Efficacy, dose-response, and aerosol delivery of dry powder synthetic lung surfactant treatment in surfactant-deficient rabbits and premature lambs

Abstract

Background: Dry powder (DP) synthetic lung surfactant may be an effective means of noninvasive delivery of surfactant therapy to premature infants supported with nasal continuous positive airway pressure (nCPAP) in low-resource settings.

Methods: Four experimental DP surfactant formulations consisting of 70% of phospholipids (DPPC:POPG 7:3), 3% Super Mini-B (SMB) or its sulfur-free derivate B-YL as SP-B peptide mimic, 25% of lactose or trehalose as excipient, and 2% of NaCl were formulated using spray drying. In vitro surface activity was confirmed with captive bubble surfactometry. Surfactant particle size was determined with a cascade impactor and inhaled dose was quantified using a spontaneously breathing premature lamb lung model supported with CPAP. In vivo surfactant efficacy was demonstrated in three studies. First, oxygenation and lung compliance were monitored after intratracheal instillation of resuspended DP surfactant in intubated, ventilated, lavaged, surfactant-deficient juvenile rabbits. In dose-response studies, ventilated, lavaged, surfactant-deficient rabbits received 30, 60, 120 or 240 mg/kg of DP B-YL:Lactose or B-YL:Trehalose surfactant by aerosol delivery with a low flow aerosol chamber via their endotracheal tube. Noninvasive aerosolization of DP B-YL:Trehalose surfactant via nasal prongs was tested in spontaneous breathing premature lambs supported with nCPAP. Intratracheal administration of 200 mg/kg of Curosurf^®, a liquid porcine surfactant, was used as a positive control.

Results: Mass median aerosol diameter was 3.6 μm with a geometric standard deviation of 1.8. All four experimental surfactants demonstrated high surface efficacy of intratracheal instillation of a bolus of ~ 100 mg/kg of surfactant with improvement of oxygenation and lung compliance. In the dose-response studies, rabbits received incremental doses of DP B-YL:Lactose or B-YL:Trehalose surfactant intratracheally and showed an optimal response in oxygenation and lung function at a dose of 120-240 mg/kg. Aerosol delivery via nasal prongs of 1 or 2 doses of ~ 100 mg/kg of B-YL:Trehalose surfactant to premature lambs supported with nCPAP resulted in stabilization of spontaneous breathing and oxygenation and lung volumes comparable to the positive control.

Conclusion: These studies confirm the clinical potential of DP synthetic lung surfactant with B-YL peptide as a SP-B mimic to alleviate surfactant deficiency when delivered as a liquid bolus or as an aerosol.

Keywords: B-YL peptide; Dry powder (DP) Synthetic lung surfactant; Lactose; Low flow aerosolization chamber (LFAC); Noninvasive ventilation; Premature lambs; Respiratory distress syndrome (RDS); Super Mini-B (SMB) peptide; Surfactant protein B (SP-B); Surfactant-deficient rabbits; Trehalose.

Fig. 1

Arterial PO₂ and dynamic compliance (mean ± SEM) in the six groups of 4–5 surfactant-deficient rabbits treated intratracheally with one of the four experimental DP synthetic lung surfactants resuspended in distilled water (30 mg/mL), the positive control Curosurf and the negative control (Lipids), described in Table 1. *p = 0.002 for B-YL:Trehalose vs Curosurf; ^#p = 0.032 for B-YL:Trehalose vs SMB:Lactose

Fig. 2

Oxygenation (PaO_2, mmHg) and dynamic compliance (mL/kg/cm H₂O) (mean ± SEM) of surfactant-deficient rabbits treated with intratracheal aerosol delivery of dry powder B-YL:Lactose (top) or B-YL:Trehalose (bottom) surfactant. Animals are sorted according to the total dose of surfactant administered over 1 or 2 doses. *p = 0.045, respectively 0.015, for B-YL:Lactose 30 or 60 vs 120 and 240 mg/kg; ^#p = 0.03, respectively 0.015, for B-YL:Trehalose 30 or 60 vs 120 and 240 mg/kg at 120 min post-surfactant

Fig. 3

Phospholipid (DPPC and POPG) and B-YL concentrations (mean ± SEM) in lung tissue (µg/g) from surfactant-deficient rabbits measured 2 h after intratracheal insufflation of dry powder. A Lung DPPC and POPG concentrations after aerosol delivery of DP B-YL:Lactose surfactant. B Lung DPPC and POPG concentrations after DP B-YL:Trehalose surfactant treatment. C B-YL peptide concentration in lung tissue after B-YL:Lactose and B-YL:Trehalose surfactant treatment. *p = 0.0285 for B-YL 30 vs 120 mg/kg; **p = 0.0348 for DPPC 30 vs 120 mg/kg; ^▲p = 0.0385 for POPG 30 vs 120 mg/kg; ^#p = 0.0080 for DPPC + POPG 30 vs 120 mg/kg. Lower limit of quantitation (LLOQ) was 0.1 µg/mL for DPPC and POPG and 50 ng/mL for B-YL

Fig. 4

Rescue sequence of medical treatment (doxapram in red) and nasal mechanical ventilation (NIV in yellow) during the 180 min period starting after completion of (first) surfactant treatment (t = 0), divided into 5 min intervals

Fig. 5

Arterial pH, partial arterial oxygen pressure (PaO₂), and partial arterial carbon dioxide pressure (PaCO₂), and lung volume (mean ± SEM) in the three groups of premature lambs supported with nCPAP and 100% oxygen and treated with 1 or 2 doses of aerosolized B-YL:Trehalose surfactant or the positive control Curosurf. Data reflect the period from birth until 180 min post-surfactant treatment for PaO₂ (A), PaCO₂ (B), and pH (C), whereas lung volumes were derived from postmortem pressure–volume curves (D). MV: mechanical ventilation. *p < 0.02 for 2-dose B-YL:Trehalose and Curosurf groups vs the 1-dose B-YL:Trehalose group; #p = 0.045 for the Curosurf vs the 1- and 2-dose B-YL:Trehalose groups; ^▲p = 0.012 for Curosurf vs the 1-dose BYL:Trehalose group

Fig. 6

Mean ± SEM phospholipid (DPPC and POPG) and B-YL peptide concentrations in lung tissue of premature lambs treated with aerosol delivery of 1 or 2 doses of dry powder B-YL:Trehalose surfactant, intratracheal instillation of one dose of the positive control Curosurf, or untreated controls. *p ≤ 0.04 for 1- and 2-dose B-YL:Trehalose vs Curosurf; ^#p = 0.03 Curosurf vs controls