Influence of lipid composition on the phase transition temperature of liposomes composed of both DPPC and HSPC.

Objective: Phase transition of the lipid membrane is one of the most important properties of liposomes. The objective of this study was to investigate the influence of molar ratio of 1,2-dipalmitoyl-sn-glycero-3-phosphocholine (DPPC) and hydrogenated soy phosphatidylcholine (HSPC) on the phase transition temperature (T(m)) of the liposomes.

Materials And Methods: The T(m)s of the liposomes with different phosphatidylcholine (PC) composition were determined by calcein release test and differential scanning calorimetry (DSC).

Results: Only one phase transition was observed for liposomes composed of both DPPC and HSPC, indicating that DPPC and HSPC might combine into one phase with single phase transition. The T(m) of the liposomes composed of both DPPC and HSPC was directly dependent on the molar ratio of the two PCs. Moreover, DPPC percentage and T(m) relationship could be fitted with a linear equation (r(2) > 0.98). In addition, the serum stability of the liposomes at 37°C was directly increased with the increase of DPPC percentage. When 10% DSPE-PEG2000 was added, the significant increase of calcein release at T(m) and decrease at 37°C were observed.

Discussion: It is easy to obtain liposomes with a T(m) in between that of DPPC and HSPC by modifying the molar ratio of DPPC and HSPC.

Conclusion: With the modification of T(m), the liposomes containing various ratios of DPPC and HSPC may have promising application potential in the field of thermosensitive liposomes (TSLs). After 10% DSPE-PEG2000 is added, a formulation of sterically stabilized liposomes with the proper thermal sensitivity can be obtained.