Nerve growth factor loaded hypotonic eye drops for corneal nerve repair

Neurotrophic keratopathy is a degenerative disease caused by corneal nerve damage, leading to corneal ulceration. Recombinant human nerve growth factor (rhNGF) was approved for neurotrophic keratitis therapy; however, the excipients of the eye drops are not optimized for its controlled release. To this aim, we introduce the hypotonic hydrogel PF127 as an excipient for rhNGF in eye drops. We confirmed the formation of a hydrogel using a vial-inversion test and based on rheological properties. The hydrogel exerts shear-thinning behavior upon sweep test with a favorable transmittance and a natural refractive index. Moreover, the hydrogel exhibited fast and sustained rhNGF release kinetic, along with constant dissolution and the formation of a network-like structure. The release of rhNGF was confirmed by the proliferation of PC12 cells and its protective effect on damaged axons of dorsal root ganglia cells. The hydrogel performed accordingly in the in-situ ocular gelation and ocular surface retention test. We further confirmed that labeled proteins were released from the hydrogel to the cornea. Preclinical testing in mice showed that rhNGF hydrogels supported the recovery from corneal epithelial defects: they reduced the defect size and increased corneal nerve density. Schirmer's test revealed improved corneal nerve function based on tear secretion. The hydrogel resists clearance from blinking and enhances the intraocular absorption of rhNGF. The ocular surface, retinal thickness, and the ciliary body and retina remained unchanged. Together, these findings suggest that the hypotonic PF127 hydrogel is a suitable rhNGF delivery system to prepare eye drops for potential use in neurotrophic keratopathy.