Investigation Of Exenatide Loaded PLGA Microspheres/Hydrogel Multilayer Drug Delivery System

Exenatide(EXT)is a naturally occurring 39-amino-acid peptide isolated from thesalivary secretions of the lizard Helodermasuspectum,and it shares an approximately53%sequence homology with the mammalian gut hormone,GLP-1.Byetta(?),the EXTsolution for injection,has been approved by both the United States(2005)and European Union(2006)for the treatment of type 2 diabetes mellitus.However,the clinicalapplications of Byetta(?) are limited by the need for very frequent and long-term administration,which has a very negative effect on patient compliance.Thus,a great deal of effort has beendevoted to developing a long-acting drug delivery system for EXT to improve the complianceof patients with type 2 diabetes mellitus.EXT loaded PLGA microspheres(Ms)and thermosensitive hydrogel were widely investigated as long-term drug delivery system.However,initial burst release,fast release rate and incompleted release can not be ignored.In this study,thermosensitive hydrogel and Ms were used to prepare multilayer drug delivery system,with sustained EXT release and high bioactivity.Firstly,Electrostatic spraying was investigated for preparing PLGA microspheres.And TP5 was chosen as a model peptide drug.Some PLGA microspheres with different gel-core were prepared by electrostatic spraying,and the materials of gel-core include PVP-K30、PEO-WSR1105、PVA-217、F127 and alginate calcium.The results showed that,encapsulation efficiency of formulation F11(gel-core was F127)was not higher than Ms without gel-core,and similar with microspheres prepared by double emulsion-solvent evaporation.And TP5 release from formulation F11 could last for 20 days,without brust release.However,synthesizes the feasibility and convenience of the preparation process,Double emulsion-solvent evaporation method was chosen as the suitable one to prepare microspheres in the following study.A series of mixed hydrogels of F127 and PEG were synthesized,and investigated in terms of their thermosensitive properties.Then,some mixed hydrogelwas selected to prepare EXT loaded multilayer drug delivery system.EXT dissolved in mixture of F127 and PEG,which was loaded in Ms,to prepare F-Depot-gel-Ms.The interior structure and distribution of EXT/hydrogel within F-Depot-gel-Ms were investigated by optical microscope and raman imaging.Ms and F-Depot-gel-Ms were compared in terms of change in distribution of EXT/hydrogel within F-Depot-gel-Ms,the rate of PLGA degradation and the drug release kinetics.A sustained EXT release was observed in F-Depot-gel-Ms for 22 days,which was shower than Ms.In pharmacodynamics study,the obtained results demonstrated that a single injection of F-Depot-gel-Ms allowed the mice to maintain a stable blood glucose concentration for two weeks and their body weight was reduced more effectively than that in the Ms group.In addition,F-Depot-gel-Ms had a longer interval between dosing(two weeks)and a lower dosage(2.4μg/kg)than Bydureon(?)(one week,33μg/kg).The bioactivity and release of macromolecular Exenatide was improved by the multi-gel-core structure.A series of mixed hydrogels of PLGA-PEG-PLGA and PCLA-PEG-PCLA were synthesized,and investigated in terms of their critical micelle concentration,stability of micelle structure and thermosensitive properties.Then,Blended-PPP-3(one kind of mixture of PLGA-PEG-PLGA and PCLA-PEG-PCLA,50:50)was selected to prepare EXT loaded multilayer drug delivery system.The Blended-PPP-3(25%)and Ms was used to prepare a triple-barrier Depot-gel-in-Ms-in-Matrix-gel system.The mechanism of EXT release involved drug diffusion,hydrogel diffusion,PLGA erosion and mixed hydrogel erosion.The results obtained showed that EXT release was at a sustained rate for 46 days,because it is controlled by the inner deport-gel,the Ms matrix and the outer Matrix-gel successively.No burst release or platform were observed due to the interception function and control function of the outer Matrix-gel.In addition,the biological activity of EXT in releae medium was tested by oral glucose tolerance test.Results shown that,the the biological activity of EXT was protected.A single injection of Depot-gel-in-Ms-in-Matrix-gel allowed mice to maintain a stable blood glucose concentration(BGC)and well-controlled body weight for 20 days.On the 20th day of the pharmacodynamics study,an oral glucose tolerance test was carried out,there was no fluctuations in BGC in Depot-gel-in-Ms-in-Matrix-gel group.However,a serious fluctuation was observed in the Ms group,and the AUC of BGC in Ms group was nearly double that in the Depot-gel-in-Ms-in-Matrix-gel system group.And H&E staining results suggested that Depot-gel-in-Ms-in-Matrix-gel exhibited an acceptable biocompatibility in vivo.In summary,the triple-barrier Depot-gel-in-Ms-in-Matrix-gel system based Ms and thermosensitve hydrogel mixture(PLGA-PEG-PLGA and PCLA-PEG-PCLA)was shown to be a promising hydrophilic protein and polypeptide-loaded long-acting formulation with a sustained drug release and high drug bioactivity.