ALKALI BURN-INDUCED SYNTHESIS OF INFLAMMATORY EICOSANOIDS IN RABBIT CORNEAL EPITHELIUM

Purpose. Alkali burning of the rabbit cornea is a well-established mod el for the study of anterior surface inflammation, neovascularization, and wound-healing processes. 12-hydroxyeicosanoids have been implicat ed as mediators of such responses. 12(S)-hydroxyeicosatetraenoic acid (12[S]-HETE) is a lipoxygenase-derived arachidonate metabolite and 12( R)-hydroxyeicosatetraenoic acid (12[R]-HETE) is formed by a cytochrome P450 monooxygenase; both give rise to the potent angiogenic factor 12 (R)-hydroxyeicosatrienoic acid (12[R]-HETrE). In this study, the autho rs correlate the pattern of their synthesis in the corneal epithelium with the inflammatory response after alkali injury. Methods. New Zeala nd albino rabbits were anesthetized and alkali burns created with 10-m m filter paper discs (1 N NaOH for 2 minutes). Corneas were then rinse d; 1 to 7 days later, corneal epithelium was scraped and used to asses s C-14-arachidonic acid conversion to 12-HETE and 12-HETrE enantiomers in the presence of NADPH by chiral high-pressure liquid chromatograph y. The inflammatory response secondary to the alkali burn was quantifi ed through area measurements of reepithelialization and neovasculariza tion. Results. Alkali burn induced a time-dependent production of corn eal epithelial 12-HETE and 12-HETrE. A marked increase in 12-HETE and 12-HETrE synthesis was evident at day 2 (from 22 +/- 7 to 139 +/- 22 n g/hour) after injury, increasing to 800 +/- 68 ng/hour at day 7. Chira l analysis revealed a time-dependent synthesis of the R and S enantiom ers of 12-HETE (24% R, 76% S) and 12-HETrE (72% R, 28% S). Total arach idonate metabolism, as well as the formation of 12(R)-HETrE, correlate d with the area of neovascularization (P < 0.01 and P < 0.02, respecti vely). Conclusions. The results demonstrate that surviving and regener ating epithelium has an increased capacity of synthesizing 12(S)-HETE and 12(R)-HETE and that maximal production of 12(R)-HETrE, a known dir ect and indirect angiogenic factor, coincides with neovascularization in this model. Thus, the lipoxygenase and cytochrome P450-dependent ac tivities increased in a time-dependent manner, indicating the potentia l involvement of both pathways in the inflammatory response to alkali bum. The formation of significant quantities of 12(R)HETE and 12(R)-HE TrE is a novel finding in this alkali injury model.