Studies On Quantitative Analysis & Absorption-Mechanism Of Oral Insulin Formulation

A stable self-emulsifying oral insulin formulation was successfully developed and provided a new drug carrier system for oral administration of protein and peptide. In this paper, several in vitro experiments were carried out, including quantitative analysis of insulin, physicochemical parameters and the absorption-mechanism of the oral insulin formulation. In addition, a two cross-over trial was conducted in diabetic Beagle dogs as an in vivo model to evaluate the potential application of this preparation in blood glucose control.Several pretreatment methods were applied and optimized for quantitative analysis insulin in self-micro-emulsifying formulations by reversed-phase high performance liquid chromatography(RP-HPLC). As a result, a 96% recovery of insulin was obtained when the insulin-loaded formulation was pretreated by Triton X-100 solution(0.01%, v/v). This pretreatment method, which set a platform for quality control and stability study of the formulaiotn, was simple, reproducible,highly sensitive and specific for quantitative determination of insulin in oily formulations.The formulation was evaluated by various physicochemical parameters such as droplet size, insulin encapsulation efficiency and stability. The influence of this formulation on Caco-2 monolayer cells was assessed in terms of apparent permeability coefficients (Papp) and trans-epithelial electrical resistance (TEER).This formulation enabled changes in barrier properties of Caco-2 mono-layers, as referred TEER and Papp of the para-cellular marker Ranitidine (20-fold greater than control) but not trans-cellular marker Propranolol, suggesting that the opening of tight junctions was involved.In diabetic Beagle dogs, the bioavailability of this formulation was up to 15.2% at a dose of 2.5 IU/kg in comparison with the hypoglycemic effect of native insulin (0.5 IU/kg) delivered by subcutaneous injection. This formulation, recently approved by China SFDA (State Food and Drug Administration) to enter clinical trials, was stable, degradation-protected and absorption-enhanced, and provided a promising formulation for oral insulin delivery.