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pp.311-323
Selenium (Se) obtained from dietary sources is an essential micronutrient for normal body function and it functions as an essential constituent of selenoproteins. We investigated the influence of Se on the formation of colonic aberrant crpyt foci (ACF) and tumor formation induced by azoxymethane (AOM) and dextran sodium sulfate (DSS) in male ICR mice. Five-week old ICR mice were acclimated for one week and fed on the low iron diet (LFe, 4.5 ppm) and different Se diet [Lse (0.02 ppm), Normal Se (0.1 ppm), HSe (0.5 ppm)] for 12 weeks. Animals received intraperitoneal injections of AOM (10㎎/㎏ B.W. in saline weekly for 3 weeks), followed by 2% DSS (molecular weight 36,000～50,000) in the drinking water for a week. There were five experimental groups, including a normal control group, AOM/DSS,
LFe+AOM/DSS, LFe+AOM/DSS+LSe, LFe+AOM/DSS+HSe. After sacrifice of animals, the total numbers of AC and ACF were measured in the colonic mucosa. The number of mice bearing tumors was expressed as tumor incidence rate. The iron and selenium liver concentration was measured using ICP-AES. Glutathione peroxidase (GPx) activity was determined using a GPx assay kit in the liver and colon. TUNEL and proliferating cell nuclear antigen (PCNA) staining were performed to examine the cell apoptosis and cell proliferation. In addition, immunohistochemistry of β-catenin was also performed on the mucous membrane tissue of colon. In AOM/DSS-induced colon carcinogenesis animal model, LFe diet decreased the number of 2.95±2.5 ACF/cm2 to 1.85±1.1 ACF/cm2 but it increased the total number of 5.06±4.2 AC/cm2 to 6.19±4.8 AC/cm2 compared with normal iron diet. In the iron-deficient mice, selenium did not affect the either the number of ACF or AC. The tumor incidence rate was higher in LFe diet groups than in normal iron diet group and high selenium diet weakly reduced the tumor incidence. Low selenium diet decreased the activity of GPx in the liver and colon. Apoptotic positive cells were decreased in the low selenium diet group. In addition, on the β-catenin staining, positive cells were increased in the low selenium diet group while they were decreased in the high selenium diet group. These findings indicate that the dietary levels of selenium was not highly enough to exhibit a significant protection against colon carcinogenesis in the iron-deficient mice. However, our results also indicate that dietary selenium might exert a protecting effect against colon cancer by increasing GPx activity and apoptosis and by inhibiting cell proliferation and β-catenin over-expression.
Introduction
Materials and Methods
1. Materials
2. Animals
3. Experimental designs
4. Experimental diets
5. Carcinogen treatment
6. Sample collection
7. Blood analysis
8. Histopathological examination
9. Iron and selenium analysis in liver
10. Glutathione peroxidase activity
11. AC and ACF counts
12. Tumor incidence
13. TUNEL assay
14. Immunohistochemistry of PCNA
15. Immunohistochemistry of β-catenin
16. Statistical analysis
Results
1. Body weights of mice
2. Blood analysis
3. Iron concentrations in liver
4. Selenium concentrations in liver
5. GPx activity in the liver and colon
6. Aberrant crypt foci (ACF)
7. Tumor incidence
8. Apoptosis in tumor sections
9. Immunohistochemistry of PCNA
10. Immunohistochemistry of β-catenin
Discussion
References
