Shedding light on the glass state
11th August 2011
Schematic representation of proteins dried with (a) and without (b) carbohydrate. The circles and hexagons represent the protein and the black semicircles reactive patches
In a special issue of the European Journal of Pharmaceutics and Biopharmaceutics (EJPB) Dr Roger Parker and Dr Natalia Perez described new work which shed light on the molecular basis of stabilising proteins in the glass state.
IFR, which is strategically funded by the Biotechnology and Biological Sciences Research Council (BBSRC), has had a long standing interest in the glass state of carbohydrates, polysaccharides and proteins which is relevant to their processing behaviour and mechanical and storage properties in diverse situations ranging from plant tissues to foods and biodegradable thermoplastics.
Although it is well known that adding a carbohydrate to a protein prior to drying confers stability to it in the dry state, the mechanism by which this is achieved is unclear. Using β-lactoglobulin as a model protein allowed the researchers to study a deteriorative reaction in solid systems ranging from the pure protein to dilute protein-carbohydrate mixtures.
At low concentrations the addition of the disaccharides sucrose and trehalose slowed the reaction as did low concentrations of the polysaccharide dextran. The results support a modified “water substitute hypothesis” and, in this instance, addition of the disaccharide trehalose did not provide any enhanced stability beyond that of the other carbohydrates.
“We propose that the function of the added carbohydrate is both to separate potentially reactive groups and reduce structural distortion on drying” said Dr Roger Parker.
These new insights led the paper to be included in an EJPB issue devoted to ‘Unmet needs in Protein Formulation Science.’
Reference: The aggregative stability of beta-lactoglobulin in glassy mixtures with sucrose, trehalose and dextran. European Journal of Pharmaceutics and Biopharmaceutics 78 (2), 264-270 doi:10.1016/j.ejpb.2011.02.002
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