Abstract
Background:
Acidic urine pH is associated with rapid hydrolysis of N-glucuronide conjugates of aromatic amines into metabolites that may undergo metabolism in the bladder lumen to form mutagenic DNA adducts. We previously reported that consistently acidic urine was associated with increased bladder cancer risk in a hospital-based case–control study in Spain. Here, we conducted a separate study in northern New England to replicate these findings.
Methods:
In a large, population-based case–control study conducted in Maine, New Hampshire, and Vermont, we examined bladder cancer risk in relation to consistent urine pH, measured twice daily by participants over 4 consecutive days using dipsticks. In parallel, we collected spot urine samples and conducted laboratory measurements of urinary acidity using a pH meter. Unconditional logistic regression was used to estimate associations, adjusting for age, gender, race, Hispanic status, and state. Analyses were further stratified by smoking status.
Results:
Among 616 urothelial carcinoma cases and 897 controls, urine pH consistently ≤ 6.0 was associated with increased bladder cancer risk (OR = 1.27; 95% confidence interval, 1.02–1.57), with the effect limited to ever-smokers. These findings were supported by analyses of a spot urine, with statistically significant exposure–response relationships for bladder cancer risk overall (Ptrend = 5.1×10−3) and among ever-smokers (Ptrend = 1.2×10−3).
Conclusions:
Consistent with a previous study in Spain, our findings suggest that acidic urine pH is associated with increased bladder cancer risk.
Impact:
Our findings align with experimental results showing that acidic urine pH, which is partly modifiable by lifestyle factors, is linked to hydrolysis of acid-labile conjugates of carcinogenic aromatic amines.
Introduction
Some aromatic amines found in cigarette smoke as well as in the manufacture of dye, rubber, and chemicals are well-known bladder carcinogens (1, 2). N-glucuronidation is an important mechanism by which aromatic amines are hepatically metabolized into more water-soluble conjugates, which then allows passage into the bladder lumen via urine (3, 4). While N-glucuronide conjugates of aromatic amines are relatively stable at neutral pH (5, 6), increasing acidity of pH is associated with more rapid hydrolysis resulting in a regeneration of the parent amine or unconjugated metabolite (5–7). In vitro evidence specifically examining aromatic amines derived from cigarette smoke, such as 4-aminobiphenyl (4-ABP), indicated that the half-life of N-glucuronide conjugates of 4-ABP was more than 17 times shorter at a pH of 5.5 versus 7.4 before hydrolysis into its unconjugated form (8). Unconjugated aromatic amines are then capable of binding covalently to nucleic acids to form DNA adducts after further metabolic activation in the bladder (9, 10). N’-(3′-monophospho-deoxyguanosin-8-yl)-N-acetylbenzidine (dGp-ABZ), the major adduct present in exfoliated human bladder cells in workers exposed to benzidine (11), has been shown to cause frameshift mutations, point mutations, and sister chromatid exchanges in in vitro systems, and Ras proto-oncogene mutations in tumors (12–15). In humans, subjects with urine pH < 6 had 10-fold higher levels of exfoliated urothelial cell dGp-ABZ adduct formation than subjects with urine pH> 7, after controlling for internal dose of the examined urinary aromatic amines (16).
We examined subjects with consistently acidic urine over a 4-day study period with the intention of identifying individuals predisposed to having a bladder microenvironment that is conducive to mutagenic activity from unconjugated aromatic amines. We previously reported an association between consistently acidic urine pH and increased risk of bladder cancer in a hospital-based case–control study conducted in Spain (17). The primary aim of the current study is to further examine the association between consistent acidic urine over a period of several days and risk of bladder cancer based on data from a population-based case–control study conducted in northern New England.
Materials and Methods
Study design and data collection
This case–control study conducted in Maine, Vermont, and New Hampshire was described in detail (18). Briefly, the study included 1,171 cases aged 30 to 79 years at diagnosis with histologically confirmed urothelial cell carcinoma of the bladder diagnosed between September 1, 2001 and October 31, 2004 (Maine and Vermont) or between January 1, 2002 and July 31, 2004 (New Hampshire). We interviewed 1,418 population controls that were randomly selected from the state Department of Motor Vehicle records (ages 30–64 years) and Centers for Medicare and Medicaid Services beneficiary records (ages 65–79 years), frequency matched to cases by state, gender, and age within 5 years of diagnosis. The study was approved by the NCI SSIRB and all study participants provided written informed consent. The study was conducted in accordance with the ethical principles of the Declaration of Helsinki.
A trained interviewer obtained detailed information on demographics, use of tobacco products, and other factors using a computer-assisted personal interview. Never-smokers were defined as subjects who had ever smoked <100 cigarettes, while ever-smokers (including occasional and regular smokers) had smoked ≥100 cigarettes over their lifetime.
Study participants were trained to measure urine pH with dipsticks at home and record results into a diary. In total, 616 cases (52.6%) and 897 controls (63.3%) returned diaries with complete data on urine pH, measured twice daily (first morning void, early evening) for four consecutive days after the interview. Patients were considered to have consistently acidic urine if all eight urine pH values were ≤6.0. Among cases who returned a urine diary, the median number of days between cancer diagnosis and interview was 166 days [interquartile range (IQR), 108–286 days]. There was no association between time since diagnosis and urine pH (P = 0.94). In parallel to the self-measured urine samples, we collected independent spot urine samples from participants during in-home visits and conducted laboratory measurements of urinary acidity using a standard pH meter.
Spanish bladder cancer study and urine pH
The purpose of the current study of urine pH and bladder cancer in northern New England was to replicate the findings previously reported in the Spanish Bladder Cancer Study, a large multicenter, hospital-based case–control study in Spain that explores the etiology of bladder cancer. The study design and analyses of urinary pH and bladder cancer risk in Spain were previously reported in detail (17, 19, 20). In the Spanish study, subjects were categorized as having a consistently acidic urine pH using the same criteria as the current analyses. As urine pH can reflect time-varying exposures and factors, this conservative definition was used to increase the probability that individuals would have had a long-term tendency to have acidic urine.
Statistical analysis
We estimated the ORs and 95% confidence intervals (CI) for bladder cancer in relation to a dichotomous variable reflecting consistently acidic urine pH using unconditional logistic regression, adjusting for age, gender, race, Hispanic status, and state of residence. Among current or former smoking controls and current or former smoking cases, there was no correlation between smoking duration, smoking intensity, or cigarettes smoked in the last 48 hours prior to spot urine collection and consistent urinary pH measured by study participants, or the spot urine pH measured in a laboratory (all Spearman ρ < 0.11, all P values were nonsignificant). Further, we did not observe statistical evidence of confounding when the urine pH and bladder cancer risk models were adjusted for various measures of smoking (risk estimates changed <10%) or usual body mass index (BMI); therefore, we did not include these variables in our final models but do show these results in Supplementary Table S1.
To test for linear trends, we computed the Wald statistic, treating the categorized exposure variable in the controls as ordinal. To test for interaction between two risk factors, we added a cross product term to the logistic models and conducted likelihood ratio tests. To combine our current results with those from the previous case–control study conducted in Spain, we performed random effects meta-analyses and tested for heterogeneity in the effect estimates.
All analyses were performed using SAS software version 9.4 (SAS Institute, Cary, NC;RRID:SCR_008567) except for analyses conducted in the Spanish study and the meta-analysis of the New England and Spanish studies that evaluated urine pH and bladder cancer risk by smoking status, which were performed using STATA 11. Results for urine pH and bladder cancer risk for current smokers, who made up 28% of ever-smokers, and former smokers were similar, and the two groups were combined to increase statistical power.
Data availability
Data were generated by the authors but are not publicly available due to subject privacy. Data requests can be made by contacting the corresponding author. Reasonable data requests will be considered by the senior authors.
Results
Subjects who returned a urine diary were similar to those who did not with regard to average age (65.0 vs. 64.5 years, respectively; P = 0.66), gender (25.2% vs. 25.2% female; P > 0.99), education (52.0% vs. 49.4% with at least a high school education; P = 0.20), and average usual adult BMI (26.0 vs. 26.4 kg/m2; P = 0.07). Table 1 shows the distribution of gender, age, race, Hispanic status, state of residence, usual BMI, and smoking variables (i.e., smoking status, smoking intensity, and smoking duration) among cases and controls. Urine pH was not correlated with usual BMI (Spearman ρ = 0.07).
Table 1.
Selected characteristics of subjects in the urine pH analysis, New England Bladder Cancer Study, 2001 to 2004.
| Subject characteristics | Controls n = 897 (%) | Cases n = 616 (%) |
|---|---|---|
| Gender | ||
| Female | 234 (26.1) | 147 (23.9) |
| Male | 663 (73.9) | 469 (76.1) |
| Age (years) | ||
| <55 | 138 (15.4) | 101 (16.4) |
| 55–64 | 225 (25.1) | 159 (25.8) |
| 65–74 | 367 (40.9) | 238 (38.6) |
| 75+ | 167 (18.6) | 118 (19.2) |
| Race | ||
| White | 854 (95.2) | 586 (95.1) |
| Native American/White | 31 (3.5) | 27 (4.4) |
| Other races | 11 (1.2) | 3 (0.5) |
| Unknown | 1 (0.1) | 0 (0.0) |
| Hispanic | ||
| Yes | 15 (1.7) | 11 (1.8) |
| No | 881 (98.2) | 605 (98.2) |
| Unknown | 1 (0.1) | 0 (0.0) |
| State of residence | ||
| Maine | 495 (55.2) | 305 (49.5) |
| Vermont | 134 (14.9) | 92 (14.9) |
| New Hampshire | 268 (29.9) | 219 (35.6) |
| Usual BMI (kg/m2) | ||
| <18.5 | 8 (0.9) | 9 (1.5) |
| 18.5–<25.0 | 375 (41.8) | 254 (41.2) |
| 25.0–<30.0 | 387 (43.1) | 239 (38.8) |
| ≥30.0 | 115 (12.8) | 106 (17.2) |
| Unknown | 12 (1.3) | 8 (1.3) |
| Smoking status | ||
| Never-smoker | 296 (33.0) | 93 (15.1) |
| Ever-smoker | 600 (66.9) | 522 (84.7) |
| Unknown | 1 (0.1) | 1 (0.2) |
| Usual smoking intensity | ||
| Never-smoker | 296 (33.0) | 93 (15.1) |
| 1–19 cigarettes/day | 177 (19.7) | 111 (18.0) |
| 20–39 cigarettes/day | 286 (31.9) | 287 (46.6) |
| 40+ cigarettes/day | 108 (12.0) | 109 (17.7) |
| Unknown | 30 (3.3) | 16 (2.6) |
| Smoking duration | ||
| Never-smoker | 296 (33.0) | 93 (15.1) |
| <20 years | 199 (22.2) | 93 (15.1) |
| 20–<30 years | 137 (15.3) | 93 (15.1) |
| 30–<40 years | 94 (10.5) | 125 (20.3) |
| 40+ years | 139 (15.5) | 196 (31.8) |
| Unknown | 32 (3.6) | 16 (2.6) |
Urine pH consistently ≤6.0 was associated with an increased risk of bladder cancer (OR = 1.27; 95% CI, 1.02–1.57; Table 2). The association was apparent among ever-smokers (OR = 1.33; 95% CI, 1.04–1.71), but not among never-smokers (OR = 0.92; 95% CI, 0.55–1.52; Pinteraction = 0.27). We found a similar pattern with spot urine pH analyzed as a continuous variable; there was an exposure–response relationship between greater urine acidity and increased risk of bladder cancer (Ptrend = 5×10−3), which was apparent among ever-smokers (Ptrend = 1.2×10−3) but not among never-smokers (P = 0.80; Table 2).
Table 2.
Urine pH and risk of bladder cancer in in the New England Bladder Cancer Study.
| Cases | Controls | I) Consistently acidic urine over 4 days |
II) Spot urine, continuous |
||
|---|---|---|---|---|---|
| Urine pH | OR (95% CI) | OR per 1 unit pH decrease (95% CI) | P trend | ||
| All Subjects | |||||
| 378 | 600 | >6.0a | 1 (Ref) | ||
| 238 | 297 | ≤6.0b | 1.27 (1.02–1.57) | 1.24 (1.07–1.44) | 5.1×10−3 |
| Never-smokers | |||||
| 63 | 198 | >6.0 | 1 (Ref) | ||
| 30 | 98 | ≤6.0 | 0.94 (0.56–1.57) | 1.04 (0.74–1.47) | 0.80 |
| Ever-smokers | |||||
| 315 | 401 | >6.0 | 1 (Ref) | ||
| 207 | 199 | ≤6.0 | 1.33 (1.04–1.71) | 1.33 (1.12–1.59) | 1.2×10−3 |
>6.0: at least one of eight urine pH values >6.0.
≤6.0: all eight urine pH values ≤6.0.
ORs and 95% CI were adjusted for age (<55, 55–64, 65–74, 75+ years), gender (male, female), race (White, Native American/White, other races, unknown), Hispanic status (yes, no, unknown), and state of residence (Maine, Vermont, New Hampshire).
II) 9 cases and 21 controls were excluded for having spot urine pH values <2.
Bladder cancer risk estimates for both measures of urine pH showed similar associations among former and current smokers (Supplementary Table S2). Further, among current smokers, adjustment for number of cigarettes smoked in the last 48 hours had a negligible impact on bladder cancer risk for either measure of urine pH [e.g., for the spot urine, OR = 1.45 (95% CI, 1.04–2.00); Ptrend = 0.03 unadjusted vs. 1.43 (95% CI = 1.03–1.98); Ptrend = 0.03 adjusted). When the continuous spot urine pH was categorized into pH ≤6.0 versus pH >6, we observed the same pattern identified with the urine pH obtained by self-testing; no association among never-smokers, a statistically significant association among ever-smokers, and similar associations among former and current smokers (Supplementary Table S3).
When ever-smokers with consistently acidic urine at pH ≤6.0 were further subdivided into subjects with at least one urine pH measurement >5.0 and subjects whose urine pH was always ≤5.0, we observed a trend in bladder cancer risk with increasing acidity [ORs of 1.32 (95% CI, 1.03–1.70) and 1.53 (95% CI, 0.58–4.04), respectively; Ptrend = 0.02; Supplementary Table S1]. We observed negligible change of this exposure–response relationship among ever-smokers when adjusting for usual BMI, ever smoking, usual smoking intensity, smoking duration, or both usual intensity and duration of smoking (Supplementary Table S2). In addition, among cases, no significant association was observed between consistently acidic urine pH and either cancer stage or grade.
We stratified on urine pH and examined bladder cancer risk by smoking status, usual smoking intensity, and smoking duration; patterns of risk were consistently higher among subjects with urine pH consistently ≤6.0 as compared with subjects without consistently acidic urine pH, although the interaction tests did not achieve significance (Table 3). For example, in terms of usual smoking intensity, risk estimates for never-smokers, 1–19 cigarettes per day, and 20+ cigarettes per day were 1.0 (reference), 2.6 (95% CI, 1.5–4.6), and 4.1 (95% CI, 2.5–6.6) among subjects with consistently acidic urine, compared with 1.0 (reference), 1.8 (95% CI, 1.2–2.7), and 3.1 (95% CI, 2.2–4.3) among subjects without consistently acidic urine; Pinteraction = 0.48).
Table 3.
Risk of bladder cancer by smoking stratified by urine pH in the New England Bladder Cancer Study.
| Urine pH >6.0a OR (95% CI)c Cases/controls | Urine pH ≤6.0b OR (95% CI) Cases/controls | P interaction e | |
|---|---|---|---|
| Smoking status | |||
| Never-smokers | 1.0 (Ref) | 1.0 (Ref) | |
| 63/198 | 30/98 | ||
| Ever-smokers | 2.5 (1.8–3.5) | 3.5 (2.2–5.6) | |
| 315/401 | 207/199 | 0.27 | |
| Smoking intensity | |||
| Never-smokers | 1.0 (Ref) | 1.0 (Ref) | |
| 63/198 | 30/98 | ||
| 1–19 cigarettes/day | 1.8 (1.2–2.7) | 2.6 (1.5–4.6) | |
| 66/120 | 45/57 | ||
| 20+ cigarettes/day | 3.1 (2.2–4.3) | 4.1 (2.5–6.6) | |
| 237/261 | 159/133 | ||
| Ptrend < 0.0001d | Ptrend < 0.0001 | 0.48 | |
| Smoking duration | |||
| Never-smoker | 1.0 (Ref) | 1.0 (Ref) | |
| 63/198 | 30/98 | ||
| <30 years | 1.7 (1.2–2.5) | 2.0 (1.2–3.4) | |
| 118/226 | 68/110 | ||
| 30–<40 years | 4.0 (2.6–6.3) | 5.1 (2.7–9.4) | |
| 75/63 | 50/31 | ||
| 40+ years | 4.2 (2.8–6.4) | 6.5 (3.7–11.5) | |
| 113/93 | 83/46 | ||
| Ptrend < 0.0001 | Ptrend < 0.0001 | 0.63 | |
Urine pH >6.0: at least one of eight urine pH values >6.0.
Urine pH ≤6.0: all eight urine pH values ≤6.0.
ORs and 95% CI were adjusted for age (<55, 55–64, 65–74,75+ years), gender (male, female), race (white only, native/white only, other races, don’t know), Hispanic (yes, no, don’t know), and state of residence (Maine, Vermont, New Hampshire).
P value for linear trend was computed using the Wald statistic, treating the median value of each exposure category among control subjects as continuous.
Interaction between urine pH and each smoking variable was tested by adding a cross product term to the logistic model and conducting a likelihood ratio test.
Urine pH is primarily determined by a combination of body surface area and dietary intake, in which fruits and vegetables generally raise urine pH, while meat, fish, and dairy products generally contribute to the acidification of urine pH (21). Adjustment for usual consumption of these dietary items over the past five years had negligible impact on risk estimates.
Discussion
In a large population-based case–control study conducted in northern New England, we found that consistently acidic urine pH ≤6.0 was associated with an increased risk of bladder cancer. This association was apparent among ever-smokers, but not among never-smokers. Further, among ever-smokers, we observed an exposure–response relationship in which increasing urine acidity was associated with increasing risk of bladder cancer. These findings were further supported by parallel analyses of spot urine samples that were measured in the laboratory. Here, we also found significant exposure–response relationships between increased urinary acidity in spot urine and bladder cancer risk.
Our findings are consistent with results from our hospital-based case–control study conducted in Spain (17), which included 712 cases and 611 controls from 18 hospitals who tested their urine pH at home following discharge and followed the same protocol as the current study. The Spanish study found that acidic urine pH was a risk factor only among ever-smokers (OR = 1.54; 95% CI, 1.19–1.99) versus never-smokers (OR = 1.03; 95% CI, 0.60–1.8; compare to Table 2). Further, in a meta-analysis of the New England and Spanish studies, the test for interaction between acidic urine pH and risk of bladder cancer among ever-smokers versus never-smokers was borderline significant (P = 0.066). In addition, the Spanish study found a very similar association for trend in bladder cancer risk with increasing urine acidity among ever-smokers (ORs = 1.41; 95% CI, 1.09–1.82 and 1.53, 95% CI, 0.90–2.61 for urine pH > 5.0–6.0 and ≤ 5.0, respectively; Ptrend = 0.007; compare to Supplementary Table S2). These findings are supported by in vitro studies showing that lower urine pH is associated with more rapid hydrolysis of N-glucuronide conjugates of aromatic amines from cigarette smoke and other sources into metabolites (5–8) that can form mutagenic DNA adducts in the bladder urothelium (11).
Strengths of our study include the population-based study design, large sample size, and ability to examine trends in urine pH over multiple days. In addition, we have shown that urine dipstick readings were highly correlated with those obtained by a pH meter (Spearman ρ = 0.98; P < 0.001) and that essentially all individuals with urinary pH ≤ 6.0 for every first morning and evening void over a 4-day period maintained this pattern over a 7-day period (22). In addition, we obtained an independent spot urine sample from study subjects and measured pH in the laboratory and found a similar association with bladder cancer risk.
A limitation of the study is the inability to determine whether urine pH changed after cancer diagnosis given the case–control design of the study. We found no association between time since diagnosis and urine pH (P = 0.94) which provides evidence against treatment effects on urine pH. We also conducted several analyses in our previous report on the Spanish Bladder Cancer Study to investigate potential disease and treatment bias. We found that urine pH was not influenced by tumor stage or grade, that experimental microscopic hematuria did not influence urine pH, and that urine pH did not change between the week before bladder cancer surgery and within 10 days to three weeks after surgery (17).
In conclusion, we found evidence for an association between consistently acidic urine pH and increased risk of bladder cancer, which was limited to ever-smokers. These findings in a New England population support similar results from a Spanish population and are consistent with experimental findings showing that acidic urine pH, which is modifiable in part by multiple lifestyle factors, increases the rate of hydrolysis of acid-labile conjugates of aromatic amines that are carcinogenic to the human bladder.
Supplementary Material
Acknowledgments
This study was funded by the Intramural Research Program of the NIH, NCI ZIA CP010125–28 and contract number N02-CP-01037.
We thank Anna McIntosh, Paul Hurwitz, Patricia Clark, and Vanessa Olivo (Westat, Rockville, MD) for their support in study and data management, and Anne Taylor [Information Management Services (IMS), Silver Spring, MD] and Mary McAdams (formerly at IMS) for their programming support. We would like to acknowledge Dr. Michael Jones (Maine Medical Center), Sue Ledoux and Dawn Nicolaides (Maine Cancer Registry), Kimberley Walsh and Christina Robinson (Dartmouth Medical School), Dr. Masatoshi Kida (University of Vermont), William Apao and Carolyn Greene (Vermont Cancer Registry) for their contributions during the fieldwork and data collection phases. We also thank all fieldwork staff, interviewers, and data abstractors for their dedicated work, and our study participants for agreeing to be part of this study.
Footnotes
Authors’ Disclosures
No disclosures were reported.
Supplementary data for this article are available at Cancer Epidemiology, Biomarkers & Prevention Online (http://cebp.aacrjournals.org/).
References
- 1.Case RA, Hosker ME, Mc DD, Pearson JT. Tumors of the urinary bladder in workmen engaged in the manufacture and use of certain dyestuff intermediates in the British chemical industry. I. The role of aniline, benzidine, alpha-naphthylamine, and beta-naphthylamine. Br J Ind Med 1954;11:75–104 [DOI] [PMC free article] [PubMed] [Google Scholar]
- 2.Silverman DT, Koutros S, Figueroa JD, Prokunina-Olsson L, Rothman N. Bladder cancer. In: Thun M, Linet M, Cerhan J, Haiman C, Schottenfeld D, editors. Schottenfeld and Fraumeni cancer epidemiology and prevention. 4th ed. New York: Oxford University Press; 2018. p. 977–96. [Google Scholar]
- 3.Dutton GJ. Bladder cancer. In: Thun M, Linet M, Cerhan J, Haiman C, Schottenfeld D, editors. Glucuronidation of drugs and other compounds. Boca Raton, Florida: CRC Press; 1980. p.13. [Google Scholar]
- 4.Mulder GJ, Coughtrie MWH, Burchell B. Bladder cancer. In: Mulder G, editor. Conjugation reactions in drug metablolism. New York: Taylor & Francis; 1990. p. 51–105. [Google Scholar]
- 5.Babu SR, Lakshmi VM, Hsu FF, Zenser TV, Davis BB. Role of N-glucuronidation in benzidine-induced bladder cancer in dog. Carcinogenesis 1992;13:1235–40. [DOI] [PubMed] [Google Scholar]
- 6.Kadlubar FF, Miller JA, Miller EC. Hepatic microsomal N-glucuronidation and nucleic acid binding of N-hydroxy arylamines in relation to urinary bladder carcinogenesis. Cancer Res 1977;37:805–14. [PubMed] [Google Scholar]
- 7.Babu SR, Lakshmi VM, Hsu FF, Kane RE, Zenser TV, Davis BB. N-acetylbenzidine-N’-glucuronidation by human, dog and rat liver. Carcinogenesis 1993;14:2605–11. [DOI] [PubMed] [Google Scholar]
- 8.Babu SR, Lakshmi VM, Huang GP, Zenser TV, Davis BB. Glucuronide conjugates of 4-aminobiphenyl and its N-hydroxy metabolites. pH stability and synthesis by human and dog liver. Biochem Pharmacol 1996;51:1679–85. [DOI] [PubMed] [Google Scholar]
- 9.Flammang TJ, Yamazoe Y, Benson RW, Roberts DW, Potter DW, Chu DZ, et al. Arachidonic acid-dependent peroxidative activation of carcinogenic arylamines by extrahepatic human tissue microsomes. Cancer Res 1989;49:1977–82. [PubMed] [Google Scholar]
- 10.Wise RW, Zenser TV, Kadlubar FF, Davis BB. Metabolic activation of carcinogenic aromatic amines by dog bladder and kidney prostaglandin H synthase. Cancer Res 1984;44:1893–7. [PubMed] [Google Scholar]
- 11.Rothman N, Bhatnagar VK, Hayes RB, Zenser TV, Kashyap SK, Butler MA, et al. The impact of interindividual variation in NAT2 activity on benzidine urinary metabolites and urothelial DNA adducts in exposed workers. Proc Natl Acad Sci USA 1996;93:5084–9. [DOI] [PMC free article] [PubMed] [Google Scholar]
- 12.Beland FA, Beranek DT, Dooley KL, Heflich RH, Kadlubar FF. Arylamine-DNA adducts in vitro and in vivo: their role in bacterial mutagenesis and urinary bladder carcinogenesis. Environ Health Perspect 1983;49:125–34. [DOI] [PMC free article] [PubMed] [Google Scholar]
- 13.Fox TR, Schumann AM, Watanabe PG, Yano BL, Maher VM, McCormick JJ. Mutational analysis of the H-ras oncogene in spontaneous C57BL/6 x C3H/He mouse liver tumors and tumors induced with genotoxic and nongenotoxic hepatocarcinogens. Cancer Res 1990;50:4014–9. [PubMed] [Google Scholar]
- 14.Heflich RH, Morris SM, Beranek DT, McGarrity LJ, Chen JJ, Beland FA. Relationships between the DNA adducts and the mutations and sister-chromatid exchanges produced in Chinese hamster ovary cells by N-hydroxy-2-aminofluorene, N-hydroxy-N’-acetylbenzidine and 1-nitrosopyrene. Mutagenesis 1986;1:201–6. [DOI] [PubMed] [Google Scholar]
- 15.Melchior WB Jr, Marques MM, Beland FA. Mutations induced by aromatic amine DNA adducts in pBR322. Carcinogenesis 1994;15:889–99. [DOI] [PubMed] [Google Scholar]
- 16.Rothman N, Talaska G, Hayes RB, Bhatnagar VK, Bell DA, Lakshmi VM, et al. Acidic urine pH is associated with elevated levels of free urinary benzidine and N-acetylbenzidine and urothelial cell DNA adducts in exposed workers. Cancer Epidemiol Biomarkers Prev 1997;6:1039–42. [PubMed] [Google Scholar]
- 17.Alguacil J, Kogevinas M, Silverman DT, Malats N, Real FX, Garcia-Closas M, et al. Urinary pH, cigarette smoking, and bladder cancer risk. Carcinogenesis 2011;32:843–7. [DOI] [PMC free article] [PubMed] [Google Scholar]
- 18.Baris D, Karagas MR, Verrill C, Johnson A, Andrew AS, Marsit CJ, et al. A case–control study of smoking and bladder cancer risk: emergent patterns over time. J Natl Cancer Inst 2009;101:1553–61. [DOI] [PMC free article] [PubMed] [Google Scholar]
- 19.Garcia-Closas M, Malats N, Silverman D, Dosemeci M, Kogevinas M, Hein DW, et al. NAT2 slow acetylation, GSTM1 null genotype, and risk of bladder cancer: results from the Spanish bladder cancer Study and meta-analyses. Lancet 2005;366:649–59. [DOI] [PMC free article] [PubMed] [Google Scholar]
- 20.Samanic C, Kogevinas M, Dosemeci M, Malats N, Real FX, Garcia-Closas M, et al. Smoking and bladder cancer in Spain: effects of tobacco type, timing, environmental tobacco smoke, and gender. Cancer Epidemiol Biomarkers Prev 2006;15:1348–54. [DOI] [PubMed] [Google Scholar]
- 21.Remer T, Manz F. Potential renal acid load of foods and its influence on urine pH. J Am Diet Assoc 1995;95:791–7. [DOI] [PubMed] [Google Scholar]
- 22.Alguacil J, Pfeiffer RM, Moore LE, Del Fresno MR, Medina-Lopez R, Kogevinas M, et al. Measurement of urine pH for epidemiological studies on bladder cancer. Eur J Epidemiol 2007;22:91–8. [DOI] [PubMed] [Google Scholar]
Associated Data
This section collects any data citations, data availability statements, or supplementary materials included in this article.
Supplementary Materials
Data Availability Statement
Data were generated by the authors but are not publicly available due to subject privacy. Data requests can be made by contacting the corresponding author. Reasonable data requests will be considered by the senior authors.