Title : A3 adenosine receptor agonists did not protect hippocampal slices under excitotoxicity conditions
Abstract:
A neuroprotective function of adenosine against ischemic/excitotoxic cell damage has been demonstrated. The adenosine receptors named A1, A2A, A2B, and A3 have been implicated in a wide range of biological functions as well as in pathological states such as ischemic injury. However, the involvement of A3 receptor is unclear and controversial. The aim of this study was to investigate the effect of A3 adenosine agents, NECA and HEMADO on glutamate-induced excitotoxicity model using hippocampal slices of Wistar rats. Male Wistar rats aged 3 months (n=6 per group) were killed and hippocampi were quickly dissected out; transverse sections (400 µm) using a McIlwain tissue chopper were obtained. This study was approved by the Local Ethics Committee (CEUA—Comissão de Ética no Uso de Animais—UFRGS; nr.29819). Hippocampal slices were incubated with Krebs-Henseleit medium containing the adenosinergic compounds NECA [5-(N-ethylcarboxamido)-adenosine] or HEMADO [2-(1-Hexynyl)-N6-methyladenosine]. After, the slices were incubated with a solution containing 10 nM of glutamate for 60 min at 37 °C to induce excitotoxicity followed by a recovery period (150 min). Then, the cell viability was determined through the ability of cells to reduce MTT (3-(4,5-dimethylthiazol-2-yl-diphenyltetrazolium bromide). The glutamate incubation, in the tested times and concentrations, increases the mitochondrial activity (about 20%). The HEMADO in vitro incubation did not alter the mitochondrial activity either in basal conditions neither in slices submitted to glutamate-induced toxicity. In despite of the in vitro incubation of NECA, we observed a tendency to decrease the mitochondrial activity in basal conditions as well an increase in a glutamate-induced toxicity (not statistically significant). It is possible to conclude that A3 agents were unable to protect hippocampal slices under excitotoxiciy conditions, suggesting that A3 receptors are not associated with protective adenosine effects. However, further experiments evaluating different glutamate concentrations, incubation times and other damage models are necessary to better understand the role of A3 receptor in ischemic injury.
