Sustained Release of Tacrolimus From a Topical Drug Delivery System Promotes Corneal Reinnervation

Abstract

Purpose Corneal nerve fibers provide sensation and maintain the epithelial renewal process. Insufficient corneal innervation can cause neurotrophic keratopathy. Here, topically delivered tacrolimus is evaluated for its therapeutic potential to promote corneal reinnervation in rats. Methods A compartmentalized neuronal cell culture was used to determine the effect of locally delivered tacrolimus on sensory axon regeneration in vitro. The regenerating axons but not the cell bodies were exposed to tacrolimus (50 ng/mL), nerve growth factor (50 ng/mL), or a vehicle control. Axon area and length were measured after 48 hours. Then, a biodegradable nanofiber drug delivery system was fabricated via electrospinning of a tacrolimus-loaded polycarbonate–urethane polymer. Biocompatibility, degradation, drug biodistribution, and therapeutic effectiveness were tested in a rat model of neurotrophic keratopathy induced by stereotactic trigeminal nerve ablation. Results Sensory neurons whose axons were exposed to tacrolimus regenerated significantly more and longer axons compared to vehicle-treated cultures. Trigeminal nerve ablation in rats reliably induced corneal denervation. Four weeks after denervation, rats that had received tacrolimus topically showed similar limbal innervation but a significantly higher nerve fiber density in the center of the cornea compared to the non-treated control. Topically applied tacrolimus was detectable in the ipsilateral vitreal body, the plasma, and the ipsilateral trigeminal ganglion but not in their contralateral counterparts and vital organs after 4 weeks of topical release. Conclusions Locally delivered tacrolimus promotes axonal regeneration in vitro and corneal reinnervation in vivo with minimal systemic drug exposure. Translational Relevance Topically applied tacrolimus may provide a readily translatable approach to promote corneal reinnervation.

The Role of Sensory Innervation in Homeostatic and Injury-Induced Corneal Epithelial Renewal

“…Sustained local delivery of low-dose tacrolimus directly at the repair site of peripheral nerves increases the number of regenerating nerve fibers and accelerates their rate of regeneration [ 138 , 139 , 140 ]. Daeschler et al adapted this approach, namely the sustained local delivery of the drug from a biodegradable drug delivery system, to promote reinnervation of denervated corneas in rats [ 65 ]. The density of regenerated nerve fibers in the central cornea was found to be significantly higher four weeks post-denervation, as compared to non-treated control rats [ 65 ].…”

“…Daeschler et al adapted this approach, namely the sustained local delivery of the drug from a biodegradable drug delivery system, to promote reinnervation of denervated corneas in rats [ 65 ]. The density of regenerated nerve fibers in the central cornea was found to be significantly higher four weeks post-denervation, as compared to non-treated control rats [ 65 ].…”

“…The field’s prevailing conceptual model is that corneal epithelial wound healing and maintenance depend on sensory axons providing direct trophic stimulation of LSCs [ 35 , 36 , 37 , 38 , 39 , 40 , 41 , 42 , 43 , 44 , 45 , 46 , 47 , 48 , 49 , 50 , 51 ]. Two conceptually different therapeutic approaches for NK have evolved: (i) a novel surgical procedure termed “minimally invasive corneal neurotization” (MICN), designed to restore or provide corneal sensory innervation, and (ii) development of a topical treatment in attempt to maintain or recover a physiological trophic milieu that is lost following pathological corneal denervation [ 64 , 65 , 66 ]. Despite progress in treatments for NK, nearly 30–40% of NK patients fail to respond to either of the available treatments.…”

“…Sci. 2023, 24, x FOR PEER REVIEW 3 of 16 restore or provide corneal sensory innervation, and (ii) development of a topical treatment in attempt to maintain or recover a physiological trophic milieu that is lost following pathological corneal denervation [64][65][66]. Despite progress in treatments for NK, nearly 30-40% of NK patients fail to respond to either of the available treatments.…”

Advancing Nerve Regeneration: Translational Perspectives of Tacrolimus (FK506)

“…Rodents that were treated with these biodegradable local delivery devices as an adjunct to the gold standard epineural nerve repair demonstrated more motor and sensory neurons that regenerated their axons distal to the nerve repair site [ 65 , 70 , 71 ] and an earlier return of motor function [ 71 ]. Even in the cornea, the local and sustained release of tacrolimus has been demonstrated to accelerate ocular surface reinnervation following ophthalmic nerve injury [ 72 ].…”