Nanoscale cationic micelles of amphiphilic copolymers based on star-shaped PLGA and PEI cross-linked PEG for protein delivery application

To enhance the bioavailability of protein therapeutants and improve the stability of storage and delivery, a series of branched amphiphilic block copolymers consisting of cholic acid (CA) initiated poly(D,L-lactide-co-glycolide) (CA-PLGA) and water-soluble polyethyleneimine cross-linked polyethylene glycol (PEI-PEG) denoted as CA-PLGA-b-(PEI-PEG) were synthesized and characterized. CA-PLGA-b-(PEI-PEG) presented low cytotoxicity by MTT and cck-8 assay. The cationic CA-PLGA-b-(PEI-PEG) micelles (diameter about 100 nm and zeta potential 34–61 mV) were prepared through self-assembly method, and complexed with insulin via electrostatic interaction to obtain nanoscale micelle/insulin complexes. The micelle/insulin complexes-loaded CA-PLGA microspheres (MIC-MS, 10.4 ± 3.85 μm) were manufactured by employing a double emulsion (W1/O/W2) method. The in vitro insulin release behavior and in vivo hypoglycaemic effect of MIC-MS on streptozotocin (STZ) induced diabetic rats were compared with those of the insulin-loaded CA-PLGA microspheres (INS-MS, 7.8 ± 2.57 μm). The initial burst in vitro release of MIC-MS was markedly lower than that of INS-MS (P < 0.01), and the pharmacological availability of MIC-MS via subcutaneous administration was 148.9% relative to INS-MS. Therefore, the cationic CA-PLGA-b-(PEI-PEG) micelles can effectively increase the bioavailability of insulin in CA-PLGA microspheres and can be considered as a potential protein carrier.