Identification of prostamides, fatty acyl ethanolamines and their biosynthetic precursors in rabbit cornea.

Arachidonoyl ethanolamine (anandamide) and prostaglandin ethanolamines (prostamides) are biologically active derivatives of arachidonic acid. Although available through different precursor phospholipids, there is considerable overlap between the biosynthetic pathways of arachidonic acid-derived eicosanoids and anandamide-derived prostamides. Prostamides exhibit physiological actions and are involved in ocular hypotension, smooth muscle contraction and inflammatory pain. Although topical application of bimatoprost, a structural analogue of prostaglandin F2a ethanolamide (PGF2a-EA), is currently a first line treatment for ocular hypertension, the endogenous production of prostamides and their biochemical precursors in corneal tissue have not yet been reported. In this study we report the presence of anandamide, palmitoyl-, stearoyl-, alpha-linoleoyl-, docosahexaenoyl-, linoleoyl- and oleoyl-ethanolamines in rabbit cornea, and following treatment with anandamide, the formation of PGF2a-EA, PGE2-EA, PGD2-EA by corneal extracts (all analysed by LC/ESI-MS/MS). A number of N-acyl phosphatidylethanolamines, precursors of anandamide and other fatty acyl ethanolamines were also identified in corneal lipid extracts using ESI-MS/MS. These findings suggest that the prostamide and fatty acid ethanolamine pathways are operational in the cornea, and may provide valuable insight into corneal physiology and their potential influence on adjacent tissues and the aqueous humour.