Hypoxic injury provokes inflammation of many tissues including the ocular surface. In rabbit corneal epithelial cells, both peroxisome proliferator-activated receptor (PPAR)-inducible cytochrome P450 4B1 and cyclooxygenase-2 (COX-2) mRNAs were increased by hypoxia. PPAR ␣ and  but not ␥ mRNAs were detected in these cells. The PPAR activator, WY-14,643 increased COX-2 expression. Similarly, non-steroidal anti-inflammatory drugs with the ability to activate PPARs induced COX-2 independently of prostaglandin synthesis inhibition. COX-2 protein overexpression by hypoxia and PPAR activation was not associated with a parallel increase in prostaglandin E 2 accumulation. However, the enzyme regained full catalytic activity when: 1) hypoxic cells were re-exposed to normoxic conditions in the presence of heme and arachidonic acid, and 2) WY-14,643-treated cells were depleted of intracellular GSH. Consistent with previous observations showing that the corneal production of cytochrome P450-derived inflammatory eicosanoids is elevated by hypoxia and inflammation, the current data suggest that hypoxic injury is a model of inflammation in which molecules other than COX-derived arachidonic acid metabolites play a major proinflammatory role. This study also suggests that increased cellular GSH may be the mechanism responsible for the characteristic dissociation of PPAR-induced COX-2 expression and activity. Moreover, we provide new insights into the commonly observed lack of efficacy of classical non-steroidal anti-inflammatory drugs in the treatment of hypoxia-related ocular surface inflammation.
The present study documents the increased expression of CYP4B1 isoform in the corneal epithelium during hypoxic injury in vivo. It also demonstrates the presence of VEGF mRNA in the corneal epithelium and its increased expression in this model of hypoxic injury. All together, the results of this study raise the possibility of interaction between these autocoids, VEGF and CYP4B1-12(R)-HETrE, in mediating the neovascularization response induced by the prolonged hypoxic state brought about by closed eye contact lens wear.
By combining the use of BD Biosciences Fluoro Blok ™ membrane-based Boyden chambers with the Cellomics HCS Array Scan, a more sensitive method formeasuring cellmigration has been developed. This assay is based on counting nuclei ofmigrated cells on the bottomof the filter rather than conventional approaches, which usemeasurement of totalwell fluorescence. This cellmigration assay provides approximately 10-fold increased signal/background compared to conventional approaches and can be used to assess the effects of growth factors on endothelial cell migration and to screen chemical compounds for inhibitory effects on growth factor–mediated endothelial cell migration.
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