Carcinogenicity of the food additive furylfuramide in foetal and young mice

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.

Tofu products: A review of their raw materials, processing conditions, and packaging

Tofu is a traditional product made mainly from soybeans, which has become globally popular because of its inclusion in vegetarian, vegan, and hypocaloric diets. However, with both commercial production of tofu and scientific research, it remains a challenge to produce tofu with high quality, high nutrition, and excellent flavor. This is because tofu production involves multiple complicated steps, such as soybean selection, utilization of appropriate coagulants, and tofu packaging. To make high-quality tofu product, it is important to systematically understand critical factors that influence tofu quality. This article reviews the current research status of tofu production. The diversity of soybean seeds (the raw material), protein composition, structural properties, and nutritional values are reviewed. Then, selection of tofu coagulants is reviewed to provide insights on its role in tofu quality, where the focus is on the usage of mix coagulants and recent developments with new coagulants. Moreover, a comprehensive summary is provided on recent development in making high-fiber tofu using Okara (the major by-product during tofu production), which has a number of potential applications in the food industry. To help encourage automatic, environmental friendly, and high-efficient tofu production, new developments and applications in production technology, such as ultrasound and high-pressure process, are reviewed. Tofu packaging, including packaging materials and techniques, is evaluated as it has been found to have a positive impact on extending the shelf life and improving the quality of tofu products. Finally, the future research directions and potential areas for new developments are discussed.

Effect of episomally encoded DNA polymerases on chemically induced mutagenesis at the hisG46 target in Ames test

BACKGROUND

The standard Ames test strains owe their high sensitivity to chemical and physical mutagens to the episomal Y-family DNA polymerase RI encoded by the mucAB operon. The S. typhimurium test strains carry also another related samAB operon on a 60-kDa cryptic plasmid. In contrast to the chromosomally encoded Y-family DNA polymerases V and IV, these plasmid born polymerase genes have no direct counterpart in mammalian cells. By replicating damaged templates, DNA polymerases play a central role in mutagenesis and genome stability. It is therefore imperative to investigate their specificity to understand differences in mutagenesis between the prokaryotic versus eukaryotic (mammalian) systems. To this end we have isolated and separately expressed the DNA polymerase subunits encoded by the mucAB and samAB operons. After demonstrating how these enzymes control chemical and UV mutagenesis at the standard hisD3052 and hisG428 Ames test targets, we are now adding the third Ames test target hisG46 to the trilogy.

RESULTS

Four new Ames tester strains based on the hisG46 target have been constructed expressing the activated DNA polymerase MucA' and SamA' accessory subunits combined with the MucB and SamB catalytical subunits under the control of lac promoter. These polymerase assemblies were substituted for the endogenous PolRI, PolV and SamAB polymerases present in the standard TA100 strain and tested for their abilities to promote chemically induced mutagenesis. SamA' + SamB has been able to promote mutagenesis induced by AF-2 and 1,8-DNP to higher extent than SamA' + MucB. The MucA' + MucB (PolRI*) more efficiently promoted MMS as well as spontaneous mutagenesis than its wild type counterpart but was less efficient for other mutagens including AFB1. Strikingly azide mutagenesis was inhibited by PolRI and also SamA'B.

CONCLUSION

A new system for SOS-independent overexpression of the activated DNA polymerases RI and SamA'B and their chimeras in the hisG46 Ames test background has been established and validated with several representative mutagens. Overall, the TA100 strain showed the highest sensitivity towards most tested mutagens. The observed inhibition of azide mutagenesis by PolRI* suggests that this type of Y-family DNA polymerases can perform also "corrective" error free replication on a damaged DNA.

Effect of glutathione modulation on molecular interaction of [14C]-chloroacetonitrile with maternal and fetal DNA in mice

Binding of haloacetonitriles or their reactive metabolites to macromolecules of fetal tissue may be responsible for reproductive toxicity. To investigate the role of glutathione (GSH) in the metabolism and reproductive toxicity of haloacetonitriles, irreversible interaction of chloroacetonitrile (CAN) with maternal uterine and fetal DNA was assessed in a time course study among normal and among glutathione-depleted mice treated with [2-14C]-CAN. GSH was depleted in maternal and fetal tissues by treating of animals with diethylmaleate (DEM) 1 h before [2-14C]-CAN administration. Maternal urinary excretion of thiocyanate was 5 times higher in glutathione-depleted mice than in controls. At 8 and 24 h following [2-14C]-CAN administration, total radioactivity uptake in maternal uterine tissue, amniotic fluid, and fetal tissue was higher in glutathione-depleted mice than in control. Also the interaction of CAN or its reactive metabolites with maternal uterine DNA was enhanced following glutathione depletion. At 24 h after treatment, the covalent binding to DNA in fetal tissue was significantly increased in glutathione depleted mice (205% of control). The magnitude of interaction of CAN in fetal DNA was about 4 times higher than that in uterine DNA. The time course study in either maternal uterine or fetal DNA revealed elevated and persistent levels of covalent binding of [ C]-CAN to DNA at 72 h after treatment. Enhancement of the molecular interaction of CAN in maternal and fetal DNA following GSH depletion indicates an important role for GSH in CAN metabolism.

Inhibition of T cell mitogenesis by nitrofurans

A group of nitrofurans (5-nitro-2-furaldehyde, nifuroxime, nitrofurazone, nitrofurantoin, 5-nitro-2-furoic acid and 2-nitrofuran) were evaluated for inhibition of mitogenesis (DNA synthesis) in human peripheral blood T cells. T cells, either triggered by phorbol myristate acetate (PMA) or in the presence of accessory cells, were activated with a specified mitogen [phytohemagglutin (PHA), concanavalin A (ConA), or anti-CD3] and the amount of tritiated thymidine incorporated into DNA was determined. The results obtained indicate that nitrofurans inhibit mitogenesis irrespective of activator. 5-Nitro-2-furaldehyde was much more inhibitory than the other compounds, while 2-nitrofuran was less inhibitory. When the aldehyde group (5-nitro-2-furaldehyde) was replaced by a carboxyl group (5-nitro-2-furoic acid), the inhibitory activity was also reduced greatly. These results show that while the nitro group alone confers inhibitory activity to the furan ring, the group at the 2 position is crucial. In general, the mitogenic response of purified T cells (lacking accessory cells) triggered by PMA (phorbol ester) was inhibited less than that of the T cell-accessory cell system. With the latter, 50% inhibition of T cell mitogenesis was achieved by nifuroxime, nitrofurazone, and nitrofurantoin at 45-51 and 34-39 microM with PHA and ConA respectively. When purified T cells were used, the values were 71-85 and 55-60 microM respectively. For a given drug concentration, mitogenesis was more inhibited when induced by ConA or anti-CD3 than by PHA. The importance of using a single cell system (purified T cells) was emphasized by the interesting finding that only this system showed enhancement of mitogenesis, up to 35-40% at low drug levels. With the exception of the nitrofuraldehyde, the nitrofurans at strongly inhibitory levels were only moderately cytotoxic, exhibiting 62-85% cell survival after exposure to drug for 68 hr. Our results suggest that nitrofurans inhibit T cell mitogenesis by a relatively non-toxic mechanism; these results are comparable to those obtained for mammalian cells under aerobic conditions.

Genetic toxicology: can we design predictive in vivo assays?

The present analysis examines the assumptions in, the perceptions and predictivity of and the need for short-term tests (STTs) for genotoxicity in light of recent findings that most noncarcinogens from the National Toxicology Program are genotoxic (i.e., positive in one or more in vitro STTs). Reasonable assumptions about the prevalence for carcinogens (1-10% of all chemicals), the sensitivity of these STTs (ca. 90% of all carcinogens are genotoxic) and their estimated "false positive" incidence (60-75%) imply that the majority of chemicals elicit genotoxic responses and, consequently, that most in vitro genotoxins are likely to be noncarcinogenic. Thus, either the usual treatment conditions used in these in vitro STTS are producing a large proportion of artifactual and meaningless positive results or else in vitro mutagenicity is too common a property of chemicals to serve as a useful predictor of carcinogenicity or other human risk. In contrast, the limited data base on in vivo STTs suggests that the current versions of these assays may have low sensitivity which appears unlikely to improve without dropping either their 'short-term' aspect or the rodent carcinogenicity benchmark. It is suggested that in vivo genotoxicity protocols be modified to take into consideration both the fundamentals of toxicology as well as the lessons learned from in vitro genetic toxicology. In the meantime, while in vivo assays are undergoing rigorous validation, genetic toxicology, as currently practiced, should not be a formal aspect of chemical or drug development on the grounds that it is incapable of providing realistic and reliable information on human risk. It is urged that data generated in new, unvalidated in vivo genotoxicity assays be exempted from the normal regulatory reporting requirements in order to encourage industry to participate in the laborious and expensive development of this next phase of genetic toxicology.

X-ray- and chemically induced germ-line mutation causing phenotypical anomalies in mice

A large and significant increase of phenotypical anomalies was observed in the progeny of ICR parent mice treated before mating with X-rays, urethane, 7,12-dimethylbenz[a]anthracene, ethylnitrosourea (ENU), and 4-nitroquinoline 1-oxide, but the increase was not significant with furylfuramide. Major types of induced anomalies were cleft palate, dwarf, open eyelid, tail anomalies, and exencephalus. Dwarf, open eyelid and tail anomalies were predominant types of viable anomalies and were inherited as if they were dominant mutations with varying expressivity or penetrance. Incidence of prenatal anomalies increased with treated doses of X-rays, urethan, or ENU for both spermatozoa and spermatogonia. Spermatogonia were less sensitive to X-rays and urethane than spermatozoa, while ENU induced a very high incidence of prenatal anomalies by the spermatogonial treatment. In contrast to the previous works with X-rays, there was a clear, almost linear increase of anomalies in the dose range from 0 to 216 rad after spermatogonial exposure. For treatment of oocytes, there was also a clear increase with doses of X-rays and urethane. Doubling doses of X-rays for prenatal anomalies were 12 rad for spermatozoa, 27 rad for spermatogonia, and 19 rad for mature oocytes. These values are similar to those for ordinary mouse mutations. However, the mean rate of prenatal anomalies per rad (1.2 X 10(-4), 6.6 X 10(-5) and 9.1 X 10(-5) for spermatozoa, spermatogonia and mature oocytes, respectively) and that for 1 micrograms/g of ENU (3.4 X 10(-4) for spermatogonia) were 4-40 times higher than that of ordinary mutation in mice, because overall phenotypical abnormalities were scored in this study. Information obtained from the work on phenotypical anomalies is valuable to assess genetic risk of radiation and chemicals, because a majority of human genetic diseases show this kind of irregular and uncertain inheritance and most of the induced anomalies are similar to those found in humans.

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)

Mutagenicity in drug development: interpretation and significance of test results

The use of mutagenicity data has been proposed and widely accepted as a relatively fast and inexpensive means of predicting long-term risk to man (i.e., cancer in somatic cells, heritable mutations in germ cells). This view is based on the universal nature of the genetic material, the somatic mutation model of carcinogenesis, and a number of studies showing correlations between mutagenicity and carcinogenicity. An uncritical acceptance of this approach by some regulatory and industrial concerns is over-conservative, naive, and scientifically unjustifiable on a number of grounds: Human cancers are largely life-style related (e.g., cigarettes, diet, tanning). Mutagens (both natural and man-made) are far more prevalent in the environment than was originally assumed (e.g., the natural bases and nucleosides, protein pyrolysates, fluorescent lights, typewriter ribbon, red wine, diesel fuel exhausts, viruses, our own leukocytes). "False-positive" (relative to carcinogenicity) and "false-negative" mutagenicity results occur, often with rational explanations (e.g., high threshold, inappropriate metabolism, inadequate genetic endpoint), and thereby confound any straightforward interpretation of mutagenicity test results. Test battery composition affects both the proper identification of mutagens and, in many instances, the ability to make preliminary risk assessments. In vitro mutagenicity assays ignore whole animal protective mechanisms, may provide unphysiological metabolism, and may be either too sensitive (e.g., testing at orders-of-magnitude higher doses than can be ingested) or not sensitive enough (e.g., short-term treatments inadequately model chronic exposure in bioassay). Bacterial systems, particularly the Ames assay, cannot in principle detect chromosomal events which are involved in both carcinogenesis and germ line mutations in man. Some compounds induce only chromosomal events and little or no detectable single-gene events (e.g., acyclovir, caffeine, methapyrilene). In vivo mutagenicity assays are more physiological but appear to be relatively insensitive due to the inability to achieve sufficiently high acute plasma levels to mimic cumulative long-term effects. Examination of the mutagenicity of naturally occurring analogs may indicate the irrelevance of a test compound's mutagenicity (e.g., deoxyguanosine and the structurally related antiviral drug, acyclovir, have identical mutagenicity patterns). Life-threatening or severe debilitating diseases (e.g., cancer, severe psychoses, severe crippling arthritis, sight-threatening diseases) may justify treatment with mutagenic or even carcinogenic therapeutic agents (benefit/risk considerations).(ABSTRACT TRUNCATED AT 400 WORDS)

The predictive value of batteries of short-term tests for carcinogens

Carcinogenesis is a multistage process in which many factors may affect the outcome. No single short-term test, measuring a single endpoint, can predict chemically induced carcinogenesis with infallibility. Therefore it is necessary to use a battery of tests when screening new compounds. Ideally, tests to be used in this way should be validated rigorously. Test batteries should not be used in isolation but should be complemented by information from studies of metabolism, pharmacokinetics, etc. Such an approach is proving valuable for the detection of carcinogens already present in the environment and for screening new chemicals for latent hazards.

Specific gene mutations in L5178Y cells in culture

The predominant test system uses a near-diploid L5178Y mouse lymphoma cell line and is based on the quantitation of forward mutations occurring at the heterozygous thymidine kinase (TK) locus (TK+/- leads to TK-/-). (Other markers, such as ouabain- or methothrexate-resistance and alanine independence, in other L5178Y mouse lymphoma cells were also examined, but our criteria for the acceptability of data or the paucity of data considerably reduced the value of these mutagenesis test systems to this study.) The biochemical basis for the L5178Y/TK+/- assay depends on the ability of TK-competent cells to phosphorylate 5-bromo-2'-deoxyuridine or trifluorothymidine. The phosphorylated product or its metabolites kill these cells, thus, medium containing 5-bromo-2'-deoxyuridine or trifluorothymidine is capable of selecting for cells that are lacking the TK enzyme (TK-/-). TK-/- cells eventually give rise to a bimodal distribution of colony sizes. The relative proportion of small and large colonies appears to be characteristic of the mutagen, its dose, and the length of the expression period. A total of 108 references were reviewed and 48 chemical agents were evaluated. Of these, in vivo carcinogenicity data existed for 44 and covered a wide variety of chemical classes (43 compounds) and a complex mixture. In this system, 39 agents were positive, 1 was negative, and 4 yielded inconclusive results. The 44 test substances evaluated were insufficient to single out agents or agent classes for which the assay was particularly well suited; however, with the exception of thymidine analogs, the system seems to be versatile. The correlation of the TK locus assay results with the carcinogenicity data revealed that 2 agents were definite false positives (sodium azide and methotrexate) and 1 agent was a definite false negative (1,1-dimethylhydrazine). Further evaluation suggested that 4-acetylaminofluorene and diphenylnitrosamine were questionable false positives, while benzo[e]pyrene was a questionable false negative. (The term questionable was used to imply uncertainties concerning the mutagenicity and/or carcinogenicity data). Thus, the assay is of value in the battery approach to mutagenicity/carcinogenicity screening.

Mutagenicity of nitro derivatives induced by exposure of aromatic compounds to nitrogen dioxide

Mutagenic nitro derivatives were readily induced when 6 kinds of chemicals were exposed to 10 ppm of nitrogen dioxide (NO2). Single nitro derivatives were formed from pyrene, phenanthrene, fluorene or chrysene. Carbazole and fluoranthene each produced 2 derivatives substituted with nitro groups at different positions. The formation of nitro derivatives was enhanced by exposure of pyrene to NO2 containing nitric acid (HNO3, less than 100-fold enhancement) or sulphur dioxide (SO2, less than 15-fold enhancement). After 24 h of exposure the yields of the nitro derivative were 0.02% with 1 ppm of NO2 in air and 2.85% with NO2 (1 ppm) containing traces of HNO3. The nitro derivatives from all but phenanthrene and carbazole were chemically identified by means of gas chromatography (GC) and mass spectrometry (MS), and the mutagenicity of the 4 kinds of authentic nitro derivatives was tested by using Salmonella strains TA98 and TA1538 with or without the S9 fraction from rat liver treated with Aroclor 1254. The nitro derivative induced from pyrene was determined to be 1-nitropyrene; that of chrysene was 6-nitrochrysene; that of fluorene was 2-nitrofluorene; and those of fluoranthene were 3-nitrofluoranthene, and 8-nitrofluoranthene. Tested with strain TA98 in the absence of the S9 fraction, the first 4 of these derivatives yielded, respectively, 3050, 269, 433 and 13 400 revertants per nmole. Thus, each nitro derivative formed was potentially a direct-acting frameshift-type mutagen. Each compound exposed to NO2 showed a decreased mutagenic activity when tested in the presence of S9 mix. A possible explanation comes from experiments in which 1-nitropyrene was incubated with the S9 mix at 37 degree C for 10 min, and 1-aminopyrene was formed. The mutagenic activity of 1-aminopyrene was appreciable, but only about one-tenth of that of 1-nitropyrene in the Ames test.

Deactivation of furyl furamide (AF-2) by rat-liver microsomes and its implication in short-term tests for mutagenicity/carcinogenicity

The genetic activity of AF-2 in both bacteria and yeast rapidly disappeared in the presence of rat-liver microsomal fraction (S9 mix). Incubation of AF-2 with S9 mix even for 10 min at 37 degrees C was sufficient to inactivate it completely. Data available in the literature suggest that activation of AF-2 is necessary for its geno-toxic effect. The activation step may involve reduction of the nitrofuran to an amino group probably by the enzyme reductase I. Most cultured cell systems, such as bacteria, yeast, Neurospora, mammalian cells and human lymphocytes, can probably bring about this reduction. However, the rapid disappearance of the genetic activity of AF-2 in the presence of rat-liver homogenate suggests that rat-liver microsomes may further metabolize the reduction products to inactive forms. Thus, it becomes necessary to test even those chemicals that are mutagenic per se, with mammalian microsomal preparations before their mutagenic/carcinogenic potentialities can be assessed in short-term tests.

Validation and characterization of the L5178Y/TK+/- mouse lymphoma mutagen assay system

The current status of the L5178Y/TK+/- leads to TK-/- mouse-lymphoma mutagenicity assay is described. Dose-survival-mutagenic response data are shown for 43 chemicals. Mutagenicity and cytotoxicity in the presence or absence of non-induced and/or Aroclor-induced rat-liver S-9 are compared for most of these chemicals, 25 of these for which usuable carcinogenicity data exist have been used to construct an approximately linear relationship between oncogenic potency in vivo and mutagenic potency in this system in vitro; linearity between these two endpoints extends over a greater than 100,000-fold range in potencies. Several carcinogens which are negative or difficult to detect in the standard Ames assay are mutagenic in this mammalian cell system. These include natulan, sodium saccharin (lot S-1022), p,p'-DDE (metabolite of DDT), dimethylnitrosamine, diethylnitrosamine and diethylstilbestrol. Characterization of the TK-/- mutants suggests that two mutagenic mechanisms contribute to their final yield. Large-colony TK-/- mutants probably represent point or gene mutations affecting the TK locus. In addition, a class of small-colony TK(/- mutants are described and characterized as being heritably growth-deficient; this and other properties suggest that these small-colony TK-/- mutants originate by a heritable and viable chromosomal aberration. Most carcinogens and mutagens tested produce both classes of TK-/- mutants in this system; the relative proportions of small- and large-colony mutants are both mutagen- and dose-dependent. Comparative studies have been done at the rapidly-expressing TK locus and the slowly-expressing HGPRT locus in these cells. Several carcinogens detected at the TK locus are non- or very weakly mutagenic at the HGPRT locus. This findings is consistent with the induction of slow-growing specific locus mutants by a chromosomal mechanism and their subsequent dilution during this long expression time.

Determination of radiation equivalence of the chemical furylfuramide (AF-2) for the induction of gene conversion in diploid yeast and estimation of genetic risk to the Japanese population

Dose--effect relationships for the induction of gene conversion by AF-2 in diploid yeast have been established. On the basis of these, the rec value for AF-2 for induction of gene conversion has been calculated to be 0.085 microgram/ml.h. This compares well with the rec values obtained with other test systems and other genetic end-points. The genetic burden to the Japanese population due to consumption of AF-2 is estimated to be equivalent to 55 millirec. However, uncertainties in the consumption of AF-2 per person and its metabolic detoxication tend to lower this value to, probably, a small fraction of that due to natural background ionizing radiation.

Malignant transformation of cryopreserved early passage syrian golden hamster cells by 2-(2-furyl)-3-(5-nitro-2-furyl)-acrylamide

2-(2-Furyl)-3-(5-nitro-2-furyl)-acrylamide (AF-2) induced the malignant transformation of secondary cultures of Syrian golden hamster embryo cells prepared from cryopreserved primary cells. Transformed cells grew in semi-solid agar medium and formed sarcomas when inoculated subcutaneously into non-immunosuppressed suckling hamsters.

Nitrofurantoin damages DNA of human cells

Nitrofurantoin causes damage to DNA of cultured diploid human fibroblasts. As a consequence DNA synthesis is blocked. The damage is removed by the normal enzymatic DNA repair system. Xeroderma pigmentosum fibroblasts which are defective in the excision endonuclease fail to repair nitrofurantoin-caused lesions.

The action of AF 2 on cultured hamster and human cells under aerobic and hypoxic conditions

AF 2 (2-(2-furyl)-3-(5-nitro-furyl)acrylamide) was toxic to Chinese hamster V 79 cells and normal human fibroblasts in aerobic media. However, the toxicity of the drug was increased many times by hypoxia. Similarly, the frequency of AF 2-induced azaguanine- and ouabain-resistant mutants of V 79 cells was much higher in hypoxia than under aerobic conditions. Both hamster V 79 cells and human fibroblasts metabolized AF 2 and other nitrofurans rapidly only under hypoxic conditions. Human fibroblasts were more sensitive to AF 2 both under aerobic conditions and in hypoxia than were V 79 cells under similar conditions. The Chinese hamster cells consistently gave survival curves with marked shoulders while human cells did not. Aerobic cultures of fibroblasts derived from xeroderma pigmentosum (XP) patients were markedly sensitive to AF 2 while fibroblasts from two ataxia telangeictasia patients had normal sensitivity. Under hypoxic conditions the sensitivity of both types of cells was increased but the XP line remained 5--10-fold more sensitive than normal or ataxia cells. These results suggest that the DNA lesions produced by AF 2 may be regarded as similar to those produced by ultraviolet light, at least in terms of their repairability in human cells.

Mutagenic effect of orally given AF-2 on embryonic cells in pregnant Syrian hamsters

Pregnant hamsters were given various doses of AF-2 by stomach tube; then the cells of their embryos were isolated and cultured in normal medium. Chromosome preparations were made within 24 h after the start of primary culture, and examined for chromosomal aberrations. Marked chromosomal abnormalities were observed in cells of embryos of animals treated with AF-2 at over 20 mg/kg. Samples of surviving cells were also cultured in normal medium for 48 h, and then selected in medium containing 8AG or 6TG. This treatment with AF-2 caused marked dose-dependent induction of 8AG- or 6TG-resistant mutations: mutant colonies were even obtained after a single treatment with 2 mg of AF-2 per kg. These results show that this is a sensitive and useful mammalian system for detecting environmental mutagens.

Neoplastic transformation induced by furylfuramide and nitromethylfuran of embryonic hamster cells in tissue culture

Secondary cultures of Syrian hamster embryonic fibroblasts were tested for transformation and neoplastic properties after exposure in vitro to furylfuramine (AF-2) and other nitrofurans. Typical morphological transformation was seen in five of six cultures between 30 and 186 days following treatment with 5-10X10(6) M AF-2 for 24 h. Transformation was seen in only one of four cultures 145 days after treatment for 6 h with AF-2. Treatment with 5-10X10(6) M NMF (5-nitro-2-methylfuran) for 24 h also induced transformation after 50 and 118 days in two cultures. In contrast, untreated cultures and cultures treated with 5-10X10(-6) M NFT [4-(5-nitro-2-furyl)thiazole] for 24 h were not transformed within 200 days. Three of the six lines transformed by AF-2 and both lines transformed by NMF also became tumorigenic 7-24 days after morphologic transformation. The other three transformed lines produced nodules which regressed within a few weeks of transplantation. Untreated and treated non-transformed lines did not produce tumors during an observation period of 6 months. The tumors were classified as fibrosarcomas. The ability to form colonies in soft agar was acquired by only one tumorigenic line.

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

The carcinogenicity of a food additive, 2-(2-furyl)-3-(5-nitro-2-furyl)acrylamide (AF-2), was studied in Wistar rats and CDF1 mice. The rats developed mammary tumors; the first appearing 9 months after the start of the experiment. In mice fed AF-2 diet, squamous cell carcinoma of the forestomach was observed in the 11th month. Some mice had metastases in the liver, spleen, lymph nodes and peritoneal cavity.

Mutagenicity of nitrovin--a nitrofuran feed additive

Nitrovin, a nitrofuran feed additive, is shown to be directly mutagenic in Salmonella typhimurium TA 98 and TA 100 between 0.1 and 2.5 microgram per plate (0.09--2.3 micrometer). Addition of a rat-liver homogenate reduces the mutation rates. Nitrovin inhibits growth of the same bacteria in suspension cultures at concentrations above 0.09 micrometer.

Carcinogenicity of a food additive, AF-2, in hamsters and mice

The carcinogenicity of a food additive, 2-(2-furyl)-3-(5-nitro-2-furyl) acrylamide (trade name, AF-2), was studied. A diet containing AF-2 at a rate of 0.25% was administered to male golden hamsters and male ddY mice. The hamsters developed squamous cell carcinomas in the forestomach after the 49th day from the start of administration. In mice fed a AF-2 diet for 308 days, squamous cell carcinoma was observed in the forestomach after the 381th day from the start of the experiment; in some cases the carcinoma metastasized to the lung and liver.

Short term screening tests for carcinogens

There are now short term tests with a high predictive value for mammalian carcinogens. Many of them are based on the ability to detect damage to DNA in bacteria or mammalian cells after metabolic activation by microsomal enzymes. Their introduction will enable provisional safety assessments to be made for the many thousands of industrial and environmental chemicals for which long-term animal testing cannot at present be considered.

Detection of carcinogens as mutagens in the Salmonella/microsome test: assay of 300 chemicals: discussion

About 300 carcinogens and non-carcinogens of a wide variety of chemical types have been tested for mutagenicity in the simple Salmonella/microsome test. The test uses bacteria as sensitive indicators of DNA damage, and mammalian liver extracts for metabolic conversion of carcinogens to their active mutagenic forms. There is a high correlation between carcinogenicity and mutagenicity: 90% (157/175) of the carcinogens were mutagenic in the test, including almost all of the known human carcinogens that were tested. Despite the severe limitations inherent in defining non-carcinogenicity, few "non-carcinogens" showed any degree of mutagenicity [McCann et al. (1975) Proc. Nat. Acad. Sci. USA 72, 5135-5139]. In the present paper, carcinogens negative in the test andapparent false positives are discussed. We also discuss evidence that chemical carcinogens and radiation, likely to initiate most human cancer and genetic defects do so by damage to DNA. The Salmonella test can play a central role in a program of prevention: to identify mutagenic chemicals in the environment (all indications are there are many) and to aid in the development of non-mutagenic products to prevent future human exposure.