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E Zeiger

Publications and source records attributed to E Zeiger.

At least 91 records · Page 5Linked to original sources
PubMed1989

Chromosome aberration and sister chromatid exchange tests in Chinese hamster ovary cells in vitro: II. Results with 20 chemicals.

Twenty chemicals were tested for their ability to induce sister chromatid exchanges (SCEs) and chromosomal aberrations (ABs) in cultured Chinese hamster ovary cells (CHO). These chemicals were tested with and without an added metabolic activation system (rat liver S9 fraction). Four chemicals were negative in both assays, 1 induced ABs only, and 15 were positive for SCEs; 6 of these 15 also induced ABs. The effect of cell harvest time on the ability to detect the induction of chromosomal aberrations was examined for six chemicals. Five of these had caused at least one of the following: cell cycle delay, aberrations observed in first division metaphase cells in the SCE assay, or a weak response in the standard AB assay (10-12-hr growth period). Three chemicals, chlorinated trisodium phosphate, 1,2-dibromo-3-chloropropane, and tetrakis(hydroxymethyl)phosphonium chloride, were positive using both the standard and extended harvest times. N-Nitrosodimethylamine and diphenhydramine HCl were only positive using an extended harvest time, and malonaldehyde was negative using both standard and extended harvest times.

Animals↗
PubMed1989

Chromosome aberration and sister chromatid exchange tests in Chinese hamster ovary cells in vitro. III. Results with 27 chemicals.

Twenty-seven chemicals previously tested in rodent carcinogenicity assays were tested for induction of chromosomal aberrations (ABS) and sister chromatid exchanges (SCE) in Chinese hamster ovary (CHO) cells as part of a larger analysis of the correlation between results of in vitro genetic toxicity assays and carcinogenicity bioassays. Chemicals were tested up to toxic doses with and without exogenous metabolic activation. Seventeen of the chemicals tested were carcinogens; only two of these were negative for both ABS and SCE. Of the eight noncarcinogens tested, four were negative for both endpoints (ABS and SCE) and four gave a positive response for at least one endpoint. Of the remaining two chemicals, one, diallyl phthalate, gave an equivocal response in the bioassay and a positive response in these CHO cell cytogenetics tests. The other chemical, 2,4-toluene diisocyanate, was tested for carcinogenicity as a mixture with the 2,6-isomer; the mixture was carcinogenic, but the cytogenetic test results for the 2,4-isomer were negative. Only six of the 27 chemicals tested produced an effect in one endpoint alone; the other 21 were either positive or negative for both ABS and SCE. Only one of the 27 chemicals tested required S9 for a positive response in the SCE test; two chemicals required S9 for a positive result in the ABS test. Experiments with unsynchronized CHO cells demonstrated that mean SCE frequency increased with increasing culture time, and this may have been a factor in the positive results obtained for five chemicals in the SCE test under conditions of delayed harvest.

Animals↗
PubMed1989

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].

Animals↗
PubMed1989

Mutagenicity of the human carcinogen treosulphan in Salmonella.

The human carcinogen treosulphan was mutagenic in Salmonella typhimurium TA100 and TA1535, as was dl-1,2:3,4-diepoxybutane (DEB), a proposed hydrolysis product of treosulphan. Another proposed hydrolysis product, methane- sulfonic acid, was not mutagenic in these strains. The pattern of the mutagenic responses at pH 6,7, and 8 to treosulphan and DEB suggests that DEB formation may be responsible for the mutagenicity of treosulphan.

Busulfan↗
PubMed1989

Chromosomal aberrations and sister chromatid exchange tests in Chinese hamster ovary cells in vitro. IV. Results with 15 chemicals.

The National Toxicology Program has undertaken a study to assess the ability of four genetic toxicology assays to predict the carcinogenicity of chemicals in 2-year rodent studies [Tennant et al.: Science 236:933-941, 1987]. Two of the assays, used for evaluating in vitro cytogenetic damage, were the SCE and chromosome aberration assays in Chinese hamster ovary cells. The results and data for 15 of the chemicals tested in these two assays are presented here. Each chemical was tested with and without exogenous metabolic activation. The chemicals tested were bisphenol A, 2-chloroethanol, C.I. acid orange 10, C.I. disperse yellow 3, C.I. solvent yellow 14, cytembena, D&C red 9, 1,2-dibromoethane, FD&C yellow 6, malaoxon, D,L-menthol, phenol, sulfisoxazole, titanium dioxide, and tris(2-ethylhexyl)phosphate. In vitro cytogenetic results from the other chemicals presented by Tennant et al. (Science 236:933-941, 1987) have been published by Galloway et al. (Environmental and Molecular Mutagenesis 10(Suppl 10): 1-175, 1987), Gulati et al. (Environmental and Molecular Mutagenesis 13:133-193, 1989), and Love-day et al. (Environmental Mutagenesis 13:60-94).

Animals↗
PubMed1989

Effect of pH on mutagenesis by thiols in Salmonella typhimurium TA102.

The mutagenicity of thiol (SH)-containing compounds was tested in Salmonella typhimurium TA102 in the liquid preincubation method. Cysteinyl-glycine (CG), cysteine ethyl ester (CEE), L- and D-penicillamine (PA), cysteine (Cys) and glutathione (GSH) were mutagenic to strain TA102 without metabolic activation. On a molar basis, CG was the most potent mutagen. The mutagenicity of the remaining compounds decreased in the order specified above. The mutagenic response of each thiol-containing compound was a function of the pKa of the thiol group and the pH of the preincubation mixture. This indicates that a thiolate anion, rather than a free thiol, is required for mutagenesis.

Chemical Phenomena↗
PubMed1989

Classification according to chemical structure, mutagenicity to Salmonella and level of carcinogenicity of a further 42 chemicals tested for carcinogenicity by the U.S. National Toxicology Program.

This paper is an extension and update of an earlier review published in this journal (Ashby and Tennant, 1988). A summary of the rodent carcinogenicity bioassay data on a further 42 chemicals tested by the U.S. National Toxicology Program (NTP) is presented. An evaluation of each chemical for structural alerts to DNA-reactivity is also provided, together with a summary of its mutagenicity to Salmonella. The 42 chemicals were numbered and evaluated as an extension of the earlier analysis of 222 NTP chemicals. The activity patterns and conclusions derived from the earlier study remain unchanged for the larger group of 264 chemicals. Based on the extended database of 264 NTP chemicals, the sensitivity of the Salmonella assay for rodent carcinogens is 58% and the specificity for the non-carcinogens is 73%. A total of 32 chemicals were defined as equivocal for carcinogenicity and, of these, 11 (34%) are mutagenic to Salmonella. An evaluation is made of instances where predictions of carcinogenicity, based on structural alerts, disagree with the Salmonella mutagenicity result (12% of the database). The majority of the disagreements are for structural alerts on non-mutagens, and that places these alerts as a sensitive primary screen with a specificity lower than that of the Salmonella assay. That analysis indicates some need for assays complementary to the Salmonella test when screening for potential genotoxic carcinogens. It also reveals that the correlation between structural alerts and mutagenicity to Salmonella is probably greater than 90%. Chemicals predicted to show Michael-type alkylating activity (i.e., CH2 = CHX; where X = an electron-withdrawing group, e.g. acrylamide) have been confirmed as a structural alert, and the halomethanes (624 are possible) have been classified as structurally-alerting. To this end an extended carcinogen-alert model structure is presented. Among the 138 NTP carcinogens now reviewed, 45 (33%) are non-mutagenic to Salmonella and possess a chemical structure that does not alert to DNA-reactivity. These carcinogens therefore either illustrate the need for complementary genetic screening tests to the Salmonella assay, or they represent the group of non-genotoxic carcinogens referred to most specifically by Weisburger and Williams (1981); the latter concept is favoured.

Animals↗
PubMed1989

Prostaglandin hydroperoxidase-dependent activation of heterocyclic aromatic amines.

Heterocyclic aromatic amines, derived from the pyrolysis of amino acids and proteins, are potent mutagens in the Ames Salmonella assay with rodent liver activation. Additionally, heterocyclic aromatic amines are multipotent carcinogens. We report evidence that these compounds are substrates for the hydroperoxidase activity of prostaglandin H synthase, as measured by alterations in UV/visible spectra, and are bioactivated to macromolecule-reactive species by this enzyme. Indirect electron paramagnetic resonance studies indicate that this activation may occur via a one-electron mechanism. 2-Amino-3-methylimidazo[4,5f]quinoline (IQ), 2-amino-3,4-dimethylimidazo[4,5-f]quinoline (MeIQ), and 3-amino-1-methyl-5H-pyrido[4,3-b]indole (Trp-P-2) are direct-acting mutagens in TA98. The mutagenicity of IQ and MeIQ, but not Trp-P-2, were enhanced by activation with ram seminal vesicle microsomes (a rich source of prostaglandin H synthase). Subsequent experiments utilized the newly constructed tester strain TA1538/1,8-DNP6 (pYG 121), which has enhanced arylamine N-acetyltransferase activity. In this strain IQ, MeIQ and 2-amino-6-methyldipyrido-[1,2-a:3',2'-d]imidazole (Glu-P-1) were mutagenic with ram seminal vesicle microsome activation. 3-Amino-1,4-dimethyl-5H-pyrido[4,3-b]indole (Trp-P-1) was a weak direct-acting mutagen, and was not activated by the ram seminal vesicles (RSV) system. The responses of IQ and MeIQ were markedly enhanced in TA1538/1.8-DNP6 (pYG 121), relative to TA98. These data are consistent with the involvement of prostaglandin H synthase-catalyzed activation in heterocyclic aromatic amine-induced extrahepatic neoplasia.

Amines↗
PubMed1989

Isolation of Guard Cell Protoplasts from Mechanically Prepared Epidermis of Vicia faba Leaves.

A method for isolating guard cell protoplasts (GCP) from mechanically prepared epidermis of Vicia faba is described. Epidermis was prepared by homogenizing leaves in a Waring blender in a solution of 10% Ficoll, 5 millimolar CaCl(2), and 0.1% polyvinylpyrrolidone 40 (PVP). Attached mesophyll and epidermal cells were removed by shaking epidermis in a solution of Cellulysin, mannitol, CaCl(2), PVP, and pepstatin A. Cleaned epidermis was transferred to a solution of mannitol, CaCl(2), PVP, pepstatin A, cellulase "Onozuka" RS, and pectolyase Y-23 for the isolation of GCP. Preparations made by this method included both adaxial and abaxial GCP and contained </=0.017% mesophyll protoplasts, </=0.6% mesophyll fragments, and no epidermal cell contaminants. Yields averaged 9 x 10(4) protoplasts/leaflet and 98 to 100% of the GCP excluded trypan blue, concentrated neutral red, and hydrolyzed fluorescein diacetate. Isolated GCP increased in diameter by 2.2 micrometers after incubation in darkness in 10 micromolar fusicoccin, 0.4 molar mannitol, 5 millimolar KCl, and 1 millimolar CaCl(2). Illumination of GCP with 800 micromoles per square meter per second of red light resulted in alkalinization of their suspension medium. When 10 micromolar per square meter per second of blue light was superimposed onto the red light background, the medium acidified. Measurements of chlorophyll a fast fluorescence transients from isolated GCP indicated that GCP were capable of electron transport, and slow transients contained the "M" peak usually associated with a functional photosynthetic carbon reduction pathway.

Journal Article↗
PubMed1989

Sensory transduction and electrical signaling in guard cells.

Guard cells are a valuable model system for the study of photoreception, ion transport, and osmoregulation in plant cells. Changes in stomatal apertures occur when sensing mechanisms within the guard cells transduce environmental stimull into the ion fluxes and biosynthesis of organic solutes that regulate turgor. The electrical events mediating sensory transduction in guard cells can be characterized with a variety of electrophysiological recording techniques. Recent experiments applying the patch clamp method to guard cell protoplasts have demonstrated activation of electrogenic pumps by blue and red light as well as the presence of potassium channels in guard cell plasmalemma. Light activation of electrogenic proton pumping and the ensuing gating of voltage-dependent ion channels appear to be components of sensory transduction of the stomatal response to light. Mechanisms underlying stomatal control by environmental signals can be understood by studying electrical events associated with ion transport.

Journal Article↗
PubMed1988

Weak and unexpected mutagenicity to Salmonella of the rat hepatocarcinogen methapyrilene.

The rat liver carcinogen methapyrilene is shown to be a selective mutagen to strain TA1535 of Salmonella typhimurium when tested in the absence of S9 mix and using the standard plate-incorporation assay protocol. The activity observed was weak but was reproducible for a range of samples on many occasions of test and was not due to impurities. These data contrast with six earlier reports of the inactivity of this chemical in the Salmonella mutation assay.

Aminopyridines↗
PubMed1988

DNA binding and mutagenicity of ethyl methanesulfonate in wild-type and uvrB cells of Salmonella typhimurium.

The extent of DNA ethylation and the influence of excision repair on ethyl methanesulfonate (EMS) mutagenesis of Salmonella typhimurium were examined. The relationship between the dose to DNA and the exposure concentration of EMS was linear. EMS induction of his+ revertants followed exponential kinetics and did not parallel the increase in total DNA ethylation. Mutant induction was influenced by the cells' nucleotide excision repair ability. Although mutagenized to a larger extent than the wild-type (uvr+) strain at high doses, the uvrB strain was more resistant to the mutagenic effect of low doses of EMS.

Alkylation↗
PubMed1988

Red light stimulates an electrogenic proton pump in Vicia guard cell protoplasts.

Stomatal opening in response to light has a component that matches the absorption spectrum of chlorophyll; however, the intervening sensory transduction steps are not well understood. To study this process, we illuminated Vicia faba guard cell protoplasts with red light and simultaneously recorded current flow across the plasma membrane, utilizing the patch clamp technique in the whole cell configuration. We report evidence that under voltage clamp conditions, red light (1 mmol of photons.m-2.S-1) stimulated an outward current. This response required ATP (2.5 mM) and orthophosphate (1 mM) at the cytoplasmic side of the membrane. Both red-light-stimulated currents and currents activated in the dark by the proton pump agonist fusicoccin (10 microM) were abolished by the protonophore carbonylcyanide m-chlorophenylhydrazone at 10 microM, indicating that these responses were carried by protons. Pump currents were inhibited by orthovanadate applied to the cytoplasmic side of the membrane (50% inhibition at 3.5 microM), implicating a H+ -ATPase. Elimination of the current by the photosynthetic inhibitor 3-(3,4-dichlorophenyl)-1,1-dimethylurea, in the presence of saturating concentrations of ATP, pointed to a requirement for photosynthetically active chloroplasts. We conclude that red light stimulates an electrogenic proton pump at the plasmalemma of Vicia guard cells and that chloroplasts modulate this response.

Carbonyl Cyanide m-Chlorophenyl Hydrazone↗
PubMed1988

Glutathione mutagenesis in Salmonella typhimurium is a gamma-glutamyltranspeptidase-enhanced process involving active oxygen species.

Reduced glutathione (GSH) is mutagenic in Salmonella in the presence of gamma-glutamyltranspeptidase (GGT), with the highest response obtained in strain TA102. Reduced cysteinylglycine, one of the products of GGT metabolism of GSH, is mutagenic in the absence of GGT. In strain TA102, GSH mutagenesis was dependent on molecular oxygen, enhanced by iron, inhibited by EDTA, desferrioxamine mesylate, mannitol, butylated hydroxyanisole, peroxidase and catalase, but not by superoxide dismutase. Binding of GSH or its GGT-dependent metabolites to DNA in vitro was not detected. This is consistent with a model of an indirect mechanism of mutagenesis, i.e. cleavage of GSH by GGT, followed by facile auto-oxidation of the resulting cysteinylglycine, with the production of free radicals which lead to the (pen)ultimate mutagen, H2O2.

Catalase↗
PubMed1988

Photosynthetic Carbon Fixation in Guard Cell Protoplasts of Vicia faba L. : Evidence from Radiolabel Experiments.

Photosynthetic carbon fixation in guard cells was reexamined in experiments with highly purified guard cell protoplasts from Vicia faba L. irradiated with red light. The fate of (14)CO(2) (4.8 microcuries of NaHCO(3); final concentration: 100 micromolar) supplied to these preparations was investigated with two-dimensional paper, and thin layer chromatography. Rates of CO(2) fixation were 5- to 8-fold higher in the light than in darkness. Separation of acid-stable products into water-insoluble, neutral, and anionic fractions showed that more radioactivity was incorporated into the neutral fraction in the light than in the dark. In the dark, malate and aspartate comprised 90% of the radiolabel found in the anionic fraction, whereas in the light, radioactivity was also found in 3-phosphoglyceric acid (PGA), sugar monophosphates, sugar diphosphates, and triose phosphates. Phosphorylated compounds contained up to 60% of the label in the light-treated anionic fraction. Phosphatase treatment and rechromatography of labeled sugar diphosphate showed the presence of ribulose, a specific metabolite of the photosynthetic carbon reduction pathway (PCRP). In time-course experiments, labeled PGA was detected within 5 seconds. With time, the percentage of label in PGA decreased and that in sugar monophosphate increased. We conclude that PGA is a primary carboxylation product of the PCRP in guard cells and that the activity of the PCRP, and phosphoenolpyruvate-carboxylase is metabolically regulated.

Journal Article↗
PubMed1988

Light quality and osmoregulation in vicia guard cells : evidence for involvement of three metabolic pathways.

Osmoregulation in opening stomata of epidermal peels from Vicia faba L. leaves was investigated under a variety of experimental conditions. The K(+) content of stomatal guard cells and the starch content of guard cell chloroplasts were examined with cobaltinitrite and iodine-potassium iodide stains, respectively; stomatal apertures were measured microscopically. Red light (50 micromoles per square meter per second) irradiation caused a net increase of 3.1 micrometers in aperture and a decrease of -0.4 megapascals in guard cell osmotic potential over a 5 hour incubation, but histochemical observations showed no increase in guard cell K(+) content or starch degradation in guard cell chloroplasts. At 10 micromoles per square meter per second, blue light caused a net 6.8 micrometer increase in aperture over 5 hours and there was a substantial decrease in starch content of chloroplasts but no increase in guard cell K(+) content. At 25 micromoles per square meter per second of blue light, apertures increased faster (net gain of 5.7 micrometers after 1 hour) and starch content decreased. About 80% of guard cells had a higher K(+) content after 1 hour of incubation but that fraction decreased to 10% after 5 hours. In the absence of KCl in the incubation medium, stomata opened slowly in response to 25 micomoles per square meter per second of blue light, without any K(+) gain or starch loss. In dual beam experiments, stomata irradiated with 50 micomoles per square meter per second of red light for 3 hours opened without detectable starch loss or K(+) gain; addition of 25 micomoles per square meter per second of blue light caused a further net gain of 4.4 micometers in aperture accompanied by substantial K(+) uptake and starch loss. Comparison of K(+) content in guard cells of opened stomata in epidermal peels with those induced to open in leaf discs showed a substantially higher K(+) content in the intact tissue than in isolated peels. These results are not consistent with K(+) (and its counterions) as the universal osmoticum in guard cells of open stomata under all conditions; rather, the data point to sugars arising from photosynthesis and from starch degradation as additional osmotica. Biochemical confirmation of these findings would indicate that osmoregulation during stomatal opening is the result of three key metabolic processes: ion transport, photosynthesis, and sugar metabolism.

Journal Article↗