Mutagenicity, metabolism and DNA adduct formation of 6-nitrochrysene in Salmonella typhimurium

The mutagenic activities of 6-nitrochrysene (6-NC) and its previously identified metabolites were evaluated in Salmonella typhimurium TA100 and TA98 in the presence and absence of metabolic activation by 9000 g supernatant from the livers of rats treated with Aroclor. 6-Aminochrysene (6-AC) and trans-1,2-dihydro-1,2-dihydroxy-6-aminochrysene (1,2-DHD-6-AC) were the most active mutagens in TA100 upon metabolic activation. 6-NC and 6-AC were the most active mutagens in TA100 in the absence of metabolic activation. Upon metabolic activation, 6-AC was the most active in TA98; the other compounds were weak or inactive depending on the conditions of the assay. In the absence of metabolic activation, the mutagenic activities of 6-NC and its metabolites in TA98 were comparable to those observed in TA100. The major metabolite formed upon incubation of [3H]6-NC with S.typhimurium TA100 and 9000 g supernatant from the livers of Aroclor-induced rats was identified as trans-1,2-dihydro-1,2-dihydroxy-6-nitrochrysene (1,2-DHD-6-NC); trans-9,10-dihydro-9,10-dihydroxy-6-nitrochrysene and 1,2-dihydroxy-6-nitrochrysene were also identified. The major DNA adduct formed in TA100 under these conditions was chromatographically identical to that previously detected in vivo in the liver and lungs of newborn mice treated with 6-NC, as well as to that obtained upon incubation of 1,2-DHD-6-AC with calf thymus DNA in the presence of rat liver microsomes. The DNA adducts derived from 6-NC in S.typhimurium TA100 without activation were identical to those adducts previously identified after incubation of 6-hydroxylaminochrysene with calf thymus DNA.(ABSTRACT TRUNCATED AT 250 WORDS)     

Synthesis and mutagenicity of 1-nitropyrene 4,5-oxide and 1-nitro-pyrene 9,10-oxide, microsomal metabolites of 1-nitropyrene

[4,5,9,10-³H]1-Nitropyrene was incubated with liver microsomesprepared from guinea pigs treated with Aroclor 1254 and theproducts were examined by h.p.l.c. The previously reported metabolites,1-nitropyrene trans-4,5-diliydrodiol, 1-nitropyrene trans-9,10-dihydrodiol,and 3-, 6-, and 8-hydroxy-1-nitropyrene were detected. In addition,h.p.l.c., nuclear magnetic resonance and mass spectral analysesindicated the presence of 1-nitropyrene 4,5-oxide and 1-nitro-pyrene9,10-oxide. The epoxide hydrase inhibitor, 1,2-epoxy-3,3,3-trichloropropane,decreased the concentration of the 4,5- and 9,10-dihydrodiolsin the microsomal incubations and increased the concentrationof their corresponding oxides. Reaction of 1-nitropyrene withm-chloroperoxybenzoic acid gave a mixture of 1-nitropyrene 4,5-oxideand 1-nitropyrene 9,10-oxide, which was separated by chromatography.The mutagenicity of the oxides was determined in Salmonellatyphimurium strains TA98, TA98NR, and TA98/1,8-DNP₆, both withand without exogenous activation by a rat liver homogenate fraction(S9). In the absence of S9, both oxides showed maximum activityin TA98, slightly decreased mutagenicity in the acetylase-deficientstrain TA98/1,8-DNP₆, and much reduced activity in the nitroreductase-deficientstrain, TA98NR. When assayed in the presence of S9, 1-nitropyrene4,5-oxide had maximum mutagenicity in TA98, and was 50 and 95%less mutagenic in TA98NR and TA98/1,8-DNP₆, respectively. 1-Nitropyrene9,10-oxide had a similar strain sensitivity, except that itstotal mutagenicity was lower. Since 1-nitropyrene is metabolizedby oxidative pathways in vivo, these K-region oxides may contributeto the toxicities elicited by this compound. ⁴To whom correspondence should be addressed     

Inhibitory effect of lichen constituents on mutagenicity induced by heterocyclic amines

Physodic acid, one of the main constituents of Hypogymnia enteromorpha, inhibited the mutagenicity of indirect mutagens, including benzo[a]pyrene and heterocyclic amines in Salmonella typhimurium TA 98. In contrast, it was not effective against direct mutagens such as 6-nitropiperonal and adriamycin. Its antimutagenicity was not associated with free-radical scavenging or antioxidative activities. Physodic acid seemed to inhibit the formation of reactive metabolites, such as N-hydroxy-Trp-P-2, by blocking the hepatic microsomal oxidation systems. Another component of H. enteromorpha, physodalic acid, also inhibited mutagenicity of a heterocyclic amine, Trp-P-2, in S. typhimurium TA 98, even though it was reportedly mutagenic in S. typhimurium TA 100.     

Glucuronide conjugation reduces the cytotoxicity but not the mutagenicity of benzo(a)pyrene in the CHO/HGPRT assay

Benzo(a)pyrene (B[a]P) is biotransformed by the mixed-function oxidase (MFO) system to numerous metabolites some of which are cytotoxic and/or mutagenic to mammalian cells. However, conjugation of B(a)P metabolites with glucuronic acid in vivo is a major pathway of detoxication and elimination. The effects of glucuronide conjugation on B(a)P-induced cytotoxicity and mutagenicity were studied using the CHO/HGPRT assay with a rat liver homogenate preparation containing MFO system cofactors (S9 mix) and uridine diphosphate alpha-D-glucuronic acid (UDPGA). B(a)P metabolites proximate to the biologically active B(a)P quinones (B[a]P 6-OH) and to the B(a)P 7,8-diol-9,10 epoxide isomers (B[a]P 7,8-diol), were also assayed with S9 mix in the absence and presence of UDPGA. The addition of UDPGA to S9 mix reduced B(a)P-induced cytotoxicity but did not affect mutagenicity. B(a)P 6-OH-mediated cytotoxicity was also reduced in the presence of UDPGA. UDPGA had no effect on B(a)P 7,8-diol-induced cytotoxicity or mutagenicity. B(a)P phenols have been shown to be the preferred B(a)P-metabolite substrates for UDP-glucuronyltransferase enzymes. Thus, the reduction of B(a)P and B(a)P 6-OH-induced cytotoxicity by glucuronide conjugation is likely due to the elimination of cytotoxic phenols and quinones. Since B(a)P 7,8-diol is a poor substrate for UDP-glucuronyltransferase enzymes, no effects on B(a)P-induced mutagenicity or B(a)P 7,8-diol-induced cytotoxicity and mutagenicity were observed.     

Mutagenicity of (R) and (S) styrene 7,8-oxide and the intermediary mercapturic acid metabolites formed from styrene 7,8-oxide

We have tested the two enantiomers of styrene 7,8-oxide and various thioether metabolites of racemic styrene 7,8-oxide for their direct mutagenicity in Salmonella typhimurium TA100. The mutagenicity data suggests that the (R) enantiomer is more mutagenic than the (S) enantiomer, with the racemic mixture intermediate between the two. The thioether metabolites were not mutagenic. The difference in the mutagenicities of enantiomers probably resulted from a stereoselective process in the Salmonella tester strain. At the present time it is not clear whether the rate-limiting reaction is the interaction of the enantiomers with DNA or some other cellular component.     

Genotoxicity of 5-aminolevulinic and 4,5-dioxovaleric acids in the salmonella/microsuspension mutagenicity assay and SOS chromotest

5-Aminolevulinic acid (ALA) is a heme precursor that accumulates in some porphyric disorders and in lead poisoning which can undergo metal-catalyzed oxidation producing reactive oxygen species and the keto-aldehyde, 4,5-dioxovaleric acid (DOVA). Evidence in vitro of ALA-induced DNA lesions suggests that ALA and DOVA have mutagenic potential that could possibly contribute to an increased frequency of hepatocellular carcinoma (HCC) in patients with acute intermittent porphyria (AIP). In this study, we evaluated the genotoxic potential of ALA and DOVA. In the absence of exogenous metabolic activation, ALA and DOVA were mutagenic in Salmonella typhimurium tester strain TA104. ALA was also mutagenic in S. typhimurium TA102, but not in TA98, TA100, or TA1535, indicating an oxidative mechanism. Removal of H(2)O(2) with catalase gave only partial protection, suggesting generation of other mutagenic species. Both ALA and DOVA damaged the DNA of Escherichia coli PQ37, inducing the SOS response detected by an increase in beta-galactosidase activity. These results verified the potential mutagenic activity of ALA and DOVA and reinforce the hypothesis that DNA damage induced by ALA may be associated with the development of HCC in individuals suffering from AIP.     

Synthesis and mutagenic activity of nitro-imidazoarenes. A study on the mechanism of the genotoxicity of heterocyclic arylamines and nitroarenes

A series of nitro-imidazoarenes (nitro-IAs) were synthesized from the corresponding amino-imidazoarenes (amino-IAs). These two classes of compounds are structurally related to the potent food mutagen and carcinogen, 2-amino-3-methylimidazo[4,5-f]quinoline (IQ). The mutagenic activities of the nitro-IAs were assayed in the Salmonella typhimurium frameshift tester strains TA98, TA98/1,8-DNP6 and TA98NR without use of extracellular metabolization. Nitro-IQ, the nitro counterpart of IQ, was two times more mutagenic than IQ. In general, the mutagenic activities of the nitro-IAs varied over 50,000-fold. The relationships between the chemical structures and mutagenic activities are identical with those previously reported for the corresponding amino-IAs: the methyl group on the imidazole ring and the quinoline-nitrogen were found to be required for potent mutagenic activity. The reductive activation of the nitro-IAs is not carried out primarily by the 'classical' nitroreductase of Salmonella which is defective in TA98NR. The O-acetyltransferase defective in TA98/1,8-DNP6 is required for the efficient production of the ultimate mutagens of the nitro-IAs. The interchangeability of the structure-activity relationships of the nitro-IAs and amino-IAs reflects a basic similarity of the mechanisms of the mutagenicity of the two classes of compounds. It is likely that N-hydroxy compounds are proximate metabolites common to the nitro-IAs and amino-IAs; they are further activated by an acetyl-CoA-dependent O-acetyltransferase of Salmonella. It is very likely a property of the ultimate mutagen, possibly a nitrenium ion, which governs the mutagenic potency of the different nitro- and amino-IAs and thus determines the structure-activity relationships.     

Antibacterial activity and mutagenicity studies of water-soluble phosphazene high polymers.

Eight water-soluble phosphazene high polymers, [NPR2]n (R, organic, water-solubilizing side-group; n, approx: 15,000) and the small-molecule counterparts of the polymers were examined for antibacterial activity against six different strains of bacteria (Escherichia coli, Salmonella typhimurium (TA 100), Salmonella pullorum, Streptococcus faecalis, Bacillus subtilis and Pseudomonas aeruginosa). Antibacterial testing was carried out by measuring zones of inhibition and changes in solution turbidity over time. In addition, the antibacterial activity of the surfaces of cross-linked poly[di(methoxyethoxyethoxy)phosphazene] (MEEP) hydrogels were investigated. A number of the high polymers, as well as the MEEP hydrogels, impeded bacterial growth. Only E. coli was unaffected by the phosphazenes. A possible explanation for the antibacterial character of the polymers is presented. The same compounds were monitored for potential mutagenic activity using the Salmonella typhimurium tester strains TA 100 and TA 98. None of the high polymers or their small-molecule analogues showed mutagenic activity in either strain of Salmonella at the concentrations tested. The use of these materials as coatings for artificial implants is discussed.     

Mutagenicity of N-substituted phenanthrene 9,10-imines in Salmonella typhimurium and Chinese hamster V79 cells

We previously showed that some (nonsubstituted) aziridines derived from polycyclic aromatic hydrocarbons (arene imines) elicit various mutagenic and genotoxic effects in bacteria and mammalian cells and that these arene imines are active at much lower concentrations than the corresponding epoxide analogues. In the present study, N-substituted derivatives of phenanthrene 9,10-imine were investigated. All 10 derivatives studied showed direct mutagenicity in Salmonella typhimurium TA100. Some of the compounds additionally exhibited weak effects in the strains TA98 and TA1537. Most N-substituted derivatives were weaker mutagens than unsubstituted phenanthrene 9,10-imine but stronger mutagens than phenanthrene 9,10-oxide. Bulky substituents reduced the mutagenicity more than did small substituents. In addition, the derivatives with electron-withdrawing substituents (with the exception of N-chlorophenanthrene 9,10-imine) were weaker mutagens than those with electron-donating substituents. Phenanthrene 9,10-imine and five N-substituted derivatives were investigated to determine whether they induce gene mutations at the hgprt locus in V79 cells. Four compounds, including the parent aziridine, were positive in the V79 test. The other two compounds were negative. The mutagenic potencies in the V79 cell system did not correlate well with those obtained with the Salmonella system. Overall, the study shows that in addition to unsubstituted arene imines, N-substituted derivatives are mutagenic. This finding is of interest, as metabolic pathways leading from aromatic compounds to N-substituted arene imines are conceivable.     

Effects of epoxide hydratase inhibitors in forward and reversion bacterial mutagenesis assay systems

Cyclohexene oxide (CCHO) and 1,1,1-trichloropropene-2,3-oxide (TCPO) are inhibitors of epoxide hydratase and have been used in studies of the mechanisms of mutagenesis in bacterial mutagenesis assays. The present studies were designed to investigate the mutagenic activity of CCHO and TCPO in Salmonella typhimurium employing the Ames histidine-reversion assays (TA98, TA100, TA1535, TA1537, TA1538) and a forward mutation assay that uses 8-azaguanine resistance in TM677 as the genetic marker. In the reverse mutation assay, TCPO (10⁻³ M) produced a mutagenic response in strains TA100 and TA1535 in the absence or presence of a rat liver metabolizing system (S9), indicating that TCPO causes base-pair substitution mutations. CCHO (10⁻³ M) showed a slight but significant mutagenic effect in strain TA100, with or without S9 and, in strain TA1535, only in the absence of S9. In the forward assay, TCPO was a strong mutagen at concentrations above 5 × 10⁻⁵ M and was toxic to the bacteria. The mutagenic and toxic effects of TCPO were slightly reduced in the presence of the S9 preparation, suggesting that the epoxide may be metabolized by the microsomal enzymes. In the forward assay, CCHO showed no mutagenic activity but some toxicity at 3 × 10⁻³ M. When epoxide hydratase activity was measured under the conditions of the forward mutation assay, 85% inhibition of activity was observed at 10⁻³ M TCPO, a concentration that caused a 45-fold increase in the mutation frequency. CCHO (3 × 10⁻³ M) produced a 55% inhibition of epoxide hydratase activity without exhibiting mutagenic effects in TM677. These results indicate that CCHO should be employed in preference to TCPO when inhibition of epoxide hydratase activity is required in bacterial mutagenesis studies.     

Electronic considerations in the mutagenesis of some 4,5-bridged chrysenes

The mutagenic activity of four 4,5-bridged chrysene derivatives, benz(a)aceanthrylene, and 5-methylchrysene was examined using histidine auxotrophic strains TA98 and TA100 of Salmonella typhimurium. All compounds showed a positive mutagenic response with both TA100 and TA98 in the presence of S-9. A correlation between the electronic character of the bridging group and mutagenic activity for the chrysene derivatives is proposed.     

Evaluation of the genotoxicity of gentian violet in bacterial and mammalian cell systems

Previous studies indicate that gentian violet (GV), a triphenylmethane dye used in agriculture and human medicine, is a clastogen in vitro and a carcinogen in chronically exposed mice and rats. Data on its genotoxic activity, however, have been incomplete and partly contradictory. Mutagenesis and DNA damage experiments were conducted to re-evaluate the genotoxic potential of GV in both bacterial and mammalian cell systems. GV was mutagenic in Salmonella typhimurium tester strains TA97 and TA104, but there was little mutagenic activity detected in strains TA98 and TA100. A rat liver homogenate fraction (S9) tended to increase mutagenicity. The major microsomal metabolites of GV, pentamethylpararosaniline and N,N,N',N'-tetramethylpararosaniline were less mutagenic in TA97 and TA104, while N,N,N',N"-tetramethylpararosaniline was a weak mutagen in Salmonella. GV was not mutagenic in Chinese hamster ovary (CHO) cell strain CHO-K1-BH4, and was a questionable mutagen in CHO-AS52 cells. While GV produced DNA damage as measured by sedimentation of nucleotids derived from B6C3F1 mouse lymphocytes treated in vitro, no damage was found in lymphocytes isolated from mice dosed with GV. GV was also a weak producer of gene amplification in an SV40-transformed Chinese hamster cell line. The results indicate that GV is a point mutagen in bacteria; however, since similar exposure conditions produced weak mutagenic activity in mammalian cells, GV may be carcinogenic by virtue of its clastogenic activity.     

Evaluation of the mutagenicity of an N-nitroso contaminant of the sunscreen Padimate O: N-nitroso-N-methyl-p-aminobenzoic acid, 2-ethylhexyl ester (NPABAO).

The nitrosamine contaminant, N-nitroso-N-methyl-p-aminobenzoic acid, 2-ethylhexyl ester (NPABAO), of the major sunscreen ingredient Padimate O (4-N,N'-dimethylamino-benzoic acid, 2-ethylhexyl ester) was synthesized and tested for mutagenicity in the Salmonella typhimurium and mouse lymphoma L5178Y TK +/- assays. In contrast to the previously reported positive responses in S. typhimurium tester strains TA100 and TA1535 [Loeppky et al., 1991], there were no increases in the number of revertants with strains TA98, TA100, TA1535, and TA1538 in either the Salmonella plate incorporation [Ames et al., 1975] or preincubation [Yahagi et al., 1977] assays. Additional testing with Salmonella, following the modified preincubation procedure [Rogan, 1990] that gave the initial positive response, was also negative. Data from the mouse lymphoma assays were also uniformly negative. During synthesis of NPABAO, small amounts of 4-N,N'-dimethylamino-3-nitrobenzoic acid, 2-ethylhexyl ester (DMANBAO) can be formed. To determine whether the reported positive mutagenicity response of NPABAO could be the result of trace amounts of DMANBAO in the NPABAO, that compound was also synthesized and tested for mutagenicity with Salmonella. Positive responses were obtained with tester strains TA98 and TA 1538 but not with TA100 and TA1535, indicating that DMANBAO was not responsible for the increase in revertants originally reported.     

Mutagenicity of oxidized microsomal metabolites of 1-nitropyrene in Chinese hamster ovary cells

1-Nitropyrene, a tumorigenic environmental pollutant, is mutagenic in Chinese hamster ovary (CHO) cells in the presence of a liver homogenate 9000 g supernatant fraction (S9). The metabolic pathways involved in this response were studied by comparing the mutagenicities at the hypoxanthine-guanine phosphoribosyl transferase locus of 1-nitropyrene, some oxidized microsomal metabolites of 1-nitropyrene, and related compounds. In the absence of S9, pyrene 4,5-oxide and 6-hydroxy-1-nitropyrene displayed the highest mutagenicities, followed by 1-nitropyrene 9,10-oxide and 1-nitropyrene 4,5-oxide; 3- and 8-hydroxy-1-nitropyrene were weaker mutagens, while pyrene and 1-nitropyrene were essentially without activity. With S9, the order of mutagenic potency was 1-nitropyrene 4,5-oxide greater than 6-hydroxy-1-nitropyrene approximately 1-nitropyrene 9,10-oxide greater than 1-nitropyrene approximately 3-hydroxy-1-nitropyrene approximately 8-hydroxy-1-nitropyrene greater than pyrene approximately pyrene 4,5-oxide, with the latter two compounds being essentially inactive. Inclusion of the epoxide hydrolase inhibitor 1,2-epoxy-3,3,3-trichloropropane during the S9-mediated treatment of CHO cells with 1-nitropyrene increased mutation induction 5-fold. Also, liver microsomes prepared from guinea-pigs treated with Aroclor 1254 mediated a stronger mutagenic response with 1-nitropyrene than microsomes from Aroclor-treated rats. 1-Nitropyrene was essentially non-mutagenic in the presence of microsomes from untreated and phenobarbital-treated rats. Examination of the 1-nitropyrene metabolites produced during the microsomal incubations indicated that Aroclor-induced guinea-pig microsomes yielded substantial amounts of 1-nitropyrene 4,5-dihydrodiol, while Aroclor-induced rat microsomes produced 6-fold more 6- and 8-hydroxy-1-nitropyrene than phenobarbital microsomes.(ABSTRACT TRUNCATED AT 250 WORDS)     

Cyclopenta[cd]fluoranthene and its precursors in combustion exhausts: a survey of their bacterial mutagenic activity

Cyclopenta[cd]fluoranthene (1) and 3-ethynylfluoranthene (2) have both recently been identified in combustion exhausts. In this study, their mutagenic activities were compared to that of fluoranthene (3), one of the most abundant polycyclic aromatic hydrocarbons (PAHs) in combustion exhausts, in the Salmonella/microsome reversion assay (Ames assay) using S. typhimurium strain TA98. The mutagenicity of 1 was modest in comparison to other active cyclopenta PAHs. Unexpectedly, 2 was mutagenic both with and without exogenous metabolic activation (rat liver S9). Furthermore, cyclopenta[cd]fluoranthene-3,4-epoxide (6) was synthesized in order to evaluate its role as the ultimate mutagenic active form of 1. The epoxide 6 was a direct-acting mutagen. In addition, a pyrolysate containing a mixture of 1 (85%), 2 (2%), and 3 (13%) obtained by flash vacuum thermolysis of 3-(1-chloroethenyl)fluoranthene (2a) at 1,050 degrees C was also mutagenic, but a significant mutagenic response was detected only in the presence of S9 activation. The results of this study indicate that 1 and 2 can contribute to the mutagenic activity of combustion exhausts.     

Influence of the triazine ring on the mutagenicity of triazinoindoles and some congeners.

Three compounds, which could be considered as precursors or derivatives of the 3-(4'-substituted-benzylidenamino)5H- 1,2,3-triazin[5,4b]indol-4-one series, were selected from the study of their mutagenic activity. Ames tests were performed study of their mutagenic activity. Ames tests were performed using the Salmonella typhimurium strains TA97, TA98, TA100, and TA102, according to the preincubation procedure, both with and without metabolic activation. The 3-amino-5H-1,2,3-triazin[5,4b]indol-4-one has been shown to be a strong S9-independent mutagen, which reverts frameshift and substitution mutations. Nevertheless its potency increases with the addition of microsomal fraction. In contrast, the 2-benzyliden-1-(3-aminoindol)-2-carbohydrazide and the 3-aminoindol-2-carbohydrazide congeners were not mutagenic. These results suggest that the 1,2,3-triazine ring is the principle substructure responsible for the mutagenicity of the triazinoindole congeners studied.     

Identification of human and murine sulfotransferases able to activate hydroxylated metabolites of methyleugenol to mutagens in Salmonella typhimurium and detection of associated DNA adducts using UPLC-MS/MS methods

Methyleugenol, a secondary metabolite present in many herbal spices, is carcinogenic in various tissues of mice and rats but negative in standard in vitro mutagenicity tests. Several observations indicate that hydroxylation followed by sulfation is an important activation pathway in the carcinogenicity and DNA adduct formation by methyleugenol and other alkenylbenzenes in animal models. However, sulfation is not taken into account in standard in vitro tests. Therefore, we have studied whether expression of murine or human sulfotransferases (SULTs) in the target strain, Salmonella typhimurium TA100, leads to the activation of hydroxylated metabolites of methyleugenol [(+)-1'-hydroxymethyleugenol, (-)-1'-hydroxymethyleugenol and (E)-3'-hydroxymethylisoeugenol]. Human SULT1A1 (a form expressed at high levels in many tissues) and SULT1C2 (expressed primarily in foetal tissues) activated all three compounds even at very low substrate concentrations. At higher concentrations, activation was also observed with human SULT1A2 and SULT1E1. Murine Sult1a1 required higher substrate concentrations than its human orthologue. Other SULT forms (human 1A3, 1C1, 1C3, 2A1 and 2B1b as well as murine 1d1) did not activate any methyleugenol metabolites studied. Furthermore, we developed isotope-dilution mass-spectrometric methods for the sensitive and specific detection of DNA adducts formed by methyleugenol metabolites. All three hydroxylated metabolites formed the same DNA adducts in S. typhimurium TA100-hSULT1A1: high levels of N (2)-(trans-methylisoeugenol-3'-yl)-2'-deoxyguanosine and modest levels of N (6)-(trans-methylisoeugenol-3'-yl)-2'-deoxyadenosine. Adduct levels correlated with the mutagenic effects induced. No adducts were formed by the test compounds in the SULT-deficient standard strain TA100. In conclusion, several methyleugenol metabolites are activated to DNA-reactive mutagens in S. typhimurium upon incorporation of appropriate sulfation capacity. We have identified human and murine SULT forms able to catalyse this activation. Methods were developed that may be utilised to analyse DNA samples from human tissues specifically for the possible presence of methyleugenol adducts.     

Mutagenic potential of Mancozeb in Salmonella typhimurium.

Mancozeb, a dithiocarbamate fungicide, was examined for its possible mutagenic activity using Salmonella typhimurium tester strains TA97a, TA98, TA100, and TA102. We found that Mancozeb exhibited toxic effects at the dose of 40 microg/plate and higher with all tester strains. Mancozeb showed dose-dependent increases in the number of revertants with and without metabolic activation when it was dissolved in DMSO or acetone with strain TA97a; however, the number of revertants at the highest dose was less than two-fold compared to control values. We postulate that the true mutagenic potential of Mancozeb may be masked by its toxic effect to the tester strain used.     

Mutability of salmonella tester strains TA1538 (hisD3052) and TA1535 (hisG46) containing the UmuD' and UmuC proteins of escherichia coli

We have studied the mutability of Salmonella typhimurium tester strains carrying plasmids in which either the umuDC or the umuD'C operon of Escherichia coli have been cloned. Reversion of the hisD3052 frameshift mutation by benzo[a]pyrene (B[a]P), aflatoxin B1 (AFB1) and 1-nitropyrene (1-NP), was very efficiently promoted by UmuD' (the activated form of UmuD) and UmuC proteins. In contrast, UmuD'C proteins promoted a moderate reversion of the missense hisG46 allele by B[a]P, and were not effective in mediating this reversion by AFB1. The Salmonella tester strain carrying the hisD3052 allele and containing the E. coli UmuD'C proteins has a sensitivity toward frameshift mutagens similar to that of the MucAB containing strain TA98, and may be useful for obtaining a high level of mutants generated by the SOS mutagenic mechanism in the absence of MucAB proteins. © 1994 Wiley-Liss, Inc.     

Mutagenic activity and mutational specificity of antiprotozoal drugs with and without nitrite treatment

We examined the mutagenic activities of six antiprotozoal drugs (three diaminopyrimidine compounds [pyrimethamine, diaveridine, and trimethoprim] and three 8-aminoquinoline derivatives [primaquine, pentaquine, and pamaquine]) in Escherichia coli WP2uvrA/pKM101 and Salmonella typhimurium TA100 and TA98 with and without nitrite treatment. The diaminopyrimidine compounds showed no mutagenic activity under any condition in any strain. The 8-aminoquinoline derivatives after nitrite treatment at 5-20 mM for 5 min at pH 3, on the contrary, showed clear mutagenicity in TA100 and WP2uvrA/pKM101 in the presence and absence of S9 mix. We concluded that 8-aminoquinoline derivatives became mutagenic following nitrite treatment. In the Lac(+) reversion assay with E. coli WP3101P-WP3106P, these nitrite-treated compounds induced G:C --> A:T transitions and G:C --> T:A transversions in the absence of S9 mix. On the other hand, A:T --> T:A transversions were induced only in the presence of S9 mix, suggesting a different kind of products may be responsible for the mutagenicity.