Trimerization Dictates Solution Opalescence of a Monoclonal Antibody.
Opalescence, sometimes observed in antibody solutions, is thought to be mediated by light scattering of soluble oligomers or insoluble particulates. However, mechanistic features, such as stoichiometry and self association affinity of oligomeric species related to opalescence, are poorly understood. Here, opalescence behavior of a monoclonal antibody (mAb 1) solution was studied over a wide range of solution conditions including different protein concentrations, pH, and in the presence or absence of salt. Hydrodynamic and thermodynamic properties of mAb 1 solutions were studied by analytical ultracentrifugation and dynamic light scattering. Opalescence in mAb 1 solutions is pH and concentration dependent. The degree of opalescence correlates with reversible monomer trimer equilibrium detected by analytical ultracentrifugation. Increased trimer formation corresponds to increased opalescence in mAb 1 solutions at higher pH and protein concentrations. Addition of NaCl shifts this equilibrium toward monomer and reduces solution opalescence. This study demonstrates that opalescence in mAb 1 solutions does not arise from the light scattering of monomer or random molecular self associations but is strongly correlated with a specific self association stoichiometry and affinity. Importantly, at pH 5.5 (far below isoelectric point of mAb 1) the solution is not opalescent and with nonideal behavior. This study also dissects several parameters to describe the hydrodynamic and thermodynamic nonideality.
Journal of pharmaceutical sciences