Co-delivery of neurotrophic factors and a zinc chelator substantially increases retinal ganglion cell survival and axon protection in the optic nerve crush model.

Abstract

Traumatic optic neuropathies lead to retinal ganglion cell (RGC) death and axonal degeneration, primarily due to disrupted neurotrophic factor (NTF) supply from the brain and a neurotoxic cascade, potentially mediated by elevated retinal Zn²⁺ levels. Ciliary neurotrophic factor (CNTF) and brain-derived neurotrophic factor (BDNF) are two major NTFs known to support RGC survival and axon protection. Dipicolylamine (DPA), a Zn²⁺ chelator with high selectivity and affinity, offers a strategy to reduce excess Zn²⁺. To achieve sustained NTF delivery and Zn²⁺ reduction, we developed sulfonated poly(serinol hexamethylene urea) nanoparticles (S-PSHU NPs) co-loaded with CNTF, BDNF, and DPA. In vitro release studies demonstrated sustained release of CNTF and BDNF for up to 8 weeks and DPA for up to 4 weeks. In a rat optic nerve crush (ONC) model, DPA-loaded S-PSHU NPs showed dose-dependent elimination of retinal Zn²⁺. Additionally, in primary RGC culture, RGC activity and axon growth correlated with CNTF and BDNF dosage. In vivo, NTF-DPA-loaded S-PSHU NPs significantly enhanced RGC survival and axon protection post-ONC, as evidenced by cholera toxin subunit B (CTB)-labeled axons in the central visual centers of the brain, including the suprachiasmatic nucleus, lateral geniculate nucleus, and superior colliculus. STATEMENT OF SIGNIFICANCE: • Co-delivery of neurotrophic factors (NTFs: CNTF and BDNF) and a zinc chelator (dipicolylamine, DPA) promotes retinal ganglion cell (RGC) axon survival and protection. • Sustained release of NTFs for up to 8 weeks and DPA for up to 4 weeks. • DPA-loaded nanoparticles effectively eliminate excess retinal zinc after optic nerve injury. • NTF-DPA-loaded nanoparticles significantly improve RGC survival and axon protection in a rat optic nerve crush model.