Subchronic mercury treatment of rats in different phases of ontogenesis: functional effects on the central and peripheral nervous system

N-acetyl cysteine and selenium protects mercuric chloride-induced oxidative stress and antioxidant defense system in liver and kidney of rats: a histopathological approach

Mercury exposure is second-most common cause of metal poisoning which is quite stable and biotransformed to highly toxic metabolites thus eliciting biochemical alterations and oxidative stress. The aim of present study describes the protective effect of selenium either alone or in combination with N-acetyl cysteine (NAC) against acute mercuric chloride poisoning. The experiment was carried out in male albino Sprague Dawley rats (n=30) which was divided into five groups. Group 1 served as control. Groups 2-5 were administered mercuric chloride (HgCl2: 12mol/kg, i.p.) once only, group 2 served as experimental control. Animals of groups 3, 4 and 5 were received N-acetyl cysteine (NAC: 0.6mg/kg, i.p.) and selenium (Se: 0.5mg/kg, p.o.) and NAC with Se in combination. Acute HgCl2 toxicity caused significant rise in serum alanine aminotransferase, aspartate aminotransferase, alkaline phosphatase, lactate dehydrogenase, albumin, bilirubin, γ-glutamyl transpeptidase, cholesterol, triglycerides, protein, urea, creatinine, uric acid and blood urea nitrogen content. Animals also showed significantly higher mercury content in liver and kidney, significant rise in lipid peroxidation level with concomitant decrease in reduced glutathione content and the antioxidant enzyme activities of superoxide dismutase and catalase after HgCl2 exposure. Results of the present investigation clearly showed that combination therapy with NAC+Se provide maximum protection against mercury toxicity than monotherapy (alone treated groups) by preventing oxidative degradation of biological membrane from metal mediated free radical attacks.

Chronic inorganic mercury exposure induces sex-specific changes in central TNFα expression: importance in autism?

Mercury is neurotoxic and increasing evidence suggests that environmental exposure to mercury may contribute to neuropathologies including Alzheimer's disease and autism spectrum disorders. Mercury is known to disrupt immunocompetence in the periphery, however, little is known about the effects of mercury on neuroimmune signaling. Mercury-induced effects on central immune function are potentially very important given that mercury exposure and neuroinflammation both are implicated in certain neuropathologies (i.e., autism). Furthermore, mounting evidence points to the involvement of glial activation in autism. Therefore, we utilized an in vivo model to assess the effects of mercury exposure on neuroimmune signaling. In prairie voles, 10 week mercury exposure (60ppm HgCl(2) in drinking water) resulted in a male-specific increase in TNFα protein expression in the cerebellum and hippocampus. These findings are consistent with our previously reported male-specific mercury-induced deficits in social behavior and further support a role for heavy metals exposure in neuropathologies such as autism. Subsequent studies should further evaluate the mechanism of action and biological consequences of heavy metals exposure. Additionally, these observations highlight the potential of neuroimmune markers in male voles as biomarkers of environmental mercury toxicity.

Prenatal exposure to methylmercury and PCBs affects distinct stages of information processing: an event-related potential study with Inuit children

Methylmercury (MeHg) and polychlorinated biphenyls (PCBs) are seafood contaminants known for their adverse effects on neurodevelopment. This study examines the relation of developmental exposure to these contaminants to information processing assessed with event-related potentials (ERPs) in school-aged Inuit children from Nunavik (Arctic Québec). In a prospective longitudinal study on child development, exposure to contaminants was measured at birth and 11 years of age. An auditory oddball protocol was administered at 11 years to measure ERP components N1 and P3b. Multiple regression analyses were performed to examine the associations of levels of the contaminants to auditory oddball performance (mean reaction time, omission errors and false alarms) and ERP parameters (latency and amplitude) after control for potential confounding variables. A total of 118 children provided useable ERP data. Prenatal MeHg exposure was associated with slower reaction times and fewer false alarms during the oddball task. Analyses of the ERP parameters revealed that prenatal MeHg exposure was related to greater amplitude and delayed latency of the N1 wave in the target condition but not to the P3b component. MeHg effects on the N1 were stronger after control for seafood nutrients. Prenatal PCB exposure was not related to any endpoint for sample as a whole but was associated with a decrease in P3b amplitude in the subgroup of children who had been breast-fed for less than 3 months. Body burdens of MeHg and PCBs at 11 years were not related to any of the behavioural or ERP measures. These data suggest that prenatal MeHg exposure alters attentional mechanisms modulating early processing of sensory information. By contrast, prenatal PCB exposure appears to affect information processing at later stages, when the information is being consciously evaluated. These effects seem to be mitigated in children who are breast-fed for a more extended period.

The interaction of selenium and mercury in the accumulations and oxidative stress of rat tissues

This study evaluates the interaction of selenium (Se) and mercury (Hg) in the accumulations and oxidative stress of rat tissues. Rats were divided into five groups including one control (n=9) and four treated groups including M-Hg (n=9), L-Hg+Se (n=11), M-Hg+Se (n=10), and H-Hg+Se (n=10) group. Treated groups of rats were instilled with different amounts of mercuric chloride (HgCl(2)) and dl-selenomethionine (SeMet) by gavage since pregnancy of their mothers. Atomic fluorescence spectroscopy (AFS) was applied for mercury and selenium quantification. Glutathione (GSH), malondialdehyde (MDA), and total superoxide dismutase (SOD) activity of tissues were detected using biochemical methods. Results showed that Hg was deposited mainly in kidney. Se could decrease Hg content in kidney but increase it in blood and liver. Hg decreased GSH and SOD and increased MDA levels in most detected tissues, while Se took on a counteraction effect in same tissues. This study suggests that interactions of Se and Hg affect their accumulation and Se may antagonize Hg-induced inhibition on organic activities.

Subchronic heavy metal and alcohol treatment in rats: changes in the somatosensory evoked cortical activity

Young adult male Wistar rats were treated, by gavage, with 80 or 320 mg/kg Pb2+ (lead acetate), 0.4 or 1.6 mg/kg Hg2+ (mercuric chloride) or both by combining the lower doses. For combination with alcohol, ethanol was added to the rats' drinking water in 5 v/v %. After 12 weeks of treatment, electrophysiological recording was made from the somatosensory cortex in urethane anaesthesia. Evoked potentials obtained by stimulation of the whiskers were recorded. Both metals, and alcohol alone, increased significantly the latency of the evoked response. Alcohol seemed to abolish the effect of Pb, but not of Hg. Fatigue, calculated form the response amplitude, was increased by Pb and Hg treatment and this effect of Hg was reduced by ethanol. Evoked activity and its dynamic characteristics were sensitive to the complex neurotoxic effect induced in the rats and can provide a basis for developing functional markers.