Cancer as development gone awry: the case for bisphenol-A as a carcinogen

Systematic review of the potential carcinogenicity of bisphenol A in humans

Bisphenol A (BPA) is a synthetic chemical to which humans are exposed through a variety of environmental sources. We have conducted a comprehensive, systematic review of 29 epidemiology studies and 27 experimental animal studies, published through May 2022, evaluating the potential carcinogenicity of BPA to contribute to the understanding of whether BPA is carcinogenic in humans. We conducted this review according to best practices for systematic reviews and incorporating established frameworks for study quality evaluation and evidence integration. The epidemiology studies have many limitations that increase the risk of biased results, but overall, the studies do not provide clear and consistent evidence for an association between BPA exposure and the development of any type of cancer. The experimental animal studies also do not provide strong and consistent evidence that BPA is associated with the induction of any malignant tumor type. Some of the proposed mechanisms for BPA carcinogenicity are biologically plausible, but the relevance to human exposures is not clear. We conclude that there is inadequate evidence to support a causal relationship between BPA exposure and human carcinogenicity, based on inadequate evidence in humans, as well as evidence from experimental animal studies that suggests a causal relationship is not likely.

Matrix Composition Modulates Vitamin D3's Effects on 3D Collagen Fiber Organization by MCF10A Cells

Vitamin D3 (vitD3) has been implicated in various cellular functions affecting multiple tissue types. Epidemiological and laboratory studies suggest that vitD3 may be effective as a preventive or therapeutic option for breast cancer. However, randomized clinical trials have yet to confirm these suggestions. Breast neoplasias can arise from developmental alterations; based on this evidence, we seek to understand vitD3's role in normal breast development, particularly its role in epithelial morphogenetic processes such as ductal elongation, branching, and alveolar formation. These processes require extensive changes in the extracellular microenvironment, such as collagen fiber organization, and are largely influenced by hormones. Here, we build upon our past work to shed light on calcitriol's effects on collagen fiber organization by breast epithelial cells, and how such effects are modulated by extracellular matrix composition. We embedded MCF10A normal human breast epithelial cells in two different matrices-collagen type I and collagen type I + 10% Matrigel; treatment with calcitriol resulted in flatter epithelial structures. Next, using two-photon microscopy, we examined changes in collagen fiber organization and corresponding changes in epithelial structures. Applying a novel three-dimensional (3D) image analysis method, we show that increasing doses of calcitriol result in denser collagen fiber bundles in the localized area surrounding the epithelial structures, and that these bundles are aligned in a more parallel direction to epithelial structures when exposed to the highest vitD3 dose. Changed patterns in fiber organization may explain the flattening of epithelial structures; in turn, changes in biophysical forces in the matrix abutting these structures may be responsible for changes in the referred patterns. Addition of 10% Matrigel dampened the effects of calcitriol on both epithelial morphogenesis and fiber organization. Overall, we report novel functions of calcitriol in the breast epithelium and add to the growing body of evidence documenting how hormones affect biophysical processes.

From Wingspread to CLARITY: a personal trajectory

In the three decades since endocrine disruption was conceptualized at the Wingspread Conference, we have witnessed the growth of this multidisciplinary field and the accumulation of evidence showing the deleterious health effects of endocrine-disrupting chemicals. It is only within the past decade that, albeit slowly, some changes regarding regulatory measures have taken place. In this Perspective, we address some historical points regarding the advent of the endocrine disruption field and the conceptual changes that endocrine disruption brought about. We also provide our personal recollection of the events triggered by our serendipitous discovery of oestrogenic activity in plastic, a founder event in the field of endocrine disruption. This recollection ends with the CLARITY study as an example of a discordance between 'science for its own sake' and 'regulatory science' and leads us to offer a perspective that could be summarized by the motto attributed to Ludwig Boltzmann: "Nothing is more practical than a good theory".

A Combined Morphometric and Statistical Approach to Assess Nonmonotonicity in the Developing Mammary Gland of Rats in the CLARITY-BPA Study

BACKGROUND

The Consortium Linking Academic and Regulatory Insights on Bisphenol-A (CLARITY-BPA) is a rare collaboration of guideline-compliant (core) studies and academic hypothesis-based studies to assess the effects of bisphenol A (BPA).

OBJECTIVES

We aimed to a) determine whether BPA showed effects on the developing rat mammary gland using new quantitative and established semiquantitative methods in two laboratories, b) develop a software tool for automatic evaluation of quantifiable aspects of the mammary ductal tree, and c) compare those methods.

METHODS

Sprague-Dawley rats were exposed to BPA, vehicle, or positive control [ethinyl estradiol (EE2)] by oral gavage beginning on gestational day (GD)6 and continuing with direct dosing of the pups after birth. There were two studies: subchronic and chronic. The latter used two exposure regimes, one stopping at postnatal day (PND)21 (stop-dose) the other continuing until tissue harvest (continuous). Glands were harvested at multiple time points; whole mounts and histological specimens were analyzed blinded to treatment.

RESULTS

The subchronic study's semiquantitative analysis revealed no significant differences between control and BPA dose groups at PND21, whereas at PND90 there were significant differences between control and the lowest BPA dose and between control and the lowest EE2 dose in animals in estrus. Quantitative, automatized analysis of the chronic PND21 specimens displayed nonmonotonic BPA effects, with a breaking point between the 25 and 250μg/kg body weight (BW) per day doses. This breaking point was confirmed by a global statistical analysis of chronic study animals at PND90 and 6 months analyzed by the quantitative method. The BPA response was different from the EE2 effect for many features.

CONCLUSIONS

Both the semiquantitative and the quantitative methods revealed nonmonotonic effects of BPA. The quantitative unsupervised analysis used 91 measurements and produced the most striking nonmonotonic dose-response curves. At all time points, lower doses resulted in larger effects, consistent with the core study, which revealed a significant increase of mammary adenocarcinoma incidence in the stop-dose animals at the lowest BPA dose tested. https://doi.org/10.1289/EHP6301.

The Case for BPA as an Obesogen: Contributors to the Controversy

Since the inception of the term endocrine disruptor, the idea that the environment is an important determinant of phenotype has motivated researchers to explore the effect of low dose exposure to BPA during organogenesis. The syndrome observed was complex, affecting various endpoints such as reproduction and reproductive tissues, behavior, mammary gland development and carcinogenesis, glucose homeostasis, and obesity. This constellation of impacted endpoints suggests the possibility of complex interactions among the multiple effects of early BPA exposure. One key finding of our rodent studies was alterations of energy and amino-acid metabolism that were detected soon after birth and continued to be present at all time points examined through 6 months of age. The classical manifestations of obesity and associated elements of metabolic disease took a longer time to become apparent. Here we examine the validity of the often-mentioned lack of reproducibility of obesogenic effects of BPA, starting from the known environmental causes of variation, which are diverse and range from the theoretical like the individuation process and the non-monotonicity of the dose-response curve, to the very pragmatic like housing, feed, and time and route of exposure. We then explore environmental conditions that may hinder reproducibility and discuss the effect of confounding factors such as BPA-induced hyperactivity. In spite of all the potential sources of variation, we find that some obesogenic or metabolic effects of BPA are reproducibly observed when study conditions are analogous. We recommend that study authors describe details of their study conditions including the environment, husbandry, and feed. Finally, we show that when experimental conditions are strictly maintained, reproducibility, and stability of the obese phenotype is consistently observed.

Prenatal exposure to BPA alters the epigenome of the rat mammary gland and increases the propensity to neoplastic development

Exposure to environmental estrogens (xenoestrogens) may play a causal role in the increased breast cancer incidence which has been observed in Europe and the US over the last 50 years. The xenoestrogen bisphenol A (BPA) leaches from plastic food/beverage containers and dental materials. Fetal exposure to BPA induces preneoplastic and neoplastic lesions in the adult rat mammary gland. Previous results suggest that BPA acts through the estrogen receptors which are detected exclusively in the mesenchyme during the exposure period by directly altering gene expression, leading to alterations of the reciprocal interactions between mesenchyme and epithelium. This initiates a long sequence of altered morphogenetic events leading to neoplastic transformation. Additionally, BPA induces epigenetic changes in some tissues. To explore this mechanism in the mammary gland, Wistar-Furth rats were exposed subcutaneously via osmotic pumps to vehicle or 250 µg BPA/kg BW/day, a dose that induced ductal carcinomas in situ. Females exposed from gestational day 9 to postnatal day (PND) 1 were sacrificed at PND4, PND21 and at first estrus after PND50. Genomic DNA (gDNA) was isolated from the mammary tissue and immuno-precipitated using anti-5-methylcytosine antibodies. Detection and quantification of gDNA methylation status using the Nimblegen ChIP array revealed 7412 differentially methylated gDNA segments (out of 58207 segments), with the majority of changes occurring at PND21. Transcriptomal analysis revealed that the majority of gene expression differences between BPA- and vehicle-treated animals were observed later (PND50). BPA exposure resulted in higher levels of pro-activation histone H3K4 trimethylation at the transcriptional initiation site of the alpha-lactalbumin gene at PND4, concomitantly enhancing mRNA expression of this gene. These results show that fetal BPA exposure triggers changes in the postnatal and adult mammary gland epigenome and alters gene expression patterns. These events may contribute to the development of pre-neoplastic and neoplastic lesions that manifest during adulthood.