Platelet-activating factor acetylhydrolases in Caco-2 cells and epithelium of normal and ulcerative colitis patients.
OBJECTIVE
Platelet-activating factor (PAF) is a potent inflammatory mediator implicated in the pathogenesis of inflammatory bowel disease and necrotizing enterocolitis. Metabolism by platelet-activating factor acetylhydrolase (PAF-AH) is the major pathway for platelet-activating factor degradation. The aim of this study was to investigate the possible role of intestinal epithelium as a source of PAF-AH.


METHODS
Intracellular and secreted PAF-AHs were characterized in human colonic epithelial cells isolated from histologically normal mucosa and inflamed mucosa from patients with ulcerative colitis and in the human intestinal epithelial cell line Caco-2 by measuring the metabolism of [3H]-PAF to [3H]lysoPAF.


RESULTS
Human colonic epithelial cells and Caco-2 cells synthesize and secrete PAF-AH as shown by in vitro hydrolysis of [3H]PAF to [3H]-lysoPAF in cell lysates and conditioned media. Both intracellular and secreted PAF-AHs are calcium-independent and substrate-specific for phospholipids similar to PAF. Epithelial cells from involved areas of resections for ulcerative colitis had increased levels of secreted PAF-AH and decreased levels of intracellular PAF-AH compared with epithelial cells from histologically normal areas.


CONCLUSIONS
Human colonic epithelial cells and Caco-2 cells produce intracellular and secreted PAF-AHs, which are distinct proteins. This is the first demonstration of PAF-AH production by epithelial cells.
D043203:1-Alkyl-2-acetylglycerophosphocholine Esterase; D015153:Blotting, Western; D018938:Caco-2 Cells / Q000201:enzymology*; D002118:Calcium / Q000378:metabolism; D002478:Cells, Cultured; D003093:Colitis, Ulcerative / Q000201:enzymology*; D003106:Colon / Q000201:enzymology*; D004591:Electrophoresis, Polyacrylamide Gel; D004848:Epithelium / Q000201:enzymology; D006801:Humans; D007413:Intestinal Mucosa / Q000201:enzymology; D010741:Phospholipases A / Q000378:metabolism*; D011233:Precipitin Tests
D010741:Phospholipases A; D043203:1-Alkyl-2-acetylglycerophosphocholine Esterase; D002118:Calcium