Effects of roselle (Hibiscus sabdariffa Linn.), a Thai medicinal plant, onthe mutagenicity of various known mutagens in Salmonella typhimurium and on formation of aberrant crypt foci induced by the colon carcinogens azoxymethane and 2-amino-1-methyl-6-phenylimidazo[4,5-b]pyridine in F344 rats

The 80% ethanol extract of roselle (Hibiscus sabdariffa Linn.), a medicinal plant in Thailand, was examined for antimutagenic and chemopreventive acti vity in a colon carcinogenesis model. It reduced about 60-90% of the mutage nicity induced by 2-amino-1-methyl-6-phenylimidazo[4,5-b]pyridine (PhIP) an d other heterocyclic amines 2-amino-3-methylimidazo[4,5-f]quinoline (IQ),2- amino-3,4-dimethylimidazo[4,5-f]quinoline(MeIQ),2-amino-3,8-dimethylidazo[4 ,5-f]quinoxaline(MeIQx),3-amino-1,4-dimethyl-5H-pyrido[4,3-b]indole (Trp-P- 1), 3-amino-1-methyl-5H-pyrido[4,3-b]indole (Trp-P2),2-amino-6-methyldipyri do[1,2-a:3',2'-d]imidazole (Glu-P-1),2-aminodipyrido[1,2-a:3',2'-d]imidazle (Glu-P-2), at a concentration of 12.5 mg/plate in the Salmonella mutation assay. The extract showed no mutagenicity and no antibacterial activity bel ow this dose. Mutagenicity of methylazoxymethanol (MAM) acetate, which, lik e PhIP, is a colon carcinogen,was also efficiently inhibited by the roselle extract. To investigate chemoprevention by roselle in a colon carcinogenes is model, we examined the inhibitory effects of the roselle extract in F344 rats in which aberrant crypt focus (ACF) formation was induced by azoxymet hane (AOM) and PhIP. In the initiation stage, the number of AOM-induced ACF in the colon was significantly decreased by roselle (17-25%) compared with that in rats treated with AOM alone. The amount of O-6-methylguanine in th e colonic mucosa tended to be decreased in the roselle-treated rats. The nu mber of PhIP-induced ACF was also significantly decreased by roselle treatm ent (22%) at a concentration of 1.0 g/kg body weight in the initiation stag e. However, in the post-initiation stage of AOM-induced ACF formation, rose lle increased the number of ACF, especially the number of foci which had mo re than three crypts/focus. These results indicate that roselle has antimut agenic activity against MAM acetate and heterocyclic amines and that it dec reases the number of AOM- and PhIP-induced ACF in the initiation stage, alt hough it rather increased the number of ACF in the post-initiation stage. ( C) 1999 Elsevier Science Ltd. All rights reserved.