Organotypic retinal cultures as an ex vivo screening platform for PLGA-based neuroprotective microspheres

In this study, the suitability of organotypic cultures of neonatal rat retina as a controlled ex vivo platform for the evaluation of intraocular microparticulate drug delivery systems is assessed, while also exploring their ability to identify formulation-dependent differences. Poly(lactic-co-glycolic acid) (PLGA) microspheres loaded with glial cell line-derived neurotrophic factor (GDNF) and/or α-tocopherol acetate (VitE) were evaluated in short-term (7 days) and long-term (20 days) retinal explant cultures. Retinas from wild-type rats were explanted at postnatal day 9 or 10 and cultured with GDNF/VitE-loaded microspheres with different VitE content (PLGA-E20-GDNF and PLGA-E40-GDNF), VitE-loaded microspheres (PLGA-E20 and PLGA-E40), blank microspheres (PLGA), or left untreated. After exposures, retinal sections were analyzed by immunohistochemistry and TUNEL assay. In short-term cultures, both GDNF/VitE-loaded formulations significantly reduced photoreceptor cell death, whereas in long-term cultures a significant reduction of TUNEL-positive cells was only observed for the PLGA-E40-GDNF formulation. The formulation containing higher VitE content showed a greater neuroprotective effect despite lower GDNF loading, suggesting a possible contribution of VitE to the overall effect. No signs of cytotoxicity or structural damage were observed. The concordance between the present ex vivo findings and previously reported in vivo data in terms of neuroprotective efficacy and biocompatibility supports the use of organotypic retinal cultures as an intermediate ex vivo model to evaluate ocular drug delivery systems.