Dextranol: A better lyoprotectant

Abstract

Dextranol, a reduced dextran, prevents damage to stored dry protein samples that unmodified dextran would otherwise cause. Lyoprotectants like the polysaccharide dextran are critical for preserving dried protein samples by forming rigid a glass that protects entrapped protein molecules. Stably dried proteins are important for maintaining critical information in clinical samples like blood serum. However, we found that dextran reacts with serum proteins during storage, producing high-molecular weight Amadori-product conjugates. These conjugates appeared in a matter of days or weeks when stored at elevated temperatures (37{degrees} or 45{degrees}C), but also appeared on a timescale of months when stored at room temperature. We synthesized a less reactive dextranol by reducing dextrans anomeric carbon from an aldehyde to an alcohol. Serum samples dried in a dextranol- based matrix protected the serum proteins from forming high-molecular weight conjugates. The levels of four cancer-related serum biomarkers (prostate specific antigen, neuropilin-1, osteopontin, and metalloproteinase 7) decreased, as measured by immunoassay, when serum samples were stored for one to two weeks in dextran- based matrix. Switching to a dextran-based lyoprotection matrix slightly reduced the damage to osteopontin and completely stopped any detectable damage during storage in the other three biomarkers when for a period of two weeks at 45{degrees}C. Dextranol offers a small and easy modification to dextran that significantly improves the molecules function as a lyoprotectant by eliminating the potential for damaging protein-polysacharide conjugation.