title: Evaluation of effects of pH and ionic strength on colloidal stability of IgG solutions by PEG-induced liquid-liquid phase separation.
abstract: Colloidal stability of IgG antibody solutions is important for pharmaceutical and medicinal applications. Solution pH and ionic strength are two key factors that affect the colloidal stability of protein solutions. In this work, we use a method based on the PEG-induced liquid-liquid phase separation to examine the effects of pH and ionic strength on the colloidal stability of IgG solutions. We found that at high ionic strength (≥0.25M), the colloidal stability of most of our IgGs is insensitive to pH, and at low ionic strength (≤0.15M), all IgG solutions are much more stable at pH 5 than at pH 7. In addition, the PEG-induced depletion force is less efficient in causing phase separation at pH 5 than at pH 7. In contrast to the native inter-protein interaction of IgGs, the effect of depletion force on phase separation of the antibody solutions is insensitive to ionic strength. Our results suggest that the long-range electrostatic inter-protein repulsion at low ionic strength stabilizes the IgG solutions at low pH. At high ionic strength, the short-range electrostatic interactions do not make a significant contribution to the colloidal stability for most IgGs with a few exceptions. The weaker effect of depletion force at lower pH indicates a reduction of protein concentration in the condensed phase. This work advances our basic understanding of the colloidal stability of IgG solutions and also introduces a practical approach to measuring protein colloidal stability under various solution conditions.
authors.affiliation: Process and Product Development, Amgen Inc., Seattle, Washington 98119, USA.
authors.forename: Ronald W
authors.initials: RW
authors.lastname: Thompson
authors.affiliation: Process and Product Development, Amgen Inc., Seattle, Washington 98119, USA.
authors.forename: Ramil F
authors.initials: RF
authors.lastname: Latypov
authors.affiliation: Materials Processing Center, Massachusetts Institute of Technology, 77 Massachusetts Avenue, Cambridge, Massachusetts 02139, USA.
authors.forename: Ying
authors.initials: Y
authors.lastname: Wang
authors.affiliation: Materials Processing Center, Massachusetts Institute of Technology, 77 Massachusetts Avenue, Cambridge, Massachusetts 02139, USA.
authors.forename: Aleksey
authors.initials: A
authors.lastname: Lomakin
authors.affiliation: Process and Product Development, Amgen Inc., Seattle, Washington 98119, USA.
authors.forename: Julie A
authors.initials: JA
authors.lastname: Meyer
authors.affiliation: Process and Product Development, Amgen Inc., Seattle, Washington 98119, USA.
authors.forename: Suresh
authors.initials: S
authors.lastname: Vunnum
authors.affiliation: Materials Processing Center, Massachusetts Institute of Technology, 77 Massachusetts Avenue, Cambridge, Massachusetts 02139, USA.
authors.forename: George B
authors.initials: GB
authors.lastname: Benedek
mesh_terms: D003102:Colloids; D006801:Humans; D006863:Hydrogen-Ion Concentration; D007074:Immunoglobulin G / Q000737:chemistry*; D008958:Models, Molecular; D009994:Osmolar Concentration; D011092:Polyethylene Glycols / Q000494:pharmacology*; D011487:Protein Conformation; D055550:Protein Stability / Q000187:drug effects; D012995:Solubility; D012996:Solutions; D013696:Temperature
chemical_list: D003102:Colloids; D007074:Immunoglobulin G; D012996:Solutions; D011092:Polyethylene Glycols