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Xenon-mediated neuroprotection in response to sustained, low-level excitotoxic stress

View Article: PubMed Central - PubMed

ABSTRACT

Noble gases such as xenon and argon have been reported to provide neuroprotection against acute brain ischemic/anoxic injuries. Herein, we wished to evaluate the protective potential of these two gases under conditions relevant to the pathogenesis of chronic neurodegenerative disorders. For that, we established cultures of neurons typically affected in Alzheimer's disease (AD) pathology, that is, cortical neurons and basal forebrain cholinergic neurons and exposed them to L-trans-pyrrolidine-2,4-dicarboxylic acid (PDC) to generate sustained, low-level excitotoxic stress. Over a period of 4 days, PDC caused a progressive loss of cortical neurons which was prevented substantially when xenon replaced nitrogen in the cell culture atmosphere. Unlike xenon, argon remained inactive. Xenon acted downstream of the inhibitory and stimulatory effects elicited by PDC on glutamate uptake and efflux, respectively. Neuroprotection by xenon was mimicked by two noncompetitive antagonists of NMDA glutamate receptors, memantine and ketamine. Each of them potentiated xenon-mediated neuroprotection when used at concentrations providing suboptimal rescue to cortical neurons but most surprisingly, no rescue at all. The survival-promoting effects of xenon persisted when NMDA was used instead of PDC to trigger neuronal death, indicating that NMDA receptor antagonism was probably accountable for xenon’s effects. An excess of glycine failed to reverse xenon neuroprotection, thus excluding a competitive interaction of xenon with the glycine-binding site of NMDA receptors. Noticeably, antioxidants such as Trolox and N-acetylcysteine reduced PDC-induced neuronal death but xenon itself lacked free radical-scavenging activity. Cholinergic neurons were also rescued efficaciously by xenon in basal forebrain cultures. Unexpectedly, however, xenon stimulated cholinergic traits and promoted the morphological differentiation of cholinergic neurons in these cultures. Memantine reproduced some of these neurotrophic effects, albeit with less efficacy than xenon. In conclusion, we demonstrate for the first time that xenon may have a therapeutic potential in AD.

No MeSH data available.


Impact of xenon on the uptake and release of [3H]-D-aspartate in cortical cultures exposed to PDC. (a) [3H]-D-aspartate uptake measured in cortical cultures exposed acutely or not to PDC (30 μM) under an atmosphere containing 75% N2 or 75% Xe, in the presence or not of memantine (10 μM). Error bars indicate mean±S.E.M. (n=6). ***P<0.001 relative to control cultures under N2 atmosphere. (b) [3H]-D-aspartate released in cortical cultures exposed or not to PDC (30 μM) in an atmosphere containing 75% N2 or 75% Xe, in the presence or not of memantine (10 μM). Error bars indicate mean±S.E.M. (n=9). ***P<0.001 relative to control cultures under N2 atmosphere. Impact of an atmosphere containing 75% Xe on [3H]-D-aspartate release evoked by a depolarizing treatment with 4-aminopyridine (4-AP; 2.5 mM) and bicuculline (Bic; 50 μM). Error bars indicate mean±S.E.M. (n=9). **P<0.01, ***P<0.001 relative to control cultures maintained under N2 atmosphere.
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fig3: Impact of xenon on the uptake and release of [3H]-D-aspartate in cortical cultures exposed to PDC. (a) [3H]-D-aspartate uptake measured in cortical cultures exposed acutely or not to PDC (30 μM) under an atmosphere containing 75% N2 or 75% Xe, in the presence or not of memantine (10 μM). Error bars indicate mean±S.E.M. (n=6). ***P<0.001 relative to control cultures under N2 atmosphere. (b) [3H]-D-aspartate released in cortical cultures exposed or not to PDC (30 μM) in an atmosphere containing 75% N2 or 75% Xe, in the presence or not of memantine (10 μM). Error bars indicate mean±S.E.M. (n=9). ***P<0.001 relative to control cultures under N2 atmosphere. Impact of an atmosphere containing 75% Xe on [3H]-D-aspartate release evoked by a depolarizing treatment with 4-aminopyridine (4-AP; 2.5 mM) and bicuculline (Bic; 50 μM). Error bars indicate mean±S.E.M. (n=9). **P<0.01, ***P<0.001 relative to control cultures maintained under N2 atmosphere.

Mentions: We studied whether some of the effects of xenon resulted from direct interference with the mechanism of action of PDC. To do so, we used a non-metabolizable analog of L-glutamate, [3H]-D-aspartate, that labels the cytosolic and vesicular pools of endogenous excitatory amino acids.37 Our data show that an acute application of PDC (30 μM) reduced the uptake of [3H]-D-aspartate by more than 70%. The uptake of [3H]-D-aspartate was not restored by xenon and it also remained impaired in the presence of memantine (10 μM) (Figure 3a). Noticeably, the uptake of [3H]-D-aspartate was not significantly affected by xenon in control conditions.


Xenon-mediated neuroprotection in response to sustained, low-level excitotoxic stress
Impact of xenon on the uptake and release of [3H]-D-aspartate in cortical cultures exposed to PDC. (a) [3H]-D-aspartate uptake measured in cortical cultures exposed acutely or not to PDC (30 μM) under an atmosphere containing 75% N2 or 75% Xe, in the presence or not of memantine (10 μM). Error bars indicate mean±S.E.M. (n=6). ***P<0.001 relative to control cultures under N2 atmosphere. (b) [3H]-D-aspartate released in cortical cultures exposed or not to PDC (30 μM) in an atmosphere containing 75% N2 or 75% Xe, in the presence or not of memantine (10 μM). Error bars indicate mean±S.E.M. (n=9). ***P<0.001 relative to control cultures under N2 atmosphere. Impact of an atmosphere containing 75% Xe on [3H]-D-aspartate release evoked by a depolarizing treatment with 4-aminopyridine (4-AP; 2.5 mM) and bicuculline (Bic; 50 μM). Error bars indicate mean±S.E.M. (n=9). **P<0.01, ***P<0.001 relative to control cultures maintained under N2 atmosphere.
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Related In: Results  -  Collection

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fig3: Impact of xenon on the uptake and release of [3H]-D-aspartate in cortical cultures exposed to PDC. (a) [3H]-D-aspartate uptake measured in cortical cultures exposed acutely or not to PDC (30 μM) under an atmosphere containing 75% N2 or 75% Xe, in the presence or not of memantine (10 μM). Error bars indicate mean±S.E.M. (n=6). ***P<0.001 relative to control cultures under N2 atmosphere. (b) [3H]-D-aspartate released in cortical cultures exposed or not to PDC (30 μM) in an atmosphere containing 75% N2 or 75% Xe, in the presence or not of memantine (10 μM). Error bars indicate mean±S.E.M. (n=9). ***P<0.001 relative to control cultures under N2 atmosphere. Impact of an atmosphere containing 75% Xe on [3H]-D-aspartate release evoked by a depolarizing treatment with 4-aminopyridine (4-AP; 2.5 mM) and bicuculline (Bic; 50 μM). Error bars indicate mean±S.E.M. (n=9). **P<0.01, ***P<0.001 relative to control cultures maintained under N2 atmosphere.
Mentions: We studied whether some of the effects of xenon resulted from direct interference with the mechanism of action of PDC. To do so, we used a non-metabolizable analog of L-glutamate, [3H]-D-aspartate, that labels the cytosolic and vesicular pools of endogenous excitatory amino acids.37 Our data show that an acute application of PDC (30 μM) reduced the uptake of [3H]-D-aspartate by more than 70%. The uptake of [3H]-D-aspartate was not restored by xenon and it also remained impaired in the presence of memantine (10 μM) (Figure 3a). Noticeably, the uptake of [3H]-D-aspartate was not significantly affected by xenon in control conditions.

View Article: PubMed Central - PubMed

ABSTRACT

Noble gases such as xenon and argon have been reported to provide neuroprotection against acute brain ischemic/anoxic injuries. Herein, we wished to evaluate the protective potential of these two gases under conditions relevant to the pathogenesis of chronic neurodegenerative disorders. For that, we established cultures of neurons typically affected in Alzheimer's disease (AD) pathology, that is, cortical neurons and basal forebrain cholinergic neurons and exposed them to L-trans-pyrrolidine-2,4-dicarboxylic acid (PDC) to generate sustained, low-level excitotoxic stress. Over a period of 4 days, PDC caused a progressive loss of cortical neurons which was prevented substantially when xenon replaced nitrogen in the cell culture atmosphere. Unlike xenon, argon remained inactive. Xenon acted downstream of the inhibitory and stimulatory effects elicited by PDC on glutamate uptake and efflux, respectively. Neuroprotection by xenon was mimicked by two noncompetitive antagonists of NMDA glutamate receptors, memantine and ketamine. Each of them potentiated xenon-mediated neuroprotection when used at concentrations providing suboptimal rescue to cortical neurons but most surprisingly, no rescue at all. The survival-promoting effects of xenon persisted when NMDA was used instead of PDC to trigger neuronal death, indicating that NMDA receptor antagonism was probably accountable for xenon&rsquo;s effects. An excess of glycine failed to reverse xenon neuroprotection, thus excluding a competitive interaction of xenon with the glycine-binding site of NMDA receptors. Noticeably, antioxidants such as Trolox and N-acetylcysteine reduced PDC-induced neuronal death but xenon itself lacked free radical-scavenging activity. Cholinergic neurons were also rescued efficaciously by xenon in basal forebrain cultures. Unexpectedly, however, xenon stimulated cholinergic traits and promoted the morphological differentiation of cholinergic neurons in these cultures. Memantine reproduced some of these neurotrophic effects, albeit with less efficacy than xenon. In conclusion, we demonstrate for the first time that xenon may have a therapeutic potential in AD.

No MeSH data available.