Modulation of experimental colon tumorigenesis by types and amounts of dietary fatty acids

Epidemiological studies and laboratory animal model assays suggest that a high intake of dietary fat promotes colorectal cancer. Several in vivo and in vitro studies support the hypothesis that omega-6 fatty acids promote colon tumorigenesis, whereas omega-3 fatty acids lack promoting activity. Fat intake in the United States traditionally includes high amounts (30% of total caloric intake) of saturated fat rather than omega-6 fatty acids. Therefore, the present study was designed to compare the modulatory effects of a high-fat diet containing mixed lipids (HFML), a diet rich in saturated fatty acids (the average American diet), a diet with fish oil (HFFO) that is rich in omega-3 fatty acids, and a low-fat corn oil diet (LFCO) on the formation of chemically induced colonic aberrant crypt foci (ACF) and tumors, cyclooxygenase (COX)-2 activity, and apoptosis during experimental colon carcinogenesis. At 5 weeks of age, groups of male F344 rats were fed a 5% corn oil diet (LFCO). At 7 weeks of age, rats intended for carcinogen treatment received s.c. injections of azoxymethane at a dose level of 15 mg/kg of body weight once weekly for 2 weeks. Beginning 1 day after the carcinogen treatment, groups of rats were then maintained on experimental diets containing 20% HFML or 20% HFFO. Rats were killed at 8, 23, or 38 weeks after azoxymethane treatment. Colonic ACF and tumors were evaluated histopathologically, and apoptosis was evaluated by the terminal deoxynucleotidyl transferase-mediated nick end labeling method. Colonic mucosae and tumor samples harvested at week 38 were analyzed for COX-2 synthetic activity and expression. The rats fed the HFML diet showed significantly increased total colonic ACF (P < 0.001-0.0001) with a multiplicity of > or = 4 aberrant crypts/focus (P < 0.0001) compared with the effects of the HFFO or LFCO diets at week 8, 23, and 38. Interestingly, there was a 2- to 3-fold increase (> or = 4) in multicrypt foci in rats given the HFML diet as compared with such foci in rats fed the HFFO or LFCO diets. By week 23, the HFML diet had significantly increased the incidence of colonic tumors (30-60%) and their multiplicity (100-141%) when compared with the effects of the LFCO or HFFO diets. At week 38, the HFML diet had induced 100% colon tumor incidence and a 4-fold multiplicity of adenocarcinomas compared with the LFCO and HFFO diets. At weeks 23 and 38, a significantly lower percentage of apoptotic colonic epithelial cells were observed in the tumors of animals fed the HFML diet as compared with those fed the HFFO diet. The HFML diet caused significantly increased levels of COX-2 activity in colon tumors (P < 0.05-0.01), and these tumors had enhanced levels of COX-2 expression as compared with those in assays with LFCO or HFFO diets. These observations demonstrate for the first time that HFML diets containing high levels of saturated fatty acids (such as those in Western diets) promote colon carcinogenesis. Although the mechanisms involved in colon tumor promotion by a HFML diet are not fully known, our results indicate that the modulation of eicosanoid production via the influence on COX activity and the suppression of apoptosis may play a key role in HFML diet-induced colon tumorigenesis.     

Prevention of colon cancer by low doses of celecoxib, a cyclooxygenase inhibitor, administered in diet rich in omega-3 polyunsaturated fatty acids

Epidemiologic and animal studies suggest that a high-fat diet containing mixed lipids promotes colorectal cancer, whereas fish oil lacks promoting effect. Although cyclooxygenase-2 (COX-2) inhibitors are effective chemopreventive agents against colon carcinogenesis, administration of high doses of these agents over time may induce side effects. Here, we compared the efficacy of moderately high and low doses of celecoxib administered in diets high in mixed lipids (HFML) or fish oil (HFFO) against azoxymethane-induced colon carcinogenesis in male F344 rats. One day after the last azoxymethane treatment (15 mg/kg body weight once weekly for 2 weeks), groups of rats were fed the HFML and HFFO diets containing 0, 250, 500, and 1,000 ppm celecoxib. Rats were killed 26 weeks later and colon tumors were subjected to histopathologic examination and analyzed for total COX and COX-2 synthetic activities and COX-2 expression. Rats fed the HFFO diet showed significantly lower colon tumor incidence and multiplicity compared with rats fed the HFML diet. Celecoxib at 250, 500, and 1,000 ppm in either diet significantly suppressed colon carcinogenesis. Inhibition of colon adenocarcinomas were more pronounced in animals given 250 ppm celecoxib in HFFO diet compared with 250 ppm celecoxib given in HFML diet, suggesting some synergism between omega-3 polyunsaturated fatty acids (PUFA) and celecoxib. Inhibition of colon tumors by celecoxib was associated with lower levels of COX-2 activity and expression in colon tumors. These studies support the use of low doses of celecoxib in omega-3 PUFA-rich diet as a promising approach for clinical trials.     

Promoting effects of high-fat corn oil and high-fat mixed lipid diets on 7,12-dimethylbenz[a]anthracene-induced mammary tumorigenesis in F344 rats

Epidemiological studies and laboratory animal model assays suggest that a high intake of dietary fat promotes mammary carcinogenesis as well as colon tumorigenesis. Fat intake in the United States traditionally includes high amounts (30% of total caloric intake) of saturated fatty acids (SFAs) compared to polyunsaturated fatty acids (PUFAs). A recent study suggested that a high-fat mixed-lipid diet (HFML), which simulates the mixed-lipid and high SFAs composition of the average American diet, strongly promotes rat colon carcinogenesis, even when compared to another high-fat diet containing PUFA-rich corn oil. On the other hand, some reports suggest that a high-fat diet rich in n-6 PUFAs promotes mammary carcinogenesis more strongly than a high-fat diet rich in SFAs. Therefore, the present study was designed to compare the effects of HFML, high-fat corn oil diet (HFCO) that is rich in n-6 PUFAs, and a low-fat corn oil diet (LFCO) on 7,12-dimethylbenz[a]anthracene (DMBA)-induced mammary carcinogenesis in female F344 rats. At 7 weeks of age, female F344 rats intended for carcinogen treatment received a gavage of DMBA at a dose level of 65 mg/kg of body weight. Beginning 1 week after carcinogen treatment, groups of rats were then maintained on experimental diets containing LFCO, HFCO or HFML. All rats were evaluated weekly by palpation of mammary tumors and sacrificed 20 weeks after the DMBA treatment. Palpable tumors of mammary glands were detected at the 8, 11, and 19 weeks in the HFCO, HFML and LFCO groups, respectively. Histopathological observation revealed that the incidence and number of mammary tumors in the HFCO group were significantly higher than in the LFCO group. Rats on the HFML diet tended towards a higher incidence and number of mammary tumors compared with the LFCO group, although the correlation was not statistically significant. These results suggest that, for this animal model, both the HFCO and HFML diets promote DMBA-induced mammary carcinogenesis when compared to the LFCO diet, and that the HFCO diet is more tumor-promotional than the HFML diet.     

Effect of different levels of omega-3 and omega-6 fatty acids on azoxymethane-induced colon carcinogenesis in F344 rats

The effect of various levels of dietary Menhaden fish oil containing omega-3 fatty acids plus corn oil containing omega-6 fatty acids fed during the postinitiation phase of colon carcinogenesis was studied in male F344 rats. Starting at 5 weeks of age, groups of animals were fed the 5% corn oil (5% CO) diet. At 7 weeks of age, all animals except the vehicle-treated controls were administered s.c. injections of azoxymethane (15 mg/kg body wt/week for 2 weeks). 4 days after carcinogen or vehicle treatment, groups of animals were transferred to experimental diets containing 4% Menhaden oil + 1% corn oil (4% MO + 1% CO), 23.5% corn oil (23.5% CO), 17.6% corn oil + 5.9% Menhaden oil (17.6% CO + 5.9% MO), 11.8% corn oil + 11.8% Menhaden oil (11.8% CO + 11.8% MO), or 5.9% corn oil + 17.6% Menhaden oil (5.9% CO + 17.6% MO) and fed these diets until termination of the experiment at Week 38 after carcinogen treatment. An additional group consuming a 5% CO diet was continued on these diets. Colon mucosal ornithine decarboxylase activity and microsomal fatty acid composition of colon mucosa were measured in vehicle-treated animals fed experimental diets for 14 weeks. Fatty acids were also analyzed in the microsomal fraction of colon tumors at termination of the experiment. The body weights of animals fed various experimental diets were comparable. Feeding of high fat diets containing 17.6% CO + 5.9% MO, 11.8% CO + 11.8% MO, or 5.9% CO + 17.6% MO significantly inhibited the incidence (percentage of animals with tumors) of colon adenocarcinomas compared to that of 23.5% CO diet. However, the multiplicity (number of tumors/rat) of colon adenocarcinomas was significantly inhibited only in groups fed the 5.9% CO + 17.6% MO compared to those fed the 23.5% CO diet. The incidence and multiplicity of adenocarcinomas were greater in animals fed the 23.5% CO diet compared to those fed the 5% CO diet. Colonic mucosal ornithine decarboxylase activity was lower in animals fed the 11.8% CO + 11.8% MO, 5.9% CO + 17.6% MO, 5% CO, and 4% MO + 1% CO diets compared to the levels in animals fed the 23.5% CO diet. The increasing levels of Menhaden oil in the diet significantly increased the omega-3 fatty acids such as eicosapentaenoic acid and docosahexaenoic acid and decreased the omega-6 fatty acids such as linoleic acid, linolenic acid, and arachidonic acid in microsomal fractions from colonic mucosa and tumors.     

Effect of different levels of dietary trans fat or corn oil on azoxymethane-induced colon carcinogenesis in F344 rats

The effect of various levels of dietary corn oil or trans fat on azoxymethane (AOM; CAS: 25843-45-2)-induced carcinogenesis was investigated in female F344 rats fed the AIN-76 semipurified diets. Starting at 5 weeks of age, groups of rats were fed the low-fat diet containing 5% corn oil (designated as low-fat control diet). At 7 weeks of age, all animals except the vehicle-treated controls, were given sc injections of AOM (15 mg/kg body wt, once weekly) for 3 weeks. After 1 week, groups of animals were transferred to semipurified diets containing 13.6% corn oil and 23.5% corn oil or high-fat diets containing 5.9% corn oil plus 5.9% trans fat plus 11.8% Oleinate (low trans fat), 5.9% corn oil plus 11.8% trans fat plus 5.9% Oleinate (intermediate trans fat), and 5.9% corn oil plus 17.6% trans fat (high trans fat). Fecal bile acids were measured in vehicle-treated rats. All animals were necropsied 34 weeks after the last AOM injection. The animals fed the 23.5% corn oil diet had a higher incidence of colon tumors than did those in the groups fed the 5 and 13.6% corn oil diets. There was no difference in colon tumor incidence between the 5 and 13.6% corn oil diet groups. The animals fed the high-fat diets containing low trans fat, intermediate trans fat, and high trans fat developed significantly fewer liver and colon tumors and more small intestinal tumors than did the rats fed 23.5% corn oil diet. The excretion of fecal deoxycholic acid, lithocholic acid, and 12-ketolithocholic acid was higher in animals fed the 23.5% corn oil diet compared to the excretion in animals fed the other diets.     

Effect of dietary fish oil on azoxymethane-induced colon carcinogenesis in male F344 rats

The effect of dietary intake of different levels of Menhaden fish oil on azoxymethane-induced carcinogenesis was examined in male F344 rats fed the semipurified diets. Starting at 5 weeks of age, groups of animals were fed the 5% corn oil (low corn oil) diet. At 7 weeks of age, all animals except the vehicle-treated controls were given s.c. injections of azoxymethane (15 mg/kg body weight/week for 2 weeks). After 4 days, groups of animals were fed the diets containing 4% Menhaden oil + 1% corn oil (low fish oil), 22.5% Menhaden oil + 1% corn oil (high fish oil), 5% corn oil, and 23.5% corn oil (high corn oil). Thirty-four weeks after azoxymethane injections, all animals were necropsied. High fish oil diet had no tumor promoting effect in the large intestine when compared to the high corn oil diet. There was no difference in large intestinal tumor incidence among the other dietary groups. The results of this study indicate that fish oils rich in highly polyunsaturated n-3 fatty acids do not enhance large bowel carcinogenesis and that the fatty acid composition of the dietary fat is one of the determining factors in large bowel carcinogenesis.     

Steady state levels of transforming growth factor-beta1 and -beta2 mRNA and protein expression are elevated in colonic tumors in vivo irrespective of dietary lipids intervention

Colonic tumors of human origin produce abundant transforming growth factor (TGF)-beta suggesting that TGF-beta is critical to their growth. Dietary lipids regulate a number of growth factors including TGF-beta. Whether elevated TGF-beta levels are consistently expressed in colonic tumors irrespective of the environmental milieu in an in vivo model is not known and forms the main objective of the present study. Male F344 rats were injected with azoxymethane, 10 weeks later, rats bearing preneoplastic lesions were fed a low fat (5% corn oil) diet and 3 high fat (5% corn oil with 18% corn oil, fish oil or beef tallow) diets for 16 weeks. Colonic tumors and mucosae were processed and assessed for TGF-beta status. TGF-beta1 and -beta2 mRNA levels were upregulated in colonic tumors more than in mucosae of all diet groups. Dietary lipids modulated TGF-beta mRNA in both tumors and mucosae, high corn and fish oil diets upregulated TGF-beta1 significantly more than the low fat corn oil or high fat beef tallow diets. Immunohistochemical assessments of tissues with different biological features revealed that TGF-beta1 and -beta2 were elevated in tumors and in selected microscopic preneoplastic lesions compared to normal mucosae. This is the first in vivo study, documenting that developing colonic tumors acquire upregulated TGF-beta phenotype even in the presence of lipid environments capable of differentially regulating TGF-beta in normal mucosae. Elevated expression of TGF-beta in a selected subset of microscopic preneoplastic lesions suggests that TGF-beta plays an important role on both early and late stages of colon carcinogenesis.     

Influence of omega-3 fatty acids on the growth of human colon carcinoma in nude mice

The present study investigated the influence of dietary omega-3 fatty acid supplementation on the growth of human colon carcinoma xenograft in athymic nude mice. Four diets were fed to evaluate the effect of levels and types of fat on colon tumor growth. Animals were maintained on a standard diet modified by addition of fats containing omega-3 and omega-6 fatty acids to represent high and low fat intakes for 53 days. The final mean estimated tumor weight for the high fat corn oil (24%) fed group was 2,302 mg, whereas the low fat (8% corn oil) group was 1,681 mg. The final mean tumor weight of the high fat menhaden oil fed group was 782 mg representing a 66% decrease in growth compared to the high fat corn oil group and a decrease of 54% compared to the low corn oil fed group. The high fat golden algae oil fed group resulted in a mean final tumor weight of 223 mg representing a 90% inhibition of tumor growth relative to the high fat corn oil fed group and 87% inhibition of growth compared to the low fat corn oil fed group. These findings indicate that dietary omega-3 fatty acids possess significant tumor suppressing properties and that the primary tumor suppressing fatty acid is docosahexaenoic acid. Histopathologic examination of control and treated tumors and expression array analyses (human cytokine and apoptosis arrays) support the tumor growth inhibition data and provide evidence for discussion of possible mechanisms for the observed growth inhibition.     

Differential-effects of omega-3 and omega-6 Fatty-acids on primary tumor-growth and metastasis

The amount and type of dietary lipid can significantly influence spontaneous tumor development and tumor progression. To determine the effect of fish oil (rich in omega-3 polyunsaturated fatty acids) and corn oil (rich in omega-6 polyunsaturated fatty acids) on primary tumor growth, metastasis and carcass weight, 45 female Lewis/Wistar rats with subcutaneous mammary tumor implants (MAC-33) were randomized to 1 of 3 diets with 30% lipid consisting of: (i) corn oil alone, (ii) combined 50%:50% corn oil:fish oil, or (iii) fish oil alone. Primary tumor weight was significantly reduced in animals which were fed fish oil or corn oil alone compared to animals given combined corn oil:fish oil diet. Biochemical analysis (protein, DNA, RNA) of the primary revealed no difference between dietary groups. Cell cycle analysis of the primary tumor showed no difference in percent G(0)-G(1), S, G(2)-M or growth fraction (% S + G(2)-M) between dietary groups. In contrast, lung metastasis, was reduced in animals fed the combined corn oil:fish oil diet. Thus, dietary, lipid intake can significantly influence primary tumor growth and tumor metastasis. Differential effects of omega-3 and omega-6 polyunsaturated fatty acids occur on primary tumor growth and development of distant pulmonary metastases in this animal model.     

Carcinogen and dietary lipid regulate ras expression and localization in rat colon without affecting farnesylation kinetics.

Epidemiological and experimental data suggest that dietary fiber and fat are major determinants of colorectal cancer. However, the mechanisms by which these dietary constituents alter the incidence of colon cancer have not been elucidated. Evidence indicates that dominant gain-of-function mutations short-circuit protooncogenes and contribute to the pathogenesis of cancer. Therefore, we began to dissect the mechanisms whereby dietary fat and fiber, fed during the initiation, promotion and progression stages of colon tumorigenesis, regulate ras p21 localization, expression and mutation frequency. Male Sprague-Dawley rats (140) were provided with corn oil or fish oil and pectin or cellulose plus or minus the carcinogen azoxymethane (AOM) in a 2 x 2 x 2 factorial design and killed after 34 weeks. We have previously shown adenocarcinoma incidence in these animals to be 70.3% (52/74) for corn oil + AOM and 56.1% (37/66) for fish oil + AOM (P < 0.05). Total ras expression as well as ras membrane:cytosol ratio was 4- to 6-fold higher in colon tumors than in mucosa from AOM- or saline-injected rats. Expression of ras in the mucosal membrane fraction was 13% higher for animals fed corn oil compared with fish oil feeding (P < 0.05), which is noteworthy since ras must be localized at the plasma membrane to function. The elevated ras membrane:cytosol ratio in tumors was not due to increased farnesyl protein transferase activity or prenylation state, as nearly all detectable ras was in the prenylated form. Phosphorylated p42 and p44 mitogen activated protein kinase (ERK) expression was two-fold higher in tumor extracts compared with uninvolved mucosa from AOM- and saline-injected rats (P < 0.05). The frequency of K-ras mutations was not significantly different between the various groups, but there was a trend toward a greater incidence of mutations in tumors from corn oil fed rats (85%) compared with fish oil fed rats (58%). Our results indicate that the carcinogen-induced changes in ras expression and membrane localization are associated with the in vivo activation of the ERK pathway. In addition, suppression of tumor development by dietary n-3 polyunsaturated fatty acids may be partly due to a combined effect on colonic ras expression, membrane localization, and mutation frequency.     

Tissue-specific attenuation of endogenous DNA I-compounds in rats by carcinogen azoxymethane: possible role of dietary fish oil in colon cancer prevention.

I-compounds are bulky covalent DNA modifications that are derived from metabolic intermediates of nutrients. Some I-compounds may play protective roles against cancer, aging, and degenerative diseases. Many carcinogens and tumor promoters significantly reduce I-compound levels gradually during carcinogenesis. Colon cancer is the second leading cause of cancer death in the United States, whereas cancer of the small intestine is relatively rare. Here we have studied levels of I-compounds in DNA of colon and duodenum of male Sprague-Dawley rats treated with azoxymethane. The effects of dietary lipids (fish oil or corn oil) on colon and duodenal DNA I-compounds were also investigated. Rats fed a diet containing fish oil or corn oil were treated with 15 mg/kg azoxymethane. Animals were terminated 0, 6, 9, 12, or 24 hours after injection. I-compound levels were analyzed by the nuclease P1-enhanced (32)P-postlabeling assay. Rats treated with azoxymethane displayed lower levels of I-compounds in colon DNA compared with control groups (0 hour). However, I-compound levels in duodenal DNA were not diminished after azoxymethane treatment. Animals fed a fish oil diet showed higher levels of I-compounds in colonic DNA compared with corn oil groups (mean adduct levels for fish and corn oil groups were 13.35 and 10.69 in 10(9) nucleotides, respectively, P = 0.034). Taken together, these results support claims that fish oil, which contains a high level of omega-3 polyunsaturated fatty acids, may have potent chemopreventive effects on carcinogen-induced colon cancer. The fact that duodenal I-compounds were not diminished by azoxymethane treatment may have been due to the existence of tissue-specific factors protecting against carcinogenesis. In conclusion, our observations show that endogenous DNA adducts may serve not only as sensitive biomarkers in carcinogenesis and cancer prevention studies, but are also helpful to further our understanding of the chemopreventive properties of omega-3 fatty acids and mechanisms of carcinogenesis.     

Effect of diets high in omega-3 and omega-6 fatty acids on initiation and postinitiation stages of colon carcinogenesis.

The effect of dietary menhaden oil containing omega-3 fatty acids and corn oil rich in omega-6 fatty acids fed during the initiation and/or postinitiation stages of colon carcinogenesis was investigated in male F344 rats. At 5 weeks of age, all animals were divided into seven groups (39 rats/group) and fed the semipurified diets containing 5% corn oil (LCO), 23.5% corn oil (HCO), or 18.5% menhaden oil plus 5% corn oil (HFO). At 7 weeks of age, all animals except the vehicle (normal saline)-treated groups were given two weekly s.c. injection of azoxymethane (AOM) at a dose rate of 15 mg/kg body weight, once weekly. Three days after the second injection of AOM, groups of animals fed LCO, LCO, HCO, HCO, HCO, HFO, or HFO diets were transferred, respectively, to LCO, HCO, LCO, HCO, HFO, HCO, or HFO and continued on these diets until termination of the experiment. All animals were necropsied 42 weeks after carcinogen treatment. Body weights of animals fed various experimental diets during the initiation and postinitiation periods were comparable. As expected, the HCO diet fed during the postinitiation period significantly increased the AOM-induced incidence and multiplicity of colon adenocarcinomas, whereas the HCO diet fed during the initiation phase of carcinogenesis had no effect. Colon tumor incidence and multiplicity were significantly reduced in groups fed the HFO diet at either initiation and/or postinitiation phases of carcinogenesis as compared with those fed the HCO diet. Whereas the precise mechanisms producing the difference between the high menhaden oil (HFO) diet as compared with high corn oil (HCO) diet remain to be elucidated, it is likely that the effect during the initiation and postinitiation phases may be due to alteration in carcinogen metabolism and to modulation of prostaglandin synthesis, respectively.     

Dietary fish oil inhibits the expression of farnesyl protein transferase and colon tumor development in rodents

Although epidemiological and experimental studies indicate a strong relationship between different dietary fats and risk of colon cancer, the modulating effects of these nutritional factors at the molecular level are not fully elucidated. Activated ras genes have been implicated in the etiology of many human malignancies, including colon cancer. It is well established that the transforming ability of ras-p21 depends on its correct localization in plasma membrane. We have previously demonstrated that ingestion of a relatively higher amount of dietary fish oil leads to reduced plasma membrane levels of ras-p21 with concomitant increase in its cytoplasmic contents during the promotion and progression phases of chemically-induced colon tumorigenesis. In this follow-up experiment, we have found that intake of a high amount of corn oil, one of the most widely used fats in the American diet, enhances the expression of farnesyl protein transferase (FPTase). This enzyme catalyses farnesylation of ras precursors in a critical step during post-translational modification of ras oncoproteins, thereby enabling their anchorage to plasma membrane. In contrast, consumption of high amounts of fish oil, which is rich in omega-3 polyunsaturated fatty acids, reduces the levels of FPTase expression, thus inhibiting post-translational processing of ras precursors resulting in decreased ras function both in colonic mucosa as well as in colon tumors. These results correlate with increased incidence and multiplicity of grossly visibly colon tumors in carcinogen-treated animals fed a high corn oil diet versus decreased incidence and multiplicity of colon tumors in their counterparts fed the high fish oil diet. This dietary inhibition of FPTase may have a practical chemopreventive potential.      

Effect of different levels of dietary corn oil and lard during the initiation phase of colon carcinogenesis in F344 rats

The effect of various levels of polyunsaturated fat (corn oil) and saturated fat (lard) fed during the initiation stage of colon carcinogenesis was studied in male F344 rats. The animals were fed the diets containing 5, 13.6, and 23.5% corn oil or lard 2 weeks before, during, and until 1 week after sc injection of 15 mg azoxymethane [(AOM) CAS: 25843-45-2]/kg body weight, once weekly for 2 weeks (designated as initiation). One week after AOM treatment, groups of animals were transferred to their respective 5% corn oil or lard diets. Additional groups consuming 5% corn oil or lard were transferred to 23.5% corn oil or lard, respectively (post-initiation stage). All animals were fed these diets until the termination of the experiment. Fecal bile acids and colonic mucosal ornithine decarboxylase activity were measured in vehicle-treated animals fed the experimental diets for 14 weeks. Body weights and intakes of total calories, protein, nonnutritive fiber, and micronutrients were comparable among the various dietary groups. The animals fed the 23.5% corn oil diet during the postinitiation stage had a higher incidence of colon tumors than did those fed the 5% corn oil diet, whereas feeding of 23.5 and 13.6% corn oil diets during the initiation stage had no effect. In contrast, animals fed the 23.5 and 13.6% lard diet during the initiation stage and 23.5% lard diet during the postinitiation stage developed more colon adenocarcinomas than did those fed the 5% lard diet. The excretion of fecal deoxycholic acid, lithocholic acid, and 12-ketolithocholic acid and the activity of colonic mucosal ornithine decarboxylase activity were higher in animals fed the 23.5% corn oil or lard diet during the postinitiation compared to the levels in animals fed the 5% corn oil or lard diet.     

Modifying effect of tuna orbital oil rich in docosahexaenoic acid and vitamin D3 on azoxymethane-induced colonic aberrant crypt foci in rats

The modifying effect of dietary tuna (Thunnus thynnus orientalis) orbital oil rich in docosahexaenoic acid (DHA) and vitamin D3 (VD3) on the development of azoxymethane (AOM)-induced colonic aberrant crypt foci (ACF) was investigated in male F344 rats. Animals were given three weekly subcutaneous injections of AOM (15 mg/kg body weight) to induce ACF. The rats were fed the experimental diet containing 5% tuna orbital oil (low fish oil), 23.5% tuna orbital oil (high fish oil), 5% corn oil (low corn oil) or 23.5% corn oil (high corn oil) for 5 weeks, starting 1 week before the first dose of AOM. Animals were sacrificed 2 weeks after the last AOM injection to count colonic ACF and assay the expression of cyclooxygenase (COX)-1 and -2. High corn oil diet significantly increased the development of ACF, when compared with low corn oil diet (P<0.005). High fish oil diet also increased ACF formation compared with low fish oil diet (P<0.01), but the increase was smaller than high corn oil diet. The frequency of ACF was significantly lower in the rats fed high fish oil diet than high corn oil diet (P<0.02). Moreover, frequency of ACF consisted of 4 or more crypts in rats fed the high fish oil diet was significantly lower than that of rats given high corn oil diet. COX-1 and COX-2 expression did not significantly differ among the groups. These results suggest that fish oil derived from tuna, which contains high amounts of DHA and VD3, suppresses the formation and growth of ACF without affecting COX-1 and COX-2 expression, and may have a preventive effect on colon carcinogenesis.     

Both dietary calorie and fat affect the growth of transplanted mammary-tumors in riii/sa mice - the effect of calorie is more profound than the effect of fat

The effects of dietary calories and/or fat on the growth of mammary tumor transplants, their expression of mouse mammary tumor virus (MMTV) and the incidence of lung metastasis were examined in RIII/Sa mice. Starting at 3-4 weeks of age, groups of female mice were fed either high isocaloric diets (16 kcal/day/mouse) containing 25% or 5% corn or fish oil or low isocaloric (10 kcal/day/mouse) diets containing 25% or 5% fish or corn oil. After one week, small pieces (2x2x2 mm) of tumor tissue, prepared from a transplantable mammary tumor, were inserted into the fourth pair of mammary glands of mice, and the mice maintained on their respective diets until sacrifice. All mice developed palpable tumors during a period of 3-4 weeks. After 12 weeks, all those mice that were assessed for tumor burden were sacrificed, tumor weight in each mouse determined, and the level of the expression of MMTV in the tumors evaluated by dot blot hybridization. Our results show that low isocalorie diets, regardless of the type or amount of fat, inhibited tumor growth by at least 60% in comparison to high isocalorie diets. However, mice fed low isocaloric diets containing fish oil were also found to produce smaller tumors (20-40%) as opposed to those mice fed similar, but corn oil containing diets. Fatty acid analyses of mammary tumors and liver tissue of mice fed corn oil and fish oil containing diets revealed that while normal and tumor tissues from both groups contained high levels of polyunsaturated fatty acids, the tissues of mice fed corn oil had the n-6, whereas the mice fed fish oil had the n-3 family of fatty acids. The levels of MMTV expression were found to be unaffected by either caloric or fat content in the diet. In a separate set of experiments, the effect of a low calorie diet on lung metastasis was determined, It was found that mice fed a low calorie diet produced significantly less metastatic lung nodules than those mice fed a high calorie diet: the mean survival time for the former group of mice was 106 days, as compared to only 71 days for the latter group of mice. In conclusion, we suggest that the amount of calories in a diet is more important than the amount or the type of fat in suppressing the growth of transplanted tumors and that a low calorie diet may also lower the incidence of lung metastasis.     

Inhibition of the promotional phase of azoxymethane-induced colon carcinogenesis in the F344 rat by calcium lactate: effect of simulating two human nutrient density levels

The effects of 2 levels of dietary calcium and 2 types of dietary fat on the promotional phase phase of azoxymethane-induced colon cancer in the F344 rat were investigated. During the initiation phase of carcinogenesis all animals were fed a 5% corn oil AIN-76A diet containing 0.32% Ca in the form of calcium lactate. Rats were then injected with azoxymethane (AOM) weekly for 8 weeks. Thereafter, the rats were fed 1 of 3 diet formulations: a 5% corn oil diet or a 20% corn oil or 20% American Blend oil fat diet, with the level of Ca set at either 0.32% of the diet, a nutrient density simulating a daily human intake of approximately 1700 mg Ca/day, or at 0.04% of the diet, reflecting a human daily intake of approximately 200-250 mg of Ca/day, thus modeling 2 human nutrient density levels for calcium. Measurements of fecal pH during the experiment indicated an acidic adaptation of the large bowel to the lactate anion. Analysis of collected fecal samples showed more total fatty acids to be present in the colon when higher amounts of calcium were consumed. However, results of the tumorigenesis study indicated that calcium lactate fed at the 0.32% level significantly inhibited the development of colonic adenocarcinoma in all dietary groups. Taken together, this investigation supports the hypothesis that calcium supplementation can inhibit colon neoplasia in rats fed a high fat diet; however, under the conditions of this study, the 20% fat level did not significantly promote colon cancer as compared to a 5% fat level.     

Influence of dietary-fat on growth of mda-mb231 human breast carcinomas maintained in female athymic nude-mice

The purpose of this study was to assess the effects of the type of dietary fat [corn oil (controls), olive oil, linseed oil, primrose oil, canola oil and fish (Menhaden) oil] and the amount of dietary fat on the growth of MDA-MB231 human breast carcinomas in female athymic nude mice. The different types of fats examined in these studies differ widely in their omega-3, -6 and -9 fatty acid contents, fatty acid chain length and their degree of unsaturation. These fats were fed to the carcinoma bearing mice at 20% of the diet by weight and for 5 to 8 weeks. No significant effect of these diets on mouse body weight gains throughout the study was observed. Compared to the corn oil controls, none of the dietary fats significantly affected the growth of the human breast carcinomas in these animals, with the exception of fish oil which consistently and significantly (P<0.05 to P<0.001) suppressed carcinoma growth. DNA synthesis of the human breast carcinomas derived from the fish oil fed mice was assessed by BrdU and PCNA labeling indices and by H-3-thymidine autoradiographic analysis. Despite the fact that the carcinomas derived from the fish oil fed mice were significantly smaller than the carcinomas from the corn oil fed mice, there were no significant differences in any of these parameters of DNA synthesis between the two groups (corn oil and fish oil) of carcinomas. In contrast, in the human breast carcinomas derived from the fish oil fed mice, a significant increase (P<0.01 to P<0.001) in the rate of (125)IUrd loss (K-L/day) and a significant increase (P<0.05 to P<0.001) in the cell loss factor (phi) (phi=1-T-P/T-D) was observed, compared to carcinomas derived from corn oil fed mice. Analysis of the human breast carcinomas for TBARS, a measure of secondary products of lipid peroxidation, revealed that the carcinomas derived from the fish oil fed mice had significantly increased (P<0.001) concentrations of these products compared to carcinomas derived from corn oil fed mice. These results provide evidence that the suppression of growth of human breast carcinoma MDA-MB231 in athymic nude mice by dietary fish oil appears to be due primarily to an increase in the loss of cells from the carcinomas in lieu of a suppression of DNA synthesis, a phenomenon that may be due to the increased concentration of lipid peroxidation products in the tumor tissue. In the studies designed to examine the effect of the amount of fat on growth of MDA-MB231 human breast carcinomas in athymic nude mice, one group of mice was fed a high fat diet (corn oil, 29%) and a second group of mice was fed a low fat diet (corn oil, 1.8%). Both diets were fed at a restricted level, i.e., 65% of ad libitum. A third group of mice was fed a high fat diet (corn oil, 18.1%) ad libitum. The diets were formulated to assure that mice of each group consumed equal amounts of protein, vitamins, minerals and fiber; mice fed the high fat diets (ad libitum and restricted) consumed equal amounts of fat. Growth of the human breast carcinomas in mice fed the high fat and low fat restricted diets was not significantly different despite the large difference in fat consumption. Growth of the carcinomas in mice fed the high fat diet ad libitum was substantially greater than carcinoma growth in mice fed the restricted high fat diet (P<0.001) despite equal amounts of fat consumption. These results demonstrate that in an environment of energy (caloric) restriction, high levels of dietary fat will not enhance growth of MDA-MB231 human breast carcinomas in athymic nude mice, thus emphasizing the important role for energy (calories) in the enhancement of mammary (breast) tumorigenic processes by high fat diets.     

Effect of dietary fat on growth of MCF-7 and MDA-MB231 human breast carcinomas in athymic nude mice: relationship between carcinoma growth and lipid peroxidation product levels

Human breast carcinoma cell lines MCF-7 and MDA-MB231 were transplanted s.c. to female athymic nude mice at 3-4 weeks of age. At 7-10 days after transplantation, the mice were divided into groups and fed for 6-8 weeks one of the following semi-purified diets containing different amounts and types of fat, i.e. 5% corn oil, 20% corn oil, 20% butter, 19% beef tallow/1% corn oil and 19% fish (Menhaden) oil/1% corn oil. In addition experiments, the fish oil diets were supplemented with antioxidants (vitamin E, 8 g or 2000 IU/kg diet plus tertiary butyl hydroquinone, TBHQ, 4 g/kg diet) or ferric citrate (3 g/kg diet). Tumor peroxidation product levels were assessed by measuring 2-thiobarbituric acid reactants (TBA assay). At the termination of the studies (6-8 weeks of diet feeding) mean human breast carcinoma volume (MCF-7 and MDA-MB231) was the largest in mice fed the 20% corn oil diet, intermediate in mice fed the butter or beef tallow diets and the least in mice fed the fish oil diet. The difference in mean tumor volumes among mice fed the 20% corn oil diet and those fed the fish oil diet was significant (P less than 0.01). When comparing low (5% corn oil) and high (20% corn oil) fat diets, numerical increases in human breast carcinoma volume (MCF-7 and MDA-MB231) were consistently observed in the high-fat diet groups but these differences were not always significant. Tumor lipid peroxidation product levels were determined on the MDA-MB231 tumors; tumor lipid peroxidation levels were significantly (P less than 0.01) increased only in mice fed the fish oil diets. Supplementation of the fish oil diets with antioxidants (vitamin E + TBHQ) significantly reduced the level of tumor peroxidation products and significantly increased tumor volume (P less than 0.05). When tumor lipid peroxidation product levels in the fish oil plus antioxidant fed mice were reduced to the level of that observed in the tumors of the corn oil fed mice, no significant differences in tumor volumes were observed in these two groups. In contrast, supplementation of the fish oil diets with ferric citrate, significantly (P less than 0.05) increased tumor lipid peroxidation product levels and decreased tumor volume. Thus, the type of dietary fat can clearly affect the growth of human breast carcinomas (MCF-7 and MDA-MB231) maintained in athymic nude mice.(ABSTRACT TRUNCATED AT 400 WORDS)     

Effects of high-fat diets rich in either omega-3 or omega-6 fatty acids on UVB-induced skin carcinogenesis in SKH-1 mice

Our previous studies reported that caffeine or voluntary exercise decreased skin tumor multiplicity, in part, by decreasing fat levels in the dermis. These data suggest that tissue fat may play an important role in regulating ultraviolet light (UV) B-induced skin tumor development. In the present study, we explored the effects of high-fat diets rich in either omega-3 or omega-6 fatty acids on UVB-induced skin carcinogenesis. SKH-1 mice were irradiated with 30 mJ/cm(2) of UVB once a day, two times per week for 39 weeks. During UVB treatment, one group of mice was given a high-fat fish oil (HFFO) diet rich in omega-3 fatty acids and the other group of mice was given a high-fat mixed-lipids (HFMLs) diet rich in omega-6 fatty acids. The results showed that, compared with HFML diet, HFFO treatment (i) increased latency for the development of UVB-induced skin tumors; (ii) decreased the formation of papilloma, keratoacanthoma and carcinoma by 64, 52 and 46%, respectively and (iii) decreased the size of papilloma, keratoacanthoma and carcinoma by 98, 80 and 83%, respectively. Mechanistic studies with antibody array revealed that compared with HFML diet, administration of HFFO to the mice significantly decreased the UVB-induced increases in the levels of TIMP-1, LIX and sTNF R1 as well as other several proinflammatory cytokines and stimulated the UVB-induced apoptosis in the epidermis. Our results indicate that omega-3 fatty acids in HFFO diet have beneficial effects against UVB-induced skin carcinogenesis, and these effects may be associated with an inhibition on UVB-induced inflammatory response.