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Department of Hygiene and * First Department of Internal Medicine, Hirosaki University School of Medicine, Hirosaki, 036-8562 Japan
1To whom correspondence should be addressed. E-mail: nakaji{at}cc.hirosaki-u.ac.jp.
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ABSTRACT |
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 TOP ABSTRACT MATERIALS AND METHODSRESULTSDISCUSSIONLITERATURE CITED |
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KEY WORDS: • dietary fiber • cellulose • fat • lard • large bowel tumorigenesis
Dietary fiber (DF) and dietary fat may be associated with colon carcinogenesis (1–5). DF enhances stool bulk, which may stimulate intestinal transit and thereby decrease exposure to intraluminal carcinogens. In addition, DF reduces the concentration of procarcinogenic secondary bile acids and may increase anticarcinogenic SCFA (6). Finally, water-soluble fibers delay starch absorption, stabilizing the serum insulin level that might otherwise increase and promote intestinal tumorigenesis (7). Dietary fat has been postulated to variously affect epithelial mitogenesis, bile acid secretion, serum insulin concentrations, prostaglandin E2, host immunocompetence, and tumor membrane characteristics (8). Furthermore, Reddy et al. (9) reported that the lipid fraction of wheat bran had strong colon tumor inhibitor properties in a rat experiment. However, the exact mechanism(s) by which the lipid fraction of wheat bran inhibited colon carcinogenesis in addition to altering inducible nitric oxide synthase activity and cyclooxygenase activity remain to be elucidated.
Nevertheless, since Fuchs’ report in 1999 (10) and the reports of Schatzkin and Alberts in 2000 (11,12) on the protective effects of DF against colon carcinogenesis, many researchers have questioned the benefit of DF. Furthermore, Giovannucci and Goldin (13) stated that neither previous case-control nor cohort studies found that the total fat composition of the diet increased the risk of colon cancer.
However, we should be careful in evaluating the effects of dietary factors on carcinogenesis, including colon carcinogenesis, because the protective/promotive effects may be mediated by a balance of dietary factors in the total diet, or by the interaction of dietary fiber, nutrients, and other foods.
There have been several studies that compared the effects of fat and DF intakes on rat colon tumorigenesis, and most studies reported that the preventive effect of DF was greater than the promotive effect of fat (14–18), although the findings of some researchers did not demonstrate this (19) or indicate any preventive effect (9).
In this study, we compared the effects of cellulose (representing dietary fiber) and lard (representing animal fat) on rat large intestine tumorigenesis. Rats treated with 1,2-dimethylhydrazine (DMH) were examined frequently by colonofiberscopy (20). This allowed consecutive examinations of the large intestine of each rat, thus facilitating a comparison of the number of tumors appearing in the large intestine of individual rats, and the numbers of rats with tumors from each group.
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MATERIALS AND METHODS |
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TOPABSTRACTMATERIALS AND METHODSRESULTSDISCUSSIONLITERATURE CITED |
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150 g were assigned to the following 6 groups. Rats were fed a diet without cellulose (Otsuka Shokuhin; Table 1) that contained 5, 10, and 15 g/100 g lard (n = 15/subgroup) or diets containing 15 g/100 g cellulose and the same concentrations of lard (n = 15/subgroup). This diet contained the following energy and nutrients (per 100 g): energy, 1831 J; casein, 16.2 g; dextrin, 72.7 g; and rice oil, 9.6 g. The basal diet was a non-DF diet (HINEX, Otsuka Pharmaceutical). The cellulose used was in the form of cellulose powder (Macherey Nagel; particle size; 20–100 µm, purity; 99.0 g/100 g, origin; citrus). Lard (39.2 g/100 g SFA, 55.8 g/100 g unsaturated fatty acids, and 0.1 g/100 g cholesterol) was purchased from Nisshin Seifun. Rice oil (extracted from rice bran using the resolvent, myristic acid 0.2–0.3 g/100 g, palmitic acid 16.3–16.4 g/100 g, palmitoleic acid 0.2 g/100 g, stearic acid 1.5–1.7 g/100 g, oleic acid 41.9–42.2 g/100 g, linoleic acid 35.4–36.1 g/100 g, linolenic acid 1.3 g/100 g) was purchased from Otsuka Pharmaceutical. Rats were maintained in cages under constant conditions (room temperature 24 ± 2°C, humidity 60%) and consumed water and food ad libitum.
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Endoscopic examination of the large intestine. Endoscopic examination was begun at wk 19 of DMH treatment and continued until week 28, at intervals of 1–2 wk. Rats were deprived of food (although water was consumed ad libitum) for 24 h as the only pretreatment; they were anesthetized with i.p. pentobarbital (25 mg/kg). The endoscope had an external diameter at the tip of 4.8 mm, the angles of the curvature were 180° up and 60° down, and the effective length was 595 mm (type BF 4B2, Olympus). The endoscopic examination was performed by the same person throughout the study.
Measurement of food intake, dry fecal output, and transit time. At wk 14 of DMH treatment, daily food intake and dry fecal output in each group were measured. At 15 wk of DMH treatment, the rats were derived of food for 24 h. Indigo Carmine (Wako Pure Chemical Industries) was then spread on the surface of the next food portion as a coloring and the whole gut transit time was measured from when the rats started eating until they excreted colored feces.
Histopathological study. At week 28 of DMH treatment, all rats were killed while under anesthesia with diethyl ether, the excised large intestine was opened from the side attached to the mesentery, and the tissue was fixed in formalin. Tissue from any unusual protrusion of the large intestine was examined histologically after being stained with hematoxylin and eosin. The tissue from an area was diagnosed as "carcinoma" when any atypical glandular tubular structure had invaded the submucosal layer.
Statistical analysis.
Data for food consumption, fecal output, digestive transit time, number of tumors (carcinomas), and number of lymph follicles were evaluated by 2-way ANOVA and post-hoc by Duncan’s multiple range tests. A 
2 test was used to determine differences among groups in the incidence of carcinomas at wk 28 of DMH treatment and at autopsy. Furthermore, Cox proportional hazards regression was used to estimate the hazard ratios [relative risks (RR)] of tumor incidence associated with the intakes of cellulose and lard. Estimated RR are presented with 95% CI. P-values (two-sided) < 0.05 were considered significant. Statistical analyses were performed with the Stata Statistical Software Release 8.2 (Stata Corporation) (21).
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RESULTS |
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TOPABSTRACTMATERIALS AND METHODSRESULTSDISCUSSIONLITERATURE CITED |
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All lesions detected by endoscopy were carcinomas. Of the 97 carcinomas detected histologically, 90% were identified by endoscopic examination. The diagnostic accuracy of endoscopy for distal colon carcinoma was 95% and that for proximal colon carcinoma was 79%, percentages that did not differ (2 = 0.36, P = 0.55, Table 2).
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The large intestine was visible up to the proximal end with the endoscope. The proximal side of the intestine was not observable in 1 rat in the 0% cellulose, 5% lard group because of obstruction of the large intestine during the experiment. However, no protruding lesion was observed in the oral side in that rat at autopsy. Moreover, because the cecum was at a sharp angle to the proximal large intestine, the probe of the endoscope could not be inserted deeply into the cecum.
The first tumors were observed in all groups at wk 22 of DMH treatment. The difference in tumor incidence was greatest between the 0% and 15% cellulose groups in wk 22 and 24; thereafter, this difference decreased until wk 28 when the groups did not differ (2 = 0.12, P = 0.73) (Fig. 1).
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A total of 151 protrusions were found in the colon specimens of 78 rats. No adenomas were found. Furthermore, no cases were found with lymph follicles containing microscopic adenocarcinomas. The proportion of carcinoma-bearing rats was not affected by the dietary lard concentration (Table 3). The numbers of carcinoma lesions in the 0% cellulose groups (1.5 ± 0.6, 1.5 ± 0.6, and 1.7 ± 0.7, for the 5, 10, and 15% lard groups, respectively) were greater than those in the 15% cellulose diet groups (1.0 ± 0.5, 1.0 ± 0.5, and 0.8 ± 0.4 for the 5, 10, and 15% lard groups, respectively, P < 0.05). However, the number of carcinoma lesions did not differ among the 3 lard subgroups in both the 0% and 15% cellulose groups.
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DISCUSSION |
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TOPABSTRACTMATERIALS AND METHODSRESULTSDISCUSSIONLITERATURE CITED |
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The use of the endoscope also had some limitations, one of which was the discrepancy between the endoscopic and autopsy diagnoses of the number of tumors. The presence of feces in the large intestine is a probable cause of the failure to detect some of the protruding lesions endoscopically. In this study, the diagnostic accuracy of endoscopy for distal colon carcinoma was 95%, whereas that for proximal colon carcinoma was 87%, percentages that did not differ. To overcome this disadvantage, we evaluated the results from both endoscopic and histological findings.
The important finding in this study is that the induction rates of tumor growth in the 15% cellulose groups were significantly lower than in the 0% cellulose groups. The tumor induction rates, however, were independent of the lard concentration.
An increase in the weight and volume of feces may be one of the main mechanisms of suppression of large bowel carcinogenesis by water-insoluble fibers including cellulose (20,22–24), with a resulting decrease in the relative proportions of carcinogenic substances in the feces (20,22–24). In addition, the transit time in the large intestine may be reduced (25,26), so that the time during which carcinogenic substances in the feces are in contact with the mucous membranes of the large intestine is reduced (1,27–32). This hypothesis is supported by the present finding that the weight of the feces in the rats from the 15% cellulose group was 8–10 times that in the rats fed 0% cellulose. However, whole transit time and carcinoma development were not associated in this study.
There have been several studies to date in which the effects of fat and DF intakes on rat colon tumorigenesis have been compared; different results were reported, although most studies concluded that the preventive effect of DF was greater than the promotive effect of fat (14–18). Jacobs (33) reported that wheat bran given during the initiation phase of dimethylhydrazine-induced colon tumorigenesis had an enhancing effect, whereas an inhibitory effect occurred when bran was given during the promotion phase of carcinogenesis. In our study, however, the DMH challenge was repeated 19 times rather than just 2 or 3 as in other studies; consequently, separating the initiation and promotion phases of colon cancer (and the respective effects of fat and DF on them) becomes very difficult, but closely resembles the actual conditions in the everyday life of humans. Because the effect of fat on colon carcinogenesis occurs primarily in the promotion phase (34), it is likely that the effect of fat and DF was the result of a complex interaction of the respective inhibitory and enhancing effects of DF and fat in both the initiation and promotion phases of colon carcinogenesis. Reddy and Murayma (35) reported that a diet high in lard consumed during the initiation stage of azoxymethane-induced colon carcinogenesis in rats resulted in more adenocarcinomas than did a diet low in lard. These data may pose a further complication in explaining our findings regarding the lack of any relationship between lard concentrations and tumorigenesis.
In the current experiment, cellulose and lard as the representative DF and fat, a possible limitation as discussed above, were administered during both the initiation and promotion phases of colon carcinogenesis. The reason for this was to try and emulate an everyday diet, in which humans ingest a mixture of DF (cellulose) and fat (lard) during both the initiation and promotion stages of colon carcinogenesis.
The current study did not demonstrate any effect of lard intake on carcinoma development, whereas cellulose supplementation inhibited rat colon tumorigenesis. We used a DF density that is far higher than the density of the actual Japanese diet; however, the concentrations of fat used in this study approach the density of the actual Japanese diet, in that 5% is lower than, 10% is similar to, and 15% is greater than the average Japanese fat intake (36). Under these conditions, our data suggest that the preventive effect of cellulose is greater than the promotive effect of lard. Clearly, more studies are warranted to elucidate the underlying mechanisms of the effects of dietary fat and DF on colon carcinogenesis, particularly experiments that distinguish between the initiation and promotion phases of colon cancer, and also use an experimental DF density more similar to the actual density in the Japanese diet.
It is very interesting that although the tumor induction rate in the 15% cellulose groups did not differ from that of the 0% cellulose groups at wk 28 of DMH treatment, the rats differed over the whole course of endoscopic observation. Conventional experiments of this type have adopted the method of killing rats at certain times for autopsy. The disadvantage of this method is that it introduces a confounding factor in that rats killed at different times differ in tumorogenetic stage, making it difficult to compare the courses midway. Killing a rat too early or too late, for instance, makes it difficult to accurately confirm the difference. To evaluate this effect, Freeman et al. (37) autopsied 3–4 rats every 4 wk to evaluate the effect of DF. However, this method obviously does not permit the repeated examination of the large intestine in the same rat.
In conclusion, the preventive effect of cellulose against large bowel tumorigenesis is greater than the promotive effect of lard under the current experimental conditions.
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FOOTNOTES |
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Manuscript received 18 August 2003. Initial review completed 3 October 2003. Revision accepted 6 January 2004.
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LITERATURE CITED |
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TOPABSTRACTMATERIALS AND METHODSRESULTSDISCUSSIONLITERATURE CITED |
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1. Burkitt, D. P. (1971) Epidemiology of cancer of the colon and rectum. Cancer 28:3-13.[Medline]
2. Lipkin, M., Reddy, B., Newmark, H. & Lamprecht, S. A. (1999) Dietary factors in human colorectal cancer. Annu. Rev. Nutr. 19:545-586.[Medline]
3. Levin, B. (1992) Nutrition and colorectal cancer. Cancer 70:1723-1726.[Medline]
4. Boutron, M. C., Wilpart, M. & Faivre, J. (1991) Diet and colorectal cancer. Eur. J. Cancer Prev. (suppl. 2):13-20.
5. for the European Prospective Investigation into Cancer and NutritionBingham, S. A., Day, N. E., Luben, R., Ferrari, P., Slimani, N., Norat, T., Clavel-Chapelon, F., Kesse, E. & Nieters, A., et al (2003) Dietary fibre in food and protection against colorectal cancer in the European Prospective Investigation into Cancer and Nutrition (EPIC): an observational study. Lancet 361:1496-1501.[Medline]
6. Hawk, E. T., Limburg, P. J. & Viner, J. L. (2002) Epidemiology and prevention of colorectal cancer. Surg. Clin. Am. 82:905-941.
7. Giovannucci, E. (1995) Insulin and colon cancer. Cancer Causes Control 6:164-179.[Medline]
8. Giovannucci, E. & Goldin, B. (1997) The role of fat, fatty acids, and total energy intake in the etiology of human colon cancer. Am. J. Clin. Nutr. 66(suppl. 6):1564S-1571S.
9. Reddy, B. S., Hirose, Y., Cohen, L. A., Simi, B., Cooma, I. & Rao, C. V. (2000) Preventive potential of wheat bran fractions against experimental colon carcinogenesis: implications for human colon cancer prevention. Cancer Res. 60:4792-4797.
10. Fuchs, C. S., Giovannucci, E. L., Colditz, G. A., Hunter, D. J., Stampfer, M. J., Rosner, B., Speizer, F. E. & Willett, W. C. (1999) Dietary fiber and the risk of colorectal cancer and adenoma in women. N. Engl. J. Med. 340:169-176.
11. Schatzkin, A., Lanza, E., Corle, D., Lance, P., Iber, F., Caan, B., Shike, M., Weissfeld, J., Burt, R., Cooper, M. R., Kikendall, J. W. & Cahill, J. (2000) Lack of effect of a low-fat, high-fiber diet on the recurrence of colorectal adenomas. Polyp Prevention Trial Study Group. N. Engl. J. Med. 342:1149-1155.
12. Alberts, D. S., Martinez, M. E., Roe, D. J., Guillen-Rodriguez, J. M., Marshall, J. R., van Leeuwen, J. B., Reid, M. E., Ritenbaugh, C., Vargas, P. A., Bhattacharyya, A. B., Earnest, D. L. & Sampliner, R. E. (2000) Lack of effect of a high-fiber cereal supplement on the recurrence of colorectal adenomas. Phoenix Colon Cancer Prevention Physicians’ Network. N. Engl. J. Med. 342:1156-1162.
13. Giovannucci, E. & Goldin, B. (1997) The role of fat, fatty acids, and total energy intake in the etiology of human colon cancer. Am. J. Clin. Nutr. 66(suppl. 6):S1564-S1571.
14. Wijnands, M. V., Appel, M. J., Hollanders, V. M. & Woutersen, R. A. (1999) A comparison of the effects of dietary cellulose and fermentable galacto-oligosaccharide, in a rat model of colorectal carcinogenesis: fermentable fibre confers greater protection than non-fermentable fibre in both high and low fat background. Carcinogenesis 20:651-656.
15. Coleman, L. J., Landstrom, E. K., Royle, P. J., Bird, A. R. & McIntosh, G. H. (2002) A diet containing 
-cellulose and fish oil reduces aberrant crypt foci formation and modulates other possible markers for colon cancer risk in azoxymethane-treated rats. J. Nutr. 132:2312-2318.
16. Hardman, W. E. & Cameron, I. L. (1995) Site specific reduction of colon cancer incidence, without a concomitant reduction in cryptal cell proliferation, in 1,2-dimethylhydrazine treated rats by diets containing 10% pectin with 5% or 20% corn oil. Carcinogenesis 16:1425-1431.
17. Hardman, W. E., Cameron, I. L., Heitman, D. W. & Contreras, E. (1991) Demonstration of the need for end point validation of putative biomarkers: failure of aberrant crypt to predict colon cancer incidence. Cancer Res. 51:6388-6392.
18. Trudel, J. L., Senterman, M. K. & Brown, R. A. (1983) The fat/fiber antagonism in experimental colon carcinogenesis. Surgery 94:691-696.[Medline]
19. Sinkeldam, E. J., Kuper, C. F., Bosland, M. C., Hollanders, V. M. & Vedder, D. M. (1990) Interactive effects of dietary wheat bran and lard on N-methyl-N'-nitro-N-nitrosoguanidine-induced colon carcinogenesis in rats. Cancer Res. 50:1092-1096.
20. Iwane, S. (1989) Endoscopic study on the effect of dietary fiber against 1,2-dimethylhydrazine-induced colonic carcinogenesis rats (in Japanese). Jpn. J. Gastroenterol. 86:2713-2720.
21. Stata Corporation (2003) Stata Statistical Software: Release 8.2 2003 Stata Press College Station, TX.
22. Heitman, D. W., Ord, V. A., Hunter, K. E. & Cameron, I. L. (1989) Effect of dietary cellulose on cell proliferation and progression of 1,2-dimethylhydrazine-induced colon carcinogenesis in rats. Cancer Res. 49:5581-5585.
23. Sloan, D. A., Fleiszer, D. M., Richards, G. K., Murray, D., Brown, R. A., Richards, G. K., Murray, D. & Brown, R. A. (1993) The effect of the fiber components cellulose and lignin on experimental colon neoplasia. J. Surg. Oncol. 52:77-82.[Medline]
24. Kritchevsky, D. & Klurfeld, D. M. (1997) Interaction of fiber and energy restriction in experimental colon carcinogenesis. Cancer Lett. 114:51-52.[Medline]
25. Hillman, L., Peters, S., Fisher, A. & Pomare, E. W. (1983) Differing effects of pectin, cellulose and lignin on stool pH, transit time and weight. Br. J. Nutr. 50:189-195.[Medline]
26. Hillemeier, C. (1995) An overview of the effects of dietary fiber on gastrointestinal transit. Pediatrics 96:997-999.
27. Burkitt, D. P., Walker, A.R.P. & Painter, N. S. (1974) Dietary fiber and diseases. J. Am. Med. Assoc. 229:1069-1074.
28. Spiller, G. A., Chernoff, M. C., Shipley, E. A., Beigler, M. A. & Briggs, G. M. (1977) Can fecal weight be used to establish a recommended intake of dietary fiber (plantix). Am. J. Clin. Nutr. 30:659-661.
29. Nakaji, S., Sugawara, K., Ohta, M., Iwane, S., Aisawa, T. & Munakata, A. (1996) Endoscopic evaluation of the preventive effect of wheat bran against 1,2-dimethylhydrazine induced large bowel carcinogenesis in rats. Nutr. Res. 16:1521-1527.
30. Bingham, S. A. (1990) Mechanisms and experimental and epidemiological evidence relating dietary fibre (non-starch polysaccharides) and starch to protection against large bowel cancer. Proc. Nutr. Soc. 49:153-171.[Medline]
31. Lewin, M. R. (1991) Is there a fibre-depleted aetiology for colorectal cancer? Experimental evidence. Rev. Environ. Health 9:17-30.[Medline]
32. Faivre, J., Wilpart, M. & Boutron, M. C. (1991) Primary prevention of large bowel cancer. Recent Results Cancer Res. 122:85-99.[Medline]
33. Jacobs, L. R. (1983) Enhancement of rat colon carcinogenesis by wheat bran consumption during the stage of 1,2-dimethylhydrazine administration. Cancer Res. 43:4057-4061.
34. Bull, A. W., Soullier, B. K., Wilson, P. S., Hayden, M. T. & Nigro, N. D. (1979) The promotion of azoxymethane-induced intestinal cancer by high-fat diet in rats. Cancer Res. 39:4956-4959.
35. Reddy, B. S. & Murayama, H. (1986) Effect of different levels of dietary corn oil and lard during the initiation phase of colon carcinogenesis in F 344 rats. J. Natl. Cancer Inst. 77:815-822.
36. Freeman, H. J., Spiller, G. A. & Kim, Y. S. (1978) A double-blind study on the effect of purified cellulose dietary fiber on 1,2-dimethylhydrazine-induced rat colonic neoplasia. Cancer Res. 38:2912-2917.
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