Biomedical subjects

A Seidel

Publications and source records attributed to A Seidel.

At least 19 recordsLinked to original sources

PubMed2006

Modified nucleosides: an accurate tumour marker for clinical diagnosis of cancer, early detection and therapy control.

Modified nucleosides, regarded as indicators for the whole-body turnover of RNAs, are excreted in abnormal amounts in the urine of patients with malignancies. To test their usefulness as tumour markers and to compare them with the conventional tumour markers, fractionated urine samples were analysed using chromatography. The excretion patterns of nucleosides of 68 cancer patients with malignant and benign tumours and 41 healthy controls have been studied. Significant elevations in the total sum and the concentrations of at least three (or four) of indicator nucleosides cytidine, pseudouridine, 2-pyridone-5-carboxamide-N1-ribofuranoside, N2,N2-dimethylguanine, 1-methylguanosine, 2-methylguanosine and 1-methyladenosine indicate a tumour with a sensitivity of 54% (77%) and a specificity of 86% (98%). Using an artificial neural network analysis, a sensitivity of 97% and a specificity of 85% were achieved in differentiating between tumour and control volunteers. The comparison with carcinoembryonic antigen, cancer antigen 15-3 und tissue polypeptide antigen indicates that urinary nucleosides may be useful tumour markers. This study suggests that the simultaneous determination of modified nucleosides and creatinine in urine samples of patients with cancer leads to an advantage to current methods and is a useful method to detect cancer early and to control the success of therapy.

Adult↗

PubMed2005

Genotoxic risk assessment in white blood cells of occupationally exposed workers before and after alteration of the polycyclic aromatic hydrocarbon (PAH) profile in the production material: comparison with PAH air and urinary metabolite levels.

OBJECTIVE: Workers in various industries can be exposed to polycyclic aromatic hydrocarbons (PAHs). The relationship between biomarkers of genotoxic risk, PAH compounds in air (ambient monitoring) and PAH metabolites in urine (internal exposure) were studied in 17 workers exposed to PAHs in a fireproof-material producing plant before and 3 months after the PAH profile was altered in the binding pitch. METHODS: Two biomarkers of exposure, specific DNA adducts of (+/-)-r-7,t-8-dihydroxy-t-9,10-oxy-7,8,9,10-tetrahydrobenzo[a]pyrene (anti-BPDE) and non-specific DNA adduct of 8-oxo-7,8-dihydro-2'-deoxyguanosine (8-oxodGuo) were determined in white blood cells (WBCs). In addition, DNA strand breaks were analysed in lymphocytes by single-cell gel electrophoresis in a genotoxic risk assessment. Sixteen PAH compounds in air were determined by personal air sampling, and hydroxylated metabolites of phenanthrene, pyrene and naphthalene were determined in urine. RESULTS: After substitution of the binding pitch the concentrations of benzo[a]pyrene in air decreased (P<0.01). No changes could be observed for pyrene, while levels of phenanthrene (P=0.0013) and naphthalene (P=0.0346) in air increased. Consequently, median DNA adduct rates of anti-BPDE decreased after alteration of the production material (from 0.9 to <0.5 adducts/10(8) nucleotides). No changes in the excretion of 1-hydroxypyrene in urine could be determined, whereas increased levels of 1-, 2+9-, 3- and 4-hydroxyphenanthrene (P<0.0001) and 1-naphthol and 2-naphthol (P=0.0072) were found in urine. In addition, a statistically significant increase in DNA strand break frequencies (P<0.01) and elevated 8-oxodGuo adduct levels (P=0.7819, not statistically significant) were found in the WBCs of exposed workers 3 months after the PAH profile in the binding pitch had been altered. CONCLUSION: The results presented here show that the increased concentration of naphthalene and/or phenanthrene in the air at the work place could induce the formation of DNA strand breaks and alkali-labile sites in WBCs of exposed workers.

Adult↗

PubMed2005

The Influence of long-chain polyunsaturated fatty acids on total lipid fatty acid composition of a canine mastocytoma cell line.

Cutaneous mast cells are considered as key immune effectors in the pathogenesis of canine atopic dermatitis (CAD). These cells release immediate-phase and late-phase mediators of inflammation. Dietary fatty acids are incorporated in cellular membranes and seem to influence mediator production and release. A dietary intervention with n6- and n3-fatty acids is thought to alleviate clinical symptoms in atopic dogs. The purpose of this study was to examine the effects of n6- and n3-fatty acids on the fatty acid composition of canine mastocytoma cells (C2) as a possible model for CAD. The C2 was cultured in a basic medium called Dulbecco's modified Eagle's medium (DEH) or with additional 14 mum linoleate (C18:2n6, DEH-LA), gamma-linolenate (C18:3n6, DEH-GLA), arachidonate (C20:4n6, DEH-AA), alpha-linolenate (C18:3n3, DEH-LnA), eicosapentaenoate (C20:5n3, DEH-EPA) or docosahexaenoate (C22:6n3, DEH-DHA). Cell growth was examined for 11 days in all media. Cell growth increased from days 1 to 8 and decreased thereafter in all media conditions. The fatty acids supplied did not influence cell growth. The cells were harvested after 8 days for fatty acid analysis. The fatty acid composition was determined by gas chromatography after extraction and trans-esterification of the lipids. The added fatty acids increased the concentration of these fatty acids in C2 differently (LA 4.9-fold, GLA 6.9-fold, AA 6-fold, LNA 9.3-fold, EPA 6.5-fold and DHA 8.4-fold). Furthermore, elongated and Delta6-desaturated products of the corresponding fatty acids were significantly elevated. However, Delta5-desaturated products were not measurable. These results let us assume that C2 has no measurable activity of the Delta5-desaturase. In case the low activity of Delta5-desaturase is one of the mechanisms underlying the pathogenesis of CAD, C2 seems to be an adequate model for investigations in CAD.

Animals↗

PubMed2004

Induction of gene expression of xenobiotic metabolism enzymes and ABC-transport proteins by PAH and a reconstituted PAH mixture in human Caco-2 cells.

It was shown recently that in epithelial Caco-2 cells the food contaminant benzo[a]pyrene (B[a]P) is metabolized and B[a]P-sulfate metabolites were transported out of the cells. The aim of this study was to investigate whether B[a]P and other polycyclic aromatic hydrocarbons (PAH) such as chrysene, phenanthrene, benzo[k]fluoranthene (B[k]F), dibenzo[a,l]pyrene (DB[a,l]P), and pyrene alone or in a mixture in a ratio as they occur in tobacco smoke have effects on gene expression of intestinal cytochrome P450 enzymes (CYP), Phase II enzymes and ATP-binding cassette (ABC)-transport proteins in the human Caco-2 cells. B[a]P induced its own metabolism. Treatment of the Caco-2 cells with B[a]P, chrysene, B[k]F, or DB[a,l]P induced mRNA expression of CYP1A1 and CYP1B1 specifically as measured by RT-PCR. In contrast, the mRNA expression of the microsomal epoxide hydrolase (mEH) was not affected by PAH. The gene expression of the Phase II enzymes UDP-glucuronosyltransferase 1A6 (UGT1A6) and UGT1A7 was also induced by these PAH but treatment with them had no effect on gene expression of sulfotransferases (SULT) at all. Of the ABC-transport proteins, MDR1 mRNA expression was induced by treatment with carcinogenic PAH, whereas MRP2 mRNA expression was not changed. The mixture of PAH also induced CYP1A1, CYP1B1, UGT1A6, and UGT1A7 mRNA expression. We conclude that B[a]P, chrysene, B[k]F, and DB[a,l]P have specific effects on intestinal CYP1A1, CYP1B1, UGT1A6, and UDP1A7 mRNA expression but no effects on the expression of SULT.

ATP-Binding Cassette Transporters↗

PubMed2004

Consequences of eicosapentaenoic acid (n-3) and arachidonic acid (n-6) supplementation on mast cell mediators.

Mast cells are important players in the pathogenesis of atopic diseases. These cells release immediate-phase and late-phase mediators of inflammation. Fatty acids are incorporated in cellular membranes and therefore seem to influence mediator production and release. A study was conducted to assess the effects of eicosapentaenoic acid (EPA, 20:5n-3) and arachidonic acid (AA, 20:4n-6) on mast cell mediators in a canine mastocytoma cell line (C2). Cells were cultured in a basic medium (Dulbecco's modified Eagle's medium/HAM's F12 1 : 1, DEH), DEH supplemented with 14.0 microm EPA (DEH-EPA) or 14 microm AA (DEH-AA). The DEH-AA cultured cells had increased spontaneous and mastoparan-stimulated PGE2 production and histamine release. Furthermore, the tryptase activity was increased. The DEH-EPA cultured cells rendered elevated levels of PGE2 and histamine release compared with DEH only after stimulation. These levels were significantly lower in comparison to DEH-AA. The increased PGE2 production of C2 cultured in DEH-AA is the consequence of the AA enrichment, because AA is the precursor of PGE2. However, the different effects by AA and EPA on mast cell mediators possibly reflect the higher susceptibility of long chain polyunsaturated fatty acids (PUFA) to undergo lipid peroxidation, because it is known that altered cellular redox state influences mediator production and release.

Animals↗

PubMed2003

Effects of essential fatty acids on mediators of mast cells in culture.

The objective of this study was to investigate the effects of alpha-linolenic acid (18:3n-3) and linoleic acid (18:2n-6) on the fatty acid composition and the activity and release of mast cell mediators in the canine mastocytoma cell line C2. Cells were cultured in Dulbecco's modified Eagle's medium mixed with 50% Ham's F12 (containing linoleic acid 0.14 micro M). The basic medium (DEH) was supplemented with 0.14 micro M alpha-linolenic acid. 14.0 micro M alpha-linolenic acid (DEH-n-3) or 14.0 micro M linoleic acid (DEH-n-6) was added. Eight days after culturing of C2 in DEH-n-3 we measured elevated levels of n-3 fatty acids up to 22:3. The tryptase activity and the stimulated PGE2 production and histamine release were reduced. In contrast, after culturing of C2 in DEH-n-6 we determined elevated levels of n-6 fatty acids up to 20:3, increased tryptase activity and stimulated histamine release. Thus 18:3n-3 has anti-inflammatory effects in cultured canine mastocytoma cells.

Animals↗

PubMed2001

Occupational hand dermatitis in food industry apprentices: results of a 3-year follow-up cohort study.

OBJECTIVE: The aim of this prospective follow-up study was to quantify the impact of hand dermatitis (HD) in bakers, confectioners and bakery shop assistants, and to investigate related risk factors. METHOD: Bakers', confectioners' and bakery-shop assistants were included in a prospective follow-up study in the region of East Thuringia starting in August 1996. At the beginning of their vocational training 91 apprentices were interviewed and examined in a standardised way. Follow-up examinations and interviews were done after 6 months (n = 79), 12 months (n = 63) and at the end of the training (n = 69) after 36 months. RESULTS: In their case histories 3.3% (n = 3) of the apprentices reported previous HD in childhood and adolescence. The first assessment after 2 to 4 weeks of vocational training revealed HD in 17.5% (n = 16) of the individuals. At the follow-up examination after 6 months, point prevalence of HD was 29.1% (n = 23), after 12 months 27.0% (n = 17) and after 36 months 27.5% (n = 19). Mild to moderate irritant contact dermatitis was the most frequent finding. Finally, an atopic skin diathesis (> 10 points, "atopy score") (OR = 4.89; CI 95% 1.15-20.79), previous HD (OR = 41.1; CI 95% 4.99-339.13) as well as flexural dermatitis (OR = 6.8; CI 95% 1.72-27.22) proved to be predictive factors for the development of HD. No association was found to respiratory atopy (OR = 1.29; CI 95% 0.35-4.7) and metal sensitisation (OR = 1.1; CI 95% 0.29-4.35). Exogenous irritant factors did not show a strong association towards a risk increase. Wet work in general, as well as distinct occupational tasks showed only a tendency for being a risk factor for HD. However, leisure time activities, especially house building and rebuilding (OR = 5.4; CI 95% 1.05-27.81), were associated with an elevated risk. CONCLUSIONS: Endogenous and exogenous factors contribute to the development of HD in bakers' and confectioners' apprentices.

Adolescent↗

PubMed2001

Effects of the (-)-anti-11R,12S-dihydrodiol 13S,14R-epoxide of dibenzo.

The tumor suppressor protein p53 plays an important role in recognition of DNA damage and induction of subsequent cell cycle arrest. One of its target genes encodes the protein p21(WAF1), which is involved in mediation of growth arrest after DNA damage has occurred. Dibenzo[a,l]pyrene (DB[a,l]P) is a polycyclic aromatic hydrocarbon which is an exceptionally potent carcinogen. A reactive secondary metabolite of DB[a,l]P, the fjord region (-)-anti-11R,12S-dihydrodiol 13R,14S-epoxide [(-)-anti-DB[a,l]PDE] was used to investigate DNA damage via adduct formation and cell cycle arrest in human diploid fibroblast cell cultures (HDF). Synchronous HDF were exposed to increasing concentrations (0.014, 0.028 and 0.07 microM) of (-)-anti-DB[a,l]PDE and at 1, 12, 24 and 42 h after treatment cell pellets were analyzed for DNA adduct formation and cell cycle arrest. Exposure of HDF to 0.07 microM (-)-anti-DB[a,l]PDE caused a total DNA binding level of 113 pmol adducts/mg DNA (42 h after treatment). G(1) arrest was induced by this treatment, with 91% of the cells remaining in G(1) phase compared with the solvent-treated control cultures (50%) as analyzed by propidium iodide staining and flow cytometry. Further investigation of the percentage of cells in S phase by 5-bromo-2'-deoxyuridine incorporation confirmed the G(1) arrest in HDF treated with 0.07 microM (-)-anti-DB[a,l]PDE, with only 1.5% of the cells moving into S phase compared with 39% in the control 42 h after treatment. Induction of p53 and p21(WAF1) was demonstrated by western blot analysis.

Benzopyrenes↗

PubMed2001

First pass annotation of promoters on human chromosome 22.

The publication of the first almost complete sequence of a human chromosome (chromosome 22) is a major milestone in human genomics. Together with the sequence, an excellent annotation of genes was published which certainly will serve as an information resource for numerous future projects. We noted that the annotation did not cover regulatory regions; in particular, no promoter annotation has been provided. Here we present an analysis of the complete published chromosome 22 sequence for promoters. A recent breakthrough in specific in silico prediction of promoter regions enabled us to attempt large-scale prediction of promoter regions on chromosome 22. Scanning of sequence databases revealed only 20 experimentally verified promoters, of which 10 were correctly predicted by our approach. Nearly 40% of our 465 predicted promoter regions are supported by the currently available gene annotation. Promoter finding also provides a biologically meaningful method for "chromosomal scaffolding", by which long genomic sequences can be divided into segments starting with a gene. As one example, the combination of promoter region prediction with exon/intron structure predictions greatly enhances the specificity of de novo gene finding. The present study demonstrates that it is possible to identify promoters in silico on the chromosomal level with sufficient reliability for experimental planning and indicates that a wealth of information about regulatory regions can be extracted from current large-scale (megabase) sequencing projects. Results are available on-line at http://genomatix.gsf.de/chr22/.

Algorithms↗

PubMed2000

Contribution to the Determination of Kinetic Parameters of the Sol-Gel Transformation by Rheological Measurements.

The system tetraethoxysilane(TEOS)-water-ethanol has been studied by rheological measurements. Different molar ratios of TEOS : water (1 : 4, 1 : 10, and 1 : 20) are studied at different temperatures (30, 40, and 50 degrees C). The dynamic viscosity (rotating mode) at a constant shear rate (100 s(-1)) and the elastic and viscous moduli (oscillating mode) at a constant frequency (1 Hz) are determined. The viscosity-time curves are evaluated by application of a nucleation and particle growth model. Good agreement between experiments and theory is observed. The model allows the determination of the complex rate constant of silica precipitation. The temperature-dependent measurements gave the possibility to determine the apparent energy of activation by common methods. The results are in agreement with data from the literature. The gel time defined as intersection point of elastic and plastic moduli and its dependence on temperature are evaluated by the Smoluchowski model. The energy of activation for the coagulation was determined and found to be in the correct order of magnitude. Copyright 2000 Academic Press.

Journal Article↗

PubMed2000

New and highly efficient synthesis of cis- and trans-opened Benzo[a]pyrene 7,8-diol 9,10-epoxide adducts at the exocyclic N(2)-amino group of deoxyguanosine.

We describe a new and facile method for the synthesis of both cis- and trans-opened N(2)-deoxyguanosine (dG) adducts of (+/-)-7alpha, 8beta-dihydoxy-9beta,10beta-epoxy-7,8,9,10-tetra hydrobenzo[a]pyrene and (+/-)-7alpha,8beta-dihydoxy-9alpha,10alpha -epoxy-7,8,9, 10-tetrahydrobenzo[a]pyrene at C-10. The key step in our approach is the direct coupling of O(6)-allyl-3', 5'-di-O-(tert-butyldimethylsilyl)-2'-deoxyguanosine with these epoxides followed by the separation of the mixtures of cis- and trans-diastereomers produced. Overall coupling yields ranged from 45 to 65%. Stereochemistry of addition of the N(2)-exocyclic amino group of dG (cis-trans, approximately 1:1) was assigned by NMR, and the absolute configuration of the dG adducts was unequivocally assigned by CD spectroscopy after separation of each individual diastereomer and cleavage of the allyl protecting group. A strong CD band at 279 nm in the O(6)-protected adduct was found to be diagnostic for configuration at C-10, with a negative band correlating with 10R configuration. The synthetic methodology described allows easy access to cis- and trans-opened N(2)-dG adducts which are valuable building blocks for the synthesis of adduct-containing oligonucleotides for physical and biochemical studies.

7,8-Dihydro-7,8-dihydroxybenzo(a)pyrene 9,10-oxide↗

PubMed2000

Unrepaired fjord region polycyclic aromatic hydrocarbon-DNA adducts in ras codon 61 mutational hot spots.

The fjord region diol-epoxide metabolites of polycyclic aromatic hydrocarbons display stronger tumorigenic activities in rodent studies than comparable bay region diol-epoxides, but the molecular basis for this difference between fjord and bay region derivatives is not understood. Here we tested whether the variable effects of these genotoxic metabolites of polycyclic aromatic hydrocarbons may result from different DNA repair reactions. In particular, we compared the repairability of DNA adducts formed by bay region benzo[a]pyrene (B[a]P) diol-epoxides and the structurally similar but significantly more tumorigenic fjord region diol-epoxide metabolites of benzo[c]phenanthrene (B[c]Ph). For that purpose, we incorporated both types of polycyclic aromatic hydrocarbon adducts into known hot spot sites for carcinogen-induced proto-oncogene activation. Synthetic DNA substrates were assembled using a portion of human N-ras or H-ras that includes codon 61, and stereospecific B[a]P or B[c]Ph adducts were synthesized on adenine N6 at the second position of these two ras codon 61 sequences. DNA repair was determined by incubating the site-directed substrates in human cell extracts, followed by electrophoretic visualization of radiolabeled oligonucleotide excision products. These cell-free assays showed that all tested bay region B[a]P-N6-dA adducts are removed by the human nucleotide excision repair system, although excision efficiency varied with the particular stereochemical configuration of each B[a]P residue. In contrast, all fjord region B[c]Ph-N6-dA adducts located in the identical sequence context and with exactly the same stereochemical properties as the corresponding B[a]P lesions were refractory to the nucleotide excision repair process. These findings indicate that the exceptional tumorigenic potency of B[c]Ph or related fjord region diol-epoxides may be attributed, at least in part, to slow repair of the stable base adducts deriving from the reaction of these compounds with DNA.

Adenine↗

PubMed2000

Detection of carcinogenic aromatic amines in the urine of non-smokers.

Smoking is thought to be one of the most important anthropogenic risk factors involved in the development of urinary bladder cancer in humans. Tobacco smoke contains a complex mixture of chemicals including potent carcinogens such as aromatic amines. In the present study the amounts of several freebase aromatic amines including the potent carcinogens 2-aminonaphthalene and 4-aminobiphenyl have been analyzed in the urine of 48 German urban living smokers and non-smokers. The results indicate that (i) both groups excrete the identical set of four aromatic amines; (ii) smokers excrete approximately twice the total amount of these amines, but similar amounts of 2-aminonaphthalene and 4-aminobiphenyl are found in non-smokers; and (iii) the excreted aromatic amines are decomposed in the urine within a few hours thus, explaining why aromatic amines are difficult to detect in this matrix. Their decomposition could be prevented by adding small amounts of p-toluidine to the freshly collected urine. Unlike smokers the origin of aromatic amines detected in the urine of non-smokers is at present unknown. Based on the cotinine levels found in the urine of non-smokers environmental tobacco smoke can be excluded as a major source of aromatic amines. In addition, neither diesel exhaust-related nitroarenes nor the corresponding amino-derivatives, to which they may be metabolically converted, were found. The detected urinary levels of aromatic amines arising from sources other than tobacco smoke or diesel exhaust may play a role in the bladder cancer etiology of non-smokers.

2-Naphthylamine↗

PubMed2000

Formation of stable DNA adducts and apurinic sites upon metabolic activation of bay and fjord region polycyclic aromatic hydrocarbons in human cell cultures.

Carcinogenic polycyclic aromatic hydrocarbons (PAH), such as benzo[a]pyrene (B[a]P), 7,12-dimethylbenz[a]anthracene (DMBA), and dibenzo[a,l]pyrene (DB[a,l]P), are metabolically activated to electrophilically reactive bay or fjord region diol epoxides that bind to the exocyclic amino groups of purine bases in DNA to form stable adducts. In addition, it has been reported that these PAH can be enzymatically oxidized to yield radical cations that form apurinic (AP) sites in DNA via depurinating adducts. The formation of stable adducts and AP sites in DNA of human cells exposed to PAH was examined in cytochrome P450 (P450)-expressing mammary carcinoma MCF-7 cells and in leukemia HL-60 cells, which display a high peroxidase but no P450-mediated activity, after exposure to these PAH. Stable DNA adducts were assessed by (33)P-postlabeling/HPLC analysis, and the induction of AP sites in DNA was analyzed by an aldehyde reactive probe (ARP) and a slot blot method. After exposure for 4 h, the levels of stable DNA adducts were comparable in MCF-7 cells treated with B[a]P and DMBA, but significantly lower than those observed in MCF-7 cells treated with the stronger carcinogen DB[a,l]P. While the levels of stable adducts increased more than 10-fold (B[a]P and DMBA) or 100-fold (DB[a,l]P) after exposure for 24 h, the levels of AP sites remained low after both treatment periods. Thus, the levels of stable adducts were approximately 5-fold higher than the levels of AP sites after treatment with B[a]P or DMBA and more than 100-fold higher in cells exposed to DB[a,l]P for 24 h. None of these carcinogenic PAH formed detectable levels of stable DNA adducts or AP sites in HL-60 cells. The results demonstrate that metabolic activation of B[a]P, DMBA, and DB[a,l]P is catalyzed by P450 enzymes leading to diol epoxides that form predominantly stable DNA adducts but only low levels of AP sites.

9,10-Dimethyl-1,2-benzanthracene↗

PubMed2000

Polymorphisms in P450 CYP1B1 affect the conversion of estradiol to the potentially carcinogenic metabolite 4-hydroxyestradiol.

Most drug metabolizing cytochrome P450s (P450) are predominantly expressed in the liver. In contrast, human CYP1B1 is an extrahepatic P450 which is overexpressed in many tumours and has been strongly implicated in the activation of carcinogens. Rare allelic variants of the CYP1B1 gene which encode an inactive protein have been identified. However, four polymorphisms which most likely do not abolish functionality have been described. In this report, we have characterized the functional consequences of these. A CYP1B1 cDNA, identical to a cDNA published previously, served as a template to introduce allelic changes either separately or in combination. The resulting effects on CYP1B1 activity were determined in membranes isolated from Escherichia coli which coexpressed CYP1B1 together with P450 reductase. None of the allelic changes affected the CYP1B1 expression level. The allelic changes Arg48 to Gly, Ala19 to Ser and Asn453 to Ser had little influence on the Vmax and the Km of the CYP1B1 mediated 2- and 4-hydroxylation of estradiol. In contrast, the Km of these metabolic pathways was increased at least three-fold by the allelic change Va432 to Leu or by simultaneously changing Val432 to Leu and Asn453 to Ser. However, these alterations had little effect on the kinetic parameters of other CYP1B1 mediated reactions such as the epoxidation of (-)-trans-(7R,8R)-benzo[a]pyrene 7,8-dihydrodiol as determined by (r-7,t-8,t-9,c-10)-benzo[a]pyrene tetraol formation, or such as the O-dealkylation of ethoxyresorufin and the 1'-hydroxylation of bufuralol. Molecular modelling suggests that amino acid residue 432 of CYP1B1 may be involved in the interaction between CYP1B1 and P450 reductase. Since 4-hydroxyestradiol has been implicated in hormonal carcinogenesis and CYP1B1 is expressed in target tissues, the data presented demonstrate that polymorphisms in CYP1B1 have the potential to affect disease susceptibility.

Alleles↗

PubMed1999

The K-region trans-8,9-diol does not significantly contribute as an intermediate in the metabolic activation of dibenzo[a,l]pyrene to DNA-binding metabolites by human cytochrome P450 1A1 or 1B1.

Metabolic activation of the K-region trans-8,9-diol of the highly carcinogenic hexacyclic aromatic hydrocarbon dibenzo[a,l]pyrene (DB[a,l]P) by human cytochrome P-450 (P450) 1A1 and 1B1 was investigated in Chinese hamster V79 cell lines expressing human P450 1A1 or 1B1. P450 1A1 and 1B1 are the major P450s involved in metabolic activation of polycyclic aromatic hydrocarbons in human cells. The major DNA adducts formed by metabolism of DB[a,l]P in cultures expressing P450 1A1 or 1B1 resulted mainly from the fjord region (-)-anti-DB[a,l]P-11,12-diol 13,14-epoxide [(-)-anti-DB[a,l]PDE] and, to a lesser extent, (+)-syn-DB[a,l]PDE. In V79 cells expressing human P450 1A1, high amounts of as yet unidentified highly polar DNA adducts are formed in addition to the DNA adducts derived from DB[a,l]PDEs. Human P450 1A1 has been found to metabolize DB[a,l]P on its K-region to the trans-8,9-diol, and it has been proposed that the DNA binding of the parent compound in P450 1A1-expressing tissues may be partially mediated by activation of the K-region trans-8,9-diol to form bis-diol epoxides. V79 cells expressing human P450 1A1 or 1B1 formed only low amounts of DNA adducts after treatment with high doses of the K-region trans-8,9-diol. None of the adducts formed were identical to the main adducts formed in the same cell lines by metabolic activation of DB[a,l]P or (-)-DB[a,l]P-trans-11,12-diol. These results demonstrate that the K-region trans-8,9-diol does not significantly contribute to the genotoxicity of the very potent carcinogen DB[a,l]P in human cells or tissues expressing P450 1A1 or 1B1.

Animals↗

PubMed1999

Comparison of cytochrome P450- and peroxidase-dependent metabolic activation of the potent carcinogen dibenzo[a,l]pyrene in human cell lines: formation of stable DNA adducts and absence of a detectable increase in apurinic sites.

The potent carcinogen dibenzo[a,l]pyrene (DB[a,l]P) has been reported to form both stable and depurinating DNA adducts upon activation by cytochrome P450 enzymes and/or cellular peroxidases. Only stable DB[a,l]P-DNA adducts were detected in DNA after reaction of DB[a,I]P-11,12-diol-13,14-epoxides in solution or cells in culture. To determine whether DB[a,l]P can be activated to metabolites that form depurinating adducts in cells with either high peroxidase (human leukemia HL-60 cell line) or cytochrome P450 activity (human mammary carcinoma MCF-7 cell line), cultures were treated with DB[a,l]P for 4 h, and the levels of stable adducts and apurinic (AP) sites in the DNA were determined. DNA samples from DB[a,l]P-treated HL-60 cells contained no detectable levels of either stable adducts or AP sites. MCF-7 cells exposed to 2 microM DB[a,l]P for 4 h contained 4 stable adducts per 10(6) nucleotides, but no detectable increase in AP sites. The results indicate that metabolic activation of DB[a,l]P by cytochrome P450 enzymes to diol epoxides that form stable DNA adducts, rather than one-electron oxidation catalyzed either by cytochrome P450 enzymes or peroxidases to form AP sites, is responsible for the high carcinogenic activity of DB[a,l]P.

Apurinic Acid↗

PubMed1999

Mono- and Diglucuronide formation from benzo[a]pyrene and chrysene diphenols by AHH-1 cell-expressed UDP-glucuronosyltransferase UGT1A7.

Polycyclic aromatic hydrocarbon (PAH)-type compounds induce at least two rat UDP-glucuronosyltransferase isoforms, UGT1A6 and UGT1A7. Among the glucuronidation reactions of PAH metabolites studied, mono- and diglucuronide formation of benzo[a]pyrene and chrysene-3,6-diphenol showed the highest induction factors in rat liver microsomes. Availability of AHH-1 cells stably expressing UGT1A7 allowed us to study whether this PAH-inducible isoform could catalyze benzo[a]pyrene and chrysene-3,6-diphenol glucuronidation. It was found that UGT1A7 indeed catalyzed mono- and diglucuronide formation of both benzo[a]pyrene and chrysene 3,6-diphenols. V79 cell-expressed rat UGT1A6 also catalyzed these reactions, except for chrysene diphenol diglucronide formation (Bock et al., Mol Pharmacol 42: 613-618, 1992). Enzyme kinetic studies of the glucuronidation of 6-hydroxychrysene (used as a stable PAH phenol) indicated that UGT1A7 conjugated this compound with a lower apparent Km value (0.1 microM) than UGT1A6 (10 microM). The results suggest that the two PAH-inducible UGTs may cooperate in conjugating PAH metabolites, but that UGT1A7 is more efficient.

Benzo(a)pyrene↗