RELEASE OF PLATELET-ACTIVATING-FACTOR (PAF) AND EICOSANOIDS IN UVC-IRRADIATED CORNEAL STROMAL CELLS

Ultraviolet (UV) irradiation provokes acute inflammation of the eye, a nd can be used to model processes that occur in response to damage to the anterior segment. This study characterized ultraviolet-C (UVC, 254 nm) irradiation-induced PAF synthesis, and arachidonic acid (20:4) an d eicosanoid release in rabbit corneal stromal cells maintained in vit ro. PAF was measured by radioimmunoassay (RIA) after exposing cultured corneal stromal cells to UVC irradiation (20 min, 2, 5, 10 mW/cm(2)). C-14-20:4-labeled stromal cells were also stimulated with UVC and rad iolabeled phospholipids, neutral lipids and eicosanoids were measured. Synthesis of cell-associated and secreted PAF from corneal stromal ce lls was increased by UV irradiation. UV irradiation (254 nm, 5mW/cm(2) ) enhanced 20:4 release from triacylglycerols, phosphatidy linositol, phosphatidylserine and phosphatidylethanolamine, and increased levels of 20:4-diacylglycerol and unesterified 20:3. The released 20:4 entere d both the cyclooxygenase and lipoxygenase pathways after UVC irradiat ion. The PAF antagonist, BN52021 (10 mu M) reduced UVC irradiation-ind uced stimulation of prostaglandin production, but failed to inhibit UV C-induced 20:4 release and synthesis of lipoxygenase products. Further more, exogenous PAF (1 mu M) stimulated prostaglandin production, but did not increase the synthesis of lipoxygenase products from radiolabe led 20:4. The effects of PAF on prostaglandin synthesis were inhibited by BN52021. These findings indicate that responses to injury in cultu red corneal stromal cells include PAF synthesis, release of 20:4 from glycerolipids, accumulation of diacylglycerol and synthesis of eicosan oids. The data further suggest that during UVC irradiation in vitro, P AF is not a primary or initial mediator of 20:4 release and synthesis of lipoxygenase products, but may mediate UVC-induced prostaglandin sy nthesis.