Oxygen free radicals and neurodegeneration in Parkinson's disease: a role for nitric oxide

Glycine nano-selenium prevents brain oxidative stress and neurobehavioral abnormalities caused by MPTP in rats

BACKGROUND

Parkinson's disease (PD) is a common degenerative disease of the central nervous system in the elderly. In recent years, the results of clinical and experimental studies have shown that oxidative stress is one of the important pathogenesis of PD. Selenium is one of the minor elements reported to possess antioxidant properties. Thus, the purpose of this study was to investigate the recovery effect of glycine nano-selenium on neurobehavioral abnormalities and oxidative stress caused by 1-methyl-4-phenyl-1,2,3,6-tetrahydropyridine (MPTP) in rat.

MATERIALS AND METHODS

SD male rats weighing 280-310 g were purchased from the Chengdu Dossy Experimental Animals Company, China. All rats were housed in a temperature-controlled room, with a 12 h light-dark cycles and had free access to food and water ad libitum. Rats were randomly divided into 4 groups with 8 animals in each group: the control group (normal saline), 1-methyl-4-phenyl-1,2,3,6-tetrahydropyridine group (MPTP), MPTP + 0.05 mg/kg glycine nano-selenium (MPTP + 0.05 Se), MPTP + 0.1 mg/kg glycine nano-selenium (MPTP + 0.1 Se). Behavioral assessment, clinical symptoms, Immunohistochemistry analysis of tyrosine hydroxylase (TH) and antioxidant activity were accessed to determine the protective effects glycine nano-selenium have on PD rats.

RESULTS

From the results, Rats showed a decrease in spontaneous motor behavior and an increase in pole test score. Also, the number of TH⁺ neurons were also significantly decreased (P < 0.05) after treated with MPTP for 7 days indicating that MPTP could successfully induce neurobehavioral abnormalities in rats. Furthermore, the lipid peroxide (MDA) levels of the PD model group were significantly increased and the antioxidant activities (SOD and GSH-PX) were significantly inhibited (P < 0.05) compared to the control group indicating the important role oxidative stress played in dopaminergic neuron death and neurobehavioral abnormalities in PD rats. Compared with the PD model group, glycine nano-selenium administration could significantly improve behavior and increase the number of TH⁺ neurons (P < 0.05) to protect against the loss of dopaminergic neurons. At the same time, glycine nano-selenium could decrease the MDA levels and increase the activities of SOD and GSH-PX significantly (P < 0.05).

CONCLUSION

In conclusion, PD rat model was successfully developed by intraperitoneal injection of MPTP and the intragastric administration of glycine nano-selenium reduced neurobehavioral abnormalities by decreasing oxidative stress in rat brain.

Beneficial effects of L-arginine on 1-methyl-4-phenyl-1,2,3,6-tetrahydropyridine-induced neuronal degeneration in substantia nigra of Balb/c mice

BACKGROUND

L-arginine has been recently investigated and proposed to reduce neurological damage after various experimental models of neuronal cellular damage. In this study, we aim to evaluate the beneficial effects of L-arginine administration on the numerical density of dark neurons (DNs) in the substantia nigra pars compacta (SNc) of Balb/c mice subjected to 1-methyl-4-phenyl-1,2,3,6-tetrahydropyridine (MPTP) administration.

MATERIALS AND METHODS

Male Balb/c mice were randomly divided into 4 groups (n = 7 each): MPTP only; saline only (control); MPTP + L-arginine; and L-arginine only. The animals were infused intranasally with a single intranasal administration of the proneurotoxin MPTP (1 mg/nostril). L-arginine (300 mg/kg) was administrated intraperitoneally once daily for 1-week starting from 3 days after MPTP administration. Cavalieri principle method was used to estimate the numerical density of DNs in the SNc of different studied groups.

RESULTS

Twenty days following MPTP administration, the number of DNs was significantly increased when compared to sham-control and L-arginine-control groups (P < 0.05). Nevertheless, our results showed that L-arginine administration significantly decreased the numerical density of DNs in SNc of mice.

CONCLUSION

This investigation provides new insights in experimental models of Parkinson's disease, indicating that L-arginine represents a potential treatment agent for dopaminergic neuron degeneration in SNc observed in Parkinson's disease patients.

Protective effects of TREK-1 against oxidative injury induced by SNP and H2O2

AIM

TREK-1 (TWIK-related K+ channel-1) is a 2-pore-domain K+ channel subtype. The present study investigated the role of TREK-1 in cell death induced by oxidative stress.

METHODS

The cell viability of wild-type Chinese hamster ovary (CHO) and TREK-1-transfected CHO cells (TREK-1/CHO cells) was measured using 3-(4,5-dimethylthiazol-2-yl)-2,5-diphenyltetrazolium bromide (MTT) assay in the presence of sodium nitroprusside (SNP) or hydrogen peroxide (H2O2). Apoptosis of wild-type CHO and TREK-1/CHO cells was detected using Hoechst33342 staining.

RESULTS

Both SNP and H2O2 caused dose- and time-dependent growth inhibition of wild-type CHO and TREK-1/ CHO cells. Following a 12 h exposure to SNP, the 50% inhibition (IC(50)) values for wild-type CHO and TREK-1/CHO cells were calculated as 0.69 mmol/L and 1.14 mmol/L, respectively. The IC(50) values were 0.07 mmol/L and 0.09 mmol/L in H2O2-treated wild-type CHO and TREK-1/CHO cells, respectively, following 12 h exposure to H2O2. Moreover, SNP/H2O2 induced less apoptosis in TREK-1/ CHO cells than that in wild-type CHO cells (P<0.05).

CONCLUSION

The results demonstrated that TREK-1 played a protective role against oxidative injury.

Defects of mitochondrial electron transport chain in bipolar disorder: implications for mood-stabilizing treatment

OBJECTIVE

Converging lines of evidence indicate that defects in the mitochondrial electron transport chain (ETC) are associated with bipolar disorder (BD), and that mood-stabilizing drugs produce neuroprotective effects. Our objective is to review the most recent findings regarding this research.

METHOD

We searched MEDLINE and have reviewed here the most recently published articles.

RESULTS

There are deletions, mutation, and decreased expression of mitochondrial ETC complexes in BD. Because ETC is a major source of reactive oxygen species, these factors, along with decreased expression of antioxidant enzymes in BD, suggest the presence of oxidative damage in this disorder. Numerous recent studies have shown that mood-stabilizing drugs produce neuroprotective effects against oxidative damage and increase expression and activities of endogenous antioxidant enzymes in the rat brain.

CONCLUSION

These findings indicate that the process of oxidative damage could be a significant therapeutic target for the treatment of BD with mood-stabilizing drugs.

Complex-1 activity and 18F-DOPA uptake in genetically engineered mouse model of Parkinson's disease and the neuroprotective role of coenzyme Q10

Regional distribution of coenzyme Q10 and mitochondrial complex-1 activity were estimated in the brains of control-(C57BL/6), metallothionein knock out-, metallothionein transgenic-, and homozygous weaver mutant mice; and human dopaminergic (SK-N-SH) cells with a primary objective to determine the neuroprotective potential of coenzyme Q10 in Parkinson's disease. Complex-1 activity as well as coenzyme Q10 were significantly higher in the cerebral cortex as compared to the striatum in all the genotypes examined. Complex-1 activity and coenzyme Q10 were significantly reduced in weaver mutant mice and metallothionein knock out mice, but were significantly increased in metallothionein transgenic mice. The reduced complex-1 activity and 18F-DOPA uptake occurred concomitantly with negligible differences in the coenzyme Q10 between in the cerebral cortex and striatum of weaver mutant mice. Administration of coenzyme Q10 increased complex-1 activity and partially improved motoric performance in weaver mutant mice. Direct exposure of rotenone also reduced coenzyme Q10, complex-1 activity, and mitochondrial membrane potential in SK-N-SH cells. Rotenone-induced down-regulation of complex-1 activity was attenuated by coenzyme Q10 treatment, suggesting that complex-1 may be down regulated due to depletion of coenzyme Q10 in the brain. Therefore, metallothionein-induced coenzyme Q10 synthesis may provide neuroprotection by augmenting mitochondrial complex-1 activity in Parkinson's disease.

NADPH oxidase mediates lipopolysaccharide-induced neurotoxicity and proinflammatory gene expression in activated microglia

Parkinson's disease is characterized by the progressive degeneration of dopaminergic neurons in the substantia nigra. We have previously reported that lipopolysaccharide (LPS)-induced degeneration of dopaminergic neurons is mediated by the release of proinflammatory factors from activated microglia. Here, we report the pivotal role of NADPH oxidase in inflammation-mediated neurotoxicity, where the LPS-induced loss of nigral dopaminergic neurons in vivo was significantly less pronounced in NADPH oxidase-deficient (PHOX-/-) mice when compared with control (PHOX+/+) mice. Dopaminergic neurons in primary mensencephalic neuron-glia cultures from PHOX+/+ mice were significantly more sensitive to LPS-induced neurotoxicity in vitro when compared with PHOX-/- mice. Further, PHOX+/+ neuron-glia cultures chemically depleted of microglia failed to show dopaminergic neurotoxicity with the addition of LPS. Neuron-enriched cultures from both PHOX+/+ mice and PHOX-/- mice also failed to show any direct LPS-induced dopaminergic neurotoxicity. However, the addition of PHOX+/+ microglia to neuron-enriched cultures from either strain resulted in reinstatement of LPS-induced dopaminergic neurotoxicity, supporting the role of microglia as the primary source of NADPH oxidase-generated insult and neurotoxicity. Immunostaining for F4/80 in mensencephalic neuron-glia cultures revealed that PHOX-/- microglia failed to show activated morphology at 10 h, suggesting an important role of reactive oxygen species (ROS) generated from NADPH oxidase in the early activation of microglia. LPS also failed to elicit extracellular superoxide and produced low levels of intracellular ROS in microglia-enriched cultures from PHOX-/- mice. Gene expression and release of tumor necrosis factor alpha was much lower in PHOX-/- mice than in control PHOX+/+ mice. Together, these results demonstrate the dual neurotoxic functions of microglial NADPH oxidase: 1) the production of extracellular ROS that is toxic to dopamine neurons and 2) the amplification of proinflammatory gene expression and associated neurotoxicity.

Metallothionein attenuates 3-morpholinosydnonimine (SIN-1)-induced oxidative stress in dopaminergic neurons

Parkinson's disease is characterized by a progressive loss of dopaminergic neurons in the substantia nigra zona compacta, and in other subcortical nuclei associated with a widespread occurrence of Lewy bodies. The causes of cell death in Parkinson's disease are still poorly understood, but a defect in mitochondrial oxidative phosphorylation and enhanced oxidative stress have been proposed. We have examined 3-morpholinosydnonimine (SIN-1)-induced apoptosis in control and metallothionein-overexpressing dopaminergic neurons, with a primary objective to determine the neuroprotective potential of metallothionein against peroxynitrite-induced neurodegeneration in Parkinson's disease. SIN-1 induced lipid peroxidation and triggered plasma membrane blebbing. In addition, it caused DNA fragmentation, alpha-synuclein induction, and intramitochondrial accumulation of metal ions (copper, iron, zinc, and calcium), and enhanced the synthesis of 8-hydroxy-2-deoxyguanosine. Furthermore, it down-regulated the expression of Bcl-2 and poly(ADP-ribose) polymerase, but up-regulated the expression of caspase-3 and Bax in dopaminergic (SK-N-SH) neurons. SIN-1 induced apoptosis in aging mitochondrial genome knockout cells, alpha-synuclein-transfected cells, metallothionein double-knockout cells, and caspase-3-overexpressed dopaminergic neurons. SIN-1-induced changes were attenuated with selegiline or in metallothionein-transgenic striatal fetal stem cells. SIN-1-induced oxidation of dopamine to dihydroxyphenylacetaldehyde was attenuated in metallothionein-transgenic fetal stem cells and in cells transfected with a mitochondrial genome, and enhanced in aging mitochondrial genome knockout cells, in metallothionein double-knockout cells and caspase-3 gene-overexpressing dopaminergic neurons. Selegiline, melatonin, ubiquinone, and metallothionein suppressed SIN-1-induced down-regulation of a mitochondrial genome and up-regulation of caspase-3 as determined by reverse transcription-polymerase chain reaction. The synthesis of mitochondrial 8-hydroxy-2-deoxyguanosine and apoptosis-inducing factors were increased following exposure to 1-methyl-4-phenylpyridinium ion or rotenone. Pretreatment with selegiline or metallothionein suppressed 1-methyl-4-phenylpyridinium ion-, 6-hydroxydopamine-, and rotenone-induced increases in mitochondrial 8-hydroxy-2-deoxyguanosine accumulation. Transfection of aging mitochondrial genome knockout neurons with mitochondrial genome encoding complex-1 or melanin attenuated the SIN-1-induced increase in lipid peroxidation. SIN-1 induced the expression of alpha-synuclein, caspase-3, and 8-hydroxy-2-deoxyguanosine, and augmented protein nitration. These effects were attenuated by metallothionein gene overexpression. These studies provide evidence that nitric oxide synthase activation and peroxynitrite ion overproduction may be involved in the etiopathogenesis of Parkinson's disease, and that metallothionein gene induction may provide neuroprotection.

Pre- and post-treatment with pirlindole and dehydropirlindole protects cultured brain cells against nitric oxide-induced death

We have previously shown that pirlindole and dehydropirlindole, two monoamine oxidase type-A inhibitors, protect cultured brain cells against iron-induced toxicity through a mechanism unrelated to monoamine oxidase type-A inhibition. The current study was performed to test whether the protective effect of pirlindole and dehydropirlindole could be extended to a nitric oxide (NO)-induced insult. A comparison with other monoamine oxidase inhibitors (brofaromine, moclobemide and deprenyl) and with trolox was made. In a first series of experiments, rat hippocampal or cortical cultured cells were exposed to a drug for 3 h, then 5 microM sodium nitroprusside, a NO donor, was added and the incubation was continued for 16 h. Cell survival assessment showed that pirlindole, dehydropirlindole and trolox significantly protected cultures against NO-induced toxicity in a concentration-dependent manner with respective EC(50)'s of 7, 3 and 17 microM. Similarly, pirlindole, dehydropirlindole or trolox, at a concentration of 50 microM, significantly decreased both intracellular peroxide production and lipoperoxidation. Other drugs were ineffective. In a post-hoc treatment protocol (3- or 6-h pre-incubation in the presence of sodium nitroprusside, then addition of one of the above mentioned compounds), only pirlindole and dehydropirlindole significantly improved cell survival in a concentration-dependent manner with respective EC(50)'s of 9 and 4 microM. The maximal protection in terms of cell survival was 90% and 78% after 3 and 6 h, respectively. They also reduced the production of both lipoperoxides and endoperoxides. Our results show that pirlindole and dehydropirlindole protect neurons against NO-induced toxicity at pharmacologically relevant concentrations. Moreover, their protective effect is still apparent when they are applied after the start of the insult. Therefore, our preclinical study suggests a new strategy that may be efficient to reduce NO-induced damage in the central nervous system.

Role of the JAK/STAT signal transduction pathway in the regulation of gene expression in CNS

Over the last 20 years the JAK/STAT signal transduction pathway has been extensively studied. An enormous amount of data on different cell signal transduction pathways is now available. The JAK/STAT signal transduction pathway is one of the intracellular signaling pathways activated by cytokines and growth factors that was first studied in the hematopoietic system, but recent data demonstrate that this signal transduction is also greatly utilized by other systems. The JAK/STAT pathway is a signaling cascade that links the activation of specific cell membrane receptors to nuclear gene expression. This review is focused on the role of JAK/STAT signal transduction pathway activation in the central nervous system (CNS).

Gö6976 protects mesencephalic neurons from lipopolysaccharide-elicited death by inhibiting p38 MAP kinase phosphorylation

Glial activation is associated with inflammation-related neuron degeneration in the brain. A variety of protein kinases are assumed to contribute to the expression of inflammation-related products, such as nitric oxide (NO) and proinflammatory cytokines, however, the mechanisms of glial activation and glia-mediated neurotoxicity remain unclear. We found that the indolocarbazole, Gö6976, originally known as a selective protein kinase C (PKC) inhibitor, protects neurons from glia-mediated damage and suppresses lipopolysaccharide (LPS)-induced microglial production of inflammatory factors. The purpose of the study we report here was to determine the mechanism underlying the neuroprotective effect of Gö6976 in mesencephalic neuron/glia cultures. Gö6976 suppressed LPS-induced neurotoxicity in mesencephalic neuron/glia cultures and the protective effect of Gö6976 paralleled the suppression of p38 mitogen activated protein kinase (MAPK) activation and inhibition of NO production. Gö6976 did not directly inhibit the activity of p38 MAPK; rather, the inhibitor suppressed the phosphorylation of p38 MAPK, suggesting that the target of Gö6976 is a signaling event upstream of p38 MAPK. Although Gö6976 was originally known to be a selective PKC inhibitor, the neuroprotection was not mediated through its reputed effects on PKC activity. This paper demonstrates that the neuroprotective effect of Gö6976 against LPS-induced damage is mediated through the inhibition of proinflammatory factors, such as NO from microglia, by inhibiting the phosphorylation of p38 MAPK.

p38 MAP kinase is involved in lipopolysaccharide-induced dopaminergic neuronal cell death in rat mesencephalic neuron-glia cultures

Immune stimulants, such as the bacterial endotoxin, lipopolysaccharide (LPS), the human immunodeficiency virus-1 coat protein gp120, or beta-amyloid peptides, lead to glial activation and production of various immune mediators, such as nitric oxide (NO) and proinflammatory cytokines in the brain. These mediators appear to contribute to neuronal cell death in neurodegenerative diseases. However, the signaling pathways, which mediate the neurotoxic effect by the endotoxin, are not understood. The purpose of this study was to determine the role of mitogen-activated protein kinase (MAPK) in LPS-induced neurodegeneration using mesencephalic dopaminergic neuron/glia cultures. We have found that the p38 MAPK is important in LPS-induced death of mesencephalic neurons in rat neuron-glia mixed cultures. Upon treatment with 10 ng/ml LPS, the number of dopaminergic neurons decreased by 80% within 48 h, preceded by a significant production of NO by glia. Neuroprotection by selective inhibition of p38 MAPK activity paralleled a decrease in LPS-induced inducible nitric oxide synthase (iNOS) expression. These events were significantly reduced by the selective p38 MAPK inhibitor, SB202190, but not by the inactive analogue SB202474. Inhibition of iNOS activity and NO production by treatment with GW274150 was also neuroprotective. Although the p38 MAPK inhibitor afforded significant neuroprotection from LPS toxicity in the neuron-glia mixed culture, it failed to protect dopaminergic neurons from 6-hydroxy-dopamine-induced toxicity, which acts directly on dopaminergic neurons by inducing hydroxyl radical formation from the mitochondria. The results suggest that p38 MAPK in glia plays a significant role in the LPS-induced death of mesencephalic neurons through induction of nitric oxide synthase and resulting NO production.

Signaling and gene expression in the neuron-glia unit during brain function and dysfunction: Holger Hydén in memoriam

Holger Hydén demonstrated almost 40 years ago that learning changes the base composition of nuclear RNA, i.e. induces an alteration in gene expression. An equally revolutionary observation at that time was that a base change occurred in both neurons and glia. From these findings, Holger Hydén concluded that establishment of memory is correlated with protein synthesis, and he demonstrated de novo synthesis of several high-molecular protein species after learning. Moreover, the protein, S-100, which is mainly found in glial cells, was increased during learning, and antibodies towards this protein inhibited memory consolidation. S-100 belongs to a family of Ca(2+)-binding proteins, and Holger Hydén at an early point realized the huge importance of Ca(2+) in brain function. He established that glial cells show more marked and earlier changes in RNA composition in Parkinson's disease than neurons. Holger Hydén also had the vision and courage to suggest that "mental diseases could as well be thought to depend upon a disturbance of processes in glia cells as in the nerve cells", and he showed that antidepressant drugs cause profound changes in glial RNA. The importance of Holger Hydén's findings and visions can only now be fully appreciated. His visionary concepts of the involvement of glia in neurological and mental illness, of learning being associated with changes in gene expression, and of the functional importance of Ca(2+)-binding proteins and Ca(2+) are presently being confirmed and expanded by others. This review briefly summarizes highlights of Holger Hydén's work in these areas, followed by a discussion of recent research, confirming his findings and expanding his visions. This includes strong evidence that glial dysfunction is involved in the development of Parkinson's disease, that drugs effective in mood disorders alter gene expression and exert profound effects on astrocytes, and that neuronal-astrocytic interactions in glutamate signaling, NO synthesis, Ca(2+) signaling, beta-adrenergic activity, second messenger production, protein kinase activities, and transcription factor phosphorylation control the highly programmed events that carry the memory trace through the initial, signal-mediated short-term and intermediate memory stages to protein synthesis-dependent long-term memory.

JAK/STAT signaling pathway mediates cytokine-induced iNOS expression in primary astroglial cell cultures

The production of nitric oxide by the calcium-independent inducible nitric oxide synthase (iNOS) in glial cells has been implicated in the neuropathogenesis of various diseases. It is well known that in response to lipopolysaccharide (LPS) and cytokines, such as IFN-gamma, glial cells are induced to synthesize large amount of nitric oxide (NO) (Bolaños et al., 1996; Nicoletti et al., 1998). The signaling transduction pathways for iNOS transcription in astroglial cells have however not yet been established. Because IFN-gamma receptor chains are associated with Janus tyrosine kinases (JAK1 and JAK2) (Darnell et al., 1994), we analyzed the involvement of the JAK/STAT signal transduction pathway in iNOS expression. Our study shows increased JAK2 and STAT1 alpha/beta tyrosine phosphorylation in primary astroglial cell culture after treatment with IFN-gamma and LPS. A temporal correlation was observed between JAK2 and STAT1 alpha/beta tyrosine phosphorylation, the appearance of interferon-regulatory factor-1 (IRF-1) mRNA and the iNOS expression. Inhibition experiments showed that JAK2 and STAT1 alpha/beta tyrosine phosphorylation were necessary for IFN gamma-mediated iNOS induction in astroglial cells. We conclude that JAK2 and STAT1 alpha/beta tyrosine phosphorylation is an early event involved in the expression of iNOS in astroglial cells.

Impaired iron homeostasis in Parkinson's disease

Despite physiological systems designed to achieve iron homeostasis, increased concentrations of brain iron have been demonstrated in a range of neurodegenerative diseases. These including the parkinsonian syndromes, the trinucleotide repeat disorders and the dementia syndromes. The increased brain iron is confined to those brain regions most affected by the degeneration characteristic of the particular disorder and is suggested to stimulate cell damage via oxidative mechanisms. Changes in central iron homeostasis have been most closely investigated in PD, as this disorder is well characterised both clinically and pathologically. PD is associated with a significant increase in iron in the degenerating substantia nigra (SN) and is measureable in living PD patients and in post-mortem brain. This increase, however, occurs only in the advanced stages of the disease, suggesting that this phenonoma may be a secondary, rather than a primary initiating event, a hypothesis also supported by evidence from animal experiments. The source of the increased iron is unknown but a variety of changes in iron homeostasis have been identified in PD, both in the brain and in the periphery. The possibility that an increased amount of iron may be transported into the SN is supported by data demonstrating that one form of the iron-binding glycoprotein transferrin family, lactotransferrin, is increased in surviving neurons in the SN in the PD brain and that this change is associated with increased numbers of lactotransferrin receptors on neurons and microvessels in the parkinsonian SN. These changes could represent one mechanism by which iron might concentrate within the PD SN. Alternatively, the measured increased in iron might result from a redistribution of ferritin iron stores. Ferritin is located in glial cells while the degenerating neurons do not stain positive for ferritin. As free radicals are highly reactive, it is unlikely that glial-derived free radicals diffuse across the intracellular space in sufficent quantities to damage neuronal constituents. If intracellular iron release contributes to neuronal damage it seems more probable that an intraneuronal iron source is responsible for oxidant-mediated damage. Such a iron source is neuromelanin (NM), a dark-coloured pigment found in the dopaminergic neurons of the human SN. In the normal brain, NM has the ability to bind a variety of metals, including iron, and increased NM-bound iron is reported in the parkinsonian SN. The consequences of these phenomena for the cell have not yet been clarified. In the absence of significant quantities of iron NM can act as an antioxidant, in that it can interact with and inactivate free radicals. On the other hand, in the presence of iron NM appears to act as a proxidant, increasing the rate of free radical production and thus the oxidative load within the vulnerable neurons. Given that increased iron is only apparent in the advanced stages of the disease it is unlikely that NM is of importance for the primary aetiology of PD. A localised increase in tissue iron and its interaction with NM may be, however, important as a secondary mechanism by increasing the oxidative load on the cell, thereby driving neurodegeneration.

Time dependency of the action of nitric oxide in lipopolysaccharide-interferon-gamma-induced neuronal cell death in murine primary neuron-glia co-cultures

We investigated the time-dependency of the action of nitric oxide (NO) on glia-mediated neuronal cell death. Cortical neuron-glia co-cultures were treated with lipopolysaccharide and interferon gamma (LPS/IFNgamma). The production of NO was first detectable 9 h after the exposure to LPS/IFNgamma and increased for up to 48 h. A significant neuronal cell death was observed 36-48 h after treatment with LPS/IFNgamma. The NO generated at the initial stage of NO synthesis (about 12 h) following exposure to LPS/IFNgamma was found to be critical for LPS/IFNgamma-induced neurotoxicity. Furthermore, the rate of NO production at the initial stage of NO synthesis was correlated linearly with the extent of neuronal cell death. These findings suggest that the maximal rate of NO synthesis, instead of the accumulated NO(2)(-) level, is a sensitive index for predicting endotoxin-induced cytotoxicity.

Agmatine suppresses nitric oxide production in microglia

We investigated the effect of agmatine, an arginine metabolite synthesized in the brain, in cultured microglia obtained from neonatal rat cerebral cortex. Agmatine (1-300 microM) did not affect viability of cultured microglia. Activation of microglia by lipopolysaccharide (LPS, 1 microg/ml) caused the expression of inducible nitric oxide synthase (iNOS) and the production of nitric oxide (NO) assessed as the accumulation of nitrite in the culture supernatants. Agmatine had no effect on the expression of iNOS, but significantly suppressed the LPS-induced NO production in a concentration-dependent manner. Agmatine was also effective in suppressing the production of NO induced by a combination of interferon-gamma (500 U/ml) and amyloid beta protein (10 microM). In co-cultures of rat cortical neurons and microglia, LPS caused significant loss of neuron viability. The LPS neurotoxicity was not observed in the absence of microglia, and was completely blocked by the NOS inhibitor diphenyleneiodoium chloride. The neuronal death induced by microglia-derived NO was significantly attenuated by the presence of agmatine. These results suggest that agmatine works to protect neurons by inhibiting the production of NO in microglia.

Post-transcriptional inhibition of lipopolysaccharide-induced expression of inducible nitric oxide synthase by Gö6976 in murine microglia

Glia in the brain respond to various toxins with an increased expression of inducible nitric oxide synthase (iNOS) and an increased production of nitric oxide (NO). Here, we report that lipopolysaccharide (LPS)-induced expression of iNOS was down-regulated post-transcriptionally through the destabilization of iNOS mRNA by the indolocarbazole compound, Gö6976, in murine microglia. This Gö6976 effect is specific for iNOS since tumor necrosis factor alpha was unaffected by the compound. Interestingly, the post-transcriptional effects ascribed to Gö6976 were not observed with other inhibitors of protein kinase A, C (PKC), G, or protein tyrosine kinases. Instead, these kinases appear to affect the iNOS/NO system at the transcriptional level. In the past, Gö6976 has been reported to be a rather specific inhibitor of PKC in vitro. Results from our experiments, through prolonged treatment with phorbol esters and with the various PKC inhibitors including phorbol ester-insensitive PKC isotype inhibitor, suggest that the Gö6976-mediated post-transcriptional regulation of iNOS gene expression and NO production in microglia is not mediated through its reputed effects on PKC activity. Since the effects of various neurotoxins and certain neurodegenerative diseases may be manifested through alterations in the iNOS/NO system, post-transcriptional control of this system may represent a novel strategy for therapeutic intervention.

The indolocarbazole Gö6976 protects neurons from lipopolysaccharide/interferon-gamma-induced cytotoxicity in murine neuron/glia co-cultures

The expression of inducible nitric oxide synthase (iNOS) and the production of nitric oxide (NO) after exposure to endotoxins has been implicated in immune-mediated neurotoxicity. The indolocarbazole compound Gö6976, which has been described as a selective protein kinase C (PKC) inhibitor in vitro, rescued neurons from lipopolysaccharide/interferon-gamma (LPS/IFNgamma)- or interleukin-1alpha/tumor necrosis alpha/IFNgamma (IL-1alpha/TNFalpha/IFNgamma)-induced cytotoxicity in murine primary neuron-glia co-cultures. Other compounds known to inhibit PKC, Ro31-8220, GF109203X, Gö7874, H7, staurosporine and H89, failed to rescue neurons from the LPS/IFNgamma-induced cytotoxicity. These results suggest that the neuroprotection by Gö6976 from the LPS/IFNgamma-induced neuronal cell death is not mediated through its reputed effects on PKC activity. The neuroprotection paralleled the inhibition of iNOS gene expression and NO production. However, further analyses correlating NO production with the extent of neurotoxicity suggested that additional mechanism(s) besides the inhibition of the iNOS/NO system may be responsible for the neuroprotective effects of Gö6976. An understanding of the mechanism underlying the neuroprotective effect of Gö6976 may provide key insights into potential interventions for immune-mediated neurodegenerative diseases.

Induction of superoxide in glioma cell line U87 stimulated with lipopolysaccharide and interferon-gamma: ESR using a new flow-type quartz cell

The production of superoxide and nitric oxide induced in U87 glioma treated with lipopolysaccharide (LPS) and interferon-gamma (IFN-gamma) was examined by electron spin resonance (ESR) spectroscopy using a newly designed flow-type quartz cuvette without detaching cells from the culture plate. ESR spectra of 2,2,6, 6-tetramethyl-4-hydroxy-1-piperidinyloxy (TEMPOL) with U87 cells on a quartz culture plate were measured at 15 min intervals. The signal intensity of TEMPOL decreased in the presence of U87 cells at the pseudo-first order rate. The signal decay was accelerated in the U87 cells treated with LPS/IFN-gamma for 24 h, and was suppressed in the presence of superoxide dismutase and catalase. By the spin-trapping method, nitric oxide from U87 cells pretreated with LPS/IFN-gamma for 24 h was measured by the ESR, but only a weak signal of nitric oxide adducts was detected. Further, the nitrite and nitrate levels in the medium did not increase for 24 h. By the ESR measurement of cells on culture plates without detachment stress, it was found that the production of superoxide was induced by LPS/IFN-gamma, but that of nitric oxide was not, in U87 glioma cells.

Free radical scavengers: chemical concepts and clinical relevance

Free radicals are involved in the pathology of many CNS disorders, like Parkinson's disease, Alzheimer's disease, or stroke. This discovery lead to the development of many radical scavengers for the clinical treatment of neurodegenerative diseases. In this review, the different chemical concepts for free radical scavenging will be discussed: nitrons, thiols, iron chelators, phenols, and catechols. Especially catechols, like the naturally occurring flavonols, the synthetic drug nitecapone, or the endogenous catacholamines and their metabolites, are of great interest, as they combine iron chelating with radical scavenging activity. We present data on the radical scvenging activity of dopamine and apomorphine, which prevent lipid peroxidation in rat brain mitochondria and protect PC12 cells against H2O2-toxicity.

The protective role of plasmalogens in iron-induced lipid peroxidation

The role of plasmalogens in iron-induced lipid peroxidation was investigated in two liposomal systems. The first consisted of total brain phospholipids with and without plasmalogens, and the second of phosphatidylethanolamine/phosphatidylcholine liposomes with either diacyl- or alkenylacyl-phosphatidylethanolamine. By measuring thiobarbituric acid reactive substances, oxygen consumption, fatty acids and aldehydes, we show that plasmalogens effectively protect polyunsaturated fatty acids from oxidative damage, and that the vinyl ether function of plasmalogens is consumed simultaneously. Furthermore, the lack of lag phase, the increased antioxidant efficiency with time, and the experiments with lipid- and water-soluble azo compounds, indicate that plasmalogens probably interfere with the propagation rather than the initiation of lipid peroxidation, and that the antioxidative effect cannot be related to iron chelation.

Antioxidant properties of the triaminopyridine, flupirtine

Flupirtine is a triaminopyridine-derived centrally acting analgesic, which interacts with mechanisms of noradrenergic pain modulation. Recently, it has been found to display neuroprotective effects in various models of excitotoxic cell damage, global and focal ischemia. Although this profile suggests that flupirtine acts as an antagonist of the N-methyl-D-aspartate (NMDA) and glutamate-triggered Ca2+ channel, there is no direct interaction with the receptor. In this paper, we examined whether flupirtine can act as an antioxidant and prevent free radical-mediated structural damage. Flupirtine at 5-30 microM inhibited ascorbate/ Fe2+ (1-10 microM)-stimulated formation of thiobarbituric reactive substances, an indicator of lipid peroxidation, in rat brain mitochondria. Interestingly, we found an increasing effectiveness of the drug at higher iron concentrations. Additionally, higher concentrations of flupirtine also provided protection against protein oxidation, as demonstrated by a decrease in protein carbonyls formed after treatment of rat brain homogenates with ascorbate/Fe2+. In PC12 cell culture, flupirtine at 10-100 microM was able to attenuate H2O2-stimulated cell death and improve the survival by 33%.

Expression of iron transport proteins and excessive iron accumulation in the brain in neurodegenerative disorders

New findings on the role of LfR (lactotransferrin receptor), MTf (melanotransferrin), CP (ceruloplasmin) and DCT1 (Divalent Cation Transporter) in brain iron transport, obtained during the past 3 years, are important advances in the fields of physiology and pathophysiology of brain iron metabolism. According to these findings, disruption in the expression of these proteins in the brain is probably one of the important causes of the altered brain iron metabolism in age-related neurodegenerative diseases, including Parkinson's Disease, Alzheimer's disease, Huntington's disease and amyotrophic lateral sclerosis. Further studies on the involvement of LfR, MTf and DCT1 in iron uptake by and CP in iron egress from different types of brain cells as well as control mechanisms of expression of these proteins in the brain are critical for elucidating the causes of excessive accumulation of iron in the brain and neuronal death in neurodegenerative diseases.

Age-related neurodegeneration and oxidative stress: putative nutritional intervention

This review describes age-related changes that occur in neuronal function and cites evidence to show that these alterations may be the result of increased sensitivity to oxidative stress (OS). Evidence is presented to show that the abilities to mitigate the OS effects and to repair the damage from OS show decline as a function of age. Results from age- and OS-sensitive tests are given; these results indicate that one of the major sites of action of OS is the membranes, especially if compromised by high amounts of sphingomyelin, and one of the major effects of OS is to further alter the calcium disregulation in aging. It is suggested that attempts to increase antioxidant protection through diets comprised of fruits and vegetables identified as being high in total antioxidant activity might prevent or reverse the deleterious OS effects on neuronal aging.

Role of poly(ADP-ribose)synthetase in inflammation

Peroxynitrite and hydroxyl radicals are potent initiators of DNA single strand breakage, which is an obligatory stimulus for the activation of the nuclear enzyme poly(ADP-ribose)synthetase (PARS). Rapid activation of PARS depletes the intracellular concentration of its substrate, NAD+, slowing the rate of glycolysis, electron transport and ATP formation. This process can result in acute cell dysfunction and cell necrosis. Accordingly, inhibitors of PARS protect against cell death under these conditions. In addition to the direct cytotoxic pathway regulated by DNA injury and PARS activation, PARS also appears to modulate the course of inflammation by regulating the expression of a number of genes, including the gene for intercellular adhesion molecule 1, collagenase and the inducible nitric oxide synthase. The research into the role of PARS in inflammatory conditions is now supported by novel tools, such as novel, potent inhibitors of PARS, and genetically engineered animals lacking the gene for PARS. In vivo data demonstrate that inhibition of PARS protects against various forms of inflammation, including zymosan or endotoxin induced multiple organ failure, arthritis, allergic encephalomyelitis, and diabetic islet cell destruction. Pharmacological inhibition of PARS may be a promising novel approach for the experimental therapy of various forms of inflammation.

Hydroxyl radical formation resulting from the interaction of nitric oxide and hydrogen peroxide

The highly reactive and cytotoxic hydroxyl radical (OH) was found by electrochemical detection to be produced in reactions involving hydrogen peroxide (H2O2) and the nitric oxide (NO) donor diethylamine- NO complex. Using aromatic hydroxylation of salicylate as a specific indicator of OH, three salicylate hydroxylation products were identified; catechol, 2,3- and 2,5-dihydroxybenzoic acid. Four additional compounds were detected but not identified. The interactions of H2O2 and NO represent a biologically feasible reaction mechanism that can account for OH-induced damage in cellular environments where transition metal ions are unavailable for participation in the superoxide-mediated Fenton reaction. The ability of the NO/H2O2 complex to generate OH independently of iron or other transition metals provides a new focus for studies concerned with the origin of tissue-specific damage caused by oxygen-derived species.

Effects of ozone exposure in rats on memory and levels of brain and pulmonary superoxide dismutase

Exposure to ozone results in increased production of free radicals, which causes oxidative stress. The objective of this study was to determine the effect of different doses of ozone exposure on memory and to correlate this with pulmonary and brain Cu/Zn superoxide dismutase (SOD) levels. Male Wistar rats were exposed for 4 h to one of the following ozone concentrations: 0, 0.1, 0.2, 0.5, or 1 ppm. Subsequently, they were tested in a passive avoidance conditioning protocol to measure short and long-term memory. Motor activity was determined 1 and 24 h after ozone exposure. Cu/Zn SOD levels in the brain and pulmonary tissue were also measured. Rats exposed for 4 h to 0.2, 0.5, and 1 ppm ozone showed long-term memory deterioration and decreased motor activity, which was reversed 24 h later. Brain and pulmonary Cu/Zn SOD levels were increased in animals exposed to 0.1, 0.2, and 0.5 ppm ozone doses, but decreased in animals exposed to 1 ppm ozone. The results suggest that ozone exposure affects long-term memory possibly in association oxidative stress.

Comparison of inducible nitric oxide synthase expression in the brains of Listeria monocytogenes-infected cattle, sheep, and goats and in macrophages stimulated in vitro

The expression of inducible nitric oxide synthase (iNOS) was studied in the brains of cattle, sheep, and goat that succumbed to a natural infection with Listeria monocytogenes. The lesions in infected brains are characterized by microabscesses, perivascular cuffs, gliosis, glial nodules, and large areas of malacia. Using immunocytochemistry, we detected bacteria in microabscesses, particularly in sheep and goats, and in areas without signs of inflammation, but not in perivascular infiltrates. iNOS was expressed by macrophage (Mphi)-type cells of microabscesses and glial nodules but rarely by Mphi in areas of malacia, as determined by immunohistochemistry with iNOS-specific antibodies. iNOS was not detected in perivascular cuffs. Major histocompatibility complex class II molecules (MHC-II), another marker of cell activation, showed a different pattern of distribution. Perivascular cuffs contained high numbers of MHC-II-positive cells, including some with Mphi characteristics. Microabscesses in sheep and goats showed low expression of MHC-II, particularly in iNOS-expressing cells. In cattle, the expression of markers for activated or recruited phagocytes, the calcium-binding proteins S100A8 and S100A9 (formerly called MRP-8 and MRP-14, respectively), was largely restricted to cells showing weak or undetectable iNOS expression; iNOS-positive Mphi showed a low expression of S100A8 and S100A9. Thus, iNOS is expressed by a restricted subset of Mphi in listeric encephalitis. In cultured sheep and goat Mphi, a low proportion of cells expressed iNOS upon activation by L. monocytogenes and gamma interferon, resulting in nitrite generation at least 1 order of magnitude lower than that in similarly treated cattle Mphi. Since these species differences were much less obvious in vivo, it appears that the well-known species variation in iNOS expression by Mphi could reflect an in vitro phenomenon.

Effects of respiratory burst inhibitors on nitric oxide production by human neutrophils

Human neutrophils (PMN) activated by N-formylmethionyl-leucyl-phenylalanine (fMLP) simultaneously release nitric oxide (.NO), superoxide anion (O2.-) and its dismutation product, hydrogen peroxide (H2O2). To assess whether .NO production shares common steps with the activation of the NADPH oxidase, PMN were treated with inhibitors and antagonists of intracellular signaling pathways and subsequently stimulated either with fMLP or with a phorbol ester (PMA). The G-protein inhibitor, pertussis toxin (1-10 micrograms/ml) decreased H2O2 yield without significantly changing .NO production in fMLP-stimulated neutrophils; no effects were observed in PMA-activated cells. The inhibition of tyrosine kinases by genistein (1-25 micrograms/ml) completely abolished H2O2 release by fMLP-activated neutrophils; conversely, .NO production increased about 1.5- and 3-fold with fMLP and PMA, respectively. Accordingly, orthovanadate, an inhibitor of phosphotyrosine phosphatase, markedly decreased .NO production and increased O2.- release. On the other hand, inhibition of protein kinase C with staurosporine and the use of burst antagonists like adenosine, cholera toxin or dibutyryl-cAMP diminished both H2O2 and .NO production. The results suggest that the activation of the tyrosine kinase pathway in stimulated human neutrophils controls positively O2.- and H2O2 generation and simultaneously maintains .NO production in low levels. In contrast, activation of protein kinase C is a positive modulator for O2.- and .NO production.

Cholesterol: a two-edged sword in brain aging

Previous research from several laboratories has indicated that cholesterol (CHO) accumulates in neuronal membranes and alters their structural and signal transduction (ST) properties during aging. The possible reasons for these increases in membrane CHO have not been specified. However, present findings suggest that such accumulation may actually serve to protect neuronal tissue from oxidative damage. Striatal slices (6, 24 month rats) were preincubated in 1 mM CHO (30 min) followed by incubation with H2O2 (10 microM, 30 min). The slices were then either superfused with 30 mM KCl in the presence or absence of 500 microM oxotremorine (Ox), and K(+)-evoked dopamine release (K(+)-ERDA) examined or assessed for carbachol-stimulated low K(m) GTPase activity. The results indicated that CHO incubation prior to H2O2 in either age group was effective in preventing H2O2 reductions in both non-Ox-enhanced K(+)-ERDA and Ox conditions, as well as sodium nitroprusside (SNP 150 microM)-induced decreases in K(+)-ERDA. In addition, H2O2-induced deficits in carbachol-stimulated low K(m) GTPase activity were reduced in the striatal tissue from the old animals pretreated with CHO. However, if the slices were incubated in H2O2 prior to CHO exposure, CHO enhanced the H2O2 effects in the tissue from the old animals. Thus, depending upon the order of exposure, CHO functioned to enhance or retard the effects of oxidative stress, in an age-dependent manner.

Dopaminergic neuronal degeneration and motor impairments following axon terminal lesion by instrastriatal 6-hydroxydopamine in the rat

6-Hydroxydopamine-induced nerve terminal lesion of the nigrostriatal system may provide a partial lesion model of Parkinson's disease useful for the assessment of neuroprotective treatments and behavioral recovery after therapeutic intervention. The aim of the present study was to assess the retrograde degenerative changes in the dopaminergic neurons of the substantia nigra and the associated behavioral and neurochemical consequences of intrastriatal injections of 6-hydroxydopamine in young adult rats. Four groups of rats were stereotaxically injected in the right striatum with graded doses of 6-hydroxydopamine ranging from 0 to 20 mu g. Structural and functional deficits were quantified by tyrosine hydroxylase-immunoreactive nigral cell numbers, striatal dopamine content, skilled paw use, and drug-induced rotation. The results show that striatal 6-hydroxydopamine lesions produce dose-dependent decreases in striatal dopamine levels and tyrosine hydroxylase-immunoreactive cell numbers in the ipsilateral substantia nigra, accompanied by a significant long-lasting atrophy of the remaining dopaminergic neurons. Paw reaching test scores on the side contralateral to the lesion were non-linearly correlated with dopaminergic neuronal cell loss and exhibited a clear symptomatic threshold such that impaired paw use appeared only after >50% loss of nigral dopamine neurons or a reduction of 60-80% of striatal dopamine levels. The behavioral, cellular, and neurochemical effects of the nerve terminal lesion thus bear some resemblance to the early stages of Parkinson's disease, where the severity of motor impairment is correlated with the loss of dopamine in the striatum and dopaminergic neuronal loss in the substantia nigra. Rats with intrastriatal 6-hydroxydopamine lesions thus provide a model of progressive dopamine neuron degeneration useful not only for the exploration of neuroprotective therapeutic intervention but also for the study of mechanisms of functional and structural recovery after subtotal damage of the nigrostriatal dopamine system.

Modulation of lipopolysaccharide-induced tumor necrosis factor-alpha and nitric oxide production by dopamine receptor agonists and antagonists in mice

The effects of various agonist and antagonists of dopamine D1 and D2 receptors on lipopolysaccharide (LPS)-induced tumor necrosis factor-alpha (TNF-alpha) and nitric oxide (NO) production was investigated in mice. Pretreatment of animals with bromocryptine or quinpirole, agonists of dopamine D2 receptors caused a blunting of both the TNF-alpha and NO responses to LPS injected intraperitoneally. Sulpiride, an antagonist of dopamine D2 receptors, decreased the LPS-induced TNF-alpha plasma levels in a dose-dependent manner and inhibited the LPS-induced NO production by peritoneal macrophages. Bromocryptine or quinpirole blunted both the TNF-alpha and NO response to LPS. SCH-23390, an antagonist of dopamine D1 receptors did not alter LPS-induced TNF-alpha production, but inhibited LPS-induced NO production. These results indicate that while the D2 subtype of dopamine receptors is involve in the modulation of both LPS-induced TNF-alpha and NO production, dopamine D1 receptors only regulate the production of NO. Since several drugs possess effect on dopamine D2 receptors, the present observations may be of clinical relevance.

(-)-Deprenyl reduces neuronal apoptosis and facilitates neuronal outgrowth by altering protein synthesis without inhibiting monoamine oxidase

(-)-Deprenyl stereospecifically reduces neuronal death even after neurons have sustained seemingly lethal damage at concentrations too small to cause monoamine oxidase-B (MAO-B) inhibition. (-)-Deprenyl can also influence the process growth of some glial and neuronal populations and can reduce the concentrations of oxidative radicals in damaged cells at concentrations too small to inhibit MAO. In accord with the earlier work of others, we showed that (-)-deprenyl alters the expression of a number mRNAs or proteins in nerve and glial cells and that the alterations in gene expression/protein synthesis are the result of a selective action on transcription. The alterations in gene expression/protein synthesis are accompanied by a decrease in DNA fragmentation characteristic of apoptosis and the death of responsive cells. The onco-proteins Bcl-2 and Bax and the scavenger proteins Cu/Zn superoxide dismutase (SOD1) and Mn superoxide dismutase (SOD2) are among the 40-50 proteins whose synthesis is altered by (-)-deprenyl. Since mitochondrial ATP production depends on mitochondrial membrane potential (MMP) and mitochondrial failure has been shown to be one of the earliest events in apoptosis, we used confocal laser imaging techniques in living cells to show that the transcriptional changes induced by (-)-deprenyl are accompanied by a maintenance of mitochondrial membrane potential, a decrease in intramitochondrial calcium and a decrease in cytoplasmic oxidative radical levels. We therefore propose that (-)-deprenyl acts on gene expression to maintain mitochondrial function and to decrease cytoplasmic oxidative radical levels and thereby to reduce apoptosis. An understanding of the molecular steps by which (-)-deprenyl selectively alters transcription may contribute to the development of new therapies for neurodegenerative diseases.

Molecular mechanisms of microglial activation

Microglial cells are brain macrophages which serve specific functions in the defense of the central nervous system (CNS) against microorganisms, the removal of tissue debris in neurodegenerative diseases or during normal development, and in autoimmune inflammatory disorders of the brain. In cultured microglial cells, several soluble inflammatory mediators such as cytokines and bacterial products like lipopolysaccharide (LPS) were demonstrated to induce a wide range of microglial activities, e.g. increased phagocytosis, chemotaxis, secretion of cytokines, activation of the respiratory burst and induction of nitric oxide synthase. Since heightened microglial activation was shown to play a role in the pathogenesis of experimental inflammatory CNS disorders, understanding the molecular mechanisms of microglial activation may lead to new treatment strategies for neurodegenerative disorders, multiple sclerosis and bacterial or viral infections of the nervous system.