Activation of NADPH oxidase and extracellular superoxide production in seizure-induced hippocampal damage

Pharmacological elevation of glutathione inhibits status epilepticus-induced neuroinflammation and oxidative injury

Glutathione (GSH) is a major endogenous antioxidant, and its depletion has been observed in several brain diseases including epilepsy. Previous studies in our laboratory have shown that dimercaprol (DMP) can elevate GSH via post-translational activation of glutamate cysteine ligase (GCL), the rate limiting GSH biosynthetic enzyme and inhibit neuroinflammation in vitro. Here we determined 1) the role of cysteamine as a new mechanism by which DMP increases GSH biosynthesis and 2) its ability to inhibit neuroinflammation and neuronal injury in the rat kainate model of epilepsy. DMP depleted cysteamine in a time- and concentration-dependent manner in a cell free system. To guide the in vivo administration of DMP, its pharmacokinetic profile was determined in the plasma, liver, and brain. The results confirmed DMP's ability to cross the blood-brain-barrier. Treatment of rats with DMP (30 mg/kg) depleted cysteamine in the liver and hippocampus that was associated with increased GCL activity in these tissues. GSH levels were significantly increased (20 %) in the hippocampus 1 h after 30 mg/kg DMP administration. Following DMP (30 mg/kg) administration once daily, a marked attenuation of GSH depletion was seen in the SE model. SE-induced inflammatory markers including cytokine release, microglial activation, and neuronal death were significantly attenuated in the hippocampus with DMP treatment. Taken together, these results highlight the importance of restoring redox status with rescue of GSH depletion by DMP in post epileptogenic insults.

Activatable Dual-Optical Molecular Probe for Bioimaging Superoxide Anion in Epilepsy

Superoxide anion (O2•-) plays a pivotal role in the generation of other reactive oxygen species within the body and is closely linked to epilepsy. Despite this connection, achieving precise imaging of O2•- during epilepsy pathology remains a formidable challenge. Herein, we develop an activatable molecular probe, CL-SA, to track the fluctuation of the level of O2•- in epilepsy through simultaneous fluorescence imaging and chemiluminescence sensing. The developed probe CL-SA demonstrated its efficacy in imaging of O2•- in neuronal cells, showcasing its dual optical imaging capability for O2•- in vitro. Furthermore, CL-SA was successfully used to observe aberrantly expressed O2•- in a mouse model of epilepsy. Overall, CL-SA provides us with a valuable tool for chemical and biomedical studies of O2•-, promoting the investigation of O2•- fluctuations in epilepsy, as well as providing a reliable means to explore the diagnosis and therapy of epilepsy.

NOX-induced oxidative stress is a primary trigger of major neurodegenerative disorders

Neurodegenerative diseases (NDDs) causing cognitive impairment and dementia are difficult to treat due to the lack of understanding of primary initiating factors. Meanwhile, major sporadic NDDs share many risk factors and exhibit similar pathologies in their early stages, indicating the existence of common initiation pathways. Glucose hypometabolism associated with oxidative stress is one such primary, early and shared pathology, and a likely major cause of detrimental disease-associated cascades; targeting this common pathology may therefore be an effective preventative strategy for most sporadic NDDs. However, its exact cause and trigger remain unclear. Recent research suggests that early oxidative stress caused by NADPH oxidase (NOX) activation is a shared initiating mechanism among major sporadic NDDs and could prove to be the long-sought ubiquitous NDD trigger. We focus on two major NDDs - Alzheimer's disease (AD) and Parkinson's disease (PD), as well as on acquired epilepsy which is an increasingly recognized comorbidity in NDDs. We also discuss available data suggesting the relevance of the proposed mechanisms to other NDDs. We delve into the commonalities among these NDDs in neuroinflammation and NOX involvement to identify potential therapeutic targets and gain a deeper understanding of the underlying causes of NDDs.

Therapeutic Strategies to Ameliorate Neuronal Damage in Epilepsy by Regulating Oxidative Stress, Mitochondrial Dysfunction, and Neuroinflammation

Epilepsy is a central nervous system disorder involving spontaneous and recurring seizures that affects 50 million individuals globally. Because approximately one-third of patients with epilepsy do not respond to drug therapy, the development of new therapeutic strategies against epilepsy could be beneficial. Oxidative stress and mitochondrial dysfunction are frequently observed in epilepsy. Additionally, neuroinflammation is increasingly understood to contribute to the pathogenesis of epilepsy. Mitochondrial dysfunction is also recognized for its contributions to neuronal excitability and apoptosis, which can lead to neuronal loss in epilepsy. This review focuses on the roles of oxidative damage, mitochondrial dysfunction, NAPDH oxidase, the blood-brain barrier, excitotoxicity, and neuroinflammation in the development of epilepsy. We also review the therapies used to treat epilepsy and prevent seizures, including anti-seizure medications, anti-epileptic drugs, anti-inflammatory therapies, and antioxidant therapies. In addition, we review the use of neuromodulation and surgery in the treatment of epilepsy. Finally, we present the role of dietary and nutritional strategies in the management of epilepsy, including the ketogenic diet and the intake of vitamins, polyphenols, and flavonoids. By reviewing available interventions and research on the pathophysiology of epilepsy, this review points to areas of further development for therapies that can manage epilepsy.

Spatial, temporal, and cell-type-specific expression of NADPH Oxidase isoforms following seizure models in rats

The NADPH Oxidase (NOX) enzymes are key producers of reactive oxygen species (ROS) and consist of seven different isoforms, distributed across the tissues and cell types. The increasing level of ROS induces oxidative stress playing a crucial role in neuronal death and the development of epilepsy. Recently, NOX2 was reported as a primary source of ROS production, activated by NMDA receptor, a crucial marker of epilepsy development. Here, we demonstrate spatial, temporal, and cellular expression of NOX2 and NOX4 complexes in in-vitro and in-vivo seizure models. We showed that the expression of NOX2 and NOX4 was increased in the initial 24 h following a brief seizure induced by pentylenetetrazol. Interestingly, while this elevated level returns to baseline 48 h following seizure in the cortex, in the hippocampus these levels remain elevated up to one week following the seizure. Moreover, we showed that 1- and 2- weeks following status epilepticus (SE), expression of NOX2 and NOX4 remains significantly elevated both in the cortex and the hippocampus. Furthermore, in in-vitro seizure model, NOX2 and NOX4 isoforms were overexpressed in neurons and astrocytes following seizures. These results suggest that NOX2 and NOX4 in the brain have a transient response to seizures, and these responses temporally vary depending on, seizure duration, brain region (cortex or hippocampus), and cell types.

Crosstalk between neuroinflammation and oxidative stress in epilepsy

The roles of both neuroinflammation and oxidative stress in the pathophysiology of epilepsy have begun to receive considerable attention in recent years. However, these concepts are predominantly studied as separate entities despite the evidence that neuroinflammatory and redox-based signaling cascades have significant crosstalk. Oxidative post-translational modifications have been demonstrated to directly influence the function of key neuroinflammatory mediators. Neuroinflammation can further be controlled on the transcriptional level as the transcriptional regulators NF-KB and nrf2 are activated by reactive oxygen species. Further, neuroinflammation can induce the increased expression and activity of NADPH oxidase, leading to a highly oxidative environment. These factors additionally influence mitochondria function and the metabolic status of neurons and glia, which are already metabolically stressed in epilepsy. Given the implication of this relationship to disease pathology, this review explores the numerous mechanisms by which neuroinflammation and oxidative stress influence one another in the context of epilepsy. We further examine the efficacy of treatments targeting oxidative stress and redox regulation in animal and human epilepsies in the literature that warrant further investigation. Treatment approaches aimed at rectifying oxidative stress and aberrant redox signaling may enable control of neuroinflammation and improve patient outcomes.

The metabolic basis of epilepsy

The brain is a highly energy-demanding organ and requires bioenergetic adaptability to balance normal activity with pathophysiological fuelling of spontaneous recurrent seizures, the hallmark feature of the epilepsies. Recurrent or prolonged seizures have long been known to permanently alter neuronal circuitry and to cause excitotoxic injury and aberrant inflammation. Furthermore, pathological changes in bioenergetics and metabolism are considered downstream consequences of epileptic seizures that begin at the synaptic level. However, as we highlight in this Review, evidence is also emerging that primary derangements in cellular or mitochondrial metabolism can result in seizure genesis and lead to spontaneous recurrent seizures. Basic and translational research indicates that the relationships between brain metabolism and epileptic seizures are complex and bidirectional, producing a vicious cycle that compounds the deleterious consequences of seizures. Metabolism-based treatments such as the high-fat, antiseizure ketogenic diet have become mainstream, and metabolic substrates and enzymes have become attractive molecular targets for seizure prevention and recovery. Moreover, given that metabolism is crucial for epigenetic as well as inflammatory changes, the idea that epileptogenesis can be both negatively and positively influenced by metabolic changes is rapidly gaining ground. Here, we review evidence that supports both pathophysiological and therapeutic roles for brain metabolism in epilepsy.

Neuroprotective role of apocynin against pentylenetetrazole kindling epilepsy and associated comorbidities in mice by suppression of ROS/RNS

Epilepsy is a neurological disease that transpires due to the unusual synchronized neuronal discharge within the central nervous system, which drives repetitious unprovoked seizures. Nicotinamide adenine dinucleotide phosphate (NADPH) oxidase is a complex enzyme accountable for reactive oxygen species (ROS) production, neurodegeneration, neurotoxicity, memory impairment, vitiates normal cellular processes, long term potentiation, and thus, implicated in the pathogenesis of epilepsy. Therefore, the present study was sketched to examine the neuroprotective effect of apocynin, NADPH oxidase inhibitor in pentylenetetrazole kindling epilepsy, and induced comorbidities in mice. Mice (either sex) were given pentylenetetrazole (35 mg/kg, i.p.) every other day up to 29 days, and a challenge test was executed on the 33^rd day. Pretreatment with apocynin (25, 50, and 100 mg/kg, i.p.) was carried out from 1^st to 33^rd day. Rotarod and open field test were performed on the 1^st, 10^th, 20^th, and 30^th days of the study. Animals were tutored on the morris water maze from 30^th to 33^rd day, and the retention was registered on the 34^th day. Tail suspension test and elevated plus maze were sequentially performed on the 32^nd and 33^rd day of the study. On the 34^th day, animals were sacrificed, and their brains were isolated to conduct biochemical estimation. NADPH oxidase activation due to chronic pentylenetetrazole treatment resulted in generalized tonic-clonic seizures, enhanced oxidative stress, remodeled neurotransmitters' level, and resulted in comorbidities (anxiety, depression, and memory impairment). Pretreatment with apocynin significantly restricted the pentylenetetrazole induced seizure severity, ROS production, neurotransmitter alteration, and comorbid conditions by inhibiting the NADPH oxidase enzyme.

Melissa officinalis L. ameliorates oxidative stress and inflammation and upregulates Nrf2/HO-1 signaling in the hippocampus of pilocarpine-induced rats

Epilepsy is characterized by recurrent epileptic seizures, and its effective management continues to be a therapeutic challenge. Oxidative stress and local inflammatory response accompany the status epilepticus (SE). This study evaluated the effect of Melissa officinalis extract (MOE) on oxidative stress, inflammation, and neurotransmitters in the hippocampus of pilocarpine (PILO)-administered rats, pointing to the involvement of Nrf2/HO-1 signaling. Rats received PILO via intraperitoneal administration and were treated with MOE for 2 weeks. MOE prevented neuronal loss; decreased lipid peroxidation, Cox-2, PGE2, and BDNF; and downregulated glial fibrillary acidic protein in the hippocampus of PILO-treated rats. In addition, MOE enhanced GSH and antioxidant enzymes, upregulated Nrf2 and HO-1 mRNA abundance, and increased the nuclear translocation of Nrf2 in the hippocampus of epileptic rats. Na⁺/K⁺-ATPase activity and GABA were increased, and glutamate and acetylcholine were decreased in the hippocampus of epileptic rats treated with MOE. In conclusion, MOE attenuated neuronal loss, oxidative stress, and inflammation; activated Nrf2/HO-1 signaling; and modulated neurotransmitters, GFAP, and Na⁺/K⁺-ATPase in the hippocampus of epileptic rats. These findings suggest that M. officinalis can mitigate epileptogenesis, pending further studies to explore the exact underlying mechanisms.

Imbalance of Systemic Redox Biomarkers in Children with Epilepsy: Role of Ferroptosis

To assess if ferroptosis, a new type of programmed cell death accompanied by iron accumulation, lipid peroxidation, and glutathione depletion, occurs in children with epilepsy, and in order to identify a panel of biomarkers useful for patient stratification and innovative-targeted therapies, we measured ferroptosis biomarkers in blood from 83 unrelated children with a clinical diagnosis of epilepsy and 44 age-matched controls. We found a marked dysregulation of three ferroptosis key markers: a consistent increase of 4-hydroxy-2-nonenal (4-HNE), the main by-product of lipid peroxidation, a significant decrease of glutathione (GSH) levels, and a partial inactivation of the enzyme glutathione peroxidase 4 (GPX4), the mediator of lipid peroxides detoxification. Furthermore, we found a significant increase of NAPDH oxidase 2 (NOX2) in the blood of children, supporting this enzyme as a primary source of reactive oxygen species (ROS) in epilepsy. Additionally, since the nuclear factor erythroid 2-related factor 2 (NRF2) induction protects the brain from epileptic seizure damage, we also evaluated the NRF2 expression in the blood of children. The antioxidant and anti-inflammatory transcription factor was activated in patients, although not enough to re-establish a correct redox homeostasis for counteracting ferroptosis. Ferroptosis-mediated oxidative damage has been proposed as an emergent mechanism underlying the pathogenesis of epilepsy. Overall, our study confirms a crucial role for ferroptosis in epilepsy, leading to the identification of a panel of biomarkers useful to find new therapeutic targets. Developing innovative drugs, which act by inhibiting the ferroptosis signaling axis, may represent a promising strategy for new anti-seizure medications.

Circulating glutathione peroxidase and superoxide dismutase levels in patients with epilepsy: A meta-analysis

PURPOSE

Glutathione peroxidase (GSH-Px) and superoxide dismutase (SOD) are assessed as oxidative stress markers to determine the impact of oxidation on the levels of GSH-Px and SOD in patients with epilepsy (PWE) and healthy controls.

METHODS

A meta-analysis was completed on twenty-nine published studies. A total of 636 PWE and 665 healthy controls, 303 PWE and 191 controls, and 22 PWE and 22 controls were included to study GSH-Px levels in erythrocytes, serum and plasma, respectively. For SOD studies, there were 610 PWE and 680 controls, 464 PWE and 382 controls, and 62 PWE with 77 controls for erythrocytes, serum and plasma, respectively.

RESULTS

Meta-analysis showed that the erythrocyte SOD level was significantly lower in PWE than in healthy controls (SMD =-1.96; 95% CI [-2.93, -0.99]; P<0.0001). Moreover, the meta-analysis demonstrated that in serum and plasma, SOD levels in PWE were significantly lower than those in healthy controls (SMD =-1.47; 95% CI [-2.47, -0.48]; P<0.0001). Erythrocyte GSH-Px levels had a tendency to decrease in PWE compared with healthy controls (SMD =-0.31; 95% CI [-1.48, 0.85]; P=0.598), but the results showed no significant difference.

CONCLUSION

Our results showed reduced SOD levels in erythrocytes, serum and plasma in PWE, which may be an indicator of oxidative damage in epilepsy. This is the first meta-analysis of circulating GSH-Px and SOD levels in PWE and healthy controls.

Diapocynin, an NADPH oxidase inhibitor, counteracts diisopropylfluorophosphate-induced long-term neurotoxicity in the rat model

Organophosphate (OP) nerve agents are a threat to both the military and civilians. OP exposure causes cholinergic crisis and status epilepticus (SE) because of irreversible inhibition of acetylcholinesterase that can be life-threatening if left untreated. OP survivors develop long-term morbidity, such as cognitive impairment and motor dysfunction, because of oxidative stress and progressive neuroinflammation and neurodegeneration, which act as disease promoters. Current medical countermeasures (MCMs) do not mitigate these pathologies. Therefore, our goal was to target these disease promoters using diapocynin (DPO), an NADPH oxidase inhibitor, in addition to MCMs, in a rat diisopropylfluorophosphate (DFP) model. The DFP-intoxicated rats were treated with DPO (300 mg/kg, oral, six doses, 12-h intervals) or vehicle 2 h following behavioral SE termination with diazepam. The DPO treatment significantly rescued DFP-induced motor impairment and attenuated epileptiform spiking during the first 72 h after DFP exposure in severely seizing rats despite no difference in epileptiform spike rate between the vehicle and DPO groups in mild SE rats. DPO significantly reduced DFP-induced reactive astrogliosis, neurodegeneration, GP91phox , glutathiolated protein, serum nitrite, and proinflammatory cytokines and chemokines, such as interleukins (ILs) IL-1α, IL-6, IL-2, IL-17A, leptin, and IP-10, in the hippocampus. Collectively, these data support a neuroprotective role of DPO in an OP-induced neurotoxicity model.

Seizure-Induced Oxidative Stress in Status Epilepticus: Is Antioxidant Beneficial?

Epilepsy is a common neurological disorder which affects patients physically and mentally and causes a real burden for the patient, family and society both medically and economically. Currently, more than one-third of epilepsy patients are still under unsatisfied control, even with new anticonvulsants. Other measures may be added to those with drug-resistant epilepsy. Excessive neuronal synchronization is the hallmark of epileptic activity and prolonged epileptic discharges such as in status epilepticus can lead to various cellular events and result in neuronal damage or death. Unbalanced oxidative status is one of the early cellular events and a critical factor to determine the fate of neurons in epilepsy. To counteract excessive oxidative damage through exogenous antioxidant supplements or induction of endogenous antioxidative capability may be a reasonable approach for current anticonvulsant therapy. In this article, we will introduce the critical roles of oxidative stress and further discuss the potential use of antioxidants in this devastating disease.

Inflammatory and immune mechanisms underlying epileptogenesis and epilepsy: From pathogenesis to treatment target

Epilepsy is a brain disease associated with epileptic seizures as well as with neurobehavioral outcomes of this condition. In the last century, inflammation emerged as a crucial factor in epilepsy etiology. Various brain insults through activation of neuronal and non-neuronal brain cells initiate a series of inflammatory events. Growing observations strongly suggest that abnormal activation of critical inflammatory processes contributes to epileptogenesis, a gradual process by which a normal brain transforms into the epileptic brain. Increased knowledge of inflammatory pathways in epileptogenesis has unveiled mechanistic targets for novel antiepileptic therapies. Molecules specifically targeting the pivotal inflammatory pathways may serve as promising candidates to halt the development of epilepsy. The present paper reviews the pieces of evidence conceptually supporting the potential role of inflammatory mechanisms and the relevant blood-brain barrier (BBB) disruption in epileptogenesis. Also, it discusses the mechanisms underlying inflammation-induced neuronal-glial network impairment and highlights innovative neuroregulatory actions of typical inflammatory molecules. Finally, it presents a brief analysis of observations supporting the therapeutic role of inflammation-targeting tiny molecules in epileptic seizures.

Modulating neuroinflammation and oxidative stress to prevent epilepsy and improve outcomes after traumatic brain injury

Traumatic brain injury (TBI) is a leading cause of death and disability in young adults worldwide. TBI survival is associated with persistent neuropsychiatric and neurological impairments, including posttraumatic epilepsy (PTE). To date, no pharmaceutical treatment has been found to prevent PTE or ameliorate neurological/neuropsychiatric deficits after TBI. Brain trauma results in immediate mechanical damage to brain cells and blood vessels that may never be fully restored given the limited regenerative capacity of brain tissue. This primary insult unleashes cascades of events, prominently including neuroinflammation and massive oxidative stress that evolve over time, expanding the brain injury, but also clearing cellular debris and establishing homeostasis in the region of damage. Accumulating evidence suggests that oxidative stress and neuroinflammatory sequelae of TBI contribute to posttraumatic epileptogenesis. This review will focus on possible roles of reactive oxygen species (ROS), their interactions with neuroinflammation in posttraumatic epileptogenesis, and emerging therapeutic strategies after TBI. We propose that inhibitors of the professional ROS-generating enzymes, the NADPH oxygenases and myeloperoxidase alone, or combined with selective inhibition of cyclooxygenase mediated signaling may have promise for the treatment or prevention of PTE and other sequelae of TBI. This article is part of the special issue entitled 'New Epilepsy Therapies for the 21st Century - From Antiseizure Drugs to Prevention, Modification and Cure of Epilepsy'.

Solid Lipid Nanoparticles Enhanced the Neuroprotective Role of Curcumin against Epilepsy through Activation of Bcl-2 Family and P38 MAPK Pathways

Oxidative stress of neurons caused by a series of complex neuropathological processes will induce certain neurodegenerative disorders including epilepsy. Curcumin (Cur) is an effective natural antioxidant compound; however, the poor bioavailability obstructs its neural protective applications. In this study, Cur is encapsulated in solid lipid nanoparticles (SLNs) for better neuroprotective efficacy. In vitro study certified that Cur-SLNs functioned obviously better against neuronal apoptosis than Cur, by significantly decreasing the level of free radical and reversing mitochondrial function through the activation of the Bcl-2 family. In vivo experiments showed that SLNs transported Cur through the blood-brain barrier (BBB). The behavioral performance of epileptic mice was improved by Cur-SLNs, with more NeuN but less TUNEL positive cells observed in hippocampus. The in vivo mechanism was also explored. Cur-SLNs reduced neuronal apoptosis through Bcl2 family and P38 MAPK pathways. Overall, Cur-SLNs have better protective effects toward oxidative stress in neurons than free Cur both in vitro and in vivo, which suggests they may be a promising agent against neurodegenerative disorders including epilepsy.

Activation of the phagocyte NADPH oxidase/NOX2 and myeloperoxidase in the mouse brain during pilocarpine-induced temporal lobe epilepsy and inhibition by ketamine

Excessive reactive oxygen species (ROS) production can induce tissue injury involved in a variety of neurodegenerative disorders such as neurodegeneration observed in pilocarpine-induced temporal lobe epilepsy. Ketamine, a noncompetitive N-methyl-D-aspartate (NMDA) receptor antagonist has beneficial effects in pilocarpine-induced temporal lobe epilepsy, when administered within minutes of seizure to avoid the harmful neurological lesions induced by pilocarpine. However, the enzymes involved in ROS productions and the effect of ketamine on this process remain less documented. Here we show that during pilocarpine-induced epilepsy in mice, the expression of the phagocyte NADPH oxidase NOX2 subunits (NOX2/gp91^phox, p22^phox, and p47^phox) and the expression of myeloperoxidase (MPO) were dramatically increased in mice brain treated with pilocarpine. Interestingly, treatment of mice with ketamine before or after pilocarpine administration decreased this process, mainly when injected before pilocarpine. Finally, our results showed that pilocarpine induced p47^phox phosphorylation and H₂O₂ production in mice brain and ketamine was able to inhibit these processes. Our results show that pilocarpine induced NOX2 activation to produce ROS in mice brain and that administration of ketamine before or after the induction of temporal lobe epilepsy by pilocarpine inhibited this activation in mice brain. These results suggest a key role of the phagocyte NADPH oxidase NOX2 and MPO in epilepsy and identify a novel effect of ketamine.

Antioxidant drug therapy as a neuroprotective countermeasure of nerve agent toxicity

The use of chemical warfare agents is an ongoing, significant threat to both civilians and military personnel worldwide. Nerve agents are by far the most formidable toxicants in terms of their lethality and toxicity. Nerve agents initiate neurotoxicity by the irreversible inhibition of acetylcholinesterase and resultant accumulation of acetylcholine in excitable tissues. The cholinergic toxidrome presents as miosis, lacrimation, diarrhea, fasciculations, seizures, respiratory arrest and coma. Current medical countermeasures can attenuate acute mortality and confer limited protection against secondary neuronal injury when given rapidly after exposure. However, there is an urgent need for the development of novel, add-on neuroprotective therapies to prevent mortality and long-term toxicity of nerve agents. Increasing evidence suggests that pathways other than direct acetylcholinesterase inhibition contribute to neurotoxicity and secondary neuronal injury. Among these, oxidative stress is emerging as a key therapeutic target for nerve agent toxicity. In this review, we discuss the rationale for targeting oxidative stress in nerve agent toxicity and highlight research investigating antioxidant therapy as a neuroprotective medical countermeasure to attenuate oxidative stress, neuroinflammation and neurodegeneration.

Rosiglitazone attenuates cell apoptosis through antioxidative and anti-apoptotic pathways in the hippocampi of spontaneously hypertensive rats

Oxidative stress serves an important role in hypertensive brain damage. Peroxisome proliferator‑activated receptor γ (PPAR‑γ) agonists possess antioxidative and anti‑apoptotic effects. The present study verified the possibility that rosiglitazone serves a neuroprotective role by alleviating oxidative stress and cell apoptosis in the hippocampi of spontaneously hypertensive rats (SHRs). SHRs and age‑matched Wistar‑Kyoto (WKY; both 56 weeks old) rats received gavage administration of vehicle or rosiglitazone (5 mg/kg/day) for eight weeks. Systolic blood pressure (SBP) was measured by the indirect tail‑cuff method. The expression ratio of activated astrocytes was analyzed by glial fibrillary acidic protein immunohistochemistry. PPAR‑γ, inducible nitric oxide synthase (iNOS), gp47phox, B‑cell lymphoma 2 (Bcl‑2), Bcl‑2‑associated X protein (Bax) and caspase‑3 expression were investigated by quantitative polymerase chain reaction and western blot analysis. The number of apoptotic cells in the hippocampus of four groups was detected using the terminal deoxynucleotidyl transferase‑mediated dUTP end‑labeling (TUNEL) method. Compared with the WKY group, the SHR group exhibited decreased Bcl‑2 and PPAR‑γ expression, increased SBP, increased ratio of activated astrocytes and TUNEL‑positive cells, increased expression of iNOS, gp47phox, caspase‑3 and Bax. Rosiglitazone administration increased Bcl‑2 and PPAR‑γ expression, decreased the ratio of activated astrocytes and TUNEL‑positive cells, decreased iNOS, gp47phox, caspase‑3 and Bax expression in the hippocampi of SHRs. However, rosiglitazone did not significantly decreased SBP in the SHR group. Therefore, rosiglitazone exerts neuroprotective effect through antioxidative and anti‑apoptotic pathways, which was independent of blood pressure control.

A Metabolic Paradigm for Epilepsy

There is a resurgence of interest in the role of metabolism in epilepsy. Long considered ancillary and acknowledged only in the context of clinical application of ketogenic diets, metabolic control of epilepsy is gaining momentum and mainstream interest among researchers. A metabolic paradigm for epilepsy rests upon known perturbations in three major interconnected metabolic nodes and therapeutic targets therefrom (i.e., glycolysis, mitochondria, and redox balance).

Glial responses during epileptogenesis in Mus musculus point to potential therapeutic targets

The Mesio-Temporal Lobe Epilepsy syndrome is the most common form of intractable epilepsy. It is characterized by recurrence of focal seizures and is often associated with hippocampal sclerosis and drug resistance. We aimed to characterize the molecular changes occurring during the initial stages of epileptogenesis in search of new therapeutic targets for Mesio-Temporal Lobe Epilepsy. We used a mouse model obtained by intra-hippocampal microinjection of kainate and performed hippocampal whole genome expression analysis at 6h, 12h and 24h post-injection, followed by multilevel bioinformatics analysis. We report significant changes in immune and inflammatory responses, neuronal network reorganization processes and glial functions, predominantly initiated during status epilepticus at 12h and persistent after the end of status epilepticus at 24h post-kainate. Upstream regulator analysis highlighted Cyba, Cybb and Vim as central regulators of multiple overexpressed genes implicated in glial responses at 24h. In silico microRNA analysis indicated that miR-9, miR-19b, miR-129, and miR-223 may regulate the expression of glial-associated genes at 24h. Our data support the hypothesis that glial-mediated inflammatory response holds a key role during epileptogenesis, and that microglial cells may participate in the initial process of epileptogenesis through increased ROS production via the NOX complex.

Treatment with NADPH oxidase inhibitor apocynin alleviates diabetic neuropathic pain in rats

Increased reactive oxygen species by the activation of NADPH oxidase (NOX) contributes to the development of diabetic complications. Apocynin, a NOX inhibitor, increases sciatic nerve conductance and blood flow in diabetic rats. We investigated potential protective effect of apocynin in rat diabetic neuropathy and its precise mechanism of action at molecular level. Rat models of streptozotocin-induced diabetes were treated with apocynin (30 and 100 mg/kg per day, intragastrically) for 4 weeks. Mechanical hyperalgesia and allodynia were determined weekly using analgesimeter and dynamic plantar aesthesiometer. Western blot analysis and histochemistry/immunohistochemistry were performed in the lumbar spinal cord and sciatic nerve respectively. Streptozotocin injection reduced pain threshold in analgesimeter, but not in aesthesiometer. Apocynin treatment increased pain threshold dose-dependently. Western blot analysis showed an increase in catalase and NOX-p47phox protein expression in the spinal cord. However, protein expressions of neuronal and inducible nitric oxide synthase (nNOS, iNOS), superoxide dismutase, glutathion peroxidase, nitrotyrosine, tumor necrosis factor-α, interleukin-6, interleukin-1β, aldose reductase, cyclooxygenase-2 or MAC-1 (marker for increased microgliosis) in the spinal cord remained unchanged. Western blot analysis results also demonstrated that apocynin decreased NOX-p47phox expression at both doses and catalase expression at 100 mg/kg per day. Histochemistry of diabetic sciatic nerve revealed marked degeneration. nNOS and iNOS immunoreactivities were increased, while S-100 immunoreactivity (Schwann cell marker) was decreased in sciatic nerve. Apocynin treatment reversed these changes dose-dependently. In conclusion, decreased pain threshold of diabetic rats was accompanied by increased NOX and catalase expression in the spinal cord and increased degeneration in the sciatic nerve characterized by increased NOS expression and Schwann cell loss. Apocynin treatment attenuates neuropathic pain by decelerating the increased oxidative stress-mediated pathogenesis in diabetic rats.

Metabolic Dysfunction and Oxidative Stress in Epilepsy

The epilepsies are a heterogeneous group of disorders characterized by the propensity to experience spontaneous recurrent seizures. Epilepsies can be genetic or acquired, and the underlying mechanisms of seizure initiation, seizure propagation, and comorbid conditions are incompletely understood. Metabolic changes including the production of reactive species are known to result from prolonged seizures and may also contribute to epilepsy development. In this review, we focus on the evidence that metabolic and redox disruption is both cause and consequence of epileptic seizures. Additionally, we discuss the promise of targeting redox processes as a therapeutic option in epilepsy.

Metabolic and Homeostatic Changes in Seizures and Acquired Epilepsy-Mitochondria, Calcium Dynamics and Reactive Oxygen Species

Acquired epilepsies can arise as a consequence of brain injury and result in unprovoked seizures that emerge after a latent period of epileptogenesis. These epilepsies pose a major challenge to clinicians as they are present in the majority of patients seen in a common outpatient epilepsy clinic and are prone to pharmacoresistance, highlighting an unmet need for new treatment strategies. Metabolic and homeostatic changes are closely linked to seizures and epilepsy, although, surprisingly, no potential treatment targets to date have been translated into clinical practice. We summarize here the current knowledge about metabolic and homeostatic changes in seizures and acquired epilepsy, maintaining a particular focus on mitochondria, calcium dynamics, reactive oxygen species and key regulators of cellular metabolism such as the Nrf2 pathway. Finally, we highlight research gaps that will need to be addressed in the future which may help to translate these findings into clinical practice.

p47Phox/CDK5/DRP1-Mediated Mitochondrial Fission Evokes PV Cell Degeneration in the Rat Dentate Gyrus Following Status Epilepticus

Parvalbumin (PV) is one of the calcium-binding proteins, which plays an important role in the responsiveness of inhibitory neurons to an adaptation to repetitive spikes. Furthermore, PV neurons are highly vulnerable to status epilepticus (SE, prolonged seizure activity), although the underlining mechanism remains to be clarified. In the present study, we found that p47Phox expression was transiently and selectively increased in PV neurons 6 h after SE. This up-regulated p47Phox expression was accompanied by excessive mitochondrial fission. In this time point, CDK5-tyrosine 15 and dynamin-related protein 1 (DRP1)-serine 616 phosphorylations were also increased in PV cells. Apocynin (a p47Phox inhibitor) effectively mitigated PV cell loss via inhibition of CDK5/DRP1 phosphorylations and mitochondrial fragmentation induced by SE. Roscovitine (a CDK5 inhibitor) and Mdivi-1 (a DRP1 inhibitor) attenuated SE-induced PV cell loss by inhibiting aberrant mitochondrial fission. These findings suggest that p47Phox/CDK5/DRP1 may be one of the important upstream signaling pathways in PV cell degeneration induced by SE via excessive mitochondrial fragmentation.

Scavenging reactive oxygen species inhibits status epilepticus-induced neuroinflammation

Inflammation has been identified as an important mediator of seizures and epileptogenesis. Understanding the mechanisms underlying seizure-induced neuroinflammation could lead to the development of novel therapies for the epilepsies. Reactive oxygen species (ROS) are recognized as mediators of seizure-induced neuronal damage and are known to increase in models of epilepsies. ROS are also known to contribute to inflammation in several disease states. We hypothesized that ROS are key modulators of neuroinflammation i.e. pro-inflammatory cytokine production and microglial activation in acquired epilepsy. The role of ROS in modulating seizure-induced neuroinflammation was investigated in the pilocarpine model of temporal lobe epilepsy (TLE). Pilocarpine-induced status epilepticus (SE) resulted in a time-dependent increase in pro-inflammatory cytokine production in the hippocampus and piriform cortex. Scavenging ROS with a small-molecule catalytic antioxidant decreased SE-induced pro-inflammatory cytokine production and microglial activation, suggesting that ROS contribute to SE-induced neuroinflammation. Scavenging ROS also attenuated phosphorylation of ribosomal protein S6, the downstream target of the mammalian target of rapamycin (mTOR) pathway indicating that this pathway might provide one mechanistic link between SE-induced ROS production and inflammation. Together, these results demonstrate that ROS contribute to SE-induced cytokine production and antioxidant treatment may offer a novel approach to control neuroinflammation in epilepsy.

Neurovascular-neuroenergetic coupling axis in the brain: master regulation by nitric oxide and consequences in aging and neurodegeneration

The strict energetic demands of the brain require that nutrient supply and usage be fine-tuned in accordance with the specific temporal and spatial patterns of ever-changing levels of neuronal activity. This is achieved by adjusting local cerebral blood flow (CBF) as a function of activity level - neurovascular coupling - and by changing how energy substrates are metabolized and shuttled amongst astrocytes and neurons - neuroenergetic coupling. Both activity-dependent increase of CBF and O₂ and glucose utilization by active neural cells are inextricably linked, establishing a functional metabolic axis in the brain, the neurovascular-neuroenergetic coupling axis. This axis incorporates and links previously independent processes that need to be coordinated in the normal brain. We here review evidence supporting the role of neuronal-derived nitric oxide (^•NO) as the master regulator of this axis. Nitric oxide is produced in tight association with glutamatergic activation and, diffusing several cell diameters, may interact with different molecular targets within each cell type. Hemeproteins such as soluble guanylate cyclase, cytochrome c oxidase and hemoglobin, with which ^•NO reacts at relatively fast rates, are but a few of the key in determinants of the regulatory role of ^•NO in the neurovascular-neuroenergetic coupling axis. Accordingly, critical literature supporting this concept is discussed. Moreover, in view of the controversy regarding the regulation of catabolism of different neural cells, we further discuss key aspects of the pathways through which ^•NO specifically up-regulates glycolysis in astrocytes, supporting lactate shuttling to neurons for oxidative breakdown. From a biomedical viewpoint, derailment of neurovascular-neuroenergetic axis is precociously linked to aberrant brain aging, cognitive impairment and neurodegeneration. Thus, we summarize current knowledge of how both neurovascular and neuroenergetic coupling are compromised in aging, traumatic brain injury, epilepsy and age-associated neurodegenerative disorders such as Alzheimer's disease and Parkinson's disease, suggesting that a shift in cellular redox balance may contribute to divert ^•NO bioactivity from regulation to dysfunction.

Altered MT1 and MT2 melatonin receptors expression in the hippocampus of pilocarpine-induced epileptic rats

Clinical and experimental findings show that melatonin may be used as an adjuvant to the treatment of epilepsy-related complications by alleviates sleep disturbances, circadian alterations and attenuates seizures alone or in combination with AEDs. In addition, it has been observed that there is a circadian component on seizures, which cause changes in circadian system and in melatonin production. Nevertheless, the dynamic changes of the melatoninergic system, especially with regard to its membrane receptors (MT₁ and MT₂) in the natural course of TLE remain largely unknown. The aim of this study was to evaluate the 24-hour profile of MT₁ and MT₂ mRNA and protein expression in the hippocampus of rats submitted to the pilocarpine-induced epilepsy model analyzing the influence of the circadian rhythm in the expression pattern during the acute, silent, and chronic phases. Melatonin receptor MT₁ and MT₂ mRNA expression levels were increased in the hippocampus of rats few hours after SE, with MT₁ returning to normal levels and MT₂ reducing during the silent phase. During the chronic phase, mRNA expression levels of both receptors return to levels close to control, however, presenting a different daily profile, showing that there is a circadian change during the chronic phase. Also, during the acute and silent phase it was possible to verify MT₁ label only in CA2 hippocampal region with an increased expression only in the dark period of the acute phase. The MT₂ receptor was present in all hippocampal regions, however, it was reduced in the acute phase and it was found in astrocytes. In chronic animals, there is a reduction in the presence of both receptors especially in regions where there is a typical damage derived from epilepsy. Therefore, we conclude that SE induced by pilocarpine is able to change melatonin receptor MT₁ and MT₂ protein and mRNA expression levels in the hippocampus of rats few hours after SE as well as in silent and chronic phases.

Effect of Oxidative Stress on ABC Transporters: Contribution to Epilepsy Pharmacoresistance

Epilepsy is a neurological disorder affecting around 1%–2% of population worldwide and its treatment includes use of antiepileptic drugs to control seizures. Failure to respond to antiepileptic drug therapy is a major clinical problem and over expression of ATP-binding cassette transporters is considered one of the major reasons for pharmacoresistance. In this review, we have summarized the regulation of ABC transporters in response to oxidative stress due to disease and antiepileptic drugs. Further, ketogenic diet and antioxidants were examined for their role in pharmacoresistance. The understanding of signalling pathways and mechanism involved may help in identifying potential therapeutic targets and improving drug response.

Pathophysiology of status epilepticus

Status epilepticus (SE) is the maximal expression of epilepsy with a high morbidity and mortality. It occurs due to the failure of mechanisms that terminate seizures. Both human and animal data indicate that the longer a seizure lasts, the less likely it is to stop. Recent evidence suggests that there is a critical transition from an ictal to a post-ictal state, associated with a transition from a spatio-temporally desynchronized state to a highly synchronized state, respectively. As SE continues, it becomes progressively resistant to drugs, in particular benzodiazepines due partly to NMDA receptor-dependent internalization of GABA(A) receptors. Moreover, excessive calcium entry into neurons through excessive NMDA receptor activation results in activation of nitric oxide synthase, calpains, and NADPH oxidase. The latter enzyme plays a critical part in the generation of seizure-dependent reactive oxygen species. Calcium also accumulates in mitochondria resulting in mitochondrial failure (decreased ATP production), and opening of the mitochondrial permeability transition pore. Together these changes result in status epilepticus-dependent neuronal death via several pathways. Multiple downstream mechanisms including inflammation, break down of the blood-brain barrier, and changes in gene expression can contribute to later pathological processes including chronic epilepsy and cognitive decline.

NADPH oxidase isoform expression is temporally regulated and may contribute to microglial/macrophage polarization after spinal cord injury

Spinal cord injury (SCI) results in both acute and chronic inflammation, as a result of activation of microglia, invasion of macrophages and activation of the NADPH oxidase (NOX) enzyme. The NOX enzyme is a primary source of reactive oxygen species (ROS) and is expressed by microglia and macrophages after SCI. These cells can assume either a pro- (M1) or anti-inflammatory (M2) polarization phenotype and contribute to tissue response to SCI. However, the contribution of NOX expression and ROS production to this polarization and vice versa is currently undefined. We therefore investigated the impact of SCI on NOX expression and microglial/macrophage polarization over time in a mouse model of contusion injury. Adult C57Bl/6 mice were exposed to a moderate T9 contusion SCI and tissue was assessed at acute, sub-acute and chronic time points for NOX isoform expression and co-expression with M1 and M2 microglia/macrophage polarization markers. Two NOX isoforms were increased after injury and were associated with both M1 and M2 markers, with an M1 preference for NOX2 acutely and NOX4 chronically. M2 cells were primarily found at acute time points only; the peak of NOX2 expression was associated with the decline in M2 polarization. In vitro, NOX2 inhibition shifted microglial polarization toward the M2 phenotype. These results now show that microglial/macrophage expression of NOX isoforms is independent of polarization state, but that NOX activity can influence subsequent polarization. These data can contribute to the therapeutic targeting of NOX as a therapy for SCI.

WONOEP appraisal: Molecular and cellular biomarkers for epilepsy

Peripheral biomarkers have myriad potential uses for treatment, prediction, prognostication, and pharmacovigilance in epilepsy. To date, no single peripheral biomarker has demonstrated proven effectiveness, although multiple candidates are in development. In this review, we discuss the major areas of focus including inflammation, blood-brain barrier dysfunction, redox alterations, metabolism, hormones and growth factors.

Anti-Inflammatory Small Molecules To Treat Seizures and Epilepsy: From Bench to Bedside

As a crucial component of brain innate immunity, neuroinflammation initially contributes to neuronal tissue repair and maintenance. However, chronic inflammatory processes within the brain and associated blood-brain barrier (BBB) impairment often cause neurotoxicity and hyperexcitability. Mounting evidence points to a mutual facilitation between inflammation and epilepsy, suggesting that blocking the undesired inflammatory signaling within the brain might provide novel strategies to treat seizures and epilepsy. Neuroinflammation is primarily characterized by the upregulation of proinflammatory mediators in epileptogenic foci, among which cyclooxygenase-2 (COX-2)/prostaglandin E2 (PGE2), interleukin-1β (IL-1β), transforming growth factor-β (TGF-β), toll-like receptor 4 (TLR4), high-mobility group box 1 (HMGB1), and tumor necrosis factor-α (TNF-α) have been extensively studied. Small molecules that specifically target these key proinflammatory perpetrators have been evaluated for antiepileptic and antiepileptogenic effects in animal models. These important preclinical studies provide new insights into the regulation of inflammation in epileptic brains and guide drug discovery efforts aimed at developing novel anti-inflammatory therapies for seizures and epilepsy.

Orexin Receptor Antagonism Improves Sleep and Reduces Seizures in Kcna1-null Mice

STUDY OBJECTIVE

Comorbid sleep disorders occur in approximately one-third of people with epilepsy. Seizures and sleep disorders have an interdependent relationship where the occurrence of one can exacerbate the other. Orexin, a wake-promoting neuropeptide, is associated with sleep disorder symptoms. Here, we tested the hypothesis that orexin dysregulation plays a role in the comorbid sleep disorder symptoms in the Kcna1-null mouse model of temporal lobe epilepsy.

METHODS

Rest-activity was assessed using infrared beam actigraphy. Sleep architecture and seizures were assessed using continuous video-electroencephalography-electromyography recordings in Kcna1-null mice treated with vehicle or the dual orexin receptor antagonist, almorexant (100 mg/kg, intraperitoneally). Orexin levels in the lateral hypothalamus/perifornical region (LH/P) and hypothalamic pathology were assessed with immunohistochemistry and oxygen polarography.

RESULTS

Kcna1-null mice have increased latency to rapid eye movement (REM) sleep onset, sleep fragmentation, and number of wake epochs. The numbers of REM and non-REM (NREM) sleep epochs are significantly reduced in Kcna1-null mice. Severe seizures propagate to the wake-promoting LH/P where injury is apparent (indicated by astrogliosis, blood-brain barrier permeability, and impaired mitochondrial function). The number of orexin-positive neurons is increased in the LH/P compared to wild-type LH/P. Treatment with a dual orexin receptor antagonist significantly increases the number and duration of NREM sleep epochs and reduces the latency to REM sleep onset. Further, almorexant treatment reduces the incidence of severe seizures and overall seizure burden. Interestingly, we report a significant positive correlation between latency to REM onset and seizure burden in Kcna1-null mice.

CONCLUSION

Dual orexin receptor antagonists may be an effective sleeping aid in epilepsy, and warrants further study on their somnogenic and ant-seizure effects in other epilepsy models.

Orexin Receptor Antagonism Improves Sleep and Reduces Seizures in Kcna1-null Mice

STUDY OBJECTIVE

Comorbid sleep disorders occur in approximately one-third of people with epilepsy. Seizures and sleep disorders have an interdependent relationship where the occurrence of one can exacerbate the other. Orexin, a wake-promoting neuropeptide, is associated with sleep disorder symptoms. Here, we tested the hypothesis that orexin dysregulation plays a role in the comorbid sleep disorder symptoms in the Kcna1-null mouse model of temporal lobe epilepsy.

METHODS

Rest-activity was assessed using infrared beam actigraphy. Sleep architecture and seizures were assessed using continuous video-electroencephalography-electromyography recordings in Kcna1-null mice treated with vehicle or the dual orexin receptor antagonist, almorexant (100 mg/kg, intraperitoneally). Orexin levels in the lateral hypothalamus/perifornical region (LH/P) and hypothalamic pathology were assessed with immunohistochemistry and oxygen polarography.

RESULTS

Kcna1-null mice have increased latency to rapid eye movement (REM) sleep onset, sleep fragmentation, and number of wake epochs. The numbers of REM and non-REM (NREM) sleep epochs are significantly reduced in Kcna1-null mice. Severe seizures propagate to the wake-promoting LH/P where injury is apparent (indicated by astrogliosis, blood-brain barrier permeability, and impaired mitochondrial function). The number of orexin-positive neurons is increased in the LH/P compared to wild-type LH/P. Treatment with a dual orexin receptor antagonist significantly increases the number and duration of NREM sleep epochs and reduces the latency to REM sleep onset. Further, almorexant treatment reduces the incidence of severe seizures and overall seizure burden. Interestingly, we report a significant positive correlation between latency to REM onset and seizure burden in Kcna1-null mice.

CONCLUSION

Dual orexin receptor antagonists may be an effective sleeping aid in epilepsy, and warrants further study on their somnogenic and ant-seizure effects in other epilepsy models.

Fish oil provides protection against the oxidative stress in pilocarpine model of epilepsy

Temporal lobe epilepsy (TLE), the most common form of epilepsy is often resistant to pharmacological treatment. Neuronal loss observed in epileptic brain may be result of an overproduction of free radicals (oxidative stress). Oxidative stress is characterized by an imbalance between antioxidant defenses and oxidizing agents (free radicals), which can lead to tissue injury. The n-3 PUFAs are important for the development and maintenance of central nervous system functions. Research by our group has shown that chronic treatment with fish oil, immediately after status epilepticus (SE), exhibits both neuroprotective effects and effects on neuroplasticity. The main purpose of this research was to evaluate if fish oil exhibits a protective effect against oxidative stress. Animals were subjected to TLE model by pilocarpine administration. After 3 h of SE they were randomly divided into the following groups: control animals treated daily with vehicle or with 85 mg/kg of fish oil and animals with epilepsy treated daily with vehicle or with 85 mg/kg of fish oil. After 90 days, superoxide anion production, enzymatic activity of superoxide dismutase (SOD) and catalase (CAT) and protein expression of NAD(P)H oxidase subunits (p47(PHOX) and gp91(PHOX)) were analyzed. Our results showed evidences that reactive oxygen species are increased in animals with epilepsy and that fish oil supplementation could counteract it. Fish oil supplementation promoted protection against oxidative stress by multiple ways, which involved the reduction of activity and expression of NAD(P)H oxidase subunits and increased the activity and expression of antioxidants enzymes, contributing to well-known neuroprotective effect in epilepsy.

Peripheral inflammation increases seizure susceptibility via the induction of neuroinflammation and oxidative stress in the hippocampus

BACKGROUND

Neuroinflammation with activation of microglia and production of proinflammatory cytokines in the brain plays an active role in epileptic disorders. Brain oxidative stress has also been implicated in the pathogenesis of epilepsy. Damage in the hippocampus is associated with temporal lobe epilepsy, a common form of epilepsy in human. Peripheral inflammation may exacerbate neuroinflammation and brain oxidative stress. This study examined the impact of peripheral inflammation on seizure susceptibility and the involvement of neuroinflammation and oxidative stress in the hippocampus.

RESULTS

In male, adult Sprague-Dawley rats, peripheral inflammation was induced by the infusion of Escherichia coli lipopolysaccharide (LPS, 2.5 mg/kg/day) into the peritoneal cavity for 7 days via an osmotic minipump. Pharmacological agents were delivered via intracerebroventricular (i.c.v.) infusion with an osmotic minipump. The level of cytokine in plasma or hippocampus was analyzed by ELISA. Redox-related protein expression in hippocampus was evaluated by Western blot. Seizure susceptibility was tested by intraperitoneal (i.p.) injection of kainic acid (KA, 10 mg/kg). We found that i.p. infusion of LPS for 7 days induced peripheral inflammation characterized by the increases in plasma levels of interleukin-1β (IL-1β), interleukin-6 (IL-6) and tumor necrosis factor-α (TNF-α). This is associated with a significant increase in number of the activated microglia (Iba-1(+) cells), enhanced production of proinflammatory cytokines (including IL-1β, IL-6 and TNF-α), and tissue oxidative stress (upregulations of the NADPH oxidase subunits) in the hippocampus. These cellular and molecular responses to peripheral inflammation were notably blunted by i.c.v. infusion of a cycloxygenase-2 inhibitor, NS398 (5 μg/μl/h). The i.c.v. infusion of tempol (2.5 μg/μl/h), a reactive oxygen species scavenger, protected the hippocampus from oxidative damage with no apparent effect on microglia activation or cytokine production after peripheral inflammation. In the KA-induced seizure model, i.c.v. infusion of both NS398 and tempol ameliorated the increase in seizure susceptibility in animals succumbed to the LPS-induced peripheral inflammation.

CONCLUSIONS

Together these results indicated that LPS-induced peripheral inflammation evoked neuroinflammation and the subsequent oxidative stress in the hippocampus, resulting in the increase in KA-induced seizure susceptibility. Moreover, protection from neuroinflammation and oxidative stress in the hippocampus exerted beneficial effect on seizure susceptibility following peripheral inflammation.

Oxidative stress in murine Theiler's virus-induced temporal lobe epilepsy

Temporal lobe epilepsy (TLE) is the most common form of acquired epilepsy that can be caused by several inciting events including viral infections. However, one-third of TLE patients are pharmacoresistant to current antiepileptic drugs and therefore, there is an urgent need to develop antiepileptogenic therapies that prevent the development of the disease. Oxidative stress and redox alterations have recently been recognized as important etiological factors contributing to seizure-induced neuronal damage. The goal of this study was to determine if oxidative stress occurs in the TMEV (Theiler's murine encephalomyelitis virus) model of temporal lobe epilepsy (TLE). C57Bl/6 mice were injected with TMEV or with PBS intracortically and observed for acute seizures. At various time points after TMEV injection, hippocampi were analyzed for levels of reduced glutathione (GSH), oxidized glutathione (GSSG) and 3-nitrotyrosine (3 NT). Mice infected with TMEV displayed behavioral seizures between days 3 and 7 days post-infection (dpi). The intensity of seizures increased over time with most of the seizures being a stage 4 or 5 on the Racine scale at 6 days p.i. Mice exhibiting at least one seizure during the observation period were utilized for the biochemical analyses. The levels of GSH were significantly depleted in TMEV infected mice at 3, 4 and 14 days p.i. with a concomitant increase in GSSH levels as well as an impairment of the redox status. Additionally, there was a substantial increase in 3 NT levels in TMEV infected mice at these time points. These redox changes correlated with the occurrence of acute seizures in this model. Interestingly, we did not see changes in any of the indices in the cerebellum of TMEV-infected mice at 3 dpi indicating that these alterations are localized to the hippocampus and perhaps other limbic regions. This is the first study to demonstrate the occurrence of oxidative stress in the TMEV model of infection-induced TLE. The redox alterations were observed at time points coinciding with the appearance of acute behavioral seizures suggesting that these changes might be a consequence of seizure activity. Our results support the hypothesis that redox changes correlate with seizure activity in acquired epilepsies, regardless of the inciting insults, and suggest oxidative stress as a potential therapeutic target for their treatment.

Anti-oxidative effects produced by environmental enrichment in the hippocampus and cerebral cortex of male and female rats

Both physical and intellectual activity may reduce the incidence of neurodegenerative disorders. There is evidence that environmental enrichment (EE) can induce profound behavioral, neurochemical and neuroanatomical changes, thus producing lasting improvements in memory and learning tasks. In this study we evaluated the anti-oxidative effects produced by EE in the hippocampus and the cerebral cortex of male and female rats. The animals had been reared in either EE or control conditions. The parameters studied were: thiobarbituric acid reactive substances (TBARS), protein oxidation, total radical antioxidant parameter, catalase, superoxide dismutase and superoxide anion activity. The results showed that our EE protocol reduced markers of oxidative stress in the hippocampus and in the cerebral cortex. Overall, the measures taken in the two cerebral regions revealed that EE rats showed higher values for antioxidant measures and lower values for oxidative stress parameters than control animals. More importantly, a consistent sex difference was found, indicating that in female rats the hippocampus and cerebral cortex are plastic brain regions receptive to external stimulation such as EE. Although EE males have higher levels for antioxidant capacity, catalase and SOD, it is likely that females do not need to activate all the antioxidant defenses since they have a greater capacity to assimilate external stimuli. This is suggested by the similarity of protein oxidation and TBARS levels in hippocampus in both sexes, and the even lower levels of protein oxidation and superoxide anion activity in the cerebral cortex in EE females.

Seizure-induced oxidative stress in temporal lobe epilepsy

An insult to the brain (such as the first seizure) causes excitotoxicity, neuroinflammation, and production of reactive oxygen/nitrogen species (ROS/RNS). ROS and RNS produced during status epilepticus (SE) overwhelm the mitochondrial natural antioxidant defense mechanism. This leads to mitochondrial dysfunction and damage to the mitochondrial DNA. This in turn affects synthesis of various enzyme complexes that are involved in electron transport chain. Resultant effects that occur during epileptogenesis include lipid peroxidation, reactive gliosis, hippocampal neurodegeneration, reorganization of neural networks, and hypersynchronicity. These factors predispose the brain to spontaneous recurrent seizures (SRS), which ultimately establish into temporal lobe epilepsy (TLE). This review discusses some of these issues. Though antiepileptic drugs (AEDs) are beneficial to control/suppress seizures, their long term usage has been shown to increase ROS/RNS in animal models and human patients. In established TLE, ROS/RNS are shown to be harmful as they can increase the susceptibility to SRS. Further, in this paper, we review briefly the data from animal models and human TLE patients on the adverse effects of antiepileptic medications and the plausible ameliorating effects of antioxidants as an adjunct therapy.

Mitochondrial respiration deficits driven by reactive oxygen species in experimental temporal lobe epilepsy

Metabolic alterations have been implicated in the etiology of temporal lobe epilepsy (TLE), but whether or not they have a functional impact on cellular energy producing pathways (glycolysis and/or oxidative phosphorylation) is unknown. The goal of this study was to determine if alterations in cellular bioenergetics occur using real-time analysis of mitochondrial oxygen consumption and glycolytic rates in an animal model of TLE. We hypothesized that increased steady-state levels of reactive oxygen species (ROS) initiated by epileptogenic injury result in impaired mitochondrial respiration. We established methodology for assessment of bioenergetic parameters in isolated synaptosomes from the hippocampus of Sprague-Dawley rats at various times in the kainate (KA) model of TLE. Deficits in indices of mitochondrial respiration were observed at time points corresponding with the acute and chronic phases of epileptogenesis. We asked if mitochondrial bioenergetic dysfunction occurred as a result of increased mitochondrial ROS and if it could be attenuated in the KA model by pharmacologically scavenging ROS. Increased steady-state ROS in mice with forebrain-specific conditional deletion of manganese superoxide dismutase (Sod2(fl/fl)NEX(Cre/Cre)) in mice resulted in profound deficits in mitochondrial oxygen consumption. Pharmacological scavenging of ROS with a catalytic antioxidant restored mitochondrial respiration deficits in the KA model of TLE. Together, these results demonstrate that mitochondrial respiration deficits occur in experimental TLE and ROS mechanistically contribute to these deficits. Furthermore, this study provides novel methodology for assessing cellular metabolism during the entire time course of disease development.

Post-status epilepticus treatment with the cannabinoid agonist WIN 55,212-2 prevents chronic epileptic hippocampal damage in rats

Repeated seizures are often associated with development of refractory chronic epilepsy, the most common form of which is temporal lobe epilepsy. G-protein-coupled cannabinoid receptors (CB1 and CB2 receptors) regulate neuronal excitability and have been shown to mediate acute anticonvulsant effects of cannabinoids in animal models. However, the potential of cannabinoids to prevent chronic neuronal damage and development of epilepsy remains unexplored. We hypothesized that treatment with a CB receptor agonist after an episode of status epilepticus--but before development of spontaneous recurrent seizures--might prevent the development of functional changes that lead to chronic epilepsy. Using the rat pilocarpine model, a therapeutic approach was simulated by administering the CB agonist, WIN 55,212-2 after an episode of status epilepticus. Epileptic behavior was monitored during development of spontaneous recurrent seizures for up to 6 months. Histology, neurochemistry, redox status and NMDA receptor subunit expression were assessed at 6 months after pilocarpine-induced seizures. Sub-acute treatment with WIN 55,212-2 (for 15 days starting 24h after PILO injection) dramatically attenuated the severity, duration and frequency of spontaneous recurrent seizures. Further, in contrast to vehicle-treated animals, hippocampi from WIN 55,212-2-treated animals showed: normal thiol redox state, normal NR2A and NR2B subunit expression, preservation of GABAergic neurons and prevention of abnormal proliferation of GABAergic progenitors. This study shows for the first time that, after a known inciting event, treatment with a compound targeting CB receptors has the potential to prevent the epileptogenic events that result in chronic epileptic damage.

Seizure activity results in calcium- and mitochondria-independent ROS production via NADPH and xanthine oxidase activation

Seizure activity has been proposed to result in the generation of reactive oxygen species (ROS), which then contribute to seizure-induced neuronal damage and eventually cell death. Although the mechanisms of seizure-induced ROS generation are unclear, mitochondria and cellular calcium overload have been proposed to have a crucial role. We aim to determine the sources of seizure-induced ROS and their contribution to seizure-induced cell death. Using live cell imaging techniques in glioneuronal cultures, we show that prolonged seizure-like activity increases ROS production in an NMDA receptor-dependent manner. Unexpectedly, however, mitochondria did not contribute to ROS production during seizure-like activity. ROS were generated primarily by NADPH oxidase and later by xanthine oxidase (XO) activity in a calcium-independent manner. This calcium-independent neuronal ROS production was accompanied by an increase in intracellular [Na(+)] through NMDA receptor activation. Inhibition of NADPH or XO markedly reduced seizure-like activity-induced neuronal apoptosis. These findings demonstrate a critical role for ROS in seizure-induced neuronal cell death and identify novel therapeutic targets.

Temporal and spatial increase of reactive nitrogen species in the kainate model of temporal lobe epilepsy

Steady-state levels of reactive oxygen species (ROS) and oxidative damage to cellular macromolecules are increased in the rodent hippocampus during epileptogenesis. However, the role of reactive nitrogen species (RNS) in epileptogenesis remains to be explored. The goal of this study was to determine the spatial and temporal occurrence of RNS i.e. nitric oxide levels in a rat model of temporal lobe epilepsy (TLE). Rats were injected with a single high dose of kainate and monitored by video for behavioral seizures for 6weeks to determine the onset and severity of chronic seizures. RNS and tissue/mitochondrial redox status (glutathione redox couple and coenzyme A:glutathione redox couple) were measured in the hippocampus at 8h, 24h, 48h, 1wk, 3wk and 6wk following kainate to assess the level of reactive species in subcellular compartments. We observed a biphasic increase in RNS levels with a return to control values at the 48h time point. However, both tissue and mitochondrial redox status showed permanent and significant decreases during the entire time course of epilepsy development. 3 nitrotyrosine (3NT) protein adducts were found to gradually increase throughout epileptogenesis, conceivably as a result of the local environment under oxidative and nitrosative stress. Colocalization of 3NT immunostaining with neuron- or astrocyte-specific markers revealed neuron-specific localization of 3NT in hippocampal principal neurons. Persistent and concurrent glutathione oxidation and nitrosative stress occur during epileptogenesis suggesting a favorable environment for posttranslational modifications.

Oxidative stress markers in the neocortex of drug-resistant epilepsy patients submitted to epilepsy surgery

PURPOSE

While there is solid experimental evidence of brain oxidative stress in animal models of epilepsy, it has not been thoroughly verified in epileptic human brain. Our purpose was to determine and to compare oxidative stress markers in the neocortex of epileptic and non-epileptic humans, with the final objective of confirming oxidative stress phenomena in human epileptic brain.

METHODS

Neocortical samples from drug-resistant epilepsy patients submitted to epilepsy surgery (n=20) and from control, non-epileptic cortex samples (n=11) obtained from brain bank donors without neurological disease, were studied for oxidative stress markers: levels of reactive oxygen species (ROS), such as superoxide anion (O2(-)); activity of antioxidant enzymes: superoxide dismutase (SOD), catalase, glutathione peroxidase (GPx), and glutathione reductase (GR); and markers of damage to biomolecules (lipid peroxidation and DNA oxidation).

RESULTS

Compared with non-epileptic controls, the neocortex of epileptic patients displayed increased levels of superoxide anion (P≤0.001), catalase (P≤0.01), and DNA oxidation (P≤0.001); a decrease in GPx (P≤0.05), and no differences in SOD, GR and lipid peroxidation.

CONCLUSIONS

Our findings in humans are in agreement with those found in animal models, supporting oxidative stress as a relevant mechanism also in human epilepsy. The concurrent increase in catalase and decrease in GPx, together with unchanged SOD levels, suggests catalase as the main antioxidant enzyme in human epileptic neocortex. The substantial increase in the levels of O2(-) and 8-oxo-dG in epileptic patients supports a connection between chronic seizures and ROS-mediated neural damage.

Mitochondrial involvement and oxidative stress in temporal lobe epilepsy

A role for mitochondria and oxidative stress is emerging in acquired epilepsies such as temporal lobe epilepsy (TLE). TLE is characterized by chronic unprovoked seizures arising from an inciting insult with a variable seizure-free "latent period." The mechanism by which inciting injury induces chronic epilepsy, known as epileptogenesis, involves multiple cellular, molecular, and physiological changes resulting in altered hyperexcitable circuitry. Whether mitochondrial and redox mechanisms contribute to epileptogenesis remains to be fully clarified. Mitochondrial impairment is revealed in studies from human imaging and tissue analysis from TLE patients. The collective data from animal models suggest that steady-state mitochondrial reactive oxygen species and resultant oxidative damage to cellular macromolecules occur during different phases of epileptogenesis. This review discusses evidence for the role of mitochondria and redox changes occurring in human and experimental TLE. Potential mechanisms by which mitochondrial energetic and redox mechanisms contribute to increased neuronal excitability and therapeutic approaches to target TLE are delineated.

Changes in gene expression in the frontal cortex of rats with pilocarpine-induced status epilepticus after sleep deprivation

Sleep and epilepsy present a bidirectional interaction. Sleep complaints are common in epilepsy, and sleep deprivation may provoke seizures. However, the mechanisms underlying this relationship are unknown. Thus, this study investigated the effects of paradoxical sleep deprivation (PSD24h) and total sleep deprivation (TSD6h) in the expression of genes related to reactive oxygen species and nitric oxide production in the frontal cortex of a rodent model of temporal lobe epilepsy (PILO). The data show that PILO rats had increased NOX-2 expression and decreased SOD expression, independent of sleep. Higher NOX-2 expression was observed only in PILO rats subjected to the control condition and TSD6h. Also, eNOS and DDAH1 were increased in the PILO group submitted to TSD6h. Moreover, CAT expression in the frontal cortex of PILO rats submitted to PSD24h was reduced compared to that of PILO rats that were not sleep-deprived. The molecular changes found in the frontal cortex of PILO rats following sleep deprivation suggest a mechanism via oxidative stress.

Post-treatment of an NADPH oxidase inhibitor prevents seizure-induced neuronal death

The present study sought to evaluate the neuroprotective effects of apocynin, an NADPH oxidase assembly inhibitor, on seizure-induced neuronal death. Apocynin, also known as acetovanillone, is a natural organic compound isolated from the root of Canadian hemp (Apocynum cannabium). It has been extensively studied to determine its disease-fighting capabilities and application in several brain insults, such as traumatic brain injury and stroke. Here we tested the hypothesis that post-treatment of apocynin may prevent seizure-induced neuronal death by suppression of NADPH oxidase-mediated superoxide production. Temporal lobe epilepsy (TLE) was induced by intraperitoneal injection of pilocarpine (25mg/kg) in male rats. Apocynin (30mg/kg, i.p.) was injected into the intraperitoneal space two hours after seizure onset. A second injection was performed 24h after seizure. To test whether apocynin inhibits NADPH oxidase activation-induced reactive oxygen species (ROS) production, dihydroethidium (dHEt, 5mg/kg, i.p.) was injected before onset of seizure and ROS production was detected five hours after seizure onset. Neuronal oxidative injury (4HNE), neuronal death (Fluoro Jade-B), blood brain barrier (BBB) disruption (IgG leak), neurotrophil infiltration (MPO) and microglia activation (CD11b) in the hippocampus was evaluated at three days after status epilepticus (SE). Pilocarpine-induced seizure increased p47 immunofluorescence in the plasma membrane of hippocampal neurons at 12h post-insult and apocynin treatment prevented this increase. The present study found that apocynin post-treatment decreased ROS production and lipid peroxidation after seizure and decreased the number of degenerating hippocampal neurons. Apocynin also reduced seizure-induced BBB disruption, neurotrophil infiltration and microglial activation. Taken together, the present results suggest that inhibition of NADPH oxidase by apocynin may have a high therapeutic potential to reduce seizure-induced neuronal dysfunction.

A role of fluoride on free radical generation and oxidative stress in BV-2 microglia cells

The generation of ROS and lipid peroxidation has been considered to play an important role in the pathogenesis of chronic fluoride toxicity. In the present study, we observed that fluoride activated BV-2 microglia cell line by observing OX-42 expression in immunocytochemistry. Intracellular superoxide dismutase (SOD), glutathione (GSH), malondialdehyde (MDA), reactive oxygen species (ROS), superoxide anions (O₂^∙−), nitric oxide synthase (NOS), nitrotyrosine (NT) and nitric oxide (NO), NOS in cell medium were determined for oxidative stress assessment. Our study found that NaF of concentration from 5 to 20 mg/L can stimuli BV-2 cells to change into activated microglia displaying upregulated OX-42 expression. SOD activities significantly decreased in fluoride-treated BV-2 cells as compared with control, and MDA concentrations and contents of ROS and O₂^∙− increased in NaF-treated cells. Activities of NOS in cells and medium significantly increased with fluoride concentrations in a dose-dependent manner. NT concentrations also increased significantly in 10 and 50 mg/L NaF-treated cells compared with the control cells. Our present study demonstrated that toxic effects of fluoride on the central nervous system possibly partly ascribed to activiting of microglia, which enhanced oxidative stress induced by ROS and reactive nitrogen species.