continuous 95% oxygen for 7 d and then allocated them into 6 groups to evaluate whether treatment with zileuton and zafirlukast, 2 agents which decrease the effects of leukotrienes, lessened the pulmonary effects of short-term hyperoxia. After 7 d, lung tissue was collected for light and electron microscopy. Pulmonary changes including edema, hemorrhage, alveolar macrophage influx, and Type II pneumocyte proliferation were graded on a numerical scoring system. Compared with controls exposed to hyperoxia [corrected] and saline, rats exposed to hyperoxia and treated with zileuton had significantly reduced levels of alveolar macrophage influx and Type II pneumocyte proliferation, but those exposed to hyperoxia [corrected] and treated with zafirlukast showed no significant reduction in any pulmonary changes. This study helps define pulmonary changes induced secondary to hyperoxia in rat pups and presents new information on the mechanisms of leukotriene inhibition in decreasing the severity of hyperoxic lung injury.