Carcinogenesis Advance Access originally published online on November 20, 2006
Carcinogenesis 2007 28(5):1122-1130; doi:10.1093/carcin/bgl224
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Induction of inducible nitric oxide synthase: a protective mechanism in colitis-induced adenocarcinoma
1 Gastrointestinal Research Group, Department of Physiology and Biophysics, Faculty of Medicine, University of Calgary, Calgary, Alberta, Canada T2N 4N1
2 Department of Digestive Disease, Second Hospital of Shanxi Medical University, Taiyuan, Shanxi 030001, China
3 Department of Pathology, University of Calgary, Calgary, Alberta, Canada T2N 4N1
* To whom correspondence should be addressed. Tel: +1 403 210 9714; Fax: +1 403 283 3028; Email: dmmccaff{at}ucalgary.ca
A close association between inflammatory bowel disease (IBD) and increased risk of developing adenocarcinoma exists. Moreover, chronic induction of high levels of nitric oxide (NO) produced from inducible nitric oxide synthase (iNOS) is a consistent observation in IBD. In this study we made interleukin-10/inducible nitric oxide synthase double-deficient (IL-10–/–/iNOS–/–) mice and studied the development of adenocarcinoma. Mice >6 months of age were compared with healthy wild-type (WT) controls. Inflammation was assessed using macroscopic/histological scores and myeloperoxidase activity as an indication of granulocyte infiltration. Mucosal polyps were scored macroscopically and hyperproliferation was quantified by 5-bromo-2-deoxyuridine immunohistochemistry. Dysplastic changes were assessed histologically based on cytologic and architectured atypia as well as the presence of submucosal invasion. The p53 and ß-catenin messenger RNA mRNA and protein expression were assessed using real-time polymerase chain reaction and immunohistochemistry, respectively.
Inflammatory indices were significantly elevated in interleukin-10-deficient (IL-10–/–) over WT and not significantly different from IL-10–/–/iNOS–/– mice. The incidence of mucosal polyps was similar between IL-10–/– (79%) and IL-10–/–/iNOS–/– (83%) mice; however, significantly higher numbers of polyps were observed in the absence of iNOS (P < 0.05). Hyperproliferation was noted in both groups. Signs of dysplasia and submucosal invasion were significantly higher in IL-10–/–/iNOS–/– compared with IL-10–/– mice (P < 0.05). No significant increase in p53 and ß-catenin mRNA levels was observed in IL-10–/– over WT mice; however, a 2-fold (P = 0.06) and 3-fold (P < 0.05) increase, respectively, was noted in IL-10–/–/iNOS–/– mice. Our data suggest exposure to chronic NO limits abnormal p53 and ß-catenin expression and reduces incidence of adenocarcinoma in IL-10–/– mice.
Abbreviations: BrdU, 5-bromo-2-deoxyuridine; cDNA, complementary DNA; GAPDH, glyceraldehyde-3-phosphate dehydrogenase; IBD, inflammatory bowel disease; IL-10–/–, interleukin-10 deficient; IL-10–/–/iNOS–/–, interleukin-10/inducible nitric oxide synthase double deficient; iNOS, inducible nitric oxide synthase; MPO, myeloperoxidase; mRNA, messenger RNA; NO, nitric oxide; PCR, polymerase chain reaction; UC, ulcerative colitis; WT, wild-type
Received June 13, 2006; revised November 7, 2006; accepted November 8, 2006.