Probing the mechanism of insulin aggregation during agitation.

Agitation of insulin during its storage and transport has been reported to denature the protein, resulting in its inactivation. The physical changes accompanying the denaturation process which result in aggregation of insulin are poorly understood. In this work, we study the aggregates formed following agitation of insulin under defined conditions by different physical and chemical techniques. We show that both non-disulphide-mediated covalent bonds as well as non-covalent interactions are involved in the formation of aggregates. The two-step kinetics of aggregation could be clearly seen, with discrete 'early' and 'late' stages of fibrillation. Understanding the nature of agitation-induced aggregates will help in devising a strategy to protect this therapeutic protein against instability during its storage and transport.