Chiho Yabuta

Galectin-3 Enhances Epithelial Cell Adhesion and Wound Healing in Rat Cornea

Background/Aims: To investigate if galectin-3: (1) enhances adhesion of rat corneal epithelial cells onto a collagen IV substrate and (2) promotes wound healing in rat corneal explants. Methods: Primary cultures of rat corneal epithelial cells were fixed and immunostained with galectin-3 antibody. To test cellular adherence onto plates coated with collagen type IV, isolated corneal epithelial cells from rats were cultured for 24 h with or without recombinant galectin-3. The attached cells were counted after fixing and staining with 0.1% crystal violet. Direct binding of galectin-3 to collagen IV was tested using a biotin label transfer method. To evaluate wound healing, explants with a 3.5-mm diameter wound in the central corneal epithelium from rats were incubated for 16 h with or without recombinant galectin-3. Changes in the size of the wound were measured with a digital microscope after staining with 5% fluorescein sodium. Results: In rat corneal epithelial cells, galectin-3 was stained throughout the cytoplasm, with increasing density adjacent to the plasma membrane. Exogenous galectin-3, but not epidermal growth factor (EGF), significantly promoted adhesion of corneal epithelial cells onto the collagen IV substrate. Galectin-3 directly bound to collagen IV in vitro. Exogenous galectin-3 significantly enhances wound healing in the corneal explants, which was partially inhibited by β-lactose. Conclusion: Galectin-3 promotes adhesion of corneal epithelial cells onto collagen IV and enhances wound healing in corneal explants. Since galectin-3 functions in promoting wound healing by a different mechanism than that used by EGF, exogenous galectin-3 may be a candidate drug for enhancing epithelial cell wound healing in disorders of the cornea.

Topical FK962 Facilitates Axonal Regeneration and Recovery of Corneal Sensitivity After Flap Surgery in Rabbits

PURPOSE To test if the drug FK962 (N-(1-acetylpiperidin-4-yl)-4-fluorobenzamide) facilitates axonal elongation and recovery of corneal sensitivity after creation of a corneal flap in rabbits. DESIGN Animal study. METHODS Primary cultures of rabbit trigeminal ganglion cells were used to test if FK962 promoted nerve elongation in vitro. A 130 μm-thick×8.6 mm-diameter flap was created in rabbit corneas where topical 10(-6) M FK962 was administered 4 times daily. After treatment of 7 days, corneal mechanical sensitivity was measured using a Cochet-Bonnet esthesiometer. Whole-mount corneal sections were prepared, sensory nerve axons were stained with antibody for neurofilament, and axonal elongation from transected nerve termini were scored using standardized criteria. Ocular pharmacokinetics modeling was used to predict permeation of topical FK962 into cornea. RESULTS FK962 accelerated sprouting and elongation of neurites in cultured neuronal cells from rabbit trigeminal ganglia. In the in vivo rabbit model, distal axons from transected nerve termini in corneas disappeared soon after flap surgery; but with time, axons regenerated and elongated. Topical application of 10(-6) M FK962 for 7 days significantly enhanced axonal elongation and increased corneal sensitivity. Increased corneal sensitivity was directly and significantly correlated with axonal elongation, suggesting functional enhancement of re-innervation by FK962. CONCLUSIONS Results from a rabbit model of laser in situ keratomileusis (LASIK) surgery showed that topical FK962 facilitated corneal re-innervation leading to recovery of sensitivity. Results suggested that topical application of FK962 might decrease complications in patients after LASIK surgery.

FK962 promotes neurite elongation and regeneration of cultured rat trigeminal ganglion cells: possible involvement of GDNF.

PURPOSE Amputation of the trigeminal nerve leads to decreased corneal sensitivity and dry eye. Our previous study showed that the drug FK962 (N-[1-acetylpiperidin-4-yl]-4-fluorobenzamide) induced neurite elongation from trigeminal ganglion (TG) cells and accelerated recovery of corneal sensitivity in a rabbit model of in situ keratomileusis (LASIK) surgery. However, the molecular pathways leading to FK962-induced neurite elongation and regeneration are not well defined. Thus, the purposes of the present experiments were to determine if FK962 induces elongation and regeneration of cultured rat TG cells and to investigate the mechanism of FK962-induced neurite elongation. METHODS Mixed TG cells were cultured with or without FK962, and immunocytochemistry was used to detect stimulation of neurite elongation. Neurite regeneration was also tested in an in vitro model of neuronal ablation. ELISA was used to detect glial cell line-derived neurotrophic factor (GDNF) and somatostatin (SST) release, and mRNA expression was measured by qPCR. Antibody neutralization was used to determine the mechanism for FK962-induced neurite elongation/regeneration. RESULTS FK962 enhanced elongation and regeneration of neurites in TG neurons. GDNF treatment-induced neurite elongation and GDNF antibody significantly inhibited neurite elongation induced by GDNF and FK962. Nerve growth factor (NGF) treatment also induced neurite elongation, which was inhibited by NGF antibody, but NGF antibody did not inhibit FK962-induced neurite elongation. CONCLUSIONS Our data suggested that FK962 stimulated induction of GDNF from TG cells. GDNF may be a part of the signaling pathway for FK962-induced neurite elongation/regeneration in rat TG neurons.

In Silico Ocular Pharmacokinetic Modeling: Delivery of Topical FK962 to Retina

PURPOSES To establish the in silico ocular pharmacokinetic modeling for eye drops, and to simulate the dose regimen for FK962 in human choroid/retinal diseases. METHODS Pharmacokinetics for FK962 in vivo was performed by a single instillation of drops containing 0.1% 14C-FK962 in rabbit eyes. Permeation of FK962 across the cornea, sclera, and choroid/retina was measured in vitro. Neurite elongation by FK962 was measured in cultured rat retinal ganglion cells. Parameters from the experimental data were used in an improved in silico model of ocular pharmacokinetics of FK962 in man. RESULTS The mean concentration of FK962 in ocular tissues predicted by in silico modeling was consistent with in vivo results, validating the in silico model. FK962 rapidly penetrated into the anterior and posterior segments of the eye and then diffused into the vitreous body. The in silico pharmacokinetic modeling also predicted that a dose regimen of 0.0054% FK962 twice per day would produce biologically effective concentrations of FK962 in the choroid/retina, where FK962 facilitates rat neurite elongation. CONCLUSIONS Our in silico model for ocular pharmacokinetics is useful (1) for predicting drug concentrations in specific ocular tissues after topical instillation, and (2) for suggesting the optimal dose regimens for eye drops. The pharmacodynamics for FK962 produced by this model may be useful for clinical trials against retinal neuropathy.