Tip-enhanced Raman scattering for tracking of invasomes in the stratum corneum.

Stratum corneum is the primary skin barrier to percutaneous absorption. Since 1980, topical liposomal formulations have been proposed and successfully employed for increasing the drug penetration through the skin. There is no clear consensus on the drug penetration mechanism from topically applied liposomes, despite a vast amount of research. One of the reasons for the ambiguity is that the interactions between the stratum corneum and liposomes are in nanoscale, which makes them difficult to probe. In this study, we employed tip-enhanced Raman scattering (TERS) to gain a better understanding of the interactions between the human stratum corneum and topically applied liposomal system called invasomes. TERS is capable of imaging at nanometer spatial resolution and can provide structural information at the nanometer scale. A sample preparation technique was developed and calibrated to enable TERS on complex stratum corneum samples. Invasomes prepared from a head deuterated phospholipid were employed to aid identification of topically applied liposomal phospholipid in the stratum corneum. Results presented in this study give for the first time a strong spectroscopic evidence along with high-resolution images to show intact invasome vesicles deep in the stratum corneum upon topical application.

Cationic liposomes formulated with DMPC and a gemini surfactant traverse the cell membrane without causing a significant bio-damage.

Cationic liposomes have been intensively studied both in basic and applied research because of their promising potential as non-viral molecular vehicles. This work was aimed to gain more information on the interactions between the plasmamembrane and liposomes formed by a natural phospholipid and a cationic surfactant of the gemini family. The present work was conducted with the synergistic use of diverse experimental approaches: electro-rotation measurements, atomic force microscopy, ζ-potential measurements, laser scanning confocal microscopy and biomolecular/cellular techniques. Electro-rotation measurements pointed out that the interaction of cationic liposomes with the cell membrane alters significantly its dielectric and geometric parameters. This alteration, being accompanied by significant changes of the membrane surface roughness as measured by atomic force microscopy, suggests that the interaction with the liposomes causes locally substantial modifications to the structure and morphology of the cell membrane. However, the results of electrophoretic mobility (ζ-potential) experiments show that upon the interaction the electric charge exposed on the cell surface does not vary significantly, pointing out that the simple adhesion on the cell surface of the cationic liposomes or their fusion with the membrane is to be ruled out. As a matter of fact, confocal microscopy images directly demonstrated the penetration of the liposomes inside the cell and their diffusion within the cytoplasm. Electro-rotation experiments performed in the presence of endocytosis inhibitors suggest that the internalization is mediated by, at least, one specific pathway. Noteworthy, the liposome uptake by the cell does not cause a significant biological damage.