Stabilization of recombinant human keratinocyte growth factor by osmolytes and salts

Keratinocyte growth factor (KGF) has limited stability in aqueous media, as it undergoes denaturation followed by aggregation at 37 degrees C. Heparin and anionic polymers have been shown to increase the denaturation temperatures and extend the half-life of the monomeric, native form of KGF during storage. These polymers, however, bind more than one protein molecule with high affinity, and such tight complex formation may cause problems for clinical use. In this study, we have tested low molecular weight additives, such as osmolytes and salts, for their effects on the stability of KGF against thermal denaturation and high-temperature storage. Salts such as NaCl, sodium phosphate, ammonium sulfate, and sodium citrate were highly effective in increasing both the denaturation temperature and storage stability. The fact that the same additives stabilize KGF against both stresses is consistent with the idea that the storage stability is determined by denaturation followed by aggregation. Among the osmolytes tested, N,N'-dimethylglycine, trehalose, and sucrose were also effective stabilizers. However, quantitative comparison of the osmolytes tested indicated that their effectiveness on the thermal denaturation and the storage stability is not exactly parallel, suggesting that other factors also contribute to the storage stability.