Guanosine enhances glutamate uptake and oxidation, preventing oxidative stress in mouse hippocampal slices submitted to high glutamate levels

Abstract Glutamate (Glu) is the main mammalian brain neurotransmitter. Concerning the glutamatergic neurotransmission, excessive levels of glutamate in the synaptic cleft are extremally harmful. This phenomenon, named as excitotoxicity is involved in various acute and chronic brain diseases. Guanosine (GUO), an endogenous guanine nucleoside, possesses neuroprotective effects in several experimental models of glutamatergic excitotoxicity, an effect accompanied by an increase in astrocytic glutamate uptake. Therefore, the objective of this study was to investigate the involvement of an additional putative parameter, glutamate oxidation to CO2, involved in ex-vivo GUO neuroprotective effects in mouse hippocampal slices submitted to glutamatergic excitotoxicity. Mice were sacrificed by decapitation, the hippocampi were removed and sliced. The slices were incubated for various times and concentrations of Glu and GUO. First, the concentration of Glu that produced an increase in L-[14C(U)]-Glu oxidation to CO2 without cell injury was determined at different time points (between 0 and 90 minutes); 1000 μM Glu increased Glu oxidation between 30-60 minutes of incubation without cell injury. Under these conditions (Glu concentration and incubation time), 100 μM GUO increased Glu oxidation (35%). Additionally, 100 μM GUO increased L-[3,4-3H]-glutamate uptake (45%) in slices incubated with 1000 μM Glu (0-30 minutes). Furthermore, 1000 μM Glu increased reactive species levels, SOD activity, and decreased GPx activity, and GSH content after 30 and 60 minutes; 100 μM GUO prevented these effects. This is the first study demonstrating that GUO simultaneously promoted an increase in the uptake and utilization of Glu in excitotoxicity-like conditions preventing redox imbalance.