Effects of Gamma Irradiation on the Physical Stability of Liposomal Phospholipids

Abstract

The effects of liposome composition and gamma irradiation on the phase transition, size, zeta potential and pH were investigated using factorial designs. In addition, the effect of irradiation on the leak-in rate of calcein was evaluated for one of the liposome composition. The liposomes were stored for 6 months in order to reveal any possible long term effects. The phospholipids used were dipalmitoyl phosphatidyl choline (DPPC) or egg phosphatidyl choline (egg PC). Charge was introduced to the liposomal bilayers by the addition of 10% dipalmitoyl phosphatidyl glycerol (DPPG) or egg phosphatidyl glycerol (egg PG). The liposome-suspensions were obtained by the extrusion method. After gamma irradiation changes in the phase transition, zeta potential and pH of the liposomes were observed. The size of the liposomes was not affected by the irradiation, but the irradiation prevented the neutral DPPC-liposomes from aggregation. This was confirmed by cryo-electron microscopy. No change in the leak-in rate was observed. During storage, a significant increase in size was observed only for the non-irradiated egg PC-liposomes. For all the liposome-suspensions composed of unsaturated phospholipids, a significant drop in pH and an increased zeta potential (more negative) was measured. Changes in the phase transition for the neutral DPPC-liposomes (non-irradiated and irradiated) were observed during