Neuroprotective effect of guanosine against glutamate‐induced cell death in rat hippocampal slices is mediated by the phosphatidylinositol‐3 kinase/Akt/ glycogen synthase kinase 3β pathway activation and inducible nitric oxide synthase inhibition

Abstract

Excitotoxicity and cell death induced by glutamate are involved in many neurodegenerative disorders. We have previously demonstrated that excitotoxicity induced by millimolar concentrations of glutamate in hippocampal slices involves apoptotic features and glutamate-induced glutamate release. Guanosine, an endogenous guanine nucleoside, prevents excitotoxicity by its ability to modulate glutamate transport. In this study, we have evaluated the neuroprotective effect of guanosine against glutamate-induced toxicity in hippocampal slices and the mechanism involved in such an effect. We have found that guanosine (100 μM) was neuroprotective against 1 mM glutamate-induced cell death through the inhibition of glutamate release induced by glutamate. Guanosine also induced the phosphorylation and, thus, activation of protein kinase B (PKB/Akt), a downstream target of phosphatidylinositol-3 kinase (PI3K), as well as phosphorylation of glycogen synthase kinase 3β, which has been reported to be inactivated by Akt after phosphorylation at Ser9. Glutamate treated hippocampal slices showed increased inducible nitric oxide synthase (iNOS) expression that was prevented by guanosine. Slices preincubated with SNAP (an NO donor), inhibited the protective effect of guanosine. LY294002 (30 μM), a PI3K inhibitor, attenuated guanosine-induced neuroprotection, guanosine prevention of glutamate release, and guanosine-induced GSK3β(Ser9) phosphorylation but not guanosine reduction of glutamate-induced iNOS expression. Taken together, the results of this study show that guanosine protects hippocampal slices by a mechanism that involves the PI3K/Akt/GSK3β(Ser9) pathway and prevention of glutamate-induced glutamate release. Furthermore, guanosine also reduces glutamate-induced iNOS by a PI3K/Akt-independent mechanism.

Benzothiazepine CGP37157 and Its Isosteric 2′-Methyl Analogue Provide Neuroprotection and Block Cell Calcium Entry

“…Glutamate caused a 32% reduction of cell viability in nontreated tissues, analogously to the observed in previous reports from our group and others; 46 this neuronal lesion was prevented by increasing concentrations of compound ITH12505, in a concentration-dependent manner, with a maximal protection at 30 μM (Figure 6a). At this concentration, MTT was reduced by 85% compared to control, having 52% more viability than that found in glutamate slices.…”

Guanosine prevents nitroxidative stress and recovers mitochondrial membrane potential disruption in hippocampal slices subjected to oxygen/glucose deprivation

“…Effects of NOS isoforms inhibition on cellular viability and cell membrane permeability of hippocampal slices GUO treatment prevented iNOS expression in hippocampal slices subjected to OGD and to an in vitro glutamate challenge [33,34]. Here, we used NOS activity inhibitors to understand the involvement of the NOS isoforms in the mechanism of OGD-induced cell damage and in the neuroprotective effect of GUO.…”

Gliopreventive effects of guanosine against glucose deprivation in vitro

“…Although there is increasing evidence showing the neuroprotective effects of guanosine on models of neurotoxicity, its mechanisms are not fully understood. However, guanosine may mediate its effects through the modulation of the mitogen-activated protein kinases (MAPKs) and the phosphoinositide 3-kinase (PI3K) signaling pathways [22,23].…”