Mercurial uncertainties in environmental health

Multifactorial Origin of Neurodevelopmental Disorders: Approaches to Understanding Complex Etiologies

A significant body of evidence supports the multifactorial etiology of neurodevelopmental disorders (NDDs) affecting children. The present review focuses on early exposure to environmental chemicals as a risk factor for neurodevelopment, and presents the major lines of evidence derived from epidemiological studies, underlying key uncertainties and research needs in this field. We introduce the exposome concept that, encompassing the totality of human environmental exposures to multiple risk factors, aims at explaining individual vulnerability and resilience to early chemical exposure. In this framework, we synthetically review the role of variable gene backgrounds, the involvement of epigenetic mechanisms as well as the function played by potential effect modifiers such as socioeconomic status. We describe laboratory rodent studies where the neurodevelopmental effects of environmental chemicals are assessed in the presence of either a “vulnerable” gene background or adverse pregnancy conditions (i.e., maternal stress). Finally, we discuss the need for more descriptive and “lifelike” experimental models of NDDs, to identify candidate biomarkers and pinpoint susceptible groups or life stages to be translated to large prospective studies within the exposome framework.

Tremor secondary to neurotoxic exposure: mercury, lead, solvents, pesticides

Lead, mercury, solvents, and pesticide exposures are common in certain occupations and may cause nervous system dysfunction. Tremors may be the herald manifestation among a constellation of acute toxicity signs and symptoms. However, since tremors may also be the only sign on clinical presentation and since tremors also occur in other diseases, relating tremors to a specific occupational exposure can be challenging. Diagnosis of tremor etiology must be based on other findings on physical exam, laboratory results, and/or imaging. Discerning whether the tremor resulted from the occupational environment versus other etiologies requires knowledge of potential exposure sources, additional detail in history taking, and support of other health and industrial professionals. Reduction or removal from the exposure source remains the key first step in treating patients suffering from tremor that had resulted from occupational exposure toxicity.

Cardiac autonomic activity and blood pressure among Nunavik Inuit adults exposed to environmental mercury: a cross-sectional study

BACKGROUND

Mercury is a contaminant that reaches high levels in Nunavik (North of Quebec). It is transformed into methylmercury (MeHg) and accumulated in marine mammals and predator fish, an important part of the traditional Inuit diet. MeHg has been suggested to affect BP in adults and children while the influence on HRV has only been studied in children. We aimed to assess the impact of MeHg levels on HRV and BP in Inuit adults from Nunavik.

METHODS

In the fall of 2004, the <<Qanuippitaa?>> Health Survey was conducted in Nunavik (Quebec, Canada) and information on HRV was collected among 280 adults aged 40 years and older. Indicators of the time and frequency domains of HRV were derived from a 2-hour Holter recording. BP was measured according to the Canadian Coalition for High Blood Pressure technique. Pulse pressure (PP) was the difference between systolic (SBP) and diastolic blood pressure (DBP). Blood mercury concentration was used as exposure biomarker. Statistical analysis was conducted through linear regression and multivariable linear regression was used to control for confounders.

RESULTS

Mercury was negatively correlated with low frequency (LF) (r = -0.18; p = 0.02), the standard deviation of RR intervals (SDNN) (r = -0.14; p = 0.047) and the coefficient of variation of RR intervals (CVRR) (r = -0.18; p = 0.011) while correlations with other HRV parameters did not reach statistical significance. After adjusting for confounders, the association with LF (beta = -0.006; p = 0.93) became non significant. However, the association with SDANN became statistically significant (beta = -0.086; p = 0.026) and CVRR tended to decrease with blood mercury concentrations (beta = -0.057; p = 0.056). Mercury was positively correlated with SBP (r = 0.25; p < 0.0001) and PP (r = 0.33; p < 0.0001). After adjusting for confounders, these associations remained statistically significant (beta SBP = 4.77; p = 0.01 and beta PP = 3.40; p = 0.0036). Moreover, most of the HRV parameters correlated well with BP although SBP the best before adjustment for mercury exposure.

CONCLUSION

The results of this study suggest a deleterious impact of mercury on BP and HRV in adults. SBP and PP increased with blood mercury concentrations while SDANN decreased with blood mercury concentrations.

Effects of 2,3-dimercapto-1-propanesulfonic acid (DMPS) on methylmercury-induced locomotor deficits and cerebellar toxicity in mice

Chelating therapy has been reported as a useful approach for counteracting mercurial toxicity. Moreover, 2,3-dimercapto-1-propanesulfonic acid (DMPS), a tissue-permeable metal chelator, was found to increase urinary mercury excretion and decrease mercury content in rat brain after methylmercury (MeHg) exposure. We evaluated the capability of DMPS to reduce MeHg-induced motor impairment and cerebellar toxicity in adult mice. Animals were exposed to MeHg (40 mg/L in drinking water, ad libitum) during 17 days. In the last 3 days of exposure (days 15-17), animals received DMPS injections (150 mg/kg, i.p.; once a day) in order to reverse MeHg-induced neurotoxicity. Twenty-four hours after the last injection (day 18), behavioral tests related to the motor function (open field and rotarod tasks) and biochemical analyses on oxidative stress-related parameters (cerebellar glutathione, protein thiol and malondyaldehyde levels, glutathione peroxidase and glutathione reductase activities) were carried out. Histological analyses for quantifying cellular damage and mercury deposition in the cerebellum were also performed. MeHg exposure induced a significant motor deficit, observed as decreased locomotor activity in the open field and decreased falling latency in the rotarod apparatus. DMPS treatment displayed an ameliorative effect toward such behavioral parameters. Cerebellar glutathione and protein thiol levels were not changed by MeHg or DMPS treatment. Conversely, the levels of cerebellar thiobarbituric acid reactive substances (TBARS), a marker for lipid peroxidation, were increased in MeHg-exposed mice and DMPS administration minimized such phenomenon. Cerebellar glutathione peroxidase activity was decreased in the MeHg-exposed animals, but DMPS treatment did not prevent such event. Histological analyses showed a reduced number of cerebellar Purkinje cells in MeHg-treated mice and this phenomenon was completely reversed by DMPS treatment. A marked mercury deposition in the cerebellar cortex was observed in MeHg-exposed animals (granular layer>Purkinje cells>molecular layer) and DMPS treatment displayed a significant ameliorative effect toward these phenomena. These findings indicate that DMPS displays beneficial effects on reversing MeHg-induced motor deficits and cerebellar damage in mice. Histological analyses indicate that these phenomena are related to its capability of removing mercury from cerebellar cortex.

Acute exposure to methylmercury opens the mitochondrial permeability transition pore in rat cerebellar granule cells

Cerebellar granule cells are preferentially targeted during methylmercury (MeHg) poisoning. Following acute MeHg exposure, granule cells in culture undergo an increase in intracellular Ca2+ concentration ([Ca2+]i) that apparently contributes to cell death. This effect consists of several temporally and kinetically distinct phases. The initial elevation arises from release of Ca2+(i) stores; the second phase results from entry of Ca2+(e). In these experiments, we tested the hypothesis that release of mitochondrial Ca2+ through the mitochondrial permeability transition pore (MTP) contributes to the initial release of Ca2+(i). Neonatal rat cerebellar granule cells in culture and single cell microfluorimetry were used to examine MeHg-induced changes in [Ca2+]i and mitochondrial membrane potential (Psi(m)). Pretreatment with the MTP inhibitor cyclosporin A (CsA, 5 microM) delayed the initial phase of increased [Ca2+]i induced by 0.2 and 0.5 microM MeHg, but not 1.0 microM MeHg. CsA (5 microM) also delayed the irreversible loss of Psi(m) induced by 0.5 microM MeHg. Ca2+(e) was not required for either effect, because the effect of CsA on the first phase increase in [Ca2+]i and loss of Psi(m) was not altered in nominally Ca2+-free buffer. Increasing concentrations of MeHg (0.2-2.0 microM) caused increasing incidence of cell death at 24 h postexposure. Treatment with CsA provided protection against cytotoxicity at lower MeHg concentrations (0.2-0.5 microM), but not at higher MeHg concentrations (1.0-2.0 microM). Thus, the MTP appears to play a significant role in the cellular effects following acute exposure of cerebellar granule neurons to MeHg.