Analysis of interactions between the corneal epithelium and liposomes: qualitative and quantitative fluorescence studies of a corneal epithelial cell line.

Transcorneal drug transport is normally limited by the intrinsic permeation characteristics of the corneal epithelium. However, liposomes, i.e., phospholipid vesicles composed of phospholipid membranes, have recently attracted attention as carriers of topically applied agents. The present study therefore describes a qualitative and quantitative laboratory investigation of interactions between corneal epithelial cells and liposomes. The lipid bilayers and interior spaces of liposomes were labelled with different fluorophores. Fluorescence microscopy revealed a rapid uptake of rhodamine B-labelled liposome bilayer components by the epithelial cell membrane and the cytoplasm. Simultaneously, intracellular uptake of aqueous liposome content was indicated by uniform fluorescence of the cytoplasm due to carboxyfluorescein (CF). The fluorimetric experiments showed that the uptake of liposomes by SIRC cells depended on liposome concentrations and the time of exposure of the cells to the liposomes, and that saturation effect characteristics were present. Cell fluorescence dropped by approximately 45% when the incubation temperature of the cells was reduced from 37 degrees C to 4 degrees C. Both this phenomenon and a significant reduction in liposome uptake (p < 0.05 and p < 0.01) after incubation with the metabolic inhibitors 2-deoxyglucose and sodium azide indicated active, energy-dependent processes. Phagocytosis in cell-liposome interactions was directly shown by a significant reduction in cell fluorescence (p < 0.05) after application of the actin inhibitor cytochalasin B. The results presented here give concrete data on interactions between liposomes and superficial cells of the eye in vitro.