Cytokine‐Induced Arginase Expression in Intestinal Epithelial Cells Reduce Nitric Oxide Production and Apoptosis

Abstract

Intestinal epithelial cells are involved in disease progression of inflammatory bowel diseases such as necrotizing entercolitis in preterm neonates. Intestinal epithelial cells metabolize arginine to either nitric oxide (NO) by NO synthase (NOS) or to L-ornithine and urea by arginase. L-ornithine is the first step in polyamine synthesis important for cell viability, while NO production can lead to apoptosis. The hypothesis of this study is that in intestinal epithelial cells inflammation increases both NOS and arginase expression, and that arginase activity mitigates NO production and apoptosis. Rat intestinal epithelial cells (rIEC-6) were incubated with conditioned media (CM) from RAW 264.7 cells (a macrophage cell line) treated with LPS (E.coli 0127:B8; 1μg/ml) for 4 hours. rIEC-6 cells incubated with CM had significantly higher levels of iNOS, cleaved caspase-3, and arginase II protein levels than did control cells. Levels of arginase I were not different between controls and CM treated cells. rIEC-6 incubated in CM had significantly greater NO production than did untreated rIEC-6, and NO production in CM-treated cells was further increased when the arginase inhibitor nor-NOHA was added to the media. Viable cell number was significantly lower after 24 hours with CM than in controls, and inhibition of arginase activity with nor-NOHA resulted in a further significant decrease in viable cell numbers. These data suggest that cytokine-induced arginase expression in rIEC-6 cells tempers cytokine-induced iNOS-derived NO production and apoptosis.