Chemopreventive Effect Of Mofezolac On Beef Tallow -promoted Colon Carcinogenesis In Rats

Backgroud:Colon cancer remains one of the leading causes of cancer deaths worldwide, and the incidence is rising quickly in recent years in China. Colon carcinogenesis refers to multistep and multiphase. Epidemiologies and aminal experiments have proven that fatty acids diets exert important effect on colon carcinogenesis. The countries feeding on saturated fatty acids often have the high colon cancer incidence, such as America and European countries. We have previously studied the corn oil, oliver oil, fish oil and beef tallow. We found that the beef tallow accelerated the proliferation of colon mucosa, elevated the cytosolicβ-catenin expression, increased the numbers of ACF and tumors in AOM-treated rats. Although beef tallow-fed rats with saline treatment didn't show significant elevation of ACF (only a few observed) and tumor formation, proliferation of colon mucosa and cytosolicβ-catenin expression were all increased. Therefore, beef tallow promoted colon carcinogenesis in rats and it is necessary to carry out chemoprevention on colon carcinogenesis in the populations with high fat intake. Many researches have demonstrated that COX plays an important role during colon carcinogenesis. COX-1, as well as COX-2, plays a role during colon carcinogenesis, which involves even at an earlier stage. COX-1 can protect stem cells from DNA damage-induced death, maintain tumor growth during early stage. Genetic disruption of the COX-1 gene and selective COX-1 inhibitor were shown to significantly decrease the number of colon tumors on animal models. Objectives:1. To observe the effect of selective COX-1 inhibitor mofezolac on beef tallow diet-promoted colon carcinogenesis in rats.2. To investigate the potential mechanism of mofezolac on affecting colon carcinogenesis in rats fed with beef tallow diet.Methods:1. Male SD rats were injected with AOM or saline. Saline-treated rats were given a 10% beef tallow diet without (beef tallow group) or with 1200ppm mofezolac (beef tallow+mofezolac group). AOM-treated rats were given a 10% beef tallow diet without (beef tallow+AOM group) or with 1200ppm mofezolac (beef tallow+AOM+mofezolac group). The rats were supplied with the diets respectively until killed.2. 12 weeks after the last injection of AOM or saline, some rats were killed, the colon were fixed in 10% buffered formalin. The colon was then stained with methylene blue and rinsed with physiological saline. After staining, the colon was observed using a stereoscopic microscope.3. 44 weeks after the last injection of AOM or saline, some rats were killed, the colon were fixed in 10% buffered formalin. Tumors were counted; some rats were intraperitoneally injected with BrdU labeling reagent in each group. The rats were sacrificed 2h after the injection of the labeling reagent, the colon was fixed in 10% neutral-buffered formalin. Distal colon was cut to get the tissue (if groups developed tumors, get normal-appearing colonic tissue surrounding the the tumor), then embedded in paraffin and sectioned, followed by immunohistochemistry to evaluate the colon crypt proliferation, observe the alteration of proliferative cell distribution in the crypts, count the number of the proliferative cells in the crypt. 4. At 44 weeks, some rats were killed in each group, colonic mucosa was harvested by scraping of the epithelium using a glass slide (scrape normal-appearing colonic mucosa surrounding the tumor in groups with tumors). The protein was extracted, COX-1 and cytoplasmicβ-catenin were checked by western blot.Results:1. At 12 weeks, beef tallow and beef tallow+mofezolac groups had few ACF (data not shown); the number of ACF per colon and the ACF multiplicity were significantly lower in beef tallow+AOM+mofezolac than in beef tallow+AOM group.2. At 44 weeks, tumors developed only in the AOM-treated groups. Beef tallow+AOM+mofezolac group had significant lower tumor multiplicity than Beef tallow+AOM group (2.5±2.3 vs. 5.3±1.2, P<0.05). Besides, tumor incidence was also reduced by mofezolac supplement (66.7% vs. 100%, P<0.05).3. At 44 weeks, mofezolac decreased the number of proliferative cells in the distal colon crypts in both the beef tallow group (5.00±0.82 vs. 3.25±0.50, P<0.05) and beef tallow+AOM (7.75±0.96 vs . 4.75±0.50, P<0.05) groups, which were often observed in the basal compartment of the crypts.4. At 44 weeks, the expression of COX-1 and cytoplasmicβ-catenin was reduced by mofezolac supplement in both beef tallow and beef tallow +AOM groups.Conclusions:1. Selective COX-1 inhibitor mofezolac effectively suppressed colon carcinogenesis in rats fed on beef tallow diet.2. Inhibition of COX-1 and cytosolicβ-catenin expression probably involved in the suppression effect of mofezolac on colon carcinogenesis.3. Mofezolac was a probable candidate for colon cancer chemoprevention and may be appropriate for populations with a high fat intake.