Hot topics in and new strategies for surfactant research.
Explore the source record for details and available documents.
Animals↗
Biomedical subjects
A H Jobe
Publications and source records attributed to A H Jobe.
Lung function in premature lambs and rabbits treated with a recombinant SP-C surfactant.
We evaluated the efficacy of a recombinant surfactant protein-C (rSP-C) surfactant in vitro and in vivo, using ventilated preterm lambs and rabbits. The surface tension measured with a Wilhelmy balance of the rSP-C surfactant was lower than the surface tension of natural sheep surfactant (containing SP-B and SP-C). The rSP-C and natural surfactants were equivalently sensitive to inhibition by plasma. Over a 5-h study period, lambs treated with 100 mg/kg rSP-C and natural surfactants at birth had similar PCO2, lung mechanics, and FRC values. Indicators of injury also were not different. In preterm rabbits ventilated with 3 cm H2O positive end-expiratory pressure (PEEP), similar compliance responses were measured for the rSP-C and natural surfactant. Large-aggregate surfactants recovered from alveolar washes of the lambs treated with rSP-C or natural surfactant retained their function when tested in preterm rabbits. In conclusion, the rSP-C surfactant was effective in preterm animals with surfactant deficiency.
Animals↗
Effects of ventilation style on surfactant metabolism and treatment response in preterm lambs.
We investigated whether the style of ventilation would influence respiratory physiology or surfactant metabolism in surfactant-treated preterm lambs. Preterm lambs were delivered at 131 +/- 1 d gestation and treated with an organic solvent extract of sheep surfactant (100 mg/kg). The lambs were randomized to ventilation peiods of 2 h, 5 h, 10 h, or 24 h, and to ventilation with a low rate (15 breaths/min) and high VT (15 ml/kg), with a high rate (50 breaths/min) and low VT (8 ml/kg), or with high-frequency oscillatory ventilation (HFOV). Gas exchange and lung volumes were similar across time and for the different ventilation styles. Saturated phosphatidylcholine (SatPC) in alveolar lavage was lower for the HFOV group than for the other ventilation groups at 10 h and 24 h. The rate of loss of surfactant protein B (SP-B) from these preterm animals' lungs was slow and not influenced by ventilation style. The percentages of surfactants in large-aggregate forms were not changed by style of ventilation, and the large-aggregate surfactants had excellent function when tested in surfactant-deficient preterm rabbits. Alveolar lavage protein was low (30 ml/kg), and tissue hyaluronan did not change with time or ventilation style. In preterm lambs ventilated without causing injury, the extreme styles of ventilation examined in the study had minimal effects on lung function, surfactant function, or surfactant metabolism.
Animals↗
Surfactant homeostasis in corticotropin-releasing hormone deficiency in adult mice.
Glucocorticoids are essential for lung maturation and pharmacologic doses of glucocorticoids increase surfactant in adult rats. Therefore, we asked if glucocorticoid deficiency in corticotropin-releasing hormone-deficient mice (CRH-/-) with very low plasma corticosterone levels would alter surfactant pool sizes and precursor incorporation into saturated phosphatidylcholine (Sat PC). Alveolar and lung tissue Sat PC pool sizes were not different for CRH-/- mice and wild-type mice. The incorporation of [3H]choline into Sat PC also was similar for the two strains of mice. Glucocorticoids are not a major regulator of surfactant homeostasis in the adult mouse.
Animals↗
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.
1,2-Dipalmitoylphosphatidylcholine↗
Surfactant protein-C in ventilated premature lamb lung.
Although surfactants containing only lipids and surfactant protein C (SP-C) or SP-C analogs can be effective for the treatment of surfactant deficiency in animal models, there is no information concerning the alveolar or lung clearance of SP-C. Because the other lipid and protein components of surfactant are cleared very slowly from the preterm lung, we hypothesized that SP-C also would be cleared slowly. Therefore, we compared the losses of iodinated native SP-C (nSP-C) and a recombinant SP-C analog (rSP-C, phenylalanines in positions 4 and 5 and isoleucine in position 32 of the human sequence) to [14C]dipalmitoylphosphatidylcholine (DPPC) after airway administration at birth of trace or treatment doses of surfactant given to preterm lambs. In preterm lambs given trace doses at 134-136 d gestation, alveolar [14C]DPPC and [125I]rSP-C decreased to 14.7% recovery for DPPC and 8.3% recovery for rSP-C after 2 h ventilation. There was no loss of [14C]DPPC from the total lungs (alveolar wash + lung tissue), and approximately 20% of the [125I]rSP-C was lost from the lungs. For 128 d gestational age lambs treated with 100-mg/kg doses of surfactants containing nSP-C or 2% rSP-C, the alveolar and total lung recoveries for [125I]nSP-C or [125I]rSP-C were equivalent to that of [14C]DPPC after 5 h ventilation. These results demonstrate that nSP-C and rSP-C have alveolar clearances and accumulations into preterm lung tissue that are similar to those of DPPC.
1,2-Dipalmitoylphosphatidylcholine↗
Fetal versus maternal and gestational age effects of repetitive antenatal glucocorticoids.
BACKGROUND: Although single courses of antenatal glucocorticoids decrease respiratory distress syndrome and mortality, repetitive courses of antenatal glucocorticoids are being given to women at risk of preterm delivery without evidence of benefit or appreciation of potential risks. OBJECTIVES: To evaluate the effects of single and repetitive antenatal glucocorticoid exposures on fetal growth and postnatal lung function in sheep. METHODS: Pregnant ewes were randomized to three protocols that included one or three doses (at 7-day intervals) of 0.5 mg/kg of betamethasone (beta) given to the ewe or fetus beginning at gestations ranging from 104 to 128 days' gestation with delivery at 125, 135, and 146 days' gestation. Postnatal assessments included measurements of gas exchange, compliance, ventilation efficiency, static lung volume, and lung tissue and alveolar wash saturated phosphatidylcholine. RESULTS: Single or repetitive maternal beta but not fetal beta caused fetal growth retardation at delivery at 125, 135, and 146 days' gestation. Single-dose fetal beta had no effect on postnatal lung function whereas single-dose maternal beta significantly increased compliance, lung volume, and tissue and alveolar surfactant after preterm delivery. Although three-dose fetal beta improved all indicators of postnatal lung function, three-dose maternal beta resulted in larger responses. The added benefits of repetitive beta relative to a single-dose beta on postnatal lung function after preterm delivery were not as great when therapy was begun later in gestation. Postnatal lung function after delivery at 146 days' gestation (term is 150 days) was improved after repetitive maternal beta at early gestational age. CONCLUSIONS: In sheep, single or repetitive maternal beta causes growth retardation from 104 to 121 days' gestation and the growth retardation persists to term. In contrast, single or repetitive fetal beta does not cause fetal growth retardation and is less potent at improving postnatal lung function and increasing surfactant pools. There are potential benefits as well as risks for the use of repetitive antenatal glucocorticoids. Randomized, controlled trials in humans are essential given the widespread use of repetitive courses of antenatal glucocorticoids in women at risk of preterm delivery. respiratory distress syndrome, maturation, prematurity, growth retardation, surfactant.
Animals↗
Rescue of SP-B knockout mice with a truncated SP-B proprotein. Function of the C-terminal propeptide.
The function of the 102-amino acid C-terminal propeptide of surfactant protein B (SP-B) was analyzed by characterizing the phenotype associated with loss of expression of this peptide domain in transgenic mice. A construct encoding the signal peptide, N-terminal propeptide, and mature peptide of human SP-B (hSP-BDeltac) was cloned under the control of the 3.7-kilobase human SP-C promoter and injected into fertilized eggs of the FVB/N mouse strain. Founder mice expressing the hSP-BDeltac transgene were bred with heterozygous SP-B knockout mice (SP-B +/-). Offspring containing the transgene and one allele of mouse SP-B were identified and subsequently crossed to generate a transgenic line that expressed SP-BDeltac in a null background (SP-B(-/-)/hSP-BDeltac(+/+)). Expression of hSP-BDeltac in SP-B(-/-) mice was restricted to type II cells and resulted in a 2-fold increase in mature SP-B relative to wild type littermates. These mice survived without any evidence of respiratory problems and had normal lung function, normal alveolar surfactant phospholipid pool sizes, and typical tubular myelin indicating that the 102-residue C-terminal propeptide of SP-B is not required for normal structure and function of extracellular surfactant. However, proteolytic processing of the SP-C proprotein was perturbed resulting in the accumulation of a processing intermediate, Mr = 11,000, similar to the phenotype detected in SP-B(-/-) mice; furthermore, lamellar bodies in type II cells of SP-B(-/-)/hSP-BDeltac(+/+) mice were much larger than in the wild type animal and saturated phosphatidylcholine content in lung tissue was significantly increased although the incorporation of choline into saturated phosphatidylcholine was normal. Collectively, these results demonstrate a role for the C-terminal propeptide of SP-B in SP-C proprotein processing and the maintenance of lamellar body size. The C-terminal propeptide may be an important determinant of intracellular surfactant pool size.
Animals↗
Preterm lung function after retreatment with antenatal betamethasone in preterm lambs.
OBJECTIVE: We hypothesized that two doses of betamethasone administered 1 week apart would further enhance postnatal pulmonary function in preterm lambs (compared with a single dose). STUDY DESIGN: Fetal sheep (121 days' gestation) randomly received saline solution or betamethasone (0.5 mg/kg) as a single injection. Six days later fetal sheep were retreated with either saline solution or corticosteroid, and postnatal lung function was evaluated 1 day later. RESULTS: Betamethasone improved compliance and ventilation efficiency index nearly 50%, and total lung volume increased twofold. No effects of treatment-to-delivery interval (1 vs 7 days) or corticosteroid retreatment on pulmonary function were apparent. Although surfactant pool sizes increased as a function of duration of exposure, no additional effect of corticosteroid retreatment was noted. Antenatal betamethasone increased messenger ribonucleic acid levels for the surfactant proteins A and C, and retreatment augmented surfactant protein B messenger ribonucleic acid levels but suppressed surfactant protein A and C messenger ribonucleic acid. CONCLUSION: Improved postnatal lung function resulting from antenatal betamethasone was not augmented by retreatment.
Animals↗
Surfactant metabolism in surfactant protein A-deficient mice.
In the present study we asked if surfactant metabolism was altered in surfactant protein (SP) A-deficient mice in vivo. Although previous studies in vitro demonstrated that SP-A modulates surfactant secretion and reuptake by type II cells, mice made SP-A deficient by homologous recombination grow and reproduce normally and have normal lung function. Alveolar and lung tissue saturated phophatidylcholine (Sat PC) pools were 50 and 26% larger, respectively, in SP-A(-/-) mice than in SP-A(+/+) mice. Radiolabeled choline and palmitate incorporation into lung Sat PC was similar both in vivo and for lung tissue slices in vitro from SP-A(+/+) and SP-A(-/-) mice. Percent secretion of radiolabeled Sat PC was unchanged from 3 to 15 h, although SP-A(-/-) mice retained more labeled Sat PC in the alveolar lavages at 48 h (consistent with the increased surfactant pool sizes). Clearance of radiolabeled dipalmitoylphosphatidylcholine and SP-B from the air spaces after intratracheal injection was similar in SP-A(-/-) and SP-A(+/+) mice. Lack of SP-A had minimal effects on the overall metabolism of Sat PC or SP-B in mice.
Animals↗
Surfactant metabolic consequences of overexpression of GM-CSF in the epithelium of GM-CSF-deficient mice.
Granulocyte macrophage colony-stimulating factor (GM-CSF) is a regulator of surfactant metabolism because GM-CSF-deficient mice have abnormally slow clearance and catabolism of saturated phosphatidylcholine (Sat PC) and surfactant protein (SP)-A in airspaces and lung tissue. Overexpression of GM-CSF only in respiratory epithelial cells of mice deficient in GM-CSF using the SP-C promotor (GM-/-,SP-C-GM+/+) resulted in increased type II cell numbers and normalization of alveolar Sat PC pool sizes. Metabolic measurements demonstrated that incorporation of radiolabeled choline and palmitate was increased more than twofold, but the amount of radiolabeled Sat PC that accumulated in airspaces relative to the amount incorporated was decreased by 50% relative to normal GM+/+ mice. The clearance of dipalmitoylphosphatidylcholine and SP-B from the airspaces was more rapid for GM-/-,SP-C-GM+/+ mice than for GM+/+ mice. Loss of Sat PC and SP-B from the lungs (alveolar plus lung tissue) was similar in the two strains of mice. The normal surfactant pools in the GM-/-,SP-C-GM+/+ mice were achieved by the net effects of increases in type II cell numbers, increased incorporation, decreased accumulation, and increased reuptake rates for surfactant components, demonstrating the multiple effects of GM-CSF on surfactant metabolism.
1,2-Dipalmitoylphosphatidylcholine↗
Pulmonary dysfunction in neonatal SP-B-deficient mice.
Pulmonary function was assessed in newborn wild-type and homozygous and heterozygous surfactant protein B (SP-B)-deficient mice after birth. SP-B +/+ and SP-B+/- mice became well oxygenated and survived postnatally. Although lung compliance was decreased slightly in the SP-B+/- mice, lung volumes and compliances were decreased markedly in homozygous SP-B-/- mice. They died rapidly after birth, failing to inflate their lungs or oxygenate. SP-B proprotein was absent in the SP-B-/- mice and was reduced in the SP-B+/- mice, as assessed by Western analysis. Surfactant protein A, surfactant proprotein C, surfactant protein D, and surfactant phospholipid content in lungs from SP-B+/- and SP-B-/- mice were not altered. Lung saturated phosphatidylcholine and precursor incorporation into saturated phosphatidylcholine were not influenced by SP-B genotype. Intratracheal administration of perfluorocarbon resulted in lung expansion, oxygenation, and prolonged survival of SP-B-/- mice and in reduced lung compliance in SP-B+/+ and SP-B+/- mice. Lack of SP-B caused respiratory failure at birth, and decreased SP-B protein was associated with reduced lung compliance. These findings demonstrate the critical role of SP-B in perinatal adaptation to air breathing.
Animals↗
Glucocorticoid regulation of surfactant components in immature lambs.
To assess effects of dose and duration of glucocorticoid exposure on maturation of the fetal lung, we administered single or multiple doses of betamethasone (0.5 mg/kg im) to pregnant sheep for 2 or 21 days before preterm delivery at 125 days of gestation. Lung function (compliance, lung volume at 40 cmH2O pressure, and ventilatory efficiency index) was increased after two to four weekly doses of glucocorticoid (2.5- to 4-fold increase) and after 48 h of exposure (1.4- to 2.3-fold). Total protein of lavage fluid decreased similarly with three doses, four doses, and 48 h of treatment. In lambs with long-term exposure to betamethasone, there was a similar, dose-dependent increase in concentrations of saturated phosphatidylcholine and surfactant proteins A (SP-A) and B (SP-B) (maximal 2- to 3-fold in tissue and 10- to 15-fold in lavage fluid). Levels of SP-A and SP-B were closely correlated in lavage fluid. In animals treated for 48 h, only tissue SP-B was increased (2.7-fold). We conclude that 48 h of glucocorticoid treatment improves lung function in the premature lamb without a detectable increase in lavage surfactant components and that longer exposure to antenatal glucocorticoid increases surfactant lipid and proteins in a coordinated fashion. The enhanced response with repetitive dosing indicates that the process of glucocorticoid-induced lung maturation is either reversible and/or gestational age dependent.
Animals↗
Preterm newborn lamb renal and cardiovascular responses after fetal or maternal antenatal betamethasone.
The optimal dose, route of administration, and treatment-to-delivery interval necessary to induce beneficial extrapulmonary effects of glucocorticoids are not known. Pregnant ewes (127 days gestation) were randomized to receive maternal or fetal intramuscular injections of betamethasone (0.2 or 0.5 mg/kg body wt) or saline 24 h before cesarean delivery of their lambs. Three hours after delivery, low-dose maternal vs. control lamb mean arterial pressure [64 +/- 4 vs. 47 +/- 2 (SE) mmHg], glomerular filtration rate (1.7 +/- 0.2 vs. 0.7 +/- 0.1 ml.min-1.kg-1), and total renal sodium reabsorption (219 +/- 31 vs. 85 +/- 12 mueq.min-1.kg-1) were increased. Comparable increases were observed in the high-dose maternal and fetal groups without effects in the low-dose fetal group. This study provides the first quantitative data demonstrating that even short-term (24-h) antenatal betamethasone exposure alters preterm newborn cardiovascular and renal functions. These responses are route and dose dependent and are comparable to glucocorticoid-induced maturational effects after longer-term antenatal exposure.
Administration, Topical↗
Postnatal lung function and protein permeability after fetal or maternal corticosteroids in preterm lambs.
We evaluated postnatal lung function and intravascular albumin loss to tissues of 123-days-gestation preterm surfactant-treated and ventilated lambs 15 h after direct fetal (n = 8) or maternal (n = 9) betamethasone treatment or saline placebo (n = 9). The betamethasone-treated groups had similar increases in dynamic compliances, ventilatory efficiency indexes, and lung volumes relative to controls (P < 0.05). The losses of 125I-labeled albumin from blood, a marker of intravascular integrity, and the recoveries of 125I-albumin in muscle and brain were similar for control and betamethasone-exposed lambs. Betamethasone-treated lambs had lower recoveries of 125I-albumin in lung tissues and in alveolar washes than did controls (P < 0.01). Although blood pressures were higher for the treated groups (P < 0.05), all groups had similar blood volumes, cardiac outputs, and organ blood flows. Maternal or fetal treatment with betamethasone 15 h before preterm delivery equivalently improved postnatal lung function, reduced albumin recoveries in lungs, and increased blood pressures. However, prenatal betamethasone had no effects on the systemic intravascular losses of albumin or did not change blood volumes.
Adrenal Cortex Hormones↗
Tidal volume effects on surfactant treatment responses with the initiation of ventilation in preterm lambs.
We hypothesized that initiation of ventilation in preterm lambs with high volumes would cause lung injury and decrease the subsequent response to surfactant treatment. Preterm lambs were randomized to ventilation for 30 min after birth with 5 ml/kg (VT5), 10 ml/kg (VT10), or 20 ml/kg (VT20) tidal volumes and then ventilated with approximately 10 ml/kg tidal volumes to achieve arterial PCO2 values of approximately 50 Torr to 6 h of age. VT20 lambs had lower compliances, lower ventilatory efficiencies, higher recoveries of protein, and lower recoveries of surfactant in alveolar lavages and in surfactant that had decreased compliances when tested in preterm rabbits than VT5 or VT10 lambs. Other lambs randomized to treatment with surfactant at birth and ventilation with 6, 12, or 20 ml/kg tidal volumes for 30 min had no indicators of lung injury. An initial tidal volume of 20 ml/kg decreased the subsequent response to surfactant treatment, an effect that was prevented with surfactant treatment at birth.
1,2-Dipalmitoylphosphatidylcholine↗
Testing surfactant treatment responses: a comparison of two models.
We have compared treatment responses of two surfactants in two animal models of respiratory distress syndrome. Preterm rabbits at 27 days gestation and premature lambs at 126 days gestation were treated with natural sheep surfactant Survanta (Ross Laboratories), or no surfactant and then were ventilated with the same ventilation style to achieve tidal volumes of 8 ml/kg. Dynamic compliances at 15 min were higher for control and surfactant-treated rabbits than for preterm lambs. Sheep surfactant and Survanta increased compliances in rabbits, but only sheep-surfactant-treated lambs had compliances higher than controls at 15 min of age. Maximal lung volumes (milliliters per kilogram) of the rabbits (after 15 min ventilation) were about twice those of the lambs (after 4 h of ventilation). Lung volumes of sheep-surfactant-treated rabbits were larger than for Survanta-treated rabbits, but no differences in lung volume were evident between the surfactant-treated lambs. The two models for testing surfactants do not give the same results when directly compared.
Analysis of Variance↗
Surfactant protein-B and lung function in surfactant-treated preterm lambs.
We asked if the amount of SP-B (range 37-410 micrograms/ml) in surfactants used to treat preterm lambs at 123 days of gestation correlated with postnatal lung function or the SP-B content of surfactant recovered by alveolar washes after 10 h ventilation. Ventilation was initiated using a low tidal volume strategy to minimize early lung injury. There were small increases in compliance for the lambs treated with surfactants containing more than 37 micrograms/ml SP-B and an increased lung volume for lambs treated with a surfactant containing 385 micrograms/ml/ml relative to the surfactant containing 37 micrograms/ml SP-B. The amount of SP-B in the surfactant used for treatment correlated linearly with the amount of SP-B in the surfactant recovered from the lambs (r = 0.95, p < 0.001). Albumin leak from the vasculature to the airspace was low as was total protein in alveolar washes, indicating minimal lung injury. The SP-B content of surfactant (from 37 to 410 micrograms/ml) had minimal effects on postnatal lung function over a 10-hour study period in lambs ventilated in a manner to minimize lung injury.
Biological Products↗