Adenosines scavenged hydroxyl radicals and prevented posttraumatic epilepsy

Functioning and Gene Expression of Adenosine A1 Receptor During Zebrafish (Danio rerio) Development

The A1 adenosine receptor is the most widely expressed P1 receptor in vertebrates, performing inhibitory tone of the nervous system. Increased levels of adenosine are crucial to promote tissue protection in threatening situations, such as convulsion and hypoxia. Zebrafish is an established model organism for studies on health and disease. In this study, we evaluated the functionality of A1 adenosine receptor through development of zebrafish (6-7-day-, 3-, 8-, and 24-month-old), assessing: (I) the effects of the agonist N6-cyclopenthyladenosine (CPA) over locomotor parameters, (II) the anticonvulsant properties of CPA and adenosine per se in the pentylenetetrazol-induced seizure, and (III) the gene expression of adora1b through development. CPA promoted decreased distance traveled in the highest concentrations/doses tested (larvae: 75 to 500 μM; adults: 20 mg.kg-1), altered mean velocity (larvae: 50-500 μM; adults: 20 mg.kg-1) and time in the bottom zone of apparatus (adults: decrease in 20 mg.kg-1). Adenosine increased the latency of the larvae to reach stage II at 5 and 10 μM. CPA anticonvulsant effect against convulsive stage II was reached at 75 μM, although it decreased basal locomotor activity in larvae. For adults, CPA 10 mg.kg-1 was effective as anticonvulsant without locomotory effects. Adenosine had minor anticonvulsant effects in the concentration tested (larvae: 5 and 10 μM). The level of gene expression of adora1b was stable in brain from adult animals (8- and 24-month-old animals). These results suggest that zebrafish has similar responses to CPA as mammals. To avoid confounding factors, such as locomotor effects, during any brain function investigation using A1 adenosine receptor as a target, the concentration below 75 μM or below the dose of 20 mg.kg-1 of CPA is ideal for zebrafish at larval and adult stages, respectively.

Chemical Kindling as an Experimental Model to Assess the Conventional Drugs in the Treatment of Post-traumatic Epilepsy

BACKGROUND

Traumatic brain injury (TBI) is one of the leading causes of morbidity and mortality today, which will surpass many infectious diseases in the coming years/decades. Posttraumatic epilepsy (PTE) is one of the most common debilitating consequences of TBI. PTE is a secondary, acquired epilepsy that causes recurrent, spontaneous seizures more than a week after TBI. The extent of head injury in individuals who develop PTE is unknown; however, trauma is thought to account for 20% of symptomatic epilepsy worldwide. Understanding the mechanisms of epilepsy following TBI is crucial for the discovery of new anticonvulsant drugs for the treatment of PTE, as well as for improving the quality of life of patients with PTE.

OBJECTIVE

This review article explains the rationale for the usage of a chemical model to access new treatments for post-traumatic epilepsy.

RESULTS

There are multiple methods to control and manage PTE. The essential and available remedy for the management of epilepsy is the use of antiepileptic drugs. Antiepileptic drugs (AEDs) decrease the frequency of seizures without affecting the disease's causality. Antiepileptic drugs are administrated for the prevention and treatment of PTE; however, 30% of epilepsy patients are drug-resistant, and AED side effects are significant in PTE patients. There are different types of animal models, such as the liquid percussion model, intracortical ferric chloride injection, and cortical subincision model, to study PTE and neurophysiological mechanisms underlying the development of epilepsy after head injury. However, these animal models do not easily mimic the pathological events occurring in epilepsy. Therefore, animal models of PTE are an inappropriate tool for screening new and putatively effective AEDs. Chemical kindling is the most common animal model used to study epilepsy. There is a strong similarity between the kindling model and different types of human epilepsy.

CONCLUSION

Today, researchers use experimental animal models to evaluate new anticonvulsant drugs. The chemical kindling models, such as pentylenetetrazol, bicuculline, and picrotoxin-induced seizures, are important experimental models to analyze the impact of putative antiepileptic drugs.

Iron Metabolism and Ferroptosis in Epilepsy

Epilepsy is a disease characterized by recurrent, episodic, and transient central nervous system (CNS) dysfunction resulting from an excessive synchronous discharge of brain neurons. It is characterized by diverse etiology, complex pathogenesis, and difficult treatment. In addition, most epileptic patients exhibit social cognitive impairment and psychological impairment. Iron is an essential trace element for human growth and development and is also involved in a variety of redox reactions in organisms. However, abnormal iron metabolism is associated with several neurological disorders, including hemorrhagic post-stroke epilepsy and post-traumatic epilepsy (PTE). Moreover, ferroptosis is also considered a new form of regulation of cell death, which is attributed to severe lipid peroxidation caused by the production of reactive oxygen species (ROS) and iron overload found in various neurological diseases, including epilepsy. Therefore, this review summarizes the study on iron metabolism and ferroptosis in epilepsy, in order to elucidate the correlation between iron and epilepsy. It also provides a novel method for the treatment, prevention, and research of epilepsy, to control epileptic seizures and reduce nerve injury after the epileptic seizure.

Label-free imaging of hemoglobin degradation and hemosiderin formation in brain tissues with femtosecond pump-probe microscopy

The degradation of hemoglobin in brain tissues results in the deposition of hemosiderin, which is a major form of iron-storage protein and closely related to neurological disorders such as epilepsy. Optical detection of hemosiderin is vitally important yet challenging for the understanding of disease mechanisms, as well as improving surgical resection of brain lesions. Here, we provide the first label-free microscopy study of sensitive hemosiderin detection in both an animal model and human brain tissues. Methods: We applied spectrally and temporally resolved femtosecond pump-probe microscopy, including transient absorption (TA) and stimulated Raman scattering (SRS) techniques, to differentiate hemoglobin and hemosiderin in brain tissues. The label-free imaging results were compared with Perls' staining to evaluate our method for hemosiderin detection. Results: Significant differences between hemoglobin and hemosiderin transient spectra were discovered. While a strong ground-state bleaching feature of hemoglobin appears in the near-infrared region, hemosiderin demonstrates pure excited-state absorption dynamics, which could be explained by our proposed kinetic model. Furthermore, simultaneous imaging of hemoglobin and hemosiderin can be rapidly achieved in both an intracerebral hemorrhage (ICH) rat model and human brain surgical specimens, with perfect correlation with Perls' staining. Conclusion: Our results suggest that rapid, label-free detection of hemosiderin in brain tissues could be realized by femtosecond pump-probe microscopy. Our method holds great potential in providing a new tool for intraoperative detection of hemosiderin during brain surgeries.

Effectiveness of deferoxamine on ferric chloride-induced epilepsy in rats

Iron overload has been regarded as a common cause for refractory epilepsies in patients after hemorrhagic strokes. This study is to examine the potential epilepsy control effect of deferoxamine (DFO), an iron chelator, on a ferric chloride-induced epilepsy rat model. Twenty four rats were divided into 4 groups: group I is blank control group, group II is sham group with intracortical injection of saline, group III is epilepsy group with intracortical injection of iron and saline treatment, group IV is treatment group with intracortical injection of iron and DFO treatment. For the DFO intervention group, a daily dose of 100mg/kg DFO via peritoneal injection was applied for 14days. Outcomes were evaluated by behavioral study, electroencephalography (EEG), magnetic resonance imaging (MRI) scan and tissue analysis. Epilepsies according to behavioral observations and EEG analysis were significantly suppressed after intervention of DFO. Reduction of iron content in the brain cortex was proved by diminished low signal area on T2-MRI images (p=0.006) and tissue analysis (p<0.001), simultaneously the superoxide dismutase (SOD) activity increased (p<0.001). Western blot analysis demonstrated the decreasing of local transferrin after DFO treatment. DFO is efficient at Fe clearance, thus helpful in epilepsy control. This finding implies potential therapeutic value of DFO in patients with refractory epilepsy after hemorrhagic stroke.

Base deficit and serum lactate concentration in patients with post traumatic convulsion

Introduction:

Traumatic brain injury is a major cause of morbidity and mortality worldwide, and has been reported to be one of the risk factors for epileptic seizures. Abnormal blood lactate (LAC) and base deficit (BD) reflects hypoperfusion and could be used as metabolic markers to predict the outcome. The aim of this study is to assess the prognostic value of BD and LAC levels for post traumatic convulsion (PTC) in head injury patients.

Materials and Methods:

All head injury patients with PTC were studied for the demographics profile, mechanism of injury, initial vital signs, and injury severity score (ISS), respiratory rates, CT scan findings, and other laboratory investigations. The data were obtained from the trauma registry and medical records. Statistical analysis was done using SPSS software.

Results:

Amongst 3082 trauma patients, 1584 were admitted to the hospital. Of them, 401 patients had head injury. PTC was observed in 5.4% (22/401) patients. Out of the 22 head injury patients, 10 were presented with the head injury alone, whereas 12 patients had other associated injuries. The average age of the patients was 25 years, comprising predominantly of male patients (77%). Neither glasgow coma scale nor ISS had correlation with BD or LAC in the study groups. The mean level of BD and LAC was not statistically different in PTC group compared to controls. However, BD was significantly higher in patients with associated injuries than the isolated head injury group. Furthermore, there was no significant correlation amongst the two groups as far as LAC levels are concerned.

Conclusion:

Base deficit but not lactic acid concentration was significantly higher in head injury patients with associated injuries. Early resuscitation by pre-hospital personnel and in the trauma room might have impact in minimizing the effect of post traumatic convulsion on BD and LAC.

Oxidative injury in epilepsy: potential for antioxidant therapy?

Biological ill effects of oxidative injury from excess free radical production are implicated in many human conditions. Epilepsy is a chronic, dynamic neurological disorder associated with ongoing neuronal damage, particularly when uncontrolled. Oxidative injury may play a role in the initiation and progression of epilepsy, and therapies aimed at reducing oxidative stress may ameliorate tissue damage and favorably alter the clinical course. There is abundant in vivo evidence of oxidative injury in animal models of epilepsy and for efficacy of antioxidant therapy in reducing this injury in animal models of epileptogenesis. However, there is sparse direct clinical data on the use of antioxidants in human epilepsy. This review examines the evidence for the role of oxidative injury in epilepsy, the rationale for use of antioxidant therapy in epilepsy and appraises the current clinical performance of the studies of antioxidant therapies.

Epilepsy and epileptic syndrome

Epilepsy is one of the most common neurological disorders. In most patients with epilepsy, seizures respond to available medications. However, a significant number of patients, especially in the setting of medically-intractable epilepsies, may experience different degrees of memory or cognitive impairment, behavioral abnormalities or psychiatric symptoms, which may limit their daily functioning. As a result, in many patients, epilepsy may resemble a neurodegenerative disease. Epileptic seizures and their potential impact on brain development, the progressive nature of epileptogenesis that may functionally alter brain regions involved in cognitive processing, neurodegenerative processes that relate to the underlying etiology, comorbid conditions or epigenetic factors, such as stress, medications, social factors, may all contribute to the progressive nature of epilepsy. Clinical and experimental studies have addressed the pathogenetic mechanisms underlying epileptogenesis and neurodegeneration.We will primarily focus on the findings derived from studies on one of the most common causes of focal onset epilepsy, the temporal lobe epilepsy, which indicate that both processes are progressive and utilize common or interacting pathways. In this chapter we will discuss some of these studies, the potential candidate targets for neuroprotective therapies as well as the attempts to identify early biomarkers of progression and epileptogenesis, so as to implement therapies with early-onset disease-modifying effects.

Neuroprotective effects of ethyl pyruvate on brain energy metabolism after ischemia-reperfusion injury: a 31P-nuclear magnetic resonance study

The neuroprotective effects of ethyl pyruvate (EP), a stable derivative of pyruvate, on energy metabolism of rat brain exposed to ischemia-reperfusion stress were investigated by (31)P-nuclear magnetic resonance ((31)P-NMR) spectroscopy. Recovery level of phosphocreatine after ischemia was significantly greater when superfused with artificial cerebrospinal fluid (ACSF) with 2 mM EP than when superfused with ACSF without EP. EP was neuroprotective against ischemia only when administered before the ischemic exposure. Intracellular pH during ischemia was less acidic when superfused ahead of time with EP. EP did not show neuroprotective effects in neuron-rich slices pretreated with 100 microM fluorocitrate, a selective glial poison. It was suggested that both the administration of EP before ischemic exposure and the presence of astrocytes are required for EP to exert neuroprotective effects. We suggest the potential involvement of multiple mechanisms of action, such as less acidic intracellular pH, glial production of lactate, and radical scavenging ability.

Inhibitory role of Acorus calamus in ferric chloride-induced epileptogenesis in rat

The roots and rhizomes of Acorus calamus (Family: Araceae) have been used in the ancient systems of medicine for the treatment of various neurological disorders. Of the various methods used for inducing experimental epileptic models, the intracortical administration of ferric chloride (FeCl(3)) into sensorimotor cortex induces recurrent seizures and epileptic discharge similar to human post-traumatic epilepsy through the generation of free radicals. The present study focuses on the effect of Acorus calamus on the behavioral, electroencephalographic, and antioxidant changes in FeCl(3)-induced rat epileptogenesis. Topical administration of FeCl(3) (5 microL; 100 mM) into the sensorimotor cortex of rats showed an increase in the wet dog shake behavior, spike wave discharges together with an significant increase in antioxidant enzyme activity, such as superoxide dismutase and catalase, resulting in an increase in the level of lipid peroxidation in cerebral cortex. Pretreatment with Acorus calamus (200 mg/kg b.w., p.o. for 14 days) and also diazepam (DZ, 20 mg/kg b.w., i.p.) decreased the WDS behavior, spike wave discharges with single isolated positive waves, and a significant decrease in activity of superoxide dismutase and level of lipid peroxidation was observed in cerebral cortex with respect to those observed in FeCl(3)-induced epileptic group. Data presented in this study clearly show that Acorus calamus possesses the ability for preventing the development of FeCl(3)-induced epileptogenesis by modulating antioxidant enzymes, which in turn exhibit the potentiality of Acorus calamus to be developed as an effective anti-epileptic drug.

Iron-induced experimental cortical seizures: Electroencephalographic mapping of seizure spread in the subcortical brain areas

The iron-induced model of post-traumatic chronic focal epilepsy in rats was studied by depth-electrode mapping to investigate the spread of epileptiform activity into subcortical brain structures after its onset in the cortical epileptic focus. Electrical seizure activity was recorded in the hippocampal CA1 and CA3 areas, amygdala and caudate-putamen, in rats with iron-induced chronic cortical focal epilepsy. These experiments showed that the epileptiform activity with its onset in the cortical focus synchronously propagated into the studied subcortical brain areas. Seizure behaviours seemed to increase in correspondence with the spread of the epileptic electrographic activity in subcortical areas. Comparison of the cortical focus electroencephalographic and associated multiple-unit action potential recordings with those from the subcortical structures showed that the occurrence and evolution of the epileptiform activity in the subcortical structures were in parallel with that in the cortical focus. The intracerebral anatomic progression and delineation of seizure spread (mapped by field potential (EEG) and multiple-unit action potentials (MUA) recordings) indicated participation of these regions in the generalization of seizure activity in this model of epilepsy. The seizure-induced activation of the hippocampus appeared to evolve into an epileptic focus independent of the cortical focus. The present study demonstrates the propagation of epileptic activity from the cortical focus into the limbic and basal ganglia regions. Treatment of iron-induced epileptic rats with ethosuximide, an anti-absence drug, resulted in suppression of the epileptiform activity in the cortical focus as well as in the subcortical brain areas.

Prevention and treatment of post-traumatic epilepsy

Post-traumatic epilepsy is reported after 2-5% of closed head injuries but up to 50% or more following penetrating head injury. Despite several studies, no drug strategy has been able, to date, to quench the biochemical events leading to epileptogenesis. One possibility is that treatment with available antiepileptic drugs has been implemented too late, and thus, ultra-early treatment might still be able to stop the neurochemical epileptogenic cascade dead in its tracks. However, currently drug therapy should be instituted only after the first late unprovoked seizure.

Nucleotides and inorganic phosphates as potential antioxidants

Highly reactive OH radicals, formed in an iron-ion catalyzed Fenton reaction, are implicated in many pathological conditions. The quest for Fenton reaction inhibitors, either radical scavenger or metal-ion chelator antioxidants, spans the previous decades. Purine nucleotides were previously studied as natural modulators of the Fenton reaction; however, the modulatory role of purine nucleotides remained in dispute. Here, we have resolved this long-standing dispute and demonstrated a concentration-dependent biphasic modulation of the Fenton reaction by nucleotides. By electron spin resonance measurements with 0.1 mM Fe(II), we observed an increase of *OH production at low purine nucleotide concentrations (up to 0.15 mM), while at higher nucleotide concentrations, an exponential decay of *OH concentration was observed. We found that the phosphate moiety, not the nucleoside, determines the pro/antioxidant properties of a nucleotide, suggesting a chelation-based modulation. Furthermore, the biphasic modulation mode is probably due to diverse nucleotide-Fe(II) complexes formed in a concentration-dependent manner. At ATP concentrations much greater than Fe(II) concentrations, multiligand chelates are formed which inhibit the Fenton reaction owing to a full Fe(II) coordination sphere. In addition to natural nucleotides, we investigated a series of base- or phosphate-modified nucleotides, dinucleotides, and inorganic phosphates, as potential biocompatible antioxidants. Ap5A, inorganic thiophosphate and ATP-gamma-S proved highly potent antioxidants with IC50 values of 40, 30, and 10 microM, respectively. ATP-gamma-S proved 100 and 20 times more active than ATP and the potent antioxidant Trolox, respectively. In the presence of 30 microM ATP-gamma-S no *OH was detected after 5 min in the Fenton reaction mixture. The most potent antioxidants identified inhibit the Fenton reaction by forming full coordination sphere chelates.

Animal models of post-traumatic epilepsy

Epilepsy is a major unfavorable long-term consequence of traumatic brain injury (TBI). Moreover, TBI is one of the most important predisposing factors for the development of epilepsy, particularly in young adults. Understanding the molecular and cellular cascades that lead to the development of post-traumatic epilepsy (PTE) is key for preventing its development or modifying the disease process in such a way that epilepsy, if it develops, is milder and easier-to-treat. Tissue from TBI patients undergoing epileptogenesis is not available for such studies, which underscores the importance of developing clinically relevant animal models of PTE. The goal of this review is to (1) provide a description of PTE in humans, which is critical for the development of clinically relevant models of PTE, (2) review the characteristics of currently available PTE models, and (3) provide suggestions for the development of future models of PTE based on our current understanding of the mechanisms of TBI and epilepsy. The development of clinically relevant models of PTE is critical to advance our understanding of the mechanisms of post-traumatic epileptogenesis and epilepsy, as well as for producing breakthroughs in the development and testing of novel antiepileptogenic treatments.

Posttraumatic epilepsy with special emphasis on prophylaxis and prevention

Posttraumatic epileptic seizures have an incidence of about 10% in series of severe head injuries. Control of "early seizures", i.e. those occurring in the first week after injury, is mandatory. Attacks, especially if recurrent, may add secondary damage to the injured brain: intravenous phenythoin with therapeutic plasma level allows control of the attacks. Seizures occurring months or years after injury are called "late seizures": recurring "late seizures" make up the clinical syndrome of "posttraumatic epilepsy". "Prophylaxis" should mean that drug treatment, given for a more or less prolonged period of time, blocks permanently the ripening of the epileptogenic foci avoiding the occurrence of seizures. In animal "prophylaxis" by antiepileptic drugs seems efficacious in many experimental models including iron induced epilepsy which is considered a model of posttraumatic epilepsy and vice versa. In the human being "prophylaxis" has been attempted with: phenytoin, phenobarbital, carbamazepine, valproate but without success. During treatment period the occurrence of seizures is prevented but, after discontinuation of the drug, seizures occur just as in non treated patients. The ripening of the epileptic focus in posttraumatic epilepsy, as in iron induced epilepsy, seems to be due to a cascade of events beginning with haemorrhage, haemolysis, iron or heme compound liberation, free radical formation, peroxidation and cell death. Experimentally free radical scavengers and antiperoxidants have marked prophylactic effect. Some of them (phosphate diester of vitamin E and C, melatonin, vanillyl alcohol) may be employed in clinical practice, but up to date there is no controlled study in human beings.

Protective effect of adenosine in rat model of Parkinson's disease: neurobehavioral and neurochemical evidences

Normal cellular metabolism produces oxidants which are neutralized within the cell by antioxidant enzymes and other antioxidants. An imbalance between oxidant and antioxidant has been postulated to lead the degeneration of dopaminergic neurons in Parkinson's disease. In this study, we examined whether adenosine, an antioxidant, can prevent or slowdown neuronal injury in 6-hydroxydopamine (6-OHDA) model of Parkinsonism. Rats were treated with adenosine (500, 250, 125 mg/kg b.wt.) once before surgery and five times after surgery (1 h interval). 2 microl 6-OHDA (12.5 microg in 0.2% ascorbic acid in normal saline) was infused in the right striatum. Two weeks after 6-OHDA infused rats were tested for neurobehavioral activity and sacrificed after 3 weeks of 6-OHDA infusion, for the estimation of glutathione peroxidase, glutathione-S-transferase, glutathione reductase, glutathione content, lipid peroxidation and dopamine and its metabolites. Adenosine was found to be successful in up-regulating the antioxidant status, lowering the dopamine loss and functional recovery returned close to the baseline dose. This study revealed that adenosine, which is an essential part of our body, might be helpful in slowing down the progression of neurodegeneration in Parkinsonism.

The role of mitochondria and oxidative stress in neuronal damage after brief and prolonged seizures

Studies in vitro and in other disease states where excitotoxicity is believed to be important have demonstrated that mitochondrial function is a critical determinant of cell death, reflecting key roles in intracellular calcium homeostasis, energy production and oxidative stress. Central to this is the process of mitochondrial permeability transition, for which there are numerous influencing factors, although many, if not all, may specifically act though effects on the redox state of the cell and oxidative stress. Mitochondrial function in relation to seizure-induced cell death has been little studied until recently, but there is now accumulating evidence that similar mechanisms operate, certainly in cell death, following prolonged seizures. To what extent these same mechanisms might contribute to non-fatal but pathologically significant functional cellular changes in epilepsy, and the significance of reported free radical production after brief seizures is as yet uncertain. However, with the wide range of established techniques available to study mitochondrial function and oxidative stress, and those currently under development, these questions are undoubtedly answerable in the near future. Increased understanding of the mechanisms involved in seizure-induced cellular damage is an essential basis for the development of rational neuroprotective strategies.

alpha-Tocopheryl-L-ascorbate-2-O-phosphate diester, a hydroxyl radical scavenger, prevents the occurrence of epileptic foci in a rat model of post-traumatic epilepsy

Intracortical injection of iron ions has been used to model post-traumatic epilepsy. The results obtained using these models suggest that oxidation of neural membranes by active oxygen free radicals may be involved in the etiology of post-traumatic epilepsy. This is a study of the effects of alpha-tocopheryl-L-ascorbate-2-O-phosphate diester potassium salt (EPC-K1), known as a hydroxyl radical scavenger, on the peroxidation of neural membranes by FeCl(3) in vitro and on the occurrence of epileptic discharges in the FeCl(3) injected post-traumatic epilepsy model rats. EPC-K1 dose-dependently inhibited the production of thiobarbituric acid reactive substances (TBARS) and protein carbonyl (P-Carb), both indices of biogenic macromolecular peroxidation. In vivo studies, sporadic spike discharges and/or epileptiform activities were observed in electrocorticograms (ECoG) of male Sprague-Dawley rat 15-90 min after 500 nmol of FeCl(3) was injected into the motor cortex. On the other hand, when 200 mg/kg of EPC-K1 was injected intraperitoneally 60 min prior to the injection of FeCl(3), the occurrence of epileptic discharges was prevented or delayed. When EPC-K1 (2.5-5 nmol) was injected along with the ferric ions, the occurrence of epileptiform activities was also prevented or delayed. EPC-K1 prevented the induction of early convulsion, the major risk factor of post-traumatic epilepsy. Rats in the Fe+EPC group were injected with 500 nmol of FeCl(3) into the left motor cortex and were given an EPC-K1-diet (CE-2 chow contained 0.2% of EPC-K1, and daily EPC-K1 intake was about 80 mg/kg/day). In the Fe+EPC group rats, the percent induction of epileptic discharges in ECoGs was significantly lower than that in the Fe+CE group rats, which were fed CE-2 after FeCl(3) injection. In the homotropic contra lateral cortex, TBARS and P-Carb content did not show any changes. However, the relative TBARS content in the focal area significantly increased in the Fe+CE and Fe+EPC group rats 3 h after the injection. It became normal 3 days after in the Fe+EPC group. The relative P-Carb content in the focal area significantly increased in the Fe+CE and Fe+EPC group rats 3 h after the injection. However, it became normal after 3 days. In the present study, EPC-K1, which consists of vitamins E and C connected by a phosphate, protected the oxidation of neural membranes and prevented the occurrence of ferric ion-induced epileptic discharges by its radical scavenger activity. These data suggest that EPC-K1 may be clinically useful in not only preventing the focus formation of post-traumatic epilepsy, but also in treating and attenuating the progression of free radical-induced degenerative disorders.

Changes in cortical and hippocampal ectonucleotidase activities in mice lacking cellular prion protein

Animals lacking cellular prion protein (PrP(c)) expression are more susceptible to seizures. Adenosine is an endogenous anticonvulsant agent and it levels in the synaptic cleft are regulated by ectonucleotidases. We evaluated ectonucleotidase activities in synaptosomes from hippocampus and cerebral cortex of adult PrP(c) null mice and wild-type mice (genetic background 129/Sv X C57BL/6J). There was an increase (47%) in adenosine triphosphate (ATP) hydrolysis in hippocampal synaptosomes of PrP(c) knockout mice as compared with the wild-type animals. In cortical synaptosomes, ATP hydrolysis was similar in both PrP(c) mice and controls. However, there was a significant decrease in adenosine diphosphate (ADP) hydrolysis in both hippocampal (-39%) and cortical (-25%) synaptosomes in PrP(c) null animals compared to wild-type mice. Changes in brain ectonucleotidases activities related to modifications in the PrP(c) expression may contribute, at least in part, to the higher sensitivity to seizures of PrP(c) null mice.

Lipid peroxidation in hippocampus early and late after status epilepticus induced by pilocarpine or kainic acid in Wistar rats

Oxidative stress has been implicated in a variety of acute and chronic neurologic conditions, including epilepsy. Both the kainic acid and pilocarpine are useful models of temporal lobe epilepsy in rodents. As an index of lipid peroxidation the level thiobarbituric acid reactive substances (TBARS) was measured after the status epileticus induced by pilocarpine or kainic acid. In hippocampus there was a slight enhancement in the TBARS levels measured 12-14 h after the end of status epileticus induced by pilocarpine and kainic acid. The TBARS levels in pilocarpine treated animals was significantly decreased late after status epileticus and in kainic acid model the TBARS returned to basal levels. These results indicating a putative role of reactive oxygen species in kainic acid and pilocarpine induced epilepsy.

Pharmacological prophylaxis of post-traumatic epilepsy

Early and late epileptic seizures are a frequent complication of severe head traumas. The administration of anticonvulsant drugs immediately after head injury is commonly implemented as a prophylactic measure; however, there is a lack of consensus on the usefulness of prophylaxis with anticonvulsants for the prevention of late post-traumatic epilepsy (PTE). The inconsistent evidence accumulated so far from clinical studies, most nonrandomised and uncontrolled in design, and the limited knowledge of the processes underlying post-traumatic epileptogenesis, do not warrant empirical pharmacological prophylaxis with long term administration of conventional anticonvulsants. Phenytoin and phenobarbital (phenobarbitone) are used to a large extent in this indication. As a general rule, a benefit/risk analysis in individual patients should drive prophylactic drug prescription in PTE as it can have potential detrimental effects on a patient's recovery. New compounds, such as free-radical scavengers and antiperoxidants, show encouraging experimental results, but their clinical use is still very limited.

Adenosine A2A receptors regulate the extracellular accumulation of excitatory amino acids upon metabolic dysfunction in chick cultured retinal cells

The role of endogenous extracellular adenosine as a tonic modulator of the extracellular accumulation of excitatory amino acids (glutamate and aspartate) caused by metabolic inhibition was investigated in cultured retinal cells. The selective adenosine A2A receptor antagonist, 4-[2-[7-amino-2-(2-furyl)(1,2,4)-triazin-5-ylamino]-ethyl]ph enol (ZM241385) (50 nM), increased the release of glutamate (three- to four-fold) and of aspartate (nearly two-fold) upon iodoacetic acid-induced glycolysis inhibition, in the presence or in the absence of Ca2+. Blockade of tonic activation of A2A receptors by ZM241385 also increased (nearly two-fold) the ischemia-induced release of glutamate and aspartate. Furthermore, another selective A2A receptor antagonist, 5-amino-7-(2-phenylethyl)-2-(2-furyl)pyrazolo[4,3-e]-1,2,4-triazolo[1,5- c] pyrimidine (SCH58261), also increased the release of aspartate and glutamate by about two-fold in cells submitted to glycolysis inhibition. In contrast, the selective adenosine A1 receptor antagonist, 1,3-dipropyl-8-cyclopentylxanthine (DPCPX) (100 nM), did not significantly modify the extracellular accumulation of either glutamate or aspartate caused by inducers of chemical ischemia or glycolytic inhibitors. Inhibition of glycolysis also increased (about three-fold) the extracellular accumulation of GABA, which was virtually unchanged by ZM241385. Furthermore, the GABAA receptor antagonist, bicuculline (10 microM), only increased (nearly two-fold) the iodoacetic acid-induced Ca(2+)-dependent release of glutamate, whereas the GABAB receptor antagonist, 3-aminopropyl(diethoxymethyl) phosphinic acid, CGP35348 (100 microM), was devoid of effects on the extracellular accumulation of glutamate and aspartate. These results show that endogenous extracellular adenosine, which rises under conditions of inhibited glycolysis, tonically inhibits the extracellular accumulation of excitatory amino acid through the activation of A2A, but not A1, adenosine receptors, and this effect is independent of GABAA and GABAB functions in the cultured retinal cells.

Ameliorative effect of adenosine on hypoxia-reoxygenation injury in LLC-PK1, a porcine kidney cell line

We studied the effects of adenosine on injury caused by hypoxia and reoxygenation in LLC-PK1 cells. Lactate dehydrogenase and gamma-glutamyltranspeptidase were released from cells exposed to hypoxia for 6 hr and then reoxygenation for 1 hr. The addition of adenosine at 100 microM to the medium before hypoxia began significantly decreased enzyme leakage into medium during both hypoxia and reoxygenation. The adenosine A1-receptor agonist, R(-)-N6-(2-phenylisopropyl)adenosine (R-PIA), at the concentration of 100 microM, did not affect enzyme release, but the adenosine A2-receptor agonist 2-p-[2-car-boxyethyl]phenethyl-amino-5'-N-ethylcarboxamido-adenosi ne hydrochloride (CGS 21680) at the concentration of 100 nM, suppressed the injury caused by hypoxia and reoxygenation. There were decreases in cAMP contents and ATP levels in LLC-PK1 cells injured by hypoxia and reoxygenation. Adenosine (100 microM) restored ATP levels in the cells during reoxygenation. With adenosine, the intracellular cAMP level was increased prominently during reoxygenation. These results suggest that adenosine protects LLC-PK1 cells from injury caused by hypoxia and reoxygenation by increasing the intracellular cAMP level via adenosine A2 receptor.

Amplification of the inflammatory cellular redox state by human immunodeficiency virus type 1-immunosuppressive tat and gp160 proteins

In the course of our studies on oxidative stress as a component of pathological processes in humans, we showed that microintrusion into cells with microcapillary and ultramicroelectrochemical detection could mimic many types of mechanical intrusion leading to an instant (0.1 s) and high (some femtomoles) burst release of H2O2. Specific inhibitors of NADPH enzymes seem to support the assumption that this enzyme is one of the main targets of our experiments. Also, human immunodeficiency virus type 1 (HIV-1) gp160 inhibits the cooperative response of uninfected T cells as well as Tat protein release by infected cells does. In this study, we analyzed in real time, lymphocyte per lymphocyte, the T-cell response following activation in relation to the redox state. We showed that the immunosuppressive effects of HIV-1 Tat and gp160 proteins and oxidative stress are correlated, since the native but not the inactivated Tat and gp160 proteins inhibit the cellular immune response and enhance oxidative stress. These results are consistent with a role of the membrane NADPH oxidase in the cellular response to immune activation.

Phenylarsine oxide inhibits ex vivo HIV-1 expression

Phenylarsine oxide (PAO), which is described as an inhibitor of tyrosine phosphatase activity, inhibits H2O2 release from human peripheral blood mononuclear cells (PBMCs) as measured by electrochemistry. Since human immunodeficiency virus type 1 (HIV-1) replication is known to be favored under oxidative stress conditions, ex vivo experiments using uninfected PBMCs, primary monocytes or a latently infected promonocytic U1 cell line show that HIV-1 replication and reactivation, monitored by p24 antigen measurement, are inhibited by PAO in a time- and concentration-dependent manner. These observations can be linked with the inhibition of NF-kappa B activation when uninfected monocytes are induced by either tumor necrosis factor alpha (TNF-alpha) phorbol 12-myristate 13-acetate (PMA) or lipopolysaccharide (LPS).

Regional vulnerability to oxidative stress in a model of experimental epilepsy

We evaluated oxidative stress associated with a model of experimental epilepsy. Male Wistar rats were injected i.p. with 150 mg/kg convulsant 3-mercaptopropionic acid and decapitated in two stages: during seizures or in the post-seizure period. Spontaneous chemiluminescence, levels of thiobarbituric acid reactive substances, total antioxidant capacity and antioxidant enzyme activities were measured in cerebellum, hippocampus, cerebral cortex and striatum. In animals killed at seizure, increases of 42% and 90% were observed in spontaneous chemiluminescence of cerebellum and cerebral cortex homogenates, respectively, accompanied by a 25% increase in cerebral cortex levels of thiobarbituric acid reactive substances. In the post-seizure stage, emission completely returned to control levels in cerebral cortex and partly in cerebellum, thus showing oxidative stress reversibility in time. Hippocampus and striatum seemed less vulnerable areas to oxidative damage. A 30% decrease in glutathione peroxidase activity was only observed in cerebral cortex during seizures, while catalase and superoxide dismutase remained unchanged in all four areas during either stage. Likewise, total antioxidant capacity was unaffected in any of the studied areas. It is suggested that oxidative stress in this model of epilepsy arises from an increase in oxidant species rather than from depletion of antioxidant defences.

Antiepileptic effects of allopurinol on EL mice are associated with changes in SOD isoenzyme activities

We have investigated the potential antiepileptic action of superoxide dismutase (SOD) activities in the brain of the epileptic mutant EL mouse. EL mice which experienced frequent seizures (EL[s]) had abnormally low levels of SOD isoenzyme activity in the hippocampal area. Once epileptogenicity was established in these animals, activity of cyanide-sensitive Cu,Zn-SOD was maintained at significantly lower levels than in control mice. However, cyanide-insensitive Mn-SOD activity was not different from non-epileptic controls. In EL mice which had not experienced seizure provoking stimulations and exhibited no seizures (EL[ns]) there was moderately lower levels of SOD isoenzyme activities compared to controls. In spite of the low level of Cu,Zn-SOD activity in EL[s] mice, the Cu,Zn-SOD protein content was high in the hippocampus of these animals, suggesting that inactive Cu,Zn-SOD might be induced during development. After allopurinol (ALP) was given orally to EL[s] mice, Cu,Zn-SOD activities increased dramatically in the hippocampus and seizure activity was decreased. Even after 48 h, when antiepileptic action of ALP was lost, the SOD activity was maintained at the high level associated with initial ALP administration. EL[s] mice also showed DNA fragmentation in the hippocampal CA1 region and the parietal cortex, detected with in situ terminal transferase-mediated dUTP nick labeling with the aid of alkaliphosphatase or peroxidase. The degree of DNA fragmentation was less severe in EL[ns] mice. We propose that abnormalities in region specific Cu,Zn-SOD isoenzyme activity might produce free radicals, leading to DNA fragmentations and cell loss. This might contribute to hippocampal epileptogenesis in EL mice.

Oxidative injury in the nervous system

A free radical is a highly reactive chemical species that can react with organic macromolecules leading to cell and tissue damage and consequent functional disruption. Free radical or oxidative injury is increasingly recognized as an important factor in the pathophysiology of many human diseases, including those that affect the nervous system. This review summarizes important evidence implicating oxidative injury in the pathogenesis and progression of many important neurological disorders, including cerebrovascular disease, epilepsy, amyotrophic lateral sclerosis, and Huntington's disease. Results of controlled clinical trials of various antioxidant therapies in neurological disease performed to date are also highlighted.

Melatonin inhibits iron-induced epileptic discharges in rats by suppressing peroxidation

PURPOSE

Intracortical injection of iron ion induces recurrent seizures and epileptic discharges in the electrocorticogram. This observation may be used as a model of posttraumatic epilepsy. The involvement of iron-mediated oxygen free radical species and neuronal lipid peroxidation in iron-induced seizure has been suggested. Melatonin exerts free radical scavenging properties. In this study, we examined the protective effect of melatonin against iron-induced seizures.

METHODS

We examined the protective effect of melatonin against in vitro iron-induced oxidative damage in homogenates from rat cerebral cortex, by measuring the concentration of thiobarbituric acid reactive substances (TBARS), as an index of oxidative damage. We also examined the effect of melatonin on the appearance of epileptic discharges in the EEG following injection of FeCl3 into the sensorimotor cortex in anesthetized rats, and by measuring the concentration of TBARS in the brain tissue.

RESULTS

FeCl3 increased the concentration of TBARS in brain homogenates in a concentration-dependent manner, and melatonin reduced FeCl3-induced rise in TBARS in a dose-response fashion. Pretreatment with melatonin suppressed or delayed the development of FeCl3-induced epileptic discharges and decreased the concentration of TBARS in brain tissues.

CONCLUSIONS

Our results suggest that iron ion generates oxygen free radical species that induce neuronal macromolecular peroxidation and seizure, and that melatonin inhibits iron-induced seizures by scavenging free radicals.

R-phenylisopropyladenosine attenuates noise-induced hearing loss in the chinchilla

Reactive oxygen species, which are cytotoxic to living tissues, are thought to be partly responsible for noise-induced hearing loss. In this study R-phenylisopropyladenosine (R-PIA), a stable non-hydrolyzable adenosine analogue which has been found effective in upregulating antioxidant enzyme activity levels, was topologically applied to the round window of the right ears of chinchillas. Physiological saline was applied to the round window of the left ears (control). The animals were then exposed to a 4 kHz octave band noise at 105 dB SPL for 4 h. Inferior colliculus evoked potential thresholds and distortion product otoacoustic emissions (DPOAE) were measured and hair cell damage was documented. The mean threshold shifts immediately after the noise exposure were 70-90 dB at frequencies between 2 and 16 kHz. There were no significant differences in threshold shifts at this point between the R-PIA-treated and control ears. By 4 days after noise exposure, however, the R-PIA-treated ears showed 20-30 dB more recovery than saline-treated ears at frequencies between 4 and 16 kHz. More importantly, threshold measurements made 20 days after noise exposure showed 10-15 dB less permanent threshold shifts in R-PIA-treated ears. The amplitudes of DPOAE also recovered to a greater extent and outer hair cell losses were less severe in the R-PIA-treated ears. The results suggest that administration of R-PIA facilitates the recovery process of the outer hair cell after noise exposure.

Suppression of drug-induced epileptiform discharges by cyclic AMP in rat hippocampus

The effect of cyclic adenosine 3',5'-monophosphate (cAMP) on epileptiform activity in rat hippocampal slices was investigated. Bath-applied cAMP reversibly decreased the frequency of extracellularly recorded discharges in the CA3 subfield induced by bethanechol- or theophylline-containing solutions. Because cAMP was presumed to be relatively membrane impermeant, we developed and tested the hypothesis that this cAMP-mediated effect occurred extracellularly through the catabolic conversion of cAMP to 5'-AMP and, in turn, to adenosine, a known inhibitory neuromodulator. Three predictions derived from this catabolic hypothesis were tested. First, blockers of the enzymes involved were predicted to antagonize this effect of cAMP. In contrast, the coapplication of a cAMP-phosphodiesterase inhibitor, 3-isobutyl-1-methylxanthine (IBMX), or a 5'-nucleotidase inhibitor, adenosine 5'-[alpha, beta-methylene] diphosphate (AMP-CP), enhanced the cAMP-induced suppressive effect. Second, the nonhydrolyzable cAMP analogs, dibutyryl- and 8-bromo-cAMP, were predicted to be ineffective. Low concentrations (5-40 microM) of these two derivatives, however, also suppressed bethanechol-induced discharges, while, at a higher concentration (100 microM), both analogs increased discharge frequencies. Third, enzymatic catabolism of adenosine was predicted to antagonize cAMP's effect, but coapplying adenosine deaminase (10 U/mL) did not diminish this action. Because these data did not support the catabolic hypothesis, other, as yet undefined, mechanisms must be responsible for the discharge-suppressant effect of cAMP.