Nerve Growth Factor Eye Drops Cross the Ocular–Blood Barrier Reaching the Retina and Optic Nerve in the Rat

Abstract

Abstract: : Purpose: Intraocular or retrobulbar administration of nerve growth factor (NGF) inhibits experimental retinal ganglion cell degeneration. We evaluated if NGF topically applied on the conjunctiva reaches the retina and the optic nerve in the rat. Methods: 1 µg of ¹²⁵I–NGF eye drops in 10 µl of saline solution was administrated on the ocular surface of 15 Sprague Dawley rats. Animals were sacrificed at 2 h, 6 h and 24 h following NGF treatment (n=5 for each group) and autoradiography was used to identify the presence of radiolabelled NGF in intraocular tissues. Seventy–two additional rats were treated with three different concentrations of NGF eye drops (10 µg/ml, 200 µg/ml and 500 µg/ml). Animals were sacrificed at the same time points (n=8 for each group) and NGF protein and NGF–mRNA expression were evaluated in the retina, optic nerve, lens, sclera and serum by ELISA and ELISA RT–PCR respectively. As control, a group of rats was treated with saline solution.To evaluate if NGF eye drops exert biological activity on intraocular tissues, changes of production and expression of BDNF were evaluated in the retina. Results: Two hours following NGF administration, the presence of ¹²⁵I–NGF reactivity was observed in the conjunctiva, sclera, choroid and optic nerve as well as a weakly presence in the retina. After six hours, the presence of radiolabelled NGF increased in all ocular tissues including the retina. No radiolabelled NGF was detectable in any ocular tissue 24 hours following exogenous NGF administration. All the NGF doses evaluated induced a significant increase of NGF protein levels in the ocular tissues and serum (p<0.05). The maximum increase was observed at six hours and at the concentration of 200 µg/ml in the retina and optic nerve when compared to both baseline and controls (p< 0.01). No significant increase of NGF mRNA levels was observed in the retina for all the evaluated concentrations of NGF. NGF eye drops (200µg/ml) induced a significant increase of retinal BDNF production and expression, starting 2 hours after administration and returning to baseline after 24 hours. Conclusions:Our experimental data showed that NGF eye drops reach active concentrations on the retina in a dose and time dependent fashion.

Keywords: pharmacology • growth factors/growth factor receptors • retina