Mutagenic and genotoxic effects of theophylline and theobromine in Salmonella assay and in vivo sister chromatid exchanges in bone marrow cells of mice.

The mutagenic and genotoxic effects of two methylxanthines, theophylline (TH) and theobromine (TB), were assessed in the Ames mutagenicity assay (in strains TA97a, TA100, TA102 and TA104) and in vivo sister chromatid exchanges (SCEs) in bone marrow cells of mice. These are the two most commonly used nervous system stimulators throughout the world. TH is used in the long-term treatment of asthma. Bacterial mutagenicity assay showed very weak mutagenic effects of both drugs in Salmonella strains TA102 and TA104 only in certain concentrations when S9 was added to it. No mutagenic effects were observed in any other strains used in this assay either with or without metabolic activation. But results of in vivo SCE assay indicate that these two drugs can induce significant SCE in bone marrow cells of mice.     

Mutagenic and genotoxic effects of Anilofos with micronucleus,chromosome aberrations,sister chromatid exchanges and Ames test

We aimed to evaluate the mutagenic effect of Anilofos, organophosphate pesticide, by using Ames/Salmonella/microsome test. Its cytotoxic and genotoxic effects were also determined by chromosome aberration (CA), sister chromatid exchange (SCE) and micronucleus (MN) test in human peripheral blood lymphocytes. In the Ames test, five different concentrations of Anilofos were examined on TA97, TA98, TA100 and TA102 strains in the absence and presence of S9 fraction. According to the results all concentrations of this pesticide have not shown any mutagenic activity on TA97, TA100 and TA102 strains in the absence and presence of S9 fraction. But, 10, 100 and 1000 µg/plate concentrations of Anilofos were determined to be mutagenic on TA98 strain without S9 fraction. Lymphocytes were treated with various concentrations (25, 50, 100 and 200 µg/ml) of Anilofos for 24 and 48 h. The results of the assays showed that Anilofos did not induce SCE frequency, replication index and MN formation at all concentrations for both treatment periods. Anilofos significantly increased CA frequency at 100 and 200 µg/ml concentrations at 24 h treatment periods and at 50, 100 and 200 µg/ml concentrations in 48 h treatment periods. Additionally, it was determined that this pesticide decreased mitotic index and nuclear division index significantly. It was concluded that Anilofos has genotoxic and cytotoxic effects in human peripheral lymphocytes.     

Effects of nitrilotriacetic acid on the induction of gene mutations and sister-chromatid exchanges by insoluble chromium compounds

The influence of nitrilotriacetic acid trisodium salt (NTA) on the mutagenic and clastogenic activity of several water-insoluble or poorly soluble chromium compounds was determined by means of the Salmonella/microsome assay (plate test on TA100 strain) and the sister-chromatid exchange (SCE) test in mammalian cell cultures (CHO line). NTA in itself did not induce gene mutations nor did it increase the frequency of SCE. Cr(VI) compounds (Pb, Ba, Zn, Sr and Ca chromates) and an industrial Cr(VI) pigment, chromium orange (containing PbCrO4 PbO), were inactive or scarcely active mutagens in the Salmonella/microsome test when dissolved in water, but they were increasingly mutagenic when solubilized by 0.5 N NaOH or NTA (10 or 100 mg/ml). Also, the mutagenic activity of Cr(VI), contaminating an industrial Cr(III) pigment (chromite), was slightly enhanced by NTA. Mutagenicity of chromates was correlated with the amounts of Cr(VI) solubilized by NTA or alkali, as determined by the colorimetric reaction with diphenylcarbazide and atomic absorption spectrophotometry, and was decreased by incubation with microsomes, due to reduction of Cr(VI) to the genetically inactive Cr(III) form. In the SCE assay, the insoluble or poorly soluble Ba, Zn, Sr and Ca chromates and the insoluble Cr(VI) pigments zinc yellow (containing ZnCrO4 Zn(OH2], chromium yellow and molybdenum orange (both containing PbCrO4) were directly clastogenic due to cellular endocytosis taking place in prolonged treatments, and NTA significantly increased their chromosome-damaging activity.     

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.     

Collaborative study of mutagenicity with Salmonella typhimurium TA102.

Thirty compounds of various chemical classes were investigated for mutagenicity in a collaborative study (3 laboratories) using Salmonella typhimurium TA102. With 5 compounds, namely hydrazine sulfate, phenylhydrazine, hydralazine, glutardialdehyde and glyoxal, mutagenicity was detected by all laboratories. Formaldehyde was assessed as weakly mutagenic in only 1 of 3 laboratories. The remaining 24 agents were uniformly described as non-genotoxic in TA102. In spite of the overall good qualitative agreement in the mutagenicity results between the 3 laboratories some quantitative discrepancies occurred in the dose response of the mutagenic compounds. Varying inter- and intra-laboratory differences in the spontaneous rate of revertants were obtained. The usefulness of the tester strain TA102 in routine mutagenicity testing is discussed.     

Genotoxic activity of potassium permanganate in acidic solutions

Potassium permanganate (KMnO4) combined with sulfuric acid is a strongly oxidizing mixture which has been recommended for the destruction and the decontamination of various mutagens/carcinogens in the publication series of the International Agency for Research on Cancer. Evaluation of the genotoxicity of 4 potassium permanganate solutions was performed using a microtechnique of the Ames test with the tester strains TA97, TA98, TA100 and TA102 with and without metabolic activation. Presence of direct-acting mutagens was detected in all the samples with the tester strain TA102 without S9 mix (163-357 revertants/microliters of the solutions). Three samples containing either acetone or ethanol as an organic solvent also induced a mutagenic response on tester strain TA100 without S9 mix (167-337 revertants/microliters). In addition, DNA damage in human peripheral blood lymphocytes was also measured for one of the mixtures by a new technique: the single-cell gel assay (SCGA). A sample with no organic solvent induced DNA damage in human lymphocytes with a dose-response relationship as determined by SCGA. The major mutagenic agent generated by the permanganate solutions was found to be manganese ion (Mn2+). Both manganese sulfate (MnSO4) and manganese chloride (MnCl2) gave mutagenic dose-response relationships on tester strain TA102 without S9 mix. The mutagenic potencies were 2.8 and 2.4 revertant/nmole for MnSO4 and MnCl2 respectively. MnCl2 also induced DNA damage in human lymphocytes as determined by the SCGA. The genotoxic effects of KMnO4 in acidic conditions were probably mediated by the conversion of MnO4- to Mn2+. KMnO4 in alkaline solutions did not produce mutagenic species and may offer an alternative for the degradation of genotoxic compounds.     

Butylated hydroxyanisole, butylated hydroxytoluene and tert.-butylhydroquinone are not mutagenic in the Salmonella/microsome assay using new tester strains

The phenolic antioxidants butylated hydroxyanisole (BHA), butylated hydroxytoluene (BHT) and tert.-butylhydroquinone (TBHQ) were reassessed for mutagenic activity using the recently developed Salmonella tester strains TA97, TA102 and TA104, and in addition TA100. None of the phenolic antioxidants showed mutagenic activity, either with or without metabolic activation. At doses of 100 micrograms/plate and higher all 3 phenolic antioxidants exhibited toxic effects. A modification of the assay using the preincubation procedure with strain TA104 did not affect mutation frequencies. Combinations of BHA and BHT, tested to detect possible synergistic effects, did not exert mutagenic activity.     

Investigation of the mutagenicity of ethylphenylglycidate

EPG and an in vitro digest of EPG by pepsin and pancreatin simulating mammalian digestion have been examined for genotoxicity in 4 mutagenicity tests employing different genetic endpoints. In the Salmonella reverse mutation assay, EPG showed only slight mutagenic activity against TA100, a strain responsive to base-pair exchange activity, in the presence of S9 mix. In vitro EPG was mutagenic for CHO-K1-BH4 cells with or without metabolic activation, the activity being greater in the presence of metabolic activation. In the in vitro SCE test, EPG was clastogenic for CHO-K1-BH4 cells independent of metabolic activation. EPG also induced transformation of C3H T10 1/2 mouse fibroblasts in vitro, producing both type II and type III foci. Subjecting an EPG solution to a simulated mammalian digestion process lowers the genotoxic activity of the solution.     

Mutagenicity of products formed by ozonation of naphthoresorcinol in aqueous solutions

The mutagenicity of products formed by ozonation of naphthoresorcinol in aqueous solution was assayed with Salmonella typhimurium strains TA97, TA98, TA100, TA102 and TA104 in the presence and absence of S9 mix from phenobarbital- and 5,6-benzoflavone-induced rat liver. Ozonated naphthoresorcinol was mutagenic in TA97, TA98, TA100 and TA104 without S9 mix. By the addition of S9 mix, the mutagenic activity of ozonated naphthoresorcinol was markedly suppressed in TA98 and TA100, but became positive in TA102. High-performance liquid chromatography (HPLC) after derivatization to 2,4-dinitrophenylhydrazones demonstrated the formation of glyoxal as an ozonation product of naphthoresorcinol. Ion chromatographic technique also demonstrated the formation of o-phthalic acid, muconic acid, maleic acid, mesoxalic acid, glyoxylic acid and oxalic acid as ozonation products. The mutagenicity assays of these identified products with five Salmonella showed that glyoxal and glyoxylic acid were directly mutagenic; the former in TA100, TA102 and TA104, the latter in TA97, TA100 and TA104. In the presence of S9 mix, glyoxylic acid gave a positive response of mutagenicity for TA102. The experimental evidence supported that glyoxal and glyoxylic acid may contribute to the mutagenicity of ozonated naphthoresorcinol.     

Sister-chromatid exchanges in lymphocytes and mutagenicity in urine of nurses handling cytostatic drugs

Sister-chromatid exchanges (SCE) in peripheral blood lymphocytes and mutagenicity of urine (Ames test) were measured in a group of 21 nurses professionally handling antineoplastic drugs and in a group of 21 unexposed controls. No differences in SCE frequencies and in urinary mutagenic activity between exposed and unexposed groups were detected. A clear positive increase in urinary mutagenicity in the TA98 Salmonella strain was observed with increasing number of cigarettes smoked, whereas no evident influence of smoking on SCE was seen. Age, coffee and alcohol consumption did not show any detectable effect in the two tests.     

Mutagenic activity of nine N,N-disubstituted hydrazines in the Salmonella/mammalian microsome assay.

The mutagenic activity of N,N-dimethyl-, N,N-diethyl-, N,N-dibutyl-, N,N-diisobutyl-, N,N-di(p-tolyl)-, N-ethyl-N-phenyl-, N,N-dibenzyl-, N,N-diphenyl- and N,N-diisopropylhydrazine was examined in the Salmonella/mammalian microsome assay using the strains TA1535, TA1537, TA97, TA98, TA100, TA102 and TA1530. All nine hydrazines were mutagenic in at least one tester strain, although of borderline significance for some of the compounds. The mutagenic potencies of the hydrazines varied 2-3 orders of magnitude, from very weak to moderate mutagenic activity. In general, the addition of S9 resulted in a lowering of the mutagenic activity and a lowering of the toxic properties of the hydrazines. The test results were relatively difficult to evaluate due to toxic effects of many of the test compounds on the test bacteria which may have resulted in an underestimation of the mutagenic potencies of some of the compounds. The pattern of mutagenic activity of the hydrazines in the different tester strains indicates that more than one mechanism of action may be involved in the mutagenicity.     

Preferential induction of AT-TA transversion, but not deletions, by chlorambucil at the hisG428 site of Salmonella typhimurium TA102.

The chemotherapeutic agent chlorambucil effectively induces deletion mutations in mouse germ cells. The possibility that this chemical also effectively induces deletion mutations in bacterial DNA was examined using Ames Salmonella tester strains. Chlorambucil was mutagenic only to strains TA102 (hisG428, rfa/pKM101) and YG2975 (hisG46, rfa/pKM101) when S9 mix was absent. Since strain TA102 can detect short deletions, the mutational changes of TA102 induced by this agent without S9 mix were directly determined by the DNA sequencing technique. It turned out that chlorambucil did not induce deletion mutations but preferentially induced AT-TA transversions at the hisG428 site of plasmid pAQ1 of strain TA102. These results caution that the positive results induced by chlorambucil in mutagenicity tests do not necessarily mean the occurrence of deletions.     

Activity of bromochlorodifluoromethane (BCF) in three mutation tests

The halocarbon BCF was tested in 3 assays to assess its mutagenicity and clastogenicity. It produced a positive response in Salmonella typhimurium strain TA1535 but was negative in TA1537, TA1538, TA98 and TA100. In an L5178Y mouse lymphoma microwell assay (TK locus), BCF was negative. BCF was administered at 5000 and 50 000 ppm in air for 6 h to groups of C57B1/6J mice of both sexes. Animals were killed at 24, 48 and 72 h after cessation of exposure and the incidence of bone marrow micronuclei per 1000 PCEs determined. There was no significant difference in the incidences of micronuclei between untreated animals and those exposed to either concentration of BCF at any of the sampling times. These results suggest that BCF is mutagenic in vitro in only one strain of Salmonella; in mammalian cells the compound induced no gene mutation in vitro nor clastogenic activity in vivo at doses that also produced clear evidence of toxicity.     

Evaluation of the mutagenic and cytostatic potential of aristolochic acid (3,4-methylenedioxy-8-methoxy-10-nitrophenanthrene-1-carboxylic acid) and several of its derivatives

Aristolochic acid (1), a constituent of Aristolochia species, has been used for medicinal purposes since the Graeco-Roman period. Following the observation that the compound was mutagenic and carcinogenic, it was removed from pharmaceutical products. Consistent with previous reports, we have found that 1 serves as a direct-acting mutagen in Salmonella typhimurium strains TA100, TA102, TA1537 and TM677, but was not active in the nitroreductase-deficient strains TA98NR and TA100NR. However, aristolic acid (2), a compound that differs in structure only by the absence of the nitro group, was also found to be a direct-acting mutagen in Salmonella strains TA98, TA100, TA102, TA1537, and TM677, as well as strains TA98NR and TA100NR. Both compounds (1 and 2) were active mutagens when evaluated with cultured Chinese hamster ovary cells. Thus, in contrast to previous suggestions, the nitro group at position 10 is not required to induce a mutagenic response. Also, a series of structural relatives (the methyl esters of 1 and 2 (3 and 4, respectively), aristolochic acid-D (5), aristolactam (6), aristolactam A-II (7), and aristolactam-N-beta-D-glucoside (8)) were evaluated for mutagenic potential with Salmonella typhimurium strain TM677 and found to be inactive. Since compounds 3 and 4 were found to be active mutagens with Salmonella typhimurium strains TA98, TA100, TA102 and TA1537 (sufficient quantities of compounds 5-8 were not available for testing), differential sensitivity of the tester strains unrelated to mutagenic potential is suggested. Further, compounds 1, 2, and 6-8 were evaluated for potential to inhibit growth with cultured KB or P388 cells. P388 cells were substantially more sensitive, and compound 1 was the most active of the materials tested (ED5 = 0.58 microM). Compound 6 also demonstrated appreciable activity (ED50 = 4.2 microM), as did compound 8 (ED50 = 6.0 microM). It therefore appears that phenanthrene-ring substituents, in addition to the nitro group at position 10, serve important roles for biological potential. In considering the carcinogenic event induced by aristolochic acid, these functionalities should also be taken into account.     

Evaluation of secondary nitroalkanes, their nitronates, primary nitroalkanes, nitrocarbinols, and other aliphatic nitro compounds in the Ames Salmonella assay.

The secondary nitroalkanes 2-nitropropane, 2-nitrobutane, 3-nitropentane and nitrocyclopentane, as well as their anionic forms (nitronates); the primary nitroalkanes 1-nitropropane, 1-nitrobutane, and 1-nitropentane and their respective nitronates; the nitrocarbinols 2-nitro-1-propanol, 2-nitro-1-butanol, 3-nitro-2-butanol, and 3-nitro-2-pentanol and their respective nitronates; 2-methyl-2-nitropropane, and 2-nitroso-2-nitropropane were tested in the Ames Salmonella assay using strains TA98, TA100 and TA102. Nitronates of the secondary nitroalkanes 2-nitropropane, 2-nitrobutane, 3-nitropentane, and nitrocyclopentane were significantly mutagenic in Salmonella strains TA100 and TA102 at 10-80 mumoles/plate, but the parent compounds were mutagenic at only a single dose level or were not mutagenic at all in the same dose range. The primary nitroalkanes and the nitrocarbinols were not mutagenic, or only marginally so, at the concentrations tested. The nitronates of the primary nitroalkanes and the nitrocarbinols reprotonated too rapidly under the conditions of the assay for adequate evaluation of mutagenicity. 2-Methyl-2-nitropropane was not mutagenic in strains TA100 and TA102; 2-nitroso-2-nitropropane was also not mutagenic in strains TA100 and TA102, but induced an equivocal mutagenic response in TA98. The positive Salmonella mutation data for the nitronates of the secondary nitroalkanes studied correlate very well with the very slow rate of reprotonation of secondary nitroalkane nitronates at pH 7.7 (Conaway et al. (1991) Cancer Res., 51, 3143), and provide further evidence that nitronates of secondary nitroalkanes, rather than the neutral parent forms with which they may be in equilibrium, are the more proximate mutagenic species.     

Further examination of the effects of nitrosylation on Alternaria alternata mycotoxin mutagenicity in vitro

Previously, Alternaria extract and metabolite mutagenicities+/-nitrosylation were characterized using Ames Salmonella strains TA98 and TA100, which are both reverted at GC sites. To examine other targets for mutation, the metabolites Altertoxin I (ATX I), Altenuene (ALT), Alternariol (AOH), Alternariol monomethyl ether (AME), Tentoxin (TENT), Tenuazonic acid (TA) and Radicinin (RAD) were reexamined+/-nitrosylation, using Ames Salmonella strain TA97, sensitive to frameshift mutations at a run of C's, as well as strains TA102 and TA104, reverted by base pair mutations at AT sites and more sensitive to oxidative damage. ATX I was also assessed for mammalian mutagenicity at the Hprt gene locus in Chinese hamster V79 lung fibroblasts and rat hepatoma H4IIE cells. When tested from 1 to 100 microg/plate without nitrosylation, ATX I was mutagenic in TA102+/-rat liver S9 for activation and weakly mutagenic in TA104+/-S9, demonstrating direct-acting AT base pair mutagenicity. AOH was also directly mutagenic at AT sites in TA102+/-S9 while AME was weakly mutagenic in TA102+/-S9 and TA104+S9. Nitrosylation of ATX I enhanced mutagenicity at AT sites in TA104+/-S9 but produced little change in TA102+/-S9 compared to native ATX I. However, nitrosylated ATX I generated a potent direct-acting frameshift mutagen at C sites in TA97+/-S9. While ATX I was not mutagenic in either V79 cells or H4IIE cells, 5 and 10 microg/ml nitrosylated ATX I produced a doubling of 6-thioguanine resistant V79 colonies and 0.5 and 1 microg/ml were mutagenic to H4IIE cells, becoming toxic at higher concentrations. These results suggest ATX I, AME and AOH induce mutations at AT sites, possibly through oxidative damage, with nitrosylation enhancing ATX I frameshift mutagenicity at runs of C's. Nitrosylated ATX I was also directly mutagenic in mammalian test systems.     

Evaluation of the mutagenic potential of mycotoxins using Salmonella typhimurium and Saccharomyces cerevisiae.

The mutagenic effects of fiteen mycotoxins on Salmonella typhimurium strains TA1535, TA1537 and TA1538 and Saccharomyces cerevisiae strain D-3 were tested. Only aflatoxin B1 and sterigmatocystin were mutagenic. Both were active against S. typhimurium strain TA1538 and S. cerevisiae strain D-3; however, both required activation by the hepatic S-9 enzyme preparation. A positive correlation between the other mycotoxins reported to be carcinogenic and the two in vitro test systems employed was not demonstrated in our hands.     

Laser pyrolysis products-genotoxic, clastogenic and mutagenic effects of the particulate aerosol fractions

Laser therapy has gained wide acceptance and application in many medical disciplines. Nevertheless, during surgical procedures, the thermal destruction of tissue creates a smoke plume. Recent research data indicate that pyrolysates liberated during vaporisation of tissue induce DNA damage. However, assessing potential health hazards during medical laser treatment requires comprehensive insight into the cytotoxic, genotoxic, clastogenic and mutagenic capacity of laser pyrolysis products (LPP). Therefore, the aim of this study was to evaluate the cytotoxic, genotoxic, clastogenic and mutagenic potential of substances resulting from laser irradiation. Four different types of porcine tissues were irradiated with a surgical CO2 laser, the aerosols were sampled under defined conditions and subjected to the SCE test, micronucleus test and the HPRT test. The results showed that the pyrolysis products are strong inducers of cytotoxic effects. The pyrolysis products induced positive effects in the SCE test, micronucleus test and the HPRT test. The ability and extent to induce genotoxic and mutagenic effects turned out to be dependent on the type of tissue that had been irradiated. In general, the effects were most pronounced with liver pyrolysate. In all test systems, a clear dose relationship could be established. In conclusion, we were able to prove that the particulate fraction of laser pyrolysis aerosols originating from biological tissues undoubtedly have to be classified as cytotoxic, genotoxic, clastogenic and mutagenic. Therefore, they could be potential health hazards for humans.     

Genotoxicity evaluation of tetramethylbenzenes

The three tetramethyl isomers of benzene (prenitene, 1,2,3,4-; izodurene, 1,2,3,5-; and durene, 1,2,4,5-tetramethylben- zene) were studied using in vitro mutagenicity and in vivo genotoxicity tests. Potency of mutate induction by these solvents was evaluated in Salmonella typhimurium cells with, and without S9-mix made from Aroclor 1254-induced rat liver S9. The potency of induction of micronuclei (MN) and sister chromatid exchanges (SCEs) by solvents was evaluated in bone marrow of mice. Izodurene displayed mutagenic potency in strains TA97a, TA98 and TA100 only in the absence of the S9-mix. In MN tests, all three tetramethylbenzenes demonstrated no clastogenic activity on the bone marrow cells. All the tested solvents were active as genotoxic compounds in the SCE tests, demonstrating a dose-response relationships.     

Mutagenicity studies on coffee. The influence of different factors on the mutagenic activity in the Salmonella/mammalian microsome assay

Recently, mutagenic activity on several strains of Salmonella typhimurium has been found in many heat-processed foodstuffs. The previously reported direct-acting mutagenic activity of coffee in Salmonella typhimurium TA100 (Ames assay) was confirmed in our study. In addition to TA100, a mutagenic effect of coffee was also found by using the newly developed strain TA102. The mutagenic activity was abolished by the addition of rat-liver homogenate. 10% S9 mix completely eliminated the mutagenic activity of 30 mg of coffee per plate. The addition of reduced glutathione to active S9 further decreased the mutagenic activity and also reduced the mutagenicity together with inactivated S9. The compound or compounds responsible for this inactivation are heat-labile and seem to be located in the cytosol fraction of the S9. Part of the mutagenicity of coffee was also lost spontaneously upon incubation at temperatures between 0 degrees and 50 degrees C. The loss of activity was dependent on temperature, being more pronounced at 50 degrees C compared to 0 degrees C (at 50 degrees C approximately 50% of the mutagenic activity was lost after 6 h). As anaerobic conditions prevented this loss of mutagenicity almost totally, oxidative processes are probably responsible for the inactivation. The stability of the mutagen was not influenced by incubation at low pH values (pH 1-3), with or without the addition of pepsinogen. The mutagenic properties of methylglyoxal, which to some extent could be responsible for the mutagenic activity of coffee, were compared with those of coffee. Methylglyoxal was strongly mutagenic towards Salmonella typhimurium TA100 and TA102. Its mutagenic activity was partially inactivated by the addition of 10% S9. Glyoxalase I and II together with reduced glutathione abolished the mutagenic activity of methylglyoxal but reduced the mutagenicity of coffee by only 80%. Since these enzymes occur in mammalian cells, the mutagenic compound(s) of coffee could also be degraded in vivo. This conclusion is supported by the fact that a long-term carcinogenicity study with rats was negative. These results clearly demonstrate that the effects observed in vitro do not necessarily also occur in vivo, but that in vitro experiments may contribute to the understanding of fundamental mechanisms of chemical carcinogenesis.