Avaliação do potencial neuroprotetor do zinco e da quercetina em modelos de isquemia e estresse oxidativo

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Avaliação do potencial neuroprotetor do zinco e da quercetina em modelos de isquemia e estresse oxidativo

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Title: Avaliação do potencial neuroprotetor do zinco e da quercetina em modelos de isquemia e estresse oxidativo
Author: Bahl, Marina Mônica
Abstract: Cerebral ischemia is characterized by a transitory or a permanent reduction in the blood flow in a specific area of the central nervous system, producing glucose and oxygen deprivation (OGD) to cells. Events such as glutamatergic excitotoxicity and oxidative stress can lead to necrotic or apoptotic neuronal cell death. Besides being an essential element in the structure and function of a number of proteins, Zinc is released concurrently with glutamate in the glutamatergic synaptic transmission, exerting a modulatory role. Quercetin is a flavonoid obtained through the food, displaying known neuroprotective effects. The objective of this study was to develop neuroprotection strategies utilizing a model of ischemia and a model of oxidative stress by using hippocampal slices of adult rats. The animals treated in vivo with ZnCl2 (300 mg/L; p.o.) during 30 days did not show any evidence of neuroprotection in the hippocampal slices in the ex vivo ischemia model. The cell viability and permeability tests indicated impairment in the cell condition after 15 or 60 min of ischemia. The total glutathione (GSH-t) levels were decreased only after 2 hours of reperfusion. Protein thiol (PSH) content remained unchanged in all treatment conditions. In the in vitro treatment with ZnCl2 the response was dual, when the cell viability was evaluated, ZnCl2 10 and 100 ìM was able to protect hippocampal slices exposed to 15 minutes OGD followed by 2 hours of reperfusion, however, ZnCl2 100 ìM was neurotoxic when these slices were subjected to 60 minutes of OGD followed, or not, by 2 hours of reperfusion. In the cell permeability assay, ZnCl2 100 ìM was neuroprotective in the reperfusion period. Still, GSH-t and PSH content decreased after 15 or 60 min PGO specially at the highest ZnCl2 (10 and/or 100 ìM) tested concentration. In hippocampal slices incubated for 1 ctivity of the antioxidant enzyme glutathione reductase (GR), as did the GR specific inhibitor carmustine (BCNU). The GR inhibition by BCNU did not alter the ischemic response, indicating that GR inhibition is a secondary event in the toxicity induced by the ischemic insult, which is in accordance with published data. In the in vitro treatment using quercetin it was possible to unravel neuroprotection at quercetin 10 and 30 ìM when the cell viability was tested during the ischemic or in the reperfusion period. Quercetin at different concentration was unable to reverse the GSH-t content decrease in the 2-hours reperfusion period. The PSH levels remained unchanged in all treatments. Quercetin at 30 and 100 ìM produced neuroprotection in the cell viability test when the hippocampal slices were exposed to 2.5 mM H2O2, but was unable to reverse the GSH-t decrease when hippocampal slices were exposed to 1.0 or 2.5 mM H2O2. The PSH content remained unaltered after H2O2 treatment. These results suggest that ZnCl2 did not cause neuroprotection when administered in vivo, while, in vitro it caused a dual effect, being neurotoxic or neuropretective, depending on the parameter tested. Inhibition of GR is not a relevant fator in the ischemic model employed. Quercetin, demonstrated a strong neuroprotective action in the in vitro ischemia model and a moderate neuroprotective effect against H2O2.
Description: Dissertação (mestrado) - Universidade Federal de Santa Catarina, Centro de Ciências Biológicas. Programa de Pós-Graduação em Neurociências.
URI: http://repositorio.ufsc.br/xmlui/handle/123456789/90779
Date: 2007

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