Spermidine attenuates the inhibitory effect of ethanol on NMDA-induced neurotoxicity

Abstract

The exact site(s) and the molecular mechanism(s) by which ethanol inhibits the activity of NMDA receptors in the brain have so far not been identified although the involvement of several NMDA receptor modulatory sites activated by glycine, Mg2+, Zn2+, polyamines and red-ox agents has been suggested. In this study we investigated the effects of spermidine, a polyamine site agonist, on NMDA-induced neurotoxicity and its ability to modulate the inhibitory action of ethanol on neurotoxicity produced by the maximal neurotoxic concentration of NMDA as measured by the MTT assay in rat cerebellar granule cells. This assay measures the enzymatic activity in mitochondria and/or endosome/lysosome compartment that closely correlates with the cell viability. Spermidine dramatically potentiated NMDA-induced responses both at nontoxic and maximally neurotoxic NMDA concentrations. Ethanol, as expected, concentration-dependently inhibited the maximal neurotoxicity produced by NMDA. The potentiating effect of spermidine observed at nontoxic concentrations of NMDA was not altered by ethanol evidenced by the fact that the EC(50) value for spermidine was not significantly changed in the presence of ethanol. This suggests that ethanol and spermidine produce their effects by acting at different sites within the NMDA receptor complex. In contrast, the inhibitory effect of ethanol on the maximally neurotoxic action of NMDA was significantly reduced by spermidine in a concentration-dependent manner, suggesting that the spermidine enhancement of NMDA receptor function in this situation is more potent and is able mask the inhibitory action of ethanol on other sites within the NMDA receptor.

Effects of Apocynin and Ethanol on Intracerebral Haemorrhage‐induced Brain Injury in Rats

“… 42 . Low‐dose ethanol produces N ‐methyl‐ d ‐aspartate (NMDA) receptor antagonism and free radical‐scavenging effects 41,43–46 . In the present study, a predominant free radical‐scavenging mechanism does not seem likely because no reduction in lipid peroxidation was observed.…”

Difluoromethylornithine Decreases Long‐Lasting Protein Oxidation Induced by Neonatal Ethanol Exposure in the Hippocampus of Adolescent Rats

“…N ‐methyl‐ d ‐aspartate receptors are comprised of an assembly of subunits (an NR1 subunit plus at least 1 type of NR2 subunit) with a number of modulatory sites, including a polyamine binding site, which is present in the NR2B subunit (Chenard and Menniti, 1999). The polyamine binding site of the NMDA receptor seems to be particularly relevant, from the pharmacological point of view, as it regulates important CNS functions, such as learning and memory (Berlese et al, 2005; Rubin et al, 2004) and alters the susceptibility to the neurotoxic effects of glutamate and ethanol (Cebere et al, 2002; Ferrani‐Kile et al, 2003; Gibson et al, 2003; Honse et al, 2003; Mayer et al, 2002; Mikolajczak et al, 2003), Interestingly, eliprodil, which inhibits NMDA receptor activity by interacting allosterically with the polyamine modulatory site on NMDA receptors, reduces the severity of learning deficits associated with developmental alcohol exposure (Thomas et al, 2004). In fact, in vitro studies have suggested a role for polyamines in ethanol withdrawal‐induced neurotoxicity, as not only polyamine binding site antagonists, but also polyamine synthesis inhibitors protect against ethanol withdrawal‐induced neurotoxicity (Gibson et al, 2003; Nagy et al, 2004).…”