Mark A. Watson

The colon-selective spasmolytic otilonium bromide inhibits muscarinic M 3 receptor-coupled calcium signals in isolated human colonic crypts

Otilonium bromide (OB) is a smooth muscle relaxant used in the treatment of irritable bowel syndrome. Otilonium bromide has been shown to interfere with the mobilization of calcium in intestinal smooth muscle, but the effects on other intestinal tissues have not been investigated. We identified the muscarinic receptor subtype coupled to calcium signals in colonic crypt derived from the human colonic epithelium and evaluated the inhibitory effects of OB. Calcium signals were monitored by fluorescence imaging of isolated human colonic crypts and Chinese hamster ovary cells stably expressing the cloned human muscarinic M3 receptor subtype (CHO‐M3). Colonic crypt receptor expression was investigated by pharmacological and immunohistochemical techniques. The secretagogue acetylcholine (ACh) stimulated calcium mobilization from intracellular calcium stores at the base of human colonic crypts with an EC50 of 14 μM. The muscarinic receptor antagonists 4‐DAMP, AF‐DX 384, pirenzepine and methroctamine inhibited the ACh‐induced calcium signal with the following respective IC50 (pKb) values: 0.78 nM (9.1), 69 nM (7.2), 128 nM (7.1), and 2510 nM (5.8). Immunohistochemical analyses of muscarinic receptor expression demonstrated the presence of M3 receptor subtype expression at the crypt‐base. Otilonium bromide inhibited the generation of ACh‐induced calcium signals in a dose dependent manner (IC50=880 nM). In CHO‐M3 cells, OB inhibited calcium signals induced by ACh, but not ATP. In addition, OB did not inhibit histamine‐induced colonic crypt calcium signals. The present studies have demonstrated that OB inhibited M3 receptor‐coupled calcium signals in human colonic crypts and CHO‐M3 cells, but not those induced by stimulation of other endogenous receptor types. We propose that the M3 receptor‐coupled calcium signalling pathway is directly targeted by OB at the level of the colonic epithelium, suggestive of an anti‐secretory action in IBS patients suffering with diarrhoea.

MTHFR (C677T and A1298C) Polymorphisms and Risk of Sporadic Distal Colorectal Adenoma in the UK Flexible Sigmoidoscopy Screening Trial (United Kingdom)

ObjectiveThe purpose of this study was to further evaluate the role of low activity MTHFR variants as well as to explore interactive effects between alcoholic drink consumption and MTHFR variants and risk of distal colorectal adenomatous polyps.MethodsWe examined the relationship between MTHFR C677T and A1298C gene polymorphisms and risk of distal adenomas in one of the largest case control studies of 946 polyp-free controls and 894 cases, all participants of the UK Flexible Sigmoidoscopy Screening Trial (UKFSS).ResultsInvestigation of the effect of the MTHFR C677T polymorphism in this large UKFSS study revealed no overall association on adenoma risk (P>0.05). However the MTHFR 1298C allele was linked, for the first time, to high risk adenomas, although in males only (odds ratio (OR) for A/C+C/C compared with A/A 1.55; 95% confidence interval (CI), 1.08–2.22; P=0.018).ConclusionsIn this, the largest study of these polymorphisms in relation to colorectal adenoma, there was no evidence for an interaction with alcohol in combination with the variant forms of MTHFR (P>0.05).

No Association between Cytochrome P450 and Glutathione S-Transferase Gene Polymorphisms and Risk of Colorectal Adenoma: Results from the UK Flexible Sigmoidoscopy Screening Trial

Genetic variation in carcinogen metabolizing enzymes has been proposed as a susceptibility marker for colorectal neoplasia. The cytochrome P450 (CYP) and glutathione S -transferase (GST) enzymes metabolize several classes of carcinogen in the human diet and tobacco smoke. Epidemiologic studies that

Dietary factors affecting the prevalence of distal colorectal adenomas and metaplastic polyps

INTRODUCTION When compared with colorectal cancer, relatively little is known regarding the effect of diet on the development of colorectal adenomatous and metaplastic polyps. Dietary assessments in case-control studies are subject to bias as dietary recall may be modified by the development of symptoms and knowledge of the diagnosis. We have assessed dietary intake in 3488 volunteers having a screening flexible sigmoidoscopy in four regions of the UK (Norwich, Leeds, Portsmouth, Harrow). METHODS People attending for a screening flexible sigmoidoscopy completed a food frequency questionnaire prior to their test. Those investigated for lower GI symptoms during the previous 2 years or with a history of colitis or colorectal neoplasia were excluded. Food frequency was divided into high and low (above and below the median) and compared in cases and polyp free controls.