SUPPRESSION OF AZOXYMETHANE-INDUCED RAT COLON CARCINOGENESIS BY DIETARY ADMINISTRATION OF NATURALLY-OCCURRING XANTHOPHYLLS ASTAXANTHIN AND CANTHAXANTHIN DURING THE POSTINITIATION PHASE

The modulating effects of dietary feeding of two xanthophylls, astaxan thin (AX) and canthaxanthin (CX) during the postinitiation phase on co lon carcinogenesis initiated with azoxymethane (AOM) were investigated in male F344 rats, Animals were initiated with AOM by weekly s,c. inj ections of 15 mg/kg body wt for 3 weeks and then they were fed the die ts containing AX or CX at concentrations of 100 and 500 p,p,m, for 34 weeks, The others contained the groups of rats treated with AX or CX a lone and untreated, At the end of the study (week 37), the incidence a nd multiplicity of neoplasms (adenoma and adenocarcinoma) in the large intestine of rats initiated with AOM and followed by AX or CX contain ing diet at a high dose (500 p,p,m,) were significantly smaller than t hose of rats given AOM alone (P < 0.001), In addition, AX or CX feedin g significantly inhibited the development of aberrant crypt foci induc ed by AOM, Dietary exposure to AX or CX also decreased cell proliferat ion activity as revealed by measuring 5'-bromodeoxyuridine-labeling in dex in crypt cells, colonic mucosal ornithine decarboxylase activity a nd blood polyamine levels, These results indicate that AX and CX are p ossible chemopreventers for carcinogenesis of colon in addition to uri nary bladder and oral cavity and such effects may be partly due to sup pression of cell proliferation.