Formation and persistence of benzo(a)pyrene metabolite-DNA adducts

The interaction effects of zinc and polygenic risk score with benzo[a]pyrene exposure on lung cancer risk: A prospective case-cohort study among Chinese populations

The relationship of exposure to benzo[a]pyrene (BaP) with lung cancer risk has been firmly established, but whether this association could be modified by other environmental or genetic factors remains to be explored. To investigate whether and how zinc (Zn) and genetic predisposition modify the association between BaP and lung cancer, we performed a case-cohort study with a 5.4-year median follow-up duration, comprising a representative subcohort of 1399 participants and 359 incident lung cancer cases. The baseline concentrations of benzo[a]pyrene diol epoxide-albumin adduct (BPDE-Alb) and Zn were quantified. We also genotyped the participants and computed the polygenic risk score (PRS) for lung cancer. Our findings indicated that elevated BPDE-Alb and PRS were linked to increased lung cancer risk, with the HR (95%CI) of 1.54 (1.36, 1.74) per SD increment in ln-transformed BPDE-Alb and 1.27 (1.14, 1.41) per SD increment in PRS, but high plasma Zn level was linked to a lower lung cancer risk [HR (95%CI)=0.77 (0.66, 0.91) per SD increment in ln-transformed Zn]. There was evidence of effect modification by Zn on BaP-lung cancer association (P for multiplicative interaction = 0.008). As Zn concentrations increased from the lowest to the highest tertile, the lung cancer risk per SD increment in ln-transformed BPDE-Alb decreased from 2.07 (1.48, 2.89) to 1.33 (0.90, 1.95). Additionally, we observed a significant synergistic interaction of BPDE-Alb and PRS [RERI (95%CI) = 0.85 (0.03, 1.67)], with 42% of the incident lung cancer cases among individuals with high BPDE-Alb and high PRS attributable to their additive effect [AP (95%CI) = 0.42 (0.14, 0.69)]. This study provided the first prospective epidemiological evidence that Zn has protective effect against BaP-induced lung tumorigenesis, whereas high genetic risk can enhance the harmful effect of BaP. These findings may provide novel insight into the environment-environment and environment-gene interaction underlying lung cancer development, which may help to develop prevention and intervention strategies to manage BaP-induced lung cancer.

EGFR Targeted Redox Sensitive Chitosan Nanoparticles of Cabazitaxel: Dual-Targeted Cancer Therapy, Lung Distribution, and Targeting Studies by Photoacoustic and Optical Imaging

In this research, we have modified tocopheryl polyethylene glycol succinate (TPGS) to a redox-sensitive material, denoted as TPGS-SH, and employed the same to develop dual-receptor-targeted nanoparticles of chitosan loaded with cabazitaxel (CZT). The physicochemical properties and morphological characteristics of all nanoparticle formulations were assessed. Dual-receptor targeting redox-sensitive nanoparticles of CZT (F-CTX-CZT-CS-SH-NPs) were developed by a combination of pre- and postconjugation techniques by incorporating synthesized chitosan-folate (F) and TPGS-SH during nanoparticle synthesis and further postconjugated with cetuximab (CTX) for epidermal growth factor receptor (EGFR) targeting. The in vitro release of the drug was seemingly higher in the redox-sensitive buffer media (GSH, 20 mM) compared to that in physiological buffer. However, the extent of cellular uptake of dual-targeted nanoparticles was significantly higher in A549 cells than other control nanoparticles. The IC50 values of F-CTX-CZT-CS-SH-NPs against A549 cells was 0.26 ± 0.12 μg/mL, indicating a 6.3-fold and 60-fold enhancement in cytotoxicity relative to that of dual-receptor targeted, nonredox sensitive nanoparticles and CZT clinical injection, respectively. Furthermore, F-CTX-CZT-CS-SH-NPs demonstrated improved anticancer activity in the benzo(a)pyrene lung cancer model with a higher survival rate. Due to the synergistic combination of enhanced permeability and retention (EPR) effect of small-sized nanoparticles, the innovative and redox sensitive TPGS-SH moiety and the dual folate and EGFR mediated augmented endocytosis have all together significantly enhanced their biodistribution and targeting exclusively to the lung which is evident from their ultrasound/photoacoustic and in vivo imaging system (IVIS) studies.

Association of air pollution with postmenopausal breast cancer risk in UK Biobank

BACKGROUND

We investigated the association of several air pollution measures with postmenopausal breast cancer (BCa) risk.

METHODS

This study included 155,235 postmenopausal women (of which 6146 with BCa) from UK Biobank. Cancer diagnoses were ascertained through the linkage to the UK National Health Service Central Registers. Annual exposure averages were available from 2005, 2006, 2007, and 2010 for NO2, from 2007 and 2010 for PM10, and from 2010 for PM2.5, NOX, PM2.5-10 and PM2.5 absorbance. Information on BCa risk factors was collected at baseline. Cox proportional hazards regression was used to evaluate the associations of year-specific and cumulative average exposures with BCa risk, overall and with 2-year exposure lag, while adjusting for BCa risk factors.

RESULTS

PM10 in 2007 and cumulative average PM10 were positively associated with BCa risk (2007 PM10: Hazard ratio [HR] per 10 µg/m3 = 1.18, 95% CI 1.08, 1.29; cumulative average PM10: HR per 10 µg/m3 = 1.99, 95% CI 1.75, 2.27). Compared to women with low exposure, women with higher 2007 PM10 and cumulative average PM10 had greater BCa risk (4th vs. 1st quartile HR = 1.15, 95% CI 1.07, 1.24, p-trend = 0.001 and HR = 1.35, 95% CI 1.25, 1.44, p-trend < 0.0001, respectively). No significant associations were found for any other exposure measures. In the analysis with 2-year exposure lag, both 2007 PM 10 and cumulative average PM10 were positively associated with BCa risk (4th vs. 1st quartile HR = 1.19, 95% CI 1.10, 1.28 and HR = 1.29, 95% CI 1.19, 1.39, respectively).

CONCLUSION

Our findings suggest a positive association of 2007 PM10 and cumulative average PM10 with postmenopausal BCa risk.

Race Differences in Telomere Length in Benign Prostate Biopsies and Subsequent Risk of Prostate Cancer

BACKGROUND

Telomere shortening is linked to aging and may be associated with increased risk for cancer. Most cancer studies have used telomere length in leukocytes rather than in the target tissue of cancer origin.

METHODS

A case-control study of 524 case-control pairs with a benign prostate biopsy nested within a historical cohort of 10,478 men was conducted to determine whether premalignant prostate telomere length (assessed using a modified qRT-PCR) is associated with prostate cancer risk.

RESULTS

Telomere lengths in benign prostate biopsies of cases versus controls were similar (1.46 ± 0.38 vs. 1.45 ± 0.42; P = 0.49). African American (AA) men had significantly shorter telomeres compared with White men (1.51 ± 0.38 vs. 1.63 ± 0.39; P < 0.0001). In race-stratified analyses, increasing telomere length was more strongly associated with prostate cancer risk in White men, wherein those with telomere length in the highest quartile had 1.9-fold greater adjusted risk of prostate cancer compared with men with prostate telomere lengths in the lowest quartile [OR = 1.90; 95% confidence interval (CI) = 1.08-3.36]. Men in the highest telomere length quartile also had a greater risk of aggressive prostate cancer compared with men with telomere lengths in the lowest quartile (OR = 2.78; 95% CI = 1.25-6.19).

CONCLUSIONS

White men have longer telomeres in benign prostate tissue compared with AA men, and those with the longest telomeres may be at increased risk for prostate cancer, particularly the more aggressive form of the disease.

IMPACT

Race-specific telomere length measures may be an early biomarker of aggressive prostate cancer.

The Chemopreventive Effects of Polyphenols and Coffee, Based upon a DMBA Mouse Model with microRNA and mTOR Gene Expression Biomarkers

Polyphenols are capable of decreasing cancer risk. We examined the chemopreventive effects of a green tea (Camellia sinensis) extract, polyphenol extract (a mixture of blackberry (Rubus fruticosus), blackcurrants (Ribes nigrum), and added resveratrol phytoalexin), Chinese bayberry (Myrica rubra) extract, and a coffee (Coffea arabica) extract on 7,12-dimethylbenz[a]anthracene (DMBA) carcinogen-increased miR-134, miR-132, miR-124-1, miR-9-3, and mTOR gene expressions in the liver, spleen, and kidneys of CBA/Ca mice. The elevation was quenched significantly in the organs, except for miR-132 in the liver of the Chinese bayberry extract-consuming group, and miR-132 in the kidneys of the polyphenol-fed group. In the coffee extract-consuming group, only miR-9-3 and mTOR decreased significantly in the liver; also, miR-134 decreased significantly in the spleen, and, additionally, miR-124-1 decreased significantly in the kidney. Our results are supported by literature data, particularly the DMBA generated ROS-induced inflammatory and proliferative signal transducers, such as TNF, IL1, IL6, and NF-κB; as well as oncogenes, namely RAS and MYC. The examined chemopreventive agents, besides the obvious antioxidant and anti-inflammatory effects, mainly blocked the mentioned DMBA-activated factors and the mitogen-activated protein kinase (MAPK) as well, and, at the same time, induced PTEN as well as SIRT tumor suppressor genes.

Phosphorylation of p53 by Cdk5 contributes to benzo[a]pyrene-induced neuronal apoptosis

Benzo[a]pyrene (B[a]P) is a ubiquitous carcinogenic pollutant in the environment, however, the potential neurotoxic effects of B[a]P has not been elucidated clearly. In the present study, we explored the potential involvement of p53 phosphorylation by Cdk5 in B[a]P-induced neuronal apoptosis at both in vitro and in vivo settings. For in vitro studies, primary cortical neurons isolated from the brains of Sprague Dawley (SD) rat pup were exposed to 0, 10, 20, and 40 μM of B[a]P for 12, 24, or 48 h. For in vivo studies, SD rats were injected intraperitoneally with 0, 1.0, 2.5, and 6.25 mg/kg of B[a]P every other day for 1, 2, or 3 months. Our results demonstrated that exposure to B[a]P caused a dose- and a time-dependent increase in neuronal apoptotic ratio in both in vitro and in vivo studies. There was also a dose- and a time-dependent upregulation of p35, p25, Cdk5, and phosphorylated p53 at Ser15 after B[a]P exposure. In order to explore whether B[a]P-induced increased neuronal apoptosis was through Cdk5/p53 pathway, roscovitine, a specific Cdk5 inhibitor, was applied to pretreat neurons prior to B[a]P exposure. The results showed that pretreatment of neurons with roscovitine partially rescued cells from B[a]P-induced apoptosis, and alleviated B[a]P-induced upregulation of phosphorylated p53 at Ser15. Our results suggest that Cdk5/p53 signaling pathway may be involved in B[a]P-induced neuronal apoptosis, which will provide information to further elucidate the molecular mechanisms of B[a]P-induced neurotoxicity.

A Review of Stable Isotope Labeling and Mass Spectrometry Methods to Distinguish Exogenous from Endogenous DNA Adducts and Improve Dose-Response Assessments

Cancer remains the second most frequent cause of death in human populations worldwide, which has been reflected in the emphasis placed on management of risk from environmental chemicals considered to be potential human carcinogens. The formation of DNA adducts has been considered as one of the key events of cancer, and persistence and/or failure of repair of these adducts may lead to mutation, thus initiating cancer. Some chemical carcinogens can produce DNA adducts, and DNA adducts have been used as biomarkers of exposure. However, DNA adducts of various types are also produced endogenously in the course of normal metabolism. Since both endogenous physiological processes and exogenous exposure to xenobiotics can cause DNA adducts, the differentiation of the sources of DNA adducts can be highly informative for cancer risk assessment. This review summarizes a highly applicable methodology, termed stable isotope labeling and mass spectrometry (SILMS), that is superior to previous methods, as it not only provides absolute quantitation of DNA adducts but also differentiates the exogenous and endogenous origins of DNA adducts. SILMS uses stable isotope-labeled substances for exposure, followed by DNA adduct measurement with highly sensitive mass spectrometry. Herein, the utilities and advantage of SILMS have been demonstrated by the rich data sets generated over the last two decades in improving the risk assessment of chemicals with DNA adducts being induced by both endogenous and exogenous sources, such as formaldehyde, vinyl acetate, vinyl chloride, and ethylene oxide.

Daytime Restricted Feeding Modifies the Temporal Expression of CYP1A1 and Attenuated Damage Induced by Benzo[a]pyrene in Rat Liver When Administered before CYP1A1 Acrophase

The aryl hydrocarbon receptor (AhR) is a ligand-activated transcription factor that heterodimerizes with the AhR nuclear translocator (ARNT) to modulate CYP1A1 expression, a gene involved in the biotransformation of benzo[a]pyrene (BaP). The AhR pathway shows daily variations under the control of the circadian timing system. Daytime restricted feeding (DRF) entrains the expression of genes involved in the processing of nutrients and xenobiotics to food availability. Therefore, we evaluate if temporal AhR, ARNT, and CYP1A1 hepatic expression in rats are due to light/dark cycles or fasting/feeding cycles promoted by DRF. Our results show that AhR oscillates throughout the 24 h period in DRF and ad libitum feeding rats (ALF), showing maximum expression at the same time points. DRF modified the peak of ARNT expression at ZT5; meanwhile, ALF animals showed a peak of maximum expression at ZT17. An increased expression of CYP1A1 was linked to the meal time in both groups of animals. Although a high CYP1A1 expression has been previously associated with BaP genotoxicity, our results show that, compared with the ALF group, DRF attenuated the BaP-CYP1A1 induction potency, the liver DNA-BaP adducts, the liver concentration of unmetabolized BaP, and the blood aspartate aminotransferase and alanine aminotransferase activities when BaP is administered prior to the acrophase of CYP1A1 expression. These results demonstrate that DRF modifies the ARNT and CYP1A1 expression and protects from BaP toxicity.

BaP Metabolism and DNA-adduct Formation in Cultured Human Lymphocytes TreatedIn Vitrowith BaP and (-)-BaP-7,8-dihydrodiol

Nine samples of human lymphocytes from six healthy subjects were treated in vitro for 24 hours with [3H]-benzo[a]pyrene (BaP) and unlabelled (-)-BaP-7,8-dihydrodiol; 1μg/ml and 0.5μg/ml, respectively. The separation by HPLC of BaP-DNA adducts showed a significant formation of syn-BaPDE-dGuo adducts in five out of the nine human lymphocyte samples treated in vitro with [3H]-BaP. BaP-(7,10/8,9) tetrol and BaP-(7/8,9,10) tetrol derived from (+)-anti-BaPDE were the predominant isomers extracted from the culture medium of all the lymphocyte samples treated with (-)-BaP-7,8-dihydrodiol (mean ratio of anti-BaPDE/syn-BaPDE tetrols 5.6 + 1.2), suggesting that the metabolic activation of (-)-BaP-7,8-dihydrodiol occurred by its epoxidation to (+)-anti-BaPDE much more frequently (4–8 times) than by epoxidation to the (-)-syn-BaPDE form. In contrast to the predominant formation of anti-BaPDE tetrols, the analysis by HPLC of DNA adducts in the five subjects examined also revealed the significant formation of syn-BaPDE-DNA adducts (mean adduct ratio of (+)-anti-/(-)-syn-BaPDE-DNA = 2.6 ± 0.7). In six human lymphocyte samples treated in vitro with anti-BaPDE and syn-BaPDE, the anti-BaPDE bound to DNA 2–5 times more efficiently than did the syn-BaPDE. However, after 24 hours, the level of anti-BaPDE-DNA adducts significantly decreased almost to the level of the syn-BaPDE-DNA adducts, suggesting that a stereoselective repair mechanism could have preferentially removed the anti-BaPDE-DNA adducts.

Effects of Gut Microbiome on Carcinogenic DNA Damage

The human intestine is host to a vast microbial community: the gut microbiome (GM). The GM has been considered as a key modulator of human health in the past decade. In particular, several studies have supported that altered GM is associated with cancer, such as colorectal cancer, adenocarcinoma, and pancreatic cancer. The formation of a DNA adduct is one of the key events in carcinogenesis, and whether GM can influence DNA adducts has yet to be examined. This study analyzed 10 DNA adducts (N²-Me-dG, N⁶-Me-dA, N²-Et-dG, OH-Me-dG, OH-Me-dA, N²-EtD-dG, O⁶-Me-dG, 1,N²-ε-dG, 8-oxo-dG, and 5-Cl-dC), attributed to various endogenous processes and physiological stressors, using highly sensitive LC-MS/MS in germ-free (GF) and conventionally raised (CONV-R) mice. Our results showed that significant differences in specific DNA adducts appeared in liver, colon, and small intestine samples between GF and CONV-R mice. The differences in adduct levels may indicate that GM can locally or systemically regulate endogenous processes including neutrophil bactericidal activity (represented by 5-Cl-dC), lipid peroxidation (1,N²-ε-dG), oxidative stress generation (8-oxo-dG), and endogenous aldehyde metabolism (OH-Me-dA). Further studies are warranted to elucidate how the GM influences endogenous process, DNA damage, and the risks of developing cancer.

Phenanthrene alters oxidative stress parameters in tadpoles of Euphlyctis cyanophlyctis (Anura, Dicroglossidae) and induces genotoxicity assessed by micronucleus and comet assay

Phenanthrene (PHE), a tricyclic polycyclic aromatic hydrocarbon (PAH), is ubiquitously found in aquatic environments. It is one of the major components in PAH mixtures. It has been identified as one of the 16 priority PAHs for toxicological evaluations. PHE is reported to induce lethal and sub-lethal toxicity in various aquatic indicator organisms. However, no toxicological data of PHE in anuran amphibians could be found. Amphibian larvae (tadpoles) develop in aquatic habitats. Therefore, exposure to PHE could negatively impact their development and fitness in later periods as they move in to the terrestrial habitat following metamorphosis. In the present study, we have analyzed the effects of PHE in Euphlyctis cyanophlyctis tadpoles. PHE induced concentration-dependent lethal effects in the tadpoles. The estimated LC₅₀ values were 16.52, 15.29, 13.69, and 12.28 mg/L at 24, 48, 72, and 96 h of exposure respectively. These LC₅₀ values are significantly higher than the reported environmental concentration of PHE. However, the strong negative correlation (R² = 0.997, p < 0.001) between the LC₅₀ value and exposure time indicates that longer exposure to lower concentration may cause significant lethal effects. Besides, PHE at environmentally relevant concentrations induced significant sub-lethal toxicities. Exposure to sub-lethal concentrations was found to be genotoxic in erythrocyte micronucleus as well as comet assays. Sub-lethal concentrations of PHE significantly increased superoxide dismutase activity and tissue glutathione level as well as induced lipid peroxidation. The present findings clearly indicate that PHE is a potential threat to the early life stages of amphibians. Further investigations are necessary to ascertain the implications of these early effects during adult life stages.

Synthesis of N2 -Aryl-2'-Deoxyguanosine Modified Phosphoramidites and Oligonucleotides

The N² -position of 2'-deoxyguanosine (N² -position in dG) is well known for forming carcinogenic minor groove DNA adducts, which originate from environmental pollutants, chemicals, and tobacco smoke. The N² -dG DNA adducts have strong implications on biological processes such as DNA replication and repair and may, therefore, result in genomic instability by generating mutations or even cell death. It is crucial to know the role of DNA polymerases when they encounter the N² -dG damaged site in DNA. To get detailed insights on the in vitro DNA damage tolerance or bypass mechanism, there is a need to synthetically access N² -dG damaged DNAs. This article describes a detailed protocol of the synthesis of N² -aryl-dG modified nucleotides using the Buchwald-Hartwig reaction as a main step and incorporation of the modified nucleotides into DNA. In Basic Protocol 1, we focused on the synthesis of five different N² -dG modified phosphoramidites with varying bulkiness (benzyl to pyrenyl). Basic Protocol 2 describes the details of synthesizing N² -dG modified oligonucleotides employing the standard solid phase synthesis protocol. This strategy provides robust synthetic access to various modifications at the N² -position of dG; the modified dGs serve as good substrates to study translesion synthesis and repair pathways. Overall data presented in this article are based on earlier published reports. © 2019 by John Wiley & Sons, Inc.

Air pollution and body burden of persistent organic pollutants at an electronic waste recycling area of China

This paper reviews the concentrations of persistent organic pollutants (POPs) in atmosphere of an electronic waste (e-waste) recycling town, Guiyu, in Southeast China, focusing on polybrominated diphenyl ethers (PBDEs), polychlorinated dibenzo-p-dioxin and dibenzofurans (PCDD/Fs), polychlorinated biphenyls (PCBs), and polycyclic aromatic hydrocarbons (PAHs). We assess the evidence for the association between air pollution and human body burden, to provide an indication of the severity of respiratory exposure. Compared with standards and available existing data for other areas, it clearly shows that four typical POPs, derived from recycling processes, lead to serious atmospheric pollution and heavy body burden. From published data, the estimated respiratory exposure doses of Guiyu adults and children, varied between 2.48-10.37 and 3.25-13.6 ng kg^-1 body weight (bw) day^-1 for PBDEs, 2.31-7.6 and 4.09-13.58 pg World Health Organization-Toxic Equivalent Quantity (WHO-TEQ) kg^-1 bw day^-1 for PCDD/Fs, 5.57 and 20.52 ng kg^-1 bw day^-1 for PCBs, and 8.59-50.01 and 31.64-184.14 ng kg^-1 bw day^-1 for PAHs, respectively. These results show that air pollution is more harmful to children. Furthermore, except for PBDEs, the hazard quotient (HQ) of the other three pollutants was rated more than 1 by respiratory exposure only, and all of them are at risk of carcinogenesis. So we speculate these pollutants enter the body mainly through air inhalation, making respiratory exposure may be more important than dietary exposure in the Guiyu e-waste recycling area. Effective management policies and remediation techniques are urgently needed to prevent the deterioration of ambient air quality in the e-waste recycling area.

Significant interactions between maternal PAH exposure and single nucleotide polymorphisms in candidate genes on B[ a ]P-DNA adducts in a cohort of non-smoking Polish mothers and newborns

Polycyclic aromatic hydrocarbons (PAH) are a class of chemicals common in the environment. Certain PAH are carcinogenic, although the degree to which genetic variation influences susceptibility to carcinogenic PAH remains unclear. Also unknown is the influence of genetic variation on the procarcinogenic effect of in utero exposures to PAH. Benzo[ a ]pyrene (B[ a ]P) is a well-studied PAH that is classified as a known human carcinogen. Within our Polish cohort, we explored interactions between maternal exposure to airborne PAH during pregnancy and maternal and newborn single nucleotide polymorphisms (SNPs) in plausible B[ a ]P metabolism genes on B[ a ]P-DNA adducts in paired cord blood samples. The study subjects included non-smoking women ( n = 368) with available data on maternal PAH exposure, paired cord adducts, and genetic data who resided in Krakow, Poland. We selected eight common variants in maternal and newborn candidate genes related to B[ a ]P metabolism, detoxification, and repair for our analyses: CYP1A1 , CYP1A2 , CYP1B1 , GSTM1 , GSTT2 , NQO1 , and XRCC1 . We observed significant interactions between maternal PAH exposure and SNPs on cord B[ a ]P-DNA adducts in the following genes: maternal CYP1A1 and GSTT2 , and newborn CYP1A1 and CYP1B1 . These novel findings highlight differences in maternal and newborn genetic contributions to B[ a ]P-DNA adduct formation and have the potential to identify at-risk subpopulations who are susceptible to the carcinogenic potential of B[ a ]P.

Association between air pollution and mammographic breast density in the Breast Cancer Surveilance Consortium

Background

Mammographic breast density is a well-established strong risk factor for breast cancer. The environmental contributors to geographic variation in breast density in urban and rural areas are poorly understood. We examined the association between breast density and exposure to ambient air pollutants (particulate matter <2.5 μm in diameter (PM_2.5) and ozone (O₃)) in a large population-based screening registry.

Methods

Participants included women undergoing mammography screening at imaging facilities within the Breast Cancer Surveillance Consortium (2001–2009). We included women aged ≥40 years with known residential zip codes before the index mammogram (n = 279,967). Breast density was assessed using the American College of Radiology’s Breast Imaging-Reporting and Data System (BI-RADS) four-category breast density classification. PM_2.5 and O₃ estimates for grids across the USA (2001–2008) were obtained from the US Environmental Protection Agency Hierarchical Bayesian Model (HBM). For the majority of women (94%), these estimates were available for the year preceding the mammogram date. Association between exposure to air pollutants and density was estimated using polytomous logistic regression, adjusting for potential confounders.

Results

Women with extremely dense breasts had higher mean PM_2.5 and lower O₃ exposures than women with fatty breasts (8.97 vs. 8.66 ug/m³ and 33.70 vs. 35.82 parts per billion (ppb), respectively). In regression analysis, women with heterogeneously dense vs. scattered fibroglandular breasts were more likely to have higher exposure to PM_2.5 (fourth vs. first quartile odds ratio (OR) = 1.19, 95% confidence interval (CI) 1.16 − 1.23). Women with extremely dense vs. scattered fibroglandular breasts were less likely to have higher levels of ozone exposure (fourth vs. first quartile OR = 0.80, 95% CI 0.73–0.87).

Conclusion

Exposure to PM_2.5 and O₃ may in part explain geographical variation in mammographic density. Further studies are warranted to determine the causal nature of these associations.

Cancer risk to First Nations' people from exposure to polycyclic aromatic hydrocarbons near in-situ bitumen extraction in Cold Lake, Alberta

BACKGROUND

The Alberta oil sands are an important economic resource in Canada, but there is growing concern over the environmental and health effects as a result of contaminant releases and exposures. Recent studies have shown a temporal and spatial trend of increased polycyclic aromatic hydrocarbon (PAH) concentrations in sediments and snowpack near the Athabasca oil sands operations (i.e., open pit mines), but thus far similar studies have not been done for the Cold Lake region where steam assisted gravity drainage (in situ) extraction is performed.

METHODS

Many PAHs are known mutagenic carcinogens, and this study measured soil and atmospheric concentrations of PAHs in the Cold Lake region to assess the excess lifetime cancer risk posed to the First Nations' inhabitants of the region. Using both deterministic and probabilistic risk assessment methods, excess lifetime cancer risks were calculated for exposures from inhalation or inadvertent soil ingestion.

RESULTS

The mean excess cancer risk for First Nations' people through ingestion who engage in traditional wilderness activities in the Cold Lake region was 0.02 new cases per 100,000 with an upper 95% risk level of 0.07 cases per 100,000. Exposure to PAHs via inhalation revealed a maximum excess lifetime cancer risk of less than 0.1 cases per 100,000.

CONCLUSIONS

Excess lifetime risk values below 1 case per 100,000 is generally considered negligible, thus our analyses did not demonstrate any significant increases in cancer risks associated with PAH exposures for First Nations people inhabiting the Cold Lake region.

Significant interactions between maternal PAH exposure and haplotypes in candidate genes on B[a]P-DNA adducts in a NYC cohort of non-smoking African-American and Dominican mothers and newborns

Polycyclic aromatic hydrocarbons (PAH) are a class of chemicals common in the environment. Certain PAH are carcinogenic, although the degree to which genetic variation influences susceptibility to carcinogenic PAH remains unclear. Also unknown is the influence of genetic variation on the procarcinogenic effect of in utero exposures to PAH. Benzo[a]pyrene (B[a]P) is a well-studied PAH that is classified as a probable human carcinogen. Within our New York City-based cohort, we explored interactions between maternal exposure to airborne PAH during pregnancy and maternal and newborn haplotypes (and in one case, a single-nucleotide polymorphism) in key B[a]P metabolism genes on B[a]P-DNA adducts in paired cord blood samples. The study subjects included non-smoking African-American (n = 132) and Dominican (n = 235) women with available data on maternal PAH exposure, paired cord adducts and genetic data who resided in the Washington Heights, Central Harlem and South Bronx neighborhoods of New York City. We selected seven maternal and newborn genes related to B[a]P metabolism, detoxification and repair for our analyses: CYP1A1, CYP1A2, CYP1B1, GSTM3, GSTT2, NQO1 and XRCC1. We found significant interactions between maternal PAH exposure and haplotype on cord B[a]P-DNA adducts in the following genes: maternal CYP1B1, XRCC1 and GSTM3, and newborn CYP1A2 and XRCC1 in African-Americans; and maternal XRCC1 and newborn NQO1 in Dominicans. These novel findings highlight differences in maternal and newborn genetic contributions to B[a]P-DNA adduct formation, as well as ethnic differences in gene-environment interactions, and have the potential to identify at-risk subpopulations who are susceptible to the carcinogenic potential of B[a]P.

Polycyclic aromatic hydrocarbons-induced ROS accumulation enhances mutagenic potential of T-antigen from human polyomavirus JC

Polycyclic aromatic hydrocarbons (PAHs) are the products of incomplete combustion of organic materials, which are present in cigarette smoke, deep-fried food, and in natural crude oil. Since PAH-metabolites form DNA adducts and cause oxidative DNA damage, we asked if these environmental carcinogens could affect transforming potential of the human Polyomavirus JC oncoprotein, T-antigen (JCV T-antigen). We extracted DMSO soluble PAHs from Deepwater Horizon oil spill in the Gulf of Mexico (oil-PAHs), and detected several carcinogenic PAHs. The oil-PAHs were tested in exponentially growing cultures of normal mouse fibroblasts (R508), and in R508 stably expressing JCV T-antigen (R508/T). The oil-PAHs were cytotoxic only at relatively high doses (1:50-1:100 dilution), and at 1:500 dilution the growth and cell survival rates were practically unaffected. This non-toxic dose triggered however, a significant accumulation of reactive oxygen species (ROS), caused oxidative DNA damage and the formation of DNA double strand breaks (DSBs). Although oil-PAHs induced similar levels of DNA damage in R508 and R508/T cells, only T-antigen expressing cells demonstrated inhibition of high fidelity DNA repair by homologous recombination (HRR). In contrast, low-fidelity repair by non-homologous end joining (NHEJ) was unaffected. This potential mutagenic shift between DNA repair mechanisms was accompanied by a significant increase in clonal growth of R508/T cells chronically exposed to low doses of the oil-PAHs. Our results indicate for the first time carcinogenic synergy in which oil-PAHs trigger oxidative DNA damage and JCV T-antigen compromises DNA repair fidelity.

Simultaneous measurement of benzo[a]pyrene-induced Pig-a and lacZ mutations, micronuclei and DNA adducts in Muta™ Mouse

In this study we compared the response of the Pig-a gene mutation assay to that of the lacZ transgenic rodent mutation assay, and demonstrated that multiple endpoints can be measured in a 28-day repeat dose study. Muta™Mouse were dosed daily for 28 days with benzo[a]pyrene (BaP; 0, 25, 50 and 75 mg/kg body weight/day) by oral gavage. Micronucleus (MN) frequency was determined in reticulocytes (RETs) 48 hr following the last dose. 72 h following the last dose, mice were euthanized, and tissues (glandular stomach, small intestine, bone marrow and liver) were collected for lacZ mutation and DNA adduct analysis, and blood was evaluated for Pig-a mutants. BaP-derived DNA adducts were detected in all tissues examined and significant dose-dependent increases in mutant Pig-a phenotypes (i.e., RET(CD24-) and RBC (CD24-)) and lacZ mutants were observed. We estimate that mutagenic efficiency (i.e., rate of conversion of adducts into mutations) was much lower for Pig-a compared to lacZ, and speculate that this difference is likely explained by differences in repair capacity between the gene targets, and differences in the cell populations sampled for Pig-a versus lacZ. The BaP doubling doses for both gene targets, however, were comparable, suggesting that similar mechanisms are involved in the accumulation of gene mutations. Significant dose-related increases in % MN were also observed; however, the doubling dose was considerably higher for this endpoint. The similarity in dose response kinetics of Pig-a and lacZ provides further evidence for the mutational origin of glycosylphosphatidylinositol (GPI)-anchor deficiencies detected in the Pig-a assay.

Phase-II conjugation ability for PAH metabolism in amphibians: characteristics and inter-species differences

The present study examines amphibian metabolic activity - particularly conjugation - by analysis of pyrene (a four ring, polycyclic aromatic hydrocarbon) metabolites using high-performance liquid chromatography (HPLC) with fluorescence detector (FD), a mass spectrometry detector (MS) system and kinetic analysis of conjugation enzymes. Six amphibian species were exposed to pyrene (dissolved in water): African claw frog (Xenopus laevis); Tago's brown frog (Rana tagoi); Montane brown frog (Rana ornativentris); Wrinkled frog (Rana rugosa); Japanese newt (Cynops pyrrhogaster); and Clouded salamander (Hynobius nebulosus); plus one fish species, medaka (Oryzias latipes); and a fresh water snail (Clithon retropictus), and the resultant metabolites were collected. Identification of pyrene metabolites by HPLC and ion-trap MS system indicated that medaka mainly excreted pyrene-1-glucuronide (PYOG), while pyrene-1-sulfate (PYOS) was the main metabolite in all amphibian species. Pyrene metabolites in amphibians were different from those in invertebrate fresh water snails. Inter-species differences were also observed in pyrene metabolism among amphibians. Metabolite analysis showed that frogs relied more strongly on sulfate conjugation than did Japanese newts and clouded salamanders. Furthermore, urodelan amphibians, newts and salamanders, excreted glucose conjugates of pyrene that were not detected in the anuran amphibians. Kinetic analysis of conjugation by hepatic microsomes and cytosols indicated that differences in excreted metabolites reflected differences in enzymatic activities. Furthermore, pyrenediol (PYDOH) glucoside sulfate was detected in the Japanese newt sample. This novel metabolite has not been reported previously to this report, in which we have identified unique characteristics of amphibians in phase II pyrene metabolism.

Polycyclic aromatic hydrocarbons-aromatic DNA adducts in cord blood and behavior scores in New York city children

BACKGROUND

Airborne polycyclic aromatic hydrocarbons (PAH) are widespread urban pollutants that can bind to DNA to form PAH-DNA adducts. Prenatal PAH exposure measured by personal monitoring has been linked to cognitive deficits in childhood in a prospective study conducted by the Columbia Center for Children's Environmental Health.

OBJECTIVES

We measured PAH-DNA and other bulky aromatic adducts in umbilical cord white blood cells using the 32P-postlabeling assay to determine the association between this molecular dosimeter and behavioral/attention problems in childhood.

METHODS

Children born to nonsmoking African-American and Dominican women residing in New York City (NYC) were followed from in utero to 7-8 years of age. At two time points before 8 years of age (mean ages, 4.8 years and 7 years), child behavior was assessed using the Child Behavior Checklist (CBCL). To estimate and test the association between adducts and behavioral outcomes, both CBCL continuous raw scores and dichotomized T-scores were analyzed.

RESULTS

Higher cord adducts were associated with higher symptom scores of Anxious/Depressed at 4.8 years and Attention Problems at 4.8 and 7 years, and with Diagnostic and Statistical Manual of Mental Disorders, 4th edition-oriented Anxiety Problems at 4.8 years.

CONCLUSIONS

These results suggest that PAH exposure, measured by DNA adducts, may adversely affect child behavior, potentially affecting school performance.

Biotransformation of benzo[a]pyrene in Ahr knockout mice is dependent on time and route of exposure

Benzo[a]pyrene (BP) is an ubiquitous environmental pollutant with potent mutagenic and carcinogenic properties. The Ah receptor (Ahr) is important in the metabolic activation of BP and is therefore central to BP-induced carcinogenesis. Although Ahr(-/-) mice are refractory to BP-induced carcinogenesis, higher levels of BP-DNA and -protein adducts were formed in them than in wild-type mice. These results indicated the presence of an Ahr-independent and/or a slower biotransformation of BP in Ahr knockout mice. To address this issue further, we have now performed a time-course experiment, with mice receiving a single oral dose of BP (100 mg/kg). Wild-type mice have an effective clearance of BP metabolites, mainly through 3-hydroxybenzo[a]pyrene and 9-hydroxybenzo[a]pyrene in the feces with reduced levels of DNA and protein adducts in the examined tissues. On the other hand, the Ahr(-/-) mice appear to have a lower metabolic clearance of BP resulting in increased levels of DNA and protein adducts and of unmetabolized BP. In addition, we have performed an administration route experiment and found that skin-exposed Ahr(-/-) mice showed lower levels of protein adducts along with markedly reduced P450 1B1 expression, but only in the exposed area, as compared with the wild-type mice. In addition, the systemic uptake of BP is increased in the Ahr(-/-) mice as compared with the wild-type mice. Hence, the lack of a functional Ah receptor results in an Ahr-independent biotransformation of BP with a slower clearance of BP and higher levels of DNA and protein adducts, but the distribution and levels of BP and BP-protein adducts are clearly dependent on the route of exposure.

DNA adduct kinetics in reproductive tissues of DNA repair proficient and deficient male mice after oral exposure to benzo(a)pyrene

Benzo(a)pyrene (B[a]P) can induce somatic mutations, whereas its potential to induce germ cell mutations is unclear. There is circumstantial evidence that paternal exposure to B[a]P can result in germ cell mutations. Since DNA adducts are thought to be a prerequisite for B[a]P induced mutations, we studied DNA adduct kinetics by (32)P-postlabeling in sperm, testes and lung tissues of male mice after a single exposure to B[a]P (13 mg/kg bw, by gavage). To investigate DNA adduct formation at different stages of spermatogenesis, mice were sacrificed at Day 1, 4, 7, 10, 14, 21, 32, and 42 after exposure. In addition, DNA repair deficient (Xpc(-/-)) mice were used to study the contribution of nucleotide excision repair in DNA damage removal. DNA adducts were detectable with highest levels in lung followed by sperm and testis. Maximum adduct levels in the lung and testis were observed at Day 1 after exposure, while adduct levels in sperm reached maximum levels at approximately 1 week after exposure. Lung tissue and testis of Xpc(-/-) mice contained significantly higher DNA adduct levels compared to wild type (Wt) mice over the entire 42 day observation period (P < 0.05). Differences in adduct half-life between Xpc(-/-) and Wt mice were only observed in testis. In sperm, DNA adduct levels were significantly higher in Xpc(-/-) mice than in Wt mice only at Day 42 after exposure (P = 0.01). These results indicate that spermatogonia and testes are susceptible for the induction of DNA damage and rely on nucleotide excision repair for maintaining their genetic integrity.

Assessment of interactions between PAH exposure and genetic polymorphisms on PAH-DNA adducts in African American, Dominican, and Caucasian mothers and newborns

Polycyclic aromatic hydrocarbons (PAH) are widespread pollutants commonly found in air, food, and drinking water. Benzo[a]pyrene is a well-studied representative PAH found in air from fossil fuel combustion and a transplacental carcinogen experimentally. PAHs bind covalently to DNA to form DNA adducts, an indicator of DNA damage, and an informative biomarker of potential cancer risk. Associations between PAH-DNA adduct levels and both cancer risk and developmental deficits have been seen in previous experimental and epidemiologic studies. Several genes have been shown to play an important role in the metabolic activation or detoxification of PAHs, including the cytochrome P450 genes CYP1A1 and CYP1B1 and the glutathione S-transferase (GST) genes GSTM1, and GSTT2. Genetic variation in these genes could influence susceptibility to adverse effects of PAHs in polluted air. Here, we have explored interactions between prenatal PAH exposure and 17 polymorphisms in these genes (rs2198843, rs1456432, rs4646903, rs4646421, rs2606345, rs7495708, rs2472299, rs162549, rs1056837, rs1056836, rs162560, rs10012, rs2617266, rs2719, rs1622002, rs140194, and gene deletion GSTM1-02) and haplotypes on PAH-DNA adducts in cord blood of 547 newborns and in maternal blood of 806 mothers from three different self-described ethnic groups: African Americans, Dominicans, and Caucasians. PAHs were measured by personal air monitoring of mothers during pregnancy. Significant interactions (p < 0.05) were observed between certain genetic polymorphisms and CYP1A1 haplotype and PAHs in mothers and their newborns in the three ethnic groups. However, with our limited sample size, the current findings are suggestive only, warranting further study.

Effects of environmental air pollution on endogenous oxidative DNA damage in humans

Epidemiological studies conducted in metropolitan areas have demonstrated that exposure to environmental air pollution is associated with increases in mortality. Carcinogenic polycyclic aromatic hydrocarbons (c-PAHs) are the major source of genotoxic activities of organic mixtures associated with respirable particulate matter, which is a constituent of environmental air pollution. In this study,we wanted to evaluate the relationship between exposure to these genotoxic compounds present in the air and endogenous oxidative DNA damage in three different human populations exposed to varying levels of environmental air pollution. As measures of oxidative DNA damage we have determined 8-oxo-7,8-dihydro-2'-deoxyguanosine (8-oxodG) by liquid chromatography-tandem mass spectrometry (LC-MS/MS) and cyclic pyrimidopurinone N-1,N(2) malondialdehyde-2'-deoxyguanosine (M(1)dG) by the immunoslot blot assay from lymphocyte DNA of participating individuals. The level of endogenous oxidative DNA damage was significantly increased in individuals exposed to environmental air pollution compared to unexposed individuals from Kosice (8-oxodG adducts) and Sofia (M(1)dG adducts). However, there was no significant difference in the level of endogenous oxidative DNA and exposure to environmental air pollution in individuals from Prague (8-oxodG and M(1)dG adducts) and Kosice (M(1)dG adducts). The average level of M(1)dG adducts was significantly lower in unexposed and exposed individuals from Kosice compared to those from Prague and Sofia. The average level of 8-oxodG adducts was significantly higher in unexposed and exposed individuals from Kosice compared to those from Prague. A significant increasing trend according to the interaction of c-PAHs exposure and smoking status was observed in levels of 8-oxodG adducts in individuals from Kosice. However, no other relationship was observed for M(1)dG and 8-oxodG adduct levels with regard to the smoking status and c-PAH exposure status of the individuals. The conclusion that can be made from this study is that environmental air pollution may alter the endogenous oxidative DNA damage levels in humans but the effect appears to be related to the country where the individuals reside. Genetic polymorphisms of the genes involved in metabolism and detoxification and also differences in the DNA repair capacity and antioxidant status of the individuals could be possible explanations for the variation observed in the level of endogenous oxidative DNA damage for the different populations.

Quantitative analysis of benzo[a]pyrene biotransformation and adduct formation in Ahr knockout mice

Benzo[a]pyrene (BP) is an ubiquitous environmental pollutant with potent mutagenic and carcinogenic properties. The Ah receptor (Ahr) is involved in the metabolic activation of BP and is therefore important in the induction of chemical carcinogenesis. In this study, the relationship between Ahr genotype and biotransformation of BP in internal organs was investigated in Ahr (+/+), Ahr (+/-) and Ahr (-/-) mice. The mice were treated with BP (100mg/kg) by gavage. Gene expression was measured after 24h by real-time RT-PCR and showed induction of Cyp1a1 in liver and lung, and Cyp1b1 in lung in both Ahr (+/+) and Ahr (+/-). No induction of the Cyp genes was observed in the Ahr (-/-). There was a significant basal expression of Cyp1b1 in the liver of all genotypes, and this expression was independent of the BP exposure. Analyzed by HPLC-fluorescence, there were increased levels of protein and DNA adducts, metabolites, conjugates and unmetabolized BP in the internal organs of Ahr (-/-) as compared to Ahr (+/+) and Ahr (+/-) mice. This may be partly explained by a delayed bioactivation of BP in the Ahr deficient mice. The BP metabolism observed in the Ahr (-/-) mice is also evidence of an Ahr independent biotransformation of BP.

Epimerization and stability of two new cis-benzo[a]pyrene tetrols by the use of liquid chromatography-fluorescence and mass spectrometry

Quantitative determination of the hydrolysis products from proteins and DNA gives valuable information regarding the reactive metabolite that forms the protein and DNA adduct. Quantification of protein-benzo[a]pyrene (BP) adducts represents a more sensitive method than quantification of BP-DNA adducts. The aim of the present study was to identify two hydrolysis products from BP-derived protein adducts found in vitro and in vivo in a previous study. Male Wistar rats were injected i.p. with BP, and serum albumin was isolated and subjected to acid hydrolysis at 70 degrees C for 3 h. The hydrolysate was subjected to LC separation, and fractions of the two unknown compounds were collected. The molecular masses of the two unknown compounds were in accordance with being tetrols as judged by LC electrospray mass spectrometry. The fragmentation patterns were characteristic of tetrols with formation of the molecular ion and the loss of water molecules. In addition, the compounds were subjected to acid hydrolysis at 70 degrees C with 0.1 M HCl for 3 h. We observed that two of the known tetrols epimerized to the two unknown tetrols and vice versa. This is probably a characteristic epimerization involving not only position C(10)-OH but also another site like position C(7)-OH. The in vivo findings of the two unknown adducts are probably the result of the formation of BPDE III in the metabolism of BP. These two tetrols must then have the C(7)-OH and C(8)-OH groups in a cis position.

Dose-dependent benzo(a)pyrene [B(a)P]-DNA adduct levels and persistence in F-344 rats following subchronic dietary exposure to B(a)P

In order to investigate the relationship between BaP-DNA adduct formation and long-term exposure to benzo(a)pyrene (BaP), DNA adduct levels in liver and lung tissues of male and female F-344 rats subchronically exposed to BaP were determined. Doses of 0, 5, 50, and 100mg/kg BaP, representing control, low, intermediate, and high doses, respectively, were administered in the animal diet over a 90-day period. After dosing, animals were sacrificed, liver and lung tissues were removed, DNA was isolated and analyzed for BaP-induced DNA adducts by the (32)P-postlabeling method using a four-directional thin-layer chromatography system. At low and intermediate BaP doses, DNA adduct levels in the tissues were significantly correlated with exposure. However, at high BaP doses, the dose-DNA adduct relationship became non-linear. Similarly, the relative DNA adducts persistence at intermediate and high doses were significantly higher than that measured at low dose. The low and intermediate dose linearity and high dose non-linearity may be due to saturation of metabolic activation and detoxification enzymes, and DNA repair processes.

DNA damage from polycyclic aromatic hydrocarbons measured by benzo[a]pyrene-DNA adducts in mothers and newborns from Northern Manhattan, the World Trade Center Area, Poland, and China

Polycyclic aromatic hydrocarbons (PAH), of which benzo[a]pyrene is a representative member, are combustion-related environmental pollutants and include known carcinogens. Laboratory animal studies indicate that the dose of PAHs to the fetus is on the order of a 10th that to the mother and that there is heightened susceptibility to PAH-induced carcinogenesis during the fetal and infancy periods. Carcinogen-DNA adducts, a measure of procarcinogenic genetic damage, are considered a biomarker of increased cancer risk. Here we compare the levels of benzo[a]pyrene-DNA adducts as a proxy for PAH-DNA damage measured in maternal blood and newborn cord blood obtained at delivery in four different populations of mothers (total of 867) and newborns (total of 822), representing a 30-fold range of exposure to ambient PAHs. The populations include residents in Northern Manhattan, participants in a study of the effects of the World Trade Center disaster, residents in Krakow, Poland, and residents in Tongliang, China. Mean adduct concentrations in both maternal and cord blood and the proportion of samples with detectable adducts, increased across the populations [Northern Manhattan < World Trade Center (WTC) < Krakow < Tongliang], consistent with the trend in estimated ambient exposure to PAHs (P < 0.001). For mothers, the means in the respective populations were Northern Manhattan (0.21 adducts per 10(8) nucleotides), WTC (0.23 adducts per 10(8) nucleotides), Krakow (0.28 adducts per 10(8) nucleotides), Tongliang (0.31 adducts per 10(8) nucleotides); the corresponding means in the newborns were Northern Manhattan (0.23), WTC (0.24), Krakow (0.29), Tongliang (0.31). The percentage of mothers with detectable levels of adducts in the respective populations were Northern Manhattan (36.8%), WTC (57.5%), Krakow (72.9%), Tongliang (73.4%); the corresponding percentages among the newborns were Northern Manhattan (42.4%), WTC (60.6%), Krakow (71.1%), Tongliang (79.5%). Despite the estimated 10-fold lower PAH dose to the fetus based on laboratory animal experiments, the adduct levels in the newborns were similar to or higher than in the mothers. This study suggests that the fetus may be 10-fold more susceptible to DNA damage than the mother and that in utero exposure to polycyclic aromatic hydrocarbons may disproportionately increase carcinogenic risk. The data support preventive policies to limit PAH exposure to pregnant women and children.

Use of the local lymph node assay in assessment of immune function

The murine local lymph node assay (LLNA) was originally developed as a predictive test method for the identification of chemicals with sensitizing potential. In this study we demonstrated that an adapted LLNA can also be used as an immune function assay by studying the effects of orally administered immunomodulating compounds on the T-cell-dependent immune response induced by the contact sensitizer 2,4-dinitrochlorobenzene (DNCB). C57Bl/6 mice were treated with the immunotoxic compounds cyclosporin A (CsA), bis(tri-n-butyltin)oxide (TBTO) or benzo[a]pyrene, (B[a]P). Subsequently, cell proliferation and interferon-gamma (IFN-gamma) and interleukin (IL)-4 release were determined in the auricular lymph nodes (LNs) after DNCB application on both ears. Immunosuppression induced by CsA, TBTO and B[a]P was clearly detectable in this application of the LLNA. Cytokine release measurements proved valuable to confirm the results of the cell proliferation assay and to obtain an indication of the effect on Th1/Th2 balance. We believe to have demonstrated the applicability of an adapted LLNA as an immune function assay in the mouse.

Modulation of adult rat benzo(a)pyrene (BaP) metabolism and DNA adduct formation by neonatal diethylstilbestrol (DES) exposure

This study seeks to elucidate the role of diethylstilbestrol (DES), a synthetic estrogen on benzo(a)pyrene (BaP) metabolism in the male rat reproductive tissues. Offspring of timed-pregnant Sprague-Dawley rats were neonatally treated on days 2, 4, and 6 post-partum with 1.45 micromol/kg of DES. Ten weeks after birth, the adult rats were challenged with radiolabeled benzo(a)pyrene (3H BaP) (10 micromol/kg) and the rats were sacrificed 2 h after BaP exposure. Prostrate, testis, lung, liver, urine and feces samples were collected and extracted using a mixture of H2O, MeOH and CHCl3. The extracts were analyzed by reverse phase HPLC. The concentrations of BaP organic metabolites in DES rats were lower compared to controls (vehicle-treated rats). On the other hand, concentrations of aqueous metabolites were significantly increased in DES treated animals. The toxication to detoxication ratios were significantly decreased in DES rats compared to controls. This trend is also reflected in the decreased concentrations of BaP-DNA adducts in DES rats. Collectively these results suggest that DES is capable of modulating the metabolic pathway of BaP towards detoxification thereby preventing the manifestation of toxicity.

Biomarkers in maternal and newborn blood indicate heightened fetal susceptibility to procarcinogenic DNA damage

Polycyclic aromatic hydrocarbons (PAHs) such as benzo[a]pyrene (BaP) are widespread air contaminants released by transportation vehicles, power generation, and other combustion sources. Experimental evidence indicates that the developing fetus is more susceptible than the adult to carcinogenic effects of PAHs, although laboratory studies in rodents suggest that the dose to fetal tissues is an order of magnitude lower than that to maternal tissues. To assess fetal versus adult susceptibility to PAHs and environmental tobacco smoke (ETS), we compared carcinogen-DNA adducts (a biomarker associated with increased cancer risk) and cotinine (a biomarker of tobacco smoke exposure) in paired blood samples collected from mothers and newborns in New York City. We enrolled 265 nonsmoker African-American and Latina mother-newborn pairs in New York City between 1997 and 2001 (estimated average ambient air BaP concentrations < 0.5 ng/m3). Despite the estimated 10-fold lower fetal dose, mean levels of BaP-DNA adducts as determined by high-performance liquid chromatography-fluorescence were comparable in paired New York City newborn and maternal samples (0.24 adducts per 10(8) nucleotides, 45% of newborns with detectable adducts vs. 0.22 per 10(8) nucleotides, 41% of mothers with detectable adducts). However, by the Wilcoxon signed-rank test, the levels in newborns were higher (p = 0.02). Mean cotinine was higher in newborns than in mothers (1.7 ng/mL, 47% detectable vs. 1.28 ng/mL, 44% detectable). Consistent with our prior study in a Caucasian Polish population, these results indicate increased susceptibility of the fetus to DNA damage and reduced ability to clear ETS constituents. The findings have implications for risk assessment, given the need to protect children as a sensitive subset of the population.

CYP1A1 and CYP1B1 in blood-brain interfaces: CYP1A1-dependent bioactivation of 7,12-dimethylbenz(a)anthracene in endothelial cells

Immunohistochemistry and autoradiography were used to identify sites of the cytochrome P450 enzymes (P450) 1A1 and 1B1 expression and activation of 7,12-dimethylbenz(a)anthracene (DMBA), in the brain of rodents pretreated with the aryl hydrocarbon receptor (AhR) agonists beta-naphthoflavone (BNF), 3,3',4,4',5-pentachlorobiphenyl or vehicle. Immunohistochemistry revealed that CYP1A1 was preferentially induced in endothelial cells (EC) in the choroid plexus, in veins in the leptomeninges, and in cerebral veins of AhR agonist-pretreated mice. No induction occurred in cerebral capillary EC. In vehicle-treated mice no localization of CYP1A1 in EC was observed. CYP1B1 was expressed in smooth muscle cells of arteries in the leptomeninges, in cerebral arteries/arterioles and to a low extent in ependymal cells of AhR agonist- and vehicle-treated mice. No CYP1B1 was detected in capillary loops of the choroid plexus or in cerebral capillaries. Following administration of [(3)H]DMBA to BNF-pretreated mice, a marked irreversible binding in EC of the choroid plexus and of veins in the leptomeninges was observed but not in cerebral capillaries. In vehicle-treated mice, there was no [(3)H]DMBA-binding at these sites. Furthermore, a high level of irreversibly bound [(3)H]DMBA occurred in EC at these sites in precision-cut mouse/rat brain slices and in excised blood-brain interfaces incubated with [(3)H]DMBA. Since [(3)H]DMBA binding sites corresponded with the sites of CYP1A1 induction, we conclude that rodents express a constitutively low but highly inducible and functional CYP1A1 in EC of some of the blood-brain interfaces. The role of CYP1A1/1B1 and environmental pollutants in the etiology of cerebrovascular disease needs further consideration.

Analysis of DNA and protein adducts of benzo[a]pyrene in human tissues using structure-specific methods

We review studies which investigate the presence, using structure-specific analytical methods, of DNA or protein adducts of the carcinogen benzo[a]pyrene (BaP) in human tissues. The analytical methods include high performance liquid chromatography with fluorescence detection and gas chromatography-mass spectrometry. Although, for DNA detection these methods are somewhat less sensitive than non-specific techniques such as 32P-postlabeling and immunoassay, they have the distinct advantage of providing reliable structural information. In order to achieve adequate sensitivity, these methods often require the use of fairly large amounts of DNA (>100 microg) or protein (50-100mg). Most studies reviewed here measured tetraols released from DNA or protein by hydrolysis of adducts derived from (7R,8S)-dihydroxy-(9S,10R)-epoxy-7,8,9,10-tetrahydrobenzo[a]pyrene (BPDE), a major ultimate carcinogen of BaP. BPDE-DNA adducts were detected in 39% of 705 samples analyzed. BPDE-protein adducts were found in 59% of 772 samples. There was no single exposure situation that led to an overwhelming presence of detectable adducts. For example, BPDE-DNA adducts were detected in 45% of smokers, 33% of former smokers, 52% of non-smokers, 39% of occupationally exposed individuals, and 34% of environmentally exposed people. Adduct levels were influenced by polymorphisms in carcinogen metabolizing genes such as GSTM1, the presence of which was frequently protective. The relatively high occurrence of non-detectable adducts may result from low levels of BaP exposure and host factors such as genetic polymorphisms. Our analysis demonstrates that the presence of BaP adducts in human tissues cannot be assumed, even in situations where exposure to BaP is relatively high.

Selective induction of gene expression in rat lung by hexavalent chromium

Multigene-expression analysis provides a formidable tool for evaluating cellular functions, under either physiological or pathological conditions, and for assessing their modulation by exogenous agents. We investigated multigene expression in the liver and lung of rats receiving intratracheal instillations of sodium dichromate for 3 consecutive days. Nylon membrane cDNA arrays were hybridized with standardized amounts of (32)P-labeled probes, and the results were normalized by making reference to housekeeping genes. The basal expression of 52 of 216 tested genes was 2.1-11.1 times higher in the liver than in the lung of control rats. No alteration of gene expression occurred in the liver of chromium(VI)-treated rats, consistent with the fact that this metal species, being reduced upstream, can exert effects only locally but not at a distance from the respiratory tract. In contrast, the expression of 56 genes was increased 2.1 to 3.0 times in the lung as an early response to chromium(VI) administration. The altered genes are involved in the metabolic reduction of chromium(VI) and in a variety of interconnected functions, such as multidrug resistance and stress response, protein and DNA repair mechanisms, signal transduction pathways, apoptosis, and cell-cycle modulation. Thus, short-term treatment with chromium(VI) by intratracheal administration triggered a variety of defense processes in the lung. Although the use of selected genes does not provide an exhaustive picture of overall gene expression, these findings contribute to our understanding of chromium toxicology and provide a further mechanistic support to the involvement of thresholds in chromium(VI) carcinogenesis.

Effects of benzyl isothiocyanate and phenethyl isothiocyanate on benzo[a]pyrene metabolism and DNA adduct formation in the A/J mouse

Benzyl isothiocyanate (BITC) inhibits lung tumorigenesis induced in A/J mice by benzo[a]pyrene (B[a]P). In contrast, phenethyl isothiocyanate (PEITC) does not. We tested the hypothesis that BITC inhibits B[a]P tumorigenicity in mouse lung by inhibiting DNA adduct formation, and compared the effects of BITC and PEITC. In mouse liver or lung microsomal incubations, BITC and PEITC inhibited formation of 7,8-dihydro-7,8-dihydroxybenzo[a]pyrene (B[a]P-7, 8-diol) and some other B[a]P metabolites. The metabolism of B[a]P was compared in mouse lung and liver microsomes, 6 or 24h after treatment with BITC or PEITC. In lung, 6 h after treatment, B[a]P-7, 8-diol and some other metabolites were inhibited by BITC and PEITC. However, 24 h after treatment, no inhibition of B[a]P-7,8-diol was observed in microsomes from BITC-treated mice, whereas it was substantially increased in mice treated with PEITC. Effects on B[a]P metabolism in liver microsomes were generally modest. Conversion of B[a]P-7,8-diol to mutagens by mouse liver microsomes was more strongly inhibited by BITC than PEITC. Effects on 7,8-dihydroxy-9, 10-epoxy-7,8,9,10-tetrahydrobenzo[a]pyrene (BPDE)-DNA adduct formation were evaluated in DNA from mice treated with isothiocyanates and B[a]P, and killed 2-120h later. The area under the curve (AUC) for BPDE-DNA adducts in lung was 29.5% less (P = 0. 001) in the BITC-B[a]P treated mice and 19.0% less (P = 0.02) in the PEITC-B[a]P mice than in the mice treated with B[a]P alone. Similar results were obtained in liver DNA. There were no significant differences between the reduction of BPDE-DNA AUC values by BITC versus PEITC. The results of this study support the hypothesis that BITC inhibits B[a]P-induced lung tumorigenesis in A/J mice by inhibiting the metabolic activation of B[a]P to BPDE-DNA adducts. However, differences in BPDE-DNA adduct formation do not appear to explain fully the contrasting effects of BITC and PEITC on B[a]P-induced lung tumorigenesis.

LacI mutation spectra following benzo[a]pyrene treatment of Big Blue mice

The mutation spectrum of the lacI gene from the liver of C57Bl6 Big Blue transgenic mice treated with benzo[a]pyrene (B[a]P) has been compared with the spectrum of spontaneous mutations observed in the liver of untreated Big Blue mice. Mice were treated with B[a]P for 3 days followed by a partial hepatectomy one day after the last injection. Liver tissue was removed for analysis at hepatectomy and, again, 3 days later at the time of sacrifice. Earlier, we reported that the lacI mutant frequency in these B[a]P-treated mice was elevated in the liver both at the time of hepatectomy and at sacrifice; however, a statistically significant increase in the mutant frequency was observed only at sacrifice. In this study, the DNA sequence spectra of lacI mutations observed in the liver of B[a]P-treated Big Blue mice at hepatectomy and at time of sacrifice were compared with each other and with the spectrum of spontaneous liver mutations. No differences were observed between the two B[a]P-treatment spectra. However, mutation frequencies of both GC-->TA and GC-->CG at the time of hepatectomy and at sacrifice were significantly elevated compared with the spontaneous frequency of these same transversions. Also, the frequency of AT-->TA transversions was significantly higher than the spontaneous frequency at the time of hepatectomy but not at sacrifice. The frequency of all other classes of mutations scored was not significantly different from the frequency of these same events in the spontaneous spectra. These data support the view that B[a]P treatment results in the induction of GC-->TA and GC-->CG transversions within 1 day of the last injection and they provide insights regarding the relative roles of benzo[a]pyrene-7,8-diol-9, 10-epoxide and radical cations of B[a]P in B[a]P-induced mutagenesis in vivo. Finally, these data provide evidence for B[a]P-induced mutagenesis under conditions where no statistical increase in mutant frequency could be shown.

Multiple organ mutation in the lacZ transgenic mouse (Muta mouse) 6 months after oral treatment (5 days) with benzo[a]pyrene

We have recently demonstrated that not all organs with high rates of mutation in the lacZ transgene develop tumors using the Muta Mouse. To better understand the role of in vivo mutation in carcinogenesis, we examined the mutant frequencies (MF) of the lacZ transgene in tumor-bearing and non tumor-bearing organs. MF, recovered after 2 weeks (the data taken from our previous study) and after 26 weeks following oral doses of 125 mg kg-1 day-1 benzo[a]pyrene (BP) for five days were compared. The organs examined included the target organs (forestomach, spleen, and lung) and non-target organs (colon, glandular stomach, and liver) for BP carcinogenesis. The data indicated that lacZ MF were markedly increased over spontaneous frequencies in the organs examined and that the organ which showed the highest MF was the colon, followed by the forestomach>spleen>glandular stomach, liver, and lung in that order. These findings indicate that the MF of the lacZ transgene in each organ, even 26 weeks after the start of the treatment does not fully correlate with the known target organs of BP. Furthermore, the lacZ MF in a non-papilloma region of a forestomach with a papilloma was equivalent to the two highest MF observed in the healthy colon (non-target organ) of mice at 26 weeks. These observations also indicate that the generation of tumors requires the induction of mutations as well as other factor(s) specific to the target organs. These results clearly suggest that highly mutated organs do not always progress to tumors in the transgenic mouse.

32P-Postlabeling analysis of lipophilic DNA adducts resulting from interaction with (+/-)-3-hydroxy-trans-7,8-dihydroxy-9,10-epoxy-7,8,9,10-tetrahydrobenzo [a]pyrene

Bay-region diol epoxides are considered the putative ultimate carcinogens of polynuclear aromatic hydrocarbons. However, the results of studies on tumorigenesis and DNA binding of benzo[a]pyrene (BP) and its bay-region diol epoxide, (+)-trans-7,8-dihydroxy-anti-9,10-epoxy-7,8,9,10-tetrahydrobenzo[a]pyren e [(+)-anti-BPDE] suggest that, in addition to anti-BPDE, other reactive metabolite(s) of BP may also be involved in BP-induced carcinogenesis. Recent studies have demonstrated that 3-hydroxy-trans-7,8-dihydroxy-anti-9,10-epoxy-7,8,9,10-tetrahydrobenzo[a ]pyrene (anti-BPTE) is another highly reactive metabolite of BP. In order to identify syn- and anti-BPTE-derived DNA adducts and their base selectivity, we synthesized both compounds by two different methods and reacted in vitro with calf thymus DNA and individual nucleotides. The resultant adducts were analyzed by nuclease P1-enhanced 32P-postlabeling. Anti-BPTE produced three major and several minor adducts with DNA; dAp and dGp were the preferred substrates, while dCp and dTp were the least reactive. In contrast, syn-BPTE produced two major adducts each with DNA and dGp; dAp generated only one adduct. Co-chromatography of anti-BPTE-derived DNA adducts with those of mononucleotide adducts revealed that the major adducts in DNA were guanine derived. Further, co-chromatographic results revealed that the anti-BPTE-DNA adducts were distinctly different from that of anti-BPDE-DNA adducts. These observations indicate that both syn- and anti-BPTE can react with DNA bases and these DNA adducts may also contribute to BP-induced carcinogenesis.

Comparison between in vivo mutagenicity and carcinogenicity in multiple organs by benzo[a]pyrene in the lacZ transgenic mouse (Muta Mouse)

To evaluate whether the in vivo mutagenicity test system using the lacZ transgenic mice (Muta Mouse) may be applied to carcinogenesis studies, both the in vivo mutagenicity and carcinogenicity of benzo[a]pyrene (BP) was tested in mice under the same administration conditions. The eleven organs of the mice on the 14th day after the final oral administration of BP at a dose of 125 mg kg(-1) day(-1) or corn oil for 5 consecutive days were tested for in vivo mutation by the positive-selection method. The data show that the colon had the highest lacZ mutant frequency (37-fold increase over the spontaneous frequency), followed by the ileum > forestomach > bone marrow, spleen > glandular stomach > liver, lung > kidney and heart. No significant mutations were found in the brain. These results may suggest that, in general, the organs with rapidly proliferative tissues have a marked increase in vivo mutant frequencies under the conditions of this experimental design. The forestomach and lymphatic organs including the spleen (malignant lymphoma) were the main target organs for BP carcinogenesis by 5 daily oral doses of 75 and 125 mg kg(-1) day(-1). These results suggest that the mutation results from the transgenic assay with BP reflect the carcinogenicity of BP in the mouse. They also indicate, however, that the magnitude of the in vivo lacZ mutant frequencies induced by BP in different organs did not fully correlate with the target organs for carcinogenicity.

Variability in PAH-DNA adduct measurements in peripheral mononuclear cells: implications for quantitative cancer risk assessment

Biomarkers such as DNA adducts have significant potential to improve quantitative risk assessment by characterizing individual differences in metabolism of genotoxins and DNA repair and accounting for some of the factors that could affect interindividual variation in cancer risk. Inherent uncertainty in laboratory measurements and within-person variability of DNA adduct levels over time are putatively unrelated to cancer risk and should be subtracted from observed variation to better estimate interindividual variability of response to carcinogen exposure. A total of 41 volunteers, both smokers and nonsmokers, were asked to provide a peripheral blood sample every 3 weeks for several months in order to specifically assess intraindividual variability of polycyclic aromatic hydrocarbon (PAH)-DNA adduct levels. The intraindividual variance in PAH-DNA adduct levels, together with measurement uncertainty (laboratory variability and unaccounted for differences in exposure), constituted roughly 30% of the overall variance. An estimated 70% of the total variance was contributed by interindividual variability and is probably representative of the true biologic variability of response to carcinogenic exposure in lymphocytes. The estimated interindividual variability in DNA damage after subtracting intraindividual variability and measurement uncertainty was 24-fold. Inter-individual variance was higher (52-fold) in persons who constitutively lack the Glutathione S-Transferase M1 (GSTM1) gene which is important in the detoxification pathway of PAH. Risk assessment models that do not consider the variability of susceptibility to DNA damage following carcinogen exposure may underestimate risks to the general population, especially for those people who are most vulnerable.

Benzo(a)pyrene-albumin adducts in humans exposed to polycyclic aromatic hydrocarbons in an industrial area of Poland

OBJECTIVES

The interaction of benzo(a)pyrene with serum albumin was measured in an attempt to identify the actual exposure and to evaluate albumin adduct measurements as biomarkers for exposure monitoring.

METHODS

Benzo(a)pyrene-diol-epoxide (BPDE)-albumin adducts were measured by competitive enzyme linked immunosorbent assay (ELISA) in plasma of coke oven plant workers from three plants and from people living in a highly industrialised area of Silesia in Poland. Due to the high air concentrations of polycyclic aromatic hydrocarbons (PAHs) in this area, a control group was selected from a rural non-industrialised area in Poland. Breathing zone air measurements of PAHs were collected from some of the participants.

RESULTS

Coke oven plant workers and non-occupationally exposed people had similar concentrations of albumin adducts whereas the rural controls were significantly lower (2.74 fmol adducts/microgram albumin (SEM 0.124)). The mean concentration of BPDE-albumin adduct in plasma of both the occupational and the environmental groups were significantly higher in the summer samples (4.34 fmol adducts/microgram albumin (SEM 0.335) and 4.55 fmol adducts/microgram albumin (SEM 0.296), respectively) than in the winter samples (3.06 fmol adducts/microgram albumin (SEM 0.187) and 3.04 fmol adducts/microgram albumin (SEM 0.184), respectively) even though the air measurements showed higher concentrations of PAHs in the winter. The statistical analysis did not show any effects of air exposures on concentrations of BPDE-albumin adduct.

CONCLUSIONS

A multiple regression analysis of the measured concentrations of BPDE-albumin adducts for all the groups, during both seasons, indicates that occupational exposures do not contribute significantly to the formation of adducts. In general, the concentrations of albumin adducts found vary within relatively small limits for the two seasons and between the various groups of participants. No extreme differences were found.