Application of systematic evidence mapping to identify available data on the potential human health hazards of selected market-relevant azo dyes.

BACKGROUND: Azo dyes are used in textiles and leather clothing. Human exposure can occur from wearing textiles containing azo dyes. Since the body's enzymes and microbiome can cleave azo dyes, potentially resulting in mutagenic or carcinogenic metabolites, there is also an indirect health concern on the parent compounds. While several hazardous azo dyes are banned, many more are still in use that have not been evaluated systematically for potential health concerns. This systematic evidence map (SEM) aims to compile and categorize the available toxicological evidence on the potential human health risks of a set of 30 market-relevant azo dyes. METHODS: Peer-reviewed and gray literature was searched and over 20,000 studies were identified. These were filtered using Sciome Workbench for Interactive computer-Facilitated Text-mining (SWIFT) Review software with evidence stream tags (human, animal, in vitro) yielding 12,800 unique records. SWIFT Active (a machine-learning software) further facilitated title/abstract screening. DistillerSR software was used for additional title/abstract, full-text screening, and data extraction. RESULTS: 187 studies were identified that met populations, exposures, comparators, and outcomes (PECO) criteria. From this pool, 54 human, 78 animal, and 61 genotoxicity studies were extracted into a literature inventory. Toxicological evidence was abundant for three azo dyes (also used as food additives) and sparse for five of the remaining 27 compounds. Complementary search in ECHA's REACH database for summaries of unpublished study reports revealed evidence for all 30 dyes. The question arose of how this information can be fed into an SEM process. Proper identification of prioritized dyes from various databases (including U.S. EPA's CompTox Chemicals Dashboard) turned out to be a challenge. Evidence compiled by this SEM project can be evaluated for subsequent use in problem formulation efforts to inform potential regulatory needs and prepare for a more efficient and targeted evaluation in the future for human health assessments.

Systematic evidence map (SEM) template: Report format and methods used for the US EPA Integrated Risk Information System (IRIS) program, Provisional Peer Reviewed Toxicity Value (PPRTV) program, and other "fit for purpose" literature-based human health analyses.

BACKGROUND: Systematic evidence maps (SEMs) are gaining visibility in environmental health for their utility to serve as problem formulation tools and assist in decision-making, especially for priority setting. SEMs are now routinely prepared as part of the assessment development process for the US Environmental Protection Agency (EPA) Integrated Risk Information System (IRIS) and Provisional Peer Reviewed Toxicity Value (PPRTV) assessments. SEMs can also be prepared to explore the available literature for an individual chemical or groups of chemicals of emerging interest. OBJECTIVES: This document describes the typical methods used to produce SEMs for the IRIS and PPRTV Programs, as well as "fit for purpose" applications using a variety of examples drawn from existing analyses. It is intended to serve as an example base template that can be adapted as needed for the specific SEM. The presented methods include workflows intended to facilitate rapid production. The Populations, Exposures, Comparators and Outcomes (PECO) criteria are typically kept broad to identify mammalian animal bioassay and epidemiological studies that could be informative for human hazard identification. In addition, a variety of supplemental content is tracked, e.g., studies presenting information on in vitro model systems, non-mammalian model systems, exposure-level-only studies in humans, pharmacokinetic models, and absorption, distribution, metabolism, and excretion (ADME). The availability of New Approach Methods (NAMs) evidence is also tracked (e.g., high throughput, transcriptomic, in silico, etc.). Genotoxicity studies may be considered as PECO relevant or supplemental material, depending on the topic and context of the review. Standard systematic review practices (e.g., two independent reviewers per record) and specialized software applications are used to search and screen the literature and may include the use of machine learning software. Mammalian bioassay and epidemiological studies that meet the PECO criteria after full-text review are briefly summarized using structured web-based extraction forms with respect to study design and health system(s) assessed. Extracted data is available in interactive visual formats and can be downloaded in open access formats. Methods for conducting study evaluation are also presented which is conducted on a case-by-case basis, depending on the usage of the SEM.

Use of systematic evidence maps within the US environmental protection agency (EPA) integrated risk information system (IRIS) program: Advancements to date and looking ahead.

Systematic evidence maps (SEMs) are increasingly used to inform decision-making and risk management priority-setting and to serve as problem formulation tools to refine the focus of questions that get addressed in full systematic reviews. Within the U.S. Environmental Protection Agency (EPA) Office of Research and Development (ORD) Integrated Risk Information System (IRIS), SEMs have been used to inform data gaps, determine the need for updated assessments, inform assessment priorities, and inform development of study evaluation considerations, among other uses. Increased utilization of SEMs across the environmental health field has the potential to increase transparency and efficiency for data gathering, problem formulation, read-across, and evidence surveillance. Use of the SEM templates published in the companion text (Thayer et al.) can promote harmonization in the environmental health community and create more opportunities for sharing extracted content.

Application of systematic evidence mapping to assess the impact of new research when updating health reference values: A case example using acrolein.

BACKGROUND: The environmental health community needs transparent, methodologically rigorous, and rapid approaches for updating human health risk assessments. These assessments often contain reference values for cancer and/or noncancer effects. Increasingly, the use of systematic review methods are preferred when developing these assessments. Systematic evidence maps are a type of analysis that has the potential to be very helpful in the update process, especially when combined with machine-learning software advances designed to expedite the process of conducting a review. OBJECTIVES: To evaluate the applicability of evidence mapping to determine whether new evidence is likely to result in a change to an existing health reference value, using inhalation exposure to the air pollutant acrolein as a case example. METHODS: New literature published since the 2008 California Environmental Protection Agency's Office of Environmental Health Hazard Assessment (OEHHA) Reference Exposure Level (REL) for acrolein was assessed. Systematic review methods were used to search the literature and screening included the use of machine-learning software. The Populations, Exposures, Comparators and Outcomes (PECO) criteria were kept broad to identify studies that characterized acute and chronic exposure and could be informative for hazard characterization. Studies that met the PECO criteria after full-text review were briefly summarized before their suitability for chronic point of departure (POD) derivation and calculation of a reference value was considered. Studies considered potentially suitable underwent a targeted evaluation to determine their suitability for use in dose-response analysis. RESULTS: Over 15,000 studies were identified from scientific databases. Both machine-learning and manual screening processes were used to identify 60 studies considered PECO-relevant after full-text review. Most of these PECO-relevant studies were short-term exposure animal studies (acute or less than 1 month of exposure) and considered less suitable for deriving a chronic reference value when compared to the subchronic study in rats used in the 2008 OEHHA assessment. Thirteen epidemiological studies were identified but had limitations in the exposure assessment that made them less suitable for dose-response compared to the subchronic rat study. Among the 13 studies, there were four controlled trial studies that have the potential to be informative for future acute reference value derivation. Thus, the 2008 subchronic rat study used by OEHHA appears to still be the most appropriate study for chronic reference value derivation. In addition, advances in dosimetric modeling for gases, including new evidence pertinent to acrolein, could be considered when updating existing acrolein toxicity values. CONCLUSIONS: Evidence mapping is a very useful tool to assess the need for updating an assessment based on understanding the potential impact of new studies on revising an existing health reference value. In this case example, the focus was to identify studies suitable for chronic exposure dose-response analysis, while also identifying studies that may be important to consider for acute exposure scenarios, hazard identification, or for future research. This allows the evidence map to be a useful resource for a range of decision-making contexts. Specialized systematic review software increased the efficiency of the process in terms of human resources and time to conduct the analysis.

Assessment of Health Effects of Exogenous Urea: Summary and Key Findings.

PURPOSE OF REVIEW: Urea has been utilized as a reductant in diesel fuels to lower emission of nitrogen oxides, igniting interest in probable human health hazards associated with exposure to exogenous urea. Here, we summarize and update key findings on potential health effects of exogenous urea, including carcinogenicity. RECENT FINDINGS: No definitive target organs for oral exposure were identified; however, results in animal studies suggest that the liver and kidney could be potential target organs of urea toxicity. The available human-subject literature suggests that the impact on lung function is minimal. Based on the literature on exogenous urea, we concluded that there was inadequate information to assess the carcinogenic potential of urea, or perform a quantitative assessment to derive reference values. Given the limited information on exogenous urea, additional research to address gaps for exogenous urea should include long-term cancer bioassays, two-generation reproductive toxicity studies, and mode-of-action investigations.

Correlation between CYP1A1 transcript, protein level, enzyme activity and DNA adduct formation in normal human mammary epithelial cell strains exposed to benzo[a]pyrene.

The polycyclic aromatic hydrocarbon (PAH) benzo(a)pyrene (BP) is thought to bind covalently to DNA, through metabolism by cytochrome P450 1A1 (CYP1A1) and CYP1B1, and other enzymes, to form r7, t8, t9-trihydroxy-c-10-(N(2)-deoxyguanosyl)-7,8,9,10-tetrahydro-benzo[a]-pyrene (BPdG). Evaluation of RNA expression data, to understand the contribution of different metabolic enzymes to BPdG formation, is typically presented as fold-change observed upon BP exposure, leaving the actual number of RNA transcripts unknown. Here, we have quantified RNA copies/ng cDNA (RNA cpn) for CYP1A1 and CYP1B1, as well as NAD(P)H: quinone oxidoreductase 1 (NQO1), which may reduce formation of BPdG adducts, using primary normal human mammary epithelial cell (NHMEC) strains, and the MCF-7 breast cancer cell line. In unexposed NHMECs, basal RNA cpn values were 58-836 for CYP1A1, 336-5587 for CYP1B1 and 5943-40112 for NQO1. In cells exposed to 4.0 µM BP for 12h, RNA cpn values were 251-13234 for CYP1A1, 4133-57078 for CYP1B1 and 4456-55887 for NQO1. There were 3.5 (mean, range 0.2-15.8) BPdG adducts/10(8) nucleotides in the NHMECs (n = 16), and 790 in the MCF-7s. In the NHMECs, BP-induced CYP1A1 RNA cpn was highly associated with BPdG (P = 0.002), but CYP1B1 and NQO1 were not. Western blots of four NHMEC strains, chosen for different levels of BPdG adducts, showed a linear correlation between BPdG and CYP1A1, but not CYP1B1 or NQO1. Ethoxyresorufin-O-deethylase (EROD) activity, which measures CYP1A1 and CYP1B1 together, correlated with BPdG, but NQO1 activity did not. Despite more numerous levels of CYP1B1 and NQO1 RNA cpn in unexposed and BP-exposed NHMECs and MCF-7cells, BPdG formation was only correlated with induction of CYP1A1 RNA cpn. The higher level of BPdG in MCF-7 cells, compared to NHMECs, may have been due to a much increased induction of CYP1A1 and EROD. Overall, BPdG correlation was observed with CYP1A1 protein and CYP1A1/1B1 enzyme activity, but not with CYP1B1 or NQO1 protein, or NQO1 enzyme activity.

Use of genomic data in risk assessment case study: II. Evaluation of the dibutyl phthalate toxicogenomic data set.

An evaluation of the toxicogenomic data set for dibutyl phthalate (DBP) and male reproductive developmental effects was performed as part of a larger case study to test an approach for incorporating genomic data in risk assessment. The DBP toxicogenomic data set is composed of nine in vivo studies from the published literature that exposed rats to DBP during gestation and evaluated gene expression changes in testes or Wolffian ducts of male fetuses. The exercise focused on qualitative evaluation, based on a lack of available dose-response data, of the DBP toxicogenomic data set to postulate modes and mechanisms of action for the male reproductive developmental outcomes, which occur in the lower dose range. A weight-of-evidence evaluation was performed on the eight DBP toxicogenomic studies of the rat testis at the gene and pathway levels. The results showed relatively strong evidence of DBP-induced downregulation of genes in the steroidogenesis pathway and lipid/sterol/cholesterol transport pathway as well as effects on immediate early gene/growth/differentiation, transcription, peroxisome proliferator-activated receptor signaling and apoptosis pathways in the testis. Since two established modes of action (MOAs), reduced fetal testicular testosterone production and Insl3 gene expression, explain some but not all of the testis effects observed in rats after in utero DBP exposure, other MOAs are likely to be operative. A reanalysis of one DBP microarray study identified additional pathways within cell signaling, metabolism, hormone, disease, and cell adhesion biological processes. These putative new pathways may be associated with DBP effects on the testes that are currently unexplained. This case study on DBP identified data gaps and research needs for the use of toxicogenomic data in risk assessment. Furthermore, this study demonstrated an approach for evaluating toxicogenomic data in human health risk assessment that could be applied to future chemicals.

CYP1A1 and CYP1B1 gene expression and DNA adduct formation in normal human mammary epithelial cells exposed to benzo[a]pyrene in the absence or presence of chlorophyllin.

Benzo[a]pyrene (BP) is a potent pro-carcinogen and ubiquitous environmental pollutant. Here, we examined the induction and modulation of CYP1A1 and CYP1B1 and 10-(deoxyguanosin-N(2)-yl)-7,8,9-trihydroxy-7,8,9,10-tetrahydrobenzo[a]pyrene (BPdG) adduct formation in DNA from 20 primary normal human mammary epithelial cell (NHMEC) strains exposed to BP (4muM) in the absence or presence of chlorophyllin (5muM). Real-time polymerase chain reaction (RT-PCR) analysis revealed strong induction of both CYP1A1 and CYP1B1 by BP, with high levels of inter-individual variability. Variable BPdG formation was found in all strains by r7, t8-dihydroxy-t-9, 10 epoxy-7,8,9,10-tetrahydrobenzo[a]pyrene (BPDE)-DNA chemiluminescence assay (CIA). Chlorophyllin mitigated BP-induced CYP1A1 and CYP1B1 gene expression in all 20 strains when administered with BP. Chlorophyllin, administered prior to BP-exposure, mitigated CYP1A1 expression in 18/20 NHMEC strains (p<0.005) and CYP1B1 expression in 17/20 NHMEC strains (p<0.005). Maximum percent reductions of CYP1A1 and CYP1B1 gene expression and BPdG adduct formation were observed when cells were pre-dosed with chlorophyllin followed by administration of the carcinogen with chlorophyllin (p<0.005 for CYP1A1 and CYP1B1 expression and p<0.0005 for BPdG adducts). Therefore, chlorophyllin is likely to be a good chemoprotective agent for a large proportion of the human population.

Immune response signatures of benzo{alpha}pyrene exposure in normal human mammary epithelial cells in the absence or presence of chlorophyllin.

Carcinogenic polycylic aromatic hydrocarbons can alter immune responses. Changes in immune response gene expression profiles in multiple human mammary cell strains exposed to benzo(alpha)pyrene (BP) (4 microM) in vitro, in the presence or absence of chlorophyllin (5 microM), were observed using Affymetrix gene arrays. Expressions of five immune response genes were altered ~3.0-fold by BP exposure and 24 genes by BP in the presence chlorophyllin. In silico pathway analysis revealed altered immune response genes form interactive gene networks with many cellular processes, suggesting their role in a complex multigenic response to toxins. Additionally, it was suggestive of the possible immunomodulatory potential of chlorophyllin apart from various other well-documented mechanisms of action. Gene expression matrices revealed consistent alteration patterns involving IL1B, SECTM1 and CXCL14 on exposure to BP, and IL1RN, CD86, IF144 and GIP2 in the presence of chlorophyllin and BP, suggesting some of these genes might constitute putative immune response biomarkers of PAH exposure. This study has therefore identified a battery of potential immune response biomarkers of PAH exposure, amidst several genes, for future validation studies.

Chlorophyllin significantly reduces benzo[a]pyrene-DNA adduct formation and alters cytochrome P450 1A1 and 1B1 expression and EROD activity in normal human mammary epithelial cells.

We hypothesized that chlorophyllin (CHLN) would reduce benzo[a]pyrene-DNA (BP-DNA) adduct levels. Using normal human mammary epithelial cells (NHMECs) exposed to 4 microM BP for 24 hr in the presence or absence of 5 microM CHLN, we measured BP-DNA adducts by chemiluminescence immunoassay (CIA). The protocol included the following experimental groups: BP alone, BP given simultaneously with CHLN (BP+CHLN) for 24 hr, CHLN given for 24 hr followed by BP for 24 hr (preCHLN, postBP), and CHLN given for 48 hr with BP added for the last 24 hr (preCHLN, postBP+CHLN). Incubation with CHLN decreased BPdG levels in all groups, with 87% inhibition in the preCHLN, postBP+CHLN group. To examine metabolic mechanisms, we monitored expression by Affymetrix microarray (U133A), and found BP-induced up-regulation of CYP1A1 and CYP1B1 expression, as well as up-regulation of groups of interferon-inducible, inflammation and signal transduction genes. Incubation of cells with CHLN and BP in any combination decreased expression of many of these genes. Using reverse transcription real time PCR (RT-PCR) the maximal inhibition of BP-induced gene expression, >85% for CYP1A1 and >70% for CYP1B1, was observed in the preCHLN, postBP+CHLN group. To explore the relationship between transcription and enzyme activity, the ethoxyresorufin-O-deethylase (EROD) assay was used to measure the combined CYP1A1 and CYP1B1 activities. BP exposure caused the EROD levels to double, when compared with the unexposed controls. The CHLN-exposed groups all showed EROD levels similar to the unexposed controls. Therefore, the addition of CHLN to BP-exposed cells reduced BPdG formation and CYP1A1 and CYP1B1 expression, but EROD activity was not significantly reduced.

Transcriptional profiles of benzo(a)pyrene exposure in normal human mammary epithelial cells in the absence or presence of chlorophyllin.

Benzo(a)pyrene (BP) exposure causes alterations in gene expression in normal human mammary epithelial cells (NHMECs). This study used Affymetrix Hu-Gene133A arrays, with 14,500 genes represented, to evaluate modulation of BP-induced gene expression by chlorophyllin in six NHMEC strains derived from different donors. A major goal was to seek potential biomarkers of carcinogen exposure and how they behave in the presence of a chemopreventive agent. NHMECs (passage 6 and 70% confluence) were exposed for 24h to either vehicle control, or BP, or chlorophyllin followed by BP and chlorophyllin together. BP exposure resulted in approximately 3-fold altered expression of 49 genes in at least one of the six NHMEC strains. When cells were exposed to chlorophyllin pre-treatment followed by BP plus chlorophyllin, expression of 125 genes was similarly altered. Genes in the functional categories of xenobiotic metabolism, cell signaling, cell motility, cell proliferation, cellular transcription, metabolism, cell cycle control, apoptosis and DNA repair were identified. Only CYP1B1 and ALDH1A3 were consistently up-regulated by approximately 3-fold in most of the cell strains (at least 4) when exposed to BP. Cluster analysis identified a suite of 13 genes induced by BP where induction was mitigated in the presence of chlorophyllin. Additionally, cluster analysis identified a suite of 16 genes down-regulated by BP where induction was partially restored in the presence of chlorophyllin.

An evaluation of the mode of action framework for mutagenic carcinogens case study: Cyclophosphamide.

In response to the 2005 revised US Environmental Protection Agency (EPA) Cancer Guidelines, a Risk Assessment Forum's Technical Panel has devised a strategy in which genetic toxicology data combined with other information are assessed to determine whether a carcinogen operates through a mutagenic mode of action (MOA). This information is necessary for EPA to decide whether age-dependent adjustment factors (ADAFs) should be applied to the cancer risk assessment. A decision tree has been developed as a part of this approach and outlines the critical steps for analyzing a compound for carcinogenicity through a mutagenic MOA (e.g., data analysis, determination of mutagenicity in animals and in humans). Agents, showing mutagenicity in animals and humans, proceed through the Agency's framework analysis for MOAs. Cyclophosphamide (CP), an antineoplastic agent, which is carcinogenic in animals and humans and mutagenic in vitro and in vivo, was selected as a case study to illustrate how the framework analysis would be applied to prove that a carcinogen operates through a mutagenic MOA. Consistent positive results have been seen for mutagenic activity in numerous in vitro assays, in animals (mice, rats, and hamsters) and in humans. Accordingly, CP was processed through the framework analysis and key steps leading to tumor formation were identified as follows: metabolism of the parent compound to alkylating metabolites, DNA damage followed by induction of multiple adverse genetic events, cell proliferation, and bladder tumors. Genetic changes in rats (sister chromatid exchanges at 0.62 mg/kg) can commence within 30 min and in cancer patients, chromosome aberrations at 35 mg/kg are seen by 1 hr, well within the timeframe and tumorigenic dose range for early events. Supporting evidence is also found for cell proliferation, indicating that mutagenicity, associated with cytotoxicity, leads to a proliferative response, which occurs early (48 hr) in the process of tumor induction. Overall, the weight of evidence evaluation supports CP acting through a mutagenic MOA. In addition, no data were found that an alternative MOA might be operative. Therefore, the cancer guidelines recommend a linear extrapolation for the risk assessment. Additionally, data exist showing that CP induces mutagenicity in fetal blood and in the peripheral blood of pediatric patients; thus, the ADAFs would be applied.

Reduction in tamoxifen-induced CYP3A2 expression and DNA adducts using antisense technology.

Tamoxifen (TAM) is widely used in the treatment and prevention of breast cancer. There is clear evidence that cytochrome P450 (CYP) 3A enzymes play an important role in TAM metabolism, resulting in metabolites that lead to formation of TAM-DNA adducts. We have investigated the effect of CYP3A2 antisense (AVI-4472) exposure on CYP3A2 transcription, enzyme activity, translation, and TAM-DNA adducts, in livers of rats administered TAM (50 mg/kg body weight [bw]/day) for 7 days. The study design included administration of 0, 0.5, 2.5, or 12.5 mg AVI-4472/kg bw/day for 8 days, beginning 1 day before TAM exposure. The specific activity of CYP3A2 was increased after TAM administration, and decreased significantly (approximately 70%) in the presence of 12.5 mg AVI-4472. CYP3A2 protein levels, determined by immunoblot analysis, showed a similar pattern. Hepatic TAM-DNA adduct levels were measurable in all TAM-exposed groups. However, when rats were co-treated with 2.5 and 12.5 mg AVI-4472/kg bw/day, statistically significant (approximately 50%) reductions in TAM-DNA adduct levels (2.0-2.8 adducts/10(8) nucleotides) were observed compared to rats treated with TAM alone (5.1 adducts/10(8) nucleotides). Rat toxicology U34 arrays (Affymetrix) were used to investigate the modulation of gene expression patterns on co-administration of TAM with AVI-4472. Results indicated that several CYP genes were down regulated although no significant induction of CYP3A2 was observed in the TAM-exposed rats co-treated with AVI-4472. Overall the data suggest the utility of antisense technology in the redirection of TAM metabolism thereby lowering TAM genotoxicity in rat liver.

Transcriptional signatures of environmentally relevant exposures in normal human mammary epithelial cells: benzo[a]pyrene.

Changes in gene expression in a panel of primary normal human mammary epithelial cell strains, developed from healthy breast tissue obtained at reduction mammoplasty from different donors, in response to benzo[a]pyrene exposure have been investigated. It was expected that both gene expression changes common to cell strains derived from different donors as well as inter-individual variation would be observed. Therefore, the strategy that has been adopted is to identify potentially important changes, or useful changes from a biomonitoring perspective, using gene-array technology and a small number of donors; then investigate selected transcription responses using a large number of tissue donors and a cheaper method of transcript detection (real-time polymerase chain reaction). Here we report results from four primary normal human mammary epithelial cell strains that were treated with benzo[a]pyrene in vitro for either 6 or 24 h. Transcription was monitored using high-density oligonucleotide arrays (Affymetrix HuGeneFL). Total RNA was used for the preparation of labeled targets that were hybridized to microarrays containing probes representing more than 6800 human genes and expressed sequence tags. Gene expression data were analyzed using the GeneChip software (MAS 5.0). Altered gene expression patterns were observed in response to benzo[a]pyrene in human mammary epithelial cell strains from different donors. Specifically, the dioxin inducible cytochrome P450 CYP1B1 was consistently induced in response to 6 and 24 h exposure to benzo[a]pyrene in cell strains from all four donors. Two other genes that were relatively consistently induced were IL1beta and MMP1. Less consistent changes in other metabolism genes (CYP1A1, CYP11B2, and NQO1) and certain cell cycle control genes GOS2 and AF1Q were also induced, while EGR1 was suppressed. Although no change in p53 transcription was observed, an accumulation of p53 protein was detected using antibodies. A similar accumulation of Waf1 (p21) was also observed using immunohistochemistry, this was expected since p53 is p21's transcription factor. Significant inter-individual variations in both the levels and patterns of gene expression were observed, in response to benzo[a]pyrene exposure. These studies provide a complementary approach to molecular epidemiology for the investigation of differential susceptibility to chemical carcinogens, and specifically polycyclic aromatic hydrocarbons.

Induction of CYP1A1 and CYP1B1 and formation of carcinogen-DNA adducts in normal human mammary epithelial cells treated with benzo[a]pyrene.

Inter-individual variation in formation of carcinogen-DNA adducts and induction of cytochrome P450 genes was measured in 23 cultured normal human mammary epithelial cell (NHMEC) strains established from reduction mammoplasty tissue. Semi-confluent cells were exposed to 4 microM benzo[a]pyrene (BP) for 12 h and BP-DNA adduct levels were measured by chemiluminescence immunoassay using antiserum elicited against DNA modified with r7, t8-dihydroxy-t-9, 10-epoxy-7,8,9,10-tetrahydrobenzo[a]pyrene (BPDE). BP-DNA adduct levels for 22 of 23 different cell strains ranged from non-detectable (three samples) to about 15 adducts/10(8) nucleotides. Increases in levels of CYP1A1 and CYP1B1 were detected using both oligonucleotide arrays and reverse transcription/quantitative real-time polymerase chain reactions (RT-PCRs). For CYP1A1 and CYP1B1, the oligonucleotide array data and RT-PCR data were highly correlated (r=0.73 and 0.70, respectively), suggesting that oligonucleotide arrays are a suitable gene discovery tool, and demonstrating that the complementary and efficient RT-PCR may be used to confirm microarray data for a specific gene in a large number of samples. As measured by RT-PCR, inter-individual variation in CYP1A1 induction was 100-fold, while the variation in CYP1B1 induction was almost 40-fold. On a per-person basis, CYP1A1 and CYP1B1 induction were well-correlated (r=0.88, P<0.001), which is to be expected as they are under the control of a common transcriptional regulation mechanism in response to BP exposure. Inter-individual variation in carcinogen-DNA adduct formation could not be explained only by variation in levels of CYP1A1 or CYP1B1 induction, as neither was well-correlated with BPDE-DNA adduct level (r=0.40 and 0.50 for CYP1A1 and CYP1B1, respectively). Evaluation of glutathione-S-transferase M1 genotype (GSTM1 positive or null) revealed an apparent correlation between positive GSTM1 genotype and BPDE-DNA adduct levels (r=0.84 and 0.77 for CYP1A1 and CYP1B1, respectively); however, after removal of the single outlier this relationship was not significant. Overall the data suggest that BPDE-DNA adduct levels in normal human breast tissue may be modulated by multiple factors that include, but are not exclusive to, CYP1A1 and CYP1B1 inducibility and the presence or absence of GSTM1.

Altered gene expression patterns in MCF-7 cells induced by the urban dust particulate complex mixture standard reference material 1649a.

Human exposures to polycyclic aromatic hydrocarbon (PAH) occur in complex mixtures. Here, gene expression patterns were investigated using standard reference material (SRM) 1649a (urban dust). MCF-7 cells were exposed to SRM 1649a alone or SRM 1649a with either benzo[a]pyrene (BP) or dibenzo[a,l]pyrene (DBP) for 24 hours. Global analyses of the gene expression data revealed alterations of 41 RNA transcripts with at least 2-fold change (signal log ratio /= 1) in response to SRM 1649a exposure. Increase in expression of cytochrome P450 (CYP) genes was observed in response to BP exposure (CYP1A1 and CYP1B1; signal log ratio of 4.7 and 2.5, respectively). An additive induction of CYP1A1 and CYP1B1 was observed with cotreatment of SRM 1649a and BP. On the contrary, no change in gene expression of CYP1A1 and CYP1B1 was observed when the cells were exposed to DBP. Furthermore, to study the effect of complex PAH mixtures on the metabolic activation of carcinogenic PAH to DNA-binding derivatives and to relate this with gene expression studies, PAH-DNA adduct formation was determined. SRM 1649a decreased the total level of BP-DNA adducts in comparison with BP alone. No significant difference in adduct levels was observed in response to either DBP alone or in combination with SRM 1649a. These results provide a transcriptional signature for chemical carcinogen exposure; in addition, they suggest a major factor in carcinogenic activity of PAH within complex mixtures is their ability to promote or inhibit the activation of carcinogenic PAH by the induction of CYP enzymes.

Effects of suberoylanilide hydroxamic acid and trichostatin A on induction of cytochrome P450 enzymes and benzo[a]pyrene DNA adduct formation in human cells.

In this study, we investigated the effects of histone deacetylase (HDAC) inhibitors suberoylanilide hydroxamic acid (SAHA) and trichostatin A (TSA) on the metabolism of polycyclic aromatic hydrocarbons (PAH) in human mammary carcinoma derived MCF-7 cells in culture. Benzo[a]pyrene (B[a]P) induces cytochrome P450 (CYP) 1A1, CYP1B1 and other xenobiotic metabolizing enzymes. Results from our study indicated a significant increase in CYP activity in comparison to vehicle control in cells treated with SAHA or TSA as measured by ethoxyresorufin-O-deethylase assay. However, co-treatment with 1.0 microM SAHA and BP, reduced the mRNA levels of CYP1B1 relative to B[a]P alone. When co-treated with 1.0 microM TSA and BP, a reduction in the mRNA levels of both CYP1A1 and CYP1B1 was observed relative to BP alone. We further investigated to ascertain if the differential expression and activity of CYP1A1 and CYP1B1 influenced levels of B[a]P DNA adduct formation. MCF-7 cells co-treated with B[a]P and SAHA or TSA formed DNA adducts, although no significant differences in levels of DNA binding were revealed. These results suggest that while CYP enzyme activity and gene expression were affected by the HDAC inhibitors SAHA and TSA, they had no apparent influence on B[a]P DNA binding.

Transcriptional signatures of normal human mammary epithelial cells in response to benzo[a]pyrene exposure: a comparison of three microarray platforms.

Microarrays are used to study gene expression in a variety of biological systems. A number of different platforms have been developed, but few studies exist that have directly compared the performance of one platform with another. The goal of this study was to determine array variation by analyzing the same RNA samples with three different array platforms. Using gene expression responses to benzo[a]pyrene exposure in normal human mammary epithelial cells (NHMECs), we compared the results of gene expression profiling using three microarray platforms: photolithographic oligonucleotide arrays (Affymetrix), spotted oligonucleotide arrays (Amersham), and spotted cDNA arrays (NCI). While most previous reports comparing microarrays have analyzed pre-existing data from different platforms, this comparison study used the same sample assayed on all three platforms, allowing for analysis of variation from each array platform. In general, poor correlation was found with corresponding measurements from each platform. Each platform yielded different gene expression profiles, suggesting that while microarray analysis is a useful discovery tool, further validation is needed to extrapolate results for broad use of the data. Also, microarray variability needs to be taken into consideration, not only in the data analysis but also in specific probe selection for each array type.

CYP3A4 polymorphisms--potential risk factors for breast and prostate cancer: a HuGE review.

The steroid hydroxylase CYP3A4 is the most abundant P-450 enzyme in the human liver, and CYP3A enzymes metabolize more than 50% of prescription drugs. The CYP3A4 gene is expressed in the liver, gut, colon, prostate, and breast. Individual variation in CYP3A4 may play a role in breast and prostate carcinogenesis through modulation of sex hormone metabolite levels. Alternatively, CYP3A4 can metabolically activate exogenous carcinogens. CYP3A4 activity varies widely in humans, and more than 78 DNA sequence polymorphisms are known. These observations prompted the hypothesis that variant CYP3A4 may be involved in breast and prostate cancer. Two epidemiologic studies of breast cancer and five of prostate cancer examined CYP3A4 genotypes. A US study showed that inheritance of CYP3A4*1B correlates with early menarche, a breast cancer risk factor. However, an Australian breast cancer case-control study found no association with CYP3A4*1B. Two Scottish prospective studies showed CYP3A4*1B to be a risk factor for prostate cancer among men with benign prostatic hyperplasia. Three other studies were undertaken in the United States: two were case-only studies and the other was a case-sibling control study. Although results for African Americans were inconsistent, these studies suggested that CYP3A4*1B was associated with markers of advanced disease. These observations support the notion that development of robust, conventional molecular epidemiologic case-control studies to address these questions, including gene-gene and gene-environment interactions, will be timely.