Surfactant for the treatment of respiratory distress syndrome

A multicenter randomized masked comparison trial of synthetic surfactant versus calf lung surfactant extract in the prevention of neonatal respiratory distress syndrome

OBJECTIVE

To compare the efficacy and safety of a synthetic surfactant (Exosurf Neonatal, Burroughs Wellcome Co) and a surfactant extract of calf lung lavage (Infasurf, IND #27,169, ONY, Inc) in the prevention of neonatal respiratory distress syndrome (RDS).

DESIGN AND SETTING

Ten-center randomized masked comparison trial.

PATIENTS

Premature infants (n = 871) <29 weeks gestational age by best obstetric estimate.

INTERVENTIONS

Infants were randomly assigned to a course of treatment with Exosurf Neonatal (n = 438) or Infasurf (n = 433) at birth, and if still intubated, at 12 and 24 hours of age. Crossover treatment was allowed within 72 hours of age if severe respiratory failure (defined as two consecutive a/A PO2 ratios </=.10) persisted after three doses of the randomized surfactant.

PRIMARY OUTCOME MEASURES

Three primary outcome measures of efficacy [the incidence of RDS; the incidence of RDS death; and the incidence of survival without bronchopulmonary dysplasia at 28 days after birth] were compared using linear regression techniques.

RESULTS

Of 871 randomized infants, 18 infants did not receive treatment with a study surfactant, and 25 infants did not meet all eligibility criteria. The primary analysis of efficacy was performed in the 846 eligible infants and analysis of safety outcomes in the 853 infants who received study surfactant. Demographic characteristics did not differ between the two treatment groups. Compared with Exosurf, Infasurf treatment resulted in a 62% decrease in the incidence of RDS (Infasurf, 16% vs Exosurf, 42%) and a 70% decrease in RDS death (Infasurf, 1.7% vs Exosurf, 5.4%) but did not increase the incidence of survival without bronchopulmonary dysplasia at 28 days. Treatment with Infasurf resulted in significant improvement in several secondary outcome measures. Infasurf-treated infants had lower average FIO2 (Infasurf, .33 [SEM] vs Exosurf, .42; difference .08; 95% confidence interval [CI], .06 to .11) and average mean airway pressure (Infasurf, 6.0 cm H2O vs Exosurf, 7.1 cm H2O; difference 1.1 cm H2O; 95% CI, .7 to 1.6 cm H2O) for the first 72 hours of life. Crossover surfactant treatment was significantly less frequent in the Infasurf compared with the Exosurf group (Infasurf, 1% vs Exosurf, 6%). Complications (bradycardia, clinical airway obstruction, and transcutaneous arterial desaturation) associated with second and third, but not initial, surfactant treatments were observed more frequently in the Infasurf treatment group. Infasurf-treated infants had significantly less air leak (</=7 days) (Infasurf, 8% vs Exosurf, 14%; adjusted relative risk [ARR] .55; 95% CI, .37 to .81). Severe intraventricular hemorrhage (IVH) (grade 3 and 4) did not differ between the two groups (Infasurf, 11.8% vs Exosurf, 8.3%; ARR 1.41; 95% CI, .94 to 2.09) but total IVH occurred more frequently in Infasurf-treated infants (Infasurf, 39.0% vs Exosurf, 29.9%; ARR, 1.30; 95% CI, 1.08 to 1.57).

CONCLUSION

Significant reductions in the incidence of RDS, the severity of early respiratory disease, the incidence of pulmonary air leaks associated with RDS, and the mortality attributable to RDS suggest that Infasurf is a more effective surfactant preparation than Exosurf Neonatal in the prophylaxis of RDS. However, Infasurf prophylaxis as used in this study was also associated with a greater risk of total but not severe IVH.

Surfactant inhibition by plasma: gestational age and surfactant treatment effects in preterm lambs

The preterm infant with respiratory distress syndrome has edematous lungs and small amounts of surfactant that do not function normally. We reported that surfactant recovered from preterm lambs after surfactant treatment can have decreased sensitivity to inhibition of surface tension by plasma. We asked whether this augmented resistance to inhibition was dependent on lung development (gestational age) by testing sensitivity to plasma inhibition of 1) endogenous surfactant from preterm lambs and 2) surfactant from preterm lambs after treatment with an organic solvent-extracted natural sheep surfactant. Surfactant recovered after surfactant treatment of 121- or 128-days-gestation lambs had the same sensitivity to plasma inhibition as did the surfactant used to treat the lambs. Surfactant recovered from 134-days-gestation lambs had decreased sensitivity to inhibition. Lung maturation is a variable influencing surfactant inhibition by plasma.

Influence of bilirubin on surface tension properties of lung surfactant

AIM

To investigate the influence of bilirubin on the surface tension activity of a porcine derived (Curosurf) and synthetic (Exosurf) surfactant.

METHODS

The captive bubble surfactometer at phospholipid doses of 0.5 mg/ml (low dose) and 1 mg/ml (high dose) in solutions of increasing bilirubin concentrations (0.25, 0.5, and 1.0 mg/ml) was used.

RESULTS

Curosurf (without bilirubin) showed a higher surface f1p4ion activity than Exosurf, as shown by area compression of 30 (SD 0.6)% compared with 76(1.4)% at low surfactant dose and 25 (0.9)% compared with 85 (0.5)% at high dose (P < 0.01). Bilirubin showed negligible surface activity at the concentrations studied. At low phospholipid dose (0.5 mg/ml Curosurf), bilirubin increased film area compression of lipid extract surfactant from 30 (0.6)% to 55 (1.6)%, 59 (0.1)%, and 68 (0.5)% at the three studied bilirubin concentrations, respectively (P < 0.01). At high phospholipid dose (1 mg/ml Curosurf), bilirubin had the same adverse, although less pronounced, effect on film area compression of porcine lipid extract surfactant (25 (0.9)% vs 26 (0.9)%, 39 (1.3)%, and 44 (1.1)%, respectively) (P < 0.01). Using synthetic surfactant (Exosurf), with a much lower original surface activity, bilirubin did not further inhibit its surface tension properties at any of the phospholipid doses studied.

CONCLUSION

These results indicate that in vitro bilirubin impairs the surface tension activity of porcine lipid extract surfactant, but does not affect synthetic surfactant activity.

Pulmonary hemorrhage: a novel complication after extracorporeal life support

Pulmonary hemorrhage (PH) occurs infrequently as a complication in neonates with respiratory failure. Major PH has been observed at the authors' institution in several neonates after "successful" completion of extracorporeal life support (ECLS) therapy. The authors sought to determine the incidence of PH and the risk factors associated with this unique and newly described morbidity after ECLS. The hospital records of all patients who had PH after ECLS were reviewed. The control patients were the first three infants who underwent ECLS just before each PH case. PH was defined as the occurrence of bloody tracheal secretions associated with a deterioration in pulmonary status. Demographics, ventilator/ECLS parameters, fluid management, coagulation, and laboratory studies were evaluated in the pre-ECLS, during ECLS, and in the post-ECLS period. From 1985 to 1993, 13 (6%) of 214 neonates suffered major PH, at a mean time of 43.2 +/- 9.2 hours after the ECLS course. The overall mortality rate for children with PH was 38%, compared with 5% among the control patients. In the pre-ECLS phase, patients with PH required more fluid (153.6 +/- 20.2 mL/kg/d v 106.8 +/- 10.2 mL/kg/d) and were acidemic for a longer period (2.3 +/- 1.2 hours v 0.6 +/- 0.2 hours; pH < 7.25). No differences were noted in AaDo2 or oxygenation index criteria. During ECLS, inotropes were required more often (23% v 0%; P < .01) because hypotension was more common (77% v 33%; P < .05). Activated clotting times (ACT) and heparin requirements were equivalent for the two groups. After ECLS the patients with PH required longer ventilatory assistance (184.9 +/- 48.2 hours v 83.4 +/- 16.7 hours) and supplemental oxygen (24.3 +/- 3.0 days v 17.2 +/- 1.9 days). No coagulation abnormalities were identified at the time of PH. Higher SGPT (185.4 +/- 146.4 U/L v 22.6 +/- 3.5 U/L; P < .05) and BUN (69.3 +/- 7.5 mg/dL v 47.2 +/- 5.9 mg/dL; P < .05) also were noted for the patients with PH. PH represents an important and novel morbidity in neonates after ECLS. Prolonged acidosis, a high fluid requirement before ECLS, the need for blood pressure support during ECLS, and evidence of renal and/or hepatic dysfunction serve to identify patients who have a high risk for the development of this complication.

Appropriate surfactant usage in 1996

Surfactant therapy has been proven effective in the prevention and treatment of respiratory distress syndrome. Over 6,000 infants have been studied in randomized controlled trials. These studies have demonstrated that both prophylactic administration of surfactant and administration of surfactant to premature infants with established respiratory distress syndrome will decrease the risk of pneumothorax and decrease the risk of mortality. Currently, over 50% of very low birth weight infants in North America receive some sort of surfactant preparation. However, many questions remain regarding optimal usage of surfactant preparations. Recent randomized controlled trials have evaluated issues regarding surfactant dosage, treatment strategy, method of administration, and surfactant preparation. Initial doses in the range of 100-200 mg/kg with repeat doses to selected infants who relapse appears to be the best approach to therapy. Prophylactic surfactant therapy leads to a small but statistically significant reduction in the risk of pneumothorax and mortality. The clinical relevance of these advantages and the cost effectiveness of this care remains under debate. A variety of methods of administration have been used in randomized controlled trials. Trials which compare these methods of administration demonstrate the adequacy of currently tested bolus administration. However, other methods of administration, such as slow infusion of surfactant leads to uneven distribution of surfactant and poor response. Both synthetic surfactants and natural surfactant extracts have been proven effective in the care of these infants. However, randomized controlled trials which directly compare these two preparations demonstrate a small advantage to the use of natural surfactant extracts. Natural surfactant extracts improve initial ventilatory status and decrease the risk of pneumothorax. Surfactant replacement therapy has proven to be effective in the treatment of very low birth weight premature infants. Current clinical trials support the early institution of treatment either prophylactically or as soon as possible in intubated babies with signs of respiratory distress syndrome. Repeat treatment may be important in optimizing outcome due to surfactant inactivation. Currently available natural surfactant extracts improve early clinical outcome and decrease pneumothorax compared to the available synthetic preparations.

Exogenous pulmonary surfactant as a drug delivering agent: influence of antibiotics on surfactant activity

1. It has been proposed to use exogenous pulmonary surfactant as a drug delivery system for antibiotics to the alveolar compartment of the lung. Little, however, is known about interactions between pulmonary surfactant and antimicrobial agents. This study investigated the activity of a bovine pulmonary surfactant after mixture with amphotericin B, amoxicillin, ceftazidime, pentamidine or tobramycin. 2. Surfactant (1 mg ml-1 in vitro and 40 mg ml-1 in vivo) was mixed with 0.375 mg ml-1 amphotericin B, 50 mg ml-1 amoxicillin, 37.5 mg ml-1 ceftazidime, 1 mg ml-1 pentamidine and 2.5 mg ml-1 tobramycin. Minimal surface tension of 50 microliters of the mixtures was measured in vitro by use of the Wilhelmy balance. In vivo surfactant activity was evaluated by its capacity to restore gas exchange in an established rat model for surfactant deficiency. 3. Surfactant deficiency was induced in ventilated rats by repeated lavage of the lung with warm saline until PaO2 dropped below 80 cmH2O with 100% inspired oxygen at standard ventilation settings. Subsequently an antibiotic-surfactant mixture, saline, air, or surfactant alone was instilled intratracheally (4 ml kg-1 volume, n = 6 per treatment) and blood gas values were measured 5, 30, 60, 90 and 120 min after instillation. 4. The results showed that minimal surface tensions of the mixtures were comparable to that of surfactant alone. In vivo PaO2 levels in the animals receiving ceftazidime-surfactant or pentamidine-surfactant were unchanged when compared to the surfactant group. PaO2 levels in animals receiving amphotericin B-surfactant, amoxicillin-surfactant or tobramycin-surfactant were significantly decreased compared to the surfactant group. For tobramycin it was further found that PaO2 levels were not affected when 0.2 M NaHCO3 (pH = 8.3) buffer was used for suspending surfactant instead of saline. 5. It is concluded that some antibiotics affect the in vivo activity of a bovine pulmonary surfactant. Therefore, before using surfactant-antibiotic mixtures in clinical trials, interactions between the two agents should be carefully evaluated.

Surfactant replacement therapy for adult respiratory distress syndrome in children

Surfactant replacement therapy may have a role in the treatment of ARDS in children. The current studies suggest that rapid instillation of exogenous surfactant is more effective than slow tracheal instillation or aerosolized delivery. Studies suggest that exogenous surfactant given early in the development of ARDS is more effective than therapy provided late in the course of the disease. Natural surfactants appear to be more effective than artificial surfactants due to the presence of SP-B and SP-C, which prevent inhibition of the exogenous surfactant by the protein leakage into the alveolus that is characteristic of ARDS. Exogenous surfactant replacement therapy appears to be safe and well tolerated. A surfactant that can be delivered by aerosol would be useful since this is more easily tolerated by the patients, requires less surfactant, and would be more cost effective when compared with tracheal instillation. Aerosolized surfactant could be given to patients who have not yet required mechanical ventilation, thus potentially preventing the progression of the acute lung injury to respiratory failure. The recent failure of a large multi-center trial of aerosolized Exosurf for the treatment of sepsis-related ARDS72 may have been due to the failure of the delivery system as opposed to the surfactant used in the trial; therefore, further research into aerosol delivery systems is needed. There may be different responses to exogenous surfactant therapy by patients with ARDS of different etiologies, such as aspiration pneumonia, sepsis, or trauma. Well-planned placebo-controlled trials will be required to determine these differences. The data supporting the role of surfactant replacement for the treatment of ARDS in children is growing. However, before widespread use of surfactant is considered, a multi-center, placebo-controlled trial will be required to establish the safety and efficacy of surfactant replacement in such patients.

A multicenter randomized, masked comparison trial of natural versus synthetic surfactant for the treatment of respiratory distress syndrome

OBJECTIVE

To compare the efficacy and safety of two surfactant preparations in the treatment of respiratory distress syndrome (RDS).

METHODS

We conducted a randomized, masked comparison trial at 21 centers. Infants with RDS who were undergoing mechanical ventilation were eligible for treatment with two doses of either a synthetic (Exosurf) or natural (Infasurf) surfactant if the ratio of arterial to alveolar partial pressure of oxygen was less than or equal to 0.22. Crossover treatment was allowed within 96 hours of age if severe respiratory failure (defined as two consecutive arterial/alveolar oxygen tension ratios < or = 0.10) persisted after two doses of the randomly assigned surfactant. Four primary outcome measures of efficacy (the incidence of pulmonary air leak (< or = 7 days); the severity of RDS; the incidence of death from RDS; and the incidence of survival without bronchopulmonary dysplasia (BPD) at 28 days after birth) were compared by means of linear regression techniques.

RESULTS

The primary analysis of efficacy was performed in 1033 eligible infants and an analysis of safety outcomes in the 1126 infants who received study surfactant. Preentry demographic characteristics and respiratory status were similar for the two treatment groups, except for a small but significant difference in mean gestational age (0.5 week) that favored the infasurf treatment group. Pulmonary air leak (< or = 7 days) occurred in 21% of Exosurf- and 11% of infasurf-treated infants (adjusted relative risk, 0.53; 95% confidence interval, 0.40 to 0.71; p < or = 0.0001). During the 72 hours after the initial surfactant treatment, the average fraction of inspired oxygen (+/-SEM) was 0.47 +/- 0.01 for Exosurf- and 0.39 +/- 0.01 for infasurf-treated infants (difference, 0.08; 95% confidence interval, 0.06 to 0.10; p < 0.0001); the average mean airway pressure (+/-SEM) was 8.6 +/- 0.1 cm H2O; for Exosurf- and 7.2 +/- 0.1 cm H2O for Infasurf-treated infants (difference, 1.4 cm H2O; 95% confidence interval, 1.0 to 1.8 cm H2O; p < 0.0001). The incidences of RDS-related death, total respiratory death, death to discharge, and survival without bronchopulmonary dysplasia at 28 days after birth did not differ. The number of days of more than 30% inspired oxygen and of assisted ventilation, but not the duration of hospitalization, were significantly lower in Infasurf-treated infants.

CONCLUSION

Compared with Exosurf, Infasurf provided more effective therapy for RDS as assessed by significant reductions in the severity of respiratory disease and in the incidence of air leak complications.

Developmental regulation of phospholipid secretion by fetal type II pneumocytes

Surfactant sufficiency is dependent upon adequate synthesis and secretion of surfactant by the type II alveolar epithelium. Our laboratory has previously shown that basal secretion of surfactant phospholipid by differentiated fetal type II cells is lower than the basal secretion by adult cells. The purposes of this study were to determine if undifferentiated fetal type II cells can secrete phosphatidylcholine, to determine if terbutaline, a beta-adrenergic agonist, stimulates secretion of surfactant phospholipids by undifferentiated fetal cells and to examine the effects of differentiation on secretion of surfactant phospholipids by fetal cells. Constitutive (basal) secretion of phosphatidylcholine increased linearly as a function of time in both undifferentiated and differentiated cells, but the rate of secretion was greater in differentiated cells than the rate of secretion in undifferentiated cells. Terbutaline caused a concentration-dependent increase in secretion in both undifferentiated and differentiated cells. Maximal effective concentration and EC50 were similar for undifferentiated (10(-6) M, 0.2 microM) and differentiated (10(-5) M, 0.3 microM) cells. The relative stimulation of secretion above control values was greater for undifferentiated cells. The kinetics of terbutaline stimulation varied significantly with cellular differentiation. Terbutaline resulted in 230% stimulation of secretion in undifferentiated cells at 30 min followed by a decline in the response to terbutaline at 60 to 120 min. In contrast, terbutaline stimulated secretion by differentiated cells showed a sustained linear increase from 0 to 120 min. This regulation of stimulated secretion is not present in undifferentiated cells. We conclude that undifferentiated type II cells are capable of the secretion of phosphatidylcholine and that terbutaline stimulates secretion by undifferentiated cells. Furthermore, basal secretion increases as a function of differentiation of type II cells and the regulation of stimulated secretion seen in differentiated cells is not developed in undifferentiated cells. The developmental regulation of the secretion of surfactant is complex and probably involves both excitatory as well as inhibitory mechanisms which develop at different stages of differentiation of the type II cell.

Glutathione metabolism in newborns: evidence for glutathione deficiency in plasma, bronchoalveolar lavage fluid, and lymphocytes in prematures

Respiratory distress in premature newborns is associated with deficiency of surfactant in the bronchoalveolar lining fluid; this may be influenced by a local deficiency of antioxidants. Severe L-buthionine-S,R-sulfoximine-induced depletion of glutathione (GSH, a major antioxidant) in rodents is associated with lung type 2 cell lamellar body damage and decreased concentrations in lung and bronchoalveolar lavage fluid (BALF) of phosphatidyl choline (a major component of surfactant). At birth, prematurely born newborns (30-34 weeks) had lower peripheral venous plasma GSH concentrations than term (> 36 weeks) babies; these levels decreased further with increasing prematurity (< 27 weeks, with respiratory distress). On day 2, the peripheral venous plasma GSH concentrations reached a nadir, and the lowest levels were found in the most premature newborns. Lymphocyte GSH concentrations were lowest on day 2 and day 7, and in prematures (< 27 weeks, with respiratory distress) remained below adult lymphocyte GSH levels for at least 4 weeks. At birth, prematures (< 27 weeks, with respiratory distress) had a central plasma arterio-venous (A-V) GSH gradient across the lung (an estimate of lung uptake of GSH) of 0.72 +/- 0.15 (mean +/- SD) mumol/L; on day 2, the A-V gradient did not change significantly (0.49 +/- 0.09 mumol/L). At birth, these prematures had markedly decreased BALF GSH concentrations (compared with adult levels), and they were not significantly changed during the first 4 weeks of life. These results suggest that GSH deficiency is present in prematures and that it increases with the degree of prematurity. At birth, GSH deficiency will compromise the lungs' defense against oxidative stress injury. Oxidative stress is likely to increase if hyperoxic treatment is given for respiratory distress in these infants.

Outcome at 1-year adjusted age of 957 infants weighing more than 1250 grams with respiratory distress syndrome randomized to receive synthetic surfactant or air placebo. American and Canadian Exosurf Neonatal Study Groups

This study determined outcomes at 12-months adjusted age of 957 infants weighing more than 1250 gm at birth who were subjects in a randomized, double-blind, controlled trial of synthetic surfactant or air placebo administered in a rescue trial at 23 hospitals in the United States and 13 hospitals in Canada. Follow-up results were available for 475 of 563 surviving infants who received air placebo (84%) and 482 of 571 infants who received synthetic surfactant (84%). Developmental outcome was equivalent in the two groups. Morbidity was less in the synthetic surfactant group as assessed by the need for medication for chronic lung disease (52 of 475 (11%) for the air placebo group vs 32 of 482 (7%) for the synthetic surfactant group) or respiratory support (10 of 475 (2%) for the air placebo group vs 1 of 482 (< 1%) for the synthetic surfactant group) at 1-year adjusted age. Bayley Scales of Infant Development (mental development Index: 102 for both the air placebo and synthetic surfactant groups; psychomotor development index: 95 for the air placebo group vs 94 for the synthetic surfactant group) and impairment rates (94 of 475 (20%) for the air placebo group vs 86 of 482 (18%) for the synthetic surfactant group) were similar in the two groups. Infants weighing more than 1250 gm who have respiratory distress syndrome have previously been shown to have improved survival rates and lower neonatal morbidity after treatment with synthetic surfactant. These follow-up data confirm that developmental outcome as determined at 12-months adjusted age is at least as good in those receiving synthetic surfactant.

Association of surfactant protein C with isolated alveolar type II cells

Surfactant protein C (SP-C) is a small hydrophobic protein that is synthesized and secreted by alveolar type II cells. The mechanism of clearance of SP-C from the alveolar airspace is not well understood, although previous studies demonstrated that recombinant SP-C instilled into the lungs of spontaneously breathing anaesthetized rats was taken up by type II cells and incorporated into lamellar bodies. The current investigation was undertaken to characterize the interaction of a complex of SP-C and surfactant-like lipids with freshly isolated rat alveolar type II cells under conditions in which the extracellular milieu can be regulated. SP-C was isolated from alveolar proteinosis lavage fluid and radiolabeled with 125I-Bolton-Hunter reagent. The radiolabeled protein retained its ability to facilitate adsorption of phospholipids to an air/liquid interface. Labeled human SP-C associated with isolated type II cells in a concentration-dependent manner that was also dependent upon temperature and time. The association of labeled SP-C with isolated type II cells did not saturate up to 150 micrograms/ml. SP-A significantly enhanced the association of SP-C with isolated type II cells. Under the experimental conditions tested, SP-C was not degraded to TCA-soluble products. These results are consistent with the hypothesis that association or uptake of SP-C by type II cells may be enhanced by SP-A and that like SP-A, SP-C is recycled by type II cells.

Mechanisms of bilirubin toxicity

Possible mechanisms of bilirubin toxicity on the brain and lung were studied in animal experiments and in vitro. The uptake of tyrosine as precursor of dopamine in rat synaptosomes was evaluated to study the role of different bilirubin concentrations on synaptic neurotransmission. The results of this study show a statistically significant correlation between bilirubin levels and tyrosine uptake, supporting the hypothesis that the effect of bilirubin on neuronal excitability is dose-dependent. Concerning bilirubin toxicity on the lung, we studied the effect of different bilirubin concentrations on surface activity of modified natural surfactant (Curosurf) and synthetic surfactant (Exosurf), both in current clinical use for treatment of neonatal respiratory distress syndrome. Surface activity of Curosurf and Exosurf was investigated with the captive bubble surfactometer. The results of this study show that bilirubin impairs, in vitro, the surface tension activity of natural surfactant in a dose dependent manner and has no effect on surface tension activity of artificial surfactant. These data suggest that bilirubin interferes with surfactant proteins SP-B and/or SP-C, thus impairing surfactant activity at the air-liquid interface. We conclude that bilirubin shows its toxic effect reacting with different biological systems in a dose-dependent fashion.

Biomimetic pulmonary surfactants

Considerable progress has been made in the development of defined mixtures of proteins or peptides with phospholipids which mimic the activity of natural pulmonary surfactants. Several of these biomimetic surfactants are active in animal models and clinical syndromes of surfactant deficiency. This review summarizes the structure and composition of natural surfactants and the development of defined mixtures of peptides and lipids that may be useful in the treatment of respiratory distress.

Pulmonary mechanics in ventilated preterm infants with respiratory distress syndrome after exogenous surfactant administration: a comparison between two surfactant preparations

The effects of two surfactant preparations on lung mechanics have been studied on 24 ventilated premature infants with respiratory distress syndrome (RDS): 13 were given artificial surfactant (Exosurf Neonatal, Burroughs-Wellcome) and 11 natural porcine surfactant (Curosurf, Laboratoire Serono France). Measurements of respiratory system compliance (Cdyn, Crs) and resistance (Rrs) were performed immediately before surfactant administration and repeated 6, 18, 24, 48, and 72 hours later. With Exosurf treatment, 6 hours after surfactant administration inhaled O2 concentration (FlO2) could be lowered from (0.72 +/- 0.20, to 0.62 +/- 0.33; P < 0.05), whereas Crs did not change (0.37 mL/cmH2O/kg, +/- 0.14 vs. 0.39 +/- 0.12, NS). After 24 hours and during the following days a significant increase in Crs occurred (24 hours post-Exosurf: 0.51 +/- 0.18, P < 0.05). With Curosurf treatment, the improvement in oxygenation was greater and FlO2 could be lowered much more after 6 hours (from FlO2, 0.78 +/- 0.23 to 0.34 +/- 0.11, P < 0.01). This was associated with an increase in Crs (from 0.39 +/- 0.09 to 0.59 +/- 0.17, P < 0.05). During the following days, Crs was significantly higher in the group treated with Curosurf. Resistance was not altered by the type of surfactant preparation used except after 72 hours, when Rrs increased in the group treated with Exosurf. In conclusion, Curosurf appears to be more effective than Exosurf with regard to immediate pulmonary changes in ventilator treated premature infants with RDS. A rapid increase in Crs after Curosurf treatment indicates that recruitment of new functional areas of the lung is likely to be associated with a stabilization of small airways and alveolar units.

A conformation transition of lung surfactant lipids probably involved in respiration

X-ray scattering and freeze-fracture electron microscopy of a lung surfactant extract show the existence of a complex lamellar phase, L gamma, over a wide range of concentrations and temperatures. This lamellar phase, which consists of two bilayer motifs comprised of monolayers with stiff chains alternating with monolayers with disordered chains, allows us to propose a structural model of a collapse phase at the alveolar pulmonary interface. This model accounts for the increase in surface pressure during the compression as well as the easy respreading upon expansion of the interface during the respiratory cycle.

Host defence capacities of pulmonary surfactant: evidence for 'non-surfactant' functions of the surfactant system

The most well characterized function of pulmonary surfactant is its ability to reduce surface tension at the alveolar air-liquid interface, thereby preventing lung collapse. However, several lines of evidence suggest that surfactant may also have 'non-surfactant' functions: specific components of surfactant (proteins and phospholipids) may interact with different alveolar cells, inhaled particles and micro-organisms modulating pulmonary host defence systems. SP-A, the most abundant surfactant protein, binds to alveolar macrophages via a specific surface receptor with high affinity [128]. Such binding effects the release of reactive oxygen species from resident alveolar macrophages if SP-A is properly presented to the target cell. SP-A also stimulates chemotaxis of alveolar macrophages [142], and serves as an opsonin in the phagocytosis of herpes simplex virus [161] Candida tropicalis [138] and various bacteria [137]. In addition, SP-A enhances the uptake of particles by monocytes and culture-derived macrophages [140] and improves bacterial killing. SP-D, another hydrophobic surfactant-associated protein, might interact with alveolar macrophages as well, stimulating the release of oxygen radicals [148], while for the hydrophilic surfactant proteins SP-B and SP-C no macrophage interactions have been described so far. SP-A and SP-D are members of the so-called 'collectins', pattern recognition molecules involved in first line defence. While some surfactant proteins appear to stimulate certain macrophage defence functions, surfactant phospholipids seem to inhibit those of lymphocytes. Suppressed lymphocyte functions include lymphoproliferation in response to mitogens and alloantigens, B cell immunoglobulin production and natural killer cell cytotoxicity. Concerning surfactant's phospholipid composition phosphatidylglycerol is more suppressive than phosphatidylcholine on a molar basis [38]. Bovine surfactant has an immunosuppressive effect on the development of hypersensitivity pneumonitis in a guinea pig model [150]. Despite these interesting observations, several important questions concerning the interactions of surfactant components with pulmonary host defence systems remain unanswered. Sufficient host defence in the lungs works through various humoral-cellular systems in conjunction with the specific anatomy of the airways and the gas exchange surface--how does the surfactant system fit into this network? Surfactant and alveolar cells are both altered during lung injury--is there a relationship between alveolar cells from RDS patients and the endogenous surfactant isolated from such patients? How does exogenous surfactant as used for substitution therapy modulate the defence system of the host? Some of those artificial surfactants have been shown to inhibit the endotoxin-alveolar macrophages, PMNs and monocytes including IL-1, IL-6 and TNF [139,152].(ABSTRACT TRUNCATED AT 400 WORDS)

Surfactant replacement therapy in late-stage adult respiratory distress syndrome

In four adult patients with late-stage acute respiratory distress syndrome (ARDS), a single dose of the artificial surfactant ALEC was given by intrabronchial instillation. There was no sustained clinical improvement, but bronchoalveolar lavage measurements indicated that phosphatidylcholine (PC) at 24 h after treatment had increased up to 4.4 fold and phosphatidylglycerol up to 34.7 fold. However, PC relative to total phospholipid remained below normal, and protein contamination relative to PC remained above normal. Thus, therapeutic formulations and regimens to achieve greater and more sustained supplementation of PC may be required in patients with late-stage ARDS.

Role of alveolar type II cells and of surfactant-associated protein C mRNA levels in the pathogenesis of respiratory distress in mink kits infected with Aleutian mink disease parvovirus

Neonatal mink kits infected with Aleutian mink disease parvovirus (ADV) develop an acute interstitial pneumonia with clinical symptoms and pathological lesions that resemble those seen in preterm human infants with respiratory distress syndrome and in human adults with adult respiratory distress syndrome. We have previously suggested that ADV replicates in the alveolar type II epithelial cells of the lung. By using double in situ hybridization, with the simultaneous use of a probe to detect ADV replication and a probe to demonstrate alveolar type II cells, we now confirm this hypothesis. Furthermore, Northern (RNA) blot hybridization showed that the infection caused a significant decrease of surfactant-associated protein C mRNA produced by the alveolar type II cells. We therefore suggest that the severe clinical symptoms and pathological changes characterized by hyaline membrane formation observed in ADV-infected mink kits are caused by a dysfunction of alveolar surfactant similar to that observed in respiratory distress syndrome in preterm infants. However, in the infected mink kits the dysfunction is due to the replication of ADV in the lungs, whereas the dysfunction of surfactant in preterm infants is due to lung immaturity.

Extensive intraalveolar pulmonary hemorrhage in infants dying after surfactant therapy

To assess the possible relationship between exogenous surfactant therapy and pulmonary hemorrhage in premature infants, we compared autopsy findings in 15 infants treated with exogenous surfactant and in 29 who died before the introduction of surfactant therapy. Infants who met the following criteria were included: birth weight 501 to 1500 gm, survival 4 hours to 7 days, and no congenital anomalies. Average birth weight, gestational age, and age at death were equivalent for the two groups. High rates of pulmonary hemorrhage were present in both groups (treated 80% vs untreated 83%). The untreated group had higher incidences of interstitial hemorrhage and lung hematomas and significantly more large interstitial hemorrhages: 31% untreated versus 0% treated (p < 0.05). The overall rate of intraalveolar hemorrhage was similar in the two groups, but surfactant-treated infants were more likely to have extensive intraalveolar hemorrhage: 53% versus 14% (p < 0.05). Most surfactant-treated infants who survived more than 24 hours had extensive intraalveolar hemorrhage (8/9). Patients who had extensive intraalveolar hemorrhage, with or without prior surfactant therapy, frequently had clinically significant pulmonary hemorrhage (7/12). These findings indicate that infants who die after surfactant therapy have higher rates of a specific type of pulmonary hemorrhage--extensive intraalveolar hemorrhage.

The fate of exogenous surfactant in neonates with respiratory distress syndrome

Respiratory distress syndrome (RDS) in newborn neonates is characterised by deficient secretion of surfactant from type III alveolar cells. Administration of surfactant to airways acutely decreases the degree of respiratory failure and increases the survival rate in neonates with RDS. Clinically available surfactants are lipid extracts derived from animal lung lavage or from whole lung. Synthetic surfactants contain phospholipids or additional spreading agents. An optimal exogenous surfactant would be efficacious, nontoxic and nonimmunogenic, resistant to oxidants and proteolytic agents, widely available at reasonable cost and manufactured with little batch-to-batch variability. Surfactant has been instilled into the airways as a bolus infusion through the endotracheal tube. In addition, surfactant may be given by aerosolisation or continuous infusion into the airways. Suggested dosages range from 50 to 200 mg/kg. Exogenous surfactant is cleared from the epithelial lining fluid (ELF) mainly by alveolar epithelial cells, although alveolar macrophages and the central airways may also contribute to clearance of the drug. Only small quantities of surfactant actually enter the blood stream. A significant fraction of surfactant is taken up, processed, and secreted back into the alveolar space by type II alveolar cells. This process is termed recycling. Phosphatidylglycerol, given to small premature neonates as a component of exogenous human surfactant, has an apparent pulmonary half-life of 31 +/- 3 hours (n = 11). The apparent pulmonary half-life of the main surfactant component dipalmitoyl phosphatidylcholine is 45 hours (n = 3) and that of surfactant protein A is about 9 hours (n = 4). A relationship between the dose of exogenous surfactant and its concentration in the ELF has been demonstrated. Some neonates with RDS respond poorly to surfactant therapy. The reasons for this include insufficient levels of surfactant in the ELF, uneven distribution of exogenous surfactant, inability of exogenous surfactant to enter the metabolic pathways, inhibition of surface activity by plasma-derived proteins, or inactivation of surfactant as a result of proteases, phospholipases, or oxygen free radicals. In addition, surfactant therapy may be ineffective in neonates with respiratory failure caused by factors other than surfactant deficiency. The efficacy of exogenous surfactant can be improved by increasing the dosage of surfactant and by administration of surfactant very early in respiratory failure.

Liposomes in pulmonary applications: physicochemical considerations, pulmonary distribution and antioxidant delivery

The application of liposomes for improved drug delivery to the lung is promising. Liposome-mediated pulmonary drug delivery promotes an increase in drug retention-time in the lung and more importantly, a reduction in extrapulmonary side-effects, invariably resulting in enhanced therapeutic efficacies. The engineering of an effective liposomal drug formulation for inhalation therapy must take into consideration the leakage problem associated with the nebulization process; vesicle stability and release kinetics within the pulmonary milieu; and, the altered pharmacokinetics of the entrapped drug. The delivery of liposome-entrapped antioxidants via the tracheobronchial route has been found to be very useful in increasing the half-times of the administered agents, thus providing a sustained release effect for prolonged drug action. The entrapment in liposomes of alpha-tocopherol, an extremely insoluble but highly effective antioxidant, has been shown to be very effective in ameliorating oxidant-induced injuries in the lung. The use of bifunctional liposomes containing two antioxidants have been determined to provide excellent resistance to an oxidative challenge and appears to hold promise for improved clinical applications in antioxidant therapy.

Acute effects of a single dose of porcine surfactant on patients with the adult respiratory distress syndrome

In an attempt to restore functional surfactant to the lungs of patients with the adult respiratory distress syndrome (ARDS), we have treated six patients within the first 2 days of the onset of ARDS with a single dose of hydrophobic components of porcine surfactant. Surfactant (4 g in 50 ml) delivered via a bronchoscope in aliquots to each of the lobar bronchi was well tolerated and caused a modest transient improvement in gas exchange. No significant changes in chest radiograph or lung compliance were detected. Analysis of bronchoalveolar lavage (BAL) fluid showed no change in albumin, alpha-1-proteinase inhibitor specific activity, or cell count. Bronchoalveolar lavage phospholipid concentrations were elevated 3 h after surfactant administration relative to preadministration levels and fell by 24 h. In addition, in two patients we found reduced inhibition of surfactant function in BAL after surfactant replacement. These observations suggest a role for surfactant replacement in the treatment of patients with ARDS and support the need for continuing investigation.

Aerosolized versus instilled exogenous surfactant in a nonuniform pattern of lung injury

Previous studies have shown that the underlying patterns of lung injury influence subsequent responses to aerosolized exogenous surfactant. The purpose of this study was to compare aerosolized versus tracheally instilled surfactant in a nonuniform lung injury. Adult sheep underwent whole lung lavage with subsequent HCl instillation into the right middle lobe (RML) and lingula (LING) to create a nonuniform injury. Animals were treated with either nebulized surfactant (Neb.Surf.), tracheally instilled surfactant (Inst.Surf.), or nebulized saline (Neb. Saline). PaO2, alveolar-arterial O2 gradient (PAO2-PaO2), PaCO2, and peak inspiratory pressure (PIP) values all significantly improved during 180 min of continuous aerosolization for Neb.Surf. animals compared with pretreatment values (p < 0.01) and with the other two treatment groups (p < 0.01). Although PaO2 and (PAO2-PaO2) values improved for the Inst.Surf. group by 180 min after treatment (p < 0.05), PaCO2 and PIP values were significantly increased 30 min after surfactant instillation (p < 0.05). Neb. Saline animals had no significant changes in physiologic parameters over 180 min. Approximately 8% of the total aerosolized surfactant deposited in lung tissue was recovered from the more severely damaged RML and LING, compared with approximately 50% of the total instilled surfactant recovered from these lobes. This resulted in significantly greater percentages of the total aerosolized surfactant deposited in each of the remaining lobes compared with the percent deposition of instilled surfactant (p < 0.05). Both the underlying pattern of lung injury and the exogenous surfactant delivery technique may influence clinical responses to surfactant therapy in patients with the adult respiratory distress syndrome (ARDS).

Changes in exogenous surfactant in ventilated preterm lamb lungs

Preterm lambs were treated with either a surfactant from bovine lung (Survanta) or three synthetic surfactants (Exosurf), a 69:22:9 mixture of dipalmitoylphosphatidylcholine, phosphatidylglycerol, and palmitic acid prepared by heat annealing (Lipid Mixture 1) or with glass beads (Lipid Mixture 2). After 5 h of ventilation, large and small aggregate surfactant fractions were isolated from alveolar washes by centrifugation. SP-A was used as an indicator for the association of endogenous surfactant components with the treatment surfactants. The large aggregate fraction from Survanta-treated lambs contained more SP-A than did the fractions from the lambs treated with the other surfactants (p < 0.05). The surfactants used to treat the sheep and the large aggregate surfactants from alveolar washes increased compliances when tested in surfactant-deficient, immature rabbits, relative to that in control animals. The large aggregate fractions in alveolar washes from lambs treated with Survanta, Lipid Mixture 1, and Lipid Mixture 2 improved compliances in the preterm rabbits to a greater extent than did the surfactants used to treat the lambs. The small aggregate fractions were inactive as surfactants. The function of exogenous surfactant can be improved after exposure to the preterm lung. The improvement may result from the association of exogenous surfactant with components of endogenous surfactant.

99mTc-DTPA clearance in preterm lambs. Effect of surfactant therapy and ventilation

Surfactant therapy and high-frequency oscillatory ventilation (HFO) may minimize damage to the pulmonary epithelium of surfactant-deficient newborns. Using pulmonary clearance of insufflated, aerosolized 99mTc-DTPA (molecular weight 492) as an index of lung epithelial permeability, we examined the effects of 300 mg bovine lipid extract surfactant (S) administered at birth to preterm lambs ventilated by either HFO or conventional mechanical ventilation (CMV). Four groups of lambs, delivered by cesarean section at 129 to 133 days of gestation, were studied: (1) HFO + S, (2) CMV + S, (3) HFO, and (4) CMV. 99mTc-DTPA clearance was assessed at 2, 4, and 5.5 h after birth. Surfactant treatment improved oxygenation and lung pressure-volume relationships, with oxygenation best maintained by the combination of HFO + S. All groups had similar biexponential clearance curves at the three time points, however, and there was no significant difference in the mean rates of clearance (k) between the four groups at 2 h (k = 6.03 +/- 0.60 [SEM], 7.04 +/- 1.46, 5.67 +/- 0.91, and 7.23 +/- 0.97 %/min for Groups 1, 2, 3, and 4, respectively), 4 h (k = 6.95 +/- 0.77, 5.60 +/- 0.51, 6.39 +/- 0.64, and 6.78 +/- 1.71 %/min), and 5.5 h (k = 7.43 +/- 0.78, 6.08 +/- 0.80, 7.86 +/- 0.90, and 7.95 +/- 0.66 %/min). These data suggest that neither surfactant nor HFO significantly alters pulmonary epithelial permeability to a small radiolabeled molecule in preterm lambs.

Multicentre randomised trial comparing high and low dose surfactant regimens for the treatment of respiratory distress syndrome (the Curosurf 4 trial)

A randomised trial was conducted in 82 centres using the porcine surfactant extract, Curosurf, to compare two regimens of multiple doses to treat infants with respiratory distress syndrome and arterial to alveolar oxygen tension ratio < 0.22. Infants were randomly allocated to a low dosage group (100 mg/kg initially, with two further doses at 12 and 24 hours to a maximum cumulative total of 300 mg/kg; n = 1069) or a high dosage group (200 mg/kg initially with up to four further doses of 100 mg/kg to a maximum cumulative total of 600 mg/kg; n = 1099). There was no difference between those allocated low and high dosage in the rates of death or oxygen dependency at 28 days (51.1% v 50.8%; difference -0.3%, 95% confidence interval (CI) -4.6% to 3.9%), death before discharge (25.0% v 23.5%; difference -1.5%, 95% CI -5.1% to 2.2%), and death or oxygen dependency at the expected date of delivery (32.2% v 31.0%; difference -1.2%, 95% CI -5.2% to 2.7%). For 14 predefined secondary measures of clinical outcome there were no significant differences between the groups but the comparison of duration of supplemental oxygen > 40% did attain significance; 48.4% of babies in the low dose group needed > 40% oxygen after three days compared with 42.6% of those in the high dose group. The total amount of surfactant administered in the low dose regimen (mean 242 mg phospholipid/kg) was probably enough to replace the entire pulmonary surfactant pool. Adopting the low dose regimen would lead to considerable cost savings, with no clinically significant loss in efficacy.

Optimizing alveolar expansion prolongs the effectiveness of exogenous surfactant therapy in the adult rabbit

We evaluated four ventilator patterns after the administration of 80 mg/kg bovine lipid extract surfactant (LES) to anesthetized, paralyzed, saline-lavaged New Zealand white rabbits. Two ventilator types were compared: high frequency oscillatory ventilation (HFO) versus conventional mechanical ventilation (CMV), each at high (HI) and low (LO) end-expiratory lung volumes (EELV); n = 6, each group; treatment duration = 4 h. Target PaO2 ranges were > 350 mm Hg for groups with high EELV (i.e., HFO-HI and CMV-HI) and 70 to 100 mm Hg for those with low EELV (i.e., HFO-LO and CMV-LO). Ventilator pressures were limited to < or = 39/9 cm H2O in the CMV-HI group. Five of six CMV-HI-treated animals did not maintain target PaO2 levels. Both ventilator type and strategy influenced outcome significantly. Animals managed with HFO had higher mean arterial pressures (p = 0.004), lower mean airway pressures (Paw) (p < 0.00008) and HCO3- requirements (p < 0.02), larger inflation (p = 0.003) and deflation (p < 0.00001) respiratory system volumes at 10 cm inflation pressure, and higher lung lamellar body (p = 0.0006) and lavage fluid (p = 0.003) phospholipid quantities than did CMV-treated animals. The deflation P-V curve (p = 0.0004), lamellar body (p < 0.00001) and lavage fluid (p = 0.0002) phospholipid levels were superior after the high EELV strategy. We conclude that ventilator pattern strongly influences exogenous surfactant efficacy. Benefits arise from keeping EELV high enough to prevent atelectasis and using small (approximately 2 ml/kg) tidal volumes to prevent overdistension.(ABSTRACT TRUNCATED AT 250 WORDS)

A function of lung surfactant protein SP-B

The primary function of lung surfactant is to form monolayers at the alveolar interface capable of lowering the normal surface tension to near zero. To accomplish this process, the surfactant must be capable of maintaining a coherent, tightly packed monolayer that avoids collapse during expiration. The positively charged amino-terminal peptide SP-B1-25 of lung surfactant-specific protein SP-B increases the collapse pressure of an important component of lung surfactant, palmitic acid (PA), to nearly 70 millinewtons per meter. This alteration of the PA isotherms removes the driving force for "squeeze-out" of the fatty acids from the primarily dipalmitoylphosphatidylcholine monolayers of lung surfactant. An uncharged mutant of SP-B1-25 induced little change in the isotherms, suggesting that a specific charge interaction between the cationic peptide and the anionic lipid is responsible for the stabilization. The effect of SP-B1-25 on fatty acid isotherms is remarkably similar to that of simple poly-cations, suggesting that such polymers might be useful as components of replacement surfactants for the treatment of respiratory distress syndrome.

Corticosteroids and surfactant for prevention of neonatal RDS

Two main strategies are available for the prevention of neonatal respiratory distress syndrome (RDS) in cases of preterm delivery: antenatal administration of hormones that accelerate fetal lung maturation, and prophylactic treatment with surfactant soon after birth. The efficacy of each of these therapeutic regimens has been well documented in large randomized clinical trials, and recent data furthermore indicate that, in preterm babies with lowered risk of RDS after antenatal corticosteroid treatment, the odds for developing RDS are not further reduced by prophylactic treatment with surfactant. Corticosteroids and surfactant operate by clearly different mechanisms. The steroids stimulate (via the fibroblast-pneumonocyte factor) production of surfactant phospholipids by alveolar type II cells, enhance the expression of surfactant-associated proteins, reduce microvascular permeability, and accelerate overall structural maturation of the lungs. However, the increment in pool size of surfactant resulting from antenatal treatment with corticosteroids is trivial relative to the dose of exogenous surfactant required for successful prophylaxis at birth. Data from animal experiments indicate that antenatal corticosteroids and postnatal surfactant treatment have synergistic beneficial effects on neonatal lung function, and that these effects can be further potentiated by adding antenatal administration of thyrotrophin releasing hormone (TRH). Promising results have been obtained in recent clinical trials combining antenatal treatment with corticosteroids and TRH for prevention of RDS.

Exogenous surfactant rapidly increases PaO2 in mature rabbits with lungs that contain large amounts of saline

Neonatal respiratory distress syndrome (RDS) is characterized by a relative surfactant deficiency and air-space edema. We tested the hypothesis that exogenous surfactant would improve gas exchange in mature surfactant-replete lungs containing large amounts of saline. Healthy young rabbits weighing 550 to 1,000 g were anesthetized and tracheotomized, and they received assisted ventilation with a FlO2 = 1. Baseline PaO2 decreased when 20 ml/kg of warmed saline (n = 6) was instilled into the lung; average PaO2 was stable and remained less than 200 mm Hg during the next 180 min. When either 50 mg/kg of natural surfactant (n = 6) or lipid-extracted surfactant (LES) (n = 6) was included in the saline solution, the PaO2 was higher (p < 0.05) than in the saline-alone group. To evaluate the effect of delayed addition of the surfactant we performed six additional experiments; the PaO2 fell to 60 +/- 6.9 SEM mm Hg after saline instillation, but within 15 min of administering LES, the PaO2 increased to 246 +/- 44.1 mm Hg, and it rose to 469 +/- 29.6 mm Hg by the end of the experiment (t = 180 min). Similar ventilator settings maintained comparable PaCO2 values in untreated and surfactant-treated groups. Gravimetric lung water contents (ml/kg body weight or ml/total lung hydroxyproline content) were markedly increased, but similar, in all groups. These studies show that the increase in PaO2 after surfactant administration to mature lungs containing large amounts of saline is similar to the increase in PaO2 seen when surfactant is given to premature infants with RDS.(ABSTRACT TRUNCATED AT 250 WORDS)

Adsorption, compression and stability of surface films from natural, lipid extract and reconstituted pulmonary surfactants

A pulsating bubble surfactometer was used to study the surface activities and surface film stabilities of bovine pulmonary surfactants (10 mg/ml) and a reconstituted surfactant (10 mg/ml). Pulmonary surfactants were natural surfactant (NS), lipid extract surfactant [LES(chol)] and lipid extract surfactant without neutral lipids (LES). NS is composed of phospholipids, neutral lipids and surfactant-associated proteins (SP-A, SP-B and SP-C). Both LES(chol) and LES are organic solvent extracts of NS. LES(chol) retains all the components of NS except SP-A. Reconstituted surfactant was dipalmitoylphosphatidylcholine (DPPC): 1-palmitoyl-2-oleoyl-phosphatidylglycerol (POPG): SP-B/7:3:1%. All three pulmonary surfactants attained the equilibrium surface tension almost instantaneously at 37 degrees C. The adsorption rates of NS and LES(chol) at 24 degrees C were similar to those at 37 degrees C, while LES exhibited a lower adsorption rate at 24 degrees C. Reconstituted surfactant adsorbed slower than any of the pulmonary surfactants. Film stability was studied by recording the spontaneous increase in the pressure gradient of a static bubble at the minimum size (Rmin) once near zero surface tension was attained. The order of surface film stabilities were: reconstituted surfactant > > NS > LES > LES(chol). Surface films of NS and LES could be stabilized by prolonged pulsation, while film stability of LES(chol) was only moderately affected by pulsation. These results indicate that SP-A in NS promotes formation of some unique structure, possibly tubular myelin, which induces selective adsorption of lipids into the surface.

Rapid improvement of static compliance after surfactant treatment in preterm infants with respiratory distress syndrome

Respiratory mechanics were measured in 20 preterm infants before and in the 24-hr period after treatment with surfactant. All infants were enrolled in the rescue clinical trial with Curosurf carried out in the Neonatal Intensive Care Unit. They received a dose of 200 mg/kg lipid surfactant intratracheally after birth. Static compliance of the respiratory system (Crs) was measured by the single breath occlusion technique during both spontaneous and mechanical ventilation. Resistance of the respiratory system (Rrs) and expiratory time constant (Trs) were also measured. As early as 3 hr after surfactant administration a significant improvement of 45% in Crs measured during mechanical ventilation (CrsV) was noted (0.40 +/- 0.14 vs 0.58 +/- 0.17 mL/cm H2O/kg, P < 0.001), together with a significant improvement of the arterial/alveolar O2 tension ratio (Pa/AO2) (0.12 +/- 0.03 vs 0.30 +/- 0.16, P < 0.01). The improvement of CrsV and Pa/AO2 was confirmed 24 hr later (0.55 +/- 0.15 mL/cm H2O/kg and 0.33 +/- 0.18, respectively). A significant correlation was found between Crs and Pa/AO2 ratio (r = 0.56, P < 0.001). Time constant values were significantly higher after surfactant treatment (0.15 +/- 0.07 vs 0.09 +/- 0.03 sec; P < 0.01). Rrs remained unchanged. These data indicate that Curosurf given intratracheally after birth determines a rapid improvement of respiratory mechanics as soon as 3 hr after dosing, together with the improvement of oxygenation. From the findings obtained with the present study we show evidence that respiratory system mechanics may be a useful physiological measure to guide ventilatory strategy following surfactant therapy.

Amphipathic alpha-helical peptides based on surfactant apoprotein SP-A

Three peptides based on the putative amphipathic helical region of the major pulmonary surfactant apoprotein (SP-A) were synthesized by solid-phase techniques, mixed with DPPC and tested for efficacy as lung surfactants in an in vitro adult rat lavaged lung model. The peptides correspond to residues 81-102 (SP-A81-102) and 78-101 (SP-A78-101) of the native human sequence and an analog with increased hydrophobicity, Leu84,90SP-A78-101. Neither native sequence was effective in simple mixtures with DPPC. However, substitution of leucine residues for Asp84 and Thr90 of SP-A81-102 yielded a peptide which was active in mixtures with DPPC, restoring quasi-static lung compliance to 90% of the unlavaged value. In the absence of peptide, DPPC had no effect on the P-V curve of the lavaged lung. The activity of the Leu84,90 analog correlated with an increased amphipathic alpha-helical potential and an improvement in several predictive parameters for lipid-binding. The similarities between this active peptide and other active amphipathic alpha-helical peptides lend support to the hypothesis that amphipathic alpha-helical potential and the size of the hydrophobic face are critical for functional synthetic surfactant peptides in simple mixtures with dipalmitoylphosphatidylcholine.

99mTc-DTPA-surfactant inhalation in adult respiratory distress syndrome (ARDS): a new diagnostic-therapeutic tool

ARDS is a life-threatening pulmonary disease with a rapidly progressive decline due mainly to multi-organ failure. Death occurs in 50-75% of ARDS cases. The diagnosis and therapy should start in the first six days of this fatal disease when mortality is at its lowest level. The 99mTc-DTPA-measured pulmonary alveolar epithelial permeability (PAEP) is strikingly increased in ARDS even in comparison to heavy smokers. Furthermore, surfactant inhalation has been shown to be of therapeutic value. In five ARDS patients with increased PAEP (T0.5 = 12% pred.) 20 mg/kg of aerosolized surfactant determined a dramatic improvement in blood gases and PAEP (51.8% pred.) No patient remained dependent on ventilatory treatment.

Differential glucocorticoid regulation of the pulmonary hydrophobic surfactant proteins SP-B and SP-C

Glucocorticoids increase expression of the genes for the pulmonary surfactant-associated proteins SP-B and SP-C in fetal lung both in vivo and in vitro. To examine the mechanism of these effects, we studied induction of SP-B and SP-C mRNAs in human fetal lung cultured as explants. Both mRNA levels rose rapidly in response to 100 nM dexamethasone (Dex), with a faster response for SP-B: maximal levels of induction were achieved in < or = 12 h for SP-B (3.5-fold versus control) versus approximately 24 h for SP-C mRNA (35-fold versus control). Cycloheximide (2.5 micrograms/ml) did not affect glucocorticoid induction of SP-B mRNA but markedly decreased induction of SP-C mRNA. In control cultures, cycloheximide did not significantly reduce levels of either transcript. In nuclear run-on assays, Dex increased the rate of gene transcription for both SP-B (2.8 +/- 0.3-fold versus control, n = 4) and SP-C (10- to 30-fold). Using actinomycin D to assess mRNA stability, the t1/2 of SP-B mRNA was increased from 7.5 +/- 0.4 h to 18.8 +/- 2.9 h by Dex treatment (P < 0.05), whereas the t1/2 of SP-C mRNA was not affected (9.3 +/- 1.7 h versus 8.1 +/- 1.2 h; NS). A similar increase in SP-B mRNA t1/2 with Dex (from 6 h to 19 h) was observed in label-chase studies with [3H]uridine. We conclude that glucocorticoids regulate the hydrophobic surfactant proteins of alveolar type II cells by different mechanisms: induction of SP-B is a primary response and includes an increase in both transcription rate and mRNA stability, whereas induction of SP-C is a secondary process, requiring ongoing protein synthesis, involving increased transcription rate without a change in mRNA stability.