Dextranol: A better lyoprotectant

Abstract

19Dextranol, a reduced dextran, prevents damage to stored dry protein samples that unmodified dextran 20 would otherwise cause. Lyoprotectants like the polysaccharide dextran are critical for preserving dried protein 21 samples by forming rigid a glass that protects entrapped protein molecules. Stably dried proteins are important 33 molecule's function as a lyoprotectant by eliminating the potential for damaging protein-polysacharide 34 conjugation.35 41 polysaccharides. Large uncharged polymers like polysaccharides protect proteins by molecular crowding, water 42 replacement, and glass formation (4-8). 43Dextran has frequently been used as a polysaccharide lyoprotectant in dry protein formulations, mainly 44 due to its high glass transition temperature, which enables room temperature storage (4,9,10). As an inert 45 additive (11), dextran is particularly suitable to be used as a preservative in pharmaceutical products (12-17). 46As a result, there have been numerous drugs on the market that contain dextran as a preservative (18,19), 47 including biologics (20,21). 48Dextran has one drawback, discovered in the food science field in early 1990s; storage of proteins with 49 dextran in low-moisture conditions can facilitate formation of protein-dextran conjugates. (22-25). This 50 reaction has been well documented to occur with various proteins (26-30). Dextran is a branched D-glucose 51 polymer by α-1,6 linkages and α-1,3 linkages at branch points with a single reducing end and multiple non-52 reducing ends. The conjugation is formed via a Mailard reaction between dextran's reducing end and protein's 53 primary amines (N-terminus and/or lysine side chains) leading via a Schiff base to the Amadori product. While 54 these conjugates are mostly shown to form at elevated temperatures (≥50°C) over a time period of days, there 55 are reports of protein-sugar conjugates forming even at lower temperatures, typically over longer time scales. 56 (31-36) 57 Dextran-protein conjugates are larger and more soluble than un-modified proteins. The size of dextrans, 58 like proteins, covers the low to high kilodalton range and thus, conjugation can easily double or triple the size 59 of the un-modified protein. Like pegylation, dextran conjugation also increases a protein's solubility (37) and 60 also makes it a better emulsifier (23,38-40). Conjugation of carbohydrates with proteins also causes acidification 61 (lowering of isoelectric point) by removing positive charges from lysine residues (41,42). 62 Dry storage is an attractive alternative to the typical cryogenic storage for stabilization of proteinaceous 63 biomarkers in clinical biofluid samples like blood serum. Many clinical samples are collected each year and 64 stored in archival biobanks for diagnostic and retrospective biomarker discovery research. The ten largest