FK962 enhances neurite elongation in cultured rat retinal ganglion cells

Abstract

Purpose: Glaucoma is a progressive optic neuropathy, and a major risk factor is elevated intraocular pressure (IOP). Various drugs to reduce IOP are widely used to treat glaucoma, but control of IOP is not fully successful. Neuroprotection is a new proposed treatment for glaucoma. Damage to axons in the optic nerve disturbs axonal transport and leads to retinal ganglion cell death. Endogenous neurotrophic factors contribute to the regeneration of axons. Our previous study showed that FK962 induces neurite elongation in cultured trigeminal ganglion cells from rabbits and rats via induction of glial cell-line derived neurotrophic factor. The purpose of the present experiments was to test if FK962 promotes neurite elongation in retinal ganglion cells. An in silico pharmacokinetics model was also used to predict efficacy of topical application of FK962.

Methods: Neuronal cells (~75% retinal ganglion cells) and isolated rat retinal ganglion cells were cultured with and without FK962, and with (mixed cell culture) and without (pure culture) glial cells. Cells with neurite elongation were counted after the cells were fixed and immunolabeled with antibodies for neurofilaments or calcein AM. For the in silico pharmacokinetics study, a modified cylindrical eye model was used with parameters obtained from permeation studies with rabbit sclera and sclera-choroid-retina preparations mounted side-by-side in Ussing diffusion chambers.

Results: FK962 significantly increased the number of neuronal cells with elongated neurites in mixed cell culture. FK962 also increased the number of ganglion cells with elongated neurites in pure culture. The in silico pharmacokinetics study predicted that 10^-10 to 10^-9 M FK962, which facilitated neurite elongation in vitro, would be delivered to retina-choroid when a single dose of 0.0001% or 0.001% FK962 was topically applied.

Conclusions: FK962 may be a good candidate for the therapy of axonal degeneration caused by glaucoma and optic nerve injury. Dr. Shearer receives a research contract and consulting fees from, and Dr. Azuma is an employee of Senju Pharmaceutical Co., Ltd.

Keywords: 531 ganglion cells • 503 drug toxicity/drug effects • 695 retinal degenerations: cell biology