Involvement of Neutrophil Phospholipase D in the Production of Reactive Oxygen Metabolites in Experimental Rat Colitis

Background & Aims : Phospholipase D (PLD) hydrolyzes phosphatidylcholine and produces lipid second messengers including phosphatidic acid (PA) and diacylglycerol (DG). Although cellular PLD has recently been recognized as an important signal-transmitting enzyme, the roles of PLD in pathophysiological conditions are largely unknown. The aim of this study is to elucidate the roles of PLD in the production of reactive oxygen metabolites in experimental rat colitis. Methods : Colitis was induced in rats by oral administration of dextran sulfate sodium. Luminol amplified chemiluminescences of the colonic mucosa and polymorphonuclear leukocytes were both measured. Results and Conclusions : Oleate-dependent PLD was activated in the colitic mucosa. Chemiluminescence and myeloperoxidase activity of the colitic mucosa were significantly higher than those of the control normal mucosa. Preincubation of the mucosa in vitro with PLD, PA, or DG significantly enhanced chemiluminescence of the colitic, but not of normal mucosa. On the other hand, administration of glycerol, which inhibits the production of PA and DG by PLD, significantly decreased chemiluminescence induced by exogenous PLD. In rat polymorphonuclear leukocytes suspension, the addition of PLD, PA, or DG significantly increased chemiluminescence and propranolol significantly decreased the chemiluminescence induced by both PA and DG. These results suggest that PLD in neutrophils may be relevant to the production of reactive oxygen metabolites in experimental rat colitis.