title: Controlled release of bioactive PDGF-AA from a hydrogel/nanoparticle composite.
abstract: Polymer excipients, such as low molar mass poly(ethylene glycol) (PEG), have shown contradictory effects on protein stability when co-encapsulated in polymeric nanoparticles. To gain further insight into these effects, platelet-derived growth factor (PDGF-AA) was encapsulated in polymeric nanoparticles with vs. without PEG. PDGF-AA is a particularly compelling protein, as it has been demonstrated to promote cell survival and induce the oligodendrocyte differentiation of neural stem/progenitor cells (NSPCs) both in vitro and in vivo. Here we show, for the first time, the controlled release of bioactive PDGF-AA from an injectable nanoparticle/hydrogel drug delivery system (DDS). PDGF-AA was encapsulated, with high efficiency, in poly(lactide-co-glycolide) nanoparticles, and its release from the drug delivery system was followed over 21 d. Interestingly, the co-encapsulation of low molecular weight poly(ethylene glycol) increased the PDGF-AA loading but, unexpectedly, accelerated the aggregation of PDGF-AA, resulting in reduced activity and detection by enzyme-linked immunosorbent assay (ELISA). In the absence of PEG, released PDGF-AA remained bioactive as demonstrated with NSPC oligodendrocyte differentiation, similar to positive controls, and significantly different from untreated controls. This work presents a novel delivery method for differentiation factors, such as PDGF-AA, and provides insights into the contradictory effects reported in the literature of excipients, such as PEG, on the loading and release of proteins from polymeric nanoparticles.
  
  
  CONCLUSIONS
  Previously, the polymer poly(ethylene glycol) (PEG) has been used in many biomaterials applications, from surface coatings to the encapsulation of proteins. In this work, we demonstrate that, unexpectedly, low molecular weight PEG has a deleterious effect on the release of the encapsulated protein platelet-derived growth factor AA (PDGF-AA). We also demonstrate release of bioactive PDGF-AA (in the absence of PEG). Specifically, we demonstrate the differentiation of neural stem and progenitor cells to oligodendrocytes, similar to what is observed with the addition of fresh PDGFAA. A differentiated oligodendrocyte population is a key strategy in central nervous system regeneration. This work is the first demonstration of controlled PDGF-AA release, and also brings new insights to the broader field of protein encapsulation.
authors.affiliation: Department of Chemical Engineering and Applied Chemistry, University of Toronto, Canada; Institute of Biomaterials and Biomedical Engineering, University of Toronto, Canada.
authors.forename: Irja
authors.initials: I
authors.lastname: Elliott Donaghue
authors.affiliation: Department of Chemical Engineering and Applied Chemistry, University of Toronto, Canada; Institute of Biomaterials and Biomedical Engineering, University of Toronto, Canada; Department of Chemistry, University of Toronto, Canada. Electronic address: molly.shoichet@utoronto.ca.
authors.forename: Molly S
authors.initials: MS
authors.lastname: Shoichet
mesh_terms: D000818:Animals; D002470:Cell Survival / Q000187:drug effects; D003692:Delayed-Action Preparations; D016503:Drug Delivery Systems; D004797:Enzyme-Linked Immunosorbent Assay; D020136:Hydrogel, Polyethylene Glycol Dimethacrylate / Q000737:chemistry*; D008297:Male; D039902:Multipotent Stem Cells / Q000166:cytology / Q000187:drug effects; D053758:Nanoparticles / Q000737:chemistry*; D058953:Neural Stem Cells / Q000166:cytology / Q000187:drug effects; D010982:Platelet-Derived Growth Factor / Q000494:pharmacology*; D011092:Polyethylene Glycols / Q000737:chemistry; D017208:Rats, Wistar
chemical_list: D003692:Delayed-Action Preparations; D010982:Platelet-Derived Growth Factor; C075278:platelet-derived growth factor A; D020136:Hydrogel, Polyethylene Glycol Dimethacrylate; D011092:Polyethylene Glycols; C000595213:polyethylene glycol 400
keywords: Controlled release; Drug delivery; Hydrogel; Nanoparticle; Neural stem cell; Oligodendrocyte; PDGF-AA; PEG; PLGA; Protein delivery; Spinal cord injury