Strain-dependent differences in the metabolism of 3-methylcholanthrene by maternal, placental, and fetal tissues of C57BL/6J and DBA/2J mice

C57BL/6J (B6) and DBA/2J (D2) mice have different susceptibilities to developmental toxicity and transplacental carcinogenesis induced by in utero exposure to polycyclic aromatic hydrocarbons, which has been associated with polycyclic aromatic hydrocarbon metabolism and inducibility at the Ah locus. The distribution of total 3-methylcholanthrene (3-MC)-associated radioactivity in maternal, placental, and fetal tissues of beta-naphthoflavone-pretreated pregnant B6 and D2 mice was determined up to 12 h after p.o. exposure to [6-14C]-3-MC (63 mg/kg, 20 mu Ci) on gestational day 17. 3-MC-associated radioactivity in maternal plasma was not significantly different in the two strains. However, D2 tissue homogenates had consistently higher levels of 3-MC-associated radioactivity, which included both bound and free parent compound and metabolites. Increased metabolism of 3-MC by B6 maternal liver was suggested by the induced levels of aryl hydrocarbon hydroxylase activity in that tissue and by the observation that levels of total radioactivity decreased more rapidly in B6 tissues than in D2 tissues. The D2 fetal lung, the target tissue for 3-MC-induced transplacental carcinogenesis, appeared to accumulate 3-MC-associated radioactivity for a longer period of time than either the D2 fetal liver or the B6 fetal tissues. This study suggests that the genetic differences in fetal susceptibility to the developmental toxicity and transplacental carcinogenesis of 3-MC may be related to the presystemic elimination of the compound from both maternal and fetal tissues.

Methylcholanthrene: a possible pseudosubstrate for adrenocortical 17 alpha-hydroxylase and aryl hydrocarbon hydroxylase

In cultured bovine adrenocortical cells, loss of 17 alpha-hydroxylase activity was observed after incubation with 3-methylcholanthrene (3-MC). The suppression of 17 alpha-hydroxylase by 3-MC was rapid (50% loss of activity in 10 hr at 1 microM 3-MC), did not exhibit a lag period, and was not affected by cycloheximide. Direct effects of 3-MC on 17 alpha-hydroxylase were observed only at high concentrations, but the concentration for 50% loss of activity was 0.3 microM when 3-MC was added for 24 hr prior to assay of 17 alpha-hydroxylase. High concentrations (to 40 microM) of substrate (progesterone), did not affect the loss of activity due to 3-MC. Loss of 17 alpha-hydroxylase activity was specific; 11 beta-hydroxylase was unaffected and cell growth was unaltered. However, 22-amino-23,24-bisnorchol-5-en-3 beta-ol, an inhibitor of 17 alpha-hydroxylase, partially prevented the loss of 17 alpha-hydroxylase at 1-30 nM. 3-MC is thought to induce cytochrome P-450s via a receptor with high affinity for 2,3,7,8-tetrachlorodibenzo-p-dioxin (TCDD). TCDD was without effect on 17 alpha-hydroxylase over the range of 10 nM to 10 microM. Benz[a]anthracene, 7,12-dimethylbenz[a]anthracene, benzo[a]pyrene, chrysene, and methylphenanthrenes suppressed 17 alpha-hydroxylase at high concentrations (10-50 microM for 50% loss of activity). Some steroids that lack a substituent at position 17 also caused loss of 17 alpha-hydroxylase. Like 17 alpha-hydroxylase, bovine adreno-cortical cell AHH was found to be suppressed by exposure to 3-MC. Compounds that caused loss of 17 alpha-hydroxylase caused loss of AHH, with a similar order of potency and at similar concentrations. Suppression of AHH by 3-MC did not require protein synthesis and was prevented by an inhibitor of enzymatic activity, alpha-naphthoflavone. This implies a degree of similarity of the cytochrome P-450s for 17 alpha-hydroxylase and adrenal AHH, but the activities were shown to be likely due to different enzymes. The suppression of 17 alpha-hydroxylase and AHH by 3-MC appears not to occur by a receptor-mediated mechanism but to be similar to the suppression of 11 beta-hydroxylase and 21-hydroxylase by steroid pseudosubstrates previously observed.

The reaction of a 3-methylcholanthrene diol epoxide with DNA in relation to the binding of 3-methylcholanthrene to the DNA of mammalian cells

DNA prelabelled in the purine or pyrimidine bases was reacted with anti-7,8-epoxy-trans-9,10-dihydroxy-7,8,9,10-tetra-hydro-3-methylchol ant hrene (anti-3MCDE). Enzymic degradation and column chromatography allowed the isolation of a number of hydrocarbon--nucleoside derivatives. The major product was shown to result from reaction with the 2-amino-group of guanine, but minor products containing guanine, adenine and cytosine were also obtained. One of the minor products, probably resulting from reaction at N7-guanine, led to rapid depurination. Anti-3MCDE was an efficient mutagen at the hprt-locus of V79 cells even at low doses which caused no cytotoxicity. In all the above properties anti-3MCDE closely resembled the anti-diol-epoxide of benzo[a]-pyrene. A similar study of DNA derived from mouse embryo cells which had been exposed to tritium labelled 3-methylcholanthrene (3MC) yielded a series of nucleoside adducts, only a minority of which were derived by reaction of anti-3MCDE with DNA. Two major in vivo products were shown to derive from 3MC alcohols, particularly 3-hydroxymethyl-cholanthrene, and probably involved both syn and anti-diol-epoxide metabolites.

The role of the Peyer's patch in carcinogenesis. I. The adsorption from the gut and retention of 3-methylcholanthrene by Peyer's patches

Radiotracer methods were used to determine the distribution of 3-methylcholanthrene (3-MC) within the lymphoid organs of rats following i.g. intubation, i.l. injection into the small intestine, i.v. injection or direct injection of the Peyer's patches with 3-[6-14C]methylcholanthrene (14C-MC). The data indicate that the gut-associated Peyer's patches and mesenteric lymph nodes were exposed to higher amounts of orally administered 14C-MC than any of the other lymphoid organs. Whereas the Peyer's patches exhibited the highest sp. act. for longer periods of time when low amounts of 14C-MC were administered, the sp. act. of the mesenteric lymph node were greater when rats were intubated with higher amounts of 14C-MC. Furthermore, the Peyer's patches were exposed to higher amounts of possible metabolites of 14C-MC. Injection of 14C-MC into the small intestinal lumen resulted in increased ratios of the Peyer's patch sp. act. to mesenteric lymph node sp. act., indicating that by-passing the stomach altered the distribution patterns. Data from rats injected i.v. with 14C-MC demonstrated that mesenteric lymph nodes but not Peyer's patches adsorbed and retained 14C-MC from the blood and indicated that the 14C-MC associated with Peyer's patches of i.g. treated rats was adsorbed from the gut rather than from the blood. Results obtained from rats which were exposed to 3-MC by directly injecting Peyer's patches with 14C-MC also indicated that the Peyer's patches were able to retain 3-MC once localized within this lymphoid organ, to metabolize the 3-MC and to possibly excrete the polycyclic aromatic hydrocarbon into the small intestine. Collectively the data indicate that Peyer's patches have an important role in the adsorption from the gut and subsequent retention of 3-MC and hence may be a likely target organ for lymphoid carcinogenesis following oral exposure to carcinogenic polycyclic aromatic hydrocarbons.

Electrofluorescence study of polycyclic hydrocarbon diol-epoxide binding to DNA

By the use of a novel electrofluorescence method, estimates have been made of the geometry of binding to DNA of racemic mixtures of the anti-diol-epoxide derivatives of three polycyclic hydrocarbon carcinogens. These anti-configurations bind in a manner consistent with the planar diol-epoxide ring's being inclined at approximately 50 degrees to the DNA axis. This is true for the derivatives of benzo(a)pyrene, benz(a)anthracene and 3-methylcholanthrene. This binding is thus different from the regular intercalative interaction associated with the native hydrocarbons. As the (+ anti)-diol-epoxides are thought to be the initiatory compounds for carcinogenesis, the common binding characteristics for the three hydrocarbons may be significant in understanding the molecular interactions precursive to cancer.

Carcinogen-binding proteins in the rat ventral prostate: specific and nonspecific high-affinity binding sites for benzo(a)pyrene, 3-methylcholanthrene, and 2,3,7,8-tetrachlorodibenzo-p-dioxin

The polychlorinated dibenzodioxin [3H]-2,3,7, 8-tetrachlorodibenzo-p-dioxin (TCDD) and the carcinogens [3H]benzo(a)pyrene and [3H]-3-methylcholanthrene bound to saturable binding sites in cytosol from the rat ventral prostate. Analysis of equilibrium binding parameters in diluted cytosol preparations indicated an apparent Kd of approximately 2 nM and a binding capacity of approximately 1 nmol/mg cytosolic protein, corresponding to approximately 5% of the total protein content. However, gel permeation chromatography analysis as well as velocity sedimentation analysis on sucrose gradients of [3H]TCDD-labeled rat prostatic cytosol indicated binding of [3H]TCDD to two discrete species. These analyses indicated a sedimentation coefficient of 3.6-3.8S, a Stokes radius of 25-28 A, and a calculated relative molecular weight of 42,000-45,000 for the most abundant binding species. The other binding species sedimented at 4-5S under high ionic strength conditions and at 8-10S under low ionic strength conditions and had a Stokes radius of approximately 60 A, a relative molecular weight of approximately 100,000 and an estimated concentration of 5-20 fmol/mg cytosolic protein. Binding of [3H]TCDD to this species was displaceable by a 200-fold M excess of 2,3,7,8-tetrachlorodibenzofuran. Therefore, this species was tentatively identified as the TCDD receptor. The properties of the high-capacity binder of [3H]TCDD were found to be similar to the characteristics of a protein previously purified from the rat ventral prostate, prostatic secretory protein, which binds androgens as well as estramustine, a nitrogen mustard derivative of estradiol. The binding of estramustine to diluted prostatic cytosol was shown to be competitively inhibited by 2,3,7,8-tetrachlorodibenzofuran. Moreover, purified prostatic secretory protein bound [3H]TCDD, [3H]benzo(a)pyrene, as well as [3H]-3-methylcholanthrene. It is suggested that binding to this protein is responsible for the high-binding capacity of carcinogens in cytosol from the rat ventral prostate.

Cytochrome P-450 induction by 3-methylcholanthrene and its antagonism by 2,2-dimethyl-5-t-butyl-1,3-benzodioxole

Previous studies in this laboratory have shown 2,2-dimethyl-5-t-butyl-1,3-benzodioxole (DBBD) to antagonize 3-methylcholanthrene induction of cytochrome P-450 in Dub:ICR mice yet have no effect on phenobarbital induction. In the present experiments, C57BL/6 mice, an Ah responsive strain, produced a similar response under the same experimental conditions. The hypothesis that DBBD, although not a cytochrome P-450 inducer, competes with 3-methylcholanthrene for binding to the Ah receptor was tested. Using sucrose density gradients, the Ah receptor was measured in hepatic cytosol from Dub:ICR and C57BL/6 male mice. DBBD was unable to displace either 2,3,7,8-tetra-chlorodibenzo-p-dioxin or 3-methylcholanthrene from the Ah receptor, in vitro. However, in in vivo experiments, DBBD treatment of Dub:ICR mice caused Ah receptor depression at 6 and 24 hr with complete recovery in between, while 3-methylcholanthrene treatment caused a 2-fold Ah receptor reduction at 2 hr followed by complete recovery after 12 hr. When 3-methylcholanthrene and DBBD were coadministered, the depression of the Ah receptor was additive. DBBD-pretreated mice had a 2.25-fold reduction in Ah receptor level, effectively blocking the ability of 3-methylcholanthrene to increase the cytochrome P-450 content and either benzo[a]pyrene hydroxylase or ethoxyresorufin O-deethylase activities. Sodium dodecyl sulfate-polyacrylamide gel electrophoresis confirmed that 3-methylcholanthrene induction of cytochrome P-450 was inhibited by DBBD pretreatment. Hence, although DBBD does not displace 3-methylcholanthrene from the Ah receptor in vitro, it does antagonize 3-methylcholanthrene induction of cytochrome P-450 and also reduces the amount of available receptor in vivo. This interaction may be due either to antagonism or to downregulation of the Ah receptor.

Protection against tumorigenesis by 3-methylcholanthrene in mice by beta-naphthoflavone as a function of inducibility of methylcholanthrene metabolism

The noncarcinogenic enzyme inducer beta-naphthoflavone (beta-NF) causes an increase in both rate of activation and of detoxification of polycyclic aromatic hydrocarbon carcinogens in tissues of mice of induction-responsive strains. An experiment was carried out to test whether pretreatment with beta-NF would potentiate, protect against, or have no effect on the tumorigenicity of methylcholanthrene (MC) administered intragastrically to mice of varying responsiveness to induction of MC metabolism. The mouse strains used were C57BL/6, BALB/c, and C3H (inbred, highly responsive to induction), Swiss (random-bred, moderately responsive), and DBA/2 and AKR (inbred, nonresponsive). Twelve weekly treatments with 20 mg MC/kg intragastrically were preceded 24 h earlier each week by 150 mg beta-NF/kg i.p. or oil. Mice were killed when moribund or 1 year after start of treatment. During this period the beta-NF-pretreatment greatly reduced mortality due to cancer among the responsive inbred mice, by 100% for the C57BL/6, 89% for the BALB/c, and 65% for the C3H, compared with 50% for the Swiss, 23% for the DBA/2 and 0% for the AKR. There were significant reductions in MC-caused tumor incidences as a result of beta-NF pretreatment for: sarcomas, lymphomas, and forestomach and skin tumors for the C57BL/6 mice; sarcomas, mesotheliomas, and mammary carcinomas for the C3H mice; mesotheliomas for the BALB/c mice; sarcomas and tumors of the skin, forestomach, and lung for the Swiss mice; and lymphomas for the DBA/2 mice. beta-NF pretreatment did not cause an increase in the incidence of any type of tumor. These results are consistent with the conclusion that inducers of mixed function oxygenase activity generally provide protection against tumorigenesis by systemically administered polycyclic aromatic hydrocarbon carcinogens, probably by increasing rate of detoxification.

Distribution and reproducibility of aryl hydrocarbon hydroxylase inducibility in a prospective population study of middle-aged male smokers and nonsmokers

Aryl hydrocarbon hydroxylase (AHH) inducibility was determined in a lymphoblast test system in 2,000 consecutive middle-aged male smokers, 304 ex-smokers, and 218 never-smokers in the same birth-year cohorts. Intraindividual, intraobserver, and interobserver, as well as temporal, reproducibility was checked in a special double-blind quadruplet sample series from 20 other consecutive middle-aged men. The results showed a three-modal phenotype distribution of AHH inducibility with high (fold induction greater than or equal to 3.6), intermediate (2.6-3.6) and low (less than or equal to 2.5) levels ranging between 7.6% to 10.5%, 38.5% to 43.0%, and 46.5% to 53.9%, respectively, in all the smoking categories. The reproducibility of the measurements was excellent, with one-way variance in the order of 0.007 to 0.033, and the applied assay method can therefore be used in large-scale prospective population investigations. Such are required in order to establish a cause-effect association between high AHH inducibility and smoking-related malignancies of the respiratory tract and oral cavity, as has been suggested from earlier retrospective studies in more limited clinical materials of cancers and precanceroses of these varieties.

Polycyclic Aromatic Hydrocarbon Binding Macromolecules. Identification, Characterization and Temperature Activation of a 4.5 S Binding Nucleoprotein

A macromolecule binding3H-methyIcholanthrene (3H-MCA) and3H-benzo(a)pyrene (3H-BaP) and sedimenting in the 4-5 S region of sucrose gradient (4.5 S) was identified in rat liver cytosol. The binding was displaced by 100-fold molar excess unlabeled ligands whereas 2,3,7,8-tetrachloro-dibenzo-p-dioxin (TCDD) was ineffective. The dissociation constant for both polycyclic aromatic hydrocarbons (PAHs) was of the order of 10−3M or lower. Both3H-MCA and3H-BaP bound to 4.5 S in a non covalent manner, since 92 % of the bound radioactivity was extractable with ethyl ether. Furthermore the binding was stronghly reduced by urea 8 M and by guanidine. HCl 4 M (99 and 70 % respectively). Thin layer chromatography of the ehtyl ether-solubilized radioactivity showed a peak comigrating with PAHs used as standards. When chromatographed on Sephadex G-200, 4.5 S was eluted as a sharp peak with an apparent molecular weight of 50-60,000 daltons. Enzyme treatment of liver cytosol showed that the 4.5 S binding sites were destroyed by micrococcal nuclease (92 % of inhibition). Papain and phosphodiesterase I and II reduced the binding to 50 %, whereas DNase I, DNase II, RNase, phospholipase A2andC and trypsin were ineffective. These data suggest that the PAHs binding macromolecule of rat liver cytosol is a protein associated with a polynucleotide. The binding of both PAHs was enhanced by increasing the incubation temperature, the maximum being reached after 20-30 min at 37 °C. After 2.5 min at 65 °C, binding sites were completely destroyed. The same temperature-induced « activation » was obtained also by prewarming the cytosol at 37 °C in the absence of ligands.

Tumor-initiating activity of the 9,10-dihydrodiol- and 9,10-dihydrodiol-7,8-epoxide of 3-methylcholanthrene in SENCAR mice

The skin tumor-initiating activities of several bay-region metabolites of 3-methylcholanthrene (3-MCA) were determined in SENCAR mice. 3-MCA-anti-9,10-diol-7,8-epoxide possessed weak tumor-initiating activity when tested at 100 and 200 nmol/mouse doses (0.27 and 0.67 papillomas per mouse after 18 weeks of promotion with 12-O-tetradecanoylphorbol-13-acetate (TPA)). 3-MCA-trans-9,10-diol at initiating doses of 50 and 100 nmol/mouse was as active as 3-MCA. 3-MCA-trans-9,10-diol was also tested for mutagenic activity toward V79 cells in cell-mediated assays and found to be approximately 2-times more potent than 3-MCA. The data suggest that 3-MCA-trans-9,10-diol is a proximate carcinogen for mouse skin.

Fetal mouse susceptibility to transplacental lung and liver carcinogenesis by 3-methylcholanthrene: positive correlation with responsiveness to inducers of aromatic hydrocarbon metabolism

The role of metabolic activation of carcinogens in fetal tissue as a determinant of sensitivity in transplacental carcinogenesis was investigated in a pharmacogenetic experiment utilizing backcrosses of C57BL/6 (AhbAhb, responsive to induction of aromatic hydrocarbon metabolism) and DBA/2 (AhdAhd, non-responsive) mice. Responsive (C57BL/6 X DBA/2)F1 and non-responsive DBA mothers, all carrying both responsive (AhbAhd) and non-responsive (AhdAhd) fetuses, were given i.p. doses of the carcinogen 3-methylcholanthrene (MC) ranging from 5 to 175 mg/kg on gestation day 17. At 10 months of age the metabolic phenotype of each offspring was determined, and correlated with number of lung and liver tumors. Both male and female AhbAhd (responsive) offspring in most dose groups presented a consistent two- to three-fold higher incidence of lung tumors than did non-responsive AhdAhd littermates. The difference held for offspring of both (C57BL/6 X DBA)F1 and DBA mothers and it was of statistical significance for one or both sexes at most dosage levels. Hepatocellular tumors were also significantly more frequent in responsive male AhbAhd progeny of (C57BL/6 X DBA/2)F1 mothers than in non-responsive AhdAhd littermates. Progeny of the DBA mothers exhibited significantly more liver and lung tumors than did those of the (C57BL/6 X DBA/2)F1 mothers receiving the same dose. These results suggest that in this model system both maternal and fetal genotype for responsiveness to induction of aromatic hydrocarbon metabolism are important factors modulating fetal carcinogenic risk.

The induction of cytochrome P-450 by isosafrole and related methylenedioxyphenyl compounds

Using sucrose gradients, the Ah receptor and a 3-4S binding peak were measured in hepatic cytosol from Dub: ICR, C57BL/6, and DBA/2 male mice. Isosafrole, piperonyl butoxide, and 5-t-butyl-1,3-benzodioxole were unable to displace 2,3,7,8-tetrachlorodibenzo-p-dioxin or 3-methylcholanthrene from either the Ah receptor or the 3-4S binding peak, in vitro. In in vivo experiments, treatment of C57BL/6 mice with 3-methylcholanthrene caused a 4-fold reduction in Ah receptor binding 2 h after i.p. injection; whereas, isosafrole caused a 2-fold enhancement of the Ah receptor after 24 h. This increase in the Ah receptor binding following isosafrole treatment may be due to induction. 3-Methylcholanthrene treatment of C57BL/6 mice also caused a 3-fold reduction in the 3-4S binding peak 2 h after i.p. injection; isosafrole treatment had little or no effect on the 3-4S peak in C57BL/6 or DBA/2 mice. Both in vivo and in vitro data appear to demonstrate that there is no direct role for the Ah receptor or the 3-4S protein in the regulation of cytochrome P-450 by methylenedioxyphenyl compounds. Using Sephadex G-100 chromatography, a cytosolic protein fraction was obtained from C57BL/6 and Dub:ICR mice which was previously implicated by others as a carrier in the metabolism of benzo[a]pyrene (B[a]P). This fraction was applied to sucrose gradients and sedimented in the 3-4S region. Hence it appears that the 3-4S binding peak may be the carrier described by these workers.

Chemoprotective effect of progesterone on carcinoma formation in mice and rats

The protective effect of progesterone on the development of chemically induced carcinomas (squamous cell carcinomas in mice and basal cell carcinomas in rats) by 3-methylcholanthrene [(MCA) CAS: 56-49-5] was studied. Progesterone administration decreased the average number, size, and weight of carcinomas by 45-50% as compared to those of tumors treated with MCA alone at any time interval. DNA radioactivity and autoradiographic studies with the use of [3H]thymidine showed an inhibition of DNA synthesis in the neoplastic cell nuclei following a concomitant administration of progesterone and MCA (18.4%) as compared to the DNA synthesis following administration of MCA alone (35.0%). Electron microscopic and cytologic observations revealed salient ultrastructural findings following progesterone administration, with advanced cytolysis, tumefied mitochondria, large populations of secondary lysosomes, and autophagic formations; also, cell differentiation tended to be of a glandular-adenomatoid type following progesterone and MCA administration as compared to the characteristic squamous cell and basal cell carcinomas after treatment with MCA alone. In addition, scanning electron microscopic observations revealed advanced cytolytic areas with several disintegrated neoplastic cells and cell debris intermingled with red blood cells, following progesterone and MCA administration. The present findings demonstrate that progesterone in pharmacologic doses exerts important chemoprotective effects on carcinoma formation, possibly by interfering with MCA metabolism and inhibiting DNA synthesis in the epidermal neoplastic cells, and thus plays an important role in tumorigenesis.

Relationships between carcinogen metabolism, adduct binding and DNA damage in 3-methylcholanthrene-exposed lung

The extent to which structural damage in DNA, isolated from rats receiving an intratracheal dose of 3-methylcholanthrene (3-MC), was affected by change in microsomal mixed-function oxidase activity, has been examined. Instillation of 3-MC causes a characteristic pattern of structural change in lung DNA as determined by stepwise elution from benzoylated DEAE-cellulose (BD-cellulose). The proportion of lung DNA containing single stranded regions was increased biphasically, relative maxima occurring 14 and 72 h after treatment, the first increase being proportional to the dose of 3-MC. Binding of 3-MC to lung DNA increased progressively for 24 h after treatment and decreased rapidly from 48 h onward. Cytochrome P-450 content of pulmonary, and also of hepatic microsomes from treated animals, was measured. On this basis, 3-MC metabolism was modified, carbon tetrachloride being an effective inhibitor when administered 4 h in advance of treatment whilst maximum self-induction of 3-MC metabolism required 24 h. BD-cellulose analysis of lung DNA of 3-MC-treated rats subjected to inhibiting or inducing treatment suggested that the extent of structural damage was primarily determined by the capacity of lung tissue to metabolise the carcinogen. In particular, inhibition of 3-MC metabolism by prior treatment with carbon tetrachloride prevented production of single stranded regions, whilst modifying 3-MC binding to DNA. The data indicate that structural analysis of DNA is a sensitive means of assessing levels of genomic injury by carcinogens. This procedure may be used to study the effects of complicated treatments, and specifically agents which modify carcinogen metabolism.

Comparison of primary hepatocytes and S9 metabolic activation systems for the C3H-10T 1/2 cell transformation assay

Three metabolic activation systems, primary rat hepatocytes, primary mouse hepatocytes and Aroclor 1254-induced rat liver S9 fraction were examined as exogenous activation systems for the C3H-10T 1/2 cell transformation assay. Under the conditions of the assay the primary mouse hepatocytes were more effective than the rat S9 fraction in mediating the transformation of C3H-10T 1/2 cells by the antineoplastic drug cyclophosphamide. However, the S9 fraction was more consistent than the mouse hepatocytes in the activation of dimethylnitrosamine. The primary rat hepatocytes were ineffective for activating either cyclophosphamide or dimethylnitrosamine in the transformation of C3H-10T 1/2 cells. The presence of mouse hepatocytes, but not the S9 fraction, inhibited transformation of C3H-10T 1/2 cells by 3-methylcholanthrene. These results demonstrate that the three systems were differentially effective in the activation of procarcinogens.

The metabolism of 1-hydroxy- and 2-hydroxy-3-methylcholanthrene by liver microsomes: effect of enzyme inducing agents

The metabolism of both 1-hydroxy-3-methylcholanthrene (1-OH-3-MC) and 2-hydroxy-3-methylcholanthrene (2-OH-3-MC) by rat liver microsomes was investigated. Metabolites were separated by high pressure liquid chromatography (HPLC). Both compounds were shown to be substrates for further metabolism. Metabolism of 1-OH-3-MC gave rise to at least 13 products while 2-OH-3-MC showed the formation of at least 10 metabolites. At least 3 products of the 1-OH-3-MC metabolism are diol derivatives of the substrate. Using 2-OH-3-MC as substrate generated one major diol derivative that represented between 20% and 50% of total metabolite formation. Pretreatment of animals with known microsomal enzyme inducing agents did not result in the expected induction patterns. In some instances, the microsomes from induced animals were less efficient at metabolizing substrate than those from control. The discovery of a major peak from 2-OH-3-MC metabolism is of extreme importance considering the potency of the parent hydroxy compound in tumor initiation studies.

Direct enantiomeric resolution of cyclic alcohol derivatives of polycyclic aromatic hydrocarbons by chiral stationary phase high-performance liquid chromatography

The enantiomers of some cyclic alcohol derivatives of phenanthrene, benz[a]anthracene, benzo[a]pyrene, cholanthrene, and 3-methylcholanthrene were resolved by high-performance liquid chromatography using a commercially available preparative column packed with an (R)-N-(3,5-dinitrobenzoyl)phenylglycine ionically bonded to gamma-aminopropylsilanized silica. Resolution of enantiomers was confirmed by ultraviolet-visible absorption, mass and circular dichroism spectral analyses. This method has been applied to the determination of optical purity of 1-hydroxycholanthrene and 1-hydroxy-3-methylcholanthrene formed in the metabolism of cholanthrene and 3-methylcholanthrene, respectively, by rat liver microsomes.

Effects of hypophysectomy on sex differences in the induction and depression of hepatic drug-metabolizing enzymes in the rat

The role of the pituitary gland in the effects of treatment with phenobarbital, methylcholanthrene and morphine on hepatic drug metabolism in adult male and adult female rats has been investigated. A marked sex difference in the effects of treatment with these three compounds on hepatic drug metabolizing enzymes in intact adult rats was observed. No sex differences in the effects of phenobarbital methylcholanthrene or morphine on hepatic drug metabolizing enzymes were observed after treatment of hypophysectomized adult male and hypophysectomized adult female rats. The results indicate that the pituitary gland plays an important role in the determination of sex differences in the response of hepatic drug metabolizing enzymes to inducing agents.

Elevated binding of 2,3,7,8-tetrachlorodibenzo-p-dioxin and 3-methylcholanthrene to the Ah receptor in hepatic cytosols from phenobarbital-treated rats and mice

Binding of 3-methylcholanthrene (MC), 2,3,7,8-tetrachlorodibenzo-p-dioxin (TCDD), and other "MC-type" inducers to cytosolic Ah receptor sites is the first specific step in induction of aryl hydrocarbon hydroxylase (AHH; cytochrome P1-450) by these compounds. [3H]TCDD and [3H]MC were used as radioligands to quantitate and characterize Ah receptor in hepatic cytosols from genetically "responsive" C57BL/6J mice, genetically "nonresponsive" DBA/2J mice, and AHH-inducible Sprague-Dawley rats. Injection of 50-100 mg/kg of phenobarbital (PB) for 3 days more than doubled the concentration of Ah receptor in hepatic cytosol from Sprague-Dawley rats. In C57BL/6J mice, PB injection at 25 mg/kg X 3 days significantly increased (P less than 0.01) the Ah receptor concentration in hepatic cytosol. No cytosolic Ah receptor was detectable in hepatic cytosol from untreated DBA/2J mice, nor did any Ah receptor appear after PB treatment in this "nonresponsive" strain. Although PB significantly elevated Ah receptor in hepatic cytosols of responsive rodents, many previous studies have shown that the maximal level of AHH activity in animals given PB and an "MC-type" inducer simultaneously is additive rather than synergistic. Ah receptor concentrations can be doubled by PB treatment without doubling the subsequent AHH-induction response to "MC-type" compounds. Thus, the cytosolic Ah receptor concentration per se may not be the primary determinant of a given tissue's maximal capacity for AHH induction by "MC-type" compounds.

The binding of polycyclic aromatic hydrocarbon diol-epoxides to DNA

Diol-epoxide derivatives of polycyclic aromatic hydrocarbons are the ultimate carcinogenic forms of these compounds encountered in vivo. Using a novel electro-fluorescence apparatus, we report that, like the (+/-)-anti-diol-epoxide of benzo[a]pyrene (BP), the similar diol-epoxides of benzo[a]anthracene (BA) and 3-methylcholanthrene (3MC) also bind to the DNA helix at an inclination of approximately 50 degrees. This compares with the essentially perpendicular, intercalative-type binding generally found with saturated aromatic compounds, such as the native hydrocarbons, and may indicate a systematic behavior in the molecular associations precursive to carcinogenesis.

Physicochemical characterization of specific and nonspecific polyaromatic hydrocarbon binders in rat and mouse liver cytosol

The aryl hydrocarbon hydroxylase inducers 2,3,7,8-tetrachlorodibenzo-p-dioxin (TCDD), 3-methylcholanthrene, and benzo(a)pyrene were all shown to bind in a saturable manner to a distinct component in cytosol from both rat and C57BL/6J mouse liver. This component was analyzed by gel permeation chromatography on Sephacryl S-300 and by sucrose density gradient centrifugation and was found to have a Stokes radius of 61 +/- 1.5 A and a sedimentation coefficient of 4.4 S under high salt conditions. Based on these parameters, which were identical for the rat and mouse receptor, a molecular weight of 111,000 was calculated. The same Stokes radius and sedimentation coefficient were observed regardless of the ligand used for labeling of the receptor protein [(3H]TCDD, 3-[3H]methylcholanthrene or [3H]benzo(a)pyrene). On the other hand, 3-[3H]methylcholanthrene and [3H]benzo(a)-pyrene exhibited much more nonspecific binding than [3H]TCDD, at least partially due to contaminating serum components, and it cannot be excluded that some previous findings on low molecular weight hepatic "receptors" for these polyaromatic hydrocarbons may actually be explained in this way. Clearly, use of thoroughly perfused livers would seem to be a prerequisite for investigations on specific binding of aryl hydrocarbon hydroxylase inducers to liver cytosol. The rat hepatic TCDD receptor was also shown to be retained on DEAE-Sepharose (eluted at 0.2-0.3 M NaCl), hydroxylapatite (eluted at 0.15-0.17 M phosphate), and heparin-Sepharose (eluted at 0.3-0.4 M NaCl). In conclusion, the TCDD receptor showed similar physicochemical and chromatographic characteristics to those previously reported for the androgen and glucocorticoid receptors. However, ligand competition experiments indicated that the TCDD receptor is not identical to any steroid receptor. In line with this, monoclonal anti-glucocorticoid receptor-IgG antibodies did not react with the TCDD receptor.

Polycyclic aromatic hydrocarbon toxicity and induction of metabolism in cultivated esophageal and epidermal keratinocytes

Serially cultivated keratinocytes of human and rat epidermis and esophagus were compared with respect to their sensitivity to toxic effects of 3-methylcholanthrene and ability to metabolize benzo(a)pyrene. 3-Methylcholanthrene was highly toxic to the human keratinocytes and to early-passage rat epidermal keratinocytes, as evidenced by markedly reduced growth upon continuous exposure or reduced colony-forming ability after 1-day exposure to concentrations of 0.4 to 40 microM in the culture medium. Rat esophageal and late-passage rat epidermal cells appeared insensitive to 3-methylcholanthrene by these criteria. All the cell types except late-passage rat epidermal cells metabolized benzo(a)pyrene at comparable rates, and expressed aryl hydrocarbon hydroxylase maximally inducible by similar concentrations of 3-methylcholanthrene. Biotransformation in the human cells was greatly inhibited by alpha-naphthoflavone, a specific inhibitor of aryl hydrocarbon hydroxylase. The lack of toxicity of 3-methylcholanthrene toward late-passage rat epidermal cells can be attributed to the low constitutive rate of biotransformation these cells exhibit. The insensitivity of rat esophageal cells despite substantial metabolic activity reflects the importance of intrinsic differences among keratinocytes derived from different epithelia and species in determining toxic response. Human cervical and monkey esophageal keratinocyte cultures also actively metabolized benzo(a)pyrene, illustrating further the utility of the culture system for exploring differences among species and epithelial cell types.