RELATIONSHIP BETWEEN CYCLOOXYGENASES AND RENAL ISCHEMIA-REPERFUSION INJURY:

P60 Aim: Renal ischemia-reperfusion (I/R) injury is a clinically significant problem and invariable consequence of renal transplantation that may result from aortic cross-clamping and resusciation after systemic hypotension. During the process of I/R injury, inflammatory reactions are activated, resulting in the formation of inflammatory cytokines, such as tumor necrosis factor-alpha, interleukin-1beta and arachidonic acid (AA) metabolites. AA is metabolized to produce a host of pro-inflammatory substrates called eicosanoids, through pathways involving lipoxygenases and cyclooxygenases (COX-1 and COX-2). Conversion of AA to thromboxane and prostaglandin is catalyzed by COX, while leukotrienes are catalyzed by lipoxygenase. COX-1 and –2 catalyze the initial key enzymatic steps in the metabolism of AA. COX-1 is constitutively expressed in most tissues, whereas COX-2 is induced in response to pro-inflamamatory cytokines and stress. In this study, we researched the expression of COX-1 and -2 in renal I/R injury of the rat. Method: The right kidney was harvested and the left renal artery and vein were clamped under laparotomy. The kidney was reperfused after 90 min of ischemia, and rats were killed at 0, 1.5, 3, 5, 12 and 24 hrs after reperfusion. COX-2 expression was analyzed by immunohistochemical staining using monoclonal antibody. To quantify the acute tubular necrosis (ATN), the degree of ATN was graded on a scale of 0 to 3 by two blind observers using HE staining. Similarly, COX-1 and COX-2 staining was graded on a scale of 0 to 4 according to the intensity of staining. All results are presented as the mean ± SD. Analyses of data are made using the analysis of variance (AVOVA). Results: COX-2 expression was observed only in endothelial cells of normal kidney. From 1.5 to 3 hr after reperfusion, COX-2 expression gradually became stronger on endothelial cells. COX-2 expression was most intense on endothelial cells at 3 and 5 hr after reperfusion. Five hours after reperfusion, internal spaces of the tubular epithelial cells were expanded, and slight destruction of the tubular epithelial cells appeared. Twelve hours after reperfusion, necrosis extended throughout the ischemic kidney and nearly all the tubular epithelial cells were destroyed, but from 12 to 24 hrs after reperfusion, COX-2 expression gradually became weaker on endothelial cells. However, there were no differences in COX-2 expression in the hours after reperfusion. ATN scores gradually became higher at time flow after reperfusion (0 hr; 0.1 ± 0.2, 1.5 hr; 0.2 ± 0.3, 3 hr; 0.6 ± 0.4, 5 hr; 1.2 ± 0.4, 12 hr; 2.5 ± 0.4, 24 hr; 2.9 ± 0.3). COX-1 expression scores revealed no significant differences in the following time intervals: (0 hr; 1.2 ± 0.7, 1.5 hr; 1.4 ± 0.7, 3 hr: 1.5 ± 0.8, 5 hr: 1.6 ± 0.8, 12 hr: 1.8 ± 0.8, 24 hr; 1.4 ± 0.6, before ischemia; 1.1 ± 0.6). However, COX-2 expression scores were significantly higher at 1.5, 3, 5, 12 and 24 hrs after reperfusion than at 0 hr after reperfusion. (0 hr; 0.8 ± 0.4, 1.5 hr; 1.9 ± 0.6, 3 hr: 3.1 ± 0.5, 5 hr: 3.3 ± 0.6, 12 hr: 2.5 ± 0.7, 24 hr; 1.8 ± 0.7, before ischemia; 0.6 ± 0.5). Conclusions: Although COX-1 expressions revealed no difference in the hours after reperfusion, COX-2 was expressed in rat model having renal I/R injury. Several hours after the maximum of COX-2 expression, the maximum of renal I/R injury was observed. These results may indicate a significant relationship between COX-2 expression and renal I/R injury.