Inflammation at Site of Insulin Infusion Diminishes Glycemic Control

Abstract

The approximation of euglycemia is the most effective means of preventing diabetic complications, which is achieved through effective insulin delivery. Recent reports indicate that insulin phenolic preservatives, which are found in all commercial insulin formulations, are cytotoxic, pro-inflammatory and induce secondary fibrosis. Therefore, we hypothesize that these preservatives induce an inflammatory response at the site of insulin infusion leading to diminished glycemic control and adverse pharmacokinetic outcomes. Insulin degradation by inflammatory cell proteases was quantitated following protease treatment in vitro. A modified murine air pouch model was utilized to evaluate the relative inflammatory responses following infusions of saline, insulin preservatives, and insulin, utilizing the adjuvant irritant thioglycolate. Blood glucose levels were monitored in diabetic mice with and without air pouch irritation. A pharmacokinetic analysis evaluated insulin effectiveness for diabetic mice between these two conditions. Inflammatory cells are significantly present in insulin preservative-induced inflammation, which effects diminished blood glucose control by both insulin uptake and degradation. Insulin containing these preservatives resulted in similar degrees of inflammation as observed with the irritant thioglycolate. These studies imply that the preservative agents found in commercial insulin formulations induce an intense localized inflammatory reaction. This inflammatory reaction may be responsible for the premature failure of insulin infusion devices. Future studies directed at reducing this inflammatory reaction may prove to be an important step in extending the lifespan of insulin infusion devices.

Mast Cell Deficiency in Mice Attenuates Insulin Phenolic Preservative-Induced Inflammation

“…Previous studies have indicated that IPP-induced inflammation leads to edema in the air pouch tissue of mice following infusion for up to 7 days [ 10 ]. To evaluate the impact of MCs on edema following IPP infusion, total protein in the lavage fluid was quantified following the infusion of either saline or diluent into the air pouch of non-diabetic mice ( Figure 4 ).…”

“…Of note is the significantly increased total leukocyte count mainly driven by an increased neutrophil influx at 3 days in the air pouch of non-diabetic control mice ( C57BL/ 6J) ( Figure 2 A,B). This was not repeated at day 7 or in the HSD:CD-1 strains [ 6 , 7 , 8 , 10 , 11 ]. Although, reduced PMN chemotaxis [ 38 ], including the reduced leukocyte recruitment in diabetes patients [ 39 ] compared to that in non-diabetic controls, has been demonstrated, the reduced immune response in IPP-induced leukocyte influx in STZ-induced diabetic C57BL/6 J mice over a 3-day period warrants further investigation.…”

“…The air pouch model and its analysis have been described in previous publications [ 6 , 7 , 8 , 10 ]. Briefly, 3 mL of filtered air was injected subcutaneously into the shaved backs of the mice to create a sustained compartment one day prior to inserting the infusion cannulas.…”

“…The approved usage duration for commercial continuous-glucose-monitoring systems is 10+ days, whereas subcutaneous insulin infusion is 3+ limiting the possibility of an automated insulin-delivery system [ 1 ]. Several hypotheses have been proposed regarding the limited insulin infusion set functional lifespan, including inflammation induced by the material–tissue interface [ 2 , 3 , 4 ], insulin aggregate formation [ 5 , 6 ], or the toxicity of insulin phenolic preservatives (IPPs), such as phenol and m-cresol [ 7 , 8 , 9 , 10 ]. Specifically, our laboratory reported that these IPPs lead to unwanted cell and tissue toxicity [ 6 , 7 , 10 ], whereas Cromolyn sodium, an MC membrane stabilizer, significantly minimized IPP-induced inflammation [ 11 ].…”

“…Several hypotheses have been proposed regarding the limited insulin infusion set functional lifespan, including inflammation induced by the material–tissue interface [ 2 , 3 , 4 ], insulin aggregate formation [ 5 , 6 ], or the toxicity of insulin phenolic preservatives (IPPs), such as phenol and m-cresol [ 7 , 8 , 9 , 10 ]. Specifically, our laboratory reported that these IPPs lead to unwanted cell and tissue toxicity [ 6 , 7 , 10 ], whereas Cromolyn sodium, an MC membrane stabilizer, significantly minimized IPP-induced inflammation [ 11 ]. These Cromolyn studies targeting MCs highlighted the potential to improve on automated insulin-delivery systems by mitigating the inflammatory response.…”