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

Neuromelanin: Its role in the pathogenesis of idiopathic Parkinson's disease and potential as a therapeutic target

Parkinson's disease is an increasingly prevalent condition that involves the marked loss of dopaminergic neurons in the substantia nigra pars compacta. These neurons pigmented with neuromelanin along with other regions of the brain are almost exclusively victims of neurodegeneration in the disease. The link between neuromelanin and Parkinson's disease has been widely studied for decades. While many studies have outlined the pigment's neuroprotective function as a potent free radical scavenger, antioxidant, and ion-chelator, it has also been observed to play a role in cell death due to mitochondrial dysfunction and oxidative stress, especially in the parkinsonian disease state. This is due to the damaging effects of neuromelanin precursors, neuromelanin-related ion dysregulation and intra- and extraneuronal neuromelanin accumulation. Current and emerging therapeutic endeavours guided by these pathological processes may include antioxidant therapy, proteostasis enhancement, ion chelation and neuromelanin-targeted immunotherapy to prevent the accumulation, formation and effects of neuromelanin and oxidative neuromelanin precursors. Some of these therapeutic strategies are already in nascent stages, while others have produced mixed results in clinical trials. This review aims to provide an update on how neuromelanin and neuromelanin-related substances may be linked to the pathogenesis of Parkinson's disease and how future therapeutic strategies may be able to hamper or prevent neuromelanin-related pathological processes and ultimately modify disease progression in Parkinson's.

A novel highly selective FRET sensor for Fe(III) and DFT mechanistic evaluation

A novel FRET-based sensor has been designed and developed through the conjugation of naphthyl and rhodamine via propylamine spacer, Naph-Rh. The naphthyl moiety serves as a FRET donor due to its emission spectrum overlapping with the rhodamine B absorption band. Naph-Rh exhibited a selectivity for sensing Fe³⁺ over other metal ions with a visual color change and fluorescent enhancement. The ratio of the Naph-Rh and Fe³⁺ was determined to be 1:1 based on Job's plot analysis with a detection limit of 83 nM. The probe exhibited a linear response to Fe³⁺ in the range of 0-120 μM. Furthermore, the density functional theory (DFT) calculations of Naph-Rh were carried out to rationalize the design and portray the plausible Fe³⁺ sensing mechanism.

Sensitive, Selective and Reliable Detection of Fe3+ in Lake Water via Carbon Dots-Based Fluorescence Assay

In this study, C-dots were facilely synthesized via microwave irradiation using citric acid and ethylenediamine as carbon precursors. The fluorescence emissions of the C-dots could be selectively quenched by Fe³⁺, and the degree of quenching was linearly related to the concentrations of Fe³⁺ presented. This phenomenon was utilized to develop a sensitive fluorescence assay for Fe³⁺ detection with broad linear range (0–250, 250–1200 μmol/L) and low detection limit (1.68 μmol/L). Most importantly, the assay demonstrated high reliability towards samples in deionized water, tap water and lake water, which should find potential applications for Fe³⁺ monitoring in complicated environments.

Iron as the concert master in the pathogenic orchestra playing in sporadic Parkinson's disease

About 60 years ago, the discovery of a deficiency of dopamine in the nigro-striatal system led to a variety of symptomatic therapeutic strategies to supplement dopamine and to substantially improve the quality of life of patients with Parkinson's disease (PD). Since these seminal developments, neuropathological, neurochemical, molecular biological and genetic discoveries contributed to elucidate the pathology of PD. Oxidative stress, the consequences of reactive oxidative species, reduced antioxidative capacity including loss of glutathione, excitotoxicity, mitochondrial dysfunction, proteasomal dysfunction, apoptosis, lysosomal dysfunction, autophagy, suggested to be causal for ɑ-synuclein fibril formation and aggregation and contributing to neuroinflammation and neural cell death underlying this devastating disorder. However, there are no final conclusions about the triggered pathological mechanism(s) and the follow-up of pathological dysfunctions. Nevertheless, it is a fact, that iron, a major component of oxidative reactions, as well as neuromelanin, the major intraneuronal chelator of iron, undergo an age-dependent increase. And ageing is a major risk factor for PD. Iron is significantly increased in the substantia nigra pars compacta (SNpc) of PD. Reasons for this finding include disturbances in iron-related import and export mechanisms across the blood-brain barrier (BBB), localized opening of the BBB at the nigro-striatal tract including brain vessel pathology. Whether this pathology is of primary or secondary importance is not known. We assume that there is a better fit to the top-down hypotheses and pathogens entering the brain via the olfactory system, then to the bottom-up (gut-brain) hypothesis of PD pathology. Triggers for the bottom-up, the dual-hit and the top-down pathologies include chemicals, viruses and bacteria. If so, hepcidin, a regulator of iron absorption and its distribution into tissues, is suggested to play a major role in the pathogenesis of iron dyshomeostasis and risk for initiating and progressing ɑ-synuclein pathology. The role of glial components to the pathology of PD is still unknown. However, the dramatic loss of glutathione (GSH), which is mainly synthesized in glia, suggests dysfunction of this process, or GSH uptake into neurons. Loss of GSH and increase in SNpc iron concentration have been suggested to be early, may be even pre-symptomatic processes in the pathology of PD, despite the fact that they are progression factors. The role of glial ferritin isoforms has not been studied so far in detail in human post-mortem brain tissue and a close insight into their role in PD is called upon. In conclusion, "iron" is a major player in the pathology of PD. Selective chelation of excess iron at the site of the substantia nigra, where a dysfunction of the BBB is suggested, with peripherally acting iron chelators is suggested to contribute to the portfolio and therapeutic armamentarium of anti-Parkinson medications.

Smoking and Neuropsychiatric Disease-Associations and Underlying Mechanisms

Despite extensive efforts to combat cigarette smoking/tobacco use, it still remains a leading cause of global morbidity and mortality, killing more than eight million people each year. While tobacco smoking is a major risk factor for non-communicable diseases related to the four main groups—cardiovascular disease, cancer, chronic lung disease, and diabetes—its impact on neuropsychiatric risk is rather elusive. The aim of this review article is to emphasize the importance of smoking as a potential risk factor for neuropsychiatric disease and to identify central pathophysiological mechanisms that may contribute to this relationship. There is strong evidence from epidemiological and experimental studies indicating that smoking may increase the risk of various neuropsychiatric diseases, such as dementia/cognitive decline, schizophrenia/psychosis, depression, anxiety disorder, and suicidal behavior induced by structural and functional alterations of the central nervous system, mainly centered on inflammatory and oxidative stress pathways. From a public health perspective, preventive measures and policies designed to counteract the global epidemic of smoking should necessarily include warnings and actions that address the risk of neuropsychiatric disease.

Elemental mapping of Neuromelanin organelles of human Substantia Nigra: correlative ultrastructural and chemical analysis by analytical transmission electron microscopy and nano-secondary ion mass spectrometry

Neuromelanin (NM) is a compound which highly accumulates mainly in catecholamine neurons of the substantia nigra (SN), and is contained in organelles (NM-containing organelles) with lipid bodies and proteins. These neurons selectively degenerate in Parkinson's disease and NM can play either a protective or toxic role. NM-containing organelles of SN were investigated by Analytical Electron Microscopy (AEM) and Nano-Secondary Ion Mass Spectrometry (NanoSIMS) within human tissue sections with respect to ultrastructure and elemental composition. Within the NM-containing organelle, the single NM granules and lipid bodies had sizes of about 200-600 nm. Energy-Dispersive X-ray microanalysis spectra of the NM granules and lipid bodies were acquired with 100 nm beam diameter in AEM, NanoSIMS yielded elemental maps with a lateral resolution of about 150 nm. AEM yielded the quantitative elemental composition of NM granules and bound metals, e.g., iron with a mole fraction of about 0.15 atomic percent. Chemical analyses by AEM and NanoSIMS were consistent at the subcellular level so that nanoSIMS measurements have been quantitated. In NM granules of SN from healthy subjects, a significant amount of S, Fe, and Cu was found. In lipid bodies an amount of P consistent with the presence of phospholipids was measured. The improved detection limits of nanoSIMS offer new possibilities for chemical mapping, high-sensitivity trace element detection, and reduced acquisition times. Variations between individual NM granules can now be investigated effectively and quantitatively by NanoSIMS mapping Cu and Fe. This should yield new insight into the changes in chemical composition of NM pigments during healthy aging and disease. Neuromelanin-containing organelles of dopamine neurons in normal human substantia nigra were investigated by analytical electron mircoscopy and secondary ion mass spectroscopy (NanoSIMS) yielding the ultrastructure and elemental composition. In neuromelanin granules a significant amount of S, Fe and Cu was found. In lipid bodies an amount of P consistent with the presence of phospholipids was measured. The improved sensitivity of NanoSIMS shows differences in chemical composition between individual neuromelanin granules and allows to study chemical changes of neuromelanin organelles during aging and disease.

Peculiarities of copper binding to alpha-synuclein

Heavy metals have been implicated as the causative agents for the pathogenesis of the most prevalent neurodegenerative disease. Various mechanisms have been proposed to explain the toxic effects of metals ranging from metal-induced oxidation of protein to metal-induced changes in the protein conformation. Aggregation of a-synuclein is implicated in Parkinson's disease (PD), and various metals, including copper, constitute a prominent group of alpha-synuclein aggregation enhancers. In this study, we have systematically characterized the a-synuclein-Cu21 binding sites and analyzed the possible role of metal binding in a-synuclein fibrillation using a set of biophysical techniques, such as electron paramagnetic resonance (EPR), electron spin-echo envelope modulation (ESEEM), circular dichroism (CD), and size exclusion chromatography (SEC). Our analyses indicated that a-synuclein possesses at least two binding sites for Cu21. We have been able to locate one of the binding sites in the N-terminal region. Furthermore, based on the EPR studies of model peptides and Beta-synuclein, we concluded that the suspected His residue did not appear to participate in strong Cu21 binding.

Appraising the Role of Iron in Brain Aging and Cognition: Promises and Limitations of MRI Methods

Age-related increase in frailty is accompanied by a fundamental shift in cellular iron homeostasis. By promoting oxidative stress, the intracellular accumulation of non-heme iron outside of binding complexes contributes to chronic inflammation and interferes with normal brain metabolism. In the absence of direct non-invasive biomarkers of brain oxidative stress, iron accumulation estimated in vivo may serve as its proxy indicator. Hence, developing reliable in vivo measurements of brain iron content via magnetic resonance imaging (MRI) is of significant interest in human neuroscience. To date, by estimating brain iron content through various MRI methods, significant age differences and age-related increases in iron content of the basal ganglia have been revealed across multiple samples. Less consistent are the findings that pertain to the relationship between elevated brain iron content and systemic indices of vascular and metabolic dysfunction. Only a handful of cross-sectional investigations have linked high iron content in various brain regions and poor performance on assorted cognitive tests. The even fewer longitudinal studies indicate that iron accumulation may precede shrinkage of the basal ganglia and thus predict poor maintenance of cognitive functions. This rapidly developing field will benefit from introduction of higher-field MRI scanners, improvement in iron-sensitive and -specific acquisition sequences and post-processing analytic and computational methods, as well as accumulation of data from long-term longitudinal investigations. This review describes the potential advantages and promises of MRI-based assessment of brain iron, summarizes recent findings and highlights the limitations of the current methodology.

The neurotoxicity of iron, copper and manganese in Parkinson's and Wilson's diseases

Impaired cellular homeostasis of metals, particularly of Cu, Fe and Mn may trigger neurodegeneration through various mechanisms, notably induction of oxidative stress, promotion of α-synuclein aggregation and fibril formation, activation of microglial cells leading to inflammation and impaired production of metalloproteins. In this article we review available studies concerning Fe, Cu and Mn in Parkinson's disease and Wilson's disease. In Parkinson's disease local dysregulation of iron metabolism in the substantia nigra (SN) seems to be related to neurodegeneration with an increase in SN iron concentration, accompanied by decreased SN Cu and ceruloplasmin concentrations and increased free Cu concentrations and decreased ferroxidase activity in the cerebrospinal fluid. Available data in Wilson's disease suggest that substantial increases in CNS Cu concentrations persist for a long time during chelating treatment and that local accumulation of Fe in certain brain nuclei may occur during the course of the disease. Consequences for chelating treatment strategies are discussed.

Vitamin D as a potential therapy in amyotrophic lateral sclerosis

Vitamin D has been demonstrated to influence multiple aspects of amyotrophic lateral sclerosis (ALS) pathology. Both human and rodent central nervous systems express the vitamin D receptor (VDR) and/or its enzymatic machinery needed to fully activate the hormone. Clinical research suggests that vitamin D treatment can improve compromised human muscular ability and increase muscle size, supported by loss of motor function and muscle mass in animals following VDR knockout, as well as increased muscle protein synthesis and ATP production following vitamin D supplementation. Vitamin D has also been shown to reduce the expression of biomarkers associated with oxidative stress and inflammation in patients with multiple sclerosis, rheumatoid arthritis, congestive heart failure, Parkinson's disease and Alzheimer's disease; diseases that share common pathophysiologies with ALS. Furthermore, vitamin D treatment greatly attenuates hypoxic brain damage in vivo and reduces neuronal lethality of glutamate insult in vitro; a hallmark trait of ALS glutamate excitotoxicity. We have recently shown that high-dose vitamin D3 supplementation improved, whereas vitamin D3 restriction worsened, functional capacity in the G93A mouse model of ALS. In sum, evidence demonstrates that vitamin D, unlike the antiglutamatergic agent Riluzole, affects multiple aspects of ALS pathophysiology and could provide a greater cumulative effect.

Involvement of NF kappa B in potentiated effect of Mn-containing dithiocarbamates on MPP(+) induced cell death

Humans are exposed to various chemical mixtures daily. The toxic response to a mixture of chemicals could be potentiated or suppressed. This study demonstrates that non-toxic doses of pesticides can induce cellular changes that increase cell sensitivity to other toxins or stress. Pesticide exposure is an environmental risk factor for Parkinson's disease. Manganese (Mn) is essential but high dose exposure may results in neurological dysfunction. Mn-containing dithiocarbamates, maneb (MB) and mancozeb (MZ), are primarily used as pesticides. Studies have shown that MB can augment dopaminergic damage triggered by sub-toxic doses of Parkinsonian mimetic MPTP. However, the mechanism underlying this effect is not clear. Activation of nuclear factor kappa B (NF-κB) has been implicated in MPTP toxicity. Mn stimulates the activation of NF-κB and subsequently induces neuronal injury via an NF-κB dependent mechanism. We speculate that MB and MZ enhance MPTP active metabolite (methyl-4-phenylpyridine ion, MPP(+)) toxicity by activating NF-κB. The activation of NF-κB was observed using Western blot analysis and NF-κB response element driven Luciferase reporter assay. Western blot data demonstrated the nuclear translocation of NF-κB p65 and the degradation of IkBα after MB and MZ 4-h treatments. Results of NF-κB response element luciferase reporter assay confirmed that MB and MZ activated NF-κB. The NF-κB inhibitor (SN50) was also shown to alleviate cytotoxicity induced by co-treatment of MB or MZ and MPP(+). This study demonstrates that activation of NF-κB is responsible for the potentiated toxic effect of MB and MZ on MPP(+) induced cytotoxicity.

Neuroprotective effects of luteolin against apoptosis induced by 6-hydroxydopamine on rat pheochromocytoma PC12 cells

CONTEXT

Apoptotic neuronal cell death plays an important role in Parkinson's disease (PD), a progressive neurodegenerative disorder. Luteolin, a flavonoid, has been shown to possess various pharmacological properties including strong antioxidant capacity.

OBJECTIVE

This study investigated the neuroprotective effect of luteolin against cytotoxicity induced by 6-hydroxy-dopamine (6-OHDA) (250 µM) in rat pheochromocytoma (PC12) cell line.

MATERIALS AND METHODS

The neuroprotective effect of luteolin against 6-OHDA-induced cytotoxicity in PC12 was evaluated by using cell viability test, nuclear staining and flow cytometry. In addition, the apoptotic role of luteolin was unveiled by monitoring mRNA expression of proapoptotic and anti-apoptotic genes.

RESULTS

Pretreatment with luteolin (3.13, 6.25, 12.5, 25 or 50 µM) could markedly attenuate 6-OHDA-induced PC12 cell viability loss in a concentration-dependent manner. Cell morphologic analysis and nuclear staining assays showed that luteolin (3.13, 12.5 or 50 µM) protected the cells from 6-OHDA-induced damage. As shown in the flow cytometry assay, the increased apoptotic rate induced by 6-OHDA could be significantly (p < 0.001) suppressed by luteolin (12.5 or 50 µM) pretreatment. The protection of luteolin (50 µM) against 6-OHDA-induced cell damage was shown to be through suppressing the over-expression of Bax gene (p < 0.01), inhibiting the reduction of Bcl-2 gene expression (p < 0.05) and markedly depressing the enhanced Bax/Bcl-2 ratio. Luteolin also downregulated the gene expression level of p53.

DISCUSSION AND CONCLUSION

Luteolin has protective effects against 6-OHDA-induced cell apoptosis and might be a potential nutritional supplement which could be used to prevent neurodegenerative diseases such as PD.

Rodent models and contemporary molecular techniques: notable feats yet incomplete explanations of Parkinson's disease pathogenesis

Rodent models and molecular tools, mainly omics and RNA interference, have been rigorously used to decode the intangible etiology and pathogenesis of Parkinson's disease (PD). Although convention of contemporary molecular techniques and multiple rodent models paved imperative leads in deciphering the role of putative causative factors and sequential events leading to PD, complete and clear-cut mechanisms of pathogenesis are still hard to pin down. The current article reviews the implications and pros and cons of rodent models and molecular tools in understanding the molecular and cellular bases of PD pathogenesis based on the existing literature. Probable rationales for short of comprehensive leads and future possibilities in spite of the extensive applications of molecular tools and rodent models have also been discussed.

Α-synuclein misfolding and Parkinson's disease

Substantial evidence links α-synuclein, a small highly conserved presynaptic protein with unknown function, to both familial and sporadic Parkinson's disease (PD). α-Synuclein has been identified as the major component of Lewy bodies and Lewy neurites, the characteristic proteinaceous deposits that are the hallmarks of PD. α-Synuclein is a typical intrinsically disordered protein, but can adopt a number of different conformational states depending on conditions and cofactors. These include the helical membrane-bound form, a partially-folded state that is a key intermediate in aggregation and fibrillation, various oligomeric species, and fibrillar and amorphous aggregates. The molecular basis of PD appears to be tightly coupled to the aggregation of α-synuclein and the factors that affect its conformation. This review examines the different aggregation states of α-synuclein, the molecular mechanism of its aggregation, and the influence of environmental and genetic factors on this process.

Role of metal ions in aggregation of intrinsically disordered proteins in neurodegenerative diseases

Neurodegenerative diseases constitute a set of pathological conditions originating from the slow, irreversible, and systematic cell loss within the various regions of the brain and/or the spinal cord. Depending on the affected region, the outcomes of the neurodegeneration are very broad and diverse, ranging from the problems with movements to dementia. Some neurodegenerative diseases are associated with protein misfolding and aggregation. Many proteins that misfold in human neurodegenerative diseases are intrinsically disordered; i.e., they lack a stable tertiary and/or secondary structure under physiological conditions in vitro. These intrinsically disordered proteins (IDPs) functionally complement ordered proteins, being typically involved in regulation and signaling. There is accumulating evidence that altered metal homeostasis may be related to the progression of neurodegenerative diseases. This review examines the effects of metal ion binding on the aggregation pathways of IDPs found in neurodegenerative diseases.

A two-site mechanism for the inhibition of IAPP amyloidogenesis by zinc

Human islet amyloid polypeptide (hIAPP) is a highly amyloidogenic protein co-secreted with insulin in response to glucose levels. The formation of hIAPP amyloid plaques near islet cells has been linked to the death of insulin-secreting β-cells in humans and the progression of type II diabetes. Since both healthy individuals and those with type II diabetes produce and secrete hIAPP, it is reasonable to look for factors involved in storing hIAPP and preventing amyloidosis. We have previously shown that zinc inhibits the formation of insoluble amyloid plaques of hIAPP; however, there remains significant ambiguity in the underlying mechanisms. In this study, we show that zinc binds unaggregated hIAPP at micromolar concentrations similar to those found in the extracellular environment. By contrast, the fibrillar amyloid form of hIAPP has low affinity for zinc. The binding stoichiometry obtained from isothermal titration calorimetry experiments indicates that zinc favors the formation of hIAPP hexamers. High-resolution NMR structures of hIAPP bound to zinc reveal changes in the electron environment along residues that would be located along one face of the amphipathic hIAPP α-helix proposed as an intermediate for amyloid formation. Results from electrospray ionization mass spectroscopy investigations showed that a single zinc atom is predominantly bound to hIAPP and revealed that zinc inhibits the formation of the dimer. At higher concentrations of zinc, a second zinc atom binds to hIAPP, suggesting the presence of a low-affinity secondary binding site. Combined, these results suggest that zinc promotes the formation of oligomers while creating an energetic barrier for the formation of amyloid fibers.

Metal emissions and urban incident Parkinson disease: a community health study of Medicare beneficiaries by using geographic information systems

Parkinson disease associated with farming and exposure to agricultural chemicals has been reported in numerous studies; little is known about Parkinson disease risk factors for those living in urban areas. The authors investigated the relation between copper, lead, or manganese emissions and Parkinson disease incidence in the urban United States, studying 29 million Medicare beneficiaries in the year 2003. Parkinson disease incidence was determined by using beneficiaries who had not changed residence since 1995. Over 35,000 nonmobile incident Parkinson disease cases, diagnosed by a neurologist, were identified for analysis. Age-, race-, and sex-standardized Parkinson disease incidence was compared between counties with high cumulative industrial release of copper, manganese, or lead (as reported to the Environmental Protection Agency) and counties with no/low reported release of all 3 metals. Parkinson disease incidence (per 100,000) in counties with no/low copper/lead/manganese release was 274.0 (95% confidence interval (CI): 226.8, 353.5). Incidence was greater in counties with high manganese release: 489.4 (95% CI: 368.3, 689.5) (relative risk = 1.78, 95% CI: 1.54, 2.07) and counties with high copper release: 304.2 (95% CI: 276.0, 336.8) (relative risk = 1.1, 95% CI: 0.94, 1.31). Urban Parkinson disease incidence is greater in counties with high reported industrial release of copper or manganese. Environmental exposure to metals may be a risk factor for Parkinson disease in urban areas.

Extracellular dopamine potentiates mn-induced oxidative stress, lifespan reduction, and dopaminergic neurodegeneration in a BLI-3-dependent manner in Caenorhabditis elegans

Parkinson's disease (PD)-mimicking drugs and pesticides, and more recently PD-associated gene mutations, have been studied in cell cultures and mammalian models to decipher the molecular basis of PD. Thus far, a dozen of genes have been identified that are responsible for inherited PD. However they only account for about 8% of PD cases, most of the cases likely involving environmental contributions. Environmental manganese (Mn) exposure represents an established risk factor for PD occurrence, and both PD and Mn-intoxicated patients display a characteristic extrapyramidal syndrome primarily involving dopaminergic (DAergic) neurodegeneration with shared common molecular mechanisms. To better understand the specificity of DAergic neurodegeneration, we studied Mn toxicity in vivo in Caenorhabditis elegans. Combining genetics and biochemical assays, we established that extracellular, and not intracellular, dopamine (DA) is responsible for Mn-induced DAergic neurodegeneration and that this process (1) requires functional DA-reuptake transporter (DAT-1) and (2) is associated with oxidative stress and lifespan reduction. Overexpression of the anti-oxidant transcription factor, SKN-1, affords protection against Mn toxicity, while the DA-dependency of Mn toxicity requires the NADPH dual-oxidase BLI-3. These results suggest that in vivo BLI-3 activity promotes the conversion of extracellular DA into toxic reactive species, which, in turn, can be taken up by DAT-1 in DAergic neurons, thus leading to oxidative stress and cell degeneration.

Pharmacological therapy in Parkinson's disease: focus on neuroprotection

Although the number of available therapeutic approaches in Parkinson's disease (PD) is steadily increasing the search for effective neuroprotective agent is continuing. Such research is directed at influencing the key steps in the pathomechanism: the mitochondrial dysfunction, the oxidative stress, the neuroinflammatory processes and the final common apoptotic pathway. Earlier-developed symptomatic therapies were implicated to be neuroprotective, and promising novel disease modifying approaches were brought into the focus of interest. The current review presents a survey of our current knowledge relating to the pathomechanism of PD and discusses the putative neuroprotective therapy.

Oxidative damage to RNA: mechanisms, consequences, and diseases

Overproduction of free radicals can damage cellular components resulting in progressive physiological dysfunction, which has been implicated in many human diseases. Oxidative damage to RNA received little attention until the past decade. Recent studies indicate that RNA, such as messenger RNA and ribosomal RNA, is very vulnerable to oxidative damage. RNA oxidation is not a consequence of dying cells but an early event involved in pathogenesis. Oxidative modification to RNA results in disturbance of the translational process and impairment of protein synthesis, which can cause cell deterioration or even cell death. In this review, we discuss the mechanisms of oxidative damage to RNA and the possible biological consequences of damaged RNA. Furthermore, we review recent evidence suggesting that oxidative damage to RNA may contribute to progression of many human diseases.

Antioxidant defense system in rats simultaneously intoxicated with agrochemicals

The effect of dimethoate, zineb and glyphosate administered alone or in combination on liver, kidney, brain and plasma antioxidant defense system was investigated. Lipid peroxidation, and RNS production were increased in all tissues studied, especially in those groups that received a combination of drugs. Intoxicated rats exhibited lower antioxidant ability, higher oxidized protein and glutathione levels in plasma with a decreased concentration of α-tocopherol in brain and liver, between 30% and 60% of control. Superoxide dismutase was decreased in liver and brain. Glutathione reductase was inhibited in liver while glutathione peroxidase and transferase were unaffected. Plasma lactate dehydrogenase and γ-glutamyl transpeptidase activities were both increased. The associations of drugs produce more damage than individual administration being the effects observed strongly dependent on the kind of tissue analyzed. In conclusion, the present paper evidenced both the role of the oxidative stress as a mechanism of action of some pesticides and the potential additive effects of a simultaneous exposure to more than one compound. In addition, results suggest a potential contribution of pesticide mixtures to the aetiology of some neurodegenerative diseases.

Chronic expression of H-ferritin in dopaminergic midbrain neurons results in an age-related expansion of the labile iron pool and subsequent neurodegeneration: implications for Parkinson's disease

While ferritin elevation within dopaminergic (DA) neurons of the substantia nigra (SN) is protective against neurodegeneration elicited by two toxin models of Parkinson's disease (PD), MPTP and paraquat, in young animals, its prolonged elevation results in a selective age-related neurodegeneration. A similar age-related neurodegeneration has been reported in iron regulatory protein 2-deficient (IRP2 -/-) mice coinciding with increased ferritin levels within degenerating neurons. This has been speculated to be due to subsequent reductions in the labile iron pool (LIP) needed for the synthesis of iron-sulfur-containing enzymes. In order to assess whether LIP reduction is responsible for age-related neurodegeneration in our ferritin transgenics, we examined LIP levels in ferritin-expressing transgenics with increasing age. While LIP levels were reduced within DA SN nerve terminals isolated from young ferritin transgenics compared to wildtype littermate controls, they were found to be increased in older transgenic animals at the age at which selective neurodegeneration is first noted. Furthermore, administration of the bioavailable iron chelator, clioquinol (CQ), to older mice was found to protect against both increased LIP and subsequent dopaminergic neurodegeneration. This suggests that age-related neurodegeneration in these mice is likely due to increased iron availability rather than its reduction. This may have important implications for PD and other related neurodegenerative conditions in which iron and ferritin have been implicated.

Identification of L-ferritin in neuromelanin granules of the human substantia nigra: a targeted proteomics approach

In the pigmented dopaminergic neurons of the human substantia nigra pars compacta the system relevant in iron storage is the polymer neuromelanin (NM). Although in most cells this function is mainly accomplished by ferritin, this protein complex appears not to be expressed in NM-containing neurons. Nevertheless the conceivable presence of iron-storing proteins as part of the NM granules has recently been discussed on the basis of Mössbauer spectroscopy and synchrotron x-ray microspectroscopy. Intriguingly by combining subcellular fractionation of NM granules, peptide sequencing via tandem mass spectrometry, and the additional confirmation by multiple reaction monitoring and immunogold labeling for electron microscopy, L-ferritin could now be unambiguously identified and localized in NM granules for the first time. This finding not only supports direct evidence for a regulatory role of L-ferritin in neuroectodermal cell pigmentation but also integrates a new player within a complicated network governing iron homeostasis in the dopamine neurons of the human substantia nigra. Thus our finding entails far reaching implications especially when considering etiopathogenetic aspects of Parkinson disease.

Raman, IR, UV-vis and EPR characterization of two copper dioxolene complexes derived from L-dopa and dopamine

The anionic complexes [Cu(L(1-))3](1-), L(-)=dopasemiquinone or L-dopasemiquinone, were prepared and characterized. The complexes are stable in aqueous solution showing intense absorption bands at ca. 605 nm for Cu(II)-L-dopasemiquinone and at ca. 595 nm for Cu(II)-dopasemiquinone in the UV-vis spectra, that can be assigned to intraligand transitions. Noradrenaline and adrenaline, under the same reaction conditions, did not yield Cu-complexes, despite the bands in the UV region showing that noradrenaline and adrenaline were oxidized during the process. The complexes display a resonance Raman effect, and the most enhanced bands involve ring modes and particularly the nuCC+nuCO stretching mode at ca. 1384 cm(-1). The free radical nature of the ligands and the oxidation state of the Cu(II) were confirmed by the EPR spectra that display absorptions assigned to organic radicals with g=2.0005 and g=2.0923, and for Cu(II) with g=2.008 and g=2.0897 for L-dopasemiquinone and dopasemiquinone, respectively. The possibility that dopamine and L-dopa can form stable and aqueous-soluble copper complexes at neutral pH, whereas noradrenaline and adrenaline cannot, may be important in understanding how Cu(II)-dopamine crosses the cellular membrane as proposed in the literature to explain the role of copper in Wilson disease.

Impairment of emotional behavior and spatial learning in adult Wistar rats by ferrous sulfate

The aim of this study was to investigate the effects of FeSO(4) on the behavior of adult Wistar rats. Rats were treated with moderate doses of iron (1.5 or 3.0 mg/kg) for 5 consecutive days, and the effects of iron supplementation on emotional behavior were studied. One group of rats was tested in elevated plus-maze and in open field, and other group was tested for learning abilities in water maze and for motor skills in rotarod task. Iron level in the brain was measured in the frontal cortex, cerebellum, basal ganglia and hippocampus. The effects of the iron treatment (in particular, a dose of 3.0 mg/kg) on emotional behavior in the elevated plus maze and in the open field were significant. The effects of iron on spatial learning were less pronounced, but significant impairments due to the treatment were observed during the probe test. Motor skills and procedural learning in the rotarod task were not significantly affected by the treatment. These behavioral impairments were associated with significant iron accumulations in the hippocampus and basal ganglia of rats treated with 3.0 mg/kg iron and are discussed in terms of possible neuronal impairments of these structures. Thus, FeSO(4) administration at 3.0 mg/kg for 5 consecutive days in adult rats overcomes the mechanisms that shield the brain from iron intoxication and leads to behavioral impairments, in particular with respect to emotional behavior.

Topographic trace-elemental analysis in the brain of Wistar rats by X-ray microfluorescence with synchrotron radiation

Knowledge about the spatial distribution and the local concentration of trace elements in tissues is of great importance, since trace elements are involved in many biological functions of living organisms. However, there are few methods available to measure the spatial (two (three)-dimensional) elemental distribution in animal brain. X-ray microfluorescence with synchrotron radiation is a multielemental mapping technique, which was used in this work to determine the topographic of iron, zinc and copper in coronal sections of female Wistar rats of different ages. Young (14 days old) and middle-aged (20 months old) rats (n = 8) were analyzed. The measurements were carried out at the XRF beam line at the Synchrotron Light National Laboratory (Campinas, Brazil). Two-dimensional scanning was performed in order to study the tendency of elemental concentration variation. The acquisition time for each pixel was 10 s/step and the step size was 300 microm/step in both directions. It was observed that the iron distribution was more conspicuous in the cortical area, thalamus and bellow the thalamus. On the other hand, the zinc distribution was more pronounced in the hippocampus. The iron, copper and zinc levels increased with advancing age. Therefore, this study reinforces the idea that these elements are involved in the chemical mechanisms of the brain that induce some neurological diseases, since they are also present in high levels in specific areas of the brain, such as the hippocampus and the substantia nigra of patients with these disorders.

Reversion of age-related recognition memory impairment by iron chelation in rats

It is now generally accepted that iron accumulates in the brain during the ageing process. Increasing evidence demonstrate that iron accumulation in selective regions of the brain may generate free radicals, thereby possessing implications for the etiology of neurodegenerative disorders. In a previous study we have reported that aged rats present recognition memory deficits. The aim of the present study was to evaluate the effect of desferoxamine (DFO), an iron chelator agent, on age-induced memory impairment. Aged Wistar rats received intraperitoneal injections of saline or DFO (300mg/kg) for 2 weeks. The animals were submitted to a novel object recognition task 24h after the last injection. DFO-treated rats showed normal recognition memory while the saline group showed long-term recognition memory deficits. The results show that DFO is able to reverse age-induced recognition memory deficits. We also demonstrated that DFO reduced the oxidative damage to proteins in cortex and hippocampus. Thus, the present findings provide the first evidence that iron chelators might prevent age-related memory dysfunction.

Contribution of disturbed iron metabolism to the pathogenesis of Parkinson’s disease

Extensive research has revealed a complex pathophysiology in Parkinson’s disease, with different factors contributing to the progressive neurodegeneration. Within this complex pathophysiology, a central role of iron and iron-induced oxidative stress has been discussed for many years, as elevated tissue iron levels, especially within the substantia nigra, have been detected by different techniques in a number of postmortem studies. These findings could be verified intra vitam by advancing MRI techniques, and more recently transcranial ultrasound. Different causes, such as disruption of the BBB, local changes in the normal iron-regulatory system, release of iron from intracellular storages or intraneuronal transportation from iron-rich areas, as well as genetic variations leading to changes in brain iron metabolism, are being discussed to be responsible for the increased tissue iron levels. Although it is still not clear whether increased iron levels constitute a primary or secondary phenomenon in the etiology of Parkinson’s disease, its interaction with many pathophysiologcial cascades and contribution to all forms of Parkinson’s disease, idiopathic as well as monogenetic, stresses the importance of further elucidating the mechanism of brain iron homeostasis and its possible alterations to finally develop pharmacological interventions that may disrupt the chain of pathological events leading to neurodegeneration.

Stage-dependent vulnerability of fetal mesencephalic neuroprogenitors towards dopaminergic neurotoxins

Although extensive knowledge exists on selective vulnerability of dopaminergic neurons against parkinsonism-inducing neurotoxins, there is a complete lack of such data on immature neuroprogenitors. Here we investigated the toxicity of 1-methyl-4-phenylpyridinium (MPP+), 6-hydroxydopamine (6-OHDA) and the free radical generator H2O2 on various developmental stages of predopaminergic mesencephalic neuroprogenitors (mNPCs) to evaluate stage-dependency of selective dopaminergic neurotoxicity. Striatal NPCs (sNPCs) without dopaminergic differentiation potential served as controls. Exposure of both undifferentiated NPCs to MPP+ resulted in concentration-dependent cell death at concentrations of >10 microM after 72 h without differences between both cell types, while 6-OHDA led to relevant cell death at 1000 microM after 24h with significant higher sensitivity of mNPCs compared to sNPCs. H2O2 did not induce relevant cell death in all cell types. In NPC cultures differentiated for 14 days, MPP+ showed enhanced toxicity compared to the undifferentiated counterparts, but no significant differences between both NPC type and differentiation conditions. 6-OHDA showed similar toxicity pattern in differentiated compared to undifferentiated NPCs. By evaluating the toxicity of MPP+ on MAP2ab+ neurons derived from both mNPCs and sNPCs as well as tyrosine hydroxylase (TH)+ dopaminergic cells from mNPCs, we found concentration-dependent cell death of all cell types with no increased vulnerability of TH+ cells. Primary TH+ neurons showed significantly higher vulnerability to MPP+. Together, we demonstrated stage-dependent vulnerability of NPCs towards dopaminergic neurotoxins, but no selective vulnerability of NPC-derived TH+ dopaminergic cells towards MPP+. This cell system seems not suitable as a screening tool for selective dopaminergic toxicity.

Genetic findings in Parkinson's disease and translation into treatment: a leading role for mitochondria?

Parkinson's disease (PD) is a progressive neurodegenerative movement disorder and in most patients its aetiology remains unknown. Molecular genetic studies in familial forms of the disease identified key proteins involved in PD pathogenesis, and support a major role for mitochondrial dysfunction, which is also of significant importance to the common sporadic forms of PD. While current treatments temporarily alleviate symptoms, they do not halt disease progression. Drugs that target the underlying pathways to PD pathogenesis, including mitochondrial dysfunction, therefore hold great promise for neuroprotection in PD. Here we summarize how the proteins identified through genetic research (alpha-synuclein, parkin, PINK1, DJ-1, LRRK2 and HTRA2) fit into and add to our current understanding of the role of mitochondrial dysfunction in PD. We highlight how these genetic findings provided us with suitable animal models and critically review how the gained insights will contribute to better therapies for PD.

Functional consequences of iron overload in catecholaminergic interactions: the Youdim factor

The influence of postnatal iron overload upon implications of the functional and interactive role of dopaminergic and noradrenergic pathways that contribute to the expressions of movement disorder and psychotic behaviours in mice was studied in a series of experiments. (1) Postnatal iron overload at doses of 7.5 mg/kg (administered on Days 10-12 post partum) and above, invariably induced a behavioural syndrome consisting of an initial (1st 20-40 min of a 60-min test session) hypoactivity followed by a later (final 20 min of a 60-min test session) hyperactivity, when the mice were tested at adult ages (age 60 days or more). (2) Following postnatal iron overload, subchronic treatment with the neuroleptic compounds, clozapine and haloperidol, dose-dependently reversed the initial hypoactivity and later hyperactivity induced by the metal. Furthermore, DA D(2) receptor supersensitivity (as assessed using the apomorphine-induced behaviour test) was directly and positively correlated with iron concentrations in the basal ganglia. (3) Brain noradrenaline (NA) denervation, using the selective NA neurotoxin, DSP4, prior to administration of the selective DA neurotoxin, MPTP, exacerbated both the functional (hypokinesia) and neurochemical (DA depletion) effects of the latter neurotoxin. Treatment with L-Dopa restored motor activity only in the animals that had not undergone NA denervation. These findings suggest an essential neonatal iron overload, termed "the Youdim factor", directing a DA-NA interactive component in co-morbid disorders of nigrostriatal-limbic brain regions.

Impact of selenium, iron, copper and zinc in on/off Parkinson's patients on L-dopa therapy

We have quantitated CSF and serum levels of Selenium, iron, copper and zinc by Atomic absorption spectrophotometer in 36 patients with parkinson's disease all on L-dopa therapy. Out of these 19 showed on or positive response to L-dopa where as 21 patients showed on and off response. These data were compared with 21 healthy controls. The results showed that serum levels of iron, copper and zinc remained unchanged where as in CSF, significant decrease in zinc was found in both on and on/off PD patients indicating the deficiency of zinc which continues in the worsening clinical condition of off patients. The level of copper remained unchanged in both on and on/off PD patients. Iron and selenium increase in CSF of both patients which is a clear evidence of relationship between increased iron and selenium level in brain which could be correlated with decrease in dopamine levels and oxidative stress in PD Patients.

Phosphoproteomic profiling of human SH-SY5Y neuroblastoma cells during response to 6-hydroxydopamine-induced oxidative stress

Dopaminergic neurons are known to be vulnerable to age-related neuronal disorders due to reactive oxygen species (ROS) generated during dopamine metabolism. However, it remains unclear what kinds of proteins are involved in the response to oxidative stress. We examined changes in whole proteins and phosphoproteins in the human dopaminergic neuroblastoma cell line SH-SY5Y under oxidative stress induced by the dopaminergic neurotoxin 6-hydroxydopamine (6-OHDA). Proteins of SH-SY5Y cells at various stages of oxidative stress were separated by two-dimensional gel electrophoresis for comparative analysis. Increase in glutathione-S-transferase pi was detected on SYPRO Ruby-stained gels by computer-aided image analysis. Stress-induced alterations in phosphoproteins were detected by Pro-Q Diamond staining. Elongation factor 2, lamin A/C, T-complex protein 1, and heterogeneous nuclear ribonucleoprotein H3 were identified by MALDI-TOF mass spectrometry as stress-responsive elements.

Brain lipid composition in postnatal iron-induced motor behavior alterations following chronic neuroleptic administration in mice

Several studies have shown that deficient uptake or excessive break down of membrane phospholipids may be associated with neurodegenerative and psychiatric disorders. The purpose of the present study was to examine the effects of postnatal iron administration in lipid composition and behavior and whether or not the established effects may be altered by subchronic administration of the neuroleptic compounds, clozapine and haloperidol. In addition to motor activities such as locomotion, rearing and activity, a targeted lipidomics approach has been used to investigated the brains of eight groups of mice (four vehicle groups and four iron groups) containing six individuals in each group treated with vehicle, low dose clozapine, high dose clozapine and haloperidol. Lipids were extracted by the Folch method and analyzed using reversed-phase capillary liquid chromatography coupled on-line to electrospray ionization mass spectrometry (LC/ESI/MS). Identification of phosphatidylcholine (PC) and sphingomyelin (SM) molecular species was based on their retention time, m/z ratio, head group specific up-front fragmentation and analysis of the product ions produced upon fragmentation. A comparison between the Ve-groups and Fe-groups showed that levels of PC and SM molecular species and motor activities were significantly lower in Fe-Ve compared to Ve-Ve. The effects of neuroleptic treatment with and without iron supplementation were studied. In conclusion our results support the hypothesis that an association between psychiatric disorders and lipid and behavior abnormalities in the brain exists.