A scanning electron-microscopic study of the effects of methylmercury on the neuronal cytoskeleton

Effects of glyphosate, mancozeb and their combinations on mouse neuroblastoma cells

Pesticides-related toxicities have long been studied. Data regarding the effects of combined exposure to environmentally relevant pesticides however remain lacking. The herbicide glyphosate and the fungicide mancozeb are extensively used in agriculture. Residues of both compounds are frequently found in food and water and therefore, environmental exposure to both pesticides is a possibility. Neurotoxicity of glyphosate, mancozeb and their combinations were investigated using mouse neuroblastoma cells. Cytotoxicity observed with the glyphosate and mancozeb combinations was higher than that observed when glyphosate was tested alone. Combinations of glyphosate followed by mancozeb increased copper, manganese, and zinc levels. Mixture of mancozeb + glyphosate increased manganese and zinc levels. Combination of mancozeb followed by glyphosate increased copper and zinc levels. Glutathione ratio was decreased as a result of combinations of glyphosate and mancozeb. The decrease in glutathione ratio was greater in the combination groups than in glyphosate alone.

Selenium Compounds Prevent the Effects of Methylmercury on the in Vitro Phosphorylation of Cytoskeletal Proteins in Cerebral Cortex of Young Rats

In this study we investigated the protective ability of the selenium compounds ebselen and diphenyldiselenide against the effect of methylmercury on the in vitro incorporation of 32P into intermediate filament (IF) proteins from the cerebral cortex of 17-day-old rats. We observed that methylmercury in the concentrations of 1 and 5 microM was able to inhibit the phosphorylating system associated with IF proteins without altering the immunocontent of these proteins. Concerning the selenium compounds, diselenide (1, 15, and 50 microM) did not induce alteration of the in vitro phosphorylation of IF proteins. Conversely, 15 microM diselenide was effective in preventing the toxic effects induced by methylmercury. Otherwise, ebselen induced an altered in vitro phosphorylation of the cytoskeletal proteins in a dose-dependent manner. Ebselen at intermediate concentrations (15 and 30 microM) increased the in vitro phosphorylation. However, at low (5 microM) or high (50 and 100 microM) concentrations it was ineffective in altering the cytoskeletal-associated phosphorylating system. Furthermore, 5 microM ebselen presented a protective effect against the action of methylmercury on the phosphorylating system. In conclusion, our results indicate that the selenium compounds ebselen and diselenide present protective actions toward the alterations of the phosphorylating system associated with the IF proteins induced by methylmercury in slices of the cerebral cortex of rats.

Differential effects of methylmercury on the phosphorylation of protein species in the brain of acutely intoxicated rats

The in vivo effect of methylmercury (MeHg) on the phosphorylation in vitro of the brain cytosol fraction was examined in acutely poisoned rats (10 mg/kg/day, for 7 days). The total phosphorylation activity, determined in the presence or absence of protein kinase effectors (Ca2+ and cAMP) and substrates (casein, histone and protein kinase C substrate), did not markedly change with the progress of intoxication. Two-dimensional electrophoretic analysis of the phosphorylated cytosol fractions from control and MeHg-treated rats revealed that (1) the extents of phosphorylation of the 24 major protein species in the control rats differed greatly from each other, (2) the effect of MeHg on the phosphorylation was not uniform regarding the individual 24 proteins or the period of intoxication, and (3) in the symptomatic period, many protein species including tubulin subunits showed elevated phosphorylation, while a few protein species showed decreased phosphorylation. These results suggest that the neurotoxic action of MeHg could be mediated through, at least in part, the modification of functional protein species due to excess phosphorylation that leads to impairment of the normal cellular processes.

Glutathione S-transferases in the organ of Corti of the rat: enzymatic activity, subunit composition and immunohistochemical localization

Glutathione S-transferases (GSTs), a family of ubiquitous cytosolic isozymes, catalyze the detoxification of electrophilic substrates with reduced glutathione and participate in intracellular binding and transport of lipophilic substances. This study measured GST activity biochemically in the inner ear of the rat; determined the isozyme profile by Western blotting; and identified, immunohistochemically, the distribution of the mu and pi class GSTs in the organ of Corti. GST enzymatic activity in inner ear tissues ranged from 117 to 348 nmoles glutathione converted/min/mg protein, values somewhat higher than those found in brain (130) and much lower than in liver (1011). Of the GST isoforms, the pi class (identified by antibodies against the Yp subunit) was most prominent, the mu class (Yb1 subunit) clearly evident while the alpha class (Y(a) subunit) was barely detectable on Western blots. Immunocytochemical analysis showed differential distribution of the Yb1 and Yp subunits. The Yb1 subunit was present in the sensory cells, while supporting cells were not specifically stained. At the subcellular level, the isozyme was localized in the apical zones of inner (IHCs) and outer hair cells (OHCs) close to the cuticular plate. The extent of staining, however, varied between OHCs and IHCs. In the OHCs, staining appeared in discrete spots in the apical areas only, whereas in IHCs staining extended further towards the center of the cells. The Yp subunit was mainly localized to Deiters cell processes and pillar cells. Both Yb1 and Yp colocalized with tubulin-specific antibody. The functional significance of GST in the cochlear receptor cells is speculative. However, a role analogous to that in other tissues (detoxification, prostaglandin synthesis) can be assumed. In addition, an association of GST with the microtubule system is possible based on immunohistochemical colocalization with tubulin.