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PubMed1986

Mutagenic activity of biliary metabolites of 6-hydroxymethylbenzo[a]pyrene.

The biliary excretion of the carcinogen 6-hydroxy-methylbenzo[a]pyrene was investigated in rats after i.p. administration. Mutagenicity of the parent compound and its biliary metabolites was tested in Ames Salmonella/microsome mutagenicity assay. Approximately 40% of the dose administered (0.25-0.5 mg/kg) to the rats was excreted in the bile within 6 h. 6-Hydroxymethylbenzo[a]pyrene was excreted primarily as water-soluble metabolites, including glucuronide and sulfate conjugates. Negligible quantities of unchanged 6-hydroxymethylbenzo[a]pyrene were excreted in the bile. In the presence of Aroclor-induced S9, 6-hydroxymethylbenzo[a]pyrene was a potent mutagen. The mutagenicity of bile from rats treated with 6-hydroxymethylbenzo[a]pyrene was variable in the absence of an activation system. However, the same bile samples were mutagenic in the presence of beta-glucuronidase and/or S9. These results indicate that biliary metabolites of 6-hydroxymethylbenzo[a]pyrene can be metabolically activated to mutagenic species.

Animals↗
PubMed1990

Stimulation of binding of benzo[a]pyrene metabolites to DNA by diet-induced peroxidative stress.

To investigate the influence of unsaturation of dietary fat on the oxidation of benzo[a]pyrene-7,8-dihydrodiol to DNA binding products, we fed diets containing 10% by weight of either safflower oil or lard to weanling rats. Compared with the group fed lard, the group fed safflower oil had 2.0- to 2.5-fold higher levels of unstimulated and peroxidation-stimulated activation of benzo[a]pyrene-7,8-dihydrodiol to DNA-binding metabolites, respectively, in hepatic nuclei. The rats fed safflower oil had a significant 75% higher level of lipid peroxidation as measured by the thiobarbituric acid assay. Rats fed safflower oil also showed 30% greater binding of (-)-benzo[a]pyrene-7,8-dihydrodiol oxidation products to DNA compared with animals fed lard, following administration of this dihydrodiol enantiomer through the hepatic portal vein. Significant diet-dependent differences were not apparent in DNA binding of the (+)-isomer, or in the tetrol production from either isomer; however, rats fed safflower oil showed a trend towards production of higher levels of anti-benzo[a]pyrene diol epoxide-derived tetrols. Activities of hepatic nuclear and microsomal aryl hydrocarbon hydroxylase and of cytosolic and microsomal glutathione S-transferases were not significantly affected by diet, nor was the activity of microsome-mediated binding of (+)- or (-)-benzo[a]pyrene-7,8-dihydrodiol to DNA in vitro. The results indicate that polyunsaturated fat in quantities as low as 10% by weight of the diet is sufficient to increase significantly the extent to which DNA-binding metabolites of benzo[a]pyrene are produced, and that this increased metabolism is likely to be independent of mixed-function oxidases.

Animals↗
PubMed2006

Molecular modeling benzo[a]pyrene N2-dG adducts in the two overlapping active sites of the Y-family DNA polymerase Dpo4.

The potent, ubiquitous environmental mutagen/carcinogen benzo[a]pyrene (B[a]P) induces a single major adduct [+ta]-B[a]P-N2-dG, whose bypass in most cases results in either no mutation (dCTP insertion) or a G-->T mutation (dATP insertion). Translesion synthesis (TLS) of [+ta]-B[a]P-N2-dG generally requires DNA polymerases (DNAPs) in the Y-family, which exist in cells to bypass DNA damage caused by chemicals and radiation. A molecular dynamics (MD) study is described with dCTP opposite [+ta]-B[a]P-N2-dG in Dpo4, which is the best studied Y-family DNAP from a structural point of view. Two orientations of B[a]P-N2-dG (BPmi5 and BPmi3) are considered, along with two orientations of the dCTP (AS1 and AS2), as outlined next. Based on NMR studies, the pyrene moiety of B[a]P-N2-dG is in the minor groove, when paired with dC, and can point toward either the base on the 5'-side (BPmi5) or the 3'-side (BPmi3). Based on published X-ray structures, Dpo4 appears to have two partially overlapping active sites. The architecture of active site 1 (AS1) is similar to all other families of DNAPs (e.g., the shape of the dNTP). Active site 2 (AS2), however, is non-canonical (e.g., the beta- and gamma-phosphates in AS2 are approximately where the alpha- and beta-phosphates are in AS1). In the Dpo4 models generated herein, using the BPmi3 orientation the pyrene moiety of [+ta]-B[a]P-N2-dG points toward the duplex region of the DNA, and is accommodated without distortions in AS1, but with distortions in AS2. Considering the BPmi5 orientation, the pyrene moiety points toward the ss-region of DNA in Dpo4, and sits in a hole defined by the fingers and little fingers domain ("chimney"); BPmi5 is accommodated in AS2 without significant distortions, but poorly in AS1. In summary, when dCTP is paired with [+ta]-B[a]P-N2-dG in the two overlapping active sites in Dpo4, the pyrene in the BPmi3 orientation is accommodated better in active site 1 (AS1), while the pyrene in the BPmi5 orientation is accommodated better in AS2. Finally, we discuss why Y-family DNAPs might have two catalytic active sites.

Benzopyrenes↗
PubMed1989

Quenching of fluorescence of pyrene-substituted lecithin by tetracyanoquinodimethane in liposomes.

In this work we have applied a kinetic scheme derived from fluorescence kinetics of pyrene-labeled phosphatidylcholine in phosphatidylcholine membrane to explain the fluorescence quenching of 1-palmitoyl-2-(10-[pyrenl-yl]-sn-glycerol-3-phosphatidylchol ine (PPDPC) liposomes by tetracyanoquinodimethane (TCNQ). The scheme was also found to be applicable to neat PPDPC and the effect of the quencher could be attributed to certain steps of the proposed mechanism. The TCNQ molecules influence the fluorescence of pyrene moieties in PPDPC liposome in two ways. Firstly, an interaction between the quencher molecule and the pyrene monomer in the excited state quenches monomer fluorescence and effectively prevents the diffusional formation of the excimer. Secondly, an interaction between the quencher molecule and the excited dimer quenches the excimer fluorescence. The TCNQ molecule does not prevent the formation of the excimer in pyrene moieties aggregated in such a way that they require only a small rotational motion to attain excimer configuration. The diffusional quenching rate constant is calculated to be 1.0 x 10(8) M-1 s-1 for the pyrene monomer quenching and 1.3 x 10(7) M-1 s-1 for the pyrene excimer quenching. The diffusion constant of TCNQ is 1.5 x 10(-7) cm2 s-1 for the interaction radii of 0.8-0.9 nm. The TCNQ molecules are practically totally partitioned in the membrane phase.

Diffusion↗
PubMed2002

Stability and aromaticity of the cyclopenta-fused pyrene congeners.

The aromaticity of all possible cyclopenta-fused pyrene congeners has been investigated at various levels of theory. On the basis of the calculated resonance energies and magnetic properties (delta(1)H data, magnetic susceptibility anisotropies, and NICS values), the overall aromaticity of these compounds is found to decrease gradually with increasing number of externally fused five-membered rings. The relatively small differences (<5 kcal/mol) in thermodynamic stability of the isomeric dicyclopentapyrenes (E(tot): dicyclopenta[cd,fg]- > dicyclopenta[cd,jk]- > dicyclopenta[cd,mn]pyrene), which differs from the aromaticity order based on the magnetic criteria (dicyclopenta[cd,mn]- > dicyclopenta[cd,fg]- > dicyclopenta[cd,jk]pyrene), is shown by model calculations to be dominated by sigma-strain imposed on the pyrene skeleton by sequential cyclopenta-fusion. This is supported by the computed homodesmotic reaction energies and aromatic stabilization energy (ASE(isom)) from isodesmic aromatic-nonaromatic isomerization, and by the model calculations on "distorted" cyclopenta[cd]pyrenes. The elusive tetracyclopenta[cd,fg,jk,mn]pyrene is computed to be bowl-shaped; its corresponding planar geometry is the transition state for bowl-bowl interconversion.

Journal Article↗
PubMed2005

Probing intermolecular communication with surface-attached pyrene.

We report on the covalent attachment of pyrene derivatives to solid substrates and their spectroscopic and electrochemical characterization. We have constructed several molecular assemblies attached to silica and indium-doped tin oxide surfaces where pyrene molecules are co-immobilized with other functionalities. It was shown that the addition of hydrophobic molecules to the pyrene-containing interface results in a significant decrease in the pyrene I1/I3 vibronic emission band ratio and an increase in the water drop contact angle due to increased hydrophobicity of the interface. The co-attachment of perylenedodecanoic acid, for which the absorption band overlaps with the emission spectrum of pyrene, shows significant intermolecular communication between these species. The co-immobilization of ferrocene serves as an effective fluorescence quencher for tethered pyrene. In all cases, our data point to significant intermolecular communication between adsorbate species, and the combination of spectroscopic and electrochemical interrogation provides insight into the loading density and local environment(s) characteristic of these interfaces.

Journal Article↗
PubMed2005

Probing interfacial organization in surface monolayers using tethered pyrene. 1. Structural mediation of electron and proton access to adsorbates.

We have synthesized and characterized a family of self-assembled monolayers containing pyrene derivatives on gold and indium-doped tin oxide (ITO) substrates. The covalently bound pyrene functionalities serve as either spectroscopic or electrochemical probes of their immediate environment, and we explore their electrochemical response in this paper. When these compounds are the only constituents bound to the interfaces, the molecules enjoy significant structural freedom. The addition of aliphatic adsorbates to the interfaces serves to place the pyrene derivatives in a more restricted environment. Cyclic voltammetry shows that the organization of a monolayer with pyrene derivatives, and the position of the terminal pyrene within such monolayer, depend sensitively on the length of the pyrene tether and the presence or absence of aliphatic interfacial species, as well as the identity of the substrate.

Journal Article↗
PubMed2000

Enzyme-mediated dialdehyde formation: an alternative pathway for benzo[a]pyrene 7,8-dihydrodiol bioactivation.

Polycyclic aromatic hydrocarbons, such as benzo[a]pyrene, are widespread environmental carcinogens of human concern. Several enzymatic systems have been shown to activate benzo[a]pyrene 7, 8-dihydrodiol, the proximate carcinogenic metabolite of benzo[a]pyrene, to a reactive species which produces both a chemiluminescence response and genotoxic lesions. The chemiluminescence response has been proposed to be the result of the formation of a dioxetane which upon ring opening forms a reactive dialdehyde intermediate. In in vitro incubations involving phorbol ester-stimulated human polymorphonuclear leukocytes or an isolated enzyme system consisting of myeloperoxidase, taurine, and hydrogen peroxide, a prolonged (>60 min) chemiluminescence response was observed from benzo[a]pyrene 7,8-dihydrodiol. HPLC analysis of the reaction mixture revealed the existence of a product which is dependent upon both taurine and the hydrocarbon. Characterization of this product using UV, NMR, and MS indicated that the product is a pyrene with two side chains resulting from bond breakage of a ring, yielding a dialdehyde. These side chains contain a portion of taurine covalently attached through imine formation with the aldehydes resulting from dioxetane ring opening. Replacement of taurine with either protein or DNA also produced a prolonged chemiluminescence response. These results demonstrate for the first time the formation of a novel electrophilic species from benzo[a]pyrene 7,8-dihydrodiol which along with an increased production of photons from this activation mechanism may lead to DNA and/or protein damage that is different from that elicited by diol epoxides.

Aldehydes↗
PubMed2006

Pyrene-p-tert-butylcalixarenes inclusion complexes formation: a surface photochemistry study.

Diffuse reflectance and luminescence techniques were used to study the photophysics and photochemistry of pyrene within p-tert-butylcalix[n]arenes with n = 4, 6, and 8, and to study their ability to form inclusion complexes in heterogeneous media. Evidences for inclusion complex formation were found for the three hosts under study. Ground state diffuse reflectance results have shown the formation of ground state dimers of pyrene inside the cavity of calix[6]arene and calix[8]arene, with this feature much more evident for calix[6]arene. For calix[4]arene, only a monomer fits inside the cavity and the presence of pyrene microcrystals outside the cavity was detected. A luminescence lifetime distribution analysis was performed, revealing the presence of prompt emissions from the pyrene microcrystals outside the cavity in the case of calix[4]arene and from the constrained dimers inside the cavities of calix[6]arene and calix[8]arene. Transient absorption results have shown the presence of pyrene radical cation and also of trapped electrons for the three hosts under study. The formation of the phenoxyl radical of the calixarene following the laser pulsed excitation of pyrene at 355 nm is increased for calix[6]arene and calix[8]arene. This feature is particularly relevant for calix[6]arene, suggesting a very favourable situation for the hydrogen atom abstraction to occur. The analysis of the degradation products revealed the presence of hydroxypyrene as a major photodegradation product for the three hosts. Dihydro-hydroxypyrene was also formed in the case of calix[6]arene and calix[8]arene. The formation of the calixarene's phenoxyl radical and subsequent hydrogen abstraction is consistent with the formation of dihydro-dihydroxypyrene.

Journal Article↗
PubMed1976

Carcinogenicity of benzo[a]pyrene 4,5-, 7,8-, and 9,10-oxides on mouse skin.

Benzo[a]pyrene and three arene oxides of benzo[a]pyrene (benzo[a]pyrene 4,5-, 7,8-, and 9,10-oxides) have been tested for carcinogenicity in mice by topical application of each compound (0.1 or 0.4 mumol) once every 2 weeks for 60 weeks. At the high dose, benzo[a]pyrene and the 7,8-oxide were highly carcinogenic, whereas the 4,5-oxide (K-region oxide) was weakly active and the 9,10-oxide was inactive. At the low dose, only benzo[a]pyrene was highly carcinogenic. The carcinogenic activities of the three arene oxides of benzo[a]pyrene were not correlated with their stabilities or mutagenic activities.

Animals↗
PubMed1976

Elucidation of hydrocarbon structure in an enzyme-catalyzed benzo[a]pyrene-poly (G) covalent complex.

The carcinogen, benzo[a]pyrene, was covalently attached to poly (G) by liver microsomes from rats pretreated with 3-methylcholanthrene. The complex was hydrolyzed with enzymes or base and products were isolated by Sephadex chromatography. Absorbance and fluorescence spectra of the products fit that of red-shifted pyrene aromatic system and suggest that metabolism has occurred at the 7-, 8-, 9-, and 10-positions of the hydrocarbon. Benzanthracene or chrysene fluorescence were not observed in these preparations. Benzo[a]pyrene derivatives were synthesized and purified by high-pressure liquid chromatography. Dehydration of 7,8-dihydroxy-7,8,9,10-tetrahydrobenzo[a]pyrene resulted in the formation of small amounts of 7-oxo-7,8,9,10-tetrahydrobenzoa[a]pyrene. A 7-keto species was also observed after similar treatment of the hydrocarbon-poly(G) hydrolysis products. Evidence of dehydration at the 9,10-positions was not observed. The hydrocarbon covalently bound to poly(G) is, therefore, a derivative of 7,8-dihydroxy-7,8,9,10-tetrahydrobenzol[a]pyrene with nucleic acid substitution at C-10 or 9.

Benzopyrenes↗
PubMed1982

Application of fluorescence and linear dichroism techniques to the characterization of the covalent adducts derived from interaction of (+/-)-trans-9,10-dihydroxy-anti-11,12-epoxy-9,10,11,12-tetrahydro-benzo[e]pyrene with DNA.

Spectroscopic techniques including absorption, fluorescence excitation and emission spectra, fluorescence decay profiles (determined by single photon counting techniques), and electric linear dichroism are applied to a study of the conformation of covalent adducts derived from a reaction of 9,10-dihydroxy-11,12-epoxy-9,10,11,12-tetrahydro[e]pyrene (B[e]PDE) with DNA. The characteristics of non-covalent adducts obtained from the intercalative binding of 9,10,11,12-tetrahydroxytetrahydrobenzo[e]pyrene (B[e]PT) (derived from the hydrolysis of B[e]PDE) with DNA are compared to those of the covalent B[e]PDE--DNA adducts. It is shown that there are two types of binding sites in B[e]PDE--DNA adducts: (1) an exterior binding site similar to the one observed with the isomeric 7,8-dihydroxy-9,10-epoxy-7,8,9,10-tetrahydrobenzo[a]pyrene (B[a]PDE)--DNA adducts, and (2) a quasi-intercalative type of binding site in which the properties of the pyrene chromophore are similar to those of an intercalated pyrene moiety, but in which the red shift in the absorption maximum, and fluorescence quenching are less pronounced. This latter conformation is not observed in covalent B[a]PDE--DNA adducts. It is shown that the DNA concentration is an important parameter in determining the relative number of pyrene chromophores at these two binding sites. The extent of covalent binding of B[e]PDE is 4-8 times less than the binding of B[a]PDE to DNA under the same experimental conditions. The reduced reactivity of B[e]PDE is tentatively attributed to steric hindrance due to quasi-diaxial conformations of the two hydroxyl groups in one of the two bay-regions of B[e]PDE.

Benzopyrenes↗
PubMed1968

Benzo(a)pyrene in gasoline partially persists in automobile exhaust.

On average 36 percent of the benzo[a]pyrene in an automobile's exhaust gas comes from the benzo[a]pyrene originally in the gasoline. Between 0.1 and 0.2 percent of the benzo[a]pyrene in the gasoline survives the combustion process and is recovered from the exhaust; 5 percent accumulates in the crankcase oil. Some of the benzo[a]pyrene in the gasoline is converted into other polynuclear aromatic hydrocarbons and other more polar compounds. For our experiments we used commercial gasoline containing benzo[a]pyrene at 1.0 part per million to which was added benzo[a]pyrene-8,9-(14)C at 1.1 parts per million as a radioactive tracer.

Benzopyrenes↗
PubMed1978

beta-Glucuronidase catalyzed hydrolysis of benzo(a)pyrene-3-glucuronide and binding to DNA.

beta-Glucuronidase catalyzes the hydrolysis of benzo[a]pyrene-3-glucuronide to 3-hydroxybenzo[a]pyrene. During the enzymatic hydrolysis, a benzo[a]pyrene derivative is formed which binds to DNA to a far greater extent than either the 3-hydroxybenzo[a]pyrene or its glucuronide. These results suggest that conjugates of benzo(a)pyrene may be converted by beta-glucuronidase at intracellular and organ sites distal to the initial sites of oxygenation and conjugation of benzo(a)pyrene to activated intermediates that are possibly carcinogenic.

Benzopyrenes↗
PubMed1980

DNA binding of benzo[a]pyrene metabolites. Effects of substrate and microsomal protein concentration in vitro, dietary contaminants, and tissue differences.

The binding of reactive benzo[a]pyrene metabolites to deproteinized DNA in vitro can be drastically changed, both quantitatively and qualitatively, in vitro by changes in the substrate concentration or the substrate/P-450 ratio, and in the intact animal by starvation or substitution of a 'purified protein test diet' for the regular laboratory chow. Liver, lung, and bowel microsomes from C57BL/6N and DBA/2N mice were examined. These data demonstrate the importance of dietary contaminants or nutrition during benzo[a]pyrene tumorigenesis. The profile of DNA binding of benzo[a]pyrene metabolites is also shown to be an extremely sensitive test for detecting minute amounts of induced cytochrome P1-450 and its associated aryl hydrocarbon (benzo[a]pyrene) hydroxylase (EC 1.14.14.2) activity. A direct correlation is not necessarily observed, however, between 'aryl hydrocarbon hydroxylase activity' and the amount of benzo[a]pyrene metabolites bound covalently to DNA. 'Untreated' genetically responsive mice are shown to have greater 'control' levels of benzo[a]pyrene metabolism in their various tissues than genetically nonresponsive mice simply on the basis that responsive mice have a lower threshold for 'responsiveness' to exogenous inducers inhaled and/or ingested in their crude diet, i.e., responsive 'control' animals already have partially induced enzymes.

Animals↗
PubMed1979

The effects of cytochrome P-450-448 inhibitors on the binding of benzo(a)pyrene and derivatives to DNA upon microsomal activation.

1. [3H]Benzo(a)pyrene and 6-substituted derivatives of [3H]benzo(a)pyrene are covalently bound to calf thymus DNA upon reaction with microsomal preparations from rats pretreated with 3-methylcholanthrene in the presence of NADPH. Two different types of cytochrome P-450-448 inhibitors, alpha-naphthoflavone and 1-benzylimidazole, show greater than 80% inhibition of the binding of benzo(a)pyrene to DNA. 2. In the presence of these inhibitors, 6-hydroxymethylbenzo(a)pyrene, 6-methylbenzo(a)pyrene and 6-formylbenzo(a)pyrene show varying degrees of inhibition of binding to DNA depending upon the inhibitor employed. 3. Polyguanylic acid is the most effective substrate for the binding of each activated polynuclear aromatic hydrocarbon; polyadenylic acid and DNA show essentially equivalent binding.

Animals↗
PubMed1980

The metabolism of benzo(a)pyrene by Chinese hamster ovary cells in culture.

1. The metabolism off the carcinogenic polycyclic hydrocarbon, benzo(a)pyrene, in Chinese hamster ovary cells in culture has been investigated. 2. Products with the properties on h.p.l.c. of 3-hydroxybenzo(a)pyrene and the trans-4,5-, 7,8- and 9,10-dihydrodiols of benzo(a)pyrene were detected in the cell medium when cells were incubated with benzo(a)pyrene for 24 h. 3. Examination of the nucleoside adducts present in hydrolysates of the DNA of Chinese hamster ovary cells that had been incubated with benzo(a)pyrene showed the presence of a product that co-chromatographed on Sephadex LH20 columns with the nucleoside adduct obtained from DNA that was allowed to react with the anti-isomer of the 7,8-dihydrodiol 9,10-epoxide of benzo(a)pyrene.

Animals↗
PubMedDate not supplied

Studies on the properties of highly purified cytochrome P-448 and its dependent activity benzo[a]pyrene hydroxylase, from Saccharomyces cerevisiae.

The yeast Saccharomyces cerevisiae, produces a cytochrome P-450 enzyme with a Soret peak in the reduced-CO difference spectrum at 448 nm. The enzyme purified to homogeneity (88-97% pure on a specific content basis) has a molecular wt. of 55 500 as determined by SDS-PAGE. Amino acid analysis of yeast cytochrome P-448 revealed 407 amino acid residues per molecule with a 43% complement of hydrophobic residues. Although the number of residues is smaller than cytochrome P-448 enzymes from mammalian sources, the percentage of hydrophobic residues is almost identical. Estimation of the haem content of yeast cytochrome P-448 showed that one haem group was present per molecule. Phospholipid was present at very low levels. The molecular wt. of the polypeptide chain plus an estimated 5-6 units of hexose and of hexosamine is in good agreement with the molecular wt. value obtained from SDS-PAGE. A reconstituted system of purified cytochrome P-448, purified NADPH-cytochrome P-450 (c) reductase and phospholipid showed aryl hydrocarbon hydroxylase activity towards benzo[a]pyrene. Both protein components, NADPH and dilauroyl phosphatidylcholine (or emulgen 911) were necessary for full activity. The NADPH requirement could be replaced by cumene hydroperoxide or H2O2 generated in situ from a glucose oxidase system; in each case Vmax is increased, but the apparent affinity for benzo[a]pyrene, as measured by an increased Km, is lowered. The spin state of purified yeast cytochrome P-448 was 94% low spin (22 degrees C) as determined from the temperature-dependent spin-state equilibrium. The addition of benzo[a]pyrene to this enzyme resulted in a change to higher spin state (18% high spin at 22 degrees C). Equilibrium gel filtration analysis of the number of benzo[a]pyrene binding sites per mole of enzyme monomer showed a value of 1 for purified yeast cytochrome P-448 and 6 for this enzyme in microsomal form. The corresponding values for purified and microsomal cytochrome P-450 from phenobarbital-pretreated rats are 1 and 6, respectively. However, purified cytochrome P-448 from beta-naphthoflavone-induced rats gave a value of 6 benzo[a]pyrene binding sites. Type I binding spectra with purified yeast cytochrome P-448 were observed with benzo[a]pyrene, lanosterol, ethylmorphine, dimethylnitrosamine, sodium phenobarbitone and perhydrofluorene. Type II spectral changes were observed with imidazole, aniline and benzphetamine. Cytochrome P-448 from Saccharomyces cerevisiae is identified as a distinct enzyme of the P-450 family. This enzyme however has many properties in common with cytochrome P-448 from mammalian sources.(ABSTRACT TRUNCATED AT 400 WORDS)

Amino Acids↗