Double base lesions of DNA by a metabolite of carcinogenic benzo[a]pyrene.

Carcinogenic benzo[a]pyrene (BP) is generally considered to show genotoxicity by forming DNA adducts of its metabolite, BP-7,8-diol-9,10-epoxide. We investigated oxidative DNA damage and its sequence specificity induced by BP-7,8-dione, another metabolite of BP, using (32)P-5'-end-labeled DNA. Formamidopyrimidine-DNA glycosylase treatment induced cleavage sites mainly at G residues of 5'-TG-3' sequence and at poly(C) sequences, in DNA incubated with BP-7,8-dione in the presence of NADH and Cu(II), whereas piperidine treatment induced cleavage sites at T mainly of 5'-TG-3'. BP-7,8-dione strongly damaged the G and C of the ACG sequence complementary to codon 273 of the p53 gene. Catalase and a Cu(I)-specific chelator attenuated the DNA damage, indicating the involvement of H(2)O(2) and Cu(I). BP-7,8-dione with NADH and Cu(II) also increased 8-oxo-7,8-dihydro-2'-deoxyguanosine formation. We conclude that oxidative DNA damage, especially double base lesions, may participate in the expression of carcinogenicity of BP in addition to DNA adduct formation.     

Identification and quantitation of benzo[a]pyrene-derived DNA adducts formed at low adduction level in mice lung tissue

The two major metabolic pathways of benzo[a]pyrene (BP) that lead to DNA lesions are monooxygenation that results in diolepoxides (BPDE) and one-electron oxidation that yields a BP radical cation. These pathways result in formation of stable and depurinating DNA adducts, respectively. Most in vivo animal studies with BP, however, have employed dosage/DNA adduct levels several orders of magnitude higher than the DNA damage level expected from environmentally relevant exposures. Presented are results of experiments in which A/J strain mice were intraperitoneally exposed to 50-microg/g doses of BP. It is shown that non-line-narrowed fluorescence and fluorescence line-narrowing spectroscopies possess the selectivity and sensitivity to distinguish between helix-external, base-stacked, and intercalated conformations of DNA-BPDE adducts formed in lung tissue. Concentrations measured by 32P postlabeling 2 and 3 days after intraperitoneal injection were 420-430 and 600-830 amol BPDE-type adducts per microg DNA. The external and base-stacked conformations are attributed mainly to (+)-trans-anti-BPDE-N2dG and the intercalated conformations to (+)-cis-anti adducts. A stable adduct derived from 9-OH-BP-4,5-epoxide was also detected at a concentration about a factor of 10 lower than the above concentrations. The DNA supernatants were analyzed for the presence of depurinating BP-derived adducts by capillary electrophoresis laser-induced fluorescence and high-performance liquid chromatography mass spectrometry.     

Extending the understanding of mutagenicity: structural insights into primer-extension past a benzo[a]pyrene diol epoxide-DNA adduct

DNA polymerase enzymes employ a number of innate fidelity mechanisms to ensure the faithful replication of the genome. However, when confronted with DNA damage, their fidelity mechanisms can be evaded, resulting in a mutation that may contribute to the carcinogenic process. The environmental carcinogen benzo[a]pyrene is metabolically activated to reactive intermediates, including the tumorigenic (+)-anti-benzo[a]pyrene diol epoxide, which can attack DNA at the exocyclic amino group of guanine to form the major (+)-trans-anti-[BP]-N(2)-dG adduct. Bulky adducts such as (+)-trans-anti-[BP]-N(2)-dG primarily block DNA replication, but are occasionally bypassed and cause mutations if paired with an incorrect base. In vitro standing-start primer-extension assays show that the preferential insertion of A opposite (+)-trans-anti-[BP]-N(2)-dG is independent of the sequence context, but the primer is extended preferentially when dT is positioned opposite the damaged base in a 5'-CG*T-3' sequence context. Regardless of the base positioned opposite (+)-trans-anti-[BP]-N(2)-dG, extension of the primer past the lesion site poses the greatest block to polymerase progression. In order to gain insight into primer-extension of each base opposite (+)-trans-anti-[BP]-N(2)-dG, we carried out molecular modeling and 1.25 ns unrestrained molecular dynamics simulations of the adduct in the +1 position of the template within the replicative pol I family T7 DNA polymerase. Each of the four bases was modeled at the 3' terminus of the primer, incorporated opposite the adduct, and the next-to-be replicated base was in the active site with its Watson-Crick partner as the incoming nucleotide. As in our studies of nucleotide incorporation, (+)-trans-anti-[BP]-N(2)-dG was modeled in the syn conformation in the +1 position, with the BP moiety on the open major groove side of the primer-template duplex region, leaving critical protein-DNA interactions intact. The present work revealed that the efficiency of primer-extension past this bulky adduct opposite each of the four bases in the 5'-CG*T-3' sequence can be rationalized by the stability of interactions between the polymerase protein, primer-template DNA and incoming nucleotide. However, the relative stabilization of each nucleotide opposite (+)-trans-anti-[BP]-N(2)-dG in the +1 position (T > G > A > or = C) differed from that when the adduct and partner were the nascent base-pair (A > T > or = G > C). In addition, extension past (+)-trans-anti-[BP]-N(2)-dG may pose a greater block to a high fidelity DNA polymerase than does nucleotide incorporation opposite the adduct because the presence of the modified base-pair in the +1 position is more disruptive to the polymerase-DNA interactions than it is within the active site itself. The dN:(+)-trans-anti-[BP]-N(2)-dG base-pair is strained to shield the bulky aromatic BP moiety from contact with the solvent in the +1 position, causing disruption of protein-DNA interactions that would likely result in decreased extension of the base-pair. These studies reveal in molecular detail the kinds of specific structural interactions that determine the function of a processive DNA polymerase when challenged by a bulky DNA adduct.     

P-Postlabeling high-performance liquid chromatographic improvements to characterize DNA adduct stereoisomers from benzo[a]pyrene and benzo[c]phenanthrene, and to separate DNA adducts from 7,12-dimethylbenz[a]anthracene

Single compounds can generate complex DNA adduct patterns by reactions through different pathways, with different target nucleotides and through different configurations of the products. DNA adduct analysis by ³²P-HPLC was improved by adding an isocratic plateau in an otherwise linear gradient, thereby enhancing resolution of predictable retention time intervals. This enhanced ³²P-HPLC technique was used to analyze and at least partly resolve 14 out of 16 available benzo[c]phenanthrene deoxyadenosine and deoxyguanosine adduct standards, 8 out of 8 available benzo[a]pyrene deoxyadenosine and deoxyguanosine adduct standards, and 51 peaks from 7,12-dimethylbenz[a]anthracene-calf thymus DNA reaction products. The same type of gradient modifications could be used to enhance resolution in analyses of other complex DNA adduct mixtures, e.g., in vivo in humans.     

Propolis protects human spermatozoa from DNA damage caused by benzo[a]pyrene and exogenous reactive oxygen species

Many environmental, physiological and genetic factors have been implicated in defective sperm function, the most common cause of infertility. In addition, sperm preparation techniques such as centrifugation, used prior to in vitro fertilization, are associated with the generation of reactive oxygen species (ROS) and an increase in the level of DNA damage. Factors that can offer spermatozoa protection are, therefore, of great importance. This study was designed to examine in vitro the effect of a Chilean propolis ethanolic extract on human spermatozoa treated with benzo[a]pyrene and exogenous reactive oxygen species. Our experimental evidence demonstrated that the natural drug under investigation is able to protect genomic DNA by damage induced by benzo[a]pyrene, hydrogen peroxide (H2O2) and hydrogen peroxide in combination with adenosine 5'-diphosphate (ADP) and ferrous sulfate (FeSO4), determining a significant reduction of the intracellular oxidants. An increase in membrane damage, measured by monitoring the formation of thiobarbituric acid-reactive substances (TBARS) and lactic dehydrogenase (LDH) release, was observed only in sperm treated with H2O2, ADP and FeSO4. The propolis extract was shown to possess the capacity to protect sperm membrane from the deleterious action of oxidative attack, reducing TBARS formation and LDH release. In summary, our results evidence that the protective effect exhibited by this natural compound in human spermatozoa is correlated, at least in part, to the antioxidant capacity of its active components, and suggest that propolis may have a role in protection against male infertility.     

Inhibition of ischemia-induced angiogenesis by benzo[a]pyrene in a manner dependent on the aryl hydrocarbon receptor

We have investigated the effect of benzo[a]pyrene (B[a]P), a carcinogen of tobacco smoke and an agonist for the aryl hydrocarbon receptor (AHR), on hypoxia-induced angiogenesis. Ischemia was induced by femoral artery ligation in wild-type and AHR-null mice, and the animals were subjected to oral administration of B[a]P (125 mg/kg) once a week. Exposure to B[a]P up-regulated the expression of metallothionein in the ischemic hindlimb and markedly inhibited ischemia-induced angiogenesis in wild-type mice. The amounts of interleukin-6 and of vascular endothelial growth factor (VEGF) mRNA in the ischemic hindlimb of wild-type mice were reduced by exposure to B[a]P. These various effects of B[a]P were markedly attenuated in AHR-null mice. Our observations suggest that the loss of the inhibitory effect of B[a]P on ischemia-induced angiogenesis apparent in AHR-null mice may be attributable to maintenance of interleukin-6 expression and consequent promotion of angiogenesis through up-regulation of VEGF expression.     

The role of repair protein Rad51 in synergistic cytotoxicity and mutagenicity induced by epidermal growth factor receptor inhibitor (Gefitinib, IressaR) and benzo[a]pyrene in human lung cancer

Rad51 protein is essential for homologous recombination repair of DNA damage, and is over-expressed in chemo- or radioresistant carcinomas. The polycyclic hydrocarbon carcinogen benzo[a]pyrene (B[a]P) affects MAPKs transduction pathways. Gefitinib (IressaR, ZD1839) is a selective epidermal growth factor receptor tyrosine kinase inhibitor that blocks growth factor-mediated cell proliferation and ERK1/2 activation. We hypothesized that gefitinib enhances B[a]P-mediated cytotoxicity by decreasing ERK1/2 activation. Exposure of human lung cancer cells to gefitinib decreased B[a]P-elicited ERK1/2 activation and induced Rad51 protein expression. Gefitinib and B[a]P co-treatment decreased Rad51 protein stability by triggering degradation via a 26S proteasome-dependent pathway. Expression of constitutive active MKK1/2 vectors (MKK1/2-CA) rescues the decreased ERK1/2 activity, and restores Rad51 protein level and stability under gefitinib and B[a]P co-treatment. Gefitinib enhances B[a]P-induced growth inhibition, cytotoxicity and mutagenicity. Co-treatment with gefitinib and B[a]P can further inhibit cell growth significantly after depletion of endogenous Rad51 by siRad51 RNA transfection. Enhancement of ERK1/2 activation by MKK1-CA expression decrease B[a]P- and gefitinib-induced cytotoxicity, and B[a]P-induced mutagenicity. Rad51 protein protects lung cancer cells from synergistic cytotoxic and mutagenic effects induced by gefitinib and B[a]P. Suppression of Rad51 protein expression may be a novel lung cancer therapeutic modality to overcome drug resistance to gefitinib.     

Coexposure to benzo[a]pyrene plus UVA induced DNA double strand breaks: visualization of Ku assembly in the nucleus having DNA lesions

Benzo[a]pyrene (BaP) is a ubiquitous environmental pollutant with potential carcinogenicity. It has been shown that BaP, upon UVA irradiation, synergistically induced oxidative DNA damage, but other DNA damage was not confirmed. In this study, we examined whether coexposure to BaP plus UVA induces double strand breaks (DSBs) using xrs-5 cells, deficient in the repair of DSBs (Ku80 mutant), and whether Ku translocates involving the formation of DSBs. BaP plus UVA had a significant cytotoxic effect on CHO-K1 cells and an even more drastic effect on Ku80-deficient, xrs-5 cells, suggesting that the DSBs were generated by coexposure to BaP plus UVA. The DSBs were repaired in CHO-K1 cells within 30 min, but not in xrs-5 cells, indicating the involvement of a non-homologous end joining, which needs Ku proteins. Furthermore, we succeeded in visualizing that Ku80 rapidly assembled to the exposed region, in which DSBs might be generated, and clarified that the presence of both Ku70 and Ku80 was important for their accumulation.     

Different mechanisms involved in apoptosis following exposure to benzo[a]pyrene in F258 and Hepa1c1c7 cells

The present study compares and elucidates possible mechanisms why B[a]P induces different cell signals and triggers apparently different apoptotic pathways in two rather similar cell lines (hepatic epithelial cells of rodents). The rate and maximal capacity of metabolic activation, as measured by the formation of B[a]P-tetrols and B[a]P-DNA adducts, was much higher in mouse hepatoma Hepa1c1c7 cells than in rat liver epithelial F258 cells due to a higher induced level of cyp1a1. B[a]P increased intracellular pH in both cell lines, but this change modulated the apoptotic process only in F258 cells. In Hepa1c1c7 cells reactive oxygen species (ROS) production appeared to be a consequence of toxicity, unlike F258 cells in which it was an initial event. The increased mitochondrial membrane potential found in F258 cells was not observed in Hepa1c1c7 cells. Surprisingly, F258 cells cultured at low cell density were somewhat more sensitive to low (50nM) B[a]P concentrations than Hepa1c1c7 cells. This could be explained partly by metabolic differences at low B[a]P concentrations. In contrast to the Hepa1c1c7 model, no activation of cell survival signals including p-Akt, p-ERK1/2 and no clear inactivation of pro-apoptotic Bad was observed in the F258 model following exposure to B[a]P. Another important difference between the two cell lines was related to the role of Bax and cytochrome c. In Hepa1c1c7 cells, B[a]P exposure resulted in a "classical" translocation of Bax to the mitochondria and release of cytochrome c, whereas in F258 cells no intracellular translocation of these two proteins was seen. These results suggest that the rate of metabolism of B[a]P and type of reactive metabolites formed influence the resulting balance of pro-apoptotic and anti-apoptotic cell signaling, and hence the mechanisms involved in cell death and the chances of more permanent genetic damage.     

Probing the microenvironmental of benzo[a]pyrene diol epoxide-DNA adducts by triplet excited state quenching methods

Triplet flash photolysis techniques, coupled with quenching of the triplets by molecular oxygen, are utilized as probes of the microenvironment of polycyclic aromatic molecules bound covalently and non-covalently to DNA. The triplet-oxygen quenching properties of the following adducts in aqueous solutions at 25±1°C were investigated: covalent adducts derived from the reaction of (±)-7β,8α-dihydroxy-9α,10α-epoxy -7,8,9,10-tetrahydrobenzo[a]pyrene (BaPDE) and of (±)-9,10-epoxy-7,8,9,10-tetrahydrobenzo[a]pyrene (BaPE) with DNA, and non-covalent intercalation complexes of acridine orange (AO) and DNA. In all cases the quenching follows the Stern-Volmer quenching law with a quenching constant of K_O2^T≈10⁹ M^?1·s^?1 for the covalent BaPDE-DNA and BaPE-DNA complexes in aqueous solution. This value of K_O2^T is characteristic of free molecules (not bound to DNA) and indicates that the pyrene chromophore is totally accessible to oxygen, and is thus not located at an intercalation-type of binding site in these covalent adducts. In contrast, the AO-DNA complexes are characterized by values of K_O2^T≈10⁸ M^?1·s^?1 indicating that the intercalated AO molecules are about ten times less accessible to molecular oxygen than free AO molecules. The K_O2^T values for the covalent BaPDE-DNA and BaPE-DNA adducts decrease when the DNA concentration is increased in the 1·10^?4?3·10^?3 M range (expressed in nucleotide concentration). This effect is attributed to intermolecular DNA-DNA interactions in which segments of adjacent DNA molecules tend to cover the pyrene chromophores on other strands, thus decreasing their accessibility to oxygen. In contrast the values of K_O2^T for the non-covalent AO-DNA intercalation complexes are independent of DNA concentration, as expected for interior binding sites.     

Ellagic acid toxicity and interaction with benzo[a]pyrene and benzo[a]pyrene 7,8-dihydrodiol in human bronchial epithelial cells

Ellagic acid, a plant phenol present in various foods consumed by humans, has been reported to have both anti-mutagenic and anti-carcinogenic potential. To evaluate the potential anti-carcinogenic property of ellagic acid, we tested its effects on the toxicity of ben-zo[a]pyrene and benzo[a]pyrene, 7,8-dihydrodiol and binding of benzo[a]yrene to DNA in cultured human bronchial epithelial cells. The toxicity of ellagic acid itself for human bronchial epithelial cells was also determined. Using a colony-forming efficiency assay, it was found that a nontoxic concentration of ellagic acid (5 g/ml) enhanced the toxicity of benzo[a]pyrene.7,8-dihydrodiol in human bronchial epithelial cells. In contrast, ellagic acid at concentrations of l.5 and 3.0 g/ml inhibited binding of benzo[a]pyrenemetabolites to DNA in these cells. An explanation for the potentiating effect of ellagic acid on the toxicity of benzo[a]pyrene, 7,8-dihydrodiol will require further investigation into the possible mechanisms of interaction between these two compounds.Abbreviations B[a]P benzo[a]pyrene - B[a]P 7,8-DHD (±)trans-7,8-dihydro-7,8-dihydroxybenzo[a]pyrene - B[a]PDE-1 (±)-7,8-dihydroxy-9,10-epoxy-7,8,9,10-tetrahydrobenzo[a]pyrene - B[a]PDE-2 (±) 7,8-dihydroxy-9,10-epoxy-7,8,9,10-tetrahydrobenzo[a]pyrene - B[a]PDE-1:dG N²-]10{7,8,9-dihydroxy-7,8,9,10-tetrahydrobenzo[a]pyrene]yl}:deoxyguanosine - B[a]PDE-2:dG NZ-{10-[7,8,9-trihydroxy-7,8,9,10-tetrahydrobenzo[a]pyrene]yl}:deoxyguanosine - CFE colony forming efficiency - EA ellagic acid - HBE human bronchial epithelial     

Differential metabolism of benzo[alpha]pyrene in vitro by human placental tissues exposed to active maternal cigarette smoke

OBJECTIVES: Generation of different metabolites and DNA-adduct(s) of metabolites of benzo[alpha]pyrene (B[alpha]P) in vitro by placental tissues (microsomes) of mothers who actively smoked cigarettes (tobacco) and those who did not smoke were analyzed to determine the variability in metabolism of the B[alpha]P substrate among individual placental samples. METHODS: Overall B[alpha]P metabolism was assayed by alkaline aqueous extraction of metabolites, and reactive metabolites by DNA adducts of B[alpha]P-metabolites produced by salmon sperm DNA added to the incubation mixtures of the substrate and microsomes of exposed- and unexposed-placentas to maternal cigarette smoke. Array of B[alpha]P-metabolites produced by the same incubations were identified by high pressure liquid chromatography of the aqueous extracts. RESULTS: Subsets of smoke-exposed placentas assessed by cluster analysis had augmented metabolic activity, others did not respond to smoke exposure. CYP1A1 expression in trophoblast cells analyzed by immunohistochemistry did not correlate with smoke exposure. The DNA-adducts generated was variable, regardless of verbally reported levels of maternal exposure. The amounts of different B[alpha]P-metabolites produced by individual samples matched for similar levels of exposure during pregnancy by self-reported smoking (1 pack/day) were also not comparable. Metabolism of B[alpha]P into different metabolites, and production of toxic DNA adducts from metabolites in vitro by human placenta were variable and unrelated to the extent of smoke exposure. CONCLUSIONS: The metabolic characteristic of human placenta for xenobiotic exposure substrates is based on the expression and function of diverse enzymes, and such metabolism exhibited inter-individual variation for toxic metabolite production or detoxification of the substrates in response to maternal smoke exposure.     

Conformations of adducts formed between the genotoxic benzo[a]pyrene-7,8-dione and nucleosides studied by density functional theory

Benzo[a]pyrene (BP) is a widely distributed environmental pollutant that is metabolized by mammalian cells to a variety of genotoxic and carcinogenic intermediates that form covalent adducts with cellular DNA. One such pathway involves the metabolic activation of BP by members of the aldo-keto-reductase (AKR) family of enzymes to the highly reactive ortho-quinone, benzo[a]pyrene-7,8-dione (BPQ). This compound has been reported to react with the 2'-deoxynucleosides, dA and dG, under physiological conditions. Four BPQ-dG adducts and two -dA adducts were identified by mass spectrometry and NMR methods [Balu et al. (2004) Chem. Res. Toxicol. 17, 827-838]. However, the detailed conformations and absolute configurations around the linkage site have not been resolved. In order to determine the full conformations of these purine adducts, we carried out quantum mechanical geometry optimization using density functional theory. In the case of the BPQ-guanine adducts, six possible structures, each of which consists of two isomers, were identified. However, in the case of the adenine adducts, only four isomers were identified. The results suggest that stereoisomeric adduct pairs are expected to adopt opposite orientations with respect to the 5'-->3' direction of the modified DNA strands. The stereochemistry-dependent variations in adduct orientation may produce different biological effects, as has been observed in the case of DNA adducts derived from other metabolites of polycyclic aromatic hydrocarbons.     

Distant Neighbor Base Sequence Context Effects in Human Nucleotide Excision Repair of a Benzo[a]pyrene-derived DNA Lesion

The effects of non-nearest base sequences, beyond the nucleotides flanking a DNA lesion on either side, on nucleotide excision repair (NER) in extracts from human cells were investigated. We constructed two duplexes containing the same minor groove-aligned 10S (+)-trans-anti-B[a]P-N²-dG (G?) DNA adduct, derived from the environmental carcinogen benzo[a]pyrene (B[a]P): 5′-C-C-A-T-C-G?-C-T-A-C-C-3′ (CG?C-I), and 5′-C-A-C3-A4-C5-G?-C-A-C-A-C-3′ (CG?C-II). We used polyacrylamide gel electrophoresis to compare the extent of DNA bending, and molecular dynamics simulations to analyze the structural characteristics of these two DNA duplexes. The NER efficiencies are 1.6(± 0.2)-fold greater in the case of the CG?C-II than the CG?C-I sequence context in 135-mer duplexes. Gel electrophoresis and self-ligation circularization experiments revealed that the CG?C-II duplex is more bent than the CG?C-I duplex, while molecular dynamics simulations showed that the unique -C3-A4-C5- segment in the CG?C-II duplex plays a key role. The presence of a minor groove-positioned guanine amino group, the Watson-Crick partner to C3, acts as a wedge; facilitated by a highly deformable local -C3-A4- base step, this amino group allows the B[a]P ring system to produce a more enlarged minor groove in CG?C-II than in CG?C-I, as well as a local untwisting and enlarged and flexible Roll only in the CG?C-II sequence. These structural properties fit well with our earlier findings that in the case of the family of minor groove 10S (+)-trans-anti-B[a]P-N²-dG lesions, flexible bends and enlarged minor groove widths constitute NER recognition signals, and extend our understanding of sequence context effects on NER to the neighbors that are distant to the lesion.     

Reactions of benzo]pa]pyrene diol-epoxides with DNA and nucleosomes in aqueous solutions

The rate of solvolysis of benzo[$\text{a}$]pyrene diol-epoxide in aqueous solutions can be followed by fluorescence spectroscopy. When DNA was present the rat of breakdown of benzo[$\text{a}$]pyrene diol-epoxide was substantially enhanced, while at the same time fluorescence intensity was decreased. This decrease, however, was due to noncovalently bound tetraols and does not seem to be a function of the covalent adducts formed. Nucleosomal core particles, reacted under identical conditions, showed very little quenching of the pyrene-like chromophore. When increasing amounts of cysteine were present the covalent binding could be prevented in both free DNA and nucleosomal DNA. Analysis of the distribution of the carcinogen to nucleosomal DNA showed that the covalently bound carcinogen was located at or within 10 bases of the 5′-OH region of the nucleosomal DNA.     

Method for determining monohydroxybenzo[a]pyrene isomers using column-switching high-performance liquid chromatography

A method for determining monohydroxybenzo[a]pyrene (OHBaP) isomers using column-switching high-performance liquid chromatography with fluorescence detection was developed. Eleven of 12 isomers of OHBaP (all except 6-OHBaP) were separated on an alkylamide-type reversed-phase column and, via column-switching, on a beta-cyclodextrin-bonded silica gel column. The detection limits for the OHBaPs were in the range 0.3-8 pg/injection (S/N=3). By using this method, 1-, 3-, and 9-OHBaPs were identified as major metabolites of benzo[a]pyrene in vitro by human recombinant p450 1A1. The method was used to determine OHBaPs in the urine of a nonsmoker subject. After enzymatic hydrolysis of the conjugated metabolites by beta-glucuronidase/aryl sulfatase, the analytes were selectively adsorbed on blue rayon (a cellulose-supported copper phthalocyanine) from the urine matrix. Methanol as the eluting solvent from the rayon gave the best recoveries of OHBaPs and 1-hydroxypyrene (1-OHP) in the range of 91-103%, which was superior to that of the solid-phase extraction method. 1-OHP, a well-known biomarker of the exposure to polycyclic aromatic hydrocarbons, was simultaneously analyzed. Intra- and interday accuracy values for the determination of 3-OHBaP in 200 ml of urine were 95.5 and 100.9%, and those for 1-OHP were 96.4 and 103.6%, respectively. The intra- and interday precision values were 3.9 and 2.4% for 3-OHBaP and 2.4 and 3.2% for 1-OHP, respectively. In 11 kinds of isomers, only 3-OHBaP was detected in the human urine. Urinary concentration of 3-OHBaP was quantified at 0.5 ng/g creatinine concentration and the 3-OHBaP/1-OHP ratio was approximately 1/130.     

In vivo evidence that phenylalanine 171 acts as a molecular brake for translesion DNA synthesis across benzo[a]pyrene DNA adducts by human DNA polymerase κ

Humans possess multiple specialized DNA polymerases that continue DNA replication beyond a variety of DNA lesions. DNA polymerase kappa (Pol κ) bypasses benzo[a]pyrene diolepoxide-N²-deoxyguanine (BPDE-N²-dG) DNA adducts in an almost error-free manner. In the previous work, we changed the amino acids close to the adducts in the active site and examined the bypass efficiency. The substitution of alanine for phenylalanine 171 (F171A) enhanced by 18-fold in vitro, the efficiencies of dCMP incorporation opposite (−)- and (+)-trans-anti-BPDE-N²-dG. In the present study, we established human cell lines that express wild-type Pol κ (POLK+/−), F171A (POLK F171A/−) or lack expression of Pol κ (POLK−/−) to examine the in vivo significance. These cell lines were generated with Nalm-6, a human pre-B acute lymphoblastic leukemia cell line, which has high efficiency for gene targeting. Mutations were analyzed with shuttle vectors having (−)- or (+)-trans-anti-BPDE-N²-dG in the supF gene. The frequencies of mutations were in the order of POLK−/− > POLK+/− > POLK F171A/− both in (−)- and (+)-trans-anti-BPDE-N²-dG. These results suggest that F171 may function as a molecular brake for bypass across BPDE-N²-dG by Pol κ and raise the possibility that the cognate substrates for Pol κ are not BP adducts in DNA but may be lesions in DNA induced by endogenous mutagens.