Effect of Shiitake mushroom dose on colon tumorigenesis in azoxymethane-treated male Sprague-Dawley rats

We determined the effects of diets containing dry powdered Shiitake mushroom on frequency of azoxymethane-induced colon aberrant crypt foci (ACF) and intestinal tumors in male Sprague-Dawley rats. Pregnant rat dams and their progeny were fed AIN-93G diets containing casein (20%; control diet) or casein supplemented with Shiitake (1% or 4% wt/wt). Casein- and 1% Shiitake-fed rats exhibited identical growth curves, whereas those fed the 4% Shiitake diet were of slightly reduced body weight. The 4% Shiitake diet elicited increased active energy expenditure and reduced adiposity of rats. Small bowel and colon tumors and colon ACF were evaluated in the male progeny at 18 weeks after azoxymethane treatment. Aberrant crypt foci and tumors were most prevalent in the mid and distal regions of the colon. Shiitake intake had no effect on the relative incidence of tumors in the colon or small intestine (duodenum). Consumption of 1% Shiitake stimulated growth of invasive adenocarcinomas in the mid colon (P < .005) and favored a nonsignificant increase in median frequency of ACF in this same region. In contrast, Shiitake at 4% intake elicited a reduction in colon tumor multiplicity. Results demonstrate stimulatory actions of 1% and inhibitory actions of 4% Shiitake mushroom on indices of rat colon tumorigenesis, which may be associated with altered metabolism.