Probucol Increases Glutathione Peroxidase-1 Activity and Displays Long-Lasting Protection against Methylmercury Toxicity in Cerebellar Granule Cells

Abstract

Methylmercury (MeHg) is an environmental neurotoxicant whose molecular mechanisms underlying toxicity remain elusive. Here, we investigated molecular events involved in MeHg-induced neurotoxicity in cultured cerebellar granule cells (CGCs) as well as potential protective strategies for such toxicity. Glutathione peroxidase, isozyme 1 (GPx-1) activity was significantly (p = 0.0017) decreased at 24 h before MeHg-induced neuronal death (day in vitro 4). This event was related to enhanced susceptibilities to hydrogen peroxide or tert-butyl peroxide and increased lipid peroxidation. However, intracellular calcium levels, glutamate uptake, and glutathione levels, as well as glutathione reductase and catalase activities, were not changed by MeHg exposure at this time point. Probucol (PB), a lipid-lowering drug, displayed a long-lasting protective effect against MeHg-induced neurotoxicity. The beneficial effects of PB were correlated with increased GPx-1 activity and decreased lipid peroxidation. The protection afforded by PB was significantly higher when compared to the antioxidants, ascorbic acid and trolox. In vitro studies with the purified GPx-1 proved that MeHg inhibits and PB activates the enzyme activity. Overexpression of GPx-1 prevented MeHg-induced neuronal death. These data indicate that (1) GPx-1 is an important molecular target involved in MeHg-induced neurotoxicity and (2) PB, which increases GPx-1 activity in CGCs, induces enduring protection against such toxicity. The results bring out new insights on the potential therapeutic strategies for poisonings to MeHg and other pathological conditions related to increased production and/or decreased detoxification of peroxides.

<i>S</i>-Mercuration of cellular proteins by methylmercury and its toxicological implications

“…There have also been many reports of MeHg causing decreased GPx activity in vitro Hirota et al, 1980;Kromidas et al, 1990). Farina et al (2009) reported that the overexpression of GPx1, which is the most abundant version of GPx, prevented MeHg-induced neuronal death, indicating that GPx1 is an important molecular target that is involved in MeHg-induced neurotoxicity. They didn't determine how GPx1 was inhibited, but suggested that selenol groups (which have lower pKa values than do thiol groups) in the enzyme were involved.…”

Influence of prenatal exposure to environmental pollutants on human cord blood levels of glutamate

“…Specific attention should be paid to its organometallic compound, methylmercury, because: i) it has recognized properties as a human neurodevelopmental toxicant (Grandjean and Landrigan, 2006); ii) poisoning incidents with methylmercury have demonstrated the potential of this pollutant as neurotoxicant and its serious health consequences (Castoldi et al, 2008;Ekino et al, 2007;Grandjean et al, 2010;Nakagawa et al, 2002); iii) millions of people are nowadays chronically exposed to this contaminant and there is epidemiological (Marsh et al, 1987; Pinheiro et al, 2007;Yokoo et al, 2003) and experimental (Castoldi et al, 2008;Farina et al, 2009;Vendrell et al, 2007Vendrell et al, , 2010 evidence of the toxic effects of chronic exposure to this metal especially for the nervous system; and iv) previous results from the INMA birth cohort of Valencia (Spain) showed elevated levels of this pollutant in umbilical cord blood, where 70% of newborns had mercury levels above US EPA recommended level, i.e. 5.8 μg/L of MeHg (Ramon et al, 2008).…”

Strategies and tools for preventing neurotoxicity: To test, to predict and how to do it

“…At the same time, probucol increased GPx activity. Likewise, overexpression of GPx-1 in cultured cerebellar granule cells resulted in neuroprotection against methylmercury-induced cell death (Farina et al, 2009). Figure 2 summarizes some of these findings.…”

“…Figure 2 summarizes some of these findings. On the other hand, no effects were found in reduced and oxidized glutathione levels, glutathione reductase and catalase activity, nor on neuronal glutamate uptake or intracellular calcium, after using the same protocol for methylmercury exposure (Farina et al, 2009). Altogether, these results suggest that oxidative stress driven by inhibition of glutathione peroxidase may be one of the first hallmarks of methylmercury-induced neurotoxicity in the development of cerebellar granule cells, a finding also observed in mice exposed to methylmercury (Franco et al, 2009).…”