| Background: Epidemiologic study shows that: chemical carcinogenic agents play an important role in human carcinogenesis. Now, since the diet structure of our country's people has gradually changed: containing more energy, more protein, more fat but less fiber. These make the chemical carcinogenic agents around the environment easier lead to carcinogenesis. It is reported that the disease incidence and the case fatality of colorectal cancer increase in Shanghai. And the case fatality has ranked the second in malignant tumors'. The occurrence and development of colorectal cancer have intimate relationship with recurrent attacks of colitis. Clinical data show the patients who suffer from colitis over 30 yeas, more liable to get colon cancer, the cancerated rate could be as high as 40%. Then, looking for a novel and useful treatment target and inhibiting the development of colitis are important for preventing the occurrence of colitis related colorectal cancer. Galectin-3 is a beta-galactoside-binding protein whose expression has been correlated with progression and metastasis in colon cancer. It is a multifunctional protein expressed broadly in normal and tumor cells and was shown to be involved in cell growth, cell adhesion, cell differentiation, and tumor progression and metastasis mainly through binding to glycoproteins. It is found in the cytoplasm, on the cell surface, in the nucleus, and is secreted by tumor and inflammatory cells. And it is expressed at elevated levels in a variety of neoplastic cells. Most studies have also found a positive correlation between galectin-3 and colon cancer progression. Galectin-3 concentrations have been found to be higher in those with metastatic disease than in patients with localized tumors. Also, galectin-3 is thought to be a pro-inflammatory factor. It is downregulated in IBD patients. While the inflammation reaction decreased in Galectin-3 gene knock-out mice.However, the expression of galectin-3 during the process from colitis to colorectal cancer hasn't been reported mainly due to the lack of an available and effective colitis-related colorectal cancer model.Methods: First, making a colitis-related colorectal cancer model. A total of 320 male ICR mice were randomly divided into seven-experimental and one-control groups. Groups 1, 2 and 3 were given a single intraperitoneal (i.p.) injection of 1,2-dimethylhydrazine ( DMH) at the dose of 10, 15 or 20 mg/kg body weight, respectively. 1 week after the injection, animals in groups 1–3 were given 2% (w/v) dextran sodium sulfate (DSS) in drinking water for consecutive 7 days. Groups 4, 5 and 6 were given DMH 10, 15 and 20 mg/kg body weight alone, respectively. Group 7 was given 2% DSS only. Group 8 was an untreated control. Monitoring the body weight and food-intake of the mice every week, and then, we sacrificed some mice at week4, 9, and 13 to observe the colitis canceration. All mice were sacrificed at week 20. After the success of model-making, we went on to next step. A total of 160 male ICR mice were divided into 5 big groups, the mice of the group 1(40 mice) received saline only, the mice of the group 2 (60 mice) received DMH+DSS, the mice in groups 3-5 (20 mice respectively) received DMH+DSS, then treated with polysaccharides at three different doses. Except for the mice received saline only, the animals in groups 2-5 were given a single intraperitoneal injection of DMH (15mg/kg body weight) at the first week. Starting one week after the DMH injection, animals were administered with 2%DSS in drinking water for 7 days, then the mice in group 2 were given no further treatment. Mice in groups 3-5 were maintained on the basal diets mixed with one polysaccharides (2.5%, 5%, 10%, w/w) for 14 weeks, starting 4 week after the stop of DSS administration. The mice in group1 and group3 were sacrificed separately at the week of 3, 5, 9, 12, 15, and 20. Then, all animals were sacrificed at the end of the study (Week 20). The colons with the length of 8 cm were weighed and numbers of the colon tumors were recorded. Colon samples were then excised; a little piece of colons were fixed in 10% buffered formalin for at least 24 hours. Histopathological examinations were performed on paraffin-embedded sections after hematoxylin and eosin (H & E) staining. The colonal mucosa was carefully scraped off with a glass slide and snap-frozen in liquid nitrogen, then stored at -80°C for further assays of RT- PCR and western-blot. All the processes were handling in ice bath.Results: The bloody stools appeared in approximate 40% mice at week 4, 30% at week 9.And prolapse were observed in 10% mice at week 13, 40% at week 20. Within 20 weeks, all mice which had been given DMH/ DSS developed colonic adenocarcinoma. From the results of H.E stain, we found that the pathological changes of colon were from inflammation to colon cancer basically. And the level of galecin-3 in mucous membrane of colon underwent four phases'changes: 1) At the early stage of inflammation, galectin-3 in cytoplasm of clonic mucosa cells decreased significantly, and the ratio of nucleis to cytoplasm decreased too. 2) At the middle and advanced stage of inflammation, galectin-3 in cytoplasm were still lower than normal, but had increased compared with the early stage. While the galectin-3 in nucleis increased significantly, and the ratio of nucleis to cytoplasm increased. 3) When carcinoma in situ of colon developed, galectin-3 in cytoplasm had no significant change compared with normal, but the ratio of nucleis to cytoplasm increased.4) After using PS to treat, both galectin-3 in cytoplasm and nucleis increased, and the ratio increased.Conclusion:1. The alteration and location of galectin-3 involve in the repeatly damage, repair, hyperplasia and neoplasia during the colitis progression.2. The change of galectin-3 in cytoplasm coincided with the situation in human colitis and colon cancer, which demonstrates that this model can simulate the expression of galectin-3 in human colitis and colon cancer effectively.3. The expression of galectin-3 in nucleus and the change of galectin-3 in nucleus to cytoplasm have intimate relationship with the colitis canceration.4. The ligand of galectin-3 could prevent the colitis canceration effectly, which indicates galectin-3 could be a preventive target of colitis canceration. |
PDF Full Text Request