[Retinal protective effects of zinc-loaded magnesium oxide nanoparticles in a glutamate-excitotoxicity glaucoma...

Glaucoma is pathologically characterized by the progressive loss of retinal ganglion cells (RGCs). Currently, effective strategies for protection of RGCs in glaucoma remain lacking, and nanomaterials represent promising drug-delivery carriers. This study aims to investigate the effects of zinc-loaded magnesium oxide nanoparticles (MgO-Zn²⁺ nanoparticles, MgO-Zn NPs) on glutamate-induced RGC injury, and to evaluate their in vivo and in vitro biocompatibility and neuroprotective potential.

MgO-Zn NPs were prepared and characterized by transmission electron microscope and energy-dispersive spectroscopy. In vitro cytotoxicity was systematically evaluated in the R28 rat retinal precursor cell line using the cell counting kit-8 (CCK-8) assay. In vivo, an excitotoxic retinal injury model was established in C57/BL mice by intravitreal injection of N-methyl-D-aspartate (NMDA), followed by MgO-Zn NP intervention. RGC numbers and apoptosis were evaluated using terminal deoxynucleotidyl transferase-mediated dUTP nick end labeling (TUNEL) staining. Retinal-layer structure was examined by hematoxylin and eosin (HE) staining. Flash visual evoked potential (F-VEP) was used to evaluate RGC visual-conduction function, and RNA sequencing was performed to analyze pathways and functions of differentially expressed genes, with further validation of associated protein-expression differences.

Transmission electron microscope and energy-dispersive spectroscopy confirmed the morphological and compositional characteristics of MgO-Zn NPs, indicating successful composite synthesis. CCK-8 results showed that MgO-Zn NPs at 75 µg/mL exhibited no cytotoxicity in R28 cells. After intravitreal injection of MgO-Zn NPs in mice, no significant ocular surface or corneal adverse reactions were observed, indicating favorable ocular tolerance. TUNEL staining showed that RGC numbers in the excitotoxic model were significantly lower than those in normal mice (P<0.05), confirming successful model establishment, whereas MgO-Zn NPs significantly reduced NMDA-induced RGC apoptosis (P<0.05). HE staining showed partial structural restoration of retinal layers after MgO-Zn NP intervention (P<0.05). F-VEP measurements showed prolonged P2 latency and decreased amplitude in model mice (both P<0.001), while MgO-Zn NP intervention resulted in partial recovery of P2 latency and amplitude (both P<0.05). RNA sequencing indicated that MgO-Zn NPs alleviated NMDA-induced retinal transcriptome abnormalities, with differentially expressed genes mainly associated with the phosphatidylinositol-3-kinase (PI3K)-protein kinase B (Akt) pathway and the mammalian target of rapamycin (mTOR) signaling pathway. Immunofluorescence staining further showed that MgO-Zn NPs significantly decreased retinal p-Akt and p-mTOR expression levels (both P<0.01).

MgO-Zn NPs may serve as a dual-functional glaucoma treatment candidate, providing retinal-neuron protection while acting as an intraocular drug-delivery carrier.