Preparation Of Phenylboronic Acid-modified Polymeric Carriers For Oral Delivery Of Insulin

In recent years,diabetes is a common global disease that causes immense suffering for individuals and heavy burden for the health care system.There are 415 million adults were living with diabetes in 2015 and this number is expected to increase to around 642 million or one in ten adults by 2040,according to a report from International Diabetes Federation(IDF).Polymer-based nanocarriers have attracted increasing attention due to their widely application in the drug-loaded and controlled drug release systems.In addition,oral administration via target polymer not only can enhance the smart response,but also reduce the pain of injection,with high efficiency and sustained release.Boronic acid group has been known to bind to sugars.Therefore,it has important significance to introduce phenylboronic acid into the polymer to control insulin release after oral administration.In this thesis,phenylboronic acid-modified glucose sensitive oral insulin carriers were prepared using three different methods,respectively.The drug release properties and oral administration were also investigated in vitro and in vivo triggered by different stimulis.More specifically,it contains three parts as follows:1.The phenylboronic acid-modified glucose-responsive and fluorescent copolymer was prepared via combining RAFT polymerization and enzymatic transesterification.The as-prepared copolymer tended to self-assemble into spherical micelles that were confirmed using 1H NMR,FT-IR,transmission electron microscopy(TEM)and dynamic light scattering(DLS)analysis.Due to the attachment of fluorescent side groups,the optical properties of the micelles were analyzed using confocal laser scanning microscopy(CLSM).Owing to the amphiphilic and glucoseresponsive properties,the micelles could be used as carriers for loaded insulin.The insulin release behavior was evaluated when triggered by glucose in vitro.In addition,the resultant micelles exhibited relatively lower cytotoxicity and excellent stability against a protein solution.The insulin retained its structure stability after release,investigated through circular dichroism(CD)spectra analysis.These results showed that the obtained phenylboronic acid-modified glucose-responsive and fluorescent polymer micelles with a good biological imaging performance and biocompatibility could be one of the effective candidate carriers for controllable release of insulin.2.Development of an oral delivery strategy for insulin therapeutics has drawn much attention in recent years.In this study,a phenylboronic acid-modified glucoseresponsive nanocarriers for loading of insulin has been prepared firstly.The resultant nanocarriers exhibited relative low cytotoxicity against Caco-2 cells and excellent stability against protein solution.The insulin release behaviors were evaluated triggered by pH and glucose in vitro.In order to enhance the oral bioavailability of insulin,the insulin-loaded phenylboronic acid-modified glucose-responsive nanocarriers were further encapsulated into a three-dimensional(3D)hyaluronic acid(HA)hydrogel environment for overcoming multiple barriers and providing multi-protection for insulin during the transport process.The hypoglycemic effect for oral delivery of insulin was studied in vivo.After oral administration to the diabetic rats,the released insulin from hydrogel systems containing insulin-loaded phenylboronic acid-modified glucose-responsive nanocarriers exhibited an effective hypoglycemic effect for longer time compared with insulin-loaded phenylboronic acid-modified nanocarriers.3.To overcome multiple barriers for oral delivery of insulin,the chitosan-based multifunctional nanocarriers modified by L-valine(LV,used as a target ligand to facilitate the absorption of the small intestine)and phenylboronic acid have been designed and evaluated in this study.The resultant nanocarriers exhibited low cytotoxicity against HT-29 cells and excellent stability against protein solution.The insulin release behaviors were evaluated triggered by p H and glucose in vitro.The chemical stability of loaded insulin against digestive enzyme were established in presence of simulated gastric fluid(SGF)containing pepsin and simulated intestinal fluid(SIF)containing pancreatin,respectively.The uptake behavior of HT-29 cells was evaluated by CLSM.After oral administration to the diabetic rats,an effective hypoglycemic effect was obtained compared with subcutaneous injection of insulin.This work suggests that L-valine modified chitosan-based multifunctional nanocarriers may be a promising drug delivery carrier for oral administration of insulin.