Introduction to the 2nd Meeting on Immunity and Inflammation in Epilepsy (IIE2016)

Distinct peripheral pro-inflammatory profile associated with tuberous sclerosis complex and epilepsy

OBJECTIVE

Tuberous sclerosis complex (TSC) is a monogenetic disorder associated with sustained mechanistic target of rapamycin (mTOR) activation, leading to heterogeneous clinical manifestations. Epilepsy and renal angiomyolipoma are the most important causes of morbidity in adult people with TSC (pwTSC). mTOR is a key player in inflammation, which in turn could influence TSC-related clinical manifestations. Reliable biomarkers are lacking to monitor and predict evolution and response to treatment for epilepsy in pwTSC. Inflammation has been implicated in epileptogenesis in non-TSC-related epilepsy. We aimed to characterize the relation between markers of neuroglial activation/injury, markers of peripheral inflammation, and active epilepsy in pwTSC to identify accessible biomarkers and potential new therapeutic targets.

METHODS

We performed a cross-sectional study to investigate markers of central nervous system (CNS) (neurofilament light [NfL] and glial fibrillary acidic protein [GFAP]) and peripheral (45 cytokines) inflammation in the peripheral blood of pwTSC (n = 46) vs age- and sex-matched healthy controls (HCs) (n = 26). In pwTSC, markers associated with active epilepsy (n = 23/46) were compared to non-TSC epilepsy controls (n = 18). Observations on markers of neuroglial activation/injury (GFAP, NfL) were confirmed in an independent TSC cohort (n = 45; 69% with active epilepsy).

RESULTS

We report that TSC is characterized by elevated serum levels of marker of astrogliosis (GFAP), pro-inflammatory molecules (interleukin 1β [IL-1β], CXCL8) and trophic factor (epidermal growth factor [EGF]) compared to HCs and to non-TSC-related epilepsy controls. Among pwTSC, renal angiomyolipoma presence and size was associated with IL-15. It is notable that active epilepsy in pwTSC was associated with higher levels of GFAP compared to pwTSC without epilepsy, which was confirmed in an external validation cohort, and with elevated levels of pro-inflammatory cytokines (IL-17A, IL-17C, tumor necrosis factor α [TNF-α]), not significantly related to seizure activity or treatment with mTOR inhibitor. These associations remained significant after adjusting for age and sex.

SIGNIFICANCE

These results suggest that key inflammatory mediators could contribute to epileptogenesis and represent novel biomarkers and therapeutic targets in TSC.

Inflammatory response in epilepsy is mediated by glial cell gap junction pathway (Review)

Epilepsy is a common neurological disease that affects more than 50 million people worldwide. Neuroinflammation plays an important role in epilepsy. Activation of the immune system and an excessive inflammatory response can increase the frequency of seizures and increase the susceptibility to epilepsy. Therefore, anti-inflammatory therapies may have antiepileptic effects. Connexin 43 (Cx43) is a major component of astroglial hemichannels and gap junctions. Gap junctions are important for the direct exchange of substances and information between cells, as well as regulating the neuroinflammatory response, changing neuronal excitability, neuronal apoptosis, and synaptic remodeling. Cx43-mediated gap junction pathway can be crucial in epilepsy-induced neuroinflammatory cascades. Further, pro-inflammatory cytokines may in turn directly affect the expression of the Cx43 protein in astrocytes. Therefore, examining the association between neuroinflammation and epilepsy can be instrumental in uncovering the pathogenesis of epilepsy, which can lead to the development of novel and more effective antiepileptic drugs.

Electrographic seizures induced by activation of ETA and ETB receptors following intrahippocampal infusion of endothelin-1 in immature rats occur by different mechanisms

We have demonstrated previously that activation of either the ET_A or ET_B receptor can induce acute electrographic seizures following the intrahippocampal infusion of endothelin-1 (ET-1) in immature (P12) rats. We also demonstrated that activation of the ET_A receptor is associated with marked focal ischemia, while activation of the ET_B receptor is not. Exploring the mechanisms underlying seizures induced by these two ET-1 receptor interactions can potentially provide insight into how focal ischemia in immature animals produces seizures and whether ischemiarelated seizures differ from seizures not associated with ischemia. To explore these seizure mechanisms we used microdialysis to determine biomarkers associated with seizures in P12 rats following the intrahippocampal infusion of two different agents: (1) ET-1, which activates both the ET_A and ET_B receptors and causes focal ischemia and (2) Ala-ET-1, which selectively activates only the ET_B receptor and does not cause ischemia. Our results show that seizures associated with combined ET_A and ET_B receptor activation (and ischemia) have a different temporal distribution and microdialysis profile from seizures associated with ET_B activation alone (and without ischemia). Seizures with combined activation peak within the first hour after infusion and the microdialysis profile is characterized by a significant increase in the ratio of glutamic acid to GABA. By contrast, seizures with activation of only the ET_B receptor peak in the second hour after infusion and microdialysis shows a significant increase in the ratio of leukotriene B4 to prostaglandin E2. These findings suggest that ischemia-related seizures in immature animals involve an imbalance of excitation and inhibition, while non-ischemiarelated seizures involve an inflammatory process resulting from an excess of leukotrienes.

Febrile infection-related epilepsy syndrome (FIRES): prevalence, impact and management strategies

Febrile infection-related epilepsy syndrome (FIRES) is a rare catastrophic epileptic encephalopathy with a yet undefined etiology, affecting healthy children. It is characterized by acute manifestation of recurrent seizures or refractory status epilepticus preceded by febrile illness, but without evidence of infectious encephalitis. To date, the absence of specific biomarkers poses a significant diagnostic challenge; nonetheless, early diagnosis is very important for optimal management. FIRES is mostly irreversible and its sequelae include drug-resistant epilepsy and neuropsychological impairments. The treatment of FIRES represents a significant challenge for clinicians and is associated with low success rates. Early introduction of ketogenic diet seems to represent the most effective and promising treatment. This review aims to highlight the most recent insights on clinical features, terminology, epidemiology, pathogenesis, diagnostic challenges and therapeutic options.