Rodent models for carcinoma of the colon

Assessment of antitumor activity of BP-C1, a platinum-based anticancer agent with a lignin-derived polymeric ligand, in autochthonous induced and spontaneous carcinogenesis rodent models

BACKGROUND

A standard approach to study the anticancer activity of novel drugs is their testing in animals with inoculated tumors, which has some limitations. An alternative is the use of spontaneous or carcinogen-induced tumor models as they have better translation potential. The carcinogen-induced and transgenic tumor models were used to assess the antitumor activity of BP-C1, a platinum-containing drug with lignin-derived polymeric ligand.

METHODS

We used female Swiss-H-derived mice and Wistar female rats to induce autochthonous tumors via exposure to benzo[a]pyrene and 1,2-dimethylhydrazine, respectively. Additionally, transgenic HER-2/neu FVB/N female mice, prone to the development of spontaneous mammary carcinomas, were used.

RESULTS

Antitumor activity of BP-C1 was observed in soft tissue sarcomas, induced by benzo[a]pyrene. The animals treated with BP-C1 exhibited more stabilizations and therapy responses compared to placebo controls. The efficacy of BP-C1 was somewhat reduced compared to cyclophosphamide; however, their combination resulted in an enhanced antitumor effect. For the 1,2-dimethylhydrazine-induced rat colon cancer model, BP-C1 reduced tumor multiplicity by 21-41 %. For mammary adenocarcinomas in HER-2/neu FVB/N mice, short-termed complete responses were observed in the BP-C1 groups with a frequency of 12-13 %, while complete responses were absent in the placebo group.

CONCLUSION

The results acquired indicated a wide spectrum of antitumor activity of BP-C1.

Estradiol and progesterone regulate proliferation and apoptosis in colon cancer

Epidemiological studies describe estrogens as protectors in the development of colon cancer in postmenopausal women treated with hormone replacement therapy. However, the role of progesterone in colon cancer has been minimally studied and the results are controversial. For the above, the objective of this work was to determine the hormonal regulation exerted by natural ovarian steroids on proliferation and apoptosis in an experimental model of colon cancer in ovariectomized rats treated with 17-beta estradiol and progesterone. Sprague-Dawley rats were exposed to the carcinogen 1,2-dimethylhydrazine to induce colon tumors. Thirty days later, the rats were ovariectomized and treated with estradiol (60 μg/kg), progesterone (10 mg/kg), estradiol plus progesterone (60 μg/kg and 10 mg/kg) or vehicle. We observed no significant differences in colon cancer incidence and tumor multiplicity between the groups. Nevertheless, we observed a decrease in PCNA expression and a greater number of apoptotic index, higher expression of caspase 3, cleaved PARP and cleaved caspase 8 in tumors, confirming the activation of the extrinsic pathway of apoptosis by the combined treatment. In addition, we observed a higher expression of estrogen receptor beta in these tumors. We conclude that the action of both hormones, estradiol and progesterone, is necessary to reduce proliferation and increase apoptosis in colon tumors, probably through estrogen receptor beta activation.

Metformin prevents hormonal and metabolic disturbances and 1,2-dimethylhydrazine-induced colon carcinogenesis in non-diabetic rats

Effects of two doses of the anti-diabetic drug, metformin (MF), on hormonal and metabolic levels of serum of non-diabetic male Wistar rats with 1,2-dimethylhydrazine (DMH)-induced colon tumor adenocarcinomas were studied. Carcinogenesis in the animals was also observed. Rats with DMH-induced colon adenocarcinomas had elevated levels of serum glucose, insulin, insulin-like growth factor-1, total cholesterol, triglycerides, catalase, malonic dialdehyde, glycated hemoglobin, aspartate aminotransferase, and alanine aminotransferase and decreased hemoglobin. Treatment with two doses of MF normalized majority of these changes in DMH-treated rats, whereas the drug was ineffective in rats without DMH treatment. The only exception was the decreased triglyceride levels in MF-treated rats. A 100 mg/kg dose of MF increased DMH-induced exophytic colon carcinomas and decreased endophytic tumors compared with untreated rats. Moreover, both MF doses increased DMH-induced and highly differentiated tumors and decreased the invasiveness of colon carcinomas compared with rats provided with DMH and water. Therefore, effects of MF on metabolic homeostasis are critical for preventing colon cancer.

WNT-pathway components as predictive markers useful for diagnosis, prevention and therapy in inflammatory bowel disease and sporadic colorectal cancer

The key role of the Wnt/β-catenin signaling in colorectal cancer (CRC) insurgence and progression is now recognized and several therapeutic strategies targeting this pathway are currently in developing. Wnt/β-catenin signaling not only dominates the early stages of sporadic colorectal cancer (SCC), but could also represent the connection between inflammatory bowel diseases (IBD) and increased risk of developing SCC. The knowledge on the sequential molecular events of Wnt-signaling cascade in IBD and during colorectal carcinogenesis, might provide new diagnostic/prognostic markers and could be helpful for optimizing the treatment protocols, thus improving the efficacy of Wnt-targeting therapies. We performed a comparative evaluation of the expression of some crucial molecules participating to Wnt signaling in an animal model of chemically-induced CRC and in human tissues obtained from patients suffering from IBD or at sequential stages of SCC. Specifically, we analyzed upstream events of Wnt signaling including β-catenin nuclear translocation and loss of E-cadherin and APC functions, and downstream events including c-Myc and Cyclin-D1 expression. We demonstrated that these crucial components of the Wnt/β-catenin pathway, when evaluated by immunohistochemistry using a multiparametric approach that includes the analyses of both expression and localization, could be potent markers for diagnosis, prevention and therapy in IBD and SCC, also possessing a predictive value for responsiveness to Wnt-targeting therapies. Furthermore, we showed that the animal model of chemically-induced CRC mimics the molecular events of Wnt signaling during IBD and SCC development in humans and may therefore be suitable for testing chemopreventive or therapeutic drugs targeting this pathway.

Dietary folate suppresses DMH-induced colon carcinogenesis in a rat model and affects DMH-induced expression of four DNA repair enzymes

This study investigated the potential role of folate in the dimethylhydrazine (DMH) colon cancer model in male Wistar rats. For induction of colon cancer, group 1 rats were injected subcutaneously with 30 mg DMH/kg body weight weekly for 30 wk. Group 2 received DMH vehicle. Group 3 rats received DMH as in Group 1 but their diet was supplemented with 8 mg folate/kg diet. Group 4 was fed diet supplemented with 8 mg folate/kg diet. Upregulation of DNA damage repair genes Apurinic/apyrimidinic endonuclease 1, X-ray repair complementing defective repair in Chinese hamster cells 5, 8-oxoguanine-DNA glycosylase, and proliferating cell nuclear antigen, associated with a reduction of folic acid level was observed in colons of DMH group. Reductions of these gene upregulations and a significant increase of colonic folic acid level occurred in the DMH group supplemented with folic acid and this group also had significant inhibition of tumor incidence, normal survival rate and histologically nearly normal colonic architecture. It can be concluded that folate supplementation exerts a potent protective effect on rat colon carcinogenesis via significant modulation of DNA repair, providing a mechanism by which it plays a role in the etiology of human cancer.

Zinc and zinc related enzymes in precancerous and cancerous tissue in the colon of dimethyl hydrazine treated rats

Trace element zinc deficiency or excess is implicated in the development or progression of some cancers. The exact role of zinc in the etiology of colon cancer is unclear. To cast light on this question, an experimental model of colon carcinogenesis was applied here. Six week old rats were given sub cutaneous injections of DMH (30 mg/kg body weight) twice a week for three months and sacrificed after 4 months (precancer model) and 6 months (cancer model). Plasma zinc levels showed a significant decrease (p<0.05) at 4 months and a greater significant decrease at 6 months (p<0.01) as compared with controls. In the large intestine there was a significant decrease in tissue zinc levels (p<0.005) and in CuZnSOD, and alkaline phosphatase activity (p<0.05) in the pre-cancerous model and a greater significant decrease in tissue zinc (p<0.0001), and in CuZnSOD and alkaline phosphatase activity (p<0.001), in the carcinoma model. The tissue zinc levels showed a significant decrease in the small intestine and stomach (p<0.005) and in liver (p<0.05) in the cancer model. 87% of the rats in the precancer group and 92% rats in the cancer group showed histological evidence of precancerous lesions and carcinomas respectively in the colon mucosa. This study suggests that the decrease in plasma zinc, tissue zinc and activity of zinc related enzymes are associated with the development of preneoplastic lesions and these biochemical parameters further decrease with progression to carcinoma in the colon.

Polycyclic aromatic hydrocarbons and digestive tract cancers: a perspective

Cancers of the colon are most common in the Western world. In majority of these cases, there is no familial history and sporadic gene damage seems to play an important role in the development of tumors in the colon. Studies have shown that environmental factors, especially diet, play an important role in susceptibility to gastrointestinal (GI) tract cancers. Consequently, environmental chemicals that contaminate food or diet during preparation become important in the development of GI cancers. Polycyclic aromatic hydrocarbons (PAHs) are one such family of ubiquitous environmental toxicants. These pollutants enter the human body through consumption of contaminated food, drinking water, inhalation of cigarette smoke, automobile exhausts, and contaminated air from occupational settings. Among these pathways, dietary intake of PAHs constitutes a major source of exposure in humans. Although many reviews and books on PAHs and their ability to cause toxicity and breast or lung cancer have been published, aspects on contribution of diet, smoking and other factors toward development of digestive tract cancers, and strategies to assess risk from exposure to PAHs have received much less attention. This review, therefore, focuses on dietary intake of PAHs in humans, animal models, and cell cultures used for GI cancer studies along with epidemiological findings. Bioavailability and biotransformation processes, which influence the disposition of PAHs in body and the underlying causative mechanisms of GI cancers, are also discussed. The existing data gaps and scope for future studies is also emphasized. This information is expected to stimulate research on mechanisms of sporadic GI cancers caused by exposure to environmental carcinogens.

Farnesol attenuates 1,2-dimethylhydrazine induced oxidative stress, inflammation and apoptotic responses in the colon of Wistar rats

Colon cancer is the major health hazard related with high mortality and it is a pathological consequence of persistent oxidative stress and inflammation. Farnesol, an isoprenoid alcohol, has been shown to possess antioxidant, anti-inflammatory and chemopreventive properties. The present study was performed to evaluate the protective efficacy of farnesol against 1,2-dimethylhydrazine (DMH) induced oxidative stress, inflammatory response and apoptotic tissue damage. Farnesol was administered once daily for seven consecutive days at the doses of 50 and 100 mg/kg body weight in corn oil. On day 7, a single injection of DMH was given subcutaneously in the groin at the dose of 40 mg/kg body weight. Protective effects of farnesol were assessed by using caspase-3 activity, tissue lipid peroxidation (LPO) and antioxidant status as end point markers. Further strengthening was evident on histopathological observations used to assess the protective efficacy of farnesol. Prophylactic treatment with farnesol significantly ameliorates DMH induced oxidative damage by diminishing the tissue LPO accompanied by increase in enzymatic viz., superoxide dismutase (SOD), catalase, glutathione peroxidase (GPx), glutathione reductase (GR), glutathione-S-transferase (GST) and quinone reductase (QR) and non-enzymatic viz., reduced glutathione (GSH) antioxidant status. Farnesol supplementation significantly decreased caspase-3 activity in colonic tissue. Histological findings also revealed that pretreatment with farnesol significantly reduced the severity of submucosal edema, regional destruction of the mucosal layer and intense infiltration of the inflammatory cells in mucosal and submucosal layers of the colon. The data of the present study suggest that farnesol effectively suppress DMH induced colonic mucosal damage by ameliorating oxidative stress, inflammatory and apoptotic responses.

Selenium as a chemopreventive agent in experimentally induced colon carcinogenesis

AIM: To elucidate the chemopreventive efficacy of selenium during experimentally induced colon carcinogenesis.

METHODS: Thirty-two male wistar rats were divided into four groups: group I (normal control); group II [1,2-dimethylhydrazine (DMH) treated]; group III (selenium treated); and group IV (DMH + selenium treated). Groups II and IV were given subcutaneous injections of DMH (30 mg/kg body weight) every week for 20 wk. Selenium, in the form of sodium selenite, was given to groups III and IV at 1 ppm in drinking water ad libitum for 20 wk. At the end of the study, rats were sacrificed and their colons were analyzed for the development of tumors, antioxidant enzyme levels and histological changes.

RESULTS: 100% of the DMH treated rats developed tumors, which was reduced to 60% upon simultaneous selenium supplementation. Similarly, tumor multiplicity decreased to 1.1 following selenium supplementation to DMH treated rats. Levels of lipid peroxidation, glutathione-S-transferase, superoxide dismutase (SOD), catalase, and glutathione peroxidase (GPx) decreased following DMH treatment, whereas levels of glutathione (GSH) and glutathione reductase (GR) significantly increased in DMH treated rats. Selenium administration to DMH treated rats led to an increase in the levels of lipid peroxidation, SOD, catalase, glutathione-S-transferase and GPx, but decreased the levels of GSH and GR. Histopathological studies on DMH treated rats revealed dysplasia of the colonic histoarchitecture, which showed signs of improvement following selenium treatment.

CONCLUSION: The study suggests the antioxidative potential of selenium is a major factor in providing protection from development of experimentally induced colon carcinogenesis.

Folate and colorectal cancer: an evidence-based critical review

Currently available evidence from epidemiologic, animal, and intervention studies does not unequivocally support the role of folate, a water-soluble B vitamin and important cofactor in one-carbon transfer, in the development and progression of colorectal cancer (CRC). However, when the portfolio of evidence from these studies is analyzed critically, the overall conclusion supports the inverse association between folate status and CRC risk. It is becoming increasingly evident that folate possesses dual modulatory effects on colorectal carcinogenesis depending on the timing and dose of folate intervention. Folate deficiency has an inhibitory effect whereas folate supplementation has a promoting effect on the progression of established colorectal neoplasms. In contrast, folate deficiency in normal colorectal mucosa appears to predispose it to neoplastic transformation, and modest levels of folic acid supplementation suppress, whereas supraphysiologic supplemental doses enhance, the development of cancer in normal colorectal mucosa. Several potential mechanisms relating to the disruption of one-carbon transfer reactions exist to support the dual modulatory role of folate in colorectal carcinogenesis. Based on the lack of compelling supportive evidence and on the potential tumor-promoting effect, routine folic acid supplementation should not be recommended as a chemopreventive measure against CRC at present.

Zinc mediated normalization of histoarchitecture and antioxidant status offers protection against initiation of experimental carcinogenesis

The present study evaluated the inhibitory effects of zinc on colonic antioxidant defense system and histoarchitecture during 1,2 dimethylhydrazine (DMH) induced colon carcinogenesis in male Spraque Dawley rats. The rats were segregated into four groups viz., normal control, DMH treated, zinc treated, DMH + zinc treated. Colon carcinogenesis was induced through weekly subcutaneous injections of DMH (30 mg/kg body weight) for 8 weeks. Zinc (in the form of zinc sulphate) was supplemented to rats at a dose level of 227 mg/l in drinking water, ad libitum for the entire duration of the study. Increased lipid peroxidation was accompanied by a decrease in reduced glutathione (GSH), glutathione reductase (GR), glutathione-s-transferase (GST), superoxide dismutase (SOD), and catalase. Administration of zinc to DMH treated rats significantly decreased the lipid peroxidation levels with simultaneous enhancement of GSH, GR, GST, SOD, and Catalase. Histopathological studies from DMH treated rats revealed disorganization of colonic histoarchitecture. However, zinc treatment to DMH treated rats greatly restored normalcy in the colonic histoarchitecture, with no apparent signs of abnormality. Energy Dispersive X-Ray Fluorescence (EDXRF) studies revealed a significant decrease in tissue concentrations of zinc in the colon following DMH treatment, which upon zinc supplementation were recovered to near normal levels. In conclusion, the results of this study suggest that zinc has a beneficial effect during the initiation of key events leading to the development of experimentally induced carcinogenesis.

Chemopreventive effects of lupulone, a hop {beta}-acid, on human colon cancer-derived metastatic SW620 cells and in a rat model of colon carcinogenesis

The bitter acids of hops (Humulus lupulus L.) mainly consist of humulones or alpha-acids and lupulones or beta-acids. We aimed to evaluate the antiproliferative mechanisms of lupulones on a human metastatic colon carcinoma-derived cell line (SW620 cells) and to assess their chemopreventive effects in a model of colon carcinogenesis. SW620 cell growth was inhibited by 70% after a 48 h exposure to lupulones (40 microg/ml). Lupulones up-regulated the expression of Fas receptor (Fas) and Fas ligand (FasL) as well as TNF-related apoptosis inducing ligand (TRAIL)-R1 (DR4) and -R2 (DR5) receptor proteins, suggesting the involvement of Fas and TRAIL receptors-mediated pathways in lupulone-induced apoptosis. Lupulones also increased the mitochondrial membrane permeability. Colon carcinogenesis was initiated in Wistar rats by intra-peritoneal injections of azoxymethane (AOM), once a week for 2 weeks. One week after the last injection, rats received lupulones (0.001 or 0.005%) in drinking water, and AOM-control rats received the excipient. After 7 months of treatment, the colon of rats receiving 0.001 and 0.005% lupulones showed, respectively, a 30 and a 50% reduction (P < 0.05) of the number of preneoplastic lesions (aberrant crypt foci). In addition, we observed a drastic reduction (70-80%) of the total number of tumors in the colon of rats treated with lupulones when compared with the AOM control group. Lupulones induced apoptosis in SW620 colon-derived metastatic cells by activating both Fas and TRAIL death receptor signaling pathways, and antagonize at a low dose (4 mg/kg/day) colon cancer development. These observations suggest the use of lupulones for colon cancer chemoprevention trials.

Beta-Catenin mutations in a mouse model of inflammation-related colon carcinogenesis induced by 1,2-dimethylhydrazine and dextran sodium sulfate

In a previous study, we developed a novel mouse model for colitis-related carcinogenesis, utilizing a single dose of azoxymethane (AOM) followed by dextran sodium sulfate (DSS) in drinking water. In the present study, we investigated whether colonic neoplasms can be developed in mice initiated with a single injection of another genotoxic colonic carcinogen 1,2-dimethylhydrazine (DMH), instead of AOM and followed by exposure of DSS in drinking water. Male crj: CD-1 (ICR) mice were given a single intraperitoneal administration (10, 20 or 40 mg/kg body weight) of DMH and 1-week oral exposure (2% in drinking water) of a non-genotoxic carcinogen, DSS. All animals were killed at week 20, histological alterations and immunohistochemical expression of beta-catenin, cyclooxygenase (COX-2) and inducible nitric oxide synthase (iNOS) were examined in induced colonic epithelial lesions (colonic dysplasias and neoplasms). Also, the beta-catenin gene mutations in paraffin-embedded colonic adenocarcinomas were analyzed by the single strand conformation polymorphism method, restriction enzyme fragment length polymorphism and direct sequencing. The incidences of colonic neoplasms with dysplastic lesions developed were 100% with 2.29+/-0.95 multiplicity, and 100% with 10.38+/-4.00 multiplicity in mice given DMH at doses of 10 mg/kg or 20 mg/kg and 2%DSS, respectively. Although approximately half of the mice given DMH at a dose of 40 mg/kg bodyweight were dead after 2-3 days after the injection, mice who received DMH 40 mg/kg and 2%DSS had 100% incidence of colonic neoplasms with 9.75+/-6.29 multiplicity. Immunohistochemical investigation revealed that adnocarcinomas, induced by DMH at all doses and 2%DSS, showed positive reactivities against beta-catenin, COX-2 and iNOS. In DMH/DSS-induced adenocarcinomas, 10 of 11 (90.9%) adenocacrcinomas had beta-catenin gene mutations. Half of the mutations were detected at codon 37 or 41, encoding serine and threonine that are direct targets for phosphorylation by glycogen synthase kinase-3beta. The present results suggests that, as in the previously reported model (AOM/DSS) our experimental protocol, DMH initiation followed by DSS, may provide a novel and useful mouse model for investigating inflammation-related colon carcinogenesis and for identifying xenobiotics with modifying effects.

Ethylene diamine tetraacetic acid induced colonic crypt cell hyperproliferation in rats

AIM: To investigate the effect of ethylene diamine tetraacetic acid (EDTA) on proliferation of rat colonic cells.

METHODS: EDTA was administered into Wistar rats, carcinogenesis induced by 1,2-dimethylhydrazine (DMH) in rats was studied with immunohistochemistry.

RESULTS: Marked regional differences in cell proliferation were found in all groups. In EDTA-treated animals, total labelling indexes in both proximal (10.00 ± 0.44 vs 7.20 ± 0.45) and distal (11.05 ± 0.45 vs 8.65 ± 0.34) colon and proliferative zone size (21.67 ± 1.13 vs 16.75 ± 1.45, 27.73 ± 1.46 vs 21.74 ± 1.07) were significantly higher than that in normal controls (P < 0.05) and lower than that in DMH group (10.00 ± 0.44 vs 11.54 ± 0.45, 11.05 ± 0.45 vs 13.13 ± 0.46, 21.67 ± 1.13 vs 35.52 ± 1.58, 27.73 ± 1.46 vs 39.61 ± 1.32, P < 0.05). Cumulative frequency distributions showed a shift of the EDTA distal curve to the right (P < 0.05) while the EDTA proximal curve did not change compared to normal controls. Despite the changes of proliferative parameters, tumours did not develop in EDTA treated animals.

CONCLUSION: Hyperproliferation appears to be more easily induced by EDTA in distal colon than in proximal colon. Hyperproliferation may need to exceed a threshold to develop colonic tumours. EDTA may work as a co-factor in colonic tumorigenesis.

Folate, colorectal carcinogenesis, and DNA methylation: lessons from animal studies

Folate, a water-soluble B vitamin and cofactor in one-carbon transfer, is an important nutritional factor that may modulate the development of colorectal cancer (CRC). Epidemiologic and clinical studies indicate that dietary folate intake and blood folate levels are inversely associated with CRC risk. Collectively, these studies suggest an approximately 40% reduction in the risk of CRC in individuals with the highest dietary folate intake compared with those with the lowest intake. Animal studies using chemical and genetically predisposed rodent models have provided considerable support for a causal relationship between folate depletion and colorectal carcinogenesis as well as a dose-dependent protective effect of folate supplementation. However, animal studies also have shown that the dose and timing of folate intervention are critical in providing safe and effective chemoprevention; exceptionally high supplemental folate levels and folate intervention after microscopic neoplastic foci are established in the colorectal mucosa promote, rather than suppress, colorectal carcinogenesis. These animal studies, in conjunction with clinical observations, suggest that folate possesses dual modulatory effects on carcinogenesis depending on the timing and dose of folate intervention. Folate deficiency has an inhibitory effect, whereas folate supplementation has a promoting effect on the progression of established neoplasms. In contrast, folate deficiency in normal epithelial tissues appears to predispose them to neoplastic transformation, and modest levels of folate supplementation suppress the development of tumors in normal tissues. Notwithstanding the limitations associated with animal models, these studies suggest that the optimal timing and dose of folate intervention must be established for safe and effective chemoprevention in humans. Folate is an important factor in DNA synthesis, stability, and integrity, the repair aberrations of which have been implicated in colorectal carcinogenesis. Folate may also modulate DNA methylation, which is an important epigenetic determinant in gene expression (an inverse relationship), in the maintenance of DNA integrity and stability, in chromosomal modifications, and in the development of mutations. A mechanistic understanding of how folate status modulates colorectal carcinogenesis further strengthens the case for a causal relationship and provides insight into a possible chemopreventive role of folate.

Role of Folate in Colon Cancer Development and Progression

Folate, a water-soluble B vitamin and important cofactor in 1-carbon transfer, is an important nutritional factor that may modulate the development of colorectal cancer. Epidemiologic and clinical studies indicate that dietary folate intake and blood folate levels are inversely associated with colorectal cancer risk. Collectively, these studies suggest an approximately 40% reduction in the risk of colorectal cancer in individuals with the highest dietary folate intake compared with those with the lowest intake. Animal studies using chemical and genetically predisposed rodent models have provided considerable support for a causal relationship between folate depletion and colorectal carcinogenesis as well as a dose-dependent protective effect of folate supplementation. However, animal studies have also shown that the dose and timing of folate intervention are critical in providing safe and effective chemoprevention; exceptionally high supplemental folate levels and folate intervention after microscopic neoplastic foci are established in the colorectal mucosa promote rather than suppress colorectal carcinogenesis. These animal studies in conjunction with clinical observations suggest that folate possesses the dual modulatory effects on carcinogenesis depending on the timing and dose of folate intervention. Folate deficiency has an inhibitory effect whereas folate supplementation has a promoting effect on progression of established neoplasms. In contrast, folate deficiency in normal epithelial tissues appears to predispose them to neoplastic transformation, and modest levels of folate supplementation suppress the development of tumors in normal tissues. Notwithstanding the limitations associated with animal models, these animal studies suggest that the optimal timing and dose of folate intervention need to be established for safe and effective chemoprevention in humans.

Sphingomyelin in the suppression of colon tumors: prevention versus intervention

Intestinal cells are regularly exposed to sphingolipid metabolites, i.e., ceramide and sphingoid bases, after hydrolysis of complex sphingolipids from the diet. These metabolites are known regulators of cell growth, differentiation, and death. Non-pharmacological amounts in the diet have been shown to inhibit early stages of chemically induced colon cancer in mice. To distinguish between chemopreventive and chemotherapeutic effects of sphingomyelin supplements, mice were fed sphingomyelin before and after tumor initiation. Both applications drastically reduced tumor formation, without a significant difference among the groups, indicating that sphingolipids are as effective in the chemoprevention of tumors as in early intervention. The normalization of cell proliferation and rate of apoptosis, but not the induction of differentiation, seem to be key players in the suppression of tumor formation by dietary sphingomyelin. This may have implications for the development of a cancer prevention or treatment strategy with sphingolipids as an alternative to conventional drugs.

Increased frequency of gastrin-releasing peptide receptor gene mutations during colon-adenocarcinoma progression

Epithelial cells lining the mature human colon do not normally express receptors for gastrin-releasing peptide (GRPR). In contrast, we have shown that when aberrantly expressed in functional form in colon cancer, this protein acted as a morphogen where it caused tumor cells to adopt a better-differentiated phenotype. Importantly, GRPR mRNA is ubiquitously mutated in human colon cancer cell lines, with inactivating mutations detected in all cell lines not expressing functional receptor. Since colon cancers are heterogeneously differentiated, we set out to determine if the GRPR gene was mutated as a function of tumor cell differentiation in archived human colon cancers. We used laser capture microscopy to dissect out 67 regions of defined differentiation from 20 human colon cancers randomly selected from the UIC GI Tumor Bank. Except for two polymorphisms, the GRPR gene was not mutated in nonmalignant epithelial cells. In contrast, 42 distinct mutations were identified in malignant cells. Overall mutation number inversely correlated with the degree of tumor cell differentiation. Within any cancer, all GRPR mutations found within better-differentiated cells were conserved in more poorly-differentiated cells; while all poorly-differentiated cells contained mutations resulting in GRPR pharmacological inactivation. These data suggest that accumulation of mutations within the GRPR gene ultimately resulting in the production of nonfunctional receptors may represent a previously unappreciated mechanism allowing for the dedifferentiation of tumor cells within any particular colon cancer; and that poorly-differentiated tumor cells within any individual cancer may arise clonally from their better-differentiated precursors.

Abnormalities of the cadherin-catenin complex in chemically-induced colo-rectal carcinogenesis

Beta-Catenin is a multifunctional protein originally identified as a component of the cadherin cell-cell adhesion complex. It also binds the adenomatous polyposis coli (APC) tumour suppressor which controls beta-catenin cellular levels through its degradation. (beta-Catenin and/or APC mutations result in increased cytoplasmic Beta-catenin and nuclear translocation. The aim of the present study was to examine the expression and cellular localisation of alpha and beta-catenin, p120 and E-cadherin in a chemically-induced mouse model of colo-rectal cancer using 1,2-dimethylhydrazine (DMH). Female Balb/C mice were injected subcutaneously with a solution providing 25 mg DMH base/kg body weight for 17 weeks. Animals were killed and tumours identified in the intestine with a dissecting microscope. Formalin-fixed paraffin-embedded sections of normal and dysplastic colonic mucosa were stained by an indirect avidin-biotin immunohistochemical technique using mouse monoclonal antibodies, and membranous, cytoplasmic and nuclear cellular localisation was assessed by light microscopy. Staining distribution scored as follows: 3, > 90 % positive epithelial cells; 2, >50 % positive epithelial cells; 1, <50 % positive epithelial cells. Non-dysplastic colonic epithelial cells revealed beta-catenin expression at the membrane (33/41 scored 3),areas of cytoplasmic expression (24/41 scored 1) and no nuclear staining. Dysplastic colonic epithelium revealed increased membranous and cytoplasmic, beta-catenin immunoreactivity (39/41 and 38/41 both scored 3) with focal nuclear staining (14/41). Expression patterns for ac-catenin, p120, and E-cadherin were similar to beta-catenin with increased membranous and cytoplasmic immunoreactivity in dysplastic mucosa, although no nuclear staining was observed. Increased cytoplasmic expression and nuclear localisation of beta-catenin are consistent with a possible mutation in its gene, and this finding was in keeping with the mutational analysis of exon 3 by single-strand conformational polymorphism. Increased immunoreactivity of the other catenins also suggests further disruption in catenin regulation. In summary, alterations in the beta-catenin expression and cellular localisation in the DMH-induced tumours are similar to those seen inhuman sporadic colorectal tumours. The DMH is therefore a useful model for studying the abnormalities of the E-cadherin-catenin pathway in colorectal carcinogenesis.

A noncarcinogenic small dose of n-methylnitrosourea enhances colon tumorigenesis in F344 rats

Very small amount of carcinogens such as nitroso compounds and heterocyclic amines has been found in human feces. This study was designed to investigate in F344 rats whether an intrarectal noncarcinogenic small dose of n-methylnitrosourea (0.2 mg, 3 times weekly) affects colon carcinogenesis initiated with an intrarectal large dose (2 mg, 3 times weekly) of this carcinogen. The colon tumor yield at week 50 in 12 rats receiving the large dose for 2 weeks and then the small dose for the next 30 weeks significantly increased as compared to 23 rats receiving only the large dose for 2 weeks: 100% vs. 70% in tumor incidence and 4.3 vs. 1.2 in mean number of tumors per rat. No tumors were found in 12 rats receiving only the small dose for 30 weeks. The results indicate that a very small amount of carcinogens could participate in a tumor-enhancing effect on the high-risk colon induced with a large dose of carcinogens, even though their less amounts insufficient to complete carcinogenesis process. Further study is needed to elucidate if administration of such a small dose could induce epigenetic alterations or further genetic changes in the initiated colonic cells.

Variability of cell proliferation in the proximal and distal colon of normal rats and rats with dimethylhydrazine induced carcinogenesis

AIM: To investigate the patterns of cell proliferation in proximal and distal colons in normal rats and rats with 1,2-dimethylhydrazine (DMH) induced carcinogenesis using the thymidine analogue bromodeoxyuridine.

METHODS: Colonic crypt cell proliferation was immunohistochemically detected using the anti-bromodeoxyuridine Bu20a monoclonal antibody.

RESULTS: Marked regional differences were found in both groups. Total labelling index (LI) and proliferative zone size in both normal (8.65 ± 0.34 vs 7.2 ± 0.45, 27.74 ± 1.07 vs 16.75 ± 1.45) and DMH groups (13.13 ± 0.46 vs 11.55 ± 0.45, 39.60 ± 1.32 vs 35.52 ± 1.58) were significantly higher in distal than in proximal colon (P < 0.05), although the number of cells per proximal crypt was greater (31.45 ± 0.20 vs 34.45 ± 0.39, 42.68 ± 0.53 vs 49.09 ± 0.65, P < 0.0001). Crypt length, total LI and proliferative zone size all increased in both proximal and distal regions of DMH rats compared to normal controls (P < 0.0001). In DMH-treated rat colon a shift of labelled cells to higher crypt cell positions was demonstrated distally whilst a bi-directional shift was evident proximally (P < 0.05).

CONCLUSION: Our results show that changes in cell proliferation patterns, as assessed by bromodeoxyuridine uptake, can act as a reliable intermediate marker of colonic cancer formation. Observed differences between proliferation patterns in distal and proximal colon may be associated with the higher incidence of tumors in the distal colon.

Prevention by natural food anthocyanins, purple sweet potato color and red cabbage color, of 2-amino-1-methyl-6-phenylimidazo[4,5-b]pyridine (PhIP)-associated colorectal carcinogenesis in rats initiated with 1,2-dimethylhydrazine

The potential of purple sweet potato color (PSPC) and red cabbage color (RCC), natural anthocyanin food colors, to modify colorectal carcinogenesis was investigated in male F344/DuCrj rats, initially treated with 1,2-dimethylhydrazine (DMH) and receiving 2-amino-1-methyl-6-phenylimidazo[4,5-b]pyridine (PhIP) in the diet. After DMH initiation, PSPC and RCC were given at a dietary level of 5.0% in combination with 0.02% PhIP until week 36. No PSPC or RCC-treatment-related changes in clinical signs and body weight were found. Incidences and multiplicities of colorectal adenomas and carcinomas in rats initiated with DMH were clearly increased by PhIP. In contrast, lesion development was suppressed by RCC, or tended to be inhibited by PSPC administration. Furthermore, in the non-DMH initiation groups, induction of aberrant crypt foci (ACF) by PhIP was significantly decreased by RCC supplementation. The results thus demonstrate that while PhIP clearly exerts promoting effects on DMH-induced colorectal carcinogenesis, these can be reduced by 5.0% PSPC or 5.0% RCC in a diet under the present experimental conditions.

Pronounced inhibition by a natural anthocyanin, purple corn color, of 2-amino-1-methyl-6-phenylimidazo[4,5-b]pyridine (PhIP)-associated colorectal carcinogenesis in male F344 rats pretreated with 1,2-dimethylhydrazine

The potential of purple corn color (PCC), a natural anthocyanin, to modify colorectal carcinogenesis was investigated in male F344/DuCrj rats, initially treated with 1,2-dimethylhydrazine (DMH), receiving 2-amino-1-methyl-6-phenylimidazo[4,5-b]pyridine (PhIP) in the diet. After DMH initiation, PCC was given at a dietary level of 5.0% in combination with 0.02% PhIP until week 36. No PCC-treatment-related changes in clinical signs, body weight and food consumption were found. Incidences and multiplicities of colorectal adenomas and carcinomas in rats initiated with DMH were clearly increased by PhIP. In contrast, lesion development was suppressed by PCC administration. Furthermore, in the non-DMH initiation groups, induction of aberrant crypt foci by PhIP tended to be decreased by the PCC supplementation. The results thus demonstrate that while PhIP clearly exerts promoting effects on DMH-induced colorectal carcinogenesis, these can be reduced by 5.0% PCC in the diet, under the present experimental conditions.

Dietary fiber and colorectal neoplasia

PURPOSE

Dietary fiber has been implicated in colorectal neoplasia, despite conflicting evidence. This is a review of the currently available data on the role of dietary fiber in colorectal carcinogenesis.

METHODS

A literature search was conducted using the MEDLINE database. All case-control, longitudinal, and randomized, controlled studies published in English between 1988 and 2000 were identified, as were animal model studies in the period 1986 to 2000. Data from the various studies were tabulated and systematically analyzed, with particular emphasis on the effect of dietary fiber on tumor incidence and luminal parameters such as short chain fatty acids.

RESULTS

Epidemiologic correlation studies show a high intake of dietary fiber to be associated with a lower risk of colorectal neoplasia. Thirteen of the 24 case-control studies reviewed demonstrated a protective effect of dietary fiber against colorectal neoplasia, and 16 showed a protective effect of vegetables or vegetable fiber. On the other hand, of 13 longitudinal studies in various cohorts, only 3 demonstrated a protective effect of fiber and 4 a protective effect of vegetables or vegetable fiber. The five published randomized, controlled trials all investigated the effect of increased fiber intake on short-term adenoma recurrence; however, none showed any significant protective effect. Among 19 experimental studies in animal models, 15 showed a protective effect of fiber against tumor induction compared with controls. Animal studies also showed that poorly fermentable fibers (e.g., wheat bran and cellulose) were more protective than soluble fibers (e.g., guar gum and oat bran), which sometimes enhanced carcinogenesis. No clear correlation was found between luminal pH or short chain fatty acids and tumor induction.

CONCLUSIONS

On the basis of current data, there is little evidence to support the use of dietary fiber supplements to reduce the risk of colorectal neoplasia. Lifelong and early exposure may be important but are difficult to study. Other risk factors interact with the effects of dietary fiber.

Probiotics: future directions

Clinical studies have shown that certain probiotics may be useful in treating a variety of diarrheal disorders, including rotavirus diarrhea, antibiotic-associated diarrhea, Clostridium difficile diarrhea, and traveler's diarrhea. New data suggest that probiotics might be useful in controlling inflammatory diseases, treating and preventing allergic diseases, preventing cancer, and stimulating the immune system, which may reduce the incidence of respiratory disease. Different modes of administering probiotics are currently being investigated, which may ultimately lead to the widespread use of probiotics in functional foods. It is important that such practices be directed by carefully controlled clinical studies published in peer-reviewed journals.

Are dietary fiber-induced alterations in colonic epithelial cell proliferation predictive of fiber's effect on colon cancer?

Alterations in cell proliferation of the colon have been observed as a result of changes in amount and type of dietary fiber and in relation to risk of developing colon cancer. Although some human observational and intervention studies contribute to the database, most information results from experiments on rodents. Because of numerous contradictory reports linking dietary fiber, cell proliferation, and colon cancer, we undertook a critical review of existing methods in an attempt to explain the inconsistencies. Although there may be some individual types of dietary fiber that protect against chemically induced colon cancer, dietary fiber as a single entity does not appear to afford any consistent protection. Because of significant differences in experimental protocols among laboratories, it is not yet possible to state with certainty that increases in cell proliferation, induced by fiber consumption, are predictive of increased tumorigenesis. Much of what has been observed and interpreted as elevation of risk may simply be normal homeostatic changes in cell proliferation. Even though fermentation to short-chain fatty acids is a mechanistically attractive hypothesis to explain why fiber modulates cytokinetics, data do not consistently support short-chain fatty acids as biological intermediates in risk of colon cancer. The state of the art in this field has not yet progressed to the point where a clear effect of dietary fiber on cytokinetics and colon carcinogenesis can be assessed with any degree of certainty. Additional markers of apoptosis, differentiation, and cell-cell communication may be required for a more accurate analysis of the relation among fiber, cytokinetics, and colon cancer.

DNA repair: kinetics and thresholds

DNA damage is a critical factor in the initiation of chemically induced toxicities (including cancer), and the repair of this damage represents the cell's first line of defense against the deleterious effects of these agents. The various mechanisms of DNA repair are reviewed briefly and the actions of the DNA repair protein O6-alkylguanine DNA alkyltransferase (ATase) are used to illustrate how DNA repair can protect cells against alkylating agent-induced toxicities, mutagenesis, clastogenesis, and carcinogenesis. The effectiveness of this repair protein can be measured based on its ability to deplete levels of its promutagenic substrate O6-methylguanine (O6-meG) in the DNA of cells. These studies reveal that the repair of O6-meG from DNA occurs heterogeneously, both intra- and intercellularly. Even in cells that repair O6-meG hyperefficiently, certain regions of chromatin DNA are repaired with difficulty, and in other regions they are not repaired at all; most likely this lack of repair is a result of the location of the lesion in the DNA sequence. When individual cells are compared within a tissue, some cells are clearly repair deficient, because the O6-meG can persist in DNA for many weeks, whereas in other cells, it is removed within a matter of hours. The role of these repair-deficient cells as targets for alkylating agent induced carcinogenesis is considered. The mechanisms of the homeostatic control of DNA repair function in mammalian cells are not yet well understood. Because there are now indications of the mechanisms by which the level of DNA damage may be sensed (and so influence the activity of the ATase repair protein), this is an important area for future study.

The relationship between 1,2-dimethylhydrazine dose and the induction of colon tumours: tumour development in female SWR mice does not require a K-ras mutational event

In this study we have investigated the relationship between the dose of 1,2-dimethylhydrazine (DMH) and the yield (and location) of tumours in a mouse strain susceptible to colon tumour induction. Female SWR mice were injected with 6.8 mg/kg DMH i.p. once a week for 1, 5, 10 and 20 weeks and the animals were followed for almost 2 years. Administration of increasing doses of DMH resulted in a dose-dependent decrease in survival time. Colon tumours developed in 26, 76 and 87% of mice given a total dose of 34, 68 and 136 mg/kg DMH, respectively: no tumours were detected in animals treated with a total dose of 6.8 mg/kg. Most colon tumours (79%) were located in the distal colon with the remainder being found in the mid colon and none were detected in either the proximal colon or small intestine. As mutations in the K-ras gene are thought to be key events in the pathogenesis of human and rodent colon tumours, we determined the frequency of codon 12 and 13 K-ras mutations in these tumours by restriction site mutation analysis and/or DNA sequencing. A total of 50 colon tumour samples were analysed for codon 12 mutations and of these 29 were also screened for codon 13 mutations. No mutations were detected in either of these codons. The mutational activation of the K-ras gene is not an essential step in the development of DMH-induced colon tumours in female SWR mice and if similar considerations apply to humans, then the aetiological role of alkylating agents may be underestimated from the prevalence of K-ras GC-->AT transitions in human tumours.

Absence of p53 gene mutations in rat colon carcinomas induced through the synergistic interaction between methylazoxymethanol and X-irradiation

p53 is one the most frequently mutated genes found in human colonic tumors. Because colonic neoplasms induced in rats by certain chemical carcinogens are similar to human colonic tumors in their histological features and proliferation characteristics, the rat has been used as an experimental model to study the pathogenesis of colon cancer. However, p53 mutations were not detected in the chemically induced colonic tumors analyzed for p53 mutations. X-irradiation has also been shown to induce colonic neoplasms in rats that resemble human colonic tumors histopathologically. Because the incidence of colonic tumors induced by methylazoxymethanol (MAM) in rats was shown to be enhanced by X-irradiation, we immunohistochemically analyzed these colonic carcinomas for the presence of p53 gene mutations. The immunohistochemical analyses clearly showed the absence of nuclear immunoreactivity in all ten tumors examined. The results from the present study indicate that point mutations in p53, at least in the coding region, are not involved in the development of colon cancer induced by the combination of MAM and X-irradiation. Our observations, together with the data from previous studies, further suggest that rat colon carcinogenesis, unlike human colon cancer, may not involve p53 mutation as an obligatory event.

Colon carcinogenesis in shrews by intrarectal infusion of N-methyl-N-nitrosourea

Intrarectal infusion of a 0.15 ml solution containing 1.5 mg or 0.5 mg of N-methyl-N-nitrosourea (MNU) was given to female shrews from 6 weeks of age. Fifteen shrews were given 16 doses of 1.5 mg MNU administered biweekly (group 1), 15 shrews were given 24 doses of 0.5 mg MNU weekly (group 2), and four untreated shrews served as controls (group 3). Moribund shrews were killed during the course of the experiment and all remaining animals were killed at 37 weeks of age and terminated the experiment. The mean age when killed was 30.8 weeks in group 1 and 36.2 weeks in group 2. All autopsied shrews in group 1 and group 2, 13 shrews each, had colon cancers, and there were a few small intestinal cancers and uterine squamous cell carcinomas, while no tumors were seen in the untreated shrews. The colonic lesions were of both exophytic and endophytic type with a variety of histologies and depths of invasion. Mesenteric lymph node metastasis was seen in 31% (4/13) of group 1 and 23% (3/13) of group 2. Thus, MNU, a colonotrophic carcinogen in rodents, also induced colon cancer in shrews in the present study.

Sulindac and indomethacin inhibit formation of aberrant crypt foci in the colons of dimethyl hydrazine treated rats

Aberrant crypt foci are microscopic lesions found in the colons of rodents treated with carcinogens, and in patients with premalignant colorectal conditions. They consist of single or multiple abnormal crypts and show cellular changes ranging from dysplasia to microscopic adenomacarcinoma. It is thought that these lesions represent the initial stages of the adenomacarcinoma path that results in the development of colorectal neoplasia. We have examined the effect of sulindac and indomethacin on the formation of aberrant crypt foci in rats treated with dimethylhydrazine (DMH). Aberrant crypt foci were induced in male Sprague-Dawley rats with two oral doses of dimethyl hydrazine at 25 mg/kg per dose. Rats were randomized to receive sulindac at 3 mg/kg (n = 20) or 10 mg/kg (n = 18) b.d., indomethacin at 1 mg/kg per day (n = 18) or 2 mg/kg per day (n = 19) or control (n = 37). Drug treatment was started on the day following the first dose of carcinogen and continued for 3 weeks. Colons were fixed flat overnight in 10% formalin and stained with 0.2%. Methylene Blue solution before being studied. There was a significant reduction in the number of aberrant crypt foci in rats treated with 10 mg/kg b.d., sulindac (P = 0.001) and indomethacin at 2 mg/kg per day (P = 0.0002). Sulindac, at 3 mg/kg b.d., and indomethacin, at 1 mg/kg per day, did not have a statistically significant effect (P = 0.089 and P = 0.052, respectively). None of the drug treatments affected the relative frequency of single crypt vs multiple crypt foci. Previous studies have shown that sulindac and indomethacin will significantly inhibit the growth and development of tumours in DMH treated rats. The current data suggest that one of the pathways of action of NSAID is to inhibit the formation of early preneoplastic lesions.

The effect of Lactobacillus GG on the initiation and promotion of DMH-induced intestinal tumors in the rat

Male Fischer 344 rats were fed a 20% or a 5% corn oil diet and were injected subcutaneously with dimethylhydrazine (DMH) weekly for 16 weeks. In addition, an approximately equal number of animals challenged with DMH were fed daily, until the end of the study, 2 x 10(10) Lactobacillus casei subsp. rhamnosus strain GG starting three weeks before DMH administration or after the ninth weekly injection. The feeding of the Lactobacillus GG before and during carcinogen treatment resulted in a significant decrease in the incidence of colon tumors and the number of small intestinal and colon tumors per tumor-bearing animal for rats fed a 20% corn oil diet. This decrease in tumor incidence or number of tumors was not seen when animals were fed the Lactobacillus after the ninth week of carcinogen treatment. Animals fed a 5% corn oil diet had a lower tumor incidence and number of tumors resulting from the decrease in dietary fat; in addition the feeding of Lactobacillus GG before the carcinogen challenge resulted in a lower incidence of colon tumors. These studies show that a specific strain of L. casei subsp. rhamnosus designated GG can interfere with the initiation or early promotional stages of DMH-induced intestinal tumorigenesis, and this effect is most pronounced for animals fed a high-fat diet.

Cruciferous vegetables and glutathione: their effects on colon mucosal glutathione level and colon tumor development in rats induced by DMH

The effect of a diet containing 10-40% lyophilized cabbage or broccoli as cruciferous vegetable or 10-40% lyophilized potato as noncruciferous vegetable fed for 14 days on the colon mucosal glutathione (GSH) level was studied in male rats. The GSH levels of the duodenum mucosa and the liver were also measured. Cabbage and broccoli enhanced the colon and duodenum mucosal GSH levels in a dose-related manner; potato had no effect. All three vegetables had no effect on the liver GSH level. The effect of GSH on colon tumorigenesis induced by 1,2-dimethylhydrazine (DMH) was also examined in rats. Male Sprague-Dawley rats were injected with DMH (20 mg/kg body wt) weekly for 20 weeks. DMH lowered the colon mucosal GSH level. GSH (100 mg/day/rat) dissolved in the drinking water and given to rats during and after DMH injections had little or no effect on tumor incidence and total number of colon tumors. Tumors were larger in rats that received GSH than in those that received water. This study shows that the colon mucosal GSH level can be enhanced by feeding rats a diet high in cabbage or broccoli and that GSH added to the drinking water did not affect DMH-induced colon tumorigenesis under the experimental conditions used.

Diet and adenomatous polyp risk

Studies of risk factors for colonic adenomatous polyps have been reported in greater numbers in 1993 than in all previous years combined. This explosion in interest in polyps has not arisen because polyps themselves cause serious illness. They are in the vast majority of cases asymptomatic. However, adenomas have become the surrogate for colon cancer in a number of phase III dietary intervention trials. These trials were undertaken at a time when very little was known of adenoma risk factors. Data accumulated in the past 18 months in general demonstrate a similarity in risk factors for cancer and polyp. Since it has also been recently established that polypectomy diminishes colon cancer risk, the adenomatous polyp has been established as an ethical and convenient surrogate for cancer of the colon. Prevention of colorectal cancer is the goal of all the above studies, and it is hoped that the dietary intervention trials currently under way will generate the data that will make prevention possible.

Effect of dietary vitamin D3 (cholecalciferol) on colon carcinogenesis induced by 1,2-dimethylhydrazine in male Fischer 344 rats

This study examined the effect of increasing dietary vitamin D on chemically induced colon carcinogenesis. Male Fischer 344 rats were first injected with 1,2-dimethylhydrazine (200 mg/kg) and then fed one of five dietary levels of vitamin D as cholecalciferol (250, 1,000, 2,000, 4,000, and 10,000 IU/kg diet) for nine months. Dietary vitamin D3 had no effect on weight gain. Plasma 25-hydroxyvitamin D3 levels were similar for the 1,000 and 2,000 IU/kg groups but varied in a dose-related manner for the other groups. Vitamin D did not significantly alter the tumor incidence in either the distal or the proximal colon. No significant differences in the labeling index were found in either the proximal or the distal colon. Within the distal colon, the proliferative zone increased in a dose-related manner. Distribution of labeled cells within the crypt compartments was not affected by dietary vitamin D. Bone and serum minerals in general were unaffected by dietary vitamin D. This study shows that, at this level of dietary calcium, vitamin D did not affect 1,2-dimethylhydrazine-induced colon carcinogenesis.

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.

Effects of fat and fiber on human colon cancer xenografted to athymic nude mice

The effects of unsaturated fat and fiber (cellulose) on the growth of human colon cancer explanted to athymic nude mice was evaluated. Eighty-seven male nude mice bearing xenografts of human HT29 or WiDr colon cancer were divided into three groups of equal weight and tumor volume. Each group was fed one of three diets: normal fat/no fiber (N/N), high fat/no fiber (H/N) or high fat/high fiber (H/H). To equalize caloric intake, animals in the H/N group received 4 g of food per day and the other animals were fed 5 g of food per day. At sacrifice tumor volume and weight was recorded, and tumors were analyzed for protein and DNA content and ornithine decarboxylase activity. Tumor volume, weight, and protein were greater in the H/N group compared to the N/N group for both colon cancer cell lines. Tumor DNA content was greater in the HT29 H/N group compared to the N/N group (P less than 0.05) and tumor ornithine decarboxylase activity in the WiDr H/N group was greater than the N/N animals (P less than 0.002). The tumor growth-promoting effects of the high unsaturated fat diet were attenuated by the addition of fiber. Animal weight was higher in the H/N group compared to the N/N and H/H groups. This study suggested that a high-fat diet stimulated and fiber decreased the growth of human colon cancer explanted to athymic nude mice. The growth-promoting effects of a high-fat diet in colorectal cancer may be due in part to a circulating trophic factor since these tumors were remote from the large intestine.

Alterations in lectin binding in the proximal and distal colon of Sprague-Dawley rats with 1,2 dimethylhydrazine administration

Sequential changes in rhodamine or fluorescein isothiocyanate-conjugated lectin binding of proximal and distal colonic crypts were studied during and after the administration of the 1,2 dimethylhydrazine (DMH). Five adult its unexposed to DMH or vehicle served as baseline controls. Tissue from normal appearing colon and tumor tissue was incubated with Ulex europaeus agglutinin 1 (UEA), Arachis hypogaea (PNA), Dolichos biflorus (DBA) and Griffonia simplicafolia 1 (GSA1). Distinct regional differences were noted in the baseline controls. UEA, PNA and DBA binding were absent in the distal colonic crypt cells. In the proximal colon minimal UEA and PNA binding was noted in the lower crypt whereas DBA binding was intense. GSA1 binding was diffuse in the upper and lower crypt of both regions. During carcinogenesis a progressive increase in PNA binding was noted in normal appearing colonic crypts from both regions. A progressive increase in PNA binding in proximal and distal colonic tumors was noted over time. Similar to normal tissue, DBA bound markedly to proximal colon tumors but was absent in most distal colonic tumors. UEA stained all proximal tumors intensely at all time points. In distal colonic tumors, UEA staining was diminished at 30 weeks compared to tumors analyzed at 16, 22 and 26 weeks. Mucin depletion was also a feature of tumor tissue compared to adjacent normal and hyperplastic glands. This study documents the region specific changes in lectin binding in normal and neoplastic colonic crypts induced by DMH.

Quantitative review of studies of dietary fat and rat colon carcinoma

A quantitative overview of 14 studies of rat colon carcinogenesis was undertaken to examine the relationship between fat intake, and fat intake by degree of saturation, on the incidence of colon carcinoma while controlling for calorie consumption. Calorie consumption was not recorded in 11 of the 14 studies. Hence, two types of analyses were conducted. The first examines carcinoma incidence as a function of percent fat (by weight), with calories controlled for by including weight gain per week in the analysis. The second estimates calories per day, for studies not providing such information, using weight gain per week and age at death, followed by a joint analysis of estimated fat calories and estimated total calories. With either approach, a rather strong positive relationship between colon carcinoma incidence and fat intake is indicated for Fischer 344 rats, but no association is apparent for Sprague-Dawley rats. This situation is somewhat clarified when the degree of saturation is taken into account: both strains gave results that suggest a negative relationship between colon cancer incidence and omega-3 fatty acids intake and a positive relationship with non-omega-3 polyunsaturated fat intake among Fischer 344 rats. These analyses suggest an important and specific role for dietary fat in the promotion of rat colon carcinoma.

Dose- and time-response of colon carcinogenesis in Fischer-344 rats after a single dose of 1,2-dimethylhydrazine

The purpose of this experiment was to examine the development of colon tumors after the injection of a single dose of 1,2-dimethylhydrazine (DMH) in rats. Male Fischer-344 rats were injected with 0, 10, 30, 100 or 200 mg/kg of DMH dihydrochloride. No tumors were seen after 3 or 5 months at any dose, but were seen after 7 or 9 months. At 9 months, tumors were induced in a dose-dependent manner, with 64.7% of rats receiving the 200 mg/kg dose developing tumors. This study shows that a high incidence of colon tumors can be induced by a single dose of DMH after a 9-month latency period.

The essential fatty acid requirement for azoxymethane-induced intestinal carcinogenesis in rats

The essential fatty acid requirement for the development of intestinal carcinogenesis was determined and compared to the overall essential fatty acid status of the animals as measured by the triene/tetraene ratio in the plasma, liver and colon. To induce tumors, male Sprague-Dawley rats were given two weekly injections (20 mg/kg body wt) of azoxymethane. Two weeks after the last injection, the rats were divided into groups of 25 and given one of six diets containing various levels of essential fatty acids (as linoleate). The diets contained 5% total fat and were prepared by mixing safflower oil (high essential fatty acids, beef fat (low essential fatty acids), and medium chain triglyceride oil (no essential fatty acids). One group of rats was fed a 20% beef fat diet. The range of essential fatty acids was from less than 0.03% to 1.28% (w/w). Twenty-six weeks after the first azoxymethane injection, the animals were killed and intestinal tumor incidence and multiplicity were determined. Samples of plasma, liver and colon were also taken for measurement of the triene/tetraene ratio by gas chromatography. Large bowel tumor incidence showed a dependence on the essential fatty acid content of the diet. The results were as follows: (percent essential fatty acids: percent tumor incidence) Group A (1.28: 72.4), Group B (0.60: 73.3), Group C (0.11: 55.2), Group D (0.08: 39.3), Group E (less than 0.03: 37.9) and Group F, which was fed 20% beef fat, (0.34: 88.5).(ABSTRACT TRUNCATED AT 250 WORDS)

A comparison of dietary fish oil and corn oil in experimental colorectal carcinogenesis

Rats fed either fish oil (n = 16) or corn oil (n = 16) in calorically and nutritionally balanced diets were injected with 1,2-dimethylhydrazine, which is a colorectal specific carcinogen; differential colorectal tumor induction was then measured. In addition, plasma peroxide concentrations were measured in rats in each dietary group as well as in a group receiving a low-fat diet, either with or without prior carcinogen treatment (n = 3 for each of the 6 groups). Tumor incidence did not differ between groups fed corn oil and fish oil. Tumor yield in the left colon was significantly lower in rats fed fish oil (p = 0.0499). Total colorectal tumors induced were also fewer in the rats fed fish oil (p = 0.065). Plasma peroxide concentrations were difficult to interpret because of the wide variation within groups. The data on tumor yield in the left colon support the hypothesis that a diet rich in n-3 fatty acids, which are found in fish oil, may be less supportive of colorectal tumor development than a diet rich in n-6 fatty acids, which is found in corn oil. However, the mechanism by which fish oil decreases tumor induction is still unknown.