Pan He

Glucose-sensitive polypeptide micelles for self-regulated insulin release at physiological pH

Three novel phenylboronic acid functionalized block copolymers, monomethoxy poly(ethylene glycol)-b-poly(L-glutamic acid-co-N-3-L-glutamylamidophenylboronic acid) (mPEG-b-P(GA-co-GPBA)), were synthesized by modifying mPEG-b-PGA with 3-aminophenylboronic acid (APBA). The resultant diblock copolymers self-assembled into micelles in phosphate buffer at physiological pH (pH 7.4). More interestingly, at pH 7.4, the hydrodynamic radii (Rh) of the micelles increased with an increase in glucose concentration by formation of hydrophilic PBA–glucose complex. Thus, insulin, a model drug, was loaded into the glucose-sensitive polypeptide micelles. The in vitro release profiles revealed that the release of insulin from the micelles could be triggered by glucose, i.e. less insulin was released under healthy blood glucose level (1 mg mL−1 glucose), while quick release occurred under diabetic blood glucose level (above 2 mg mL−1 glucose). Furthermore, in vitro methyl thiazolyl tetrazolium (MTT) assays and hemolysis tests suggested that the copolymers had good biocompatibility. Therefore, the phenylboronic acid functionalized block copolymers with high glucose-sensitivity and good biocompatibility may have potential as self-regulated insulin release systems.

Novel Biodegradable and pH-Sensitive Poly(ester amide) Microspheres for Oral Insulin Delivery

Biodegradable and pH-sensitive PEAs based on dual amino acids are designed, synthesized, and characterized. Insulin can be loaded into the PEA microspheres by a solid-in-oil-in-oil technique with high encapsulation efficiency. The feasibility of PEA microspheres as oral insulin delivery carriers is evaluated in vitro and in vivo. The hydrophobic leucine groups on PEA seem to play an important role in the pH-dependent release mechanism and cytotoxicity of PEA microspheres. Oral administration of insulin-loaded PEA microspheres to streptozotocin-induced diabetic rats at 60 IU kg(-1) is able to reduce fasting plasma glucose levels to 49.4%. These results indicate that PEA microspheres are potential new vehicles for insulin oral delivery.

Insulin nanoparticle preparation and encapsulation into poly(lactic-co-glycolic acid) microspheres by using an anhydrous system

Insulin has been encapsulated in poly(lactic-co-glycolic acid) (PLGA) microspheres by solid-in-oil-in-oil (S/O/O) emulsion technique using DMF/corn oil as new solvent pairs. To get better encapsulation efficiency, insulin nanoparticles were prepared by the modified isoelectric point precipitation method so that it had good dispersion in the inner oil phase. The resulting microspheres had drug loading of 10% (w/w), while the encapsulation efficiency could be up to 90-100%. And the insulin release from the microspheres could last for 60 days. Microspheres encapsulated original insulin with the same method had lower encapsulation efficiency, and shorter release period. Laser scanning confocal microscopy indicated the insulin nanoparticle and original insulin had different distribution in microspheres. The results suggested that using insulin nanoparticle was better than original insulin for microsphere preparation by S/O/O method. Study about the secondary structure of insulin by Fourier transform infrared spectroscopy (FTIR) indicated high insulin structural integrity during the process. In vivo test showed insulin in microspheres retained its bioactivity. In addition, cytotoxicity evaluation by the MTT assay has proved that no extra toxicity was introduced into the microspheres during the emulsion process.

Facile one-pot synthesis of glucose-sensitive nanogel via thiol-ene click chemistry for self-regulated drug delivery

A novel glucose-sensitive nanogel was conveniently prepared through one-pot thiol-ene copolymerization of pentaerythritol tetra(3-mercaptopropionate), poly(ethylene glycol) diacrylate, methoxyl poly(ethylene glycol) acrylate and N-acryloyl-3-aminophenylboronic acid. The formation of core-shell nanogel was verified by proton nuclear magnetic resonance, dynamic laser scattering (DLS) and transmission electron microscopy. The successful incorporation of phenylboronic acid (PBA) in the nanogel was confirmed through Fourier transform infrared spectroscopy, inductively coupled plasma mass spectrometry and fluorescence technology. Owing to the presence of PBA, the nanogel exhibited high glucose sensitivity in phosphate-buffered saline determined by DLS and fluorescence technology. The increased amount of glucose causes an increase in the hydrodrodynamic radius and a decrease in the fluorescence intensity of PBA-alizarin red S (ARS) complex in the nanogel at pH 7.4 because of the competitive substitution of ARS to form the hydrophilic PBA-glucose complex. ARS and insulin were loaded into this glucose-sensitive nanogel. In vitro release profiles revealed that the drug release from the nanogel could be triggered by the presence of glucose. The more glucose in the release medium, the more drug was released and the faster the release rate. Furthermore, in vitro methyl thiazolyl tetrazolium assay, lactate dehydrogenase assay and hemolysis test suggested that the nanogel was biocompatible. Therefore, the PBA-incorporated nanogel with high glucose-sensitivity and good biocompatibility may have great potential for self-regulated drug release.

Surface Modification of Hydroxyapatite Nanoparticles with Thermal-Responsive PNIPAM by ATRP

Hydroxyapatite (HA) nanoparticles grafted by poly(N-isopropylacrylamide) (PNIPAM) brushes (PNIPAM-g-HA) have been synthesized by the surface-initiated atom transfer radical polymerization (ATRP) of N-isopropylacrylamide (NIPAM). The surface grafting amount of PNIPAM ranges from 15.5% to 46.4%. PNIPAM-g-HA has been characterized by FT-IR spectroscopy, thermal gravimetric analysis, X-ray diffraction, and scanning electron microscopy (SEM). The UV transmittance spectra and the particle size analysis of PNIPAM-g-HA in aqueous solution demonstrates that the PNIPAM-g-HA possess reversible thermal stimuli responsive properties. An in vitro bioactivity assessment indicates that PNIPAM-g-HA can induce the mineralization of Ca(2+) and HPO(4) (2-) and possesses an excellent bioactivity. The cell culture results show that the cells adhered to the surface of PNIPAM-g-HA grow better than on HA, and the area of the cells on the surface of PNIPAM-g-HA is much greater than for HA, which proves that the PNIPAM-g-HA has a better biocompatibility than HA.

Poly(ester amide) blend microspheres for oral insulin delivery

This study developed a novel oral insulin formulation centered on microspheres consisting of a blend of biodegradable poly(ester amide) (PEA). In the formulation, L-lysine-/L-leucine-based PEA with pendant COOH groups (PEA-COOH) was used as a pH-responsive material for the protection of insulin from the harsh environmental conditions of the stomach. Arginine-based PEA (Arg-PEA) was introduced to improve the intestinal absorption of the drug. The influence of both the hydrophobicity of PEA-COOH and the content of Arg-PEA was investigated in detail on microsphere surface morphology, drug loading, and the in vitro release profile of insulin. The PEA-COOH/Arg-PEA blend microspheres protected the loaded insulin in simulated gastric fluid and released insulin in a fast and sustained manner in simulated intestinal fluid. The in vivo test demonstrated that the oral administration of insulin-loaded PEA blend microspheres could effectively suppress the blood glucose level in diabetic rats for 10h, and the oral bioavailability was improved to 5.89+1.84% in healthy rats. These results indicate that the PEA blend microspheres are promising vehicles for the oral delivery of insulin.

Synthesis of temperature and pH-responsive crosslinked micelles from polypeptide-based graft copolymer

A polypeptide-based double hydrophilic graft copolymer was synthesized by the sequential grafting of poly(N-isopropylacrylamide) (PNIPAM) and 2-hydroxyethyl methacrylate (HEMA) onto poly(l-glutamic acid) (PGA) backbone. The copolymers were sensitive to both temperature and pH. The phase transition and aggregation behaviors of the graft copolymers in aqueous solutions were investigated by the turbidity measurements and dynamic laser scattering (DLS). The light transmittance decrease of the copolymers at temperature above lower critical solution temperature (LCST) was remarkably weakened at pH around 6.5 due to the coil to α helix change of PGA chain induced by pH. The copolymers can self-assembly into micelles with PNIPAM cores in the aqueous solution at pH 8.0 and 60°C. Subsequently, polymerization of HEMA led to the facile preparation of crosslinked micelles, which were observed directly by transmission electron microscopy (TEM). The temperature controlled shrinkage behaviors of crosslinked micelles highly depended on the pH values of the solution. The crosslinked micelles aggregated at pH 5.0 due to the increased hydrophobic interactions among them induced by the protonation of PGA component. These crosslinked micelles have promising applications as intelligent drug delivery vehicles.

An efficient pH sensitive oral insulin delivery system enhanced by deoxycholic acid

Summary A permeation enhancer, positively charged deoxycholyl-hyperbranched oligoethylenimine (DCO), was prepared and used to form complexes with negatively charged insulin based on electrostatic interaction. DCO/insulin complexes can be loaded into poly ( l -glutamic acid) (PGA) microspheres by the oil-in-oil (O/O) emulsion and solvent evaporation technique. Because of the specific pH sensitive properties of PGA, these insulin encapsulated microspheres are stable in the stomach and disaggregate in the small intestine, and the bioavailability of oral insulin administration will be improved due to DCOs permeation enhancement function.

Thermosensitive polyion complex micelles prepared by self-assembly of two oppositely charged diblock copolymers

Polyion complex (PIC) micelles were spontaneously formed in aqueous solutions through electrostatic interaction between two oppositely charged block copolymers, poly(N-isopropylacrylamide)-b-poly(L-glutamic acid) and poly(N-isopropylacrylamide)-b-poly(L-lysine). Their controlled synthesis was achieved via the ring opening polymerization of N-carboxyanhydrides (NCA), γ-benzyloxycarbonyl-L-lysine (Lys(Z)-NCA) or γ-benzyl-L-glutamate (BLG-NCA) with amino-terminated poly(N-isopropylacrylamide) macroinitiator and the subsequent deprotection reaction. The formation of PIC micelles was confirmed by dynamic light scattering and transmission electron microscopy. Turbidimetric characterization suggested that the formed PIC micelles had a concentration-dependent thermosensitivity and their phase transition behaviors could be easily adjusted either by the block length of coplymers or the concentration of micelles.