Synergistic Effect of Cavitation and Agitation on Protein Aggregation

It was recently reported that dropping induces protein aggregation due to the occurrence of cavitation. Agitation also causes protein aggregation. In this study, vials filled with antibody solution were subjected to a cycle of dropping and shaking using the friability testing apparatus to examine the combined effect of cavitation and agitation on protein aggregation. A cycle of dropping and shaking generated a massive amount of subvisible particles. Comparison of aggregation rate at different fill volumes indicated that shaking plays an important role in protein aggregation due to combination stress. Furthermore, the impact of dropping on aggregate formation was apparent because aggregation rate under combination stress was much faster than that under shaking stress alone. Increase in aggregate concentration was observed after shaking of the antibody solution, which was freshly filled into vials that had been previously used in the dropping and shaking test. Polysorbate 80 was effective in inhibiting aggregate formation under combination stress. These results suggest the following particle formation pathway: cavitation caused by dropping promotes antibody unfolding, the unfolded antibodies adsorb on the inner surface of the vial, and subsequent shaking yields subvisible particles by desorbing the adsorbed antibodies.