Mutagenicity of 2-amino-3-methylimidazo[4,5-f]quinoline in human lymphoblastoid cells.

2-Amino-3-methylimidazo[4,5-f]quinoline (IQ), a heterocyclic aromatic amine that has been identified in cooked meats and cigarette condensates, is mutagenic in human lymphoblastoid TK6 cells at the thymidine kinase and hypoxanthine-guanine phosphoribosyl transferase (hprt) loci. Treatment of the cells with IQ following activation with either an exogenous metabolizing mixture (S9) or following photoactivation of the azido-derivative of IQ (N3-IQ) showed that the photolytic-derivative of N3-IQ was more active. This observation is consistent with other reports that indicate that the weak mutagenicity of IQ in mammalian cells is caused by the lack of enzymes required for the ultimate activation of the compound within the cells. Two DNA adducts were found by 32P-post-labelling in the cells treated with the photoactivated N3-IQ. The major adduct was identified as N-(deoxyguanosin-8-yl)-2-amino-3-methylimidazo[4,5-f]quinoline (dG-C8-IQ) and the minor adduct as 5-(deoxyguanosin-N2-yl)-2-amino-3-methylimidazo[4,5-f]quinoline (dG-N2-IQ). The ratio of the dG-C8IQ to the dG-N2-IQ adducts was approximately 3:1 and did not significantly change in cultures treated with different concentrations of the mutagen. Approximately 50% of the adducts were removed 9 h after treatment with IQ and <10% of these adducts remained after 24 h. There was no significant preferential repair of either adduct under the experimental conditions used. The identification of 15 mutations induced at the hprt locus (of the 44 mutants analysed) showed IQ to be efficient at inducing single base deletions in a run of guanines. Six single guanine deletions were observed in the run of six guanines in exon III and one deletion of a single guanine was observed in a non-repetitive sequence in exon VI. Other mutations observed were two GC-->TA transversions, two GC-->CG transversions, one AT-->TA transversion and one GC-->AT transition. In addition, two multiple mutations were found. The majority of the identified mutations (12/15) occurred at GC base pairs and suggests either the dG-C8-IQ or the dG-N2-IQ adduct to be the pre-mutagenic lesion.

Analysis of the content of the diterpenes cafestol and kahweol in coffee brews.

The diterpenes cafestol and kahweol have been implicated as the components in boiled coffee responsible for its hypercholesterolaemic effects. These particular coffee constituents have also been shown to possess anticarcinogenic effects. A simple and sensitive reverse-phase HPLC method using solid-phase extraction has been developed for the analysis of cafestol and kahweol in coffee brews. This method was used to confirm that the method of coffee brewing is a major determinant of the cup content and hence level of consumption of these diterpenes. Scandinavian-style boiled coffee and Turkish-style coffee contained the highest amounts, equivalent to 7.2 and 5.3 mg cafestol per cup and 7.2 and 5.4 mg kahweol per cup, respectively. In contrast, instant and drip-filtered coffee brews contained negligible amounts of these diterpenes, and espresso coffee contained intermediate amounts, about 1 mg cafestol and 1 mg kahweol per cup. These findings provide an explanation for the hypercholesterolaemic effect previously observed for boiled coffee and Turkish-style coffee, and the lack of effect of instant or drip-filtered coffee brews. This methodology will be of value in more correctly assessing the human exposure to these diterpenes through the consumption of coffee, and hence the potential physiological effects of different brews.

Inhibition by coffee of nitrosourea-mediated DNA damage in mice.

Oral administration of coffee at doses ranging from 150 mg to 1 g per kg body weight significantly decreased endogenously formed nitrosourea-mediated DNA damage in bone marrow as well as in colon epithelial cells in mice that had simultaneously received oral administration of methylurea and sodium nitrite. Since coffee (1 g/kg body weight) did not decrease DNA damage when administered orally together with performed methylnitrosourea, it was hypothesized that coffee inhibits nitrosation in the stomach of mice. The lowest effective level of coffee, when compared on the basis of body weight, corresponds to a human intake of about 5 cups of coffee. Both chlorogenic acid (150 mg/kg body weight) and premelanoidins (1 g/kg body weight), which occur as ingredients in, or are formed during roasting of, coffee, were shown to inhibit nitrosourea-induced DNA damage in mice.

The effect of caffeine in the in vivo SCE and micronucleus mutagenicity tests.

Caffeine which was administered per os to outbred mice either twice, 30 and 6 h before sacrifice or once, 30 h before sacrifice, at dose levels of 50, 75 or 100 mg/kg body weight only caused a weak induction of micronuclei at the highest dose. Again a level of 100 mg caffeine per kg body weight was required before a weak but not significant effect could be observed in the micronucleus test using a mutagen-sensitive inbred strain of mice. In Chinese hamsters caffeine doses of 45, 75, 150 or 300 mg/kg body weight either given once or twice per os at the same time schedule as used for the mice also caused a clear cut induction of micronuclei only at the highest dose level. In the SCE test with Chinese hamster again 300 mg of caffeine were necessary to obtain a mutagenic effect although this test is considered to be more sensitive to mutagenic damage than the micronucleus test. It can therefore be concluded that caffeine causes DNA damage only at dose levels in the LD50 range which is higher for hamsters than for mice.