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At least 271 records · Page 15Linked to original sources
PubMed1978

Modification of DNA by the benzo[a]pyrene metabolite diol-epoxide r-7,t-8-dihydroxy-t-9,10-oxy-7,8,9,10-tetrahydrobenzo[a]pyrene.

The structural modification of double-stranded circular DNA of simian virus 40 and plasmid ColE1 by in vitro binding of r-7,t-8-dihydroxy-t-9,10-oxy-7,8,9,10-tetrahydrobenzo[a]pyrene was studied. Stepwise hydrolysis with endonuclease S1 and DNase followed by DNA base analysis by thin-layer chromatography provided evidence that binding to adenine caused the local denaturation of DNA, whereas the more than 10-fold greater binding to guanine did not create such local denaturation. Of the two synthetic double-stranded polymers, poly(dA-dT).poly(dA-dT) and poly(dG-dC).poly(dG-dC), bound to the diol-epoxide, only the former showed a marked hydrolysis after endonuclease S1 treatment, whereas binding occurred 24-fold more on the latter.

Benzopyrenes↗
PubMed1993

Formation of the adduct 6-(deoxyguanosin-N2-yl)-3-amino-benzo[a]pyrene from the mutagenic environmental contaminant 3-nitrobenzo[a]pyrene.

3-Nitrobenzo[a]pyrene (3-nitro-B[a]P) is a potent bacterial mutagen as a result of nitroreduction. Reaction of N-hydroxy-3-amino-B[a]P, prepared in situ from reduction of 3-nitro-B[a]P with calf thymus DNA, was studied. After enzymatic digestion of the DNA, the resulting modified nucleosides were analyzed by thermospray HPLC-MS and high-resolution proton NMR spectroscopy. The major adduct was identified as 6-(deoxyguanosin-N2-yl)-3-amino-B[a]P. The same adduct was obtained from incubation of DNA with 3-nitro-B[a]P in the presence of the mammalian nitroreductase xanthine oxidase, and hypoxanthine. These data indicate that a mammalian nitroreductase can metabolize 3-nitro-B[a]P to an activated derivative that reacts with DNA to give a novel adduct distant from the site of N-hydroxylation.

Animals↗
PubMed1981

The molecular structure of (+/-)- 7 alpha, 8 beta-dihydroxy-7,8-dihydrobenzo[a]pyrene, an early metabolite of benzo[a]pyrene.

The molecular structure of (+/-)-7 alpha, 8 beta-dihydroxy-7,8-dihydrobenzo[a]pyrene has been determined by X-ray crystallographic methods. The analysis has shown that the two hydroxyl groups are trans to each other and di-equatorial to the ring. The dihydrobenzene group adopts a distorted half-chair pucker. Trends in several bond distances indicate reactive points in the molecule.

Benzopyrenes↗
PubMed1979

The irreversible binding of benzo[a]pyrene to rat liver macromolecules in vivo and in vitro: effects of agents that influence benzo[a]pyrene metabolism.

The present study was carried out to determine the effects of agents that influence benzo[a]pyrene (BP) metabolism in vitro on the irreversible binding of BP to rat hepatic macromolecules in vivo. The irreversible binding of [3H]BP was found to be both dose and time dependent after its intraperitoneal administration to male Wistar rats. The SKF 525-A, at doses of 50 and 75 mg/kg, ip 3 h before BP, decreased the level of binding from control by 31 and 34%, respectively. At 35 mg/kg, SKF-525-A had no effect. Diethyl maleate (0.6 mL/kg, ip) and cysteine (150 mg/kg, ip), 30 and 5 min before BP, respectively, did not alter the binding of BP from control. Oral methadone treatment, previously shown to increase selectively epoxide hydrase activity in male Wistar rats, also failed to alter the amount of BP bound to hepatic macromolecules. 3-Methylcholanthrene (20 mg/kg per day, ip, for 2 days) administered 24 h before BP, decreased the level of binding from control by 30%. Parallel in vitro studies were carried out with the various agents used in vivo.

Animals↗
PubMed1990

Influence of D-galactosamine on the kinetics of metabolic processes for two intermediate metabolites, 9-hydroxybenzo(a)pyrene and 3-hydroxybenzo(a)pyrene, in 3T3 and RTG2 cells.

PAH metabolism is known to proceed in two successive steps, the first step resulting in the production of activated metabolites which are subsequently transformed by the different pathways involved in the second step. Microspectrofluorometry enables the study of the kinetics of these steps in living intact cells into which no imbalance has been artificially introduced. We used this technique to check the influence of pre-incubation with D-galactosamine on the kinetics of the detoxification step. 9- and 3-hydroxybenzo(a)pyrene (OH-B(a)P) were selected as fluorescent substrates because they are potential substrates for the different pathways of the second step. The physiological cell status was controlled at the level of the intrinsic cellular fluorescence. Pre-incubation with D-galactosamine results in a strong decrease of the experimental rate constants characteristic of the metabolism of 9- and 3-OH-B(a)P in both RTG2 and 3T3 cells. Moreover, such pre-incubation leads to a strong decrease of the transitory intracellular accumulation of 3-O-glucuronide when 3-OH-B(a)P is used as substrate for 3T3 cells. Nevertheless, it cannot be said that both phenols cannot be used as substrates by MFOs and STase, at least in rigorous experimental conditions.

Animals↗
PubMed1981

Effects of Aroclor 1254-induced rat liver S-9 fraction on benzo[a]pyrene-mediated DNA damage and benzo[a]pyrene metabolism in cultured human skin fibroblasts.

Incubation of cultured normal human skin fibroblasts with benzo[a]pyrene (B[a]P) resulted in covalent binding of B[a]P to protein, RNA and DNA. B[a]P adduct formation was increased when the cultured cells were also treated with the 9,000 g hepatic microsomal supernatant (S-9) fraction from rats pretreated with Aroclor 1254, a commercial preparation of polychlorinated biphenyls (PCBs). Comparison with control experiments which included the incubation with corn oil-induced S-9 fraction indicated that the enhanced B[a]P-adduct formation in the host cells was related to the induction of hepatic NADPH-dependent microsomal monooxygenase activity by Aroclor 1254 in the S-9 fraction. Parallel experiments showed that this Aroclor-induced enzymic activity was responsible for B[a]P-mediated DNA damage as measured by unscheduled DNA synthesis (UDS) in the cells. Similarly, administration of rat hepatic S-9 induced by 3-methylcholanthrene (MC) and phenobarbitone (PB) caused B[a]P-mediated DNA damage in cultured human skin fibroblasts.

Animals↗
PubMed1988

Comparison of DNA adducts in mouse and rat epidermis versus dermis after topical application of (+/-)r-7,t-8-dihydroxy-t-9,10-oxy-7,8,9,10-tetrahydrobenzo(a)pyrene and (+/-) benzo(a)pyrene-4,5-oxide.

Mice and rats were treated topically with the BP metabolites, anti-BPDE and BPO. Rat epidermal DNA was extensively modified by BPO, while mouse epidermal DNA was preferentially modified by anti-BPDE. Anti-BPDE-dGuo adducts were observed only in mouse dermal DNA. DNA adducts were absent from the rat dermis. This adduct formation could be the reason for the very different in vivo biological effects of BP metabolites in the two species.

7,8-Dihydro-7,8-dihydroxybenzo(a)pyrene 9,10-oxide↗
PubMed1987

The binding efficiency of polyclonal and monoclonal antibodies to DNA modified with benzo[a]pyrene diol epoxide is dependent on the level of modification. Implications for quantitation of benzo[a]pyrene-DNA adducts in vivo.

A number of polyclonal antibodies specific for DNA modified with (+/-)trans-7,8-dihydroxy-anti-9,10-epoxy-7,8,9,10-tetrahydrobenzo[a]pyre ne (BPDE) were obtained from the sera of New Zealand white rabbits immunized with BPDE-DNA, complexed with methylated bovine serum albumin (mBSA). Monoclonal antibodies were developed by fusion of mouse myeloma cells with spleen cells isolated from BALB/c mice immunized with the same complex of BPDE-DNA and mBSA. These antibodies have been characterized for specificity in a highly sensitive, enzyme-linked immunosorbent assay (ELISA). All antibodies showed a very high affinity for single-stranded BPDE-DNA, but had lower affinity towards native BPDE-DNA. The affinity for the free mononucleoside BPDE-dG was at least 100-fold lower than that for BPDE-DNA, and no affinity was detected for BP tetrols or DNA modified with N-acetoxy-N-acetyl-2-aminofluorene. A high cross reactivity was observed with DNA modified with (+/-)-trans-1,2-dihydroxy-anti-3,4-epoxy-1,2,3,4-tetrahydrochrysene++ +. Using five different antibodies, monoclonal or polyclonal, we observed that the antibody affinity for BPDE-DNA was dependent on the level of modification; in the competitive ELISA as little as 4 fmol BPDE-DNA (50 pmol/micrograms) was sufficient for 50% inhibition with our best antisera, but 17 fmol of the adduct was required when [3H]BPDE-DNA of low modification (1-10 fmol/micrograms) was used as inhibitor. When samples of [3H]BP-DNA isolated from the livers of mice, treated i.p. with different doses of [3H]BP were examined by competitive ELISA and calibrated with [3H]BPDE-DNA of low modification (1-10 fmol/micrograms), binding values calculated from the immunoassay were in good agreement with those obtained from radioactivity measurements. In contrast, when this DNA was quantitated in competitive ELISA using highly modified BPDE-DNA as standards, values by ELISA were 20-40% of those obtained by radioactivity. These results indicate that the use of serially diluted BPDE-DNA of high modification as standard competitor in the ELISA will lead to erroneous results in the measurement of adducts in DNAs modified to a low extent (biological samples). The property of antisera specific for BP-DNA, recognizing highly modified DNA more efficiently than DNA modified to a low extent, may be common to all antisera elicited against highly modified DNA immunogens. Therefore we conclude that antibody affinity must be tested also with DNA samples of low modification, obtained either in vitro or in vivo.

2-Acetylaminofluorene↗