Inhibitory effect of cryptoporic acid E, a product from fungus Cryptoporus volvatus, on colon carcinogenesis induced with N-methyl-N-nitrosourea in rats and with 1,2-dimethylhydrazine in mice.

The antitumorigenic effect of cryptoporic acid E (CPA-E), a dimeric drimane sesquiterpenoid isolated from the fungus Cryptoporus volvatus, on colon carcinogenesis was investigated. Female F344 rats given an intrarectal instillation of 2 mg of N-methyl-N-nitrosourea 3 times weekly in weeks 1 and 2 were fed diet containing 0.2% CPA-E from week 3. Female ICR mice given 15 weekly intraperitoneal injections of 10 mg of 1,2-dimethylhydrazine/kg body weight during weeks 1 to 15 were fed diet containing 0.06% CPA-E from week 1. The experiment was terminated at week 35 for rats and at week 25 for mice. The incidence and the number of tumors per animal were reduced in CPA-E-fed animals compared to the controls: 31% vs. 75% (P less than 0.05) and 0.4 +/- 0.2 (SEM) vs. 0.9 +/- 0.2 (0.1 greater than P greater than 0.05) in rats, and 31% vs. 63% (0.1 greater than P greater than 0.05) and 0.4 +/- 0.2 vs. 2.4 +/- 0.8 (P less than 0.05) in mice (16 animals in each group). Intrarectal deoxycholic acid-induced colonic mucosal ornithine decarboxylase activity was significantly lowered in CPA-E-fed animals compared to controls. This shows an antipromoting activity of CPA-E against colon carcinogenesis. Thus, it was concluded that CPA-E inhibits colon cancer development in both rats and mice treated with 2 different colon carcinogens.     

Prevention of N-Methylnitrosourea-induced Colon Tumorigenesis by Ursodeoxycholic Acid in F344 Rats

Bile acids are known to promote colon carcinogenesis. However, there is one study showing that ursodeoxycholic acid (UDCA) supplemented in the diet at the concentration of 0.4% prevented azoxymethane-induced rat colon tumorigenesis. The aim of our study was to explore the inhibitory effect of a much smaller dose of UDCA on colon carcinogenesis in rats. One hundred 7-week-old F344 rats were given 2 mg of N-methylnitrosourea 3 times a week for 3 weeks by intrarectal instillation, and were fed a 0% (control), 0.4% or 0.08% UDCA-supplemented diet for the next 27 weeks. All the rats were killed and examined for tumor development at week 30. The tumor incidence and number were significantly lower and smaller, respectively, in the UDCA-fed rats than in the control rats: 40% and 36% vs. 68%; 0.5±0.1 (mean±SEM) and 0.4±0.1 vs. 1.0±0.2. All the tumors were located in the distal half of the colon and were plaque-shaped or polypoid, being well-differentiated adenocarcinomas restricted to the mucosa or submucosa. Bile acids in the feces and the blood obtained at weeks 20 and 30, respectively, were analyzed by HPLC. A significant increase of UDCA was confirmed in both the faces and the blood of the UDCA-fed rats compared with the control rats. The results suggest that the continuous feeding of a small dose of UDCA may prevent colon carcinogenesis.     

Modifying effects of Terminalia catappa on azoxymethane-induced colon carcinogenesis in male F344 rats.

The modifying effects of dietary administration of an herb, Terminalia catappa (TC), were investigated on rat colon carcinogenesis induced by a carcinogen azoxymethane (AOM). The number of aberrant crypt foci (ACF) and beta-catenin accumulated crypts (BCACs) in the colon, and proliferating cell nuclear antigen (PCNA) labelling index in the colonic epithelium were examined in a total of 36 male F344 rats. All animals were randomly divided into five experimental groups (4-10 rats in each group). At 6 weeks of age, rats in groups 1, 2 and 3 were given s.c. injections of AOM once a week for 2 weeks at a concentration of 20 mg/kg body weight. One week before the first injection of AOM, rats in groups 2 and 3 were fed a diet containing 0.02 and 0.1% TC, respectively, throughout the experiment. Rats in group 4 were fed a diet containing 0.1% TC. Rats in group 5 were served as untreated controls. All animals were sacrificed at the experimental week 5 after the start of the experiment. Oral administration of TC at both doses significantly decreased the numbers of both ACF/colon/rat (P<0.05 for 0.02% TC, P<0.005 for 0.1% TC) and BCAC/cm/rat (P<0.05 for both 0.02 and 0.1% TC), when compared with the control group (group 1). Colonic PCNA labelling index in groups 2 and 3 was also significantly lower than that in group 1 (P<0.001 for 0.02% TC, P<0.005 for 0.1% TC). These results suggest that TC has a potent short-term chemopreventive effect on biomarkers of colon carcinogenesis and this effect may be associated with the inhibition of the development of ACF and BCACs.     

Effect of Konjac mannan on 1,2-dimethylhydrazine-induced intestinal carcinogenesis in Fischer 344 rats

The effect of Konjac mannan (KM) on 1,2-dimethylhydrazine (DMH-induced intestinal carcinogenesis was studied in male F344 rats. Rats were fed a diet containing 5% KM at 5 weeks of age. At 6 weeks of age, all animals were given a weekly intraperitoneal injection of 20 mg DMH/kg body wt for 13 weeks and autopsied 13 weeks after the last injection of DMH. The weight gain was lower in rats fed the KM diet than in rats fed the control diet throughout the experiment (P less than 0.05). The incidence of DMH-induced colon tumors was lower in animals fed the KM diet compared to animals fed the control diet (P less than 0.05). The number of colon adenocarcinoma per animal was also lower in animals fed the KM than in animals fed the control diet (P less than 0.05). However, the incidence of tumors of the small intestine did not significantly differ between the groups fed the KM and control diets. The present study demonstrated that colon tumorigenesis induced by DMH in F344 rat was inhibited by maintaining the KM diet.     

A Ferulic Acid Derivative, Ethyl 3-(4'-Geranyloxy-3-methoxyphenyl)-2-propenoate, as a New Candidate Chemopreventive Agent for Colon Carcinogenesis in the Rat

The inhibitory influence of ferulic acid (FA), a rice germ component, and its geranylated derivative 3-(4'-geranyloxy-3-methoxyphenyl)-2-propenoate (EGMP) on the post-initiation stage of azoxy-methane (AOM)-induced colon carcinogenesis was studied in male F344 rats given two s.c. injections of AOM (15 mg/kg body weight) during week 1. Diets containing EGMP or FA at doses of 0.1 or 0.2% were then fed for 3 weeks from week 2 to 5, when the animals were sacrificed. The numbers of aberrant crypt foci (ACF) and aberrant crypts (AC) per rat in the group given 0.2% FA were significantly decreased (P<0.001) as compared to the AOM alone group. Furthermore, the numbers of ACF and AC per rat fed the 0.2% and 0.1% EGMP were significantly reduced (P<0.001 and P<0.01, respectively). Colonic epithelial cells in S-phase, as measured by bromodeoxy-uridine (BrdU) labeling, in rats fed EGMP were significantly decreased in the 0.2 and 0.1% EGMP groups as compared to the AOM alone group (P<0.05). BrdU labeling indices in rats fed FA and EGMP assessed by a test using a coefficient for linear contrast were also significantly decreased as compared to the AOM alone value (P<0.05, P<0.01, respectively). The results indicate that FA and EGMP have inhibitory effects on ACF and AC development, EGMP being more potent, possibly due to stronger suppressive effects on cell proliferation. No toxic effects were observed in rats given either compound in terms of body and organ weights, and liver or kidney histology. The findings thus suggest that EGMP and FA, especially the former, might have potential as chemopreventive agents against colon tumor development.     

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).     

Possible Chemopreventive Effects of Bovine Lactoferrin on Esophagus and Lung Carcinogenesis in the Rat

A milk component, bovine lactoferrin (bLF), previously shown by us to be a strong chemopreventive of colon carcinoma development, was examined for its influence on other organs using a rat multi-organ carcinogenesis model. Male F344 rats, aged 6 weeks, were treated sequentially with diethylnitrosamine (DEN, i.p.), dihydroxy-di- N -propylnitrosamine (DHPN, in drinking water) and N -nitrosomethylbenzylamine (NMBA, s.c.) during the first 8 weeks (DDN treatment), and then bLF was administered in the basal diet, at a dose of 2, 0.2, 0.02 or 0.002%. Other groups were given DDN treatment or bLF alone as controls. All surviving animals were killed at week 41, and major organs were examined histopathologically for neoplastic lesions. In the esophagus, a tendency for reduction in development of papillomas was evident in the bLF-treated animals, along with a significant suppression of relatively large-sized papillomas (more than 50 mm³ volume) at the 0.2% dose ( P <0.05, 11% of the control). The multiplicity of tumors (adenomas and carcinomas) in the lung was also decreased in animals fed 0.02% bLF (1.98±0.41 per cm² lung tissue section, P <0.05) compared to the control group (3.48±0.33). No enhancing or inhibitory effects of bLF on tumor development in other organs were noted. The present results indicate that bLF exerts chemopreventive effects in the esophagus and lung in addition to the colon.     

Effects of arctiin on PhIP-induced mammary, colon and pancreatic carcinogenesis in female Sprague-Dawley rats and MeIQx-induced hepatocarcinogenesis in male F344 rats

Chemopreventive effects of arctiin, a lignan isolated from Arctium lappa (burdock) seeds, on the initiation or post initiation period of 2-amino-1-methyl-6-phenylimidazo[4,5-b]pyridine (PhIP) induced mammary carcinogenesis in female rats and on 2-amino-3, 8-dimethylimidazo[4,5-f]quinoxaline (MeIQx)-associated hepatocarcinogenesis in male rats were examined. In experiment 1, female Sprague-Dawley (SD) rats were given intragastric doses of 100 mg/kg body wt of PhIP once a week for 8 weeks as initiation. Groups of 20 rats each were treated with 0.2 or 0.02% arctiin during or after PhIP initiation. Control rats were fed 0.2 or 0.02% arctiin, or basal diet alone during the experimental period. Animals were killed at the end of week 48. Although the incidence of mammary carcinomas did not significantly differ among the PhIP-treated groups, multiplicity was significantly decreased in rats given 0.2 (0.7+/-0.7, P<0.05) or 0.02% (1.0+/-1.1, P<0.05) arctiin after PhIP initiation as compared with the PhIP alone controls (2.1+/-2.5). The average number of colon aberrant crypt foci was also significantly decreased in these two groups. Pancreas acidophilic foci were induced in PhIP treated animals with slight decrease in the multiplicity with arctiin during the initiation phase. For liver carcinogenesis, groups of 15 male F344 rats were given a single intraperitoneal injection of diethylnitrosamine (DEN) and starting 2 weeks later, they were administered 0.03% MeIQx in the diet, MeIQx together with 0.5% arctiin, 0.1% arctiin or basal diet for 6 weeks. They were subjected to two-third partial hepatectomy 3 weeks after DEN initiation and killed at the end of week 8 for glutathione S-transferase placental form (GST-P) immunohistochemistry. The numbers and areas of preneoplastic GST-P positive foci were elevated by the treatment with MeIQx, and further increased by the simultaneous treatment with arctiin. These results indicate that arctiin has a protective effect on PhIP-induced carcinogenesis particularly in the mammary gland in the promotion period. On the other hand, it may have a weak co-carcinogenic influence on MeIQx-induced hepatocarcinogenesis. In addition, the results suggested that PhIP is a weak pancreatic carcinogen in female SD rats, targeting acinar cells.     

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.     

Chemopreventive Effect of N-(2-Cyclohexyloxy-4-nitrophenyl)methane Sulfonamide (NS-398), a Selective Cyclooxygenase-2 Inhibitor, in Rat Colon Carcinogenesis Induced by Azoxymethane

Non-steroidal anti-inflammatory drugs (NSAIDs) such as sulindac and indomethacin inhibit colon carcinogenesis, and selective cyclooxygenase (COX)-2 inhibitors are considered to be potential chemopreventive agents without the side effects of usual NSAIDs. We reported that NS-398, N-(2-cyclohexyloxy-4-nitrophenyl)methane sulfonamide, suppressed the formation of preneoplastic lesions, aberrant crypt foci (ACF), induced by azoxymethane (AOM) in a short-term assay of rat colon carcinogenesis. In this study, we examined the effects of long-term NS-398 administration on rat colon carcinogenesis. After three AOM treatments at weekly intervals, a dose of 10 mg/kg of NS-398 in 5% Arabic gum solution was administered by gavage three times per week in group 2 until the termination of the experiment. Rats in group 1 were fed in a basal diet and given 5% Arabic gum solution alone after AOM treatment. At 40 weeks after the first AOM treatment, all rats were killed and the whole intestines including colon were examined. While the incidences of whole intestinal and colon neoplasms in group 1 were 84.6% and 80.8%, respectively, those in group 2 (given NS-398) were 51.9% and 44.4% respectively ( P =0.0177 and P =0.0103 by Fisher's exact test, respectively). The multiplicities in group 2 (0.67 ± 0.78 and 0.48 ± 0.58) were also decreased significantly compared with those (1.39 ± 1.10 and 1.08 ± 0.74) in group 1 ( P < 0.01 by Welch's method and P < 0.002 by Student's t test, respectively). In immunohistochemistry for proliferative cell nuclear antigen (PCNA), the PCNA-stained cell index (7.40 ± 0.5) in group 2 was significantly decreased from that in group 1 (14.03 ± 0.82) ( P < 0.001 by Welch's method). The results suggest that NS-398, a selective COX inhibitor, has a chemopreventive activity against colon carcinogenesis without side-effects such as gastric ulceration.     

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.     

Modulation of experimental colon tumorigenesis by types and amounts of dietary fatty acids

Epidemiological studies and laboratory animal model assays suggest that a high intake of dietary fat promotes colorectal cancer. Several in vivo and in vitro studies support the hypothesis that omega-6 fatty acids promote colon tumorigenesis, whereas omega-3 fatty acids lack promoting activity. Fat intake in the United States traditionally includes high amounts (30% of total caloric intake) of saturated fat rather than omega-6 fatty acids. Therefore, the present study was designed to compare the modulatory effects of a high-fat diet containing mixed lipids (HFML), a diet rich in saturated fatty acids (the average American diet), a diet with fish oil (HFFO) that is rich in omega-3 fatty acids, and a low-fat corn oil diet (LFCO) on the formation of chemically induced colonic aberrant crypt foci (ACF) and tumors, cyclooxygenase (COX)-2 activity, and apoptosis during experimental colon carcinogenesis. At 5 weeks of age, groups of male F344 rats were fed a 5% corn oil diet (LFCO). At 7 weeks of age, rats intended for carcinogen treatment received s.c. injections of azoxymethane at a dose level of 15 mg/kg of body weight once weekly for 2 weeks. Beginning 1 day after the carcinogen treatment, groups of rats were then maintained on experimental diets containing 20% HFML or 20% HFFO. Rats were killed at 8, 23, or 38 weeks after azoxymethane treatment. Colonic ACF and tumors were evaluated histopathologically, and apoptosis was evaluated by the terminal deoxynucleotidyl transferase-mediated nick end labeling method. Colonic mucosae and tumor samples harvested at week 38 were analyzed for COX-2 synthetic activity and expression. The rats fed the HFML diet showed significantly increased total colonic ACF (P < 0.001-0.0001) with a multiplicity of > or = 4 aberrant crypts/focus (P < 0.0001) compared with the effects of the HFFO or LFCO diets at week 8, 23, and 38. Interestingly, there was a 2- to 3-fold increase (> or = 4) in multicrypt foci in rats given the HFML diet as compared with such foci in rats fed the HFFO or LFCO diets. By week 23, the HFML diet had significantly increased the incidence of colonic tumors (30-60%) and their multiplicity (100-141%) when compared with the effects of the LFCO or HFFO diets. At week 38, the HFML diet had induced 100% colon tumor incidence and a 4-fold multiplicity of adenocarcinomas compared with the LFCO and HFFO diets. At weeks 23 and 38, a significantly lower percentage of apoptotic colonic epithelial cells were observed in the tumors of animals fed the HFML diet as compared with those fed the HFFO diet. The HFML diet caused significantly increased levels of COX-2 activity in colon tumors (P < 0.05-0.01), and these tumors had enhanced levels of COX-2 expression as compared with those in assays with LFCO or HFFO diets. These observations demonstrate for the first time that HFML diets containing high levels of saturated fatty acids (such as those in Western diets) promote colon carcinogenesis. Although the mechanisms involved in colon tumor promotion by a HFML diet are not fully known, our results indicate that the modulation of eicosanoid production via the influence on COX activity and the suppression of apoptosis may play a key role in HFML diet-induced colon tumorigenesis.     

Silk protein, sericin, suppresses colon carcinogenesis induced by 1,2-dimethylhydrazine in mice

Male 5-week old ICR mice were examined for the effect of feeding silk protein, sericin on colon carcinogenesis. In experiment 1, mice were fed the diets supplemented with 1.5% or 3% sericin for five weeks, and given weekly injections of 1,2-dimethylhydrazine (DMH) for the initial three weeks. Supplemental sericin caused a dose-dependent decrease in the development of colonic aberrant crypt foci. In experiment 2, mice were fed the diet supplemented with 3% sericin for 115 days, and given weekly injections of DMH for the initial ten weeks. The incidence and number of colon tumors were suppressed by consumption of sericin. The results suggest a potential usefulness of sericin as a chemopreventive agent for colon carcinogenesis.     

Chemoprevention by Nimesulide, a Selective Cyclooxygenase-2 Inhibitor, of 2-Amino-1-methyl-6-phenylimidazo[4,5-b]pyridine (PhIP)-induced Mammary Gland Carcinogenesis in Rats

Breast cancer is common in women all over the world, and exploration of chemopreventive approaches to this cancer is very important. Nimesulide, a selective inhibitor of cyclooxygenase-2 (COX-2), is a good candidate as a chemopreventive agent with low toxicity. We examined its effects on mammary tumor development in female Sprague-Dawley rats induced with the environmental carcinogen 2-amino-1-methyl-6-phenylimidazo[4,5- b ]pyridine (PhIP). Rats at 7 weeks of age received intragastric intubations of PhIP (85 mg/kg body weight) 4 times weekly for 2 weeks and were maintained on control diet (high fat diet) or experimental diet (high fat diet supplemented with 400 ppm nimesulide) throughout the experiment. COX-2 protein was over-expressed in epithelial cancer cells and stromal cells of the PhIP-induced mammary carcinomas, but was weak or not apparent in normal mammary gland cells. The development of mammary carcinomas was clearly suppressed by administration of nimesulide. The carcinoma incidence was 51% as compared to 71% for the control diet group. The average multiplicity of carcinomas in the experimental diet group was 1.2±0.2 ( P < 0.05), significantly smaller than the control diet group value (2.6±0.5). The size of carcinomas was also clearly decreased; 1.1±0.4 cm³/rat in experimental diet group ( P < 0.05), 4.1±1.3 cm³/rat in the control diet group. The results therefore provide evidence that the selective COX-2 inhibitor, nimesulide, possesses chemopreventive activity against PhIP-induced mammary carcinogenesis in rats.     

Inhibitory Effects of 1'-Acetoxychavicol Acetate on N-Nitrosobis(2-oxopropyl)-amine-induced Initiation of Cholangiocarcinogenesis in Syrian Hamsters

The influence of 1'-acetoxychavicol acetate (ACA) during the initiation stage was investigated in the N -nitrosobis(2-oxopropyl)amine (BOP)-initiated hamster tumorigenesis model. Ninety male 5-week-old hamsters were divided into three groups, each consisting of 30 animals, and s.c. injected with 20 mg/kg of BOP twice with a one-week interval. Groups 1 through 3 were fed diet supplemented with ACA at concentrations of 500, 100 and 0 ppm, respectively, for 3 weeks starting one week before the first carcinogen application. At the termination of experimental week 54, the total incidence and multiplicity of cholangiocellular adenomas and carcinomas in group 1 (17.9% and 0.3±0.9) were significantly ( P < 0.05 and P < 0.01) decreased as compared to the group 3 values (50.0% and 0.7±0.8). The ACA treatments also showed a tendency to reduce the development of preneoplastic lesions in the pancreas, a main target organ of BOP, although this was not statistically significant. Our results thus indicate that ACA exerts an inhibitory effect on BOP-induced cholangiocarcinogenesis in hamsters. Taken together with previous findings of inhibited colon, oral and skin carcinogenesis in rats and mice, they suggest that ACA is a candidate chemopreventive agent with a wide spectrum of activity.     

Preventive effect of fermented brown rice and rice bran against colon carcinogenesis in male F344 rats

Epidemiological and preclinical studies demonstrate that nutrition plays an important role in the etiology of cancer. It has been reported that rice components, especially rice germ plays a key role in prevention of cancer. The experiments described here examined the potential anticancer properties of brown rice fermented by Aspergillus Oryzae (FBRA) in male F344 rats using inhibition of the formation of azoxymethene (AOM) induced aberrant crypt foci (ACF) and tumors in the colon as the measure of preventive efficacy. The agent was administered at 2.5 and 5% levels in the diet during the initiation phase (during and until 1 week after carcinogen treatment) and/or post-initiation phase (beginning 1 week after carcinogen treatment) of carcinogenesis. In the ACF and tumor studies, rats were sacrificed 5 or 40 weeks after the initiation of AOM treatment (15 mg/kg body weight, once weekly for 3 weeks), respectively. Colonic ACF and tumors were evaluated histopathologically. Administration of 2.5 and 5% FBRA in the diet continuously during initiation and post-initiation period significantly inhibited the ACF formation in rats treated with AOM, compared with rats treated with AOM alone (99+/-24.1 and 79+/-18.4 vs. 139.5+/-27.7, respectively). In addition, administration of 5% FBRA in the diet during the post-initiation phase significantly suppressed the incidence (44 vs.18%) and multiplicity (0.93+/-0.96 vs. 0.18+/-0.40) of colon adenocarcinomas as compared to those given the control diet. In addition, 5% FBRA in the diet during post-initiation phase caused significant inhibition of cell proliferation in the colonic mucosa as compared to the group fed the control diet (81% reduction, p<0.05). These observations demonstrated for the first time that FBRA inhibits colon tumor development in rats, and suggest that it is a promising dietary supplement for prevention of human colon cancer.     

Inhibitory effects of ursodeoxycholic acid on N-methylnitrosourea-induced colon carcinogenesis and colonic mucosal telomerase activity in F344 rats.

Bile acids are known to promote colon carcinogenesis. However, one study showed that ursodeoxychlic acid (UDCA) prevented azoxymethane-induced rat colon tumorigenesis. The aim of the present study with 3 sets of experiments was to explore the inhibitory effect of UDCA supplemented in the diet on colon carcinogenesis induced by the intrarectal administration of N-methylnitrosourea (MNU) in F344 rats. In experiment I, 5 rats per group were fed a diet supplemented with 0% (control), 0.4%, 0.08% or 0.016% UDCA or chenodeoxycholic acid (CDCA) for 5 weeks after receiving 3 intrarectal doses of 4 mg MNU in week 1. The formation of colonic aberrant crypt foci (ACFs, preneoplastic lesions) at week 6 showed a 24% and 23% reduction in the 0.4% and 0.08% UDCA groups, respectively, as compared to the control group, while it increased for the 0.4% and 0.08% CDCA groups, and was unaffected in the 0.016% UDCA and CDCA groups. In experiment II based on the results of experiment I, all rats received an intrarectal dose of 2 mg MNU 3 times a week for 3 weeks, and then were administered with 0%, 0.4% or 0.08% UDCA for 27 weeks. At week 30, the incidence of colon tumors in the UDCA groups was significantly lower than that in the control group: 20/50 (40%) and 9/25 (36%) vs. 17/25 (68%). The number of large-sized ACFs with 4 or more ACs showed a 47% and 59% reduction in the normal-appearing mucosa in the UDCA groups as compared to the control group, while the number of small-sized ACFs with 1-3 ACs was similar in all groups. The normal-appearing mucosa showed a noticeable level of telomerase activity (semiquantitative PCR-based TRAP assay) in the control group, and significantly reduced levels in the UDCA groups compared to the control group: 19.8 and 32.7 vs. 71.0 TPG unit in mean value. The colon tumors showed a high level of enzyme activity in both the control and UDCA groups. In experiment III, 6 rats per group were fed a diet supplemented with 0%, or 0.4% UDCA or CDCA for 5 weeks after receiving 3 intrarectal doses of 4 mg MNU in week 1. Two control groups did not receive any treatment with MNU and bile acids. The MNU-treated groups showed significantly elevated levels of colonic mucosal telomerase activity at week 6 as compared to the control group (6.5 TPG unit in mean value). It was noted that both UDCA and CDCA administration reduced the enzyme activity as compared to the group with MNU treatment alone: 24.7 and 25.2 vs. 40.1 TPG unit in mean value. Thus, the present study suggested that orally administered UDCA inhibited the growth of ACFs and the development of carcinomas in the colon of rats treated with MNU. Also, UDCA may suppress MNU-induced telomerase activation in normal-appearing but ACF-containing colon mucosa, and its mechanism appears to be different from that responsible for the anti-tumor promoting action of UDCA.     

Mucin-depleted foci (MDF) in the colon of rats treated with azoxymethane (AOM) are useful biomarkers for colon carcinogenesis

Crypt foci with absent or scant mucous production (mucin-depleted foci, MDF) were recently described by our group in the colon of azoxymethane (AOM)-treated rats. Since MDF are dysplastic and easy to quantify, we think that MDF are pre-neoplastic lesions that could be used as biomarkers for carcinogenesis. To test this hypothesis, we studied MDF in azoxymethane (AOM)-initiated rats treated with cholic acid (CHA), a promoter of colon carcinogenesis or with piroxicam (PXC), a colon cancer-inhibiting drug. Aberrant crypt foci (ACF) were determined as well. F344 male rats were treated with AOM (15 mg/kg x 2, s.c.) and then divided into: controls, which were fed AIN76 diet; CHA group, which was fed AIN76 diet containing CHA 0.5% w/w; PXC group, which was fed AIN76 diet containing PXC 0.02% w/w. Ten weeks after the first dose of AOM, the total number of MDF was significantly increased in rats treated with CHA (P<0.05) and drastically reduced (P<0.01) in rats treated with PXC (MDF/colon were 6.10 +/- 1.26, 10.59 +/- 1.96 and 1.31 +/- 0.21 in controls, CHA and PXC groups, respectively, means +/- SE). The multiplicity of MDF was also increased in CHA-treated rats. On the contrary, ACF multiplicity was significantly decreased by CHA. In PXC-treated rats there were fewer ACF with lower multiplicity. The effect of PXC was also investigated 15 weeks after the first AOM dose and the results showed that the total number of MDF in the PXC group was significantly lower than in controls. The number of 'large' MDF, formed by 12 or more crypts, was also reduced (P<0.01) by PXC ('large' MDF were 1.7 +/- 0.5 and 0.4 +/- 0.2 in control and PXC groups, respectively). Since CHA promotes and PXC reduces colon cancer, MDF are correlated with carcinogenesis and can be proposed as endpoints to study the modulation of colon carcinogenesis in short-term experiments.     

Dietary n-3 PUFA increases the apoptotic response to 1,2-dimethylhydrazine, reduces mitosis and suppresses the induction of carcinogenesis in the rat colon

The effect of dietary fish oil on colonic crypt cell apoptosis and proliferation was examined in male Wistar rats, 24 and 48 h after administration of 1,2-dimethylhydrazine (DMH), and its influence on the induction of aberrant crypt foci (ACF) in the distal colon was assessed. Rats (125-150 g) fed a high-fat semi-synthetic diet containing corn oil (CO) were given DMH (30 mg/kg body wt) or a sham injection of EDTA/NaCl. Animals were then fed either the CO diet or a diet in which fish oil (EPA 18.7%; DHA 8%) was substituted for corn oil. Subgroups of rats (n = 5) were killed after 24 and 48 h, and crypt cell apoptosis and proliferation were quantified by morphological criteria in isolated intact crypts from the mid and distal colon. Consumption of the fish oil diet (FO) was associated with increased apoptotic cell death (P < 0.001) and suppression of proliferation (P < 0.05) in colonic crypts both 24 and 48 h after DMH. In a second experiment, animals were given three injections of DMH or sham injections of carrier at weekly intervals. For 48 h after each injection animals were fed either the CO or FO diet, but otherwise maintained on the CO throughout. The number and crypt multiplicity of ACF in the distal colon were determined after 18 weeks, and animals given the FO diet for the 48 h period following carcinogen administration were found to have significantly fewer ACF than rats fed the CO diet (P < 0.05). The data demonstrate that the fatty acid composition of the diet is an important determinant in the induction of carcinogenesis by DMH. The proliferative and apoptotic response of the colonic crypt to carcinogen and fish oil, coupled with the reduced incidence of ACF, suggest n-3 PUFA can protect against the carcinogenic effects of DMH by mediating changes in the balance proliferation and cell death.