Effects of a high-fat diet on azoxymethane-induced aberrant crypt foci and fecal biochemistry and microbial activity in rats

Protective Properties of Intestinal Alkaline Phosphatase Supplementation on the Intestinal Barrier: Interactions and Effects

The intestinal barrier is critical for maintaining intestinal homeostasis, and its dysfunction is associated with various diseases. Recent findings have revealed the multifunctional role of intestinal alkaline phosphatase (IAP) in diverse biological processes, including gut health maintenance and function. This review summarizes the protective effects of IAP on intestinal barrier integrity, encompassing the physical, chemical, microbial, and immune barriers. We discuss the results and insights from in vitro, animal model, and clinical studies as well as the available evidence regarding the impact of diet on IAP activity and expression. IAP can also be used as an indicator to assess intestinal-barrier-related diseases. Further research into the mechanisms of action and long-term health effects of IAP in maintaining overall intestinal health is essential for its future use as a dietary supplement or functional component in medical foods.

Consumption of the Total Western Diet Promotes Colitis and Inflammation-Associated Colorectal Cancer in Mice

Consumption of a Western type diet is a known risk factor for colorectal cancer. Our group previously developed the total Western diet (TWD) for rodents with energy and nutrient profiles that emulate a typical Western diet. In this study, we tested the hypothesis that consumption of the TWD would enhance colitis, delay recovery from gut injury and promote colon tumorigenesis. In multiple experiments using the azoxymethane + dextran sodium sulfate or Apc^Min/+ mouse models of colitis-associated colorectal carcinogenesis (CAC), we determined that mice fed TWD experienced more severe and more prolonged colitis compared to their counterparts fed the standard AIN93G diet, ultimately leading to markedly enhanced colon tumorigenesis. Additionally, this increased tumor response was attributed to the micronutrient fraction of the TWD, and restoration of calcium and vitamin D to standard amounts ameliorated the tumor-promoting effects of TWD. Finally, exposure to the TWD elicited large scale, dynamic changes in mRNA signatures of colon mucosa associated with interferon (IFN) response, inflammation, innate immunity, adaptive immunity, and antigen processing pathways, among others. Taken together, these observations indicate that consumption of the TWD markedly enhanced colitis, delayed recovery from gut injury, and enhanced colon tumorigenesis likely via extensive changes in expression of immune-related genes in the colon mucosa.

Enrichment of conjugated linoleic acid (CLA) in hen eggs and broiler chickens meat by lactic acid bacteria

1. The aim of this work was to compare conjugated linoleic acid (CLA) concentrations in chickens supplemented with 4 American Tissue Culture Collection (ATCC) bacterial strains, Lactobacillus plantarum, Lactobacillus lactis, Lactobacillus casei and Lactobacillus fermentum, and 4 isolates of Lactobacillus reuteri from camel, cattle, sheep and goat rumen extracts. 2. Micro-organisms were grown anaerobically in MRS broth, and 10(6) CFU/ml of bacteria were administered orally to mixed-sex, 1-d-old broiler chickens weekly for 4 weeks and to 23-week-old layer hens weekly for 6 weeks. 3. The 4 strains were evaluated for their effects on synthesis of CLA in hen eggs and broiler meat cuts. 4. Administration of pure Lactobacillus and isolated L. reuteri strains from camel, cattle, goat and sheep led to significantly increased CLA concentrations of 0.2-1.2 mg/g of fat in eggs and 0.3-1.88 mg/g of fat in broiler chicken flesh homogenates of leg, thigh and breast. 5. These data demonstrate that lactic acid bacteria of animal origin (L. reuteri) significantly enhanced CLA synthesis in both eggs and broiler meat cuts.

Metabonomic variations associated with AOM-induced precancerous colorectal lesions and resveratrol treatment

Resveratrol (Res), 3,5,4'-trihydroxy-trans-stilbene, is an antioxidant found in the skin of red grapes and in several other plants. This phenolic compound has been recently reported to possess cancer chemopreventive activity that inhibits the process of carcinogenesis. However, the mechanisms underlying its anticancer effects remain largely unresolved. In this study, we investigated the chemoprotective effects of dietary Res in an azoxymethane (AOM) induced precancerous colorectal lesion model in male Wistar rats. The metabolic alterations in urine, sera, and colonic tissues of experimental rats perturbed by AOM intervention as well as the Res treatment were measured by a gas chromatography time-of-flight mass spectrometry (GC-TOFMS) analysis. Significant alterations of metabolites were observed in AOM group in urine, sera, and colonic tissues, which were attenuated by Res treatment and concurrent with the histopathological improvement with significantly decreased aberrant crypt foci (ACF) incidence. Representative metabolites include depleted glucose, β-hydroxybutyrate (ketone body), hypoxanthine, and elevated branched chain amino acids (isoleucine and valine) and tryptophan in colonic tissue, as well as elevated serum aminooxyacetate and urinary 4-hydroxyphenylacetate and xanthurenate. These metabolic changes suggest that the preventive effect of Res is associated with attenuation of impaired glucose and lipid metabolism and elevated protein breakdown in colonic tissues from AOM-exposed rats. It also appears that Res induced significant metabolic alterations independent of the AOM-induced metabolic changes. The significantly altered metabolites identified in Res-AOM group relative to AOM group include arachidonate, linoleate, glutamate, docosahexaenoate, palmitelaidate, 2-aminobutyrate, pyroglutamate, and threonate, all of which are involved in inflammation and oxidation processes. This suggests that Res exerts the chemopreventive effects on ACF formation by anti-inflammatory and antioxidant mechanisms in addition to amelioration of AOM-induced mitochondrial disruption.

Linoleic-acid-induced growth suppression induces quiescent cancer cell nests in nude mice

We examined the effect of linoleic acid (LA) on tumor formation. Cell growth was suppressed by LA in a dose-dependent manner in MKN28 and Colo320 cells. Continuous treatment with LA provided growth arrest in both cells at 5-7 weeks after the treatment. LA-pretreated MKN28 and Colo320 cells showed higher tumorigenicity (9/10 and 10/10, respectively) than nontreated cells (2/10 and 3/10, respectively; p < 0.01) in nude mice. In contrast, LA-pretreated MKN28 and Colo320 cells showed more suppressed tumor growth than nontreated cells (p < 0.01). LA-pretreated MKN28 and Colo320 cells with LA administration after the inoculation did not form macroscopic tumors. Histological examination revealed small cancer cell aggregations, which showed no proliferative activity. In LA-treated MKN28 and Colo320 cells, protein production of Bcl-2 was increased, whereas Bak, EGFR and VEGF levels were decreased. These findings suggest that LA might induce quiescence and subsequent dormancy in cancer cells.

Orlistat-associated adverse effects and drug interactions: a critical review

Orlistat, an anti-obesity drug, is a potent and specific inhibitor of intestinal lipases. In light of the recent US FDA approval of the over-the-counter sale of orlistat (60 mg three times daily), clinicians need to be aware that its use may be associated with less well known, but sometimes clinically relevant, adverse effects. More specifically, the use of orlistat has been associated with several mild-to-moderate gastrointestinal adverse effects, such as oily stools, diarrhoea, abdominal pain and faecal spotting. A few cases of serious hepatic adverse effects (cholelithiasis, cholostatic hepatitis and subacute liver failure) have been reported. However, the effects of orlistat on non-alcoholic fatty liver disease are beneficial. Orlistat-induced weight loss seems to have beneficial effects on blood pressure. No effect has been observed on calcium, phosphorus, magnesium, iron, copper or zinc balance or on bone biomarkers. Interestingly, the use of orlistat has been associated with rare cases of acute kidney injury, possibly due to the increased fat malabsorption resulting from the inhibition of pancreatic and gastric lipase by orlistat, leading to the formation of soaps with calcium and resulting in increased free oxalate absorption and enteric hyperoxaluria. Orlistat has a beneficial effect on carbohydrate metabolism. No significant effect on cancer risk has been reported with orlistat.Orlistat interferes with the absorption of many drugs (such as warfarin, amiodarone, ciclosporin and thyroxine as well as fat-soluble vitamins), affecting their bioavailability and effectiveness. This review considers orlistat-related adverse effects and drug interactions. The clinical relevance and pathogenesis of these effects is also discussed.

The Roles of Dietary PPARgamma Ligands for Metastasis in Colorectal Cancer

Dietary peroxisome proliferator-activated receptor (PPAR)gamma ligands, linoleic acid (LA) and conjugated linoleic acid (CLA), showed anticancer effects in colorectal carcinoma cells. LA is metabolized by two pathways. Cyclooxygenase (COX)-2 produces procarcinogenic prostaglandin E2, whereas 15-lipoxygenase (LOX)-1 produces PPARgamma ligands. The 15LOX-1 pathway, which is dominant in colorectal adenomas, was downregulated and inversely COX-2 was upregulated in colorectal cancer. LA and CLA inhibited peritoneal metastasis of colorectal cancer cells in nude mice. The inhibitory effect was abrogated by PPARgamma antisense treatment. A continuous LA treatment provided cancer cells quiescence. These quiescent cells formed dormant nests in nude mice administrated LA. The quiescent and dormant cells showed downregulated PPARgamma and upregulated nucleostemin. Thus, short-term exposure to dietary PPARgamma ligands inhibits cancer metastasis, whereas consistent exposure to LA provides quiescent/dormant status with possible induction of cancer stem and/or progenitor phenotype. The complicated roles of dietary PPARgamma ligands are needed to examine further.

Reversal of expression of 15-lipoxygenase-1 to cyclooxygenase-2 is associated with development of colonic cancer

AIMS

Two different pathways of linoleic acid (LA) metabolism have opposite effects on the development of colonic cancer: a protumoral prostaglandin cascade metabolized by cyclooxygenase (COX)-2, and an antitumoral peroxisome proliferator-activated receptor (PPAR)-gamma ligands metabolized by 15-lipooxygenase (LOX)-1. The aim was to examine the switching of the two LA metabolic pathways in colonic adenomas and carcinomas.

MATERIALS AND METHODS

The expression of 15LOX-1 mRNA and COX-2 protein was examined in 54 adenomas, 21 pTis carcinoma-in-adenoma lesions and 36 pT3/p Stage II carcinomas of the colon by in-situ hybridization and immunohistochemistry, respectively.

RESULTS

15LOX-1 expression was found in 89% (48 of 54) of adenomas, 43% (nine of 21) of adenomas and 10% (two of 21) of carcinomas in carcinoma-in-adenoma lesions, but not in pT3 carcinomas (P < 0.0001). In contrast, COX-2 production was found in 11% (six of 54) of adenomas, 52% (11 of 21) of adenomas and 71% (15 of 21) of carcinomas in carcinoma-in-adenoma lesions, and 92% (33 of 36) of pT3 carcinomas (P < 0.0001). Concurrence of 15LOX-1 down-regulation and COX-2 up-regulation was found in 6% (three of 54) of adenomas, 33% (seven of 21) of adenomas and 71% (15 of 21) of carcinomas in carcinoma-in-adenoma lesions, and 92% (33 of 36) of pT3 carcinomas (P < 0.0001).

CONCLUSIONS

These results suggest that switching of LA metabolism by reversal of the expression of 15LOX-1 and COX-2 is associated with acquisition of malignant potential in colonic neoplasia.

Inhibitory effect of linoleic acid on transformation of IEC6 intestinal cells by in vitro azoxymethane treatment

The effect of linoleic acid (LA) on growth and transformation of IEC6 intestinal cells was examined. IEC6 cells expressed mRNAs of 15-lipooxygenase (LOX15) and peroxisome proliferator-activated receptor (PPAR)gamma but not COX-2. Cell growth was suppressed by LA in a dose-dependent manner in IEC6 cells. Three-week treatment with LA provided IEC6 cells a quiescent state. LA-induced growth inhibition was abrogated by exposure to antisense S-oligodeoxynucleotides (S-ODNs) for LOX15 and/or PPARgamma. In an in vitro carcinogenesis model, IEC6 cells, which had confirmed CYP2E1 expression and activity, were continuously treated with AOM and/or LA for 40 weeks. DNA injury in AOM-treated cells was suppressed to the control level by concurrent LA treatment. Colony formation of AOM-treated cells in soft agar was suppressed by treatment with LA, which was reversed by exposure to antisense S-ODNs for LOX15 and/or PPARgamma. AOM-treated IEC6 cells formed s.c. tumors in 9 of 12 mice, whereas AOM+LA-treated cells formed no tumor. IEC6 cells showed no remarkable alteration of protein production by AOM treatment, whereas cells treated with AOM+LA showed decreased epidermal growth factor receptor (EGFR) and phospho-EGFR and increased BAX. These findings suggest that LA inhibited AOM-induced transformation of COX-2-negative IEC6 cells, which was possibly mediated with PPARgamma ligands generated by LOX15 from LA.

The anti-obesity agent Orlistat is associated to increase in colonic preneoplastic markers in rats treated with a chemical carcinogen

Orlistat is an anti-obesity agent that increases the fecal fat excretion, which promotes colon carcinogenesis. Therefore, the present study was designed to verify the effects of Orlistat on the formation of rat colonic aberrant crypt foci (ACF) and cell proliferation evaluated by the PCNA method. Male Wistar rats received either a standard diet or a high fat diet (HFD), supplemented or not with Orlistat (200mg/kg chow) and two doses of the carcinogen dimethyl-hydrazine (25mg/Kg). After 30 days, Orlistat was associated to a significant increase in the number of colonic ACFs and cell proliferation in DMH-treated animals, independently of the HFD.

Bile acid induced gene expression in LT97 colonic adenoma cells

LT97 human colonic adenoma cells reflecting early premalignant genotype and growth characteristics have been posed to tumor promoting bile acids in order to identify marker genes that permit identification of tumor promoters in vitro. Physiologically relevant concentrations of desoxycholate (DOC) and chenodesoxycholate (CDC) upregulated expression of c-fos and COX-2 in a concentration- and time-dependent manner. Transient induction of c-fos was seen with the non-promoting taurodesoxycholate (TDOC) as well as DOC, however extended induction at 3 h was only achieved by DOC and CDC reaching 3-6-fold as compared to the control. Stimulation of COX-2 expression was completely specific for the tumor promoting analogs DOC and CDC. It was about 4-fold in the 80 microM DOC and CDC groups after 3 h and increased to 12- and 7-fold respectively after 6 h. Expression of VEGF was stimulated 4-5-fold in the tumor promoter (DOC and CDC) groups and about 2-fold in the non-promoting controls TDOC and GCDC. At later times the tumor promoter specific difference was lost. Our results show that all three genes are modulated in a tumor promoter dependent way and that their upregulation in LT97 adenoma cells can be used for in vitro testing of colon tumor promoters and chemopreventive compounds.

Lactobacillus growth and membrane composition in the presence of linoleic or conjugated linoleic acid

Five Lactobacillus strains of intestinal and food origins were grown in MRS broth or milk containing various concentrations of linoleic acid or conjugated linoleic acid (CLA). The fatty acids had bacteriostatic, bacteriocidal, or no effect depending on bacterial strain, fatty acid concentration, fatty acid type, and growth medium. Both fatty acids displayed dose-dependent inhibition. All strains were inhibited to a greater extent by the fatty acids in broth than in milk. The CLA isomer mixture was less inhibitory than linoleic acid. Lactobacillus reuteri ATCC 55739, a strain capable of isomerizing linoleic acid to CLA, was the most inhibited strain by the presence of linoleic acid in broth or milk. In contrast, a member of the same species, L. reuteri ATCC 23272, was the least inhibited strain by linoleic acid and CLA. All strains increased membrane linoleic acid or CLA levels when grown with exogenous fatty acid. Lactobacillus reuteri ATCC 55739 had substantial CLA in the membrane when the growth medium was supplemented with linoleic acid. No association between level of fatty acid incorporation into the membrane and inhibition by that fatty acid was observed.

Most effective colon cancer chemopreventive agents in rats: a systematic review of aberrant crypt foci and tumor data, ranked by potency

Potential chemopreventive agents for colorectal cancer are assessed in rodents. We speculated that the magnitude of the effect is meaningful and ranked all published agents according to their potency. Data were gathered systematically from 137 articles with the aberrant crypt foci (ACF) end point and from 146 articles with the tumor end point. The potency of each agent to reduce the number of ACF is listed in one table and the potency of each agent to reduce the tumor incidence in another table. Both tables are shown in this review and on a website with sorting abilities (http://www.inra.fr/reseau-nacre/sci-memb/corpet/indexan.html). Potency was estimated as the ratio of the value in control rats to the value in treated rats. From each article, only the most potent agent was kept, except in articles reporting the effect of more than seven agents. Among the 186 agents in the ACF table, the median agent reduced the number of ACF by one-half. The most potent agents to reduce azoxymethane-induced ACF were Pluronic, polyethylene glycol, perilla oil with beta-carotene, and sulindac sulfide. Among the 160 agents in the tumor table, the median agent reduced the tumor incidence in rats by one-half. The most potent agents to reduce the incidence of azoxymethane-induced tumors were celecoxib, a protease inhibitor from soy, difluoromethylornithine with piroxicam, polyethylene glycol, and a thiosulfonate. For the 57 agents present in both tables, a significant correlation (r) was found between the potencies against ACF and tumors (r = 0.45, P < 0.001); without celecoxib, a major outlying point in the correlation, r = 0.68 (P < 0.001, n = 56). In conclusion, this review gathers most known chemopreventive agents, ranks the most promising agents against colon carcinogenesis in rats or mice, and further supports the use of ACF as a surrogate end point for tumors in rats.

Bile salt deconjugation by lactobacillus plantarum 80 and its implication for bacterial toxicity

The effects of bile salts on the survival of lactobacilli were investigated using glycocholic acid, cholic acid and deoxycholic acid as model compounds and the bile salt hydrolase active Lactobacillus plantarum 80 (BSH+) and its BSH negative mutant. The detrimental effects of cholic acid, i.e. growth inhibition and cytotoxicity at a concentration of 1 and 5 mmol l-1, respectively, were considered to be due to the hydrophobic protonated form of the molecule, which brings about membrane damage. The conversion of glycocholic acid to cholic acid by the BSH active L. plantarum 80 caused a growth inhibition which was comparable with the inhibition observed in the broth supplemented with 1 mmol l-1 cholic acid. Deoxycholic acid caused toxicity through membrane damage when the compound was in solution. Its toxicity disappeared in the culture broth as the molecule precipitated. In case of cholic acid, the toxicity could be removed by buffering the solution at pH 7.0. It was calculated that at this pH most of the cholic acid molecules were ionized. The results led to the formulation of an extended hypothesis about the ecological significance of bile salt transformations. Primary deconjugation is carried out to counteract intracellular acidification. Yet, the deconjugated molecule can be harmful at moderately acidic pH-values. In this case, the BSH+ strains could effectively profit from their activity in case they are associated with 7alpha-dehydroxylating bacteria which dehydroxylate the deconjugated bile salts. The dehydroxylated molecule has a low solubility and precipitates at moderately acidic pH.

Overexpression of protein kinase C betaII induces colonic hyperproliferation and increased sensitivity to colon carcinogenesis

Protein kinase C betaII (PKC betaII) has been implicated in proliferation of the intestinal epithelium. To investigate PKC betaII function in vivo, we generated transgenic mice that overexpress PKC betaII in the intestinal epithelium. Transgenic PKC betaII mice exhibit hyperproliferation of the colonic epithelium and an increased susceptibility to azoxymethane-induced aberrant crypt foci, preneoplastic lesions in the colon. Furthermore, transgenic PKC betaII mice exhibit elevated colonic beta-catenin levels and decreased glycogen synthase kinase 3beta activity, indicating that PKC betaII stimulates the Wnt/adenomatous polyposis coli (APC)/beta-catenin proliferative signaling pathway in vivo. These data demonstrate a direct role for PKC betaII in colonic epithelial cell proliferation and colon carcinogenesis, possibly through activation of the APC/beta-catenin signaling pathway.

Comparative effects of secondary bile acids, deoxycholic and lithocholic acids, on aberrant crypt foci growth in the postinitiation phases of colon carcinogenesis

The objective of this study was to investigate the effect of deoxycholic (DCA) and lithocholic (LCA) acids on the postinitiation phases of colon cancer. Male Sprague-Dawley rats (n = 170) were injected with azoxymethane (2 injections at 15 mg/kg body wt sc given 1 wk apart) and fed a control (CON) AIN-93 diet. Two weeks after the second azoxymethane injection, 10 animals were killed and aberrant crypt foci (ACF) were enumerated. The remaining animals were randomly assigned to four diet groups: 1) CON, 2) DCA, 3) LCA, and 4) high fat (HF, a positive control group). Bile acid diets consisted of 0.2% by weight DCA or LCA; HF diets consisted of 20% fat (5% soybean oil + 15% beef tallow by weight). Animals were killed at Weeks 3, 12, and 20 (from 1st carcinogen injection), and number and growth features of ACF and adenomatous lesions were enumerated in the colon. At Week 12, ACF number and small, medium, and large (1-3, 4-6, and > or = 7 crypts/focus, respectively) ACF were higher in the HF group than in the DCA, LCA, and CON groups (p < or = 0.05). By Week 20, ACF number and small, medium, and large ACF were similar in the LCA and HF groups, whereas the response was similar in the DCA and CON groups. Average crypt multiplicity was higher in the HF and LCA groups than in the DCA and CON groups (p < or = 0.05). Microadenoma (MA) incidence was higher in the HF group than in the CON and LCA groups (p < or = 0.05). Regional distribution patterns for ACF number were similar to MA and tumor distribution patterns within the CON, DCA, and HF groups. In the LCA group, ACF number and MA showed a proximal predominance in regional distribution, whereas tumors showed a distal predominance. HF diets provided the most stimulatory environment, immediately enhancing the number and growth of ACF and MA incidence. In conclusion, HF and LCA diets exerted distinct effects on postinitiation phases of colon cancer, whereas the DCA diet did not.

Effect of dietary deoxycholic acid and cholesterol on fecal steroid concentration and its impact on the colonic crypt cell proliferation in azoxymethane-treated rats

To elucidate the role of fecal steroids in the malignant tumor formation of colonic epithelial cells, we examined the effects of dietary deoxycholic acid (DCA) and cholesterol (CHL) on fecal steroid concentrations and their impact on colonic crypt cell proliferation. Twenty 5-week-old male Fischer 344 rats were provided with either a control semisynthetic diet or the same diet supplemented with 0.15% DCA and 1% CHL (steroid diet) over a 5-week period. The effects of these two diets were compared among rats that were either injected with azoxymethane (AOM), a known gastrointestinal carcinogen, or saline. In a 2 x 2 factorial design, rats fed each of these diets were given two weekly subcutaneous injections of either AOM (15 mg/kg b.w.) or saline at 6 and 7 weeks of age. At 9 weeks of age, fecal samples were obtained for analysis of bile acids, CHL and its bacterial metabolites of intestinal microflora. At 10 weeks of age, animals were sacrificed and colonic proliferation was assessed as vincristine-accumulated mitotic figures per crypt. Rats fed the steroid diet had significantly elevated fecal bile acid (5x, P < 0.001) and neutral steroid (10x, P < 0.01) levels when compared to those fed the control diet. AOM treatment did not appear to influence these levels. However, rats injected with AOM had a significant increase (P < 0.001) in their rate of colonic cell proliferation as compared to saline-injected control animals on both diets. Furthermore, rats fed the steroid diet had a significantly higher (P < 0.001) cell proliferation rate than animals fed the control diet. The effects of AOM treatment and the steroid diet on cell proliferation were additive. Our results demonstrate that high concentrations of neutral and acid steroids in the colonic lumen can enhance carcinogen-induced elevated cell proliferation and thus may play a key role in the etiology of colon cancer.

Specific species of intestinal bacteria influence the induction of aberrant crypt foci by 1,2-dimethylhydrazine in rats

To shed light on the association of intestinal microflora with the development of colon cancer, we studied the modifying effects of intestinal microflora on the occurrence of 1,2-dimethylhydrazine (DMH)-induced colonic aberrant crypt foci (ACF) in germfree (GF), gnotobiotic (GB) and conventionalized (Cvd) rats. In the first part of this study, 10 week old germfree Fischer-344 rats were randomly assigned to three groups and two groups of rats were orally inoculated with mixtures of pure culture of Escherichia coli, Enterococcus faecium, and several strains of Bacteroides and Clostridium species (GB), or feces from conventional rats (Cvd). Inoculated rats were given two weekly i.p. injections of DMH (20 mg/kg body wt) at 13 and 14 weeks of age. Rats were sacrificed 11 or 34 weeks after the last DMH injection for ACF scoring. The total number of ACF, ACF with four or more crypts/focus, and mean number of aberrant crypts per focus (crypt multiplicity) in GB rats sacrificed at week 34 were 168% (P < 0.001), 442% (P < 0.001) and 138% (P < 0.001) of those in GF rats, respectively. On the other hand, the same values in Cvd rats were 42% (P < 0.001), 147% (P = 0.246) and 159% (P < 0.001) of those in GF rats, respectively. Similar results were observed in rats that were sacrificed at week 11. In the second part of this study, the effect of colonization of Bifidobacterium breve on the ACF profiles was examined in GB rats. The number of ACF with four or more crypts/focus and crypt multiplicity in GB plus B. breve rats at week 11 were significantly lower than those of GB rats (P < 0.01, and P < 0.05, respectively), although the former was not statistically significant at week 34. These findings suggest that some intestinal bacteria might behave as promoters and some as anti-promoters in colon carcinogenesis.