Biosurfactant MEL-A dramatically increases gene transfection via membrane fusion

Biosurfactants, which are surface-active compounds produced by microorganisms growing on water-insoluble substrates, have many biological activities. We studied here three different biosurfactants, mannosylerythritol lipid (MEL) or 4-O-[(4',6'-di-O-acetyl-2',3'-di-O-alkanoyl)-beta-D-mannopyranosyl] meso-erythritol (MEL-A), 4-O-[(6'-O-acetyl-2',3'-di-O-alkanoyl)-beta-D-mannopyranosyl] meso-erythritol (MEL-B) and 4-O-[(4'-O-acetyl-2',3'-di-O-alkanoyl)-beta-D-mannopyranosyl] meso-erythritol (MEL-C). MEL-A enhanced the efficiency of gene transfection by cationic liposomes, but MEL-B and MEL-C did not. We also studied the localization of FITC-conjugated antisense DNAs (15-mer oligonucleotides; phosphorothioate) in the target cells by confocal laser scanning microscopy (CLSM). The FITC-conjugated antisense oligonucleotides were temporarily on the plasma membrane of the target cells, thereafter they were transferred into the nucleus of the target cells. In the case of MEL-B and MEL-C, such localization of DNA was not observed both in the plasma membrane and in the nucleus. The results obtained by CLSM images were in good agreement with the transfection efficiency. This suggests that MEL-A induces the membrane fusion between the target cells and the cationic liposomes, accelerating the efficiency of gene transfection dramatically.