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.     

Inhibitory effect of dietary monoglucosylceramide 1-O-beta-glucosyl-N-2'-hydroxyarachidoyl-4,8-sphingadienine on two different categories of colon preneoplastic lesions induced by 1,2-dimethylhydrazine in F344 rats

Sphingolipids display a wide spectrum of biological activities, including cell growth, differentiation and apoptosis. However, precise mechanisms by which these compounds exert anticancer or cancer-preventive effects are not known. In the present study, we evaluated the preventive efficacy of enriched dietary monoglucosylceramide 1-O-beta-glucosyl-N-2'-hydroxyarachidoyl-4,8-sphingadienine (G(1)CM) on 1,2-dimethylhydrazine (DMH)-induced aberrant crypt foci (ACF) and beta-catenin-accumulated crypt (BCAC) formation in F344 rats during initiation stage. We also examined whether G(1)CM affects cell proliferation and apoptosis in these lesions. Pure G(1)CM was isolated from rice bran. Forty-two rats were divided randomly into five experimental groups. Rats in groups 1-3 were given subcutaneous injections of DMH (40 mg/kg body weight) once a week for 2 weeks. One week before the first injection of DMH, rats in groups 2 and 3 were fed a diet containing 200 and 1,000 p.p.m. G(1)CM, respectively, for 5 weeks. Rats in group 4 were fed a diet containing 1,000 p.p.m. G(1)CM. Rats in group 5 were given the basal diet alone and served as untreated controls. The experiment was terminated 5 weeks after the start. Dietary G(1)CM at both doses (groups 2 and 3) significantly inhibited the induction of ACF and BCAC (P<0.001) when compared to group 1 treated with DMH alone. In groups 2 and 3, the proliferating cell nuclear antigen labeling indices of epithelial cells in ACF and BCAC were also lower than in group 1 (P<0.0001 for ACF, P<0.05 for BCAC). These results, that dietary G(1)CM has possible chemopreventive effects in the present short-term colon carcinogenesis bioassays, suggest that longer exposure may cause suppression of tumor development.     

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.     

Suppression of Azoxymethane-induced Rat Colon Aberrant Crypt Foci by Dietary Protocatechuic Acid

The modifying effect of dietary exposure to protocatechuic acid (PCA) on the development of azoxymethane (AOM)-induced colonic aberrant crypt foci (ACF) was investigated in male F344 rats. The effects of PCA feeding on the silver-stained nucleolar organizer regions protein (AgNORs) count in the colonic epithelial cells and on the ornithine decarboxylase (ODC) activity in the colonic mucosa were also estimated. Animals were given weekly s.c. injections of AOM (15 mg/kg body weight) for 3 weeks to induce ACF. These rats were fed diet containing 1000 or 2000 ppm PCA for 5 weeks, starting one week before the first dosing of AOM. All rats were killed 2 weeks after the last AOM injection, to measure the number of ACF, ODC activity, and AgNORs count per nucleus in the colon. In rats given AOM and PCA, the frequency of ACF/colon was significantly decreased compared with that in rats given AOM alone ( P < 0.005 at 1000 and P < 0.05 at 2000 ppm). ODC activity in the colon of rats given AOM and PCA at both doses was also significantly lower than that of rats treated with AOM alone ( P < 0.05). Similarly, the mean AgNORs count in rats fed PCA was significantly smaller than that of rats treated with AOM alone ( P < 0.0001). Treatment with PCA alone did not affect these three biomarkers. These results provide further evidence that PCA could be a chemopreventive agent against rat colon carcinogenesis.     

The modifying effect of Peucedanum japonicum, a herb in the Ryukyu Islands, on azoxymethane-induced colon preneoplastic lesions in male F344 rats

The modifying effect of dietary Peucedanum japonicum (PJ), which is a traditional herb in the Ryukyu Islands and is an anti-oxidant, on azoxymethane (AOM)-induced rat colon carcinogenesis was examined. Male F344 rats were divided into six groups: rats in groups 1-4 were given subcutaneous injection of AOM (20 mg/kg body weight) once a week for 2 weeks. Rats in groups 2, 3 and 4 were fed the diets containing 0.2 and 1% PJ and 0.025% chlorogenic acid, respectively. We observed modification of the preneoplastic lesions of both aberrant crypt foci (ACF) and beta-catenin accumulated crypts (BCAC) in colon carcinogenesis, microscopically and immunohistochemically. The numbers of ACF consisting of more than four aberrant crypts per rat in groups 2 (3.2+/-1.7) and 3 (3.0+/-3.2) were significantly lower than that of group 1 (10.8+/-4.9; P<0.05, respectively). The mean number of BCAC in both groups 2 (0.88+/-0.48/cm2/rat) and 3 (0.81+/-0.34/cm2/rat) was significantly lower than that in group 1 (2.13+/-0.54/cm2/rat; P < 0.0001, respectively). In addition, proliferating cell nuclear antigen labeling indices in group 2 (10.98+/-2.03) and group 3 (9.85+/-2.62) were significantly lower than that in group 1 (14.87+/-3.93; P < 0.001 and P < 0.0001, respectively). These findings indicate that PJ inhibits both ACF formation and accumulation of beta-catenin, and that PJ also reduces the cell proliferation activity, suggesting that PJ may have chemopreventive potential for colon carcinogenesis.     

Induction of Apoptosis by Sulindac in Azoxymethane-induced Possible Colonic Premalignant Lesions in Rats

We have reported that β-catenin-accumulated crypts (BCAC), which do not have the appearance of aberrant crypt foci (ACF) are possible colonic premalignant lesions in rats. Suppression of the occurrence and advancement of such lesions should have critical relevance to cancer prevention. This study examined whether sulindac, a chemopreventive nonsteroidal anti-inflammatory drug is able to induce apoptosis in such premalignant lesions. At 6 weeks of age, rats groups 1–3 were given azoxymethane (AOM) (15 mg/kg-body weight) once weekly for 3 weeks. Two groups were given sulindac in the diet (200 and 400 ppm), starting at 9 weeks of age. The rats were sacrificed at the termination, and the colons were carefully examined. The incidence and crypt multiplicity of BCAC and ACF were significantly less than those of the control group. The effect of sulindac on the expression of BCAC was greater than that on ACF. Exposure to sulindac significantly increased the apoptotic index (terminal deoxynucleotide transferase dUTP nick-end labeling (TUNEL)-positive cells) in BCAC. However, no significant increase of the index was found in the case of ACF. These results suggest that the chemopreventive effect of sulindac in rats is related to the induction of apoptosis in premalignant lesions. Our results also provide additional evidence that BCAC are premalignant lesions in colon carcinogenesis in rodents.     

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.     

Induction of apoptosis by sulindac in azoxymethane-induced possible colonic premalignant lesions in rats.

We have reported that beta-catenin-accumulated crypts (BCAC), which do not have the appearance of aberrant crypt foci (ACF) are possible colonic premalignant lesions in rats. Suppression of the occurrence and advancement of such lesions should have critical relevance to cancer prevention. This study examined whether sulindac, a chemopreventive nonsteroidal anti-inflammatory drug is able to induce apoptosis in such premalignant lesions. At 6 weeks of age, rats groups 1 - 3 were given azoxymethane (AOM) (15 mg/kg-body weight) once weekly for 3 weeks. Two groups were given sulindac in the diet (200 and 400 ppm), starting at 9 weeks of age. The rats were sacrificed at the termination, and the colons were carefully examined. The incidence and crypt multiplicity of BCAC and ACF were significantly less than those of the control group. The effect of sulindac on the expression of BCAC was greater than that on ACF. Exposure to sulindac significantly increased the apoptotic index (terminal deoxynucleotide transferase dUTP nick-end labeling (TUNEL)-positive cells) in BCAC. However, no significant increase of the index was found in the case of ACF. These results suggest that the chemopreventive effect of sulindac in rats is related to the induction of apoptosis in premalignant lesions. Our results also provide additional evidence that BCAC are premalignant lesions in colon carcinogenesis in rodents.     

Modifying effect of tuna orbital oil rich in docosahexaenoic acid and vitamin D3 on azoxymethane-induced colonic aberrant crypt foci in rats

The modifying effect of dietary tuna (Thunnus thynnus orientalis) orbital oil rich in docosahexaenoic acid (DHA) and vitamin D3 (VD3) on the development of azoxymethane (AOM)-induced colonic aberrant crypt foci (ACF) was investigated in male F344 rats. Animals were given three weekly subcutaneous injections of AOM (15 mg/kg body weight) to induce ACF. The rats were fed the experimental diet containing 5% tuna orbital oil (low fish oil), 23.5% tuna orbital oil (high fish oil), 5% corn oil (low corn oil) or 23.5% corn oil (high corn oil) for 5 weeks, starting 1 week before the first dose of AOM. Animals were sacrificed 2 weeks after the last AOM injection to count colonic ACF and assay the expression of cyclooxygenase (COX)-1 and -2. High corn oil diet significantly increased the development of ACF, when compared with low corn oil diet (P<0.005). High fish oil diet also increased ACF formation compared with low fish oil diet (P<0.01), but the increase was smaller than high corn oil diet. The frequency of ACF was significantly lower in the rats fed high fish oil diet than high corn oil diet (P<0.02). Moreover, frequency of ACF consisted of 4 or more crypts in rats fed the high fish oil diet was significantly lower than that of rats given high corn oil diet. COX-1 and COX-2 expression did not significantly differ among the groups. These results suggest that fish oil derived from tuna, which contains high amounts of DHA and VD3, suppresses the formation and growth of ACF without affecting COX-1 and COX-2 expression, and may have a preventive effect on colon carcinogenesis.     

Formation of Early Lesions in 1,2-dimethylhydrazine-induced Colon Carcinogenesis in Rats

Aberrant crypt foci (ACF) are recognized as preneoplastic lesions for colon cancer, and ACF in rodents arewidely used as an intermediate biomarker to predict tumorigenicity in the colon. However, a lack of correlationsbetween the formation of ACF and the development of colonic tumors has been reported in several studies. Forexample, 2-(carboxyphenyl) retinamide (2-CPR) and genistein were reported to inhibit the carcinogen-inducedformation of ACF, whereas both of them were later found to enhance colon tumorigenesis in rats treated withazoxymethane (AOM). Recently, we have identified β-catenin-accumulated crypts (BCAC) in the colon of ratsshortly after administration of AOM, and provided evidence that these are independent early lesions of classicalACF, and BCAC might be direct precursors for colon cancers. In the present study, we performed a comparativeanalysis of the modifying effects of 2-CPR and genistein on 1,2-dimethylhydrazine (DMH)-induced BCAC andACF in male F344 rats. Dietary administration of 2-CPR (315 ppm) significantly reduced the total number,multiplicity and size of ACF in DMH-exposed colonic mucosa, while genistein (250 ppm) had no significant effectson DMH-induced ACF formation. In contrast, both of 2-CPR and genistein significantly enhanced the multiplicityand size of DMH-induced BCAC when compared with DMH alone group. In addition, both 2-CPR and genisteinsignificantly increased the proliferating cell nuclear antigen (PCNA) index preferentially in BCAC. Togetherwith previous findings that 2-CPR and genistein are tumor promoters in the colon, our results support the conceptthat BCAC are precursors of colon tumors and suggest that these lesions are more reliable short-term biomarkersfor colon carcinogenesis in rodents than ACF.     

Regressive Effects of Various Chemopreventive Agents on Azoxymethane-induced Aberrant Crypt Foci in the Rat Colon

Regressive effects of four chemopreventive agents [5-hydroxy-4-(2-phenyl-( E )-ethenyl)-2(5 H fura-none (KYN-54), S-methyl metbanethiosulfonate (MMTS), chlorogenic acid (CA), and piroxicam] on azoxymethane (AOM)-induced aberrant crypt foci (ACF) in the colon of male F344 rats were examined by dietary exposure. At six weeks of age, 60 rats of groups 1 through 5 received subcutaneous injections of AOM (15 mg/kg body weight) once a week for three weeks. Twelve weeks after the first carcinogen injection, wben the occurrence of ACF was maximal, the rats in groups 2 through 5 were started on diet containing the test chemicals as follows: group 2, KYN-54 (0.02%); group 3, MMTS (0.01%); group 4, CA (0.025%); and group 5, piroxicam (0.0125%). Group 1 (20 rats) was kept on the basal diet alone, and group 6 (12 rate) served as an untreated control. Rats in each group were killed at 6, 12, 18, or 24 weeks after the start of the experiment, and the yield of ACF in the colon of each group at 18 or 24 weeks was compared with that at 12 weeks. The number of ACF per rat colon of each group at 18 or 24 weeks was smaller than that at 12 weeks. The reduction rates at 18 weeks were 7% in group 1 (AOM alone), 11% in group 2 (AOM+KYN-54), 10% in group 3 (AOM+MMTS), 51% in group 4 (AOM + CA) ( P 0.01), and 33% in group 5 (AOM+piroxicam) ( P <0.02), while at 24 weeks they were 12%, 26%, 51% ( P <0.002), 43% ( P <0.05), and 70% ( P <0.001), respectively. These results indicate that chemopreventive agents for large bowel carcinogenesis, i.e., KYN-54, MMTS, CA, and piroxicam, are not only able to prevent the development of ACF, but also can regress ACF, which are regarded as precursor lesions of colorectal cancer.     

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.      

Azoxymethane-induced beta-catenin-accumulated crypts in colonic mucosa of rodents as an intermediate biomarker for colon carcinogenesis

It is now well established that bile acids act as colon tumor promoters. However, a previous study provided conflicting data showing that dietary exposure of cholic acid (CHA), a primary bile acid, inhibits the carcinogen-induced formation of aberrant crypt foci (ACF), possible preneoplastic lesions, in colonic mucosa of rodents. Recently we found beta-catenin-accumulated crypts (BCAC) in colonic mucosa of rats initiated with azoxymethane (AOM) and provided evidence that BCAC might be preneoplastic lesions independent from ACF. In the present study, we investigated the modifying effects of dietary CHA on the formation of BCAC as well as ACF in male F344 rats after exposure to AOM to determine if the differences in the effect of CHA on these lesions could account for this discrepancy. The results indicate that administration of CHA (0.5%) in the diet during the post-initiation phase significantly reduced the total number, multiplicity and size of ACF (P < 0.00001) in AOM-exposed colonic mucosa as reported previously. The number of ACF even with >4 aberrant crypts/focus was also decreased significantly (P < 0.0002), suggesting that the large ACF are little resistant to continuous feeding of 0.5% CHA diet. Interestingly, the dietary CHA significantly enhanced both the multiplicity (P < 0.002) and size (P < 0.00001), but not the incidence, of AOM-induced BCAC when compared with the control diet group. Importantly, the number of large BCAC with >6 crypts/lesion was increased significantly by the dietary CHA (P < 0.003). Our results support the concept that BCAC are precursors of colon tumors and indicate the usefulness of BCAC as intermediate biomarkers for colon carcinogenesis, although the methodology for their detection requires further improvement.     

Inhibition by dietary benzylselenocyanate of hepatocarcinogenesis induced by azoxymethane in Fischer 344 rats

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 semipurified 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.     

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.     

Chemoprevention of azoxymethane-induced rat colon carcinogenesis by dietary capsaicin and rotenone

The modifying effects of dietary administration of capsaicin, which is the principal pungent capsicum fruit, and rotenone, which is a naturally occurring pesticide derived from Derris and Lonchorcarpus species, on azoxymethane (AOM)-induced colon tumorigenesis were investigated in male F344 rats. Gavage with capsaicin and rotenone significantly elevated phase II enzymes, glutathione S-transferase (GST) and quinone reductase (QR), in the liver and colon. In an aberrant crypt foci (ACF) bioassay, feeding of capsaicin and rotenone at a dose of 500 ppm for 4 weeks significantly inhibited ACF formation induced by AOM (20 mg/kg body weight, once a week for 2 weeks). In a subsequent long-term study designed to confirm the protective effects of both compounds on ACF development, one group was treated with AOM alone and four other groups received the carcinogen treatment plus diets containing 500 ppm test compounds for 4 weeks (initiation phase) and for 34 weeks (post-initiation phase). Two groups were treated with capsaicin or rotenone alone (500 ppm in diet) and one group was maintained on the basal diet. At the termination of the study, dietary exposure of capsaicin during the initiation phase was found to significantly reduce the incidence of colonic adenocarcinoma (60% vs. 24%, 60% reduction, P=0.0407). Rotenone feeding during the post-initiation phase also reduced the frequency of colonic adenocarcinoma (60% vs. 19%, 68% reduction, P=0.0226). Our results suggest that two natural compounds, capsaicin and rotenone, might be useful for the prevention of human colon cancers.     

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.     

Prevention by long-term fermented miso of induction of colonic aberrant crypt foci by azoxymethane in F344 rats.

The present study was designed to investigate the effects of fermented miso in the diet on the induction of aberrant crypt foci (ACF) by azoxymethane (AOM) in male F344 rats. A total of 50 rats, 8 weeks of age, were divided into 5 groups and given weekly subcutaneous injections of AOM (15 mg/kg body wt) for 3 weeks. Rats were fed a normal control MF solid diet, or solid diet containing 10% long-term fermented (aged), medium- or short-term fermented miso, or 2.2% NaCl for 5 weeks, starting one week before the first AOM dosing. It was found that, compared to the control (MF) diet, the long-term fermented diet significantly decreased (by 22.2%) ACF/colon, but increased (by 18.2%) the number of aberrant crypts (Acs)/focus. The latter was also increased by the medium-term fermented diet (by 25.3%). The PCNA labeling index was only affected by the short-term fermented diet (36.9% increase) and by 2.2% NaCl diet (27.2% increased). The present results indicate that aged or completely fermented miso supplemented into the diet, could act as a chemopreventive agent for colon carcinogenesis.     

A rapid dual organ rat carcinogenesis bioassay for evaluating the chemoprevention of breast and colon cancer

In this study we evaluated the effect of dietary administration of a high fat, low fiber diet (HRD) with or without 2% phytic acid (PA) on the development of mammary cancer and/or colon cancer in rats exposed to methylnitrosourea (MNU), azoxymethane (AOM) or MNU + AOM. The rats were fed a HRD alone or a HRD + 2% PA. At the end of week 2, the rats were given either a s.c. injection of MNU (50 mg/kg body wt) or one of normal saline (vehicle). At the end of weeks 3 and 4, the rats were given either a s.c. injection of AOM (15 mg/kg body wt per week) or one of normal saline (vehicle). Nine weeks after the injection of MNU or saline, 10 rats from each group were sacrificed and the mammary tumor incidence and the number of colonic aberrant crypt foci (ACF) were compared between different groups. The administration of different diets was continued for an additional 21 weeks and the mammary tumor and colon tumor incidence between different groups were compared. Results showed that rats injected with MNU alone did not develop ACF or colon tumors while those injected with AOM alone did not develop mammary tumors. Linear regression analysis of the number of ACF at 11 weeks versus colonic tumor incidence at 32 weeks, and the linear regression analysis of mammary tumor incidence at 11 weeks versus mammary tumor incidence at 32 weeks, both showed good linear correlation. These results demonstrate the potential value of the short term dual organ carcinogenesis bioassay for screening chemopreventive agents for their relative ability to inhibit the development of mammary cancer and/or colon cancer while on high risk diet.     

A water-soluble extract from cultured medium of Ganoderma lucidum (Rei-shi) mycelia suppresses azoxymethane-induction of colon cancers in male F344 rats

The present study was designed to investigate the protective effect of a dietary water-soluble extract from cultured medium of Ganoderma lucidum (Rei-shi or Mannentake) mycelia (designated as MAK) on the induction and development of azoxymethane (AOM)-induced colon tumors in male F344/Du Crj rats. A total of 80 animals were divided into five groups at six weeks of age, groups 2, 3 and 4 being given weekly subcutaneous injections of AOM (15 mg/kg body weight) for the initial 3 weeks to induce colon tumors. Rats in group 1 and 5 were injected with the vehicle, 0.9% (w/v) saline, following the same schedule. Rats in groups 1, 2, 3, 4 and 5 were fed MF, MF, 1.25% MAK, 2.5% MAK and 2.5% MAK diets, respectively, starting 1 week before AOM treatment and throughout the six-month experimental period. There were no significant differences in number of ACF, total AC and AC per site among groups 2 to 4, but the tumor incidence was significantly lower, and tumor size was smaller in group 4 (AOM + 2.5% MAK) than in group 2 (AOM + MF). Additionally, beta-catenin positive tumor cell nuclei were significantly decreased in the MAK-fed rats (groups 3 and 4), which also demonstrated lowering of the PCNA labeling index and a shortened germinal region in the colon. The present results thus indicate that dietary MAK could act as a potent chemopreventive agent for colon carcinogenesis.