The effect of endotoxin on 1,2-dimethylhydrazine-induced colonic tumors in rats

The effect of endotoxin on colon tumors was studied in male Sprague-Dawley rats. Colon tumors were induced in weanling rats by the administration of 20 weekly subcutaneous injections of 1,2-dimethylhydrazine (DMH). When colon tumors were detected by colonoscopy in 80% of the rats around week 24 after DMH injection, the animals were divided randomly into two groups. One group served as the control. The other group received six endotoxin (Escherichia coli) treatments every fifth day. The first dose was 50 micrograms/100 g (intraperitoneally); the remaining doses were 100 micrograms/100 g (subcutaneously). Rats were killed 2 weeks after the last endotoxin injection. Endotoxin treatments resulted in larger colon tumors. The median tumor size was 71 mm2 for endotoxin-treated and 31 mm2 for untreated rats (P less than 0.02). Endotoxin treatments also resulted in a significantly higher incidence (P less than 0.05) of ulcer development in the small intestine, that is 47% in the endotoxin-treated versus 23% in the untreated rats. After a single subcutaneous injection of endotoxin (100 micrograms/100 g), the colon mucosal reduced glutathione (GSH) level was raised by 21% at 16 hours, reached a peak on day 2, then decreased to baseline by day 4. The increased GSH level in the colon mucosa was maintained up to the third endotoxin injection. By the fifth injection, no increase in the GSH level was observed. These results suggest that the growth of colon tumors in rats induced by DMH could be enhanced by endotoxin treatments. The enhanced tumor growth may be due to an increase in the colon GSH level and/or other mediators released by macrophages as a result of endotoxin treatments.     

Calcium inhibits colon carcinogenesis in an experimental model in the rat

Different dietary factors can affect colorectal cancer incidence. However, the effect of increased levels of dietary calcium on neoplasms is unclear. The present study was designed to examine the effect of a low calcium supplement on experimental colon carcinogenesis induced by parenteral administration of dimethylhydrazine (DMH). One hundred and twenty 10-week-old Sprague-Dawley rats were divided into five groups of equal sex distribution. The 10 rats in group A (control group) received no treatment; the 30 rats in group B (DMH group) were injected subcutaneously with 18 weekly doses of 21 mg/kg DMH; the 20 rats in group C (EDTA control group) received EDTA solution only; the 30 rats in group D (calcium group) received calcium at 3.2 g/l by adding calcium lactate to the drinking water from the start until the conclusion of the experiment; and the 30 rats in group E (DMH + calcium group) received oral calcium supplements at the same dose as the rats in group D (calcium group) and the same DMH injections as the rats in group B (DMH group). The rats were sacrificed at 25-34 weeks. In group E, we observed a significant diminution in the number of tumours (P = 0.01); an increase in the number of tumour-free animals (P = 0.006); a change in tumour location towards the distal colon (P < 0.025); more adenomas (P = 0.02); and a diminution of adenocarcinomas and mucinous carcinomas, although this was not significant. We conclude that a low dietary calcium supplement in rats inhibits colon cancer carcinogenesis induced by DMH, and changes tumour location towards the distal colon.     

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.     

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.     

Inhibitory effect of synthetic interferon inductor Cycloferone on 1,2-dimethylhydrazine-induced colon carcinogenesis in rats

The effect of a synthetic interferon inductor Cycloferone on colon carcinogenesis was firstly studied in rats. Seventy-five 2-month-old outbred female LIO rats were subdivided into three groups and were weekly exposed to 15 s.c. injections of 1,2-dimethylhydrazine (DMH) at a single dose of 7 mg/kg body wt. From the day of the fist injection of DMH rats from group 2 were given weekly i.p. injections of Cycloferone (62.5 mg/kg) until the end of the experiment. DMH-treated rats (group 3) were exposed to weekly i.p. injections of Cycloferone (62.5 mg/kg) starting in the week after the last injection of the carcinogen. Rats from group 1 were exposed to DMH and treated weekly with 0.2 ml i.p. of normal saline. Additional groups of rats were treated weekly with Cycloferone (62.5 mg/kg) or with 0.2 ml of saline. The experiment was ended 6 months after the first injection of DMH. In DMH-treated rats (groups 1, 2 and 3) colon adenocarcinomas developed in 87, 61 and 59%, respectively. The number of colon tumors per tumor-bearing rat was 2.5, 1.9 and 1.3 in groups 1, 2 and 3, respectively. Treatment with Cycloferone significantly inhibits carcinogenesis in ascending and descending colon. The incidence of tumors of the rectum was decreased in the group 2 as compared with the group 1. There were no cases of tumors of rectum in rats from group 3. The treatment with Cycloferone alone as well as with normal saline failed to induce any tumors in rats. Thus, our results demonstrated inhibitory effect of Cycloferone on colon carcinogenesis induced by DMH in rats.     

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.     

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.     

Modification by five antioxidants of 1,2-dimethylhydrazine-initiated colon carcinogenesis in F344 rats

The effects of antioxidants given in the post initiation phaseof colon tumor development were investigated in male F344 ratstreated with 1 ,2-dimethylhydrazine (DMH). Animals (20/group)were given s.c. injections of DMH at a dose of 20 mg/kg oncea week for four consecutive weeks. One week after the last injection,rats were fed diet containing 5% sodium L-asorbate (SA), 0.5%butylated hydroxyanisole (BHA), 0.8% ethoxyquin (EQ), 1.0% propylgallate or 0.5% butylated hydroxytoluene (BHT) for 36 weeks.A control group was fed the basal diet not containing antioxidants.The experiment was terminated 40 weeks after the first injectionof DMH and all intestinal tumors were confirmed histologically.SA significantly increased the incidence of adenomas and thenumber of tumors per rat of the colon (especially of the distalcolon). Although EQ and BHT did not affect the number of ratswith colon tumors, the number of tumors per rat occurring inthe distal colon was significantly increased by EQ while beingdecreased by BHT. No modification of tumor development was observedwith BHA or PG. Thus, modification of tumor development by SA,EQ and BHT was apparent, mainly in the distal colon.     

The effects of chronic ethanol administration on polyamine content during dimethylhydrazine-induced colorectal carcinogenesis in the rat

Chronic ethanol (EtOH) consumption has been implicated as aco-carcinogen, selectively promoting rectal tumor formation.We studied the effects of EtOH consumption on tumor formationand polyamine content (putrescine, spermidine and spermine)in proximal and distal colon and rectum of Sprague-Dawley ratstreated with the procarcinogen 1,2-dimethylhydrazine (DMH).Sixty-four adult male rats were pair fed nutritionally completeliquid diets with 36% of calories supplied as EtOH or isocaloriccarbohydrates. Both groups received 4 weeks of the liquid dietfollowed by 4 weeks of standard laboratory chow during which50% of the rats in each group received DMH (30 mg/kg) or vehicles.c. weekly. This cycle was repeated four times (32 weeks).Animals were sacrificed at the end of each 8 week cycle andnormal appearing and available tumor bearing tissue from proximaland distal colon and rectum was obtained for polyamine contentand histology. Five animals, unexposed to DMH or EtOH servedas baseline controls. There were no consistent regional differencesin putrescine, spermidine or spermine of baseline controls.A progressive decrease in tissue putrescine was seen in allthree regions of the control group and was significant at 24and 32 weeks versus baseline controls. In all three regions,chronic EtOH consumption prevented the decrease in tissue putrescine.Spermidine content was also significantly increased in the distalcolon of EtOH-treated animals compared to baseline values. Consistentchanges in spermine content were seen in any treatment groupor region. A significant increase in putrescine content of normalappearing and tumor-bearing tissue of DMH treated animals at32 weeks was noted. Chronic EtOH administration did not augmentrectal or colonic polyamine content in DMH-treated animals.Likewise, chronic EtOH consumption did not alter the number,size or distribution of large bowel tumors of DMH treated animals.     

Inhibitory effect of peptide Epitalon on colon carcinogenesis induced by 1,2-dimethylhydrazine in rats

The effect of synthetic pineal peptide Epitalon (Ala-Glu-Asp-Gly) on colon carcinogenesis was firstly studied in rats. Eighty 2-month-old outbred male LIO rats were subdivided into four groups and were weekly exposed to five subcutaneous injections of 1,2-dimethylhydrazine (DMH) at a single dose of 21 mg/kg body weight. Additionally, 5 days a week, some of the rats were given subcutaneous injections of saline at a dose of 0.1 ml during the whole experiment (group 1, control) or Epitalon at a single dose of 1 microg during the whole experiment (group 2), Epitalon after termination of carcinogen injections (group 3) or during the period of DMH exposure (group 4). Colon carcinomas developed in 90-100% of DMH-treated rats. The number of total colon tumors per rat was 4.1; 2.7; 3.7; 2.9 in groups 1, 2, 3, 4, respectively (the difference in groups 2 and 4 compared with group 1 is significant). In rats from group 2, colon tumors were smaller than in control animals. In group 2, the incidence, as well the multiplicity of tumors in ascending and descending colon, were significantly decreased in comparison with group 1. In group 4, the mean number of tumors per rat was significantly decreased, too. A trend to decrease the number of tumors in the rectum in rats from groups 2, 3 and 4, treated with Epitalon was found. Epitalon inhibited also the development of tumors in jejunum and ileum. Thus, our results demonstrated an inhibitory effect of Epitalon on chemically induced bowel carcinogenesis in rats.     

Post-initiation effects of chlorophyllin and indole-3-carbinol in rats given 1,2-dimethylhydrazine or 2-amino-3-methyl- imidazo

Chlorophyllin (CHL) is a water-soluble derivative of chlorophyll, the ubiquitous pigment in green and leafy vegetables, whereas indole-3-carbinol (I3C) is present in cruciferous vegetables such as cabbage, broccoli and cauliflower. In rats initiated with 1,2-dimethylhydrazine (DMH), CHL and I3C reportedly promoted or enhanced the incidence of colon tumors when they were administered after, or during and after the carcinogen exposure, respectively. The same compounds given post-initiation inhibited the formation of colonic aberrant crypts induced by heterocyclic amines, such as 2-amino-3-methylimidazo[4,5-f]quinoline (IQ), but tumor suppression was not examined in the latter studies. In the present investigation, male F344 rats were treated with IQ or DMH during the first 5 weeks of a 1 year study; IQ was given in the diet (0.03%), whereas DMH was administered once a week by s.c. injection (20 mg/kg body wt). Beginning 1 week after the last dose of IQ or DMH until sacrifice, rats received 0.001, 0.01 or 0.1% (w/v) CHL in the drinking water or 0.001, 0.01 or 0.1% I3C in the diet. Compared with controls given carcinogen alone, 0.1% I3C treatment suppressed the multiplicity of IQ-induced colon tumors, and CHL inhibited in a dose-related manner the incidence of IQ-induced liver tumors. However, 0.001% CHL increased significantly the multiplicity of DMH-induced colon tumors while having no effect on the colon tumors induced by IQ. These results indicate that both the choice of carcinogen as well as the dose of the tumor modulator can be important determinants of the events that occur during post-initiation exposure to CHL or I3C. Based on the present findings and data in the literature, it is possible for CHL and I3C to act as tumor promoters or anticarcinogens, depending upon the test species, initiating agent and exposure protocol.     

Interaction of dietary fat and route of carcinogen administration on 1,2-dimethylhydrazine-induced colon tumorigenesis in rats

Since the results of an earlier study indicating no effect ofdietary fat on dimethylhydrazine (DMH)-induced colon cancerin rats differed from those of other investigators, the presentstudy was initiated to determine if the modulating effect offat intake on colon tumorigenesis was dependent on the routeof DMH administration. Male weanling Sprague-Dawley rats (160)were fed one of two nutritionally balanced diets containing5% or 24% corn oil (CO). Following 3 weeks adaptation to theirrespective diets, 40 rats from each diet group were treatedwith five doses of DMH (30 mg/kg) by intragastric i.g.) gavageor subcutaneous (s.c.) injection, over a 3 week period. Ratswere sacrificed when they showed clinical signs of colon tumorand surviving animals were killed 51 weeks after the initialDMH treatment. The cumulative probability of death with coloncarcinoma did not differ between the dietary or treatment groups.There was no effect of route of administration or dietary faton total intestinal tumor incidence. The number of rats withcolon carcinoma was: 5%CO.IG=25; 24%CO.IG=27; 5%CO.SC=23; 24%CO.SC=19.Polypoid tumor incidence was significantly higher in the 24%CO.SCgroup (12/40) compared to the 5%CO.SC group (3/40) (Chi-squared= 5.25; p <0.03) while sessile tumor incidence was the inverse.Marginally significant differences in tumor morphology werenoted between the IG groups.     

Effect of dietary sodium ascorbate on 1,2-dimethylhydrazine- or methylnitrosourea-induced colon carcinogenesis in rats

The effect of dietary sodium ascorbate (SA) on colon carcinogenesisevoked by 1,2-dimethylhydrazine (DMH) or N-methyl-N-nitrosourea(MNU) was studied in female F344 rats. Animals were fed dietscontaining 0, 0.25 and 1% of SA and given s.c. a single doseof 150 mg DMH/kg body wt., 10 weekly s.c. injections of 20 mgDMH/kg body wt. or intrarectal administration of 2 mg MNU, twicea week for 2 weeks. The incidence of colon and kidney tumorswas lower in rats fed the 0.25 or 1% SA and treated with a singledose of DMH than in the animals fed the diet without SA; however,the tumor incidences did not differ between the SA- and controldiet-fed animals and treated with multiple doses of DMH or MNU.     

Effects of dietary perilla oil, soybean oil and safflower oil on 7,12-dimethylbenz[a]anthracene (DMBA) and 1,2-dimethyl-hydrazine (DMH)-induced mammary gland and colon carcinogenesis in female SD rats

The effects of diet supplemented with perilla oil, which contains a large amount of n-3 alpha-linolenic acid, and n-6 linoleic acid rich soybean and safflower oil supplemented diets on 7,12-dimethylbenz[a]anthracene (DMBA)- and 1,2-dimethylhydrazine (DMH)-induced mammary gland and colon carcinogenesis were investigated in female SD rats. Groups of 23 or 24, 5 week old animals were first given three s.c. injections of 40 mg/kg body wt DMH followed by a single intragastric administration of 50 mg/kg body wt DMBA within 2 weeks of the commencement. Starting 1 week after the DMBA treatment, they were administered pellet diet containing 10% perilla oil, soybean oil or safflower oil for the succeeding 33 weeks. Histological examination revealed that the resultant numbers of mammary tumors per rat were significantly lower in rats given perilla oil diet (4.4 +/- 2.5) than in the soybean oil diet group (6.5 +/- 3.9). Furthermore, colon tumor incidence was significantly lower in animals receiving the perilla oil supplement (18.2%) than in those given safflower oil diet (47.4%), and the numbers of colon tumors per rat tended to be lowest in rats administered perilla oil. Also the incidence of nephroblastomas in rats receiving perilla oil diet (0%) was significantly lower than that for the soybean oil diet group (23.8%). The results thus indicate that the alpha-linolenic acid (n-3)-rich perilla oil diet inhibits development of mammary gland, colon and kidney tumors as compared to linoleic acid (n-6)-rich safflower or soybean oil diet.     

Effects of sodium cholate on experimental carcinogenesis and cell proliferation in an excluded colonic segment

Bile salts appear to be important promoters of colon carcinogenesis. This study was designed to assess the importance of the fecal stream in cholic acid-induced colon tumor promotion. Male Sprague-Dawley rats underwent transverse colostomy after induction with dimethylhydrazine (DMH) and the excluded distal colon was irrigated with saline or sodium cholate (23 microM) 5 times per week until sacrifice. Controls initially injected with saline were similarly treated. All surviving animals were sacrificed at 28 weeks after the last DMH injection. Five animals from each group were randomly chosen to assess tritiated thymidine labeling and distribution by autoradiography in normal appearing colon mucosa of irrigated bowel. Cholate irrigation failed to increase tumor yield or modify the proportion of adenomas and adenocarcinomas in this model. Paradoxically, fewer tumors per affected rat were noted with sodium cholate irrigation. Cholate irrigation also failed to affect crypt cellularity, thymidine labeling indices, and labeling distribution in DMH-treated rats and controls. An effect of DMH was seen, however, with an increase in thymidine labeling index and increased labeling in the top half of the crypt in all DMH-treated groups. This study suggests that tumor promotion with primary bile salts is not a direct affect and may result from further bile salt metabolism within the fecal stream. DMH-induced changes in cell proliferation were reproduced with this model. Use of an excluded colon segment to assess the effect of suspected tumor promoters on carcinogenesis or colon mucosal cell proliferation is feasible and may be a useful model for future studies.     

Prolonged chronic inflammation progresses to dysplasia in a novel rat model of colitis-associated colon cancer

Inflammatory bowel disease (IBD) is a gastrointestinal disorder of unknown etiology or cure. One complication of IBD is an increased risk for development of colon cancer. The aims of this study were to use a previously established rat model of colitis to develop a new model of colitis-associated colon cancer and ascertain the involvement of three cancer-related genes: K-ras, adenomatous polyposis coli (APC), and p53. Four groups of rats were used: reactivated 1,2-dimethylhydrazine [DMH; trinitrobenzene sulfonic acid (TNBS) was used to induce colitis followed by a weekly s.c. dose of DMH], prolonged reactivation (inflammation was induced with TNBS, then maintained twice a week), saline-DMH (animals received saline instead of TNBS followed by a weekly dose of DMH), and normal (received no treatment). Animals were sacrificed at 5, 10, or 15 weeks, and colon samples were taken for pathologic analysis and gene mutation detection. No dysplasia was found in the normal group. The highest incidences of dysplasia were as follows: prolonged reactivation group at 5 weeks (60%), reactivated DMH group at 10 weeks (83%), and saline-DMH group at 15 weeks (67%). Carcinoma was found in both the prolonged reactivation and saline-DMH groups. No mutations were found in the K-ras oncogene; however 62% of the APC samples (exon 15 at nucleotide 2778) and 76% of p53 (exon 6 at nucleotide 1327) showed substitutions. The prolonged reactivation group may be considered a new model of colitis-associated colon cancer, offering the potential to study cancer prevention strategies for patients with IBD.     

Urinary excretion of N1-acetylspermidine and other acetylated and free polyamines in the 1,2-dimethylhydrazine model of experimental rat colon cancer

1,2-Dimethylhydrazine (DMH) is a potent procarcinogen with selectivity for the colon. Recently, it has been demonstrated that levels of N1-acetylspermidine were elevated 2-3-fold in colonic tumors induced by this agent compared to control tissues. To determine whether alterations in the urinary levels of this acetylated polyamine or other polyamines were useful biochemical markers for colon cancer in this experimental model, rats were given s.c. injections of DMH (20 mg/kg body weight/week) or diluent for 26 weeks. One week after the last injection, control and DMH-treated animals were placed in separate metabolic cages and their urine was collected for 24 h. The urinary levels (expressed as nmol/mg creatinine) of putrescine, spermidine, spermine, N1-acetylspermidine, and N8-acetylspermidine were then analyzed by high-performance liquid chromatography. Animals from each group were then sacrificed and their colons were examined for tumors. The results of these studies demonstrated that the urinary level of N1-acetylspermidine was an excellent biochemical marker for colonic tumors induced by DMH. At 18.3 nmol/mg creatinine, N1-acetylspermidine was 100% sensitive and specific for colon cancer. Moreover, urinary levels of N1-acetylspermidine were better for this purpose than the N1-acetylspermidine/N8-acetylspermidine molar ratio, a marker previously suggested to be more specific for certain cancers than free polyamines.     

Use of polar solvents in chemoprevention of 1,2-dimethylhydrazine-induced colon cancer

To examine the effect of the polar solvents on 1,2-dimethylhydrazine (DMH)-induced colon cancer, 100 male Sprague-Dawley rats were randomly allocated to a control and three treatment groups. Treated animals received N-methylformamide (NMF), dimethylsulfoxide (DMSO), or methylsulfonylmethane (MSM) added to drinking water 1 week before carcinogen injections commenced and for the duration of the experiment. Primary tumors were detected by serial laparotomy under ether anesthesia performed at 2-month intervals and commencing after carcinogen injections had been completed. The average time to tumor onset was significantly delayed in rats receiving NMF and MSM (P = 0.0141 and 0.0398 respectively, Mantel-Haenszel test). In addition, fewer poorly differentiated tumors were noted in treatment groups. No weight loss or toxicity was observed. These findings demonstrate that the polar solvents significantly reduce the latent period to tumor onset in DMH-induced colon cancer and indicate the need to further investigate such compounds as chemopreventive agents.     

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.