Reduction of colonic carcinogenesis by wheat bran independent of fecal bile acid concentration

It has been reported previously that populations with a decreased concentration of fecal bile acids have a lower incidence of colon cancer. We examined the importance of fecal bile acid dilution by wheat bran (WB) in inhibiting colonic tumorigenesis in an experimental animal model. Male F344 rats received oral doses of the colon carcinogen 1,2-dimethylhydrazine [CAS: 540-73-8] and were assigned randomly to groups fed one of four semipurified diets for 26 weeks. The diets were fiber-free (FF), 10% WB, FF + bile salts, or WB + bile salts. The amount of bile salts added was adjusted to produce a fecal bile acid concentration in the group fed WB + bile salts equal to that found in the FF groups. Fecal bile acid concentrations at 12 and 24 weeks in the WB + bile salts group were similar to those in the FF group. Gross and microscopic findings at necropsy revealed a reduced total number and multiplicity of colon tumors in both bran-fed groups. Although the fecal bile acid concentrations of the FF and WB + bile salts groups were equal, the latter showed a significant reduction in tumor yield.     

Ursodeoxycholic acid inhibits the initiation and postinitiation phases of azoxymethane-induced colonic tumor development.

Colonic tumorigenesis involves the processes of initiation and promotion/progression from normal epithelial cells to tumors. Studies in both humans and experimental models of colon cancer indicate that secondary bile acids promote tumor development. In contrast, we have demonstrated previously that another bile acid, ursodeoxycholic acid (UDCA), inhibits the development of azoxymethane (AOM)-induced colon cancer in rats. More recently, we have shown that UDCA inhibits AOM-induced hyperproliferation, and aberrant crypt formation and growth. In our previous studies, we supplemented UDCA throughout the experiment. The efficacy of a chemopreventive agent may depend on the timing of administration, which has important clinical implications. In the present investigation, we examined the ability of UDCA, when administered only in the initiation or the promotion/progression phase, to block tumor development. Male Fisher 344 rats were divided in a 2 x 3 factorial design, with animals receiving AOM or vehicle, and fed an unsupplemented diet or diet supplemented with 0.4% UDCA in the initiation or promotion/progression phase. Thirty-two weeks later, rats were sacrificed and tumor histology determined, and colons were examined for aberrant crypt foci (ACF). In the carcinogen-treated dietary control group, tumor incidence was 72.3%, and tumor multiplicity was 1.9 tumors per tumor-bearing rat. UDCA, in the initiation or promotion/progression phase, significantly decreased tumor incidence to 46.2% and 38.4% (P < 0.05), respectively; and tumor multiplicity to 1.4 and 1.3 tumors per tumor-bearing rat (P < 0.05), respectively. UDCA did not alter tumor size, histology, or location, although there were trends for smaller tumors and less advanced histological grades in the group given UDCA during the promotion phase. UDCA, in the initiation but not the promotion phase, inhibited ACF formation and growth. In summary, UDCA significantly inhibited AOM-induced colonic carcinogenesis during either tumor initiation or in the promotion/progression phase. In contrast, UDCA inhibited ACF formation only when administered in the initiation phase, suggesting that the mechanisms of chemoprevention by this bile acid differ in these two phases.     

An association between genetic polymorphisms in the ileal sodium-dependent bile acid transporter gene and the risk of colorectal adenomas.

Epidemiological and experimental studies have implicated bile acids (particularly secondary bile acids) as important factors in the development of colorectal cancer. The ileal sodium-dependent bile acid transporter (ISBT) is a crucial player in the enterohepatic circulation of bile acids. Genetic defects in ISBT may result in malabsorption of bile acids and a loss of bile acids into the large intestine, with a resultant increase in the cytotoxic secondary bile acids in the colon. In a case-control study, we investigated the association between two sequence variations in SLC10A2, the gene encoding ISBT, and colorectal adenomas, a precursor lesion of colorectal cancer. The frequency of the missense mutation in codon 171 of exon 3 (a nucleotide transversion from G to T resulting in an alanine to serine substitution) was not significantly different between cases and controls. However, we found a 2-fold higher risk of colorectal adenomas associated with a C-->T nucleotide transition in codon 169 of exon 3 (odds ratio = 2.06; 95% confidence interval: 1.10-3.83). Logistic regression analysis using A171S/169 C-->T haplotypes as the allelic markers showed that among AA wild-type homozygotes for A171S mutation, this C-->T nucleotide transition in codon 169 was associated with a 2.42 times increased risk (odds ratio = 2.42; 95% confidence interval: 1.26-4.63). This initial observation of an association between a polymorphism in the SLC10A2 gene and the risk of colorectal adenomatous polyps would, if confirmed by other studies, support the role of bile acids in the carcinogenesis of colorectal cancer.     

Oral administration of cholic acid promotes growth of liver tumors initiated by diethylnitrosamine in rats.

The effect of dietary administration of cholic acid on tumorigenesis in the liver was investigated in male Fischer-344 rats after carcinogenic initiation by diethylnitrosamine (DEN); progression of liver tumors was examined in the rats fed 0.4% cholic acid-containing diet (CA group) and the rats fed standard diet (C group) at 15, 20 and 25 weeks after administration of DEN. The total bile acids and cholic acid in serum of CA group were 150 nmol/ml and 117 nmol/ml, being 31-fold and 51-fold higher than those in C group (p<0.0001, each). Serum AST and ALT were significantly higher in CA group than in C group at 15 weeks (p<0.01). Serum ALP was significantly higher in CA group than C group at each time point (p<0.01, each). Liver tumors, whose histology was hepatocellular carcinoma, developed at 15 weeks in both CA and C groups. However, tumor volume and tumor weight were significantly increased in CA group, compared to those in C group at each time point (p<0.001, p<0. 001, p<0.01, p<0.001, p<0.01 and p<0.05). The percentage of apoptotic cells in CA group at each time point was significantly lower than C group (p<0.05, p<0.01 and p<0.05). The percentage of bcl-2 positive tumor cells in C group at 20 weeks was 1.88+/-2.59%. However, it dramatically increased to 34.00+/-13.67% in CA group (p<0.0001). It was also higher in CA group than in C group at 15 and 25 weeks (p<0.05 and p<0.01). In addition, the bax-positive cells were higher in CA group than in C group at 20 weeks (p<0.05). These data suggest that oral administration of cholic acid promotes liver tumorigenesis initiated by DEN through reducing apoptosis mediated by overexpression of bcl-2.     

Anatomical site-specific response to DNA damage is related to later tumor development in the rat azoxymethane colon carcinogenesis model.

There is now general agreement that the etiology of proximal and distal colon cancers may differ, thus prompting renewed interest in understanding anatomical site-specific molecular mechanisms of tumor development. Using a 2x2x2 factorial design with male Sprague-Dawley rats (corn oil, fish oil; pectin, cellulose; plus or minus azoxymethane injection) we found a greater than 2-fold difference (P < 0.001) in tumor incidence proximally versus distally (prox/dist ratio: corn oil, 2.25; fish oil, 2.61). The purpose of the present study was to determine if the higher degree of proximal versus distal tumors in our model system could be accounted for by differences between these two sites in initial DNA damage, response to that damage or an effect of diet at one site but not the other. DNA damage was assessed by quantitative immunohistochemistry of O(6)-methylguanine adducts; repair by measurement of O(6)-methylguanine-DNA alkyltransferase and removal was determined by measurement of targeted apoptosis. Although overall initial DNA damage was similar at both sites, in the distal colon there was a greater expression of repair protein (P < 0.001) and a greater degree of targeted apoptosis (P < 0.0001). There was also a reduction in DNA damage in the distal colon of rats consuming fish oil. Together, these results suggest that the lower tumor incidence in the distal colon may be a result of the capacity to deal with initial DNA damage by the distal colon, as compared with the proximal colon. Therefore, the determination of site-specific mechanisms in tumor development is important because distinct strategies may be required to protect against cancer at different sites.     

局部晚期宫颈癌后装腔内联合组织间插植剂量学及临床疗效分析

目的 研究后装腔内/组织间插植近距离治疗(IC/ISBT)与传统后装腔内近距离治疗(ICBT)相比较的剂量学差异及其近期疗效。方法 45例局部晚期宫颈癌患者采用IC/ISBT及ICBT方法进行后装近距离治疗,分别对两种治疗方法的A点(A1、A2)、D90%、D100%以及膀胱、结肠、直肠、小肠受量进行计算,同时观察近期疗效。结果 IC/ISBT比ICBT放疗A点剂量显著提升(P<0.05);并且IC/ISBT的D90%、D100%也均明显高于ICBT (P<0.05)。外照射后残存肿瘤直径≥3cm时,IC/ISBT比ICBT可获得较高的靶区剂量提升(P<0.05)。IC/ISBT与ICBT的膀胱、直肠、结肠、小肠D2cm³、D0.1cm³相近(P>0.05)。疗后1、3、6个月的近期疗效IC/ISBT与ICBT相近(P>0.05)。结论 局部晚期宫颈癌(残存肿瘤直径≥3cm)后装近距离治疗中IC/ISBT在不增加危及器官受量及降低近期疗效前提下显著地提高了靶区、A点剂量,具有明显剂量学优势。     

Analysis of dosimetry and clinical efficacy of intracavitary/interstitial brachytherapy in locally advanced cervical cancer

Objective To study the dosimetric differences and short-term efficacy between intracavitary/interstitial brachytherapy (IC/ISBT) and conventional intracavitary brachytherapy (ICBT). Methods Forty-five patients with locally advanced cervical cancer were treated with IC/ISBT and ICBT. Points A (A1,A2), D90%, D100%, organs at risk, and the doses of bladder, colon, rectum and small intestine were calculated and the short-term efficacy was observed between two groups. Results Point A dose was significantly improved in IC/ISBT compared with ICBT (P<0.05). The D90% and D100% in IC/ISBT were significantly higher than those in ICBT (both P<0.05). After brachytherapy, IC/ISBT could obtain a significantly larger increase in target dose when residual tumor diameter was ≥3 cm compared with ICBT (P<0.05). The D2cm³ and D0.1cm³ of bladder, rectum, colon and small intestine did not significantly differ between IC/ISBT and ICBT (all P>0.05). The 1-,3-and 6-month clinical efficacy did not significantly differ between two technologies (all P>0.05). Conclusion During brachytherapy for locally advanced cervical cancer (residual tumor diameter ≥3 cm), IC/ISBT significantly increases the doses of target area and point A without increasing the dose of organs at risk or lowering the short-term clinical efficacy, which has significant dosimetric advantages.     

Promoting effect of 5 beta-chol-3-en-24-oic acid on N-methyl-N-nitrosourea-induced colonic tumorigenesis in rats

The effect of 5 beta-chol-3-en-24-oic acid (delta 3) on N-methyl-N-nitrosourea (MNU)-induced colonic tumorigenesis was studied by intrarectal injection of these compounds in rats. Female Fischer rats received 0.5 ml of distilled water (DW) alone or DW containing 2.5 mg of MNU twice in one week followed by 0.5 ml of peanut oil (PO) alone or PO containing 1 mg of delta 3, or 1 mg of lithocholic acid (LC) thrice weekly for 48 weeks. Thus, 6 groups were employed as follows: group I, DW + PO (n = 12); group II, DW + delta 3 (n = 30); group III, DW + LC (n = 30); group IV, MNU + PO (n = 30); group V, MNU + delta 3 (n = 30) and group VI, MNU + LC (n = 37). Fecal bile acid profiles were analyzed before and during the treatment. Numbers of rats bearing colonic tumor were none in the groups without MNU, but 5 (17%) in group IV, 15 (50%) in group V and 12 (32%) in group VI (corrected X2 = 6.07, P less than 0.025 for group IV vs V, and 1.42, P less than 0.3 for group IV vs VI). Total numbers of tumors were 7, 17 and 15 in group IV, V and VI, respectively, and they were mostly adenomas and adenocarcinomas. A breast fibroadenoma in one rat of group VI was the sole extracolonic neoplasm in these rats. Total fecal bile acids ranged from 7.7 to 10.5 mumol/g dry feces during the study without any significant quantitative or qualitative difference with respect to with or without bile acids and MNU treatment. These results indicated that delta 3 promoted MNU-induced colonic tumorigenesis in rats without alteration in bile acid metabolism.     

Effect of Konjac mannan on 1,2-dimethylhydrazine-induced intestinal carcinogenesis in Fischer 344 rats

The effect of Konjac mannan (KM) on 1,2-dimethylhydrazine (DMH-induced intestinal carcinogenesis was studied in male F344 rats. Rats were fed a diet containing 5% KM at 5 weeks of age. At 6 weeks of age, all animals were given a weekly intraperitoneal injection of 20 mg DMH/kg body wt for 13 weeks and autopsied 13 weeks after the last injection of DMH. The weight gain was lower in rats fed the KM diet than in rats fed the control diet throughout the experiment (P less than 0.05). The incidence of DMH-induced colon tumors was lower in animals fed the KM diet compared to animals fed the control diet (P less than 0.05). The number of colon adenocarcinoma per animal was also lower in animals fed the KM than in animals fed the control diet (P less than 0.05). However, the incidence of tumors of the small intestine did not significantly differ between the groups fed the KM and control diets. The present study demonstrated that colon tumorigenesis induced by DMH in F344 rat was inhibited by maintaining the KM diet.     

Experimental colon cancer in the absence of intestinal contents in Sprague-Dawley rats

The proximal and distal ends of the transverse colons of 16 noninbred Sprague-Dawley rats were severed and stitched to their abdominal walls. The ascending and descending colons were anastomosed end-to-end. The disarticulated colon loop was rinsed 30 times over 15 days to remove all traces of dimethylhydrazine (21 mg/kg body wt) for 27 weeks. When rats were killed 3 weeks later, 4 had invasive carcinomas and 2 had tubular adenomas in the end-to-end anastomosed (function-isolated) colons. Three rats developed invasive carcinomas in the isolated (defunctionalized) colon loops. The carcinogen probably reached the isolated colon loop through the circulation and induced (independently of bile acids) mucosal changes that led to invasive carcinoma.     

Predictive value of proliferation, differentiation and apoptosis as intermediate markers for colon tumorigenesis

In order to determine the prognostic significance of proliferation, differentiation, and apoptosis as intermediate markers for colon tumor development, these indices were measured during the promotion phase of tumorigenesis. Two hundred and sixty male Sprague-Dawley rats were provided with one of two fats (corn oil and fish oil) and two fibers (pectin and cellulose) plus or minus the carcinogen azoxymethane (AOM) and killed at two time points (18 and 36 wk) in a 2x2x2x2 factorial design. In vivo cell proliferation was measured immunohistochemically using incorporation of bromodeoxyuridine into DNA. Differentiation was assessed by binding of Dolichos biflorus agglutinin (DBA) to colonocytes. Apoptosis was measured by immunoperoxidase detection of digoxigenin-labeled genomic DNA. Adenocarcinoma incidence results at week 36 were 70.3% for corn oil + AOM and 56.1% for fish oil + AOM treatment (P < 0.05); no main effect of fiber was observed. At week 18, AOM treatment increased the number of cells per crypt column in the proximal colon compared with saline controls (P = 0.0358) and increased the proliferative zone in the distal colon compared with controls (P = 0.0073). However, changes in cell proliferation at week 18 did not predict the beneficial effect of fish oil versus corn oil. In contrast, DBA binding (the marker for differentiation) was higher in fish oil versus corn oil fed animals in both the proximal and distal colon and in each portion of the crypt (P = 0.0001). There were a greater number of apoptotic cells/crypt column in the proximal colon (P = 0.0019) and distal colon (P = 0.0358) with fish oil compared with corn oil, and indices of apoptosis also predicted certain fat/fiber interactions. Measurements of differentiation and apoptosis had greater prognostic value to detect dietary effects on tumor incidence than did measurements of cell proliferation.      

Inhibitory effect of dietary perilla oil rich in the n-3 polyunsaturated fatty acid alpha-linolenic acid on colon carcinogenesis in rats.

The inhibitory effect of dietary perilla oil rich in the n-3 polyunsaturated fatty acid alpha-linolenic acid against colon carcinogenesis was investigated in rats. Four groups of 26 F344 rats each received an intrarectal dose of 2 mg of N-methyl-N-nitrosourea 3 times a week for 2 weeks, and received a diet containing 12% perilla oil, 6% or 12% safflower oil (rich in the n-6 polyunsaturated fatty acid linoleic acid), or 12% palm oil (rich in saturated and monounsaturated fatty acids). At week 35, the incidence of colon cancer was significantly lower in perilla oil-fed rats than in other dietary groups; 19% vs. 46%, 56% and 58%. When examined at week 10, the concentration of fecal bile acids, known to be tumor promoters, was not significantly different among the dietary groups, and the intrarectal deoxycholic acid-induced colonic mucosal ornithine decarboxylase activity, a marker of tumor promotion, was significantly lower in perilla oil-fed group than in other groups. The serum and colonic mucosal fatty acid compositions and the blood plasma prostaglandin E2 level directly reflected the fatty acid composition of each dietary fat. The results suggest that the anti-tumor-promoting effect of dietary perilla oil was a result of a decreased sensitivity of colonic mucosa to tumor promoters arising from the altered fatty acid composition in membrane phospholipid of colonic epithelial cells, and was not a consequence of a decrease of promoters such as bile acids.     

Effects of oral administration of sulfolithocholic acid disodium salt and lithocholic acid sodium salt on N-methyl-N-nitrosourea-induced colonic tumorigenesis in conventional rats

Effects of p.o. administration of sulfolithocholic acid disodium salt (SLCNa) and lithocholic acid sodium salt (LCNa) on N-methyl-N-nitrosourea (MNU)-induced colonic tumorigenesis were studied in conventional rats. Female F344 rats received either 0.5 ml of distilled water (DW) alone or DW containing 2.5 mg of MNU twice in 1 wk intrarectally. Then rats were fed freely on a basal diet (PCE-2) or PCE-2 containing LCNa or SLCNa (both at 0.5 mmol/100 g of PCE-2) for 40 wk. Thus, 6 groups were completed: MNU + PCE-2 (n = 30); MNU + LCNa (n = 29); MNU + SLCNa (n = 22); DW + PCE-2 (n = 17); DW + LCNa (n = 20); and DW + SLCNa (n = 19). Numbers of rats bearing colonic tumor were 3 (10%) in MNU + PCE-2, 2 (7%) in MNU + LCNa, and 8 (36%) in MNU + SLCNa group (uncorrected x2 = 9.35 among the 3 groups), but none in those groups without MNU. Total fecal bile acids in the rats given bile salts showed about 2-fold increase compared with those without bile salts. Fecal bile acid profiles between the LCNa and SLCNa groups were indistinguishable except for a slight increase of sulfolithocholic acid in the SLCNa groups. These results indicated that p.o. administration of SLCNa but not LCNa promoted MNU-induced colonic tumorigenesis in conventional rats. Fecal bile acid profiles did not support the higher tumor incidence in the MNU + SLCNa group compared with the MNU + LCNa group, which suggested that an unrecognized mechanism probably relating to desulfation of SLCNa was involved in this phenomenon.     

The inhibitory effect of magnesium hydroxide on the bile acid-induced cell proliferation of colon epithelium in rats with comparison to the action of calcium lactate

The modulating effects of magnesium hydroxide and calcium lactateon the cholic acid-induced hyperproliferation of cells In ratcolon epithelium were investigated. Rats were divided into sixgroups (10 rats/group) and fed the following diets for 8 weeks:0.25% cholic acid alone (group 1), cholic acid plus 0.2% magnesiumhydroxide (group 2), chollc acid plus 1.18% calcium in the formof calcium lactate (group 3), calcium lactate alone (group 4),magnesium hydroxide alone (group 5) and the basal diet alone(group 6). At the end of the experiment, all rats were killedfor the immunocytochemical examination of 5-bromo-2'-deoxyuridine(BrdU) incorporation in the cell nuclei of colonic epithelium.Magnesium hydroxide reduced the cholic acid induced BrdU incorporationby 33% at the distal part and 40% at the proximal part. Calciumlactate also reduced the BrdU incorporation by 48% and 51% respectively.Exposure of magnesium hydroxide or calcium lactate alone hadno influence on BrdU incorporation. The results suggest thatmagnesium hydroxide might exert anti-carcinogenic effects asdoes calcium by reducing increased cell proliferation of colonicepithelium induced by toxic effects of bile acids, which areregarded as colon tumor promoters or cocarcinogens.     

The TP53 colorectal cancer international collaborative study on the prognostic and predictive significance of p53 mutation: influence of tumor site, type of mutation, and adjuvant treatment.

PURPOSE: The aims of the TP53 Colorectal Cancer (CRC) International Collaborative Study were to evaluate the possible associations between specific TP53 mutations and tumor site, and to evaluate the prognostic and predictive significance of these mutations in different site, stage, and treatment subgroups. PATIENTS AND METHODS: A total of 3,583 CRC patients from 25 different research groups in 17 countries were recruited to the study. Patients were divided into three groups according to site of the primary tumor. TP53 mutational analyses spanned exons 4 to 8. RESULTS: TP53 mutations were found in 34% of the proximal colon tumors and in 45% of the distal colon and rectal tumors. They were associated with lymphatic invasion in proximal tumors. In distal colon tumors, deletions causing loss of amino acids were associated with worse survival. In proximal colon tumors, mutations in exon 5 showed a trend toward statistical significance (P < .05) when overall survival was considered. Dukes' C tumors with wild-type TP53 and those with mutated TP53 (proximal tumors) showed significantly better prognosis when treated with adjuvant chemotherapy. CONCLUSION: Analysis of TP53 mutations from a large cohort of CRC patients has identified tumor site, type of mutation, and adjuvant treatment as important factors in determining the prognostic significance of this genetic alteration.     

Modulation of experimental colon tumorigenesis by types and amounts of dietary fatty acids

Epidemiological studies and laboratory animal model assays suggest that a high intake of dietary fat promotes colorectal cancer. Several in vivo and in vitro studies support the hypothesis that omega-6 fatty acids promote colon tumorigenesis, whereas omega-3 fatty acids lack promoting activity. Fat intake in the United States traditionally includes high amounts (30% of total caloric intake) of saturated fat rather than omega-6 fatty acids. Therefore, the present study was designed to compare the modulatory effects of a high-fat diet containing mixed lipids (HFML), a diet rich in saturated fatty acids (the average American diet), a diet with fish oil (HFFO) that is rich in omega-3 fatty acids, and a low-fat corn oil diet (LFCO) on the formation of chemically induced colonic aberrant crypt foci (ACF) and tumors, cyclooxygenase (COX)-2 activity, and apoptosis during experimental colon carcinogenesis. At 5 weeks of age, groups of male F344 rats were fed a 5% corn oil diet (LFCO). At 7 weeks of age, rats intended for carcinogen treatment received s.c. injections of azoxymethane at a dose level of 15 mg/kg of body weight once weekly for 2 weeks. Beginning 1 day after the carcinogen treatment, groups of rats were then maintained on experimental diets containing 20% HFML or 20% HFFO. Rats were killed at 8, 23, or 38 weeks after azoxymethane treatment. Colonic ACF and tumors were evaluated histopathologically, and apoptosis was evaluated by the terminal deoxynucleotidyl transferase-mediated nick end labeling method. Colonic mucosae and tumor samples harvested at week 38 were analyzed for COX-2 synthetic activity and expression. The rats fed the HFML diet showed significantly increased total colonic ACF (P < 0.001-0.0001) with a multiplicity of > or = 4 aberrant crypts/focus (P < 0.0001) compared with the effects of the HFFO or LFCO diets at week 8, 23, and 38. Interestingly, there was a 2- to 3-fold increase (> or = 4) in multicrypt foci in rats given the HFML diet as compared with such foci in rats fed the HFFO or LFCO diets. By week 23, the HFML diet had significantly increased the incidence of colonic tumors (30-60%) and their multiplicity (100-141%) when compared with the effects of the LFCO or HFFO diets. At week 38, the HFML diet had induced 100% colon tumor incidence and a 4-fold multiplicity of adenocarcinomas compared with the LFCO and HFFO diets. At weeks 23 and 38, a significantly lower percentage of apoptotic colonic epithelial cells were observed in the tumors of animals fed the HFML diet as compared with those fed the HFFO diet. The HFML diet caused significantly increased levels of COX-2 activity in colon tumors (P < 0.05-0.01), and these tumors had enhanced levels of COX-2 expression as compared with those in assays with LFCO or HFFO diets. These observations demonstrate for the first time that HFML diets containing high levels of saturated fatty acids (such as those in Western diets) promote colon carcinogenesis. Although the mechanisms involved in colon tumor promotion by a HFML diet are not fully known, our results indicate that the modulation of eicosanoid production via the influence on COX activity and the suppression of apoptosis may play a key role in HFML diet-induced colon tumorigenesis.     

Dietary resistant starch type 3 prevents tumor induction by 1,2-dimethylhydrazine and alters proliferation, apoptosis and dedifferentiation in rat colon

Some epidemiological and experimental studies suggest that consumption of resistant starch is preventive against colon cancer. Resistant starch leads to a fermentation-mediated increase in the formation of short-chain fatty acids, with a particularly high butyrate fraction in large bowel. Butyrate is considered to be protective against colon cancer because it causes growth arrest and apoptosis and regulates expression of proteins involved in cellular dedifferentiation in various tumor cell lines in culture. We sought to investigate these processes under conditions of a carcinogenicity experiment in vivo. In the present study, 1,2-dimethylhydrazine-treated Sprague-Dawley rats were fed standard diet (n=12) or diet with 10% hydrothermally modified Novelose 330, a resistant starch type 3 (RS3), replacing digestible starch (n=8). After 20 weeks tumor number, epithelial proliferation, apoptosis, immunoreactivity of carcinogenesis-related proteins [protein kinase C-delta (PKC-delta), heat shock protein 25 (HSP25) and gastrointestinal glutathione peroxidase (GI-GPx)], as well as mucin properties were evaluated in proximal and distal colon in situ. No tumors developed under RS3 diet, compared to a tumor incidence of 0.6+/-0.6 (P<0.05) under the standard diet. RS3 decreased the number of proliferating cells, the length of the proliferation zone and the total length of the crypt in the distal colon, but not proximal colon, and enhanced apoptosis in both colonic segments. It induced PKC-delta and HSP25 expression, but inhibited GI-GPx expression in the epithelium of distal colon. RS3 increased the number of predominantly acidic mucin containing goblet cells in the distal colon, but had no effect on the goblet cell count. We conclude that hydrothermally treated RS3 prevented colon carcinogenesis, and that this effect was mediated by enhanced apoptosis of damaged cells accompanied by changes in parameters of dedifferentiation in colonic mucosa.     

Prevention of N-Methylnitrosourea-induced Colon Tumorigenesis by Ursodeoxycholic Acid in F344 Rats

Bile acids are known to promote colon carcinogenesis. However, there is one study showing that ursodeoxycholic acid (UDCA) supplemented in the diet at the concentration of 0.4% prevented azoxymethane-induced rat colon tumorigenesis. The aim of our study was to explore the inhibitory effect of a much smaller dose of UDCA on colon carcinogenesis in rats. One hundred 7-week-old F344 rats were given 2 mg of N-methylnitrosourea 3 times a week for 3 weeks by intrarectal instillation, and were fed a 0% (control), 0.4% or 0.08% UDCA-supplemented diet for the next 27 weeks. All the rats were killed and examined for tumor development at week 30. The tumor incidence and number were significantly lower and smaller, respectively, in the UDCA-fed rats than in the control rats: 40% and 36% vs. 68%; 0.5±0.1 (mean±SEM) and 0.4±0.1 vs. 1.0±0.2. All the tumors were located in the distal half of the colon and were plaque-shaped or polypoid, being well-differentiated adenocarcinomas restricted to the mucosa or submucosa. Bile acids in the feces and the blood obtained at weeks 20 and 30, respectively, were analyzed by HPLC. A significant increase of UDCA was confirmed in both the faces and the blood of the UDCA-fed rats compared with the control rats. The results suggest that the continuous feeding of a small dose of UDCA may prevent colon carcinogenesis.     

Effect of dietary corn bran and autohydrolyzed lignin on 3,2'-dimethyl-4-aminobiphenyl-induced intestinal carcinogenesis in male F344 rats

The effect of dietary corn bran and autohydrolyzed lignin on 3,2'-dimethyl-4-aminobiphenyl (DMAB)-induced intestinal carcinogenesis was studied in male inbred F344 rats. Groups of weanling rats were fed semipurified diets containing 15% corn bran or 7.5% lignin or a semipurified diet without these fibers (control diet). At 7 weeks of age, all animals, except vehicle-treated controls, were given sc injections of 50 mg DMAB/kg body weight/week for 20 weeks. All animals were autopsied 20 weeks after the last injection of DMAB. The incidence of colon tumors (percentage of animals with tumors) and colon tumor multiplicity (tumors/animal) were increased in rats fed the corn bran diet as compared to the tumor incidence and multiplicity in rats fed the control diet. The incidence of small intestinal tumors was slightly lower in rats fed the corn bran diet as compared to the incidence in rats fed the control diet. The concentrations (mg/g dry feces) of fecal deoxycholic acid and total bile acids and the daily output of fecal deoxycholic acid, lithocholic acid, hyodeoxycholic acid, and total bile acids were increased in rats fed the corn bran diet as compared to the concentrations and daily output in rats fed the control diet. The incidence and multiplicity of small intestinal tumors as well as the number of colon adenocarcinomas per tumor-bearing animal were lower in animals fed the lignin diet than in those fed the control diet. Lignin had no effect on the concentrations of fecal bile acids, but the daily output of total bile acids was increased in animals fed the lignin diet as compared to the daily output in rats fed the control diet. This study thus indicates that the protection against colon cancer depends on the type of fiber.     

Distal bowel selectivity in the chemoprevention of experimental colon carcinogenesis by the non-steroidal anti-inflammatory drug nabumetone

Use of non-steroidal anti-inflammatory drugs (NSAIDs) for chemoprevention of colon cancer has been hindered by their potential gastro-intestinal toxicity. Nabumetone, which is approximately 10 to 36 times safer than conventional NSAIDs, was evaluated in 2 models of experimental colon carcinogenesis. In azoxymethane (AOM)-treated Fisher 344 rats, nabumetone caused dose-dependent inhibition of aberrant crypt foci (ACF), with 750 and 1,500 ppm resulting in 15% and 37% reductions, respectively (p < 0.05). Moreover, complex ACF were reduced by 48% in the latter group. MIN mice studies confirmed the chemopreventive efficacy of nabumetone, with 900 ppm suppressing approximately half of the intestinal tumors. Interestingly, inhibition of intermediate biomarkers in both models was markedly greater in the distal than the proximal bowel. To mechanistically evaluate this regional selectivity, we assessed cyclo-oxygenase-2 (COX-2) expression in the uninvolved mucosa and demonstrated a 3- to 4-fold excess in the distal relative to the proximal bowel in both MIN mice and AOM-treated rats. We then investigated another putative NSAID target, peroxisome proliferator-activated receptor-delta (PPAR-delta) and demonstrated up-regulation during AOM-induced colonic tumorigenesis. Furthermore, in pre-neoplastic mucosa, there was a 3-fold excess of PPAR-delta in the distal colon. We demonstrate that nabumetone is an effective protective agent in both experimental models of colon carcinogenesis. The striking distal predilection of nabumetone may be, at least partially, explained by distal bowel over-expression of COX-2 and PPAR-delta.