Increased nigral iron content in postmortem parkinsonian brain

6-Hydroxydopamine increases ubiquitin-conjugates and protein degradation: implications for the pathogenesis of Parkinson's disease

One of the hallmarks of Parkinson's disease (PD) is pathological structure, termed Lewy body, containing inclusions of ubiquitinated proteins in the dopaminergic neurons in the substantia nigra. The mechanism leading to the formation of these aggregates is unclear, although it has been shown that mutations in alpha-synuclein or in the ubiquitin-related enzyme UCH-L1 might induce such protein aggregation. We, therefore, examined the possible role of 6-hydroxydopamine (6-OHDA), a dopaminergic neurotoxin used in PD experimental models, in causing protein degradation and its association with the ubiquitin system. Using antiubiquitin antibodies we found that exposure of SH-SY5Y neuroblastoma and PC-12 cell lines to 6-OHDA increased the levels of free ubiquitin and ubiquitin-conjugated proteins, in a dose-dependent manner. Furthermore, metabolic labeling with 35S-methionine, demonstrated that 6-OHDA markedly increased protein degradation, as indicated by the secretion of protein metabolites to the medium. Inhibition of the proteasome activity by the specific inhibitor MG132, attenuated the protein degradation induced by 6-OHDA and potentiated its toxicity. Administration of the antioxidant N-acetylcysteine to the 6-OHDA-treated cells, increased cell survival and reduced protein degradation. In conclusion, our findings suggest that 6-OHDA toxicity is associated with protein degradation and ubiquitin-proteasome system activation.

Neonatal iron exposure induces oxidative stress in adult Wistar rat

Oxidative stress and excess of iron in the brain has been implicated in a variety of acute and chronic neurological conditions. The neonatal period is critical for the establishment of normal iron content in the adult brain. In the present study, the long-term oxidative effects of iron exposure during this period were assessed by treating Wistar rats orally with 0, 7.5 or 15 mg Fe(+2)/kg of body weight on postnatal days 10-12. Thiobarbituric acid reactive species, protein carbonyl, superoxide dismutase activity were measured at the age of 3 months. It was found that there was an increase in thiobarbituric acid reactive species and protein carbonyl in the substantia nigra of iron treated rats. In contrast, oxidative stress in the striatum was decreased. Superoxide dismutase activity was decreased in the substantia nigra iron treated rats. There were no differences in cerebellum measures among the groups. Our results demonstrated that iron supplementation in a critical neonatal period induced oxidative stress and modulated SOD activity in the adult life in selective brain regions.

Chronic L-DOPA administration is not toxic to the remaining dopaminergic nigrostriatal neurons, but instead may promote their functional recovery, in rats with partial 6-OHDA or FeCl(3) nigrostriatal lesions

In this study, we have examined the effects of chronic L-3,4-dihydroxyphenylalanine (L-DOPA) administration on the remaining dopaminergic neurons in rats with 6-hydroxydopamine (6-OHDA) or buffered FeCl(3) partial lesions to the nigrostriatal tract. L-DOPA administration increased the turnover of dopamine in the striatum. L-DOPA administration for 1 week produced an increase in the level of striatal RTI-121 binding, a specific marker for dopamine uptake sites on the dopaminergic nerve terminals in the striatum. However, longer periods of L-DOPA treatment decreased the level of RTI-121 binding in the striatum. In the partial 6-OHDA lesion model, L-DOPA treatment had a time-dependent effect on the number of neurons demonstrating a dopaminergic phenotype i.e., neurons that are tyrosine hyrdoxylase (TH)-immunopositive, on the lesioned side of the brain. In the first few weeks of treatment, L-DOPA decreased the number of TH-positive neurons but with long-term treatment, i.e., 24 weeks, L-DOPA increased the number of neurons demonstrating a dopaminergic phenotype. Even in the buffered FeCl(3) infusion model, where the levels of iron were increased, L-DOPA treatment did not have any detrimental effects on the number of TH-positive neurons on the lesioned side of the brain. Consequently, chronic L-DOPA treatment does not have any detrimental effects to the remaining dopaminergic neurons in rats with partial lesions to the nigrostriatal tract; indeed in the 6-OHDA lesion model, long-term L-DOPA may increase the number of neurons, demonstrating a dopaminergic phenotype.

Neonatal iron potentiates adult MPTP-induced neurodegenerative and functional deficits

The interactive effects of neonatal iron and adult MPTP treatment groups of C57 Bl/6 mice were studied through adminustration of iron (Fe(2+)) 7.5mg/kg b.w., p.o. or vehicle (saline) on days 10-12 post partum, followed at 3months of age by administration of either MPTP (2x20 or 2x40mg/kg, s.c.) or saline. Neonatal iron administration to mice-induced hypoactivity during the first 20-min period of testing and hyperactivity during the 3rd and final 20-min period for all three parameters of motor activity tested at 4months of age. MPTP treatment caused a dose-related hypokinesia throughout the 3x20-min test periods; in the mice that received both neonatal iron and MPTP severe deficits of motor activity (akinesia) were obtained. Iron treatment impaired the ability of mice to habituate to the novel testing environment and later administration of MPTP potentiated the impairment markedly. Neurochemical analyses of striatal and frontal cortical dopamine (DA) and DA metabolites demonstrated that the depletions were potentiated under conditions of combined neonatal iron and adult MPTP. The analysis of total iron content (µg/g) in brain regions indicated notably elevated levels in the basal ganglia, but not in the frontal cortex, of mice administered Fe(2+). Iron-overload combined with MPTP treatment induced functional and neurochemical deficits with interactive consequences beyond a mere additive effect that may have implications for the neurodegenerative process in parkinsonism.

Mitochondrial dysfunction and oxidative stress in aging and neurodegenerative disease

A major risk factor for neurodegenerative diseases such as Parkinson's disease (PD), Huntington's disease (HD), amyotrophic lateral sclerosis (ALS), Alzheimer's disease (AD) and progressive supranuclear palsy (PSP) is aging. Two processes that have been implicated in aging are free radical-induced oxidative damage and mitochondrial dysfunction. A progressive impairment of mitochondrial function and/or increased oxidative damage has been suggested to play critical roles in the pathogenesis of these neurodegenerative diseases. For example, decreased complex I activity, increased oxidative damage and altered activities of antioxidant defense enzymes have been demonstrated in PD. In AD, decrements in complex IV activity and increased oxidative damage have been reported. Reductions in complex II activity, increased cortical lactate levels and oxidative damage have been described in HD. Some familial ALS cases are associated with mutations in the gene for Cu,Zn superoxide dismutase (SOD1) while increased oxidative damage is observed in sporadic ALS. Studies in PSP have demonstrated regionally specific reductions in brain and muscle mitochondrial function, hypofrontality and increased oxidative damage. Altogether, the age-dependent onset and progressive course of these neurodegenerative diseases may ultimately highlight an association between aging, mitochondrial impairment and oxidative stress.

The biochemistry of aging

Although philosophers and scientists have long been interested in the aging process, general interest in this fascinating and highly important topic was minimal before the 1960s. In recent decades, however, interest in aging has greatly accelerated, not only since the elderly form an ever-increasing percentage of the population, but because they utilize a significant proportion of the national expenditures. In addition, many people have come to the realization that one can now lead a very happy, active, and productive life well beyond the usual retirement age. Scientifically, aging is an extremely complex, multifactorial process, and numerous aging theories have been proposed; the most important of these are probably the genomic and free radical theories. Although it is abundantly clear that our genes influence aging and longevity, exactly how this takes place on a chemical level is only partially understood. For example, what kinds of genes are these, and what proteins do they control? Certainly they include, among others, those that regulate the processes of somatic maintenance and repair, such as the stress-response systems. The accelerated aging syndromes (i.e., Hutchinson-Gilford, Werner's, and Down's syndromes) are genetically controlled, and studies of them have decidedly increased our understanding of aging. In addition, C. elegans and D. melanogaster are important systems for studying aging. This is especially true for the former, in which the age-1 mutant has been shown to greatly increase the life span over the wild-type strain. This genetic mutation results in increased activities of the antioxidative enzymes, Cu-Zn superoxide dismutase and catalase. Thus, the genomic and free radical theories are closely linked. In addition, trisomy 21 (Down's syndrome) is characterized by a significantly shortened life span; it is also plagued by increased oxidative stress which results in various free radical-related disturbances. Exactly how this extra chromosome results in an increased production of reactive oxygen species is, however, only partially understood. There is considerable additional indirect evidence supporting the free radical theory of aging. Not only are several major age-associated diseases clearly affected by increased oxidative stress (atherosclerosis, cancer, etc.), but the fact that there are numerous natural protective mechanisms to prevent oxyradical-induced cellular damage speaks loudly that this theory has a key role in aging [the presence of superoxide dismutase, catalase, glutathione peroxidase, and glutathione reductase, among others; various important intrinsic (uric acid, bilirubin, -SH proteins, glutathione, etc.) and extrinsic (vitamins C, E, carotenoids, flavonoids, etc.) antioxidants; and metal chelating proteins to prevent Fenton and Haber-Weiss chemistry]. In addition, a major part of the free radical theory involves the damaging role of reactive oxygen species and various toxins on mitochondria. These lead to numerous mitochondrial DNA mutations which result in a progressive reduction in energy output, significantly below that needed in body tissues. This can result in various signs of aging, such as loss of memory, hearing, vision, and stamina. Oxidative stress also inactivates critical enzymes and other proteins. In addition to these factors, caloric restriction is the only known method that increases the life span of rodents; studies currently underway suggest that this also applies to primates, and presumably to humans. Certainly, oxidative stress plays an important role here, although other, as yet unknown, factors are also presumably involved. Exactly how the other major theories (i.e., immune, neuroendocrine, somatic mutation, error catastrophe) control aging is more difficult to define. The immune and neuroendocrine systems clearly deteriorate with age. (ABSTRACT TRUNCATED)

NT-4/5 exacerbates free radical-induced neuronal necrosis in vitro and in vivo

Neurotrophins render neurons highly vulnerable to certain injuries. We examined the possibility that NT-4/5 would enhance free radical neurotoxicity in vivo as well as in vitro. Striatal neurons exposed to 10 microM Fe(2+) or 1 mM l-buthionine-[S, R]-sulfoximine (BSO) underwent mild degeneration within 24 h. With concurrent addition of 10-100 ng/ml NT-4/5, neuronal death following exposure to Fe(2+) or BSO was significantly increased and suppressed by addition of 100 microM trolox, an antioxidant. In the adult brain, the intrastriatal injections of 20 nmol Fe(2+) revealed features of neuronal necrosis such as swelling cell body and mitochondria, fenestration of plasma membrane prior to nuclear membrane, and scattering condensation of nuclear chromatin. Cotreatment with 1.8 microg NT-4/5 augmented the striatal damage 24 h following the injections of Fe(2+). This study implies that free radicals produce necrotic degeneration in vivo as well as in vitro that becomes more sensitive in the presence of neurotrophins.

Maze learning and motor activity deficits in adult mice induced by iron exposure during a critical postnatal period

Newborn mice were administered Fe(2+) (iron succinate: 7.5 mg/kg, b. wt) on either Days 3-5, 10-12 or 19-21, or vehicle (saline) at the same times, postnatally. Spontaneous motor behaviour and radial arm maze learning were tested at the age of 3 months. It was found that mice treated with Fe(2+) during postnatal Days 10-12 were markedly hypokinetic during the 1st 20-min test period and hyperkinetic during the 3rd and final 20-min test period. These mice showed an almost complete lack of habituation of spontaneous motor activity parameters to the test chambers. In the radial arm maze, the Days 10-12 treatment group evidenced significantly both more errors in arm choices and longer latencies to acquire all eight pellets; these mice showed also a severe trial-to-trial retention deficit as indexed by retention quotients. These behavioural deficits were observed also in animals treated with Fe(2+) during postnatal Days 3-5, but the effects were less pronounced, indicating the higher susceptibility of the brain for Fe(2+)-induced damage during Days 10-12 postpartum. Treatment with Fe(2+) on Days 19-21 did not induce behavioural alterations in comparison with its respective control (vehicle) group. Analysis of total brain iron content indicated significantly more iron (microg/g) accumulation in the basal ganglia, but not frontal cortex, of mice from the Days 3-5 and 10-12 Fe(2+) (7.5 mg/kg) treatment groups. The contribution of iron overload during the immediate postnatal to later functional deficits seems to implicate symptoms of Parkinsonism but the kinetics of iron uptake to the brain and its regional distribution at this critical period of development awaits elucidation.

Local striatal infusion of MPP+ does not result in increased hydroxylation after systemic administration of 4-hydroxybenzoate

In vivo bilateral microdialysis in the rat striatum was used to investigate hydroxyl radical formation under basal conditions and after intrastriatal administration of the neurotoxin, 1-methyl-4-phenylpyridinium (MPP+). After a short equilibration period, 4-hydroxybenzoate (4HBZ), which scavenges hydroxyl radicals to produce 3,4-dihydroxybenzoate (34DHB), was injected intraperitoneally 15 min before infusion of MPP+. To evaluate the enzymatic contribution to hydroxyl radical formation, two other series of microdialyses were performed following administration of monoamine oxidase B inhibitors, either 1-deprenyl (selegiline) or MDL 72,974A [(E)-2-(4-fluorophenethyl)-3-fluoroallylamine hydrochloride]. Microdialysate samples were analyzed by high-performance liquid chromatography for catecholamines, 3,4-dihydroxyphenylacetate (DOPAC), homovanillate (HVA), along with the hydroxyl radical adduct, 34DHB and its precursor, 4HBZ. MPP+ administration resulted in a massive release of dopamine along with a decrease in DOPAC and HVA in all three groups. A striking effect in all three groups was noted in which MPP+ resulted in a decrease in interstitial 4HBZ to < 50% of the non-MPP+ -treated side. In absolute terms, the amount of 34DHB produced was low but similar in all three groups, even after unilateral MPP+ infusion. When 34DHB was normalized to 4HBZ release to account for differences in precursor availability, there were no significant differences in the 34DHB/4HBZ ratios either with or without MAO inhibitor treatment or after local MPP+ infusion. Systemic 4HBZ administration appears to result predominantly in intra-cellular sampling of hydroxyl radicals which produces different results from local infusion of trapping agents such as salicylate.

Neonatal iron exposure induces neurobehavioural dysfunctions in adult mice

Excess iron in the brain has been implicated in the pathogenesis of several human neurodegenerative disorders, i.e., Parkinson's and Alzheimer's disease. The neonatal period is critical for the establishment of normal iron content in the adult brain. In the present study, the long-term neurobehavioral effects of iron exposure during this period were assessed by treating NMRI mice orally with 0.0, 3.7, or 37.0 mg Fe(2+)/kg body wt on postnatal days 10-12. Spontaneous motor behavior and radial arm maze learning were tested at the age of 3 months. It was found that the mice treated with the higher dose of Fe(2+), 37.0 mg/kg body wt, were hypoactive during the first 20 min of testing but hyperactive during the final 20 min, showing an almost complete lack of habituation of spontaneous activity in the test chambers. These changes were also seen in animals treated with the lower dose of Fe(2+), 3.7 mg/kg body wt, but the effects were less pronounced, indicating a dose-response relationship. In the radial arm maze, the Fe(2+) 37.0 mg/kg group evidenced significantly both more errors in arm choices and longer latencies to acquire all eight pellets. Both dose groups showed attenuated performance increments on successive trials. Analysis of brain iron content indicated significantly more total iron (microgram/g) in the basal ganglia, but not frontal cortex, of the higher, 37 mg/kg, dose group. The knowledge of the long-term effects of iron entering the brain during this critical period of rapid brain growth is limited. Increased amounts of iron in the brain, especially in the basal ganglia, may contribute to neurodegenerative processes.

Evidence for oxidative stress in the subthalamic nucleus in progressive supranuclear palsy

Increased free radical production and oxidative stress have been proposed as pathogenic mechanisms in several neurodegenerative disorders. Free radicals interact with biological macromolecules, such as lipids, which can lead to lipid peroxidation. A well-established marker of oxidative damage to lipids is malondialdehyde (MDA). We measured tissue MDA levels in the subthalamic nucleus (STN) and cerebellum from 11 progressive supranuclear palsy (PSP) cases and 11 age-matched control cases using sensitive HPLC techniques. In PSP, a significant increase in tissue MDA levels was observed in the STN when compared with the age-matched control group. By contrast, no significant difference between tissue MDA content was observed in cerebellar tissue from the same PSP and age-matched control cases. These results indicate that lipid peroxidation may play a role in the pathogenesis of PSP.

Pathogenesis and preclinical course of Parkinson's disease

Idiopathic parkinsonism (IP) is defined by its classic symptomology, its responsiveness to therapies which elevate dopamine levels, and by the failure to identify a specific etiological factor. The progressive and irreversible degeneration of dopaminergic neurons projecting from the substantia nigra pars compacta (SNc) to the striatum and the presence of SNc Lewy bodies are regarded as the essential pathological bases of IP, but neither the initiator(s) nor the nature of the degeneration have been determined, nor its relationship with degenerative changes in other parts of the IP brain. This paper discusses the various hypotheses that have been proposed to explain these phenomena, arguing that IP be regarded as a multisystem disorder, both at the level of individual neurons and at the whole brain level. It is probable that IP is the result of a multifactorial process, and that a cascade of interacting and overlapping biochemical mechanisms determine the course of the disease.

Iron in the basal ganglia in Parkinson's disease. An in vitro study using extended X-ray absorption fine structure and cryo-electron microscopy

Iron is found in high concentration in some areas of the brain, and increased iron in the substantia nigra is a feature of Parkinson's disease. The purpose of this study was to investigate the physical environment of brain iron in post-mortem tissue to provide information on the possible role of iron in neurodegeneration in Parkinson's disease. Iron has also been implicated as the cause of signal loss in areas of high brain iron on T2-weighted MRI sequences. Knowledge of the physical environment of the brain iron is essential in interpreting the cause of signal change. Post-mortem tissue was obtained from six cases of Parkinson's disease and from six age-matched controls. Iron levels were measured using absorption spectrophotometry. Extended X-ray absorption fine structure was used to evaluate the atomic environment of iron within the substantia nigra and both segments of the globus pallidus. Cryo-electron transmission microscopy was used to probe the iron storage proteins in these areas. Iron levels were increased in the parkinsonian nigra and lateral portion of the globus pallidus. Spectra from the extended X-ray absorption fine structure experiments showed that ferritin was the only storage protein detectable in both control and parkinsonian tissue in all areas studied. Cryo-electron transmission microscopy studies showed that ferritin was more heavily loaded with iron in Parkinson's disease when compared with age-matched controls. In summary we have shown that iron levels are increased in two areas of the brain in Parkinson's disease including the substantia nigra, the site of maximal neurodegeneration. This produces increased loading of ferritin, which is the normal brain iron storage protein. It is possible that increased loading of ferritin may increase the risk of free radical-induced damage. Differences in ferritin loading may explain regional differences in iron's effect on the T2 signal.

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.

Neuroprotection by bromocriptine against 1-methyl-4-phenyl-1,2,3,6-tetrahydropyridine-induced neurotoxicity in mice

Mice were treated with 1-methyl-4-phenyl-1,2,3,6-tetrahydropyridine (MPTP; 30 mg/kg i.p. twice, 16 h apart). This resulted in changes in motor performance and toxic insult of nigral neurons as evidenced by dopamine depletion in nucleus caudatus putamen. In vitro and in vivo treatment of MPTP caused the generation of hydroxyl radicals (.OH) as measured by a sensitive salicylate hydroxylation procedure. A dopamine agonist, bromocriptine (10 microM and 10 mg/kg i.p.), blocked .OH formation caused by MPTP in vitro (20 microM) and in vivo (30 mg/kg i.p.). An MPTP-induced increase in the activity of catalase and superoxide dismutase in substantia nigra on the seventh day was reduced by bromocriptine pretreatment. Bromocriptine blocked MPTP-induced behavioral dysfunction as well as glutathione and dopamine depletion, indicating its potent neuroprotective action. This study suggests that bromocriptine stimulates antioxidant mechanisms in the brain and acts as a free radical scavenger in addition to its action at dopamine receptors, thus indicating its strength as a valuable neuroprotectant.

Neuroprotection by nitric oxide against hydroxyl radical-induced nigral neurotoxicity

We investigated the effects of nitric oxide on an in vitro and in vivo generation of hydroxyl radicals, and in vivo neurotoxicity caused by intranigral infusion of ferrous citrate in rats. The formation of hydroxyl radicals in vitro, without exogenous hydrogen peroxide, was dose-dependent. Some nitric oxide donors (e.g. sodium nitroprusside) stimulated, while others (nitroglycerin, diethylamine/nitric oxide, nitric oxide in Ringer's solution) suppressed hydroxyl radical generation in vitro. A significant increase in extra-cellular hydroxyl radicals was detected in a brain microdialysis study. Intranigral infusion of ferrous citrate caused long-lasting lipid peroxidation and dopamine depletion in the ipsilateral nigral region and striatum, respectively. Sub-acute dopamine depletion in the striatum was positively correlated with acute lipid peroxidation in substantia nigra. Intranigral administration of nitric oxide did not affect striatal dopamine. Interestingly, nitric oxide in Ringer's protected nigral neurones against the oxidative injury. The results demonstrate that a regional increase in the levels of iron can result in hydroxyl radical generation and lipid peroxidation leading to neurotoxicity. It also demonstrates that exogenous nitric oxide can act as hydroxyl radical scavenger and protect neurones from oxidative injury.

Tyrosine hydroxylase and Parkinson's disease

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

Glial pathology but absence of apoptotic nigral neurons in long-standing Parkinson's disease

The cause and mechanism of neuronal cell death in the substantia nigra of patients with Parkinson's disease (PD) are unknown. There is also controversy about whether the cell death results from a single event followed by cell loss consistent with aging or whether there is an ongoing pathologic process. Using postmortem tissue obtained from the Parkinson's Disease Society Brain Tissue Bank in London, we have sought to establish whether apoptosis, or more specifically DNA fragmentation of neurons, is a prominent feature of nigral pathology. In addition, we have studied microglial activation in the substantia nigra as an indicator of ongoing pathology using the highly sensitive markers CR3/43 and EBM11. Reactive astrocytes have been assessed using immunostaining for glial fibrillary acidic protein (GFAP). Ten patients with pathologically proven PD were studied. In all cases, regardless of disease duration, severity, drug treatment, or age of the patient, there was no evidence of apoptosis in the substantia nigra as assessed by in situ end-labeling of DNA fragments using biotinylated dUTP and terminal deoxynucleotidyl transferase (TdT). In contrast, a case of multiple system atrophy (MSA) served as a positive control for the technique. In this case, positive DNA end-labeling could be found in neurons and non-neuronal cells in the brain stem. In the PD cases, there was, however, localized pathology in the substantia nigra as revealed by the CR3/ 43 and EBM11 markers for activated microglia. This process seemed independent of disease duration and was florid even in patients with severe neuronal loss. It remains to be determined to what extent the activation of glial cells reflects progressive nigral pathology, and whether those factors which are classically associated with prominent apoptotic neuronal cell death in vivo, such as neurotrophic factor deprivation, are prime causes of nigral neuronal loss in PD. Future studies should focus on recent-onset PD or incidental Lewy body disease to further address these questions.

Involvement of iron in MPP+ toxicity in substantia nigra: protection by desferrioxamine

Desferrioxamine (DES) protective effect against 1-methyl-4-phenylpyridinium (MPP+) toxicity was evaluated by microdialysis in the substantia nigra. DES (1 microM to 10 mM) co-perfused with MPP+ (2.5 mM) on day 1, produced on day 2 a higher dopamine extracellular output after perfusion of MPP+ than in control-MPP+ perfusion experiments, in which no DES was administered on day 1. Both Ringer's perfusion alone (control-Ringer) and co-perfusion of DES (10 mM) with MPP+ (2.5 mM) on day 1 produced on day 2 similar increases in dopamine extracellular output after a second MPP+ perfusion. In the control-Ringer experiment, note that the MPP+ on day 2 is the first MPP+ perfusion. Perfusion of FeCl3 (200 microM) along with MPP+ (2.5 mM) and DES (100 microM) on day 1 completely abolished on day 2 the neuroprotective effect found with MPP+ (2.5 mM) and DES (100 microM). The ability of DES to protect against MPP+ toxicity may indicate a therapeutic strategy in the treatment of diseases when iron is implicated.

EPR investigations of the iron domain in neuromelanin

The interactions between iron and neuromelanin (NM) have been studied by means of EPR spectroscopy. The variable temperature EPR spectral features of a specimen of NM extracted from normal human midbrains clearly indicate that iron is present as polynuclear oxy-hydroxy ferric aggregates as well as isolated Fe(III) centres. Ferric oxy-hydroxy phases are typical of the iron storage proteins ferritin and hemosiderin, but the comparison of the variable temperature EPR spectra of ferritin and NM highlights significant differences between the two iron(III)oxy-hydroxy domains. Moreover, further investigations on melanin models synthesised in the presence of either ferritin or a ferric salt as iron sources suggest that the same pathway of formation and inclusion of the polynuclear iron oxide is operating in NM and in the model systems, whatever is the source of iron.

Essential trace element alterations in amyotrophic lateral sclerosis

Although trace elements have been implicated in the pathogenesis of amyotrophic lateral sclerosis (ALS) for a long time, new evidence has connected familial ALS with the metalloenzyme copper-zinc superoxide dismutase, thus reinforcing the study of their metabolism. This work presents the results of serum and cerebrospinal fluid levels of copper, zinc, manganese and magnesium, by atomic absorption spectrophotometry. Statistically significant decreased cerebrospinal fluid and serum copper levels were found in patients compared to the control group (20.25 +/- 7.09 vs. 30.86 +/- 16.02 SD micrograms/l and 913.21 +/- 165.55 vs. 1020.17 +/- 197.76 SD micrograms/l) while serum manganese levels were found to be increased in patients (3.59 +/- 0.89 SD micrograms/l) compared to controls (3.03 +/- 1.23 SD micrograms/l). Zinc and magnesium levels were unchanged. Our findings indicate an essential trace element imbalance in the disease.

Characterization of brain beta-carboline-2-N-methyltransferase, an enzyme that may play a role in idiopathic Parkinson's disease

The activity of beta-carboline-2-N-methyltransferase results in the formation of neurotoxic N-methylated beta-carbolinium compounds. We have hypothesized that these N-methylated beta-carbolinium cations may contribute to the development of idiopathic Parkinson's disease. This report describes experiments undertaken to optimize assay conditions for bovine brain beta-carboline-2-N-methyltransferase activity. The activity of beta-carboline-2-N-methyltransferase is primarily localized in the cytosol, has a pH optimum of 8.5-9, and obeys Michaelis-Menten kinetics with respect to its substrates, 9-methylnorharman (9-MeNH) and S-adenosyl-L-methionine (SAM). Kinetic constants, KM and Vmax, with respect to 9-MeNH, are 75 microM and 48 pmol/h/mg protein, respectively. The KM for SAM is 81 microM and the Vmax is 53 pmol/h/mg protein. In addition, enzyme activity is inhibited by S-adenosyl-L-homocysteine (SAH) or zinc, and is increased 2-fold in the presence of iron or manganese. Enzyme characterization is a prerequisite to the purification of this N-methyltransferase from bovine brain as well as comparison of its activity in human brain from control and Parkinson's disease individuals.

Mitochondrial respiratory enzyme function and superoxide dismutase activity following brain glutathione depletion in the rat

In substantia nigra from patients with Parkinson's disease, there are decreased levels of reduced glutathione (GSH) and diminished activities of mitochondrial complex I and alpha-ketoglutarate dehydrogenase (alpha-KGDH), along with increased activity of superoxide dismutase (SOD). However, the interrelationship among these events is uncertain. We now report the effect of decreased brain GSH levels on SOD and mitochondrial respiratory enzyme activity in rat brain. In addition, we have investigated the ability of thioctic acid, an endogenous antioxidant, to alter these parameters. Unilateral or bilateral intracerebroventricular (ICV) administration of buthionine sulphoximine (BSO; 1 x 3.2 mg or 2 x 1.6 mg) over a 48-hr period reduced cortical GSH by 55-70%. There was no change in the activity of complex I, II/III, or IV or of citrate synthase in cortex. Similarly, there was no alteration of mitochondrial or cytosolic SOD activity. Thioctic acid (50 or 100 mg/kg IP) alone had no effect on cortical GSH levels in control animals and did not reverse the decrease in GSH levels produced by unilateral or bilateral ICV BSO administration. Thioctic acid (50 or 100 mg/kg IP) had no overall effect on complex I, II/III, or IV or on citrate synthase activity in control animals. Thioctic acid also did not alter cortical mitochondrial respiratory enzyme activity in BSO-treated rats. At the lower dose, thioctic acid tended to increase mitochondrial and cytosolic SOD activity in control animals and in BSO-treated rats. However, at the higher dose, thioctic acid tended to decrease mitochondrial SOD activity. Overall, there was no consistent effect of thioctic acid (50 or 100 mg/kg IP) on SOD activity in control or BSO-treated animals. This study shows that BSO-induced glutathione deficiency does not lead to alterations in mitochondrial respiratory enzyme activity or to changes in SOD activity. GSH depletion in Parkinson's disease therefore may not account for the alterations occurring in complex I and mitochondrial SOD in substantia nigra. Thioctic acid did not alter brain GSH levels or mitochondrial function. Interestingly, however, it did produce some alterations in SOD activity, which may reflect either its antioxidant activity or its ability to act as a thiol-disulphide redox couple.

Oxidative stress and apoptosis in neurodegeneration

The pathogenesis of neurodegenerative diseases such as Parkinson's diseases, amyotrophic lateral sclerosis and Alzheimer's disease is unknown. These diseases are characterized by a slow, progressive loss of particular subsets of neurons. Much evidence has accumulated which supports the hypothesis that oxidative stress and damage by free radicals may play an important part in these diseases. In particular recent studies with the inherited form of amyotrophic lateral sclerosis have revealed mutations in the superoxide dismutase gene, which is one of the cell's main defence mechanisms against oxidative stress. These findings suggest a direct link between oxidative stress and the development of a neurodegenerative disease.

Autoradiography of transferrin receptors in the human brain

Transferrin is the major protein concerned with iron transport in the serum and may provide a route by which iron enters the brain. This study was designed to show the optimal binding conditions for in vitro transferrin receptor autoradiography and to show the regional distribution of transferrin receptors in the human brain. Optimal binding conditions were: 120 min incubation with 5.0 nM 125I-transferrin at 37 degrees C. Transferrin receptors degrade quickly even with storage at -70 degrees C, therefore binding studies should be performed within 7 days post mortem. Transferrin receptors were widely distributed in the human brain, with high density in the neocortex, moderate densities in the putamen and caudate nuclei, and very low densities in the globus pallidus and substantia nigra. Therefore transferrin receptor density shows a mismatch with the known distribution of iron in the human brain. The presence and distribution of transferrin receptors in the human brain are important because they may provide a route to deliver lipophobic substances across the blood-brain barrier by binding them to antibodies raised against transferrin receptors.

Different mechanisms of glutamate-induced neuronal death between dopaminergic and non-dopaminergic neurons in rat mesencephalic culture

Parkinson's disease is characterized by dopaminergic neuronal degeneration, but its pathogenic mechanism is still unknown. In the dopaminergic neurons, oxygen radicals such as hydrogen peroxide are released through dopamine oxidation. Many factors are involved in radical formation, but glutamate and nitric oxide (NO) are the major effectors of the radical-induced neurotoxicity mediated primarily through calcium influx. In the cultured embryonic rat mesencephalon, we investigated the dopaminergic and non-dopaminergic neuronal death induced by glutamate and by NO-generating agents. Although glutamate had a neurotoxic effect on both dopaminergic and non-dopaminergic neurons, it showed slightly greater effect in the dopaminergic neurons. In contrast to glutamate, NO-generating agents (S-nitrosocysteine and sodium nitroprusside) showed neurotoxic effects restricted exclusively to non-dopaminergic neurons. Although N omega-nitro-L-arginine, and NO synthase inhibitor, had no significant effect on the glutamate-induced cytotoxicity in dopaminergic neurons, it had a significant antagonistic effect on that in non-dopaminergic neurons. These findings indicate the presence of two different mechanisms of glutamate-induced neuronal death, one being neurotoxicity not mediated by NO, found in dopaminergic neurons, and the other being that mediated via NO, found in non-dopaminergic neurons.

Glutamate and Parkinson's disease

Altered glutamatergic neurotransmission and neuronal metabolic dysfunction appear to be central to the pathophysiology of Parkinson's disease (PD). The substantia nigra pars compacta--the area where the primary pathological lesion is located--is particularly exposed to oxidative stress and toxic and metabolic insults. A reduced capacity to cope with metabolic demands, possibly related to impaired mitochondrial function, may render nigral highly vulnerable to the effects of glutamate, which acts as a neurotoxin in the presence of impaired cellular energy metabolism. In this way, glutamate may participate in the pathogenesis of PD. Degeneration of dopamine nigral neurons is followed by striatal dopaminergic denervation, which causes a cascade of functional modifications in the activity of basal ganglia nuclei. As an excitatory neurotransmitter, glutamate plays a pivotal role in normal basal ganglia circuitry. With nigrostriatal dopaminergic depletion, the glutamatergic projections from subthalamic nucleus to the basal ganglia output nuclei become overactive and there are regulatory changes in glutamate receptors in these regions. There is also evidence of increased glutamatergic activity in the striatum. In animal models, blockade of glutamate receptors ameliorates the motor manifestations of PD. Therefore, it appears that abnormal patterns of glutamatergic neurotransmission are important in the symptoms of PD. The involvement of the glutamatergic system in the pathogenesis and symptomatology of PD provides potential new targets for therapeutic intervention in this neurodegenerative disorder.

Oxidative stress and antioxidant therapy in Parkinson's disease

Parkinson's disease, known also as striatal dopamine deficiency syndrome, is a degenerative disorder of the central nervous system characterized by akinesia, muscular rigidity, tremor at rest, and postural abnormalities. In early stages of parkinsonism, there appears to be a compensatory increase in the number of dopamine receptors to accommodate the initial loss of dopamine neurons. As the disease progresses, the number of dopamine receptors decreases, apparently due to the concomitant degeneration of dopamine target sites on striatal neurons. The loss of dopaminergic neurons in Parkinson's disease results in enhanced metabolism of dopamine, augmenting the formation of H2O2, thus leading to generation of highly neurotoxic hydroxyl radicals (OH.). The generation of free radicals can also be produced by 6-hydroxydopamine or MPTP which destroys striatal dopaminergic neurons causing parkinsonism in experimental animals as well as human beings. Studies of the substantia nigra after death in Parkinson's disease have suggested the presence of oxidative stress and depletion of reduced glutathione; a high level of total iron with reduced level of ferritin; and deficiency of mitochondrial complex I. New approaches designed to attenuate the effects of oxidative stress and to provide neuroprotection of striatal dopaminergic neurons in Parkinson's disease include blocking dopamine transporter by mazindol, blocking NMDA receptors by dizocilpine maleate, enhancing the survival of neurons by giving brain-derived neurotrophic factors, providing antioxidants such as vitamin E, or inhibiting monoamine oxidase B (MAO-B) by selegiline. Among all of these experimental therapeutic refinements, the use of selegiline has been most successful in that it has been shown that selegiline may have a neurotrophic factor-like action rescuing striatal neurons and prolonging the survival of patients with Parkinson's disease.

Changed transferrin sialylation in Parkinson's disease

Variation in the sialylation pattern of transferrin was studied in serum and cerebrospinal fluid (CSF) of 90 patients with Parkinson's disease (PD), dementing and non-dementing, de novo and treated, and was compared with the variation observed in a group of 21 age-matched healthy controls. In serum and CSF of PD patients the proportional contribution of the different sialo-transferrins was independent of sex or dementia. However, a significant shift was found towards the more sialylated fractions for serum transferrin in both de novo and treated PD patients. This shift was not observed for CSF transferrin. The contribution of the tau-transferrin fraction, reduced in de novo PD patients, returns on treatment to the level observed for healthy controls. These observations may be important, as the degree of sialylation of transferrin in serum and CSF plays a role in the homeostasis of iron, and suggest that alterations in transferrin sialylation may play a role in the pathophysiology of PD.

Regional differences in late-onset iron deposition, ferritin, transferrin, astrocyte proliferation, and microglial activation after transient forebrain ischemia in rat brain

With use of iron histochemistry and immunohistochemistry, regional changes in the appearance of iron, ferritin, transferrin, glial fibrillary acidic protein-positive astrocytes, and activated microglia were examined from 1 to 24 weeks after transient forebrain ischemia (four-vessel occlusion model) in rat brain. Expression of the C3bi receptor and the major histocompatibility complex class II antigen was used to identify microglia. Neuronal death was confirmed by hematoxylin-eosin staining only in pyramidal cells of the hippocampal CA1 region, which is known as the area most vulnerable to ischemia. Perls' reaction with 3,3'-diaminobenzidine intensification revealed iron deposits in the CA1 region after week 4, which gradually increased and formed clusters by week 24. Iron also deposited in layers III-V of the parietal cortex after week 8 and gradually built up as granular deposits in the cytoplasm of pyramidal cells in frontocortical layer V. An increasing astroglial reaction and the appearance of ferritin-immunopositive microglia paralleled the iron accumulation in the hippocampal CA1 region, indicating that iron deposition was probably produced in the process of gliosis. Neither neuronal death nor atrophy was found in the cerebral cortex. Nevertheless, an astroglial and ferritin-immunopositive microglial reaction became evident at week 8 in the parietal cortex. On the other hand, the granular iron deposition in the pyramidal neurons of frontocortical layer V was not accompanied by any glial reaction in the chronic stage of ischemia. Three different types of iron deposition in the chronic phase after transient forebrain ischemia were shown in this study. In view of the neuronal damage caused by iron-catalyzed free radical formation, the late-onset iron deposition may be relevant to the pathogenesis of the chronic brain dysfunction seen at a late stage after cerebral ischemia.

Bioenergetic and oxidative stress in neurodegenerative diseases

Aging is a major risk factor for several common neurodegenerative diseases, including Parkinson's disease (PD), amyotrophic lateral sclerosis (ALS), Alzheimer's disease (AD), and Huntington's disease (HD). Recent studies have implicated mitochondrial dysfunction and oxidative stress in the aging process and also in the pathogenesis of neurodegenerative diseases. In brain and other tissues, aging is associated with progressive impairment of mitochondrial function and increased oxidative damage. In PD, several studies have demonstrated decreased complex I activity, increased oxidative damage, and altered activities of antioxidant defense systems. Some cases of familial ALS are associated with mutations in the gene for Cu, Zn superoxide dismutase (Cu, Zn SOD) and decreased Cu, Zn SOD activity, while in sporadic ALS oxidative damage may be increased. Defects in energy metabolism and increased cortical lactate levels have been detected in HD patients. Studies of AD patients have identified decreased complex IV activity, and some patients with AD and PD have mitochondrial DNA mutations. The age-related onset and progressive course of these neurodegenerative diseases may be due to a cycling process between impaired energy metabolism and oxidative stress.

Oxidative stress in Parkinson's disease

Oxidative damage and mitochondrial dysfunction are now considered to be important events in the cause of dopaminergic cell death in Parkinson's disease (PD). It is not known whether these biochemical abnormalities represent primary causes of PD or whether they are the end result of a series or reactions precipitated by environmental and genetic factors. Both oxidative damage and complex I deficiency are linked in a reciprocal manner and can potentially produce a toxic cellular environment capable of attacking a variety of biomolecules as well as inhibiting energy production. Defining the roles that these two biochemical defects play in nigral neuronal loss will provide important insights into the aetiology of PD.

Complex I, iron, and ferritin in Parkinson's disease substantia nigra

Elevated iron levels, enhanced oxidative damage, and complex I deficiency have been identified in the substantia nigra of Parkinson's disease patients. To understand the interrelationship of these abnormalities, we analyzed iron levels, ferritin levels, and complex I activity in the substantia nigra of patients with Parkinson's disease. Total iron levels were increased significantly, ferritin levels were unchanged, and complex I activities were decreased significantly in the substantia nigra samples. The failure of ferritin levels to increase with elevated iron concentrations suggests that the amount of reactive iron may increase in the substantia nigra of Parkinson's disease patients. There was no correlation between the iron levels and complex I activity or the iron-ferritin ratio and complex I activity in the substantia nigra samples.

Ferrous-citrate complex and nigral degeneration: evidence for free-radical formation and lipid peroxidation

Increased nigral iron content in the parkinsonian brain is now well documented and is implicated in the pathogenesis of this movement disorder. Free iron in the pigmented DA-containing neurons catalyze DA autoxidation and Fenton reaction to produce cytotoxic .OH, initiating lipid peroxidation and consequent cell damage. The present results clearly demonstrate that a regional increase in the levels of the "labile iron pool" can result in the degeneration of dopaminergic nigral neurons as reflected by a significant inhibition in the expression of tyrosine hydroxylase mRNA and DA depletion. Iron-complex-induced damage of dopaminergic neurons in the substantia nigra, might have resulted from a sequence of cytotoxic events including the .OH generation and lipid peroxidation as demonstrated in this study. This free-radical-induced oxidative nigral injury may be a reliable free-radical model for studying parkinsonism and may be relevant to idiopathic Parkinson's disease. This apparent nigral injury stimulated by Fe(2+)-citrate is more severe than that produced by ferric iron and its citrate complex. Moreover, these data indicate that Fe(2+)-citrate is as potent as MPP+ in causing oxidative injury to the substantia nigral neurons. However, the nigral toxicity of MPTP and its congeners are not progressive, while Fe(2+)-citrate complex may produce a progressive degeneration of the nigrostriatal neurons which is similar to the progression of ideopathic Parkinson's disease. Thus, this unique Fe(2+)-citrate complex animal model could be used for studying neuroprotective treatments for retarding or halting the progressive nigrostriatal degeneration caused by free radicals in the iron-rich basal ganglia.

Antioxidant mechanism and protection of nigral neurons against MPP+ toxicity by deprenyl (selegiline)

The current research has demonstrated that MPP+ can induce lipid peroxidation in the nigrostriatal system of rat in vivo. Antioxidant agent U-78517F and .OH scavenger DMSO may protect against MPP+ toxicity through the inhibition of .OH radical-mediated oxidative injury in the substantia nigra. These findings indicate that the cytotoxic hydroxyl radical generated from dopamine oxidation in the iron-rich basal ganglia may contribute to the mechanism underlying the selective A9 melanized nigral degeneration in MPTP-Parkinsonism and possibly in idiopathic Parkinson's disease. In addition, the present studies also clearly demonstrate that deprenyl can substantially protect dopaminergic neurons against MPP+ toxicity in the substantia nigra zona compacta in vivo. The neuroprotective effect provided by deprenyl may not be the consequence of its inhibition of MAO-B activity or prevention of the uptake of MPP+ by dopaminergic neurons. A unique antioxidant property of deprenyl by suppressing .OH formation and associated oxidative injury induced by MPP+ may contribute to the apparent neuroprotective action. In perspective, this putative antioxidant effect of deprenyl may provide another mechanism to its overt neuroprotective effects against oxygen radical-mediated oxidative injury in some neurotoxic chemicals, such as 6-OHDA and DSP-4, and probably in Alzheimer's disease and senescent changes. Finally, based on the present data, a possible neuroprotective therapeutic window of deprenyl in the treatment of early Parkinson's disease has been proposed. It is suggested that deprenyl should be introduced as early as possible in de novo Parkinsonian patients to achieve its full neuroprotective effect on nigral degeneration. Moreover, a combination of early detection of individuals at risk of developing Parkinson's disease and early intervention of deprenyl and/or other centrally active antioxidants to these patients may provide a new preventive therapeutic strategy in the future, in addition to the current conventional levodopa treatment of Parkinson's disease.

Peripheral iron metabolism in patients with Parkinson's disease

To elucidate the possible role of peripheral metabolism of iron in the risk for developing Parkinson's disease (PD), we compared serum levels of iron, transferrin and ferritin, and 24-h iron excretion in urine after a single intramuscular dose of 1 mg/kg desferrioxamine, in 68 PD patients and their spouses as the control group. All these values did not differ significantly between the groups, they were not influenced by antiparkinsonian therapy, and they did not correlate with age, age at onset and duration of the disease, scores of the Unified PD Rating Scale or the Hoehn and Yahr staging in the PD group, with the exception of the 24-h urinary iron excretion with the duration of the disease (r = 0.32, p < 0.05). These results suggest that peripheral metabolism of iron is apparently unrelated to the risk of developing PD.

Ironic catastrophes: one's food--another's poison

Iron deficiency is an important nutritional problem in third world countries because it diminishes work performance. In meat-eating countries, iron excess may be more important than iron deficiency. Heme iron is more efficiently absorbed from the diet than inorganic iron, and iron excess can produce cellular oxidation in association with superoxide dismutase. Metal ion catalysis is linked to aging, coronary artery disease, stroke, carcinogenesis, neurodegenerative disorders, and inflammatory disorders. Prudence is advised in the excessive consumption of meat and iron supplementation of the diet until this process is more thoroughly investigated.

Cerebrospinal fluid ferritin levels of patients with Parkinson's disease, Alzheimer's disease, and multiple system atrophy

Iron is believed to play a role in the pathogenesis of both Parkinson's disease (PD) and Alzheimer's disease (AD). We measured ferritin, which is considered to be the iron storage protein, in CSF of patients with PD, AD, and multiple system atrophy (MSA) as well as control subjects. We found a significant increase in CSF ferritin in AD compared with both PD and age-matched controls. No significant differences were found between PD patients with dementia (PDD) and non-demented PD patients. For non-demented PD patients a positive correlation between CSF ferritin and age was found. Our results may indicate that iron has a role in the pathophysiology of AD.

Unaltered aconitase activity, but decreased complex I activity in substantia nigra pars compacta of patients with Parkinson's disease

Substantia nigra pars compacta of seven patients who had died of Parkinson's disease, has been investigated for the iron-depending aconitase (reactions I and II). In addition we analysed respiratory chain enzymes. While complex I activity of the respiratory chain was significantly reduced, other enzymes of this pathway were unaltered. The citric acid cycle enzyme aconitase (reactions I and II) showed no difference between patients and controls. Thus this ferrous iron dependent and oxidatively sensitive enzyme is not affected by the unphysiological high amount of ferric iron and the 'oxidative stress' present in substantia nigra of parkinsonian patients.

Antioxidant properties of bromocriptine, a dopamine agonist

It has been suggested that free radicals may adversely influence the pathogenesis of Parkinson's disease. We conducted this study to determine whether bromocriptine, an agent widely used for treating parkinsonism, possesses antioxidant effects. Bromocriptine scavenged superoxide produced from a superoxide generating system (hypoxanthine-xanthine oxidase) by the spin-trapping method using electron spin resonance. Bromocriptine had a strong scavenging effect on the 5,5-dimethyl-1-pyrroline-N-oxide hydroxide signal produced from Fenton's reaction. Bromocriptine also attenuated the stable free radical diphenyl-p-picrylhydrazyl signal. This drug inhibited the autooxidation of rat brain homogenates in a dose-dependent manner in vitro. Autooxidation of brain homogenates collected from rats treated with bromocriptine (2.5 mg/kg, i.p., daily for 3 days) was significantly reduced as compared with values in untreated rat homogenates. These observations suggest that bromocriptine is a free radical scavenger and a potent antioxidant.

Iron accumulation in the substantia nigra of 1-methyl-4-phenyl-1,2,3,6-tetrahydropyridine (MPTP)-induced hemiparkinsonian monkeys

The mechanism of abnormal iron accumulation in the substantia nigra (SN) pars compacta of patients with Parkinson's disease (PD) is unknown. To explore this question, we made a hemiparkinsonism model in monkeys by injecting 1-methyl-4-phenyl-1,2,3,6-tetrahydropyridine (MPTP) into the caudate or putamen on one side, and compared iron content in the SN and other basal ganglia structures by histochemistry. The injected side, especially the SN pars compacta, showed a marked increase in iron staining. Our study indicates that an injury to the nigrostriatal system by MPTP injection can induce iron accumulation in the SN.

Increased levels of lipid hydroperoxides in the parkinsonian substantia nigra: an HPLC and ESR study

Previous studies examining the involvement of oxidative stress in the substantia nigra in Parkinson's disease have measured terminal products of lipid peroxidation or the function of antioxidant defense systems. We report a more specific early marker of lipid peroxidation, lipid hydroperoxides, in a high-performance liquid chromatography (HPLC) and electron spin resonance (ESR) investigation. HPLC-chemiluminescent detection revealed two classes of lipid hydroperoxides in brain tissue extracts--free fatty acid hydroperoxides and cholesterol lipid hydroperoxides. Only cholesterol lipid hydroperoxides were consistently detected in all tissue extracts. Cholesterol lipid hydroperoxides had a 10-fold increase in the Parkinson's disease substantia nigra compared to control subjects. ESR detection of radical degradation products, including those of lipid hydroperoxides, in nigral homogenates incubated with the spin trap N-t-butyl-alpha-phenyl nitrone (PBN) showed a marked variation in ESR signal between tissues. Despite the increased levels of lipid hydroperoxides in parkinsonian substantia nigra, there was no overall difference in ESR signal intensity between nigral tissues from controls and from patients with Parkinson's disease. The increased levels of an early component of the peroxidation chain in substantia nigra in Parkinson's disease support the hypothesis of a continuous toxic process involving oxygen radical activity. However, using previously frozen tissue, ESR evidence for increased radical formation could not be demonstrated.

Indices of oxidative stress and mitochondrial function in individuals with incidental Lewy body disease

Brain tissue from normal individuals with incidental Lewy bodies and cell loss in pigmented substantia nigra neurons (asymptomatic Parkinson's disease) and age-matched control subjects without nigral Lewy bodies was examined biochemically. There was no difference in dopamine levels or dopamine turnover in the caudate and putamen of individuals with incidental Lewy body disease compared to control subjects. There were no differences in levels of iron, copper, manganese, or zinc in the substantia nigra or other brain regions from the individuals with incidental Lewy body disease compared to those from control subjects. Similarly, ferritin levels in the substantia nigra and other brain areas were unaltered. There was no difference in the activity of succinate cytochrome c reductase (complexes II and III) or cytochrome oxidase (complex IV) between incidental Lewy body subjects and control subjects. Rotenone-sensitive NADH coenzyme Q1 reductase activity (complex I) was reduced to levels intermediate between those in control subjects and those in patients with overt Parkinson's disease, but this change did not reach statistical significance. The levels of reduced glutathione in substantia nigra were reduced by 35% in patients with incidental Lewy body disease compared to control subjects. Reduced glutathione levels in other brain regions were unaffected and there were no changes in oxidized glutathione levels in any brain region. Altered iron metabolism is not detectable in the early stages of nigral dopamine cell degeneration. There may be some impairment of mitochondrial complex I activity in the substantia nigra in Parkinson's disease.(ABSTRACT TRUNCATED AT 250 WORDS)

Regulation of iron absorption: proteins involved in duodenal mucosal uptake and transport

Newly identified iron (Fe)-binding proteins isolated from both rat and human duodenal mucosa permit a better understanding of Fe absorption. Mucins bind Fe at acid pH to keep it soluble and available for absorption at the more alkaline pH of the duodenum; this explains the development of Fe deficiency in achlorhydric subjects. Integrin was identified on the surface of enterocytes in association with radioiron and is believed to facilitate the transfer of Fe through the microvillous membrane. Mobilferrin, a 56 kDa Fe-binding protein, was identified in enterocyte cytosol. It coprecipitates with integrin and appears in close association with integrin in the apical cytoplasm of absorptive cells. We postulate it accepts dietary Fe from integrin and acts as the shuttle protein from Fe in the cytoplasm. Since Fe in enterocytes remains in equilibrium with body stores, we postulate mucosal Fe uptake is regulated by the number of Fe-binding sites either occupied or unoccupied by Fe on mobilferrin. Fe repletion of enterocytes from body stores is probably accomplished via transferrin receptors on the basal membranes of enterocytes. Increased transfer of Fe from blood into absorptive enterocytes occurs in Fe-replete animals to inhibit mucosal uptake of dietary Fe. Little transfer of Fe from plasma to enterocytes occurs in Fe deficiency. Enhanced mucosal transfer into the body occurs with increased body need for Fe. The exact mechanism for mucosal transfer of Fe into the plasma has not been defined but may also be mediated by an integrin.(ABSTRACT TRUNCATED AT 250 WORDS)

Iron induced oxidative stress and mitochondrial dysfunction: relevance to Parkinson's disease

Inactivation of the mitochondrial respiratory chain in response to iron-induced oxidative stress has been studied in cultured cells. Iron loading resulted in malonaldehyde production, decreased levels of glutathione and reduced specific activities of both complexes I and IV of the respiratory chain. These results are discussed with respect to idiopathic Parkinson's disease, which is associated with increased iron levels and a specific decrease in complex I activity in the substantia nigra.

Pallidonigroluysian degeneration with iron deposition: a study of three autopsy cases

In the basal ganglia of three autopsy cases of pallidonigroluysian degeneration, we found marked iron deposition, a finding which has not been mentioned previously in the literature. Besides severe astrogliosis and neuronal loss in the pallidum, Luysian body and nigra, granular deposits of brown pigments were found in the neuropil, microglias, oligodendrocytes and astrocytes in three such the nuclei and the striatum. These brown pigments proved histochemically to be iron. Our histochemical semiquantitative study showed a significantly stronger reaction for iron in the degenerated nuclei in these three cases than in control cases comprising non-degenerative and the other degenerative diseases. Quantitative study with inductively coupled emission spectrometry also demonstrated a markedly higher iron content in the globus pallidus and the striatum in comparison with the control cases. The possibility is discussed that iron deposition plays a role in generating the lesions of pallidonigroluysian degeneration.

MRI, brain iron and experimental Parkinson's disease

Abnormal levels of brain iron have been reported in parkinsonism, which is characterized principally by degeneration of dopaminergic (DA) nigrostriatal neurons. There are conflicting reports, however, of both increased and decreased iron in parkinsonism. An animal model of parkinsonism was used to clarify the contribution of the loss of nigrostriatal DAergic neurons to abnormal iron accumulations. In rats with 6-hydroxydopamine induced unilateral DA depletion, brain iron deposition and its day-to-day stability was studied in vivo using T2-weighted magnetic resonance imaging (MRI) scans taken on 4 consecutive days beginning 1-2 months post-surgery and post-mortem by Perls'-DAB histochemical stain. Unilateral DA depletion (parkinsonism model) produced large day-to-day fluctuations in T2 relaxation time in the striatum. The T2 relaxation time in Sham control rats was relatively minor. The uptake and transport of iron by intrinsic cells of the striatum may vary, and this variability may have been exaggerated by the destruction of DAergic nigrostriatal neurons, which are known to modulate the activity of the intrinsic cells. Inconsistent reports of increased or decreased iron in parkinsonism may reflect, in part, single time-point measures of widely fluctuating iron.

Iron accumulation in the rat basal ganglia after excitatory amino acid injections--dissociation from neuronal loss

The current study examines in an animal model the relation of excessive iron accumulation in the basal ganglia to the pathology of Parkinsonism and Hallervoden-Spatz disease. Following a unilateral microinjection of excitatory amino acids, kainate, or quinolinate to the anterior olfactory nucleus/ventral striatal region, an increase in histochemical iron concentration was observed in the ipsilateral ventral pallidum, the islands of calleja, the globus pallidus, the entopeduncular nucleus, the ventral thalamus, and the substantia nigra pars reticulata. The iron was observed both in glia and as intensification of patches in the neuropil. In a second group of rats, after microinjection of ibotenate or quisqualate to the nucleus basalis of Meynert, iron accumulated in the ipsilateral entopeduncular nucleus and pars reticulata of substantia nigra. Increased iron accumulation, compared to that in the contralateral side, was stable for months after a single microinjection. In the basal ganglia distal from the site of EAA injection, no gross morphological changes were associated with the increased iron accumulation. The implications of these findings to the pathology of Parkinson's and Hallervorden-Spatz diseases are discussed.