Abstract
Though MC insulin preparations are said to have been developed from which the heterogeneous peptic contaminants have been removed, for the purpose of lowering the immunogenicity of insulin, a recent report claims the detection of considerable quantities of both substances with molecular weights higher than that of insulin and desamidoinsulin. Hence, a comparative study was made of MC insulin and conventional insulin as to purity and stability, using gel chromatography, polyacrylamide disc-gel electrophoresis, bio-assay (J. P. rabbit method) and other physical/chemical methods.
With gel chromatography applied to three vials of conventional insulin (400 U/10 ml/vial), bcomponent (23%) was detected besides c-component, but no b-component was detected in ten vials of MC-insulin (400 U/10 ml/vial) treated similarly with gel-filtration. With polyacrylamide disc-gel electrophoresis applied to 80 jug of various insulin preparations, it was demonstrated that conventional insulin contained proinsulin like substances (2-3%), arginineinsulin (2.5-3%) and monodesamidoinsulin (10-42%), but MC-insulin contained only traces of monodesamidoinsulin.
The stability of MC-insulin preparations was determined after storage for different periods at 5°C and at 30°C. It was found that there were no significant changes in biological potency, nitrogen content, zinc, or crystalline shapes and sizes after storage for twentyfour months at 5°C or after three months at 30°C. High molecular weight substances were not formed during these periods, but monodesamidoinsulin became slightly increased as storage was prolonged. This tendency was higher after storage at 30°C and was more noticeable in neutral soluble insulin than in an insulin zinc suspension.
Based on the above findings, it was assumed that MC-insulin preparations were more highly purified than was conventional insulin, and were very stable for long periods in cool places. For further development of MC-insulin, studies on the possible immunogenicity of desamidoinsulin and the prevention of its formation and its increase during storage are required.
