Effect of Glycocalyx on Drug Delivery Carriers Targeted to Endothelial Cells

Animal models have shown that coupling ligands, targeted to endothelium surface receptors, with drug delivery carriers (DDC) can optimize the treatment of diseases by specific vascular delivery. The endothelium is exposed to hydrodynamic forces that modulate the expression of these cellular adhesion molecules (CAMs) and affect the structural and biological activity of endothelial cells (ECs). In order to investigate how delivery of targeted DDC can be optimized, we investigated carriers binding to flow adapted ECs under flow conditions. Comparison of live ECs to fixed cells from our previous experiments give insight into the effect of receptor motility on the cell surface as well as the effect of other factors such as glycocalyx (a protective layer of carbohydrates on the surface of cells) and actin remodeling. A flow chamber model is used to investigate how DDC size variation alters binding under flow conditions. Binding experiments were done with and without glycocalyx in order to elucidate its protective effect. Using fluorescence microscopy we determined the real time binding and rolling speeds of DDC under flow conditions. We also demonstrate the presence of glycocalyx and image actin filament remodeling. The binding of 1 µm carriers to ECs decreased after flow adaptation, in both non-activated and TNF-α activated ECs compared to non-flow adapted live cells. After removal of the glycocalyx by degrading enzymes binding increased in quiescent ECs, but only increased in activated cells after 2 hr of perfusion with particles. The binding with 100 nm carriers also decreased after flow adaptation but to a lesser extent and partially increased after enzyme degradation. These experiments give insight as to how tunable affinity parameters can be optimized to enhance therapeutic capabilities.