Transplacental effect of a 15% olive-oil diet on functional activity of immune components in the spleen and colon tumors of rat offspring

We studied whether feeding pregnant female rats a 15% olive-oil diet affects the activity of lymph cells in the spleen and tumors in offspring with chemically-induced colon tumors. Rat mothers were fed either a 7% corn-oil or a 15% olive-oil diet. Five-week-old male offspring were divided into 3 groups. A control group was fed the 7% corn-oil diet similar to their mothers. The experimental group I was fed the 7% corn-oil diet whereas their mothers were fed the 15% olive-oil diet. The experimental group II was fed the same 15% olive-oil diet as their mothers. Experimental rats were injected weekly for 8 weeks with the carcinogen, 1,2-dimethylhydrazine (DMH), 20 mg/kg b.w. Results of experiments were studied 6 months later. The area of zones in the spleen responsible for producing B and T lymphocytes were measured and the number of cells counted. The activity of lymphoid elements of the spleen and of tumors were studied using immunohistochemical methods for evaluating the synthesis of CD8(+) lymphocytes and proliferative activity of lymphocytes in spleens and tumors. Feeding pregnant or lactating mothers with the 15% olive-oil diet had no marked tumor-protective effect on chemically-induced colon cancer in offspring. Diet-dependent changes were found at the cellular level. In the spleen of control offspring, the presence of a tumor was accompanied by an increase in the number of Ki-67(+) cells and CD8(+) lymphocytes in the red pulp. In experimental group I, DMH significantly increased the total cell number and the number of CD8(+) lymphocytes in the red pulp of the spleen in both tumor-bearing and tumor-free rats. In experimental group II, the total number of lymph cells and the number of CD8(+) lymphocytes increased compared to offspring fed a control diet. Tumor formation activated the proliferative activity of lymph elements. The total number of cells in infiltrates of the colon mucosa decreased in tumor-bearing rats compared to tumor-free counterparts, and this was seen in all three dietary groups of rats. In tumors from offspring of experimental group II, only the number of CD8(+) lymphocytes increased compared to those in offspring of experimental group I. The findings indicate that feeding mothers the 15% olive-oil diet had a cancer-inhibiting role in offspring, predominantly changes at the cellular level.     

Transplacental effects of a 15% olive-oil diet on chemically-induced tumorigenesis in offspring

We evaluated whether feeding pregnant female rats a diet high in olive-oil, that showed a tumor-preventive effect in adults, has a similar preventive effect on chemically-induced cancer in offspring (i.e. mammary glands and colon cancer in rats). The control group was fed the same 7% corn-oil diet as their mothers. Experimental group I was fed a 7% corn-oil diet while their mothers received a 15% olive-oil diet. Experimental group II was fed the same 15% olive-oil diet as their mothers. Female offspring were twice administered 7,12-dimethylbenz(a)antracene (DMBA) in doses of 10 mg/rat. Male offspring were injected 6 times with 1, 2-dimethylhydrazine (DMH) in doses of 20 mg/kg body weight. Effect of DMBA was manifested in a high rate of tumorigenesis: the number of tumor-bearing rats in control offspring reached 52.0%. This effect increased to 60.6% among offspring of experimental group II and to 67.7% in offspring of experimental group I. The mean tumor size increased significantly in control offspring. Following administration of DMH number of tumor-bearing rats was similar in all groups of offspring: 36.7%, 40.7% and 42.8%. Tumor types differed: the majority of tumors in the control group were benign polyps and adenomas (72.1%) and the number of adenocarcinomas was low (27.9%). The number of malignant tumors increased to 37.5% in offspring of experimental group II and to 45.5% in offspring of experimental group I. In control group offspring, a distinct tendency to increased body weight and a significant increase in spleen weight were seen. The findings indicate that feeding mothers a diet high in fat concentrations, even those with known tumor preventive significance in adults, lose this cancer-inhibiting role in offspring.     

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.     

Effect of Konjac mannan on 1,2-dimethylhydrazine-induced intestinal carcinogenesis in Fischer 344 rats

The effect of Konjac mannan (KM) on 1,2-dimethylhydrazine (DMH-induced intestinal carcinogenesis was studied in male F344 rats. Rats were fed a diet containing 5% KM at 5 weeks of age. At 6 weeks of age, all animals were given a weekly intraperitoneal injection of 20 mg DMH/kg body wt for 13 weeks and autopsied 13 weeks after the last injection of DMH. The weight gain was lower in rats fed the KM diet than in rats fed the control diet throughout the experiment (P less than 0.05). The incidence of DMH-induced colon tumors was lower in animals fed the KM diet compared to animals fed the control diet (P less than 0.05). The number of colon adenocarcinoma per animal was also lower in animals fed the KM than in animals fed the control diet (P less than 0.05). However, the incidence of tumors of the small intestine did not significantly differ between the groups fed the KM and control diets. The present study demonstrated that colon tumorigenesis induced by DMH in F344 rat was inhibited by maintaining the KM diet.     

Effect of dietary corn bran and autohydrolyzed lignin on 3,2'-dimethyl-4-aminobiphenyl-induced intestinal carcinogenesis in male F344 rats

The effect of dietary corn bran and autohydrolyzed lignin on 3,2'-dimethyl-4-aminobiphenyl (DMAB)-induced intestinal carcinogenesis was studied in male inbred F344 rats. Groups of weanling rats were fed semipurified diets containing 15% corn bran or 7.5% lignin or a semipurified diet without these fibers (control diet). At 7 weeks of age, all animals, except vehicle-treated controls, were given sc injections of 50 mg DMAB/kg body weight/week for 20 weeks. All animals were autopsied 20 weeks after the last injection of DMAB. The incidence of colon tumors (percentage of animals with tumors) and colon tumor multiplicity (tumors/animal) were increased in rats fed the corn bran diet as compared to the tumor incidence and multiplicity in rats fed the control diet. The incidence of small intestinal tumors was slightly lower in rats fed the corn bran diet as compared to the incidence in rats fed the control diet. The concentrations (mg/g dry feces) of fecal deoxycholic acid and total bile acids and the daily output of fecal deoxycholic acid, lithocholic acid, hyodeoxycholic acid, and total bile acids were increased in rats fed the corn bran diet as compared to the concentrations and daily output in rats fed the control diet. The incidence and multiplicity of small intestinal tumors as well as the number of colon adenocarcinomas per tumor-bearing animal were lower in animals fed the lignin diet than in those fed the control diet. Lignin had no effect on the concentrations of fecal bile acids, but the daily output of total bile acids was increased in animals fed the lignin diet as compared to the daily output in rats fed the control diet. This study thus indicates that the protection against colon cancer depends on the type of fiber.     

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.     

Mammary tumors in splenectomized rats.

The objective of this study was to examine how splenectomy affects the immune response, particularly T cells, in chemically-induced mammary tumors. Female rats were splenectomized and then exposed to 9,10-dimethyl-1,2-benz(a)anthracene (DMBA) to induce mammary tumors. Splenectomy significantly decreased the rate of tumor appearance and their malignant transformation. The tumor latency period in splenectomized rats was 12.0+/-0.9 weeks compared to 9.7+/-0.5 wk in intact controls, and malignancy appeared in 45% of splenectomized rats, compared to 70% in controls. By the end of the experiment, the total number of tumors and their size were similar in both groups. Blood CD4+ and CD8+ T cell concentrations were similar in tumor-bearing and tumor-free splenectomized animals, but in both groups CD4- and CD8- lymphocytes decreased sharply compared to control animals. In tumor-bearing rats, splenectomy also resulted in significantly more circulating natural killer cells. The spleens of tumor-bearing control rats had significantly fewer CD4+ and CD8+ lymphocytes and more CD4- and CD8- lymphocytes and natural killer cells than did their blood. In conclusion, splenectomy inhibits the early stages of tumorigenesis and reduces the rate of malignant transformation of benign tumors, but does not prevent the progress of carcinogenesis. Differences between splenectomized (operated) and intact rats to the effect of DMBA can be explained by an increase in non-specific resistance of splenectomized rats as a result of operation.     

Chemoprevention of 2-amino-1-methyl-6-phenylimidazo- [4,5-b]pyridine-induced colon carcinogenesis by 1-O-hexyl-2,3,5-trimethylhydroquinone after initiation with 1,2-dimethylhydrazine in F344 rats

The aim of this study is to investigate the chemopreventive effects of the synthetic phenolic antioxidant 1-O-hexyl-2,3, 5-trimethylhydroquinone (HTHQ) on 2-amino-1-methyl-6-phenylimidazo[4,5-b]pyridine (PhIP)-associated colon carcinogenesis in rats after initiation with 1,2-dimethylhydrazine (DMH) in male F344 rats. Groups of 20-22, 6-week-old male F344 rats were given four subcutaneous injections of 40 mg/kg body wt of DMH during the initial 4 weeks. They were then maintained on powdered basal diet containing 0.03% PhIP alone, PhIP together with 0.5 or 0.125% HTHQ, 0.5 or 0.125% HTHQ alone or basal diet for 32 weeks. A small number (1.1 +/- 1.1/rat) of colon tumors were induced by DMH treatment alone. After initiation with DMH, the number of colon tumors was greatly increased to 8.3 +/- 5.6 by the administration of PhIP. Additional treatment with HTHQ dose-dependently decreased the multiplicity of colon adenocarcinomas to 4.9 +/- 2.8 and 2.6 +/- 1.4 with 0.125 and 0.5%, respectively. This treatment similarly reduced atypical hyperplasias of the ventral prostate. Furthermore, HTHQ significantly reduced the multiplicity of duodenal adenocarcinomas induced by DMH + PhIP or DMH alone. Immunohistochemically, HTHQ was revealed to suppress PhIP-DNA adduct formation in the epithelial cells of the colon and prostate in a separate 2 weeks experiment. The present results clearly showed that HTHQ has chemopreventive potential for PhIP-associated colon and prostate carcinogenesis. The observed inhibition may largely be due to interference with PhIP-DNA adduct formation. In addition, HTHQ has been demonstrated to inhibit duodenal carcinogenesis in the post-initiation stage.     

Response of T and B lymphocytes in the spleen, lymph nodes and mammary tumors in rats treated with human soluble tumor-associated antigens and commercial human albumin

We showed previously that soluble tumor-associated antigens (sTAA) isolated from breast cancer patients could suppress chemically-induced tumorigenesis in rats in comparison to the effect of commercial human albumin (CHA). Herein we analyze the possible mechanism of those findings. The following groups of mammary tumor-bearing rats were used in the studies: i) control rats treated with saline; ii) rats treated with CHA; and iii) rats treated with human sTAA. Different zones of the spleen, regional lymph nodes and tumors and their cellular content (B and T cells) were analyzed using the methods of morphometry and immunohistochemistry. Treatment of tumor-bearing rats with CHA resulted in a significant decrease in the size of the germinal center of the follicles. The number of B lymphocytes in the mantle layer of the follicles, the marginal zone and red pulp decreased significantly. The number of CD8+ T cells also decreased in the marginal zone and red pulp, whereas the number of CD4+ T cells increased in the periarterial lymph sheath (PALS) and the red pulp. Reaction of the spleen to vaccination with sTAA manifested in a significant increase in the size of most areas of the white pulp and in the number of B lymphocytes. In lymph nodes from control rats or those treated with CHA, CD8+ lymphocytes mainly accumulated in the paracortical zone. In rats treated with sTAA, CD8+ lymphocytes accumulated also in the medulla. The number of CD4+ T cells in these rats sharply increased and accumulated mainly in the medulla around the vessels. The total number of lymphocytes was changed differently in different areas of tumors (peripheral vs. at depth). The number of CD8+ cells significantly increased at depth of tumors, and also the ratio in the number of these cells at depth of tumors compared to a periphery increased. No difference was found in response of lymph cells to different types of treatment. All findings indicated a strict antitumor effect of vaccination with the sTAA, which prevents the development of insufficiency of the immune system when an intensive immune reaction takes place.     

Multiple dietary factors in the enhancement of dimethylhydrazine carcinogenesis: main effect of indole-3-carbinol

The effects of multiple dietary influences on 1,2-dimethylhydrazine [(DMH) CAS: 540-73-8]-induced colon cancer in rats were studied. A 2(4) factorial experimental design was used to examine the main and interactive effects of 15% wheat bran (WB), 1% cholesterol (CH) with cholic acid, 20% beef tallow (BT), and 0.1% indole-3-carbinol (IC) on 160 male F344 rats treated ip with DMH (10 mg/kg) weekly for 16 weeks. The test diets were fed for 3 weeks before, 16 weeks during, and 12 weeks after DMH administration. At necropsy, total weight gain, liver and spleen weights, serum CH levels, liver aryl hydrocarbon hydroxylase (AHH) activity, and the size, number, incidence, and location of intestinal tumors were analyzed for dietary factor effects. The most significant inducer of tumors was the combination of CH + BT + IC acting in synergism. The single main effect most responsible for tumor morbidity was IC, which appeared to enhance tumorigenesis via its role as an inducer of AHH activity. The WB decreased tumor incidence and burden when added to diets also containing CH, but it otherwise increased tumor burden per tumor-bearing animal and incidence in all other diets. This study demonstrated the need for examining synergistic and antagonistic interactions among dietary initiators and/or promoters of colon carcinogenesis, as well as implicating IC as a significant factor in the development of DMH-induced tumors in rats.     

Effect of dietary carbohydrates on the growth of dysplastic crypt foci in the colon of rats treated with 1,2-dimethylhydrazine

The effect of dietary starch and sucrose on the growth of foci of dysplastic crypts in the colon (FDC) was studied in female Sprague Dawley rats treated twice p.o. with 25 mg/kg of 1,2-dimethylhydrazine (DMH). After DMH administration, the animals were fed high-fat (23% corn oil, w/w)/low-calcium (0.1%, w/w)/low-cellulose (2%, w/w) diets in which carbohydrates were represented by corn starch (starch diet) or sucrose (sucrose diet) (46%, w/w). The animals were fed for either 30 or 105 days with the experimental diets. The number of FDC was not significantly affected by diet. However, after 30 days the percentage of small FDC (formed by 1-2 dysplastic crypts) was higher in the animals fed the starch diet compared to the animals fed the sucrose diet [90.3 +/- 1.1% (SE) and 82.6 +/- 3.1%, respectively; P less than 0.05]. In contrast, foci formed by 3-4 dysplastic crypts were decreased by the starch diet (P less than 0.05). After 105 days of feeding, the starch diet induced a number of dysplastic crypts/focus lower than that induced by the sucrose diet (2.6 +/- 0.1 and 2.9 +/- 0.1, respectively; P less than 0.05). The percentage of small FDC was also higher in the animals fed the starch diet compared to animals fed the sucrose diet (P less than 0.01). After 30 days of feeding, DMH treatment increased colon proliferative activity in both dietary groups (P less than 0.05). But after 105 days of feeding, proliferation was similar in controls and DMH-treated rats and markedly reduced in animals fed the starch diet (mean labeling index values for both controls and DMH-treated rats were 10.4 +/- 0.8 and 4.4 +/- 0.5 in the sucrose and starch diets, respectively; P less than 0.001). The overall results suggest that starch in high-fat/low-calcium/low-cellulose diets has a protective role against DMH-colon carcinogensis in the rat.     

Suppression of a a carcinogen (1,2-dimethylhydrazine dihydrochloride)-induced increase in mitotic activity in the colonic crypts of rats by addition of dietary cellulose

Serial injections of the colon carcinogen, 1,2-dimethylhydrazine (DMH), have been reported to increase the proliferative activity in the colonic crypts preceding development of tumors. Can addition of purified cellulose to a fiber-free AIN-76 rat diet be used to suppress this increase in proliferative activity? To answer this question rats were divided into two groups, and one group was given eight weekly injections of the DMH base at 9.5 mg/kg of body weight. Throughout this period and for 2 additional wk the rats were isocalorically fed a defined nutritionally complete diet both with and without different dietary levels of cellulose (0, 5, and 15%). The rats were given injections of colchicine 3 h prior to sacrifice to arrest and to collect dividing cells at metaphase. Analysis of variance was performed on various morphometric parameters obtained from histological sections of midaxial crypts from the descending colon. Our results confirm that DMH induced a significant increase in the mitotic activity as measured by the number of metaphase figures per crypt. The presence of dietary cellulose did cause a significant suppression of the DMH-induced increase in the crypt mitotic activity.     

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.      

Effect of dietary wheat bran and dehydrated citrus fiber on 3,2'-dimethyl-4-aminobiphenyl-induced intestinal carcinogenesis in F344 rats

The effect of dietary wheat bran and dehydrated citrus fiberon 3,2'-dimethyl-4-aminobiphenyl (DMAB)-induced colon and smallintestinal carcinogenesis was studied in male F344 rats. Weanlingrats were fed semipurified diets containing 5% alphacel, 5%alphacel + 15% wheat bran or 5% alphacel + 15% citrus fiber.At 7 weeks of age, all animals, except vehicle-treated controls,received weekly s.c. injections of 50 mg DMAB/kg body weightfor 20 weeks. The DMAB- or vehicle-treated groups were autopsied20 weeks after the last injection of DMAB. The animals fed thewheat bran diet and treated with DMAB had a lower incidence(number of animals with tumors) and multiplicity (number oftumors/tumor-bearing animal) of colon and small intestinal tumorsthan did those fed the control diet and treated with DMAB. Animalsfed the diet containing citrus fiber developed fewer small intestinaltumors (incidence and multiplicity) than did the rats fed thecontrol diet; the number of adenocarcinomas was reduced in ratsfed the citrus fiber diet. This study thus indicates that dietscontaining wheat bran and citrus fiber reduce the risk for DMAB-inducedintestinal cancer and that the protection against colon cancerdepends on the type of fiber.     

High tumor-preventive effects of polyclonal IgG generated against p53 tumor-associated protein obtained from benign-tumor bearing rats

We have shown the different effects of rabbit IgG generated against various types of p53 tumor-associated protein on chemically induced colon cancer in rats. p53 protein was isolated in the form of cytoplasmic, soluble, protein from sera obtained from: a) rats with colon cancer and b) rats with benign colon tumors. The isolation was performed using the affinity chromatography columns with,eel fiberglass membranes. Anti-p53 IgG were obtained from rabbits vaccinated with the above mentioned types of p53. Sprague Dawley rats were vaccinated with anti-p53 IgG (100 mu g/rat) at two-week intervals for 2 months and then monthly for 3 months. The induction of colon cancer was caused by weekly injections with 1,2-dimethylhydrazine (20 mg/kg) for 7 weeks and was initiated 8 weeks after the start of the vaccination. Results of experiments were evaluated 6 months after the start of cancer induction. It was found that vaccination of rats with IgG generated against the p53 protein isolated from cancer-bearing rats did not exhibit significant protective effect. Only IgG generated against p53 protein from benign tumor-bearing rats significantly prevented the carcinogenic effect of DMH. The number of tumor-bearing rats in vaccinated group decreased to 44% as compared with 93% in the control group. In vaccinated rats, the number of tumors/rat was 0.8 as compared to 9.3 in controls. The number of malignant tumors in vaccinated rats was half that in controls: 29% and 58%, respectively. In the controls, metastases were found in 6 of 45 rats (13%). Anti-p53 IgG not only has an anti-tumor effect but also prevented benign tumors from becoming malignant. We suggest that the anticancer role of a vaccine generated against p53 protein from benign tumor-bearing rats is related to a wild-type p53 protein. Further studies will be performed to clarify this hypothesis.     

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.     

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.     

Effects of dietary saturated and unsaturated fatty acids on fecal bile acids and colon carcinogenesis induced by azoxymethane in rats

To determine whether the kind of dietary fat affects colon carcinogenesis, male Donryu rats were fed a 5% fat diet containing linoleate, an unsaturated fat, or stearate, a saturated fat, in semipurified fat-free chow. The rats were given azoxymethane (7.4 mg/kg body weight) s.c. once a week for 11 weeks and killed 15 weeks after the last injection of the carcinogen. The rats on the unsaturated fat diet had a significantly higher incidence of colon tumors. Fatty acid analysis of cholesterol esters in the liver and examination of the amount of fecal bile acids showed that the unsaturated fat diet increased the level of cholesterol linoleate and arachidonate in the liver and also increased the fecal excretion of bile acids, especially that of lithocholic acid. The colon tumors in rats on the unsaturated fat diet, compared with those in rats on the saturated fat diet, contained a higher level of lysophosphatidylcholine. These results suggest that increased fecal excretion of bile acids due to increased polyunsaturated cholesterol esters in the liver stimulates phospholipase A2 activity of colon initiated cells and enhances colon carcinogenesis in rats on the unsaturated fat diet.     

Melatonin and colon carcinogenesis. IV. Effect of melatonin on proliferative activity and expression of apoptosis-related proteins in the spleen of rats exposed to 1,2-dimethylhydrazine

The suppression of 1,2-dimethylhydrazine (DMH)-induced colon carcinogenesis by melatonin was previously demonstrated. The objective of the present work was to evaluate histologically and immunohistochemically the splenic immune response to the induced cancer and to melatonin. Spleens from rats, either untreated, injected with DMH, fed with melatonin or treated with both carcinogen and melatonin, were studied. The exposure to the carcinogen and the consequential carcinogenesis resulted in splenic changes that reflected the insufficiency of the immune response, as manifested in significant reduction of the white pulp and the simultaneous expansion of the red pulp. The effects of melatonin on most splenic components were inverse to those of DMH. The anti-carcinogenic properties of melatonin were evidenced from the reversal of the inhibitory effects of DMH, especially when the densities of lymphocytes in different parts of the spleen were compared. The combined treatment of the rats with DMH and melatonin resulted in the expansion of the splenic zones by 106% to 125%, compared to those from DMH-treated rats, and the numbers of CD8+ lymphocytes and Fas-positive cells increased sharply. Therefore we conclude that anti-carcinogenic effects of melatonin are related to activation of several elements of the host's lymphatic system.     

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.