The pathogen reduction treatment of platelets with S-59 HCl (Amotosalen) plus ultraviolet A light: genotoxicity profile and hazard assessment

Despite restrictive donor criteria and screening procedures, infections resulting from the transfusion of bacterially contaminated platelet products continue to occur. Pathogen reduction technologies targeting nucleic acids have been developed. However, concerns about the safety of these procedures exist; the main concern being the possible mutagenic and carcinogenic effects of the pathogen-inactivated preparation in the recipient. This report reviews the genotoxicity profile of the S-59 (Amotosalen) plus long wavelength ultraviolet light (UVA) pathogen reduction technology, and assesses the mutagenic and carcinogenic hazards in recipients of treated platelets. S-59, a synthetic heterocyclic psoralen, non-covalently intercalates into the nucleic acids of pathogens and forms crosslinks when UVA photoactivated. Before clinical use, the levels of residual S-59 and free photoproducts are greatly reduced using a 'compound adsorption device' (CAD). In vitro, S-59 is mutagenic in Salmonella typhimurium and mouse lymphoma L5178Y TK(+/-) cells, and is clastogenic in CHO cells. There is reduced activity (Salmonella, CHO cells) or no activity (mouse lymphoma cells) with metabolic activation (S9 mix). When tested up to toxic dose levels, S-59 was negative in the mouse bone marrow micronucleus assay and the rat hepatocyte unscheduled DNA synthesis (UDS) test. Based on comparative studies conducted with S-59 plus UVA-treated platelets (up to 25 times without CAD), any genotoxic effects can be attributed to residual S-59. Considering (1) the known genotoxic mechanism of action for S-59, (2) the negative in vivo studies for S-59 at multiples >40,000x over clinical peak plasma levels, and (3) the fact that the positive in vitro genotoxicity effects for the end product seem due to residual S-59, any mutagenic hazard to a recipient of S-59 plus UVA-treated platelets is negligible and there is no concern about a carcinogenic potential as a consequence of a mutagenic activity. This conclusion is supported by a negative p53(+/-) mouse carcinogenicity study.     

The pathogen reduction treatment of platelets with S-59 HCl (Amotosalen) plus ultraviolet A light: Genotoxicity profile and hazard assessment

Despite restrictive donor criteria and screening procedures, infections resulting from the transfusion of bacterially contaminated platelet products continue to occur. Pathogen reduction technologies targeting nucleic acids have been developed. However, concerns about the safety of these procedures exist; the main concern being the possible mutagenic and carcinogenic effects of the pathogen-inactivated preparation in the recipient. This report reviews the genotoxicity profile of the S-59 (Amotosalen) plus long wavelength ultraviolet light (UVA) pathogen reduction technology, and assesses the mutagenic and carcinogenic hazards in recipients of treated platelets. S-59, a synthetic heterocyclic psoralen, non-covalently intercalates into the nucleic acids of pathogens and forms crosslinks when UVA photoactivated. Before clinical use, the levels of residual S-59 and free photoproducts are greatly reduced using a ‘compound adsorption device’ (CAD). In vitro, S-59 is mutagenic in Salmonella typhimurium and mouse lymphoma L5178Y TK^+/− cells, and is clastogenic in CHO cells. There is reduced activity (Salmonella, CHO cells) or no activity (mouse lymphoma cells) with metabolic activation (S9 mix). When tested up to toxic dose levels, S-59 was negative in the mouse bone marrow micronucleus assay and the rat hepatocyte unscheduled DNA synthesis (UDS) test. Based on comparative studies conducted with S-59 plus UVA-treated platelets (up to 25 times without CAD), any genotoxic effects can be attributed to residual S-59. Considering (1) the known genotoxic mechanism of action for S-59, (2) the negative in vivo studies for S-59 at multiples >40,000× over clinical peak plasma levels, and (3) the fact that the positive in vitro genotoxicity effects for the end product seem due to residual S-59, any mutagenic hazard to a recipient of S-59 plus UVA-treated platelets is negligible and there is no concern about a carcinogenic potential as a consequence of a mutagenic activity. This conclusion is supported by a negative p53^+/− mouse carcinogenicity study.     

Mutagenicity testing of imidazole and related compounds.

Ames tests have been performed with imidazole and its principal metabolites, hydantoin and hydantoic acid. N-Acetyl-imidazole, a potential metabolite resulting from the action of intestinal bacteria, and histamine, a structurally related compound which is widely distributed in mammalian tissues, have also been tested. Imidazole and histamine were also tested in the UDS assay in primary rat hepatocytes, while imidazole alone was tested in the M2-C3H mouse fibroblast malignant transformation assay. Imidazole gave consistently negative results in the Ames test, the UDS assay and the transformation assay. The three metabolites of imidazole, namely hydantoin, hydantoic acid and N-acetyl-imidazole, all gave negative results in the Ames test. Histamine gave no evidence of mutagenic activity in the Ames test or of genotoxicity in the UDS assay. These results indicate that imidazole and its metabolites are unlikely to present a mutagenic or carcinogenic hazard.     

On the mutagenicity of nitroimidazoles

Regarding mutagenicity, metronidazole is one of the best-investigated compounds of the nitroimidazoles. This drug is mutagenic on bacteria, especially if base-pair tester strains are used and bacterial nitroreductases are present. The serum levels attained in man after intake of this drug are sufficient to cause mutations in bacteria. Furthermore, interaction with and binding to DNA occurs under anaerobic conditions and sometimes DNA breaks are observed. However, metronidazole does not show mutagenic activity in mammalian cells in vitro; the micronucleus test is negative and chromosome aberrations are only found under anaerobic conditions. With microbial systems the mutagenicity of 47 nitroimidazoles has been investigated. Only 4 compounds were always negative in the applied test systems. Because with base-pair tester strains mutagenicity was assessed, this class of compounds should be regarded as a base-pair mutagen. In fungi, some compounds (e.g. ZK 26173 and azathioprine) are potent mutagens, whilst with most investigated nitroimidazoles only a weak or no mutagenic activity could be detected. Somewhat similar observations have been made in tests with Drosophila melanogaster, a test for gene mutations in mammalian cells, the micronucleus test, cytogenic tests and the dominant lethal test. The reduction products of metronidazole, misonidazole and 1-methyl-2-nitro-5-vinylimidazole, cause DNA damage if the nitro group is reduced in the presence of DNA. Reduction products are formed by microbes in the gut or by mammalian cells under anaerobic conditions. No teratological effect due to metronidazole or most other nitroimidazoles has been observed. Metronidazole is carcinogenic in mice and rats, and dimetridazole in rats. Up to the present, no carcinogenic effects have been observed in man. Azathioprine is probably carcinogenic for man. It is unlikely that the therapeutic applications of the presently used nitroimidazoles, except for azathioprine, will cause an increase in the tumor incidence in man or will cause other genotoxic effects, although such effects cannot be excluded with certainty.     

Comparative mutagenicity of chemicals selected for test in the International Program on Chemical Safety''s collaborative study on plant systems for the detection of environmental mutagens

A review has been made of the four compounds (maleic hydrazide, methyl nitrosourea, sodium azide, azidoglycerol) tested in the International Program on Chemical Safety's collaborative study systems. Maleic hydrazide (MH) is a weak cytotoxic/mutagenic chemical in mammalian tissues and is classified as a class 4 chemical. In contrast, with few exceptions such as Arabidopsis, MH is a potent mutagen/clastogen in plant systems. The difference in its response between plant and animal tissue is likely due to differences in the way MH is metabolized. MH appears to be noncarcinogenic and has been given a negative NCI/NTP carcinogen rating.

Methyl nitrosourea (MNU) is a toxic, mutagenic, radiomimetic, carcinogenic, and teratogenic chemical. It has been shown to be a mutagen in bacteria, fungi, Drosophila, higher plants, and animal cells both in vitro and in vivo. MNU is a clastogen in both animal and human cell cultures, plant root tips and cell cultures inducing both chromosomes and chromatid aberrations as well as sister-chromatid exchanges. Carcinogenicity has been confirmed in numerous studies and involves the nervous system, intestine, kidney, stomach, bladder and uterus, in the rat, mouse, and hamster. MNU produces stage-specific teratogenic effects and also interferes with embryonic development. The experimental evidence that strongly indicates the mutagenic effects of MNU underlines the possible hazard of this compound to human beings. The experimental evidence for the stringent handling of this compound is clear.

Sodium azide (NaN₃) is cytotoxic in several animal and plant systems and functions by inhibiting protein synthesis and replicative DNA synthesis at low dosages. It is mutagenic in bacteria, higher plants and human cells and has been used as a positive control in some systems. In general, tests for clastogenicity have been negative or weakly positive. No evidence of carcinogenicity has been reported in a 2-year study seeking carcinogenic activity in male and female rats. Its advantages in comparison to other efficient mutagens are claimed to be a high production of gene mutations accompanied by a low frequency of chromosomal rearrangements and safer handling because of its nonclastogenic and noncarcinogenic action on humans.     

Normal chromosomal aberration frequencies in peripheral lymphocytes of healthy human volunteers exposed to a maximum daily dose of paracetamol in a double blind trial.

Paracetamol (acetaminophen) has been examined for mutagenic potential in numerous studies: gene mutation tests consistently gave negative results while in vitro chromosomal aberration tests showed equally consistently positive effects. In vivo studies for chromosome breaking activity gave clearly negative, equivocal or weakly positive results. In particular two reports have indicated that human volunteers taking a maximum daily dose of paracetamol (3 x 1000 mg over 8 h) exhibited significantly elevated frequencies of chromatid breaks in their peripheral lymphocytes 24 h later. In the one study evaluating the time course, levels returned to normal between 3 and 7 days later. We performed a carefully controlled double-blind study in which volunteers were pre-screened for normal liver function, they all were non-smoking and their diet and environmental exposures were controlled during the study. Cell-cycle kinetics were monitored and paralleled and a placebo group was included. Although a larger number of cells than in the other studies was analysed we were unable to reproduce their findings. No significant increases in structural chromosome aberrations (CA) were found either when the paracetamol group (male, female or both) post-dosing values were compared with pre-dosing values, or when treated groups at any sampling time were compared with the placebo groups. There was not even any evidence that individuals responded to the clastogenic potential of paracetamol or that a group response may have been masked by non-responders. In conjunction with the recently published results of the NTP bioassay, showing no carcinogenic activity in mice and no carcinogenic activity in rats except an increase of mononuclear cell leukaemia in female rats which is of doubtful relevance, the study presented here argues that paracetamol does not pose an unacceptable (if any) genotoxic/carcinogenic risk to man.     

Principles of formalizing a quantitative evaluation of the genetic danger of chemical compounds for man

Specific characteristics of the mutagenic effect of chemicals, which must be taken into account in developing the test system to assess the potential genetic risk caused by chemical substances, are considered. The organizational principles of the procedures currently available for testing and ranking chemicals by their mutagenic and carcinogenic hazard to humans are discussed. The use of selective information suggested by Wiener and Shannon as an efficiency measure of testing and estimating the potential genetic hazard of chemical substances is substantiated. The feasibility of this approach was demonstrated by testing the efficiency of the battery of two short-term in vitro tests as an example. It was shown that selective information is able to serve as an integral universal criterion of the efficiency of testing, if either one test or the test battery were used.     

Polychlorinated biphenyls (PCBs): mutagenicity and carcinogenicity

The potential mutagenicity and carcinogenicity of commercial PCBs has been investigated in both in vivo and in vitro systems and several conclusions can be drawn from these studies. (1) PCBs can covalently adduct DNA both in vivo and in vitro (using a source of metabolic activation); the more highly chlorinated biphenyls are poorly metabolized and these compounds tend to exhibit very low binding to DNA. Based on the structure-activity relationships for PCBs (Safe, 1984) it is unlikely that the more toxic compounds such as 3,3',4,4',5-penta- and 3,3',4,4',5,5'-hexachlorobiphenyl, would form covalent adducts with DNA. (2) PCB mixtures and individual compounds exhibit minimal mutagenic activity in most assay systems. (3) The more highly chlorinated PCB mixtures (i.e. greater than 50% Cl by weight) are hepatocarcinogens in rodents whereas data from a limited number of studies suggest that the lower chlorinated mixtures are not carcinogenic. (4) In some model systems, the higher chlorinated PCB mixtures act as promoters of preneoplastic lesions and hepatocellular carcinomas in rodents treated with a variety of initiators. (5) Aroclor 1254 acts as a promoter of skin papilloma formation in HRS/J hairless mice and structure-activity and genetic studies suggest that the Ah receptor is necessary but not sufficient for the activity of halogenated aryl hydrocarbons as promoters in hairless mice. (6) Individual PCB congeners and higher chlorinated commercial mixtures also exhibit anti-carcinogenic activity in the CD-1 mouse skin cancer model. (7) Results from occupational studies suggest that individuals exposed to PCBs may have an excess of cancer at some sites, however, the most comprehensive study (Brown, 1987) suggests that there are no significant increases in the overall cancer rate in workers exposed to PCBs. Follow-up and continuing epidemiological studies on the PCB-exposed workers are required to further clarify the potential carcinogenic effects of PCBs on humans. In several strains of rats and mice, there is a high incidence of hepatic preneoplastic lesions and carcinomas and these lesions can be induced by diverse promoting agents (Schulte-Hermann et al., 1983; Weinstein, 1984). Since PCBs are not mutagenic and do not readily form covalent adducts with cellular DNA, it is likely that the higher chlorinated biphenyls are not genotoxic and act as promoters of carcinogenesis in rodents. A comparable mechanism has been suggested for 2,3,7,8-TCDD (Shu et al., 1987; Weinstein, 1984). For PCBs, the role of the Ah receptor in mediating their activity as promoters has not been delineated.(ABSTRACT TRUNCATED AT 400 WORDS)     

Relationships between structures and mutagenic potencies of 16 heterocyclic nitrogen mustards (ICR compounds) in Salmonella typhimurium

16 heterocyclic nitrogen mustards (ICR compounds), which were synthesized for use as possible antitumor agents by Creech and coworkers, were tested for mutagenicity in Salmonella typhimurium strains TA1535, TA1536, TA1537, TA1538, TA98 and TA100. The compounds were incorporated into the top agar at 5 doses: 0.5, 1, 2.5, 5 and 10 micrograms/plate. All of the compounds were negative in TA1535 except ICR 449, which was positive in all 6 strains. The other 15 compounds were positive in the remaining strains with the following exceptions: ICR 371 and 355 were negative in TA100; ICR 445 was negative in TA98 and TA100; and ICR 360 was negative in TA1537, TA1538, TA98 and TA100. Good qualitative agreement was observed between the mutagenic and antitumor activities of the 16 compounds, and between the mutagenic and carcinogenic activities of the 5 compounds that have been tested for carcinogenicity by Peck and coworkers. However, no significant correlation was found between mutagenic potency in Salmonella and antitumor potency in mice for the 16 compounds. Also, for the 5 compounds that have been tested for carcinogenicity, no significant correlation was found between their mutagenic potency in Salmonella and their carcinogenic potency in mice. In Salmonella, the secondary (2 degrees) amines generally were more mutagenic than their tertiary (3 degrees) amine homologs, although the opposite result has been reported in certain eukaryotes. Relationships between structures and potencies for the different nuclei of the 16 ICR compounds are discussed, as are similarities and differences in strain sensitivities. We conclude that the Salmonella his reversion test is not a good predictor of the antitumor and carcinogenic potencies of these ICR compounds.     

Mutagenicity of fungal metabolites related to aflatoxin biosynthesis.

Fungal metabolites identified as the intermediates in aflatoxin biosynthetic pathway were screened for their mutagenic activity to Salmonella typhimurium TA98. Norsolorinic acid, averufin, and versiconal acetate were found to possess questionable mutagenic activity, but versicolorin A, and sterigmatocystin were significant mutagens relative to aflatoxin B1. The mutagenic activity appears to be related to the bisfuran and not the anthraquinone moiety of the molecule, even though the latter is a key structure of such potent carcinogenic mycotoxin as luteoskyrin.     

Mutagenicity of benzidine and benzidine-congener dyes and selected monoazo dyes in a modified Salmonella assay

We have evaluated the mutagenic activity of a series of diazo compounds derived from benzidine and its congeners o-tolidine, o-dianisidine and 3,3'-dichlorobenzidine as well as several monoazo compounds. The test system used was a modification of the standard Ames Salmonella assay in which FMN, hamster liver S9 and a preincubation step are used to facilitate azo reduction and detection of the resulting mutagenic aromatic amines. All of the benzidine and o-tolidine dyes tested were clearly mutagenic. The o-dianisidine dyes except for Direct Blue 218 were also mutagenic. Direct Blue 218 is a copper complex of the mutagenic o-dianisidine dye Direct Blue 15. Pigment Yellow 12, which is derived from 3,3'-dichlorobenzidine, could not be detected as mutagenic, presumably because of its lack of solubility in the test reaction mixture. Of the monoazo dyes tested, methyl orange was clearly mutagenic, while C.I. Acid Red 26 and Acid Dye (C.I. 16155; often referred to as Ponceau 3R) had marginal to weak mutagenic activity. Several commercial dye samples had greater mutagenic activity with the modified test protocol than did equimolar quantities of their mutagenic aromatic amine reduction products. Investigation of this phenomenon for Direct Black 38 and trypan blue showed that it was due to the presence of mutagenic impurities in these samples. The modified method used appears to be suitable for testing the mutagenicity of azo dyes, and it may also be useful for monitoring the presence of mutagenic or potentially carcinogenic impurities in otherwise nonmutagenic azo dyes.     

Mutagens that are not carcinogens: faulty theory or faulty tests?

In the National Toxicology Program database of 172 chemicals that were judged non-carcinogenic or equivocal in 2 year rodent studies in both sexes of rats and mice, there are 38 chemicals that were mutagenic in Salmonella. All but two of the chemicals had structural alerts for mutagenicity. The largest proportion of the mutagenic non-carcinogens were benzeneamines and substituted benzeneamines. In all, 12 of the mutagenic non-carcinogens had mutagenic carcinogen analogues, and for two chemicals, the carcinogenic analogues were not mutagenic. Non-carcinogens that were mutagenic in Salmonella also tended to be mutagenic and clastogenic in mammalian in vitro tests. The mutagenic responses are discussed and explanations offered for the mutagenicity and lack of carcinogenic activity of these chemicals.     

Mutagenicities of N-nitrosamines on Salmonella.

The mutagenic activities of 11 N-nitrosamines were tested using Salmonella typhimurium TA100 and TA98. All the carcinogenic N-nitrosamines were mutagenic on TA100 with a drug-activating system from the rat liver, whereas N,N-diphenylnitrosamine, a non-carcinogen, was not mutagenic. None of the N-nitrosamines was mutagenic on TA98, except N,N-diethylnitrosamine which was weakly mutagenic. To detect the mutagenicity of N,N-dimethylnitrosamine, the pre-incubation of bacteria and N,N-dimethylnitrosamine with S-9 Mix before if was poured onto plates was obligatorily required. Dimethyl sulfoxide inhibited the mutagenic effect of N,N-dimethylnitrosamine.     

Mutagenicity,carcinogenicity and teratogenicity of vanadium compounds

The mutagenic, carcinogenic and teratogenic effects of vanadium and its compounds are reviewed. It is concluded that vanadium is not clastogenic and only weakly mutagenic; it has marked mitogenic activity affecting the distribution of chromosomes during mitosis and possibly causing aneuploidy. The few positive data on effects of vanadium during development leave it open whether direct effects on the embryo or fetus or physiological disturbances in the mother are responsible. No data exist indicating that vanadium is carcinogenic in animals or man, but since it interferes with mitosis and chromosome distribution, the possibility that vanadium might be carcinogenic under certain conditions cannot be dismissed offhand.     

Formation of mutagenic N-nitroso compounds from the pesticides prometryne, dodine and carbaryl in the presence of nitrite at pH 1

Environmental chemicals including pesticides carrying secondary and tertiary amino groups are suggested to be a health hazard to man since potentially carcinogenic nitroso compounds may be formed in the presence of nitrite at low pH values resembling conditions in the human stomach. Nitrosation of the isopropylamino-triazine Prometryne, the n-dodecyl guanidine Dodine and the N-methylcarbamate carbaryl was investigated in the presence of HCl and acetic acid at pH 1 and excess sodium nitrite for 4 h at 37 degrees C. The reaction products were extracted with CCl4 and were analyzed qualitatively and quantitatively by infrared spectroscopy, nuclear-resonance spectrometry, GC/mass spectrometry and by spectrophotometry. All compounds investigated formed N-nitroso derivatives in the following yields: carbaryl 67%, Dodine 12% and Prometryne 14%. The N-nitroso derivatives per se were not or only slightly mutagenic to Escherichia coli K12 or Salmonella typhimurium TA 1538. However, significantly increased mutation frequencies were seen after metabolic activation by mouse-liver microsomes. These results add to the observations that among environmental chemicals not only those containing methyl- or ethyl-substituted amino groups form potentially carcinogenic nitroso derivatives but also those with iso-propylamino groups as well as alkyl-substituted guanidine derivatives.     

Detoxification of aflatoxin B1 by manganese peroxidase from the white-rot fungus Phanerochaete sordida YK-624

Aflatoxin B(1) (AFB(1) ) is a potent mycotoxin with mutagenic, carcinogenic, teratogenic, hepatotoxic, and immunosuppressive properties. In order to develop a bioremediation system for AFB(1) -contaminated foods by white-rot fungi or ligninolytic enzymes, AFB(1) was treated with manganese peroxidase (MnP) from the white-rot fungus Phanerochaete sordida YK-624. AFB(1) was eliminated by MnP. The maximum elimination (86.0%) of AFB(1) was observed after 48 h in a reaction mixture containing 5 nkat of MnP. The addition of Tween 80 enhanced AFB(1) elimination. The elimination of AFB(1) by MnP considerably reduced its mutagenic activity in an umu test, and the treatment of AFB(1) by 20 nkat MnP reduced the mutagenic activity by 69.2%. (1) H-NMR and HR-ESI-MS analysis suggested that AFB(1) is first oxidized to AFB(1) -8,9-epoxide by MnP and then hydrolyzed to AFB(1) -8,9-dihydrodiol. This is the first report that MnP can effectively remove the mutagenic activity of AFB(1) by converting it into AFB(1) -8,9-dihydrodiol.     

Absence of mutagenic activity of WHR-1142A, lidamidine hydrochloride, in 4 short-term tests for mutagenic/carcinogenic potential

WHR-1142A, lidamidine hydrochloride, an antidiarrhoeal agent, was tested for possible mutagenic/carcinogenic activity in the Ames Salmonella typhimurium/metabolic activation test, the micronucleus test, by analysis of metaphase chromosomes obtained from human lymphocytes grown in culture and in a cell transformation assay. No evidence of mutagenic/carcinogenic activity due to WHR-1142A, lidamidine hydrochloride, was found in any of the 4 tests.     

Antimutagenic effect of eight natural foods on moldy foods in a high liver cancer incidence area.

Ames test procedures were used to test 8 natural food extracts for their antimutagenic activity against the mutagenic activity induced in S. typhimurium strains TA98 and TA100 by aflatoxin B1 (AFB1) or metabolic extracts from A. versicolor or A. ochraceus. The tested substances were extracted repeatedly with acetone. The revertants induced by AFB1, metabolic extracts of A. versicolor or A. ochraceus were significantly decreased when extracts of the 8 natural foods were added to the media. The results showed that these extracts had marked inhibitory effects on the mutagenic activity induced by AFB1 or metabolic extracts of the two molds and also suggested that antimutagenic substances were present in these natural foods. These experiments provide a scientific basis for the study of food substances for the prevention of carcinogenesis. It is considered that these 8 natural food extracts produce marked antimutagenic effects and are practically valuable in the field of chemoprophylaxis of liver cancer in humans.     

High mutagenic potency of several polycyclic aromatic hydrocarbons induced by liver postmitochondrial fractions from control and xenobiotic-treated immature carp

The metabolism of carcinogens in fish was examined by measuring the activation of different polycyclic aromatic hydrocarbons (PAH) by carp (Cyprinus carpio L.) liver post-mitochondrial fractions (S9) using the Salmonella typhimurium TA100 reverse mutation assay. For this study, 1 non-carcinogen, anthracene (AN), and 4 carcinogens, chrysene (CHR), benzo[a]pyrene (BaP), 3-methylcholanthrene (3MC) and 7,12-dimethylbenzanthracene (DMBA), were chosen. The bioactivating potency of the metabolic systems of carp pretreated with phenobarbital (PB), 3MC or Aroclor 1254 (ARO) were compared to uninduced carp liver. The results show that carp liver has the ability to metabolize carcinogenic PAH into mutagenic metabolites, which is enhanced when carp are pretreated with 3MC or ARO, but not with PB. A positive correlation between the induction of aryl hydrocarbon hydroxylase (AHH) activity in carp liver and the mutagenic potencies of CHR, BaP, DMBA and 3MC, has been observed. The bioactivating ability of carp liver S9 was compared with the ability of the same fractions from female Wistar rats (this study) as well as from Sprague-Dawley rats (literature data). When the mutagenic potencies of selected PAH had been normalized on the activity of BaP, the following order of mutagenic activities with S9 fractions from ARO-treated animals was obtained: (1) BaP (1) greater than DMBA (0.26) greater than 3MC (0.22) greater than CHR (0.05) greater than AN (0) for carp; (2) BaP (1) greater than 3MC (0.48) greater than CHR (0.31) greater than DMBA (0.16) greater than AN (0) for Sprague-Dawley rats; and (3) BaP (1) greater than 3MC (0.17) greater than DMBA (0.11) greater than CHR (0) = AN (0) for female Wistar rats. We conclude that carp and rats are very similar in their ability to activate carcinogenic PAH into mutagenic metabolites, which suggests that carp may be very susceptible to the carcinogenic activity of these compounds. According to our results from the mutagenicity study, as well as from the enzyme induction study, we propose the use of carp as a suitable model system for the study of chemical carcinogens.     

Metabolic studies and the evaluation of genetic risk from the viewpoint of industrial toxicology

In recent years some important industrial chemicals, e.g. solvents, and monomers used in the production of plastics, have been found to be more dangerous than had been suspected. Some of them are mutagens and carcinogens. The active substance may be the compound itself, but more frequently it is a reactive intermediate, an alkylating agent, formed from the parent compound by oxidation under the influence of liver-microsome mixed-function oxidases. Trichloroethylene, vinyl chloride, 1,1-dichloroethylene and 2-chloro-1,3-butadiene can be mentioned as examples, where mutagenic or carcinogenic activity has been demonstrated; similar activity of some others is to be suspected. Metabolic studies may explain unexpected effects or they may allow one to predict such effects. Tests on microorganisms with a metabolic activation in vitro seem to be extremely valuable for fast and efficient screening of man-made chemicals to be introduced into the environment, because such tests combine the use of liver microsomes and bacteria for the detection and classification of the effect. Mutagenicity tests in mammals do not lose their usefulness, since they take into account the distribution of the compound in the body, its transport to the target organ, species-specific differences etc. As exposures of workers to chemicals mentioned above have been quantitatively measured regularly, epidemiological studies should be performed with regard to mutagenic and carcinogenic effects in relation to the degree of exposure. Here is a chance for better understanding of how to extrapolate experimental results to human populations and how to establish safe levels of chemicals in the environment if at all possible and acceptable.