Restoration of surfactant activity by polymyxin B in lipopolysaccharide-potentiated injury of immature rabbit lungs

Abstract

During postnatal adaptation pulmonary surfactant may be inactivated by lipopolysaccharide (LPS). We evaluated the effect of surfactant therapy in combination with antibiotic polymyxin B (PxB) in double-hit model of neonatal lung injury. Surfactant (poractant alfa, Curosurf) was exposed to smooth (S) LPS without/with PxB and tested in captive bubble surfactometer. Preterm rabbits received intratracheally saline (control) or S-LPS and were ventilated with 100% oxygen. After 30 min, LPS-treated animals received no treatment, or surfactant (200 mg/kg) without/with 3% PxB; controls received the same dose of surfactant. Animals were ventilated for further 2 h. In vitro, addition of 5% S-LPS to surfactant increased minimum surface tension (γmin) and addition of 1-3% PxB to surfactant/S-LPS mixture restored γmin to low values. Animals only given S-LPS had lower lung compliance and lung gas volume (LGV) compared to surfactant groups. Treatment with surfactant/PxB, but not with surfactant only, restored LGV. Addition of PxB to the surfactant increased the alveolar expansion. S-LPS interferes with surface activity of the pulmonary surfactant and PxB improves the resistance of surfactant to LPS-induced inactivation. In our neonatal model of respiratory distress syndrome surfactant gives positive response even in simultaneous exposure to S-LPS, when enriched with PxB.

Figure 1

Schematic diagram of double-hit model of lung immaturity and acute lung injury by bacterial lipopolysaccharide (LPS) instillation in premature newborn rabbits and the overview of experimental protocol.

Figure 2

(A–D) Dynamic surface properties of poractant alfa at 5 mg of PL/ml without and with LPS at 1, 3 and 5% (A); poractant alfa at 3 mg of PL/ml without and with LPS at 1, 3 and 5% (B); poractant alfa at 3 mg of PL/ml with LPS at 5% and PxB at 0.5–3% (C) at minimum (empty columns) and maximum (striped columns) bubble size. Area of compression needed to reach minimum surface tension of 5 mN/m of poractant at 3 mg PL/ml and with LPS at 1, 3 and 5% (2D left), and poractant alfa/LPS 5% with PxB at 0.5, 1, 2 and 3% (2D right). All values were obtained during the 5th cycle in the captive bubble surfactometer and are shown as mean ± SD.

Figure 3

Representative diagrams of the behavior of the poractant alfa at 3 mg/ml (up), poractant alfa 3 mg/ml and 5% LPS (middle) and poractant alfa 3 mg/ml, 5% LPS and 3% PxB (down) in captive bubble surfactometer. Speed of absorption at the surface of the air bubble (left) and surface tension at 1st, 2nd and 5th cycle during compression (right).

Figure 4

Lung-thorax compliance during the experiment in preterm newborn rabbits exposed to LPS (negative control) or saline (positive control) at delivery and treated with poractant alfa with or without PxB at 30 min of ventilation. Statistical analysis: at all time points since 45th min, all groups > LPS; P < 0.001; at 45th min, LPS/poractant alfa/PxB < saline/poracant alfa, P < 0.05.

Figure 5

Representative macroscopic appearance of the lungs in preterm newborn rabbits after administration of saline and poractant alfa (A), LPS and no further treatment (B), LPS and poractant alfa (C), and LPS and poractant alfa with PxB (D).