DNA damage and mutagenicity induced by endosulfan and its metabolites

Endosulfan is a widely used broad-spectrum organochlorine pesticide, which acts as a contact and stomach poison. Nontarget species, such as cattle, fish, birds, and even humans, are also affected. Studies on the genotoxicity and mutagenicity of endosulfan have been inconsistent and nothing is known about the genotoxicity of its metabolites. In the present study, endosulfan (as a commercial isomeric mixture and as the alpha- and beta-isomers), and metabolites of endosulfan (the sulfate, lactone, ether, hydroxyether, and diol derivatives) were assayed for their ability to induce DNA damage in Chinese hamster ovary (CHO) cells and human lymphocytes using the Comet assay and were assayed for their mutagenicity using the Salmonella reversion assay (Ames test with TA98, TA97a, TA102, TA104, and TA100, with and without S9 activation). The compounds produced statistically significant (P < 0.01), concentration-dependent (0.25-10 microM) increases in DNA damage in both CHO cells and human lymphocytes. Endosulfan lactone caused the most DNA damage in CHO cells, while the isomeric mixture of endosulfan produced the greatest response in lymphocytes. The test compounds also were mutagenic in Salmonella strains at concentrations of 1-20 mug/plate (P < 0.05), with TA98 being the most sensitive strain and the diol and hydroxyether metabolites producing the highest responses. The results indicate that exposure to sublethal doses of endosulfan and its metabolites induces DNA damage and mutation. The contribution of the metabolites to the genotoxicity of the parent compound in Salmonella and mammalian cells, however, is unclear, and the pathways leading to bacterial mutation and mammalian cell DNA damage appear to differ.     

Studies on the induction of gene mutations in bacterial and mammalian cells by the ring-opened benzene metabolites trans,trans-muconaldehyde and trans,trans-muconic acid

t,t-Muconaldehyde and t,t-muconic acid have been investigated for the induction of gene mutations in Salmonella typhimurium (reversion of the his- strains TA97, TA98, TA100, TA102, TA104 and TA1535), Escherichia coli (reversion of the trp- strain WP2 uvrA) and Chinese hamster V79 cells (acquisition of resistance toward 6-thioguanine). t,t-Muconaldehyde proved weakly mutagenic in strain TA104 in the presence and absence of NADPH-fortified postmitochondrial fraction from rat liver homogenate (S9 mix). In strains TA97, TA100 and TA102, weak positive responses were observed only in the presence of S9 mix. In strains TA98, TA1535 and WP2 uvrA, the result was negative. In V79 cells, the mutation frequency was increased from approximately 7 X 10(-6) to 90 X 10(-6) in cultures exposed to t,t-muconaldehyde at optimal concentration (1.7-3 microM in separate experiments). The concentration-response curve showed pronounced hyperlinearity, with no mutagenic effect being observed at a third of the optimal concentration. t,t-Muconic acid was greater than 100 times less toxic than t,t-muconaldehyde in both bacteria and mammalian cells, and it did not show any mutagenic effect. These results complete a previous mutagenicity study, carried out on benzene and 13 metabolites. It is concluded that the newly investigated metabolites cannot account for the bacterial mutagenicity of bioactivated benzene and benzene-trans-1,2-dihydrodiol, since these compounds exhibited their strongest response in strain TA1535. t,t-Muconaldehyde showed similarities in its mutagenicity to p-benzoquinone and hydroquinone. All three compounds showed, at most, weak effects in bacteria, but were strongly mutagenic in V79 cells.(ABSTRACT TRUNCATED AT 250 WORDS)     

Use of rat/hamster S-9 mixture in the Ames mutagenicity assay

Based on the findings of Nagao et al [1978] that phenacetin is negative in the standard Ames test with Aroclor induced rat S-9 and positive with hamster S-9, the test was performed with a mixture of rat/hamster S-9. Phenacetin was mutagenic with the mixture. The activity of the mixture was compared to the rat S-9 alone with low concentrations of 2-aminoanthracene (a strong promutagen for Salmonella typhimurium TA 1535, TA 100, TA 1537, and TA 98), nitrosopiperidine (a weak promutagen), and 1,2 epoxybutane (a weak, direct-acting mutagen). Except for an increased mutagenic activation by the mixture with nitrosopiperidine the mixture was comparable to the rat S-9 alone, indicating that replacing rat S-9 with a rat/hamster S9 mixture in the standard Ames test could increase the sensitivity of the test without interfering with rat S-9 activity.     

Mutagenicity of chili extract and capsaicin in short-term tests

Vanillin, capsaicin and chili extracts were tested for mutagenicity in Salmonella typhimurium histidine-deficient tester strains TA 98, TA 100, TA 1535, TA 1537, and TA 1538. Vanillin was nonmutagenic, whereas chili extract and capsaicin were mutagenic with metabolic activation. Capsaicin, an active component of chili extract, was the more potent mutagen. The positive samples were also tested in two mammalian test systems: the micronucleus test and the 8-azaguanine-resistant mutagenesis assay that used V79 Chinese hamster cells. It was observed that both were negative for the latter test at the dose level tested, whereas in the micronucleus test, only capsaicin was positive near the LD50 dose. Capsaicin also inhibited DNA synthesis in the testes of Swiss mice injected at two dose levels.     

Mutagenic activity in synthetic pyrethroids in Salmonella typhimurium

Four pyrethroids, allethrin, resmethrin, permethrin and fen-valerate,were tested for mutagenicity in bacterial reversion assay systemswith seven strains (TA1535, TA100, TA1538, TA98, TA1537, TA97and TA104) of Salmonella typhimurium. Our results show thatthree pyrethroids, namely resmethrin, permethrin and fenvalerate,were not found to be mutagenic in S. typhimurium in the presenceor absence of a rat liver activation system. Allethrin was foundto be mutagenic with TA100, TA104 and TA97 strains and requiredmetabolic activation (S9 mix) in order to show its activity,mainly with TA100 and TA104 strains.     

Comparative mutagenic and genotoxic effects of three antimalarial drugs, chloroquine, primaquine and amodiaquine

Comparative mutagenic and genotoxic effects of three antimalarialdrugs, chloroquine, primaquine and amodiaquine, were assessedin the Ames mutagenicity assay (in strains TA97a, TA100, TA102and TA104) and in vivo sister chromatid exchange (SCE) and chromosomeaberration (CA) assays in bone marrow cells of mice. These arethe most commonly used antimalarial drugs available at presentthroughout the world. The results of the bacterial mutagenicityassays showed a very weak mutagenic effect of all three drugsin Salmonella strains TA97a and TA100 both with and withoutS9 mix and in TA104 only with S9 mix. The results of the invivo SCE and CA assays indicate that these three drugs are genotoxicin bone marrow cells of mice. ³To whom correspodence should be addressed. Tel: +91 33 473 3491; Fax: +91 33 473 5197; Email: iichbio{at}giascl01.vsnl.net.in     

In vitro genotoxicity of dyes present in colored smoke munitions

Genetic toxicology studies were conducted on organic dyes and mixtures used in colored smoke munitions. The dyes studied included Solvent Red 1; two different batches (Lot 1 and Lot 2) of Disperse Red 11; terephthalic acid; and a mixture of 25 parts Solvent Red 1, 5 parts Disperse Red 11, and 16 parts terephthalic acid. The dyes were evaluated for their ability to produce mutations in Salmonella bacterial strains and in Chinese hamster ovary (CHO) cells. The dyes were also tested in CHO cells to determine cytotoxicity and the induction of sister chromatid exchanges and chromosome aberration. None of the dyes were genotoxic in the standard Ames assay using bacterial strain TA1535 or TA100 with or without the addition of S-9 or in TA98 and TA1538 without S-9. With S-9, Disperse Red 11 (Lot 2) showed significant mutagenic activity in TA98 and TA1538 which increased as a function of S-9 concentration. However, the maximum level of mutagenic activity detected was low (3.8 revertants/micrograms). The azo dye Solvent Red 1 was also negative in a pre-incubation assay designed to reduce azo compounds to free amines. Solvent Red 1 was cytotoxic to mammalian cells, caused a significant increase in SCE, but was not mutagenic or clastogenic. Disperse Red 11 (Lot 1 and Lot 2) were not cytotoxic or clastogenic but produced an increase in cell cycle time and SCE frequency. Only Disperse Red 11 (Lot 2) increased mutations in the CHO/hypoxanthine-guanine phosphoribosyltransferase (HGPRT) assay. The mutagenic activity of the dye mixture was not significant, suggesting no synergistic interaction between the dyes. These studies demonstrated that none of the dyes was clastogenic and that a contaminant in Disperse Red 11 (Lot 2) may be responsible for the weak mutagenic activity in both mammalian and bacterial cell systems.     

Hydrogen peroxide mutagenicity towards Salmonella typhimurium

In bioassays conducted under controlled, comparable conditions, weak direct mutagenicity responses were observed for hydrogen peroxide in the standard (Ames test) agar plate incorporation bioassay with Salmonella typhimurium strains TA97, TA98, TA102, and TA1537, in a 20 min preincubation test with strains TA97, TA98, TA100, TA102, TA1537, and TA1538, and in a liquid incubation modification using strain TA1537. These results conclusively demonstrate that hydrogen peroxide is a weak mutagen, especially in strains that are sensitive to oxidative damage under suitable bioassay conditions.     

The effectiveness of Salmonella strains TA100, TA102 and TA104 for detecting mutagenicity of some aldehydes and peroxides

Several aldehydes and peroxides were tested for mutagenicityusing Salmonella typhimurium tester strains TA97a, TA100, TA102and TA104, in the presence and absence of Aroclor-induced liverS9 mix from F344 rats and B6C3F₁ mice, in either preincubationor vapour phase rotocols. Some chemicals were tested in additionalSalmonella strains. Benzaldehyde, butyraldehyde, benzoyl peroxide,4-chlorobenzaldehyde, isobutyraldehyde, propionaldehyde andveratraldehyde were non-mutagenic Acetaldehyde and dicumyl peroxidegave inconsistent results and furfural gave equivocal responsesin TA100 and TA104. Cumene hydroperoxide, formaldehyde and glutaraldehydewere mutagenic in TA100, TA102 and TA104. trans-Cinnamaldehydeexhibited a weak mutagenic response in TA100 with mouse liverS9 only. 2,4,5-Trimethoxybenzaldehyde was mutagenic only instrain TA1538 with rat liver S9. With the exception of butanoneperoxide, which was mutagenic only in TA104, all chemicals mutagenicin strains TA102 and/or TA104 were also mutagenic in TA100.The data do not, therefore, support the preferential use ofstrains TA102 and TA104 for screening aldehydes and peroxidesfor mutagenicity. For a number of these chemicals the advantagesof using TA102 or TA104 was in the increased responses comparedwith those obtained with TA100. Two of the four peroxides weremutagenic and one of these was mutagenic only with TA104. Thissuggests that strains TA102 and TA104 be used if peroxides arenot mutagemc in TA100 or TA97. ⁴Present addresses: ⁴British American Tobacco Ltd, SouthamptonSO15 8TL, UK ⁵FRAME, Nottingham NG1 4EE, UK ³To whom correspondence should be addressed. Tel: +1 919 541 4482; Fax: +1 919 541 2242; Email: zeiger{at}niehs.nih.gov      

Antimutagenic effects of centchroman--a contraceptive and a candidate drug for breast cancer in multiple mutational assays

Centchroman (CC), a non-steroidal oral contraceptive and a candidate drug for breast cancer, has been reported to exhibit partial to complete remission of lesions in 40.5% of breast cancer patients. The potent anti-oestrogenic activity, negligible side-effects and anti-breast cancer activity of CC prompted us to evaluate the antimutagenic effects of this compound in a bacterial mutagenicity assay and CHO/HPRT and AS52/GPT mutation assays in vitro and in vivo in female Swiss albino mice as measured by both sister chromatid exchange (SCE) and chromosome aberrations (CA) against three known positive mutagen compounds, dimethylbenz[a]anthracene (DMBA), cyclophosphamide (CP) and mitomycin C (MMC). Antimutagenicity assays in Salmonella strains TA97a, TA100, TA98 and TA102 were carried out against commonly used known positive mutagens, sodium azide, 4-nitro-o-phenylenediamine, cumine hydroperoxide, 2-aminofluorene and danthron. A significantly reduced number of bacterial histidine revertant colonies was observed in the plates treated with 0.1, 1, 5 and 10 microg/plate CC and a positive compound when compared with bacterial plates treated with the respective positive compound alone. Ethyl methanesulfonate (EMS), a commonly used positive mutagen for CHO/HPRT and AS52/GPT gene mutation assays, was used for antimutagenicity assay in these cells. CC exhibited protective effects against the mutagenicity of EMS in these two mammalian cell mutation assays, CHO/HPRT and AS52/GPT. In the in vivo studies, pretreatment with CC reduced DMBA-induced SCE and CA and CP- and MMC-induced CA when compared with the group treated only with the positive compounds. These results indicate that CC can reduce the mutagenic effects of known genotoxic compounds.     

Mutagenic and cytotoxic potencies of a series of anthracycline derivatives as measured by His+ reversion, 8-azaguanine resistance and direct plating cytotoxicity tests in Salmonella typhimurium

His+ reversion at multiple his- loci, 8-azaguanine resistance, and a previously reported direct plating cytotoxicity test were used to measure the genotoxic potencies of a series of anthracycline derivatives in Salmonella typhimurium. N-demethylated amino sugar monosaccharide anthracyclines reverted most his- tester strains and were positive with 8-azaguanine selection. Reversion of strain TA98 was the most sensitive end point for measuring the mutagenic activity of the N-demethylated anthracyclines. N,N-dimethyl amino sugar derivatives of Adriamycin and daunomycin were negative as measured by His+ reversion in tester strain TA98, but generated positive responses in tester strain TA102 that were equal to or greater than those of the demethylated parent compounds. Similarly, N,N-dimethyl amino sugar derivatives of pyrromycinone and 1-deoxypyrromycinone had no mutagenic activity as measured by His+ reversion except in tester strains TA102 and TA104. These later compounds also gave positive responses with 8-azaguanine selection. In view of these results, the importance of amino sugar dialkylation and anthracycline mechanisms of mutagenesis are discussed.     

Metabolic activation of organic extracts from diesel, coke oven, roofing tar, and cigarette smoke emissions in the Ames assay

Four environmental emissions samples were ranked by their genotoxic potency in several bioassays. Although the relative potency of a series of automotive emissions (diesel and gasoline) in the Ames assay correlated well with the relative potency in mammalian cell and mouse skin, this was not the case for the coke oven, roofing tar, and cigarette smoke condensate (CSC) emissions. This study examines the role of metabolic activation in determining the difference between a microbial and a mammalian bioassay in ranking the genotoxic potency of these environmental emissions. Uninduced and Aroclor 1254-induced S9 from both rat and hamster liver were compared as the metabolic activator in the Ames assay with Salmonella typhimurium TA98. The diesel emissions sample was direct-acting while the other samples required activation. The standard S9 concentration (only Aroclor-induced rat, approximately 1.25 mg protein/plate) also produced the maximum mutagenic activity. Induced S9s produced higher mutagenic activity than uninduced. The hamster S9 gave significantly higher mutagenic activities than rat S9 for the coke oven and CSC. The relative potency of these four samples was not significantly different between the microbial (Ames), mammalian cell (mouse lymphoma), and tumor initiation (mouse skin) assays. These results suggest that the differences observed between the relative mutagenic activity of these emissions in the mammalian cell and microbial assays was not due to a lack of optimization of the S9 system but may be inherent in the different response of the indicator cells to different chemical classes.     

Evaluation of mutagenic activity in an extract of pepper tree stem bark (Schinus terebinthifolius Raddi)

An extract (decoction) from pepper tree stem bark (Schinus terebinthifolius Raddi) is widely used in Brazil as a topical antiinflammatory agent and to cicatrize wounds. The extract contains catechin, tannins, terpenes, flavonoids, and saponins; of these components, both mutagenic potential and antioxidant properties have been ascribed to flavonoids. The mutagenicity of some flavonoids is believed to be associated with the formation of reactive oxygen species and seems to depend on the number and position of hydroxyl groups. In the present study, we evaluated an extract of S. terebinthifolius in a series of cell-free and bacterial assays in order to determine its genotoxic potential. The extract was negative in a cell-free plasmid DNA test, indicating that it did not directly break DNA. Positive results, however, were obtained in the SOS chromotest, in a forward mutagenesis assay employing CC104 and CC104mutMmutY strains of Escherichia coli, and in the Salmonella reversion assay, using strains TA97, TA98, TA100, and TA102. All the bacterial tests were performed without exogenous metabolic activation due to the topical use of this preparation. The results indicate that pepper tree stem bark extract produces DNA damage and mutation in bacteria, and that oxidative damage may be responsible for the genotoxicity.     

Ozone is mutagenic in Salmonella.

Ozone is a highly reactive gas that has been tested for genotoxicity in a number of systems. Induced genetic damage resulting from ozone treatment may not be readily observed because of the high toxicity of the chemical and difficulties in generating and administering controlled concentrations. The mutagenicity of ozone was investigated in Salmonella typhimurium using a plate test protocol designed for reactive vapours and gases. Ozone, at two to three consecutive doses, induced weak, albeit statistically significant, mutagenic responses in tester strain TA102 with and without Aroclor-induced rat liver S9 (lowest effective mean concentration of 0.019 ppm; 35 min total exposure). However, dose-related responses were not always obtained. No mutagenicity was detected in strains TA98, TA100, or TA1535, with or without S9. In strain TA104, ozone induced a weak response only at a single dose with S9; this response was not reproducible. Mutagenicity was dependent on the ozone flow rate and total exposure time, with variations in the optimum dose-time regimen leading to toxicity or complete inactivity. The data show that ozone is a very weak bacterial mutagen and only when tested under narrowly prescribed, subtoxic dosing conditions.     

Effects of Salmonella genotypes and testing protocols on H2O2-induced mutation

Hydrogen peroxide (H2O2) was shown to be mutagenic in a number of strains of Salmonella typhimurium. Strain SB1106p (hisC3108, hisO1242, pKM101), a newly-constructed strain carrying the histidine mutation at a UGA chain-terminating codon, was more responsive to H2O2 than TA104 or TA102, the two hisG428 strains originally developed for detecting oxidative mutagens. The largest proportional increase in revertants of strain TA104 was in the fraction of intragenic deletions. Three other strains (TA97, SB1111 and SB1106) gave unequivocal positive responses to H2O2 in both the liquid pre-incubation procedure and standard plate incorporation procedure. The response of TA100 varied among experiments, ranging from negative to a weak positive. Variations in the catalase content among the tester strains did not correlate with the relative responses obtained in the mutagenicity assays.     

Mutagenicity spectra in Salmonella typhimurium strains of glutathione, L-cysteine and active oxygen species

Glutathione and L-cysteine, in the presence of rat kidney post-mitochondrialsupernatant (S9) fraction, and various forms of active oxygenwere investigated for mutagenicity in seven his^– strainsof Salmonella typhimurium. Glutathione and L-cysteine showedqualitatively and quantitatively virtually identical mutagenicactivities. The number of mutants induced in strain TA97 was3–4 times higher than in TA100, the strain in which themutagenicity was originally detected. Mutagenic effects werealso observed in strains TA92, TA102 and TA104, but not in TA1535and TA1537. Hydrogen peroxide, superoxide and glucose/glucoseoxidase in the presence and absence of kidney S9 fraction showedpronounced mutagenic effects in strains TA104 and TA102. Additionally,weak mutagenic effects were observed in TA100, while the remainingstrains, including TA97, were not responsive. These mutagenicityspectra suggest that the mutagenic species formed from glutathioneand L-cysteine are similar, if not identical, and are differentfrom hydrogen peroxide, superoxide and other oxygen speciesderived from them. Further support for this notion was givenwhen it was observed that catalase did not affect the mutagenicityof glutathione and that superoxide dismutase showed a significanteffect only when used in milligram quantities. This study showsthat mutagenicity spectra may be useful in the elucidation ofactivation pathways. Furthermore, it is interesting to notethat all the compounds and preparations showing a positive responsein the Ames test in the present study occur endogenously inorganisms: glutathione, L-cysteine, hydrogen peroxide, superoxide,glucose, glucose oxidase and kidney S9 fraction (which was mutagenicin several strains).     

Effect of some phthalate esters in human cells in the comet assay.

Phthalate esters are among the most extensively used industrial chemicals and are widely distributed in the environment. Di-(2-ethylhexyl)phthalate (DEHP) and its hydrolysis product mono-(2-ethylhexyl)phthalate (MEHP) have been examined for genotoxic activity on previous occasions. Only MEHP was found to cause chromosome damage in CHO cells but was without effect in the sister chromatid exchange and hypoxanthine guanine phosphoribosyl assay. DEHP was found to be a weak direct acting mutagen in Salmonella typhimurium strain TA100, the mutagenic activity of which could be abolished by rat liver microsomes (S9 mix). The clastogenicity and weak mutagenicity suggest a possible contributory role for these compounds in the observed carcinogenicity of the phthalates, which have been thought predominantly to be linked to cancer pathology through proliferation of hepatic peroxisomes. The present study showed that these compounds could produce DNA damage in human blood cells in the Comet assay and also, that rat liver microsomes could abolish the effect of DEHP. Thus in the intact animal, no response may be observed.     

Conditions affecting the mutagenicity of trichloroethylene in Salmonella

Trichloroethylene (TCE) is a high production volume chemical frequently stabilized with oxiranes. These oxiranes may be responsible for the mutagenic activity of TCE in Salmonella, which has been occasionally, but not consistently, reported. High purity and oxirane-stabilized TCE samples were tested for their mutagenic potential in Salmonella typhimurium strains TA 1535, TA 98, and TA 100. Stabilized TCE was tested using a preincubation protocol up to a dose level of 10,000 micrograms per plate, but no mutagenic response was observed in either the presence or absence of a supplementary metabolic activation system (S9 mix) derived from Aroclor 1254-induced male rat liver. TCE without oxirane stabilizers also was nonmutagenic when tested in a vapor delivery system at nominal concentrations of up to 20% and using S9 mix derived from either rat or hamster. TCE containing 0.5-0.6% 1,2-epoxybutane did induce mutagenic responses from strains TA 1535 and TA 100 in the presence and absence of S9 mix. The lowest effective dose was about 0.63% in TA 1535 in the absence of S9 mix. Vapor-phase tests with 1,2-epoxybutane showed that an atmospheric concentration of 0.009% could induce 12-fold and 3-fold increases, respectively, in strains TA 1535 and TA 100. These increases would account for the mutagenic activity of the stabilized TCE sample. Epichlorohydrin (another commonly used stabilizer) induced similar increases in mutant numbers at an atmospheric concentration of 0.0009%. The absence of a significant response caused by unstabilized TCE in the presence of S9 mix is probably due to a lack of assay sensitivity, since chloral, a metabolite of TCE, is a mutagen in TA 100 [Haworth et al.: Environ Mutagen [Supplement 1] 5:3-142, 1983].     

Analysis of rat lymphocyte activation of benzo[a]pyrene, 2-acetylaminofluorene, and several of their metabolites to mutagenic and DNA-damaging species in vitro.

Rat lymphocytes are a potentially useful and convenient cell system for monitoring the genotoxic effects of chemicals in vivo, but little is known about the ability of these cells to metabolize promutagens to genotoxic species. In this study, Fischer 344 rat lymphocytes were treated in vitro with benzo[a]pyrene (BaP), 2-acetylaminofluorene (2-AAF), and several of their metabolites, and DNA damage was measured using nucleoid sedimentation analysis. Of the BaP derivatives, BaP 4,5-oxide and BaP 7,8-diol-9, 10-epoxide decreased lymphocyte nucleoid sedimentation, whereas BaP and BaP 7,8-dihydrodiol had little effect. Among the 2-AAF derivatives, N-acetoxy-2-AAF, N-hydroxy-2-AAF, and N-hydroxy-2-aminofluorene damaged rat lymphocyte nucleoids, whereas 2-AAF, 2-aminofluorene, and fluorene produced little detectable damage. The decrease in nucleoid sedimentation produced by N-hydroxy-2-AAF was not inhibited by paraoxon, salicylamide, or 2-aminofluorene, whereas paraoxon inhibited damage produced by N-acetoxy-2-AAF. In co-culture assays, rat lymphocytes increased the mutagenicity of N-hydroxy-2-AAF in Salmonella typhimurium strain TA98, but mediated little or no mutagenic response with BaP, BaP 7,8-dihydrodiol, and 2-AAF. Also, human lymphocytes, but not rat lymphocytes, mediated a positive mutagenic response with BaP 7,8-dihydrodiol in Chinese hamster ovary UV5 cells. Although rat lymphocytes may metabolize certain proximal genotoxic chemicals to DNA-damaging species (e.g., N-hydroxy-2-AAF), these data suggest that in vivo lymphocyte DNA damage is more likely to result from lymphocytes encountering reactive chemical derivatives produced by other cells. It is also clear that differences exist between the ability of human and rat lymphocytes to activate promutagens, and this may impact on the use of the rat model to predict the genotoxicity of chemicals in humans.     

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.