Inhibition of poly(ADP-ribose) polymerase preserves surfactant synthesis after hydrogen peroxide exposure.

Exposure to hydrogen peroxide (H2O2) decreases phosphatidylcholine (PC) synthesis in rabbit type II pneumocytes. Activation of poly(ADP-ribose) polymerase (PARP) may play a role in this process. Exposure of type II pneumocytes to H2O2 resulted in a 53% decrease in the rate of incorporation of [3H]choline into PC (P < 0.001). Cell NAD and ATP levels were decreased by 52% (P < 0.001) and 39% (P < 0.01), respectively, without significant changes in cell viability. Exposure to H2O2 also resulted in a 52% (P < 0.05) increase in the activity of PARP. Preincubation of type II cells with inhibitors of PARP (nicotinamide; 3-aminobenzamide) before H2O2 exposure prevented the increase in PARP activity, and blocked the decreases in ATP, NAD, and rate of PC synthesis. These results suggest that the energy depletion associated with activation of PARP contributes to the effects of oxidant stress on type II cell metabolic function and may be ameliorated by pharmacological agents in vitro.

Hyperoxic lung injury reduces exogenous surfactant clearance in vivo.

We studied the rate of clearance of treatment doses of radiolabeled calf lung surfactant extract, which was instilled into the lungs of young adult rabbits exposed to air (control) or 100% oxygen for 64 h. More than 75% of the instilled surfactant remained lung-associated at all time points up to 24 h post-instillation in both groups; however, significantly more of the labeled phosphatidylcholine (PC) remained in the alveolar wash of oxygen-exposed rabbits (44 +/- 9% in 100% O2 versus 27 +/- 5% in controls at 6 h and 27 +/- 2% in 100% O2 versus 6 +/- 1% in control rabbits at 24 h, p < 0.05). Less of the labeled PC could be found in type II pneumocytes isolated from the oxygen exposed animals than in control animals, both at 6 h (24 +/- 2 cpm/10(6) cells in O2 versus 38 +/- 7 cpm/10(6) cells in control) and 24 h (42 +/- 5 cpm/10(6) cells in O2 versus 70 +/- 12 cpm/10(6) cells in control) post-instillation. Type II cells from animals exposed to 100% oxygen also demonstrated significantly lower PC synthesis rates than cells from lungs of control animals. Interestingly, clearance of exogenous surfactant in rabbits exposed to 100% oxygen for 48 h, an exposure that does not cause significant type II pneumocyte dysfunction, was not different from control. We concluded that injury to type II pneumocytes may result in decreased clearance of instilled surfactant from the alveolar space and may be important in determining dosing regimens for the use of surfactant therapy in adult respiratory distress syndrome.

Infant sleep position: pediatricians' advice to parents.

OBJECTIVE: The American Academy of Pediatrics' (AAP) recommendation for side or supine sleep position in healthy babies has generated much controversy. We surveyed primary care physicians to determine the effect of the AAP statement on physician attitude toward infant sleep position and advice to parents. METHODS: We sent a 23-question survey to 194 physicians in Western New York. The survey addressed their attitude toward the AAP recommendations and its impact on their advice to parents. RESULTS: Of the 149 physicians treating newborns, 121 (82%) completed the questionnaire; 98% were aware of the AAP statement. The most common sources of information were the AAP (86%) and professional literature (77%). Of the respondents, 79% agreed with the AAP statement. Reasons for reservation were lack of data (64%), potential adverse consequences of supine position (52%), and their own experience (47%). Gender, years in practice, and type of reimbursement did not influence attitude toward the AAP recommendation. The AAP statement increased the frequency with which physicians routinely discussed sleep position from 34 to 70% (P < .02). Physicians recommending the prone position decreased from 57 to 7% (P < .001), while those recommending supine sleep position increased from 10 to 42% (P < .001). CONCLUSIONS: Most physicians agreed with the AAP statement and more frequently discussed sleep position following the AAP recommendations. However, they did not routinely recommend supine sleep position. The majority (69%) recommended the side position even though it is unstable. Although the AAP statement has increased discussion of infant sleep position by primary care physicians in WNY, only a minority recommend that infants sleep supine.

Increased expression of tissue inhibitor of metalloproteinases (TIMP-I) and metallothionein in murine lungs after hyperoxic exposure.

Acute exposure to hyperoxia results in well-described pathophysiologic responses in the lungs, beginning with subtle, subcellular changes and ending with severe pulmonary inflammation and edema. The biologic events that underlie or accompany this injury are not well understood. Our previous studies in rabbits have shown that hyperoxia induces large increases in the mRNAs encoding metallothionein (MT) and the tissue inhibitor of metalloproteinases (TIMP-I). Here we report studies of hyperoxic lung injury in two strains of mouse that differ in their relative resistance to O2 toxicity. O2-sensitive (C57BL/6J) mice and O2-resistant (C3H/HeJ) mice were exposed to 100% O2 for up to 96 h. Lung mRNAs were assayed by primer extension and slot blot hybridization. By 72 h of hyperoxia, the sensitive strain showed large increases in MT-I, MT-II, and TIMP-I mRNAs. The resistant strain showed similar changes but with a 24-h delay. In situ hybridization demonstrated that hyperoxic lung injury was accompanied by obvious increases in TIMP-I and MT transcripts in cells surrounding arteries and large airways, where many inflammatory cells were localized. With prolonged exposure, hybridization to MT transcripts had spread throughout lung parenchyma. The two strains showed the same patterns of in situ hybridization for TIMP-I and MT transcripts but, as with the whole lung homogenates, followed a different time course. Corresponding increases in MT protein were shown to occur, using a cadmium binding assay and by immunohistochemistry. The strong spatial correlation between the presence of localized inflammation and increased TIMP-I and MT expression further supports the importance of TIMP-I and MT in acute lung injury.

Inter-strain variation in susceptibility to hyperoxic injury of murine airways.

The contribution of genetic background in susceptibility to hyperoxic lung injury is not clear. We utilized inbred mice to: 1) characterize inter-strain variation in hyperoxia-induced effects on lavageable indicators of airway epithelial injury; 2) test the hypothesis that hyperoxia-induced change in airway permeability is under Mendelian control. Male mice (5-7 wk, 20-25 g) from six inbred strains were exposed to 95-99% oxygen (O2) or room air for 0, 48, or 72 h. Hyperoxia-induced alteration in lung permeability was estimated by changes in lung wet weight:dry weight ratio and total bronchoalveolar lavage (BAL) protein concentration. The airway inflammatory response to O2 was assessed by changes in cellular profiles in BAL fluid. At least two distinct phenotypes were found among the strains exposed to O2 for 72 h. The susceptible phenotype (exemplified by C57BL/6J [B6] mice) was characterized by mean BAL protein concentration that was approximately 10 times greater than the resistant phenotype (e.g. C3H/HeJ [C3] mice). Hyperoxia caused LWW:LDW to double in susceptible B6 mice relative to controls, while no significant change was found in resistant C3 mice. Compared to air-exposed controls, hyperoxia also decreased the mean number of BAL alveolar macrophages and increased polymorphonuclear leukocytes in B6 mice, but the inflammatory cell profile of C3 mice was not affected after 72 h. The observed ratios of resistant to susceptible phenotypes of F1, F2, and back-cross progeny from B6 and C3 progenitors were not consistent with the hypothesis that susceptibility to hyperoxia is under Mendelian control.(ABSTRACT TRUNCATED AT 250 WORDS)

Impact of lung surfactant therapy on chronic lung diseases in premature infants.

Bronchopulmonary dysplasia (BPD) and chronic lung disease remain common complications of prematurity. This article addresses the evolution of BPD since its description in 1967, and the impact of surfactant replacement therapy on the incidence and characteristics of BPD. It also addresses the emergence of a form of chronic lung disease now seen in surfactant-treated premature infants who had no acute lung disease.

A controlled clinical comparison of four different surfactant preparations in surfactant-deficient preterm lambs.

Four pulmonary surfactant preparations (natural sheep surfactant, Exosurf, Infasurf, and Survanta) were compared with no treatment in 29 newborn lambs at 126 +/- 1 days gestation. Fetuses were delivered by Cesarean section under general anesthesia and treated with either the manufacturer's recommended dose of a commercial surfactant, 100 mg phospholipid/kg of natural sheep surfactant, or no surfactant (control group). Lambs were mechanically ventilated with 100% oxygen until moribund from respiratory failure or until killed at 24 h after delivery. Lambs surviving to 12 h received surfactant retreatment (of the same type) if hypoxemic. All lambs were surfactant deficient at birth, having less than 0.1 mg/ml of phospholipid measured in the lung liquid. All control lambs developed early respiratory failure and died within 8 h after delivery. Survival was significantly prolonged by natural surfactant (p less than 0.02), Infasurf (p less than 0.0001), and Survanta (p less than 0.02). Natural surfactant, Infasurf, and Survanta significantly improved arterial oxygenation and ventilatory compliance compared with no treatment. These effects lasted as long as 24 h in lambs given Infasurf, but no more than 6 h in lambs given natural surfactant or Survanta. After death, static pressure-volume lung mechanics were significantly better for lambs given natural sheep surfactant, Infasurf, or Survanta. Lambs given Exosurf were no different than control lambs in any variable measured. Thus, in 126-day gestation surfactant-deficient newborn lambs, natural sheep surfactant, Infasurf, and Survanta, but not Exosurf, Improve oxygenation, lung mechanics, and survival.

Acute ozone-induced change in airway permeability: role of infiltrating leukocytes.

The role of infiltrating polymorphonuclear leukocytes (PMNs) in acute lung injury and inflammation is still controversial. In inbred mice, acute ozone (O3) exposure induces airway inflammation that is characterized by a maximal influx of lavageable PMNs 6 h after exposure and a maximal increase in lung permeability 24 h after O3. We tested the hypothesis that O3-induced change in airway epithelial permeability of O3-susceptible C57BL/6J mice is due to infiltrating PMNs. Male mice (6-8 wk) were treated with a nonsteroidal anti-inflammatory drug (indomethacin), a chemotactic inhibitor (colchicine), or an immunosuppressant (cyclophosphamide) to deplete or inhibit PMNs from infiltrating the airways. After drug or vehicle treatment, mice were exposed for 3 h to 2 ppm O3 or filtered air, and pulmonary inflammation was assessed by inflammatory cell counts and total protein content (a marker of airway permeability) in bronchoalveolar lavage (BAL) fluid. Filtered air exposure did not affect the parameters of pulmonary inflammation at any time after exposure. Compared with vehicle controls, each of the drug treatments resulted in significant reduction of PMN influx 6 and 24 h after O3. However, total BAL protein content was not attenuated significantly by the three treatments at either 6 or 24 h postexposure. Results of these experiments suggest that the influx of PMNs and the change in total BAL protein are not mutually dependent events in this model and suggest that infiltrating PMNs do not play a major role in acute O3-induced changes in permeability of the murine lung.

Mechanisms of H2O2-mediated injury to type II cell surfactant metabolism and protection with PEG-catalase.

Alterations in type II pneumocyte function, including surfactant biosynthesis, may play a significant role in the development and pathophysiology of oxidant-induced lung injury. The results of this study showed that type II cells exposed to 50-300 microM H2O2 demonstrated a dose-dependent decrease in phosphatidylcholine (PC) synthesis with only minimal changes in cell viability. The activities of the choline-phosphate cytidyltransferase and cholinephosphotransferase, specific enzymes of PC synthesis, were not significantly decreased by the exposure. However, the activity of glycerol-3-phosphate acyltransferase, a sulfhydryl-dependent enzyme involved in an early stage of phospholipid synthesis, was decreased by the exposures in a manner that was similar to that seen for PC synthesis. Further studies showed that incubation of type II cells with polyethylene glycol-conjugated catalase for 1 h resulted in an increase in the cell-associated catalase activity (53 +/- 5 vs. 6.7 +/- 1.5 units/mg protein for controls). Confocal microscopy analysis showed that a significant portion of this activity was located intracellularly. More importantly, these cells were protected from changes in PC synthesis rates when subsequently incubated with 300 microM H2O2. These results indicate that the deleterious effects of H2O2 on type II cell surfactant synthesis may be pharmacologically modified in vitro, a concept that may have utility with regard to the modulation of in vivo lung injuries.

Hypocapnia does not alter collateral ventilation in sheep.

Hypocapnic constriction has been proposed as a mechanism by which collateral pathways might rapidly alter ventilation to match perfusion. We studied the changes in response to hypocapnia with age in sheep, a species with collateral resistance (Rcoll) similar to those measured in humans. Measurements of Rcoll were made with either 5 or 10% CO2 and with air (hypocapnia) in 29 anesthetized sheep, ages 6 mo to 10 yr, with the wedged bronchoscope technique. Rcoll was 0.42 +/- 0.12, 0.58 +/- 0.18, 0.32 +/- 0.18, and 0.17 +/- 0.04 (SE) cmH2O.ml-1.min in 6-mo- and 1-, 2-, and 10-yr-old animals, respectively. These values were unchanged with hypocapnia. Despite the lack of a change in Rcoll with hypocapnia, administration of histamine aerosol (8 animals) through the bronchoscope increased Rcoll by 151 +/- 35% (P less than 0.05). These data suggest that although collateral pathways exist in sheep and are capable of constriction, they do not respond to hypocapnia. Furthermore, the response to hypocapnia is not influenced by age.

Home oxygen therapy for chronic lung disease in extremely low-birth-weight infants.

Chronic lung disease that requires prolonged oxygen therapy commonly complicates the recovery of extremely low-birth-weight infants (less than 1000 g). We report follow-up data through 18.5 +/- 0.9 (mean +/- SEM) months of age in 30 extremely low-birth-weight infants (birth weight, 783 +/- 24 g; gestational age, 26.0 +/- 0.3 weeks) who were discharged home receiving supplemental oxygen. Oxygen was prescribed to maintain arterial oxygen saturation at 95% or greater. At discharge, postconceptional age was 40.5 +/- 0.6 weeks, and weight was 2220 +/- 50 g. Duration of home oxygen therapy was 4.5 +/- 0.5 months. The mean weight percentile increased from less than 5 to 23 between discharge and the last follow-up. All infants survived; only 6 required hospitalization for acute medical illnesses. We conclude that carefully supervised home oxygen therapy permits the safe early discharge of selected extremely low-birth-weight infants with chronic lung disease.