The metabolism of 7-ethylbenz[a]anthracene by rat liver microsomal preparations

7-Ethylbenz[a]anthracene (7-EBA) is a much weaker carcinogen than the 7-methyl analogue (7-MBA), and this difference may be based upon differences in the pathways by which the two compounds are metabolized and activated. In the present work, 7-EBA and the related 7 alpha- and 7 beta-hydroxyethyl derivatives (7-OHEBA and 7-beta-OHEBA) have been incubated with microsomes prepared from the livers of rats pretreated with 3-methylcholanthrene, the metabolites were extracted and purified by TLC, and the products present in the dihydrodiol band were examined by analytical HPLC. Metabolites were identified by comparison with authentic reference standards and by their chromatographic, UV, fluorescence, mass, and NMR spectral characteristics. The 7-EBA metabolites included the 1,2- 3,4, 5,6- 8,9- and 10,11-dihydrodiols, the 3,4- 8,9- and 10,11-dihydrodiols of 7-alpha-OHEBA, and three phenolic dihydrodiols that were not completely characterized. No 7-beta-OHEBA derivatives were detected as metabolites of 7-EBA. The results obtained so far have not revealed any qualitative differences in the routes by which 7-EBA and 7-MBA are metabolized in rat liver microsomal preparations.

Formation of DNA adducts in mouse skin treated with metabolites of chrysene

Analysis by 32P-postlabelling of DNA isolated from mouse skin that had been treated in vivo with the polycyclic hydrocarbon chrysene revealed the presence of 7 adducts. All 7 adducts were also present in DNA from mice treated with trans-1,2-dihydro-1,2-dihydroxychrysene (chrysene-1,2-diol), and one of them, adduct 2, was formed from the triol derivative 9-hydroxy-trans-1,2- dihydro-1,2-dihydroxychrysene (9-hydroxychrysene-1,2-diol) and from 3-hydroxychrysene. Adducts were not detected in DNA from mice treated with trans-3,4-dihydro-3,4-dihydroxychrysene (chrysine-3,4-diol) or with 1-, 2-, 4-, 5- or 6-hydroxychrysene. In vitro modification of DNA by the anti-isomer of the bay-region diol-epoxide yielded adducts 3-7, while the corresponding triol-epoxide yielded adducts 2. It is concluded that chrysene activation in mouse skin proceeds principally via the bay-region diol-epoxide and to a lesser extent via the related bay-region triol-epoxide.

The method of information synthesis and its use in the assessment of health care technology

This paper compares information synthesis to literature review and meta-analysis as tools for the researcher trying to summarize published information and identify information gaps on emerging technologies. Because information synthesis is narrowly focused and addresses the question of what is not known, as well as what is known, it is a good precursor to a full-scale technology assessment. An example of information synthesis is given, comparing cost-effectiveness of extracorporeal shock wave lithotripsy to two other treatments for kidney stones.

Aromatic DNA adducts in human bone marrow and peripheral blood leukocytes

DNA from normal human bone marrow mononuclear and non-mononuclear cells was analysed by 32P-post-labelling for the presence of aromatic adducts. Ten out of 10 individuals showed the presence of adducts at levels of 1-9 adducts per 10(8) nucleotides that were not detected in four samples of human foetal bone marrow. Inter-individual variations in the patterns of these presumed aromatic adducts were observed. Similar adducts were also present in the DNA of peripheral white blood cells of both smokers and non-smokers, although at lower levels than in bone marrow. The data suggest that the adducts result from environmental exposure to an as-yet-unidentified genotoxic agent or agents.

Metabolism of the bay-region diol-epoxide of chrysene to a triol-epoxide and the enzyme-catalysed conjugation of these epoxides with glutathione

Metabolic activation of chrysene in mouse skin appears to involve r-1,t-2-dihydroxy-t-3,4-oxy-1,2,3,4-tetrahydrochrysene (anti-chrysene-1,2-diol 3,4-oxide) and 9-hydroxy-r-1,t-2-dihydroxy-t-3,4-oxy-1,2,3,4-tetrahydrochrysene (anti-9-OH-chrysene-1,2-diol 3,4-oxide). The enzyme-catalysed conjugation of these epoxides with [35S]glutathione has been studied in experiments in which the glutathione conjugates were separated by h.p.l.c. and examined by fluorescence spectrophotometry. Both anti-chrysene-1,2-diol 3,4-oxide and anti-9-OH-chrysene-1,2-diol 3,4-oxide formed conjugates nonenzymically and both were shown to be substrates for rat liver glutathione transferases. When anti-chrysene-1,2-diol 3,4-oxide was incubated with [35S]glutathione and a rat liver microsomal metabolizing system, glutathione conjugates with h.p.l.c. and fluorescence spectral characteristics identical to those of conjugates formed from both anti-chrysene-1,2-diol 3,4-oxide and anti-9-OH-chrysene-1,2-diol 3,4-oxide were detected. This finding provides evidence that anti-chrysene-1,2-diol 3,4-oxide can be further metabolized to the triol-epoxide, anti-9-OH-chrysene-1,2-diol 3,4-oxide by rat liver microsomal systems.

Effects of inducers on the regio- and stereoselective metabolism of benzo[a]pyrene by mouse tissue microsomes

The metabolism of benzo[a]pyrene (BP) by microsomal fractions of the skin, lungs and liver of the mouse, and the effects on this process of pretreatment with the xenobiotics phenobarbital (PB) and 3-methylcholanthrene (3-MC) were examined. Differences between the untreated tissues were found both in terms of the total amounts of diol recovered and in the relative proportions of the individual diols extracted following incubation. Induction with PB or 3-MC significantly altered the profiles of metabolic diols obtained with epidermal and hepatic microsomes compared with their respective controls. Pulmonary microsomes showed similar trends to those obtained with liver microsomes but these were not statistically significant. The optical purity of the BP-7,8-diol that was formed by each microsomal type was examined by direct resolution of the enantiomers on HPLC using a chiral stationary phase. In each case the (-)-7R,8R-enantiomer predominated. Pretreatment with 3-MC significantly decreased the optical purity of BP-7,8-diol recovered from incubations with skin microsomes, but significantly increased the optical purity of the diol extracted from incubations with lung and liver microsomes. In addition to the diols, an unidentified BP metabolite was found that eluted between BP-9,10- and 4,5-diol on a reverse-phase high-performance liquid chromatography (HPLC) system and which represented a major product in extracts of incubations of BP with both induced and uninduced skin and lung microsomal fractions.

Pathways involved in the metabolism and activation of polycyclic hydrocarbons

The metabolism and activation of the polycyclic aromatic hydrocarbons has been reviewed and the original contributions made to this area by Professor E. Boyland have been placed in context. The reactions involved in the formation, via epoxides, of hydroxylated derivatives have been outlined and conjugations with glucuronic and sulphuric acids and with glutathione have been discussed. Examples of secondary hydroxylation reactions have been given and the possible role that phenolic hydroxyl groups may play in activating epoxides considered. Mechanism by which polycyclic hydrocarbons are activated by metabolism to epoxides of various types have been included, mainly by reference to benzo[a]pyrene, benz[a]anthracene and chrysene. The tissue and species specific effects of polycyclic hydrocarbons have been referred to and the tissues that may act as targets in man for the initiation of malignancy by polycyclic hydrocarbons mentioned.

Mutagenic potential of DNA adducts formed by diol-epoxides, triol-epoxides and the K-region epoxide of chrysene in mammalian cells

The syn- and anti-isomers of chrysene-1,2-diol-3,4-oxide (syn-diol-epoxide and anti-diol-epoxide) and of 9-hydroxychrysene-1,2-diol-3,4-oxide (syn-triol-epoxide and anti-triol-epoxide), and chrysene-5,6-oxide, the K-region epoxide, were tested for their ability to induce 6-thioguanine-resistant mutants in V79 Chinese hamster cells. The levels of DNA adducts formed by each compound in the V79 cells were determined by 32P-post-labelling analysis. The most potent mutagen, in terms of the mutation frequency/nmol compound administered, was the anti-triol-epoxide, which was 1.7 times as active as the anti-diol-epoxide. The anti-diol-epoxide was approximately 10 times more active than both the syn-triol-epoxide and the syn-diol-epoxide, which in turn were several times more active than the K-region epoxide. However, when the results were expressed as mutations/pmol total adducts formed, the anti-triol-epoxide and anti-diol-epoxide were shown to be of similar potency and approximately twice as active as the other three compounds. Thus differences in the conformation of adducts formed with DNA by syn- and anti-isomers may be responsible for their different mutagenic potentials; the presence of a phenolic OH-group at the 9-position of a chrysene-1,2-diol-3,4-oxide appears to increase its chemical reactivity.

The effect of neighbouring bases on G-specific DNA cleavage mediated by treatment with the anti-diol epoxide of benzo[a]pyrene in vitro

Three 5'-end-labelled double-stranded linear DNA fragments of defined sequence were treated with r-7, t-8-dihydroxy-t-9, 10-oxy-7,8,9,10-tetrahydrobenzo[a]pyrene (anti-BPDE). The DNA samples were then examined by gel electrophoresis both before and after denaturation and treatment with alkali. The extent of modification of deoxyguanosine (dG) residues was estimated from changes in electrophoretic mobility: at saturation less than 25% of the dG residues appeared to be modified by reaction with anti-BPDE. The determination of the sites of G-specific strand cleavage in a total of 0.5 kbp of DNA by sequencing gel electrophoresis showed that scission at dG residues is sequence specific and that whilst, for example, cleavage occurred at the central dG residues of all 5'-CGG-3' (21/21), of all 5'-TGG-3' (14/14), of all 5'-TGT-3' (7/7) and of all 5'-CGT-3' (5/5) sequences examined, it did not occur in any of the 5'-GGA-3' (0/12) or 5'-GGC-3' (0/15) sequences and only occurred rarely in the 5'-GGG-3' (1/48) and 5'-GGT-3' (2/11) sequences. No cleavage was found at internal dG residues within poly(dG)9 or poly(dG)18 sequences. The data may permit prediction of the sites of strand scission in DNA molecules of known sequence that have been modified by diol-epoxides of polycyclic hydrocarbons.

Mutagenic and cell-transforming activities of triol-epoxides as compared to other chrysene metabolites

The syn- and anti-isomers of the bay-region diol-epoxides of chrysene and of 3-hydroxychrysene and their metabolic precursors have been investigated for mutagenicity in Salmonella typhimurium (reversion to histidine prototrophy) and V79 Chinese hamster cells (acquirement of resistance to 6-thioguanine) and for transforming activity in M2 mouse prostate cells. Other known and potential chrysene metabolites have been included in mutagenicity experiments. Direct mutagenic activity in S. typhimurium TA 100 exhibited, in order of potency, anti-triol-epoxide greater than syn-triol-epoxide greater than anti-diol-epoxide greater than syn-diol-epoxide greater than chrysene 5,6-oxide much greater than chrysene-1,2-quinone, chrysene-3,4-quinone, and chrysene 5,6-quinone. Chrysene, the six isomeric chrysenols, and the trans-dihydrodiols [trans-1,2-dihydroxy-1,2-dihydrochrysene (chrysene-1,2-diol), trans-3,4-dihydroxy-3,4-dihydrochrysene, trans-5,6-dihydroxy-5,6-dihydrochrysene, and 9-hydroxy-trans-1,2-dihydroxy-1,2-dihydrochrysene (9-hydroxychrysene-1,2-diol)] were inactive per se but were activated to mutagens in the presence of reduced nicotinamide adenine dinucleotide phosphate-fortified postmitochondrial fraction (S9 mix) of liver homogenate from Arochlor 1254-treated rats. Chrysene, 3-hydroxychrysene, chrysene-1,2-diol, and 9-hydroxychrysene-1,2-diol were activated efficiently; the other compounds were activated weakly. In S. typhimurium TA 98, the mutagenic activities of the chrysene derivatives were weak in comparison with those in the strain TA 100. trans-3,4-Dihydroxy-3,4-dihydrochrysene (in the presence of S9 mix) was the most efficacious mutagen in strain TA 98. The relative mutagenic potencies of the directly active compounds differed from the results obtained in strain TA 100, in that in strain TA 98 the anti-diol-epoxide was more mutagenic than the triol-epoxides and chrysene 5,6-oxide was more mutagenic than syn-diol-epoxide and syn-triol-epoxide. In V79 cells, the order of mutagenic potency was: anti-triol-epoxide greater than anti-diol-epoxide greater than syn-triol-epoxide greater than syn-diol-epoxide greater than chyrsene 5,6-oxide greater than chrysene-1,2-diol (in the presence of S9 mix) greater than 9-hydroxychrysene-1,2-diol (in the presence of S9 mix) greater trans-3,4-dihydroxy-3,4-dihydrochrysene in the presence of S9 mix). Chrysene, 3-hydroxychrysene, 5-hydroxychrysene, and 6-hydroxychrysene showed no mutagenic effects in V79 cells, either in the presence or absence of S9 mix.(ABSTRACT TRUNCATED AT 400 WORDS)

Studies on the further activation of benzo[a]pyrene diol epoxides by rat liver microsomes and nuclei

The syn- and anti-diastereoisomers of trans-7,8-dihydroxy-9,10-oxy-7,8,9,10-tetrahydrobenzo[a]pyrene (BPDE) were further metabolized by rat liver microsomes obtained from 3-methylcholanthrene(MC)-pretreated rats and NADPH to reactive intermediates, presumably 1,7,8- and 3,7,8-trihydroxy-9,10-oxy-7,8,9,10-tetrahydrobenzo[a]pyrenes (triol-epoxides), that bound to macromolecules or decomposed to products consistent with pentahydroxy derivatives of benzo[a]pyrene (BP-pentols). Three major metabolites of syn-BPDE and four major metabolites of anti-BPDE were isolated by high performance liquid chromatography and characterized by spectroscopic techniques. When fluorescence spectroscopy was employed all metabolites exhibited very similar spectral properties and showed substantial shifts in excitation and emission maxima to longer wavelengths when measured under alkaline conditions, consistent with the presence of a phenolic hydroxyl group. Furthermore, the spectral properties of the metabolites from syn- and anti-BPDE were similar to those of 1-hydroxypyrene. Previous data from this laboratory together with the data presented in this study thus strongly suggest that further metabolism of BPDE involves hydroxylation at the 1- and 3-positions to yield the corresponding triol-epoxides and various BP-pentols. The pentols could also be formed by incubating tetrols derived from syn- and anti-BPDE with microsomes and NADPH. However, the rate of formation of pentols from the BP-tetrols was much slower than the rate of further metabolism of BPDE. Accordingly, the major route of BP-pentol formation is likely to be via the intermediate formation of triol-epoxides. Isolated liver nuclei from MC-pretreated rats were also found to catalyze the activation of anti-BPDE in presence of NADPH to reactive intermediates. This resulted in a substantial increase in binding to histone and non-histone proteins, with a concomitant decrease in binding to DNA. No qualitative change in the distribution of DNA-bound products of anti-BPDE could be demonstrated as a result of the further metabolism of anti-BPDE.

The metabolism of 9-methylanthracene by rat-liver microsomal preparations

The metabolism of 9-methylanthracene by liver microsomal preparations from 3-methylcholanthrene-treated rats was examined. The principal metabolites identified were 9-hydroxymethylanthracene, the 1,2- and 3,4-dihydrodiols of the parent hydrocarbon and the 3,4-dihydrodiol of the 9-hydroxymethyl derivative. A small amount of a product that appeared to be a phenolic derivative of the hydrocarbon was also formed. The structures of the major metabolites were confirmed by u.v., n.m.r., and mass-spectral analysis and, wherever possible, by direct comparison of their chromatographic properties with those of the authentic compounds. 9-Hydroxymethylanthracene was further metabolized by rat-liver microsomal preparations to the 3,4-dihydrodiol but not to the related 1,2-dihydrodiol.

Aberrant activation of benzo(a)pyrene in cultured rat mammary cells in vitro and following direct application to rat mammary glands in vivo

Primary cultures of epithelial cell aggregates and fibroblasts derived from mammary tissue from female Wistar rats were treated with benzo(a)pyrene (BP), and their DNA was isolated and analyzed. At least seven BP-DNA adducts were detected in DNA hydrolysates by high-performance liquid chromatography, none of which had the chromatographic properties characteristic of adducts formed by the putative ultimate carcinogen r-7, t-8-dihydroxy-t-9, 10-oxy-7, 8,9,10-tetrahydrobenzo(a)pyrene (anti-BP-7, 8-diol-9, 10-oxide) or other known electrophilic metabolites of BP. Similar profiles of adducts were obtained from mammary DNA of rats that had been treated with BP by injection into their mammary fat pads. Chromatography on boronate columns indicated that five of the seven adducts contained cis-hydroxyl groups. In contrast, when BP was administered by i.p. injection to female Wistar rats, anti-BP-7,8-diol-9,10-oxide-DNA adducts were detected in each of seven tissues, including mammary gland, that were examined.

Comparative studies of the metabolic activation of chrysene in rodent and human skin

Metabolism and activation of chrysene was examined in mouse, rat and human skin using a short-term organ culture technique. Mouse skin released larger quantities of free dihydrodiols into the culture medium than either rat or human skin and greater quantities of chrysene metabolites became covalently bound to the DNA of mouse skin. The stereochemistry of the chrysene-1,2-diol that was formed by each skin type was examined using high-performance liquid chromatography (HPLC) with a chiral stationary phase to resolve the enantiomers. It was found that in each case the (-)-enantiomer predominated. When hydrolysates of DNA extracted from rodent or human skin that had been treated with 3H-labelled chrysene were chromatographed on Sephadex LH-20 columns, the elution profiles of the hydrocarbon-DNA adducts were found to vary between the species studied. Further examination using HPLC showed that some of the adducts formed in skin had the chromatographic characteristics of adducts formed when the anti-isomer of the 'bay-region' diol-epoxide of chrysene (r-1,t-2-dihydroxy-t-3,4-oxy-1,2,3,4-tetrahydrochrysene) reacted with DNA and that others had the characteristics of triol-epoxide adducts.

Evidence for N-(deoxyguanosin-8-yl)-1-aminopyrene as a major DNA adduct in female rats treated with 1-nitropyrene

[3H]1-Nitropyrene was administered at a dose of 25 mg/kg by i.p. injection to female Wistar rats. Animals were killed 24 h later and DNA was isolated from kidney, liver and mammary gland, enzymically hydrolysed and analysed by reverse-phase h.p.l.c. A major adduct peak was detected in DNA from each of the three organs. Enzymic hydrolysates of DNA, which had been reacted in vitro with 1-nitropyrene in the presence of xanthine oxidase, were similarly analysed by h.p.l.c. One major adduct peak was obtained which had the same retention time as the in vivo product. Confirmatory evidence that the in vivo adduct and the in vitro adduct were structurally similar was obtained from the determination of the pH-dependent solvent partitioning profiles. Further, treatment of the in vivo adduct from liver, kidney or mammary gland DNA hydrolysates and the in vitro adduct with sodium hydroxide resulted in the formation of a more polar product which eluted earlier on h.p.l.c. This behaviour is consistent with scission of the imidazole ring of a deoxyguanosine adduct. The major DNA adduct formed in vitro following xanthine oxidase reduction of 1-nitropyrene has previously been identified by others as N-(deoxyguanosin-8-yl)-1-aminopyrene. The present data suggest that the in vivo 1-nitropyrene-DNA adduct has the same structure.

Metabolic activation of 7,12-dimethylbenz[a]anthracene in rat mammary tissue: fluorescence spectral characteristics of hydrocarbon-DNA adducts

The hydrocarbon-deoxyribonucleoside adducts present in DNA isolated from the mammary glands of rats that had been treated with 7,12-dimethylbenz[a]anthracene (DMBA) were separated by Sephadex LH20 column chromatography, purified by high performance liquid chromatography (HPLC), and examined by photon-counting spectrophotofluorimetry. The adducts were found to have anthracene-like fluorescence spectra which is consistent with the reaction of diol-epoxides formed in the 1,2,3,4-ring of DMBA with mammary gland DNA.

The formation of 9-hydroxychrysene-1,2-diol as an intermediate in the metabolic activation of chrysene

9-Hydroxy-trans-1,2-dihydro-1,2-dihydroxychrysene (9-hydroxychrysene-1,2-diol), which may be the triol involved in the formation of a chrysene triol-epoxide-DNA adduct in mouse skin, was not detected when chrysene was incubated with rat-liver microsomal preparations. In separate experiments an excess of synthetic 9-hydroxychrysene-1,2-diol was added during the incubation of 3H-labelled chrysene with rat-liver microsomes and was then re-isolated. The triol was found to contain a radioactive product that had chromatographic properties identical to those of 9-hydroxychrysene-1,2-diol when examined by reverse-phase h.p.l.c., both before and after acetylation, by normal-phase h.p.l.c. and by t.l.c. both before and after oxidation. When treated with m-chloroperoxybenzoic acid, the synthetic 9-hydroxychrysene-1,2-diol formed products that possessed alkylating activity and that reacted with DNA in vitro. Examination of the triol-epoxides produced by oxidation of a mixture of synthetic and metabolic 9-hydroxychrysene-1,2-diol by t.l.c. suggested that the anti-isomer was formed.

The metabolism of 9,10-dimethylanthracene by rat liver microsomal preparations

The metabolism of the weakly-carcinogenic hydrocarbon, 9,10-dimethylanthracene (DMA) by rat-liver microsomal preparations has been examined. 9-Hydroxymethyl-10-methylanthracene (9-OHMeMA) and 9,10-dihydroxymethyl-anthracene (9,10-DiOHMeA) were identified as metabolites by comparing their chromatographic and spectral properties with those of the authentic compounds. The trans-1,2-dihydro-1,2-dihydroxy derivative of DMA (DMA 1,2-diol) was the major metabolite formed which was identified by its chromatographic, u.v., n.m.r. and mass spectral properties. The dihydrodiol was also formed in the oxidation of DMA in an ascorbic acid-ferrous sulphate-EDTA system. Two other dihydrodiols that were formed from DMA by metabolism appeared to be the trans-1,2- and 3,4-dihydrodiols of 9-OHMeMA (9-OHMeMA 1,2-diol and 9-OHMeMA 3,4-diol) and the further metabolism of DMA 1,2-diol yielded both of these dihydrodiols. When 9-OHMeMA was further metabolized, two main metabolites were formed; one was identified as 9,10-DiOHMeA and the other appeared to be 9-OHMeMA 3,4-diol. No metabolites were detected when 9,10-DiOHMeA was incubated with rat-liver microsomal fractions.

Microsome-mediated reactions of phenols of polycyclic hydrocarbons with DNA

Phenolic metabolites of 7 polycyclic hydrocarbons were incubated with rat-liver microsomal fractions in the presence of DNA. Hydrocarbon-nucleoside adducts with chromatographic properties similar to those of diol-epoxide-deoxyribonucleoside adducts, were detected in hydrolysates of DNA that had been incubated with phenols of benzo[a]pyrene, benz[a]anthracene and chrysene. Adducts were not detected when phenols of phenanthrene, pyrene, dibenz[a,c]anthracene or dibenz[a,h]anthracene were further metabolised. The possible contribution of phenolic metabolites to the carcinogenic activity and DNA binding of polycyclic hydrocarbons is discussed.

Biologically-active and chemically-reactive polycyclic hydrocarbon metabolites

The mechanism by which polycyclic hydrocarbons produce tumours in mammalian tissues exposed to them involves biotransformation of the compounds to chemically-reactive species that covalently modify cellular informational macromolecules. In all cases known, epoxides of some form are the reactive species involved. The most common pathway is the formation of vicinal diol-epoxides, the reactive centre of the molecule commonly being adjacent to the 'bay-region'. With some hydrocarbons, the involvement in DNA binding of non-'bay-region' diol-epoxides, of a phenol epoxide and of a 'bay-region' diol-epoxide containing a phenolic function (a triol-epoxide) has also been demonstrated. The relative importance to the carcinogenic process of the different pathways leading to DNA-binding products may be reflected by the biological activities of the intermediates involved.

The metabolism of 7,12-dimethylbenz[a]anthracene and 7-hydroxymethyl-12-methylbenz[a]anthracene by rat liver and adrenal homogenates and by rat adrenocortical cells

The metabolism of 3H-labelled 7,12-dimethylbenz[a]anthracene (DMBA) and of 7-hydroxymethyl-12-methylbenz[a]anthracene (7-OHM-12-MBA) into solvent- and water-soluble and protein-bound derivatives has been examined in rat liver and adrenal homogenates and in rat adrenocortical cells in culture. Although the overall extents of metabolism of the substrates by the two types of homogenate were similar, there was twice as much binding to protein in incubations with the 7-hydroxymethyl derivative. Rat adrenal cells in culture metabolized DMBA more extensively than 7-OHM-12-MBA and converted much more of the parent hydrocarbon into water-soluble derivatives. Both hydrocarbons were metabolized to yield dihydrodiols that were separated and identified by high performance liquid chromatography (HPLC). The 8,9-dihydrodiol was the major dihydrodiol formed from DMBA but, with 7-OHM-12-MBA as substrate, metabolism was diverted to the 10,11- and 3,4-positions in adrenal and hepatic preparations respectively. The viability of rat adrenocortical cells in culture, as measured by trypan blue exclusion, did not appear to be affected by treatment with DMBA, 7-OHM-12-MBA, the sulphate ester of 7-OHM-12-MBA or by 3,4-dihydro-3,4-dihydroxy-7-hydroxymethyl-12-methylbenz[a]anthracene.

Inactivation of a diol-epoxide and a K-region epoxide with high efficiency by glutathione transferase X

Four glutathione transferases (EC 2.5.1.18), glutathione transferases A, B, and C and a hitherto unknown form, termed X, were purified to apparent homogeneity from rat liver cytosol. They were investigated for their abilities to inactivate two mutagenic epoxides derived from the polycyclic aromatic hydrocarbon benz(a)anthracene, the K-region epoxide benz(a)anthracene 5,6-oxide and the diol-epoxide r-8,t-9-dihydroxy-t-10,11-oxy-8,9,10, 11-tetrahydrobenz(a)anthracene. Mutagenic activity was determined using Salmonella typhimurium his- strain TA100. Glutathione alone had little if any influence on the mutagenicity of the diol-epoxide but significantly decreased the mutagenic effect of the K-region epoxide. This inactivation was enhanced by the addition of glutathione transferases. Both epoxides were inactivated by glutathione in the presence of each of the four enzymes, but with varying efficiencies. Inactivation of the K-region epoxide (in terms of its mutagenicity in the presence of glutathione) required extremely little enzyme, about 1000 times less than for the diol-epoxide. On a molar basis, glutathione transferase X (followed by C greater than A greater than or equal to B) was clearly the most efficient enzyme in inactivating both substrates and also more efficient than were three other purified enzymes (microsomal epoxide hydrolase, cytosolic epoxide hydrolase, and dihydrodiol dehydrogenase) previously investigated in this test system. Taking into account the amounts of enzyme present in rat liver, the glutathione transferases C and X were most effective in inactivating the epoxides examined. Thus, the newly discovered glutathione transferase X appears to be of substantial significance in the inactivation of two structural prototypes of epoxides derived from polycyclic aromatic hydrocarbons, a K-region epoxide and a non-bay-region vicinal diol-epoxide.

Metabolic activation of chrysene in mouse skin: evidence for the involvement of a triol-epoxide

All three possible dihydrodiols of chrysene and a chrysene triol, formed from the further metabolism of the chrysene-1,2-diol, were detected when ether extracts of mouse skin that had been treated with 3H-labelled chrysene were examined by h.p.l.c. The major deoxyribonucleoside-hydrocarbon adducts present in hydrolysates of DNA isolated from the mouse skin were examined by chromatography on Sephadex LH20 and by h.p.l.c. on Zorbax ODS. One adduct had chromatographic properties identical to those of the major adduct formed when r-1,t-2-dihydroxy-t-3,4-oxy-1,2,3,4-tetrahydrochrysene reacts with DNA. A second major adduct was present that had chromatographic properties that were indistinguishable from those of an adduct that was formed when either chrysene-1,2-diol or 3-hydroxychrysene were incubated with DNA in a rat liver microsomal metabolising system. The results provide evidence that this new adduct is formed via the reaction of a 'triol-epoxide', that appears to be 9-hydroxy-chrysene-1,2-diol 3,4-oxide, with DNA in mouse skin.