A study of zwitterionic/cationic vesicle formation and the influence of hyaluronan on this formation

The aggregation behavior of the biocompatible and naturally occurring zwiterionic phospholipid 1,2-dipalmitoyl-sn-glycero-3-phosphatidylcholine (DPPC) combined with its synthetic cationic analogue 1,2-dipalmitoyl-3-trimetylammonium-propan (DPTAP) was studied. Further, the physical properties of the formed DPPC/DPTAP liposomes were determined. The phase transition temperature of DPPC/DPTAP mixtures was studied using the steady-state fluorescence of laurdan, and the results were compared with those obtained from microcalorimetry measurements. The phase transition temperature was higher for all DPPC/DPTAP mixtures compared to that for pure DPPC and DPTAP, this increase being particularly pronounced for equimolar mixtures of DPPC and DPTAP. Membrane fluidity was determined by means of 1,6-diphenyl-1,3,5-hexatriene fluorescence anisotropy measurements. While the ratio of DPPC in DPPC/DPTAP liposomes was increased, the results suggest the formation of more tightly packed membranes. The interaction of DPPC/DPTAP liposomes with hyaluronan (Hya) was also studied. The formation of complexes was observed at a specific DPTAP/Hya concentration ratio independently of DPPC concentration or the molecular weight of Hya.