Transdermal Insulin Delivery Using Ionic Liquid-Mediated Nanovesicles for Diabetes Treatment

Transdermal insulin delivery is a promising method for diabetes management, providing the potential for controlled, sustained release and prolonged insulin effectiveness. However, the large molecular weight of insulin hinders its passive absorption through the stratum corneum (SC) of the skin, and high doses of insulin are required, which limits the commercial viability. We developed ethosome (ET) and trans-ethosome (TET) nanovesicle formulations containing a biocompatible lipid-based ionic liquid, [EDMPC][Lin], dissolved in 35% ethanol. TET formulations were obtained by adding isopropyl myristate (IPM), Tween-80, or Span-20 as surfactants to ET formulations. Dynamic light scattering, ζ-potential, transmission electron microscopy, and confocal laser scanning microscopy studies revealed that the nanovesicles had a stable particle size. The formulations remained stable at 4 °C for more than 3 months. ET and TET formulations containing IPM (TET1) significantly (p < 0.0001) enhanced the transdermal penetration of FITC-tagged insulin (FITC-Ins) in both mouse and pig skin, compared with that of the control FITC-Ins solution and other TET formulations, by altering the molecular structure of the SC layer. These nanovesicles were found to be biocompatible and nonirritants (cell viability >80%) in the in vitro and in vivo studies on three-dimensional (3D) artificial human skin and a diabetic mouse model, respectively. The ET and TET1 formulations were applied to the skin of diabetic mice at an insulin dosage of 30 IU/kg. The nanovesicle formulations significantly reduced blood glucose levels (BGLs) compared with the initial high BGL value (>150 mg/dL). The nanovesicle-treated mice maintained low BGLs for over 15 h, as opposed to only 2 h in the injection group. The ET and TET1 formulations reduced the BGLs by 62 and 34%, respectively, of the initial value. These ET and TET1 formulations have a high potential for use in commercial transdermal insulin patches, enhancing comfort and adherence in diabetes treatment.