The future of exogenous surfactant therapy.

Since the identification of surfactant deficiency as the putative cause of the infant respiratory distress syndrome (RDS) by Avery and Mead in 1959, our understanding of the role of pulmonary surfactant in respiratory physiology and the pathophysiology of acute lung injury (ALI) has advanced substantially. Surfactant replacement has become routine for the prevention and treatment of infant RDS and other causes of neonatal lung injury. The role of surfactant in lung injury beyond the neonatal period, however, has proven more complex. Relative surfactant deficiency, dysfunction, and inhibition all contribute to the disturbed physiology seen in ALI and acute respiratory distress syndrome (ARDS). Consequently, exogenous surfactant, while a plausible therapy, has proven to be less effective in ALI/ARDS than in RDS, where simple deficiency is causative. This failure may relate to a number of factors, among them inadequacy of pharmaceutical surfactants, insufficient dosing or drug delivery, poor drug distribution, or simply an inability of the drug to substantially impact the underlying pathophysiology of ALI/ARDS. Both animal and human studies suggest that direct types of ALI (eg, aspiration, pneumonia) may be more responsive to surfactant therapy than indirect lung injury (eg, sepsis, pancreatitis). Animal studies are needed, however, to further clarify aspects of drug composition, timing, delivery, and dosing before additional human trials are pursued, as the results of human trials to date have been inconsistent and largely disappointing. Further study and perhaps the development of more robust pharmaceutical surfactants offer promise that exogenous surfactant will find a place in our armamentarium of treatment of ALI/ARDS in the future.

Nanostructure of the aqueous form of lung surfactant of different species visualized by cryo-transmission electron microscopy.

Cryogenic temperature transmission electron microscopy (cryo-TEM) makes it possible to study the nanostructure of a wide range of fluid phases with a high degree of preservation. Most studies based on scanning electron microscopy or TEM employ specimen preparation techniques that give extraordinary results for tissues, but alter the native structure of complex fluid substances such as lung surfactant. In this paper, we evaluated direct-imaging cryo-TEM as a method to study the morphology of the aqueous form of lung surfactant. We compared the morphology of samples obtained from different species, and cryo-TEM data to data obtained by staining-and-drying. We demonstrate that cryo-TEM preserves and images much better sample morphology and fine details of the surfactant structures. We show that cryo-TEM, a method based on physical fixation, which avoids chemical changes and aggregate rearrangement, is a most useful tool to further our understanding of lung surfactant and its function.

Surfactant for respiratory distress syndrome: are there important clinical differences among preparations?

PURPOSE OF REVIEW: Respiratory distress syndrome is the leading cause of mortality and morbidity among infants born prematurely. The disorder arises from the developmental and biochemical abnormalities associated with preterm delivery. The decreased number of type II alveolar pneumocytes results in absent or reduced surfactant production, which leads to alveolar instability and a tendency to collapse during expiration and increased work of breathing necessitating the institution of supplemental oxygen therapy and positive pressure mechanical ventilation. RECENT FINDINGS: Exogenous surfactant replacement therapy has been shown to be effective in the treatment of neonatal respiratory distress syndrome and has become a standard of care in neonatal intensive care units. A number of controversies still exist over a number of issues, however, such as the comparative effectiveness of one surfactant preparation over another, timing of administration, dosing volumes and short versus long-term benefits. Furthermore, the emergence of a newer generation of synthetic, peptide-containing surfactants has opened a new era in surfactant therapy which may have implications for future practice and research. SUMMARY: This paper discusses these developments and analyses the effectiveness of surfactant therapy against respiratory distress syndrome by appraising the evidence produced from published trials and systemic reviews.

Surfactante pulmonar / Pulmonary Surfactante

La terapia con surfactante ha constituido un importante avance en el manejo de recién nacidos prematuros con EMH. Tanto surfactantes naturales como sintéticos llevan a la mejoría clínica y disminución de la mortalidad. El uso profiláctico, después de la estabilización inicial del recién nacido, tiene beneficios sobre la terapia de rescate una vez establecida la EMH. En prematuros que no han sido tratados en forma profiláctica, la administración de rescate precoz (antes de las 2 horas) tiene beneficios sobre la terapia tardía. Los efectos adversos de esta terapia son infrecuentes y usualmente no serios. Futuras investigaciones demostrarán la utilidad de los nuevos surfactantes y la optimización del tratamiento junto con otras intervenciones respiratorias.

Effects of Stachybotrys chartarum on surfactant convertase activity in juvenile mice.

We have shown recently that alveolar type II cells are sensitive to exposure to Stachybotrys chartarum spores, both in vitro and in an in vivo juvenile mouse model. In mice, this sensitivity is manifest in part as a significant increase in the newly secreted, biologically active, heavy aggregate form of alveolar surfactant (H) and the accumulation of the lighter, "metabolically used", biologically inactive alveolar surfactant forms (L(vivo)) in the interalveolar space. Conversion of the heavy, surface-active alveolar surfactant to the light metabolically used, nonsurface active forms is believed to involve the activity of an enzyme, namely convertase, which is thought to be derived from lamellar bodies (LB) in alveolar type II cells. The purpose of this study was to evaluate the effects of S. chartarum spores on mouse H and LB convertase activity by measuring their rates of conversion to L(vivo) using the in vitro surface area cycling technique. It was determined whether there were concurrent changes in the protein and phospholipid concentrations of the raw bronchoalveolar lavage fluid (RL) and LB fractions that could be correlated with changes in convertase activity. Conversions of H to L(vivo) in untreated control mice and saline-, isosatratoxin F-, and Cladosporium cladosporioides-exposed mice were not significantly different (p > 0.05). However, conversion from H to L(vivo) in the mice exposed to S. chartarum spores was significantly higher than all other treatment groups (p < 0.001). LB to L(vivo) conversions in untreated and saline-exposed mice were not significantly different, although they were significantly higher than the H to L(vivo) conversions in these two animal treatment groups (p < 0.005), which supports the position that LB is a source of convertase activity in animals. LB to L(vivo) conversion from C. cladosporioides-, isosatrotoxin F-, and S. chartarum-exposed mice were all significantly depressed (p < 0.003) compared to the LB to L(vivo) conversion values obtained from untreated and saline-exposed mice. Protein concentrations in RL, H, L(vivo), and LB from mice exposed to S. chartarum spores were significantly elevated compared to those from the other treatment groups (p < 0.001). Protein concentration in H isolated from C. cladosporioides-exposed mice was also significantly elevated above untreated and saline control animal levels. Phospholipid concentrations in H isolated from S. chartarum-exposed mice were significantly elevated compared to those from other treatment groups, while LB phospholipid concentrations were significantly increased compared to saline and untreated control animal groups. These results show that S. chartarum spores significantly alter convertase activity in both the H and LB surfactant fractions in juvenile mice and that these changes can be related to changes in protein and phospholipid concentrations in alveolar lavage fractions. As surfactant promotes lung stability by reducing the surface tension of the air-alveolar interface, these results further support our position that inhalation exposure to S. chartarum spores in exposed individuals may lead to altered surfactant metabolism, and possibly to lung dysfunction through diminished alveolar surfactant surface tension attributes, and lung stability.

The amoebapore superfamily.

Amoebapores, synthesized by human protozoan parasites, form ion channels in target cells and artificial lipid membranes. The major pathogenic effect of these proteins is due to their cytolytic capability which results in target cell death. They comprise a coherent family and are homologous to other proteins and protein domains found in eight families. These families include in addition to the amoebapores (1) the saposins, (2) the NK-lysins and granulysins, (3) the pulmonary surfactant proteins B, (4) the acid sphingomyelinases, (5) acyloxyacyl hydrolases and (6) the aspartic proteases. These amoebapore homologues have many properties in common including membrane binding and stability. We note for the first time that a new protein, countin, from the cellular slime mold, Dictyostelium discoideum, comprises the eighth family within this superfamily. All currently sequenced members of these eight families are identified, and the structural, functional and phylogenetic properties of these proteins are discussed.

Pumactant and poractant alfa for treatment of respiratory distress syndrome in neonates born at 25-29 weeks' gestation: a randomised trial.

BACKGROUND: Exogenous surfactant preparations vary in their constitution and biophysical properties. Synthetic and animal-derived preparations lower the rate of death compared with controls. No significant differences in mortality or important long-term clinical outcomes have been shown between them in randomised trials. We did a randomised controlled trial to compare pumactant, a synthetic surfactant, with poractant alfa, an animal-derived surfactant, both of which are widely used in the UK. METHODS: We enrolled 212 neonates born between 25 weeks' and 29 weeks and 6 days' gestation who were intubated for presumed surfactant deficiency and were free from life-threatening malformations. We randomly assigned 105 neonates poractant alfa, and 107 pumactant. The primary outcome was duration of high-dependency care and mortality was a secondary outcome. Analysis was by intention to treat. FINDINGS: Outcome data were analysed for 199 babies. The trial was stopped on the recommendation of the data and safety monitoring committee because mortality assumed a greater importance than the primary outcome. Predischarge mortality differed significantly between groups, in favour of poractant alfa (14.1 vs 31.0%, p=0.006; odds ratio 0.37 [95% CI 0.18-0.76). This difference was sustained after adjustment for centre, gestation, birthweight, sex, plurality, and use of antenatal steroids. INTERPRETATION: Mortality was unexpectedly lower among neonates who received poractant alfa than among those who received pumactant, and was independent of all the variables we investigated. Stopping the trial early may have widened the difference between the treatment groups.

Local effect of lung contusion on lung surfactant composition in multiple trauma patients.

OBJECTIVE: The aim of this study was to investigate the direct influence of lung contusion on pulmonary surfactant in multiple trauma patients. DESIGN: Prospective, nonrandomized study. SETTING: University hospital, trauma intensive care unit. PATIENTS: Eighteen multiple trauma patients with unilateral lung contusions and Injury Severity Scores >19 were studied prospectively. INTERVENTIONS: Bronchoalveolar lavage was performed daily until either day 7 or extubation. Samples from the side of lung contusion (n = 62) and the contralateral, uninjured side (n = 62) were obtained at the same time in 14 patients. Total phospholipids, total phospholipid classes, and surfactant apoprotein A were quantified. Additionally, surfactant function was measured with a pulsating bubble surfactometer in four patients. All data are presented as mean +/- SEM. Statistical analyses were performed using programs of SPSS for Windows 6.1.3 (SPSS Inc., Chicago, IL) (Student's t-test; p < .05). MEASUREMENTS AND MAIN RESULTS: Total phospholipids were significantly increased on the side of lung contusion (contusion side, 40+/-7 microg/mL; contralateral side, 21+/-3 microg/mL; p = .004). The percentage contents of phosphatidylcholine (contusion side, 87.1%+/-1.0%; contralateral side, 84.3%+/-1.0%; p = .04) and sphingomyelin (contusion side, 2.9%+/-0.3%; contralateral side, 1.9%+/-0.2%; p = .004) were significantly higher. In contrast, the percentage content of phosphatidylglycerol was significantly decreased (contusion side, 4.1%+/-0.1%; contralateral side, 6.9%+/-0.6%; p = .001). No alterations were found for the relative contents of phosphatidylethanolamine (contusion side, 2.4%+/-0.2%; contralateral side, 2.2%+/-0.2%; p = .47), phosphatidylinositol (contusion side, 3.5%+/-0.4%; contralateral side, 4.6%+/-0.5%; p = .06), and surfactant apoprotein A (contusion side, 7177+/-1404 ng/mL; contralateral side, 4513+/-787 ng/mL, p = .10). There was no statistical difference for minimal surface tension measured with the pulsating bubble surfactometer after 5 mins of oscillation (contusion side, 29.5+/-2.3 mN/m; contralateral side, 23.7+/-2.1 mN/m; p = .08). CONCLUSIONS: Direct damage of lung parenchyma by lung contusion alters the composition of surfactant. No additional changes in surfactant function were observed that would argue in favor of functional compensation.

Ultrastructural alterations in intraalveolar surfactant subtypes after experimental ischemia and reperfusion.

Ischemia and reperfusion (I/R) result in surfactant dysfunction. Whether the impairment of surfactant is a consequence or a cause of intraalveolar edema formation is still unknown. The cumulative effects of lung perfusion, ischemic storage, and subsequent reperfusion on surfactant ultrastructure and pulmonary function were studied in a rat isolated perfused lung model. The left lungs were fixed for electron microscopy by vascular perfusion either immediately after excision (control; n = 5) or after perfusion with modified Euro-Collins solution (EC), storage for 2 h at 4 degrees C in EC, and reperfusion for 40 min (n = 5). A stereological approach was chosen to discriminate between intraalveolar surfactant subtypes of edematous regions and regions free of edema. Intraalveolar edema seen after I/R in the EC group occupied 36 +/- 6% (mean +/- SEM) of the gas exchange region as compared with control lungs (1 +/- 1%; p = 0.008). Relative intraalveolar surfactant composition showed a decrease in surface active tubular myelin (3 +/- 1 versus 12 +/- 0%; p = 0.008) and an increase in inactive unilamellar forms (83 +/- 2 versus 64 +/- 5%; p = 0.008) in the EC group. These changes occurred both in edematous (tubular myelin, 3 +/- 1%; unilamellar forms, 88 +/- 6%) and in nonedematous regions (tubular myelin, 4 +/- 3%; unilamellar forms, 77 +/- 5%). The ultrastructural changes in surfactant were associated with an increase in peak inspiratory pressure during reperfusion. In conclusion, surfactant alterations seen after I/R are not directly related to the presence of edema fluid in the alveoli. Disturbances in intraalveolar surfactant after I/R are not merely the result of inactivation due to plasma protein leakage but may instead be responsible for an increased permeability of the blood-air barrier, resulting in a vicious cycle of intraalveolar edema formation and progressing surfactant impairment.

Damage to surfactant-specific protein in acute respiratory distress syndrome.

BACKGROUND: Acute respiratory distress syndrome (ARDS) develops in association with many serious medical disorders. Mortality is at least 40%, and there is no specific therapy. A massive influx of activated neutrophils, which damage pulmonary vascular endothelium and alveolar epithelium, leads to alveolar oedema and pulmonary surfactant dysfunction. In-vitro studies show that neutrophil elastase can cleave surfactant-specific proteins and impair surfactant function. If this happens in vivo in ARDS, the response to surfactant therapy will be limited. METHODS: Samples of pulmonary surfactant were obtained from the lungs of 18 patients with ARDS and six healthy controls by bronchoalveolar lavage. We separated proteins in these samples according to molecular weight by sodium dodecyl sulphate polyacrylamide gel electrophoresis (SDS-PAGE). We then used western blotting with monoclonal antibody E8 to detect the major surfactant-specific protein A (SP-A). FINDINGS: By contrast with controls, 14 of 18 patients had evidence of in-vivo damage to SP-A that resembled damage caused to SP-A when it is cleaved by neutrophil elastase. Controls showed a single band of normal dimers at 66 kDa, whereas 14 of 18 patients showed multiple bands at 66 kDa, 55 kDA, and 30-36 kDa, and six showed additional bands at 36-40 kDa. INTERPRETATION: Direct damage to surfactant-specific proteins occurs in lungs of patients with ARDS, probably by proteolysis. Trials of protein-containing therapeutic surfactant are in progress in ARDS, and our results indicate that the frequent failure to maintain response may result from continuing damage to surfactant by products of activated neutrophils. A combination of surfactant and antiprotease therapy may improve therapeutic prospects.

Protein-lipid interactions and enzyme requirements for light subtype generation on cycling reconstituted surfactant.

Surfactant convertase is required for conversion of heavy density (H) natural surfactant to light density (L) subtype during cycling in vitro, a technique that reproduces surfactant metabolism. To study mechanisms of H to L conversion, we prepared liposomes of dipalmitoylphosphatidylcholine (DPPC) and phosphatidylglycerol (PG), or the phospholipids (PL) in combination with either surfactant protein A (SP-A), surfactant protein B (SP-B), or both SP-A and SP-B. Phospholipids alone showed time-dependent conversion from heavy to light subtype on cycling in the absence of convertase, which was decreased by adding SP-B, but not SP-A, to phospholipids (p < 0.01 for PL+SP-B, or PL+SP-A+SP-B vs. PL, or PL+SP-A). The ultrastructure, surface activity, buoyant density, and L subtype generation on cycling PL+SP-A+SP-B with partially purified convertase or with phospholipase D were similar to those of natural TM. In conclusion, a reconstituted surfactant mimics the behavior of natural surfactant on cycling, and reveals that interaction of SP-B with phospholipids decreases L subtype generation. In addition, esterase/ phospholipase D activity is required for conversion of heavy to light subtype on cycling.

Changes in pulmonary artery pressure during the acute phase of respiratory distress syndrome treated with three different types of surfactant.

We studied the changes in acceleration time/right ventricular ejection time ratio (AT/RVET; indicative of changes in pulmonary artery pressure) calculated from Doppler ultrasound examinations performed before and 1, 6, and 12 h after the first and second doses of surfactant following the administration of each of three different surfactants during the acute phase of the respiratory distress syndrome. Maximum fractional inspired oxygen concentration (F(I,O2)) and peak inspiratory pressure (PIP) were recorded during each 4 h period from birth for the first 24 h and subsequently every 24 h until 72 h. Eighty-three infants were studied. Fifty patients weighing > 1 kg received Exosurf (n = 29) or ALEC (n = 21) and 33 weighing < or = 1 kg received Exosurf (n = 22) or Survanta (n = 11). The AT/RVET rose rapidly after administration of all three surfactants. There was no significant difference in the change in AT/RVET between those > 1 kg who received Exosurf and those who received ALEC (a synthetic surfactant). Similarly, there was no difference between those infants < or = 1 kg who received Exosurf and those who received Survanta. The F(I,O2) requirements, but not PIP, were lower in those infants who received Survanta at 12 and 20 h compared with those who received Exosurf. There was no significant difference in the F(I,O2) or PIP requirements between infants > 1 kg who received Exosurf compared with those who received ALEC. The rise in AT/RVET found in this study after administration of ALEC, Exosurf, or Survanta suggests that similar and rapid falls in pulmonary artery pressure occur after all three surfactant administrations, despite the difference in clinical response demonstrated between Exosurf and Survanta.

Effects of lung injury on pulmonary surfactant aggregate conversion in vivo and in vitro.

Within the alveolar space pulmonary surfactant is converted from the surface active large aggregates (LA) to the inactive small aggregates (SA). This conversion is affected by a change in surface area, lung injury, breathing pattern, and protease activity. This study examined the effect of N-nitroso-N-methylurethane-induced acute lung injury on aggregate conversion in mechanically ventilated and spontaneously breathing rabbits. Both the in vitro surface area cycling techniques and the in vivo technique of intratracheally injecting radiolabeled LA were used for analyzing aggregate conversion. Mechanical ventilation of injured lungs resulted in increased aggregate conversion and increased surfactant aggregate ratios compared with controls. Spontaneously breathing injured animals had aggregate conversion and aggregate ratios that were not significantly different from controls. In vitro aggregate conversion was slower for LA obtained from injured animals compared with normal animals. We conclude that the mechanical stress of mechanical ventilation results in increased aggregate conversion and aggregate ratios. Furthermore, in vitro conversion of isolated LA does not necessarily reflect the conversion of aggregates within the alveoli.

Surfactante artificial, su uso en recién nacidos prematuros / Artificial pulmonary surfactant: its use in premature newborm

El síndrome de dificultad respiratoria (SDR) neonatal o Enfermedad de Membrana Hialina (EMH), continúa siendo una de las principales causas de mortalidad entre los recién nacidos prematuros. El tratamiento convencional de esta enfermedad es estrictamente sintomático y de sostén, para permitir al paciente llegar hasta el momento en que es capaz de sintetizar su propio material surfactante. Consiste en asegurar un ambiente térmico adecuado, aportes hidroelectrolíticos suficientes y asistencia respiratoria. En las últimas décadas ha comenzado a desarrollarse en forma exitosa un tratamiento más racional y específico, dirigido a tratar la causa primaria de la enfermedad. Ya que la falta de surfactante durante los primeros 2 ó 3 días del naciemiento es la causa del problema, se implementó una terapéutica de reemplazo. Las modalidades utilizadas hasta la fecha pueden reunirse en dos, una como tratamiento de pacientes afectados y otra como profilaxis en el momento del nacimiento en prematuros con alto riesgo de desarrollar la enfermedad

[Natural or artificial surfactants? Arguments in favour of natural surfactants]. / Surfactant naturel ou artificiel? Les arguments en faveur des surfactants naturels.

The use of exogenous surfactant (ES) is an essential component for prevention and treatment of hyaline membrane disease (HMD). The ES available for clinical use are of two therapeutic classes: natural surfactants prepared from mammalian lung and artificial surfactants. The choice between these two classes of ES is controversial. In this overview, we present the arguments in favour of the preferential use of natural ES. The presence of hydrophobic specific proteins (SP-B and SP-C) provides to natural ES better surface tension properties than artificial ES. The in vitro greater efficacy of natural ES has been confirmed in vivo in experimental models of surfactant deficiency, human pharmacodynamic studies, and comparative clinical trials. Furthermore, the excellent clinical tolerance and harmlessness of natural ES has been firmly established. A meta-analysis of the comparative clinical trials between natural ES and one artificial ES (enrolling as many as 4400 babies treated for HMD) suggests that the use of natural ES compared to this artificial ES significantly reduces the neonatal mortality by 20%. In conclusion, all these arguments are in favor of the preferential use of natural ES for prevention and treatment of HMD.