Preparation and characteristics of W/O microemulsion stabilized with polyglycerylpolyricinoleate as a potential system for oral insulin delivery

Aim. The aim of the present work was to develop the composition and study the characteristics of water-in-oil microemulsion stabilized with polyglycerylpolyricinoleate — Tween 80 — ethanol mixture as a potential system for oral insulin delivery. Materials and methods. To determine the boundaries of the regions of existence of water-in-oil microemulsion in the pseudo-three component systems water — polyglycerylpolyricinoleate (PG-3-PR, Gobiotics BV, Netherlands)/ Tween 80/ethanol — paraffin oil, mixtures of paraffin oil and surfactants with oil — surfactant ratios from 9.5:0.5 to 0.5: 9.5 (wt.) were thoroughly mixed and titrated with an aqueous phase (distilled water).Compositions with the value of hydrophilic-lipophilic balance of the PG-3-PR — Tween 80 mixture equal to 6.15 were studied. Among several types of formed systems, a single-phase region corresponding to a homogeneous, optically transparent, liquid water-in-oil microemulsion was determined. The kinetic and thermodynamic stability of a number of compositions, including those containing insulin (Actrapid HM, Novo Nordisk А/С, Denmark), was studied. The values of the effective viscosity of microemulsions at different ratios of surfactant — oil and surfactant — co-surfactant were determined using a vibration viscometer. Based on the results obtained, a composition was selected to study the kinetics of insulin release into a model environment that simulated the environment of the small intestine. Insulin solution (the control sample) and the insulin-containing microemulsion were placed in the dialysis bags and immersed in 50 mL of PBS (pH 7.4) in a shaking incubator at 180 rpm and 37 ° С. At predetermined intervals, the aliquots of dissolution media were withdrawn, and the concentration of the released peptide was determined by the Bradford assay using a UV spectrophotometer at 595 nm. Results. The composition with 9:1 surfactant — co-surfactant ratio, containing 10 % of the aqueous phase (an insulin solution with a concentration of 100 IU / ml), which remained stable both during three cycles of freezing/thawing and heating/cooling, and after long-term storage at room temperature, was selected to study the kinetics of in vitro release of the peptide into the model medium. The effective viscosity of the sample was 2.4±0.04 Pa.s. The microemulsion sample demonstrated a prolonged release of insulin within 48 hours of the experiment (43 %). Conclusions. As a result, the boundaries of the existence of microemulsion regions in pseudo-three — component systems water — polyglycerylpolyricinoleate / Tween 80 / ethanol — paraffin oil were established, as well as the values of the effective viscosity of a number of compositions were determined. The study of the kinetic and thermodynamic stability of the obtained systems, including those containing insulin, as well as the study of the kinetics of the release of biologically active substance from the microemulsion into the model medium, allowed us to determine the optimal composition for further development of nanoscale dosage forms intended for prolonged delivery of insulin to the gastrointestinal tract.