Opalescence of an IgG1 Monoclonal Antibody Formulation is Mediated by Ionic Strength and Excipients - Can increase in ionic strength result in higher viscosity? - BioPharm International

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Opalescence of an IgG1 Monoclonal Antibody Formulation is Mediated by Ionic Strength and Excipients
Can increase in ionic strength result in higher viscosity?


BioPharm International
Volume 22, Issue 4

Impact of Ionic Strength on Viscosity


Figure 7
To further explore the effect of ionic strength on the MAb1 formulation, the viscosity of formulations with increasing amounts of NaCl and concentration were evaluated. It was determined that the viscosity increased in a concentration-dependent manner (Figure 7). Additionally, as the ionic strength was increased with NaCl, the viscosity also increased (Figure 7). MAb1 at 100 mg/mL in 150 mM NaCl had a viscosity of ~20 cP (Figure 7). The most significant change in viscosity (~90 cP) occurred in the 100 mg/mL sample containing 500 mM NaCl (Figure 7).

Differential Scanning Calorimetry of MAb1 with Increasing Amounts of NaCl


Figure 8
Differential scanning calorimetry (DSC) was performed on MAb1 at a concentration of 1 mg/mL IgG1, PS-80, pH 6.0 with increasing amounts of NaCl. It was determined that the first transition (Tm1 = 69.7 C) shifted to a lower temperature (67.1 C) as the amount of NaCl was increased to 250 mM. The second transition (Tm2 = 88.1 C) also decreased (85.5 C) as the NaCl concentration was increased to 250 mM (Figure 8).

Stability Studies


Figure 9
It was also investigated whether the ionic strength had an effect on the stability of MAb1 formulations. MAb1 formulations at 24 mg/mL IgG1 containing increasing amounts of NaCl, a buffer, and PS-80 were placed on stability for four weeks at 4 C and 45 C. Samples were analyzed using SEC–HPLC at different time points. In formulations stored for four weeks at 4 C, there were no changes detected (data not shown). After four weeks at 45 C in the absence of NaCl, approximately 2.5% dimers were present (Figure 9). However, in samples containing 250 mM NaCl that were incubated for four weeks at 45 C, the amount of dimers increased to approximately 5% (Figure 9). A systematic trend of increasing dimers was observed with an increase in NaCl concentration (Figure 9).

Osmotic Second Virial Coefficient of the MAb1 Formulation

The osmotic second virial coefficient is commonly indicated by the term A2 or B22. When the second virial coefficient is measured using light scattering, it reflects protein–protein interactions as well as contributions from protein–cosolute interactions and protein nonideality.16,17 A positive B22 value correlates to net repulsive forces between solute molecules, and negative B22 values indicate net attractive forces between solute molecules.16,18,19 Several methods can be used to measure the B22 value of a formulation, one of which is the use of multi-angle light scattering with dilutions of the formulation. This method was used to obtain second virial coefficient values for MAb1.


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