Seizure suppression and neuroprotection by targeting the purinergic P2X7 receptor during status epilepticus in mice

Abstract

Prolonged seizures [status epilepticus (SE)] constitute a neurological emergency that can permanently damage the brain. SE results from a failure of the normal mechanisms to terminate seizures; in particular, γ-amino butyric acid-mediated inhibition, and benzodiazepine anticonvulsants are often incompletely effective. ATP acts as a fast neurotransmitter via ionotropic ligand-gated P2X receptors. Here we report that SE induced by intra-amygdala kainic acid in mice selectively increased hippocampal levels of P2X7 receptors relative to other P2X receptors. Using transgenic P2X7 reporter mice expressing enhanced green fluorescent protein, we identify dentate granule neurons as the major cell population transcribing the P2X7 receptor after SE. Pretreatment of mice with an intracerebroventricular microinjection of 1.75 nmol A438079, a P2X7 receptor antagonist, reduced seizure duration by 58% and reduced seizure-induced neuronal death by 61%. Injection of brilliant blue G (1 pmol), another selective antagonist, reduced seizure duration by 48% and was also neuroprotective. A438079 was seizure-suppressive when injected shortly after induction of SE, and coinjection of A438079 with lorazepam 60 min after triggering SE, when electrographic seizure-responsiveness to lorazepam had decreased, also terminated SE. Our results suggest that P2X7 receptor antagonists may be a promising class of drug for seizure abrogation and neuroprotection in SE.

Adenosine A2A receptor and ecto-5′-nucleotidase/CD73 are upregulated in hippocampal astrocytes of human patients with mesial temporal lobe epilepsy (MTLE)

“…The tight association between ecto-5′-nucleotidase/CD73 and A 2A receptors expression in astrocytes of the epileptic human hippocampus allow us to consider the possibility that the manipulation of ecto-5′-nucleotidase/CD73 activity might also afford an antiepileptic benefit similar to selective A 2A receptor blockade. Moreover, given the hazardous concerted action of extracellular ATP accumulation and consequent adenosine formation favoring nerve-terminal P2X7 and astrocytic A 2A receptor activation in the epileptic human brain, one may speculate about the potential benefit of combining selective A 2A antagonists together with blockade of the P2X7 channel (see, e.g., [33,35,[68][69][70]) to control intractable MTLE. …”

Bax Regulates Neuronal Ca2+Homeostasis

“…Brain samples were removed and 12 m sections from each sample were collected at the level of dorsal hippocampus (Paxinos and Franklin, 2001). Measurement of cell death was assessed by Fluoro-Jade B (FJB; Millipore) staining as described previously (Engel et al, 2012). FJB is a polyanionic fluorescein derivitave that specifically stains degenerating neurons.…”

“…2A, top). Hippocampal sections from mice subjected to status epilepticus for 24 h (Engel et al, 2010) showed strong TUNEL in the CA3 and served as positive controls ( Fig. 2A, bottom).…”

“…Upon a variety of apoptotic stimuli, Bax undergoes conformational changes, leading to its translocation, oligomerization, and insertion into the outer mitochondrial membrane (Youle and Strasser, 2008). Bax oligomerization initiates outer mitochondrial membrane permeabilization (MOMP) and promotes caspase-dependent or -independent apoptosis , Goping et al, 1998, De Giorgi et al, 2002, Youle and Strasser, 2008, Galluzzi et al, 2009. Neurons deficient in bax have been shown to be protected from growth factor withdrawal-, denervation-, proteotoxic-, and oxidative stress-induced neuronal injury (Xiang et al, 1998, Siu and Alway, 2006, Steckley et al, 2007.…”

Epilepsy and the inflammasome: Targeting inflammation as a novel therapeutic strategy for seizure disorders

“…ATPmediated activation of the P2X7 receptor is well known to activate the NLRP3 inflammasome and recently this target has been investigated for its role in seizures [48]. P2X7 receptor antagonists reduce kainate-induced seizure behaviour [49] and seizure activity [50] and this effect is maintained even when administered 15 minutes after SE induction [50]. P2X7 receptor antagonists in combination with lorazepam halt SE when given 1 hour post SE, a time when neither is fully effective alone [50].…”