Ilene R S Sosenko

Bronchopulmonary dysplasia: changes in pathogenesis, epidemiology and definition.

Bronchopulmonary dysplasia (BPD) continues to be one of the most common long-term complications associated with preterm birth. Its incidence is increasing as the survival of extreme premature infants improves, but its clinical presentation is milder than the original description of Northway and collaborators. In contrast to the classic BPD that was strongly related to mechanical injury and oxygen toxicity, current forms of the condition are more related to immaturity, perinatal infection and inflammation, persistent ductus arteriosus and disrupted alveolar and capillary development. Many different definitions of BPD have been proposed, most of which are based on the duration of supplemental oxygen requirement. The different definitions can produce strikingly different incidence figures, which may account for the wide variations in the condition reported in the literature. Some of the limitations of the criteria most commonly used to diagnose BPD are discussed in this article.

Influence of infection on patent ductus arteriosus and chronic lung disease in premature infants weighing 1000 grams or less

OBJECTIVES To test the hypotheses that (1) infection increases ductal dilatory prostaglandins and inflammatory mediators that may influence the closure of a patent ductus arteriosus (PDA), increasing the incidence of late episodes of PDA (after 7 days) and the rate of closure failures, and (2) the concurrence of PDA and infection increases the risk of chronic lung disease (CLD). METHODS One hundred fourteen premature infants (birth weight, 500 to 1000 gm) were prospectively assessed for PDA and infection. Serum levels of 6-ketoprostaglandin F1 alpha and tumor necrosis factor alpha were measured routinely in all infants and when PDA or infection was present. Multivariate assessment of risk factors for PDA closure failure and for CLD was done by logistic regression, and expressed as an odds ratio and as 95% confidence intervals. RESULTS Late PDA episodes were more frequent in infants with infection than in those without infection. A temporally related infection (<5 days between both diagnoses) was associated with an increased risk of PDA closure failure (odds ratio, 19.1 (confidence interval, 4 to 90)). In addition to birth weight and the severity of initial respiratory failure, PDA and infection increased the risk of CLD (odds ratio, 11.7 (confidence interval, 1.7 to 81) for PDA; odds ration, 3.1 (confidence interval, 1 to 11) for infection). Furthermore, when both factors were temporally related, they further increased the risk of CLD (odds ratio, 29.6 (confidence interval, 4.5 to >100)). Infants with infection and those with PDA had higher levels of 6-ketoprostaglandin F1 alpha than did control subjects. Levels of tumor necrosis factor alpha were also elevated in infants with infection and in those with late PDA. CONCLUSIONS Infection adversely influences PDA outcome by increasing the risk of late ductal reopening and PDA closure failures. Increased levels of prostaglandins and tumor necrosis factor alpha in infants with infection may explain the poor PDA outcome. The concurrence of PDA and infection potentiates their negative effects on the risk of CLD.

Failure of Premature Rabbits to Increase Antioxidant Enzymes During Hyperoxic Exposure: Increased Susceptibility to Pulmonary Oxygen Toxicity Compared with Term Rabbits

ABSTRACT: Although the prematurely born are known to have decreased baseline levels of protective antioxidant enzymes (Frank L, Sosenko IRS: J Pediatr 110:9 and 106, 1987), the ability to augment the baseline values during high O2 exposure is the key factor determining O2 tolerance versus O2 susceptibility. We have compared the pulmonary antioxidant enzyme responses of prematurely delivered rabbits (gestational d 29 of 32) and full-term rabbits to 48–72 h of hyperoxic exposure. We found that although full-term newborns exposed to >90% O2 consistently showed elevated superoxide dismutase, catalase, glutathione peroxidase, and glucose-6-phosphate dehydrogenase activities, the premature animals repeatedly failed to respond to hyperoxia with increased antioxidant enzyme activity levels. Consistent with the comparative antioxidant enzyme responses were the evidences of O2 toxicity in the two age groups. The prematurely born rabbits had significantly increased lung lavage protein content, lung conjugated diene levels, and more severe light microscopic lung pathology compared with the full-term animals during equal O2 exposure time. This first reported comparison of prematurely born versus full-term animal responses to hyperoxia might help to explain the clinical observation that the very prematurely born infant is excessively prone to the development of O2-induced lung injury and the progressive development of bronchopulmonary dysplasia.

Effect of early initiation of intravenous lipid administration on the incidence and severity of chronic lung disease in premature infants

OBJECTIVE To investigate whether intravenous administration of lipid nutrition (Intralipid) within 12 hours of birth to ventilator-dependent premature infants would decrease the incidence or severity, or both, of chronic lung disease. METHOD We randomly assigned 133 infants to Intralipid or control groups, using two weight strata: 42 Intralipid versus 37 control subjects in the 600 to 800 gm stratum, and 28 Intralipid versus 26 control subjects in the 801 to 1000 gm stratum. The Intralipid group received 20% Intralipid at < 12 hours after birth, starting at a dose of 0.5 gm/kg and increasing to a maximum of 1.5 gm/kg, maintained through day 7. Control infants received no lipid until after day 7. Neither group received enteral feedings until after day 7. RESULTS No significant differences in mortality rates were present in the total population (23/70 = 32.9% vs 16/63 = 25.4%; p = 0.35, Intralipid vs control); however, the mortality rate increased significantly in 600 to 800 gm infants receiving Intralipid versus the control infants (20/41 = 47.5% vs 9/37 = 24.3%; p = 0.032). No significant differences were found in the number of infants in whom chronic lung disease developed (requiring oxygen for > or = 28 days), proportion requiring oxygen for > or = 60 days, number of survivors without chronic lung disease, or total oxygen and ventilation requirements. However, 600 to 800 gm infants receiving Intralipid had significantly more pulmonary hemorrhage, and greater numbers of infants receiving Intralipid in both weight categories required supplemental oxygen at day 7. The incidence of other complications of prematurity, time required to regain birth weight, and duration of hospital stay did not differ between groups. CONCLUSION Intralipid administration initiated at < 12 hours after birth failed to protect very low birth weight premature infants from chronic lung disease. Some of the results raise questions about possible deleterious effects of Intralipid when administered early in the first week of life.

A randomized, double-blind, placebo- controlled trial on intravenous ibuprofen L-lysine for the early closure of nonsymptomatic patent ductus arteriosus within 72 hours of birth in extremely low-birth-weight infants

A multicenter, double-blind, randomized, placebo-controlled trial was conducted to evaluate the efficacy and safety of intravenous (IV) ibuprofen (L-lysine) for the early closure of nonsymptomatic patent ductus arteriosus (PDA) within 72 hours of birth in extremely low-birth-weight (ELBW) infants with evidence of ductal shunting by echocardiogram. Eleven sites enrolled 136 infants with nonsymptomatic early PDA (gestational age < 30 weeks; body weight 500 to 1000 g) to receive a 3-day course (10 mg/kg, 5 mg/kg, and 5 mg/kg) of IV ibuprofen ( N = 68) or placebo ( N = 68). Cardiac echocardiogram was performed on study days 1 and 14, and with rescue. Infants were followed to 36 weeks postconceptional age. Patient demographics, mean (standard deviation), were similar between ibuprofen and placebo: birth weight: 798.5 g (128.7) versus 797.3 g (132.8); gestational age: 26.1 weeks (1.3) versus 26.2 weeks (1.4); and age at first dose: 1.5 days (0.7). The intent-to-treat analysis of the primary endpoint, subjects rescued, died, or dropped through study day 14, was 21/68 (30.9%) with ibuprofen and 36/68 (52.9%) for placebo ( P = 0.005). Death, intraventricular hemorrhage, necrotizing enterocolitis, daily fluid intake/output, liver function, bronchopulmonary dysplasia, and retinopathy of prematurity did not differ. A trend toward decreased periventricular leukomalacia by ibuprofen was noted. IV ibuprofen was effective and safe in the early closure of PDA in preterm neonates.

Menhaden Fish Oil, n-3 Polyunsaturated Fatty Acids, and Protection of Newborn Rats from Oxygen Toxicity

ABSTRACT: We have previously reported that newborn rats born to mothers fed a high n-6 polyunsaturated fatty acid (PUFA) (safflower oil) diet demonstrated increased n-6 PUFA in lung lipids and superior tolerance to high oxygen exposure. In the present study, we explored whether high n-3 PUFA might also protect against hyperoxic damage and by what mechanism. Adult female rats were fed either regular rat chow, a high n-3 (menhaden fish oil-based) diet, or a high n-6 (safflower oil-based) diet for 6 wk before and then throughout pregnancy and lactation. Newborn offspring of the high n-3 (fish oil) dams demonstrated increased n-3 PUFA {i.e. eicosapentaenoic and docosahexaenoic acid) and decreased n-6 PUFA {i.e. linoleic and arachidonic acid) in their lung lipids compared to the other two diet groups. The high n-6 (safflower oil) offspring had the opposite PUFA lung lipid pattern (with increases in total n-6 fatty acids and decreases in total n-3 fatty acids). The high n-3 offspring demonstrated markedly decreased lung levels of prostaglandin E2, vja and thromboxane B2, whereas the high n-6 offspring had higher eicosanoid levels than the regular diet offspring. Offspring of both high n-6 and high n-3 diet dams demonstrated essentially the same superior hypperoxic tolerance compared to regular diet offspring [7-d (>95% O2) survival rates of 110/115 and 99/109, respectively, versus 70/91, p<0.01]. These studies lend further support to the speculation that increasing lung PUFA content may provide the newborn lung with increased ability to scavenge oxygenfree radicals and thus may serve to protect against oxygen toxicity.

Intralipid increases lung polyunsaturated fatty acids and protects newborn rats from oxygen toxicity

ABSTRACT: Intralipid, derived from soybean oil and containing a high percentage of n-6 family polyunsaturated fatty acids (PUFA) and also linolenic acid, an n-3 family PUFA, is commonly the first fat source provided to very low birth weight premature infants. Following up on our previous reports that newborn rats born to dams fed high-PUFA diets demonstrate superior tolerance to hyperoxia, we examined whether the high-PUFA fat source Intralipid might also protect against oxygen toxicity. Adult female rats were fed either regular Rat Chow or fat-free diet containing 20%-Intralipid as the fat source for 3 wk before and then throughout pregnancy and lactation. One- and 5-d-old offspring of Intralipid diet-fed dams demonstrated significant increases in lung lipid n-6 family PUFA plus elevated linolenic acid compared with regular diet-fed offspring. These characteristic fatty acid patterns, apparent in total lung lipids, were even more pronounced in the triglyceride fraction compared with the phospholipid fraction. Associated with these fatty acid changes were significantly improved hyperoxic survival rates (89 out of 95 = 94% survival after 7 d of >95% O2 exposure) in Intralipid offspring (versus 89 out of 106 = 84%, p < 0.05 in regular diet offspring) and evidence of superior clinical/pathologic status. No differences in pulmonary antioxidant enzyme or surfactant system development, response of antioxidant enzymes to hyperoxic exposure, or lung prostaglandin E2, 6-keto PGF2-α or leukotrienes C4-F4 were present. These findings continue to support the hypothesis that increasing lung PUFA content may provide increased O2 free radical scavenging capacity, thus protecting against hyperoxic lung damage. The results also suggest a role for Intralipid administration in protecting the lungs of high oxygen-exposed very low birth weight premature infants.

Failure of premature rabbits to increase lung antioxidant enzyme activities after hyperoxic exposure: antioxidant enzyme gene expression and pharmacologic intervention with endotoxin and dexamethasone.

ABSTRACT: Premature rabbits, unlike full-term rabbits, are unable to mount a protective increase in pulmonary antioxidant enzyme (AOE) activities in response to 48 h of hyperoxic exposure and demonstrate increased pulmonary O2 toxicity compared with full-term rabbits. To examine AOE gene expression of CuZn superoxide dismutase (SOD), Mn SOD, catalase, and glutathione peroxidase in preterm versusterm rabbits in response to hyperoxia, 29.5 d preterm rabbits (delivered by hysterotomy) and term rabbits (spontaneously vaginally delivered) were exposed to 48 h of >90% O2 or room air. Preterm rabbits had a significant increase in CuZn SOD mRNA without corresponding AOE activity increases, suggesting translational/posttranslational inhibition. In full-term rabbits, the magnitude of lung AOE mRNA changes was associated with concordant magnitude changes in activities of CuZn SOD, Mn SOD, and catalase, suggesting pretranslational regulation of AOE gene expression; glutathione peroxidase, however, appears to be regulated translationally/posttranslationally. To investigate potential pharmacologic means of overcoming the susceptibility of the preterm rabbit to O2 toxicity, 29.5 d preterm rabbits received 20–40 μg/kg of Salmonella typhimuriumendotoxin or diluent S.C. (after birth and at 24 h); in separate experiments, pregnant rabbits received intramuscular injections of dexamethasone (0.01–0.05 mg/kg) or saline on gestational d 27.5 and 28.5 and underwent hysterotomy at 29.5 d. After hyperoxic exposure, postnatal endotoxin treatment of preterm rabbits resulted in significant increases in CuZn SOD activity and CuZn SOD mRNA, suggesting a reversal of the translational/posttranslational inhibition characteristic of the preterm rabbit, improved hyperoxic survival (74/81 = 91% versus70/92 = 76%, p< 0.05; endotoxin versuscontrols), and protection against hyperoxia-induced increases in lung lavage protein (+4% endotoxin versus+28% controls, p< 0.05). Prenatal dexamethasone neither improved hyperoxic survival, protected against O2 toxicity, nor produced increases in any of the AOE after 48 h of hyperoxia relative to air-breathing preterm rabbits.

Metyrapone Delays Surfactant and Antioxidant Enzyme Maturation in Developing Rat Lung

ABSTRACT. The surfactant system and the antioxidant enzyme system of the fetal lung have chronologically similar developmental patterns and both can be accelerated by the administration of exogenous glucocorticoids. To test whether the antioxidant enzyme system, like the surfactant system, is regulated, at least in part, by endogenous glucocorticoids, we injected pregnant rats for 3 days prior to delivery with metyrapone, an adrenal 11-β hydroxylase inhibitor which crosses the placenta and blocks endogenous glucocorticoid synthesis, or saline. Metyrapone offspring had significantly decreased lung tissue disaturated phosphatidylcholine and disaturated phosphatidylcholine/total phospholipids (p < 0.05) compared to controls at days 21 and 22 of gestation. Activities of the antioxidant enzymes superoxide dismutase, catalase, and glutathione peroxidase were similarly significantly reduced (p < 0.01) in the lungs of metyrapone offspring at both gestational days studied. One day premature metyrapone pups demonstrated poorer survival than control pups from 25 min after delivery (44% survival versus 83%, p < 0.05) to 90 min (6% survival versus 78%, p < 0.01). These findings of delayed maturation of the surfactant and antioxidant enzyme systems following adrenal glucocorticoid blockade suggest that both systems are regulated, at least in part, by an endogenous glucocorticoid mechanism.

IL-1α causes lung inflammation and maturation by direct effects on preterm fetal lamb lungs

Intra-amniotic endotoxin induces IL-1, causes chorioamnionitis, lung inflammation, lung injury and lung maturation in preterm lambs. Intra-amniotic IL-1α also causes chorioamnionitis, lung inflammation and lung maturation. We asked if IL-1α effects on the preterm lung are mediated by direct signaling to the lung rather than by indirect effects from the chorioamnionitis. To study IL-1 effects independently of chorioamnionitis, the lungs and the amniotic fluid were surgically separated in fetal sheep by diverting fetal lung fluid via a tracheostomy tube to a sialastic bag. A mini-osmotic pump delivered an intratracheal infusion of recombinant sheep IL-1α (10 μg) or saline (control) over 24 h. Preterm lambs were delivered 1d or 7d after the start of the infusion at 124d gestational age (Term = 150d). IL-1α recruited inflammatory cells and increased pro-inflammatory cytokine mRNA expression in the fetal lungs. Compared with controls, IL-1α did not alter lung antioxidant enzyme activity or alveolar numbers. IL-1α had minimal effects on the mRNA or protein expression of proteins essential for vascular development. IL-1α induced large increases in alveolar surfactant saturated phosphatidylcholine and increased lung gas volumes. Lung inflammation and maturation result from direct exposure of the fetal lung to a single cytokine - IL-1α.