Immunohistochemical detection of pulmonary cytochrome P450IA and metabolic activities associated with P450IA1 and P450IA2 isozymes in lung cancer patients

Genetic and epigenetic modulations in toxicity: The two-sided roles of heavy metals and polycyclic aromatic hydrocarbons from the environment

This study emphasizes the importance of considering the metabolic and toxicity mechanisms of environmental concern chemicals in real-life exposure scenarios. Furthermore, environmental chemicals may require metabolic activation to become toxic, and competition for binding sites on receptors can affect the severity of toxicity. The multicomplex process of chemical toxicity is reflected in the activation of multiple pathways during toxicity of which AhR activation is major. Real-life exposure to a mixture of concern chemicals is common, and the composition of these chemicals determines the severity of toxicity. Nutritional essential elements can mitigate the toxicity of toxic heavy metals, while the types and ratio of composition of PAH can either increase or decrease toxicity. The epigenetic mechanisms of heavy metals and PAH toxicity involves either down-regulation or up-regulation of some non-coding RNAs (ncRNAs) whereas specific small RNAs (sRNAs) may have dual role depending on the tissue and circumstance of expression. Similarly, decrease DNA methylation and histone modification are major players in heavy metals and PAH mediated toxicity and FLT1 hypermethylation is a major process in PAH induced carcinogenesis. Overall, this review provides the understanding of the metabolism of environmental concern chemicals, emphasizing the importance of considering mixed compositions and real-life exposure scenarios in assessing their potential effects on human health and diseases development as well as the dual mechanism of toxicity via genetic or epigenetic axis.

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.

Genetic polymorphisms of human cytochrome P450 CYP1A1 in an Egyptian population and tobacco-induced lung cancer

Background

Cytochrome P450 CYP1A1 helps detoxify the potential carcinogens in tobacco smoke, it was reported that polymorphisms in the coding gene result in variation in the expression and activity levels which alter metabolism and clearance of carcinogens and therefore modify cancer risk. In this work, we aimed to identify CYP1A1 gene polymorphisms associated with lung cancer in Egyptian population and to examine the interaction effect with Tobacco smoking in modulating disease risk.

Methods

A case–control study was conducted on 150 unrelated lung cancer patients and 150 unrelated control subjects. Genomic DNA was extracted and sequencing analysis of CYP1A1 gene was performed on ABI PRISM 3100 genetic analyzer.

Results

Three variants in CYP1A1 gene were identified in heterozygous forms in lung cancer patients I462V, T461N and I286T. A combined variant T461N/ I462V associated with lung cancer and those who carried this variant were 2-times more likely to develop lung cancer (OR = 2.03, 95% CI = 1.81-2.29, P = 0.04), specially the non-small cell type (NSCLC) (OR = 2.20, 95% CI = 1.93–2.50, P = 0.02). Wild type was more frequent among smoker controls (83.3%) compared to smoker lung cancer patients (54.8%), P = 0.03. Association studies to examine the interaction effect of identified variants with Tobacco smoking in modulating disease risk showed no significant associations. Identified polymorphisms showed no significant implication on the stage or the prognosis of the disease.

Conclusion

Our findings support that CYP1A1 polymorphisms play a role in the pathogenesis of lung cancer. In Egyptian population, CYP1A1 I462V, T461N and I286T variants were identified among lung cancer patients and combined T461N/ I462V was a risk variant for NSCLC in non smokers.

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.

CYP1A1 gene polymorphisms increase lung cancer risk in a high-incidence region of Spain: a case control study

Background

A rural region in south-west Spain has one of the highest lung cancer incidence rates of the country, as revealed by a previous epidemiological 10-year follow-up study. The present work was undertaken to ascertain the role of CYP1A1 gene polymorphisms and their interaction with tobacco smoking in the development of the disease in this location.

Methods

One-hundred-and-three cases of lung cancer and 265 controls participated in the study. The participants were screened for the presence of four CYP1A1 polymorphisms, namely MspI, Ile462Val, T3205C, and Thr461Asn. Lung cancer risk was estimated as odds ratios (OR) and 95% confidence intervals (CI) using unconditional logistic regression models adjusting for age, sex, and smoking.

Results

The distribution of the variant CYP1A1 alleles was different from that described for other Caucasian populations, with CYP1A1*2A showing an uncommonly high frequency (p < 0.01). The CYP1A1*2B allele (carrying MspI and Ile462Val mutations) was strongly associated with high lung cancer risk (OR = 4.59, CI:1.4-12.6, p <0.01). The Ile462Val polymorphism was also shown to increase the risk for the disease (OR = 4.51, CI:1.8-11.9; p <0.01) and particularly for squamous-cell (OR = 5.01; CI: 1.6-14.3, p < 0.01) and small-cell lung carcinoma (SCLC) (OR = 6.97, CI: 1.2-81.3; p = 0.04). Moreover, the Thr461Asn polymorphism was found to be associated with SCLC in a Caucasian population for the first time to our knowledge (OR = 8.33, CI: 1.3-15.2, p = 0.04).

Conclusion

The results suggest that CYP1A1 polymorphisms contribute to increase lung cancer susceptibility in an area with an uncommon high incidence rate.

Association between the CYP1A1 gene polymorphism and susceptibility to emphysema and lung cancer

Aim-To investigate cytochrome P4501A1 (CYP1A1) polymorphism and susceptibility to emphysema and lung cancer.Methods-A novel polymerase chain reaction (PCR) for genotyping the CYP1A1 polymorphism, corresponding to putative low or high enzyme activity, was developed to genotype lung cancer resection samples which had been assessed macroscopically for the presence of centriacinar and panacinar emphysema. Samples were collected and genotyped from a group of patients with chronic obstructive airways disease. A control group of anonymous blood donations was genotyped to determine the basal levels of the polymorphism in the Scottish population.Results-The high activity allele of the CYP1A1 gene is associated with susceptibility to centriacinar emphysema and lung cancer but not panacinar emphysema. CYP1A1 polymorphism is not linked to lung cancer in the absence of emphysema, nor to chronic obstructive airways disease which is the clinical manifestation of emphysema, particularly of the panacinar type.Conclusions-Susceptibility to emphysema and lung cancer is associated with polymorphism of the P4501A1 gene. A trend towards damage of centriacinar pattern has been detected, which supports the theory that centriacinar emphysema results from local, direct damage to the respiratory bronchioles from exposure to cigarette smoke.

Update information on drug metabolism systems--2009, part II: summary of information on the effects of diseases and environmental factors on human cytochrome P450 (CYP) enzymes and transporters

The present paper is an update of the data on the effects of diseases and environmental factors on the expression and/or activity of human cytochrome P450 (CYP) enzymes and transporters. The data are presented in tabular form (Tables 1 and 2) and are a continuation of previously published summaries on the effects of drugs and other chemicals on CYP enzymes (Rendic, S.; Di Carlo, F. Drug Metab. Rev., 1997, 29(1-2), 413-580., Rendic, S. Drug Metab. Rev., 2002, 34(1-2), 83-448.). The collected information presented here is as stated by the cited author(s), and in cases when several references are cited the latest published information is included. Inconsistent results and conclusions obtained by different authors are highlighted, followed by discussion of the major findings. The searchable database is available as an Excel file, for information about file availability contact the corresponding author.

Critical appraisal of the expression of cytochrome P450 enzymes in human lung and evaluation of the possibility that such expression provides evidence of potential styrene tumorigenicity in humans

Styrene is widely used with significant human exposure, particularly in the reinforced plastics industry. In mice it is both hepatotoxic and pneumotoxic, and this toxicity is generally thought to be associated with its metabolism to styrene oxide. Styrene causes lung tumors in mice but not in rats. The question is how the tumorigenic effect in mouse lung may relate to the human. This review examines the comparison of the metabolic activation rates (1) between the liver and lung and (2) for the lung, between the rodent and human. Emphasis is placed on the specific cytochromes P450 present in the lungs of humans and what role they might play in the bioactivation of styrene and other compounds. In general, pulmonary metabolism is very slow compared to hepatic metabolism. Furthermore, metabolic rates in humans are slow compared to those in rats and mice. There is a wide difference in what specific cytochromes P450 investigators have reported as being present in human lung which makes comparisons, both inter-species and inter-organ, difficult. The general low activity for cytochrome P450 activity in the lung, especially for CYP2F1, the human homolog for CYP2F2 which has been identified in mice as being primarily responsible for styrene metabolism, argues against the hypothesis that human lung would produce enough styrene oxide to damage pulmonary epithelial cells leading to cell death, increased cell replication and ultimately tumorigenicity, the presumed mode of action for styrene in the production of the mouse lung tumors.

Characterisation of the xenobiotic-metabolizing Cytochrome P450 expression pattern in human lung tissue by immunochemical and activity determination

The lung represents an important target for the toxic effects of chemicals. Many of the chemicals require enzymatic activation to exert their adverse effects, which is mostly catalysed by Cytochrome P450 (CYP) enzymes. Although there is considerable evidence that individual members of the xenobiotic-metabolizing P450 family are expressed in human lung tissue at the mRNA level, there is conflicting evidence concerning the following issues: (I) the qualitative expression pattern of CYP isoenzymes; (II) CYP expression at the protein and/or activity level; and (III) interindividual variability of CYP enzymes in human lung. The latter can be the basis for individual susceptibility towards the adverse effects of lung toxicants. In preparing for studying factors to explain interindividual variability of CYP expression in lung tissue, we investigated the qualitative pulmonary expression pattern of xenobiotic-metabolizing CYP enzymes and elaborated the optimal conditions for quantification at the protein and activity level. By using either individual human lung samples or pooled microsomes from different individuals, immunoreactive bands specific for the following CYP enzymes could be determined by Western blotting: CYP1A1, CYP1A2, CYP2E1 and CYP3A5. Western blotting experiments were also supportive of the presence of CYP2A, CYP2B6, CYP2D6 and CYP3A4 in human lung. By using antibodies specific for CYP2C enzymes and CYP1B1, respectively, immunoreactive bands, which differed slightly in mobility from corresponding standards, were detectable. In addition, we measured methoxy- and ethoxyresorufin dealkylase activities and chlorzoxazone (CLX)-hydroxylase activity in human lung and confirmed the specifities of the latter two activities by inhibition experiments. In summary, we have established methodologies to quantify a panel of CYP enzymes in human lung samples among which there are CYP enzymes whose expression at the protein and activity level has not been evidenced so far.

A common CYP1B1 polymorphism is associated with 2-OHE1/16-OHE1 urinary estrone ratio

Cytochrome P450 (CYP) is a multigene family of enzymes involved in important life functions; some of these genes are inducible and are implicated in the oxidative metabolic activation and detoxification of many endogenous and exogenous compounds.

Differences in cytochrome P450 forms involved in the metabolism of N,N-dipropyl-2-[4-methoxy-3-(2-phenylethoxy)phenyl]ethylamine monohydrochloride (NE-100), a novel sigma ligand, in human liver and intestine

N,N-Dipropyl-2-[4-methoxy-3-(2-phenylethoxy)phenyl]ethylamine monohydrochloride (NE-100) has been developed to treat subjects with schizophrenia. This drug is mainly excreted in the form of oxidative metabolites. In the present study, identification of p450 forms involved in the metabolism was carried out using human livers and intestinal microsomes (HLM and HIM). Eadie-Hofstee plots for NE-100 disappearance in HLM were biphasic, thus indicating the involvement of at least two p450 forms. The metabolism of NE-100 was mediated with recombinant CYP1A1, CYP1A2, CYP2C9, CYP2C19, CYP2D6, and CYP3A4. A significant correlation was observed between activities of NE-100 metabolism and dextromethorphan O-demethylation (a specific activity for CYP2D6) or testosterone 6beta-hydroxylation (a specific activity for CYP3A4) in HLM. The activity of NE-100 metabolism was inhibited by approximately 80% by an anti-CYP2D6 antibody and only by quinidine among the p450-selective inhibitors at a low substrate concentration (0.1 microM). In contrast, with a high substrate concentration (10 microM), the activity was inhibited by an anti-CYP3A4 antibody and by ketoconazole. On the other hand, in HIM, the Eadie-Hofstee plots for NE-100 disappearance were monophasic, and the metabolism was strongly inhibited by an anti-CYP3A4 antibody and by ketoconazole but not by other inhibitors used. These results strongly suggest that NE-100 has different profiles regarding metabolism between liver and intestine. During absorption, NE-100 is mainly metabolized by CYP3A4 in the intestine and thereafter by CYP2D6 in the liver in the presence of therapeutic doses.

Expression and regulation of xenobiotic-metabolizing cytochrome P450 (CYP) enzymes in human lung

Pathogenesis of lung diseases, such as lung cancer and chronic obstructive pulmonary disease, is tightly linked to exposure to environmental chemicals, most notably tobacco smoke. Many of the compounds associated with these diseases require an enzymatic activation to exert their deleterious effects on pulmonary cells. These activation reactions are mostly catalyzed by cytochrome P450 (CYP) enzymes. Interindividual differences in the in situ activation and inactivation of chemical toxicants may contribute to the risk of developing lung diseases associated with these compounds. This review summarizes in detail the expression of individual CYP forms in human pulmonary tissue and gives a view on the significance of the pulmonary expression of CYP enzymes. The localization of individual CYP enzymes in various cell types of human lung and the emerging field of regulation of human pulmonary CYP enzymes are discussed. At least CYP1A1 (in smokers), CYP1B1, CYP2B6, CYP2E1, CYP2J2, and CYP3A5 proteins are expressed in human lung, and also other CYP forms are likely to be expressed. Xenobiotic-metabolizing CYP enzymes are mostly expressed in bronchial and bronchiolar epithelium, Clara cells, type II pneumocytes, and alveolar macrophages in human lung, although individual CYP forms have different patterns of localization in pulmonary tissues. Problems in animal to human lung toxicity extrapolation and several specific aspects requiring more detailed assessment are identified.

Use of biomarkers in risk assessment

The systematic development and application of biomarkers in environmental health risk assessment is a relatively new field. At first, the major interest was in biomarkers of exposure, borrowing concepts from pharmacology, then it moved from the external estimates of exposure to internal measures of dose, and ultimately, to markers of target dose. While these markers provide evidence of exposures, they do not provide evidence of that toxicological damage has occurred. For this reason, measurements of DNA adducts and protein adducts are of interest, since they may provide bridges between exposures and disease end-points. In parallel, more quantitative and more sensitive end-points for diseases have been sought. Again, with advancing techniques in cytogenetics, extensive studies were conducted on such markers as chromosomal aberrations, micronuclei and other changes deemed to represent genomic damage. However, these types of end-points are quite unspecific for application to new hazards of uncertain human toxic (carcinogenic) potential. Recent work focusing on more specific early-effect markers such as certain oncogenes and tumour-suppressor genes have substantial promise as shown by work with aflatoxins and vinyl chloride. Such studies have also enhanced mechanistic insight. The advances in molecular genetics have led to an upsurge in interest in most susceptibility factors, and identification of polymorphisms of various enzymes has become possible. Ongoing search for "ultra-high risk" individuals may be fruitful, but probably only relevant to a small segment of potentially exposed populations. Factors associated with a small differential risk, however theoretically or mechanistically important, offer only little practical use.

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.

Evaluation of benzo(a)pyrene-induced DNA damage in human endothelial cells using alkaline single cell gel electrophoresis

The alkaline version of the 'comet assay' was used to evaluate DNA damage in human umbilical vein endothelial cells (HUVEC) exposed to 0.1, 1.0, or 10 microM benzo(a)pyrene for 90min. The genotoxicity was monitored in HUVEC pretreated with the Ah-receptor agonist beta-naphthoflavone (BNF), previously shown to induce cytochrome P4501A1 (CYP1A1) activity in these cells, and in vehicle-treated HUVEC with only constitutive levels of this enzyme. Increased DNA damage was observed only in cells that had been exposed to 10 microM benzo(a)pyrene, cells exposed to BNF being subjected to the most extensive damage. The CYP1A/B-inhibitor alpha-naphthoflavone (ANF) reduced the benzo(a)pyrene-induced DNA-damage in the BNF-treated HUVEC to the same level as in the uninduced cells. The fact that benzo(a)pyrene induced DNA damage in vehicle-treated HUVEC suggests that there may be at least one alternative route of bioactivation for benzo(a)pyrene in these cells. Consequently, judging from the present results it seems as if tobacco-related polycyclic aromatic hydrocarbons (PAHs) may disrupt the function of the endothelial lining in blood vessels with low monooxygenase activity. It is proposed that exposure to Ah receptor agonists via, for example, tobacco smoke, may enhance the DNA-damaging effects of smoke-related genotoxic PAHs in human endothelial cells. The role of PAHs in endothelial dysfunction of tobacco smokers should therefore be further studied.

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 of drug metabolising enzymes: pharmacokinetic and toxicological consequences in humans

Currently, 5 different main mechanisms of induction are distinguished for drug-metabolising enzymes. The ethanol type of induction is mediated by ligand stabilisation of the enzyme, but the others appear to be mediated by intracellular 'receptors'. These are the aryl hydrocarbon (Ah) receptor, the peroxisome proliferator activated receptor (PPAR), the constitutive androstane receptor (CAR, phenobarbital induction) and the pregnane X receptor [PXR, rifampicin (rifampin) induction]. Enzyme induction has the net effect of increasing protein levels. However, many inducers are also inhibitors of the enzymes they induce, and the inductive effects of a single drug may be mediated by more than one mechanism. Therefore, it appears that every inducer has its own pattern of induction; knowledge of the main mechanism is often not sufficient to predict the extent and time course of induction, but may serve to make the clinician aware of potential dangers. The possible pharmacokinetic consequences of enzyme induction depend on the localisation of the enzyme. They include decreased or absent bioavailability for orally administered drugs, increased hepatic clearance or accelerated formation of reactive metabolites, which is usually related to local toxicity. Although some severe drug-drug interactions are caused by enzyme induction, most of the effects of inducers are not detected in the background of nonspecific variation. For any potent inducer, however, its addition to, or withdrawal from, an existing drug regimen may cause pronounced concentration changes and should be done gradually and with appropriate monitoring of therapeutic efficacy and adverse events. The toxicological consequences of enzyme induction in humans are rare, and appear to be mainly limited to hepatoxicity in ethanol-type induction.

Studies on biomarkers in cancer etiology and prevention: a summary and challenge of 20 years of interdisciplinary research

Sensitive, specific methods have been developed that allow quantitative measurements of the metabolites of carcinogen metabolites and of DNA and protein adducts in humans exposed occupationally, environmentally and endogenously to genotoxic agents. The interrelationship between exposure to carcinogens, host risk factors and the responses of biomarkers has been examined in cross-sectional, ecological and case-control studies which provided new insights into the causes of cancer and the mechanisms of carcinogenesis. The identification of hitherto unknown DNA-reactive chemicals formed in the human body from dietary precursors and of carcinogenic components of complex mixtures has increased the possibility of establishing causal relationships in etiology. The identification of individuals and subgroups heavily exposed to carcinogens has led to the development of measures for avoiding or decreasing exposure to carcinogenic risk factors. New, ultrasensitive methods for measuring DNA adducts allow the quantification and structural elucidation of specific DNA damage in humans arising from oxidative stress and lipid peroxidation (LPO), which have been found to be the driving forces in several human malignancies. Background DNA damage in "unexposed" individuals has been shown unequivocally to be due to LPO products, and a significant interindividual variation in adduct levels has been shown in individuals with comparable exposure to carcinogens. Thus, pharmacogenetic variants with higher susceptibility to carcinogenic insults, due to genetic polymorphism in xenobiotic-metabolizing enzymes, have been characterized by a combination of genotyping and measurements of macromolecular adducts. Dosimetry has been used in human studies to evaluate the efficacy of interventions with chemopreventive agents like ascorbic acid, dietary phenols and green tea. Advances in the application of selected biomarkers in human studies are reviewed and illustrated by examples from the author's research conducted during the past two decades.

Use of biomarkers--new frontiers in occupational toxicology and epidemiology

The incorporation of biomarkers into occupational toxicology and epidemiology some 25 years ago marked a turning-point for the discipline. The advances in molecular biology have provided new tools. At first, the major interest was in biomarkers of exposure, borrowing concepts from pharmacology, then it moved from the external estimates of exposure to internal measures of dose, and ultimately, to markers of target dose. Concerted efforts to measure carcinogens at the molecular level, e.g. DNA adducts, occupied a substantial fraction of the biomarkers work. In parallel, more quantitative and more sensitive end-points for etiological studies were sought earlier. Again, with advancing techniques in cytogenetics, extensive studies were conducted on such markers as sister chromatid exchanges (SCEs), micronuclei and other changes deemed to represent genomic damage. However, these types of end-points were quite unspecific for application to new hazards of uncertain human carcinogenic potential. Recent work focusing on more specific early-effect markers such as certain oncogenes and tumour-suppressor genes have substantial promise as shown by work with aflatoxins and vinyl chloride. Such studies have also enhanced mechanistic insight. The advances in molecular genetics have led to an upsurge in interest in most susceptibility factors, and identification of polymorphisms of various enzymes has become possible. Ongoing search for 'ultra-high risk' individuals may be fruitful, but probably only relevant to a small segment of potentially exposed populations. Factors associated with a small differential risk, however theoretically or mechanistically important, offer only little practical use.

Localization of cytochrome P4501A1 and covalent binding of a mutagenic heterocyclic amine in blood vessel endothelia of rodents

Immunohistochemistry was used to examine the cellular localization of cytochrome P4501A1 (CYP1A1) in various types of endothelial linings in muscle tissues of rats and mice treated with the Ah receptor agonist beta-naphthoflavone (BNF). In addition, light microscopic autoradiography was used to localize sites of metabolic activation of 3H-labeled Trp-P-1 (3-amino-1,4-dimethyl-5H-pyrido[4,3-b]indole), a heterocyclic amine known to be metabolized by CYP1A1, in rodent tissue slices. The results showed a colocalization of CYP1A1 immunoreactivity and covalent binding of 3H-Trp-P-1 in endothelial linings of capillaries and veins of heart, skeletal muscle, and uterus in BNF-treated rodents, indicating the presence of catalytically active CYP1A1 at these sites. The immunohistochemical staining and covalent binding of 3H-Trp-P-1 in endothelia of arteries and arterioles was generally weak with the exception of uterine arterioles. In lymph nodes of BNF-treated rats, there was an intense CYP1A1 staining of high endothelial venules. The results suggest that endothelial linings of capillaries and veins in muscle tissues but also uterine arterioles and high endothelial venules in lymph nodes may be targets for CYP1A1-mediated metabolic products of endogenous and exogenous substances following exposure to CYP1A1 inducing agents.

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

Cytochrome P4501A1 (CYP1A1) is involved in the bioactivation of polycyclic aromatic hydrocarbons into their reactive epoxide metabolites. CYP1A1 is considered to be important with regard to individual susceptibility to lung cancer since phenotypic and genotypic polymorphisms of CYP1A1 have been associated with an increased risk of lung cancer in a number of studies. We examined here the expression and localization of CYP1A1 mRNA in human lung tissue using in situ hybridization with a CYP1A1-specific RNA probe. A centrilobular expression of CYP1A1 mRNA was observed in the peripheral lung. The expression was intense in bronchiolar epithelium of peripheral lung, especially in terminal cuboidal epithelium. Type II alveolar epithelial cells were also intensely labelled. Type I alveolar epithelial cells and vascular epithelium exhibited binding but the hybridization signals were less intense. Our results are in good agreement with our previous work on immunohistochemical localization of CYP1A protein, in which we used the 1-7-1 MAb that recognizes both CYP1A1 and CYP1A2. In serial sections analyzed with in situ hybridization and immunohistochemistry, a similar distribution of CYP1A1 mRNA and CYP1A protein was observed. CYP1A1 mRNA is thus expressed in human lungs and the expression is particularly intense in the cell types involved in the development of peripheral lung cancers.

Quantitative RT-PCR measurement of cytochromes p450 1A1, 1B1, and 2B7, microsomal epoxide hydrolase, and NADPH oxidoreductase expression in lung cells of smokers and nonsmokers

Bronchial epithelial cells (BEC) are the progenitors of bronchogenic carcinomas and are exposed to polycyclic aromatic hydrocarbon (PAH) procarcinogens through inhalation of combustion products. PAH are converted to carcinogenic molecules through a combination of monoxygenation by cytochrome p450 (CYP) enzymes in the presence of NADPH oxidoreductase (OR) and hydrolysis by microsomal epoxide hydrolase (mEH). In artificial systems, the relative expression of these genes determines whether carcinogenic or noncarcinogenic species are generated during metabolism. This relationship was explored in humans by using quantitative competitive reverse transcriptase polymerase chain reaction amplification to determine the range of expression of CYP1A1, CYP1B1, mEH, and NADPH OR in BEC recovered from 10 nonsmokers and 9 smokers. CYP2B7 expression was evaluated because, although little is known of its substrate specificity, it is expressed at high levels in human lung tissue. CYP1A1 and CYP1B1 were expressed in BEC at significantly different levels (P < 0.05) in the 9 smokers at 1.4 +/- 2.3 x 10(4) and 2.4 +/- 3.2 x 10(3) molecules/10(6) beta-actin molecules (mean +/- STD), respectively, but each was measurable in only one of the 10 nonsmokers. There was significant inter-individual variation (P < 0.05) in both CYP1A1 and CYP1B1 expression among the subjects for whom sufficient data were obtained. The inducibility of human BEC CYP1A1 gene by PAH exposure was confirmed in vitro by incubating cultured immortalized human BEC with beta-naphthoflavone and observing a > 6-fold induction of CYP1A1 after 24 h. In contrast to BEC, alveolar macrophages expressed CYP1A1 at low (30-70 molecules/10(6) beta-actin molecules) to unmeasurable levels in both smokers and nonsmokers. There was no significant difference in expression of mEH, CYP2B7, or NADPH OR in smokers compared with nonsmokers. The inter-individual variation in absolute and relative expression of PAH metabolism enzymes in BEC reported here supports the hypothesis that inter-individual variation in ability to activate/inactivate inhaled PAH carcinogens accounts for at least some of the inter-individual variation in risk for bronchogenic carcinoma.

In vitro kinetics of two human CYP1A1 variant enzymes suggested to be associated with interindividual differences in cancer susceptibility

A genetic polymorphism (A4889-->G) in the human CYP1A1 gene which creates an Ile462-->Val amino acid substitution has been suggested to cause altered enzymatic properties of CYP1A1. Since several epidemiological studies have shown an association between the CYP1A1-Val allele and lung cancer, we considered it of importance to evaluate the in vitro kinetic properties of the two CYP1A1 variants after expression of each cDNA in yeast. No differences were found in K(m) or Vmax for CYP1A1 dependent O-dealkylation of ethoxyresorufin and 3-hydroxylation of benzo(a)pyrene between the two variants. The data indicate that the Ile/Val polymorphism in human CYP1A1 is not functionally important.

United States lung carcinoma incidence trends: declining for most histologic types among males, increasing among females

BACKGROUND

Lung carcinoma is now the most frequently diagnosed major cancer in the world and is also the most common cause of cancer deaths in males and females in the United States and worldwide. Based on trends in cigarette smoking and on analysis of lung cancer rates by birth cohort, it was predicted that a decline would occur in age-adjusted lung cancer rates, initially in males, and approximately 10 years later in females. We evaluated age-adjusted lung cancer incidence rates for changes in trends by race, sex and histologic type to determine if and when rates may have started declining.

METHODS

We analyzed population-based incidence data from the National Cancer Institute's Third National Cancer Survey conducted between 1969 and 1971 and from the Surveillance, Epidemiology and End-results (SEER) program conducted between 1974 and 1991. Age-adjusted rates were plotted by time period using a logarithmic scale for the ordinate. We used regression methods for grouped time-to-response data to fit a model to the disease rate for age, and calendar year to estimate the calendar year of maximum disease rate.

RESULTS

During this period, the overall age-adjusted lung cancer incidence rate rose from 37.8 to 68.2 per 100,000. Lung cancer rates in both white and black males climaxed around 1984 and declined subsequently. Furthermore, among white and black males, the rates of squamous cell carcinoma, small cell carcinoma, and large cell carcinoma declined after peaks in 1981 and 1982, 1986 and 1987, and 1986 and 1988, respectively. The rates for adenocarcinoma in black males peaked in 1987 whereas the rates in white males appeared to have plateaued between 1989 and 1991. Total lung cancer rates in males exceeded those in females, with rates in black males exceeding rates in white males. Age-adjusted lung carcinoma rates among white and black females continued to increase for all histologic types with the exception of large cell carcinoma among whites, bronchioloalveolar carcinoma among whites and blacks, and adenosquamous carcinoma among blacks.

CONCLUSIONS

The cumulative effect of these trends has resulted in a plateau of total lung carcinoma incidence in all persons combined, and a decline might be expected soon, as has already been observed among males. Most of these changes reflect past cigarette smoking patterns. Demonstration of declines and tapering increases among several population subgroups suggests impending reductions in the incidence and mortality rate for this highly fatal cancer.

The role of individual susceptibility in cancer burden related to environmental exposure

Individual susceptibility to cancer may result from host factors including differences n metabolism, DNA repair, altered expression of protooncogenes and tumor suppressor genes, and nutritional status. Since most carcinogens require metabolic activation before binding to DNA, variations in an individual's metabolic phenotype that have detected in enzymes involved in activation and detoxification should play an essential role in the development of environmental cancer. This phenotypic metabolic variation has now been related to genetic polymorphisms, and many genes encoding carcinogen-metabolizing enzymes have been identified and cloned. Consequently, allelic variants or genetic defects that give rise to the observed variation and new polymorphisms have been recognized. Development of simple polymerase chain reaction (PCR)-based assays has enabled identification of an individual's genotype for a variety of metabolic polymorphisms. Thus, recent knowledge of the genetic basis for individual metabolic variation has opened new possibilities of studies focusing on increased individual susceptibility to environmentally induced cancer, which are reviewed with special reference to smoking-induced lung cancer. Cancer susceptibility due to chemical exposure is likely to be determined by an individual's phenotype for a number of enzymes (both activating and detoxifying) relevant to that of a single carcinogen or mixtures of carcinogens. Given the number and variability in expression of carcinogen-metabolizing enzymes and the complexity of chemical exposures, assessment of a single polymorphic enzyme (genotype) may not be sufficient. Mutations in the p53 gene are among the most common genetic changes in human cancer. The frequency and type p53 mutations can act as a fingerprint of carcinogen exposure and may therefore provide information about external etiological agents, intensity of exposure, and host factors affecting the tumorigenesis process. In human lung cancer, p53 mutations (both the mutation pattern and frequency) have been linked with tobacco smoking; the type of mutation most frequently observed is G:C to T:A transversion, a mutation preferentially induced by benzo[a]pyrene diol epoxide. An association between the presence of this transversion and the genotype deficient in glutathione S-transferase M1-mediated detoxification has been observed in lung cancer. Taken together, these findings suggest that determination of metabolic at risk genotypes in combination with levels of DNA adducts in target (surrogate) tissues and the p53 mutation pattern should allow the identification of susceptible individuals and subgroups in carcinogen-exposed populations.

Lung injury: cell-specific bioactivation/deactivation of circulating pneumotoxins

Many of the blood-borne xenobiotics which result in injury to the lung are not inherently pneumotoxic but cause damage within the target cells following metabolic activation. This injury is usually restricted to those cells capable of bioactivation and thus, in addition to its clinical significance, it provides a valuable indicator of the normal metabolic activity within the numerous cell types present in lung. Not surprisingly, injury does not simply reflect the presence or absence of a particular enzyme but rather the balance between mechanisms for activation and deactivation. A change in the balance between different enzymes may also determine whether activation results in injury or tumorigenesis (Foster et al. 1992). Changes in particular types of cells cannot be determined by analysing whole lung homogenates. Isolation of particular cell types can provide valuable information but this approach does not address the differences between adjacent cells of the same type (Forkert & Moussa 1989; Dinsdale et al. 1992). Further progress may require the correlation of the injury with the status of individual cells; the quantitation of histochemical and immunocytochemical data is notoriously labour intensive but this approach may well be inescapable.

Biomarkers for Great Lakes priority contaminants: halogenated aromatic hydrocarbons

One of the major goals of the Great Lakes Action Plan is to actively accumulate and assess toxicological information on persistent toxic substances found in the Great Lakes basin. As part of Health Canada's commitment to this plan, a review of biomarkers for the environmental contaminants polychlorinated biphenyls (PCBs) and polychlorinated dibenzodioxins/dibenzofurans (PCDDs/PCDFs) was conducted. In general, while food consumption was identified as the major source of human exposure to both contaminant groups, certain commodities, such as fish, milk and dairy products, and meat, were found to predominate. Due to the ubiquitous nature of these environmental contaminants and their propensity to bioaccumulate, all humans will have detectable body burdens, which in certain cases can be positively associated with the consumption of particular foods (i.e., PCBs and freshwater fish from the Great Lakes). When dealing with environmental exposure only, relating specific effect biomarkers to contaminant exposure or tissue levels was difficult, due in part to the complex nature of the exposure and the nonspecific nature of the effect. For PCBs, the most likely biomarkers of effect included some form of alteration in lipid metabolism (serum triglyceride/cholesterol levels) and elevation of hepatic-related enzymes, aspartate aminotransferase (AST) and gamma-glutamyltransferase (GGT). Cross-species extrapolation also indicates the potential for neurotoxicologic effects to occur in humans. For PCDDs/PCDFs, dermatologic lesions (chloracne) and indications of hepatic enzyme induction have been documented, but primarily due to occupational or high acute accidental exposures. Recent evidence suggests that neonates may represent a potential at-risk population due to relatively high exposure to PCDDs/PCDFs, as with PCBs, during breast feeding as compared to standard adult dietary intake. Future areas of potential benefit for biomarker development include immunologic and endocrine effects, primarily based on biologic plausibility from experimental animal research.

Role of the lung in accumulation and metabolism of xenobiotic compounds--implications for chemically induced toxicity

The mammalian lung is exposed to and affected by many airborne and bloodborne foreign compounds. This review summarizes the role of lung in accumulation and metabolism of xenobiotics, some of which are spontaneously reactive or are metabolically activated to toxic intermediates. The specific architectural arrangement of mammalian lung favors that so-called pneumophilic drugs are filtered out of the blood and are retained within the tissue as shown in particular for amphetamine, chlorphentermine, amiodarone, imipramine, chlorpromazine, propranolol, local anaesthetics, and some miscellaneous therapeutics. There is strong evidence that intrapulmonary distribution activity and regulation of drug-metabolizing enzymes in lung is distinct from liver. This review focuses on the metabolic rate of selected compounds in lung such as 5-fluoro-2'-deoxyuridine, local anesthetics, nicotine, benzo(alpha)pyrene, ipomeanol, 4-methylnitrosamino-1-(3-pyridyl)-1-butanone. It is widely accepted that the formation of radical species is a key event in the pneumotoxic mechanisms induced by bleomycin, paraquat, 3-methylindole, butylhydroxytoluene, or nitrofurantoin. Finally, methodological approaches to assess the capacity of lung to eliminate foreign compounds as well as biochemical features of the pulmonary tissue are evaluated briefly.

Pretranslational induction of cytochrome P4501A enzymes by beta-naphthoflavone and 3-methylcholanthrene occurs in different liver zones

Most of the cytochrome P450 (CYP) genes are expressed in an uneven, zonated pattern in the liver. Factors regulating this regionally restricted expression are not well known. In this study we have analysed cell lysates obtained from opposite zones of rat liver by infusing digitonin to the perfused liver to study the zonation of CYP1A1 and CYP1A2 induction. 3-Methylcholanthrene induced CYP1A1 protein in perivenous cells, while a low dose of beta-naphthoflavone caused periportal induction. Analysis of CYP1A1 mRNA from cell lysates by reverse transcriptase-coupled polymerase chain reaction (RT-PCR) and in situ hybridization experiments both demonstrated that this inducer-specific differently localized effect occurred at the pretranslational level. A corresponding difference in the regional pattern of CYP1A2 induction was seen: induction by beta-naphthoflavone reversed the constitutive perivenous pattern into a periportal CYP1A2 mRNA pattern while induction after 3-methylcholanthrene treatment was more panacinar. Attempts to identify the regiospecific factors involved were made by comparing the in vitro induction of CYP1A1 by beta-naphthoflavone and 3-methylcholanthrene in hepatocytes isolated from the periportal and perivenous region. However, after isolation, induction seemed to be independent of the source of the cells. Our results demonstrate the existence in the liver of regionally acting factors that mediate the induction of CYP1A1 and 1A2 in a local and inducer-specific fashion. These factors could be Ah receptor associated binding proteins operating in vivo, but no longer in isolated cells.

Detection of ras gene mutations in human lung cancer: comparison of two screening assays based on the polymerase chain reaction

We studied the prevalence of point mutations in ras oncogenes (K-ras and N-ras) in DNA from white blood cells and tumor tissue from 36 untreated patients with non-small-cell lung cancer, all of whom were smokers or ex-smokers. We observed somatic K-ras mutations in one-third of the lung carcinomas studied but no N-ras mutation. K-ras codon 12 mutations were found more frequently in adenocarcinomas than in the other histopathological subtypes studied. More than 60% (10/16) of the lung adenocarcinomas had a codon 12 mutation, most of which were G to T transversions. No mutations was found in white blood cell DNA. Two polymerase chain reaction screening methods, oligonucleotide hybridization and denaturing gradient gel electrophoresis (DGGE), were used to detect the mutations. The oligonucleotide method appears to be more sensitive than DGGE, but DGGE proved to be a reliable nonradioactive method for rapid screening of point mutations in genes relevant to carcinogenesis.