Does leakage of the blood-brain barrier mediate epileptogenesis?

Blood-brain Barrier Damage is Pivotal for SARS-CoV-2 Infection to the Central Nervous System

Transsynaptic transport is the most accepted proposal to explain the SARS-CoV-2 infection of the CNS. Nevertheless, emerging evidence shows that neurons do not express the SARS-CoV-2 receptor ACE2, which highlights the importance of the blood-brain barrier (BBB) in preventing virus entry to the brain. In this study, we examine the presence of SARS-CoV-2 messenger ribonucleic acid (mRNA) and the cytokine profile in cerebrospinal fluids (CSF) from two patients with a brain tumor and COVID-19. To determine the BBB damage, we evaluate the Q- albumin index, which is an indirect parameter to assess the permeability of this structure. The Q-albumin index of the patient with an intraventricular brain tumor suggests that the BBB is undamaged, preventing the passage of SARS-CoV-2 and pro-inflammatory molecules. The development of brain tumors that disrupt the BBB (measured by the Q-albumin index), in this case, a petroclival meningioma (Case 1), allows the free passage of the SARS-CoV-2 virus and probably lets the free transit of pro-inflammatory molecules to the CNS, which leads to a possible activation of the microglia (astrogliosis) and an exacerbated immune response represented by IL-13, IFN-γ, and IL-2 trying to inhibit both the infection and the carcinogenic process.

tPA Modulation of the Blood-Brain Barrier: A Unifying Explanation for the Pleiotropic Effects of tPA in the CNS

The plasminogen activation (PA) system is best known for its role in fibrinolysis. However, it has also been shown to regulate many nonfibrinolytic functions in the central nervous system (CNS). In particular, tissue-type plasminogen activator (tPA) is reported to have pleiotropic activities in the CNS, regulating events such as neuronal plasticity, excitotoxicity, and cerebrovascular barrier integrity, whereas urokinase-type plasminogen activator is mainly associated with tissue remodeling and cell migration. It has been suggested that the role tPA plays in controlling barrier integrity may provide a unifying mechanism for the reported diverse, and often opposing, functions ascribed to tPA in the CNS. Here we will review the possibility that the pleiotropic effects reported for tPA in physiologic and pathologic processes in the CNS may be a consequence of its role in the neurovascular unit in regulation of cerebrovascular responses and subsequently parenchymal homeostasis. We propose that this might offer an explanation for the ongoing debate regarding the neurotoxic versus neuroprotective roles of tPA.

Identification of a neurovascular signaling pathway regulating seizures in mice

OBJECTIVE

A growing body of evidence suggests that increased blood-brain barrier (BBB) permeability can contribute to the development of seizures. The protease tissue plasminogen activator (tPA) has been shown to promote BBB permeability and susceptibility to seizures. In this study, we examined the pathway regulated by tPA in seizures.

METHODS

An experimental model of kainate-induced seizures was used in genetically modified mice, including mice deficient in tPA (tPA (-/-) ), its inhibitor neuroserpin (Nsp (-/-) ), or both (Nsp:tPA (-/-) ), and in mice conditionally deficient in the platelet-derived growth factor receptor alpha (PDGFRα).

RESULTS

Compared to wild-type (WT) mice, Nsp (-/-) mice have significantly reduced latency to seizure onset and generalization; whereas tPA (-/-) mice have the opposite phenotype, as do Nsp:tPA (-/-) mice. Furthermore, interventions that maintain BBB integrity delay seizure propagation, whereas osmotic disruption of the BBB in seizure-resistant tPA (-/-) mice dramatically reduces the time to seizure onset and accelerates seizure progression. The phenotypic differences in seizure progression between WT, tPA (-/-) , and Nsp (-/-) mice are also observed in electroencephalogram recordings in vivo, but absent in ex vivo electrophysiological recordings where regulation of the BBB is no longer necessary to maintain the extracellular environment. Finally, we demonstrate that these effects on seizure progression are mediated through signaling by PDGFRα on perivascular astrocytes.

INTERPRETATION

Together, these data identify a specific molecular pathway involving tPA-mediated PDGFRα signaling in perivascular astrocytes that regulates seizure progression through control of the BBB. Inhibition of PDGFRα signaling and maintenance of BBB integrity might therefore offer a novel clinical approach for managing seizures.

Real-time hemodynamic response and mitochondrial function changes with intracarotid mannitol injection

Disruption of blood brain barrier (BBB) is used to enhance chemotherapeutic drug delivery. The purpose of this study was to understand the time course of hemodynamic and metabolic response to intraarterial (IA) mannitol infusions in order to optimize the delivery of drugs for treating brain tumors.

PRINCIPAL RESULTS

We compared hemodynamic response, EEG changes, and mitochondrial function as judged by relative changes in tissue NADH concentrations, after intracarotid (IC) infusion of equal volumes of normal saline and mannitol in our rabbit IC drug delivery model. We observed significantly greater, though transient, hyperemic response to IC infusion of mannitol compared to normal saline. Infusion of mannitol also resulted in a greater increase in tissue NADH concentrations relative to the baseline. These hemodynamic, and metabolic changes returned to baseline within 5min of mannitol injection.

CONCLUSION

Significant, though transient, changes in blood flow and brain metabolism occur with IA mannitol infusion. The observed transient hyperemia would suggest that intravenous (IV) chemotherapy should be administered either just before, or concurrent with IA mannitol injections. On the other hand, IA chemotherapy should be delayed until the peak hyperemic response has subsided.

Brain-reactive antibodies and disease

Autoimmune diseases currently affect 5-7% of the world's population; in most diseases there are circulating autoantibodies. Brain-reactive antibodies are present in approximately 2-3% of the general population but do not usually contribute to brain pathology. These antibodies penetrate brain tissue only early in development or under pathologic conditions. This restriction on their pathogenicity and the lack of correlation between serum titers and brain pathology have, no doubt, contributed to a delayed appreciation of the contribution of autoantibodies in diseases of the central nervous system. Nonetheless, it is increasingly clear that antibodies can cause damage in the brain and likely initiate or aggravate multiple neurologic conditions; brain-reactive antibodies contribute to symptomatology in autoimmune disease, infectious disease, and malignancy.

A cell-free extract from human adipose stem cells protects mice against epilepsy

PURPOSE

Stem cell-based therapies are being considered for various neurologic diseases, such as epilepsy. Recent studies have suggested that some effects of transplanted stem cells are due to bystander effects that modulate the host environment, rather than direct effects of cell replacement. The extract from human adipose stem cells (ASCs) that secrete multiple growth factors including cytokines and chemokines may be a potential source of bystander effects for the treatment of epilepsy, in which inflammation is thought to play an important role. Here, we investigated the effects of a cytosolic extract of human ASCs (ASCs-E) in a mouse model of epilepsy.

METHODS

Human ASCs-E, boiled ASCs-E, or fibroblast-extract (fibroblast-E) was intraperitoneally administrated to C57BL/6 mice 15 min before pilocarpine-induced status epilepticus (SE) or during chronic epileptic stage. Blood-brain barrier (BBB) leakage was evaluated by measuring Evans blue dye extravasation. Spontaneous recurrent seizure (SRS) was investigated by long-term video-electroencephalography (EEG) monitoring. The mice performed elevated plus maze, open-field, light/dark transition, and novel object recognition tasks.

KEY FINDINGS

Acute application of human ASCs-E before SE led to earlier attenuation of seizure spike activities after treatment with diazepam, reduction of BBB leakage, and inhibition of the development of epilepsy. Human ASCs-E treatment (for 7 days) during the chronic epileptic stage suppressed SRS and reduced abnormal epileptic behavioral phenotypes. However, neither boiled ASCs-E nor fibroblast-E had any effects in the experimental epilepsy model.

SIGNIFICANCE

Our results demonstrate that human ASCs-E prevents or inhibits epileptogenesis and SRS in mice. They also suggest a stem cell-based, noninvasive therapy for the treatment of epilepsy.

Molecular cascades that mediate the influence of inflammation on epilepsy

Experimental evidence strongly indicates a significant role for inflammatory and immune mediators in initiation of seizures and epileptogenesis. Here we will summarize data supporting the involvement of IL-1β, TNF-α and toll-like receptor 4 in seizure generation and the process of epileptogenesis. The physiological homeostasis and control over brain immune response depends on the integrity of the blood-brain barrier, transforming growth factor (TGF)-β signaling and leukocyte migration. To what extent targeting the immune system is successful in preventing epileptogenesis, and which signaling pathway should be beleaguered is still under intensive research.

The emerging role for chemokines in epilepsy

Epilepsy has been considered mainly a neuronal disease, without much attention to non-neuronal cells. In recent years growing evidence suggest that astrocytes, microglia, blood leukocytes and blood-brain barrier breakdown are involved in the pathogenesis of epilepsy. In particular, leukocyte-endothelium interactions and eventually subsequent leukocyte recruitment in the brain parenchyma seem to represent key players in the epileptogenic cascade. Chemokines are chemotactic factors controlling leukocyte migration under physiological and pathological conditions. In the light of recent advances in our understanding of the role of inflammation mechanisms in the pathogenesis of epilepsy, pro-inflammatory chemokines may play a critical role in epileptogenesis.

Acute effects of calvarial damage on dural mast cells, pial vascular permeability, and cerebral cortical histamine levels in rats and mice

Neurological complications after mild head injury can include vasogenic edema and/or subsequent development of epilepsy, conditions associated with elevated histamine. In the present study we assessed the potential of mast cells located in the dura mater to contribute to elevated cortical histamine and breakdown of the blood-brain barrier after minor head injury, modeled by either a parietal craniectomy or producing a groove in (scoring) the parietal bone surface to model a grazing head injury. We measured the following effects at 5-20 min after a unilateral parietal craniectomy (rats) or unilateral scoring of the parietal bone (mice): (1) mast cell integrity in subjacent dura mater; (2) subjacent vs. contralateral histamine in dura mater and cerebral cortex; (3) vascular permeability of cerebral cortical blood vessels subjacent to the injury, and; (4) the effects of an H(2)-receptor antagonist on cerebral cortical vascular permeability.

RESULTS

Dural mast cells subjacent to the craniectomy became activated (degranulated) concomitant with (1) decreased histamine in dura mater subjacent to the craniectomy; (2) increased histamine in the subjacent cerebral cortex; and (3) extravasation of Evans blue-albumin which stained the subjacent cerebral cortex, indicating a localized breakdown of the blood-brain barrier. Similar results were observed in mice after scoring the parietal bone surface and, additionally, pretreatment with the histamine H(2)-receptor antagonist zolantadine (1 h before injury) dose-dependently inhibited extravasation of Evans blue-albumin. We conclude that even a minor grazing injury of the skull, in the absence of penetrating brain injury or concussion, can activate dural mast cells and elevate cortical histamine, a novel mechanism with potential contributions to neurotraumatic complications arising from a relatively minor or grazing head wound.