Respiratory failure in mice caused by a hybridoma making antibodies to the 15 kDa surfactant apoprotein

SP-B refining of pulmonary surfactant phospholipid films

Pulmonary surfactant stabilizes the alveoli by lining the air-fluid interface with films that reduce surface tension to near 0 mN/m (gamma(min)). Surfactant protein B (SP-B) enhances the surface activity of surfactant phospholipids. A captive bubble tensiometer (CBT) was used to study the properties of adsorbed films of dipalmitoylphosphatidylcholine (DPPC) with acidic 1-palmitoyl-2-oleoyl-sn-glycero-3-[phospho-rac-(1-glycerol)] (POPG) or neutral 1-palmitoyl-2-oleoyl-sn-glycerol-3-phosphocholine with (7:3) and without 1% dimeric SP-B. SP-B enhanced the adsorption rate of DPPC-containing neutral or acidic lipid suspensions (1 mg/ml) to a similar extent. Quasi-static cycling of these films revealed that SP-B significantly decreased the film area reduction required to reach gamma(min) for the acidic but not for the neutral system. The results obtained with DPPC-phosphatidylglycerol (PG)-SP-B were consistent with selective DPPC adsorption into the surface monolayer during film formation. Film area reduction required to reach gamma(min) with this system (with and without calcium) approached that of pure DPPC, suggesting selective DPPC insertion and PG squeeze-out. Dynamic cycling of such films showed that larger film area reductions were required to reach gamma(min) for the neutral than for acidic system, even after 20 cycles. Fluorescence microscopy of solvent-spread DPPC-POPG-SP-B planar films revealed highly condensed structures at approximately 25 mN/m, although no specific PG phase-segregated structures could be identified. The study suggests that specific interactions of SP-B with acidic phospholipids of surfactant may be involved in the generation and maintenance of DPPC-rich films in the alveoli.

Effects of surfactant proteins SP-B and SP-C on dynamic and static mechanics of immature lungs

To investigate the effects of surfactant proteins B (SP-B) and C (SP-C) on lung mechanics, we compared tidal and static lung volumes of immature rabbits anesthetized with pentobarbital sodium and given reconstituted test surfactants (RTS). With a series of RTS having various SP-B concentrations (0-0.7%) but a fixed SP-C concentration (1.4%), both the tidal volume with 25-cmH2O insufflation pressure and the static volume deflated to 5-cmH2O airway pressure increased, significantly correlating with the SP-B concentration: the former increased from 6.5 to 26.0 ml/kg (mean), and the latter increased from 6.4 to 31.8 ml/kg. With another series of RTS having a fixed SP-B concentration (0.7%) but various SP-C concentrations (0-1.4%), the tidal volume increased from 5.1 to 24.8 ml/kg, significantly correlating with the SP-C concentration, whereas the static volume increased from 3.4 to 32.0 ml/kg, the ceiling value, in the presence of a minimal concentration of SP-C (0. 18%). In conclusion, certain doses of SP-B and SP-C were indispensable for optimizing dynamic lung mechanics; the static mechanics, however, required significantly less SP-C.

Synthetic protein analogues in artificial surfactants

Today, airway instillation of surfactant preparations is a generally used treatment for respiratory distress syndrome in premature infants. Most commercially available surfactants are purified from animal lungs and contain lipids, mainly phospholipids, and about 2% of the hydrophobic surfactant proteins B and C (SP-B and SP-C). During the last half-decade the main structural properties of these proteins have been clarified and this knowledge now makes it possible to design synthetic analogues for future use in artificial surfactants.

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.

Inactivation of surfactant in rat lungs

Although surfactant replacement therapy has dramatically improved the outcome of premature infants with respiratory distress syndrome, approximately 30% of treated infants show a transient or no response. Nonresponse to surfactant replacement therapy may be due to extreme lung immaturity and possibly surfactant inactivation. Surfactant inactivation involves aspecific biophysical events, such as interference with the formation or activity of an alveolar monolayer, and specific interactions with serum proteins, including antibodies, leaking into the alveolar space. As formulations containing surfactant proteins appear to better tolerate serum inactivation, we used an excised rat lung model to compare the susceptibility to serum inactivation of a mixture of synthetic phospholipids selected from surfactant lipid constituents, Exosurf (a protein-free synthetic surfactant), Survanta [containing surfactant proteins B and C (SP-B and -C)], and a porcine surfactant (containing SP-A, -B, and -C). For each of these preparations, we used pressure/volume determinations as an in situ measure of surfactant activity and retested the same preparations after mixing with human serum, a nonspecific surfactant inactivator. Human serum inactivated porcine surfactant to a lesser extent than Survanta, Exosurf, or synthetic phospholipids. Temperature exerted a significant effect on deflation stability, as shown by a greater lung compliance in untreated, normal lungs and a larger improvement in compliance after treating lavaged lungs with synthetic phospholipids at 37 degrees C than at 22 degrees C. We conclude that surfactant containing SP-A, -B, and -C is only moderately susceptible to inactivation with whole serum and may therefore exert a greater clinical response than protein-free surfactants or those containing only SP-B and -C.

Treatment responses to surfactants containing natural surfactant proteins in preterm rabbits

The in vivo function of surfactants reconstituted using natural surfactant lipid and protein constituents was evaluated in 27-day-gestation preterm rabbits. The animals were treated with protein-free surfactant lipids (LH-20), LH-20 + 5% SP-A, LH-20 + 1% SP-B, LH-20 + 1% SP-C, LH-20 + 5% SP-A + 1% SP-B + 1% SP-C (SP-ABC), natural sheep surfactant, or 4 ml/kg 0.45% NaCl (control) and then ventilated with tidal volumes of 8 ml/kg and 3 cm H2O positive end-expiratory pressure (PEEP). Ventilatory pressures (peak pressures minus PEEP) and dynamic compliances of the LH-20 + SP-C rabbits were greater (p < 0.01) than those of control, LH-20, and LH-20 + SP-A groups but lower (p < 0.05) than in the LH-20 + SP-B, LH-20 + SP-ABC, and sheep surfactant groups. Recoveries of intravascular labeled albumin in the lungs were comparable in the LH-20 + SP-B, LH-20 + SP-C, LH-20 + SP-ABC, and sheep surfactant groups and less (p < 0.01) than in LH-20 + SP-A rabbits, which had lower (p < 0.05) recoveries than did the control and LH-20 groups. The postventilation pressure-volume curves for LH-20 + SP-B and LH-20 + SP-ABC rabbits had significantly lower opening pressures, larger maximal lung volumes, and larger retained volumes on deflation relative to the LH-20 + SP-C, LH-20, and control groups.(ABSTRACT TRUNCATED AT 250 WORDS)

Surfactant inactivation and surfactant replacement in experimental models of ARDS

Lung structure and function, and the effect of surfactant replacement, were studied in three animal models of adult respiratory distress syndrome (ARDS): surfactant depletion by repeated lung lavage, proteinaceous pulmonary edema induced by prolonged exposure to hyperoxia, and inoculation with hybridoma making an antibody to the hydrophobic surfactant-associated protein, SP-B. Surfactant replacement therapy restored normal gas exchange in respiratory failure induced by repeated lung lavage but was ineffective in animals with severe lung parenchymal lesions induced by hyperoxia or antibody to SP-B. Lung edema fluid from animals exposed to hyperoxia inhibited surfactant function in a concentration-dependent manner. These observations indicate that, in experimental ARDS, the effect of surfactant replacement depends on the type of animal model and, especially, on the degree of lung injury present at the time of therapy.