Nonspecific delivery of substances into pancreatic islet cells by pH-sensitive liposomes in vitro.

The aim of this study was to evaluate the suitability of different liposome preparations for translocation of substances into the pancreatic islet cell in vitro. For this purpose, isolated islets, either fresh or cultured or dispersed islet cells from the rat were incubated with different liposome preparations containing 6-carboxyfluorescein. The composition of the liposomes was either phosphatidylcholine/ganglioside (pH-insensitive) or phosphatidylethanolamine/oleic acid (pH-sensitive). Non-specific immunoglobulin was attached to the liposome membrane by means of covalent conjugation or by dialysis. Following incubation with the different liposomes, the islets were dispersed and examined in a fluorescence microscope for assessment of intracellular fluorescence emitted by the liposome-delivered fluorescein. It was found that the delivery of liposomal contents into islet cells was the least when using the pH-insensitive liposomes. The delivery could be slightly increased if immunoglobulin was conjugated to these liposomes. Intracellular fluorescence arising from pH-sensitive liposomes was clearly stronger than that from pH-insensitive liposomes. The use of pH-sensitive liposomes with conjugated IgG, however, failed to improve the delivery. When the proportions of fluorescent cells in the different islet preparations were compared, there was a higher percentage of such cells in the freshly isolated islets and in the dispersed islet cells than in the cultured islet cells. To quantitate the liposome mediated delivery of substances, cells in suspension, from a insulin producing tumor cell line (RINm5F) of from dispersed rat islets, were incubated with carboxyfluorescein containing liposomes and the intracellular release of the fluorescein was followed spectrofluorometrically.(ABSTRACT TRUNCATED AT 250 WORDS)