Differences in mitochondrial function between brain and heart of senile rats exposed to acute hypobaric hypoxia. Role of nitric oxide.

Rat brain and heart display different endogenous protective responses against hypobaric hypoxia in an age-dependent way. The aim of the present work was to evaluate the effects of acute hypobaric hypoxia (HH, 48 h) on brain and heart mitochondrial function as well as the participation of nitric oxide (NO) in old rats (22-month old). Cortical mitochondria from rats exposed to HH decreased respiratory rates (37 %, state 3) and membrane potential (20 %), but NO and H2O2 production increased by 48 %, and 23 %, respectively. Hippocampal mitochondria preserved O2 consumption and H2O2 production, decreased membrane potential (18 %) and increased NO production (46 %). By contrast, HH decreased NO production (53 %) in mitochondria from left heart ventricles associated with increased cytochrome oxidase activity (39 %) and decreased NADPH oxidase activity (31 %). Also, a tendency to increase complex I-III (24 %) and complex II-III (65 %) activity was observed. In conclusion, after HH hippocampal and cortical mitochondria showed mild uncoupling and increased NO production. However, only the hippocampus preserved O2 consumption and H2O2 levels. Interestingly, heart mitochondria showed a decreased ROS production through increased cytochrome oxidase activity associated with a decrease in NO production. This may be interpreted as a self-protective mechanism against hypoxia.

Changes in motor function and brain cortex mitochondrial active oxygen species production in aged mice.

Neuronal ageing is a complex physiological process, associated to metabolic and motor changes. In this study, 3 and 17 months old male Swiss mice were used. Aged mice exhibited a significant reduction in motor performance and walking footprint pattern. Synaptosomes and mitochondrial fractions were isolated from mouse brain cortex. Active oxygen species and cardiolipin content were measured in both subcellular fractions. Synaptosomal acetylcholinesterase activity was measured in both animal age groups. Results showed that superoxide levels were 42.9% lower in synaptosomes from old mice as compared with young animals, while no changes were observed in non-synaptic mitochondria. Succinate-glutamate dependent H2O2 production rate was 27.5% decreased in non-synaptic mitochondria from aged mice. Cardiolipin content was 21% decreased in synaptosomes from 17-months old animals, while no changes were observed in non-synaptic mitochondria. Acetylcholinesterase activity decreased 16% in 17-months old mice, as compared with young animals. Age-related alterations in neuronal function could be associated with changes in active oxygen species at synapses, with parallel motor deficiencies.

Impairment of striatal mitochondrial function by acute paraquat poisoning.

Mitochondria are essential for survival. Their primary function is to support aerobic respiration and to provide energy for intracellular metabolic pathways. Paraquat is a redox cycling agent capable of generating reactive oxygen species. The aim of the present study was to evaluate changes in cortical and striatal mitochondrial function in an experimental model of acute paraquat toxicity and to compare if the brain areas and the molecular mechanisms involved were similar to those observed after chronic exposure. Sprague-Dawley rats received paraquat (25 mg/Kg i.p.) or saline and were sacrificed after 24 h. Paraquat treatment decreased complex I and IV activity by 37 and 21 % respectively in striatal mitochondria. Paraquat inhibited striatal state 4 and state 3 KCN-sensitive respiration by 80 % and 62 % respectively, indicating a direct effect on respiratory chain. An increase of 2.2 fold in state 4 and 2.3 fold in state 3 in KCN-insensitive respiration was observed in striatal mitochondria from paraquat animals, suggesting that paraquat redox cycling also consumed oxygen. Paraquat treatment increased hydrogen peroxide production (150 %), TBARS production (42 %) and cardiolipin oxidation/depletion (12 %) in striatal mitochondria. Also, changes in mitochondrial polarization was induced after paraquat treatment. However, no changes were observed in any of these parameters in cortical mitochondria from paraquat treated-animals. These results suggest that paraquat treatment induced a clear striatal mitochondrial dysfunction due to both paraquat redox cycling reactions and impairment of the mitochondrial electron transport, causing oxidative damage. As a consequence, mitochondrial dysfunction could probably lead to alterations in cellular bioenergetics.

Alcohol hangover induces mitochondrial dysfunction and free radical production in mouse cerebellum.

Alcohol hangover (AH) is defined as the temporary state after alcohol binge-like drinking, starting when ethanol (EtOH) is absent in plasma. Previous data indicate that AH induces mitochondrial dysfunction and free radical production in mouse brain cortex. The aim of this work was to study mitochondrial function and reactive oxygen species production in mouse cerebellum at the onset of AH. Male mice received a single i.p. injection of EtOH (3.8g/kg BW) or saline solution. Mitochondrial function was evaluated 6h after injection (AH onset). At the onset of AH, malate-glutamate and succinate-supported state 4 oxygen uptake was 2.3 and 1.9-fold increased leading to a reduction in respiratory control of 55% and 48% respectively, as compared with controls. Decreases of 38% and 16% were found in Complex I-III and IV activities. Complex II-III activity was not affected by AH. Mitochondrial membrane potential and mitochondrial permeability changes were evaluated by flow cytometry. Mitochondrial membrane potential and permeability were decreased by AH in cerebellum mitochondria. Together with this, AH induced a 25% increase in superoxide anion and a 92% increase in hydrogen peroxide production in cerebellum mitochondria. Related to nitric oxide (NO) metabolism, neuronal nitric oxide synthase (nNOS) protein expression was 52% decreased by the hangover condition compared with control group. No differences were found in cerebellum NO production between control and treated mice. The present work demonstrates that the physiopathological state of AH involves mitochondrial dysfunction in mouse cerebellum showing the long-lasting effects of acute EtOH exposure in the central nervous system.

Mitochondrial function in rat cerebral cortex and hippocampus after short- and long-term hypobaric hypoxia.

Taking into account the importance of aerobic metabolism in brain, the aim of the present work was to evaluate mitochondrial function in cerebral cortex and hippocampus in a model of sustained hypobaric hypoxia (5000 m simulated altitude) during a short (1 mo) and a long (7 mo) term period, in order to precise the mechanisms involved in hypoxia acclimatization. Hippocampal mitochondria from rats exposed to short-term hypobaric hypoxia showed lower respiratory rates than controls in both states 4 (45%) and 3 (41%), and increased NO production (1.3 fold) as well as eNOS and nNOS expression associated to mitochondrial membranes, whereas mitochondrial membrane potential decreased (7%). No significant changes were observed in cortical mitochondria after 1 mo hypobaric hypoxia in any of the mitochondrial functionality parameters evaluated. After 7 mo hypobaric hypoxia, oxygen consumption was unchanged as compared with control animals both in hippocampal and cortical mitochondria, but mitochondrial membrane potential decreased by 16% and 8% in hippocampus and cortex respectively. Also, long-term hypobaric hypoxia induced an increase in hippocampal NO production (0.7 fold) and in eNOS expression. A clear tendency to decrease in H2O2 production was observed in both tissues. Results suggest that after exposure to hypobaric hypoxia, hippocampal mitochondria display different responses than cortical mitochondria. Also, the mechanisms responsible for acclimatization to hypoxia would be time-dependent, according to the physiological functions of the brain studied areas. Nitric oxide metabolism and membrane potential changes would be involved as self-protective mechanisms in high altitude environment.

Oxygen metabolism in human placenta mitochondria.

Due to the high metabolic demands of the placental tissue during gestation, we decide to analyzed the mitochondrial bioenergetic functions in the human term placenta. Different mitochondrial morphological parameters, membrane potential and cardiolipin content were determined by flow cytometry. Oxygen uptake, hydrogen peroxide production and cytochrome P450 content, were also measured. Some apoptotic mitochondrial proteins were also analyzed by western blot. Two isolated mitochondrial fractions were observed: large/heavy and small/light with different functional characteristics. Oxygen uptake showed a respiratory control (RC) of 3.4 ± 0.3 for the heavy mitochondria, and 1.1 ± 0.4 for light mitochondria, indicating a respiratory dysfunction in the light fraction. Good levels of polarization were detected in the heavy fraction, meanwhile the light population showed a collapsed ΔΨm. Increased levels of cytochrome P450, higher levels of hydrogen peroxide, and low cardiolipin content were described for the light fraction. Three pro-apoptotic proteins p53, Bax, and cytochrome c were found increased in the heavy mitochondrial fraction; and deficient in the light fraction. The heavy mitochondrial fraction showed an improved respiratory function. This mitochondrial fraction, being probably from cytotrophoblast cells showed higher content of proteins able to induce apoptosis, indicating that these cells can effectively execute an apoptotic program in the presence of a death stimulus. Meanwhile the light and small organelles probably from syncytiotrophoblast, with a low oxygen metabolism, low level of ΔΨm, and increased hydrogen peroxide production, may not actively perform an apoptotic process due to their deficient energetic level. This study contributes to the characterization of functional parameters of human placenta mitochondria in order to understand the oxygen metabolism during the physiological process of gestation.

Effect of melatonin on motor performance and brain cortex mitochondrial function during ethanol hangover.

Increased reactive oxygen species generation and mitochondrial dysfunction occur during ethanol hangover. The aim of this work was to study the effect of melatonin pretreatment on motor performance and mitochondrial function during ethanol hangover. Male mice received melatonin solution or its vehicle in drinking water during 7 days and i.p. injection with EtOH (3.8 g/kg BW) or saline at the eighth day. Motor performance and mitochondrial function were evaluated at the onset of hangover (6h after injection). Melatonin improved motor coordination in ethanol hangover mice. Malate-glutamate-dependent oxygen uptake was decreased by ethanol hangover treatment and partially prevented by melatonin pretreatment. Melatonin alone induced a decrease of 30% in state 4 succinate-dependent respiratory rate. Also, the activity of the respiratory complexes was decreased in melatonin-pretreated ethanol hangover group. Melatonin pretreatment before the hangover prevented mitochondrial membrane potential collapse and induced a 79% decrement of hydrogen peroxide production as compared with ethanol hangover group. Ethanol hangover induced a 25% decrease in NO production. Melatonin alone and as a pretreatment before ethanol hangover significantly increased NO production by nNOS and iNOS as compared with control groups. No differences were observed in nNOS protein expression, while iNOS expression was increased in the melatonin group. Increased NO production by melatonin could be involved in the decrease of succinate-dependent oxygen consumption and the inhibition of complex IV observed in our study. Melatonin seems to act as an antioxidant agent in the ethanol hangover condition but also exhibited some dual effects related to NO metabolism.

Mitochondrial susceptibility in a model of paraquat neurotoxicity.

Paraquat is a highly toxic herbicide capable of generating oxidative stress and producing brain damage after chronic exposure. The aim of this research was to investigate the contribution of mitochondria to the molecular mechanism of apoptosis in an in vivo experimental model of paraquat neurotoxicity. Sprague-Dawley adult female rats received paraquat (10 mg/kg i.p.) or saline once a week during a month. Paraquat treatment increased cortical and striatal superoxide anion levels by 45% and 18%, respectively. As a consequence, mitochondrial aconitase activity was significantly inhibited in cerebral cortex and striatum. Paraquat treatment increased cortical and striatal lipid peroxidation levels by 16% and 28%, respectively, as compared with control mitochondria Also, cortical and striatal cardiolipin levels were decreased by 13% and 49%, respectively. Increased Bax and Bak association to mitochondrial membranes was observed after paraquat treatment in cerebral cortex and striatum. Also, paraquat induced cytochrome c and AIF release from mitochondria. These findings support the conclusion that a weekly dose of paraquat during four weeks induces oxidative damage that activates mitochondrial pathways associated with molecular mechanisms of cell death. The release of apoptogenic proteins from mitochondria to cytosol after paraquat treatment would be the consequence of an alteration in mitochondrial membrane permeability due to the presence of high superoxide anion levels. Also, our results suggest that under chronic exposure, striatal mitochondria were more sensitive to paraquat oxidative damage than cortical mitochondria. Even in the presence of a high oxidative stress in striatum, equal levels of apoptosis were attained in both brain areas.

Paraquat induces behavioral changes and cortical and striatal mitochondrial dysfunction.

Paraquat is a highly toxic quaternary nitrogen herbicide capable of increasing superoxide anion production. The aim of this research was to evaluate various behavioral changes and study cortical, hippocampal, and striatal mitochondrial function in an experimental model of paraquat toxicity in rats. Paraquat (10mg/kg ip) was administered weekly for a month. Anxiety-like behavior was evidenced in the paraquat-treated group as shown by a diminished time spent in, and fewer entries into, the open arms of an elevated-plus maze. Also, paraquat treatment induced a deficit in the sense of smell. In biochemical assays, NADH-cytochrome c reductase activity was significantly inhibited by 25 and 34% in cortical and striatal submitochondrial membranes, respectively. Striatal cytochrome oxidase activity was decreased by 24% after paraquat treatment. Also, cortical and striatal mitochondria showed 55 and 74% increased State 4 respiratory rates, respectively. Paraquat treatment decreased striatal State 3 oxygen consumption by 33%. Respiratory controls were markedly decreased in cortical and striatal mitochondria, indicating mitochondrial dysfunction after paraquat treatment, together with mitochondrial depolarization and increased hydrogen peroxide production rates. We demonstrate that paraquat induced alterations in nonmotor symptoms and cortical and striatal mitochondrial dysfunction.

Age-related alterations in mitochondrial physiological parameters and nitric oxide production in synaptic and non-synaptic brain cortex mitochondria.

Brain aging has been associated with mitochondrial dysfunction and changes in nitric oxide levels. The aim of this study was to evaluate the susceptibility of synaptic and non-synaptic mitochondria to aging-dependent dysfunction. State 3 respiratory rate and respiratory control were 43% and 33% decreased, respectively in brain cortex synaptosomes from 14-month-old animals, as compared with synaptosomes from 3-month-old mice. Respiratory rates were not significantly affected by aging in non-synaptic mitochondrial fractions. Mitochondrial dysfunction was associated with increases of 84% and 38% in H2O2 production rates in brain cortex synaptosomes and non-synaptic mitochondria, respectively, from 14-month-old mice, as compared with young animals. Synaptic mitochondria seem to be more susceptible to calcium insult in 14-month-old mice, as compared with non-synaptic mitochondria, as measured by response of both types of fractions to calcium-induced depolarization. With aging, nitric oxide (NO) production was 44% and 27% decreased both in synaptosomal and non-synaptic mitochondrial fractions, respectively. The results of this study suggest that with aging, mitochondrial function at the nerve terminals would be more susceptible to suffer alterations by the constant calcium changes occurring as a consequence of synaptic activity. Non-synaptic mitochondria would be more resistant to age-related dysfunction and oxidative damage.

Mitochondrial dysfunction as a mediator of hippocampal apoptosis in a model of hepatic encephalopathy.

In this study, we describe the presence of apoptosis, associated with a mitochondrial dysfunction in the hippocampus of animals in an experimental model defined as minimal hepatic encephalopathy (MHE). This experimental model was studied after 10 days of induced portal vein calibrated stricture, leading to portal hypertension and to a moderate hyperammonemia, without the presence of other evident central nervous system changes. The molecular mechanisms here proposed indicate the presence of apoptotic intrinsic pathways that point to hippocampal mitochondria as an important mediator of apoptosis in this experimental model. In this model of MHE, the presence of DNA fragmentation is documented by 2.3-times increased number of TUNEL-positive cells. These findings together with a higher ratio of the Bcl-2 family members Bax/Bcl-xL in the outer mitochondrial membrane of the MHE animals together with 11% of cytochrome c release indicate the presence of apoptosis in this experimental model. A detailed analysis of the hippocampal mitochondrial physiology was performed after mitochondrial isolation. The determination of the respiratory rate in the presence of malate plus glutamate and ADP showed a 45% decrease in respiratory control in MHE animals as compared with the sham group. A marked decrease of cytochrome oxidase (complex IV of the electron transport chain) was also observed, showing 46% less activity in hippocampal mitochondria from MHE animals. In addition, mitochondria from these animals showed less ability to maintain membrane potential (ΔΨ (m)) which was 13% lower than the sham group. Light scattering experiments showed that mitochondria from MHE animals were more sensitive to swell in the presence of increased calcium concentrations as compared with the sham group. In addition, in vitro studies performed in mitochondria from sham animals showed that mitochondrial permeability transition (MPT) could be a mitochondrial mediator of the apoptotic signaling in the presence of NH(4) (+) and calcium.

Mitochondrial function and nitric oxide production in hippocampus and cerebral cortex of rats exposed to enriched environment.

Male rats (21days) were assigned to enriched environment (EE) or to standard environment (SE) for 1year. Oxygen consumption and the sensitivity to calcium induced mitochondrial permeability transition (MPT), through mitochondrial membrane potential (DeltaPsi(m)) and swelling, were determined in isolated hippocampal and cerebral cortex mitochondria. Mitochondrial H(2)O(2) production rate, and NOS activity and expression associated with mitochondrial membranes were also assayed. Results showed that state 3 respiratory rate was increased by 80% in cerebral cortex mitochondria from EE rats and no changes were observed in hippocampal mitochondria after EE exposure. Calcium induced-swelling was 40% and 53% lower in hippocampal and cerebral cortex mitochondria from EE rats, as compared with SE rats. Calcium loading induced membrane depolarization in cerebral cortex mitochondria from EE rats but did not affect mitochondrial DeltaPsi(m) in hippocampal mitochondria from EE animals, probably due to decreased H(2)O(2) formation. NO production associated to mitochondrial membranes was increased by 195% in cerebral cortex mitochondria but decreased by 47% in hippocampal mitochondria from EE rats, as compared with SE rats. Western blot analysis from nNOS protein expression associated to mitochondrial samples revealed a similar pattern. Our results suggest that in hippocampus and cerebral cortex, EE exposure protects mitochondria against calcium-induced MPT maintaining a convenient membrane potential, which assures a continuous energy supply.

Exposure to enriched environments increases brain nitric oxide synthase and improves cognitive performance in prepubertal but not in young rats.

Rats were randomly assigned to enriched (EE) or standard environments (SE) at 21 or 73 days of age, for 17 days. Half of the rats of each rearing condition were trained in a radial maze (RM). At 38 days (pre-pubertal) or 90 days (young), rats were sacrificed and brain cytosolic and mitochondrial nitric oxide synthase (mtNOS) activity was assayed. Western blot analysis of brain mtNOS was conducted. In the pre-pubertal group, EE rats improved their performance in the RM while SE rats did not. In the young group, SE and EE rats showed a random performance in the RM. In SE pre-pubertal rats, training increased brain cytosolic NOS and mtNOS activity by 68% and 82%. In EE non-trained pre-pubertal rats, brain cytosolic NOS and mtNOS activity increased by 80% and 60%, as compared with SE non-trained pre-pubertal rats. In EE pre-pubertal rats that were trained, brain cytosolic NOS and mtNOS activity increased by 70% and 90%, as compared with SE pre-pubertal rats that were not trained. A higher protein expression of brain mtNOS was found in EE rats, as compared with SE animals. Mitochondrial complex I activity was higher in EE than in SE rats. Training had no effect on complex I activity neither in SE nor in EE rats. In young rats, no significant differences in enzyme activities were found between EE and SE rats. These results support the hypothesis that brief exposure to EE and training produce effects on behavioral performance and on biochemical parameters in an age-dependent manner.

Improvement of mouse brain mitochondrial function after deprenyl treatment.

Deprenyl is a selective monoamine oxidase (MAO) B inhibitor, widely used for treatment of Parkinson's disease. The present study shows that deprenyl treatment was able to improve mitochondrial function. Fourteen month old mice were injected i.p. with deprenyl (20 mg/kg) and killed 1.5 h after the administration. Different brain subcellular fractions were isolated from control and deprenyl-treated animals to evaluate the effect of deprenyl on nitric oxide synthase (NOS) activity. Oxygen consumption, hydrogen peroxide (H(2)O(2)) production, mitochondrial membrane potential and calcium-induced permeability transition (MPT) were studied in intact mitochondria. In addition, the effect of deprenyl on respiratory complexes and MAO activities were evaluated in submitochondrial particles (SMP). Monoamine oxidase activity was found to be decreased by 55% in mitochondria from deprenyl-treated animals and as a consequence, H(2)O(2) production was significantly decreased. Deprenyl inhibited NOS activity in cytosolic fractions and SMP by 40% and 55%, respectively. In similar conditions, SMP from deprenyl-treated animals showed increased cytochrome oxidase activity. A 51% increase in the oxygen uptake in state 3 (active respiration state) was found after deprenyl treatment, but no significant changes were observed in state 4 (resting respiration state). Deprenyl treatment protected against calcium-induced depolarization and was able to inhibit calcium-induced MPT. This work provides evidence that deprenyl treatment exerts an improvement of brain mitochondrial function, through a reduction of free radical production, prevention of calcium-induced MPT and maintaining a mitochondrial transmembrane potential.

Extensive enriched environments protect old rats from the aging dependent impairment of spatial cognition, synaptic plasticity and nitric oxide production.

In aged rodents, neuronal plasticity decreases while spatial learning and working memory (WM) deficits increase. As it is well known, rats reared in enriched environments (EE) show better cognitive performances and an increased neuronal plasticity than rats reared in standard environments (SE). We hypothesized that EE could preserve the aged animals from cognitive impairment through NO dependent mechanisms of neuronal plasticity. WM performance and plasticity were measured in 27-month-old rats from EE and SE. EE animals showed a better spatial WM performance (66% increase) than SE ones. Cytosolic NOS activity was 128 and 155% higher in EE male and female rats, respectively. Mitochondrial NOS activity and expression were also significantly higher in EE male and female rats. Mitochondrial NOS protein expression was higher in brain submitochondrial membranes from EE reared rats. Complex I activity was 70-80% increased in EE as compared to SE rats. A significant increase in the area of NADPH-d reactive neurons was observed in the parietotemporal cortex and CA1 hippocampal region of EE animals.

Free radical chemistry in biological systems.

Mitochondria are an active source of the free radical superoxide (O2-) and nitric oxide (NO), whose production accounts for about 2% and 0.5% respectively, of mitochondrial O2 uptake under physiological conditions. Superoxide is produced by the auto-oxidation of the semiquinones of ubiquinol and the NADH dehydrogenase flavin and NO by the enzymatic action of the nitric oxide synthase of the inner mitochondrial membrane (mtNOS). Nitric oxide reversibly inhibits cytochrome oxidase activity in competition with O2. The balance between NO production and its utilization results in a NO intramitochondrial steady-state concentration of 20-50 nM, which regulates mitochondrial O2 uptake and energy supply. The regulation of cellular respiration and energy production by NO and its ability to switch the pathway of cell death from apoptosis to necrosis in physiological and pathological conditions could take place primarily through the inhibition of mitochondrial ATP production. Nitric oxide reacts with O2- in a termination reaction in the mitochondrial matrix, yielding peroxynitrite (ONOO-), which is a strong oxidizing and nitrating species. This reaction accounts for approximately 85% of the rate of mitochondrial NO utilization in aerobic conditions. Mitochondrial aging by oxyradical- and peroxynitrite-induced damage would occur through selective mtDNA damage and protein inactivation, leading to dysfunctional mitochondria unable to keep membrane potential and ATP synthesis.

Free radical chemistry in biological systems

Mitochondria are an active source of the free radical superoxide (O2-) and nitric oxide (NO), whose production accounts for about 2% and 0.5% respectively, of mitochondrial O2 uptake under physiological conditions. Superoxide is produced by the auto-oxidation of the semiquinones of ubiquinol and the NADH dehydrogenase flavin and NO by the enzymatic action of the nitric oxide synthase of the inner mitochondrial membrane (mtNOS). Nitric oxide reversibly inhibits cytochrome oxidase activity in competition with O2. The balance between NO production and its utilization results in a NO intramitochondrial steady-state concentration of 20-50 nM, which regulates mitochondrial O2 uptake and energy supply. The regulation of cellular respiration and energy production by NO and its ability to switch the pathway of cell death from apoptosis to necrosis in physiological and pathological conditions could take place primarily through the inhibition of mitochondrial ATP production. Nitric oxide reacts with O2- in a termination reaction in the mitochondrial matrix, yielding peroxynitrite (ONOO-), which is a strong oxidizing and nitrating species. This reaction accounts for approximately 85% of the rate of mitochondrial NO utilization in aerobic conditions. Mitochondrial aging by oxyradical- and peroxynitrite-induced damage would occur through selective mtDNA damage and protein inactivation, leading to dysfunctional mitochondria unable to keep membrane potential and ATP synthesis.

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.

Chemiluminescence and antioxidant levels during peroxisome proliferation by fenofibrate.

Fenofibrate, the hypolipidemic drug and peroxisome proliferator, was given to mice (0.23% w/w in the diet) during 1-3 weeks and H2O2 and TBARS steady state concentrations, liver chemiluminescence and antioxidant levels were measured. Administration of fenofibrate during 2 weeks induced an increase of 89% in H2O2 steady state concentration. Spontaneous chemiluminescence was decreased by 57% during fenofibrate treatment, while no significant effect was observed on TBARS concentration. Hydroperoxide-initiated chemiluminescence was decreased by 56% after 15 days of fenofibrate treatment, probably due to an increase in endogenous antioxidant levels. Total and oxidized glutathione increased gradually after fenofibrate administration, obtaining maximal increases of 67% and 58% respectively, after 22 days of treatment. An increase of 55% was found in ubiquinol levels in treated mice, as compared with the controls. alpha-tocopherol content was decreased by 51% in the liver of fenofibrate-treated mice. According to our findings, the high rate of H2O2 production associated with peroxisome proliferation, would not lead to an increase in lipid peroxidation. This can be explained by the presence of high levels of ubiquinols, which act as an antioxidant. The increased production of H2O2, would lead to DNA damage directly, and not through lipid peroxidation processes.