Developmental Fluoride Neurotoxicity: A Systematic Review and Meta-Analysis

Background: Although fluoride may cause neurotoxicity in animal models and acute fluoride poisoning causes neurotoxicity in adults, very little is known of its effects on children’s neurodevelopment.Objective: We performed a systematic review and meta-analysis of published studies to investigate the effects of increased fluoride exposure and delayed neurobehavioral development.Methods: We searched the MEDLINE, EMBASE, Water Resources Abstracts, and TOXNET databases through 2011 for eligible studies. We also searched the China National Knowledge Infrastructure (CNKI) database, because many studies on fluoride neurotoxicity have been published in Chinese journals only. In total, we identified 27 eligible epidemiological studies with high and reference exposures, end points of IQ scores, or related cognitive function measures with means and variances for the two exposure groups. Using random-effects models, we estimated the standardized mean difference between exposed and reference groups across all studies. We conducted sensitivity analyses restricted to studies using the same outcome assessment and having drinking-water fluoride as the only exposure. We performed the Cochran test for heterogeneity between studies, Begg’s funnel plot, and Egger test to assess publication bias, and conducted meta-regressions to explore sources of variation in mean differences among the studies.Results: The standardized weighted mean difference in IQ score between exposed and reference populations was –0.45 (95% confidence interval: –0.56, –0.35) using a random-effects model. Thus, children in high-fluoride areas had significantly lower IQ scores than those who lived in low-fluoride areas. Subgroup and sensitivity analyses also indicated inverse associations, although the substantial heterogeneity did not appear to decrease.Conclusions: The results support the possibility of an adverse effect of high fluoride exposure on children’s neurodevelopment. Future research should include detailed individual-level information on prenatal exposure, neurobehavioral performance, and covariates for adjustment.     

Human Neurospheres as Three-Dimensional Cellular Systems for Developmental Neurotoxicity Testing

Background

Developmental neurotoxicity (DNT) of environmental chemicals is a serious threat to human health. Current DNT testing guidelines propose investigations in rodents, which require large numbers of animals. With regard to the “3 Rs” (reduction, replacement, and refinement) of animal testing and the European regulation of chemicals [Registration, Evaluation, and Authorisation of Chemicals (REACH)], alternative testing strategies are needed in order to refine and reduce animal experiments and allow faster and less expensive screening.

Objectives

The goal of this study was to establish a three-dimensional test system for DNT screening based on human fetal brain cells.

Methods

We established assays suitable for detecting disturbances in basic processes of brain development by employing human neural progenitor cells (hNPCs), which grow as neurospheres. Furthermore, we assessed effects of mercury and oxidative stress on these cells.

Results

We found that human neurospheres imitate proliferation, differentiation, and migration in vitro. Exposure to the proapoptotic agent staurosporine further suggests that human neurospheres possess functioning apoptosis machinery. The developmental neurotoxicants methylmercury chloride and mercury chloride decreased migration distance and number of neuronal-like cells in differentiated hNPCs. Furthermore, hNPCs undergo caspase-independent apoptosis when exposed toward high amounts of oxidative stress.

Conclusions

Human neurospheres are likely to imitate basic processes of brain development, and these processes can be modulated by developmental neurotoxicants. Thus, this three-dimensional cell system is a promising approach for DNT testing.     

Photoacoustic-Ultrasound Tomography: A New Window into Developmental Toxicity

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Worldwide, birth defects affect 3%–6% of infants and account for 20% of all infant deaths.¹ With mounting evidence for links between environmental exposures and birth outcomes,^2,3 there is an need for accurate screening strategies for timely diagnosis and treatment of fetal abnormalities. According to the authors of a recent study published in Environmental Health Perspectives, early detection of developmental defects in mice was achieved using a novel dual-modality imaging technique that can overcome some of the challenges of traditional ultrasound technology.⁴Birth defects arise from unknown causes in roughly half of all cases.^5,6 Congenital heart defects are the most common type of birth defect⁷ and are among the top eight causes of infant mortality.⁸ Mixed evidence associates congenital heart defects with prenatal proximity to landfills and exposures to air pollution, metals, pesticides, solvents, disinfection by-products, and high ambient temperatures.^9,10,11Ultrasound imaging techniques can detect some developmental defects before birth, but despite significant advances, their use is limited to later stages of development. However, even in the second trimester more than 50% of congenital heart abnormalities are not detected by routine fetal ultrasound.¹² In addition, conventional ultrasound cannot measure functional parameters such as tissue oxygen saturation (SaO2) and hemoglobin content (HbT). These two early indicators of alterations in embryo circulation typically precede gross morphological changes.^13,14Open in a separate windowLeft: The heart bulge of this 12-day-old mouse embryo is visible in the center of its body. Scanning electron micrograph, magnification 20× when printed at 10cm wide. Right: A new tomographic technique enabled investigators to pinpoint when heart abnormalities started in embryos that received low (middle) and high (bottom) doses of MMC (the top panel shows the control). Images, left to right: © Steve Gschmeissner/Science Photo Library; Qiu et al.⁴ A newer tool, photoacoustic-ultrasound (PA-US) tomography, combines the specificity, high contrast, and deep-tissue penetration of optical and acoustic imaging technologies to provide details about organ structure and function.¹⁵ In this hybrid technology, optical energy is delivered into biological tissues, resulting in ultrasonic emissions that can be analyzed to produce images.¹⁶ Because optical absorption is directly related to physiological properties such as SaO2 and HbT content, different tissues will produce different photoacoustic signals, which can be translated into extremely detailed three-dimensional pictures of the target area.¹⁷ Although PA-US tomography is a promising clinical tool broadly applied in disease monitoring, functional imaging, and therapy and surgery guidance,¹⁸ this is the first time it was tested for assessing developmental toxicity.In the study, investigators used dual-modality PA-US imaging to examine early embryo morphology and markers of embryonic tissue oxygenation and function in mice, after exposure to methylmercury chloride (MMC), a potential neuro- and cardiotoxicant. Pregnant dams received either a high MMC dose, low MMC dose, or saline control for 6 consecutive days. Exposure occurred during a period equivalent to weeks 2–4 of human gestation, when early organogenesis begins and the risk of developmental abnormalities and miscarriage is highest.^19,20 Embryos from treated and control dams were evaluated for pathological changes using PA-US imaging. That technique enabled detection of differences between the high-dose and control groups in overall embryo size and cardiovascular function, results that were confirmed by ex vivo histopathological analyses. In the low-dose group, quantification of SaO2 and HbT values allowed detection of functional abnormalities that preceded apparent morphological changes and would have eluded diagnosis by conventional ultrasound alone.Fuller Bazer, chair of the Physiology of Reproduction Program at Texas A&M University, notes that the dosages used in the study were high relative to concentrations that are toxic to humans. However, the authors’ main focus was testing the technology’s performance. Given the results, says Bazer, who was not involved in the study, PA-US imaging shows promise as a noninvasive means of detecting developmental abnormalities. With further refinement, he suggests, PA-US imaging could prove instrumental in identifying unique developmental changes during normal gestation, or in mouse models of disease with detrimental effects on fetal and placental development.“Our study provides a new high-resolution, real-time imaging method for in vivo evaluation of embryonic development,” says Qingliang Zhao, senior author of the study. “We believe that dual-modality PA-US imaging has great potential in developmental biology research.” The technology is not yet ready for use in humans, Zhao says. However, he asserts that the application of photoacoustic contrast agents and the optimization of detector bandwidth—both of which are the subject of published studies^21,22—would drastically improve the resolution and imaging depth of the PA-US system. Such an approach could prove useful in preclinical studies and clinical applications.     

甲醛和苯单独及联合染毒对小鼠神经系统的毒性作用

[目的]研究甲醛和苯单独及联合染毒对小鼠神经系统的毒性作用,为综合评价甲醛和苯的联合毒性提供科学依据。[方法]选用健康清洁级昆明种纯系小鼠60只,随机分为10组,每组6只,雌雄各半,分别是阴性对照组（清洁空气）（GO）;低（1mg／m^3）（G1）、中（3mg／m^3）（G2）、高（5mg／m^3）（G3）剂量甲醛组;低（500mg／m^3）（G4）、中（1500mg／m^3）（G5）、高（2500mg／m^3）（G6）剂量苯组;低（0．5mg／m^3甲醛＋250mg／m^3苯）（G7）、中（1．5mg／m^3甲醛＋750mg／m^3苯）（G8）、高（2．5mg／m^3甲醛＋1250mg／m^3苯）（G9）剂量联合组。采用静式吸入染毒,每天2h,连续染毒14d。染毒结束后,采用Morris水迷宫实验检测小鼠的学习记忆能力,并测定脑组织的氧化损伤水平。[结果]Morris水迷宫实验结果显示：在定位航行实验中,高剂量甲醛组,中、高剂量苯组和各联合剂量组小鼠逃避潜伏期长于对照组（P〈0．05）;与甲醛、苯单独组比较,中、高剂量联合组逃避潜伏期明显延长（P〈0．05）;在空间探索实验中,与对照组比较,中、高剂量甲醛组和高剂量苯组及各联合剂量组在目标象限游泳时间所占百分比减小（P〈0．05）;与甲醛、苯单独染毒组比较,各联合剂量组在目标象限游泳时间所占百分比均明显减小（P〈0．05）。甲醛和苯单独染毒中、高剂量组及各联合剂量组的SOD活力均低于阴性对照组（P〈0．05）;各剂量甲醛组、高剂量苯组和各联合剂量组MDA含量均高于其阴性对照组（P〈0．05）。与甲醛、苯单独染毒组比较,各联合剂量组SOD活力明显下降（P〈0．05）,MDA含量明显升高（P〈0．05）。[结论]较高剂量甲醛和苯单独染毒对小鼠神经系统有一定毒性作用,甲醛和苯联合染毒对小鼠神经系统的毒性作用大于甲醛、苯单独染毒时的作用,二者联合毒性可能具有协同作用。     

Gender Constancy Judgments in Children with Gender Identity Disorder: Evidence for a Developmental Lag

Gender constancy judgments in children referredfor problems in their gender identity development (N =206) and controls (N = 95) were compared. On Slaby andFrey's (1975) gender constancy interview, the gender-referred children performed more poorlythan the controls at three stage levels: genderidentity, gender stability, and gender consistency. Onthe Boy-Girl Identity Task, a second measure of gender constancy (Emmerich et al., 1977), thegender-referred children also performed more poorly.Gender-referred children who had not attained genderconsistency engaged in significantly less same-sex-typed play on a free-play task than thegender-referred children who had, but there were nogender consistency effects for the controls. Two othermeasures of sex-typed behavior were unrelated to genderconsistency. In the gender-referred group alone, childrenwho failed the gender identity or genderstability stages were more likely to draw anopposite-sex person first on the Draw-a-Person test andto evince more affective gender confusion on the GenderIdentity Interview (Zucker et al., 1993) than childrenwho had passed. It is concluded thatchildren referred for problems in their gender identitydevelopment have a developmental lag in gender constancyacquisition. Possible reasons for the lag arediscussed.     

Domoic Acid Poisoning as a Possible Cause of Seasonal Cetacean Mass Stranding Events in Tasmania,Australia

The periodic trend to cetacean mass stranding events in the Australian island state of Tasmania remains unexplained. This article introduces the hypothesis that domoic acid poisoning may be a causative agent in these events. The hypothesis arises from the previously evidenced role of aeolian dust as a vector of iron input to the Southern Ocean; the role of iron enrichment in Pseudo-nitzschia bloom proliferation and domoic acid production; and importantly, the characteristic toxicosis of domoic acid poisoning in mammalian subjects leading to spatial navigation deficits. As a pre-requisite for quantitative evaluation, the plausibility of this hypothesis was considered through correlation analyses between historical monthly stranding event numbers, mean monthly chlorophyll concentration and average monthly atmospheric dust loading. Correlation of these variables, which under the domoic acid stranding scenario would be linked, revealed strong agreement (r = 0.80–0.87). We therefore advocate implementation of strategic quantitative investigation of the role of domoic acid in Tasmanian cetacean mass stranding events.     

鲜淡菜中软骨藻酸的液相色谱紫外法研究

[目的]根据美国FDA对软骨藻酸(domoic acid)的控制指标，建立一种简便的水产品中软骨藻酸液相色谱紫外测定方法。[方法]采用含甲醇的水溶液，选择性地提取鲜淡菜中软骨藻酸，经离心、过滤等手段进行样品处理，在最优化的条件下进行液相色谱检测。[结果]本研究方法的实际测定生物样品——鲜淡菜中软骨藻酸范围为0．12．50mg／kg，最低检测限达到0．007mg／kg，并且在现有分离条件下无明显干扰物存在；同时经与原分析方法比对，具有很好的一致性。[结论]本方法建立了生物样品鲜淡菜中软骨藻酸的液相色谱紫外测定方法，具有简便、快速的特点，能适合在一般分析实验室开展此项检测工作。     

软骨藻酸对H4细胞血红素氧化酶-1的诱导

[目的 ]研究软骨藻酸对H4细胞血红素氧化酶 1(hemeoxygenase 1,HO 1)的诱导。 [方法 ]流式细胞仪检测0、0 .0 64、0 .64、6.4μmol/L软骨藻酸作用细胞 2 4h后HO 1蛋白表达、HO 1mRNA转录和HO 1酶活性。[结果 ]HO 1蛋白表达 :0 .0 64、0 .64、6.4μmol/L浓度组的荧光强度分别为 ( 68.0 7± 7.0 7)、( 81.3 4± 8.64 )和 ( 81.95± 8.3 0 ) ,与对照组 ( 60 .60± 5 .3 6)比较 ,差异均有显著性 (P <0 .0 1)。HO 1mRNA转录 :0 .0 64 μmol/L组相对表达量为 ( 0 .43 9± 0 .0 0 7) ,与对照组( 0 .411± 0 .0 0 8)比较差异无显著性 (P >0 .0 5 ) ;0 .64 μmol/L和 6.4μmol/L组分别为 ( 0 .5 0 6± 0 .0 13 )和 ( 0 .63 1± 0 .0 3 6) ,与对照组比较差异有显著性 (P <0 .0 1)。HO 1酶活性 :0 .0 64mol/L组为 ( 3 89.3 2± 3 4.75 )pmol/(mg·h) ,与对照组 ( 3 2 6.75±2 7.0 5 )pmol/(mg·h)相比 ,差异无显著性 (P >0 .0 5 ) ;0 .64和 6.4μmol/L组分别为 ( 4 61.75± 2 7.84)和 ( 687.5 0± 3 5 .93 )pmol/(mg·h) ,与对照组相比 ,差异有显著性 (P <0 .0 1)。前述 3指标结果均有随剂量浓度增加而逐渐升高的趋势。 [结论 ]软骨藻酸能诱导H4细胞HO 1蛋白表达、HO 1mRNA转录和HO 1酶活性升高     

Perfluorooctanoic Acid Exposure and Cancer Outcomes in a Contaminated Community: A Geographic Analysis

Background: Perfluorooctanoic acid (PFOA) has been linked to cancer in occupational mortality studies and animal toxicologic research.Objective: We investigated the relationship between PFOA exposure and cancer among residents living near the DuPont Teflon-manufacturing plant in Parkersburg, West Virginia (WV).Methods: Our analyses included incident cases of 18 cancers diagnosed from 1996 through 2005 in five Ohio (OH) counties and eight WV counties. For analyses of each cancer outcome, controls comprised all other cancers in the study data set except kidney, pancreatic, testicular, and liver cancers, which have been associated with PFOA in animal or human studies. We applied logistic regression models to individual-level data to calculate adjusted odds ratios (AORs) and confidence intervals (CIs). For the combined analysis of OH and WV data, the exposure of interest was resident water district. Within OH, geocoded addresses were integrated with a PFOA exposure model to examine the relationship between cancer odds and categories of estimated PFOA serum.Results: Our final data set included 7,869 OH cases and 17,238 WV cases. There was a positive association between kidney cancer and the very high and high serum exposure categories [AOR = 2.0 (95% CI: 1.0, 3.9) n = 9 and 2.0 (95% CI: 1.3, 3.2) n = 22, respectively] and a null association with the other exposure categories compared with the unexposed. The largest AOR was for testicular cancer with the very high exposure category [2.8 (95% CI: 0.8, 9.2) n = 6], but there was an inverse association with the lower exposure groups, and all estimates were imprecise because of small case numbers.Conclusions: Our results suggest that higher PFOA serum levels may be associated with testicular, kidney, prostate, and ovarian cancers and non-Hodgkin lymphoma. Strengths of this study include near-complete case ascertainment for state residents and well-characterized contrasts in predicted PFOA serum levels from six contaminated water supplies.     

Blood Manganese as an Exposure Biomarker: State of the Evidence

Despite evidence of adverse health effects resulting from exposure to manganese (Mn), biomarkers of exposure are poorly understood. To enhance understanding, mean blood Mn (MnB) and mean air Mn (MnA) were extracted from 63 exposure groups in 24 published papers, and the relationship was modeled using segmented regression. On a log/log scale, a positive association between MnA and MnB was observed among studies reporting MnA concentrations above about 10 μg/m³, although interpretation is limited by largely cross-sectional data, study design variability, and differences in exposure monitoring methods. Based on the results of the segmented regression, we hypothesize that below the concentration of about 10 μg/m³, Mn in the body is dominated by dietary Mn, and additional inhaled Mn only causes negligible changes in Mn levels unless the inhaled amount is substantial. However, stronger study designs are required to account for temporal characteristics of the MnA to MnB relationships that reflect the underlying physiology and toxicokinetics of Mn uptake and distribution. Thus, we present an inception cohort study design we have conducted among apprentice welders, and the analytical strengths this study design offers. To determine if blood could be a useful biomarker for Mn to be utilized by industrial hygienists in general industry requires additional time-specific analyses, which our inception cohort study design will allow.     

Species-Specific Differential AhR Expression Protects Human Neural Progenitor Cells against Developmental Neurotoxicity of PAHs

Background

Because of their lipophilicity, persistent organic pollutants (POPs) cross the human placenta, possibly affecting central nervous system development. Most POPs are known aryl hydrocarbon receptor (AhR) ligands and activators of AhR signaling. Therefore, AhR activation has been suggested to cause developmental neurotoxicity (DNT).

Objective

We studied the effects of AhR ligands on basic processes of brain development in two comparative in vitro systems to determine whether AhR-activation is the underlying mechanism for reported DNT of POPs in humans.

Methods

We employed neurosphere cultures based on human neural progenitor cells (hNPCs) and wild-type and AhR-deficient mouse NPCs (mNPCs) and studied the effects of different AhR agonists [3-methylcholanthrene (3-MC), benzo(a)pyrene [B(a)P], and 2,3,7,8-tetrachlorodibenzo-p-dioxin (TCDD)] and an antagonist [3′-methoxy-4′-nitroflavone (MNF)] on neurosphere development. Moreover, we analyzed expression of AhR and genes involved in AhR signaling.

Results

In contrast to wild-type mNPCs, hNPCs and AhR-deficient mNPCs were insensitive to AhR agonism or antagonism. Although AhR modulation attenuated wild-type mNPC proliferation and migration, hNPCs and AhR-deficient mNPCs remained unaffected. Results also suggest that species-specific differences resulted from nonfunctional AhR signaling in hNPCs.

Conclusion

Our findings suggest that in contrast to wild-type mNPCs, hNPCs were protected against polycyclic aromatic hydrocarbon–induced DNT because of an absence of AhR. This difference may contribute to species-specific differences in sensitivity to POPs.