Division of Cell Biology, Department of Human Biology, Neuroscience Institute and Institute of Infectious Disease and Molecular Medicine, Faculty of Health Sciences, University of Cape Town, Cape Town, South Africa.
Department of Paediatric Neurology, Red Cross War Memorial Children's Hospital, Neuroscience Institute, University of Cape Town, Cape Town, South Africa.
Brain. 2019 Nov 1;142(11):3482-3501. doi: 10.1093/brain/awz283.
Status epilepticus is defined as a state of unrelenting seizure activity. Generalized convulsive status epilepticus is associated with a rapidly rising mortality rate, and thus constitutes a medical emergency. Benzodiazepines, which act as positive modulators of chloride (Cl-) permeable GABAA receptors, are indicated as first-line treatment, but this is ineffective in many cases. We found that 48% of children presenting with status epilepticus were unresponsive to benzodiazepine treatment, and critically, that the duration of status epilepticus at the time of treatment is an important predictor of non-responsiveness. We therefore investigated the cellular mechanisms that underlie acquired benzodiazepine resistance, using rodent organotypic and acute brain slices. Removing Mg2+ ions leads to an evolving pattern of epileptiform activity, and eventually to a persistent state of repetitive discharges that strongly resembles clinical EEG recordings of status epilepticus. We found that diazepam loses its antiseizure efficacy and conversely exacerbates epileptiform activity during this stage of status epilepticus-like activity. Interestingly, a low concentration of the barbiturate phenobarbital had a similar exacerbating effect on status epilepticus-like activity, while a high concentration of phenobarbital was effective at reducing or preventing epileptiform discharges. We then show that the persistent status epilepticus-like activity is associated with a reduction in GABAA receptor conductance and Cl- extrusion capability. We explored the effect on intraneuronal Cl- using both gramicidin, perforated-patch clamp recordings and Cl- imaging. This showed that during status epilepticus-like activity, reduced Cl- extrusion capacity was further exacerbated by activity-dependent Cl- loading, resulting in a persistently high intraneuronal Cl-. Consistent with these results, we found that optogenetic stimulation of GABAergic interneurons in the status epilepticus-like state, actually enhanced epileptiform activity in a GABAAR dependent manner. Together our findings describe a novel potential mechanism underlying benzodiazepine-resistant status epilepticus, with relevance to how this life-threatening condition should be managed in the clinic.
癫痫持续状态被定义为一种持续不断的癫痫发作状态。全身性惊厥性癫痫持续状态与死亡率的迅速上升有关，因此构成了医疗紧急情况。苯二氮䓬类药物作为氯离子（Cl-）通透性 GABAA 受体的正调节剂，被列为一线治疗药物，但在许多情况下无效。我们发现，48%出现癫痫持续状态的儿童对苯二氮䓬类药物治疗无反应，而且重要的是，治疗时癫痫持续状态的持续时间是无反应的一个重要预测指标。因此，我们使用啮齿动物器官型和急性脑切片研究了导致获得性苯二氮䓬类药物耐药的细胞机制。去除 Mg2+离子会导致癫痫样活动的演变模式，最终导致反复放电的持续状态，这强烈类似于癫痫持续状态的临床 EEG 记录。我们发现，地西泮在这种癫痫持续状态样活动的阶段失去了其抗惊厥作用，反而加剧了癫痫样活动。有趣的是，低浓度的巴比妥类药物苯巴比妥对癫痫持续状态样活动也有类似的加剧作用，而高浓度的苯巴比妥则有效减少或预防癫痫样放电。然后，我们表明持续的癫痫持续状态样活动与 GABAA 受体电导和 Cl-外排能力的降低有关。我们使用革兰氏菌素、穿孔贴片钳记录和 Cl-成像来研究神经元内 Cl-的影响。这表明，在癫痫持续状态样活动期间，活性依赖性 Cl-加载进一步加剧了 Cl-外排能力的降低，导致神经元内持续的高 Cl-。与这些结果一致，我们发现，在癫痫持续状态样状态下，光遗传学刺激 GABA 能中间神经元实际上以 GABAAR 依赖的方式增强了癫痫样活动。我们的研究结果共同描述了一种潜在的新型苯二氮䓬类药物耐药性癫痫持续状态的机制，与如何在临床上管理这种危及生命的疾病有关。
