Effects of acidic N + 1 residues on asparagine deamidation rates in solution and in the solid state

Effects of acidic N + 1 residues on asparagine deamidation rates in solution and in the solid state
January 2005
Bei Li 1, Eric M. Gorman 2, Kimberly D. Moore 3, Todd Williams 3, Richard L. Schowen 1, Elizabeth M. Topp 1, Ronald T. Borchardt 1 *
1Department of Pharmaceutical Chemistry, The University of Kansas, 2095 Constant Avenue, Lawrence, Kansas 66047
2College of Pharmacy, Drake University, Des Moines, Iowa 50311
3Mass Spectrometry Laboratory, The University of Kansas, Lawrence, Kansas 66047
Journal of Pharmaceutical Sciences, Volume 94, Issue 3 , Pages 666 - 675
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Abstract
The deamidation kinetics of four model peptides (AcGQNGG, AcGQNDG, AcGQNEG, and AcGQNQG) were studied in solution (70?C, pH 5-10) and in lyophilized solids [70?C, 50% relative humidity, effective pH (pH) 5-10] containing polyvinyl pyrrolidone. AcGQNGG, AcGQNEG, and AcGQNQG degraded exclusively through Asn deamidation, whereas AcGQNDG also displayed Asp isomerization, and Asp-Gly peptide bond cleavage. The pH/pH-rate profiles were consistent with a shift in the rate-determining step of Asn deamidation from carbonyl addition to expulsion of ammonia with increasing pH. In solution, AcGQNGG deamidated up to 38-fold faster than the other peptides, indicating the importance of steric effects of the N + 1 residue. AcGQNGG and AcGQNQG had up to 60 times slower rates of deamidation in the solid state than in solution. In contrast, the deamidation rates of AcGQNEG and AcGQNDG in the solid state were similar to those in solution. N + 1 Glu or Asp residue may enhance local hydration, so that the deamidation of Asn in the solid formulations actually proceeds in a solution-like environment. ? 2005 Wiley-Liss, Inc. and the American Pharmacists Association J Pharm Sci 94:666-675, 2005