Inhibition of the prostaglandin receptor EP2 following status epilepticus reduces delayed mortality and brain inflammation

Abstract

Prostaglandin E2 is now widely recognized to play critical roles in brain inflammation and injury, although the responsible prostaglandin receptors have not been fully identified. We developed a potent and selective antagonist for the prostaglandin E2 receptor subtype EP2, TG6-10-1, with a sufficient pharmacokinetic profile to be used in vivo. We found that in the mouse pilocarpine model of status epilepticus (SE), systemic administration of TG6-10-1 completely recapitulates the effects of conditional ablation of cyclooxygenase-2 from principal forebrain neurons, namely reduced delayed mortality, accelerated recovery from weight loss, reduced brain inflammation, prevention of blood-brain barrier opening, and neuroprotection in the hippocampus, without modifying seizures acutely. Prolonged SE in humans causes high mortality and morbidity that are associated with brain inflammation and injury, but currently the only effective treatment is to stop the seizures quickly enough with anticonvulsants to prevent brain damage. Our results suggest that the prostaglandin receptor EP2 is critically involved in neuroinflammation and neurodegeneration, and point to EP2 receptor antagonism as an adjunctive therapeutic strategy to treat SE.inflammatory cytokine | electroencephalography | epileptogenesis | gliosis | neuronal injury A s a dominant product of cyclooxygenase-2 (COX-2 or PTGS2) in the brain, prostaglandin E2 (PGE 2 ) is emerging as a crucial mediator of many COX-2-driven pathological events in the central nervous system (CNS) (1). PGE 2 acts on four G protein-coupled receptors named EP1, EP2, EP3, and EP4. Among these, the EP2 receptor is widely expressed in the brain and plays important physiologic functions, such as in neuronal plasticity (2, 3). However, recent studies have identified a possible link between EP2 signaling and secondary neurotoxicity in models of chronic inflammation and neurodegeneration (1,(4)(5)(6). In a rodent model of amyotrophic lateral sclerosis, for example, EP2 receptor knockout mice exhibit improved survival, down-regulation of proinflammatory enzymes, and reduced oxidative stress (6).Prolonged status epilepticus (SE) in humans is associated with brain injury and substantial morbidity. Mortality is high during refractory SE that requires general anesthesia (7,8), and the 30-d mortality is about 35-37% for adults who experience at least 60 min of SE (9). Outcome in humans is dependent upon age, etiology, and SE duration (8-10), and currently the only effective treatment is to stop the seizures quickly enough to prevent brain damage (10). Most deaths from nonrefractory SE occur in the 2-wk period after successful treatment rather than during the seizure episode itself (9), pointing to a delayed but cascading set of responsible events. In mice, prolonged SE induced by pilocarpine causes >25% delayed mortality (11), and is associated with a series of molecular and cellular events in the brain, including neurodegeneration, and selective inflammatory reactions involving reactive microglia and a...

Infiltrating monocytes promote brain inflammation and exacerbate neuronal damage after status epilepticus

“…We have previously shown that, during the 24 h following SE, rodents quickly lose 10-20% of their body weight and then gradually begin to recover in the following days (6,8,39). As expected, animals subject to SE lost ∼13% of their body weight in the 24 h after SE onset, independent of Ccr2 genotype (Fig.…”

“…These admittedly sparse clinical findings are consistent with the much more extensive animal literature in demonstrating a florid inflammatory response of the brain to SE (5). We and others have provided evidence in animal models of epilepsy that quenching inflammation after SE can provide neuroprotection, prevent BBB opening, alleviate morbidity, and rescue behavioral deficits (6)(7)(8)(9)(10).…”

“…One possibility is that neuron-released prostaglandin E 2 , a product of cyclooxygenase-2 (COX-2), induces microglial CCL2 expression via EP2 receptors. Indeed, genetic removal of neuronal COX-2 or EP2 antagonism can mitigate the induction of CCL2 mRNA in the brain (6,8,9) or in purified microglia (57). Another possibility is that neuronal ATP release increases CCL2 in microglia via P2X7 receptors (58).…”

“…Control mice of each genotype received methylscopolamine and terbutaline, followed by saline solution injection instead of pilocarpine. Seizures were classified as previously described (6,67) as follows. A score of 0 represents normal behavior (walking, exploring, sniffing, grooming); a score of 1 represents immobile, staring, jumpy/ curled-up posture; a score of 2 represents automatisms (repetitive blinking, chewing, head bobbing, vibrissae twitching, scratching, face-washing, "stargazing"); a score of 3 represents partial body clonus, occasional myoclonic jerks, shivering; a score of 4 represents whole-body clonus, "corkscrew" turning and flipping, loss of posture, rearing and falling; a score of 5 (SE onset) represents nonintermittent seizure activity, stage 3 or 4 repeatedly; a score of 6 represents wild running, bouncing, and tonic seizures; and a score of 7 represents death.…”

“…Degradation of the BBB can occur after insults to the brain, including seizures (6,40,41). Serum albumin was detected by Western blot analysis in the PBS solution-perfused cortex four days following pilocarpine-induced SE in wild-type mice, compared with minimal albumin in saline solution-treated wild-type animals (Fig.…”