Maurice R. Bennink

10 Soyfoods, isoflavones and risk of colonic cancer: a review of the in vitro and in vivo data

Soy foods and soybean components have received considerable attention of late for their potential role in reducing cancer risk. Although the relationship between soy intake and the risk of breast and prostate cancer has been the focus of most interest, the relationship between soy intake and other cancers, including colorectal cancer, has also been studied. Several anti-carcinogens have been identified in soybeans, but most enthusiasm for the potential anti-cancer effects of soy undoubtedly stems from work involving soybean isoflavones. Isoflavones have a limited distribution in nature, and, for practical purposes, soyfoods are the only nutritionally relevant dietary source of these phytochemicals. Isoflavones are weak oestrogens but possess other potentially important biological attributes independent of their ability to bind to the oestrogen receptor. The isoflavone genistein inhibits the growth of most types of hormone-dependent and hormone-independent cancer cells in vitro, including colonic cancer cells. Several mechanisms for the in vitro anti-cancer effects of genistein have been proposed, including effects on signal transduction. A number of epidemiological studies, primarily of Asian origin, have examined the relationship between soy intake and the risk of colorectal cancer. Although these studies provide little support for a protective effect of soy, concerns have been raised about the completeness of the soy intake data, since soy was not the focus of these studies and most of this research was conducted prior to the recent interest in the anti-cancer effects of soy. The effect of soy/isoflavone intake has also been studied in rodents, but again these data are conflicting and provide only modest support for a protective effect. Although the relationship between soy intake and colonic cancer risk is certainly worthy of further investigation, there is, at the moment, very limited support for soy exerting a protective effect against this type of cancer.

Prevention of precancerous colonic lesions in rats by soy flakes, soy flour, genistein, and calcium

The main purpose of this research was to determine whether diets containing soy products would inhibit the early stages of azoxymethane-induced colon cancer in F344 rats. Additional objectives were to determine whether feeding starch instead of sucrose, feeding additional calcium (0.5% compared with 0.1%), or feeding a low-fiber powdered enteral formula would influence early colon carcinogenesis. Colon cancer was initiated with 2 injections of azoxymethane (15 mg/kg body wt) and a 12-wk dietary treatment period was started 1 wk after the second injection. Precancerous colon lesions were assessed as foci with aberrant crypts (FAC). The mean numbers of FAC were 133 [soy concentrate (low concentration of phytochemicals)], 111 (starch substituted for sucrose), 98 [full-fat soy flakes (whole soybeans)], 87 (defatted soy flour), 77 (0.015% genistein), and 70 (0.5% Ca). The soy flour and full-fat soy flake diets contained 0.049% genistein derivatives (primarily glycosides), but were less effective in inhibiting the formation of FAC than the diet containing 0.015% genistein (as the aglycone). Eating soybeans and soy flour may reduce the early stages of colon cancer.

Whole Grape Intake Impacts Cardiac Peroxisome Proliferator-Activated Receptor and Nuclear Factor κB Activity and Cytokine Expression in Rats With Diastolic Dysfunction

Prolonged hypertension is the leading cause of heart failure. Failing hearts show reduced peroxisome proliferator-activating receptor (PPAR) activity and enhanced nuclear factor &kgr;B (NF-&kgr;B) activity, which together modify cardiac inflammation and fibrosis. In vitro studies suggest that phytochemicals alter PPAR and NF-&kgr;B activity, but the capabilities of a phytochemical-rich diet are less understood. Grapes contain an array of commonly consumed dietary phytochemicals. In Dahl salt-sensitive hypertensive rats, we showed previously that dietary provision of whole table grape powder (3% weight:weight) for 18 weeks reduced blood pressure, cardiac hypertrophy, and diastolic dysfunction. The hypothesis tested here is that, in this model, phytochemical provision from whole grape powder impacts cardiac PPAR and NF-&kgr;B activity and their related gene transcripts. Grape-fed rats had enhanced PPAR-&agr; and PPAR-&ggr; DNA binding activity but reduced NF-&kgr;B DNA binding activity. RT-PCR revealed that grape-fed rats showed upregulated mRNA for PPAR-&agr;, PPAR-&ggr; coactivator-1&agr;, PPAR-&ggr;, and the cytosolic NF-&kgr;B inhibitor, inhibitor-&kgr;B&agr;. By contrast, grape-fed rats showed downregulated mRNA for tumor necrosis factor-&agr; and transforming growth factor-&bgr;1. Finally, grape-fed rats showed significantly reduced cardiac tumor necrosis factor-&agr; and transforming growth factor-&bgr; protein expression, increased inhibitor-&kgr;B&agr; expression, and reduced cardiac fibrosis. In the Dahl salt-sensitive rat, chronic intake of grapes altered cardiac transcripts related to PPAR and NF-&kgr;B that may be significant to the observed diet-associated cardioprotection.

Dietary Cooked Navy Beans and Their Fractions Attenuate Colon Carcinogenesis in Azoxymethane-Induced Ob/Ob Mice

Based on the protective effects of cooked dry bean consumption in a human intervention study, we evaluated which fraction of cooked dry beans is responsible for its cancer-preventive effects. Cooked navy beans (whole beans), the insoluble fraction (bean residue) or soluble fraction of the 60% (vol:vol) ethanol extract of cooked navy beans (bean extract), or a modified AIN-93G diet (16.6% fat including 12.9% lard) as control diet were fed to 160 male obese ob/ob mice after 2 azoxymethane injections. In comparison to control-fed mice, dysplasia, adenomas, or adenocarcinomas were detected in fewer mice on either bean fraction diet (percent reduction from control: whole beans 54%, P = 0.10; bean residue 81%, P = 0.003; bean extract 91%, P = 0.007), and any type of colon lesions, including focal hyperplasia, were found in fewer mice on each of the 3 bean diets percent reduction from control: whole bean 56%, P = 0.04; bean residue 67%, P = 0.01; bean extract 87%, P = 0.0003. These results suggest that both the soluble and the insoluble fraction of the extract contribute to the cancer-protective effect of cooked navy beans.

Enhancement of 1,2-dimethylhydrazine-induced colon carcinogenesis in mice by dietary agar

The effect of dietary agar on colon carcinogenesis was investigated. The frequency and number of tumours of the colon induced by subcutaneous injections of 1,2-dimethylhydrazine (DMH) was examined in male CF1 mice fed different levels of agar and fat in the diet. The mice were fed one of four diets: a low-fat, low-fibre control diet, the control diet with added agar, a high-fat diet, or a high-fat, agar-containing diet. The mice were injected with 20 mg DMH/kg body weight weekly for 20 wk. Controls were injected with saline. The mice fed agar had significantly more colon tumours per animal than those fed diets that did not contain agar and there was a slightly increased frequency of malignant tumours in agar-fed mice compared with that in mice given the control diet. Feeding high-fat diets only slightly increased the incidence of malignant tumours and did not significantly affect the number of tumours per animal. No tumours occurred in mice injected with saline. Since it has been suggested that faecal steroids have a co-carcinogenic role in colon carcinogenesis, faecal bile acids and neutral sterols were determined. Feeding agar decreased the faecal neutral sterol and bile-acid concentrations, whereas feeding high-fat diets did not affect the faecal bile-acid concentrations and increased faecal neutral sterol concentrations only when agar was also in the diet. The results of this study show that dietary agar enhances DMH-induced colon carcinogenesis in mice even though the level of faecal steroids is lowered.

Dietary Soy Reduces Colon Carcinogenesis in Human and Rats

The anti-cancer activity of individual soy phytochemicals (non-nutritive plant components with biological activity) have been extensively studied in vitro and in vivo. There is much less data relating soy consumption and colon cancer. This chapter will summarize epidemiologic studies and discuss the animal experiments and one intervention study that have evaluated the potential of dietary soy to inhibit colon carcinogenesis.

Inflammation-associated serum and colon markers as indicators of dietary attenuation of colon carcinogenesis in ob/ob mice.

Although inflammatory cytokines and obesity-associated serum proteins have been reported as biomarkers of colorectal adenoma risk in humans, little is known of biomarkers of response to interventions that attenuate tumorigenesis. Dietary navy beans and their fractions attenuate colon carcinogenesis in carcinogen-induced genetically obese mice. We hypothesized that this attenuation would be associated with changes in inflammatory cytokines and obesity-related serum proteins that may serve as measures of efficacy. ob/ob mice (n = 160) were injected with the carcinogen azoxymethane (AOM) to induce colon cancer and randomly placed on one of four diets (control, whole navy bean, bean residue fraction, or bean extract fraction) for 26 to 28 wk. Serum was analyzed for 14 inflammation- or obesity-related proteins, and colon RNA was analyzed for expression of 84 inflammation-associated genes. Six of 14 serum proteins were increased [i.e., interleukin (IL)-4, IL-5, IL-6, IL-10, IFNγ, granulocyte macrophage colony-stimulating factor] in hyperplastic/dysplastic stages of colon carcinogenesis. Bean-fed mice had significantly higher monocyte chemoattractant protein-1 and lower IL-6 levels in serum. In colon mucosa, 55 of 84 inflammation-associated genes differed between AOM-induced and noninduced mice. Of the 55 AOM-induced genes, 5 were counteracted by bean diets, including IL-6 whose increase in expression levels was attenuated by bean diets in AOM-induced mice. In summary, IL-6 emerged as a serum protein that was increased in hyperplastic/dysplastic stages of colon carcinogenesis, but attenuated with bean-based diet in serum and colon mucosa. Changes in a subset of inflammation-associated serum proteins and colon gene expression may serve as response indicators of dietary attenuation of colon carcinogenesis.

Diet-relevant phytochemical intake affects the cardiac AhR and nrf2 transcriptome and reduces heart failure in hypertensive rats.

Intake of phytochemical-rich diets is inversely related to hypertension. Phytochemicals alter in vitro aryl hydrocarbon receptor (AhR) and NF-E2 related factor (nrf2) transcription factor activity and related genes pertinent to antioxidant defense. However, it is unknown if these molecular effects occur in the heart with dietary intake of physiologically relevant phytochemicals and if this correlates with reduced hypertension-associated heart failure. This extended feeding study used whole grapes as a model of a phytochemical-rich food and hypertensive heart failure-prone rats to assess mechanisms of effect. Grape intake reduced cardiac hypertrophy and fibrosis and improved diastolic function. At the development of diastolic dysfunction, hypertensive rats show reduced AhR activity, reduced expression of AhR-regulated genes, reduced glutathione and reduced activity of glutathione-regulating proteins. However, grape intake significantly increased cardiac AhR and nrf2 activity, Phase I/II gene transcripts and protein activity related to antioxidant defense. Heart failure is the leading cause of morbidity and mortality in the aged and the intake of phytochemicals from fruits and vegetables decreases with age. Concentrated antioxidant nutrient trials have failed to affect heart failure. However, this study demonstrates that diet-relevant intake of non-nutrient phytochemicals significantly reduces heart failure progression. Therefore, this study suggests that higher intake of phytochemical-containing foods may achieve cardiac benefits that isolated antioxidant supplements may not. In summary, intake of diet-relevant phytochemicals altered the cardiac antioxidant transcriptome, antioxidant defense, oxidative damage and fibrosis. Regular phytochemical intake may therefore increase cardiac resistance to cardiac pathology instigated by prolonged hypertension.

Incorporation of n-3 fatty acids into WB-F344 cell phospholipids inhibits gap junctional intercellular communication

In this investigation, we demonstrate that rat liver epithelial (WB-F344) cells grown in medium supplemented with n−3 fatty acids (FA) results in the inhibition of gap junctional intercellular communication (GJIC). Cells incubated for 48 hr in medium containing 50 μM α-linolenate (18∶3n−3) resulted in a 60% inhibition of GJIC, compared to control cells, while treatment with γ-linolenate (18∶3n−6) had no effect. Supplementation with octadecatetraenoate (18∶4n−3), eicosapentaenoate (20∶5n−3), and docosahexaenoate (22∶6n−3), inhibited GJIC by 42%, 28%, and 18%, respectively. Incubation with each of the n−3 FA markedly increased the total n−3 FA content of cellular phospholipids (PL). Growing cells in medium containing 50 μM arachidonate (20∶4n−6) plus 50 μM 18∶3n−3 partially attenuated the inhibition of GJIC induced by 18∶3n−3. The mechanism by which n−3 FA inhibit GJIC remains to be determined.

Metabolism of 1,2‐dimethylhydrazine by cultured rat colon epithelial cells

The colon carcinogen 1,2-dimethylhydrazine (DMH) was cultured with rat colon epithelial cells to determine if these cells have the ability to metabolize DMH. Colon epithelial cells isolated from conventional and germfree Sprague-Dawley rats were incubated in CMRL 1066 supplemented medium containing 14C-DMH. Cells from both groups of rats metabolized DMH to gaseous metabolites, to metabolites in the medium that were putatively identified as azoxymethane and methylazoxymethanol, and to products that bound to DNA. Cells from germfree rats metabolized DMH at an equal or greater rate than cells from conventional rats for the criteria examined. This report demonstrates that rat colon epithelial cells can metabolize DMH without previous metabolism by other tissues or colon bacteria.