Mitigating fibrosis-An impediment to corneal re-innervation following lamellar flap surgery

Abstract

Restoration of corneal sensitivity is of utmost importance to maintain corneal homeostasis following any injury or insult, for which, both corneal nerve regeneration and re-innervation are essential. Fibrosis poses a major impediment for re-innervation. We have in this study evaluated the influence of various nerve growth factors and corneal fibrosis on corneal nerve regeneration and reinnervation following lamellar flap surgery (LFS) and its modulation using antifibrotic drug pirfenidone. To achieve this, trigeminal ganglion cells were treated with pirfenidone, NGF, and NT-3 to evaluate their effect on trigeminal cell neurite growth. Following LFS, the gene expression of nerve growth factors NGF, BDNF and NT-3, Gap 43, Nogo-A and profibrotic factors Tenascin C, TGF-beta 1 were evaluated with and without pirfenidone. Wound fibrosis and corneal nerve regeneration using pirfenidone following LFS were evaluated by staining whole corneal mounts with α SMA and β tubulin 3. Safety of NGF and pirfenidone topical drops in normal unoperated cornea and its efficacy in enhancing corneal healing was evaluated following LFS. Our study shows, pirfenidone did not influence trigeminal cell neurite elongation; NGF and NT-3 significantly enhanced trigeminal cell neurite elongation. NT-3 also significantly increased neurite branching. There was significant increase in the gene expression of NGF, BDNF, NT-3, Gap- 43, TGF beta-1, Tenascin C, Nogo-A genes in the operated cornea compared to normal cornea, treatment of operated corneas with pirfenidone prevented the increased expression of these genes except Gap 43 which remained unchanged. The treatment of operated eyes with combination of NGF and pirfenidone positively influenced corneal healing compared to treatment with NGF alone, and had no adverse influence on the cornea. Pirfenidone appreciably reduced corneal fibrosis which aided in re-innervation. Both NGF and NT3 positively influence trigeminal neurite elongation. NGF and pirfenidone have complementary influence on corneal wound healing.