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Biomedical subjects

A Dipple

Publications and source records attributed to A Dipple.

At least 73 records · Page 4Linked to original sources
PubMed1989

Mutagenic specificity of a potent carcinogen, benzo[c]phenanthrene (4R,3S)-dihydrodiol (2S,1R)-epoxide, which reacts with adenine and guanine in DNA.

Mutations were induced in the supF gene of the pS189 shuttle vector by treatment with optically active benzo[c]phenanthrene (4R,3S)-dihydrodiol (2S,1R)-epoxide in vitro and replication in human cells. The induced mutation frequency was 60-fold greater than the spontaneous rate, and most of the mutations analyzed were transversions (86%), which principally consisted of similar numbers of A.T----T.A and G.C----T.A changes. The unusual susceptibility of A.T pairs to mutation by this chemical agent is consistent with its chemical reactivity toward adenine and argues that the mutations are targeted to the adducts formed. The central base in the sequences 5'-AGA-3', 5'-AAC-3', and 5'-GAG-3' was particularly susceptible to mutation. Twelve "hotspots" in the supF gene accounted for most mutations seen. Some of these hotspots differed from those found by others for racemic benzo[a]pyrene dihydrodiol epoxide and, even when a hotspot was common, the mutagenic changes were not always the same. Although adenine insertion opposite a noninstructional lesion could account for most of the data, no single mutagenic mechanism could encompass all of it. The cellular machinery that converts chemical damage to mutations must determine the mutational result to a large extent, but the findings herein show that the chemical agent itself plays a large role in determining both the location and the nature of the mutations that arise.

Adenine↗
PubMed1989

Absolute stereochemistry of the major 7,12-dimethylbenz[alpha]anthracene- DNA adducts formed in mouse cells.

In recent work we assigned partial structures to individual 7,12-dimethylbenz[alpha]anthracene (DMBA)--deoxyribonucleoside bisphosphates separated by TLC after postlabeling with [32P]ATP. We have now been able to postlabel DNA adducts formed in cells exposed to either the (4R,3R)- or (4S,3S)-dihydrodiol of DMBA and thereby to assign absolute stereochemistry to the 2-, 3- and 4- positions in the major DMBA-DNA adducts. It is found that the major anti dihydrodiol epoxide-DNA adducts arise from the (4R,3S)-dihydrodiol (2S,1R)-epoxide and that the major syn dihydrodiol epoxide-DNA adducts arise from the (4S,3R)-dihydrodiol (2S,1R)-epoxide.

9,10-Dimethyl-1,2-benzanthracene↗
PubMed1988

7,12-Dimethylbenz[a]anthracene-DNA adducts in mouse skin, dermis and epidermis.

Female NIH Swiss mice were treated topically with either 0.01 or 0.1 mumol 7,12-[3H]dimethylbenz[a]anthracene and DNA was isolated either from the whole skin, the dermis or the epidermis. Levels of binding to DNA and levels of individual adducts formed were similar in all 3 tissue fractions for a given dose of carcinogen with levels for the epidermis being marginally greater than in the other fractions. In all tissue fractions, the syn dihydrodiol epoxide-deoxyribonucleoside adducts were responsible for a greater fraction of total binding at the higher, than at the lower, carcinogen dose. The mechanism of metabolic activation of 7,12-dimethylbenz[a]anthracene for DNA binding is, therefore, qualitatively the same in both the dermis and epidermis. Quantification of adducts suggests some subtle differences between the DMBA activating systems in dermis and epidermis.

9,10-Dimethyl-1,2-benzanthracene↗
PubMed1988

Comparison of 32P-postlabeling and high pressure liquid chromatographic analyses for 7,12-dimethylbenz[a]anthracene--DNA adducts.

[3H]7,12-Dimethylbenz[a]anthracene-modified DNA obtained from mouse cells in culture was enzymatically hydrolyzed to nucleoside 3'-phosphates, postlabeled with [32P]phosphate, and the carcinogen-modified nucleoside bisphosphates were separated by thin layer chromatography. Each adduct spot was eluted, dephosphorylated and the resulting [3H]nucleoside adducts were analyzed by high pressure liquid chromatography so that the structural information available for the liquid chromatographic peaks could be applied to the spots obtained from the postlabeling procedure. After this cross referencing, specific dihydrodiol epoxide-nucleotide adducts can now be monitored by the postlabeling technique.

9,10-Dimethyl-1,2-benzanthracene↗
PubMed1988

A metabolite of the carcinogen 7,12-dimethylbenz[a]anthracene that reacts predominantly with adenine residues in DNA.

Four 7,12-dimethylbenz[a]anthracene--deoxyribonucleoside adducts formed in mouse epidermis in vivo arise from the syn dihydrodiol epoxide metabolite of this carcinogen. With the synthetic syn dihydrodiol epoxide it was possible to identify three of these as deoxyadenosine adducts and to establish their structures. These three adducts account for the large majority of DNA adduct arising from this metabolite in vivo. The in vivo metabolite is unusual, therefore, in that it reacts almost exclusively with adenine residues in DNA while most carcinogen metabolites react preferentially with guanine residues.

9,10-Dimethyl-1,2-benzanthracene↗
PubMed1987

Stereochemical specificity in the metabolic activation of benzo(c)phenanthrene to metabolites that covalently bind to DNA in rodent embryo cell cultures.

Benzo(c)phenanthrene (BcPh) has only weak carcinogenic activity in rodent bioassays. However, bay-region diol-epoxides of BcPh have the highest tumor-initiating activities of all hydrocarbon diol-epoxides tested to date. To determine whether BcPh is metabolically activated to bay-region diol-epoxides that bind to DNA in cells, Sencar mouse, Syrian hamster, and Wistar rat embryo cell cultures were exposed to [5-3H]-BcPh, and the BcPh-deoxyribonucleoside adducts formed were analyzed by immobilized boronate chromatography and reverse-phase high-performance liquid chromatography. Greater than 74% of the BcPh-deoxyribonucleoside adducts formed in all 3 species resulted from reaction of (4R,3S)-dihydroxy-(2S,1R)-epoxy-1,2,3,4-tetrahydro-BcPh [(-)-BcPhDE-2] with DNA to yield deoxyadenosine and deoxyguanosine adducts in a ratio of 3:1. A much smaller proportion of BcPh-deoxyribonucleoside adducts were formed by reaction of (4S,3R)-dihydroxy-(2S,1R)-epoxy-1,2,3,4-tetrahydro-BcPh [(+)-BcPhDE-1] with deoxyadenosine. No BcPh-deoxyribonucleoside adducts arising from either (+)-BcPhDE-2 or (-)-BcPhDE-1 were detected. The absence of adducts from these isomers of BcPhDE was not due to failure of these isomers to react with DNA in cells, for reaction of (+/-)-BcPhDE-1 or (+/-)-BcPhDE-2 with DNA in solution or in hamster embryo cell cultures resulted in the formation of DNA adducts from both the (+)- and (-)-enantiomers of each BcPhDE. These results indicate that both the (+)- and (-)-3,4-dihydrodiols of BcPh are formed and that their metabolic activation to diol-epoxides occurs with high stereospecificity in cells from all 3 species of rodents. The finding that the major DNA-binding metabolite is (-)-BcPhDE-2, the diol-epoxide with the (R,S)-diol-(S,R)-epoxide absolute configuration that is associated with high carcinogenic activity of diol-epoxides of other hydrocarbons, demonstrates that these cells are able to activate BcPh to an ultimate carcinogenic metabolite. The fact that a high proportion of the BcPh-DNA adducts are deoxyadenosine adducts suggests that BcPh has DNA-binding properties similar to those of the potent carcinogen 7,12-dimethylbenz(a)anthracene. The stereospecificity observed in the metabolic activation of BcPh to DNA-binding metabolites and the reaction of these metabolites with both deoxyguanosine and deoxyadenosine suggest that studies of the interactions of BcPh with DNA in vivo may be a valuable approach for establishing the role of specific activation pathways and DNA adducts in tumor induction.

Animals↗
PubMed1987

Resistance of 7,12-dimethylbenz[a]anthracene-deoxyadenosine adducts in DNA to hydrolysis by snake venom phosphodiesterase.

In enzymatic hydrolyses of 7,12-dimethylbenz[a]anthracene (DMBA)-modified DNA isolated from fetal mouse cell cultures, a low concentration of venom phosphodiesterase was sufficient for complete release of DMBA-deoxyguanosine adducts. However, efficient release of DMBA-deoxyadenosine adducts required much higher levels of phosphodiesterase. If these adducts exhibit similarly differential susceptibilities to exonucleases involved in DNA metabolism or repair, each adduct could result in significantly different biological effects in vivo.

9,10-Dimethyl-1,2-benzanthracene↗
PubMed1987

Characterization of 5-methylchrysene-1,2-dihydrodiol-3,4-epoxide-DNA adducts.

Products of reaction of the racemic anti bay region 1,2-dihydrodiol-3,4-epoxide of 5-methylchrysene with DNA were identified by comparison with the products formed in reactions with individual nucleotides. The latter products, i.e. two deoxyguanosine adducts and four deoxyadenosine adducts, were characterized by various spectroscopic methods. In DNA, in addition to the major deoxyguanosine adduct already identified by Melikian et al. (Cancer Res., 44, 2524, 1984), we have now identified a second deoxyguanosine adduct arising from the trans opening of the epoxide ring by the amino group of deoxyguanosine. This differs from the adduct characterized by Melikian et al. only in that it arises from the opposite enantiomer of the dihydrodiol epoxide. Three deoxyadenosine adducts were also found in DNA. Two of these arose from the trans opening of the epoxide ring of each dihydrodiol epoxide enantiomer by the amino group of deoxyadenosine and the third from the cis opening of the epoxide ring of one enantiomer. Approximately 32% of the racemic dihydrodiol epoxide reacts with DNA rather than with water and this high extent of reaction with DNA is attributed to the out-of-plane deformations arising from the methyl substitution in the bay region.

Carcinogens↗
PubMed1985

Acid lability of the hydrocarbon-deoxyribonucleoside linkages in 7,12-dimethylbenz[a]anthracene-modified deoxyribonucleic acid.

DNA containing bound radioactive 7,12-dimethylbenz[a]anthracene was isolated from mouse fetal cell cultures exposed to this carcinogen. The carcinogen-deoxyriboside adducts within the DNA were found to be sensitive to acid-catalyzed hydrolysis. Adducts derived from reaction of a syn-dihydrodiol epoxide with deoxyadenosine residues in DNA were the most sensitive to acid and were hydrolyzed to yield a 1,2,3,4-tetrahydrotetraol of 7,12-dimethylbenz[a]anthracene under mild conditions. The structure of this tetraol was established by synthesis and mass spectrometry. Although definitive structures cannot be assigned at present to the nucleic acid adducts of this potent carcinogen, the present findings confirm and extend earlier work assigning partial structures to the major adducts.

9,10-Dimethyl-1,2-benzanthracene↗
PubMed1985

Selective effects of selenium selenite on 7,12-dimethylbenz(a)anthracene-DNA binding in fetal mouse cell cultures.

Sodium selenite inhibits the binding of 7,12-dimethylbenz(a)anthracene (DMBA) to DNA in tertiary cultures of fetal mouse cells in a rather selective fashion. Inhibition can be demonstrated at 6 but not at 3 h after DMBA addition to the cells. Inhibition is seen after treatment of the cells with DMBA concentrations of 0.05 or 0.1 micrograms/ml but not after treatment at 0.01 micrograms/ml. Furthermore the inhibition seen with up to 1 microgram selenium/ml is selective in that products from the anti bay region dihydrodiol epoxide metabolite (where the epoxide oxygen is trans to the 4-hydroxy group) are suppressed while those from the syn-dihydrodiol-epoxide (where the epoxide oxygen is cis to the 4-hydroxy group) are not affected. In the absence of selenite, it was found that syn-dihydrodiol epoxide-DNA adducts are formed in a roughly linear fashion with time over a range of DMBA concentration. In contrast, the capacity of the cells to generate anti-dihydrodiol-epoxide adducts in a 3-h interval is saturated at concentrations of DMBA above 0.025 micrograms/ml and after the initial 3-h period the cells generate these adducts at up to a 6-fold greater rate than during the initial 3 h. This increase in rate of formation of anti-dihydrodiol-epoxide products is inhibited by actinomycin D and appears to be a consequence of DMBA inducing an enzyme activity which selectively generates the anti-dihydrodiol-epoxide and not the syn-dihydrodiol-epoxide. The selective action of sodium selenite in inhibiting only anti-dihydrodiol-epoxide product formation and doing this only at certain times and at certain doses of DMBA is a result of the fact that it inhibits the induction process. Once induction has occurred, sodium selenite is no longer inhibitory of DMBA-DNA binding. The chemopreventive action of selenium in chemical carcinogenesis could be partially attributable to effects such as those described herein on carcinogen-DNA binding. It is also possible, however, that the chemopreventive actions of selenium might be attributable to effects on the expression of genes other than those involved in carcinogen metabolism.

9,10-Dimethyl-1,2-benzanthracene↗
PubMed1984

7,12-Dimethylbenz[alpha]anthracene-DNA adducts in cultured cells from mouse fetuses of different gestational ages.

Primary cell cultures prepared from individual litters of NIH Swiss mouse fetuses of different gestational ages were incubated with 7,12-[3H]dimethylbenz[a]anthracene (DMBA) for 24 h. Levels of binding of DMBA to DNA and the distribution of individual DMBA-deoxyribonucleoside adducts were similar in all cultures derived from fetuses of 13-15 days of gestation. However, in cells from fetuses at 17-19 days changes in DMBA-DNA binding were noted. In particular the syn bay region dihydrodiol epoxide of DMBA was responsible for a significantly greater fraction of the total DMBA-DNA binding in the cultures from the more mature fetuses.

9,10-Dimethyl-1,2-benzanthracene↗
PubMed1984

7,12-dimethylbenz[a] anthracene--DNA binding in mouse skin: response of different mouse strains and effects of various modifiers of carcinogenesis.

7,12-Dimethylbenz[a]anthracene (DMBA)--deoxyribonucleoside adducts formed in mouse skin DNA were quantified in order to determine whether these changed in any systematic fashion under conditions where the tumorigenic activity of DMBA is modified. Similar distributions of adducts were found in male NIH Swiss mice and C57BL mice which exhibit different sensitivities to initiation-promotion using DMBA as initiator, though in both these strains of mice the bay region syn dihydrodiol epoxide is responsible for a greater fraction of total binding at higher DMBA doses. Pretreatment with various chemicals known to inhibit the tumor initiating activity of DMBA in mouse skin did not lead to selective inhibition of the formation of any adduct in female NIH Swiss mice. However, the effects of these agents ranged from a clear inhibition of overall DNA binding (7,8-benzoflavone) to little or no effect on overall binding (butylated hydroxyanisole, butylated hydroxytoluene). The lack of any effect of the antioxidants on DMBA--DNA adduct formation suggests that they may affect some step in tumor initiation other than adduct formation.

9,10-Dimethyl-1,2-benzanthracene↗