Ingestion of sugar beet fiber enhances irradiation-induced aberrant crypt foci in the rat colon under an apoptosis-suppressed condition

Abstract

The induction of aberrant crypt foci (ACF) by irradiation of gamma-rays (60Co), and the effect of dietary sugar beet fiber (SBF) on irradiation-induced ACF were examined. We found that abdominal irradiation of gamma-rays could induce ACF in the rat colon. The irradiation was performed once a week at a dose rate of 2 or 3 Gy per irradiation. Irradiation-induced ACF were observed in the colon at 10 weeks after the first irradiation at dose of 2 Gy for six times or 3 Gy for four times. Dietary SBF had no effect on the number of ACF, aberrant crypts (AC) or AC/focus induced by abdominal gamma-irradiation. However, an ingestion of SBF resulted in an increase in the number of these parameters in apoptosis-suppressed rats by cycloheximide (CHX). An injection of CHX suppressed irradiation-induced apoptosis of the colonic epithelial cells for at least 6 h after the irradiation. In CHX-injected rats, an ingestion of SBF significantly increased the number of ACF, AC and AC/focus compared with fiber-free fed rats at 9 weeks after the first irradiation. On the other hand, in saline-injected rats, no significant difference was found between SBF and fiber-free diets in the number of ACF, AC and AC/focus through the experimental period. These results suggest that dietary SBF may be involved in the elimination of abnormal cells from an irradiated colon through the apoptosis of colonic epithelial cells. In this study, we have shown a new method for inducing ACF by using gamma-rays which were not influenced by luminal contents such as bacterial enzyme, at least in the initiation stage.

Fig. 1.

Changes in mean food intake for 9 weeks after the first γ-irradiation. Rats were irradiated on their abdomens once a week six times at 2 Gy (broken arrows) or four times at 3 Gy (solid arrows).

Fig. 2.

Effect of CHX injection on irradiation-induced apoptosis of epithelial cells in the distal colon. Injection of CHX was performed 10–15 min before and 3 h after γ-irradiation. Control rats were injected with saline. Values are means ± SEM (3 h after irradiation, n = 3; 6 h after irradiation, n = 7; 9 h after irradiation, n = 13). *, Significantly different from control group (P < 0.05). Bars not sharing a letter are significantly different (P < 0.05).

Fig. 3.

Effect of ingestion of SBF (filled bars) or fiber-free (open bars) on ACF induced by γ-irradiation in CHX-treated or untreated rats. Control rats were injected with saline. Values are means ± SEM (n = 6, except for fiber-free and control group at 9 weeks, n = 4; fiber-free group at 5 and 7 weeks, n = 5). *, Significantly different from fiber-free and CHX-injected group at the same time point; §, significantly different from SBF group at 5 weeks; +, significantly different from SBF and CHX-injected group at the same time point.