Brain iron and ferritin in Parkinson's and Alzheimer's diseases

Regulation of heme oxygenase-1 expression by dopamine in cultured C6 glioma and primary astrocytes

Heme oxygenase-1 (HO-1) is an inducible enzyme involved in heme catabolism, tissue iron homeostasis and the cellular response to oxidative stress. Elevated HO-1 expression in astrocytes has been observed in association with abnormal iron deposition and increased oxidative stress in Parkinson's disease (PD). Since HO-1 could contribute to these aspects of PD pathobiology we have investigated its regulation in cultured astrocytes and C6 glioma cells. Here we report that dopamine is a potent inducer of HO-1. This induction is not mediated by a classical dopamine receptor and is not mimicked by a range of catecholamines and dopamine metabolites. When the time-course of HO-1 expression was compared between dopamine and hemin, the latter induced the gene immediately while the former did so with a lag. This suggested two distinct signal transduction pathways. However, cycloheximide blocked both hemin- and dopamine-induced HO-1 expression, suggesting that both pathways may involve proteins with short half-lives. Ascorbic acid blocked dopamine induction of HO-1 but had no effect on hemin-induced expression. This suggested that dopamine may signal upstream of the unstable protein by producing pro-oxidant metabolites or byproducts. Inhibition of monoamine oxidases A or B or catechol-O-methyl transferase did not block HO-1 induction by dopamine, indicating that these enzymes were not converting dopamine to an active metabolite. These results suggest that dopamine, released or secreted from affected neurons, may trigger HO-1 expression in neighboring astrocytes. HO-1 and its metabolites could then contribute to the oxidative stress and iron deposition associated with PD.

Glial HO-1 expression, iron deposition and oxidative stress in neurodegenerative diseases

The mechanisms responsible for the pathological deposition of brain iron in Parkinson's disease, Alzheimer's disease and other human neurodegenerative disorders remain poorly understood. In rat primary astrocyte cultures, we demonstrated that dopamine, cysteamine, H(2)O(2) and menadione rapidly induce heme oxygenase-1 (HO-1) expression (mRNA and protein) followed by sequestration of non-transferrin-derived (55)Fe by the mitochondrial compartment. The effects of dopamine on HO-1 expression were inhibited by ascorbate implicating a free radical mechanism of action. Dopamine-induced mitochondrial iron trapping was abrogated by administration of the heme oxygenase inhibitors, tin mesoporphyrin (SnMP) or dexamethasone (DEX) indicating that HO-1 upregulation is necessary for subsequent mitochondrial iron deposition in these cells. Overexpression of the human HO-1 gene in cultured rat astroglia by transient transfection also stimulated mitochondrial (55)Fe deposition, an effect that was again preventible by SnMP or DEX administration. We hypothesize that free ferrous iron and carbon monoxide generated by HO-1-mediated heme degradation promote mitochondrial membrane injury and the deposition of redox-active iron within this organelle. We have shown that the percentages of GFAP-positive astrocytes that co-express HO-1 in Parkinson-affected substantia nigra and Alzheimer-diseased hippocampus are significantly increased relative to age-matched controls. Stress-induced up-regulation of HO-1 in astroglia may be responsible for the abnormal patterns of brain iron deposition and mitochondrial insufficiency documented in various human neurodegenerative disorders.

Time course of dopaminergic cell death and changes in iron, ferritin and transferrin levels in the rat substantia nigra after 6-hydroxydopamine (6-OHDA) lesioning

Parkinson's disease is characterized by dopaminergic cell death in the substantia nigra. The underlying mechanism is, however, unknown. Though there are increasing lines of evidence showing iron accumulation in the Parkinsonian substantia nigra, it still remains obscure whether increased iron is the primary cause of dopaminergic cell death, or just a consequence of the pathological process. It is also unclear how iron gains access to the Parkinsonian SN. To gain more understanding in these areas, the present study investigated the time course of dopaminergic cell death and of changes in the level of iron, ferritin and transferrin. The results showed that iron was increased after the significant nigral dopaminergic cell death induced by 6-hydroxydopamine injection into the rat substantia nigra. On the other hand, the expression of transferrin was decreased. However, there was a temporal increase in the number of ferritin positive microglia. The results indicated that iron increase was not the primary cause of dopaminergic cell death in the Parkinsonian rat. It was most likely the result of an accumulation of iron-laden microglia.

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.

Potent neuroprotective and antioxidant activity of apomorphine in MPTP and 6-hydroxydopamine induced neurotoxicity

Apomorphine is a potent radical scavenger and iron chelator. In vitro apomorphine acts as a potent iron chelator and radical scavenger with IC50 of 0.3 microM for iron (2.5 microM) induced lipid peroxidation in rat brain mitochondrial preparation, and it inhibits mice striatal MAO-A and MAO-B activities with IC50 values of 93 microM and 241 microM. Apomorphine (1-10 microM) protects rat pheochromocytoma (PC12) cells from 6-hydroxydopamine (150 microM) and H2O2 (0.6 mM) induced cytotoxicity and cell death. The neuroprotective property of (R)-apomorphine, a dopamine D1-D2 receptor agonist, has been studied in the MPTP (N-methyl-4-phenyl-1,2,3,6-tetrahydropyridine) model of Parkinson's disease. (R)-apomorphine (5-10 mg/kg, s.c.) pretreatment in C57BL mice, protects against MPTP (24 mg/kg, i.p.) induced loss of nigro-striatal dopamine neurons, as indicated by striatal dopamine content, tyrosine hydroxylase content and tyrosine hydroxylase activity. It is suggested that the neuroprotective effect of (R)-apomorphine against MPTP neurotoxicity derives from its radical scavenging and MAO inhibitory actions and not from its agonistic activity, since the mechanism of MPTP dopaminergic neurotoxicity involves the generation of oxygen radical species induced-oxidative stress.

Mitochondrial iron sequestration in dopamine-challenged astroglia: role of heme oxygenase-1 and the permeability transition pore

Little is currently known concerning the mechanisms responsible for the excessive deposition of redox-active iron in the substantia nigra of subjects with Parkinson's disease (PD). In the present study, we demonstrate that dopamine promotes the selective sequestration of non-transferrin-derived iron by the mitochondrial compartment of cultured rat astroglia and that the mechanism underlying this novel dopamine effect is oxidative in nature. We also provide evidence that up-regulation of the stress protein heme oxygenase-1 (HO-1) is both necessary and sufficient for mitochondrial iron trapping in dopamine-challenged astroglia. Finally, we show that opening of the mitochondrial transition pore (MTP) mediates the influx of non-transferrin-derived iron into mitochondria of dopamine-stimulated and HO-1-transfected astroglia. Our findings provide an explanation for the pathological iron sequestration, mitochondrial insufficiency, and amplification of oxidative injury reported in the brains of PD subjects. Pharmacological blockade of transition metal trapping by "stressed" astroglial mitochondria (e.g., using HO-1 inhibitors or modulators of the MTP) may afford effective neuroprotection in patients with PD and other neurological afflictions.

T1 and T2 in the brain of healthy subjects, patients with Parkinson disease, and patients with multiple system atrophy: relation to iron content

PURPOSE

To investigate the potential of magnetic resonance imaging for identification and quantification of brain iron in healthy subjects, patients with Parkinson disease, and patients with multiple system atrophy.

MATERIALS AND METHODS

Forty-nine subjects were studied at 1.5 T. Regional T1 and T2 values were compared among groups and also with histopathologic estimates of iron concentration.

RESULTS

In healthy subjects, interregional T1 and T2 differences in the cortex and basal ganglia showed a good correlation with reported values for iron concentration, and intraregional variations were generally consistent with reported variability of iron concentration. Patients with multiple system atrophy had T1 and T2 shortening in the globus pallidus consistent with reported increases in ferritin-bound iron and changes in the putamen consistent with accumulation of hemosiderin (posterior portion) and neuromelanin (remainder). Both groups of patients had changes in the cortex that are consistent with decreased ferritin concentration and T2 changes in white matter consistent with demyelination. Patients with Parkinson disease also had a (nonsignificant) T2 shortening in the substantia nigra that was suggestive of iron accumulation.

CONCLUSION

Most of the T1 and T2 findings appear to be related to changes in iron content and form and may possibly be used as indicators of such changes.

Pathophysiology of Parkinson's disease

Parkinson's disease is a progressive disease with selective dopaminergic neuronal loss. The pathophysiology is at present better understood with plurifactorial etiology, including genetic predisposition and environmental toxic factors. The mechanisms of cell death are based upon oxidative stress and apoptosis. The heterogeneity of dopaminergic neuronal loss leads to etiopathogenic clues. In the same way, the model of functional organization of basal ganglia circuitry gives a basis for further experimental and therapeutic research.

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

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

MRI evaluation of brain iron in earlier- and later-onset Parkinson's disease and normal subjects

Tissue iron levels in the extrapyramidal system of earlier- and later-onset Parkinson's disease (PD) subjects were evaluated in vivo using a magnetic resonance imaging (MRI) method. The method involves scanning subjects in both high- and low-field MRI instruments, measuring tissue relaxation rate (R2), and calculating the field-dependent R2 increase (FDRI) which is the difference between the R2 measured with the two MRI instruments. In tissue, only ferritin iron is known to increase R2 in a field-dependent manner and the FDRI measure is a specific measure of this tissue iron pool. Two groups of male subjects with PD and two age-matched groups of normal control males were studied. The two groups of six subjects with PD consisted of subjects with earlier- or later-onset (before or after age 60) PD. FDRI was measured in five subcortical structures: the substantia nigra reticulata (SNR), substantia nigra compacta (SNC), globus pallidus, putamen, and caudate nucleus, and in one comparison region; the frontal white matter. Earlier-onset PD subjects had significant (p < 0.05) increases in FDRI in the SNR, SNC, putamen, and globus pallidus, while later-onset PD subjects had significantly decreased FDRI in the SNR when compared to their respective age-matched controls. Controlling for illness duration or structure size did not meaningfully alter the results. Published post-mortem studies on SN iron levels indicate decreased ferritin levels and increased free iron levels in the SN of older PD subjects, consistent with the decreased FDRI observed in our later-onset PD sample, which was closely matched in age to the post-mortem PD samples. The FDRI results suggest that disregulation of iron metabolism occurs in PD and that this disregulation may differ in earlier- versus later-onset PD.

The role of iron in neurodegeneration: prospects for pharmacotherapy of Parkinson's disease

Although the aetiology of Parkinson's disease (PD) and related neurodegenerative disorders is still unknown, recent evidence from human and experimental animal models suggests that a misregulation of iron metabolism, iron-induced oxidative stress and free radical formation are major pathogenic factors. These factors trigger a cascade of deleterious events leading to neuronal death and the ensuing biochemical disturbances of clinical relevance. A review of the available data in PD provides the following evidence in support of this hypothesis: (i) an increase of iron in the brain, which in PD selectively involves neuromelanin in substantia nigra (SN) neurons; (ii) decreased availability of glutathione (GSH) and other antioxidant substances; (iii) increase of lipid peroxidation products and reactive oxygen (O2)species (ROS); and (iv) impaired mitochondrial electron transport mechanisms. Most of these changes appear to be closely related to interactions between iron and neuromelanin, which result in accumulation of iron and a continuous production of cytotoxic species leading to neuronal death. Some of these findings have been reproduced in animal models using 6-hydroxydopamine, N-methyl-4-phenyl-1,2,3,6-tetrahydropyridine (MPTP), iron loading and beta-carbolines, although none of them is an accurate model for PD in humans. Although it is not clear whether iron accumulation and oxidative stress are the initial events causing cell death or consequences of the disease process, therapeutic efforts aimed at preventing or at least delaying disease progression by reducing the overload of iron and generation of ROS may be beneficial in PD and related neurodegenerative disorders. Current pharmacotherapy of PD, in addition to symptomatic levodopa treatment, includes 'neuroprotective' strategies with dopamine agonists, monoamine oxidase-B inhibitors (MAO-B), glutamate antagonists, catechol O-methyltransferase inhibitors and other antioxidants or free radical scavengers. In the future, these agents could be used in combination with, or partly replaced by, iron chelators and lazaroids that prevent iron-induced generation of deleterious substances. Although experimental and preclinical data suggest the therapeutic potential of these drugs, their clinical applicability will be a major challenge for future research.

Free radicals in Alzheimer's disease

Alzheimer's disease is a neurodegenerative disorder comprising multisystem atrophies probably caused by multifactorial processes. The disease is characterized by typical neuropathology, impaired synaptic function and massive cell loss. The pathobiochemistry of this disorder involves oxidative stress, which accumulates free radicals leading to excessive lipid peroxidation and neuronal degeneration in certain brain regions. Moreover, radical induced disturbances of DNA, proteins and lipid membranes have been measured. The hypothesis has been proposed that cellular events involving oxidative stress may be one basic pathway leading to neurodegeneration in Alzheimer's disease. In this work we report evidence for increased oxidative stress and disturbed defense mechanisms in Alzheimer's disease, which may result in a self-propagating cascade of neurodegenerative events. Furthermore it is evident from experimental data, that aggregation of beta-amyloid and beta-amyloid toxicity is favourably caused by oxidative stress. Therefore, oxidative stress plays a key role in the conversion of soluble to unsoluble beta-amyloid, suggesting that oxidative stress is primary to the beta-amyloid cascade.

Lipid peroxides in the free radical pathophysiology of brain diseases

1. Polyunsaturated fatty acids are essential for normal cell membrane functioning because many membrane properties, such as fluidity and permeability, are closely related to the presence of unsaturated and polyunsaturated side chains. Lipid peroxidation results in loss of membrane polyunsaturated fatty acids and oxidized phospholipids as polar species contributing to increased membrane rigidity. 2. Polyunsaturated fatty acids are released from membrane phospholipids by a number of enzymic mechanisms involving the receptor-mediated stimulation of phospholipase A2 and phospholipase C/diacylglycerol lipase pathways. 3. The overstimulation of excitatory amino acid (EAA) receptors stimulates the activities of lipases and phospholipases, and this stimulation produces changes in membrane phospholipid composition, permeability, and fluidity, thus decreasing the integrity of plasma membranes. 4. Alterations in properties of plasma membranes may be responsible for the degeneration of neurons seen in neurodegenerative diseases. Two major processes may be involved in neuronal injury caused by the overstimulation of EAA receptors. One is a large Ca2+ influx and the other is an accumulation of free radicals and lipid peroxides as a result of neural membrane phospholipid degradation. It is suggested that calcium and free radicals act in concert to induce neuronal injury in acute trauma (ischemia and spinal cord injury) and in neurodegenerative diseases.

Induction of nitric oxide synthase and microglial responses precede selective cell death induced by chronic impairment of oxidative metabolism

Abnormal oxidative processes including a reduction in thiamine-dependent enzymes accompany many neurodegenerative diseases. Thiamine deficiency (TD) models the cellular and molecular mechanisms by which chronic oxidative aberrations associated with thiamine-dependent enzyme deficits cause selective neurodegeneration. The mechanisms underlying selective cell death in TD are unknown. In rodent TD, the earliest region-specific pathological change is breakdown of the blood-brain barrier (BBB). The current studies tested whether nitric oxide and microglia are important in the initial events that couple BBB breakdown to selective neuronal loss. Enhanced expression of endothelial nitric oxide synthase and nicotinamide adenine dinucleotide phosphate diaphorase reactivity in microvessels, as well as the presence of numerous inducible nitric oxide synthase-immunoreactive microglia, accompanied the increases in BBB permeability. Nitric oxide synthase induction appears critical to TD pathology, because immunoreactivity for nitrotyrosine, a specific nitration product of peroxynitrite, also increased in axons of susceptible regions. In addition, TD elevated iron and the antioxidant protein ferritin in microvessels and in activated microglia, suggesting that these cells are responding to an oxidative challenge. All of these changes occurred in selectively vulnerable regions, preceding neuronal death. These findings are consistent with the hypothesis that the free radical-mediated BBB alterations permit entry of iron and extraneuronal proteins that set in motion a cascade of inflammatory responses culminating in selective neuronal loss. Thus, the TD model should help elucidate the relationship between oxidative deficits, BBB abnormalities, the inflammatory response, ferritin and iron elevation, and selective neurodegeneration.

Astrocyte mitochondria: a substrate for iron deposition in the aging rat substantia nigra

Little is currently known concerning the cellular substrates for, and the mechanisms mediating the pathological deposition of, redox-active brain iron in Parkinson's disease. In various subcortical brain regions, populations of astroglia progressively accumulate peroxidase-positive cytoplasmic inclusions derived from effete, iron-laden mitochondria. In the present study, histochemical, ultrastructural, and elemental microanalytical techniques were used to demonstrate the existence of peroxidase-positive astroglia in the substantia nigra of adult rats. At 4 months of age and earlier, few GFAP-positive nigral astroglia contained small, electron-dense cytoplasmic inclusions which exhibited faint endogenous peroxidase activity (diaminobenzidine reaction product) and no detectable iron by microprobe analysis. In contrast, by 14-18 months of age, there was a significant, fourfold increase in numbers of peroxidase-positive astrocyte inclusions in the substantia nigra. The nigral gliosomes in the older animals were heterogeneously electron dense, immunoreactive for ubiquitin and a mitochondrial epitope, and often exhibited X-ray emission peaks for iron. Copper peaks were also detected in a minority of nigral gliosomes. Previous in vitro work indicated that the iron-mediated peroxidase activity in these cells promotes the bioactivation of dopamine and other catechols to neurotoxic free radical intermediates. Thus, mitochondrial sequestration of redox-active iron in aging nigral astroglia may be one factor predisposing the senescent nervous system to parkinsonism and other neurodegenerative disorders.

Quantitative analysis of T2 signal intensities in Alzheimer's disease

Hypointensities (focal areas of decreased signal intensity) have been reported on T2 weighted magnetic resonance images (MRI) in normal aging and in some neurological disease processes. Increased concentrations of iron have been suggested as one cause of these hypointensities. In Alzheimer's Disease, data suggests that there is both a disruption in iron metabolism as well as the presence of T2 hypointensities. We endeavored to determine if the decreased signal intensities could be quantitatively determined and, if so, in what regions, in an effort to establish a non-invasive biological marker and diagnostic aide. We performed a quantitative analysis of the T2 signal intensities in 13 MRIs from AD patients and 16 age- and sex-matched control subjects. We found that while there were statistically significant differences in the intensities of the putamen and red nucleus, these differences were small. We were unable to detect differences in intensities in a whole slice or the frontal lobe. To our knowledge this is the first quantitative comparison of MRI signal intensities in Alzheimer's Disease.

Neuronal death: is there a role for astrocytes?

Astrocytes are ubiquitous in the brain and have multiple functions. It is becoming increasingly clear that they play an important role in monitoring the neuromicroenvironment in CNS and in information processing or signaling in the nervous system in normal conditions and respond to CNS injuries in a gradual and varied way. It is still debated whether such reactions are beneficial or detrimental. It was believed that reactive astrogliosis observed in most neurological disorders may regulate the removal of toxic compounds produced by damaged neurons and support neuronal growth by releasing trophic factors. However it was also suggested that astrocytes contribute to a decline of neurologic function, for example by accumulation and release of excitotoxic aminoacids after ischemia and oxidative stress, formation of epileptogenic scars in response to CNS injury and metabolism of protoxins to potent toxins. In a number of metabolic diseases astrocytes, not neurons, may be the primary target. The astrocyte's role in normal and pathological conditions will be discussed in the light of recent information about their metabolism, receptor distribution and release.

Neural heme oxygenase-1 expression in idiopathic Parkinson's disease

Heme oxygenase-1 is a cellular stress protein expressed in brain and other tissues in response to oxidative challenge and other noxious stimuli. In the present study, immunohistochemistry was used to assess HO-1 expression in various postmortem human brain specimens derived from PD and control subjects. In the substantia nigra of both PD and control specimens, moderate HO-1 immunoreactivity was consistently observed in neuromelanin-containing (dopaminergic) neurons. Lewy bodies in PD nigra neurons exhibited intense HO-1 immunostaining in their peripheries. In both PD and control specimens, neuronal HO-1 staining was faint or nondetectable in the other brain regions surveyed. The fraction of GFAP-positive astroglia expressing HO-1 in PD substantia nigra (77.1 +/- 12.3) was significantly greater than that observed in the substantia nigra of control subjects (18.7 +/- 7.1; P = 0.0015). In the other regions examined, percentages of GFAP-positive astroglia coexpressing HO-1 were relatively low and did not differ significantly (P > 0.05) between control and PD specimens. Upregulation of HO-1 in the substantia nigra of PD subjects supports the view that the affected tissue is experiencing chronic oxidative stress. In addition, excessive cellular levels of heme-derived free iron and carbon monoxide resulting from HO-1 overactivity may contribute to the pathogenesis of PD.

A new MRI ratio method for in-vivo estimation of signal hypointensity in aging and Alzheimer's disease

1. Alzheimer's Disease (AD) is accompanied by a disruption in iron metabolism. There is no universally accepted method for detecting brain iron. 2. The authors have developed a novel "ratio" method which uses the red nucleus as an internal reference. We postulated that this method would improve our sensitivity in detecting differences in MRI signal intensities and that it would allow us to measure brain iron deposition. 3. The ratio method reasonably reproduced previous reports of the normal deposition of iron in brain that occurs with aging. It failed to distinguish any differences in three brain areas: putamen, left frontal lobe and whole slice in AD patients versus age and sex matched controls. 4. It also failed to detect differences with AD progression or severity. 5. The ratio method itself warrants further investigation.

Intranigral iron infusion in the rat. Acute elevations in nigral lipid peroxidation and striatal dopaminergic markers with ensuing nigral degeneration

Iron is known to induce lipid peroxidation and recent evidence indicates that both iron and lipid peroxidation are elevated in the substantia nigra in Parkinson's disease (PD). To test whether excess intranigral iron induces lipid peroxidation, we infused an iron citrate solution (0.63 nmol in 0.25 microL) into the rat substantia nigra and measured nigral thiobarbituric acid reactive products at 1-h, 1-d, 1-wk, and 1-mo postinfusion. In a separate group of iron-infused animals, histologic analysis within the substantia nigra through 1-mo postinfusion was accomplished by thionine- and iron-staining, with concurrent assessment of striatal neurochemical markers. Concentrations of nigral thiobarbituric acid reactive products were significantly elevated at 1 h and 1 d in iron-infused animals compared to vehicle-infused and unoperated animals, with a return to control values by 1 wk. Similarly, striatal dopamine turnover was acutely elevated, suggesting damage to dopaminergic neurons, which was confirmed histologically. Although iron-staining within the iron diffusionary area was increased through the postinfusion month, there was an apparent progression of the cellular character of staining from predominantly neuronal to reactive glial and finally to oligodendroglial by 1 mo postinfusion. This progression of cellular iron-staining may indicate a shifting of infused iron to a more bound unreactive form, thus explaining only an acute elevation in lipid peroxidation through 1 d following intranigral iron infusion. The data indicate that damage to nigral neurons induced by iron infusion is transciently associated with a marker of oxidative damage and supports the possibility that iron-induced oxidative stress contributes to the pathogenesis of PD.

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.

Blood transferrin and ferritin in Alzheimer's disease

In the present study we found a significant correlation between severity of dementia of Alzheimer's type (DAT) and both transferrin and ferritin serum levels. Levels of transferrin in serum of 41 DAT patients tended to be lower than those of 19 age-matched controls, while levels of ferritin were not significantly different in DAT patients compared to controls. These results are interpreted in line with previous findings of higher brain ferritin and lower brain transferrin levels in DAT and are a circumstantial support for the oxygen radical hypothesis of degenerative brain disease.

Increased susceptibility of Alzheimer's disease temporal cortex to oxygen free radical-mediated processes

Reactive oxygen-mediated processes are though to contribute to the pathogenesis of Alzheimer's disease (AD). To investigate this hypothesis we studied autopsy tissue from 11 pairs of AD cases and control individuals matched for age, postmortem delay, and tissue storage time. The temporal neocortex, which is severely involved by AD pathology, and the cerebellum, which is spared, were analyzed for tissue markers of lipid peroxidation (LPO). The average chemiluminescence formed from bond breakage in tissue homogenates during a 3-h incubation, without the presence of catalysts such as metal ions or ascorbate, was significantly increased in the AD temporal cortex to 130% of matched controls. Basal tissue content of LPO products (thiobarbituric acid reactive substances--TBARs) was not different between groups. However, TBARs were significantly elevated in AD temporal cortex to 135% of control after the incubation. In contrast, in the cerebellum there was no difference between AD and control tissue, indicating a disease-specific tissue effect. Because the use of oral antioxidants have received considerable attention in the last few years, the results seen in the testing of an AD patient who took daily vitamin E supplements for 4 years is particularly interesting. The time course for CL reactivity in the temporal cortex was considerably delayed compared to all other samples. This observation is consistent with the hypothesis that antioxidants within tissue will quench ROS-mediated reactions. This study indicates that there is increased susceptibility to ROS in the AD temporal cortex that may contribute to the pathogenesis of the disease. Furthermore, our observation suggest that oral antioxidant supplementation may be protective against LPO in the human brain.

MR evaluation of age-related increase of brain iron in young adult and older normal males

The purposes of this study were to extend the investigation of age-related increases in brain iron to a younger age group, replicate previously published results, and further evaluate the validity of a novel noninvasive magnetic resonance (MR) method for measuring tissue iron (ferritin) levels with specificity. The method consists of measuring the dependence of tissue transverse relaxation rates (R2) on the field strength of MR instruments. Two MR instruments operating at 1.5 and 0.5 T were used to measure the field-dependent R2 increase (FDRI) in the frontal white matter, caudate, putamen, and globus pallidus. A group of 13 normal adult males (ages 21-77), with seven subjects below and six above age 35, was examined. As expected from postmortem and prior FDRI data, robust and significant age-related increases in FDRI were observed in the caudate, putamen, and globus pallidus, with the globus pallidus FDRI increasing sharply in the second decade and reaching a plateau after age 30. In addition, we replicated previous reports showing very high correlations between FDRI and published brain iron levels for the four regions examined. The data replicate and extend previous FDRI observations on brain aging and are consistent with postmortem data on age-related increases in brain iron. These results are relevant to the investigation of age-related neurodegenerative diseases in which iron may catalyze toxic free radical reactions.

Neuronal vulnerability in Parkinson's disease

Although Parkinson's disease is characterized by a loss of dopaminergic neurons in the substantia nigra not all dopaminergic neurons degenerate in this disease. This suggests that some specific factors make subpopulations of dopaminergic neurons more susceptible to the disease. Here, we show that the most vulnerable neurons are particularly sensitive to oxidative stress and rise in intracellular calcium concentrations. Because both events seem to occur in Parkinson's disease this may explain why some dopaminergic neurons degenerate and other do not.

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.

Iron in parkinsonian and control substantia nigra--a Mössbauer spectroscopy study

We used Mössbauer spectroscopy to study the iron content, the redox state, and the binding site of iron in substantia nigra (SN) from parkinsonian (PD) and control brains. Measurements performed on fresh-frozen, formalin-fixed, and lyophilized samples demonstrated the presence of ferric (Fe3+) iron only, both in PD and control SN. Ferrous iron, if present at all, may represent at most 5% of the total iron. We found no difference in the total amount of iron in SN between PD and control brains. The Mössbauer spectra observed at 4.1 K in fresh (frozen or lyophilized) samples were different from those obtained in formalin-fixed (frozen or lyophilized) samples. In the fresh samples, only ferritin-like iron was observed, whereas in the samples frozen or lyophilized from formalin, non-ferritin iron was detected.

Glia-dependent neurotoxicity and neuroprotection in mesencephalic cultures

Dopaminergic neurotoxicities of 6-hydroxydopamine (6-OHDA) and the lipopolysaccharide (LPS) were compared in rat mesencephalic cultures plated on poly-L-lysine or on glial monolayers. In the neuron-enriched cultures plated on polylysine, 6-OHDA killed 89% of the tyrosine hydroxylase (TH)-immunopositive neurons, but LPS was not neurotoxic. Conversely, in mixed neuron/glial cultures, 6-OHDA killed only 27% of the TH-immunopositive neurons while LPS killed 70%. The mixed neuronal/glial mesencephalic culture offers a better in vitro model for studying possible mechanisms involved in Parkinson's disease.

Magnetic resonance imaging of brain iron in health and disease

Brain iron is a major contributor to magnetic resonance imaging (MRI) contrast in normal gray matter, and its role in the pathogenesis of different neurological disorders has also become apparent. Non-heme brain iron is present in the brain mainly in the form of ferritin. The unique magnetic properties of ferritin determine different signal changes on both T1- and T2-weighted images, and the T2 relaxation rates have a linear dependence on applied field strength. This finding is typical for ferric oxyhydroxide cores. The resulting T2-shortening also depends on echo-spacing used in the imaging sequence as well as on the water diffusion coefficient and the size of the ferritin cluster. Quantitation of non-heme brain iron by MRI aids in the diagnosis and monitoring of different neurological diseases.

The role of transition metals in the pathogenesis of Parkinson's disease

The mechanisms that lead to degeneration of melanized dopaminergic neurons in the brain stem, and particularly in the substantia nigra (SN) in patients with Parkinson's disease (PD) are still unknown. Demonstration of increased iron (Fe) in SN of PD brain has suggested that Fe-melanin interaction may contribute to oxidative neuronal damage. Energy dispersive X-ray electron microscopic analysis of the cellular distribution of trace elements revealed significant Fe peaks, similar to those of a synthetic melanin-Fe3+ complex, in intraneuronal electron-dense neuromelanin granules of the SN zona compacta, with highest levels in a case of PD and Alzheimer's disease (AD). No Fe increase was found in Lewy bodies or in SN neurons of control specimens. The relevance of the in vitro chemical reactions of dopamine (DA), 5-hydroxydopamine (5-OHDA), and 6-hydroxydopamine (6-OHDA) with Fe3+ and with dioxygens for the pathogenesis of PD was investigated. An initiating mechanism for a chain reaction is suggested by which excessive Fe3+ arises. Melanin can act as an efficient antioxidant and in the presence of Fe can promote the formation of cytotoxic hydroxyl free radicals (.OH) which, in turn, initiate lipid peroxidation and consequent cell damage. While in vitro studies indicate that DA oxidation leading to melanin formation is independent of metal ions, saturation of melanin with large amounts of Fe3+ causes a significant generation of free .OH radicals. The relevance of the events induced by the melanin-Fe complex for the degeneration of dopaminergic neurons in PD is discussed. Free redox-active metal ions in the cytoplasm may cause site-specific peroxidation and thus exert neurotoxic effects. Excessive hydrogen peroxide in post mortem frontal cortex of a patient with PD and AD could be shown by confocal fluorescence microscopy, and this observation may be a direct indicator of oxidative stress.

Expression of lactoferrin receptors is increased in the mesencephalon of patients with Parkinson disease

The degeneration of nigral dopaminergic neurons in Parkinson disease is believed to be associated with oxidative stress. Since iron levels are increased in the substantia nigra of parkinsonian patients and this metal catalyzes the formation of free radicals, it may be involved in the mechanisms of nerve cell death. The cause of nigral iron increase is not understood. Iron acquisition by neurons may occur from iron-transferrin complexes with a direct interaction with specific membrane receptors, but recent results have shown a low density of transferrin receptors in the substantia nigra. To investigate whether neuronal death in Parkinson disease may be associated with changes in a pathway supplementary to that of transferrin, lactoferrin (lactotransferrin) receptor expression was studied in the mesencephalon. In this report we present evidence from immunohistochemical staining of postmortem human brain tissue that lactoferrin receptors are localized on neurons (perikarya, dendrites, axons), cerebral microvasculature, and, in some cases, glial cells. In parkinsonian patients, lactoferrin receptor immunoreactivity on neurons and microvessels was increased and more pronounced in those regions of the mesencephalon where the loss of dopaminergic neurons is severe. Moreover, in the substantia nigra, the intensity of immunoreactivity on neurons and microvessels was higher for patients with higher nigral dopaminergic loss. These data suggest that lactoferrin receptors on vulnerable neurons may increase intraneuronal iron levels and contribute to the degeneration of nigral dopaminergic neurons in Parkinson disease.

The effect of a synthetic neuromelanin on yield of free hydroxyl radicals generated in model systems

Neuromelanin is an amorphous pigment of the catecholamine origin that accumulates in certain dopaminergic neurons of the substantia nigra of human brain. In Parkinson's disease, there appears to be selective degeneration of the most heavily pigmented neurons of the substantia nigra, and this process has been linked to the presence of neuromelanin. It has been postulated that neuromelanin could increase the risk of oxidative stress reactions. On the other hand, melanin is usually considered to be an efficient antioxidant. Here we analyze experimental conditions that stimulate, or inhibit, antioxidant properties of neuromelanin. Using electron spin resonance (ESR)--spin trapping technique and salicylate hydroxylation assay, we monitored the formation of free hydroxyl radicals generated by a Fenton system in the presence of varying concentration of dopamine-melanin, a synthetic model for neuromelanin. Our data clearly indicate that the antioxidant action of neuromelanin is predominantly due to its ability to sequester redox-active metal ions such as iron. Using direct ESR spectroscopy, we have shown that ferric complexes with neuromelanin are resistant to reduction by mild biological reductants such as ascorbate. We have demonstrated that dopamine-melanin saturated with ferric ions, could enhance the formation of free hydroxyl radicals by redox activation of the ions. Thus, under the conditions that stimulate the release of accumulated metal ions, neuromelanin may actually become an efficient prooxidant. It is conceivable that neuromelanin, which normally is able to protect pigmented dopaminergic neurons against metal-ion related toxicity, could under extreme conditions have a cytotoxic role.

Localization of a new ferritin heavy chain sequence present in human brain mRNA to chromosome 11

Two types of ferritin heavy (H) chain clones have been isolated from cDNA libraries of human fetal and adult brain: one corresponds to the ferritin H chain mRNA that is abundant in liver and is called "liver-like" brain cDNA; the other contains an additional 279 nucleotide (nt) sequence in the 3' untranslated region and is called brain ferritin H chain cDNA. To map the 279-nt sequence, polymerase chain reaction (PCR) amplification was carried out using DNA from rodent x human hybrid cell lines containing single human chromosomes as templates, and oligomeric primers homologous to the 3' end of the 279-nt sequence (primer A) and to a coding sequence just 5' to the 279-nt sequence. Significant PCR product of the size expected from analysis of the brain ferritin H chain cDNA clones and a genomic ferritin H chain clone (487 bp) was generated only from hybrid-cell DNA containing human chromosome 11. This PCR product and the "liver-like" brain cDNA (lacking the 279-nt sequence) both hybridized to chromosome 11 fragments that are known to define the well-characterized functional liver ferritin H chain gene and a putative pseudogene. Preliminary data indicate that primer A (and thus the 279-nt sequence) maps to the functional ferritin H chain gene fragments, but binding to the pseudogene has not been ruled out.

Role of mitochondria in the etiology and pathogenesis of Parkinson's disease

We discuss the etiology and pathogenesis of Parkinson's disease (PD). Our group and others have found a decrease in complex I of the mitochondrial electron transfer complex in the substantia nigra of patients with PD; in addition, we reported loss of the alpha-ketoglutarate dehydrogenase complex (KGDHC) in the substantia nigra. Dual loss of complex I and the KGDHC will deleteriously affect the electron transport and ATP synthesis; we believe that energy crisis is the most important mechanism of nigral cell death in PD. Oxidative stress has also been implicated as an important contributor to nigral cell death in PD, but we believe that oxidative stress is a secondary phenomenon to respiratory failure, because respiratory failure will increase oxygen free-radical formation and consume glutathione. The primary cause of mitochondrial respiratory failure has not been elucidated yet, but additive effect of environmental neurotoxins in genetically predisposed persons appears to be the most likely possibility.

Point mutations of mitochondrial genome in Parkinson's disease

Oxidative stress and subsequent energy crisis have been proposed as the cause of nigral neuronal cell death in Parkinson's disease. We have reported defects in the mitochondrial respiratory chain and increased amount of deleted mitochondrial genome in the nigrostriatal system of patients with Parkinson's disease. Deletion in mitochondrial DNA could be ascribed to somatically acquired premature aging leading to cell death. To elucidate the contribution of maternally transmitted point mutations in mitochondrial DNA to the premature DNA damages, we employed a direct sequencing system and analyzed the total nucleotide sequences of mitochondrial DNA in the brains of five patients with idiopathic Parkinson's disease. There were no predominant point mutations among the patients in contrast to some neuromuscular diseases. However, each patient had several point mutations that would result in a significant change in the gene products. Some of these mutations may be involved either in the increased production of oxygen radicals from the mitochondrial respiratory chain or in the increased susceptibility of the respiratory chain components to oxidative damage. We propose that some of these mutations can be regarded as one of the risk factors accelerating degeneration of nigrostriatal pathway in Parkinson's disease.

Pharmacological and clinical implications of MAO-B inhibitors

Although the involvement of monoamine oxidase B (MAO-B) in physiological function is not yet well understood, its inhibitors have been shown to be quite useful in the treatment of various neuropsychiatric disorders. Platelet MAO-B activity has been found to be reduced in several psychiatric disorders, related to substance abuse and associated with different personalities. 1-Deprenyl (selegiline), an archetypical MAO-B inhibitor, alone does not seem to exert an antidepressive effect, however, it may become useful when administered in combination with amine neurotransmitter precursors. MAO-B inhibitors are useful adjunct drugs to 1-DOPA in the symptomatic treatment of Parkinson's disease. Interestingly, 1-deprenyl alone can slow down the progress of otherwise disabled syndromes of Parkinson's disease. It has been proposed that 1-deprenyl may play a role in neuroprotection and neurorescue. MAO-B inhibitors can selectively and dramatically increase the level of beta-phenylethylamine, which has been shown to potentiate dopamine and noradrenaline function in the central nervous system. Several new types of highly selective, reversible and irreversible MAO-B inhibitors have recently been developed. The mechanism(s) of neuroprotective and rescue actions of 1-deprenyl and other MAO-B inhibitors will help to shed some light on our understanding of the neurodegenerative process.

Degeneration of nigrostriatal dopaminergic neurons increases iron within the substantia nigra: a histochemical and neurochemical study

Parkinson's-diseased (PD) brains have increased levels of iron in the zona compacta of the substantia nigra (SNc). To determine whether these elevated nigral iron levels may be caused secondarily by degeneration of nigrostriatal dopaminergic (NS-DA) neurons, the NS-DA pathway was unilaterally lesioned in rats through 6-hydroxydopamine (6-OHDA) infusion and nigral iron levels evaluated three weeks later. A significant increase was observed in both iron concentration (+35%) and iron content (+33) within the substantia nigra (SN) ipsilateral to comprehensive 6-OHDA lesions. Moreover, ferric iron staining was dramatically increased within the SNc following 6-OHDA lesions, primarily due to the appearance of iron-positive SNc neurons and infiltrating reactive glial cells. Iron staining in the SN zona reticularis was modestly increased after 6-OHDA lesions, but staining in the neostriatum and globus pallidus was unaffected. These results indicate that loss of NS-DA neurons is associated with increased iron levels in the SN. This suggests that increased nigral iron levels in PD may be secondary to some neurodegenerative process. Nonetheless, even a secondary increase in nigral iron levels may be of pathogenic importance in PD because of iron's ability to catalyze neurotoxic free radical formation and perpetuate neurodegeneration.

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.

Biochemistry of Parkinson's disease with special reference to the dopaminergic systems

The cardinal neurochemical abnormality in Parkinson's disease is the decreased dopamine content in the striatum, resulting from the loss of dopaminergic neurons in the mesencephalon. Precise analysis of the dopaminergic neurons in the midbrain demonstrates, however, that this cell loss is not uniform. Some dopaminergic cell groups are more vulnerable than others. The degree of cell loss is severe in the substantia nigra pars compacta, intermediate in the ventral tegmental area and cell group A8, but nonexistent in the central gray substance. This heterogeneity provides a good paradigm for analyzing the factors implicated in this differential vulnerability. So far, the neurons that degenerate have been shown to contain neuromelanin, high amounts of iron, and no calbindin28K, and to be poorly protected against oxidative stress. By contrast, the neurons that survive in Parkinson's disease are free of neuromelanin, calbindinD28-positive, contain low amounts of iron, and are better protected against oxidative stress. The analysis of the pattern of cell loss in Parkinson's disease may thus bring new clues as to the mechanism of nerve cell death in Parkinson's disease.

The iron-binding protein lactotransferrin is present in pathologic lesions in a variety of neurodegenerative disorders: a comparative immunohistochemical analysis

Lactotransferrin is a glycoprotein that specifically binds and transports iron. This protein is also believed to transport other metals such as aluminum. Several lines of evidence indicate that iron and aluminum are involved in the pathogenesis of many dementing diseases. In this context, the analysis of the iron-binding protein distribution in the brains of patients affected by neurodegenerative disorders is of particular interest. In the present study, the distribution of lactotransferrin was analyzed by immunohistochemistry in the cerebral cortex from patients presenting with Alzheimer's disease, Down syndrome, amyotrophic lateral sclerosis/parkinsonism-dementia complex of Guam, sporadic amyotrophic lateral sclerosis, or Pick's disease. The results show that lactotransferrin accumulates in the characteristic lesions of the different pathologic conditions investigated. For instance, in Alzheimer's disease and Guamanian cases, a subpopulation of neurofibrillary tangles was intensely labeled in the hippocampal formation and inferior temporal cortex. Senile plaques and Pick bodies were also consistently labeled. These staining patterns were comparable to those obtained with antibodies to the microtubule-associated protein tau and the amyloid beta A4 protein, although generally fewer neurofibrillary tangles were positive for lactotransferrin than for tau protein. Neuronal cytoplasmic staining with lactotransferrin antibodies, was observed in a subpopulation of pyramidal neurons in normal aging, and was more pronounced in Alzheimer's disease, Guamanian cases, Pick's disease, and particularly in Down syndrome. Lactotransferrin was also strongly associated with Betz cells and other motoneurons in the primary motor cortex of control, Alzheimer's disease, Down syndrome, Guamanian and Pick's disease cases. These same lactotransferrin-immunoreactive motoneurons were severely affected in the cases with amyotrophic lateral sclerosis. It is possible that in these neurodegenerative disorders affected neurons either take up or synthesize lactotransferrin to an abnormally elevated rate. An excessive accumulation of lactotransferrin, as well as transported iron and aluminum, may lead to a cytotoxic effect resulting in the formation of intracellular lesions and neuronal death.

The roles of neuromelanin, binding of metal ions, and oxidative cytotoxicity in the pathogenesis of Parkinson's disease: a hypothesis

A characteristic feature of both Parkinson's disease (idiopathic paralysis agitans) and normal aging is loss of pigmented neurons in the substantia nigra. This has been found to correlate with the accumulation of neuromelanin and with oxidative stress in this brain region, but a clear association between these factors has not been established. Based on our recent demonstration that neuromelanin is a true melanin, containing bound metal ions in situ, we present a general model for its accumulation in vivo and the hypotheses (1) that it has a cytoprotective function in the sequestration of redox-active metal ions under normal conditions but (2) that it has a cytotoxic role in the pathogenesis of Parkinson's disease. Thus, neuromelanin accumulates normally through the autooxidation of catecholamines and serves tightly to bind redox-active metal ions, processes which would accelerate under conditions of intracellular or extracellular oxidative stress. Based on the known properties of melanin, however, neuromelanin also has the potential for exacerbating oxidative stress, eg by generating H2O2 when it is intact or by releasing redox-active metal ions if it loses its integrity; these reactions also would modulate the reactivity of the neuromelanin. By overwhelming intracellular antioxidative defense mechanisms, such a positive-feedback cycle could turn a condition of chronic or repeated oxidative stress in vulnerable neurons into an acute crisis, leading to cellular death. If the cumulative stress in duration and/or degree is severe enough, neuronal depletion could be sufficient to cause Parkinson's disease during life. One possible trigger for this cascade is suggested by the increased nigral iron contents in postmortem parkinsonian brains and the correlation of this disease with urban living where exposure to heavy metal ions is high: the saturation of neuromelanin with redox-active metal ions. Parkinson's disease therefore may be a form of accelerated aging in the substantia nigra associated with environmental toxins in which neuromelanin has a central, active role.

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.