Thyroid Hormone Disruptors Interfere with Molecular Pathways of Eye Development and Function in Zebrafish.

The effects of thyroid hormone disrupting chemicals (THDCs) on eye development of zebrafish were investigated. We expected THDC exposure to cause transcriptional changes of vision-related genes, which find their phenotypic anchoring in eye malformations and dysfunction, as observed in our previous studies. Zebrafish were exposed from 0 to 5 days post fertilization (dpf) to either propylthiouracil (PTU), a thyroid hormone synthesis inhibitor, or tetrabromobisphenol-A (TBBPA), which interacts with thyroid hormone receptors. Full genome microarray analyses of RNA isolated from eye tissue revealed that the number of affected transcripts was substantially higher in PTU- than in TBBPA-treated larvae. However, multiple components of phototransduction (e.g., phosphodiesterase, opsins) were responsive to both THDC exposures. Yet, the response pattern for the gene ontology (GO)-class "sensory perception" differed between treatments, with over 90% down-regulation in PTU-exposed fish, compared to over 80% up-regulation in TBBPA-exposed fish. Additionally, the reversibility of effects after recovery in clean water for three days was investigated. Transcriptional patterns in the eyes were still altered and partly overlapped between 5 and 8 dpf, showing that no full recovery occurred within the time period investigated. However, pathways involved in repair mechanisms were significantly upregulated, which indicates activation of regeneration processes.

Network Analysis Reveals Similar Transcriptomic Responses to Intrinsic Properties of Carbon Nanomaterials in Vitro and in Vivo.

Understanding the complex molecular alterations related to engineered nanomaterial (ENM) exposure is essential for carrying out toxicity assessment. Current experimental paradigms rely on both in vitro and in vivo exposure setups that often are difficult to compare, resulting in questioning the real efficacy of cell models to mimic more complex exposure scenarios at the organism level. Here, we have systematically investigated transcriptomic responses of the THP-1 macrophage cell line and lung tissues of mice, after exposure to several carbon nanomaterials (CNMs). Under the assumption that the CNM exposure related molecular alterations are mixtures of signals related to their intrinsic properties, we inferred networks of responding genes, whose expression levels are coordinately altered in response to specific CNM intrinsic properties. We observed only a minute overlap between the sets of intrinsic property-correlated genes at different exposure scenarios, suggesting specific transcriptional programs working in different exposure scenarios. However, when the effects of the CNM were investigated at the level of significantly altered molecular functions, a broader picture of substantial commonality emerged. Our results imply that in vitro exposures can efficiently recapitulate the complex molecular functions altered in vivo. In this study, altered molecular pathways in response to specific CNM intrinsic properties have been systematically characterized from transcriptomic data generated from multiple exposure setups. Our computational approach to the analysis of network response modules further revealed similarities between in vitro and in vivo exposures that could not be detected by traditional analysis of transcriptomics data. Our analytical strategy also opens a possibility to look for pathways of toxicity and understanding the molecular and cellular responses identified across predefined biological themes.

Current knowledge of environmental exposure in children during the sensitive developmental periods / O estado atual do conhecimento sobre a exposição ambiental no organismo infantil durante os períodos sensíveis de desenvolvimento

Abstract: Objective: This study aims to identify the scientific evidence on the risks and effects of exposure to environmental contaminants in children during sensitive developmental periods. Data source: The search was performed in the Bireme database, using the terms: children's health, environmental exposure, health vulnerability, toxicity pathways and developmental disabilities in the LILACS, MEDLINE and SciELO systems. Data synthesis: Children differ from adults in their unique physiological and behavioral characteristics and the potential exposure to risks caused by several threats in the environment. Exposure to toxic agents is analyzed through toxicokinetic processes in the several systems and organs during the sensitive phases of child development. The caused effects are reflected in the increased prevalence of congenital malformations, diarrhea, asthma, cancer, endocrine and neurological disorders, among others, with negative impacts throughout adult life. Conclusion: To identify the causes and understand the mechanisms involved in the genesis of these diseases is a challenge for science, as there is still a lack of knowledge on children's susceptibility to many environmental contaminants. Prevention policies and more research on child environmental health, improving the recording and surveillance of environmental risks to children's health, should be an ongoing priority in the public health field.

Resumo: Objetivo: O presente estudo busca identificar as evidências científicas sobre os riscos e efeitos da exposição de contaminantes ambientais no organismo infantil durante os períodos sensíveis de seu desenvolvimento. Fonte de dados: As pesquisas foram feitas pelo banco de dados da Bireme, com os termos children's health, environmental exposure, health vulnerability, toxicity pathways e developmental disabilities nos sistemas Lilacs, Medline e SciELO. Síntese de dados: A criança difere do adulto por suas características singulares de ordem fisiológica, comportamental e do potencial de exposição a riscos frente às ameaças do ambiente. A exposição a agentes tóxicos é analisada por meio dos processos toxicocinéticos nos sistemas e órgãos durante as janelas sensíveis do desenvolvimento infantil. Os efeitos causados transparecem no aumento da prevalência de malformações congênitas, diarreia, asma, cânceres, distúrbios endócrinos e neurológicos, entre outros, com impactos negativos ao longo da vida adulta. Conclusão: Identificar as causas e compreender os mecanismos envolvidos na gênese desses agravos é um desafio que se impõe à ciência, visto que ainda há uma lacuna de conhecimento sobre a suscetibilidade infantil para muitos contaminantes ambientais. Políticas de prevenção e mais pesquisas em saúde ambiental infantil, que impulsionem o registro e a vigilância epidemiológica dos riscos ambientais à saúde da criança, devem ser uma prioridade contínua no campo da saúde pública.

Current knowledge of environmental exposure in children during the sensitive developmental periods.

OBJECTIVE: This study aims to identify the scientific evidence on the risks and effects of exposure to environmental contaminants in children during sensitive developmental periods. DATA SOURCE: The search was performed in the Bireme database, using the terms: children's health, environmental exposure, health vulnerability, toxicity pathways and developmental disabilities in the LILACS, MEDLINE and SciELO systems. DATA SYNTHESIS: Children differ from adults in their unique physiological and behavioral characteristics and the potential exposure to risks caused by several threats in the environment. Exposure to toxic agents is analyzed through toxicokinetic processes in the several systems and organs during the sensitive phases of child development. The caused effects are reflected in the increased prevalence of congenital malformations, diarrhea, asthma, cancer, endocrine and neurological disorders, among others, with negative impacts throughout adult life. CONCLUSION: To identify the causes and understand the mechanisms involved in the genesis of these diseases is a challenge for science, as there is still a lack of knowledge on children's susceptibility to many environmental contaminants. Prevention policies and more research on child environmental health, improving the recording and surveillance of environmental risks to children's health, should be an ongoing priority in the public health field.

Information-dependent enrichment analysis reveals time-dependent transcriptional regulation of the estrogen pathway of toxicity.

The twenty-first century vision for toxicology involves a transition away from high-dose animal studies to in vitro and computational models (NRC in Toxicity testing in the 21st century: a vision and a strategy, The National Academies Press, Washington, DC, 2007). This transition requires mapping pathways of toxicity by understanding how in vitro systems respond to chemical perturbation. Uncovering transcription factors/signaling networks responsible for gene expression patterns is essential for defining pathways of toxicity, and ultimately, for determining the chemical modes of action through which a toxicant acts. Traditionally, transcription factor identification is achieved via chromatin immunoprecipitation studies and summarized by calculating which transcription factors are statistically associated with up- and downregulated genes. These lists are commonly determined via statistical or fold-change cutoffs, a procedure that is sensitive to statistical power and may not be as useful for determining transcription factor associations. To move away from an arbitrary statistical or fold-change-based cutoff, we developed, in the context of the Mapping the Human Toxome project, an enrichment paradigm called information-dependent enrichment analysis (IDEA) to guide identification of the transcription factor network. We used a test case of activation in MCF-7 cells by 17ß estradiol (E2). Using this new approach, we established a time course for transcriptional and functional responses to E2. ERα and ERß were associated with short-term transcriptional changes in response to E2. Sustained exposure led to recruitment of additional transcription factors and alteration of cell cycle machinery. TFAP2C and SOX2 were the transcription factors most highly correlated with dose. E2F7, E2F1, and Foxm1, which are involved in cell proliferation, were enriched only at 24 h. IDEA should be useful for identifying candidate pathways of toxicity. IDEA outperforms gene set enrichment analysis (GSEA) and provides similar results to weighted gene correlation network analysis, a platform that helps to identify genes not annotated to pathways.

Grouping of histone deacetylase inhibitors and other toxicants disturbing neural crest migration by transcriptional profiling.

Functional assays, such as the "migration inhibition of neural crest cells" (MINC) developmental toxicity test, can identify toxicants without requiring knowledge on their mode of action (MoA). Here, we were interested, whether (i) inhibition of migration by structurally diverse toxicants resulted in a unified signature of transcriptional changes; (ii) whether statistically-identified transcript patterns would inform on compound grouping even though individual genes were little regulated, and (iii) whether analysis of a small group of biologically-relevant transcripts would allow the grouping of compounds according to their MoA. We analyzed transcripts of 35 'migration genes' after treatment with 16 migration-inhibiting toxicants. Clustering, principal component analysis and correlation analyses of the data showed that mechanistically related compounds (e.g. histone deacetylase inhibitors (HDACi), PCBs) triggered similar transcriptional changes, but groups of structurally diverse toxicants largely differed in their transcriptional effects. Linear discriminant analysis (LDA) confirmed the specific clustering of HDACi across multiple separate experiments. Similarity of the signatures of the HDACi trichostatin A and suberoylanilide hydroxamic acid to the one of valproic acid (VPA), suggested that the latter compound acts as HDACi when impairing neural crest migration. In conclusion, the data suggest that (i) a given functional effect (e.g. inhibition of migration) can be associated with highly diverse signatures of transcript changes; (ii) statistically significant grouping of mechanistically-related compounds can be achieved on the basis of few genes with small regulations. Thus, incorporation of mechanistic markers in functional in vitro tests may support read-across procedures, also for structurally un-related compounds.

Review: toxicometabolomics.

Metabolomics use in toxicology is rapidly increasing, particularly owing to advances in mass spectroscopy, which is widely used in the life sciences for phenotyping disease states. Toxicology has the advantage of having the disease agent, the toxicant, available for experimental induction of metabolomics changes monitored over time and dose. This review summarizes the different technologies employed and gives examples of their use in various areas of toxicology. A prominent use of metabolomics is the identification of signatures of toxicity - patterns of metabolite changes predictive of a hazard manifestation. Increasingly, such signatures indicative of a certain hazard manifestation are identified, suggesting that certain modes of action result in specific derangements of the metabolism. This might enable the deduction of underlying pathways of toxicity, which, in their entirety, form the Human Toxome, a key concept for implementing the vision of Toxicity Testing for the 21st century. This review summarizes the current state of metabolomics technologies and principles, their uses in toxicology and gives a thorough overview on metabolomics bioinformatics, pathway identification and quality assurance. In addition, this review lays out the prospects for further metabolomics application also in a regulatory context.

In vitro Toxicity Testing in the Twenty-First Century.

The National Research Council (NRC) article "Toxicity Testing in the 21st Century: A vision and A Strategy" (National Research Council, 2007) was written to bring attention to the application of scientific advances for use in toxicity tests so that chemicals can be tested in a more time and cost efficient manner while providing a more relevant and mechanistic insight into the toxic potential of a compound. Development of tools for in vitro toxicity testing constitutes an important activity of this vision and contributes to the provision of test systems as well as data that are essential for the development of computer modeling tools for, e.g., system biology, physiologically based modeling. This article intends to highlight some of the issues that have to be addressed in order to make in vitro toxicity testing a reality in the twenty-first century.