Neuroprotection mediated by the EP₄ receptor avoids the detrimental side effects of COX-2 inhibitors following ischaemic injury

Although COX-2 inhibition in animal models of ischaemia has shown neuroprotection, clinical trials revealed long term side effects with COX-2 inhibitors. A more focussed approach is necessary to retain the therapeutic effects of prostaglandins. This study investigated the role of the PGE 2 EP4 receptor using both in vitro and in vivo models of ischaemia. To demonstrate whether targeting the EP4 receptor is as neuroprotective as COX-2 inhibition, simultaneous experiments were carried out using a selective COX-2 inhibitor. Organotypic hippocampal sliced cultures, exposed to 2 h of oxygen glucose deprivation, were treated with; DMSO only, COX-2 inhibitor (NS-398), EP4 agonist (L-902688) or EP4 antagonist (GW627368X) and cell death was assessed. The EP4 agonist and the COX-2 inhibitor significantly reduced cell death following in vitro ischaemia, whereas treatment with the EP4 antagonist significantly increased cell death in hippocampal cultures. Following a 1 h occlusion of middle cerebral artery, mice were treated with the COX-2 inhibitor (10 mg kg, I.P), EP4 agonist (0.75 μg/kg, I.P) or vehicle (I.P), at the onset of reperfusion and again at 24 h post stroke. The COX-2 inhibitor and EP 4 agonist treated animals showed a significant reduction in infarct volume (P < .05) at 48 h post stroke compared to the vehicle treated group. These results show that selective activation of the EP4 receptor following acute ischaemic damage is neuroprotective, and support the concept of targeting protective prostaglandin receptor signalling as a potential therapeutic target for cerebral stroke.