Carcinogenic activity of 2-(2-furyl)-3-(5-nitro-2-furyl)-acrylamide, a food additive, in mice and rats

Carcinogenic risk of food additive AF-2 banned in Japan: a case study on reassessment of genotoxicity

BACKGROUND

Carcinogenic risk assessment studies have been repeatedly improved and are still being debated to find a goal. Evaluation might be changed if new approaches would be applied to some chemicals which means that new approaches may change the final assessment. In this paper, the risk assessment of a chemical, in particular the proper carcinogenicity, is examined using the long-banned food additive, 2-(2-furyl)-3-(5-nitro-2-furyl)-acrylamide, AF-2, as a case study.

RESULTS

First, Ames tests were carried out using strains TA1535, TA100, TA1538, and TA98 and their nitroreductase-deficient strains YG7127, YG7128, YG7129, and YG7130. The results showed that mutagenic activity was reduced by about 50% in the nitroreductase-deficient strains, indicating that part of the mutagenic activity shown in Ames test was due to bacterial metabolism. Second, in vivo genotoxicity tests were conducted, including the one that had not been developed in 1970's. Both a micronucleus test and a gene mutation assay using transgenic mice were negative. Third, assuming it is a genotoxic carcinogen, the virtual safety dose of 550 μg/day was calculated from the TD50 in rats with a probability of 10-5.

CONCLUSION

AF-2 has been shown to be carcinogenic to rodents and has previously been indicated to be genotoxic in vitro. However, the present in vivo genotoxicity study, it was negative in the forestomach, a target organ for cancer, particularly in the gene mutation assay in transgenic mice. Considering the daily intake of AF-2 in the 1970s and its virtually safety dose, the carcinogenic risk of AF-2 could be considered acceptable.

Improvement of carcinogen identification in BALB/3T3 cell transformation by application of a 2-stage method

The present studies intend to heighten the sensitivity of BALB/3T3 cells to chemical carcinogens in a transformation assay, by including exposure of carcinogen-treated cells to a tumor promoter, 12-O-tetradecanoylphorbol 13-acetate (TPA). In the assay, cells were first treated with a known or suspected carcinogen for 72 h, cultured in normal medium for 3 days, exposed to media with and without TPA for 2 weeks, and cultured in normal medium for an additional 3 weeks. Benzo[a]pyrene, a potent carcinogen with a polycyclic aromatic hydrocarbon structure, caused transformation in the presence and absence of TPA. N-Methyl-N'-nitro-N-nitrosoguanidine (MNNG), a carcinogen with direct-acting alkylating ability, did not induce significant transformation without TPA, while treatment with MNNG followed by TPA produced numerous transformed foci, classifying MNNG as an initiating agent of transformation under the condition presented in this report. 3-Amino-1,4-dimethyl-5H-pyrido[4,3-b]indole (Trp-P-1), 3-amino-1-methyl-5H-pyrido[4,3-b]indole (Trp-P-2), 2-(2-furyl)-3-(5-nitro-2-furyl)acrylamide (AF-2), sodium nitrite and butylated hydroxyanisole (BHA), which are carcinogenic and/or mutagenic, produced transformed foci in significant numbers of treated dishes in the presence but not in the absence of TPA. Butylated hydroxytoluene (BHT) and sodium saccharin, which are considered to be a modifier and a promoter of carcinogenesis, did not cause significant transformation with or without TPA treatment. These studies suggest that this 2-stage transformation system is capable of detecting a wider range of chemical carcinogens as initiating agents than the standard assay. Studies on the transformation assay schedule revealed that the proportion of dishes with foci, the number of foci per dish and sizes of foci all increased in the normal medium after the termination of TPA treatment. Therefore, transformed cells appear to proliferate independently of TPA after those cells are released by TPA from postconfluence inhibition of cell division.

Chemical carcinogens. A review and analysis of the literature of selected chemicals and the establishment of the Gene-Tox Carcinogen Data Base. A report of the U.S. Environmental Protection Agency Gene-Tox Program

The literature on 506 selected chemicals has been evaluated for evidence that these chemicals induce tumors in experimental animals and this assessment comprises the Gene-Tox Carcinogen Data Base. Three major sources of information were used to create this evaluated data base: all 185 chemicals determined by the International Agency for Research on Cancer to have Sufficient evidence of carcinogenic activity in experimental animals, 28 selected chemicals bioassayed for carcinogenic activity by the National Toxicology Program/National Cancer Institute and found to induce tumors in mice and rats, and 293 selected chemicals which had been evaluated in genetic toxicology and related bioassays as determined from previous Gene-Tox reports. The literature data on the 239 chemicals were analyzed by the Gene-Tox Carcinogenesis Panel in an organized, rational and consistent manner. Criteria were established to assess individual studies employing single chemicals and 4 categories of response were developed: Positive, Negative, Inconclusive (Equivocal) and Inconclusive. After evaluating each of the individual studies on the 293 chemicals, the Panel placed each of the 506 chemicals in an overall classification category based on the strength of the evidence indicating the presence or absence of carcinogenic effects. An 8-category decision scheme was established using a modified version of the International Agency for Research on Cancer approach. This scheme included two categories of Positive (Sufficient and Limited), two categories of Negative (Sufficient and Limited), a category of Equivocal (the evidence of carcinogenicity from well-conducted and well-reported lifetime studies had uncertain significance and was neither clearly positive nor negative), and three categories of Inadequate (the evidence of carcinogenicity was insufficient to make a decision, however, the data suggested a positive or negative indication). Of the 506 chemicals in the Gene-Tox Carcinogen Data Base, 252 were evaluated as Sufficient Positive, 99 as Limited Positive, 40 as Sufficient Negative, 21 as Limited Negative, 1 as Equivocal, 13 as Inadequate with the data suggesting a positive indication, 32 as Inadequate with the data suggesting a negative indication, and 48 Inadequate with the data not suggesting any indication of activity. This data base was analyzed and examined according to chemical class, using a 29 chemical class scheme.(ABSTRACT TRUNCATED AT 400 WORDS)

Carcinogens and mutagens that may occur in foods

The principal carcinogens and mutagens that have been identified in human foods are reviewed. These agents may occur in foods as naturally occurring components (e.g., metabolites made by plant or fungal cells), components of contaminating plants or microorganisms, food additives (usually unintentional), or products that arise during processing or cooking. In the mixed diets of developed countries the levels of the known carcinogens and mutagens are very low. However, serious contamination of foods by the potent hepatocarcinogen aflatoxin B1 has occurred in some parts of the world; contamination by N-nitroso compounds or their precursors is another important concern. Extrapolation of the data on the carcinogenicity and mutagenicity of chemicals that can occur in foods to an accurate estimation of the potential hazard to human populations is not yet possible.

Teratogenic effects of carcinogenic agents on limb regeneration in the Japanese newt Cynops pyrrhogaster

Normal regeneration of the amputated forelimb of the Japanese newt Cynops pyrrhogaster and regeneration after a single intraperitoneal injection of three potent mutagenic/carcinogenic agents was investigated. Three dose levels of each agent and controls were tested for teratogenicity in this newt model with the following chemicals: N-methyl-N'-nitro-N-nitrosoguanidine (MNNG), 4-nitro-quinoline-1-oxide, and 2-(2-furyl)-3-(5-nitrofuryl)acrylamide. These chemicals were administered at 10 days (late dedifferentiation stage), 20 days (late bud stage), and 30 days (early digits stage) after amputation at the midforelimb. A total of 628 newts, with 16-20 animals per group, were used. Normal forelimb regeneration in Cynops pyrrhogaster closely paralleled that reported for other species. A variety of deformities, including syndactyly, polydactyly, oligodactyly, brachydactyly, and digital branching, were occasionally observed in control regenerating forelimbs, with syndactyly occurring at highest incidence (17.5%). All three mutagens at all tested dose levels enhanced the incidence of teratogenic changes, though increases were not always statistically significant. MNNG, particularly when administered at the time of initial chondrogenesis (20 days, late bud stage), was especially teratogenic. The type of forelimb deformity was not mutagen-specific in this experiment. As Cynops pyrrhogaster is easily and inexpensively maintained and tolerates surgery well, this model with the regenerating forelimb should prove useful for further studies on teratogen screening. Also, studies directed toward mutagenic and epigenetic effects of exogenous agents on rapidly proliferating and differentiating tissues can be investigated with this model, which obviates transplacental excursion and metabolism of test compounds.

Mutagen formation in browning model systems

A browning model system, consisting of diacetyl and ammonia, produced frameshift and base-pair substitution mutagens when the system was heated over 20 min and 120 min, respectively. The major product was 2,4,5- trimethylimidazole , which showed no mutagenicity toward Salmonella typhimurium strains TA98 and TA100 with or without metabolic activation. When furfural was reacted with nitrate under mild conditions (for 30 min to 3 h at 0-25 degrees C and pH 2-7), it did not produce mutagenic nitrofuran derivatives. However, the ethyl ether extract obtained from the reaction mixture of furfural and nitrate with hydrochloric acid exhibited strong mutagenic activities toward S. typhimurium strains TA98 and TA100 in the presence of metabolic activation. The major product of this reaction mixture, 4- nitrofurfural , exhibited no mutagenicity toward tester strains TA98 and TA100 with or without metabolic activation. Pure active mutagen(s) was (were) not, however, identified in either system.

Mutagenic factors in cooked foods

The charred surface of fish and beef showed strong mutagenic activity in Salmonella typhimurium test strains when activated by S-9 mix of rat liver. The pyrolysis products of proteins and amino acids were also highly mutagenic. Among the pyrolysis products of amino acids, those of tryptophan, serine, and glutamic acid were most active. The new gamma-carboline derivatives, 3-amino-1,4-dimethyl-5H-pyrido[4,3-b]indole and 3-amino-1-methyl-5H-pyrido[4,3-b]indole, were purified from the pyrolysis products of tryptophan. These new compounds were stronger mutagens than aflatoxin B1 towards S. typhimurium TA98, a frameshift type mutant, and they also transformed cryopreserved Syrian hamster embryo cells in vitro. Tryptophan pyrolysate also contained the beta-carboline derivatives, norharman and harman, which are not mutagenic alone, but act as comutagens. A mixture of norharman or harman and nonmutagenic aniline or o-toluidine was strongly mutagenic. The mutagenicities of charred products of other foods, such as seaweed and garlic, are reviewed in this article. Flavonoids, such as kaempferol and quercetin, and glycosides of these flavonoles were mutagenic. The mutagenicity of cooked vegetables depends partly on these flavonoid derivatives. The already-known existence of benzol[a]pyrene and nitroso compounds in cooked food is also reviewed.