Kainic acid–induced albumin leak across the blood–brain barrier facilitates epileptiform hyperexcitability in limbic regions

Abstract

Dr. Francesco M. No e is a researcher with experience in EEG and animal models of epilepsy. SUMMARYObjective: Systemic administration of kainic acid (KA) is a widely used procedure utilized to develop a model of temporal lobe epilepsy (TLE). Despite its ability to induce status epilepticus (SE) in vivo, KA applied to in vitro preparations induces only interictal-like activity and/or isolated ictal discharges. The possibility that extravasation of the serum protein albumin from the vascular compartment enhances KA-induced brain excitability is investigated here. Methods: Epileptiform activity was induced by arterial perfusion of 6 lM KA in the in vitro isolated guinea pig brain preparation. Simultaneous field potential recordings were carried out bilaterally from limbic (CA1, dentate gyrus [DG], and entorhinal cortex) and extralimbic regions (piriform cortex and neocortex). Blood-brain barrier (BBB) breakdown associated with KA-induced epileptiform activity was assessed by parenchymal leakage of intravascular fluorescein-isothiocyanate albumin. Seizureinduced brain inflammation was evaluated by western blot analysis of interleukin (IL)-1b expression in brain tissue. Results: KA infusion caused synchronized activity at 15-30 Hz in limbic (but not extralimbic) cortical areas, associated with a brief, single seizure-like event. A second bolus of KA, 60 min after the induction of the first ictal event, did not further enhance excitability. Perfusion of serum albumin between the two administrations of KA enhanced epileptiform discharges and allowed a recurrent ictal event during the second KA infusion. Significance: Our data show that arterial KA administration selectively alters the synchronization of limbic networks. However, KA is not sufficient to generate recurrent seizures unless serum albumin is co-perfused during KA administration. These findings suggest a role of serum albumin in facilitating acute seizure generation. KEY WORDS: In vitro guinea pig brain preparation, Status epilepticus, Beta-gamma activity, Neuronal network synchronization, IL-1 beta.Pathologic features mimicking mesial temporal lobe epilepsy (mTLE) can be reproduced in experimental animals by systemic and intracerebral application of kainic acid (KA).1 Intrahippocampal administration of KA at high doses (≥5 mM) is effective in inducing convulsive 2 and nonconvulsive 3 status epilepticus (SE), eventually followed by recurrent spontaneous limbic seizures, between 5 days and 1 month after SE. 3,4 In this in vivo model of TLE, altered patterns of rhythmic activity in the gamma frequency range (30-80 Hz) occur during the acute SE and before the onset

Peripheral blood mononuclear cell activation sustains seizure activity

“…15,31 Furthermore, serum albumin uptake by astrocytes through the transforming growth factor β receptors (TGF-β Rs), has been linked to a rapid downregulation of astrocytic K + -inward-rectifying (K IR ) channels, resulting in a reduced buffering and subsequent accumulation of potassium in the extracellular space and in an increased brain excitability. 32 In our experimental conditions, 15 hALB is perfused at 4 mg/mL, which falls within the range associated with BBB damage occurring in a pathology associated condition. 33 Co-perfusion of LPS, hALB, and na-PBMCs (and autologous resting guinea pig splenocytes) never generated SLEs or microgliosis.…”

“…As mentioned previously, BBB permeability leads to the extravasation into the brain parenchyma of serum proteins and immune cells, triggering inflammation and ictogenesis. Serum albumin extravasation, due to its negative charge, alters the neuronal membrane charge, contributing to an acute increase in neuronal excitability 30 and, at the same time, is able to disrupt the neuronal and glial membrane homeostasis 15,31 . Furthermore, serum albumin uptake by astrocytes through the transforming growth factor β receptors (TGF‐β Rs), has been linked to a rapid downregulation of astrocytic K + ‐inward‐rectifying (K IR ) channels, resulting in a reduced buffering and subsequent accumulation of potassium in the extracellular space and in an increased brain excitability 32 .…”

“…Brains were isolated from young adult (3/4 weeks old) Hartley guinea‐pigs ( n = 35; 150–200 g; Charles River Laboratories) according to the standard technique described elsewhere 12 . Human recombinant albumin (hALB; Sigma‐Aldrich, 4 gr/L) and the endotoxin lipopolysaccharide (LPS; Sigma Aldrich, 100 ng/ml), were applied by arterial perfusion 14,15 …”

“…The morphologic and functional integrity of the BBB in the in vitro isolated guinea pig brain preparation has been demonstrated. 13,15 We assessed the presence of BBB breakdown by perfusing fluorescein-iso-thio-cyanate (FITC)-albumin (Sigma-Aldrich, 50 mg/10 ml) for 4 minutes immediately before the brains were fixed after the electrophysiological experiment for histologic analysis of FITC-albumin extravasation (at least n = 3 for each protocol).…”

Macrophage stimulating protein preserves blood brain barrier integrity after intracerebral hemorrhage through recepteur d'origine nantais dependent GAB1/Src/β‐catenin pathway activation in a mouse model

“…A large number of studies have confirmed that BBB is an important barrier to the central nervous system (CNS) (Friedman & Kaufer 2015). In epilepsy (Noe et al . 2016), Alzheimer’s disease (Lecler et al .…”