Increased neocortical expression of the P2X7 receptor after status epilepticus and anticonvulsant effect of P2X7 receptor antagonist A‐438079

Abstract

Summary Purpose ATP is an essential transmitter/cotransmitter in neuron function and pathophysiology and has recently emerged as a potential contributor to prolonged seizures (status epilepticus) through the activation of the purinergic ionotropic P2X7 receptor (P2X7R). Increased P2X7R expression has been reported in the hippocampus, and P2X7R antagonists reduced seizure‐induced damage to this brain region. However, status epilepticus also produces damage to the neocortex. The present study was designed to characterize P2X7R in the neocortex and assess effects of P2X7R antagonists on cortical injury after status epilepticus. Methods Status epilepticus was induced in mice by intraamygdala microinjection of kainic acid. Specific P2X7R inhibitors were administered into the ventricle before seizure induction, and cortical electroencephalography and behavior was recorded to assess seizure severity. P2X7R expression was examined in neocortex up to 24 h after status epilepticus, in epileptic mice, and in resected neocortex from patients with pharmacoresistent temporal lobe epilepsy (TLE). In addition, the induction of P2X7R after status epilepticus was investigated using transgenic P2X7R reporter mice, which express enhanced green fluorescent protein under the control of the p2x7r promoter. Key Findings Status epilepticus resulted in increased P2X7R protein levels in the neocortex of mice. Neocortical P2X7 receptor levels were also elevated in mice that developed epilepsy after status epilepticus and in resected neocortex from patients with pharmacoresistent TLE. Immunohistochemistry determined that neurons were the major cell population transcribing the P2X7R in the neocortex within the first 8 h after status epilepticus, whereas in epileptic mice, P2X7R up‐regulation occurred in microglia as well as in neurons. Pretreatment of mice with the specific P2X7R inhibitor A‐438079 reduced electrographic and clinical seizure severity during status epilepticus and reduced seizure‐induced neuronal death in the neocortex. Significance Our findings identify neurons in the neocortex as an important site of P2X7R up‐regulation after status epilepticus and in epilepsy, and provide support for the possible use of P2X7R antagonists for the treatment of status epilepticus and prevention of seizure‐induced brain damage.

The P2X7 Receptor Channel: Recent Developments and the Use of P2X7 Antagonists in Models of Disease

“…This finding was supported by the use of three P2X7 antagonists (oATP, A438079, and A740003), each of which enhanced disease symptoms in status epilepticus . In contrast, opposite outcomes were reported using two antagonists (BBG and A438079) in this disorder (Engel et al, 2012;Jimenez-Pacheco et al, 2013).…”

“…Although P2X7 has been identified on a number of cell types, less is known about the relative distribution of P2X7 between different cell types within whole tissues. Recently, transgenic P2X7 reporter mice expressing enhanced green fluorescent protein downstream of the P2RX7 promoter have been generated (Engel et al, 2012;Garcia-Huerta et al, 2012;Jimenez-Pacheco et al, 2013), which is an important step toward addressing the distribution of P2X7 in vivo. For example, these mice have been used to localize P2X7 expression in the central nervous system after prolonged seizures, with P2X7 identified to be upregulated on neurons, but not upregulated on microglia or astrocytes, in the hippocampus and neocortex (Engel et al, 2012;Jimenez-Pacheco et al, 2013).…”

“…Recently, transgenic P2X7 reporter mice expressing enhanced green fluorescent protein downstream of the P2RX7 promoter have been generated (Engel et al, 2012;Garcia-Huerta et al, 2012;Jimenez-Pacheco et al, 2013), which is an important step toward addressing the distribution of P2X7 in vivo. For example, these mice have been used to localize P2X7 expression in the central nervous system after prolonged seizures, with P2X7 identified to be upregulated on neurons, but not upregulated on microglia or astrocytes, in the hippocampus and neocortex (Engel et al, 2012;Jimenez-Pacheco et al, 2013). Although the P2X7 expression on microglia and astrocytes was weak in these studies, P2X7 expression in these cell types is well established from immunohistochemical studies (see Verkhratsky et al, 2012).…”

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. …”

Seizures Due to a KCNQ2 Mutation: Treatment with Vitamin B6

“…This activation modulates neurotransmitter release, promotes activation and release of interleukin 1b (a proconvulsant) from microglia and acts on oligodendrocytes and astrocytes to trigger cell death (Henshall et al 2013). P2X7R antagonists have been reported to have potent anticonvulsant effects (Jimenez-Pacheco et al 2013); thus, it is possible that PLP is having anticonvulsant effects by acting as a P2X7R antagonist. It is also possible that the action of PLP is not only limited to P2X receptors.…”