Studies On Oral Administration Of Insulin Based On Hydrophobic Ion Pairing Method

Insulin as the mainstay of drug therapy for patients with insulin-dependent diabetes mellitus (IDDM) and adjuvant therapy for patients with non insulin-dependent diabetes mellitus (NIDDM) is widely used. Injections are the most normal mode of delivery of insulin to patients, but this route is inconvenient and not acceptable by patients because of frequent subcutaneous administration, which often causes low patient compliance. Oral administration is one of the most acceptable routes for patients, but it is very difficult because of the intrinsic characteristics of insulin (molecular weight is too large to penetrate mucosa of GI tract; degraded by protease, acid or basic and so on). Insulin loaded nanoparticles was studied in this paper based on research achievements at home and abroad. It was reported that sodium oleate can be used as absorption enhancer for many drugs, so insulin-sodium oleate complex (Ins-S.O complex), Ins-S.O complex loaded PLGA nanoparticles and composite microcapsules were prepared. Evaluation in vitro and in vivo showed it was promising for diabetes.Firstly, the Ins-S.O complex was prepared by hydrophobic ion pairing (HIP) method and the structure characters were assessed by various methods such as FTIR, DSC, Zeta potential analysis, and so on. It was confirmed that the Ins-S.O complex was successfully prepared. The preparation parameters such as pH of reaction solvent, the molar ratio of sodium oleate to insulin, stirring rate, reaction time, reaction temperature and so on were studied to get the maximal complexation efficiency (CE). The CE was reached up to 96.6±0.41% and the mean diameter of the Ins-S.O complex was sized about 80 nm under the optimal conditions. The partitioning coefficient was enhanced by 3 orders of magnitude compared with native insulin. The insulin bioactivity of the complex was evaluated by in vivo test. When 1 IU/kg insulin or insulin equivalent Ins-S.O 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-S.O complex, respectively) over 1 h. It was shown 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 and insulin equivalent Ins-S.O complex was given to Wistar rats by intragastric administration respectively. In the case of the Ins-S.O complex, the plasma glucose level reduced to 59.5±6.29% from the initial one within the first 4 h, but it recovered to 80% at 6 h. The pharmacological bioavailability of Ins-S.O complex was about 7.41%.Based on the preliminary study, Ins-S.O complex loaded poly(lactide-co-glycolide) (PLGA) nanoparticles was prepared via emulsion solvent diffusion method to get a long hypoglycemic effect. The effects of key parameters such as concentration of PVA, concentration of PLGA, initial-loaded drug, preparation temperature, preparation stirring rate and so forth on the properties of the nanoparticles were investigated. The insulin encapsulation efficiency reached up to 91.2% and the mean diameter of the nanoparticles was sized about 160 nm under the optimal conditions. The study of drug loading mechanism proved that more than 50% of insulin was absorbed on the surface of nanoparticles. The in vitro drug release was characterized by an initial burst and subsequent delayed release in various dissolution mediums.The pharmacological effects of the nanoparticles made of PLGA were further studied to evaluate their potential suitability for oral delivery. When Ins-S.O complex loaded PLGA nanoparticles was administered to STZ-induced diabetic rats by oral administration, the plasma glucose level reduced to 23.85% from the initial one 12 h post oral administration and this continued for 24 h. It was shown that the use of Ins-S.O complex loaded PLGA nanoparticles is an effective method to reduce plasma glucose levels. The pharmacological bioavailability of the PLGA nanoparticles in STZ-induced diabetic rats was about 11.41%,and the pharmacokinetics bioavailability was about 6.72%. The insulin nanoparticles also improved the glycemic response to an oral glucose challenge. The absorption mechanism of PLGA nanoparticles was also studied in this study.In order to inhibit the burst release of insulin from PLGA nanoparticles and make full use of insulin in colon, Ins-S.O complex loaded PLGA nanoparticles was encapsulated into microcapsules by spray drying method. Eudragit FS30D was used as the microcapsule carrier. It was found that all of PLGA nanoparticles was encapsulated in microcapsules.The in vitro release profile showed that the burst release was inhibited in pH 1.2 and pH 6.8 dissolution medium. The pharmacological bioavailability of the composite microcapsules in STZ-induced diabetic rats was about 14.05%, which suggested that the composite microcapsules harboring PLGA nanoparticles have the potential for oral administration.