The levels and the structure of fecal α 1-antitrypsin in patients with inflammatory bowel disease

Abstract

Fecal ct 1-antitrypsin (ct 1-AT) clearance is now a standard test for the assessment of intestinal protein loss. In patients with inflammatory bowel disease(IBD), the sources of fecal a 1-AT remains uncleared and molecular heterogeneity of fecal a 1-AT has been reported. AIMS: 1) To examine the levels and the structure of a 1-AT in feces and sera of patients with IBD. 2) To examine the synthesis and secretion of a 1-AT in intestinal epithelial cells and hepatocytes. METHODS: We studied 36 patients with ulcerative colitis(UC), 26 patients with Crohn's disease(CD), and 20 control subjects. The stool samples were collected at 4 °C over a period of 48 hours and were homogenized. We also used human intestinal epithelial cell lines, Caco-2 and HT-29, and a hepatocellular cell line, HepG2. These cells were stimulated with interleukin-6 (IL-6), interleukin-1 13 and tumor necrosis factor a. The level of <x 1-AT protein was measured by ELISA, and the expression of <x 1-AT mRNA by RT-PCR. The a 1-AT molecules were examined by Western blotting and the reactivity with Concanavalin A (Con A) was studied by Con Aa 1-AT Ab sandwich EIA. RESULTS: 1) Fecal ct 1-AT concentrations were significantly higher in active UC and CD (medians 1465, and 3482 lag/g respectively) than in inactive UC, CD and control subjects (medians 411,651, and 327 laglg respectively). In all disease groups and control subjects, serum a 1-AT showed an apparent molecular weight (MW) of-52 kDa and fecal a 1-AT showed fragments of various sizes. In active UC and CD, the apparent MW of the main band of fecal ct I-AT was higher than in inactive patients and control subjects. In active UC and CD, ConA-bound ct 1-AT was rich in the feces. 2) The synthesis and secretion of a 1-AT were increased after stimulation with IL-6 (10, 100 ng/ml) in Caco-2 cells, and HT-29 cells as well as HepG2. The percentage of ct I-AT released extracellularly was also increased. The level of ¢t 1-AT mRNA expression reached a peak within 120 mins of stimulation of IL-6. Neither IL-1 13 nor TNF a was a potent stimulant. CONCLUSIONS: An increase of fecal a 1-AT level is at least partly due to an increase of its secretion from intestinal epithelial cells in patients with intestinal inflammation. The structural analysis of fecal a I-AT is useful for assessment of disease activity in IBD.