Inhibitory actions of the gamma-aminobutyric acid in pediatric Sturge-Weber syndrome

Reappraisal of anoxic spreading depolarization as a terminal event during oxygen-glucose deprivation in brain slices in vitro

Anoxic spreading depolarization (aSD) has been hypothesized as a terminal event during oxygen–glucose deprivation (OGD) in submerged cortical slices in vitro. However, mechanical artifacts caused by aSD-triggered edema may introduce error in the assessment of neuronal viability. Here, using continuous patch-clamp recordings from submerged rat cortical slices, we first confirmed that vast majority of L4 neurons permanently lost their membrane potential during OGD-induced aSD. In some recordings, spontaneous transition from whole-cell to out-side out configuration occurred during or after aSD, and only a small fraction of neurons survived aSD with reperfusion started shortly after aSD. Secondly, to minimize artifacts caused by OGD-induced edema, cells were short-term patched following OGD episodes of various duration. Nearly half of L4 cells maintained membrane potential and showed the ability to spike-fire if reperfusion started less than 10 min after aSD. The probability of finding live neurons progressively decreased at longer reperfusion delays at a rate of about 2% per minute. We also found that neurons in L2/3 show nearly threefold higher resistance to OGD than neurons in L4. Our results suggest that in the OGD ischemia model, aSD is not a terminal event, and that the “commitment point” of irreversible damage occurs at variable delays, in the range of tens of minutes, after OGD-induced aSD in submerged cortical slices.

Sturge-Weber syndrome: an update on the relevant issues for neurosurgeons

PURPOSE

Sturge-Weber syndrome (SWS) is a neurocutaneous facomatosis characterized by facial and leptomeningeal angioma, glaucoma, seizures, and neurological disability. Therefore, a challenging multidisciplinary interaction is required for its management. The goal of this paper is to review the main aspects of SWS and to present an illustrative pediatric series.

METHODS

The pertinent literature has been analyzed, focused mainly on etiopathogenesis, pathology, clinical features, diagnostic tools, management, and outcome of the disease. Moreover, a series of 11 children operated on for refractory epilepsy between 2005 and 2015 (minimum follow-up 5 years, mean follow-up 9.6 years) is reported. The series consists of six boys and five girls with 6.5-month and 16.2-month mean age at seizure onset and at surgery, respectively. Seizures affected all children, followed by hemiparesis and psychomotor delay (81%), glaucoma (54%), and other neurological deficits (45%).

RESULTS

All children underwent hemispherectomy (anatomical in three cases, functional in two cases, hemispherotomy in six cases); one patient needed a redo hemispherotomy. Mortality was nil; disseminated intravascular coagulation and interstitial pneumonia occurred in one patient each; three children had subdural fluid collection. Eight patients (72%) are in the ILAE Class 1 (completely seizure and aura free), two in Class 2 (only auras, no seizure), and one in Class 3 (1-3 seizure days per year). AEDs discontinuation was possible in 73% of cases. The most important news from the literature concerned the pathogenesis (role of the mutation of the GNAQ gene in the abnormal SWS vasculogenesis), the clinical findings (the features and pathogenesis of the stroke-like episodes are being understood), the diagnostic tools (quantitative MRI and EEG), and both the medical (migraine, seizures) and surgical management (epilepsy). The epileptic outcome of SWS patients is very good (80% are seizure-free), if compared with other hemispheric syndromes. The quality of life is affected by the neurological and cognitive deficits.

CONCLUSIONS

SWS still is an etiological and clinical challenge. However, the improvements over the time are consistent. In particular, the neurosurgical treatment of refractory epilepsy provides very good results as long as the indication to treatment is correct.

Off-Label Use of Bumetanide for Brain Disorders: An Overview

Bumetanide (BTN or BUM) is a FDA-approved potent loop diuretic (LD) that acts by antagonizing sodium-potassium-chloride (Na-K-Cl) cotransporters, NKCC1 (SLc12a2) and NKCC2. While NKCC1 is expressed both in the CNS and in systemic organs, NKCC2 is kidney-specific. The off-label use of BTN to modulate neuronal transmembrane Cl⁻ gradients by blocking NKCC1 in the CNS has now been tested as an anti-seizure agent and as an intervention for neurological disorders in pre-clinical studies with varying results. BTN safety and efficacy for its off-label use has also been tested in several clinical trials for neonates, children, adolescents, and adults. It failed to meet efficacy criteria for hypoxic-ischemic encephalopathy (HIE) neonatal seizures. In contrast, positive outcomes in temporal lobe epilepsy (TLE), autism, and schizophrenia trials have been attributed to BTN in studies evaluating its off-label use. NKCC1 is an electroneutral neuronal Cl⁻ importer and the dominance of NKCC1 function has been proposed as the common pathology for HIE seizures, TLE, autism, and schizophrenia. Therefore, the use of BTN to antagonize neuronal NKCC1 with the goal to lower internal Cl⁻ levels and promote GABAergic mediated hyperpolarization has been proposed. In this review, we summarize the data and results for pre-clinical and clinical studies that have tested off-label BTN interventions and report variable outcomes. We also compare the data underlying the developmental expression profile of NKCC1 and KCC2, highlight the limitations of BTN’s brain-availability and consider its actions on non-neuronal cells.

Why Malformations of Cortical Development Cause Epilepsy

Malformations of cortical development (MCDs), a complex family of rare disorders, result from alterations of one or combined developmental steps, including progenitors proliferation, neuronal migration and differentiation. They are an important cause of childhood epilepsy and frequently associate cognitive deficits and behavioral alterations. Though the physiopathological mechanisms of epilepsy in MCD patients remain poorly elucidated, research during the past decade highlighted the contribution of some factors that will be reviewed in this paper and that include: (i) the genes that caused the malformation, that can be responsible for a significant reduction of inhibitory cells (e.g., ARX gene) or be inducing cell-autonomous epileptogenic changes in affected neurons (e.g., mutations on the mTOR pathway); (ii) the alteration of cortical networks development induced by the malformation that will also involve adjacent or distal cortical areas apparently sane so that the epileptogenic focus might be more extended that the malformation or even localized at distance from it; (iii) the normal developmental processes that would influence and determine the onset of epilepsy in MCD patients, particularly precocious in most of the cases.

NMDA Receptors as Voltage Sensors

The membrane potential is an essential parameter of a living cell. However, measurements of the membrane potential using conventional techniques are associated with a number of artifacts. Cell-attached recordings of the currents through NMDA receptor channels enable noninvasive measurements of the neuronal membrane potential. This approach overcomes the problem of a leak conductance introduced during intracellular sharp electrode recordings and whole-cell patch-clamp recordings. Here, we describe the procedures of using cell-attached recordings of NMDA receptor channels to measure the true membrane potential.

Potential biological targets for bioassay development in drug discovery of Sturge-Weber syndrome

Sturge-Weber Syndrome (SWS) is a neurocutaneous disease with clinical manifestations including ocular (glaucoma), cutaneous (port-wine birthmark), neurologic (seizures), and vascular problems. Molecular mechanisms of SWS pathogenesis are initiated by the somatic mutation in GNAQ. Therefore, no definite treatments exist for SWS and treatment options only mitigate the intensity of its clinical manifestations. Biological assay design for drug discovery against this syndrome demands comprehensive knowledge on mechanisms which are involved in its pathogenesis. By analysis of the interrelated molecular targets of SWS, some in vitro bioassay systems can be allotted for drug screening against its progression. Development of such platforms of bioassay can bring along the implementation of high-throughput screening of natural or synthetic compounds in drug discovery programs. Regarding the fact that study of molecular targets and their integration in biological assay design can facilitate the process of effective drug discovery; some potential biological targets and their respective biological assay for SWS drug discovery are propounded in this review. For this purpose, some biological targets for SWS drug discovery such as acetylcholinesterase, alkaline phosphatase, GABAergic receptors, Hypoxia-Inducible Factor (HIF)-1α and 2α are suggested.

NKCC1 Chloride Importer Antagonists Attenuate Many Neurological and Psychiatric Disorders

In physiological conditions, adult neurons have low intracellular Cl^- [(Cl^-)_I] levels underlying the γ-aminobutyric acid (GABA)ergic inhibitory drive. In contrast, neurons have high (Cl^-)_I levels and excitatory GABA actions in a wide range of pathological conditions including spinal cord lesions, chronic pain, brain trauma, cerebrovascular infarcts, autism, Rett and Down syndrome, various types of epilepsies, and other genetic or environmental insults. The diuretic highly specific NKCC1 chloride importer antagonist bumetanide (PubChem CID: 2461) efficiently restores low (Cl^-)_I levels and attenuates many disorders in experimental conditions and in some clinical trials. Here, I review the mechanisms of action, therapeutic effects, promises, and pitfalls of bumetanide.

Failure of the Nemo Trial: Bumetanide Is a Promising Agent to Treat Many Brain Disorders but Not Newborn Seizures

The diuretic bumetanide failed to treat acute seizures due to hypoxic ischemic encephalopathy (HIE) in newborn babies and was associated with hearing loss (NEMO trial, Pressler et al., 2015). On the other hand, clinical and experimental observations suggest that the diuretic might provide novel therapy for many brain disorders including Autism Spectrum Disorders (ASD), schizophrenia, Rett syndrome, and Parkinson disease. Here, we discuss the differences between the pathophysiology of severe recurrent seizures in the neonates and neurological and psychiatric disorders stressing the uniqueness of severe seizures in newborn in comparison to other disorders.

Imaging increased glutamate in children with Sturge-Weber syndrome: Association with epilepsy severity

BACKGROUND

Sturge-Weber syndrome (SWS) is strongly associated with epilepsy. Brain tissue studies have suggested that epileptic activity in SWS is driven by glutamatergic synaptic activity. Here, we used proton magnetic resonance spectroscopic imaging (MRSI) to test if glutamate (GLU) concentrations are increased in the affected hemisphere and if such increases are associated with severity of epilepsy in children with SWS. We also studied the metabolic correlates of MRSI abnormalities, using glucose positron emission tomography (PET) imaging.

METHODS

3T MRI and glucose PET were performed in 10 children (age: 7-78 months) with unilateral SWS and a history of epilepsy. MRSI data were acquired from the affected (ipsilateral) and non-affected (contralateral) hemispheres. GLU, N-acetyl-aspartate (NAA) and creatine (Cr) were quantified in multiple voxels; GLU/Cr and NAA/Cr ratios were calculated and compared to seizure frequency as well as glucose PET findings.

RESULTS

The highest GLU/Cr ratios were found in the affected hemisphere in all children except one with severe atrophy. The maximum ipsilateral/contralateral GLU/Cr ratios ranged between 1.0 and 2.5 (mean: 1.6). Mean ipsilateral/contralateral GLU/Cr ratios were highest in the youngest children and showed a strong positive correlation with clinical seizure frequency scores assessed at the time of the scan (r=0.88, p=0.001) and also at follow-up (up to 1 year, r=0.80, p=0.009). GLU increases in the affected hemisphere coincided with areas showing current or previous increases of glucose metabolism on PET in 5 children. NAA/Cr ratios showed no association with clinical seizure frequency.

CONCLUSIONS

Increased glutamate concentrations in the affected hemisphere, measured by MRSI, are common in young children with unilateral SWS and are associated with frequent seizures. The findings lend support to the role of excess glutamate in SWS-associated epilepsy.

Depolarizing GABA and developmental epilepsies

Early in development, GABA, which is the main inhibitory neurotransmitter in adult brain, depolarizes immature neurons and exerts dual--excitatory and shunting/inhibitory--effects in the developing neuronal networks. The present review discusses some general questions, including the properties of excitation at depolarizing GABAergic synapse and shunting inhibition by depolarizing GABA; technical issues in exploration of depolarizing GABA using various techniques and preparations, including the developmental aspects of traumatic injury and what is known (or rather unknown) on the actions of GABA in vivo; complex roles of depolarizing GABA in developmental epilepsies, including a contribution of depolarizing GABA to enhanced excitability in the immature networks, caused by repetitive seizures accumulation of intracellular chloride concentration that increases excitatory GABA power and its synchronizing proconvulsive effects, and correction of chloride homeostasis as a potential strategy to treat neonatal seizures.

The developing cortex

Cortical maturation is associated with a series of developmental programs encompassing neuronal and network-driven patterns. Thus, voltage-gated and synapse-driven ionic currents are very different in immature and adult neurons with slower kinetics in the former than in the latter. These features are neuron and developmental stage dependent. GABA, which is the main inhibitory neurotransmitter in adult brain, depolarizes and excites immature neurons and its actions are thought to exert a trophic role in developmental processes. Networks follow a parallel sequence with voltage-gated calcium currents followed by calcium plateaux and synapse-driven patterns in vitro. In vivo, early activity exhibits discontinuous temporal organization with alternating bursts. Early cortical patterns are driven by sensory input from the periphery providing a basis for activity-dependent modulation of the cortical networks formation. These features and notably the excitatory GABA underlie the high susceptibility of immature neurons to seizures. Alterations of these sequences play a central role in developmental malformations, notably migration disorders and associated neurological sequelae.

Sturge-Weber syndrome

Sturge-Weber syndrome (SWS) is a rare sporadic neurocutaneous syndrome defined by the association of a facial capillary malformation in the ophthalmic distribution of the trigeminal nerve, with ipsilateral vascular glaucoma and vascular malformation of the eye, and a leptomeningeal angioma. SWS is suspected at birth in the presence of facial angioma in the trigeminal nerve area. MRI with gadolinium enhancement and pondered T1, T2, FLAIR and diffusion sequences is today the technique of choice to visualize the leptomeningeal angioma or to suspect it by indirect signs, even before the development of neurological signs, from the first months of life. The prognosis of SWS with leptomeningeal angioma is related to the severity of neurological signs that are absent at birth and develop later in life (epilepsy, hemiparesis, and mental delay). Seizures are usually the presenting neurological symptom. Status epilepticus might inaugurate the epilepsy and remains frequent in infancy. Repetitive seizures are thought to increase the atrophy of brain tissue in regard to the leptomeningeal angioma. Preventive presymptomatic treatment with antiepileptic drugs is often recommended, and parents are trained to use rescue benzodiazepines in case of seizures. After epilepsy onset, in patients intractable to antiepileptic drugs, surgery should be considered.

Excitatory action of GABA on immature neurons is not due to absence of ketone bodies metabolites or other energy substrates

Brain slices incubated with glucose have provided most of our knowledge on cellular, synaptic, and network driven mechanisms. It has been recently suggested that γ-aminobutyric acid (GABA) excites neonatal neurons in conventional glucose-perfused slices but not when ketone bodies metabolites, pyruvate, and/or lactate are added, suggesting that the excitatory actions of GABA are due to energy deprivation when glucose is the sole energy source. In this article, we review the vast number of studies that show that slices are not energy deprived in glucose-containing medium, and that addition of other energy substrates at physiologic concentrations does not alter the excitatory actions of GABA on neonatal neurons. In contrast, lactate, like other weak acids, can produce an intracellular acidification that will cause a reduction of intracellular chloride and a shift of GABA actions. The effects of high concentrations of lactate, and particularly of pyruvate (4-5 mm), as used are relevant primarily to pathologic conditions; these concentrations not being found in the brain in normal "control" conditions. Slices in glucose-containing medium may not be ideal, but additional energy substrates neither correspond to physiologic conditions nor alter GABA actions. In keeping with extensive observations in a wide range of animal species and brain structures, GABA depolarizes immature neurons and the reduction of the intracellular concentration of chloride ([Cl(-)](i)) is a basic property of brain maturation that has been preserved throughout evolution. In addition, this developmental sequence has important clinical implications, notably concerning the higher incidence of seizures early in life and their long-lasting deleterious sequels. Immature neurons have difficulties exporting chloride that accumulates during seizures, leading to permanent increase of [Cl(-)](i) that converts the inhibitory actions of GABA to excitatory and hampers the efficacy of GABA-acting antiepileptic drugs.

Transient focal cortical increase of interictal glucose metabolism in Sturge-Weber syndrome: implications for epileptogenesis

PURPOSE

To investigate clinical correlates and longitudinal course of interictal focal cortical glucose hypermetabolism in children with Sturge-Weber syndrome (SWS).

METHODS

Fluorodeoxyglucose positron emission tomography (FDG-PET) scans of 60 children (age range 3 months to 15.2 years) with Sturge-Weber syndrome and epilepsy were assessed prospectively and serially for focal hypo- or hypermetabolism. Thirty-two patients had two or more consecutive PET scans. Age, seizure variables, and the occurrence of epilepsy surgery were compared between patients with and without focal hypermetabolism. The severity of focal hypermetabolism was also assessed and correlated with seizure variables.

KEY FINDINGS

Interictal cortical glucose hypermetabolism, ipsilateral to the angioma, was seen in nine patients, with the most common location in the frontal lobe. Age was lower in patients with hypermetabolism than in those without (p=0.022). In addition, time difference between the onset of first seizure and the first PET scan was much shorter in children with increased glucose metabolism than in those without (mean: 1.0 vs. 3.6 years; p=0.019). Increased metabolism was transient and switched to hypometabolism in all five children where follow-up scans were available. Focal glucose hypermetabolism occurred in 28% of children younger than the age of 2 years. Children with transient hypermetabolism had a higher rate of subsequent epilepsy surgery as compared to those without hypermetabolism (p=0.039).

SIGNIFICANCE

Interictal glucose hypermetabolism in young children with SWS is most often seen within a short time before or after the onset of first clinical seizures, that is, the presumed period of epileptogenesis. Increased glucose metabolism detected by PET predicts future demise of the affected cortex based on a progressive loss of metabolism and may be an imaging marker of the most malignant cases of intractable epilepsy requiring surgery in SWS.

Antiepileptic effects of endogenous beta-hydroxybutyrate in suckling infant rats

Physiological ketosis is a hallmark of metabolism in suckling infants. However, little is known on the impact of physiological ketosis on brain excitability. We addressed this question in suckling rats in vivo. 16-channel extracellular field potential recordings were performed from somatosensory barrel cortex at postnatal days 5-9 non-anaesthetized rat pups. Seizures were induced by the volatile convulsant agent flurothyl. One hour after blockade of physiological ketogenesis using combined administration of beta-oxidation inhibitors mercaptoacetate, insulin and glucose to prevent hypoglycemia, we found no significant change in the flurothyl-induced electrographic seizures. However, build-up of seizures during two repetitive flurothyl applications was strongly aggravated in the animals with blocked ketogenesis. The effect of ketogenesis inhibitors was reversed by exogenous beta-hydroxybutyrate. Diazepam exerted anticonvulsive action both under physiological ketosis and after blockade of ketogenesis, and bumetanide had no significant anticonvulsive effects in both conditions. Thus, physiological ketosis reduces excitability in the immature brain and elimination of physiological ketosis results in elimination of this anticonvulsant effect. Our study raises concern that the changes in diet, and pharmacological manipulations such as glucose infusion, and pathologies such as hyperinsulinism which break natural ketosis, may be a potential risk factor for epileptogenesis in nursing infants.

Neuronal chloride accumulation and excitatory GABA underlie aggravation of neonatal epileptiform activities by phenobarbital

Phenobarbital produces its anti-epileptic actions by increasing the inhibitory drive of γ-aminobutyric acid. However, following recurrent seizures, γ-aminobutyric acid excites neurons because of a persistent increase of chloride raising the important issue of whether phenobarbital could aggravate persistent seizures. Here we compared the actions of phenobarbital on initial and established ictal-like events in an in vitro model of mirror focus. Using the in vitro three-compartment chamber preparation with the two hippocampi and their commissural fibres placed in three different chambers, kainate was applied to one hippocampus and phenobarbital contralaterally, either after one ictal-like event or after many recurrent ictal-like events that produce an epileptogenic mirror focus. Field, perforated patch and single-channel recordings were used to determine the effects of γ-aminobutyric acid and their modulation by phenobarbital, and alterations of the chloride cotransporters were investigated using sodium-potassium-chloride cotransporter 1 and potassium chloride cotransporter 2 antagonists, potassium chloride cotransporter 2 immunocytochemistry and sodium-potassium-chloride cotransporter 1 knockouts. Phenobarbital reduced initial ictal-like events and prevented the formation of a mirror focus when applied from the start. In contrast, phenobarbital aggravated epileptiform activities when applied after many ictal-like events by enhancing the excitatory actions of γ-aminobutyric acid due to increased chloride. The accumulation of chloride and the excitatory actions of γ-aminobutyric acid in mirror foci neurons are mediated by the sodium-potassium-chloride cotransporter 1 chloride importer and by downregulation and internalization of the chloride-exporter potassium-chloride cotransporter 2. Finally, concomitant applications of the sodium-potassium-chloride cotransporter 1 antagonist bumetanide and phenobarbital decreased excitatory actions of γ-aminobutyric acid and prevented its paradoxical actions on mirror focus. Therefore, the history of seizures prior to phenobarbital applications determines its effects and rapid treatment of severe potentially epileptogenic-neonatal seizures is recommended to prevent secondary epileptogenesis associated with potassium chloride cotransporter 2 downregulation and acquisition of the excitatory γ-aminobutyric acid phenotype.