Perturbation of the quaternary state of insulin aspart formulation after prolonged storage in a closed-vial, real-world setting

People with diabetes from many developing countries find it challenging to follow manufacturers’ guidelines regarding strict storage conditions for insulin. What happens to insulin formulations exposed to real-world scenarios is important to understand before adjusting the current recommendations to decrease wastage and increase global accessibility. Upon investigating the effect on the potency of insulin formulations lacking refrigeration during the summer in India, we observed a subtle (≤ 5%) decline in the relative potency over the four months in our previous study. In this report, we present the biophysical characterization of the ‘rapid-acting’ analogue insulin aspart using Nuclear Magnetic Resonance (NMR), Thioflavin T (ThT) fluorescence assay, Size Exclusion Chromatography coupled with Multi-Angle Light Scattering (SEC-MALS), and Native PAGE to decipher the cause behind this subtle potency decline upon prolonged storage. We report that insulin aspart undergoes a time-dependent gradual establishment of insulin quaternary structure equilibrium, without any detectable formation of fibrils upon prolonged storage at elevated temperature. This crucial information about temperature-associated changes in insulin aspart might aid in better preparation and handling of insulin in developing countries. • Study of insulin aspart formulation thermostability in a real-world setting • Biophysical characterization of ‘rapid-acting’ analogue insulin aspart formulations • Gradual establishment of insulin quaternary structure equilibrium observed. • No detectable presence of fibrils was found.