Effect of CaCl2 on the Structure of DODAB Vesicles Containing the Ganglioside GD3

Abstract

CaCl2 has been successfully used in the formulation and stabilization of vaccines. Vesicles made of the disialoganglioside GD3 and the cationic lipid DODAB are promising immunotherapeutic tools, by combining the targeting properties of GD3 and the adjuvant properties of DODAB. In this work, the effects of CaCl2 on the structure of DODAB and DODAB+GD3 vesicles have been compared by Differential Scanning Calorimetry (DSC) and Electron Paramagnetic Resonance (EPR) spectroscopy. EPR spectra show that CaCl2 does not induce the formation of GD3 domains by lateral phase separation. DSC thermograms show that CaCl2 hinders the formation of a subgel phase for vesicles cooled below 15 °C. CaCl2 also decreases the hysteresis between gel–fluid and fluid–gel transitions in both pure and mixed vesicles. EPR data show that CaCl2 increases the superficial rigidity of DODAB and DODAB+GD3 vesicles at temperatures below the gel–fluid transition. In this temperature range, CaCl2 does not affect the packing of the DODAB vesicle core but increases the packing of the DODAB+GD3 vesicle core. EPR data also show that CaCl2 decreases the rigidity of both types of vesicles at temperatures above the gel–fluid transition. These results might help overcome the challenges of vaccine and immunotherapy cold chain logistics.