Why and when are seizures bad for the brain?

Neurofilament light chain as a biomarker of meningoencephalitis of unknown etiology in dogs

BACKGROUND

Neurofilament light chain (NfL) is a neuron-specific cytoskeletal protein expressed in axons. Damaged axons of the central nervous system release NfLs into the cerebrospinal fluid (CSF) and the blood. In humans with neurologic diseases, NfL is used as a biomarker.

OBJECTIVES

To identify the potential of NfL as a supportive tool for the diagnosis, prognosis, and monitoring of meningoencephalitis of unknown etiology (MUE) in dogs.

ANIMALS

Twenty-six client-owned healthy dogs, 10 normal Beagle dogs, and 38 client-owned MUE dogs.

METHODS

Cohort study. The concentrations of NfL in serum and CSF were measured using single-molecule array technology.

RESULTS

Median NfL concentration was significantly higher in MUE dogs (serum, 125 pg/mL; CSF, 14 700 pg/mL) than in healthy dogs (serum, 11.8 pg/mL, P < .0001; CSF, 1410 pg/mL, P = .0002). The areas under the receiver operating characteristic curves of serum and CSF NfL concentrations were 0.99 and 0.95, respectively. The cut-off values were 41.5 pg/mL (serum) and 4005 pg/mL (CSF) for differentiating between healthy and MUE dogs, with sensitivities of 89.19% and 90%, respectively, and specificities of 96.97% and 100%, respectively. The NfL concentration showed a significant decrease (pretreatment, 122 pg/mL; posttreatment, 36.6 pg/mL; P = .02) in the good treatment-response group and a significant increase (pretreatment, 292.5 pg/mL; posttreatment, 1880 pg/mL, P = .03) in the poor treatment-response group.

CONCLUSIONS AND CLINICAL IMPORTANCE

Neurofilament light chain is a potential biomarker for diagnosing MUE and evaluating response to treatment.

Anti-convulsant action and amelioration of oxidative stress by Glycyrrhiza glabra root extract in pentylenetetrazole- induced seizure in albino rats

Objectives:

The aim of the present study was to evaluate the anti-convulsant potential of aqueous and ethanol e xtract of Glycyrrhiza glabra (AEGG and EEGG) and its action on markers of oxidant stress in albino rats.

Materials and Methods:

The aqueous and ethanol extract of Glycyrrhiza glabra was tested at three doses viz. 100, 200, and 400 mg/kg i.p. for its anti-convulsant activity using pentylenetetrazole (PTZ)-induced seizure in rat. The effect of EEGG (400 mg/kg, i.p.) on oxidative stress markers like malondialdehyde (MDA), superoxide dismutase (SOD), and catalase (CAT) of rat brain tissue homogenate was tested.

Results:

The onset of seizure was delayed (P < 0.01) by all the three doses of EEGG, but the duration of convulsion was reduced (P < 0.01) only in higher dose level (200 and 400 mg/ kg), whereas AEGG up to 400 mg/kg did not alter any of the parameters significantly. Biochemical analysis of rat brain tissue revealed that MDA was increased (P < 0.01), whereas SOD and CAT were decreased (P < 0.01) in PTZ-induced seizure rat, whereas pre-treatment with EEGG (400 mg/kg) decreased (P < 0.01) the MDA and increased (P < 0.01) both SOD and CAT, indicating attenuation of lipid peroxidation due to increase in antioxidant enzymes.

Conclusion:

The results demonstrated that EEGG poses anti-convulsant potential and ameliorates ROS induced neuronal damage in PTZ-induced seizure.

Neurofilament heavy chain and heat shock protein 70 as markers of seizure-related brain injury

PURPOSE

  Status epilepticus (SE) has deleterious effects on brain tissue, but whether brief recurrent seizures may also damage neurons represents a matter of controversy. Therefore, it remains a central area of epilepsy research to identify individuals at risk where disease progression can be potentially prevented. Biomarkers may serve as tools for such identification. Thus the present study aimed at analyzing the levels of heat shock protein 70 (HSP-70, also designated as HSPA1A) and neurofilament heavy chain protein (NfH(SMI35) ) in cerebrospinal fluid (CSF) of patients with seizures of different severity.

METHODS

  Forty-one patients were included, of whom 20 patients had a single generalized tonic-clonic seizure (GTCS) episode (SS), 11 had repetitive GTCS (RS), and 10 experienced convulsive SE. The control group consisted of 18 subjects. HSP-70 levels were measured using a conventional enzyme-linked immunosorbent assay (ELISA), whereas the NfH(SMI35) protein levels were detected by an electrochemiluminescence (ECL) immunoassay.

KEY FINDINGS

  Patients with SE (p < 0.001) and RS (p < 0.05) had significantly higher NfH(SMI35) levels than controls, and SE was associated with increased concentrations when compared with SS (p < 0.001). NfH(SMI35) levels in SS did not differ from controls. Patients with SE had significantly raised HSP-70 levels compared to RS (p < 0.05), SS (p < 0.05), and controls (p < 0.001). SS and RS did not differ from each or from controls. Levels of NfH(SMI35) and HSP-70 showed a significant correlation (r = 0.34; p = 0.007) in the group of all study subjects, which was not apparent when controls and patients with seizures were considered separately. The correlation between NfH(SMI35) and HSP-70 tended to be inverse in patients with SE, but it did not reach statistical significance (r = -0.3; p > 0.05).

SIGNIFICANCE

  Studying biochemical markers as additional quantitative tools for the measurement of neuronal damage (especially subclinical), complementary to available techniques of imaging, and clinical assessment might prove useful for identifying patients at risk of accumulating neuronal injury resulting from uncontrolled seizures. NfH(SMI35) and HSP-70 are of potential value as sensitive and specific biomarkers of seizure-related pathologic events. Future longitudinal studies are needed to monitor such patients by correlating biochemical, neuroimaging, and clinical methods of assessment.

Acute confusion or altered mental state: consider nonconvulsive status epilepticus

BACKGROUND

The diagnosis of nonconvulsive status epilepticus (NCSE) is particularly challenging in elderly patients. Confusion, personality change, dysphasia, subtle motor activity and nystagmus may be the only presenting signs.

OBJECTIVE

To review current knowledge about NCSE with special focus on older people.

METHODS

Systematic review of the current literature via Medline search.

CONCLUSION

Although prospective studies are still lacking, NCSE may be one of the most frequently missed diagnoses in patients presenting with altered mental status. Elderly patients are at particular risk of diagnostic errors because of the broad range of presentations of NCSE, significant comorbidities (especially cerebrovascular disease), limited awareness of this particular seizure emergency or difficulties with access to electroencephalography. Although diagnostic criteria and treatment remain controversial, the diagnosis of NCSE is important because it is potentially reversible.

Repeated brief epileptic seizures by pentylenetetrazole cause neurodegeneration and promote neurogenesis in discrete brain regions of freely moving adult rats

Recurrent epileptic seizures are known to provoke various forms of cellular reorganization in the brains of humans and experimental animals. However, little is known about the mechanism of neuronal cell death resulting from epileptic seizures elicited by GABA antagonists. In the present study, we explored the effect on the central nervous systems of freely moving adult rats, of repeated brief epileptic seizures induced by systemic injection of pentylenetetrazole, a GABA-A receptor antagonist. Starting with minor convulsions, repeated epileptic seizures elicited a progressive increase in seizure severity, culminating in the fully kindled state. Histological examination showed that the epileptic seizures caused overt neuronal cell death in the limbic system, including the hippocampus and amygdala, and its adjoining cortex. During the recurrent epileptic seizures, neurogenesis occurred in the subgranular zone of the hippocampus, the subventricular zone of the lateral ventricle, and the amygdala. This type of pentylenetetrazole-induced neurogenesis was seen at an early stage of epileptogenesis in some regions in which massive cell loss was not evident. This suggests that neurogenesis is not a secondary consequence of neuronal cell death, but rather an independent effect of recurrent epileptic seizures.

Diagnosing and predicting refractory epilepsy

Over 30% of people with epilepsy will never achieve remission with antiepileptic drug (AED) therapy. These individuals are often severely disabled by their condition, have an unsatisfactory quality of life, and are at increased risk of sudden unexpected death. Early identification of refractory epilepsy would allow prompt referral to specialist services, where the diagnosis can be confirmed, seizures and syndromes classified, AED therapy optimized, and suitability for surgery assessed. Recent studies suggest that patients with symptomatic or cryptogenic epilepsy, those who experience multiple seizures before AED treatment initiation, and those with febrile convulsions, a family history of epilepsy, or psychiatric comorbidities are least likely to respond to drug therapy. Failure to achieve good seizure control with the first one or two AED monotherapies is usually sufficient to highlight the possibility of subsequent refractory epilepsy. For most of these individuals, combination therapy using AEDs with complementary modes of action is the recommended treatment approach.

Treatment of seizure emergencies: Convulsive and non-convulsive status epilepticus

Status epilepticus (SE), defined as recurrent epileptic seizures without complete recovery between seizures, is one of the most serious manifestations of epilepsy. Generalized convulsive status epilepticus (GCSE) is the most common and most life-threatening form of SE, and aging increases the mortality risk. In a recent study of treatment of GCSE, 226 of 518 evaluable patients (43.6%) were of age 65 or older. In the 157 elderly patients with overt GCSE, phenobarbital was successful as first-line treatment in 71.4%, lorazepam in 63%, diazepam and phenytoin in 53.3%, and phenytoin alone in 41.5%. Phenobarbital and lorazepam were more successful than phenytoin alone. In the 69 elderly patients with subtle GCSE, success as the first treatment was 30.8% for phenobarbital, 14.3% for lorazepam, 11.8% for phenytoin, and 7.7% for diazepam and phenytoin. Overall, the results were similar to those reported for the entire study. Lorazepam, because of ease of use, is probably the best drug for the initial treatment of overt GCSE in the elderly; phenobarbital may be the best drug for subtle GCSE in this group, but more data are needed. The term "nonconvulsive SE" has been used to include complex partial SE and absence SE - both of which present as an "epileptic twilight state" - and SE in comatose patients. The diagnosis can be challenging, particularly in the elderly, as overlapping clinical features and electroencephalogram patterns can be seen in SE and in a variety of encephalopathic conditions. There is a suggestion that aggressive treatment of elderly patients with nonconvulsive SE may worsen prognosis. Clearly, there is a need for more data to better understand management of elderly patients with both convulsive and nonconvulsive SE.

Medical therapy of epilepsy: when to initiate treatment and when to combine?

Most patients reporting more than one well-documented or witnessed seizure require prophylactic antiepileptic (AED) therapy. Those with an underlying brain disorder and/or an abnormal electroencephalogram should probably be treated after their first event. The goal should be maintenance of a normal lifestyle by complete seizure control with no or minimal side-effects. Failure of the first AED due to lack of efficacy implies refractoriness. A policy of consecutive substitutions is unlikely to be an effective strategy. Thus, if the first or second monotherapy improves control but does not produce seizure freedom, an AED with different and perhaps multiple mechanisms of action should be added. Strategies for combining drugs should involve individual assessment of patient-related factors, including seizure type and epilepsy syndrome classifications coupled with an understanding of the pharmacology, side-effects and interaction profile of the AEDs. Reducing the dose of one or more AEDs may help accommodate the introduction of a second or third drug. An orderly approach to the pharmacological management and, when appropriate, surgical investigations for each epilepsy syndrome will optimise the chance of perfect seizure control and help more people achieve safer and more fulfilled lives.

Caffeic acid phenethyl ester exerts a neuroprotective effect on CNS against pentylenetetrazol-induced seizures in mice

Since overexcitation of excitatory amino acid is an important mechanism in seizure genesis wherein free radicals have recently been suggested to play a critical role, we explored the effects of caffeic acid phenethyl ester (CAPE) administration in pentylenetetrazole (PTZ)-induced seizure in mice. CAPE prevents the oxidative damage in brain tissue induced by PTZ, scavenging reactive oxygen species (ROS). Our results demonstrate that CAPE treatment which prevents free radical production and ameliorates seizure severity may be useful at least as an adjunctive treatment of seizure disorders.

The influence of anticonvulsant and antioxidant drugs on nitric oxide level and lipid peroxidation in the rat brain during penthylenetetrazole-induced epileptiform model seizures

Nitric oxide (NO) generation in the brain cortex of Wistar rats was measured by direct method of electron paramagnetic resonance (EPR) spectroscopy. Dramatic (fivefold) elevation of NO production was found during penthylenetetrazole (PTZ)-induced epileptiform seizures. The level of secondary products of lipid peroxidation (LPO; thiobarbituric acid reactive substances, TBARS) was also significantly increased in the cerebral cortex of rats with PTZ-evoked seizures. The effects of anticonvulsant drugs phenobarbital, lamotrigine, phenazepam, as well as antioxidant substances alpha-tocopherol and novel original Russian synthetic drug mexidol (2-ethyl-6-methyl-3-oxypiridine succinate), were investigated. All the substances studied significantly decreased seizure manifestations and partially prevented both enhancement of NO generation and increase in TBARS formation. Mexidol and phenobarbital were found to be the most effective in the preventing of PTZ-induced seizures among all the substances studied. The data obtained support our speculation that neuroprotective action of mexidol may correlate with its ability to inhibit not only excessive reactive oxygen species (ROS) formation but also NO generation. While the molecular mechanism underlying action of mexidol and phenobarbital still remains unclear, it is likely that the effect of these drugs on NO production is contributing to their neuroprotective action. It might be concluded that both the suppression of seizure-induced NO generation and LPO enhancement may be involved in the mechanism of action of antiepileptic drugs.

Brain levels of N-acylethanolamine phospholipids in mice during pentylenetetrazol-induced seizure

The N-acylethanolamine phospholipids (NAPE) are precursors for N-acylethanolamines (NAE), including anandamide (20:4-NAE), which is a ligand for the cannabinoid receptors. Previously, NAPE were believed to be found only in injured tissue, e.g., after neurodegenerative insults. Neuronal injury may occur in response to seizure activity. Therefore, we investigated the effect of pentylenetetrazol (PTZ)-induced seizures in PTZ-kindled mice on the level of NAPE in the brain. Male NMRI mice were kindled with PTZ injections 3 times/wk, thereby developing clonic seizures in response to PTZ. Mice were killed within 30 min after the clonic seizure on the test day (12th injection) and the brains were collected. Eight species of NAPE were analyzed as the glycerophospho-N-acylethanolamines by high-performance liquid chromatography-coupled electrospray ionization mass spectrometry. No effect of the PTZ kindling on the NAPE levels in murine brains was observed. Total NAPE in control mice cortex (n = 4) was 16.4 +/- 3.0 micromol/g wet weight of which 20:4-NAPE accounted for 3.6 mol%, and the major species was 16:0-NAPE, accounting for 52.1 mol%. Determination of the activity of NAPE-hydrolyzing phospholipase D and of N-acyltransferase in brain membrane preparations from adult and 3-d-old mice revealed an enzyme pattern in the adult mice that was favorable for NAE accumulation as opposed to NAPE accumulation. Thus, there was no difference in NAPE levels; at present, however, this does not exclude that NAE may accumulate during seizure.

Modulation of cortical nitric oxide synthase, glutamate, and redox state by nifedipine and taurine in PTZ-kindled mice

PURPOSE

Correlation between pentylenetetrazol (PTZ)-induced kindling and the cortical nitric oxide synthase (NOS), intracellular calcium [Ca2+]i, glutamate, and free radicals was studied in mice, as well as the modulatory action of nifedipine and taurine on these parameters.

METHODS

Male Swiss albino mice were used. Mice in one group received a single convulsive dose of PTZ (50 mg/kg, i.p), and were killed 24 h later. To induce kindling, PTZ was injected in a subconvulsive dose (40 mg/kg, i.p.) every other day for 3 weeks. One kindled group was used as control, whereas two other groups were injected 30 min before PTZ with either nifedipine (30 mg/kg, i.p) or taurine (100 mg/kg, i.p). All three kindled groups were killed 24 h after the last injection.

RESULTS

Compared with normal control group, PTZ-kindled mice had significantly higher levels of [Ca2+]i, malonaldehyde (MDA), NOS, and lactate dehydrogenase (LDH) but had lower levels of superoxide dismutase (SOD) and reduced glutathione (GSH). Acute seizures of the same intensity did not induce these alterations, indicating their link to the kindling phenomenon and not to seizure activity. The effect of taurine, known as an antioxidant, was more pronounced than that of the Ca2+-channel blocker, nifedipine. The first drug reversed the PTZ-kindled action on [Ca2+]i, NOS, LDH, GSH, and SOD, whereas nifedipine restored only LDH and GSH levels. However, both drugs did not restore the elevated MDA level.

CONCLUSIONS

This study suggests that free radicals, as well as NOS, are implicated in PTZ-induced kindling, and that antioxidants could play a role in controlling the accompanying changes.