Beef induces and rye bran prevents the formation of intestinal polyps in ApcMin mice: relation to β-catenin and PKC isozymes

Abstract

Epidemiological studies suggest that high consumption of red meat and saturated fat and low consumption of fiber are associated with an increased risk of colon cancer. Therefore, we studied whether diets high in red meat or high in different grain fibers as well as inulin, polydisperse β(2→1) fructan, could affect the formation of intestinal polyps in Apc^Min mice. Min mice were fed the following high-fat (40% of energy) diets for 5–6 weeks; a high-beef diet and a casein-based diet without added fiber or casein-based diet with 10% (w/w) oat, rye or wheat bran, or 2.5% (w/w) inulin. One group had a normal low-fat AIN93-G diet. The mice fed the rye-bran diet had the lowest number of polyps in the distal small intestine [15.4 ± 8.7 (mean ± SD)], and in the entire intestine (26.4 ± 12.1). The rye-bran group differed significantly (P = 0.001–0.004) from the beef group (36.6 ± 9.4 and 52.8 ± 13.2). In addition, the beef group differed significantly from the AIN93-G group (P = 0.009) and also from the wheat-bran group (21.0 ± 6.1 and 35.0 ± 8.2; P = 0.02) in the distal small intestine. The inulin group (32.9 ± 14.3 and 49.3 ± 16.3), on the other hand, was close to the beef group and it differed significantly from the rye-bran group in the distal small intestine. The number of animals bearing tumors in the colon + caecum was only 33% in the rye-bran group when compared with 89% in the beef and 100% in the inulin groups. The mice fed the rye-bran and beef diets had the lowest levels of cytosolic β-catenin (0.60 ± 0.42 and 0.67 ± 0.26) and they differed significantly (P = 0.040 and 0.062) from the mice fed the oat-bran diet (1.46 ± 0.43). No differences between groups in expression of protein kinase C (PKC) α, βII, δ and ζ were found. The four PKC isozymes were positively correlated with cytosolic β-catenin levels (r = 0.62–0.68; P < 0.0001).