INTRODUCTION
Epilepsy is
characterized by the spontaneous periodic occurrences of seizures and affects
nearly 1-2% of the general population. Etiologically, epilepsy is either
symptomatic secondary to structural brain changes or idiopathic; that is mostly
genetic. Experimental evidence in rodents have showed the ability of different
brain insults as trauma, stroke and febrile seizures, to induce inflammation in
the brain1. The clinical observation of the efficacy of selected
anti-inflammatory drugs; like steroids to control seizures that are resistant
to anti-epileptic drugs, has marked a list of studies that incriminated
inflammation in the etiopathogenesis of symptomatic epilepsy.2
Cytokines are chemical mediators of inflammation and immune responses. The
interleukin (IL) -1β was found to be linked to seizure susceptibility and
epileptogensis. Its administration in experimental seizure models has worsened
the seizure activity while its depression, suppressed this activity.3
Most of clinical studies on IL-1β were done on patients with chronic
symptomatic epilepsy and its results are still controversial. The aim of this
study was to examine IL-1β in patients with idiopathic epilepsy and those with
newly diagnosed epilepsy immedietly following seizure activity to understand its
pathological role.
PATIENTS AND METHODS
Patients with idiopathic
epilepsy admitted to Neurology department, Mansoura University
for investigation or treatment, were recruited if they develop in hospital
-spontaneous epileptic seizure activity for less than 5 minutes. Patients were
selected to serve two main groups; newly diagnosed epilepsy and chronic
epilepsy. Patients with an evidence of status epilepticus, recent trauma,
electrolyte imbalance, history of drug intoxication, acute neurological
diseases, inflammatory, metabolic or neoplastic diseases were excluded from the
study. Evidence of infection was
excluded by history, clinical examination and C-reactive protein assessment. A
group of patients with cryptogenic epilepsy served as control. All patients
didn’t experience another seizure within 24-hours of the index seizure. All
patients had Magnetic resonance imaging (MRI) of the brain using a high
resolution 1.5 Tesla MRI scan and reported to be normal. Plasma samples were
collected within 6 hours of the index seizure. Another plasma sample for 20
patients 24-hours after the index seizure to detect the basal level of IL-1β.
The serum samples were immediately centrifuged and frozen at -80 C. IL-1β were
measured by commercially available ELISA (Enzyme Linked Immunosorbent Assay)
kits (Human IL-1β ELISA Kit, Boster Biological
Technology Ltd) according to the manufacturers’ instructions.
Data
entry and statistical analyses were performed using SPSS (statistical package
of social sciences) version 16.0 (SPSS Inc., Chicago, IL, USA). Parametric data were
expressed in mean ± standard deviation. Non parametric data were expressed in
median, minimum and maximum. Normality of data was first tested by one sample
K-S test. In addition, independent t test was used to compare means for
continous parametric variables of each two different groups. Also, Mann-Whitney
U test (z) was used to compare non parametric continuous variables in two
different groups. Pearson Chi-square tests were used to compare the categorical
variables between the both cases and control groups. P-value < 0.05 was
considered as statistically significant.
The study was approaved
by the Neurology departmental council and the ethical committee for research of
Mansoura Faculty of Medicine.
RESULTS
Sixty patients were
recruited for the study. Four patients were excluded because of sample lyses
and 56 patients were considered for statistical analysis. The clinical
characteristics of patients are presented in Table (1). Seven patients (12.5%)
were considered cryptogenic because they had secondary generalized tonic-clonic
seizures (sGTCS) after complex partial seizures (CPS) and their MRI were
normal. Polytherapy was found in half of the patients reflecting their
drug-refractory pattern. Table 2 and 3 summarizes IL-1β results in different
situations. Patients with seizure onset within the last 6 months were
considered new onset epilepsy. IL-1β was significantly higher than those of the
normal population (P<0.001*). The normal concentration of IL-1β reported in
healthy general population is 0.3pg/ml.(4,5). To know if this is the basal
level, we reassessed 20 patients 24 hours after the index seizure. The level
significantly dropped but still significantly higher than normal concentrations
(P=0.003*). The rise of IL-1β following the index seizure was significantly
higher among adults when compared to children (P=0.01*). The levels of IL-1β
were not significantly different between idiopathic epilepsy and cryptogenic
type, new-onset epilepsy and chronic one, and childhood-onset and adult- onset.
The level was also not significantly increased with higher seizure frequency or
poly therapy.
DISCUSSION
Epilepsy
is chronic medical illness irrespective of the current treatment with AEDs
because they don't work with every patient with epilepsy. Even those, who
responded to AEDs, have a nearly 50% chance of seizure recurrence within 10
years.6 This clinical observation suggests that the locus of control
of epilepsy is outside the repertoire of AEDs. One plausible hypothesis for
seizure recurrence is brain inflammation and because epilepsy has enduring
predisposition to generate seizures, a relationship between the later and
inflammation was the focus of several research works. Studies have shown that
inflammation, irrespective of its cause, can cause seizures and also seizures
can cause inflammation. In this study, we measured the level of IL-1β in the
sera of patients with idiopathic epilepsy whether new onset or chronic one. The
study showed significant rise of IL-1β immediately following seizure activity
suggesting cause-effect relationship. In animal epilepsy models, seizure
induction by different electrical and chemical stimuli triggered rapid
induction of inflammatory mediators in brain regions of seizure activity onset
and propagation7-11. The proinflammatory cytokines like IL –1β and
their receptors are expressed in neurons as well as microglia and astrocytes.12
Clinical studies in temporal lobe epilepsy and extratemporal lobe epilepsy has
shown evidence of increased interleukin-1 receptor antagonist (IL-1Ra), which
is mainly induced by IL-1β reflecting the activation of IL-1 system3,13,14.
However most of the studies failed to show rise of IL-1β either because of the
time of assay or the small rise. Peltola and his group's assay on patients with
primary generalized or secondary generalized seizures showed no significant
rise when they did the assay 72- and 24-hours following seizure activity15,16.
While Uldag et al. found significant rise of IL-1Ra, within 12 hours from
seizure activity, but the ratio of IL-1β/IL-Ra has not changed suggesting increase
of IL-1β level. They attributed that to the small and rapid rise of IL-1β that
was overcome by increased IL-Ra activity.3
We
re-assayed the plasma level of IL-1β after 24-hours of the index seizure and it
significantly decreased confirming the short-lived response as suggested by
Peltola et al.15,16. However the basal level attained by 20 patients
after the index seizure is significantly higher than normal population. This
could reflect a state of mild chronic inflammation in epileptic patients that facilitate
occurrences of seizures. In a nice review about the role of inflammation in
epilepsy, Vezzani et al. suggested three different mechanisms through which,
brain inflammation might lead to seizures; all has involved IL-1β. The first is
the positive evidence that IL-1β, TNF, IL-6, prostaglandin E2, and complement
cascade can generate and perpetuate seizures. The second evidence is also
mediated by IL-1β as a response to fever that accompany most inflammatory
processes as happens in febrile seizures and the later development of mesial
temporal sclerosis and temporal lobe epilepsy. The third evidence came from a
systemic injection of inflammation–inducer; lipopolysaccharide into rats
lowering their seizure threshold and electrographic discharge in animal model
of petit mal epilepsy. These changes were also brought by the effect of brain
cytokines; namely IL-1β or TNF. 17
The rise of IL-1β, in
our results was not significantly changed by seizure frequency, epilepsy
duration or the number of AEDs. This is in agreement with Uludag et al whose
cases were both idiopathic and symptomatic epilepsy. That finding denotes that
inflammation and its cytokine generators starts very early during the process
of epileptogenesis.
In this study we ascertained
the involvement of IL-1β as a seizure response and a possible role in seizure
generation in patients with idiopathic epilepsy. We didn't measure IL-6 and the
IL-1Ra that reflects the rest of interleukin activity. We also didn't do CSF
assay of these cytokines that reflects more brain activity because of the cost
and the invasive technique of the later.
We conclude that IL-1β is seizure-related in idiopathic
epilepsy and presumably its pathogenesis and introducing it as a possible
target in epilepsy management.
[Disclosure: Authors report no conflict
of interest]
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