Modulation of colonic xenobiotic metabolizing enzymes by feeding bile acids: comparative effects of cholic, deoxycholic, lithocholic and ursodeoxycholic acids

Immunotoxicity and the mechanisms of aflatoxin B1-induced growth retardation in shrimp and alleviating effects of bile acids

Aflatoxin B1 (AFB1) is one of the most toxic mycotoxins prevalent in the environment and food chain, posing severe health risks to humans and animals. Bile acids are natural detergents synthesized from cholesterol and play a key role in the excretion of toxins in vertebrates. Here, pacific white shrimp (Litopenaeus vannamei) served as an animal model to examine the toxicity mechanisms of AFB1 and assess the potential alleviating effects of bile acids against AFB1. Our results revealed that AFB1 exposure significantly inhibited the growth performance and immune response of shrimp, accompanied by AFB1 accumulation and histological damage. Mechanistically, AFB1-induced DNA damage activated DNA repair mechanisms and induced the arrest of cell cycle via the ATR-cyclin B/cdc2 pathway. Additionally, AFB1 directly suppressed the immune response and growth performance of shrimp by inhibiting Toll and IMD pathways and the secretion of digestive enzymes. Notably, dietary bile acids significantly reduced AFB1 accumulation and alleviated AFB1-induced growth retardation and immunotoxicity in shrimp, and CCKAR, ATR, and Relish may be key mediators of the alleviating effects of bile acids. Our study provided new insights into the toxicity mechanisms of AFB1 in invertebrates and highlighted the potential of bile acids to alleviate AFB1 toxicity.

Benign gallbladder disease is a risk factor for colorectal cancer, but cholecystectomy is not: A propensity score matching analysis

Background

Previous studies reported controversial results on the relationship between cholecystectomy (CHE) and colorectal cancer (CRC). We hypothesized that gallbladder disease (GBD), instead of cholecystectomy, increased the risk of CRC. We aimed to investigate the incidence of benign gallbladder disease (BGBD) and CHE in CRC patients and local adults undergoing annual health examination by analyzing large data from a tertiary hospital in southwest China.

Methods

A propensity score matching (PSM) analyzed, retrospective study from January 1, 2013, to August 31, 2020, including 7,471 pathologically confirmed CRC patients and 860,160 local annual health examination adults in the First Affiliated Hospital of Chongqing Medical University, was conducted. The prevalence of BGBD and the CHE rate were analyzed before and after a 1:1 PSM.

Results

Of the 7,471 CRC patients, 7,160 were eligible for the case group. In addition, 860,160 local health examination adults were included for comparison. The incidence of BGBD was higher in the CRC patients than in the local adults (19.2% vs. 11.3%, P < 0.001), but no significant difference in CHE rate existed between the case group and the control group (5.0% vs. 4.8%, P = 0.340). In the subgroup analysis, patients with BGBD had a higher risk of colon cancer than rectal cancer (20.4% vs. 18.2%, P = 0.024) and more significantly in the right colon (P = 0.037). A weakly positive correlation between CHE and right colon cancer was observed before PSM but no longer existed after PSM (P = 0.168).

Conclusions

Benign gallbladder disease was positively correlated with colorectal cancer, especially right colon cancer. Cholecystectomy did not increase the risk of colorectal cancer.

Effects of dietary chenodeoxycholic acid supplementation in a low fishmeal diet on growth performance, lipid metabolism, autophagy and intestinal health of Pacific white shrimp, Litopenaeus vannamei

An 8-week feeding trial was conducted to evaluate the effects of chenodeoxycholic acid (CDCA) on growth performance, body composition, lipid metabolism, and intestinal health of juvenile white shrimp, Litopenaeus vannamei fed a low fishmeal diet. Four practical diets were formulated: HFM (25% fishmeal), LFM (15% fishmeal), LB1 (LFM + 0.04% CDCA), LB2 (LFM + 0.08% CDCA). Each diet was assigned to four tanks with forty shrimp (initial weight 0.33 ± 0.03 g) per tank. The results indicated that the growth performance of shrimp were similar between the four groups; the crude lipid content of shrimp fed the LB2 diet was significantly lower than those fed the HFM diet (P < 0.05). The lipase activity content in hepatopancreatic were significantly higher in the two CDCA supplemented groups than that in LFM group; the contents of total cholesterol, low-density lipoprotein cholesterol, high-density lipoprotein cholesterol in hemolymph were significantly lower in LFM group, LB1 group and LB2 group than that in HFM group (P < 0.05). The shrimp fed LB1 diet was significantly decreased the intestinal expression levels of tube than those fed in HFM diet; the intestinal gene expression of imd and toll were significantly lower in LB2 group than those in HFM group (P < 0.05). The results of hepatopancreas gene expression suggest that shrimp fed the LFM diet showed significantly upregulated expression levels of sterol regulatory element-binding protein (srebp), acetyl-CoA carboxylase (acc), and carnitine palmitoyltransferase 1 (cpt-1) than those fed the HFM diet; shrimp fed the LB1 diet showed significantly upregulated expression levels of srebp, acc, and AMP-activated protein kinase (ampk) than those fed the HFM diet; shrimp fed the LB2 diet had higher expression levels of srebp, acc, and cpt-1 than those fed the HFM diet (P < 0.05). In the hepatopancreas, the shrimp fed the LFM diet shown significantly up-regulated the expression levels of beclin1 compared to those fed HFM diet; the expression levels of autophagy-related protein13 (atg3), autophagy-related protein 12 (atg12) of in shrimp fed the LB1 diet were significantly higher than those fed the HFM diet; and the expression levels of autophagy-related protein13 (atg13), beclin1, atg3, atg12, autophagy-related protein 9 (atg9) of shrimp fed LB2 diet were significantly higher than those fed the HFM diet (P < 0.05). The atg3 in intestine of shrimp fed the LB2 diet were significantly higher than those fed the HFM diet (P < 0.05). Intestinal mucous fold were damaged, hepatic tubules were disorganized and B cells appeared to be swollen in LFM group. The fold height and width of shrimp fed the diets supplemented with CDCA increased significantly than those fed the LFM diet (P < 0.05), the hepatic tubules were neatly arranged, and R cells increased. In conclusion, supplementary CDCA in a low fishmeal diet promoted lipid metabolism, enhanced autophagy of shrimp, also improved the health of the intestine and hepatopancreas.

Effects of bile acids on aflatoxin B1 bioaccumulation, detoxification system, and growth performance of Pacific white shrimp

The potential of bile acids (BAs) to reduce aflatoxin B₁ (AFB₁) residues and toxicity in Litopenaeus vannamei was evaluated. Both juveniles and subadults were treated with 0, 0.05, 0.15 and 0.25 g/kg BAs for 60 days followed by 10-d AFB₁ exposure (2000 μg/kg), and fifteen shrimp (five shrimp were pooled into one sample, n = 3) from each treatment were collected at five time points (30, 60, 63, 66 and 70 d). All parameters were determined using accepted and standard methods with acceptable accuracy (recovery) of 90-110%. Results demonstrated that BAs reduced the AFB₁ residues in shrimp (limit of detection: 0.01 μg/L, relative standard deviation < 10% and recovery: 92.1-96.8%). BAs increased the detoxification of AFB₁ and decreased the levels of oxidative stress products by increasing Phase II and antioxidant systems, avoiding AFB₁-induced deterioration of shrimp meat and health risks to human. The confidence level was 95%.

Predicting Carcinogenic Mechanisms of Non-Genotoxic Carcinogens via Combined Analysis of Global DNA Methylation and In Vitro Cell Transformation

An in vitro cell transformation assay (CTA) is useful for the detection of non-genotoxic carcinogens (NGTXCs); however, it does not provide information on their modes of action. In this study, to pursue a mechanism-based approach in the risk assessment of NGTXCs, we aimed to develop an integrated strategy comprising an in vitro Bhas 42 CTA and global DNA methylation analysis. For this purpose, 10 NGTXCs, which were also predicted to be negative through Derek/Sarah structure-activity relationship analysis, were first tested for transforming activity in Bhas 42 cells. Methylation profiles using reduced representation bisulfite sequencing were generated for seven NGTXCs that were positive in CTAs. In general, the differentially methylated regions (DMRs) within promoter regions showed slightly more bias toward hypermethylation than the DMRs across the whole genome. We also identified 13 genes associated with overlapping DMRs within the promoter regions in four NGTXCs, of which seven were hypermethylated and six were hypomethylated. Using ingenuity pathway analysis, the genes with DMRs at the CpG sites were found to be enriched in cancer-related categories, including "cell-to-cell signaling and interaction" as well as "cell death and survival". Moreover, the networks related to "cell death and survival", which were considered to be associated with carcinogenesis, were identified in six NGTXCs. These results suggest that epigenetic changes supporting cell transformation processes occur during non-genotoxic carcinogenesis. Taken together, our combined system can become an attractive component for an integrated approach for the testing and assessment of NGTXCs.

Modulatory effect of troxerutin on biotransforming enzymes and preneoplasic lesions induced by 1,2-dimethylhydrazine in rat colon carcinogenesis

Colon cancer is the third most global oncologic problem faced by medical fraternity. Troxerutin, a flavonoid present in tea, coffee, cereal grains, and a variety of fruits and vegetables, exhibits various pharmacological and biological activities. This study was carried out to investigate the effect of troxerutin on xenobiotic metabolizing enzymes, colonic bacterial enzymes and the development of aberrant crypt foci (ACF) during 1,2-dimethylhydrazine (DMH) induced experimental rat colon carcinogenesis. Male albino Wistar rats were randomly divided into six groups. Group 1 served as control. Group 2 received troxerutin (50 mg/kg b.w., p.o. every day) for 16 weeks. Groups 3-6 received subcutaneous injections of DMH (20 mg/kg b.w.) once a week, for the first four weeks. In addition, groups 4-6 received different doses of troxerutin (12.5, 25, 50 mg/kg b.w., p.o. every day respectively) along with DMH injections. Our results reveal that DMH treated rats exhibited elevated activities of phase I enzymes such as cytochrome P450, cytochrome b5, cytochrome P4502E1, NADPH-cytochrome P450 reductase and NADH-cytochrome b5 reductase and reduced activities of phase II enzymes such as glutathione-S-transferase (GST), DT-diaphorase (DTD) and uridine diphospho glucuronyl transferase (UDPGT) in the liver and colonic mucosa of control and experimental rats. Furthermore, the activities of fecal and colonic mucosal bacterial enzymes, such as β-glucronidase, β-glucosidase, β-galactosidase and mucinase were found to be significantly higher in DMH alone treated rats than those of the control rats. On supplementation with troxerutin to DMH treated rats, the alterations in the activities of the biotransforming enzymes, bacterial enzymes and the pathological changes were significantly reversed, the effect being more pronounced when troxerutin was supplemented at the dose of 25 mg/kg b.w. Thus troxerutin could be considered as a good chemopreventive agent against the formation of preneoplastic lesions in a rat model of colon carcinogenesis.

The impact of cholesterol and its metabolites on drug metabolism

INTRODUCTION

Global prevalence of Western-type diet has increased in the last decades resulting in occurrence of certain chronic diseases. This type of diet is also linked to high-cholesterol intake and increase in blood cholesterol. Many of the molecular mechanisms of dealing with increased levels of cholesterol and its metabolites have been elucidated in animal models and humans. It is also evident that cholesterol metabolism is closely connected to drug metabolism. Cholesterol/bile acids and drugs share many transporters, enzymes and regulatory proteins which are key points in the crosstalk.

AREAS COVERED

This review presents an overview of the effect of cholesterol and its metabolites on drug metabolism with special emphasis on species-specific differences. The article focuses on the role of nuclear receptors farnesoid X receptor, vitamin D receptor and liver X receptor in the regulation of drug metabolism genes and the role of cholesterol biosynthesis intermediates, oxysterols and bile acids in the induction of drug metabolism through pregnane X receptor.

EXPERT OPINION

Studies show that the regulation of drug metabolism by sterols is multileveled. Many species-dependent differences were observed which hinder the transfer of findings from model animals to humans. As of now, there is little evidence available for cholesterol impact on drug metabolism in vivo in humans. There is also the need to confirm the results obtained in animal models and in vitro analyses in human cells but this is very difficult given the current lack of tools.

Bile-acid-induced cell injury and protection

Several studies have characterized the cellular and molecular mechanisms of hepatocyte injury caused by the retention of hydrophobic bile acids (BAs) in cholestatic diseases. BAs may disrupt cell membranes through their detergent action on lipid components and can promote the generation of reactive oxygen species that, in turn, oxidatively modify lipids, proteins, and nucleic acids, and eventually cause hepatocyte necrosis and apoptosis. Several pathways are involved in triggering hepatocyte apoptosis. Toxic BAs can activate hepatocyte death receptors directly and induce oxidative damage, thereby causing mitochondrial dysfunction, and induce endoplasmic reticulum stress. When these compounds are taken up and accumulate inside biliary cells, they can also cause apoptosis. Regarding extrahepatic tissues, the accumulation of BAs in the systemic circulation may contribute to endothelial injury in the kidney and lungs. In gastrointestinal cells, BAs may behave as cancer promoters through an indirect mechanism involving oxidative stress and DNA damage, as well as acting as selection agents for apoptosis-resistant cells. The accumulation of BAs may have also deleterious effects on placental and fetal cells. However, other BAs, such as ursodeoxycholic acid, have been shown to modulate BA-induced injury in hepatocytes. The major beneficial effects of treatment with ursodeoxycholic acid are protection against cytotoxicity due to more toxic BAs; the stimulation of hepatobiliary secretion; antioxidant activity, due in part to an enhancement in glutathione levels; and the inhibition of liver cell apoptosis. Other natural BAs or their derivatives, such as cholyl-N-methylglycine or cholylsarcosine, have also aroused pharmacological interest owing to their protective properties.

Hesperetin exerts dose dependent chemopreventive effect against 1,2-dimethyl hydrazine induced rat colon carcinogenesis

Colon cancer is still one of the leading causes of death in USA and is increasing at an alarming rate in Asia. It is one of the major causes of death in industrialized countries, and its etiology is known to be a combination of hereditary, environmental, dietary factors and lack of physical activity. Chemoprevention plays a potential role in colorectal cancer. The present study was performed to evaluate the efficacy of hesperetin supplementation on colonic aberrant crypt foci, lipid peroxidation and antioxidant defense system in 1,2-dimethylhydrazine (DMH) induced colon carcinogenesis in male Wistar rats. The rats were segregated into six groups viz., group 1, control rats received modified pellet diet; group 2 rats received modified pellet diet along with hesperetin (30 mg/kg body weight/day); groups 3-6 administrated DMH (20 mg/kg body weight) subcutaneous injection once a week for the first 4 weeks; in addition groups 4-6 received hesperetin at three different doses of 10, 20 and 30 mg/kg body weight/day for 16 weeks. All the rats were sacrificed at the end of the experimental period of 16 weeks. Increased tumor incidence and increased number aberrant crypt foci (ACF) accompanied by a decrease in the tissue lipid peroxidation, glutathione S-transferase (GST), glutathione peroxidase (GPx), superoxide dismutase (SOD), and catalase (CAT) activities were observed in DMH-treated rats. Administration of hesperetin to DMH treated rats significantly decreased the tumor incidence, the number of aberrant crypt foci with simultaneous enhancement of tissue lipid peroxidation, GST, GPx, SOD, and CAT activities. The results of this study suggest that hesperetin at a dose of 20 mg/kg body weight showed a significant beneficial effect against chemically induced colonic carcinogenesis in rats as compared to the other two doses.

Decreased levels of mucosal detoxification enzymes in the pouch of patients with familial adenomatous polyposis

BACKGROUND

Adenomas can develop in the pouch after colectomy with ileal pouch-anal anastomosis (IPAA) in patients with familial adenomatous polyposis (FAP). Glutathione S-transferases (GSTs) have a protective role in carcinogenesis. GST activity is much higher in the ileum than in the colon. The present study examined the hypothesis that the protective capacity of GSTs may be lowered as a result of colonic metaplasia of the ileal pouch.

METHODS

Levels of GSTs, glutathione and cysteine, and the degree of inflammation and colonic metaplasia were quantified in biopsies from the pouch and afferent loop of 26 patients with FAP.

RESULTS

GST enzyme activity, and levels of GST alpha, glutathione and cysteine in the pouch were significantly lower than those in the afferent loop (308 versus 398 nmol per min per mg protein (P<0.001), 4604 versus 5286 ng per mg protein (P=0.010), 27.1 versus 34.8 nmol per mg protein (P=0.023) and 0 versus 4.8 nmol per mg protein (P=0.009) respectively). No correlation was found between inflammation or colonic metaplasia of the pouch and GST enzyme activity in the pouch.

CONCLUSION

After IPAA, GST detoxification activity in the pouch is significantly lower than that in the afferent ileal loop, which may promote tumorigenesis.

Interactions of high amylose starch and deoxycholic acid on gut functions in rats

OBJECTIVE

This study evaluated whether high amylose cornstarch (HAS) could prevent adverse physiologic effects induced by deoxycholic acid (DCA) in the gut of rats.

METHODS

Thirty-two male Sprague-Dawley rats were provided with a low amylose cornstarch (LAS) diet or a 50/50 mixture of LAS and HAS diets for 4 wk; each of these diets was supplemented with 0 or 2 g of DCA per kilogram of diet. Therefore, there were four groups.

RESULTS

Cecal content pH was lower in rats fed the HAS diets compared with rats fed the LAS diets (P < 0.05). Bifidobacteria number in cecal contents, cecal pools of acetate, butyrate, and total short-chain fatty acids were highest in rats fed the HAS diet; moreover, the HAS/DCA diet resulted in increased Bifidobacteria growth and short-chain fatty acid production numerically compared with the LAS/DCA diets (P = 0.06). Production of prostaglandin-E2 in colonic mucosa was highest in rats fed the LAS/DCA diet, and the intake of HAS significantly decreased prostaglandin-E2 levels (P < 0.05).

CONCLUSIONS

In this study, DCA may have inhibited fermentation in the large intestine and increased prostaglandin-E2 production, and concurrent administration of HAS and DCA may have decreased the adverse effects on the gut induced by DCA.

Chemoprevention of N-methylnitrosourea-induced colon carcinogenesis by ursodeoxycholic acid-5-aminosalicylic acid conjugate in F344 rats

Bile acids enhance colon carcinogenesis in animal models, whereas ursodeoxycholic acid (UDCA) suppresses it. Nonsteroid anti-inflammatory drugs prevent colon cancer development in animals and humans. The aim of the present study was to explore the inhibitory effect of UDCA conjugate with 5-aminosalicylic acid (5-ASA), UDCA-5-ASA conjugate (UDCA-5-ASA), against colon carcinogenesis in rats. One-hundred-and-twenty-nine 7-week-old F344 rats received an intrarectal instillation of 2 mg of N-methylnitrosourea 3 times a week for 3 weeks, and were fed a 0% (control), 0.11% or 0.02% UDCA-5-ASA-, 0.08% UDCA- or 0.03% 5-ASA-supplemented diet for the next 27 weeks. The test diets contained an equimolar amount of a test agent, 2.0 mmol/kg diet, except for the 0.02% UDCA-5-ASA diet. The tumor incidence and the mean number of tumors/rat at week 30 were significantly lower and smaller in the UDCA-5-ASA diet groups, 48% and 0.7 in both, and marginally lower in the UDCA and 5-ASA diet groups, 56% and 0.9, and 64% and 0.8, compared to the control group, 83% and 1.3. All the tumors were polypoid in shape, and most of them were differentiated adenocarcinomas restricted to the mucosa or submucosa. An analysis by HPLC for bile acids and 5-ASA in the feces and serum collected at week 30 showed that one-half of ingested UDCA-5-ASA was cleaved into UDCA and 5-ASA in the colon. Thus, the two moieties may have independently affected the promotion stage of carcinogenesis.

Glutathione S-transferase-pi overexpression is closely associated with K-ras mutation during human colon carcinogenesis

BACKGROUND & AIMS

In colorectal adenoma and carcinoma, glutathione S-transferase-pi (GSTP1-1) is highly expressed. K-ras mutation is also known to occur frequently in colorectal adenoma and carcinoma, as well as in the putative precursor of adenoma, aberrant crypt foci (ACF). Further, forced expression of v-H-ras in rat liver epithelial cells has been shown to enhance rat pi-class GST expression. The aim of the present study is, therefore, to investigate the causative relationship between GSTP1-1 overexpression and K-ras mutation in these lesions.

METHODS

Twenty-seven specimens of colorectal carcinoma, 24 of adenoma, and 28 of ACF were examined in this study. The expression of GSTP1-1 or p21(K-ras) was examined by immunohistochemistry. The GSTP1-1 messenger RNA levels were measured by TaqMan reverse-transcription polymerase chain reaction (PCR). K-ras mutation was detected by two-step PCR restriction fragment length polymorphism. v-K-ras transfection to RPMI-4788 colon carcinoma cells was carried out by the lipofection method. Activities of GSTP1-1 promoters containing AP-1 and Sp1 responsive elements in the v-K-ras transfectants were measured by a secreted form of human placental alkaline phosphatase (SEAP) assay. Nuclear protein from these transfectants bound to the GSTP1-1 promoter was analyzed by electrophoretic mobility shift assay (EMSA).

RESULTS

In human colorectal carcinoma, adenoma, and ACF, close association of increased expression of GSTP1-1 with K-ras mutation was observed. v-K-ras transfectants showed significantly higher SEAP activity than that of mock-transfectant activity. EMSA showed specific interaction of AP-1 with promoter of GSTP1-1.

CONCLUSIONS

It is highly plausible that GSTP1-1 overexpression in ACF, colorectal adenoma, and carcinoma is induced by K-ras mutation via AP-1 activation.

Evaluation of fecal mutagenicity and colorectal cancer risk

Colorectal cancer is one of the most common internal malignancies in Western society. The cause of this disease appears to be multifactorial and involves genetic as well as environmental aspects. The human colon is continuously exposed to a complex mixture of compounds, which is either of direct dietary origin or the result of digestive, microbial and excretory processes. In order to establish the mutagenic burden of the colorectal mucosa, analysis of specific compounds in feces is usually preferred. Alternatively, the mutagenic potency of fecal extracts has been determined, but the interpretation of these more integrative measurements is hampered by methodological shortcomings. In this review, we focus on exposure of the large bowel to five different classes of fecal mutagens that have previously been related to colorectal cancer risk. These include heterocyclic aromatic amines (HCA) and polycyclic aromatic hydrocarbons (PAH), two exogenous factors that are predominantly ingested as pyrolysis products present in food and (partially) excreted in the feces. Additionally, we discuss N-nitroso-compounds, fecapentaenes and bile acids, all fecal constituents (mainly) of endogenous origin. The mutagenic and carcinogenic potency of the above mentioned compounds as well as their presence in feces, proposed mode of action and potential role in the initiation and promotion of human colorectal cancer are discussed. The combined results from in vitro and in vivo research unequivocally demonstrate that these classes of compounds comprise potent mutagens that induce many different forms of genetic damage and that particularly bile acids and fecapentaenes may also affect the carcinogenic process by epigenetic mechanisms. Large inter-individual differences in levels of exposures have been reported, including those in a range where considerable genetic damage can be expected based on evidence from animal studies. Particularly, however, exposure profiles of PAH and N-nitroso compounds (NOC) have to be more accurately established to come to a risk evaluation. Moreover, lack of human studies and inconsistency between epidemiological data make it impossible to describe colorectal cancer risk as a result of specific exposures in quantitative terms, or even to indicate the relative importance of the mutagens discussed. Particularly, the polymorphisms of genes involved in the metabolism of heterocyclic amines are important determinants of carcinogenic risk. However, the present knowledge of gene-environment interactions with regard to colorectal cancer risk is rather limited. We expect that the introduction of DNA chip technology in colorectal cancer epidemiology will offer new opportunities to identify combinations of exposures and genetic polymorphisms that relate to increased cancer risk. This knowledge will enable us to improve epidemiological study design and statistical power in future research.

Fecal excretion pattern of bile acids in rats fed high fat diets and neomycin in induced colon tumorigenesis

Neomycin augments colon tumorigenesis in 1,2 - dimethylhydrazine treated rats fed polyunsaturated fat diet and decreases fecal cholic acid excretion, while it inhibits tumorigenesis with increased cholic acid and decreased deoxycholic acid excretions in rats fed high cholesterol diet. Participation of other fecal bile acids seems to be insignificant in relation to colon carcinogenesis.

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.