Background: The delivery of genes to the airways holds promise for the treatment of lung diseases such as cystic fibrosis and asthma. Current non-viral gene delivery systems lack sufficient transfection efficiency. Pulmonary surfactant has been reported to be a barrier to gene transfer into the airways. Here we analyze the interaction of liposomal and polycationic transfection complexes with pulmonary surfactant.
Methods: The efficiency of non-viral transfection of cultured human airway epithelial cells (16HBE14o-), COS7 cells and porcine primary airway epithelial cells was studied in the presence of various surfactant preparations in order to model the conditions prevailing in the airways during transfection.
Results: The natural pulmonary surfactant, Alveofact, an extract from bovine lung lavage, was found to inhibit lipofection with lipofectAMINE for all cell lines investigated. Dendrimer meditated polyfection was unaffected for pulmonary cell lines and was weakly affected for COS7 cells. PEI-mediated polyfection was unaffected for all cell lines tested. The synthetic surfactant preparation Exosurf containing L-alpha-phosphatidylcholine-dipalmitoyl (DPPC) as the sole lipid ingredient had no statistically significant effect on polymer- and lipid-mediated transfection. The transfection efficiencies are related to structural changes in the DNA complexes as demonstrated by DNase-accessibility tests and fluorescence spectroscopy. In the presence of the phospholipid POPG, which is a constituent of Alveofact, DNA condensed in lipofectAMINE lipoplexes became accessible to DNaseI, while DNA condensed with PAMAM dendrimer or PEI was less accessible to DNase I as compared to lipoplexes. Consistently, the fluorescence of a DNA-intercalating dye increased after addition of Alveofact only in the case of lipoplexes.
Conclusions: In contrast to lipofection, gene transfer with cationic polymers to airway epithelial cells is not inhibited by pulmonary surfactant in vitro. Depending on the surfactant concentration even an increase in polymermediated transfection can be seen. In conclusion, cationic polymers appear to be the more stable gene delivery systems for topical application into the airways.