Free radicals in brain metabolism and pathology

Altered plasma antioxidant status in subjects with Alzheimer's disease and vascular dementia

OBJECTIVES

Oxygen-free radicals and lipid hydroperoxides may have an aetiological role in the development of lesions in the central nervous system in patients with Alzheimer's disease and in those with vascular dementia. This study aimed to make a cross-sectional comparison of blood markers of oxidative stress in two groups of patients with these disorders and a control group.

DESIGN

Cross-sectional comparative study.

SETTING

Established memory clinics in Cardiff organized by a University Department of Geriatric Medicine within an acute care NHS Trust.

METHODS

Following a dietary assessment, postprandial venous blood samples were obtained from the following: 25 subjects with probable Alzheimer's disease (AD) (mean age 74.3; 10 F, 15 M); 17 subjects with probable vascular dementia (VD) (mean age 75.5; 5 F, 12 M); and 41 controls (mean age 73.4; 24 F, 17 M) for measurement of circulating lipid peroxides (LP), total antioxidant capacity (TAC), vitamin C (VitC), vitamin E (VitE) and beta-carotene (BC).

RESULTS

Plasma levels of VitC were significantly lower in subjects with vascular dementia compared with controls (VD, 6.5 (4.8, 8.2); controls, 10.0 (8.38, 11.6); VD vs controls, p = 0.015), but no significant difference was seen between controls and patients with Alzheimer's disease (AD, mean 8.3 (6.2, 10.4)). VitE levels were significantly lower in subjects with AD compared with controls (31.1 (28.2, 34.0) vs 36.0 (32.8, 39.2), p = 0.035). BC levels were similar in subjects with AD and controls, but significantly elevated in those with VD (AD, 0.28 (0.2, 0.34); VD, 0.40, (0.27, 0.53); controls, 0.28 (0.22, 0.34); VD vs controls, p = 0.046). There were no significant differences in LP or TAC between the three groups.

CONCLUSIONS

Subjects with dementia attributed to Alzheimer's disease or to vascular disease have a degree of disturbance in antioxidant balance which may predispose to increased oxidative stress. This may be a potential therapeutic area for antioxidant supplementation.

Free radicals as mediators of neuronal injury

1. Free radicals may play an important role in several pathological conditions of the central nervous system (CNS) where they directly injure tissue and where their formation may also be a consequence of tissue injury. 2. Free radicals produce tissue damage through multiple mechanisms, including excito-toxicity, metabolic dysfunction, and disturbance of intracellular homeostasis of calcium. 3. Oxidative stress can significantly worsen acute insults, such as ischemia, as well as chronic neurodegenerative disorders including amyotrophic lateral sclerosis (ALS) and Parkinson's disease. 4. For instance, recent findings suggest a causal role for chronic oxidative stress in familial ALS, as this disease is linked to missence mutations of the copper/zinc superoxide dismutase (SOD). 5. Thus, therapeutic approaches which limit oxidative stress may be potentially beneficial in several neurological diseases.

Effect of aluminum on superoxide dismutase activity in the adult rat brain

Male rats were treated daily with an intraperitoneal injection of 15 mg aluminum (Al chloride)/kg body weight for 17 d, in order to study the effects on superoxide dismutase (SOD) activities in the brain (cortex). No significant difference between control and treated animals was registered in the Cu/Zn and Mn SOD activities in the gray matter of the cortex. High Al levels were found in the plasma, the spleen, and the liver of the treated animals in comparison to the controls, but not in the cortex homogenates (gray matter). In addition, Al induced a significant decrease in food ingestion and weight gain.

The comparison of the antioxidant defense potential of brain to liver of rats after methanol ingestion

The antioxidant enzymatic and nonenzymatic potential in the brain of rats given methanol orally was investigated for 7 days consecutively and compared to that one in the liver. Glutathione (GSH) and the activities of superoxide dismutase (Cu, Zn-SOD), glutathione peroxidase (GSH-Px) and glutathione reductase (GSSG-R) were reduced in the brain after the first 24 h, whereas in the liver these parameters were diminished after 6 h. The brain catalase (CAT) activity was very low and constant in contrast to high and changeable CAT in the liver. At the beginning of intoxication, the activities of Cu, Zn-SOD and CAT in the liver were increased; after 5 days they were restored to normal values while Cu, Zn-SOD diminished gradually in the brain. An early change that occurred 6 h after intoxication was a decrease of ascorbate in the brain and in the liver. The increase in thiobarbituric acid-reactive substances (TBA-rs) in the liver was preceded by their increase in the brain. Our findings indicate decreased antioxidative potential both in the brain and in the liver of rats after methanol ingestion. The regulatory mechanisms of the antioxidant enzymes in the brain of intoxicated rats differ from those ones in the liver.

Influence of twinline, an elemental diet, on the generation of nitric oxide and reactive-oxygen intermediates from mouse peritoneal macrophages and polymorphonuclear leukocytes

The influence of Twinline (SNN-6010), an elemental diet containing medium-chain triglycerides, on the generation of nitric oxide (NO) and superoxide (O2.-) has been examined in mouse peritoneal macrophages and polymorphonuclear leukocytes (PMN). When PMN and peritoneal macrophages obtained from untreated mice were cultured in medium containing 0.1% and 1% (v/v) Twinline for 48h and stimulated with phorbol myristate acetate or N-formyl-methionyl-leucyl-phenylalanine, their chemiluminescence and O2.- generation were strongly suppressed, as was NO generation from peritoneal macrophages. PMN and peritoneal macrophages obtained from mice fed Twinline for 30 days generated much smaller amounts of 02.- and NO compared with PMN and peritoneal macrophages from control mice. In conjunction with this suppressed NO generation, inducible NO synthase and its mRNA expression in peritoneal macrophages were suppressed by Twinline both in-vivo and ex-vivo. Although phagocytosis of PMN and peritoneal macrophages was not suppressed by Twinline; their candida-killing activity was markedly suppressed. These results indicate that Twinline suppresses the host-defence function of PMN and peritoneal macrophages by down-regulating their generation of reactive-oxygen intermediates and NO.

Time-level relationship for lipid peroxidation and the protective effect of alpha-tocopherol in experimental mild and severe brain injury

OBJECTIVE

Oxygen free radical-mediated lipid peroxidation has been proposed to be one of the major mechanisms of secondary damage in traumatic brain injury. The first purpose of this study was to establish the time-level relationship for lipid peroxidation in injured brain tissue. The second purpose was to examine the protective effect of alpha-tocopherol against lipid peroxidation.

METHODS

For this study, 65 guinea pigs in five groups were studied. Five of the animals were identified as a control group, and the remaining 60 animals were divided equally into four groups (Groups A, B, C, and D). Mild injury (200 g x cm) (Groups A and C) and severe injury (1000 g x cm) (Groups B and D) were produced by the method of Feeney et al. Alpha-tocopherol (100 mg/kg) was administered intraperitoneally before brain injury in Groups C and D. Five animals from each group were killed immediately after trauma, five after 1 hour, and the remaining five animals after 36 hours. Lipid peroxidation in traumatized brain tissues was assessed using the thiobarbituric acid method.

RESULTS

In all groups with traumatic brain injuries, levels of malondialdehyde, a lipid peroxidation product, were higher than in the control group. The amount of lipid peroxidation was increased by the severity of the trauma. Alpha-tocopherol significantly suppressed the rise in lipid peroxide levels in traumatized brain tissues.

CONCLUSION

This study demonstrates that lipid peroxidation is increased by the severity of trauma and that alpha-tocopherol has a protective effect against oxygen free radical-mediated lipid peroxidation in mild and severe brain injury.

Tyrosine hydroxylase and Parkinson's disease

A consistent neurochemical abnormality in Parkinson's disease (PD) is degeneration of dopaminergic neurons in substantia nigra, leading to a reduction of striatal dopamine (DA) levels. As tyrosine hydroxylase (TH) catalyses the formation of L-DOPA, the rate-limiting step in the biosynthesis of DA, the disease can be considered as a TH-deficiency syndrome of the striatum. Similarly, some patients with hereditary L-DOPA-responsive dystonia, a neurological disorder with clinical similarities to PD, have mutations in the TH gene and decreased TH activity and/or stability. Thus, a logical and efficient treatment strategy for PD is based on correcting or bypassing the enzyme deficiency by treatment with L-DOPA, DA agonists, inhibitors of DA metabolism, or brain grafts with cells expressing TH. A direct pathogenetic role of TH has also been suggested, as the enzyme is a source of reactive oxygen species (ROS) in vitro and a target for radical-mediated oxidative injury. Recently, it has been demonstrated that L-DOPA is effectively oxidized by mammalian TH in vitro, possibly contributing to the cytotoxic effects of DOPA. This enzyme may therefore be involved in the pathogenesis of PD at several different levels, in addition to being a promising candidate for developing new treatments of this disease.

Autoxidation of rat brain homogenate: evidence for spontaneous lipid peroxidation. Comparison with the characteristics of Fe2+- and ascorbic acid-stimulated lipid peroxidation

Aerobically-incubated brain homogenates are known to undergo autoxidation characterized by spontaneous TBARS production, presumably as a result of lipid peroxidation. However, TBARS measurement alone, because of its lack of specificity, is not sufficient to demonstrate the occurrence of lipid peroxidation in complex biological systems. This study, undertaken to determine whether or not spontaneous oxidation of rat brain homogenate is due to lipid peroxidation, measured different specific markers of this process (fatty acids, lipid aldehydes and the formation of fluorescence products) and studied changes in alpha-tocopherol. Incubation of rat brain homogenates at 37 degrees C under air led to spontaneous TBARS formation, which was accompanied by lipid aldehydes and lipid fluorescence products as well as polyunsaturated fatty acid (PUFA) degradation. Alpha-tocopherol was also consumed. On the whole, these results demonstrate that autoxidation of brain homogenate is a spontaneous lipid peroxidation process. When homogenates were exposed to Fe2+ and ascorbic acid-induced oxidative stress, lipid peroxidation was enhanced. However, spontaneous and stimulated peroxidation showed similar patterns not characteristic of classical lipid peroxidation, i.e. without the lag and accelerating phases typical of a propagating chain reaction. PUFA degradation was limited despite stimulation of peroxidation.

Prostaglandins act as neurotoxin for differentiated neuroblastoma cells in culture and increase levels of ubiquitin and beta-amyloid

Although chronic inflammatory reactions have been proposed to cause neuronal degeneration associated with Alzheimer's disease (AD), the role of prostaglandins (PGs), one of the secretory products of inflammatory reactions, in degeneration of nerve cells has not been studied. Our initial observation that PGE1-induced differentiated neuroblastoma (NB) cells degenerate in vitro more rapidly than those induced by RO20-1724, an inhibitor of cyclic nucleotide phosphodiesterase, has led us to postulate that PGs act as a neurotoxin. This study has further investigated the effects of PGs on differentiated NB cells in culture. Results showed that PGA1 was more effective than PGE1 in causing degeneration of differentiated NB cells as shown by the cytoplasmic vacuolation and fragmentation of soma, nuclei, and neurites. Because increased levels of ubiquitin and beta-amyloid have been implicated in causing neuronal degeneration, we studied the effects of PGs on the levels of these proteins during degeneration of NB cells in vitro by an immunostaining technique, using primary antibodies to ubiquitin and beta-amyloid. Results showed that PGs increased the intracellular levels of ubiquitin and beta-amyloid prior to degeneration, whereas the degenerated NB cells had negligible levels of these proteins. These data suggest that PGs act as external neurotoxic signals which increase levels of ubiquitin and beta-amyloid that represent one of the intracellular signals for initiating degeneration of nerve cells.

Modification of ion homeostasis by lipid peroxidation: roles in neuronal degeneration and adaptive plasticity

Oxyradicals attack double bonds of unsaturated fatty acids in cell membranes in a process called membrane lipid peroxidation (MLP).This process occurs in many different acute and chronic neurodegenerative conditions, and to a lesser extent during normal physiological activity in neuronal circuits. It can modify neurotransmitter release and uptake, ion-channel activity, the function of ion-motive ATPases and glucose transporters,and the coupling of cell-surface receptors to GTP-binding proteins. MLP can also impair mitochondrial function and promote a cascade of events that culminates in apoptotic cell death. The lipid peroxidation product 4-hydroxynonenal might play a central role in MLP-induced alterations in plasma membrane and mitochondrial protein functions. The modification of processes such as outgrowth of neurites and long-term potentiation of synaptic transmission by agents that suppress or promote MLP suggests roles for subtoxic levels of MLP in neuronal plasticity.

Effect of selenium on vanadium toxicity in different regions of rat brain

The protective effect of selenium on the neurotoxicity of vanadium in different brain regions of rats was investigated. The lipid peroxidation was significantly accentuated after intraperitoneal (i.p.) administration of vanadium (1.5 mg kg-1 b.wt) for a period of 12 consecutive days to rats. The increase in lipid peroxidation was inhibited by selenium treatment (0.02 mg kg-1 b.wt., i.p.) for 12 consecutive days. Vanadium exposure produced a decrease in nonprotein sulfhydryl group. Selenium treatment prevented the depression in nonprotein sulfhydryl group in all the brain regions of the vanadium exposed rats. The concentration of ascorbic acid was decreased after co-administration of selenium and vanadium. These results suggest that selenium protects neuronal cells against neurotoxic effects of vanadium by maintaining the availability of antioxidant nonprotein sulfhydryl groups. The decrease in ascorbic acid levels may have been due to its consumption in forming complexes with vanadium.

Regional and ultrastructural immunolocalization of copper-zinc superoxide dismutase in rat central nervous system

We examined the distribution of copper-zinc superoxide dismutase (CuZnSOD) in adult rat central nervous system by light and electron microscopic immunocytochemistry, using an affinity-purified polyclonal antibody. The enzyme appeared to be exclusively localized in neurons. No immunoreactivity was seen in non-neuronal cells. The staining intensity was variable, depending on the brain region and, within the same region, on the neuron type. Highly immunoreactive elements included cortical neurons evenly distributed in the different layers, hippocampal interneurons, neurons of the reticular thalamic nucleus, and Golgi, stellate, and basket cells of the cerebellar cortex. Other neurons, i.e., pyramidal cells of the neocortex and hippocampus, Purkinje and granule cells of the cerebellar cortex, and the majority of thalamic neurons, showed much weaker staining. In the spinal cord, intense CuZnSOD immunoreactivity was present in many neurons, including motor neurons. Pre-embedding immunoelectron microscopy of the neocortex, hippocampus, reticular thalamic nucleus, and cerebellar cortex showed cytosolic and nucleoplasmic labeling. Moreover, single membrane-limited immunoreactive organelles identified as peroxisomes were often found, even in neurons that appeared weakly stained at the light microscopic level. In double immunogold labeling experiments, particulate CuZnSOD immunoreactivity co-localized with catalase, a marker enzyme for peroxisomes, thus demonstrating that in neural tissue CuZnSOD is also present in peroxisomes.

Neurodegenerative disorders in humans: the role of glutathione in oxidative stress-mediated neuronal death

Oxidative stress has been implicated in both normal aging and in various neurodegenerative disorders and may be a common mechanism underlying various forms of cell death including necrosis, apoptosis, and excitotoxicity. In this review, we develop the hypothesis that oxidative stress-mediated neuronal loss may be initiated by a decline in the antioxidant molecule glutathione (GSH). GSH plays multiple roles in the nervous system including free radical scavenger, redox modulator of ionotropic receptor activity, and possible neurotransmitter. GSH depletion can enhance oxidative stress and may also increase the levels of excitotoxic molecules; both types of action can initiate cell death in distinct neuronal populations. Evidence for a role of oxidative stress and diminished GSH status is presented for Lou Gehrig's disease (ALS), Parkinson's disease, and Alzheimer's disease. Potential links to the Guamanian variant of these diseases (ALS-PD complex) are discussed. In context to the above, we provide a GSH-depletion model of neurodegenerative disorders, suggest experimental verifications of this model, and propose potential therapeutic approaches for preventing or halting these diseases.

Cytotoxic and genotoxic effects of 4-hydroxynonenal in cerebral endothelial cells

Oxygen free radicals are produced in the central nervous system (CNS) as a consequence of normal physiological metabolic reactions of neuronal cells, but there is evidence accumulating that they are also implicated in the processes leading to a number of pathological changes in the brain. A general mechanism whereby oxygen free radicals induce tissue damage is lipid peroxidation (LPO), which generates a large variety of water-soluble carbonyl compounds. Due to their high reactivity, we focused our investigations on 4-hydroxyalkenals, in particular on 4-hydroxynonenal (HNE), the major 4-hydroxyalkenal. Two phenotypes of cerebral endothelial cells (cECs) were treated with various concentrations of 4-hydroxynonenal and the cyto- and genotoxic effects studied. The cytogenetic endpoints determined were chromosomal aberrations and the induction of micronuclei. Three hours of incubation with HNE induced significantly elevated levels of chromosomal aberrations at concentrations > or = 1 microM and micronuclei at concentrations > or = 10 microM in both cEC phenotypes, compared to the controls. Cytotoxicity was observed at a concentration of 50 microM HNE and was significantly higher in the elongated and spindle-shaped cEC phenotype (type II) than in the epithelial cEC phenotype (type I). The results indicate that cECs are affected by HNE even at low concentrations with minor differences between the two cEC phenotypes.

Short-term impairment of energy production in isolated rat liver mitochondria by hypoxia/reoxygenation: involvement of oxidative protein modification

The aim of the present study was to elucidate the role of mitochondria in liver impairment after ischaemia/reperfusion. It is commonly assumed that mitochondria are in part responsible for tissue damage by impaired oxidative phosphorylation as a consequence of the attack of radicals generated within the mitochondria. The principal support for this hypothesis was found by exposing isolated mitochondria to temporary hypoxia in combination with alterations of substrate supply. Rat liver mitochondria treated in this way responded with impaired ADP-stimulated respiration after reoxygenation, which decreased with time of hypoxia and reoxygenation. The decline of the activity of the NADH-cytochrome c-oxidoreductase complex found under these conditions is likely to cause the drop in active respiration. No changes in the content of respiratory chain complexes, determined by Blue Native PAGE, could be demonstrated. However, oxidative modifications of mitochondrial proteins, indicated by carbonyl formation, were found. Likewise, products of lipid peroxidation, such as lipid peroxides and malondialdehyde, were formed. Mitochondria were still able to build up a transmembrane potential and did not show drastic changes in membrane conductivity after hypoxia/reoxygenation stress. The presence of water-soluble antioxidants exhibited a beneficial effect, diminishing the decline of active respiration after 5 min of hypoxia and 10 min of reoxygenation. These observations strongly suggest that mitochondria play a pathogenic role in ischaemia/reperfusion injury, which is at least in part mediated by an oxygen-derived free-radical-linked mechanism.

Evidence for a high free radical state in low-grade astrocytomas

OBJECTIVE

It is postulated that reactive oxygen species may play an inductive role in neuro-oncogenesis. However, data pertaining to the redox state of astrocytomas are limited, which prompted us to undertake this study.

METHODS

Intraoperative snap-frozen samples were obtained from the surface and core of 8 low-grade and 11 high-grade astrocytomas. Small portions of each specimen were fixed in 10% neutral formalin or cacodylate-buffered glutaraldehyde. Lipid peroxidation was estimated by measuring thiobarbituric acid-reactive substances, and total glutathione levels were determined. Light microscopy was performed to define the relevant histopathology, and electron microscopy was used to quantitate peroxisomal content.

RESULTS

Thiobarbituric acid-reactive substance values for low-grade astrocytomas were significantly elevated compared to those for malignant lesions, as was the case for total glutathione. This discrepancy was especially marked at the tumor surface. Peroxisomes predominated in the low-grade category.

CONCLUSION

We speculate regarding malignant transformation as a possible consequence of this decline in antioxidant capacity, as well as regarding the role of seizures and astrocytoma glutamate receptors in the initiation of free radical cascades. The therapeutic and teleological implications are considerable.

Abeta25-35 induces rapid lysis of red blood cells: contrast with Abeta1-42 and examination of underlying mechanisms

Amyloid beta-peptide (A beta) is produced by many different cell types and circulates in blood and cerebrospinal fluid in a soluble form. In Alzheimer's disease (AD), A beta forms insoluble fibrillar aggregates that accumulate in association with cells of the brain parenchyma and vasculature. Both full-length A beta (A beta1-40/42) and the A beta25-35 fragment can damage and kill neurons by a mechanism that may involve oxidative stress and disruption of calcium homeostasis. Circulating blood cells are exposed to soluble A beta1-40/42 and may also be exposed to A beta aggregates associated with the luminal surfaces of cerebral microvessels. We therefore examined the effects of A beta25-35 and A beta1-42 on human red blood cells (RBCs) and report that A beta25-35, in contrast to A beta1-42, induces rapid (10-60 min) lysis of RBCs. The mechanism of RBC lysis by A beta25-35 involved ion channel formation and calcium influx, but did not involve oxidative stress because antioxidants did not prevent cell lysis. In contrast, A beta1-42 induced a delayed (4-24 h) damage to RBCs which was attenuated by antioxidants. The damaging effects of both A beta25-35 and A beta1-42 towards RBCs were completely prevented by Congo red indicating a requirement for peptide fibril formation. A beta1-42 induced membrane lipid peroxidation in RBC, and basal levels of lipid peroxidation in RBCs from AD patients were significantly greater than in age-matched controls, suggesting a possible role for A beta1-42 in previously reported alterations in RBCs from AD patients.

Oxidative stress in closed-head injury: brain antioxidant capacity as an indicator of functional outcome

It has been suggested that reactive oxygen species (ROS) play a role in the pathophysiology of brain damage. A number of therapeutic approaches, based on scavenging these radicals, have been attempted both in experimental models and in the clinical setting. In an experimental rat and mouse model of closed-head injury (CHI), we have studied the total tissue nonenzymatic antioxidant capacity to combat ROS. A major mechanism for neutralizing ROS uses endogenous low-molecular weight antioxidants (LMWA). This review deals with the source and nature of ROS in the brain, along with the endogenous defense mechanisms that fight ROS. Special emphasis is placed on LMWA such as ascorbate, urate, tocopherol, lipoic acid, and histidine-related compounds. A novel electrochemical method, using cyclic voltammetry for the determination of total tissue LMWA, is described. The temporal changes in brain LMWA after CHI, as part of the response of the tissue to high ROS levels, and the correlation between the ability of the brain to elevate LMWA and clinical outcome are addressed. We relate to the beneficial effects observed in heat-acclimated rats and the detrimental effects of injury found in apolipoprotein E-deficient mice. Finally, we summarize the effects of cerebroprotective pharmacological agents including the iron chelator desferal, superoxide dismutase, a stable radical from the nitroxide family, and HU-211, a nonpsychotoropic cannabinoid with antioxidant properties. We conclude that ROS play a key role in the pathophysiology of brain injury, and that their neutralization by endogenous or exogenous antioxidants has a protective effect. It is suggested, therefore, that the brain responds to ROS by increasing LMWA, and that the degree of this response is correlated with clinical recovery. The greater the response, the more favorable the outcome.

4-Hydroxynonenal, an aldehydic product of membrane lipid peroxidation, impairs glutamate transport and mitochondrial function in synaptosomes

Removal of extracellular glutamate at synapses, by specific high-affinity glutamate transporters, is critical to prevent excitotoxic injury to neurons. Oxidative stress has been implicated in the pathogenesis of an array of prominent neurodegenerative conditions that involve degeneration of synapses and neurons in glutamatergic pathways including stroke, and Alzheimer's, Parkinson's and Huntington's diseases. Although cell culture data indicate that oxidative insults can impair key membrane regulatory systems including ion-motive ATPases and amino acid transport systems, the effects of oxidative stress on synapses, and the mechanisms that mediate such effects, are largely unknown. This study provides evidence that 4-hydroxynonenal, an aldehydic product of lipid peroxidation, mediates oxidation-induced impairment of glutamate transport and mitochondrial function in synapses. Exposure of rat cortical synaptosomes to 4-hydroxynonenal resulted in concentration- and time-dependent decreases in [3H]glutamate uptake, and mitochondrial function [assessed with the dye 3-(4,5-dimethylthiazol-2-yl)-2,5-diphenyltetrazolium bromide (MTT)]. Other related aldehydes including malondialdehyde and hexanal had little or no effect on glutamate uptake or mitochondrial function. Exposure of synaptosomes to insults known to induce lipid peroxidation (FeSO4 and amyloid beta-peptide) also impaired glutamate uptake and mitochondrial function. The antioxidants propyl gallate and glutathione prevented impairment of glutamate uptake and MTT reduction induced by FeSO4 and amyloid beta-peptide, but not that induced by 4-hydroxynonenal. Western blot analyses using an antibody to 4-hydroxynonenal-conjugated proteins showed that 4-hydroxynonenal bound to multiple cell proteins including GLT-1, a glial glutamate transporter present at high levels in synaptosomes. 4-Hydroxynonenal itself induced lipid peroxidation suggesting that, in addition to binding directly to membrane regulatory proteins, 4-hydroxynonenal potentiates oxidative cascades. Collectively, these findings suggest that 4-hydroxynonenal plays important roles in oxidative impairment of synaptic functions that would be expected to promote excitotoxic cascades.

Expression of superoxide dismutase following axotomy

Oxidative injury has been implicated in the pathophysiology of neuronal injury and neurodegenerative disease. Antioxidant proteins provide an endogenous defense against such oxidative injury and may yield important clues to mechanisms of cytoprotection and neuronal recovery. Axotomy is the simplest model of neuronal injury and lesioning the sciatic nerve allows concurrent study of both motor (spinal cord) and sensory (dorsal root ganglia, DRG) neurons affected by the same injury. This study was designed to examine the expression of superoxide dismutase (SOD), an essential antioxidant protein, in motor and sensory neurons following complete axotomy of peripheral nerve. Immunocytochemical, quantitative immunoblot, and enzymatic activity assay techniques are used. By 12 days after axotomy, immunocytochemical expression of Mn-SOD is markedly increased in affected DRG and spinal cord. A similar increase in Cu/Zn-SOD is not seen in DRG or spinal cord. This immunocytochemical staining is associated with a significant increase in specific activity and Mn-SOD protein content as measured on quantitative immunoblots. This report suggests, for the first time, that Mn-SOD and not Cu/Zn-SOD increases in sensory neurons of the DRG and motor neurons of the spinal cord following distal axotomy of the sciatic nerve. Quantitative measurements of Mn-SOD following axotomy reveals that the increase in immunocytochemical reactivity is associated with an approximately 30% increase in specific activity when comparing lesioned and contralateral spinal cord samples. These data suggest that Mn-SOD may have a more significant role in the pathophysiology of neuronal injury than Cu/Zn-SOD.

Impaired mitochondrial function, oxidative stress and altered antioxidant enzyme activities following traumatic spinal cord injury

Glutamate-induced excitotoxicity involving the formation of reactive oxygen species (ROS) has been implicated in neuronal dysfunction and cell loss following ischemic and traumatic injury to the central nervous system (CNS). ROS are formed in mitochondria when energy metabolism is compromised, and are inactivated by the ROS scavengers superoxide dismutase (SOD), catalase, and glutathione (GSH). ROS can impair the function of several cellular components including proteins, nucleic acids, and lipids. In the present study, we measured indicators of mitochondrial metabolic activity, ROS formation, lipid peroxidation, and antioxidant enzyme activities in synaptosomes obtained from rat spinal cord at early times following traumatic injury. Mitochondrial metabolic activity was found to significantly decrease as early as 1 h following injury, and continued to be compromised over the remaining postinjury time points. ROS formation was found to be significantly increased at 4 and 24 h following injury, while lipid peroxidation levels were found to be significantly increased in the injured spinal cord at 1 and 24 h, but not 4 h following injury. SOD enzyme activity was unchanged at all postinjury time points, while catalase activity and GSH levels were significantly increased at 24 h following injury. These findings indicate that impaired mitochondrial function, ROS, and lipid peroxidation occur soon after traumatic spinal cord injury, while the compensatory activation of molecules important for neutralizing ROS occurs at later time points. Therapeutic strategies aimed at facilitating the actions of antioxidant enzymes or inhibiting ROS formation and lipid peroxidation in the CNS may prove beneficial in treating traumatic spinal cord injury, provided such treatments are initiated at early stages following injury.

Evidence that 4-hydroxynonenal mediates oxidative stress-induced neuronal apoptosis

Oxidative stress is believed to play important roles in neuronal cell death associated with many different neurodegenerative conditions (e.g., Alzheimer's disease, Parkinson's disease, and cerebral ischemia), and it is believed also that apoptosis is an important mode of cell death in these disorders. Membrane lipid peroxidation has been documented in the brain regions affected in these disorders as well as in cell culture and in vivo models. We now provide evidence that 4-hydroxynonenal (HNE), an aldehydic product of membrane lipid peroxidation, is a key mediator of neuronal apoptosis induced by oxidative stress. HNE induced apoptosis in PC12 cells and primary rat hippocampal neurons. Oxidative insults (FeSO4 and amyloid beta-peptide) induced lipid peroxidation, cellular accumulation of HNE, and apoptosis. Bcl-2 prevented apoptosis of PC12 cells induced by oxidative stress and HNE. Antioxidants that suppress lipid peroxidation protected against apoptosis induced by oxidative insults, but not that induced by HNE. Glutathione, which binds HNE, protected neurons against apoptosis induced by oxidative stress and HNE. PC12 cells expressing Bcl-2 exhibited higher levels of glutathione and lower levels of HNE after oxidative stress. Collectively, the data identify that HNE is a novel nonprotein mediator of oxidative stress-induced neuronal apoptosis and suggest that the antiapoptotic action of glutathione may involve detoxification of HNE.

Seasonal variation in the antioxidant defense system of the brain of the ground squirrel (Citellus citellus) and response to low temperature compared with rat

Seasonal variation in the activity of antioxidant enzymes (superoxide dismutase (EC 1.15.1.1.; SOD), catalase (EC 1.11.1.6; CAT), glutathione peroxidase (EC 1.11.1.9; GSH-Px), glutathione reductase (EC 1.6.4.2; GR), glutathione-S-transferase (EC 2.5.1.18; GST) and low-molecular-weight antioxidants: ascorbic acid (AsA), vitamin E (VIT E) and glutathione (CSH+GSSG) were examined in the brain of the ground squirrels (Citellus citellus) maintained at 30 degrees C during the whole year. The highest activity (per mg protein) of antioxidant defense (AD) enzymes was found in the spring and was much lower in the summer. A further decrease in activity of CAT, GSH-Px and GST was observed in the winter. The highest levels of AsA and glutathione were recorded in winter in comparison with spring and summer. AD system in the brain of the ground squirrel and rates (maintained at thermoneutrality) exposed to low temperature (4 degrees C) for 3, 6 or 24 hr during the summer was studied as well. Summer was chosen as a period of stable euthermia for ground squirrels and in thermoregulation similar to rats. Consumption of free fatty acid and glucose during the acute exposure to low temperature was found to be species specific. In the ground squirrel, an increase in the specific activities of SOD, after 3, 6 and 24 hr, CAT after 3 and 6 hr and GR after 6 hr of exposure to low temperature was detected. When activities were expressed in U/g wet mass, an increase of SOD after 3, 6 and 24 hr (P < 0.02, P < 0.02, P < 0.005) and CAT and GSH-Px 3 hr (P < 0.01) upon exposure to low temperature was observed. In the rats, no changes in the specific activities of these enzymes after exposure to low temperature were recorded and only an increase in GST activity (U/g wet mass) after 6 hr exposure was registered. Low-molecular-weight AD components in both animal species were unchanged upon short-term exposure to low temperature. The species-specific differences in brain AD between the rats and the ground squirrels after short exposure to low temperature may be ascribed to seasonal changes of the brain activity in the latter.

The relation between antioxidants and memory performance in the old and very old

OBJECTIVES

Aging processes, and among them brain aging, are thought to be associated with free radical action. It is hypothesized that plasma antioxidant vitamin levels correlate with cognitive performance in healthy older subjects.

DESIGN

Longitudinal and cross-sectional comparisons.

SETTING

The city of Basle, considered representative of the older urban population in Switzerland.

PARTICIPANTS

A total of 442 subjects aged 65 to 94 years (mean: 75 years; 312 male, 132 female) was selected from a random sample.

MEASUREMENTS

In 1993, participants were tested for memory, and plasma vitamin levels were measured for the three antioxidants alpha-tocopherol, ascorbic acid, and beta-carotene. These vitamin parameters, measured previously in 1971 in the same sample, were integrated in our analyses. In addition, plasma cholesterol, ferritin, and systolic blood pressure were taken into account. Memory variables were priming, working-memory, free recall, recognition and the WAIS-R vocabulary test (semantic memory).

RESULTS

Correlations showed significant stability of the plasma antioxidants over the time lag of 22 years (alpha-tocopherol: r = .47, P < or = .001; beta-carotene: r = .43, P < .001; ascorbic acid: r = .22, P < .001). Free recall, recognition, and vocabulary (but not priming and working-memory) correlated significantly with ascorbic acid and beta-carotene in the cross-sectional 1993 data as well as in the longitudinal 1971-1993 analysis. These two antioxidants remained significant predictors, especially of semantic memory, after controlling for possible confounding variables like age, education, and gender using multiple regression analyses and ANOVAs.

CONCLUSION

Among people aged 65 and older, higher ascorbic acid and beta-carotene plasma level are associated with better memory performance. These results indicate the important role played by antioxidants in brain aging and may have implications for prevention of progressive cognitive impairments.

Rapid alteration of tau in oligodendrocytes after focal ischemic injury in the rat: involvement of free radicals

Glial inclusions containing the microtubule-associated protein tau are present in a variety of chronic neurodegenerative conditions. We now report a rapid and time-dependent increase of tau immunoreactivity within oligodendrocytes after focal cerebral ischemia in the rat. The number of tau positive oligodendrocytes in the ipsilateral subcortical white matter increased six- to eightfold by 40 minutes after permanent middle cerebral artery occlusion (MCAO). Tau was detected using antibodies that label both the N- and C-terminal of the protein, suggesting accumulation of full-length protein within these cells. Pretreatment with the spin trap agent alpha-phenyl-tert-butyl-nitrone (PBN)(100mg/kg) reduced the number of tau-positive oligodendrocytes by 55% in the subcortical white matter of the ischemic hemisphere compared with untreated animals at 40 minutes after MCAO. In contrast, pretreatment with glutamate receptor antagonists MK-801 (0.5 mg/kg) or 2,3-dihydroxy-6-nitro-7-sulpfamoyl-benzo(f)quinoxaline (NBQX) (2 x 30 mg/kg), failed to reduce the number of tau-positive oligodendrocytes after 40 minutes of ischemia. The results indicate that oligodendrocytes respond rapidly to an ischemic challenge and that free radical-mediated mechanisms are involved in the cascade leading to increased tau immunoreactivity.

Ozone produces functional deficits in the rat visual pathway

The effects of ozone (O3) have been studied mainly in reference to the respiratory pathways, though some reports have shown that this gas produces noxious effects in brain. The aim of the present work was to study the O3 effects on the central nervous system, focusing on the visual pathway by means of visual evoked potentials technique recording in the visual cortex and the lateral geniculate nucleus of rats exposed to three different concentrations of O3 (0.75, 1.5 and 3.0 ppm). Our results showed that P1, N1 and P2 components were significantly delayed in the visual cortex and lateral geniculate nucleus in those rats exposed to 3.0 ppm of O3. Moreover, the N1 component in the visual cortex was also affected even under exposure to 1.5 ppm of O3. Results suggest that O3 exposure affects the conduction mechanisms and synaptic excitability of the visual pathway. It is known that inhalation of O3 produce a cascade of ozonation products capable of producing lipid peroxidation in the brain. Unevenness of some neurotransmitters has also been referred in animals exposed to this gas. Thus we consider that the delay found in the primary components of the visual evoked potentials could obey to a neurochemical disorder produced by O3 inhalation.

Fused 2-thiohydantoin derivatives: evaluation as potential antioxidants

A series of fused 5,5-diphenyl and 5-arylidene-2-thiohydantoin derivatives were examined for their oxygen free radical inhibitory and radical scavenging properties (RSC) using both an enzymic and non-enzymic biological generators of free radicals. Non-enzymic lipid peroxidation (OH. radicals) was assayed as the amount of malondialdehyde (MDA) that had been formed during incubation of boiled rat liver microsomes in the presence of ascorbic acid and ferric ions. Superoxide anions (.O2- anion radicals) were generated enzymatically in the xanthine-xanthine oxidase system. Among the 20 investigated compounds only four fused arylidene 2-thiohydantoin derivatives showed weak antioxidant activity scavenging OH. radicals. There is a relationship between the electrophilic OH. radical scavenging properties (RSC) of the tested molecules and the value of their HOMO energy derived from semiempirical MO calculations.

Changes in some pro- and antioxidants in rat cerebellum after chronic alcohol intake

Some pro- and antioxidants were measured in the cerebellum from ethanol-fed rats using ethanol administration in drinking water as a model of moderate alcohol intoxication. After 4 weeks of ethanol intake, a 30% increase in the nonheme iron content in the cerebellum occurred in ethanol-fed rats as compared to control animals. The low-molecular-weight-chelated iron (LMWC-Fe) content as well as the percentage of total nonheme iron represented by LMWC-Fe were increased in the cerebellar cytosol after chronic ethanol administration. Cerebellar copper and selenium concentrations were lower and zinc concentration higher in ethanol-fed rats than in controls. Ethanol consumption decreased the cerebellar vitamin E level. Glutathione S-transferase [EC 2. 5. 1. 18] activity was higher, whereas glutathione peroxidase [glutathione: H2O2 oxidoreductase, EC 1. 11. 1. 9] activity was not altered by ethanol treatment. No significant changes in cerebellar lipid peroxidation, carbonyl protein content, or glutamine synthetase [L-glutamate:ammonia ligase (ADP-forming) EC 6. 3. 1. 2] activity were observed. These results suggest that adaptative increases in some elements of the antioxidant defense may counteract the increase in LMWC-Fe, a pro-oxidant factor, and prevent the occurrence of overt cellular lipid and protein damage. However, after 8 weeks of ethanol intake, the activity of glutamine synthetase, an enzyme specially sensitive to inactivation by oxygen radicals, was decreased, suggesting that this prevention was not totally achieved.

Lipid peroxides are generated by the fetal rat brain after episodes of global ischemia in utero

Complete arrest of maternal-fetal blood supply for up to 30 min caused a time-dependent increase in the endogenous levels of lipid peroxides (LPO) in fetal brain and liver extracts and fetal blood and amniotic fluids as indicated by the appearance of thiobarbituric acid reactive substances (TBARS). A steady increase of TBARS from 48.0 +/- 2.2 pmol/g wet weight to 75.0 +/- 5.6 pmol/g wet weight up to 30 min restriction was noticed in the fetal brain. The fetal liver TBARS values increased by approximately 69% after 5 min restriction and remained high, above the control level, for 30 min. After two days reperfusion following 30 min restriction, the TBARS levels in the fetal brain were 1.8 fold higher above the control, while those of the liver returned to control values. The levels of the lipid-soluble antioxidant alpha-tocopherol were reduced by about 40% and 50% in the placenta and brain tissues after 5 min restriction, respectively. Slices of fetal brain incubated at 37 degrees C in DMEM under oxygen in the presence of 50 microM Fe2+ were able to generate LPO in a time- and tissue concentration-dependent manner. After 15 min incubation, about 6.3 fold increase in total TBARS levels could be measured in the presence of 50 microM Fe2+, most of which was released in the medium. The iron chelator desferrioxamine (25 microM) and the antioxidant alpha-tocopherol (10 microM) added to the incubation medium, each inhibited by about 88% TBARS production. After 20 min episode of ischemia, fetal brain slices released into the medium 138.5 +/- 9.8 nmol/15 min/mg DNA compared to 75.9 +/- 4.5 nmol/15 min/mg DNA released by the sham preparations. After 3 h reperfusion, brain slices from fetuses exposed to 20 min ischemia continued to produce TBARS above control levels, whereas those of brief ischemia (5 min) returned to control levels. The data indicate that the limited resistance of the fetal brain to brief, rather than prolonged, periods of ischemia, is likely due to a lack of free FA for LPO generation, rather than the levels of tissue lipid antioxidants.

Oxidative damage and fibrogenesis

Various chronic disease processes are characterized by progressive accumulation of connective tissue under-going fibrotic degeneration. Evidence of oxidative reactions is often associated with fibrogenesis occurring in liver, lung, arteries, and nervous system. Moreover, an increasing bulk of experimental and clinical data supports a contributory role of oxidative stress in the pathogenesis of this kind of disease. Indeed, many etiological agents of fibrogenesis stimulate free radical reactions either directly or through inflammatory stimuli. Free radicals, as well as products of their reaction with biomolecules, appear to modulate the activity of the two cellular types mainly involved in the process, namely phagocytes and extracellular matrix-producing cells. Lipid peroxidation and certain lipid peroxidation products induce genetic overexpression of fibrogenic cytokines, the key molecules in the pathomechanisms of fibrosis, as well as increased transcription and synthesis of collagen. Both these events can be downregulated, at least in experimental models, by the use of antioxidants. The effect of oxidative stress on cytokine gene expression appears to be an important mechanism by which it promotes connective tissue deposition.

High metabolic rates of 4-hydroxynonenal in brain capillary endothelial cells during hypoxia/reoxygenation

We measured the accumulation of 4-hydroxynonenal (HNE), a major lipid peroxidation product during hypoxia/reoxygenation of brain capillary endothelial cells (BCEC). The concentration of HNE after 2 h of hypoxia was 0.23 nmol/mg protein and rose up to 0.28 nmol/mg protein after 30 min of reoxygenation. That reflects a 1.5-fold increase, whereas aortic endothelial cells (AEC) increased the HNE level 5-fold, compared to the control. Therefore, the ability of BCEC to degrade exogenously added HNE was tested. The HNE consumption in BCEC achieved a rate of about 600 nmol.min-1.mg protein-1, about two times higher than in AEC. The higher ability of BCEC to degrade HNE is probably the reason of the 2-fold higher IC50 value against the aldehyde. Therefore, we concluded that the high ability of BCEC to degrade HNE is a substantial part of the secondary antioxidative defense of the brain.

Oxidative-stress associated parameters (lactoferrin, superoxide dismutases) in serum of patients with Alzheimer's disease

In this case/control study, serum levels of oxidative stress related parameters such as Fe-binding lactoferrin (LTF), Mn- and Zn,Cu-superoxide dismutase (SOD) were determined by enzyme linked immunoassays in patients suffering from the Alzheimer's dementia as well as in non-demented controls. The Mn-SOD concentration was significantly (P<0.05, U-test) reduced in patients suffering from Alzheimer's disease if compared to non-demented controls. The other parameters investigated did not differ significantly between both groups. Our findings give evidence for the hypothesis of a disturbed free radical metabolism in Alzheimer's disease. The specificity of these results remains to be clarified. Further studies are needed to elucidate the relevance of oxidative stress in the etiopathogenesis of the Alzheimer's disease.

Antioxidant defence system in a patient with cerebrovascular accident

The increased production of reactive oxygen metabolites in the central nervous system may result in cellular damage and vascular-parenchymal injury. Vascular injury is also a cause of the vasoregulation deficiency. In this case report, a 60-year-old woman was admitted to the department of neurology, with a diagnosis of cerebrovascular accident. During 18 days of follow-up, the status of the antioxidant system was determined by measuring red cell superoxide dismutase and catalase activity. Red cell and plasma copper, zinc and magnesium concentrations were also measured. Red cell superoxide dismutase activity increased markedly by Day 2, reached a peak on Day 6 before decreasing to normal 18 days after the injury. Red cell catalase activity was below normal values during the whole of the 18-day study period and was at its lowest between days 6 and 7. Plasma copper, zinc and magnesium concentrations showed corresponding alterations.

Relations between the selenium status and the low T3 syndrome after major trauma

OBJECTIVE

Thyroxine (T4) is deiodinated to triiodothyronine (T3) by the hepatic type I iodothyronine deiodinase, a selenoprotein that is sensitive to selenium (Se) deficiency. After severe injury, T4 deiodination is decreased, leading to the low T3 syndrome. Injury increases free radical production, which inactivates the iodothyronine deiodinase. The aims were to study the Se status after major trauma and to investigate its relation to the low T3 syndrome.

DESIGN

Preliminary prospective descriptive study.

SETTING

Intensive care unit at a university teaching hospital.

PATIENTS AND METHODS

11 patients aged 41 +/- 4 years (mean +/- SEM), with severe multiple injuries (Injury Severity Score 29 +/- 2 points). A balance study was performed from day 1 to day 7. Serum and urine samples were collected from the time of admission until day 7, then on days 10, 15, 20, 25 and 30. Non-parametric tests and Pearson's correlation coefficients were used for analysis.

RESULTS

Cumulated Se losses were 0.88 +/- 0.1 mumol/24h. Serum Se was decreased from admission to day 7. T3, free T3, and the T3/T4 ratio were low until day 5, being lowest on day 2; T4 and thyroid stimulating hormone were normal. Serum Se was correlated with T3 (r = 0.55, p = 0.0001), and with free T3 (r = 0.35).

CONCLUSION

Se status is altered after trauma, with decreased Se serum levels upon admission to the ICU but with no major Se losses. Se is probably redistributed to the tissues. The correlation between Se and T3, along with the parallel decrease in T4 deiodination, indicates that reduced deiodination might be related to the transient decrease in serum Se.

Acute acidosis elevates malonaldehyde in rat brain in vivo

Oxidative stress in brain tissue was measured experimentally in situ using microdialysis to sample the extracellular environment for a lipid peroxidation breakdown product and antioxidants. The extracellular concentrations of the lipid peroxidation product malonaldehyde (MDA) and the antioxidants ascorbic acid (AA) and uric acid (UA) were measured in rat cortex and striatum in vivo using microdialysis coupled to HPLC with UV detection. Tissue acidosis following ischaemia and epileptic seizures may contribute to neuronal damage, which may be mediated by reactive oxygen species. Perfusion of microdialysis probes with acidic artificial cerebrospinal fluid (pH 6) led to a significant increase in the sampled concentration of MDA and the antioxidant ascorbic acid. Simultaneous perfusion of ascorbate (5 mM) with acidic ACSF (pH 6) completely attenuated the rise in lipid peroxidation. This study provides in vivo evidence for acidosis induced oxidative stress in brain tissue and an antioxidant action of ascorbate. The methodology described here can provide direct in vivo information in respect of oxidative stress in experimental situations. The method could equally be applied to the assessment of oxidative stress in a number of pathological models not necessarily confined to the CNS.

Effects of ethanol administration on cerebral non-protein sulfhydryl content in rats exposed to styrene vapour

Glutathione (GSH) and other non-protein sulfhydryls (NPS) are known to protect cells from oxidative stress and from potentially toxic electrophiles formed by biotransformation of xenobiotics. This study examined the effect of a simultaneous administration of styrene and ethanol on NPS content and lipid peroxidation in rat liver and brain. Hepatic cytochrome P450 and cytochrome b5 content, aniline hydroxylase and aminopyrine N-demethylase activities as well as the two major urinary metabolites of styrene, mandelic and phenylglyoxylic acids were also measured. Groups of rats given ethanol for 3 weeks in a liquid diet were exposed, starting from the second week, to 326 ppm of styrene (6 h daily, 5 days a week, for 2 weeks). In control pair-fed animals, styrene produced about 30% depletion of brain NPS and 50% depletion of hepatic NPS. Subchronic ethanol treatment did not affect hepatic NPS levels, but caused 23% depletion of brain NPS. Concomitant administration of ethanol and styrene caused a NPS depletion in brain tissue in the order of 60%. These results suggest that in the rat, simultaneous exposure to ethanol and styrene may lead to considerable depletion of brain NPS. This effect is seen when both compounds are given on a subchronic basis, a situation which better resembles possible human exposure.

Frontal lobe phosphorus metabolism and neuropsychological function in aging and in Alzheimer's disease

31P Magnetic resonance spectroscopy of the frontal lobe was performed in 17 patients with Alzheimer's disease (AD), 8 elderly controls (EC), and 17 young controls (YC). The phosphocreatine/inorganic phosphate (PCr/Pi) ratio in AD (2.32 +/- 0.26 SD) was significantly lower than in EC (2.65 +/- 0.41). In AD patients, a correlation was observed between the PCr/Pi ratio and the dementia rating scale (r = -0.50, p = 0.04). A significant positive correlation between PCr/Pi ratio and age was observed in both AD (r = 0.67, p = 0.003) and YC (r = 0.63, p = 0.006) groups, however, suggesting caution in interpretation of this ratio in AD. We did not find differences between AD, EC, or YC in any other spectroscopic measure. A significant sex difference in the phosphomonoester/phosphodiester ratio (PME/PDE) ratio was observed in AD brain. Females had a lower PME/PDE ratio than males.

Reversibility of manganese-induced learning defect in rats

In this study the mechanism by which manganese (Mn) induces learning defect and its reversibility has been investigated in rats. Female albino rats were dosed orally with 357 micrograms Mn/kg body weight for 15 or 30 days. Attempts were made to correct the Mn-induced learning defect by (1) co-administration of mevinolin and Mn for 30 days; (2) administration of mevinolin for 15 days after 15 days of dosing with Mn, and (3) by withdrawal of Mn treatment (15 days dosing with Mn followed by 15 days without Mn). Mevinolin was given orally at 235.7 micrograms/kg body weight. Significant increases in the Mn and cholesterol levels in the hippocampus were accompanied by an obvious slowness in learning of rats exposed to Mn. After one training period (day 29) the time required to reach the exit of a T-maze was 104.5 +/- 13.8 sec for rats dosed with Mn for 30 days, whereas that of the controls was 28.7 +/- 11.4 sec on day 30. This delay was completely corrected (to 30.7 +/- 6.0 sec) in rats co-administered mevinolin (an inhibitor of cholesterol biosynthesis) with Mn. Withdrawal of Mn, with or without inhibiting the cholesterol biosynthesis, also corrected the Mn-induced learning defect. These results suggest that Mn toxicity produces learning disability by increasing cholesterol biosynthesis and this reversible disability in learning can be corrected by withdrawal of Mn exposure.

Peroxyl radical scavenging activity of Ginkgo biloba extract EGb 761

Antioxidant mechanisms have been proposed to underlie the beneficial pharmacological effects of EGb 761, an extract from Ginkgo biloba leaves used for treating peripheral vascular diseases and cerebrovascular insufficiency in the elderly. In vitro evidence has been reported that EGb 761 scavenges various reactive oxygen species, i.e. nitric oxide, and the superoxide, hydroxyl, and oxoferryl radicals. However, the ability of EGb 761 to scavenge peroxyl radicals (reactive species mainly involved in the propagation step of lipid peroxidation) has not been investigated. To characterize further the antioxidant action of EGb 761, we measured the protective effects of EGb 761 during: (1) the oxidation of B-phycoerythrin by peroxyl radicals generated in aqueous solution by 2,2'-azobis (2-amidinopropane) hydrochloride (AAPH); and (2) the reaction of luminol or cis-parinaric acid with peroxyl radicals generated from 2,2'-azobis (2,4-dimethylvaleronitrile) (AMVN) in liposomes or in human low density lipoprotein (LDL), respectively. To evaluate the peroxyl radical scavenging activity of EGb 761 in a more physiologically relevant model of damage to lipid-containing systems, we also analyzed the effect of the extract on the oxidation of human LDL exposed to the azo-initiators in terms of: (1) accumulation of cholesterol linoleate ester hydroperoxides, (2) depletion of alpha-tocopherol and beta-carotene, and (3) changes in intrinsic tryptophan fluorescence. EGb 761 afforded protection against oxidative damage in all the systems we analyzed; thus, it is an efficient scavenger of peroxyl radicals. This result extends the oxygen radical scavenging properties of the extract and supports the hypothesis of an antioxidant therapeutic action of EGb 761.

Brain peroxidative and glutathione status after moderate hypoxia in normal weight and intra-uterine growth-restricted newborn piglets

In order to investigate the pathogenetic factors causing the relatively frequent occurrence of brain injury in intrauterine growth-restricted newborns, lipid peroxidation products (TBAR), glutathione (GSH, GSSG) and in vitro production of reactive oxygen species (chemiluminescence, stimulated lipid peroxidation, H2O2 formation) were studied in the brain of normal weight (NW) and intra-uterine growth-restricted newborn piglets (IUGR) after 1 hour of hypoxia (FiO2 11%) and 90 min reoxygenation. Cardiocirculatory parameters and catecholamine release into the blood were also measured. In the cerebellum, higher GSH content, but also higher in vitro production of lucigenin amplified chemiluminescence were found in comparison to other brain regions, independent of growth restriction and hypoxia. Moderate hypoxia without acidosis and hypercapnia resulted in GSH depletion especially in the brain of IUGR, but no changes in GSSG concentrations were measured. Though TBAR decreased after hypoxia/reoxygenation, in some brain areas of IUGR higher TBAR values were found in comparison to NW. H2O2 formation, stimulated lipid peroxidation and lucigenin and luminol amplified chemiluminescence in the 9000 x/g supernatant of brain tissue did not reveal special response of IUGR to hypoxia/reoxygenation. Hypoxia-induced circulatory centralisation due to increased release of catecholamines into the plasma prevented oxygen deficiency also in the brain of IUGR. The role of brain monoamine metabolism in the production of reactive oxygen species, followed by greater GSH depletion and higher in vivo formation of lipid peroxides in IUGR is discussed.

Lipid peroxidation inhibits acyl-CoA:-1-acyl-sn-glycero-3-phosphocholine O-acyltransferase but not CTP: phosphocholine cytidylyltransferase activity in rat brain membranes

In brain tissue in vivo peroxidized according to three model systems, we determined two microsomal enzyme activities involved in phospholipid biosynthesis. The first, short-term model, was based on the i.v. administration to normal rats, twice a day, for a period of 1 week, of a sonicated emulsion of a peroxidized mixture of phospholipids and linoleate (4:1, w/w; 500 mg/day; hydroperoxides: 200-250 nmol/mg lipid). The half-life time of the injected toxic lipid species in the blood circulation was about 1 h. At the end of the week's treatment, brain and liver malondialdehyde, conjugated diene and lipid hydroperoxide levels were significantly higher in treated rats than in the controls. The second model consisted of the acute injection of aqueous Fe2+ solution (50 mM) into lateral ventricles, and the collection of brain tissue 2 h later. The third model was based on two consecutive injections of hydroperoxylinoleate (1 mg each) into lateral ventricles over a period of 18 h, and the collection of brain tissue 2 h after the second administration. In brain microsomal membranes prepared from peroxide- or iron-treated rats, lysophosphatidylcholine acyltransferase activity exhibited a significant inhibition. On the contrary, in microsomal preparations derived from the short-term model, CTP:phosphocholine cytidylyltransferase activity was slightly stimulated. Intraventricular injection of linoleate or linoleic acid hydroperoxide left this enzyme activity unchanged. The effect of in vitro membrane peroxidation on both microsomal enzyme activities was investigated. By using an Fe2+ (20 microM)-ascorbate (0.25 mM) peroxidation system, the residual acyltransferase and cytidylyltransferase activities were 80 and 72% of initial activity respectively. Significant dose-dependent inactivation of acyltransferase (maximum loss of 45% of initial activity) was seen when 0.1-10 mumol of photooxidized phospholipids were preincubated with 100 micrograms of microsomal membranes. Unoxidized or photooxidized phospholipids (1 mM) promoted a slight stimulation of cytidylyltransferase activity. Altogether, the results suggest a link between oxygen radical generation and the perturbation of the membrane structure in which the enzymes are located.

Role of antioxidants in health maintenance

Free radicals are produced in the body as by products of normal metabolism and as a result of exposure to radiation and some environmental pollutants. Because they are highly reactive, they can damage cellular components and are implicated in a variety of diseases. Free radicals are normally neutralized by efficient systems in the body that include the antioxidant enzymes (superoxide dismutase, catalase, and glutathione peroxidase) and the nutrient-derived antioxidant small molecules (vitamin E, vitamin C, carotenes, flavonoids, glutathione, uric acid, and taurine). In healthy individuals, a delicate balance exists between free radicals and antioxidants. In some pathologic conditions such as diabetes, and in critically ill patients, oxidative stress causes the level of antioxidants to fall below normal. Antioxidant supplements for such conditions are expected to be of benefit. As a preventive measure against certain diseases, the best approach for healthy individuals is to regularly consume adequate amounts of antioxidant-rich foods, eg, fruits and vegetables.

The role of free radicals in toxicity and disease

Free radicals are defined as atoms or molecules that contain one or more unpaired electrons. The toxicity of many xenobiotics is associated with the metabolic activation of foreign compounds to form free radicals or with the production of reactive oxygen species as superoxide anion, hydroxyl radicals or hydrogen peroxide which are responsible for the tissue damaging effects as lipid peroxidation, and DNA and protein damage. Oxidative stress associated with production of reactive oxygen species is believed to be involved not only in the toxicity of xenobiotics but also in the pathophysiology of aging, and various age-related diseases, including cataracts, atherosclerosis, neoplastic diseases, diabetes, diabetic retinopathy, chronic inflammatory diseases of the gastrointestinal tract, aging of skin, diseases associated with cartilage, Alzheimer's disease, and other neurologic disorders. The cellular sources of free radicals and reactive oxygen species, the biological targets of free radicals, and clinical conditions which are associated with free radical production and tissue damage are reviewed. In addition, potential therapeutic approaches to the prevention of free radical damage are considered. Free radical-induced injury can explain many clinical conditions.

Influence of the xanthine derivative denbufylline and the anti-inflammatory agent nabumetone on microsomal free radical production and lipid peroxidation in rat liver

The influence of denbufylline, nabumetone and its main metabolite BRL 10,720 on iron stimulated lipid peroxidation (LPO), cytochrome P 450 dependent H2O2 and chemiluminescence (CL) production was investigated in rat liver microsomes in vitro (10(-5)-10(-3) M) and in vivo after treatment of rats (5-300 mg/kg b.m. orally on three consecutive days). In rat liver slices the release of thiobarbituric acid reactants (TBAR) was measured after 1 hour of incubation with the drugs. Denbufylline, nabumetone and BRL 10,720 exerted a significant inhibition of iron stimulated LPO in vitro. Nabumetone showed the strongest antioxidative activity, which was also seen in liver slices. These antioxidative effects were not found after in vivo treatment of rats. Denbufylline (10(-3) M) additionally inhibited H2O2 formation and the luminol and lucigenin amplified CL in vitro. Unexpectedly, nabumetone increased H2O2 formation both in vitro and in vivo, but in vitro only lucigenin amplified CL. BRL 10,720 increased microsomal H2O2 production in vivo. Moreover, BRL 10,720 enhanced CL in vitro and in vivo significantly, which is interpreted as an increase of the production of superoxide anion radicals and other reactive oxygen species such as H2O2, but lipid peroxidation in liver microsomes was not enhanced. These results suggest that denbufylline, nabumetone and BRL 10,720 in contrast to the in vitro effects did not exert antioxidative activities after treatment of rats. On the contrary, BRL 10,720 was found to support the formation of reactive oxygen species in liver microsomes.