John Peterson Myers

A Clash of Old and New Scientific Concepts in Toxicity, with Important Implications for Public Health

Background A core assumption of current toxicologic procedures used to establish health standards for chemical exposures is that testing the safety of chemicals at high doses can be used to predict the effects of low-dose exposures, such as those common in the general population. This assumption is based on the precept that “the dose makes the poison”: higher doses will cause greater effects. Objectives We challenge the validity of assuming that high-dose testing can be used to predict low-dose effects for contaminants that behave like hormones. We review data from endocrinology and toxicology that falsify this assumption and summarize current mechanistic understanding of how low doses can lead to effects unpredictable from high-dose experiments. Discussion Falsification of this assumption raises profound issues for regulatory toxicology. Many exposure standards are based on this assumption. Rejecting the assumption will require that these standards be reevaluated and that procedures employed to set health standards be changed. The consequences of these changes may be significant for public health because of the range of health conditions now plausibly linked to exposure to endocrine-disrupting contaminants. Conclusions We recommend that procedures to establish acceptable exposure levels for endocrine-disrupting compounds incorporate the inability for high-dose tests to predict low-dose results. Setting acceptable levels of exposure must include testing for health consequences at prevalent levels of human exposure, not extrapolations from the effects observed in high-dose experiments. Scientists trained in endocrinology must be engaged systematically in standard setting for endocrine-disrupting compounds.

Regulatory decisions on endocrine disrupting chemicals should be based on the principles of endocrinology

For years, scientists from various disciplines have studied the effects of endocrine disrupting chemicals (EDCs) on the health and wellbeing of humans and wildlife. Some studies have specifically focused on the effects of low doses, i.e. those in the range that are thought to be safe for humans and/or animals. Others have focused on the existence of non-monotonic dose-response curves. These concepts challenge the way that chemical risk assessment is performed for EDCs. Continued discussions have clarified exactly what controversies and challenges remain. We address several of these issues, including why the study and regulation of EDCs should incorporate endocrine principles; what level of consensus there is for low dose effects; challenges to our understanding of non-monotonicity; and whether EDCs have been demonstrated to produce adverse effects. This discussion should result in a better understanding of these issues, and allow for additional dialog on their impact on risk assessment.

Why public health agencies cannot depend on good laboratory practices as a criterion for selecting data: The case of Bisphenol A

Background In their safety evaluations of bisphenol A (BPA), the U.S. Food and Drug Administration (FDA) and a counterpart in Europe, the European Food Safety Authority (EFSA), have given special prominence to two industry-funded studies that adhered to standards defined by Good Laboratory Practices (GLP). These same agencies have given much less weight in risk assessments to a large number of independently replicated non-GLP studies conducted with government funding by the leading experts in various fields of science from around the world. Objectives We reviewed differences between industry-funded GLP studies of BPA conducted by commercial laboratories for regulatory purposes and non-GLP studies conducted in academic and government laboratories to identify hazards and molecular mechanisms mediating adverse effects. We examined the methods and results in the GLP studies that were pivotal in the draft decision of the U.S. FDA declaring BPA safe in relation to findings from studies that were competitive for U.S. National Institutes of Health (NIH) funding, peer-reviewed for publication in leading journals, subject to independent replication, but rejected by the U.S. FDA for regulatory purposes. Discussion Although the U.S. FDA and EFSA have deemed two industry-funded GLP studies of BPA to be superior to hundreds of studies funded by the U.S. NIH and NIH counterparts in other countries, the GLP studies on which the agencies based their decisions have serious conceptual and methodologic flaws. In addition, the U.S. FDA and EFSA have mistakenly assumed that GLP yields valid and reliable scientific findings (i.e., “good science”). Their rationale for favoring GLP studies over hundreds of publically funded studies ignores the central factor in determining the reliability and validity of scientific findings, namely, independent replication, and use of the most appropriate and sensitive state-of-the-art assays, neither of which is an expectation of industry-funded GLP research. Conclusions Public health decisions should be based on studies using appropriate protocols with appropriate controls and the most sensitive assays, not GLP. Relevant NIH-funded research using state-of-the-art techniques should play a prominent role in safety evaluations of chemicals.

Bisphenol A and Risk of Metabolic Disorders

IN THIS ISSUE OF JAMA, LANG AND COLLEAGUES 1 REPORT the results of the first major epidemiologic study to examine the health effects associated with the ubiquitous estrogenic chemical bisphenol A (BPA). This compound is the base chemical (monomer) used to make polycarbonate plastic food and beverage containers, the resin lining of cans, and dental sealants; it also is found in “carbonless” paper used for receipts as well as a wide range of other common household products. Based on their analysis of data from the National Health and Nutrition Examination Survey 2003-2004, Lang et al report a significant relationship between urine concentrations of BPA and cardiovascular disease, type 2 diabetes, and liver-enzyme abnormalities in a representative sample of the adult US population. This report, suggesting links between BPA and some of the most significant and economically burdensome human diseases, is based on a cross-sectional study and therefore cannot establish causality; follow-up longitudinal studies should thus be a high priority. Yet many peer-reviewed published studies report on related adverse effects of BPA in experimental animals, and cell culture studies identify the molecular mechanisms mediating these responses. These experimental findings add biological plausibility to the results reported by Lang et al. Based on this background information, the study by Lang et al, while preliminary with regard to these diseases in humans, should spur US regulatory agencies to follow the recent action taken by Canadian regulatory agencies, which have declared BPA a “toxic chemical” requiring aggressive action to limit human and environmental exposures. Alternatively, Congressional action could follow the precedent set with the recent passage of federal legislation designed to limit exposures to another family of compounds, phthalates, also used in plastic. Like BPA, phthalates are detectable in virtually everyone in the United States. This bill moves US policy closer to the European model, in which industry must provide data on the safety of a chemical before it can be used in products. Subsequent to an unexpected observation in 1997, numerous laboratory animal studies have identified lowdose drug-like effects of BPA at levels less than the dose used by the US Food and Drug Administration (FDA) and the Environmental Protection Agency to estimate the current human acceptable daily intake dose (ADI) deemed safe for humans. These studies have shown adverse effects of BPA on the brain, reproductive system, and—most relevant to the findings of Lang et al—metabolic processes, including alterations in insulin homeostasis and liver enzymes. However, no prior studies examining BPA for effects on cardiovascular function have been conducted in laboratory animals or humans. Epidemiologists are informed by animal studies that identify potential human health hazards when the animal models and exposure levels are relevant and effects are mediated via response mechanisms present in humans. For example, when adult rats were fed a 0.2-μg/kg per day dose of BPA for 1 month (a dose 250 times lower than the current ADI), BPA significantly decreased the activities of antioxidant enzymes and increased lipid peroxidation, thereby increasing oxidative stress. When adult mice were administered a 10-μg/kg dose of BPA once a day for 2 days (a dose 5 times lower than the ADI), BPA stimulated pancreatic cells to release insulin. After administration of 100 μg/kg per day of BPA via injection or feeding for 4 days, mice developed insulin resistance and postprandial hyperinsulinemia. Follow-up studies showed that stimulation of mouse -cell insulin production and secretion by between 0.1 to 1 nM of estradiol or BPA (23-230 pg/mL of BPA) is mediated by activation of the extracellular signal-related protein kinase 1/2 pathway by binding of BPA to estrogen receptor and that via this nonclassical estrogen-response mechanism, BPA and estradiol have equal potency and efficacy. BPA and estradiol are also equipotent at inhibiting adiponectin release from human adipocytes at 1 nM, further implicating BPA at current human exposure levels in insulin resistance and the metabolic syndrome.

Human exposures to bisphenol A: mismatches between data and assumptions

Abstract Human exposure to bisphenol A (BPA), a synthetic estrogen found in numerous consumer products, is widespread. However, scientific knowledge about the sources and routes of exposure remains incomplete. Although human biomonitoring studies report small amounts of bioactive BPA in the blood of most subjects, toxicokinetic models suggest that circulating levels should be undetectable. The conflict between reported data and toxicokinetic models has spurred considerable debate, with some suggesting that data from analyses of human blood should be dismissed in their entirety. This review addresses the assumptions used by previous risk assessment panels regarding the sources and routes of exposure to BPA (specifically, that BPA exposures occur solely via a few dietary sources) and how these assumptions have affected the interpretation of BPA studies. Given new experimental evidence that route of exposure influences BPA pharmacokinetics, we consider the implications of basing regulatory decisions on limited data that have provided incomplete information about the products that contain this chemical and how it enters the body. We also address evidence that challenges the assumption that humans metabolize BPA rapidly enough to result in undetectable levels in blood and therefore determine that there is a possibility of harm from current exposure levels. Our conclusions are consistent with the large number of hazards and adverse effects identified in laboratory animals exposed to low doses of BPA.

Concerns over use of glyphosate-based herbicides and risks associated with exposures: A consensus statement

The broad-spectrum herbicide glyphosate (common trade name “Roundup”) was first sold to farmers in 1974. Since the late 1970s, the volume of glyphosate-based herbicides (GBHs) applied has increased approximately 100-fold. Further increases in the volume applied are likely due to more and higher rates of application in response to the widespread emergence of glyphosate-resistant weeds and new, pre-harvest, dessicant use patterns. GBHs were developed to replace or reduce reliance on herbicides causing well-documented problems associated with drift and crop damage, slipping efficacy, and human health risks. Initial industry toxicity testing suggested that GBHs posed relatively low risks to non-target species, including mammals, leading regulatory authorities worldwide to set high acceptable exposure limits. To accommodate changes in GBH use patterns associated with genetically engineered, herbicide-tolerant crops, regulators have dramatically increased tolerance levels in maize, oilseed (soybeans and canola), and alfalfa crops and related livestock feeds. Animal and epidemiology studies published in the last decade, however, point to the need for a fresh look at glyphosate toxicity. Furthermore, the World Health Organization’s International Agency for Research on Cancer recently concluded that glyphosate is “probably carcinogenic to humans.” In response to changing GBH use patterns and advances in scientific understanding of their potential hazards, we have produced a Statement of Concern drawing on emerging science relevant to the safety of GBHs. Our Statement of Concern considers current published literature describing GBH uses, mechanisms of action, toxicity in laboratory animals, and epidemiological studies. It also examines the derivation of current human safety standards. We conclude that: (1) GBHs are the most heavily applied herbicide in the world and usage continues to rise; (2) Worldwide, GBHs often contaminate drinking water sources, precipitation, and air, especially in agricultural regions; (3) The half-life of glyphosate in water and soil is longer than previously recognized; (4) Glyphosate and its metabolites are widely present in the global soybean supply; (5) Human exposures to GBHs are rising; (6) Glyphosate is now authoritatively classified as a probable human carcinogen; (7) Regulatory estimates of tolerable daily intakes for glyphosate in the United States and European Union are based on outdated science. We offer a series of recommendations related to the need for new investments in epidemiological studies, biomonitoring, and toxicology studies that draw on the principles of endocrinology to determine whether the effects of GBHs are due to endocrine disrupting activities. We suggest that common commercial formulations of GBHs should be prioritized for inclusion in government-led toxicology testing programs such as the U.S. National Toxicology Program, as well as for biomonitoring as conducted by the U.S. Centers for Disease Control and Prevention.

Estimating Burden and Disease Costs of Exposure to Endocrine-Disrupting Chemicals in the European Union

CONTEXT Rapidly increasing evidence has documented that endocrine-disrupting chemicals (EDCs) contribute substantially to disease and disability. OBJECTIVE The objective was to quantify a range of health and economic costs that can be reasonably attributed to EDC exposures in the European Union (EU). DESIGN A Steering Committee of scientists adapted the Intergovernmental Panel on Climate Change weight-of-evidence characterization for probability of causation based upon levels of available epidemiological and toxicological evidence for one or more chemicals contributing to disease by an endocrine disruptor mechanism. To evaluate the epidemiological evidence, the Steering Committee adapted the World Health Organization Grading of Recommendations Assessment, Development and Evaluation (GRADE) Working Group criteria, whereas the Steering Committee adapted definitions recently promulgated by the Danish Environmental Protection Agency for evaluating laboratory and animal evidence of endocrine disruption. Expert panels used the Delphi method to make decisions on the strength of the data. RESULTS Expert panels achieved consensus at least for probable (>20%) EDC causation for IQ loss and associated intellectual disability, autism, attention-deficit hyperactivity disorder, childhood obesity, adult obesity, adult diabetes, cryptorchidism, male infertility, and mortality associated with reduced testosterone. Accounting for probability of causation and using the midpoint of each range for probability of causation, Monte Carlo simulations produced a median cost of €157 billion (or

Flawed Experimental Design Reveals the Need for Guidelines Requiring Appropriate Positive Controls in Endocrine Disruption Research

209 billion, corresponding to 1.23% of EU gross domestic product) annually across 1000 simulations. Notably, using the lowest end of the probability range for each relationship in the Monte Carlo simulations produced a median range of €109 billion that differed modestly from base case probability inputs. CONCLUSIONS EDC exposures in the EU are likely to contribute substantially to disease and dysfunction across the life course with costs in the hundreds of billions of Euros per year. These estimates represent only those EDCs with the highest probability of causation; a broader analysis would have produced greater estimates of burden of disease and costs.

Should oral gavage be abandoned in toxicity testing of endocrine disruptors

Frederick S. vom Saal,* Benson T. Akingbemi,† Scott M. Belcher,‡ David A. Crain,§ David Crews,{ Linda C. Guidice,jj Patricia A. Hunt,jjj Csaba Leranth,jjjj John Peterson Myers,# Angel Nadal,** Nicholas Olea,†† Vasantha Padmanabhan, Cheryl S. Rosenfeld, Alan Schneyer, Gilbert Schoenfelder, Carlos Sonnenschein, Ana M. Soto, Richard W. Stahlhut, Shanna H. Swan, Laura N. Vandenberg, Hong-Sheng Wang, Cheryl S. Watson, Wade V. Welshons, and Robert T. Zoeller

Exposure to endocrine-disrupting chemicals in the USA: a population-based disease burden and cost analysis

For decades, hazard assessments for environmental chemicals have used intra-gastric gavage to assess the effects of ‘oral’ exposures. It is now widely used – and in some cases required – by US federal agencies to assess potential toxicity of endocrine disrupting chemicals (EDCs). In this review we enumerate several reasons why gavage is not appropriate for the assessment of EDCs using bisphenol A (BPA) as a main example. First, whereas human dietary exposures interact with the oral mucosa, gavage exposures avoid these interactions, leading to dramatic differences in absorption, bioavailability and metabolism with implications for toxicokinetic assumptions and models. Additionally, there are well acknowledged complications associated with gavage, such as perforation of the esophagus that diminish its value in toxicological experiments. Finally, the gavage protocol itself can induce stress responses by the endocrine system and confound the assessment of EDCs. These serious flaws have not been taken into account in interpreting results of EDC research. We propose the exploration of alternatives to mimic human exposures when there are multiple exposure routes/sources and when exposures are chronic. We conclude that gavage may be preferred over other routes for some environmental chemicals in some circumstances, but it does not appropriately model human dietary exposures for many chemicals. Because it avoids exposure pathways, is stressful, and thus interferes with endocrine responses, gavage should be abandoned as the default route of administration for hazard assessments of EDCs.