γ-ray irradiation of liposomes of polymerizable phospholipids containing octadeca-2,4-dienoyl groups and characterization of the irradiated liposomes

The synthesis of a variety of polymerizable phospholipids containing the octadeca-2,4-dienoyl moiety on 2-acyl chains and the characteristics of liposomes containing those phospholipids of the gamma-irradiation are described. We synthesized three different polymerizable phosphocholines that have different 1-acyl chain lengths with the octadeca-2,4-dienoyl moiety on the 2-acyl chain: myristoyl (MODPC), palmitoyl (PODPC) and stearoyl (SODPC). The liposomes were prepared by extrusion through polycarbonate filters with a pore size of 0.2 mu m, and were polymerized by gamma-irradiation with various dose rates. The polymerization rate increased in the order SODPC > MODPC > PODPC. The mechanism of the polymerization of SODPC was the same as that of 1,2-bis-[(E,E)-octadeca-2,4-dienoyl]-sn-glycero-3-phosphocholine (DODPC), but differed from that of MODPC and PODPC. Freeze-thaw testing was used to evaluate the stability of the polymerizable liposomes. The MODPC liposome was more stable than other monofunctional liposomes. For similar irradiation, the polymerization behavior of the liposomes was significantly affected by the 1-acyl length.