Effect of dietary galacto-oligosaccharides on azoxymethane-induced aberrant crypt foci and colorectal cancer in Fischer 344 rats

The aim of the present study was to investigate the effects of galacto-olig osaccharides (GOS, Elix'or) on the development of aberrant crypt foci (ACF) and colorectal tumours in rats treated with azoxymethane (AOM), Two groups of 102 male Fischer 344 rats were injected twice with AOM to induce colore ctal tumours, and fed diets containing either a low [5% (w/w); LGOS] or a h igh [20% (w/w); HGOS] concentration of GOS, Four weeks after the last AOM i njection, 18 animals from each group were killed and their colon was remove d for scoring ACF. Half of the animals in the LGOS group were switched to a n HGOS diet (L/HGOS) and half of those in the HGOS group to an LGOS diet (H /LGOS), Six weeks after the change in diet, nine animals per group were kil led for scoring ACF. Ten months after the start of the study the remaining animals were killed for scoring colorectal tumours, The aberrant crypt mult iplicity scored after 13 weeks and the colorectal tumour incidence in rats fed an HGOS diet were significantly lower than those in rats fed an LGOS di et. However, the induction of ACF by AOM, the proliferation rate and apopto tic index of the adenomas, and the size and multiplicity of colorectal tumo urs were not influenced by the amount of GOS in the diet, The aberrant cryp t multiplicity, scored after 13 weeks, was predictive for the tumour outcom e at the end of the study, It was concluded that an HGOS diet has a protect ive effect against the development of colorectal tumours in rats and that t his protective effect is exerted during the promotion phase rather than the initiation phase of carcinogenesis.