Introduction

Proinflammatory mediators can alter neuronal excitability and affect neurotransmission leading to decrease the threshold of seizures and induce neuronal damage. Epilepsy animal models and human brain autopsy studies revealed that recurrent seizures can induce chronic brain inflammation that further more increase the neuronal excitability and induce neuronal injury even in absence of underlying infection or autoimmune disease [1]. Additional evidence has been gained from the therapeutic use of anti-inflammatory medication including steroids in patient with refractory epilepsy [2].

Chemerin is an immunomodulation factor that induces chemotaxis during inflammatory response. Chemerin level increased in response to proinflammatory mediators to induce the migration of natural killer cells, macrophages, and dendritic cells to the site of inflammation [3]. Circulating chemerin level is correlated to altered glucose, lipid, and cytokine homeostasis. Elevated chemerin may serve as a biomarker for chronic inflammation in various tissues and organs including the central nervous system [4]. Experimental studies demonstrated that hypoxia activates proinflammatory cytokine cascades that upregulate the expression of chemerin in a time- and dose-dependent manner [5].

Irisin was initially identified as a skeletal muscle-derived myokine that increased during exercise to improve energy and glucose homeostasis by stimulation of the browning of white adipose tissue. It also expressed in various tissues and organs including the brain [6]. There is emerging evidence exploring the effects of irisin on the brain function. Irisin is involved in regulation of neuronal differentiation, metabolism, and energy expenditure, in addition to its protective role against ischemia-induced neuronal injury [7]. There is increasing interest in the role of irisin in ischemic cerebrovascular insult; however, there is insufficient data about its role in seizures induced neuronal damage.

The current study explores the predictive role of irisin and chemerin for seizure control in children with idiopathic epilepsy and its relation to clinical characteristics of the patients.

Patients and methods

This case-control study included 50 children with confirmed diagnosis of idiopathic epilepsy aged 5–10 years and 30 age- and sex-matched healthy children as a control group. Children with epilepsy were randomly selected from pediatric neurology clinic while control group were selected from pediatric outpatient clinic at Alzahraa University hospital, Al-Azhar University, Cairo, Egypt, during the period from March 2016 to February 2017. An informed written consent was obtained from the caregivers of all included children in adherence with the principles of the Declaration of Helsinki and in accordance with ethics committee of Al-Azhar University. The study has been approved by the local ethics committee of Egyptian national research center institute.

Children with history of hypoxic or traumatic brain insults, neurological, psychological disorders, developmental disabilities, mental retardation, obesity, and acute or chronic medical illness (e.g., cardiac, respiratory, metabolic, endocrine, liver, renal diseases) were excluded from the study.

All the studied children were subjected to detailed medical history including sociodemographic data, neurological manifestation, age of onset of seizures, duration of illness, previous investigation, current medication, and seizure frequency over the previous 6 months. Complete systematic and neurological clinical examination, assessment of seizure severity by Chalfont severity scale [8], and neuroimaging were done for children with epilepsy to exclude any underlying traumatic, perinatal asphyxia and infectious or structural brain lesion. Digital interictal EEG was done using a Nihon Kohden 1200 digital EEG instrument at pediatric neurophysiology unite at Alzahraa University hospital. Intermittent photic stimulation, sleep deprivation, and hyperventilation activation procedures were done. The type of epilepsy was identified according to the commission on classification and terminology of the international league against epilepsy [9].

Biochemical investigations

Three milliliters of venous blood samples were drawn under complete aseptic condition (alcohol swab 70%) in plain gel separator vacutainer. Serum coagulation at room temperature for 10–20 min and centrifuge at speed of 2000–3000 rpm for 20 min was done. Serum was stored according to manufacture till time for analysis. Serum chemerin level was determined according to Zabel et al. [10] using ELISA kit (Boster’s Human/chemerin Kit, B Valley Ave, Pleasanton, CA, USA). Determination of serum irisin level was done according to Yang et al. [11] using ELISA kit (Irisin ELISA kit EK-067-16; Phoenix Pharmaceuticals, Burlingame, CA).

Statistical analysis

Data analysis was done using the Statistical Package for Social Sciences (version 20; SPSS Inc., Chicago, IL, USA). Quantitative data were expressed as mean ± SD. Differences between two groups were analyzed using independent t student test while differences between more than two groups were analyzed with ANOVA test. Further analysis between groups was done using post hoc Tukey’s test. Nonparametric data were expressed as number and percentage and were compared using the chi-square test. Correlations were performed using Pearson correlation coefficients. Logistic regression analysis for predictors of uncontrolled seizures in children with idiopathic epilepsy was done. Receiver operating characteristic curves (ROC) were used to identify the optimal cutoff points of Chalfont score, chemerin, and irisin level for prediction of uncontrolled seizures in children with idiopathic epilepsy. P values < 0.05 were considered significant.

Results

This study included 50 children with confirmed diagnosis of idiopathic epilepsy (52% male and 48% female). Regarding EEG, 31 (62%) of them had focal epilepsy, 9 (18%) had focal with secondary generalization, and 10 (20%) had generalized epilepsy. The age of onset of seizures ranged between 1.5 and 6.5 years with a mean duration of epilepsy of 3.816 ± 1.955 years. All of them received proper antiepileptic drug with proper doses including at least two antiepileptic drugs at maximum dose for those with uncontrolled seizures. Serum levels of valproic acid and carbamazepine were done to confirm appropriate drug serum level in those with uncontrolled seizures. Twenty-five of them were controlled on antiepileptic drugs for the previous 6 months. Another 30 age- and sex-matched healthy children (50% male and 50% female) were selected as controls. There was no significant difference in age or gender between patients and control (p value = 0.063, 0.862 respectively).

Children with uncontrolled seizures have statistically significant increase in Chalfont severity score than those with controlled seizures. However, no significant difference in other clinical data between both groups was detected as shown in Table 1.

Table 1 Comparison of clinical data and electroencephalographic findings in children with controlled and uncontrolled seizures over the previous 6 months
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In comparison to healthy controls, serum levels of chemerin and irisin were significantly higher in children with epilepsy especially those with uncontrolled seizures as shown in Table 2.

Table 2 Comparison of serum irisin and chemerin level in children with epilepsy and healthy controls
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Pearson correlation analysis showed that serum levels of chemerin and irisin had significant positive correlation with Chalfont severity score of seizures and the duration of epilepsy as demonstrated in Table 3.

Table 3 Correlation between clinical data and serum level of chemerin and irisin in children with epilepsy
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Regression analysis showed that elevated Chalfont severity score and serum levels of chemerin and irisin are predictors for uncontrolled seizures as demonstrated in Table 4.

Table 4 Logistic regression analysis for predictors of uncontrolled seizures in children with idiopathic epilepsy
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Circulating chemerin and irisin have 80% and 76% sensitivity and 88% and 92% specificity at cutoff point > 191.38 ng/ml and > 151.2 ng/ml respectively for prediction of uncontrolled seizures in children with idiopathic epilepsy as demonstrated in Table 5 and Fig. 1.

Table 5 Sensitivity, specificity, and predictive values for predictors of uncontrolled seizures in children with epilepsy
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Fig. 1
figure 1

Receiver operating characteristic (ROC) curve for predictors of uncontrolled seizures in children with epilepsy

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Discussion

The pathophysiological mechanism of epilepsy and its relation to inflammation is complex. Identifying the pathogenesis of neuroinflammation is critical not only for diagnostic or prognostic proposes but also to improve treatment modalities [12].

There are emerged evidences suggesting the role of immune activation and chronic inflammation in the pathogenesis and comorbidity of epilepsy. Chemerin expression has been reported in several previous studies during either acute or chronic progressive inflammation suggesting its role in the pathogenesis and progression of inflammatory disorders in different tissues and organs [13, 14]; however, there is limited data regarding its role in neurological disorders. The current study demonstrated elevated chemerin level in children with epilepsy that was significantly related to seizure severity scores and seizure control over the previous 6 months. Previous studies demonstrated elevated chemerin expression in neurological disorders including stroke [15], multiple sclerosis [16], and autoimmune encephalitis [17]. Furthermore, neuronal cell inflammation can be reduced after blocking of chemerin receptors in animal models of autoimmune inflammatory diseases suggesting a potential therapeutic target [18]. Chemerin is a chemoattractant protein that induces endothelial cell inflammation, triggers angiogenesis, and induces cellular damage through activation of proinflammatory mediator and recruitment of leucocytes and macrophages [19]. Binding of chemerin to its cell membrane receptors suppresses the adenylate cyclase activity and increases the expression of cyclic adenosine monophosphate leading to elevated intracellular calcium concentration and increased neuronal excitability [15].

In addition to the adverse effect of chronic inflammation, patient with frequent uncontrolled seizures are at high risk for hypoxemia that may exacerbate epileptogenesis [20]. Periictal hypoxemia and hypercapnia have been reported in about one third of patients undergoing electroencephalographic telemetry [21]. Previous studies demonstrated that irisin has protective effects against hypoxic insults, oxidative stresses, and apoptosis in different animal models, in addition to its anti-inflammatory property [22, 23]. The current study revealed higher irisin serum levels in children with epilepsy especially those with active seizures that were significantly correlated to seizure severity and duration of epilepsy. Animal models reveal that elevated irisin level in the brain increases the expression of brain-derived neurotrophic factors that maintain neuronal survival and proliferation. Irisin level may be elevated as a protective mechanism against seizure-induced neuroinflammation [24]. Animal model of oxygen-glucose deprivation revealed that an irisin-protective effect could be mediated through inhibition of reactive oxygen species-NOD-like receptor pyrin 3 inflammatory signaling pathways [25] and activation of the intracellular Akt and ERK1/2 signaling pathways [26].

Assessment of seizure severity and seizure response to antiepileptic medications are important aspects during management of childhood epilepsy [27]. The current study demonstrated that elevated chemerin and irisin level are independent predictors of poor response to antiepileptic medication in the previous 6 months. Chalfont score is a subjective tool to assess seizure severity that depends mainly on history from parents. Using of biomarkers reflecting disease pathophysiology provides an objective, accurate, and dynamic tool to guide the diagnosis, improve risk stratification, and monitor treatment response [28]. However, both markers have lower sensitivity than Chalfont score for prediction of uncontrolled seizures.

There is controversial data linking elevated circulating chemerin level to body mass index [3, 29]. To eliminate the effect of adiposity on circulating chemerin level, children with obesity were excluded from our study. Additionally, it was reported that irisin acts as a trigger for the activation of hypothalamic neuronal network and its serum level is elevated during initial phase of puberty [30], so we include prepubertal children only in the study.

The small number of included children and the cross-sectional designs of the study are considered as two major limitations of our study. The current study identifies a relevant relationship between chemerin and irisin level and epilepsy but cannot confirm the cause-effect relationship. So, longitudinal studies are required to explore the changes of serum chemerin and irisin level during the course of the disease.

Conclusion

Elevated circulating level of irisin and chemerin may predict poor seizure control in children with idiopathic epilepsy suggesting the role of hypoxia-triggered neuroinflammation in the pathogenesis and drug response of childhood idiopathic epilepsy. Further studies are required to identify the therapeutic potential of blocking neuroinflammation for proper seizure control in children with epilepsy.