Trans-meningeal drug delivery to optic nerve ganglion cell axons using a nanoparticle drug delivery system

• Optic nerve meninges were dissected from eyes at the time of enucleation.
• Meningeal samples were mounted in a diffusion cell with dural side facing donor.
• Donor chamber was filled with brimonidine or nanoparticle loaded with brimonidine.
• UV–vis spectrophotometer absorbance over time demonstrates diffusion across dura.
• Nanoparticle encapsulation controls delivery across the optic nerve dura.

The purpose of this study was to investigate if neuroprotective drugs can cross the optic nerve sheath in vitro. Four optic nerves were used for this study. Two porcine nerves were harvested at the time of euthanasia and two human nerves were obtained at the time of therapeutic globe enucleation. The optic nerve sheaths were dissected and placed as a membrane in a two chamber diffusion cell to test meningeal penetration by both brimonidine alone and brimonidine encapsulated in nanoparticle (NP-brimonidine). Brimonidine concentration was assayed by UV–vis spectrometer measurement of absorbance at 389 nm. Increasing concentration of brimonidine on the receiver side of the chamber was measured in both the brimonidine alone and the brimonidine encapsulated experiments. The human data were fitted with a two parameter exponential regression analysis (brimonidine alone donor r2 = 0.87 and receiver r2 = 0.80, NP-brimonidine donor r2 = 0.79 and receiver r2 = 0.84). Time constant (τ) was 10.2 h (donor) and 13.1 h (receiver) in the brimonidine study, and 24.0 h (donor) and 15.9 h (receiver) in the NP-brimonidine study. Encapsulated brimonidine had a longer time to reach equilibrium. Passage of brimonidine through the optic nerve sheath was demonstrated in the experiments. Increase in time constants when comparing the NP-brimonidine with the brimonidine curves in the human studiesindicates that diffusion is delayed by the initial parameter of drug being loaded in NP. Direct treatment of injured optic nerve axons may be possible by trans-meningeal drug diffusion.