Inactivation of pulmonary surfactant by silicone oil in vitro and in ventilated immature rabbits

Efficient protein production inspired by how spiders make silk

Membrane proteins are targets of most available pharmaceuticals, but they are difficult to produce recombinantly, like many other aggregation-prone proteins. Spiders can produce silk proteins at huge concentrations by sequestering their aggregation-prone regions in micellar structures, where the very soluble N-terminal domain (NT) forms the shell. We hypothesize that fusion to NT could similarly solubilize non-spidroin proteins, and design a charge-reversed mutant (NT*) that is pH insensitive, stabilized and hypersoluble compared to wild-type NT. NT*-transmembrane protein fusions yield up to eight times more of soluble protein in Escherichia coli than fusions with several conventional tags. NT* enables transmembrane peptide purification to homogeneity without chromatography and manufacture of low-cost synthetic lung surfactant that works in an animal model of respiratory disease. NT* also allows efficient expression and purification of non-transmembrane proteins, which are otherwise refractory to recombinant production, and offers a new tool for reluctant proteins in general.

Phospholipid Composition in Synthetic Surfactants Is Important for Tidal Volumes and Alveolar Stability in Surfactant-Treated Preterm Newborn Rabbits

BACKGROUND

The development of synthetic surfactants for the treatment of lung pulmonary diseases has been going on for many years.

OBJECTIVES

To investigate the effects of phospholipid mixtures combined with SP-B and SP-C analogues on lung functions in an animal model of respiratory distress syndrome.

METHODS

Natural and synthetic phospholipid mixtures with/without SP-B and/or SP-C analogues were instilled in ventilated premature newborn rabbits. Lung functions were evaluated.

RESULTS

Treatment with Curosurf or phospholipids from Curosurf combined with SP-B and SP-C analogues gave similar results. Treatment with phospholipids from adult rabbit lungs or liver combined with dipalmitoylphosphatidylcholine (DPPC) and palmitoyloleoylphosphatidylglycerol (POPG) gave tidal volumes (VT) well above physiological levels, but alveolar stability at end-expiration was only achieved when these phospholipids were combined with analogues of SP-B and SP-C. Treatment with egg yolk-PC mixed with DPPC with and without POPG gave small VT, but after addition of both analogues VT was only somewhat lower and lung gas volumes (LGV) similar to those obtained with Curosurf. Substitution of egg yolk-PC (≥99% PC) with 1-palmitoyl-2-oleoyl-sn-glycero-3-phosphocholine and 1-palmitoyl-2-linoleoyl-sn-glycero-3-phosphocholine, and combining them with DPPC, POPG and 2% each of the SP-B and SP-C analogue gave a completely synthetic surfactant with similar effects on VT and LGV as Curosurf.

CONCLUSIONS

Phospholipid composition is important for VT while the SP-B and SP-C analogues increase alveolar stability at end-expiration. Synthetic surfactant consisting of unsaturated and saturated phosphatidylcholines, POPG and the analogues of SP-B and SP-C has similar activity as Curosurf regarding VT and LGV in an animal model using preterm newborn rabbits ventilated without positive end-expiratory pressure.

Prophylactic intratracheal polymyxin B/surfactant prevents bacterial growth in neonatal Escherichia coli pneumonia of rabbits

In neonatal pneumonia, the surface activity of pulmonary surfactant is impaired and microorganisms may invade by passing the air-liquid interface. Previously, we have shown that addition of the antimicrobial peptide polymyxin B (PxB) to modified porcine surfactant (pSF) improves resistance to surfactant inactivation in vitro while antimicrobial activity of PxB is maintained. In this study, we investigated pSF/PxB in vivo. Neonatal near-term rabbits were treated with intratracheal pSF and/or PxB. Rabbits treated with only saline served as controls. Animals were ventilated with standardized tidal volumes and received ∼10(7) Escherichia coli intratracheally. Plethysmographic pressure-volume curves were recorded every 30 min. After 240 min, animals were killed, the right lung and left kidney were excised, and bacterial growth was determined. The left lung was used for histologic analysis. Intratracheal administration of PxB ± pSF significantly reduced the growth of E. coli compared with control animals or animals receiving only pSF. This was accompanied by reduction of severe inflammatory tissue destruction and significantly reduced bacterial translocation to the left kidney. Animals receiving pSF + PxB had no difference in lung compliance compared with the pSF- or PxB-treated group. Mixtures of PxB and pulmonary surfactant show antimicrobial effects in neonatal rabbits and prevent systemic spreading of E. coli.