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PubMed1979

The metabolic activation of benzo(a)pyrene and 9-hydroxybenzo(a)pyrene by liver microsomal fractions.

A rat liver microsome-mediated bacterial mutagenicity test showed 9-hyroxybenzo(a)pyrene to be significantly more effective as a pre-mutagen than benzo(a)pyrene. Experiments measuring the ability of these compounds to be metabolically activated to moieties that alkylate exogenous DNA demonstrated that 9-hydroxybenzo(a)pyrene was almost six times more effective than benzo(a)pyrene itself. Addition of trichloropropene-2,3-oxide to the reaction mixture enhanced the mutagenicity and DNA alkylation by benzo(a)pyrene but had little or no effect on the 9-hydroxybenzo(a)pyrene-mediated mutagenicity and alkylation. On the other hand, 7,8-benzoflavone inhibited the microsome-mediated mutagenicity and DNA alkylating activity of both hydrocarbons.

Alkylation↗

PubMed1997

6-sulfooxymethylbenzo[a]pyrene is an ultimate electrophilic and carcinogenic form of the intermediary metabolite 6-hydroxymethylbenzo[a]pyrene.

Previous experiments have demonstrated that the intermediary metabolite 6-hydroxymethylbenzo[a] pyrene (HMBP) can be activated to the electrophilic mutagen, 6-sulfooxymethylbenzo[a]pyrene (SMBP), by rat and mouse liver PAPS-dependent sulfotransferase activity or by chemical synthesis. This aralkylating metabolite and 6-hydroxymethylbenzo[a]pyrene were individually administered to groups of 12 female Sprague-Dawley rats, at a 0.2 micromol dose three times weekly for 20 doses. SMBP induced sarcomas at the site of injection in 12 of 12 rats by 33 weeks, whereas HMBP induced sarcomas at the site of injection in 12 of 12 rats by 31 weeks. These results, taken together with the results of previous studies, strongly support the hypothesis that the electrophilic mutagen SMBP accounts for most, if not all, of the complete carcinogenicity of the intermediary metabolite HMBP and probably at least some of the complete carcinogenicity of 6-methylbenzo[a]pyrene (MBP), 6-formylbenzo[a]pyrene (formylBP), and even benzo[a]pyrene (BP), all of which are metabolized to HMBP.

Animals↗

PubMed1978

Tumorigenicity of the optical enantiomers of the diastereomeric benzo[a]pyrene 7,8-diol-9,10-epoxides in newborn mice: exceptional activity of (+)-7beta,8alpha-dihydroxy-9alpha,10alpha-epoxy-7,8,9,10-tetrahydrobenzo[a]pyrene.

The tumorigenicities of benzo[a]pyrene and each optical enantiomer of the diastereomeric benzo[a]pyrene 7,8-diol-9,10-epoxides derived from trans-7,8-dihydroxy-7,8-dihydrobenzol[a]pyrene were tested by sequential intraperitoneal injection of mice with 1,2, and 4 nmol, or with 2, 4, and 8 nmol of each compound on the 1st, 8th, and 15th day of life, respectively. The experiment was terminated when the animals were 34--37 weeks old. (+)-7beta, 8alpha-dihydroxy-9alpha,10alpha-epoxy-7,8,9,10-tetrahydrobenzol[a]pyrene [(+)-BP-7beta,8alpha-diol-9alpha,10alpha-epoxide 2] had exceptional tumorigenicity, whereas benzo[a]-pyrene and the other three optically pure isomers of the benzo[a]pyrene 7,8-diol,9,10-epoxides had little or no activity. These results demonstrate differences in the carcinogenic activities of optically active isomers of a polycyclic hydrocarbon diol epoxide. Eleven percent of control mice had pulmonary tumors, whereas 71% and 100% of the mice treated with a total dose of 7 or 14 nmol of (+)-BP-7beta,8alpha-diol-9alpha,10alpha-epoxide 2, respectively, had pulmonary tumors. Control mice had an average of 0.12 pulmonary tumors per mouse, whereas mice treated with a total dose of 7 or 14 nmol of (+)-BP-7beta,8alpha-diol-9alpha,10alpha-epoxide 2 had 1.72 and 7.67 pulmonary tumors per mouse, respectively. Mice treated with 14 nmol of (-)-BP-7alpha,8beta-diol-9beta,10beta-epoxide 2, (-)-BP-7beta,8alpha-diol-9beta,10beta-epoxide 1, or (+)-BP-7alpha,8beta-diol-9alpha,10alpha-epoxide 1 had 0.13, 0.25, and 0.34 pulmonary tumors per animal, respectively.

Animals↗

PubMed1977

Epidermal hyperplasia after topical application of benzo (a) pyrene, benzo (a) pyrene diol epoxides, and other metabolites.

The effects of benzo(a)pyrene (BP) and 22 derivatives upon the number of nuclei per unit length of epidermis, the number of cell layers of epidermis, and the thickness of the epidermal layer were studied. Several derivatives of BP induced changes in epidermal morphology that are typical of those produced by various agents that promote skin tumorigenesis after application of an initiator. The most potent compounds tested were the BP diol epoxides, (+/-)-7beta,8alpha-dihydroxy-9beta, 10beta-epoxy-7,8,9,10-tetrahydrobenzo-(a)pyrene (diol epoxide 1) and (+/-)-7beta,8alpha-dihydroxy-9alpha, 10alpha-epoxy-7,8,9,10-tetrahydrobenzo(a)pyrene (diol epoxide 2). These derivatives were followed in activity by 9-hydroxybenzo(a)pyrene, 2-hydroxybenzo(a)pyrene, and by 9,10-epoxy-7,8,9,10-tetrahydrobenzo(a)pyrene. The possible implications of these results with regard to the carcinogenicity of BP on mouse skin are discussed.

Administration, Topical↗

PubMed1992

Percutaneous absorption and metabolism of pyrene, benzo[a]pyrene, and di(2-ethylhexyl) phthalate: comparison of in vitro and in vivo results in the hairless guinea pig.

The in vitro and in vivo absorption and metabolism of pyrene, benzo[a]pyrene, and di(2-ethylhexyl) phthalate (DEHP) were investigated in the hairless guinea pig. The in vitro method, which involved the use of flow-through diffusion cells and Hepes-buffered Hanks' balanced salt solution containing 4% bovine serum albumin as perfusate, was demonstrated to be a suitable system for predicting in vivo absorption of the above lipophilic compounds. The successful application of the in vitro technique for these compounds is significant because no satisfactory in vitro method has hitherto been developed to predict in vivo absorption of highly lipophilic chemicals. Quantification of parent compounds and metabolites that permeated into perfusates and those that remained in skin discs provided insight into the process by which the chemicals penetrated through the skin. Pyrene was absorbed primarily by a passive diffusion process, although a small fraction of the administered dose was biotransformed into metabolites in the skin and partitioned into the receptor fluid. Absorption of benzo[a]pyrene was mediated by biotransformation processes. A metabolite derived from the ultimate carcinogen of this compound, benzo[a]pyrene r-7, t-8,9,10-tetrahydrotetrol, was identified in the receptor fluid. Most of the administered DEHP remained in the skin and only a very small fraction of the dose partitioned into the receptor fluid in either viable or nonviable skin. Data from the present study led to the conclusion that the in vitro method can be utilized to predict in vivo absorption for compounds of high lipophilicity and that dermal metabolism facilitates partitioning of metabolites into the receptor fluid and hence may affect the biological activities of dermally applied compounds.

Administration, Cutaneous↗

PubMedDate not supplied

Phototoxicity of pyrene and benzo[a]pyrene to embryo-larval stages of the Pacific oyster Crassostrea gigas.

There is a growing body of evidence to suggest that certain polycyclic aromatic hydrocarbons (PAHs) pose a greater hazard to aquatic organisms than previously demonstrated, due to their potential to cause photo-induced toxicity when exposed to ultraviolet (UV) radiation. The consequences of photo-induced toxicity are reported here for embryo-larval stages of the pacific oyster Crassostrea gigas, following exposure to pyrene and benzo[a]pyrene. During laboratory investigations, significant increases in toxicity were observed in the presence of environmentally attainable levels of UV-radiation, compared with embryos exposed to PAH alone, at levels previously deemed to have little acute biological effect. The phototoxicity of pyrene and benzo[a]pyrene completely inhibited the development to the D-shell larval stage when embryos were simultaneously exposed to 5 microg l(-1) PAH and ultraviolet light (UVB = 6.3 +/- 0.1 microW/cm2 and UVA = 456.2 +/- 55 microW/cm2). A linear relationship was also demonstrated for benzo[a]pyrene phototoxicity with decreasing UV light intensity.

Animals↗

PubMed2006

Removal of pyrene and benzo(a)pyrene from contaminated water by sequential and simultaneous ozonation and biotreatment.

The removal of pyrene and benzo(a)pyrene from contaminated water by sequential and simultaneous ozonation-bioremediation techniques was investigated. During the sequential treatment, ozonation using 0.5 or 2.5 mg/L ozone was used as a pretreatment process, whereas, during the simultaneous treatment process, ozonation of hydrocarbon-contaminated water at a predetermined duration using 0.5 mg/L ozone was made in the presence of microbial biomass. Ozonation was not beneficial for the removal of pyrene. However, despite a decreased specific biodegradation rate, ozonation improved the overall elimination of benzo(a)pyrene during both treatment processes. The overall removal of benzo(a)pyrene increased from 23 to 91% after exposure of the water to 0.5 mg/L ozone for 30 minutes during the simultaneous treatment process and further to 100% following exposure to 2.5 mg/L ozone for 60 minutes during the sequential treatment mode, demonstrating the benefits of combined ozonation-biological treatment for the removal of polycyclic aromatic hydrocarbons.

Benzo(a)pyrene↗

PubMed1999

Seasonal effect on airborne pyrene, urinary 1-hydroxypyrene, and benzo(a)pyrene diol epoxide-hemoglobin adducts in the general population.

Exposure to airborne polycyclic aromatic hydrocarbons (PAHs) in 65 employees (40 sampled both in summer and winter, 15 sampled in summer only, and 10 sampled in winter only) with no occupational exposure to PAHs was assessed by measuring: personal exposure to pyrene, urinary excretion of 1-hydroxypyrene (1-OHP), and benzo(a)pyrene diol epoxide adducts to hemoglobin (BPDE-Hb). Overall, office employees were exposed to significantly higher levels of pyrene in winter (4.54 +/- 2.35 ng/m3, mean +/- SD) than in summer (1.67 +/- 1.92 ng/m3, mean +/- SD; P < 0.001), but no such seasonal variability was observed in 1-OHP excretion. Tobacco smoking was the major determinant of 1-OHP excretion. BPDE-Hb adducts were measured by gas chromatography-mass spectrometry as benzo(a)pyrene tetrols (BPT) released from adducted hemoglobin. In the 65 employees analyzed, mean BPT levels +/- SD were higher in winter (0.14 +/- 0.38 fmol/mg Hb) than summer (0.031 +/- 0.022 fmol/mg Hb). This difference was not statistically significant, probably because of the small proportion of subjects with detectable adducts (11% in summer and 16% in winter). BPDE-Hb adducts were not significantly associated with sex, age, diet, smoking habits, or with pyrene levels and 1-OHP excretion. This is the first report providing reference BPDE-Hb adduct values for the general population not occupationally exposed to environmental PAHs and shows a tendency to seasonal variability, with higher BPT levels in winter when environmental PAHs are also high.

Adolescent↗

PubMed1989

Roles of individual human cytochrome P-450 enzymes in the bioactivation of benzo(a)pyrene, 7,8-dihydroxy-7,8-dihydrobenzo(a)pyrene, and other dihydrodiol derivatives of polycyclic aromatic hydrocarbons.

Human liver microsomes oxidized 7,8-dihydroxy-7,8-dihydrobenzo(a)pyrene [B(a)P-7,8-diol] to products that yield DNA adduct formation and umu gene expression in the tester system Salmonella typhimurium TA1535/pSK1002. The umu response is correlated to levels of microsomal cytochrome P-450NF (P-450NF) and nifedipine oxidation in different human liver samples used for activation, and both the (+)- and (-)-enantiomers of B(a)P-7,8-diol gave similar results in these and other assays. The microsomal umu response was inhibited by antibodies raised against P-450NF. 7,8-Benzoflavone stimulated the B(a)P-7,8-diol-dependent umu response observed with purified P-450NF and human liver and lung microsomes. Thus, P-450NF appears to be the major enzyme involved in the activation of B(a)P-7,8-diol in human liver and possibly lung. Similar results were obtained for the activation of trans-9,10-dihydroxy-9,10-dihydrobenzo(b)fluoranthene and trans-3,4-dihydroxy-3,4-dihydro-7,12-dimethylbenz(a)anthracene, compounds that are known to form highly tumorigenic diol-epoxides. The major product of the oxidation of (+)-B(a)P-7,8-diol was the cis-syn isomer of benzo(a)pyrene-7,8,9,10-tetraol[7 beta, 8 alpha, 9 beta, 10 beta-tetrahydroxy-7,8,9,10-tetrahydrobenzo(a)pyrene]. Studies on the nature of the human liver enzymes involved in the formation of B(a)P-7,8-diol [from benzo(a)pyrene] indicate that neither P-450NF, P-450PA, P-450j, P-450DB, nor P-450MP is involved. The correlation of 7,8-diol formation with phenacetin O-deethylation in a set of liver samples and the partial inhibition of the reaction by 7,8-benzoflavone and anti-rat P-450 beta NF-B suggest that the enzyme involved may be P1-450, the human ortholog of rat P-450 beta NF-B, which catalyzes both the formation of B(a)P-7,8-diol and its subsequent oxidation in tissues of polycyclic hydrocarbon-treated rats. The differential effects of inhibitors indicate that benzo(a)pyrene 3-hydroxylation, 4,5-epoxidation, and 9,10-epoxidation are catalyzed by an enzyme(s) distinct from that which forms the 7,8-epoxide. The roles of the human P-450 enzymes differ from the rodent orthologs in the paradigm for bioactivation of polycyclic hydrocarbons; further, flavones appear to have opposing effects on diol formation and further epoxidation in both human liver and lung.

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

PubMed1985

Quantitation of benzo(a)pyrene metabolite: DNA adducts in selected hepatic and pulmonary cell types isolated from [3H]benzo(a)pyrene-treated rabbits.

Benzo(a)pyrene metabolite: deoxyribonucleoside adducts were analyzed in hepatic and pulmonary cells isolated from rabbits 24 h after i.v. administration of [3H]BP (1 mg/kg; 50 mCi/kg). The major adduct in each of the cell types analyzed was (+)-r-7, t-8-dihydroxy-t-9, 10-oxy-7, 8, 9, 10-tetrahydrobenzo(a)pyrene: deoxyguanosine, but (+/-)-r-7, t-8-dihydroxy-c-9, 10-oxy-7, 8, 9, 10-tetrahydrobenzo(a)pyrene: deoxyguanosine and very low levels of (-)-r-7, t-8-dihydroxy-t-9, 10-oxy-7, 8, 9, 10-tetrahydrobenzo(a)pyrene -deoxyguanosine and an unidentified adduct were also observed. The level of the major adduct was similar in each of the isolated cell types and was at least as high in cells with very low cytochrome P-450-dependent monooxygenase activity (hepatic nonparenchymal cells and alveolar macrophages) as in those with higher activity (hepatocytes, alveolar type II cells, and Clara cells). The binding of benzo(a)pyrene metabolites to proteins was also determined, and again binding levels did not correlate with differences in cytochrome P-450 activity.

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

PubMed2007

Humic acid effect on pyrene degradation: finding an optimal range for pyrene solubility and mineralization enhancement.

The addition of humic acid (HA) to polycyclic aromatic hydrocarbon (PAH) contaminated systems has been shown to enhance, inhibit, or have no effect on the biodegradation of these PAHs. In this study, the surfactant effects of Elliott soil HA (ESHA) at two pH values were tested. At pH 7.0, ESHA did not behave as a surfactant. At pH 11.8, ESHA acted as a surfactant, as displayed by a decrease in surface tension with increasing concentrations of ESHA. The effect of ESHA on pyrene solubility was tested by adding 0 to 800 microg ESHA/g soil to soil-slurries. Enhancement of pyrene apparent solubility demonstrated a dose- and time-related effect. Broader doses from 0 to 10,080 microg ESHA/g soil and three higher doses from 3,360 to 10,080 microg ESHA/g soil were tested for their effects on pyrene mineralization by indigenous soil microorganisms and a novel PAH-degrading Mycobacterium sp. KMS in soil microcosms, respectively. ESHA amendments between 20 and 200 microg ESHA/g soil were found to consistently increase pyrene mineralization by indigenous microorganisms, while the 10,080 microg ESHA/g soil produced inhibition and all other doses presented no effects. Pyrene degradation by M. KMS was significantly inhibited by the addition of the highest dose of ESHA.

Biodegradation, Environmental↗

PubMedDate not supplied

S-Adenosyl-L-methionine is a carbon donor in the conversion of benzo[alpha]pyrene to 6-hydroxymethylbenzo[alpha]pyrene by rat liver S-9.

In earlier studies we reported that 6-hydroxymethylbenzo[alpha]pyrene is a metabolite of benzo[alpha]pyrene and of 6-methylbenzo[alpha]pyrene when these substrates are incubated with homogenates or microsomal preparations of liver and microsomal preparations of subcutaneous tissue from Sprague--Dawley rats. However, the origin of the carbon donor was not established. We now report that S-adenosyl-L-methionine (SAM) can serve as a carbon donor in the metabolic formation of 6-hydroxymethylbenzo[alpha]pyrene from benzo[alpha]pyrene by the S-9 fraction of rat liver.

Animals↗

PubMed1999

Fate of phenanthrene, pyrene and benzo[a]pyrene during biodegradation of crude oil added to two soils.

The release of 14CO2 from 9-[14C]phenanthrene, 4,5,9,10-[14C]pyrene and 7-[14C]benzo[a]pyrene, added to Brent/Fortes crude oil and mixed into a pristine sand soil (0.40% organic C) and a pristine organic soil (22.9% organic C), was determined. After 244 days at 25 degrees C, 11.1 +/- 3.5% (sand) and 17.1 +/- 0.30% (organic) phenanthrene-14C and 9.77 +/- 2.8% (sand) and 5.86 +/- 1.4% (organic) benzo[a]pyrene-14C was released. After 210 days, 3.65 +/- 0.5% (sand) and 4.43 +/- 0.33% (organic) pyrene-14C was released. Inoculation of these two soils with DC1 and PD2 (bacteria capable of accelerating the phenanthrene and pyrene mineralisation in soil in the absence of crude oil) either at day 0 or after release as 14CO2 by indigenous degraders had ceased, failed to increase or initiate further mineralisation. Thus, aged PAH residues were non-bioavailable to these metabolically competent degrading microorganisms. At the end of the first period of incubation (210 days or 244 days), the total aromatic hydrocarbons recovered using Soxhlet extraction was 0.18% (sand) and 42.8% (organic) compared with approximately 100% from bio-inhibited soils. This confirmed that the indigenous microbiological activity not only caused a limited amount of PAH mineralisation but also reduced the extractability of residues, possibly due to the generation of metabolites which were chemisorbed and bound (and non extractable) in 'aged' soils.

Benzopyrenes↗

PubMed1977

Laser photolysis and fluorescence studies on pyrene-thiazide and pyrene-diazoxide systems.

The laser photolysis studies on pyrene, pyrene-thiazides and pyrene-diazoxide systems in acetonitrile revealed that thiazides and diazoxide can scavenge the photoejected electron. It was found that the pyrene fluorescence is quenched by the present diuretics and related compounds and both static and dynamic quenching constants were obtained. Thiazides quench the fluorescence through both static and dynamic mechanism, while the small static quenching constant and no lifetime shortening of pyrene were observed in the case of diazoxide quencher. This difference may correspond to the difference of their diuretic activity.

Diazoxide↗

PubMed1984

Benzo(e)pyrene-induced alterations in the metabolic activation of benzo(a)pyrene and 7,12-dimethylbenz(a)anthracene by hamster embryo cells.

Benzo(e)pyrene (BeP) is a cocarcinogen with benzo(a)pyrene (BaP) and an anticarcinogen with 7,12-dimethylbenz(a)anthracene (DMBA) in mouse skin initiation-promotion assays (Slaga, T.J., Jecker, L., Bracken, W.M. and Weeks C.E. Cancer Lett. 7: 51-59, 1979). We have investigated the effects of BeP on the metabolic activation of BaP and DMBA in early-passage cultures of Syrian hamster embryo cells. BeP had no effect on BaP-induced mutation frequencies in hamster embryo cell-mediated assays with V79 target cells. However, it inhibited the DMBA-induced mutagenesis by as much as 10-fold at the highest dose tested. Low doses of BeP did not affect the total amount of BaP metabolized, but the proportion of water-soluble metabolites was reduced, and the proportions of trans-7,8-dihydro-7,8-dihydroxybenzo(a)pyrene and trans-9,10-dihydro-9,10-dihydroxybenzo(a)pyrene were increased. Higher doses did decrease BaP metabolism and caused similar alterations in the metabolite profile. In cultures treated with trans-7,8-dihydro-7,8-dihydroxybenzo(a)pyrene, BeP greatly reduced the oxidative metabolism of this diol. BeP inhibited DMBA metabolism at all doses tested; the proportion of water-soluble metabolites formed was decreased, and the proportions of trans-8,9-dihydro-8,9-dihydroxy-7,12-dimethylbenz(a)anthracene and trans-3,4-dihydro-3,4-dihydroxy-7,12-dimethylbenz(a)anthracene were increased. The results demonstrate that BeP is an effective inhibitor of the secondary oxidation of carcinogenic hydrocarbon diols required to convert diols which are proximate carcinogens to ultimate carcinogens such as diol-epoxides. The balance between (a) limited inhibition with consequent increase in total exposure to the ultimate carcinogenic form and (b) sufficient inhibition to reduce exposure to the ultimate carcinogenic form may determine whether BeP acts as a co- or anticarcinogen with a particular carcinogenic hydrocarbon.

9,10-Dimethyl-1,2-benzanthracene↗

PubMed1986

Inhibition of the mutagenicity and metabolism of 6-methyl-benzo[a]pyrene and 6-hydroxymethyl-benzo[a]pyrene.

Previously reported inhibitors of benzo[a]pyrene (BaP) mutagenicity in Salmonella typhimurium strain TA98 were tested for their effectiveness against the mutagenicity of 6-methyl-benzo[a]pyrene (6-CH3-BaP), 6-hydroxymethyl-benzo[a]pyrene (6-CH2OH-BaP) and 6-acetoxymethyl-benzo[a]pyrene (6-CH3COOCH2-BaP). Dose-response curves obtained for phenothiazine (PTH), 2-chlorophenothiazine (2Cl-PTH), phenylisothiocyanate (PHN), phenethylisothiocyanate (PNE), trans-retinol (TR) and disulfiram (TETD) showed a variety of degrees of inhibition of mutagenicity. Additionally, glutathione (GSH) was found to inhibit the mutagenicity of 6-CH3COOCH2-BaP, and the mutagenicity of 6-CH2OH-BaP was enhanced by the addition of supplemental ATP, Na2SO4 and EDTA. Only 2Cl-PTH was equally as good an inhibitor of 6-CH3-BaP and BaP, reducing revertant colonies to less than 50% of control at 10 X BaP concentration. To probe the mechanism of inhibition, the effect of 2Cl-PTH on the binding of BaP and the 6-substituted benzo[a]pyrenes to cytochrome P-450 was investigated by difference spectroscopy. Also, the effect of 2Cl-PTH on the subsequent metabolism of 6-CH3-BaP and 6-CH2OH-BaP was investigated by rapid scan difference spectroscopy and high-performance liquid chromatographic separation of products. The results are consistent with a major mechanism of inhibition for 2Cl-PTH involving a competition for the cytochrome P-450 binding site.

Benzopyrenes↗

PubMed1980

A benzo[alpha]pyrene-7,8-dihydrodiol-9,10-epoxide is the major metabolite involved in the binding of benzo[alpha]pyrene to DNA in isolated viable rat hepatocytes.

Benzo[alpha]pyrene is metabolised by isolated viable hepatocytes from both untreated and 3-methylcholanthrene pretreated rats to reactive metabolites which covalently bind to DNA. The DNA from the hepatocytes was isolated, purified and enzymically hydrolysed to deoxyribonucleosides. The hydrocarbon-deoxyribonucleoside products after initial separation, on small columns of Sephadex LH-20, from unhydrolysed DNA, oligonucleotides and free bases, were resolved by high pressure liquid chromatography (HPLC). The qualitative nature of the adducts found in both control and pretreated cells was virtually identical; however pretreatment with 3-methylcholanthrene resulted in a quantitatively higher level of binding. The major hydrocarbon-deoxyribonucleoside adduct, found in hepatocytes co-chromatographed with that obtained following reaction of the diol-epoxide, (+/-) 7 alpha,8 beta-dihydroxy-9 beta,10 beta-epoxy-7,8,9,10-tetrahydrobenzo[alpha]pyrene with DNA. Small amounts of other adducts were also present including a more polar product which co-chromatographed with the major hydrocarbon-deoxyribonucleoside adduct formed following microsomal activation of 9-hydroxybenzo[alpha]-pyrene and subsequent binding to DNA. In contrast to the results with hepatocytes, when microsomes were used to metabolically activate benzo[alpha]-pyrene, the major DNA bound-product co-chromatographed with the more polar adduct formed upon further metabolism of 9-hydroxybenzo[alpha]pyrene. These results illustrate that great caution must be exercised in the extrapolation of results obtained from short-term mutagenesis test systems, utilising microsomes, to in vivo carcinogenicity studies.

Animals↗

PubMed1977

Nucleoside adducts from the in vitro reaction of benzo[a]pyrene-7,8-dihydrodiol 9,10-oxide or benzo[a]pyrene 4,5-oxide with nucleic acids.

The covalent binding of benzo[a]pyrene 4,5-oxide and benzo[a]pyrene-7,8-dihydrodiol 9,10-oxide isomer I and isomer II to nucleic acids in aqueous acetone solution has been investigated. Benzo[a]pyrene 4,5-oxide reacted preferentially with guanosine residues. On the other hand, benzo[a]pyrene-7,8-dihydrodiol 9,10-oxide isomer I and II reacted extensively with guanosine, adenosine, and cytidine residues. Time course studies showed that the reactivity of isomer I or isomer II with homopolyribonucleotides followed the order poly(G) greater than poly(A) greater than poly(C). Alkaline or enzymatic hydrolysis of the modified nucleic acids and subsequent chromatography on Sephadex LH-20 columns yielded benzo[a]pyrene-nucleotide adducts. These were enzymatically converted to the corresponding nucleosides which were resolved into several distinct components by high-pressure liquid chromatography. Evidence was obtained for the presence of multiple nucleoside adducts of guanosine, adenosine, cytidine, deoxyguanosine, deoxyadenosine, and deoxycytidine. The HPLC profiles of adducts formed with isomer I were different from the corresponding profiles of adducts formed with isomer II. Structural aspects of these nucleoside adducts are discussed.

Alcohols↗