SP-A deficiency in primate model of bronchopulmonary dysplasia with infection. In situ mRNA and immunostains

Ibuprofen-induced patent ductus arteriosus closure: physiologic, histologic, and biochemical effects on the premature lung

OBJECTIVE

The goal was to study the pulmonary, biochemical, and morphologic effects of a persistent patent ductus arteriosus in a preterm baboon model of bronchopulmonary dysplasia.

METHODS

Preterm baboons (treated prenatally with glucocorticoids) were delivered at 125 days of gestation (term: 185 days), given surfactant, and ventilated for 14 days. Twenty-four hours after birth, newborns were randomly assigned to receive either ibuprofen (to close the patent ductus arteriosus; n = 8) or no drug (control; n = 13).

RESULTS

After treatment was started, the ibuprofen group had significantly lower pulmonary/systemic flow ratio, higher systemic blood pressure, and lower left ventricular end diastolic diameter, compared with the control group. There were no differences in cardiac performance indices between the groups. Ventilation index and dynamic compliance were significantly improved with ibuprofen. The improved pulmonary mechanics in ibuprofen-treated newborns were not attributable to changes in levels of surfactant protein B, C, or D, saturated phosphatidylcholine, or surfactant inhibitory proteins. There were no differences in tracheal concentrations of cytokines commonly associated with the development of bronchopulmonary dysplasia. The groups had similar messenger RNA expression of genes that regulate inflammation and remodeling in the lung. Lungs from ibuprofen-treated newborns were significantly drier (lower wet/dry ratio) and expressed 2.5 times more epithelial sodium channel protein than did control lungs. By 14 days after delivery, control newborns had morphologic features of arrested alveolar development (decreased alveolar surface area and complexity), compared with age-matched fetuses. In contrast, there was no evidence of alveolar arrest in the ibuprofen-treated newborns.

CONCLUSIONS

Ibuprofen-induced patent ductus arteriosus closure improved pulmonary mechanics, decreased total lung water, increased epithelial sodium channel expression, and decreased the detrimental effects of preterm birth on alveolarization.

Elevated expression of surfactant proteins in newborn rats during adaptation to hyperoxia

The mechanisms whereby lung adaptation to hyperoxia occurs in the newborn period are incompletely understood. Pulmonary surfactant has been implicated in lung protection against hyperoxic injury, and elevated expression of certain surfactant proteins occurs in lungs of adult rats during adaptation to sublethal oxygen (85% O(2)). Here we report that newborn rats, which can adapt to even higher levels of hyperoxia (100% O(2)) than do adult rats, manifest changes in the lung surfactant proteins (SP), especially SP-A and SP-D. In newborn rats exposed to hyperoxia on Days 3 through 10 of life, lung messenger RNAs (mRNAs) for SP-A and SP-B gradually and progressively increased, relative to levels in age-matched, air-exposed newborns, over this 8-d period. By contrast, SP-C and SP-D mRNAs were maximally increased relative to values in simultaneously air-exposed control rats after 4 d of exposure. Lung mRNA for CC-10, a protein specific for Clara cells, was greater in hyperoxia-exposed rats than in air-exposed control rats on Day 4 of exposure, but not on other days. Lung mRNA for thyroid transcription factor (TTF)-1 was marginally increased on Days 1, 2, 4, and 6, and significantly increased on Day 8. Both SP-A and SP-D proteins were increased in lung lavage samples taken from hyperoxia-exposed newborns, relative to those taken from air-exposed controls, with the greatest increases occurring on Days 6 and 8 of exposure. However, the patterns of increase of the proteins were not identical to those of the respective mRNAs. In situ hybridization studies demonstrated increases in SP-D, and to a lesser extent in SP-A, in peripheral lung tissues from oxygen-exposed newborns. Taken together, these data indicate that specific surfactant proteins are upregulated at both the pretranslational and post-translational levels in distal lung epithelium during adaptation to hyperoxia in the newborn rat.

Deficiencies in lung surfactant proteins A and D are associated with lung infection in very premature neonatal baboons

Surfactant proteins A (SP-A) and D (SP-D) are important in the innate host defense against pathogenic microorganisms. A deficit in these proteins in premature infants, either because of immaturity or as a consequence of superimposed chronic lung disease (CLD), could increase their susceptibility to infection. The study reported here examined infection in CLD in the premature newborn baboon, and correlated it with the amounts of SP-A and SP-D in lung tissue and lavage fluid. Two groups of baboons were delivered prematurely, at 125 d gestational age (g.a.), and differed principally in whether they developed naturally acquired pulmonary infections and sepsis. Group I animals were ventilated with clinically appropriate oxygen for 6 d and 14 d without clinical incident. Group II animals were ventilated for 5 to 71 d, but differed from those in Group I in that most developed pulmonary infection and/or sepsis. In Group I animals, tissue pools of both SP-A and SP-D were equal to or exceeded those in adults, and lavage pools of SP-A increased progressively with the time of ventilation to about 35% of adult levels after 14 d. In contrast, most Group II animals had concentrations of lavage SP-A that were less than 20% of that in adult animals. A low concentration of lavage SP-A correlated with the release of interleukin-8, and with a high "infection index" based on histopathology, microbiologic cultures, and clinical indications of sepsis. Our data suggest that the amounts of SP-A and SP-D in lavage fluid are indicators of the risk of infection in the evolution of neonatal CLD. Deficits in the amount of lavage SP-A, even after 60 d of ventilation, may have inhibited the resolution of infection and thereby contributed to the developing injury among our Group II animals.

Degree of lung maturity determines the direction of the interleukin-1- induced effect on the expression of surfactant proteins

Intra-amniotic interleukin (IL)-1 increases surfactant components in immature fetal lung, whereas high IL-1 after birth is associated with surfactant dysfunction. Our aim was to investigate whether the fetal age influences the responsiveness of surfactant proteins (SPs) to IL-1. Rabbit lung explants from fetuses at 19, 22, 27, and 30 d of gestation and 1-d-old newborns were cultured in serum-free medium in the presence of recombinant human (rh) IL-1alpha or vehicle. The influence of IL-1alpha on SP-A, -B, and -C messenger RNA (mRNA) content was dependent on the conceptional age. In very immature lung on Day 19, rhIL-1alpha (570 ng/ml for 20 h) increased SP-A, -B, and -C mRNA by 860+/-15%, 314+/-108%, and 64+/-17%, respectively. The increase in SP-A mRNA was evident within 4 to 6 h. IL-1alpha increased the SP-A concentration in alveolar epithelial cells and in the culture medium within 20 h. In contrast, at 27 to 30 d of gestation and in newborns, IL-1alpha decreased SP-C, -B, and -A mRNA by means of 64 to 67%, 48 to 59%, and 12 to 15%, respectively. SP-B protein decreased by 45 to 60%. The decrease in mRNA became evident within 8 to 12 h and was dependent on IL-1 concentration. On Day 27, IL-1alpha accelerated the degradation of SP-B mRNA in the presence of actinomycin D. IL-1 did not increase the degradation rate of SP-A mRNA unless both actinomycin D and cycloheximide were added to the explants. The present findings may explain some of the contrasting associations between inflammatory cytokines and lung diseases during the perinatal period. The determinants of the direction of the IL-1 effect on the expression of SPs remain to be identified.

Abnormal surfactant metabolism and function in preterm ventilated baboons

We evaluated surfactant metabolism and function and the effects of antenatal glucocorticoids in very preterm baboons. Pregnant baboons were randomized to receive saline (controls) or 6 mg betamethasone (beta) 48 and 24 h before delivery at 125 +/- 2 d gestation (term is 184 d). The newborn baboons were treated with [14C]dipalmitoylphosphatidylcholine-labeled surfactant and ventilated for 6 d. Lung function for six control and six betamethasone-treated animals was similar. Recoveries of 14C-saturated phosphatidylcholine (Sat PC) were similar: 4.8% (control) and 3.6% (beta) in alveolar wash and 15.4% (control) and 17.7% (beta) in total lungs. Alveolar and total lung pool sizes of Sat PC were about 23 and 190 micromol/kg, respectively. The preterm baboons secreted 8.7% (control) and 6.5% (beta) of de novo synthesized Sat PC labeled with 3H-palmitate from Day 5 to Day 6. These preterm baboons had high estimated Sat PC synthetic and net tissue accumulation rates but low secretion of Sat PC. The large aggregate surfactant fractions from the preterm baboons had high minimal surface tensions and were less effective when used to treat surfactant-deficient preterm rabbits than surfactant from newborn or adult baboons. Ventilation of the preterm baboon was associated with surfactant functional and metabolic abnormalities that were not altered by antenatal glucocorticoids.