Single nucleotide polymorphisms, metabolic activation and environmental carcinogenesis: why molecular epidemiologists should think about enzyme expression

J.A. Williams

Institute of Cancer Research, Haddow Laboratories, Cotswold Road, Sutton, SM2 5NG, UK


    Abstract
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 Abstract
 Introduction
 Myeloperoxidase expression in...
 Expression of N...
 Expression of cytochrome P450...
 Peroxidases in the breast
 Summary and future perspectives
 References
 
This commentary was written to stimulate thoughts on, and consideration of, enzyme expression data in target organs when investigating possible associations between polymorphisms in carcinogen activation enzymes, lifestyle/dietary factors and cancer risk. The lung and breast are taken as examples. There is overwhelming evidence for a genotoxic mechanism in lung cancer development, and compelling evidence for the contribution of genotoxins to breast cancer aetiology. A consistent association has been shown where lung cancer risk is decreased by a G->A polymorphism in the myeloperoxidase (MPO) gene, which is expressed in neutrophils recruited to the lung after chemical or immunological insults. In the breast, a consistent lack of association has been observed for women who are fast N-acetyltransferase type 2 (NAT2) acetylators consuming cooked meat. This could be explained by the lack of detectable NAT2-associated sulfamethazine acetylation activity in cytosols prepared from mammary tissue, suggesting a minor contribution to carcinogen activation. The recent identification in mammary cytosols of detectable sulfotransferase isoforms (SULT1A1 and SULT1A3), which have high catalytic efficiency for activating N-hydroxylated heterocyclic amines (HCAs, mutagens in cooked meat), offers a more important role for these enzymes in the metabolic activation of genotoxins in the breast. The possible contribution of MPO and lactoperoxidase enzymes to carcinogen activation in mammary tissue is also considered. Sulfotransferases and peroxidases have wide substrate specificity in terms of carcinogen activation (HCAs, aromatic amines and polycyclic aromatic hydrocarbons—all present in cooked meat and tobacco smoke) compared with NATs (HCAs and aromatic amines only). For gene–environment interactions, investigations into functional polymorphisms in SULT and peroxidase genes may, therefore, offer new evidence for the involvement of genotoxins in the initiation of carcinogenesis. Identification of the isoforms (if any) of carcinogen activation enzymes that are expressed in the organs of interest will help to determine which genes to investigate in these studies.

Abbreviations: CYP, cytochrome P450; HCAs, heterocyclic amines; MPO, myeloperoxidase; NAT, N-acetyltransferase; PAHs, polycyclic aromatic hydrocarbons; SULT, sulfotransferase.


    Introduction
 Top
 Abstract
 Introduction
 Myeloperoxidase expression in...
 Expression of N...
 Expression of cytochrome P450...
 Peroxidases in the breast
 Summary and future perspectives
 References
 
Epidemiological studies in combination with mechanistic studies can determine the causes of cancer at various organ sites (1). The mutational spectra of the TP53 gene in lung and breast tumours suggests that exogenous agents may play a greater part in carcinogenesis here than in other tissues, such as the colon (2). Knowledge of the aetiological agents responsible for and the mechanisms leading to tumour formation is essential for achieving cancer prevention (36). It is argued in this article that assessment of enzyme expression studies in the target organ should be incorporated into molecular epidemiology studies when investigating the potential effects of polymorphisms in carcinogen metabolizing enzymes on cancer risk. This is particularly appropriate for organs such as the lung and breast (7) where evidence exists for the involvement of a genotoxic mechanism in the carcinogenic process (2,811) and where evidence of metabolic activation of suspected carcinogens exists in the form of DNA adducts (3,5,12). First, the effect of polymorphisms in the myeloperoxidase (MPO) gene on lung cancer risk will be briefly reviewed. Secondly, reasons will be suggested for the apparent lack of association between polymorphisms in the N-acetyltransferase 2 (NAT2) gene, levels of meat consumption and breast cancer risk. Further, suggestions will be made as to why the recent characterization of sulfotransferase (SULT) isoforms in cytosols prepared from mammary tissues should direct molecular epidemiologists to investigate SULT1A polymorphisms in gene–environment interaction studies. Full characterization of the carcinogen-activating enzymes expressed in prostatic tissues could establish whether exposures to environmental agents are risk factors for cancer at these sites. Finally, it will be suggested that when associating genotype and lifestyle or environmental factors with cancer risk, investigation of polymorphisms in genes encoding enzymes with wide substrate specificity with regard to carcinogen activation (e.g. peroxidases and SULTs) will be more fruitful than studies of those polymorphic genes encoding enzymes with a narrow substrate specificity (e.g. NATs).

Pathways of activation of three classes of suspected human chemical carcinogens catalyzed by human xenobiotic-metabolizing enzymes are shown in Figure 1Go. The enzymes catalyzing metabolic activation of these compounds include cytochrome P450 (CYP) enzymes, NATs, SULTs and peroxidase enzymes.



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Fig. 1. Pathways of metabolic activation of suspected human carcinogens. References are given in parentheses. *Refers to rat enzyme

 

    Myeloperoxidase expression in the lung
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 Abstract
 Introduction
 Myeloperoxidase expression in...
 Expression of N...
 Expression of cytochrome P450...
 Peroxidases in the breast
 Summary and future perspectives
 References
 
Neutrophil recruitment into lung tissue occurs after exposure to a variety of insults known to increase lung cancer risk, including tobacco smoke particulates, infection, asbestos and ozone (1315). Following immunological and/or chemical insults, neutrophils release MPO (13) and undergo a `respiratory burst', which is characterized by a massive increase in oxygen consumption and a consequent NADPH-dependent production of superoxide and other free radicals. MPO is present in the primary granules of neutrophils and catalyzes the production of the potent bacteriotoxic oxidizing agent hypochlorous acid (a one- and two-electron oxidant that can attack endogenous molecules including DNA) from hydroxyl radicals and chloride ions. A significant proportion (25–40%) of the hydrogen peroxide formed by activated neutrophils may be converted to hypochlorous acid (16,17). MPO metabolically activates a wide range of tobacco smoke mutagens and environmental pollutants to DNA-damaging metabolites, including aromatic amines (18), the promutagenic derivatives of polycyclic aromatic hydrocarbons (PAHs) (1921) and heterocyclic amines (HCAs) (22) (Figure 1Go).

A G->A transition at position –463 in the promoter region of the MPO gene, which leads to the loss of a SP1 transcription binding site in an Alu hormone-responsive element (23), has been shown to reduce MPO mRNA expression (24). The wild-type G allele is present in 75% of Caucasians (2527). A study of American Caucasians (182 cases, 459 controls) and African Americans (157 cases, 244 controls) gave the first indication that possession of two copies of the A allele of the MPO gene reduced the risk of lung cancer (25). Possession of the A/A genotype (8–10% of the population) was associated with a 70% reduction in lung cancer risk in Caucasians (odds ratio, 0.30; 95% confidence interval, 0.10–0.93; P = 0.04) and a 39% reduction (not statistically significant) in African Americans (odds ratio, 0.61; 95% confidence interval, 0.26–1.41) compared with those with two G alleles (25). A second study (26) of populations with Caucasian, Japanese or Hawaiian ethnicity (323 cases, 437 controls) reported an overall 50% reduction in risk (95% confidence interval, 0.2–1.3) for those with the A/A genotype compared with those with two G alleles. In a matched case-control study of 196 lung cancer, 245 laryngeal cancer and 255 pharyngeal cancer patients from the Berlin area (27), possession of one or two A alleles was suggested as being a protective factor for cancer of the lung (relative risk, 0.47; 95% confidence interval 0.28–0.79; P = 0.004) and larynx (relative risk, 0.66; 95% confidence interval, 0.44–1.01; P = 0.054) but not for cancer of the pharynx (relative risk, 0.75; 95% confidence interval, 0.51–1.12; P = 0.16), after adjusting for age, gender and extent of cigarette habit. A smaller matched case-control study (93 cases, 121 controls) of Caucasians (28) reported an overall reduction in risk of 48% for those possessing the variant A allele (odds ratio, 0.52; 95% confidence interval 0.30–0.90; P = 0.02). The consistency of agreement between these studies, which provide data on 800 cases and 1500 controls, suggests an important role for MPO in lung cancer aetiology, possibly through activation of carcinogens and/or production of free radicals in or near the target cells (Figure 1Go).


    Expression of N-acetyltransferases and sulfotransferases in the breast
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 Abstract
 Introduction
 Myeloperoxidase expression in...
 Expression of N...
 Expression of cytochrome P450...
 Peroxidases in the breast
 Summary and future perspectives
 References
 
The majority of lung cancer cases (87%) can be attributed to a single agent, tobacco smoking (29), but the aetiology of breast cancer is obscure and most likely multifactorial. Studies of polymorphisms in carcinogen-metabolizing enzymes have promised much but delivered little in the identification of at-risk groups of women within the general population. A useful example is provided by investigations into the suggested links between cooked meat consumption and breast cancer risk.

Cooked meat contains a variety of mutagens (30), including HCAs formed from the cooking of proteinaceous foodstuffs (particularly meat and fish) at high temperatures. These compounds are carcinogens in the rat mammary (31) and prostate (32) glands following high-dose oral administration, and are suspected of being mammary carcinogens in women (33) and prostate carcinogens in men (32,34). HCAs require metabolic activation to form DNA-damaging metabolites (Figure 1Go). This can occur via a two-step pathway involving first a CYP catalyzed N-hydroxylation (22,35) followed by O-esterification catalyzed by NAT and/or SULT enzymes (Figure 1Go). The acetoxy or sulfoxy esters formed are unstable and generate a nitrenium ion as the ultimate DNA-reactive intermediate (Figure 1Go), and quantitatively, N-(deoxyguanosin-8-yl)–HCAs are the major adducts formed (36). Parent HCAs can also be activated by peroxidases to generate nitrenium ions (22,37).

Determination of NAT and SULT (38,39) enzyme expression in the breast has revealed the major isoforms to be NAT1, SULT1A1 and SULT1A3, all of which can metabolically activate promutagenic derivatives of HCAs to DNA-reactive metabolites (3941) (Figure 1Go). In mammary cytosols, NAT1-specific para-aminobenzoic acid acetylation activity was measurable (with a 6-fold interindividual variation), whereas NAT2-specific sulfamethazine acetylation activity was below the limit of detection (38,39). Although reverse transcription–polymerase chain reaction and immunohistochemical analyses have shown that the NAT2 gene is expressed in the ductal epithelial cells of the breast (39), the absence of enzyme activity is consistent with low mammary expression of NAT2. These advances in the determination of enzyme expression in the breast, and others detailed below, may explain why no association has been found between polymorphisms in the NAT2 gene, cooked meat consumption and breast cancer risk; for example, in studies by Ambrosone et al. (42) (740 cases, 810 controls), Gertig et al. (43) (466 cases, 466 controls) and Delfino et al. (44) (114 cases, 280 controls).

The liver plays a major role in the control of systemic levels of xenobiotics, and for some compounds, such as nitrosamines (45) or PAHs (46,47), there is evidence that hepatic metabolic activation produces short-lived electrophiles that could damage DNA in extra-hepatic organs (for review on carcinogen metabolism see ref. 48). For heterocyclic and aromatic amines, however, local metabolic activation at the target site (i.e. the breast) may be more important than hepatic activation (7,4951).

There are 26 reported alleles of the NAT2 gene (for the NAT allele website see http://www.louisville.edu/medschool/pharmacology/NAT.html) but NAT2 activities in the human population are bimodally distributed (50–60% of Caucasians have low acetylation activity for NAT2 substrates, and are designated `slow acetylators') (52). The influence of the NAT2 genotype on NAT2 enzyme activity has been well characterized (40). An important opportunity was therefore presented to study gene–environment interactions, since the slow NAT2 phenotype is present in a significant proportion of the Caucasian population, and the enzyme has potential human carcinogens as substrates (53) (Figure 1Go). These include carcinogenic aromatic amines that are good substrates for hepatic clearance by N-acetylation. However, where genotoxic carcinogens are metabolically activated by NAT2 (via NAT-catalyzed O-acetylation of N-hydroxylated aromatic or HCAs), expression at the target site, e.g. the breast, is likely to be more important since the short-lived acetoxy esters would not be expected to survive transport to the breast.

The identification of the SULT isoforms expressed in mammary tissue (39) may be more promising in providing information on breast cancer aetiology. The SULTs are a supergene family (54), and one of the two isoforms detected in mammary cytosols, SULT1A1 (the other is SULT1A3) (39) has the highest O-esterification activity for N-hydroxylated heterocylic amines (41). SULT enzymes metabolically activate a wider range of promutagenic substrates (39,5557) and rodent mammary carcinogens than NATs (Figure 1Go). It might therefore be expected that functional polymorphisms in the SULT1A1 and SULT1A3 genes would have more influence on breast cancer risk than NAT polymorphisms, especially as humans are most often exposed to mixtures of genotoxins through a particular potential risk factor e.g. consumption of well-done meat resulting in exposure to mixtures of PAHs and HCAs (30,58). In model systems, methylated PAHs such as 7,12-dimethylbenz[a]anthracene can be activated via sulfation of the 7-hydroxylated derivative (57,59). However the major pathway of metabolic activation of PAHs via sulfation is thought to occur via conjugation of a tetrol derivative (56). The relative importance of these SULT-requiring pathways in human tissues is unknown. A functional polymorphism has been described for the SULT1A1 gene (60), a G->A transition in codon 213 (Arg213->His213). The frequency of the 1A1*Arg allele in Caucasian population samples has been reported to be 0.63 in Germany, (60), 0.69 in the USA (61) and 0.68 in the UK (62). In a Nigerian population the frequency of the 1A1*Arg allele was reported to be 0.63 (62). The His->Arg213 polymorphism has been reported to decrease mutagen activation by 10–300-fold (63). The high frequency of the low activity sulfation allele in the study population, coupled with wide substrate specificity, could offer a practical method of identifying populations at risk of developing cancer in the mammary gland and in other organs where SULT1A1 is expressed.


    Expression of cytochrome P450 enzymes in prostate and pancreatic tissues
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 Abstract
 Introduction
 Myeloperoxidase expression in...
 Expression of N...
 Expression of cytochrome P450...
 Peroxidases in the breast
 Summary and future perspectives
 References
 
The mutagenic activity of PAHs and HCAs present in cooked meat provides a plausible mechanism for carcinogenesis in human tissues. There is an association between levels of cooked meat consumption and risk of prostate (64) and pancreatic cancer (64), but a case-control study based in Auckland, New Zealand (317 patients and 480 age-matched controls), found no clear association between intake of known HCAs and prostate cancer risk (65). In this New Zealand-based study, however, an increased risk for prostate cancer was observed for high intake-levels of well-done beefsteak. CYP1A2 is expressed in the prostate (34) and pancreas (66,67) and in experiments using recombinantly-expressed CYP1 enzymes, the catalytic efficiency for N-hydroxylation of 2-amino-1-methyl-6-phenylimidazo[4,5-b]pyridine was far greater for CYP1A1 and CYP1A2 than for CYP1B1 (68). An association between CYP1A2 expression, HCA activation and cancer risk could be investigated if functional polymorphisms in the CYP1A2 gene could be fully understood (6971).


    Peroxidases in the breast
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 Abstract
 Introduction
 Myeloperoxidase expression in...
 Expression of N...
 Expression of cytochrome P450...
 Peroxidases in the breast
 Summary and future perspectives
 References
 
Two interesting epidemiological studies have shown that women with allergies/atopic diseases (i.e. those associated with inflammation and elevated peroxidase activity), compared with women without atopic diseases, have an elevated risk of developing cancer of the breast [relative risk 2.5; 95% confidence interval 1.01–5.16 (72) and relative risk, 1.25; 95% confidence interval 0.76–2.07 (90)]. A mechanistic role for peroxidase-activation of mutagens has been suggested (22,37,73,74) (Figure 1Go). Levels of MPO-containing neutrophils are elevated in inflamed mammary tissues (75) compared with non-inflamed tissues, and are present in breast milk and breast secretions. The gene encoding the human form of another peroxidase enzyme, lactoperoxidase (76), is arranged `tail-to-tail' with the MPO gene. The enzyme encoded by this gene also has bacteriocidal functions, and is secreted into the milk ducts. The catalytic activity of the human form of this enzyme has not been well studied, but the bovine form of this enzyme can activate 17ß-estradiol (77), aromatic amines (78) and HCAs (37) to mutagenic metabolites. A possible causal link between peroxidase-catalyzed carcinogen activation and/or free radical production and breast carcinogenesis could be investigated by assessing the effect of the reported MPO polymorphism (2527) and/or functional single nucleotide polymorphisms in the lactoperoxidase gene on breast cancer risk.


    Summary and future perspectives
 Top
 Abstract
 Introduction
 Myeloperoxidase expression in...
 Expression of N...
 Expression of cytochrome P450...
 Peroxidases in the breast
 Summary and future perspectives
 References
 
It would be particularly informative to make a quantitative assessment of the contributions of metabolizing enzymes to carcinogen activation in the organs of interest. This could be done by measuring mRNA levels and enzyme activity levels in the target tissues, inter-individual variations in carcinogen metabolism and/or enzyme activity, as well as catalytic efficiency of the enzymes for metabolically activating carcinogenic substrates. Allocation of an endogenous role for carcinogen metabolizing enzymes will help our understanding of enzyme expression in target tissues; e.g. a role for folate metabolism has recently been shown for NAT1 (79).

The functional effects of single nucleotide polymorphisms on enzyme expression can be assessed by measuring gene transcription (25), mRNA stability, immunoreactive protein or enzyme activity (60,80; see ref. 7 for a review). Caution should be taken when using just one method of measurement, as enzyme activity levels do not always correspond to mRNA transcript levels (39,81). Furthermore, for metabolizing enzymes, increases in protein are not always mirrored by increases in active enzyme (82). If possible, a combination of methods should be employed to increase confidence in the perceived functional effect of a single nucleotide polymorphism on the expression level or activity of the enzyme (7).

In summary, knowledge of tissue-specific enzyme expression can provide useful information for molecular epidemiologists when investigating gene–environment interactions. This can include profiling of the isoforms expressed (39,83,84), localization of enzyme expression within the tissue (38,39,67,83,84) and quantitative determination of enzyme activity within sub-cellular tissue fractions (38,39,83,84). Information on all the competing pathways of metabolic activation and detoxication of suspected human carcinogens should also be taken into account. Peroxidases and SULT enzymes have wider substrate specificities than NAT enzymes. Thus, while NAT enzymes are limited to activation of N-hydroxylated heterocyclic and aromatic amines, peroxidases can metabolically activate both parent and hydroxylated heterocyclic and aromatic amines and hydroxylated PAHs, and SULTs can activate the hydroxylated promutagenic derivatives of all three classes of mutagens. Such mixtures are more representative of the mixtures present in cooked meat and tobacco smoke. Investigation of polymorphisms in enzymes with wide substrate specificity, with regard to carcinogen activation therefore looks promising for the detection of links between environmental or lifestyle factors and cancer risk.


    Notes
 
Present address: Department of Drug Disposition, Lilly Research Laboratories, Drop Code 0730, Eli Lilly and Company, Lilly Corporate Center, Indianapolis, IN 46285, USA Email: williams_james_andrew{at}lilly.com


    Acknowledgments
 
I thank David Phillips, Philip Grover and Richard Houlston for critical comments.


    References
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 Abstract
 Introduction
 Myeloperoxidase expression in...
 Expression of N...
 Expression of cytochrome P450...
 Peroxidases in the breast
 Summary and future perspectives
 References
 

  1. Ames,B.N. (1999) Cancer prevention and diet: help from single nucleotide polymorphisms. Proc. Natl Acad. Sci. USA, 96, 12216–12218.[Free Full Text]
  2. Biggs,P.J., Warren,W., Venitt,S. and Stratton,M.R. (1993) Does a genotoxic carcinogen contribute to human breast cancer? The value of mutational spectra in unravelling the aetiology of cancer. Mutagenesis, 8, 275–283.[Abstract]
  3. Perera,F.P., Estabrook,A., Hewer,A., Channing,K., Rundle,A., Mooney,L.A., Whyatt,R. and Phillips,D.H. (1995) Carcinogen-DNA adducts in human breast tissue. Cancer Epidemiol. Biomarkers Prev., 4, 233–238.[Abstract]
  4. Martin,F.L., Carmichael,P.L., Crofton-Sleigh,C., Venitt,S., Phillips,D.H. and Grover,P.L. (1996) Genotoxicity of human mammary lipid. Cancer Res., 56, 5342–5346.[Abstract]
  5. Pfau,W., Stone,E.M., Brockstedt,U., Carmichael,P.L., Marquardt,H. and Phillips,D.H. (1998) DNA adducts in human breast tissue: association with N-acetyltransferase-2 (NAT2) and NAT1 genotypes. Cancer Epidemiol. Biomarkers Prev., 7, 1019–1025.[Abstract]
  6. Martin,F.L., Cole,K.J., Harvey,D.P., Weaver,G., Williams,J.A., Millar,B.C., Phillips,D.H. and P.L.,G. (2000) DNA damage in human breast milk cells and its induction by `early' and `late' milk extracts. Carcinogenesis, 21, 799–804.[Abstract/Free Full Text]
  7. Williams,J.A. and Phillips,D.H. (2000) Mammary expression of xenobiotic-metabolising enzymes and their potential role in breast cancer: a review. Cancer Res., 60, 4667–4677.[Abstract/Free Full Text]
  8. Doll,R. and Peto,R. (1981) The causes of cancer: quantitative estimates of avoidable risks of cancer in the United States today. J. Natl Cancer Inst., 66, 1191–1308.[ISI][Medline]
  9. Tokunaga,M., Land,C.E., Yamamoto,T., Asano,M., Tokuoka,S., Ezaki,H. and Nishimori,I. (1987) Incidence of female breast cancer among atomic bomb survivors, Hiroshima and Nagasaki, 1950–1980. Radiat. Res., 112, 243–272.[ISI][Medline]
  10. Welp,E.A., Weiderpass,E., Boffetta,P., Vainio,H., Vasama-Neuvonen,K., Petralia,S. and Partanen,T.J. (1998) Environmental risk factors of breast cancer. Scand. J. Work Environ. Health, 24, 3–7.
  11. Weiderpass,E., Pukkala,E., Kauppinen,T., Mutanen,P., Paakkulainen,H., Vasama-Neuvonen,K., Boffetta,P. and Partanen,T. (1999) Breast cancer and occupational exposures in women in Finland. Am. J. Ind. Med., 36, 48–53.[ISI][Medline]
  12. Mollerup,S., Ryberg,D., Hewer,A., Phillips,D.H. and Haugen,A. (1999) Sex differences in lung CYP1A1 expression and DNA adduct levels among lung cancer patients. Cancer Res., 59, 3317–3320.[Abstract/Free Full Text]
  13. Hunninghake,G.W., Gadek,J.E., Kawanami,O., Ferrans,V.J. and Crystal,R.G. (1979) Inflammatory and immune processes in the human lung in health and disease: evaluation by bronchoalveolar lavage. Am. J. Pathol., 97, 149–206.[Abstract]
  14. Schmekel,B., Hornblad,Y., Linden,M., Sundstrom,C. and Venge,P. (1990) Myeloperoxidase in human lung lavage. II. Internalization of myeloperoxidase by alveolar macrophages. Inflammation, 14, 455–461.[ISI][Medline]
  15. Schmekel,B., Karlsson,S.E., Linden,M., Sundstrom,C., Tegner,H. and Venge,P. (1990) Myeloperoxidase in human lung lavage. I. A marker of local neutrophil activity. Inflammation, 14, 447–454.[ISI][Medline]
  16. Foote,C.S., Goyne,T.E. and Lehrer,R.I. (1983) Assessment of chlorination by human neutrophils. Nature, 301, 715–716.[ISI][Medline]
  17. Prutz,W.A. (1996) Hypochlorous acid interactions with thiols, nucleotides, DNA and other biological substrates. Arch. Biochem. Biophys., 332, 110–120.[ISI][Medline]
  18. Tsuruta,Y., Subrahmanyam,V.V., Marshall,W. and PJ,O.B. (1985) Peroxidase-mediated irreversible binding of arylamine carcinogens to DNA in intact polymorphonuclear leukocytes activated by a tumor promoter. Chem. Biol. Interact., 53, 25–35.[ISI][Medline]
  19. Trush,M.A., Seed,J.L. and Kensler,T.W. (1985) Oxidant-dependent metabolic activation of polycyclic aromatic hydrocarbons by phorbol ester-stimulated human polymorphonuclear leukocytes: possible link between inflammation and cancer. Proc. Natl Acad. Sci. USA, 82, 5194–5198.[Abstract]
  20. Mallet,W.G., Mosebrook,D.R. and Trush,M.A. (1991) Activation of (+–)-trans-7,8-dihydroxy-7,8-dihydrobenzo[a]pyrene to diolepoxides by human polymorphonuclear leukocytes or myeloperoxidase. Carcinogenesis, 12, 521–524.[Abstract]
  21. Petruska,J.M., Mosebrook,D.R., Jakab,G.J. and Trush,M.A. (1992) Myeloperoxidase-enhanced formation of (+–)-trans-7,8-dihydroxy-7,8-dihydrobenzo[a]pyrene-DNA adducts in lung tissue in vitro: a role of pulmonary inflammation in the bioactivation of a procarcinogen. Carcinogenesis, 13, 1075–1081.[Abstract]
  22. Williams,J.A., Stone,E.M., Millar,B.C., Gusterson,B.A., Grover,P.L. and Phillips,D.H. (1998) Determination of the enzymes responsible for activation of the heterocyclic amine 2-amino-3-methylimidazo[4,5-f]quinoline in the human breast. Pharmacogenetics, 8, 519–528.[ISI][Medline]
  23. Piedrafita,F.J., Molander,R.B., Vansant,G., Orlova,E.A., Pfahl,M. and Reynolds,W.F. (1996) An Alu element in the myeloperoxidase promoter contains a composite SP1-thyroid hormone-retinoic acid response element. J. Biol. Chem., 271, 14412–14420.[Abstract/Free Full Text]
  24. Austin,G.E., Lam,L., Zaki,S.R. et al. (1993) Sequence comparison of putative regulatory DNA of the 5' flanking region of the myeloperoxidase gene in normal and leukemic bone marrow cells. Leukemia, 7, 1445–1450.[ISI][Medline]
  25. London,S.J., Lehman,T.A. and Taylor,J.A. (1997) Myeloperoxidase genetic polymorphism and lung cancer risk. Cancer Res., 57, 5001–5003.[Abstract]
  26. Le Marchand,L., Seifried,A., Lum,A. and Wilkens,L.R. (2000) Association of the myeloperoxidase –463G->A polymorphism with lung cancer risk. Cancer Epidemiol. Biomarkers Prev., 9, 181–184.[Abstract/Free Full Text]
  27. Cascorbi,I., Henning,S., Brockmoller,J., Gephart,J., Meisel,C., Muller,J.M., Loddenkemper,R. and Roots,I. (2000) Substantially reduced risk of cancer of the aerodigestive tract in subjects with variant–463A of the myeloperoxidase gene. Cancer Res., 60, 644–649.[Abstract/Free Full Text]
  28. Schabath,M.B., Spitz,M.R., Zhang,X., Delclos,G.L. and Wu,X. (2000) Genetic variants of myeloperoxidase and lung cancer risk. Carcinogenesis, 21, 1163–1166.[Abstract/Free Full Text]
  29. American Cancer Society. (2000) Cancer Prevention and Early Detection, Facts and Figures 2000. The American Cancer Society, Atlanta, GA.
  30. Knize,M.G., Salmon,C.P., Pais,P. and Felton,J.S. (1999) Food heating and the formation of heterocyclic aromatic amine and polycyclic aromatic hydrocarbon mutagens/carcinogens. Adv. Exp. Med. Biol., 459, 179–193.[Medline]
  31. Nagao,M., Ushijima,T., Wakabayashi,K., Ochiai,M., Kushida,H., Sugimura,T., Hasegawa,R., Shirai,T. and Ito,N. (1994) Dietary carcinogens and mammary carcinogenesis. Induction of rat mammary carcinomas by administration of heterocyclic amines in cooked foods. Cancer, 74, 1063–1069.[ISI][Medline]
  32. Shirai,T., Sano,M., Tamano,S. et al. (1997) The prostate: a target for carcinogenicity of 2-amino-1-methyl-6-phenylimidazo[4,5-b]pyridine (PhIP) derived from cooked foods. Cancer Res., 57, 195–198.[Abstract]
  33. Zheng,W., Gustafson,D.R., Sinha,R., Cerhan,J.R., Moore,D., Hong,C.P. anderson,K.E., Kushi,L.H., Sellers,T.A. and Folsom,A.R. (1998) Well-done meat intake and the risk of breast cancer. J. Natl Cancer Inst., 90, 1724–1729.[Abstract/Free Full Text]
  34. Williams,J.A., Martin,F.L., Muir,G.H., Grover,P.L. and Phillips,D.H. (2000) Metabolic activation of carcinogens and expression of various cytochromes P450 in human prostate tissue. Carcinogenesis, 21, 1683–1689.[Abstract/Free Full Text]
  35. Stone,E.M., Williams,J.A., Grover,P.L., Gusterson,B.A. and Phillips,D.H. (1998) Interindividual variation in the metabolic activation of heterocyclic amines and their N-hydroxy derivatives in primary cultures of human mammary epithelial cells. Carcinogenesis, 19, 873–879.[Abstract]
  36. Schut,H.A. and Snyderwine,E.G. (1999) DNA adducts of heterocyclic amine food mutagens: implications for mutagenesis and carcinogenesis. Carcinogenesis, 20, 353–368.[Abstract/Free Full Text]
  37. Williams,J.A., Stone,E.M., Millar,B.C., Hewer,A. and Phillips,D.H. (2000) Pathways of heterocyclic amine activation in the breast: DNA adducts of 2-amino-3-methylimidazo[4,5-f]quinoline (IQ) formed by peroxidases and in human mammary epithelial cells and fibroblasts. Mutagenesis, 15, 149–154[Abstract/Free Full Text]
  38. Sadrieh,N., Davis,C.D. and Snyderwine,E.G. (1996) N-acetyltransferase expression and metabolic activation of the food- derived heterocyclic amines in the human mammary gland. Cancer Res., 56, 2683–2687.[Abstract]
  39. Williams,J.A., Stone,E.M., Fakis,G., Johnson,N., Meinl,W., Glatt,H., Sim,E. and Phillips,D.H. (2000) Human mammary NAT and SULT enzymes metabolically activate N-hydroxylated heterocyclic amines, but NAT enzyme activity is not influenced by NAT genotype. Proc. Am. Assoc. Cancer Res. 41, 551.
  40. Grant,D.M., Hughes,N.C., Janezic,S.A., Goodfellow,G.H., Chen,H.J., Gaedigk,A., Yu,V.L. and Grewal,R. (1997) Human acetyltransferase polymorphisms. Mutat. Res., 376, 61–70.[ISI][Medline]
  41. Yamazoe,Y., Nagata,K., Yoshinari,K., Fujita,K., Shiraga,T. and Iwasaki,K. (1999) Sulfotransferase catalyzing sulfation of heterocyclic amines. Cancer Lett., 143, 103–107.[ISI][Medline]
  42. Ambrosone,C.B., Freudenheim,J.L., Sinha,R., Graham,S., Marshall,J.R., Vena,J.E., Laughlin,R., Nemoto,T. and Shields,P.G. (1998) Breast cancer risk, meat consumption and N-acetyltransferase (NAT2) genetic polymorphisms. Int. J. Cancer, 75, 825–830.[ISI][Medline]
  43. Gertig,D.M., Hankinson,S.E., Hough,H., Spiegelman,D., Colditz,G.A., Willett,W.C., Kelsey,K.T. and Hunter,D.J. (1999) N-acetyl transferase 2 genotypes, meat intake and breast cancer risk. Int. J. Cancer, 80, 13–17.[ISI][Medline]
  44. Delfino,R.J., Sinha,R., Smith,C. et al. (2000) Breast cancer, heterocyclic aromatic amines from meat and N-acetyltransferase 2 genotype. Carcinogenesis, 21, 607–615.[Abstract/Free Full Text]
  45. Umbenhauer,D.R. and Pegg,A.E. (1981) Alkylation of intracellular and extracellular DNA by dimethylnitrosamine following activation by isolated rat hepatocytes. Cancer Res., 41, 3471–3474.[Abstract]
  46. Kapitulnik,J., Wislocki,P.G., Levin,W., Yagi,H., Jerina,D.M. and Conney,A.H. (1978) Tumorigenicity studies with diol-epoxides of benzo (a)pyrene which indicate that (+/–)-trans-7beta,8alpha-dihydroxy-9alpha,10alpha-epoxy-7,8,9,10-tetrahydrobenzo(a)pyrene is an ultimate carcinogen in newborn mice. Cancer Res., 38, 354–358.[Abstract]
  47. Shen,A.L., Fahl,W.E. and Jefcoate,C.R. (1980) Metabolism of benzo (a)pyrene by isolated hepatocytes and factors affecting covalent binding of benzo(a)pyrene metabolites to DNA in hepatocyte and microsomal systems. Arch. Biochem. Biophys., 204, 511–523.[ISI][Medline]
  48. Guengerich,F.P. (2000) Metabolism of chemical carcinogens. Carcinogenesis, 21, 345–351.[Abstract/Free Full Text]
  49. Malfatti,M.A., Kulp,K.S., Knize,M.G. et al. (1999) The identification of [2-(14)C]2-amino-1-methyl-6-phenylimidazo[4,5-b]pyridine metabolites in humans. Carcinogenesis, 20, 705–713.[Abstract/Free Full Text]
  50. King,R.S., Teitel,C.H., Shaddock,J.G., Casciano,D.A. and Kadlubar,F.F. (1999) Detoxification of carcinogenic aromatic and heterocyclic amines by enzymatic reduction of the N-hydroxy derivative. Cancer Lett., 143, 167–171.[ISI][Medline]
  51. Langouet,S., Welti,D.H., Keriguy,N., Fay,L.B., Markovic,J., Guengerich,F.P., Guillouzo,A. and Turesky,R.J. (2000) The metabolism of 2-amino-3,8-dimethylimdiazo[4,5-f]quinoxaline in human hepatocytes. Proc. Am. Assoc. Cancer Res., 41, 836.
  52. Bell,D.A., Taylor,J.A., Butler,M.A., Stephens,E.A., Wiest,J., Brubaker,L.H., Kadlubar,F.F. and Lucier,G.W. (1993) Genotype/phenotype discordance for human arylamine N-acetyltransferase (NAT2) reveals a new slow-acetylator allele common in African-Americans. Carcinogenesis, 14, 1689–1692.[Abstract]
  53. Hein,D.W., Doll,M.A., Fretland,A.J., Leff,M.A., Webb,S.J., Xiao,G.H., Devanaboyina,U.S., Nangju,N.A. and Feng,Y. (2000) Molecular genetics and epidemiology of the NAT1 and NAT2 acetylation polymorphisms. Cancer Epidemiol. Biomarkers Prev., 9, 29–42.[Abstract/Free Full Text]
  54. Weinshilboum,R.M., Otterness,D.M., Aksoy,I.A., Wood,T.C., Her,C. and Raftogianis,R.B. (1997) Sulfotransferase molecular biology: 1. cDNAs and genes. FASEB J., 11, 3–14.[Abstract/Free Full Text]
  55. Glatt,H.R. (1997) Bioactivation of mutagens via sulfation. FASEB J., 11, 314–321.[Abstract/Free Full Text]
  56. Glatt,H.R., Bartsch,I., Christoph,S. et al. (1998) Sulfotransferase-mediated activation of mutagens studied using heterologous expression systems. Chem. Biol. Interact., 109, 195–219.[ISI][Medline]
  57. Watabe,T., Ishizuka,T., Isobe,M. and Ozawa,N. (1982) A 7-hydroxymethyl sulfate ester as an active metabolite of 7,12-dimethylbenz[a]anthracene. Science, 215, 403–405.[ISI][Medline]
  58. Keating,G.A., Layton,D.W. and Felton,J.S. (1999) Factors determining dietary intakes of heterocyclic amines in cooked foods. Mutat. Res., 443, 149–156.[ISI][Medline]
  59. Surh,Y.J., Lai,C.C., Miller,J.A. and Miller,E.C. (1987) Hepatic DNA and RNA adduct formation from the carcinogen 7-hydroxymethyl-12-methylbenz[a]anthracene and its electrophilic sulfuric acid ester metabolite in preweanling rats and mice. Biochem. Biophys. Res. Commun., 144, 576–582.[ISI][Medline]
  60. Engelke,C.E., Meinl,W., Boeing,H. and Glatt,H. (2000) Association between functional genetic polymorphisms of human sulfotransferases 1A1 and 1A2. Pharmacogenetics, 10, 163–169.[ISI][Medline]
  61. Raftogianis,R.B., Wood,T.C., Otterness,D.M., van Loon,J.A. and Weinshilboum,R.M. (1997) Phenol sulfotransferase pharmacogenetics in humans: association of common SULT1A1 alleles with TS PST phenotype. Biochem. Biophys. Res. Commun., 239, 298–304.[ISI][Medline]
  62. Coughtrie,M.W., Gilissen,R.A., Shek,B., Strange,R.C., Fryer,A.A., Jones,P.W. and Bamber,D.E. (1999) Phenol sulphotransferase SULT1A1 polymorphism: molecular diagnosis and allele frequencies in Caucasian and African populations. Biochem. J., 337, 45–49.[ISI][Medline]
  63. Glatt,H., Engelke,C.E., Pabel,U., Teubner,W., Jones,A.L., Coughtrie,M.W., Andrae,U., Falany,C.N. and Meinl,W. (2000) Sulfotransferases: genetics and role in toxicology. Toxicol. Lett., 112–113, 341–348.[ISI]
  64. WHO (1997) The World Health Report. World Health Organisation, Geneva, Switzerland.
  65. Norrish,A.E., Ferguson,L.R., Knize,M.G., Felton,J.S., Sharpe,S.J. and Jackson,R.T. (1999) Heterocyclic amine content of cooked meat and risk of prostate cancer. J. Natl Cancer Inst., 91, 2038–2044.[Abstract/Free Full Text]
  66. Wacke,R., Kirchner,A., Prall,F. et al. (1998) Up-regulation of cytochrome P450 1A2, 2C9 and 2E1 in chronic pancreatitis. Pancreas, 16, 521–528.[ISI][Medline]
  67. Foster,J.R., Idle,J.R., Hardwick,J.P., Bars,R., Scott,P. and Braganza,J.M. (1993) Induction of drug-metabolizing enzymes in human pancreatic cancer and chronic pancreatitis. J. Pathol., 169, 457–463.[ISI][Medline]
  68. Crofts,F.G., Sutter,T.R. and Strickland,P.T. (1998) Metabolism of 2-amino-1-methyl-6-phenylimidazo[4,5-b]pyridine by human cytochrome P4501A1, P4501A2 and P4501B1. Carcinogenesis, 19, 1969–1973.[Abstract]
  69. Chida,M., Yokoi,T., Fukui,T., Kinoshita,M., Yokota,J. and Kamataki,T. (1999) Detection of three genetic polymorphisms in the 5'-flanking region and intron 1 of human CYP1A2 in the Japanese population. Jpn J. Cancer Res., 90, 899–902.[ISI][Medline]
  70. Sachse,C., Brockmoller,J., Bauer,S. and Roots,I. (1999) Functional significance of a C->A polymorphism in intron 1 of the cytochrome P450 CYP1A2 gene tested with caffeine. Br. J. Clin. Pharmacol., 47, 445–449.[ISI][Medline]
  71. Welfare,M.R., Aitkin,M., Bassendine,M.F. and Daly,A.K. (1999) Detailed modelling of caffeine metabolism and examination of the CYP1A2 gene: lack of a polymorphism in CYP1A2 in Caucasians. Pharmacogenetics, 9, 367–375.[ISI][Medline]
  72. Eriksson,N.E., Holmen,A., Hogstedt,B., Mikoczy,Z. and Hagmar,L. (1995) A prospective study of cancer incidence in a cohort examined for allergy. Allergy, 50, 718–722.[ISI][Medline]
  73. Josephy,P.D. and Coomber,B.L. (1998) The 1996 Veylien Henderson Award of the Society of Toxicology of Canada. Current concepts: neutrophils and the activation of carcinogens in the breast and other organs. Can. J. Physiol. Pharmacol., 76, 693–700.[ISI][Medline]
  74. Dubuisson,J.G. and Gaubatz,J.W. (1998) Bioactivation of the proximal food mutagen 2-hydroxyamino-1-methyl-6- phenylimidazo[4,5-b]pyridine (N-OH-PhIP) to DNA-binding species by human mammary gland enzymes. Nutrition, 14, 683–686.[ISI][Medline]
  75. Bundred,N.J., Dover,M.S., Aluwihare,N., Faragher,E.B. and Morrison,J.M. (1993) Smoking and periductal mastitis. BMJ, 307, 772–773.[ISI][Medline]
  76. Ueda,T., Sakamaki,K., Kuroki,T., Yano,I. and Nagata,S. (1997) Molecular cloning and characterization of the chromosomal gene for human lactoperoxidase. Eur J. Biochem., 243, 32–41.[Abstract]
  77. Sipe,H.J.Jr, Jordan,S.J., Hanna,P.M. and Mason,R.P. (1994) The metabolism of 17 beta-estradiol by lactoperoxidase: a possible source of oxidative stress in breast cancer. Carcinogenesis, 15, 2637–2643.[Abstract]
  78. Yamazoe,Y., Zenser,T.V., Miller,D.W. and Kadlubar,F.F. (1988) Mechanism of formation and structural characterization of DNA adducts derived from peroxidative activation of benzidine. Carcinogenesis, 9, 1635–1641.[Abstract]
  79. Sim,E. (2000) N-acetyltransferases: the second phase. Drug Metab. Rev. 32, Suppl.1.
  80. Hughes,N.C., Janezic,S.A., McQueen,K.L., Jewett,M.A., Castranio,T., Bell,D.A. and Grant,D.M. (1998) Identification and characterization of variant alleles of human acetyltransferase NAT1 with defective function using p-aminosalicylate as an in-vivo and in-vitro probe. Pharmacogenetics, 8, 55–66.[ISI][Medline]
  81. Berkhout,T.A., Simon,H.M., Patel,D.D., Bentzen,C., Niesor,E., Jackson,B. and Suckling,K.E. (1996) The novel cholesterol-lowering drug SR-12813 inhibits cholesterol synthesis via an increased degradation of 3-hydroxy-3-methylglutaryl-coenzyme A reductase. J. Biol. Chem., 271, 14376–14382.[Abstract/Free Full Text]
  82. Watkins,P.B., Wrighton,S.A., Schuetz,E.G., Molowa,D.T. and Guzelian,P.S. (1986) Macrolide antibiotics inhibit the degradation of the glucocorticoid-responsive cytochrome P450p in rat hepatocytes in vivo and in primary monolayer culture. J. Biol. Chem., 261, 6264–6271.[Abstract/Free Full Text]
  83. Stanley,L.A., Coroneos,E., Cuff,R., Hickman,D., Ward,A. and Sim,E. (1996) Immunochemical detection of arylamine N-acetyltransferase in normal and neoplastic bladder. J. Histochem. Cytochem., 44, 1059–1067.[Abstract/Free Full Text]
  84. Hickman,D., Pope,J., Patil,S.D., Fakis,G., Smelt,V., Stanley,L.A., Payton,M., Unadkat,J.D. and Sim,E. (1998) Expression of arylamine N-acetyltransferase in human intestine. Gut, 42, 402–409.[Abstract/Free Full Text]
  85. Butler,M.A., Iwasaki,M., Guengerich,F.P. and Kadlubar,F.F. (1989) Human cytochrome P-450PA (P-450IA2), the phenacetin O-deethylase, is primarily responsible for the hepatic 3-demethylation of caffeine and N-oxidation of carcinogenic arylamines. Proc. Natl Acad. Sci. USA, 86, 7696–7700.[Abstract]
  86. Larsen,M.C., Angus,W.G., Brake,P.B., Eltom,S.E., Sukow,K.A. and Jefcoate,C.R. (1998) Characterization of CYP1B1 and CYP1A1 expression in human mammary epithelial cells: role of the aryl hydrocarbon receptor in polycyclic aromatic hydrocarbon metabolism. Cancer Res., 58, 2366–2374[Abstract]
  87. Shou,M., Gonzalez,F.J. and Gelboin,H.V. (1996) Stereoselective epoxidation and hydration at the K-region of polycyclic aromatic hydrocarbons by cDNA-expressed cytochromes P450 1A1, 1A2 and epoxide hydrolase. Biochemistry, 35, 15807–15813[ISI][Medline]
  88. Lu,A.Y., Thomas,P.E., Ryan,D., Jerina,D.M. and Levin,W. (1979) Purification of human liver microsomal epoxide hydrase. Differences in the properties of the human and rat enzymes. J. Biol. Chem., 254, 5878–5881.[Abstract]
  89. Mallet,W.G., Mosebrook,D.R. and Trush,M.A. (1991). Activation of (+–)-trans-7,8-dihydroxy-7,8-dihydrobenzo[a]pyrene to diolepoxides by human polymorphonuclear leukocytes or myeloperoxidase. Carcinogenesis, 12, 521–524.[Abstract]
  90. Mills,P.K., Beeson,W.L., Fraser,G.E. and Phillips,R.L. (1992) Allergy and Cancer: organ site-specific results from the Adventist Health Study Am J Epidemiol 136, 287–295.[Abstract]
Received September 11, 2000; accepted November 2, 2000.