methylnitronitrosoguanidine and 2--3-dimethyl-4-aminobiphenyl

Yogurt is milk fermented by a mixture of two bacteria: Lactobacillus delbrueckii ssp. bulgaricus and Streptococcus salivarius ssp. thermophilus. Epidemiological studies have correlated a reduced risk of colon cancer with yogurt consumption. Independent studies have established that yogurt and extracts thereof are antimutagenic. Although multiple explanations can account for yogurt's putative anticarcinogenicity, we are interested in testing the hypothesis that antimutagenic compounds produced during fermentation are responsible. We recently reported on the antimutagenicity of an acetone extract of yogurt against the experimental carcinogens N-methyl-N'-nitro-N-nitrosoguanidine (MNNG) and 3.2'dimethyl-4-aminobiphenyl (DMAB) (Mutation Res. (1995) 334, 213-224). We are now aware that palmitic acid is an active ingredient against MNNG.

Topics: Aminobiphenyl Compounds; Antimutagenic Agents; Fatty Acids; Fermentation; Methylnitronitrosoguanidine; Mutagenicity Tests; Mutagens; Palmitic Acid; Palmitic Acids; Salmonella typhimurium; Yogurt

Reconstituted non-fat dry milk powder, fermented by a mixture of Streptococcus thermophilus CH3 and Lactobacillus bulgaricus 191R to produce yogurt, was freeze-dried and extracted in acetone. After evaporation of the acetone, the extract was dissolved in dimethyl sulfoxide (DMSO) and tested for antimutagenicity. In the Ames test, significant dose-dependent activity was observed against N-methyl-N'-nitro-N-nitrosoguanidine (MNNG), 4-nitro-quinoline-N-oxide (4NQO), 3,2'-dimethyl-4-aminobiphenyl (DMAB), 9,10-dimethyl-1,2-benz[a]anthracene (DMBA), and 3-amino-1-methyl-5H-pyrido[4,3-b]indole acetate (Trp-P-2). Weak activity was observed against 1,2,7,8-diepoxyoctane (DEO), and no activity was observed against methyl methanesulfonate (MMS), ethyl methanesulfonate (EMS), or aflatoxin B1 (AFB1). In a related assay (Saccharomyces cerevisiae D7), significant antimutagenic activity was detected against MNNG and 4NQO. Activity against the experimental colon carcinogens MNNG and DMAB was examined further, as assayed in the Ames test (Salmonella typhimurium TA100). Compounds responsible for both activities were less soluble in aqueous solutions than in DMSO. Adjustment of yogurt pH to 3, 7.6, or 13 prior to freeze-drying and acetone extraction did not significantly alter the amount of anti-MNNG activity recovered. In contrast, extractability of anti-DMAB activity was significantly greater at acidic pH. Conjugated linoleic acid, a known dairy anticarcinogen, failed to inhibit mutagenesis caused by either mutagen, suggesting that other yogurt-derived compound(s) are responsible. Unfermented milk was treated with lactic acid, yogurt bacteria without subsequent growth, or both, to determine if formation of antimutagenic activity required bacterial growth. Extracts of the milk treatments exhibited the same weak antimutagenicity observed in unfermented milk, approximately 2.5-fold less than in the yogurt extracts, suggesting that antimutagenic activity is associated with bacterial growth.

Topics: 4-Nitroquinoline-1-oxide; 9,10-Dimethyl-1,2-benzanthracene; Acetone; Aminobiphenyl Compounds; Analysis of Variance; Anticarcinogenic Agents; Antimutagenic Agents; Carbolines; Dose-Response Relationship, Drug; Hydrogen-Ion Concentration; Lactobacillus; Methylnitronitrosoguanidine; Mutagenicity Tests; Saccharomyces cerevisiae; Salmonella typhimurium; Streptococcus; Yogurt

Reconstituted nonfat dry milk was fermented by Lactobacillus helveticus CH65, Lactobacillus acidophilus BG2FO4, Streptococcus salivarius ssp. thermophilus CH3, Lactobacillus delbrueckii ssp. bulgaricus 191R, and by a mixture of the latter two organisms. The fermented milks were then freeze-dried, extracted in acetone, dissolved in dimethylsulfoxide, and assayed for antimutagenicity in the Ames test (Salmonella typhimurium TA 100) against N-methyl, N'-nitro, N-nitroso-guanidine, and 3,2'-dimethyl-4-amino-biphenyl. Dose-dependent activity was significant against both mutagens in all extracts. Maximal inhibitory activity against 3,2'-dimethyl-4-aminobiphenyl and N-methyl, N'-nitro, N-nitroso-guanidine was 2- and 2.7-fold greater, respectively, than that exhibited by extracts of unfermented milk. Extracts of milk fermented by L. delbrueckii ssp. bulgaricus 191R were examined further. Compounds that were responsible for activity against both mutagens were less soluble in aqueous solutions than in dimethylsulfoxide. Adjustment of milk fermented by L. delbrueckii ssp. bulgaricus 191R to pH 3, 7.6, or 13 prior to freeze-drying and acetone extraction did not significantly alter the activity specific for 3,2'-dimethyl-4-aminobiphenyl. In contrast, compounds with activity specific for N-methyl, N'-nitro, N-nitrosoguanidine were less extractable at pH 7.6. The weak antimutagenicity of unfermented milk was not increased by addition of 2% L-lactic acid.

Topics: Aminobiphenyl Compounds; Animals; Antimutagenic Agents; Fermentation; Hydrogen-Ion Concentration; Lactobacillus; Methylnitronitrosoguanidine; Milk; Statistics as Topic