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

A diet containing alpha-cellulose and fish oil reduces aberrant crypt foci formation and modulates other possible markers for colon cancer risk in azoxymethane-treated rats

There is a need for better understanding of the roles of dietary fats and fibers in colon cancer risk. We examined the effect of different dietary fiber and fat sources on an azoxymethane (AOM)-induced colon cancer in rats. In a 2 x 3 factorial design, rats were fed a semipurified diet containing soy-derived fiber (Fibrim), alpha-cellulose (Solkafloc) or resistant starch (RS; Hi-maize) at 10 g dietary fiber/100 g diet, combined with fish oil (FO) or sunflower seed oil (SSO) at 10 g/100 g diet, and lard added to all diets at 10 g/100 g, to provide a total of 20 g mixed fat/100 g diet. Sprague-Dawley rats (28 d of age) consumed diets for 4 wk and then two doses of AOM (15 mg/kg body) were administered 1 wk apart by subcutaneous injection. Rats were killed after 13 wk of consuming experimental diets. Colons were fixed in formalin and aberrant crypt foci (ACF) were quantified after staining. ACF counts were higher (+66%, P < 0.01) in rats fed SSO and RS, than in those fed alpha-cellulose and FO. Rats fed FO had 19% fewer ACF than those fed SSO (P < 0.05). alpha-Cellulose was associated with the highest cecal butyrate concentration (P < 0.001), the highest beta-glucuronidase specific activity (P < 0.001) and the lowest cecal water cytotoxicity (P < 0.001) relative to soy fiber- and RS-fed rats. There were inverse correlations between the number of ACF and cecal butyrate concentration (r = -0.33, P < 0.05) and between cecal water cytotoxicity and beta-glucuronidase activity (r = -0.70, P < 0.001). The greatest protection was associated with alpha-cellulose as the fiber source and FO as the fat source as measured by colon ACF numbers in rats.

Phyto-oestrogens and cancer

Phyto-oestrogens have been suggested to have a preventive effect against various cancers. This review includes a discussion of the consumption of phyto-oestrogen-rich foods such as soy, a source of isoflavones, and whole grain products, which contain lignans, and their role in the prevention of breast, prostate, and colon cancer. In women, a soy-containing diet is only slightly protective against breast cancer, if at all, but is more likely to be beneficial if initiated before puberty or during adolescence. These findings are supported by conclusions of studies of immigrants and other epidemiological studies. However, in one case-control study and one prospective study, a low-lignan diet increased the risk of breast cancer. Experimental evidence also exists for an inhibitory effect of soy and rye bran on prostate-cancer growth and for rye bran or isolated lignans on colon cancer. Whether these observed protective effects are caused by the presence of dietary phyto-oestrogens, or whether they are merely indicators of a healthy diet in general, has not been established.

Synergistic effect of genistein and BCNU on growth inhibition and cytotoxicity of glioblastoma cells

OBJECTIVE

Recent experiments have shown that dietary soy isoflavones such as genistein can significantly suppress invasiveness and growth of a number of human malignancies. This study examined whether genistein, at a concentration typical of plasma levels following soy diet intake, in combination with 1,3-bis(2-chloroethyl)-1-nitrosourea (BCNU, carmustine) exhibited an additive or synergistic inhibitory effect on the growth of glioma cells.

METHODS

The human glioblastoma multiforme (GBM) cell line U87 and the rodent C6 glioma were treated with genistein at 4 microM, combined with BCNU (0-50 microM). Monolayer cell growth and cytotoxicity, as measured by colonigenic survival in soft agarose, were then compared in control and drug-treated cultures. Presence of apoptosis, using the DNA ladder assay and laser scanning cytometry (LSC), was investigated in all cell lines at those concentrations where an enhancement of antiproliferative effect of BCNU in presence of genistein was observed.

RESULTS

A 32-41% increase in monolayer growth inhibition and a 28-42% increase in colony cytotoxicity in the U87 cell line were observed when genistein (4 microM) was added to BCNU in the 0-10 microM dose range. In the C6 cell line, a 30-36% increase in monolayer growth inhibition and a 39-54% increase in colony cytotoxicity were observed with the BCNU dose range of 0-50 microM. All experiments showed a significant increase in growth inhibition and a decrease in colonogenic survival (P < 0.05). We were unable to detect apoptosis in any of the lines when genistein was combined with BCNU.

CONCLUSION

These results indicate that genistein at typical adult dietary plasma levels can significantly enhance the antiproliferative and cytotoxic action of BCNU. The implication for treatment of GBM may be a reduction in the chemotherapeutic dose recommendations of these agents and subsequently a decrease in the risk of treatment sequelae for these patients.

Amelioration of cisplatin toxicity by a fermented grain food product

The most noticeable hypothesis regarding the pathogenesis of cisplatin toxicity, seen mainly in kidney and intestine, is oxidative stress, an imbalance between free-radical generating cisplatin and radical scavenging systems. This paper describes the role of the antioxidant system in cisplatin-induced toxicity and the protective effect by a processed grain food (Antioxidant Biofactor: AOB), which has been shown to exhibit strong antioxidant activity. Male Fischer 344 rats were used. They were pre-fed either a basal diet (control, 15 g/day) or the diet supplemented with AOB to provide 6.5% or 20% of total diet throughout the experiment. Cisplatin (5 mg/kg, i.v.) was administered at the start of the experiment, and the animals were sacrificed 5 days later. Blood urea nitrogen (BUN) and plasma creatinine, NO2(-) and NO3(-) (NOx) were determined from the plasma. The levels of 4-hydroxy-2-nonenal (a lipid peroxidation product), 8-hydroxy-deoxyguanosine (8-OHdG, an oxidatively modified DNA adduct) and nitrotyrosine were histologically analyzed. The cisplatin administration resulted in a loss of body weight and elevations of BUN, serum creatinine and NOx levels, whereas AOB supplement reversed these effects. The severe morphological damages induced in the kidney and intestine by the cisplatin administration were markedly improved in the AOB group. The levels of lipid peroxidation, 8-OHdG, and nitrotyrosine all paralleled the morphological damage. The AOB effect was dose dependent. In conclusion, the present study suggests that certain food additives like AOB may be of benefit against the side effects of cisplatin.

Clinical characteristics and pharmacokinetics of purified soy isoflavones: single-dose administration to healthy men

BACKGROUND

Soy isoflavones are potential cancer chemoprevention treatments.

OBJECTIVE

We conducted safety studies of purified unconjugated genistein, daidzein, and glycitein, and defined pharmacokinetic parameters for their absorption and metabolism.

DESIGN

Thirty healthy men ingested a single dose of 1 of 2 isoflavone preparations purified from soy. The delivered doses of genistein (1, 2, 4, 8, or 16 mg/kg body wt) were higher than those previously administered to humans. Formulation A was composed of 90 +/- 5% genistein, 10% daidzein, and 1% glycitein. Formulation B was composed of 43% genistein, 21% daidzein, and 2% glycitein.

RESULTS

We observed no clinically significant behavioral or physical changes after treatment. We observed elevations in lipoprotein lipase and hypophosphatemia that were possibly related to the treatment but that were associated with no clinical toxicity. Considerable quantities of isoflavones were excreted in urine as conjugates. The terminal elimination rate, elimination half-life, area under the curve, maximum plasma concentration, apparent systemic clearance, and volume of distribution were estimated for genistein and daidzein. The mean elimination half-lives with both formulations were 3.2 h for free genistein and 4.2 h for free daidzein. The mean pseudo half-lives were 9.2 h for total genistein and 8.2 h for total daidzein.

CONCLUSIONS

Dietary supplements of purified unconjugated isoflavones administered to humans in single doses exceeding normal dietary intake manyfold resulted in minimal clinical toxicity. Genistein and daidzein (free and total) were rapidly cleared from plasma and excreted in urine.

Isolating antigenotoxic components and cancer cell growth suppressors from agricultural by-products

Commercial processing wastes or by-products of crops were found to be sources of antimutagens and human tumor cell growth suppressors. We developed a microplate method to measure genomic DNA damage in Chinese hamster ovary cells with a modified single cell gel electrophoresis (SCGE) assay. This allowed us to measure the repression of 2-acetoxyacetylaminofluorene (2AAAF)-induced DNA damage by very small amounts of complex mixtures, fractions or individual chemicals isolated from agricultural by-products. We previously demonstrated that PCC, an ethanol extract of a commercial soybean processing by-product, repressed induced genomic DNA damage in mammalian cells. PCC was separated into a series of chemically defined fractions and two fractions (PCC70 and PCC100) repressed mutagen-induced damage. Of the isoflavones isolated from soybean fraction PCC70, daidzein expressed antigenotoxic activity, however, genistin and genistein enhanced DNA damage. An antigenotoxic response also was observed with a fraction isolated from corn distillate solids (CDS40). We developed a microplate assay to measure the suppression of the growth rate of human cancer cells in which the cytostatic/cytotoxic status at each concentration of the test sample was quantitatively determined. Genistein, genistin, daidzein and daidzin isolated from soybean fraction PCC70 expressed a wide range of growth suppression of HT-29 human colon cancer cells. The biological assays were integrated with, and directed, the separation and analytical chemistry component of this project. Compounds were purified from biologically active fractions and the structure of individual chemicals was determined with analytical HPLC and LC-mass spectroscopy (LC-MS). This research may lead to the isolation of novel chemoprotectants from agronomic commercial processing products and by-products.

The influence of dietary proteins on colon cancer risk

Experimental evidence is accumulating from animal models and in vitro data which shows that dietary proteins can influence cancer expression, some having a promotional influence, others a preventative effect relative to an arbitrarily established standard diet. This result will to a degree be determined by the nature of the cancer model under study. Dairy proteins have been shown to be relatively protective when compared with defatted soybean meal and cooked red meat in the rat dimethylhydrazine-induced (DMH) colon cancer model. Some epidemiological evidence supports these experimental observations. Both protein and fat appear to be influencing outcome, with potential for interactive effects. A number of possible mechanisms have been postulated as to how these proteins and closely associated factors could be influencing colon cancer risk, an area that deserves more investigation. Combinations of foods such as dairy foods with cereals and/or probiotic bacteria provide potentially interesting alliances in reducing colon cancer risk. The combining of relatively protective agents deserves more investigation as to its potential, in devising functional foods and diets worthy of further evaluation, in animal models of cancer, and human intervention studies using relevant endpoint markers.

Selective estrogen receptor modulators in reproductive medicine and biology

Estrogen replacement therapy has significant potential benefits for postmenopausal women, such as improvement of menopausal symptoms and protection from osteoporosis, but it may also increase a woman's risk of breast cancer. Also, some women do not take hormone replacement therapy because of such undesirable side effects as breast tenderness and uterine bleeding. Therefore, there is much interest in the development of compounds that provide the benefits of estrogen replacement therapy without the risks and side effects. The selective estrogen receptor modulators make up one class of compounds with both estrogen agonist and antagonist activity. This review discusses the clinical indications, risks, benefits, and mechanisms of action of selective estrogen receptor modulators and related compounds.

Diet and prevention of colorectal cancer

There is a 20-fold difference in incidence rates of colorectal cancer between the areas of highest incidence (North America and Australia) and lowest incidence (India). Animal studies, epidemiologic research, and clinical trials continue to focus on diet in the search for responsible environmental factors. Between 1997 and 1999, a number of research areas have had considerable activity, and they provide the focus for this review. Among foods, vegetables, cereals, and soy have been topics of recent research. Nutrients from foods and supplements have also gained attention, including n-3 fatty acids, calcium, and B vitamins. Gene-environment interactions are beginning to be studied in populations. Studies of the interaction between polymorphisms in the gene for methylenetetrahydrofolate reductase (MTHFR) and dietary components for risk of both colorectal cancer and adenomatous polyps provide a glimpse into the future of diet and cancer research.

Promotion of health by soy isoflavones: efficacy, benefit and safety concerns

Cardiovascular diseases, osteoporosis-related hip fractures, and various cancers of the colon, prostate, uterus, and breast are remarkably less prevalent in Asia than in other industrialized countries. It is believed that the large consumption of soy products in Asian countries is contributory to the reduction of these chronic disorders. Genistein is a major isoflavone found in most soy products and plays an important role in the promotion of human health. Extensive epidemiological, in vitro, and animal studies have been performed, and most studies indicate that genistein has beneficial effects on a multitude of human disorders, including cancers, cardiovascular diseases, osteoporosis, and postmenopausal symptoms. To date, there is an abundance of promising studies supporting genistein's potential uses, but further research is still needed to validate its preventative and therapeutic efficacy. In addition, the adverse effects of genistein have drawn public attention. More studies are required to assess the potential detrimental effect of genistein, and a benefit-risk ratio should be considered before future clinical studies are performed.

Isoflavonoids and chronic disease: mechanisms of action

Soy and its isoflavones are associated with a reduced risk of chronic disease. The mechanisms of action of isoflavones include their roles as weak estrogens, inhibitors of tyrosine kinase-dependent signal transduction processes and as cellular antioxidants. Although estrogen receptor beta binds genistein with an affinity close to that of 17beta-estradiol, it remains to be determined whether it is a mediator of genistein's activity in vivo. Genistein's inhibition of protein tyrosine kinases is not limited to direct effect on these kinases, but may result from alteration in kinase expression. Genistein is not a particularly good scavanger of cellular oxidants; however, it reacts vigorously with the prooxidant hypochlorous acid, produced by neutrophils as part of the inflammatory response. The chlorinated isoflavones may have altered biochemical and biological effects compared to their parent compounds and may provide increased protection against inflammatory disease.