Anti–inflammatory lipid mediators markedly accelerate wound healing and inhibit neo–vascularization: Evidence for novel protective lipid circuits in the cornea.

Abstract

Abstract: : Purpose: Injury to the cornea leads to formation of distinct classes of mediators that initiate and amplify inflammatory cascades and neo–vascularization. However, endogenous pathways that counter–regulate these signals and minimize corneal damage remain to be elucidated. To this end, we assessed whether recently described novel anti–inflammatory lipid circuits, namely the Lipoxin A₄ and the docosahexaenoic acid (DHA)–initiated 17S–resolvin circuit, are present in the cornea and have a role in keratitis, wound healing and/or neo–vascularization. Methods: Corneal injury in Balb/c male mice was induced by thermal cautery. Wound healing, re–epithelialization, opacity and neo–vascularization were assessed by slit lamp vital microscopy. Eyes or cornea were collected at different stages of wound healing and inflammatory markers quantitated by ELISA, myeloperoxidase assay, and/or RT–PCR. Oligonucleotide primers were designed to quantitate RNA expression of 12/15–lipoxygenase and the LXA₄ receptor. 17S–series resolvins were biosynthesized from DHA and purified by column chromatography and RP–HPLC. Mice were treated with 1 µg LXA₄ or the resolvin precursor 17S–hydroxy–DHA by eye drop and tail vein injection for 4 days post–injury. Results: Eye and cornea expressed 12/15–lipoxygenase, a key enzyme for the formation of lipoxins and resolvins, as well as the LXA₄ receptor. Treatment with either LXA₄ or 17S–hydroxy–DHA caused a pronounced inhibition of corneal neo–vascularization, inflammation and corneal opacity and dramatically accelerated wound repair. Conclusions: Taken together these findings provide the first evidence for anti–inflammatory lipid circuits in the cornea, namely expression of their biosynthetic pathways as well as receptors. The dramatic impact of LXA₄ and 17S–Resolvins on wound repair and neo–vascularization provides evidence for a potential role for these endogenous lipid circuits in minimizing corneal damage. Moreover, they may provide a novel therapeutic approach to accelerate or promote corneal healing following injury or refractive surgery.

Keywords: cornea: epithelium • inflammation • wound healing