Controlled Release of Insulin Granules from PLGA Microparticles for Glucose Modulation in Diabetes

Diabetes is a chronic disease deriving from the insufficient production or utilization of insulin. So far, the treatment of diabetes relies on the daily subcutaneous injection of insulin. However, this approach suffers of poor patient compliance and fluctuations in blood glucose levels that increases the risk of hypoglycemia, cardiovascular disease, non-healing wounds and other comorbidities. In this work, a delivery system is proposed for the controlled release of insulin and regulation of glycaemia. Nanoscale granules of insulin were synthesized and encapsulated within the porous matrix of PLGA microparticles (i-μPLs). The granules were obtained with an accurate crystallization process returning spherical nanoparticles with a diameter of 209.9±15.8 nm. μPLs were prepared via a top-down approach resulting in 20 x 5 μm square microparticles, made out of a biodegradable polymer - poly(lactic-co-glycolic acid) (PLGA) - which is already used in clinical applications. In vitro studies were conducted on different cells, including macrophages, fibroblasts and endothelial cells, and confirmed the safety and biological activity of i-μPLs. After insulin stimulation, phosphorylated AKT at Ser473 was assessed in cell lysate using a commercial kit (In-Cell ELISA): i-μPL activity was comparable to that of free, commercial insulin. As preliminary in vivo studies, i-μPLs (0.25 U) or empty μPLs (control) were implanted in the spleen of mice. Twenty-four hours post implantation, fasted mice underwent an oral glucose tolerance test (1 g glucose/Kg body weight). In i-μPL treated mice, the mean blood glucose level was lower as compared to controls at time zero (before gavage) and at 15, 30, 60 and 120 min. Consequently, the glycaemia AUC was reduced in i-μPLs-treated vs. control mice (17828±1527 vs. 20543±413, p=0.06). This preliminary data would suggest that i-μPLs could be effectively used to modulate glucose content in diabetes.