The effects of a "low-risk" diet on tumor incidence in chemically induced colon cancer in rats

Most effective colon cancer chemopreventive agents in rats: a systematic review of aberrant crypt foci and tumor data, ranked by potency

Potential chemopreventive agents for colorectal cancer are assessed in rodents. We speculated that the magnitude of the effect is meaningful and ranked all published agents according to their potency. Data were gathered systematically from 137 articles with the aberrant crypt foci (ACF) end point and from 146 articles with the tumor end point. The potency of each agent to reduce the number of ACF is listed in one table and the potency of each agent to reduce the tumor incidence in another table. Both tables are shown in this review and on a website with sorting abilities (http://www.inra.fr/reseau-nacre/sci-memb/corpet/indexan.html). Potency was estimated as the ratio of the value in control rats to the value in treated rats. From each article, only the most potent agent was kept, except in articles reporting the effect of more than seven agents. Among the 186 agents in the ACF table, the median agent reduced the number of ACF by one-half. The most potent agents to reduce azoxymethane-induced ACF were Pluronic, polyethylene glycol, perilla oil with beta-carotene, and sulindac sulfide. Among the 160 agents in the tumor table, the median agent reduced the tumor incidence in rats by one-half. The most potent agents to reduce the incidence of azoxymethane-induced tumors were celecoxib, a protease inhibitor from soy, difluoromethylornithine with piroxicam, polyethylene glycol, and a thiosulfonate. For the 57 agents present in both tables, a significant correlation (r) was found between the potencies against ACF and tumors (r = 0.45, P < 0.001); without celecoxib, a major outlying point in the correlation, r = 0.68 (P < 0.001, n = 56). In conclusion, this review gathers most known chemopreventive agents, ranks the most promising agents against colon carcinogenesis in rats or mice, and further supports the use of ACF as a surrogate end point for tumors in rats.

Dietary modulation of experimental neoplastic development: role of fat and fiber content and calorie intake

Cancer is still one of the major causes of death in the industrialized countries but locally prevailing lifestyles may dictate the kinds of cancer seen among populations of different geographical areas. Dietary habits and, in particular, the nature and/or the amount of fat, calorie and/or vegetable fiber which are consumed in these countries are among the most frequently quoted etiological factors which may account for this situation. Epidemiological and experimental evidence has accumulated which, even though it can be used to support these conclusions, is still a matter of considerable debate. Modulation of neoplastic development is a concept which has been elaborated to overcome the fact that many experimental observations are not really taken into consideration by the classical 2-step theory of carcinogenesis. It is defined as the effect of any treatment which given before, during or after the initiation of a full carcinogenic process modifies the pattern of neoplastic development as evaluated by the kinetics of appearance, the incidence and/or the yield of histologically characterized malignant tumors. It is said to be positive or negative depending on whether it accelerates or slows down the process and increases or decreases the yield of malignant tumors respectively. From a review of the available experimental data, it is concluded that fat per se has, most probably, no modulating effect but that unbalanced diets rich in lipids could act as a positive modulator of chemically induced carcinogenesis by virtue of their capacity to cause a break in metabolic and proliferative homeostasis; that vegetable fibers as well as restriction in calorie intake could act as negative modulators of the same process because they could restore or help restore this homeostasis. It is thus proposed that to maintain dietary balance either by increasing fiber and/or by reducing total calorie intake is the most effective way to negatively modulate chemically induced carcinogenesis in experimental animals. To make the same recommendation to humans could most probably help preventing major cancers like breast and colon cancers.

The effect of early caloric restriction on colonic cellular growth in rats

Although the inhibitory effect of caloric restriction on tumorigenesis is substantial and well known, the pertinent mechanisms remain to be determined. We recently suggested that the risk of cancer may be directly related to the total number of dividing cells within an affected organ. This study evaluates the effects of early caloric restriction on the cellular growth of the colon. The experiment began one day postpartum and ended six weeks later with the killing of all animals. It consisted of two consecutive periods: a) three weeks of suckling and b) three weeks postweaning. Animals whose food was restricted only during the suckling period showed normal colons when killed at six weeks. Caloric restriction (40%) for three weeks postweaning resulted in colons of lower weight with fewer cells (less total DNA) and reduced total DNA synthesis [( 3H]thymidine uptake, dpm/colon) when compared with animals fed ad libitum postweaning. Conversely, only rats fed ad libitum from birth through the first three weeks after weaning demonstrated an increase (21%) in the rate of DNA synthesis (dpm/mg DNA) compared with other animals. In addition, the colonic crypts showed no differences in the number of cells or the number of dividing cells, as determined by autoradiography. By contrast, the total number of crypts (and/or the number of mucosal cells between crypts) are reduced, and hence the total number of colonic mucosal cells dividing at any given time are similarly decreased. The reduced number of dividing cells in the colons of these animals (i.e., those restricted postweaning) could explain previous data suggesting that they are resistant to the induction of colon cancer.

Effects of psyllium fiber and short-chain organic acids derived from fiber breakdown on colonic epithelial cells from high-risk patients

The effect of a purified fiber, psyllium and the short-chain organic acids derived from fiber breakdown, were assayed on isolated colonic epithelial cells primary-cultured from patients at high-risk of colon cancer, due to adenoma growth or family history of colon cancer. Psyllium fiber provided colonocytes some protection from deoxycholic acid-induced lysis. Propionic acid, a product of fiber breakdown, was a potent colonocyte mitogen, suggesting that fiber could indirectly protect the colon by providing colonocyte nutrients.