The nonfermentable dietary fiber lignin alters putative colon cancer risk factors but does not protect against DMH-induced colon cancer in rats

Dietary fiber in the prevention of obesity and obesity-related chronic diseases: From epidemiological evidence to potential molecular mechanisms

Obesity is a mostly preventable diet-related disease and currently a major challenge for human populations worldwide. Obesity is a major risk factor for diseases such as type 2 diabetes mellitus (T2DM), cardiovascular disease (CVD) and certain cancers. Dietary fiber is a complex mixture of non-digestible molecules, mostly polysaccharides. Multiple epidemiological studies have demonstrated statistically significant reductions in risks of obesity, T2DM, CVD, colorectal cancer, and pre-menopausal breast cancer with higher dietary fiber intakes. Various direct and indirect mechanisms have been proposed including altered digestion and absorption, stimulation of gut hormones including glucagon-like-peptide-1 (GLP-1) and peptide YY (PYY), reduced appetite, and altered metabolism of bile and cholesterol. These may act via pathways involving G-protein-coupled receptors (GPRs), histone deacetylase (HDAC), and aromatase enzymes. Ultimately, fiber intake contributes to improving glucose levels and insulin sensitivity, lowering risk of T2DM, CVD and certain cancers. Therefore, diets rich in dietary fiber should be encouraged to prevent obesity and associated chronic disease.

Lignin - An underutilized, renewable and valuable material for food industry

Lignin is the second most abundant biorenewable polymers only next to cellulose and is ubiquitous in various plant foods. In food industry, lignin often presented as a major component of by-products from plant foods. In the last decade, the food and nutritional interests of lignin attracted more and more attentions and great progresses have been accomplished. In the present review, the structure, physicochemical properties, dietary occurrence and preparation methods of lignin from food resources were summarized. Then, the versatile activities of food lignin were introduced under the subtitles of antioxidant, antimicrobial, antiviral, antidiabetic and other activities. Finally, the potential applications of food lignin were proposed as a food bioactive ingredient, an improver of food package films and a novel material in fabricating drug delivery vehicles and contaminant passivators. Hopefully, this review could bring new insights in exploiting lignin from nutrition- and food-directed views.

Evaluation of blueberry juice in mouse azoxymethane-induced aberrant crypts and oxidative damage

Blueberry is a plant with a number of nutritional and biomedical capabilities. In the present study we initially evaluated the capacity of its juice (BJ) to inhibit the number of aberrant crypts (AC) induced with azoxymethane (AOM) in mouse. BJ was administered daily by the oral route to three groups of animals during four weeks (1.6, 4.1, and 15.0 μL/g), respectively, while AOM (10 mg/kg) was intraperitoneally injected to the mentioned groups, twice a week, in weeks two and three of the assay. We also included two control groups of mice, one administered distilled water and the other the high dose of BJ. A significant increase of AC was observed in the AOM treated animals, and a mean protection of 75.6% was determined with the two low doses of BJ tested; however, the high dose of the juice administered together with AOM increased the number of crypts more than four times the value observed in animals administered only AOM. Furthermore, we determined the antioxidant potential of BJ with an ex vivo DPPH assay and found a dose-dependent decrease with a mean of 19.5%. We also determined the DNA oxidation/antioxidation by identifying 8-hydroxy-2'-deoxyguanosine adducts and found a mean decrease of 44.3% with the BJ administration with respect to the level induced by AOM. Our results show a complex differential effect of BJ related to the tested doses, opening the need to further evaluate a number of factors so as to determine the possibility of a cocarcinogenic potential.

Soy Saponins Meditate the Progression of Colon Cancer in Rats by Inhibiting the Activity of β -Glucuronidase and the Number of Aberrant Crypt Foci but Not Cyclooxygenase-2 Activity

Objective. The effect of extracted crude soybean saponins on preneoplastic lesions, aberrant crypt foci (ACF), and the related mechanism were investigated. Research Methods and Procedures. Rats were assigned into five groups according to different doses of extracted crude soybean saponins and received 1,2-dimethylhydrazine (DMH) injection in week 5. In week 15, all rats were sacrificed. The number of ACFs, the cyclooxygenase-2 (COX-2) protein expression, the level of prostaglandins E2 (PGE2), and the activity of β-glucuronidase were examined. Results. Results revealed that the consumption of extracted crude soybean saponins decreased the number of ACFs and the activity of β-glucuronidase in rats, while the expression of COX-2 protein and PGE2 level were not affected. Conclusions. Soybean saponins were effective in inhibiting colon cancer by downregulating the activity of β-glucuronidase in colonic mucosa but not the COX-2 protein expression and PGE2 level.

Zinc and zinc related enzymes in precancerous and cancerous tissue in the colon of dimethyl hydrazine treated rats

Trace element zinc deficiency or excess is implicated in the development or progression of some cancers. The exact role of zinc in the etiology of colon cancer is unclear. To cast light on this question, an experimental model of colon carcinogenesis was applied here. Six week old rats were given sub cutaneous injections of DMH (30 mg/kg body weight) twice a week for three months and sacrificed after 4 months (precancer model) and 6 months (cancer model). Plasma zinc levels showed a significant decrease (p<0.05) at 4 months and a greater significant decrease at 6 months (p<0.01) as compared with controls. In the large intestine there was a significant decrease in tissue zinc levels (p<0.005) and in CuZnSOD, and alkaline phosphatase activity (p<0.05) in the pre-cancerous model and a greater significant decrease in tissue zinc (p<0.0001), and in CuZnSOD and alkaline phosphatase activity (p<0.001), in the carcinoma model. The tissue zinc levels showed a significant decrease in the small intestine and stomach (p<0.005) and in liver (p<0.05) in the cancer model. 87% of the rats in the precancer group and 92% rats in the cancer group showed histological evidence of precancerous lesions and carcinomas respectively in the colon mucosa. This study suggests that the decrease in plasma zinc, tissue zinc and activity of zinc related enzymes are associated with the development of preneoplastic lesions and these biochemical parameters further decrease with progression to carcinoma in the colon.

Dietary fibre on cell proliferation in large bowel mucosal crypts near or away from lymphoid nodules and on mineral bioavailability

The effect of consumption for 24 weeks of different amounts (0%, 5% or 10% w/w) of fermentable (pectin and guar gum) or nonfermentable (cellulose and lignin) dietary fibres on cell proliferation and other parameters in large bowel mucosal crypts was studied in rats. In all 12 dietary groups, the crypts located over the distal aggregate of lymphoid nodules (ALN) had more colchicine arrested metaphase figures per midaxial crypt section (MC) and a longer crypt column height than crypts located three to four cm away from this ALN. These differences are attributed to the tropic influence of nodular cells in the ALN. Consumption of fermentable fibre decreased pH in the lumen of the caecum, and glucose, Zn and Cu in serum but increased Ca and Mg in serum. The decrease in caecal pH and serum glucose was significantly correlated with a decrease in MC. Increased intake of the nonfermentable fibre types increased faecal bulk but had no significant correlation with the other measured crypt parameters. Multiple regression analyses was used to model the relationships between the mucosal crypt criterion variables and the two measured predictor variables, caecal pH and serum glucose. Relationships between dietary fibre, ALN, MC, bioavailability of dietary minerals and risk of colorectal cancer are discussed.

Effects of adlay on azoxymethane-induced colon carcinogenesis in rats

Adlay (Coix lachryma-jobi L. var. ma-yuen Stapf) is a grass crop used in traditional Chinese medicine and as a nutritious food. It has been reported that adlay has anti-inflammatory and anti-tumor activity. Cyclooxygenase-2 (COX-2) is an inducible enzyme functionally related to both inflammation and colon carcinogenesis and is the target of many chemopreventive agents. This study investigated the effect of adlay on colon carcinogenesis and COX-2 expression. In a short-term experiment, male F344 rats were fed diets containing different doses of dehulled adlay and received the colon-specific carcinogen, azoxymethane (AOM), by intraperitoneal injection. All rats were killed after 5 weeks of feeding, and the colons were examined for the preneoplastic lesion, aberrant crypt foci (ACF). Dietary dehulled adlay at levels of 10%, 20%, or 40% significantly reduced the numbers of ACF and aberrant crypts. Dehulled adlay reduced the number of ACF of different sizes but did not affect the crypt multiplicity. Most ACF were found in the middle and distal colons; dehulled adlay significantly suppressed the formation of ACF in the middle colon. In a long-term experiment, male F344 rats were fed diets containing different doses of dehulled adlay and injected with AOM. All rats were killed after 52 weeks of feeding, and colons were examined for tumors and COX-2 protein expression. The results indicated that dehulled adlay did not inhibit colon tumors in spite of a slight suppressing effect in the proximal colon. Rats fed diets containing 20% dehulled adlay had less COX-2 protein expression in both proximal and distal colon tumors. The inconsistent effects between COX-2 protein expression and tumor outcome may be due to regional differences in the colon and the malignancy of the tumors. These findings suggest that dehulled adlay suppresses early events in colon carcinogenesis but not the formation of tumors.

The gastrointestinal tract as the portal of entry for foreign macromolecules: fate of DNA and proteins

The gastrointestinal tract (GIT) of mammals is the main portal of entry for foreign DNA and proteins. We have documented the fate of orally administered DNA or protein in the GIT of the mouse. The gene for the Green Fluorescent Protein (GFP) (4.7 kb) and the genomes of bacteriophage M13 (7.25 kb) and adenovirus type 2 (Ad2; 35.9 kb) were used as test DNAs. Persistence of these DNAs in the GIT was monitored by Southern hybridization and fluorescent in situ hybridization (FISH) or by PCR. For studies on proteins, recombinant glutathione-S-transferase was fed to mice. Survival of the protein in the GIT was then assessed by Western blotting. Depending on feeding schedules and food regimens, but irrespective of mouse strain or DNA length, fragments of the GFP gene or other DNAs were detectable for up to 18 h after feeding by Southern blot analysis. The GFP DNA could be visualized by FISH in cecal epithelia. A high fiber diet reduced the time required for food to pass through the GIT, and foreign DNA was cleared more rapidly. A high fat diet or complexing of the foreign DNA with protamine or lipofectin did not extend DNA persistence times. Undegraded GST protein was detected only in foregut contents up to 30 min after feeding. At 15 and 30 min post feeding, trace amounts of GST were found in extracts of the kidney. The GIT is constantly exposed to highly recombinogenic fragments of foreign DNA and to intact foreign proteins. Our data have implications for studies on carcinogenesis and mutagenesis, and on the pathogenicity of infectious proteins such as prions.

Changing concepts of dietary fiber: implications for carcinogenesis

The dietary fiber (DF) hypothesis suggested that DF, as plant cell walls, protected against colorectal cancer. The implicit assumption in much historic literature was that the readily analyzed and quantified nonstarch polysaccharide (NSP) component was critical in cancer protection. However, the presence of polymeric phenolic components such as lignin or suberin has profound effects on the physicochemical properties of the cell walls and largely determines their physiological properties in humans. In certain groups of food plants, degradation of cell walls that contain neither lignin nor suberin releases ferulic acid and other hydroxycinnamic acids. These acids have antioxidant, antimutagenic, and other anticancer effects, including modulation of gene expression and immune response. Reexamination of literature on cancer protection suggests that plant cell walls containing significant amounts of phenolic components may be the most likely to protect against cancer. In the last 30 years, the definition of DF has been incrementally expanded to incorporate NSP extracted from plant cell walls and from sources other than plant cell walls, then resistant starch, and most recently nondigestible oligosaccharides. On the early definitions, increased consumption of DF could only be achieved by increasing the intake of whole grains, brans, or other food plant material that would increase the intake of plant cell walls containing significant amounts of phenolic components. However, the new definitions make it possible to increase "dietary fiber" without consuming any such materials. We suggest that this could have negative connotations for cancer risk in human populations.

Dietary fiber and colorectal neoplasia

PURPOSE

Dietary fiber has been implicated in colorectal neoplasia, despite conflicting evidence. This is a review of the currently available data on the role of dietary fiber in colorectal carcinogenesis.

METHODS

A literature search was conducted using the MEDLINE database. All case-control, longitudinal, and randomized, controlled studies published in English between 1988 and 2000 were identified, as were animal model studies in the period 1986 to 2000. Data from the various studies were tabulated and systematically analyzed, with particular emphasis on the effect of dietary fiber on tumor incidence and luminal parameters such as short chain fatty acids.

RESULTS

Epidemiologic correlation studies show a high intake of dietary fiber to be associated with a lower risk of colorectal neoplasia. Thirteen of the 24 case-control studies reviewed demonstrated a protective effect of dietary fiber against colorectal neoplasia, and 16 showed a protective effect of vegetables or vegetable fiber. On the other hand, of 13 longitudinal studies in various cohorts, only 3 demonstrated a protective effect of fiber and 4 a protective effect of vegetables or vegetable fiber. The five published randomized, controlled trials all investigated the effect of increased fiber intake on short-term adenoma recurrence; however, none showed any significant protective effect. Among 19 experimental studies in animal models, 15 showed a protective effect of fiber against tumor induction compared with controls. Animal studies also showed that poorly fermentable fibers (e.g., wheat bran and cellulose) were more protective than soluble fibers (e.g., guar gum and oat bran), which sometimes enhanced carcinogenesis. No clear correlation was found between luminal pH or short chain fatty acids and tumor induction.

CONCLUSIONS

On the basis of current data, there is little evidence to support the use of dietary fiber supplements to reduce the risk of colorectal neoplasia. Lifelong and early exposure may be important but are difficult to study. Other risk factors interact with the effects of dietary fiber.

Comparative effects of three resistant starch preparations on transit time and short-chain fatty acid production in rats

A high-fiber diet may protect against colon cancer because of the butyrate generated in the colon by bacterial fermentation of nonstarch polysaccharides. Butryrate can reverse neoplastic changes, at least in vitro, and resistant starch (RS) represents a source of butyrate in vivo. We examined the effects of replacing normal maize starch in the diet of rats with three preparations of RS on the amounts of starch, butyrate, and other short-chain fatty acids in the cecum. We examined the effects on fecal bulking and transit time, which have been suggested to protect against colon cancer. The RS preparations that we tested were potato starch, high-amylose maize starch, and an alpha-amylase-treated high-amylose maize starch. All had major effects on fecal weight and on the weight of the cecum but only slightly shortened transit times. All increased the amount of starch reaching the cecum and increased short-chain fatty acid production in the cecum; potato starch had the greatest effect and high-amylose maize starch the least. Potato starch, unlike high-amylose maize starch, enhanced the proportion of butyrate. Thus there were marked differences among sources of RS, even though these were all classified as RS2. The significance for colon cancer is discussed.

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.

Dietary fibres may protect or enhance carcinogenesis

Dietary fibre (DF) is widely considered to protect against cancer, especially colorectal cancer. However, a large prospective epidemiological study has shown no apparent effect of DF intake on the development of colorectal cancer. We suggest that this may be because the term DF represents a wide range of materials, some able to protect, but some able to enhance carcinogenesis. This is consistent with data from animal carcinogenesis experiments. Most of the DF in western diets is in the form of plant cell walls, but these vary in their composition and it is unlikely that all types are protective. The few data available indicate that plant cell walls containing suberin or lignin may be the most protective, although they are present in only small amounts in food plants. DFs are also added to foods. These include components obtained from plant cell walls, such as pectins, as well as soluble DFs from other sources. In general, animal carcinogenesis experiments indicate that soluble DFs do not protect and some may enhance carcinogenesis. Few human intervention studies have been done on DF or sources of DF, with the exception of wheat bran, a good source of DF, which has been shown to protect. Possible mechanisms whereby DF may enhance carcinogenesis are discussed. In addition to DFs, resistant starches and non-digestible oligosaccharides are added to foods; these, like DF, escape digestion in the small intestine. However, so far only a few animal carcinogenesis experiments have been reported using these materials, and no human intervention studies. We believe caution should be exercised in the addition of such materials to food.