Localization of CYP1A1 mRNA in human lung by in situ hybridization: comparison with immunohistochemical findings

Bioluminescence imaging of Cyp1a1-luciferase reporter mice demonstrates prolonged activation of the aryl hydrocarbon receptor in the lung

Aryl hydrocarbon receptor (AHR) signalling integrates biological processes that sense and respond to environmental, dietary, and metabolic challenges to ensure tissue homeostasis. AHR is a transcription factor that is inactive in the cytosol but upon encounter with ligand translocates to the nucleus and drives the expression of AHR targets, including genes of the cytochrome P4501 family of enzymes such as Cyp1a1. To dynamically visualise AHR activity in vivo, we generated reporter mice in which firefly luciferase (Fluc) was non-disruptively targeted into the endogenous Cyp1a1 locus. Exposure of these animals to FICZ, 3-MC or to dietary I3C induced strong bioluminescence signal and Cyp1a1 expression in many organs including liver, lung and intestine. Longitudinal studies revealed that AHR activity was surprisingly long-lived in the lung, with sustained Cyp1a1 expression evident in discrete populations of cells including columnar epithelia around bronchioles. Our data link diet to lung physiology and also reveal the power of bespoke Cyp1a1-Fluc reporters to longitudinally monitor AHR activity in vivo.

Genic-intergenic polymorphisms of CYP1A genes and their clinical impact

The humancytochrome P450 1A (CYP1A) subfamily genes, CYP1A1 and CYP1A2, encoding monooxygenases are critically involved in biotransformation of key endogenous substrates (estradiol, arachidonic acid, cholesterol) and exogenous compounds (smoke constituents, carcinogens, caffeine, therapeutic drugs). This suggests their significant involvement in multiple biological pathways with a primary role of maintaining endogenous homeostasis and xenobiotic detoxification. Large interindividual variability exist in CYP1A gene expression and/or catalytic activity of the enzyme, which is primarily due to the existence of polymorphic alleles which encode them. These polymorphisms (mainly single nucleotide polymorphisms, SNPs) have been extensively studied as susceptibility factors in a spectrum of clinical phenotypes. An in-depth understanding of the effects of polymorphic CYP1A genes on the differential metabolic activity and the resulting biological pathways is needed to explain the clinical implications of CYP1A polymorphisms. The present review is intended to provide an integrated understanding of CYP1A metabolic activity with unique substrate specificity and their involvement in physiological and pathophysiological roles. The article further emphasizes on the impact of widely studied CYP1A1 and CYP1A2 SNPs and their complex interaction with non-genetic factors like smoking and caffeine intake on multiple clinical phenotypes. Finally, we attempted to discuss the alterations in metabolism/physiology concerning the polymorphic CYP1A genes, which may underlie the reported clinical associations. This knowledge may provide insights into the disease pathogenesis, risk stratification, response to therapy and potential drug targets for individuals with certain CYP1A genotypes.

Expression of xenobiotic metabolising enzymes in lungs of horses with or without histological evidence of lower airway inflammation

Mild, moderate and severe equine asthma is a problem for equine welfare. The aetiology of the disease is not known in detail but is likely multi‐factorial. One important factor may be inhaled dust which carries harmful substances which may be bioactivated and thus can lead to local inflammation in the airways. The aim of this study was to investigate gene expression and protein localisation of cytochrome P450 (CYP) enzymes, superoxide dismutase and glutathione‐S‐transferases (GST) involved in bioactivation and detoxification of harmful substances in lungs of horses with or without histological evidence of lower airway inflammation. Significantly lower gene expression of CYP2A13 and GSTM1 was observed in lungs from horses with histological evidence of lower airway inflammation compared with horses without. A higher expression, although not significant, was found for CYP1A1 in horses with histological evidence of lower airway inflammation. There were no differences in gene expression of GSTP1 and SOD3. The proteins were localised in the respiratory epithelium which is of relevance as a defence to local exposure of inhaled harmful substances. In conclusion, our study reports differential gene expression of enzymes involved in bioactivation and detoxification of foreign substances in the lungs of horses with histological evidence of lower airway inflammation compared with horses without.

Xenobiotica-metabolizing enzymes in the lung of experimental animals, man and in human lung models

The xenobiotic metabolism in the lung, an organ of first entry of xenobiotics into the organism, is crucial for inhaled compounds entering this organ intentionally (e.g. drugs) and unintentionally (e.g. work place and environmental compounds). Additionally, local metabolism by enzymes preferentially or exclusively occurring in the lung is important for favorable or toxic effects of xenobiotics entering the organism also by routes other than by inhalation. The data collected in this review show that generally activities of cytochromes P450 are low in the lung of all investigated species and in vitro models. Other oxidoreductases may turn out to be more important, but are largely not investigated. Phase II enzymes are generally much higher with the exception of UGT glucuronosyltransferases which are generally very low. Insofar as data are available the xenobiotic metabolism in the lung of monkeys comes closed to that in the human lung; however, very few data are available for this comparison. Second best rate the mouse and rat lung, followed by the rabbit. Of the human in vitro model primary cells in culture, such as alveolar macrophages and alveolar type II cells as well as the A549 cell line appear quite acceptable. However, (1) this generalization represents a temporary oversimplification born from the lack of more comparable data; (2) the relative suitability of individual species/models is different for different enzymes; (3) when more data become available, the conclusions derived from these comparisons quite possibly may change.

Health risk assessment for air pollutants: alterations in lung and cardiac gene expression in mice exposed to Milano winter fine particulate matter (PM2.5)

Oxidative stress, pulmonary and systemic inflammation, endothelial cell dysfunction, atherosclerosis and cardiac autonomic dysfunction have been linked to urban particulate matter exposure. The chemical composition of airborne pollutants in Milano is similar to those of other European cities though with a higher PM2.5 fraction. Milano winter fine particles (PM2.5win) are characterized by the presence of nitrate, organic carbon fraction, with high amount of polycyclic aromatic hydrocarbons and elements such as Pb, Al, Zn, V, Fe, Cr and others, with a negligible endotoxin presence. In BALB/c mice, we examined, at biochemical and transcriptomic levels, the adverse effects of repeated Milano PM2.5win exposure in lung and heart. We found that ET-1, Hsp70, Cyp1A1, Cyp1B1 and Hsp-70, HO-1, MPO respectively increased within lung and heart of PM2.5win-treated mice. The PM2.5win exposure had a strong impact on global gene expression of heart tissue (181 up-regulated and 178 down-regulated genes) but a lesser impact on lung tissue (14 up-regulated genes and 43 down-regulated genes). Focusing on modulated genes, in lung we found two- to three-fold changes of those genes related to polycyclic aromatic hydrocarbons exposure and calcium signalling. Within heart the most striking aspect is the twofold to threefold increase in collagen and laminin related genes as well as in genes involved in calcium signaling. The current study extends our previous findings, showing that repeated instillations of PM2.5win trigger systemic adverse effects. PM2.5win thus likely poses an acute threat primarily to susceptible people, such as the elderly and those with unrecognized coronary artery or structural heart disease. The study of genomic responses will improve understanding of disease mechanisms and enable future clinical testing of interventions against the toxic effects of air pollutant.

Genotoxic bioactivation of constituents of a diesel exhaust particle extract by the human lung

The ability of the human lung to catalyze genotoxic bioactivation of constituents of diesel exhaust particle (DEP) extract (DEPE) and the identity of the lung enzymes involved in the bioactivation were investigated using human lung tissues obtained from surgical resections. Genotoxicity was determined by lung S9-catalyzed mutagenicity of DEPE constituents to Salmonella typhimurium TA98NR in the Ames test and by DEPE-induced pneumocyte DNA damage response as determined by γH2Ax expression in ex vivo tissues. S9 was prepared from lung explants treated ex vivo with either DEPE to induce pulmonary enzymes (DEPE-S9) or vehicle only (CON-S9). TA98NR served as the tester strain for the purpose of enhancing and minimizing the contribution of lung S9 and Salmonella, respectively, to DEPE bioactivation. DEPE-S9 was 2.2-fold more active than CON-S9 or rat liver S9 in DEPE bioactivation and the bioactivation was inhibited 58, 45, 22, and 16% by α-naphthoflavone, dicumarol, ketoconazole, and ticlopidine, respectively. Alveolar S9 was less active than bronchioalveolar S9 in DEPE bioactivation. DEPE and diesel exhaust particles (DEP) induced γ-pH2Ax expression in pulmonary cells. Pulmonary CYP1A1 and NQO1 were induced by DEPE treatment, with the constitutive and induced CYP1A1 distributed throughout all peripheral lung regions, whereas NQO1 was limited in distribution to bronchiolar epithelium. The results show that the human lung is highly active in catalyzing genotoxic bioactivation of diesel emission constituents and that CYP1A and NQO1 play major roles in the reaction. The findings underscore the usefulness of human lung tissues in studies of the pneumotoxicity potential of chemicals to humans.

Haplotypes in the 5'-untranslated region of the CYP1A2 gene are inversely associated with lung cancer risk but do not correlate with caffeine metabolism

In this study, we analyzed the influence of CYP1A2 genetic variation and enzyme activity on lung cancer risk in a high-incidence area. A total of 95 lung cancer patients and 196 controls were genotyped for the -3860G/A, -3113A/G, -2467T/delT, -739T/G, and -163C/A polymorphisms in the 5'-untranslated region of the gene. In addition, a subset of 70 patients and 115 controls were phenotyped by high-performance liquid chromatography determination of the caffeine metabolic ratio (CMR). The -2467T/delT polymorphism and the CYP1A2*1V haplotype (-163C>A, -2467T>delT) were inversely associated with lung cancer risk (odds ratio [OR] = 0.47 [0.2-0.9]; P = 0.02 and OR = 0.13 [0.02-1.0]; P = 0.04; respectively). In addition, the CYP*1A/*1V and *1F (-163C>A)/*1D (-163C>A, -2467T>delT) diplotypes were absent in the patients group, whereas accounting for 7.1% (P = 0.017) and 5.6% (P = 0.037) of controls, respectively. Mean CMR was significantly higher in patients than in controls (10.50 ± 17.31 vs. 6.52 ± 6.26, P = 0.01) but regression analyses did not yield significant ORs for the association with lung cancer risk. Similarly, no significant correlations were found between any genetic variant and enzyme activity. Several CYP1A2 haplotypes and diplotypes containing the -2467delT variant were associated with lower lung cancer risk; however, they did not correlate with significant changes in CYP1A2 metabolic activity toward caffeine.

CYP1A1*2A polymorphism as a predictor of clinical outcome in advanced lung cancer patients treated with EGFR-TKI and its combined effects with EGFR intron 1 (CA)n polymorphism

BACKGROUND

Mutations in the epidermal growth factor receptor (EGFR) have been confirmed as predictors of efficacy for EGFR-tyrosine kinase inhibitors (TKIs). We investigated whether polymorphisms of the EGFR and cytochrome P450, family 1, member A1 (CYP1A1) genes were associated with clinical outcome in NSCLC patients treated with EGFR-TKI.

METHODS

Genotypes for the intron 1 (CA)n repeat and R497K polymorphisms in the EGFR gene and the *2A (3801 T→C) and *2C (2455 A→G) polymorphisms in CYP1A1 gene were evaluated in 115 NSCLC patients by PCR-RFLP and DNA sequencing. Genetic polymorphisms were correlated with clinical outcomes of EGFR-TKIs. From a subgroup of patients whose tumour tissues were available, associations between somatic EGFR mutations, EGFR expression, and genomic polymorphisms were also analysed.

RESULTS

EGFR intron 1 (CA)n and CYP1A1*2A polymorphisms were independent predictive factors (p=0.046, p=0.011, respectively) and the latter was also a prognostic factor (p=0.001) for patients treated with EGFR-TKIs. We also observed a strong synergistic effect from two genotypes. Specifically, patients with both the T/T allele of the CYP1A1 gene and shorter intron 1 CA repeats (≤ 16 CA) of the EGFR gene showed an improved response (p=0.002) compared with patients with the T/C or C/C allele and longer intron 1 CA repeats (both alleles >16 CA). In contrast, for R497K and CYP1A1*2C, no relationship was observed with clinical outcome for patients treated with EGFR-TKIs (p=0.573; p=0.629, respectively). Both SNPs in the CYP1A1 gene showed a correlation with EGFR somatic mutations.

CONCLUSIONS

The findings of this study suggest that the CYP1A1*2A polymorphism is a predictor for clinical outcome in NSCLC patients treated with EGFR-TKI therapy, and combining analysis of both CYP1A1*2A and EGFR intron 1 (CA)n polymorphisms may be useful for predicting treatment outcome in NSCLC patients treated with EGFR-TKIs.

Cytochrome P450-mediated pulmonary metabolism of carcinogens: regulation and cross-talk in lung carcinogenesis

Lung cancer is strongly associated with exogenous risk factors, in particular tobacco smoking and asbestos exposure. New research data are accumulating about the regulation of the metabolism of tobacco carcinogens and the metabolic response to oxidative stress. These data provide mechanistic details about why well known risk factors cause lung cancer. The purpose of this review is to evaluate the present knowledge of the role of cytochrome P450 (CYP) enzymes in the metabolism of tobacco carcinogens and associations with tobacco and asbestos carcinogenesis. Major emphasis is placed on human data and regulatory pathways involved in CYP regulation and lung carcinogenesis. The most exciting new research findings concern cross-talk of the CYP-regulating aryl hydrocarbon receptor with other transcription factors, such as nuclear factor-erythroid 2-related factor 2, involved in the regulation of xenobiotic metabolism and antioxidant enzymes. This cross-talk between transcription factors may provide mechanistic evidence for clinically relevant issues, such as differences in lung cancers between men and women and the synergism between tobacco and asbestos as lung carcinogens.

Mouse lung CYP1A1 catalyzes the metabolic activation of 2-amino-1-methyl-6-phenylimidazo[4,5-b]pyridine (PhIP)

2-Amino-1-methyl-6-phenylimidazo[4,5-b]pyridine (PhIP) carcinogenesis is initiated by N(2)-hydroxylation, mediated by several cytochromes P450, including CYP1A1. However, the role of CYP1A1 in PhIP metabolic activation in vivo is unclear. In this study, Cyp1a1-null and wild-type (WT) mice were used to investigate the potential role of CYP1A1 in PhIP metabolic activation in vivo. PhIP N(2)-hydroxylation was actively catalyzed by lung homogenates of WT mice, at a rate of 14.9 +/- 5.0 pmol/min/g tissue, but <1 pmol/min/g tissue in stomach and small intestine, and almost undetectable in mammary gland and colon. PhIP N(2)-hydroxylation catalyzed by lung homogenates of Cyp1a1-null mice was approximately 10-fold lower than that of WT mice. In contrast, PhIP N(2)-hydroxylation activity in lung homogenates of Cyp1a2-null versus WT mice was not decreased. Pretreatment with 2,3,7,8-tetrachlorodibenzo-p-dioxin increased lung Cyp1a1 mRNA and lung homogenate PhIP N(2)-hydroxylase activity approximately 50-fold in WT mice, where the activity was substantially inhibited (70%) by monoclonal antibodies against CYP1A1. In vivo, 30 min after oral treatment with PhIP, PhIP levels in lung were similar to those in liver. After a single dose of 0.1 mg/kg [(14)C]PhIP, lung PhIP-DNA adduct levels in Cyp1a1-null mice, but not in Cyp1a2-null mice, were significantly lower (P = 0.0028) than in WT mice. These results reveal that mouse lung has basal and inducible PhIP N(2)-hydroxylase activity predominantly catalyzed by CYP1A1. Because of the high inducibility of human CYP1A1, especially in cigarette smokers, the role of lung CYP1A1 in PhIP carcinogenesis should be considered. (237 words).

CYP2A13 in human respiratory tissues and lung cancers: an immunohistochemical study with a new peptide-specific antibody

Human cytochrome P450 2A13 (CYP2A13) is highly efficient in the metabolic activation of a tobacco-specific carcinogen, 4-(methylnitrosamino)-1-(3-pyridyl)-1-butanone (NNK), and another potent carcinogen, aflatoxin B1 (AFB1). Although previous studies demonstrated that CYP2A13 mRNA is predominantly expressed in human respiratory tissues, expression of CYP2A13 protein in these tissues and the involved cell types have not been determined because of the lack of CYP2A13-specific antibodies. To explore the toxicological and physiological function of CYP2A13, it is important to understand the tissue/cellular distribution of CYP2A13 protein. In this study, we generated a peptide-specific antibody against human CYP2A13 and demonstrated by immunoblot analysis that this antibody does not cross-react with heterologously expressed human CYP2A6 and mouse CYP2A5 proteins, both sharing a high degree of amino acid sequence similarity with CYP2A13. Nor does the antibody cross-react with heterologously expressed human CYP3A4, CYP2S1, or any of the cytochrome P450 enzymes present in the human liver microsomes. Using this highly specific antibody for immunohistochemical staining, we detected a high level of CYP2A13 protein expression in the epithelial cells of human bronchus and trachea, but a rare distribution in the alveolar cells. There was little expression of CYP2A13 protein in different types of lung cancers. In consideration of the high efficiency of CYP2A13 in NNK metabolic activation, our result is consistent with the reported observations that most smoking-related human lung cancers are bronchogenic and supports that CYP2A13-catalyzed in situ activation may play a critical role in human lung carcinogenesis related to NNK and AFB1 exposure.

Preferential induction of CYP1A1 and CYP1B1 in CCSP-positive cells

Both benzo[a]pyrene (BaP) and 2,3,7,8-tetrachlorodibenzo-p-dioxin (TCDD) are potent ligands of aryl hydrocarbon receptors (AhR). Although animal studies indicate that both compounds induce pathological changes in the peripheral lung, the specific cell type involved remains unclear. Clara cells, expressing Clara cell specific protein (CCSP) and abundant in cytochrome P450, are nonciliated bronchiolar epithelial cells in the peripheral lung. Here we explore the hypothesis that CCSP-positive Clara cells are highly responsive to AhR ligands and are the primary cell type involved in BaP- and TCDD-induced toxicities. The responsiveness to AhR ligands was evaluated by measuring the respective mRNA and protein levels of cytochrome P450 1A1 (CYP1A1) and 1B1 (CYP1B1) using real-time RT-PCR and immunocytochemistry assays. Two in vitro models were used: primary cultures of human small airway epithelial (SAE) cells and rat lung slice cultures. In the presence of calcium, human SAE cells differentiated into CCSP-positive cells. BaP- and TCDD-induced mRNA and protein levels of CYP1A1 and CYP1B1 levels were significantly elevated in CCSP-positive cell cultures. Similarly, AhR mRNA and protein levels were increased in CCSP-positive cell cultures, as determined by real-time RT-PCR and Western blot analysis. When rat lung slice cultures were treated with BaP or TCDD for 24 h, CYP1A1 and CYP1B1 proteins were strongly induced in Clara cells. These results indicate that, in the peripheral lung of both rats and humans, CCSP-positive cells (Clara cells) may be more sensitive to AhR ligands than other cell types.

CYP2S1: A short review

A new member of the cytochrome P450 superfamily, CYP2S1, has recently been identified in human and mouse. In this paper, we review the data currently available for CYP2S1. The human CYP2S1 gene is located in chromosome 19q13.2 within a cluster including CYP2 family members CYP2A6, CYP2A13, CYP2B6, and CYP2F1. These genes also show the highest homology to the human CYP2S1. The gene has recently been found to harbor genetic polymorphism. CYP2S1 is inducible by dioxin, the induction being mediated by the Aryl Hydrocarbon Receptor (AHR) and Aryl Hydrocarbon Nuclear Translocator (ARNT) in a manner typical for CYP1 family members. In line with this, CYP2S1 has been shown to be inducible by coal tar, an abundant source of PAHs, and it was recently reported to metabolize naphthalene. This points to the involvement of CYP2S1 in the metabolism of toxic and carcinogenic compounds, similar to other dioxin-inducible CYPs. CYP2S1 is expressed in epithelial cells of a wide variety of extrahepatic tissues. The highest expression levels have been observed in the epithelial tissues frequently exposed to xenobiotics, e.g., the respiratory, gastrointestinal, and urinary tracts, and in the skin. The observed ubiquitous tissue distribution, as well as the expression of CYP2S1 throughout embryogenesis suggest that CYP2S1 is likely to metabolize important endogenous substrates; thus far, retinoic acid has been identified. In conclusion, CYP2S1 exhibits many features of interest for human health and thus warrants further investigation.

Tumor suppressive effects of tocotrienol in vivo and in vitro

Tocotrienols have been reported to have higher biological activities than tocopherols. We investigated the antitumor effect of tocotrienols both in vivo and in vitro. Oral administration of tocotrienols resulted in significant suppression of liver and lung carcinogenesis in mice. In human hepatocellular carcinoma HepG2 cells, delta-tocotrienol exerted more significant antiproliferative effect than alpha-, beta-, and gamma-tocotrienols. delta-Tocotrienol induced apoptosis, and also tended to induce S phase arrest. On the other hand, gene expression analysis showed that delta-tocotrienol increased CYP1A1 gene, a phase I enzyme. Although further study will be necessary to investigate possible adverse effect, the data obtained in present study suggest that tocotrienols could be promising agents for cancer prevention.

Metabolism and bioactivation of toxicants in the lung. The in vitro cellular approach

Lung is a target organ for the toxicity of inhalated compounds. The respiratory tract is frequently exposed to elevated concentrations of these compounds and become the primary target site for toxicity. Occupational, accidental or prolonged exposure to a great variety of chemicals may result in acute or delayed injury to cells of the respiratory tract. Nevertheless, lung has a significant capability of biotransforming such compounds with the aim of reducing its potential toxicity. In some instances, the biotransformation of a given compound can result in the generation of more reactive, and frequently more toxic, metabolites. Indeed, lung tissue is known to activate pro-carcinogens (i.e. polycyclic aromatic hydrocarbons or N-nitrosamines) into more reactive intermediates that easily form DNA adducts. Lungs express several enzymes involved in the metabolising of xenobiotics. Among them, cytochrome P450 enzymes are major players in the oxidative metabolism as well metabolic bioactivation of many organic toxicants, including pro-carcinogens. Xenobiotic-metabolising P450 enzymes are expressed in bronchial and bronchiolar epithelium, Clara cells, type II pneumocytes, and alveolar macrophages Individual CYP isoforms have different patterns of localisation within pulmonary tissue. With the aid of sensitive techniques (i.e. reverse transcriptase-polymerase chain reaction, RT-PCR) it has become possible to detect CYP1A1, CYP1B1, CYP2A6, CYP2B6, CYP2E1 and CYP3A5 mRNAs in lung cells. Less conclusive results have been obtained concerning CYP2Cs, CYP2D6 and CYP3A4. CYP3A5 protein appears to be widely present in all lung samples and is localised in the ciliated and mucous cells of the bronchial wall, bronchial glands, bronchiolar ciliated epithelium and in type I and type II alveolar epithelium. Lung cells also express Phase II enzymes such as epoxide hydrolase, UGT1A (glucuronyl transferase) and GST-P1 (glutathione S-transferase), which largely act as detoxifying enzymes. A key question concerning organ-specific chemical toxicity is whether the actual target has the capacity to activate (or efficiently inactivate) chemicals. Results of several studies indicate that the different xenobiotic-metabolising CYPs, present in the human lung and lung-derived cell lines, likely contribute to in situ activation of pulmonary toxins, among them, pro-carcinogens. Some CYPs, in particular CYP1A, are polymorphic and inducible. Interindividual differences in the expression of these CYPs may explain the different risk of developing lung toxicity (possibly cancer), by agents that require metabolic activation. Few cell lines, principally A549, have been used with variable success as an experimental model for investigating the mechanisms of toxicity. Although RT-PCR analysis has evidenced the presence of the major human pulmonary CYP mRNAs, the measurable P450 specific activities are, however, far below those present in human lungs. Detection of the toxicity elicited by reactive metabolites requires the use of metabolically competent cells; consequently, better performing cells are needed to ensure realistic in vitro prediction of toxicity. Genetic manipulation of lung-derived cells allowing them to re-express key biotransformation enzymes appear to be a promising strategy to improve their functionality and metabolic performance.

Localization of cytochrome P450 CYP2S1 expression in human tissues by in situ hybridization and immunohistochemistry

CYP2S1 is a recently discovered dioxin-inducible member of the cytochrome P450 superfamily. It has been shown to be involved in the metabolism of some aromatic hydrocarbons as well as retinoic acid, suggesting a role in biotransformation of both exogenous and endogenous compounds. In this study, we used mRNA in situ hybridization and immunohistochemistry to investigate the cellular localization of CYP2S1 in various human tissues using tissue microarrays. High expression levels were observed mainly in epithelial cell types, especially in the epithelia frequently exposed to xenobiotics. In the respiratory tract, the expression was strong in nasal cavity, bronchi, and bronchioli, whereas it was low in the alveolar lining cells. Similarly, CYP2S1 was highly expressed in the epithelial cells throughout the gastrointestinal tract. Strong epithelial expression was also observed in uterine cervix, urinary bladder, and skin. In many exocrine glands (e.g., adrenal gland and pancreas), secretory epithelial cells showed moderate to strong expression levels. In the liver, the expression was low. CYP2S1 was highly expressed in epithelial cells that are major targets for carcinogen exposure and common progenitor cells to tumor development. Indeed, we found strong CYP2S1 expression in many tumors of epithelial origin.

Mechanisms in pulmonary toxicology

Specific accumulation and biotransformation of drugs cause cell injury in the lung. Evoked mechanisms are oxidative injury, direct cytotoxic effects, intracellular deposition of phospholipids, and immune reaction. Individual susceptibility can be due to genetically determined metabolic idiosyncrasy or to immune-mediated hypersensitivity.

Overexpression of aryl hydrocarbon receptor in human lung carcinomas

Exposure to polycylic aromatic hydrocarbons (PAH) has been associated with increased risk of lung cancer. Aryl hydrocarbon receptor (AhR) is known to play an essential role in PAH-induced toxicity. The objectives of this study were to identify and evaluate AhR expression in normal human lung tissues and in lung carcinomas. AhR protein and mRNA levels in human lung cell lines were evaluated with immunoblot and quantitative real-time RT-PCR assays, respectively. AhR protein expression was high in cytosol homogenates of adenocarcinoma (AD) cell lines and AhR mRNA levels corresponded well with AhR protein levels in these cell lines. AhR expression in human lung tissues and carcinomas were examined by means of immunohistochemical staining method. In normal lung tissues, immunostaining was found in the cytosol of bronchiolar epithelial cells. AhR immunostaining was more intense in AD than in squamous cell carcinomas. When AhR expression was compared with noral bronchiolar epithelial cells and neoplastic cells in the same specimens, the neoplastic cells, especially those of AD, demonstrated an increased staining. The upregulation of AhR mRNA expression was also demonstrated among 2 of 4 paired tissues with the quantitative real-time RT-PCR assay. Our data indicated that AhR expression was upregulated in lung AD and suggested that AhR and its expression might play an important role in the development of lung AD.

CYP1A1 levels in lung tissue of tobacco smokers and polymorphisms of CYP1A1 and aromatic hydrocarbon receptor

Induction of a polycyclic aromatic hydrocarbon-metabolizing cytochrome P450 isoform CYP1A1 is regulated by aromatic hydrocarbon receptor (AHR). High inducibility of CYP1A1, possibly due to genetic polymorphisms, has been considered to be a risk factor for lung cancer in tobacco smokers. The relationship between low or high pulmonary expression of CYP1A1 and polymorphic genotypes of CYP1A1 and AHR was investigated in 73 active smokers. CYP1A1 expression was determined in surgical lung samples by measuring ethoxyresorufin O-deethylase (EROD) activity and by immunostaining for CYP1A1 protein. The most common allelic variants of CYP1A1 and AHR in Finns, i.e. the MspI variant (CYP1A1*2A), I462V variant (CYP1A1*2B), and -459C to T variant of CYP1A1 and the R554K variant (AHR*2) of AHR were studied using polymerase chain reaction based methods. EROD activity correlated positively with the daily cigarette consumption (r = 0.45). There was additional variation in EROD activity independent of the amount of smoking e.g. among those who smoked one pack per day until the day of operation, EROD activity ranged from 4-142 (median 48) pmol/min/mg. The frequencies of the MspI, 462V, and -459T variant alleles of CYP1A1 and 554K variant allele of AHR were 0.158, 0.055, 0.055 and 0.075, respectively. No differences were observed in the frequencies of polymorphic genotypes between the smokers with low and those with high expression, when the relationship was studied using a regression analysis adjusted for cigarette consumption. Our results thus indicate that the interindividual variation of CYP1A1 levels in smokers' lung tissue is not attributable to genetic polymorphisms of CYP1A1 or AHR tested in this study.

Induction and regulation of the carcinogen-metabolizing enzyme CYP1A1 by marijuana smoke and delta (9)-tetrahydrocannabinol

Induction of the carcinogen-metabolizing enzyme cytochrome P4501A1 (CYP1A1) is a key step in the development of tobacco-related cancers. To determine if marijuana smoke activates CYP1A1, a murine hepatoma cell line expressing an inducible CYP1A1 gene (Hepa-1) was exposed in vitro to tar extracts prepared from either tobacco, marijuana, or placebo marijuana cigarettes. Marijuana tar induced higher levels of CYP1A1 messenger RNA (mRNA) than did tobacco tar, yet resulted in much lower CYP1A1 enzyme activity. These differences between marijuana and tobacco were primarily due to Delta(9)-tetrahydrocannabinol (Delta(9)-THC), the psychoactive component of marijuana. Here we show that Delta(9)-THC acts through the aryl hydrocarbon receptor complex to activate transcription of CYP1A1. A 2-microg/ml concentration of Delta(9)-THC produced an average 2.5-fold induction of CYP1A1 mRNA, whereas a 10- microg/ml concentration of Delta(9)-THC produced a 4.3-fold induction. No induction was observed in Hepa-1 mutants lacking functional aryl-hydrocarbon receptor or aryl-hydrocarbon receptor nuclear translocator genes. At the same time, Delta(9)-THC competitively inhibited the CYP1A1 enzyme, reducing its ability to metabolize other substrates. Spiking tobacco tar with Delta(9)-THC resulted in a dose-dependent decrease in the ability to generate CYP1A1 enzyme activity as measured by the ethoxyresorufin-o-deethylase (EROD) assay. This inhibitory effect was confirmed by Michaelis-Menton kinetic analyses using recombinant human CYP1A1 enzyme expressed in insect microsomes. This complex regulation of CYP1A1 by marijuana smoke and the Delta(9)-THC that it contains has implications for the role of marijuana as a cancer risk factor.

Differential response of cultured human umbilical vein and artery endothelial cells to Ah receptor agonist treatment: CYP-dependent activation of food and environmental mutagens

In the present study, 7-ethoxyresorufin O-deethylase (EROD), 7, 12-dimethylbenz[a]anthracene (DMBA)-hydroxylase, and covalent binding of (3)H-labeled 3-amino-1,4-dimethyl-5H-pyrido[4,3-b]indole ((3)H-Trp-P-1) and (3)H-DMBA were examined in human umbilical vein endothelial cells (HUVEC) and human umbilical artery endothelial cells (HUAEC) exposed to the aryl hydrocarbon (Ah) receptor agonist beta-naphthoflavone (BNF) or vehicle only. The results revealed a marked induction of enzymatic activity in BNF-treated HUVEC compared with vehicle-treated cells, whereas no similar response was observed in BNF-treated HUAEC. EROD, DMBA hydroxylase, and covalent binding of (3)H-Trp-P-1 and (3)H-DMBA in BNF-treated HUVEC were reduced in the presence of the CYP1A inhibitor ellipticine. Addition of other CYP1A inhibitors alpha-naphthoflavone, miconazole, 1-ethynylpyrene, 1-(1-propynyl)pyrene), or the CYP1A substrate ethoxyresorufin to the incubation buffer of BNF-treated HUVEC reduced covalent binding of (3)H-Trp-P-1 by 93-98%. Western blot analysis confirmed an induction of CYP1A1 in BNF-treated HUVEC, but not in BNF-treated HUAEC. CYP1A1 was, however, detected in both vehicle- and BNF-treated HUAEC. The results showed that BNF exposure induced CYP1A1 and metabolic activation of xenobiotics in HUVEC, whereas the catalytic activity remained low in BNF-treated HUAEC. Our results suggest that endothelial lining of human veins may be a target for adverse effects of xenobiotics activated into reactive metabolites by Ah receptor-regulated enzymes. Several studies have detected CYP1A1 in endothelial linings, whereas expression of CYP1A2 and CYP1B1 seems to be negligible at this site. This suggests that the metabolic activation and covalent binding of (3)H-Trp-P-1 and (3)H-DMBA in HUVEC are most likely mediated by CYP1A1.

An uncommon phenotype of poor inducibility of CYP1A1 in human lung is not ascribable to polymorphisms in the AHR, ARNT, or CYP1A1 genes

Cigarette smoking can induce CYP1A1 in the lung. Induction requires the aryl hydrocarbon receptor (AHR) and aryl hydrocarbon receptor nuclear translocator (ARNT) proteins. Lung samples from seven of 75 Finnish patients who smoked until the time of surgery exhibited absent or low levels of CYP1A1 protein, mRNA and enzymatic activity, suggesting that these individuals might be genetically non or poorly inducible for CYP1A1. All seven lung samples expressed normal levels of AHR mRNA and ARNT mRNA, indicating that they did not carry inactivating polymorphisms in the 5' upstream regulatory regions of these genes. Sequencing of cDNAs encompassing the complete coding regions of AHR and ARNT identified a previously known codon 554 polymorphism in AHR, which was present in the homozygous state in one individual. This polymorphism, which leads to an amino acid substitution, has previously been reported either to have no effect or to enhance CYP1A1 induction. Previously unreported silent single nucleotide polymorphisms were identified in codon 44 of AHR and codon 189 of ARNT. 1500 bp of genomic sequence from the 5' upstream regulatory sequence of the CYP1A1 gene was also sequenced in the non-inducible individuals. A nucleotide substitution polymorphism at position -459 was detected in the heterozygous state in two individuals. This polymorphic site does not reside in any known regulatory sequence. The complete CYP1A1 coding sequence and intron/exon boundaries were then sequenced. None of the non or poorly inducible individuals exhibited any polymorphisms, either homozygous or heterozygous compared to representative inducible individuals or the previously published CYP1A1 sequence. Thus, no polymorphisms in the AHR, ARNT or CYP1A1 genes were identified that could be responsible for the non/low inducibility phenotype observed.

Induction and regulation of xenobiotic-metabolizing cytochrome P450s in the human A549 lung adenocarcinoma cell line

Several cytochrome P450 (CYP) enzymes are expressed in the human lung, where they participate in metabolic inactivation and activation of numerous exogenous and endogenous compounds. In this study, the expression pattern of all known xenobiotic-metabolizing CYP genes was characterized in the human alveolar type II cell-derived A549 adenocarcinoma cell line using qualitative reverse transcriptase/polymerase chain reaction (RT-PCR). In addition, the mechanisms of induction by chemicals of members in the CYP1 and CYP3A subfamilies were assessed by quantitative RT-PCR. The expression of messenger RNAs (mRNAs) of CYPs 1A1, 1B1, 2B6, 2C, 2E1, 3A5, and 3A7 was detected in the A549 cells. The amounts of mRNAs of CYPs 1A2, 2A6, 2A7, 2A13, 2F1, 3A4, and 4B1 were below the limit of detection. 2,3,7,8-tetrachlorodibenzo-p-dioxin (TCDD) induced CYP1A1 and CYP1B1 mRNAs 56-fold and 2.5-fold, respectively. CYP3A5 was induced 8-fold by dexamethasone and 11-fold by phenobarbital. CYP3A4 was not induced by any of the typical CYP3A4 inducers used. The tyrosine kinase inhibitor genistein and the protein kinase C inhibitor staurosporine blocked TCDD-elicited induction of CYP1A1, but they did not affect CYP1B1 induction. Protein phosphatase inhibitors okadaic acid and calyculin A enhanced TCDD-induction of CYP1B1 slightly, but had negligible effects on CYP1A1 induction. These results suggest that CYP1A1 and CYP1B1 are differentially regulated in human pulmonary epithelial cells and give the first indication of the induction of CYP3A5 by glucocorticoids in human lung cells. These results establish that having retained several characteristics of human lung epithelial cell CYP expression, the A549 lung cell line is a valuable model for mechanistic studies on induction of the pulmonary CYP system.

Induction of UDP-glycosyltransferase family 1 genes in rat liver: different patterns of mRNA expression with two inducers, 3-methylcholanthrene and beta-naphthoflavone

Uridine diphosphate (UDP)-glucuronosyltransferases (UGTs), presently called UDP-glycosyltransferases, catalyse the detoxification of many toxic and carcinogenic compounds. Glucuronidation is also a major metabolic pathway for numerous drugs. The UGT1A6 gene (formerly known as UGT1*06 and UGT1A1) has been suggested to belong to the aryl hydrocarbon (Ah) gene battery, which consists of several genes encoding for drug-metabolising enzymes regulated by dioxin and other ligands of the Ah receptor. In this study, we analysed the localisation of UGT1A6 expression in rat liver by in situ hybridisation to mRNA. Two different RNA probes were used, one which was specific to UGT1A6 and the other against the C terminal sequence shared by all UGT1 genes. In this study, no UGT1A6 mRNA was detected in the control animals. However, other gene(s) of the UGT1 family were expressed in the perivenous region surrounding the central veins as detected by hybridisation with the probe against the common region of the UGT1 genes. Treatment with the lower dose (5 mg/kg) of 3-methylcholanthrene (3MC) induced expression of UGT1A6 perivenously. Treatment with the higher dose (25 mg/kg) of 3-Methylcholanthrene resulted in a more panacinar expression pattern. In contrast to the perivenous induction observed with 3-methylcholanthrene, treatment with 15 mg/kg of beta-naphthoflavone (BNF) resulted in strong induction in the periportal region. The results reveal an inducer-specific pattern of UGT1A6 expression similar to that demonstrated earlier for other Ah battery genes, namely CYP1A1, CYP1A2, GSTYalpha and ALDH3. The finding further supports the notion that common factors regulate the regional hepatic expression of Ah battery genes.