Efficacy of synthetic peptide-containing surfactant in the treatment of respiratory distress syndrome in preterm infant rhesus monkeys

The role of surfactant proteins in DPPC enrichment of surface films

A pressure-driven captive bubble surfactometer was used to determine the role of surfactant proteins in refinement of the surface film. The advantage of this apparatus is that surface films can be spread at the interface of an air bubble with a different lipid/protein composition than the subphase vesicles. Using different combinations of subphase vesicles and spread surface films a clear correlation between dipalmitoylphosphatidylcholine (DPPC) content and minimum surface tension was observed. Spread phospholipid films containing 50% DPPC over a subphase containing 50% DPPC vesicles did not form stable surface films with a low minimum surface tension. Addition of surfactant protein B (SP-B) to the surface film led to a progressive decrease in minimum surface tension toward 1 mN/m upon cycling, indicating an enrichment in DPPC. Surfactant protein C (SP-C) had no such detectable refining effect on the film. Surfactant protein A (SP-A) had a positive effect on refinement when it was present in the subphase. However, this effect was only observed when SP-A was combined with SP-B and incubated with subphase vesicles before addition to the air bubble containing sample chamber. Comparison of spread films with adsorbed films indicated that refinement induced by SP-B occurs by selective removal of non-DPPC lipids upon cycling. SP-A, combined with SP-B, induces a selective adsorption of DPPC from subphase vesicles into the surface film. This is achieved by formation of large lipid structures which might resemble tubular myelin.

Synthetic surfactants to treat neonatal lung disease

Pulmonary surfactant is a complex of surface-active lipids mixed with specific proteins. Two of these, SP-B and SP-C, are essential for adsorption of surfactant lipids to the air-liquid interfaces of the lungs and, hence, are also essential for alveolar stability and effective gas exchange. Surfactant substitutes must contain at least one of these proteins (or analogues of them) to be optimally effective when administered into the airways of babies with surfactant deficiency or dysfunction. This review describes how an increased understanding of the properties of surfactant proteins has led to the development of improved synthetic surfactants with the potential to treat a wide range of respiratory disorders.

Exogenous surfactant therapy and mucus rheology in chronic obstructive airway diseases

Exogenous surfactant is a specialized biomaterial used for substitution of the lipoprotein mixture normally present in the lungs-pulmonary surfactant. Respiratory Distress Syndrome is a disease of preterm infants mainly caused by pulmonary immaturity as evidenced by a deficiency of mature lung surfactant. Pulmonary surfactant is known to stabilize small alveoli and prevent them from collapsing during expiration. However, apart from alveoli, surfactant also lines the narrow conducting airways of the tracheobronchial tree. This paper reviews the role of this surfactant in the airways and its effect on mucus rheology and mucociliary clearance. Its potential role as a therapeutic biomaterial in chronic obstructive airway diseases, namely asthma, chronic bronchitis, and respiratory manifestations of cystic fibrosis, are discussed. This paper also attempts to elucidate the exact steps in the pathogenic pathway of these diseases which could be reversed by supplementation of exogenous surfactant formulations. It is shown that there is great potential for the use of present day surfactants (which are actually formulated for use in Respiratory Disease Syndrome) as therapy in the aforementioned diseases of altered mucus viscoelasticity and mucociliary clearance. However, for improved effectiveness, specific surfactant formulations satisfying certain specific criteria should be tailor-made for the clinical condition for which they are intended. The properties required to be fulfilled by the optimal exogenous surfactant in each of the above clinical conditions are enumerated in this paper.

Bronchoalveolar lavage with KL4-surfactant in models of meconium aspiration syndrome

As a model of the meconium aspiration syndrome (MAS) of human infants, adult rabbits and newborn rhesus monkeys received intratracheal instillation of human meconium to induce pulmonary injury. Injured rabbits were ventilated with 100% O2 and divided into four treatment groups, receiving: 1) bronchoalveolar lavages (BAL) with dilute KL4-Surfactant; 2) lavages with equal volumes of sterile saline; 3) a single intratracheal bolus of KL4-Surfactant, 100 mg/kg; and 4) no treatment. The untreated rabbits developed atelectasis, a fall in pressure-volume levels and in partial pressure of O2 in arterial blood (PaO2) from approximately 500 to < 100 mm Hg, and severe pulmonary inflammation between 3 and 5 h after instillation of meconium. Rabbits treated by BAL with dilute KL4-Surfactant showed rapid and sustained recovery of PaO2 to approximately 300 mm Hg within minutes, a return toward normal pressure-volume levels, and diminished inflammation. Rabbits receiving BAL with saline failed to show recovery, and rabbits treated with a bolus of surfactant intratracheally exhibited a transient response by 1-2 h after treatment, but then returned to the initial atelectatic state. Newborn rhesus monkeys, after receiving human meconium intratracheally before the first breath, developed severe loss of pulmonary function. Treatment of these monkeys 1-5 h after birth with BAL with dilute KL4-Surfactant produced clearing of chest radiographs and a rapid improvement in pulmonary function with ratios of partial pressure of O2 in arterial blood to the fraction of O2 in the inspired air rising into the normal range where they remained through the 20-h period of study. The studies indicate that pulmonary function in two models of severe meconium injury respond rapidly to BAL with dilute KL4-Surfactant.

Protein composition of synthetic surfactant affects gas exchange in surfactant-deficient rats

Synthetic surfactant peptides offer an opportunity to standardize the protein composition of surfactant. We tested the effect of phospholipids (PL) with synthetic full-length SP-B1-78 (B), mutant B (Bser), KL4 peptide (UCLA-KL4), and palmitoylated SP-C1-35 (C) on oxygenation and lung function in a surfactant-deficient rat model. Sixty-four adult rats were ventilated with 100% oxygen, a tidal volume of 7.5 mL/kg, and a rate of 60/min. Their lungs were lavaged with saline until the arterial PO2 dropped below 80 torr, when 100 mg/kg surfactant was instilled. Surfactant preparations included: PL (PL surfactant), PL + 3% B (B surfactant), PL + 3% B and 1% C (BC surfactant), PL + 3% UCLA-KL4 (KL4 surfactant), PL + 3% Bser (Bser surfactant), and PL + 3% B and 1% UCLA-KL4 (BKL4 surfactant). Sixty minutes after surfactant instillation, positive end-expiratory pressure was applied for 5 min, and pressure-volume curves were determined in situ. The six surfactant preparations had a minimum surface tensions <10 mN/m on a Langmuir/Wilhelmy balance. Instillation of PL, Bser, and BKL4 surfactant increased mean arterial/alveolar PO2 (aADO2) ratios by 50-100% over postlavage values, whereas KL4 surfactant increased aADO2 ratios by 118%, B surfactant by 191%, and BC surfactant by 225%. Lung volumes at 30 cm H2O pressure were highest after treatment with BC surfactant, intermediate after B and KL4 surfactants, and lowest after BKL4, Bser, and PL surfactants. These data suggest that a surfactant preparation with a combination of synthetic B and C peptides surpasses synthetic B and KL4 surfactants in improving oxygenation and lung compliance in surfactant-deficient rats.

Effects of a cationic and hydrophobic peptide, KL4, on model lung surfactant lipid monolayers

We report on the surface behavior of a hydrophobic, cationic peptide, [lysine-(leucine)4]4-lysine (KL4), spread at the air/water interface at 25 degrees C and pH 7.2, and its effect at very low molar ratios on the surface properties of the zwitterionic phospholipid 1,2-dipalmitoylphosphatidylcholine (DPPC), and the anionic forms of 1-palmitoyl-2-oleoylphosphatidylglycerol (POPG) and palmitic acid (PA), in various combinations. Surface properties were evaluated by measuring equilibrium spreading pressures (pi(e)) and surface pressure-area isotherms (pi-A) with the Wilhelmy plate technique. Surface phase separation was observed with fluorescence microscopy. KL4 itself forms a single-phase monolayer, stable up to a surface pressure pi of 30 mN/m, and forms an immiscible monolayer mixture with DPPC. No strong interaction was detected between POPG and KL4 in the low pi region, whereas a stable monolayer of the PA/KL4 binary mixture forms, which is attributed to ionic interactions between oppositely charged PA and KL4. KL4 has significant effects on the DPPC/POPG mixture, in that it promotes surface phase separation while also increasing pi(e) and pi(max), and these effects are greatly enhanced in the presence of PA. In the model we have proposed, KL4 facilitates the separation of DPPC-rich and POPG/PA-rich phases to achieve surface refinement. It is these two phases that can fulfill the important lung surfactant functions of high surface pressure stability and efficient spreading.

Spiking Survanta with synthetic surfactant peptides improves oxygenation in surfactant-deficient rats

The hypothesis that the in vivo function of Survanta (Beractant) can be improved by supplementation with synthetic surfactant peptides B and C was tested in a surfactant-deficient rat model. Full length surfactant protein-B (SP-B1-78) (B) and palmitoylated surfactant protein-C (SP-C1-35) (C), and synthetic KL4 peptide were added to Survanta after extraction, creating extracted Survanta (ES) with 1% B, 2% B, and 2% B plus 1% C, or mixed with Survanta without extraction, creating modified Survanta (S) with 2% B, 2% B plus 1% C, and 2% KL4. Adult rats were ventilated with 100% oxygen, tidal volumes (VT) of 7.5 ml/kg and a rate of 60/min, and were lavaged until the PaO2 dropped below 80 mm Hg, when 100 mg/kg of surfactant was instilled. After 15 to 60 min of ventilation, pressure-volume (P-V) curves were generated in situ. Instillation of ES or S with 2% B plus 1% C led to the greatest increase in oxygenation, closely followed by ES and S with 2% B, and more distantly by S plus 2% KL4. TLC was comparable among the ES and S groups, but greater than that of air-placebo controls. These data suggest that spiking of Survanta with synthetic SP-B and SP-C increased oxygenation more effectively than B or KL4 alone in this surfactant-deficient rat model.