Methodological optimization of polyethylenimine (PEI)‐based gene delivery to the lungs of mice via aerosol application

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Abstract
Background Polyethylenimine (PEI) has been successfully used for gene delivery to the lungs of mice via aerosol application using a whole body nebulization device. In this report we optimized the design of such an aerosol device. Methods Aerosol devices were constructed as either serial inhalation apparatus or as a whole body nebulization chamber connected to an aerosol spacer placed in a horizontal or vertical position. PEI‐based gene vectors were nebulized using a standard jet nebulizer and luciferase gene expression of various tissues was examined. Results Using a whole body aerosol device resulted in luciferase gene expression in the lungs of mice at the same level as compared with a serial inhalation apparatus. Whereas gene expression was enhanced in the presence of 5% CO2‐in‐air, anesthesia of mice strongly decreased gene expression even when mice were intubated with an intravascular cannula. Reduction of the median mass aerodynamic diameter (MMAD) of the aerosol from 3.4 to 0.27 µm by interposition of an aerosol spacer increased gene expression significantly 3‐fold. Drying of the aerosol by silica gel additionally increased gene delivery significantly 3‐fold. Reporter gene expression mediated by branched PEI 25 kDa was 9‐ and 15‐fold higher as compared with linear PEIs of 22 and 25 kDa, respectively, and was dependent on the DNA concentration. Gene expression was detectable as soon as 6 h after gene vector application and reached a maximum after 72 h but was still detectable after 14 days. The presence of Zn2+ did not increase gene expression. Conclusion We propose aerosol drying as a novel and simple method of optimizing PEI‐based gene delivery to the lungs. Copyright © 2004 John Wiley & Sons, Ltd.