Wild-type K-ras has a tumour suppressor effect on carcinogen-induced murine colorectal adenoma formation

K-ras mutations are found in ~40% of human colorectal adenomas and carcinomas and contribute to colorectal tumour formation at an early stage. Wild-type K-ras has been reported to be deleted in some tumours, but the consequences of changes in wild-type K-ras copy number for experimental colorectal carcinogenesis have not been investigated. To characterize the effects of K-ras copy number changes on formation of carcinogen-induced colorectal neoplasms in mice, wild-type (K-ras(+/+) ) and heterozygous K-ras exon 1 knockout (K-ras(+/-) ) mice were given 10 weekly treatments of 1, 2-dimethylhydrazine (DMH) to induce colorectal tumours. Colorectal expression levels of K-ras 4A and 4B transcripts in K-ras(+/-) mice were ~50% decreased compared with K-ras(+/+) mice. One year after DMH treatment, survival of K-ras(+/-) mice decreased from 88 to 82% compared with wild-type mice. Colorectal adenomas significantly increased from 0.52 ± 0.15 in K-ras(+/+) mice to 0.87 ± 0.14 in K-ras(+/-) mice (mean ± SEM per mouse, P < 0.01); total tumour volume increased 2.13-fold (P < 0.05). Comparing K-ras(+/+) with K-ras(+/-) murine adenomas, Ki-67-positive proliferating tumour cells significantly increased from 7.77 ± 0.64% to 9.15 ± 0.92% and cleaved caspase-3-positive apoptotic tumour cells decreased from 1.40 ± 0.37% to 0.80 ± 0.22% (mean ± SEM, P < 0.05 for both). No K-ras or B-raf mutations were detected in the adenomas. Immunohistochemical studies showed no significant changes in extracellular signal regulating kinase/mitogen-activated protein kinase (Erk/MapK) or PI3K/Akt pathway activation in the adenomas. In conclusion, the data collectively show that a 50% reduction in K-ras gene dosage and RNA expression promoted experimental colorectal tumourigenesis, consistent with wild-type K-ras having a tumour suppressor effect on carcinogen-induced murine colorectal adenoma formation.

Modulatory effect of troxerutin on biotransforming enzymes and preneoplasic lesions induced by 1,2-dimethylhydrazine in rat colon carcinogenesis

Colon cancer is the third most global oncologic problem faced by medical fraternity. Troxerutin, a flavonoid present in tea, coffee, cereal grains, and a variety of fruits and vegetables, exhibits various pharmacological and biological activities. This study was carried out to investigate the effect of troxerutin on xenobiotic metabolizing enzymes, colonic bacterial enzymes and the development of aberrant crypt foci (ACF) during 1,2-dimethylhydrazine (DMH) induced experimental rat colon carcinogenesis. Male albino Wistar rats were randomly divided into six groups. Group 1 served as control. Group 2 received troxerutin (50 mg/kg b.w., p.o. every day) for 16 weeks. Groups 3-6 received subcutaneous injections of DMH (20 mg/kg b.w.) once a week, for the first four weeks. In addition, groups 4-6 received different doses of troxerutin (12.5, 25, 50 mg/kg b.w., p.o. every day respectively) along with DMH injections. Our results reveal that DMH treated rats exhibited elevated activities of phase I enzymes such as cytochrome P450, cytochrome b5, cytochrome P4502E1, NADPH-cytochrome P450 reductase and NADH-cytochrome b5 reductase and reduced activities of phase II enzymes such as glutathione-S-transferase (GST), DT-diaphorase (DTD) and uridine diphospho glucuronyl transferase (UDPGT) in the liver and colonic mucosa of control and experimental rats. Furthermore, the activities of fecal and colonic mucosal bacterial enzymes, such as β-glucronidase, β-glucosidase, β-galactosidase and mucinase were found to be significantly higher in DMH alone treated rats than those of the control rats. On supplementation with troxerutin to DMH treated rats, the alterations in the activities of the biotransforming enzymes, bacterial enzymes and the pathological changes were significantly reversed, the effect being more pronounced when troxerutin was supplemented at the dose of 25 mg/kg b.w. Thus troxerutin could be considered as a good chemopreventive agent against the formation of preneoplastic lesions in a rat model of colon carcinogenesis.

Caloric restriction reduced 1, 2-dimethylhydrazine-induced aberrant crypt foci and induces the expression of Sirtuins in colonic mucosa of F344 rats

BACKGROUND

Caloric restriction (CR), a lowering of caloric intake without malnutrition, is associated with longevity. CR also decreases incidences of age-related diseases including cancer. The sirtuins (SIRTs) have been implicated as a key mediator for the beneficial effects of CR on longevity. However, the underlying mechanisms by which CR decreases cancer risk have not yet been fully elucidated.

MATERIALS AND METHODS

The present study was conducted to determine whether CR would modify the growth of preneoplastic colonic aberrant crypt foci (ACF). We also analyzed the expression of SIRTs to elucidate the molecular mechanisms of cancer-preventive effects of CR. F344 rats were fed a CR diet (60% of ad libitum diet) or a basal diet ad libitum. Then, the animals were given subcutaneous injection of either 1, 2-dimethylhydrazine (DMH) that enhances cell proliferation of colonic mucosa or saline. All animals were sacrificed at 5 weeks after the beginning of the experiment.

RESULTS

The number of ACF in colonic mucosa was significantly decreased in DMH-treated rats with CR as compared to in those without CR. No ACF was found in DMH-untreated animals with or without CR. Also, we found that CR decreased the cell proliferation of colonic mucosa in DMH-treated rats. The expressions of anti-apoptotic gene, Survivin, and cell cycle progression-associated gene, Cyclin D1, were increased by DMH-treatment. Both of the genes expressions were declined by CR in those of DMH-treated rats. The expressions of all SIRT1-7 mRNAs were significantly increased by CR in DMH-treated rats.

CONCLUSION

As previous studies demonstrated that SIRT1 down-regulates Survivin and Cyclin D1, our findings suggest that at least SIRT1 protect colonic mucosa from formation and development of ACF by increasing apoptosis and reducing excessive cell growth in colon epithelial cells.

Influence of gilaburu (Viburnum opulus) juice on 1,2-dimethylhydrazine (DMH)-induced colon cancer

In this study, the effects of gilaburu (Viburnum opulus) juice on colon tumorogenesis were investigated. Eight weeks old Balb-C male mice received subcutaneous injections of 1,2-dimethylhydrazine (DMH) (20 mg/kg body weight) once a week for 12 weeks. Both the sham control (group 1) and the DMH control (group 2) groups received drinking water alone, whereas the mice of groups 3 and 4 received gilaburu juice for 30 weeks (started with first DMH injection) and for 18 weeks (started after last DMH injection), respectively. Eighteen weeks after the last DMH injection, all mice were killed and the histogenesis of colon tumors was investigated from the paraffin-embedded sections of colon, which were stained with hematoxylin-eosin. The sites and incidences of tumoral lesions (low-grade dysplasia, high-grade dysplasia, intramucosal carcinoma and invasive carcinoma) were analyzed and compared with control. The results showed that the body weights of the mice were similar in all the groups. No tumoral lesions were found in group 1. Colon tumors developed in all DMH-treated mice (groups 2, 3 and 4). In these groups, the greatest numbers of tumor lesions were detected in the distal colon, followed by the mid-colon and only a few in the proximal colon. There was a reduction in the mean total number of tumor lesion in groups 3 (8.5) and 4 (8.3), when compared to group 2 (11.3). The incidence of invasive carcinoma in group 3 was significantly lower than group 2 (p < 0.05). On the basis of these results, we conclude that gilaburu juice may be useful for the prevention of colon cancer at the initiation stage.

A novel model of colitis-related colorectal cancer

AIM: To duplicate a colitis-related colorectal cancer model that is cheap, simple and accessible.

METHODS: A total of 320 male ICR mice were randomly divided into 7 experimental groups (group A-G) and 1 control group. Groups A, B and C were given a single intraperitoneal injection of 1, 2-dimethylhydrazine (DMH) at the dose of 10, 15 and 20 mg/kg body weight, respectively. one week after injection, the animals in group A, B and C were treated with 20 g/L dextran sodium sulfate (DSS) in drinking water for consecutive 7 days. Group D, E and F were administered with DMH 10, 15 and 20 mg/kg body weight only, respectively. Group G was given 20 g/L DSS only. The weight and food intake of mice in each group were recorded every week. Several mice were killed to observed the progression to carcinoma of colitis in week 4, 9 and 13. All the mice were executed for observation in week 20.

RESULTS: After administered with DMH and DSS, the bloody stools appeared in 40% mice in week 4, 30% in week 9, and rectal prolapse was observed in 10% mice in week 13, 40% in week 20. Within 20 weeks, all the mice, which had been given DMH and DSS, developed colonic adenocarcinoma. The weights of spleen and colon were increased significantly, while the weight of thymus was decreased obviously in group A, B, C in comparison with those in the control group (spleen: 0.64 ± 0.03, 0.75 ± 0.03, 0.78 ± 0.01 g vs 0.16 ± 0.05 g, P < 0.01; colon: 0.93 ± 0.06, 0.96 ± 0.02, 0.01 ± 0.06 g vs 0.31 ± 0.06 g, P < 0.01; thymus: 0.027 ± 0.001 g vs 0.045 ± 0.004 g, P < 0.05; 0.026 ± 0.002 g vs 0.045 ± 0.004 g, P < 0.05; 0.016 ± 0.003 g vs 0.045 ± 0.004 g, P < 0.01).

CONCLUSION: DMH and DSS can effectively induce the formation of colonic cancer in ICR mice, which can well simulate the progression of colitis to carcinoma. The method used in this study is a cheap, simple and accessible.