Polymer Therapeutics for Sustained, Controllable Release of Growth Factors to Promote Cranial Nerve Repair and Regeneration by Stem Cells.

Objectives: Nerve injuries in the craniofacial region are common, difficult to treat and often result in unpredictable sub-optimal functional outcomes. Attempts to induce healing using stem cell implantation have shown some success. To facilitate stem cell proliferation and differentiation, growth factor (GF) supplementation is essential. However, rapid clearance of exogenous GFs from the target site and premature inactivation by proteolytic enzymes and reactive oxygen species have limited clinical success. This study investigated the ability of two model dextrin-GF conjugates (dextrin-EGF and dextrin-bFGF) to support in vitro stem cell proliferation and differentiation by sustained, controllable GF release and demonstrate their potential as a supplement for stem cell therapy.
Methods: Dextrin-EGF and -bFGF conjugates were synthesized (using 51,000 g/mol dextrin with ~30 mol% succinoylation) having a protein content (BCA assay) of 3.9 and 6.7% w/w and a molecular weight (by GPC) of 190,000 and 180,000 g/mol, respectively. Proliferation and apoptosis of mouse neural stem cell (mNSC) was assessed over 7 days by MTT and TUNEL assays, respectively. Multipotency and differentiation of mNSCs was assessed immunocytochemically and quantified by fluorescent confocal microscopy.
Results: In vitro supplementation of mNSC monolayer and 3-dimensional spheres with dextrin-GF conjugates led to greater and prolonged proliferation compared to unbound GF controls. Cells grown with a combination of dextrin-EGF/dextrin-bFGF conjugates showed the greatest and most prolonged proliferation profile, with no detectable apoptosis after 7 days of treatment, demonstrating their ability to controllably release GFs over time. Immunocytochemical detection of multipotency (nestin) and differentiation (olig2, MAP2, GFAP) markers of dextrin-GF-treated mNSCs verified that controlled release of GFs preserves the multipotency of mNSCs and enhances their ability to differentiate into nerve cells, compared to ‘free GF’-treated cells.
Conclusions: These results show the improved stem cell survival and differentiation in the presence of dextrin-GFs, and demonstrate the potential that dextrin-GFs may offer for localised delivery of therapeutic agents for nervous tissue repair, including cranial nerve repair and regeneration.