Chemical rearrangement of phenol-epoxide metabolites of polycyclic aromatic hydrocarbons to quinone-methides

Evidence of the involvement of triol-epoxide and phenol-epoxide metabolites in the metabolic activation of polycyclic hydrocarbons is accumulating. It is proposed that the phenolic OH-groups present in such epoxides will activate the epoxide moieties and permit their rearrangement to quinone-methides. These quinone-methides are highly reactive, potentially-isolable chemical entities with strong alkylating activity. In one resonance form they are resonance-stabilized carbonium ions. Only epoxides that also possess phenolic OH-groups in certain positions will form quinone-methides: these appear to include 9-hydroxybenzo [a] pyrene 4,5-oxide and the triol-epoxides 9-hydroxy-trans-1,2-dihydro-1,2-dihydroxychrysene 3,4-oxide and 2-hydroxy-trans-9,10-dihydro-9,10-dihydroxybenzo[a]pyrene 7,8-oxide.

Formation of the 1,2-diol as a metabolite of 7,12-dimethylbenz[a]-anthracene by rodent and human skin

Rodent and human skin maintained in short-term organ culture was treated with 3H-labelled 7,12-dimethylbenz[a]-anthracene. Extracts of the rodent tissue and culture fluid in which either mouse, rat or human skin had been maintained were found to contain radioactive material that possessed the chromatographic characteristics of trans-1,2-dihydro-1,2-dihydroxy-7,12-dimethylbenz[a]anthracene when it was examined in two different h.p.l.c. systems. When the metabolite was treated with hot mineral acid, the two radioactive products formed co-chromatographed with the phenols that were formed when the reference dihydrodiol was similarly treated. Acetylation of the isolated metabolite yielded a single product that had chromatographic properties identical to those of the diacetate of the reference dihydrodiol. Taken together these data show that the 1,2-dihydrodiol of 7,12-dimethylbenz[a]anthracene is formed as a metabolite of this hydrocarbon by rodent and human skin maintained in short-term organ culture.

A simple method for the removal of contaminating fibroblasts from cultures of rat mammary epithelial cells

A simple method of removing fibroblasts from cultured mammary epithelial cells is described. Primary cultures of both fibroblasts and epithelial cells have been prepared from rat mammary tissue dissociated with collagenase and hyaluronidase. Fibroblasts present as contaminants in the epithelial cell cultures have been selectively removed by incubating cultures at 37 degrees C in Hanks' balanced salt solution that contained antibiotics (100 micrograms/ml) and fungizone (5 micrograms/ml, a treatment which does not appear to decrease cell viability.

Metabolic activation of chrysene by hamster embryo cells: evidence for the formation of a 'bay-region' diol-epoxide-N2-guanine adduct in RNA

Ribonucleoside-hydrocarbon adducts present in hydrolysates of RNA isolated from hamster embryo cells treated with 3H-labelled chrysene were examined by chromatography on Sephadex LH20 and by h.p.l.c. on Zorbax ODS. Two adducts formed in cells had chromatographic properties identical to those of two synthetic adducts formed when r-1,t-2-dihydroxy-t-3,4-oxy-1,2,3,4-tetrahydrochrysene (antichrysene 1,2-diol 3,4-oxide) reacted with poly G in vitro. Another adduct formed in cells had chromatographic properties identical to those of a synthetic adduct formed when antichrysene 1,2-diol 3,4-oxide reacted with poly A. In addition to the characterized adducts, other minor adducts were detected whose structures are not known. The structure of the more abundant guanosine--hydrocarbon adduct formed in cells was investigated by determining its pK values and stability in 1 M KOH. The structures of the synthetic guanosine--hydrocarbon adducts were investigated by 1H-n.m.r. spectroscopy. The data show that, in the hydrocarbon--guanosine adducts studied, the hydrocarbon moiety is attached to the exocyclic amino group of guanine.

Metabolic activation of benzo[a]pyrene in human skin maintained in short-term organ culture

The metabolic activation of benzo[a]pyrene (BP) was examined in six samples of human skin after topical application of the hydrocarbon to the skin in short-term organ culture. The results show that all of the samples were capable of metabolizing BP to water-soluble products and to ether-soluble products that included the 4,5-, 7,8- and 9,10-dihydrodiols and a product which had chromatographic properties identical with those of authentic trans-11,12-dihydro-11,12-dihydroxybenzo[a]pyrene (BP-11,12-diol). The major BP-deoxyribonucleoside adduct detected in each skin sample appeared to be formed from the reaction of r-7,t-8-dihydroxy-t-9,10-oxy-7,8,9,10-tetrahydrobenzo[a]pyrene (anti-BP-7,8-diol 9,10-oxide) with deoxyguanosine residues in DNA.

Tumour-initiating activities of dihydrodiols of dibenz[a,c]anthracene

The tumor-initiating activities of dibenz[a,c]anthracene (DBA) and of the related trans-1,2-, 3,4- and 10,11-dihydrodiols have been examined on mouse skin subsequently promoted with 12-O-tetradecanoyl-phorbol-13-acetate (TPA). The 1,2- and 10,11-dihydrodiols were active and were more active than equivalent doses of either the parent hydrocarbon or the 3,4-dihydrodiol. The data are discussed in relation to possible mechanisms that may be involved in the metabolic activation of DBA.

Preferential binding of polycyclic hydrocarbons to matrix-bound DNA in rat-liver nuclei

The reactions of benzo[a]pyrene and 7,12-dimethylbenz[a]anthracene metabolites and of r-7,t-8-dihydroxy-t-9,10-oxy-7,8,9,10-tetrahydrobenzo[a]pyrene with the DNA of matrix-bound and released chromatin fractions of rat-liver nuclei have been examined. Qualitatively there were no differences between the DNA-bound metabolites in each fraction but more binding to matrix-bound DNA occurred. Evidence was obtained that the increased binding of hydrocarbon to matrix-bound DNA was not dependent upon the proximity of hydrocarbon-metabolizing enzymes and Sephadex LH20 chromatography showed that the differences between the fractions were not due to contamination of DNA with residual proteins. The conformation of the matrix-bound chromatin may make its DNA more accessible to reactive metabolites than that of released chromatin.

Metabolism and activation of benzo[a]pyrene by mouse and rat skin in short-term organ culture and in vivo

The metabolic activation of BP was examined in mouse and rat skin in vivo and in short-term organ culture. In mouse skin, larger quantities of ether- and water-soluble metabolites were formed and more BP became bound covalently to DNA and protein than in rat skin. Qualitative differences in the formation of dihydrodiol metabolites and of BP-deoxyribonucleoside adducts between mouse and rat skin were also observed. Organ culture techniques may not provide a true model of metabolic activation in vivo because it was found that the covalent binding of BP to DNA and protein was reduced in skin maintained in culture despite an accumulation of dihydrodiol and other ether-soluble metabolites. In addition, the proportions of the syn- and anti-isomers of BP-7,8-diol 9,10-oxide involved in the formation of adducts with deoxyguanosine differed between skin treated in organ culture and in vivo.

Inactivation of a diol epoxide by dihydrodiol dehydrogenase but not by two epoxide hydrolases

The mutagenicity of r-8,t-9-dihydroxy-t-10, 11-oxy-8,9,10,11-tetrahydrobenz[a]anthracene (BA-8,9-diol 10, 11-oxide) toward Salmonella typhimurium TA 100 is not decreased by the presence of large amounts of highly purified microsomal or cytosolic epoxide hydrolase. However, highly purified dihydrodiol dehydrogenase inactivates this diol epoxide, which is a major DNA-binding metabolite of benz[a]anthracene. The K-region epoxide, benz[a]anthracene 5,6-oxide (BA 5,6-oxide) is efficiently inactivated by microsomal epoxide hydrolase, is much less readily inactivated by cytosolic epoxide hydrolase, and is not inactivated by dihydrodiol dehydrogenase. This inactivation of a diol epoxide by dihydrodiol dehydrogenase points to a new significance of this enzyme and a new level of control for diol epoxides.

The metabolism and activation of polycyclic aromatic hydrocarbons in epithelial cell aggregates and fibroblasts prepared from rat mammary tissue

The metabolism of 7,12-dimethylbenz[a]anthracene (DMBA), benzo[a]pyrene (BP) and benz[a]anthracene (BA) by epithelial cell aggregates and fibroblasts in culture has been investigated using mammary tissue obtained from female Wistar rats. The results show that: (a) both types of mammary cells metabolise all three hydrocarbons into ether- and water-soluble derivatives; (b) the patterns of metabolites produced by epithelial cells and fibroblasts are similar but that fibroblasts form more of the water-soluble materials; (c) the major dihydrodiols formed are the 8,9-dihydrodiols of BA and DMBA and the 7,8- and 9,10-dihydrodiols of BP; (d) all three hydrocarbons are metabolise to form products that bind covalently to protein but only the potent carcinogens BP and DMBA are metabolised to form derivatives that react covalently with DNA; and (e) the chromatographic profiles of the hydrocarbon-deoxyribonucleoside adducts formed in epithelial cells treated with either BP or DMBA are similar to those obtained in analogous experiment with fibroblasts.

The metabolic activation of chrysene by hamster embryo cells

The major deoxyribonucleoside--hydrocarbon adducts present in hydrolysates of DNA isolated from hamster embryo cells treated with chrysene were examined by chromatography on Sephadex LH20 and by h.p.l.c. on Zorbax ODS. The results show that both major adducts have chromatographic properties identical to those of adducts formed when r-1,t-2-dihydroxy-t-3,4-oxy-1,2,3,4-tetrahydrochrysene reacts with DNA and provide evidence that metabolic activation of chrysene occurs via the formation of this 'bay-region' diol-epoxide.

Academic anxiety, locus of control, and achievement in medical school

Programs designed to assist medical students in academic difficulty typically fail to consider the importance of such factors as academic anxiety and the individual's mechanisms for coping with stress. The authors have addressed this issue by examining relationships among prior achievement, academic anxiety, locus of control, and performance in the first year of medical school. Academic anxiety not only was found to be significantly related to first year performance, but also, when combined with a measure of prior achievement, resulted in a significant increase in prediction. Additional evidence is presented which suggests that the relationship between academic anxiety and achievement may be curvilinear. Locus of control was found to correlate significantly with academic anxiety and tended to shift in a direction of greater externality during the first year of medical school. Findings are discussed within the framework of existing psychological research, and implications are presented for medical admissions, curricula, and counseling.

Fluorescence spectra of nucleoside-hydrocarbon adducts formed in mouse skin treated with 7,12-dimethylbenz[a]anthracene

Hydrolysates of DNA that had been isolated from mouse skin treated with 3H-labelled 7,12-dimethylbenz[a]anthracene (DMBA) were subjected to chromatography on Sephadex LH20 columns and 3H-labelled products that eluted in the region expected for nucleoside-hydrocarbon adducts were purified further by high pressure liquid chromatography (h.p.l.c.). The fluorescence spectra of three major products that were resolved by this method were determined using photoncounting spectrophotofluorimetry. The fluorescence spectra of all three products were anthracene-like and similar to the spectra of nucleoside-hydrocarbon adducts obtained from DNA that was incubated with 3,4-dihydro-3,4-dihydroxy-7,12-dimethylbenz[a]anthracene 1,2-oxide (DMBA-3,4-diol 1,2-oxide). This is consistent with the idea that the metabolic activation of DMBA in mouse skin occurs through the formation of 'bayregion' diol-epoxides in the 1,2,3,4-ring.

The metabolic and activation of dibenz[a,c]anthracene

In rat liver microsomal preparations, the 10,11-dihydrodiol of dibenz[a,c]anthracene (DBA) is metabolized to r-10,t-11-dihydroxy-t-12,13-oxy-10,11,12,13-tetrahydrodibenz[a,c]anthracene (anti-DBA 10,11-diol 12,13-oxide), the anti isomer of a non-bay-region diol-epoxide of DBA. When 3H-labelled DBA or trans-10,11-dihydro-10,11-dihydroxydibenz[a,c]anthracene were metabolized in this system in the presence of DNA or when 3H-labelled DBA was added to primary cultures of hamster embryo cells, covalent reactions of hydrocarbon metabolites with DNA occurred. The chromatographic characteristics of the radioactive hydrocarbon-deoxyribonucleoside adducts formed in these reactions were examined using Sephadex LH20 column chromatography and high pressure liquid chromatography. The results showed that whilst some of the radioactive hydrocarbon-deoxyribonucleoside adducts formed were indistinguishable from adducts that were formed when anti-DBA 10,11-diol 12,13-oxide reacted with DNA, other, unidentified adducts, which did not apparently arise from reactions of this diol-epoxide with DNA, were also present. Hydrocarbon-nucleoside adducts were not detected in hydrolysates of nucleic acids that were isolated from mouse skin that had been treated in vivo with DBA.

The metabolic activation of benz[alpha]anthracene in three biological systems

The 3,4- and 8,9-dihydrodiols of benz[alpha]anthracene (BA) are formed as metabolites of the parent hydrocarbon by rat-liver microsomes, by mouse skin and by hamster embryo cells. In incubations with rat-liver microsomal fractions, only small amounts of the 3,4-dihydrodiol of BA were detected relative to other dihydrodiol metabolites and only small amounts of BA-deoxyribonucleoside adducts derived from the related diol-epoxide, t-3, r-4-dihydroxy-t-1,2-oxy-1,2,3,4-tetrahydrobenz[alpha]anthracene (anti-BA-3,4-diol 1,2-oxide), were detected relative to adducts derived from r-8,t-9-dihydroxy-t-10,11-oxy-8,9,10,11-tetrahydrobenz[alpha]anthracene (anti-BA-8,9-diol 10,11-oxide). However, in studies with mouse skin and hamster embryo cells, larger amounts of free 3,4-dihydrodiol were detected and a larger proportion of the hydrocarbon-deoxyribonucleoside adducts resulted from the reaction of anti-BA-3,4-diol 1,2-oxide with DNA.

Mutagenicity of benzo[a]pyrene 7,8-dihydrodiol and 7,12-dimethylbenz[a]anthracene 3,4-dihydrodiol in S. typhimurium mediated by microsomes from rat liver and mouse skin

The mutagenic activities of trans-7,8-dihydro-7,8-dihydroxybenzo[a]-pyrene (BP 7,8-diol) and of trans-3,4-dihydroxy-7,12-dimethylbenz[a]-anthracene (DMBA 3,4-diol) towards S. typhimurium TA100 were measured in assays that were carried out on a micro-scale in liquid medium in the presence of microsomal fractions prepared from mouse skin or rat liver. In the presence of an NADPH-generating system, microsomal enzymes converted both diols into mutagens that were probably the respective 'bay-region' diol-epoxides. The rate of the enzyme-catalysed conversion of the BP 7,8-diol into mutagens by microsomal preparations from mouse epidermis was similar to that occurring with microsomes from rat liver. Pretreatment of mice by the topical application of benz[a]anthracene (BA) or 7,12-dimethylbenz[a]-anthracene (DMBA) increased the mutagenic activity of BP 7,8-diol mediated by mouse skin microsomal preparations by 2-fold and this was paralleled by a 4-fold increase in epidermal aryl hydrocarbon (benzo[a]pyrene) hydroxylase (AHH) activity. The results are discussed in relation to the high susceptibility of mouse skin to polycyclic aromatic hydrocarbon (PAH) carcinogenesis.

Polycyclic hydrocarbon activation and metabolism in epithelial cell aggregates prepared from human mammary tissue

The metabolism of benz(a)anthracene (BA), 7,12-dimethylbenz(a)anthracene (DMBA) and benzo(a)pyrene (BP) by human mammary epithelial cell aggregates in culture has been investigated using non-neoplastic tissues obtained from eight patients undergoing reduction mammoplasty. All three hydrocarbons were metabolized to water-soluble and organic solvent-soluble products and the latter included both K-region and non-K-region dihydrodiols. The major dihydrodiols detected as metabolites of the parent hydrocarbons were the 8,9-dihydrodiols of BA and DMBA and the 9,10-dihydrodiol of BP. The 1,2-dihydrodiols of BA and DMBA and the 11,12-dihydrodiol of BP were not detected. The hydrocarbons also became bound to the proteins and DNA of the epithelial cells but there were wide differences in the extents of binding occurring with the different hydrocarbons and in the extents of metabolism and binding occurring with tissue preparations from different patients. Some of the hydrocarbon-deoxyribonucleoside adducts formed from DMBA and BP appeared to have arisen through reactions of "bay-region" diol-epoxides with DNA, but only very low levels of reaction with DNA were detected in tissue preparations treated with BA.

The metabolic activation of benz[a]anthracene in hamster embryo cells: evidence that diol-epoxides react with guanosine, deoxyguanosine and adenosine in nucleic acids

The principal nucleoside-hydrocarbon adducts present in hydrolysates of RNA and DNA isolated from hamster embryo cells treated with benz[a]anthracene (BA) were examined by chromatography on Sephadex LH 20 and by high pressure liquid chromatography (HPLC) on Spherisorb 5 ODS. The results extend the previous finding that a non-'bay-region' diol-epoxide, anti-BA-8,9-diol 10,11-oxide (r-8,t-9-dihydroxy-t-10,11-oxy-8,9,10,11-tetrahydrobenz[a] anthracene) is involved in the binding of BA to cellular nucleic acids and show that this diol-epoxide most probably reacts with guanosine and adenosine in RNA and with deoxyguanosine in DNA. The results also show that a 'bay-region' diol-epoxide anti-BA-3,4-diol 1,2-oxide (t-3,-4-dihydroxy-t-1,2-oxy-1,2,3,4-tetrahydrobenz[a]anthracene, which is thought to be involved in the binding of benz[a]anthracene, which is thought to be involved in the binding of benz[a]anthracene to DNA in some situations, reacts mainly with deoxyguanosine.

An accounting/recharge system for educational media services

An accounting/recharge system can aid the educational media manager in more efficient use of resources to accomplish organizational goals. A system for cataloging, billing, and analyzing the productivity and relative efficiency of media production and services is outlined. Benefits derived from such a system include an improved basis for planning and rationing of resources, greater efficiency in utilization and production, improved internal communications, and an increased sense of accomplishment.