Dietary Sugar Beet Fiber Prevents the Increase in Aberrant Crypt Foci Induced by γ-Irradiation in the Colorectum of Rats Treated with an Immunosuppressant

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Abstract
We demonstrated recently that γ-irradiation can induce aberrant crypt foci (ACF) in the rat colorectum. The aim of this study was to evaluate the effect of dietary sugar beet fiber (SBF) on the distribution of the CD8+ intraepithelial lymphocyte (IEL) in the colorectum and on the number of γ-irradiation–induced ACF of rats administered anti-asialo GM1 (αAGM1) as an immunosuppressant. Wistar/ST rats fed a fiber-free diet or the diet supplemented with SBF (100 g/kg diet) were administrated αAGM1 or normal rabbit serum as a control during the initiation period with γ-irradiation. At 5 and 9 wk after the first irradiation, ACF and total aberrant crypts (AC) per area in the colorectum were counted. The numbers of ACF (P = 0.0010) and AC (P = 0.0635) per unit area were lower in the SBF-fed group than in the rats fed the fiber-free diet. αAGM1 administration significantly raised the number of ACF (P = 0.0001) and AC (P = 0.0006) per area in the colorectum. Moreover, αAGM1 administration during the initiation period reduced the number of CD8+ IEL per 100 cells in the epithelial layer (P = 0.0001) of the colon. These results demonstrate that reduction of the number of CD8+ IEL per 100 cells in the epithelial layer as a result of αAGM1 administration promotes the formation of irradiation-induced ACF in the colorectum. The number of CD8+ IEL per 100 cells in epithelial layer was lower in the group fed the fiber-free diet than in the SBF-fed group (P = 0.0522). These results indicated that the ingestion of dietary SBF suppressed γ-irradiation–induced ACF formation through the immune surveillance in the colorectal mucosa.