Neurobehavioral effects of postnatal exposure to low-level mercury vapor and/or methylmercury in mice

Neurobehavioral effects of the exposure to mercury vapor and methylmercury during postnatal period on mice

In this study, we investigated the neurobehavioral alterations and modifications of gene expression in the brains of female mice exposed to low-level mercury vapor and/or methylmercury during postnatal development. The mice were exposed to low-level mercury vapor at a mean concentration of 0.094 mg/m3 and supplied with tap water containing 5 ppm methylmercury from postnatal day 11 to 12 weeks of age. Behavioral analyses were performed at 17 weeks of age. Total locomotor activity in the open field test and the retention trial performance in the passive avoidance test were significantly reduced in the combined exposure group compared with those in the control group. The differences in locomotor activity and performance in the retention trial at 17 weeks were no longer detected at 45 weeks. These results suggest that the effect of aging on the behavioral abnormalities resulting from postnatal exposure to mercury complexes are not significant. In the microarray analysis of brains in the combined exposure group, the gene expression levels of Ano2 and Sgk1 were decreased. Real-time RT-PCR analysis confirmed these changes caused by combined mercury exposure, showing significant downregulation of Ano2 and Sgk1 in the cerebrum. These genes play key roles in the brain as a calcium-activated chloride channel and as a kinase that responds to cellular stress, respectively. Our findings provide insight into the neurobehavioral changes caused by combined mercury exposure.

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.

Association of blood mercury exposure with depressive symptoms in the Chinese oldest old

Depressive symptoms have a significant impact on the quality-of-life among the oldest old (aged ≥ 80 years) in the population. Current research on the association of blood mercury with depressive symptoms has mainly targeted the general population. However, it is unclear whether this association is present in the oldest old. We used data from the Healthy Aging and Biomarker Cohort Study carried out in 2017-2018, with 1154 participants aged ≥ 80 years eligible for analysis. Inductively coupled plasma mass spectrometry (ICP-MS) was employed to detect blood mercury (Hg) levels, while the CES-D10 depression scale was used to assess depressive symptoms. The association between blood mercury levels and depressive symptoms was investigated using log-binomial and Poisson regression models. We also used restricted cubic splines (RCS) to assess the linear or nonlinear association of blood mercury with depressive symptoms scores. The 1154 participants ranged in age from 80 to 120 years, while the geometric mean of blood mercury concentration was 1.01 μg/L. After adjustment for covariates, log-binomial and Poisson regression analyses revealed a statistically significant, positive association of blood mercury with depressive symptoms. In comparison to the first tertile, the adjusted relative risks of blood mercury and the presence of depressive symptoms in the second and third tertiles were 1.55 (1.20-1.99) and 1.45 (1.11-1.90), respectively. The RCS model showed a linear association between blood mercury level and depressive symptoms scores. In conclusion, among the oldest old, we demonstrated that blood mercury levels were positively associated with depressive symptoms. Further surveys, especially cohort studies and clinical trials are needed to confirm these results.

Mercury Exposure and Its Health Effects in Workers in the Artisanal and Small-Scale Gold Mining (ASGM) Sector—A Systematic Review

Gold is one of the most valuable materials but is frequently extracted under circumstances that are hazardous to artisanal and small-scale gold miners’ health. A common gold extraction method uses liquid mercury, leading to a high exposure in workers. Therefore, a systematic review according to the PRISMA criteria was conducted in order to examine the health effects of occupational mercury exposure. Researching the databases PubMed^®, EMBASE^® and Web of Science^TM yielded in a total of 10,589 results, which were screened by two independent reviewers. We included 19 studies in this review. According to the quantitative assessment, occupational mercury exposure may cause a great variety of signs and symptoms, in particular in the field of neuro-psychological disorders, such as ataxia, tremor or memory problems. However, many reported symptoms were largely unspecific, such as hair loss or pain. Most of the included studies had a low methodological quality with an overall high risk of bias rating. The results demonstrate that occupational mercury exposure seriously affects miners’ health and well-being.

Developmental exposure to mercury chloride impairs social behavior in male offspring dependent on genetic background and maternal autoimmune environment

To date, the connection between inorganic mercury (Hg) and social behavior remains incompletely understood. The aim of this study was to investigate the influence of maternal autoimmunity by inorganic Hg (Hg²⁺) exposure on social behavior of offspring. Wild-type (WT) and immunoglobulin deficient (Ig^-/-) B10.S dams fertilized by male WT B10.S or SJL mice were treated with 50 μM Hg chloride (HgCl₂). Non-pregnant female WT B10.S mice were used to investigate factors regulating HgCl₂-induced autoimmunity to brain. HgCl₂ selectively impaired social behavior in male offspring, but not female offspring from WT B10.S dams × male SJL, in that only male offspring displayed reduced time distribution with the stranger mouse, decreased sniffing to the stranger mouse and increased self-grooming. HgCl₂ did not disrupt social behavior of male or female offspring from WT B10.S dams × male WT B10.S or Ig^-/- B10.S dams × male SJL. The offspring from WT and Ig^-/- B10.S dams × male SJL had equivalent autoimmunity to brain antigens during HgCl₂ exposure, indicating that maternal, but not offspring-derived anti-brain antibodies (Ab) impaired social behavior of the offspring. Non-pregnant WT B10.S mice treated with HgCl₂ had increased anti-brain Ab dependent on increase in CD4 T cell activation and IFNγ signaling to macrophages. IFNγ interaction with macrophages drove B cells and plasma cells to produce IgG. Therefore, HgCl₂ selectively impaired social behavior in males with certain genetic background via maternally derived anti-brain Ab production, thus providing a novel insight into our current understanding of Hg toxicity.

Effect of Metallothionein-III on Mercury-Induced Chemokine Gene Expression

Mercury compounds are known to cause central nervous system disorders; however the detailed molecular mechanisms of their actions remain unclear. Methylmercury increases the expression of several chemokine genes, specifically in the brain, while metallothionein-III (MT-III) has a protective role against various brain diseases. In this study, we investigated the involvement of MT-III in chemokine gene expression changes in response to methylmercury and mercury vapor in the cerebrum and cerebellum of wild-type mice and MT-III null mice. No difference in mercury concentration was observed between the wild-type mice and MT-III null mice in any brain tissue examined. The expression of Ccl3 in the cerebrum and of Cxcl10 in the cerebellum was increased by methylmercury in the MT-III null but not the wild-type mice. The expression of Ccl7 in the cerebellum was increased by mercury vapor in the MT-III null mice but not the wild-type mice. However, the expression of Ccl12 and Cxcl12 was increased in the cerebrum by methylmercury only in the wild-type mice and the expression of Ccl3 in the cerebellum was increased by mercury vapor only in the wild-type mice. These results indicate that MT-III does not affect mercury accumulation in the brain, but that it affects the expression of some chemokine genes in response to mercury compounds.