Trivalent Chromium has no Effect on Delaying Azoxymethane-Induced Colorectal Cancer in FVB/NJ Mice

As Cr(III) compounds have been shown to increase insulin sensitivity and decrease plasma cholesterol and triglycerides in rodent models of diabetes and insulin resistance and as colorectal cancer risk has been associated with insulin resistance and diabetes, the effects of the Cr(III) compound Cr3 ([Cr3O(O2CCH2CH3)6(H2O)3](+)) were investigated in male and female FVB/NJ mice with azoxymethane-induced colorectal cancer. In contrast to a previous study on the effects of Cr3 on 1,2-dimethylhydrazine-induced colorectal cancer in Sprague Dawley rats, no effects of Cr3 at daily doses of 1 and 10 mg Cr/kg body mass were observed, leaving in question whether administration of Cr(III) compounds can delay or prevent the onset of colorectal cancer.

Mixed tocopherols inhibit azoxymethane-induced aberrant crypt foci in rats

Gamma (gamma) tocopherol, but not alpha (alpha) tocopherol (vitamin E), has previously been reported as an effective inhibitor of cyclooxygenase (COX) enzyme activity. In a pilot study of 17 rats, mixed tocopherols containing more than 50% gamma-tocopherol, added at 0.1% to an AIN-76A diet, produced a significant inhibition (about 55%) of azoxymethane-induced aberrant crypt foci in the colon of rats. Mixed tocopherols also reduced tetradecanoyl phorbol acetate-induced ear inflammation in mice when topically applied.

Epidermal growth factor receptor signaling is required for microadenoma formation in the mouse azoxymethane model of colonic carcinogenesis

Colonic carcinogenesis involves the progressive dysregulation of homeostatic mechanisms that control growth. The epidermal growth factor (EGF) receptor (EGFR) regulates colonocyte growth and differentiation and is overexpressed in many human colon cancers. A requirement for EGFR in colonic premalignancy, however, has not been shown. In the current study, we used a specific EGFR antagonist, gefitinib, to investigate this role of the receptor in azoxymethane colonic premalignancy. The azoxymethane model shares many clinical, histologic, and molecular features of human colon cancer. Mice received azoxymethane i.p. (5 mg/kg/wk) or saline for 6 weeks. Animals were also gavaged with gefitinib (10 mg/kg body weight) or vehicle (DMSO) thrice weekly for 18 weeks, a dose schedule that inhibited normal receptor activation by exogenous EGF. Compared with control colonocytes [bromodeoxyuridine (BrdUrd), 2.2+/-1.2%], azoxymethane significantly increased proliferation (BrdUrd, 12.6+/-2.8%), whereas gefitinib inhibited this hyperproliferation (BrdUrd, 6.2+/-4.0%; <0.005). Azoxymethane significantly induced pro-transforming growth factor-alpha (6.4+/-1.3-fold) and increased phospho-(active) EGFR (5.9+/-1.1-fold), phospho-(active) ErbB2 (2.3+/-0.2-fold), and phospho-(active) extracellular signal-regulated kinase (3.3+/-0.4-fold) in premalignant colonocytes. Gefitinib inhibited activations of these kinases by >75% (P<0.05). Gefitinib also significantly reduced the number of large aberrant crypt foci and decreased the incidence of colonic microadenomas from 75% to 33% (P<0.05). Gefitinib concomitantly decreased cell cycle-regulating cyclin D1 and prostanoid biosynthetic enzyme cyclooxygenase-2 in microadenomas, suggesting that these regulators are key targets of EGFR in colonic carcinogenesis. These results show for the first time that EGFR signaling is required for early stages of colonic carcinogenesis. Our findings suggest, moreover, that inhibitors of EGFR might be useful in chemopreventive strategies in individuals at increased risk for colonic malignancies.

Selenised casein protects against AOM-induced colon tumors in Sprague Dawley rats

Selenium (Se) has been shown to be protective against cancers in animal models at concentrations exceeding those considered essential for normal nutritional requirements. Organic forms of Se provided as dairy proteins were obtained from cows fed diets supplemented with yeast Se. The casein extracted from milk was found to contain approximately half the Se of the Se-enriched milk. This casein was included in a semi-purified AIN rodent diet so as to provide 1 ppm Se and 25% protein and was compared with AIN diets containing no added Se (control, 0.05 ppm), 1 ppm and 4 ppm Se as selenised yeast (Sel-Plex) Their influence on colon tumor expression was examined in rats induced with azoxymethane, the diets being introduced post-induction. The selenised casein diet at this concentration was effective in reducing colon tumor incidence (by 29%) and burden (decreased 52%, P < 0.05) relative to the control in rats 26 wk post-induction. Selenised yeast, when added at similar (1 ppm) and increased Se concentration (4 ppm), did not influence significantly colon tumor expression. However, in a second study, with Se yeast providing Se at 1 ppm, 4 ppm, and 8 ppm throughout the experiment, a significant reduction in tumors was observed with 8 ppm Se (colon tumor incidence was 15% lower and colon tumor burden was 35% lower, P < 0.05). However this was associated with a significantly lower body weight in the rats (down 10.5%, P < 0.05) indicating a possible disturbance with normal energy intake or metabolism. The form in which Se is presented in the diet may influence significantly its bioavailability and/or anticancer potential at given concentrations within a safe range. The efficacy of selenised casein and indeed other potential dietary sources deserve further investigation with regard to their ability to prevent colon tumors at concentrations considered safe in the diet.

Inhibitory effects of Centella asiatica on azoxymethane-induced aberrant crypt focus formation and carcinogenesis in the intestines of F344 rats

Effects of the water extract of Centella asiatica Linn. on formation of azoxymethane (AOM)-induced aberrant crypt foci (ACF) and intestinal tumorigenesis in male F344 rats were investigated. Treatment with the extract significantly decreased the number of larger ACF (with four or more crypts per focus) in the large intestine in the early stage, while the number of methylated DNA adducts was not decreased compared with that in the AOM-treated group. In the post-initiation stage, the extract significantly decreased the total number of ACF and the number of larger ACF, accompanied by a decrease in the 5-bromo-2'-deoxyuridine-labeling index and an increase in the induction of apoptotic cells in the colonic mucosa. The incidences of neoplasms, the numbers of adenocarcinomas in the small intestines and entire intestines, and sizes of neoplasms in the entire intestines in rats fed C. asiatica extract at a dose of 10 mg/kg were smaller than those in rats given AOM alone (p < 0.05). The extract at a dose of 100 mg/kg significantly reduced the multiplicity of neoplasms in the small intestine (p < 0.05). These results suggest that inhibition of the formation of AOM-induced ACF by C. asiatica extract is associated with modification of cell proliferation and induction of apoptosis in colonic crypts and that the extract has a chemopreventive effect on colon tumorigenesis.

Effects of adlay on azoxymethane-induced colon carcinogenesis in rats

Adlay (Coix lachryma-jobi L. var. ma-yuen Stapf) is a grass crop used in traditional Chinese medicine and as a nutritious food. It has been reported that adlay has anti-inflammatory and anti-tumor activity. Cyclooxygenase-2 (COX-2) is an inducible enzyme functionally related to both inflammation and colon carcinogenesis and is the target of many chemopreventive agents. This study investigated the effect of adlay on colon carcinogenesis and COX-2 expression. In a short-term experiment, male F344 rats were fed diets containing different doses of dehulled adlay and received the colon-specific carcinogen, azoxymethane (AOM), by intraperitoneal injection. All rats were killed after 5 weeks of feeding, and the colons were examined for the preneoplastic lesion, aberrant crypt foci (ACF). Dietary dehulled adlay at levels of 10%, 20%, or 40% significantly reduced the numbers of ACF and aberrant crypts. Dehulled adlay reduced the number of ACF of different sizes but did not affect the crypt multiplicity. Most ACF were found in the middle and distal colons; dehulled adlay significantly suppressed the formation of ACF in the middle colon. In a long-term experiment, male F344 rats were fed diets containing different doses of dehulled adlay and injected with AOM. All rats were killed after 52 weeks of feeding, and colons were examined for tumors and COX-2 protein expression. The results indicated that dehulled adlay did not inhibit colon tumors in spite of a slight suppressing effect in the proximal colon. Rats fed diets containing 20% dehulled adlay had less COX-2 protein expression in both proximal and distal colon tumors. The inconsistent effects between COX-2 protein expression and tumor outcome may be due to regional differences in the colon and the malignancy of the tumors. These findings suggest that dehulled adlay suppresses early events in colon carcinogenesis but not the formation of tumors.

Fructooligosaccharide associated with celecoxib reduces the number of aberrant crypt foci in the colon of rats

According to Burkitt's hypothesis, dietary fibres may protect against the development of colorectal cancer. In rats, studies have shown that only butyrate-producing fibres are protective. In parallel, in humans, non-steroidal anti-inflammatory drugs, which target cyclooxygenases, have been shown to display a protective effect against colorectal cancer. Among them, COX-2-selective inhibitors which present less side effects than non-selective agents, are promising as chemopreventive agents. Our aim was to analyse the effect of an association between butyrate-producing fibres and the COX-2 inhibitor on the development of aberrant crypt foci (ACF) in rats. Fisher F344 rats were fed with (1) a standard low fibre control diet; (2) the standard diet supplemented with 1500 ppm celecoxib; (3) a diet supplemented with 6% fructo-oligosaccharide (FOS); and (4) a diet with both celecoxib and FOS. Three weeks later, the rats were injected twice with azoxymethane and the number of ACF was determined 15 weeks later. In the control group, 43.8 +/- 6.4 ACF were found. This number was not significantly modified by the addition of FOS or celecoxib alone to the diet. However, the association of FOS and celecoxib resulted in a 61% reduction in the number of ACF (P < 0.01). The number of aberrant crypt per foci was also reduced. Thus, although no significant effect of celecoxib or FOS alone was identified, the association of butyrate-producing fibre and celecoxib was effective in preventing the development of ACF. This preliminary study argues for a strong protective effect of such an association which deserves further studies.

Effects of high fat fish oil and high fat corn oil diets on initiation of AOM-induced colonic aberrant crypt foci in male F344 rats

Modulating effects of high fat fish oil (HFFO) and high fat corn oil (HFCO) diets on azoxymethane (AOM)-induced colonic aberrant crypt foci (ACF) were studied in male F344 rats following 8 weeks of dietary treatment. The incidence of AOM-induced ACF was significantly lower in the proximal colon of rats fed the HFFO diets compared with rats fed the HFCO diets. No differential effects were found on enzyme activities that are involved in metabolic activation and detoxification of AOM. Activities of hepatic P450 IAI and P450 IIBI and hepatic and feacal levels of lipid peroxidation were increased by feeding the HFFO diet. Hepatic GST activity and plasma levels of PGE(2) were significantly lower in rats fed the HFFO diets compared with those fed the HFCO diets. These observations demonstrate that HFFO diets with high levels of n-3 PUFAs are also protective against preneoplastic lesions in the early stages of chemically induced colon carcinogenesis. It seems unlikely from our results that the inhibitory effect of a HFFO diet can be attributed to an altered metabolic activation and detoxification of AOM. Other mechanisms such as oxidative stress or reduction of PGE(2) levels may play an important role in the anticarcinogenic effects of n-3 PUFAs.

Inhibition of azoxymethane-induced DNA adduct formation by Aloe arborescens var. natalensis

To clarify the possible mechanisms of inhibition of azoxymethane (AOM)-induced aberrant crypt foci (ACF) in the rat colorectum by freeze-dried whole leaves of Aloe arborescens var. natalensis (Kidachi aloe) (hereinafter referred to as ALOE) and commercial crude aloin (Sigma A-0451; from Curacao aloe) (hereinafter ALOIN), we studied the effects of ALOE and ALOIN on the formation of AOM-induced DNA adducts (O6-methylguanine; O6-MeG) in rats. Male F344 rats (4 weeks old) were fed a basal diet, or experimental diets containing 5%ALOE or 0.25%ALOIN for 5 weeks. All rats were injected s.c. twice with 15 mg/kg AOM, once at the end of week 1, and once at the end of week 2. The animals were sacrificed 6 hours after the second injection to analyze DNA adducts (O6-MeG) in the colorectum. Dietary administration of ALOE significantly inhibited the O6-MeG levels (50% reduction) compared with controls, whereas the O6-MeG levels in the ALOIN-fed rats showed a tendency to decrease (by 30%), although not significantly. In this study, we also measured the enzyme activity and mRNA level of cytochrome (CYP) 2E1, known to be responsible for the activation of AOM, in rat liver. ALOE-fed rats showed significantly reduced CYP2E1 enzymatic activity (27% reduction) compared with controls. On the other hand, the activity in ALOIN-fed rats tended to decrease by 11%, although not significantly. The CYP2E1 mRNA levels in ALOE- and ALOIN-fed rats were slightly reduced (9.7% and 5.2%, respectively). These results may explain, at least in part, the previously observed inhibitory effects of ALOE and ALOIN, especially ALOE on AOM-induced ACF formation in the rat colorectum.

Antimutagenicity of Murdannia loriformis in the Salmonella mutation assay and its inhibitory effects on azoxymethane-induced DNA methylation and aberrant crypt focus formation in male F344 rats

An 80% ethanol extract of Murdannia loriformis, a Thai medicinal plant, was examined for antimutagenic activity and cancer chemopreventive activity. In the Salmonella mutation assay, the extract showed antimutagenicity against 2-amino-3-methylimidazo [4,5-f]quinoline, 2-amino-3,4-dimethylimidazo[4,5-f]quinoline, 2-amino-3,8-dimethylimidazo [4,5-f]quinoxaline, 2-amino-1-methyl-6-phenylimidazo[4,5-b]pyridine, 2-amino-1,4-dimethyl-5H-pyrido[4,3-b]indole, 3-amino-1-methyl-5H-pyrido[4,3-b]indole, 2-amino-6-methyldipyrido [1,2-a:3',2'-d] imidazole, 2-aminodipyrido[1,2-a:3',2'-d]imidazole, 2-aminoanthracene, 2-(2-furyl)-3-(5-nitro-2-furyl) acrylamide, N-methyl-N'-nitro-N-nitrosoguanidine and methylazoxymethanol acetate and reduced their mutagenicities to 31.4-67.9% at the dose of 10 mg/plate. However, it did not inhibit the mutagenicities of 2-amino-9H-pyrido[2,3-b]indole, 2-amino-3-methyl-9 H-pyrido[2,3-b]indole, benzo[a]pyrene,N-ethyl-N'-nitro-N-nitrosoguanidine and 1-nitropyrene. The extract itself showed no mutagenicity. The chemopreventive activity of M. loriformis was examined using azoxymethane (AOM)-induced aberrant crypt focus (ACF) formation in the colon of F344 rats. The extract at doses of 0.1-1.0 g/kg wt significantly inhibited ACF formation in the initiation stage (21-51%), although it was more effective at a lower dose. In the post-initiation stage, the extract also tended to inhibit ACF formation (12-27%) and significantly decreased the number of larger ACFs that have more than 3 aberrant crypts per focus. The extract inhibited the formation of O6-methylguanine and N7-methylguanine in the colonic mucosa and muscular layers but not or increased in the liver. These results indicate that M. loriformis extract has antimutagenic activity toward various known mutagens and that it inhibits AOM-induced ACF formation both in the initiation and post-initiation stages in the rat colon.

Effect of ursodeoxycholic acid on azoxymethane-induced aberrant crypt foci formation in rat colon: in vitro potential role of intracellular Ca2+

The studies were conducted to examine the precise nature of the suppressive effect of ursodeoxycholic acid (UDCA) on colonic aberrant crypt foci (ACF) formation. Fischer 344 rats were treated with a single dose of azoxymethane (AOM) (20 mg/kg, s.c.) and fed basal diet (MF) supplemented with UDCA (0.4%) during an initiation or a post-initiation stage. ACF were enumerated at the 2nd, 5th and 8th weeks after AOM administration (15-18 rats/group). The number of ACF in the UDCA treated group was decreased significantly in the initiation and post-initiation stages at the 2nd (P < 0.01, P < 0.0001) and 8th weeks (P < 0.001, P < 0.0001), respectively, compared with untreated controls. In the time-course experiments, the effect of continuous feeding of UDCA (0.4%) on ACF formation was evaluated. ACF number was decreased significantly (P < 0.005) until the 16th week. UDCA showed a significant dose-dependent suppression of ACF number from a range of 0.1-0.4% UDCA. To approach the subcellular mechanisms of the effect of bile acids, the intracellular free Ca2+ concentration ([Ca2+]i) of bile acid-treated rat colonic cancer cells (ACL-15) was examined. DCA and CDCA, which are promotive on ACF formation, induced a rapid increase in [Ca2+]i, while UDCA and CA, which are suppressive or non-effective on ACF formation, did not. These findings suggest that the promotive effect of bile acids may involve intracellular Ca2+ signaling.

Evaluation of a selective prostaglandin E receptor EP1 antagonist for potential properties in colon carcinogenesis

BACKGROUND

Cyclooxygenases (COXs) and prostanoids play pivotal roles in colon carcinogenesis. This study was designed to determine the chemopreventive effects of ONO-8711, a selective prostaglandin E receptor EP1 antagonist, on the development of azoxymethane (AOM)-induced colonic aberrant crypt foci (ACF) in male F344 rats and to compare its potential with that of nimesulide, a well-documented selective COX-2 inhibitor.

MATERIALS AND METHODS

Five-week-old male F344 rats received s.c. injections of AOM (15 mg/kg body weight) or the saline vehicle once weekly for two weeks and were fed the control diet (AIN-76A) or the experimental diets containing 400 or 800 ppm of ONO-8711 or 400 ppm nimesulide for 5 weeks.

RESULTS

Administration of ONO-8711 at 800 ppm significantly reduced the total number of ACF/colon and 5-bromodeoxyuridine (BrdUrd) labeling index as compared to the control diet group (by 31% and 66%, respectively). As expected, dietary administration of nimesulide also suppressed the development of ACF and BrdUrd labeling index in the colon, by about 39% and 54%, respectively.

CONCLUSION

Our finding that ONO-8711 significantly suppresses colonic ACF formation and cell proliferation strengthens the hypothesis that the selective prostaglandin E receptor EP1 antagonists possesses chemopreventive activity against colon cancer development.

Prevention of azoxymethane-induced intestinal tumors by a crude ethyl acetate-extract and tryptanthrin extracted from Polygonum tinctorium Lour

The effect of a crude ethyl acetate (AcOEt)-extract and tryptanthrin extracted from the Indigo plant (Polygonum tinctorium Lour.) on azoxymethane (AOM)-induced intestinal tumors was examined in F344 rats. The rats were given subcutaneous (s.c.) injections of either AOM (15 mg/kg body weight (b.w.)) once a week for 3 weeks to induce atypical crypt foci (ACF) as a known cancer precursor, or AOM (7.5 mg/kg b.w.) once a week for 10 weeks to induce intestinal tumors. The rats were also administered the AcOEt-extract (500 mg/kg b.w.) or tryptanthrin (50 mg/kg b.w.) orally, 5 days a week, for 7 or 30 weeks, starting two days before the first administration of AOM. All rats were killed 4 or 20 weeks after the last treatment. In the short-term experiment, the incidence of ACE and atypical crypts (AC) in the groups receiving the AcOEt-extract and tryptanthrin was significantly lower than in the control group. In the tumor-inducing experiment, intestinal tumor incidence in the tryptanthrin group was lower than in the AOM-control group (5% versus 26%), and small intestine tumor incidence in the AcOEt-extract and tryptanthrin groups were lower than in the AOM-control group (0% and 0% versus 23%). These results show that the AcOEt-extract of Indigo and tryptanthrin have cancer chemopreventive activity.

Chemoprevention of colon cancer by a glutathione conjugate of 1,4-phenylenebis(methylene)selenocyanate, a novel organoselenium compound with low toxicity

We have consistently shown that several synthetic Organoselenium compounds are superior cancer chemopreventive agents and less toxic than selenite or certain naturally occurring selenoamino acids. 1,4-Phenylenebis(methylene)selenocyanate (p-XSC) is the lead Organoselenium compound in that it has been shown to be the most effective and the least toxic agent in several experimental cancer models. It is not known whether p-XSC or one of its metabolites is responsible for its chemopreventive efficacy. As an initial step, we synthesized one of its putative metabolites, i.e., the glutathione conjugate of p-XSC (p-XSe-SG), and determined its stability in the pH range from 2 to 8 and in the diet under normal feeding conditions. We also assessed its maximum tolerated dose and examined its chemopreventive efficacy against azoxymethane (AOM)-induced colon carcinogenesis in male F344 rats. p-XSe-SG proved to be very stable over the pH range tested. The maximum tolerated dose of p-XSe-SG determined in a 6-week subchronic toxicity study was found to be >210 ppm (>40 ppm selenium) when the compound was added to AIN-76A high-fat diet. To assess the efficacy of this agent in the postinitiation period of colon carcinogenesis, male F344 rats 6 weeks of age were fed the high-fat diet, and at beginning of weeks 7 and 8, all of the rats intended for carcinogen treatment were given AOM at a dose of 15 mg/kg body weight by s.c. injection. Two days after the carcinogen treatment, the groups of rats consuming the high-fat control diet began their respective high-fat experimental diet regimens with 0, 56, or 84 ppm p-XSe-SG (0.1, 10, and 15 ppm of selenium) supplementation. All animals continued on their respective diets for 38 weeks after the AOM-treatment and were then killed. Colon tumors were evaluated histologically using routine procedures and were also analyzed for cyclooxygenase (COX)-1 and COX-2 expression and enzymatic activities. The results indicate that p-XSeSG administered during the post-initiation stage significantly inhibited both the incidence (P < 0.05-0.01) and the multiplicity (P < 0.05-0.005) of AOM-induced colon adenocarcinomas. This agent also greatly suppressed the multiplicity (P < 0.01-0.001) of AOM-induced exophytic adenocarcinomas in a dose-dependent manner. Feeding of 56 or 84 ppm p-XSe-SG in the diet significantly suppressed total COX activity (P < 0.02 to -0.01) and COX-2 specific activity (P < 0.005-0.0005) but had minimal effect on the protein expression levels of COX-1 and COX-2. These results suggest that the newly developed synthetic Organoselenium compound, p-XSe-SG, is stable in the diet and at wide pH ranges, inhibits colon carcinogenesis when administered during the postinitiation stage, and inhibits COX activity. Compared with previous efficacy studies and considering the toxicity associated with selenium, p-XSe-SG seems to be the least toxic Organoselenium chemopreventive agent thus far tested in the experimental colon carcinogenesis. Studies are in progress to delineate whether p-XSe-SG is also effective when administered during the progression stage of colon carcinogenesis.

Troglitazone, a ligand for peroxisome proliferator-activated receptor gamma, inhibits chemically-induced aberrant crypt foci in rats

The biological roles of peroxisome proliferator-activated receptors (PPARs) in various diseases, including inflammation and cancer, have been highlighted recently. Although PPARgamma ligand is suspected to play an important role in carcinogenesis, its effects on colon tumorigenesis remain undetermined. The present time-course study was conducted to investigate possible modifying effects of a PPARgamma ligand, troglitazone, on the development and growth of aberrant crypt foci (ACF), putative precursor lesions for colon carcinoma, induced by azoxymethane (AOM) or dextran sodium sulfate (DSS) in male F344 rats. Oral troglitazone (10 or 30 mg / kg body weight (b.w.)) significantly reduced AOM (two weekly subcutaneous injections, 20 mg / kg b.w.)-induced ACF. Treatment with troglitazone increased apoptosis and decreased polyamine content and ornithine decarboxylase (ODC) activity in the colonic mucosa of rats treated with AOM. Gastric gavage of troglitazone also inhibited colitis and ACF induced by DSS (1% in drinking water), in conjunction with increased apoptosis and reduced colonic mucosal polyamine level and ODC activity. Our results suggest that troglitazone, a synthetic PPARgamma ligand, can inhibit the early stage of colon tumorigenesis with or without colitis.

Soybean resistant proteins interrupt an enterohepatic circulation of bile acids and suppress liver tumorigenesis induced by azoxymethane and dietary deoxycholate in rats

We found that azoxymethane and dietary deoxycholate induced liver tumors in rats. The incidence and the development of the tumor were closely related to the enterohepatic circulation of bile acids. The feeding of a high-molecular-weight fraction of soy protein digest (HMF) suppressed the tumorigenesis, probably due to the inhibitory effect of soybean resistant protein on reabsorption of bile acids in the intestine.

Ligands for peroxisome proliferator-activated receptors alpha and gamma inhibit chemically induced colitis and formation of aberrant crypt foci in rats

The biological role of the peroxisome proliferator-activated receptors (PPARs) in various diseases, including inflammation and cancer, has been highlighted recently. Although PPARgamma ligands have been found to inhibit mammary carcinogenesis in rodents, the effects on colon tumorigenesis are controversial. In the present study, three different experiments were conducted to investigate the modifying effects of PPARs ligands (PPARalpha and PPARgamma) on colitis and an early phase of colitis-related colon carcinogenesis in male F344 rats. In the first experiment, gastric gavage of troglitazone (PPARgamma ligand, 10 or 100 mg/kg body weight) or bezafibrate (PPARalpha ligand, 10 or 100 mg/kg body weight) inhibited colitis induced by dextran sodium sulfate (DSS) and lowered trefoil factor-2 content in colonic mucosa. In the second experiment, dietary administration (0.01 or 0.05% in diet) of troglitazone and bezafibrate for 4 weeks significantly reduced azoxymethane (AOM, two weekly s.c. injections, 20 mg/kg body weight)-induced formation of aberrant crypts foci, which are precursor lesions for colon carcinoma. In the third experiment, dietary administration (0.01% in diet for 6 weeks) of pioglitazone (PPARgamma ligand), troglitazone, and bezafibrate effectively suppressed DSS/AOM-induced ACF. Administration of both ligands significantly reduced cell proliferation activity in colonic mucosa exposed to DSS and AOM. Our results suggest that synthetic PPARs ligands (PPARalpha and PPARgamma) can inhibit the early stages of colon tumorigenesis with or without colitis.

Inhibition of azoxymethane-induced colon carcinogenesis in male F344 rats by the citrus limonoids obacunone and limonin

The modifying effects of dietary administration of the citrus limonoids obacunone and limonin on azoxymethane (AOM)-induced colon tumorigenesis were investigated in two experiments in male F344 rats. In a pilot study, we examined the modifying effects of obacunone and limonin on AOM-induced (20 mg/kg body wt, once a week for 2 weeks) formation of aberrant crypt foci (ACF). Dietary feeding of both compounds at dose levels of 200 and 500 p.p.m. during AOM exposure for 4 weeks ('initiation' feeding) or after AOM treatment for 4 weeks ('post-initiation' feeding) significantly inhibited ACF formation (55-65% reduction by 'initiation' feeding, P < 0.001; 28-42% reduction by 'post-initiation' feeding, P < 0.05-0.002). In a long-term study designed to confirm the protective effects of obacunone and limonin on ACF development, one group was treated with AOM alone and another four groups received the carcinogen treatment plus diets containing 500 p.p.m. test compounds for 3 weeks (initiation phase) or 29 weeks (post-initiation phase). Two groups were treated with obacunone or limonin alone (500 p.p.m. in diet) and one group was maintained on the basal diet. At the termination of the study, dietary exposure to obacunone or limonin during the initiation phase was found to have significantly reduced the incidence of colonic adenocarcinoma (72 versus 25 or 6%, P = 0.004 or 0.00003). Obacunone or limonin feeding during the post-initiation phase also reduced the frequency of colonic adenocarcinoma (72 versus 13%, P = 0.0002). Our results suggest that the citrus limonoids obacunone and limonin might be useful for the prevention of human colon cancers.

The effect of an oral administration of Lactobacillus casei strain shirota on azoxymethane-induced colonic aberrant crypt foci and colon cancer in the rat

The preventive effect of oral administration of viable Lactobacillus casei strain Shirota (LcS) on azoxymethane (AOM)-induced colonic aberrant crypt foci (ACF) and colon cancers in the rat was investigated. The study consisted of two experiments; in a short-term experiment (Exp-I), the inhibitory effect of 8- and 12-week treatments with LcS. Forty rats each received weekly a subcutaneous injection of AOM at a dose of 15 mg/kg of body weight for 5 weeks. Eight and twelve weeks after the start of the carcinogen treatment, each subgroup of rats were sacrificed, and the colon and the mesenteric lymph nodes (MLN) were removed. The number of ACFs and the surface marker of lymphocytes derived from the MLN were investigated. The large ACF (those comprising four or more aberrant crypts per focus) had significantly decreased in the rats which had consumed the LcS diet. And oral administration of viable LcS significantly recovered CD8 positive lymphocytes to the levels in the control group. In a long-term experiment (Exp-II), 30 rats each received weekly a subcutaneous injection of AOM at a dose of 7. 4 mg/kg of body weight for 10 weeks. Twenty-five weeks after the start of the carcinogen treatment, each subgroup of rats were sacrificed, and the colon were removed. The number and incidence of colon cancers were investigated. The number of rats with colon cancers and the number of colon cancers per rat, were significantly decreased in the rats which had consumed the LcS diet. LcS inhibited chemically-induced colon carcinogenesis in the rat. CD8 positive T lymphocytes may play a key role in the preventive effect against colon carcinogenesis.

Modifying effects of ferulic acid on azoxymethane-induced colon carcinogenesis in F344 rats

The modifying effects of dietary administration of ferulic acid (FA) on azoxymethane (AOM)-induced colon carcinogenesis were examined in three experiments with male 344 rats. In the first experiment, the modifying effect of FA on AOM (15 mg/kg body weight, once a week, for 3 weeks)-induced formation of aberrant crypt foci (ACF) was examined in five groups. Numbers of ACF/colon of groups 2 (AOM+250 ppm FA) and 3 (AOM+500 ppm FA) at the termination (5 weeks after the start) were smaller than of group 1 (AOM alone). Those of ACF/cm(2) of group 3 were also smaller than of group 1 (P<0.05). In the second experiment, a long-term assay for the effects of FA was conducted with seven groups. At the termination (35 weeks), groups 2 and 3 which were given FA during the initiation phase at doses of 250 and 500 ppm, respectively, had lower incidences of colonic carcinomas (23 and 27%, respectively) than group 1 which was given AOM alone (59%; P<0.05). In the third experiment, to determine whether FA could modify the activities of phase II detoxifying enzymes, glutathione S-transferase (GST) and quinone reductase (QR) in liver and colon, 60 rats were gavaged with FA at four doses (0, 25, 50, 100 mg/kg body weight). Dosing of 100 mg/kg significantly elevated GST activity in liver (P<0.03), and QR activities in liver and colonic mucosa (P<0.01 and P<0.02, respectively), suggesting that detoxifying enzymes are related to the blocking effect of FA on AOM-induced colon carcinogenesis.

Suppressive effect of the herbal medicine Oren-gedoku-to on cyclooxygenase-2 activity and azoxymethane-induced aberrant crypt foci development in rats

The present study is part of a program to obtain effective chemopreventive agents with low toxicity from medicinal herbs and traditional herbal medicines. We previously reported that Oren (Coptidis rhizoma) and Ogon (Scutellariae radix) inhibit azoxymethane (AOM)-induced aberrant crypt foci (ACF) formation. In the present investigation, we found Sanshishi (Gardeniae fructus) and the traditional herbal medicine Oren-gedoku-to (OGT), composed of Ogon, Oren, Sanshishi and Obaku, also have preventive potential. Sanshishi and OGT decreased the numbers of ACF to 25.2 and 59.4% of the control value at 2% in the diet, respectively. Adverse effects, evidenced by body weight loss, were weaker with OGT than component herbs. To investigate their mechanisms of action, the influence on cyclooxygenase-1 (COX-1) and cyclooxygenase-2 (COX-2) activities was studied. Both OGT and Sanshishi inhibited COX-2 but not COX-1, this presumably contributing to their suppressive effects on ACF development. The results suggest that OGT may be useful for colon cancer chemoprevention in terms of efficacy and toxicity.

Prevention by aspirin and its combination with alpha-difluoromethylornithine of azoxymethane-induced tumors, aberrant crypt foci and prostaglandin E2 levels in rat colon

The dose-response relationship in male F344 rats was determined for the ability of aspirin administered in the diet to prevent azoxymethane (AOM)-induced colon cancer and aberrant crypt foci (ACF) and to reduce prostaglandin E2 (PGE2) levels. Starting at either 7 or 22 weeks of age, the rats received aspirin. All rats received two doses of AOM (15 mg/kg each on days 7 and 14) and were killed on day 36. The lowest concentrations of aspirin to prevent ACF or reduce PGE2 levels were 600 and 400 mg/kg, respectively. To evaluate the prevention of tumors, rats received either 0 or 400 mg/kg aspirin for a total of 39 weeks with AOM (30 mg/kg) administered 7 days after the start of treatment. Aspirin had no effect on the yield of colon tumors. In a second experiment, rats started to receive 0, 200, 600 or 1800 mg/kg aspirin or 1000 mg/kg alpha-difluoromethylornithine (DFMO) +/- aspirin. Eight and 15 days later, all the rats received 15 mg/kg AOM. Eleven weeks later, animals that were receiving the control diet started to receive 0, 200, 600 or 1800 mg/kg aspirin; 1000 or 3000 mg/kg DFMO; or 1000 mg/kg DFMO + 200 or 600 mg/kg aspirin. The animals were killed 32 weeks later. DFMO effectively reduced the yield of colon tumors when administered starting either before or after AOM while aspirin was much weaker. The combination of aspirin + DFMO administered after AOM was synergistic. Both aspirin and DFMO decreased the Mitotic Index, while apoptosis was increased only by DFMO. Our results demonstrated that aspirin and DFMO could prevent colon cancer when administered after AOM. Furthermore, aspirin reduced ACF, PGE2 levels and mitosis at concentrations that did not prevent cancer. In contrast, the ability to enhance apoptosis did correlate with the prevention of cancer.

The chemopreventive role of ursodeoxycholic acid in azoxymethane-treated rats: suppressive effects on enhanced group II phospholipase A2 expression in colonic tissue

Great interest has been focused on the chemoprevention of colonic carcinogenesis by oral administration of ursodeoxycholic acid (UDCA) because its administration reportedly reduces the incidence of colon cancer in animal experiments. To elucidate the precise role of UDCA in the chemoprevention of azoxymethane-induced colon carcinogenesis, we examined the expression levels of group II phospholipase A2 in the colonic tissue of UDCA-treated and untreated rats and correlated the levels with the findings of aberrant crypt foci, putative preneoplastic lesions. Twelve weeks after azoxymethane exposure, the total number of aberrant crypt foci in 0.4% UDCA-fed rats and 1% UDCA-fed rats was significantly decreased compared to the untreated animals. The mucosal concentrations of PGE2 and 6-keto PGF1alpha were significantly lower in the UDCA-treated rats than in untreated rats. In correlation with lowering, the enhanced activity, protein mass and mRNA levels of group II phospholipase A2 were significantly attenuated in the UDCA-treated animals. The chemopreventive role of UDCA in colon carcinogenesis may lie in its modulation of the arachidonate metabolism in colonic mucosa.

Fish oil blocks azoxymethane-induced rat colon tumorigenesis by increasing cell differentiation and apoptosis rather than decreasing cell proliferation

The purpose of this study was to determine whether the protective effect of fish oil against colon carcinogenesis is due to decreased proliferation, increased differentiation and/or increased apoptosis. Male Sprague Dawley rats (n = 260) were fed one of two oils (corn or fish) and two fibers (pectin or cellulose), plus or minus the carcinogen azoxymethane (AOM). Rats were killed at wk 18 (n = 80) or 36 (n = 180) for cytokinetic measurements. In vivo cell proliferation was measured by incorporation of bromodeoxyuridine into DNA, differentiation by binding of Dolichos biflorus agglutinin and apoptosis by immunoperoxidase detection of digoxigenin labeled genomic DNA. Fish oil resulted in a lower adenocarcinoma incidence (56.1 vs. 70.3%) compared with corn oil. There was no effect of fat or fiber on number of proliferative cells/crypt column in either the proximal or distal colon. In contrast, fish oil resulted in a greater degree of differentiation compared with corn oil in both colonic sites. In addition, fish oil resulted in a higher number of apoptotic cells/crypt column in both the proximal and distal colon as compared with corn oil. AOM treatment increased the ratio of proliferative cells/crypt column to apoptotic cells/crypt column in both the proximal and distal colon compared with saline controls. Fish oil, however, resulted in a lower ratio in both sites in the colon as compared with corn oil. These results suggest that an increase in apoptosis and differentiation, rather than a decrease in proliferation, accounts for the protective effect of fish oil against experimentally induced colon tumorigenesis.

Dry beans inhibit azoxymethane-induced colon carcinogenesis in F344 rats

Epidemiological studies show a low incidence of colon cancer in many Latin American countries where the consumption of dry beans (e.g., pinto) is high. The purpose of this study was to use rats as an animal model to obtain experimental data on the inhibition of colon carcinogenesis by dry beans. Fifty-three 5-wk-old weanling male F344 rats were randomly assigned by weight to the following groups: control (11 rats), casein diet (21 rats), and bean diet (21 rats). Animals fed the casein and bean diets were treated with the carcinogen azoxymethane (AOM) once weekly for 2 wk. Rats in the control group also consumed the casein diet but were not exposed to AOM. All diets were isocaloric. The protein concentration of the diets was adjusted to 18 g/100 g with casein, and the fat concentration was adjusted to 5 g/100 g with corn oil. Rats fed the bean diet had significantly fewer colon adenocarcinomas (P < 0.05) than rats fed the casein diet (5 vs. 22 tumors), and significantly fewer rats fed the bean diet (P < 0.05) had colonic tumors than did casein-fed rats (24 vs. 50%). Tumor multiplicity was also significantly lower for the bean-fed rats, and significantly fewer (P < 0.05) tumors per tumor-bearing rat were observed in bean-fed rats than in casein-fed rats (1.0 +/- 0.0 vs. 2.5 +/- 0.6). This study demonstrates that dry beans contain anticarcinogenic compounds capable of inhibiting AOM-induced colon cancer in rats. However, the specific anticarcinogenic components within dry beans have not been identified, and it is unclear whether dietary fiber, phytochemicals or other components within dry beans are primarily responsible for the anticarcinogenic properties of beans.

Dietary fat and fiber modulate the effect of carcinogen on colonic protein kinase C lambda expression in rats

To elucidate the mechanisms by which dietary factors influence the risk of colon cancer, we investigated the effect of select dietary fats and fibers on atypical protein kinase C (PKC) lambda expression. Azoxymethane- and saline (control)-injected rats were fed diets containing either corn oil or fish oil (15 g/100 g) and either cellulose or pectin (6 g/100 g) and killed at two time points (15 and 37 wk) in a 2 x 2 x 2 x 2 factorial design. Colonic PKC lambda protein and mRNA levels were determined using immunoblotting and relative competitive polymerase chain reaction, respectively. Azoxymethane suppressed cytosolic PKC lambda protein levels compared with the saline controls at both time points, and this suppression was partially blocked by fish oil feeding at 15 wk and pectin at 37 wk. Also, at 15 wk, azoxymethane-injected rats fed corn oil had higher levels of membrane PKC lambda relative to the other treatment groups. Overall, expression of PKC lambda mRNA was not correlated with differences in the respective isozyme protein levels. Therefore, the chemopreventive effects of dietary fish oil and pectin are associated with the blockage of azoxymethane-induced alterations in colonic PKC lambda protein expression.

Inhibition of azoxymethane-initiated colon tumor by bovine lactoferrin administration in F344 rats

The influence of bovine lactoferrin (bLF) on colon carcinogenesis was investigated in male F344 rats treated with azoxymethane (AOM). Following three weekly injections of AOM, the animals received 2 or 0.2% bLF for 36 weeks. No effects indicative of toxicity were noted, but significant reduction in both the incidence and number of adenocarcinomas of the large intestine was observed with both doses. Thus, the incidences of adenocarcinomas in the groups receiving 2% and 0.2% bLF were 15% and 25%, respectively, in contrast to the 57.5% control value (P < 0.01 and P < 0.05, respectively). The results indicate that bLF might find application for chemoprevention of colon cancer.

Suppression of azoxymethane-induced aberrant crypt foci in rat colon by nimesulide, a selective inhibitor of cyclooxygenase 2

Non-steroidal anti-inflammatory drugs, such as piroxicam and sulindac, are known to inhibit development of aberrant crypt foci (ACF) and cancer in the colon. However, these agents cause gastrointestinal side-effects. Nimesulide is a selective inhibitor of cyclooxygenase 2 and has been shown to have a more potent anti-inflammatory action than piroxicam, but be less ulcerogenic and, therefore, a potentially more useful chemopreventive agent. To assess this possibility the inhibitory effects of nimesulide on the formation of ACF induced by azoxymethane in rat colon were investigated, and compared with those of piroxicam and sulindac. Male F344 rats were treated s.c. with 15 mg/kg body weight azoxymethane once a week for 2 weeks and given 50, 100 or 200 ppm nimesulide, 200 ppm piroxicam, or 200 ppm sulindac in their diet from the day before the first carcinogen treatment until the end of the experiment at week 4. At this time, nimesulide at doses of 50, 100 and 200 ppm had reduced the numbers of azoxymethane-induced ACF to 75%, 71% and 65% respectively compared to the control. The number of azoxymethane-induced ACF per colon in the group given 200 ppm nimesulide was almost the same as in those given 200 piroxicam, and lower than that in the group given 200 ppm sulindac. These results suggest that nimesulide, a selective cyclooxygenase 2 inhibitor, warrants attention as a candidate for chemopreventive agent with low toxicity, active against colon carcinogenesis.

Suppression of azoxymethane-induced rat colon carcinogenesis by dietary administration of naturally occurring xanthophylls astaxanthin and canthaxanthin during the postinitiation phase

The modulating effects of dietary feeding of two xanthophylls, astaxanthin (AX) and canthaxanthin (CX) during the postinitiation phase on colon carcinogenesis initiated with azoxymethane (AOM) were investigated in male F344 rats. Animals were initiated with AOM by weekly s.c. injections of 15 mg/kg body wt for 3 weeks and then they were fed the diets containing AX or CX at concentrations of 100 and 500 p.p.m. for 34 weeks. The others contained the groups of rats treated with AX or CX alone and untreated. At the end of the study (week 37), the incidence and multiplicity of neoplasms (adenoma and adenocarcinoma) in the large intestine of rats initiated with AOM and followed by AX or CX containing diet at a high dose (500 p.p.m.) were significantly smaller than those of rats given AOM alone (P < 0.001). In addition, AX or CX feeding significantly inhibited the development of aberrant crypt foci induced by AOM. Dietary exposure to AX or CX also decreased cell proliferation activity as revealed by measuring 5'-bromodeoxyuridine-labeling index as crypt cells, colonic mucosal ornithine decarboxylase activity and blood polyamine levels. These results indicate that AX and CX are possible chemopreventers for carcinogenesis of colon in addition to urinary bladder and oral cavity and such effects may be partly due to suppression of cell proliferation.

Inhibition of 1,2-dimethylhydrazine-induced oxidative DNA damage by green tea extract in rat

Following subcutaneous injection of 1,2-dimethylhydrazine (DMH), which is carcinogenic to rat colon and liver, to Sprague-Dawley rats, a significant increase of 8-hydroxydeoxyguanosine (8-OHdG) was observed in the DNA of colonic mucosa and liver. The 8-OHdG formation reached the maximal level at about 24 h after the DMII injection. On the other hand, no increase of 8-OHdG was observed in the DNA of the kidney. Drinking green tea extract (GTE) for ten days prior to the DMH injection significantly inhibited the formation of 8-OHdG in the colon. These findings demonstrate that DMH causes oxidative damage to the DNA of its target organ, and that GTE protects colonic mucosa from this oxidative damage.

Selective preservation of protein kinase C-zeta in the chemoprevention of azoxymethane-induced colonic tumors by piroxicam

While nonsteroidal anti-inflammatory drugs have been shown to exert preventive effects against the development of colonic tumors in humans and in chemically-induced tumors in animal models, the mechanism(s) involved in this phenomenon is unclear. We have recently demonstrated that one such agent, piroxicam, when supplemented (75 ppm) in the diets of rats administered azoxymethane, reduced the incidence of rats bearing tumors. To date, the effects of piroxicam on protein kinase C, a family of serine/threonine kinases which may be intimately involved in the colonic malignant transformation process, have not been examined. It was, therefore, of interest to determine whether piroxicam altered the expression of one or more isoforms of this kinase in these tumors. The present studies demonstrate that dietary piroxicam selectively preserved the expression of protein kinase C-zeta in azoxymethane-induced tumors; suggesting that this is at least one mechanism involved in this agent's chemopreventive actions in this organ.

Chemoprevention of digestive organs carcinogenesis by natural product protocatechuic acid

The worldwide increase in cancer mortality demands a practical and effective chemopreventive approach to this problem. Using animal bioassay, the authors demonstrated protocatechuic acid (PCA, 3,4-dihydroxybenzoic acid), a simple and antioxidative phenolic acid present in fruits, vegetables, and nuts, to be an efficacious agent in reducing the carcinogenic action of 4-nitroquinoline 1-oxide in oral cavity, N-methyl-N-nitrosourea in glandular stomach, azoxymethane in colon, and diethylnitrosamine in liver. PCA exerts its chemopreventive action partly through inhibition of cell proliferation induced by carcinogens in the target organs. The prospect of this agent as chemopreventive against human cancer warrants a thorough investigation, such as dose-dependent efficacy and its potential toxicity at an effective dose level in other species of animals. Considering its promising anticarcinogenic potency, proliferation biomarkers, including tissue and blood polyamine levels, might eventually be useful in assessing the possible role of PCA intake in high risk populations for cancers of these organs.

Omeprazole inhibits colorectal carcinogenesis induced by azoxymethane in rats

Numerous clinical and experimental studies suggest that gastrin plays an important part in the development of colorectal cancer in humans. This study was done to assess the influence of omeprazole induced hypergastrinaemia on the development of colorectal tumours in an experimental animal model. Forty female Sprague-Dawley rats received either omeprazole (40 mumol/kg) or vehicle (0.25% methylcellulose) by once daily oral gavage throughout the experiment. All animals received 12 consecutive weekly subcutaneous injections of azoxymethane (10 mg/kg/week) beginning at week 6. Serum gastrin concentrations were measured during weeks 1 and 5 and at death (week 27). Chronic omeprazole treatment resulted in appreciable hypergastrinaemia during the study, mean gastrin concentrations in omeprazole treated rats being raised by up to nine to 10 fold, compared with vehicle treated control rats (p < 0.001). Despite this, tumour incidence in the omeprazole group was significantly lower at 63%, compared with 95% in the vehicle only group (p < 0.02). The median number of tumours in the omeprazole group (1) compared with the vehicle group (3) was also significantly lower (p = 0.02). Average tumour size, site distribution, and the comparative frequencies of adenomas and adenocarcinomas were similar in the two groups. This study shows that omeprazole protects against colorectal carcinogenesis in this model despite causing appreciable hypergastrinaemia. The mechanism by which this occurs is unclear and merits further investigation. Because of the compounding protective effects of omeprazole, this model is not a suitable one for studying the longterm trophic effects of gastrin on the colon.

Inhibitory effect of aspirin on azoxymethane-induced colon carcinogenesis in F344 rats

Epidemiologic studies suggest that sustained use of aspirin may reduce the risk of development of and mortality due to colon cancer. Previous preclinical studies have shown that several non-steroidal anti-inflammatory drugs act as potential chemopreventive agents in experimentally induced colon cancer models. The present study was designed to investigate the chemopreventive effect of 40 and 80% maximum tolerated dose (MTD) levels of aspirin administered in the diet on azoxymethane (AOM)-induced colon carcinogenesis in male F344 rats. The MTD of aspirin as determined in male F344 rats was 500 p.p.m. Beginning at 5 weeks of age, all animals were randomly divided into various experimental groups (48 rats/group) and fed one of the semipurified diets containing 0, 200 p.p.m. (40% MTD), or 400 ppm (80% MTD) of aspirin. Two weeks later, all animals (36 rats/group) except the vehicle-treated groups (12 rats/group) were administered s.c. injections of AOM at a dose level of 15 mg/kg body wt, once weekly for 2 weeks. All animals were continued on their respective dietary regimen for additional 52 weeks and necropsied. Histopathologic evaluation of colon tumors was performed by routine procedures. Basal levels and ex vivo production of colonic mucosal and tumor prostaglandin E2 (PGE2) were measured in all groups. The results indicate that daily oral administration of 200 and 400 p.p.m. aspirin significantly inhibited the incidence (% animals with tumors) and multiplicity (tumors/animal) of invasive adenocarcinomas of the colon as well as the size of adenocarcinomas. Colonic mucosal and tumor PGE2 levels (basal and ex vivo production) were significantly reduced in animals administered 200 and 400 p.p.m. aspirin. The results of this study support the epidemiologic evidence that ingestion of aspirin inhibits colon carcinogenesis. Although the precise mechanisms of aspirin-induced colon tumor inhibition remain to be determined, it is likely that the effect may be mediated through the modulation of prostaglandin synthesis.

Reduction of aberrant crypt foci induced in rat colon with azoxymethane or methylnitrosourea by feeding cholic acid

Recent studies in our laboratory have demonstrated that feeding cholic acid (CHA) to rats treated with a single dose of azoxymethane (AOM) reduces the growth of putative preneoplastic lesions, aberrant crypt foci (ACF), in a dose-dependent manner. This finding was unexpected since CHA has been reported to promote colon cancer in rats receiving multiple treatments of the colon carcinogen, methylnitrosourea (MNU). The main objective of the present investigation was to evaluate the effect of the type of carcinogen and treatment protocol on the induction and growth of ACF in conjunction with CHA treatment. Male Sprague-Dawley rats received 0, 1 or 2 treatments with AOM or MNU and were fed either the AIN-76A or AIN-76A plus 0.2% CHA diet for 4 weeks. The total number and average size of ACF were significantly reduced in CHA-fed animals regardless of the type or number of treatments of carcinogen. The greatest reduction of ACF due to CHA-feeding was seen in the distal colon. The average crypt multiplicity (number of crypts in each ACF) was not altered by diet or carcinogen treatment. Colonic cell proliferation (crypt height and number of mitotic figures) was significantly increased in CHA-fed animals compared to control diet animals. Therefore, feeding CHA for 4 weeks reduced the number and size of ACF in rats induced by 1 or 2 injections of AOM or MNU, despite stimulation of colonic cell proliferation. These findings suggest further investigation is needed to understand the mechanism of promotion by cholic acid and the value of number and growth characteristics of ACF as a biological endpoint in the pathogenesis of colon cancer.

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

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

Inhibition by putrescine of experimental carcinogenesis in rat colon induced by azoxymethane

The effects of putrescine on the incidence and number of colon tumors induced by azoxymethane, and on the labelling index and the activity of ornithine decarboxylase (ODC) in the colon mucosa were investigated in Wistar rats. Rats received 10 weekly injections of 7.4 mg/kg body weight of azoxymethane and i.p. injections of 300 mumol/kg body weight of putrescine every 2 days until the end of the experiment at week 40. This prolonged treatment with putrescine significantly reduced the incidence and number of colon tumors. Administration of putrescine also significantly decreased the labelling index and the ODC activity in the colon mucosa during, but not after, treatment with the carcinogen. These last effects may be related to the action of putrescine in inhibiting the development of colonic tumors.

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

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

Importance of the duration of inhibition on intestinal carcinogenesis by difluoromethylornithine in rats

The effect of the duration and sequence of inhibition of intestinal tumor formation in rats was studied to determine whether part time inhibition has any value. Four groups of male Sprague-Dawley rats were given 8 weekly s.c. injections of azoxymethane (AOM) 8 mg/rat. Three groups were given the inhibitor, difluoromethylornithine (DFMO) in the drinking water; one for the entire 26 weeks of the study, one for the first 13 weeks only, and one for the last 13 weeks. A control group was not given the inhibitor. While the continuous treatment group developed the least number of tumors per rat (1.5 vs. 5 for controls), still both groups given the inhibitor for just 13 weeks also developed fewer tumors than controls 5 vs. 3.2 (early treatment) and 5 vs. 2.8 (late treatment). These results show that part time inhibition, including its late application, does reduce intestinal tumor formation in rats.

Inhibitors for the mutagenicities of colon carcinogens, 1,2-dimethylhydrazine and azoxymethane, in the host-mediated assay

Inhibitory effects of several chemicals on the mutagenicities of 1,2-dimethylhydrazine (DMH) and azoxymethane (AOM) for Salmonella typhimurium G46 in the host-mediated assay were investigated. They were carbon disulfide (CS2), tetraethylthiuram disulfide (disulfiram, DSF), sodium diethyldithiocarbamate (SDDC), ethylene-bis(dithiocarbamato) manganese (Maneb), pyrazole (PZ), aminoacetonitrile hydrogen sulfate (AAN), and sodium selenite (SE). All the compounds, except for SE, inhibited the mutagenicities of DMH and AOM.

Inhibits of of colon carcinogenesis

Disulfiram (tetraethylthiuram disulfide, Antabuse) and sodium diethyldithiocarbamate, when added to the diet, inhibit 1,2-dimethylhydrazine (DMH)-induced neoplasia of the large bowel in female CF1 mice. Ethylene bis(dithiocarbamato)manganese (Maneb) and bis(ethylxanthogen), two pesticides with structural similarities to disulfiram, produce comparable inhibition of DHM. In other work, disulfiram was found to inhibit the carcinogenic effect of azoxymethane (AOM) on the large bowel. Under comparable conditions the inhibition of AOM was considerably less than that obtained with DMH as the carcinogen. The data suggest that disulfiram inhibits DMH metabolism at more than one oxidative step.