Significant progress in diabetes device technology has been realized over the past two decades. These novel technologies improve glycemic control over daily injections thus reducing the probability of encountering diabetic complications. Insulin infusion pump sets provide dosing flexibility and enhanced clinical efficacy in terms of reducing HbA1c and severe hypoglycemic events. Despite these technological improvements in insulin delivery systems, current best-practice set wear is typically limited to three days. Current challenges to extending the lifespan of subcutaneous insulin administration sets and infusion pumps involve unreliable insulin efficacy through the development of skin pathologies. Currently, all commercially available insulin formulations contain insulin phenolic preservatives (IPP) known as excipients that are a double edge sword. While they provide insulin protein stability, sterility and prolong insulin shelf life, our laboratory has recently shown that these are cytotoxic, induce inflammation and secondary fibrosis. Subsequently, our data in murine and porcine models demonstrated that proximate pre-infusion IPP removal significantly reduces infusion site inflammation while maintaining protein functionality. Thus, the two major obstacles to increased infusion set wear time are the chemotoxicity of the IPP and the transdermal cannula induced tissue injury, both of which are inflammation driven. Mature mast cells (MC) reside in cutaneous tissue. Thus, MC are one of the first responder in skin injury and are key contributors in orchestrating the inflammatory response once the skin is breached. Therefore, our central hypothesis, supported by our published and preliminary data, is that accumulative IPP and the transdermal injection and infusion devices contribute to local skin irritation due to mast cell activation and subsequent leukocyte recruitment, thus initiating the inflammatory cascade. As MC interact with macrophages (MQ) we further hypothesize that increased MC degranulation promotes M1 phenotype leading to phagocytosis insulin uptake/degradation by neutrophils & MQ and thus altering blood glucose control. Therefore, our overall goals are, first, to determine how MC activation occurs, and, second, the contribution to the resulting tissue reactions (inflammation and fibrotic cascades) while correlating IPP concentration and composition for the duration of the infusion period. We will test our hypothesis in three specific aims: 1) determine IPP induced MC activation and insulin degradation, 2) employ novel transgenic mouse models (Cre/loxP) to determine the mechanisms and mediators of IPP and device MC induced inflammation, and 3) preserve long-term tissue integrity during insulin infusion pump therapy in a pre-clinical porcine model. Ultimately, the successful accomplishment of this proposal could result in transforming current diabetes management practices that would achieve the goals of increasing the lifespan of insulin infusion devices and most importantly, sustaining a tissue site available for future recurrent insulin administrations.

PROJECT NARRATIVE This proposed research project has significant public health implications given the profound increase in the incidence of diabetes mellitus and the ensuing exponential increase in health care expenditures required to treat its complications. Diabetic complications are optimally prevented when euglycemia is achieved through the use of insulin infusion pumps that approximate normal glucose homeostasis for insulin-dependent diabetes patients. The resultant knowledge will extend infusion pump lifetime by providing additional insights into the causal role of mast cell activation and products following insulin excipient and device induced tissue reaction to allow the identification of new targets that will advance the development of more effective and specific approaches that will optimize future diabetes therapies.