Graduate Thesis Or Dissertation
 

Antimutagenic potency of wheat grain and berry extracts in vitro and anticarcinogenicity of wheat grain in vivo

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  • The antimutagenic potency of wheat grain and berry extracts was studied in vitro against several heterocyclic amines (HCAs) using the Salmonella mutagenicity assay and the anticarcinogencity of wheat grain was studied in vivo using the rat colonic aberrant crypt focus assay. Wheat bran, which binds HCAs in vitro, as well as refined wheat and unrefined whole wheat, inhibited the mutagenic activities of 2-amino-3- methylimidazo [4, 5-f] quinoline (IQ), 2-amino-1-methyl-6-phenylimidazo[4, 5-b]pyridine (PhIP) and 2-amino-3,8-dimethylimidazo[4,5-f]quinoxaline (MeIQx) when they were co-incubated and the supernatant (minus grain) was added to the Salmonella mutagenicity assay. The water-soluble fraction alone from refined and unrefined wheat, but not bran, also inhibited these mutagens in vitro. In vivo, AIN- 93G diets containing refined wheat or unrefined wheat were examined for their ability to inhibit IQ-induced colonic aberrant crypt foci (ACF) in the F344 rat. A slight increase in the number of aberrant crypts/ACF (AC/ACF) was seen after 16 weeks in rats treated post-initiation with refined wheat (p<0.05), and fewer foci with 2 or 3 aberrant crypts (ACF-2) were found in rats given unrefined whole wheat post-initiation compared with animals treated with the same diet during the initiation phase (p<0.05). There was no significant difference in the profile of IQ urinary metabolites or excretion of promutagens 0-48 hours after carcinogen dosing, and grains had no effect on hepatic cytochrome P450 (CYP) 1A1, CYP1A2, aryl sulfotransferase, or N-acetyltransferase activities; however, a slightly higher UDP-glucuronosyl transferase activity was observed in rats fed unrefined wheat compared with refined wheat diets (p<0.05). Thus, despite their antimutagenic activities in vitro, only marginal effects were seen with refined and unrefined wheat in vivo with respect to induction of hepatic enzyme activities, carcinogen metabolism, or IQ-induced ACF in the rat colon. The fresh juice and extract of crandall black currant (Ribes aureum) were not mutagens in the Salmonella mutagenicity assay. Berry extract or fresh juice at levels to 50 μl (22 mg berry) in a 500 μl pre-incubation system significantly inhibited the mutagenicity of IQ, a mutagen from cooked meat, by 32% when rat liver S9 bioactivation system was present. One hundred μl of crandall black currant extract gave 89% inhibition of IQ mutagenicity (p<0.05). However, the mutagenicity of 2-hydroxyamino-3-methylimidazo[4,5-f] quinoline (N-hydroxy- IQ), a direct-acting metabolite of IQ, was not affected. An in vitro fluorometric assay showed the activity of cytochrome P 450 (CYP) 1A1 and CYP 1A2 was decreased. Inhibition of CYP 1A2 activity may be an important mechanism of antimutagenicity of crandall black currant extract. Similar results were also observed with other berry samples. Key word: cereal grains, black currant, berry, aberrant crypt foci, heterocyclic amines, CYP1A1, CYP1A2, Salmonella mutagenicity assay.
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