A thermodynamic analysis of the binding interaction between polysorbate 20 and 80 with human serum albumins and immunoglobulins: a contribution to understand colloidal protein stabilisation.

The development of liquid therapeutic protein drugs imposes the presence of specific stabilisation agents to prevent protein degradation in order to reach shelf-lives of at least 2 years for drugs stored at 2-8 degrees C. Non-ionic detergents are used to avoid protein adsorption and the formation of protein aggregates. Depending on the protein and excipient (detergent) used the stabilisation effect is quite different and cannot be predicted up to now. One reason for this is the inadequate understanding of the principles that govern the stabilisation of proteins in the presence of detergents. One stabilisation mechanism discussed implicates a direct binding of detergent molecules to the hydrophobic surface area(s) of the protein in order to minimise protein-protein interactions and thus protein aggregation. Therefore, the presented study considers the interaction and binding of polysorbate 20 and 80 to various human serum albumins and immunoglobulins of different subtypes. The interaction is analysed by means of isothermal titration calorimetry (ITC) and differential scanning calorimetry (DSC). From ITC the binding constant is derived as well as the thermodynamic parameters. The thermal protein stability is obtained from DSC. The results show that binding of the two detergents to human serum albumin is observed with binding constants of approximately approximately 10(3) M(-1), with 1-3 detergent molecules binding to the albumins. The exact polysorbate-albumin ratio depends on the used albumin fraction. The interaction of the detergent is also obvious from the DSC results, showing an increase of the denaturation temperature. However, the binding of the detergent to the three investigated immunoglobulins is quite low and negligible, thus showing that for immunoglobulins a direct and strong polysorbate binding to the protein is not the reason for the colloidal stabilisation effect of immunoglobulins in solution in the presence of polysorbate 20 or 80.