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.
Available from: Maciej Skotak
- "Contrary to normal subjects, where more Fe 2+ is deposited in the SN pars reticulata, in PD Fe 2+ is deposited abundantly in the SNpc containing pigmented neurons (Sian-Hulsmann et al., 2011). Together with paraquat, Fe 2+ enhances dopaminergic neurodegeneration (Peng et al., 2007). Low levels of ferritin in the SNpc of PD patients and incidental Lewy body disease cases have been reported. "
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ABSTRACT: Oxidative stress is a common hallmark of neuronal cell death associated with neurodegenerative disorders such as Alzheimer's disease, Parkinson's disease, as well as brain stroke/ischemia and traumatic brain injury. Increased accumulation of reactive species of both oxygen (ROS) and nitrogen (RNS) has been implicated in mitochondrial dysfunction, energy impairment, alterations in metal homeostasis and accumulation of aggregated proteins observed in neurodegenerative disorders, which lead to the activation/modulation of cell death mechanisms that include apoptotic, necrotic and autophagic pathways. Thus, the design of novel antioxidant strategies to selectively target oxidative stress and redox imbalance might represent important therapeutic approaches against neurological disorders. This work reviews the evidence demonstrating the ability of genetically encoded antioxidant systems to selectively counteract neuronal cell loss in neurodegenerative diseases and ischemic brain damage. Because gene therapy approaches to treat inherited and acquired disorders offer many unique advantages over conventional therapeutic approaches, we discussed basic research/clinical evidence and the potential of virus-mediated gene delivery techniques for antioxidant gene therapy.
Available from: Jerome I Rotter
- "This TF-TFR2 mediated mitochondrial mechanism of pathology is likely to be only one of a number of factors contributing to PD pathology. Given that iron excess (or iron depletion) in model systems aggravates (or attenuates) pesticide toxicity (e.g., Kaur et al., 2003; Peng et al., 2007 "
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ABSTRACT: Pathologic features of Parkinson's disease (PD) include death of dopaminergic neurons in the substantia nigra, presence of α-synuclein containing Lewy bodies, and iron accumulation in PD-related brain regions. The observed iron accumulation may be contributing to PD etiology but it also may be a byproduct of cell death or cellular dysfunction. To elucidate the possible role of iron accumulation in PD, we investigated genetic variation in 16 genes related to iron homeostasis in three case-control studies from the United States, Australia, and France. After screening 90 haplotype tagging single nucleotide polymorphisms (SNPs) within the genes of interest in the US study population, we investigated the five most promising gene regions in two additional independent case-control studies. For the pooled data set (1289 cases, 1391 controls) we observed a protective association (OR=0.83, 95% CI: 0.71-0.96) between PD and a haplotype composed of the A allele at rs1880669 and the T allele at rs1049296 in transferrin (TF; GeneID: 7018). Additionally, we observed a suggestive protective association (OR=0.87, 95% CI: 0.74-1.02) between PD and a haplotype composed of the G allele at rs10247962 and the A allele at rs4434553 in transferrin receptor 2 (TFR2; GeneID: 7036). We observed no associations in our pooled sample for haplotypes in SLC40A1, CYB561, or HFE. Taken together with previous findings in model systems, our results suggest that TF or a TF-TFR2 complex may have a role in the etiology of PD, possibly through iron misregulation or mitochondrial dysfunction within dopaminergic neurons.
Available from: Richard J Smeyne
- "However, in PD patients the ratio of reduced to oxidized iron in the SN has been reported to increase , in one report to 1:3 ; a dysregulation not found in other tissues or regions of the brain  . Because numerous studies have shown that the elevated levels of reduced iron in the SN can lead to cellular toxicity    , it has been suggested that iron chelation may provide some level of neuroprotection in Parkinson disease    . "
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ABSTRACT: It has been established that oxidative stress, defined as the condition when the sum of free radicals in a cell exceeds the antioxidant capacity of the cell, contributes to the pathogenesis of Parkinson's disease. Glutathione is a ubiquitous thiol tripeptide that acts alone, or in concert with enzymes within cells to reduce superoxide radicals, hydroxyl radicals and peroxynitrites. In this review, we examine the synthesis, metabolism and functional interactions of glutathione, and discuss how this relates to protection of dopaminergic neurons from oxidative damage and its therapeutic potential in Parkinson's disease.
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