Effects of nerve growth factor on catalase and glutathione peroxidase in a hydrogen peroxide-resistant pheochromocytoma subclone

Membrane Depolarization Inhibits BIMEL Upregulation but Prevents Neuronal Apoptosis Primarily by Increasing Cellular GSH Levels

Sympathetic neurons deprived of nerve growth factor (NGF) die by apoptosis. Chronic depolarization with elevated concentrations of extracellular potassium ([K⁺]_E) supports long-term survival of these and other types of neurons in culture. While depolarization has long been used to support neuronal cultures, little is known about the mechanism. We explored how chronic depolarization of NGF-deprived mouse sympathetic neurons in culture blocks apoptotic death. First, we determined the effects of elevated [K⁺]_E on proapoptotic BH3-only proteins reported to be upregulated in sympathetic neurons after NGF withdrawal. Upregulation of BIM_EL was blocked by depolarization while upregulation of PUMA was not. BMF levels did not increase after NGF withdrawal, and elevated [K⁺]_E had no effect on its expression. dp5/HRK was not detectable. A large increase in production of mitochondria-derived reactive species (RS), including reactive oxygen species (ROS), occurs in NGF-deprived sympathetic neurons. Suppressing these RS prevents cytochrome c release from mitochondria and apoptosis. The addition of high [K⁺]_E to cultures rapidly blocked increased RS and cytochrome c release. Elevated [K⁺]_E caused an increase of the cellular antioxidant glutathione (GSH). Preventing this increase prevented the elevated [K⁺]_E from blocking cytochrome c release and death. While suppression of BIM_EL upregulation by elevated [K⁺]_E may contribute to high [K⁺]_E pro-survival effects, we conclude that elevated [K⁺]_E prevents apoptotic death of NGF-deprived sympathetic neurons primarily via an antioxidant mechanism.

Redox Signaling Mechanisms in Nervous System Development

SIGNIFICANCE

Numerous studies have demonstrated the actions of reactive oxygen species (ROS) as regulators of several physiological processes. In this study, we discuss how redox signaling mechanisms operate to control different processes such as neuronal differentiation, oligodendrocyte differentiation, dendritic growth, and axonal growth. Recent Advances: Redox homeostasis regulates the physiology of neural stem cells (NSCs). Notably, the neuronal differentiation process of NSCs is determined by a change toward oxidative metabolism, increased levels of mitochondrial ROS, increased activity of NADPH oxidase (NOX) enzymes, decreased levels of Nrf2, and differential regulation of different redoxins. Furthermore, during the neuronal maturation processes, NOX and MICAL produce ROS to regulate cytoskeletal dynamics, which control the dendritic and axonal growth, as well as the axonal guidance.

CRITICAL ISSUES

The redox homeostasis changes are, in part, attributed to cell metabolism and compartmentalized production of ROS, which is regulated, sensed, and transduced by different molecules such as thioredoxins, glutaredoxins, peroxiredoxins, and nucleoredoxin to control different signaling pathways in different subcellular regions. The study of how these elements cooperatively act is essential for the understanding of nervous system development, as well as the application of regenerative therapies that recapitulate these processes.

FUTURE DIRECTIONS

The information about these topics in the last two decades leads us to the conclusion that the role of ROS signaling in development of the nervous system is more important than it was previously believed and makes clear the importance of exploring in more detail the mechanisms of redox signaling. Antioxid. Redox Signal. 28, 1603-1625.

Cellular and molecular mechanisms involved in the neurotoxicity of opioid and psychostimulant drugs

Substance abuse and addiction are the most costly of all the neuropsychiatric disorders. In the last decades, much progress has been achieved in understanding the effects of the drugs of abuse in the brain. However, efficient treatments that prevent relapse have not been developed. Drug addiction is now considered a brain disease, because the abuse of drugs affects several brain functions. Neurological impairments observed in drug addicts may reflect drug-induced neuronal dysfunction and neurotoxicity. The drugs of abuse directly or indirectly affect neurotransmitter systems, particularly dopaminergic and glutamatergic neurons. This review explores the literature reporting cellular and molecular alterations reflecting the cytotoxicity induced by amphetamines, cocaine and opiates in neuronal systems. The neurotoxic effects of drugs of abuse are often associated with oxidative stress, mitochondrial dysfunction, apoptosis and inhibition of neurogenesis, among other mechanisms. Understanding the mechanisms that underlie brain dysfunction observed in drug-addicted individuals may contribute to improve the treatment of drug addiction, which may have social and economic consequences.

Differential cytotoxic responses of PC12 cells chronically exposed to psychostimulants or to hydrogen peroxide

Repeated abuse of stimulant drugs, cocaine and amphetamine, is associated with extraneuronal dopamine accumulation in specific brain areas. Dopamine may be cytotoxic through the generation of reactive oxygen species, namely hydrogen peroxide (H2O2), resulting from dopamine oxidative metabolism. In this work, we studied the cytotoxicity in PC12 cells (a dopaminergic neuronal model) chronically and/or acutely exposed to cocaine or amphetamine, as compared to H2O2 exposure. Chronic cocaine treatment induced sensitization to acute cocaine insult and increased cocaine-evoked accumulation of extracellular dopamine, although no changes in dihydroxyphenylacetic acid (DOPAC) levels were observed. Moreover, dopamine was depleted in cells chronically exposed to amphetamine and acute amphetamine toxicity persisted in these cells, indicating that dopamine was not involved in amphetamine cytotoxicity. PC12 cells chronically treated with H2O2 were totally resistant to acute H2O2, but not to acute cocaine or amphetamine exposure, suggesting that the toxicity induced by these stimulant drugs is unrelated to adaptation to oxidative stress. Interestingly, chronic cocaine treatment largely, but not completely, protected the cells against a H2O2 challenge, whilst a decrement in intracellular ATP was observed. This study shows that chronic treatment of PC12 cells with cocaine or H2O2 modifies the cytotoxic response to an acute exposure to these agents.

Enhancement of neuronal protection from oxidative stress by glutamic acid decarboxylase delivery with a defective herpes simplex virus vector

We have developed defective herpes simplex virus 1 (HSV-1) vectors, based on amplicon plasmids with a replication-deficient mutant, as helper for the transfer of the glutamic acid decarboxylase (GAD67) or beta-galactosidase (beta-gal) gene as control directed by HCMV promoter into neuronal-like cells (PC12) and primary neurons. GAD67 protein was detected immunochemically, while GAD67 activity in virus-producing and nonproducing cell lines was detected enzymatically or by GABA release. Infection with GAD67-expressing amplicon vectors enhanced the resistance of PC12 cells to H(2)O(2). This protection was related to increased energy metabolism, as shown by MTT reduction and ATP level, and involved the GABA shunt, as shown by the reduction in ATP level seen in the presence of gamma-vinyl GABA (GVG), a specific GABA transaminase inhibitor. Level of glutathione (GSH), which requires ATP for its synthesis, was increased by the GAD67 transgene. The activity of glucose-6-phosphate dehydrogenase involved in the maintenance of the NADPH that can be used for the regeneration of the GSH pool, was increased by infection with amplicon vectors. Thus, replication-deficient HSV-1 and the GAD67 transgene have complementary neuroprotective effects and infection with GAD67-expressing amplicon vectors was able to protect nondifferentiated cortical neurons from glutamate toxicity mediated by oxidative stress. Such defective GAD67-expressing HSV-1, as neurotropic vector, should be helpful in neurodegenerative diseases implicating alterations of energy metabolism and oxidative stress in neuronal cells expressing GABA transaminase.

Neurotrophic factors can partially reverse morphological changes induced by mepivacaine and bupivacaine in developing sensory neurons

Both bupivacaine and mepivacaine induce morphological changes in growing neurons. We designed this study to investigate the role of some neurotrophic factors (NTFs) in supporting developing neurons exposed to the deleterious effects of these drugs. Dorsal root ganglia were isolated from chick embryos and exposed to either bupivacaine or mepivacaine. After 60 min of exposure, the culture media were replaced with fresh culture media free from local anesthetics. NTFs-brain-derived NTF, glial-derived NTF, or neurotrophin-3-were added to the replacement media, and the cells were examined up to 48 h after the washout. The growth cone collapse assay was applied by a quantitative method of assessment. When the replacement media were not supported by any NTF, the growth cone collapse values were significantly larger than the control values at 20 h after the washout of mepivacaine and 48 h after the washout of either bupivacaine or mepivacaine (P < 0.05). However, when any of the NTFs were used, the collapsing activity was significantly attenuated, and growth cone collapse values showed no statistically significant differences in comparison with the control values at these time points (P > 0.05). We conclude that several NTFs support the recovery of neurons after exposure to local anesthetics. The supporting effects of NTFs on the reversibility of mepivacaine-induced collapse tended to be more obvious than those seen after the bupivacaine washout.

IMPLICATIONS

Three neurotrophic factors (NTFs) can partially support the reversibility of mepivacaine- and bupivacaine-induced growth cone collapse in growing primary cultured sensory neurons. The effect of NTFs is more apparent after mepivacaine than after bupivacaine washout.

Signal transduction and neurosurvival in experimental models of brain injury

Brain injury and neurodegenerative disease are linked by their primary pathological consequence-death of neurons. Current approaches for the treatment of neurodegeneration are limited. In this review, we discuss animal models of human brain injury and molecular biological data that have been obtained from their analysis. In particular, signal transduction pathways that are associated with neurosurvival following injury to the brain are presented and discussed.

Protective effect of nerve growth factor on neurons after traumatic brain injury

The protective effect of nerve growth factor (NGF) on neurons after traumatic brain injury (TBI) was investigated. A brain trauma model of fluid-percussion in rats was established, and 7s NGF was infused continuously in its cerebral ventricle. The activity of superoxide dismutase (SOD), glutathione peroxidase (GSH-Px) and catalase (CAT), and [Ca2+]i overloading in brain tissues was observed after giving exogenous NGF postinjury. We found that the activity of SOD, GSH-Px, and CAT was markedly higher in NGF-treated group than in the simple trauma group (P < 0.01). Although the level of [Ca2+]i in the NGF-treated group increased, the value was significantly lower than that in the simple trauma and control groups (P < 0.01). These findings suggest that exogenous NGF can (a) increase the activity of the major antioxidant enzymes in brain tissues and attenuate the injuries to neurons induced by oxygen-free radicals, (b) reduce the severe overload of [Ca2+]i and stabilize its homeostasis, and (c) provide clear protective effects on neurons after traumatic brain injury.

Thymocytes selected for resistance to hydrogen peroxide show altered antioxidant enzyme profiles and resistance to dexamethasone-induced apoptosis

Treatment of WEHI7.2 cells, a mouse thymoma-derived cell line, with dexamethasone, a synthetic glucocorticoid, causes the cells to undergo apoptosis. Previous work has shown that treatment of WEHI7.2 cells with dexamethasone results in a downregulation of antioxidant defense enzymes, suggesting that increased oxidative stress may play a role in glucocorticoid-induced apoptosis. To test whether resistance to oxidative stress causes resistance to dexamethasone-induced apoptosis, WEHI7.2 cell variants selected for resistance to 50, 100 and 200 microM H(2)O(2) were developed. Resistance to H(2)O(2) is accompanied by increased antioxidant enzyme activity, resistance to other oxidants and a delayed loss of viable cells after dexamethasone treatment. In the 200 microM H(2)O(2)-resistant cell variant the delay in cell loss is correlated with delayed release of cytochrome c from the mitochondria into the cytosol. This suggests that reactive oxygen species play a role in a signaling event during steroid-mediated apoptosis in lymphocytes.

Testosterone protects cerebellar granule cells from oxidative stress-induced cell death through a receptor mediated mechanism

It is known that steroid hormones can affect neuronal susceptibility to different types of insults, including oxidative stress. Using an in vitro/ex vivo model, we have previously shown that cerebellar granule cells prepared from neonatal rats treated with a single dose of testosterone are less vulnerable to oxidative stress-induced cell death, via a mechanism involving an upregulation of the cellular antioxidant defenses. Whether the testosterone protective action on cerebellar granule cells was direct or indirect remained to be clarified. Therefore, in this study we have investigated the effects of in vitro testosterone treatment, to see whether it also protects cerebellar granule cells from oxidative stress-induced damage. Cerebellar granule cells treated with 10(-6) M testosterone for 48 h were found less susceptible to damage induced by 50 microM hydrogen peroxide, as shown by a 30% decrease in the number of cells with apoptotic morphology. The addition of the androgen receptor antagonist flutamide abolished the protective effect of testosterone, suggesting an androgen receptor-mediated mechanism. This hypothesis was further supported by the presence of the androgen receptor in cultured cerebellar granule cells. The activity of the antioxidant enzyme catalase was also measured, and a 2-fold increase was detected in the testosterone treated cells, but not in the cells co-treated with flutamide. The present results demonstrate that cerebellar granule cells treated in vitro with testosterone are protected from oxidative stress via a mechanism mediated by the androgen receptor. Similarly to what we observed after in vivo administration of testosterone, the potentiation of the antioxidant defences seems to play a major role in the protection afforded by testosterone.

Is oxidative stress involved in the developmental neurotoxicity of chlorpyrifos?

The increasing use of chlorpyrifos (CPF) has elicited concern about neurotoxic effects on the fetus and neonate. CPF targets a number of events specific to brain development, over and above the ability of its active metabolite, CPF oxon, to inhibit cholinesterase. We used PC12 cells, a model system which displays many of the neurodevelopmental effects of CPF, in order to examine whether oxidative stress underlies the direct effects of CPF on development. Production of reactive oxygen species (ROS) was measured with a fluorescent intracellular dye. When PC12 cell suspensions were treated acutely with CPF for 10 min, ROS generation was increased in a concentration-dependent manner; CPF oxon was much less effective than the native compound. CPF also increased the ROS production in response to an acute sodium nitroprusside challenge, indicating sensitization of the cells to other oxidant stressors. Next, PC12 cells were grown in an undifferentiated state in the presence of CPF or CPF oxon for extended time periods, under conditions in which CPF inhibits mitosis, and the cells were then washed and ROS production measured. Neither compound elicited a significant change in ROS production. Finally, differentiation was initiated with nerve growth factor and the cells were exposed continuously to CPF or CPF oxon over a 72 h period; under these conditions, CPF inhibits neurite outgrowth. When the cells were washed and evaluated for ROS production, no significant differences were seen. These results indicate that CPF, but not CPF oxon, has the ability to elicit acute increases in ROS production. However, the effect disappears immediately once CPF exposure is terminated, possibly reflecting cellular defense mechanisms that lessen the impact of oxidant injury.

Repeated immunolesions display diminished stress response signal

Cholinergic basal forebrain neurons (CBFNs) retrogradely transport neurotrophins released in the hippocampus and cortex as part of a general response to injury in a process that is impaired in the aged rodent and can be spared by the exogenous addition of pharmacological doses of nerve growth factor (NGF). This observation suggests that components of stress response signal transduction pathways in the aged CNS can be exogenously activated. The extent and mechanism of the endogenous stimulation of NGF in response to injury can be mimicked via treatment with 192 IgG-saporin of rat CNS, an immunolesion model. Here we report on the use of a conditioning lesion paradigm to determine if repeated partial immunolesions have a conditioning effect on the immunolesion-induced increases in NGF protein or decreases in choline acetyltransferase (ChAT) and acetylcholinesterase (AChE) activity. We report that chronic repeated immunolesions, as used here, were not as effective as a one time equivalent immunolesion in terms of induced NGF protein increases or decreasing ChAT and AChE activity in the hippocampus and cortex. Thus, chronic lesions resulting in cholinergic impairment typical of the aged CNS may differ from acute toxic models as a result of desensitization due to a conditioning effect of chronic subthreshold lesioning events in the CNS.

Cysteamine pretreatment of the astroglial substratum (mitochondrial iron sequestration) enhances PC12 cell vulnerability to oxidative injury

Much of the excess iron reported in the substantia nigra of subjects with Parkinson's disease (PD) implicates nonneuronal (glial) cellular compartments. Yet, the significance of these glial iron deposits vis-a-vis toxicity to indigent nigrostriatal dopaminergic neurons remains unclear. Cysteamine (CSH) induces the appearance of iron-rich (peroxidase-positive) cytoplasmic inclusions in cultured rat astroglia, which are identical to glial inclusions that progressively accumulate in substantia nigra and other subcortical brain regions with advancing age. We previously demonstrated that the iron-mediated peroxidase activity in these cells oxidizes dopamine and other catechols to potentially neurotoxic semiquinone radicals. In the present study, we cocultured catecholamine-secreting PC12 cells (as low-density dispersed cells or high-density colonies) atop monolayers of either CSH-pretreated (iron-enriched) or control rat astroglial substrata. In some experiments, the PC12 cells were differentiated with nerve growth factor (NGF). The nature of the glial substratum did not appreciably affect the growth characteristics of the PC12 cells. However, undifferentiated PC12 cells grown atop CSH-pretreated astrocytes (a senescent glial phenotype) were far more susceptible to dopamine(1 microM)-H2O2(1 microM)-related killing than PC12 cells cultured on control astroglia. Differentiated PC12 cells behaved similarly although the fraction killed was about half that seen with the undifferentiated PC12 cells. In the latter experiments, PC12 cell death was abrogated by coadministration of the antioxidants, ascorbate (200 microM), melatonin (100 microM), or resveratrol (50 microM) or the iron chelator, deferoxamine (400 microM), attesting to the role of oxidative stress and catalytic iron in the mechanism of PC12 cell death in this system. The aging-associated accumulation of redox-active iron in subcortical astrocytes may facilitate the bioactivation of dopamine to neuronotoxic free radical intermediates and thereby predispose the senescent nervous system to PD and other neurodegenerative disorders.

Effect of NGF treatment on outcome measures in a rat model of middle cerebral artery occlusion

Ischemic insults to the brain result in a time-dependent increase in neuronal death that is responsible for some of the functional deficits associated with stroke. Our working hypothesis is that ischemia results in a prompt depletion of high energy phosphate species resulting in decreased pH and glutathione levels in brain in a temporal and spatial pattern that disrupts nerve growth factor homeostasis and increases neuronal apoptosis. Here we show hemispheric depletion of active phosphate species after ischemia. Also, we observed that the striatum is an early target for oxidative stress that is followed by energy metabolic impairment and altered neurotrophin levels that were detected by noninvasive magnetic resonance imaging (MRI) measurements of cytotoxicity and conventional biochemical determinations of apoptosis, glutathione, and nerve growth factor (NGF) protein levels in a pattern distinct from that observed in the hippocampus. Furthermore, early assessment of intracellular pH by 31P-magnetic resonance spectroscopy (31P-MRS) was a predictor of later infarct development as determined by MRI. We also show that pretreatment with pharmacological doses of NGF did not have overall significant beneficial consequences on irreversible ischemia in an intraluminal unilateral irreversible model of stroke in rat brain.

Herpes simplex virus type 1 vector-mediated expression of nerve growth factor protects dorsal root ganglion neurons from peroxide toxicity

Nerve growth factor beta subunit (beta-NGF) transgene delivery and expression by herpes simplex virus type 1 (HSV-1) vectors was examined in a cell culture model of neuroprotection from hydrogen peroxide toxicity. Replication-competent (tk- K mutant background) and replication-defective (ICP4(-);tk- S mutant background) vectors were engineered to contain the murine beta-NGF cDNA under transcriptional control of either the human cytomegalovirus immediate-early gene promoter (HCMV IEp) (e.g., KHN and SHN) or the latency-active promoter 2 (LAP2) (e.g., KLN and SLN) within the viral thymidine kinase (tk) locus. Infection of rat B103 and mouse N2A neuronal cell lines, 9L rat glioma cells, and Vero cells with the KHN or SHN vectors resulted in the production of beta-NGF-specific transcripts and beta-NGF protein reaching a maximum at 3 days postinfection (p.i.). NGF protein was released into the culture media in amounts ranging from 10.83 to 352.86 ng/ml, with the highest levels being achieved in B103 cells, and was capable of inducing neurite sprouting of PC-12 cells. The same vectors produced high levels of NGF in primary dorsal root ganglion (DRG) cultures at 3 days. In contrast to HCMV IEp-mediated expression, the LAP2-NGF vectors showed robust expression in primary DRG neurons at 14 days. The neuroprotective effect of vector produced NGF was assessed by its ability to inhibit hydrogen peroxide-induced neuron toxicity in primary DRG cultures. Consistent with the kinetics of vector-mediated NGF expression, HCMV-NGF vectors were effective in abrogating the toxic effects of peroxide at 3 but not 14 days p.i. whereas LAP2-NGF vector transduction inhibited apoptosis in DRG neurons at 14 days p.i. but was ineffective at 3 days p.i. Similar kinetics of NGF expression were observed with the KHN and KLN vectors in latently infected mouse trigeminal ganglia, where high levels of beta-NGF protein expression were detected at 4 wks p.i. only from the LAP2; HCMV-NGF-driven expression peaked at 3 days but could not be detected during HSV latency at 4 weeks. Together, these results indicate that (i) NGF vector-infected cells produce and secrete mature, biologically active beta-NGF; (ii) vector-synthesized NGF was capable of blocking peroxide-induced apoptosis in primary DRG cultures; and (iii) the HCMV-IEp functioned to produce high levels of NGF for several days; but (iv) only the native LAP2 was capable of long-term expression of a therapeutic gene product in latently infected neurons in vivo.

An evaluation of the role of mitochondria in neurodegenerative diseases: mitochondrial mutations and oxidative pathology, protective nuclear responses, and cell death in neurodegeneration

There is mounting evidence for mitochondrial involvement in neurodegenerative diseases including Alzheimer's and Parkinson's disease and amyotrophic lateral sclerosis. Mitochondrial DNA mutations, whether inherited or acquired, lead to impaired electron transport chain (ETC) functioning. Impaired electron transport, in turn, leads to decreased ATP production, formation of damaging free-radicals, and altered calcium handling. These toxic consequences of ETC dysfunction lead to further mitochondrial damage including oxidation of mitochondrial DNA, proteins, and lipids, and opening of the mitochondrial permeability transition pore, an event linked to cell death in numerous model systems. Although protective nuclear responses such as antioxidant enzymes and bcl-2 may be induced to combat these pathological changes, such a vicious cycle of increasing oxidative damage may insidiously damage neurons over a period of years, eventually leading to neuronal cell death. This hypothesis, a synthesis of the mitochondrial mutations and oxidative stress hypotheses of neurodegeneration, is readily tested experimentally, and clearly points out many potential therapeutic targets for preventing or ameliorating these diseases.

Induction of apoptosis in the CNS during development by the combination of hyperoxia and inhibition of glutathione synthesis

Apoptosis in the central nervous system (in contrast to necrosis) is an endogenous cell suicide mechanism triggered in response to biological factors and genotoxic stimuli often resulting from oxidative stress. Excessive neural apoptosis may result in longterm brain dysfunction. A significant proportion of prematurely born infants are exposed to high oxygen and nutritional regimens deficient in antioxidant precursors. Such infants frequently display cognitive deficits when studied in later childhood. Studies in cell culture have characterized a close relationship between oxidative stress, glutathione availability and cell death. Here, we assessed this relationship in rat brain, as a model approximation of the situation that occurs in human infants. Two day old rats were exposed to an atmosphere of 95% oxygen and treated with buthionine sulfoximine (BSO), a glutathione synthesis inhibitor. Control groups consisted of rat-pups kept in air, air plus BSO, or oxygen alone. At the end of 5 days of treatment, brains were harvested, dissected and nerve growth factor protein (NGF), glutathione, and extent of apoptosis were measured. Hyperoxia induced a decrease in NGF protein while BSO induced a decrease in glutathione concentrations. Animals treated with both hyperoxia and BSO had a dramatic increase in the extent of brain apoptosis detected. We conclude from these studies that the brains of animals exposed to both oxidative stress and limited antioxidant protection are liable to pro-apoptotic changes. Increased cell death via apoptosis reflecting changes in neurotrophin and glutathione homeostasis may represent the mechanism responsible for the induction of the longterm cognitive deficits observed in some preterm infants.

Resistance to the apoptotic effect of aggregated amyloid-beta peptide in several different cell types including neuronal- and hepatoma-derived cell lines

There is a large body of literature indicating that aggregated amyloid-beta peptide (Abeta) is toxic to neurons and suggesting that this neurotoxicity represents the final common pathway for neuronal degeneration in Alzheimer's disease. Previous studies have shown the outgrowth of a subclone of the rat neuronal cell line PC12 that is resistant to the toxic effect of aggregated Abeta peptide if the parent cell line is grown in the presence of aggregated Abeta peptide for a number of passages [Behl, Davis, Lesley and Schubert (1994) Cell 77, 817-827; Boland, Behrens, Choi, Manias and Perlmutter (1996) J. Biol. Chem. 271, 18032-18044]. To begin to characterize the mechanism by which PC12 cells become resistant to the apoptotic effect of Abeta peptide, in the present study we examined whether the resistance was specific to aggregated peptides, specific to an apoptotic form of cell death, and specific in cell type or was a general resistance to cell death that could be elicited in diverse cell types. The results show that the resistance is specific to compounds that have apoptotic effects through the generation of hydroxyl radical or H2O2, including aggregated Abeta-(25-35), Abeta-(1-40), Abeta-(1-42), Abeta-(1-43), amylin, 6-hydroxydopamine and H2O2 itself. The resistant subclones of PC12 were not resistant to other forms of apoptotic cell death or to necrotic cell death. The resistant state was also identified in a human hepatoma cell line, HepG2, when it was grown in the presence of aggregated Abeta-(25-35) for several passages, indicating that the mechanism(s) or molecule(s) responsible for this resistance are not restricted to neuronal cells and may be relevant to the pathobiology of oxidative injury in other cell types.

Oxidative stress and lipid abnormalities in renal transplant recipients with or without chronic rejection

BACKGROUND

The histological picture of chronic rejection with endothelial lesions and vascular hyperplasia resembles the early arteriosclerotic lesions. As increasing evidence suggests a role for oxidative stress in arteriosclerosis, we examined whether chronic rejection in renal transplant recipients was associated with increased oxidative stress markers.

METHODS

We investigated lipid metabolism and oxidative stress in 77 renal transplant recipients. Group I patients (n=34; 48+/-2 years old, 12 women, 22 men) had no clinical or histological signs of chronic rejection, whereas group II patients (n=43; 47+/-3 years old, 15 women, 28 men) had histologically proven chronic rejection. All patients were treated with cyclosporine and steroids. Lipid metabolism was evaluated by determining total cholesterol, triglycerides, high-density lipoprotein cholesterol, apolipoproteins AI and B, and lipoprotein (a). Oxidative stress was evaluated by determining: (i) the end product of lipid peroxidation, malonyldialdehyde (MDA), and erythrocyte polyunsaturated fatty acids; (ii) the nonenzymatic antioxidant system: erythrocyte alpha-tocopherol and glutathione; and (iii) the enzymatic antioxidant system: erythrocyte superoxide dismutase and plasma glutathione peroxidase. Results were compared with those of a control group (38 healthy volunteers).

RESULTS

Compared with controls, renal transplant recipients had significantly increased total cholesterol, triglyceride, and apolipoprotein B levels; they also had, in association with these lipid abnormalities, a significant increase in MDA and a significant decrease in erythrocyte polyunsaturated fatty acids, as well as a significant decrease in enzymatic and nonenzymatic antioxidant defense mechanisms. In contrast to lipid disturbances, where no difference was observed between groups I and II, markers of oxidative stress were significantly higher in group II compared with group I (MDA: 1.87+/-0.43 and 1.62+/-0.31 nmol/ml, respectively, P<0.05). The red blood cell antioxidative defense mechanisms were significantly decreased in group II compared with controls (erythrocyte alpha-tocopherol: 0.61+/-0.38 and 1.08+/-0.31 mg/L, respectively, P<0.01; superoxide dismutase: 1.08+/-0.2 and 1.32+/-0.31 U/mg Hb, respectively, P<0.01).

CONCLUSION

Our data show that oxidative stress with a decrease in antioxidant defenses is associated with kidney transplantation. In addition, oxidative stress markers are particularly increased in transplant recipients with chronic rejection, which suggests that oxidative stress may participate in the development and/or progression of vascular lesions observed in these patients.

Mechanisms of resistance to oxidative stress in Alzheimer's disease

It is likely that amyloid beta-protein (A beta) mediates nerve cell death in Alzheimer's disease (AD). Some nerve cell populations, however, remain undamaged in AD brain. To understand the biochemical basis for resistance to A beta toxicity, a series of cell lines were isolated which are resistant to A beta toxicity. It is shown that a major component of the resistance mechanism is the transcriptional elevation of two H2O2 degrading enzymes, glutathione peroxidase and catalase. These data support other evidence for the role of oxidative damage in A beta toxicity, and suggest strategies for clinical approaches to the disease.

Elevated reactive oxygen species and antioxidant enzyme activities in animal and cellular models of Parkinson's disease

The dopaminergic neurotoxin N-methyl,4-phenyl-1,2,3,6 tetrahydropyridine (MPTP) causes a syndrome in primates and humans which mimics Parkinson's disease (PD) in clinical, pathological, and biochemical findings, including diminished activity of complex I in the mitochondrial electron transport chain. Reduced complex I activity is found in sporadic PD and can be transferred through mitochondrial DNA, suggesting a mitochondrial genetic etiology. We now show that MPTP treatment of mice and N-methylpyridinium (MPP+) exposure of human SH-SY5Y neuroblastoma cells increases oxygen free radical production and antioxidant enzyme activities. Cybrid cells created by transfer of PD mitochondria exhibit similar characteristics; however, PD cybrids' antioxidant enzyme activities are not further increased by MPP+ exposure, as are the activities in control cybrids. PD mitochondrial cybrids are subject to metabolic and oxidative stresses similar to MPTP parkinsonism and provide a model to determine mechanisms of oxidative damage and cell death in PD.

Different effects of oxidative stress on activation of transcription factors in primary cultured rat neuronal and glial cells

We compared the cytotoxic effects of oxidative stress on neuronal and glial cells in vitro by examining the cell viability and changes in DNA-binding activities of transcription factors, AP-1 and CREB, using Trypan blue exclusion and electrophoretic mobility shift assay (EMSA), respectively. Neurotoxin 6-hydroxydopamine (6-OHDA) and H2O2 reduced the viability of both types of cells in time- and concentration-dependent manner. Both neurotoxins dose-dependently decreased DNA-binding activities in neuronal cells. The results of cell viability assay suggested that these changes may reflect the reduction in neuronal cell viability. In contrast, both reagents increased DNA-binding activities in glial cells, although they decreased cell numbers. These results suggest that the effects of oxidative stress on transcription factors is different in neuronal and glial cells. We also examined the effect of brain-derived neurotrophic factor (BDNF) on 6-OHDA- or H2O2-induced changes in DNA-binding activities. In neuronal cells, pre-treatment with BDNF prevented the decrease in DNA-binding activities induced by 6-OHDA or H2O2. In glial cells, the effect of BDNF on oxidative stress-induced changes in DNA-binding activities in the 6-OHDA-treated group were opposite to those in H2O2-treated group. Our results suggest that 6-OHDA and H2O2 may exert their cytotoxic mechanisms through different signal transduction systems.

Nerve growth factor attenuates cholinergic deficits following traumatic brain injury in rats

Traumatic brain injury (TBI) results in chronic derangements in central cholinergic neurotransmission that may contribute to posttraumatic memory deficits. Intraventricular cannula (IVC) nerve growth factor (NGF) infusion can reduce axotomy-induced spatial memory deficits and morphologic changes observed in medial septal cholinergic neurons immunostained for choline acetyltransferase (ChAT). We examined the efficacy of NGF to (1) ameliorate reduced posttraumatic spatial memory performance, (2) release of hippocampal acetylcholine (ACh), and (3) ChAT immunoreactivity in the rat medial septum. Rats (n = 36) were trained prior to TBI on the functional tasks and retested on Days 1-5 (motor) and on Day 7 (memory retention). Immediately following injury, an IVC and osmotic pump were implanted, and NGF or vehicle was infused for 7 days. While there were no differences in motor performance, the NGF-treated group had significantly better spatial memory retention (P < 0.05) than the vehicle-treated group. The IVC cannula was then removed on Day 7, and a microdialysis probe was placed into the dorsal hippocampus. After a 22-h equilibration period, samples were collected prior to and after administration of scopolamine (1 mg/kg), which evoked ACh release by blocking autoreceptors. The posttraumatic reduction in scopolamine-evoked ACh release was completely reversed with NGF. Injury produced a bilateral reduction in the number and cross-sectional area of ChAT immunopositive medial septal neurons that was reversed by NGF treatment. These data suggest that cognitive but not motor deficits following TBI are, in part, mediated by chronic deficits in cholinergic systems that can be modulated by neurotrophic factors such as NGF.

Regulation of antioxidant enzyme expression by NGF

The rapid decreases in viability seen in H2O2-treated PC12 cells reflect enhanced susceptibility of neural cell types to oxidant injury. The dose-response relationship between NGF concentration and survival after H2O2 treatment resembles that for NGF effects on PC12 survival in serumless medium. Previously we have shown that NGF treatment enhances the activity of GSH-Px and catalase which catalyze the degradation of H2O2. Here in order to ascertain whether NGF stimulates transcription, affects mRNA stability, or acts post-transcriptionally, we measured catalase and GSH-Px mRNA half-lives. While both catalase and GSH-Px transcripts are stable with a relatively long half life and a gradual decay in mRNA levels, NGF had different effects on their stability. NGF had marked effects on catalase mRNA stability. The catalase gene has a 3' flanking region with T-rich clusters and CA repeats known to be susceptible to regulation by destabilization or ubiquination. NGF maintained catalase mRNA levels of actinomycin D (ACT-D) treated PC12 cells at twice that of cells exposed to ACT-D alone, delaying the rate of decay for catalase mRNA for 24 h. The NGF induction of GSH-Px and catalase mRNA was inhibited by cycloheximide (CHX) treatment with a slight decrease in their mRNA levels due to prolonged exposure to CHX. When the CHX treatment was delayed relative to the NGF treatment there was no effect on NGF effects on catalase and GSH-Px. The GSH-Px gene has conserved sequences in the open reading frame and 3' untranslated region which forms a stem-loop structure necessary for the incorporation of Se into this selenoprotein. While Se is important in stabilizing GSH-Px transcripts, it did not affect transcription rates or mRNA stability. These results are consistent with the hypothesis that NGF regulates catalase and GSH-Px expression via a primary effect on transcription factor pathways.

Oxygen-induced apoptosis in PC12 cells with special reference to the role of Bcl-2

We previously reported that PC12h cells are killed by a high oxygen atmosphere. In this study, we further characterized this oxygen-induced cell death and found apoptotic features, as follows. Firstly, chromatin condensation was observed in cells cultured in a 50% O2 atmosphere. Secondly, cycloheximide and cordycepin, protein and RNA synthesis inhibitors, respectively, prevented the oxygen-induced cell death in PC12h cells, suggesting that it is mediated by an intracellular death program. Thirdly, NGF, CPT-cAMP and depolarization by high potassium medium also effectively inhibited this apoptotic cell death in PC12h cells. The effect of high K+ is thought to be mediated by the influx of Ca2+ into cells through voltage-dependent Ca2+ channels, because nifedipine, an L-type Ca2+ channel blocker, inhibited the effect of high K+. In addition, since the oxygen-induced apoptosis was blocked by the antioxidant vitamin E, this oxygen toxicity is suggested to be mediated by reactive oxygen species. To further characterize this oxygen-induced apoptosis at the molecular level, we used PC12 cells overexpressing the proto-oncogene bcl-2. Although a large number of PC12 cells transfected with the control vector died in a 50% O2 atmosphere within 6 days, bcl-2-transfected PC12 cells survived and proliferated. These findings suggested that our system using PC12 cells will be a useful model with which to analyze the molecular mechanisms of apoptosis induced by oxidative stress in neuronal cells.