Beef meat and blood sausage promote the formation of azoxymethane-induced mucin-depleted foci and aberrant crypt foci in rat colons

Red meat intake is associated with colon cancer risk. Puzzlingly, meat does not promote carcinogenesis in rat studies. However, we demonstrated previously that dietary heme promotes aberrant crypt foci (ACF) formation in rats given a low-calcium diet. Here, we tested the hypothesis that heme-rich meats promote colon carcinogenesis in rats treated with azoxymethane and fed low-calcium diets (0.8 g/kg). Three meat-based diets were formulated to contain varying concentrations of heme by the addition of raw chicken (low heme), beef (medium heme), or black pudding (blood sausage; high heme). The no-heme control diet was supplemented with ferric citrate and the heme control diet with hemoglobin to match iron and heme concentrations in the beef diet, respectively. After 100 d, colons were scored for ACF and mucin-depleted foci (MDF). Fecal water was assayed for lipoperoxides and cytotoxicity. Only diets with heme promoted the formation of MDF, but all meat diets promoted ACF formation. The number of MDF/colon was 0.55 +/- 0.68 in controls, but 1.2 +/- 0.6 (P = 0.13), 1.9 +/- 1.4 (P < 0.01), and 3.0 +/- 1.2 (P < 0.001) in chicken-, beef-, and black pudding-fed rats. MDF promotion by the high-heme black pudding diet was greater than that by the medium-heme beef diet. The number of ACF/colon was 72 +/- 16 in controls, but 91 +/- 18, 100 +/- 13, and 103 +/- 14 in chicken-, beef-, and black pudding-fed rats (all P < 0.001). ACF and MDF did not differ between rats fed the beef diet and those fed the heme control diet. MDF promotion was correlated with high fecal water lipoperoxides and cytotoxicity (r = 0.65, P < 0.01). This is the first study to show the promotion of experimental carcinogenesis by dietary meat and the association with heme intake.     

Effect of simple phenolic compounds on azoxymethane-induced aberrant crypt foci in rat colon

Because complex mixtures of plant polyphenols exert anticancer activity in animal models, we investigated whether low-molecular-weight natural phenolic compounds (2-OH-coumaric acid, 3-OH-coumaric acid, 4-OH-coumaric acid, 3-OH-flavone, 7-OH-flavone, 4-OH-benzoic acid, 3-OH-benzoic acid, and 2,3-OH-benzoic acid) affect azoxymethane (AOM)-induced aberrant crypt foci (ACF), which have been suggested to represent preneoplastic lesions, in the colon of rats. Male Fischer 344 rats were fed diets supplemented with 0.1% (wt/wt) of the different phenolic compounds, and after 2 wk they were treated twice (1 wk apart) with AOM (15 mg/kg s.c.); the dietary treatment continued until sacrifice, 7 wk after the first injection with AOM. The results showed that none of these phenolic compounds exerted chemopreventive activity on the ACF assay. On the contrary, 3-OH-flavone slightly, although significantly, increased (P < 0.05), the number of ACF per colon [157 +/- 7 and 198 +/- 14 (SE) in control and 3-OH-flavone groups, respectively, n = 10]. We also found that the number of "large" ACF was significantly increased in the group treated with 4-OH-benzoic acid. In conclusion, none of the phenolic compounds tested demonstrated a suppressive action on ACF induction by AOM.     

Inhibition by ginseng of 1,2-dimethylhydrazine induction of aberrant crypt foci in the rat colon

The modifying effects of dietary administration of ginseng on the induction and development of 1,2-dimethylhydrazine (DMH)-induced aberrant crypt foci (ACF) were investigated in Fischer 344 (F-344) rats. In Experiment 1, starting at six weeks of age, 65 rats were injected with DMH or saline alone once a week for four weeks. Rats in Groups 1 and 2 were fed diets containing 1% ginseng for five weeks, starting one week before the first dose of DMH. Animals in Groups 3 and 4 received ginseng for eight weeks after DMH treatment; Group 5 served as a carcinogen control group. In Experiment 2, 60 rats were injected with DMH or saline alone four times at one-week intervals. They were also fed diets containing 1% ginseng or the control diet throughout the 30 days of the experiment. In Experiment 1, numbers of foci with at least four crypts were significantly reduced in Group 2 treated with red ginseng during the initiation phase (p < 0.005). In Experiment 2, treatment with red ginseng also resulted in a decrease in the total number of DMH-induced ACF accompanied by a reduction in 5-bromo-2'-deoxyuridine labeling indexes in colonic crypts comprising ACF (p < 0.005 and p < 0.05, respectively). These findings suggest that dietary administration of red ginseng in combination with DMH suppresses colon carcinogenesis of rats, and the inhibition may be associated, in part, with suppression of cell proliferation in the colonic mucosa.     

Egg yolk proteins suppress azoxymethane-induced aberrant crypt foci formation and cell proliferation in the colon of rats

Dietary proteins can influence colonic carcinogenesis; some proteins have a promotional effect, whereas others exhibit a preventive effect. Dietary egg yolk proteins have been reported to suppress the expression of colon tumors in rats. In this study, we investigated the effect of consumption egg yolk proteins on cell proliferation in a rat model of azoxymethane (AOM)-induced colon cancer. We hypothesize, based on the literature of egg yolk protein actions, that they protect against colon tumor development. Therefore, male F344 rats were fed a purified AIN-93G diet containing either 20% casein (control) or 20% egg yolk proteins for 5 weeks. After 1 week on the experimental diet, the rats were administered weekly subcutaneous injections of saline or AOM for 2 weeks to induce aberrant crypt foci. Rats were administered an intraperitoneal injection of 5-bromo-2′-deoxyuridine 1 hour before being euthanized for examination of DNA synthesis in the colonic mucosa. The contents of the cecum were analyzed for the presence of short-chain fatty acids (SCFAs). In the AOM-injected rats, the yolk protein diet suppressed aberrant crypt foci formation and reduced the proliferative 5-bromo-2′-deoxyuridine–labeling index in the proximal colon when compared with the control diet. A significant increase in cecal SCFAs was observed in the rats that were fed egg yolk proteins. These results indicate that dietary egg yolk proteins have a preventive effect on AOM-induced large bowel carcinogenesis in rats; it exerts this effect by altering cell proliferation through SCFA production. This study suggests that the consumption of egg yolk proteins might be protective against colon carcinogenesis.     

Oral administration of butyrivibrio fibrisolvens, a butyrate-producing bacterium, decreases the formation of aberrant crypt foci in the colon and rectum of mice

Butyrivibrio fibrisolvens, a butyrate-producing ruminal bacterium, was evaluated for use as a probiotic to prevent colorectal cancer. Oral administration to Jcl:ICR mice of a new strain of B. fibrisolvens (MDT-1) that produces butyrate at a high rate (10(9) cfu/dose) increased the rate of butyrate production by fecal microbes, suggesting that MDT-1 can grow in the gut. The number of colorectal aberrant crypt foci (ACF), putative preneoplastic lesions induced by 1,2-dimethylhydrazine, was reduced after MDT-1 administration (10(9) cfu/dose, 3 times/wk for 4 wk). The number of aberrant crypts (ACs), number of foci having 3 or 4 ACs per focus, and the percentage of mice having 3 or 4 ACs per focus were also reduced, suggesting that the progress of lesions was suppressed by MDT-1. Interestingly, the MDT-1 cell homogenate did not have a similar beneficial effect. MDT-1 had low beta-glucuronidase activity, and administration of MDT-1 reduced the beta-glucuronidase activity in the colorectal contents. The numbers of natural killer (NK) and NKT cells in the spleen were markedly enhanced in response to MDT-1. Decreased beta-glucuronidase activity and increased numbers of NK and NKT cells and butyrate production may explain in part why MDT-1 administration suppressed ACF formation. These results suggest that colorectal cancer may be prevented or suppressed by the utilization of MDT-1 as a probiotic. Administration of MDT-1 had no harmful effect on the health of mice at least for 3 mo.     

A diet containing alpha-cellulose and fish oil reduces aberrant crypt foci formation and modulates other possible markers for colon cancer risk in azoxymethane-treated rats

There is a need for better understanding of the roles of dietary fats and fibers in colon cancer risk. We examined the effect of different dietary fiber and fat sources on an azoxymethane (AOM)-induced colon cancer in rats. In a 2 x 3 factorial design, rats were fed a semipurified diet containing soy-derived fiber (Fibrim), alpha-cellulose (Solkafloc) or resistant starch (RS; Hi-maize) at 10 g dietary fiber/100 g diet, combined with fish oil (FO) or sunflower seed oil (SSO) at 10 g/100 g diet, and lard added to all diets at 10 g/100 g, to provide a total of 20 g mixed fat/100 g diet. Sprague-Dawley rats (28 d of age) consumed diets for 4 wk and then two doses of AOM (15 mg/kg body) were administered 1 wk apart by subcutaneous injection. Rats were killed after 13 wk of consuming experimental diets. Colons were fixed in formalin and aberrant crypt foci (ACF) were quantified after staining. ACF counts were higher (+66%, P < 0.01) in rats fed SSO and RS, than in those fed alpha-cellulose and FO. Rats fed FO had 19% fewer ACF than those fed SSO (P < 0.05). alpha-Cellulose was associated with the highest cecal butyrate concentration (P < 0.001), the highest beta-glucuronidase specific activity (P < 0.001) and the lowest cecal water cytotoxicity (P < 0.001) relative to soy fiber- and RS-fed rats. There were inverse correlations between the number of ACF and cecal butyrate concentration (r = -0.33, P < 0.05) and between cecal water cytotoxicity and beta-glucuronidase activity (r = -0.70, P < 0.001). The greatest protection was associated with alpha-cellulose as the fiber source and FO as the fat source as measured by colon ACF numbers in rats.     

Carrageenan gel and aberrant crypt foci in the colon of conventional and human flora-associated rats

Carrageenans (CAR) are sulfated polymers from seaweed used as gelling agents in foods. Chemical carcinogen induction of tumors in the colon of rats is enhanced by CAR. We speculated that gut microflora is involved in this effect. We thus studied the initiating and promoting effects of undegraded CAR-kappa (345,000 mol wt) in conventional rats and in germ-free rats associated with a human fecal flora. The initiating effect of CAR was studied by scoring aberrant crypt foci (ACF) in the colon of Fischer 344 rats given CAR (10% in water). The promoting effect of CAR was studied by comparing the multiplicity of ACF (number of crypts/focus) in rats receiving pure water or CAR (0.25% and 2.5% in water) for 100 days, starting 7 days after azoxymethane initiation (1 dose of 20 mg/kg i.p.). Duplicate studies were conducted in conventional rats and in human flora-associated rats maintained in isolators. Results show that CAR did not initiate ACF. In conventional rats, the 2.5% CAR gel promoted the growth of ACF: 2.98 +/- 0.29 and 3.44 +/- 0.48 crypts/ACF in control and treated rats, respectively (p < 0.02). The 0.25% CAR gel did not promote ACF. CAR can thus enhance intestinal tumors in this rat model, but only at a high dose level. In contrast, we did not observe any promoting effect of the administration of the 2.5% CAR gel in human flora-associated rats: 2.81 +/- 0.18 and 2.78 +/- 0.38 crypts/ACF in control and treated rats, respectively (p = 0.80). The specific microflora of rats, but not the human gut flora, might be involved in colon tumor enhancement by CAR.     

Insulin injections promote the growth of aberrant crypt foci in the colon of rats

The main objective of the present study was to test the hypothesis that exogenous insulin would enhance colon carcinogenesis. Thirty‐six female Fischer 344 rats were fed ad libitum a low‐fat rodent chow and given a single azoxymethane injection (20 mg/kg) one week later, they were randomized into two groups. Control rats were given a subcutaneous saline injection, 5 dayslwk, and experimental rats were given Ultralente bovine insulin (20 U/kg). The promoting effect of insulin injections was assessed by the multiplicity (number of crypts) of aberrant crypt foci after 100 days of treatment (72 injections). The rats given insulin ate more and were heavier than controls (215 ± 11 vs. 182 ± 7 g, p < 0.001). Insulin injections also increased the amount of abdominal fat, plasma triglycerides, and in‐sulinemia and decreased blood glucose (all p < 0.05). The number of aberrant crypt foci was the same in both groups, but their multiplicity was significantly increased by the insulin injections (2.8 ± 03 vs. 2.5 ± 0.2 crypt/focus in controls, p = 0.007). In addition, the proportion of sialomucin‐producing foci was higher in insulin‐injected rats than in controls (p = 0.04). These data show that exogenous insulin can promote colon carcinogenesis in rats and suggest that life‐style and diets leading to low blood insulin might protect humans against colorectal cancer.     

Consumption of sericin suppresses colon oxidative stress and aberrant crypt foci in 1,2-dimethylhydrazine-treated rats by colon undigested sericin

This study was conducted to examine the mechanisms of the anti-colon tumor effect of dietary sericin. Dietary supplementation of 3% sericin reduced colon mucosal lipid peroxide and aberrant crypt foci in 1,2-dimethylhydrazine-treated rats. The colon content from sericin-fed rats had much stronger antioxidant activity compared to that from control rats not receiving sericin. The amino acid composition of undigested proteins in the colon contents from sericin-fed rats was similar to that of sericin ingested. The results suggest that the strong antioxidant activity of undigested sericin in the colon content causes lower oxidative stress and tumorigenesis in the colon.     

Fish oil decreases oxidative DNA damage by enhancing apoptosis in rat colon

To determine if dietary fish oil protects against colon cancer by decreasing oxidative DNA damage at the initiation stage of colon tumorigenesis, oxidative DNA damage, proliferation, and apoptosis were assessed by colonic crypt cell position using quantitative immunohistochemical analysis of 8-hydroxydeoxyguanosine (8-OHdG), Ki-67, and TUNEL assay, respectively. Sixty rats were provided one of two diets (corn oil or fish oil) and dextran sodium sulfate (DSS, an inducer of oxidative DNA damage) treatments (no DSS, 3% DSS, or DSS withdrawal). Fish oil feeding resulted in lower 8-OHdG levels (P = 0.038), higher levels of apoptosis (P = 0.035), and a lower cell proliferative index (P = 0.05) compared with corn oil feeding. In the top third of the crypt, fish oil caused an incremental stimulation of apoptosis with increased DNA damage (P = 0.043), whereas there was no such relationship with corn oil. Because polyps and tumors develop from DNA damage that leads to loss of growth and death control, the significant difference in fish oil vs. corn oil on these variables may account, in part, for the observed protective effect of fish oil against oxidatively induced colon cancer.     

Intrarectal administration of deoxycholate selectively reduces small aberrant crypt foci in the rat colorectum

We investigated whether intrarectal application of deoxycholate (DCA), taurine, DCA with taurine or taurodeoxycholate modifies the formation of aberrant crypts (ACs) induced by N,N′-dimethylhydrazine in the colorectum of WKAH rats. Administration of DCA led to a significant reduction in the number of aberrant crypt foci (ACF) in the colorectum. Interestingly, the administration of DCA selectively decreased the number of ACF with 1-3 aberrant crypts/focus (AC/focus) more effectively than did that of saline or taurine. As a result, there was an increasein the AC/focus ratio in the WKAH rats administered DCA. In conclusion, increased luminal concentration of DCA with enema resulted in a significant reduction in smaller ACF, which raised the AC/focus ratio in the colorectum of WKAH rats.     

Effects of green tea and high-fat diet on arachidonic acid metabolism and aberrant crypt foci formation in an azoxymethane-induced colon carcinogenesis mouse model

Excessive fat consumption is a risk factor for colon carcinogenesis, and green tea consumption may reduce the risk of colon and other cancers. The current study was designed to investigate the effects of green tea and a high-fat diet on arachidonic acid metabolism and aberrant crypt foci formation in an azoxymethane (AOM)-induced colon carcinogenesis mouse model. We also determined whether green tea consumption altered the size of regional fat pads. CF-1 female mice were maintained on either a high-fat (20% corn oil) or a low-fat (5% corn oil) diet. AOM was given subcutaneous at a dose of 7.5 mg/kg body weight at 6 wk and then a dose of 10 mg/kg at 7 wk of age. Two weeks after the second AOM injection, 0.6% green tea (6 mg tea solids/ml) was given as the drinking fluid and continued for 10 wk until the experiment was terminated. In the AOM-treated mice not receiving green tea, the high-fat diet significantly enhanced colonic levels of 5-lipoxygenase, leukotriene A4 hydrolase, and leukotriene B4, but it did not significantly alter prostaglandin E2 levels and aberrant crypt foci formation. In AOM-treated mice on the high-fat diet, green tea significantly decreased colonic levels of cytosolic phospholipase A2, 5-lipoxygenase, and leukotriene B4; green tea treatment also decreased the number of aberrant crypt foci (P < 0.05). The weights of parametrial and retroperitoneal fat pads were increased by the high-fat diet and decreased by green tea treatment. The current results indicate that green tea consumption and dietary fat modulate 5-lipoxygenase-dependent pathway of arachidonic acid metabolism during AOM-induced colon carcinogenesis. Green tea inhibits ACF formation in mice on a high corn oil diet, suggesting its possible inhibitory effect on colon carcinogenesis in populations such as those in Western countries that consume high amounts of fat.     

Effect of lactobacilli, bifidobacteria and inulin on the formation of aberrant crypt foci in rats

Summary Background Our studies were aimed at investigating the effect of lactic acid producing bacteria (LAB) or inulin, a natural source of non-digestible oligosaccharides derived from chicory, on the induction by carcinogens of aberrant crypt foci (ACF) in the colon, which are considered to be early precursor lesions of neoplasia. Methods Strains of Bifidobacterium longum, Lactobacillus casei and Lactobacillus acidophilus were administered to rats fed a purified high starch diet, under a variety of treatment protocols including daily gavage, via the drinking water and in the diet. The rats were treated with methyl-N-nitrosourea, 1,2-dimethylhydrazine, or azoxymethane (AOM) to induce ACF. Results In general, no consistent significant changes in ACF numbers were detected in these experiments. In one study, the basal diet of the rats was changed to one containing a higher level of fat (corn oil). Under these conditions, a significant decrease in AOM-induced colonic ACF was seen in rats given L. acidophilus or inulin. In a concurrent group of animals fed a low fat diet, no significant decrease in ACF was observed. Conclusions The results indicate that the type of diet fed can influence the detection of protective effects of LAB and oligosaccharides and that against the background of a diet with a level of fat typical of a Western diet, evidence for a protective effect of L. acidophilus and inulin towards colon cancer was obtained Received: 26 July 2001, Accepted: 26 November 2001     

Suppression of intestinal crypt cell proliferation and aberrant crypt foci by dietary quercetin in rats

Quercetin inhibits proliferation of human gastric and colonic cancer cells in vitro by suppressing mitosis and increasing apoptosis. Quercetin might therefore act as an anticarcinogen in the alimentary tract, but previous findings have been inconsistent. We fed rats quercetin at dietary concentrations of 1, 5, 20, and 50 g/kg. At < or = 20 g/kg, we observed a statistically significant reduction in the frequency of crypt cell mitosis in proximal, mid, and distal small intestine and in distal colon, amounting to approximately 40% of control at 1 g/kg. There was no effect on apoptosis. Quercetin metabolites, but not quercetin aglycone, were detected in plasma of rats fed quercetin at 20 and 50 g/kg. In a second experiment, rats were fed quercetin at 1 g/kg after treatment with 1,2-dimethylhydrazine to induce aberrant crypt foci. In dimethylhydrazine-treated and control rats, crypt cell mitosis was suppressed at 48 h and 42 days after injection, and there was a statistically significant reduction in the number of aberrant crypts and larger aberrant crypt foci (> 4 crypts/focus) in the distal colon of treated animals. These findings demonstrate that quercetin can inhibit intestinal crypt cell proliferation in vivo, but the effect diminishes as the level of dietary exposure increases. At low concentrations, dietary quercetin inhibits induction of aberrant crypts by a mechanism that does not involve increased crypt cell apoptosis.     

Dietary selenite and azadeoxycytidine treatments affect dimethylhydrazine-induced aberrant crypt formation in rat colon and DNA methylation in HT-29 cells

Several observations implicate a role for altered DNA methylation in cancer pathogenesis. The global level of DNA methylation is generally lower; however, DNA methyltransferase (Dnmt1) activity is usually higher in tumor cells than in normal cells. The purpose of this study was to investigate whether the Dnmt1 inhibitor, 5-aza-2'-deoxycytidine (aza-dC) would alter the effect of dietary selenium on the formation of aberrant crypts. Weanling rats (n = 60) were fed three concentrations of selenium (deficient, 0.1 and 2.0 mg/kg diet) in a Torula yeast-based diet. Half of the rats were injected weekly with aza-dC (1 mg/kg, subcutaneously) and half were injected with the vehicle control (PBS). After 3.5 wk of consuming the experimental diets, the rats were given two injections of dimethylhydrazine (DMH; 25 mg/kg, intraperitoneally). Rats fed the selenium-deficient diet and injected with PBS had significantly (P < 0.006) more aberrant crypts than rats fed 0.1 or 2.0 mg selenium/kg diet (244 +/- 21 vs. 165 +/- 9 and 132 +/- 14, respectively). In contrast, when rats were injected with aza-dC, there was a significant (P < 0.0001) reduction in aberrant crypt formation and dietary selenium had no effect (62 +/- 8 vs. 77 +/- 13 vs. 54 +/- 8, in rats fed 0, 0.1 and 2.0 mg selenium/kg diet, respectively). HT-29 cells cultured in the absence of selenium had significantly hypomethylated DNA but significantly more Dnmt1 protein expression than cells cultured in the presence of 1 or 2 micromol/L selenium. These results suggest that aza-dC treatment may protect selenium-deficient rats against carcinogen-induced aberrant crypt formation.     

饮茶对大鼠大肠变性隐窝病灶及大肠肿瘤的影响

以二甲基肼诱发Wistar大鼠大肠癌为模型,研究了绿茶和茶色素(红茶的主要成分)大肠癌的化学预防作用和对大肠肿瘤的影响。结果表明,在第16周2个饮茶组动物的变性隐窝病灶(ACF)形成数比阳性对照组显著减少(P< 0.01);在第32周时阳性对照组100% 发生了肿瘤(平均瘤数为2.6个/只,平均瘤体积为294.7m m 3/瘤)。绿茶组和茶色素组的平均瘤数抑制率分别为47.1% 和43.1% ,平均瘤体积抑制率分别为77.1% 和68.1% 。表明绿茶和茶色素对实验性大肠肿瘤具有预防作用,ACF作为一个有用的中间终点可代替癌发生率进行大肠癌化学预防剂研究     

Dietary inulin suppresses azoxymethane-induced aberrant crypt foci and colon tumors at the promotion stage in young Fisher 344 rats

This study was designed to determine the effect of 10% dietary long-chain inulin on the azoxymethane (AOM)-induced colonic preneoplastic aberrant crypt foci (ACF) and small intestinal and colon tumors at the initiation (I), promotion (P) and I + P stages (20 rats per treatment) in Fisher 344 male weanling rats. After an acclimatization period of 1 wk, groups of Fisher 344 male weanling rats were assigned to consume AIN 93G diet (control) or AIN 93G diet containing 10% inulin. All the rats received 16 mg/kg body AOM dissolved in saline subcutaneously at 7 wk of age followed by a second injection at 8 wk of age. An additional group of five rats received only saline and consumed the control diet. The rats received the assigned diets until asphyxiation by CO(2) at 16 wk of age for the ACF experiment and 45 wk for the end-point tumor experiment. Feed intake, weight gain, diarrheal index, cecal weight, cecal pH, ACF and tumors in the colon were determined. Rats fed inulin had diarrhea after 2 wk of feeding and recovered by approximately 4 wk. Cecal weight was greater in rats fed inulin and cecal pH was lower. The inulin group had more than 66% fewer aberrant crypts and 60% fewer ACF compared with the control group. Tumor incidences in the small intestine and colon of rats in the control, I, P and I + P groups were: 78, 31, 0 and 11% and 90, 73, 69 and 50%, respectively. The corresponding values for the distal portion of the colon were 87, 63, 45 and 33%, respectively. Colon tumors per tumor-bearing rat were 4.2, 3.09, 1.36 and 1.2 for the control, I, P and I + P groups, respectively. All groups differed, P < 0.05. The results of this study indicate that dietary long-chain inulin suppresses AOM-induced ACF formation, an early preneoplastic marker of colon tumorigenesis in rats, and colon tumors, particularly at the promotion stage.     

Vitamin E supplementation does not alter azoxymethane-induced colonic aberrant crypt foci formation in young or old mice

Vitamin E, part of the body's primary lipid-soluble defense against free radicals and reactive oxygen molecules, has been suggested to reduce the risk for some cancers. However, the role of vitamin E in the etiology and prevention of colon cancer, especially in the highest risk group, the aged, is not clear. Thus, this study was conducted to elucidate the effect of vitamin E supplementation on susceptibility to colon cancer by examining azoxymethane (AOM)-induced aberrant crypt foci (ACF) formation, a surrogate biomarker of colon cancer. Young (3-4 mo) and old (19-20 mo) C57BL/6JNIA mice were fed either a control diet (30 mg dl-alpha-tocopheryl acetate/kg diet) or a vitamin E-supplemented diet (500 mg dl-alpha-tocopheryl acetate/kg diet) for 16 wk. After 6 wk of dietary supplementation, young and old mice were injected with saline or AOM weekly for 5 wk to receive the same total dose of AOM (2.2 mg) and killed 10 wk after the first AOM injection. Vitamin E supplementation had no effect on the number of AOM-induced ACF in young or old mice. In addition, vitamin E supplementation did not have an effect on splenocyte interferon-gamma, interluekin-6 and tumor necrosis factor-alpha levels, natural killer cell killing activity or colonic cell proliferation in young or old mice. Thus, alpha-tocopherol does not seem to affect the initiation and early promotion stages of AOM-induced colon carcinogenesis in young or old mice. Whether vitamin E supplementation might be effective in reducing AOM-induced colon tumors is unclear.     

Diverse effect of fish oil on the growth of aberrant crypt foci and tumor multiplicity in F344 rats

The main objective of the present study was to investigate the amenability of preneoplastic lesions at different developmental stages to the growth‐regulatory effects of two types of dietary lipids. F344 male rats were given three injections of azoxymethane (15 mg/kg) and fed a low‐fat corn oil diet for 12 weeks to allow preneoplastic lesions or aberrant crypt foci (ACF) to develop. At this time, the colons of rats had a large number of ACF exhibiting various crypt multiplicities (number of crypts/focus). These rats were then randomly allocated to three dietary groups: high‐fat corn oil (HFC), high‐fat fish oil (HFF), and low‐fat corn oil (LFC). The number and crypt multiplicity of ACF and adenomatous lesions were determined after 6 and 12 weeks of dietary intervention. After six weeks, the HFF group had the highest number of ACF of all crypt multiplicities and microadenomas among the dietary groups. After 12 weeks of feeding, the HFC diet increased the number of tumors without significantly changing the number of ACF. In contrast, the HFF diet increased significantly (p < 0.05) the number of ACF with higher crypt multiplicity without affecting the number of tumors. Consequently, the total number of tumors per group in decreasing order was as follows: HFC > LFC > HFF. These findings suggest that dietary lipids varying in fatty acid composition, namely corn oil and fish oil, exerted a growth‐enhancing and ‐inhibiting effect, respectively, on different preneoplastic stages in a selective and differential manner. Most notably, transition of microscopic preneoplastic lesions to macroscopic lesions (microadenomas or adenomas) appears to be retarded by an HFF diet.     

Feeding soybean resistant protein to rats raises fecal bile acid excretion but counteracts a deoxycholate-caused decrease in colonic aberrant crypt foci.

A high-molecular-weight fraction after removal of water-soluble peptides from proteinase-treated soybean protein isolate (referred to as HMF) was examined for its effect on preneoplastic lesions in the rat colon. For this purpose, male Fisher-344 rats 7 wk old were divided into 8 groups (n = 5), of which 6 groups received 3 injections of azoxymethane (AOM, 15 mg/kg of body weight) for 3 wk once a week, while all were fed HMF or casein diets supplemented with or without deoxycholic acid (DCA) over a period of 4 wk. Two groups of AOM-treated rats were allowed free access to HMF or casein diets without supplemental DCA, respectively, while the others were pair-fed so as to be well matched in their food intake. There were no significant differences in growth parameters among the pair-fed groups. Feeding HMF diets raised fecal lipid and acidic steroid excretions to a greater extent than feeding casein diets, secondary bile acids being conspicuous among acidic steroids in the excreta irrespective of the presence or absence of DCA supplementation. As a result of observation for colonic aberrant crypt foci (ACF), the intake of HMF proved to reverse the reduction of ACF appearance by DCA. This result implies that secondary bile acids are caught and brought out by HMF, or rather its derivative "resistant protein," so as not to keep contact with colonic mucosae.