VP6: Sustained Topical Release of Tacrolimus Promotes Corneal Reinnervation in Rats

Abstract

INTRODUCTION: Corneal nerve fibers provide sensibility and maintain ocular surface health. Impaired corneal innervation results in progressive corneal breakdown and vision loss termed neurotrophic keratopathy. Non-surgical therapies that promote corneal reinnervation and thereby prevent vision loss are presently unavailable. MATERIALS AND METHODS: In a compartmentalized neuronal cell culture system only the axonal compartments were exposed to either Tacrolimus (50 ng/ml, n=15) or a vehicle (n=9). After 48h, the axonal surface area and axon length were measured. A biodegradable drug-delivery-system (DDS) was fabricated via electrospinning of a Tacrolimus loaded polycarbonte-urethane-polymer (100 µg Tacrolimus per DDS) which achieved sustained Tacrolimus release for >31 days. Effectiveness was tested in a rat model of neurotrophic keratopathy. Adult rats (n=16) underwent trigeminal nerve ablation and received either a Tacrolimus DDS topically before tarsorrhaphy or tarsorrhaphy only. After 28 days, the normalized corneal nerve fiber density was determined and Tacrolimus biodistribution was assessed via mass spectrometry. RESULTS: Sensory neurons whose axons were exposed to Tacrolimus regenerated significantly more axons (surface area: 2.46±0.7mm2 vs. 0.45±0.2mm2; p<0.001) that were significantly longer on average (2.49±0.5mm vs. 0.84±0.39 mm; p < 0.001) compared to vehicle treated cultures. In agreement with the in vitro results, rats that had received Tacrolimus topically showed significantly higher corneal nerve fiber density (1.48±0.68) compared to the non-treated control (0.19±0.18; p < 0.001) and 7-days post denervation (0.07±0.04; p < 0.001). Tacrolimus was detectable in the ipsilateral vitreal body (3.2±1.9 ng/g), the plasma (1.3±0.7 ng/ml) and the ipsilateral trigeminal ganglion (0.6±0.1 ng/g) but not in their contralateral counterparts or vital organs (liver, kidey, heart) 28-days post denervation. CONCLUSION: Local delivery of low-dose Tacrolimus accelerates sensory axon regeneration in vitro and corneal reinnervation in vivo with minimal systemic drug exposure. Therefore, topically applied Tacrolimus may provide a readily translatable approach to promote corneal reinnervation in patients suffering from corneal nerve fiber loss.