Dietary zinc inhibits the formation of colonic preneoplastic lesion induced by azoxymethane and dextran sodium sulfate in mice / 대한수의학회지

Colorectal cancer (CRC) is one of the leading causes of cancer death in western countries or in the developed countries. Zinc intake has been associated with decreased risk of CRC. We investigated the effect of zinc on the formation of colonic aberrant crypt foci (ACF) induced by azoxymethane followed by dextran sodium sulfate in mice. Five-week old ICR mice were fed with the different zinc levels (0.01, 0.1, 1 ppm) for 12 weeks. The numbers of ACF were measured in the colonic mucosa. The ACF number of HZn group was significantly low compared with LZn group or MZn group. Cytosolic superoxide dismutase activity was the highest in HZn group, while thiobarbituric acid reactive substance level for lipid peroxidation was the highest in LZn group. There was no difference in number of PCNA-positive proliferative cells among the groups. TUNEL-positive apoptotic cells were increased in HZn group compared with LZn group. The HZn group exhibited a decrease of beta-catenin immunostaining areas compared with the LZn or MZn group. These findings indicate that dietary zinc might exert a protecting effect against colon carcinogenesis by inhibiting the development of ACF in the mice.

Suppressive Effect of Zinc on the Formation of Colonic Preneoplastic Lesions in the Mouse Fed High Levels of Dietary Iron

We investigated the effect of zinc on the formation of colonic aberrant crypt foci induced by azoxymethane (AOM) followed by dextran sodium sulfate (DSS) in mice with high iron diet (HFe; 450 ppm iron). Six-week old ICR mice were fed on high iron diets with combination of three different levels of zinc in diets, low-zinc (LZn; 0.01 ppm), medium-zinc (MZn; 0.1 ppm), and high-zinc (HZn; 1 ppm) for 12 weeks. Animals were received weekly intraperitoneal injections of AOM (10 mg/kg B.W. in saline) for 3 weeks followed by 2% DSS (molecular weight 36,000~50,000) in the drinking water for a week. To confirm the iron storage in the body, the hepatic iron concentration has been determine chemically and compared with histological assessment visualized by Prussian blue reaction. Aberrant crypt (AC) and aberrant crypt foci (ACF) were analyzed in the colonic mucosa of mouse fed high dietary iron. Superoxide dismutase (SOD) activity and thiobarbituric acid-reactive substances (TBARS) level were also investigated. Apoptosis in the preneoplastic lesion was determined by terminal deoxynucleotidyl transferase-mediated dUTP nickend labeling (TUNEL). In addition, immunohistochemistry of beta-catenin was also performed on the mucous membrane of colon. The number of large ACF (> or = 4 AC/ACF), which possess greater tumorigenic potential, was significantly lower in MZn and HZn groups compared with LZn group. Cytosolic SOD activity in the liver was significantly higher in HZn group compared with LZn group. Hepatic MDA level was decreased significantly in HZn group compared with MZn and LZn groups. Apoptotic index was significantly higher in HZn group. Taken together, these findings indicate that dietary zinc might exert a protective effect against colonic preneoplastic lesion induced by AOM/DSS in ICR mice with high iron status, and suggest that dietary supplement of zinc might play a role in suppressing colon carcinogenesis in mice.