Percorrer por autor "Aschner, Michael"
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- N-acetylcysteine or sodium selenite prevent the p38-mediated production of proinflammatory cytokines by microglia during exposure to mercury (II)Publication . Branco, Vasco; Coppo, Lucia; Aschner, Michael; Carvalho, CristinaMercury (Hg) is known for its neurotoxicity and is reported to activate microglia cells at low exposure levels. Since mercury decreases the activity of the glutathione and thioredoxin systems, we hypothesize that Hg would, in turn, disrupt microglia homeostasis by interfering with redox regulation of signaling pathways. Thus, in this work, we analyzed the effect of exposure to Hg2+ on nuclear translocation and activation of NF-kB (p50) and p38 and pro-inflammatory gene transcription (IL-1ß; iNOS, TNF-alpha) considering the interaction of Hg with the glutathione system and thioredoxin systems in microglial cells. N9 (mouse) microglia cells were exposed to different concentrations of Hg2+ and the 24 h EC50 for a reduction in viability was 42.1 ± 3.7 μM. Subsequent experiments showed that at sub-cytotoxic levels of Hg2+, there was a general increase in ROS (≈40%) accompanied by a significant depletion (60–90%) of glutathione (GSH) and thioredoxin reductase (TrxR) activity. Upon 6 h of exposure to Hg2+, p38 (but not p50) accumulated in the nucleus (50% higher than in control), which was accompanied by an increase in its phosphorylation. Transcript levels of both IL1-ß and iNOS were increased over two-fold relative to the control. Furthermore, pre-exposure of cells to the p38 inhibitor SB 239063 hindered the activation of cytokine transcription by Hg2+. These results show that disruption of redox systems by Hg2+ prompts the activation of p38 leading to transcription of pro-inflammatory genes in microglia cells. Treatment of N9 cells with NAC or sodium selenite—which caused an increase in basal GSH and TrxR levels, respectively, prevented the activation of p38 and the transcription of pro-inflammatory cytokines. This result demonstrates the importance of an adequate nutritional status to minimize the toxicity resulting from Hg exposure in human populations at risk.
- Thioredoxin reductase inhibitors as potential antitumors : mercury compounds efficacy in glioma cellsPublication . Pires, Vanessa; Bramatti, Isabella; Aschner, Michael; Branco, Vasco; Carvalho, CristinaGlioblastoma multiforme (GBM) is the most aggressive and common form of glioma. GBM, like many other tumors, expresses high levels of redox proteins, such as thioredoxin (Trx) and thioredoxin reductase (TrxR), allowing tumor cells to cope with high levels of reactive oxygen species (ROS) and resist chemotherapy and radiotherapy. Thus, tackling the activity of these enzymes is a strategy to reduce cell viability and proliferation and most importantly achieve tumor cell death. Mercury (Hg) compounds are among the most effective inhibitors of TrxR and Trx due to their high affinity for binding thiols and selenols. Moreover, organomercurials such as thimerosal, have a history of clinical use in humans. Thimerosal effectively crosses the blood–brain barrier (BBB), thus reaching effective concentrations for the treatment of GBM. Therefore, this study evaluated the effects of thimerosal (TmHg) and its metabolite ethylmercury (EtHg) over the mouse glioma cell line (GL261), namely, the inhibition of the thioredoxin system and the occurrence of oxidative cellular stress. The results showed that both TmHg and EtHg increased oxidative events and triggered cell death primarily by apoptosis, leading to a significant reduction in GL261 cell viability. Moreover, the cytotoxicity of TmHg and ETHg in GL261 was significantly higher when compared to temozolomide (TMZ). These results indicate that EtHg and TmHg have the potential to be used in GBM therapy since they strongly reduce the redox capability of tumor cells at exceedingly low exposure levels.