The Association of Plain and Ligand- Bearing Neutral and Ph-Sensitive Liposomes with Various Cells

Abstract

The majority of commonly used liposomes are supposed to enter cells through an endocytotic pathway and to be delivered to the lysosomes where enzymatic degradation of the lipids and the encapsulated material can occur. Therefore liposomes that do not end up in the lysosomes have been designed. One strategy is the application of pH-sensitive liposomes. Because of their lipid composition these liposomes show increased sensitivity to reduced pH which leads to fusion with endosomal membranes and to release of encapsulated material in the cytosol before degradation in the lysosome. One more step forward is receptor-mediated targeting through specific ligands coupled onto the liposomal surface.

The exact mechanism by which liposomes are taken up by cells is still under investigation. It has become obvious in the past that it is necessary to gain individual information for every liposomal preparation and to study the effect on each cell line and primary cell culture. We have investigated the association of liposome preparations composed of the neutral lipid SPC (soy lecithin) and pH-sensitive lipids DOPE/CHEMS 3:2 mol/mol (dioleoylphos-phatidylethanolamine and cholesteryl hemisuccinate) with different cell lines: HeLa (human cervix carcinoma), COS-7 (monkey kidney, SV 40 transformed) and LMH (chicken hepatoma). Serum stability and influence of serum on the association efficiency was studied. Our data show that the presence of 10% fetal calf serum (FCS) during incubation did not reduce association efficiency significantly. Liposome encapsulated marker (FITC-dextran) was effectively delivered to HeLa and COS-7 cells by means of pH-sensitive liposomes. Receptor-mediated delivery could be achieved to LMH cells by coupling specilic ligand N-Ac-BSA to pH-sensitive liposomes.

Some of the experiments were performed at 37°C and 4°C to study the involvement of phagocytosis, a process which does not occur below 10°C.

Keywords::

• Cellular uptake
• Neutral/Ph-sensitive liposomes
• Receptor-mediated targeting
• Asialoglyco-protein-receptor
• Serum stability