Commentary on Kaushik et al.: Prostaglandin D2 is crucial for seizure suppression and postictal sleep. Novel evidence supporting a role for prostanoid receptors in seizure control

Neuroprotective effects of thromboxane receptor antagonist SQ 29,548 after pilocarpine-induced status epilepticus in mice

Thromboxane A₂ (TXA₂) is an important eicosanoid in the cardiovascular system, and increasing evidence suggests that TXA₂ receptors (TPs) and their ligands may constitute valuable tools for the development of neuroprotective drugs. However, the role of TPs on seizure-induced damage has not been investigated. Therefore, we evaluated the effects of SQ 29,548, a potent and selective TP antagonist-on neuromotor performance, neurodegeneration, reactive astrocytosis, and c-Fos protein immunoreactivity after pilocarpine-induced status epilepticus (SE) in mice. Adult C57BL/6 mice received intracerebroventricular SQ 29,548 injections 90 min and 24 h after pilocarpine-induced SE. We found that SQ 29,548 prevented the impairment of neuromotor performance (Neuroscore test) 48 h after pilocarpine-induced SE. Data analysis suggested the existence of two subgroups of SQ 29,548-treated post-SE animals. Eight out of 12 SQ 29,548-treated animals displayed Neuroscore values identical to those of vehicle-treated controls, and were considered SQ 29,548 responders. However, 4 out of 12 SQ 29,548-treated animals did not show any improvement in Neuroscore values, and were considered SQ 29,548 non-responders. Treatment with SQ 29,548 attenuated SE-induced increase in the number of FJC- or GFAP-positive cells in the hippocampus of SQ 29,548 responders. In addition, SQ 29,548 prevented the SE-elicited increase of c-Fos immunoreactivity in the hippocampus. In summary, our results suggest that the TP antagonist (SQ 29,548) improves neurological outcome after pilocarpine-induced SE in mice. The existence of SQ 29,548 responders and non-responders was suggested by results from the Neuroscore test. Additional studies are needed to understand the mechanisms underlying these findings, as well as the potential uses of TP antagonists in the treatment of seizure-induced damage.

Anticonvulsant-like effect of thromboxane receptor agonist U-46619 against pentylenetetrazol-induced seizures

Increasing evidence suggests that prostanoid receptors and their ligands may constitute valuable tools for development of new antiepileptic drugs. Thromboxane A₂ (TXA₂) is a major eicosanoid in cardiovascular homeostasis. TXA₂ exerts its action through the specific G protein-coupled TXA₂ receptor (TP). In addition to its crucial role in the cardiovascular system, TXA₂ and TPs play a role in the brain. Nevertheless, previously identified roles have been limited to cell protection of neurotoxicity, and the role of TPs on seizure activity was not investigated. Here we evaluated the effect of potent and selective TP agonist U-46619 on seizures induced by pentylenetetrazol (PTZ). Adult C57BL/6 mice received increasing doses of U-46619 (0, 30, 100 or 300 μg/kg). After 30 min we measured the latencies to myoclonic and generalized seizures induced by PTZ (60 mg/kg). We found that U-46619 increased the latency to PTZ-induced myoclonic jerks and tonic-clonic seizures. Moreover, U-46619 increased the immunocontent of phosphorylated Ser⁶⁵⁷ at protein kinase C (PKC) alpha subunit, indicating PKC activation in the hippocampus and cerebral cortex. Levels of TPs were not altered by the agonist. Administration of a TP antagonist, SQ 29,548, did not alter seizures and did not blunt the anticonvulsant-like effect of the agonist. In summary, we showed that a potent and selective TP agonist, U-46619, increased seizure latency in mice. Activation of PKC signaling pathways may underlie the anticonvulsant-like effect. Further investigation is needed to understand the potential of TPs in seizure treatment.

EP2 receptor agonist ONO-AE1-259-01 attenuates pentylenetetrazole- and pilocarpine-induced seizures but causes hippocampal neurotoxicity

Epilepsy is a common and devastating neurological disease affecting more than 50 million people worldwide. Accumulating experimental and clinical evidence suggests that inflammatory pathways contribute to the development of seizures in various forms of epilepsy. In this context, while the activation of the PGE₂ EP2 receptor causes early neuroprotective and late neurotoxic effects, the role of EP2 receptor in seizures remains unclear. We investigated whether the systemic administration of the highly selective EP2 agonist ONO-AE1-259-01 prevented acute pentylenetetrazole (PTZ)- and pilocarpine-induced seizures. The effect of ONO-AE1-259-01 on cell death in the hippocampal formation of adult male mice seven days after pilocarpine-induced status epilepticus (SE) was also evaluated. ONO-AE1-259-01 (10μg/kg, s.c.) attenuated PTZ- and pilocarpine-induced seizures, evidenced by the increased latency to seizures, decreased number and duration of seizures episodes and decreased mean amplitude of electrographic seizures. ONO-AE1-259-01 and pilocarpine alone significantly increased the number of pyknotic cells per se in all hippocampal subfields. The EP2 agonist also additively increased pilocarpine-induced pyknosis in the pyramidal cell layer of CA1 but reduced pilocarpine-induced pyknosis in the granule cell layer of the dentate gyrus (DG). Although the systemic administration of ONO-AE1-259-01 caused a significant anticonvulsant effect in our assays, this EP2 agonist caused extensive cell death. These findings limit the likelihood of EP2 receptor agonists being considered as novel potential anticonvulsant drugs.

Defining the therapeutic time window for suppressing the inflammatory prostaglandin E2 signaling after status epilepticus

Neuroinflammation is a common feature in nearly all neurological and some psychiatric disorders. Resembling its extraneural counterpart, neuroinflammation can be both beneficial and detrimental depending on the responding molecules. The overall effect of inflammation on disease progression is highly dependent on the extent of inflammatory mediator production and the duration of inflammatory induction. The time-dependent aspect of inflammatory responses suggests that the therapeutic time window for quelling neuroinflammation might vary with molecular targets and injury types. Therefore, it is important to define the therapeutic time window for anti-inflammatory therapeutics, as contradicting or negative results might arise when different treatment regimens are utilized even in similar animal models. Herein, we discuss a few critical factors that can help define the therapeutic time window and optimize treatment paradigm for suppressing the cyclooxygenase-2/prostaglandin-mediated inflammation after status epilepticus. These determinants should also be relevant to other anti-inflammatory therapeutic strategies for the CNS diseases.

Montelukast potentiates the anticonvulsant effect of phenobarbital in mice: an isobolographic analysis

Although leukotrienes have been implicated in seizures, no study has systematically investigated whether the blockade of CysLT1 receptors synergistically increases the anticonvulsant action of classic antiepileptics. In this study, behavioral and electroencephalographic methods, as well as isobolographic analysis, are used to show that the CysLT1 inverse agonist montelukast synergistically increases the anticonvulsant action of phenobarbital against pentylenetetrazole-induced seizures. Moreover, it is shown that LTD4 reverses the effect of montelukast. The experimentally derived ED50mix value for a fixed-ratio combination (1:1 proportion) of montelukast plus phenobarbital was 0.06±0.02 μmol, whereas the additively calculated ED50add value was 0.49±0.03 μmol. The calculated interaction index was 0.12, indicating a synergistic interaction. The association of montelukast significantly decreased the antiseizure ED50 for phenobarbital (0.74 and 0.04 μmol in the absence and presence of montelukast, respectively) and, consequently, phenobarbital-induced sedation at equieffective doses. The demonstration of a strong synergism between montelukast and phenobarbital is particularly relevant because both drugs are already used in the clinics, foreseeing an immediate translational application for epileptic patients who have drug-resistant seizures.