Effects of Gamma Irradiation on the Physical Stability of Liposomal Phospholipids

Sterilization methods of liposomes: Drawbacks of conventional methods and perspectives

Liposomes are targeted drug delivery systems that are of great pharmaceutical and therapeutic interest. Parenteral route is the main way used for liposome administration. In this case, their sterility is a requirement. However, due to the particular sensitivity of liposomes and their tendency to physicochemical alterations, their sterilization remains a real challenge. Conventional sterilization methods such as heat, ethylene oxide, ultraviolet and gamma irradiations are considered as unsuitable for liposome sterilization and the recommended methods for obtaining sterility of liposomes are filtration and aseptic manufacturing. Unfortunately, these recommended methods are not without limitations. This review outlines the difficulties associated with the use of these different classical methods for obtaining liposome sterility. The effects on liposome physicochemical and biopharmaceutical characteristics as well as efficacy, toxicity and practical problems of these sterilization techniques have been discussed. The search for an alternative method being therefore necessary, the applicability of supercritical carbon dioxide (ScCO₂) technology, which is nowadays a promising strategy for the sterilization of sensitive products such as liposomes, is also examined. It appears from this analysis that ScCO₂ could effectively be an interesting alternative to achieve sterility of liposomes, but for this, sterilization assays including challenge tests and optimization studies are needed.

Toxicity of gamma irradiated liposomes. 2. In vitro effects on cells in culture

In this study, the effects of liposome composition and gamma irradiation on their interactions with cell cultures were studied. The cytotoxicity test and the growth inhibition test clearly revealed toxic effects of liposomes composed of unsaturated phospholipids and gamma irradiation of these preparations enhanced their toxic effects. The murine fibroblast cell-line L 929 was less affected compared to the macrophage cell-line RAW 264 with a higher endocytic capacity. On the other hand, both gamma irradiated and non-irradiated liposomes composed of saturated phospholipids were non-toxic for the cells and irradiation did not affect their drug delivery properties. Hence, it seems that gamma irradiation is appropriate for sterilisation of these liposomes.