CHEMOPREVENTION OF MOUSE URINARY-BLADDER CARCINOGENESIS BY THE NATURALLY-OCCURRING CAROTENOID ASTAXANTHIN

The chemopreventive effects of two xanthophylls, astaxanthin (AX) and canthaxanthin (CX), on urinary bladder carcinogenesis induced by N-but yl-N(4-hydroxybutyl)nitrosamine (OH-BBN) was investigated in male ICR mice. Mice were given 250 p.p.m. OH-BBN in drinking water for 20 weeks and after a 1 week interval with tap water, water containing AX or CX at a concentration of 50 p.p.m. was administered during subsequent 20 weeks. Other groups of mice were treated with AX or CX alone or untre ated. At the end of the study (week 41), the incidences of preneoplast ic lesions and neoplasms in the bladder of mice treated with OH-BBN an d AX or CX were smaller than those of mice given OH-BBN. In particular , AX administration after OH-BBN exposure significantly reduced the in cidence of bladder cancer (transitional cell carcinoma) (P < 0.003). H owever, the inhibition of the frequencies of such lesions in mice trea ted with OH-BBN and CX was not significant. Treatment with AX or CX al so decreased the number/nucleus of silver-stained nucleolar organizer region proteins (AgNORs), a new index of cell proliferation, in the tr ansitional epithelium exposed to OH-BBN. Preneoplasms and neoplasms in duced by OH-BBN, and the antiproliferative potential, was greater for AX than CX. These results indicate that AX is a possible chemopreventi ve agent for bladder carcinogenesis and such an effect of AX may be pa rtly due to suppression of cell proliferation.