Inhibition by Dietary Benzylselenocyanate of Hepatocarcinogenesis Induced by Azoxymethane in Fischer 344 Rats1

The effect of dietary benzylselenocyanate (BSC), a novel organoselenium compound and its sulfur analog, benzylthiocyanate (BTC), on hepatocarcinogenesis induced by azoxymethane (AOM) was investigated in male F344 rats. Eighty-one weanling rats were divided into 3 groups and were raised on a semipurificd diet (control diet). Starting from 5 weeks of age, groups of animals consuming the control diet were fed one of the experimental diets containing 25 ppm BSC or BTC. An additional group was continued on the control diet. At 7 weeks of age, animals were given weekly sc injections of AOM (15 mg/kg body weight once weekly for 2 weeks). One week after the second AOM injection, those groups receiving BSC and BTC diets were transferred to the control diet and continued on this diet until termination of the experiment at 34 weeks after the last AOM injection. For quantitative analysis of enzyme-altered liver cell foci, glutathione S-transferase placental form was stained by an immunohistochemical technique. The results indicate that the incidence and the density of the enzyme-altered foci were significantly lower in AOM-treated rats fed the diet containing 25 ppm BSC (foci incidence 56%, foci density 2.43/cm²) than in AOM-treated animals fed the control diet (foci incidence 92%, foci density 4.79/cm²). The incidence of small altered foci was significantly inhibited in rats fed the BTC diet (35%) as compared to those fed the control diet (68%), but the degree of inhibition was more pronounced in animals fed the BSC diet than in those fed the BTC diet.     

Inhibition by dietary organoselenium, p-methoxybenzene-selenol, of hepatocarcinogenesis induced by azoxymethane in rats

The effect of dietary p-methoxybenzeneselenol, a new organoselenium compound, on azoxymethane (AOM)-induced hepatocarcinogenesis was examined in female F344 rats. Semipurified diets containing 0 and 5 ppm p-methoxybenzeneselenol were fed to the rats, starting at 5 weeks of age until one week after the carcinogen treatment. At 7 weeks of age, all animals except the vehicle-treated controls were given weekly sc injections of AOM (15 mg/kg body weight, 3 times). At 34 weeks after the last AOM treatment, the liver neoplasm incidence and liver tumor multiplicity as well as the incidence of altered liver cell foci were significantly lower in AOM-treated rats fed the diet containing 50 ppm p-methoxybenzeneselenol (tumor incidence 19%, tumor multiplicity 0.45/rat, foci incidence 3.47/cm2) than in AOM-treated animals fed the diet without p-methoxybenzeneselenol (tumor incidence 66%, tumor multiplicity 2.24/rat, foci incidence 12.08/cm2). These results indicate that dietary p-methoxybenzeneselenol at a dose of 50 ppm inhibits AOM-induced hepatic tumorigenesis.     

Chemoprevention of colon carcinogenesis by dietary organoselenium, benzylselenocyanate, in F344 rats

The effect of feeding benzylselenocyanate (BSC) and its sulfur analogue, benzylthiocyanate (BTC), 2 wk before, during, and until 1 wk after carcinogen administration (initiation phase) on intestinal carcinogenesis induced by azoxymethane (CAS:25843-45-2) was studied in male F344 rats. Weanling rats were raised on a semipurified diet (AIN-76A diet; control diet). Beginning at 5 wk of age, groups of animals consuming the control diet were fed one of the diets containing 25 ppm BSC or BTC. An additional group was continued on the control diet. At 7 wk of age, all animals in 3 groups, except the vehicle-treated controls, were administered s.c. injections of azoxymethane (15 mg/kg body weight, once weekly for 2 wk). Animals were continued on the control diet and BSC and BTC diets until 1 wk after carcinogen treatment, when those groups receiving BSC and BTC diets were fed the control diet until termination of the experiment. Tissue and blood plasma glutathione peroxidase activity was measured in vehicle-treated animals fed the control diet and BSC and BTC diets for 5 wk. The results indicate that body weights were comparable among the various dietary groups. BSC in the diet significantly inhibited the incidence (percentage of animals with tumors) and multiplicity (tumors/animal) of adenocarcinomas in the colon and multiplicity of adenocarcinomas in the small intestine compared to those fed the control diet. BTC in the diet had no effect on colon and small intestinal tumors. Selenium-dependent glutathione peroxidase activity was significantly increased in kidneys and colon and small intestinal mucosae of animals fed the BSC diet compared to animals fed the BTC and control diets.     

Mechanism of benzylselenocyanate inhibition of azoxymethane-induced colon carcinogenesis in F344 rats

Benzylselenocyanate (BSC), a novel organoselenium compound, has been found to inhibit azoxymethane (AOM)-induced colon carcinogenesis in rats during initiation. To investigate its mechanism of action, we examined the effects of BSC feeding on the following parameters: (a) metabolism of [14C]AOM to 14CO2 in vivo; (b) metabolic activation of AOM to MAM and of MAM to formic acid and methanol by rat liver microsomes in vitro; and (c) AOM-induced DNA methylation in rat livers and colons. Five-week-old male F344 rats were fed modified (23% corn oil) AIN-76A diets containing 0 (control), 25, or 50 ppm of BSC or benzylthiocyanate (BTC), a sulfur analogue of BSC which does not inhibit the colon carcinogenicity of AOM. After 3 weeks, rats were either sacrificed for the isolation of liver microsomes or were given 15 mg/kg of [14C]AOM s.c. to determine the rate of carcinogen metabolism in vivo. No difference in [14C]AOM metabolism was found between rats fed the BTC diets and those fed the control diet. In contrast, the rate of [14C]AOM metabolism, as determined by exhaled radioactivity, was 2-3 times higher in rats fed the BSC diets. While liver microsomes from rats fed the BTC diets metabolized AOM and MAM at rates not significantly different from those obtained with control liver microsomes, the metabolic activation of AOM as well as of MAM was stimulated severalfold when assayed with liver microsomes from rats fed the BSC diets. An increase in total liver cytochrome P-450 was also observed in the BSC-fed rats. Following the administration of 15 mg/kg AOM, significantly less O6-methylguanine and 7-methylguanine was present in the colon DNA from rats consuming the BSC diets than in rats fed the BTC or control diets. The body weight gains of rats fed the 25- and 50-ppm BSC-containing diets for 3 weeks were less (27 and 43%, respectively) than those of rats fed either the control or BTC-containing diets. These results indicate that dietary BSC significantly induces the hydroxylation of AOM and the oxidation of MAM in rat liver. An increase in the rates of AOM and MAM metabolism in the liver due to enzyme induction by BSC will result in decreased delivery of MAM to the colon via the bloodstream. This will be reflected in decreased DNA alkylation, as observed, and is likely to be a major factor in the inhibition of AOM-induced colon carcinogenesis by BSC.     

Chemoprevention of colon carcinogenesis by the synthetic organoselenium compound 1,4-phenylenebis(methylene)selenocyanate.

The chemopreventive effect of 40% and 80% maximum tolerated dose (MTD) levels of 1,4-phenylenebis(methylene)selenocyanate (p-XSC) administered in the diet during the initiation phase (2 weeks before, during, and up to 3 days after carcinogen administration) and the post-initiation phase (3 days after carcinogen treatment until termination) of azoxymethane (AOM)-induced colon carcinogenesis was studied in male F344 rats. The MTD of p-XSC was determined in male F344 rats and found to be 50 ppm. Beginning at 5 weeks of age, all animals were divided into various experimental groups (42 rats/group) and fed the high-fat semipurified diet or diets containing 20 (40% MTD) and 40 (80% MTD) ppm p-XSC. At 7 weeks of age, all animals (30 rats/group) except the vehicle-treated groups (12 rats/group) were administered s.c. injections of AOM (15 mg/kg body weight/week for 2 weeks). Three days after the second injection of AOM or vehicle (normal saline), groups of animals fed the p-XSC diets and control diet were transferred, respectively, to control diet and p-XSC diets and continued on these diets until the termination of the study. All animals were necropsied during the 36th week after AOM treatment. Colonic mucosal prostaglandin E2 and selenium-dependent glutathione peroxidase were measured in animals fed the control and p-XSC diets at the termination of the study. The results indicate that 40 ppm p-XSC administered during the initiation phase significantly inhibited the colon tumor incidence (percentage of animals with tumors). Dietary p-XSC administered at 20 and 40 ppm levels during the initiation phase significantly inhibited colon tumor multiplicity (tumors/animal and tumors/tumor-bearing animal). Colon tumor incidence and multiplicity were significantly reduced in groups fed 20 and 40 ppm p-XSC diets at the postinitiation phase of carcinogenesis. Colonic mucosal selenium-dependent glutathione peroxidase activity was increased, and prostaglandin E2 was reduced in animals fed the p-XSC diet compared to animals fed the control diet. Whereas the precise mechanisms of p-XSC-induced inhibition of colon carcinogenesis remain to be elucidated, it is likely that the effect during the initiation and postinitiation phases may be due to alteration in carcinogen metabolism and to modulation of prostaglandin synthesis and selenium-dependent glutathione peroxidase activity.     

Effect of dietary excess of inorganic selenium during initiation and postinitiation phases of colon carcinogenesis in F344 rats

The effect of supplemental inorganic selenium given during the initiation or postinitiation phase of colon carcinogenesis induced by azoxymethane [(AOM)CAS:25843-45-2] was studied in male F344 rats. Weanling animals were raised on AIN-76A semipurified (control) diet. Starting at 4 wk of age, groups of animals intended for initiation study were fed the semipurified diets containing 0.5 and 2.5 ppm selenium in the form of sodium selenite, and those intended for postinitiation study were continued on the control diet. At 7 wk of age, all animals except the vehicle-treated controls were injected s.c. with AOM (15 mg/kg body weight, once weekly for 2 wk). One wk following AOM treatment, animals in the initiation study receiving the supplemental selenium were transferred to the control diet whereas those in the postinitiation study receiving the control diet were transferred to the diets containing 0.5 and 2.5 ppm selenium. These animals were continued on this regimen until the termination of the experiment at 34 wk post-AOM injection. Tissue and blood glutathione peroxidase activity was measured in vehicle-treated animals fed the control and selenium-supplemented diets. The results indicate that body weights were comparable among the various dietary groups. Feeding of diets containing 0.5 and 2.5 ppm selenium during the initiation phase had no effect on colon tumor incidence, but the multiplicity of adenomas was slightly inhibited in animals fed the 2.5 ppm selenium diet. The incidence and multiplicity of colon adenocarcinomas and the multiplicity of colon adenomas were inhibited in animals fed the 2.5-ppm selenium diet during the postinitiation phase of carcinogenesis. The incidence of small intestinal tumors was higher in animals fed the 2.5-ppm selenium diet during the initiation phase than in animals fed the control diet and 0.5-ppm selenium diet. Selenium-dependent glutathione peroxidase activity was increased in kidneys and small and large intestinal mucosae of animals fed the 2.5-ppm selenium diet compared to those fed the 0.5-ppm selenium and control diets.     

Effect of different levels of dietary trans fat or corn oil on azoxymethane-induced colon carcinogenesis in F344 rats

The effect of various levels of dietary corn oil or trans fat on azoxymethane (AOM; CAS: 25843-45-2)-induced carcinogenesis was investigated in female F344 rats fed the AIN-76 semipurified diets. Starting at 5 weeks of age, groups of rats were fed the low-fat diet containing 5% corn oil (designated as low-fat control diet). At 7 weeks of age, all animals except the vehicle-treated controls, were given sc injections of AOM (15 mg/kg body wt, once weekly) for 3 weeks. After 1 week, groups of animals were transferred to semipurified diets containing 13.6% corn oil and 23.5% corn oil or high-fat diets containing 5.9% corn oil plus 5.9% trans fat plus 11.8% Oleinate (low trans fat), 5.9% corn oil plus 11.8% trans fat plus 5.9% Oleinate (intermediate trans fat), and 5.9% corn oil plus 17.6% trans fat (high trans fat). Fecal bile acids were measured in vehicle-treated rats. All animals were necropsied 34 weeks after the last AOM injection. The animals fed the 23.5% corn oil diet had a higher incidence of colon tumors than did those in the groups fed the 5 and 13.6% corn oil diets. There was no difference in colon tumor incidence between the 5 and 13.6% corn oil diet groups. The animals fed the high-fat diets containing low trans fat, intermediate trans fat, and high trans fat developed significantly fewer liver and colon tumors and more small intestinal tumors than did the rats fed 23.5% corn oil diet. The excretion of fecal deoxycholic acid, lithocholic acid, and 12-ketolithocholic acid was higher in animals fed the 23.5% corn oil diet compared to the excretion in animals fed the other diets.     

Effect of dietary alfalfa, pectin, and wheat bran on azoxymethane-or methylnitrosourea-induced colon carcinogenesis in F344 rats.

The effect of dietary alfalfa, pectin, and wheat bran on colon carcinogenesis was studied in female inbred F344 rats. Weanling rats were fed semipurified diets containing 0 or 15% alfalfa, pectin, or wheat bran. At 7 weeks of age, all animals except controls were given azoxymethane (AOM) sc at a dose rate of 8 mg/kg body weight/week for 10 weeks or methylnitrosourea (MNU) intrarectally at a dose rate of 2 mg/rat twice a week for 3 weeks. The AOM-treated group was autopsied 40 weeks and the MNU-treated group 30 weeks after the first injection of the carcinogen. No tumors were observed in the colon or other organs of untreated rats fed the various diets. The animals fed the alfalfa diet and treated with MNU had a higher incidence of colon tumors than did those fed the control diet or the diets containing pectin or wheat bran. The incidence of MNU-induced colon tumors did not differ between the animals fed the control diet or the diets containing pectin or wheat bran. However, the incidence of AOM-induced colon tumors in rats fed diets containing pectin or wheat bran was lower than that in rats fed the control diet or the alfalfa diet. These results thus indicate that the effect of fiber in colon carcinogenesis depends on the type of fiber and, possibly, the fiber's mode of action.     

Inhibitory effect of dietary p-methoxybenzeneselenol on azoxymethane-induced colon and kidney carcinogenesis in female F344 rats

The effect of dietary p-methoxybenzeneselenol on colon carcinogenesis induced by azoxymethane [(AOM) CAS: 25843-45-2] was studied in female F344 rats. Starting at 5 weeks of age, animals were fed the high-fat diet (control diet) or high-fat diet to which 50 ppm of p-methoxybenzeneselenol (experimental diet) had been added. At 7 weeks of age, all animals except the vehicle-treated controls were administered sc injections of AOM (15 mg/kg body wt, once weekly for 3 wk). Animals were fed the control and experimental diets until 1 week after carcinogen treatment when those animals receiving the p-methoxybenzeneselenol diet were fed the control diet until termination of the experiment. p-Methoxybenzeneselenol in the diet significantly inhibited the incidence (percentage of animals with tumors) of tumors in the colon and kidney, as well as the colon tumor multiplicity (adenomas and adenocarcinomas per animal).     

Chemoprevention of experimental mammary carcinogenesis by the synthetic organoselenium compound, benzylselenocyanate, in rats

The effect of the dietary organoselenium compound, benzylselenocyanate (BSC) along with its sulphur analogue, benzylthiocynanate (BTC) and sodium selenite (Na2SeO3), on 7,12-dimethylbenz[a]anthracene (DMBA)-induced mammary carcinogenesis was examined in female Sprague-Dawley rats during the initiation phase of carcinogenesis. Semipurified diets containing 25 p.p.m. of BSC and 25 p.p.m. BTC, and 4 p.p.m. Selenium as Na2SeO3 in drinking water were given to 5-week-old rats for 3 weeks starting 2 weeks before, during and until 1 week after carcinogen treatment. At 7 weeks of age animals were given a single dose of DMBA (10 mg) in 1 ml olive oil by oral intubation. One week after DMBA treatment, the groups receiving BSC- and BTC-supplemented diets were transferred to the unsupplemented standard diets and the group of rats receiving Na2SeO3 in drinking water was transferred to regular tap water for the duration of the experiment. The results indicate that the rats receiving BSC in their diet showed a highly significant inhibition of tumor incidence and tumor multiplicity as well as a prolonged latency period when compared to the group fed the control diet. Neither BTC nor Na2SeO3 had any effect on the subsequent development of mammary tumors. These results indicate that dietary BSC inhibits mammary tumor incidence during the initiation phase of carcinogenesis and is a considerably more potent inhibitor than its sulphur analogue BTC and inorganic selenium. This is the first report that demonstrates the inhibition of mammary carcinogenesis by a synthetic organoselenium compound.     

The effect of dietary omega-3 fatty acids (fish oil) on azoxymethanol-induced focal areas of dysplasia and colon tumor incidence

MaxEPA (MA), a fish oil high in omega-3 fatty acids, was combined with various levels of corn oil (CO), rich in omega-6 fatty acids, and fed to female CF1 mice. The three fish oil blends with CO and the two CO levels of the diets studied were as follows: 16.0% CO + 4.4% MA (Diet 1); 10.2% CO + 10.2% MA (Diet 2); 4.4% CO + 16.0% MA (Diet 3); 20.4% CO (Diet 4); and 4.4% CO (Diet 5). The diets were provided 2 weeks before weekly subcutaneous injection of saline or azoxymethanol (AOM). Studies of epithelial cell proliferation and the incidence of focal areas of dysplasia (FAD) involved six weekly AOM injections. One week after the last AOM injection and 1 hour before killing, mice were injected with tritiated thymidine (3HTdR). No differences in any proliferative parameters were found among the five groups of saline-treated mice. Among the AOM-treated animals, those fed Diet 3 showed significantly fewer cells per crypt and significantly fewer labeled cells/gland than CO Diets 4 and 5. Additionally, the distribution of S-phase cells in crypts of AOM-treated mice fed Diet 3 most closely resembled that of the saline controls. The greatest alteration in the distribution of proliferative cells was observed in the high-CO diet (Diet 4) and the lowest MA level (Diet 1). Mice fed Diets 2 and 3 had significantly fewer FAD/500 microns of distal colonic serial sections than those fed the high CO diet (Diet 4). Mice involved in chronic tumor incidence studies received only three weekly injections of the same dose of AOM. Regardless of diet, approximately 88% of all tumors arose in the distal colon. A significantly larger tumor-bearing population was observed in both the high-CO Diet 4 and the lowest MaxEPA (MA) diet (Diet 1) compared with the incidence in MA Diets 2 and 3 and the low-CO Diet 5. A diet with a ratio of omega-6 to omega-3 fatty acids of approximately 1.0 apparently prevented the development of an adenoma-type proliferative pattern thereby reducing FAD numbers and subsequent tumor incidence.     

Effect of diets high in omega-3 and omega-6 fatty acids on initiation and postinitiation stages of colon carcinogenesis.

The effect of dietary menhaden oil containing omega-3 fatty acids and corn oil rich in omega-6 fatty acids fed during the initiation and/or postinitiation stages of colon carcinogenesis was investigated in male F344 rats. At 5 weeks of age, all animals were divided into seven groups (39 rats/group) and fed the semipurified diets containing 5% corn oil (LCO), 23.5% corn oil (HCO), or 18.5% menhaden oil plus 5% corn oil (HFO). At 7 weeks of age, all animals except the vehicle (normal saline)-treated groups were given two weekly s.c. injection of azoxymethane (AOM) at a dose rate of 15 mg/kg body weight, once weekly. Three days after the second injection of AOM, groups of animals fed LCO, LCO, HCO, HCO, HCO, HFO, or HFO diets were transferred, respectively, to LCO, HCO, LCO, HCO, HFO, HCO, or HFO and continued on these diets until termination of the experiment. All animals were necropsied 42 weeks after carcinogen treatment. Body weights of animals fed various experimental diets during the initiation and postinitiation periods were comparable. As expected, the HCO diet fed during the postinitiation period significantly increased the AOM-induced incidence and multiplicity of colon adenocarcinomas, whereas the HCO diet fed during the initiation phase of carcinogenesis had no effect. Colon tumor incidence and multiplicity were significantly reduced in groups fed the HFO diet at either initiation and/or postinitiation phases of carcinogenesis as compared with those fed the HCO diet. Whereas the precise mechanisms producing the difference between the high menhaden oil (HFO) diet as compared with high corn oil (HCO) diet remain to be elucidated, it is likely that the effect during the initiation and postinitiation phases may be due to alteration in carcinogen metabolism and to modulation of prostaglandin synthesis, respectively.     

Anti-carcinogenic properties of omeprazole against human colon cancer cells and azoxymethane-induced colonic aberrant crypt foci formation in rats

Omeprazole is a proton pump inhibitor, a widely used drug to treat ulcers and gastroesophageal refluxdisease. We have evaluated colon cancer chemopreventive properties of omeprazole using azoxymethane (AOM)-induced colonic aberrant crypt foci (ACF) in male F344 rats and analyzed cell growth inhibition and apoptosis induction in human colon cancer cells. Five-week-old male F344 rats were fed a control or experimental diet containing two doses of omeprazole (200 and 400?ppm). After one week, all animals were s.c. injected with AOM (15?mg/kg body weight, once weekly for two weeks). Rats continued on experimental diets for seven more weeks before being sacrificed. Colons were histopathologically evaluated for ACF. Human colon cancer HCT-116 and HCA-7 cells treated with omeprazole were evaluated for different markers associated with proliferation and apoptotic markers using Western blot technique. Rats fed with 200 and 400?ppm of omeprazole significantly suppressed total colonic ACF formation (~30%, P<0.001) and showed significant suppression of multi-crypt foci (~30-50%, P<0.05-0.001). Omeprazole produced significant dose-response effects on inhibition of multi-crypt foci (≥4). Omeprazole treatment in human colon cancer cell lines HCT-116 and HCA-7 cells resulted in induction of p21waf1/cip1 and decreased the expression of anti-apoptotic proteins Bcl-2, Bcl-XL and survivin in a dose-dependent manner. Anticancer properties observed in colon cancer cell lines suggest that omeprazole may induce key signaling molecules of antiproliferation and inhibition of anti-apoptotic proteins.     

Effect of different levels of dietary corn oil and lard during the initiation phase of colon carcinogenesis in F344 rats

The effect of various levels of polyunsaturated fat (corn oil) and saturated fat (lard) fed during the initiation stage of colon carcinogenesis was studied in male F344 rats. The animals were fed the diets containing 5, 13.6, and 23.5% corn oil or lard 2 weeks before, during, and until 1 week after sc injection of 15 mg azoxymethane [(AOM) CAS: 25843-45-2]/kg body weight, once weekly for 2 weeks (designated as initiation). One week after AOM treatment, groups of animals were transferred to their respective 5% corn oil or lard diets. Additional groups consuming 5% corn oil or lard were transferred to 23.5% corn oil or lard, respectively (post-initiation stage). All animals were fed these diets until the termination of the experiment. Fecal bile acids and colonic mucosal ornithine decarboxylase activity were measured in vehicle-treated animals fed the experimental diets for 14 weeks. Body weights and intakes of total calories, protein, nonnutritive fiber, and micronutrients were comparable among the various dietary groups. The animals fed the 23.5% corn oil diet during the postinitiation stage had a higher incidence of colon tumors than did those fed the 5% corn oil diet, whereas feeding of 23.5 and 13.6% corn oil diets during the initiation stage had no effect. In contrast, animals fed the 23.5 and 13.6% lard diet during the initiation stage and 23.5% lard diet during the postinitiation stage developed more colon adenocarcinomas than did those fed the 5% lard diet. The excretion of fecal deoxycholic acid, lithocholic acid, and 12-ketolithocholic acid and the activity of colonic mucosal ornithine decarboxylase activity were higher in animals fed the 23.5% corn oil or lard diet during the postinitiation compared to the levels in animals fed the 5% corn oil or lard diet.     

Effect of restricted caloric intake on azoxymethane-induced colon tumor incidence in male F344 rats

The effect of 30% caloric restriction on azoxymethane (AOM)-induced colon carcinogenesis was investigated in male F344 rats. Starting at 5 weeks of age, groups of animals were fed ad libitum a high-fat (23.5%) semipurified diet. At 7 weeks of age, all animals except the vehicle-treated groups were s.c. injected with AOM (15 mg/kg body wt, once weekly for 2 weeks). Four days after the second AOM injection, groups of animals were continued on high-fat diet and fed ad libitum (ad libitum group) whereas other groups were restricted to 70% of total calories (calorie-restricted group) consumed by the ad libitum group, but received same amounts of fiber, vitamins, and minerals. Thirty-two weeks after AOM injections, all animals were necropsied. The animals in the calorie-restricted group developed significantly fewer colon tumors and had a lower colon tumor incidence than did the rats in the ad libitum group. The size of colon tumors was also reduced in the calorie-restricted group.     

The effects of dietary selenomethionine on polyamines and azoxymethane-induced aberrant crypts

We evaluated the effects of dietary selenomethionine supplementation on colonic polyamine levels and the ability of L-selenomethionine supplementation to modulate the carcinogenic activity of azoxymethane (AOM) in the rat colon. Four-week-old male F344 rats were treated with 15 mg/kg body weight of AOM once a week for 2 weeks. Dietary selenomethionine at a concentration of either 1 or 2 ppm was administered in AIN-76A rodent diet to AOM-treated animals for 16 weeks. Aberrant crypt foci (ACF), precursor lesions of colon cancer, were investigated after the 16 week treatment course. Selenomethionine given in the diet at 2 ppm markedly reduced the number of aberrant crypt foci. The multiplicity of ACFs (i.e. the number of aberrant crypts/focus) and the percentage of microadenomas were also affected by selenomethionine in a dose dependent manner. However, evaluation of the colonic tissue polyamine levels between control and treated groups showed no significant difference. These results demonstrate that selenomethionine can modulate the development of AOM-induced premalignant lesions through a polyamine-independent mechanism.     

The Dietary Effect of Monoglucosyl-rutin on Azomethane-Induced Colon Carcinogenesis

The dietary effect of monoglucosyl-rutin (M-R), a flavonoid, on azoxymethane (AOM)-induced colon carcinogenesis ‍was investigated in two experiments with 5 week old, F344 male rats. In the first experiment (5 weeks study), effects ‍of MR on AOM (15 mg/kg body weight 3 times weekly)-induced formation of aberrant crypt foci (ACF) in five ‍groups were assessed. In this experiment, group 3 given 500 ppm M-R with AOM had a significantly smaller number ‍of ACF containing 4 or more aberrant crypts than group 1 with AOM alone, and groups 2 and 3 given 100 ppm or ‍500 ppm M-R respectively had significantly lower BrdU labeling indices in the epithelial cells of large bowel than ‍group 1. For the second experiment, rats were divided into 8 groups. Groups 1-5 were given AOM as in the first ‍experiment. Groups 2-5 were fed diets containing 100ppm or 500ppm M-R for 4 weeks in the initiation phase or 36 ‍weeks in the post-initiation phase. Group 6 was given 500ppm M-R throughout the experiment, and group 7 was ‍kept on the basal diet and served as a control. At the termination of the experiment (40 weeks after the start), groups ‍2-5 had significantly smaller numbers of positive cells with anti-proliferating cell nuclea antigen (PCNA) antibody ‍than group 1. Furthermore, group 5 treated with 500ppm M-R for 36 weeks demonstrated tendencies for decrease in ‍the incidence and multiplicity of colon tumors. These data suggest that M-R has the potential to inhibit AOMinduced ‍colon carcinogenesis.     

Promotion of azoxymethane-induced intestinal cancer by high-fat diet in rats.

Promotional properties of a high-fat diet in intestinal cancer were studied by feeding a 30% beef fat diet to 8 groups of rats (25 rats/group) for time periods varying from 1 to 21 weeks after 8 weekly s.c. injections of azoxymethane (AOM) (8 mg/ kg). Two other groups were fed the high-fat diet, one for 8 weeks prior to and the other during AOM injections. A 5% fat diet was fed to rats when not on the 30% fat diet and to a control group of 25 animals. High fat diet increased intestinal tumor frequency up to 2-fold when given for at least 4 weeks after but not during or prior to AOM injections; this increase occurred even after a prolonged interval (10 weeks) between the last AOM injection and the high-fat diet. In general, tumor frequency increased according to the length of time animals were fed the high-fat diet after AOM. Therefore, the high-fat diet in this model exhibited most of the properties of promoters developed from murine skin cancer, thus adding support to the concept that excess dietary fat acts at the promotional phase of carcinogenesis.     

Chemoprevention of Azoxymethane-induced Rat Colon Carcinogenesis by a Xanthine Oxidase Inhibitor, 1'-Acetoxychavicol Acetate

In our studies to find natural compounds with chemopreventive efficacy in foods, using azoxymethane (AOM)-induced colonic aberrant crypt foci and colonic mucosal cell proliferation as biomarkers, a x an thine oxidase inhibitor, 1′-acetoxychavicol acetate (ACA), present in the edible plant Languas galanga from Thailand was found to be effective. This study was conducted to test the ability of ACA to inhibit AOM-induced colon tumorigenesis when it was fed to rats during the initiation or post-initiation phase. Male F344 rats were given three weekly s.c. injections of AOM (15mg/kg body weight) to induce colonic neoplasms. They were fed diet containing 100 or 500 ppm ACA for 4 weeks, starting one week before the first dosing of AOM (the initiation feeding). The other groups were fed the ACA diet for 34 weeks, starting one week after the last AOM injection (the post-initiation feeding). At the termination of the study (week 38), AOM had induced 71% incidence of colonic adenocarcinoma (12/17 rats). The initiation feeding with ACA caused significant reduction in the incidence of colon carcinoma (54% inhibition by 100 ppm ACA feeding and 77% inhibition by 500 ppm ACA feeding, P=0.03 and P=0.001, respectively). The post-initiation feeding with ACA also suppressed the incidence of colonic carcinoma (45% inhibition by 100 ppm ACA feeding and 93% inhibition by 500 ppm ACA feeding, P=0.06 and P=0.00003, respectively). Such inhibition was dose-dependent and was associated with suppression of proliferation biomarkers, such as ornithine decarboxylase activity in the colonic mucosa, and blood and colonic mucosal polyamine contents. ACA also elevated the activities of phase II enzymes, glutathione S-transferase (GST) and quinone reductase (QR), in the liver and colon. These results indicate that ACA could inhibit the development of AOM-induced colon tumorigenesis through its suppression of cell proliferation in the colonic mucosa and its induction of GST and QR. The results confirm our previous finding that ACA feeding effectively suppressed the development of colonic aberrant crypt foci. These findings suggest possible chemopreventive ability of ACA against colon tumorigenesis.     

Modulating effects of diets high in omega-3 and omega-6 fatty acids in initiation and postinitiation stages of diethylnitrosamine-induced hepatocarcinogenesis in rats.

The effects of sardine fish oil or corn oil on diethylnitrosamine (DEN)-induced hepatocarcinogenesis were investigated in male F344 rats. Starting at 5 weeks of age, animals were divided into 11 groups and fed 23.5% corn oil (HCO) (groups 1 and 7) or 5% corn oil (LCO) (groups 2 and 8), 22.5% sardine oil + 1% corn oil (FO) semipurified diet (groups 3 and 9) or basal diet (CE-2) (groups 4-6, 10 and 11). At 6 weeks of age, all animals except the vehicle-treated groups were given DEN (200 mg/kg body weight, i.p. once weekly for 3 weeks). One week after the final exposure to DEN, groups 1-3 were changed to the basal diet, and groups 4-6 were switched to the HCO, LCO or FO diet, respectively. Animals in groups 1-3 and 10 were given drinking water containing 0.05% phenobarbital (PB). Liver sections from the animals at the termination of the experiment (24 weeks) were doubly stained for glutathione S-transferase placental form (GST-P) and silver-stained nucleolar organizer regions (AgNORs). The multiplicity of hepatocellular neoplasms of group 1 was significantly larger than that of group 2 or 3. The number of GST-P-positive foci of group 2 or 3 was significantly smaller than that of group 1. Among the groups fed the experimental diets in the postinitiation phase (groups 4-6), no significant difference was found in the incidence of liver tumors. AgNORs values of the enzyme-altered foci in rats of the HCO diet groups were larger than those of the other diet groups. These results indicate that the enhancing effect of a high dose of corn oil in hepatocarcinogenesis is mainly present during the initiation phase but not during postinitiation phase, and fish oil rich in polyunsaturated omega-3 fatty acids could inhibit DEN-induced hepatocarcinogenesis in rats.