Associations of prenatal methylmercury exposure and maternal polyunsaturated fatty acid status with neurodevelopmental outcomes at 7 years of age: results from the Seychelles Child Development Study Nutrition Cohort 2

Mercury-induced toxicity: Mechanisms, molecular pathways, and gene regulation

Mercury is a well-known neurotoxicant for humans and wildlife. The epidemic of mercury poisoning in Japan has clearly demonstrated that chronic exposure to methylmercury (MeHg) results in serious neurological damage to the cerebral and cerebellar cortex, leading to the dysfunction of the central nervous system (CNS), especially in infants exposed to MeHg in utero. The occurrences of poisoning have caused a wide public concern regarding the health risk emanating from MeHg exposure; particularly those eating large amounts of fish may experience the low-level and long-term exposure. There is growing evidence that MeHg at environmentally relevant concentrations can affect the health of biota in the ecosystem. Although extensive in vivo and in vitro studies have demonstrated that the disruption of redox homeostasis and microtube assembly is mainly responsible for mercurial toxicity leading to adverse health outcomes, it is still unclear whether we could quantitively determine the occurrence of interaction between mercurial and thiols and/or selenols groups of proteins linked directly to outcomes, especially at very low levels of exposure. Furthermore, intracellular calcium homeostasis, cytoskeleton, mitochondrial function, oxidative stress, neurotransmitter release, and DNA methylation may be the targets of mercury compounds; however, the primary targets associated with the adverse outcomes remain to be elucidated. Considering these knowledge gaps, in this article, we conducted a comprehensive review of mercurial toxicity, focusing mainly on the mechanism, and genes/proteins expression. We speculated that comprehensive analyses of transcriptomics, proteomics, and metabolomics could enhance interpretation of "omics" profiles, which may reveal specific biomarkers obviously correlated with specific pathways that mediate selective neurotoxicity.

The impact of prenatal mercury on neurobehavioral functioning longitudinally assessed from a young age to pre-adolescence in a Spanish birth cohort

The objective is to investigate the relation between cord blood mercury concentrations and child neurobehavioural functioning assessed longitudinally during childhood until pre-adolescence.

METHODS

The study involves mothers and their offspring engaged in the Spanish INMA birth cohort (n = 1147). Total mercury (THg) was determined in cord blood. Behavioural problems were assessed several times during childhood using the ADHD-DSM-IV at age 4, SDQ at ages 7 and 11, CPRS-R:S and the CBCL at ages 7, 9 and 11. Covariates were obtained through questionnaires during the whole period. Multivariate generalised negative binomial (MGNB) models or mixed-effects MGNB (for those tests with information at one or more time points, respectively) were used to investigate the relation between cord blood THg and the children's punctuations. Models were adjusted for prenatal fish intake. Effect modification by sex, prenatal and postnatal fish intake, prenatal fruit and vegetable intake, and maternal polychlorinated biphenyl concentrations (PCBs) was assessed by interaction terms.

RESULTS

The geometric mean ± standard deviation of cord blood THg was 8.22 ± 2.19 μg/L. Despite adjusting for fish consumption, our results did not show any statistically significant relationship between prenatal Hg and the children's performance on behavioural tests conducted between the ages of 4 and 11. Upon assessing the impact of various factors, we observed no statistically significant interaction.

CONCLUSION

Despite elevated prenatal THg exposure, no association was found with children's behavioural functioning assessed from early childhood to pre-adolescence. The nutrients in fish could offset the potential neurotoxic impact of Hg. Further birth cohort studies with longitudinal data are warranted.

Patterns of perinatal polyunsaturated fatty acid status and associated dietary or candidate-genetic factors

Perinatal exposure to omega-3 and omega-6 polyunsaturated fatty acids (PUFAs) can be characterized through biomarkers in maternal or cord blood or breast milk. Objectives were to describe perinatal PUFA status combining multiple biofluids and to investigate how it was influenced by dietary intake during pregnancy and maternal FADS and ELOVL gene polymorphisms. This study involved 1,901 mother-child pairs from the EDEN cohort, with PUFA levels measured in maternal and cord erythrocytes, and colostrum. Maternal dietary PUFA intake during the last trimester was derived from a food frequency questionnaire. Twelve single-nucleotide polymorphisms in FADS and ELOVL genes were genotyped from maternal DNA. Principal component analysis incorporating PUFA levels from the three biofluids identified patterns of perinatal PUFA status. Spearman's correlations explored associations between patterns and PUFA dietary intake, and linear regression models examined pattern associations with FADS or ELOVL haplotypes. Five patterns were retained: "High omega-3 LC-PUFAs, low omega-6 LC-PUFAs"; "Omega-6 LC-PUFAs"; "Colostrum LC-PUFAs"; "Omega-6 precursor (LA) and DGLA"; "Omega-6 precursor and colostrum ALA". Maternal omega-3 LC-PUFA intakes were correlated with "High omega-3 LC-PUFAs, low omega-6 LC-PUFAs" (r(DHA) = 0.33) and "Omega-6 LC-PUFAs" (r(DHA) = -0.19) patterns. Strong associations were found between FADS haplotypes and PUFA patterns except for "High omega-3 LC-PUFAs, low omega-6 LC-PUFAs". Lack of genetic association with the "High omega-3 LC-PUFAs, low omega-6 LC-PUFAs" pattern, highly correlated with maternal omega-3 LC-PUFA intake, emphasizes the importance of adequate omega-3 LC-PUFA intake during pregnancy and lactation. This study offers a more comprehensive assessment of perinatal PUFA status and its determinants.

Nutritional Quality Implications: Exploring the Impact of a Fatty Acid-Rich Diet on Central Nervous System Development

Given the comprehensive examination of the role of fatty acid-rich diets in central nervous system development in children, this study bridges significant gaps in the understanding of dietary effects on neurodevelopment. It delves into the essential functions of fatty acids in neurodevelopment, including their contributions to neuronal membrane formation, neuroinflammatory modulation, neurogenesis, and synaptic plasticity. Despite the acknowledged importance of these nutrients, this review reveals a lack of comprehensive synthesis in current research, particularly regarding the broader spectrum of fatty acids and their optimal levels throughout childhood. By consolidating the existing knowledge and highlighting critical research gaps, such as the effects of fatty acid metabolism on neurodevelopmental disorders and the need for age-specific dietary guidelines, this study sets a foundation for future studies. This underscores the potential of nutritional strategies to significantly influence neurodevelopmental trajectories, advocating an enriched academic and clinical understanding that can inform dietary recommendations and interventions aimed at optimizing neurological health from infancy.

Dietary selenium and mercury intakes from fish consumption during pregnancy: Seychelles Child Development Study Nutrition Cohort 2

Some health agencies have issued precautionary principle fish advisories to pregnant women based on the presence of methylmercury (MeHg) in fish that could possibly be harmful to the developing fetus. Fish, however, is a rich source of selenium (Se) and other nutrients essential for normal brain development. Selenium is also thought to have a key role in alleviating MeHg toxicity. We estimated the dietary Se and MeHg intakes and dietary Se:Hg molar ratios from the fish consumed in a high fish-eating pregnant cohort where no adverse associations of fish consumption and outcomes has been reported. We used dietary data collected as part of the Seychelles Child Development Study Nutrition Cohort 2 (n = 1419). In this cohort 98% of participants consumed fish, with an average intake of 106.2 g per day. Daily Se intakes from fish consumption were 61.6 µg/ d, within the range recommended during pregnancy. The mean dietary Se:Hg molar ratios was 6. These findings demonstrate that fish consumption exposes pregnant Seychellois women to Se in excess of MeHg. Based on these findings, fish consumption, especially fish with Se:Hg ratios above 1, may help pregnant women achieve optimum dietary Se intakes, which may protect against MeHg toxicity.

Prenatal Metal Exposures and Child Social Responsiveness Scale Scores in 2 Prospective Studies

Background

Prenatal exposure to metals is hypothesized to be associated with child autism. We aim to investigate the joint and individual effects of prenatal exposure to urine metals including lead (Pb), mercury (Hg), manganese (Mn), and selenium (Se) on child Social Responsiveness Scale (SRS) scores.

Methods

We used data from 2 cohorts enriched for likelihood of autism spectrum disorder (ASD): Early Autism Risk Longitudinal Investigation (EARLI) and the Markers of Autism Risk in Babies-Learning Early Signs (MARBLES) studies. Metal concentrations were measured in urine collected during pregnancy. We used Bayesian Kernel Machine Regression and linear regression models to investigate both joint and independent associations of metals with SRS Z-scores in each cohort. We adjusted for maternal age at delivery, interpregnancy interval, maternal education, child race/ethnicity, child sex, and/or study site.

Results

The final analytic sample consisted of 251 mother-child pairs. When Pb, Hg, Se, and Mn were at their 75th percentiles, there was a 0.03 increase (95% credible interval [CI]: -0.11, 0.17) in EARLI and 0.07 decrease (95% CI: -0.29, 0.15) in MARBLES in childhood SRS Z-scores, compared to when all 4 metals were at their 50th percentiles. In both cohorts, increasing concentrations of Pb were associated with increasing values of SRS Z-scores, fixing the other metals to their 50th percentiles. However, all the 95% credible intervals contained the null.

Conclusions

There were no clear monotonic associations between the overall prenatal metal mixture in pregnancy and childhood SRS Z-scores at 36 months. There were also no clear associations between individual metals within this mixture and childhood SRS Z-scores at 36 months. The overall effects of the metal mixture and the individual effects of each metal within this mixture on offspring SRS Z-scores might be heterogeneous across child sex and cohort. Further studies with larger sample sizes are warranted.

Resveratrol alleviates perinatal methylmercury-induced neurobehavioral impairments by modulating the gut microbiota composition and neurotransmitter disturbances

Methylmercury (MeHg), a potent neurotoxic substance, causes adverse health outcomes by modulating metabolites through altered gut microbiota patterns. Among the many metabolites, neurotransmitters play a particularly important role in the nervous system and behavior. Resveratrol (RSV) has been investigated as an antiaging, antioxidant, anti-inflammatory, and neuroprotective agent. The current study evaluated that RSV is protective of neurodevelopmental toxicity induced by MeHg and further explored the underlying mechanisms. Sprague-Dawley rats were treated with 1.2 mg/kg/d of MeHg, and the effects were evaluated after supplementation with RSV (20 mg/kg/d). The results indicated that MeHg had adverse effects on early neurodevelopmental indicators in the experimental group offspring as compared to control pups. Interestingly, RSV significantly improved the MeHg-induced delays in the neurobehavioral reflexes and reduced the total mercury (THg) concentration in the colons of the offspring rats. In agreement, RSV administration improved the gut microbiota diversity and structure by increasing the abundance of probiotics and upregulating the expression of tight junction proteins. It also ameliorated the MeHg-induced abnormalities in the expression profiles of neurotransmitters. Furthermore, eight key bacteria that were strongly linked with the neurotransmitters and neuroreflex parameters were identified. Taken together, these results demonstrate that RSV treatment effectively reduces the occurrence of neurodevelopmental toxicity caused by perinatal MeHg exposure by modulating the intestinal flora and neurotransmitter metabolism. These findings provide a new therapeutic approach for treating MeHg-induced neurotoxicity. The cover image is based on the Research Article Resveratrol alleviates perinatal methylmercury-induced neurobehavioral impairments by modulating the gut microbiota composition and neurotransmitter disturbances by Fang Chen et al., https://doi.org/10.1002/tox.23973.

Potential role of selenium in modifying the effect of maternal methylmercury exposure on child neurodevelopment - A review

Selenium (Se) is an essential trace element for normal neurodevelopment. It is incorporated into multiple selenoenzymes which have roles in the brain and neurological function, the synthesis of thyroid hormones, the antioxidant defense system, DNA synthesis, and reproduction. Fish is a source of both Se and neurotoxic methylmercury (MeHg). Selenium is known to ameliorate the effects of MeHg in experimental animals, but studies in children exposed to both Se and MeHg through prenatal fish consumption have been inconclusive. Research on Se's implications for pregnancy and child neurodevelopment is limited. The aims of this review are to summarize the literature on the biological roles of Se during pregnancy and the potential role in mitigating the effects of MeHg exposure from fish consumption on human health. This review has shown that Se concentrations among pregnant women globally appear insufficient, with the majority of pregnant women reporting Se concentrations below 70 µg/L during pregnancy. The role of Se in child development and its interactions with MeHg in children are inconclusive. Further investigation of the interaction between Se and MeHg in relation to child neurodevelopment in high fish-eating populations is required to fully elucidate effects.

Associations between serum taurine concentrations in mothers and neonates and the children's anthropometrics and early neurodevelopment: Results from the Seychelles Child Development Study, Nutrition Cohort 2

BACKGROUND

High concentrations of taurine are present in the developing human brain and maternal breast milk. Taurine is thought to influence fetal growth and brain development based on experimental rodent studies. As fish is an important dietary source of taurine, we investigated associations between taurine concentrations and child outcomes in a high fish consuming population.

OBJECTIVE

To examine associations between maternal and cord serum taurine concentrations and birth anthropometric measures and cognitive development in children at 20 months of age.

METHODS

Pregnant women were recruited between 2008 and 2011 as part of Nutrition Cohort 2 (NC2) of the Seychelles Child Development Study (SCDS). Maternal taurine serum concentrations were measured at 28 week's gestation and in cord serum. Child weight, length and head circumference were measured at birth and neurodevelopment was assessed using Bayley Scales of Infant Development II (BSID-II) at 20 months of age. Associations between taurine status, birth measures and neurodevelopmental outcomes were examined (n = 300) using regression models and adjusted for relevant covariates.

RESULTS

Mean (SD) maternal and cord taurine concentrations were 124.9 (39.2) µmol/L (range 28.2-253.9 µmol/L) and 187.6 (60.0) µmol/L (range 55.0-417.4 µmol/L) respectively. We found no associations between maternal taurine concentrations and child anthropometric and neurodevelopmental measures (weight β = -0.001, SE=0.001; length β = -0.006, SE=0.006; head circumference β = -0.002, SE=0.002; MDI β = -0.005, SE=0.015; PDI β = -0.004, SE=0.016; all P > 0.05), or between cord taurine concentrations and outcomes (weight β = -0.001, SE<0.000; length β = -0.001, SE=0.004; head circumference β < 0.000, SE=0.002; MDI β = 0.004, SE=0.010; PDI β = -0.015, SE=0.012; all P > 0.05).

CONCLUSION

The Seychellois population have high maternal and cord taurine concentrations owing to their high fish intake and may be considered taurine replete compared to individuals who consume a Westernised diet. This high taurine status may explain why there were no significant associations between maternal and cord taurine concentrations and outcomes after adjusting for covariates.

KEAP1 polymorphisms and neurodevelopmental outcomes in children with exposure to prenatal MeHg from the Seychelles Child Development Study Nutrition Cohort 2

BACKGROUND

Humans differ in the metabolism of the neurotoxicant methyl mercury (MeHg). This variation may be partially due to variation in genes encoding the transcription factor Nuclear factor E2-related factor 2 (NRF2) and its negative regulator Kelch-like ECH-Associated Protein 1 (KEAP1), which regulate glutathione and related transporter and antioxidant proteins that play a role in the metabolism and neurotoxicity of MeHg.

AIM

To elucidate a potential risk from genetic variation in NFE2L2 (encoding NRF2) and KEAP1 toward prenatal mercury exposure and child neurodevelopmental outcomes at 20 months and 7 years of age in a population with variable prenatal exposure to MeHg from maternal fish consumption.

MATERIAL AND METHODS

Nutrition Cohort 2 is a mother-child cohort in the Republic of Seychelles. Children were genotyped for NFE2L2 (rs2364723, rs13001694) and KEAP1 (rs8113472, rs9676881) polymorphisms (N = 1285 after removing siblings). Total mercury (Hg) was measured in cord blood as a biomarker for prenatal MeHg exposure. Child neurodevelopmental outcomes included the Bayley Scales of Infant Development II administered at 20 months of age, and outcomes across multiple neurodevelopmental domains from 14 tests administered in children and 3 instruments completed by parents when children were 7 years of age.

RESULTS

The mean cord blood MeHg concentration was 34 (95% CI 11, 75) µg/L. None of the four polymorphisms had a significant association (p < 0.05) with either cord MeHg or neurodevelopmental test results at 20 months. There were no significant associations between either NFE2L2 polymorphism and any developmental test scores. At 7 years, children carrying KEAP1 rs8113472 CA showed significantly worse performance on psychomotor function than children with the CC variant (finger tapping, dominant hand: β - 1.19, SE 0.34; finger tapping, non-dominant hand: β - 0.92, SE 0.31) and worse social communication (SCQ Total: β 0.65, SE 0.27). Children carrying rs8113472 AA, versus children with CC, showed significantly better performance on social communication (SRS Total: β - 8.88, SE 3.60). Children carrying KEAP1 rs9676881 AG, versus children with GG, showed significantly worse performance on psychomotor function (trailmaking A time: β 8.66, SE 3.37) and cognition (KBIT Matrices: β - 0.96, SE 0.36).

CONCLUSION

No associations between NFE2L2 and KEAP1 polymorphisms and MeHg concentration were identified. However, at 7 years, KEAP1 polymorphisms were associated with differences in neurodevelopmental outcomes in children from a population with high fish intake.

Postnatal methylmercury exposure and neurodevelopmental outcomes at 7 years of age in the Seychelles Child Development Study Nutrition Cohort 2

BACKGROUND

Consumption of fish yields many nutritional benefits, but also results in exposure to methylmercury (MeHg). The developing brain is known to be particularly susceptible to MeHg toxicity in high doses. However, the potential impact of low-level environmental exposure from fish consumption on children's neurodevelopment remains unclear.

METHODS

We investigated postnatal MeHg exposure at 7 years and its association with a battery of 17 neurodevelopmental outcomes in a subset of children (n = 376) from 1535 enrolled mother-child pairs in Nutrition Cohort 2 of the Seychelles Child Development Study (SCDS NC2). Each outcome was modeled in relation to postnatal MeHg exposure using linear regression, adjusting for prenatal MeHg exposure, levels of maternal polyunsaturated fatty acids (PUFA), and several other covariates known to be associated with neurodevelopmental outcomes.

RESULTS

Median postnatal MeHg exposure at 7 years was 2.5 ppm, while the median prenatal MeHg exposure was 3.5 ppm. We found no statistically significant associations between postnatal MeHg exposure and any of the 17 neurodevelopmental outcomes after adjusting for prenatal MeHg exposure and other covariates.

CONCLUSIONS

These findings are consistent with previous cross-sectional analyses of the SCDS Main Cohort. Continued follow-up of the entire NC2 cohort at later ages with repeated exposure measures is needed to further confirm these findings.

Maternal fish consumption and child neurodevelopment in Nutrition 1 Cohort: Seychelles Child Development Study

Maternal fish consumption exposes the fetus to beneficial nutrients and potentially adverse neurotoxicants. The current study investigated associations between maternal fish consumption and child neurodevelopmental outcomes. Maternal fish consumption was assessed in the Seychelles Child Development Study Nutrition Cohort 1 (n 229) using 4-day food diaries. Neurodevelopment was evaluated at 9 and 30 months, and 5 and 9 years with test batteries assessing twenty-six endpoints and covering multiple neurodevelopmental domains. Analyses used multiple linear regression with adjustment for covariates known to influence child neurodevelopment. This cohort consumed an average of 8 fish meals/week and the total fish intake during pregnancy was 106·8 (sd 61·9) g/d. Among the twenty-six endpoints evaluated in the primary analysis there was one beneficial association. Children whose mothers consumed larger quantities of fish performed marginally better on the Kaufman Brief Intelligence Test (a test of nonverbal intelligence) at age 5 years (β 0·003, 95 % CI (0, 0·005)). A secondary analysis dividing fish consumption into tertiles found no significant associations when comparing the highest and lowest consumption groups. In this cohort, where fish consumption is substantially higher than current global recommendations, maternal fish consumption during pregnancy was not beneficially or adversely associated with children's neurodevelopmental outcomes.

Hair and cord blood element levels and their relationship with air pollution, dietary intake, gestational diabetes mellitus, and infant neurodevelopment

BACKGROUND & AIMS

Exposure to a range of elements, air pollution, and specific dietary components in pregnancy has variously been associated with gestational diabetes mellitus (GDM) risk or infant neurodevelopmental problems. We measured a range of pregnancy exposures in maternal hair and/or infant cord serum and tested their relationship to GDM and infant neurodevelopment.

METHODS

A total of 843 pregnant women (GDM = 224, Non-GDM = 619) were selected from the Complex Lipids in Mothers and Babies cohort study. Forty-eight elements in hair and cord serum were quantified using inductively coupled plasma-mass spectrometry analysis. Binary logistic regression was used to estimate the associations between hair element concentrations and GDM risk, while multiple linear regression was performed to analyze the relationship between hair/cord serum elements and air pollutants, diet exposures, and Bayley Scales of infant neurodevelopment at 12 months of age.

RESULTS

After adjusting for maternal age, BMI, and primiparity, we observed that fourteen elements in maternal hair were associated with a significantly increased risk of GDM, particularly Ta (OR = 9.49, 95% CI: 6.71, 13.42), Re (OR = 5.21, 95% CI: 3.84, 7.07), and Se (OR = 5.37, 95% CI: 3.48, 8.28). In the adjusted linear regression model, three elements (Rb, Er, and Tm) in maternal hair and infant cord serum were negatively associated with Mental Development Index scores. For dietary exposures, elements were positively associated with noodles (Nb), sweetened beverages (Rb), poultry (Cs), oils and condiments (Ca), and other seafood (Gd). In addition, air pollutants PM2.5 (LUR) and PM10 were negatively associated with Ta and Re in maternal hair.

CONCLUSIONS

Our findings highlight the potential influence of maternal element exposure on GDM risk and infant neurodevelopment. We identified links between levels of these elements in both maternal hair and infant cord serum related to air pollutants and dietary factors.

Association between maternal erythrocyte PUFAs during pregnancy and neurodevelopment in children at 2 years of age: a birth cohort study

Background: Previous studies on prenatal polyunsaturated fatty acids (PUFAs) and children's neurodevelopment have shown inconsistent results, and evidence from the Asian population is scarce. Objective: To investigate the association between maternal erythrocyte PUFAs and neurodevelopment in children in the Chinese population. Methods: We included 242 mother-child pairs from the Yuexiu birth cohort. The composition of maternal erythrocyte fatty acids during pregnancy was measured by gas chromatography. Each PUFA was divided into 3 tertiles. Neurodevelopment in children was evaluated with the Ages and Stages Questionnaire at 2 years of age, including 5 domains of development: communication, gross motor, fine motor, problem solving, and personal-social skills. Results: Maternal eicosapentaenoic acid (EPA) [OR (95% CI): 0.34 (0.15, 0.74) for tertile 2, and 0.31 (0.13, 0.70) for tertile 3] was associated with a reduced risk of potential developmental delay in gross motor skills. Conversely, arachidonic acid (AA) [OR (95% CI): 2.54 (1.17, 5.70) for tertile 3] was associated with an increased risk of potential developmental delay in personal-social skills. The ratio of AA/EPA [OR (95% CI): 2.64 (1.18, 6.15) for tertile 3] was associated with an increased risk of potential developmental delay in gross motor skills. No significant association was found between other PUFAs and neurodevelopment. Conclusion: This birth cohort has first shown a beneficial association between maternal EPA and gross motor skills of children. Meanwhile, maternal AA and the ratio of AA/EPA have negative associations with neurodevelopment in children.

Epigenetics of methylmercury

PURPOSE OF REVIEW

Methylmercury (MeHg) is neurotoxic at high levels and particularly affects the developing brain. One proposed mechanism of MeHg neurotoxicity is alteration of the epigenetic programming. In this review, we summarise the experimental and epidemiological literature on MeHg-associated epigenetic changes.

RECENT FINDINGS

Experimental and epidemiological studies have identified changes in DNA methylation following in utero exposure to MeHg, and some of the changes appear to be persistent. A few studies have evaluated associations between MeHg-related changes in DNA methylation and neurodevelopmental outcomes. Experimental studies reveal changes in histone modifications after MeHg exposure, but we lack epidemiological studies supporting such changes in humans. Experimental and epidemiological studies have identified microRNA-related changes associated with MeHg; however, more research is needed to conclude if these changes lead to persistent and toxic effects.

SUMMARY

MeHg appears to interfere with epigenetic processes, potentially leading to persistent changes. However, observed associations of mercury with epigenetic changes are as of yet of unknown relevance to neurodevelopmental outcomes.

Embryonic mercury exposure in zebrafish: Alteration of metabolites and gene expression, related to visual and behavioral impairments

The widespread presence of mercury, a heavy metal found in the environment and used in numerous industries and domestic, raises concerns about its potential impact on human health. Nevertheless, the adverse effects of this environmental toxicant at low concentrations are often underestimated. There are emerging studies showing that accumulation of mercury in the eye may contribute to visual impairment and a comorbidity between autism spectrum disorders (ASD) trait and visual impairment. However, the underlying mechanism of visual impairment in humans and rodents is challenging. In response to this issue, zebrafish larvae with a cone-dominated retinal visual system were exposed to 100 nM mercury chloride (HgCl₂), according to our previous study, followed by light-dark stimulation, a social assay, and color preference to examine the functionality of the visual system in relation to ASD-like behavior. Exposure of embryos to HgCl₂ from gastrulation to hatching increased locomotor activity in the dark, reduced shoaling and exploratory behavior, and impaired color preference. Defects in microridges as the first barrier may serve as primary tools for HgCl₂ toxicity affecting vision. Depletion of polyunsaturated fatty acids (PUFAs), linoleic acid, arachidonic acid (ARA), alpha-linoleic acid, docosahexaenoic acid (DHA), stearic acid, L-phenylalanine, isoleucine, L-lysine, and N-acetylputrescine, along with the increase of gamma-aminobutyric acid (GABA), sphingosine-1-phosphate, and citrulline assayed by liquid chromatography-mass spectrometry (LC-MS) suggest that these metabolites serve as biomarkers of retinal impairments that affect vision and behavior. Although suppression of adsl, shank3a, tsc1b, and nrxn1a gene expression was observed, among these tsc1b showed more positive correlation with ASD. Collectively, these results contribute new insights into the possible mechanism of mercury toxicity give rise to visual, cognitive, and social deficits in zebrafish.

The association of auditory function measures with low-level methylmercury from oceanic fish consumption and mercury vapor from amalgam: The Seychelles Child Development Study Nutrition 1 Cohort

BACKGROUND

Some authors have reported that low-level exposure to methylmercury (MeHg) adversely impacts measures of auditory function. These reports, however, are not consistent in their findings. Consequently, we examined auditory function in a population exposed to low-level methylmercury (MeHg) exposure from fish consumption and to mercury vapor (Hg0) from dental amalgams. We analyzed their associations with the participants hearing acuity, absolute and interwave ABR latencies, and otoacoustic emissions (distortion product/DPOAE and click evoked/CEOAE).

DESIGN

We administered an audiometry test battery to 246 participants from the Seychelles Child Development Study (SCDS) Nutrition Cohort 1 (NC1) at 9 years of age. The test battery included standard pure-tone audiometry, tympanometry, Auditory Brainstem Responses (ABR) and Distortion Product and Click Evoked Otoacoustic Emissions (DPOAE and CEOAE) testing. We measured prenatal MeHg exposure in maternal hair and postnatal MeHg in children's hair. We approximated prenatal Hg0 exposure using maternal amalgam surface area and postnatal Hg0 using children amalgam surface area. Complete exposure records and audiometric data were available on 210 participants and in them we analyzed the association of MeHg and Hg0 exposures with auditory outcomes using covariate-adjusted linear regression models adjusted for sex and tympanometric pressure.

RESULTS

Hg exposures were similar for both sexes. Seven of the 210 evaluable participants examined had either a mild (5) or moderate (2) hearing loss. Four had a mild monaural hearing loss and 3 had either a mild (1) or moderate (2) bilateral hearing loss. No participant had greater than a moderate hearing loss in either ear. Hg exposures were higher in participants with either a mild or moderate hearing loss, but these differences were not statistically significant. Among the 210 with complete data, neither prenatal nor postnatal MeHg nor Hg0 exposure was statistically significantly associated with any of the ABR endpoints (p > 0.05 for all 72 associations). Neither prenatal nor postnatal Hg0 exposure was associated with any of the OAE endpoints (p > 0.05). MeHg exposure was statistically associated with 6 of the 56 DPOAE endpoints (p-values between 0.0001 and 0.023), but none of the 40 CEOAE endpoints. Two of the associations occurred with prenatal MeHg exposures and 1 of those would suggest a beneficial effect. Four of the other associations occurred with postnatal MeHg exposures with only 2 found in left ears of both males and females and the other 2 in the left and right ear of females at only one frequency.

CONCLUSION

Overall, these data do not present a clear and consistent pattern to suggest that the auditory system is negatively affected by low-level methylmercury exposure due to dietary consumption of oceanic fish or mercury vapor exposure from dental amalgams.

Marine Capture Fisheries from Western Indian Ocean: An Excellent Source of Proteins and Essential Amino Acids

The Republic of Seychelles is located in Western-Central Indian Ocean, and marine capture fisheries play a key role in the country's economic and social life in terms of food security, employment, and cultural identity. The Seychellois are among the highest per capita fish-consuming people in the world, with a high reliance on fish for protein. However, the diet is in transition, moving towards a Western-style diet lower in fish and higher in animal meat and easily available, highly processed foods. The aim of this study was to examine and evaluate the protein content and quality of a wide range of marine species exploited by the Seychelles industrial and artisanal fisheries, as well as to further to assess the contribution of these species to the daily intake recommended by the World Health Organization (WHO). A total of 230 individuals from 33 marine species, including 3 crustaceans, 1 shark, and 29 teleost fish, were collected from the Seychelles waters during 2014-2016. All analyzed species had a high content of high-quality protein, with all indispensable amino acids above the reference value pattern for adults and children. As seafood comprises almost 50% of the consumed animal protein in the Seychelles, it is of particular importance as a source of essential amino acids and associated nutrients, and as such every effort to sustain the consumption of regional seafood should be encouraged.

Prenatal mercury exposure, fish intake and child emotional behavioural regulation in the Norwegian Mother, Father and Child Cohort Study

Objective

While maternal fish consumption in pregnancy has consistently been linked to better cognitive and emotional outcomes in children, fish is also a primary source of exposure to methyl mercury (MeHg), which has been linked to poorer child cognitive outcomes. The aim of this study was to evaluate the associations between MeHg exposure, using calculated MeHg exposure from maternal diet and total mercury (Hg) concentration in maternal blood during pregnancy, and child internalising and externalising behaviours at 3 and 5 years of age.

Design and participants

The study sample comprised 51 238 mother-child pairs in the Norwegian Mother, Father and Child Cohort Study. Data on maternal blood Hg concentration in gestational week 18 were available for a sub-sample of 2936 women. Maternal MeHg exposure from diet was calculated from a validated Food Frequency Questionnaire answered in mid-pregnancy. Mothers reported children's emotional behaviour at age 3 and 5 years by questionnaires including twenty items from the Child Behaviour Checklist. Longitudinal associations were examined using generalised estimating equations, adjusted for potential confounders and stratified by maternal fish intake.

Results

Maternal blood Hg concentration (median=1.02 µg/L, 90th percentile=2.22, range=0-13.8) was not associated with emotional behaviour in children. Increasing dietary MeHg intake (median 0.15 µg/kg body weight/week, 90th percentiles=0.31, range=0-1.86) was significantly associated with lower internalising β=-0.03 (95% CI -0.05 to -0.00) and externalising child behaviours β=-0.04 (95% CI -0.07 to -0.02) in adjusted models. The inverse associations were also apparent when stratifying by low/high maternal fish intake (<400 and ≥400 g/week).

Conclusions

The results indicated that prenatal MeHg exposure, well below the weekly tolerable intake established by European Food Safety Authority (1.3 µg/kg bw), did not adversely affect child emotional regulation. Children of mothers consuming fish regularly were less likely to show signs of emotional behavioural problems.

The Human LRRK2 Modulates the Age-Dependent Effects of Developmental Methylmercury Exposure in Caenorhabditis elegans

Methylmercury (MeHg) neurotoxicity exhibits age-dependent effects with a latent and/or persistent neurotoxic effect on aged animals. Individual susceptibility to MeHg neurotoxicity is governed by both exposure duration and genetic factors that can magnify or mitigate the pathologic processes associated with this exposure. We previously showed the G2019S mutation of leucine-rich repeat kinase 2 (LRRK2) modulates the response of worms to high levels of MeHg, mitigating its effect on neuronal morphology in pre-vesicles in cephalic (CEP) dopaminergic neurons. Here we sought to better understand the long-term effects of MeHg exposure at low levels (100-fold lower than that in our previous report) and the modulatory role of the LRRK2 mutation. Worms exposed to MeHg (10 or 50 nM) at the larval stage (L1 stage) were compared at adult stages (young age: day 1 adult; middle age: day 5 adult; old age: day 10 adult) for the swimming speeds in M9 buffer, moving speeds during locomotion on an OP50-seeded plate, and the numbers of CEP dopaminergic pre-vesicles, vesicular structures originating from the dendrites of CEP for exportation of cellular content. In addition, the expression levels of Caenorhabditis elegans homologs of dopamine transporter (dat-1) and tyrosine hydroxylase (cat-2) were also analyzed at these adult stages. Our data showed that swimming speeds were reduced in wild-type worms at the day 10 adult stage at 50 nM MeHg level; yet, reduced swimming speeds were noted in the G2019S LRRK2 transgenic line upon MeHg exposures as low as 10 nM. Compared to locomotor speeds, swimming speeds appear to be more sensitive to the behavioral effects of developmental MeHg exposures, as the locomotor speeds were largely intact and indistinguishable from controls following MeHg exposures. Furthermore, we showed an age-dependent modulation of dat-1 and cat-2 expressions, which could also be modified by the LRRK2 mutation. Although MeHg exposures did not change the number of pre-vesicles, the LRRK2 mutation was associated with increased numbers of pre-vesicles in aged worms. Our data suggest that the latent behavioral effects of MeHg are sensitized by the G2019S LRRK2 mutation, and the underlying mechanism likely involves age-dependent changes in dopaminergic signaling.

Combined association of early exposure to long-chain n-3 polyunsaturated fatty acids, mercury and selenium with cognitive performance in 1-year-old infants

BACKGROUND

Previous studies on long-chain n-3 polyunsaturated fatty acids (LCn3PUFAs) and infant neurodevelopment did not consider effect modifications of mercury (Hg) and selenium (Se).

OBJECTIVES

To examine the joint association of prenatal LCn3PUFAs, Hg and Se with infant cognitive performance, and to explore whether DNA methylation may explain this potential association.

METHODS

A total of 484 newborns were enrolled from the Shanghai Birth Cohort with available data on cord blood LCn3PUFA, nail Hg and Se during 2015-2016. Cord blood LCn3PUFA concentrations were assessed by gas chromatography, and nail Hg and Se concentrations were measured using clippings collected within 6 months of birth by inductively coupled plasma mass spectrometry. Five aspects of infant neurodevelopment (communication, gross motor, fine motor, problem-solving, and personal-social skills) were assessed using the Age and Stage Questionnaire (ASQ) at ages 6 and 12 months. Multivariable-adjusted generalized estimating equations models were performed to examine the associations between cord blood LCn3PUFA concentrations and ASQ test scores, and these associations were stratified by nail Hg and Se levels. Epigenome-wide DNA methylation in cord blood was compared in a random subgroup consisting of 19 infants from the highest and 21 from the lowest decile of LCn3PUFA concentrations.

RESULTS

LCn3PUFAs were not significantly associated with any ASQ test scores. However, in the subgroup with lower Hg (<median 0.13 ppm) and higher Se (≥median 0.87 ppm) levels, infants with higher LCn3PUFA concentrations had higher ASQ scores indicating better performance in gross motor skills [quartile 4 vs. 1: mean difference = 7.78; 95% confidence interval=(3.47, 12.09); P_trend<0.01; P_interaction = 0.03]. Additionally, twenty CpG sites were differentially methylated when comparing high to low LCn3PUFA groups.

CONCLUSION

The association of prenatal LCn3PUFA concentrations with infant neurodevelopment, particularly gross motor skills, may be observed among infants with high Se and low Hg levels.

Delivery Mode and Child Development at 20 Months of Age and 7 Years of Age in the Republic of Seychelles

OBJECTIVE

To determine if cesarean delivery is adversely associated with child neurodevelopment as measured at 20 months and 7 years.

METHODS

In a prospective cohort study (n = 1328) in the Republic of Seychelles, we examined the association between mode of delivery and 22 measures of child neurodevelopment spanning multiple domains: cognition, executive and psychomotor function, language development, behavior, scholastic achievement, and social communication. Using multivariable linear regression, we evaluated the relationship between delivery mode (Cesarean/vaginal delivery) and each developmental outcome, while controlling for relevant covariates including child sex and age, maternal age, maternal IQ, whether both parents lived with the child, and Hollingshead socioeconomic status.

RESULTS

At 20 months, children born via cesarean delivery had slightly higher scores (β = 0.11, 95% confidence interval: 0.00, 0.21) on the Infant Behavior Questionnaire-Revised Positive Affectivity/Surgency subtest, a measure of infant temperament, as compared to vaginal delivery. Delivery mode was not associated with any of the 7-year developmental outcomes.

CONCLUSIONS FOR PRACTICE

Our study does not support the notion that cesarean delivery is associated with child neurodevelopmental outcomes.

Methylmercury-Induced Metabolic Alterations in Caenorhabditis elegans Are Diet-Dependent

Methylmercury (MeHg) is a well-known neurotoxicant; however, its role in metabolic diseases has been gaining wider attention. Chronic exposure to MeHg in human populations shows an association with diabetes mellitus and metabolic syndrome (MS). As the incidences of both obesity and MS are on the rise globally, it is important to understand the potential role of MeHg in the development of the disease. There is a dearth of information on dietary interactions between MeHg and lipids, which play an important role in developing MS. We have previously shown that MeHg increases food seeking behaviors, lipid levels, fat storage, and pro-adipogenic gene expression in C. elegans fed the standard OP50 Escherichia coli diet. However, we hypothesized that these metabolic changes could be prevented if the worms were fed a bacterial diet lower in lipid content. We tested whether C. elegans developed metabolic alterations in response to MeHg if they were fed two alternative E. coli strains (HT115 and HB101) that are known absorb significantly less lipids from their media. Additionally, to explore the effect of a high-lipid and high-cholesterol diet on MeHg-induced metabolic dysfunction, we supplemented the OP50 strain with twice the standard concentration of cholesterol in the nematode growth media. Wild-type worms fed either the HB101 or HT115 diet were more resistant to MeHg than the worms fed the OP50 diet, showing a significant right-hand shift in the dose–response survival curve. Worms fed the OP50 diet supplemented with cholesterol were more sensitive to MeHg, showing a significant left-hand shift in the dose–response survival curve. Changes in sensitivity to MeHg by differential diet were not due to altered MeHg intake in the worms as measured by inductively coupled mass spectrometry. Worms fed the low-fat diets showed protection from MeHg-induced metabolic changes, including decreased food consumption, lower triglyceride content, and lower fat storage than the worms fed either of the higher-fat diets. Oxidative stress is a common characteristic of both MeHg exposure and high-fat diets. Worms fed either OP50 or OP50 supplemented with cholesterol and treated with MeHg had significantly higher levels of reactive oxygen species, carbonylated proteins, and loss of glutathione than the worms fed the HT115 or HB101 low-lipid diets. Taken together, our data suggest a synergistic effect of MeHg and dietary lipid levels on MeHg toxicity and fat metabolism in C. elegans, which may affect the ability of MeHg to cause metabolic dysfunction.

Prenatal exposure to metals and autism spectrum disorder: Current status and future directions

Autism spectrum disorder (ASD) is a heterogeneous neurodevelopmental disorder with genetic and environmental contributors to etiology. Many metals have the potential to be neurotoxic and their exposures are widespread. The field of metals exposure and ASD research is emerging, and in this review article we assess the current state of the literature, with emphasis on the previous two years. Epidemiology studies are discussed with respect to exposure timing, exposure matrix, and outcome assessment. Toxicology studies are described for exposure dosing and timing, as well as behavioral and molecular outcomes. Further epidemiological and toxicological investigations can identify the timing and importance of metals as ASD risk factors and uncover biological mechanisms for risk mitigation and therapeutic strategies.