Effect of protein and solution properties on the donnan effect during the ultrafiltration of proteins

Abstract

Formulation of protein biopharmaceuticals as highly concentrated liquids can improve the drug substance storage and supply chain, improve the target product profile, and allow greater flexibility in dosing methods. The Donnan effect can cause a large offset in pH from the target value established with the diafiltration buffer during the concentration and diafiltration of charged proteins with ultrafiltration membranes. For neutral formulations, the pH will typically increase above the diafiltration buffer pH for basic monoclonal antibodies and decline below the diafiltration buffer pH for acidic Fc-fusion proteins. In this study, new equations for the Donnan effect during the diafiltration and concentration of proteins in solutions containing monovalent and divalent ions were derived. The new Donnan models obey mass conservation laws, account for the buffering capacity of proteins, and account for protein-ion binding. Data for the pH offsets of an Fc-fusion protein and a monoclonal antibody were predicted in both monovalent and divalent buffers using these equations. To compensate for the pH offset caused by the Donnan effect, diafiltration buffers with pH and excipient values offset from the ultrafiltrate pool specifications can be used. The Donnan offset observed during the concentration of an acidic Fc-fusion protein was mitigated by operating at low temperature. It is important to account for the Donnan effect during preformulation studies. The excipients levels in an ultrafiltration pool may differ from the levels in a protein solution obtained by adding buffers into concentrated protein solutions due to the Donnan effect.

Buffer‐free therapeutic antibody preparations provide a viable alternative to conventionally buffered solutions: From protein buffer capacity prediction to bioprocess applications

“…When developing a buffering approach, it is important to consider the specific production history of the mAb [8][9][10][11]; despite vigorous UF/DF, some residual storage buffer can remain, due to the Donnan effect and further protein-ion interactions. [8] Here, we call a solution condition "buffer free" if all residual buffers combined provide less than 5% of the total buffer capacity (e.g., as inferred from the buffer excipient concentration determined by the methods outlined in "Carboxylic acid analytics," below).…”

Viscosity Behavior of High-Concentration Monoclonal Antibody Solutions: Correlation with Interaction Parameter and Electroviscous Effects

“…At low ionic strength, the pH and ionic strength of the solutions were monitored during ultrafiltration/diafiltration to ensure constant ionic strength and achieve a targeted solution pH as described in the literature. [18][19] A brief explanation of the Donnan and excluded volume calculations for three solution pH conditions employed in this work are discussed in the Appendix section. For higher ionic strength studies, sodium chloride was added to adjust the total solution ionic strength to 150 mM and was chosen to achieve an ionic strength similar to that of an isotonic solution (0.9% NaCl solution = 154 mM ionic strength).…”

“…A description of the theoretical and practical approach to these effects have been detailed by Stoner et al 19 and recently by Bolton et al, 18 wherein the contribution of the Donnan effect on the final solution ionic strength and pH of the retentate can be estimated at any given protein concentration with a known Z and diafilterate buffer composition.…”

Improving impurities clearance by amino acids addition to buffer solutions for chromatographic purifications of monoclonal antibodies

“…The use of the same buffer agent, histidine, provided that the concentration in the CEX pool is higher than that in the formulation buffer, may also minimize the transition in pH or histidine concentration from the target value by the Donnan effect [38] during the ultrafiltration/diafiltration process, especially for highly concentrated mAbs. Further studies will be needed to examine these hypotheses.…”