Depletion of copper and manganese in brain after MPTP treatment of mice

Combined chronic copper exposure and aging lead to neurotoxicity in vivo

The environment, containing pollutants, toxins, and transition metals (copper, iron, manganese, and zinc), plays a critical role in neurodegenerative disease development. Copper occupational exposure increases Parkinson's disease (PD) risk. Previously, we determined the mechanisms by which copper induces dopaminergic cell death in vitro. The copper transporter protein 1 (Ctr1) overexpression led to intracellular glutathione depletion potentiating caspase-3 mediated cell death; oxidative stress was primarily cytosolic, and Nrf2 was upregulated mediating an antioxidant response; and protein ubiquitination, AMPK-Ulk1 signaling, p62, and Atg5-dependent autophagy were increased as a protective mechanism. However, the effect of chronic copper exposure on the neurodegenerative process has not been explored in vivo. We aimed to elucidate whether prolonged copper treatment reproduces PD features and mechanisms during aging. Throughout 40 weeks, C57BL/6J male mice were treated with copper at 0, 100, 250, and 500 ppm in the drinking water. Chronic copper exposure altered motor function and induced dopaminergic neuronal loss, astrocytosis, and microgliosis in a dose-dependent manner. α-Synuclein accumulation and aggregation were increased in response to copper, and the proteasome and autophagy alterations, previously observed in vitro, were confirmed in vivo, where protein ubiquitination, AMPK phosphorylation, and the autophagy marker LC3-II were also increased by copper exposure. Finally, nitrosative stress was induced by copper in a concentration-dependent fashion, as evidenced by increased protein nitration. To our knowledge, this is the first study combining chronic copper exposure and aging, which may represent an in vivo model of non-genetic PD and help to assess potential prophylactic and therapeutic approaches. DATA AVAILABILITY: The data underlying this article are available in the article.

Unscrambling the Role of Redox-Active Biometals in Dopaminergic Neuronal Death and Promising Metal Chelation-Based Therapy for Parkinson's Disease

Biometals are all metal ions that are essential for all living organisms. About 40% of all enzymes with known structures require biometals to function correctly. The main target of damage by biometals is the central nervous system (CNS). Biometal dysregulation (metal deficiency or overload) is related to pathological processes. Chronic occupational and environmental exposure to biometals, including iron and copper, is related to an increased risk of developing Parkinson's disease (PD). Indeed, biometals have been shown to induce a dopaminergic neuronal loss in the substantia nigra. Although the etiology of PD is still unknown, oxidative stress dysregulation, mitochondrial dysfunction, and inhibition of both the ubiquitin-proteasome system (UPS) and autophagy are related to dopaminergic neuronal death. Herein, we addressed the involvement of redox-active biometals, iron, and copper, as oxidative stress and neuronal death inducers, as well as the current metal chelation-based therapy in PD.

Copper biodistribution after acute systemic administration of copper gluconate to rats

Neurodegenerative disorders have been linked to the decrease of copper concentrations in different regions of the brain. Therefore, intake of micronutrient supplements could be a therapeutic alternative. Since the copper distribution profile has not been elucidated yet, the aim of this study was to characterize and to analyze the concentration profile of a single administration of copper gluconate to rats by two routes of administration. Male Wistar rats were divided into three groups. The control group received vehicle (n = 5), and the experimental groups received 79.5 mg/kg of copper orally (n = 4-6) or 0.64 mg/kg of copper intravenously. (n = 3-4). Blood, striatum, midbrain and liver samples were collected at different times. Copper concentrations were assessed using atomic absorption spectrophotometry. Copper concentration in samples from the control group were considered as baseline. The highest copper concentration in plasma was observed at 1.5 h after oral administration, while copper was quickly compartmentalized within the first hour after intravenous administration. The striatum evidenced a maximum metal concentration at 0.25 h for both routes of administration, however, the midbrain did not show any change. The highest concentration of the metal was held by the liver. The use of copper salts as replacement therapy should consider its rapid and discrete accumulation into the brain and the rapid and massive distribution of the metal into the liver for both oral and intravenous routes. Development of controlled-release pharmaceutical formulations may overcome the problems that the liver accumulation may imply, particularly, for hepatic copper toxicity.

Copper Ions and Parkinson's Disease: Why Is Homeostasis So Relevant?

The involvement of copper in numerous physiological processes makes this metal ion essential for human life. Alterations in copper homeostasis might have deleterious consequences, and several neurodegenerative disorders, including Parkinson’s disease (PD), have been associated with impaired copper levels. In the present review, we describe the molecular mechanisms through which copper can exert its toxicity, by considering how it can interfere with other cellular processes known to play a role in PD, such as dopamine metabolism, oxidative stress, and α-synuclein aggregation. The recent experimental evidence that associates copper deficiency and the formation of superoxide dismutase 1 (SOD1) aggregates with the progression of PD is also discussed together with its therapeutic implication. Overall, the recent discoveries described in this review show how either copper deficiency or excessive levels can promote detrimental effects, highlighting the importance of preserving copper homeostasis and opening unexplored therapeutic avenues in the definition of novel disease-modifying drugs.

Nexus between mitochondrial function, iron, copper and glutathione in Parkinson's disease

Parkinson's disease is neuropathologically characterised by loss of catecholamine neurons in vulnerable brain regions including substantia nigra pars compacta and locus coeruleus. This review discusses how the susceptibility of these regions is defined by their shared biochemical characteristics that differentiate them from other neurons. Parkinson's disease is biochemically characterised by mitochondrial dysfunction, accumulation of iron, diminished copper content and depleted glutathione levels in these regions. This review also discusses this neuropathology, and provides evidence for how these pathological features are mechanistically linked to each other. This leads to the conclusion that disruption of mitochondrial function, or iron, copper or glutathione metabolism in isolation provokes the pathological impairment of them all. This creates a vicious cycle that drives pathology leading to mitochondrial failure and neuronal cell death in vulnerable brain regions.

Copper sulfate pretreatment prevents mitochondrial electron transport chain damage and apoptosis against MPP+-induced neurotoxicity

Intrastriatal injection of 1-methyl-4-phenylpyridinium (MPP⁺) is considered a model to reproduce some biochemical alterations observed in Parkinson's disease (PD) patients. Among those alterations, inhibition of mitochondrial complex I activity, increased free radical production and reduced antioxidant responses have been reported. Copper (Cu) plays an important role in the metabolism and antioxidative responses through its participation as a cofactor in the cytochrome c oxidase enzyme (COX), Cu/Zn-superoxide dismutase (Cu/Zn-SOD), and metallothioneins. We tested the effect of copper sulfate (CuSO₄) pretreatment on the mitochondrial electron transport chain (METC) in the striatum after MPP⁺ toxicity in rats. The results showed that the MPP⁺ intrastriatal injection reduced mitochondrial complex I, II, IV and V activities; while 10 μmol of CuSO₄ pretreatment counteracted this damage. Activities of complexes I, II and IV, were coincident with ATP recovery. Moreover, Cu/Zn-SOD activity was reduced as a consequence of MPP⁺ damage; however, copper pre-treatment kept the striatal Cu/Zn-SOD activity unchanged in MPP⁺-damaged animals. We observed that MPP⁺ also reduced the metallothionein (MT) content and that CuSO₄ pretreatment maintained baseline values. CuSO₄ pretreatment also reduced the striatal caspase-3 and caspase-9 activities that were increased three days after MPP⁺-induced damage. The present study provided evidence that copper pretreatment reduced MPP⁺-induced apoptotic damage, probably through direct action on copper-dependent proteins or indirectly on proteins in the apoptotic pathway.

Targeting mitochondrial metal dyshomeostasis for the treatment of neurodegeneration

Mitochondrial impairment and metal dyshomeostasis are suggested to be associated with many neurodegenerative disorders including Alzheimer's disease, Parkinson's disease, Huntington's disease, amyotrophic lateral sclerosis and Friedreich's ataxia. Treatments aimed at restoring metal homeostasis are highly effective in models of these diseases, and clinical trials hold promise. However, in general, the effect of these treatments on mitochondrial metal homeostasis is unclear, and the contribution of mitochondrial metal dyshomeostasis to disease pathogenesis requires further investigation. This review describes the role of metals in mitochondria in health, how mitochondrial metals are disrupted in neurodegenerative diseases, and potential therapeutics aimed at restoring mitochondrial metal homeostasis and function.

Copper and copper proteins in Parkinson's disease

Copper is a transition metal that has been linked to pathological and beneficial effects in neurodegenerative diseases. In Parkinson's disease, free copper is related to increased oxidative stress, alpha-synuclein oligomerization, and Lewy body formation. Decreased copper along with increased iron has been found in substantia nigra and caudate nucleus of Parkinson's disease patients. Copper influences iron content in the brain through ferroxidase ceruloplasmin activity; therefore decreased protein-bound copper in brain may enhance iron accumulation and the associated oxidative stress. The function of other copper-binding proteins such as Cu/Zn-SOD and metallothioneins is also beneficial to prevent neurodegeneration. Copper may regulate neurotransmission since it is released after neuronal stimulus and the metal is able to modulate the function of NMDA and GABA A receptors. Some of the proteins involved in copper transport are the transporters CTR1, ATP7A, and ATP7B and the chaperone ATOX1. There is limited information about the role of those biomolecules in the pathophysiology of Parkinson's disease; for instance, it is known that CTR1 is decreased in substantia nigra pars compacta in Parkinson's disease and that a mutation in ATP7B could be associated with Parkinson's disease. Regarding copper-related therapies, copper supplementation can represent a plausible alternative, while copper chelation may even aggravate the pathology.

Consequences of manganese administration for striatal dopamine and motor behavior in 1-methyl-4-phenyl-1,2,3,6-tetrahydropyridine-exposed C57BL/6 mice

Environmental compounds may be important contributors to Parkinson's disease etiology. Epidemiological and experimental evidence for the facilitation of parkinsonism by manganese is equivocal. This work addressed methodological concerns in the few studies of manganese modulation of 1-methyl-4-phenyl-1,2,3,6-tetrahydropyridine (MPTP)-induced toxicity in C57BL/6 mice. Male, retired breeder mice received 0 or 100 mg/kg of manganese chloride (MnCl₂; subcutaneously on days 1, 4 and 7) and 0 or 20 mg/kg of MPTP (intraperitoneally on day 8) and survived up to day 15 or 22. On the day of sacrificing, horizontal (grid crossing) and vertical (rearing) open field movement, swimming, grip strength and grip fatigue were examined. Striata were analyzed for dopamine and 3,4-dihydroxyphenylacetic acid (DOPAC) using high-performance liquid chromatography. MPTP produced a main effect decrease in striatal dopamine (48.8%) and DOPAC (38.1%), but there was no main effect of MnCl₂ or MnCl₂ x MPTP interaction. However, modulatory interactions were observed between the effects of MnCl₂ and MPTP for grid crossing, rearing and grip strength. Interestingly, these interactions reduced the severity of behavioral deficits attributable to either of these compounds alone. For rearing and grip strength, the MnCl₂ x MPTP interaction was dependent upon survival time. The mechanistic nature of the MnCl₂ x MPTP interaction upon these behaviors, in the absence of such an interaction for striatal dopamine and DOPAC, remains to be clarified.

Effects of pergolide mesilate on metallothionein mRNAs expression in a mouse model for Parkinson disease

Dopamine agonists have neuroprotective properties in addition to their original pharmacologic function. We examined the effects of pergolide mesilate (PM) on the levels of metallothionein mRNA expression and lipid peroxidation in the corpus striata of 1-methyl 4-phenyl 1,2,3,6-tetrahydropyridine (MPTP)-induced Parkinsonian mice. Mice were administered normal saline (vehicle as a control), PM, or MPTP. A consecutive 7-d administration of MPTP via a gastric tube at a dose of 30 mg/kg significantly decreased metallothionein (MT)-I mRNA expression but did not influence MT-III mRNA expression. Lipid peroxidation, measured as the production of malondialdehyde reactive substances, did not increase after MPTP treatment. Although PM administration alone did not effect MT-I expression, an additional consecutive 7-d administration of PM (30 mug/kg) following MPTP treatment recovered the decreased MT-I level and increased MT-III expression. Lipid peroxidation was significantly suppressed. These results suggest that PM exerts an antioxidative property through the induction of MT-I and MT-III mRNAs simultaneously in response to cellular and/or tissue injury.

Cerebral bioimaging of Cu, Fe, Zn, and Mn in the MPTP mouse model of Parkinson's disease using laser ablation inductively coupled plasma mass spectrometry (LA-ICP-MS)

Laser ablation inductively coupled plasma mass spectrometry (LA-ICP-MS) has been established as a powerful technique for the determination of metal and nonmetal distributions within biological systems with high sensitivity. An imaging LA-ICP-MS technique for Fe, Cu, Zn, and Mn was developed to produce large series of quantitative element maps in native brain sections of mice subchronically intoxicated with 1-methyl-4-phenyl-1,2,3,6-tetrahydropyridin (MPTP) as a model of Parkinson's disease. Images were calibrated using matrix-matched laboratory standards. A software solution allowing a precise delineation of anatomical structures was implemented. Coronal brain sections were analyzed crossing the striatum and the substantia nigra, respectively. Animals sacrificed 2 h, 7 d, or 28 d after the last MPTP injection and controls were investigated. We observed significant decreases of Cu concentrations in the periventricular zone and the fascia dentata at 2 h and 7d and a recovery or overcompensation at 28 d, most pronounced in the rostral periventricular zone (+40%). In the cortex Cu decreased slightly to -10%. Fe increased in the interpeduncular nucleus (+40%) but not in the substantia nigra. This pattern is in line with a differential regulation of periventricular and parenchymal Cu, and with the histochemical localization of Fe, and congruent to regions of preferential MPTP binding described in the rodent brain. The LA-ICP-MS technique yielded valid and statistically robust results in the present study on 39 slices from 19 animals. Our findings underline the value of routine micro-local analytical techniques in the life sciences and affirm a role of Cu availability in Parkinson's disease.

Effect of EGb761 supplementation on the content of copper in mouse brain in an animal model of Parkinson's disease

OBJECTIVE

EGb761 is a well-defined mixture of active compounds extracted from Ginkgo biloba leaves with neuroprotective effects in an animal model of Parkinson's disease induced by 1-methyl-4-phenylpyridinium (MPP(+)). Because copper has been implicated in Parkinson's disease, we investigated whether the protective effect of EGb761 in MPP(+) neurotoxicity is related to the regulation of copper in the brain.

METHODS

C-57BL/6 mice were pretreated with EGb761 (10 mg/kg) daily for 17 d followed by administration of MPP(+) (0.72 mg/kg); the mice were sacrificed 24 h later. The copper content of the striatum, midbrain, hippocampus, frontal cortex, and cerebellum was analyzed by graphite furnace atomic absorption spectrophotometry. Copper content is expressed as mug of copper per gram of wet tissue.

RESULTS

Copper content was reduced in the corpus striatum (45%; P < 0.05), and increased in the midbrain (65%; P < 0.05) and hippocampus (116%; P < 0.001) after MPP(+) administration. EGb761 pretreatment of the MPP(+) group prevented changes in the copper content of the striatum, midbrain, and hippocampus. No significant changes were found in the copper content of the cerebellum and frontal cortex in all treatment groups.

CONCLUSION

We showed that the protective effect of EGb761 against MPP(+) neurotoxicity may be due in part to the regulation of copper homeostasis in the brain.

Free copper, ferroxidase and SOD1 activities, lipid peroxidation and NO(x) content in the CSF. A different marker profile in four neurodegenerative diseases

The understanding of oxidative damage in different neurodegenerative diseases could enhance therapeutic strategies. Our objective was to quantify lipoperoxidation and other oxidative products as well as the activity of antioxidant enzymes and cofactors in cerebrospinal fluid (CSF) samples. We recorded data from all new patients with a diagnosis of either one of the four most frequent neurodegenerative diseases: Parkinson's disease (PD), Alzheimer's disease (AD), Huntington's disease (HD) and lateral amyotrophic sclerosis (ALS). The sum of nitrites and nitrates as end products of nitric oxide (NO) were increased in the four degenerative diseases and fluorescent lipoperoxidation products in three (excepting ALS). A decreased Cu/Zn-dependent superoxide dismutase (SOD) activity characterized the four diseases. A significantly decreased ferroxidase activity was found in PD, HD and AD, agreeing with findings of iron deposition in these entities, while free copper was found to be increased in CSF and appeared to be a good biomarker of PD.

Role of Lipoamide Dehydrogenase and Metallothionein on 1-Methyl-4-phenyl-1,2,3,6- tetrahydropyridine-induced Neurotoxicity

In the present study, we investigated the effects of 1-methyl-4-phenyl-1,2,3,6-tetrahydropyridine (MPTP) on lipoamide dehydrogenase activity and metallothionein content. Lipoamide dehydrogenase is a flavoprotein enzyme, which reduces lipoamide and low molecular weight thiols. This enzyme has also been involved in the conversion of ubiquinone (coenzyme Q-10, oxidized form) to ubiquinol (reduced form). Lipoamide dehydrogenase activity was measured spectrophotometrically following its incubation with different doses of MPTP, MPP+, and divalent metals. MPTP at higher concentrations inhibited the lipoamide dehydrogenase activity, whereas it's potent toxic metabolite 1-methyl-4-phenylpyridinium (MPP+) had a similar effect at lower concentration. Calcium and copper did not affect the enzyme activity at any of the doses tested, whereas, zinc dose dependently enhanced the lipoamide dehydrogenase activity. Additionally, levels of metallothionein in the mouse nigrostriatal system were measured by cadmium affinity method following administration of MPTP. Metallothionein content was significantly reduced in the substantia nigra (SN), and not in the nucleus caudatus putamen (NCP) following a single administration of MPTP (30 mg/kg, i.p.). Our results suggests that both lipoamide dehydrogenase activity and metallothionein levels may be critical for dopaminergic neuronal survival in Parkinson's disease and provides further insights into the neurotoxic mechanisms involved in MPTP-induced neurotoxicity.

The copper chelator, D-penicillamine, does not attenuate MPTP induced dopamine depletion in mice

In MPTP (N-methyl-4-phenyl-1,2,3,6-tetrahydropyridine) and 6-hydroxydopamine induced dopaminergic neurotoxicity and Parkinson's disease iron accumulates in substantia nigra pars compacta which has been suggested to participate in oxidative stress induced neurodegeneration. Pretreatment with iron chelators desferal, clioquinol, VK-28 and M30 are neuroprotective in both models. To determine the specificity of chelation neuroprotective activity we have examined the effect of D-penicillamine, a relatively specific copper chelator, in the mice model of MPTP-induced dopamine depletion. Our studies show that D-penicillamine, employed for removal of copper in Wilson disease is relatively weak in preventing dopaminergic neurotoxicity induced by MPTP, as compared to iron chelators previously studied. The results indicate that for prevention of MPTP-induced dopamine depletion and dopamine neurodegeneration, iron rather than copper chelation may be more effective and specific.

Reduction of Zinc-Positive Terminal Fields in Striatum of Mouse after 1-Methyl-4-Phenylpyridinium Neurotoxicity

Zinc is an essential trace element in the central nervous system and is located in three distinct pools: free zinc, vesicular zinc and protein-bound zinc. Zinc may serve as an endogenous neuromodulator and has been associated with neuropathologies. This study was undertaken to determine whether levels of vesicular zinc in neuronal terminals would decrease in response to the dopaminergic neurotoxin 1-methyl-4-phenylpyridinium ion (MPP+). Adult male C-57 black mice were injected with MPP+ (0.72 mg/kg) into their right lateral ventricle. All animals were killed at 1, 2, 24 h and 7 days after MPP+ or saline administration. The brains were stained for zinc sulfides and the density of zinc-positive terminal fields was evaluated after MPP+ administration. The relative optical density analysis of zinc-positive terminal fields showed significant decreases in the striatum at 1, 2 and 24 h (24, 18 and 14%, respectively, versus control) and ventricular epithelium (1, 2, 24 h and 7 days). The hippocampus showed increase in the stratum oriens and stratum radiatum at different times. MPP+ administration reduced dopamine levels at 24h and 7 days (36 and 40%, respectively, versus control) as a result of the neurotoxic action of MPP+. The decrease of zinc-positive neuronal terminal fields in the striatum after MPP+ administration is most likely due to a neuronal release of vesicular zinc in response to its dopaminergic neurotoxicity.

Effect of manganese exposure on MPTP neurotoxicities

We used a 1-methyl-4-phenyl-1,2,3,6-tetrahydropyridine (MPTP)-treated mice model to evaluate whether manganese (Mn) exposure can affect MPTP-induced neurotoxicity. We randomly assigned adult male C57BL/6 mice (n=5-7 per group) the following treatments: SO, Mn(-) x MPTP(-); MO, Mn(+) x MPTP(-); SM, Mn(-) x MPTP(+); MM, Mn(+) x MPTP(+). Mn (MnCl(2).4H(2)O) was administered intraperitoneally at a dose of 2 mg/kg daily for 3 weeks. MPTP was then administered intraperitoneally at a dose of 30 mg/kg daily for 5 days in the SM and MM groups. Seven days after the last MPTP injection, the animals were sacrificed. Blood Mn levels were elevated in the Mn-exposed groups. Striatal Mn levels were not influenced by Mn treatment alone, however, they were decreased following MPTP. Tyrosine hydroxylase (TH)-immunoreactive (ir) neurons in the substantia nigra pars compacta (SNpc) were decreased significantly in the MPTP-exposed groups. Densities of TH- and dopamine transporter (DAT)-ir axon terminals in the caudate-putamen (CPU) were also decreased in the MPTP-treated groups. Furthermore, glial fibrillary acidic protein (GFAP)-ir astrocytes increased in the CPU with MPTP treatment. However, no effects were observed with Mn exposure. Concentrations of dopamine (DA), 3,4-dihydrophenyl acetic acid (DOPAC) and homovanillic acid (HVA) in the corpus striatum were also decreased significantly with MPTP treatment alone, but Mn had no effect. Thus, decreased dopaminergic activities with MPTP led to decreased DA and its metabolites. Significant hypertrophies of GFAP-ir astrocytes in the globus pallidus (GP) were observed in Mn-exposed groups, especially in the MM group. MPTP targeted dopaminergic systems whereas Mn neurotoxicities occurred in the GP. In conclusion, our data suggest that Mn does not potentiate the neurotoxicity of MPTP.

EGb761 blocks MPP+-induced lipid peroxidation in mouse corpus striatum

EGb761 has been suggested to be an antioxidant and free radical scavenger. Excess generation of free radicals, leading to lipid peroxidation (LP), has been proposed to play a role in the damage to striatal neurons induced by 1-methyl-4-phenylpyridinium (MPP+). We investigated the effects of EGb761 pretreatment on MPP+ neurotoxicity. C-57 black mice were pretreated with EGb761 for 17 days at different doses (0.63, 1.25, 2.5, 5 or 10 mg/kg) followed by administration of MPP+, (0.18, 0.36 or 0.72 mg/kg). LP was analyzed in corpus striatum at 30 min, 1 h, 2 h and 24 h after MPP+ administration. Striatal dopamine content was analyzed by HPLC at the highest EGb761 dose at 2 h and 24 h after MPP+ administration. MPP+-induced LP was blocked (100%) by EGb761 (10 mg/kg). Pretreatment with EGb761 partially prevented (32%) the dopamine-depleting effect of MPP+ at 24 h. These results suggest that supplements of EGb761 may be effective at preventing MPP+-induced oxidative stress.

Neuroprotective effect of acute and chronic administration of copper (II) sulfate against MPP+ neurotoxicity in mice

Neurodegenerative effects of MPP+, the main metabolite of MPTP include dopamine (DA) depletion and enhanced lipid peroxidation (LPO) in mice striata, both associated to free radicals overproduction. Since copper is related to several antioxidant enzymes, we tested its neuroprotective effect against MPP+-induced neurotoxicity (20 microg/3 microl). CuSO4 pretreatment was administrated by either acute (2.5 mg/kg, i.p.) or chronic (350 or 700 mg/l doses through drinking water, for 30 days) schemes. Acute administration blocked MPP+-induced striatal LPO only when administered 16 or 24 hours before MPP+, and prevented the DA-depleting effect only at 24 hours. Chronic CuSO4 prevented the LPO increase, and blocked the DA depletion only at the higher dose used (700 mg/l). Neuroprotective effect of CuSO4 was dependent on the dose and the time of pretreatment, which suggest that this lag could be related with mechanisms of activation or synthesis of copper-dependent proteins responsible of cellular defense against MPP+.

Participation of manganese-superoxide dismutase in the neuroprotection exerted by copper sulfate against 1-methyl 4-phenylpyridinium neurotoxicity

Neurodegenerative effects of 1-methyl-4-phenylpyridinium (MPP+), the main metabolite of the neurotoxin 1-methyl-4-phenyl-1,2,3,6-tetrahydropyridine (MPTP) include enhancement of lipid peroxidation in the striatum of mice, associated to overproduction of free radicals. Copper acts as a prosthetic group of several copper-dependent antioxidant enzymes, and we previously showed the neuroprotective effect of CuSO4 pretreatment against the MPP+-induced neurotoxicity. In those studies, acute administration of CuSO4 (2.5 mg/kg) blocked MPP+-induced striatal lipid peroxidation, suggesting the activation of Cu-dependent proteins that defend neurons from damage elicited by free radicals. In the present study, we evaluated the activity of superoxide dismutase in mice pretreated with CuSO4 16 h or 24 h prior to MPP+ administration. Copper administration produced a specific and significant increase in manganese superoxide dismutase activity in both the CuSO4/saline (fivefold increase) and the CuSO4/MPP+ groups of animals (sevenfold increase). The Na2SO4/MPP+ group showed a twofold increase in manganese superoxide dismutase activity versus control levels. The results suggest that the load of copper activating manganese-dependent superoxide dismutase could be responsible for neuroprotection against the MPP+ insult.

MPTP decreases MT-I mRNA in mouse striatum

1-Methyl-4-phenyl-1,2,3,6-tetrahydropyridine (MPTP) is a drug that induces parkinsonism in humans and non-human primates. Free radicals are thought to be involved in its mechanism of action. Recently, metallothionein has been proposed to play a role as a scavenger of free radicals. In the present work, we studied the effect of MPTP neurotoxicity on brain metallothionein-I (MT-I) mRNA expression. Male C-57 black mice were treated with MPTP (30 mg/kg, i.p., daily) for 3 or 5 days. All animals were killed by cervical dislocation 7 days after the last MPTP dose. The brains were removed quickly and immediately frozen, and quantitative in situ hybridization was performed using MT-I cDNA probe. MT-I mRNA content in striatum, a region which is known to be highly predisposed and sensitive to MPTP-induced oxidative stress, decreased by 30% (3 days) and 39% (5 days) respectively, after the last MPTP administration. These results suggest that MT-I gene expression is decreased in MPTP neurotoxicity. It is suggested that the reduction of MT, an anti-oxidant and a free radical scavenger, in the striatum by MPTP enables the neurotoxin to exert maximal oxidative damage to the striatum.

Changes of metallothionein I + II proteins in the brain after 1-methyl-4-phenylpyridinium administration in mice

1-methyl-4-phenylpyridinium (MPP+) is a drug that induces a Parkinson's-like syndrome in several species. Oxidative stress resulting from either excess generation or reduced scavenging of free radicals has been proposed to play a role in its neurotoxicity. It has been suggested that metallothionein (MT) protects against oxidative damage of the central nervous system produced by overproduction of free radicals. This study examined the effect of MPP+ on metallothionein I+II protein content in different brain regions. NIH mice were injected with MPP+ (4.5, 9.0 or 18 microg/3 microl) into their right lateral ventricle. Corpus striatum, cerebellum, midbrain, frontal cortex and hippocampus were dissected out and their metallothionein concentrations were analyzed by radioimmunoassay. MPP+ reduced the concentration of MT I+II proteins (38%) only in the striatum. The results suggest that changes in MT I+II content may be associated with MPP+ neurotoxicity.

Metallothionein-I and -II knock-out mice are not more sensitive than control mice to 1-methyl-4-phenyl-1,2,3,6-tetrahydropyridine neurotoxicity

Oxidative stress, resulting from either excess generation or reduced scavenging of free radicals, has been proposed to play a role in damaging striatal neurons in 1-methyl-4-phenyl-1,2,3,6-tetrahydropyridine (MPTP) neurotoxicity. Metallothionein (MT) is a scavenger of oxygen-derived free radicals and it has been suggested that MT protects against oxidative damage in the central nervous system. In the present study we compared MT-I and -II null mice (MT-null) and the parental strain with intact metallothionein genes (control mice) to determine whether the absence of MT protein alters MPTP neurotoxicity. Control and MT-null mice were treated with MPTP at different doses (30, 40 and 50 mg/kg, i.p.) for 11 days. Seven days after the last dose, brains were removed and dopamine (DA) and homovanillic acid (HVA) contents were analyzed in striatum and midbrain by high pressure liquid chromatography (HPLC). Striatal DA content in MPTP-treated control mice was reduced by 53, 74 and 84% after 30, 40 and 50 mg/kg, respectively. Similar decreases were observed in MT-null mice treated with MPTP. MT-null mice were not more sensitive than control mice to MPTP neurotoxicity. The data suggest that MT-I and -II proteins do not play a role in protecting against MPTP neurotoxicity.

Reduced ferroxidase activity in the cerebrospinal fluid from patients with Parkinson's disease

Recent evidence suggest the implication of transition metals leading to overproduction of free radicals as a possible causal factor in the death of nigral cells associated to Parkinson's disease (PD). Iron depots in the basal ganglia of PD patients have been described; in addition, contents of nigral copper have been found decreased, while its concentration in cerebrospinal fluid (CSF) is raised, particularly the free form of the metal. To search for a possible link between altered copper concentrations and PD, we advanced the hypothesis that ferroxidase activity of ceruloplasmin is decreased in the CSF of PD patients. We studied 35 untreated PD patients, 14 L-3,4-dihydroxyphenylalanine (L-DOPA)-treated PD patients and 26 controls. Both CSF ferroxidase activity and CSF copper content were measured and correlated with the clinical stage of the disease. We found that untreated PD patients had a significant reduction of 40% in CSF ferroxidase while CSF copper was slightly increased as compared with both the values in L-DOPA-treated PD patients and controls. We also found that the fraction of copper linked to ferroxidase in untreated PD is inversely related to the clinical stage of the disease.

Metallothionein inducers protect against 1-methyl-4-phenyl-1,2,3,6-tetrahydropyridine neurotoxicity in mice

1-methyl-4-phenyl-1,2,3,6-tetrahydropyridine (MPTP) is a drug that induces parkinsonism in human and non-human primates. Free radicals are thought to be involved in its mechanism of action. Recently, the participation of metallothionein as scavenger of free radicals has been proposed. In this work, we studied the effect of metallothionein inducers in MPTP neurotoxic action. Male swiss albino mice were pretreated either with cadmium (1 mg/kg) or dexamethasone (5 mg/kg), two well-known inducers of metallothionein synthesis, and 5 hours later with an MPTP administration (30 mg/kg). Treatment schedule was repeated daily for either 3 or 5 consecutive days. All animals were killed 7 days after the last administration, and striatal dopamine and homovanillic acid contents were analyzed as an end-point of MPTP neurotoxicity. Striatal dopamine content of cadmium plus MPTP-treated animals (3-days) increased by 32%, and 48% (5-days) vs MPTP-alone animals. Dexamethasone plus MPTP-treated group also showed increased dopamine levels 28% (3-days) and 43% (5-days). MPTP treatment reduced striatal metallothionein concentration (49% vs control animals). Dexamethasone and cadmium increased metallothionein concentrations in MPTP-treated groups, by 77% and 82% respectively. Results suggest that metallothionein induction provide a significant resistance factor against the deleterious effect of MPTP.

Quinolinic acid neurotoxicity: in vivo increased copper and manganese content in rat corpus striatum after quinolinate intrastriatal injection

Copper and manganese, two essential metals involved in physiological and physiopathological processes in the brain, were measured in corpora striata of rats 7 days after intrastriatal injection of quinolinic acid (QUIN, 240 nmol/l microliters), an N-methyl-D-aspartate (NMDA) receptor agonist with toxic activity. Seven days after QUIN administration, copper and manganese contents were assessed by graphite furnace atomic absorption spectrophotometry. Total copper content was increased by 152% in QUIN-treated rats (18.74 +/- 2.05 micrograms/g) as compared to control animals (7.44 +/- 1.15 micrograms/g), whereas manganese striatal levels were enhanced by 35% (0.30 +/- 0.02 microgram/g) vs. control values (0.22 +/- 0.02 microgram/g). Quinolinate-induced striatal increase in copper and manganese levels were prevented by 23% (9.18 +/- 1.43 micrograms/g) and -0.45% (0.22 +/- 0.03 microgram/g) vs. control values, respectively, in rats pretreated with an NMDA receptor antagonist, dizocilpine (MK-801, 10 mg/kg, i.p.), 60 min before QUIN administration. As an index of QUIN neurotoxicity, striatal GABA levels were also measured 7 days after QUIN injection. GABA content was decreased by-55% in QUIN-lesioned rats (96.37 +/- 8.92 micrograms/g), whereas MK-801 was able to block QUIN-induced GABA depletion by 2% (219.37 +/- 10.60) vs. control values (214.2 +/- 21.88 micrograms/g). These findings suggest that increased concentrations of transition metals can be mediated by selective overactivation of NMDA receptors and might be a consequence of neural loss as well as glial response to damage.

Short-term manganese pretreatment partially protects against 1-Methyl-4-phenyl-1,2,3,6-tetrahydropyridine neurotoxicity

1-Methyl-4-phenyl-1,2,3,6-tetrahydropyridine (MPTP) is a neurotoxin that induces parkinsonism in human and non-human primates. Its mechanism of action is not fully elucidated. Recently, the participation of trace metals, such as manganese, on its neurotoxic action has been postulated. In this work, we studied the effect of manganese administration on the neurochemical consequences of MPTP neurotoxic action. Male Swiss albino mice were treated with manganese chloride (MnCl2.4H2O; 0.5 mg/ml or 1.0 mg/ml of drinking water) for 7 days, followed by three MPTP administrations (30 mg/kg, intraperitoneally). Seven days after the last MPTP administration, mice were sacrificed and dopamine and homovanillic acid contents in corpus striatum were analyzed. Striatal concentration of dopamine was found increased by 60% in mice pretreated with 0.5 mg/ml and 52% in the group treated of 1.0 mg/ml as compared versus animals treated with MPTP only. Homovanillic acid content in both groups treated with manganese was the same as those in control animals. The results indicate that manganese may interact with MPTP, producing an enhancement of striatal dopamine turnover, as the protective effect of manganese was more pronounced in the metabolite than in the neurotransmitter.