Blog 12 – Oxidative Stress and Epilepsy
Oxidative stress is thought to be the underlying cause of major brain diseases including epilepsy. In association with neuroinflammation (Blog 11 Sleep Disturbances and Epilepsy – Adversaries), oxidative stress is considered an important facilitator in epilepsy that eventually leads to brain damage. On this point, there exist numerous reviews and animal studies supporting a causative role of oxidative stress in epilepsy. Sadly, there are only a handful of clinical trials that have tested this role.
Scientists know very little about the development and progression of epilepsy. It is clear that abnormal repetitive neuronal activity called seizures, are the major symptom of the disease. A small percentage of epilepsies are due to known genetic mutations. The remainder, termed acquired epilepsies, have possible origins in known neurological insults e.g. trauma, illness. However, the cause of acquired epilepsy for most, remains unknown. Therefore, studies that might identify a common biological pathway such as oxidative stress, for the majority of epilepsies, may lead to better therapies and a possible cure.
Recall that approximately 30-40 percent of patients with epilepsy do not respond to anti-seizure medication. Those that do, however, must endure side effects, some of which cause patients to stop their medication. Furthermore, anti-seizure medication treats the symptoms and not the underlying pathological processes. Thus, it is vital that research into the basic mechanism(s) of epilepsy is front and center. Evaluation of the role of oxidative stress in epilepsy is a reasonable place to start.
What is Oxidative Stress?
Metabolic processes in our cells, whether dependent on enzymes or not, constantly produce substances (small molecules, particles) that are highly reactive with nearby essential compounds. These reactive species (RS) contain oxygen, nitrogen or carbon that promote oxidative changes. Importantly, there is an abundance of RS in our cells and at high concentrations, all RS may directly harm neighboring indispensable compounds, such as proteins, DNA and fats. Specifically, if the damaged compound is not repaired, these random oxidative changes hinder and subsequently prohibit normal cellular functions. The outcome is that cells die prematurely and create a state of inflammation.
Fortunately, humans possess a wealth of anti-oxidative defense mechanisms to prevent random oxidative destruction. These mechanisms include the well-known anti-oxidative compounds e.g. vitamin C and E, selenium, polyphenols, lycopene and flavonoids, all found in fruits and vegetables. Lesser known mechanisms but of higher overall benefits are the anti-oxidative enzymes e.g. superoxide dismutase (SOD), catalase and glutathione peroxidase. Additionally, sophisticated repair mechanisms exist that exclusively identify and repair oxidized DNA and proteins.
Oxidative stress occurs when the amount of RS overwhelms the antioxidative systems. Therefore, key components are not repaired and become dysfunctional. Fortunately, our anti-oxidative mechanisms are so effective that oxidative stress is minimal. However, with age, illness, injury, extreme stress, and initial stages of chronic disease, oxidative stress is evident and harmful.
Role of Oxidative Stress in Epilepsy
Several recent reviews summarize the experimental data supportive of a role of oxidative stress in seizures and progression of epilepsy (Lin et al., 2020; Parsons et al., 2022). Mainly, oxidative stress as defined above is considered “one of the early cellular events and a critical factor to determine the fate of neurons in epilepsy.” (Lin et al., 2020).
Supportive Data that Oxidative Stress is a Key Mechanism in Epilepsy
1. Epilepsies due to genetic mutations and genetic animal models of epilepsy show production of reactive species, deficiency of anti-oxidative mechanisms and subsequent neuronal damage (Pearson-Smith et al., 2017).
2. The amount of oxidative metabolites and antioxidative potential in children and adults with severe epilepsy correlate with seizure frequency (Morimoto et al., 2016). Additionally, altered anti-oxidative systems have been identified in patients with temporal lobe epilepsy (Keskin et al., 2016). Analysis of resected human brain tissue (those undergoing surgery) show evidence of oxidative damage and neuronal cell damage and death (Pecorelli et al., 2015).
3. Results of numerous experiments in experimental models of epilepsy report that anti-oxidants e.g. N-acetyl-cysteine, melatonin, vitamin C and vitamin E inhibit seizure-induced oxidative damage. Also, artificial activation of the genetic network that promotes anti-oxidative mechanisms prevents oxidative stress, preserves neurons and reduces seizures in animal models of epilepsy.
Clinical Trials
Armed with aforementioned findings, clinicians began to assess the efficacy of anti-oxidant therapy in patients with epilepsy. Nineteen antioxidant compounds have been successfully evaluated in animal models of epilepsy (Lin et al.,2020). Of these, 7 compounds (N-acetyl cysteine; ubiquinone; vitamin C, selenium/sildenafil; vitamin E and melatonin) have undergone clinical trials in man. Despite the fact that many trials ended more than 7 years ago, results for only two of these compounds, vitamin E and melatonin, are publically available.
Vitamin E
Vitamin E is a fat soluble anti-oxidant found in nuts, plant-based oils (e.g. olive, sunflower) and avocados, for example. Two clinical trials using vitamin E as an add-on to anti-seizure medication produced contrasting results. The first study of 12 patients with epilepsy reported that vitamin E, daily for six months significantly reduced seizure frequency in 10 of the 12 patients (Ogunmekan and Hwang, 1989). In contrast, daily use of vitamin E for 3 months in 43 patients was without effect on seizure frequency or severity (Raju et al., 1994). Both studies used what clinicians consider to be very high doses of vitamin E (more than 15 times the recommended daily allowance).
Melatonin
Melatonin is a sleep regulating hormone produced by the pineal gland in the brain. It is commercially available in extended release form to enhance sleep duration and quality. Additionally, due to its structure, it acts as an anti-oxidant. Since epilepsy is associated with sleep disturbances (Sleep Disturbances and Epilepsy – Adversaries), the use of melatonin as an add-on therapy for drug resistant (intractable epilepsy) is reasonable.
There have been six published clinical trials evaluating melatonin in epilepsy. Five of the 6 studies pertain to children and evaluated melatonin efficacy in 6-37 youngsters with epilepsy for generally a 3 month period. Melatonin significantly improved sleep characteristics and improved seizure severity in 2 of the 5 studies. Due to the small number of participants, it is impossible to know why positive results occurred in some but not all studies. One study in adults with generalized epilepsy found melatonin added on to therapy of valproate for 8 weeks improved both sleep characteristics and reduced the seizure frequency and severity (Verma et al., 2021). Although larger than trials with children, this trial evaluated only 52 patients.
Conclusions
There is considerable experimental data supporting the hypothesis that oxidative stress is instrumental in creating an abnormal environment that continues to perpetuate seizures and maintain the disease state. Clinical evaluations of more effective antioxidative compounds would be worthwhile. The positive results of melatonin in adults is a good start that needs confirmation with a larger study.
Select References
Keskin Guler, S et al., Antioxidative-oxidative balance in epilepsy patients on antiepileptic therapy: A prospective case-control study. Neurol. Sci. 5: 763–767, 2016.
Lin T-K et al., Seizure-Induced Oxidative Stress in Status Epilepticus: Is Antioxidant Beneficial? Antioxidants 9: 1029, 2020
Morimoto M et al., Oxidative Stress Measurement and Prediction of Epileptic Seizure in Children and Adults With Severe Motor and Intellectual Disabilities. J Clin Med Res. 8(6): 437-444,2016.
Ogunmekaan AO, Hwang PA. A randomized, double-blind, placebo-controlled, clinical trial of D-alpha-tocopheryl acetate (vitamin E), as add-on therapy, for epilepsy in children. Epilepsia. 30(1): 84-9, 1989.
Parsons ALM et al., The Interconnected Mechanisms of Oxidative Stress and Neuroinflammation in Epilepsy. Antioxidants 11: 157, 2022.
Pecorelli A et al., NADPH oxidase activation and 4-hydroxy-2-nonenal/aquaporin-4 adducts as possible new players in oxidative neuronal damage presents in drug-resistant epilepsy. Biochim Biophys Acta. 1852(3): 507-19, 2015..
Raju GB, Behari M, Prasad K, Ahuja GK. Randomized, double-blind, placebo-controlled, clinical trial of D-alpha-tocopherol (vitamin E) as add-on therapy in uncontrolled epilepsy. Epilepsia. 35(2): 368-72,1994.
Verma N et al., Effect of add-on melatonin on seizure outcome, neuronal damage, oxidative stress, and quality of life in generalized epilepsy with generalized onset motor seizures in adults: A randomized controlled trial. J Neurosci Res. 99(6): 1618-1631, 2021.