Selenium inhibition of benzo[a]pyrene, 3-methylcholanthrene, and 3-methylcholanthrylene mutagenicity in Salmonella typhimurium strains TA98 and TA100

Selenium (Se) decreased the mutagenicity of benzo[a]pyrene (BP), 3-methylcholanthrene (3MC), and 3-methylcholanthrylene (3MCE) in Salmonella typhimurium strains TA98 and TA100. Metabolism of BP, 3MC and 3MCE to mutagens was accomplished with the liver S9 fraction from Aroclor 1254-treated male Sprague-Dawley rats. Exposure of the bacteria to 4 nmoles BP, 10 nmoles 3MC, or 10 nmoles 3MCE in the presence of S9, and up to 200 nmoles Se as Na2SeO3 resulted in decreased mutagenicities up to 39, 66 and 60% of their respective control activities without Se in TA98 and up to 46, 52 and 64% of their respective control activities without Se in TA100. Se (200 nmoles) alone was not mutagenic in strains TA98 or TA100 with or without S9. BP, 3MC and 3MCE were not mutagenic in either strain without S9. None of the tested concentrations of BP, 3MC, 3MCE and Se were cytotoxic. Assays of the aryl hydrocarbon hydroxylase (AHH) activity in the S9 preparation revealed decreased AHH activity with increase in Se concentration. The decreased mutagenicity and AHH activity were Se (as Na2SeO3) dependent and could not be duplicated by sulfur (S as Na2SO3). Inhibition of AHH activity by Se provides an explanation of the mechanism of Se inhibition of BP, 3MC and 3MCE mutagenicities in S. typhimurium TA98 and TA100.     

Metabolic activation of N-acetylbenzidine and N,N'-diacetylbenzidine to mutagens, using isolated hepatocytes and the 9000 X g liver supernatant from rat, hamster and guinea pig

The metabolic activation of MABZ and DABZ, forming products mutagenic towards Salmonella typhimurium TA1538, was studied with isolated hepatocytes from rat, hamster and guinea pig and the S9 fraction (9000 X g supernatant) prepared from these hepatocytes. Special attention was given to the influence of acetyl-CoA, the cofactor for N-acetylation, on the mutagenicity of these arylamides. The rat and guinea pig S9 preparation activated MABZ as well as DABZ to a much higher degree than the intact hepatocytes of these animal species. Addition of acetyl-CoA to the S9 preparation decreased the mutagenicity of MABZ and DABZ. On the contrary, for the hamster the mutagenicity of MABZ and DABZ appeared to be lower with the S9 preparation than with intact hepatocytes. Addition of acetyl-CoA to the S9 here increased the mutagenic activity of these arylamides. In the presence of intact hepatocytes obvious interspecies differences were observed in the activation of MABZ and DABZ. DABZ was far more effectively activated by hamster hepatocytes than by rat hepatocytes. This was not found with MABZ. Both substrates were poorly activated by guinea pig hepatocytes.     

Mutagenic activities of cyclophosphamide (NSC-26271) and its main metabolites in Salmonella typhimurium, human peripheral lymphocytes and Chinese hamster ovary cells

Cyclophosphamide (CPA) and its main metabolites were analyzed with respect to their mutagenic activities in Salmonella, human peripheral lymphocytes (PL), and Chinese hamster ovary (CHO) cells. In Salmonella, the compounds were activated with S9 mix from rat livers, which were unstimulated or stimulated with Aroclor 1254 or phenobarbital. For the enzyme inducers the following order of efficiency was found for all test compounds except carboxyphosphamide: phenobarbital greater than Aroclor 1254 greater than non-induced. The most potent mutagens in all 3 test systems were 4-OH-CPA, PAM and nor-HN2. S9 mix transforms 4-OH-CPA to strong mutagenic compounds in the Salmonella assay. All metabolites tested in the Salmonella assay were activated by S9 mix to higher mutagenic potential.     

Enhanced mutagenicity of anisidine isomers in bacterial strains containing elevated N-acetyltransferase activity.

In previous studies on the mutagenicity of anisidine isomers, the ortho isomer was considered to be mutagenic towards standard Ames tester strains, while the para isomer gave equivocal results. In the present study we show that both para- and ortho-anisidine isomers are mutagenic in a Salmonella typhimurium tester strain containing elevated levels of N-acetyltransferase (YG1029). p-Anisidine gave a positive mutagenic response using either hamster S9 or ram seminal vesicle microsomes (RSVM) as an activating system, while o-anisidine gave a positive response only with the hamster S9 fraction. The mutagenic response from p-anisidine was greater than with o-anisidine in each case. In tests with p-anisidine and RSVM, the addition of arachidonic acid was not necessary to observe a mutagenic response. Catalase produced a dose-dependent decrease in the mutagenic response with p-anisidine and RSVM; this indicates that endogenous hydrogen peroxide from the bacteria acts as a substrate for the peroxidase activity of RSVM prostaglandin H synthase. These results demonstrate that both anisidine isomers are mutagenic and that N-acetyltransferase enzymes play an important role in their metabolism to mutagenic species.     

Mutagenic activation of 2-acetylaminofluorene by guinea-pig liver homogenates: essential involvement of cytochrome P-450 mixed-function oxidases

2-Acetylaminofluorene (AAF) was highly mutagenic to Salmonella typhimurium strain TA98, when activated by a liver post-mitochondrial supernatant fraction (S9 fraction) from guinea-pigs, in spite of the resistance of this species to AAF carcinogenesis and the low capacity of the liver of this species for N-hydroxylation of AAF. The mutagenicity was comparable to or higher than that resulting from activation by mouse- or rat-liver S9 fraction, and was not enchanced by treatment with cytochrome P-450 inducers, a combination of phenobarbital and 5,6-benzoflavone. In an attempt to understand this unexpected result we examined whether a cytochrome P-450 mixed-function oxidase system participated in the mutagenic activation of AAF by guinea-pig liver, as it does in the case of mouse liver. The mutagenic activation was: (1) completely dependent on the addition of a co-factor, NADPH, to the mutation assay system, (2) completely suppressed by antiserum against NADPH--cytochrome c reductase, and (3) sensitive to a cytochrome P-450 inhibitor, 7,8-benzoflavone. These results indicate that the cytochrome P-450 enzyme system is essentially involved even in the mutagenic activation of AAF by guinea-pig-liver S9 fraction. Based on both the present and other data, the mechanism of the mutagenic activation is discussed to explain the observed high mutagenic potential of AAF in the presence of guinea-pig-liver S9 fraction.     

Bacterial mutagenicity of some tobacco aromatic nitrogen bases and their mixtures

The first aim was to compare the genotoxicities of two tobacco-specific nitrosamines (TSNA), 4-(methylnitrosamino)-(3-pyridyl)-1-butanone (NNK) and N'-nitrosonornicotine (NNN) in two types of tests, the Salmonella reverse mutation assay (250-2000 microg per plate) and the Mutatox test (up to 1000 microg/ml) using dark mutant M-169 of Vibrio fischeri. The second aim was to assess the effects of single other tobacco chemicals and metabolites (nicotine (NIC), cotinine (COT), trans-3-hydroxycotinine (3HC), cotinine-N-oxide (CNO) and nicotine-N-oxide (NNO)) on the mutagenic responses at relative concentrations observed physiologically. The Salmonella strains were TA100, TA7004, TA7005, and TA7006, all showing missense backmutations that are characteristic of the TSNA. NNN was a direct mutagen to strains TA100, TA7004, and in the Mutatox test, and was not mutagenic in the presence of rat or hamster S9. NNK was mutagenic only in strain TA7004 with rat and hamster S9, but not in TA100, but was directly mutagenic in the Mutatox test. While all the other tobacco chemicals were not mutagenic alone to strains TA100 and TA7004 in the presence and absence of rat or hamster S9, the Mutatox test produced direct mutagenicity for COT, 3HC, and NNO, but not CNO. The latter was mutagenic in the Mutatox test with rat or hamster S9, but only rat S9 was effective for COT, NNO and 3HC. Inhibitory potentiations of NNN by NIC and COT were observed on strain TA7004, and by NIC on strain TA100. There were no interactions on NNK in the presence of S9 for strain TA7004 or TA100. In contrast, a complex inhibition and enhancement behavior occurred in the Mutatox test for each interaction, but no effects were observed for CNO on NNK without S9, and few for NIC on NNK with hamster S9. Compounds which showed no activity alone modulated the genotoxicity of two potent TSNAs in both types of tests.     

Evaluation of genotoxicity of N-nitrosodibenzylamine in Chinese hamster V79 cells and in Salmonella

Health concerns have arisen due to the formation of N-nitrosodibenzylamine (NDBzA; CAS No. 5336-53-8) in pork processed in a new type of rubber netting. In view of the potent carcinogenicity of related nitrosamines (e.g. N-nitroso-n-dibutylamine and N-nitrosodiethylamine), NDBzA was evaluated for genotoxicity in vitro in both Chinese hamster V79 cells and in Salmonella. In V79 cells, concentrations up to 25 micrograms/ml were tested with and without activation by rat or hamster hepatocytes. Significant elevation of SCE frequency was seen only at 25 micrograms/ml in the presence of uninduced hamster hepatocytes. Mutation to 6-thioguanine resistance was observed at 25 micrograms/ml, in the absence of hepatocytes and in the presence of induced (Aroclor 1254) or uninduced hamster hepatocytes, but not with rat hepatocytes. With uninduced rat hepatocytes, a small but significant (p less than 0.05) increase in the mutation frequency was seen with 10 micrograms/ml NDBzA. In the Salmonella assay, using a pre-incubation protocol and concentrations up to 1000 micrograms/ml, NDBzA was negative in strain TA98, and in TA100 with rat S9, but was positive at the highest dose in TA100 with hamster S9, and more strongly with Aroclor 1254-induced hamster S9. When activated by uninduced rat or hamster hepatocytes, as opposed to S9, NDBzA was negative with all tester strains. Hamster hepatocytes activated more than rat in the V79 studies, and hamster S9 was more strongly activating in the Salmonella assay. These results indicate that NDBzA is weakly mutagenic to both Salmonella and V79 cells.     

Application of modified Salmonella/microsome prescreen to petroleum-derived complex mixtures and polynuclear aromatic hydrocarbons (PAH)

In some cases, the Salmonella mutagenicity assay may fail to predict the carcinogenic potential of PAH (and of complex mixtures containing PAH) because of nonoptimal in vitro metabolic activation parameters. In this study, 7 petroleum-derived complex mixtures, as well as a number of individual PAH which were representative constituents of such mixtures, were tested in a Salmonella prescreen using quadrant plates with rat or hamster S9 at concentrations approximately 2-8 times those used in the standard assay. Some PAH (perylene, quinoline, benzo[b]chrysene, phenanthrene, anthracene) were optimally activated to mutagens by S9 at 400 microliters/plate. Rat S9 was similar to hamster S9 for most tested PAH, but anthracene and quinoline mutagenicity was enhanced by hamster S9. All 7 complex mixtures were more mutagenic with 200-400 microliters/plate S9; rat was generally slightly more efficient than hamster. Modifying this assay to include a prescreen using a range of S9 concentrations (and perhaps from species other than rat) may improve prediction of the potential carcinogenicity of complex petroleum-derived mixtures.     

Mutagenic activation of 2-amino-3-methylimidazo[4,5-f]-quinoline (IQ) and 2-amino-3,4-dimethylimidazo[4,5-f]-quinoline (MeIQ) by subcellular fractions and cells isolated from small intestine,kidney and liver of the rat

The mutagenic activity of the pyrolysis products 2-amino-3-methylimidazo[4,5-f]-quinoline and 2-amino-3,4-dimethylimidazo[4,5-f]-quinoline in Salmonella typhimurium TA98 using rat intestinal and renal subcellular fractions as activation systems was approximately 1 and 5 revertants per nmol, respectively. This was 1,000 times less than the activity with a subcellular fraction from rat liver. The mutagenic activity of both compounds was considerably increased using intestinal, renal and hepatic preparations isolated from PCB (Aroclor 1254)-pretreated rats, compared to preparations from control animals. In addition, both compounds displayed a moderate direct-acting mutagenic activity at concentrations above 10^-5 M. Isolated cells from small intestine, kidney and liver incubated in nucleopore chambers were able to convert both compounds into products which mutated bacteria outside the chambers. The concentrations of chemicals required to yield responses of a similar magnitude were approximately 3 orders of magnitude higher in the intestinal and renal systems compared to the hepatic system. The formation of metabolites mutagenic for Salmonella typhimurium by hepatic subcellular and cellular systems was shown to be superior to the respective intestinal and renal systems.Abbreviations AHH arylhydrocarbon hydroxylase - IQ 2-amino-3-methylimidazo[4,5-f]-quinoline - MC 3-methylcholanthrene - MeIQ 2-amino-3,4-dimethylimidazo[4,5-f]-quinoline - PCB polychlorinated biphenyls (Aroclor 1254) - S9 the 9,000 g supernatant tissue fraction - TCDD 2,3,7,8-tetrachlorodibenzo-p-dioxin     

Comparative induction of gene mutations and chromosome damage by 1-methoxy-1,3,5-cycloheptatriene (MCHT), 1. Results from a battery of standard tests

The ability of 1-methoxy-1,3,5-cycloheptatriene (MCHT) to induce gene mutations and chromosome breaks has been examined in a battery of standard assays. MCHT was not mutagenic to 5 strains of Salmonella, with or without S9 fraction. In L5178Y TK+/- mouse lymphoma cells, MCHT induced TK-/- mutants in the presence but not in the absence of S9 fraction. In V79 Chinese hamster cells, MCHT induced azaguanine-resistant mutants in the presence and absence of S9 but the effect was considerably reduced in the absence of S9. MCHT resulted in no increases in chromosome aberrations in cultured human lymphocytes, with or without S9 fraction, neither was there any increase in micro-nucleated polychromatic erythrocytes in treated mice. MCHT thus appears on the basis of these results, to be possibly a specific gene mutagen (rather than clastogen) for mammalian cells. This uncommon mutagenicity profile has been investigated further in an accompanying paper (Cole et al., 1990) and has proved to be an oversimplification.     

Mutagenicity of benzidine and 4-aminobiphenyl after metabolic activation with isolated hepatocytes and liver 9000 × g supernatant from rat,hamster and guinea pig

The mutagenicity of benzidine and 4-aminobiphenyl towards Salmonella typhimurium strain TA1538 was measured in the presence of isolated hepatocytes from rat, hamster and guinea pig. The mutagenic potency of these compounds was also assayed with S9 (9000 × g supernatant) prepared from disrupted hepatocytes of these aryl amines was investigated.For all 3 animal species it was found that the mutagenicity of benzidine is higher with intact hepatocytes than with S9 prepared from disrupted hepatocytes. Addition of acetyl coenzyme A to the S9 fraction increased the mutagenicity of benzidine. In contrast to benzidine, the mutagenicity of 4-aminobiphenyl appeared to be lower with hepatocytes than with S9. Addition of acetyl coenzyme A to the S9 fraction decreased the mutagenicity of 4-aminobiphenyl.The mutagenic potency of 4-aminobiphenyl was almost equal in the presence of the liver preparations from the 3 different species, whereas obvious species differences were seen with benzidine.     

Mutagenicity and DNA adduct formation of PAH, nitro-PAH, and oxy-PAH fractions of atmospheric particulate matter from São Paulo, Brazil

Urban particulate matter (UPM) contributes to lung cancer incidence. Here, we have studied the mutagenic activity and DNA adduct-forming ability of fractionated UPM extractable organic matter (EOM). UPM was collected with a high-volume sampler in June 2004 at two sites, one at street level adjacent to a roadway and the other inside a park within the urban area of the city of S?o Paulo, Brazil. UPM was extracted using dichloromethane, and the resulting EOM was separated by HPLC to obtain PAH, nitro-PAH, and oxy-PAH fractions which were tested for mutagenicity with the Salmonella strains TA98 and YG1041 with and without S9 metabolic activation. The PAH fraction from both sites showed negligible mutagenic activity in both strains. The highest mutagenic activity was found for the nitro-PAH fraction using YG1041 without metabolic activation; however, results were comparable for both sites. The nitro-PAH and oxy-PAH fractions were incubated with calf thymus DNA under reductive conditions appropriate for the activation of nitro aromatic compounds, then DNA adduct patterns and levels were determined with thin-layer chromatography (TLC) 32P-postlabeling method using two enrichment procedures-nuclease P1 digestion and butanol extraction. Reductively activated fractions from both sites produced diagonal radioactive zones (DRZ) of putative aromatic DNA adducts on thin layer plates with both enrichment procedures. No such DRZ were observed in control experiments using fractions from unexposed filters or from incubations without activating system. Total adduct levels produced by the nitro-PAH fractions were similar for both sites ranging from 30 to 45 adducts per 10(8) normal nucleotides. In contrast, the DNA binding of reductively activated oxy-PAH fractions was three times higher and the adduct pattern consisted of multiple discrete spots along the diagonal line on the thin layer plates. However, DNA adduct levels were not significantly different between the sampling sites. Both samples presented the same levels of mutagenic activity. The response in the Salmonella assay was typical of nitroaromatics. Although, more mutagenic activity was related to the nitro-PAH fraction in the Salmonella assay, the oxy-PAH fractions showed the highest DNA adduct levels. More studies are needed to elucidate the nature of the genotoxicants occurring in S?o Paulo atmospheric samples.     

Mutagenicity and metabolism of dimethylnitrosamine and benzo[alpha]pyrene in tissue homogenates from inbred Syrian hamsters treated with phenobarbital, 3-methylcholanthrene or polychlorinated biphenyls.

There are significant differences between mice and hamsters in polycyclic hydrocarbon and nitrosamine metabolism. Homogenates of liver, lung and intestinal mucosa from 6 strains of Syrian golden hamster were compared for their ability to metabolize benzo[alpha]pyrene (BP) and dimethylnitrosamine (DMN) to mutagens. Females of strains MHA/SSLak, LSH/SlLak, CB/SsLak, PD4/Lak LHC/Lak and Lak:LVG (SYR) were either untreated or received phenobarbital (PB), 3-methylcholanthrene (MC) or polychlorinated biphenyls (AR) to induce drug-metabolizing enzymes. Salmonella typhimurium TA92 and TA98 were used as indicators of the formation of mutagans. Dimethylnitrosamine demethylase (DMND) was assayed using 1 mM DMN as substrate. Aryl hydrocarbon hydroxylase (AHH) was measured using benzo[alpha]pyrene as substrate. MC does not induced AHH activity in hamster liver, but is an excellent inducer of enzymes converting BP to mutagens. This lack of correlation between increased AHH activity and increased metabolism of BP to mutagen in liver is in marked contrast to correlations seen in mice. MC induces AHH in hamster lung and intestinal mucosa. AR induces AHH in liver, lung and intestinal mucosa. Activity of DMND in liver is not affected by treatment of hamsters with BP or AR, but is repressed approx. 30% by treatment with MC. Activity of DMND and conversion of DMN to mutagen are correlated (r = 0.59) in hamster liver. Microsomes of hamster liver are more effective than those from mouse in converting DMN to mutagen, despite similar DMND activities in livers from the two species.     

Inhibitory effects of thiols on a mutagenic contaminant from the synthesis of N-nitrosothiazolidine

The effect of S9 and various thiols were studied for potential modifying effects on a mutagenic trace artifact ('NTHZ') formed during the synthesis of N-nitrosothiazolidine (NTHZ) from cysteamine, formaldehyde and nitrite. Induced and uninduced S9 prepared from Syrian hamster livers reduced mutagenic activity in Salmonella TA100. Incorporation of boiled S9 into the preincubation medium produced similar effects, indicating a non-enzymatic mechanism for the detoxification reaction. Thiols alone also lowered revertant yields, and inhibitory efficacy was, in general, related to the pKa of the compound. At equimolar concentrations mutagenic activity was reduced in the following order (pKa values in parentheses): Thioglycolate (10.7) greater than mercaptoethanol (9.6) greater than reduced glutathione (8.8) greater than cysteine (8.35) greater than cystine (8.2). N-Acetylcysteine (9.52) and cysteamine (8.35), however, did not fit this pattern. The results of this study suggest that normal hepatic mechanisms may minimize 'NTHZ' genotoxicity thereby reducing potential health risks associated with its exposure.     

The activity of S9-liver fractions from seven species in the Salmonella/mammalian-microsome mutagenicity test

A comparative study was made of the metabolizing activity of microsomal fractions of the liver of the rat, mouse, Chinese hamster, dog, mini-pig, rhesus monkey and baboon, with and without pretreatment of the animals with Aroclor (500 mg/kg i.p.). The activity of the fractions was determined by means of the Salmonella/mammalian-microsome mutagenicity test. The protein content of the S9 fractions was standardized (36.14 mg/ml) to eliminate species-specific and inter-individual differences. Strain TA100 of Salmonella typhimurium was used as test organism. The substances tested, namely benzo[a]pyrene, cyclophosphamide, diethylnitrosamine, β-naphthylamine and o-aminoazotoluene, are all known mutagens or carcinogens belonging to various chemical classes.

The tests made with S9 fractions from animals that had not been pretreated with Aroclor revealed distinct species-specific differences in the metabolizing activity of the fractions and also differences from one substance to another. The fractions from mice and Chinese hamster had only a weakly positive effect with some of the substances, those from the rat and the mini-pig only with 2 and 3 of the 5, resp. The dog-liver fraction gave positive results with all substances except benzo[a]pyrene. The fractions from the baboon and the rhesus monkey had positive to strongly positive effects with all the substances.

In the experiments in which the animals had been pretreated with Aroclor, the S9 fractions from all species produced positive effects with all substances, and the mutagenic effects provoked by various substances, when fractions from untreated animals were used, remained of the same degree or became more distinct. Species-specific differences were no longer discernible.

Demethylase activity in all the S9 fractions used was determined with ethylmorphine. Without prior activation, the fractions from the mouse, Chinese hamster, rat and dog gave highly divergent values. In the fractions from the mini-pig, the baboon and, in particular, the rhesus monkey, the activity was relatively more pronounced. Enzyme induction with Aroclor led to a distinct increase in demethylase activity in the livers of almost all species. Only a very rough quantitative relation was evident between the demethylase activity of the individual S9 fractions and their influence on the substances tested for mutagenicity.     

Activation of mutagens by hepatocytes and liver 9000 X g supernatant from human origin in the Salmonella typhimurium mutagenicity assay. Comparison with rat liver preparations

The mutagenicity of 10 known genotoxic compounds, of several chemical classes, was measured in Salmonella typhimurium mutagenicity assays comprising isolated human hepatocytes or human liver 9000 X g supernatant (S9) from 4 different individuals, as activating system. The mutagenic activity of several compounds as determined with the Salmonella/hepatocyte suspension assay showed obvious differences when compared with the values obtained in the Salmonella/S9 plate assay. For instance, the mutagenic activity of BZ, DMN and DEN appeared to be much higher in the hepatocyte assay than in the S9 assay. However, 2-AF and 2-AAF were activated more effectively into mutagens in the S9 assay than in the hepatocyte assay. 2-AF was slightly more mutagenic than 2-AAF in the hepatocyte assay, whereas it was far more mutagenic than 2-AAF in the S9 assay. DMN was found more mutagenic than DEN in the hepatocyte assay, whereas in the S9 assay DEN appeared to be slightly more mutagenic. Furthermore, great interindividual differences in the metabolic activation of certain compounds, e.g. BZ and DMN, were observed in the hepatocyte suspension assay, whereas these variations were less evident in the S9 plate assay. Comparison of the mutagenicity data obtained with the human liver preparations, with those obtained with rat liver preparations, showed great interspecies differences in the capacity to activate certain chemicals into mutagens. The use of human liver preparations, in particular isolated human hepatocytes, may be of great value in studies on inter- and intraspecies variations in metabolic activation of genotoxic agents.     

Antimutagenic effects of several subfractions of extract from wheat sprout toward benzo[a]pyrene-induced mutagenicity in strain TA98 of Salmonella typhimurium

The aqueous extract from wheat sprouts contains some antimutagenic factor(s). The factor(s) abolish(es) the activity of aryl hydrocarbon (benzo[a]pyrene) hydroxylase (AHH) in the S9 fraction from Aroclor-treated rat livers and also inhibit(s) the mutagenic activity of benzo[a]pyrene (B(a)P) in the Ames test. The extract (fraction S30) was subjected to initial fractionation by thermal treatment, 3 24-h cycles of dialysis and ultrafiltration. The antigenotoxic activity of fraction S30 amounted to 98% and was unchanged by thermal treatment (100 degrees C, 10 min). Both the dialysate and the dialysis fluid inhibited the mutagenic effect of B(a)P by 48.4 and 48% respectively. The microsomal subfraction inhibited the mutagenicity only in 10%, and the postmicrosomal subfraction in 68%. It is concluded that the extract from wheat sprouts contains at least 2 heat-resistant compounds (or groups of compounds) located within the cell cytosol and showing antimutagenic activity: one group is of low molecular weight and another of high MW. Alternatively, low-molecular compounds could either be free or bound to high-molecular compound(s).     

Re-evaluation of the mutagenic potential of quinacrine dihydrochloride dihydrate.

Quinacrine has been used for voluntary female non-surgical sterilization for its ability to produce tubal occlusion. Safety issues regarding quinacrine have been raised because it has been shown to intercalate with DNA. Therefore, safety issues need to be resolved by appropriate toxicology studies to support a review for human transcervical use. Such toxicology studies include mutagenicity assays. Here we report an evaluation of the genotoxicity of quinacrine dihydrochloride dihydrate (QH) using a battery of assays. In the bacterial mutagenicity assay, QH was strongly positive in Salmonella typhimurium tester strain TA1537 with and without S9-activation and in S. typhimurium tester strain TA98 with S9-activation; QH was also strongly positive in Escherichia coli WP2 uvrA without S9-activation. QH was not mutagenic in S. typhimurium tester strains TA100 and TA1535 with and without S9-activation. QH was mutagenic in the mouse lymphoma assay in the absence of S9-activation. QH was clastogenic in Chinese hamster ovary (CHO) cells, with and without S9-activation. QH was negative for polyploidy in the same chromosome aberration test. Using a triple intraperitoneal injection treatment protocol in both male and female mice, QH was negative in the in vivo mouse micronucleated erythrocyte (micronucleus) assay. These results confirm that QH is mutagenic and clastogenic in vitro and suggest a potential risk to human health due to QH exposure after intrauterine exposure.     

Mutagenicity of the coccidiostat diaveridine in the Salmonella/mammalian microsome assay

The coccidiostat diaveridine was tested for mutagenicity in the Salmonella/microsome assay with tester strains TA100 and TA98. This compound was not mutagenic in either tester strain in the presence and absence of rat S9 mix, but was found to be mutagenic in strain TA100 after metabolic activation with hamster S9 mix.     

Diethylstilbestrol and 11 derivatives: a mutagenicity study with Salmonella typhimurium.

Diethylstilbestrol was tested for mutagenicity with his- S. typhimurium strains under 10 different matabolic situations (no exogenous metabolizing system; S9 mix from liver homogenate of rats induced with Aroclor 1254, with or without inhibition of epoxide hydratase; liver and/or kidney S9 mix from control or hamsters treated with Aroclor 1254; horse-radish peroxidase + H2O2). Under none of these conditions did diethylstilbestrol give any indication of a mutagenic effect. Furthermore, 11 metabolites and other derivatives of diethylstilbestrol, 2 of them potent inducers of sister-chromatid exchange in cultured fibroblasts, were not mutagenic with any of the 4 tester strains (S. typhimurium TA100, TA98, TA1537, TA1535) in the presence or absence of S9 mix from liver homogenate of rats induced with Aroclor 1254. Thus, one of the few known human carcinogens is very resistant to detection by the mammalian enzyme-mediated Salmonella typhimurium mutagenicity test (Ames test). This is especially remarkable since the metabolizing systems used included: (1) some of very high metabolic activity (S9 mix from liver homogenate of rats and hamsters induced with Aroclor 1254); (2) metabolizing systems from organs susceptible to the carcinogenic activity of diethylstilbestrol (hamster kidney); as well as (3) a mixture of (1) and (2) in case both activities are required for the carcinogenic effect in the whole animal.