Liver Aryl Hydrocarbon Hydroxylase Research Articles

Purification and biochemical characterization of two major cytochrome P-450 isoforms induced by 2,3,7,8-tetrachlorodibenzo-p-dioxin in chick embryo liver.

Two cytochrome P-450 isoforms induced by 2,3,7,8-tetrachlorodibenzo-p-dioxin (TCDD) in chick embryo liver microsomes were purified. The P-450s exhibit catalytic selectivity either for arachidonic acid metabolism, particularly epoxygenation (P-450 TCDDAA, 55 kDa), or for aryl hydrocarbon hydroxylase (AHH) and 7-ethoxyresorufin deethylase (7-EROD) (P-450 TCDDAHH, 54.5 kDa). Turnover numbers for arachidonic acid epoxygenation, AHH, and 7-EROD, respectively, were 24.2, 0.23, and 0.45 for TCDDAA and 0.57, 9.7, and 35.5 for TCDDAHH. Both P-450s were low spin, with carbon monoxide-binding peaks at 448 nm. Their N-terminal amino acid sequences showed 80% homology and contained the sequence: PXXXSATEXL, common to CYP1A P-450s but not others. Polyclonal antibodies to TCDDAA and TCDDAHH cross-reacted with both P-450s on Western blots and immunoinhibited all TCDD-induced liver microsomal arachidonic acid metabolism, AHH, and 7-EROD. Immunoquantitation using antibodies made monospecific by immunoadsorption against the heterologous P-450 showed that TCDDAA and TCDDAHH were coinduced in liver in equal amounts and accounted for all of the TCDD-induced P-450. Enzyme assays and Western blots also showed expression of both TCDDAA and TCDDAHH in kidney but only of TCDDAHH in heart, indicating that these P-450s can be independently regulated and selectively induced. On Western blots non-immunopurified anti-TCDDAA and anti-TCDDAHH antisera recognized rat and guinea pig CYP1A1 and CYP1A2. Immunopurified TCDDAA antiserum only recognized rat CYP1A2, indicating that TCDDAA is more closely related immunochemically to CYP1A2 than to CYP1A1. The evidence that pleotropic responses to Ah receptor ligands can include induction of a P-450 that can form biologically active products from the endogenous membrane lipid, arachidonic acid, suggests that organ- and cell-specific expression of TCDD-induced P-450s could affect responses to TCDD.

Aryl hydrocarbon hydroxylase activity in chemically induced and toremifene‐treated mammary tumors in rats

Aryl hydrocarbon hydroxylase (AHH) and NADPH-cytochrome P450 reductase (NCR) activity of microsomes from liver, lungs, uterus and mammary tumors in dimethylbenzanthracene-induced and toremifene-treated female Sprague-Dawley rats were studied. AHH and NCR activity in tumors and uteri was low compared with that in livers and lungs. The distribution of AHH in tumors was wide and skewed. It varied in different tumors of the same animal as widely as between different animals. The enzyme activity in tumors did not correlate with that in the liver, lungs or uterus of the same animal. Toremifene had no effect on AHH or NCR in tumor or liver, but it decreased them in lungs. Tumor AHH activity correlated with its overall growth rate and development stage. The results suggest that malignant transformation leading to the defect in growth regulation also confuses the complex regulatory system of AHH activity.

Retinoids: From metabolism to environmental monitoring

Adult herring gulls, Larus argentatus, were captured on their nests at various colonies on the Great Lakes and retinoids (vitamin A) analyzed in the liver by reverse-phase HPLC. All- trans-retinol and all- trans-retinyl palmitate concentrations showed significant differences between colonies. Colonies having the highest concentrations of 2,3,7,8-tetrachlorodibenzo- p-dioxin had the lowest retinoid concentrations. Particularly low levels of hepatic retinoids occurred in Lake Ontario gulls in 1987; and all- trans-retinol was negatively correlated with liver aryl hydrocarbon hydroxylase activity. Liver retinoids were identified in the white sucker, Catostomus commersoni, using reverse-phase HPLC with diode array detection. All- trans-retinol, all- trans-retinyl palmitate, and 3,4-didehydroretinyl esters were detected. In the case of adult white suckers sampled from a contaminated river near Montreal and a control site, significantly lower levels of all- trans-retinol and all- trans-retinyl palmitate were found in the contaminated population.

Xenobiotic metabolizing enzyme activity in the liver and kidney of the brown bullhead ( Ictalurus nebulosus)

Activities of aryl hydrocarbon hydroxylase (AHH), epoxide hydrase (EH), glutathione-S-transferase (GST) and UDP-glucuronyl transferase (UDPGT) were easily detected in brown bullhead ( Ictalurus nebulosus) liver. AHH (substrate— 3H-benzo(a)pyrene). GST (substrate—l-chloro-2,4-dinitrobenzene) and EH (substrate— 3H-benzo(a)pyrene-4,5-oxide) activities in kidney were 4, 60 and 183%, respectively, of the corresponding values in liver. UDPGT (substrate —p-nitrophenol) was not detected in the kidney of control or 3-methylcholanthrene (3-MC)-treated fish. Treatment of bullhead with 3-MC enhanced the activity of AHH in liver and kidney nearly 14- and 33-fold, respectively, with little or no effect on EH or GST activity at the time point tested. The types of benzo(a)pyrene (BP) metabolites formed by liver and kidney microsomes were qualitatively similar, but there were considerable differences in the patterns of the metabolites produced by the microsomes from the two tissues. The liver microsomes from control fish converted a substantially greater proportion of BP to quinones than did the kidney microsomes.

Monocyte aryl hydrocarbon hydroxylase (AHH) activity mimics Kupffer cell and hepatocyte AHH activity in an animal model of liver disease

We have previously reported that monocyte aryl hydrocarbon hydroxylase (AHH) activity is depressed in patients with liver disease and is decreased more in cirrhosis than in early stage liver disease. To determine if monocyte AHH activity reflects liver AHH activity, we studied an animal model of cirrhosis, i.e., yellow phosphorus induced cirrhosis in the pig. AHH activity was detectable in monocytes isolated from peripheral blood of normal pigs (0.32 +/- 0.13 nmol.mg-1 P.h-1, n = 11) and was comparable to the level of AHH activity in hepatic Kupffer cells isolated from wedge or needle biopsies of livers of normal pigs (0.38 +/- 0.21, n = 7). The AHH level in pig Kupffer cells was approximately 10% of the AHH level in hepatocytes and microsomes. To induce liver disease, pigs were administered yellow phosphorus (0.6 mg/kg) 5 days per week for 16 weeks. At 4 weeks of treatment, monocyte AHH activity was not different from control and liver histology was normal. Depression of monocyte AHH activity was evident at 8 weeks of treatment when liver fibrosis was seen histologically. At 12 weeks of treatment when histology revealed extensive liver fibrosis and collagen levels were elevated, the level of monocyte AHH activity was decreased 67% compared with controls. Similar changes were observed at 12 weeks in Kupffer cell AHH activity (86% decrease) and hepatocyte AHH activity (70% decrease) compared with controls. These results suggest that monocyte AHH activity reflects liver AHH activity and may be a good indicator of change in liver enzyme function in liver disease in the pig model of cirrhosis.

Effects of 3-methylsulphonyl-4,5,3′,4′-tetrachlorobiphenyl and 7,8-benzoflavone on mouse liver aryl hydrocarbon hydroxylase activity in vitro

The activity of aryl hydrocarbon hydroxylase (AHH) in mouse liver microsomes was assayed in the presence of 3-methylsulphonyl-4,5,3′,4′-tetrachlorobiphenyl (3-MSF-TCB). The mice had been previously injected with a fixed amount of the AHH inducer 3-methylcholanthrene (MC) or 2,3,7,8-tetrachlorodibenzo- p-dioxin (TCDD) or with the vehicle (olive oil) alone. The dose-effect patterns for 3-MSF-TCB were markedly different according to the genetic responsiveness of the mice towards aromatic hydrocarbons ( Ah responsiveness); in Ah responsive strains 3-MSF-TCB inhibited the MC-induced AHH activity as did 7,8-benzoflavone (ANF), which is known to be a potent inhibitor of AHH, whereas in Ah non-responsive strains 3-MSF-TCB (and ANF) greatly enhanced the same activity. On the other hand, the dose-response patterns were similar for both types of mice for TCDD-induced activity or basal activity (mice injected with the vehicle alone). The dose-effect curves for 3-MSF-TCB were quite distinct from those for ANF, particularly with respect to the basal AHH activity, for both Ah responsive and non-responsive strains. These results indicate that both ANF and 3-MSF-TCB can have either an inhibitory or an activating effect on AHH, depending on the dose, the Ah phenotype and previous induction with MC or TCDD.

Pharmacological and toxicological properties of arotinoids SMR-2 and SMR-6 in mice

Studies were conducted to define primary pharmacological and toxicological properties of two arotinoids, SMR-2 and SMR-6, in male B6D2F1 mice. Mice were gavaged daily for up to 22 days with retinoids in corn oil (0.1, 0.2, or 0.4 mg/kg day SMR-2 or SMR-6 or 2.5, 10, or 30 mg/kg all- trans-retinoic acid as a reference control). Toxicological and biochemical endpoints were assayed after 8, 15, and 22 days. At toxic doses, i.e., those inducing weight loss, morphological changes were observed in skin, lymph nodes, spleen, bone marrow, liver, thymus, forestomach, adrenal, bone, and testes. Biochemical alterations included elevated serum alkaline phosphatase, corticosterone, and interleukins-1, -2, and -3. Additional immune alterations included increased responsiveness of spleen cells to both thymus-dependent and thymus-independent mitogens and increases in the total number of B cells in the spleen. At doses not inducting weight loss, target organ effects included the appearance of plasma cells and infiltration of polymorphonuclear cells in lymph nodes; myeloid cell hypercellularity in bone marrow; hematopoiesis in spleen; subacute inflammation in forestomach; and periportal cytoplasmic vacuolization in liver. At the low doses, SMR-2 resulted in decreased responsiveness of spleen cells to mitogens and SMR-6 caused increased responsiveness. SMR-6 also increased interleukin-1 and -2 production at low doses. Biochemical effects included reduced activities of liver aryl hydrocarbon hydroxylase (AHH) and soluble brain protein kinase C. Overall, the results suggest that leukcopoiesis and reduced liver AHH and reduced soluble protein kinase C activities are the primary and initial pharmacological and toxicological effects of retinoids.

Differential induction of fetal mouse liver and lung cytochromes P-450 by -naphthoflavone and 3-methylcholanthrene

Previous studies have shown that the incidences of liver and lung tumors in mice exposed transplacentally to 3-methyl-cholanthrene (MC) were significantly influenced by the sensitivity of both mothers and fetuses to induction of cytochrome(s) P-450 by polycyclic aromatic hydrocarbons. In order to delineate further the biochemical and molecular processes underlying the observed biological effects, the inductive effect of MC and beta-naphthoflavone (beta NF) on cytochrome P-450 was determined at the biochemical and molecular levels. C57BL/6 females were mated with DBA/2 males and treated i.p. on day 17 of gestation with olive oil alone, 150 mg/kg of beta NF or different doses of MC. At various times after injection the mothers were sacrificed and the fetuses removed for biochemical and molecular studies. MC caused maximal induction of aryl hydrocarbon hydroxylase (AHH) activity by 8 h in both the liver and lung. beta NF caused nearly maximal induction of AHH activity by 8 h in the lung but had little effect on liver AHH activity at this time. Maximal induction with beta NF occurred by 24 h in both organs. Addition of monoclonal antibody 1-7-1, specific for the MC-inducible forms of cytochrome P-450 (P-450IA1 and A2), to the incubation mixtures resulted in a 55-70% inhibition of AHH activity in both lung and liver assays, regardless of the inducing agent used, while having no effect on AHH activity from oil-treated mice. RNA blot analysis carried out in parallel with enzyme assays demonstrated that the levels of enzyme activity correlated very well with the levels of steady-state RNAs. MC caused maximal induction of P-450IA1 RNA levels 4 h after injection in both organs and a biphasic secondary increase was observed in the lung. Maximal levels of P-450IA1 RNA were seen at 12-16 h following injection of beta NF. However, the ratio of P-450IA1 RNAs present at 16 versus 2 h in the beta NF-treated liver appeared greater than that in the lung. P-450IA2 was also induced in fetal liver and lung, but at low levels relative to P-450IA1. The results indicate that the increase in functional AHH activity was primarily due to induction of cytochrome P-450IA1. The differences in induction kinetics observed for cytochromes P-450IA1 and A2 suggest that these enzymes exhibit both tissue- and inducer-dependent specificity.

Effect of chronic cysteamine treatment on mouse liver aryl hydrocarbon hydroxylase activity.

Patients receive chronic cysteamine in the management of nephropathic cystinosis. In a previous report our results indicated that acute cysteamine treatment inhibited cytochrome P-450. Cysteamine (85 mg/kg i.p.) was administered daily to female Swiss mice for 1.5 and 8.5 months. Cysteamine treatment (8.5 months) did not affect hepatic microsomal aryl hydrocarbon hydroxylase (AHH) activity compared with controls. A small decrease in liver AHH activity was seen after 1.5 months of treatment with cysteamine. Liver histology, body weight, liver and spleen weights, and serum aminotransferase activity after chronic and subchronic treatment did not differ from controls. Chronic in vivo cysteamine treatment, unlike acute in vitro treatment did not decrease AHH activity. Incubation of isolated murine hepatocytes with cysteamine significantly inhibited AHH activity compared with controls. The inhibition occurred in a concentration-related manner, with 65% inhibition at 8.8 mM (1 mg/mL) (equivalent to the predicted plasma concentration using the maximally tolerable human dose), and 100% inhibition at 44 mM (5 mg/mL). The concentrations used in vitro were not cytotoxic. This suggests that chronic cysteamine treatment may not result in drug interactions and that in vitro results are not always good indicators of in vivo effects.

Effects of SO2 or NOx on toxic and genotoxic properties of chemical carcinogens. II. Short term in vivo studies.

Short term in vivo studies were performed to study biological effects of the common air pollutants SO2 or NOx and their influence on the genotoxic activities of nitrosamines. Hepatocytes and lung cells were isolated from Sprague-Dawley rats which had inhaled 50 p.p.m. of SO2 or NOx for 2 weeks. After incubating the cells for 1 h, genotoxicity was determined in hepatocytes by measuring DNA single-strand breaks induced by N-nitroso-acetoxymethylmethylamine, N-nitrosodimethylamine and N-nitrosomethylbenzylamine. Parameters of toxicity (trypan blue exclusion and leakage of serum enzymes) were determined in both liver and lung cells also following 1 h incubation. The activities of aryl hydrocarbon hydroxylase (AHH), nitrosodimethylamine demethylase (NDMA-D) and glutathione-S-transferase (GST) were determined in subcellular microsomal fractions isolated from lung and liver tissues. Finally, as a measure of overall toxicity, the activities of various serum enzymes were determined in the blood serum of the rats. It was found that the induction of DNA single-strand breaks by three nitrosamines was decreased in hepatocytes from SO2-treated animals. The viability of rat hepatocytes and of rat lung cells, as determined by trypan blue exclusion, was similar in all three treatment groups immediately after isolation, as well as after 1 h incubation with DMSO or with the nitrosamines. In contrast, the leakage of enzymes was different in hepatocytes of SO2-treated rats, since lactate dehydrogenase activity was decreased. Leakage of enzymes from the lung cells did not differ from group to group, but was lower than from hepatocytes. Foreign compound metabolizing enzymes were mainly decreased in NOx-treated animals, namely AHH, NDMA-D and GST in liver and GST in the lung. For SO2-treated animals NDMA-D was increased in liver and GST was decreased in lung. Blood serum enzyme levels were not greatly different from each other, except for lactate dehydrogenase which was elevated in SO2-exposed animals.

The effect of cigarette smoking on 7-ethoxyresorufin O-deethylase and other monooxygenase activities in human liver: analyses with monoclonal antibodies.

Four cytochrome P-450 enzyme activities, 7-ethoxyresorufin O-deethylase (ERDE), coumarin 7-hydroxylase (CH), 7-ethoxycoumarin O-deethylase (ECDE) and aryl hydrocarbon hydroxylase (AHH) were measured in human liver needle biopsy samples from smokers and non-smokers. Cigarette smoking was verified and quantitated by measuring plasma cotinine levels. Enzyme inhibitory monoclonal antibodies (MAb) to a 3-methylcholanthrene-induced (MAb 1-7-1) and phenobarbitone-induced (MAb 2-66-3) rat hepatic cytochrome P-450 were used to measure the contribution of MAb-defined, epitope-specific cytochromes P-450 to the total reaction measured for each of the above activities. ERDE activity was significantly elevated in the livers of cigarette smokers, whereas AHH, CH or ECDE activities were not affected by cigarette smoking. No correlation was observed between plasma cotinine concentration and ERDE activity. MAb 1-7-1 inhibited hepatic ERDE activity to a variable extent (from 0 to 65%), but had very little or no effect on AHH, CH or ECDE activities. The inhibitory effect of MAb 1-7-1 on ERDE activity was greater than 50% in the non-smokers. MAb 2-66-3 had no inhibitory effect on any of the enzyme activities studied. In contrast to liver both ERDE and AHH on human placental microsomes from cigarette smokers were inhibited by MAb 1-7-1. The MAb 2-66-3 was without effect. Cigarette smoking induces a form of P-450 in human liver, responsible for ERDE activity, that contains an epitope recognized by MAb 1-7-1. This form of cytochrome P-450 is insensitive to MAb 2-66-3 and is not contributing to AHH, CH or ECDE activities of human liver.

Multiple Dietary Factors in the Enhancement of Dimethylhydrazine Carcinogenesis: Main Effect of Indole-3-carbinol<xref ref-type="fn" rid="FN1">2</xref>

The effects of multiple dietary influences on 1,2-dimethylhydrazine [(DMH) CAS: 540-73-8]-induced colon cancer in rats were studied. A 2(4) factorial experimental design was used to examine the main and interactive effects of 15% wheat bran (WB), 1% cholesterol (CH) with cholic acid, 20% beef tallow (BT), and 0.1% indole-3-carbinol (IC) on 160 male F344 rats treated ip with DMH (10 mg/kg) weekly for 16 weeks. The test diets were fed for 3 weeks before, 16 weeks during, and 12 weeks after DMH administration. At necropsy, total weight gain, liver and spleen weights, serum CH levels, liver aryl hydrocarbon hydroxylase (AHH) activity, and the size, number, incidence, and location of intestinal tumors were analyzed for dietary factor effects. The most significant inducer of tumors was the combination of CH + BT + IC acting in synergism. The single main effect most responsible for tumor morbidity was IC, which appeared to enhance tumorigenesis via its role as an inducer of AHH activity. The WB decreased tumor incidence and burden when added to diets also containing CH, but it otherwise increased tumor burden per tumor-bearing animal and incidence in all other diets. This study demonstrated the need for examining synergistic and antagonistic interactions among dietary initiators and/or promoters of colon carcinogenesis, as well as implicating IC as a significant factor in the development of DMH-induced tumors in rats.

Behavioral effects of drugs as a function of maternal polybrominated biphenyl body burden

Prior to breeding, female rats were dosed orally for 20 days with either 0.5 mg/kg polybrominated biphenyl (PBB), 5.0 mg/kg PBB, or the lecithin liposome vehicle. Male offspring of these 3 treatment groups did not differ with respect to the learning of an operant discrimination task. However, administration of phenobarbital or d-amphetamine impaired the behavior of the offspring of low-dose PBB dams less than that of the offspring of controls. The behavioral effects of the drugs were generally inversely related to levels of liver PBB and activities of liver aryl hydrocarbon hydroxylase (AHH).

Monoclonal antibody-directed phenotyping of cytochrome P-450-dependent aryl hydrocarbon hydroxylase and 7-ethoxycoumarin deethylase in mammalian tissues.

The distribution of cytochromes P-450 that catalyze aryl hydrocarbon hydroxylase and 7-ethoxycoumarin O-deethylase were studied with monoclonal antibody (MAb) 1-7-1 which completely inhibits these activities of a purified 3-methylcholanthrene-induced rat liver cytochrome P-450. The degree of inhibition by MAb 1-7-1 quantitatively assesses the contribution of different cytochromes P-450 in the liver, lung, and kidney microsomes from untreated, 3-methylcholanthrene- and phenobarbital (PB)-treated rats, mice, guinea pigs, and hamsters. Enzyme sensitivity to MAb 1-7-1 inhibition defines two types of cytochrome P-450 contributing to aryl hydrocarbon hydroxylase and 7-ethoxycoumarin O-deethylase. The MAb 1-7-1-sensitive cytochrome P-450 is a major contributor to aryl hydrocarbon hydroxylase in rat liver, lung, and kidney of 3-methylcholanthrene-treated rats, C57BL/6 mice, guinea pigs, and hamsters; this type is also present in lesser amounts in the extrahepatic tissues of the control and PB-treated animals, and in the lungs of the relatively "noninducible" DBA/2 mice treated with 3-methylcholanthrene. This form however makes little or no contribution to liver aryl hydrocarbon hydroxylase of control or PB-treated animals. 7-Ethoxycoumarin O-deethylase is also a function of both the MAb 1-7-1-sensitive and insensitive classes of cytochrome P-450. The ratio of the classes contributing to aryl hydrocarbon hydroxylase and 7-ethoxycoumarin O-deethylase differs in the various tissues and species and after inducer treatment. All of the 7-ethoxycoumarin O-deethylase activity in guinea pigs and hamsters is a function of cytochromes P-450 different than the MAb 1-7-1-sensitive cytochrome P-450 responsible for aryl hydrocarbon hydroxylase activity. Thus, the MAb 1-7-1 antigenically defines the type of cytochromes P-450 contributing to each reaction. Cytochromes P-450 can be viewed as paradigmatic for enzyme systems in which the nature and amount of product is regulated by multiple isoenzymic forms. Analyses using monoclonal antibodies to specific isoenzymes may thus have broad application to a variety of other complex systems which are composed of multiple isoenzymes.

Effect of steroid hormone treatment on aryl hydrocarbon hydroxylase activity in the Syrian hamster kidney

Aryl hydrocarbon hydroxylase (AHH) activity was determined in castrate and intact male Syrian hamster kidney and liver microsomes following in vivo treatment with either diethylstilbestrol (DES) or 17β-estradiol as well as other steroid hormones. After 1 month of estrogen treatment, there was a 5-fold decline in AHH activity in castrated hamster kidneys compared with untreated castrate levels. the amount of AHH activity in the kidney was depressed more than 75% of untreated castrate levels even after the estrogen had been withdrawn for 6 days. Consistent with a nearly 2.5-fold higher renal AHH activity observed in intact male hamsters compared to castrates was the finding of a 1.7-fold elevation in the activity of this enzyme after treatment of castrated animals with androgen[5α-dihydrotestrosterone (5α-DHT)] for 1 month. Moreover, following withdrawal of estrogen from intact hamsters, the increase in AHH activity in the kidney essentially paralleled the rise in serum testosterone levels. In castrated animals, the depression of AHH activity by estrogen was partially reversed by concomitant 5α-DHT treatment. However, no appreciable changes were seen in liver AHH activity with androgen treatment in the presence or absence of estrogen. Similarly, the level of AHH activity, which was nearly 7- and 14-fold higher than intact and castrate kidney levels, respectively, was not altered by estrogen treatment. Neither progesterone nor cortisone had any effect on the levels of AHH activity in either the kidney or liver. Therefore, AHH activity in the male hamster kidney, but not the liver, is responsive to both estrogens and androgenic hormone.

Effect of topical application of defined constituents of coal tar on skin and liver aryl hydrocarbon hydroxylase and 7-ethoxycoumarin deethylase activities

A single topical application of coal tar solution (USP) to neonatal rats resulted in the induction of aryl hydrocarbon hydroxylase (AHH) and 7-ethoxycoumarin O-deethylase activities in skin, liver, lung, kidney, and intestine. The induction response of AHH in these tissues was in the order of skin > liver > intestine > lung > kidney. The induction response of 7-ethoxycoumarin O-deethylase was highest in the lung and followed the order of lung > kidney > skin > liver > intestine. Twenty-eight defined chemical constituents present in coal tar solution were individually analyzed for their induction effect on skin and liver AHH and 7-ethoxycoumarin O-deethylase activities. A single topical application of anthracene, 1,2-benzanthracene, 2,3-benzanthracene, benzo( a)pyrene, 2,3-benzofluorene, carbazole, chrysene, coronene, 1,2,3,4-dibenzanthracene, 1,2,5,6-dibenzanthracene, 7,12-dimethylbenzanthracene, fluorene, isoquinoline, 3-methylcholanthrene, or phenanthrene at a dose of 1 mg/10 g body weight to neonatal rats resulted in statistically significant induction of skin and liver AHH and 7-ethoxycoumarin O-deethylase activities. The induction response varied from chemical to chemical. Acridine was found to be an inducer of the skin enzymes only. Topical application of triphenylene, benzo(ghi)perylene, fluoranthene, 1-methylphenanthrene, and perylene caused induction of liver enzymes without producing effects on skin enzymes. These studies indicate that several hydrocarbons present in coal tar solution have induction effects on drug and carcinogen metabolism in skin and liver and that there are tissue-specific responses to some of these hydrocarbons.

Induction of Neonatal Rat Skin and Liver Aryl Hydrocarbon Hydroxylase by Coal Tar and Its Constituents

Topical application of coal tar solution (USP) to neonatal rats resulted in the induction of skin and liver aryl hydrocarbon hydroxylase (AHH) activities. Furthermore indirect exposure of the animals to coal tar vapors resulted in induction of the enzyme in skin and liver. Cutaneous application of coal tar to pregnant rats resulted in induction of skin and liver AHH activity in both mothers and prenatal rats. Among several defined constituents of coal tar tested benzo(a)pyrene (BP), anthracene and acridine were found to have measurable induction effects on neonatal rat skin and liver AHH. These studies indicate that therapeutic coal tar solution as well as selected defined chemical constituents of coal tar are capable of altering the activity of AHH in skin and liver.

Hydrocarbon metabolism and cortisol balance in oil-exposed ringed seals, Phoca hispida

1. Ringed seals were exposed experimentally to oil contamination, by feeding of a [ 14C]naphthalene marked crude oil in fish for up to 4 days at a rate of 5 ml/day. 2. Mixed function oxygenase (MFO) activity, measured as aryl hydrocarbon hydroxylase in liver and kidney, was found to be induced, in particular in kidney tissue where the activity increased 3-fold. 3. MFO induction correlated with a high degree of conversion of crude oil hydrocarbons to water-soluble metabolites. Most of the radioactivity was found in the polar fraction of plasma and urine. 4. Plasma cortisol levels were somewhat elevated by captive holding, and increased markedly after oil-exposure. Cortisol half-life decreased after oil exposure from 1 3 4 to 1 hr.

Murine colonic mucosal metabolism and cytotoxicity of benzo [alpha] pyrene.

Homogenates of colonic mucosa from seven mouse strains metabolized 14 C-benzol [alpha] pyrene (BP) to alkali-soluble and water-phase products. In those strains in which liver aryl hydrocarbon hydroxylase activity is inducible by beta-naphthoflavone (beta-NF), the C57Bl/6, BALB/c, C3H and random-bred Swiss CD-1, colonic metabolism of BP was also induced by intraperitoneal treatment with 150 mg/kg beta-NF 24 h before assay. No increase in the colonic metabolism of BP was seen after beta-NF treatment of the noninducible strains, AKR, DBA and SWR. A detailed study of the products formed was carried out with C57BL/6 male mice. High-performance liquid-chromatography analysis of the products of BP metabolism revealed that phenolic derivatives predominated, but that a small percentage of the BP was converted into the proximate carcinogen, the BP-7,8-diol. Addition of uridine 5'-diphosphoglucuronic acid to the incubation mixture caused an increase in total product formation and a shift from alkali-soluble to water-phase products. Of the water-phase products formed by beta-NF-induced colonic mucosal homogenates, about 40% were nondialyzable and associated with precipitable material. In a study of the cellular effects of BP on the colonic mucosa, intrarectal administration of 1 mg BP had a significant cytotoxic effect, as indicated by the number of pyknotic cells and 3H-thymidine-labeling index, and prior treatment with beta-NF afforded significant protection against this cytotoxicity.

Effect of various xenobiotics and steroids on aryl hydrocarbon hydroxylase activity of intestinal and hepatic microsomes from male rats.

The effects of four solvents and 37 xenobiotics and endogenous steroids on intestinal and hepatic microsomal aryl hydrocarbon hydroxylase (AHH) activity were determined. In general, hepatic AHH was more sensitive than intestinal AHH to inhibition by a wide variety of xenobiotics. Acetone, ethanol, dimethyl formamide, triamcinolone acetonide, 17 alpha-propyltestosterone, metronidazole, cimetidine and butylated hydroxyanisole (BHA) activated or stimulated intestinal AHH activity while inhibiting hepatic AHH activity at the same concentrations. Ethoxyquin, progesterone, pregnenolone acetate, deoxycorticosterone acetate, tamoxifen and SKF 525-A exerted markedly different concentration-dependent inhibitions of intestinal and liver AHH activities. The most potent inhibitors of AHH activity were captan, BHA, chlorpromazine, thioridazine, disulfiram and menadione. The ability of steroids to inhibit AHH activity correlated well with lipophilicity.