SEARCH · PubMed Health

Results for “Pyrenes”

Explore indexed PubMed citations for clinical trials, systematic reviews and public health research. Read source abstracts and follow each citation to its original PubMed record.

Quote a phrase for an exact phrase match. Source license links do not imply unrestricted reuse.

At least 145 records · Page 8Linked to original sources

PubMed1989

Benzo[a]pyrene-DNA-adducts and monooxygenase activities in mice treated with benzo[a]pyrene, cigarette smoke or cigarette smoke condensate.

Synchronous fluorescence spectrophotometry (SFS), developed to study benzo[a]pyrene-7,8-diol-9,10-epoxide(BPDE)-DNA, was used to measure the in vivo formation of DNA-adducts in genetically responsive C57BL/6 (B6) and non-responsive DBA/2 (D2) mice. Treatment with cigarette smoke by inhalation for 3-16 days, or i.p. injection of cigarette smoke condensate or neutral fraction did not lead to detectable levels of BPDE-DNA-adducts in either lungs or liver, although aryl hydrocarbon hydroxylase (AHH) activity, an indicator of benzo[a]pyrene (BP) metabolism, was clearly induced in lungs of B6 mouse. A dose-dependent amount of BPDE-DNA-adducts in lung and somewhat less in liver was found after i.p. injection with BP (20-80 mg/kg). Mice treated with vehicle or 4 mg/kg of BP were negative for adducts by SFS. In B6 mice AHH was induced both in lungs and livers while there was no AHH induction in D2 mice although the levels of BPDE-DNA-adducts were somewhat higher than in B6 mice. Thus, no clear correlation seems to exist between AHH activity and the formation of BPDE-DNA-adducts. Also, according to our results SFS can be used to quantitate adduct-formation in in vivo animal studies.

7-Alkoxycoumarin O-Dealkylase↗

PubMed1990

Metabolism of benzo[a]pyrene and (-)-trans-benzo[a]pyrene-7,8-dihydrodiol by freshly isolated hepatocytes of brown bullheads.

The metabolism of [3H]benzo[a]pyrene (BP) and (-)-trans-[14C]7,8-dihydroxy-7,8-dihydrobenzo[a]pyrene (BP-7,8-diol) was studied in freshly isolated hepatocytes of the wild benthic fish, brown bullhead (Ictalurus nebulosus). Bullhead hepatocytes incubated with 40 microM [3H]BP for 1 h metabolized BP to water soluble metabolites which were separated on silica gel t.l.c. plates to reveal conjugates with glucuronic acid, glutathione, and sulfate (51%, 14% and 4% of total metabolites, respectively). Additional metabolites that were extractable with ethyl acetate were separated by reversed phase HPLC to reveal only two major metabolites: BP-9,10-dihydrodiol and BP-7,8-diol (13% and 2.6% of total metabolites, respectively). Hepatocytes isolated from individual fish displayed an 11-fold variability in the rates at which they metabolized BP (756 +/- 167 pmol x mg dry wt-1 x h-1), which correlated negatively (r = -0.7, P less than 0.01) with an 18-fold variability in the glycogen content of the cells. Hepatocytes isolated from the same fish, in parallel incubations under the same optimum conditions, metabolized BP-7,8-diol 4.5-fold faster than they metabolized BP. The variability in the rate of BP-7,8-diol metabolism was about 7-fold. Major metabolites included glutathione conjugates, glucuronides and sulfates (35%, 25% and 30% of total metabolites, respectively). These conjugates, like those formed from BP, were degradable with gamma-glutamyltransferase, beta-glucuronidase and arylsulfatase, respectively. Ethyl acetate extractable metabolites were predominantly isomeric benzo-ring tetrahydrotetrols (9% of total metabolites). In summary, this study indicates that during short-term incubations bull-head hepatocytes metabolize BP and BP-7,8-diol primarily to conjugated derivatives. The usefulness of thin-layer chromatography for the convenient determination of the rate of BP-7,8-diol metabolism is demonstrated.

Animals↗

PubMed1987

Modulation of the cytotoxicity and mutagenicity of benzo[a]pyrene and benzo[a]pyrene 7,8-diol by glutathione and glutathione S-transferases in mammalian cells (CHO/HGPRT assay).

Biologically reactive metabolites of benzo[a]pyrene (BP) and benzo[a]-pyrene 7,8-diol (BP-diol), formed by the mixed-function oxidase (MFO) system, are substrates for conjugation and detoxication by glutathione (GSH) when catalyzed by glutathione S-transferases (GSHT). We have investigated the detoxication of BP- and BP-diol-induced cytotoxicity and mutagenicity with GSH by supplementing the S9 mix used in the Chinese hamster ovary cells/hypoxanthine-guanine phosphoribosyltransferase (CHO/HGPRT) assay with GSH (6.5 mM) or GSH plus GSHT. The addition of GSH to the S9 mix resulted in a reduction of BP- and BP-diol induced cytotoxicity. GSH plus GSHT eliminated BP-induced cytotoxicity and reduced the mutagenicity of BP. GSH inhibited the mutagenicity at low (essentially non-lethal) concentrations of BP-diol, but did not do so at toxic concentrations. GSH plus GSHT inhibited the cytotoxicity and mutagenicity of BP-diol at concentrations not affected by GSH alone. These studies indicate that biochemical mechanisms of detoxication can affect the biological activity of a carcinogen, such as BP or BP-diol as profoundly as bioactivation by the MFO system.

Animals↗

PubMed1990

Formation of hemoglobin-benzo[a]pyrene adducts in human erythrocytes incubated with benzo[a]pyrene and hamster embryo cells.

Evidence is accumulating that the levels of covalent carcinogen-macromolecule adducts, including adducts with hemoglobin, reflect biologically effective levels of carcinogen exposure. The purposes of the present study were (a) to establish a cellular system for obtaining adducts between intracellular human hemoglobin and metabolites of polycyclic aromatic hydrocarbons (PAH), and (b) to evaluate techniques for chromatographic characterization of the adducts. We showed that hemoglobin-benzo[a]pyrene adducts were formed when human erythrocytes were treated with [3H]benzo[a]pyrene (BP) in the presence of hamster embryo fibroblasts, which are known to be effective for BP metabolism. After lysis of the erythrocytes, noncovalently bound BP and its metabolites were effectively removed from hemoglobin under mild conditions by using hydrophobic interaction and size-exclusion liquid chromatography. Three to five distinct adducts were resolved by reversed-phase and ion-exchange liquid chromatography. As determined by a two-step, reversed-phase liquid chromatographic procedure, trypsin treatment of globin from the cellular system yielded at least three of the four 7,8,9,10-tetrahydro-7,8,9,10-tetrahydroxy BP tetrols known to arise from mammalian metabolism of BP. This observation is consistent with both (a) the recently described formation of labile carboxyl esters via reaction of BP-7,8-dihydrodiol-9,10-epoxide (BPDE) with hemoglobin and (b) the known formation of both anti- and syn-BPDE in hamster embryo fibroblasts. In addition, high-performance liquid chromatographic analysis demonstrated the presence of other products presumed to be BP-peptide adducts because of their susceptibility to thermolysin treatment.

Animals↗

PubMed1992

Chinese medicinal herbs modulate mutagenesis, DNA binding and metabolism of benzo[a]pyrene 7,8-dihydrodiol and benzo[a]pyrene 7,8-dihydrodiol-9,10-epoxide.

Oldenlandia diffusa(OD) and Scutellaria barbata (SB) have been used in traditional Chinese medicine for treating liver, lung and rectal tumors. In this study, the effects of aqueous extracts of these two herbs on benzo[a]pyrene 7,8-dihydrodiol. (BaP 7,8-DHD) and benzo[a]pyrene 7,8-dihydrodiol-9,10-epoxide (BPDE)-induced mutagenesis using Salmonella typhimurium TA100 as the bacterial tester strain and rat liver 9000 x g supernatant (S9) as the metabolic activation system were assessed. We also determined the effects of these two herbs on BaP 7,8-DHD and BPDE binding to calf thymus DNA. Organosoluble metabolites of BaP 7,8-DHD and water-soluble conjugates of BaP 7,8-DHD and BPDE were analyzed by high-performance liquid chromatography (HPLC) and alumina column liquid chromatography. Mutagenesis assays revealed that these two herbs produced a significant concentration-dependent inhibition of histidine-independent (His+) revertants induced by BaP 7,8-DHD and BPDE. OD and SB also inhibited BPDE-induced mutagenesis in a concentration-dependent manner in the absence of S9. SB had a greater inhibitory effect than OD. SB significantly inhibited BaP 7,8-DHD and BPDE binding to DNA while OD significantly enhanced DNA binding of both compounds. OD and SB inhibited the formation of organosoluble metabolites of BaP 7,8-DHD and decreased the formation of water-soluble conjugates of BaP 7,8-DHD and BPDE. However, the fraction of the total radioactivity in the water-soluble conjugates present as sulfate and glutathione was increased by OD and SB. Glucuronide fraction was decreased. The results of this study affirm our previous work suggesting that these two Chinese medicinal herbs possess antimutagenic properties and further suggest that they act as blocking agents through a scavenging mechanism.

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

PubMed1992

The co-carcinogen benzo[e]pyrene increases the binding of a low dose of the carcinogen benzo[a]pyrene to DNA in Sencar mouse epidermis.

The mechanism of the co-carcinogenic activity of benzo[e]pyrene (BeP) was investigated by determining the effects of BeP on the binding of the carcinogen benzo[a]pyrene (BaP) to DNA in Sencar mouse epidermis. The dose of BaP used was 20 nmol/mouse, a dose which is not carcinogenic in a single application but is carcinogenic after multiple treatments such as those in the BaP-BeP co-carcinogenesis experiments described by Van Duuren and Goldschmidt (J. Natl. Cancer Inst., 56, 1237, 1976). After 3 h of exposure to [3H]BaP and BeP at BaP:BeP dose ratios of 1:3 and 1:10, [3H]BaP-DNA adducts in both BeP-treated groups were lower than in an acetone-BaP control group. After 12 and 24 h of exposure, the BaP-BeP (1:10) group contained 19% and 33% higher [3H]BaP-DNA adduct levels than the control. In the BaP-BeP (1:3) group, the amount of [3H]BaP-DNA adduct levels was higher than the control after 12 h. BeP co-treatment with either [3H]BaP-7,8-dihydrodiol or anti-[3H]BaPDE had no effect on the amount of BaPDE-DNA adducts present. These results demonstrate that the co-carcinogen BeP increases the amount of a low dose of BaP that binds to mouse epidermal DNA and indicate that the increase in BaP-DNA adducts results from increased metabolism of BaP to the proximate carcinogen BaP-7,8-dihydrodiol.

Animals↗

PubMed1993

Exceptional tumor-initiating activity of 4-fluorobenzo[j]-fluoranthene on mouse skin: comparison with benzo[j]-fluoranthene, 10-fluoro-benzo[j]fluoranthene, benzo[a]pyrene, dibenzo[a,l]pyrene and 7,12-dimethylbenz[a]anthracene.

Exceptional tumorigenic potency was observed with 4-fluorobenzo[j]fuoranthene (4-fluoroB[j]F) relative to benzo[j]fluoranthene (B[j]F) and 10-fluorobenzo[j]fluoranthene (10-fluoroB[j]F) in a mouse skin initiation promotion bioassay. Comparison of the tumorigenic response obtained at total initiating doses of 50, 100, and 1000 nmol firmly established the greater tumorigenic potency of 4-fluoroB[j]F. B[j]F produced a significant tumorigenic response only at total initiating doses of 100 and 1000 nmol per mouse. 10-FluoroB[j]F produced a significant tumorigenic response only at the highest initiating dose, 1000 nmol per mouse. In contrast, 4-fluoroB[j]F produced a significant tumorigenic response at all three doses. At a total initiating dose of 50 nmol, a 90% incidence of tumor-bearing mice with an average of 3.05 tumors per mouse was observed with 4-fluoroB[j]F. A second initiation promotion bioassay was performed to establish the tumorigenic potency of 4-fluoroB[j]F relative to benzo[a]-pyrene (B[a]P), 7,12-dimethylbenz[a]anthracene (DMBA), and dibenzo[a,l]pyrene (DB[a,l]P). 4-FluoroB[j]F did exhibit significant tumor-initiating activity at doses of 10 and 25 nmol per mouse, inducing a 45 and 60% incidence of tumor-bearing mice with an average of 0.75 and 1.65 tumors per mouse, respectively. While B[a]P was not tumorigenic at these doses, DMBA and DB[a,l]P exhibited significant tumorigenic activity at doses of 1, 4, 10, and 25 nmol per mouse. DB[a,l]P induced a 95% incidence of tumor-bearing mice with an average of 5.0 tumors per mouse at a total initiator dose of 1 nmol. DMBA at this dose produced an 85% incidence of tumor-bearing mice with an average of 1.30 tumors per mouse. The results of these initiation promotion bioassays clearly demonstrate that 4-fluoroB[j]F is significantly more active than B[j]F, 10-fluoroB[j]F and B[a]P and less active than either DMBA or DB[a,l]P as a tumor initiator on mouse skin.

9,10-Dimethyl-1,2-benzanthracene↗

PubMed1997

Tissue distribution of DNA adducts in rats treated by intramammillary injection with dibenzo[a,l]pyrene, 7,12-dimethylbenz[a]anthracene and benzo[a]pyrene.

Dibenzo[a,l]pyrene (DBP) has recently emerged as a potent environmental carcinogen having greater carcinogenicity in the rat mammary epithelial glands than 7,12-dimethylbenz[a]anthracene (DMBA), previously considered to be the most potent mammary carcinogen and benzo[a]pyrene (BP), a ubiquitous environmental carcinogen. Previous studies on the tumor-initiating potential of DBP, DMBA, and BP demonstrated that DBP was 2.5 times more potent in inducing the tumors in mouse skin and rat mammary glands than DMBA; BP was a weak mammary carcinogen in these animals. The present study was designed to investigate if the significantly increased mammary carcinogenicity of DBP over DMBA and BP was related to increased DNA adduction at the target site. Female Sprague-Dawley rats were treated by intramammillary injection with an equimolar dose of 0.25 micromol/gland of DBP, DMBA, and BP at the 3rd, 4th and 5th mammary glands on both sides. 32P-Postlabeling analysis of mammary epithelial DNA of rats treated with DBP produced two major (nos. 3 and 6) and at least 5 minor adducts. DMBA treatment resulted in one major and 4 minor DNA adducts while BP produced one major and two minor adducts. Quantitation of the adduct radioactivity revealed that DNA adduction was 6- and 9-fold greater in DBP-treated animals than in BP- and DMBA-treated animals, respectively. The adduct levels per 10(9) nucleotides in mammary epithelial cells for DBP, BP and DMBA were in the following descending order: 1828 +/- 378, 300 +/- 45 and 207 +/- 72, respectively. Tissue distribution of DNA adducts in non-target organs following DBP treatment showed similar adduct pattern as found in the mammary epithelial cells except the liver, which resulted in 4 additional adduct spots; vehicle-treated tissue DNA processed in parallel did not show any detectable adducts. DMBA- and BP-DNA adduct patterns in various tissues were similar to that found in mammary epithelial cells, however, significant quantitative differences were found; BP-DNA adducts were undetectable in the pancreas and bladder. Quantitation of adduct radioactivity showed a 15- to 60-fold lower DBP-DNA adduction in these tissues than the levels found in the mammary tissue; similarly 5-20 and 30-100 times lower DNA adduction was found following treatment with DMBA and BP, respectively. The significantly increased binding of DBP to the mammary epithelial DNA over BP and DMBA is in concordance with its known higher mutagenicity and tumorigenicity.

9,10-Dimethyl-1,2-benzanthracene↗

PubMed1998

Comparative tumorigenicity of 1- and 3-nitrobenzo[a]pyrenes, and 3,6- and 1,6-dinitrobenzo[a]pyrenes in F344/DuCrj rats.

Our earlier study revealed that 1- and 3-nitrobenzo[a]pyrene (NBP), 1,6- and 3,6-dinitrobenzo[a]pyrene (DNBP), nitrated derivatives of benzo[a]BP (BP), are present in the environment. These derivatives are potent mutagens for Salmonella tester strains and we have preliminarily reported them to be carcinogenic in F344/DuCrj rats. In this study, the tumorigenic action of 1- and 3-NBP, 1.6- and 3,6-DNBP, and BP induced by subcutaneous injection into rats was found to differ according to the NO2-substitution in the BP structure. The chemicals were suspended in equal volumes of beeswax and tricaprylin, and rats were subcutaneously injected with single doses of 500, 1000, and 2000 microg for 1- and 3-NBP, and of 8, 40, 200, and 1000 microg for 3,6- and 1,6-DNBP, and BP as a positive control. 3,6-DNBP and BP induced tumors in a dose-dependent manner at the injection site. Rats given 1000 microg of 3,6-DNBP (2924 nmol) and BP (3968 nmol) developed subcutaneous tumors at the rate of 70 and 80%, respectively, and those given a minimum dose of 23 nmol for 3.6-DNBP and 32 nmol for BP per rat developed tumors at a rate of 4.8 and 18.2%, respectively. However, rats given 500 and 1000 microg of 1- and 3-NBP did not develop any tumors while those given a high dose, 2000 microg, of each chemical developed tumors at only one of ten animals used. It was concluded, therefore, that these chemicals are weak carcinogens. Histologically, most of the tumors were malignant fibrous histiocytomas. Rats given various doses of 1,6-DNBP did not develop any tumors at the injection site. The failure of 1,6-DNBP to induce tumors may involve its metabolites because of the lower mutagenicity of its reduction products, 1-nitroso-6-NBP and 1-amino-6-NBP. It is suggested, therefore, that tumorigenicities of NBPs and DNBPs differ according to the NO2-substitution on the chemical structure, which may be due to the possible nitroreduction of the chemicals.

Animals↗

PubMed1982

Carcinogenic epoxides of benzo[a]pyrene and cyclopenta[cd]pyrene induce base substitutions via specific transversions.

We have determined the spectrum of base-pair substitution mutations induced in the lacI gene of a uvrB- strain of Escherichia coli by two polycyclic aromatic hydrocarbons--(+/-)7 alpha,8 beta-dihydroxy-9 beta,10 beta-epoxy-7,8,9,10 tetrahydrobenzo[a]pyrene (BPDE), and 3,4-epoxycylopenta[cd]pyrene (CPPE). Approximately 10% of all lacI mutations induced by either BPDE or CPPE are nonsense mutations, suggesting that base-pair substitutions are a large fraction of the mutational events induced by these agents in the uvrB- bacteria. Both carcinogens specifically induced the G . C leads to T . A and, to a lesser extent, the A . T leads to T . A transversions. One possible mechanism for transversion induction at G . C sites by BPDE might involve carcinogen binding to the exocyclic amino group of guanine in the template strand followed by a rotation of the modified base around its glycosylic bond from the anti to the syn conformation. This could allow specific pairing of modified bases with an imino tautomer of adenine.

Benzopyrenes↗

PubMed1992

Peroxidase-mediated glutathione conjugation of benzo[a]pyrene-7,8-dihydrodiol is enhanced by benzo[a]pyrene phenols in vitro.

We reported previously that glutathione (GSH) is oxidized by peroxidases to a thiyl radical that can react with a number of chemicals, including the penultimate carcinogenic metabolite benzo[a]pyrene-7,8-dihydrodiol (7,8-B[a]PD), to give GSH conjugates. Here, we report that phenolic metabolites of benzo[a]pyrene (B[a]P) enhance the peroxidase-mediated formation of glutathione conjugates of 7,8-B[a]PD. The GSH conjugation of 7,8-B[a]PD in a horseradish peroxidase/peroxide system was increased over control values as follows: 9-OH-B[a]P by 4-fold, 7-OH-B[a]P by 3-fold, 1-OH-B[a]P by 2-fold. In contrast 3-OH-B[a]P was ineffective. A phenolic derivative of another polycyclic aromatic hydrocarbon (PAH), benz[a]anthracene, also enhanced GSH conjugation of 7,8-B[a]PD. The enhancement was dependent upon the presence of the phenol, horseradish peroxidase and peroxide. The phenolic compounds, including 3-OH-B[a]P, were also efficient reducing cofactors for the peroxidase. With the exception of 3-OH-B[a]P, the phenolic metabolites of PAH enhanced peroxidase-mediated formation of thiyl radical as detected by electron spin resonance spectrometry. Since both phenols and dihydrodiols are metabolites of B[a]P catalyzed by the cytochromes P450 system, enhancement of peroxidase-dependent 7,8-B[a]PD-GSH conjugation by phenols suggests a possible interaction between peroxidases and cytochromes P450 systems. This interaction may contribute to the detoxication of the penultimate carcinogenic PAH-dihydrodiols and other chemicals.

Benzo(a)pyrene↗

PubMed1993

Tumor-initiating activity and carcinogenicity of dibenzo[a,l]pyrene versus 7,12-dimethylbenz[a]anthracene and benzo[a]pyrene at low doses in mouse skin.

Dibenzo[a,l]pyrene (DB[a,l]P) is an extremely potent carcinogen that may be present in environmental samples. Dose-response studies were conducted at low doses in mouse skin by initiation-promotion and repeated application to compare its activity to that of 7,12-dimethylbenz[a]anthracene (DMBA), benzo[a]pyrene (B[a]P), DB[a,l]P-8,9-dihydrodiol and DB[a,l]P-11,12-dihydrodiol. Female SENCAR mice were initiated with 1 or 0.25 nmol of DB[a,l]P, DMBA, B[a]P or DB[a,l]P-11,12-dihydrodiol and promoted with phorbol ester acetate. At 1 nmol, DB[a,l]P induced 2.6 tumors/mouse, whereas DB[a,l]P-11,12-dihydrodiol and DMBA induced 0.17 and 0.29 tumors/mouse respectively. At the low dose, DB[a,l]P induced 0.79 tumors/mouse, but the other two compounds were virtually inactive. B[a]P, tested only at 1 nmol, was inactive. These three compounds, as well as DB[a,l]P-8,9-dihydrodiol, were tested by repeated application twice weekly for 40 weeks at 1 and 4 nmol per dose. In addition, DB[a,l]P, DMBA and B[a]P were also tested at 8 nmol. At 8 and 4 nmol, DB[a,l]P induced malignant tumors in 91 and 70% of mice respectively. At 4 nmol DB[a,l]P-11,12-dihydrodiol elicited only benign tumors in 36% of mice. At 4 nmol DMBA induced two carcinomas in one mouse and at 8 nmol it induced one papilloma and one sebaceous gland adenoma. B[a]P and DB[a,l]P-8,9-dihydrodiol were inactive at all doses tested. These results demonstrate that DB[a,l]P is a much more potent carcinogen than DMBA, the aromatic hydrocarbon previously considered to be the most potent. Combination of these results with previous comparisons of DB[a,l]P, DB[a,l]P-11,12-dihydrodiol, DMBA and B[a]P at higher doses (E.L. Cavalieri et al. (1991) Carcinogenesis, 12, 1939-1944) shows clearly the interference of toxicity with the tumorigenicity of DB[a,l]P and its 11,12-dihydrodiol.

9,10-Dimethyl-1,2-benzanthracene↗

PubMed1981

The uptake and release of benzo[a]pyrene and benzo[e]pyrene in vitro by Syrian hamster embryo cells as a function of serum concentration.

A quantitative study on the in vitro uptake of benzo[a]pyrene (B[a]P) and benzo[e]pyrene (B[e]P) by Syrian hamster embryo cells and the induction of sister chromatid exchange (SCE) has been carried out. The amounts of B[a]P and B[e]P taken up by the cells decreases as does the induction of SCEs by B[a]P when the concentration of serum in the culture medium increases. It appears that serum prevents (B[a]P or B[e]P uptake. We have observed no significant differences between the two hydrocarbons regarding uptake by cells; chromatographic results show however that B[a]P is metabolized by these cells, while B[e]P is not. Our results suggest that serum inhibits B[a]P and B[e]P uptake and hence decreases the number of SCEs.

Animals↗

PubMed1982

Glutathione conjugation and DNA-binding of (+/-)-trans-7,8-dihydroxy-7,8-dihydrobenzo[a]pyrene and (+/-)-7 beta,8 alpha-dihydroxy-9 alpha,10 alpha-epoxy-7,8,9,10-tetrahydrobenzo[a]pyrene in isolated rat hepatocytes.

Isolated rat liver hepatocytes, previously depleted of glutathione (GSH) by treatment with diethylmaleate, were allowed to incorporate [3H]glycine into their GSH. Incubation of 3H-labelled cells with 14C-labelled (+/-)-trans-7,8-dihydroxy-7,8-dihydrobenzo[a]pyrene ((+/-)-BP-7,8-dihydrodiol) or (+/-)-7 beta,8 alpha-dihydroxy-9 alpha,10 alpha-epoxy-7,8,9,10-tetrahydrobenzo[a]pyrene ((+/-)-BPDE) revealed the formation of double labelled products. This together with evidence from amino acid analysis indicates formation of GSH-conjugates of the highly carcinogenic BP-derivatives. Incubation of hepatocytes isolated from 3-methylcholanthrene (MC) treated rats with 3H-labelled (+/-)-BP-7,8-dihydrodiol or (+/-)-BPDE resulted in binding of radioactivity to DNA. Reduction of the intracellular level of GSH to approximately 40% of the normal level resulted in an approximate 2-fold increase in the DNA-binding of either substrate. In addition there was a concurrent decrease in the amount of GSH-conjugates formed. These data clearly demonstrate that GSH participates in conjugation reactions with carcinogenic (+/-)-BP-7,8-dihydrodiol and (+/-)-BPDE and that the intracellular level of GSH is important in preventing reactive intermediates from reacting with the DNA in intact cells.

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

PubMed1984

Benzo[e]pyrene-induced alterations in the binding of benzo[a]pyrene to DNA in hamster embryo cell cultures.

Benzo[e]pyrene (B[e]P), a weakly carcinogenic polycyclic aromatic hydrocarbon (PAH) modifies tumor induction in mouse skin and the induction of mutation in mammalian cells by carcinogenic PAH. To determine how B[e]P alters the metabolic activation of the carcinogen benzo[a]pyrene (B[a]P), early passage Syrian hamster embryo cell cultures were exposed to [3H]B[a]P or [3H]trans-7,8-dihydro-7,8-dihydroxyB[a]P (B[a]P-7,8-diol) in the presence of various concentrations of B[e]P for 24 h. The DNA was isolated, degraded to deoxyribonucleosides and the B[a]P-deoxyribonucleoside adducts were analyzed by h.p.l.c. As the dose of B[e]P increased, the amount of B[a]P bound to DNA decreased and the ratio of anti-B[a]P-7,8-diol-9,10-epoxide (B[a]PDE)-deoxyguanosine adduct to syn-B[a]PDE-deoxyguanosine adduct decreased. B[e]P treatment inhibited the binding of B[a]P-7,8-diol to DNA to a greater extent than it inhibited the binding of B[a]P and decreased the ratio of anti- to syn-B[a]PDE-deoxyguanosine adducts formed from the 7,8-diol. These results indicate that B[e]P decreases the activation of B[a]P to DNA-binding intermediates in these cells; especially the oxidation of B[a]P-7,8-diol to a diol-epoxide. The B[e]P-induced alterations in the ratio of DNA adducts formed from the syn- and anti-isomers of B[a]PDE suggest that B[e]P selectively inhibited certain pathways of metabolic activation of B[a]P. Thus, B[e]P-induced modifications in the biological activity of PAH may result from alteration in both the amounts and the relative proportions of various isomeric forms of the ultimate carcinogenic metabolites formed from PAH.

Animals↗

PubMed1984

Metabolism of benzo[a]pyrene-7,8-dihydrodiol and benzo[a]pyrene-7,8-dihydrodiol-9,10-epoxide to protein-binding products and glutathione conjugates in isolated rat hepatocytes.

Isolated hepatocytes from 3-methylcholanthrene (MC)-treated rats metabolized trans-7,8-dihydroxy-7,8-dihydrobenzo[a]pyrene (BP-7,8-diol) and (+/-)-7 beta,8 alpha-dihydroxy-9 alpha,10 alpha-oxy-7,8,9,10-tetrahydrobenzo[a]pyrene (anti-BPDE) to water soluble conjugates including glutathione (GSH) conjugates. Under the conditions employed 35% of total water soluble products derived from BP-7,8-diol could be accounted for by GSH conjugates. The corresponding figure for anti-BPDE was estimated to be greater than or equal to 80%. Isolated hepatocytes metabolized BP-7,8-diol and anti-BPDE to GSH conjugates at maximal rates of 0.5 and 9 nmol per 10(6) cells per min, respectively. Thus, identifying the rate limiting step in the reaction sequence as the metabolism of BP-7,8-diol to the GSH conjugating intermediates. In addition to the direct conjugation of anti-BPDE with GSH, anti-BPDE but not the corresponding BP-tetraols, was further metabolized to reactive intermediates that subsequently bound to cellular proteins or reacted with GSH forming water soluble conjugates. The identity or identities of these novel reactive intermediates is discussed.

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

PubMed1987

Binding of benzo[a]pyrene metabolites in the rat intestinal lumen by magnetic polyethyleneimine microcapsules following an intragastric dose of [14C]benzo[a]pyrene.

Semi-permeable magnetic polyethyleneimine (PEI) microcapsules have been developed to trap carcinogens and their metabolites in vivo and their time-dependent binding of a model carcinogen, [14C]benzo[a]pyrene [( 14C]BaP), is studied within the intestinal lumen. Overall, approximately 0.5% of an intragastric BaP dose was bound by these microcapsules recovered from faeces with specific binding of metabolites (nmol/10(6) recovered microcapsules) being similar in the 0-24-h and 24-48-h periods, but approximately 10-fold lower in the 48-72-h period. Successive extractions of microcapsules with ammoniacal methanol, 2.5 N HCl, methanol and dimethylsulfoxide released approximately 60% of bound radiolabeled and the unextracted radiolabel was presumed to have been bound covalently. By contrast, greater than 90% of bound radiolabel was extractable from the faeces of the treated animals and from microcapsules treated in vitro with [14C]7,8-dihydroxy-9,10-epoxytetrahydrobenzo[a]pyrene (BaPDE), indicating that the in vivo microcapsule-bound metabolites were not derived either from adsorbed faecal material or from [14C]BaPDE formed in situ. A time-dependent appearance of BaP 3,6-dione was found. Also the qualitative and quantitative patterns of metabolites trapped by microcapsules, as assayed by h.p.l.c., were consistent only with a unique set of BaP metabolites being bound within the intestinal lumen. Hence these carcinogen-binding microcapsules can be used to investigate the in situ formation of carcinogen metabolites within the intestinal tract.

Animals↗

PubMed1988

Persistence of benzo[a]pyrene and 7,8-dihydro-7,8-dihydroxybenzo[a] pyrene in Fischer 344 rats: time distribution of total metabolites in blood, urine and feces.

A comparison of the rates of elimination of [3H]benzo[a] pyrene (BaP) and 7,8-dihydro-7,8-diol-[3H]benzo[a]pyrene (BPD), after subcutaneous injection into Fischer 344 rats, shows they are both eliminated at about the same rates and with the same pattern over at least 7 days post-exposure. The end-rate of combined urinary and fecal excretion was approximately 40 nmol/day. About 20% of the injected BaP and approximately 3% of the injected BPD remained at the site of injection for at least 9 days. The remainder was distributed throughout the animal. If the rate of excretion continued at the observed steady-state rates, the BaP and BPD could persist for up to 40 days for each milligram of injected substance. The concentration of excretion products were highest during day 1 and day 2 following exposure, decreased exponentially to a concentration of approximately 0.5 microM (mixed metabolites) by day 5 following exposure, and then continued to be excreted at that rate. Feces contained the highest total amounts of radioactivity, which were approximately 2- to 4-fold higher than the amounts in urine and approximately 15- to 50-fold higher than in total blood. The conversion of organic 3H to 3H2O during the experimental period indicates that whole-body phenol(quinone) formation was significant for BaP metabolism, but was much less for BPD metabolism. When BaP was injected, both blood and urine contained water-soluble, volatile tritium counts (3H2O). Injection of BPD resulted in volatile 3H2O in urine but not in blood. The persistence of BaP and BPD metabolites in skin, blood, urine and feces compartments indicates there is a substantial reservoir of the chemical(s) that could be used to replenish repaired or discarded DNA adducts.

Animals↗