Albrecht Seidel - Academia.edu (original) (raw)
Papers by Albrecht Seidel
Angewandte Chemie, 1993
5j: Eine Mischung aus 4 j (0.32 mmol), 9-Bromphenanthren (0.96 mmol) und [Pd(PPh,),] (0.1 mmol) i... more 5j: Eine Mischung aus 4 j (0.32 mmol), 9-Bromphenanthren (0.96 mmol) und [Pd(PPh,),] (0.1 mmol) in Methanol'Toluol (30 mL, 1. 1) wurde 5 mill geruhrt. AiischlieBend wurde eine 2 M NaZCO,-Lbsung (3 mL) zugegeben. Die Reaktionsmischung wurde welter geruhrt und 5 h bei 140'C untcr Ruckflun erhitzt. Nach Zugabe von Wasser (50 mL) und Ahkuhlen auf Raumtemperatur wurdc die Mischung mil Ether extrahiert (3 x 20 mL). Die vereinigten organischen Phasen wurden mit Wasser gewaschen. getrocknet (MgSO,) und emgeengt.
![Research paper thumbnail of Fjord-region diol-epoxides of benzo[c]chrysene are potent inducers of micronuclei in murine bone marrow](https://attachments.academia-assets.com/87648331/thumbnails/1.jpg)
](Mutation Research - Fundamental and Molecular Mechanisms of Mutagenesis, 1994
Vicinal diol-epoxides are the best established carcinogenic metabolites of polycyclic aromatic hy... more Vicinal diol-epoxides are the best established carcinogenic metabolites of polycyclic aromatic hydrocarbons. Numerous studies have demonstrated their high genotoxic activity in various in vitro test systems. However, in vivo mutagenicity data are not available. The fjord-region diol-epoxides of benzo[c]chrysene combine high mutagenic activity in vitro with high hydrolytic stability. They were tested for the induction of micronuclei in the bone marrow following intraperitoneal administration to NMRI mice. The anti diastereomer of the diol-epoxide enhanced the frequency of micronucleated polychromatic erythrocytes strongly (7-19-fold above the value in untreated controls) over a very wide dose range (2.5-300/zmol/kg body weight). The syn diastereomer demonstrated similar effects, but required about 5 times higher doses. The corresponding proximate mutagen, benzo[c]chrysene-trans-9,10-dihydrodiol, was only moderately active, whereas the positive control substance, benzo[a]pyrene-trans-7,8-dihydrodiol, was strongly active. The study indicates that intraperitoneally administered diol-epoxides of benzo[c]chrysene may reach the bone marrow. Therefore, it will be possible to study the influence of metabolic modulation, e.g. by enzyme induction, on the effects of these ultimate mutagens and their metabolic precursors in vivo.
![Research paper thumbnail of Interaction between Metabolism and Transport of Benzo[a]pyrene and Its Metabolites in Enterocytes](https://attachments.academia-assets.com/87648332/thumbnails/1.jpg)
](Toxicology and Applied Pharmacology, 2002
Epithelial cells of the small intestine are responsible for the resorption of different food comp... more Epithelial cells of the small intestine are responsible for the resorption of different food components as well as potentially toxic agents such as benzo[a]pyrene (B[a]P), a particular contaminant of charcoal-grilled meat. This study was undertaken to investigate any functional relationship between the metabolism of B[a]P and the unidirectional transport of metabolites back into the intestinal lumen mediated by ATP-binding cassette (ABC) transport proteins. The human intestinal Caco-2 cell line was used. In addition, mdr1-and mrp2-transfected MDCK cells were employed to characterize the possible role of these ABC transport proteins in the polarized transport. After incubations of Caco-2 cells with B[a]P, HPLC analysis revealed that the primary metabolites of B[a]P were B[a]P-1-sulfate and B[a]P-3-sulfate. Other metabolites, such as B[a]P-3-glucuronide, B[a]P-9,10-diol, or B[a]P-3,6-quinone, could be detected only in small amounts. The transport experiments using Transwell chambers clearly showed that B[a]P-1-and B[a]P-3-sulfate were actively transported toward the apical (luminal) region. This transport increased after induction of CYP1A1/CYP1B1 (Phase 1)-metabolism, although a decrease was observed during concomitant inhibition. Inhibition studies using chemical inhibitors of P-glycoprotein, MRPs, showed no effects. A comparison between the transport of B[a]P-1-and B[a]P-3-sulfate in wild-type and mrp2-transfected MDCKII cells revealed no differences at all. The results indicate that B[a]P is metabolized by Caco-2 cells mainly to B[a]P-1-and B[a]P-3-sulfate, which are subject to an apically directed transport. Furthermore ABC transport proteins P-glycoprotein, MRP1, and MRP2 are not involved in this polarized B[a]P-sulfate secretion.
![Research paper thumbnail of Activated Fjord-Region Metabolites of Dibenzo[a,l]pyrene: Synthesis and Mutagenic Activities of the Diastereomericsyn− andanti−11,12-Dihydrodiol 13,14-Epoxides](https://attachments.academia-assets.com/87648327/thumbnails/1.jpg)
](Polycyclic Aromatic Compounds, 1994
A growing body of literature documents the importance of trauma-informed and trauma-specific serv... more A growing body of literature documents the importance of trauma-informed and trauma-specific services and systems change in both addiction treatment and child welfare fields. The overall aim of this qualitative study was to explore barriers, benefits, and facilitating factors associated with a trauma-informed systems assessment and improvement initiative conducted in the context of a family drug treatment court (FDTC). Semi-structured in-depth interviews with 12 key informants and historical analyses of project documents over a 4-year time span were conducted. Results underscore the relevance of trauma-informed systems change in collaborative contexts designed to address the complex needs of children and families.
Polycyclic Aromatic Compounds, 1990
A glazing façade subjected to blast loads has a structural behaviour that strongly differs from t... more A glazing façade subjected to blast loads has a structural behaviour that strongly differs from the typical response of a glazing system subjected to ordinary loads. Consequently, sophisticated modelling techniques are required to identify correctly its criticalities. The paper investigates the behaviour of a cable-supported façade subjected to high-level blast loading. Nonlinear dynamic analyses are performed in ABAQUS/Explicit using a sophisticated FE-model (M01), calibrated to dynamic experimental and numerical results. The structural effects of the total design blast impulse, as well as only its positive phase, are analyzed. At the same time, the possible cracking of glass panels is taken into account, since this phenomenon could modify the response of the entire façade. Finally, deep investigations are dedicated to the bearing cables, since subjecting them to elevated axial forces and their collapse could compromise the integrity of the cladding wall. Based on results of previous studies, frictional devices differently applied at their ends are presented to improve the response of the façade under the impact of a high-level explosion. Structural effects of various solutions are highlighted through dynamic simulations. Single vertical devices, if appropriately calibrated, allow reducing significantly the axial forces in cables, and lightly the tensile stresses in glass panes.
Polycyclic Aromatic Compounds, 2000
Page 1. Po/i,r.drc .Arumuric Compoimndr. 1999. Vol. 16. pp. 191-203 Reprints available dircctl) f... more Page 1. Po/i,r.drc .Arumuric Compoimndr. 1999. Vol. 16. pp. 191-203 Reprints available dircctl) from the publisher Photocopymp permitted b) license only C 1999 OPA (Overseas Publishers Asswiationj NV Published by license ...
Polycyclic Aromatic Compounds, 2008
Polycyclic Aromatic Compounds, 2004
The fjord-region PAH dibenzo[a,l]pyrene (DBP) is considerably more carcinogenic than the bay-regi... more The fjord-region PAH dibenzo[a,l]pyrene (DBP) is considerably more carcinogenic than the bay-region benzo[a]pyrene (BP). This fact can be ascribed to differences in DNA binding efficiency of their ultimate carcinogenic diol epoxide (DEs) intermediates, differences in structural features of the DNA adducts, and differences in DNA adduct recognition and the subsequent lesion removal by nucleotide excision repair (NER). In order to
Polycyclic Aromatic Compounds, 1996
In the present work we have used a DNA polymerase assay to investigate the primer extension with ... more In the present work we have used a DNA polymerase assay to investigate the primer extension with T7 DNA polymerase (Sequenase 2.0) and the Klenow fragment of Escherichia coli DNA polymerase I (exo KF) on chemically synthesized 21mer templates representing partial sequences of the human Ha-ras protooncogene with site-specifically positioned trans-N -dA adducts of (-)- (adduct 1) and (+)-anti-benzo[c]phenanthrene 3,4-dihydrodiol
Polycyclic Aromatic Compounds, 1996
Abstract Phenanthrene, benz[a]anthracene, chrysene, benzo[c]phenanthrene, and benzo[a]pyrene have... more Abstract Phenanthrene, benz[a]anthracene, chrysene, benzo[c]phenanthrene, and benzo[a]pyrene have been studied for their regiospecific oxidation by five human (1A1, 1A2, 2A6, 2E1, 3A4) and three rat (1A1, 1A2, 2B1) CYP isoforms. All substrates are preferentially metabolized by CYP1A1 and CYP1A2 in human and rat. Other isoforms play a minor role if at all. Significant differences between human and rat CYP isoforms can be recognized with regard to the regiospecific oxidation of PAH. For instance, K-region oxidation is more pronounced in rat than in human CYP1A1 and CYP1A2. Hence, extrapolation from metabolism studies in rodents to human may be limited.
Polycyclic Aromatic Compounds, 1996
ABSTRACT
Environmental Health Perspectives, 1990
Methylated polycyclic aromatic hydrocarbons are common in the human environment. Many of them are... more Methylated polycyclic aromatic hydrocarbons are common in the human environment. Many of them are stronger carcinogens than their purely aromatic congeners. They may be metabolized to benzylic alcohols. We report here on biochemical and toxicological characteristics of 1-hydroxymethylpyrene (HMP), a typical representative of this class of compounds. Rat liver cytosol, fortified with 3'-phosphoadenosine-5'-phosphosulfate, converted HMP into its sulfate ester (HMPS). HMPS bound covalently to isolated DNA. In physiological buffer at 370C, HMPS had a half-life of 2 min, the major decomposition product being HMP. Thus, cyclic activation is possible. When Cl-anions were present at physiological concentrations, an additional reaction product of HMPS, 1-chloromethylpyrene (CIMP), could be identified on the basis of its chromatographic properties and its mass spectrum, using the authentic standard for comparison. CIMP was shorter-lived in buffer than HMPS. CIMP reacted with DNA, the adduct pattern in the 32P-postlabeling analysis being similar, or identical, to that of HMPS. CIMP proved to be a very potent mutagen in Salmonella typhimurium, whereas HMPS, and HMP in the presence of a sulfateconjugating system, showed strong mutagenicity only when Cl-or Br-ions were present in the exposure buffer. It is concluded that HMPS is capable of reacting with DNA, but is hampered in its distribution by membrane barriers. Strikingly, a CIMP intermediate is produced, which can act as a transport form to overcome membrane barriers. Among 10 investigated tissues, HMP-activating sulfotransferases were found at appreciable levels only in the liver, and there the activity in parenchymal cells exceeded that in Kupffer cells by a factor of-200. Distribution processes and their restrictions may, therefore, be important factors determining the toxicology of benzylic alcohols and other compounds activated through conjugation with sulfate.
Environmental Health Perspectives, 1990
V79 cells, genetically engineered to express active cytochromes P450IIB1 and P450IA1, were used t... more V79 cells, genetically engineered to express active cytochromes P450IIB1 and P450IA1, were used to study the cytotoxicity and mutagenicity of cyclophosphamide and ifosfamide. Cyclophosphamide, tested up to a concentration of 2 mM, was not cytotoxic in V79 nor in the P450IA1-expressing V79-derived cell line XEM2. Pronounced cytotoxicity was, however, observed in the P450IIB1-expressing V79-derived cell line SDL. Induction of gene mutations (acquisition of 6-thioguanine resistance) was observed in SD1 cells as well, but the effects were weak. Ifosfamide was inactive in V79 cells, but was cytotoxic in SDl cells. Ifosfamide mustard, an active metabolite of ifosfamide, was equally cytotoxic and showed similar mutagenic effects in SDl and parental V79 cells. The results indicate that cyclophosphamide and ifosfamide are metabolically activated by cytochrome P4501IB1. In contrast, cytochrome P450IA1 was not capable of activating cyclophosphamide. Thus, V79-derived cell lines defined for their expression of a specific form of cytochrome P-450 can be used as diagnostic tools to identify the cytochrome P-450 that is responsible for the metabolic activation of drugs.
Environmental Health Perspectives, 1990
The ability of isolated rat liver endothelial and Kupffer cells to activate benzo(a)pyrene (BP), ... more The ability of isolated rat liver endothelial and Kupffer cells to activate benzo(a)pyrene (BP), trans-7,8-dihydroxy-7,8-dihydrobenzo(a)pyrene (DDBP), trans-1,2-dihydroxy-1,2-dihydrochrysene (DDCH), and aflatoxin B, (AFB%) to mutagenic metabolites was assessed by means of a cell-mediated bacterial mutagenicity assay and compared with the ability of parenchymal cells to activate these compounds. Endothelial and Kupffer cells from untreated rats were able to activate AFB, and DDBP; DDBP was activated even in the absence of an NADPH-generating system. Pretreating the animals with Aroclor 1254 strongly enhanced the mutagenicity of the dihydrodiol, whereas the mutagenicity of AFB, showed a slight increase. BP and DDCH were only activated by endothelial and Kupffer cells isolated from Aroclor 1254-pretreated rats. Parenchymal cells from untreated animals activated all four carcinogens tested; Aroclor 1254 enhanced the parenchymal cell-mediated mutagenicity of BP and DDCH but did not affect that of DDBP and clearly reduced that of AFB,. The reduced mutagenicity of AFB, correlates with the decrease in the amount of 2a-hydroxytestosterone formed when testosterone was incubated with parenchymal cell microsomes from Aroclor 1254-pretreated rats (compared with microsomes from untreated animals): the formation of 2a-hydroxytestosterone is specifically catalyzed by cytochrome P-450h, a hemoprotein thought to be involved in the activation of AFB,. These results show that not only rat liver parenchymal cells, but also endothelial and Kupffer cells, activate several carcinogens to mutagenic metabolites.
Chemico-Biological Interactions, 1991
Rat liver dihydrodiol dehydrogenase (DDH, E.C. 1.3.1.20) has recently been shown to oxidize the h... more Rat liver dihydrodiol dehydrogenase (DDH, E.C. 1.3.1.20) has recently been shown to oxidize the highly carcinogenic benz[a]anthracene-3,4-dihydrodiol in an NADP÷-dependent reaction to its corresponding catechol [22]. The present study is a systematic investigation of the substrate specificity of the purified enzyme towards synthetic trans-dihydrodiol metabolites of phenanthrene, benz[a]anthracene, chrysene, dibenz[a, hlanthracene and benzo[a]pyrene. DDH exhibited a remarkable regiospecificity of enzymatic catalysis with regard to the site of the dihydrodiol moiety of the parent hydrocarbon. M-region-and, with lower efficiency, bay-region dihydrodiols were found to be good substrates of the enzyme with maximal velocities between 20-80 nmol/min per mg enzyme and Km values in the micromolar range. K-region dihydrodiols were not accepted as substrates. Dihydrodiols situated at the terminal ring of an anthracene-type structure such as benz[a]anthracene-8,9-dihydrodiol as well as the corresponding dihydrodiol epoxides were also not oxidized by DDH at measurable rates. The results provide evidence for a detoxifying role of DDH in the metabolism of the chemical carcinogens benz[a]anthracene, chrysene and dibenz[a,h]anthracene.
![Research paper thumbnail of On the species-specific biotransformation of dibenzo[a,l]pyrene](https://attachments.academia-assets.com/87648381/thumbnails/1.jpg)
](Chemico-Biological Interactions, 2006
We were aimed at investigating the activation of the carcinogenic polycyclic aromatic hydrocarbon... more We were aimed at investigating the activation of the carcinogenic polycyclic aromatic hydrocarbon (PAH) dibenzo[a,l]pyrene (DB[a,l]P) in Chinese hamster V79 cells that express single human, rat or fish cytochrome P450 (CYP) enzymes. DB[a,l]P is detectable in environmental samples and has been characterized as the most potent carcinogenic species among all PAHs as yet tested in rodent bioassays. Metabolite profiles and metabolite-dependent cytotoxic and clastogenic activities were monitored. The total turnover of CYP-mediated transformation of DB[a,l]P was as follows: human CYP1B1 > fish CYP1A1 ≈ human CYP1A1 rat CYP1A2 > rat CYP1A1. By contrast, enzyme forms that are not classified as being members of family CYP1, such as CYP2A6, 2E1, 2B1, and 3A4, failed to catalyze any detectable conversion of this substrate. All CYP1A1 enzymes tested formed both the K-region trans-8,9-and the trans-11,12-dihydrodiol, whereas human CYP1B1 failed to catalyze K-region activation. In cells expressing human or fish CYP1A1, human CYP1B1, and rat CYP1A2, the (−)-trans-11,12-dihydrodiol was formed enantiospecifically. DB[a,l]Pdependent cytotoxicities (EC 50) were found in the following order: human CYP1A1 (12 nM) > fish CYP1A1 (30 nM) > human CYP1B1 (45 nM) other forms. In addition, an appreciable micronuclei formation was detected in human CYP1A1-and 1B1expressing cells during exposure to DB[a,l]P. Our study demonstrates that human CYP1A1, 1B1 and fish CYP1A1 are able to transform DB[a,l]P into genotoxic derivatives in appreciable amounts. In contrast, CYP enzymes from rat predominantly target the K-region of DB[a,l]P and thus are serving more a rather protective route of biotransformation. Together our data suggest that humans might be more susceptible to DB[a,l]P-induced carcinogenicity than rats.
![Research paper thumbnail of Conformational Studies of Stereoisomeric Tetrols Derived from syn- and anti -Dibenzo[ a,l ]pyrene Diol Epoxides](https://attachments.academia-assets.com/87648335/thumbnails/1.jpg)
](Chemical Research in Toxicology, 1997
An understanding of the conformational behavior of the stereoisomeric tetrols at the 11,12,13,14-... more An understanding of the conformational behavior of the stereoisomeric tetrols at the 11,12,13,14-positions of dibenzo[a,l]pyrene (DB[a,l]P) is essential for the spectroscopic identification of DNA adducts derived from the biologically highly active fjord region syn-and anti-DB[a,l]P-11,12-diol 13,14-epoxides. Conformational effects are expected to play an important role in DNA-DB[a,l]P diol epoxide reactivity, base-sequence specificity, and conformation dependent repair. The results of conformational studies on trans-anti-, cis-anti-, and cis-syn-DB[a,l]P tetrol isomers are presented and compared to the results obtained previously for trans-syn-DB[a,l]P tetrol (Carcinogenesis 17, 829-837, 1996). Molecular mechanics, dynamical simulations, and semiempirical calculations of electronic transitions are used to interpret the low-temperature fluorescence spectra and 1 H NMR data. Molecular dynamics simulations (in vacuo) identified two conformers (I and II) for each of the tetrol isomers; in all conformations the aromatic ring system is severely distorted. Fluorescence line-narrowing (FLN) spectroscopy identified two distinct conformational species for the transanti isomer, one occurring in ethanol and the other occurring in a glycerol/water matrix. The corresponding structures are assigned based on the S 1 r S 0 transition energies calculated for conformers I and II, respectively. 1 H NMR spectroscopy confirmed the structure of conformer I at room temperature. In contrast to trans-syn-DB[a,l]P tetrol (where the major conformation was identified as a boat structure), both conformations of trans-anti-DB[a,l]P tetrol feature a half-chair structure for the cyclohexenyl ring with different orientations of the hydroxyl groups. For cis-anti-and cis-syn-DB[a,l]P tetrols, only a single conformer is detected by FLN spectroscopy. The NMR results for the latter appear to be most consistent with a mixture of two half-chair conformers I and II, while for the cis-anti isomer a flattened, boatlike conformation was observed. The generally good agreement between the NMR coupling constants and those estimated theoretically indicates that these structures should serve as good starting points for spectroscopic or computational studies of DNA adducts derived from DB[a,l]P diol epoxides.
![Research paper thumbnail of Structure, Conformations, and Repair of DNA Adducts from Dibenzo[ a , l ]pyrene: 32 P-Postlabeling and Fluorescence Studies](https://attachments.academia-assets.com/87648334/thumbnails/1.jpg)
](Chemical Research in Toxicology, 1998
The nature of stable DNA adducts derived from the very potent carcinogen dibenzo[a,l]pyrene (DB[a... more The nature of stable DNA adducts derived from the very potent carcinogen dibenzo[a,l]pyrene (DB[a,l]P) in the presence of rat liver microsomes in vitro and in mouse skin in vivo has been studied using 32 P-postlabeling and laser-based fluorescence techniques. Analysis of DB[a,l]P-DNA adducts via 32 P-postlabeling has been obtained by comparison of the adduct patterns to those obtained from reactions of synthetic (()-anti-, (+)-anti-, (-)-anti-, and (()-syn-DB[a,l]P-11,12-diol 13,14-epoxide (DB[a,l]PDE) with single nucleotides and calf thymus DNA. anti-DB[a,l]PDE-dA adducts derived from the (-)-enantiomer are the major adducts formed in calf thymus DNA and in mouse skin DNA. The ratio of deoxyadenosine to deoxyguanosine modification is approximately 2:1 in mouse skin exposed to DB[a,l]P; activation by rat liver microsomes leads to a similar profile of adducts but with two additional spots. The conformations of DB[a,l]P adducts in native DNA, as well as the possibility of conformationdependent repair, have been explored by low-temperature fluorescence spectroscopy. These studies have been performed using polynucleotides and calf thymus DNA reacted in vitro with DB[a,l]PDE and native DNA from mouse epidermis exposed to DB[a,l]P. The results show that adducts are heterogeneous, possess different structures, and adopt different conformations. External, external but base-stacked and intercalated adduct conformations are observed in calf thymus DNA and in mouse skin DNA samples. Differences in adduct repair rates are also revealed; namely, the analysis of mouse skin DNA samples obtained at 24 and 48 h after exposure to DB[a,l]P clearly shows that external adducts are repaired more efficiently than intercalated adducts. These results, taken together with those for B[a]P-DNA adducts [Suh et al. (1995) Carcinogenesis 16, 2561-2569], indicate that the repair of DNA damage resulting from PAH diol epoxides is conformation-dependent.
![Research paper thumbnail of Structure Elucidation of the Adducts Formed by Fjord Region Dibenzo[ a , l ]pyrene-11,12-dihydrodiol 13,14-Epoxides with Deoxyguanosine](https://attachments.academia-assets.com/87648323/thumbnails/1.jpg)
](Chemical Research in Toxicology, 1999
Dibenzo[a,l]pyrene-11,12-dihydrodiol 13,14-epoxide {(()-anti-DB[a,l]PDE} was reacted with deoxygu... more Dibenzo[a,l]pyrene-11,12-dihydrodiol 13,14-epoxide {(()-anti-DB[a,l]PDE} was reacted with deoxyguanosine (dG) in dimethylformamide at 100°C for 30 min, and two sets of adducts were isolated: a mixture of (()-anti-cis-&-trans-N 2 dG (43%) and a mixture of (()anti-cis-&-trans-N7Gua (45%). Both are mixtures of four stereoisomers that cannot be separated by HPLC. Similarly, (()-syn-DB[a,l]PDE was reacted with dG under the same conditions, and (()-syn-cis-&-trans-N 2 dG (38%) and (()-syn-cis-&-trans-N7Gua (59%) were obtained. The structures of the adducts were determined by a combination of NMR and fast atom bombardment mass spectrometry. By reacting (-)-anti-DB[a,l]PDE or (+)-syn-DB[a,l]-PDE with dG under the same conditions, however, optically pure N 2 dG and N7Gua isomers were obtained: (-)-anti-cis-N 2 dG (12%), (-)-anti-trans-N 2 dG (17%), (-)-anti-trans-N7Gua (43%), (+)-syn-cis-N 2 dG (7%), (+)-syn-trans-N 2 dG (3%), (+)-syn-cis-N7Gua (36%), and (+)-syntrans-N7Gua (22%). The structures of the optically pure adducts were assigned by NMR. synand anti-DB[a,l]PDE-N 2 dG adducts can be distinguished by fluorescence line-narrowing spectroscopy (FLNS). Moreover, distinction between cis-and trans-stereochemistry of the adducts is also straightforward by FLNS, because the FLN spectra for the four DB[a,l]PDE-N 2 dG adducts, anti-cis, anti-trans, syn-cis, and syn-trans, are spectroscopically unique.
Angewandte Chemie, 1993
5j: Eine Mischung aus 4 j (0.32 mmol), 9-Bromphenanthren (0.96 mmol) und [Pd(PPh,),] (0.1 mmol) i... more 5j: Eine Mischung aus 4 j (0.32 mmol), 9-Bromphenanthren (0.96 mmol) und [Pd(PPh,),] (0.1 mmol) in Methanol'Toluol (30 mL, 1. 1) wurde 5 mill geruhrt. AiischlieBend wurde eine 2 M NaZCO,-Lbsung (3 mL) zugegeben. Die Reaktionsmischung wurde welter geruhrt und 5 h bei 140'C untcr Ruckflun erhitzt. Nach Zugabe von Wasser (50 mL) und Ahkuhlen auf Raumtemperatur wurdc die Mischung mil Ether extrahiert (3 x 20 mL). Die vereinigten organischen Phasen wurden mit Wasser gewaschen. getrocknet (MgSO,) und emgeengt.
Mutation Research - Fundamental and Molecular Mechanisms of Mutagenesis, 1994
Vicinal diol-epoxides are the best established carcinogenic metabolites of polycyclic aromatic hy... more Vicinal diol-epoxides are the best established carcinogenic metabolites of polycyclic aromatic hydrocarbons. Numerous studies have demonstrated their high genotoxic activity in various in vitro test systems. However, in vivo mutagenicity data are not available. The fjord-region diol-epoxides of benzo[c]chrysene combine high mutagenic activity in vitro with high hydrolytic stability. They were tested for the induction of micronuclei in the bone marrow following intraperitoneal administration to NMRI mice. The anti diastereomer of the diol-epoxide enhanced the frequency of micronucleated polychromatic erythrocytes strongly (7-19-fold above the value in untreated controls) over a very wide dose range (2.5-300/zmol/kg body weight). The syn diastereomer demonstrated similar effects, but required about 5 times higher doses. The corresponding proximate mutagen, benzo[c]chrysene-trans-9,10-dihydrodiol, was only moderately active, whereas the positive control substance, benzo[a]pyrene-trans-7,8-dihydrodiol, was strongly active. The study indicates that intraperitoneally administered diol-epoxides of benzo[c]chrysene may reach the bone marrow. Therefore, it will be possible to study the influence of metabolic modulation, e.g. by enzyme induction, on the effects of these ultimate mutagens and their metabolic precursors in vivo.
Toxicology and Applied Pharmacology, 2002
Epithelial cells of the small intestine are responsible for the resorption of different food comp... more Epithelial cells of the small intestine are responsible for the resorption of different food components as well as potentially toxic agents such as benzo[a]pyrene (B[a]P), a particular contaminant of charcoal-grilled meat. This study was undertaken to investigate any functional relationship between the metabolism of B[a]P and the unidirectional transport of metabolites back into the intestinal lumen mediated by ATP-binding cassette (ABC) transport proteins. The human intestinal Caco-2 cell line was used. In addition, mdr1-and mrp2-transfected MDCK cells were employed to characterize the possible role of these ABC transport proteins in the polarized transport. After incubations of Caco-2 cells with B[a]P, HPLC analysis revealed that the primary metabolites of B[a]P were B[a]P-1-sulfate and B[a]P-3-sulfate. Other metabolites, such as B[a]P-3-glucuronide, B[a]P-9,10-diol, or B[a]P-3,6-quinone, could be detected only in small amounts. The transport experiments using Transwell chambers clearly showed that B[a]P-1-and B[a]P-3-sulfate were actively transported toward the apical (luminal) region. This transport increased after induction of CYP1A1/CYP1B1 (Phase 1)-metabolism, although a decrease was observed during concomitant inhibition. Inhibition studies using chemical inhibitors of P-glycoprotein, MRPs, showed no effects. A comparison between the transport of B[a]P-1-and B[a]P-3-sulfate in wild-type and mrp2-transfected MDCKII cells revealed no differences at all. The results indicate that B[a]P is metabolized by Caco-2 cells mainly to B[a]P-1-and B[a]P-3-sulfate, which are subject to an apically directed transport. Furthermore ABC transport proteins P-glycoprotein, MRP1, and MRP2 are not involved in this polarized B[a]P-sulfate secretion.
Polycyclic Aromatic Compounds, 1994
A growing body of literature documents the importance of trauma-informed and trauma-specific serv... more A growing body of literature documents the importance of trauma-informed and trauma-specific services and systems change in both addiction treatment and child welfare fields. The overall aim of this qualitative study was to explore barriers, benefits, and facilitating factors associated with a trauma-informed systems assessment and improvement initiative conducted in the context of a family drug treatment court (FDTC). Semi-structured in-depth interviews with 12 key informants and historical analyses of project documents over a 4-year time span were conducted. Results underscore the relevance of trauma-informed systems change in collaborative contexts designed to address the complex needs of children and families.
Polycyclic Aromatic Compounds, 1990
A glazing façade subjected to blast loads has a structural behaviour that strongly differs from t... more A glazing façade subjected to blast loads has a structural behaviour that strongly differs from the typical response of a glazing system subjected to ordinary loads. Consequently, sophisticated modelling techniques are required to identify correctly its criticalities. The paper investigates the behaviour of a cable-supported façade subjected to high-level blast loading. Nonlinear dynamic analyses are performed in ABAQUS/Explicit using a sophisticated FE-model (M01), calibrated to dynamic experimental and numerical results. The structural effects of the total design blast impulse, as well as only its positive phase, are analyzed. At the same time, the possible cracking of glass panels is taken into account, since this phenomenon could modify the response of the entire façade. Finally, deep investigations are dedicated to the bearing cables, since subjecting them to elevated axial forces and their collapse could compromise the integrity of the cladding wall. Based on results of previous studies, frictional devices differently applied at their ends are presented to improve the response of the façade under the impact of a high-level explosion. Structural effects of various solutions are highlighted through dynamic simulations. Single vertical devices, if appropriately calibrated, allow reducing significantly the axial forces in cables, and lightly the tensile stresses in glass panes.
Polycyclic Aromatic Compounds, 2000
Page 1. Po/i,r.drc .Arumuric Compoimndr. 1999. Vol. 16. pp. 191-203 Reprints available dircctl) f... more Page 1. Po/i,r.drc .Arumuric Compoimndr. 1999. Vol. 16. pp. 191-203 Reprints available dircctl) from the publisher Photocopymp permitted b) license only C 1999 OPA (Overseas Publishers Asswiationj NV Published by license ...
Polycyclic Aromatic Compounds, 2008
Polycyclic Aromatic Compounds, 2004
The fjord-region PAH dibenzo[a,l]pyrene (DBP) is considerably more carcinogenic than the bay-regi... more The fjord-region PAH dibenzo[a,l]pyrene (DBP) is considerably more carcinogenic than the bay-region benzo[a]pyrene (BP). This fact can be ascribed to differences in DNA binding efficiency of their ultimate carcinogenic diol epoxide (DEs) intermediates, differences in structural features of the DNA adducts, and differences in DNA adduct recognition and the subsequent lesion removal by nucleotide excision repair (NER). In order to
Polycyclic Aromatic Compounds, 1996
In the present work we have used a DNA polymerase assay to investigate the primer extension with ... more In the present work we have used a DNA polymerase assay to investigate the primer extension with T7 DNA polymerase (Sequenase 2.0) and the Klenow fragment of Escherichia coli DNA polymerase I (exo KF) on chemically synthesized 21mer templates representing partial sequences of the human Ha-ras protooncogene with site-specifically positioned trans-N -dA adducts of (-)- (adduct 1) and (+)-anti-benzo[c]phenanthrene 3,4-dihydrodiol
Polycyclic Aromatic Compounds, 1996
Abstract Phenanthrene, benz[a]anthracene, chrysene, benzo[c]phenanthrene, and benzo[a]pyrene have... more Abstract Phenanthrene, benz[a]anthracene, chrysene, benzo[c]phenanthrene, and benzo[a]pyrene have been studied for their regiospecific oxidation by five human (1A1, 1A2, 2A6, 2E1, 3A4) and three rat (1A1, 1A2, 2B1) CYP isoforms. All substrates are preferentially metabolized by CYP1A1 and CYP1A2 in human and rat. Other isoforms play a minor role if at all. Significant differences between human and rat CYP isoforms can be recognized with regard to the regiospecific oxidation of PAH. For instance, K-region oxidation is more pronounced in rat than in human CYP1A1 and CYP1A2. Hence, extrapolation from metabolism studies in rodents to human may be limited.
Polycyclic Aromatic Compounds, 1996
ABSTRACT
Environmental Health Perspectives, 1990
Methylated polycyclic aromatic hydrocarbons are common in the human environment. Many of them are... more Methylated polycyclic aromatic hydrocarbons are common in the human environment. Many of them are stronger carcinogens than their purely aromatic congeners. They may be metabolized to benzylic alcohols. We report here on biochemical and toxicological characteristics of 1-hydroxymethylpyrene (HMP), a typical representative of this class of compounds. Rat liver cytosol, fortified with 3'-phosphoadenosine-5'-phosphosulfate, converted HMP into its sulfate ester (HMPS). HMPS bound covalently to isolated DNA. In physiological buffer at 370C, HMPS had a half-life of 2 min, the major decomposition product being HMP. Thus, cyclic activation is possible. When Cl-anions were present at physiological concentrations, an additional reaction product of HMPS, 1-chloromethylpyrene (CIMP), could be identified on the basis of its chromatographic properties and its mass spectrum, using the authentic standard for comparison. CIMP was shorter-lived in buffer than HMPS. CIMP reacted with DNA, the adduct pattern in the 32P-postlabeling analysis being similar, or identical, to that of HMPS. CIMP proved to be a very potent mutagen in Salmonella typhimurium, whereas HMPS, and HMP in the presence of a sulfateconjugating system, showed strong mutagenicity only when Cl-or Br-ions were present in the exposure buffer. It is concluded that HMPS is capable of reacting with DNA, but is hampered in its distribution by membrane barriers. Strikingly, a CIMP intermediate is produced, which can act as a transport form to overcome membrane barriers. Among 10 investigated tissues, HMP-activating sulfotransferases were found at appreciable levels only in the liver, and there the activity in parenchymal cells exceeded that in Kupffer cells by a factor of-200. Distribution processes and their restrictions may, therefore, be important factors determining the toxicology of benzylic alcohols and other compounds activated through conjugation with sulfate.
Environmental Health Perspectives, 1990
V79 cells, genetically engineered to express active cytochromes P450IIB1 and P450IA1, were used t... more V79 cells, genetically engineered to express active cytochromes P450IIB1 and P450IA1, were used to study the cytotoxicity and mutagenicity of cyclophosphamide and ifosfamide. Cyclophosphamide, tested up to a concentration of 2 mM, was not cytotoxic in V79 nor in the P450IA1-expressing V79-derived cell line XEM2. Pronounced cytotoxicity was, however, observed in the P450IIB1-expressing V79-derived cell line SDL. Induction of gene mutations (acquisition of 6-thioguanine resistance) was observed in SD1 cells as well, but the effects were weak. Ifosfamide was inactive in V79 cells, but was cytotoxic in SDl cells. Ifosfamide mustard, an active metabolite of ifosfamide, was equally cytotoxic and showed similar mutagenic effects in SDl and parental V79 cells. The results indicate that cyclophosphamide and ifosfamide are metabolically activated by cytochrome P4501IB1. In contrast, cytochrome P450IA1 was not capable of activating cyclophosphamide. Thus, V79-derived cell lines defined for their expression of a specific form of cytochrome P-450 can be used as diagnostic tools to identify the cytochrome P-450 that is responsible for the metabolic activation of drugs.
Environmental Health Perspectives, 1990
The ability of isolated rat liver endothelial and Kupffer cells to activate benzo(a)pyrene (BP), ... more The ability of isolated rat liver endothelial and Kupffer cells to activate benzo(a)pyrene (BP), trans-7,8-dihydroxy-7,8-dihydrobenzo(a)pyrene (DDBP), trans-1,2-dihydroxy-1,2-dihydrochrysene (DDCH), and aflatoxin B, (AFB%) to mutagenic metabolites was assessed by means of a cell-mediated bacterial mutagenicity assay and compared with the ability of parenchymal cells to activate these compounds. Endothelial and Kupffer cells from untreated rats were able to activate AFB, and DDBP; DDBP was activated even in the absence of an NADPH-generating system. Pretreating the animals with Aroclor 1254 strongly enhanced the mutagenicity of the dihydrodiol, whereas the mutagenicity of AFB, showed a slight increase. BP and DDCH were only activated by endothelial and Kupffer cells isolated from Aroclor 1254-pretreated rats. Parenchymal cells from untreated animals activated all four carcinogens tested; Aroclor 1254 enhanced the parenchymal cell-mediated mutagenicity of BP and DDCH but did not affect that of DDBP and clearly reduced that of AFB,. The reduced mutagenicity of AFB, correlates with the decrease in the amount of 2a-hydroxytestosterone formed when testosterone was incubated with parenchymal cell microsomes from Aroclor 1254-pretreated rats (compared with microsomes from untreated animals): the formation of 2a-hydroxytestosterone is specifically catalyzed by cytochrome P-450h, a hemoprotein thought to be involved in the activation of AFB,. These results show that not only rat liver parenchymal cells, but also endothelial and Kupffer cells, activate several carcinogens to mutagenic metabolites.
Chemico-Biological Interactions, 1991
Rat liver dihydrodiol dehydrogenase (DDH, E.C. 1.3.1.20) has recently been shown to oxidize the h... more Rat liver dihydrodiol dehydrogenase (DDH, E.C. 1.3.1.20) has recently been shown to oxidize the highly carcinogenic benz[a]anthracene-3,4-dihydrodiol in an NADP÷-dependent reaction to its corresponding catechol [22]. The present study is a systematic investigation of the substrate specificity of the purified enzyme towards synthetic trans-dihydrodiol metabolites of phenanthrene, benz[a]anthracene, chrysene, dibenz[a, hlanthracene and benzo[a]pyrene. DDH exhibited a remarkable regiospecificity of enzymatic catalysis with regard to the site of the dihydrodiol moiety of the parent hydrocarbon. M-region-and, with lower efficiency, bay-region dihydrodiols were found to be good substrates of the enzyme with maximal velocities between 20-80 nmol/min per mg enzyme and Km values in the micromolar range. K-region dihydrodiols were not accepted as substrates. Dihydrodiols situated at the terminal ring of an anthracene-type structure such as benz[a]anthracene-8,9-dihydrodiol as well as the corresponding dihydrodiol epoxides were also not oxidized by DDH at measurable rates. The results provide evidence for a detoxifying role of DDH in the metabolism of the chemical carcinogens benz[a]anthracene, chrysene and dibenz[a,h]anthracene.
Chemico-Biological Interactions, 2006
We were aimed at investigating the activation of the carcinogenic polycyclic aromatic hydrocarbon... more We were aimed at investigating the activation of the carcinogenic polycyclic aromatic hydrocarbon (PAH) dibenzo[a,l]pyrene (DB[a,l]P) in Chinese hamster V79 cells that express single human, rat or fish cytochrome P450 (CYP) enzymes. DB[a,l]P is detectable in environmental samples and has been characterized as the most potent carcinogenic species among all PAHs as yet tested in rodent bioassays. Metabolite profiles and metabolite-dependent cytotoxic and clastogenic activities were monitored. The total turnover of CYP-mediated transformation of DB[a,l]P was as follows: human CYP1B1 > fish CYP1A1 ≈ human CYP1A1 rat CYP1A2 > rat CYP1A1. By contrast, enzyme forms that are not classified as being members of family CYP1, such as CYP2A6, 2E1, 2B1, and 3A4, failed to catalyze any detectable conversion of this substrate. All CYP1A1 enzymes tested formed both the K-region trans-8,9-and the trans-11,12-dihydrodiol, whereas human CYP1B1 failed to catalyze K-region activation. In cells expressing human or fish CYP1A1, human CYP1B1, and rat CYP1A2, the (−)-trans-11,12-dihydrodiol was formed enantiospecifically. DB[a,l]Pdependent cytotoxicities (EC 50) were found in the following order: human CYP1A1 (12 nM) > fish CYP1A1 (30 nM) > human CYP1B1 (45 nM) other forms. In addition, an appreciable micronuclei formation was detected in human CYP1A1-and 1B1expressing cells during exposure to DB[a,l]P. Our study demonstrates that human CYP1A1, 1B1 and fish CYP1A1 are able to transform DB[a,l]P into genotoxic derivatives in appreciable amounts. In contrast, CYP enzymes from rat predominantly target the K-region of DB[a,l]P and thus are serving more a rather protective route of biotransformation. Together our data suggest that humans might be more susceptible to DB[a,l]P-induced carcinogenicity than rats.
Chemical Research in Toxicology, 1997
An understanding of the conformational behavior of the stereoisomeric tetrols at the 11,12,13,14-... more An understanding of the conformational behavior of the stereoisomeric tetrols at the 11,12,13,14-positions of dibenzo[a,l]pyrene (DB[a,l]P) is essential for the spectroscopic identification of DNA adducts derived from the biologically highly active fjord region syn-and anti-DB[a,l]P-11,12-diol 13,14-epoxides. Conformational effects are expected to play an important role in DNA-DB[a,l]P diol epoxide reactivity, base-sequence specificity, and conformation dependent repair. The results of conformational studies on trans-anti-, cis-anti-, and cis-syn-DB[a,l]P tetrol isomers are presented and compared to the results obtained previously for trans-syn-DB[a,l]P tetrol (Carcinogenesis 17, 829-837, 1996). Molecular mechanics, dynamical simulations, and semiempirical calculations of electronic transitions are used to interpret the low-temperature fluorescence spectra and 1 H NMR data. Molecular dynamics simulations (in vacuo) identified two conformers (I and II) for each of the tetrol isomers; in all conformations the aromatic ring system is severely distorted. Fluorescence line-narrowing (FLN) spectroscopy identified two distinct conformational species for the transanti isomer, one occurring in ethanol and the other occurring in a glycerol/water matrix. The corresponding structures are assigned based on the S 1 r S 0 transition energies calculated for conformers I and II, respectively. 1 H NMR spectroscopy confirmed the structure of conformer I at room temperature. In contrast to trans-syn-DB[a,l]P tetrol (where the major conformation was identified as a boat structure), both conformations of trans-anti-DB[a,l]P tetrol feature a half-chair structure for the cyclohexenyl ring with different orientations of the hydroxyl groups. For cis-anti-and cis-syn-DB[a,l]P tetrols, only a single conformer is detected by FLN spectroscopy. The NMR results for the latter appear to be most consistent with a mixture of two half-chair conformers I and II, while for the cis-anti isomer a flattened, boatlike conformation was observed. The generally good agreement between the NMR coupling constants and those estimated theoretically indicates that these structures should serve as good starting points for spectroscopic or computational studies of DNA adducts derived from DB[a,l]P diol epoxides.
Chemical Research in Toxicology, 1998
The nature of stable DNA adducts derived from the very potent carcinogen dibenzo[a,l]pyrene (DB[a... more The nature of stable DNA adducts derived from the very potent carcinogen dibenzo[a,l]pyrene (DB[a,l]P) in the presence of rat liver microsomes in vitro and in mouse skin in vivo has been studied using 32 P-postlabeling and laser-based fluorescence techniques. Analysis of DB[a,l]P-DNA adducts via 32 P-postlabeling has been obtained by comparison of the adduct patterns to those obtained from reactions of synthetic (()-anti-, (+)-anti-, (-)-anti-, and (()-syn-DB[a,l]P-11,12-diol 13,14-epoxide (DB[a,l]PDE) with single nucleotides and calf thymus DNA. anti-DB[a,l]PDE-dA adducts derived from the (-)-enantiomer are the major adducts formed in calf thymus DNA and in mouse skin DNA. The ratio of deoxyadenosine to deoxyguanosine modification is approximately 2:1 in mouse skin exposed to DB[a,l]P; activation by rat liver microsomes leads to a similar profile of adducts but with two additional spots. The conformations of DB[a,l]P adducts in native DNA, as well as the possibility of conformationdependent repair, have been explored by low-temperature fluorescence spectroscopy. These studies have been performed using polynucleotides and calf thymus DNA reacted in vitro with DB[a,l]PDE and native DNA from mouse epidermis exposed to DB[a,l]P. The results show that adducts are heterogeneous, possess different structures, and adopt different conformations. External, external but base-stacked and intercalated adduct conformations are observed in calf thymus DNA and in mouse skin DNA samples. Differences in adduct repair rates are also revealed; namely, the analysis of mouse skin DNA samples obtained at 24 and 48 h after exposure to DB[a,l]P clearly shows that external adducts are repaired more efficiently than intercalated adducts. These results, taken together with those for B[a]P-DNA adducts [Suh et al. (1995) Carcinogenesis 16, 2561-2569], indicate that the repair of DNA damage resulting from PAH diol epoxides is conformation-dependent.
Chemical Research in Toxicology, 1999
Dibenzo[a,l]pyrene-11,12-dihydrodiol 13,14-epoxide {(()-anti-DB[a,l]PDE} was reacted with deoxygu... more Dibenzo[a,l]pyrene-11,12-dihydrodiol 13,14-epoxide {(()-anti-DB[a,l]PDE} was reacted with deoxyguanosine (dG) in dimethylformamide at 100°C for 30 min, and two sets of adducts were isolated: a mixture of (()-anti-cis-&-trans-N 2 dG (43%) and a mixture of (()anti-cis-&-trans-N7Gua (45%). Both are mixtures of four stereoisomers that cannot be separated by HPLC. Similarly, (()-syn-DB[a,l]PDE was reacted with dG under the same conditions, and (()-syn-cis-&-trans-N 2 dG (38%) and (()-syn-cis-&-trans-N7Gua (59%) were obtained. The structures of the adducts were determined by a combination of NMR and fast atom bombardment mass spectrometry. By reacting (-)-anti-DB[a,l]PDE or (+)-syn-DB[a,l]-PDE with dG under the same conditions, however, optically pure N 2 dG and N7Gua isomers were obtained: (-)-anti-cis-N 2 dG (12%), (-)-anti-trans-N 2 dG (17%), (-)-anti-trans-N7Gua (43%), (+)-syn-cis-N 2 dG (7%), (+)-syn-trans-N 2 dG (3%), (+)-syn-cis-N7Gua (36%), and (+)-syntrans-N7Gua (22%). The structures of the optically pure adducts were assigned by NMR. synand anti-DB[a,l]PDE-N 2 dG adducts can be distinguished by fluorescence line-narrowing spectroscopy (FLNS). Moreover, distinction between cis-and trans-stereochemistry of the adducts is also straightforward by FLNS, because the FLN spectra for the four DB[a,l]PDE-N 2 dG adducts, anti-cis, anti-trans, syn-cis, and syn-trans, are spectroscopically unique.