Protective effect of montmorillonite on plasmid DNA in oral gene delivery into small intestine

Montmorillonite, a bioinert clay mineral, was examined as a novel vector for an oral gene-delivery system. The complex of montmorillonite and plasmid DNA encoding the enhanced green fluorescent protein (EGF-P) gene was prepared at various weight ratios, and then transfected into cultured intestinal epithelial cells (IEC-6) in vitro. The EGFP gene was clearly transcribed when the transfection was performed using the montmorillonite-plasmid complex at a weight ratio of 0.05:1. In contrast, no gene expression was detected by reverse transcription-polymerase chain reaction (RT-PCR) analysis when the transfection was per-formed with naked plasmid. Various plasmid preparations were given orally to mice, and the gene expression in the stomach and small intestine was examined by, RT-PCR. Although no gene expression was detected in the mice receiving an oral administration of naked plasmid or polyethyleneimine-plasmid complex. the EGFP gene complexed with montmo-rillonite was expressed in the small intestine. These results indicate that montmorillonite protected the plasmid DNA from the acidic environment in the stomach and DNA-degrading enzymes in the intestine. and successfully delivered it into cells of the small intestine.