Inflammation as Treatment Target for Status Epilepticus

Abstract

Background

Status epilepticus (SE) is a serious neurological disease that manifests as prolonged seizures that last more than 5 minutes and between such episodes, patients do not regain consciousness. It can result in cognitive defects, brain damage, or even death. It is commonly known that one of the causes can be an inflammatory process, but here we will focus on inflammation as a result of new onset refractory status epilepticus and, related to this, new promising forms of SE treatment. Particular emphasis has been focused on new-onset refractory status epilepticus (NORSE).

Methods

Based on public research databases, drugs with anti-inflammatory activity – commonly used in different spheres of medicine – have been reviewed as potentially treating status epilepticus.

Results

There is seizable clinical research suggesting that drugs that decrease inflammatory processes might be effective in terminating status epilepticus.

Conclusion

There is growing evidence showing that adding anti-inflammatory drugs to basic antiepileptic treatment enhances the efficiency of the therapeutic process, with special potential in NORSE cases.

1. INTRODUCTION

1.1. Definition and Epidemiology

Status epilepticus (SE) is a life-threatening neurological condition defined as prolonged seizures which last at least 5 minutes and are followed by a lack of consciousness recovery between episodes. Accordingly, it increases the risk of dangerous ramifications such as cognitive defects and neuro infection and is associated with increased mortality. Furthermore, in around 40% [1] of patients, it may lead to drug refractory SE, which cannot be aborted by antiepileptic drugs (AED), even if used in maximal doses.

SE is considered a major neurological mortal condition, such as cerebrovascular disease [2]. Significantly, the highest incident rate occurs in pediatric patients (especially during the first 12 months of life) and elderly people (above 60 years old), creating a “U-shaped” curve [2, 3]. Also, those who developed SE more often were males [4-6].

Population-based research indicates that status epilepticus ranges between 10 in Switzerland [7] and 61 in Richmond, Virginia, USA [8] per 100,000 per year. The most hazardous type of SE is refractory (i.e., drug-resistant) SE, representing about 25-45% of cases [9].

1.2. Status Epilepticus and Inflammation-vicious Cycle Relationship

It is commonly known that one of the causes of SE may be the inflammatory process, such as neuro infection (viral: HSV1, HSV2, CMV, EBV, VZV, mumps, measles, Japanese/ West Nile encephalitis and HIV; bacterial: neurosyphilis, tuberculosis, neuroborreliosis, listeriosis; fungal, prional and parasitis), autoimmune diseases related to the presence of neural-specific antibodies including leucine-rich glioma-inactivated protein 1 (LGI1), N-methyl-D-aspartate receptor (NMDA-R), and glutamic acid decarboxylase 65 (GAD65) IgG.

In recent years there has been growing evidence showing that SE may generate inflammatory processes as secondary events leading to a “vicious circle” [10]. To illustrate, in some clinical cases, serum levels of various proinflammatory mediators, such as IL-1β, IL-6, COX-2, TNF- α, HMGB1, etc., were elevated in patients suffering from SE [11]. In our review, not only do we focus on the pathophysiology of inflammation caused by idiopathic and new-onset refractory SE, clinical studies based on patients during hospitalization, but also on possible ways of treatment. Further research on biomarkers of neuroinflammation and oxidative stress enables physicians to use them as predictive and prognostic factors. However, the best group of patients to be analyzed in this study is one with new-onset refractory SE of unknown etiology (NORSE). SE is possible due to the lack of organic diseases among these patients, excluding inflammation-related reasons.

2. MOLECULAR BACKGROUND

To fully understand the role of the inflammatory process in SE, we need to deeply examine a variety of biomarkers and signaling pathways. SE might distract the brain-blood barrier (BBB) and cause the activation of microglia, astrocytes, monocyte-macrophages, and neutrophils. They release factors, such as IL-1, TNF-α, HMGB1, and IL-6, which activate consecutive receptors: IL-1R, TNFR, and TLR4. In vitro studies have shown that activated astrocytes have a stronger expression of inflammatory cytokines such as IL-1 and TLR than resting cells.

According to the latest findings, most reaction cascades are related to the activation of NF-kB [11]. When NF-kB is phosphorylated, it leads to the generation of inflammatory cytokines. To illustrate, preclinical studies in rodents have shown that those without SE had low NF-kB phosphorylation levels in the microglia and ones with SE had significantly higher levels.

Other pathways involved in inflammatory responses are mTOR, MAPK, COX-2, prostaglandin E2, P2X7R, and TGFβ. When activated, for instance, by seizures, the mTOR cascade may lead to SE by stimulating the activity of NF-kB. Studies have proved that inhibiting those reactions, such as resveratrol, adenosine, and mTOR inhibitors, can reduce inflammation and consequently the frequency of seizures. Moreover, COX-2 is one of the major inflammatory factors, and while generating it in the brain, PGE2 is produced and binds with the EP2 receptor [11-13]. IL-1R1, EP2, and TLR4 antagonists given to patients during or after SE can protect neuronal tissue and prevent death [14].

P2X7R and MAGL inhibitors or anakinra can have similar effects, which decrease the level of IL-1β in the hippocampus. Those drugs can become new potential forms of treatment for refractory SE.

SE also results in the damage of BBB and its permeability. This enables albumins to bind with TGF-β receptors in the brain parenchyma and stimulate the NF-kB pathway, which triggers inflammation [11]. Leakage of BBB is caused by different pathological processes like high blood pressure, oxidative stress, inflammation, angiogenesis, and increasing glutamate levels. During SE, the level of glutamate increases significantly. Research has proved that early activation of glutamate receptors can be a trigger point leading to BBB damage [15]. Additionally, glutamase, which is also released during seizures, contributes to increasing matrix-matallo-proteinase 2 and 9 (MMP-2, MMP-9) levels. These factors cause BBB deficits as well. This interdependence may be path-breaking in understanding the mechanisms responsible for SE, but because it was studied only in rats, further human research is needed [16]. Moreover, BBB destruction can also result from VEGF impact, which has recently been qualified as an inflammatory factor. Moreover, IL-1 and TNF-α upregulate VEGF. Consequently, likelihood of seizures increases [17-20].

All the chemical reactions and molecules mentioned above contribute to harmful and severe changes in the brain, such as epileptogenesis, oxidative stress, neuronal death, and cognitive defects. Thus, the convulsant threshold becomes lower, and neurons are much more excitable, which puts patients at a higher risk of recurrent, prolonged, and severe seizures. The longer the seizures last, the worse the prognosis is.

The pathogenic scenario of major steps in the cascade of molecular events during NORSE in relation to the inflammatory process is presented in Fig. (1).

Fig. (1).

Cascade of events in the status epilepticus pathogenesis.

According to scientific knowledge about inflammatory mechanisms related to SE, we already have some medications that can be used. But until we fully understand the correlation between SE and inflammatory reactions, we will not be able to gain satisfactory therapeutic results. That is why further research is in urgent need (Table 1).

Table 1.

Molecular targets for therapeutic intervention in the etatus epilepticus pathogenesis.

Molecules Involved in the Inflammatory Cascade Leading to SE	Type of Molecule and Mode of Action	Drug with Target Point Corresponding to the Signaling Pathway of the Molecule
IL-1	Activates IL-1R, leading to the phosphorylation of NF-κB in the NF-κB signaling pathway [11]	Anakinra (IL-1 β antagonist) [12]; dexamethasone
TNF-α	Activates TNFR, leading to the phosphorylation of NF-κB in the NF-κB signaling pathway [11]	Dexamethasone
HMGB-1	Cytokine mediator and protein organizing the DNA and regulating transcription; activates TLR4, leading to the phosphorylation of NF-κB in the NF-κB signaling pathway [11]	-
NF-κB	A protein complex that acts as a transcription factor; its phosphorylation leads to the release of pro-inflammatory cytokines [11]	-
mTOR kinase	A serine-threonine kinase which regulates cell growth, proliferation and movement, translation and transcription processes; its activation leads to the phosphorylation of NF-κB in the NF-κB signaling pathway [11]	Resveratrol; mTOR inhibitors; adenosine; rapamycin [11, 38]
MAPK	Group of serine-threonine protein kinases; they affect gene expression, division, differentiation, movement, and apoptosis of cells; their activation leads to increased expression of COX-2 [11]	Leptomycin B (relieve angioedema after BBB disruption) [11]
COX-2	Cyclooxygenase enzyme; catalyzes the synthesis of prostanoids from arachidonic acid; influences the initiation and prolongation of inflammation leading to SE [11]	COX-2 inhibitors [11]
PGE-2	Inflammatory mediator that is generated by cyclooxygenase 2 (COX2); activates EP1, EP2, EP3, EP4 receptors, increases Ca2+ release; its action lowers the seizure threshold [11]	EP2 receptor agonists (pretreatment) EP2 receptor inhibitors [11]
P2X7R	A protein which belongs to the family of purinoceptors for ATP; its activation leads to the release of IL-1β, PGE-2, TNF-α, and NF-κB phosphorylation in the NF-κB signaling pathway [11]	P2X7R inhibitors [22]
IL-6	Cytokine secreted under the influence of IL-1 and other proinflammatory cytokines; strongly stimulates inflammatory processes [11]	Tocilizumab [37]; dexamethasone
TGF-βR	Single pass serine / threonine kinase receptor activated by albumin that leaks through a defective BBB; its activation causes NF-κB phosphorylation in the NF-κB signaling pathway [11]	-

3. LABORATORY CHANGES AND BIOMARKERS

3.1. Blood and Cerebrospinal Fluid

According to the clinical data collected from several studies, patients suffering from SE have upregulation of common inflammatory markers in serum CSF and display specific neuroimaging changes. Unfortunately, biomarkers are not yet used in clinical practice, but they might be promising in diagnosing SE, monitoring treatment effects, and predicting its outcome.

By monitoring S100-B and cytokines such as High Mobility Group Box 1 (HMGB1), it is possible to recognize gliosis, the result of neuroinflammation. The advantage of HMGB1 is that it meets many criteria of a good biomarker and has good blood stability [21].

Acute phase proteins such as procalcitonin (PCT), C reactive protein (CRP), and albumin indicate an ongoing inflammatory process in the body. It has been proved that procalcitonin levels were higher in patients with SE, did not correspond with infection, and had adverse aftereffects [22]. Additionally, from 2010-2018 a cohort study was performed on patients with NORSE [23]. NORSE is a syndrome defined as an SE observed in a patient for the first time with no past neurological medical history, without an obvious cause, and unresponsive to the first and the second line of AED. Patients with NORSE were observed to have increased ESR and CRP serum levels. Not counting those with known etiology (thromboembolism and infection), 71% had an ESR of 30 and CRP 9,3 (references: ESR 1-15 mm/h; CRP <0.5 mg/dL). 60% had inflammatory changes in CSF, such as pleocytosis, oligoclonal bands, and an elevated IgG index. Patients with febrile infection-related epilepsy syndrome (FIRES), considered a type of NORSE, also had increased inflammatory markers – even after excluding infection and thromboembolism – especially IL-1 and IL-6 in CSF and blood. In patients with refractory SE, IL-6, IL-8, and CXCL10 were significantly higher than in patients with other neuronal diseases. Those interleukins stimulate the production of CRP. According to the examination of mortal cases, BBB dysfunction led to albumin leakage and its presence in the brain tissue. Albumin is a protein synthesized in the liver; therefore, its increased concentration in CSF indicates damage to the BBB. In patients with SE, the CSF albumin to serum ratio was higher than in patients without seizures [21].

Moreover, mediators of oxidative stress, such as the cystine/glutamate antiporter system and inducible nitric oxide synthase (iNOS), were found in the CSF of adults and children with SE [12]. 141 patients with SE were studied to verify the role of uric acid as an endogenous antioxidant and reactive oxygen/nitrite scavenger. It was found that patients with higher levels of uric acid had more difficulty controlling seizures. They also had longer periods of hospitalization, and their functional outcomes were worse [24].

4. NEUROIMAGING

4.1. MRI

Patients with SE should have MRI done to exclude different causes of SE. Monitoring SE-related signal changes due to prolonged seizure activity is also important. Over 70% of patients have T2/fluid-attenuated inversion recovery (FLAIR), the hyper signal in limbic and neocortical parts (often bilaterally) in basal ganglia and peri-insular areas. Moreover, diffuse atrophy has been observed in every third patient [25]. Among patients who underwent brain MRI, 80% had abnormal changes, and in 60% of cases, hyperintensity T2 was observed in the medial temporal lobe [23].

In children, around 25% had abnormal signals in temporal lobes, 7% in basal ganglia, 5% in the insula and peri-insular areas, and 11% in white matter. Normal imaging during the chronic phase is presented in around 19% [26].

MRI can also monitor BBB dysfunction, which occurs in neuroinflammation and oxidative stress. Analyzing images of MRI with contrast and T2 signals in the piriform cortex may be helpful while monitoring the development of epilepsy in patients with SE because of its specificity [22]. MRI changes appearing during SE do not have a specific etiology.

4.2. PET

Numerous studies have been conducted to determine the potential role of FDG-PET as a biomarker of disease activity in NORSE. In a cohort study of 12 patients with NORSE [27], it was found that the results of FDG-PET imaging may help locate epileptogenous areas in the brain – altered images in FDG-PET may correspond with changes in the course of the disease and that the FDG-PET results correlate with the results of the treatment. It is important that, in the initial, acute phase of SE, both hypermetabolism and hypometabolism are dominant, while in the chronic phase, hypometabolic changes become the majority. Additionally, it was found that areas like the amygdala, hippocampus, occipital cortex, sensorimotor cortex, and striatum are susceptible to epileptogenesis. The presence of hypermetabolic changes in FDG-PET does not allow the etiology of SE to be determined [28]. However, it was discovered through studies on rats [29] that there is a protein–translocator protein (TSPO) – an inflammatory biomarker that was upregulated in PET 2 weeks after the onset of SE and was downregulated 4 weeks after SE. Upregulation has been associated with the onset of epilepsy in both animals and patients. It was confirmed that an increased level of TSPO correlates with a greater frequency of spontaneous recurrent seizures (SRS) and with the severity of depressive-like and sensorimotor-like comorbidities. This study confirms that neuroinflammation correlates with SE changes in PET.

5. CLINICAL AND DEMOGRAPHIC CHARACTERISTICS

It is important to study the clinical characteristics of patients suffering from NORSE. The recognition of NORSE is based on excluding a wide range of possible causes. Physicians should deeply examine patients and do blood tests, antibody panels, imaging, CSF analysis, and EEG to eliminate the major causes of SE, which may be a stroke, injury, neuro infections, autoimmune diseases, metabolic causes, and CNS tumors.

Patients diagnosed with NORSE may develop symptoms of SIRS, indicating that inflammation can be a consequence of SE. To diagnose SIRS, patients should match at least two from the following criteria, and SE must last at least 12 h from the onset: temperature higher than 38°C or lower than 36°C, heart rate higher than 90 bpm, a respiratory rate higher than 20 breaths per minute, white blood count lower than 4000/mm³ or higher than 12,000/mm³, and the number of polymorphonuclear leukocytes higher than 10%.

Those who had infections or autoimmune diseases were excluded. All patients were treated according to the appropriate guideline - intravenous benzodiazepines as a first line, valproic acid and phenytoin as the second line, and anesthetic drugs (propofol and thiopental), if inducing coma was necessary. 85 of 127 patients met the criteria; in 47% of cases, it was their first onset of SE. In 43% of cases, SE coexists with SIRS, and 16% of inflammatory response is idiopathic. Mortality was noted as 35% and 30% in cases with SIRS. According to the mentioned statistics, SIRS was a negative predictive factor as it leads to refractory SE. Moreover, it is suspected that SIRS can develop from SE spontaneously, with no evident cause, which supports the thesis of our review [30].

Other relevant clinical studies are based on the introduction of anti-inflammatory treatment in NORSE patients and the observation of drug response.

For example, there is a study involving 3 NORSE patients (aged between 26 and 34) already receiving AEDs [31]. All patients had negative CSF results for evidence of infection (HSV, VZV, EBV). They all had prodromal symptoms such as headache, neck pain, vomiting, fever, myalgia, generalized tonic-clonic seizure (in one patient alongside complex partial seizures), or acute confusion. Standard treatment with AEDs had been unsuccessful.

The results of this study were as follows: one patient who was ordered to administer IV methylprednisolone, PO prednisolone, and IV immunoglobulins had some neurological deficits but could re-enter his workplace while continuing AED treatment with mycophenolate mofetil (after withdrawal of corticosteroids the seizures returned, so treatment with steroids had to be prolonged). The second patient also received steroids and IV. immunoglobulins. His outcome was also satisfying, without bigger deficits, but he had to continue AED treatment. In the third patient, as immunotherapy, only steroids were administered. His results after SE were a moderate cognitive deficit and only seizures that were partially controlled by AED (no absolute resolution of seizure activity). For comparison, this study also included 2 NORSE patients (with similar prodromal symptoms and aged 22 to 23) who did not receive any additional anti-inflammatory treatment to the standard treatment of AEDs. Their results were much worse – one died during hospitalization and the second’s outcome is unknown. Still, she was transported back to her country in a state of coma after 16 days of hospitalization.

The same results were obtained from another patient report (a 75-year-old woman) with refractory status epilepticus, in which basic treatment was unsuccessful. Only adding dexamethasone allowed the seizures to be controlled, and the patient went into remission [32].

The fact that there are studies supporting the positive effects of adding anti-inflammatory treatment in patients with RS/SE also supports the theory that status epilepticus causes inflammation.

6. TREATMENT

If seizures last despite the 1^st and the 2^nd line treatment of SE, the patient is considered to have developed a refractory SE which requires adding non-sedative anesthetics, which does not require mechanical ventilation (3^rd line): propofol, pentobarbital, midazolam, and thiopental. According to the latest statistics, one in five patients do not respond effectively to those medications, and from now on, the state should be referred to as super-refractory SE [33]. So far, strict recommendations have not been established, but some substances have undergone clinical tests and have achieved satisfying results.

Knowing that status epilepticus may induce an inflammatory reaction, it is rational to consider anti-inflammatory drugs as a potential treatment adjective to standard anti-epileptic regimes. Firstly, dexamethasone is one of the best tested and broadly available [32]. Clinicians from Louisiana State University Health Sciences Center conducted a study on 4 patients with RSE. In order to terminate their seizures, which did not respond to any line of traditional treatment, they added appropriate doses of dexamethasone intravenously to AEDs such as levetiracetam, valproate, lorazepam, and lacosamide. After 3-4 days from the first dose, all patients achieved SE resolution in continuous EEG, and no seizures were observed [32]. Another stride that can be useful is methylprednisolone given intravenously for 5 days, followed by prednisone for 1 week intravenously for 3-4 days [25, 34]. The studies mentioned above do not provide concrete evidence but suggest some potential benefits of dexamethasone and methylprednisolone. So far, no studies with a control group have been conducted, and we should treat it cautiously.

Anakinra, as an IL-1 β antagonist, was recently used to treat children with FIRES and may be used in adults. It reduces SE time and makes SE less severe, has neuroprotective effects, and decreases mortality [22]. In the case of a 32-month girl with FIRES [25] and some other cases, for example, in a 21-year-old woman, anakinra had a positive impact [35]. This drug also had anti-neuroinflammatory activity. Together with EP2 antagonists, it also had a neuroprotective impact when given 3-4 hours from the SE onset [2]. In addition, the rat model has demonstrated that an IL-1 β blockade reduced IL-1 β levels and stopped cell decline in the brain [36].

Another drug worth attention to is tocilizumab. It specifically binds to IL-6 receptors (sIL-6R and mIL-6R), which reduces the activity of this interleukin. This is important because IL-6 plays a key role in inflammation-induced neuronal damage and stimulates pro-inflammatory cell differentiation. Studies have been conducted to check the therapeutic potential of tocilizumab [37]. The effect of an IL-6 inhibitor was tested in 7 NORSE patients who did not respond to conventional immunotherapy (5 of them had been treated with rituximab). The desired therapeutic effect was achieved in 6 out of 7 patients. In this group, after administration of 1 or 2 doses of tocilizumab, the SE was inhibited, and no further events were found during follow-up. However, attention should be paid to the fact that 2 patients experienced a serious infection-related adverse reaction; therefore, tocilizumab should be used with caution.

Another possible form of treatment may be rapamycin, an immunosuppressive drug commonly used in transplantology that inhibits the mTOR pathway. Serving that drug before seizures protects the brain from astrogliosis and pyramidal cell dispersion; it aborts epileptogenesis. Given after the start of seizures, a positive impact was also noticed. In rats with pilocarpine-induced SE, it is suggested that seizures can be re-established [38].

We cannot overlook such a widely known, easily available, and relatively cheap drug as alpha-tocopherol (Vit. E). After serving it to rodents, it proved its neuroprotective impact and reduced neuroglial activation. Administering the drug before inducing SE protects against oxidative stress, while giving it after seizures reduce astrocytosis and weakens inflammatory processes [39].

Recently, more attention has been paid to the ketogenic diet (KD) as a non-pharmacological, promising form of treatment for SE. This diet is high in fat, and the ratio of fats to proteins and carbohydrates is 4:1. Until now, it was only successfully used in treating drug-resistant epilepsy, and its anti-inflammatory and neuroprotective properties contributed to its administration in other neurological disorders. Numerous factors contribute to the anti-inflammatory effect of KD, including ketone bodies, caloric restriction, polyunsaturated fatty acids, adenosine modulation, ROS reduction, and intestinal microbiome [40]. KD is also the treatment of choice in febrile epilepsy syndrome (FIRES) [41]. A retrospective cohort study (conducted between 2010-2018) involved 20 adult patients with NORSE. In 10 of them, the ketogenic diet was used, and all of them achieved ketonuria (≥ 40 mg/dl urine acetoacetate). In 7 of them, SE was inhibited, 6 after achieving ketonuria, and 1 before (mean 13.5 days after the onset of ketonuria). Two patients died during treatment [23].

Moreover, studies conducted in 2017 have proven that anesthetic agents decrease immune processes in the human body (both directly and due to their impact on neuroendocrine interactions) [42].

One promising drug may be ketamine. It blocks NMDA receptors, decreasing neuronal excitability in the brain and aborting SE. Studies on animals have shown that after one hour, seizures were restrained. Moreover, combining ketamine with benzodiazepines (diazepam and midazolam) empowers anticonvulsant effects [33].

CONCLUSION

In conclusion, there is growing evidence that prolonged status epilepticus generates a secondary inflammatory process which, in part, might be an important mechanism leading to refractoriness and neuronal damage. We propose that diagnostic and therapeutic algorithms should include imaging and laboratory tests that enable early detection of the inflammatory process and initiate targeted anti-inflammatory treatment added to standard antiepileptic drugs. In particular, NORSE represents a clearly defined clinical entity in which such an approach might prove the most effective. Patients should be thoroughly monitored based on EEG and laboratory and imaging methods to detect early features of an inflammatory process. SIRS assessment seems to be the easiest and most basic approach, and further investigation should be directed to the specific pathological mechanism as an adjunct to the standard antiepileptic therapy.

LIST OF ABBREVIATIONS

AED

Antiepileptic Drugs

BBB

Brain-Blood Barrier

CRP

C Reactive Protein

FIRES

Febrile Infection-Related Epilepsy Syndrome

HMGB1

High Mobility Group Box 1

KD

Ketogenic Diet

NMDA-R

N-methyl-D-aspartate Receptor

SE

Status Epilepticus

SRS

Spontaneous Recurrent Seizures

CONSENT FOR PUBLICATION

Not applicable.

FUNDING

None.

CONFLICT OF INTEREST

The authors declare no conflict of interest, financial or otherwise.