Preparation and characterization of biodegradable nanoparticles entrapping immunodominant peptide conjugated with PEG for oral tolerance induction

PEG-conjugated immunodominant peptides for collagen-induced arthritis (CIA) were prepared for oral tolerance induction instead of whole Type II collagen (CII), because a small peptide can be converted to a macromolecule soluble in methylene chloride by the coupling of poly-ethylene glycol (PEG). PEG-pep1 was synthesized from a peptide and mPEG-NH₂ (Mw ∼5000) using SPDP as a linker, whereas PEG-pep2 was prepared by the direct disulfide coupling between PEG-OD (Mw ∼10,000) and the peptide. PEG-pep1 and PEG-pep2 were purified by gel permeation chromatography (GPC), and the peak fractions of GPC were identified by GPC and MALDI-TOF mass spectroscopy. The peptide coupling gave much earlier retention times for PEG-pep1 (11.26 min) and PEG-pep2 (10.61 min) than for mPEG-SPDP (15.63 min) and mPEG-OD (14.58 min). The Mw's of mPEG-NH ₂, mPEG-SPDP, PEG-pep1, mPEG-OD and PEG-pep2 were 5451, 5588, 7035, 10,360 and 11,826, respectively, suggesting that PEG-pep1 and PEG-pep2 of high purity could be obtained. The nanoparticles entrapping PEG-pep1 and PEG-pep2 (NP/PEG-pep1 and NP/PEG-pep2) were prepared by the o/w solvent evaporation method, whereas the peptide-loaded nanoparticles (NP/pep) were prepared by the w/o/w double emulsion method. Although all the nanoparticles had a similar spherical morphology under scanning electron microscopy, NP/pep showed up as having a larger mean size than the others, which was confirmed by dynamic light scattering analysis (NP/pep, 499.7 ± 27.2 nm; NP/PEG-pep1, 333.0 ± 16.8 nm; NP/PEG-pep2, 342.4 ± 15.1 nm). The lower encapsulation efficiency of NP/pep (21.0 ± 1.6%) than NP/PEG-pep1 (66.5 ± 5.0%) and NP/PEG-pep2 (73.8 ± 5.5%) can also be attributed to the preparation method. In in vitro release studies, NP/PEG-pep1 and NP/PEG-pep2 displayed a similar release profile, close to a linear release pattern, whereas NP/pep displayed a tri-phasic release profile. From these results, it was demonstrated that nanoparticles entrapping a PEG-conjugated peptide could be an alternative delivery method for the induction of oral tolerance rather than CII and peptide.