Neurodegeneration, Neuroprotection, and Disease-Oriented NeuroscienceResearch PaperGuanosine is neuroprotective against oxygen/glucose deprivation in hippocampal slices via large conductance Ca2+-activated K+ channels, phosphatidilinositol-3 kinase/protei

Guanine derivatives (GD) have been implicated in many relevant brain extracellular roles, such as modulation of glutamate transmission and neuronal protection against excitotoxic damage. GD are spontaneously released to the extracellular space from cultured astrocytes and during oxygen/glucose deprivation (OGD). The aim of this study has been to evaluate the potassium channels and phosphatidilinositol-3 kinase (PI3K) pathway involvement in the mechanisms related to the neuroprotective role of guanosine in rat hippocampal slices subjected to OGD. The addition of guanosine (100 μM) to hippocampal slices subjected to 15 min of OGD and followed by 2 h of re-oxygenation is neuroprotective. The presence of K+ channel blockers, glibenclamide (20 μM) or apamin (300 nM), revealed that neuroprotective effect of guanosine was not dependent on ATP-sensitive K+ channels or small conductance Ca2+-activated K+ channels. The presence of charybdotoxin (100 nM), a large conductance Ca2+-activated K+ channel (BK) blocker, inhibited the neuroprotective effect of guanosine. Hippocampal slices subjected to OGD and re-oxygenation showed a significant reduction of glutamate uptake. Addition of guanosine in the re-oxygenation period has blocked the reduction of glutamate uptake. This guanosine effect was inhibited when hippocampal slices were pre-incubated with charybdotoxin or wortmanin (a PI3K inhibitor, 1 μM) in the re-oxygenation period. Guanosine promoted an increase in Akt protein phosphorylation. However, the presence of charybdotoxin blocked such effect. In conclusion, the neuroprotective effect of guanosine involves augmentation of glutamate uptake, which is modulated by BK channels and the activation of PI3K pathway. Moreover, neuroprotection caused by guanosine depends on the increased expression of phospho-Akt protein.

Schematic diagram of the mechanism of neuroprotection promoted by guanosine against oxygen/glucose deprivation. In hippocampal slices subjected to oxygen/glucose deprivation (OGD) and re-oxygenation, charybdotoxin (a BK channels blocker) and Wortmanin (a PI3K inhibitor) prevented GUO-induced neuroprotection. Guanosine (GUO) modulates BK channels activation, promoting Akt phosphorylation and blocking the reduction in glutamate uptake induced by OGD damage, thus resulting in neuroprotection.69Highlights▶OGD promotes reduction of cell viability and glutamate uptake in hippocampal slices. ▶Guanosine promotes neuroprotection and prevents reduction of the glutamate uptake. ▶Guanosine-induced neuroprotection involves the activation of BK channels. ▶Guanosine is neuroprotective via activation of PI3-K pathway and AKT phosphorylation.