Active seizures represent a major risk factor for oxidation stress in children with epilepsy. The developing brain is highly vulnerable to oxidation stress induced injury due to its great lipid content and high oxygen consumption. Neuronal exposure to oxidation stress enhances lipid peroxidation that may alter membrane excitability, disturb neurotransmitters and impairs both morphological and functional aspects of developing brain [1-6].
Production of free radicals and reactive oxygen/nitrogen species is tightly regulated by physiological anti-oxidant defense. Oxidation stress occurred due to imbalance in oxidants/antioxidant defense balance leading to activation of inflammatory signals, disruption of cellular morphology, and function. Endogenous antioxidants include both enzymatic molecules (e.g., glutathione peroxidase, glutathione reductase, catalase, superoxide dismutase, and glucose-6-phosphate dehydrogenase) and non-enzymatic molecules (e.g., vitamin C, E, omega-3, bilirubin, melatonin, coenzyme Q, reduced Glutathione, and uric acid) .
Cognitive impairment represents serious comorbidity of childhood epilepsy that adversely affects the quality of life and learning. The interaction between epilepsy and cognition is complex and multifactorial. Seizure activities in addition to use of antiepileptic medications are involved in the pathogenesis of cognitive dysfunction . Epilepsy related factors include the underlying etiology, age of onset, frequency of seizures, duration, and type of epilepsy. Cognitive affection may precede the initiation of antiepileptic medications and can be persist even in those with controlled seizures. Cognitive dysfunction can be transient following seizure activity. However, several studies reported a long term cognitive impairment with ageing and dementia .
Malondialdehyde (MDA) is a lipid peroxidation end product that is produced by oxidation of polyunsaturated fatty acids. Advanced oxidation protein products (AOPP) is another biomarker that reflects protein damage induced by oxidative stress.
Both biomarkers are widely used as an indicator of increased oxidation stress in various tissues and organs. Evidence showed that oxidative stress toxicity involving cellular lipid and protein molecules are associated with increased the psychological comorbidities in subjects with temporal lobe epilepsy [10, 11].
Oxidation stress and free radicals formation together with impaired anti-oxidative defense capacity are involved in the initiation and progression of epilepsy and the development of its comorbidities [12, 13]. However, the impact of unbalanced oxidation stress on cognitive function in children with temporal lobe epilepsy apart from the effect of antiepileptic medications and refractory seizures is not fully explored. Evaluation of cognitive abilities and detection of risk factors that may add more burdens in such children can help individualization of treatment strategies.
The current study was conducted to explore the relation between oxidation stress/anti-oxidative imbalance, and cognitive function in children with newly diagnosed temporal lobe epilepsy.
Materials and Methods
A cross-sectional comparative study involved 42 children with newly diagnosed temporal lobe epilepsy who were recruited from children referred to Pediatric and Neurology Department at Al-Azhar University hospitals, Cairo, Egypt. A control group consisted of 42 healthy children of matched age and sex to epilepsy group was selected consecutively from attendance of pediatric outpatient clinics of Al-Azhar and Sayed Galal Hospital.
Inclusion criteria: Include children with confirmed temporal lobe epilepsy who were newly diagnosed and did not receive any previous antiepileptic drugs; their age ranged between 6 and 8 years old. Based on neurological examination and neuroimaging assay only those with idiopathic etiology were included. Control group were apparently healthy children who did not have family history of neuropsychiatric disorders or febrile seizures.
Exclusion criteria: Include children with any acute infection or inflammation, children with chronic medical disorders (e.g., metabolic, renal, hematological, cardiac, respiratory, and hepatic diseases), children with history of developmental delay, perinatal hypoxia or neuromuscular disability, children with structural brain abnormalities, children with mental retardation (IQ<70 by Wechsler intelligence quotient, the 3th edition), children with any psychological disorders and children who received any medications affect cognitive function within the previous 1 week as antihistaminic.
Diagnosis of epilepsy
A detailed medical history was obtained including socio demographic data (age, sex, level of education, and parent education), perinatal, developmental history, age of onset, seizures semiology, aura characteristics, seizures frequency, neurological manifestation, and previous investigations, or medications. Complete general and neurological clinical examinations were done.
Diagnosis of temporal lobe epilepsy was based on history of focal onset seizures either with retained or impaired awareness from reliable eye witness together with electroencephalography confirm the presence of temporal region epileptic discharge. Epilepsy was classified according to the principles of international league against epilepsy . Interictal EEG was done using a Nihon Kohden 1200 digital EEG instrument at pediatric neurology unit of Al-Zahraa Hospital. Intermittent photic stimulation, sleep deprivation, and hyperventilation activation procedures were done for children with epilepsy to confirm temporal lobe epileptic discharge. Neuroimaging was done for children with epilepsy to exclude any underlying organic brain lesions (trauma, hypoxia, infections, mesial temporal sclerosis, or structural malformation).
Newly diagnosed epilepsy includes subjects with more than two unprovoked seizures who are initially diagnosed with epilepsy who have not received any antiepileptic medications before enrolling in the study.
Children with newly diagnosed temporal lobe epilepsy and healthy controls were age and gender matched. Likewise, with matched parent education, socio-economic status, and children level of education to eliminate the impact of other factors that may affect children cognitive abilities. Regarding nutrition all including children received ordinary traditional food with no history of specific medications affecting the cognitive functions (e.g., Omega-3, multivitamin, antihistamines, and antipsychotics).
Cognitive function assessment
All included children were interviewed and subjected to psychological assessment to exclude psychological disorders. Cognitive function was evaluated by the Arabic Version of Wechsler Intelligence Scale for Children-The Third Edition (WISC-III) . This scale consists of performance and verbal subtests used to assess general intelligence and obtain total intelligence quotient (IQ) score, verbal IQ score, and performance IQ score. Verbal IQ score is obtained by doing 5 subscales (information that evaluate general knowledge and long term memory, similarities that evaluate logic thinking and verbal reasoning, arithmetic, digit span that evaluate working memory, and comprehension scales that evaluate social knowledge). While performance IQ score is score is obtained by doing another 5 subscales (picture completion that evaluate identification of related items, coding that evaluate organization, block design that evaluate analysis, designing, picture arrangement that evaluate visual-motor coordination, and object assembly scales that evaluate the identification of item parts). Total IQ score is based on the scores of both verbal and performance IQ scales. Assessment was done before initiating any antiepileptic medications. IQ score ≥130 is very superior, score 120-129 is superior, score 110-119 is high average, score 90-109 is average, score 80-89 is low average, score 70- 79 is borderline, and score ≤ 69 is extremely low. Time needed to complete the test ranges from 60 to 90 minutes.
Under complete aseptic condition, 4 ml venous blood were collected in ethylenediamine tetraacetic acid tubes (EDTA tubes), centrifuged for 15 minutes at 1000 x g within 30 minutes of collection and stored at -80°C according to manufacture till the time for analysis.
Plasma Human Advanced Oxidation Protein Products (AOPP) was measured by competitive enzyme-linked immunosorbent assay (ELISA) technique using Abbexa (Catalog No: abx258311) kits. The detection range was 61.7 ng/ml - 5000 ng/ml and the sensitivity was less than 23.7 ng/ml.
Plasma Total Antioxidant Capacity (TAC) was measured by competitive enzyme-linked immunosorbent assay (ELISA) technique using Cell Biolabs’ OxiSelect™ TAC Assay Kit (Catalog Number STA-360).
Plasma Malondialdehyde (MDA) was measured by competitive enzyme-linked immunosorbent assay (ELISA) technique using Elabscience kits (Catalog No: E-EL-0060). The detection range was 31.25-2000 ng/mL and the sensitivity was 18.75 ng/mL.
Plasma catalase was measured by competitive enzyme-linked immunosorbent assay (ELISA) technique using Elabscience kits (Catalog No: E-BC-K031-M). The detection range was 1.12-150 U/ml and the sensitivity was 1.12 U/mL.
The study follows the principles of the Declaration of Helsinki. Consent was obtained from caregivers of all children before they get enrolled in the study according to guideline of Local Ethics Committee of Al-Zharaa University.
Data analysis was done using the Statistical Package for Social Sciences (SPSS version 26, USA). Quantitative data were expressed as mean ± SD. Difference between groups was analyzed using independent student t-test and chi-square test. Correlations were performed using Pearson correlation coefficients. Logistic regression analysis was performed to detect predictors of cognitive dysfunction in children with epilepsy. P-value <0.05 was considered significant.
Results and Discussion
The current study included 42 children with newly diagnosed temporal lobe epilepsy (23 males and 19 females) and 42 healthy controls (21 males and 21 females). The age of onset of seizures ranged between 6 to 8 years. No significant difference was detected in age, sex, education, body weight, height, and body mass index between the two studied groups (Table 1).
There was a higher significant level of circulating malondialdehyde, advanced oxidation protein products, and lower catalase, total antioxidant capacity and cognition ability scores in children with temporal lobe epilepsy compared to the healthy controls (Table 2).
Cognition ability scores have a negative significant correlation with malondialdehyde and advanced oxidation protein products levels and significant positive correlation with the age of onset of seizures, circulating catalase, and total antioxidant capacity levels (Table 3).
Stepwise linear regression analysis revealed that younger age of onset and increased advanced oxidation protein products level represent independent predictors for cognitive performance in children with temporal lobe epilepsy as shown in (Table 4).
Epilepsy is a chronic neurologic disorder that adversely affects cognitive performance. Cognition impairment may persist even after seizures control and extend into adult life . The relation between epilepsy and cognition is complex. Some hypotheses suggest the cognitive dysfunction is a consequence of epilepsy while others suggests that both disorders are related to the same underlying etiology .
Evidences showed that cognitive impairment is occurred at the early stage of epilepsy even before initiation of antiepileptic medications .
Our studies revealed lower cognitive abilities performance in children with newly diagnosed temporal lobe epilepsy than their healthy peers which is in a good agreement with previous studies indicating that cognitive impairment is already present at the time of diagnosis of epilepsy and may antedates the initial recognized seizure .
Table 1: Comparison of socio-demographic data between children with epilepsy and healthy controls
Table 2: Comparison of cognition ability scores and circulating oxidants/antioxidants level between children with epilepsy and healthy controls
Table 3: Correlation between age of onset of seizures, oxidants/antioxidants level, and cognitive ability scores
Table 4: Stepwise linear regression analysis for the association between circulating oxidants/antioxidants level, age of onset, and total intelligence quotient of the studied children
Despite that IQ of children with idiopathic epilepsy is usually within the normal range, our findings showed that children with newly diagnosed temporal lobe epilepsy have about10 points lower mean IQ scores than healthy controls. Our study showed that children with newly diagnosed temporal epilepsy had lower scores for verbal and performance IQ than their healthy peers.
The presence of cognitive impairment at the time of epilepsy diagnosis in absence of structural brain lesion suggests the presence of a common pathophysiological mechanism inducing both disorders . The current study investigated oxidation stress as a link between epilepsy and cognition and revealed higher level of oxidants and lower level of antioxidants in children with newly diagnosed epilepsy. Furthermore, this oxidants/antioxidants imbalance was strongly correlated with lower cognitive ability scores in children with temporal lobe epilepsy.
Increased oxidation stress is one of the key factors involved in the process of epileptogenesis. The high lipid content of neuronal cells in addition to its high level of oxygen consumption making the brain at greater risk for oxidation stress induced cellular damage. When oxidation stress exceeds antioxidant capacity of the brain, those oxidants may disturb neuronal cells structural components, induce neuronal dysfunction leading to cell apoptosis or necrosis . Moreover, exposure to oxidation stress may activate pro-inflammatory signaling pathways leading to release of pro-inflammatory cytokines that induce neuro-inflammation and neuro-degeneration leading to the development of numerous epilepsy comorbidities even when seizure activity is controlled .
Several studies revealed that unbalanced oxidation stress is linked to psycho-behavioral comorbidities in children with newly diagnosed, refractory epilepsy or even in healthy subjects [23, 24]. Animal models showed that oxidation stress may implement in cognitive decline through inducing endothelial dysfunction and impairing cerebral blood flow . In human studies oxidation stress is one of the hypothesized mechanisms included in age related decline in learning and memory . Our study demonstrated that younger age of onset, higher levels of oxidants and lower level of antioxidants defenses were significantly associated with lower cognitive performance in children with temporal lobe epilepsy. Previous studies showed a strong association between oxidative stress and cognitive dysfunction in several disorders. However, no sufficient data was reported in epilepsy. Liu et al.  reported that elevated MDA level represent an independent predictor of post-stroke cognitive impairment . Previous studies reveled decreased total antioxidant capacity in newly diagnosed and untreated epileptic subjects improved after initiation of antiepileptic medications and achieving seizure control [29, 30]. Animal model of epilepsy showed improved cognition and memory performance using medications that eliminate the oxidative stress . Pearson et al.  demonstrated that exposure to oxidative stress in animal model of temporal lobe epilepsy induce cognitive dysfunction. Furthermore, pharmacological removal of reactive oxygen species may improve cognitive performance in such animal model.
Identification of baseline cognitive abilities at the time of diagnosis of epilepsy and regular monitoring of cognitive performance are required to adjust treatment plan, and avoid further cognition impairment and learning disabilities especially in children with younger age of onset of seizures.
The first limitation is the small number of the studied children. The second limitation is the cross sectional designs of this study that interferes with assessment of cause-effect relationship.
Oxidation stress may be associated with impaired cognitive abilities in children with newly diagnosed temporal lobe epilepsy. Treatment strategy for children with newly diagnosed temporal lobe epilepsy should be adjusted to decrease oxidation stress to avoid worsening of cognitive performance.
Conflict of Interest
The authors declare that there is no conflict of interest in this article.
Authors did not receive any funding source to declare.
All authors contributed to data analysis, drafting, and revising of the article and agreed to be responsible for all the aspects of this work.
Heba Tawfik Okda
Mohamed Farouk Ahmed
Rasha M. Gouda
Rasha Sobhy Elattar
Seham Eelsaid Abdelsadek
Talal Abd Allah Mohammed Dawa
Mohammad Fathi Abdulsalam
Fathy Mahmoud Mansour
Adel M. Othman
Shahinaz El Attar
Rayyh A.M. Saleh
HOW TO CITE THIS ARTICLE
Marwa Elhady, Heba Tawfik Okda, Mohamed Farouk Ahmed, Rasha M. Gouda, Rasha Sobhy Elattar, Seham Eelsaid Abdelsadek, Talal Abd Allah Mohammed Dawa, Mohammad Fathi Abdulsalam, Fathy Mahmoud Mansour, Adel M. Othman, Doaa Ibrahim Hassan Ibrahim, Shaimaa A.Maklad, Shahinaz El Attar, Walaa Shipl, Rayyh A.M. Saleh, Esraa Ali. Oxidative stress and cognitive performance in children with temporal lobe epilepsy. J. Med. Chem. Sci., 2024, 7(1) 24-33.