Interleukin-1 receptor is a target for adjunctive control of diazepam-refractory status epilepticus in mice
Introduction
Status epilepticus (SE) is a life-threatening neurological emergency, characterized by continuous or intermittent seizures without full recovery between seizures (Betjemann et al., 2015). Refractory SE is defined by the failure of adequate amounts of two intravenous drugs to stop seizures, which occurs in about one-third of patients (Chen and Wasterlain, 2006). Those SEs without timely termination may result in later neuronal damage, cognitive alterations and epileptogenesis (Sadarangani et al., 2008, Ferlisi and Shorvon, 2012, Ferro et al., 2014). By convention, first-line antiepileptic drugs (ADEs) of convulsive SE are benzodiazepines, such as diazepam (DZP). DZP refractory/resistant SE refers to SE that cannot be terminated following the rational intravenous DZP, which was usually also resistant to other parenteral benzodiazepines and high possibly resistant to a second or third line of ADEs (Treiman et al., 1998, Chen and Wasterlain, 2006). DZP (or benzodiazepine) refractory SE seems dependent on the duration of SE, and it occurs especially when SE was prolonged (typically 0.5–1 h) in both patients and rodents (Loscher, 2009, Prasad et al., 2014). A recent prospective observational cohort study found that the time elapsed from SE onset to the first benzodiazepine administration is delayed with a median time of 30 min (Sanchez Fernandez et al., 2015). DZP refractory SE may be further controlled using other classes of AEDs and even general anesthesia (Shorvon, 2011). However, most of these drugs may lead to severe side-effects and complications (Bell, 1969, Sutter et al., 2014). Therefore, it is urgent to develop new therapeutic strategies for SE, especially for the benzodiazepine refractory prolonged SE.
Although several potential mechanisms for benzodiazepine refractory SE have been previously reported, such as internalization of GABAergic receptors (Naylor et al., 2005) and increase in membranous AMPA (alpha-amino-3-hydroxy-5-methyl-4-isoxazolepropionic acid) as well as NMDA (N-methyl-d-aspartic acid) receptors during SE (Wasterlain and Chen, 2008), the exact mechanisms underlying the DZP refractoriness of SE remains obscure. Recently, increasing evidence supports that the neural inflammations may be a crucial factor promoting the refractoriness of SE. For example, Spatola et al. found that inflammatory SE was more often refractory to initial antiepileptic treatment (Spatola et al., 2015). Besides, Gaspard et al, reported autoimmune encephalitis is the most commonly identified cause of new-onset refractory SE (Gaspard et al., 2015). Moreover, purinergic P2X7 receptor antagonists can enhance the inhibitory effect of DZP on SE (Jimenez-Pacheco et al., 2013), which may also act anti-inflammatory effects (Kim et al., 2010). Thus, these results lead us to consider the neuroinflammatory mechanism of refractory SE, which is still little studied.
Interleukin-1 beta (IL-1β) is a seizure-related proinflammatory mediator, which may be accumulated in the brain during SE (Rijkers et al., 2009, Vezzani et al., 2011). Whether the IL-1β contributes to the pharmacological refractoriness of SE remains unclear. It has been reported that the mRNA of IL-1β highly increases at 7.5 h after the SE, suggesting that the induction of IL-1β by SE may not develop rapidly enough to explain time dependent resistance of SE to AEDs (Kuteykin-Teplyakov et al., 2009). However, recently, Librizzi et al. found that the IL-1β induced by the proceeding seizure is sufficient to exacerbate the seizures resurrected within a short time delay in the in vitro isolated guinea-pig brain (Librizzi et al., 2012). We also found interleukin-1 receptor antagonist (IL-1RA) enhances postictal suppression of kindled seizures in wild-type but not IL-1R1 knock-out (KO) mice (Tao et al., 2015). Athough these results were not in a SE condition, they at least suggest the increase of endogenic IL-1β or its receptor may be rapidly enough even during a self-limited seizure.
Therefore, we hypothesis that IL-1β may be accumulated during SE and contribute to the DZP-refractory phenomenon of prolonged SE. Using a DZP-refractory prolonged SE mice model induced by kainic acid (KA), we tested whether pharmacological blockade or KO of IL-1R1 could reverse the time-dependent DZP-refractory phenomenon of prolonged SE.
Section snippets
Animals
Age-matched wild-type (WT) C57BL/6 mice and IL-1R1-KO mice (generated on a C57BL/6 background, from Jackson Laboratory, stock number: 003245) were used in this study. All animals (aged 10–12 weeks) were maintained in individual cages with a 12-h light/dark cycle (lights on from 8:00 to 20:00). Water and food were given ad libitum. Experiments were conducted between 10:00 and 17:00. All experiments were in complete compliance with the National Institutes of Health Guide for the Care and Use of
Prolonged SE up-regulated IL-1β and is DZP-refractory in WT mice
We sought to investigate whether the IL-1β is rapid enough up-regulated during refractory SE. We first confirmed that low dose of DZP (1 mg/kg) failed to terminate the SE (both behavioral seizures and ictal EEGs) when it was given 40 min after the onset of SE, while DZP rapidly suppressed behavioral seizures within several minutes and terminated ictal EEGs when it was given 10 min after the onset of SE (Fig. 1B). Then, we examined the expression of IL-1β in mouse hippocampus by western blot at 10
Discussion
In present study, we confirmed that DZP became ineffective when given at 40 min after the SE onset induced by intrahippocampal injection of KA in mice, which is consistent with previous studies in other animal models (George and Kulkarni, 1996) and in line with clinical findings (Prasad et al., 2014). Using this DZP-refractory SE model, we provided IL-1β is a key modulator of DZP-refractory SE by its receptor IL-1R1, and suggest IL-1R1 may be a potent target for adjunctive control of refractory
Conclusion
The present study provides direct evidence that IL-1R1 is a potent target for adjunctive control of DZP refractory SE in mice. Both pharmacological block and gene KO of IL-1R1 may reverse or prevent the progressive DZP-refractoriness of SE in mice. Thus, combination of IL-1R1 antagonists with DZP may be a novel strategy for the treatment of refractory prolonged SE.
Competing interests
The authors declare that they have no competing interests.
Acknowledgments
This work was funded by the National Natural Science Foundation of China (81302749, 91332202, 81273492), and partly supported by the Program for Zhejiang Leading Team of S&T Innovation (2011R50014) and the Research Program of Zhejiang Chinese Medical University (2014ZR05 & 2015ZG03).
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