The iron chelator desferrioxamine (Desferal) retards 6-hydroxydopamine-induced degeneration of nigrostriatal dopamine neurons

A dibenzoylmethane derivative protects dopaminergic neurons against both oxidative stress and endoplasmic reticulum stress

The enhancement of intracellular stresses such as oxidative stress and endoplasmic reticulum (ER) stress has been implicated in several neurodegenerative disorders including Parkinson's disease (PD). During a search for compounds that regulate ER stress, a dibenzoylmethane (DBM) derivative 14-26 (2,2′-dimethoxydibenzoylmethane) was identified as a novel neuroprotective agent. Analysis in SH-SY5Y cells and in PC12 cells revealed that the regulation of ER stress by 14-26 was associated with its anti-oxidative property. 14-26 prevented the production of reactive oxygen species (ROS) when the cells were exposed to oxidants such as hydrogen peroxide and 6-hydroxydopamine (6-OHDA) or an ER stressor brefeldin A (BFA). 14-26 also prevented ROS-induced damage in both the ER and the mitochondria, including the protein carbonylation in the microsome and the reduction of the mitochondrial membrane potential. Further examination disclosed the presence of the iron-chelating activity in 14-26. In vivo, 14-26 suppressed both oxidative stress and ER stress and prevented neuronal death in the substantia nigra pars compacta (SNpc) after injection of 6-OHDA in mice. These results suggest that 14-26 is an antioxidant that protects dopaminergic neurons against both oxidative stress and ER stress and could be a therapeutic candidate for the treatment of PD.

Neurodegeneration and peroxidases

Alzheimer's disease (AD), Parkinson's disease (PD) and amyotrophic lateral sclerosis (ALS) are neurodegenerative diseases that affect different parts of the central nervous system. However, a review of the literature indicates that certain biochemical reactions involved in neurodegeneration in these three diseases are quite similar and could be partly identical. This article critically examines the similarities and, based on data from our own and other laboratories, proposes a novel explanation for neurodegeneration in these three diseases. We identified about 20 commonalities that exist in the neurodegenerative process of each disease. We hypothesize that there are two enzyme-catalyzed pathways that operate in affected neurons: an oxidative pathway leading to destruction of various neuronal proteins and lipids, and an apoptotic pathway which the body normally uses to remove unwanted and dysfunctional cells. Data from many laboratories indicate that oxidative reactions are primarily responsible for neurodegeneration, whereas apoptosis may well be a secondary response to the presence of neurons that have already been severely damaged by oxidative reactions. Attempts to inhibit apoptosis for the purpose of attenuating progression of these diseases may therefore be only of marginal benefit. Specific oxidative reactions within affected neurons led us to propose that one or more heme peroxidases may be the catalyst(s) involved in oxidation of proteins and lipids. Support for this proposal is provided by the recent finding that amyloi-beta peptide may act as a peroxidase in AD. Possible participation of the peroxidase activity of cytochrome c, herein designated as cytochrome c(px) to distinguish it from yeast cytochrome c peroxidase, is discussed. Of special interest is our recent finding that many compounds that cause attenuation of neurodegeneration are inhibitors of the peroxidase activity of cytochrome c. Several inhibitors were subsequently identified as suicide substrates. Such inhibitors could be ideally suited for targeted clinical approaches aimed at arresting progression of neurodegeneration. Finally, it is possible that immobilized yet still active peroxidase(s) may be present in protein aggregates in AD, PD, and ALS. This activity could be the catalyst for the slow, self-perpetuating and irreversible degeneration of affected neurons that occurs over long periods of time in these neurodegenerative diseases.

Desferoxamine reverses neonatal iron-induced recognition memory impairment in rats

We have previously demonstrated that rats given iron neonatally presented memory deficits. The aim of the present study was to evaluate the effect of desferoxamine, a metal chelating agent, on memory deficits in an iron overload model in rats. Male rats received vehicle or iron orally at postnatal days 12-14 and desferoxamine (30 or 300 mg/kg) in the adulthood. After desferoxamine treatment, they were trained in a novel-object recognition task. Iron-treated rats showed recognition memory impairments when compared to controls. Iron-treated rats that received desferoxamine 300 mg/kg, showed normal recognition memory, suggesting that desferoxamine can reverse recognition memory deficits associated with iron accumulation. Further research is required to examine whether the findings from animal models of iron overload have implications for humans.

Iron and paraquat as synergistic environmental risk factors in sporadic Parkinson's disease accelerate age-related neurodegeneration

Extensive epidemiological data in humans and studies in animal models of Parkinson's disease (PD) suggest that sporadic forms of the disorder are not strictly genetic in nature but most likely because of combined environmental exposures over the period of the life-span coupled with increased genetic susceptibilities. Environmental paraquat and neonatal iron exposure have both been separately suggested as potential risk factors for sporadic forms of the disease. In this study, we demonstrate that combined environmental exposure to these two agents results in accelerated age-related degeneration of nigrostriatal dopaminergic neurons. Furthermore, pretreatment with the synthetic superoxide dismutase/catalase mimetic, EUK-189, significantly attenuated neuronal death mediated by combined paraquat and iron treatment. These findings support the notion that environmental PD risk factors may act synergistically to produce neurodegeneration associated with the disorder and that iron and paraquat may act via common oxidative stress-mediated mechanisms.

Iron in chronic brain disorders: imaging and neurotherapeutic implications

Iron is important for brain oxygen transport, electron transfer, neurotransmitter synthesis, and myelin production. Though iron deposition has been observed in the brain with normal aging, increased iron has also been shown in many chronic neurological disorders including Alzheimer's disease, Parkinson's disease, and multiple sclerosis. In vitro studies have demonstrated that excessive iron can lead to free radical production, which can promote neurotoxicity. However, the link between observed iron deposition and pathological processes underlying various diseases of the brain is not well understood. It is not known whether excessive in vivo iron directly contributes to tissue damage or is solely an epiphenomenon. In this article, we focus on the imaging of brain iron and the underlying physiology and metabolism relating to iron deposition. We conclude with a discussion of the potential implications of iron-related toxicity to neurotherapeutic development.

Iron dysregulation in Alzheimer's disease: multimodal brain permeable iron chelating drugs, possessing neuroprotective-neurorescue and amyloid precursor protein-processing regulatory activities as therapeutic agents

Considering the multi-etiological character of Alzheimer's disease (AD), the current pharmacological approaches using drugs oriented towards a single molecular target possess limited ability to modify the course of the disease and thus, offer a partial benefit to the patient. In line with this concept, novel strategies include the use of a cocktail of several drugs and/or the development of a single molecule, possessing two or more active neuroprotective-neurorescue moieties that simultaneously manipulate multiple targets involved in AD pathology. A consistent observation in AD is a dysregulation of metal ions (Fe(2+), Cu(2+) and Zn(2+)) homeostasis and consequential induction of oxidative stress, associated with beta-amyloid aggregation and neurite plaque formation. In particular, iron has been demonstrated to modulate the Alzheimer's amyloid precursor holo-protein expression by a pathway similar to that of ferritin L-and H-mRNA translation through iron-responsive elements in their 5'UTRs. This review will discuss two separate scenarios concerning multiple therapy targets in AD, sharing in common the implementation of iron chelation activity: (i) novel multimodal brain-permeable iron chelating drugs, possessing neuroprotective-neurorescue and amyloid precursor protein-processing regulatory activities; (ii) natural plant polyphenols (flavonoids), such as green tea epigallocatechin gallate (EGCG) and curcumin, reported to have access to the brain and to possess multifunctional activities, such as metal chelation-radical scavenging, anti-inflammation and neuroprotection.

Disturbance of Iron Metabolism as a Contributing Factor to SN Hyperechogenicity in Parkinson’s Disease: Implications for Idiopathic and Monogenetic Forms

A number of investigations have provided evidence for a central role of iron in the pathogenesis of Parkinson's disease (PD). Recently it could be demonstrated that iron related changes of the substantia nigra may be one important factor contributing to the hyperechogenicity typicall visualized by transcranial sonography in idiopathic PD. Moreover, also patients with monogenetically caused PD show this hyperechogenicity, although to a lesser extent. According to numerous findings and experiments it seems plausible that iron also contributes to the pathophysiological cascades in the monogenetic forms of PD. Therefore, it is not only essential to acknowledge the pivotal role of iron for PD, but also to enhance the effort in finding therapeutic strategies to prevent the impact of iron on neurodegenerative processes. Moreover, early detection of subjects at risk is essential for the application of therapeutic strategies at a stage at which neuroprotection is still possible.

Iron metabolism in Parkinsonian syndromes

Growing evidence suggests an involvement of iron in the pathophysiology of neurodegenerative diseases. Several of the diseases are associated with parkinsonian syndromes, induced by degeneration of basal ganglia regions that contain the highest amount of iron within the brain. The group of neurodegenerative disorders associated with parkinsonian syndromes with increased brain iron content can be devided into two groups: (1) parkinsonian syndromes associated with brain iron accumulation, including Parkinson's disease, diffuse Lewy body disease, parkinsonian type of multiple system atrophy, progressive supranuclear palsy, corticobasal ganglionic degeneration, and Westphal variant of Huntington's disease; and (2) monogenetically caused disturbances of brain iron metabolism associated with parkinsonian syndromes, including aceruloplasminemia, hereditary ferritinopathies affecting the basal ganglia, and panthotenate kinase associated neurodegeneration type 2. Although it is still a matter of debate whether iron accumulation is a primary cause or secondary event in the first group, there is no doubt that iron-induced oxidative stress contributes to neurodegeneration. Parallels concerning pathophysiological as well as clinical aspects can be drawn between disorders of both groups. Results from animal models and reduction of iron overload combined with at least partial relief of symptoms by application of iron chelators in patients of the second group give hope that targeting the iron overload might be one possibility to slow down the neurodegenerative cascade also in the first group of inevitably progressive neurodegenerative disorders.

Role of iron in neurodegenerative disorders

Although the pathophysiology underlying a number of neurodegenerative diseases is complex and, in many aspects, only partly understood, increased iron levels in pathologically relevant brain areas and iron-mediated oxidative stress seem to play a central role in many of them. Much has been learned from monogenetically caused disturbances of brain iron metabolism including pantothenate kinase-associated neurodegeneration type 2, hereditary ferritinopathies affecting the basal ganglia, and aceruloplasminemia that may well be applied to the most common neurodegenerative disorders associated with brain iron accumulation including Parkinson disease and Alzheimer disease. Iron-mediated oxidative stress in neurodegenerative diseases caused by other genetic pathways like Huntington disease and Friedreich ataxia underscore the complex interaction of this trace metal and genetic variations. Therapeutical strategies derived from application of iron chelators in monogenetically caused disturbances of brain iron metabolism and new iron and oxidative stress diminishing substances in animal models of Parkinson disease are promising and warrant further investigational effort.

Green tea catechins as brain-permeable, non toxic iron chelators to "iron out iron" from the brain

Evidence to link abnormal metal (iron, copper and zinc) metabolism and handling with Parkinson's and Alzheimer's diseases pathology has frequently been reported. The capacity of free iron to enhance and promote the generation of toxic reactive oxygen radicals has been discussed numerous times. Metal chelation has the potential to prevent iron-induced oxidative stress and aggregation of alpha-synuclein and beta-amyloid peptides. The efficacy of iron chelators depends on their ability to penetrate the subcellular compartments and cellular membranes where iron dependent free radicals are generated. Thus, natural, non-toxic, brain permeable neuroprotective drugs, are preferentially advocated for "ironing out iron" from those brain areas where it preferentially accumulates in neurodegenerative diseases. This review will discuss the most recent findings from in vivo and in vitro studies concerning the transitional metal (iron and copper) chelating property of green tea, and its major polyphenol, (-)-epigallocatechin-3-gallate with respect to their potential for the treatment of neurodegenerative diseases.

Metal specificity of an iron-responsive element in Alzheimer's APP mRNA 5'untranslated region, tolerance of SH-SY5Y and H4 neural cells to desferrioxamine, clioquinol, VK-28, and a piperazine chelator

Iron closely regulates the expression of the Alzheimer's Amyloid Precursor Protein (APP) gene at the level of message translation by a pathway similar to iron control of the translation of the ferritin L- and H mRNAs by Iron-responsive Elements in their 5' untranslated regions (5'UTRs). Using transfection based assays in SH-SY5Y neuroblastoma cells we tested the relative efficiency by which iron, copper and zinc up-regulate IRE activity in the APP 5'UTR. Desferrioxamine (high affinity Fe3+ chelator), (ii) clioquinol (low affinity Fe/Cu/Zn chelator), (iii) piperazine-1 (oral Fe chelator), (iv) VK-28 (oral Fe chelator), were tested for their relative modulation of APP 5' UTR directed translation of a luciferase reporter gene. Iron chelation based therapeutic strategies for slowing the progression of Alzheimer's disease (and other neurological disorders that manifest iron imbalance) are discussed with regard to the relative neural toxic action of each chelator in SH-SY5Y cells and in H4 glioblastoma cells.

Molecular basis of 6-hydroxydopamine-induced caspase activations due to increases in oxidative stress in the mouse striatum

To clarify the possible role of in the in vivo toxic effects of 6-hydroxydopamine (6-OHDA), especially caspase activations, we examined its effects on striatal lipid peroxidation (LPO) and caspase activations in 6-OHDA-lesioned mice. Both dopamine (DA) levels and DA turnover were significantly changed by the 6-OHDA i.c.v. injection compared with the pre-injection level in the striatum. In addition, the striatal glutathione (GSH) content fluctuated and was significantly decreased both at 3 and 14 days after 6-OHDA i.c.v. injection. Moreover, superoxide dismutase (SOD) activity at 7 days after 6-OHDA i.c.v. injection was transiently and significantly increased compared with the pre-injection level. The levels of thiobarbituric acid-reactive substances (TBA-RS) were significantly increased at 1, 3 and 14 days. 6-OHDA significantly increased the activities of all three caspases, except for the caspase-3 activity at 7 days throughout the experimental period compared with the pre-injection level. In conclusion, 6-OHDA-induced dopaminergic dysfunction is mainly due to caspase activations by increases in oxidative stress in the mouse striatum.

Multifunctional drugs with different CNS targets for neuropsychiatric disorders

The multiple disease etiologies that lead to neuropsychiatric disorders, such as Parkinson's and Alzheimer's disease, amyotrophic lateral sclerosis, Huntington disease, schizophrenia, depressive illness and stroke, offer significant challenges to drug discovery efforts aimed at preventing or even reversing the progression of these disorders. Transcriptomic tools and proteomic profiling have clearly indicated that such diseases are multifactorial in origin. Further, they are thought to be initiated by a cascade of molecular events that involve several neurotransmitter systems. In response to this complexity, a new paradigm has recently emerged that challenges the widely held assumption that 'silver bullet' agents are superior to 'dirty drugs' in therapeutic approaches aimed at the prevention or treatment of neuropsychiatric diseases. A similar pattern of drug development has occurred in strategies for the treatment of cancer, AIDS and cardiovascular diseases. In this review, we offer an overview of therapeutic strategies and novel investigative drugs discovered or developed in our own and other laboratories, that address multiple CNS etiological targets associated with an array of neuropsychiatric disorders.

Iron: a new target for pharmacological intervention in neurodegenerative diseases

Iron (Fe) is an essential element that is imperative for the redox-driven processes of oxygen transport, electron transport, and DNA synthesis. However, in the absence of appropriate storage or chelation, excess-free Fe readily participates in the formation of toxic-free radicals, inducing oxidative stress and apoptosis. A growing body of evidence suggests that Fe may play some role in neurodegenerative diseases such as Huntington disease, Alzheimer's disease, Parkinson's disease, and particularly Friedreich's ataxia. This review examines the role of Fe in the pathology of these conditions and the potential use of Fe chelators as therapeutic agents for the treatment of neurodegenerative disorders. Consideration is given to the features that comprise a clinically successful Fe chelator, with focus on the development of ligands such as desferrioxamine, clioquinol, pyridoxal isonicotinoyl hydrazone, and other novel aroylhydrazones.

Nucleotides and inorganic phosphates as potential antioxidants

Highly reactive OH radicals, formed in an iron-ion catalyzed Fenton reaction, are implicated in many pathological conditions. The quest for Fenton reaction inhibitors, either radical scavenger or metal-ion chelator antioxidants, spans the previous decades. Purine nucleotides were previously studied as natural modulators of the Fenton reaction; however, the modulatory role of purine nucleotides remained in dispute. Here, we have resolved this long-standing dispute and demonstrated a concentration-dependent biphasic modulation of the Fenton reaction by nucleotides. By electron spin resonance measurements with 0.1 mM Fe(II), we observed an increase of *OH production at low purine nucleotide concentrations (up to 0.15 mM), while at higher nucleotide concentrations, an exponential decay of *OH concentration was observed. We found that the phosphate moiety, not the nucleoside, determines the pro/antioxidant properties of a nucleotide, suggesting a chelation-based modulation. Furthermore, the biphasic modulation mode is probably due to diverse nucleotide-Fe(II) complexes formed in a concentration-dependent manner. At ATP concentrations much greater than Fe(II) concentrations, multiligand chelates are formed which inhibit the Fenton reaction owing to a full Fe(II) coordination sphere. In addition to natural nucleotides, we investigated a series of base- or phosphate-modified nucleotides, dinucleotides, and inorganic phosphates, as potential biocompatible antioxidants. Ap5A, inorganic thiophosphate and ATP-gamma-S proved highly potent antioxidants with IC50 values of 40, 30, and 10 microM, respectively. ATP-gamma-S proved 100 and 20 times more active than ATP and the potent antioxidant Trolox, respectively. In the presence of 30 microM ATP-gamma-S no *OH was detected after 5 min in the Fenton reaction mixture. The most potent antioxidants identified inhibit the Fenton reaction by forming full coordination sphere chelates.

Increased murine neonatal iron intake results in Parkinson-like neurodegeneration with age

Iron elevation is well-documented in the Parkinsonian midbrain but its cause and contribution to subsequent neurodegeneration remain unknown. Mice administered iron at doses equivalent to those found in iron-fortified human infant formula during a developmental period equivalent to the first human year of life display progressive midbrain neurodegeneration and enhanced vulnerability to toxic injury. This may have major implications for the impact of neonatal iron intake as a potential risk factor for later development of Parkinson's disease (PD).

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

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

Reduction of iron-regulated amyloid precursor protein and beta-amyloid peptide by (-)-epigallocatechin-3-gallate in cell cultures: implications for iron chelation in Alzheimer's disease

Brain iron dysregulation and its association with amyloid precursor protein (APP) plaque formation are implicated in Alzheimer's disease (AD) pathology and so iron chelation could be considered a rational therapeutic strategy for AD. Here we analyzed the effect of the main polyphenol constituent of green tea, (-)-epigallocatechin-3-gallate (EGCG), which possesses metal-chelating and radical-scavenging properties, on the regulation of the iron metabolism-related proteins APP and transferrin receptor (TfR). EGCG exhibited potent iron-chelating activity comparable to that of the prototype iron chelator desferrioxamine, and dose dependently (1-10 microm) increased TfR protein and mRNA levels in human SH-SY5Y neuroblastoma cells. Both the immature and full-length cellular holo-APP were significantly reduced by EGCG, as shown by two-dimensional gel electrophoresis, without altering APP mRNA levels, suggesting a post-transcriptional action. Indeed, EGCG suppressed the translation of a luciferase reporter gene fused to the APP mRNA 5'-untranslated region, encompassing the APP iron-responsive element. The finding that Fe(2)SO(4) reversed the action of EGCG on APP and TfR proteins reinforces the likelihood that these effects are mediated through modulation of the intracellular iron pool. Furthermore, EGCG reduced toxic beta-amyloid peptide generation in Chinese hamster ovary cells overexpressing the APP 'Swedish' mutation. Thus, the natural non-toxic brain-permeable EGCG may provide a potential therapeutic approach for AD and other iron-associated disorders.

Green tea catechins as brain-permeable, natural iron chelators-antioxidants for the treatment of neurodegenerative disorders

Neurodegeneration in Parkinson's, Alzheimer's, or other neurodegenerative diseases appears to be multifactorial, where a complex set of toxic reactions, including oxidative stress (OS), inflammation, reduced expression of trophic factors, and accumulation of protein aggregates, lead to the demise of neurons. One of the prominent pathological features is the abnormal accumulation of iron on top of the dying neurons and in the surrounding microglia. The capacity of free iron to enhance and promote the generation of toxic reactive oxygen radicals has been discussed numerous times. The observations that iron induces aggregation of inert alpha-synuclein and beta-amyloid peptides to toxic aggregates have reinforced the critical role of iron in OS-induced pathogenesis of neurodegeneration, supporting the notion that a combination of iron chelation and antioxidant therapy may be one significant approach for neuroprotection. Tea flavonoids (catechins) have been reported to possess divalent metal chelating, antioxidant, and anti-inflammatory activities, to penetrate the brain barrier and to protect neuronal death in a wide array of cellular and animal models of neurological diseases. This review aims to shed light on the multipharmacological neuroprotective activities of green tea catechins with special emphasis on their brain-permeable, nontoxic, transitional metal (iron and copper)-chelatable/radical scavenger properties.

M30, a novel multifunctional neuroprotective drug with potent iron chelating and brain selective monoamine oxidase-ab inhibitory activity for Parkinson's disease

Iron and monoamine oxidase activity are increased in brain of Parkinson's disease (PD). They are associated with autoxidation and oxidative deamination of dopamine by MAO resulting in the generation of reactive oxygen species and the onset of oxidative stress to induce neurodegeneration. Iron chelators (desferal, Vk-28 and clioquinol) but not copper chelators have been shown to be neuroprotective in the 6-hydroxydoapmine and MPTP models of Parkinson's disease (PD), as are monoamine oxidase B inhibitors such as selegiline and rasagiline. These findings prompted the development of multifunctional anti PD drugs possessing iron chelating phamacophore of VK-28 and the propargylamine MAO inhibitory activity of rasagiline. M30 is a potent iron chelator, radical scavenger and brain selective irreversible MAO-A and B inhibitor, with little inhibition of peripheral MAO. It has neuroprotective activity in in vitro and in vivo models of PD and unlike selective MAO-B inhibitors it increases brain dopamine, serotonin and noradrenaline. These findings indicate beside its anti PD action, it may also possess antidepressant activity, similar to selective MAO-A and nonselective MAO inhibitors. These properties make it an ideal anti PD drug for which it is being developed.

Marker for a preclinical diagnosis of Parkinson's disease as a basis for neuroprotection

Neuroprotective therapy is a pivotal aim in the treatment of the relentlessly progressive disorder Parkinson's disease. However, more than 60% of the dopaminergic neurons of the substantia nigra have already degenerated, when the diagnosis may be established. At this "advanced stage" neuroprotective strategies will - if at all - only have limited effect. It is, therefore, essential to establish markers to identify subjects at risk before motor manifestation. A number of such "premotor" signs have been discovered and investigated lately. Such signs include a genetic vulnerability and hyperechogenicity of the substantia nigra as well as premotor symptoms like olfactory and autonomic dysfunction, depression, REM sleep behaviour disorder, visual and neuropsychological impairment. Moreover, first signs of affection of the substantia nigra like PET and SPECT abnormalities and slight motor signs can be included, as they may be detected before a definite diagnosis can be made. Although most of these signs and symptoms are unspecific if singularly evaluated a combination of these features may indeed be valuable to detect a subgroup of the population at risk for PD. However, future studies are necessary to establish the predictive value of these "markers" singularly and in combination.

Parkin-deficient mice are not more sensitive to 6-hydroxydopamine or methamphetamine neurotoxicity

Background

Autosomal recessive juvenile parkinsonism (AR-JP) is caused by mutations in the parkin gene which encodes an E3 ubiquitin-protein ligase. Parkin is thought to be critical for protecting dopaminergic neurons from toxic insults by targeting misfolded or oxidatively damaged proteins for proteasomal degradation. Surprisingly, mice with targeted deletions of parkin do not recapitulate robust behavioral or pathological signs of parkinsonism. Since Parkin is thought to protect against neurotoxic insults, we hypothesized that the reason Parkin-deficient mice do not develop parkinsonism is because they are not exposed to appropriate environmental triggers. To test this possibility, we challenged Parkin-deficient mice with neurotoxic regimens of either methamphetamine (METH) or 6-hydroxydopamine (6-OHDA). Because Parkin function has been linked to many of the pathways involved in METH and 6-OHDA toxicity, we predicted that Parkin-deficient mice would be more sensitive to the neurotoxic effects of these agents.

Results

We found no signs consistent with oxidative stress, ubiquitin dysfunction, or degeneration of striatal dopamine neuron terminals in aged Parkin-deficient mice. Moreover, results from behavioral, neurochemical, and immunoblot analyses indicate that Parkin-deficient mice are not more sensitive to dopaminergic neurotoxicity following treatment with METH or 6-OHDA.

Conclusion

Our results suggest that the absence of a robust parkinsonian phenotype in Parkin-deficient mice is not due to the lack of exposure to environmental triggers with mechanisms of action similar to METH or 6-OHDA. Nevertheless, Parkin-deficient mice could be more sensitive to other neurotoxins, such as rotenone or MPTP, which have different mechanisms of action; therefore, identifying conditions that precipitate parkinsonism specifically in Parkin-deficient mice would increase the utility of this model and could provide insight into the mechanism of AR-JP. Alternatively, it remains possible that the absence of parkinsonism in Parkin-deficient mice could reflect fundamental differences between the function of human and mouse Parkin, or the existence of a redundant E3 ubiquitin-protein ligase in mouse that is not found in humans. Therefore, additional studies are necessary to understand why Parkin-deficient mice do not display robust signs of parkinsonism.

Novel multifunctional neuroprotective iron chelator-monoamine oxidase inhibitor drugs for neurodegenerative diseases: in vitro studies on antioxidant activity, prevention of lipid peroxide formation and monoamine oxidase inhibition

Iron-dependent oxidative stress, elevated levels of iron and of monoamine oxidase (MAO)-B activity, and depletion of antioxidants in the brain may be major pathogenic factors in Parkinson's disease, Alzheimer's disease and related neurodegenerative diseases. Accordingly, iron chelators, antioxidants and MAO-B inhibitors have shown efficacy in a variety of cellular and animal models of CNS injury. In searching for novel antioxidant iron chelators with potential MAO-B inhibitory activity, a series of new iron chelators has been designed, synthesized and investigated. In this study, the novel chelators were further examined for their activity as antioxidants, MAO-B inhibitors and neuroprotective agents in vitro. Three of the selected chelators (M30, HLA20 and M32) were the most effective in inhibiting iron-dependent lipid peroxidation in rat brain homogenates with IC50 values (12-16 microM), which is comparable with that of desferal, a prototype iron chelator that is not has orally active. Their antioxidant activities were further confirmed using electron paramagnetic resonance spectroscopy. In PC12 cell culture, the three novel chelators at 0.1 microM were able to attenuate cell death induced by serum deprivation and by 6-hydroxydopamine. M30 possessing propargyl, the MAO inhibitory moiety of the anti-Parkinson drug rasagiline, displayed greater neuroprotective potency than that of rasagiline. In addition, in vitro, M30 was a highly potent non-selective MAO-A and MAO-B inhibitor (IC50 < 0.1 microM). However, HLA20 was more selective for MAO-B but had poor MAO inhibition, with an IC50 value of 64.2 microM. The data suggest that M30 and HLA20 might serve as leads in developing drugs with multifunctional activities for the treatment of various neurodegenerative disorders.

Novel multifunctional neuroprotective iron chelator-monoamine oxidase inhibitor drugs for neurodegenerative diseases. In vivo selective brain monoamine oxidase inhibition and prevention of MPTP-induced striatal dopamine depletion

Several multifunctional iron chelators have been synthesized from hydroxyquinoline pharmacophore of the iron chelator, VK-28, possessing the monoamine oxidase (MAO) and neuroprotective N-propargylamine moiety. They have iron chelating potency similar to desferal. M30 is a potent irreversible rat brain mitochondrial MAO-A and -B inhibitor in vitro (IC50, MAO-A, 0.037 +/- 0.02; MAO-B, 0.057 +/- 0.01). Acute (1-5 mg/kg) and chronic [5-10 mg/kg intraperitoneally (i.p.) or orally (p.o.) once daily for 14 days]in vivo studies have shown M30 to be a potent brain selective (striatum, hippocampus and cerebellum) MAO-A and -B inhibitor. It has little effects on the enzyme activities of the liver and small intestine. Its N-desmethylated derivative, M30A is significantly less active. Acute and chronic treatment with M30 results in increased levels of dopamine (DA), serotonin(5-HT), noradrenaline (NA) and decreases in DOPAC (dihydroxyphenylacetic acid), HVA (homovanillic acid) and 5-HIAA (5-hydroxyindole acetic acid) as determined in striatum and hypothalamus. In the mouse MPTP (N-methy-4-phenyl-1,2,3,6-tetrahydropyridine) model of Parkinson's disease (PD) it attenuates the DA depleting action of the neurotoxin and increases striatal levels of DA, 5-HT and NA, while decreasing their metabolites. As DA is equally well metabolized by MAO-A and -B, it is expected that M30 would have a greater DA neurotransmission potentiation in PD than selective MAO-B inhibitors, for which it is being developed, as MAO-B inhibitors do not alter brain dopamine.

Novel potential neuroprotective agents with both iron chelating and amino acid-based derivatives targeting central nervous system neurons

Antioxidants and iron chelating molecules are known as neuroprotective agents in animal models of neurodegenerative disorders such as Alzheimer's disease (AD) and Parkinson's disease (PD). In this study, we designed and synthesized a novel bifunctional molecule (M10) with radical scavenging and iron chelating ability on an amino acid carrier likely to be a substrate for system L, thus targeting the compound to the central nervous system (CNS). M10 had a moderate iron affinity in HEPES buffer (pH 7.4) with logK(3)=12.25+/-0.55 but exhibited highly inhibitory action against iron-induced lipid peroxidation, with an IC(50) value (12microM) comparable to that of desferal (DFO). EPR studies indicated that M10 was a highly potent *OH scavenger with an IC(50) of about 0.3 molar ratio of M10 to H(2)O(2). In PC12 cell culture, M10 was at least as potent as the anti-Parkinson drug rasagiline in protecting against cell death induced by serum-deprivation and by 6-hydroxydopamine (6-OHDA). These results suggest that M10 deserves further investigation as a potential agent for the treatment of neurodegenerative disorders such as AD and PD.

Design, synthesis, and evaluation of novel bifunctional iron-chelators as potential agents for neuroprotection in Alzheimer's, Parkinson's, and other neurodegenerative diseases

Several novel antioxidant-iron chelators bearing 8-hydroxyoxyquinoline moiety were synthesized, and various properties related to their iron chelation, and neuroprotective action were investigated. All the chelators exhibited strong iron(III) chelating and high antioxidant properties. Chelator 9 (HLA20), having good permeability into K562 cells and moderate selective MAO-B inhibitory activity (IC50 110 microM), displayed the hightest protective effects against differentiated P19 cell death induced by 6-hydroxydopamine. EPR studies suggested that Chelator 9 also act as radical scavenger to directly scavenge hydroxyl radical.

p-Quinone mediates 6-hydroxydopamine-induced dopaminergic neuronal death and ferrous iron accelerates the conversion of p-quinone into melanin extracellularly

Parkinson's disease (PD) is characterized by the selective loss of dopaminergic neurons in the substantia nigra (SN). 6-Hydroxydopamine (6-OHDA), a dopaminergic neurotoxin, is detected in human brains and the urine of PD patients. Using SH-SY5Y, a human neuroblastoma cell line, we demonstrated that 6-OHDA toxicity was determined by the amount of p-quinone produced in 6-OHDA auto-oxidation rather than by reactive oxygen species (ROS). Glutathione (GSH), which conjugated with p-quinone, provided significant protection whereas catalase, which detoxified hydrogen peroxide and superoxide anions, failed to block cell death caused by 6-OHDA. Although iron accumulated in the SN of patients with PD can cause dopaminergic neuronal degeneration by enhancing oxidative stress, we found that extracellular ferrous iron promoted the formation of melanin and reduced the amount of p-quinone. The addition of ferrous iron to the culture medium inhibited caspase-3 activation and apoptotic nuclear morphologic changes and blocked 6-OHDA-induced cytotoxicity in SH-SY5Y cells and primary cultured mesencephalic dopaminergic neurons. These data suggested that generation of p-quinone played a pivotal role in 6-OHDA-induced toxicity and extracellular iron in contrast to intracellular iron was protective rather than harmful because it accelerated the conversion of p-quinone into melanin.

Iron protects astrocytes from 6-hydroxydopamine toxicity

The role of iron in 6-hydroxydopamine (6-OHDA) toxicity towards astrocytes was investigated in vitro using rat primary astrocytes, rat astrocytoma cell line C6, and human astrocytoma cell line U251. The assessment of mitochondrial respiration or lactate dehydrogenase release has shown a dose-dependent decrease in the viability of astrocytes treated with 6-OHDA, which coincided with DNA fragmentation and the changes in cellular morphology. This was a consequence of the oxidative stress mediated by 6-OHDA autoxidation products hydrogen peroxide, superoxide anion, and hydroxyl radical. Both FeSO(4) and FeCl(3) markedly alleviated detrimental effects of 6-OHDA treatment, while MgSO(4) was without effect. The protective action of iron was neutralized by a membrane-permeable iron chelator o-phenanthroline, which also augmented astrocyte killing in the absence of exogenous iron. The mechanisms responsible for iron-mediated protection of astrocytes did not involve interference with either 6-OHDA autoxidation, hydrogen peroxide toxicity, or 6-OHDA-induced activation of extracellular signal-regulated kinase. Finally, the addition of iron potentiated and its chelation blocked 6-OHDA toxicity towards neuronal PC12 cells, suggesting the opposite roles for this transition metal in regulating the survival of astrocytes and dopaminergic neurons.

Multifunctional Activities of Green Tea Catechins in Neuroprotection

Many lines of evidence suggest that oxidative stress resulting in reactive oxygen species (ROS) generation and inflammation play a pivotal role in the age-associated cognitive decline and neuronal loss in neurodegenerative diseases including Alzheimer's (AD), Parkinson's (PD) and Huntington's diseases. One cardinal chemical pathology observed in these disorders is the accumulation of iron at sites where the neurons die. The buildup of an iron gradient in conjunction with ROS (superoxide, hydroxyl radical and nitric oxide) are thought to constitute a major trigger in neuronal toxicity and demise in all these diseases. Thus, promising future treatment of neurodegenerative diseases and aging depends on availability of effective brain permeable, iron-chelatable/radical scavenger neuroprotective drugs that would prevent the progression of neurodegeneration. Tea flavonoids (catechins) have been reported to possess potent iron-chelating, radical-scavenging and anti-inflammatory activities and to protect neuronal death in a wide array of cellular and animal models of neurological diseases. Recent studies have indicated that in addition to the known antioxidant activity of catechins, other mechanisms such as modulation of signal transduction pathways, cell survival/death genes and mitochondrial function, contribute significantly to the induction of cell viability. This review will focus on the multifunctional properties of green tea and its major component (-)-epigallocatechin-3-gallate (EGCG) and their ability to induce neuroprotection and neurorescue in vitro and in vivo. In particular, their transitional metal (iron and copper) chelating property and inhibition of oxidative stress.

Manganese superoxide dismutase protects against 6-hydroxydopamine injury in mouse brains

Dopaminergic neurons of the substantia nigra are susceptible to toxin-based insults. Intrastriatal injection of 6-hydroxydopamine results in selective toxicity to these neurons. A mechanistic role for reactive oxygen species is supported by observations that antioxidants confer protection from 6-hydroxydopamine. Although cell culture studies have suggested extracellular or nonmitochondrial mechanisms in 6-hydroxydopamine toxicity, the compartmentalization of oxidative injury mechanisms is incompletely defined in vivo. Transgenic mice overexpressing mitochondrial manganese superoxide dismutase or extracellular superoxide dismutase received unilateral intrastriatal injections of 6-hydroxydopamine. Mice that overexpress manganese superoxide dismutase showed significantly smaller striatal lesions than littermate controls. There were no differences in nonspecific striatal injury associated with contralateral vehicle injection. Manganese superoxide dismutase overexpression also protected against loss of neuronal cell bodies in the substantia nigra. In contrast, mice overexpressing extracellular superoxide dismutase showed no protection from 6-hydroxydopamine toxicity in either brain region. Protection of the nigrostriatal system by overexpression of manganese superoxide dismutase supports a role for mitochondrially derived superoxide in 6-hydroxydopamine toxicity. Mitochondrial oxidative stress appears to be a common mechanism among diverse models of Parkinson disease, whether involving toxins, mutated genes, or cybrid cells containing patient mitochondria. Antioxidant therapies that target this subcellular compartment may prove promising.

Failure of FK506 (tacrolimus) to alleviate apomorphine-induced circling in rat Parkinson model in spite of some cytoprotective effects in SH-SY5Y dopaminergic cells

The mechanism of action of the neurotoxin 6-hydroxydopamine (6-OHDA) is thought to involve the generation of free radicals and subsequent apoptotic processes. We have demonstrated in vitro that the neuroimmunophilin, FK506 (10-100 nM), dose dependently and significantly restored the ROS production to the control level, increased the Bcl-2 protein level, partly inhibited the cytochrome C release from mitochondria and reduced the caspase-3 activation in SH-SY5Y cells. On the other hand, there was no significant restoration of the ATP level by FK506 and the toxin activated proteins, p53 and Bax, were not normalized by FK506. In support of these latter results, daily administration of FK506 for 7 days to rats (0.5, 1 and 3 mg/kg i.p.) did not significantly prevent the apomorphine-induced contralateral circling, measured 2 weeks after unilateral nigral lesioning. Moreover, FK506 pretreatment did not significantly lower the toxin elevated lipid peroxidation levels, indicating that oxidative stress was present even after the FK506 treatment in the lesioned striatum. Taken together, our results with FK506 are inconsistent. We confirm the antioxidant nature of FK506, that is, it blocks ROS production in SH-SY5Y cells. However, there were no significant protective effects in any apoptotic analyses in SH-SY5Y cells and in animal studies, a 7-day FK506 pre-treatment was not able to reverse the toxic effect of 6-OHDA in a rat model of Parkinson's disease.

Bifunctional drug derivatives of MAO-B inhibitor rasagiline and iron chelator VK-28 as a more effective approach to treatment of brain ageing and ageing neurodegenerative diseases

Degeneration of nigrostriatal dopamine neurons and cholinergic cortical neurones are the main pathological features of Parkinson's disease (PD) and for the cognitive deficit in dementia of the Alzheimer' type (AD) and in dementia with Lewy bodies (DLB), respectively. Many PD and DLB subjects have dementia and depression resulting from possible degeneration of cholinergic and noradrenergic and serotonergic neurons. On the other hand, AD patients may also develop extrapyramidal features as well as depression. In both PD and AD there is, respectively, accumulation of iron within the melanin containing dopamine neurons of pars compacta and with in the plaques and tangle. It has been suggested that iron accumulation may contribute to the oxidative stress induced apoptosis reported in both diseases. This may result from increased glia hydrogen peroxide producing monoamine oxidase (MAO) activity that can generate of reactive hydroxyl radical formed from interaction of iron and hydrogen peroxide. We have therefore prepared a series of novel bifunctional drugs from the neuroprotective-antiapoptotic antiparkinson monoamine oxidase B inhibitor, rasagiline, by introducing a carbamate cholinesterase (ChE) inhibitory moiety into it. Ladostigil (TV-3326, N-propargyl-3R-aminoindan-5yl)-ethyl methylcarbamate), has both ChE and MAO-AB inhibitory activity, as potential treatment of AD and DLB or PD subjects with dementia Being a brain selective MAO-AB inhibitor it has limited potentiation of the pressor response to oral tyramine and exhibits antidepressant activity similar to classical non-selective MAO inhibitor antidepressants by increasing brain serotonin and noradrenaline. Ladostigil inhibits brain acetyl and butyrylcholinesterase in rats and antagonizes scopolamine-induced inhibition of spatial learning. Ladostigil like MAO-B inhibitor it prevents MPTP Parkinsonism in mice model and retains the in vitro and in vivo neuroprotective activity of rasagiline. Ladostigil, rasagiline and other propargylamines have been demonstrated to have neuroprotective activity in several in vitro and in vivo models, which have been shown be associated with propargylamines moiety, since propargylamines itself possess these properties. The mechanism of neuroprotective activity has been attributed to the ability of propargylamines-inducing the antiapoptotic family proteins Bcl-2 and Bcl-xl, while decreasing Bad and Bax and preventing opening of mitochondrial permeability transition pore. Iron accumulates in brain regions associated with neurodegenerative diseases of PD, AD, amyotrophic lateral sclerosis and Huntington disease. It is thought to be involved in Fenton chemistry oxidative stress observed in these diseases. The neuroprotective activity of propargylamines led us to develop several novel bifunctional iron chelator from our prototype brain permeable iron chelators, VK-28, possessing propargylamine moiety (HLA-20, M30 and M30A) to iron out iron from the brain. These compounds have been shown to have iron chelating and monoamine oxidase A and B selective brain inhibitory and neuroprotective-antiapoptotic actions.

Iron, brain ageing and neurodegenerative disorders

There is increasing evidence that iron is involved in the mechanisms that underlie many neurodegenerative diseases. Conditions such as neuroferritinopathy and Friedreich ataxia are associated with mutations in genes that encode proteins that are involved in iron metabolism, and as the brain ages, iron accumulates in regions that are affected by Alzheimer's disease and Parkinson's disease. High concentrations of reactive iron can increase oxidative-stress induced neuronal vulnerability, and iron accumulation might increase the toxicity of environmental or endogenous toxins. By studying the accumulation and cellular distribution of iron during ageing, we should be able to increase our understanding of these neurodegenerative disorders and develop new therapeutic strategies.

The cytotoxic activity of lactoperoxidase: enhancement and inhibition by neuroactive compounds

Neuronal death associated with Parkinson's disease is commonly believed to be caused by oxygen- and nitrogen-derived free radical species. Some years ago, however, we showed that peroxidase from the midbrain of dogs is able to kill various cell types, including neuroblastoma cells (M. B. Grisham et al., J. Neurochem. 48: 876-882: 1987). We postulated that a nigral peroxidase may play a significant role in the degeneration of dopaminergic neurons in Parkinson's disease. To further establish proof of principle, we recently performed a series of experiments using horseradish peroxidase and lactoperoxidase. We showed that the cytotoxic activity of lactoperoxidase is fully inhibited by physiological concentrations of dopamine, reduced glutathione, and L-cysteine, as well as by micromolar concentrations of apomorphine, desferal, aspirin, and uric acid. l-Methyl-4-phenyl-1,2-dihydropyridine (MPDP) and l-methyl-4-phenylpyridinium (MPP+) augment the cytotoxic activity, whereas l-methyl-4-phenyl-1,2,3,6-tetrahydropyridine, deprenyl, and pargyline had minimal or no effect. We also showed that horseradish peroxidase catalyzes the oxidation of MPDP to MPP+. Thus, contrary to the generally accepted theory that the in vivo oxidation of MPDP occurs spontaneously, this reaction may be catalyzed by a brain peroxidase. These observations lend further support to the suggestion that a brain peroxidase may play an important role in the metabolic events associated with Parkinson's disease.

Redox imbalance

Substantial evidence implies that redox imbalance attributable to an overproduction of reactive oxygen species or reactive nitrogen species that overwhelm the protective defense mechanism of cells contributes to all forms of Parkinson's disease. Factors such as dopamine, neuromelanin, and transition metals may, under certain circumstances, contribute to the formation of oxygen species such as H(2)O(2), superoxide radicals, and hydroxyl radicals and react with reactive nitrogen species such as nitric oxide or peroxinitrite. Mitochodrial dysfunction and excitotoxicity may be a cause and a result of oxidative stress. Consequences of this redox imbalance are lipid peroxidation, oxidation of proteins, DNA damage, and interference of reactive oxygen species with signal transduction pathways. These consequences become even more harmful when genetic variations impair the normal degradation of altered proteins. Therefore, therapeutic strategies must aim at reducing free-radical formation and scavenging free-radicals.

Catechin polyphenols: neurodegeneration and neuroprotection in neurodegenerative diseases

Neurodegeneration in Parkinson's, Alzheimer's, and other neurodegenerative diseases seems to be multifactorial, in that a complex set of toxic reactions including inflammation, glutamatergic neurotoxicity, increases in iron and nitric oxide, depletion of endogenous antioxidants, reduced expression of trophic factors, dysfunction of the ubiquitin-proteasome system, and expression of proapoptotic proteins leads to the demise of neurons. Thus, the fundamental objective in neurodegeneration and neuroprotection research is to determine which of these factors constitutes the primary event, the sequence in which these events occur, and whether they act in concurrence in the pathogenic process. This has led to the current notion that drugs directed against a single target will be ineffective and rather a single drug or cocktail of drugs with pluripharmacological properties may be more suitable. Green tea catechin polyphenols, formerly thought to be simple radical scavengers, are now considered to invoke a spectrum of cellular mechanisms of action related to their neuroprotective activity. These include pharmacological activities like iron chelation, scavenging of radicals, activation of survival genes and cell signaling pathways, and regulation of mitochondrial function and possibly of the ubiquitin-proteasome system. As a consequence these compounds are receiving significant attention as therapeutic cytoprotective agents for the treatment of neurodegenerative and other diseases.

Does cellular iron dysregulation play a causative role in Parkinson's disease?

Selective dopaminergic cell loss in Parkinson's disease is correlated with increased levels of cellular iron. It is still hotly debated as to whether the increase in iron is an upstream event which acts to promote neurodegeneration via formation of oxidative stress or whether iron accumulates as a by-product of the neuronal cell loss. Here we review evidence for loss of iron homeostasis as a causative factor in disease-associated neurodegeneration and the primary players which may be involved. A series of recent studies suggest that iron regulatory proteins (IRPs) coordinate both cellular iron levels and energy metabolism, both of which are disrupted in Parkinson's disease (PD) and may in turn contribute to increased levels of oxidative stress associated with the disease. Iron has also been recently been implicated in promotion of alpha-synuclein aggregation either directly or via increasing levels of oxidative stress suggesting an important role for it in Lewy body formation, another important hallmark of the disease.

Nutritional iron deprivation attenuates kainate-induced neurotoxicity in rats: implications for involvement of iron in neurodegeneration

There is evidence suggesting that oxidative stress contributes to kainate neurotoxicity. Since iron promotes oxidative stress, the present study explores how change in nutritional iron content modulates kainate-induced neurotoxicity. Rats received an iron-deficient diet (ID) from 22 days of age for 4 weeks. One control group received the same diet supplemented with iron and another control group received standard rodent diet. Cellular damage after subcutaneous kainate (10 mg/kg) was assessed by silver impregnation and gliosis by staining microglia. ID reduced cellular damage in piriform and entorhinal cortex, in thalamus, and in hippocampal layers CA1-3. ID also attenuated gliosis, except in the hippocampal CA1 layer. Given involvement of zinc in hippocampal neurotransmission and in oxidative stress, we tested for a possible interaction of nutritional iron with nutritional zinc. Rats were made iron-deficient and then assigned to supplementation with iron, zinc, or iron + zinc. Controls were continued on ID diet. After 2 weeks, rats were treated with kainate. Iron supplementation abolished the protective effect of ID in piriform and entorhinal cortex. In hippocampal CA1 and dorsal thalamus, neither iron nor zinc supplementation alone abolished the protective effect of ID against cellular damage. Iron + zinc supplementation abolished ID protection in dorsal thalamus, but not in reuniens nucleus. Kainate-induced gliosis in CA1 remained unaffected by nutritional treatments. Thus, in piriform and entorhinal cortex, nutritional iron has a major impact on cellular damage and gliosis. In hippocampal CA1, gliosis may associate with synaptic plasticity not modulated by nutritional iron, while cellular damage is sensitive to nutritional iron and zinc.

Cell signaling pathways in the neuroprotective actions of the green tea polyphenol (-)-epigallocatechin-3-gallate: implications for neurodegenerative diseases

Accumulating evidence supports the hypothesis that brain iron misregulation and oxidative stress (OS), resulting in reactive oxygen species (ROS) generation from H2O2 and inflammatory processes, trigger a cascade of events leading to apoptotic/necrotic cell death in neurodegenerative disorders, such as Parkinson's (PD), Alzheimer's (AD) and Huntington's diseases, and amyotrophic lateral sclerosis (ALS). Thus, novel therapeutic approaches aimed at neutralization of OS-induced neurotoxicity, support the application of ROS scavengers, transition metals (e.g. iron and copper) chelators and non-vitamin natural antioxidant polyphenols, in monotherapy, or as part of antioxidant cocktail formulation for these diseases. Both experimental and epidemiological evidence demonstrate that flavonoid polyphenols, particularly from green tea and blueberries, improve age-related cognitive decline and are neuroprotective in models of PD, AD and cerebral ischemia/reperfusion injuries. However, recent studies indicate that the radical scavenger property of green tea polyphenols is unlikely to be the sole explanation for their neuroprotective capacity and in fact, a wide spectrum of cellular signaling events may well account for their biological actions. In this article, the currently established mechanisms involved in the beneficial health action and emerging studies concerning the putative novel molecular neuroprotective activity of green tea and its major polyphenol (-)-epigallocatechin-3-gallate (EGCG), will be reviewed and discussed.

The Relevance of Iron in the Pathogenesis of Parkinson's Disease

Investigations that revealed increased levels of iron in postmortem brains from patients with Parkinson's disease (PD) as compared to those from individuals not suffering from neurological disorders are reported. The chemical natures in which iron predominates in the brain and the relevance of neuromelanin for neuronal iron binding are discussed. Major findings have been that iron levels increase with the severity of neuropathological changes in PD, presumably due to increased transport through the blood-brain barrier in late stages of parkinsonism. Glial iron is mainly stored as ferric iron in ferritin, while neuronal iron is predominantly bound to neuromelanin. Iron overload may induce progressive degeneration of nigrostriatal neurons by facilitating the formation of reactive biological intermediates, including reactive oxygen species, and the formation of cytotoxic protein aggregates. There are indications that iron-mediated neuronal death in PD proceeds retrogradely. These results are also discussed with respect to their relevance for disease progression in relation to cytotoxic alpha-synuclein protofibril formation.

Ironing Iron Out in Parkinson's Disease and Other Neurodegenerative Diseases with Iron Chelators: A Lesson from 6-Hydroxydopamine and Iron Chelators, Desferal and VK-28

In Parkinson's disease (PD) and its neurotoxin-induced models, 6-hydroxydopamine (6-OHDA) and N-methyl-4-phenyl-1,2,3,6-tetrahydropyridine (MPTP), significant accumulation of iron occurs in the substantia nigra pars compacta. The iron is thought to be in a labile pool, unbound to ferritin, and is thought to have a pivotal role to induce oxidative stress-dependent neurodegeneration of dopamine neurons via Fenton chemistry. The consequence of this is its interaction with H(2)O(2) to generate the most reactive radical oxygen species, the hydroxyl radical. This scenario is supported by studies in both human and neurotoxin-induced parkinsonism showing that disposition of H(2)O(2) is compromised via depletion of glutathione (GSH), the rate-limiting cofactor of glutathione peroxide, the major enzyme source to dispose H(2)O(2) as water in the brain. Further, radical scavengers have been shown to prevent the neurotoxic action of the above neurotoxins and depletion of GSH. However, our group was the first to demonstrate that the prototype iron chelator, desferal, is a potent neuroprotective agent in the 6-OHDA model. We have extended these studies and examined the neuroprotective effect of intracerebraventricular (ICV) pretreatment with the prototype iron chelator, desferal (1.3, 13, 134 mg), on ICV induced 6-OHDA (250 micro g) lesion of striatal dopamine neurons. Desferal alone at the doses studied did not affect striatal tyrosine hydroxylase (TH) activity or dopamine (DA) metabolism. All three pretreatment (30 min) doses of desferal prevented the fall in striatal and frontal cortex DA, dihydroxyphenylacetic acid, and homovalinic acid, as well as the left and right striatum TH activity and DA turnover resulting from 6-OHDA lesion of dopaminergic neurons. A concentration bell-shaped neuroprotective effect of desferal was observed in the striatum, with 13 micro g being the most effective. Neither desferal nor 6-OHDA affected striatal serotonin, 5-hydroxyindole acetic acid, or noradrenaline. Desferal also protected against 6-OHDA-induced deficit in locomotor activity, rearing, and exploratory behavior (sniffing) in a novel environment. Since the lowest neuroprotective dose (1.3 micro g) of desferal was 200 times less than 6-OHDA, its neuroprotective activity may not be attributed to interference with the neurotoxin activity, but rather iron chelation. These studies led us to develop novel brain-permeable iron chelators, the VK-28 series, with iron chelating and neuroprotective activity similar to desferal for ironing iron out from PD and other neurodegenerative diseases, such as Alzheimer's disease, Friedreich's ataxia, and Huntington's disease.

Neuroprotection by a novel brain permeable iron chelator, VK-28, against 6-hydroxydopamine lession in rats

Significant increase in iron occurs in the substantia nigra pars compacta of Parkinsonian subjects, and in 6-hydroxydopamine (6-OHDA) treated rats and monkeys. This increase in iron has been attributed to its release from ferritin and is associated with the generation of reactive oxygen species and the onset of oxidative stress-induced neurodegeneration. Several iron chelators with hydroxyquinoline backbone were synthesized and their ability to inhibit basal as well as iron-induced mitochondrial lipid peroxidation was examined. The neuroprotective potential of the brain permeable iron chelator, VK-28 (5-[4-(2-hydroxyethyl) piperazine-1-ylmethyl]-quinoline-8-ol), injected either intraventricularly (ICV) or intraperitoneally (IP), to 6-OHDA lesioned rats was investigated. VK-28 inhibited both basal and Fe/ascorbate induced mitochondrial membrane lipid peroxidation, with an IC(50) (12.7 microM) value comparable to that of the prototype iron chelator, desferal, which does not cross the blood brain barrier. At an ICV pretreatment dose as low as 1 microg, VK-28 was able to completely protect against ICV 6-OHDA (250 microg) induced striatal dopaminergic lesion, as measured by dopamine (DA), dihydroxyphenylacetic acid (DOPAC) and homovanilic acid (HVA) levels. IP injection of rats with VK-28 (1 and 5 mg/kg) daily for 10 and 7 days, respectively, demonstrated significant neuroprotection against ICV 6-OHDA at the higher dose, with 68% protection against loss of dopamine at 5mg/kg dosage of VK-28. The present study is the first to show neuroprotection with a brain permeable iron chelator. The latter can have implications for the treatment of Parkinson's disease and other neurodegenerative diseases (Alzheimer's disease, Friedreich ataxia, aceruloplasminemia, Hallervorden Spatz syndrome) where abnormal iron accumulation in the brain is thought to be associated with the degenerative processes.

Neuroprotective strategies in Parkinson's disease : an update on progress

In spite of the extensive studies performed on postmortem substantia nigra from Parkinson's disease patients, the aetiology of the disease has not yet been established. Nevertheless, these studies have demonstrated that, at the time of death, a cascade of events had been initiated that may contribute to the demise of the melanin-containing nigro-striatal dopamine neurons. These events include increased levels of iron and monoamine oxidase (MAO)-B activity, oxidative stress, inflammatory processes, glutamatergic excitotoxicity, nitric oxide synthesis, abnormal protein folding and aggregation, reduced expression of trophic factors, depletion of endogenous antioxidants such as reduced glutathione, and altered calcium homeostasis. To a large extent, the 1-methyl-4-phenyl-1,2,3,6-tetrahydropyridine (MPTP) and 6-hydroxydopamine (6-OHDA) animal models of Parkinson's disease confirm these findings. Furthermore, neuroprotection can be afforded in these models with iron chelators, radical scavenger antioxidants, MAO-B inhibitors, glutamate antagonists, nitric oxide synthase inhibitors, calcium channel antagonists and trophic factors. Despite the success obtained with animal models, clinical neuroprotection is much more difficult to accomplish. Although the negative studies obtained with the MAO-B inhibitor selegiline (deprenyl) and the antioxidant tocopherol (vitamin E) may have resulted from an inappropriate choice of drug (selegiline) or an inadequate dose (tocopherol), the niggling problem that still remains is why these drugs, and others, do work in animals while they fail in the clinic. One reason for this may be related to the fact that in normal human brains the number of dopaminergic neurons falls by around 3-5% every decade, while in Parkinson's disease this decline is greater. Brain autopsy studies have shown that by the time the disease is identified, some 70-75% of the dopamine-containing neurons have been lost. More sensitive reliable methods and clinical correlative markers are required to discern between confoundable symptomatic effects versus a possible neuroprotective action of drugs, namely, the ability to delay or forestall disease progression by protecting or rescuing the remaining dopamine neurons or even restoring those that have been lost.A number of other possibilities for the clinical failure of potential neuroprotectants also exist. First, the animal models of Parkinson's disease may not be totally reflective of the disease and, therefore, the chemical pathologies established in the animal models may not cause, or contribute to, the progression of the disease clinically. Second, because of the series of events occurring in neurodegeneration and our ignorance about which of these factors constitutes the primary event in the pathogenic process, a single drug may not be adequate to induce neuroprotection and, as a consequence, use of a cocktail of drugs may be more appropriate. The latter concept receives support from recent complementary DNA (cDNA) microarray gene expression studies, which show the existence of a gene cascade of events occurring in the nigrostriatal pathway of MPTP, 6-OHDA and methamphetamine animal models of Parkinson's disease. Even with the advent of powerful new tools such as genomics, proteomics, brain imaging, gene replacement therapy and knockout animal models, the desired end result of neuroprotection is still beyond our current capability.

What have we learnt from CDNA microarray gene expression studies about the role of iron in MPTP induced neurodegeneration and Parkinson's disease?

There have been numerous hypotheses concerning the etiology and mechanism of dorsal raphe dopaminergic neurodegeneration in Parkinson's disease and its animal models, MPTP (N-methyl-4-phenyl-1,2,3,6-tetrahydropyridine) and 6-hydroxydopamine. The advent of cDNA microarray gene expression where expression of thousands of genes can be globally assessed has indicated that mechanism of neurodegeneration by MPTP is a complex cascade of vicious circles. One of these is the alteration of genes associated with iron metabolism, a transitional metal closely associated with inducing the formation of reactive oxygen species and inducing oxidative stress. cDNA gene expression analyses support the established hypothesis of oxidative induced neurodegeneration involving iron deposition in substantia nigra pars compacta (SNPC) parkinsonian brains. The regulation of cellular iron metabolism has been further enhanced by the recent discovery of two iron regulatory proteins, IRP1 and IRP2 which control the level of iron with in the cell. When the cellular level of iron increases IRP2 is degraded by ubiquitination and no further iron accumulates. The reverse occurs when the level of iron is low within the cell. Knock-out IRP1 and IRP2 mice have shown that in latter mice brain iron accumulation precedes the neurodegeneration, ataxia and bradykinesia observed in these animals. Indeed MPTP treatment, which results in iron accumulation in SNCP, abolishes IRP2 with the concomitant increase in alpha-synuclein. Iron chelators such as R-apomorphine and EGCG, which protect against MPTP neurotoxicity, prevent the loss of IRP2 and the increase in alpha-synuclein. The presence of iron together with alpha-synuclein in SNPC may be detrimental for dopaminergic neurons. Since, iron has been shown to cause aggregation of alpha-synuclein to a neurotoxic agent. The use of iron chelators penetrating the blood brain barrier as neuroprotective drugs has been envisaged.

Dopaminergic cell death precedes iron elevation in MPTP-injected monkeys

Though increasing lines of evidence suggest that iron accumulation and iron-induced oxidative stress might be important pathological factors responsible for substantia nigra (SN) cell death in Parkinson's disease (PD), it is still unknown whether iron accumulation is a primary cause or consequence of nigral cell death. Using nuclear microscopy, iron histochemistry, TUNEL method for apoptosis detection, and tyrosine hydroxylase (TH) immunohistochemistry, the present study investigated possible changes in iron contents in the SN and correlations of dopaminergic cell death progression with the process of iron accumulation in 1-methyl-4-phenyl-1,2,3,6-tetrahydropyridine(MPTP)-induced parkinsonian monkey from 1 d to 18 months after MPTP administration. Our study demonstrated that apoptosis occurred in the ipsilateral SN at 1 d after MPTP injection and the number of TH-positive cells decreased significantly from 1 week onward. However, iron content was significantly increased in the ipsilateral SN from 4.5 months to 18 months after MPTP injection, and the iron increase was significantly correlated to the extent of dopaminergic cell death. These results suggest that dopaminergic cell death induced by MPTP administration might lead to iron accumulation in the monkey SN, and increased iron might contribute to the progression of nigral degeneration.

Dopamine release rather than content in the caudate putamen is associated with behavioral changes in the iron rat model of Parkinson's disease

The effects of intranigral iron injection on dopamine (DA) release and content in the caudate putamen (CPu) and their relationship to DA-related behavioral response were investigated in rats. Different concentrations of FeCl(3) (10, 20, and 40 microg) and saline were injected separately into the left substantia nigra. In some experiments, rats were pretreated with desferrioxamine or saline before iron injection. After 3 weeks, changes in behavioral response, DA release, and DA content in the CPu were determined. In all iron injection groups (10, 20, and 40 microg), DA content in the lesioned side of the brain was significantly decreased, showing a significant linear correlation (R(2) = 0.981, P = 0.01), and DA turnover ratio significantly increased (both P = 0.01, 0.01 and 0.001 vs unlesioned sides, respectively). However, injection dosages of 10 or 20 microg of iron did not lead to significant changes in DA release in the CPu or in behavioral response. At the 40-microg dosage, it was found that DA release in the lesioned side and rearing activity both were significantly reduced (all P = 0.01 vs unlesioned side or control) and apomorphine-induced rotation was observed. Pretreatment with desferrioxamine significantly inhibited the effect of iron on DA release and content. These results demonstrate that iron injection can damage dopaminergic neurons and suggest that DA release, rather than DA content, in the CPu is associated with DA-related behavioral changes in this PD model.

Effect of postnatal iron administration on MPTP-induced behavioral deficits and neurotoxicity: behavioral enhancement by L-Dopa-MK-801 co-administration

Two experiments were performed to investigate the interactive effects of postnatal iron administration and adult MPTP treatment upon the function of C57 Bl/6 mice tested at adult age and to ascertain the possible ameliatory effects of a subthreshold dose of L-Dopa co-administered with different doses of the uncompetitive glutamate antagonist, MK-801. Experiment I indicated that postnatal iron induced marked deficits (hypoactivity), initially, in all three parameters of motor activity at the 5.0 and 7.5 mg/kg doses, and to a lesser extent at the 2.5 mg/kg dose. Later combination with MPTP (2x40 mg/kg) potentiated severely these deficits. During the final period of testing a marked hyperactivity was obtained for the two higher dose groups; this effect was abolished in mice administered MPTP. Experiment II indicated that the deficits in motor activity parameters induced by postnatal iron at 7.5 mg/kg were alleviated in a dose-related manner by the co-administration of the uncompetitive glutamate antagonist, MK-801, with a subthreshold dose of L-Dopa. Postnatal iron (7.5 mg/kg) administration followed by low doses of MPTP (2x20 mg/kg) 3 months later virtually abolished all motor activity. The combination of these compounds increased also the motor activity of mice treated with MPTP (2x20 mg/kg) or mice treated with the combination of postnatal iron and MPTP. The combination of MK-801 with L-Dopa increased locomotor (0.3 mg/kg), rearing (0.1 and 0.3 mg/kg) and total activity (0.3 mg/kg) of iron-treated mice during the initial, hypoactive 30-min period of testing. Locomotor activity (0.1 mg/kg) of MPTP-treated mice was increased too during this period. During the final 30-min period of testing all three parameters of activity (locomotion, 0.3 mg/kg; rearing and total activity, 0.1 and 0.3 mg/kg) were enhanced in the iron-treated mice, locomotion (0.1 mg/kg) and rearing (0.1 mg/kg) in the iron plus MPTP treated mice and only locomotion (0.1 mg/kg) in the MPTP-treated mice. In control mice (vehicle+saline), the higher doses of MK-801 (0.1 and 0.3 mg/kg) enhanced both locomotor and total activity. Analyses of total iron concentration in the frontal cortex and basal ganglia of Fe(2+) and vehicle treated mice indicated that marked elevations basal ganglia iron levels of the 5.0 and 7.5 mg/kg groups, later injected either saline or MPTP, were obtained (Experiment I). In Experiment II, iron concentrations in the basal ganglia were elevated in both the Fe(2+)-sal and Fe(2+)-MPTP groups to 170 and 177% of Veh.-sal values, respectively. There was a significant increase in the frontal cortex of iron-treated mice later administered either saline or MPTP (2x40 mg/kg) in Experiment I as well as in those given iron followed by MPTP (2x20mg/kg) in Experiment II. The implications of iron overload in parkinsonism seem confirmed by the interactive effects of postnatal administration of the metal followed by adult MPTP treatment upon motor activity and the activity-enhancing effects of co-administration of L-Dopa with MK-801.