Neurotoxicity, drugs and abuse, and the CuZn-superoxide dismutase transgenic mice

Mitochondrial injury and cognitive function in HIV infection and methamphetamine use

OBJECTIVE

In this work, we evaluated the association of human immunodeficiency virus (HIV) infection and methamphetamine (METH) use with mitochondrial injury in the brain and its implication on neurocognitive impairment.

DESIGN

Mitochondria carry their genome (mtDNA) and play a critical role in cellular processes in the central nervous system. METH is commonly used in HIV-infected populations. HIV infection and METH use can cause damage to mtDNA and lead to neurocognitive morbidity. We evaluated HIV infection and METH use with mitochondrial injury in the brain.

METHODS

We obtained white and gray matter from Brodmann areas 7, 8, 9, 46 of the following: HIV-infected individuals with history of past METH use (HIV+METH+, n = 16), HIV-infected individuals with no history of past METH use (HIV+METH-, n = 11), and HIV-negative controls (HIV-METH-, n = 30). We used the 'common deletion', a 4977 bp mutation, as a measurement of mitochondrial injury, and quantified levels of mtDNA and 'common deletion' by droplet digital PCR, and evaluated in relation to neurocognitive functioning [Global Deficit Score (GDS)].

RESULTS

Levels of mtDNA and mitochondrial injury were highest in white matter of Brodmann area 46. A higher relative proportion of mtDNA carrying the 'common deletion' was associated with lower GDS (P < 0.01) in HIV+METH+ but higher GDS (P < 0.01) in HIV+METH-.

CONCLUSIONS

Increased mitochondrial injury was associated with worse neurocognitive function in HIV+METH- individuals. Among HIV+METH+ individuals, an opposite effect was seen.

Striatal volume increases in active methamphetamine-dependent individuals and correlation with cognitive performance

The effect of methamphetamine (MA) dependence on the structure of the human brain has not been extensively studied, especially in active users. Previous studies reported cortical deficits and striatal gains in grey matter (GM) volume of abstinent MA abusers compared with control participants. This study aimed to investigate structural GM changes in the brains of 17 active MA-dependent participants compared with 20 control participants aged 18-46 years using voxel-based morphometry and region of interest volumetric analysis of structural magnetic resonance imaging data, and whether these changes might be associated with cognitive performance. Significant volume increases were observed in the right and left putamen and left nucleus accumbens of MA-dependent compared to control participants. The volumetric gain in the right putamen remained significant after Bonferroni correction, and was inversely correlated with the number of errors (standardised z-scores) on the Go/No-go task. MA-dependent participants exhibited cortical GM deficits in the left superior frontal and precentral gyri in comparison to control participants, although these findings did not survive correction for multiple comparisons. In conclusion, consistent with findings from previous studies of abstinent users, active chronic MA-dependent participants showed significant striatal enlargement which was associated with improved performance on the Go/No-go, a cognitive task of response inhibition and impulsivity. Striatal enlargement may reflect the involvement of neurotrophic effects, inflammation or microgliosis. However, since it was associated with improved cognitive function, it is likely to reflect a compensatory response to MA-induced neurotoxicity in the striatum, in order to maintain cognitive function. Follow-up studies are recommended to ascertain whether this effect continues to be present following abstinence. Several factors may have contributed to the lack of more substantial cortical and subcortical GM changes amongst MA-dependent participants, including variability in MA exposure variables and difference in abstinence status from previous studies.

Methamphetamine use parameters do not predict neuropsychological impairment in currently abstinent dependent adults

Methamphetamine (meth) abuse is increasingly of public health concern and has been associated with neurocognitive dysfunction. Some previous studies have been hampered by background differences between meth users and comparison subjects, as well as unknown HIV and hepatitis C (HCV) status, which can also affect brain functioning. We compared the neurocognitive functioning of 54 meth dependent (METH+) study participants who had been abstinent for an average of 129 days, to that of 46 demographically comparable control subjects (METH-) with similar level of education and reading ability. All participants were free of HIV and HCV infection. The METH+ group exhibited higher rates of neuropsychological impairment in most areas tested. Among meth users, neuropsychologically normal (n=32) and impaired (n=22) subjects did not differ with respect to self-reported age at first use, total years of use, route of consumption, or length of abstinence. Those with motor impairment had significantly greater meth use in the past year, but impairment in cognitive domains was unrelated to meth exposure. The apparent lack of correspondence between substance use parameters and cognitive impairment suggests the need for further study of individual differences in vulnerability to the neurotoxic effects of methamphetamine.

Long-term neurobiological consequences of ecstasy: a role for pre-existing trait-like differences in brain monoaminergic functioning?

This study investigated whether trait-like differences in brain monoaminergic functioning relate to differential vulnerability for the long-term neurochemical depletion effects of MDMA. Genetically selected aggressive (SAL) and non-aggressive (LAL) house-mice differing in baseline serotonergic and dopaminergic neurotransmission were administered MDMA. An acute binge-like MDMA injection protocol (three times, using either of the dosages of 0, 5, 10 and 20mg/kg i.p. with 3h interval) was employed. Three and 28 days after treatment with MDMA induced a dose-dependent depletion of striatal dopamine and its metabolites that did not differ between SAL and LAL mice. Similarly, the dose-dependent MDMA-induced serotonergic depletion did not differ between lines 3 days after treatment. Interestingly, 28 days after MDMA in LAL mice, 5-HT and 5-HIAA levels were still significantly depleted after treatment with 3x10 mg/kg, while in SAL mice 5-HT depletion was only seen after the highest dosage. Surprisingly, LAL mice did not show any long-term 5-HT depletion after treatment with the highest dose. In conclusion, only LAL mice are able to restore initial severe loss of MDMA-evoked 5-HT and 5-HIAA levels. SAL and LAL mice are differentially susceptible for the long-term but not short-term MDMA-induced serotonergic depletion in the striatum. The differentiation between both lines in the long-term striatal serotonergic response to MDMA seems to depend on the capacity of the brain to adapt to the short-term depletion of monoaminergic levels and may somehow be related to individual, trait-like characteristics of brain monoaminergic systems.

Pathways of methamphetamine toxicity

Methamphetamine (METH) is a drug of abuse which is neurotoxic for the nigrostriatal system. METH-induced neurodegeneration involves production of reactive oxygen species, triggering autophagic vacuoles within nigral neurons of chronic abusers of METH. In fact, Cu,Zn-superoxide dismutase 1 (SOD1) is a critical protein for the neurotoxic effects of METH on DA neurons. Moreover, mutations in the SOD1 gene cause amyotrophic lateral sclerosis, a dramatic neurodegenerative disorder. In the present paper we demonstrate that in G93A transgenic mice, overexpressing the ALS-linked mutant form of SOD1, surviving motor neurons share common intracellular alterations with METH-exposed DA neurons. We hypothesize that in mutant SOD1 transgenic mice, a defective autophagy might be responsible for the neurotoxic effects seen with in nigral neurons during METH toxicity.

Gene expression profiling of MPP+-treated MN9D cells: A mechanism of toxicity study

Parkinson's disease (PD) is a common neurodegenerative disease characterized by progressive loss of midbrain dopaminergic neurons with unknown etiology. MPP+ (1-methyl-4-phenylpyridinium) is the active metabolite of the neurotoxin 1-methyl-4-phenyl-1,2,3,6-tetrahydropyridine (MPTP), which induces Parkinson's-like syndromes in humans and animals. MPTP/MPP+ treatment produces selective dopaminergic neuronal degeneration, therefore, these agents are commonly used to study the pathogenesis of PD. However, the mechanisms of their toxicity have not been elucidated. In order to gain insights into MPP+-induced neurotoxicity, a gene expression microarray study was performed using a midbrain-derived dopaminergic neuronal cell line, MN9D. Utilizing a two-color reference design, Agilent mouse oligonucleotide microarrays were used to examine relative gene expression changes in MN9D cells treated with 40microM MPP+ compared with controls. Bioinformatics tools were used for data evaluation. Briefly, raw data were imported into the NCTR ArrayTrack database, normalized using a Lowess method and data quality was assessed. The Student's t-test was used to determine significant changes in gene expression (set as p<0.05, fold change >1.5). Gene Ontology for Function Analysis (GOFFA) and Ingenuity Pathway Analysis were employed to analyze the functions and roles of significant genes in biological processes. Of the 51 significant genes identified, 44 were present in the GOFFA or Ingenuity database. These data indicate that multiple pathways are involved in the underlying mechanisms of MPP+-induced neurotoxicity, including apoptosis, oxidative stress, iron binding, cellular metabolism, and signal transduction. These data also indicate that MPP+-induced toxicity shares common molecular mechanisms with the pathogenesis of PD and further pathway analyses will be conducted to explore these mechanisms.

L-carnitine protects neurons from 1-methyl-4-phenylpyridinium-induced neuronal apoptosis in rat forebrain culture

1-Methyl-4-phenylpyridinium ion (MPP+), an inhibitor of mitochondrial complex I, has been widely used as a neurotoxin because it elicits a severe Parkinson's disease-like syndrome with an elevation of intracellular reactive oxygen species (ROS) and apoptosis. L-carnitine plays an integral role in attenuating the brain injury associated with mitochondrial neurodegenerative disorders. The present study investigates the effects of L-carnitine against the toxicity of MPP+ in rat forebrain primary cultures. Cells in culture were treated for 24 h with 100, 250, 500 and 1000 microM MPP+ alone or co-incubated with L-carnitine. MPP+ produced a dose-related increase in DNA fragmentation as measured by cell death ELISA (enzyme-linked immunosorbent assay), an increase in the number of TUNEL (terminal dUTP nick-end labeling)-positive cells and a reduction in the mitochondrial metabolism of 3-(4,5-dimethylthiazol-2-yl)-2,5-diphenyltetrazolium bromide (MTT). No significant effect was observed with the release of lactate dehydrogenase (LDH), indicating that cell death presumably occurred via apoptotic mechanisms. Co-incubation of MPP+ with L-carnitine significantly reduced MPP+-induced apoptosis. Western blot analyses showed that neurotoxic concentrations of MPP+ decreased the ratio of BCL-X(L) to Bax and decreased the protein levels of polysialic acid neural cell adhesion molecules (PSA-NCAM), a neuron specific marker. L-carnitine blocked these effects of MPP+ suggesting its potential therapeutic utility in degenerative disorders such as Parkinson's disease, Alzheimer's disease, ornithine transcarbamylase deficiency and other mitochondrial diseases.

Free radical production induced by methamphetamine in rat striatal synaptosomes

The pro-oxidative effect of methamphetamine (METH) in dopamine terminals was studied in rat striatal synaptosomes. Flow cytometry analysis showed increased production of reactive oxygen species (ROS) in METH-treated synaptosomes, without reduction in the density of dopamine transporters. In synaptosomes from dopamine (DA)-depleted animals, METH did not induce ROS production. Reserpine, in vitro, completely inhibited METH-induced ROS production. These results point to endogenous DA as the main source of ROS induced by METH. Antioxidants and inhibitors of neuronal nitric oxide synthase and protein kinase C (PKC) prevented the METH-induced oxidative effect. EGTA and the specific antagonist methyllycaconitine (MLA, 50 microM) prevented METH-induced ROS production, thus implicating calcium and alpha7 nicotinic receptors in such effect. Higher concentrations of MLA (>100 microM) showed nonspecific antioxidant effect. Preincubation of synaptosomes with METH (1 microM) for 30 min reduced [(3)H]DA uptake by 0%. The METH effect was attenuated by MLA and EGTA and potentiated by nicotine, indicating that activation of alpha(7) nicotinic receptors and Ca(2+) entry are necessary and take place before DAT inhibition. From these findings, it can be postulated that, in our model, METH induces DA release from synaptic vesicles to the cytosol. Simultaneously, METH activates alpha(7) nicotinic receptors, probably inducing depolarization and an increase in intrasynaptosomal Ca(2+). This would lead to DAT inhibition and NOS and PKC activation, initiating oxidation of cytosolic DA.

Cocaine pharmacology and current pharmacotherapies for its abuse

Cocaine abuse continues to be prevalent and effective therapies for cocaine craving and addiction remain elusive. In the last decade immunopharmacotherapy has been proposed as a promising means to alleviate this illness. By using the organism's natural immune response, an anti-cocaine vaccine promotes the production of cocaine-specific antibodies that sequester the drug before their passage into the brain, where it exerts its reinforcing and thus addictive effects. A series of studies demonstrating the cocaine-blocking properties of various immunogenic conjugates will be reviewed in the context of the neuropsychopharmacological profile of the drug.

Brain-derived neurotrophic factor rescues neuronal death induced by methamphetamine

BACKGROUND

Methamphetamine (MA) induces degeneration of various regions of the brain, resulting in neuropsychiatric damage. Although the underlying mechanisms of MA-induced neurotoxicity have been studied, there are few reports to date regarding the factor(s) that can effectively prevent MA-induced neurotoxicity. Because brain-derived neurotrophic factor (BDNF) has been known to prevent many kinds of neuronal cell death, we investigated whether BDNF inhibits MA-induced neuronal death.

METHODS

Using primary cortical neurons, we examined the effect of BDNF on MA-induced neuronal death. In addition, using pharmacologic and molecular biological tools, we elucidated which pathways are involved in this effect.

RESULTS

Brain-derived neurotrophic factor dose-dependently blocked MA-induced neuronal death, and this effect was inhibited by phosphatidylinositol-3-kinase inhibitors. In addition, overexpression of activated Akt protects neurons against MA. Furthermore, expression of kinase-defective Akt blocked the effect of BDNF on MA-induced neuronal death.

CONCLUSIONS

Brain-derived neurotrophic factor effectively blocks MA-induced neuronal death, and Akt activation is necessary and sufficient for this effect.

Mice with partial deficiency of c-Jun show attenuation of methamphetamine-induced neuronal apoptosis

The regional distribution of c-Jun expression and of the number of apoptotic cells was compared in various brain areas after methamphetamine administration to mice. Our results showed that there was methamphetamine-induced overexpression of c-Jun in the cortex and striatum but not in the cerebellar cortex. There was an almost totally similar regional appearance of methamphetamine-induced apoptotic cells in the mouse brain; no apoptosis was present in the cerebellum. Additionally, in the neocortical area, more positive signals for c-Jun immunoreactivity were observed in the piriform cortex, an area that also showed more positive terminal deoxynucleotidyl transferase-mediated dUTP nick-end labeling (TUNEL) signals than the frontal and parietal cortices. These observations suggested that c-Jun might be involved in methamphetamine-induced apoptosis. This idea was confirmed by using heterozygous c-Jun knockout mice that showed much less apoptosis than wild-type controls. In addition, we found that the majority of TUNEL-positive cells were also positive for c-Jun-like immunoreactivity in both genotypes. Moreover, methamphetamine-induced caspase-3 activity and PARP cleavage were also reduced in c-Jun heterozygous knockout mice. In contrast, methamphetamine-induced hyperthermia was essentially identical in the two genotypes. When taken together, our data support the hypothesis that c-Jun is involved in methamphetamine-induced apoptosis.

Methamphetamine-induced dopaminergic neurotoxicity and production of peroxynitrite are potentiated in nerve growth factor differentiated pheochromocytoma 12 cells

Methamphetamine (METH) is a widely abused psychomotor stimulant known to cause dopaminergic neurotoxicity in rodents, nonhuman primates, and humans. METH administration selectively damages the dopaminergic nerve terminals, which is hypothesized to be due to release of dopamine from synaptic vesicles within the terminals. This process is believed to be mediated by the production of free radicals. The current study evaluates METH-induced dopaminergic toxicity in pheochromocytoma 12 (PC12) cells cultured in the presence or absence of nerve growth factor (NGF). Dopaminergic changes and the formation of 3-nitrotyrosine (3-NT), a marker for peroxynitrite production, were studied in PC12 cell cultures grown in the presence or absence of NGF after different doses of METH (100-1,000 microM). METH exposure did not cause significant alterations in cell viability and did not produce significant dopaminergic changes or 3-NT production in PC12 cells grown in NGF-negative media after 24 hours. However, cell viability of PC12 cells grown in NGF-positive media was decreased by 45%, and significant dose-dependent dopaminergic alteration and 3-NT production were observed 24 hours after exposure to METH. The current study supports the hypothesis that METH acts at the dopaminergic nerve terminals and produces dopaminergic damage by the production of free radical peroxynitrite.

Methamphetamine-induced dopaminergic neurotoxicity: role of peroxynitrite and neuroprotective role of antioxidants and peroxynitrite decomposition catalysts

Oxidative stress, reactive oxygen (ROS), and nitrogen (RNS) species have been known to be involved in a multitude of neurodegenerative disorders such as Parkinson's disease (PD), Alzheimer's disease (AD), and amyotrophic lateral sclerosis (ALS). Both ROS and RNS have very short half-lives, thereby making their identification very difficult as a specific cause of neurodegeneration. Recently, we have developed a high performance liquid chromatography/electrochemical detection (HPLC/EC) method to identify 3-nitrotyrosine (3-NT), an in vitro and in vivo biomarker of peroxynitrite production, in cell cultures and brain to evaluate if an agent-driven neurotoxicity is produced by the generation of peroxynitrite. We show that a single or multiple injections of methamphetamine (METH) produced a significant increase in the formation of 3-NT in the striatum. This formation of 3-NT correlated with the striatal dopamine depletion caused by METH administration. We also show that PC12 cells treated with METH has significantly increased formation of 3-NT and dopamine depletion. Furthermore, we report that pretreatment with antioxidants such as selenium and melatonin can completely protect against the formation of 3-NT and depletion of striatal dopamine. We also report that pretreatment with peroxynitrite decomposition catalysts such as 5, 10,15,20-tetrakis(N-methyl-4'-pyridyl)porphyrinato iron III (FeTMPyP) and 5, 10, 15, 20-tetrakis (2,4,6-trimethyl-3,5-sulfonatophenyl) porphinato iron III (FETPPS) significantly protect against METH-induced 3-NT formation and striatal dopamine depletion. We used two different approaches, pharmacological manipulation and transgenic animal models, in order to further investigate the role of peroxynitrite. We show that a selective neuronal nitric oxide synthase (nNOS) inhibitor, 7-nitroindazole (7-NI), significantly protect against the formation of 3-NT as well as striatal dopamine depletion. Similar results were observed with nNOS knockout and copper zinc superoxide dismutase (CuZnSOD)-overexpressed transgenic mice models. Finally, using the protein data bank crystal structure of tyrosine hydroxylase, we postulate the possible nitration of specific tyrosine moiety in the enzyme that can be responsible for dopaminergic neurotoxicity. Together, these data clearly support the hypothesis that the reactive nitrogen species, peroxynitrite, plays a major role in METH-induced dopaminergic neurotoxicity and that selective antioxidants and peroxynitrite decomposition catalysts can protect against METH-induced neurotoxicity. These antioxidants and decomposition catalysts may have therapeutic potential in the treatment of psychostimulant addictions.

Peroxynitrite plays a role in methamphetamine-induced dopaminergic neurotoxicity: evidence from mice lacking neuronal nitric oxide synthase gene or overexpressing copper-zinc superoxide dismutase

The use of methamphetamine (METH) leads to neurotoxic effects in mammals. These neurotoxic effects appear to be related to the production of free radicals. To assess the role of peroxynitrite in METH-induced dopaminergic, we investigated the production of 3-nitrotyrosine (3-NT) in the mouse striatum. The levels of 3-NT increased in the striatum of wild-type mice treated with multiple doses of METH (4 x 10 mg/kg, 2 h interval) as compared with the controls. However, no significant production of 3-NT was observed either in the striata of neuronal nitric oxide synthase knockout mice (nNOS -/-) or copper-zinc superoxide dismutase overexpressed transgenic mice (SOD-Tg) treated with similar doses of METH. The dopaminergic damage induced by METH treatment was also attenuated in nNOS-/- or SOD-Tg mice. These data further confirm that METH causes its neurotoxic effects via the production of peroxynitrite.

Prevention of dopaminergic neurotoxicity by targeting nitric oxide and peroxynitrite: implications for the prevention of methamphetamine-induced neurotoxic damage

Methamphetamine (METH) is a neurotoxic psychostimulant that produces catecholaminergic brain damage by producing oxidative stress and free radical generation. The role of oxygen and nitrogen radicals is well documented as a cause of METH-induced neurotoxic damage. In this study, we have obtained evidence that METH-induced neurotoxicity is the resultant of interaction between oxygen and nitrogen radicals, and it is mediated by the production of peroxynitrite. We have also assessed the effects of inhibitors of neuronal nitric oxide synthase (nNOS) as well as scavenger of nitric oxide and a peroxynitrite decomposition catalyst. Significant protective effects were observed with the inhibitor of nNOS, 7-nitroindazole (7-NI), as well as by the selective peroxynitrite scavenger or decomposition catalyst, 5,10,15,20-tetrakis(2,4,6-trimethyl-3,5-sulfonatophenyl)porphyrinato iron III (FeTPPS). However, the use of a nitric oxide scavenger, 2-phenyl-4,4,5,5-tetramethylimidazoline-1-oxyl-3-oxide (c-PTIO), did not provide any significant protection against METH-induced hyperthermia or peroxynitrite generation and the resulting dopaminergic neurotoxicity. In particular, treatment with FeTPPS completely prevented METH-induced hyperthermia, peroxynitrite production, and METH-induced dopaminergic depletion. Together, these data demonstrate that METH-induced dopaminergic neurotoxicity is mediated by the generation of peroxynitrite, which can be selectively protected by nNOS inhibitors or peroxynitrite scavenger or decomposition catalysts.

Molecular footprints of neurotoxic amphetamine action

Methamphetamine (METH) and 3,4-methylenedioxymethamphetamine (MDMA or Ecstasy) are amphetamine analogs with high abuse potential. These drugs also cause damage to dopamine and serotonin nerve terminals in vivo. The mechanisms by which these drugs cause neurotoxicity are not known, but a great deal of attention has been focused on reactive oxygen species (ROS) and reactive nitrogen species (RNS) as mediators of this toxicity. ROS and RNS have very short biological half-lives in vivo, and it is virtually impossible to measure them in brain directly. However, ROS and RNS are also characterized by their extreme reactivity with proteins and nucleotides. Tryptophan hydroxylase (TPH) and tyrosine hydroxylase (TH), the initial and rate limiting enzymes in the synthesis of serotonin and dopamine, respectively, are identified targets for the actions of METH and MDMA. Using recombinant forms of these proteins, we have found that nitric oxide, catechol-quinones, and peroxynitrite, all of which are potentially produced by the neurotoxic amphetamines, covalently modify both TPH and TH. The ROS and RNS cause reductions in catalytic function of these enzymes in a manner that is consistent with the effects of METH and MDMNA in vivo. Protein-bound ROS or RNS may serve as molecular footprints of neurotoxic amphetamine action.

Role of peroxynitrite in methamphetamine-induced dopaminergic neurotoxicity and sensitization in mice

Abstract Methamphetamine (METH)-induced dopaminergic neurotoxicity is thought to be associated with the generation of reactive oxygen species (ROS) and reactive nitrogen species (RNS). Recently, we have reported that copper/zinc(CuZn)-superoxide dismutase transgenic mice are resistant to METH-induced neurotoxicity. In the present study, we examined the role of the neuronal nitric oxide synthase (nNOS), susceptibility of nNOS knockout (KO) mice and sensitization to psychostimulants after neurotoxic doses of METH. Male SwissWebster mice were treated with or without 7-nitroindazole (7-NI) along with METH (5 mg/kg,ip,q 3h x 3) and were sacrificed 72 h after the last METH injection. Dopamine (DA) and dopamine transporter (DAT) binding sites were determined in striatum from saline and METH-treated animals. 7-NI completely protected against the depletion of DA, and DAT in striatum. In follow-up experiments nNOS KO mice along with appropriate control (C57BL/6N, SV129 and B6JSV129) mice were treated with METH (5 mg/kg,ip, q 3h x 3) and were sacrificed 72 h after dosing. This schedule of METH administrations resulted in only 10-20% decrease in tissue content of DA and no apparent change in the number of DAT binding sites in nNOS KO mice. However, this regime of METH resulted in a significant decrease in the content of DA as well as DAT binding sites in the wild-type animals. Pre-exposure to single or multiple doses of METH resulted in a marked locomotion sensitization in response to METH. However, the nNOS KO mice show no sensitization in response to METH after single or multiple injections of METH. Therefore, these studies strongly suggest the role of peroxynitrite, nNOS and DA system in METH-induced neurotoxicity and behavioral sensitization.

A new nitroxyl-probe with high retention in the brain and its application for brain imaging

In order to estimate free radical reactions and image them in the brain of living animals, a nitroxyl spin-probe, carboxy-PROXYL acetoxymethyl ester (CxP-AM) was newly synthesized. CxP-AM was designed to be hydrolyzed by esterase, but not by lipase, so that it would pass through the blood-brain barrier and be retained in the cytosolic phase of parenchymal cells in the brain after intravenous injection. The pharmacokinetics of CxP-AM was compared with those of carboxy-PROXYL (CxP) and its methyl ester (CxP-M). Carboxyl esterase almost completely hydrolyzed CxP-AM within 3 min. After intravenous injection, the brain retained 1.8 times more CxP-AM than CxP-M, and retained it for more than 30 min. Electron spin resonance computed tomographic (ESR-CT) imaging of CxP-AM in the heads of mice produced marked contrast in the encephalon region, while CxP was distributed only in the extracranial region and CxP-M was distributed in both regions, confirming the pharmacokinetics of CxP-AM. The decay rate of CxP-AM determined with time-resolved ESR-CT imaging was different in the two brain regions, suggesting regional differences in the total reducing capability. CxP-AM should become a powerful probe for the investigation and diagnosis of free radical reactions and their imaging in the brain.

Methamphetamine generates peroxynitrite and produces dopaminergic neurotoxicity in mice: protective effects of peroxynitrite decomposition catalyst

Methamphetamine (METH)-induced dopaminergic neurotoxicity is believed to be produced by oxidative stress and free radical generation. The present study was undertaken to investigate if METH generates peroxynitrite and produces dopaminergic neurotoxicity. We also investigated if this generation of peroxynitrite can be blocked by a selective peroxynitrite decomposition catalyst, 5, 10,15, 20-tetrakis(N-methyl-4'-pyridyl)porphyrinato iron III (FeTMPyP) and protect against METH-induced dopaminergic neurotoxicity. Administration of METH resulted in the significant formation of 3-nitrotyrosine (3-NT), an in vivo marker of peroxynitrite generation, in the striatum and also caused a significant increase in the body temperature. METH injection also caused a significant decrease in the concentration of dopamine (DA), 3, 4-dihydroxyphenylacetic acid (DOPAC), and homovanillic acid (HVA) by 76%, 53% and 40%, respectively, in the striatum compared with the control group. Treatment with FeTMPyP blocked the formation of 3-NT by 66% when compared with the METH group. FeTMPyP treatment also provided significant protection against the METH-induced hyperthermia and depletion of DA, DOPAC and HVA. Administration of FeTMPyP alone neither resulted in 3-NT formation nor had any significant effect on DA or its metabolite concentrations. These findings indicate that peroxynitrite plays a role in METH-induced dopaminergic neurotoxicity and also suggests that peroxynitrite decomposition catalysts may be beneficial for the management of psychostimulant abuse.

Selenium, an antioxidant, protects against methamphetamine-induced dopaminergic neurotoxicity

Dopaminergic changes were studied in the caudate nucleus of adult female mice after pre- and post-treatment with an antioxidant, selenium, 72 h after the multiple injections of methamphetamine (METH, 4x10 mg/kg, i.p. at 2-h interval) or an equivalent volume of saline. Selenium treatment prevented the depletion of dopamine (DA) and its metabolites 3,4-dihydroxyphenylacetic acid (DOPAC) and homovanillic acid (HVA) in caudate nucleus resulting from the METH treatment. These data suggest that METH-induced neurotoxicity is mediated by free radical and selenium plays a protective role against METH-induced dopaminergic neurotoxicity.

Elevation of antioxidant potency in the brain of mice by low-dose gamma-ray irradiation and its effect on 1-methyl-4-phenyl-1,2,3,6-tetrahydropyridine (MPTP)-induced brain damage

The elevation of endogenous thiol-related antioxidants and free radical scavenging enzymes in the brain of C57BL/6 female mice after low-dose gamma-ray irradiation and its inhibitory effect on 1-methyl-4-phenyl-1,2,3,6-tetrahydropyridine (MPTP)-induced brain damage were investigated. The brain level of the reduced form of glutathione (GSH) increased soon after irradiation with 50 cGy of gamma-rays, reached a maximum at 3 h post-treatment, and remained elevated until 12 h. Thioredoxin (TRX) was also transiently increased after irradiation. The activities of free radical scavenging enzymes, including Cu/Zn-superoxide dismutase, catalase and glutathione peroxidase, were significantly induced after irradiation as well. Cerebral malondialdehyde was remarkably elevated by MPTP treatment, and this elevation was suppressed by pre-irradiation (50 cGy). The contents of GSH and TRX were significantly decreased by MPTP treatment in comparison with those of the control group. These reductions both seemed to be attenuated by pre-irradiation with gamma-rays. These results suggest that low-dose gamma-ray irradiation induces endogenous antioxidative potency in the brain of mice and might be effective for the prevention and/or therapy of various reactive oxygen species-related neurodegenerative disorders, such as Parkinson's disease and Alzheimer's disease.

Reduced levels of catalase activity potentiate MPP+-induced toxicity: comparison between MN9D cells and CHO cells

1-Methyl-4-phenyl-1,2,3,6-tetrahydropyridine (MPTP) has been shown to be toxic by inducing oxygen free radicals in the mammalian nervous system, especially in the nigrostriatal dopaminergic system. The present study was designed to compare the toxic effects of MPP+, the active metabolite of MPTP, in MN9D neuronal cells that exhibit relatively low levels of catalase activity, as compared to CHO cells, which exhibit high levels of catalase activity. The survival of the MN9D cells in the presence of 250 microM MPP+ was less than 10%, whereas CHO cells exhibited 70% survival at the same concentration of MPP+. The ED50 values of MPP+ in MN9D and CHO cell lines were 60-600 microM, respectively. MN9D cells contain less catalase, an enzyme believed to be involved in the detoxification of free radicals compared to CHO cells. The catalase activity was 2 Units/mg protein in MN9D cells and 30 U/mg protein in CHO cells. The catalase activity in CHO cells increased with increasing MPP+ concentrations from 100-500 microM, however, it decreased at 1 mM MPP+. In contrast, catalase activity in MN9D remained the same at all MPP+ concentrations. When the CHO cells were pre-treated with 10-25 mM 3-aminotriazole (3-AT), which inhibits catalase activity, and exposed to MPP+ at various concentrations, they became susceptible to MPP+. It is evident from these data that the differential susceptibility to MPP+ in these two cell lines are due to differences in catalase activity. In addition, the inhibition of constituentive catalase activity in CHO cells by 3-AT treatment enhances their susceptibility. In conclusion, the study demonstrates that catalase activity represents an important defence mechanism in MPTP-induced toxicity.

Effect of acute exposure to 3-nitropropionic acid on activities of endogenous antioxidants in the rat brain

The response of endogenous antioxidants to acute exposure of the mitochondrial inhibitor, 3-nitropropionic acid (3-NPA), was investigated in selected rat brain regions. Rats treated with 3-NPA (30 mg/kg, s.c.) were sacrificed at 30, 60, 90 and 120 min after injection to examine the alterations in reduced glutathione levels (GSH), and activities of antioxidant enzymes, superoxide dismutase (SOD), glutathione peroxidase (GPx), and catalase (CAT) in the hippocampus (HIP), frontal cortex (FC), and caudate nucleus (CN). CAT activity increased in the HIP 90 min after 3-NPA treatment. While cytosolic copper/zinc SOD (CuZn-SOD) and mitochondrial manganese SOD (Mn-SOD) levels increased in the FC at 120 min, only the Mn-SOD increased in the CN 90 min after treatment. The activity of GPx decreased in the HIP 120 min after 3-NPA injection. When compared with the control, administration of 3-NPA led to GSH depletion in HIP within 120 min. The depletion of GSH and induction of antioxidant enzyme activities after the 3-NPA exposure suggest conditions favorable for oxidative stress.

Effect of 1-methyl-4-phenylpyridinium (MPP+) on mitochondrial membrane potential in cerebellar neurons: interaction with the NMDA receptor

The effect of MPP+, a dopaminergic neurotoxin, in mitochondrial membrane potential was investigated in dissociated cerebellar granule cells using rhodamine 123 and flow cytometry. MPP+ (1 mM) decreased the mitochondrial membrane potential by 30%. Antagonists of the NMDA receptor complex, such as MK-801 (IC50 value of 20.92 +/- 0.02 nM), 5,7-dichlorokynurenic acid (IC50 value of 6.46 +/- 1.06 microM) and D-AP5 (IC50 value of 8.29 +/- 0.63 microM), inhibited the action of MPP+. Neither NBQX, nor riluzole, nor desipramine modified the action of MPP+. Dibucaine restored the basal values of mitochondrial membrane potential altered by MPP+. Since, in the presence of NMDA, MPP+ antagonized the effect of this total agonist, it can be concluded that, in this preparation, MPP+ interacts with the NMDA receptor complex as a partial agonist. This interaction could be the result of an allosteric modulation of the NMDA receptor complex by MPP+. The decrease of mitochondrial membrane potential induced by MPP+ is antagonized by dibucaine, suggesting that this effect is mediated by an activation of phospholipase A2.

Elevated expression of glutathione peroxidase in PC12 cells results in protection against methamphetamine but not MPTP toxicity

In vivo administration of either 1-methyl-4-phenyl-1,2,3,6-tetrahydropyridine (MPTP) or methamphetamine (MA) produces damage to the dopaminergic nervous system which may be due in part to the generation of reactive oxygen species (ROS). The resistance of superoxide dismutase (SOD) over-expressing transgenic mice to the effects of both MPTP and MA suggests the involvement of superoxide in the resulting neurotoxicity of both compounds. Superoxide can be converted by SOD to hydrogen peroxide, which itself can cause cellular degeneration by reacting with free iron to produce highly reactive hydroxyl radicals resulting in damage to proteins, nucleic acids and membrane phospholipids. Hydrogen peroxide has also been reported to be produced via inhibition of NADH dehydrogenase by MPP + formed during oxidation of MPTP by MAO-B and by dopamine auto-oxidation following MA-induced dopamine release from synaptic vesicles within nerve terminals. To test whether hydrogen peroxide is an important factor in the toxicity of either of these two neurotoxins, we created clonal PC12 lines expressing elevated levels of the hydrogen peroxide-reducing enzyme glutathione peroxidase (GSHPx). Elevation of GSHPx levels in PC12 was found to diminish the rise in ROS levels and lipid peroxidation resulting from MA but not MPTP treatment. Elevated levels of GSHPx also appeared to prevent decreases in transport-mediated dopamine uptake produced via MA administration as well as to attenuate toxin-induced cell loss as measured by either MTT reduction or LDH release. Our data, therefore, suggest that hydrogen peroxide production likely contributes to MA toxicity in dopaminergic neurons.

Methamphetamine-induced dopaminergic toxicity in mice. Role of environmental temperature and pharmacological agents

1. Multiple injections of METH (4 x 10 mg/kg, i.p.) at room temperature (23 degrees C) produced a significant depletion of dopamine (DA) and its metabolites DOPAC and HVA in striatum at 24 and 72 hr, and 1 and 2 wk. 2. Three days post 4 x 10 mg/kg METH at 23 degrees C, an 80% decrease in striatal dopamine (DA) occurred, while the same dose at 4 degrees C produced only a 20% DA decrease, and 4 x 20 mg/kg METH at 4 degrees C produced a 54% DA decrease. A similar pattern in the decreases of the DA metabolites DOPAC and HVA was observed after METH administration. 3. At 23 degrees C (+)MK-801 completely blocked while phenobarbital (40% decrease) and diazepam (65% decrease) partially blocked decreases in striatal DA produced by 4 x 10 mg/kg METH. Decreases in DOPAC and HVA were similar to the decreases in DA after METH and antagonists. 4. Multiple injections of METH (4 x 10 mg/kg, i.p.) at room temperature also produced a significant depletion of serotonin (5-HT) in striatum at 24 and 72 hr, and 1 and 2 wk. The depletion of 5-HT metabolite 5-HIAA was found only at 72 hr post-dosing. 5. This depletion of 5-HT and its metabolite 5-HIAA at room temperature was blocked either by changing the environmental temperature to 4 degrees C, or by pretreatment with MK-801, diazepam and phenobarbital after METH treatment. 6. Therefore, these data suggest that drugs that block METH toxicity, such as haloperidol (D2 receptors), pentobarbital and phenobarbital (chloride channels) and MK-801 (NMDA/glutamate receptors), do not necessarily have the same mechanism of action but may either induce hypothermia or block induction of hyperthermia. 7. In summary, these studies show that in the mouse, environmental temperature greatly influences METH neurotoxicity, and that the protective effects of compounds such as diazepam, phenobarbital and MK-801 may be mediated by blockade of METH-induced hyperthermia.