https://www.cogsci.ucsd.edu/~mboyle/COGS163/pdf-files/W5-AR-Glia%20and%20epilepsy-%20excitability%20and%20inflammation-TINS-2013.pdf

Glia and epilepsy: excitability and inflammation

Epilepsy is a chronic neurological disease characterized by an enduring propensity for generation of seizures. The pathogenic processes of seizure generation and recurrence are the subject of intensive preclinical and clinical investigations as their identification would enable development of novel treatments that prevent epileptic seizures and reduce seizure burden. Such treatments are particularly needed for pharmacoresistant epilepsies, which affect ~30% of patients. Neuroinflammation is commonly activated in epileptogenic brain regions in humans and is clearly involved in animal models of epilepsy. An increased understanding of neuroinflammatory mechanisms in epilepsy has identified cellular and molecular targets for new mechanistic therapies or existing anti-inflammatory drugs that could overcome the limitations of current medications, which provide only symptomatic control of seizures. Moreover, inflammatory mediators in the blood and molecular imaging of neuroinflammation could provide diagnostic, prognostic and predictive biomarkers for epilepsy, which will be instrumental for patient stratification in future clinical studies. In this Review, we focus on our understanding of the IL-1 receptor-Toll-like receptor 4 axis, the arachidonic acid-prostaglandin cascade, oxidative stress and transforming growth factor-β signalling associated with blood-brain barrier dysfunction, all of which are pathways that are activated in pharmacoresistant epilepsy in humans and that can be modulated in animal models to produce therapeutic effects on seizures, neuronal cell loss and neurological comorbidities.

Neuroinflammatory pathways as treatment targets and biomarkers in epilepsy.

Diverse brain insults, including traumatic brain injury, stroke, infections, tumors, neurodegenerative diseases, and prolonged acute symptomatic seizures, such as complex febrile seizures or status epilepticus (SE), can induce “epileptogenesis,” a process by which normal brain tissue is transformed into tissue capable of generating spontaneous recurrent seizures. Furthermore, epileptogenesis operates in cryptogenic causes of epilepsy. In view of the accumulating information about cellular and molecular mechanisms of epileptogenesis, it should be possible to intervene in this process before the onset of seizures and thereby either prevent the development of epilepsy in patients at risk or increase the potential for better long-term outcome, which constitutes a major clinical need. For identifying pharmacological interventions that prevent, interrupt or reverse the epileptogenic process in people at risk, two groups of animal models, kindling and SE-induced recurrent seizures, have been recommended as potentially useful tools. Furthermore, genetic rodent models of epileptogenesis are increasingly used in assessing antiepileptogenic treatments. Two approaches have been used in these different model categories: screening of clinically established antiepileptic drugs (AEDs) for antiepileptogenic or disease-modifying potential, and targeting the key causal mechanisms that underlie epileptogenesis. The first approach indicated that among various AEDs, topiramate, levetiracetam, carisbamate, and valproate may be the most promising. On the basis of these experimental findings, two ongoing clinical trials will address the antiepileptogenic potential of topiramate and levetiracetam in patients with traumatic brain injury, hopefully translating laboratory discoveries into successful therapies. The second approach has highlighted neurodegeneration, inflammation and up-regulation of immune responses, and neuronal hyperexcitability as potential targets for antiepileptogenesis or disease modification. This article reviews these areas of progress and discusses the challenges associated with discovery of antiepileptogenic therapies.

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Prevention or Modification of Epileptogenesis after Brain Insults: Experimental Approaches and Translational Research

Epilepsy is a chronic neurologic disorder that affects over 70 million people worldwide. Despite the availability of over 20 antiseizure drugs (ASDs) for symptomatic treatment of epileptic seizures, about one-third of patients with epilepsy have seizures refractory to pharmacotherapy. Patients with such drug-resistant epilepsy (DRE) have increased risks of premature death, injuries, psychosocial dysfunction, and a reduced quality of life, so development of more effective therapies is an urgent clinical need. However, the various types of epilepsy and seizures and the complex temporal patterns of refractoriness complicate the issue. Furthermore, the underlying mechanisms of DRE are not fully understood, though recent work has begun to shape our understanding more clearly. Experimental models of DRE offer opportunities to discover, characterize, and challenge putative mechanisms of drug resistance. Furthermore, such preclinical models are important in developing therapies that may overcome drug resistance. Here, we will review the current understanding of the molecular, genetic, and structural mechanisms of ASD resistance and discuss how to overcome this problem. Encouragingly, better elucidation of the pathophysiological mechanisms underpinning epilepsies and drug resistance by concerted preclinical and clinical efforts have recently enabled a revised approach to the development of more promising therapies, including numerous potential etiology-specific drugs ("precision medicine") for severe pediatric (monogenetic) epilepsies and novel multitargeted ASDs for acquired partial epilepsies, suggesting that the long hoped-for breakthrough in therapy for as-yet ASD-resistant patients is a feasible goal. SIGNIFICANCE STATEMENT: Drug resistance provides a major challenge in epilepsy management. Here, we will review the current understanding of the molecular, genetic, and structural mechanisms of drug resistance in epilepsy and discuss how the problem might be overcome.

https://pharmrev.aspetjournals.org/content/pharmrev/72/3/606.full.pdf

Drug Resistance in Epilepsy: Clinical Impact, Potential Mechanisms, and New Innovative Treatment Options.

https://link.springer.com/content/pdf/10.1007%2Fs13311-011-0039-z.pdf

Interleukin-1β Biosynthesis Inhibition Reduces Acute Seizures and Drug Resistant Chronic Epileptic Activity in Mice

http://users.zoominternet.net/~vfazio2/index_files/Ref7_Marchietal_33_pp171-181_2009.pdf

Antagonism of peripheral inflammation reduces the severity of status epilepticus

The blood–brain barrier (BBB) protects the brain from harmful substances in the bloodstream, while supplying the brain with the nutrients required for proper function. The endothelial cell cerebrovasculature lining also regulates brain penetration of drugs. Because of the presence of such complex and yet delicate mechanisms of vascular protection, pharmacologic targeting of central nervous system (CNS) pathologies was and remains a challenge. In general, it is assumed that breaching the BBB will improve CNS drug delivery (Kroll & Neuwelt, 1998), but altered BBB function associated with CNS pathologies such as epilepsy is also a characteristic of pharmacokinetic drug resistance (Oby & Janigro, 2006). Therefore, the interplay between BBB function or failure, and drug delivery is more complex than originally believed.

Is there a link between leakage of the BBB, seizure-epileptic pathology, and multiple drug resistance? Several evidences have shown BBB damage and profound remodeling of the cerebrovasculature during or immediately after seizures (Marchi et al., 2006, 2007b). This has been interpreted as a vascular consequence of spontaneous seizures. It has also been repeatedly shown that BBB leakage is sufficient to promote seizures (Oby & Janigro, 2006; Marchi et al., 2007a,b; Uva et al., 2007) or epileptogenesis (Seiffert et al., 2004; van Vliet et al., 2007). Whatever the temporal or causal relationship between BBB leakage and seizures, it is clear that the epileptic brain is characterized by an abnormal blood–brain interface.

The integrity of the BBB is clinically evaluated with magnetic resonance imaging (MRI) techniques. Although T1-contrast enhancement (Gd++) is a reliable imaging method for direct testing of BBB permeability, structural changes at a cellular level and changes of the distribution of water between the extra- and intracellular compartments can be assessed by diffusion-weighted imaging (DWI) and by calculating the extent of passive water motion or diffusivity (apparent diffusion coefficient, ADC). Periictal and postictal human studies using DWI or diffusion tensor imaging (DTI) showed, in some cases, transiently decreased local diffusivity, potentially in concordance with the epileptic zone (Vincent et al., 1995; Flink & Atchison, 2003; Lang & Vincent, 2003; Vernino, 2007). Diffusion studies have also demonstrated areas of significantly increased diffusivity in patients with partial epilepsies during the interictal period (Diehl et al., 1999, 2001; Hufnagel et al., 2003; Diehl et al., 2005). These results suggest that abnormal cerebrovascular and parenchymal homeostatic mechanisms are altered in epileptics.

In human epilepsy, overexpression of drug-resistance efflux proteins at the BBB has been studied extensively in the framework of antiepileptic drug (AED) refractoriness, but additional mechanisms have also been proposed (Loscher & Potschka, 2005; Oby & Janigro, 2006). Given that the pathology of drug-resistant epilepsy often reveals morphologic and functional abnormalities of the BBB, protein extravasation, and brain edema, it is reasonable to hypothesize that the physical–chemical properties of AEDs will differently predict CNS drug delivery to the epileptic focus. For example, most AEDs are highly lipid soluble and tightly protein bound, and their permeability across an intact BBB is controlled by parameters. It is possible that altered brain water content or protein extravasation combined with overexpression of drug transporters may affect the distribution of AEDs.

We have focused our study on the consequences of BBB damage on serum protein extravasation and brain water content. Because this was induced acutely and by iatrogenic means, the results may bear specific relevance for sudden episodes of BBB disruption (BBBD), as seen in traumatic brain injury (Schmidt & Grady, 1993; Korn et al., 2005; Tomkins et al., 2008). For this pilot study we used the hydrophilic radiolabel compounds 3H-deoxy-glucose (DOG) and 3H-sucrose (SUC) and the lipophilic AEDs 14C-phenytoin (PHT) and 14C-diazepam (DIA).

/pdf/blood-brain-barrier-damage-and-brain-penetration-of-1ov6308uz7.pdf

Blood-brain barrier damage and brain penetration of antiepileptic drugs: role of serum proteins and brain edema.

Ca2+-activated Cl− channels (CaCCs) are involved in several physiological processes. Recently, TMEM16A/anoctamin1 and TMEM16B/anoctamin2 have been shown to function as CaCCs, but very little information is available on the structure–function relations of these channels. TMEM16B is expressed in the cilia of olfactory sensory neurons, in microvilli of vomeronasal sensory neurons, and in the synaptic terminals of retinal photoreceptors. Here, we have performed the first site-directed mutagenesis study on TMEM16B to understand the molecular mechanisms of voltage and Ca2+ dependence. We have mutated amino acids in the first putative intracellular loop and measured the properties of the wild-type and mutant TMEM16B channels expressed in HEK 293T cells using the whole cell voltage-clamp technique in the presence of various intracellular Ca2+ concentrations. We mutated E367 into glutamine or deleted the five consecutive glutamates 386EEEEE390 and 399EYE401. The EYE deletion did not significantly modify the apparent Ca2+ dependence nor the voltage dependence of channel activation. E367Q and deletion of the five glutamates did not greatly affect the apparent Ca2+ affinity but modified the voltage dependence, shifting the conductance–voltage relations toward more positive voltages. These findings indicate that glutamates E367 and 386EEEEE390 in the first intracellular putative loop play an important role in the voltage dependence of TMEM16B, thus providing an initial structure–function study for this channel.

/pdf/the-voltage-dependence-of-the-tmem16b-anoctamin2-calcium-4d1flm6tyg.pdf

The voltage dependence of the TMEM16B/anoctamin2 calcium-activated chloride channel is modified by mutations in the first putative intracellular loop.

At least two members of the TMEM16/anoctamin family, TMEM16A (also known as anoctamin1) and TMEM16B (also known as anoctamin2), encode Ca2+-activated Cl− channels (CaCCs), which are found in various cell types and mediate numerous physiological functions. Here, we used whole-cell and excised inside-out patch-clamp to investigate the relationship between anion permeation and gating, two processes typically viewed as independent, in TMEM16B expressed in HEK 293T cells. The permeability ratio sequence determined by substituting Cl− with other anions (PX/PCl) was SCN− > I− > NO3− > Br− > Cl− > F− > gluconate. When external Cl− was substituted with other anions, TMEM16B activation and deactivation kinetics at 0.5 µM Ca2+ were modified according to the sequence of permeability ratios, with anions more permeant than Cl− slowing both activation and deactivation and anions less permeant than Cl− accelerating them. Moreover, replacement of external Cl− with gluconate, or sucrose, shifted the voltage dependence of steady-state activation (G-V relation) to more positive potentials, whereas substitution of extracellular or intracellular Cl− with SCN− shifted G-V to more negative potentials. Dose–response relationships for Ca2+ in the presence of different extracellular anions indicated that the apparent affinity for Ca2+ at +100 mV increased with increasing permeability ratio. The apparent affinity for Ca2+ in the presence of intracellular SCN− also increased compared with that in Cl−. Our results provide the first evidence that TMEM16B gating is modulated by permeant anions and provide the basis for future studies aimed at identifying the molecular determinants of TMEM16B ion selectivity and gating.

https://rupress.org/jgp/article-pdf/143/6/703/1231211/jgp_201411182.pdf

Giulia Betto

Papers

Antagonism of peripheral inflammation reduces the severity of status epilepticus

Blood-brain barrier damage and brain penetration of antiepileptic drugs: role of serum proteins and brain edema.

The voltage dependence of the TMEM16B/anoctamin2 calcium-activated chloride channel is modified by mutations in the first putative intracellular loop.

Interactions between permeation and gating in the TMEM16B/anoctamin2 calcium-activated chloride channel