Decreased plasma thiol antioxidant capacity precedes neurological signs in a rat methylmercury intoxication model

The main target organ for MeHg is the nervous system, and its neurological dysfunction remains irreversible. Therefore, predictive biomarkers associated with individual susceptibility to MeHg and future clinical severity are needed to protect against the progression of MeHg toxicity. In this study, we demonstrated that plasma thiol antioxidant capacity (-SHp) is a useful predictive biomarker associated with future clinical severity using MeHg-intoxicated rats administered 1 mg/kg/day for 4 weeks. Blood samples were collected from the subclavian vein of each rat once a week to examine total blood mercury concentrations and the levels of plasma oxidative stress markers. Time course analyses of the correlation between these weekly blood examination values and hind limb crossing signs score after 4 weeks of MeHg exposure were performed, and plasma -SHp levels after 2 weeks of MeHg exposure showed strong correlations with future hind limb crossing sign scores. Neuropathological changes also developed in parallel with hind limb crossing sign scores. Quantitative analysis of vacuolar areas in the spinal cord showed a strong correlation with hind limb crossing sign scores. In conclusion, evaluation of plasma -SHp levels allowed us to detect individuals at risk for health damage and could protect the sensitive population against MeHg toxicity.

Neurotransmitter amines and antioxidant agents in neuronal protection against methylmercury-induced cytotoxicity in primary cultures of mice cortical neurons

Methylmercury (MeHg) is an environmental toxicant with detrimental effects on the developing brain and adult nervous system. The main mechanisms identified include oxidative stress, changes in intracellular calcium, mitochondrial changes, inhibition of glutamate uptake, of protein synthesis and disruption of microtubules. However, little is known about mechanisms of protection against MeHg neurotoxicity. We found that resveratrol (10 μM) and ascorbic acid (200 μM) protected MeHg-induced cell death in primary cultures of cortical neurons. In this work, we aimed at finding additional targets that may be related to MeHg mode of action in cell toxicity with special emphasis in cell protection. We wonder whether neurotransmitters may affect the MeHg effects on neuronal death. Our findings show that neurons exposed to low MeHg concentrations exhibit less mortality if co-exposed to 10 μM dopamine (DA). However, DA metabolites, HVA (homovanillic acid) and DOPAC (3,4-dihydroxyphenylacetic acid) are not responsible for such protection. Furthermore, both DA D1 and D2 receptors agonists showed a protective effect against MeHg toxicity. It is striking though that DA receptor antagonists SKF83566 (10 μM) and haloperidol (10 μM) did not inhibit DA protection against MeHg. In addition, the protective effect of 10 μM DA against MeHg-induced toxicity was not affected by additional organochlorine pollutants exposure. Our results also demonstrate that cells exposed to MeHg in presence of 100 μM acetylcholine (ACh), show an increase in cell mortality at the "threshold value" of 100 nM MeHg. Finally, norepinephrine (10 μM) and serotonin (20 μM) also had an effect on cell protection. Altogether, we propose to further investigate the additional mechanisms that may be playing an important role in MeHg-induced cytotoxicity.