Clinical Aspects of Insulin–Antigenicity

Conventional insulin such as that used for therapy displayed a series of bands in polyacrylamide disc-gel electrophoresis, representing monodesamido-insulin, insulin corresponding to Sanger's formula, the intermediates of proinsulin, arginine insulin, insulin ethyl ester, proinsulin, etc. Separation according to molecular size was achieved by molecular sieving in Sephadex columns; anion-exchange chromatography yielded essentially pure insulin. When injected as a neutral solution, this monocomponent insulin was nonimmunogenic in rabbits, while the isolated protein contaminants elicited insulin antibody formation, which explains the immunogenicity observed with conventional recrystallized insulin. The values of insulin binding to serum IgG were determined by a standard electrophoretic procedure, with a fixed concentration of added 125I-labeled insulin. The values of total serum IRI were determined after acid ethanol extraction. The IgG binding and the total IRI were determined sequentially in sera from patients from the beginning of treatment with conventional insulin preparations. In the course of a few months, both parameters became considerably elevated. Practically no elevation was observed in sera from patients after treatment with monocomponent porcine Lente insulin, there was little or no antibody response, and the total serum IRI remained normal.