Regulatory T cells as a possible new target in epilepsy?

Epilepsy is a complex chronic brain disorder with diverse clinical features that can be caused by various triggering events, such as infections, head trauma, or stroke. During epileptogenesis, various abnormalities are observed, such as altered cellular homeostasis, imbalance of neurotransmitters, tissue changes, and the release of inflammatory mediators, which in combination lead to spontaneous recurrent seizures. Regulatory T cells (Tregs), a subtype of CD4+Foxp3+ T cells, best known for their key function in immune suppression, also seem to play a role in attenuating neurodegeneration and suppressing pathological inflammation in several brain disease states. Considering that epilepsy is also highly associated with neuronal damage and neuroinflammation, modulation of Tregs may be an interesting way to modify the disease course of epilepsy and needs further investigation. In this review, we will describe the currently available information on Tregs in epilepsy.

The intracerebral injection of Aß1-42 oligomers does not invariably alter seizure susceptibility in mice.

Objectives: Epileptiform activity and seizures are present in patients with Alzheimer's disease (AD) and genetic animal models of AD. Amyloid beta 1-42 (Aß1-42) oligomers are thought to be crucial in AD and can cause neuronal hyperexcitability in vitro. However, it is unclear whether these Aß1-42 oligomers cause the increased seizure susceptibility in vivo in people with AD and in AD animal models, nor via which mechanisms it would do so. We investigated this question by injecting Aß1-42 oligomers intracerebrally in mice and assessed its impact on seizure susceptibility. Materials and methods: We performed a single intracerebral injection of synthetic Aß1-42 oligomers or scrambled Aß1-42 in NMRI mice in three different cohorts and subjected them to an i.v. infusion of a chemoconvulsant. We evoked the seizures 1.5 h, 1 week, or 3 weeks after the intracerebral injection of Aß1-42 oligomers, covering also the timepoints and injection locations that were used by others in similar experimental set-ups. Results: With a thioflavine T assay and transmission electron microscopy we confirmed that Aß1-42 monomers spontaneously aggregated to oligomers. We did not find an effect of Aß1-42 oligomers on susceptibility to seizures - evoked 1.5 h, 1 week or 3 weeks - after their intracerebral injection. Significance: The lack of effect of Aß1-42 oligomers on seizure susceptibility in our experiments contrasts with recent findings in similar experimental set-ups. Contradicting conclusions are frequent in experiments with Aß1-42 and they are often attributed to subtle differences in the various aggregation forms of the Aß1-42 used in different experiments. We confirmed the presence of Aß1-42 oligomers with state-of-the-art methods but cannot ascertain that the protein aggregates we used are identical to those used by others. Whether our findings or those previously published best represent the role of Aß1-42 oligomers on seizures in AD remains unclear.

Neurofilament light chain: A possible fluid biomarker in the intrahippocampal kainic acid mouse model for chronic epilepsy?

OBJECTIVE: In the management of epilepsy, there is an ongoing quest to discover new biomarkers to improve the diagnostic process, the monitoring of disease progression, and the evaluation of treatment responsiveness. In this regard, biochemical traceability in biofluids is notably absent in contrast to other diseases. In the present preclinical study, we investigated the potential of neurofilament light chain (NfL) as a possible diagnostic and response fluid biomarker for epilepsy. METHODS: We gained insights into NfL levels during the various phases of the intrahippocampal kainic acid mouse model of temporal lobe epilepsy-namely, the status epilepticus (SE) and the chronic phase with spontaneous seizures. To this end, NfL levels were determined directly in the cerebral interstitial fluid (ISF) with cerebral open flow microperfusion as sampling technique, as well as in cerebrospinal fluid (CSF) and plasma. Lastly, we assessed whether NfL levels diminished upon curtailing SE with diazepam and ketamine. RESULTS: NfL levels are higher during SE in both cerebral ISF and plasma in kainic acid-treated mice compared to sham-injected mice. Additionally, ISF and plasma NfL levels are lower in mice treated with diazepam and ketamine to stop SE compared with the vehicle-treated mice. In the chronic phase with spontaneous seizures, higher NfL levels could only be detected in ISF and CSF samples, and not in plasma. No correlations could be found between NfL levels and seizure burden, nor with immunohistological markers for neurodegeneration/inflammation. SIGNIFICANCE: Our findings demonstrate the translational potential of NfL as a blood-based fluid biomarker for SE. This is less evident for chronic epilepsy, as in this case higher NfL levels could only be detected in ISF and CSF, and not in plasma, acknowledging the invasive nature of CSF sampling in chronic epilepsy follow-up.

Higher susceptibility to 6 Hz corneal kindling and lower responsiveness to antiseizure drugs in mouse models of Alzheimer's disease.

OBJECTIVE: Epileptic spikes and seizures seem present early in the disease process of Alzheimer's disease (AD). However, it is unclear how soluble and insoluble amyloid beta (Aß) and tau proteins affect seizure development in vivo. We aim to contribute to this field by assessing the vulnerability to 6 Hz corneal kindling of young female mice from two well-characterized transgenic AD models and by testing their responsiveness to selected antiseizure drugs (ASDs). METHODS: We used 7-week-old triple transgenic (3xTg) mice that have both amyloid and tau mutations, and amyloid precursor protein Swedish/presenillin 1 dE9 (APP/PS1) mice, bearing only amyloid-related mutations. We assessed the absence of plaques via immunohistochemistry and analyzed the concentrations of both soluble and insoluble forms of Aß1-42 and total tau (t-tau) in brain hippocampal and prefrontal cortical tissue. Seven-week-old mice of the different genotypes were subjected to the 6 Hz corneal kindling model. After kindling acquisition, we tested the anticonvulsant effects of three marketed ASDs (levetiracetam, brivaracetam, and lamotrigine) in fully kindled mice. RESULTS: No Aß plaques were present in either genotype. Soluble Aß1-42 levels were increased in both AD genotypes, whereas insoluble Aß1-42 concentrations were only elevated in APP/PS1 mice compared with their respective controls. Soluble and insoluble forms of t-tau were increased in 3xTg mice only. 3xTg and APP/PS1 mice displayed more severe seizures induced by 6 Hz corneal kindling from the first stimulation onward and were more rapidly kindled compared with control mice. In fully kindled AD mice, ASDs had less-pronounced anticonvulsive effects compared with controls. SIGNIFICANCE: Mutations increasing Aß only or both Aß and tau in the brain enhance susceptibility for seizures and kindling in mice. The effect of ASDs on seizures measured by the Racine scale is less pronounced in both investigated AD models and suggests that seizures of young AD mice are more difficult to treat.

Plasma citrulline levels are increased in patients with multiple sclerosis.

BACKGROUND: Multiple sclerosis is an inflammatory demyelinating disorder of the central nervous system (CNS). Myelin basic protein (MBP), which is one of the main compounds of CNS myelin, appears to be hypercitrullinated in the brain of patients with MS. We hypothesized that MS is associated with an increased release of citrulline from the brain. METHODS: Twenty-five patients with MS, 25 controls without neurological disease (CwND) and 25 subjects with non-MS cerebral white matter lesions were included in this study. Groups were matched for age and gender. Clinical MS disability measures were recorded by means of Expanded Disability Status Scale (EDSS) scores and Multiple Sclerosis Severity Scores (MSSS). Citrulline was assessed in plasma obtained from an antecubital peripheral vein (PV) in all participants. Additional internal jugular vein (IJV) samples were examined in 10 patients with MS and 10 CwND. Twelve patients with MS underwent brain magnetic resonance imaging to determine total brain and T2 fluid-attenuated inversion recovery lesion volume. RESULTS: Median [IQR] PV citrulline levels were increased in patients with MS (50.47 [86.61] µM), as compared to CwND (33.58 [43.65] µM, P = 0.042) and subjects with non-MS cerebral white matter lesions (32.41 [28.86] µM, P = 0.006). Citrulline IJV levels and IJV/PV ratios were comparable between patients with MS and CwND. No significant correlations were found between PV citrulline levels and any of the clinical, nor radiological, disease measures. CONCLUSION: PV plasma levels of citrulline are elevated in patients with MS but this does not seem to result from an augmented release from the brain. Increased plasma citrulline may be a promising new biomarker in MS but the origin and significance need to be further elucidated.