Epigenetics of breast cancer: polycyclic aromatic hydrocarbons as risk factors

Cellular accumulation of crude oil compounds reduces the competitive fitness of the coral symbiont Symbiodinium glynnii

Oil spill events in the marine environment can have a deleterious impact on the affected ecosystems, such as coral reefs, with direct consequences for their socioeconomic value. The mutualistic relationship between tropical corals and their dinoflagellate symbionts (Symbiodiniaceae) provide structural and nutritional basis for a high local biodiversity in oligotrophic waters. Here, we investigated effects of crude oil water-accommodated fraction on the competitive fitness of the model zooxanthellae species Symbiodinium glynnii. Results of laboratory essays demonstrate that crude oil carbon is incorporated into the cellular biomass with a concomitant change of δ¹³C isotopic value. Carcinogenic/mutagenic polycyclic aromatic hydrocarbons were identified in the culture media and were responsible for a linear reduction in population growth of S. glynnii, presumably related to energy relocation for DNA repair. Additionally, the experiments revealed that physiological effects induced by crude oil compounds are genetically inherited by the following generations under non-contaminated growth conditions, and induce a reduction in the competitive fitness to cope with other environmental parameters, such as low salinity. We suggest that the effects of crude oil contamination represent an imparing factor for S. glynnii coping with anthropogenic drivers (e.g. warming and acidification) and interfere with the delicate symbiont-host relationship of tropical corals. This is especially relevant in the coastal areas of northeastern Brazil where an oil spill event deposited crude oil on shallow water sediments with the potential to be resuspended to the water column by physical and/or biological activity, enhancing the risk of future coral bleaching events.

Aryl Hydrocarbon Receptor and Its Diverse Ligands and Functions: An Exposome Receptor

The aryl hydrocarbon receptor (AhR) is a transcriptional factor that regulates multiple functions following its activation by a variety of ligands, including xenobiotics, natural products, microbiome metabolites, and endogenous molecules. Because of this diversity, the AhR constitutes an exposome receptor. One of its main functions is to regulate several lines of defense against chemical insults and bacterial infections. Indeed, in addition to its well-established detoxication function, it has several functions at physiological barriers, and it plays a critical role in immunomodulation. The AhR is also involved in the development of several organs and their homeostatic maintenance. Its activity depends on the type of ligand and on the time frame of the receptor activation, which can be either sustained or transient, leading in some cases to opposite modes of regulations as illustrated in the regulation of different cancer pathways. The development of selective modulators and their pharmacological characterization are important areas of research. Expected final online publication date for the Annual Review of Pharmacology and Toxicology, Volume 62 is January 2022. Please see http://www.annualreviews.org/page/journal/pubdates for revised estimates.

Research progress on the association between environmental pollutants and the resistance mechanism of PARP inhibitors in ovarian cancer

The occurrence and progression of ovarian cancer are closely related to genetics and environmental pollutants. Poly(ADP-ribose) polymerase (PARP) inhibitors have been a major breakthrough in the history of ovarian cancer treatment. PARP is an enzyme responsible for post-translational modification of proteins and repair of single-stranded DNA damage. PARP inhibitors can selectively inhibit PARP function, resulting in a synthetic lethal effect on tumor cells defective in homologous recombination repair. However, with large-scale application, drug resistance also inevitably appears. For PARP inhibitors, the diversity and complexity of drug resistance mechanisms have always been difficult problems in clinical treatment. Herein, we mainly summarized the research progress of DNA damage repair and drug resistance mechanisms related to PARP inhibitors and the impact of environmental pollutants on DNA damage repair to aid the development prospects and highlight urgent problems to be solved.

Bone Disruption and Environmental Pollutants

BACKGROUND

Endocrine Disrupting Chemicals (EDCs) are ubiquitous and may significantly contribute in environmental pollution, thus contaminating humans and wildlife. Environmental pollutants could interfere with bone homeostasis by means of different mechanisms, which include hormonal imbalance, direct osteoblasts toxicity and enanchment of osteoclasts activity, thus leading to osteopenia or osteoporosis. Among these, bisphenols, dioxins, polycyclic aromatic hydrocarbons, polychlorobiphenyls, poly- and perfluoroalkyls, phthalates, parabens, organotins and cadmium may play a role in bone distuption.

METHODS

PubMed/MEDLINE, ISI-web of knowledge and Google scholar databases were searched for medical subject headings terms and free-text word related to the aforementioned classes of chemicals and bone metabolism and remodelling for better clarifying and understanding the main mechanisms of bone disruption.

RESULTS

Several of EDCs act as xenoestrogens. Considering that estrogens play a significant role in regulating bone remodeling, most of these chemicals generate hormonal imbalance with possible detrimental consequences on bone tissue structure and its mechanical and non-mechanical properties.

DISCUSSION

A lot of evidences about bone distruptors came from in vitro studies or animal models, and conduct to equivocal results. In addition, a few data derived form humans and most of these data focused on the impact of EDCs on bone mineral density without considering their influence on long-term fracture risk. Moreover, it should be taken into account that humans are exposed to a mixture of EDCs and the final effect on bone metabolism might be the result of either a synergism or antagonist effects among them. Age of first exposure, cumulative dose exposure over time, and the usually observed non-monotonic dose-response curve for EDCs should be considered as other important variable influencing the final effect on bone metabolism.

CONCLUSION

Taking into account these variables, observational studies are needed to better analyze this issue both for echological purpose and to preserve bone health.

Elevated exposure to polycyclic aromatic hydrocarbons (PAHs) may trigger cancers in Pakistan: an environmental, occupational, and genetic perspective

Polycyclic aromatic hydrocarbons (PAHs) are carcinogenic compounds which are emitted through incomplete combustion of organic materials, fossil fuels, consumption of processed meat, smoked food, and from various industrial activities. High molecular mass and mobility make PAHs widespread and lethal for human health. A cellular system in human detoxifies these toxicants through specialized enzymatic machinery called xenobiotic-metabolizing (CYP450) and phase-II (GSTs) enzymes (XMEs). These metabolizing enzymes include cytochromes P450 family (CYP1, CYP2), glutathione s-transferases, and ALDHs. Gene polymorphisms in XMEs encoding genes can compromise their metabolizing capacity to detoxify ingested carcinogens (PAHs etc.) that may lead to prolong and elevated exposure to ingested toxicants and may consequently lead to cancer. Moreover, PAHs can induce cancer through reprograming XMEs' gene functions by altering their epigenetic markers. This review article discusses possible interplay between individual's gene polymorphism in XMEs' genes, their altered epigenetic markers, and exposure to PAHs in cancer susceptibility in Pakistan.

Consumption of reused vegetable oil intensifies BRCA1 mutations

Breast cancer (BC) is a foremost type of cancer in women globally with an increased mortality rate in developing countries. Information regarding hereditary factors, lifestyle, work environment, food habits, and personal history could be useful in diagnosing breast cancer. Among such food habits, the reuse of edible oil for preparing food is a common practice in any developing country. The repeated heating of oils enhances the oxidative degradation of oil to produce polyaromatic hydrocarbons (PAH) which could disrupt the redox balance and generate reactive oxygen species. These reactive toxic intermediates can lead to BRCA1 mutations that are responsible for breast cancer. Mutations in DNA are the main cause for the conversion of proto-oncogenes into oncogenes which leads to change in expression and an increase in cell proliferation wherein a normal cell gets transformed into a malignant neoplastic cell. This review summarizes the possible mechanism involved in the induction of breast cancer due to repeated heating of edible.

An urban-rural and sex differences in cancer incidence and mortality and the relationship with PM2.5 exposure: An ecological study in the southeastern side of Hu line

This study investigates the urban-rural and sex differences in the increased risks of the ten most common cancers in China related to high PM_2.5 concentration in the southeastern side of Hu line. Pearson correlation coefficient is estimated to reveal how the cancers closely associated with PM_2.5 long-term exposure. Then linear regression is conducted to evaluate sex- and area-specific increased risks of those cancers from high level PM_2.5 long-term exposure. The major finding is with the increase of every 10 μg/m³ of annual mean PM_2.5 concentration, the increase of relative risks for lung cancer incidence and mortality are 15% and 23% for males, and 22% and 24% for females in rural area. For urban area, the increase of relative risk for ovarian cancer incidence is 9% for females, while that for prostatic cancer increases 17% for males. For leukemia, the increase of relative risks for incidence and mortality are 22% and 19% for females in rural area, while in urban area the increase of relative risk for mortality is 9% for males and for incidence is 6% for females. It is also found that with increased PM_2.5 exposure, the risks for ovarian and prostatic cancer rise significantly in urban area, while risks for lung cancer and leukemia rise significantly in rural area. The results demonstrate the higher risks for lung cancer and leukemia with increased PM_2.5 exposure are more significant for female. This study also suggests that the carcinogenic effects of PM_2.5 have obvious sex and urban-rural differences.

Breast cancer family history and allele-specific DNA methylation in the legacy girls study

Family history, a well-established risk factor for breast cancer, can have both genetic and environmental contributions. Shared environment in families as well as epigenetic changes that also may be influenced by shared genetics and environment may also explain familial clustering of cancers. Epigenetic regulation, such as DNA methylation, can change the activity of a DNA segment without a change in the sequence; environmental exposures experienced across the life course can induce such changes. However, genetic-epigenetic interactions, detected as methylation quantitative trait loci (mQTLs; a.k.a. meQTLs) and haplotype-dependent allele-specific methylation (hap-ASM), can also contribute to inter-individual differences in DNA methylation patterns. To identify differentially methylated regions (DMRs) associated with breast cancer susceptibility, we examined differences in white blood cell DNA methylation in 29 candidate genes in 426 girls (ages 6-13 years) from the LEGACY Girls Study, 239 with and 187 without a breast cancer family history (BCFH). We measured methylation by targeted massively parallel bisulfite sequencing (bis-seq) and observed BCFH DMRs in two genes: ESR1 (Δ4.9%, P = 0.003) and SEC16B (Δ3.6%, P = 0.026), each of which has been previously implicated in breast cancer susceptibility and pubertal development. These DMRs showed high inter-individual variability in methylation, suggesting the presence of mQTLs/hap-ASM. Using single nucleotide polymorphisms data in the bis-seq amplicon, we found strong hap-ASM in SEC16B (with allele specific-differences ranging from 42% to 74%). These findings suggest that differential methylation in genes relevant to breast cancer susceptibility may be present early in life, and that inherited genetic factors underlie some of these epigenetic differences.

Oil spill off the coast of Guimaras Island, Philippines: Distributions and changes of polycyclic aromatic hydrocarbons in shellfish

The sinking of the Solar 1 tanker caused serious heavy oil pollution around Guimaras Island, Philippines. In the present study, variations of parent polycyclic aromatic hydrocarbons (PAHs) and alkylated PAHs (alkPAHs) in some shellfish were investigated around Guimaras Island and other small islands from 3months to 5years after the spill. The total PAHs and alkPAHs in shellfish were detected in high concentrations at 448 and 33,666ng/g dry weight, respectively, in November 2006. The concentrations of alkPAHs gradually decreased, while the parent PAHs in shellfish degraded more slowly than the alkPAHs, which was likely due to the persistent characteristics of PAHs. The risks based on European Union regulations were insignificant in 2008, but total PAHs in shellfish were still over 8 times higher at the investigated sites in November 2011 than that before the oil spill.

Geographic variations in female breast cancer incidence in relation to ambient air emissions of polycyclic aromatic hydrocarbons

A significant geographic variation of breast cancer incidence exists, with incidence rates being much higher in industrialized regions. The objective of the current study was to assess the role of environmental factors such as exposure to ambient air pollution, specifically carcinogenic polycyclic aromatic hydrocarbons (PAHs) that may be playing in the geographic variations in breast cancer incidence. Female breast cancer incidence and ambient air emissions of PAHs were examined in the northeastern and southeastern regions of the USA by analyzing data from the Surveillance, Epidemiology, and End Results (SEER) Program and the State Cancer Profiles of the National Cancer Institute and from the Environmental Protection Agency. Linear regression analysis was conducted to evaluate the association between PAH emissions and breast cancer incidence in unadjusted and adjusted models. Significantly higher age-adjusted incidence rates of female breast cancer were seen in northeastern SEER regions, when compared to southeastern regions, during the years of 2000-2012. After adjusting for potential confounders, emission densities of total PAHs and four carcinogenic individual PAHs (benzo[a]pyrene, dibenz[a,h]anthracene, naphthalene, and benzo[b]fluoranthene) showed a significantly positive association with annual incidence rates of breast cancer, with a β of 0.85 (p = 0.004), 58.37 (p = 0.010), 628.56 (p = 0.002), 0.44 (p = 0.041), and 77.68 (p = 0.002), respectively, among the northeastern and southeastern states. This study suggests a potential relationship between ambient air emissions of carcinogenic PAHs and geographic variations of female breast cancer incidence in the northeastern and southeastern US. Further investigations are needed to explore these interactions and elucidate the role of PAHs in regional variations of breast cancer incidence.

Biological impact of environmental polycyclic aromatic hydrocarbons (ePAHs) as endocrine disruptors

Polycyclic aromatic hydrocarbons (PAHs) are often detected in the environment and are regarded as endocrine disruptors. We here designated mixtures of PAHs in the environment as environmental PAHs (ePAHs) to discuss their effects collectively, which could be different from the sum of the constituent PAHs. We first summarized the biological impact of environmental PAHs (ePAHs) found in the atmosphere, sediments, soils, and water as a result of human activities, accidents, or natural phenomena. ePAHs are characterized by their sources and forms, followed by their biological effects and social impact, and bioassays that are used to investigate their biological effects. The findings of the bioassays have demonstrated that ePAHs have the ability to affect the endocrine systems of humans and animals. The pathways that mediate cell signaling for the endocrine disruptions induced by ePAHs and PAHs have also been summarized in order to obtain a clearer understanding of the mechanisms responsible for these effects without animal tests; they include specific signaling pathways (MAPK and other signaling pathways), regulatory mechanisms (chromatin/epigenetic regulation, cell cycle/DNA damage control, and cytoskeletal/adhesion regulation), and cell functions (apoptosis, autophagy, immune responses/inflammation, neurological responses, and development/differentiation) induced by specific PAHs, such as benz[a]anthracene, benzo[a]pyrene, benz[l]aceanthrylene, cyclopenta[c,d]pyrene, 7,12-dimethylbenz[a]anthracene, fluoranthene, fluorene, 3-methylcholanthrene, perylene, phenanthrene, and pyrene as well as their derivatives. Estrogen signaling is one of the most studied pathways associated with the endocrine-disrupting activities of PAHs, and involves estrogen receptors and aryl hydrocarbon receptors. However, some of the actions of PAHs are contradictory, complex, and unexplainable. Although several possibilities have been suggested, such as direct interactions between PAHs and receptors and the suppression of their activities through other pathways, the mechanisms underlying the activities of PAHs remain unclear. Thus, standardized assay protocols for pathway-based assessments are considered to be important to overcome these issues.

Postmenopausal Breast Cancer Risk in Relation to Antibodies Specific to Benzo[a]Pyrene, Estradiol and Progesterone

BACKGROUND

Antibodies might protect against low doses of environmental carcinogens by decreasing systemic uptake, activation of metabolic pathways, and redistribution of carcinogens within the organism. The features of antibody formation in relation to environmental carcinogens and sex steroids under natural conditions should be determined to identify breast cancer risk, then to develop cancer immune prevention strategies.

OBJECTIVES

The purpose of this study was to investigate antibodies specifications to benzo(a)pyrene, estradiol and progesterone in postmenopausal women with invasive breast cancer.

PATIENTS AND METHODS

A semi-quantitative non-competitive immunoassay of IgG antibodies to benzo(a)pyrene (IgG-Bp), estradiol (IgG-Es), and progesterone (IgG-Pg) has conducted. The assay has performed on 322 serum samples from patients with breast cancer and 179 serum samples from healthy postmenopausal women by using low-molecular-weight Bp, Es, and Pg conjugated with bovine serum albumin. ROC analysis has also conducted to determine the odds ratio (OR).

RESULTS

Combination of the high levels of IgG-Bp and IgG-Es without IpG-Pg was more frequent in breast cancer patients than that in healthy women, and the OR has increased to 3.8. Combination of the high levels of IgG-Pg with high levels of both IgG-Bp and IgG-Es were significantly more frequent in breast cancer patients (36.9%) than that in healthy women (5.6%), and the OR increased to 11.7. These differences have peculiarly expressed in breast cancer patients with hormone status ER+/PR- (OR = 26.7). The minimum OR (0.4) has obtained at low levels of the three antibodies.

CONCLUSIONS

Immunoassay of antibodies against environmental carcinogens and sex steroid hormones could use to detect breast cancer risk. Induction of antibodies against Bp for cancer immunoprevention could lead to antibody formation against steroid hormones, thereby increasing breast cancer risk.

Constitutive expression of AhR and BRCA-1 promoter CpG hypermethylation as biomarkers of ERα-negative breast tumorigenesis

Background

Only 5–10 % of breast cancer cases is linked to germline mutations in the BRCA-1 gene and occurs early in life. Conversely, sporadic breast tumors, which represent 90-95 % of breast malignancies, have lower BRCA-1 expression, but not mutated BRCA-1 gene, and tend to occur later in life in combination with other genetic alterations and/or environmental exposures. The latter may include environmental and dietary factors that activate the aromatic hydrocarbon receptor (AhR). Therefore, understanding if changes in expression and/or activation of the AhR are associated with somatic inactivation of the BRCA-1 gene may provide clues for breast cancer therapy.

Methods

We evaluated Brca-1 CpG promoter methylation and expression in mammary tumors induced in Sprague–Dawley rats with the AhR agonist and mammary carcinogen 7,12-dimethyl-benzo(a)anthracene (DMBA). Also, we tested in human estrogen receptor (ER)α-negative sporadic UACC-3199 and ERα-positive MCF-7 breast cancer cells carrying respectively, hyper- and hypomethylated BRCA-1 gene, if the treatment with the AhR antagonist α-naphthoflavone (αNF) modulated BRCA-1 and ERα expression. Finally, we examined the association between expression of AhR and BRCA-1 promoter CpG methylation in human triple-negative (TNBC), luminal-A (LUM-A), LUM-B, and epidermal growth factor receptor-2 (HER-2)-positive breast tumor samples.

Results

Mammary tumors induced with DMBA had reduced BRCA-1 and ERα expression; higher Brca-1 promoter CpG methylation; increased expression of Ahr and its downstream target Cyp1b1; and higher proliferation markers Ccnd1 (cyclin D1) and Cdk4. In human UACC-3199 cells, low BRCA-1 was paralleled by constitutive high AhR expression; the treatment with αNF rescued BRCA-1 and ERα, while enhancing preferential expression of CYP1A1 compared to CYP1B1. Conversely, in MCF-7 cells, αNF antagonized estradiol-dependent activation of BRCA-1 without effects on expression of ERα. TNBC exhibited increased basal AhR and BRCA-1 promoter CpG methylation compared to LUM-A, LUM-B, and HER-2-positive breast tumors.

Conclusions

Constitutive AhR expression coupled to BRCA-1 promoter CpG hypermethylation may be predictive markers of ERα-negative breast tumor development. Regimens based on selected AhR modulators (SAhRMs) may be useful for therapy against ERα-negative tumors, and possibly, TNBC with increased AhR and hypermethylated BRCA-1 gene.

PAHs reduce DNA synthesis and delay cell division in the widespread primary producer Prochlorococcus

The cyanobacteria Prochlorococcus is the most abundant primary producer in the ocean. In a global study across the Atlantic, Indian and Pacific Oceans, we tested the effect of organic pollutants on the growth and cell division of natural Prochlorococcus populations. Sub-lethal concentrations of Polycyclic Aromatic Hydrocarbons (PAHs) altered Prochlorococcus cell division by reducing DNA synthesis and decreasing the percentage of cells entering mitosis. Cell division time increased with PAHs dosage by 1.2 h per μg L(-1) of mixture added. At PAHs dosages >1 μg L(-1), Prochlorococcus cell division tended to arrest at S-phase (DNA synthesis). As a consequence, population growth was significantly reduced in the presence of PAHs. The presence of PAHs resulted in a predictable alteration of the cell cycle of the widespread cyanobacteria.The dosages tested are above concentrations in the open ocean, but found in the coastal ocean, where Prochlorococcus growth must be inhibited.

Dietary intake and breast cancer among carriers and noncarriers of BRCA mutations in the Korean Hereditary Breast Cancer Study

BACKGROUND

Soy intake is associated with a lower risk of breast cancer. However, it is unclear whether the same reduction in risk associated with high soy intake is also applicable to familial or genetic breast cancer.

OBJECTIVE

The aim of this study was to assess the dietary factors among carriers and noncarriers of BRCA mutations in the Korean Hereditary Breast Cancer Study (KOHBRA).

DESIGN

The KOHBRA Study is an ongoing project composed of affected breast cancer patients and familial members of breast cancer cases with BRCA mutations. To assess the association between dietary diversity and breast cancer risk, an HR was estimated by comparing affected subjects with their familial nonaffected members. To assess the interaction between the combination of BRCA mutation and diet diversity, the case-only OR (COR) was estimated by comparing BRCA mutation carriers and noncarriers only in affected subjects.

RESULTS

Soy product intake was associated with a lower risk of breast cancer in carriers (HR: 0.39; 95% CI: 0.19, 0.79 for the highest quartile). The highest quartile of meat intake was associated with a higher risk of breast cancer regardless of BRCA mutation in carriers (HR: 1.97; 95% CI: 1.13, 3.44) and noncarriers (95% CI: 1.41; 1.12, 1.78). The associations of meat intake and soybean intake for breast cancer were more prominent in BRCA2 mutation carriers. In the analysis with only cases, the highest quartile of soy intake, but not meat intake, was associated with BRCA-related breast cancer (COR: 0.57; 95% CI: 0.36, 0.91).

CONCLUSION

Our study suggests that soy product consumption is associated with lower breast cancer risk and it had an interaction with BRCA mutation.

Modulation of the rat hepatic cytochrome P4501A subfamily using biotin supplementation

Studies have found that biotin favors glucose and lipid metabolism, and medications containing biotin have been developed. Despite the use of biotin as a pharmacological agent, few studies have addressed toxicity aspects including the possible interaction with cytochrome P450 enzyme family. This study analyzed the effects of pharmacological doses of biotin on the expression and activity of the cytochrome P4501A subfamily involved in the metabolism of xenobiotics. Wistar rats were treated daily with biotin (2 mg/kg, i.p.), while the control groups were treated with saline. All of the rats were sacrificed by cervical dislocation after 1, 3, 5, or 7 days of treatment. CYP1A1 and CYP1A2 mRNAs were modified by biotin while enzyme activity and protein concentration were not affected. The lack of an effect of biotin on CYP1A activity was confirmed using other experimental strategies, including (i) cotreatment of the animals with biotin and a known CYP1A inducer; (ii) the addition of biotin to the reaction mixtures for the measurement of CYP1A1 and CYP1A2 activities; and (iii) the use of an S9 mixture that was prepared from control and biotin-treated rats to analyze the activation of benzo[a]pyrene (BaP) into mutagenic metabolites using the Ames test. The results suggest that biotin does not influence the CYP1A-mediated metabolism of xenobiotics.

Role of aryl hydrocarbon receptor in cancer

Aryl hydrocarbon receptor (AHR), a cytosolic ligand-activated transcription factor, belongs to the member of bHLH/PAS family of heterodimeric transcriptional regulators and is widely expressed in a variety of animal species and humans. Recent animal and human data suggested that AHR is involved in various signaling pathways critical to cell normal homeostasis, which covers multiple aspects of physiology, such as cell proliferation and differentiation, gene regulation, cell motility and migration, inflammation and others. Dysregulation of these physiological processes is known to contribute to events such as tumor initiation, promotion, and progression. Increasing epidemiological and experimental animal data provided substantial support for an association between abnormal AHR function and cancer, implicating AHR may be a novel drug-interfering target for cancers. The proposed underlying mechanisms of its actions in cancer involved multiple aspects, (a) inhibiting the functional expression of the key anti-oncogenes (such as p53 and BRCA1), (b) promoting stem cells transforming and angiogenesis, (c) altering cell survival, proliferation and differentiation by influencing the physiologic processes of cell-cycle, apoptosis, cell contact-inhibition, metabolism and remodel of extracellular matrix, and cell-matrix interaction, (d) cross-talking with the signaling pathways of estrogen receptor and inflammation. This review aims to provide a brief overview of recent investigations into the role of AHR and the underlying mechanisms of its actions in cancer, which were explored by the new technologies emerging in recent years.

DNA methylation program during development

DNA methylation is a key epigenetic mark when occurring in the promoter and enhancer regions regulates the accessibility of the binding protein and gene transcription. DNA methylation is inheritable and can be de novo-synthesized, erased and reinstated, making it arguably one of the most dynamic upstream regulators for gene expression and the most influential pacer for development. Recent progress has demonstrated that two forms of cytosine methylation and two pathways for demethylation constitute ample complexity for an instructional program for orchestrated gene expression and development. The forum of the current discussion and review are whether there is such a program, if so what the DNA methylation program entails, and what environment can change the DNA methylation program. The translational implication of the DNA methylation program is also proposed.

Endocrine disruptors and bone metabolism

Bone microenvironment is a complex dynamic equilibrium between osteoclasts and osteoblasts and is modulated by a wide variety of hormones and osteocyte mediators secreted in response to physiological and pathological conditions. The rate of remodeling involves tight coupling and regulation of both cells population and is regulated by a wide variety of hormones and mediators such as parathyroid hormone, prostaglandins, thyroid hormone, sex steroids, etc. It is also well documented that bone formation is easily influenced by the exposure of osteoblasts and osteoclasts to chemical compounds. Currently, humans and wildlife animals are exposed to various environmental xenoestrogens typically at low doses. These compounds, known as endocrine disruptor chemicals (EDCs), can alter the systemic hormonal regulation of the bone remodeling process and the skeletal formation. This review highlights the effects of the EDCs on mammalian bone turnover and development providing a macro and molecular view of their action.

¹H NMR-based metabolomics approach to assess toxicity of bunker a heavy oil to freshwater carp, Cyprinus carpio

Using a ¹H NMR metabolomics approach, the effects of dietary exposure of bunker A heavy oil (0.01, 0.1, 1, and 5% in diet) on freshwater carp, Cyprinus carpio, were examined. Statistical analysis by PCA score plots showed that the amount of metabolites in exposure groups 0.1, 1, and 5% differed from those in the control group. Although no discernible effects on metabolites were noted in the 0.1% exposure group as well as in the lowest concentration (0.01%) group, several metabolites such as amino acid (e.g., leucine, isoleucine, valine, glutamine, histidine, proline, and methionine), 3-D-hydroxybutyrate, and glycerol were elevated, while another metabolite such as formate was reduced in 1 and 5% groups. These changes in the metabolites associated with the tri-carboxylic-acid (TCA) cycle suggest that oil exposure resulted in the disturbance of the TCA cycle in the liver of the carp. Isobutyrate, a marker of anoxia, was also increased in 1 and 5% exposures groups and was directly related to low hemoglobin concentrations leading to reduced oxygen transport by blood. In addition, significant elevation of creatinine in the plasma of carps exposed to 5% heavy oil suggests disturbance in kidney function. Thus, metabolomics approach can detect toxic effects of hazardous pollutants on fish.

Perspectives of breast cancer etiology: synergistic interaction between smoking and exogenous hormone use

To explore breast cancer etiology, literature was searched using Medline. We explored the 1) plausibility of smoking in breast carcinogenesis; 2) physiological properties, susceptibility windows, and exposure timing of breast cells; 3) role of exogenous hormones in breast carcinogenesis; 4) biological mechanism of synergistic interactions between smoking and exogenous hormones in breast carcinogenesis; and 5) evidence from epidemiologic studies and the fitted secular trend between smoking rate, exogenous hormone use, and breast cancer incidence in past decades. We deduced that exogenous hormone use per se is not a significant cause and its association with breast cancer is distorted by chronic exposure to environmental carcinogens, especially smoking. We hypothesize that smoking is one of the causes of breast cancer and that this causality is strengthened by synergistic interaction between smoking and exogenous hormone use. Physicians should be cautious of prescribing exogenous hormones for those with chronic exposure to environmental carcinogens to prevent breast cancer.

Regulation of constitutive and inducible AHR signaling: complex interactions involving the AHR repressor

The AHR is well known for regulating responses to an array of environmental chemicals. A growing body of evidence supports the hypothesis that the AHR also plays perhaps an even more important role in modulating critical aspects of cell function including cell growth, death, and migration. As these and other important AHR activities continue to be elucidated, it becomes apparent that attention now must be directed towards the mechanisms through which the AHR itself is regulated. Here, we review what is known of and what biological outcomes have been attributed to the AHR repressor (AHRR), an evolutionarily conserved bHLH-PAS protein that inhibits both xenobiotic-induced and constitutively active AHR transcriptional activity in multiple species. We discuss the structure and evolution of the AHRR and the dominant paradigm of a xenobiotic-inducible negative feedback loop comprised of AHR-mediated transcriptional up-regulation of AHRR and the subsequent AHRR-mediated suppression of AHR activity. We highlight the role of the AHRR in limiting AHR activity in the absence of xenobiotic AHR ligands and the important contribution of constitutively repressive AHRR to cancer biology. In this context, we also suggest a new hypothesis proposing that, under some circumstances, constitutively active AHR may repress AHRR transcription, resulting in unbridled AHR activity. We also review the predominant hypotheses on the molecular mechanisms through which AHRR inhibits AHR as well as novel mechanisms through which the AHRR may exert AHR-independent effects. Collectively, this discussion emphasizes the importance of this understudied bHLH-PAS protein in tissue development, normal cell biology, xenobiotic responsiveness, and AHR-regulated malignancy.

Estrogenic activity of environmental polycyclic aromatic hydrocarbons in uterus of immature Wistar rats

Polycyclic aromatic hydrocarbons (PAHs) are an important group of environmental pollutants, known for their mutagenic and carcinogenic activities. Many PAHs are aryl hydrocarbon receptor (AhR) ligands and several recent studies have suggested that PAHs or their metabolites may activate estrogen receptors (ER). The present study investigated possible estrogenic/antiestrogenic effects of abundant environmental contaminants benzo[a]pyrene (BaP), benz[a]anthracene (BaA), fluoranthene (Fla) and benzo[k]fluoranthene (BkF) in vivo, using the immature rat uterotrophic assay. The present results suggest that BaA, BaP and Fla behaved as estrogen-like compounds in immature Wistar rats, when applied for 3 consecutive days at 10mg/kg/day, as documented by a significant increase of uterine weight and hypertrophy of luminal epithelium. These effects were likely to be mediated by ERalpha, a major subtype of ER present in uterus, as they were inhibited by treatment with ER antagonist ICI 182,780. BaA, the most potent of studied PAHs, induced a significant estrogenic effect within a concentration range 0.1-50mg/kg/day; however, it did not reach the maximum level induced by reference estrogens. The proposed antiestrogenicity of the potent AhR agonist BkF was not confirmed in the present in vivo study; the exposure to BkF did not significantly affect the uterine weight, although a weak suppression of ERalpha immunostaining was observed in luminal and glandular epithelium, possibly related to its AhR-mediated activity. The PAHs under study did not induce marked genotoxic damage in uterine tissues, as documented by the lack of Ser-15-phoshorylated p53 protein staining. With the exception of Fla, all three remaining compounds increased CYP1-dependent monooxygenation activities in liver at the doses used, suggesting that the potential tissue-specific antiestrogenic effects of PAHs mediated by metabolization of 17beta-estradiol also cannot be excluded. Taken together, these environmentally relevant PAHs induced estrogenic effects in vivo, which might affect their toxic impact and carcinogenicity.

Review of the etiology of breast cancer with special attention to organochlorines as potential endocrine disruptors

Breast cancer is the most frequently diagnosed cancer among Canadian women, accounting for about 30% of all new cancer cases each year. Although the incidence of breast cancer has increased over the past 50 years, the cause of this rise is unknown. Risk factors for breast cancer may be classified into four broad categories: (1) genetic/familial, (2) reproductive/hormonal, (3) lifestyle, and (4) environmental. Established risk factors for breast cancer include older age, later age at first full-term pregnancy, no full-term pregnancies, postmenopausal obesity, and genetic factors. However, these known risk factors cannot account for the majority of cases. In the early 1990s, it was suggested that exposure to some environmental chemicals such as organochlorine compounds may play a causal role in the etiology of breast cancer through estrogen-related pathways. The relationship between organochlorines and breast cancer risk has been studied extensively in the past decade and more, and at this point there is no clear evidence to support a causal role of most organochlorine pesticides in the etiology of human breast cancer, but more evidence is needed to assess risk associated with polychlorinated biphenyls (PCBs). Future studies need to consider the combined effects of exposures, concentrate on vulnerable groups such as those with higher levels of exposure, only consider exposures occurring during the most etiologically relevant time periods, and more thoroughly consider gene-environment interactions.

A role for the aryl hydrocarbon receptor in mammary gland tumorigenesis

The aryl hydrocarbon receptor (AhR) is an evolutionarily conserved transcription factor bound and activated by ubiquitous environmental pollutants. Historically, the AhR has been studied for its transcriptional regulation of genes encoding cytochrome P450 enzymes, which metabolize many of these chemicals into mutagenic and toxic intermediates. However, recent studies demonstrate that the AhR plays an important role in the biology of several cell types in the absence of environmental chemicals. Here, this paradigm shift is discussed in the context of a putative role for the AhR in mammary gland tumorigenesis. Data demonstrating high levels of constitutively active AhR in mammary tumors are summarized. Particular focus is placed on the likelihood that the AhR contributes to ongoing mammary tumor cell growth and on the possibility that the AhR inhibits apoptosis while promoting transition to an invasive, metastatic phenotype. A working model is proposed that may help explain the sometimes contradictory outcomes observed after AhR manipulation and that serves as a blueprint for the design of therapeutics which target the AhR in breast cancer. The theme that malignant cells reveal the functions for which the AhR has been evolutionarily conserved is presented throughout this discussion.

Enhanced micronucleus formation and modulation of BCL-2:BAX in MCF-7 cells after exposure to binary mixtures

BACKGROUND

Within mixtures, interactions between different xenobiotics may occur to give rise to additive, synergistic, inhibitory and/or stimulatory effects in target cells. The role that xenobiotics individually or in mixtures, and at environmental concentrations, play in the etiology of common human diseases often remains obscure.

METHODS

In the presence or absence of lindane, chromosomal aberrations were detected in MCF-7 cells after 24-hr treatment with benzo[a]pyrene (B[a]P) or 2-amino-1-methyl-6-phenylimidazo[4,5-b]pyridine (PhIP) using the cytokinesis-block micronucleus assay. Micronuclei were scored in 1,000 binucleate cells/treatment. We investigated intracellular responses using quantitative gene expression analyses of cyclin-dependent kinase inhibitor 1A [CDKN1A (P21(WAF1/CIP1))], B-cell leukemia/lymphoma 2 (BCL-2), BCL-2-associated X (BAX), and isoforms of cytochrome P450 (CYP), CYP1A1, CYP1A2, and CYP1B1. Immunocytochemical analyses of p53, p21(Waf1/Cip1), Bcl-2 and Bax protein expression in MCF-7 cells were also carried out.

RESULTS

After exposure to binary mixtures of B[a]P plus lindane or PhIP plus lindane, a 10-fold increase in micronucleus formation resulted; these test agents individually induced 2- to 5-fold increases. Lindane increased the ratio of Bcl-2:Bax, as did 17beta-estradiol (E(2)). Although treatment with B[a]P alone was found to elevate expression of P21(WAF1/CIP1)and CYP isoenzymes, it reduced the ratio of BCL-2:BAX mRNA transcripts. Treatment with a binary mixture of 10(-8) M B[a]P plus 10(-12) M lindane or 10(-10) M E(2) reversed B[a]P-induced reductions in the ratio of Bcl-2- to Bax-positive cells. In contrast, treatments with PhIP (known to possess hormonelike properties) plus lindane or E(2) resulted in profound reductions in Bcl-2:Bax ratio.

CONCLUSIONS

Our results suggest that low-dose treatments (i.e., close to environmental levels) may increase DNA damage while influencing survival in exposed cells and that these effects may depend on the endocrine activity of test agents.

Human breast biomonitoring and environmental chemicals: use of breast tissues and fluids in breast cancer etiologic research

Extensive research indicates that the etiology of breast cancer is complex and multifactorial and may include environmental risk factors. Breast cancer etiology and exposure to xenobiotic compounds, diet, electromagnetic fields, and lifestyle have been the subject of numerous scientific inquiries, but research has yielded inconsistent results. Biomonitoring has been used to explore associations between breast cancer and levels of environmental chemicals in the breast. Research using breast tissues and fluids to cast light on the etiology of breast cancer is, for the most part, predicated on the assumption that the tissue or fluid samples either contain measurable traces of the environmental agent(s) associated with the cancer or that they retain biological changes that are biomarkers of such exposure or precursors of carcinogenic effect. In this paper, we review breast cancer etiology research utilizing breast biomonitoring. We first provide a brief synopsis of the current state of understanding of associations between exposure to environmental chemicals and breast cancer etiology. We then describe the published breast cancer research on tissues and fluids, which have been used for biomonitoring, specifically human milk and its components, malignant and benign breast tissue, nipple aspirate fluid (NAF) and breast cyst fluid. We conclude with a discussion on recommendations for biomonitoring of breast tissues and fluids in future breast cancer etiology research. Both human milk and NAF fluids, and the cells contained therein, hold promise for future biomonitoring research into breast cancer etiology, but must be conducted with carefully delineated hypotheses and a scientifically supportable epidemiological approach.

Effects of polycyclic aromatic hydrocarbon-containing oil mixtures on generation of reactive oxygen species and cell viability in MCF-7 breast cancer cells

Clarified slurry oil (CSO), and two crude oil samples, Belridge heavy crude oil (BHCO) and Lost Hills light crude oil (LHLCO), were examined for their ability to generate reactive oxygen species (ROS) in MCF-7 cells. Intracellular ROS and cell viability were determined in a flow cytometer using dihydroxyrhodamine 123 and propidium iodide, respectively. In experiments with short-term exposure, single-cell suspensions were loaded with the fluorescent probes and then treated with the oil samples (1 or 10 ppm). Measurements were made at 5, 15, 30, 60, and 90 min after addition of oil samples. In experiments with longer term exposure, preconfluent cell cultures were treated with oil samples for 6, 12, or 24 h prior to preparing single-cell suspensions. Both short-term and longer term treatment with oil samples resulted in elevated generation of reactive oxygen species (ROS). Cell cultures also were treated with benzo[a]pyrene, a polycyclic aromatic hydrocarbon detected in all three oil samples. Treatment with benzo[a]pyrene produced a significant increase in levels of ROS. The present findings suggest that oil samples with higher concentrations of polycyclic aromatic hydrocarbons may exert adverse effects on human mammary epithelial tissue through induction of oxidative stress.

Effects of the environmental mammary carcinogen 6-nitrochrysene on p53 and p21(Cip1) protein expression and cell cycle regulation in MCF-7 and MCF-10A cells

The environmental pollutant 6-nitrochrysene (6-NC) is a potent mammary carcinogen in rats; it is more potent than numerous classical mammary carcinogens such as benzo[a]pyrene (BaP). The mechanisms that account for the remarkable carcinogenicity of 6-NC remain elusive. Similar to BaP, 6-NC is also known to induce DNA damage in rodents and in human breast tissues. As an initial investigation, we reasoned that DNA damage induced by 6-NC may alter the expression of p53 protein in a manner that differs from other DNA damaging carcinogens (e.g. BaP). Using human breast adenocarcinoma MCF-7 cells and immortalized human mammary epithelial MCF-10A cells, we determined the effects of 6-NC on the expression of p53 protein and its direct downstream target cyclin-dependent kinase inhibitor p21(Cip1) as well as on the cell cycle progression. Western blot analysis demonstrated that treatments of MCF-7 and MCF-10A cells with 6-NC for 12, 24 or 48h did not increase the level of total p53 protein; however, an increase of p21(Cip1) protein and a commitment increase of G(1) phase were observed in MCF-10A cells but not in MCF-7 cells. Further studies using 1,2-dihydroxy-1,2-dihydro-6-hydroxylaminochrysene (1,2-DHD-6-NHOH-C), the putative ultimate genotoxic metabolite of 6-NC, was conducted and showed a significant induction of p53 (p<0.05) in MCF-7 cells; however, this effect was not evident in MCF-10A cells, indicating the varied DNA damage responses between the two cell lines. By contrast to numerous DNA damaging agents such as BaP which is known to stimulate p53 expression, the lack of p53 response by 6-NC imply the lack of protective functions mediated by p53 (e.g. DNA repair machinery) after exposure to 6-NC and this may, in part, account for its remarkable carcinogenicity in the mammary tissue.

Diesel exhaust influences carcinogenic PAH-induced genotoxicity and gene expression in human breast epithelial cells in culture

The carcinogenic polycyclic aromatic hydrocarbon (PAHs) benzo[a]pyrene (B[a]P) and dibenzo[a,l]pyrene (DB[a,l]P) are widespread environmental pollutants, however their toxicological effects within a mixture is not established. We investigated the influence of diesel exhaust (DE) on B[a]P and DB[a,l]P-induced PAH-DNA adduct formation, metabolic activation, gene expression and 8-oxo-dG adduct levels in human breast epithelial cells (MCF-10A) in culture. Following 24 and 48h, cells co-exposed to DE plus B[a]P exhibited a significant decrease in PAH-DNA adduct levels, compared with B[a]P alone, as determined by (33)P-postlabeling combined with reversed-phase high performance liquid chromatography (HPLC). Cytochrome P450 (CYP) enzyme activity, as measured by the ethoxyresorufin O-deethylase (EROD) assay and CYP1B1 expression, significantly increased with co-exposure of DE plus DB[a,l]P, compared with DB[a,l]P alone. Aldo keto-reductase (AKR)1C1, AKR1C2, and AKR1C3 expression also significantly increased in cells exposed to DE plus PAH, compared with PAH exposure alone. Cell populations exhibiting 8-oxo-dG adducts significantly increased in response to exposure to B[a]P or DE plus B[a]P for 24h, compared with vehicle control, as quantified by flow cytometry. These results suggest that complex mixtures may modify the carcinogenic potency of PAH by shifting the metabolic activation pathway from the production of PAH diol-epoxides to AKR pathway-derived metabolites.

Carcinogen-Induced DNA Double Strand Break Repair in Sporadic Breast Cancer

BACKGROUND

Induction of DNA double strand breaks and alterations in the repair of these breaks is implicated in breast carcinogenesis. Prior studies have demonstrated that peripheral blood mononuclear cells (PBMC) from breast cancer patients exhibit increased numbers of DNA strand breaks after exposure to ionizing radiation, but these studies did not specifically measure DNA double strand breaks and it is not known whether chemical carcinogens produce similar effects.

MATERIALS AND METHODS

PBMC from 32 women undergoing breast surgery were genotyped at nine loci of seven DNA repair genes. DNA double strand break repair was measured using the neutral comet assay after exposure to ionizing radiation (0.5 Gy) or bioactivated benzo[a]pyrene (B[a]P, 5 microM.

RESULTS

PBMC from breast cancer patients showed higher levels of residual DNA double strand breaks 30 min after exposure to radiation than PBMC from patients with benign breast disease (1.40 times baseline [95% confidence intervals [CI] 1.29-1.51] versus 1.24 times baseline [95% CI 1.15-1.33], respectively, P = 0.04). The response to B[a]P trended in the same direction, but did not reach statistical significance. The MGMT K178R variant genotype was associated with improved DNA double strand break repair in PBMC exposed to B[a]P.

CONCLUSIONS

Reduced repair of radiation-induced DNA double strand breaks in PBMC is a robust biomarker of breast cancer risk. Reduced DNA repair capacity may have a genetic component even in sporadic breast cancer.

IGHMBP2 Thr671Ala polymorphism might be a modifier for the effects of cigarette smoking and PAH–DNA adducts to breast cancer risk

Laboratory and bioinformatics studies have suggested that immunoglobulin mu-binding protein 2 (IGHMBP2) is involved in DNA repair, replication and recombination. Using 1067 cases and 1110 controls from a population-based case-control study, we sought to clarify the potential role of the IGHMBP2 Thr671Ala polymorphism (A to G substitution) alone and as a modifier of the effects for cigarette smoking and PAH-DNA adducts on breast cancer risk. Unconditional logistic regression was used to estimate odds ratios (OR) and 95% confidence intervals (CI). Overall, there was no significant association between the IGHMBP2 variant-G allele and breast cancer risk (OR = 1.1, 95% CI = 0.9-1.3). Increased risk was found among women who had detectable PAH-DNA adducts and carried at least one variant-G allele (OR = 1.4, 95% CI = 1.0-1.8, p for trend = 0.01) compared to women carrying the wild-type AA genotype and with non-detectable adducts. Smokers carrying the IGHMBP2 variant-G allele had no significant increased breast cancer risk compared with non-smoking women with the AA genotype. Heavy smokers (>31 pack years) had a statistically significant association with breast cancer risk (OR=2.0, 95% CI=1.2-3.3) relative to nonsmokers with the AA genotype though the magnitude of association was not different than heavy smokers (> 31 pack years) with the AA genotype (OR=1.6, 95% CI=0.9-2.6). Overall our study observes only modestly higher effect estimates for PAH-DNA adduct exposure and cigarette smoking among those with the high-risk genotype, but these differences are not statistically significant. Additional studies focused on the biological function of the variant-G allele and interactions with other genetic polymorphisms are necessary to confirm our findings.

Residential environmental exposures and other characteristics associated with detectable PAH-DNA adducts in peripheral mononuclear cells in a population-based sample of adult females

The detection of polycyclic aromatic hydrocarbon (PAH)-DNA adducts in human lymphocytes may be useful as a surrogate end point for individual cancer risk prediction. In this study, we examined the relationship between environmental sources of residential PAH, as well as other potential factors that may confound their association with cancer risk, and the detection of PAH-DNA adducts in a large population-based sample of adult women. Adult female residents of Long Island, New York, aged at least 20 years were identified from the general population between August 1996 and July 1997. Among 1556 women who completed a structured questionnaire, 941 donated sufficient blood (25+ ml) to allow use of a competitive ELISA for measurement of PAH-DNA adducts in peripheral blood mononuclear cells. Ambient PAH exposure at the current residence was estimated using geographic modeling (n=796). Environmental home samples of dust (n=356) and soil (n=360) were collected on a random subset of long-term residents (15+ years). Multivariable regression was conducted to obtain the best-fitting predictive models. Three separate models were constructed based on data from : (A) the questionnaire, including a dietary history; (B) environmental home samples; and (C) geographic modeling. Women who donated blood in summer and fall had increased odds of detectable PAH-DNA adducts (OR=2.65, 95% confidence interval (CI)=1.69, 4.17; OR=1.59, 95% CI=1.08, 2.32, respectively), as did current and past smokers (OR=1.50, 95% CI=1.00, 2.24; OR=1.46, 95% CI=1.05, 2.02, respectively). There were inconsistent associations between detectable PAH-DNA adducts and other known sources of residential PAH, such as grilled and smoked foods, or a summary measure of total dietary benzo-[a]-pyrene (BaP) intake during the year prior to the interview. Detectable PAH-DNA adducts were inversely associated with increased BaP levels in dust in the home, but positively associated with BaP levels in soil outside of the home, although CIs were wide. Ambient BaP estimates from the geographic model were not associated with detectable PAH-DNA adducts. These data suggest that PAH-DNA adducts detected in a population-based sample of adult women with ambient exposure levels reflect some key residential PAH exposure sources assessed in this study, such as cigarette smoking.

Unexplained cancer clusters: common threads

A number of identified cancer clusters have followed exposures to mixtures of chemicals. The causes for these cancers could not be attributed to any of the individual chemicals in the mixtures and up to now have remained unexplained. The author presents case studies showing that these previously unexplained cancer clusters have common characteristics. First, they can be attributed to exposures to mixtures that contain at least one lipophilic and one hydrophilic chemical, with octanol:water partition coefficients, K(ow), indicative of lipophilic or hydrophilic character. Second, the specific combinations of lipophiles and hydrophiles act as individual entities and produce cancers not associated with exposure to any of the individual chemicals contained in the mixtures. The cancers that follow these exposures can be in the form of single or multiple cancers per cluster.

Long-term effects of a standardized complex mixture of urban dust particulate on the metabolic activation of carcinogenic polycyclic aromatic hydrocarbons in human cells in culture

Humans are exposed to complex mixtures of polycyclic aromatic hydrocarbons in the atmosphere. We examined the long term effects of a standard reference material (SRM) 1649a over time on the metabolic activation and DNA adduct formation by two carcinogenic PAHs, benzo[a]pyrene (BP) and dibenzo[a,l]pyrene (DBP) in the human mammary carcinoma derived cell line MCF-7. PAH-DNA adduct analysis, cytochrome P450 (CYP) enzyme activity, CYP1A1 and CYP1B1 protein expression were determined in cells treated with SRM 1649a alone or SRM 1649a with either BP or DBP for 24 to 120 h. Averaging over time, significantly higher levels of DNA adducts were observed in cells treated with BP or DBP alone than in co-treatments with SRM 1649a and BP or DBP. Ethoxyresorufin O-deethylase assay indicated a significant increase in activity in cells treated with BP alone and co-treated with SRM1649a in comparison to other treatment groups. Induction of CYP1A1 and CYP1B1 protein expression was observed by immunoblots in cells treated with BP alone or in co-treatments of SRM 1649a and BP or DBP. These data demonstrate the influence of the components of SRM 1649a in inhibiting the activation of BP or DBP by CYP enzymes in the formation of DNA adducts. It also suggests that the carcinogenic activity of PAH within a complex mixture may vary with composition and activation of the components present in the complex mixture.

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 or >/= 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.

Common risk factors of breast and ovarian cancer: recent view

Clinicians, epidemiologists, and public health specialists tend to examine breast and ovarian cancer separately. Although this seems fairly rational and expected, both malignancies are estrogen related and thus share many risk factors. In this review, we investigate the common familial, reproductive, anthropometric, nutritional, and lifestyle risk factors of breast and ovarian cancer. We believe that the parallel examination of the two cancer types could significantly contribute to an improved prevention of "gynecological cancer" as a whole.

Polycyclic aromatic hydrocarbon-DNA adducts and breast cancer: a pooled analysis

Polycyclic aromatic hydrocarbon (PAH)-DNA adducts have been associated with breast cancer in several small studies. The authors' pooled analysis included 873 cases and 941 controls from a population-based case-control study. Competitive enzyme-linked immunosorbent assay in peripheral mononuclear cells was conducted in 2 rounds, and results were pooled on the basis of round-specific quantiles. The odds ratio for breast cancer was elevated in relation to detectable PAH-DNA adducts (1.29 as compared with nondetectable adduct levels; 95% confidence interval = 1.05, 1.58), but there was no apparent dose-response relationship with increasing quantiles. No consistent pattern emerged when the results were stratified by PAH sources (e.g., active cigarette smoking or PAH-containing foods), or when the cases were categorized by stage of disease or hormone receptor status. These data provide only modest support for an association between PAH-DNA adducts and breast cancer development.

A gene-environment interaction between occupation and BRCA1/BRCA2 mutations in male breast cancer?

The association of male breast cancer (MBC) with a positive breast cancer (BC) family history and with BRCA1/2 germ-line mutations points to a genetic component; a relationship with occupation has also been reported. Recently, we identified pathogenetic BRCA1/2 mutations in a population-based series of Italian MBC patients: here in, we investigated interactions between a carrier status for BRCA1/2 mutations and occupation using a case-case design and estimating case-only odds ratios (CORs). Truck-driving was the most frequent occupation (3/4 BRCA-related cases and 2/19 unrelated cases). An interaction between carrier status and working as a truck-driver emerged, when we classified MBC cases as "ever/never-held" this job title (COR 25.5; 95% Confidence Limits (CL): 1.1-1,412.5) or according to truck-driving as the "longest-held" work (COR 54.0; 95% CL: 1.6-2,997.5). The possible modifying effect on MBC risk in subjects carrying BRCA1/2 germ-line mutations of an occupation characterised by exposure to chemicals such as polycyclic aromatic hydrocarbons (PAH) that are capable of inducing DNA damage, may provide clues to the role of environmental exposures in modifying BC risk in mutation carriers in both genders.

BRCA1 in hormone-responsive cancers

Mutations of the breast cancer susceptibility gene BRCA1 are linked to hereditary early onset breast and breast-ovarian cancer syndromes. These mutations confer an increased risk for other hormone-dependent cancers, including those of the uterus, cervix and prostate. BRCA1 expression is decreased or absent in a significant proportion of sporadic breast and ovarian cancers, suggesting a wider role in these tumor types. Multiple functions for BRCA1 have been identified, including roles in DNA repair, cell-cycle progression and apoptosis. These functions are consistent with a tumor suppressor activity, but they do not explain why BRCA1 mutation carriers develop hormone-responsive cancer types. Recent studies indicate that BRCA1 interacts with and regulates the activity of estrogen receptor alpha (ER alpha) and the androgen receptor. Its expression is regulated by carcinogens and anticarcinogens that modulate ER alpha signaling, suggesting a molecular linkage between BRCA1 and hormone-responsive cancers.