Protein preservation is becoming a critical technology. According to Robert Langer, Chair of the FDA’s Science Committee, improving protein stabilization technology is now one of the greatest challenges in the fields of biomaterials and pharmaceuticals. Preservation can be achieved by embedding a protein in a glassy matrix, typically a polyalcohol or sugar. Ideally, the stabilized protein is reconstituted under physiological conditions when its function is required. Unfortunately though, there is often a loss of activity that increases as a function of storage time. Understanding the reasons for this loss of protein activity is a complex problem. The major stabilizing forces of protein structures are hydrophobic and electrostatic. While there is consensus on the hydrophobic contributions to stability, the roles of electrostatic interactions are heavily debated.
The internal molecular motions in proteins, necessary for biological activity, are very dependent on the degree of plasticizing, which is determined by the level of hydration.1
Protein stability has been directly tied to the equilibrium structuring of water between low-density and higher density forms.2
Protein structure can be monitored by fluorescence, differential scanning calorimetry and circular dichroic spectroscopy, and this information can be correlated to protein function as determined by colorimetric or fluorimetric assays.
Storage stability of the proteins shows a reasonably good correlation with the degree of retention of native structure of proteins during drying as measured by the spectral correlation coefficient for FTIR spectra.3 Other conditions, including temperature and pH, can be used to determine optimal stability ranges for proteins under a variety of conditions.
Additionally, determination of proteolysis or (unintentional or intentional) chemical modification as a function of temperature, relative humidity, head space gases, and other factors can be explored via HPLC, peptide mapping and other methods.
A final report with optimal conditions for stability can be developed.
Screening of common excipients for protein stability is available
Cold-stage microscopy under vacuum for analysis of protein freeze drying and cycle optimization.
1 A. Pacaroni, S. Cinelli, E. Cornicchi, A. de Francesco and G. Onori, Fast fluctuations in protein powders: The role of hydration, Chem. Phys. Lett. 410 (2005) 400-403.
2 M. Klotz, Parallel change with temperature of water structure and protein behavior, J. Phys. Chem. B, 103 (1999) 5910-5916.
3 L. Chang, D. Shepherd, J. Sun, D. Ouellett, K. L. Grant, X. Tang, M. J. Pikal , Mechanism of protein stabilization by sugars during freeze-drying and storage: Native structure preservation, specific interaction, and/or immobilization in a glassy matrix? Journal of Pharmaceutical Sciences. 94, (2005) 27 - 1444.