Comparative mutagenicity of two triarylmethane food dyes in Salmonella, Saccharomyces and Drosophila

A core in vitro genotoxicity battery comprising the Ames test plus the in vitro micronucleus test is sufficient to detect rodent carcinogens and in vivo genotoxins

In vitro genotoxicity testing needs to include tests in both bacterial and mammalian cells, and be able to detect gene mutations, chromosomal damage and aneuploidy. This may be achieved by a combination of the Ames test (detects gene mutations) and the in vitro micronucleus test (MNvit), since the latter detects both chromosomal aberrations and aneuploidy. In this paper we therefore present an analysis of an existing database of rodent carcinogens and a new database of in vivo genotoxins in terms of the in vitro genotoxicity tests needed to detect their in vivo activity. Published in vitro data from at least one test system (most were from the Ames test) were available for 557 carcinogens and 405 in vivo genotoxins. Because there are fewer publications on the MNvit than for other mammalian cell tests, and because the concordance between the MNvit and the in vitro chromosomal aberration (CAvit) test is so high for clastogenic activity, positive results in the CAvit test were taken as indicative of a positive result in the MNvit where there were no, or only inadequate data for the latter. Also, because Hprt and Tk loci both detect gene-mutation activity, a positive Hprt test was taken as indicative of a mouse-lymphoma Tk assay (MLA)-positive, where there were no data for the latter. Almost all of the 962 rodent carcinogens and in vivo genotoxins were detected by an in vitro battery comprising Ames+MNvit. An additional 11 carcinogens and six in vivo genotoxins would apparently be detected by the MLA, but many of these had not been tested in the MNvit or CAvit tests. Only four chemicals emerge as potentially being more readily detected in MLA than in Ames+MNvit--benzyl acetate, toluene, morphine and thiabendazole--and none of these are convincing cases to argue for the inclusion of the MLA in addition to Ames+MNvit. Thus, there is no convincing evidence that any genotoxic rodent carcinogens or in vivo genotoxins would remain undetected in an in vitro test battery consisting of Ames+MNvit.

Short-term toxicity study of Green S in rats

Groups of 15 rats of each sex were fed Green S at dietary concentrations to provide dose levels of 0 (control), 250, 500 or 1500 mg/kg body weight/day for 13 wk. Additional groups of five animals of each sex were given the same treatments for 2 or 6 wk. There was a marked excretion of green colour in the faeces and some green colouring of the urine, although the latter may have been due to contamination. The males showed increased water and food intakes associated, particularly at the highest dose, with a higher rate of body-weight gain. Haematological examination revealed a transitory mild anaemia at the highest dose level, whilst no findings indicative of a toxic effect were found in the renal concentration tests or the serum analyses. With a dose of 1500 mg Green S/kg a greater proportion of the rats showed higher urinary protein, protein casts, increased caecal weight, thyroid degeneration in female animals and enlargement of the lymph nodes in the intestine wall. The no-effect dose level for Green S in this study was considered to be 500 mg/kg.

Studies on the mutagenicity of commercial preparations of the food colour Red 2G after purification or oxidation

The UK-permitted, monoazo food colour Red 2G (C.I. 18050) has previously been shown to induce transition mutations in bacteria when tested with metabolic activation. Whilst this result has now been confirmed, later commercial food-grade batches of the dye have also been found to exhibit dose-dependent direct activity in fluctuation tests with E. coli WP2 uvr A. HPLC analyses revealed the presence of contaminants several of which were either eliminated or reduced in amount after laboratory recrystallization. A concomitant loss of mutagenicity occurred which was gradually regained with storage of purified preparations. Since peroxidation of standard samples significantly potentiated activity over a number of doses it is concluded that commercial mixtures contain at least one mutagenic impurity which may arise by spontaneous oxidation. The data are discussed in relation to the effects of oxidation on other aromatic amines and with respect to the use of this colour in foods.

Mutagenic activity of heated potato/oil systems

Mutagens detected with Salmonella typhimurium strain TA 98 in the presence of liver S9 mix were extracted from potato slices, but not pure potato starch, after frying in oil. No mutagenic activity was detected using strain TA 100, in the presence or absence of S9 mix with either fried potato slices or potato starch. Mutagenic activity was detected at frying temperatures of 140 degrees C and above. The mutagenic activity was limited to the outer portion of the fried potato slices and increased with frying time and temperature. Mutagenic activity ratios for extraction with both (NH4)2SO4/NH4OH and Na2SO4/NaOH were similar.

UV-absorbing and other sun-protecting substances: genotoxicity of 2-ethylhexyl P-methoxycinnamate

The mutagenicity of 2-ethylhexyl p-methoxycinnamate was demonstrated when 25 sunscreen ingredients were tested in the Salmonella/microsome assay. This substance also increased the frequency of sex-linked recessive lethals in Drosophila melanogaster. A trace contaminant may be implicated because many samples were obtained from several sources and the results were batch-related.

Detection of mutagenic activity in human urine following fried pork or bacon meals

Mutagenic activity has been demonstrated in urine of human subjects after ingestion of fried pork or bacon. Activity was detected with Salmonella strains TA1538 and TA98 particularly, in the presence of liver homogenate S9, and was not enhanced by prior incubation of urine with beta-glucuronidase. Chemical and biological characteristics of the urine activity closely resemble those found in extracts of fried pork and bacon which also increase the frequency of sex-linked recessive mutations in Drosophila melanogaster. Microwave-cooked meat neither contained extractable mutagenic activity, nor contributed to urinary mutagenicity, possible due to the paucity of browning reactions in meat cooked under these conditions. If the urine and meat factors are chemically identical, then approximately one-third of the food activity is recovered from the urine. These results show that mutagenic factors, generated during cooking of pork and bacon, are ingested and absorbed and are subject to urinary clearance in biologically detectable quantities. It is possible that the potential for genetic toxicity in humans of these and related factors has been underestimated.

A review of the genotoxicity of food, drug and cosmetic colours and other azo, triphenylmethane and xanthene dyes

The genetic toxicology of the major dyestuffs used in foods, drugs and cosmetics has been reviewed. Published data for azo, triphenylmethane and xanthene dyes from short-term assays for muta-carcinogenicity have been summarized and discussed according to usage, current and previous worldwide legislative status. Certain other synthetic food dyes, commercial mixtures, natural and polymeric colourants as well as a section on aminoazobenzene and its derivatives have been included. Genotoxicity has been discussed with reference to structural chemistry, levels of exposure, absorption and metabolism and to epidemiological information. The extent of agreement between data from different tests and correlations with animal cancer assays have been considered. Synthetic dyes from the 3 major structural classes exhibit genotoxicity, whilst only 2 natural colours have proved active. Activity may be due to the presence of certain functional groups, notably nitro- and amino-substituents which are metabolized to ultimate electrophiles that may be stabilized by electronic interaction with aryl rings. Metabolic processes such as azo-reduction may be activating or detoxifying. the low but significant correlation between animal carcinogenicity and short-term test data may be increased with further screening, especially involving chromosome assays. It is suggested that a human cancer hazard may exist where significant quantities of finished benzidine dye samples are handled. Such risks from exposures to other colours and the possibility of human germ-line mutation induction by dyestuffs cannot be meaningfully assessed.