A novel insulin-sodium oleate complex for oral administration: preparation, characterization and in vivo evaluation

The aim of this study was to prepare a novel insulin-sodium oleate (Ins/SO) complex and to evaluate the characteristics of the resultant complex. The Ins/SO complex was prepared using the hydrophobic ion pairing (HIP) method and the structure characters were assessed by the FTIR and DSC analysis method. It was found that the Ins/SO complex was synthesized by the HIP method. The insulin complexation efficiency was reached up to 96.6 ± 0.41% and mean diameter of the Ins/SO complex was sized about 80 nm under optimal conditions. The insulin bioactivity of the complex was evaluated by in vivo test. When 1 IU/kg insulin or insulin equivalent Ins/SO complex was given to normal rats by subcutaneous injection, the plasma glucose level was reduced by almost the same percentage (41.0 ± 8.19% for insulin and 44.0 ± 6.29% for Ins/SO complex, respectively) over 1 h. It was showed that insulin was not out of the bioactivity during the complexation process. In order to evaluate the bioactivity of the complex for oral administration, 20 IU/kg insulin or insulin equivalent Ins/SO complex was given to rats by intragastric administration, respectively. In the case of the Ins/SO complex, the plasma glucose level reduced to 59.5 ± 6.29% of the initial one within the first 4 h and gradually recovered to 88.9 ± 8.73% within 16 h, while there was almost no hypoglycemic effect for native insulin. The results suggested that the complex has potential for oral candidates.