Arginine and its Derivatives Suppress the Opalescence of an Antibody Solution

Opalescence is a problem concerned with the stability of an antibody solution. It occurs when a high concentration of a protein is present. Arginine (Arg) is a versatile aggregation suppressor of proteins, which is among the candidates that suppress opalescence in antibody solutions. Here, we investigated the effect of various types of small molecular additives on opalescence to reveal the mechanism of Arg in preventing opalescence in antibody solution. As expected, Arg suppressed the opalescence of the immunoglobulin G (IgG) solution. Arg also concentration dependently inhibited the formation of microstructures in IgG molecules. Interestingly, the intrinsic fluorescence spectra of highly concentrated IgG solutions differed from those having low concentrations, even though IgG retained a distinct tertiary structure. Arginine ethylester was more effective in suppressing the opalescence of IgG solutions than Arg, whereas lysine and γ-guanidinobutyric acid were less effective. These results indicated that positively charged groups of both α-amine and guanidinium actively influence Arg as an additive for suppressing opalescence. Diols, which are the suppressors of the liquid-liquid phase separation of proteins were also effective in suppressing the opalescence. These results therefore provide insight into the control of opalescence of antibody solutions at high concentrations using solution additives.