Iron as catalyst for oxidative stress in the pathogenesis of Parkinson's disease?

The mechanisms leading to degeneration of melanized dopaminergic neurons in the brain stem, and particularly in the substantia nigra zona compacta (SNZC) in patients with Parkinson's disease (PD) are still unknown. Demonstration of increased iron Fe(III) in SNZC 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-Fe(III) complex in intracytoplasmic electron-dense neuromelanin granules of SNZC neurons, 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 chemical reactions of dopamine (DA), 5-hydroxydopamine (5-OHDA), and 6-hydroxydopamine (6-OHDA) with Fe(III) and with dioxygen for the pathogenesis of PD was investigated. An initiating mechanism related to interaction between Fe and neuromelanin is suggested which results in accumulation of Fe(III) and a continuous production of cytotoxic species inducing a cascade of pathogenic reactions ultimately leading to neuronal death.     

Experimental Strategy to Identify Genes Susceptible to Oxidative Stress in Nigral Dopaminergic Neurons

Neuropathological evidence from both human and experimental models of Parkinson's disease (PD) firmly supports a significant role for oxidative stress (OS) in the death of dopaminergic (DA) neurons in substantia nigra. Largely unknown are the genes underlying selective susceptibility of nigral DA neuron to OS and how they effect nigral DA cell death. The major barriers to high-throughput identification of candidate genes are the paucity of nigral DA neurons as well as the dilution effect of non-DA cells both in primary cultures and brain tissues. To overcome these barriers, we have developed a DA cell line model, SN4741, appropriate for cDNA microarray analysis. Candidate genes were selected from both the microarray analysis and the molecular implication of their pathological mechanisms (i.e., decreased mitochondrial complex I activity and proteasomal dysfunction) of PD. Subsequent secondary validation tests were devised to characterize genes including clone #45 that may underlie selective vulnerability of nigral DA neuron to OS.     

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.     

Proteomic analysis of human substantia nigra identifies novel candidates involved in Parkinson's disease pathogenesis

Parkinson's disease (PD) pathology spreads throughout the brain following a region‐specific process predominantly affecting the substantia nigra (SN) pars compacta. SN exhibits a progressive loss of dopaminergic neurons responsible for the major cardinal motor symptoms, along with the occurrence of Lewy bodies in the surviving neurons. To gain new insights into the underlying pathogenic mechanisms in PD, we studied postmortem nigral tissues dissected from pathologically confirmed PD cases (n = 5) and neurologically intact controls (n = 8). Using a high‐throughput shotgun proteomic strategy, we simultaneously identified 1795 proteins with concomitant quantitative data. To date, this represents the most extensive catalog of nigral proteins. Of them, 204 proteins displayed significant expression level changes in PD patients versus controls. These were involved in novel or known pathogenic processes including mitochondrial dysfunction, oxidative stress, or cytoskeleton impairment. We further characterized four candidates that might be relevant to PD pathogenesis. We confirmed the differential expression of ferritin‐L and seipin by Western blot and demonstrated the neuronal localization of gamma glutamyl hydrolase and nebulette by immunohistochemistry. Our preliminary findings suggest a role for nebulette overexpression in PD neurodegeneration, through mechanisms that may involve cytoskeleton dynamics disruption. All MS data have been deposited in the ProteomeXchange with identifier PXD000427 ( http://proteomecentral.proteomexchange.org/dataset/PXD000427 ).     

Iron as a vulnerability factor in nigrostriatal degeneration in aging and Parkinson's disease.

Recent findings strengthen the connection between iron accumulation in the basal ganglia, oxidative stress and nigrostriatal degeneration. Oxidative stress appears to be elevated in the normal human substantia nigra in comparison with other brain regions, and further increases occur in Parkinson's disease. Accumulation of iron may contribute to degeneration of nigral dopamine neurons by catalyzing oxidative damage to cell components and also by perturbing the network of interactions that modulate cellular redox status.     

Neuroprotection by iron chelator against proteasome inhibitor-induced nigral degeneration

The cause of the neurodegenerative process in Parkinson's disease (PD) remains unclear, but evidence suggests that failure of the ubiquitin-proteasome system may play a major role in the pathogenesis of the disease. Iron is believed to be a key contributor to PD pathology by inducing aggregation of alpha-synuclein and by generating oxidative stress. Our present studies have shown that micro-injection of the proteasome inhibitor lactacystin into the substantia nigra (SN) of C57BL/6 mice causes significant loss of dopaminergic cells and induces intracellular inclusion body formation. We have also found that co-injection of the iron chelator desferrioxamine not only attenuates the lactacystin-induced dopamine neuron loss, but also reduces the presence of ubiquitin-positive intracellular inclusions in the SN, whereas use of iron-deficient diet has no such protective effects. These results may support that iron plays a key role in proteasome inhibitor-induced nigral pathology and that reducing iron reactivity may prevent dopaminergic neuron degeneration and reduce abnormal protein aggregation.     

Prevention of progression in Parkinson’s disease

Environmental influences affecting genetically susceptible individuals seem to contribute significantly to the development of Parkinson’s disease (PD). Xenobiotic exposure including transitional metal deposition into vulnerable CNS regions appears to interact with PD genes. Such exposure together with mitochondrial dysfunction evokes a destructive cascade of biochemical events, including oxidative stress and degeneration of the sensitive dopamine (DA) production system in the basal ganglia. Recent research indicates that the substantia nigra degeneration can be decelerated by treatment with iron binding compounds such as deferiprone. Interestingly compounds known to decrease PD risk including caffeine, niacin, nicotine and salbutamol also possess iron binding properties. Adequate function of antioxidative mechanisms in the vulnerable brain cells can be restored by acetylcysteine supplementation to normalize intracellular glutathione activity. Other preventive measures to reduce deterioration of dopaminergic neurons may involve life-style changes such as intake of natural antioxidants and physical exercise. Further research is recommended to identify therapeutic targets of the proposed interventions, in particular protection of the DA biosynthesis by oxygen radical scavengers and iron binding agents.     

Inflammation and infection in Parkinson's disease

The hallmark of Parkinson's disease (PD) is a specific degeneration of dopaminergic neurons in the substantia nigra (SN). The cause of nigral dopaminergic neuronal cell death in PD and its underlying mechanisms remain elusive, however, involvement of inflammatory events has been postulated because inflammatory features have been described in the brain of PD patients. Some evidence also suggest that a possible deleterious effects of neuroinflammatory processes by infection in experimental models of neurodegenerative disease. In this review, we summarize and discuss the latest findings regarding inflammation in PD. Especially, we focused on the relationship between infection and PD.     

多巴胺代谢异常在帕金森病相关病理变化中的作用

帕金森病(Parkinson's disease,PD)是常见的中枢神经系统退行性疾病之一,其主要病理学特征是中脑黑质部的多巴胺(dopamine,DA)能神经元选择性丢失.虽然已发现基因易感性、衰老、环境毒素等因素与PD发病有关,但导致DA能神经元退行性死亡的细胞分子机制仍不明确.DA代谢是DA能神经元中的重要生理过...     

Is there a rationale for neuroprotection against dopamine toxicity in Parkinson's disease?

Parkinson's disease is a progressive neurological disease caused by rather selective degeneration of the dopaminergic neurons in the substantia nigra. Though subject to intensive research, the etiology of this nigral loss is still undetermined and treatment is basically symptomatic. The current major hypothesis is that nigral neuronal death in PD is due to excessive oxidative stress generated by auto and enzymatic oxidation of the endogenous neurotransmitter dopamine (DA), the formation of neuromelanin (NM) and the presence of a high concentration of iron. In this review article although we concisely describe the effects of NM and iron on neuronal survival, we mainly focus on the molecular mechanisms of DA-induced apoptosis. DA exerts its toxic effects through its oxidative metabolites either in vitro or in vivo The oxidative metabolites then activate a very intricate web of signals, which culminate in cell death. The signal transduction pathways and genes, which are associated with DA toxicity are described in detail.     

Mitochondrial dysfunction in Parkinson's disease

Parkinson's disease (PD) is one of the most common neurodegenerative disorders characterized by resting tremor, rigidity, and bradykinesia. The primary cause of PD is still unknown, but oxidative stress and mitochondrial dysfunction have been implicated as important contributors to neuronal death in substantia nigra (SN) of PD. Considering neurons as post-mitotic cells, neurons could have error-avoiding mechanism against oxidative DNA damage. Indeed, several DNA repairing enzymes such as MTH1, OGG1, and MUTYH express in human brain. All the three enzymes up-regulated in the SN of PD patients, suggesting these three enzymes cooperate in mitochondrial DNA repairing in PD brain.     

Mössbauer spectroscopy and ELISA studies reveal differences between Parkinson's disease and control substantia nigra

The possible role of iron in the degeneration of nervous cells in Parkinson's disease (PD) was studied with the use of M?ssbauer spectroscopy (MS) and enzyme-linked immunoabsorbent assay (ELISA). M?ssbauer data were obtained at 90 and 4.1 K from 21 samples of control and 9 samples of parkinsonian substantia nigra (SN). M?ssbauer spectra were very similar to those observed in ferritin. Small differences were detected between the spectra obtained from PD and from control SN, and could be due to a slight difference in the composition of the ferritin-like iron cores or due to the presence of about 8% of non-ferritin-like iron in parkinsonian SN. ELISA studies from 11 controls and 6 parkinsonian SN showed a decrease in the concentration of L-chains in wet tissues of PD-SN compared to control SN. The decrease in the amount of L subunits may correspond to a decreased ability of this ferritin to keep iron in a safe form. Iron released from ferritin or neuromelanin (NM) may be the source of such iron, which may cause the difference in the M?ssbauer spectra and may trigger oxidative stress leading to cell death.     

Ferroportin1 and hephaestin overexpression attenuate iron‐induced oxidative stress in MES23.5 dopaminergic cells

Elevated iron was found in the substantia nigra (SN) of patients with Parkinson's disease (PD). Our previous in vivo experiments suggested that decreased ferroportin1 (FPN1) and hephaestin (HP) expression might account for the cellular iron accumulation and resulting dopaminergic neurons loss in the SN of PD animal models. In the present study, we investigated whether increased FPN1 and/or HP expression could attenuate iron‐induced oxidative stress in the dopaminergic MES23.5 cell line. We generated MES23.5 cells with stable overexpression of FPN1 and/or HP. Our study showed that overexpression of FPN1 and/or HP increased iron efflux, lowered cellular iron level, suppressed reactive oxygen species production, and restored mitochondrial transmembrane potential, similar to the effects seen for the iron chelator deferoxamine. These results suggest that FPN1 and/or HP might directly contribute to iron efflux process from neurons in conditions of overexpression, thus prevent cellular iron accumulation and eventually protect cells from iron‐induced oxidative stress. J. Cell. Biochem. 110: 1063–1072, 2010. Published 2010 Wiley‐Liss, Inc.     

Reprint of: Revisiting oxidative stress and mitochondrial dysfunction in the pathogenesis of Parkinson disease—resemblance to the effect of amphetamine drugs of abuse

Parkinson disease (PD) is a chronic and progressive neurological disease associated with a loss of dopaminergic neurons. In most cases the disease is sporadic but genetically inherited cases also exist. One of the major pathological features of PD is the presence of aggregates that localize in neuronal cytoplasm as Lewy bodies, mainly composed of α-synuclein (α-syn) and ubiquitin. The selective degeneration of dopaminergic neurons suggests that dopamine itself may contribute to the neurodegenerative process in PD. Furthermore, mitochondrial dysfunction and oxidative stress constitute key pathogenic events of this disorder. Thus, in this review we give an actual perspective to classical pathways involving these two mechanisms of neurodegeneration, including the role of dopamine in sporadic and familial PD, as well as in the case of abuse of amphetamine-type drugs. Mutations in genes related to familial PD causing autosomal dominant or recessive forms may also have crucial effects on mitochondrial morphology, function, and oxidative stress. Environmental factors, such as MPTP and rotenone, have been reported to induce selective degeneration of the nigrostriatal pathways leading to α-syn-positive inclusions, possibly by inhibiting mitochondrial complex I of the respiratory chain and subsequently increasing oxidative stress. Recently, increased risk for PD was found in amphetamine users. Amphetamine drugs have effects similar to those of other environmental factors for PD, because long-term exposure to these drugs leads to dopamine depletion. Moreover, amphetamine neurotoxicity involves α-syn aggregation, mitochondrial dysfunction, and oxidative stress. Therefore, dopamine and related oxidative stress, as well as mitochondrial dysfunction, seem to be common links between PD and amphetamine neurotoxicity.     

Serum Uric Acid and Nigral Iron Deposition in Parkinson’s Disease: A Pilot Study

Background

Uric acid (UA) is an endogenous antioxidant which is known to reduce oxidative stress and also chelate iron ion. Recent studies have provided evidence that UA may play a neuroprotective role in Parkinson’s disease (PD). However, it is unknown whether UA relates to nigral iron deposition, which is a characteristic pathophysiological alteration in PD. The aim of this study was to determine the potential relationship of these two markers in patients with PD.

Methods

A total of 30 patients of PD and 25 age- and gender- matched healthy controls underwent 3-Tesla MRI and laboratory tests including serum UA levels. We assessed iron levels by measuring phase shift values using susceptibility-weighted image. Mean phase shift values of the substantia nigra (SN), red nucleus, head of the caudate nucleus, globus pallidus, putamen, thalamus, and frontal white matter were calculated and correlated with serum UA levels.

Results

Serum UA levels were significantly decreased in the PD patients than in the controls. Phase shift values in bilateral SN were significantly increased in the PD patients than in the controls. There was no significant correlation between serum UA levels and nigral phase shift values.

Conclusions

As previous studies, low serum UA level and increased nigral iron content in the PD was reconfirmed in this study. However, we failed to find the relationship between these two markers. Our data suggest that serum UA may not be important determinant of nigral iron deposition in PD.     

Neuroinflammation and oxidative stress: Co-conspirators in the pathology of Parkinson’s disease

Parkinson’s disease (PD) is a complex disease, with genetics and environment contributing to the disease onset. Recent studies of causative PD genes have confirmed the involvement of cellular mechanisms engaged in mitochondrial and UPS dysfunction, oxidative stress and apoptosis in the progressive degeneration of the dopaminergic neurons in PD. In addition, clinical, epidemiological and experimental evidence has implicated neuroinflammation in the disease progression. This review will discuss neuroinflammation in PD, with particular focus on the genetic and toxin-based models of the disease. These studies have confirmed elevated oxidative stress and the pro-inflammatory response occurs early in the disease and these processes contribute to and/or exacerbate the nigro-striatal degeneration. In addition, the experimental models discussed here have also provided strong evidence that these pathways are an important link between the familial and sporadic causes of PD. The potential application of anti-inflammatory interventions in limiting the dopaminergic neuronal cell death in these models is discussed with evidence suggesting that the further investigation of their use as part of multi-targeted clinical trials is warranted.     

Proteomic profiling of the substantia nigra demonstrates CNDP2 overexpression in Parkinson's disease

Despite decades of intensive investigations, the precise sequence of molecular events and the specific proteins mediating the degenerative process underlying Parkinson's disease (PD) remain unraveled. Proteomic strategies may provide unbiased tools to identify novel candidates and explore original mechanisms involved in PD. Substantia nigra pars compacta (SN) tissue, whose degeneration is the hallmark of PD, was dissected from neuropathologically confirmed PD patients (n=3) and control subjects (n=3), before being submitted to a comparative 2-DE analysis. The present study revealed a subset of neuronal and/or glial proteins that appears to be deregulated in PD and likely to contribute to neurodegeneration. Observed alterations not only consolidate well accepted concepts surrounding PD pathogenesis such as oxidative stress and mitochondrial dysfunction but also point out to novel pathways. Among the latter, cytosolic non specific dipeptidase 2 (CNDP2), a relatively unknown protein not yet reported to be associated with PD pathogenesis, was shown to be increased in the SN of PD patients, as confirmed by Western blot. Immunohistochemical analyses demonstrated the presence of CNDP2 within the cytoplasm of SN dopaminergic neurons. Altogether, our findings support a key role of CNDP2 in PD neurodegeneration, by mechanisms that could involve oxidative stress, protein aggregation or inflammation. This article is part of a Special Issue entitled: Translational Proteomics.     

Parkinson disease: from pathology to molecular disease mechanisms

Parkinson disease (PD) is a complex neurodegenerative disorder with both motor and nonmotor symptoms owing to a spreading process of neuronal loss in the brain. At present, only symptomatic treatment exists and nothing can be done to halt the degenerative process, as its cause remains unclear. Risk factors such as aging, genetic susceptibility, and environmental factors all play a role in the onset of the pathogenic process but how these interlink to cause neuronal loss is not known. There have been major advances in the understanding of mechanisms that contribute to nigral dopaminergic cell death, including mitochondrial dysfunction, oxidative stress, altered protein handling, and inflammation. However, it is not known if the same processes are responsible for neuronal loss in nondopaminergic brain regions. Many of the known mechanisms of cell death are mirrored in toxin-based models of PD, but neuronal loss is rapid and not progressive and limited to dopaminergic cells, and drugs that protect against toxin-induced cell death have not translated into neuroprotective therapies in humans. Gene mutations identified in rare familial forms of PD encode proteins whose functions overlap widely with the known molecular pathways in sporadic disease and these have again expanded our knowledge of the neurodegenerative process but again have so far failed to yield effective models of sporadic disease when translated into animals. We seem to be missing some key parts of the jigsaw, the trigger event starting many years earlier in the disease process, and what we are looking at now is merely part of a downstream process that is the end stage of neuronal death.     

Glutathione depletion in PC12 results in selective inhibition of mitochondrial complex I activity. Implications for Parkinson's disease

Oxidative stress appears to play an important role in degeneration of dopaminergic neurons of the substantia nigra (SN) associated with Parkinson's disease (PD). The SN of early PD patients have dramatically decreased levels of the thiol tripeptide glutathione (GSH). GSH plays multiple roles in the nervous system both as an antioxidant and a redox modulator. We have generated dopaminergic PC12 cell lines in which levels of GSH can be inducibly down-regulated via doxycycline induction of antisense messages against both the heavy and light subunits of gamma-glutamyl-cysteine synthetase, the rate-limiting enzyme in glutathione synthesis. Down-regulation of glutamyl-cysteine synthetase results in reduction in mitochondrial GSH levels, increased oxidative stress, and decreased mitochondrial function. Interestingly, decreases in mitochondrial activities in GSH-depleted PC12 cells appears to be because of a selective inhibition of complex I activity as a result of thiol oxidation. These results suggest that the early observed GSH losses in the SN may be directly responsible for the noted decreases in complex I activity and the subsequent mitochondrial dysfunction, which ultimately leads to dopaminergic cell death associated with PD.     

Intranigral iron infusion in the rat

Iron is known to induce lipid perocidation 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 μL) 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.