Fibre and cancer of the colon

The Role of Inositols in Endocrine and Neuroendocrine Tumors

Inositols have demonstrated a role in cancer prevention and treatment in many kinds of neoplasms. Their molecular mechanisms vary from the regulation of survival and proliferative pathways to the modulation of immunity and oxidative stress. The dysregulation of many pathways and mechanisms regulated by inositols has been demonstrated in endocrine and neuroendocrine tumors but the role of inositol supplementation in this context has not been clarified. The aim of this review is to summarize the molecular basis of the possible role of inositols in endocrine and neuroendocrine tumors, proposing it as an adjuvant therapy.

Broad Spectrum Anticancer Activity of Myo-Inositol and Inositol Hexakisphosphate

Inositols (myo-inositol and inositol hexakisphosphate) exert a wide range of critical activities in both physiological and pathological settings. Deregulated inositol metabolism has been recorded in a number of diseases, including cancer, where inositol modulates different critical pathways. Inositols inhibit pRB phosphorylation, fostering the pRB/E2F complexes formation and blocking progression along the cell cycle. Inositols reduce PI3K levels, thus counteracting the activation of the PKC/RAS/ERK pathway downstream of PI3K activation. Upstream of that pathway, inositols disrupt the ligand interaction between FGF and its receptor as well as with the EGF-transduction processes involving IGF-II receptor and AP-1 complexes. Additionally, Akt activation is severely impaired upon inositol addition. Downregulation of both Akt and ERK leads consequently to NF-kB inhibition and reduced expression of inflammatory markers (COX-2 and PGE2). Remarkably, inositol-induced downregulation of presenilin-1 interferes with the epithelial-mesenchymal transition and reduces Wnt-activation, β-catenin translocation, Notch-1, N-cadherin, and SNAI1 release. Inositols interfere also with the cytoskeleton by upregulating Focal Adhesion Kinase and E-cadherin and decreasing Fascin and Cofilin, two main components of pseudopodia, leading hence to invasiveness impairment. This effect is reinforced by the inositol-induced inhibition on metalloproteinases and ROCK1/2 release. Overall, these effects enable inositols to remodel the cytoskeleton architecture.

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.

Anticarcinogenic, hypocholesterolemic, and antagonistic activities of Lactobacillus acidophilus

Lactobacillus acidophilus is considered to possess health-promoting attributes. These include anticarcinogenic and hypocholesterolemic properties and antagonistic action against intestinal and food-born pathogens. L. acidophilus can also survive the hostile environment and establish in the complex ecosystem of the gastrointestinal tract. Therefore, the beneficial effects of ingesting L. acidophilus accrue over a longer period than those organisms that cannot colonize the gut. However, the exact mechanisms of these attributes are not known. Presumably, the anticarcinogenic activity may be attributed to production of compounds and/or conditions that inhibit the proliferation of tumor cells, suppression of microorganisms that convert procarcinogens to carcinogens, and degradation of carcinogens formed. They hypocholesterolemic effect is probably exerted by inhibition of 3-hydroxy-3-methylglutaryl CoA reductase, which is a rate-limiting enzyme in endogenous cholesterol biosynthesis in the body and by promoting the excretion of dietary cholesterol in feces as a result of coprecipitation in the presence of deconjugated bile acids in the intestine and/or adsorption by the organisms. The antagonistic effect against pathogens and other organisms is possibly mediated by competition for nutrients and adhesion sites, formation of metabolites such as organic acids, hydrogen peroxide, and production of antibiotic-like compounds and bacteriocins.

Inhibition of rat mammary carcinogenesis by inositol hexaphosphate (phytic acid). A pilot study

Since phytic acid (inositol hexaphosphate, InsP6) and inositol (Ins) have been demonstrated to have anti-tumor and anti-cell proliferative action in several experimental models of carcinogenesis, in a pilot study we have examined their effect on 7,12-dimethylbenz(a)anthracene (DMBA)-induced rat mammary tumor model. Starting a week prior to induction with DMBA, the drinking water of female Sprague-Dawley rats was supplemented with either: 15 mM InsP6, 15 mM Ins, or 15 mM InsP6 + 15 mM Ins; a control group received no inositol compounds. Animals (55-day-old) were given a single dose of DMBA (20 mg) in 1 ml of sesame oil by oral intubation. Four additional groups not receiving DMBA, but drinking tap water, InsP6, Ins, or InsP6 + Ins of the same molarity as experimental groups were observed for the duration of the study to monitor for any putative toxicity following this long-term treatment. As opposed to the DMBA-only group, rats treated with InsP6 +/- Ins showed a 48% reduction in the number of tumors/tumor bearing animal (tumor multiplicity) and a 40% reduction in the number of tumors/rat. In contrast to 20% rats in DMBA-only group, only 0-8% animals in the treatment group had 5 or more tumors. Likewise, the tumor incidence was reduced by 19% in InsP6 +/- Ins as compared to control untreated animals. The tumors in the treated groups were also 16% smaller in size. Data from this pilot study suggest that in addition to being effective against colon cancer, InsP6 +/- Ins may be protective against mammary carcinoma as well; additional studies are however warranted.

Suppression of colonic cancer by dietary phytic acid

Large differences exist between human populations in the frequency of colonic cancer. Epidemiological evidence indicates that these differences are strongly influenced by country of residence, and a negative correlation has been found between the fiber content of the diet and frequency of colonic cancer. This has prompted the hypothesis that high-fiber diets are in some way protective. However, reanalysis of the dietary data provides equally strong support for the hypothesis that the protective element may be phytic acid (inositol hexaphosphate). This heat- and acid-stable substance is present in high concentration in many food items, including cereal grains, nuts, and seeds. Phytic acid forms chelates with various metals and suppresses damaging iron-catalyzed redox reactions. Inasmuch as colonic bacteria have been shown to produce oxygen radicals in appreciable amounts, dietary phytic acid might suppress oxidant damage to intestinal epithelium and neighboring cells. Indeed, rapidly accumulating data from animal models indicate that dietary supplementation with phytic acid may provide substantial protection against experimentally induced colonic cancer. Should further investigations yield additional support for this hypothesis, purposeful amplification of dietary phytic acid content would represent a simple method for reducing the risk of colonic carcinogenesis.

Cereal fiber, calcium, and colorectal cancer

Food intake during the preceding 15 years was evaluated in detail in 41 patients treated for colorectal cancer and an equal number of matched control subjects by means of a dietary history technique that permitted quantitation of nutrients. Dietary habits of the control group could be compared against two larger groups of 371 hospital control and 430 population control subjects. Patients with cancer, who were interviewed after complete recovery from surgery, consumed more fat, protein, and carbohydrates, and thus more energy, than control subjects although these differences were not statistically significant. Per unit energy, the habitual diet of patients with cancer contained less cereal fiber (P less than 0.001), less riboflavin (P less than 0.05), less calcium (P less than 0.05), and less phosphorus (P less than 0.05) than the diet of the control subjects. A high intake of either cereal fiber, total fiber, calcium, and phosphorus in relation to energy intake was found to be associated with a reduced risk ratio of colorectal cancer. For colon cancer separately, a high intake of calcium and cereal fiber was associated with a reduced risk ratio. For rectal cancer, a high intake of total fiber and cereal fiber was associated with a reduced risk ratio. High alcohol consumption correlated with an increased risk ratio. These data are compatible with previous Scandinavian studies relating food consumption to the incidence and mortality of colorectal cancer.

Dietary factors in aetiology and prevention of cancer in man

Chemical carcinogenesis, as presently understood, involves a number of carcinogenic factors which act in series of steps. Some industrial carcinogens may pollute the natural environment and penetrate into food. Many substances which are potent carcinogens in experimental animals exist in nature and are present in the human diet. On the other hand, many substances which are known to inhibit experimental carcinogenesis also exist in human diet. The present review discusses experimental and epidemiological data connected with the human cancer and diet. It also postulates that the dietary prevention of human cancer through "prudent" modification of diet and dietary patterns may be of importance; many of the present data are still confusing and conflicting.

Diet and colorectal cancer with special reference to fiber intake

In this nested case-control study, 8,006 American Japanese men were examined and interviewed with a dietary questionnaire from 1965 to 1968. After a follow-up period of over 16 years, 102 colon and 60 rectal cancer incident cases were identified. Dietary data from these patients and from 361 cancer-free controls were analyzed for intake of dietary fiber (DF), vitamins, minerals, macronutrients, and selected food groups. We found a significant (p = 0.042) negative association of DF and colon cancer risk among low fat intake men (less than 61 g/d). In this subgroup, the men consuming less than 7.5 g/d of DF had an adjusted relative risk (RR) for colon cancer of 2.28 (95% CI 0.93-5.60), compared to those consuming greater than or equal to 14.8 g/d of DF. We also observed (among the complete group of subjects) a significant (p = 0.011) negative association between vitamin C intake and the risk of colon cancer. Men in the lowest quintile of vitamin C intake (less than 37 mg/d) had an adjusted colon cancer RR of 1.87 (95% CI 1.03-3.37), compared to men in the highest quintile (greater than or equal to 160 mg/d). We view these dietary associations with colon cancer risk with caution. There were no other significant associations of dietary variables with colon cancer risk. Also, there were no significant associations between intake levels of DF, micronutrients, or food groups and rectal cancer risk.

Dietary fiber and human cancer: critique of the literature

The relationship between dietary fiber consumption and risk of gastrointestinal cancer in humans is examined using representative studies of several types: international and intranational correlations, case-control analyses, metabolic investigations, cohort studies, and migrant studies. The strongest statistical association between diet and cancer is found in international studies in which numerous environmental variables differ. Studies on smaller groups within a single culture have not given strong support to the findings of international comparisons. Colon cancer rates within regions of the U.S. and other countries vary with sufficient magnitude that diet is unlikely to account for more than a minor proportion of risk. The evidence that a diet containing fiber-rich foods reduces risk of colon cancer must be considered tentative. Foods high in starch and fiber are statistically associated with a high rate of stomach cancer. Examination of the combined rates of colon and gastric cancer shows that the U.S. risk is low relative to countries in which a diet higher in fiber is consumed. It would be premature to suggest that a high fiber diet will confer protection against gastrointestinal cancer.

Dietary fibre consumption and its association with large bowel cancer in man

The hypothesis that lack of fibre in the diet is responsible for a variety of large bowel problems, including cancer, has stimulated much discussion and research over the past 15 years. However, the epidemiological examination of this hypothesis has been hampered by the absence of data on the fibre content of most of the world's foods. In studies in Britain and Scandinavia where consumption of the chemical fraction of dietary fibre, the non-starch polysaccharides, has been determined using accurate methods, significant negative association between colon cancer occurrence and NSP consumption have been shown. Fibre may therefore be protective to populations otherwise assumed to be at risk from a westernised type of diet. At present, methodological problems preclude the use of case-control studies in confirming or refuting these associations.

Dietary suppression of colonic cancer. Fiber or phytate?

The incidence of colonic cancer differs widely between various human populations. It has been suggested that dietary fiber content is of utmost importance and is inversely related to the occurrence of colonic cancer. However, high-fiber diets are not always correlated with low frequency of colonic cancer, suggesting the involvement of additional dietary constituents. Inositol hexaphosphate (phytic acid) is an abundant plant seed component present in many, but not all, fiber-rich diets. The authors have found that phytic acid is a potent inhibitor of iron-mediated generation of the hazardous oxidant, hydroxyl radical. Herein, the authors propose that inhibition of intracolonic hydroxyl radical generation, via the chelation of reactive iron by phytic acid, may help explain the suppression of colonic carcinogenesis and other inflammatory bowel diseases by diets rich in phytic acid.

[The effect of nutrition on intestinal flora]

In several groups of probands the influence of nutrition on the gut flora has been examined. In old people there is a striking decrease in the numbers of Bifidobacteria whereas those of Clostridium perfringens strongly increase and those of Enterobacteriaceae and Lactobacilli can be found somewhat higher than in the compared group. In a group of longevitial old aged men nourished with a fibre-rich diet these alterations are found less striking. Changing from a mixed Japanese diet to a "western diet" a tendentious decrease in the total number of bacteria and in the numbers of Bifidobacteria, Eubacteria, and in moderate, in the numbers of Streptococci, too, could be determined. Simultaneously, a considerable development of nitrosamines occurred. In C3H/Hemice a glucomannan containing (fibre-rich) diet caused a substantial increase in the evidence frequency of Bifidobacterium and in the numbers of Enterobacteriaceae. Parallel with these results incidence and average number of noduli of manifested hepatic carcinoma decreased remarkably.

Nonstarch polysaccharide consumption in four Scandinavian populations

Nonstarch polysaccharide (NSP) intake was measured in representative samples of 30 men aged 50-59 in 2 urban and 2 rural Scandinavian populations that exhibited a 3-4 fold difference in incidence of large bowel cancer. Intake was measured by chemical analysis of complete duplicate portions of all food eaten over one day by each individual. NSP intakes showed a rural-urban gradient, with 18.4 +/- 7.8 g/day in rural Finland and 18.0 +/- 6.4 g/day in rural Denmark versus 14.5 +/- 5.4 g/day in urban Finland and 13.2 +/- 4.8 g/day in urban Denmark. NSP intakes were also calculated (using food tables) from weighed food records kept over 4 days, one of which was the day on which the duplicate collection was made. Intakes were 2-2.5 g/day higher with this method than with direct chemical analysis, mainly because published tables of values have become outdated and inaccurate as a result of improved methods for measuring NSP in food. Individual variation from day to day in NSP intake was considerable. Average NSP intake and intake of some of its component sugars were inversely related to colon cancer incidence in this geographical comparison. To show a relationship at the individual level between diet and cancer risk in a prospective study would require detailed and accurate methods for the assessment of NSP consumption.

Cereal foods today and tomorrow

The present place of cereal foods in the UK diet is assessed. In particular, the role of wheat and of bread white or brown in providing nutrients is reviewed. An examination is carried out of the forces--including nutritional and medical suggestions that the health of the nation would benefit from increased use of 'unrefined' cereals--which favour or inhibit change in future production and consumption of cereals in the UK.

Introductory statement on the progress of The National Large Bowel Cancer Project: its goals, objectives, and programs

The introductory lecture updates the state of the art bearing on cancer of the large bowel. Topics discussed include etiological factors, the pathology of the disease, the role of animal models, the early diagnosis of the disease, including biochemical markers, with emphasis on immunology, and finally therapy, including surgery, radiotherapy, chemotherapy, and the immunological approaches to therapy as identified in the ongoing activities of the National Large Bowel Cancer Project. Interesting aspects of complementing the traditional ways of treating colorectal disease are noted in the discussion of new approaches to chemotherapeutic treatment based on rational developments obtained throught the study of cell kinetics and cell turnover. It is pointed out that this and other interrelationships considered in the multidisciplinary experimental and clinical approaches provide important leads toward the understanding of the mechanisms of disease, discovery of causes and means of prevention, methods of earlier diagnosis, improved rational modalities of treatment, and, one hopes, more successful management.

Metabolic epidemiology of colon cancer. Fecal bile acids and neutral sterols in colon cancer patients and patients with adenomatous polyps

Because of potential significance of bile acids and cholesterol metabolites in the pathogenesis of colon cancer, fecal neutral sterols, and bile acids were determined in patients with colon cancer, adenomatous polyps or other digestive diseases and American or Japanese controls. The fecal excretion of cholesterol, coprostanol, coprostanone, total bile acids, deoxycholic acid, lithocholic acid was higher in patients with colon cancer and patients with adenomatous polyps compared to normal American and Japanese controls as well as patients with other digestive diseases. Patients with other digestive diseases excreted comparable levels of fecal bile acids and cholesterol metabolites compared to normal American controls; Japanese controls excreted reduced levels compared to normal American controls. These findings suggest that possible interactions between bile acids and cholesterol metabolites and colonic epithelial cells may be relevant in colon carcinogenesis.