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J M Sayer

Publications and source records attributed to J M Sayer.

60 records · Page 4Linked to original sources
PubMed1981

Mutagenicity of the bay-region diol-epoxides and other benzo-ring derivatives of dibenzo(a,h)pyrene and dibenzo(a,i)pyrene.

The mutagenic activities of dibenzo(a,h)(pyrene, dibenzo(a,i)pyrene, and a total of 11 of their benzo-ring derivatives were evaluated in bacterial and mammalian cells in the absence or presence of a mammalian metabolic activation system. trans-1,2-Dihydroxy-1,2-dihydrodibenzo(a,h)pyrene and trans-3,4-dihydroxy-3,4-dihydrodibenzo(a,i)pyrene, the expected dihydrodiol precursors of bay-region diol-epoxides, were metabolized to products which were more mutagenic to strains TA98 and TA100 of Salmonella typhimurium than were the metabolic products formed from their respective parent hydrocarbons. For each dihydrodiol, replacement of the benzo-ring double bond adjacent to the diol moiety with a single bond resulted in tetrahydrodiol derivatives which could not be metabolically activated, suggesting that one or both diastereomeric bay-region diol-epoxides were the bioactivated metabolites. The authentic bay-region diol-epoxide diastereomers of dibenzo(a,h)pyrene and dibenzo(a,i)pyrene in which the benzylic hydroxyl group and the epoxide oxygen are trans (diol-epoxide 2 series) were highly mutagenic in strains TA98 and TA100 of S. typhimurium and in cultured Chinese hamster V79 cells. Neither diol-epoxide was significantly, if at all, metabolized by epoxide hydrolase. The bay-region diol-epoxide of dibenzo(a,i)pyrene was from 1.5 to 5 times more active as a mutagen than the diol-epoxide of dibenzo(a,h)pyrene, and in strain TA98 of S. typhimurium as well as Chinese hamster V79 cells, it had activity comparable to that of the highly carcinogenic bay-region diol-epoxide of benzo(a)pyrene.

Animals↗
PubMedDate not supplied

Effects of pH and salt concentration on the hydrolysis of a benzo[alpha]pyrene 7,8-diol-9,10-epoxide catalyzed by DNA and polyadenylic acid.

The time-dependent absorbance change that occurs when benzo[alpha]pyrene 7,8-diol-9,10-epoxide is added to solutions of calf thymus DNA has been shown, by an unequivocal chromatographic method, to correspond to DNA-catalyzed hydrolysis of the diol-epoxide. At 25 degrees C and mu = 0.10, the kinetics of the reaction of the diol-epoxide with polyadenylic acid or DNA are consistent with preequilibrium formation of a non-covalent complex between the diol-epoxide and the polynucleotide or DNA, followed by hydrolysis of the bound epoxide by a process that is first-order in hydronium ions. Cacodylic acid also catalyzes the hydrolysis of the epoxide bound to polyadenylic acid. The rate of the DNA-catalyzed hydrolysis exhibits little or no enantiomeric selectivity for the diol-epoxide. DNA catalyzed hydrolysis of the diol-epoxide is extraordinarily sensitive to the salt concentration in the reaction medium: the rate of hydrolysis of the bound epoxide at pH 7 is retarded by a factor of approximately 45 in the presence of 0.1 M sodium chloride compared to a 1 mM buffer containing no added salt. Thus, studies of the interactions of DNA with carcinogenic diol-epoxides must take into account the ionic environment of DNA within the cell.

7,8-Dihydro-7,8-dihydroxybenzo(a)pyrene 9,10-oxide↗
PubMedDate not supplied

Multiple fluorescence lifetimes for oligonucleotides containing single, site-specific modifications at guanine and adenine corresponding to trans addition of exocyclic amino groups to (+)-(7R,8S,9S,10R)- and (+)-(7S,8R,9R,10S) -7,8-dihydroxy-9,10-epoxy-7,8,9,10-tetrahydrobenzo[a]pyrene.

Fluorescence decay profiles of four oligonucleotide duplexes, [table: see text] ((+)- and (-)-trans-1) and [table: see text] ((+)- and (-)-trans-2), in which an exocyclic amino group of deoxyadenosine (A*) or deoxyguanosine (G*) has been alkylated by trans opening at C-10 of the epoxide group of either the (+)-(R,S,S,R)- or (-)-(S,R,R,S)-enantiomer of (+/-)-7 beta,8 alpha-dihydroxy-9 alpha,10 alpha-epoxy-7,8,9,10- tetrahydrobenzo[a]pyrene (BPDE in which the benzylic 7-hydroxy group and the epoxide oxygen are trans), exhibit more than one fluorescence lifetime. Decay profiles of the oligomers, measured at 15 degrees C with excitation and emission wavelengths of 335 and 400 nm, respectively, have been analyzed using a triple-exponential decay law. Results for (+)- and (-)-trans-1 and -2 have been compared with results for the modified, single-stranded oligonucleotides ((+)- and (-)-trans-SS-1, and (+)- and (-)-trans-SS-2) and for the cis and trans opened products formed on alkylation at the 6-amino group of 2'-deoxyadenosine 5'-phosphate by (+)-(R,S,S,R)-BPDE ((+)-trans- and (+)-cis-A). The profiles of (+)-trans- and (+)-cis-A are well represented by single-exponential decay laws with lifetimes of 86 and 110 +/- 3 ns, respectively. For the single- and double-stranded oligomer adducts, which exhibit at least three fluorescence lifetimes, two of the lifetimes are short (0.5-14 +/- 1 ns) and one is long (35-59 +/- 3 ns). The fluorescence lifetimes and the amplitudes of the long-lived components in the decay profiles of the double-stranded oligomer adducts are generally smaller than those for the corresponding single-stranded adducts. The data provide evidence that the double-stranded oligomer adducts exist as multiple conformations. Previously reported NMR results suggest that the short lifetime fluorescence components are due to major adduct conformations in which the pyrenyl group is intercalated ((+)- and (-)-trans-1) or lies in the minor groove ((+)- and (-)-trans-2). The observation of long lifetime fluorescence species for the double-stranded oligomers is consistent with the presence of minor conformations (approximately 1-5%) in which the double-stranded oligomer either is locally denatured or is a mixture of locally denatured double-stranded conformations and equilibrium concentrations of single-stranded oligomers.

7,8-Dihydro-7,8-dihydroxybenzo(a)pyrene 9,10-oxide↗
PubMedDate not supplied

Optically active benzo[c]phenanthrene diol epoxides bind extensively to adenine in DNA.

Reactions of diol epoxide metabolites of carcinogenic polycyclic aromatic hydrocarbons with DNA are thought to initiate the carcinogenic process. Although formation of a benzo[a]pyrene (BaP) diol epoxide-deoxyguanosine adduct has been held responsible for biological activity, the more potent carcinogen, 7,12-dimethylbenz[a]anthracene (DMBA) binds extensively to deoxyadenosine residues in DNA, suggesting that hydrocarbon carcinogen-deoxyadenosine adducts may be instrumental in tumour initiation. Because the bay region diol epoxides of benzo[c]phenanthrene (BcPh) are very active tumour initiators, and the relative activities of the four configurationally isomeric 3,4-diol 1,2-epoxides (Fig. 1) are known, we examined their reactions with DNA. Each BcPh diol epoxide isomer exhibits a remarkable preference for covalent binding to DNA over hydrolysis, each yields a unique distribution of products with the nucleosides of DNA and each reacts extensively with deoxyadenosine residues in DNA. The relative tumour initiating activities of these stereoisomers is best reflected by the relative yields of one of the deoxyadenosine adducts formed.

Adenine↗
PubMedDate not supplied

Barium enema or colonoscopy for the investigation of iron deficiency anaemia?

OBJECTIVE: To determine whether double contrast barium enema is adequate for excluding carcinoma of the colon in patients with iron deficiency anaemia. DESIGN: Prospective audit. SUBJECTS: One hundred and twenty-three patients with iron deficiency anaemia. INTERVENTION: All patients had upper intestinal (GI) endoscopy, duodenal biopsy and double contrast barium enema. Malignant disease and other GI pathology were treated. Patients with recurrent or persistent anaemia at follow-up were colonoscoped. OUTCOME MEASURE: Colon cancer missed on barium enema examination but detected on colonoscopic examination. RESULTS: An identified GI lesion contributing to their anaemia and 11 colon cancers were found in 71% of patients, all identified on barium enema. Two pre-cancerous conditions were missed on barium enema examination. Only 45% colonoscopies inspected the caecum. CONCLUSION: Double contrast barium enema with sigmoidoscopy is probably sufficient for excluding carcinoma of the colon in iron deficiency anaemia.

Adolescent↗