Systemic thrombin inhibition ameliorates seizures in a mouse model of pilocarpine-induced status epilepticus

Factor VII, EPCR, aPC Modulators: novel treatment for neuroinflammation

Background

Inflammation and coagulation are linked and pathogenic in neuroinflammatory diseases. Protease-activated receptor 1 (PAR1) can be activated both by thrombin, inducing increased inflammation, and activated protein C (aPC), inducing decreased inflammation. Modulation of the aPC-PAR1 pathway may prevent the neuroinflammation associated with PAR1 over-activation.

Methods

We synthesized a group of novel molecules based on the binding site of FVII/aPC to the endothelial protein C receptor (EPCR). These molecules modulate the FVII/aPC-EPCR pathway and are therefore named FEAMs—Factor VII, EPCR, aPC Modulators. We studied the molecular and behavioral effects of a selected FEAM in neuroinflammation models in-vitro and in-vivo.

Results

In a lipopolysaccharide (LPS) induced in-vitro model, neuroinflammation leads to increased thrombin activity compared to control (2.7 ± 0.11 and 2.23 ± 0.13 mU/ml, respectively, p = 0.01) and decreased aPC activity (0.57 ± 0.01 and 1.00 ± 0.02, respectively, p < 0.0001). In addition, increased phosphorylated extracellular regulated kinase (pERK) (0.99 ± 0.13, 1.39 ± 0.14, control and LPS, p < 0.04) and protein kinase B (pAKT) (1.00 ± 0.09, 2.83 ± 0.81, control and LPS, p < 0.0002) levels indicate PAR1 overactivation, which leads to increased tumor necrosis factor-alpha (TNF-α) level (1.00 ± 0.04, 1.35 ± 0.12, control and LPS, p = 0.02). In a minimal traumatic brain injury (mTBI) induced neuroinflammation in-vivo model in mice, increased thrombin activity, PAR1 activation, and TNF-α levels were measured. Additionally, significant memory impairment, as indicated by a lower recognition index in the Novel Object Recognition (NOR) test and Y-maze test (NOR: 0.19 ± 0.06, -0.07 ± 0.09, p = 0.03. Y-Maze: 0.50 ± 0.03, 0.23 ± 0.09, p = 0.02 control and mTBI, respectively), as well as hypersensitivity by hot-plate latency (16.6 ± 0.89, 12.8 ± 0.56 s, control and mTBI, p = 0.01), were seen. FEAM prevented most of the molecular and behavioral negative effects of neuroinflammation in-vitro and in-vivo, most likely through EPCR-PAR1 interactions.

Conclusion

FEAM is a promising tool to study neuroinflammation and a potential treatment for a variety of neuroinflammatory diseases.

Modulation of the Thrombin Pathway Restores LTP in a Pilocarpine Mice Model of Status Epilepticus

Background

Status epilepticus (SE) leads to memory impairment following a seizure, attributed to long-term potentiation (LTP) reduction. Thrombin, a coagulation factor that activates protease-activated receptor 1 (PAR1) is involved in cognitive impairment following traumatic brain injury by reducing hippocampal LTP and in seizures as seen in a SE pilocarpine-induced mice model. Thrombin pathway inhibition prevents this cognitive impairment. We evaluated the effect of thrombin pathway inhibition in the pilocarpine-induced SE mice model, on LTP, hippocampal, and serum markers for inflammation, the PAR1 pathway, and neuronal cell damage.

Methods

SE was induced by injecting C57BL/6J mice with pilocarpine. Before pilocarpine injection, mice were injected with either the specific thrombin inhibitor α-NAPAP [Nα-(2-naphthalene-sulfonylglycyl)-4-amidino-DL-phenylalaninepiperidide], the PAR1 antagonist SCH79797, or vehicle-only solution. Recordings of excitatory postsynaptic potentials (EPSP) were conducted from hippocampal slices 24 h following pilocarpine injection. Hippocampal real-time PCR for the quantification of the PAR1, prothrombin, and tumor necrosis factor α (TNF-α) mRNA expression levels was conducted. Serum levels of neurofilament light chain (NfL) and TNF-α were measured by a single molecule array assay.

Results

The EPSP was reduced in the pilocarpine-induced SE mice (p < 0.001). This reduction was prevented by both NAPAP and SCH79797 treatments (p < 0.001 for both treatments). Hippocampal expression of TNF-α was elevated in the pilocarpine-induced SE group compared to the control (p < 0.01), however, serum levels of TNF-α were not changed. NfL levels were elevated in the pilocarpine-induced SE group (p = 0.04) but not in the treated groups.

Conclusions

Pilocarpine-induced SE reduces LTP, in a thrombin PAR1-related mechanism. Elevation of serum NfL supports neuronal damage accompanying this functional abnormality which may be prevented by PAR1 pathway modulation.

Technology-based approaches toward a better understanding of neuro-coagulation in brain homeostasis

Blood coagulation factors can enter the brain under pathological conditions that affect the blood-brain interface. Besides their contribution to pathological brain states, such as neural hyperexcitability, neurodegeneration, and scar formation, coagulation factors have been linked to several physiological brain functions. It is for example well established that the coagulation factor thrombin modulates synaptic plasticity; it affects neural excitability and induces epileptic seizures via activation of protease-activated receptors in the brain. However, major limitations of current experimental and clinical approaches have prevented us from obtaining a profound mechanistic understanding of "neuro-coagulation" in health and disease. Here, we present how novel human relevant models, i.e., Organ-on-Chips equipped with advanced sensors, can help overcoming some of the limitations in the field, thus providing a perspective toward a better understanding of neuro-coagulation in brain homeostasis.

Neurocoagulation from a Mechanistic Point of View in the Central Nervous System

Coagulation mechanisms are critical for maintaining homeostasis in the central nervous system (CNS). Thrombin, an important player of the coagulation cascade, activates protease activator receptors (PARs), members of the G-protein coupled receptor family. PAR1 is located on neurons and glia. Following thrombin activation, PAR1 signals through the extracellular signal-regulated kinase pathway, causing alterations in neuronal glutamate release and astrocytic morphological changes. Similarly, the anticoagulation factor activated protein C (aPC) can cleave PAR1, following interaction with the endothelial protein C receptor. Both thrombin and aPC are expressed on endothelial cells and pericytes in the blood-brain barrier (BBB). Thrombin-induced PAR1 activation increases cytosolic Ca²⁺ concentration in brain vessels, resulting in nitric oxide release and increasing F-actin stress fibers, damaging BBB integrity. aPC also induces PAR1 activation and preserves BBB vascular integrity via coupling to sphingosine 1 phosphate receptors. Thrombin-induced PAR1 overactivation and BBB disruption are evident in CNS pathologies. During epileptic seizures, BBB disruption promotes thrombin penetration. Thrombin induces PAR1 activation and potentiates N-methyl-D-aspartate receptors, inducing glutamate-mediated hyperexcitability. Specific PAR1 inhibition decreases status epilepticus severity in vivo. In stroke, the elevation of brain thrombin levels further compromises BBB integrity, with direct parenchymal damage, while systemic factor Xa inhibition improves neurological outcomes. In multiple sclerosis (MS), brain thrombin inhibitory capacity correlates with clinical presentation. Both thrombin inhibition by hirudin and the use of recombinant aPC improve disease severity in an MS animal model. This review presents the mechanisms underlying the effects of coagulation on the physiology and pathophysiology of the CNS.

Role of Thrombin in Central Nervous System Injury and Disease

Thrombin is a Na+-activated allosteric serine protease of the chymotrypsin family involved in coagulation, inflammation, cell protection, and apoptosis. Increasingly, the role of thrombin in the brain has been explored. Low concentrations of thrombin are neuroprotective, while high concentrations exert pathological effects. However, greater attention regarding the involvement of thrombin in normal and pathological processes in the central nervous system is warranted. In this review, we explore the mechanisms of thrombin action, localization, and functions in the central nervous system and describe the involvement of thrombin in stroke and intracerebral hemorrhage, neurodegenerative diseases, epilepsy, traumatic brain injury, and primary central nervous system tumors. We aim to comprehensively characterize the role of thrombin in neurological disease and injury.