@article{EpeHarttigStopperetal.1990, author = {Epe, B. and Harttig, U. and Stopper, Helga and Metzler, M.}, title = {Covalent binding of reactive estrogen metabolites to microtubular protein as a possible mechanism of aneuploidy induction and neoplastic cell transformation}, url = {http://nbn-resolving.de/urn:nbn:de:bvb:20-opus-63478}, year = {1990}, abstract = {Neoplastic cell transfonnation induced by estrogens and some other carcinogen\& such as benzene appears to involve the induction of mitotic aneuploidy rather than DNA damage and point mutations. As metabolic activation may also play an important roJe in the mechanism of carcinogenesis of these nongenotoxic compounds, we have studied the Interaction of reactive quinone metabolites of various estrogens and of benzene with the major microtubular protein, tubulin, in a cell-free system. Covalent binding of the radioactively labeled metabolites to the a- and 13-subunit of tubulin was found to depend on the structure of the metabolite. When the adducted tubulins were tested in vitro for their ability to polymerize to microtubules, Inhibition of microtubule assembly was obsened in every case, although to varying extents. It is proposed that the fonnation of covalent tubulin adducts may impair the formation of mitotic spindies and thus contribute to chromosomal nondisjunction and aneuploidy induction.}, subject = {Toxikologie}, language = {en} } @article{StopperMetzler1991, author = {Stopper, Helga and Metzler, M.}, title = {Carcinogenic oestrogens induce respiration deficiency mutation in yeast}, url = {http://nbn-resolving.de/urn:nbn:de:bvb:20-opus-63466}, year = {1991}, abstract = {In addition to hormonal activity, genetic darnage has been proposed as an important factor in oestrogen-mediated carcinogenesis. However, as short-term tests for oestrogens usually fail to show DNA mutations, lesions other than dassie nuclear DNA mutation have to be considered. Oestrogeninduced mitochondrial darnage was studied in the yeast Saccharomyces cerevisiae. Stilbene-type, but not steroidal, oestrogens were found to induce respiration-dcficient petite mutation. The effect was inversely correlated with cytotoxicity and required aromatic hydroxyl groups at the stilbene molecule. It only occurred under growth conditions and apparently was not due to the A TPase inhibitory qualities of stilbene oestrogens. Other studies have shown that petite mutation clones, which can be induced by a variety of substances, contain altered mitochondrial DNA. The mechanism of petite mutation induction might be important in tumorigenesis by also acting on nuclear DNA or facilitating carcinogenesis by disturbance of mitochondrial function.}, subject = {Toxikologie}, language = {en} } @article{TasStopperKoscheletal.1991, author = {Tas, P. and Stopper, Helga and Koschel, K. and Schiffmann, D.}, title = {Influence of the carcinogenic oestrogen diethylstilboestrol on the intracellular calcium level in C6 rat glioma cells}, url = {http://nbn-resolving.de/urn:nbn:de:bvb:20-opus-63459}, year = {1991}, abstract = {The ~fthetic oes~rog~n diethylsti~boestrol (DES) causes a dose-dependent elevation of the cytoplasuuc Ca concentratton m C6 rat ghoma cells. This Ca2+ rise is caused neither by Ca2+ influx nor ~-r release from the ~a2 + stores of the endoplasmic reticulum. Therefore it seems likely that DES mob!hzes Ca2+ from a nutochondrial source. The DES-induced Ca2+ signal is remarkably similar to the one mduced by the. tumou~ promotor ~hapsigargin. As this compound causes leakage of calcium from the endoplasmt~ rettculum tt ~ms posstble that DES induces a similar leakage from mitochondrial Ca2+ stores. It remaans to be estabhshed whether the DES-mediated rise in intracellular calcium is causally related to the tumour-promoting properties of this compound}, subject = {Toxikologie}, language = {en} } @article{StopperPechanSchiffmann1992, author = {Stopper, Helga and Pechan, R. and Schiffmann, D.}, title = {5-azacytidine induces micronuclei in and morphological transformation of Syrian hamster embryo fibroblasts in the absence of unscheduled DNA synthesis}, url = {http://nbn-resolving.de/urn:nbn:de:bvb:20-opus-63443}, year = {1992}, abstract = {lt is known that 5-azacytidine (5-AC) induces tumors in several organs of rats and mice. The mechanisms of these effects are still poorly understood although it is known that 5-AC can be incorporated into DNA. Furthermore, it can inhibit DNA methylation. The known data on its clastogenic andjor gene mutation-inducing potential are still controversial. Therefore, we have investigated the kinds of genotoxic effects caused by 5-AC in Syrian hamster embryo (SHE) fibroblasts. Three different endp6ints (micronucleus formation, unscheduled DNA synthesis (UDS) and cell transforrnation) were assayed under similar conditions of metabolism and dose at target in this cell system. 5-AC induces morphological transformation of SHE cells, but not UDS. Therefore, 5-AC does not seem to cause repairable DNA lesions. Furthermore, our studies revealed that 5-AC is a potent inducer of mkronuclei in the SHE system. Immunocytochemical analysis revealed that a certain percentage of these contain kinetochores indicating that 5-AC may induce both clastogenic events and numerical chromosome changes.}, subject = {Toxikologie}, language = {en} } @article{KirchnerStopperPappetal.1993, author = {Kirchner, S. and Stopper, Helga and Papp, T. and Eckert, I. and Yoo, H. J. and Vig, B. K. and Schiffmann, D.}, title = {Cytogenetic changes in primary, immortalized and malignant mammalian cells}, url = {http://nbn-resolving.de/urn:nbn:de:bvb:20-opus-63439}, year = {1993}, abstract = {Some chromosomes in transformed rat cells and somatic cell hybrids fail to display the presence of kinetochore proteins as detected by antikinetochore antibodies. Suchchromosomes (K- Chromosomes) may constitute a novel mechanism for the genesis of aneuploidy. Wehave analyzed primary~ immortalized and malignant marnmalian cells for the presence of kinetochore proteins and micronuclei. Our resuJts suggest a correlation of the K- chromosome and micronucleus frequency with the variability in chromosome number. Upon in situ hybridization with the minor satellite and alpha satellite sequences some Kchromosomes showed a signal. This indicates that the observed lack of kinetocbores is not necessarily due to a lack of centromeric DNA. We conclude that dislocated K- chromosomes may become incorporated into micronuclei which are prone to loss. Such events would be associated with the generation of aneuploidy.}, subject = {Toxikologie}, language = {en} } @article{AdamAhrweilerSahaMoelleretal.1993, author = {Adam, W. and Ahrweiler, M. and Saha-M{\"o}ller, C. R. and Sauter, M. and Sch{\"o}nberger, A. and Epe, B. and M{\"u}ller, E. and Schiffmann, D. and Stopper, Helga and Wild, D.}, title = {Genotoxicity studies of benzofuran dioxetanes and epoxides with isolated DNA, bacteria and mammalian cells}, url = {http://nbn-resolving.de/urn:nbn:de:bvb:20-opus-63420}, year = {1993}, abstract = {1.2-Dioxetanes, very reactive and high energy molecules. are involved as labile intermediates in dioxygenase- activated aerobic metabolism and in physiological processes. Various toxico1ogica1 tests reveal that dioxetanes are indeed genotoxic. In supercoiled DNA of bacteriophage PM2 they induce endonucleasesensitive sites, most of them are FPG protein-sensitive base modifications (8-hydroxyguanine, fonnamidopyrimidines). Pyrimidinedimersand sites ofbase loss (AP sites) which were probed by UV endonuclease and exonuclease 111 are minor lesions in this system. While the alky1-substituted dioxetanes do not show any significant mutagenic activity in different Salmonella typhimurium strains, heteroarene dioxetanes such as benzofuran and furocoumarin dioxetanes are strongly mutagenic in S. typhimurium strain TA I 00. DNA adducts formed with an intermediary alkyJating agent appear to be responsible for the mutagenic activity of benzofuran dioxetane. We assume that the benzofuran epoxides, generated in situ from benzofuran dioxetanes by deoxygenation are the ultimate mutagens of the latter. since benzofuran epoxides are highly mutagenic in the S. typhimurium strain TAIOO and they form DNA adducts. as detected by the 212Ppostlabelling technique. Our results imply that the type of D NA darnage promoted by dioxetanes is dependent on the structural feature of dioxetanes. Furthermore, the direct photochemical DNA darnage by energy transfer. i.e., pyrimidine dimers, plays a minor role in the genotoxicity of dioxetanes. Instead, photooxidation dominates in isolated DNA. while radical darnage and alkylation prevail in the cellular system.}, subject = {Toxikologie}, language = {en} } @article{StopperKoerberSchiffmannetal.1993, author = {Stopper, Helga and K{\"o}rber, C. and Schiffmann, D. and Caspary, W. J.}, title = {Cell-cycle dependent micronucleus formation and mitotic disturbances induced by 5-azacytidine in mammalian cells}, url = {http://nbn-resolving.de/urn:nbn:de:bvb:20-opus-63411}, year = {1993}, abstract = {5-Azacytidine was originally developed to treat human myelogenous leukemia. However, interest in this compound has expanded because of reports of its ability to affect cell differentiation and to alter eukaryotic gene expression. In an ongoing attempt to understand the biochemical effects of this compound, we examined the effects of 5-azacytidine on mitosis and on micronucleus formation in mammalian cells. In L5178Y mouse cells, 5-azacytidine induced micronuclei at concentrations at which we and others have already reported its mutagenicity at the tk locus. Using CREST staining and C-banding studies, we showed that the induced micronuclei contained mostly chromosomal fragments although some may have contained whole chromosomes. By incorporating BrdU into the DNA of SHE cells, we determined that micronuclei were induced only when the compound was added while the cells were in S phase. Microscopically visible effects due to 5-azacytidine treatment were not observed until anaphase of the mitosis following treatment or thereafter. 5-Azacytidine did not induce micronuclei via interference with formation of the metaphase chromosome arrangement in mitosis, a common mechanism leading to aneuploidy. SupravitalUV microscopy revealed that chromatid bridges were observed in anaphase and, in some cases, were sustained into interphase. In the first mitosis after 5-azacytidine treatment we observed that many cells were unable to perform anaphase separation. All of these observations indicate that 5-azacytidine is predominantly a clastogen through its incorporation into DNA.}, subject = {Toxikologie}, language = {en} } @article{StopperKoerberSpenceretal.1993, author = {Stopper, Helga and K{\"o}rber, C. and Spencer, D. L. and Kirchner, S. and Caspary, W.J. and Schiffmann, D.}, title = {An investigation of micronucleus and mutation induction by oxazepam in mammalian cells}, url = {http://nbn-resolving.de/urn:nbn:de:bvb:20-opus-63404}, year = {1993}, abstract = {Tbe benzodiazepines are a class of d.rugs that are widely used in the treatment of various psychiatric disorders. One member of um ~' oxazepam, is also a common metabolite of sevmd other benzod.iazepines. Since the evidence for the genetic toxicity and carcinogenic properties of these compounds is incol:lsb1ent, we investigated the oxazepam-induced fonnation of micronuclei in Syrian Hamster embryo fibroblast (SHE) cells, human amniotic fluid fibroblast-like (AFFL) cells and LS178Y mouse cells. A dose-dependent increase in micronucleus fractions was found in all tbree ceU llnes. The time course of micronucleus induction in L5178Y cells showed a maximum at 5 h after treatment, suggesting that the micronuclei were fonned in the first mitosis after treatment. Kinetochore staining (CREST -antiserum) revealed the presence of kinetochores in -SO\% of the micronuclei in aU tbree ceU types. ThJs resu1t was further confinned by in situ bybridization in LS178Y cells and indicates tbe presence of wbole Chromosomes or centric fragments as weU as acentric fragments in the oxazepam-induced micronuclei. The LS178Y cells did not show a mutagenic response to oxazepam at any of the doses or expression times used.}, subject = {Toxikologie}, language = {en} } @article{StopperEckertSchiffmannetal.1994, author = {Stopper, Helga and Eckert, I. and Schiffmann, D. and Spencer, D. L. and Caspary, W. J.}, title = {Is micronucleus induction by aneugens an early event leading to mutagenesis?}, url = {http://nbn-resolving.de/urn:nbn:de:bvb:20-opus-63390}, year = {1994}, abstract = {This study was designed to investigate a previously unidentified potential mechanism for mutation induction as well as to clarify a biological comequence of micronucleus formation. We compared the induction of micronuclei with mutation inductioo as measured by trißuorothymidine (TFI') resistance in mouse L5178Y cells using four aneugens: colcemid, diethylstilbestrol, griseofulvin and vioblastine. AU four compounds induced micronuclei which appeared in the first cell cycle after treatment. More than 85\% of the micronuclei induced by each compound stained positive for the presence of kinetochores implying that the micronuclei contained wbole cbromosomes. However, these same compounds were unable to induce TFf resistance under tbree different treatment regimes. We concluded that tbese compounds, under conditions where tbey induce primarily kinetochore positive micronuclel, were not able to induce mutations. Thus, the induction of micronuclei containing wbole chromosomes barborlog a select.able gene is not an early event leadlog to mutations in these cells.}, subject = {Toxikologie}, language = {en} } @article{StopperKuehnelPodschun1994, author = {Stopper, Helga and K{\"u}hnel, A. and Podschun, B.}, title = {Combination of the chemotherapeutic agent 5-fluorouracil with an inhibitor of its catabolism results in increased micronucleus induction}, url = {http://nbn-resolving.de/urn:nbn:de:bvb:20-opus-63383}, year = {1994}, abstract = {The rate limiting step in 5-fluorouracil catabolism is catalyzed by the enzyme dihydropyrimidine dehydrogenase. Since degradation of 5-fluorouracil decreases its efficacy in chemotherapy, the inhibition of its catabolism is a promising tool. We investigated the formation of micronuclei in vitro in mouse L5178Y cells. 5-fluorouracil induced an increase in micronucleus frequency, which could significantly be enhanced by the concurrent application of 2,6-dihydroxypyridine, an inhibitor of dihydropyrimidine dehydrogenase. The 5-fluorouracil concentration necessary to reach maximal genotoxic effects could be reduced to half in the presence of inhibitor. 2,6-Dihydroxypyridine alone and the naturally occuring enzyme substrate uracil did not induce micronucleus formation. Combined application of the chemotherapeutic agent 5-fluorouracil and an inhibitor of its could reduce side-effects by lowering the effective dose of the active drug. With this study we provide further support for the usefulness of this concept.}, subject = {Toxikologie}, language = {en} } @article{LutzWinklerDunitz1971, author = {Lutz, Werner K. and Winkler, F. K. and Dunitz, J. D.}, title = {Crystal structure of the antibiotic monensin similarities and differences betweeen free acid and metal complex}, url = {http://nbn-resolving.de/urn:nbn:de:bvb:20-opus-61228}, year = {1971}, abstract = {The structure of monensin, C36H620 11 , has been deterrnined by X-ray analysis of its crystalline monohydrate (orthorhombic, a = 15.15, b = 23.61, c = 10.65 A, Z = 4, space group P212121). Phases were assigned by direct methods, malring use of the 'tangent formula'. Although the conformation of the free acid resembles that of the silver salt in being cyclic, there are differences in the hydrogen bonding pattern. These featurcs are discussed in relation to the cornplexation of metal ions by m.onensin.}, subject = {Toxikologie}, language = {en} } @article{LutzFruehSimon1971, author = {Lutz, Werner K. and Fr{\"u}h, P. U. and Simon, W.}, title = {Microcalorimetric determination of ΔH0, ΔG0 and ΔS0 for the interaction of the carrier antibiotics nigericin and monensin with sodium and potassium ions}, url = {http://nbn-resolving.de/urn:nbn:de:bvb:20-opus-61218}, year = {1971}, abstract = {The thermodynainic parameters ΔH0, ΔG0 and ΔS0 - and thereby the equilibrium constants - for the complexation of the carrier antibiotics nigericin and monensin with sodium and potassium ions in methanol at 25°C have been determined by microcalorimetry. Tbc results are discussed in terms of the nature of the interaction between ligands and cations.}, subject = {Toxikologie}, language = {en} } @article{LutzSchlatter1977, author = {Lutz, Werner K. and Schlatter, C.}, title = {Mechanism of the carcinogenic action of benzene: irreversible binding to rat liver DNA}, url = {http://nbn-resolving.de/urn:nbn:de:bvb:20-opus-61208}, year = {1977}, abstract = {No abstract available}, subject = {Toxikologie}, language = {en} } @article{LutzSchlatter1977, author = {Lutz, Werner K. and Schlatter, C.}, title = {Saccharin does not bind to DNA of liver or bladder in the rat [Short Communication]}, url = {http://nbn-resolving.de/urn:nbn:de:bvb:20-opus-61194}, year = {1977}, abstract = {No abstract available}, subject = {Toxikologie}, language = {en} } @article{VivianiLutzSchlatter1978, author = {Viviani, A. and Lutz, Werner K. and Schlatter, C.}, title = {Time course of the induction of aryl hydrocarbon hydroxylase in rat liver nuclei and microsomes by phenobarbital, 3-methylcholanthrene, 2,3,7,8-tetrachloro-dibenzo-p-dioxin, dieldrin and other inducers}, url = {http://nbn-resolving.de/urn:nbn:de:bvb:20-opus-61182}, year = {1978}, abstract = {Aryl hydrocarbon hydroxylase (AHH) has been measured in male rat Jiver nucJei and microsomes after treatment of adult animals with various inducers for up to 14 days. After daily i.p. injections of 3-methylcholanthrene (MC, 20 mg/kg) the nuclear activity increased to a maximum of 600 per cent of the control activity after 4 days whereas the microsomal activity was 400 per cent of control at the same date. After 12 days, both activities equilibrated at 400 per cent. A similar time course was found after a single i.p. injection of 2,3,7,8-tetrachloro-dibenzo-p-dioxin (TCDD, 0.01 mg/kg) with an induction to .500 and 300 per cent for nuclei and microsomes, respectiveJy. after 2 days, and to 400 per cent for both after 12 days. PhenobarbitaJ (PB) was given continuously in the drinking water (I g/1) and induced the microsomal activity to 200 per cent after 8 days and 170 per cent after 14 days. The nuclear activity was only slightly induced to a constant Ievei of 130 per cent between day 8 and 14. Dieldrin did not significantly increase the microsomal activity after daiJy i.p. injections (20 mg/kg), but the nuclear activity raised to 200 per cent after 3 days and levelled down tocontrol valuesafter 12 days. Other inducers tested were benz[a)anthracene (BA), hexachlorobenzene (HCB} and 1,1.1-trichloro-2,2-bis(p-chlorophenyl)ethane (DDT). The induction pattern with BA was similar tothat of MC, a modeJ compound for the group of cytochrome P448 inducers. The induction by HCB and DDT resembled that by PB. a typical cytochrome P450 inducer.}, subject = {Toxikologie}, language = {en} } @article{LutzViviantSchlatter1978, author = {Lutz, Werner K. and Viviant, A. and Schlatter, C.}, title = {Nonlinear dose-response relationship for the binding of the carcinogen benzo(a)pyrene to rat liver DNA in vivo}, url = {http://nbn-resolving.de/urn:nbn:de:bvb:20-opus-61179}, year = {1978}, abstract = {Wlth radioactive compound of high specific activity, the binding of carcinogene to DNA can be measured wlth doses that are ineffective ln long-term studies. The binding of tritiated benzo(a )pyrene to liver DNA of adult male rats has been determined 50 hr after a singie l.p. injection of doses between 40 1'9/kg and 4 mg/kg. The doseresponse relationship is linear up to 1 mg/kg, shows a step towards 2 mg/kg, and gives a shallow linear slope above that value. The observed binding ranges from 1.7 to 180 nmoles benzo(a)pyrene per mole DNA phosphate. The nonlinearity could be due to an induction of metabolizing enzymes. The microsomal aryl hydrocarbon hydroxylase activity increases significantly 24 hr after a single dose of 4 mg/kg and 48 hr after doses of 2 and 4 mg/kg, but no induction Ia found with 1 mg/kg. The binding from an equimolar dose is 35 times lower than the one found on mouse skin DNA and 300 times lower than that of N,Ndlmethylnitrosamine in rat liver. A good correlatlon exiats to the respective tumor formation in long-term studles.}, subject = {Toxikologie}, language = {en} } @article{JaggiLutzSchlatter1978, author = {Jaggi, W. and Lutz, Werner K. and Schlatter, C.}, title = {Covalent binding of ethinylestradiol and estrone to rat liver DNA in vivo}, url = {http://nbn-resolving.de/urn:nbn:de:bvb:20-opus-61162}, year = {1978}, abstract = {Thecovalent bindingof [6,7-\(^3\)H]ethinylestradiol (EE)and [6,7-\(^3\)H]estrone (E) to liver DNA of 200 g female ratswas measured 8 h after the administration of 80 \(\mu\)g (9.2 mCi) estrogen by gavage. The binding is 1.5 for EE and 1.1 for E, expressedas binding to DNA/dose, in units of \(\mu\)mol hormonefmol DNA phosphate/mmole honnone/kg body wt. It is in the same order of magnitude as for benzene and about 10 000 tim es below the binding of typical liver carcinogens, such as aflatoxin B\(_1\) or N,N-dimethylnitrosamine.}, subject = {Toxikologie}, language = {en} } @article{VivianiLutz1978, author = {Viviani, A. and Lutz, Werner K.}, title = {Modulation of the binding of the carcinogen benzo(a)pyrene to rat liver DNA in vivo by selective induction of microsomal and nuclear aryl hydrocarbon hydroxylase activity}, url = {http://nbn-resolving.de/urn:nbn:de:bvb:20-opus-61150}, year = {1978}, abstract = {The lnfluence of mlcrosomal and nuclear aryl hydrocarbon hydroxylase (AHH) actlvlty on the covalent blndlng of [G·3H]benzo(a )pyrene to rat llver DNA was evaluated in viWJ. lnductlon of mlcrosomal AHH was obtalned alter phenobarbltal treatment (160\% of control), whlch also lncreased DNA blndlng to 190\%, but left the nuclear actlvlty unchanged. Nuclear AHH was lnduced wlth dleldrln (150\%), and the blndlng was decreased to 75\%, whereaa the mlcrosomal AHH was at control Ievei. The lncreaslng effect of mlcrosomal AHH lnductlon as weil as the decreaslng effect of nuclear AHH lnductlon on the blndlng was shown clearly when the data of the Individual rata were uaed to solve the equatlon Binding = e•(mlcroeomal AHH) + b•(nuclear AHH) + c Multiple linear regresslon analysls wlth the data from 10 anlmala reaulted ln positive valuea for a and c, a negative value for b, and a good multiple correlatlon coefflclent of r = 0.974. Pretreatment wlth 3-methylcholanthrene ln· duced mlcrosomal AHH to 380\% of control and nuclear AHH to 590\% and lncreased the blndlng' to 175,.-o. The blndlng was hlgher than predlcted by the formula found, probably because the lncreaslng lnfluence of lnduced mlcrosomal AHH overahadowed the decreaslng effect of the nuclear AHH. The study ahows clearly that the blndlng of a forelgn compound to DNA in viWJ Ia dependent not only on mlcrosomal enzyme actlvltles but also on nuclear actlvltles even lf the latter are conslderably lower than thoae of mlcrosomes.}, subject = {Toxikologie}, language = {en} } @article{LutzBraendleZbinden1978, author = {Lutz, Werner K. and Br{\"a}ndle, E. and Zbinden, G.}, title = {Effect of gum Arabic on aminopyrine demethylation in rats}, url = {http://nbn-resolving.de/urn:nbn:de:bvb:20-opus-61146}, year = {1978}, abstract = {Stimulation of aminopyrine demethylation induced in rats by oral or i.p. administration of phenobarbital was partially inhibited in animals receiving daily treatments of 2 x 200 mg/kg gum Arabic p.o.}, subject = {Toxikologie}, language = {en} } @article{JaggiLutzSchlatter1979, author = {Jaggi, W. and Lutz, Werner K. and Schlatter, C.}, title = {Comparative studies on the covalent binding of the carcinogen benzo(a)pyrene to DNA in various model systems}, url = {http://nbn-resolving.de/urn:nbn:de:bvb:20-opus-61131}, year = {1979}, abstract = {The covalent binding of tritiated benzo(a)pyrene (BP) to DNA has been determined in rat liver in vivo, in rat liver perfused in situ, after incubation of BP with liver single cells, with liver homogenate, with liver microsomes and DNA, with fibroblasts from a rat granulorna pouch, and with · 2 cell lines. Li ver single cells were found to be a valuable compromise between the rnost sensitive system (microsomal incubation of BP with DNA) and the biologically most relevant system (in vivo ).}, subject = {Toxikologie}, language = {en} }