Induction of aryl hydrocarbon hydroxylase in human lymphocytes and pulmonary alveolar macrophages--a comparison

Exposure of animals to cigarette smoke causes an increase in the levels of aryl hydrocarbon hydroxylase (AHH) in various tissues. The innate capacity for enzyme induction is genetically determined but the extent of induction and AHH levels in various tissues may vary. AHH levels in human pulmonary alveolar macrophages (PAMs) were determined and AHH inducibility of cultured lymphocytes from corresponding volunteers was determined. The inducibility by 3-methylcholanthrene of cultured lymphocytes was similar in both smokers and nonsmokers, ranging from 0.2 – 4.2 fold induction. AHH levels in nonsmoker PAMs was 0 – 0.020 units and in smokers was 0.032 – 0.253 units. The correlation of AHH activity in PAMs with lymphocyte inducibility was significant in both nonsmokers and smokers. The regression of AHH in PAMs as compared with AHH inducibility in lymphocytes was 8.5 fold higher in smokers than nonsmokers, reflecting the induction of AHH in PAMs by smoking.     

Aryl hydrocarbon hydroxylase in cultured lymphocytes of twins.

Measurement of aryl hydrocarbon hydroxylase (AHH) in cultured lymphocytes of 18 monozygotic and 30 dizygotic twin pairs showed that basal and induced AHH activity and AHH inducibility are heritable traits. The data are consistent with AHH inducibility being determined by a single or a very few polymorphic genes.     

The relationship between aryl hydrocarbon hydroxylase activity and DNA adducts measured by 32P-postlabelling assay in lymphocytes of lung cancer patients

We have investigated the correlation between DNA adduct levels and aryl hydrocarbon hydroxylase (AHH) activity in peripheral lymphocyte samples obtained from 42 lung cancer patients. DNA adducts and AHH activity were determined by the ³²P-postlabelling technique and the fluorometric method, respectively. The mean +/- SD of DNA adduct level was 0.88 +/- 0.37 (ranged from 0.22 to 1.90) per 10⁸ nucleotides. The geometric means of non-induced and 3-methylcholanthrene (MC)-induced AHH activity, as well as AHH inducibility (MC-induced AHH activity/non-induced AHH activity) were 0.029, 0.228 pmol min^-1 10^-6 cells, and 7.776, respectively. There was no statistically significant correlation between DNA adduct levels and non-induced or MC-induced AHH activity. A tendency of positive correlation was found between DNA adduct levels and AHH inducibility for the all subjects (n = 42, r = 0.25, p = 0.11). Such a positive correlation reached statistical significance in the subjects with squamous cell carcinoma (n = 13, r = 0.70, p < 0.01). In addition, similar correlation of DNA adducts with AHH inducibility was also observed in the GSTM1 present genotype (n = 17, r = 0.44, p = 0.07) and GSTP1-AA genotype (n = 29, r = 0.37, p = 0.05) individuals. These findings suggest that DNA adduct levels are mediated by CYP1A1 enzyme, and AHH inducibility may be a more relevant indicator than specific AHH activity for explaining the variation of DNA adduct levels in lymphocytes.     

Induction of arylhydrocarbon hydroxylase and blast transformation in human blood lymphocytes

Variation in arylhydrocarbon hydroxylase(AHH) inducibility in human peripheral blood lymphocytes was studied. AHH inducibility and the degree of blast transformation were determined simultaneously using [³H]benzo(a)pyrene and [³H]thymidine, respectively. AHH inducibility in terms of induction ratio(induced level to basal) or induction ratio per unit of blast transformation varied at different culture time and at different phytohemagglutinin concentrations within the same individuals. However, the ratio of absolute induced AHH activity and unit of blast transformation gave persistent value for the same individuals, indicating that AHH inducibility of human lymphocytes should be expressed in this manner in the study of cancer susceptibility.     

The role of aromatic hydrocarbon hydroxylase in the pathogenesis of lung cancer

Aromatic hydrocarbons hydroxylase (AHH)--an enzyme of monooxydases group--catalyzes hydroxylation of polycyclic aromatic hydrocarbons yielding compounds of the direct cancerogenic properties. Inducibility determined genetically is a characteristic feature of AHH. Inducibility of AHH in patients with cancer of the lungs is higher than that in healthy population. According to some authors general population may be classified into three groups of : high, moderate, and low degree of AHH inducibility. A significant increase in the incidence of neoplasms related to an exposition to PAH was noted in patients with increased AHH inducibility. These neoplasms include: carcinoma of the lungs, mouth and larynx, cancer of the pharynx and leukoplakia. Moreover, the onset of these neoplasms is earlier than in subjects with moderate and low inducibility of AHH.     

Relationship between mitogen response and aryl hydrocarbon hydroxylase in cultured human lymphocytes

This study was conducted to determine if any relationship existed between Aryl hydrocarbon hydroxylase (AHH) inducibility and mitogen response of cultured lymphocytes from normal healty individuals. The experiments were done repeatedly on the peripheral blood lymphocytes of the same individuals at 4 months intervals during the course of a year. AHH activity was measured by spectrophotofluorometric assay procedures. Mitogen response was measured by counting the incorporation of ³H-Thymidine in cellular DNA using a liquid scintillation counter.Our study indicated large variations in mitogen response of the lymphocytes throughout the study period within the same individuals as well as among the individuals. Variations in AHH inducibility within and among the individuals were also found. The variations were without any pattern. No relationship was found between AHH inducibility and the mitogen response index, suggesting the AHH inducibility test in the mitogen stimulated cultured lymphocytes is not affected by the immune responsiveness of the cells from individual.     

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Aryl hydrocarbon hydroxylase (AHH) was present in explant cultures of human prostate obtained from surgery of benign prostatic hyperplasia and was inducible by benz[a]anthracene (BA). The induction of AHH ranged from 14- to 150-fold when compared with control values and 10-fold variation of AHH inducibility among individuals was observed. Epithelial cells grown from human prostate tissue also contained measurable AHH activity and AHH was inducible by BA and 7,12-dimethylbenz[a]anthracene (DMBA). Inducibility of AHH by BA ranged from 2- to 63-fold. The inducibility of AHH by DMBA was always less than that by BA. In cells treated with N-methyl-N′-nitro-N-nitrosoguanidine (MNNG), there were no changes in AHH activity. These findings support the view that the human prostate is susceptible to environmental polycyclic hydrocarbon carcinogens and that environmental and occupational factors might contribute to the etiology of human prostatic carcinoma.     

Suppression of aryl hydrocarbon hydroxylase activity in human primary lung carcinoma x mouse hepatoma somatic cell hybrids

Variants of the mouse hepatoma cell clone inducible for aryl hydrocarbon (benzo(a)pyrene) hydroxylase (AHH) (EC 1. 14. 14.1) activity and deficient in hypoxanthine guanine phosphoribosyl-transferase (EC 2.4.2.8), and human primary lung carcinoma cell clone noninducible for AHH activity and deficient in thymidine kinase (EC 2.7.1.21) were isolated. The variant lines characterized for AHH inducibility and drug resistant phenotype were utilized to study somatic cell hybrids for the expression of AHH induction by 2,3,7,8-tetrachlorodibenzo-p-dioxin (TCDD). In two hybrids AHH activity was not expressed. In view of these results we conclude that aryl hydrocarbon hydroxylase activity is suppressed in AHH noninducible human lung carcinoma x AHH inducible mouse hepatoma cell hybrids.     

Genetics of aryl hydrocarbon hydroxylase induction in mice: Response of the lung to cigarette smoke and 3-methylcholanthrene

When mice from different inbred strains are injected intraperitoneally with 3-methylcholanthrene (MC), the activity of aryl hydrocarbon hydroxylase (AHH) rapidly increases in livers of some strains but not others. AHH plays a role in the metabolism of polycyclic hydrocarbons. Alleles at a small number of loci account for most of the variation in inducibility of hepatic AHH among mice, when MC is used as the inducing agent. Cigarette smoke is a common source of carcinogenic polycyclic hydrocarbons in the environment. Since some of the hydrocarbons in cigarette smoke are metabolized by AHH, the activity of AHH in tissues may affect the carcinogenicity of smoke in those tissues. The purpose of these experiments was to see whether induction of AHH in lung in response to cigarette smoke is regulated by the same genes that regulate induction of AHH in liver in response to MC. Mouse strains AKR/J and C57L/J and six recombinant inbred (RI) lines derived from them were tested for the response of AHH in lung and liver to parenteral MC or inhalation of cigarette smoke. Inducibility (the ratio of MC-induced AHH activities to basal AHH activities) in liver from MC-treated RI lines is bimodal and compatible with Mendelian segregation of genes at a small number of loci. Increased activities of AHH in MC-treated liver are associated with increased ability to metabolize BP and whole smoke condensates to mutagens detected by Salmonella typhimurium TA1538. Inducibility of AHH in lung in response to MC is not bimodal, and no definite conclusion about the number of loci can be made. When actual levels of AHH activity are considered, following the administration of MC as inducing agent, there is a correlation (r=0.89, p<0.01) between AHH levels in liver and lung, suggesting that some genes affecting liver also affect lung. Basal and MC-induced AHH levels in lung are also correlated (r=0.86, p<0.01). Mice with high basal activities have two to threefold higher levels of AHH after MC treatment than do mice with low basal activities. Induction of AHH in pulmonary tissues occurs in all mice after either parenteral MC or smoke inhalation. In contrast to MC treatment, AHH activities in lungs following smoke inhalation are not correlated with AHH levels in liver after MC (r=0.49) and are only weakly correlated with basal (r=0.66, 0.05相似文献   

Aryl hydrocarbon hydroxylase induction in mouse liver cells--relationship to position in the cell cycle

The inducibility of aryl hydrocarbon hydroxylase (AHH) by benzo[a]-pyrene (BaP) has been studied in synchronously grown cultures of mouse liver cells. These cells (NMuLi cl 8) have low basal levels of AHH which can be induced greater than 100-fold by BaP. Cells were synchronized in G1(G0) by serum starvation and in S by release from serum starvation in combination with excess thymidine. When released from G1(G0) by replating at lower cell density in fresh medium with 20% serum, cells began entering S with a lag of 12 h. Addition of BaP (1 microgram/ml) 8 h before serum stimulation, at the time of stimulation or 7.5 h after stimulation all gave similar induction kinetics: the AHH activity peaked as the cells began entering S regardless of when the BaP was added. Cells blocked in various parts of S by excess thymidine were inducible for AHH activity as efficiently as cells moving through S and into G2. These results indicate that the inducibility of AHH is greater when cells are actively proliferating and may be a contributing factor to why growing cells are more sensitive to mutagenesis and transformation than quiescent cells.     

Carcinogen mmetabolism and DNA adducts in human lung tissues as affected by tobacco smoking or metabolic phenotype: a case-control study on lung cancer patients

Individual variations in activity of pulmonary enzymes that metabolize tobacco-derived carcinogens may affect an individual's cancer risk from cigarette smoking. To investigate whether some of these enzymes (e.g., cytochrome P450IA-related) can serve as markers for carcinogen-induced DNA damage accumulating in the lungs of smokers, non-tumorous lung tissue specimens were taken during surgery from middle-aged men with either lung cancer (n = 54) or non-neoplastic lung disease (n = 20). Phase I (AHH, ECDE) and phase II (EH, UDPGT, GST) enzyme activities, glutathione and malondialdehyde contents were determined in lung parenchyma and/or bronchial tissues; some samples were analyzed for DNA adducts, using ³²P-postlabeling.

Data analysis of subsets or the whole group of patients yielded the following results. (1) Phase I and II drug-metabolizing enzyme (AHH, EH, UDPGT, GST) activities in histologically normal surgical specimens of lung parenchyma were correlated with the respective enzyme activities in bronchial tissues of the same subject. (2) In lung parenchyma, enzyme (AHH, ECDE, EH, UDPGT) activities were significantly and positively related to each other, implying a similar regulatory control of their expression. (3) Mean activities of pulmonary enzymes (AHH, ECDE) were significantly (2- and 7-fold, respectively) higher in lung cancer patients who had smoked within 30 days before surgery (except GST, which was depressed) than in cancer-free subjects with a similar smoking history. (4) In the cancer patients, the time required for AHH, EH and UDPGT activities to return to the level found in non-smoking subjects was several weeks. (5) Bronchial tree and peripheral lung parenchyma preparations exhibited a poor efficiency in activating promutagens to bacterial mutagens in Salmonella. However, they decreased the mutagenicity of several direct-acting mutagens, an effect which was more pronounced in tissue from recent smokers. GSH concentration and GST activity were positively correlated with mutagen inactivation in the same sample. (6) In recent smokers, AHH activity in lung parenchyma was positively correlated with the level of tobacco smoke-derived DNA adducts. (7) Pulmonary AHH and EH activity had prognostic value in tobacco-related lung cancer patients. (8) An enhanced level of pro-oxidant state in the lungs was associated with recent cigarette smoking. Malondialdehyde level in lung parenchyma was associated with the degree of small airway obstruction, suggesting a common free radical-mediated pathway for both lung cancer induction and small airway obstruction.

These results demonstrate the pronounced effect of recent cigarette smoke exposure on pulmonary xenobiotic metabolism and lipid peroxidation and lend further support to the hypothesis that the inducibility of pulmonary AHH activity (cytochrome P450IA1 levels) in tobacco smokers is associated with lung cancer risk. Results on DNA adducts in smokers' lung tissue may help to explain why a certain metabolic phenotype accumulates more DNA damage in lung cells.     

Ah receptor for 2,3,7,8-tetrachlorodibenzo-p-dioxin: ontogeny in chick embryo liver

Aryl hydrocarbon hydroxylase (AHH, cytochrome P1-450) is induced in chick liver very early during embryonic development if embryos are treated with 3-methylcholanthrene-type compounds such as 3,4,3'4'-tetrachlorobiphenyl. In mammals, AHH induction is known to be mediated by the Ah receptor. Liver from embryonic and newly hatched chicks was found to contain a cytosolic receptor for 2,3,7,8-tetrachlorodibenzo-p-dioxin (TCDD) which has properties that are very similar to properties of the Ah receptor previously characterized in mammalian tissues. In chick embryo liver, cytosolic binding sites for TCDD were of high affinity (Kd for [3-H]-TCDD = 0.2 nM) and were specific for 3-methylcholanthrene-type inducers. The specific binding component sedimented at about 9S on sucrose density gradients prepared at low ionic strength. A high level of Ah receptor was detected in chick embryo liver by the fifth day of incubation (5 DI); this is at least 24 hours prior to the onset of AHH inducibility. The Ah receptor concentration increased from 5 DI to 8 DI, the period when chick liver is undergoing early morphological differentiation. After 8 DI, Ah receptor levels dropped substantially and remained low into the posthatching period. In contrast, AHH inducibility was high by 7 DI and remained high throughout embryonic development and into the posthatching period. The discrepancy between Ah receptor levels and the degree of AHH inducibility suggests that only a small fraction of the Ah receptor population is required for maximal AHH induction.     

Aryl hydrocarbon hydroxylase activity in pulmonary alveolar macrophages and lymphocytes from lung cancer and noncancer patients: A correlation with family histories of cancer

Aryl hydrocarbon hydroxylase (AHH) activity was measured in pulmonary alveolar macrophages (PAMs) and peripheral blood lymphocytes from cigarette smokers with and without primary lung cancer. Frequency distribution analysis of AHH induction ratios for the two groups revealed an increased number of individuals in the lung cancer patient group with high lymphocyte induction values (P less than 0.05). A similar increase was not shown for high-PAM AHH values in lung cancer patients (P greater than 0.2). When individual PAM and lymphocyte AHH values were compared between noncancer and lung cancer patients, a positive correlation was observed for noncancer patients (r=0.195, P less than 0.001), but no correlation of these values was noted for lung cancer patients. The lung cancer patients were divided into three subgroups of patients showing (I) high PAM and low lymphocyte AHH levels, (II) low PAM and low lymphocyte AHH levels, and (III) low PAM and high lymphocyte AHH levels. When the incidence of family history of cancer was compared for these subgroups, no family cancer history was recorded for persons in subgroup II; however, individuals in subgroups I and III presented family cancer history incidence of 9.5% and 39.3%, respectively. Patients in group III averaged 6 years younger than those in group I. These data suggest that familial factors may be identified among lung cancer patients and that these factors appear to associate as either a cause of an effect with the capacity of pulmonary alveolar macrophages and lymphocytes to be induced for AHH. The data support the hypothesis that high AHH values may be characteristic of lung cancer patients but show that enzyme values determined from a single tissue, either PAMs or lymphocytes, may not be appropriate for showing whether high AHH inducibility is correlated with lung cancer.     

Genetics of aryl hydrocarbon hydroxylase induction in mice: Additive inheritance in crosses between C3H/HeJ and DBA/2J

In certain strains of inbred mice, hepatic aryl hydrocarbon hydroxylase (AHH) activity is induced by parenteral injection of the carcinogen 3-methylchol-anthrene, whereas in other strains AHH activity is not induced. In most genetic crosses between inducible and noninducible strains, inducibility segregates as a single autosomal dominant gene. However, in crosses between strains C3H/HeJ (inducible) and DBA/2J (noninducible), inducibility segregates as a single gene and in an additive manner, with the inducibility of hybrid animals falling between that of the inducible parent and that of the noninducible parent. In crosses between strains C57BL/6J (inducible) and DBA/2J (the same noninducible parent crossed to C3H/HeJ), inducibility segregates as a dominant gene. This suggests that the genes responsible for inducibility of AHH in strains C3H/HeJ and C57BL/6J are not identical. Whether they represent different alleles at the same genetic locus or genes at different loci has not been determined.Formerly Postdoctoral Fellow of the Roche Institute of Molecular Biology.Recipient of Research Career Development Award 1 K4 AM CA 70, 186 from the National Institute of Arthritis and Metabolic Diseases. Formerly Chief, Mammalian Genetics Section, Roche Institute of Molecular Biology.     

Ah receptor for 2,3,7,8- tetrachlorodibenzo-p-Dioxin: Ontogeny in chick embryo liver

Aryl hydrocarbon hydroxylase (AHH, cytochrome P₁-450) is induced in chick liver very early during embryonic development if embryos are treated with 3-methylcholanthrene–type compounds such as 3,4,3′4′-tetrachlorobiphenyl. In mammals, AHH induction is known to be mediated by the Ah receptor. Liver from embryonic and newly hatched chicks was found to contain a cytosolic receptor for 2,3,7,8-tetrachlorodibenzo-p-dioxin (TCDD) which has properties that are very similar to properties of the Ah receptor previously characterized in mammalian tissues. In chick embryo liver, cytosolic binding sites for TCDD were of high affinity (K_d for [3-H]-TCDD = 0.2 nM) and were specific for 3-methylcholanthrene–type inducers. The specific binding component sedimented at about 9S on sucrose density gradients prepared at low ionic strength. A high level of Ah receptor was detected in chick embryo liver by the fifth day of incubation (5 DI); this is at least 24 hours prior to the onset of AHH inducibility. The Ah receptor concentration increased from 5 DI to 8 DI, the period when chick liver is undergoing early morphological differentiation. After 8 DI, Ah receptor levels dropped substantially and remained low into the posthatching period. In contrast, AHH inducibility was high by 7 DI and remained high throughout embryonic development and into the posthatching period. The discrepancy between Ah receptor levels and the degree of AHH inducibility suggests that only a small fraction of the Ah receptor population is required for maximal AHH induction.     

The genetics of aryl hydrocarbon hydroxylase induction in mice: A single gene difference between C57BL/6J and DBA/2J

Twenty-one inbred strains of mice were surveyed for inducibility of hepatic aryl hydrocarbon hydroxylase (AHH) activity by the carcinogen 3-methylcholanthrene (MC). In 11 strains given MC, AHH activity increased 1.3- to 5-fold (inducible), whereas ten strains responded with a less than 0.5-fold increase (noninducible). Neither the inducible nor the noninducible class was homogeneous, and in each considerable variation was found in both the basal activity of AHH and the response to MC. Strains DBA/2J and C57BL/6J were chosen to represent the noninducible and inducible classes, respectively. In the crosses (C57BL/6 × DBA/2)F₁ × DBA/2 and (C57BL/6 × DBA/2)F₂, inducibility segregated as a single autosomal dominant gene. The gene symbols Ahh ⁱ and Ahh ⁿ are proposed for the alleles present in C57BL/6J and DBA/2J, respectively. No genetic linkage was found between the Ahh locus and the following loci: b, d, Es-1, Es-3, Gpd-1, Hbb, Id-1, Pgm-1, and sex. Some implications of this work in the study of mammalian enzyme induction and chemically induced carcinogenesis are discussed. There is a positive correlation between AHH inducibility and the development of an inflammatory response to the topical application of the carcinogen 7,12-dimethylbenzanthracene.     

Species and tissue distribution of the 4S carcinogen binding protein and its possible role in cytochrome P-450 induction

A carcinogen binding protein (CBP) that is implicated in controlling the expression of rat cytochrome P-450c which is closely associated with aryl hydrocarbon hydroxylase (AHH) was examined in hepatic and extrahepatic tissues of the neonatal and adult New Zealand White (NZW) rabbits, the hepatic tissue of the BALB/cJ and DBA/2J mice, Brown Norway rat, Golden Syrian hamster and Hartley guinea pig. These animals and tissues were examined in order to determine whether there was a correlation of CBP levels and the reported presence or absence of inducibility of AHH in these tissues. The CBP was found in hepatic and extrahepatic tissue of the NZW rabbit and the hepatic tissues of all animals except the Hartley guinea pig. The Hartley guinea pig may provide a useful animal with which to further examine the role of CBP in cytochrome induction. Since the CBP is not a tissue specific protein and because it is found in both neonatal and adult NZW rabbit tissue, the data suggests that the CBP is not the limiting factor in the tissue specific induction of cytochromes nor in developmentally controlled induction of cytochromes previously reported in the rabbit.     

Effects of polyhalogenated aromatic hydrocarbons on benzo(a)pyrene hydroxylase activity in the intestine and liver

Aryl hydrocarbon hydroxylase (AHH) has been measured as benzo(a)pyrene hydroxylase in the intestine and liver of rats and mice treated with a single dose of different polyhalogenated aromatic hydrocarbons. Maximal stimulation of liver AHH activity is reached with a dose of 2, 3, 7, 8-tetrachlorodibenzo-p-dioxin (TCDD) half as great as that necessary for maximal stimulation of the intestine. The duration of the effect of TCDD on intestinal AHH differs from the constant increase that occurs in the liver. Although the magnitude of the stimulation by 1,1,1-trichloro-2,2-bis (p-chlorophenyl) ethane (DDT) is less than that of TCDD, the qualitative changes in intestinal and liver AHH are similar. The changes in activity of intestinal and hepatic AHH were not directly correlated in the tissues of rats treated with several other polyhalogenated aromatic hydrocarbons. Liver and intestinal AHH activity were affected differently by fasting. These results suggest that AHH activity in the intestine and liver has different control mechanisms.     

Induction of P-450 isoenzyme activities in Syrian golden hamster liver compared to rat liver as probed by the rate of 7-alkoxyresorufin-O-dealkylation

The activities of 7-ethoxyresorufin-O-deethylase (EROD), 7-pentoxyresorufin-O-deethylase (PROD), 7-ethoxycoumarin-O-deethylase (ECOD) and aromatic hydrocarbon hydroxylase (AHH) were measured in hepatic microsomes from male and female Wistar rats and Syrian golden hamsters in order to probe the basal activity and the inducibility by phenobarbital (PB) and 3-methylcholanthrene (MC) of different P-450 isoenzymes. The basal activities of EROD and ECOD, but not PROD and AHH, were higher in male hamsters than in male rats. No sex-related difference in enzyme activities was observed with hamsters, whereas male rats had a higher ECOD and AHH activity than female rats. Induction by PB led to a 450-fold and 250-fold increase in PROD activity in male and female rat liver microsomes, respectively, while MC had a more pronounced inductive effect on EROD activity in this species. In hamsters, EROD activity was induced by MC but not by PB. Unexpectedly PROD activity in male and female hamster liver microsomes was only moderately induced by PB, the extent being lower than on induction by MC. Therefore, the activity of PROD, which is useful as a specific enzymatic assay for P-450 IIB in the rat liver, cannot be used to probe PB-like inducers in the hamster liver.     

Aryl hydrocarbon hydroxylase activity in F-344 rats subchronically exposed to benzo(a)pyrene and fluoranthene through diet

In order to investigate the relationship between aryl hydrocarbon hydroxylase (AHH) activity and exposure to benzo[a]pyrene [B(a)p] and fluoranthene (FLA), AHH activities in liver tissues of male and female F-344 rats were determined. Based on a range-finding study, doses of 0, 5, 50, and 100 mg/kg B(a)p or 0, 150, 750, and 1500 mg/kg FLA were administered in the animal diet over a 90-day period. After dosing, animals were sacrificed, liver tissues were removed, and microsomes were isolated. AHH activities were determined by reverse-phase HPLC coupled with fluorescence detection using 3-hydroxy B(a)p, and trans-2,3-dihydroxy-1,10-epoxy-1,2,3,10b tetrahydrofluoranthene as the standards. A dose-dependent increase in enzyme activity was observed with increased B(a)p or FLA exposure in both males and females. Our results also demonstrate that B(a)p-exposed females possess a higher AHH activity than males, but there is no significant sex difference with regard to enzyme activity in the case of FLA at higher doses. Overall, our findings suggest that long-term exposure to the parent compound results in elevated levels of AHH activity, which may contribute to the formation of toxic reactive metabolites and subsequent symptoms in target organs.