Sains Malaysiana 47(6)(2018): 1235–1240 http://dx.doi.org/10.17576/jsm-2018-4706-19 Effect of Gamma Irradiation on the Physical Stability of DPPC Liposomes (Kesan Sinaran Gama ke atas Kestabilan Fizikal Liposom DPPC) LIYANA MOHD ALI NAPIA, IRMAN ABDUL RAHMAN*, MOHD YUSOF HAMZAH, FAIZAL MOHAMED, HUR MUNAWAR KABIR MOHD, INTAN SYAKEELA AHMAD BASTAMAM, SHAMELLIA SHARIN, NORSYAHIDAH MOHD HIDZIR & SHAHIDAN RADIMAN ABSTRACT Unilamellar liposomes composed of dipalmitoylphosphatidylcholine (DPPC) were prepared by the reverse-phase evaporation method and extrusion through a polycarbonate membrane filter. Liposomes at 0.7 mg/mL lipid concentration in deionized water were exposed to gamma irradiation at a dose in the range 0.5 to 25 kGy. Gamma irradiation of liposomes resulted in the degradation of DPPC lipids into free fatty acids, lysophosphatidylcholine and 1,2-palmitoyl- phosphatidic acid (DPPA). The effect of gamma irradiation towards the physical stability of liposomes was investigated by means of dynamic light scattering (DLS), transmission electron microscopy (TEM) and zeta potential analysis. From the DLS analysis, no significant changes were observed in the hydrodynamic size of liposomes. TEM images indicate that the liposomes surface became smoother and rounder as higher irradiation doses were applied. Zeta potential analysis showed that gamma irradiation of DPPC liposomes at radiation doses as low as 0.5 kGy resulted in a drastic rise in the magnitude of the zeta potential. The results also demonstrate that gamma irradiation of liposomes suspension enhanced the overall stability of liposomes. Hence, it can be concluded that gamma irradiation on DPPC liposomes may potentially produce liposomes with higher stability. Keywords: Dipalmitoylphosphatidylcholine (DPPC); gamma irradiation; physical stability; zeta potential ABSTRAK Liposom unilamela yang terbentuk daripada lipid dipalmitoilfosfatidilkolina (DPPC) telah dihasilkan menggunakan kaedah penyejatan fasa-berbalik dan penerobosan menerusi turas membran polikarbonat. Ampaian liposom dengan kepekatan lipid 0.7 mg/mL di dalam air ternyah ion dipancarkan sinaran gama pada dos 0.5 hingga 25 kGy. Penyinaran gama ke atas liposom menyebabkan degradasi lipid DPPC kepada asid lemak bebas, lisofosfatidilkolina dan 1,2-palmitoil-asid fosfatidik (DPPA). Kesan penyinaran gama terhadap kestabilan fizikal liposom dikaji menggunakan analisis penyerakan cahaya dinamik (DLS), mikroskop elektron transmisi (TEM) dan penganalisis keupayaan zeta. Daripada analisis DLS, tiada perubahan pada saiz liposom dapat dikenal pasti. Imej TEM menunjukkan bahawa permukaan liposom semakin licin dan semakin membulat apabila semakin tinggi dos penyinaran dikenakan ke atas liposom. Analisis keupayaan zeta mendedahkan bahawa penyinaran gama ke atas liposom DPPC pada dos serendah 0.5 kGy menyebabkan peningkatan drastik terhadap magnitud keupayaan zeta. Hasil analisis ini juga menunjukkan bahawa penyinaran gama ke atas ampaian liposom berupaya untuk meningkatkan kestabilan liposom. Oleh itu, penyinaran gama ke atas liposom DPPC boleh menghasilkan liposom yang berkestabilan tinggi. Kata kunci: Dipalmitoilfosfatidilkolina (DPPC); kestabilan fizikal; keupayaan zet; penyinaran gama INTRODUCTION The effects of gamma irradiation on the overall chemical structure of liposomes have been extensively investigated to understand its influence on biological systems (Albertini & Rustichelli 1993; Erdogan et al. 2006; Hur Munawar et al. 2013; Pamplona 2008; Schneider 2009; Stark 1991; Van der Paal et al. 2016). The understanding of such mechanisms is vital, because liposomes represent a good model in the study of the effect of radiation on food, cells as well as sterilization of drug carriers. Studies on the effect of gamma irradiation on dipalmitoylphosphatidylcholine (DPPC) and hyaluronic acid (HA) and the manner in which the irradiation changes the interaction between these two components has also been thoroughly investigated (Ainee Fatimah et al. 2015). In spite of all the effort done in prior work, results on physico-chemical changes, especially ones affected by irradiation-damage are still lacking, thus hindering the application of liposomes as drug carriers and the utilization of irradiation to sterilize liposomes. Liposomes, upon irradiation with gamma rays, are subjected to direct or indirect effects. Direct effects are usually associated with the degradation of chemical bonds, while indirect effects are caused by radicals formed from radiolysis of water. In the former process, liposomes directly absorb irradiation energy, resulting in chemical chain-scissioning. On the other hand, in the latter