Light and moderate doses of ethanol in chemical carcinogenesis of the colon in rats

A review of experimental models in colorectal carcinogenesis

Colorectal cancer is the leading cause of malignancy of the gastrointestinal tract. A better understanding of the molecular and cellular changes that lead to the disease is necessary to develop early diagnosis and optimal treatment modalities. Rodent models are rapid, reproducible and exhibit an adenoma-carcinoma sequence similar to that found in humans. The objective of this manuscript is to review the most common chemical carcinogens used to induce experimental tumors and the usual methods of evaluation.

Jacalin Has Chemopreventive Effects on Colon Cancer Development

Colorectal cancer, which is one of the most common causes of cancer-related deaths worldwide, has a slow natural history that provides a great opportunity for prevention strategies. Plant-derived natural products have received considerable attention because of their inherent colorectal cancer chemopreventive effects. The plant lectin jacalin specifically recognizes the tumor-associated Thomsen-Friedenreich antigen and has antiproliferative effects on human colon cancer cells, highlighting its potential antitumor activity. To evaluate jacalin's potential application in colorectal cancer chemoprevention, we studied its effects on the early stages of carcinogenesis. Balb/c mice were given 4 intrarectal deposits of 0.1 ml solution of Methyl-N'-Nitro-N-Nitroso-Guanidine (5 mg/ml) twice a week (with a 3-day interval) for 2 weeks. Starting 2 weeks before carcinogen administration, animals were treated orally with jacalin (0.5 and 25 μg) three times a week (on alternate weekdays) for 10 weeks. We show that jacalin treatment reduced the number of preneoplastic lesions in carcinogen-exposed mice. This anticarcinogenic activity was associated with decreased colonic epithelial cell proliferation and stromal COX-2 expression and with increased intestinal production of TNF-α. Our results demonstrate that jacalin is able to modulate the early stages of colon carcinogenesis and emphasize its promising chemopreventive activity in colorectal cancer.

Vitamin E supplementation in chemical colorectal carcinogenesis: a two-edged knife

This work investigated the effects of Vitamin E (VE) on aberrant crypt foci (ACF) incidence, oxidative stress parameters (serum and hepatic VE concentration, and homocysteine, glutathione (GSH), and malondialdehyde (MDA) levels), and expression of both cyclooxygenase-2 (COX2) and proliferating cellular nuclear antigen (PCNA) in experimental colorectal carcinogenesis. Male Wistar rats received subcutaneous injections of 1,2-dimethylhydrazine (DMH) twice a week, for two weeks (40 mg/kg), except for the Control group. Animals were separated into groups that received different amounts of VE in the diet: 0 IU (0×), 75 IU (recommended daily intake, RDI), 225 IU (3× RDI), or 1500 IU (20× RDI), during (dDMH) or after (aDMH) administration of carcinogen. The 0×dDMH and 3×dDMH groups showed decreased serum VE levels. Hepatic VE concentration was higher in 3×aDMH as compared with the other groups. All the groups, except the Control and the 0×aDMH groups, had reduced GSH levels. The 0×dDMH, 0×aDMH, and 20×aDMH groups exhibited increased MDA levels. The aDMH groups had higher ACF incidence and PCNA expression. The 0×aDMH group presented higher ACF rate, followed by 20×aDMH. Moreover, the 3×aDMH group displayed reduced ACF incidence and COX2 expression. Multivariate analysis revealed that GSH modulated homocysteine levels and COX2. These results suggested that 1500 IU of VE is hazardous, whereas 225 IU of VE has beneficial effects on chemical colorectal carcinogenesis.

Antiproliferative effects of fluoxetine on colon cancer cells and in a colonic carcinogen mouse model

The antidepressant fluoxetine has been under discussion because of its potential influence on cancer risk. It was found to inhibit the development of carcinogen-induced preneoplastic lesions in colon tissue, but the mechanisms of action are not well understood. Therefore, we investigated anti-proliferative effects, and used HT29 colon tumor cells in vitro, as well as C57BL/6 mice exposed to intra-rectal treatment with the carcinogen N-methyl-N’-nitro-N-nitrosoguanidine (MNNG) as models. Fluoxetine increased the percentage of HT29 cells in the G₀/G₁ phase of cell-cycle, and the expression of p27 protein. This was not related to an induction of apoptosis, reactive oxygen species or DNA damage. In vivo, fluoxetine reduced the development of MNNG-induced dysplasia and vascularization-related dysplasia in colon tissue, which was analyzed by histopathological techniques. An anti-proliferative potential of fluoxetine was observed in epithelial and stromal areas. It was accompanied by a reduction of VEGF expression and of the number of cells with angiogenic potential, such as CD133, CD34, and CD31-positive cell clusters. Taken together, our findings suggest that fluoxetine treatment targets steps of early colon carcinogenesis. This confirms its protective potential, explaining at least partially the lower colon cancer risk under antidepressant therapy.