Small molecule antagonist reveals seizure-induced mediation of neuronal injury by prostaglandin E2 receptor subtype EP2

Abstract

With interest waning in the use of cyclooxygenase-2 (COX-2) inhibitors for inflammatory disease, prostaglandin receptors provide alternative targets for the treatment of COX-2-mediated pathological conditions in both the periphery and the central nervous system. Activation of prostaglandin E2 receptor (PGE 2 ) subtype EP2 promotes inflammation and is just beginning to be explored as a therapeutic target. To better understand physiological and pathological functions of the prostaglandin EP2 receptor, we developed a suite of small molecules with a 3-aryl-acrylamide scaffold as selective EP2 antagonists. The 12 most potent compounds displayed competitive antagonism of the human EP2 receptor with K B 2-20 nM in Schild regression analysis and 268-to 4,730-fold selectivity over the prostaglandin EP4 receptor. A brain-permeant compound completely suppressed the up-regulation of COX-2 mRNA in rat cultured microglia by EP2 activation and significantly reduced neuronal injury in hippocampus when administered in mice beginning 1 h after termination of pilocarpine-induced status epilepticus. The salutary actions of this novel group of antagonists raise the possibility that selective block of EP2 signaling via small molecules can be an innovative therapeutic strategy for inflammation-related brain injury.yclooxygenase-2 (COX-2), the inducible isoform of COX, is rapidly up-regulated in damaged tissue, for example in the central nervous system (CNS) after a seizure or cerebral ischemia (1-3). COX-2 induction in CNS overall contributes to inflammation and injury mainly by producing prostanoids (4-7). However, the deleterious cardio-and cerebrovascular side effects from sustained inhibition of COX-2 suggest that some COX-2 downstream prostanoid signaling might be beneficial (8), such that modulation of a specific prostanoid receptor or synthase could be a superior therapeutic strategy compared with generic block of the entire COX-2 cascade. Prostaglandin E2 (PGE 2 ), a dominant enzymatic product of COX-2 in the brain, can activate four Gprotein-coupled receptors (GPCRs): EP1, EP2, EP3, and EP4. Among these, EP2 and EP4 receptors are positively coupled through Gαs to cAMP production (9). In turn, cAMP can initiate multiple downstream events mediated by protein kinase A (PKA) or exchange protein activated by cAMP (Epac) (9).The EP2 receptor is widely expressed in both neurons and glia (3, 10). Neuronal EP2 activation appears to mediate some beneficial effects, such as PKA-dependent neuroprotection in acute models of ischemia and excitotoxicity (3,11,12), early neuroprotection following seizures (13), and promotion of spatial learning (14). Conversely, on the basis of the phenotype of EP2 knockout mice, EP2 activation is thought to promote inflammation and neurotoxicity in animal models of neurodegenerative diseases including Alzheimer's disease (15), Parkinson's disease (16), and amyotrophic lateral sclerosis (10). Glial, especially microglial EP2, is considered to play a major role in brain inflammation associated with chronic ne...

Cerebroprotection by the neuronal PGE2 receptor EP2 after intracerebral hemorrhage in middle-aged mice

“…8 In contrast, EP2 receptor signaling protects cultured neurons under various conditions through the cAMP/PKA or cAMP/Epac pathway [9][10][11][12] and regulates microglial activation and function in vitro. [13][14][15][16] These findings reflect cell-specific differences in EP2 signaling. In vivo work has shown that the EP2 receptor has beneficial effects in models of ischemic stroke 12,17,18 but detrimental effects in models of Alzheimer's disease, 19,20 Parkinson's disease, 21 and amyotrophic lateral sclerosis.…”

EP2 Receptor Signaling Pathways Regulate Classical Activation of Microglia

“…Likewise, 100 nM or 0.3 M TG4-155 produced a parallel shift to the right in the concentration-response curves of both agonists with the magnitude of the shift being similar in both resting and activated state conditions. The estimated Schild K B is 14 nM against butaprost and 10 nM against PGE 2 , which is about a 5-fold lower potency than that measured in C6G cells overexpressing human EP2 receptors (28). These data together with pharmacological results described above demonstrate that PGE2 and butaprost up to at least 1 M act entirely on EP2 receptors in both resting and activated rat microglia, that the weaker action of butaprost on EP3 receptors (38) does not come into play under our conditions, and that the only source of cAMP in PGE 2 -stimulated microglia is EP2.…”

“…The novel EP2 potentiator TG3-95-1 (referred to as compound 1 in Ref. 27) and EP2 antagonist TG4-155 were synthesized in our laboratory (27)(28)(29). All plasticware and reagents were endotoxin-free.…”

Modulation of Immunity and the Inflammatory Response: A New Target for Treating Drug-resistant Epilepsy

“…This effect was associated with reduction of neuronal cell loss, and inhibition of mossy fibers sprouting. Jiang et al [146] also found that pharmacological inhibition of PGE2 receptor subtype EP2 is neuroprotective in pilocarpine model of SE.…”