Chemoprevention of Colon Cancer

A comparative study of the influence of differing barley brans on DMH-induced intestinal tumours in male Sprague-Dawley rats

The influence of barley brans on the incidence and burden of intestinal tumours in rats induced by 1,2-dimethylhydrazine (DMH) was studied in a 7 month feeding experiment. The basic diet was American Institute of Nutrition (AIN) 76 modified by adjustment to 20% fat and 40% starch; brans were added so as to supply 5% dietary fibre. The barley brans studied were commercial barley bran (BB1; 13.0% dietary fibre) from the aleurone/subaleurone layer, outerlayer barley bran (BB2) including the germ (25.5% dietary fibre) and spent barley grain bran (SBG; a by-product of the brewery and including the hull; 47.7% dietary fibre). They were compared with wheat bran (WB; 44% dietary fibre) and cellulose (or control; 98% dietary fibre). Commercial barley bran and wheat bran were most effective in reducing tumour incidence and burden. The incidence of tumours fell significantly from 70% (BB2) and 50% (SBG) to 10% (BB1) and 20% (WB) and tumour burden and tumour mass index (TMI) were also reduced by similar orders of magnitude. There were significantly higher short chain fatty acid (SCFA) concentrations in WB- and BB1-fed rat faecal pellets relative to cellulose- and BB2-fed rat faeces; butyrate, in particular, was affected. Regression analysis of butyrate against tumour incidence showed a trend (r = 0.898: P = 0.055), but the concentration of butyrate alone could not account for the reduction in tumour incidence observed. In a second experiment, when two brans (BBI and SBG) were introduced after DMH dosing, there were higher incidences and burdens of tumours, indicating that protection by such brans was not as effective under these circumstances. Commercially available barley bran and wheat bran appear to significantly reduce tumour incidence and burden in this model relative to other brans, influencing both the initiatory as well as promotional stages of chemically induced carcinogenesis.

Dietary factors related to colorectal neoplasms

Although the etiology of colorectal cancer is multifactorial, experimental evidence suggests a role for dietary factors in the promotion of this disease. The complex interrelations governing energy balance and the consumption of fat, fiber, and micronutrients make it difficult to define the precise role of specific dietary factors in the etiology of colorectal neoplasms. Epidemiologic studies have demonstrated a correlation between the prevalence of colorectal cancer and per capita consumption of meat and fat. Case-control studies investigating the relation between colorectal cancer and dietary fat consumption have yielded inconsistent results. Prospective studies have failed to demonstrate a relation between fat consumption and subsequent risk for colorectal cancer. There is an inverse correlation between fiber intake and the prevalence of colorectal carcinoma. A more detailed analysis of the influence of various types of dietary fiber on the subsequent risk for colorectal cancer will provide a better understanding of this relation. Fiber derived from fruits and vegetables may provide more effective protection than cereal fibers. Correlational studies have established an association between total caloric intake and the prevalence of colorectal carcinoma. The design of future studies investigating the influence of individual dietary constituents on the risk for colorectal cancer must control for variations in energy balance as a confounding variable. Recent evidence suggests that a variety of micronutrients, including calcium, vitamin D, selenium, and vitamins A, C, and E, exert an anticarcinogenic effect. Studies designed to evaluate the influence of alcohol consumption on colorectal carcinogenesis have yielded inconclusive results. The potential influence of food preparation methods on colorectal carcinogenesis requires further evaluation. There is no conclusive evidence to support any of the hypotheses proposed to explain the role of dietary factors in colorectal carcinogenesis. Intervention trials designed to monitor intermediate markers for colorectal cancer such as increased epithelial-cell proliferation rates and the development of aberrant crypt architecture provide the opportunity for testing these hypotheses in relatively short-term studies. The results from such studies can be utilized in the design of large-scale, long-term prospective studies to evaluate the influence of dietary factors on the development of colorectal neoplasms. These trials should generate the information required to develop strategies for diet modification to reduce the incidence of colorectal carcinoma.

Nutrition and colorectal cancer

Environmental and genetic factors play an important role in the cause and pathogenesis of colorectal cancer. In addition to nutritional aspects, other environmental factors include physical exercise, energy intake, obesity, and parity. Dietary components currently under study are dietary fiber, fat, fruits, vegetables, and calcium. Intermediate markers of colonic proliferation, including bromodeoxyuridine and proliferating cell nuclear antigen incorporation, are being used to evaluate the response of the colonic epithelium to putative chemopreventative agents.

Nutrition and colorectal cancer

Environmental and genetic factors play an important role in the cause and pathogenesis of colorectal cancer. In addition to nutritional aspects, other environmental factors include physical exercise, energy intake, obesity, and parity. Dietary components currently under study are dietary fiber, fat, fruits, vegetables, and calcium. Intermediate markers of colonic proliferation, including bromodeoxyuridine and proliferating cell nuclear antigen incorporation, are being used to evaluate the response of the colonic epithelium to putative chemopreventative agents.