Glutathione levels in specific brain regions of genetically epileptic (tg/tg) mice

Increasing glutathione levels by a novel posttranslational mechanism inhibits neuronal hyperexcitability

Glutathione (GSH) depletion, and impaired redox homeostasis have been observed in experimental animal models and patients with epilepsy. Pleiotropic strategies that elevate GSH levels via transcriptional regulation have been shown to significantly decrease oxidative stress and seizure frequency, increase seizure threshold, and rescue certain cognitive deficits. Whether elevation of GSH per se alters neuronal hyperexcitability remains unanswered. We previously showed that thiols such as dimercaprol (DMP) elevate GSH via post-translational activation of glutamate cysteine ligase (GCL), the rate limiting GSH biosynthetic enzyme. Here, we asked if elevation of cellular GSH by DMP altered neuronal hyperexcitability in-vitro and in-vivo. Treatment of primary neuronal-glial cerebrocortical cultures with DMP elevated GSH and inhibited a voltage-gated potassium channel blocker (4-aminopyridine, 4AP) induced neuronal hyperexcitability. DMP increased GSH in wildtype (WT) zebrafish larvae and significantly attenuated convulsant pentylenetetrazol (PTZ)-induced acute 'seizure-like' swim behavior. DMP treatment increased GSH and inhibited convulsive, spontaneous 'seizure-like' swim behavior in the Dravet Syndrome (DS) zebrafish larvae (scn1Lab). Furthermore, DMP treatment significantly decreased spontaneous electrographic seizures and associated seizure parameters in scn1Lab zebrafish larvae. We investigated the role of the redox-sensitive mammalian target of rapamycin (mTOR) pathway due to the presence of several cysteine-rich proteins and their involvement in regulating neuronal excitability. Treatment of primary neuronal-glial cerebrocortical cultures with 4AP or l-buthionine-(S,R)-sulfoximine (BSO), an irreversible inhibitor of GSH biosynthesis, significantly increased mTOR complex I (mTORC1) activity which was rescued by pre-treatment with DMP. Furthermore, BSO-mediated GSH depletion oxidatively modified the tuberous sclerosis protein complex (TSC) consisting of hamartin (TSC1), tuberin (TSC2), and TBC1 domain family member 7 (TBC1D7) which are critical negative regulators of mTORC1. In summary, our results suggest that DMP-mediated GSH elevation by a novel post-translational mechanism can inhibit neuronal hyperexcitability both in-vitro and in-vivo and a plausible link is the redox sensitive mTORC1 pathway.

N-acetylcysteine aggravates seizures while improving depressive-like and cognitive impairment comorbidities in the WAG/Rij rat model of absence epilepsy

N-acetylcysteine (NAC) is an antioxidant with some demonstrated efficacy in a range of neuropsychiatric disorders. NAC has shown anticonvulsant effects in animal models. NAC effects on absence seizures are still not uncovered, and considering its clinical use as a mucolytic in patients with lung diseases, people with epilepsy are also likely to be exposed to the drug. Therefore, we aimed to study the effects of NAC on absence seizures in the WAG/Rij rat model of absence epilepsy with neuropsychiatric comorbidities. The effects of NAC chronic treatment in WAG/Rij rats were evaluated on: absence seizures at 15 and 30 days by EEG recordings and animal behaviour at 30 days on neuropsychiatric comorbidities. Furthermore, the mechanism of action of NAC was evaluated by analysing brain expression levels of some possible key targets: the excitatory amino acid transporter 2, cystine-glutamate antiporter, metabotropic glutamate receptor 2, the mechanistic target of rapamycin and p70S6K as well as levels of total glutathione. Our results demonstrate that in WAG/Rij rats, NAC treatment significantly increased the number and duration of SWDs, aggravating absence epilepsy while ameliorating neuropsychiatric comorbidities. NAC treatment was linked to an increase in brain mGlu2 receptor expression with this being likely responsible for the observed absence seizure-promoting effects. In conclusion, while confirming the positive effects on animal behaviour induced by NAC also in epileptic animals, we report the aggravating effects of NAC on absence seizures which could have some serious consequences for epilepsy patients with the possible wider use of NAC in clinical therapeutics.

Glutathione in Brain Disorders and Aging

Glutathione is a remarkably functional molecule with diverse features, which include being an antioxidant, a regulator of DNA synthesis and repair, a protector of thiol groups in proteins, a stabilizer of cell membranes, and a detoxifier of xenobiotics. Glutathione exists in two states—oxidized and reduced. Under normal physiological conditions of cellular homeostasis, glutathione remains primarily in its reduced form. However, many metabolic pathways involve oxidization of glutathione, resulting in an imbalance in cellular homeostasis. Impairment of glutathione function in the brain is linked to loss of neurons during the aging process or as the result of neurological diseases such as Huntington’s disease, Parkinson’s disease, stroke, and Alzheimer’s disease. The exact mechanisms through which glutathione regulates brain metabolism are not well understood. In this review, we will highlight the common signaling cascades that regulate glutathione in neurons and glia, its functions as a neuronal regulator in homeostasis and metabolism, and finally a mechanistic recapitulation of glutathione signaling. Together, these will put glutathione’s role in normal aging and neurological disorders development into perspective.

Effect of levetiracetam drug on antioxidant and liver enzymes in epileptic patients: case-control study

BACKGROUND

There is a limited amount of data regarding levetiracetam (LEV), an antiepileptic drug.

OBJECTIVE

This study was conducted to assess the effect of LEV on antioxidant status and liver enzymes.

METHODS

In this case-control study, 33 epileptic patients under treatment with LEV for at least 6 months were compared with 35 healthy subjects. We measured serum total antioxidant capacity (TAC), salivary superoxide dismutase (SOD), alanine aminoteransferase (ALT), and aspartate aminoteransferase (AST) levels in both groups. Dietary intakes were collected using a Food Frequency Questionnaire (FFQ).

RESULT

The level of TAC in the healthy subjects was significantly higher than it was in the patients (P=0.02), but the mean of ALT (P=0.02) and AST (P=0.03) was significantly higher in the patients in comparison with the controls. Mean salivary SOD showed no difference between the two groups. In the patients, the duration of drug use was inversely correlated with serum TAC (p=0.04) and had a direct correlation with ALT (p=0.01) and AST (p=0.03.).

CONCLUSION

The results of our study indicated that LEV increased liver enzymes Also, treatment with this drug did not improve oxidative stress, but this could be due to the different in the dietary antioxidant intake. Routine screening of the liver and antioxidant enzymes in patients with chronic use of LEV is recommended.

Neuroprotective Effects of Low Dose Anandamide in Pentylenetetrazole-Induced Kindling in Rats

Anandamide (N-arachidonoylethanolamine) is an endogenous cannabinoid receptor CB1 ligand that exhibits neuroprotective effects in the brain. In this study, the effect of exogenously given anandamide on pentylenetetrazole (PTZ)-induced chemical kindling oxidative stress and brain damage in rats was studied. Rats were intraperitoneally (i.p.) injected with 35 mg/kg PTZ once every 48 hours for 12 times to induce seizures. Anandamide was i.p. given. 30 min prior to PTZ injection at 100 or 200 mg/kg. Injections of PTZ induced significant increase in brain lipid peroxidation (malondialdehyde: MDA), and nitric oxide associated with marked decrease in brain reduced glutathione (GSH). There were also significant decrements in acetylcholinesterase (AChE) concentration, butyrylcholinesterase (BChE) and paraoxonase-1 (PON-1) activities in brain tissue of PTZ injected rats. Meanwhile, there was no significant effect for PTZ on the concentration of brain neutrophil elastase. Anandamide administered at 100 and 200 mg/kg significantly decreased MDA and increased GSH contents and at 200 mg/kg significantly decreased nitric oxide in brain of PTZ-treated rats. The drug also caused significant increments in AChE concentration and PON-1 activity but had no significant effect on BChE or neutrophil elastase in rats treated with PTZ. Anandamide given at the dose of 200mg/kg significantly decreased the mean seizure scores over the study period by 22.3% and the frequency of myoclonic jerks and rearing (stage 3) by 56.7% compared with the vehicle-treated group. Anandamide given at 100 and 200 mg/kg completely inhibited the development of generalized tonic-clonic seizures (stage 5). It is concluded that in the PTZ-induced seizures, the cannabinoid receptor CB1 agonist anandamide decreases brain oxidative stress, neuronal injury, and exerts an antiepileptic activity.

Anticonvulsant and Antioxidant Effects of Musa sapientum Stem Extract on Acute and Chronic Experimental Models of Epilepsy

Background:

Musa sapientum (banana) plant extract has been shown to possess antioxidant activity in previous studies. Neuronal injury resulting from oxidative stress is an important factor involved in pathogenesis of epilepsy.

Objective:

The present study aimed to evaluate the anticonvulsant activity of M. sapientum stem extract (MSSE) in acute and chronic experimental models in mice and its effects on various markers of oxidative stress in the brain of pentylenetetrazole (PTZ)-kindled animals.

Material and Methods:

Maximal electroshock seizures (MES) and PTZ-induced convulsion models were used for acute studies. For the chronic study, the effect of MSSE on the development of kindling was studied. For the evaluation of the effects of MSSE on oxidative stress in brain, malondialdehyde (MDA) and reduced glutathione (GSH) levels were estimated in the brains of the kindled animals.

Results:

MSSE significantly increased the latency to onset of myoclonic jerks and the duration of clonic convulsions following PTZ administration. The MSSE pretreated group showed significantly reduced mean seizure score on PTZ-induced kindling. There was a significant increase in the brain MDA levels and decrease in GSH levels in response to PTZ-induced kindling. On MSSE pretreatment, there was a significant decrease in the MDA levels in the brains, though the increase in the GSH levels was not significant.

Conclusion:

The results from this study suggest the presence of significant anticonvulsant activity in MSSE, in both acute and chronic PTZ-induced seizure models, which could be due to its antioxidant activity, as is reflected by the change in oxidative stress markers in brain.

SUMMARY

Evaluation of the anticonvulsant activity of Musa sapientum and its effects on various markers of oxidative stress in the brain has not been done previously to the best of our knowledge

M. sapientum stem extract (MSSE) significantly increased the latency to onset of myoclonic jerks and the duration of clonic convulsions in the experimental models

The MSSE pretreated group showed significantly reduced mean seizure score on pentylenetetrazole (PTZ)-induced kindling

There was significant increase in the brain malondialdehyde (MDA) levels and decrease in glutathione (GSH) levels in response to PTZ-induced kindling

On MSSE pretreatment, there was a significant decrease in the MDA levels in the brain, though the increase in the GSH levels was not significant.

Abbreviations Used: MSSE: Musa sapientum stem extract, PTZ: Pentylenetetrazole, MES: Maximal electroshock seizures, MDA: Malondialdehyde, GSH: Glutathione, SOD: Superoxide dismutase, THLE: Tonic hindlimb extension

Low dose zinc supplementation beneficially affects seizure development in experimental seizure models in rats

The role of zinc in seizure models and with antiepileptic drugs sodium valproate (SV) and phenytoin (PHT) was studied using experimental models of seizures in rats. Male Wistar rats, 150-250 g were administered zinc 2, 20, and 200 mg/kg, orally for 14 days. Sixty minutes after the last dose of zinc, rats were challenged with pentylenetetrazole (PTZ, 60 mg/kg, ip) or maximal electroshock (MES, 70 mA, 0.2 s duration). In another group, SV (150/300 mg/kg, ip) or PHT (40 mg/kg, ip) was administered after 30 min of zinc administration followed by seizure challenge. Zinc pretreatment at all doses had no effect on MES seizures. In PTZ seizures, with the lowest dose used, i.e., 2 mg/kg, a protective effect was observed. Neither the protection offered by the 100 % anticonvulsant dose of SV (300 mg/kg) in PTZ seizures was affected by pre-treatment with zinc nor a combination of subanticonvulsant dose of SV (150 mg/kg) and zinc offer any statistically significant advantage over either drug alone. The combination of phenytoin with zinc had no effect on any of the parameters tested. Apart from this, chronic zinc administration hampered development of chemically (PTZ)-kindled seizures in rats. Zinc supplementation is unlikely to have any undesirable effect when used in epileptics rather it may offer advantage in epileptic and seizure prone patients.

Relevance of the glutathione system in temporal lobe epilepsy: evidence in human and experimental models

Oxidative stress, which is a state of imbalance in the production of reactive oxygen species and nitrogen, is induced by a wide variety of factors. This biochemical state is associated with diseases that are systemic as well as diseases that affect the central nervous system. Epilepsy is a chronic neurological disorder, and temporal lobe epilepsy represents an estimated 40% of all epilepsy cases. Currently, evidence from human and experimental models supports the involvement of oxidative stress during seizures and in the epileptogenesis process. Hence, the aim of this review was to provide information that facilitates the processing of this evidence and investigate the therapeutic impact of the biochemical status for this specific pathology.

Age-dependent and tissue-related glutathione redox status in a mouse model of Alzheimer's disease

Glutathione plays an essential role in the intracellular antioxidant defense against oxidant radicals, especially the •OH radical. To understand the early and progressive cellular changes in the development of Alzheimer's disease (AD), we investigated reduced glutathione/oxidized glutathione (GSH/GSSG) status in a double mutated AD transgenic mouse model (B6.Cg-Tg), which carries Swedish amyloid-β protein precursor mutation (AβPPswe) and exon 9 deletion of the PSEN1 gene. In this study, we quantified and compared both GSH/GSSG and mixed-disulfide (Pr-SSG) levels in blood samples and three anatomic positions in brain (cerebrum, cerebellum, and hippocampus) at 3 age stages (1, 5, and 11 months) of AD transgenic (Tg)/wild type mice. The present study was designed to characterize and provide insight into the glutathione redox state of both brain tissues and blood samples at different disease stages of this Tg model. The level of Pr-SSG increased in all AD brain tissues and blood compared with controls regardless of age. The GSH/GSSG ratio in AD-Tg brain tissue started at a higher value at 1 month, fell at the transitional period of 5 months, right before the onset of amyloid plaques, followed by an increase in GSSG and associated decrease of GSH/GSSG at 11 months. These results suggest that formation of Pr-SSG may be an early event, preceding amyloid plaque appearance, and the data further implies that tissue thiol redox is tightly regulated. Notably, the high basal levels of mixed-disulfides in hippocampus suggest a potential for increased oxidative damage under oxidizing conditions and increased GSSG in this vulnerable region.

S-Glutathionyl quantification in the attomole range using glutaredoxin-3-catalyzed cysteine derivatization and capillary gel electrophoresis with laser-induced fluorescence detection

S-glutathionylation (Pr-SSG) is a specific post-translational modification of cysteine residues by the addition of glutathione. S-Glutathionylated proteins induced by oxidative or nitrosative stress play an essential role in understanding the pathogenesis of the aging and age-related disorder, such as Alzheimer's disease (AD). The purpose of this research is to develop a novel and ultrasensitive method to accurately and rapidly quantify the Pr-SSG by using capillary gel electrophoresis with laser-induced fluorescence detection (CGE-LIF). The derivatization method is based on the specific reduction of protein-bound S-glutathionylation with glutaredoxin (Grx) and labeling with thiol-reactive fluorescent dye (Dylight 488 maleimide). The experiments were performed by coupling the derivatization method with CGE-LIF to study electrophoretic profiling in in vitro oxidative stress model-S-glutathionylated bovine serum albumin (BSA-SSG), oxidant-induced human colon adenocarcinoma (HT-29) cells, brain tissues, and whole blood samples from an AD transgenic (Tg) mouse model. The results showed almost an eightfold increase in S-glutathionyl abundance when subjecting HT-29 cells in an oxidant environment, resulting in Pr-SSG at 232 ± 10.64 (average ±SD; n=3) nmol/mg. In the AD-Tg mouse model, an initial quantitative measurement demonstrated the extent of protein S-glutathionylation in three brain regions (hippocampus, cerebellum, and cerebrum), ranging from 1 to 10 nmol/mg. Additionally, we described our developed method to potentially serve as a highly desirable diagnostic tool for monitoring S-glutathionylated protein profile in minuscule amount of whole blood. The whole blood samples for S-glutathionyl expression of 5-month-old AD-Tg mice are quantified as 16.3 μmol/L (=7.2 nmol/mg protein). Altogether, this is a fast, easy, and accurate method, reaching the lowest limit of Pr-SSG detection at 1.8 attomole (amol) level, reported to date.

Depletion of glutathione does not affect electron transport chain complex activity in brain mitochondria: Implications for Parkinson disease and postmortem studies

Glutathione is an important antioxidant in the brain that appears to be decreased, in conjunction with mitochondrial complex I activity, in Parkinson disease patients. In postmortem analysis, measurement of glutathione levels and complex I activity can be delayed up to 20h. We investigated whether depletion of glutathione in the preweanling rat induces a reduction in complex I activity in brain mitochondria and the effects that postmortem delay has on glutathione levels and electron transport chain activity. After injection with the glutamate-cysteine ligase inhibitor, buthionine sulfoximine (L-BSO), glutathione levels were decreased by 53% compared to the control values in whole-brain homogenates. During postmortem delay of 24h, in which animals were kept at 4°C, the levels of glutathione decreased in the control group by 58% and in the L-BSO-treated group by 79%. However, during this period, there were no changes in mitochondrial electron transport chain complex I, II-III, or IV activity in either group. These results suggest that a preexisting deficiency of glutathione or a loss of glutathione during postmortem delay does not influence mitochondrial respiratory chain activity in the brain.

Neuroinflammation, Oxidative Stress and the Pathogenesis of Parkinson's Disease

Neuroinflammatory processes play a significant role in the pathogenesis of Parkinson's disease (PD). Epidemiologic, animal, human, and therapeutic studies all support the presence of an neuroinflammatory cascade in disease. This is highlighted by the neurotoxic potential of microglia . In steady state, microglia serve to protect the nervous system by acting as debris scavengers, killers of microbial pathogens, and regulators of innate and adaptive immune responses. In neurodegenerative diseases, activated microglia affect neuronal injury and death through production of glutamate, pro-inflammatory factors, reactive oxygen species, quinolinic acid amongst others and by mobilization of adaptive immune responses and cell chemotaxis leading to transendothelial migration of immunocytes across the blood-brain barrier and perpetuation of neural damage. As disease progresses, inflammatory secretions engage neighboring glial cells, including astrocytes and endothelial cells, resulting in a vicious cycle of autocrine and paracrine amplification of inflammation perpetuating tissue injury. Such pathogenic processes contribute to neurodegeneration in PD. Research from others and our own laboratories seek to harness such inflammatory processes with the singular goal of developing therapeutic interventions that positively affect the tempo and progression of human disease.

Functional properties and oxidative modulation of A-type K currents in hippocampal granule cells of control and chronically epileptic rats

A-type K+ channels are crucial determinants of neuronal firing. For example, reducing the amplitude of A-type currents (I(A)) increases seizure susceptibility. We have therefore examined the functional and molecular properties of I(A) in dentate granule neurons following pilocarpine-induced status epilepticus (SE). We found that the levels of various A-type channel subunit mRNAs are unaltered following SE. Furthermore, current density and biophysical properties of I(A) recorded in outside-out and cell-attached patches from dentate granule cells are not modified by SE. However, I(A) in both control and epileptic rats was powerfully regulated by the cellular redox state. I(A) was recorded in outside-out patches with the recording pipette containing either reduced (GSH) or oxidized (GSSG) glutathione. In both control and epileptic rats, the presence of GSSG caused a similar, marked acceleration of recovery from inactivation. Additionally, GSSG produced a small but significant reduction of I(A) amplitudes only in control rats. The inactivation time course of I(A) during depolarizing voltage steps was not modified by GSH or GSSG. Cell-attached recordings, in which the intracellular milieu is conserved, revealed a slow time course of recovery more comparable to that with GSH. In summary, epileptic activity does not produce chronic changes in the molecular and functional properties of the somatic I(A) of dentate granule cells. However, I(A) is powerfully modulated by oxidation in both control and epileptic rats. This finding suggests that the availability of I(A) may be strongly regulated by changes in the GSH/GSSG ratio occurring during prolonged seizure activity or hypoxia.

Age-related changes in glutathione and glutathione-related enzymes in rat brain

The most reliable and robust risk factor for some neurodegenerative diseases is aging. It has been proposed that processes of aging are associated with the generation of reactive oxygen species and a disturbance of glutathione homeostasis in the brain. Yet, aged animals have rarely been used to model the diseases that are considered to be age-related such as Parkinson's or Alzheimer's disease. This suggests that the results from these studies would be more valuable if aged animals were used. The present study was designed to provide insight into the glutathione redox state in young and aged rat siblings of both genders by studying the enzyme activities related to glutathione synthesis, cycling, and usage. The results suggested a significant age-related reduction of reduced glutathione (GSH) level in all brain regions examined, associated with an increase of GSH oxidation to glutathione disulfide (GSSG) and decrease of the GSH/GSSG ratio. These changes were accompanied by diminished gamma-glutamylcysteine synthetase activity in de novo glutathione synthesis and increased lipid peroxidation. In addition, these changes were associated with increased enzyme activities related to the GSH usage (glutathione peroxidase, gamma-glutamyl transpeptidase, and glutathione S-transferase). The results indicate that aged animals are likely more vulnerable to oxidative stress and insinuate the roles of aged animals in modeling age-related neurodegeneration diseases.

Depletion of reduced glutathione precedes inactivation of mitochondrial enzymes following limbic status epilepticus in the rat hippocampus

The time course and critical determinants of mitochondrial dysfunction and oxidative stress following limbic status epilepticus (SE) were investigated in hippocampal sub-regions of an electrical stimulation model in rats, at time points 4-44h after status. Mitochondrial and cytosolic enzyme activities were measured spectrophotometrically, and reduced glutathione (GSH) concentrations by HPLC, and compared to results from sham controls. The earliest change in any sub-region was a fall in GSH, appearing as early as 4h in CA3 (-13%, p<0.05), and persisting at all time points. This was followed by a transient fall in complex I activity (CA3, 16h, -13%, p<0.05), and later changes in aconitase (CA1,-18% and CA3, -22% at 44h, p<0.05). The activity of the cytosolic enzyme glyceraldehyde-3-phosphate-dehydrogenase was unaffected at all time points. It is known that GSH levels are dependent both on redox status, and on the availability of the precursor cysteine, in turn dependent on the cysteine/glutamate antiporter, for which extracellular glutamate concentrations are rate limiting. Both mechanisms are likely to contribute indirectly to GSH depletion following seizures. That a relative deficiency in GSH precedes later changes in the activities of complex I and aconitase in vulnerable hippocampal sub-regions, occurring within a clinically relevant therapeutic time window, suggests that strategies to boost GSH levels and/or otherwise reduce oxidative stress following seizures, deserve further study, both in terms of preventing the biochemical consequences of SE and the neuronal dysfunction and clinical consequences.

Modulation of cortical nitric oxide synthase, glutamate, and redox state by nifedipine and taurine in PTZ-kindled mice

PURPOSE

Correlation between pentylenetetrazol (PTZ)-induced kindling and the cortical nitric oxide synthase (NOS), intracellular calcium [Ca2+]i, glutamate, and free radicals was studied in mice, as well as the modulatory action of nifedipine and taurine on these parameters.

METHODS

Male Swiss albino mice were used. Mice in one group received a single convulsive dose of PTZ (50 mg/kg, i.p), and were killed 24 h later. To induce kindling, PTZ was injected in a subconvulsive dose (40 mg/kg, i.p.) every other day for 3 weeks. One kindled group was used as control, whereas two other groups were injected 30 min before PTZ with either nifedipine (30 mg/kg, i.p) or taurine (100 mg/kg, i.p). All three kindled groups were killed 24 h after the last injection.

RESULTS

Compared with normal control group, PTZ-kindled mice had significantly higher levels of [Ca2+]i, malonaldehyde (MDA), NOS, and lactate dehydrogenase (LDH) but had lower levels of superoxide dismutase (SOD) and reduced glutathione (GSH). Acute seizures of the same intensity did not induce these alterations, indicating their link to the kindling phenomenon and not to seizure activity. The effect of taurine, known as an antioxidant, was more pronounced than that of the Ca2+-channel blocker, nifedipine. The first drug reversed the PTZ-kindled action on [Ca2+]i, NOS, LDH, GSH, and SOD, whereas nifedipine restored only LDH and GSH levels. However, both drugs did not restore the elevated MDA level.

CONCLUSIONS

This study suggests that free radicals, as well as NOS, are implicated in PTZ-induced kindling, and that antioxidants could play a role in controlling the accompanying changes.

Alterations in brain glutathione homeostasis induced by the nerve gas soman

Public awareness of the dangers of chemical and biological warfare has been heightened in recent times. In particular, chemical nerve agents such as soman and its analogs have been developed and used in war as well as recent incidents, such as in Iraq and Japan. Soman, a rapid acting acetylcholinesterase inhibitor, produces a status epilepticus that leads to extensive neuropathology in vulnerable brain regions (eg, piriform cortex and hippocampus). This study was undertaken to determine whether oxidative mechanisms are involved in brain pathology during soman toxicity. Intracellular thiols such as glutathione (GSH) and protein sulfhydryls (PrSH) are among the most critical antioxidants used to combat oxidative stress. Here we report that during the seizure phase (1 h post soman exposure), PrSH levels in piriform cortex and hippocampus were decreased without changes in glutathione (GSH) levels. However, by 24 h post soman exposure (pathology phase), GSH levels were decreased by nearly 50% in the piriform cortex with a corresponding decrease in PrSH groups. The shift to a more oxidized thiol status indicates that oxygen free radicals likely participate in the neuropathology associated with soman-induced seizures.

Neuroprotective strategies in epilepsy

Dr. Carlen reviews the evidence that seizures may cause cell death and discusses possible strategies for preventing seizure-induced brain damage.

Glutathione, iron and Parkinson's disease

Parkinson's disease (PD) is a progressive neurodegenerative disease involving neurodegeneration of dopaminergic neurons of the substantia nigra (SN), a part of the midbrain. Oxidative stress has been implicated to play a major role in the neuronal cell death associated with PD. Importantly, there is a drastic depletion in cytoplasmic levels of the thiol tripeptide glutathione within the SN of PD patients. Glutathione (GSH) exhibits several functions in the brain chiefly acting as an antioxidant and a redox regulator. GSH depletion has been shown to affect mitochondrial function probably via selective inhibition of mitochondrial complex I activity. An important biochemical feature of neurodegeneration during PD is the presence of abnormal protein aggregates present as intracytoplasmic inclusions called Lewy bodies. Oxidative damage via GSH depletion might also accelerate the build-up of defective proteins leading to cell death of SN dopaminergic neurons by impairing the ubiquitin-proteasome pathway of protein degradation. Replenishment of normal glutathione levels within the brain may hold an important key to therapeutics for PD. Several reports have suggested that iron accumulation in the SN patients might also contribute to oxidative stress during PD.

Serum copper, zinc, selenium, glutathione peroxidase and superoxide dismutase levels in epileptic children before and after 1 year of sodium valproate and carbamazepine therapy

To assess whether epileptic children have abnormal values of serum copper (Cu), zinc (Zn), selenium (Se), glutathione peroxidase (GSH-PX) and superoxide dismutase (CuZn-SOD), and to evaluate the effect of long-term therapy with sodium valproate (VPA) and carbamazepine (CBZ) on these parameters, we studied 36 epileptic patients before the beginning of therapy and after 1 year of therapy with VPA or CBZ. Before the beginning of therapy, there were no differences in levels of all parameters studied between controls and epileptics. After 1 year of therapy, patients treated with VPA and CBZ continued to show normal values. In conclusion our study demonstrates that epilepsy per se and treatment with VPA and CBZ do not affect levels of Cu, Zn, Se, GSH-PX and CuZn-SOD concentrations.

Changes in the antioxidant system in epileptic children receiving antiepileptic drugs: two-year prospective studies

The aim of this study was to measure changes in the antioxidant systems of epileptic children who had been receiving either valproate or carbamazepine monotherapy for 2 years. For this purpose, levels of erythrocyte glutathione, glutathione peroxidase, superoxide dismutase, and serum lipid peroxidation in 25 healthy children and 27 children who had previously been diagnosed as having epilepsy but who had not, prior to the study, received antiepileptic drugs were tested. Of the 27 epileptic children, 14 were given valproate, and the remaining 13 were given carbamazepine; these tests were repeated in the 13th and 24th months of treatment. The results showed that, during valproate therapy, the lipid peroxidation levels of the epileptic children increased and the glutathione peroxidase levels decreased in comparison with those levels recorded in the control and pretreatment groups. In addition, the superoxide dismutase levels were found to be increased during the first year of valproate therapy when compared with those of the pretreatment group. However, during carbamazepine therapy, lipid peroxidation levels increased when compared with the control group only, not the pretreatment group. Furthermore, the results showed that during the second year of treatment, the superoxide dismutase levels of the children receiving carbamazapine monotherapy were found to be higher than those of both the control and pretreatment groups. From these results, it can be concluded that the antioxidant systems of the children who had been receiving valproate therapy during the 2 years were more significantly affected than those of the children who had been receiving carbamazepine.

Glutathione in disease

Altered glutathione metabolism in association with increased oxidative stress has been implicated in the pathogenesis of many diseases. However, whether strategies aimed at restoring glutathione concentration and homeostasis are effective in ameliorating or modifying the natural history of these states is unknown. In this review we discuss the pathogenic role for altered glutathione metabolism in such diseases as protein energy malnutrition, seizures, Alzheimer's disease, Parkinson's disease, sickle cell anaemia, chronic diseases associated with ageing and the infected state. In addition, we discuss the efficacy of glutathione precursors in restoring glutathione homeostasis both in vitro and in vivo.

Erythrocyte glutathione, glutathione peroxidase, superoxide dismutase and serum lipid peroxidation in epileptic children with valproate and carbamazepine monotherapy

This prospective study was carried out to determine changes in the antioxidant system in epileptic children receiving long term antiepileptic drugs (AEDs). Levels of erythrocyte glutathione (GSH), glutathione peroxidase (GSH-Px), superoxide dismutase (SOD) and serum lipid peroxidation were determined in 25 healthy children and 30 epileptic children who had not yet received AEDs. Sixteen patients were treated with valproic acid (VPA) and 14 with carbamazepine (CBZ); 13 months later these parameters were retested. The results showed that SOD and lipid peroxidation levels were increased but the GSH-Px levels were decreased in epileptic children on VPA therapy compared with the control group and the results before treatment. No significant differences of these parameters were found in epileptic children on CBZ therapy compared with the control group and the results before treatment, except that lipid peroxidation level was slightly higher in epileptic patients before treatment. We conclude that antioxidant systems in epileptic children on CBZ therapy are better regulated in comparison with epileptic children on VPA therapy.

Immunocytochemical demonstration of reduced glutathione in neurons of rat forebrain

Histochemical studies show reduced glutathione (GSH) in neuroglia, whereas immunocytochemistry of glutaraldehyde-fixed tissue reveals GSH also in neurons. Using an antibody suitable for formaldehyde-fixed tissue, we find GSH staining in the cytoplasm of neurons throughout the brain. Staining was prominent in large pyramidal neurons of cerebral cortex, in basal ganglia, and in reticular and ventrobasal thalamic nuclei.

Polyhydroxylated C60, fullerenol, a novel free-radical trapper, prevented hydrogen peroxide- and cumene hydroperoxide-elicited changes in rat hippocampus in-vitro

The role of polyhydroxylated C60 (fullerenol), a novel free-radical trapper, in prevention of hydrogen peroxide- and cumene hydroperoxide-elicited damage was studied in hippocampal slices from the rat in-vitro. The interactions of polyhydroxylated C60, adenosine and 6,7-dinitroquinoxaline-2,3-dione (DNQX) were also compared. Hydrogen peroxide (0.006-0.02%) and cumene hydroperoxide (0.5-1.0 mM) both reversibly reduced the amplitudes of CA1-evoked population spikes in the hippocampal slices. Deferoxamine (1 mM) had little effect on the population spikes. Deferoxamine (1 mM) significantly prevented the hydrogen peroxide (0.006%) elicited inhibition of the population spikes. Polyhydroxylated C60 (0.1 mM) significantly prevented hydrogen peroxide- or cumene hydroperoxide-elicited reduction of the population spikes and also prevented the effects of hydrogen peroxide and cumene hydroperoxide on paired-pulse facilitation in the hippocampal slice. Adenosine reduced the amplitude of population spikes and promoted paired-pulse facilitation in the CA1 region of the hippocampus. Polyhydroxylated C60 did not alter either of the effects of adenosine on the population spikes. DNQX reduced the amplitude of the population spikes in the CA1 region but did not affect the ratio of paired-pulse facilitation. Fullerenol did not alter either effect of DNQX on the population spikes. These results suggested that polyhydroxylated C60 prevented hydrogen peroxide- and cumene hydroperoxide-elicited damage in the hippocampuss slices. These effects might be associated with the free-radical scavenging activity of polyhydroxylated C60.

Co-localization of tyrosine hydroxylase and zebrin II immunoreactivities in Purkinje cells of the mutant mice, tottering and tottering/leaner

The mutant mice tottering, leaner and the compound heterozygous tottering/leaner exhibit varying degrees of several abnormal neurological phenotypes including petit mal-like epilepsy, ataxia and an intermittent myoclonus-like movement disorder. Aberrant expression of tyrosine hydroxylase in cerebellar Purkinje cells of tottering, leaner and tottering/leaner mice has been observed previously [Austin M. C. et al. (1992) Molec. Brain Res. 15, 227-240; Hess E. J. and Wilson M. C. (1991) Neuron 6, 123-132]. In the present study, the distribution of tyrosine hydroxylase expression was compared with that of Zebrin II in Purkinje cells of adult homozygous tottering and compound heterozygous tottering/leaner mutant mice using single and double immunocytochemistry and double immunofluorescence. The pattern of Zebrin II expression in the cerebella of the mutant mice was identical to that described for normal mice [Hawkes R. et al. (1985) Brain Res. 333, 359-365; Hawkes R. and Leclerc N. (1987) J. comp. Neurol. 256, 29-41]. In addition, sections through tottering and tottering/leaner cerebella demonstrated an exact correspondence between the bands of tyrosine hydroxylase immunoreactivity and bands of Zebrin II immunoreactivity. Similarly, the compartments of the Purkinje cell layer which were negative for Zebrin II staining were also negative for tyrosine hydroxylase immunoreactivity. This study provides evidence that the cerebellar Purkinje cells of tottering and tottering/leaner mice were able to express a normal gene product, Zebrin II, in a normal spatial pattern and the same Purkinje cells can also express an aberrant gene product, tyrosine hydroxylase. This abnormal gene expression may indicate that at least some Purkinje cells in these mutant mice are not functioning normally. This possibility, taken together with the morphological changes observed in many mutant Purkinje cell axons, suggests that Purkinje cell function could be altered in tottering and tottering/leaner mice, thereby contributing to the neurological abnormalities exhibited by these mice. It is also possible that alteration in function of mutant Purkinje cells could correlate with the rostrocaudal zonation pattern described in this study.

Mutant mouse strains as models for in vivo radiotracer evaluations: [11C]methoxytetrabenazine ([11C]MTBZ) in tottering mice

The regional brain distribution of [11C]methoxytetrabenazine ([11C]MTBZ), a high affinity radioligand for the vesicular monoamine transporter, has been examined in normal and tottering mice, which are neurological mutants. The tottering mice show significantly higher radiotracer accumulation (150-195% of controls) in all brain regions examined (striatum, cortex, hippocampus, hypothalamus, cerebellum and thalamus). The increases in [11C]MTBZ binding correlate (r = 0.91) with the reported increases in norepinephrine concentrations in these regions, and are consistent with the noradrenergic hyperinnervation characteristic of the tottering mutant mouse. These studies demonstrate that a mutant mouse model of increased innervation can be used to evaluate the sensitivity of an in vivo radiotracer measure, in this case [11C]MTBZ binding to vesicular transporters, to an increase in the numbers of binding sites in specific regions of the brain.

Plasma trace element, plasma glutathione peroxidase, and superoxide dismutase levels in epileptic children receiving antiepileptic drug therapy

Some antiepileptic drugs (AEDs) may alter trace element metabolism and free radical scavenging enzyme activities in humans and experimental animals. We investigated the effect of long-term AED therapy on copper (Cu), zinc (Zn), manganese (Mn), selenium (Se), magnesium (Mg), glutathione peroxidase (GSH-PX), and superoxide dismutase (SOD) in the plasma in children with epilepsy. During treatment with valproate (VPA) or carbamazepine (CBZ) monotherapy plasma Cu, Zn, Mn, Se, and Mg concentrations of patients were not statistically different from those of control subjects. The level of serum VPA weakly correlated with the increase in plasma Zn level. Recent studies suggest that membrane lipid peroxidation may be causally involved in some forms of epilepsies, and the decreased free radical scavenging enzyme activity is believed to cause the increased risk of an idiosyncratic drug reaction encountered in the management of epilepsy. Because GSH-PX and SOD are the most important members of antioxidant defense mechanisms, we quantitated the activities of these enzymes in plasma of children with epilepsy receiving VPA or CBZ. Only plasma GSH-PX activities in VPA group were higher than those of the control group, and the difference was statistically significant.

Antibodies to reduced glutathione

Reduced glutathione was conjugated to carrier proteins with glutaraldehyde. Conjugates were reduced by sodium borohydride and injected into rabbits. Using an enzyme-linked immunosorbent assay, antibody affinity and specificity were determined by competition experiments between glutathione conjugate and related conjugated compounds. The resulting cross-reactivity ratios, calculated at half-displacement, showed that conjugated glutathione was the best recognized compound. Non-reduced glutathione conjugate was 50 x less recognized. The other related conjugates were not recognized at all. Thus, the high affinity and relative specificity make these antibodies potentially valuable tools for immunohistochemical detection of reduced glutathione in glutaraldehyde-fixed rat brain. Using purified antisera diluted at 1/5000, reduced glutathione was preferentially visualized in nerve fibers of cortex, cerebellum and spinal cord. These results suggest that concentration of GSH in rat CNS are higher in nerve fibers than in neuronal perikaryons.

Age and GSH metabolism in rat cerebral cortex, as related to oxidative and energy parameters

A comprehensive study on GSH metabolism in relation to some markers of oxidative and energy status in rat cerebral cortex as a function of age was performed. Reduced GSH, total GSH and the GSH Redox Index decreased both during growth (defined as the period between 1 and 5 months) and during aging (defined as the period between 5 and 27 months) while GSSG levels increased during the two periods, but most significantly during aging. Also GSH-associated enzymes and adenine-pyridine nucleotide levels show age characteristic changes. The obtained results suggest that decreases in oxidative and energy metabolism occur during aging. They probably contribute to decreases in the activity of the biosynthetic processes (i.e., NADP+(H) and GSH synthesis) and in the antioxidant capacity of the GSH system. However, the oxidative stress does not seem to be a typical characteristic of the aging period; as an oxidative status is present during the growth period too. Typical parameters of aging process are mainly the low levels of reduced GSH, total GSH and GSH Redox Index and the high levels of GSSG as well as the high levels of GSH peroxidase and GSH transferase and the low levels of gamma-glutamylcysteine synthetase.

Role of glutathione in repair of free radical damage in hippocampus in vitro

Depletion of glutathione (GSH), an intrinsic antioxidant, increases vulnerability to free radical damage in a number of cell systems. This study investigates the role of GSH in limiting electrophysiological damage and/or recovery from free radical exposure in slices of guinea pig hippocampus. Synaptic potentials (PSPs) and population spikes (PSs) were recorded from field CA1. Free radicals were generated from 0.006% peroxide through the Fenton reaction. Analysis of the input-output curves showed that peroxide treatment decreased PSPs and impaired ability of the PSPs to generate PSs as previously reported. Recovery was nearly total within a half hour. Treatment with 5 mM buthionine sulfoximine (BSO) for 2 h depleted hippocampal GSH to 79.2% of control values. The extent of free radical damage was not increased. Recovery, however, was only partial. GSH was further depleted by oxidation with diamide or covalent bonding with dimethyl fumarate (DMF) immediately before and during the peroxide treatment. Neither diamide nor DMF treatment in BSO-incubated tissue enhanced peroxide-induced electrophysiological deficits. Following these treatments, however, tissue showed little recovery from free radical damage. We conclude that glutathione is essential for repair processes in hippocampal neurons exposed to oxidative damage.

The tottering mouse: a critical review of its usefulness in the study of the neuronal mechanisms underlying epilepsy

The tottering mouse resulted from a recessively inherited, autosomal, single-locus mutation which produces a very characteristic neurological and cellular phenotype. Almost simultaneously and late in the development of this mutant appears a triad of symptoms: frequent episodes of absence seizures with spike-and-wave discharges; more rarely occurring episodes of focal motor seizures; and ataxia. Electrographic, behavioural and pharmacological similarities to absence epilepsy in man make the tottering mouse a useful animal model for testing new anti-absence drugs. It also affords a unique opportunity to study the effects of multiple alleles on epileptic behaviour. The neuronal mechanisms underlying the generation of absence seizures in this mutant are apparently a combination of a generalized noradrenergic hyperactivity in the brain and some gene-linked, but unknown, conditions prevailing in an earlier phase of development at specific brain areas which induce the generalized forebrain hyper-innervation by locus coeruleus terminals. Several biochemically, microscopically and electrophysiologically identified cellular differences between normal and tottering mice are potential aspects of this primary developmental defect. Research into these gene-linked neuronal characteristics co-inherited with seizures in this mutant makes the tottering mouse a powerful tool in the study of cellular mechanisms underlying genetically determined factors in epileptogenesis.

Increased methionine-enkephalin levels in genetically epileptic (tg/tg) mice

Recent experimental data indicate that endogenous brain ligands for the opioid receptors such as enkephalins, beta-endorphin (beta-End) and dynorphin (Dyn) may be involved in both generalized and partial seizures. The "tottering" (tg/tg) mouse provides an electrophysiological representation of generalized spontaneous human epilepsy. These mice exhibit behavioral absence seizures with accompanying spike-wave discharges. Methionine-enkephalin (M-Enk), beta-End and Dyn levels in various regions of brain were measured by radioimmunoassay (RIA) in 15-18-week-old tg/tg and control (+/+) mice to elucidate the relation between seizures and the opioid system. beta-End and Dyn levels were similar in tg/tg and +/+ mice. However, M-Enk levels were significantly increased in the striatum, cortex, pons and medulla of the tg/tg mice. Our data suggest that in the tottering mouse model of generalized epilepsy there is an alteration of enkephalinergic pathways and not of the endorphinergic or dynorphinergic pathways.