Insulin is a well characterized drug used to treat diabetes. A large number of insulin formulations have been investigated in order to develop the optimum time delivery suited to patient needs. In addition, a number of insulin analogs such as Insulin Glargine and LysPro insulin (Humalog) have been developed and marketed as derivatives for immediate use at meal time and a more sustained release. With the regulatory release of a number of guidances on biosimilars, a number of biopharmaceutical companies are actively pursuing versions of these marketed products to address patient needs in this multibillion dollar market. The bioavailability of all these products is strongly dependent on not only the primary structure of the analog but also the formulation. Here, analytical ultracentrifugation (AUC) is investigated as a potential tool to analyze the higher-order structure of insulin under typical formulation conditions. AUC was used to probe the effect of insulin concentration, zinc addition, and the zinc chelating agent EDTA on monomer, dimer, and hexamer formation of USP Human Insulin Reference Standard. The zinc hexamer showed EDTA concentration dependence  with  increasing  dimer  and  monomer  species  at  higher  EDTA  concentrations.  The  methods  outlined  here  highlight  the  use  of  the  Beckman  Coulter  ProteomeLab  XL-I  for  characterizing  biopharmaceuticals  in  varying  conditions for formulation development. 

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