Abstract
Purpose: Polycyclic aromatic hydrocarbons (PAHs) are byproducts of incomplete combustion of organic materials. Sources include tobacco smoke, charbroiled meat, and air pollution. Indirect evidence suggests that PAHs may be associated with carcinogenesis, but the association with gastric cancer is unclear. Methods: Using a nested case-control study design, we examined prediagnostic urinary concentrations of 1-hydroxypyrene glucuronide (1-OHPG), a PAH metabolite, in 153 gastric cancer cases and 306 matched controls within the Shanghai Women’s Health Study. Conditional logistic regression adjusted for potential risk factors was used to estimate odds ratios (ORs) and 95% confidence intervals (95% CIs). Results: Urinary 1-OHPG concentrations were slightly higher among cases than controls, with medians of 0.29 μmol/mol Cr (interquartile range, 0.16-0.48) and 0.24 μmol/mol Cr (interquartile range, 0.12-0.45), respectively. Increasing concentrations of 1-OHPG appeared to be associated with elevated risk of gastric cancer, but not within the highest category of 1-OHPG (Q4 vs Q1: OR = 1.4; 95% CI = 0.8-2.5). Conclusions: Our findings suggest that higher concentrations of 1-OHPG are related to gastric cancer risk, but no clear dose-response relationship was observed.
Keywords: 1-hydroxypyrene glucuronide, polycyclic aromatic hydrocarbons, gastric cancer, China
Introduction
Polycyclic aromatic hydrocarbons (PAHs) are large aromatic planar compounds that are formed by incomplete combustion of organic material [1,2]. PAHs are ubiquitous, and major sources of exposure include tobacco smoke [3], charbroiled meat [4], ambient air pollution [5], and occupational exposure [6]. Several of the more than 100 identified PAHs, including benzo(a)pyrene (BaP), are considered carcinogenic to animals [7]. In humans, there is also evidence supporting a causal association between PAHs or PAH-containing substances and cancers of the skin, scrotum, lung, and bladder [6,8]. However, the association between PAHs and gastric cancer is less clear.
Gastric cancer is the fourth most common type of incident cancer and the second leading cause of cancer death in the world [9]. There are some suggestions for a role of PAH in gastric carcinogenesis. Animal studies have shown that a diet contaminated with coal or BaP strongly increases the risk of forestomach cancers[7]. Indirect evidence in humans also suggests that gastric cancer may be associated with higher exposure to PAHs. For example, in a meta-analysis of gastric cancer and tobacco smoking, a major source of PAHs, a higher risk of gastric cancer was reported [10]. Exposure to diesel exhaust has also been associated with gastric cancer risk [11]. Based on the few studies that have evaluated PAHs and gastric cancer indirectly, the association remains unclear. However, to our knowledge, the association between a biomarker of PAH exposure and gastric cancer has not yet been examined in a prospective study.
Urinary 1-hydroxypyrene glucuronide (1-OHPG), a metabolite of pyrene, has been established as a biomarker of PAH exposure [12,13]. To test whether urinary 1-OHPG is associated with risk of subsequent gastric cancer, we conducted a nested case-control study in a large prospective cohort study in Shanghai, China.
Materials and methods
Study population
Cases and controls were selected from participants of the Shanghai Women’s Health Study (SWHS), a population-based prospective cohort study of women residing in Shanghai, China. The design of the study has been described elsewhere [14]. Women aged 40-70 years who were permanent residents of Shanghai were invited to participate in the study. A total of 74, 942 women agreed to participate and completed the baseline survey between 1996 and 2000. Data collected included demographics, personal habits, dietary habits, occupational history, family history of cancer, disease and surgery history, reproductive history, and weight history. H. pylori infection was determined using H. pylori enzyme-linked immunosorbent assay kits (Biohit ELISA kit, Finland) to detect serum IgG antibodies. All study participants provided written informed consent prior to interview and the study protocols were approved by the institutional review boards of the National Cancer Institute, Vanderbilt University, and the Shanghai Cancer Institute in accordance with the Declaration of Helsinki.
Of the eligible participants, 65,574 (87%) provided spot urine samples, which was collected into a sterilized 100-mL cup containing 125 mg ascorbic acid. Samples were kept in a portable insulated bag with ice packs (0-4°C) and processed within 6 h for long-term storage at −70°C. Among the participants who provided urine samples, 153 incident gastric cancer cases were diagnosed through December 2005. Incident gastric cancer cases were identified through in-person follow-up interviews and by linking to the Shanghai Cancer Registry and the Shanghai Vital Statistics Unit. Two controls were selected for each case matched by age at sample collection (± 2 years), menopausal status, time of sample collection (morning or afternoon), date of sample collection (± 1 month), and time interval since last meal (± 2 hours). Controls were also free of any cancer at the time of cancer diagnosis for their corresponding case.
Urinary 1-hydroxypyrene glucuronide assay
Urinary concentration of 1-OHPG is a PAH derivative that may be a reasonable reflection of both usual and recent PAH exposure [13]. 1-OHPG was measured using immunoaffinity chromatography and synchronous fluorescence spectroscopy [15]. Assays were performed in batches of 20 that included laboratory QC samples and blinded duplicate samples. The coefficient of variation (CV) for replicate measurements of urinary 1-OHPG concentration across batches using aliquots from a single quality control pool was 10.6%. The Spearman rank correlation coefficient for paired 1-OHPG measurements in 30 blinded duplicate samples was 0.93. The assay limit of detection was 0.1 pmol/mL. For measurements below the limit of detection (9.1% and 10.1% of cases and controls, respectively), a value of 0.05 pmol/mL was assigned.
Statistical analysis
Conditional logistic regression, adjusted for matching and potential risk factors for gastric cancer: age, body mass index (BMI: kg/m2), education level, fruit and vegetable intake, H. pylori status and smoking status (ever/never), was used to estimate adjusted odds ratios (ORs) and 95% confidence intervals (95% CIs) for the association between creatinine-adjusted urinary 1-OHPG concentration (henceforth referred as 1-OHPG) and gastric cancer. Sensitivity analyses using 1-OHPG concentrations without correction for creatinine and with creatinine concentration included as an independent variable in the statistical model were also conducted, but did not have any noticeable effects on the results. The distribution of 1-OHPG among controls was used to determine cut points for quartiles. We also evaluated 1-OHPG as a continuous variable. A one unit change was defined as half the distance between the 25th and 75th percentiles among controls. P-values for trend were calculated by modeling the median of each quartile. Sensitivity analyses included analyses excluding 32 matched sets of controls and cases diagnosed within the first two years of follow-up after sample collection, excluding 22 ever smokers, without adjustment for smoking and H. pylori, and stratified analyses by the median duration of follow-up time. All analyses were conducted using SAS version 9.1 (SAS Institute, Cary, NC).
Results
The characteristics of the 153 gastric cancer cases (11 cardia and 142 non-cardia) and 306 control subjects in this study are provided in Table 1. Cases and controls were similar in age, fruit and vegetable intake, education level, and BMI. Few of the women smoked (4% and 6% among controls and cases, respectively) or drank alcohol (1% and 2% among controls and cases). A large proportion of both cases and controls tested positive for H. pylori IgG antibodies. Urinary 1-OHPG concentration were slightly higher but not statistically different between gastric cancer cases and controls, with medians of 0.29 and 0.24 μmol/mol creatinine, respectively (Wilcoxon p-value = 0.13).
Table 1.
Distribution of selected characteristics among gastric cancer cases and control in the Shanghai Women’s Health Study
| Characteristics | Cases (n = 153) | Controls (n = 306) |
|---|---|---|
| Age in years, mean (SD) | 58.7 (8.7) | 58.7 (8.6) |
| Fresh Vegetable Intake (g/day) | 270.0 (162.2) | 296.5 (186.9) |
| Fresh Fruit intake (g/day) | 223.1 (161.0) | 252.9 (172.5) |
| Education, n (%) | ||
| College | 9 (5.9) | 30 (9.8) |
| High school | 28 (18.3) | 64 (20.9) |
| Middle school | 39 (25.5) | 83 (27.1) |
| Elementary or less | 77 (50.3) | 129 (42.2) |
| BMI (kg/m2), n (%) | ||
| <25 | 84 (54.9) | 182 (59.5) |
| 25- <30 | 60 (39.2) | 101 (33.0) |
| ≥30 | 9 (5.9) | 23 (7.5) |
| Ever smokers, n (%) | 9 (5.9) | 13 (4.3) |
| Ever exposed to passive smoking, n (%) | 75 (64.7) | 204 (74.2) |
| Ever drank alcohol, n (%) | 3 (1.9) | 4 (1.3) |
| H. pylori positive, n (%)a | 136 (96.5) | 260 (92.2) |
Note: Continuous variables are displayed as means (standard deviation) and frequencies are displayed as counts (percentages).
Available on only 423 subjects.
Overall, urinary 1-OHPG concentration was not clearly associated with risk of gastric cancer (Table 2). Increasing concentrations of 1-OHPG appeared to be associated with elevated risk of gastric cancer, but not within the highest category of 1-OHPG. Compared to the lowest quartile of 1-OHPG, those in the third quartile of 1-OHPG were associated with an OR of 1.93 (95% CI: 1.07-3.49) but those in the highest quartile of 1-OHPG were associated with an OR of 1.40 (95% CI: 0.77-2.54; p-trend = 0.30). A continuous association (where values were standardized so that a change of one unit corresponds to a change of 25% of the control distribution) was also suggestive but not statistically significant (OR = 1.06, 95% CI: 0.97-1.16). Additional adjustment for H. pylori status(one of the main risk factors for gastric cancer), which was only available on a subset of the samples (n = 282 subjects), did not change the estimates. Also, effect estimates did not change substantially when adjustment for smoking status was removed (Q4 vs Q1 OR = 1.35, 95% CI: 0.73-2.52), exclusion of ever smokers (n = 22; Q4 vs Q1 OR = 1.25, 95% CI: 0.67-2.34), or after exclusion of cases diagnosed within two years of sample collection (n = 32; Q4 vs Q1 OR = 1.35, 95% CI: 0.67-2.75). We also did not observe a difference in risk when stratified by the median duration of follow-up time (3.75 years; data not shown).
Table 2.
Association between creatinine-adjusted urinary 1-OHPG concentration and risk of gastric cancer
| 1-OHPG (µmol/mol Cr) | Cases (N) | Controls (N) | Unadjusted | Adjusteda | Adjustedb |
|---|---|---|---|---|---|
|
| |||||
| OR (95% CI) | OR (95% CI) | OR (95% CI) | |||
| Q1:< 0.12 | 28 | 76 | 1.00 | 1.00 | 1.00 |
| Q2: ≥ 0.12 to< 0.24 | 32 | 78 | 1.10 (0.61-1.99) | 1.15 (0.63-2.09) | 1.13 (0.59-2.14) |
| Q3: ≥ 0.24 to< 0.45 | 50 | 76 | 1.90 (1.06-3.41) | 1.93 (1.07-3.49) | 1.91 (1.02-3.60) |
| Q4: ≥ 0.45 | 43 | 76 | 1.56 (0.87-2.80) | 1.40 (0.77-2.54) | 1.34 (0.72-2.50) |
| P trend | 0.13 | 0.30 | 0.40 | ||
| Per 1-unit increase in 1-OHPGc | 1.07 (0.98-1.17) | 1.06 (0.97-1.16) | 1.05 (0.96-1.15) | ||
Adjusted for age, education, smoking status (ever/never), fruit intake, vegetable intake, and body mass index (BMI).
Same adjustments as above but additionally adjusted for H. pylori status within 423 subjects (141 cases and 282 controls).
A 1-unit increase was defined as half of the difference between the 25th and 75th percentiles for creatinine-adjusted 1-OHPG measurements among controls.
Discussion
In this nested case-control study within the SWHS cohort, we found that higher concentrations of 1-OHPG may be associated with gastric cancer risk, but no clear dose-response relationship was observed. Although there have been some studies that have suggested a role of PAHs in gastric cancer carcinogenesis, using a well-established biomarker of PAH exposure, we were unable to detect a clear trend with increasing urinary 1-OHPG concentrations.
1-OHPG has been associated with recent consumption of charbroiled food [16] and recent occupational exposure to PAHs [15]. However, Cross et al. recently estimated BAP intake from charbroiled meats through a dietary questionnaire and did not observe an association with gastric cancer in a large prospective study [17]. Friesen et al. also found no evidence that oil-based metal working fluids (PAH component) were associated with risk of stomach cancer in an auto worker cohort [18]. In comparison, our study suggests a possible association with gastric cancer by using a direct biomarker of PAH exposure. In a secondary analysis evaluating the relations between urinary 1-OHPG concentrations and potential determinants of PAH exposure among a combined sample of controls from this study and a related study of colorectal cancer, active and passive smoking, coal as a cooking fuel, eating cooked well done foods, and recent consumption of fried dough (e.g., yóutiáo) were associated with elevated concentrations of 1-OHPG [19]. Only active smoking and fried dough consumption achieved statistical significance in multivariate analyses. Although PAHs are a complex mixture, urinary 1-OHPG concentration appears to be a useful in assessing human PAH exposure.
To the best of our knowledge, this is the first study to evaluate urinary 1-OHPG concentrations and risk of gastric cancer. This study has several strengths which include its prospective design, collection of prediagnostic urine samples from study subjects when they were healthy, long-term follow-up, collection of data on potential confounders, and rigorous methods to ascertain outcomes. There are also several limitations in this study. Our results should be interpreted as preliminary given our relatively small sample size, which also limited our ability to evaluate potential interactions with other gastric cancer risk factors. Urine samples were collected as spot samples and not 24 hour urines; in addition, urine samples were only collected once at baseline and may not reflect long-term exposure or an etiologically relevant time period.
In summary, the results of this study do not support a clear association between 1-OHPG and risk of gastric cancer. As our study was limited by a small sample size, this association should be further explored in a larger study to confirm findings.
Acknowledgements
The authors express their appreciation to the Shanghai residents who participated in the study and thank the research staff of the Shanghai Women’s Health Study for their dedication and contributions to the study. This research was supported in part by National Institutes of Health research grant R37 CA70867 and the Intramural Research Program of the National Institutes of Health, National Cancer Institute.
Disclosure of conflict of interest
No potential conflicts of interest were disclosed.
References
- 1.Baird WM, Hooven LA, Mahadevan B. Carcinogenic polycyclic aromatic hydrocarbon-DNA adducts and mechanism of action. Environ Mol Mutagen. 2005;45:106–114. doi: 10.1002/em.20095. [DOI] [PubMed] [Google Scholar]
- 2.Phillips DH. Fifty years of benzo(a)pyrene. Nature. 1983;303:468–472. doi: 10.1038/303468a0. [DOI] [PubMed] [Google Scholar]
- 3.Hecht SS. Tobacco carcinogens, their biomarkers and tobacco-induced cancer. Nat Rev Cancer. 2003;3:733–744. doi: 10.1038/nrc1190. [DOI] [PubMed] [Google Scholar]
- 4.Kazerouni N, Sinha R, Hsu CH, Greenberg A, Rothman N. Analysis of 200 food items for benzo[a] pyrene and estimation of its intake in an epidemiologic study. Food Chem Toxicol. 2001;39:423–436. doi: 10.1016/s0278-6915(00)00158-7. [DOI] [PubMed] [Google Scholar]
- 5.Chang KF, Fang GC, Chen JC, Wu YS. Atmospheric polycyclic aromatic hydrocarbons (PAHs) in Asia: a review from 1999 to 2004. Environ Pollut. 2006;142:388–396. doi: 10.1016/j.envpol.2005.09.025. [DOI] [PubMed] [Google Scholar]
- 6.Boffetta P, Jourenkova N, Gustavsson P. Cancer risk from occupational and environmental exposure to polycyclic aromatic hydrocarbons. Cancer Causes Control. 1997;8:444–472. doi: 10.1023/a:1018465507029. [DOI] [PubMed] [Google Scholar]
- 7.Culp SJ, Gaylor DW, Sheldon WG, Goldstein LS, Beland FA. A comparison of the tumors induced by coal tar and benzo[a] pyrene in a 2-year bioassay. Carcinogenesis. 1998;19:117–124. doi: 10.1093/carcin/19.1.117. [DOI] [PubMed] [Google Scholar]
- 8.Mastrangelo G, Fadda E, Marzia V. Polycyclic aromatic hydrocarbons and cancer in man. Environ Health Perspect. 1996;104:1166–1170. doi: 10.1289/ehp.961041166. [DOI] [PMC free article] [PubMed] [Google Scholar]
- 9.Kamangar F, Dores GM, Anderson WF. Patterns of cancer incidence, mortality, and prevalence across five continents: defining priorities to reduce cancer disparities in different geographic regions of the world. J. Clin. Oncol. 2006;24:2137–2150. doi: 10.1200/JCO.2005.05.2308. [DOI] [PubMed] [Google Scholar]
- 10.Tredaniel J, Boffetta P, Buiatti E, Saracci R, Hirsch A. Tobacco smoking and gastric cancer: review and meta-analysis. Int J Cancer. 1997;72:565–573. doi: 10.1002/(sici)1097-0215(19970807)72:4<565::aid-ijc3>3.0.co;2-o. [DOI] [PubMed] [Google Scholar]
- 11.Sjodahl K, Jansson C, Bergdahl IA, Adami J, Boffetta P, Lagergren J. Airborne exposures and risk of gastric cancer: a prospective cohort study. Int J Cancer. 2007;120:2013–2018. doi: 10.1002/ijc.22566. [DOI] [PubMed] [Google Scholar]
- 12.Strickland PT, Kang D, Bowman ED, Fitzwilliam A, Downing TE, Rothman N, Groopman JD, Weston A. Identification of 1-hydroxypyrene glucuronide as a major pyrene metabolite in human urine by synchronous fluorescence spectroscopy and gas chromatography-mass spectrometry. Carcinogenesis. 1994;15:483–487. doi: 10.1093/carcin/15.3.483. [DOI] [PubMed] [Google Scholar]
- 13.Strickland P, Kang D, Sithisarankul P. Polycyclic aromatic hydrocarbon metabolites in urine as biomarkers of exposure and effect. Environ Health Perspect. 1996;104(Suppl 5):927–932. doi: 10.1289/ehp.96104s5927. [DOI] [PMC free article] [PubMed] [Google Scholar]
- 14.Zheng W, Chow WH, Yang G, Jin F, Rothman N, Blair A, Li HL, Wen W, Ji BT, Li Q, Shu XO, Gao YT. The Shanghai Women’s Health Study: rationale, study design, and baseline characteristics. Am J Epidemiol. 2005;162:1123–1131. doi: 10.1093/aje/kwi322. [DOI] [PubMed] [Google Scholar]
- 15.Kang D, Rothman N, Cho SH, Lim HS, Kwon HJ, Kim SM, Schwartz B, Strickland PT. Association of exposure to polycyclic aromatic hydrocarbons (estimated from job category) with concentration of 1-hydroxypyrene glucuronide in urine from workers at a steel plant. Occup Environ Med. 1995;52:593–599. doi: 10.1136/oem.52.9.593. [DOI] [PMC free article] [PubMed] [Google Scholar]
- 16.Kang DH, Rothman N, Poirier MC, Greenberg A, Hsu CH, Schwartz BS, Baser ME, Groopman JD, Weston A, Strickland PT. Interindividual differences in the concentration of 1-hydroxypyrene-glucuronide in urine and polycyclic aromatic hydrocarbon-DNA adducts in peripheral white blood cells after charbroiled beef consumption. Carcinogenesis. 1995;16:1079–1085. doi: 10.1093/carcin/16.5.1079. [DOI] [PubMed] [Google Scholar]
- 17.Cross AJ, Freedman ND, Ren J, Ward MH, Hollenbeck AR, Schatzkin A, Sinha R, Abnet CC. Meat consumption and risk of esophageal and gastric cancer in a large prospective study. Am J Gastroenterol. 2011;106:432–442. doi: 10.1038/ajg.2010.415. [DOI] [PMC free article] [PubMed] [Google Scholar]
- 18.Friesen MC, Costello S, Thurston SW, Eisen EA. Distinguishing the common components of oil- and water-based metalworking fluids for assessment of cancer incidence risk in autoworkers. Am J Indl Med. 2011;54:450–60. doi: 10.1002/ajim.20932. [DOI] [PMC free article] [PubMed] [Google Scholar]
- 19.Hofmann JN, Liao LM, Strickland P, Shu XO, Yang G, Ji BT, Li HL, Rothman N, Kamangar F, Gao YT, Zheng W, Chow WH. Polycyclic aromatic hydrocarbons: Determinants of urinary 1-hydroxypyrene glucuronide concentration and risk of colorectal cancer in the Shanghai Women’s Health Study. BMC Cancer. 2013;13:282. doi: 10.1186/1471-2407-13-282. [DOI] [PMC free article] [PubMed] [Google Scholar]