Neuroprotectin D1 restores corneal nerve integrity and function after damage from experimental surgery

To investigate if topical treatment of neuroprotectin D1 (NPD1) increases regeneration of functional nerves after lamellar keratectomy.

An 8-mm stromal dissection was performed in the left eye of each rabbit. The rabbits were treated with NPD1, pigment epithelial-derived factor (PEDF) in combination with docosahexaenoic acid (DHA) or vehicle for 6 weeks, and corneas were obtained at 8 weeks. After fixation, corneal wholemounts were stained with mouse monoclonal anti-βIII-tubulin antibody and double stained with chicken anti-calcitonin gene-related peptide (CGRP) antibody. Corneal sensitivity and tear secretion were measured using the Cochet-Bonnet esthesiometer and the Schirmer's test, respectively. Additional rabbits were treated with NPD1, PEDF+DHA, or vehicle, and corneal sections were stained with a rat monoclonal anti-neutrophil antibody. Cultures of trigeminal ganglia from 5-day-old mice were treated with NPD1, PEDF+DHA, lipoxin A4 (LXA4), 12- or 15-hydroxyeicosatetraenoic acid (12[S] or 15[S]-HETE), and nerve growth factor (NGF) as positive control.

NPD1 increased subepithelial corneal nerve area three times compared with vehicle-treated rabbits. The effect was similar to PEDF+DHA-treated animals. There was recovery of CGRP-positive neurons and an increase in corneal sensitivity and tear secretion in NPD1-treated animals. NPD1 decreased neutrophil infiltration after 2 and 4 days of treatment. In the in vitro cultures, NPD1 and PEDF+DHA induced a 3-fold increase in neurite outgrowth compared with cultures without supplementation. Treatments with LXA4, 12(S)-, and 15(S)- HETE did not stimulate neurite outgrowth.

NPD1 has anti-inflammatory and nerve regenerative properties. This study demonstrates that NPD1 may offer an effective treatment for neurotrophic corneas.