Correlation between DNA or protein adducts and benzo[a]pyrene diol epoxide I-triglyceride adduct detected in vitro and in vivo

A review of hazards in meat products: Multiple pathways, hazards and mitigation of polycyclic aromatic hydrocarbons

Polycyclic aromatic hydrocarbons (PAHs) are stable carcinogens that are widely distributed in the environment and food, and humans are exposed to PAHs primarily through the respiratory tracts, dermal contact, and dietary intake. Meat products are an essential part of the human diet, and the formation of PAHs during meat processing is unavoidable. Therefore, a comprehensive understanding of PAHs in meat products can be a contribution to the minimization of human exposure dose. The aim of this review is to provide a comprehensive description of the toxicological analysis of PAHs intake and the various production pathways. The distribution of different PAHs in various meat products, including poultry and aquatic products, is analyzed. The discussion focuses on controlling PAHs through the use of endogenous marinades and antioxidants as well as reducing exogenous particulate matter-PAHs attachment. In addition, potential strategies for PAHs reduction and possible directions for future research are proposed.

Indenopyrene and Blue-Light Co-Exposure Impairs the Tightly Controlled Activation of Xenobiotic Metabolism in Retinal Pigment Epithelial Cells: A Mechanism for Synergistic Toxicity

High energy visible (HEV) blue light is an increasing source of concern for visual health. Polycyclic aromatic hydrocarbons (PAH), a group of compounds found in high concentrations in smokers and polluted environments, accumulate in the retinal pigment epithelium (RPE). HEV absorption by indeno [1,2,3-cd]pyrene (IcdP), a common PAH, synergizes their toxicities and promotes degenerative changes in RPE cells comparable to the ones observed in age-related macular degeneration. In this study, we decipher the processes underlying IcdP and HEV synergic toxicity in human RPE cells. We found that IcdP-HEV toxicity is caused by the loss of the tight coupling between the two metabolic phases ensuring IcdP efficient detoxification. Indeed, IcdP/HEV co-exposure induces an overactivation of key actors in phase I metabolism. IcdP/HEV interaction is also associated with a downregulation of proteins involved in phase II. Our data thus indicate that phase II is hindered in response to co-exposure and that it is insufficient to sustain the enhanced phase I induction. This is reflected by an accelerated production of endogenous reactive oxygen species (ROS) and an increased accumulation of IcdP-related bulky DNA damage. Our work raises the prospect that lifestyle and environmental pollution may be significant modulators of HEV toxicity in the retina.

Association between polycyclic aromatic hydrocarbon exposure and blood lipid levels: the indirect effects of inflammation and oxidative stress

Although previous studies have indicated polycyclic aromatic hydrocarbons (PAHs) as cardiovascular health risk factors, evidence linking exposure to PAHs and blood lipids is still lacking, and the mechanism remains largely unknown. In this study, we evaluated the association between human internal exposure to PAHs and blood lipid levels in adults, as well as the indirect effects of inflammation and oxidative stress. The internal exposure of PAHs was assessed by determining serum PAHs and their hydroxylated metabolites (OH-PAHs) in the paired urine samples. Multivariable linear regression results demonstrated significant positive associations of individual PAHs and OH-PAHs with blood lipid biomarkers. The Bayesian kernel machine regression model revealed positive joint effects of PAH internal exposure on the fasting blood glucose, low-density lipoprotein cholesterol, total cholesterol, and total triglyceride, as well as an increased ratio of apolipoprotein B to apolipoprotein A1. In evaluating individual effects, serum phenanthrene played the most significant role in the association of increased PAH exposure with elevated fasting blood glucose. Quantile g-computation demonstrated the significant change in the levels of apolipoprotein B, ratio of apolipoprotein B to apolipoprotein A1, low-density lipoprotein cholesterol, and total cholesterol per quartile increase in PAH internal exposure. The restricted cubic spline analysis demonstrated the non-linear relationship between individual PAHs and OH-PAHs on blood lipid biomarkers. The mediation analysis indicated that PAH exposure may affect blood lipids not directly, but rather indirectly through intermediate inflammation and oxidative stress. The results demonstrated a significant association between increased PAH exposure levels and elevated blood lipids, highlighting the indirect effects of inflammation and oxidative stress.

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.

Molecular mechanisms of pulmonary carcinogenesis by polycyclic aromatic hydrocarbons (PAHs): Implications for human lung cancer

Lung cancer has the second highest incidence and highest mortality compared to all other cancers. Polycyclic aromatic hydrocarbon (PAH) molecules belong to a class of compounds that are present in tobacco smoke, diesel exhausts, smoked foods, as well as particulate matter (PM). PAH-derived reactive metabolites are significant contributors to lung cancer development. The formation of these reactive metabolites entails metabolism of the parent PAHs by cytochrome P4501A1/1B1 (CYP1A1/1B1) and epoxide hydrolase enzymes. These reactive metabolites then react with DNA to form DNA adducts, which contribute to key gene mutations, such as the tumor suppressor gene, p53 and are linked to pulmonary carcinogenesis. PAH exposure also leads to upregulation of CYP1A1 transcription by binding to the aryl hydrocarbon receptor (AHR) and eliciting transcription of the CYP1A1 promoter, which comprises specific xenobiotic-responsive element (XREs). While hepatic and pulmonary CYP1A1/1B1 metabolize PAHs to DNA-reactive metabolites, the hepatic CYP1A2, however, may protect against lung tumor development by suppressing both liver and lung CYP1A1 enzymes. Further analysis of these enzymes has shown that PAH-exposure also induces sustained transcription of CYP1A1, which is independent of the persistence of the parent PAH. CYP1A2 enzyme plays an important role in the sustained induction of hepatic CYP1A1. PAH exposure may further contribute to pulmonary carcinogenesis by producing epigenetic alterations. DNA methylation, histone modification, long interspersed nuclear element (LINE-1) activation, and non-coding RNA, specifically microRNA (miRNA) alterations may all be induced by PAH exposure. The relationship between PAH-induced enzymatic reactive metabolite formation and epigenetic alterations is a key area of research that warrants further exploration. Investigation into the potential interplay between these two mechanisms may lead to further understanding of the mechanisms of PAH carcinogenesis. These mechanisms will be crucial for the development of effective targeted therapies and early diagnostic tools.

Polycyclic Aromatic Hydrocarbons: Occurrence, Electroanalysis, Challenges, and Future Outlooks

The past several decades have seen increasing concern regarding the wide distribution of polycyclic aromatic hydrocarbons (PAHs) in environmental matrices. Primary toxicological data show PAHs' persistent characteristics and possible toxicity effects. Because of this pressing global issue, electroanalytical methods have been introduced. These methods are effective for PAH determination in environmental waters, even outclassing sophisticated analytical techniques such as chromatography, conventional spectrophotometry, fluorescence, and capillary electrophoresis. Herein, the literature published on PAHs is reviewed and discussed with special regard to PAH occurrence. Moreover, the recent developments in electrochemical sensors for PAH determination and the challenges and future outlooks in this field, are also presented.

Reduction of mitochondrial DNA copy number in peripheral blood is related to polycyclic aromatic hydrocarbons exposure in coke oven workers: Bayesian kernel machine regression

Although association between polycyclic aromatic hydrocarbons (PAHs) exposure and mitochondrial DNA copy number (mtDNAcn) was researched by traditional linear model extensively, most of these studies analyzed independent effect of each PAHs metabolite and adjust for the confounding other metabolites concomitantly, without considering others interactions. As a complex organic pollutant, a reasonable statistical method is needed to study toxic effects of PAHs. Therefore, we aimed to conduct a novel statistical approach, Bayesian Kernel Machine Regression (BKMR), to explore the effect of PAHs exposure on mtDNAcn among coke oven workers. In this cross-sectional study, the concentrations urinary of PAHs metabolites were measured using high performance liquid chromatography mass spectrometry (HPLC-MS). The mtDNAcn was measured using real-time quantitative polymerase chain reaction (RT-PCR) in peripheral blood of 696 Chinese coke oven workers. The relationship of urinary of PAHs metabolites and mtDNAcn were evaluated by BKMR model. And the results showed a significant negative effect of PAHs metabolites on mtDNAcn when PAHs metabolites concentrations were all above 35th percentile compared to the median and the statistically significant negative single-exposure effect of 2-OHNAP and 2-OHPHE on mtDNAcn when all of the other PAHs are fixed at a particular threshold (25th, 50th, 75th percentile). The changes in log 2-OHNAP and 2-OHPHE from the 25th to the 75th percentile when other PAHs metabolites were at the 50th percentile were associated with change in mtDNAcn of -0.082 (-0.021, -0.124) and -0.048 (-0.021, -0.090) respectively. And evidence of a linear effect of urinary 2-OHNAP and 2-OHPHE were found. Finally, our findings suggested that PAHs cumulative exposures and particularly single-exposure of 2-OHNAP and 2-OHPHE might compromise mitochondrial function by decreasing mtDNAcn in Chinese coke oven workers.

Curcumin Ameliorates Benzo[a]pyrene-Induced DNA Damages in Stomach Tissues of Sprague-Dawley Rats

Benzo[a]pyrene (BaP) is a well-known carcinogen formed during the cooking process. Although BaP exposure has been implicated as one of the risk factors for lung cancer in animals and humans, there are only limited data on BaP-induced gastrointestinal cancer. Therefore, this study investigated the protective effects of curcumin on BaP-induced DNA damage in rat stomach tissues. BaP (20 mg/kg/day) and curcumin (50, 100, or 200 mg/kg) were administered daily to Sprague-Dawley rats by oral gavage over 30 days. Curcumin was pre-administered before BaP exposure. All rats were euthanized, and liver, kidney, and stomach tissues were removed at 24 h after the last treatment. We observed that aspartate aminotransferase (AST), alanine aminotransferase (ALT), and glucose levels were significantly reduced in rats treated with high dose co-administration of curcumin (200 mg/kg) compared to BaP alone. The expression levels of cytochrome P450 (CYP) 1A1 and CYP1B1 were significantly increased in the liver of rats treated with BaP. However, co-administration of curcumin (200 mg/kg) with BaP markedly reduced CYP1A1 expression in a dose-dependent manner. Furthermore, plasma levels of BaP-diolepoxide (BPDE) and BaP metabolites were significantly reduced by co-administration of curcumin (200 mg/kg). Additionally, co-administration of curcumin (200 mg/kg) with BaP significantly reduced the formation of BPDE-I-DNA and 8-hydroxydeoxy guanosine (8-OHdG) adducts in the liver, kidney, and stomach tissues. The inhibition of these adduct formations were more prominent in the stomach tissues than in the liver. Overall, our observations suggest that curcumin might inhibit BaP-induced gastrointestinal tumorigenesis and shows promise as a chemopreventive agent.

Characteristics, sources, and cytotoxicity of atmospheric polycyclic aromatic hydrocarbons in urban roadside areas of Hangzhou, China

The primary objective of this study is to understand the profiles, sources and cytotoxic effects of atmospheric polycyclic aromatic hydrocarbons (PAHs), which are closely related to urban air contamination and public health, in urban roadside environments. On-road sampling campaigns were conducted from 2014 to 2015 at three urban road sites in Hangzhou, China. Sixteen gaseous and particulate matter (PM) 2.5-bound PAHs were identified and quantified using gas chromatography-mass spectrometry (GC-MS). The total PAH concentrations at the three sites ranged from 750 to1142 ng/m³ and 1050 to 1483 ng/m³ in summer and winter, respectively. Low molecular weight PAHs were the most abundant compounds (77-86%) and primarily existed in gas phase. The concentrations and phase distributions of high molecular weight PAHs were varied at three sites due to the differences in traffic volume, vehicle composition, engine loading, and nearby artificial activity. Diagnostic ratios of the principal mass (m/z,178, 202, 228 and 276) parent PAHs were statistically described to determine the PAH sources to urban roadsides; principal component analysis (PCA) was applied to apportion the sources. The results indicated that high- and low-temperature fuel processes, as well as residential and industrial emissions, were major contributors to roadside PAHs. The cytotoxic potential of the roadside PAHs was evaluated using a human epithelial lung cell line (A549). Cell viability was measured after a direct exposure to PAH extract. The results reflected the profiles of roadside PAHs at the three sites. The cytotoxicity of reference PAHs was evaluated to provide further insights into the cytotoxic potential of PAHs. We found that low molecular weight PAHs, which are less cytotoxic compounds, synergistically promoted the lethal effect of cytotoxic compounds, posing a potential threat to public health.

Polycyclic aromatic hydrocarbons: from metabolism to lung cancer

Excessive exposure to polycyclic aromatic hydrocarbons (PAHs) often results in lung cancer, a disease with the highest cancer mortality in the United States. After entry into the lung, PAHs induce phase I metabolic enzymes such as cytochrome P450 (CYP) monooxygenases, i.e. CYP1A1/2 and 1B1, and phase II enzymes such as glutathione S-transferases, UDP glucuronyl transferases, NADPH quinone oxidoreductases (NQOs), aldo-keto reductases (AKRs), and epoxide hydrolases (EHs), via the aryl hydrocarbon receptor (AhR)-dependent and independent pathways. Humans can also be exposed to PAHs through diet, via consumption of charcoal broiled foods. Metabolism of PAHs through the CYP1A1/1B1/EH pathway, CYP peroxidase pathway, and AKR pathway leads to the formation of the active carcinogens diol-epoxides, radical cations, and o-quinones. These reactive metabolites produce DNA adducts, resulting in DNA mutations, alteration of gene expression profiles, and tumorigenesis. Mutations in xenobiotic metabolic enzymes, as well as polymorphisms of tumor suppressor genes (e.g. p53) and/or genes involved in gene expression (e.g. X-ray repair cross-complementing proteins), are associated with lung cancer susceptibility in human populations from different ethnicities, gender, and age groups. Although various metabolic activation/inactivation pathways, AhR signaling, and genetic susceptibilities contribute to lung cancer, the precise points at which PAHs induce tumor initiation remain unknown. The goal of this review is to provide a current state-of-the-science of the mechanisms of human lung carcinogenesis mediated by PAHs, the experimental approaches used to study this complex class of compounds, and future directions for research of these compounds.

4-Hydroxynonenal: A Superior Oxidative Biomarker Compared to Malondialdehyde and Carbonyl Content Induced by Carbon Tetrachloride in Rats

Carbon tetrachloride (CCl4), a halogenated substance that generates free radical species during metabolism in vivo, induces hepatotoxicity, produces oxidative DNA damage, and increased levels of protein carbonyl, malondialdehyde (MDA), and 4-hydroxynonenal (4-HNE). In this study, Sprague-Dawley rats received single or repeated ip injections of carbon tetrachloride (CCl4), and formation and persistence of carbonyls, MDA, and 4-HNE in plasma were measured using gas chromatography-mass spectrometry. After a single injection of 500 mg/kg CCl4 the in vivo half-lives of MDA and carbonyl content were 1.5 d and 2 d, respectively, while that of 4-HNE was approximately 10 d. Treatment with CCl4 (50, 100, 500, or 1000 mg/kg) dose-dependently increased these oxidative biomarkers in blood. However, formation of protein carbonyls and MDA was less sensitive than 4-HNE to CCl4. Levels of serum glutamic oxaloacetic transaminase (SGOT) and glutamic pyruvic transaminase (SGPT) (hepatotoxicity markers) rose with CCl4 doses. After a single injection (500 mg/kg), the peak level of SGOT was observed after 8 h but SGPT after 24 h. Overall, 4-HNE was more dose-sensitive and showed greater formation subchronically than other biomarkers. Multiple ip treatments with 300 mg CCl4 /kg (d 1, 3, 6, 10, 14, and 21) demonstrated that 4-HNE formation was highest (18-fold, peak/control) and subchronic up to d 21 (last treatment day), unlike other biomarkers. Data suggest that 4-HNE, MDA, and carbonyl content may be useful oxidative biomarkers for exposure to free radical generating halogenated compounds. However, 4-HNE appears to be a more sensitive and sustainable biomarker for toxicological and risk assessments.

Tetrahydroxylated-benzo[a]pyrene isomer analysis after hydrolysis of DNA-adducts isolated from rat and human white blood cells

Since exposure to benzo[a]pyrene is suspected to be associated with several health issues, significant efforts have been made to develop efficient strategies for the assessment of human exposure to this ubiquitous compound. In this context, a method was developed for the analysis of four tetrahydroxylated-benzo[a]pyrene isomers resulting from the hydrolysis of their respective diol-epoxide precursors which are involved in DNA-adduct formation. The analytical sensitivity necessary to reach environmental levels of concentration was obtained by using gas chromatography-tandem mass spectrometry. The recovery determined at the four concentration levels were estimated in average at 83% for benzo[a]pyrene-r-7,t-8,t-9,c-10-tetrahydrotetrol(±), 29% for benzo[a]pyrene-r-7,t-8,t-9,t-10-tetrahydrotetrol(±), and 82% for benzo[a]pyrene-r-7,t-8,C-9,c-10-tetrahydrotetrol(±). The coefficient of determination of the calibration curve was above 0.997 for all the analytes investigated and the limit of quantification ranged from 0.5 to 2 adduct/10(8) nucleotides. The precision was between 5.3% and 22.3%. The suitability of the method was firstly evaluated by the analysis of DNA isolated from white blood cells of rats submitted after controlled exposure to benzo[a]pyrene. The four targeted tetra-OH-benzo[a]pyrenes as well as two unknown isomers were detected in all the treated animals. Benzo[a]pyrene-r-7,t-8,c-9,c-10-tetrahydrotetrol(±) appeared as the most abundant isomer in both treated and control animals followed by benzo[a]pyrene-r-7,t-8,t-9,c-10-tetrahydrotetrol(±). The method was afterwards applied to the analysis of DNA isolated from white blood cells of human volunteers. The results confirmed that this method was sufficiently sensitive to monitor environmental levels of exposure since all the specimens analyzed were above the limit of quantification for benzo[a]pyrene-r-7,t-8,t-9,c-10-tetrahydrotetrol(±) and two of them were positive for benzo[a]pyrene-r-7,t-8,c-9,c-10-tetrahydrotetrol(±), thereby highlighting interspecies differences in the nature of the tetrahydroxylated-benzo[a]pyrene isomers formed. This study confirms the necessity to focus on all the tetrahydroxylated-benzo[a]pyrene isomers, which could be indicators of benzo[a]pyrene-associated toxicity related to an individual's own metabolism, rather than limit to a single form.

Lymphocyte oxidative stress/genotoxic effects are related to serum IgG and IgA levels in coke oven workers

We investigated oxidative stress/genotoxic effects levels, immunoglobulin levels, polycyclic aromatic hydrocarbons (PAHs) levels exposed in 126 coke oven workers and in 78 control subjects, and evaluated the association between oxidative stress/genotoxic effects levels and immunoglobulin levels. Significant differences were observed in biomarkers, including 1-hydroxypyrene levels, employment time, percentages of alcohol drinkers, MDA, 8-OHdG levels, CTL levels and CTM, MN, CA frequency, and IgG, IgA levels between the control and exposed groups. Slightly higher 1-OHP levels in smoking users were observed. For the dose-response relationship of IgG, IgA, IgM, and IgE by 1-OHP, each one percentage increase in urinary 1-OHP generates a 0.109%, 0.472%, 0.051%, and 0.067% decrease in control group and generates a 0.312%, 0.538%, 0.062%, and 0.071% decrease in exposed group, respectively. Except for age, alcohol and smoking status, IgM, and IgE, a significant correlation in urinary 1-OHP and other biomarkers in the total population was observed. Additionally, a significant negative correlation in genotoxic/oxidative damage biomarkers of MDA, 8-OH-dG, CTL levels, and immunoglobins of IgG and IgA levels, especially in coke oven workers, was found. These data suggest that oxidative stress/DNA damage induced by PAHs may play a role in toxic responses for PAHs in immunological functions.

Potential application of benzo(a)pyrene-associated adducts (globin or lipid) as blood biomarkers for target organ exposure and human risk assessment

In order to investigate the potential application of blood biomarkers as surrogate indicators of carcinogen-adduct formation in target-specific tissues, temporal formation of benzo[a]pyrene (BaP)-associated DNA adducts, protein adducts, or lipid damage in target tissues such as lung, liver, and kidney was compared with globin adduct formation or plasma lipid damage in blood after continuous intraperitoneal (ip) injection of [(3)H]BaP into female ICR mice for 7 d. Following treatment with [(3)H]BaP, formation of [(3)H]BaP-DNA or -protein adducts in lung, liver, and kidney increased linearly, and persisted thereafter. This finding was similar to the observed effects on globin adduct formation and plasma lipid damage in blood. The lungs contained a higher level of DNA adducts than liver or kidneys during the treatment period. Further, the rate of cumulative adduct formation in lung was markedly greater than that in liver. Treatment with a single dose of [(3)H]BaP indicated that BaP-globin adduct formation and BaP-lipid damage in blood reached a peak 48 h after treatment. Overall, globin adduct formation and lipid damage in blood were significantly correlated with DNA adduct formation in the target tissues. These data suggest that peripheral blood biomarkers, such as BaP-globin adduct formation or BaP-lipid damage, may be useful for prediction of target tissue-specific DNA adduct formation, and for risk assessment after exposure.

Bioaccessibility of polycyclic aromatic hydrocarbons: relevance to toxicity and carcinogenesis

INTRODUCTION

Bioaccessibility is a growing area of research in the field of risk assessment. As polycyclic aromatic hydrocarbons (PAHs) are ubiquitous environmental pollutants, they are the toxicants of focus to establish cancer risks in humans. Orally ingested PAHs also cause toxicity and even affect the pharmacokinetic behavior of some therapeutic agents. Toward this end, bioaccessibility is being used as a tool to assess the risk of PAHs via dietary exposures.

AREAS COVERED

This review covers some in vitro bioaccessibility models for PAHs that have been used for the past one-and-a-half decade. This review also considers the factors that influence bioaccessibility and debates the merits and limitations of using a bioaccessibility concept for estimating risk from ingestion of PAH-contaminated soil and food. Finally, the authors discuss the implications of bioaccessibility for PAH-induced toxicity and cancers in the context of risk assessment.

EXPERT OPINION

So far, much of the focus on PAH bioaccessibility is centered on soil as a preferential matrix. However, ingestion of PAHs through diet far exceeds the amount accidentally ingested through soil. Therefore, bioaccessibility could be exploited as a tool to assess the relative risk of various dietary ingredients tainted with PAHs. While bioaccessibility is a promising approach for assessing PAH risk arising from various types of contaminated soils, none of the models proposed appears to be valid. Bioaccessibility values, derived from in vitro studies, still require validation from in vivo studies.

Comparative evaluation of different cell lysis and extraction methods for studying benzo(a)pyrene metabolism in HT-29 colon cancer cell cultures

Lysis and extraction of cells are essential sample processing steps for investigations pertaining to metabolism of xenobiotics in cell culture studies. Of particular importance to these procedures are maintaining high lysis efficiency and analyte integrity as they influence the qualitative and quantitative distribution of drug and toxicant metabolites in the intra- and extracellular milieus. In this study we have compared the efficiency of different procedures viz. homogenization, sonication, bead beating, and molecular grinding resin treatment for disruption of HT-29 colon cells exposed to benzo(a)pyrene (BaP), a polycyclic aromatic hydrocarbon (PAH) compound and a suspected colon carcinogen. Also, we have evaluated the efficiency of various procedures for extracting BaP parent compound/metabolites from colon cells and culture media prior to High Performance Liquid Chromatography (HPLC) analyses. The extraction procedures include solid phase extraction, solid-supported liquid- liquid extraction, liquid-liquid extraction, and homogeneous liquid- liquid extraction. Our findings showed that bead-beating in combination with detergent treatment of cell pellet coupled with liquid-liquid extraction yielded greater concentrations of BaP metabolites compared to the other methods employed. Our method optimization strategy revealed that disruption of HT-29 colon cells by a combination of mechanical and chemical lysis followed by liquid-liquid extraction is efficient and robust enough for analyzing BaP metabolites from cell culture studies.

Comparison of standard methods for assessing dietary intake of benzo[a]pyrene

BACKGROUND

Inconsistent presence and strength of associations between dietary benzo[a]pyrene (BaP) exposure and cancers may be due to differences in exposure assessment methods. Thus, we determined correlations of usual meat and BaP intake among three methods: food frequency questionnaires (FFQ), diet diaries, and a biomarker.

METHODS

Thirty-six nonsmokers were recruited in Baltimore, MD during 2004-2005. Meat and BaP intake estimated from baseline and follow-up FFQs combined with a BaP residue database (FFQ-RD), mean meat and BaP intake estimated from three diet diaries coupled with the residue database (Diary-RD), and mean of three urinary 1-hydroxypyrene glucuronide (1-OHPG) measurements were compared using Spearman correlations. Collections spanned approximately nine months.

RESULTS

BaP intakes from meat from the baseline [median = 6.4, interquartile range (IQR) = 13.9 ng/d] and follow-up FFQ-RD (median = 7.3, IQR = 35.7 ng/d) were higher than the Diary-RD (median = 1.1, IQR = 7.4 ng/d). Mean 1-OHPG concentration was weakly correlated with mean meat intake (r = 0.33, P = 0.05) and BaP intake from meat (r = 0.27, P = 0.11) from the Diary-RD. Mean BaP intake estimated from the Diary-RD was positively correlated with the follow-up (r = 0.35, P = 0.04) but not baseline (r = 0.20, P = 0.24) FFQ; the converse was true for meat intake.

CONCLUSIONS

Diary-RD estimates were supported by biomarker measurements, but considerable unexplained variability remained. Limited correlation among the dietary BaP exposure assessment methods could be due to differences in timeframes covered by the assessments, interpersonal variability in metabolism, deficiencies in the residue database, or nondietary exposures to BaP.

IMPACT

Limited correlation in estimated BaP intake among standard methods may contribute to inconsistent epidemiology of BaP and cancer.

Toward an "omic" physiopathology of reactive chemicals: thirty years of mass spectrometric study of the protein adducts with endogenous and xenobiotic compounds

Cancer and degenerative diseases are major causes of morbidity and death, derived from the permanent modification of key biopolymers such as DNA and regulatory proteins by usually smaller, reactive molecules, present in the environment or generated from endogenous and xenobiotic components by the body's own biochemical mechanisms (molecular adducts). In particular, protein adducts with organic electrophiles have been studied for more than 30 [see, e.g., Calleman et al., 1978] years essentially for three purposes: (a) as passive monitors of the mean level of individual exposure to specific chemicals, either endogenously present in the human body or to which the subject is exposed through food or environmental contamination; (b) as quantitative indicators of the mean extent of the individual metabolic processing which converts a non-reactive chemical substance into its toxic products able to damage DNA (en route to cancer induction through genotoxic mechanisms) or key proteins (as in the case of several drugs, pesticides or otherwise biologically active substances); (c) to relate the extent of protein modification to that of biological function impairment (such as enzyme inhibition) finally causing the specific health damage. This review describes the role that contemporary mass spectrometry-based approaches employed in the qualitative and quantitative study of protein-electrophile adducts play in the discovery of the (bio)chemical mechanisms of toxic substances and highlights the future directions of research in this field. A particular emphasis is given to the measurement of often high levels of the protein adducts of several industrial and environmental pollutants in unexposed human populations, a phenomenon which highlights the possibility that a number of small organic molecules are generated in the human organism through minor metabolic processes, the imbalance of which may be the cause of "spontaneous" cases of cancer and of other degenerative diseases of still uncharacterized etiology. With all this in mind, it is foreseen that a holistic description of cellular functions will take advantage of new analytical methods based on time-integrated metabolomic measurements of a new biological compartment, the "adductome," aimed at better understanding integrated organism response to environmental and endogenous stressors.

Dietary exposure estimation of benzo[a]pyrene and cancer risk assessment

Dietary benzo[a]pyrene (BaP) levels were analyzed by high-performance liquid chromatography with fluorescence detection (HPLC-FLD) in various foods (e.g., snack, potato chip, bread, vegetable oil, meat, cereal, etc.) to estimate dietary intake levels of BaP for the assessment of BaP related-cancer risk in Koreans. Higher levels of BaP were detected in fried chicken (5.25-5.55 BaP microg/kg) and smoked dried beef (5.47 microg/kg) compared to relatively lower levels measured in sesame oil (0.36 microg/kg) and peanut (0.44 microg/kg). The BaP levels in nonmeat items were generally low in detection, but certain potato chip products showed levels up to 4.06 BaP microg/kg. In terms of chronic daily intake of BaP, fried chicken was shown to be the highest (70.09 ng/person/d) and perilla oil was the lowest (0.05 ng/person/d). The total daily intake of BaP due to the consumption of various food items investigated was estimated to be 124.55 ng/person/d, based on daily food consumption and the contaminant level of BaP. The dietary BaP-related cancer risk using carcinogenic potency factor of BaP as 7.3E + 0 (mg/kg/d)(-1) was assessed to be 1.52 x 10(-5). These data suggest that cancer risk due to dietary exposure to BaP is of concern in Koreans and needs to be reduced either by regulatory efforts or by modifying food manufacturing procedures.

Benzo[a]pyrene impairs beta-adrenergic stimulation of adipose tissue lipolysis and causes weight gain in mice. A novel molecular mechanism of toxicity for a common food pollutant

Benzo[a]pyrene (B[a]P) is a common food pollutant that causes DNA adduct formation and is carcinogenic. The report of a positive correlation between human plasma B[a]P levels and body mass index, together with B[a]P's lipophilicity, led us to test for possible adverse effects of B[a]P on adipose tissue. In ex vivo experiments using primary murine adipocytes, B[a]P rapidly (within minutes) and directly inhibited epinephrine-induced lipolysis (up to 75%) in a dose-dependent manner. Half-maximum inhibition was obtained with a B[a]P concentration of 0.9 mg.L(-1) (3.5 microm). Lipolysis induced by beta(1)-, beta(2)- and beta(3)-adrenoreceptor-specific agonists, as well as ACTH, were also significantly inhibited by B[a]P, whereas forskolin-induced lipolysis was not B[a]P-sensitive. Similar inhibition of catecholamine-induced lipolysis by B[a]P was also seen in isolated human adipocytes; half-maximum inhibition of lipolysis was achieved with a B[a]P concentration of 0.02 mg.L(-1) (0.08 microm). In vivo treatment of C57Bl/6J mice with 0.4 mg.kg(-1) B[a]P inhibited epinephrine-induced release of free fatty acids by 70%. Chronic exposure of mice to B[a]P (0.5 mg.kg(-1) injected i.p. every 48 h) for 15 days also decreased lipolytic response to epinephrine and induced a 43% higher weight gain compared with controls (B[a]P: 2.23 +/- 0.12 g versus control: 1.56 +/- 0.18 g, P < 0.01) due to increased fat mass. The weight gain occurred consistently without detectable changes in food intake. These results reveal a novel molecular mechanism of toxicity for the environmental pollutant B[a]P and introduce the notion that chronic exposure of human population to B[a]P and possibly other polycyclic aromatic hydrocarbons could have an impact on metabolic disorders, such as obesity.

Comparison of immunnological and genotoxicological parameters in automobile emission inspectors exposed to polycyclic aromatic hydrocarbons

In this study, we investigated the immunotoxicities of polycyclic aromatic hydrocarbons in 54 automobile emission inspectors and in 84 control subjects, and evaluated associations between immunological and genotoxicological parameters. Specific surface antigens of peripheral lymphocytes, namely, CD3, CD4, CD8, CD19, and CD69 were subjected to measure immune status in automobile emission inspectors and control subjects. T-and B-cells showed no significant differences between automobile emission inspectors and control subjects (p=0.740 and 0.395). In addition, the ratio of T helper cells to T cytotoxic cells was not deferent (p=0.144). However, T-cell activation was found to be significantly higher in automobile emission inspectors (p=0.041), but not B-cell activation. The levels of two cytokines (IL-4 an INF-γ) and four immunoglobulins (IgA, IgE, IgG, and IgM) were also determined in automobile emission inspectors and control subjects. All immunoglobulin types were lower in automobile emission inspectors, but this was significant only for IgG (0.047). In addition, the levels of two cytokines, IL-4 and INF-γ, were also higher in automobile emission inspectors, though this was not significant. DNA damage in mononuclear and polynuclear lymphocytes and in the level of urinary metabolites, 1-OHP and 2-naphthol, were evaluated in automobile emission inspectors and in control subjects and significant differences were found between the two groups. Examinations of urinary metabolites, DNA damage, and immunological parameters, including leukocyte subpopulations, immunoglobulins, and cytokines, showed that the cytokines levels were associated with the levels of two urinary metabolites, 1-OHP and 2-naphthol.

Effect of estrogen receptor (ER) on benzo[a]pyrene-DNA adduct formation in human breast cancer cells

To investigate the role of estrogen and estrogen receptor (ER) during benzo[a]pyrene (BaP) carcinogenesis, BaP-DNA adduct formation, and DNA synthesis were examined in ER-positive, MCF-7, and ER-negative, MDA-MB-231, human breast cancer cell lines. In MCF-7, the ER-positive human breast cancer cell line, treated with BaP, the formation of BaP-DNA adducts and DNA synthesis were inhibited in a concentration-responsive manner, but there was no change in MDA-MB-231, the ER-negative cell line. In the [3H]BaP-DNA binding assay, an increase of BaP-DNA adduct formation was observed with 17beta-estradiol (E2)-induced ERalpha. Treatments of [3H]BaP in conjunction with the E2 induced a 2.1-fold increase in BaP-DNA adduct over BaP alone in the ER-positive MCF-7 cell line. In addition, the antiestrogen tamoxifen (TAM) blocked this effect by 82%, while E2 produced no change in the ER-negative MDA-MB-231 cell line. These observations suggest that the increased formation of BaP-DNA adducts may be mediated through the ERalpha expressed by E2.

Chemopreventive effects of aloe against genotoxicity induced by benzo[a]pyrene

Chemopreventive effects of aloe against benzo[a]pyrene (BaP) mutagenicity were investigated in the Salmonella typhimurium bacterial mutation assay, the chromosome aberration assay using Chinese hamster ovary (CHO) cells, and the mouse micronuclei test using bone-marrow cells. In the bacterial assay, aloe produced a concentration-dependent decrease in the number of mutant colonies induced by BaP. The chromosome-damaging responses of BaP in CHO cells were abolished by treatment with aloe, approximately to the level seen in control. In the in vivo mouse bone-marrow micronuclei test, pretreatment of aloe 24 h prior to BaP treatment reduced the frequency of micronucleated polychromatic erythrocytes. In the cells of CHO and bone marrow treated with aloe, glutathione (GSH) levels were shown to be higher and extracellular discharge rate increased as incubation time with aloe rose. MDR1 and MRP2 gene were more expressed in Hepa c cells than in NTCC cells, but there was no change in BCRP gene expression. The antimutagenic effects of aloe were statistically significant and concentration dependent. These results demonstrated that aloe might exert chemopreventive effects against BaP-induced mutagenicity.

Effects of benzo(a)pyrene on protein expression in Jurkat T-cells

Polycyclic aromatic hydrocarbons (PAHs) are ubiquitous environmental pollutants of air, water and soil, and are produced by the incomplete combustion of organic materials. The International Agency for Research on Cancer has characterized PAHs as carcinogens. In this study, we investigated the effects of benzo(a)pyrene (B(a)P), which is the most carcinogenic member of the PAHs, on Jurkat cell protein by proteomic analysis. Jurkat cells were treated with various concentrations of B(a)P (0, 2.5, 5, 10, 20 or 40 microM) for 24 or 48 h and 3-(4,5-dimethylthiazol-2-yl)-5-(3-carboxymethoxyphenyl)-2-(4-sulfophenyl)-2H-tetrazolium and lactate dehydrogenase assays were carried out to determine cytotoxicity and a Comet assay was used to determinate genotoxicity. The cytotoxicity assays showed that 2.5 microM of B(a)P was the maximal concentration that did not cause any toxicity, but nevertheless, at this level B(a)P produced significant DNA damage in Jurkat cells at 48 h. Proteomic analysis using three different pI ranges and large two-dimensional gel electrophoresis showed 3427 protein spots. A total of 46 (13 up- and 33 down-regulated) proteins were identified as biomarkers of B(a)P and showed dose-dependent expressions in Jurkat T-cell line exposed to B(a)P. Of these, 27 protein spots were identified by matrix-assisted laser desorption/ionization-time of flight mass spectrometry. Two functionally differentiated protein groups were found. The protein group involving apoptosis and tumor suppression were found to be up-regulated, and B(a)P down-regulated enzyme was involved in energy metabolism, DNA synthesis and in cell structure and motility.

A proposed methodology of cancer risk assessment modeling using biomarkers

A methodology for cancer risk assessment modeling was developed using a biomarker of DNA adduct, exposure dose, and tumor response. DNA adducts in the blood and lung were measured after single or multiple administration of [3H]benzo[a]pyrene (1 x BaP) in ICR mice. Making the assumption that DNA adducts are formed in a dose-dependent manner as observed in 1 x BaP treatment, kinetics patterns of DNA adducts were predicted at two other hypothetical BaP doses (2 x BaP, 1/2 x BaP) for single and continuous BaP treatments because the difference between the simulated and the experimental kinetic responses only amounted to 5.49-5.86% in terms of the integrated area under the curve. Correlations between the formation of DNA adducts and exposure doses or between blood DNA and lung DNA adducts were determined to be linear. The dose-response relationship between biomarker and exposure dose was further incorporated into a dose-tumor response equation, obtained from 2-yr bioassay, to predict cancer risk. The interrelationships between exposure dose, biomarker, and tumor response allowed the prediction of cancer risk in animals, once the information on biomarker levels was obtained. Moreover, this methodology could be further applied to human cancer risk assessment after appropriate safety factors were employed.

Effects of pH and temperature on benzo[a]pyrene-DNA, -protein, and -lipid adducts in primary rat hepatocytes

The effects of pH and temperature on benzo[a]pyrene(BaP)-DNA, -protein, and -lipid adducts were compared in rat hepatocytes treated with [3H]-BaP. In primary rat hepatocytes, BaP-DNA, -protein, and -lipid adducts were formed in a concentration-dependent manner (0.31-2.80 mmol BaP), and the formation of BaP-lipid adducts, specifically triglyceride (TG) adducts, correlated well with that of DNA or protein adducts. As incubation time increased (1-24 h), the formation of DNA or protein adducts was also elevated, while BaP-TG adducts decreased after 3 h of reaction. pH had no effect on the formation of [3H]-BaP-DNA, and -protein adducts, and the TG adducts decreased with increasing pH (3.4-11.4). With an increase in incubation temperature (30-45 degrees C), on the other hand, the adduct formation was increased with increasing temperature up to 40 degrees C and then decreased sharply. These results suggest that the physicochemical properties of BaP-DNA, -protein, and -TG adducts might be important to consider when cells or humans who have been exposed to BaP are monitored for biomarkers.