Inhibitory effect of rice bran-derived crude glycosphingolipid on colon preneoplastic biomarker lesions induced by azoxymethane in male F344 rats.

The aim of the present study was to examine whether crude glycosphingolipid (cGSL) has short-term chemopreventive effects on the preneoplastic biomarker lesions involved in carcinogen-induced rat colon carcinogenesis. We also examined whether cGSL affects cell proliferation and apoptosis in these lesions. The crude preparation was obtained by the simple ethanol extraction method. Five-week-old male F344 rats were divided into 6 groups. Rats in groups 1-4 were given subcutaneous injections of azoxymethane (AOM) (20 mg/kg body weight) once a week for 2 weeks. Starting 1 week before the first injection of AOM, the rats in groups 2, 3 and 4 were fed a diet containing 250, 1,000 and 3,000 ppm cGSL, respectively, for 5 weeks. The experiment was terminated 5 weeks after the start date, and the number of aberrant crypt foci (ACF) and mucin-depleted foci (MDF) was counted. Dietary cGSL significantly inhibited the induction of ACF (group 3, P<0.01; group 4, P<0.05) and MDF (groups 2 and 3, P<0.001; group 4, P<0.05) as compared to group 1 treated with AOM alone. In groups 3 and 4, proliferating cell nuclear antigen-positive indices of epithelial cells were significantly lower than in group 1 (group 3, P<0.05; group 4, P<0.005). Caspase-3-positive indices were significantly higher in groups 3 and 4 than in group 1 (group 3, P<0.01; group 4, P<0.001). These results suggest that dietary cGSL had a potent chemopreventive effect in the present short-term colon carcinogenesis bioassays, and that this effect may be associated with the inhibition of ACF and MDF and the induction of apoptosis.

Effects of synthetic and natural in vivo inhibitors of ß-glucuronidase on azoxymethane-induced colon carcinogenesis in rats.

D-Glucaric acid is a non-toxic natural compound found in many fruits and vegetables. Our previous studies have shown that the ß-glucuronidase inhibitor D-glucaro-1,4-lactone, an active metabolite of D-glucaric acid, inhibits chemically-induced tumorigenesis in rodents. D-Glucaro-1,4-lactone has a synthetic precursor, 2,5-di-O-acetyl-D-glucaro-1,4:6,3-dilactone or aceglatone (ACE), known as a postoperative prophylactic agent, and a natural precursor, D-glucurono-γ-lactone (GL). In the present study, we first examined the effect of ACE on the initiation phase of rat colon carcinogenesis induced by 15 mg/kg azoxymethane (AOM) administered 3 times by subcutaneous (s.c.) injection at weeks 1, 2, and 3 of a 5-week short-term experiment. ACE (0.5 or 2%) was administered as a dietary supplement for 5 weeks. At 5 weeks after the initiation of treatment, the formation of aberrant crypt foci (ACF) in the rat groups treated with AOM plus a 0.5 or 2% ACE diet was significantly reduced by 48.6 and 55.3%, respectively, compared to the group administered AOM alone. In a previous study, 0.5 and 2% ACE diets dispensed during AOM treatment had a tendency to decrease AOM-induced colonic tumor incidence. In the present long-term 36-week colon tumorigenesis experiment, GL (0.5 or 2%) administered via the diet during the initiation phase (starting 1 week before the first dose of AOM and ending 1 week after the 3rd dose) did not have any significant effects on tumor incidence. On the other hand, continued post-initiation treatment with ACE (0.5 and 2%) markedly reduced colonic tumor incidence by 70 and 80%, respectively. GL was effective to a similar extent (70% inhibition), but only at a concentration of 2%. We conclude that ACE inhibits the initiation and post-initiation stages of AOM-induced colon carcinogenesis, while GL affects only the post-initiation stages.