Dietary n-3 PUFA increases the apoptotic response to 1,2-dimethylhydrazine, reduces mitosis and suppresses the induction of carcinogenesis in the rat colon

The effect of dietary fish oil on colonic crypt cell apoptosis and proliferation was examined in male Wistar rats, 24 and 48 h after administration of 1,2-dimethylhydrazine (DMH), and its influence on the induction of aberrant crypt foci (ACF) in the distal colon was assessed. Rats (125-150 g) fed a high-fat semi-synthetic diet containing corn oil (CO) were given DMH (30 mg/kg body wt) or a sham injection of EDTA/NaCl. Animals were then fed either the CO diet or a diet in which fish oil (EPA 18.7%; DHA 8%) was substituted for corn oil. Subgroups of rats (n = 5) were killed after 24 and 48 h, and crypt cell apoptosis and proliferation were quantified by morphological criteria in isolated intact crypts from the mid and distal colon. Consumption of the fish oil diet (FO) was associated with increased apoptotic cell death (P < 0.001) and suppression of proliferation (P < 0.05) in colonic crypts both 24 and 48 h after DMH. In a second experiment, animals were given three injections of DMH or sham injections of carrier at weekly intervals. For 48 h after each injection animals were fed either the CO or FO diet, but otherwise maintained on the CO throughout. The number and crypt multiplicity of ACF in the distal colon were determined after 18 weeks, and animals given the FO diet for the 48 h period following carcinogen administration were found to have significantly fewer ACF than rats fed the CO diet (P < 0.05). The data demonstrate that the fatty acid composition of the diet is an important determinant in the induction of carcinogenesis by DMH. The proliferative and apoptotic response of the colonic crypt to carcinogen and fish oil, coupled with the reduced incidence of ACF, suggest n-3 PUFA can protect against the carcinogenic effects of DMH by mediating changes in the balance proliferation and cell death.     

Chronic Trypanosoma cruzi infection associated with low incidence of 1,2-dimethylhydrazine-induced colon cancer in rats

Experimental data have demonstrated that chronic infection with intracellular parasites may enhance resistance against some types of tumour. This phenomenon has not yet been demonstrated for experimental Trypanosoma cruzi chronic infection. This study investigated the effect of a specific colon cancer inducing drug, 1,2-dimethylhydrazine (DMH), on chronically T.cruzi infected Wistar rats. Infection was obtained by inoculation of 10(5) tripomastigote forms by subcutaneous (s.c.) route. Acute phase of the infection was monitored every other day by examination of a blood smear from each animal until negativation. In the early chronic phase of the infection, colon adenocarcinoma was induced by weekly s.c. injections of DMH at a dose of 20 mg/kg body weight for 12 weeks. 102 animals were divided in four test groups: 39 infected rats received DMH (group 1); 32 non-infected rats received DMH (group 2); 16 infected rats and 15 non-infected animals were used as control groups. Animals were killed 6 months after the first dose of DMH. The whole colon was removed and prepared for light microscopic examination. Twelve animals from group 1 and 22 from group 2 had colon adenocarcinomas, the proportion of cancer being 30.7 and 68.7%, respectively (chi(2) = 10.16; P < 0.05). The relative risk of having a colon tumor in infected animals (group 1) was 0.45 (IC 95% 0.26-0.76), which is a protective risk compared with non-infected animals. These findings show that chronic infection with T.cruzi is associated with a lower incidence of DMH-induced colon cancer in rats.     

Long term administration of granulocyte-macrophage colony stimulating factor decreases development of 1-2 dimethylhydrazine-induced colon cancer in rats

BACKGROUND AND OBJECTIVES: The antitumoral activities of granulocyte-macrophage colony stimulating factor (GM-CSF) were shown earlier. In this study, the effects of GM-CSF were investigated on colon cancer induced by 18 weeks of 1-2 dimethylhydrazine (DMH) administration in rats. METHODS: Four groups received subcutaneous saline (n = 20), 15 mg/kg DMH (n = 30), DMH +6 microg/kg GM-CSF (n = 30), and DMH +12 microg/kg (n = 30) GM-CSF. RESULTS: The average number of tumors (2.8 vs. 1.5) and mean tumor volume (179 +/- 36 vs. 27 +/- 9 mm(3); means +/- SEM) were reduced in DMH + GM-CSF groups as compared to the DMH group (n = 30, P < 0.01). DMH-induced enhancement of free radicals and lipid peroxidation were decreased in DMH + GM-CSF group (n = 8-12, P < 0.05). The magnitude of DMH-induced alterations in superoxide dismutase (SOD) and glutathione peroxidase (GPx) activities was lowered in the DMH + GM-CSF group (n = 12-16, P < 0.05). DMH-induced increases in the total nitrite/nitrate levels and the nitric oxide synthase (NOS) activity (n = 10-12, P < 0.05) were also reduced in the DMH + GM-CSF group (n = 8-9, P < 0.05). CONCLUSIONS: The results indicate that GM-CSF inhibits the development of DMH-induced colon cancer in rats and suggest that inhibition of oxidative stress and NO pathway are involved in the observed antitumoral effects.     

The effects of cholic acid and bile salt binding agents on 1,2-dimethylhydrazine-induced colon carcinogenesis in the rat

The theory that bile salts may be colon tumour promoters wastested in the dimethylhydrazine (DMH)-induced rat colon cancermodel. Fifty Wistar rats were randomly allocated to one of fiveexperimental groups (n = 10), all fed the same standard diet.One group served as saline-injected controls, while the otherfour groups received DMH (20 mg/kg body weight/rat/week s.c.)for 20 weeks. In addition, each of the DMH-injected groups concurrentlyreceived 20 weekly i.g. instillations of one of the following:cholic acid (a bile acid); cholestyramine or aluminium hydroxide(both bile acid binding agents), or water. After a years observationperiod, all the controls were alive and tumour-free, while allthe DMH-injected rats had died of histologically proven coloncancer. Irrespective of the type of gastric instillate, therewere no significant differences between the groups in termsof time to tumour presentation, survival, in the necropsy incidenceof primary or metastatic colon cancer, or in the numbers ofcolon tumours per group. The data suggest that bile salts andbile salt binding agents are not colon tumour promoters in therat. The bile salt theory of colon carcinogenesis may need reappraisal.     

Experimental colon carcinogenesis is facilitated by endogenous factors in the intestinal contents

The theory that endogenous factors in the intestinal contentsmay be pathogenic during large bowel carcinogenesis was testedin the dimethylhydrazine (DMH)-induced rat colon cancer model.Thirty female Wistar rats, each serving as their own control,had a surgical transection of the proximal colon with reanastomosisto the rectum, thereby excluding part of the colon from faecalcontact. All rats then received a course of DMH (40 mg/kg bodywt/wk s.c. for 10 weeks) while fed on Vivonex. This diet wasselected because it lacks known exogenous (dietary) cocarcinogens.It also produces mucosal atrophy in functioning (proximal) colon,to parallel the disuse atrophy induced in the defunctioned (distal)colon. Animals remained on the diet throughout the experimentand were killed when moribund or at 40 weeks. At necropsy, theanatomical distribution, number, size and histological typeof colon tumours were compared between functioning and defunctionedcolonic segments within the same animal. At autopsy, there weresignificantly fewer colon tumours in the defunctioned segment(P < 0.005). Furthermore, there were significantly fewercarcinomas (P <0.005) and fewer tumours >1 cm diameter(P <0.01) in this segment. The data indicate that endogenousfactors in the intestinal contents facilitate chemically-inducedcolon carcinogenesis. Luminal nutrition may be implicated.     

Dietary calcium and vitamin D modulate 1,2-dimethylhydrazine-induced colonic carcinogenesis in the rat

To determine whether supplemental dietary calcium and/or vitamin D deficiency are involved in modulating colon cancer induced by 1,2-dimethylhydrazine (DMH), Sprague-Dawley rats were fed diets containing either: (a) a normal content of calcium (0.87%) and phosphorus (0.60%) with 2.2 IU of vitamin D3 per g of feed (group A); (b) the same diet as group A, but with calcium and phosphorus increased to 1.80 and 0.80%, respectively (group B); or (c) a vitamin D-deficient diet with supplemental calcium (1.80%) and phosphorus (0.80%) (group C). After 6 weeks on their respective diets, one-half the animals in each group were given s.c. injections of either vehicle or DMH (20 mg/kg body weight/week) for 26 weeks. Animals were then sacrificed and the incidence of tumors as well as the number of tumors per tumor-bearing rat were determined. Colonic mucosal polyamine levels were measured after 15 weeks of exposure to vehicle or DMH, before development of histologically recognizable neoplasms. The results of these experiments demonstrated that neither calcium supplementation alone nor supplemental calcium in conjunction with vitamin D deficiency altered the incidence of colonic cancer induced by this carcinogen. Supplemental calcium, however, significantly decreased the number of rats with multiple tumors and reduced tumor size. Moreover, vitamin D deficiency abolished these protective effects of calcium on colon cancer in this experimental model. DMH treatment increased polyamine levels in the premalignant colonic mucosa in group A rats. This carcinogen-induced effect was blunted by high dietary calcium. Vitamin D-deficient, calcium-supplemented rats (group C) showed an increase in N1-acetylspermidine, but not the other polyamines, with DMH treatment.     

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.     

Effect of dioctyl sodium sulfosuccinate feeding on rat colorectal 1,2-dimethylhydrazine carcinogenesis

The 1,2-dimethylhydrazine (DMH) rodent model for colorectal carcinogenesis was used to explore the effect of dietary dioctyl sodium sulfosuccinate (DSS) on carcinogenesis. Inbred male F344 rats were divided into two groups of 84 each and fed the following diets: ground chow and 5% corn oil (control group) and ground chow, 5% corn oil, and 1% DSS (experimental group). All rats received high-dose DMH base, 20 mg/kg/week sc for 20 weeks. Twenty rats per group were killed after 3, 4, 5, and 6 months. Duodenum, small intestine, colon, and rectum were dissected out. Each tumor was measured for size and location and evaluated histologically. The percentage of rats bearing tumors in the control and experimental groups did not differ significantly. In each rat there were fewer gastrointestinal tumors in the DSS-fed group of all histologic types combined, at all organ sites, at 5 and 6 months. This difference between the control and DSS-fed rats reached the level of statistical significance for tumors of the duodenum, colon, and rectum and for total gastrointestinal tumors at the 5th month.     

Correlation of neomycin, faecal neutral and acid sterols with colon carcinogenesis in rats.

High fat diets have been implicated in incidence of colon cancer both in epidemiological and animal studies. Present investigation deals with the incidence, location and numbers of large and small bowel tumours induced by 1,2-dimethyl hydrazine (DMH) in rats fed high fat diets and neomycin. Neomycin was used to modify the faecal sterol metabolism and the relationship of the high fat diet and faecal neutral and acid sterols to the large bowel tumorigenesis was evaluated. DMH administered rats were fed with (a) 20% safflower oil; (b) 20% safflower oil and neomycin; (c) 20% safflower oil, cholesterol and cholic acid; and (d) 20% safflower oil, cholesterol, cholic acid and neomycin. Neomycin was found to be associated with both increase and decrease of tumour numbers. The faecal sterols lithocholic and deoxycholic acids were found to have no participation, while cholesterol and cholic acid were found to decrease with increase in tumour numbers. However, faecal coprostanol has been found to have a significant positive correlation with tumorigenesis in all dietary groups. Therefore coprostanol might possibly be associated with colon carcinogenesis in DMH-fed rats and cholesterol metabolism in gut appears to be related to the development of tumours.     

Chemopreventive Effect of Amorphophallus campanulatus (Roxb.) Blume Tuber Against Aberrant Crypt Foci and Cell Proliferation in 1, 2-Dimethylhydrazine Induced Colon Carcinogenesis

Colorectal cancer is one of the leading causes of cancer death, both in men and women. This study investigatedthe effects of Amorphophallus campanulatus tuber methanolic extract (ACME) on aberrant crypt foci (ACF)formation, colonic cell proliferation, lipid peroxidative damage and the antioxidant status in a long term preclinicalmodel of 1, 2-dimethylhydrazine (DMH) induced colon carcinogenesis in rats. Male Wistar rats were dividedinto six groups, viz., group I rats served as controls; group II rats treated as drug controls receiving 250 mg/kg body weight of ACME orally; group III rats received DMH (20 mg/kg body weight) subcutaneously once aweek for the first 15 weeks; groups IV, V and VI rats received ACME along with DMH during the initiation,post- initiation stages and the entire period of the study, respectively. All the rats were sacrificed at the end of 30weeks and the intestinal and colonic tissues from different groups were subjected to biochemical and histologicalstudies. Administration of DMH resulted in significant (p≤0.05) intestinal and colonic lipid peroxidation (MDA)and reduction of antioxidants such as catalase, glutathione peroxidase, glutathione reductase, glutathione-Stransferaseand reduced glutathione. Whereas the supplementation of ACME significantly (p≤0.05) improvedthe intestinal and colonic MDA and reduced glutathione levels and the activities of antioxidant enzymes inDMH intoxicated rats. ACME administration also significantly suppressed the formation and multiplicity ofACF. In addition, the DMH administered rats showed amplified expression of PCNA in the colon and decreasedexpression of this proliferative marker was clearly noted with initiation, post-initiation and entire period ofACME treatment regimens. These results indicate that ACME could exert a significant chemopreventive effecton colon carcinogenesis induced by DMH.     

Presence of well‐differentiated distal,but not poorly differentiated proximal,rat colon carcinomas is correlated with increased cell proliferation in and lengthening of colon crypts

To determine whether colon crypt proliferative parameters were significantly altered by the stage of colon carcinogenesis or the type or location of colon tumors in rats, male Sprague‐Dawley rats received an injection of the carcinogen 1,2‐dimethylhydrazine (12 mg DMH base/kg body weight) or DMH vehicle once a week for 8 weeks, then were killed 24 weeks later. Three hours before sacrifice, rats were injected with 1 mg/kg body weight colchicine to arrest mitotic cells at metaphase. Transverse sections of the colon mucosa were taken 6 cm from the anus and at least 3 cm from any tumor, fixed in formalin, then stained with hematoxylin & eosin (H&E) for analyses of proliferative parameters. Only complete, mid‐axial crypts were scored for mitotic count (MC), crypt proliferative zone (PZ) height and crypt height (CH). Serial tumor sections were stained with H&E for histological evaluation or used in immunohistochemical detection of transforming growth factor α (TGFα). DMH treatment significantly increased MC, PZ and CH regardless of tumor status. The PZ and CH of rats with a carcinoma located in the distal colon were significantly increased compared with DMH‐treated rats without an adenocarcinoma (AC) or with rats which had a tumor located in the proximal colon. Distal colon ACs were found to be well differentiated and to have greater TGFα immunoreactivity than the generally less differentiated proximal colon carcinomas. Distal colon AC production and systemic circulation of a soluble colon crypt stimulating factor such as TGFα may explain the significant increase in PZ and CH in histologically normal colonic mucosa located away from the tumor. Int. J. Cancer 80:68–71, 1999. © 1999 Wiley‐Liss, Inc.     

Promotion of colon carcinogenesis through increasing lipid peroxidation induced in rats by a high cholesterol diet

To examine the influence of hypercholesteremia on 1,2-dimethylhydrazine (DMH)-induced rat colon cancer, Sprague-Dawley rats received dietary cholesterol (CH, 0–2%) and cholic acid (CA, 0.25%) with or without DMH (20 mg/kg, s.c. injection) for 18 weeks. The rats receiving dietary cholesterol and cholic acid all significantly increased total serum cholesterol and lipids but only a high cholesterol diet (2% CH plus 0.25% CA) decreased the activity of glutathione peroxidase (GSH-Px) and increased the formation of peroxides in the colon (P < 0.01). The rats that received the combination of DMH and high cholesterol diet enhanced these effects. At the end of the experiment, the diet group administered DMH and high cholesterol (2% CH plus 0.25% CA) developed colon adenoma at 50% of incidence in pathological examination, but no colon adenoma formed in the rats treated with high cholesterol alone. It is supposed that a non-carcinogenic agent like cholesterol may potentiate the carcinogenicity of DMH in rats via an increase of lipid peroxidation and decrease in the activity of peroxidase in the target organ.     

Dietary supplementation with pectin and guar gum on 1,2-dimethylhydrazine-induced colon carcinogenesis in rats.

The effect of dietary supplementation with pectin and/or guar gum on 1,2-dimethylhydrazine (DMH)-induced colon carcinogenesis was studied using 120 male Sprague-Dawley rats. The rats were given a weekly injection of DMH for 8 weeks and were maintained on a basal fiber-free diet supplemented with 5% cellulose. The rats were then subdivided into four groups and kept on the basal fiber-free diet supplemented with either no fiber, 10% pectin, 10% guar gum or a combination of 5% pectin/5% guar gum for a period of 24 weeks. The 8 weeks of DMH administration were defined as the initiation stage of carcinogenesis and the next 24 weeks were defined as the promotional stage of carcinogenesis. Food and water were available ad libitum. The rats were killed 32 weeks after the start of the experiment and tumor incidence, location and frequency in the colon were determined. Other parameters measured were body weight and caloric intake. Dietary fiber supplementation with 10% pectin or with 10% guar gum but not with the combination of 5% pectin/5% guar gum (fed during the promotional stage of carcinogenesis), was found to suppress colon cancer incidence to a significant extent.     

Distribution of preneoplastic lesions and tumors, and beta-catenin gene mutations in colon carcinomas induced by 1,2-dimethylhydrazine plus dextran sulfate sodium

Mucin-depleted foci (MDF) are considered as useful biomarkers in rat colon carcinogenesis. The purpose of the present study was to examine the mechanism(s) underlying rat colon carcinogenesis induced by 1,2-dimethylhydrazine (DMH) plus 1% Dextran Sulfate Sodium (DSS). Twelve male F344 rats were given subcutaneous injections (40mg/kg body) of DMH twice a week. They received DSS in the drinking water for 1 week after the first injection of DMH and then were maintained on tap water. The rats were sacrificed at 10 and 14 weeks after the first injection of DMH. Colon tissues were divided into 10 segments from anus to cecum (A/J) and stained with Alcian blue (AB) to identify MDF. We found that MDF and tumors were induced in the rat colon after treatment with DMH plus DSS and that the number of MDF in each segment of the colon was significantly correlated with that of tumors (p=0.006). In addition, we found that the beta-catenin protein was accumulated in cytoplasm and nuclei of MDF and the frequent beta-catenin gene mutations in the colon tumors. These results suggest that MDF is closely related to rat colon carcinogenesis induced by DMH plus DSS.     

Anti-proliferative and Apoptotic Effects of Basella rubra (L.) Against 1, 2-Dimethyl Hydrazine-induced Colon Carcinogenesis in Rats

Colorectal cancer is a very prevalent diagnosed cancer. The current study was performed in order to examine the role of BRAE (Basella rubra aqueous extract) in regulating aberrant crypt foci (ACF) formation, cell proliferation and inhibition of apoptosis in a colon carcinogenesis model in male Wistar rats. Rats were randomly allocated into six groups. Group I served as control, and group II acted as a drug control administered BRAE (250mg/kg b.w.) orally for 30 weeks. Rats in group III-VI were given subcutaneous injections of DMH (25mg/kg b.w. weekly) for 15 weeks to initiate colon carcinogenesis. Those in group IV and VI were administered BRAE along with DMH injections. Rats in group V were administered with BRAE after cessation of DMH injection. After 30 weeks of experimental period colons were obtained from experimental groups and analyzed for ACF incidence, argyrophilic nucleolar organizing region- associated proteins (AgNOR) count, histopathological and immunohistochemical changes. Only in DMH exposed groups were ACF and AgNOR numbers increased. Administration of BRAE appreciably decreased the numbers of ACF and AgNOR in BRAE treated groups. Histopathological findings revealed a high level of dysplastic changes with decreased number of goblet cells found only in only DMH injected rats. Administration of BRAE in treated group rats reversed these changes. Expression markers for cell proliferation (PCNA and Ki67) were elevated in DMH treated rats, but reduced with BRAE treatement. This expression was reversed with apoptosis markers (p53 and Caspase-3). Thus the results results of the present study were found to be significant and confirmed the potential efficacy of BRAE against colon carcinogenesis.     

The tumor-preventing effect of a mixture of several lactic acid bacteria on 1,2-dimethylhydrazine-induced colon carcinogenesis in mice

The anti-tumor effect of a dietary supplement obtained from mixed cultures of several lactic acid bacteria was examined in the colon of tumor-inducing ICR male mice by use of a carcinogen, 1,2-dimethylhydrazine (DMH, 20 mg/kg body weight, 1 intra-muscular injection per week for 10 weeks). The animals were sacrificed either 15 weeks or 24-26 weeks after the first carcinogen injection. Macroscopically, the incidence of colon tumors at a 24-26 week period of tumor induction was apparently lower in mice treated with both the DMH and dietary supplement (76%) than in those treated with DMH alone (100%). Histologically, microadenomas were induced predominantly in the anal half of the total colon, and large lymphoid aggregates were often associated with dysplastic crypts in the distal colon. Apoptotic cell masses were shed into the distended lumen of the involved crypts. The statistical analysis at a 15-week period of tumor induction indicated that the incidence of microadenomas per tumor-induced mouse was lowered significantly by use of the dietary supplement. From the present results, it is suggested that the intake of the dietary supplement inhibits the early development of colon adenomas, and the inhibition of microadenomas results in a reduction of subsequent polyp and tumor yield in the mouse colon.     

Melatonin and colon carcinogenesis: I. Inhibitory effect of melatonin on development of intestinal tumors induced by 1,2-dimethylhydrazine in rats

The effect of pineal indole hormone melatonin on colon carcinogenesis was firstly studied in rats. Two-month-old outbred female LIO rats were weekly exposed to 15 (experiment 1, groups 1 and 2) or to five (experiment 2, groups 1 and 2) s.c. injections of 1,2-dimethylhydrazine (DMH) at a single dose of 21 mg/kg of body weight. From the day of the first injection of the carcinogen DMH, the rats from groups 2 (experiments 1 and 2) were given melatonin five days a week during the night-time (from 18:00 h to 8:00 h), dissolved in tap water at 20 mg/l. The experiment was finalized in 6 months after the first injection of DMH. In both experiments the majority of tumors were localized in the descending colon. Tumors of the small intestines developed only in rats from experiment 1. Total incidence of colon tumors as well as tumors in different parts of the colon and the mean number of tumors per rat were much higher in rats from both groups in experiment 1 than that in rats from experiment 2. In experiment 1 melatonin failed to influence the total incidence of colon tumors. However, incidence of carcinomas in the ascending colon was significantly reduced (P < 0.01). The multiplicity of total colon tumors per rat, as well as the mean number of tumors, ascending and descending colon per rat, was also decreased under the influence of melatonin (group 2 vs group 1, P < 0.01). In the same experiment, melatonin slightly decreased the depth of tumor invasion and increased number of highly differentiated colon carcinomas induced by DMH. The percentage of small tumours in the descending colon among rats from group 2 was higher than that of group 1. Treatment with melatonin was also followed by a decrease in the multiplicity of DMH- induced tumors of the duodenum (group 2 vs group 1, P < 0.05) and by a decrease in the incidence of jejunum and ileum tumors (group 2 vs group 1, P < 0.05). In experiment 2, the inhibitory effect of melatonin on DMH-induced colon carcinogenesis was much more expressed than that in experiment 1. Thus, in group 1 the incidence of total colon tumors, ascending and descending colon tumors, was significantly decreased in comparison with group 2; also melatonin reduced the number of tumors per rat in the ascending and descending colon. The number of colon tumors that invaded only mucosa was significantly higher in group 2 than in group 1, P < 0.05. The ratio of highly differentiated tumors was increased (P < 0.05) and the ratio of low-differentiated tumors was decreased (P < 0.05) in rats exposed to melatonin (group 4) as compared with group 3. The number of large size tumors in the ascending and descending colon was decreased whereas the number of small size tumors (<10 mm2) was increased in those parts of the colon that were under the influence of melatonin in experiment 2. Thus, our results demonstrate the inhibitory effect of melatonin on intestinal carcinogenesis induced by DMH in rats.      

Selenium and difluoromethylornithine additively inhibit DMH-induced distal colon tumor formation in rats fed a fiber-free diet

We investigated the effects of difluoromethylornithine, an inhibitorof ornithine decarboxylase (ODC) and selenium supplementationon tumor formation induced by the carcinogen 1, 2-dimethylhydrazine(DMH) in Sprague-Dawley rats. A biochemical link between polyaminebiosynthesis and selenium metabolism to its cancer preventativeform has been suggested by the common requirement of S-adenosylmethio-nine.One-hundred and twenty male Sprague-Dawley rats were dividedinto experimental (n = 80) and control (n = 40) groups. Experimentalanimals received DMH 20 mg/kg s.c. for 20 weeks. Animals werefed either a regular diet (selenium content 0.2 p.p.m.) or ahigh selenium diet (5 p.p.m.) with or without 0.2% DFMO in thedrinking water. At death, week 30, animal weights within experimentalor control groups were not different between the four diet treatmentgroups. Tumor number and incidence in the proximal colon wasnot affected by DFMO treatment, selenium supplementation orthe combined treatment. In contrast, in the distal colon, 19tumors developed in the DFMO treated group, 22 tumors in thehigh selenium group and only 12 tumors in the combined highselenium/DFMO treatment group compared to 32 tumors in the regulardiet group. Similarly, tumor incidence was decreased by DFMOand selenium supplementation and their effects were additive.In control animals, ODC activity was decreased by DFMO treatmentand selenium supplementation in the distal colon and liver,but not the proximal colon. ODC activity of tumor tissue wasgreater than normal colon tissue from diet paired animals forproximal and distal colon, except for distal colonic tumorsin the high selenium/DFMO treatment group. Polyamine content,however, did not correlate with ODC activity in normal or neoplastictissue. In general, S-adenosylmethionine levels from normalcolon and liver tissue were unaffected by diet treatment. Seleniumsupplementation in combination with DFMO treatment selectivelyinhibited distal colon tumor formation in rats fed a fiber-freediet.     

Chemopreventive effect of trans-resveratrol--a phytoalexin against colonic aberrant crypt foci and cell proliferation in 1,2-dimethylhydrazine induced colon carcinogenesis

Prevention of cancer remains a primary need and new chemopreventive agents must be developed for this purpose. Towards this goal, a chemoprevention study was conducted to evaluate the activity of resveratrol (Res), a phytoalexin, as an inhibitor of colon carcinogenesis. Wistar male rats were divided into six groups, group 1 were control rats, group 2 were control rats that received Res (8 mg/kg body wt p.o. everyday), rats in groups 3-6 were treated weekly with 1,2-dimethylhydrazine (DMH, 20 mg/kg body wt, s.c. x 15 times). In addition, groups 4, 5 and 6 received Res as in group 2. Modifying effects were assessed using aberrant crypt foci (ACF) and the extent of histopathological lesions as end point markers. At the end of 30 weeks, Res markedly reduced tumor incidence, the degree of histological lesions and also the size of tumors significantly (P < 0.05) as compared with the rats treated with unsupplemented DMH. The number of ACF consisting of more than six aberrant crypts per rat was observed in group 6 (6.2 +/- 1.4), group 5 (7.7 +/- 1.0) and group 4 (8.2 +/- 1.4) which were significantly lower than that of group 3 (22.3 +/- 2.4) (P < 0.05). The most pronounced inhibition of ACF development was noted in rats fed Res for the entire period and also during the post-initiation period. Also, Res administration lowered the number of argyrophilic nucleolar organizing region-associated proteins (AgNORs) per nucleus in non-lesional colonic crypts, which reflects the cell proliferation activity. Oxidative imbalance in DMH-treatment was significantly (P < 0.01) modulated on Res supplementation as indicated by optimal concentration of thiobarbituric acid reactive substances (TBARS), superoxide dismutase (SOD), catalase (CAT) and reduced glutathione (GSH). The results of our study suggest Res to be an effective chemopreventive agent, which suppresses DMH-induced colon carcinogenesis at various stages.     

Qualitative and quantitative changes in sialomucins during 1,2-dimethylhydrazine-induced colon carcinogenesis in the rat

Regional differences in goblet cell glycoproteins have been demonstrated qualitatively and, to a limited extent, quantitatively in the normal adult colon. In disease states, alterations in these glycoproteins, particularly the sialoglycoproteins (SGs), have been reported. The present study defined parallel qualitative and quantitative changes in SGs in three colon regions during 1,2-dimethylhydrazine [(DMH) CAS: 540-73-8]-induced carcinogenesis. SGs were assessed histochemically by use of high iron diamine-Alcian blue (pH 2.5) staining, and tissue sialic acid levels were measured by a modified Warren assay. Two groups of inbred SD rats (n = 28) were pair-fed nutritionally complete liquid diets with 36% of calories supplied as ethanol or isocaloric carbohydrates. The dietary alcohol was added to selectively enhance rectal tumors, a region of prevalent tumors in humans. Both groups received 4 weeks of liquid diet followed by 4 weeks of standard laboratory chow with weekly sc injections of DMH. This 8-week cycle was repeated four times (32 wk). Animals from each group were sacrificed at 8, 16, 24, and 32 weeks, and adjacent tissues from proximal and distal colon and rectum were prepared for histology and biochemical assay. The results showed a progressive increase in sialomucin staining in normal-appearing mucosa in distal colon and rectum in both groups but not in the proximal colon. In contrast, tissue sialic acid increased in all three regions as early as 8 weeks, and significant increases were consistently present by 32 weeks. A different pattern was observed in tissue from frank tumors. Compared with normal-appearing mucosa, both sialomucin staining and tissue sialic acid levels were reduced in tumor tissue by 32 weeks. These studies indicated that tissue sialic acid levels may provide a simple and reliable screening technique in the early diagnosis of premalignant change in all regions of the colon.