Organophosphate exposures during pregnancy and child neurodevelopment: Recommendations for essential policy reforms

In a Policy Forum, Irva Hertz-Picciotto and colleagues review the scientific evidence linking organophosphate pesticides to cognitive, behavioral, and neurological deficits in children and recommend actions to reduce exposures.

Meeting report: hazard assessment for nanoparticles--report from an interdisciplinary workshop

In this report we present the findings from a nanotoxicology workshop held 6-7 April 2006 at the Woodrow Wilson International Center for Scholars in Washington, DC. Over 2 days, 26 scientists from government, academia, industry, and nonprofit organizations addressed two specific questions: what information is needed to understand the human health impact of engineered nanoparticles and how is this information best obtained? To assess hazards of nanoparticles in the near-term, most participants noted the need to use existing in vivo toxicologic tests because of their greater familiarity and interpretability. For all types of toxicology tests, the best measures of nanoparticle dose need to be determined. Most participants agreed that a standard set of nanoparticles should be validated by laboratories worldwide and made available for benchmarking tests of other newly created nanoparticles. The group concluded that a battery of tests should be developed to uncover particularly hazardous properties. Given the large number of diverse materials, most participants favored a tiered approach. Over the long term, research aimed at developing a mechanistic understanding of the numerous characteristics that influence nanoparticle toxicity was deemed essential. Predicting the potential toxicity of emerging nanoparticles will require hypothesis-driven research that elucidates how physicochemical parameters influence toxic effects on biological systems. Research needs should be determined in the context of the current availability of testing methods for nanoscale particles. Finally, the group identified general policy and strategic opportunities to accelerate the development and implementation of testing protocols and ensure that the information generated is translated effectively for all stakeholders.

HSP 90 alpha and HSP 90 beta genes are present in the zebrafish and are differentially regulated in developing embryos

We have employed a polymerase chain reaction-based cloning strategy to demonstrate that both hsp 90 alpha and hsp 90 beta genes are present in the zebrafish. The fact that zebrafish represents the most primitive vertebrate in which hsp 90 genes have been isolated to date has allowed us to determine that the duplication event which generated the hsp 90 alpha and hsp 90 beta genes occurred shortly before the emergence of the teleosts from the rest of the vertebrate lineage. In expression studies using Northern blot analysis, hsp 90 beta mRNA was found to be present at control temperatures throughout normal embryonic development whereas hsp 90 alpha mRNA was barely detectable. Upon heat shock, hsp 90 alpha mRNA levels increased dramatically in all developmental stages examined. The levels of hsp 90 beta mRNA increased 2-3 fold during heat shock of early stage embryos. Thus, the hsp 90 alpha gene is strongly upregulated during heat shock in zebrafish embryos whereas expression of the hsp 90 beta gene appears to be weakly induced.

Heat shock genes and the heat shock response in zebrafish embryos

Heat shock genes exhibit complex patterns of spatial and temporal regulation during embryonic development in a wide range of organisms. Our laboratory has initiated an analysis of heat shock protein gene expression in the zebrafish, a model system that is now utilized extensively for the examination of early embryonic development of vertebrates. We have cloned members of the zebrafish hsp47, hsp70,\i and hsp90 gene families and shown them to be closely related to their counterparts in higher vertebrates. Whole mount in situ hybridization and Northern blot analyses have revealed that these genes are regulated in distinct spatial, temporal, and stress-specific manners. Furthermore, the tissue-specific expression patterns of the hsp47 and hsp90 alpha genes correlate closely with the expression of genes encoding known chaperone targets of Hsp47 and Hsp90 in other systems. The data raise a number of interesting questions regarding the function and regulation of these heat shock genes in zebrafish embryos during normal development and following exposure to environmental stress.

Specific localization of zebrafish hsp90 alpha mRNA to myoD-expressing cells suggests a role for hsp90 alpha during normal muscle development

Members of the eukaryotic hsp90 family function as important molecular chaperones in the assembly, folding and activation of a select group of cellular signalling molecules and transcription factors. Several of the molecules with which hsp90 interacts, such as the bHLH transcription factor myoD, are known to be important regulators of developmental events in vertebrates. However, little information is available in support of any specific role for hsp90 in developing embryos in vivo. In this study, we provide the first in vivo evidence that the hsp90 alpha gene may play a role in the process of myogenesis. We show that constitutive hsp90 alpha mRNA in zebrafish embryos is restricted primarily to a subset of cells within the somites and pectoral fin buds which also express myoD. Furthermore, expression of the hsp90 alpha gene is down-regulated along with myoD in differentiated muscles of the trunk at a time when levels of mRNA encoding the muscle structural protein alpha-tropomyosin remain high. No hsp90 alpha mRNA is detectable within the CNS at control temperatures. In contrast, heat shock-induced expression of the hsp90 alpha gene occurs throughout the embryo at all stages of development examined. The expression patterns strongly suggest that the hsp90 alpha gene plays a specific role in the normal process of myogenesis in addition to providing protection to all cells of the embryo during periods of environmental stress.

Methylmercury-induced decrement in neuronal migration may involve cytokine-dependent mechanisms: a novel method to assess neuronal movement in vitro

A major toxic effect associated with methylmercury (MeHg) exposure in developing humans is damage to the nervous system, which involves inhibition of cell migration, particularly in the cerebellum. The mechanisms by which MeHg impairs neural migration are not fully known, especially at low doses. In this paper we report on a novel method for observing and quantitating the movement of individual cells in primary cultures of murine neonatal cerebellar cells, which offers an opportunity to assess the role of endogenous and exogenous factors on neural migration. We have used this system to test the hypothesis that treatment with methylmercury would inhibit movement of granule cell neurons, possibly via a cytokine-mediated mechanism. We demonstrate that LPS (50 ng/ml) increases movement of neurons, concomitant with increased levels of TNF-alpha and IL-6 secreted protein, and IL-1alpha mRNA. Treatment with LPS did not increase the number of neurons that moved, but, of the cells that did move, exposure to LPS significantly increased the total distances moved. Treatment with methylmercury (0.1 microM) decreased the number of moving cells and inhibited overall distance traveled by granule cells.

Aluminum pretreatment impairs the ability of astrocytes to protect neurons from glutamate mediated toxicity

A number of laboratories have shown that astrocytes protect neurons from glutamate excitotoxicity. The experiments described in this paper were designed to address the question whether prior exposure of astrocytes to aluminum (in the form of aluminum citrate) interfered with the ability of astrocytes to protect neurons from glutamate excitotoxicity. Our culture paradigm consisted of highly enriched cultures of neurons and astrocytes grown on separate coverslips; this design enables one to subject either the neurons or the astrocytes to specific treatments and recombine the cells into the same petri dish simply by moving coverslips from dish to dish. We have confirmed findings of other laboratories that astrocytes could protect neurons from glutamate-induced death when glutamate (100 microM) is added to the culture medium. We have also demonstrated that prior treatment of astrocytes with 100 microM aluminum citrate impairs this ability of astrocytes to promote neuronal survival. No differences, however, were observed in the ability of control and aluminum-treated astrocytes to take up glutamate. These findings suggest that aluminum may cause astrocytes to: (i) secrete a factor that makes neurons more susceptible to glutamate-induced toxicity; (ii) secrete a neuronotoxic factor in the presence of glutamate; or (iii) reduce secretion of a factor that protects neurons from glutamate excitotoxicity.

HSP90alpha gene expression may be a conserved feature of vertebrate somitogenesis

We have previously demonstrated that the hsp90alpha and hsp90beta genes in zebrafish are expressed in dramatically different spatial and temporal patterns in early embryos. In the case of hsp90alpha, expression is spatially restricted within the somites to putative myogenic cells which also express mRNA encoding the myogenic bHLH transcription factor myoD and is downregulated along with myoD following myogenesis. In the present study, we have examined hsp90alpha gene expression in developing chicken embryos using a gene-specific probe. We show that hsp90alpha gene expression is also localized to a subset of cells within the somites of chicken embryos and that the expression pattern correlates closely to that observed for myoD. Furthermore, expression of the hsp90alpha gene is strongly upregulated throughout the embryo following heat shock in a manner similar to that observed in heat-shocked zebrafish embryos. The data suggest that the hsp90alpha gene may play an evolutionarily conserved role during somitogenesis in vertebrates in addition to providing protection to all cells of the embryo following stress.

Current practice and recommendations for advancing how human variability and susceptibility are considered in chemical risk assessment

A key element of risk assessment is accounting for the full range of variability in response to environmental exposures. Default dose-response methods typically assume a 10-fold difference in response to chemical exposures between average (healthy) and susceptible humans, despite evidence of wider variability. Experts and authoritative bodies support using advanced techniques to better account for human variability due to factors such as in utero or early life exposure and exposure to multiple environmental, social, and economic stressors.This review describes: 1) sources of human variability and susceptibility in dose-response assessment, 2) existing US frameworks for addressing response variability in risk assessment; 3) key scientific inadequacies necessitating updated methods; 4) improved approaches and opportunities for better use of science; and 5) specific and quantitative recommendations to address evidence and policy needs.Current default adjustment factors do not sufficiently capture human variability in dose-response and thus are inadequate to protect the entire population. Susceptible groups are not appropriately protected under current regulatory guidelines. Emerging tools and data sources that better account for human variability and susceptibility include probabilistic methods, genetically diverse in vivo and in vitro models, and the use of human data to capture underlying risk and/or assess combined effects from chemical and non-chemical stressors.We recommend using updated methods and data to improve consideration of human variability and susceptibility in risk assessment, including the use of increased default human variability factors and separate adjustment factors for capturing age/life stage of development and exposure to multiple chemical and non-chemical stressors. Updated methods would result in greater transparency and protection for susceptible groups, including children, infants, people who are pregnant or nursing, people with disabilities, and those burdened by additional environmental exposures and/or social factors such as poverty and racism.

A science-based agenda for health-protective chemical assessments and decisions: overview and consensus statement

The manufacture and production of industrial chemicals continues to increase, with hundreds of thousands of chemicals and chemical mixtures used worldwide, leading to widespread population exposures and resultant health impacts. Low-wealth communities and communities of color often bear disproportionate burdens of exposure and impact; all compounded by regulatory delays to the detriment of public health. Multiple authoritative bodies and scientific consensus groups have called for actions to prevent harmful exposures via improved policy approaches. We worked across multiple disciplines to develop consensus recommendations for health-protective, scientific approaches to reduce harmful chemical exposures, which can be applied to current US policies governing industrial chemicals and environmental pollutants. This consensus identifies five principles and scientific recommendations for improving how agencies like the US Environmental Protection Agency (EPA) approach and conduct hazard and risk assessment and risk management analyses: (1) the financial burden of data generation for any given chemical on (or to be introduced to) the market should be on the chemical producers that benefit from their production and use; (2) lack of data does not equate to lack of hazard, exposure, or risk; (3) populations at greater risk, including those that are more susceptible or more highly exposed, must be better identified and protected to account for their real-world risks; (4) hazard and risk assessments should not assume existence of a "safe" or "no-risk" level of chemical exposure in the diverse general population; and (5) hazard and risk assessments must evaluate and account for financial conflicts of interest in the body of evidence. While many of these recommendations focus specifically on the EPA, they are general principles for environmental health that could be adopted by any agency or entity engaged in exposure, hazard, and risk assessment. We also detail recommendations for four priority areas in companion papers (exposure assessment methods, human variability assessment, methods for quantifying non-cancer health outcomes, and a framework for defining chemical classes). These recommendations constitute key steps for improved evidence-based environmental health decision-making and public health protection.

A simple, yet versatile, co-culture method for examining neuron-glia interactions

There is increasing interest in examining neuron-glial interactions in the developing and the mature central nervous system. Here, we describe a system that allows examination of interactions mediated by diffusible molecules even when such interactions involve more than 2 cell populations. Our procedure involves culturing highly enriched populations of neurons and glial cells on separate coverslips. Such coverslips can be readily moved from one petri dish to another, thus enabling the investigator to subject the neurons and the glial cells to different experimental manipulations. The coverslips can then be placed in any desired combination within a petri dish. This gives one great flexibility in examining neuron-glial interactions. Using this approach, we unequivocally demonstrate that astrocytes protect neurons from glutamate excitotoxicity.

Conducting evaluations of evidence that are transparent, timely and can lead to health-protective actions

BACKGROUND

In February 2021, over one hundred scientists and policy experts participated in a web-based Workshop to discuss the ways that divergent evaluations of evidence and scientific uncertainties are used to delay timely protection of human health and the environment from exposures to hazardous agents. The Workshop arose from a previous workshop organized by the European Environment Agency (EEA) in 2008 and which also drew on case studies from the EEA reports on 'Late Lessons from Early Warnings' (2001, 2013). These reports documented dozens of hazardous agents including many chemicals, for which risk reduction measures were delayed for decades after scientists and others had issued early and later warnings about the harm likely to be caused by those agents.

RESULTS

Workshop participants used recent case studies including Perfluorooctanoic acid (PFOA), Extremely Low Frequency - Electrical Magnetic Fields (ELF-EMF fields), glyphosate, and Bisphenol A (BPA) to explore myriad reasons for divergent outcomes of evaluations, which has led to delayed and inadequate protection of the public's health. Strategies to overcome these barriers must, therefore, at a minimum include approaches that 1) Make better use of existing data and information, 2) Ensure timeliness, 3) Increase transparency, consistency and minimize bias in evidence evaluations, and 4) Minimize the influence of financial conflicts of interest.

CONCLUSION

The recommendations should enhance the production of "actionable evidence," that is, reliable evaluations of the scientific evidence to support timely actions to protect health and environments from exposures to hazardous agents. The recommendations are applicable to policy and regulatory settings at the local, state, federal and international levels.

Restricted expression of the zebrafish hsp90alpha gene in slow and fast muscle fiber lineages

Members of the heat shock protein 90 (Hsp90) family of molecular chaperones play important roles in allowing a select group of intracellular signaling molecules reach and maintain functionally active conformations. We have previously shown that hsp90alpha gene expression in early zebrafish embryos is restricted to a subgroup of paraxial-mesoderm derived somitic cells prior to muscle formation and that the gene is downregulated in mature trunk and tail muscle fibers. Here we have compared the expression of the hsp90alpha gene to muscle regulatory genes during development of slow and fast muscle fibers in normal embryos and in embryos carrying mutations which affect somitic muscle formation. We show that hsp90alpha is first expressed early during the development of slow somitic muscle progenitors shortly following myoD activation and at a point prior to or co-incident with the expression of other known muscle regulatory genes. Expression of hsp90alpha is also activated in the midline of flh mutants when these cells switch from a notochord to a muscle fate. Conversely, expression is not detectable in cells of the paraxial mesoderm lineage which fail to converge in spt mutants and which do not activate expression of other muscle specific marker genes. Finally, expression of hsp90alpha is downregulated in slow muscle fibers by 24 h of age but becomes detectable in the later developing fast fibers at this time. Thus, hsp90alpha is expressed in developing muscle progenitors during short temporal and spatial windows of both slow and fast fiber lineages in the zebrafish somite.

Heat shock genes and the heat shock response in zebrafish embryos

Heat shock genes exhibit complex patterns of spatial and temporal regulation during embryonic development in a wide range of organisms. Our laboratory has initiated an analysis of heat shock protein gene expression in the zebrafish, a model system that is now utilized extensively for the examination of early embryonic development of vertebrates. We have cloned members of the zebrafish hsp47, hsp70, and hsp90 gene families and shown them to be closely related to their counterparts in higher vertebrates. Whole mount in situ hybridization and Northern blot analyses have revealed that these genes are regulated in distinct spatial, temporal, and stress-specific manners. Furthermore, the tissue-specific expression patterns of the hsp47 and hsp90 alpha genes correlate closely with the expression of genes encoding known chaperone targets of Hsp47 and Hsp90 in other systems. The data raise a number of interesting questions regarding the function and regulation of these heat shock genes in zebrafish embryos during normal development and following exposure to environmental stress.

Human acute poisoning incidents associated with neonicotinoid pesticides in the U.S. Incident Data System (IDS) database from 2018-2022 - frequency and severity show public health risks, regulatory failures

BACKGROUND

Neonicotinoid pesticides ('neonics') - imidacloprid, thiamethoxam, clothianidin, acetamiprid, dinotefuran-are the most widely used class of insecticides in the world. They have a neurotoxic mechanism of action, similar to nicotine. They are detected in food, waterways, tap water, and breast milk.

METHODS

We make use of the non-occupational human pesticide poisoning reports in the U.S. Environmental Protection Agency (EPA) online Incident Data System (IDS). The data set contains individual incidents, and incidents aggregated and submitted in bulk to EPA. IDS reports are predominantly self-reported information of varying and often low level of detail and are not routinely validated or verified by EPA.

RESULTS

We reviewed 842 non-occupational human poisoning incidents associated with neonics in the IDS from 2018 through 2022. There are four human fatality reports, two associated with clothianidin and two with acetamiprid. Major illnesses such as seizures were reported in several cases, including with dinotefuran cockroach bait product, and an imidacloprid lawn product. Moderate poisonings make up 88% of the total poisonings (740 of 842), with most of those associated with imidacloprid (547 incidents) or dinotefuran (102 incidents). Common reported symptoms classified as moderate often included two or more of the following: headaches; dizziness; lethargy; eye or throat irritation; skin itching and rash; chemical burns and skin peeling; face swelling; muscle weakness or tremors; vomiting; diarrhea; pain and tightness in chest; open sores; and general pain. These incidents stem mainly from residential uses, such as lawn and garden insect repellents, home pest treatments for bed bugs or roaches, and products used to treat pets for fleas and ticks.

CONCLUSION

Given the evidence of neurotoxicity, EPA should use its legal authority to cancel unsafe products and unnecessary uses - including from seed treatments, and residential pet and lawncare products - to prevent further human suffering.