Effect of Sterilization on Protein Adsorption of Micro- and Nano-sized Aluminum Hydroxide Adjuvant

Abstract

Aluminum hydroxide (AH) is one of the aluminum-based adjuvants that forms needle-like crystalline structure with the average particle size of 1-20 µm. Due to their favorable safety profile, AH adjuvant has been used widely in various human vaccine in diphtheria, tetanus, pertussis, hepatitis, and papilloma virus vaccines. The antigen-adjuvant interaction is strongly governed by the adjuvant's physicochemical characters, such as shape, dimension and surface charge. Based on this concept, tremendous efforts to amplify the performance of the adjuvant have been made by modifying its particle size into nano-sized adjuvant. Also, during vaccine formulation, several physical processes may take place and potentially affect the antigen-adjuvant interaction, such as dilution, salt and aging exposure, pH change, heat, pressure and shear forces stress. Therefore, in this study we have examined the effect of sterilization and pH of AH nanoparticle (AHNp) with the average size of ~160 nm on its physical characterization and adjuvant-antigen interaction. The obtained results were compared with those from AH microparticle (AHMp) and commercial AH adjuvant (AHC).AHMp and AHNp were prepared by using common precipitation method through the addition of alkali to the solution of aluminum chloride. The aluminum content of both AH suspension is 12.1 mg/mL. The average particle size of AHMp and AHNp by static light scattering are 4.21 µm and 0.16 µm, respectively. For evaluating the effect of autoclave on AH properties, all AH samples on glass container were autoclaved at 121 °C for 30 dan 60 min. The result shows that all samples did not give significant physical character change after autoclave. All measured parameters including the solid content of AH suspension, the acquired mass after freezing dry, pH value, and visual appearance remained the same as those before autoclave. The X-ray diffractogram of AHMp and AHNp revealed that the diffraction bands were sharper after autoclaving.Following autoclaving, all fraction of (bovine serum albumin) BSA added into the adjuvant could be completely adsorbed by AHNp, AHMp, and AHC samples, as high as its pre-autoclaved condition, achieving maximum adsorption capacity. Such phenomena could be obtained even when volume ratio of adjuvant/BSA multiplied 20-times. It indicates that the binding efficiency BSA to all adjuvant