Purpose: We explored the neuroprotective effects of erythropoietin (EPO)-loaded dextran microparticle-based Poly(DL-lactide-co-glycolide)/Poly(DL-lactide) (PLGA/PLA) microspheres (EPO-dextran PLGA/PLA microspheres) on retinal ganglion cells (RGCs) in optic nerve crush rats for a prolonged period of time.
Methods: EPO-dextran PLGA/PLA microspheres were prepared first by a novel solid-in-oil-in-water (S/O/W) technique. Then, the in vitro EPO release profile was assessed. Afterward, the bioactive effect of EPO released from EPO-dextran PLGA/PLA microspheres was explored in vitro on the retinal explants. Lastly, the neuroprotective effects of EPO-dextran PLGA/PLA microspheres on RGCs were evaluated in optic nerve crush rats with TUNEL staining for apoptotic RGCs. The level of glial fibrillary acidic protein (GFAP) expressed in retina was explored by immunohistochemistry staining. Survival RGCs were observed by DiI retrograde labeling using a DiI fluorescent tracer (1,1'-dioctadecyl-3,3,3',3'-tetramethylindocarbocyanine perchlorate).
Results: The results demonstrated that a sustained release of EPO from PLGA/PLA microspheres could last for at least 60 days. EPO released from the microspheres showed as efficaciously neuroregenerative as EPO protein solution on retinal explants (P = 0.2554 for neurite density, P = 0.1004 for neurite length). TUNEL staining revealed that EPO-dextran PLGA/PLA microspheres remarkably reduced RGCs death when compared to the control (untreated) group (P < 0.01 at five days and one week post-crush, P < 0.05 at two weeks post-crush). Increased GFAP expression in retina was reduced greatly in EPO-dextran PLGA/PLA microspheres-administrated rats two weeks post optic nerve crush. DiI retrograde labeling revealed that a single injection of EPO-dextran PLGA/PLA microspheres significantly promoted RGCs survival (P < 0.01 at four and eight weeks post-crush).
Conclusions: A single intravitreal injection of EPO-dextran PLGA/PLA microspheres appeared to have a prolonged protective effect on RGCs in optic nerve crush rats. The PLGA/PLA microspheres may be a feasible protein delivery system, such as EPO, to intravitreal injection for retinal degeneration diseases.