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D Wild

Publications and source records attributed to D Wild.

At least 55 records · Page 3Linked to original sources
PubMed1990

A novel pathway to the ultimate mutagens of aromatic amino and nitro compounds.

Photolysis of arylazides in aqueous media was recently found to generate presumed nitrenium ions, species which are generally considered as the ultimate mutagens/carcinogens derived from arylamines and nitroarenes. The primary photolysis products of arylazides, the arylnitrenes, can possibly react as electrophiles themselves, or they can be protonated and thus form the electrophilic nitrenium ions. Numerous arylazides and aryldiazides can be photoactivated to short-lived mutagens detectable in Salmonella typhimurium TA98. Structure-activity comparisons between arylazides and the matching arylamines and nitroarenes show correlations; e.g., phenyl azide and methyl-substituted phenyl azides are not mutagenic or only weakly mutagenic like aniline, nitrobenzene, and their methyl homologues, whereas 4-azidodiphenyl, 2-azidofluorene, 1-azidopyrene, azido-IQ, and azido-isoIQ are increasingly mutagenic in that order, like the matching amino and nitro compounds. It is hypothesized on the basis of these data that the nitrene/nitrenium ion is the reactive intermediate common to the three mutagenic pathways and that the reaction of the nitrene/nitrenium ion with DNA is rate limiting for the overall mutagenic process in Salmonella. The photochemical generation from arylazides of the reactive species, the nitrene/nitrenium ions, opens new perspectives for the understanding of the genotoxic activity of arylamines and nitroarenes in general and, specifically, of the food mutagens/carcinogens of the IQ type.

Amines↗
PubMed1990

Photobiological studies with dioxetanes in isolated DNA, bacteria, and mammalian cells.

1,2-Dioxetanes, efficient chemical sources of triplet excited carbonyl compounds, were observed to be genotoxic in isolated DNA, bacteria, and cultured mammalian cells. In superhelical DNA of bacteriophage PM2, various alkyl- and hydroxyalkyl-substituted dioxetanes (1) induced predominantly endonuclease-sensitive base modifications and only few single strand breaks. With a specific endonuclease a small fraction of the base modifications was identified as pyrimidine dimers. The psoralen dioxetane (2a) or PsD bound photochemically to calf thymus DNA at the alpha-pyrone ring of psoralen (fluorescence measurements). Photobinding was also observed when calf thymus DNA was incubated with psoralen and 3-hydroxymethyl-3,4,4-trimethyl-1,2-dioxetane. In Syrian hamster embryo fibroblasts and HL-60 cells, dioxetanes induced DNA single strand breaks. The alkyl- and hydroxyalkyl-substituted dioxetanes 1 and 2 were efficiently inactivated by cysteine, glutathione, ascorbic acid, tocopherol, NADH and FADH2. While dioxetanes 1 and 2 were not mutagenic in Salmonella typhimurium strain TA100, benzofuran dioxetanes 3 exhibited substantial effects. Further data imply that presumably a mutagenic intermediate with a lifetime of a few minutes is produced from the benzofuran dioxetane.

Animals↗
PubMed1989

Singlet oxygen as an ultimately reactive species in Salmonella typhimurium DNA damage induced by methylene blue/visible light.

The specific recognition of various DNA modifications by repair enzymes is exploited for the analysis of DNA damage induced by visible light in the presence of methylene blue in Salmonella typhimurium. The relative frequencies of various endonuclease-sensitive sites and strand breaks are determined in the plasmid pAQ1 of the treated bacteria and are compared with those observed after exposure of isolated DNA to various conditions. This comparison of damage profiles indicates that the cellular DNA damage by illumination in the presence of methylene blue is caused predominantly by the direct action of singlet oxygen. Indirect mechanisms, e.g. involving a generation of superoxide and hydroxyl radicals or the activation of cellular nucleases, do not contribute very much. The damage is dominated by base modifications. These are subject to an efficient repair that is not mediated by uvrABC proteins and therefore most probably involves recognition by specific glycosylases. Revertant frequencies observed under these conditions in the strains TA1535, TA100, TA2638 and TA104 indicate a pronounced mutagenicity of the lesions induced. On the other hand, the DNA damage does not contribute significantly to the cytotoxicity caused by the treatment as an excision repair deficiency (uvrB) has no influence on cell killing.

DNA Damage↗
PubMed1989

Photolysis of arylazides and generation of highly electrophilic DNA-binding and mutagenic intermediates.

Photolysis of arylazides with long wavelength ultraviolet (NUV) light in an aqueous medium produces short-lived reactive chemical species which bind to DNA and deoxynucleoside 3'-phosphates and induce reversion mutations in frameshift tester strains of Salmonella typhimurium. Nitrenes are known reactive products of azide photolysis, so the DNA-binding and mutagenic species is either a nitrene or a nitrene-derivative. An N-hydroxyarylamine intermediate, potentially formed from a nitrene and water, can be excluded because the mutagenic potencies of the reactive species in TA98 and in the hydroxylamine-resistant TA98/1,8-DNP6 are of the same order, and because the life-time of this species is very short. The mutagenic potency of the arylazide photolysis products decreases in the order azido-IQ greater than 1-azidopyrene greater than azido-MeIQx greater than 6-azidochrysene greater than 2-azidofluorene greater than 4-azidobiphenyl greater than 2-azido-naphthalene greater than 1-azido-naphthalene. This potency sequence correlates with that of the corresponding arylamines. Furthermore, their DNA binding products are chromatographically identical with those obtained in cellular, metabolizing systems from nitroarenes and arylamines. Therefore, the reactive, electrophilic azide photolysis product is very likely a nitrenium ion formed by protonation of a nitrene. Nitrenium ions are also the ultimate mutagens/carcinogens formed from nitroarenes and arylamines. Arylazides can therefore be considered as stabilized forms of arylnitrenium ions. The arylazide-nitrene technique reported here is new and simple and provides ready access to presumed nitrenium ions which are otherwise difficult to obtain.

Azides↗
PubMed1989

Mutagenic nitrenes/nitrenium ions from azido-imidazoarenes and their structure-activity relationships.

New heterocyclic arylazides (azido-imidazoarenes) structurally related to the food mutagen/carcinogen 2-amino-3-methyl-imidazo[4,5-f]quinoline (IQ) have been prepared. Their photolysis yields nitrenes and/or nitrenium ions which induce mutations in Salmonella typhimurium. The relationships between the chemical structure and mutagenic activity of these species are the same as those found in our previous studies of the amino- and nitro-imidazoarenes. Therefore the efficiency of the reaction with DNA of the ultimate metabolite, the nitrene/nitrenium ion, is the critical step governing the mutagenic potency of the amino- and nitro-imidazoarenes. The efficiency of DNA-binding depends on the delocalization of the positive charge of the nitrenium ion or of the electron deficiency of the nitrene. It is typical of the N-1-substituted and N-3-substituted arenimidazolyl-nitrenium ions that they can form another nitrenium resonance structure very similar to the parent nitrenium ion structure. We suggest that this property of the nitrene/nitrenium ion, in combination with its aromatic structure facilitating carbonium ion resonance structures, is the basic reason for the extremely potent mutagenic activity of IQ and related food mutagens/carcinogens.

Amines↗
PubMed1988

Characterization of an in vitro micronucleus assay with Syrian hamster embryo fibroblasts.

The use of Syrian hamster embryo cells for assessing genotoxicity provides the unique opportunity to determine 5 different end-points (gene mutations, DNA-strand breaks, aneuploidy, DNA repair (unscheduled DNA synthesis, UDS) and neoplastic transformation) in the one cell system. This approach allows direct comparisons of results produced under identical conditions of dose at target, metabolism and bioavailability. We report here on the characterization of an additional end-point in the same cell system: the formation of micronuclei indicating chromosomal changes induced by chemicals. For a preliminary validation of this new test system we have investigated 14 carcinogens and 3 non-carcinogenic structural analogues in order to evaluate the significance of micronucleus induction for carcinogenic properties. All tested carcinogens induced micronuclei in a dose-dependent manner; all non-carcinogens yielded negative results. Correlations between the formation of micronuclei and the Ames test, induction of UDS, cell transformation and the in vivo bone marrow micronucleus test are demonstrated.

Animals↗
PubMed1988

Synthesis of 2-azido-3-methylimidazo[4,5-f]quinoline and photolytic generation of a highly reactive and mutagenic IQ derivative.

Azido-IQ (2-azido-3-methylimidazo[4,5-f]quinoline), a novel analog of the food mutagen and carcinogen IQ (2-amino-3-methylimidazo[4,5-f]quinoline) was synthesized and characterized. Both thermolysis and photolysis of this azide yield a short-lived nitrene which can react as an electrophile either directly or via protonation to a nitrenium ion. Reaction of the nitrene/nitrenium ion with water produces N-hydroxy-IQ; reactions with nucleotides and with DNA (in vitro and in cells) produce adducts efficiently. Correspondingly, high frequencies of mutations are induced in Salmonella typhimurium by photolyzed azido-IQ. Comparative mutation assays with the S. typhimurium strains TA98 and the hydroxylamine-resistant TA98/1,8-DNP6 provide evidence for a novel mechanism of mutation, direct reaction of the nitrene or nitrene-derived nitrenium ion with DNA without involvement of the hydroxylamine. The photolysis of arylazides promises to be a very convenient and generally applicable non-enzymatic procedure for the cell-free or intracellular generation of short-lived and highly reactive electrophilic species which are assumed to be identical with the metabolically formed ultimate mutagens/carcinogens of arylamines and nitroarenes.

Mutagens↗
PubMed1988

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.

4-Nitroquinoline-1-oxide↗
PubMed1987

Enzymatic transformation of mercapturic acids derived from halogenated alkenes to reactive and mutagenic intermediates.

The metabolism of the mercapturic acids S-pentachlorobutadienyl-N-acetylcysteine (N-Ac-PCBC), S-trichlorovinyl-N-acetylcysteine (N-Ac-TCVC) and S-dichlorovinyl-N-acetylcysteine (N-Ac-DCVC) by subcellular fractions from male rat liver and kidney homogenates was studied. As a model compound, N-Ac-PCBC, 14C labelled, was synthesised. It was intensively metabolised by cytosolic but not by microsomal enzymes from rat liver and kidney. The major metabolite identified by GC/MS was pentachlorobutadienylcysteine, the amount produced being highest in kidney cytosol. Metabolic conversion of 14C-N-Ac-PCBC by kidney and liver cytosol resulted in covalent binding of radioactivity to protein, binding was strongly inhibited by the beta-lyase inhibitor aminooxyacetic acid (AOAA). N-Ac-TCVC and N-Ac-DCVC were also transformed by cytosolic enzymes to the corresponding cysteine conjugates (trichlorovinylcysteine and dichlorovinylcysteine). The three mercapturic acids tested were strong mutagens in the Ames-test after addition of rat kidney cytosol. In the absence of cytosol, N-Ac-TCVC and N-Ac-DCVC were weakly but definitely mutagenic, whereas N-Ac-PCBC was not. In contrast to N-Ac-PCBC, the "direct" mutagens N-Ac-TCVC and N-Ac-DCVC were both transformed to pyruvate by bacterial (S. typhimurium TA100) homogenate 100,000 g supernatants. It is concluded that mercapturic acids are deacetylated to the corresponding cysteine conjugates by cytosolic (N-Ac-PCBC, N-Ac-TCVC and N-Ac-DCVC) and bacterial enzymes (N-Ac-TCVC and N-Ac-DCVC) and further cleaved to reactive and mutagenic intermediates by mammalian and/or bacterial beta-lyase. The observed activation mechanisms for the mercapturic acids, whose formation from hexachlorobutadiene, tetrachloroethylene and trichloroethylene has been proven, might contribute to the nephrotoxicity and nephrocarcinogenicity of the parent alkenes.

Acetylation↗
PubMed1987

Heterocyclic aromatic amine-DNA-adducts in bacteria and mammalian cells detected by 32P-postlabeling analysis.

The formation of DNA adducts by the fried meat mutagen and carcinogen 2-amino-3-methylimidazo[4,5-f]quinoline (IQ) was studied by means of 32P-postlabeling of DNA digests and four-directional t.l.c. Three major and five minor adducts were detected in assays of DNA digests obtained from Salmonella typhimurium TA98 cells after treatment with IQ and rat liver postmitochondrial supernatant (S9). A qualitatively identical adduct pattern was obtained with nitro-IQ (3-methyl-2-nitroimidazo[4,5-f]quinoline), a new analogue of IQ with a nitro instead of the amino group. These two compounds, therefore, form the same ultimate metabolite. The same adduct pattern was also found after TA98/1,8-DNP6 (acetyltransferase-deficient) cells were treated with nitro-IQ; this is probably due to a residual acetyltransferase activity in this strain. Upon treatment of TA98 cells with 1 mM IQ for 3 h one adduct was detected in 4.7 x 10(5) total bases; a considerably higher adduct frequency, one in 4.2 x 10(3), was induced by nitro-IQ (70 microM, 30 min). The IQ isomer 2-amino-1-methylimidazo[4,5-f]quinoline (isoIQ) and its nitro-analogue nitro-isoIQ (1-methyl-2-nitroimidazo[4,5-f]quinoline) also produced identical adducts. Their common adduct pattern was very similar to the IQ adduct pattern but was located in a position different from that of the IQ adduct pattern. DNA from Syrian hamster embryo (SHE) cells treated with IQ and S9 exhibited adducts apparently identical with those of Salmonella DNA.

Acetyltransferases↗
PubMed1987

Prostaglandin H synthase-dependent mutagenic activation of heterocyclic aromatic amines of the IQ-type.

Microsomes from ram seminal vesicles known as a rich source of prostaglandin H synthase (PHS) activate the food mutagen IQ (2-amino-3-methylimidazo[4,5-f]quinoline) to (a) product(s) mutagenic in Salmonella typhimurium TA98. The activation is dependent on the PHS cofactor arachidonic acid and is strongly inhibited by the PHS inhibitor indomethacin. In this system, the mutagenic potency of IQ is 22 and 110 times higher than that of 2-aminofluorene and benzidine, respectively. The high mutagenic potency of IQ observed previously with mono-oxygenase activation is thus extended to the PHS system. The mutagenic activity produced by PHS increases for 4 h; this contrasts with the relatively short lifetime of the activity produced by mono-oxygenase and suggests that different agents are involved in the two processes. The PHS-mediated mutagenic activity of IQ is strongly dependent on the bacterial O-acetyltransferase which is defective in strain TA98/1,8-DNP6. Further, the responses of the strains TA1978 and TA1538 indicate that the mutagenic activity is dependent on lack of the bacterial DNA excision repair and independent of the plasmid pkM101 coded error-prone DNA repair system. Structural analogs of IQ without a methyl group on the imidazole ring and with a naphthalene instead of the quinoline ring show greatly diminished PHS-mediated mutagenic activity. The strain response pattern and structure-activity relationships are similar to those found with mono-oxygenase activation of IQ and thus indicate a basic similarity of the IQ activation via PHS with that via mono-oxygenase. It is hypothesized that PHS may activate carcinogenic heterocyclic aromatic amines in vivo.

Biotransformation↗
PubMed1986

Bacterial beta-lyase mediated cleavage and mutagenicity of cysteine conjugates derived from the nephrocarcinogenic alkenes trichloroethylene, tetrachloroethylene and hexachlorobutadiene.

The metabolism of beta-lyase and the mutagenicity of the synthetic cysteine conjugates S-1,2-dichlorovinylcysteine (DCVC), S-1,2,2-trichlorovinylcysteine (TCVC), S-1,2,3,4,4-pentachlorobuta-1,3-dienylcysteine (PCBC) and S-3-chloropropenylcysteine (CPC) were investigated in Salmonella typhimurium strains TA100, TA2638 and TA98. The bacteria contained significantly higher concentrations of beta-lyase than mammalian subcellular fractions. Bacterial 100,000 X g supernatants cleaved benzthiazolylcysteine to equimolar amounts of mercaptobenzthiazole and pyruvate. DCVC, TCVC and PCBC produced a linear time-dependent increase in pyruvate formation when incubated with bacterial 100,000 X g supernatants; pyruvate formation was inhibited by the beta-lyase inhibitor aminooxyacetic acid (AOAA). CPC was not cleaved by bacterial enzymes to pyruvate. DCVC, TCVC and PCBC were mutagenic in three strains of S. typhimurium (TA100, TA2638 and TA98) in the Ames-test without addition of mammalian subcellular fractions; their mutagenicity was decreased by the addition of AOAA to the preincubation mixture. CPC was not mutagenic in any of the strains of bacteria tested. These results indicate that beta-lyase plays a key role in the metabolism and mutagenicity of haloalkenylcysteines when tested in S. typhimurium systems. The demonstrated formation in mammals of the mutagens DCVC, TCVC and PCBC during biotransformation of trichloroethylene (Tri), tetrachloroethylene (Tetra) and hexachlorobutadiene (HCBD) may provide a molecular explanation for the nephrocarcinogenicity of these compounds.

Animals↗
PubMed1986

Synthesis and genotoxicity of acetoxyoxirane, the epoxide of vinyl acetate.

Acetoxyoxirane, the epoxide of vinyl acetate and a potential reactive intermediate, was synthesized and characterized by 13C-nuclear magnetic resonance (13C-NMR) and mass spectroscopy. The compound induced lesions (endonuclease-sensitive and alkali-labile sites) in supercoiled PM2 DNA in vitro and was directly mutagenic toward Salmonella typhimurium TA100. The mutagenicity of the epoxide in phosphate buffer (pH 7.4, 37 degrees C) decreased, with an initial half-life of 2.8 minutes, and mutagenicity was completely abolished by addition of S-9 mix. Acetoxyoxirane did not induce unscheduled DNA synthesis on incubation with Syrian hamster embryo fibroblasts (SHE cells). These findings may possibly be explained by an effective inactivation of acetoxyoxirane by esterases when these are present in the biological system. This view is consistent with the lack of acetoxyoxirane detected in rat liver microsomal incubations of vinyl acetate.

Animals↗
PubMed1986

Chemical structure and mutagenic activity of aminoimidazoquinolines and aminonaphthimidazoles related to 2-amino-3-methylimidazo[4,5-f]quinoline.

We have synthesized 11 heterocyclic aromatic amines with chemical structures related to that of 2-amino-3-methylimidazo [4,5-f] quinoline (IQ), a potent mutagen occurring in broiled sardines, fried beef and beef extract. The mutagenic activity of these IQ analogs was studied and compared with that of IQ using the Ames test with strain TA98 of Salmonella typhimurium in presence of a metabolic activation system (S9 mix) derived from rat liver. The mutagenic activities of the IQ analogs vary over a million-fold; structure-activity comparisons indicate major contributions of the methyl substitution in the imidazole ring and of the quinoline-N, and significant contributions of methylation of the exocyclic amino group and of the geometry of the entire ring system.

Animals↗