Insulin human, containing 51 amino acids, is a small polypeptide hormone that regulates blood glucose homeostasis. Patients with insulin-dependent diabetes mellitus require insulin therapy through the administration of exogenous insulin to avoid ketoacidosis. Utilizing various genetic engineering techniques, pharmaceutical companies have developed a variety of rapid- or long-acting insulin analogues. Analytical methods for various types of insulin and insulin analogues are gradually being included in the United States Pharmacopeia (USP) and the European Pharmacopeia (Ph. Eur.), but not yet in the Chinese Pharmacopeia. Usually these insulin analogues only differ by 1 to 3 amino acids, which is too subtle to distinguish by most of analytical methods currently available. In this study a peptide mapping technique was employed to screen insulin analogues for quality assessment. Peptide mapping is capable of identifying single amino acid changes resulted from events such as errors in the reading of complementary DNA sequences or point mutations. Here we analyzed 6 insulin preparations including insulin human, insulin lispro, insulin aspart, insulin detemir, insulin glargine and insulin glulisine using peptide mapping analysis. The peptide fingerprints of the insulin products we tested all corresponded well to those of the standard materials. Our peptide mapping method is more accurate in identifying the subtle differences between the insulin analogues than chromatography is. We concluded that peptide mapping is a valuable initial screening tool for quality assessment of insulin analogues. In the future, we intend to continue to develop this technology for post-marketing surveillance of other biopharmaceuticals and biosimilars, such as somatropin, erythropoietin and G-CSF.

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