Evaluation of Liposomal composition on delivery of Hydrophilic substances and P-Glycoprotein substrates

Abstract

The aim of this study was to evaluate the effects of liposome compositions on the delivery of hydrophilic substances and P-glycoprotein (P-gp) substrates into and through epithelial cells. As the study tool, Caco-2 monolayers were validated for the integrity of the monolayer and the expression of functional P-gp. Calcein and rhodamine 123 were used as model molecules for hydrophilic substances and P-gp substrates, respectively. Calcein and rhodamine 123 containing liposomes were prepared by film hydration method followed by extrusion through 100 nm polycarbonate membranes. Uptake and transport of the model molecules were compared among liposomes with different surface charges and solution. The effect of temperature and flow cytometry were used to deduce further the mechanism of cellular uptake of liposomes. The results show that Caco-2 monolayers cultivated in this study were tight and expressed functional P-gp, which were appropriate for the purposes of the study. All liposome types could enhance uptake of calcein into Caco-2 cells. Positively charged (phosphatidylcholine/stearylamine/cholesterol) and neutral (phosphatidylcholine/cholesterol) liposomes were taken up by Caco-2 cells more efficiently than negatively charged (phosphatidylcholine/dicetylphosphate/cholesterol) liposomes. The mechanism of liposome uptake was consistent with endocytosis. Although, liposomes could increase the uptake of calcein into Caco-2 cells, transcytosis did not occur efficiently enough to enhance transport of the hydrophilic molecule across Caco-2 monolayers. For rhodamine 123, neutral liposomes could both increase the cellular uptake and facilitate the transport of the hydrophobic P-gp substrate across Caco-2 monolayers. On the other hand, the cellular uptake of both negatively and positively charged liposomes decreased from that of the control. Overall results indicate that liposomes should be useful in enhancing cellular uptake of both hydrophilic substances and P-gp substrates and in facilitating transport of P-gp substrates across Caco-2 monolayers. Physicochemical properties of liposomes such as surface charge as well as the properties of the substances contained in liposomes affected the efficiency of cellular uptake by Caco-2 cells. However, other cell types as well as other formulation factors, such as type of phospholipid and other additives, should be further explored to gain more insights in liposome-cell interaction in order to develop proper formulations to enhance delivery of such substances.