Parkinson's Disease Substantia Nigra Research Articles

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

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

Uric acid is reduced in the substantia nigra in parkinson's disease: Effect on dopamine oxidation

Postmortem caudate and substantia nigra tissue samples from human parkinsonian patients (PD) and age-matched controls (NC) were analyzed for uric acid (UA), dopamine (DA), and ascorbic acid (AA) by HPLC/UV/ED. Uric acid and DA levels were significantly lower in the substantia nigra of PD by 54% and 85%, respectively. In the caudate, DA levels were significantly lower while UA levels were nonsignificantly reduced (0.10 < p < 0.05). Ascorbic acid levels were not significantly different from the controls in either brain region. Conditions favorable for oxidative stress were evaluated by measuring the oxidation of DA in individual brain homogenates. The rate constant for DA oxidation in control caudate was 0.34 × 10 −2 min −1 and in parkinsonian caudate was 4.20 × 10 −2 min t-1 . In control and parkinsonian substantianigra DA oxidation rate constants were 2.82 × 10 −2 min t−1 and 4.57 × 10 −2 min −1, respectively. Addition of UA or catalase to parkinsonian homogenate decreased the rate of DA oxidation, while addition of uncase to control homogenate increased the rate of DA oxidation. The data support the hypothesis that UA is decreased in nigrostriatal dopamine neurons in parkinsonian patients which contributes to an environment susceptible to oxidative stress, particularly through dopamine oxidation reactions.

Evidence for mitochondrial dysfunction in Parkinson's disease--a critical appraisal.

There is now considerable evidence to support a defect of the mitochondrial respiratory chain, and complex I in particular, in Parkinson's Disease (PD). However, the site specificity of the defect within the chain, its anatomical selectivity within the brain, and its presence in other tissues still remain controversial. Much of the present confusion surrounding the mitochondrial defect can be dispelled by careful analysis of the available data. The molecular basis of the deficiency and its relevance to the pathogenesis of PD remain unknown. Nevertheless, the complex I deficiency in PD provides a direct biochemical link between the idiopathic disease and the MPTP toxin model. The relationship between the mitochondrial defect and other abnormalities within the PD substantia nigra suggests that a self amplifying cycle of events might be precipitated either by a genetic or environmentally induced abnormality of mitochondrial function or free radical metabolism. Alternatively, a biochemical event separate from these might precipitate a cascade which terminates in complex I dysfunction and free radical formation. An understanding of the molecular basis of the complex I defect in PD and its relationship to other biochemical changes will provide important insight into the potential chain of events that lead to dopaminergic cell death in PD.

Parallel alterations in Met-enkephalin and substance P levels in medial globus pallidus in Parkinson's disease patients

Met-enkephalin (Met-enk) and substance P (SP) were measured by a combined high-performance liquid chromatography/radioimmunoanalysis method in medial (GPM) and lateral globus pallidus (GPL) from controls and from Parkinson's disease (PD) patients. All patients showed a similar marked (> 90%) reduction in dopamine (DA) levels in putamen compared with controls. However, based on DA levels in the caudate nucleus, two subgroups of PD patients were differentiated. In patients with > 80% decrease in caudate nucleus DA content, there was a three-fold increase in both Met-enk and SP levels in GPM. In contrast, in patients showing an ∼ 50% reduction in DA content in caudate, levels of both peptides were markedly reduced (∼ 80%). Met-enk and SP levels in GPL were unchanged in PD. These results suggest that neurons containing Met-enk and SP projecting to GPM adapt according to the extent of degeneration in the substantia nigra in PD.

Antibody to an abnormal protein in amyotrophic lateral sclerosis identifies Lewy body-like inclusions in ALS and Lewy bodies in Parkinson's disease

Ubiquitinated cytoplasmic inclusions are a characteristic feature of the neuronal pathology of neurodegenerative diseases. Immunocytochemical techniques have identified intermediate filaments associated with ubiquitin-immunoreactive inclusions in Alzheimer's disease (AD), Parkinson's disease (PD), and Pick's disease; however, no core protein has been detected in the ubiquitinated inclusions in amyotrophic lateral sclerosis (ALS). The pathogenesis of these inclusions is not known, but the inclusion may result from an accumulation of an abnormal proteins. Here we report a novel protein of 32.5 kDa detected by polyacrylamide gel electrophoresis, in the spinal cord in ALS patients. A polyclonal antibody raised against this protein and used for Western blotting, suggests that the novel protein is related to actin. Immunocytochemical studies using this antibody indicate that the protein is found in Lewy body-like inclusions in anterior horn cells of ALS, and in Lewy bodies in the substantia nigra in PD.

Neurofilament mRNA is reduced in Parkinson's disease substantia nigra pars compacta neurons.

Lewy bodies are filamentous neuronal inclusions characteristic of Parkinson's disease, and neurofilament triplet proteins are the major components of the filaments in Lewy bodies. Since the neurofilament proteins found in Lewy bodies are abnormally phosphorylated and partially degraded, the formation of Lewy bodies may be due to the defective metabolism of these proteins, and this could lead to impairments in the structure and function of neurofilament rich neuronal processes (i.e., large caliber axons). To gain further insights into the metabolism of neurofilaments in Parkinson's disease, we evaluated neurofilament mRNA levels by semi-quantitative in situ hybridization histochemistry in postmortem tissues from Parkinson's disease and control subjects. Substantia nigra pars compacta neurons were examined with digoxigenin-UTP labeled cRNA probes to the heavy and light neurofilament mRNAs. The relative abundance of these mRNAs was measured by videodensitometric image analysis of chromogenic reaction product. Using this approach, we demonstrated that the levels of both heavy and light neurofilament mRNAs were reduced in Parkinson's disease substantia nigra pars compacta neurons. Additionally, the levels of heavy neurofilament mRNA were lowest in Lewy body containing neurons in the Parkinson's disease cases. These results suggest that the formation of neurofilament-rich Lewy bodies in substantia nigra pars compacta neurons is associated with reduced levels of the heavy and light neurofilament mRNAs in Parkinson's disease. Thus, it is possible that the accumulation of abnormal neurofilament proteins in Lewy bodies and diminished neurofilament mRNAs contribute to the degeneration of substantia nigra pars compacta neurons in Parkinson's disease.

The possible role of iron in the etiopathology of Parkinson's disease.

The identification of 6-hydroxydopamine (6-OHDA) and N-methyl-4-phenyl-1,2,3,6-tetrahydropyridine (MPTP) as dopaminergic neurotoxins that can induce parkinsonism in humans and animals has contributed to a better understanding of Parkinson's disease (PD). Although the involvement of similar neurotoxins has been implicated in PD, the etiology of the disease remains obscure. However, the recently described pathology of PD supports the view for a state of oxidative stress in the substantia nigra (SN), resulting as a consequence of the selective accumulation of iron in SN zona compacta and within the melanized dopamine neurons. Whether iron is directly involved cannot be ascertained. Nevertheless, the biochemical changes due to oxidative stress resulting from tissue iron overload (siderosis) are similar to those now being identified in parkinsonian SN. These include the reduction of mitochondrial electron transport, complex I and III activities, glutathione peroxidase activity, glutathione (GSH) ascorbate, calcium-binding protein, and superoxide dismutase and increase of basal lipid peroxidation and deposition of iron. The participation of iron-induced oxygen free radicals in the process of nigrostriatal dopamine neuron degeneration is strengthened by recent studies in which the neurotoxicity of 6-OHDA has been linked to the release of iron from its binding sites in ferritin. This is further supported by experiments with the prototype iron chelator, desferrioxamine (Desferal), a free-radical inhibitor, which protects against 6-OHDA-induced lesions in the rat. Indeed, intranigral iron injection in rats produces a selective lesioning of dopamine neurons, resulting in a behavioral and biochemical parkinsonism.

Platelet mitochondrial function in Parkinson's disease. The Royal Kings and Queens Parkinson Disease Research Group.

There is increasing evidence that defective function of the mitochondrial enzyme NADH CoQ reductase (complex I) is involved not only in 1-methyl-4-phenyl-1,2,3,6-tetrahydropyridine (MPTP) toxicity, but also in idiopathic Parkinson's disease (PD). Complex I deficiency has been identified in PD substantia nigra and appears to be disease-specific and selective for the substantia nigra within the central nervous system. We describe a method for preparation of an enriched mitochondrial fraction from 60 mL blood. Using this technique, we analyzed respiratory chain function in 25 patients with PD and 15 matched control subjects. We confirm a previous report of a specific complex I deficiency in PD platelet mitochondria. Although there was a statistically significant decrease in complex I activity in the PD group compared with the control group (p = 0.005), the defect was mild (16%); it was not possible to distinguish PD from control values on an individual basis. This deficiency is not detectable in platelet whole-cell homogenates, presumably reflecting the relative insensitivity of this preparation and the limited decrease in complex I activity in PD. The presence of a mild complex I defect in platelets together with a more severe defect in substantia nigra suggests either that the pharmacological characteristics shared by these two tissues render them susceptible to a particular toxin or toxins, or that the defect is widely distributed and other biochemical events enhance the deficiency in substantia nigra.(ABSTRACT TRUNCATED AT 250 WORDS)

The oxidant stress hypothesis in Parkinson's disease: Evidence supporting it

Oxidant stress, due to the formation of hydrogen peroxide and oxygen-derived free radicals, can cause cell damage due to chain reactions of membrane lipid peroxidation. Because the substantia nigra is rich in dopamine, which can undergo both enzymatic oxidation via monoamine oxidase and nonenzymatic autoxidation, hydrogen peroxide and oxyradicals (superoxide anion radical and hydroxyl radical) are generated in this midbrain nucleus. Although proof that oxidant stress actually causes the loss of monoaminergic neurons in patients with Parkinson's disease is lacking, there is a considerable body of evidence from studies in both animals and humans that support the concept. (1) Neurotoxins that selectively destroy the dopaminergic neurons in the nigra, such as 6-hydroxydopamine and 1-methyl-4-phenyl-1,2,3,6-tetrahydropyridine (MPTP), appear to act via oxidant stress. (2) The substantia nigra of patients with Parkinson's disease reveals evidence of oxidant stress by the findings of increased lipid peroxidation and decreased reduced glutathione. (3) Total iron is increased and ferritin is reduced in the substantia nigra pars compacta in patients with Parkinson's disease. This combination suggests that this transition metal is in a low molecular weight form, capable of catalyzing nonenzymatic oxidative reactions, especially the conversion of hydrogen peroxide to hydroxyl radical, which is the most reactive of the oxygen radicals. (4) Neuromelanin, a product of dopamine autoxidation, can serve as a reservoir for iron, promoting the generation of oxyradicals. (5) Antioxidant defense mechanisms appear to be reduced in the parkinsonian substantia nigra with the findings of decreased activities of glutathione peroxidase and catalase.(ABSTRACT TRUNCATED AT 250 WORDS)

Irreversible Inhibition of Mitochondrial Complex I by 1‐Methyl‐4‐Phenylpyridinium: Evidence for Free Radical Involvement

Incubation of 10 mM 1-methyl-4-phenylpyridinium (MPP+) with sonicated beef heart mitochondria caused an irreversible time-dependent decrease in NADH-ubiquinone-1 (CoQ1) reductase activity (52% inhibition after 1 h). Inclusion of glutathione, ascorbate, or catalase in the incubation mixture protected the NADH-CoQ1 reductase activity. These results suggest that the interaction of MPP+ with complex I induces free radical generation, which in turn leads to the irreversible inhibition of complex I activity. The generation of free radicals by neurotoxin-induced inhibition of complex I has important implications for our interpretation of the increased oxidative stress observed in Parkinson's disease substantia nigra and for our understanding of the cause(s) of dopaminergic cell death in this disorder.

Alterations in levels of iron, ferritin, and other trace metals in neurodegenerative diseases affecting the basal ganglia. The Royal Kings and Queens Parkinson's Disease Research Group.

Previously we have shown that cell death in the substantia nigra (SN) in Parkinson's disease (PD) is associated with an increase in iron content but a decrease in the level of the iron-binding protein ferritin. Alterations in other metal ion levels were also observed; copper levels were reduced, whereas zinc levels were increased. The importance of these changes in iron, ferritin, and other metal ions in the pathophysiology of PD depends on whether they are specific to the illness. We measured levels of iron, copper, zinc, manganese, and ferritin in postmortem tissue from patients with progressive supranuclear palsy (PSP) and multiple system atrophy (MSA) (which shows pathology in the SN and striatum) and Huntington's disease (HD) (which shows pathological changes in the striatum, compared with control subjects). Total iron levels were elevated in areas of the basal ganglia showing pathological changes in these disorders. In particular, total iron content was increased in SN in PD, PSP, and MSA, but not in HD. Total iron levels in the striatum (caudate nucleus and/or putamen) were increased in PSP, MSA, and HD, but not in PD. There were no consistent alterations in manganese levels in the basal ganglia in any of the diseases studied. Copper levels were decreased in the SN in PD and in the cerebellum in PSP, and were elevated in the putamen and possibly the SN in HD. Zinc levels were only increased in PD in the SN, the caudate nucleus, and the putamen.(ABSTRACT TRUNCATED AT 250 WORDS)

Role of iron and iron chelation in dopaminergic-induced neurodegeneration: implication for Parkinson's disease.

Recent studies in Parkinson's disease suggest that the degeneration of the nigrostriatal melanin-containing dopaminergic neurons results from toxic effects of free radicals, which are generated during dopamine metabolism in the substantia nigra (SN). This has been linked to the selective accumulation of iron, a known catalyst of radical formation, in the zona compacta of the SN. We have shown that interaction of iron with melanin may result in a high affinity binding of iron to melanin (KD = 13.0 +/- 0.15 nM). Indeed, x-ray analysis of melanized dopamine neurons of parkinsonian SN has shown an interaction of iron with melanin that is absent in control brains. In the presence of excess Fe3+, melanin potentiates iron-induced lipid peroxidation. Since iron chelators prevent lipid peroxidation, we have ascertained the ability of the iron chelator deferoxamine to prevent the lesion of the nigrostriatal dopamine neuron induced by 6-hydroxy dopamine (6-OHDA). Our results demonstrated that intraventricular injection of 130 ng deferoxamine to rats prior to 250 micrograms of 6-OHDA partially prevented the decrease in striatal dopamine content caused by 6-OHDA (56% reduction vs 90%, respectively). This protection was sufficient to produce normal dopamine-related behavioral responses. These results suggest that iron and iron chelators play a crucial role in the process of dopaminergic neurodegeneration and neuroprotection. The latter is further supported by our recent findings that intranigral injection of iron (50 micrograms) resulted in a substantial selective decrease of striatal dopamine (95%) and impaired dopamine-related responses.

Excitatory amino acidergic pathways and receptors in the basal ganglia

The striatum receives the majority of excitatory amino acidergic input to the basal ganglia from neocortical and allocortical sources. The subthalamic nucleus and the substantia nigra also receive excitatory amino acidergic inputs from neocortex. The subthalamic nucleus, which has prominent projections to the pallidum and nigra, is the only known intrinsic excitatory amino acidergic component of the basal ganglia. Possible excitatory amino acidergic inputs reach the basal ganglia from the intralaminar thalamic nuclei and the pedunculo-pontine nucleus. The striatum is richly endowed with all subtypes of excitatory amino acid receptors and these appear to be inhomogeneously distributed within the striatal complex. The non-striatal nuclei contain lesser levels of excitatory amino acid receptors and the relative proportion of these receptors varies between nuclei. The presence of high densities of excitatory amino acid receptors is a phylogenetically conserved feature of the striatum and its non-mammalian homologues. In Huntington's disease, there is substantial depletion ofα-amino-3-hydroxy-5-methylisoxazole-4-propionic acid, N-methyl-D-aspartate, and kainate receptors within the striatum. In Parkinson's disease substantia nigra, there is significant loss of N-methyl-D-aspartate andα-amino-3-hydroxy-5-methylisoxazole-4-propionic acid receptors.

Selective Increase of Iron in Substantia Nigra Zona Compacta of Parkinsonian Brains

Histochemical and biochemical determinations of total iron, iron (II), and iron (III) contents in brain regions from Parkinson's and Alzheimer's diseases have demonstrated a selective increase of total iron content in parkinsonian substantia nigra zona compacta but not in the zona reticulata. The increase of iron content is mainly in iron (III). The ratio of iron (II):iron (III) in zona compacta changes from almost 2:1 to 1:2. This change is thought to be relevant and may contribute to the selective elevation of basal lipid peroxidation in substantia nigra reported previously. Iron may be available in a free state and thus can participate in autooxidation of dopamine with the resultant generation of H2O2 and oxygen free radicals.

Iron and Aluminum Increase in the Substantia Nigra of Patients with Parkinson's Disease: An X‐Ray Microanalysis

The levels of different elements were studied by x-ray microanalysis in the substantia nigra and the central gray substance of patients with Parkinson's disease, progressive supranuclear palsy, and matched controls. In control brains, only iron, potassium, silicum, sodium, sulfur, and zinc were within the limit of detection of the technique. The abundance of each element was different, but their respective concentrations in the two brain regions were similar, except for sulfur levels which were higher on neuromelanin aggregates in the substantia nigra than in nigral regions lacking neuromelanin, and in the central gray substance. In Parkinson's disease, but not in progressive supranuclear palsy, nigral iron levels increased in regions devoid of neuromelanin and decreased on neuromelanin aggregates, but were unchanged in the central gray substance, when compared to control values. Concentrations of the other elements in the central gray substance and substantia nigra were not different from controls in brains from patients with Parkinson's disease and progressive supranuclear palsy. Analysis of Lewy bodies in the parkinsonian substantia nigra revealed high levels of iron and the presence of aluminum. Metal abundance was not affected in progressive supranuclear palsy, in spite of the nigral cell death. This suggests that the increased iron levels and the detection of aluminum observed in Parkinson's disease are not solely the consequence of the neuronal degeneration.

ALTERATIONS IN THE LEVELS OF IRON, FERRITIN AND OTHER TRACE METALS IN PARKINSON'S DISEASE AND OTHER NEURODEGENERATIVE DISEASES AFFECTING THE BASAL GANGLIA

Levels of iron, copper, zinc and manganese were measured by inductively coupled plasma spectroscopy in frozen postmortem brain tissue from patients with Parkinson's disease (PD), progressive supranuclear palsy (PSP), multiple system atrophy with strionigral degeneration (MSA), and Huntington's disease (HD) compared with control subjects. Total iron levels were found to be elevated in the areas of basal ganglia showing pathological change in these disorders. In particular, total iron content was increased in substantia nigra in PD, PSP and MSA, but not in HD. Total iron levels in the striatum (putamen and/or caudate nucleus) were increased in PSP, MSA and HD but not in PD. Total iron levels were decreased in the globus pallidus in PD. There were no consistent alterations of manganese levels in basal ganglia structures in any of the diseases studied. Copper levels were decreased in the substantia nigra in PD, and in the cerebellum in PSP, and were elevated in the putamen and possibly substantia nigra in HD. Zinc levels were only increased in PD, in substantia nigra and in caudate nucleus and lateral putamen. Levels of the iron binding protein ferritin were measured in the same patient groups using a radio-immunoassay technique. Increased iron levels in basal ganglia were generally associated with normal or elevated levels of ferritin immunoreactivity, for example, the substantia nigra in PSP and possibly MSA, and in putamen in MSA. The exception was PD where there was a generalized reduction in brain ferritin immunoreactivity, even in the substantia nigra. An increase in total iron content appears to be a response to neurodegeneration in affected basal ganglia regions in a number of movement disorders. However, only in PD was there an increased total iron level, decreased ferritin content, decreased copper content, and an increased zinc concentration in substantia nigra. These findings suggest an alteration of iron handling in the substantia nigra in PD. Depending on the form in which the excess iron load exists in nigra in PD, it may contribute to the neurodegenerative process.

Is Parkinson's disease a progressive siderosis of substantia nigra resulting in iron and melanin induced neurodegeneration?

Razor sharp and high iron deposits are present in the substantia nigra (SN). Although the function of such high iron content is not known, the homeostasis of brain iron is important for normal brain function. The participation of free tissue iron in oxidative stress (OS), resulting in the formation of cytotoxic hydroxyl radical (.OH) from H2O2 (Fenton reaction) and promotion of membrane lipid peroxides by .OH can no longer be questioned as a biological phenomenon. The highly selective increase of Fe2+ and Fe3+ and lipid peroxidation observed in parkinsonian SN points to OS in such brains. Lipid peroxidation proceeds with either Fe2+ or Fe3+ provided a mechanism exists to facilitate the interconversion of iron between its redox states. Indeed H2O2 derived from MAO B reaction and autooxidation of dopamine to melanin in the SN can drive the iron dependent Fenton reaction. Furthermore, interaction of iron with melanin may be even more important considering that melanin avidly binds Fe3+ and reduce it to Fe2+, resulting in .OH generation. Thus, without evoking environmental neurotoxins, the excessive accumulation of free iron in the SN and "melanin-trap" could be the trigger for accelerated cell death and Parkinsonism.

A selective increase in particulate superoxide dismutase activity in parkinsonian substantia nigra.

The total activity of superoxide dismutase (SOD) and cytosolic and particulate activity of SOD in human substantia nigra and cerebellum were measured by a spectrophotometric method based on the ability of SOD to inhibit the autoxidation of adrenaline. The cytosolic and particulate isoenzymes of SOD were differentiated by the inclusion of potassium cyanide which selectively inhibits cytosolic copper/zinc-dependent SOD activity. In autopsied human brains, there was no difference in total SOD activity, or the activity of SOD in cytosol in substantia nigra of patients dying with Parkinson's disease compared to age-matched controls. However, the activity of the particulate form of SOD was higher in the parkinsonian substantia nigra compared to control tissue. In the cerebellum there was no difference in the total, cytosolic, or particulate activity of SOD between parkinsonian patients and age-matched controls. Increased activity of SOD in particulate fraction may be a protective response to elevated levels of toxic free radicals in the parkinsonian substantia nigra. Alternatively, increased SOD activity may induce cell death through the accumulation of hydrogen peroxide.

Increased nigral iron content and alterations in other metal ions occurring in brain in Parkinson's disease.

Levels of iron, copper, zinc, manganese, and lead were measured by inductively coupled plasma spectroscopy in parkinsonian and age-matched control brain tissue. There was 31-35% increase in the total iron content of the parkinsonian substantia nigra when compared to control tissue. In contrast, in the globus pallidus total iron levels were decreased by 29% in Parkinson's disease. There was no change in the total iron levels in any other region of the parkinsonian brain. Total copper levels were reduced by 34-45% in the substantia nigra in Parkinson's disease; no difference was found in the other brain areas examined. Zinc levels were increased in substantia nigra in Parkinson's disease by 50-54%, and the zinc content of the caudate nucleus and lateral putamen was also raised by 18-35%. Levels of manganese and lead were unchanged in all areas of the parkinsonian brain studied when compared to control brains, except for a small decrease (20%) in manganese content of the medial putamen. Increased levels of total iron in the substantia nigra may cause the excessive formation of toxic oxygen radicals, leading to dopamine cell death.

Basal lipid peroxidation in substantia nigra is increased in Parkinson's disease.

Polyunsaturated fatty acid (PUFA) levels (an index of the amount of substrate available for lipid peroxidation) were measured in several brain regions from patients who died with Parkinson's disease and age-matched control human postmortem brains. PUFA levels were reduced in parkinsonian substantia nigra compared to other brain regions and to control tissue. However, basal malondialdehyde (MDA; an intermediate in the lipid peroxidation process) levels were increased in parkinsonian nigra compared with other parkinsonian brain regions and control tissue. Expressing basal MDA levels in terms of PUFA content, the difference between parkinsonian and control substantia nigra was even more pronounced. Stimulating MDA production by incubating tissue with FeSO4 plus ascorbic acid, FeSO4 plus H2O2, or air alone produced lower MDA levels in the parkinsonian substantia nigra, probably reflecting the lower PUFA content. These results may indicate that an increased level of lipid peroxidation continues to occur in the parkinsonian nigra up to the time of death, perhaps because of continued exposure to excess free radicals derived from some endogenous or exogenous neurotoxic species.