Basal Aryl Hydrocarbon Hydroxylase Research Articles

The relationship between age and cutaneous aryl hydrocarbon hydroxylase (AHH) activity.

Aryl hydrocarbon hydroxylase (AHH), a component of the mixed-function oxygenase system, has been identified in liver and in many extrahepatic tissues, including the skin. In this study, the effect of ageing on cutaneous AHH activity in both male and female Wistar and Brown Norwegian rats of two age groups (average ages being 44 and 130 weeks) was assessed using benzo(alpha)pyrene as substrate and by measuring the formation of the fluorescent metabolite 3-hydroxybenzo(alpha)pyrene. Results show that cutaneous metabolism of polycyclic aromatic hydrocarbons does not change between young adulthood and senescence in either male or female rats. Sex-related differences did occur, however, and may be explained, partly, by the existence of different molecular forms of cyt-P450. In conclusion, age does not appear to be a major determinant of basal cutaneous AHH activity in rats.

Aryl Hydrocarbon Hydroxylase Activity in Human Lung Tissue: In Relation to Cigarette Smoking and Lung Cancer

In order to investigate the relationship between aryl hydrocarbon hydroxylase (AHH) activity and smoking or lung cancer, AHH activities in fresh lungs (normal tissue, tumorous tissue, and surrounding tissue of tumor) obtained from lung cancer patients and non-lung cancer patients were measured. There were no differences in lung AHH activity in the lung lobes. In the non-lung cancer patients, AHH activities ranged from 0.13 to 2.37 (pmol 3 hydroxybenzo[ a]pyrene/20 min/mg protein), and whereas in the normal tissues of the lung cancer patients they ranged from 0.19 to 5.05. Lung AHH activities showed normal distribution, and a large variation (26 times) was observed in normal tissues in the lung cancer patients. In most cases, AHH activities in the tumorous tissues and the surrounding tissue of the tumor were lower than those in the normal tissues of the lung cancer patients. In the non-lung cancer group, the means of AHH activity of the nonsmoker subgroup (NN) and the smoker subgroup (SN) were 0.62 and 0.96, respectively. On the other hand, in the lung cancer group the means of AHH activity of the nonsmoker subgroup (NC) and smoker subgroup (SC) were 0.85 and 1.05, respectively. Statistically significant differences were observed between NN and SN, NN and NC, and NN and SC. These results suggest that human lung AHH activity was increased by cigarette smoke as in rodent lungs, and the distribution of basal AHH activity in lung tissue of the nonsmokers group in the lung cancer patients shifted toward high levels compared to the nonsmokers group in the non-lung cancer group. The effect of the histological cell types of the lung cancer on the AHH activity was not observed in this study.

Proline Is Required for Transcriptional Control of the Aromatic Hydrocarbon‐inducible P1450 Gene in C57BL/6 Mouse Monolayer‐cultured Hepatocytes

Expression of aryl hydrocarbon hydroxylase (AHH) and the corresponding gene, CyplA1 or P1450 in mice, in C57BL/6 mouse hepatocytes in primary culture was investigated after exposure to benz[a]‐anthracene with respect to proline‐related metabolic regulation. When the cells were cultivated in complete Waymouth MB752/1 (Way), prominent induction of AHH by benz[a]anthracene was observed, whereas the induction was inefficient in the same but proline‐deflcient medium [Way‐(‐pro)]. Constitutive AHH activities decreased with increasing culture period. P1450 gene transcripts were slightly expressed when the medium was changed, independently of whether the cells were cultivated in either Way or Way(‐pro), followed by decrease within 24 h and no apparent induction of AHH. However, treatment with Δ1‐pyrroline‐S‐carboxylic acid (P5C), a biosynthetic precursor for proline, dose‐dependently increased basal AHH activities in the cells cultivated in Way‐(‐pro). Benz[a]anthracene induction of AHH in cells cultivated in Way(‐pro) was additively increased in the presence of P5C as much as with proline. Treatment with o‐aminobenzaldehyde, which inactivates P5C, drastically reduced the induced AHH activities in hepatocytes cultivated in either P5C‐added Way (‐pro) or Way medium. Benz[a]anthracene induced both P1450 and P3450 mRNAs. Neither proline nor P5C increased the induced transcripts within 12 h after the start of benz[a]‐anthracene treatment, but the two compounds increased the amounts of P1450 mRNA found at later time points. After treatment with actinomycin D, the half‐life of the induced P1450 mRNA was approximately 12 h, being independent of the presence of either proline or P5C. Our observations suggest that induction of AHH after treatment with polycyclic aromatic hydrocarbon is dependent on proline‐related metabolism which influences the transcriptional process of P1450 gene expression.

Regulation of mouse P1450 gene expression in monolayer-cultured hepatocytes from responsive and non-responsive strains

Regulation of P(1)450 gene expression in mouse hepatocytes from responsive (C57BL/6) and non-responsive (DBA/2) strains in primary culture was investigated with respect to aryl hydrocarbon hydroxylase (AHH) activity and P450 transcript levels. Although significant induction of AHH activity in C57BL/6 mouse hepatocytes after exposure to benz[aanthracene (BA) or 2,3,7,8-tetrachlorodibenzo-p-dioxin (TCDD) was observed 24 h after the beginning of cultivation, the response was more prominent after longer periods. AHH induction in DBA/2 mouse hepatocytes by TCDD was also evident after 24 h treatment, but that by BA was delayed, only becoming significant after 3 days. Limited treatment with cycloheximide (CHI) for the initial 8 h affected AHH activity measured after 24 h; BA-induced AHH activity was decreased if the treatment started day 1 after seeding of the cells from either strain, whereas if started at day 3 the enzyme activities in hepatocytes from C57BL/6 strain were approximately doubled and those from DBA/2 increased to 130%. Treatment with dibutyryl cAMP or forskolin, a specific activator for adenyl cyclase, increased BA-induced AHH activities. 3-Methoxybenzamide, a specific inhibitor of poly(ADP-ribose) polymerase, significantly increased both basal and BA-induced AHH activities of hepatocytes from both strains at days 3 and 5, reduction of P(1)450 transcripts also being evident in the latter case. The observations indicate qualitatively similar but quantitatively different regulation of AHH induction in both responsive and non-responsive mouse strains. Furthermore the regulation changed with increasing cultivation period. Previously described regulation mechanisms in cultured cells were observed to operate a few days after seeding, possibly after adaptation of hepatocytes to the culture conditions.

Induction of Cytochrome P450 IA1 in Mouse Hepatoma Cells as a Short-term Bioassay

The inducibility of aryl hydrocarbon hydroxylase (AHH) in mouse hepatoma Hepa-1 cell culture has been used as a quantitative bioassay for 2,3,7,8-tetrachlorodibenzo- p-dioxin (TCDD). The detection limit was 0.5pM TCDD. The basal AHH activity was about 2U/mg protein, and the maximally induced activity was about 100U/mg protein. ED50 for TCDD was 7pM. Similar data were obtained using 7-ethoxyresorufin as a substrate (EROD activity). Extraction of several consumer paper products with acetone gave an uncharacterised mixture of AHH inducers. The estimated TCDD (equivalents) in these extracts varied between 0 and 42pg/g of paper.

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.

The Association of Age with the Induction of Drug-metabolizing Enzymes in Human Monocytes

In vivo studies in man suggest that the enzyme-inducing effect of environmental influences such as drugs or smoking may be reduced in elderly people. We have investigated the basal activity and response to induction of the oxidative enzyme, aryl hydrocarbon hydroxylase (AHH) in human monocytes. Three groups were studied: ten fit young, ten fit elderly and eight frail elderly subjects. Significant induction of AHH activity in response to the hydrocarbon benz(a)anthracene was achieved in all three groups. No impairment of basal AHH activity or in the synthesis of new enzyme protein was noted with age or frailty. There is still no direct evidence of an age-associated fall in drug metabolizing enzyme activities in man.

Altered Patterns of Cutaneous Xenobiotic Metabolism in UVB-Induced Squamous Cell Carcinoma in SKH-1 Hairless Mice

Cutaneous xenobiotic metabolizing enzymes including aryl hydrocarbon hydroxylase (AHH), 7-ethoxycoumarin O-deethylase (ECD), epoxide hydrolase (EH) and glutathione S-transferase (GST) activities were examined in SKH hairless mice chronically irradiated with UVB to induce squamous cell carcinoma (SCC). Enzyme activities in irradiated tumor-bearing skin were compared to those present in the skin of nonirradiated control animals as well as in unirradiated non-tumor bearing skin sites of the SCC-bearing mice. The inducibility of skin AHH and ECD in each set of animals was assessed following a single topical application of coal tar (1 ml/100 g). Enzyme-mediated binding of [3H]benzo(a)pyrene (BP) and its metabolite 7 beta,8 alpha-dihydroxy-9 alpha,10 alpha-epoxy-7,8,9,10-tetrahydrobenzo(a)pyrene (BPDE-I) to epidermal DNA was also evaluated. Basal AHH and ECD activities in microsomes from UVB-irradiated SCC-bearing dorsal skin were 4.6- and 4.8-fold lower than those in dorsal skin of nonirradiated control animals. Enzyme activities in non-tumor bearing ventral skin from the UVB-irradiated SCC-bearing mice also were 2.2 to 2.8-fold lower as compared to activities in the nonirradiated control animals. The reduction in AHH activity paralleled the levels of enzyme-mediated binding of radiolabeled BP metabolites and of BPDE-I to epidermal DNA. GST activity was found to be increased (173%) in non-tumor bearing ventral skin of UVB-irradiated mice whereas no difference in activity between SCC-bearing dorsal skin and dorsal skin of control animals could be detected. EH activity was unchanged in each group of animals. Treatment with topically applied coal tar resulted in higher inducibility of AHH and ECD in both SCC-bearing (13-fold) as well as in non-tumor skin sites (6-fold) of UVB-irradiated mice than in skin of control animals (3-fold). Coal tar application also increased the covalent binding of [3H]BP and of the metabolite BPDE-I to skin DNA. This was greater in SCC-bearing dorsal skin (119-129%) than in nonirradiated skin of control animals (48-62%). Our studies suggest that the metabolism of BP by cutaneous cytochrome P-450 dependent monooxygenases is impaired in skin of mice irradiated chronically with UVB. The higher inducibility of these monooxygenases by topically applied coal tar and the enhancement of the associated enzyme-mediated covalent binding of BP metabolites and BPDE-I to epidermal DNA indicate that repetitive exposure of mammalian skin to UVB radiation can profoundly alter the activity and the inducibility of drug and carcinogen metabolizing enzymes.(ABSTRACT TRUNCATED AT 400 WORDS)

Induction of cytochrome P-450-dependentmonooxygenase systems in embryos and eleutheroembryos of the killfish Fundulus Heteroclitus

Microsomal aryl hydrocarbon hydroxylase (AHH) activity was highly inducible by polychlorinated biphenyls (PCBs) in Fundulus embryos, and stages prior to the appearance of the liver rudiment were competent to respond to these inducers. Consistent with previous observations, basal AHH activity in whole eleutheroembryo microsomes was shown to increase about 9-fold within 24 h of hatching. Aminopyrine N-demethylase (APD) activity also increased with time after hatching. However, the increase in APD activity was much less than that of AHH activity, suggesting a post-hatching change in basal cytochrome P-450 isozyme composition. Also associated with hatching was an increase in the sensitivity to PCBs as inducers of AHH activity. The ED50 for induction of AHH activity in eleutheroembryos was estimated to be only one-third to one-fourth that in embryos. This developmental increase in the sensitivity to PCBs was not due to a redistribution of PCBs between the yolk and tissues with yolk absorption, and was not simply age-dependent, but appeared to require hatching. An additional change in the monooxygenase system associated with hatching was that microsomal NADPH-cytochrome c reductase activity was not inducible by PCBs prior to hatching, but was modestly inducible after hatching. High performance liquid chromatographic (HPLC) analysis of benzo[a]-pyrene (BP) metabolites formed by microsomes from control and PCB-treated eleutheroembryos demonstrated production of dihydrodiols in the 7,8- and 9,10-positions of the benzo-ring. The formation of these metabolites was completely inhibited by the epoxide hydrolase (EH) inhibitor, trichloropropene oxide, indicating the presence of EH in Fundulus eleutheroembryos. Furthermore, these results indicate the Fundulus eleutheroembryos probably can activate BP to its ultimate carcinogenic form, the 7,8-dihydrodiol-9,10-epoxide, and induction of AHH activity by PCBs is likely to increase the rate of formation of activated metabolites from BP and related compounds. However, during the most active period of organogenesis, prior to hatching, basal AHH activity was low, and prehatching stages were relatively insensitive to cytochrome P-450 inducers. The combination of these effects may help to protect these stages from damage from activated metabolites.

Aryl Hydrocarbon Hydroxylase, Epoxide Hydrolase, and Benzo[a]pyrene Metabolism in Human Epidermis: Comparative Studies in Normal Subjects and Patients with Psoriasis

Prior studies have shown that human skin possesses a cytochrome P-450-dependent microsomal enzyme that is capable of metabolizing drugs and polycyclic aromatic hydrocarbon (PAH) carcinogens. This study characterized benzo[a]pyrene (BP) metabolism in human epidermis of normal and psoriatic individuals. The basal level of the cytochrome P-450-dependent microsomal enzyme aryl hydrocarbon hydroxylase (AHH) and epoxide hydrolase (EH) were measured in freshly keratomed epidermis from 12 normal individuals and from uninvolved skin sites of 12 patients with psoriasis. The induction response of AHH following the in vitro addition of the PAH benz[a]anthracene (BA) was also assessed. The basal activity (mean +/- SE) of AHH in normal epidermis was 62.1 +/- 5.6 units (fmol 3-hydroxybenzo[a]pyrene, 3-OH-BP/min/mg protein) whereas the activity in uninvolved skin of psoriatic individuals was 62.9 +/- 5.1 units (NS), Epoxide hydrolase activity was 25.1 +/- 1.1 (pmol BP 4,5-diol/min/mg protein) unites in normal epidermis and 24.8 +/- 2.1 units in epidermis from patients with psoriasis (NS). Following addition of BA (100 microM), in vitro, AHH activity in normal epidermis increased by a mean value of 165% whereas activity in nonlesional epidermis of psoriatic individuals increased 320%. Kinetic studies in normal epidermis revealed that AHH reaction was linear up to 60 min and to 50 micrograms protein, had a pH optimum of 7.4, and the Km for BP was 0.62 microM. High-performance liquid chromatography (HPLC) confirmed that the pattern of metabolism of BP was quite similar in epidermal microsomes prepared from normal and psoriatic individuals, insofar as the formation of diols, phenols, and quinones was concerned. These studies indicate that human epidermis is capable of metabolizing BP and that there is no significant difference between normal individuals and patients with psoriasis insofar as basal AHH activity or total BP metabolism is concerned. Furthermore, the epidermal enzyme system in patients with psoriasis has a greater responsiveness to environmental PAH than does that of normal individuals.

Human fetal liver cultures: Basal activities and inducibility of epoxide hydrolases and aryl hydrocarbon hydroxylase

The environmental influence of various drugs on the epoxide hydrolase with styrene oxide (EH so) or benzo(a)pyrene-4,5-oxide (EH BPox) as substrate and the aryl hydrocarbon hydroxylase (AHH) activity was studied in monolayer cultures of human fetal hepatocytes (HFH) obtained at legal abortions. Hepatocytes were isolated by trypsin treatment of liver fragments and primary HFH cultures were maintained in Eagle's minimum essential medium supplemented with 15% newborn calf serum. The HFH were plated on culture dishes and allowed to ‘settle’ for one day before adding various drugs (in 1μl dimethylsulfoxide/ml) or solvent only and assay 1–2 days later. The basal AHH activity [assayed with 3H-benzo(a)pyrene as substrate] varied between 2 and 8.4 pmoles/min/mg protein and the basal EH so activity was 0.3–4.9 nmoles/min/mg protein ( n = 6) after one or two days' culture. The corresponding activity of EH BPox was 0.23–1.48 nmoles/min/mg protein ( n = 5). Exposure of cultures to 2 mM phenobarbital (Pb), 2.5–25.0 μM benzanthracene (BA), 0.1 mM trans-stilbene oxide (TSO), or 5 μM β-naphtoflavone (βNF) resulted in a 1.2–3.7-fold induction of EH so. Induction of EH BPox was also observed with Pb, βNF, BA and TSO as inducers. Pb gave a dose-dependent induction of both EH at 0.1, 1.0 and 2.0 mM. Our results demonstrate that EH and AHH activities in HFH cultures are inducible by classical in vivo inducers. Although difficult to prove, it is plausible that such induction takes place also in intrauterine life.

Blood monocyte aryl hydrocarbon hydroxylase activity in psoriasis.

The activity of aryl hydrocarbon hydroxylase (AHH) in monocytes from 13 healthy control subjects and in 16 patients with discoid psoriasis was measured. The mean basal monocyte AHH activities of the control and psoriatic groups were 3.4 +/- 0.47 and 4.46 +/- 0.55 respectively (pmol 3-OHBP h-1 10(-6) cells). This difference was not significant. The mean induced monocyte AHH activities in the control and psoriatic groups were 56.4 +/- 10.8 and 77.8 +/- 16.0 pmol 3-OHBP h-1 10(-6) cells respectively but this difference was not significant. The mean induction ratios in the control and psoriatic groups were 16.5 +/- 1.8 and 20.4 +/- 3.6 respectively. Again, this difference was not significant. We conclude therefore, that monocyte aryl hydrocarbon hydroxylase activity is not reduced in psoriasis.

Aryl hydrocarbon hydroxylase of rat brain mitochondria: Properties of, and effect of inhibitors and inducers on, enzyme activity

Aryl hydrocarbon hydroxylase (AHH), a typical example of mixed-function oxidase system, was studied in rat brain mitochondria. The enzyme was found to require oxygen and NADH for optimal expression of the activity. Coaddition of NADPH in the incubation system containing NADH resulted in an additive effect on the enzyme activity. NADH- and NADPH-dependent mitochondrial AHH activity was linear with respect to protein concentration and incubation time. The enzyme exhibited a sharp optima at pH 7.6. Specific activity of NADH-dependent mitochondrial AHH in rat brain was 3–4 and 8–11 times higher than that of NADPH-dependent mitochondrial and microsomal enzyme activity, respectively. Of the species investigated, NADH-dependent mitochondrial AHH followed the order: mice ⩾ guinea pig > rat, while NADPH-supported mitochondrial AHH was in the order: rat > guinea pig ⩾ mice. Specific activity of NADH-dependent mitochondrial AHH in various rat brain regions was similar with the exception of olfactory lobes which exhibited 60% higher activity than other region. When total region activities were added approximately whole brain activity was recovered. The apparent K m value of NADH-dependent mitochondrial AHH was 1.18 μ m with benzo( a)pyrene as a substrate. This K m value was five to six times lower than that of NADPH-dependent microsomal AHH in rat brain (6.66 μ m). NADH-dependent mitochondrial AHH was inhibited by KCN in a concentration-dependent manner while NADPH-supported mitochondrial AHH did not reveal any sensitivity to cyanide. Brain microsomal NADH as well as NADPH-supported AHH was also inhibited by KCN in a concentration-dependent manner. Carbon monoxide inhibited NADH-dependent mitochondrial AHH activity (48%) and had no effect on NADPH-dependent mitochondrial enzyme. Mitochondrial NADH and NADPH-dependent AHH activities were induced by 3-methylcholanthrene (64–73%) and benzo( a)pyrene (91–92%) pretreatments while no induction occurred with phenobarbital administration. 1-Benzylimidazole, SKF 525 A, metyrapone, and α-naphthoflavone inhibited both basal and 3-methylcholanthreneinduced NADH-dependent mitochondrial AHH activity. α-Naphthoflavone was more effective in inhibiting 3-methylcholanthrene-stimulated rat brain NADH-dependent mitochondrial AHH. Mitochondrial NADH-dependent AHH activity increased gradually with the onset of development and attained a steady state after 49–56 days of age. An increase of eight- to ninefold in the specific enzyme activity was observed between 7- and 56-day-old rats. No significant increase in brain mitochondrial AHH activity was observed between 56- and 91-day-old rats.

Dissociation of 12- O-tetradecanoylphorbol-13-acetate and 3-methylcholanthrene-induced induction in ornithine decarboxylase and aryl hydrocarbon hydroxylase activities in [formula omitted] mouse dermal fibroblasts in culture

The effects of 12- O-tetradecanoylphorbol-13-acetate (TPA) and 3-methylcholanthrene (MC) on ornithine decarboxylase (ODC) and aryl hydrocarbon hydroxylase (AHH) activities were studied in C57BL 6 mouse dermal fibroblasts in culture. TPA selectively induced ODC activity and MC selectively induced AHH activity in these cells. Acute (10 h) exposure of the cells to DL-α-difluoromethyl ornithine (DFMO) led to a marked inhibition of ODC activity without any significant effect on induced AHH activity. Chronic inhibition of ODC activity (4 days) resulted in a slight inhibition of basal AHH activity, but the inducibility of AHH was enhanced. α-Naphthoflavone, SKF 525 A and indomethacin exerted unequal effects on the enzyme activities. These results indicate that ODC and AHH induction processes are independent events with no causal link.

Activity and kinetic properties of basal aryl hydrocarbon hydroxylase during proliferation in the transformable C3H 10T [formula omitted]; CL8 cell line

Basal aryl hydrocarbon hydroxylase (AHH) activity and its kinetic properties were studied as a function of proliferation in C3H mouse embryo 10T 1 2 CL8 cells. Activity was low in freshly plated cells, increased during exponential growth, peaked at confluency, and then declined. The apparent K m-values for benzo[ a]pyrene (BP) and NADPH were less in proliferating (approx. 0.37 μM BP, 3.3 nM NADPH) than in confluent cells (0.74–1.39 μM BP, 33.4–53.4 nM NADPH). Cells at different growth states responded differently to benz[ a]anthracene (BA) and aminophylline, an inhibitor of cyclic nucleotide phosphodiesterases. When cells were harvested at the mid log phase of growth, 12 h of exposure to aminophylline caused maximum induction, while 24 h of BA treatment were required. In contrast, at early confluence, 12 h of BA treatment gave the greatest levels of activity, while exposure to aminophylline did not induce AHH. In fact, decreases in activity were observed. These differences are indicative of different regulatory mechanisms for BA and aminophylline induction. They also suggest the regulation of basal AHH by cyclic nucleotides changes during growth. The exposure times giving maximum activity were used to determine the kinetic properties of BA-induced activity. As with basal AHH, the K m-value for BP was less in log phase (0.2–0.4 μM BP) than in confluent cells (0.64–1.05 μM BP). Moreover, the K m-values for BP and NADPH in control cultures at confluency (0.10–0.14 μM BP, 15.4–23.2 nM NADPH) were less than those for BA-treated cells (0.64 μM BP, 37.9–54.8 nM NADPH) under the same nutritional conditions. The finding that the K m-value for BP is lower in rapidly dividing cells than in confluent cells may help to explain why proliferating cells are more susceptible to transforming agents.

Responses of rodent hepatic, renal and pulmonary aryl hydrocarbon hydroxylase following exposure to cigarette smoke

Using the British-American Tobacco Co. (B.-A.T.)-Mason inhalation system which releases a precisely-calibrated dilution of tobacco smoke into a chamber, male and female rats, guinea pigs, hamsters and gerbils were exposed to the optimum smoke concentration found to induce rat renal aryl hydrocarbon hydroxylase (AHH) (40 puffs of a 1 : 5 dilution of smoke from cigarettes prepared from a blend of Canadian flue-cured tobaccos). The tissue activity was measured in 9000 g supernatants of homogenates of lung, liver and kidney 6 h following exposure. Cigarette smoke was found to be a potent inducer of AHH, dilutions as high as 1 : 40 inducing this enzyme in rat kidney. Marked tissue, sex and species differences in basal AHH were observed. Induction up to 6-fold, was observed only in lung and kidney of male and female rats. In hamsters and gerbils, lung AHH was induced in both sexes but only renal AHH in female hamsters. In male and female guinea pigs, only the renal AHH was induced some 5-fold. Hepatic AHH was not inducible in any of the species studied. The analysis of changes in AHH activity in a responsive species and tissue(s) could be a valuable technique for the quantitative evaluation of biological effects of low concentrations of cigarette smoke.

Effects of perinatal exposure to benzo(a)pyrene on the aryl hydrocarbon hydroxylase system of adult rat liver.

Early exposure to benzo(a)pyrene, B(a(P, produces long-lasting effects on the cytochrome P-450 dependent monooxygenase system of rat liver microsomes. Adult male offspring of rats given B(a(P, 20 mg/kg i.p. during late pregnancy, showed either a small but significant depression of basal aryl hydrocarbon hydroxylase acitivity or an impaired induction response to B(a)P. Few significant changes were found in the relative amounts of the individual metabolites formed from B(a)P by microsomes from perinatally exposed rats, either in the basal or B(a)P-induced state. In addition, perinatal exposure to B(a)P tended to decrease the binding of B(a)P to calf thymus DNA in in vitro incubations.

Aryl hydrocarbon (benzo[a]pyrene) hydroxylase in rat mammary tissue during pregnancy and lactation

Rats are highly resistant to mammary tumour induction by polycyclic aromatic hydrocarbons during pregnancy and lactation. Since local changes in hydrocarbon metabolism in mammary tissue or altered hepatic metabolism might contribute to the resistance, aryl hydrocarbon hydroxylase (AHH) activity in microsomes from mammary tissue and liver was measured throughout the course of pregnancy and lactation in Sprague–Dawley rats. Basal constitutive AHH activity in mammary tissue and liver of untreated rats did not change significantly during pregnancy or lactation. In rats injected with beta-naphthoflavone (BNF), AHH activity in liver microsomes increased approximately 25-fold over basal levels and the degree of enzyme induction by BNF was relatively constant throughout pregnancy and lactation. In mammary tissue, however, the induction of AHH by BNF increased dramatically from about 10 times basal at the beginning of pregnancy to over 80 times basal on day 3 of lactation. The high inducibility of mammary AHH during late pregnancy and early lactation exists both when activity is expressed per unit microsomal protein or per unit tissue DNA. Increased inducibility of mammary AHH may contribute to the resistance rats show to hydrocarbon carcinogenesis during pregnancy and lactation. Since the activity of hepatic AHH does not change significantly during pregnancy or lactation, it seems unlikely that resistance is due to altered hepatic metabolism of the hydrocarbons. AHH activity can be associated both with 'metabolic activation' and 'detoxification' of aromatic hydrocarbons. The balance between local 'activation' and 'detoxification' of aromatic hydrocarbons by AHH in mammary tissue during different physiological states is important in determining susceptibility to carcinogenesis and requires further study.

Simple vs. complex inheritance of inducible aryl hydrocarbon hydroxylase in mouse tissues.

The genetics of induction of hepatic and lung aryl hydrocarbon hydroxylase (AHH) have been studied in Af/Ki and AKR/Ki mice and in their F1 and F2 progeny after administration of 3-methylcholanthrene (3MC). Furthermore, the induction of AHH was investigated using the fetal liver explant model system with 3MC, trans-1,2-dihydroxy-3MC, and 4'-bromoflavone as the inducers. The results obtained with the above strains were contrasted with those from the C57BL/6Ki, DBA/2+Ki, and their crosses. The present investigation revealed a complex pattern of inheritance of basal and inducible AHH in lung and liver of AKR/Ki and Af/Ki, with a poor correlation between lung and liver. Hepatic AHH was not fully inducible in the F1 hybrids, while the frequency distribution function in the F2 mice was suggestive of more than two distinct classes.