Quality control issues in the analysis of lyophilized proteins

The assessment of protein stability requires the use of many sophisticated analytical techniques. Lyophilization procedures, commonly used to improve the stability profile of protein products, may potentiate undesirable protein degradation. The potential effects of lyophilization on proteins may include denaturation, decreased potency, aggregation, oxidation, and deamidation. Methods such as high-performance size-exclusion chromatography (HPSEC), peptide mapping, sodium dodecyl sulfate polyacrylamide gel electrophoresis (SDS-PAGE), and high-performance ion-exchange chromatography (HPIEC) may be used to evaluate these effects as well as to predict the long-term stability of the product. Typical degradation mechanisms of protein products and examples of the methods used for their analysis are described. In addition, methods for monitoring residual moisture levels in lyophilized proteins are presented with emphasis on their relative advantages and disadvantages.