Suppressing Effects of 6-(2,5-Dichlorophenyl)-2,4-diamino-1,3,5-triazine and Related Synthetic Compounds on Azoxymethane-induced Aberrant Crypt Foci in Rat Colon

The modifying effects of dietary administration of 6-(2,5-dichlorophenyl)-2,4-diamino-1,3,5-triazine and 5 related compounds on the occurrence of azoxymethane (AOM)-induced colonic aberrant crypt foci (ACF) were investigated in rats. Male F344 rats were given s.c. injections of AOM (15 mg/kg body weight) once a week for 3 weeks to induce ACF. They also received the diet containing 200 ppm test compound for 5 weeks, starting one week before the first dosing of AOM. At the termination of experiment, all of the compounds had caused a significant reduction in ACF frequency, which might be associated with suppression of the expression of proliferation biomarkers. The apoptotic index in the colonic mucosal epithelium of rats killed at 6 h after the first AOM exposure revealed no blocking activity of the compounds.     

Achaete-scute homolog-1 and Notch in lung neuroendocrine development and cancer

The modifying effects of dietary feeding of extract of leaves of ginkgo (Ginkgo biloba) (EGb) and bilobalide isolated from EGb on the development of azoxymethane (AOM)-induced colonic aberrant crypt foci (ACF) were investigated in male F344 rats. We also assessed the effects of EGb and bilobalide on proliferating cell nuclear antigen (PCNA) index in ‘normal-appearing’ crypts and activities of detoxifying enzymes of cytochrome P450 (CYP), glutathione S-transferase (GST) and quinine reductase (QR) activity in the liver. To induce ACF, rats were given two weekly subcutaneous injections of AOM (20 mg/kg body wt). They also received the experimental diets containing EGb (50 or 500 ppm) and bilobalide (15 or 150 ppm) for 4 weeks, starting 1 week before the first dosing of AOM. AOM exposure produced a substantial number of ACF (106±10) at the end of the study (week 4). Dietary administration of EGb and bilobalide caused significant reduction in the frequency of ACF: 50 ppm EGb, 73±17 (31% reduction, P<0.001); 500 ppm EGb, 56±13 (47% reduction, P<0.001); 15 ppm bilobalide, 79±17 (25% reduction, P<0.01); and 150 ppm bilobalide, 71±30 (33% reduction, P<0.01). Immunohistochemically, EGb or bilobalide administration significantly lowered PCNA index in normal-appearing crypts. Feeding with EGb or bilobalide increased activities of CYP as well as GST and QR in the liver. These findings might suggest possible chemopreventive ability of EGb or bilobalide, through alterations in cryptal cell proliferation activity and drug metabolizing enzymes' activities, in colon tumorigenesis.     

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.     

A xanthine oxidase inhibitor 1'-acetoxychavicol acetate inhibits azoxymethane-induced colonic aberrant crypt foci in rats

The modifying effect of dietary administration of a xanthine oxidase inhibitor 1'-acetoxychavicol acetate (ACA) present in an edible plant Languas galanga in Thailand on the development of azoxymethane (AOM)- induced colonic aberrant crypt foci (ACF) was investigated in rats. Male F344 rats were given s.c. injections of AOM (15 mg/kg body wt) once a week for 3 weeks to induce colonic ACF. They were fed the diets containing 100 or 200 ppm ACA for 5 weeks, starting 1 week before the first dosing of AOM. At the termination of the study (week 5), AOM induced 118 +/- 28 ACF/colon. Dietary administration of ACA caused significant reduction in the frequency of ACF (41% inhibition by 100 ppm ACA feeding and 37% inhibition by 200 ppm ACA feeding, P<0.01). Such inhibition might be associated with suppression of the proliferation biomarkers' expression such as ornithine decarboxylase activity in the colonic mucosa, number of silver-stained nucleolar organizer regions' protein in the colonic mucosal cell nuclei and blood polyamine content. These results indicate that ACA could inhibit the development of AOM-induced ACF through its suppression of cell proliferation in the colonic mucosa and ACA might be a possible chemopreventive agent against colon tumourigenesis.      

Inhibition of azoxymethane-induced aberrant crypt foci in rats by natural compounds, caffeine, quercetin and morin.

The modifying effects of dietary administration of natural compounds, caffeine, quercetin and morin, which are present in our daily food, on the development of azoxymethane (AOM)-induced colonic aberrant crypt foci (ACF) were investigated in rats and compared to that of a metabolic inhibitor of AOM, disulfiram. Male F344 rats were given s. c. injections of AOM (15 mg/kg body weight) once a week for 3 weeks to induce ACF. They also received the experimental diets containing one of test compounds (500 ppm) for 5 weeks, starting one week before the first dosing of AOM. At the termination of the study (week 5), AOM exposure produced 101.0+/-10.2 ACF/rat. Disulfiram almost completely inhibited ACF development (0.60+/-0.90, 99% reduction). Dietary administration of test compounds caused significant reduction in the frequency of ACF: caffeine (70.4+/-16.6, 30% reduction), quercetin (53.0+/-8.4, 48% reduction) and morin (37. 6+/-18.1, 63% reduction). Numbers of cells positive for proliferative cell nuclear antigen in ACF and surrounding crypts were lowered by feeding of test compounds. Feeding of these test compounds also suppressed polyamine content in the colonic mucosa and blood as did disulfiram. These findings might indicate possible chemopreventive effects of caffeine, quercetin and morin, through their modulation of cell proliferation activity in crypt cells, on colon tumorigenesis.     

Preventive effects of chrysin on the development of azoxymethane-induced colonic aberrant crypt foci in rats

The modifying effects of dietary feeding with chrysin (5,7-dihydroxyflavone) on the development of azoxymethane (AOM)-induced colonic aberrant crypt foci (ACF) were investigated in male F344 rats. We also assessed the effect of chrysin on mitosis and apoptosis in 'normal appearing' crypts. To induce ACF, rats were given two weekly subcutaneous injections of AOM (20 mg/kg body weight). They also received an experimental diet containing chrysin (0.001 or 0.01%) for 4 weeks, starting 1 week before the first dose of AOM. AOM exposure produced a substantial number of ACF (73+/-13/rat) at the end of the study (week 4). Dietary administration of chrysin caused significant reduction in the frequency of ACF: 0.001% chrysin, 37+/-17/rat (49% reduction, P<0.001); and 0.01% chrysin, 40+/-10/rat (45% reduction, P<0.001). In addition, chrysin administration significantly reduced the mitotic index and significantly increased the apoptotic index in 'normal appearing' crypts. These findings might suggest a possible chemopreventive activity of chrysin in the early step of colon tumorigenesis through modulation of cryptal cell proliferation activity and apoptosis.     

Suppression of Occurrence and Advancement of β-Catenin-accumulated Crypts, Possible Premalignant Lesions of Colon Cancer, by Selective Cyclooxygenase-2 Inhibitor, Celecoxib

Suppression of occurrence and advancement of premalignant lesions is important for cancer prevention. Our previous studies clarified that β-catenin-accumulated crypts, independent of aberrant crypt foci (ACF), are probably direct precursors of colon cancers in rats. Here we investigated the effects of a selective cyclooxygenase-2 inhibitor, celecoxib, on the development of β-catenin-accumulated crypts in comparison with those on ACF. Male F344 rats were divided into 4 groups. Groups 1-3 were administered azoxymethane (AOM) s.c. at a dose of 15 mg/kg body weight, once weekly for 3 weeks to induce β-catenin-accumulated crypts. Groups 2 and 3 also received experimental diet containing celecoxib (500 and 1500 ppm, respectively) for 8 weeks, starting a week before the first dosing of AOM. At termination, the frequency and crypt multiplicity (number of crypts/lesion) of β-catenin-accumulated crypts of groups 2 and 3 were significantly less than that of group 1. Furthermore, numbers of silver-stained nucleolar organizer regions (AgNORs)/nucleus in β-catenin-accumulated crypts were also decreased by exposure to celecoxib. In this study, celecoxib had greater effects on the frequency and growth of β-catenin-accumulated crypts than on those of ACF. These findings represent additional evidence that β-catenin-accumulated crypts are premalignant lesions of colon cancer. The results also suggest that β-catenin-accumulated crypts could be a novel target for evaluation of possible chemopreventive agents against colon carcino-genesis, and indicate that possible chemopreventive effects of celecoxib on the initial stage of colon carcinogenesis may be related to modulation of cell proliferation activity in such early lesions.     

Chemopreventive properties of a selective inducible nitric oxide synthase inhibitor in colon carcinogenesis, administered alone or in combination with celecoxib, a selective cyclooxygenase-2 inhibitor.

The inducible isoforms of nitric oxide synthase (iNOS) and cyclooxygenase (COX-2) are overexpressed in colonic tumors of humans, as well as in colon tumors that develop in rats after the administration of the colon-specific carcinogen, azoxymethane (AOM). iNOS may regulate COX-2 production of proinflammatory prostaglandins, which are known to play a key role in colon tumor development. Experiments were designed to assess the potential chemopreventive properties of highly selective iNOS inhibitors, administered individually and in combination with a selective COX-2 inhibitor, on the development of AOM-induced colonic aberrant crypt foci (ACF). F344 rats were fed experimental diets containing one of the following: 0, 10, 30, or 100 parts/million (ppm) of the selective iNOS inhibitor L-N(6)-(1-iminoethyl)lysine tetrazole-amide (SC-51); 1800 ppm of the less potent, selective iNOS inhibitor aminoguanidine (AG); 500 ppm of the COX-2 inhibitor celecoxib; 320 ppm of the nonsteroidal anti-inflammatory sulindac (positive control); or 30 ppm of SC-51 with 500 ppm of celecoxib, and 100 ppm of SC-51 with 500 ppm of celecoxib. One and 2 weeks later, rats received s.c. injections of AOM at a dose of 15 mg/kg of body weight. At 17 weeks of age, all rats were sacrificed. Colons were evaluated for ACF, and colonic mucosae were assayed for COX and NOS isoform enzyme activities. Samples of venous blood, collected at various time points, were analyzed for these agents. SC-51, administered alone, demonstrated dose-dependent inhibition of the incidence of colonic ACF. The highest doses of SC-51 (100 ppm) and AG (1800 ppm) significantly suppressed the incidence of colonic ACF (P < 0.01 and < 0.001, respectively) and crypt multiplicity in terms of numbers of aberrant crypts/focus (P < 0.0001). Importantly, the combination of either low or high effective doses of SC-51 (30 or 100 ppm) and celecoxib (500 ppm) suppressed AOM-induced colonic ACF formation (P < 0.05 and < 0.001, respectively) and reduced multiplicity of four or more aberrant crypts/focus (P < 0.0001) to a greater extent than did these agents administered individually. As expected, sulindac inhibited colonic ACF formation (P < 0.001) and reduced the multiplicity of four or more aberrant crypts (P < 0.0001) to approximately 45%. The enzymatic activities of COX-2 and iNOS were significantly induced in the AOM-treated animals, and administration of the iNOS inhibitors, SC-51 and AG, significantly inhibited the activities of both iNOS and COX-2 in the colonic mucosa. The combined administration of SC-51 and celecoxib inhibited the COX-2 activity to a greater extent than did either of these agents administered alone. These findings support the hypothesis that selective iNOS inhibitors may have chemopreventive properties and that coadministration with a selective COX-2 inhibitor may have additional chemopreventive potential.     

Citrus auraptene inhibits chemically induced colonic aberrant crypt foci in male F344 rats

The modifying effect of dietary administration of auraptene isolated from the peel of citrus fruit (Citrus natsudaidai Hayata) on the development of azoxymethane (AOM)-induced colonic aberrant crypt foci (ACF) was investigated in rats. Male F344 rats were given s.c. injections of AOM (15 mg/kg body wt) once a week for 3 weeks to induce ACF. They also received diets containing 100 or 500 p.p.m. auraptene for 5 weeks, starting 1 week before the first dose of AOM. At termination of the study (week 5) dietary administration of auraptene caused a significant reduction in the frequency of ACF in a dose- dependent manner (P < 0.05). Feeding of auraptene suppressed expression of cell proliferation biomarkers (5-bromo-2'-deoxyuridine labeling- index, ornithine decarboxylase activity, polyamine content and number of silver stained nucleolar organizer region protein particles) in the colonic mucosa and the occurrence of micronuclei caused by AOM. Also, auraptene increased the activities of phase II enzymes (glutathione S- transferase and quinone reductase) in the liver and colon. These findings might suggest that inhibition of AOM-induced ACF may be associated, in part, with increased activity of phase II enzymes in the liver and colon and suppression of cell proliferation in the colonic mucosa.      

Increased Cell Proliferation of Azoxymethane-induced Aberrant Crypt Foci of Rat Colon

Aberrant crypt foci (ACF) were induced in the colon of F344 rats by s.c. injection of azoxymethane (AOM) twice in a three day-interval and examined after 4 and 12 weeks. The number and crypt multiplicity of ACF in each section of rat colon increased during this period. Histologically, aberrant crypts consisted of proliferating atypical epithelial cells. Cell proliferation of ACF consisting of 4 aberrant crypts [ACF(4)] and 2 aberrant crypts [ACF(2)], and normal crypts in the colon of rats treated with AOM [normal crypts/AOM(+)] or saline [normal crypts/AOM(-)] was investigated by measurement of the mitotic index, proliferating cell nuclear antigen-labeling index (PCNA-LI), and 5-bromo-2'-deoxyuridine-labeling index (BrdU-LI). All three parameters of the cell proliferative activity of ACF(4) were higher than those of normal crypts/AOM(+) and normal crypts/AOM(-). The PCNA-LI and BrdU-LI in ACF(2) were the same as those in ACF(4). These findings suggest that ACF have increased cell proliferative activity. The correlation of these three parameters confirmed that the PCNA-LI is also a useful parameter for evaluating cell proliferative activity in ACF. The presence of many cells stained by PCNA in the upper portion of ACF suggested that ACF have more G₁ phase cells, which readily respond to mitogenic stimulation, than G₀ phase cells, which are predominant in normal crypts.     

Termination of piroxicam treatment and the occurrence of azoxymethane-induced colon cancer in rats

Piroxicam has been shown to prevent azoxymethane (AOM)-induced colon cancer when administered during the promotion/ progression phase. The requirement for continued treatment with piroxicam in order to maintain prevention of colon cancer was investigated. Male F344 rats were administered 15 mg/kg AOM at 7 and 8 weeks of age and started to receive piroxicam (200 mg/kg) in their diet at 11 weeks after the second dose of AOM. Piroxicam was removed from the diet of some of the rats at weeks 19 and 28 and the animals were held until week 47. Other rats continued to receive piroxicam until sacrificed at week 47. Treatment with piroxicam from week 11-47 reduced the yield of colon tumors. When treatment was terminated at week 19 or 28 the yield of tumors at week 47 was not reduced. Within 1 week of the start of piroxicam treatment, the number of aberrant crypt foci (ACF)/animal was decreased. Termination of treatment resulted in the recurrence of ACF. Apoptosis in adenomas was increased when piroxicam treatment was continued to week 47 but not when treatment was terminated earlier at week 19 or 28. The proliferating cell nuclear antigen-labeling index in adenomas was not affected by piroxicam even when treatment was from week 11 to 47. In summary, termination of treatment resulted in the occurrence of ACF and colon cancer indicating that prevention by piroxicam was reversible. Furthermore, enhancement of apoptosis and not decreased cell proliferation correlated with prevention of colon cancer.     

Enhanced growth of colorectal aberrant crypt foci in fasted/refed rats involves changes in TGFbeta1 and p21CIP expressions

We previously demonstrated that fasting/refeeding enhances the initiation phase of liver and colorectal carcinogenesis in rats. The present study was undertaken to establish whether cycles of fasting/refeeding carried out during the promotion phase of carcinogenesis may also affect the formation of aberrant crypt foci (ACF), preneoplastic lesions induced in the colon by azoxymethane (AOM). We were also interested in studying whether this effect might be mediated by changes in the proliferation, apoptosis or expression of TGFbeta1 and p21CIP genes in the colon. 44 male Fisher 344 rats were given a single dose of AOM (20 mg/kg s.c.) and one week later, they were exposed to 5 cycles of 4 days fasting followed by 7-10 days of refeeding (refed rats); controls were regularly fed; the rats were killed 2, 8 or 30 days after the last cycle of fasting. Fasting/refeeding caused a dramatic increase in crypt multiplicity when compared with regularly fed rats (AC/ACF was 4.30 +/- 1.3 in refed and 2.38 +/- 0.4 in regularly fed rats, P < 0.005 means +/- SD), while no significant changes were observed in the number of ACF/colon. In the two experimental groups, cell proliferation was higher in ACF than in the surrounding mucosa, but proliferative indexes were higher and the apoptotic index lower in ACF of refed rats compared with regularly fed rats. TGFbeta1 expression was higher in the ACF of refed rats than in those of fully fed controls while p21CIP was less expressed in refed rats than in controls. These results suggest that fasting/refeeding is a risk factor for colon cancer and must be taken into account for cancer prevention in humans.     

Catalpa seed oil rich in 9t,11t,13c-conjugated linolenic acid suppresses the development of colonic aberrant crypt foci induced by azoxymethane in rats

Catalpa (Catalpa ovata) seed oil (CPO) is a unique oil that contains a high amount of 9trans,11trans,13cis-conjugated linolenic acid. In the present study, we investigated whether dietary administration with CPO affects the development of azoxymethane (AOM)-induced colonic aberrant crypt foci (ACF) in male F344 rats to elucidate its possible cancer chemopreventive efficiency. Also, the effect of CPO on the fatty acid composition of liver tissue and colonic mucosa, the serum levels of total cholesterol and triglyceride, and the mRNA expression of cyclooxygenase (COX)-2 in the colonic mucosa were measured. In addition, the cell proliferation activity and apoptotic index in the colonic mucosa were estimated immunohistochemically. Animals were given two weekly subcutaneous injections of AOM (20 mg/kg body weight). They also received the experimental diet containing 0.01%, 0.1% or 1% CPO for 4 weeks, starting one week before the first dosing of AOM. AOM exposure produced a substantial number of ACF (99+/-28) at the end of the study (week 4). Dietary administration of CPO reduced the number of ACF (AOM + 0.01% CPO, 32+/-11, P<0.001; AOM + 0.1% CPO, 35+/-18, P<0.001; AOM + 1% CPO, 18+/-10, P<0.001). 9t,11t-conjugated linoleic acid was detected in the liver tissue and colonic mucosa of rats fed the CPO-containing diet. Additionally, dietary administration with CPO decreased the serum triglyceride level and the expression of COX-2 mRNA in the colonic mucosa. The indices of cell proliferation and apoptosis in the colonic mucosa of rats treated with AOM and 1% CPO have significant differences when compared with the AOM alone group. These findings suggest the possible chemopreventive activity of CPO in the early phase of colon carcinogenesis.     

Dietary‐feeding of grape seed extract prevents azoxymethane‐induced colonic aberrant crypt foci formation in fischer 344 rats

Chemoprevention by dietary agents/supplements has emerged as a novel approach to control various malignancies, including colorectal cancer (CRC). This study assessed dietary grape seed extract (GSE) effectiveness in preventing azoxymethane (AOM)‐induced aberrant crypt foci (ACF) formation and associated mechanisms in Fischer 344 rats. Six‐week‐old rats were injected with AOM, and fed control diet or the one supplemented with 0.25% or 0.5% (w/w) GSE in pre‐ and post‐AOM or only post‐AOM experimental protocols. At 16 wk of age, rats were sacrificed and colons were evaluated for ACF formation followed by cell proliferation, apoptosis, and molecular analyses by immunohistochemistry. GSE‐feeding caused strong chemopreventive efficacy against AOM‐induced ACF formation in terms of up to 60% (P < 0.001) reduction in number of ACF and 66% (P < 0.001) reduction in crypt multiplicity. Mechanistic studies showed that GSE‐feeding inhibited AOM‐induced cell proliferation but enhanced apoptosis in colon including ACF, together with a strong decrease in cyclin D1, COX‐2, iNOS, and survivin levels. Additional studies showed that GSE‐feeding also decreased AOM‐caused increase in β‐catenin and NF‐κB levels in colon tissues. Compared to control animals, GSE alone treatment did not show any considerable change in these biological and molecular events in colon, and was nontoxic. Together, these findings show the chemopreventive efficacy of GSE against the early steps of colon carcinogenesis in rats via likely targeting of β‐catenin and NF‐κB signaling, and suggest its potential usefulness for the prevention of human CRC. © 2010 Wiley‐Liss, Inc.     

Suppression of occurrence and advancement of beta-catenin-accumulated crypts, possible premalignant lesions of colon cancer, by selective cyclooxygenase-2 inhibitor, celecoxib.

Suppression of occurrence and advancement of premalignant lesions is important for cancer prevention. Our previous studies clarified that beta-catenin-accumulated crypts, independent of aberrant crypt foci (ACF), are probably direct precursors of colon cancers in rats. Here we investigated the effects of a selective cyclooxygenase-2 inhibitor, celecoxib, on the development of beta-catenin-accumulated crypts in comparison with those on ACF. Male F344 rats were divided into 4 groups. Groups 1 - 3 were administered azoxymethane (AOM) s.c. at a dose of 15 mg / kg body weight, once weekly for 3 weeks to induce beta-catenin-accumulated crypts. Groups 2 and 3 also received experimental diet containing celecoxib (500 and 1500 ppm, respectively) for 8 weeks, starting a week before the first dosing of AOM. At termination, the frequency and crypt multiplicity (number of crypts / lesion) of beta-catenin-accumulated crypts of groups 2 and 3 were significantly less than that of group 1. Furthermore, numbers of silver-stained nucleolar organizer regions (AgNORs) / nucleus in beta-catenin-accumulated crypts were also decreased by exposure to celecoxib. In this study, celecoxib had greater effects on the frequency and growth of beta-catenin-accumulated crypts than on those of ACF. These findings represent additional evidence that beta-catenin-accumulated crypts are premalignant lesions of colon cancer. The results also suggest that beta-catenin-accumulated crypts could be a novel target for evaluation of possible chemopreventive agents against colon carcino-genesis, and indicate that possible chemopreventive effects of celecoxib on the initial stage of colon carcinogenesis may be related to modulation of cell proliferation activity in such early lesions.     

Effect of dietary galacto-oligosaccharides on azoxymethane-induced aberrant crypt foci and colorectal cancer in Fischer 344 rats

The aim of the present study was to investigate the effects of galacto-oligosaccharides (GOS, Elix'or) on the development of aberrant crypt foci (ACF) and colorectal tumours in rats treated with azoxymethane (AOM). Two groups of 102 male Fischer 344 rats were injected twice with AOM to induce colorectal tumours, and fed diets containing either a low [5% (w/w); LGOS] or a high [20% (w/w); HGOS] concentration of GOS. Four weeks after the last AOM injection, 18 animals from each group were killed and their colon was removed for scoring ACF. Half of the animals in the LGOS group were switched to an HGOS diet (L/HGOS) and half of those in the HGOS group to an LGOS diet (H/LGOS). Six weeks after the change in diet, nine animals per group were killed for scoring ACF. Ten months after the start of the study the remaining animals were killed for scoring colorectal tumours. The aberrant crypt multiplicity scored after 13 weeks and the colorectal tumour incidence in rats fed an HGOS diet were significantly lower than those in rats fed an LGOS diet. However, the induction of ACF by AOM, the proliferation rate and apoptotic index of the adenomas, and the size and multiplicity of colorectal tumours were not influenced by the amount of GOS in the diet. The aberrant crypt multiplicity, scored after 13 weeks, was predictive for the tumour outcome at the end of the study. It was concluded that an HGOS diet has a protective effect against the development of colorectal tumours in rats and that this protective effect is exerted during the promotion phase rather than the initiation phase of carcinogenesis.     

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.     

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.     

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.     

Preventive Effects of a Flavonoid Myricitrin on the Formation of Azoxymethane-induced Premalignant Lesions in Colons of Rats

The preventive effect of dietary exposure to a flavonoid myricitrin of azoxymethane (AOM)-induced aberrantcrypt foci (ACF) and beta-catenin-accumulated crypts (BCAC) formation was investigated in male F344 rats.Thirty-four rats were divided randomly into five experimental groups. Rats in groups 1-3 were given subcutaneousinjections of AOM (15 mg/kg body weight) once a week for 3 weeks. Starting 1 week before the first injection ofAOM, rats in groups 2 and 3 were fed a diet containing 500 or 1000 ppm myricitrin, respectively, for 11 weeks.Rats in group 4 were fed a diet containing 1000 ppm myricitrin. Rats in groups 1 and 5 were given the basal dietalone during the study. The experiment was terminated 11 weeks after the start. The frequency of ACF per colonin group 3 treated with AOM and 1000 ppm myricitrin was significantly lower than that in group 1 treated withAOM alone (p<0.01). Furthermore, dietary myricitrin at both doses (groups 2 and 3) significantly inhibited theformation of BCAC when compared to group 1 (p<0.05). These results indicate that myricitrin had possiblechemopreventive effects in the present short-term colon carcinogenesis bioassays and suggest that longer exposuremay cause suppression of tumor development.