T E Riehl1, W F Stenson. 1. Department of Medicine, Washington University School of Medicine, St. Louis, Missouri, USA.
Abstract
BACKGROUND & AIMS: 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.
BACKGROUND & AIMS: 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.