Formation and stability of W/O microemulsion formed by food grade ingredients and its oral delivery of insulin in mice

- Effect of components on the formation and stability of microemulsions was studied.
- Effect of environmental factors on the formation of microemulsions was evaluated.
- Conductivity and rheological behavior confirmed the formation of W/O microemulsions.
- Insulin loaded W/O microemulsions lowered peak blood glucose level of mice.

Water in oil (W/O) microemulsions are potential vehicles to deliver insulin orally. In this study, we characterized the formation and stability of W/O microemulsions formed by food grade ingredients, including different intrinsic components (oil source, surfactant, and cosurfactant). Stable microemulsions were formed with Span80-Tween80 (S80T80) (HLB = 6) or PEG-7 hydrogenated castor oil (PEG-7) (HLB = 5) as surfactants and isopropyl myristate as the oil phase under mild processing conditions. The W/O microemulsions showed good thermodynamic stability in the temperature range 20-40 °C. S80T80 microemulsions were stable to the addition of NaCl. Peak glucose response to glucose tolerance test was dramatically decreased by the insulin loaded W/O microemulsions when administered to mice, and was further decreased to 1/3 of the control when sodium taurocholate or trypsin inhibitor was incorporated into the aqueous phase. This study shows that insulin in a W/O microemulsion remains bioactive during processing and digestion, and is bioavailable to the host animal.