IntroductionThe term food allergy (FA) is defined as an immune-mediated hypersensitivity to ingested allergens. This immunologic response to nutritive antigens in the intestine is mostly an immediate type hypersensitivity depending on food-specific IgE-antibodies [1]. Food antigen and IgE-antibody crosslinking causes mast cell and eosinophil degranulation with subsequent release of histamine (H) and other mediators like leukotrienes, prostaglandins and platelet activating factor at the mucosal surface of the gut [2]. Histamine might influence the occurrence and severity of intestinal as well as extraintestinal symptoms and their duration. In the intestine H is catabolized by the enzymes diamine oxidase (DAO) and histamine-N-methyltransferase (HNMT) which are present in the epithelial cells of the small and large bowel [3]. In this context, the aim of this study was to investigate the distribution and activity of DAO in the intestinal mucosa of healthy persons and patients suffering from FA.
Materials and methodsThe study involved 12 patients with manifest FA complaining of chronic or intermittent diarrhoea (100%), abdominal pain and/or bloating (55%), vomiting and/or malabsorption (25%) and urticaria, flush or skin reactions (20%). They had colonoscopy in order to exclude other gastrointestinal diseases. In all cases, diagnosis of FA was confirmed by double-blind, placebo-controlled oral food challenge (DBPCFC) and by demonstration of food-specific IgE-antibodies in blood, skin or intestinal lavage fluid [4]. In the control group (CG), 11 individuals were included who underwent colonoscopy because of obstipation, workingup of anaemia or abdominal pain without any abnormal endoscopic or histologic findings in the lower gastrointestinal tract and without allergic diseases.The endoscopically taken biopsies (n = 64/FA, n = 57/CG) were stored immediately in liquid nitrogen. They were homogenized with 1500 ml phosphate buffer (1500 rpm, 5 min, micro-dismembrator, Braun Biotech, Germany) and centrifuged (7500 rpm = 2500 g, 4°C, 10 min). DAO activity was measured in the tissue homogenates (supernatants) adding 14 C-putrescine as substrate according to the method of Kusche et al. [5]. The DAO activity was given in cpm/hour ¥ mg wet weight (ww), mean ± SD. Intraassay variation of the DAO-assay was 16.2 %. In addition, total histamine degradation capacity (THDC, D ng histamine degradation/hour ¥ mg ww, mean ± SD, intraassay variation = 8.5 %), reflecting the enzyme activity of all histamine catabolizing enzymes, was determined from each tissue homogenate. Therefore, the histamine content was measured in duplicate at t 0 and after 60 min in 100 ml aliquots (37°C) by radioimmunoassay (Coulter-Immunodiagnostics, Germany, intraassay variation = 11.8 %, interassay variation = 21.2 %). Enzymatic histamine degradation was stopped by denaturating the enzymes by 100 ml perchloric acid (8 %) at t 0 and t 60 , respectively. For statistics the U-Test (Mann-Whitney-Wilcoxon) for independent data was used.
Results and discussionIn patien...