Guanosine promotes cytotoxicity via adenosine receptors and induces apoptosis in temozolomide-treated A172 glioma cells.

Gliomas are a malignant tumor group whose patients have survival rates around 12 months. Among the treatments are the alkylating agents as temozolomide (TMZ), although gliomas have shown multiple resistance mechanisms for chemotherapy. Guanosine (GUO) is an endogenous nucleoside involved in extracellular signaling that presents neuroprotective effects and also shows the effect of inducing differentiation in cancer cells. The chemotherapy allied to adjuvant drugs are being suggested as a novel approach in gliomas treatment. In this way, this study evaluated whether GUO presented cytotoxic effects on human glioma cells as well as GUO effects in association with a classical chemotherapeutic compound, TMZ. Classical parameters of tumor aggressiveness, as alterations on cell viability, type of cell death, migration, and parameters of glutamatergic transmission, were evaluated. GUO (500 and 1000 µM) decreases the A172 glioma cell viability after 24, 48, or 72 h of treatment. TMZ alone or GUO plus TMZ also reduced glioma cell viability similarly. GUO combined with TMZ showed a potentiation effect of increasing apoptosis in A172 glioma cells, and a similar pattern was observed in reducing mitochondrial membrane potential. GUO per se did not elevate the acidic vesicular organelles occurrence, but TMZ or GUO plus TMZ increased this autophagy hallmark. GUO did not alter glutamate transport per se, but it prevented TMZ-induced glutamate release. GUO or TMZ did not alter glutamine synthetase activity. Pharmacological blockade of glutamate receptors did not change GUO effect on glioma viability. GUO cytotoxicity was partially prevented by adenosine receptor (A1R and A2AR) ligands. These results point to a cytotoxic effect of GUO on A172 glioma cells and suggest an anticancer effect of GUO as a putative adjuvant treatment, whose mechanism needs to be unraveled.

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

Guanosine, the endogenous guanine nucleoside, prevents cellular death induced by ischemic events and is a promising neuroprotective agent. During an ischemic event, nitric oxide has been reported to either cause or prevent cell death. Our aim was to evaluate the neuroprotective effects of guanosine against oxidative damage in hippocampal slices subjected to an in vitro ischemia model, the oxygen/glucose deprivation (OGD) protocol. We also assessed the participation of nitric oxide synthase (NOS) enzymes activity on the neuroprotection promoted by guanosine. Here, we showed that guanosine prevented the increase in ROS, nitric oxide, and peroxynitrite production induced by OGD. Moreover, guanosine prevented the loss of mitochondrial membrane potential in hippocampal slices subjected to OGD. Guanosine did not present an antioxidant effect per se. The protective effects of guanosine were mimicked by inhibition of neuronal NOS, but not of inducible NOS. The neuroprotective effect of guanosine may involve activation of cellular mechanisms that prevent the increase in nitric oxide production, possibly via neuronal NOS.

Atorvastatin Prevents Cognitive Deficits Induced by Intracerebroventricular Amyloid-ß1-40 Administration in Mice: Involvement of Glutamatergic and Antioxidant Systems.

Deposition of amyloid-ß (Aß) peptides into specific encephalic structures has been pointed as an important event related to Alzheimer's disease pathogenesis and associated with activation of glial cells, neuroinflammation, oxidative responses, and cognitive deficits. Aß-induced pro-oxidative damage may regulate the activity of glutamate transporters, leading to reduced glutamate uptake and, as a consequence, excitotoxic events. Herein, we evaluated the effects of the pretreatment of atorvastatin, a HMG-CoA reductase inhibitor, on behavioral and biochemical alterations induced by a single intracerebroventricular (i.c.v.) injection of aggregated Aß1-40 in mice. Atorvastatin (10 mg/kg/day, p.o.) was administered through seven consecutive days before Aß1-40 administration. Aß1-40 caused significant cognitive impairment in the object-place recognition task (2 weeks after the i.c.v. injection) and this phenomenon was abolished by atorvastatin pretreatment. Ex vivo evaluation of glutamate uptake into hippocampal and cerebral cortices slices showed atorvastatin, and Aß1-40 decreased hippocampal and cortical Na(+)-dependent glutamate uptake. However, Aß1-40 increased Na(+)-independent glutamate uptake and it was prevented by atorvastatin in prefrontal cortex slices. Moreover, Aß1-40 treatment significantly increased the cerebrocortical activities of glutathione reductase and glutathione peroxidase and these events were blunted by atorvastatin pretreatment. Reduced or oxidized glutathione levels were not altered by Aß1-40 and/or atorvastatin treatment. These results extend the notion of the protective action of atorvastatin against neuronal toxicity induced by Aß1-40 demonstrating that a pretreatment with atorvastatin prevents the spatial learning and memory deficits induced by Aß in rodents and promotes changes in glutamatergic and antioxidant systems mainly in prefrontal cortex.