Dietary caffeine reduces the genotoxicity of MeIQx in the host-mediated assay in mice.

The influence of dietary caffeine on the genotoxicity of the cooked food mutagen 2-amino-3,8-dimethylimidazo[4,5-f]-quinoxaline (MeIQx) was evaluated using the host-mediated assay in mice. For four weeks, BALB/c mice were fed a purified diet with or without caffeine (0.01% wt/wt in the diet).

Effect of hepatic cytochrome P-450 inducing agents on mutagen activity in the host-mediated assay.

Intraperitoneal treatment of female BALB/c mice with either phenobarbitone or beta-naphthoflavone led to the induction of various hepatic enzymes associated with xenobiotic metabolism and to increased abilities of hepatic S9 fractions to convert the dietary carcinogen 2-amino-3,8-dimethylimidazo[4,5-f]quinoxaline (MeIQx) to an active bacterial mutagen. In the case of another carcinogen, aflatoxin B1 an increase in in vitro hepatic activation was seen only in mice treated with phenobarbitone. In contrast, pretreatment with either phenobarbitone or beta-naphthoflavone reduced the in vivo activity of both aflatoxin B1 and MeIQx in the host mediated bacterial mutation assay.

Development changes to gut microflora metabolism in mice.

Developmental changes in the activities of bacterial nitrate reductase, nitroreductase and beta-glucuronidase and their response to fermentable dietary fibre, were investigated in caecal contents from suckling mice (2-week-old) and in mice aged 4-24 weeks fed either a purified fibre-free diet or that diet supplemented with 5% (w/w) pectin. There was no apparent age-related trend common to the three enzymes studied. Nitrate reductase activity in the mice fed the fibre-free diet did not markedly alter with age.

Dietary fat modifies the in vivo mutagenicity of some food-borne carcinogens.

Female BALB/c mice were fed a low fat diet (1% safflower oil, by weight) or one supplemented with 25% (by weight) of beef fat or olive oil. The abilities of these diets to modify the in vitro and in vivo hepatic conversion of the dietary carcinogens aflatoxin B1, 2-amino-3, 4-dimethylimidazo[4,5-f]quinoline (MeIQ) and 3-amino-1-methyl-5H-pyrido[4,3-b]indole (Trp-P-2) to bacterial mutagens was evaluated. Dietary olive oil appeared to increase the metabolism of both MeIQ and Trp-P-2 to bacterial mutagens in vivo using the intrasanguineous host-mediated assay.

Continuous culture of human faecal bacteria as an in vitro model for the colonic microflora.

To investigate the role of human gut bacteria in the metabolism of potentially reactive compounds we have developed an in vitro model of the human faecal microflora using a two-stage continuous culture inoculated with human faeces. The cultured bacterial population retained many of the bacteriological and biochemical characteristics of the flora present in the faecal sample used for inoculation. Obligate anaerobes were the predominant bacterial types found in vitro and included Bacteroides ovatus and Bifidobacterium adolescentis.