Activation of procarcinogens by human cytochrome P450 enzymes

Effects of tobacco smoke on gene expression and cellular pathways in a cellular model of oral leukoplakia

In addition to being causally linked to the formation of multiple tumor types, tobacco use has been associated with decreased efficacy of anticancer treatment and reduced survival time. A detailed understanding of the cellular mechanisms that are affected by tobacco smoke (TS) should facilitate the development of improved preventive and therapeutic strategies. We have investigated the effects of a TS extract on the transcriptome of MSK-Leuk1 cells, a cellular model of oral leukoplakia. Using Affymetrix HGU133 Plus 2 arrays, 411 differentially expressed probe sets were identified. The observed transcriptome changes were grouped according to functional information and translated into molecular interaction network maps and signaling pathways. Pathways related to cellular proliferation, inflammation, apoptosis, and tissue injury seemed to be perturbed. Analysis of networks connecting the affected genes identified specific modulated molecular interactions, hubs, and key transcription regulators. Thus, TS was found to induce several epidermal growth factor receptor (EGFR) ligands forming an EGFR-centered molecular interaction network, as well as several aryl hydrocarbon receptor-dependent genes, including the xenobiotic metabolizing enzymes CYP1A1 and CYP1B1. Notably, the latter findings in vitro are consistent with our parallel finding that CYP1A1 and CYP1B1 levels were increased in oral mucosa of smokers. Collectively, these results offer insights into the mechanisms underlying the procarcinogenic effects of TS and raise the possibility that inhibitors of EGFR or aryl hydrocarbon receptor signaling will prevent or delay the development of TS-related tumors. Moreover, the inductive effects of TS on xenobiotic metabolizing enzymes may help explain the reduced efficacy of chemotherapy, and suggest targets for chemopreventive agents in smokers.

RT-PCR-based cytochrome P450 expression profile of oral tissue samples1

OBJECTIVE

To analyse the expression of individual forms of cytochrome P450 (CYP) at the mRNA level in five homogenized oral buccal tissue samples from four individuals with or without oral malignancy.

METHOD

Individual forms of CYPs were studied by reverse transcriptase-polymerase chain reaction (RT-PCR), using specific primers for CYPs 2B6, 2C, 2D6, 2E1, 3A3/4 and 3A5, and oral CYP expressions were compared with CYP expression in liver tissue.

RESULTS

Consistent expression of CYPs 2C, 2E1 and 3A5 was observed in oral buccal tissue at mRNA level.

CONCLUSIONS

These particular CYPs have possible roles in the protection of the body against orally ingested xenobiotics as well as influence the bioavailability of therapeutic compounds.

Strong synergistic induction of CYP1A1 expression by andrographolide plus typical CYP1A inducers in mouse hepatocytes

The effects of andrographolide, the major diterpenoid constituent of Andrographis paniculata, on the expression of cytochrome P450 superfamily 1 members, including CYP1A1, CYP1A2, and CYP1B1, as well as on aryl hydrocarbon receptor (AhR) expression in primary cultures of mouse hepatocytes were investigated in comparison with the effects of typical CYP1A inducers, including benz[a]anthracene, beta-naphthoflavone, and 2,3,7,8-tetrachlorodibenzo-p-dioxin. Andrographolide significantly induced the expression of CYP1A1 and CYP1A2 mRNAs in a concentration-dependent manner, as did the typical CYP1A inducers, but did not induce that of CYP1B1 or AhR. Interestingly, andrographolide plus the typical CYP1A inducers synergistically induced CYP1A1 expression, and the synergism was blocked by an AhR antagonist, resveratrol. The CYP1A1 enzyme activity showed a similar pattern of induction. This is the first report that shows that andrographolide has a potency to induce CYP1A1 enzyme and indicates that andrographolide could be a very useful compound for investigating the regulatory mechanism of the CYP1A1 induction pathway. In addition, our findings suggest preparing advice for rational administration of A. paniculata, according to its ability to induce CYP1A1 expression.

Genetic polymorphisms of drug-metabolizing enzymes and the susceptibility to antituberculosis drug-induced liver injury

Three first-line antituberculosis drugs, isoniazid, rifampicin and pyrazinamide, may induce liver injury, especially isoniazid. This antituberculosis drug-induced liver injury ranges from a mild to severe form, and the associated mortality cases are not rare. The major drug-metabolizing enzyme of isoniazid is N-acetyltransferase. Other possible enzymes are CYP2E1 and glutathione S-transferase. There is evidence that polymorphisms of the genes that encode these enzymes may influence the activity of the corresponding drug-metabolizing enzymes. Recent studies demonstrated that these genetic polymorphisms may be associated with the susceptibility to antituberculosis drug-induced liver injury. The proposed risk-associated genotypes are NAT2 slow acetylator (without wild-type NAT2*4 allele), CYP2E1 *1A/*1A (homozygous wild type) and homozygous null GSTM1 genotype. Although the available data in the field are still limited and warrants further confirmation in different ethnic populations with larger sample sizes, it still cast some light on the application of these pharmacogenetic or pharmacogenomic approaches to prevent grave antituberculosis drug-induced liver injury in the near future.

Transcription factor binding to a putative double E-box motif represses CYP3A4 expression in human lung cells

Two vital enzymes of the CYP3A subfamily, CYP3A4 and CYP3A5, are differentially expressed in the human lung. However, the molecular mechanisms that regulate tissue-selective expression of the genes are poorly understood. The ability of the 5' upstream promoter region of these two genes to drive luciferase reporter activities in human lung A549 cells was dramatically different. The CYP3A5 promoter region activated luciferase gene expression by 10-fold over the promoterless construct, whereas the CYP3A4 promoter did not drive expression. Sequence comparisons of the promoters identified a 57-base pair insertion in the CYP3A4 promoter region (-71 to -127) that was absent in the CYP3A5 promoter. Deletion of the 57-bp motif from CYP3A4 or insertion into the CYP3A5 promoter, showed that this motif represses CYP3A4 expression in lung. EMSA analysis using nuclear extracts from either A549 cells or human lung tissues showed two specific protein/DNA complexes formed with the (32)P-labeled CYP3A4 57-bp oligonucleotide. EMSA analyses identified two E-box motifs as the minimal specific cis-elements. Supershift assays with antibodies directed against known double- or single-E-box binding factors (TAL1, deltaEF1, E2A, HEB, etc.) failed to identify this factor as a previously characterized trans-acting double E-box binding protein. These results demonstrated that the 5'-upstream region of CYP3A4 contains an active putative double E-box repressor motif, not present in the 5'-upstream region of the CYP3A5 gene, that attenuates CYP3A4 expression in the human lung. We believe that this is the first documented case in which a cytochrome P450 gene is actively repressed in a tissue-specific manner.

Evaluation of genetic damage in Brazilian footwear-workers: Biomarkers of exposure, effect, and susceptibility

Employees in the footwear manufacturing industry are routinely exposed to complex mixtures of solvents used in cleaning and as diluents in glues, primers, and degreasers. The objective of this study was to determine the genotoxic effects in a group of footwear-workers occupationally exposed to solvent-based adhesive and solutions containing organic solvents, mainly toluene. Peripheral blood and buccal cells samples were collected from 39 footwear-workers (31 males and 8 females) and 55 controls (44 males and 11 females). As biomarker of exposure, we obtained data on hippuric acid (HA), the main metabolite of toluene in urine, and DNA damage detected by the Comet assay in blood cells. Micronucleus frequencies in binucleated lymphocytes (BNMN) and in epithelial buccal cells (EBCMN) were analyzed as biomarkers of effect, while polymorphisms in genes GSTT1, GSTM1, GSTP1, CYP1A1, and CYP2E1 were used as susceptibility biomarkers. Results of HA and Comet assay showed statistical increased values amongst footwear-workers relative to controls (P < or = 0.001). No differences were observed in BNMN and EBCMN frequencies between the groups, but a correlation test revealed that age was significantly associated with BNMN frequency in both control (r(s)=0.290; P < or = 0.05) and exposed groups (r(s)=0.674; P < or = 0.001). Regarding the results on genetic polymorphisms, GSTM1 null subjects from the control group showed a significant increase in EBCMN frequency relative to GSTM1 non-null subjects (P < or = 0.05). A significant increase in DNA damage detected by Comet assay in leukocytes was obtained for GSTP1 Ile/Val or Val/Val individuals from the exposed group relative to those with GSTP1 Ile/Ile (P < or = 0.05), especially in younger subjects (P < or = 0.01), and a suggestion of interaction with CYP2E1 polymorphism was found. In confirmation of these data, stepwise multiple regression analyses for selecting between the different independent variables showed that about 25% of levels of the DNA damage in footwear-worker can be associated with genetic polymorphisms in GSTP1 and CYP2E1 (P=0.006, F=5.876).

Polymorphism of selected enzymes involved in detoxification and biotransformation in relation to lung cancer

Available data indicate that there are significant differences in individual susceptibility to lung cancer within the human population. It is believed to be underlie by inherited genetic predispositions related to the genetic polymorphism of several enzymes involved in the detoxification and xenobiotic metabolism. In this review, we collect and discuss the evidence reported up to date on the association between lung cancer and genetic polymorphism of cytochromes P450, N-acetyltransferase, glutathione S-transferases, microsomal epoxide hydrolase, NAD(P)H:quinone oxidoreductase, myeloperoxidase and glutathione peroxidase. All these genes might appear to be candidates for lung cancer susceptibility genes, nevertheless, the present state of the art still offers only a limited explanation of the link between such polymorphisms and increased risk of lung cancer.

Lung Cancer in Never Smokers: A Review

Lung cancer is the leading cause of cancer-related death in the United States. Although tobacco smoking accounts for the majority of lung cancer, approximately 10% of patients with lung cancer in the United States are lifelong never smokers. Lung cancer in the never smokers (LCINS) affects women disproportionately more often than men. Only limited data are available on the etiopathogenesis, molecular abnormalities, and prognosis of LCINS. Several etiologic factors have been proposed for the development of LCINS, including exposure to radon, cooking fumes, asbestos, heavy metals, and environmental tobacco smoke, human papillomavirus infection, and inherited genetic susceptibility. However, the relative significance of these individual factors among different ethnic populations in the development of LCINS has not been well-characterized. Adenocarcinoma is the predominant histologic subtype reported with LCINS. Striking differences in response rates and outcomes are seen when patients with advanced non–small-cell lung cancer (NSCLC) who are lifelong never smokers are treated with epidermal growth factor receptor tyrosine kinase (EGFR-TK) inhibitors such as gefitinib or erlotinib compared with the outcomes with these agents in patients with tobacco-associated lung cancer. Interestingly, the activating mutations in the EGFR-TK inhibitors have been reported significantly more frequently in LCINS than in patients with tobacco-related NSCLC. This review will summarize available data on the epidemiology, risk factors, molecular genetics, management options, and outcomes of LCINS.

Cytochrome P4501A induction in rainbow trout gills and liver following exposure to waterborne indigo, benzo[a]pyrene and 3,3',4,4',5-pentachlorobiphenyl

We have developed a gill-filament based ethoxyresorufin O-deethylase (EROD) assay to be used as a tool to monitor cytochrome P4501A (CYP1A) induction in caged fish. The present study aimed to compare temporal patterns of EROD induction in gills and liver of rainbow trout (Oncorhynchus mykiss) exposed in the laboratory to readily metabolized and persistent CYP1A inducers, i.e. indigo, benzo[a]pyrene (BaP), and 3,3',4,4',5-pentachlorobiphenyl (PCB#126). Branchial and hepatic EROD activities were examined in fish exposed for 6, 12, or 24h and in fish exposed for 24h and then held in clean water for 2 or 14 days. Furthermore, branchial CYP1A protein expression was localized by immunohistochemistry. All compounds strongly induced branchial EROD activity within 6h. The highest EROD inductions observed for indigo, BaP, and PCB#126 were roughly similar in gills (52-, 76-, and 74-fold), but differed considerably in liver (11-, 78-, and 200-fold). In indigo- and BaP-exposed fish, both hepatic and branchial EROD activities decreased rapidly in clean water. In PCB#126-exposed fish, decreased branchial and increased hepatic EROD activities were observed following transfer to clean water. The substances gave rise to immunostaining for CYP1A at different cellular sites. All inducers increased the CYP1A-immunostaining in the gill filament secondary lamellae, but PCB#126 also induced a pronounced CYP1A immunoreactivity in cells near the basal membrane of the epithelium of the primary lamellae. The observation that the low BaP and indigo concentrations induced EROD activity markedly in the gills but only slightly or not at all in the liver, supports the contention that readily metabolized AhR agonists may escape detection when hepatic EROD activity is used for environmental monitoring. The results show that gill filament EROD activity is a sensitive biomarker both for persistent and readily metabolized AhR agonists in polluted water.

Benzo[a]pyrene-7,8-quinone-3'-mononucleotide adduct standards for 32P postlabeling analyses: detection of benzo[a]pyrene-7,8-quinone-calf thymus DNA adducts

Benzo[a]pyrene-7,8-quinone (BPQ) is one of the reactive metabolites of the widely distributed archetypal polycyclic aromatic hydrocarbon, benzo[a]pyrene (B[a]P). The formation of BPQ from B[a]P through trans-7,8-dihydroxy-7,8-dihydroB[a]P by the mediation of aldo-keto reductases and its role in the genotoxicity and carcinogenesis of B[a]P currently are under extensive investigation. Toxicity pathways related to BPQ are believed to include both stable and unstable (depurinating) DNA adduct formation as well as reactive oxygen species. We previously reported the complete characterization of four novel stable BPQ-deoxyguanosine (dG) and two BPQ-deoxyadenosine (dA) adducts (Balu et al., Chem. Res. Toxicol. 17 (2004) 827-838). However, the identification of BPQ-DNA adducts by 32P postlabeling methods from in vitro and in vivo exposures required 3'-monophosphate derivatives of BPQ-dG, BPQ-dA, and BPQ-deoxycytidine (dC) as standards. Therefore, in the current study, BPQ adducts of dGMP(3'), dAMP(3'), and dCMP(3') were prepared. The syntheses of the BPQ-3'-mononucleotide standards were carried out in a manner similar to that reported previously for the nucleoside analogs. Reaction products were characterized by UV, LC/MS analyses, and one- and two-dimensional NMR techniques. The spectral studies indicated that all adducts existed as diastereomeric mixtures. Furthermore, the structural identities of the novel BPQ-dGMP, BPQ-dAMP, and BPQ-dCMP adducts were confirmed by acid phosphatase dephosphorylation of the BPQ-nucleotide adducts to the corresponding known BPQ-nucleoside adduct standards. The BPQ-dGMP, BPQ-dAMP, and BPQ-dCMP adduct standards were used in 32P postlabeling studies to identify BPQ adducts formed in vitro with calf thymus DNA and DNA homopolymers. 32P postlabeling analysis revealed the formation of 8 major and at least 10 minor calf thymus DNA adducts. Of these BPQ-DNA adducts, the following were identified: 1 BPQ-dGMP adduct, 2 BPQ-dAMP adducts, and 3 BPQ-dCMP adducts. This study represents the first reported example of the characterization of stable BPQ-DNA adducts in isolated mammalian DNA and is expected to contribute significantly to the future BPQ-DNA adduct studies in vivo and thereby to the contribution of BPQ in B[a]P carcinogenesis.

Cruciferous vegetables and colo-rectal cancer

Cruciferous vegetables have been studied extensively for their chemoprotective effects. Although they contain many bioactive compounds, the anti-carcinogenic actions of cruciferous vegetables are commonly attributed to their content of glucosinolates. Glucosinolates are relatively biologically inert but can be hydrolysed to a range of bioactive compounds such as isothiocyanates (ITC) and indoles by the plant-based enzyme myrosinase, or less efficiently by the colonic microflora. A number of mechanisms whereby ITC and indoles may protect against colo-rectal cancer have been identified. In experimental animals cruciferous vegetables have been shown to inhibit chemically-induced colon cancer. However, the results of recent epidemiological cohort studies have been inconsistent and this disparity may reflect a lack of sensitivity of such studies. Possible explanations for the failure of epidemiological studies to detect an effect include: assessment of cruciferous vegetable intake by methods that are subject to large measurement errors; the interaction between diet and genotype has not been considered: the effect that post-harvest treatments may have on biological effects of cruciferous vegetables has not been taken into account.

Relative and absolute quantitative expression profiling of cytochromes P450 using isotope-coded affinity tags

The development of a novel method for absolute quantification of proteins based on isotope-coded affinity tagging using ICAT reagents is described. The method exploits synthetic peptide standards to determine protein content at the femtomole level in biological samples. The approach is generally applicable to any subset of proteins, but is particularly appropriate for quantitative analysis of multiple, closely related isoforms, and for hydrophobic proteins that are poorly represented in 2-D gels. Relative and absolute quantification techniques are applied to an important group of microsomal metabolic enzymes, the cytochromes P450 (P450), which are critical in determining the disposition, safety and efficacy of drugs in man. Measurement of the P450 induction profile in response to chemicals is a fundamental aspect of drug safety evaluation and is currently achieved by low-throughput methods employing poorly discriminatory antibodies or substrates. Tagging technology is shown to supersede conventional methods for P450 profiling in terms of discriminatory power and throughput, exemplified by the simultaneous detection of distinct induction profiles for cyp2c subfamily members in response to phenobarbitone: cyp2c29 expression, but not cyp2c40 or cyp2c50, was induced threefold by treatment. This technology should abbreviate the drug development pathway, and provide a widely applicable, rapid means of quantifying proteins.

Ethanol-Induced Increase in the Metabolic Clearance of 1,1,1-Trichloroethane in Human Volunteers

This study evaluated the effect of moderate doses of ethanol over a short period of time on the toxicokinetics of an organic solvent, 1,1,1-trichloroethane. A group of 10 moderate drinkers were recruited and exposed via inhalation for 2 h to a low concentration of 1,1,1-trichloroethane (175 ppm) on two separate occasions. Subjects were administered ethanol (0.35 g/kg body weight) on each of the 7 days preceding one of the exposures. Blood and urine samples were collected during and following each exposure, with blood analyzed for 1,1,1-trichloroethane and urine analyzed for the metabolites of 1,1,1-trichloroethane: trichloroethanol and trichloroacetic acid. Prior ethanol consumption resulted in a significant increase in apparent metabolic clearance of 1,1,1-trichloroethane (mean increase = 25.4%). The results of this study demonstrate that ethanol consumption over time can affect the rate at which an organic solvent is cleared through metabolism in humans. For chemicals with toxic metabolic products, this inductive effect of ethanol consumption on the rate of biotransformation could be potentially harmful to exposed individuals. Metabolic clearance of compounds with high hepatic extraction may not be affected by enzyme induction as it is likely that these compounds are essentially completely metabolized while passing through the liver.

Ketoconazole Renders Poor CYP3A Phenotype Status With Midazolam as Probe Drug

Drugs metabolized by cytochrome CYP3A isoenzymes have wide interindividual variability and normally distributed plasma clearance distributions. This makes precise dosing difficult to achieve clinically, which may compromise safe therapy. We hypothesized that with potent inhibition of CYP3A, we could clinically render patients "poor metabolizer" phenotype status, and thus reduce interindividual pharmacokinetic variability of midazolam, a well-known CYP3A substrate. Intravenous bolus midazolam at doses of 2.5 mg and 1 mg were administered to 28 and 29 patients with cancer with and without co-administration of 200 mg of oral ketoconazole twice per day respectively for 3 days, starting 1 day before midazolam. Pharmacokinetic analyses of midazolam on both groups were derived using noncompartmental methods and compared. The mean clearance (CL) of midazolam was reduced 6 times by ketoconazole. Midazolam CL were normally distributed in both groups, and ranged from 1.7 to 51.9 and 1.4 to 8.2 L/hour in the control and ketoconazole groups, respectively, corresponding to a 7-fold reduction in dispersion between the 2 groups. Area-under-the-curve variability was reduced by >100%. A limited sampling model consisting of time points at 15 and 300 minutes was validated as a phenotype for CYP3A activity to facilitate the use of midazolam as a probe drug for CYP3A activity. Potent inhibition of CYP3A by ketoconazole reduced midazolam CL and area-under-the-curve variability, allowing for more precise achievement of therapeutic target drug exposure. Prospective evaluation of this approach, together with dose adjustment based on limited sampling, seems warranted.

Effect of selenium-containing compounds on hepatic chemoprotective enzymes in mice

Selenite and organoselenium compounds have been examined at supranutritional levels for their ability to influence the activity and mRNA levels of chemoprotective enzymes in the livers of selenium-sufficient mice and the changes compared to those elicited by oltipraz. Compounds investigated included novel selenocysteine prodrugs that have previously been evaluated for their ability to reduce the tumorigenicity of 4-(methylnitrosamino)-1-(3-pyridyl)-1-butanone (NNK) in mice. Following seven daily doses (i.g.), all compounds except 2-methylselenazolidine-4(R)-carboxylic acid (MSCA) increased thioredoxin reductase activity (43-92%) but only for 2-oxoselenazolidine-4(R)-carboxylic acid (OSCA) was there an accompanying increase in mRNA. No compound enhanced glutathione peroxidase activity, although sodium selenite significantly elevated the mRNA of this enzyme. Oltipraz was an efficacious inducer of both thioredoxin reductase and glutathione peroxidase mRNAs. Sodium selenite, selenazolidine-4(R)-carboxylic acid (SCA), and OSCA elevated NAD(P)H-quinone oxidoreductase mRNA but only for OSCA was the elevation in mRNA accompanied by an increase in enzyme activity. L-Selenocystine significantly increased this activity without increasing mRNA levels. Sodium selenite, L-selenocystine, L-selenomethionine, and Se-methyl-L-selenocysteine all enhanced glutathione S-transferase activity. The increased activity with sodium selenite was accompanied by increases in mRNAs of Gst alpha, Gst mu and Gst pi classes, while for L-selenocystine and Se-methyl-L-selenocysteine, only an elevation in the mRNA for the Gst alpha class was observed. Gst alpha and Gst mu class mRNAs were elevated by OSCA without a significant elevation in enzyme activity. SCA and MSCA both elevated a Gst pi mRNA and MSCA elevated Gst mu in addition. By comparison, oltipraz only significantly elevated the mRNA of Gst mu, adding to the conclusion that across the entire study, no selenium compound appears to be acting purely through the antioxidant response typified by oltipraz. Despite their chemical similarity, the three cysteine prodrugs, SCA, MSCA, and OSCA, each produced its own unique pattern of effects on protective enzymes and none was identical to the pattern elicited by sodium selenite, L-selenocystine, L-selenomethionine, and Se-methyl-L-selenocysteine. The study also shows that after 7 days of administration, there was only occasional concordance between elevations in mRNA and enzyme activity for any selenium compound and for any protective enzyme, there was no response in common for all selenium compounds.

In silico techniques for the study and prediction of xenobiotic metabolism: a review

Knowledge about metabolism is very important to understand the health risks posed by chemicals. The biochemical process of metabolism causes activation, inactivation, toxification, detoxification as well as changes in the physicochemical properties of a chemical. The long time consumption and high costs associated with animal tests and the challenges faced by traditional quantitative structure-activity relationship (QSAR) models in dealing with situations wherein parent chemical structures are less relevant to the ultimate effects have led to the development of in silico techniques for the prediction of xenobiotic metabolism. The strengths and limitations of some of the most commonly used in silico expert systems, and their application in studying metabolism of xenobiotic chemicals, have been reviewed. The in silico metabolism simulators possessed several distinguishing features imparted in part by the nature of knowledge rules (algorithms) encoded within them and in part by the integration of QSAR libraries and computational engines.

Profiling cytochrome P450 expression in ovarian cancer: identification of prognostic markers

PURPOSE

The cytochromes P450 are a multigene family of enzymes with a central role in the oxidative metabolism of a wide range of xenobiotics, including anticancer drugs and biologically active endogenous compounds. The purpose of this study was to define the cytochrome P450 profile of ovarian cancer and identify novel therapeutic targets and establish the prognostic significance of expression of individual cytochrome P450s in this type of cancer.

EXPERIMENTAL DESIGN

Immunohistochemistry for a panel of 23 cytochrome P450s and cytochrome P450 reductase was done on an ovarian cancer tissue microarray consisting of 99 primary epithelial ovarian cancers, 22 peritoneal metastasis, and 13 normal ovarian samples. The intensity of immunoreactivity in each sample was established by light microscopy.

RESULTS

In primary ovarian cancer, several P450s (CYP1B1, CYP2A/2B, CYP2F1, CYP2R1, CYP2U1, CYP3A5, CYP3A7, CYP3A43, CYP4Z1, CYP26A1, and CYP51) were present at a significantly higher level of intensity compared with normal ovary. P450 expression was also detected in ovarian cancer metastasis and CYP2S1 and P450 reductase both showed significantly increased expression in metastasis compared with primary ovarian cancer. The presence of low/negative CYP2A/2B (log rank = 7.06, P = 0.008) or positive CYP4Z1 (log rank = 6.19, P = 0.01) immunoreactivity in primary ovarian cancer were each associated with poor prognosis. Both CYP2A/2B and CYP4Z1 were also independent markers of prognosis.

CONCLUSIONS

The expression profile of individual P450s has been established in ovarian cancer. Several P450s show increased expression in ovarian cancer and this provides the basis for developing P450-based therapeutics in ovarian cancer. Expression of CYP2A/2B or CYP4Z1 in primary ovarian cancer were independent markers of prognosis.

Xenobiotic-Metabolizing Genes and Small-for-Gestational-Age Births

BACKGROUND

Little is known about the role of xenobiotic-metabolizing gene variants as risk factors for small-for-gestational-age (SGA) births or as modifiers for the effects of exposures such as maternal smoking.

METHODS

We conducted 2 joint studies: a case-control design including 493 cases (birth weight below the 10th percentile according to gestational age and sex) and 472 controls (at or above the 10th percentile) and a family-based study (mother, father, and newborn) with approximately 250 case trios and a similar number of control trios. Logistic regression and a log-linear model were used to analyze the association between genetic variants such as CYP1A1*2A, CYP1A1*2B, CYP1A1*4, GSTT1, GSTM1, and XRCC3 and SGA. The interaction between genetic variants and maternal smoking was also studied.

RESULTS

The odds ratio (OR) for the association of complete maternal GSTT1 deletion with SGA was 0.63 (95% confidence interval = 0.41-0.97), and that for the complete newborn GSTM1 deletion was 0.74 (0.55-0.98). Newborns with the partial GSTT1 deletion had an OR of 1.40 (1.01-1.95), and newborns homozygous for CYP1A1*2A had an OR of 4.28 (1.02-18.0). These results were coherent with the trio-based results. Significant interactions were observed between maternal smoking in the third trimester and CYP1A1*2A (P = 0.03), XRCC3 (P = 0.03), and newborn GSTT1 (P = 0.01).

CONCLUSIONS

Certain genetic variants involved in the metabolism of xenobiotics increase the risk of SGA, as well as modify the effects of maternal smoking by increasing or decreasing its risk.

Effects of hydroxyl group numbers on the B-ring of 5,7-dihydroxyflavones on the differential inhibition of human CYP 1A and CYP1B1 enzymes

Flavonoids are polyphenols composed of two aromatic rings (A, B) and a heterocyclic ring (C). In order to determine the effects of the number of hydroxyl groups in the B-ring of the flavonoids on human cytochrome P450 (CYP) 1 family enzymes, we evaluated the inhibition of CYP1A-dependent 7-ethoxyresorufin omicron-deethylation activity by chrysin, apigenin and luteolin, using bacterial membranes that co-express human CYP1A1, CYP1A2, or CYP1B1 with human NADPH-cytochrome P450 reductase. Chrysin, which possesses no hydroxyl groups in its B-ring, exhibited the most pronounced inhibitory effects on CYP1A2-dependent EROD activity, followed by apigenin and luteolin. On the contrary, CYP1A1-mediated EROD activity was most potently inhibited by luteolin, which is characterized by two hydroxyl groups in its B-ring, followed by apigenin and chrysin. However, all of the 5,7-dihydroxyflavones were determined to similarly inhibit CYP1B1 activity. Chrysin, apigenin, and luteolin exhibited a mixed-type mode of inhibition with regard to CYP1A2, CYP1B1, and CYP1A1, with apparent Ki values of 2.4, 0.5, and 2.0 microM, respectively. These findings suggested that the number of hydroxyl groups in the B-ring of 5,7-dihydroxyflavone might have some influence on the degree to which CYP1A enzymes were inhibited, but not on the degree to which CYP1B1 enzymes were inhibited.

Using a combination of cytochrome P450 1B1 and beta-catenin for early diagnosis and prevention of colorectal cancer

BACKGROUND

Although fecal occult blood test and invasive endoscopic examination are common used to detect colorectal adenomas and cancers, non-invasive and specific biomarkers are still under investigation. The objective is to evaluate the biomarker CYP1B1 alone or in combination with aryl hydrocarbon receptor (AhR), nuclear beta-catenin, p53 or bcl-2 for early diagnosis and prevention of colorectal cancer.

METHODS

These biomarkers were analyzed semi-quantified across 231 colonic tissues including 97 adenocarcinomas, 85 adenomas and 49 non-neoplastic colons using immunohistochemistry. In order to differentiate non-neoplastic colons from colorectal neoplasms (adenoma and carcinoma), the values for CYP1B1, AhR, nuclear beta-catenin, p53 and bcl-2 expressions were subjected to discrimination analysis, then the cross-validation, sensitivity and specificity of these models were calculated.

RESULTS

Expressions of CYP1B1, p53, nuclear beta-catenin and bcl-2 were significantly associated with colorectal carcinogenesis (p<0.01 for the trend test). The overexpression rates for CYP1B1, p53, nuclear beta-catenin and bcl-2 were significantly higher in the adenoma and carcinoma groups than in the non-neoplastic colon group (p<0.05). The discrimination models showed that a combination of two biomarkers was better than a single biomarker, and provided specificity ranging from 39% to 100% and sensitivity ranging from 43% to 82% for colorectal carcinoma.

CONCLUSIONS

The increase in expression of CYP1B1 occurred not only in colorectal carcinoma and but also in adenoma. Moreover, a screening panel of CYP1B1 in combination with nuclear beta-catenin was the most suitable marker pair to screen for colorectal carcinoma based on this study.

Induction of hepatic cytochrome P450 isozymes, benzo(a)pyrene metabolism and DNA binding following exposure to polycyclic aromatic hydrocarbon residues generated during repeated fish fried oil in rats

In the present study the effect of repeated fish fried oil (RFFO) and its extract (RFFE) on hepatic cytochrome P450 (CYP) isozymes, benzo(a)pyrene (BP) metabolism and DNA adduct formation was undertaken. HPLC analysis of RFFO showed the presence of several polycyclic aromatic hydrocarbons. CYP in microsomes from control and RFFO-treated animals showed a peak at 450 nm; however, a shift of 2 nm in the SORET region along with significant induction was observed in microsomes prepared from 3-methylcholanthrene (MC)- and RFFE-treated animals. Activities of hepatic ethoxyresorufin-O-deethylase, methoxyresorufin-O-deethylase, aryl hydrocarbon hydroxylase and erythromycin-N-demethylase were found to be significantly (P < 0.05) induced following exposure of RFFE, whereas none of these enzymes were altered in RFFO-treated group. Immunoblot analysis revealed that RFFE and MC were potent inducers of CYP1A1, 1A1/2 and 3A1 isozymes, where as RFFO showed no change in these protein levels. RT-PCR analysis showed induction of cDNA of CYP1A1 and CYP3A1 by RFFE treatment. Hepatic microsomes prepared from RFFE exposed animals enhanced BP metabolism with a concomitant increase in the relative proportion of BP 7,8-diol. Hepatic microsomes prepared from animals pretreated with RFFE and MC significantly enhanced the binding of [(3)H]-BP to calf thymus DNA. The overall results suggest that exposure to RFFE may induce hepatic CYP isozymes thereby producing enhanced reactive metabolites with a potential to bind with DNA that may result in cancer.

PPARalpha activation potentiates AhR-induced CYP1A1 expression

CYP1A1 is an extrahepatic enzyme largely involved in the bioactivation of various procarcinogens such as polycyclic aromatic hydrocarbons (PAHs) and arylamines. CYP1A1 expression is mainly regulated by AhR. Our laboratory has recently shown a new CYP1A1 regulation pathway involving PPARalpha. The aim of this study was to evaluate, in a Caco-2 cell line, the effect of a coexposure to 3-methylcholanthrene (3MC, AhR ligand) and WY-14643 (WY, PPARalpha ligand) on CYP1A1 expression (enzymatic activity, mRNA level and promoter activity). An additive effect on CYP1A1 expression was shown in cells coexposed with 3MC (0.1 or 1 microM) and a low WY concentration (30 microM) whereas a potentiating effect was observed after coexposure with 3MC (0.1 or 1 microM) and a high WY concentration (200 microM). Furthermore, 200 microM WY, alone or with 3MC, was able to increase the AhR protein level (two-fold). In conclusion, coexposure with 3MC and the PPARalpha agonist WY leads to an additive or potentiating effect on CYP1A1 inducibility, depending on the WY concentration. Furthermore, at high concentration (200 microM), WY induced AhR expression, which could explain the potentiating effect on CYP1A1 inducibility observed after addition of an AhR ligand (3MC). This phenomenon should be taken into account for risk assessment involving CYP1A1 induction.

Cytochrome p450 profile of colorectal cancer: identification of markers of prognosis

PURPOSE

The cytochromes P450 (P450) are a multigene family of enzymes with a central role in the oxidative metabolism of a wide range of xenobiotics, including anticancer drugs, carcinogens, and endogenous compounds. The purpose of this study was to define the P450 profile of colorectal cancer and establish the prognostic significance of expression of individual P450s in colorectal cancer.

EXPERIMENTAL DESIGN

Immunohistochemistry for a panel of 23 P450s was done on a colorectal cancer tissue microarray consisting of 264 primary colorectal cancers, 91 lymph node metastasis, and 10 normal colorectal samples. The intensity of immunoreactivity in each sample was established by light microscopy.

RESULTS

The most frequently expressed form of P450 in normal colon was CYP3A4. In primary colorectal cancer, several P450s (CYP1B1, CYP2S1, CYP2U1, CYP3A5, and CYP51) were present at a significantly higher level of intensity compared with normal colon. P450 expression was also detected in lymph node metastasis and the presence of several P450s (CYP1B1, CYP2A/2B, CYP2F1, CYP4V2, and CYP39) in the lymph node metastasis strongly correlated with their presence in corresponding primary tumors. The presence of strong CYP51 (log-rank = 12.11, P = 0.0005) or strong CYP2S1 (log-rank = 6.72, P = 0.0095) immunoreactivity were associated with poor prognosis. CYP51 was also an independent marker of prognosis (P = 0.009).

CONCLUSIONS

The expression of individual P450s has been established in colorectal cancer. Several P450s show increased expression in colorectal cancer. High expression of CYP51 or CYP2S1 were associated with poor prognosis and CYP51 is an independent marker of prognosis.

Effect of sulfur dioxide inhalation on CYP1A1 and CYP1A2 in rat liver and lung

Sulfur dioxide (SO2) is a ubiquitous air pollutant, presents in low concentrations in the urban air, and in higher concentrations in the working environment. In the present study, male Wistar rats were housed in exposure chambers and treated with 14.00+/-1.53, 28.00+/-2.12 and 56.00+/-4.28 mg/m3 SO2 for 6 h/day for 7 days, while control rats were exposed to filtered air in the same condition. Highly specific substrates were used as probes of cytochrome P4501A1 (CYP1A1) and cytochrome P4501A2 (CYP1A2). The mRNA levels of CYP1A1 and 1A2 were analyzed in livers and lungs by using a real-time reverse transcription-polymerase chain reaction (real-time RT-PCR) assay. Our results showed that the activities and mRNA levels of P450 were decreased in livers and lungs of rats exposed to SO2. In the liver, a decrease down to 0.68- and 0.64-fold in the CYP1A1 activity, probed by the O-deethylation of ethoxyresorufin (EROD), was observed at higher dose of SO2 (28 and 56 mg/m3); Similarly, CYP1A1 mRNA levels were reduced in livers of rats exposed to SO2 at 28 and 56 mg/m3. For livers, CYP1A2-mediated methoxyresorufin O-demethylase activity (MROD) was unaltered by SO2 at low concentrations, except for a significant decrease in the rats exposed to SO2 at 56 mg/m3 (0.79-fold); however, SO2 at higher concentrations significantly decreased levels of CYP1A2 (28 and 56 mg/m3) (p<0.05). Significant inhibition of both EROD and MROD was observed in lungs of rats exposed to SO2 at 28 and 56mg/m3. CYP1A1 activity was repressed 0.62- and 0.53-fold, while CYP1A2 activity was reduced to 0.74- and 0.55-fold in lungs, respectively. SO2 at higher concentrations (28 and 56 mg/m3) decreased significantly pulmonary CYP1A1 and 1A2 mRNA levels relative to control animals. Furthermore, the decreases of activities and mRNA levels of these P450 enzymes caused by SO2 at different concentrations in lungs and livers of rats followed linear dose-response curves. These results lead to the conclusion that SO2 exposure can reduce CYP1A1 and 1A2 in lungs and livers of rats and ROS and/or cytokines might act as mediators of this effect according to previous studies performed in mice. Reduction of hepatic and pulmonary CYPlAl and lA2 expression during SO2 exposure may be part of an adaptive response by the liver and lung to minimize cell damage.

Cytochrome P450 humanised mice

Humans are exposed to countless foreign compounds, typically referred to as xenobiotics. These can include clinically used drugs, environmental pollutants, food additives, pesticides, herbicides and even natural plant compounds. Xenobiotics are metabolised primarily in the liver, but also in the gut and other organs, to derivatives that are more easily eliminated from the body. In some cases, however, a compound is converted to an electrophile that can cause cell toxicity and transformation leading to cancer. Among the most important xenobiotic-metabolising enzymes are the cytochromes P450 (P450s). These enzymes represent a superfamily of multiple forms that exhibit marked species differences in their expression and catalytic activities. To predict how humans will metabolise xenobiotics, including drugs, human liver extracts and recombinant P450s have been used. New humanised mouse models are being developed which will be of great value in the study of drug metabolism, pharmacokinetics and pharmacodynamics in vivo, and in carrying out human risk assessment of xenobiotics. Humanised mice expressing CYP2D6 and CYP3A4, two major drug-metabolising P450s, have revealed the feasibility of this approach.

Chemoprotective and toxic potentials of synthetic and natural chalcones and dihydrochalcones in vitro

Cytochrome P4501A activity, oxidative stress and inhibition of gap junctional intercellular communication (GJIC) are involved in metabolic activation of promutagens and tumor-promoting activity of various xenobiotics, and their prevention is considered to be an important characteristic of chemoprotective compounds. In this study, a series of 31 chalcones and their corresponding dihydroderivatives, substituted in 2,2'-, 3,3'-, 4- or 4'-position by hydroxyl or methoxy group, were tested for their ability to inhibit Fe(II)/NADPH-enhanced lipid peroxidation and cytochrome P4501A-dependent 7-cethoxyresorufin-O-deethylase (EROD) activity in rat hepatic microsomes. Effects of the compounds on GJIC were determined in rat liver epithelial WB-F344 cells. Most of the chalcones and dihydrochalcones inhibited EROD activity in a dose-dependent manner at the range 0.25-25 microM, which was comparable to model flavonoid inhibitors alpha-naphthoflavone and quercetin. The chalcones exhibited higher inhibition activity than the corresponding dihydroderivatives. Mono and dihydroxylated chalcones, and dihydrochalcones showed none or only a weak antioxidant activity; trihydroxyderivatives inhibited in vitro lipid peroxidation significantly only at 50 microM concentration. Potential adverse effects, namely inhibition of GJIC and/or cytotoxicity were detected after treatment of WB-F344 cells with a number of chalcone and dihydrochalcone derivatives, suggesting that they should be excluded from additional screening as chemoprotective compounds. Chalcones and dihydrochalcones substituted at 4- and/or 4'-position, which elicited no inhibition of GJIC, were further tested for the potential enhancing effects on GJIC. The present data seem to suggest that 4-hydroxy, 2',4'-dihydroxy-3-methoxy, 2,4,4'-trihydroxy, and 2',4,4'-trihydroxychalcone, 2',4-dihydroxy and 2'-hydroxy-3,4-dimethoxydihydrochalcone might be promising chemoprotective compounds against CYP1A activity, and partly also against oxidative damage without inducing adverse effects, such as GJIC inhibition. In general, determination of potencies of tested compounds to inhibit GJIC should be involved in any set of methods for the in vitro screening of chemoprotective characteristics of potential drugs, in order to reveal their potential adverse effects associated with tumor promotion.

Role of cytochromes P450 in chemical toxicity and oxidative stress: studies with CYP2E1

Cytochromes P450 are responsible for metabolism of most xenobiotics and are required for the efficient elimination of foreign chemicals from the body. Paradoxically, these enzymes also metabolically activate biologically inert compounds to electrophilic derivatives that can cause toxicity, cell death and sometimes cellular transformation resulting in cancer. To establish the role of these enzymes in toxicity and carcinogenicity in vivo, gene knockout mice have been developed. To illustrate the role of P450s in toxicity, CYP2E1-null mice were employed with the commonly used analgesic drug acetaminophen. CYP2E1 is the rate-limiting enzyme that initiates the cascade of events leading to acetaminophen hepatotoxicity; in the absence of this P450, toxicity will only be apparent at high concentrations. Other enzymes and nuclear receptors are also involved in activation or inactivating chemicals. CYP2E1 is induced by alcohol and the primary P450 that carries out ethanol oxidation that can lead to the production of activated oxygen species and oxidative stress that elevate ERK1/2 phosphorylation through EGRF/c-Raf signaling. Paradoxically, activation of this pathway inhibits apoptotic cell death stimulated by reactive oxygen generating chemicals but accelerates necrotic cell death produced by polyunsaturated fatty acids. CYP2E1 is thought to contribute to liver pathologies that result from alcoholic liver disease and non-alcoholic steatohepatitis.

CYP2K6 from zebrafish (Danio rerio): cloning, mapping, developmental/tissue expression, and aflatoxin B1 activation by baculovirus expressed enzyme

A full-length zebrafish (Danio rerio) cytochrome P450 (CYP) 2K6 cDNA, was obtained (GenBank accession No. AF283813) through polymerase chain reaction cloning using degenerated primers based on a consensus CYP2 sequence and the heme-binding domain. This first CYP2K family member cloned from zebrafish had 1861 bp which contained 27 bp of 5'-untranslated region (5'-UTR), an open reading frame (ORF) of 1518 bp, and a 300 bp 3'-UTR with a poly A tail. The deduced 506 amino acid sequence of CYP2K6 had 63%, 62% and 59% identity with rainbow trout CYP2K1, CYP2K4 and CYP2K3, respectively; and 45%, 42%, and 42% identity with rabbit CYP2C1, human CYP2C19 and mouse CYP2C39, respectively. CYP2K6 mapped to 107.49cR on LG3 using the LN54 radiation hybrid panel. Its mRNA was detected at 5 days post-fertilization and in the adult liver and ovary among nine tissues examined. The ORF, including the 27 bp of the 5'-UTR, was cloned into pFastBac donor vector and then transferred into the baculovirus genome (bacmid DNA) in DH10Bac competent cells. The recombinant bacmid DNA was used to infect Spodoptera frugiperda insect cells to express the CYP2K6 protein (Bv-2K6). As its ortholog, rainbow trout Bv-2K1 [Yang, Y.H., Miranda, C.L., Henderson, M.C., Wang-Buhler, J.-L., Buhler, D.R., 2000. Heterologous expression of CYP2K1 and identification of the expressed protein (Bv-2K1) as lauric acid (omega-1)-hydroxylase and aflatoxin B1 exo-epoxidase. Drug Metab. Disp. 28,1279-83.], Bv-2K6 also catalyzed the conversion of aflatoxin B1 (AFB1) to its exo-8,9-epoxide as assessed by the trapping of a glutathione (GSH) adduct in the presence of a specific mouse alpha class glutathione S-transferase. The identity of the AFB1-GSH adduct was verified by liquid chromatography-mass spectrometry (LC-MS) and mass spectrometry-mass spectrometry (MS-MS) analysis. Although rainbow trout Bv-2K1 was capable of oxidizing lauric acid, zebrafish Bv-2K6 protein showed no activity against this substrate.

Regulation of CYP3A genes in the human respiratory tract

The CYP3A gene cluster consists of four members, CYP3A4, CYP3A5, CYP3A7 and CYP3A43. Especially the CYP3A4 and CYP3A5 enzymes play a significant role in the metabolism of numerous exogenous (drugs, pollutants, procarcinogens) and endogenous (steroids, bile acids) compounds. CYP3A5 protein is present in the liver and some extrahepatic tissues, such as the gut wall, kidney, adrenal gland, prostate and many cell types in the lung. In the lung, the highest amounts of CYP3A5 protein are present in bronchial and alveolar epithelial cells, bronchial glands and alveolar macrophages. The same cells types have little or no CYP3A4 expression. Cigarette smoking markedly represses CYP3A5 content in alveolar macrophages. CYP3A5 is upregulated by glucocorticoids via the glucocorticoid receptor (GR) in lung adenocarcinoma derived A549 cells. Tissue selective distribution of CYP3A4 is controlled by tissue enriched transcription factors, such as hepatic nuclear factor 4alpha (HNF4alpha), and ligand dependent nuclear receptors, most notably pregnane X receptor (PXR) and constitutive androstane receptor (CAR). The selective expression of CYP3A5 over CYP3A4 in specific lung cells is likely to be the sum of the effects of tissue-specific upregulating and downregulating transcription factors in these cells. Since the CYP3A4/5 enzymes mediate the metabolism of many exogenous and endogenous compounds with direct relevance to pulmonary physiology and pathology, the functions of these enzymes and factors controlling them should be elucidated in much more detail.

Genetic polymorphisms influencing xenobiotic metabolism and transport in patients with primary biliary cirrhosis

Epidemiological data suggest that environmental factors may trigger autoimmunity in genetically susceptible individuals. In primary biliary cirrhosis (PBC), it has been postulated that halogenated xenobiotics can modify self-molecules, facilitating the breakdown of tolerance to mitochondrial antigens. The transport and metabolism of xenobiotics is highly dependent on key genetic polymorphisms that alter enzymatic phenotype. We analyzed genomic DNA from 169 patients with PBC and 225 geographically and sex-matched healthy subjects for polymorphisms of genes coding for cytochromes P450 (CYPs) 2D6 (CYP2D6*4, CYP2D6*3, CYP2D6*5, and CYP2D6*6) and 2E1 (cl/c2), multidrug resistance 1 (MDR1 C3435T) P-glycoprotein, and pregnane X receptor (PXR C-25385T, C8055T, and A7635G). We compared the genotype frequencies in patients and controls and also correlated polymorphisms with PBC severity. The distributions of the studied genotypes did not significantly differ between patients and controls. However, when clinical characteristics of patients with PBC were compared according to genotype, the CYP2E1 c2 allele was associated with signs of more severe disease. In conclusion, genetic polymorphisms of CYP 2D6 and 2E1, PXR, and MDR1 do not appear to play a role in the onset of PBC.

Gene-environment interaction signatures by quantitative mRNA profiling in exfoliated buccal mucosal cells

Exfoliated cytologic specimens from mouth (buccal) epithelium may contain viable cells, permitting assay of gene expression for direct and noninvasive measurement of gene-environment interactions, such as for inhalation (e.g., tobacco smoke) exposures. We determined specific mRNA levels in exfoliated buccal cells collected by cytologic brush, using a recently developed RNA-specific real-time quantitative reverse transcription-PCR strategy. In a pilot study, metabolic activity of exfoliated buccal cells was verified by 3-[4,5-dimethylthiazol-2-yl]-2,5- diphenyltetrazolium assay in vitro. Transcriptional activity was observed, after timed in vivo exposure to mainstream tobacco smoke resulted in induction of CYP1B1 in serially collected buccal samples from the one subject examined. For a set of 11 subjects, mRNA expression of nine genes encoding carcinogen- and oxidant-metabolizing enzymes qualitatively detected in buccal cells was then shown to correlate with that in laser-microdissected lung from the same individuals (Chi2 = 52.91, P < 0.001). Finally, quantitative real-time reverse transcription-PCR assays for seven target gene (AhR, CYP1A1, CYP1B1, GSTM1, GSTM3, GSTP1, and GSTT1) and three reference gene [glyceraldehyde-3-phosphate dehydrogenase (GAPDH), beta-actin, and 36B4] transcripts were performed on buccal specimens from 42 subjects. In multivariate analyses, gender, tobacco smoke exposure, and other factors were associated with the level of expression of CYP1B1, GSTP1, and other transcripts on a gene-specific basis, but substantial interindividual variability in mRNA expression remained unexplained. Within the power limits of this pilot study, gene expression signature was not clearly predictive of lung cancer case or control status. This noninvasive and quantitative method may be incorporated into high-throughput human applications for probing gene-environment interactions associated with cancer.

Proteasomal Degradation of Human CYP1B1: Effect of the Asn453Ser Polymorphism on the Post-Translational Regulation of CYP1B1 Expression

Allelic variations in CYP1B1 are reported to modulate the incidence of several types of cancer. To provide a mechanistic basis for this association, we investigated the impact of nonsilent allelic changes on the intracellular levels and post-translational regulation of CYP1B1 protein. When transiently expressed in COS-1 cells, either in the presence or absence of recombinant cytochrome P450 reductase, the cellular level of the CYP1B1.4 allelic variant (containing a Ser at the amino acid position 453; Ser453) was 2-fold lower compared with the other four allelic CYP1B1 proteins (containing Asn453), as analyzed by both immunoblotting and ethoxyresorufin O-deethylase activity. This difference was caused by post-translational regulation; as in the presence of cycloheximide, the rate of degradation of immunodetectable and enzymatically active CYP1B1.4 was distinctly faster than that of CYP1B1.1. Pulse-chase analysis revealed that the half-life of CYP1B1.4 was a mere 1.6 h compared with 4.8 h for CYP1B1.1. The presence of the proteasome inhibitor MG132 [N-benzoyloxycarbonyl (Z)-Leu-Leuleucinal] increased the stability not only of immunodetectable CYP1B1, but also--unexpectedly given the size of the proteasome access channel--increased the stability of enzymatically active CYP1B1. The data presented herein also demonstrate that CYP1B1 is targeted for its polymorphism-dependent degradation by polyubiquitination but not phosphorylation. Our results importantly provide a mechanism to explain the recently reported lower incidence of endometrial cancer in individuals carrying the CYP1B1*4 compared with the CYP1B1*1 haplo-type. In addition, the mechanistic paradigms revealed herein may explain the strong overexpression of CYP1B1 in tumors compared with nondiseased tissues.

Analysis of the involvement of human N-acetyltransferase 1 in the genotoxic activation of bladder carcinogenic arylamines using a SOS/umu assay system

Human acetyltransferase genes NAT1 or NAT2 were expressed in a Salmonella typhimurium strain used to detect the genotoxicity of bladder carcinogens. To clarify whether the human and rodent bladder carcinogenic arylamines are activated via either NAT1 or NAT2 to cause genotoxicity, a SOS/umu genotoxicity assay was used, with the strains S. typhimurium NM6001 (NAT1-overexpressing strain), S. typhimurium NM6002 (NAT2-overexpressing strain), and S. typhimurium NM6000 (O-AT-deficient parent strain). Genotoxicity was measured by induction of SOS/umuC gene expression in the system, which contained both an umuC"lacZ fusion gene and NAT1 or NAT2 plasmids. 4-Aminobiphenyl, 2-acetylaminofluorene, beta-naphthylamine, o-tolidine, o-anisidine, and benzidine exhibited dose-dependent induction of the umuC gene in strain NM6001. Although the induction of umuC by these chemicals was observed in the NM6002 strain, the induction was considerably lower than in the NM6001 strain. In the parent strain, NM6000, none of these compounds induced umuC gene expression. We also determined activation of these chemicals by recombinant human cytochrome P450 (P450 or CYP) 1A2 enzyme in three S. typhimurium tester strains. The activation of the chemicals was stronger in the NM6001 strain than that in NM6002. The specific NAT1 inhibitor 5-iodosalicylic acid inhibited umuC gene expression induced by aromatic amines used. These results could provide evidence that the bladder carcinogenic aromatic amines are mainly activated by the NAT1 enzyme to produce DNA damage rather than NAT2. The NAT1-overexpressing strain can be used to determine the genotoxic activation of bladder carcinogenic arylamines in the umu test and could provide a tool for predicting the carcinogenic potential of arylamines.

Involvement of cytochrome P450 1A2 in the biotransformation of trans-resveratrol in human liver microsomes

This study was aimed at identifying the isoform(s) of human liver cytochrome P450 (CYP) involved in the hepatic biotransformation of trans-resveratrol (trans-3,5,4'-trihydroxystilbene). Trans-resveratrol metabolism was found to yield two major metabolites, piceatannol (3,5,3',4'-tetrahydroxystilbene) and another tetrahydroxystilbene named M1. Trans-resveratrol was hydroxylated to give piceatannol and M1 with apparent K(m) of 21 and 31 microM, respectively. Metabolic rates were in the range 14-101 pmol min(-1) mg(-1) protein for piceatannol and 29-161 pmol min(-1) mg(-1) protein for M1 in the 13 human liver microsomes tested. Using microsomal preparations from different human liver samples, piceatannol and M1 formation significantly correlated with ethoxy-resorufin-O-deethylation (r(2) = 0.84 and 0.88, respectively), phenacetin-O-deethylation (r(2) = 0.92 and 0.94) and immuno-quantified CYP1A2 (r(2) = 0.85 and 0.90). Formation of these metabolites was markedly inhibited by alpha-naphthoflavone and furafylline, two inhibitors of CYP1A2. Antibodies raised against CYP1A2 also inhibited the biotransformation of trans-resveratrol. In addition, the metabolism of trans-resveratrol into these two metabolites was catalyzed by recombinant human CYP1A1, CYP1A2 and CYP1B1. Our results provide evidence that in human liver, CYP1A2 plays a major role in the metabolism of trans-resveratrol into piceatannol and tetrahydroxystilbene M1.

Disinfection byproducts and bladder cancer: a pooled analysis

BACKGROUND

Exposure to disinfection byproducts in drinking water has been associated with an increased risk of bladder cancer. We pooled the primary data from 6 case-control studies of bladder cancer that used trihalomethanes as a marker of disinfection byproducts.

METHODS

Two studies were included from the United States and one each from Canada, France, Italy, and Finland. Inclusion criteria were availability of detailed data on trihalomethane exposure and individual water consumption. The analysis included 2806 cases and 5254 controls, all of whom had measures of known exposure for at least 70% of the exposure window of 40 years before the interview. Cumulative exposure to trihalomethanes was estimated by combining individual year-by-year average trihalomethane level and daily tap water consumption.

RESULTS

There was an adjusted odds ratio (OR) of 1.24 in men exposed to an average of more than 1 microg/L (ppb) trihalomethanes compared with those who had lower or no exposure (95% confidence interval [CI] = 1.09-1.41). Estimated relative risks increased with increasing exposure, with an OR of 1.44 (1.20-1.73) for exposure higher than 50 microg/L (ppb). Similar results were found with other indices of trihalomethane exposure. Among women, trihalomethane exposure was not associated with bladder cancer risk (0.95; 0.76-1.20).

CONCLUSIONS

These findings strengthen the hypothesis that the risk of bladder cancer is increased with long-term exposure to disinfection byproducts at levels currently observed in many industrialized countries.

Selective suppression of cytochrome P450 gene expression by the medicinal herb, Thonningia sanguinea in rat liver

The effect of the administration of Thonningia sanguinea (T. S.) on the abundance of individual components of the cytochrome P450 monooxygenase enzyme was examined using Western blotting and competitive reverse-transcriptase-polymerase chain reaction (RT-PCR). We also investigated the time-course of inhibition of T. S. on drug metabolizing enzymes. A single intraperitoneal dose of T. S. extract (5 ml/kg) suppressed CYP, cytochrome b5 and NADPH-CYP reductase activity by 45%, 34% and 22% respectively 24 h after T. S. administration. While T. S. did not have any significant effect on microsomal glutathione S-transferase activity, it inhibited p-nitrophenol hydroxylase (PNPH, CYP2E1) and 7-methoxyresorufin O-demethylase (MROD, CYP 1A2) activities by 37% and 32% respectively at 12 h post-T. S. administration. PNPH, erythromycin N-demethylase (ERDM, CYP 3A1/2) and MROD activities were inhibited by 28-36% 24 h after T. S. injection. Consistent with these observations, the levels of CYP2E1, CYP1A2 and CYP3A2 proteins were also suppressed 24 h post-T. S. administration. While CYP2E1 mRNA was unaffected by T. S. administration, CYP1A2 and CYP3A2 mRNAs were decreased by T. S. Cytosolic glutathione S-transferase activity was increased by 30%, 6 h after T. S injection. These data demonstrate that administration of T. S. differentially affect CYP isoforms in the liver of rats and that T. S. selectively suppresses CYP3A2 and CYP1A2 gene expression.

Identification of cytochrome P450 isoforms involved in 1-hydroxylation of pyrene

Urinary 1-hydroxypyrene (1-OHP) has been used as a biomarker for environmental polyaromatic hydrocarbon (PAH) exposure. However, it is known that there is an interindividual variability in metabolism of pyrene to 1-OHP depending on the activities of the metabolizing enzymes, especially cytochrome P450s (CYPs). In this study, we investigated the 1-hydroxylation of pyrene by 10 forms of cDNA-expressed human P450s in order to identify the principal isoforms of P450s that are involved in the major metabolic pathway of pyrene. The pyrene 1-hydroxylation activity was found to be the highest in CYP1A1 at both 0.5 and 50microM of pyrene, followed by CYP1B1 and 1A2, whereas other enzymes, including CYP2A6, 2C8, 2C9*1, 2C19, 2D6, 2E1, 3A4, and control microsomes, showed very low or undetectable rates of 1-hydroxylation. In conclusion, CYP1A1, 1B1, and 1A2 are major metabolizing enzymes in 1-hydroxylation of pyrene in vitro. This suggests that the individual difference of these enzymes must be included in epidemiological studies to evaluate PAH exposure using urinary 1-OHP.

Effect of artificial mixtures of environmental polycyclic aromatic hydrocarbons present in coal tar, urban dust, and diesel exhaust particulates on MCF-7 cells in culture

Human exposure to polycyclic aromatic hydrocarbons (PAHs) occurs through complex mixtures. The National Institute of Standards and Technology has established standard reference materials (SRMs) for selected PAH mixtures that are composed of carcinogenic, noncarcinogenic, and weakly carcinogenic compounds, such as those derived from coal tar (SRM 1597), atmospheric particulate matter (SRM 1649), and diesel particulate matter (SRM 1650). To study the effects of PAHs with different carcinogenic potential in complex mixtures, and to investigate the metabolic activation of noncarcinogenic and weakly carcinogenic PAHs to DNA-binding derivatives, artificial mixtures (1597H, 1649H, and 1650H) were prepared in the laboratory. These artificial mixtures contained the same relative ratios of noncarcinogenic and weakly carcinogenic PAHs present in SRM 1597, SRM 1649, and SRM 1650. The human mammary carcinoma-derived cell line MCF-7 was treated with these artificial mixtures and analyzed for PAH-DNA adduct formation and the induction of cytochrome P450 (CYP) enzymes. We found that the artificial mixtures formed lower but detectable levels of DNA adducts 24 and 48 hr after treatment than benzo[a]pyrene. Induction of CYP enzyme activity was measured by the ethoxyresorufin-O-deethylase assay, and the expression of CYP1A1 and CYP1B1 was confirmed by immunoblots. Both noncarcinogenic and weakly carcinogenic PAHs present in the artificial mixtures have the ability to induce CYP1A1 and CYP1B1 in MCF-7 cells and contribute to DNA binding. Therefore, it is necessary to take into account the noncarcinogenic and weakly carcinogenic PAHs present in environmental mixtures in assessing the potential risk associated with human exposure.

Genetic polymorphisms and susceptibility to childhood acute lymphoblastic leukemia

Acute lymphoblastic leukemia (ALL) is the most common form of pediatric cancer. Although exposure to environmental agents appears to predispose individuals to this disease, little attention has been paid to the role of genetic susceptibility to environmental exposures in the etiology of childhood ALL. The enzymes GSTM1, GSTT1, GSTP1, CYP1A1, and CYP2E1 are involved in the bioactivation and detoxification of a variety of xenobiotics present in food, organic solvents, tobacco smoke, drugs, alcoholic drinks, pesticides, and environmental pollutants. Polymorphisms in the genes coding for these enzymes have been associated with increased susceptibility to different cancers, including hematologic malignancies. To investigate whether these polymorphisms represent risk-modifying factors for childhood ALL, a study was conducted involving 113 Brazilian patients of childhood ALL and 221 controls with similar ethnic backgrounds. The data revealed that carriers of the rare GSTP1 Val allele were at higher risk of ALL (odds ratio [OR] = 2.7; 95% confidence interval [CI] = 1.1-6.8; P = 0.04). No difference was found in the prevalence of the GSTM1 and GSTT1 null genotypes between ALL patients and the controls, and no association was found between CYP1A1*2 and CYP2E1*3 variants and ALL. However, when the mutant CYP1A1 and CYP2E1 alleles were considered together with the GSTM1 and GSTP1 risk-elevating genotypes, the risk of ALL was increased further (OR = 10.3; 95% CI = 1.0-111.8; P = 0.05), suggesting a combined effect. These results imply that genetic variants of xenobiotic metabolizing genes influence the risk of developing childhood ALL.

Hepatic drug metabolism and transport in patients with kidney disease

The disposition of many drugs is altered in patients with acute (AKD) and chronic kidney disease (CKD). A decline in renal clearance of several drugs has been correlated significantly with residual renal function (ie, creatinine clearance) of subjects. Reductions in nonrenal clearance of some compounds also have been reported and associated with clearance of markers of oxidative and/or conjugative metabolism or P-glycoprotein-mediated transport. Although initial accounts of reduced hepatic microsomal cytochrome P-450 (CYP) content and activity in animal models of AKD and CKD were published almost 25 years ago, it is only in the last decade that technical advances in molecular biology and clinical pharmacology have enabled researchers to begin to characterize the phenotypic expression of individual enzymes and, importantly, distinguish the molecular and/or genetic basis for these changes. The selective modulation of hepatic CYP enzyme activity observed in kidney disease is caused, at least in part, by differentially altered expression of several CYP isoforms. This review summarizes data available through June 2003 regarding the effect of AKD and CKD on drug metabolism. Knowledge of the impact and nature of these alterations associated with kidney disease may facilitate the individualization of medication management in this patient population.

A quantitative structure-activity relationship (QSAR) study of mutagenicity in several series of organic chemicals likely to be activated by cytochrome P450 enzymes

The results of quantitative structure-activity relationship (QSAR) studies on six series of compounds exhibiting indirect mutagenic activity are reported. These findings demonstrate the importance of frontier orbital energies and, in some cases, frontier orbital electronic populations to overall mutagenicity in diverse polyaromatic hydrocarbons, benzidines and aminobiphenyls, benzonitrofurans, nitrogenous cooked-food mutagens, benzanthracenes, and chrysenes. The correlations between structural parameters and mutagenic potency vary from R=0.81 to R=0.97, and these findings are discussed in the context of possible molecular mechanisms of mutagenicity. In particular, it is generally regarded that cytochrome P450-mediated activation of polyaromatic hydrocarbons and their amino derivatives plays an important role in mutagenic activity. In this respect, it is apparent that enzymes of the cytochrome P4501 (CYP1) family are closely associated with the metabolic activation of polyaromatic mutagens and carcinogens via the generation of reactive intermediates (usually electrophilic in nature) that attack DNA. The findings presented in this study indicate that QSAR analyses on several series of compounds are consistent with the known evidence of procarcinogen activation mechanisms, particularly for polyaromatic hydrocarbons and their heterocyclic/amino derivatives, pointing to the importance of frontier orbital energy values in particular.

Regulatory mechanisms controlling gene expression mediated by the antioxidant response element

The expression of genes encoding antioxidative and Phase II detoxification enzymes is induced in cells exposed to electrophilic compounds and phenolic antioxidants. Induction of these enzymes is regulated at the transcriptional level and is mediated by a specific enhancer, the antioxidant response element or ARE, found in the promoter of the enzyme's gene. The transcription factor Nrf2 has been implicated as the central protein that interacts with the ARE to activate gene transcription constitutively or in response to an oxidative stress signal. This review focuses on the molecular mechanisms whereby the transcriptional activation mediated by the interaction between the ARE and NF-E2-related factor 2 (Nrf2) is regulated. Recent studies suggest that the sequence context of the ARE, the nature of the chemical inducers, and the cell type are important for determining the activity of the enhancer in a particular gene.

Molecular epidemiology of sporadic breast cancer. The role of polymorphic genes involved in oestrogen biosynthesis and metabolism

The major known risk factors for female breast cancer are associated with prolonged exposure to increased levels of oestrogen. The predominant theory relates to effects of oestrogen on cell growth. Enhanced cell proliferation, induced either by endogenous or exogenous oestrogens, increases the number of cell divisions and thereby the possibility for mutation. However, current evidence also supports a role for oxidative metabolites, in particular catechol oestrogens, in the initiation of breast cancer. As observed in drug and chemical metabolism, there is considerable interindividual variability (polymorphism) in the conjugation pathways of both oestrogen and catechol oestrogens. These person-to-person differences, which are attributed to polymorphisms in the genes encoding for the respective enzymes, might define subpopulations of women with higher lifetime exposure to hormone-dependent growth promotion, or to cellular damage from particular oestrogens and/or oestrogen metabolites. Such variation could explain a portion of the cancer susceptibility associated with reproductive effects and hormone exposure. In this paper the potential role of polymorphic genes encoding for enzymes involved in oestrogen biosynthesis (CYP17, CYP19, and 17beta-HSD) and conversion of the oestrogen metabolites and their by-products (COMT, CYP1A1, CYP1B1, GSTM1, GSTM3, GSTP1, GSTT1 and MnSOD) in modulating individual susceptibility to breast cancer are reviewed. Although some of these low-penetrance genes appeared as good candidates for risk factors in the etiology of sporadic breast cancer, better designed and considerably larger studies than the majority of the studies conducted so far are evidently needed before any firm conclusions can be drawn.

Hepatic versus extrahepatic expression of CYP3A30 and CYP3A56 in adult killifish (Fundulus heteroclitus)

Members of the CYP3A subfamily represent the largest portion of CYP proteins in liver and intestine in vertebrates. The CYP3A enzymes are involved in metabolic clearance of numerous chemically diverse compounds including toxins, carcinogens, pesticides, therapeutic drugs, dietary products and hormones. Most studies of CYP3A have been performed in mammals, whereas relatively little is known of that in non-mammalian species. We have investigated CYP3A expression in the marine and estuarine killifish (Fundulus heteroclitus). We isolated a novel CYP3A cDNA sequence, denoted CYP3A56, from killifish intestine. The CYP3A56 sequence shared 98% nucleotide and amino acid sequence identity with CYP3A30, previously isolated from killifish liver. We hypothesize that a recent gene duplication event has occurred within the killifish CYP3A subfamily. The CYP3A30 and CYP3A56 genes were co-expressed in liver, intestine, gill, kidney, spleen, brain and ovary in several individuals. The hepatic versus extrahepatic CYP3A30/56 mRNA expression was analyzed in adult killifish of both sexes, using conventional as well as real-time semi-quantitative RT-PCR. Tissues expressing CYP3A30/56 mRNA were in a descending order of magnitude: liver>intestine>>gill>spleen>kidney>brain. Furthermore, inter-individual differences (up to 18%) in CYP3A30/56 mRNA expression were evident in killifish, in particular in extrahepatic organs. For comparison, CYP3A protein expression levels were determined using polyclonal antibodies (PAb) against rainbow trout (Oncorhynchus mykiss) CYP3A. Sexually dimorphic expression of hepatic and extrahepatic CYP3A30/56 mRNA and CYP3A proteins was observed in killifish. For example, males displayed up to 2.5-fold higher CYP3A protein expression compared with females. In agreement with CYP3A30/56 mRNA analysis, highest CYP3A protein levels were observed in liver and intestine. Low CYP3A protein levels were seen in gill, kidney and spleen. Cellular localization of CYP3A protein expression was investigated using immunohistochemistry analysis and PAb against rainbow trout CYP3A. Strong CYP3A protein staining was seen in intestinal enterocytes, in gill filaments and in renal tubular epithelial cells. Moderate CYP3A staining was seen in hepatocytes in the liver, whereas mild staining was observed in hematopoietic cells in the spleen and in follicles in the ovary. Thus, similar to mammals, CYP3A expression in fish is prominent in the digestive- and respiratory tracts and may be important for the first-pass metabolism of xenobiotics. Moreover, CYP3A expression also is evident in brain and ovary in killifish, which suggests a role for CYP3A enzymes in biotransformation of xenobiotics and fine-tuning levels of steroid hormones in situ in extrahepatic organs.

Functional evaluation of novel single nucleotide polymorphisms and haplotypes in the promoter regions of CYP1B1 and CYP1A1 genes

Interindividual variation in the expression of the carcinogen- and estrogen-metabolizing enzymes cytochrome P4501B1 and 1A1 (CYP1B1 and CYP1A1) has been detected in human lung. To search for polymorphisms with functional consequences for CYP1B1 and CYP1A1 gene expression, we examined 1.5 kb of the promoter region of each gene. Genomic DNA from 21 Caucasian individuals was amplified by polymerase chain reaction (PCR) for direct cycle sequencing. Eight single nucleotide polymorphisms (SNPs) for CYP1B1 and 13 SNPs for CYP1A1 were found. The majority of polymorphisms occurred as multiSNP combinations for individual subjects. The wild-type sequences were cloned into a luciferase reporter construct. The most frequent polymorphisms were then recreated by iterative site-directed mutagenesis, replicating single polymorphisms and multiSNP combinations. These wild-type and variant constructs were functionally evaluated in transient transfection experiments employing exposures to either the index polycyclic aromatic hydrocarbon (PAH) inducer benzo[a]pyrene (B[a]P), a composite mixture of cigarette smoke extract (CSE), or the repressor chemopreventive agent trans-3,4,5-trihydroxystilbene (reseveratrol). Results indicated that all wild-type and variant constructs responded in qualitatively concordant fashion to the inducers and to the repressor. The CYP1B1 haplotypes and the majority of CYP1A1 haplotypes were shown to have no functional consequence, as compared to those of the wild-type promoter sequences. Two constructs of composite polymorphisms of CYP1A1 appeared to result in a statistically significant increase in basal promoter activity (1.38- and 1.50-fold, respectively), but the degree of functional impact was judged unlikely to be biologically important in vivo. We conclude that the observed promoter region polymorphisms in these genes are common, but are of unclear functional consequence.

Effect of frying-meat emission particulate on 17beta-estradiol 2- and 4-hydroxylation in human lung adenocarcinoma CL5 cells

The effect of airborne frying-meat emission particulate (FMEP) on metabolism of 17beta-estradiol (E(2)) to potentially toxic catechol estrogens 2- and 4-hydroxyestradiol (2- and 4-OH-E(2)) was determined using human lung adenocarcinoma CL5 cells treated with organic extracts of beef FMEP. E(2) was incubated with microsomes prepared from untreated CL5 cells or cells treated with 200 microg/ml FMEP extract for 6 h. E(2) metabolites formed were analyzed by high-performance liquid chromatography (HPLC). The results revealed that treatment with FMEP produced three-and twofold increases of 2- and 4-hydroxylation of E(2), respectively. Monooxygenase activity and immunoblot analyses showed that FMEP markedly induced microsomal 7-ethoxyresorufin O-deethylase (EROD) activity and cytochrome P-450 (CYP) IAI and CYPIBI protein levels. Similar increases in E(2) hydroxylation, EROD activity, and CYP protein levels were observed with HepG2 human hepatoma and MCF-7 human breast cancer cells treated with FMEP or 1 microM dibenz[a,h]anthracene. Cotreatment of CL5 cells with FMEP extract and 2 microM alpha-naphthoflavone, an arylhydrocarbon receptor antagonist, blocked the inductive effects of FMEP on E(2) hydroxylation and EROD activity. Additions of 0.01, 0.1, or 1 microM alpha-naphthoflavone, a CYP inhibitor, to microsomes produced concentration-dependent decreases in E(2) 2-hydroxylation and EROD activity of CL5 cells induced by dibenz[a,h]anthracene. The present finding demonstrates that FMEP can increase formation of 2-OH-E(2) and 4-OH-E(2) by human lung cells, and induction of CYP1A1 and CYP1B1 is a potential mechanism underlying increased E(2) metabolism. The toxicological significance of FMEP and estrogen interaction warrants further investigation.

Correlation of antimutagenic activity and suppression of CYP1A with the lipophilicity of alkyl gallates and other phenolic compounds

Alkyl gallates are widely used as food antioxidants. Methyl, ethyl, propyl, lauryl, and cetyl gallates showed antimutagenicity to activated 2-aminoanthracene (2AA)-induced SOS responses in Salmonella typhimurium TA1535/pSK1002. They also exhibited a suppressive effect on 3-methylcholanthrene (3-MC)-induced cytochrome P450 1A (CYP1A) in human hepatoma HepG2 cells, as indexed by the 7-ethoxyresorufin-O-deethylase (EROD) activity, and on CYP1A protein level. Both antimutagenicity and suppression of CYP1A appeared to be dependent on alkyl chain lengths, which suggested lipophilicity dependence. Based on those results, we investigated 26 other phenolic compounds for their lipophilicity, antimutagenicity and inhibition of EROD activity. The lipophilicity correlated well with the inhibition of EROD activity (r=0.78), and the inhibition of EROD activity correlated with the antimutagenicity of those compounds (r=0.71). The results suggest that the lipophilicity of the phenolic compounds may be an important factor in their ability to inhibit EROD activity.