Phenolic Preservative Removal from Commercial Insulin Formulations Reduces Tissue Inflammation while Maintaining Euglycemia

Background: Exogenous insulin therapy requires stabilization of the insulin molecule, which is achieved through the use of excipients (e.g., phenolic preservatives (PP)) that provide protein stability, sterility and prolong insulin shelf life. However, our laboratory recently reported that PP, (e.g., m-creosol and phenol) are also cytotoxic, inducing inflammation and fibrosis. Optimizing PP levels through filtration would balance the need for insulin preservation with PP-induced inflammation. Method: Zeolite Y (Z-Y), a size-exclusion-based resin, was employed to remove PP from commercial insulin formulations (Humalog) before infusion. Results: PP removal significantly decreased cell toxicity in vitro and inflammation in vivo. Infusion site histological analysis after a 3 day study demonstrated that leukocyte accumulation increased with nonfiltered preparations but decreased after filtration. Additional studies demonstrated that a Z-Y fabricated filter effectively removed excess PP such that the filtered insulin solution achieved equivalent glycemic control in diabetic mice when compared to nonfiltered insulin. Conclusion: This approach represents the proof of concept that using Z-Y for in-line PP removal assists in lowering inflammation at the site of insulin infusion and thus could lead to extending the functional lifespan of insulin infusion sets in vivo.