Microencapsulation of Japanese encephalitis antigen in biodegradable polymers for vaccine delivery

Abstract

Japanese Encephalitis (JE) antigen was encapsulated in poly (lactide-co-glycolide) (PLGA) polymers by multiple emulsion solvent evaporation method and in chitosan by emulsion-ionotropic gelation method. Various ratio of the copolymers, PLGA 50:50, PLGA 75:25, PLGA 85:15, DL-PLA and different molecular weight of chitosan, LMW, MMW and HMW were used. The physical properties and stability of microparticles and antigen in microparticles were evaluated. Results from SEM, CRYO-SEM and laser particle size analyser revealed that most microparticles were discrete and spherical with smooth surface. They were of polymer, the amount of antigen used and the speed of sonicator for PLGA microparticles or ratio of aqueous : oil phase for chitosan microparticles. The antigen entrapment efficiency detected by bicinchoninic acid method was between 40-70% while the antigen content in microparticles was between 0.2-0.4%. The antigen release in phosphate buffer saline pH 7.4 was depended on the size of microparticle. However, the degradation of polymer detected by gel permeation chromatography exhibited prominent effect on the release. The release rate was ranked ; PLGA 50:50 > PLGA 75:25 > PLGA 85:15 > DL-PLA for PLGA microparticle due to hydrophilicity of the of the copolymer and LMW > MMW > HMW for chitosan microparticle due to their viscosity. Process of preparation did not alter the antigenic epitope of antigen. In addition the microparticlewas satisfactorily stable after storage at 40℃ for 1 month. Immune response expressed as antibody titer by enzyme-linked immunosorbent assay was determined after subcutaneous administration to rabbits of selected microparticles compared to fluid vaccine. Both PLGA and chitosan microparticles coyld augment antibody level and prolong immune response. Result from PLGA microparticles was more prominent than chitosan microparticles of the same 150 µg dose after single administration. However, both showed less response than fluid vaccine of recommended than 50 µg doses.