Breast cancer, oestrogens and environmental pollutants: a re-evaluation from a mixture perspective

New approach methodologies to facilitate and improve the hazard assessment of non-genotoxic carcinogens-a PARC project

Carcinogenic chemicals, or their metabolites, can be classified as genotoxic or non-genotoxic carcinogens (NGTxCs). Genotoxic compounds induce DNA damage, which can be detected by an established in vitro and in vivo battery of genotoxicity assays. For NGTxCs, DNA is not the primary target, and the possible modes of action (MoA) of NGTxCs are much more diverse than those of genotoxic compounds, and there is no specific in vitro assay for detecting NGTxCs. Therefore, the evaluation of the carcinogenic potential is still dependent on long-term studies in rodents. This 2-year bioassay, mainly applied for testing agrochemicals and pharmaceuticals, is time-consuming, costly and requires very high numbers of animals. More importantly, its relevance for human risk assessment is questionable due to the limited predictivity for human cancer risk, especially with regard to NGTxCs. Thus, there is an urgent need for a transition to new approach methodologies (NAMs), integrating human-relevant in vitro assays and in silico tools that better exploit the current knowledge of the multiple processes involved in carcinogenesis into a modern safety assessment toolbox. Here, we describe an integrative project that aims to use a variety of novel approaches to detect the carcinogenic potential of NGTxCs based on different mechanisms and pathways involved in carcinogenesis. The aim of this project is to contribute suitable assays for the safety assessment toolbox for an efficient and improved, internationally recognized hazard assessment of NGTxCs, and ultimately to contribute to reliable mechanism-based next-generation risk assessment for chemical carcinogens.

Application of the maximum cumulative ratio (MCR) as a screening tool for the evaluation of multiple metal mixtures in shellfish in Chinese population

The objective of this study was to investigate the potential effects from exposure to multiple metals, including cadmium (Cd), chromium (Cr), arsenic (As), mercury (Hg), nickel (Ni) and lead (Pb) that exist in shellfish in Chinese populations, and evaluate the impacts of cumulative exposures among individuals. A total 15,469 individual shellfish samples were analyzed following a protocol for elemental analysis. A total of 25,669 respondents were selected through stratified multi-stage cluster sampling from  31 survey sites in China. Individual shellfish consumption data and body weight were collected and analyzed with a 24-hour dietary recall method on three non-consecutive days. The consumers were divided into two groups: aged 2-12 years group and aged ≥13 years. Exposure levels were estimated based using a semi-probabilistic risk assessment method and cumulative exposures among individual persons using the maximum cumulative ratio (MCR) method. The mean, median and 95th percentile of all metals exposure for age 2-12 years group were higher than age ≥13 years group, but none exceeded the respective reference doses of the metals. The mean hazard indices (HI) of each metal in shellfish for both age groups were less than 1. The MCR values calculated among 1283 consumers ranged from 1.28 to 3.25 with the average MCR value was 2.22. There were 51 (3.98%) consumers in group I, 1186 (92.44%) consumers in group II, 26(2.03%) consumers in group III A, and 20 (1.56%) consumers in group III B. And cadmium (Cd) and lead (Pb) produced the HQ_Max that trigged cumulative exposures. It was concluded that heavy metals did not present a potential health risk to people solely through shellfish. The cumulative risks indicated that 7.56% of the surveyed consumers were of concern because of high HI of metals exposure, and Cd, Pb, and Ni made significant contributions to the potential risk.

The effect of environmental Bisphenol A exposure on breast cancer associated with obesity

Bisphenol A (BPA) is a widely used endocrine disrupter. Its environmental exposure is a causative factor of cell aging via decreasing telomerase activity, thus leading to shortening of telomere length. Epidemiological studies confirm positive associations between BPA exposure and the incidence of obesity and type 2 diabetes (T2DM). Increased urinary BPA levels in obese females are both significantly correlated with shorter relative telomere length and T2DM. BPA is a critically effective endocrine disrupter leading to poor prognosis via the obesity-inflammation-aromatase axis in breast cancer. Environmental BPA exposure contributes to the progression of both estrogen dependent and triple negative breast cancers. BPA is a positive regulator of human telomerase reverse transcriptase (hTERT) and it increases the expression of hTERT mRNA in breast cancer cells. BPA exposure can lead to tamoxifen resistance. Among patients treated with chemotherapy, those with persistent high telomerase activity due to BPA are at higher risk of death.

A case-control study of perfluoroalkyl substances and the risk of breast cancer in Taiwanese women

Breast cancer (BC) is a common cancer in women worldwide; however, the incidence of BC is increasing in younger women, possibly associated with the environment. Perfluoroalkyl substances (PFAS) are one of endocrine disruptors that accumulate in environment and impact human health. This study aimed to investigate whether the PFAS and BC are associated. We enrolled 120 BCE patients and 119 controls at National Taiwan University Hospital (NTUH) and also collected bio-specimen and questionnaire from 2013 to 2015. All subjects' plasma PFAS levels were analyzed by ultra-performance liquid chromatography tandem mass spectrometry method with electrospray ionization (UHPLC-ESI-MS/MS). A logistic regression model was used to estimate the association between PFAS and BC. In the ≤50 years age group, the adjusted odds ratio (OR) was 2.34 (95% CI = 1.02, 5.38) for perfluorooctane sulfonate (PFOS) exposure per natural log unit increase. After stratifying the estrogen receptor (ER) status and age group, we obtained a positive association for PFHxS and PFOS concentrations with respect to the risk of ER positive tumors for ≤50 years age group. In conclusion, we found that PFAS were associated with the BC risk of ER positive tumors in young Taiwanese women. Further studies are needed to follow and explore whether these associations are causal.

Analysis of individual and combined estrogenic effects of bisphenol, nonylphenol and diethylstilbestrol in immature rats with mathematical models

BACKGROUND

Traditional toxicological studies focus on individual compounds. However, this single-compound approach neglects the fact that the mixture exposed to human may act additively or synergistically to induce greater toxicity than the single compounds exposure due to their similarities in the mode of action and targets. Mixture effects can occur even when all mixture components are present at levels that individually do not produce observable effects. So the individual chemical effect thresholds do not necessarily protect against combination effects, an understanding of the rules governing the interactive effects in mixtures is needed. The aim of the study was to test and analyze the individual and combined estrogenic effects of a mixture of three endocrine disrupting chemicals (EDCs), bisphenol A (BPA), nonylphenol (NP) and diethylstilbestrol (DES) in immature rats with mathematical models.

METHOD

In the present study, the data of individual estrogenic effects of BPA, NP and DES were obtained in uterotrophic bioassay respectively, the reference points for BPA, NP and DES were derived from the dose-response ralationship by using the traditional no observed adverse effect (NOAEL) or lowest observed adverse effect level (LOAEL) methods, and the benchmark dose (BMD) method. Then LOAEL values and the benchmark dose lower confidence limit (BMDL10) of single EDCs as the dose design basis for the study of the combined action pattern. Mixed prediction models, the 3 × 2 factorial design model and the concentration addition (CA) model, were employed to analyze the combined estrogenic effect of the three EDCs.

RESULTS

From the dose-response relationship of estrogenic effects of BPA, NP and DES in the model of the prepuberty rats, the BMDL10(NOAEL) of the estrogenic effects of BPA, NP and DES were 90(120) mg/kg body weight, 6 mg/kg body weight and 0.10(0.25) μg/kg body weight, and the LOAEL of the the estrogenic effects of three EDCs were 240 mg/kg body weight, 15 mg/kg body weight and 0.50 μg/kg body weight, respectively. At BMDL10 doses based on the CA concept and the factorial analysis, the mode of combined effects of the three EDCs were dose addition. Mixtures in LOAEL doses, NP and DES combined effects on rat uterine/body weight ratio indicates antagonistic based on the CA concept but additive based on the factorial analysis. Combined effects of other mixtures are all additive by using the two models.

CONCLUSION

Our results showed that CA model provide more accurate results than the factorial analysis, the mode of combined effects of the three EDCs were dose addition, except mixtures in LOAEL doses, NP and DES combined effects indicates antagonistic effects based on the CA model but additive based on the factorial analysis. In particular, BPA and NP produced combination effects that are larger than the effect of each mixture component applied separately at BMDL doses, which show that additivity is important in the assessment of chemicals with estrogenic effects. The use of BMDL as point of departure in risk assessment may lead to underestimation of risk, and a more balanced approach should be considered in risk assessment.

Work and Breast Cancer: Recommendations to Address Research Needs

A review of case-control, cohort, and meta-analytic studies on breast cancer, occupation, and work-related exposures from 2002 to 2017 revealed significant methodological limitations in the current literature. As part of our review, we tabulated the demographic and life history data, breast cancer risk factors, occupational history, and exposure estimates collected and analyzed in each study. Opportunities exist for future research to explore occupation and breast cancer more rigorously and with greater nuance by gathering specific data on age at diagnosis, menopausal status, tumor characteristics, demographics, breast cancer risk factors, and occupational histories, work roles and settings, and exposures. Inclusion of workers in the planning and implementation of research on their occupational risks and exposures is one effective way to refine research questions and ensure research is relevant to workers' needs and concerns.

Statistical Methodology in Studies of Prenatal Exposure to Mixtures of Endocrine-Disrupting Chemicals: A Review of Existing Approaches and New Alternatives

BACKGROUND

Prenatal exposures to endocrine-disrupting chemicals (EDCs) during critical developmental windows have been implicated in the etiologies of a wide array of adverse perinatal and pediatric outcomes. Epidemiological studies have concentrated on the health effects of individual chemicals, despite the understanding that EDCs act together via common mechanisms, that pregnant women are exposed to multiple EDCs simultaneously, and that substantial toxicological evidence of adverse developmental effects has been documented. There is a move toward multipollutant models in environmental epidemiology; however, there is no current consensus on appropriate statistical methods.

OBJECTIVES

We aimed to review the statistical methods used in these studies, to identify additional applicable methods, and to determine the strengths and weaknesses of each method for addressing the salient statistical and epidemiological challenges.

METHODS

We searched Embase, MEDLINE, and Web of Science for epidemiological studies of endocrine-sensitive outcomes in the children of mothers exposed to EDC mixtures during pregnancy and identified alternative statistical methods from the wider literature.

DISCUSSION

We identified 74 studies and analyzed the methods used to estimate mixture health effects, identify important mixture components, account for nonmonotonicity in exposure–response relationships, assess interactions, and identify windows of exposure susceptibility. We identified both frequentist and Bayesian methods that are robust to multicollinearity, performing shrinkage, variable selection, dimension reduction, statistical learning, or smoothing, including methods that were not used by the studies included in our review.

CONCLUSIONS

Compelling motivation exists for analyzing EDCs as mixtures, yet many studies make simplifying assumptions about EDC additivity, relative potency, and linearity, or overlook the potential for bias due to asymmetries in chemical persistence. We discuss the potential impacts of these choices and suggest alternative methods to improve analyses of prenatal exposure to EDC mixtures. https://doi.org/10.1289/EHP2207.

Perfluorooctanoic acid (PFOA) exposure promotes proliferation, migration and invasion potential in human breast epithelial cells

Despite significant advances in early detection and treatment, breast cancer remains a major cause of morbidity and mortality. Perfluorooctanoic acid (PFOA) is a suspected endocrine disruptor and a common environmental pollutant associated with various diseases including cancer. However, the effects of PFOA and its mechanisms of action on hormone-responsive cells remain unclear. Here, we explored the potential tumorigenic activity of PFOA (100 nM–1 mM) in human breast epithelial cells (MCF-10A). MCF-10A cells exposed to 50 and 100 µM PFOA demonstrated a higher growth rate compared to controls. The compound promoted MCF-10A proliferation by accelerating G₀/G₁ to S phase transition of the cell cycle. PFOA increased cyclin D1 and CDK4/6 levels, concomitant with a decrease in p27. In contrast to previous studies of perfluorooctane sulfate (PFOS), the estrogen receptor antagonist ICI 182,780 had no effect on PFOA-induced cell proliferation, whereas the PPARα antagonist GW 6471 was able to prevent the MCF-10A proliferation, indicating that the underlying mechanisms involve PPARα-dependent pathways. Interestingly, we also showed that PFOA is able to stimulate cell migration and invasion, demonstrating its potential to induce neoplastic transformation of human breast epithelial cells. These results suggest that more attention should be paid to the roles of PFOA in the development and progression of breast cancer.

PFOS induces proliferation, cell-cycle progression, and malignant phenotype in human breast epithelial cells

Perfluorooctanesulfonic acid (PFOS) is a synthetic fluorosurfactant widely used in the industry and a prominent environmental toxicant. PFOS is persistent, bioaccumulative, and toxic to mammalian species. Growing evidence suggests that PFOS has the potential to interfere with estrogen homeostasis, posing a risk of endocrine-disrupting effects. Recently, concerns about a potential link between PFOS and breast cancer have been raised, but the mechanisms underlying its actions as a potential carcinogen are unknown. By utilizing cell proliferation assays, flow cytometry, immunocytochemistry, and cell migration/invasion assays, we examined the potentially tumorigenic activity of PFOS (100 nM–1 mM) in MCF-10A breast cell line. The results showed that the growth of MCF-10A cells exposed to 1 and 10 µM PFOS was higher compared to that of the control. Mechanistic studies using 10 µM PFOS demonstrated that the compound promotes MCF-10A proliferation through accelerating G₀/G_1-to-S phase transition of the cell cycle after 24, 48, and 72 h of treatment. In addition, PFOS exposure increased CDK4 and decreased p27, p21, and p53 levels in the cells. Importantly, treatment with 10 µM PFOS for 72 h also stimulated MCF-10A cell migration and invasion, illustrating its capability to induce neoplastic transformation of human breast epithelial cells. Our experimental results suggest that exposure to low levels of PFOS might be a potential risk factor in human breast cancer initiation and development.

State of the evidence 2017: an update on the connection between breast cancer and the environment

BACKGROUND

In this review, we examine the continually expanding and increasingly compelling data linking radiation and various chemicals in our environment to the current high incidence of breast cancer. Singly and in combination, these toxicants may have contributed significantly to the increasing rates of breast cancer observed over the past several decades. Exposures early in development from gestation through adolescence and early adulthood are particularly of concern as they re-shape the program of genetic, epigenetic and physiological processes in the developing mammary system, leading to an increased risk for developing breast cancer. In the 8 years since we last published a comprehensive review of the relevant literature, hundreds of new papers have appeared supporting this link, and in this update, the evidence on this topic is more extensive and of better quality than that previously available.

CONCLUSION

Increasing evidence from epidemiological studies, as well as a better understanding of mechanisms linking toxicants with development of breast cancer, all reinforce the conclusion that exposures to these substances - many of which are found in common, everyday products and byproducts - may lead to increased risk of developing breast cancer. Moving forward, attention to methodological limitations, especially in relevant epidemiological and animal models, will need to be addressed to allow clearer and more direct connections to be evaluated.

Serum levels of environmental pollutants is a risk factor for breast cancer in Inuit: a case control study

BACKGROUND

Environmental Persistent Organic Pollutants (POPs) can alter the hormone homeostasis by mimicking, interfering or blocking the function of hormones; moreover POPs are hypothesized to modify the risk of breast cancer. The association between POPs and breast cancer has been widely studied but the conclusions are inconsistent. The present study examined the associations between serum levels of POPs and breast cancer with focus on the highly exposed Greenlandic Inuit population.

METHODS

The study design was a case-control study of Inuit women from Greenland. The participants were asked to complete a questionnaire with information on reproductive history and lifestyle and to provide a blood sample. The sampling was carried out in two time periods (2000-2003 and 2011-2014). The serum levels were determined of 14 polychlorinated biphenyls (PCBs), 11 organochlorine pesticides (OCPs), 16 perfluoroalkyl acids (PFAAs), 1 polybrominated biphenyl (PBB), and 9 polybrominated diphenyl ethers (PBDEs). Independent samples t-test was used to compare differences between cases and controls and odds ratios (OR) adjusted for identified confounders were obtained using logistic regression.

RESULTS

The study population included 77 breast cancer cases and 84 controls. The majority of the measured compounds declined significantly from 2000 - 2003 to 2011-2014. However, for the perfluorinated carboxylic acids (PFCAs) an increase was observed. The serum levels were significantly higher in cases compared to controls for the majority of the compounds, and after adjusting for age the difference was maintained for ∑OCP, dichlorodiphenyldichloroethylene (p,p'-DDE), ∑PFAA, ∑perfluorinated sulfonic acids (PFSA), perfluorohexane sulfonate (PFHxS), and perfluorooctane sulfonate (PFOS). For the lipophilic POPs, high serum levels (middel/highest vs. lowest tertile) of ∑PCB, ∑estrgoenicPCB, PCB99, PCB138, PCB153, PCB170, PCB170, and PCB183 was associated with breast cancer risk; for the amphiphilic PFAAs, high serum levels of ∑PFAA, ∑PFCA, ∑PFSA, perfluorooctanoic acid (PFOA), perfluorononanoic acid (PFNA), perfluorodecanoic acid (PFDA), PFHxS, and PFOS were associated with breast cancer risk.

CONCLUSION

Significant, positive associations between breast cancer risk and PCBs and PFAAs were observed. The associations indicate that environmental exposure to POPs can be a factor increasing the risk for breast cancer in Inuit women.

Design considerations for identifying breast cancer risk factors in a population-based study in Africa

Although breast cancer is becoming more prevalent in Africa, few epidemiologic studies have been undertaken and appropriate methodologic approaches remain uncertain. We therefore conducted a population-based case-control study in Accra and Kumasi, Ghana, enrolling 2,202 women with lesions suspicious for breast cancer and 2,161 population controls. Biopsy tissue for cases prior to neoadjuvant therapy (if given), blood, saliva and fecal samples were sought for study subjects. Response rates, risk factor prevalences and odds ratios for established breast cancer risk factors were calculated. A total of 54.5% of the recruited cases were diagnosed with malignancies, 36.0% with benign conditions and 9.5% with indeterminate diagnoses. Response rates to interviews were 99.2% in cases and 91.9% in controls, with the vast majority of interviewed subjects providing saliva (97.9% in cases vs. 98.8% in controls) and blood (91.8% vs. 82.5%) samples; lower proportions (58.1% vs. 46.1%) provided fecal samples. While risk factor prevalences were unique as compared to women in other countries (e.g., less education, higher parity), cancer risk factors resembled patterns identified elsewhere (elevated risks associated with higher levels of education, familial histories of breast cancer, low parity and larger body sizes). Subjects with benign conditions were younger and exhibited higher socioeconomic profiles (e.g., higher education and lower parity) than those with malignancies, suggesting selective referral influences. While further defining breast cancer risk factors in Africa, this study showed that successful population-based interdisciplinary studies of cancer in Africa are possible but require close attention to diagnostic referral biases and standardized and documented approaches for high-quality data collection, including biospecimens.

Breast cancer and persistent organic pollutants (excluding DDT): a systematic literature review

Persistent organic pollutants (POPs) are a group of heterogeneous compounds of both natural and anthropogenic origin with highly persistent and bioaccumulative properties. They cause a range of adverse effects to human health and the environment around the world. There is growing concern that POPs may increase breast cancer risk due to their xenoestrogenic properties. The aim of this systematic literature review is to summarize and integrate the risks of breast cancer following environmental exposure to POPs (other than DDT) from primary epidemiological studies published between 2006 and 2015. After searching various databases, 14 case-control studies and one cohort study were included. Evidence of an association between increased breast cancer risk and environmental exposure to these chemicals is inconsistent and inadequate to conclude with certainty. However, most of the studies have examined exposure to the pollutants after diagnosis of breast cancer, overlooking exposure during critical windows of vulnerability. They have also largely focused on individual chemicals but ignored the combined effects of different chemicals. Therefore, major data gaps remain in examining exposure during critical windows of vulnerability and assessing combined effects of multiple chemicals. Development of better exposure assessment methods addressing these gaps is required for future research.

Adipose tissue concentrations of persistent organic pollutants and total cancer risk in an adult cohort from Southern Spain: preliminary data from year 9 of the follow-up

There is an increasing trend in the incidence of cancer worldwide, and it has been accepted that environmental factors account for an important proportion of the global burden. The present paper reports preliminary findings on the influence of the historical exposure to a group of persistent organic pollutants on total cancer risk, at year 9 in the follow-up of a cohort from Southern Spain. A cohort of 368 participants (median age 51 years) was recruited in 2003. Their historical exposure was estimated by analyzing residues of persistent organic pollutants in adipose tissue. Estimation of cancer incidence was based on data from a population-based cancer registry. Statistical analyses were performed using multivariable Cox-regression models. In males, PCB 153 concentrations were positively associated with total cancer risk, with an adjusted hazard ratio (95% confidence interval) of 1.20 (1.01-1.41) for an increment of 100 ng/g lipid. Our preliminary findings suggest a potential relationship between the historical exposure to persistent organic pollutants and the risk of cancer in men. However, these results should be interpreted with caution and require verification during the future follow-up of this cohort.

Exposure to polycyclic aromatic hydrocarbons (PAHs) and bladder cancer: evaluation from a gene-environment perspective in a hospital-based case-control study in the Canary Islands (Spain)

BACKGROUND

Exposure to polycyclic aromatic hydrocarbons (PAHs) has been linked to bladder cancer.

OBJECTIVE

To evaluate the role of PAHs in bladder cancer, PAHs serum levels were measured in patients and controls from a case-control study.

METHODS

A total of 140 bladder cancer patients and 206 healthy controls were included in the study. Sixteen PAHs were analyzed from the serum of subjects by gas chromatography-mass spectrometry.

RESULTS

Serum PAHs did not appear to be related to bladder cancer risk, although the profile of contamination by PAHs was different between patients and controls: pyrene (Pyr) was solely detected in controls and chrysene (Chry) was exclusively detected in the cases. Phenanthrene (Phe) serum levels were inversely associated with bladder cancer (OR = 0·79, 95%CI = 0·64-0·99, P = 0·030), although this effect disappeared when the allelic distribution of glutathione-S-transferase polymorphisms of the population was introduced into the model (multinomial logistic regression test, P = 0·933). Smoking (OR = 3·62, 95%CI = 1·93-6·79, P<0·0001) and coffee consumption (OR = 1·73, 95%CI = 1·04-2·86, P = 0·033) were relevant risk factors for bladder cancer.

CONCLUSIONS

Specific PAH mixtures may play a relevant role in bladder cancer, although such effect seems to be highly modulated by polymorphisms in genes encoding xenobiotic-metabolizing enzymes.

Breast cancer in Sub-Saharan Africa: opportunities for prevention

Although breast cancer is a growing health problem in sub-Saharan Africa, reasons for its increased occurrence remain unclear. We reviewed the published literature to determine the magnitude of the increase in breast cancer, associated risk factors (including for breast cancer subtypes), and ways to reduce incidence and mortality. Some of the increased breast cancer occurrence likely reflects that women are living longer and adopting lifestyles that favor higher incidence rates. However, a greater proportion of breast cancers occur among premenopausal women as compared to elsewhere, which may reflect unique risk factors. Breast cancers diagnosed among African women reportedly include a disproportionate number of poor prognosis tumors, including hormone receptor negative, triple negative, and core basal phenotype tumors. However, it is unclear how lack of standardized methods for tissue collection, fixation, and classification contribute to these rates. Given appropriate classifications, it will be of interest to compare rates with other populations and to identify risk factors that relate to specific tumor subtypes. This includes not only risk factors that have been recognized in other populations but also some that may play unique roles among African women, such as genetic factors, microbiomata, xenoestrogens, hair relaxers, and skin lighteners. With limited opportunities for effective treatment, a focus is needed on identifying etiologic factors that may be amenable to intervention. It will also be essential to understand reasons why women delay seeking care after the onset of symptoms and for there to be educational campaigns about the importance of early detection.

Low-dose effects of hormones and endocrine disruptors

Endogenous hormones have effects on tissue morphology, cell physiology, and behaviors at low doses. In fact, hormones are known to circulate in the part-per-trillion and part-per-billion concentrations, making them highly effective and potent signaling molecules. Many endocrine-disrupting chemicals (EDCs) mimic hormones, yet there is strong debate over whether these chemicals can also have effects at low doses. In the 1990s, scientists proposed the "low-dose hypothesis," which postulated that EDCs affect humans and animals at environmentally relevant doses. This chapter focuses on data that support and refute the low-dose hypothesis. A case study examining the highly controversial example of bisphenol A and its low-dose effects on the prostate is examined through the lens of endocrinology. Finally, the chapter concludes with a discussion of factors that can influence the ability of a study to detect and interpret low-dose effects appropriately.

Adipose tissue concentrations of persistent organic pollutants and prevalence of type 2 diabetes in adults from Southern Spain

There is increasing evidence that environmental factors play an important role in the development of type 2 diabetes. Several persistent organic pollutants are suspected to contribute to the increasing prevalence and risk of type 2 diabetes. The aim of this study was to investigate the association of the body burden of three organochlorine pesticides and three polychlorinated biphenyls and the overall estrogenic activity with the risk of type 2 diabetes in a sample of adults from Southern Spain. Samples of adipose tissue and serum were obtained from 386 subjects undergoing non-cancer-related surgery and were extracted using validated methodologies. Residues of persistent organic pollutants were analyzed by means of high-resolution gas chromatography with a mass spectrometry detector in tandem mode. The overall estrogenicity of the adipose tissue extracts was measured by using the total effective xenoestrogen burden (TEXB) biomarker. Data on lifestyle, dietary habits, and health status were gathered from face-to-face interviews and clinical records. Statistical analyses were performed with unconditional logistic regression and different adjustment levels. In the models adjusted for adipose tissue origin, sex, age, and body mass index, the 2nd and 3rd tertiles of adipose tissue concentrations of p,p'-dichlorodiphenyldichloroethylene (p,p'-DDE) were positively associated with the risk of diabetes [odds ratios (95% confidence interval)=3.6 (0.8-17.3) and 4.4 (1.0-21.0), respectively]. A positive association with β-hexachlorocyclohexane was also found when body mass index and adipose tissue origin were removed from the models, with odds ratios (95% confidence interval) of 3.3 (1.0-10.4) and 5.5 (1.7-17.3), for the 2nd and 3rd tertiles of exposure, respectively. In addition, a statistically significant interaction was observed between p,p'-DDE and body mass index, such that the risk of diabetes increased with tertiles of exposure in a linear manner in non-obese subjects but not in the obese, in whom an inverted U-shape pattern was observed.

Changes in male hormone profile after occupational organophosphate exposure. A longitudinal study

There is a growing concern about the endocrine effects of long-term, low-level exposure to organophosphate (OP) compounds. Studies on experimental animals have found that OP pesticides have an impact on the endocrine system and a few clinical and epidemiological studies have also shown that OPs may affect the male hormone profile, although results are inconsistent. We have evaluated the effect of exposure to OP pesticides, measured through urinary levels of six dialkylphosphate (DAP) metabolites, on male hormone profile in 136 floriculture workers from the State of Mexico and Morelos during two agricultural periods with different degree of pesticide exposure. Generalized estimated equations (GEE) models were developed and adjusted for several potential confounders, including PON1 enzyme activity, as a biomarker of susceptibility, and serum levels of p,p'-DDE, a metabolite of the pesticide DDT widely used in Mexico until 1999 for control of agricultural pests and malaria. Exposure of male floriculture workers to OP pesticides was associated with increased serum levels of follicle-stimulating hormone (FSH) and prolactin and with decreased serum testosterone and inhibin B levels. Among all DAPs tested, only DETP was inversely associated with luteinizing hormone (LH). Estradiol showed a marginally significant positive trend with DEP and DETP derivatives. In conclusion, OP pesticides may have an impact on the endocrine function because of their potential to modify the male hormone profile as a function of the type of pesticide used as well as the magnitude of exposure.

Hormones and endocrine-disrupting chemicals: low-dose effects and nonmonotonic dose responses

For decades, studies of endocrine-disrupting chemicals (EDCs) have challenged traditional concepts in toxicology, in particular the dogma of "the dose makes the poison," because EDCs can have effects at low doses that are not predicted by effects at higher doses. Here, we review two major concepts in EDC studies: low dose and nonmonotonicity. Low-dose effects were defined by the National Toxicology Program as those that occur in the range of human exposures or effects observed at doses below those used for traditional toxicological studies. We review the mechanistic data for low-dose effects and use a weight-of-evidence approach to analyze five examples from the EDC literature. Additionally, we explore nonmonotonic dose-response curves, defined as a nonlinear relationship between dose and effect where the slope of the curve changes sign somewhere within the range of doses examined. We provide a detailed discussion of the mechanisms responsible for generating these phenomena, plus hundreds of examples from the cell culture, animal, and epidemiology literature. We illustrate that nonmonotonic responses and low-dose effects are remarkably common in studies of natural hormones and EDCs. Whether low doses of EDCs influence certain human disorders is no longer conjecture, because epidemiological studies show that environmental exposures to EDCs are associated with human diseases and disabilities. We conclude that when nonmonotonic dose-response curves occur, the effects of low doses cannot be predicted by the effects observed at high doses. Thus, fundamental changes in chemical testing and safety determination are needed to protect human health.

Urinary bisphenol A concentrations in girls from rural and urban Egypt: a pilot study

BACKGROUND

Exposure to endocrine active compounds, including bisphenol A (BPA), remains poorly characterized in developing countries despite the fact that behavioral practices related to westernization have the potential to influence exposure. BPA is a high production volume chemical that has been associated with metabolic dysfunction as well as behavioral and developmental effects in people, including children. In this pilot study, we evaluate BPA exposure and assess likely pathways of exposure among girls from urban and rural Egypt.

METHODS

We measured urinary concentrations of total (free plus conjugated) species of BPA in spot samples in urban (N = 30) and rural (N = 30) Egyptian girls, and compared these concentrations to preexisting data from age-matched American girls (N = 47) from the U.S. National Health and Nutrition Examination Survey (NHANES). We also collected anthropometric and questionnaire data regarding food storage behaviors to assess potential routes of exposure.

RESULTS

Urban and rural Egyptian girls exhibited similar concentrations of urinary total BPA, with median unadjusted values of 1.00 and 0.60 ng/mL, respectively. Concentrations of urinary BPA in this group of Egyptian girls (median unadjusted: 0.70 ng/mL) were significantly lower compared to age-matched American girls (median unadjusted: 2.60 ng/mL) according to NHANES 2009-2010 data. Reported storage of food in plastic containers was a significant predictor of increasing concentrations of urinary BPA.

CONCLUSIONS

Despite the relatively low urinary BPA concentrations within this Egyptian cohort, the significant association between food storage behaviors and increasing urinary BPA concentration highlights the need to understand food and consumer product patterns that may be closing the gap between urban and rural lifestyles.

Contribution of sociodemographic characteristics, occupation, diet and lifestyle to DDT and DDE concentrations in serum and adipose tissue from a Bolivian cohort

The organochlorine pesticide p,p'-Dichlorodiphenyltrichloroethane (DDT) was widely used in the early 1960s-70s for vector control in tropical and subtropical areas of South America. Due to its persistence, DDT has a high potential to bioaccumulate in the food chain and living organisms and is a major public health concern, especially in South America. The main purpose of the present study was to investigate predictors of serum and adipose tissue concentrations of p,p'-DDT and its main metabolite, p,p'-dichlorodiphenyldichloroethylene (p,p'-DDE), in an adult cohort (n=112) from Santa Cruz de la Sierra, Bolivia, using multiple linear regression models. These models explained 29.3-47.8% of the variability in adipose tissue concentrations of p,p'-DDT and p,p'-DDE, respectively, and 32.9-47.0% of that in serum. Main exposure predictors included age, occupational class, residence, diet, smoking habit, and accumulated breastfeeding time. This is one of the few studies to explore predictors of human exposure to these chemicals using a multivariate approach in a South American population. Results show that predictors of human exposure to p,p'-DDT and p,p'-DDE in Santa Cruz de la Sierra may diverge from those found in other populations of the world, due to particular sociodemographic and lifestyle characteristics of this region.

Environmental causes of cancer: endocrine disruptors as carcinogens

Environmental endocrine disrupting chemicals (EDCs), including pesticides and industrial chemicals, have been and are released into the environment producing deleterious effects on wildlife and humans. The effects observed in animal models after exposure during organogenesis correlate positively with an increased incidence of malformations of the male genital tract and of neoplasms and with the decreased sperm quality observed in European and US populations. Exposure to EDCs generates additional effects, such as alterations in male and female reproduction and changes in neuroendocrinology, behavior, metabolism and obesity, prostate cancer and thyroid and cardiovascular endocrinology. This Review highlights the carcinogenic properties of EDCs, with a special focus on bisphenol A. However, humans and wildlife are exposed to a mixture of EDCs that act contextually. To explain this mindboggling complexity will require the design of novel experimental approaches that integrate the effects of different doses of structurally different chemicals that act at different ages on different target tissues. The key to this complex problem lies in the adoption of mathematical modeling and computer simulations afforded by system biology approaches. Regardless, the data already amassed highlight the need for a public policy to reduce exposure to EDCs.

Insulin-like growth factor-I (IGF-I) serum concentrations in healthy children and adolescents: relationship to level of contamination by DDT-derivative pesticides

CONTEXT

Serum levels of Insulin-like growth factor I (IGF-I) play a critical role in children growth and in the pathogenesis of several diseases. In addition, recent studies suggest that DDT-derivative organochlorine pesticides (OC-DDTs) could influence IGF levels in human beings.

OBJECTIVE AND DESIGN

Because it has been suggested that IGF-I peak levels at puberty could determine IGF-I levels in adulthood, we developed a cross-sectional study of the potential association between serum levels of OC-DDTs and IGF system in 160 serum samples from young people (81 boys and 79 girls) living in the Canary Islands (Spain).

RESULTS

Multivariate tests were used adjusting for confounding variables (age, height, and weight) and stratifying by gender and age: IGF-I serum levels were significantly lower in pre-pubertal male children (6-15years) who showed detectable values of p,p'-DDE, and p,p'-DDD than in pre-pubertal male children with undetectable levels of these OC-DDTs-metabolites (p=0.023 and p=0.049, respectively). In addition, in this multivariate model, a non-linear dose-response curve was observed between Total DDT body burden (sum of the three DDT-derivatives measured: p,p'-DDT, p,p'-DDE, and p,p'-DDD) and IGF-I in pre-pubertal male children (6-15years; p=0.043).

CONCLUSION

These findings suggest that OC-DDTs could modulate the IGF-system in a way that is highly influenced by gender and age. Improvements in our understanding of exogenous determinants of the IGF-system may provide new insights into the role played by environmental contaminants in IGF-related diseases.

Anthropogenic pollutants: a threat to ecosystem sustainability?

Pollutants, including synthetic organic materials and heavy metals, are known to adversely affect physiological systems in all animal species studied to date. While many individual chemicals can perturb normal functions, the combined actions of multiple pollutants are of particular concern because they can exert effects even when each individual chemical is present at concentrations too low to be individually effective. The biological effects of pollutants differ greatly between species reflecting differences in the pattern of exposure, routes of uptake, metabolism following uptake, rates of accumulation and sensitivity of the target organs. Thus, understanding of the effects of pollutants on wildlife and ecosystems will require detailed study of many different species, representing a wide range of taxa. However, such studies can be informed by knowledge obtained in more controlled conditions which may indicate likely mechanisms of action and suitable endpoint measurements. Responses may be exacerbated by interactions between the effects of pollutants and environmental stressors, such as under-nutrition or osmotic stresses and so changes in such variables associated with climatic changes may exacerbate physiological responses to pollutant burdens.

Exposure to a complex cocktail of environmental endocrine-disrupting compounds disturbs the kisspeptin/GPR54 system in ovine hypothalamus and pituitary gland

BACKGROUND

Ubiquitous environmental chemicals, including endocrine-disrupting chemicals (EDCs), are associated with declining human reproductive health, as well as an increasing incidence of cancers of the reproductive system. Verifying such links requires animal models exposed to "real-life," environmentally relevant concentrations/mixtures of EDC, particularly in utero, when sensitivity to EDC exposure is maximal.

OBJECTIVES

We evaluated the effects of maternal exposure to a pollutant cocktail (sewage sludge) on the ovine fetal reproductive neuroendocrine axes, particularly the kisspeptin (KiSS-1)/GPR54 (G-protein-coupled receptor 54) system.

METHODS

KiSS-1, GPR54, and ERalpha (estrogen receptor alpha) mRNA expression was quantified in control (C) and treated (T) maternal and fetal (110-day) hypothalami and pituitary glands using semiquantitative reverse transcription polymerase chain reaction, and colocalization of kisspeptin with LHbeta (luteinizing hormone beta) and ERalpha in C and T fetal pituitary glands quantified using dual-labeling immunohistochemistry.

RESULTS

Fetuses exposed in utero to the EDC mixture showed reduced KiSS-1 mRNA expression across three hypothalamic regions examined (rostral, mid, and caudal) and had fewer kisspetin immunopositive cells colocalized with both LHbeta and ERalpha in the pituitary gland. In contrast, treatment had no effect on parameters measured in the adult ewe hypothalamus or pituitary.

CONCLUSIONS

This study demonstrates that the developing fetus is sensitive to real-world mixtures of environmental chemicals, which cause significant neuroendocrine alterations. The important role of kisspeptin/GPR54 in regulating puberty and adult reproduction means that in utero disruption of this system is likely to have long-term consequences in adulthood and represents a novel, additional pathway through which environmental chemicals perturb human reproduction.

Effects of cadmium on estrogen receptor mediated signaling and estrogen induced DNA synthesis in T47D human breast cancer cells

Cadmium (Cd) has been shown to bind to the human estrogen receptor (ER), yet studies on Cd's estrogenic effects have yielded inconsistent results. In this study, we investigated the effects of Cd on DNA synthesis and its simultaneous effects on both genomic (mediated by nuclear ER (nER)) and non-genomic (mediated by membrane-bound ER (mER)) signaling in human breast cancer derived T47D cells. No effects on DNA synthesis were observed for non-cytotoxic concentrations of CdCl(2) (0.1-1000 nM), and Cd did not increase progesterone receptor (PgR) or pS2 mRNA levels. However, Cd stimulated phosphorylation of ERK1/2 MAPK, detectable following 10 min and 18 h of treatment. The sustained Cd-induced ERK1/2 phosphorylation was inhibited by the ER antagonist ICI 182,780, suggesting the involvement of ER. In addition, Cd enhanced DNA synthesis and pS2 mRNA levels in estrogen (10 pM estradiol) treated T47D cells. The MEK1/2 specific inhibitor U0126 blocked DNA synthesis stimulated by estradiol (E2) and the E2-Cd mixtures. These findings indicate that the ERK1/2 signaling is critical in E2-related DNA synthesis. The sustained ERK1/2 phosphorylation may contribute to the Cd-induced enhancement of DNA synthesis and pS2 mRNA in mixture with low-concentration E2.

Endocrine disrupting chemicals in indoor and outdoor air

The past 50 years have seen rapid development of new building materials, furnishings, and consumer products and a corresponding explosion in new chemicals in the built environment. While exposure levels are largely undocumented, they are likely to have increased as a wider variety of chemicals came into use, people began spending more time indoors, and air exchange rates decreased to improve energy efficiency. As a result of weak regulatory requirements for chemical safety testing, only limited toxicity data are available for these chemicals. Over the past 15 years, some chemical classes commonly used in building materials, furnishings, and consumer products have been shown to be endocrine disrupting chemicals-that is they interfere with the action of endogenous hormones. These include PCBs, used in electrical equipment, caulking, paints and surface coatings; chlorinated and brominated flame retardants, used in electronics, furniture, and textiles; pesticides, used to control insects, weeds, and other pests in agriculture, lawn maintenance, and the built environment; phthalates, used in vinyl, plastics, fragrances, and other products; alkylphenols, used in detergents, pesticide formulations, and polystyrene plastics; and parabens, used to preserve products like lotions and sunscreens. This paper summarizes reported indoor and outdoor air concentrations, chemical use and sources, and toxicity data for each of these chemical classes. While industrial and transportation-related pollutants have been shown to migrate indoors from outdoor sources, it is expected that indoor sources predominate for these consumer product chemicals; and some studies have identified indoor sources as the predominant factor influencing outdoor ambient air concentrations in densely populated areas. Mechanisms of action, adverse effects, and dose-response relationships for many of these chemicals are poorly understood and no systematic screening of common chemicals for endocrine disrupting effects is currently underway, so questions remain as to the health impacts of these exposures.

Perinatal exposure to the xenoestrogen bisphenol-A induces mammary intraductal hyperplasias in adult CD-1 mice

Humans are routinely exposed to bisphenol-A (BPA), an estrogenic compound that leaches from consumer products. Given the sensitivity of the developing organism to hormones, exposure of fetuses and infants is a concern. Here, CD-1 mice were exposed to environmentally relevant doses of BPA during gestation and the lactational period (gestational day 8 through postnatal day 16). At 3, 9 and 12-15 months of age, mammary glands from exposed offspring were examined for structural changes. BPA-exposed females demonstrated altered mammary phenotypes including the appearance of alveolar buds. Additionally, intraductal hyperplasias were observed exclusively in BPA-exposed females. These lesions had the appearance of "beaded" ducts, with epithelial cells present inside the ductal lumen and increased proliferation indexes compared to normal ducts. Similar structures have also been observed following exposure to other estrogens. These results are further evidence that perinatal BPA exposure can alter the morphology of the rodent mammary gland in adulthood.

Evidence for a programming effect of early menarche on the rise of breast cancer incidence in Hong Kong

BACKGROUND

Younger age at menarche and older age at first live birth are implicated as risk factors for breast cancer, but the extent to which these factors contribute to the sharply rising incidence of this disease in developing countries has received little study.

METHODS

We conducted a retrospective analysis of 702 consecutive breast cancer patients diagnosed at a single hospital in Hong Kong during 2003-2006. Comparisons were made between patients with different ages at cancer diagnosis (hence, belonging to different birth cohorts) and their respective ages at menarche and at first live birth. We then correlated these age-dependent differences with overall breast cancer incidence data from the Hong Kong Cancer Registry.

RESULTS

When patients diagnosed before age 40 are compared with those after 60, the age of menarche is lower in the former subgroup (12.7 vs. 14.2; p<10(-6)) while the age of first live birth is greater (28.2 vs. 25.5; p<0.01). However, registry data suggest that the progressive rise in breast cancer incidence has not affected those over 65, nor very young (20-39 years) patients.

CONCLUSION

Lifestyle variables that reduce age at menarche may contribute to the rising risk of breast cancer diagnosed after age 40 in Hong Kong, whereas earlier-onset cancers may be characterised by a distinct pathogenesis. Although retrospective, these data raise the possibility that cancer-preventive health interventions could gainfully target reversible risk factors favoring early menarche - such as formula infant feeding, high-fat diets, and lack of exercise - in children and adolescents living in developing countries such as China.

The total effective xenoestrogen burden, a biomarker of exposure to xenoestrogen mixtures, is predicted by the (anti)estrogenicity of its components

Appropriate biomarkers of human exposure are required for epidemiological studies of endocrine disruption. We addressed this issue by improving a standardized method to assess the total effective xenoestrogen burden (TEXB), a biomarker of xenoestrogen exposure. Extensive separation of xenoestrogens from endogenous hormones was made in 20 adipose tissue samples by HPLC, and two eluates were separated and tested in the E-Screen bioassay. An extensive fractionation protocol was also developed. The objective of this study was to investigate predictors of TEXB by using a multiple regression model after adjusting by confounding factors. The final model included the estrogenicity of 8 out of 11 individual 1-min fractions into which the xenoestrogen eluate was split and the marital status of patients, and it explained 97% of TEXB variability, and variables. Our results indicate that TEXB of complex mixtures can be accurately predicted from the estrogenicity of a small number of components.

In utero exposure to low doses of environmental pollutants disrupts fetal ovarian development in sheep

Epidemiological studies of the impact of environmental chemicals on reproductive health demonstrate consequences of exposure but establishing causative links requires animal models using ‘real life’ in utero exposures. We aimed to determine whether prolonged, low-dose, exposure of pregnant sheep to a mixture of environmental chemicals affects fetal ovarian development. Exposure of treated ewes (n = 7) to pollutants was maximized by surface application of processed sewage sludge to pasture. Control ewes (n = 10) were reared on pasture treated with inorganic fertilizer. Ovaries and blood were collected from fetuses (n = 15 control and n = 8 treated) on Day 110 of gestation for investigation of fetal endocrinology, ovarian follicle/oocyte numbers and ovarian proteome. Treated fetuses were 14% lighter than controls but fetal ovary weights were unchanged. Prolactin (48% lower) was the only measured hormone significantly affected by treatment. Treatment reduced numbers of growth differentiation factor (GDF9) and induced myeloid leukaemia cell differentiation protein (MCL1) positive oocytes by 25–26% and increased pro-apoptotic BAX by 65% and 42% of protein spots in the treated ovarian proteome were differently expressed compared with controls. Nineteen spots were identified and included proteins involved in gene expression/transcription, protein synthesis, phosphorylation and receptor activity. Fetal exposure to environmental chemicals, via the mother, significantly perturbs fetal ovarian development. If such effects are replicated in humans, premature menopause could be an outcome.

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.

Serum levels of insulin-like growth factor-I in relation to organochlorine pesticides exposure

CONTEXT

Insulin-like growth factor 1 (IGF-I) and organochlorine pesticides (OCs) have been involved in the pathogenesis of several diseases like cancer, diabetes and growth disorders.

OBJECTIVE AND DESIGN

The potential relationship between the serum levels of various OCs and serum IGF-I was investigated in adults (176 men and 247 women) from a representative sample of the general population of the Canary Islands (Spain).

RESULTS

After adjustment for potential confounders, which include body mass index, age, and IGF-binding protein-3 (IGFBP-3), IGF-I levels were significantly lower in the 247 women who showed detectable levels of p,p'-DDD (a DDT-metabolite) than in women who presented non-detectable levels of this pesticide (p=0.030), specially in 36-50 years old women. A similar negative relationship was also found between IGF-I and aldrin (a non-DDT-derivative) in women (p=0.049). In the group of 176 men, aldrin seemed to exert a similar negative effect on IGF-I (p=0.046) and this effect was clearly significant in the oldest group (51-65 years) (p=0.009). A non-linear dose-response curve was observed between Total Cyclodienes Body Burden (Total Cyclodienes; sum of aldrin, dieldrin and endrin) and IGF-I in men (p=0.024). These findings suggest that OCs could modulate the IGF-system in a way that is highly influenced by gender, age and by chemical or combination of chemicals implicated. Such circumstances may contribute to the development of a number of diseases related to IGF-I and should be taken into account in public health decisions.

Ten years of mixing cocktails: a review of combination effects of endocrine-disrupting chemicals

In the last 10 years, good evidence has become available to show that the combined effects of endocrine disruptors (EDs) belonging to the same category (e.g., estrogenic, antiandrogenic, or thyroid-disrupting agents) can be predicted by using dose addition. This is true for a variety of end points representing a wide range of organizational levels and biological complexity. Combinations of EDs are able to produce significant effect, even when each chemical is present at low doses that individually do not induce observable effects. However, comparatively little is known about mixtures composed of chemicals from different classes of EDs. Nevertheless, I argue that the accumulated evidence seriously undermines continuation with the customary chemical-by-chemical approach to risk assessment for EDs. Instead, we should seriously consider group-wise regulation of classes of EDs. Great care should be taken to define such classes by using suitable similarity criteria. Criteria should focus on common effects, rather than common mechanisms. In this review I also highlight research needs and identify the lack of information about exposure scenarios as a knowledge gap that seriously hampers progress with ED risk assessment. Future research should focus on investigating the effects of combinations of EDs from different categories, with considerable emphasis on elucidating mechanisms. This strategy may lead to better-defined criteria for grouping EDs for regulatory purposes. Also, steps should be taken to develop dedicated mixtures exposure assessment for EDs.

Activity of xenoestrogens at nanomolar concentrations in the E-Screen assay

BACKGROUND

Certain effects induced by endocrine-disrupting chemicals (EDCs) may occur at dose levels lower than those normally tested in toxicology, but few systematic dose-response studies have been carried out in the low-dose range.

OBJECTIVES

The high statistical power afforded by a high-throughput in vitro assay such as the E-Screen assay was exploited with the aim of producing low-dose estimates for 24 estrogenic chemicals, including endogenous hormones and xenoestrogens.

RESULTS

Unusual dose-response curves with inverted U-shapes were not observed in the low-dose range. Instead, many chemicals exhibited curves with very small gradients at low doses, and this complicated the reliable estimation of low effects. Systematic comparisons between the outcomes of hypothesis-testing procedures (lowest observed effect concentrations--LOECs, no observed effect concentrations--NOECs) and regression modeling approaches (EC(01)--effective concentration causing a 1% effect, EC(05)--effective concentration causing a 5% effect) produced estimates that agreed reasonably well. In many cases, NOECs were shown to be associated with proliferative responses of 1-2%. This is in contrast with the widespread perception of NOECs as values that signal complete absence of effects. For many of the tested xenoestrogens, the NOECs, EC(01), and EC(05) were in the nanomolar range, and comparisons with measured serum and adipose tissue levels in Europe revealed considerable overlaps in some cases.

CONCLUSIONS

Our studies illustrate the difficulties that may be encountered during the estimation of low doses in vivo. High statistical power is required when the underlying dose-response curves are shallow. Through the use of large sample sizes and numerous repeats, the experimental power of the E-Screen assay was sufficiently high to measure effect magnitudes of around 1-2% with reliability. However, such resources are usually not available for in vivo testing, with the consequence that the statistical detection limits are considerably higher. If this coincides with shallow dose-response curves in the low-effect range (which is normally not measurable in vivo), the limited resolving power of in vivo assays may seriously constrain low-dose testing.

Biomonitoring of environmental estrogens in human tissues

Two examples are presented for the application of the total effective xenoestrogen burden as biomarker of chemical exposure measured in tissue samples from patients recruited for two case-control studies. The first study focused on environmental chemicals with hormone mimicking activity, the so-called environmental estrogens, and their participation in the etiology of breast cancer. The second study investigated mother-child exposure to persistent organochlorine chemicals and assessed their combined effect on the risk of male urogenital malformations in the newborn.