Associations of early life urinary triclosan concentrations with maternal, neonatal, and child thyroid hormone levels.

BACKGROUND: Triclosan, an antimicrobial agent used in some consumer products, reduces endogenous thyroid hormone concentrations in rodents. Despite ubiquitous triclosan exposure and the importance of thyroid hormones for normal fetal development, few human studies have examined the impact of triclosan exposure on maternal, neonatal, or child thyroid hormones. METHODS: In the HOME Study, a prospective cohort from Cincinnati, OH, we measured urinary triclosan concentrations up to three times in pregnant women between 16weeks and delivery, and up to three times in children between age 1-3years. We quantified serum concentrations of thyroid stimulating hormone and total and free thyroxine and triiodothyronine in mothers at 16-weeks gestation (n=202), neonates at delivery (n=274), and children at age 3years (n=153). We estimated covariate-adjusted differences in thyroid hormones with a 10-fold increase in triclosan using linear regression and multiple informants models. RESULTS: Triclosan was not associated with thyroid hormones during pregnancy. We observed a few associations of triclosan concentrations with thyroid hormone concentrations in neonates at delivery and children at age 3years. Higher gestational triclosan, particularly around the time of delivery, was associated with lower cord serum total thyroxine (ß: 0.3µg/dL; 95% CI: -0.6, -0.0). Childhood triclosan, particularly at age 1year, was positively associated with total thyroxine at age 3years (ß: 0.7µg/dL; 95% CI: 0.3, 1.2). CONCLUSION: Our findings suggest that triclosan exposure may influence some features of neonatal and early child thyroid function. Given the large number of comparisons we made, these findings should be replicated in other cohorts.

Transient Maternal Hypothyroxinemia Potentiates the Transcriptional Response to Exogenous Thyroid Hormone in the Fetal Cerebral Cortex Before the Onset of Fetal Thyroid Function: A Messenger and MicroRNA Profiling Study.

Thyroid hormone (TH) is essential for brain development both before and after birth. We have used gene expression microarrays to identify TH-regulated genes in the fetal cerebral cortex prior to the onset of fetal thyroid function to better understand the role of TH in early cortical development. TH levels were transiently manipulated in pregnant mice by treatment with goitrogens from gestational day (GD) 13-16 and/or by injection of TH 12 h before sacrifice on GD 16. The transcriptional response to exogenous TH in the GD 16 fetal cortex was potentiated by transient goitrogen treatment, suggesting that the hypothyroxinemic brain is a different substrate upon which TH can act, or that robust compensatory mechanisms are induced by transient hypothyroxinemia. Several known TH-responsive genes were identified including Klf9, and several novel TH-responsive genes such as Appbp2, Ppap2b, and Fgfr1op2 were identified in which TH response elements were confirmed. We also identified specific microRNAs whose expression in the fetal cortex was affected by TH treatment, and determined that Ppap2b and Klf9 are the target genes of miR-16 and miR-106, respectively. Thus, a complex redundant functional network appears to coordinate TH-mediated gene expression in the developing brain.

Gestational urinary bisphenol A and maternal and newborn thyroid hormone concentrations: the HOME Study.

Bisphenol A (BPA), an endocrine disruptor used in consumer products, may perturb thyroid function. Prenatal BPA exposure may have sex-specific effects on thyroid hormones (THs). Our objectives were to investigate whether maternal urinary BPA concentrations during pregnancy were associated with THs in maternal or cord serum, and whether these associations differed by newborn sex or maternal iodine status. We measured urinary BPA concentrations at 16 and 26 weeks gestation among pregnant women in the HOME Study (2003-2006, Cincinnati, Ohio). Thyroid stimulating hormone (TSH) and free and total thyroxine (T4) and triiodothyronine (T3) were measured in maternal serum at 16 weeks (n=181) and cord serum at delivery (n=249). Associations between BPA concentrations and maternal or cord serum TH levels were estimated by multivariable linear regression. Mean maternal urinary BPA was not associated with cord THs in all newborns, but a 10-fold increase in mean BPA was associated with lower cord TSH in girls (percent change=-36.0%; 95% confidence interval (CI): -58.4, -1.7%), but not boys (7.8%; 95% CI: -28.5, 62.7%; p-for-effect modification=0.09). We observed no significant associations between 16-week BPA and THs in maternal or cord serum, but 26-week maternal BPA was inversely associated with TSH in girls (-42.9%; 95% CI: -59.9, -18.5%), but not boys (7.6%; 95% CI: -17.3, 40.2%; p-for-effect modification=0.005) at birth. The inverse BPA-TSH relation among girls was stronger, but less precise, among iodine deficient versus sufficient mothers. Prenatal BPA exposure may reduce TSH among newborn girls, particularly when exposure occurs later in gestation.

A vision for safer food contact materials: Public health concerns as drivers for improved testing.

Food contact materials (FCMs) and food contact articles are ubiquitous in today's globalized food system. Chemicals migrate from FCMs into foodstuffs, so called food contact chemicals (FCCs), but current regulatory requirements do not sufficiently protect public health from hazardous FCCs because only individual substances used to make FCMs are tested and mostly only for genotoxicity while endocrine disruption and other hazard properties are disregarded. Indeed, FCMs are a known source of a wide range of hazardous chemicals, and they likely contribute to highly prevalent non-communicable diseases. FCMs can also include non-intentionally added substances (NIAS), which often are unknown and therefore not subject to risk assessment. To address these important shortcomings, we outline how the safety of FCMs may be improved by (1) testing the overall migrate, including (unknown) NIAS, of finished food contact articles, and (2) expanding toxicological testing beyond genotoxicity to multiple endpoints associated with non-communicable diseases relevant to human health. To identify mechanistic endpoints for testing, we group chronic health outcomes associated with chemical exposure into Six Clusters of Disease (SCOD) and we propose that finished food contact articles should be tested for their impacts on these SCOD. Research should focus on developing robust, relevant, and sensitive in-vitro assays based on mechanistic information linked to the SCOD, e.g., through Adverse Outcome Pathways (AOPs) or Key Characteristics of Toxicants. Implementing this vision will improve prevention of chronic diseases that are associated with hazardous chemical exposures, including from FCMs.

Adverse effects in risk assessment: modeling polychlorinated biphenyls and thyroid hormone disruption outcomes in animals and humans.

There is a growing need for quantitative approaches to extrapolate relationships between chemical exposures and early biological perturbations from animals to humans given increasing use of biological assays to evaluate toxicity pathways. We have developed such an approach using polychlorinated biphenyls (PCBs) and thyroid hormone (TH) disruption as a case study. We reviewed and identified experimental animal literature from which we developed a low-dose, linear model of PCB body burdens and decrements in free thyroxine (FT(4)) and total thyroxine (TT(4)), accounting for 33 PCB congeners; extrapolated the dose-response from animals to humans; and compared the animal dose-response to the dose-response of PCB body burdens and TH changes from eleven human epidemiological studies. We estimated a range of potencies for PCB congeners (over 4 orders of magnitude), with the strongest for PCB 126. Our approach to developing toxic equivalency models produced relative potencies similar to the toxicity equivalency factors (TEFs) from the World Health Organization (WHO). We generally found that the dose-response extrapolated from the animal studies tends to under-predict the dose-response estimated from human epidemiological studies. A quantitative approach to evaluating the relationship between chemical exposures and TH perturbations, based on animal data can be used to assess human health consequences of thyroid toxicity and inform decision-making.

Polybrominated diphenyl ether (PBDE) exposures and thyroid hormones in children at age 3 years.

BACKGROUND: Polybrominated diphenyl ethers (PBDEs) reduce serum thyroid hormone concentrations in animal studies, but few studies have examined the impact of early-life PBDE exposures on thyroid hormone disruption in childhood. METHODS: We used data from 162 mother-child pairs from the Health Outcomes and Measures of the Environment Study (2003-2006, Cincinnati, OH). We measured PBDEs in maternal serum at 16 ±â€¯3 weeks gestation and in child serum at 1-3 years. Thyroid hormones were measured in serum at 3 years. We used multiple informant models to investigate associations between prenatal and early-life PBDE exposures and thyroid hormone levels at age 3 years. RESULTS: Prenatal PBDEs were associated with decreased thyroid stimulating hormone (TSH) levels at age 3 years. A 10-fold increase in prenatal ∑PBDEs (BDE-28, -47, -99, -100, and -153) was associated with a 27.6% decrease (95% CI -40.8%, -11.3%) in TSH. A ten-fold increase in prenatal ∑PBDEs was associated with a 0.25 pg/mL (0.07, 0.43) increase in free triiodothyronine (FT3). Child sex modified associations between prenatal PBDEs and thyroid hormones, with significant decrements in TSH among females and decreased free T4 (FT4) in males. Prenatal ∑PBDEs were not associated with TT4, FT4, or total T3. CONCLUSIONS: These findings suggest an inverse relationship between prenatal ∑PBDEs and TSH at 3 years. Associations may be sexually dimorphic, with an inverse relationship between prenatal BDE-47 and -99 and TSH in females and null associations among males.

A new approach to synergize academic and guideline-compliant research: the CLARITY-BPA research program.

Recently, medical research has seen a strong push toward translational research, or "bench to bedside" collaborations, that strive to enhance the utility of laboratory science for improving medical treatment. The success of that paradigm supports the potential application of the process to other fields, such as risk assessment. Close collaboration among academic, government, and industry scientists may enhance the translation of scientific findings to regulatory decision making. The National Toxicology Program (NTP), National Institute of Environmental Health Sciences (NIEHS), and U.S. Food and Drug Administration (FDA) developed a consortium-based research program to link more effectively academic and guideline-compliant research. An initial proof-of-concept collaboration, the Consortium Linking Academic and Regulatory Insights on BPA Toxicity (CLARITY-BPA), uses bisphenol A (BPA) as a test chemical. The CLARITY-BPA program combines a core perinatal guideline-compliant 2-year chronic toxicity study with mechanistic studies/endpoints conducted by academic investigators. Twelve extramural grantees were selected by NIEHS through an RFA-based initiative to participate in the overall study design and conduct disease-relevant investigations using tissues and animals from the core study. While the study is expected to contribute to our understanding of potential effects of BPA, it also has ramifications beyond this specific focus. Through CLARITY-BPA, NIEHS has established an unprecedented level of collaboration among extramural grantees and regulatory researchers. By drawing upon the strengths of academic and regulatory expertise and research approaches, CLARITY-BPA represents a potential new model for filling knowledge gaps, enhancing quality control, informing chemical risk assessment, and identifying new methods or endpoints for regulatory hazard assessments.