Reactivity of the K-region epoxides of some polycyclic hydrocarbons towards the nucleic acids and proteins of BHK 21 cells

Differentiation of the mammary gland and susceptibility to carcinogenesis

It has been demonstrated that in humans certain factors such as early menarche, late pregnancy, and nulliparity are associated with a higher risk of developing breast cancer, while early pregnancy acts as a protective factor. Induction of mammary cancer in rats by administration of the chemical carcinogen 7,12-dimethylbenz(a)anthracene reveals that the same factors influencing human breast cancer risk also affect the susceptibility of the rat mammary gland to the chemical carcinogen. Nulliparous rats and rats undergoing pregnancy interruption are more susceptible to developing carcinomas. This fact has been attributed to the incomplete differentiation of the gland at the time of carcinogen administration. Parous rats are resistant to the carcinogenic effect of DMBA, which is explained by the complete development of the gland attained during pregnancy and lactation. This development is manifested by the differentiation of terminal end buds into secretory units, which have a smaller proliferative compartment; the epithelial cells of these secretory units have a longer cell cycle, less avidity for binding DMBA, and possess a more efficient DNA excision repair capacity.

The metabolism of benzo(a)pyrene by Chinese hamster ovary cells in culture

1. The metabolism off the carcinogenic polycyclic hydrocarbon, benzo(a)pyrene, in Chinese hamster ovary cells in culture has been investigated. 2. Products with the properties on h.p.l.c. of 3-hydroxybenzo(a)pyrene and the trans-4,5-, 7,8- and 9,10-dihydrodiols of benzo(a)pyrene were detected in the cell medium when cells were incubated with benzo(a)pyrene for 24 h. 3. Examination of the nucleoside adducts present in hydrolysates of the DNA of Chinese hamster ovary cells that had been incubated with benzo(a)pyrene showed the presence of a product that co-chromatographed on Sephadex LH20 columns with the nucleoside adduct obtained from DNA that was allowed to react with the anti-isomer of the 7,8-dihydrodiol 9,10-epoxide of benzo(a)pyrene.

The detoxication of aflatoxin B1 with glutathione in the rat

1. The deactivation of aflatoxin B1 by glutathione (GSH) has been investigated in rat. Binding of metabolites of aflatoxin B1 to [3H]glutathione in vitro with rat liver microsomes is insignificant. Incubation with rat liver 10 000 g supernatant results in increased binding. Under identical conditions, benzo(a)pyrene metabolites are bound to [3H]glutathione much more than is aflatoxin B1. 2. Pre-treatment of rats with aflatoxin 1 (2 mg/kg) caused depletion in GSH of rat liver with a minimum at 6 h but returning to above normal at 24 h. GSH S-transferase activity was marginally increased at 6 h also and returned to normal at 24 h. 3. Kidney GSH was not significantly decreased, but kidney GSH S-transferase activity showed a sudden increase in 6 h, returning to almost normal at 24 h. 4. Pre-treatment with benzo(a)pyrene (2 mg/kg) caused greater depletion of hepatic GSH than occurred with aflatoxin B1 but did not show any effect on kidney GSH. 5. Hepatic and kidney GSH S-transferase in benzo(a)pyrene-treated rats showed greatest activity at 2 h followed by a gradual fall through 24 h. 6. GSH was therefore a less efficient nucleophile for aflatoxin B1 metabolites than for benzo(a)pyrene metabolites.

Studies of age-related changes in the metabolism of eosin in the rat

Male rats of different age groups maintained normally on laboratory chow were injected with eosin (2,4,5,7-tetrabromo-11-carboxyfluorescein) after which the biliary excretion of the dye was studied. In 3 age groups below 42 weeks, the dye was excreted as 2 compounds which were identified by thin-layer chromatography as unchanged eosin (Rf 0.90--0.91) contributing about 80--90% and one conjugated compound of Rf 0.43--0.47 (14--9%) which was shown to be a glucuronide. Eosin metabolites could not be traced in 30 and 42 week-old rats. This finding is discussed in relation to: (i) age and enzymic activity, and (ii) bio-activated metabolites of this dye which may induce biochemical or toxicological and carcinogenic lesions.

The association between mutagenicity and adduct formation of 1,2,7,8-diepoxyoctane and 1,2,5,6-diepoxycyclooctane

The mutagenicity of 1,2,5,6-diepoxycyclooctane (DECO) and 1,2,7,8-diepoxyoctane (DEO) was investigated using diploid Chinese hamster lung cells. 6-thioguanine (6-TG) resistance was used as the marker for mutagenicity testing: DEO was found to be genetically active; DECO, on the contrary, totally inactive. DEO readily formed adducts with radiolabeled nucleotides, while DECO failed to do so, as demonstrated through thin-layer chromatography (TLC) and the shift of the ultraviolet absorption maximum in DEO/nucleotide mixtures. The difference between the two compounds in chemical and genetic activities was attributed to their molecular conformations and the resulting differential flexibilities and adduct-forming abilities. Association between mutagenicity and adduct formation was conclusive.

Benzpyrene-induced sister chromatid exchanges in lymphocytes of patients with lung cancer

The effect of benzpyrene on sister chromatid exchange was determined in PHA-stimulated lymphocytes of 18 patients with lung cancer and 11 controls without cancer or bronchopulmonary diseases. Patients and controls did not differ either with respect to the spontaneous rate of sister chromatid exchanges or in their response to the carcinogen. We conclude that individual susceptibility to lung cancer cannot be detected by an individual response to benzypyrene, at least in lymphocytes and at the chromosomal level.

Mouse liver and lung glutathione s-epoxide transferase: effects of phenobarbital and 3-methylcholanthrene administration

The effects of 3-methylcholanthrene (3MC) and phenobarbital (PB) administration on the levels of glutathione-S-epoxide transferase activity in supernatant preparations of liver and lung were studied in a number of different strains of mice, C57Bl/6, C3H, C3H-f, Balb/c-, A+ and DBA/2+. Three epoxide substrates, 3MC-11,12-oxide, styrene oxide (SO) and 3,3,3-trichloro-1,2-epoxypropane (TCPO), were employed in this investigation. PB administration (75 mg/kg body weight for 3 days) resulted in 13-57% increases in enzyme activity in the liver supernatant but was ineffective in inducing activity in lung. 3MC administration (40 mg/kg body weight for 2 days) on the other hand was without any effect on glutathione-S-epoxide transferase activity in both liver and lung.

The involvement of a diol-epoxide in the metabolic activation of benzo(a)pyrene in human bronchial mucosa and in mouse skin

DNA has been isolated from human bronchial segments that have been treated in short-term organ culture with 3H-labelled benzo (a) pyrene. DNA has also been isolated from mouse skin treated with 3H-labelled samples of benzo (a) pyrene, with the related radioactive 4,5-, 7,8- and 9,10-dihydrodiols and with 3H-3-hydroxybenzo (a) pyrene. Sephadex LH20 column chromatography of hydrolysates of these DNA samples showed that the hydrocarbondeoxyribonucleoside products formed in benzo (a)-pyrene-treated human bronchial mucosa and mouse skin are indistinguishable from those that are formed when 7,8-dihydro-7,8-dihydroxybenzo (a) pyrene 9,10-oxide reacts with DNA in solution. These same hydrocarbon-deoxyribonucleoside products were also found in hydrolysates of DNA from mouse skin treated with 7,8-dihydro-7,8-dihydroxybenzo (a)-pyrene but products of this type were not detected in hydrolysates of DNA following treatment of mouse skin either with the 4,5- or 9,10-dihydrodiols or with 3-hydroxybenzo (a) pyrene. This results show that the metabolic activation of benzo (a) pyrene to a diolepoxide, 7,8-dihydro-7,8-dihydroxybenzo (a) pyrene 9,10-oxide, which reacts with DNA, is the same in human bronchial mucosa, a tissue in which this hydrocarbon is suspected of being carcinogenic, as it is in mouse skin and in hamster embryo cells, two situations in which benzo(a)pyrene is known to induce malignancy.

Metabolic pathways of 7,12-dimethylbenz[a]anthracene in hepatic microsomes

High pressure liquid chromatography has enabled quantitative analysis of the in vitro metabolism of 7,12-dimethylbenz[a]anthracene, 7-methyl-12-hydroxymethylbenz[a]anthracene, 7-hydroxymethyl-12-methylbenz[a]anthracene, and 7,12-dihydroxymethylbenz[a]anthracene by 3-methylcholanthrene-induced and control rat liver microsomes. The following previously unrecognized metabolites have been tentatively identified: 5,6-dihydro-5,6-dihydroxy-7-methyl-12-hydroxymethylbenz[a]anthracene, 3-hydroxy-7,12-dihydrodihydroxymethylbenz[a]anthracene, 4-hydroxy-7,12-dihydrodihydroxymethylbenz[a]anthracene, and 8,9-dihydro-8,9-dihydroxy-7,12-dihydroxymethylbenz[a]anthracene. The epoxide hydratase inhibitor 1,2-epoxy-3,3,3-trichloropropane was found to eliminate all dihydrodiol formation and markedly inhibit the formation of several dimethylbenzanthracene metabolites. It is proposed that the tentatively identified 3-hydroxy and 4-hydroxy derivatives are formed by an enzymatic mechanism that does not involve epoxides as intermediates. The metabolic pathways of 7,12-dimethylbenz[a]anthracene in hepatic microsomal enzymes are proposed.

Skin carcinogenesis: cholesterol-5alpha,6alpha-epoxide hydrase activity in mouse skin irradiated with ultraviolet light

Cholesterol-5alpha,6alpha-epoxide hydrase activity was 96 percent greater in skin of hairless mice that were receiving suberythemic ultraviolet light irradiation for 15 weeks than in nonirradiated controls. This enzyme system, which metabolizes cholesterol-5alpha,6alpha-epoxide (a known carcinogen), appears to be substrateinducible and is apparently responsible for the concomitant reduction of the sterol carcinogen that occurs prior to tumor induction.

Epoxy derivatives of aromatic polycyclic hydrocarbons. The synthesis of dibenz[a,c]anthracene 10,11-oxide and its metabolism by rat liver preparations

The synthesis of dibenz[a,c]anthracene 10,11-oxide is described. The oxide was unstable and was rapidly decomposed with cold mineral acid into a mixture of 10- and 11- hydroxydibenz[a,c]anthracene. The oxide was converted by rat liver microsomal preparations and homogenates into a product that is probably 10,11-dihydro-10,11-dihydroxydibenz[a,c]anthracene and which was identical with the metabolite formed when dibenz[a,c]anthracene was metabolized by rat liver homogenates. The oxide did not react either chemically or enzymically with GSH. 10,11-Dihydrodibenz[a,c]anthracene and 10,11-dihydrodibenz[a,c]anthracene 12,13-oxide were both metabolized by rat liver preparations into trans-10,11,12,13-tetrahydro-10,11-dihydroxydibenz[a,c] anthracene and the oxide was converted chemically into this dihydroxy compound, and it reacted chemically but not enzymically with GSH. In the alkylation of 4-(p-nitrobenzyl)pyridine, the ;K-region' epoxide, dibenz[a,h]anthracene 5,6-oxide, was more active than either dibenz[a,c]anthracene 10,11-oxide or 10,11-dihydrobenz[a,c]anthracene 12,13-oxide.