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Elevated homocysteine is a risk factor in cardiovascular diseases and neurodegeneration. Among the putative mechanisms of homocysteineevoked neurotoxicity, disturbances in methylation processes and NMDA receptor-mediated excitotoxicity have been suggested. Our previous studies demonstrated that group I metabotropic glutamate receptors along with NMDA receptors participate in acute homocysteine-induced neuronal damage. In this study, using propidium iodide staining, we tested whether the same mechanism may mediate chronic homocysteine neurotoxicity. Our results confirmed that the application of D,L-homocysteine in micromolar concentrations for 3 days induces neurodegeneration in primary cultures of cerebellar granule neurons. Uncompetitive NMDA receptor antagonist MK801, and mGlu1 or mGlu5 receptor antagonists (LY367385 and MPEP, respectively), given alone provided very limited neuroprotection. However, simultaneous application of the NMDA receptor antagonists MK-801, memantine or amantadine and MPEP almost completely prevented chronic homocysteine neurotoxicity. These findings suggest a novel therapeutic strategy to combat neurodegeneration induced by hyperhomocysteinemia comprising a combination of antagonists of group I metabotropic glutamate receptors and NMDA receptors.
Nicotinamide is an important cofactor in many metabolic pathways and a known neuroprotective substance, while its methylated product, 1-methylnicotinamide, is a suspected neurotoxin. Homocysteine is a risk factor in Alzheimer’s disease and neurodegeneration, causing inhibition of methylation processes and inducing excitotoxicity. In this study, using primary cultures of rat cerebellar granule cells and propidium iodide staining, we investigated the neurotoxicity of nicotinamide and 1-methylnicotinamide, and their neuroprotective potential in acute and sub-acute homocysteine neurotoxicity. Our results demonstrated that nicotinamide and 1-methylnicotinamide applied for 24 h to cultures at concentrations of up to 25 mM had no effect on neuronal viability. Moreover, nicotinamide at concentrations of 5–20 mM and 1-methylnicotinamide at 1–10 mM applied to cells 24 h before, and for 24 h after an acute 30 min application of 25 mM D,L homocysteine, reduced neuronal damage. 1-Methylnicotinamide at concentrations of 250 and 500 µM showed neuroprotective activity during a sub-acute 24-h exposure to 2.5 mM D,L-homocysteine, while 5 and 25 mM nicotinamide also evoked neuroprotection. These findings do not support suggestions that 1-methylnicotinamide may act as an endogenous neurotoxic agent; rather, they indicate the neuroprotective ability of nicotinamide and 1-methylnicotinamide in homocysteine neurotoxicity. The exact mechanisms of this neuroprotection are unclear and require further investigation.
BACKGROUND AND AIMS: Brominated flame retardant tetrabromobisphenol A (TBBPA) contaminates the environment and displays cytotoxic potential. The mechanism of its cytotoxicity in neurons encompasses interference with NMDA and ryanodine receptors (NMDARs and RyRs) resulting in increase in intracellular Ca2+ concentration (Ca2+i), and induction of oxidative stress, which may be primary, or secondary to rises in Ca2+i. The aim of this study was to assess the role of excitotoxicity and Ca2+ imbalance in TBBPA-evoked oxidative stress and cytotoxicity in neurons. METHODS: Using the primary cultures of rat cerebellar granule cells (CGC) we evaluated oxidative stress induced by an acute challenge with 10 or 25 µM TBBPA by measuring reactive oxygen species (ROS) production, intracellular glutathione (GSH) level, SOD-1 and SOD-2 level, catalase activity, and the level of Zn2+ in CGC. Zn2+ and Ca2+i were measured fluoromertically, moreover TBBPA toxicity 24 h after the exposure was evaluated using propidium iodide staining. The pharmacological tools included NMDARs antagonist MK-801, ryanodine with bastadin 12 inhibiting RyRs, and various free radical scavengers. RESULTS: TBBPA induced concentration-dependent decrease in CGC viability, increase in Ca2+i and Zn2+ level, in ROS production, decrease in GSH level, catalase activity and SOD-2 level. Co-application of NMDARs and RyRs inhibitors which completely prevented increase in Ca2+i, resulted in a significant, but not complete cytoprotection, and only partially reduced the oxidative stress in the CGC. Also administration of ROS scavengers provided only partial cytoprotection and reduction of oxidative stress. CONCLUSIONS: We conclude that the production of free radicals resulting secondarily from TBBPA-evoked excitotoxicity and increases in Ca2+ level together with oxidative stress possibly induced primarily by TBBPA, both participate in TBBPA cytotoxicity in cultured neurons. Supported by the NCN grant 2012/05/B/NZ7/03225.
BACKGROUND AND AIMS: The results of early studies suggested a role of glutamate receptors in the mechanism of increases in intracellular Ca2+ concentration ([Ca2+]i ) and cytotoxicity induced by the brominated flame retardant, tetrabromobisphenol-A (TBBPA). Although now interest has focused mainly on TBBPA-induced Ca2+ release from intracellular stores, here we revisited the former issue and tested the involvement of NMDA receptors (NMDARs) in Ca2+ imbalance in neurons induced by TBBPA. METHODS: These effects were examined in primary cultures of rat cerebellar granule cells (CGC), and then, using isolated cortical membranes we checked whether TBBPA directly interacts with the agonist and modulatory sites of the NMDAR complex. On the 7th day in vitro CGC were treated with TBBPA at low µM concentrations. 45Ca uptake was detected and changes in [Ca2+]i , and plasma membrane potential were measured using fluorescent probes fluo-3 and oxonol VI, respectively. Moreover effects of TBBPA on specific binding of [3 H]MK-801, [3 H]glutamate and [3 H]glycine to isolated fraction of the rat brain cortex membranes were studied. RESULTS: The results demonstrated that TBBPA concentrationdependently increased 45Ca uptake and [Ca2+]i in CGC, and the increase was partially inhibited by NMDARs antagonist, MK-801. This effect was additive to glutamate-induced Ca2+ transients. TBBPA increased oxonol VI fluorescence in CGC reflecting depolarization of the cultured neurons. The binding assays demonstrated potentiation by TBBPA binding of [ 3 H]MK-801 in the presence of NMDA and glycine, with maximum at 20 µM TBBPA, which was inhibited by spermidine and antagonists of the polyamines’ site; inhibition by TBBPA of [ 3 H]glutamate binding, and no significant effect on [3 H]glycine binding. CONCLUSIONS: TBBPA directly enhances the activity of NMDARs in neuronal membranes by interfering with their modulatory sites, and by inducing depolarization of neurons. Supported by the NCN grant 2012/05/B/NZ7/03225
In Mongolian gerbils, global forebrain ischemia induces enhanced locomotor activity and the disruption of nest building immediately after the insult, followed by damage to hippocampal neurons developing 3 days later. Preconditioning by a brief episode of sublethal ischemia induces the protection of CA1 hippocampal neurons against a lethal ischemic insult. We examined how preconditioning with 2-min ischemia affects disturbances in the nest building behavior and locomotor activity induced by the injurious 3-min ischemia. Morphological examination confirmed that preconditioning significantly reduced neuronal damage in CA1 evoked by injurious ischemia. Behavioral studies demonstrated that preconditioning reduced the locomotor hyperactivity and latency in nest building after test ischemia, in comparison to sham or naive animals. The results indicate that the nest building test and measurement of locomotor activity may be used for an early in vivo prediction of the extent of ischemic brain damage and tolerance induced by ischemic preconditioning.
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