Strong impact of sulfotransferases on DNA adduct formation by 4-aminobiphenyl in bladder and liver in mice.

Bladder cancer risk is 3-4 times higher in men than women, but the reason is poorly understood. In mice, male bladder is also more susceptible than female bladder to 4-aminobiphenyl (ABP), a major human bladder carcinogen; however, female liver is more susceptible than male liver to ABP. We investigated the role of sulfotransferase (Sult) in gender-related bladder and liver susceptibility to ABP. Sulfation reactions of aromatic amine bladder carcinogens catalyzed by Sult may generate highly unstable and toxic metabolites. Therefore, liver Sult may decrease bladder exposure to carcinogens by promoting their toxic reactions in the liver. Notably, the expression of several liver Sults is suppressed by androgen in male mice. Here, we show that two Sults are critical for gender-related bladder susceptibility to ABP in mice. We measured tissue level of N-(deoxyguanosin-8-yl)-4-aminobiphenyl (dG-C8-ABP), a principal ABP-DNA adduct, as readout of tissue susceptibility to ABP. We identified Sutl1a1 and to a lesser extent Sult1d1 as Sults that promote dG-C8-ABP formation in hepatic cells. In mice, gender gap in bladder susceptibility to ABP was narrowed by knocking out Sult1a1 and was almost totally eliminated by knocking out both Sutl1a1 and Sult1d1. This was accompanied by dramatic decrease in ABP genotoxicity in the liver (>97%). These results show the strong impact of the Sults on bladder and liver susceptibility to a human carcinogen. Because liver expression of both Sult1a1 and Sutl1d1 is suppressed by androgen in male mice, our results suggest that androgen renders bladder more exposed to ABP in male mice by suppressing Sult-mediated ABP metabolism in liver, which increases bladder delivery of carcinogenic metabolites.

Molecular Interactions of Carcinogenic Aromatic Amines, 4-Aminobiphenyl and 4,4'-Diaminobiphenyl, with Lactoperoxidase - Insight to Breast Cancer.

BACKGROUND/AIM: Lactoperoxidase (LPO) is an antimicrobial protein present in milk, saliva, gastric secretions, tears and upper respiratory tract secretions. LPO constitutes an important enzyme of the human immune defense system. However, LPO has also been suggested to be involved in breast cancer etiology through production of reactive free radicals and activation of carcinogenic aromatic compounds. Aromatic compounds are generally highly lipophilic and thus accumulate in highly fatty breast tissues. The aromatic compounds 4-aminobiphenyl (ABP) and 4,4'-diaminobiphenyl (BZ) are known to have carcinogenic properties. LPO catalyzes their oxidation and converts them into reactive products which bind to DNA and form adducts. These DNA adducts subsequently lead to breast cancer. MATERIALS AND METHODS: The crystal structure of LPO was obtained from Protein Data Bank. Structures of ABP and BZ were retrieved from PubChem database. Induced Fit Docking was performed using glide module from Schrodinger. RESULTS: The present study reports the structural binding of ABP and BZ with LPO using in silico approaches. The amino acid residues of LPO involved in the binding with the two aromatic ligands were characterized and binding energy values were calculated. CONCLUSION: Both ABP and BZ were placed in the substrate binding site present in the distal heme cavity of LPO with good affinity. The binding mode mimicked that of the natural substrate since these compounds did not disturb the water molecule that plays an important role in the oxidation reaction. Thus, the water molecule is potentially available for facilitating the subsequent activation of the aromatic amines to reactive species which may form DNA adducts leading to breast cancer.

Mechanisms of oxidative DNA damage induced by carcinogenic arylamines.

Most arylamines are pro-carcinogens, and require metabolic activation to yield ultimate carcinogen metabolites. O-Acetylation of the N-hydroxy form of an arylamine yields an acetoxyarylamine, which can form a highly reactive arylnitrenium ion, the ultimate metabolite responsible for DNA adduct formation. However, we demonstrate here that the N-hydroxy and nitroso forms of arylamines can also induce DNA damage, including 7,8-dihydro-8-oxo-2'-deoxyguanosine (8-oxodG) lesions, via reactive oxygen species formation. The N-hydroxy and nitroso derivatives of carcinogenic arylamines may contribute to the carcinogenic process through H2O2 formation. N-Hydroxy derivatives induce metal-mediated DNA damage, with remarkable enhancement by NADH. Nitroso derivatives induce NADH-dependent DNA damage in the presence of metal ions. Hydroxy derivatives of arylamines formed by enzymatic hydroxylation or as o- or p-aminophenols can also induce DNA damage in the presence of metal ions. The autoxidation of o-phenylenediamine and several arylamine metabolites is accelerated in the presence of SOD or manganese, resulting in the enhancement of metal-mediated DNA damage. The oxidative DNA damage induced by arylamine compounds may participate in chemical carcinogenesis, in addition to DNA adduct formation.

A modified host cell reactivation assay to measure DNA repair capacity for removing 4-aminobiphenyl adducts: a pilot study of bladder cancer.

As DNA repair plays an important role in genetic susceptibility to bladder cancer, assessment of the DNA repair phenotype is critical for the molecular epidemiology of bladder cancer. In this study, we developed and applied an assay using the luciferase (luc) reporter gene in a host-cell reactivation assay to measure DNA repair capacity for DNA damage induced by 4-aminobiphenyl (4-ABP), a well-studied aromatic amine and a known bladder carcinogen. We observed a dose-response relationship for 4-ABP dosage and DNA repair capacity (luc activity). We then applied this assay to measure DNA repair capacity in a pilot study of 89 pairs of bladder cancer patients and healthy controls matched by age, gender, and ethnicity, and we found that DNA repair capacity was significantly lower in cases than in controls (13.0% versus 14.4%; P = 0.006). Poor DNA repair capacity was associated with 3.42-fold increased bladder cancer risk. Further analysis revealed that intermediate and low levels of DNA repair capacity increased bladder cancer risk to 3.43-fold and 4.97-fold, respectively, compared with individuals with the most efficient DNA repair capacity. Moreover, ever smokers with suboptimal DNA repair capacity exhibited a 6.06-fold increased risk compared with never smokers with normal DNA repair capacity. In conclusion, our results support the hypothesis that deficient DNA repair capacity for 4-ABP induced DNA damage and increases bladder cancer risk. Our assay provides a new tool to specifically quantify DNA repair capacity in bladder cancer studies and, therefore, contributes to our goal of further elucidating bladder carcinogenesis.

Alkylaniline-hemoglobin adducts and risk of non-smoking-related bladder cancer.

BACKGROUND: Some members of the arylamine family of compounds, specifically 4-aminobiphenyl (ABP), 2-naphthylamine, and benzidine, are established human bladder carcinogens. Cigarette smoking and use of permanent hair dye contribute substantially to current arylamine exposure. Low levels of 4-ABP exposure have been associated with non-smoking-related bladder cancer. Other arylamine compounds coming from as yet unidentified environmental sources may also be human bladder carcinogens. METHODS: We conducted a population-based case-control study in Los Angeles County, California, involving 298 case subjects with bladder cancer and 308 control subjects, who were matched on age, sex, race/ethnicity, and neighborhood of residence. In-person interviews provided information on tobacco smoking and other potential risk factors for bladder cancer. To assess arylamine exposure, levels of arylamine-hemoglobin adducts of nine selected alkylanilines (2,3-dimethylaniline [2,3-DMA], 2,4-DMA, 2,5-DMA, 2,6-DMA, 3,4-DMA, 3,5-DMA, 2-ethylaniline [2-EA], 3-EA, 4-EA) were measured in peripheral blood collected from study subjects. Analysis of covariance and conditional logistic regression methods were used to analyze the relationship between arylamine-hemoglobin adducts and bladder cancer risk. All statistical tests were two-sided. RESULTS: Levels of all arylamine-hemoglobin adducts, with the exception of 2,6-DMA, were higher in smokers than in nonsmokers, and levels of all arylamine-hemoglobin adducts were higher in case subjects than in control subjects. Arylamine-hemoglobin adducts of 2,6-DMA, 3,5-DMA, and 3-EA were all independently, statistically significantly (all P<.001) associated with bladder cancer risk after adjusting for cigarette smoking at the time of blood collection, lifetime smoking history, and other potential risk factors. These adducts were also independently associated with bladder cancer risk when only nonsmokers at time of blood draw were considered (highest quartile versus lowest quartile: 2,6-DMA, relative risk [RR] of bladder cancer = 8.1, 95% confidence interval [CI] = 3.6 to 18.0; 3,5-DMA, RR = 2.7, 95% CI = 1.2 to 6.0; 3-EA, RR = 4.3, 95% CI = 1.6 to 11.6). CONCLUSIONS: Diverse arylamine exposures are strongly associated with bladder cancer risk among nonsmokers. Because arylamines may account for a substantial proportion of bladder cancers among the general population, identification of environmental sources of these compounds is needed.

Evaluation of 4-aminobiphenyl-DNA adducts in human breast cancer: the influence of tobacco smoke.

Breast cancer is one of the major cancers around the world but its etiology is still not well understood. Only approximately 50% of the disease is associated with known risk factors including highly penetrant genes and lifestyle factors. Thus, environmental carcinogens may play an important role in the etiology of breast cancer. The arylamine 4-aminobiphenyl (4-ABP) is a tobacco smoke constituent, an environmental contaminant, and a well-established bladder carcinogen in rodents and humans. In this study, we investigated the role of 4-ABP in the etiology of human breast cancer by measuring 4-ABP-DNA adducts using a monoclonal antibody based immunoperoxidase method that had been validated by comparison with gas chromatography/mass spectroscopy analysis of liver tissues from 4-ABP-treated mice. Adducts were analyzed in 150 paraffin-embedded breast tumors and in 55 adjacent normal tissues collected from cases in the Long Island Breast Cancer Study Project. The role of polymorphisms in genes involved in the metabolism of 4-ABP including N-acetyl transferase 2 (NAT2), cytochrome P4501A2 (CYP1A2) and glutathione S-transferase M1 (GSTM1) and the nucleotide excision repair gene XPD was also explored in the same patients. The mean log-transformed relative staining intensity for 4-ABP-DNA adducts was higher in normal (5.93 +/- 0.54) than in the corresponding tumor (5.44 +/- 0.62, P < 0.0001) tissues. However, a highly significant positive correlation was observed between the levels of 4-ABP-DNA in both tissues (r = 0.72, P < 0.0001). Smoking status was correlated with the levels of 4-ABP-DNA in tumor adjacent normal tissues with a significant linear trend (P = 0.04) for current, former and never smokers; adducts were not related to smoking status in tumor tissues. No correlation was observed between the levels of 4-ABP-DNA and polymorphisms in the genes analyzed even when subjects were stratified by smoking status. These results demonstrate that smoking is associated with increased levels of 4-ABP-DNA adducts in human mammary tissue. In this study, genetic polymorphisms did not significantly affect the formation of 4-ABP-DNA adducts in breast cancer cases, perhaps due to the small number of samples.

Highlights of the eighth international conference on carcinogenic/mutagenic N-substituted aryl compounds.

Research in the 20th century initially identified arylamines as causative factors in occupational carcinogenesis, especially bladder cancer, and subsequently identified arylamines as a major class of mutagens/carcinogens in the environment and diet that are potential risk factors in a variety of human cancers. Current research focuses on understanding of mechanisms of arylamine carcinogenesis, such as the role of metabolic processing, DNA adduct formation, and mutagenesis, and learning more about the molecular alterations in carcinomas induced by these compounds. Furthermore, research to identify human exposures, including developing more sensitive methods for analyzing environmental samples and identifying suitable biomarkers are important aspects of contemporary investigations. In addition, better evaluation of the risk of these compounds in human cancer especially with regard to the impact of genetic polymorphisms is a major focus of research in this field. Although current population studies have sometimes been described as equivocal, improved tools for epidemiology, refined human biomonitoring methods and collaborative endeavors to study multiple population groups now provide a better means to ultimately define the role of arylamines in human carcinogenesis. The purpose of the Eighth International Conference on Carcinogenic/Mutagenic N-Substituted Aryl Compounds, held in Washington, DC, 12-14 November 2001, was to explore the current scope of studies on arylamine carcinogenesis among scientists in basic research and epidemiology and to discuss future research priorities. With the intent of providing a view to the current field of research on aromatic amines, this review presents a synopsis of the Proceedings of the Eighth International Conference and highlights the manuscripts contained in this special issue of Mutation Research.

N-acetyltransferase 2 phenotype but not NAT1*10 genotype affects aminobiphenyl-hemoglobin adduct levels.

Aminobiphenyls (ABPs) in tobacco have been implicated in bladder cancer etiology in smokers. N-Acetylation of ABPs in the liver, predominantly by the N-acetyltransferase 2 (NAT2) isozyme, represents a detoxification pathway, whereas O-acetylation of N-hydroxy-ABPs in the bladder, predominantly by the N-acetyltransferase 1 (NAT1) isozyme, represents a bioactivation pathway. We and others have demonstrated that NAT2 phenotype affects 3- and 4-ABP-hemoglobin adduct levels (higher levels in slow acetylators), which are considered valid biomarkers of the internal dose of ABP to the bladder. We have also shown that NAT1 genotype (NAT1*10 allele) is associated with increased DNA adduct levels in urothelial tissue and higher risk of bladder cancer among smokers. It is not known whether NAT1*10 genotype influences ABP-hemoglobin adduct levels. Therefore, we assessed 403 primarily non-Hispanic white residents of Los Angeles County for their NAT2 acetylator phenotype, NAT1*10 acetylator genotype, and 3- and 4-ABP-hemoglobin adduct levels. Eighty-two subjects were current tobacco smokers of varying intensities. Tobacco smokers had significantly higher mean 3- and 4-ABP-hemoglobin adduct levels relative to nonsmokers. The levels increased with increased amounts smoked per day (two-sided, P < 0.0001 in all cases). With adjustment for NAT1 genotype and race, the smoking-adjusted geometric mean level of 3-ABP-hemoglobin adducts in NAT2 slow acetylators was 47% higher than that in NAT2 rapid acetylators (P = 0.01). The comparable value for 4-ABP-hemoglobin adducts was 17% (P = 0.02). In contrast, no association between NAT1*10 genotype and 3- or 4 ABP-hemoglobin adduct levels was observed after adjustment for NAT2 phenotype, smoking, and race. The present study suggests that the impact of the NAT1*10 genotype on 3- and 4-ABP-hemoglobin adducts is noninformative on the possible association between NAT1 activity and bladder cancer risk.

Detection of carcinogenic aromatic amines in the urine of non-smokers.

Smoking is thought to be one of the most important anthropogenic risk factors involved in the development of urinary bladder cancer in humans. Tobacco smoke contains a complex mixture of chemicals including potent carcinogens such as aromatic amines. In the present study the amounts of several freebase aromatic amines including the potent carcinogens 2-aminonaphthalene and 4-aminobiphenyl have been analyzed in the urine of 48 German urban living smokers and non-smokers. The results indicate that (i) both groups excrete the identical set of four aromatic amines; (ii) smokers excrete approximately twice the total amount of these amines, but similar amounts of 2-aminonaphthalene and 4-aminobiphenyl are found in non-smokers; and (iii) the excreted aromatic amines are decomposed in the urine within a few hours thus, explaining why aromatic amines are difficult to detect in this matrix. Their decomposition could be prevented by adding small amounts of p-toluidine to the freshly collected urine. Unlike smokers the origin of aromatic amines detected in the urine of non-smokers is at present unknown. Based on the cotinine levels found in the urine of non-smokers environmental tobacco smoke can be excluded as a major source of aromatic amines. In addition, neither diesel exhaust-related nitroarenes nor the corresponding amino-derivatives, to which they may be metabolically converted, were found. The detected urinary levels of aromatic amines arising from sources other than tobacco smoke or diesel exhaust may play a role in the bladder cancer etiology of non-smokers.

Mortalities of workers at the Nitro plant with exposure to 2-mercaptobenzothialzole.

OBJECTIVES: An update of a study of workers exposed to 2-mercaptobenzothiazole (MBT) at a rubber chemicals plant in Nitro, West Virginia is reported. The earlier study found high rates of lung cancer, prostate cancer, and bladder cancer in these workers who also had potential exposure to 4-aminobiphenyl (PAB), a potent bladder carcinogen. METHODS: This cohort mortality study examines the mortalities of 1059 full time white male production workers employed at the plant from 1955 to 1977. A detailed exposure assessment was done on the 600 workers with exposure to MBT. Nine years of additional follow up to the previous study are added. RESULTS: It was found that MBT workers have expected rates of lung (standardised mortality ratio (SMR) = 1.0 95% confidence interval (95% CI) 0.7 to 1.5) and prostate (SMR = 0.9, 95% CI 0.2 to 2.3) cancer. There was an excess of bladder cancer among MBT workers who had definite exposure to PAB (SMR = 27.1, 95% CI 11.7 to 53.4), and MBT workers with potential exposure to PAB (SMR = 4.3, 95% CI 1.4 to 10.0). However, there were no deaths from bladder cancer among workers with no exposure to PAB (SMR = 0.0, 95% CI 0.0 to 24.7), although there were only 0.2 deaths expected. CONCLUSIONS: The potential confounding of exposure to an unknown portion of PAB in the MBT workers makes it impossible to evaluate risk of bladder cancer in this population at this time. However, exposure to MBT does not seem to increase the risk of most cancers including cancers of the lung and prostate.

4-Aminobiphenyl DNA damage in liver tissue of hepatocellular carcinoma patients and controls.

Epidemiologic studies have suggested that cigarette smoking is a risk factor for the development of hepatocellular carcinoma (HCC). To further investigate this relation, the authors measured levels of 4-aminobiphenyl-DNA adducts by an immunoperoxidase method in surgical liver tissues obtained between 1984 and 1995 from 105 Taiwanese patients with histologically confirmed HCC and 37 Taiwanese patients with metastatic liver tumors or intrahepatic stones. Information on clinicopathologic characteristics, cigarette smoking, and alcohol drinking was abstracted from hospital charts. Mean relative staining intensity for 4-aminobiphenyl-DNA was slightly higher in tumor tissues than in nontumor tissues obtained from HCC patients. Both mean intensities were significantly higher than the mean intensity of control tissues taken from non-HCC patients. However, no difference in mean relative staining intensity was found between smokers and nonsmokers in tissues obtained from non-HCC patients, or in tumor or nontumor tissues taken from HCC cases. After stratification of the relative staining intensities of 4-aminobiphenyl-DNA adduct levels into tertiles according to the total numbers of control tissues analyzed, there was a monotonically increasing risk of HCC. Odds ratios were 4.14 (95% confidence interval (CI) 1.15-15.50) and 9.71 (95% CI 2.82-34.86) for medium and high adduct levels compared with low adduct levels, respectively. The linear relation between adduct levels in liver tissue and HCC risk was also significant after adjustment for covariates, including hepatitis B surface antigen (HBsAg) status. The multivariate adjusted odds ratios were 3.41 (95% CI 0.82-14.25) and 6.48 (95% CI 1.59-26.50) for medium and high adduct levels, respectively. Moreover, there were monotonically increasing HCC risks for higher adduct levels in both HBsAg carriers and noncarriers. The increased risk ratios were more pronounced in noncarriers than in carriers. However, because of the small numbers of subjects, especially controls positive for HBsAg, the interaction between HBsAg status and 4-aminobiphenyl-DNA adduct level was not significant. Among HCC cases, none of the clinicopathologic characteristics were associated with relative staining intensity. These results indicate that 4-aminobiphenyl exposure, which is primarily a result of cigarette smoking, plays a role in the development of HCC in humans.

Characterization of 4-aminobiphenyl-hemoglobin adducts in maternal and fetal blood-samples.

The maternal-fetal exchange of the potent tobacco-related human carcinogen 4-aminobiphenyl was studied in women smokers during pregnancy. The number of cigarettes smoked per day by each of the women in the study was assessed via questionnaire and by measurement by immunoassay of serum and urine cotinine in maternal and fetal blood samples. Maternal and fetal blood samples were classified as coming from nonsmokers (n = 74), individuals smoking less than 1 pack of cigarettes per day (n = 16), individuals smoking 1 pack of cigarettes per day (n = 19), individuals smoking 1-2 packs of cigarettes per day (n = 19), and individuals smoking greater than 2 packs of cigarettes per day (n = 20). Both maternal and fetal blood samples were obtained at the time of delivery. 4-Aminobiphenyl was extracted from both maternal and fetal blood samples using organic extractions and the released amine was qualitatively and quantitatively characterized by analysis of the samples by gas chromatographic and mass spectrometric analysis. Background levels of 4-aminobiphenyl-hemoglobin adducts were detected in maternal nonsmokers (18.3 +/- 12.7 pg 4-aminobiphenyl/g hemoglobin, mean +/- SD) and in fetal samples (8.88 +/- 5.8 pg/g hemoglobin). Increasing levels of 4-aminobiphenyl-hemoglobin adducts were found as the smoking status of the women increased, ranging from 144 +/- 22.2 ( < 1 pack/d) to 633 +/- 87.9 ( > 2 packs/d). A corresponding increase in the presence of fetal 4-aminobiphenyl-hemoglobin adducts was also detected (74 +/- 17.8, < 1 pack/d, to 319 +/- 50.5, > 2 packs/d). This study confirms that the potent tobacco-related carcinogen 4-aminobiphenyl crosses the human placenta and binds to fetal hemoglobin in significantly higher concentrations in smokers when compared to nonsmokers.

HPLC and GC/MS determination of 4-aminobiphenyl haemoglobin adducts in fetuses exposed to the tobacco smoke carcinogen in utero.

Maternal-fetal exchange of the potent tobacco-related human carcinogen, 4-aminobiphenyl, was studied in women nonsmokers and in women smokers as well as in the corresponding fetuses during pregnancy. Smoking status of the women in the study was assessed via questionnaire and measurement by immunoassay of serum cotinine in maternal and fetal blood samples. 4-Aminobiphenyl was extracted from both maternal and fetal blood samples using organic solvent extractions and the released amine was qualitatively and quantitatively characterized by analysis of the samples by high pressure liquid chromatography (HPLC) and gas chromatography coupled with mass spectrometry (GC/MS). Background levels (pg 4-aminobiphenyl/g haemoglobin) of 4-aminobiphenyl-haemoglobin adducts were detected in maternal smokers (mean +/- S.D; 29.6 +/- 16.2 (GC/MS); 23.7 +/- 13.5 (HPLC) and in fetal samples (14.0 +/- 6.5 (GCMS); 10.0 +/- 4.6 (HPLC). Elevated levels of 4-aminobiphenyl-haemoglobin adducts were found in maternal smokers (488 +/- 174 (GC/MS); 423 +/- 154 (HPLC). as well as in the corresponding fetal blood samples (244 +/- 91 (GC/MS); 197 +/- 77 (HPLC). This study confirms that a potent tobacco-related carcinogen, 4-aminobiphenyl, crosses the human placenta and binds to fetal haemoglobin in significantly higher concentrations in smokers when compared to nonsmokers.

DNA adducts in urothelial cells: relationship with biomarkers of exposure to arylamines and polycyclic aromatic hydrocarbons from tobacco smoke.

Markers of exposure to polycyclic aromatic hydrocarbons (urinary 1-hydroxypyrene-glucuronide) and aromatic amines (4-aminobiphenyl-hemoglobin adducts), as well as urinary mutagenicity, were measured in 47 healthy smokers and 50 nonsmokers. DNA adducts were determined by P32-postlabeling in the exfoliated bladder cells of 39 healthy subjects. Both 1-hydroxypyrene-glucuronide (1-OHPG) and 4-aminobiphenyl adducts (4-ABP-Hb) were associated with smoking habits, but only 4-ABP-Hb adducts were associated with consumption of black, air-cured tobacco. The levels of 2 DNA adducts (numbers 2 and 4) in urothelial cells were clearly associated with 4-ABP-Hb adducts, in all subjects and in smokers. Levels of one of these DNA adducts (number 2) were also associated with 1-hydroxypyrene-glucuronide in urines, but in smokers the association was not statistically significant. Overall, these observations constitute further evidence of a role of arylamines in tobacco-induced bladder cancer.

Modeling human interindividual variability in metabolism and risk: the example of 4-aminobiphenyl.

We investigate, through modeling, the impact of interindividual heterogeneity in the metabolism of 4-aminobiphenyl (ABP) and in physiological factors on human cancer risk: A physiological pharmacokinetic model was used to quantify the time course of the formation of the proximate carcinogen, N-hydroxy-4-ABP and the DNA-binding of the active species in the bladder. The metabolic and physiologic model parameters were randomly varied, via Monte Carlo simulations, to reproduce interindividual variability. The sampling means for most parameters were scaled from values developed by Kadlubar et al. (Cancer Res., 51: 4371, 1991) for dogs; variances were obtained primarily from published human data (e.g., measurements of ABP N-oxidation, and arylamine N-acetylation in human liver tissue). In 500 simulations, theoretically representing 500 humans, DNA-adduct levels in the bladder of the most susceptible individuals are ten thousand times higher than for the least susceptible, and the 5th and 95th percentiles differ by a factor of 160. DNA binding for the most susceptible individual (with low urine pH, low N-acetylation and high N-oxidation activities) is theoretically one million-fold higher than for the least susceptible (with high urine pH, high N-acetylation and low N-oxidation activities). The simulations also suggest that the four factors contributing most significantly to interindividual differences in DNA-binding of ABP in human bladder are urine pH, ABP N-oxidation, ABP N-acetylation and urination frequency.

Molecular dosimetry of aromatic amines in human populations.

Certain aromatic amines carcinogenic for the human urinary bladder, such as 4-aminobiphenyl, undergo hepatic metabolic activation to N-hydroxylamines, which are transported to the bladder. During the transport process, these reactive species come in contact with hemoglobin and react with this blood protein. The principal hemoglobin adduct formed is a cysteine sulfinamide, and quantitative methods have been developed for the analysis of sulfinamide adducts at the levels present in ordinary human blood specimens. N-acetylation is an alternative metabolic fate to N-hydroxylation. The amount of hemoglobin adduct is decreased to the extent that this pathway is increased relative to N-hydroxylation. Thus, the hemoglobin adduct is sensitive to dose, cytochrome P-450-mediated activation, and N-acetyltransferase-mediated detoxification. In addition, it has been shown that DNA adduct concentration of 4-aminobiphenyl present in human bladder epithelial cells is significantly associated with hemoglobin adduct levels. Thus, the hemoglobin adduct of 4-aminobiphenyl, and perhaps several other aromatic amines, is a good dosimeter for the target tissue dose of the ultimate carcinogenic metabolite of these amines. Several studies have been undertaken in which the hemoglobin adducts of aminobiphenyls in human blood specimens were determined quantitatively. Information concerning exposure status and acetylator phenotype of the same individuals was obtained simultaneously. The results of these studies indicate that the hemoglobin adduct of 4-aminobiphenyl is closely associated with three major risk factors for bladder cancer: cigarette smoking, type of tobacco smoked, and acetylator phenotype. They also support a major etiologic role for aromatic amines in much of human bladder cancer.

Epidemiology of cancer from exposure to arylamines.

Occupational exposure to arylamines such as benzidine, 2-naphthylamine, and 4-aminobiphenyl is associated with exceptionally elevated risks of bladder cancer (up to 100-fold or more). In one plant, all 15 workers involved in distilling naphthylamine developed bladder cancer, suggesting that for high levels of exposure to potent carcinogens individual susceptibility is irrelevant. More recently, exposure to other arylamines also has been suggested to increase the risk of bladder cancer in humans. In addition, cohort and case-control studies suggest that several job titles or exposures may involve elevated risks of bladder cancer. Some of these jobs or exposures (such as in the aluminum industry) are associated with exposure to arylamines. Arylamines are found also in tobacco smoke, and different sources of evidence suggest that they can explain the risk of bladder cancer, which has been shown clearly in smokers. Epidemiologic analyses of timing of exposure in workers occupationally exposed to arylamines or in air-cured tobacco smokers suggest that arylamines exert both an early- and a late-stage activity, compatible with a two-mutation theory of bladder carcinogenesis.