Measurement of the proliferative status of colonic epithelium as a risk marker for colon carcinogenesis: Effect of bile acid and dietary fiber

The proliferative status of mouse colonic epithelium, as affected by dietary fibers with or without cholic acid (CA), was studied by autoradiography and the metaphase arrest technique. In the first study, groups of mice were fed natural ingredient (laboratory chow) or semisynthetic diets containing 0% (control) or 0.2% (test) CA. After the mice were fed two weeks, the effect of CA was significantly more pronounced in the semisynthetic diet group than in the natural ingredient diet group with respect to labeled cells/crypt section (7.8 ± 0.8 vs. 2.9 ± 0.4) and mitotic figure (MF)/crypt section (3.0 ± 0.5 vs. 1.8 ± 0.2). In the second study, diets formulated to contain 5 or 10% cellulose (C), pectin (P), or wheat bran (WB) with or without CA (0.2%) were fed to animals for two weeks and colonic proliferative indices were measured. When compared with 5% C group, the 10% WB group exhibited lower labeling index (LI) values (4.2 ± 0.5 vs. 6.4 ± 1.0) and the 10% P group exhibited higher LI values (10.0 ± 1.1 vs. 6.4 ± 1.0). CA‐induced increases in the LI and MF values responded independently in some cases to dietary fiber. Among the CA‐treated groups, only the 10% P diet resulted in lower LI when compared with the 5% C group (p < 0.05) (7.4 ± 0.8 vs. 12.5 ± 2.8) but had no effect on MF/crypt section. However, the 5 or 10% WB diet resulted in lower MF values (1.7 ± 0.2 and 1.8 ± 0.6 vs. 2.6 ± 0.3).

A long‐term feeding study comparing 10% P with 10% C diets also demonstrated that the LI was elevated in the 10% P group without any effect on the mitotic activity of the colonic epithelium. This paradoxiclal finding suggests that the value of the LI and/or mitotic index as a risk marker of colon carcinogenesis should be further investigated.     

Effect of dietary phytosterols on cell proliferation and protein kinase C activity in rat colonic mucosa

The present study investigated the role of phytosterols in colonic cell proliferation and examined the possible role of protein kinase C (PKC) in this process. A total of 18 male Sprague‐Dawley rats weighing 240–270 g were fed, for a period of 22 days, one of three experimental diets: a control diet, a diet supplemented with 0.2% cholic acid, or a diet supplemented with 0.2% cholic acid + 2% dietary phytosterols. Two hours before decapitation, animals were injected with 5'‐bromo‐2'‐deoxyuridine (BrdU, 50 mglkg body wt ip). Cell proliferation in the proximal colon was measured using a monoclonal antibody to BrdU. PKC activity in the proximal colonic mucosa was assayed using a myelin basic protein as a substrate. Cell proliferation was significantly increased by 276% with 0.2% cholic acid feeding compared with controls. The presence of 2% phytosterols in the diet abolished the cholic acid‐induced hyperplasia. Cholic acid induced a 31% expansion of the proliferative zone. Only the cytosolic PKC was significantly lower in the phytosterol‐fed group. Neither the total PKC nor the par‐ticulate PKC demonstrated an effect of phytosterols on enzyme activity. In conclusion, we found that dietary supplementation with 2% phytosterol has a significant protective effect on enhanced cell proliferation and that this effect is not mediated through the PKC system.     

Measurement of the proliferative status of colonic epithelium as a risk marker for colon carcinogenesis: effect of bile acid and dietary fiber

The proliferative status of mouse colonic epithelium, as affected by dietary fibers with or without cholic acid (CA), was studied by autoradiography and the metaphase arrest technique. In the first study, groups of mice were fed natural ingredient (laboratory chow) or semisynthetic diets containing 0% (control) or 0.2% (test) CA. After the mice were fed two weeks, the effect of CA was significantly more pronounced in the semisynthetic diet group than in the natural ingredient diet group with respect to labeled cells/crypt section (7.8 +/- 0.8 vs. 2.9 +/- 0.4) and mitotic figure (MF)/crypt section (3.0 +/- 0.5 vs. 1.8 +/- 0.2). In the second study, diets formulated to contain 5 or 10% cellulose (C), pectin (P), or wheat bran (WB) with or without CA (0.2%) were fed to animals for two weeks and colonic proliferative indices were measured. When compared with 5% C group, the 10% WB group exhibited lower labeling index (LI) values (4.2 +/- 0.5 vs. 6.4 +/- 1.0) and the 10% P group exhibited higher LI values (10.0 +/- 1.1 vs. 6.4 +/- 1.0). CA-induced increases in the LI and MF values responded independently in some cases to dietary fiber. Among the CA-treated groups, only the 10% P diet resulted in lower LI when compared with the 5% C group (p less than 0.05) (7.4 +/- 0.8 vs. 12.5 +/- 2.8) but had no effect on MF/crypt section. However, the 5 or 10% WB diet resulted in lower MF values (1.7 +/- 0.2 and 1.8 +/- 0.6 vs. 2.6 +/- 0.3). A long-term feeding study comparing 10% P with 10% C diets also demonstrated that the LI was elevated in the 10% P group without any effect on the mitotic activity of the colonic epithelium. This paradoxical finding suggests that the value of the LI and/or mitotic index as a risk marker of colon carcinogenesis should be further investigated.     

The impact of dietary fat and fiber on intestinal carcinogenesis

The effect of dietary fiber on intestinal carcinogenesis in animals is controversial. Some find that the addition of wheat bran or cellulose inhibits intestinal cancer in rats, while others report no effect. Such mixed results often are due to differences in the design of experiments. One important aspect in this regard is the amount of fat in the diet. Some fiber supplements inhibit cancer formation when the fat content is normal but not when it is high. However, a recent epidemiological study in Scandinavia showed a lower cancer incidence in a rural population compared with an urban area, in spite of the fact that the dietary fat content was high in both regions. There was a modest difference in the amount of fiber, and this may not have accounted completely for the variation in cancer incidence. Other dietary factors might have added inhibitory response to help overcome the promotional effect of an excessive amount of fat. The interaction among dietary components must be considered when designing animal experiments to assess the effect of fiber on cancer development.     

Effect of dietary benzylselenocyanate on azoxymethane-induced colon carcinogenesis in male F344 rats.

The effect of dietary benzylselenocyanate (BSC) and its analogue, benzylthiocyanate (BTC), and sodium selenite during the initiation and postinitiation phases of azoxymethane (AOM)-induced intestinal carcinogenesis was studied in male F344 rats. Animals intended for initiation study were fed the high-fat (23.5% corn oil) diets containing 25, 50, and 100 ppm BSC (10, 20, and 40 ppm selenium, respectively) and 100 ppm BTC and 4 ppm selenium (as sodium selenite in drinking water); those intended for postinitiation study were fed the high-fat control diet. Two weeks later, all animals were injected subcutaneously with AOM (15 mg/kg body wt) once weekly for two weeks. Three days after the last AOM injection, animals in the initiation and postinitiation studies were transferred respectively to the high-fat diet and high-fat diets containing BSC and BTC and sodium selenite in drinking water. This regimen was continued until 36 weeks post-AOM injection. BSC inhibited the small intestinal and colon adenocarcinoma incidence and multiplicity of colon adenocarcinomas when fed during the postinitiation phase. Sodium selenite inhibited the incidence and multiplicity of colon adenocarcinomas only during the postinitiation phase. BTC had no inhibitory effect when fed during the initiation and postinitiation phases. The colonic mucosal ornithine decarboxylase activity was significantly inhibited by the administration of all three compounds, BSC (78%), BTC (62%), and sodium selenite (44%). It is concluded that the BSC has an inhibitory effect on the intestinal carcinogenesis in animals fed the high-fat diet.     

Effect of complex polyphenols on colon carcinogenesis

Summary Background: Complex polyphenols and tannins from wine (WCPT) are being considered increasingly as potential cancer chemopreventive agents, since epidemiological studies suggest that populations consuming a high amount of polyphenols in the diet may have a lower incidence of some types of cancer. Aim of the study: We studied the effect of WCPT on a series of parameters related to colon carcinogenesis in rats. Methods: WCPT were administered to F344 rats at a dose of 14 or 57 mg/kg/d, mixed with the diet. The higher dose is about ten times the exposure to polyphenols of a moderate drinker of red wine. In rats treated with WCPT, we measured fecal bile acids and long chain fatty acids, colon mucosa cell proliferation, apoptosis and, after administration of colon carcinogens, the number and size of aberrant crypt foci (ACF) and nuclear aberrations. Results: Colon mucosa proliferation was not varied by chronic administration (90 d) of WCPT (14 or 57 mg/kg/d). The highest dose of WCPT decreased the number of cells in the colon crypts, but did not increase apoptosis. WCPT (57 mg/kg) administered before or after the administration of azoxymethane (AOM) did not vary the number or multiplicity of ACF in the colon. The number of nuclear aberrations (NA) in colon mucosa was studied after administration of 1,2-dimethylhydrazine (DMH) and 2-amino-3-methylimidazo (4,5-f)quinoline (IQ), colon-specific carcinogens which require metabolic activation. The effect of DMH and IQ was not varied by pre-feeding WCPT (57 mg/kg) for 10 d. Similarly, the levels of total, secondary bile acids and long chain fatty acids did not varied significantly in animals fed WCPT for 90 d. Conclusions: WCPT administration does not influence parameters related to colon carcinogenesis in the rat. Received: 18 January 1999, Accepted: 18 May 1999     

The role of dietary phytosterols in colon carcinogenesis.

Epidemiological and experimental studies have shown that increased intake of plant foods and decreased meat consumption are correlated with a decreased risk for colon cancer. Many components of plant foods are suggested to mitigate colon carcinogenesis, including vitamins, minerals, and dietary fiber. Phytosterols are a common component of plant foods consumed in relatively large quantities by vegetarians, who are at lower risk for colon cancer development than individuals on a Western diet low in phytosterols. In addition, phytosterols have been shown experimentally to inhibit colon cancer development. Dietary cholesterol, although structurally similar to the phytosterols, is correlated etiologically to the incidence of colon cancer, with changes in serum cholesterol levels and fecal bile acid profiles suggested to increase susceptibility to colon tumorigenesis. The objective of this paper is to discuss the effect of dietary phytosterols on cholesterol and bile acid metabolism and how these effects may lead to a decreased risk for colon cancer development.     

Effect of a dietary fiber (beet fiber) on dimethylhydrazine-induced colon cancer in Wistar rats.

The modifying effect of a dietary fiber, Fibeta (beet fiber), on experimentally induced colorectal cancer was studied in Wistar rats. The rats were fed a powdered semisynthetic casein-based diet in which the carbohydrate pool was substituted with Fibeta as the sole source of fiber. Dimethylhydrazine dihydrochloride (DMH-2HCl) was used as initiator in a dose of 20 mg/kg body wt and given by gavage once a week for 10 weeks. Throughout the experiment the rats were offered the diets with different levels of fiber in a preinitiation period of 8 weeks, during the initiation, or in a 30-week postinitiation period. The study was terminated after one year. A protective effect of the fiber was not found at any stage of the colorectal carcinogenic process. Even though differences (not statistically significant) in tumor incidences were seen, these did not reflect any effect of the high or low fiber intake during the study. Analysis for volatile fatty acids in cecal content showed that continuous feeding with a fiber-rich diet resulted in significant increase in most of the volatile fatty acids. The relative change was highest for butyric acid. These findings do not support the hypothesis that butyric acid has a protective effect on colorectal cancer. The tumor yield in the present study was low compared with that reported in the literature, and possible causes for this are discussed.     

Superior inhibitory efficacy of butyrate over propionate and acetate against human colon cancer cell proliferation via cell cycle arrest and apoptosis: linking dietary fiber to cancer prevention

Intake of dietary fiber may protect against colon cancer. The anticancer property is associated with an increased production of short chain fatty acids (SCFAs), including acetate, propionate and butyrate, during dietary fiber fermentation in the colon. However, the mechanisms remain to be determined. We hypothesized that butyrate exhibits a stronger inhibitory potential against colon cancer cell proliferation compared with acetate and propionate. We determined the half maximal inhibitory concentrations (IC₅₀) of SCFAs in HCT116 human colon cancer cell proliferation by examining cell growth curves. At 24- and 48-hour time points, IC₅₀ (mmol/L) concentrations of acetate, propionate, and butyrate were [66.0 and 29.0], [9.2 and 3.6], and [2.5 and 1.3], respectively. Consistent with the greater anti-proliferative effect, butyrate exhibits >3-fold stronger potential for inducing cell cycle arrest at the G2 phase with a drop in S-phase fraction (including c-Myc/p21 signaling) and apoptosis when compared with acetate and propionate. Subsequently, we focused on the effect of butyrate on apoptotic gene expression. Using a PCR array analysis, we identified 17 pro-apoptotic genes, 6 anti-apoptotic genes, and 4 cellular mediator genes with >1-fold increase or decrease in mRNA levels out of 93 apoptosis related genes in butyrate-treated HCT116 cells when compared with untreated HCT116 cells. These genes were mainly involved in the TNF, NFκB, CARD, and BCL-2 regulated pathways. Taken together, our data indicate a greater inhibitory efficacy of butyrate over propionate and acetate against human colon cancer cell proliferation via cell cycle arrest and apoptosis.     

Effect of dietary calcium on colon carcinogenesis induced by a single injection of 1,2-dimethylhydrazine in rats

The purpose of this study was to determine if high levels of dietary calcium could inhibit the induction of colon tumors in rats injected with a single dose of 1,2-dimethylhydrazine (DMH). Rats were given a single subcutaneous injection of DMH (200 mg/kg body weight) 2 wk before they were fed purified diets containing 5% fat and four different levels of calcium (as calcium gluconate). After 8 mo, the following incidences of colon tumors (total) were seen: 0.2% Ca, 56%; 0.5% Ca [National Academy of Sciences/National Research Council (NAS/NRC) recommended level], 75%; 1.0% Ca, 61%; 2.0% Ca, 41%. Thus, rats fed calcium at levels above or below the NAS/NRC recommendation had lower tumor incidences. The total tumor incidence and the incidence of adenocarcinomas (with or without invasion) were not significantly affected by calcium, but the incidences of benign adenomatous polyps and of distal colon tumors were significantly affected. Autoradiographic examination of [3H]thymidine-treated rats revealed that the level of calcium did not significantly alter the cell kinetic indices in the distal colon. In the proximal colon, however, the 0.2% Ca group had a significantly larger proliferative zone, with significantly more labeled cells present at the bottom of the colon crypt. Mineral analysis of tibias and serum samples revealed that rats fed higher levels of calcium had lower bone Fe and serum Mg contents, but no significant trends were seen for Ca, P, Zn or Cu. Therefore, increasing or decreasing the calcium content above or below the NAS/NRC recommendation (supplemented to low fat diets) during the promotional phase of colon carcinogenesis altered the tumor incidence, but the effect was confined to the distal colon and to benign adenomatous polyps.     

A buckwheat protein product suppresses 1,2-dimethylhydrazine-induced colon carcinogenesis in rats by reducing cell proliferation

This study was conducted to examine the effect of consumption of buckwheat protein product (BWP) on 1,2-dimethylhydrazine (DMH)-induced colon tumor in rats. Male growing Sprague-Dawley rats were fed diets containing either casein or BWP (net protein level, 200 g/kg; n = 20/group) for 124 d. The rats were gavaged weekly with DMH (20 mg/kg body) for the first 8 wk. Food intake and growth were unaffected by dietary manipulation. Dietary BWP caused a 47% reduction in the incidence of colonic adenocarcinoma (P < 0.05), but did not affect the incidence of colonic adenomas. BWP intake tended to reduce the number of colon adenocarcinomas (P = 0.16). Consumption of BWP significantly reduced cell proliferation and expression of c-myc and c-fos proteins in colonic epithelium. The results suggest that dietary BWP has a protective effect against DMH-induced colon carcinogenesis in rats by reducing cell proliferation.     

Changing concepts of dietary fiber: implications for carcinogenesis.

The dietary fiber (DF) hypothesis suggested that DF, as plant cell walls, protected against colorectal cancer. The implicit assumption in much historic literature was that the readily analyzed and quantified nonstarch polysaccharide (NSP) component was critical in cancer protection. However, the presence of polymeric phenolic components such as lignin or suberin has profound effects on the physicochemical properties of the cell walls and largely determines their physiological properties in humans. In certain groups of food plants, degradation of cell walls that contain neither lignin nor suberin releases ferulic acid and other hydroxycinnamic acids. These acids have antioxidant, antimutagenic, and other anticancer effects, including modulation of gene expression and immune response. Reexamination of literature on cancer protection suggests that plant cell walls containing significant amounts of phenolic components may be the most likely to protect against cancer. In the last 30 years, the definition of DF has been incrementally expanded to incorporate NSP extracted from plant cell walls and from sources other than plant cell walls, then resistant starch, and most recently nondigestible oligosaccharides. On the early definitions, increased consumption of DF could only be achieved by increasing the intake of whole grains, brans, or other food plant material that would increase the intake of plant cell walls containing significant amounts of phenolic components. However, the new definitions make it possible to increase "dietary fiber" without consuming any such materials. We suggest that this could have negative connotations for cancer risk in human populations.     

A protective role of dietary vitamin D3 in rat colon carcinogenesis

The aim of the present work was to gain insight into a putative anticancer effect of dietary vitamin D3 (cholecalciferol) in a rat model of colon carcinogenesis. Male rats were assigned to three different dietary groups. The dietary regimens were based on a standard murine-defined diet (AIN-76A) or a stress diet containing 20% fat, reduced Ca2+ concentration, a high phosphorus-to-Ca2+ ratio, and either low or high vitamin D3 content. Colorectal cancer was induced by administration of the procarcinogen 1,2-dimethylhydrazine (DMH). Blood Ca2+, 1,25-dihydroxyvitamin D3 [1,25(OH)2D3], and 25-hydroxyvitamin D3 [25(OH)D3] levels were measured in DMH-treated rats and in respective weight- and age-matched dietary control groups. Colonic epithelial proliferation was assessed by determining thymidine kinase (TK) activity, bromodeoxyuridine (BrdUrd) incorporation into crypt cell DNA, and the mean labeling index along the colonic crypt continuum. Maintenance of rats on the stress diet either unmodified or supplemented with vitamin D3 in the absence of carcinogen treatment provoked a time-dependent rise in colonic TK activity and hyperproliferation of colonic epithelium. DMH treatment of rats maintained on the standard diet caused a marked increase in the proliferative indexes of colonic epithelium and in expansion of the crypt proliferative compartment. TK activity and the crypt mitotic zone were significantly augmented in the animal group fed the stress diet. Supplementary vitamin D3 abrogated the stress diet-enhanced colonic responses to the carcinogenic insult. Colon tumor multiplicity was fourfold higher in animals fed the stress diet than in animals maintained on a standard diet. The marked rise in colonic tumor multiplicity and adenocarcinoma incidence in rats fed the stress diet was obliterated by supplemental dietary vitamin D3. Cumulatively, the present results indicate that dietary vitamin D3 impedes the neoplastic process in murine large intestine and strengthen the view that inappropriate changes in dietary components and micronutrients are contributory determinants of colorectal cancer.     

Effects of dietary fiber and its components on metabolic health

Dietary fiber and whole grains contain a unique blend of bioactive components including resistant starches, vitamins, minerals, phytochemicals and antioxidants. As a result, research regarding their potential health benefits has received considerable attention in the last several decades. Epidemiological and clinical studies demonstrate that intake of dietary fiber and whole grain is inversely related to obesity, type two diabetes, cancer and cardiovascular disease (CVD). Defining dietary fiber is a divergent process and is dependent on both nutrition and analytical concepts. The most common and accepted definition is based on nutritional physiology. Generally speaking, dietary fiber is the edible parts of plants, or similar carbohydrates, that are resistant to digestion and absorption in the small intestine. Dietary fiber can be separated into many different fractions. Recent research has begun to isolate these components and determine if increasing their levels in a diet is beneficial to human health. These fractions include arabinoxylan, inulin, pectin, bran, cellulose, β-glucan and resistant starch. The study of these components may give us a better understanding of how and why dietary fiber may decrease the risk for certain diseases. The mechanisms behind the reported effects of dietary fiber on metabolic health are not well established. It is speculated to be a result of changes in intestinal viscosity, nutrient absorption, rate of passage, production of short chain fatty acids and production of gut hormones. Given the inconsistencies reported between studies this review will examine the most up to date data concerning dietary fiber and its effects on metabolic health.     

Effect of dietary fat levels on the susceptibility of colonic cells to nuclear-damaging agents

The effect of two levels and types of dietary fats on the susceptibility of colonic cells to the nuclear-damaging effect of 1,2-dimethylhydrazine dihydrochloride (DMH), 2-amino-3,4-dimethylimidazo(4,5-f)quinoline (MeIQ), and gamma-radiation was investigated. Corn oil and beef tallow were added to the semisynthetic diet at 5% and 20% levels (weight/weight). A diet-related effect was not evident until after two weeks of feeding. Animals (C57BL/6J female mice) that were given the 20% corn oil or beef tallow diets had significantly (p less than 0.05) more nuclear aberrations in their colons 24 hours following treatment with DMH (5 mg or 10 mg/kg body wt or MeIQ (100 mg/kg body weight) than did those given low-fat diets (5% corn oil or beef tallow). The nuclear-damaging effect of gamma radiation was unaffected by dietary treatments. A high-fat diet had the most pronounced effect on DMH-treated animals, and maximum nuclear aberrations were observed 24 hours following the treatment. Thus, we concluded that increased levels of dietary fats elevate the toxicity of DMH and MeIQ to colonic epithelial cells.     

谷豆复合物、谷豆复合膳食纤维及单一谷物膳食纤维对脂代谢紊乱的影响

目的观察谷豆复合物、谷豆复合膳食纤维和全谷物玉米膳食纤维(DF)对脂代谢紊乱大鼠血脂及肝脏脂肪酸合成酶(FAS)活性,及其对大鼠肝组织固醇调节元件结合蛋白-1c(SREBP-1c)mRNA表达的影响,比较谷豆复合物、谷豆复合DF与单一谷物DF改善脂毒性效果。方法 50只SD大鼠适应性喂养1周后,随机分成阴性对照组、高脂模型组、谷豆复合物组、谷豆复合DF组和玉米DF组;以相应的饲料连续喂养8周后,测定各组大鼠总胆固醇(TC)、甘油三酯(TG)、空腹血糖(FBG)、高密度脂蛋白胆固醇(HDL-C)和FAS等指标,测定各组大鼠肝脏SREBP-1c mRNA的表达。结果与阴性对照组相比,高脂模型组的大鼠血清TC、TG水平显著升高(P0.05);与高脂模型组相比,谷豆复合物组、谷豆复合DF组和玉米DF组大鼠血清TC、TG水平显著降低(P0.05);HDL-C水平显著高于高脂模型组,大鼠肝脏脂肪酸合成酶活性及SREBP-1c的表达显著降低。结论谷豆复合膳食纤维可改善脂代谢紊乱大鼠的血脂水平,降低FAS活性及SREBP-1c的表达水平。     

Kinetics of epidermal cell proliferation in experimental skin carcinogenesis

It is well known that there exists a daily rhythm in the mitotic count in the epidermis of the mouse. It has also been emphasized that the mitotic rate cannot be estimated correctly from the mitotic count unless the mitotic duration is constant.