Methylmercury induced toxicogenomic response in C57 and SWV mouse embryos undergoing neural tube closure

Differential Modulatory Effects of Methylmercury (MeHg) on Ahr-regulated Genes in Extrahepatic Tissues of C57BL/6 Mice

Methylmercury (MeHg) and 2,3,7,8-tetrachlorodibenzodioxin (TCDD) are potent environmental pollutants implicated in the modulation of xenobiotic-metabolizing enzymes, particularly the cytochrome P450 1 family (CYP1) which is regulated by the aryl hydrocarbon receptor (AHR). However, the co-exposure to MeHg and TCDD raises concerns about their potential combined effects, necessitating thorough investigation. The primary objective of this study was to investigate the individual and combined effects of MeHg and TCDD on AHR-regulated CYP1 enzymes in mouse extrahepatic tissues. Therefore, C57BL/6 mice were administrated with MeHg (2.5 mg/kg) in the absence and presence of TCDD (15 μg/kg) for 6 and 24 h. The AHR-regulated CYP1 mRNA and protein expression levels were measured in the heart, lung, and kidney, using RT real-time PCR and western blot, respectively. Interestingly, treatment with MeHg exhibited mainly inhibitory effect, particularly, it decreased the basal level of Cyp1a1 and Cyp1a2 mRNA and protein, and that was more evident at the 24 h time point in kidney followed by heart. Similarly, when mice were co-exposed, MeHg was able to reduce the TCDD-induced Cyp1a1 and Cyp1a2 expression, however, MeHg potentiated kidney Cyp1b1 mRNA expression, opposing the observed change on its protein level. Also, MeHg induced antioxidant NAD(P)H:quinone oxidoreductase (NQO1) mRNA and protein in kidney, while heme-oxygenase (HO-1) mRNA was up-regulated in heart and kidney. In conclusion, this study reveals intricate interplay between MeHg and TCDD on AHR-regulated CYP1 enzymes, with interesting inhibitory effects observed that might be significant for procarcinogen metabolism. Varied responses across tissues highlight the potential implications for environmental health.

Developmental exposure to methylmercury alters GAD67 immunoreactivity and morphology of endothelial cells and capillaries of midbrain and hindbrain regions of adult rat offspring

INTRODUCTION

Methylmercury (MeHg) is an environmental contaminant that is of particular concern in Northern Arctic Canadian populations. Specifically, organic mercury compounds such as MeHg are potent toxicants that affect multiple bodily systems including the nervous system. Developmental exposure to MeHg is a major concern, as the developing fetus and neonate are thought to be especially vulnerable to the toxic effects of MeHg. The objective of this study was to examine developmental exposure to low doses of MeHg and effects upon the adult central nervous system (CNS). The doses of MeHg chosen were scaled to be proportional to the concentrations of MeHg that have been reported in human maternal blood samples in Northern Arctic Canadian populations.

METHOD

Offspring were exposed to MeHg maternally where pregnant Sprague Dawley rats were fed cookies that contained MeHg or vehicle (vehicle corn oil; MeHg 0.02 mg/kg/body weight or 2.0 mg/kg/body weight) daily, throughout gestation (21 days) and lactation (21 days). Offspring were not exposed to MeHg after the lactation period and were euthanized on postnatal day 450. Brains were extracted, fixed, frozen, and sectioned for immunohistochemical analysis. A battery of markers of brain structure and function were selected including neuronal GABAergic enzymatic marker glutamic acid decarboxylase-67 (GAD67), apoptotic/necrotic marker cleaved caspase-3 (CC3), catecholamine marker tyrosine hydroxylase (TH), immune inflammatory marker microglia (Cd11b), endothelial cell marker rat endothelial cell antigen-1 (RECA-1), doublecortin (DCX), Bergmann glia (glial fibrillary acidic protein (GFAP)), and general nucleic acid and cellular stains Hoechst, and cresyl violet, respectively. Oxidative stress marker lipofuscin (autofluorescence) was also assessed. Both male and female offspring were included in analysis. Two-way analysis of variance (ANOVA) was utilized where sex and treatment were considered as between-subject factors (p* <0.05). ImageJ was used to assess immunohistochemical results.

RESULTS

In comparison with controls, adult rat offspring exposed to both doses of MeHg were observed to have (1) increased GAD67 in the cerebellum; (2) decreased lipofuscin in the locus coeruleus; and (3) decreased GAD67 in the anterior CA1 region. Furthermore, in the substantia nigra and periaqueductal gray, adult male offspring consistently had a larger endothelial cell and capillary perimeter in comparison to females. The maternal high dose of MeHg influenced RECA-1 immunoreactivity in both the substantia nigra and periaqueductal gray of adult rat offspring, where the latter neuronal region also showed statistically significant decreases in RECA-1 immunoreactivity at the maternal low dose exposure level. Lastly, males exposed to high doses of MeHg during development exhibited a statistically significant increase in the perimeter of endothelial cells and capillaries (RECA-1) in the cerebellum, in comparison to male controls.

CONCLUSION

Findings suggest that in utero and early postnatal exposure to MeHg at environmentally relevant doses leads to long-lasting and selective changes in the CNS. Exposure to MeHg at low doses may affect GABAergic homeostasis and vascular integrity of the CNS. Such changes may contribute to neurological disturbances in learning, cognition, and memory that have been reported in epidemiological studies.

Impact of prenatal exposure to metallic elements on neural tube defects: Insights from human investigations

Metallic elements play a pivotal role in maternal and fetal health. Metals can cross the placental barrier and be absorbed by fetuses, where they may affect closure of the neural tube during embryonic development. Neural tube defects (NTDs), which result from aberrant closure of the neural tube three to four weeks post-conception, have a multifactorial and complex etiology that combines genetic variants and environmental exposure. Recent advances in population-level association studies have investigated the link between maternal environmental exposure and NTDs, particularly the influence of metals on the incidence of NTDs. Herein, we present a broad and qualitative review of current literature on the association between maternal and prenatal metal exposure via the maternal peripheral blood, amniotic fluid, placenta, umbilical cord, and maternal hair, and the risk of developing NTDs. Specifically, we identify the various aggravating or attenuating effects of metallic exposure on the risk of NTD formation. This review provides novel insights into the association between environmental metals and NTDs and has important applications for NTD prevention and mitigating environmental exposure to metals.

Toxicogenomic signatures associated with methylmercury induced developmental toxicity in the zebrafish embryos

Methylmercury (MeHg) is a toxicant with adverse effects on embryogenesis from fish to man. The developmental outcomes of MeHg are well understood, but molecular understanding of toxicity is rather limited. We performed here a genome-wide transcriptional analyses of 6, 30, and 50 μg/L MeHg exposed zebrafish embryos from 4 to 72 h post-fertilization (hpf) using RNA-sequencing and microarray, and conducted a systematical comparison of MeHg-induced transcriptomic responses reported in this and our previous studies. We observed MeHg significantly to disrupt expression of 1050, 1931, and 2996 genes, respectively including gene ontologies in terms of visual and sensory perception, phototransduction, ferroptosis, and GABAergic synapse. Significantly altered genes were associated with ontology categorized into metabolism, such as fatty acid, amino acid, and glutathione metabolism across all experiments. Expression of genes involved in Wnt, Shh, and Notch signaling pathways previously demonstrated to be crucial for development was changed at varying levels dependent on exposure concentrations and durations. Our findings show MeHg significantly to affect expression of genes associated with tissue and/or organs developmental processing including eye, lateral line, fins, and brain, especially in embryos exposed to 6 μg/L, which did not cause obviously toxic effects on zebrafish embryos. We obtain 21 genes being significantly altered by MeHg in a concentration and stage independent manner, and might be served as signatures for developmental toxicity and/or teratogenic effects.

Total mercury concentration in placental tissue, a good biomarker of prenatal mercury exposure, is associated with risk for neural tube defects in offspring

OBJECTIVE

To examine the role of total mercury (T-Hg) in placenta as a biomarker of prenatal mercury (Hg) exposure and determine the association between prenatal Hg exposure and risk for neural tube defects (NTDs) in offspring.

METHODS

Total Hg concentrations in placental tissue were detected in 408 NTD cases and 593 healthy controls enrolled in Shanxi province in northern China. Methylmercury (MeHg) and T-Hg were also detected in the umbilical cord of 147 NTD cases and 140 healthy controls. In addition, MeHg and T-Hg were detected in fetal kidney, liver, and brain tissues of 51 NTD cases. Spearman's rank correlation (r_s) was used to evaluate the correlations between placental T-Hg and T-Hg in umbilical cord and fetal kidney, liver, and brain tissues. The Wilcoxon rank-sum test was used to compare T-Hg amounts between case and control groups. Logistic regression was used to examine the association between placental T-Hg and risk for NTDs.

RESULTS

Placental T-Hg was significantly correlated with T-Hg in umbilical cord (r_s = 0.479), kidney (r_s = 0.718), liver (r_s = 0.656), and brain (r_s = 0.512) tissues (all p < 0.001). The median (25th percentile-75th percentile) concentration for placental T-Hg in the NTD case group was 8.91 (5.00-17.1) ng/g dry weight (d.w.), significantly higher than that in the healthy control group (4.99 [3.26-7.93] ng/g d.w., p < 0.001). After adjusting for potential confounders, higher levels of T-Hg in placenta were associated with increased risk for NTDs in offspring (OR = 1.76, 95% CI: 1.13-2.76), and a dose-response relationship was found (p < 0.001).

CONCLUSION

The concentration of T-Hg in placenta is a good biomarker for estimating prenatal Hg exposure, which is associated with increased risk for NTDs.

Toxicity of mercury: Molecular evidence

Minamata disease in Japan and the large-scale poisoning by methylmercury (MeHg) in Iraq caused wide public concerns about the risk emanating from mercury for human health. Nowadays, it is widely known that all forms of mercury induce toxic effects in mammals, and increasing evidence supports the concern that environmentally relevant levels of MeHg could impact normal biological functions in wildlife. The information of mechanism involved in mercurial toxicity is growing but knowledge gaps still exist between the adverse effects and mechanisms of action, especially at the molecular level. A body of data obtained from experimental studies on mechanisms of mercurial toxicity in vivo and in vitro points to that disruption of the antioxidant system may play an important role in the mercurial toxic effects. Moreover, the accumulating evidence indicates that signaling transduction, protein or/and enzyme activity, and gene regulation are involving in mediating toxic and adaptive response to mercury exposure. We conducted here a comprehensive review of mercurial toxic effects on wildlife and human, in particular synthesized key findings of molecular pathways involved in mercurial toxicity from the cells to human. We discuss the molecular evidence related mercurial toxicity to the adverse effects, with particular emphasis on the gene regulation. The further studies relying on Omic analysis connected to adverse effects and modes of action of mercury will aid in the evaluation and validation of causative relationship between health outcomes and gene expression.

Effects of boron compounds on human reproduction

Because of the high pK_a of boric acid, inorganic borates, when taken up by the human or animal organism, exist in the body almost exclusively in the form of non-dissociated boric acid. Therefore, the variety of inorganic boron compounds is commonly addressed in the toxicological literature as "boron" (B). There is a discussion concerning categorisation of inorganic boron compounds as reproductive toxins. Boron treatment of rats, mice and dogs was dose-dependently associated with testicular toxicity, characterised by inhibited spermiation at lower dose levels and by reduction of epididymal sperm counts at higher dose levels. The NOAEL for such fertility effects of boric acid in male rats (oral feeding, Sprague Dawley strain) was evaluated to be 17.5 mg B/kg bw per day. As far as developmental toxicity is concerned, oral dosing of 9.6 mg B/kg bw daily to female pregnant Sprague Dawley rats remained without effects, with foetal skeletal effects observed at higher doses. Therefore, 9.6 mg B/kg bw (oral dosing) was evaluated as NOAEL for developmental effects of boric acid. The blood level in rats, equivalent to this NOAEL, is 1270 ng B/g. As far as B-exposed humans are concerned, field studies on the effect of boron on human reproduction are possible only in a few boron-rich geographical areas. Published field studies were conducted in China's Liaoning province, the Argentinian Andes and Western Anatolia/Turkey. Particularly relevant are studies on occupationally B-exposed groups, because the potential exposure to boron is much higher in occupational compared to environmental settings. Comparison of estimated daily B exposure levels in humans and actually measured B blood levels confirms the preference of biomonitoring for exposure assessment in environmental and occupational studies. A boron blood level scaling shows that the levels of high occupational B exposures reported in China and in Turkey are compatible. Compared to the experimental B blood levels at boron-related NOAELs for male fertility and for developmental toxicity in rats, the human blood level means of the highest occupational exposure groups in China and in Turkey are lower by factors of > 4 and > 2, respectively. Basically, concentrations of B within the body that exert reproductive toxicity in humans are not reached under the conditions of human normal handling and use, including conditions of extreme occupational exposures. In consequence, all relevant results of studies into human reproductive toxicity of B are basically negative. Considering the effective doses, there is no scientific contradiction between experimental and human results of B reproductive toxicity.

Association of maternal chronic arsenic exposure with the risk of neural tube defects in Northern China

Numerous animal studies have shown that high arsenic exposure can induce neural tube defect (NTD) formation. However, epidemiological evidence related to this finding is scarce. The key objective of our study is to evaluate whether maternal arsenic exposure is associated with NTD risk in Northern China. Our case-control study was conducted in 11 countries or cities in Shanxi and Hebei provinces during 2003-2007. A total of 774 mothers were included as participants: 511 controls and 263 cases (including 123 with anencephaly, 115 with spina bifida, 18 with encephalocele, and 7 with other NTD subtypes). The arsenic concentration was measured in a specific section of hair that grew from 3 months before to 3 months after conception. We found a higher hair arsenic concentration in the NTD cases with median (inter-quartile range) of 0.093 (0.025-0.387) μg/g hair than that in the controls with a value of 0.082 (0.030-0.414) μg/g hair. Maternal hair arsenic concentration above its median of the controls was associated with an increased risk of the total NTDs with an adjusted odds ratio (OR) of 1.32 [95% confidence interval (CI): (0.91-1.92)], which was not statistically significant (p = 0.14), although the crude OR without adjusting for the confounders of 1.68 (95% CI: 1.24-2.27; p < 0.001) suggested that hair arsenic is a risk factor of NTDs. There was no dose-response relationship between maternal hair arsenic concentration and the risk of total NTDs. Similar phenomena were found for anencephaly and spina bifida, respectively. Overall, our findings showed that maternal periconceptional arsenic exposure may not significantly contribute to the risk of NTD development in Northern China; other risk factors need to be further examined in future studies.

Genome-wide Transcriptional Analysis of Oxidative Stress-related Genes and Pathways Induced by CdTe aqQDs in Mice

Objective: Quantum dots (QDs) has widely applied in the field of science, whose potential toxic effect has increasingly become a focus concern we need pay attention to in public health. The purpose of this article was to explore the toxicity mechanism with oxidative damage from treatment with QDs at the molecular level through a gene microarray.

Methods: Mice were administered aqueously synthesized cadmium telluride QDs (CdTe aqQDs) via intravenous tail injection of a 2 µmol/kg solution (based on the molar mass of Cd), and their kidneys were collected at 1 day in strict accordance with the programs used for treated mice. We determined the hierarchical clustering of expression ratios, enriched gene ontology (GO) terms and signaling pathways through gene microarray analysis and bioinformatics analysis in kidney tissue and screened the key enzyme genes, which were verified by real-time quantitative polymerase chain reaction (real-time qPCR).

Results: Compared to control group, 459 lncRNAs (197 down-regulated and 262 up-regulated) and 256 mRNAs (103 down-regulated and 153 up-regulated) were differentially expressed. According to biological processes in enriched GO terms, the response to a redox state played a significant role in the biological processes involved altered genes. Pathway analysis showed that the signaling pathways that involved cytochrome P450 (CYP450) enzymes had a close relationship with QDs. Among these signaling pathways, gene expression profiling revealed that selected differentially expressed mRNAs (CYP19A1, CYP1B1, CYP11A1, CYP11B2, and CYP17A1 in the kidney and CYP19A1 and CYP1B1 in the liver) were validated by real-time qPCR, resulting in expression levels of CYP11A1, CYP11B2 and CYP17A1 in the kidney and CYP19A1 and CYP1B1 in the liver that were significantly increased, however in expression levels of CYP19A1 and CYP1B1 compared with control group in the kidney, there was no significant difference.

Conclusions: Our results provide a foundation for and potential insight into the role of CYP450-related genes in QD-induced oxidative stress. QDs may produce a great deal of reactive oxygen species (ROS) by promoting high expression of CYP450 enzymes and accumulating steroid hormones, which may be an important toxicity mechanism for mediating oxidative stress and tissue damage.

Form of Dietary Methylmercury does not Affect Total Mercury Accumulation in the Tissues of Zebra Finch

Exposure to mercury in humans, other mammals, and birds is primarily dietary, with mercury in the methylated form and bound to cysteine in the tissues of prey items. Yet dosing studies are generally carried out using methylmercury chloride. Here we tested whether the accumulation of total mercury in zebra finch blood, egg, muscle, liver, kidney or brain differed depending on whether dietary mercury was complexed with chloride or cysteine. We found no effect of form of mercury on tissue accumulation. Some previous studies have found lower accumulation of mercury in tissues of animals fed complexed mercury. Much remains to be understood about what happens to ingested mercury once it enters the intestines, but our results suggest that dietary studies using methylmercury chloride in birds will produce similar tissue accumulation levels to those using methylmercury cysteine.

Comparative toxicogenomic responses of mercuric and methyl-mercury

Background

Mercury is a ubiquitous environmental toxicant that exists in multiple chemical forms. A paucity of information exists regarding the differences or similarities by which different mercurials act at the molecular level.

Results

Transcriptomes of mixed-stage C. elegans following equitoxic sub-, low- and high-toxicity exposures to inorganic mercuric chloride (HgCl₂) and organic methylmercury chloride (MeHgCl) were analyzed. In C. elegans, the mercurials had highly different effects on transcription, with MeHgCl affecting the expression of significantly more genes than HgCl₂. Bioinformatics analysis indicated that inorganic and organic mercurials affected different biological processes. RNAi identified 18 genes that were important in C. elegans response to mercurial exposure, although only two of these genes responded to both mercurials. To determine if the responses observed in C. elegans were evolutionarily conserved, the two mercurials were investigated in human neuroblastoma (SK-N-SH), hepatocellular carcinoma (HepG2) and embryonic kidney (HEK293) cells. The human homologs of the affected C. elegans genes were then used to test the effects on gene expression and cell viability after using siRNA during HgCl₂ and MeHgCl exposure. As was observed with C. elegans, exposure to the HgCl₂ and MeHgCl had different effects on gene expression, and different genes were important in the cellular response to the two mercurials.

Conclusions

These results suggest that, contrary to previous reports, inorganic and organic mercurials have different mechanisms of toxicity. The two mercurials induced disparate effects on gene expression, and different genes were important in protecting the organism from mercurial toxicity.

Interpreting Stress Responses during Routine Toxicity Studies

Stress often occurs during toxicity studies. The perception of sensory stimuli as stressful primarily results in catecholamine release and activation of the hypothalamic–pituitary–adrenal (HPA) axis to increase serum glucocorticoid concentrations. Downstream effects of these neuroendocrine signals may include decreased total body weights or body weight gain; food consumption and activity; altered organ weights (e.g., thymus, spleen, adrenal); lymphocyte depletion in thymus and spleen; altered circulating leukocyte counts (e.g., increased neutrophils with decreased lymphocytes and eosinophils); and altered reproductive functions. Typically, only some of these findings occur in a given study. Stress responses should be interpreted as secondary (indirect) rather than primary (direct) test article–related findings. Determining whether effects are the result of stress requires a weight-of-evidence approach. The evaluation and interpretation of routinely collected data (standard in-life, clinical pathology, and anatomic pathology endpoints) are appropriate and generally sufficient to assess whether or not changes are secondary to stress. The impact of possible stress-induced effects on data interpretation can partially be mitigated by toxicity study designs that use appropriate control groups (e.g., cohorts treated with vehicle and subjected to the same procedures as those dosed with test article), housing that minimizes isolation and offers environmental enrichment, and experimental procedures that minimize stress and sampling and analytical bias.

This article is a comprehensive overview of the biological aspects of the stress response, beginning with a Summary (Section 1) and an Introduction (Section 2) that describes the historical and conventional methods used to characterize acute and chronic stress responses. These sections are followed by reviews of the primary systems and parameters that regulate and/or are influenced by stress, with an emphasis on parameters evaluated in toxicity studies: In-life Procedures (Section 3), Nervous System (Section 4), Endocrine System (Section 5), Reproductive System (Section 6), Clinical Pathology (Section 7), and Immune System (Section 8). The paper concludes (Section 9) with a brief discussion on Minimizing Stress-Related Effects (9.1.), and a final section explaining why Parameters routinely measured are appropriate for assessing the role of stress in toxicology studies (9.2.).

Toxicogenomic approaches in developmental toxicology testing

The emergence of toxicogenomic applications provides new tools to characterize, classify, and potentially predict teratogens. However, due to the vast number of experimental and statistical procedural steps, toxicogenomic studies are challenging. Here, we guide researchers through the basic framework of conducting toxicogenomic investigations in the field of developmental toxicology, providing examples of biological and technical factors that may influence response and interpretation. Furthermore, we review current, diverse applications of toxicogenomic-based approaches in teratology testing, including exposure-response characterization (dose and duration), chemical classification studies, and cross-model comparisons study designs. This review is intended to guide scientists through the challenging and complex structure of conducting toxicogenomic analyses, while considering the many applications of using toxicogenomics in study designs and the future of these types of "omics" approaches in developmental toxicology.

Oral exposure to methylmercury modifies the prostatic microenvironment in adult rats

Methylmercury (MeHg) is an environmental pollutant that is highly toxic to the central nervous system. As its effects on male reproductive system are poorly understood, this study was carried out to analyse the effects of MeHg on the rat prostate. To evaluate the MeHg toxicity on ventral prostate, three groups of adult male Wistar rats received oral doses of 0.5, 1.0 and 3.0 mg/kg MeHg, respectively, on a daily basis for 14 days. A fourth group was used as a control. The prostate weight was decreased in rats treated orally with 0.5 mg/kg MeHg compared to controls. Also, Hg concentration increased significantly in the prostate after treatments. There were reductions in serum testosterone levels and androgen receptor immunoreactivity in animals receiving 3.0 mg MeHg/kg. The stereological data showed changes in the prostatic epithelial, stromal and luminal compartments which varied according to the different doses. Histopathological alterations, such as chronic inflammation, stratified epithelial hyperplasia and epithelial inflammatory reactive atypia, were observed in the 0.5 mg/kg MeHg-treated group. Epithelial atrophy was observed in the 3.0 mg/kg MeHg-treated group. In conclusion, the MeHg affects prostatic homoeostasis resulting in histopathological changes that may be relevant in the pathogenesis of prostatic disease.

Mechanisms and Modifiers of Methylmercury-Induced Neurotoxicity

The neurotoxic consequences of methylmercury (MeHg) exposure have long been known, however a complete understanding of the mechanisms underlying this toxicity is elusive. Recent epidemiological and experimental studies have provided many mechanistic insights, particularly into the contribution of genetic and environmental factors that interact with MeHg to modify toxicity. This review will outline cellular processes directly and indirectly affected by MeHg, including oxidative stress, cellular signaling and gene expression, and discuss genetic, environmental and nutritional factors capable of modifying MeHg toxicity.

A review of toxicogenomic approaches in developmental toxicology

Over the past decade, the use of gene expression profiling (i.e., toxicogenomics or transcriptomics) has been established as the vanguard "omics" technology to investigate exposure-induced molecular changes that underlie the development of disease. As this technology quickly advances, researchers are striving to keep pace in grasping the complexity of toxicogenomic response while at the same time determine its applicability for the field of developmental toxicology. Initial studies suggest toxicogenomics to be a promising tool for multiple types of study designs, including exposure-response investigations (dose and duration), chemical classification, and model comparisons. In this review, we examine the use of toxicogenomics in developmental toxicology, discussing biological and technical factors that influence response and interpretation. Additionally, we provide a framework to guide toxicogenomic investigations in the field of developmental toxicology.

The embryonic stem cell test combined with toxicogenomics as an alternative testing model for the assessment of developmental toxicity

One of the most studied in vitro alternative testing methods for identification of developmental toxicity is the embryonic stem cell test (EST). Although the EST has been formally validated, the applicability domain as well as the predictability of the model needs further study to allow successful implementation of the EST as an alternative testing method in regulatory toxicity testing. Genomics technologies have already provided a proof of principle of their value in identification of toxicants such as carcinogenic compounds. Also within the EST, gene expression profiling has shown its value in the identification of developmental toxicity and in the evaluation of factors critical for risk assessment, such as dose and time responses. It is expected that the implementation of genomics into the EST will provide a more detailed end point evaluation as compared to the classical morphological scoring of differentiation cultures. Therefore, genomics may contribute to improvement of the EST, both in terms of definition of its applicability domain as well as its predictive capacity. In the present review, we present the progress that has been made with regard to the prediction of developmental toxicity using the EST combined with transcriptomics. Furthermore, we discuss the developments of additional aspects required for further optimization of the EST, including kinetics, the use of human embryonic stem cells (ESC) and computational toxicology. Finally, the current and future use of the EST model for prediction of developmental toxicity in testing strategies and in regulatory toxicity evaluations is discussed.

Effects of methylmercury on male reproductive functions in Wistar rats

In this study we investigated the effects of subacute exposure to methylmercury (MeHg) on male reproductive functions in rats by means of determination of alterations in structural and functional parameters. Adult male Wistar rats received 0, 0.5, 1.0 or 3.0 mg/kg/body weight/day orally, daily MeHg for 14 days. Sperm motility, the relative sperm count and transit time in the caput/corpus epididymis, were all reduced at all doses. The lowest dose increased the number of sperm head abnormalities; daily sperm production was elevated at the intermediate dose; while at the highest dose there was a decrease in serum testosterone levels and a rise in mercury (Hg) content in reproductive organs, liver and kidneys. In conclusion, MeHg exposure produced damages on male reproductive functions which may be attributed, at least in part, to the reduction in serum testosterone levels. These consequences could potentially result in infertility in rats.

Arsenic- and cadmium-induced toxicogenomic response in mouse embryos undergoing neurulation

Arsenic (As) and cadmium (Cd) are well-characterized teratogens in animal models inducing embryotoxicity and neural tube defects (NTDs) when exposed during neurulation. Toxicological research is needed to resolve the specific biological processes and associated molecular pathways underlying metal-induced toxicity during this timeframe in gestational development. In this study, we investigated the dose-dependent effects of As and Cd on gene expression in C57BL/6J mouse embryos exposed in utero during neurulation (GD8) to identify significantly altered genes and corresponding biological processes associated with embryotoxicity. We quantitatively examined the toxicogenomic dose-response relationship at the gene level. Our results suggest that As and Cd induce dose-dependent gene expression alterations representing shared (cell cycle, response to UV, glutathione metabolism, RNA processing) and unique (alcohol/sugar metabolism) biological processes, which serve as robust indicators of metal-induced developmental toxicity and indicate underlying embryotoxic effects. Our observations also correlate well with previously identified impacts of As and Cd on specific genes associated with metal-induced toxicity (Cdkn1a, Mt1). In summary, we have identified in a quantitative manner As and Cd induced dose-dependent effects on gene expression in mouse embryos during a peak window of sensitivity to embryotoxicity and NTDs in the sensitive C57BL/6J strain.