Antimutagenicity of some citrus fruits in Salmonella typhimurium

The antimutagenic effect of 10 citrus fruit juices was observed against the mutagenicity of N-nitro-o-phenylenediamine (NPD) in TA97a and sodium azide in TA100 tester strains of Salmonella typhimurium using the Ames test. It was noticed that the juices of all these fruits reduced significantly the NPD and sodium azide induced revertant colonies. The inhibitory activity was enhanced if the mutagen and juice were co-incubated for about 30 min at 37 degrees C prior to performing the mutagenicity assay. Dilution with distilled water led to the reduction in the inhibitory activity. The antimutagenic activity of synthetic ascorbic acid or citric acid or combined ascorbic acid and citric acid was also seen. But the results with fruit juices tempted us to believe that in addition to ascorbic acid and citric acid, the presence of other factor(s) possessing antimutagenic properties cannot be ruled out.     

Antimutagenic activity of methanolic extracts of four ayurvedic medicinal plants

Methanolic extracts of Acorus calamus (Rhizome), Hemidesmus indicus (Stem), Holarrhena antidysenterica (Bark) and Plumbago zeylanica (Root), were tested for their antimutagenic potential. These extracts, at tested concentrations, showed no sign of mutagenicity to Salmonella typhimurium tester strains. The extracts of the plants exhibited varying level of antimutagenicity. At a dose of 100 microg/plate, the extracts exhibited the inhibition of His+ revertants from 18.51% to 82.66% against direct acting mutagens, methyl methanesulphonate (MMS) and sodium azide (NaN3) induced mutagenicity in Salmonella tester strains TA 97a, TA 100, TA 102 and TA 104. However, at lower concentrations (25 and 50 mcirog/plate) of the plant extracts, a decrease in antimutagenic activity was recorded. Dose dependent antimutagenic activity of the extracts is also evident from linear regression analysis of the data. The over all antimutagenic potential of above four extracts was found to be in order of A. calamus > H. indicus > H. antidysenterica > P. zeylanica. Further, total phenolic content of these extracts did not correlate with its antimutagenic activity in A. calamus and P. zeylanica.     

Antimutagenic and anticarcinogenic effects of Phyllanthus amarus

This study aimed to examine the antimutagenic and anticarcinogenic potential of Phyllanthus amarus Schum. et Thonn. using the bacterial preincubation mutation assay and an in-vivo alkaline elution method for DNA single-strand breaks in hamster liver cells. The aqueous extract of the entire plant showed an antimutagenic effect against induction by 2-aminofluorene (AF2), 2-aminoanthracene (2AA) and 4-nitroquinolone-1-oxide (4-NQO) in Salmonella typhimurium strains TA98 and TA100, and in Escherichia coli WP2 uvrA/pKM101. All the results were dose-dependent; however, inhibition of N-ethyl-N-nitrosoguanidine (ENNG)-induced mutagenesis was observed only with S. typhimurium TA100. The extract also exhibited activity against 2-nitrofluorene (2NF) and sodium azide-induced mutagenesis with S. typhimurium TA98 and TA100, respectively. Based on the alkaline elution method, the plant extract prevented in vivo DNA single-strand breaks caused by dimethylnitrosamine (DMN) in hamster liver cells. When the extract was administered 30 min prior to the administration of DMN, the elution rate constant decreased more than 2.5 times, compared to that of control. These results indicate that P. amarus possesses antimutagenic and antigenotoxic properties.     

Antigenotoxic properties of two newly synthesized β-aminoketones against N-methyl-N'-nitro-N-nitrosoguanidine and 9-aminoacridine-induced mutagenesis

The aim of this study was to determine the antigenotoxic potential of two newly synthesized β-aminoketones against N-methyl-N'-nitro-N-nitrosoguanidine (MNNG) and 9-aminoacridine (9-AA)-induced mutagenesis. The mutant bacterial tester strains were MNNG-sensitive Escherichia coli WP2 uvrA and 9-AA-sensitive Salmonella typhimurium TA1537. Both test compounds showed significant antimutagenic activity at various tested concentrations. The inhibition rates ranged from 29.5% (compound 1: 2 mM/plate) to 47.5% (compound 2: 1.5 mM/plate) for MNNG and from 25.0% (compound 2: 1 mM/plate) to 52.1% (compound 2: 2.5 mM/plate) for 9-AA genotoxicity. Moreover, the mutagenicity of the test compounds was investigated by using the same strains. Neither test compound has mutagenic properties on the bacterial strains at the tested concentrations. Thus, the findings of the present study give valuable information about chemical prevention from MNNG and 9-AA genotoxicity by using synthetic β-aminoketones.     

Evaluation of the mutagenicity and the tumor-promoting activity of parasite extracts: Schistosoma japonicum and Clonorchis sinensis

In relation to the observed association of carcinogenesis with parasitic infections, the mutagenicity of extracts of Schistosoma japonicum and Clonorchis sinensis was examined. In the bacterial mutagenicity tests using the Ames Salmonella typhimurium strains TA98, TA100, TA97 and TA102, and Escherichia coli WP2 and WP2 uvrA pKM101 Schistosoma soluble egg antigen and a homogenate of adult Schistosoma worms showed no positive responses either in the presence or in the absence of S9 mix. Likewise, adult worm extracts of Clonorchis showed no mutagenicity. The Schistosoma soluble egg antigen showed a weak but significant activity for the induction of Epstein-Barr virus expression in viral genome-carrying human lymphoblastoid cells in culture. This phenomenon suggests that the soluble egg antigen possesses tumor-promoting activity.     

A 50 Hz, 14 mT magnetic field is not mutagenic or co-mutagenic in bacterial mutation assays

We used bacterial mutation assays to assess the mutagenic and co-mutagenic effects of power frequency magnetic fields (MF). For the former, we exposed four strains of Salmonella typhimurium (TA98, TA100, TA1535, TA1537) and two strains of Escherichia coli (WP2 uvrA, WP2 uvrA/pKM101) to 50Hz, 14mT circularly polarized MF for 48h. All results were negative. For the latter, we treated S. typhimurium (TA98, TA100) and E. coli (WP2 uvrA, WP2 uvrA/pKM101) cells with eight model mutagens (N-ethyl-N'-nitro-N-nitrosoguanidine, 2-(2-furyl)-3-(5-nitro-2-furyl) acrylamide, 4-nitroquinoline-N-oxide, 2-aminoanthracene, N(4)-aminocytidine, t-butyl hydroperoxide, cumen hydroperoxide, and acridine orange) with and without the MF. The MF induced no significant, reproducible enhancement of mutagenicity. We also investigated the effect of MF on mutagenicity and co-mutagenicity of fluorescent light (ca. 900lx for 30min) with and without acridine orange on the most sensitive tester strain, E. coli WP2 uvrA/pKM101. Again, we observed no significant difference between the mutation rates induced with and without MF. Thus, a 50Hz, 14mT circularly polarized MF had no detectable mutagenic or co-mutagenic potential in bacterial tester strains under our experimental conditions. Nevertheless, some evidence supporting a mutagenic effect for power frequency MFs does exist; we discuss the potential mechanisms of such an effect in light of the present study and studies done by others.     

Intermediate frequency magnetic fields do not have mutagenic, co-mutagenic or gene conversion potentials in microbial genotoxicity tests

We used bacterial mutation and yeast genotoxicity tests to evaluate the effects of intermediate frequency (IF; 2 kHz, 20 kHz and 60 kHz) magnetic fields (MFs) on mutagenicity, co-mutagenicity and gene conversion. We constructed a Helmholtz type exposure system that generated vertical and sinusoidal IF MFs, such as 0.91 mT at 2 kHz, 1.1 mT at 20 kHz and 0.11 mT at 60 kHz. Mutagenicity, co-mutagenicity and gene conversion assays were performed for each of the three MF exposure conditions. Mutagenicity testing was performed in four strains of Salmonella typhimurium (TA98, TA100, TA1535 and TA1537) and two strains of Escherichia coli (WP2 uvrA and WP2 uvrA/pKM101) to cover a wide spectrum of point mutations. For co-mutagenicity tests, we used four sensitive test strains (TA98, TA100, WP2 uvrA and WP2 uvrA/pKM101) with five chemical mutagens (t-butyl hydroperoxide (BH, a hydroxyl free radical precursor), 2-(2-furyl)-3-(5-nitro-2-furyl) acrylamide (AF2) and N-ethyl-N'-nitro-N-nitrosoguanidine (ENNG, DNA reactive reagents), benz[a]pyrene (BaP) and 2-aminoanthracene (2AA, DNA reactive promutagens). Gene conversion testing was performed in the yeast test strain, Saccharomyces cerevisiae XD83. We also examined the effects on the repair process of DNA damage by UV irradiation. No statistically significant effects were observed between exposed and control groups in any of the genotoxicity tests, indicating that the IF MFs (0.91 mT at 2 kHz, 1.1 mT at 20 kHz or 0.11 mT at 60 kHz) do not have mutagenic or co-mutagenic potentials for the chemical mutagens tested under these experimental conditions. Our findings also indicate that these IF MFs do not induce gene conversion or affect the repair process of DNA damage in eukaryotic cells.     

The amyloid peptide induces early genotoxic damage in human preneuron NT2

The antimutagenic activities of benzalacetone (4-phenyl-3-buten-2-one) and its structurally-related compounds were evaluated through their use as post-treatments for the UV-induced mutagenesis in Escherichia coli WP2s (uvrA) and the gamma-induced mutagenesis in Salmonella typhimurium TA2638, the latter of which is sensitive to oxidants. Structure-activity relationships were studied between IC(50) activity values, i.e. the dose (micromol/ml) at which the mutation frequency is reduced to 50% of the control, and electronic and hydrophobicity properties of the studied molecules. Benzalacetone and benzalacetone analogs, cinnamaldehyde and trans-1,1,1-trifluoro-4-phenyl-3-buten-2-one (TF), inhibited both forms of mutagenesis, but methyl cinnamate, cinnamic acid and cinnamamide did not. The IC(50) values of TF, for UV-induced mutagenesis and gamma-induced mutagenesis, were 0.028 and 0.045 micromol/ml, respectively, and one order of magnitude lower than those of cinnamaldehyde and benzalacetone. The three antimutagenic analogs listed in order of decreasing activity are: TF>cinnamaldehyde>benzalacetone. This order is proportional to the electron-withdrawing property of the terminal group attached to an alpha,beta-unsaturated carbonyl moiety in the side chain that is known to play an important role in the antimutagenicities of benzalacetone and related compounds. In UV-induced mutagenesis in E. coli WP2s, mono-substituted benzalacetones - the ring-substituents of which have electron-withdrawing properties - showed antimutagenic activity that correlated with their electronic property. In gamma-induced mutagenesis in S. typhimurium TA2638, the antimutagenic activities of mono-substituted benzalacetones were proportional to the substituent hydrophobicities (pi). The different effects on both the mutation-induced systems is suggested to be related to the relative permeability of the cell membranes and the different sensitivities to mutagens between E. coli WP2s and S. typhimurium TA2638. In addition, the antimutagenic activity against gamma-induced mutagenesis could be due to the ability of parent compounds or their derivatives to scavenge long-lived organic radicals; the radicals have been described to be generated as a result of the X-irradiation of cells by Koyama et al. [Mutat. Res. 421 (1998) 45].     

Mutagenicity arising from near-ultraviolet irradiation of N-nitrosomorpholine

When a mixture of N-nitrosomorpholine and S. typhimurium TA100 in saline was irradiated with near-ultraviolet light, mutagenesis of the bacteria took place. The same observation was made with S. typhimurium TA1535, E. coli WP2 uvrA, pKM101 and uvrA/pKM101. Several other nitrosamines showed ed the same, but weaker, effect. Evidence is presented to indicate that the mutagenicity arises from the cellular phosphate-mediated photochemical formation of direct-acting mutagen from the nitrosamine.     

Urinary mutagenicity tests in lead-exposed workers

Urinary mutagenic activity detected by the bacterial fluctuation assay, using Salmonella typhimurium TA98 and Escherichia coli WP2 uvrA with and without metabolic activation (S9 mix), was studied in a group of 21 workers exposed to inorganic lead and a control group of 22 non-occupationally exposed subjects. Occupational exposure to inorganic lead had no effect on urinary mutagenicity in the strains considered, with or without metabolic activation. In smokers (exposed and non-exposed), urinary mutagenic activity appeared to increase compared to non-smokers (exposed and non-exposed), only with Salmonella typhimurium TA98 in the presence of S9 mix.     

Antimutagenicity studies of chlorophyllin using the Salmonella arabinose-resistant assay system

Studies with the arabinose-resistant Salmonella forward mutation assay system were performed to determine the antimutagenic activity of chlorophyllin against the mutagenic activity of aflatoxin B1 (AFB1), 2-aminoanthracene (2AA), benzo[a]pyrene (BaP), N-methyl-N'-nitro-N-nitrosoguanidine (MNNG) and solvent extracts of coal dust (CD), diesel emission particles (DE), airborne particles (AP), tobacco snuff (TS), black pepper (BP) and red wine (RW). Various concentrations of each chemical and complex mixture extract were assayed for mutagenic activity with and/or without S9 in a preincubation test. One concentration of each chemical and complex mixture extract was then tested with various concentrations of chlorophyllin. Results showed that chlorophyllin, at concentrations of 2.5 mg/plate or less, completely or almost completely inhibited the mutagenicity of 2AA, AFB1, BaP, MNNG and solvent extracts of CD, DE and RW. With concentrations from 1.25 to 5 mg/plate, chlorophyllin inhibited over 50% of the mutagenicity of AP, TS and BP extracts. These results further substantiate the antimutagenic efficacy of chlorophyllin against chemicals and complex mixtures.     

Evaluation of mutagenic and antimutagenic activities of alpha-bisabolol in the Salmonella/microsome assay

alpha-Bisabolol (BISA) is a sesquiterpene alcohol found in the oils of chamomile (Matricaria chamomilla) and other plants. BISA has been widely used in dermatological and cosmetic formulations. This study was undertaken to investigate the mutagenicity and antimutagenicity of BISA in the Salmonella/microsome assay. Mutagenicity of BISA was evaluated with TA100, TA98, TA97a and TA1535 Salmonella typhimurium strains, without and with addition of S9 mixture. No increase in the number of his+ revertant colonies over the negative (solvent) control values was observed with any of the four tester strains. In the antimutagenicity assays, BISA was tested up to the highest nontoxic dose (i.e. 50 and 150 microg/plate, with and without S9 mix, respectively) against direct-acting (sodium azide, SA; 4-nitroquinoline-N-oxide, 4-NQNO; 2-nitrofluorene, 2-NF; and nitro-o-phenylenediamine, NPD) as well as indirect-acting (cyclophosphamide, CP; benzo[a]pyrene, B[a]P; aflatoxin B1, AFB1; 2-aminoanthracene, 2-AA; and 2-aminofluorene, 2-AF) mutagens. BISA did not alter mutagenic activity of SA and of NPD, and showed only a weak inhibitory effect on the mutagenicity induced by 4-NQNO and 2-NF. The mutagenic effects of AFB1, CP, B[a]P, 2-AA and 2-AF, on the other hand, were all markedly and dose-dependently reduced by BISA. It was also found that BISA inhibited pentoxyresorufin-o-depentylase (PROD, IC50 2.76 microM) and ethoxyresorufin-o-deethylase (EROD, 33.67 microM), which are markers for cytochromes CYP2B1 and 1A1 in rat liver microsomes. Since CYP2B1 converts AFB1 and CP into mutagenic metabolites, and CYP1A1 activates B[a]P, 2-AA and 2-AF, results suggest that BISA-induced antimutagenicity could be mediated by an inhibitory effect on the metabolic activation of these promutagens.     

Nickel(II) genotoxicity: potentiation of mutagenesis of simple alkylating agents

Many metals have been shown to alter the function of a wide range of enzyme systems, including those involved in DNA repair and replication. To assess the impact in vivo of such metal actions a "Microtitre" fluctuation assay was used to examine the ability of Ni(II) to act as a comutagen with simple alkylating agents. In E. coli, Ni(II) chloride potentiated the mutagenicity of methyl methanesulfonate (MMS) in polymerase-proficient strains (WP2+ and WP2-), but not in polA- strains (WP6 and WP67) or in lexA- (CM561) or recA- (CM571) strains. The absence of UV excision repair (WP2- and WP67) had little, if any, effect. An extended lag phase was seen at 2-4 h in the polA- strains following treatment with Ni(II) chloride and MMS, but normal growth resumed thereafter. Results suggested that mutations induced by MMS were fixed during log phase growth and that more than 2 h of exposure were necessary for potentiation by Ni(II) to be observed. Thus, the extended lag phase probably cannot explain the lack of potentiation. RecA-dependence of the comutagenic effect was corroborated with S. typhimurium TA1535 and TA100. Only in the pKM101 containing strain, TA100, was potentiation of ethyl methanesulfonate (EMS) and MMS by Ni(II) chloride evident. The mucAB genes carried on pKM101 increase the sensitivity of TA100 to a variety of mutagens, providing there is a functional recA gene product. Taken together, the data suggest that Ni(II) acts indirectly, as a comutagen, in bacterial systems, possibly affecting processes involving recA- and/or polA-dependent function(s).     

Investigation of the mutagenic and antimutagenic effects of Origanum compactum essential oil and some of its constituents

In the present study, the chemical composition of Origanum compactum essential oil was determined by gas chromatography and mass spectrometry, and its mutagenic and antimutagenic activities were investigated by the somatic mutation and recombination test (SMART) in Drosophila melanogaster. No significant increase in the number of somatic mutations was observed with the essential oil tested using both the standard (ST) and high bio-activation (HB) cross. In order to investigate the antimutagenic effect of the essential oil, we have tested the effect on the indirect-acting mutagen urethane (URE), as well as the direct-acting mutagen methyl methanesulfonate (MMS). O. compactum essential oil showed a strong inhibitory effect against URE-induced mutagenicity, especially with the HB cross. However, only a weak inhibitory effect on the mutagenicity induced by MMS was observed. These results suggest that the detected antimutagenicity could be mediated by an inhibitory effect on metabolic activation. The essential oil was fractionated to identify the components responsible of the suppressing effect detected. Seven fractions were obtained: two of them showed the most potent inhibitory effect against URE-induced mutagenicity and were further fractionated. The sub-fractions obtained from the second chromatographic fractionation were tested for their antimutagenic activity, together with carvacrol and thymol. The highest antimutagenic effect obtained with the sub-fractions was similar to the effect of the crude essential oil, as well as to the effect of carvacrol alone. These results suggest the absence of a synergic antimutagenic effect between the components of O. compactum essential oil and indicate that carvacrol was the most active oil component.     

Inhibitory effect of heavy water on mutability of chemically injured Escherichia coli cells

After E. coli cells (WP2 and WP2uvrA) were treated with chemical mutagens (methyl methanesulfonate, MMS; N-methyl-N-nitrosourea, MNU; 4-nitroquinoline 1-oxide, 4NQO) in 1/15 M phosphate buffer, the mutability of the treated cells plated on a D₂O-agar plate was compared with that plated on an ordinary H₂O-agar plate. The mutation frequency decreased more or less on the D₂O-agar plate. The D₂O-substitution effects, as termed by the relative mutation frequencies (MF_D2O/MF_H2O), are 0.92 for MMS, 0.29 for MNU, and 0.42 for 4NQO in WP2, and 0.68 for MMS, 0.49 for MNU, and 0.16 for 4NQO in WP2uvrA. The D₂O effect seemed to be partly related to the function of the uvrA gene-associated products. The pH dependence of mutability was discussed in connection with the D₂O-substitution effect.     

Genotoxicity assay of oil dispersants in bacteria (mutation, differential lethality, SOS DNA-repair) and yeast (mitotic crossing-over)

5 oil dispersants and a sample of paraffin were devoid of mutagenic activity in the Ames reversion test, with and without S9 mix, using 7 his- S. typhimurium strains (TA1535, TA1537, TA1538, TA97, TA98, TA100, TA102). However, 3 dispersants produced direct DNA damage in E. coli WP2, which was not repairable in repair-deficient strains (WP2uvrA, CM871, TM1080), as shown by two different DNA-repair test procedures. The uvrA excision-repair system was in all cases the most important mechanism involved in repairing the DNA damage produced by oil dispersants, while the combination of uvrA with other genetic defects (polA, recA, lexA) decreased the efficiency of the system. The observed genotoxic effects were considerably lowered in the presence of S9 mix containing liver S9 fractions from Aroclor-treated rats. The sample of oil dispersant yielding the most pronounced DNA damage in repair-deficient E. coli failed to induce gene sfiA in E. coli (strain PQ37), using the SOS chromotest, or mitotic crossing-over in Saccharomyces cerevisiae (strain D5). The direct toxicity of the oil dispersant to both bacterial and yeast cells was markedly decreased in the presence of rat-liver preparations. These two short-term tests were effective in detecting the genotoxicity of both direct-acting compounds (such as 4-nitroquinoline N-oxide and methyl methanesulfonate) and procarcinogens (such as cyclophosphamide, 2-aminoanthracene and 2-aminofluorene). Moreover, the SOS chromotest was successfully applied to discriminate the activity of chromium compounds as related to their valence (i.e. Cr(VI) genotoxic and Cr(III) inactive). Combination of oil dispersants with Cr(VI) compounds did not affect the direct mutagenicity to S. typhimurium (TA102) of a soluble salt (sodium dichromate) nor did it result in any release of a water-soluble salt (lead chromate), as also confirmed by analytical methods. On the other hand, exposure to sunlight tended to decrease, to a slow rate, the direct genotoxicity of an oil dispersant in the bacterial DNA-repair test.     

Antigenotoxic potential of glucomannan on four model test systems

Antimutagenic, anticlastogenic, and bioprotective effect of polysaccharide glucomannan (GM) isolated fromCandida utilis was evaluated in four model test systems. The antimutagenic effect of GM against 9-aminoacridine (9-AA)- and sodium azide (NaN₃)-induced mutagenicity was revealed in theSalmonella typhimurium strains TA97 and TA100, respectively. GM showed anticlastogenic effect against N-nitroso-N-methylurea (NMU) induced chromosome aberrations in theVicia sativa assay. The bioprotective effect of GM co-treated with methyl-methane-sulphonate (MMS) was also established inChlamydomonas reinhardtii repair deficient strainsuvs10 anduvs14. The statistically significant antimutagenic potential of GM was not proved against 4-nitro-quinoline-1-oxide (4-NQO)-induced mutagenicity inSaccharomyces cerevisiae D7 assay. It may be due to bioprotectivity of -mannan and -glucan, which are integral part ofS. cerevisiae cell walls. Due to the good water solubility, low molecular weight (30 kDa), antimutagenic/anticlastogenic, and bioprotective activity against chemical compounds differing in mode of action, GM appears to be a promising natural protective (antimutagenic) agent.     

Study on mutagenic effects of bisphenol A diglycidyl ether (BADGE) and its derivatives in the Escherichia coli tryptophan reverse mutation assay

The di-epoxy compound bisphenol A diglycidyl ether (BADGE), its first and second hydrolysis products (BADGE.H2O and BADGE.2H2O, respectively) and its bis-chlorohydrin derivative (BADGE.2HCl) were examined for their mutagenicity in the Escherichia coli tryptophan reverse mutation test with strains WP2, WP2uvrA and IC3327. The assays were performed in the presence and absence of exogenous metabolic activation (S9 fraction from rat liver). The di-epoxy compound BADGE was able to induce mutagenic effects in strains WP2uvrA and IC3327 and the epoxy-diol BADGE.H2O also showed a positive response with these strains, although the latter was less potent than the former. On the other hand, the lack of mutagenic activity of BADGE.2H2O and BADGE.2HCl was also demonstrated.     

Conversion of tris(8-quinolinolato-N1, O8) aluminum to 8-hydroxyquinoline and activity in bacterial reverse mutation assays

Tris(8-quinolinolato-N1, O8) aluminum (AlQ), an aluminum chelate of 8-hydroxyquinoline (8OHQ) is an important charge transfer molecule in semiconducting imaging devices. This study was conducted to evaluate AlQ and 8OHQ for the ability to induce reverse mutations, either in the presence or absence of mammalian microsomal enzymes, and to determine if AlQ decomposes or is metabolized to 8OHQ under assay conditions. The tester strains used in the mutation assay were Salmonella typhimurium TA98, TA100, TA1535 and TA1537 and Escherichia coli WP2uvrA (pKM101). The assays were conducted in the presence and absence of S9. AlQ doses were 1-1000 microg per plate while 8OHQ doses were 0.947-947 microg per plate to maintain molar equivalency. Stability studies were carried out for 4h at 37 degrees C under conditions designed to mimic mutation assays. Samples were analyzed by HPLC and LC/MS to tentatively identify potential metabolites of AlQ and 8OHQ. The results of the bacterial mutagenicity assay indicate that in the presence of S9, both AlQ and 8OHQ, caused increases in the mean number of revertants per plate with tester strains TA100 and WP2uvrA (pKM101). No increases were observed with any of the remaining tester strain/activation condition combinations. The stability study showed that AlQ degrades readily to 8OHQ under standard mutagenicity test conditions, and the positive test result with AlQ is due to the bioactivation of 8OHQ. In the presence of S9, 8OHQ is metabolized to one detectable product with molecular weight indicative of a one-oxygen insertion. 8OHQ N-oxide and 2,8-quinolinediol were ruled out as possible metabolites; 8OHQ epoxides and other quinolinediols were neither confirmed nor ruled out. Bacterial mutagenicity tests have not been shown to predict in vivo effects of 8OHQ; these assays are similarly expected to be poorly predictive of in vivo genotoxic and carcinogenic potential of AlQ.     

An investigation on the antimutagenic properties of South African herbal teas

The antimutagenic properties of South African herbal teas were investigated using the Salmonella typhimurium mutagenicity assay. Aqueous extracts of fermented and unfermented rooibos tea (Aspalathus linearis) and honeybush tea (Cyclopia intermedia) both possess antimutagenic activity against 2-acetylaminofluorene (2-AAF) and aflatoxin B(1) (AFB(1))-induced mutagenesis using tester strains TA98 and TA100 in the presence of metabolic activation. A far less inhibitory effect was noticed against the direct acting mutagens, methyl methanesulfonate (MMS), cumolhydroperoxide (CHP), and hydrogen peroxide (H(2)O(2)) using TA102, a strain designed to detect oxidative mutagens and carcinogens. Depending on the mutagen used, the unfermented tea exhibited the highest protective effect. A similar response regarding the protection against mutagenesis was obtained when utilising different variations of the double layer Salmonella assay. The double layer technique proved to be more effective to detect the protective effect of the different tea preparations against the direct acting mutagens. With respect to indirect mutagens, the highest protection was noticed when the carcinogen was metabolically activated in the presence of the tea extract as compared with when the tea extract was incubated in a separate layer with the bacteria. The current data suggest that two mechanisms seem to be involved in the antimutagenicity of the tea extracts towards carcinogens that require metabolic activation: (i) the tea components may interfere with cytochrome P450-mediated metabolism of these mutagens and (ii) the direct interaction between the tea constituents, presumably the polyphenolic compounds, with the promutagens and/or the active mutagenic metabolites. However, the mild and/or lack of protection and in some cases even enhancement of mutagenesis induced by direct acting or oxidative mutagens, provide new perspectives regarding the role of the polyphenolic compounds known to exhibit antioxidant properties, in the protection against mutagenesis in the Salmonella assay. The present study provides the first evidence on the antimutagenic activity of honeybush tea and further evidence on the antimutagenicity of rooibos tea.