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Toxic effects of dopamine metabolism in Parkinson's disease
Parkinsonism and Related Disorders 15, Supplement 1 (2009) S35–S38 www.elsevier.com/locate/parkreldis
Toxic effects of dopamine metabolism in Parkinson’s disease Nobutaka Hattori a, *, Mei Wang a , Hikari Taka b , Tsutomu Fujimura b , Asako Yoritaka a , Shin-ichiro Kubo a , Hideki Mochizuki a a Department
of Neurology and b Biochemical Research Center, Division of Proteomics and Biomolecular Sciences, Juntendo University School of Medicine, 2-1-1 Hongo, Bunkyo, Tokyo 113-8421, Japan
Abstract Levodopa is the most effective medication for Parkinson’s disease (PD). In contrast, there is evidence that levodopa and its metabolites such as dopa/dopamine quinone are toxic for nigral neurons based on in vitro studies. Moreover, there is growing evidence that oxidative stress and mitochondrial dysfunction contribute the pathogenesis of PD. Thus, studies for oxidative stress give us good information for elucidating the pathogenesis of PD. In this regard, it is mandatory to develop markers such as 4-hydroxy-nonenal (HNE). HNE is a product of lipid peroxidation. Indeed, immunohistochemical studies have revealed that HNE-modified proteins accumulate within ragged red fibers (RRFs). This finding indicated that mitochondrial impairment may be linked to oxidative stress. Moreover, HNE-modified proteins accumulate in nigral neurons. In PD, mitochondrial dysfunction such as complex I deficiency has also been reported. In addition, HNE can modify α-synuclein (SNCA). Subsequently, this modification may trigger the aggregation of this protein. At a minimum, this modification could be associated with oligomer formation or fibrillation of SNCA. © 2008 Elsevier Ltd. All rights reserved. Keywords: 4-Hydroxy-nonenal; Parkinson’s disease; Oxidative stress; Levodopa; Mitochondrial dysfunctions
1. Introduction Since the discovery of levodopa therapy, the prognosis of Parkinson’s disease (PD) has improved. However, it is clear that long-term treatment with levodopa can induce motor fluctuations such as wearing off and levodopa-induced dyskinesia. Moreover, despite continuing levodopa therapy, the signs and symptoms of parkinsonism worsen progressively. In addition, dopaminergic neurons in the substantia nigra are particularly vulnerable to oxidative stress. Indeed, studies on post-mortem brains from PD patients indicate increased lipid peroxidation [1], decreased glutathione [2], abnormalities in iron homeostasis [3], and protein aggregation [4]. There is evidence that oxidative stress contributes to the pathogenesis of PD. Levodopa is the most effective medication for management of this disorder. Although there are controversies * Correspondence to: N. Hattori, Department of Neurology, Juntendo University School of Medicine, 2-1-1 Hongo, Bunkyo, Tokyo 113-8421, Japan. Tel.: +81-3-3813-3111 ext. 3321; Fax: +81-3-5800-0547. E-mail address: [email protected] 1353-8020/$ – see front matter © 2008 Elsevier Ltd. All rights reserved.
about whether levodopa is toxic for PD patients, recent studies, such as the ELLDOPA study, indicate that levodopa is not toxic for nigral neurons [5]. The ELLDOPA study was designed to determine if levodopa affected the progression of PD. This double-blind randomized study showed that subjects treated with levodopa for 40 weeks had less severe parkinsonism than placebo-treated subjects, even after a 2week washout of medications, with the highest dose group showing the greatest benefit, suggesting that levodopa may actually have neuroprotective value. However, the study did not conclusively demonstrate slowing of disease progression, because the same result could have arisen from a long-lasting symptomatic benefit of levodopa. In this paper, we review the role of the toxic effects of dopamine (DA) metabolism in PD. 2. Familial PD gene product, α-synuclein, and oxidative stress Seven causative genes and four chromosomal loci for familial PD (FPD) have been identified. Among them, α-
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synuclein (SNCA) is a key molecule to understand the mechanisms of Lewy body formation since it is a major component of the inclusions [6]. SNCA is a small, highly conserved protein that is abundant in various regions of the brain [7] and is natively unfolded [8,9]. It is associated with membranous function such as lipid rafts [10]. We recently found that an interaction with lipid rafts is crucial for the normal, pre-synaptic localization of SNCA. In addition, we have also found that SNCA binds directly to artificial membranes whose lipid composition mimics that of lipid rafts. The binding of SNCA to these raft-like liposomes requires acidic phospholipids, with a preference for phosphatidylserine (PS). Interestingly, a variety of synthetic PS with defined acyl chains does not support binding when used individually. Rather, the interaction with SNCA requires a combination of PS with oleic (18:1) and polyunsaturated (either 20:4 or 22:6) fatty acyl chains, suggesting a role for phase separation within the membrane. Furthermore, SNCA binds with higher affinity to artificial membranes with the PS head group on the polyunsaturated fatty acyl chain rather than on the oleoyl side chain, indicating a stringent combinatorial code for the interaction of SNCA with membranes. In agreement with the membrane-related functions, SNCA has seven repeats of 11 residues in the N-terminal half of the molecule with a consensus sequence of KTKEGV. Taken together, the binding potential with lipid rafts for SNCA revealed that SNCA undergoes a conformational change from an unstructured monomer in solution to an α-helical membrane-bound protein [11,12]. There is growing evidence that oxidative stress and mitochondrial respiratory failure with attendant decrease in energy output are implicated in nigral neuronal death in PD. It is not known, however, which cellular elements (neurons or glial cells) are major targets of oxygen-mediated damage. 4-Hydroxy-2-nonenal (HNE) was shown earlier to react with proteins to form stable adducts that can be used as
markers of oxidative stress-induced cellular damage. Indeed, HNE-modified proteins accumulate within ragged red fibers in mitochondrial myopathies (unpublished data) (Fig. 1). Abnormal mitochondria accumulate within the fibers. This finding indicates that mitochondrial dysfunction could be associated with oxidative stress such as lipid peroxidation. In previous work, we reported the results of immunochemical studies using polyclonal antibodies directed against HNEprotein conjugates to label the site of oxidative damage in PD patients and control subjects. On average, 58% of nigral neurons were positively stained for HNE-modified proteins in PD; in contrast, only 9% of nigral neurons were positive in the control subjects. The difference was statistically significant (Mann-Whitney U test, p < 0.01). In contrast to the substantia nigra, oculomotor neurons in the same midbrain sections showed no or only weak staining for HNE-modified proteins in both PD and control subjects. Young control subjects did not show any immunostaining; however, aged control subjects showed weak staining in the oculomotor nucleus, suggesting age-related accumulation of HNE-modified proteins in neurons. Our results indicate the presence of oxidative stress within nigral neurons in PD, and this oxidative stress may contribute to nigral cell death. HNE is one of the highly reactive aldehydes. This molecule forms covalent adducts including HNE-cysteine (Cys), HNE-histidine (His), and HNE-lysine (Lys) via the Michael reaction. Thus, SNCA is a good target of HNE, since SNCA has a single site of His residue at position 50 and 15 Lys residues. Recently, Qin and colleagues reported the effects of the interaction of HNE with SNCA. They concluded that HNE modification of SNCA resulted in a major conformational change involving increased βsheet formation [13]. HNE-modification of SNCA led to inhibition of fibrillation in an HNE concentration-dependent manner. Furthermore, they found that the addition of HNEmodified oligomer to primary mesencephalic cultures caused
Fig. 1 Immunohistochemistry for HNE-modified proteins. Arrows show immunoreactivities for HNE-modified proteins. Bar indicates 100 μm. SDH, succinate dehydrogenese.
N. Hattori et al. / Parkinsonism and Related Disorders 15, Supplement 1 (2009) S35–S38
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Fig. 2 Aggregation of SNCA with the increase of HNE concentration in vitro. HNE-SNCA aggregation was observed after incubation of both HNE and SNCA recombinant proteins. The aggregation was shown in an HNE concentration-dependent manner. Panels A and B show the treatments without and with HNE incubation, respectively.
marked neurotoxicity. We also investigated the interaction of HNE with SNCA (unpublished data). The MS/MS spectrum mass showed HNE modified SNCA at His residue (His50) as in previous studies [14] (unpublished data) (Fig. 2). It is possible that HNE can modify SNCA at the sites of the 15 Lys residues. However, we could not detect modification at Lys residues due to the labile reaction between Lys residues and HNE. Alternatively, it could be due to trypsin digestion. Moreover, incubation of HNE with SNCA at pH 7.8 and 37°C resulted in covalent modification of the protein and the
amount of HNE modified proteins increased with increasing HNE concentration (Fig. 3). It remains unclear why dopaminergic neurons of the substantia nigra are selectively vulnerable in PD patients. Considering the specificity of the lesions in PD, it is possible that the high oxidative state associated with DA metabolism may cause deterioration of dopaminergic neurons. The mechanism underlying increased oxidative stress may involve DA itself, because oxidation of cytosolic levodopa/DA may be deleterious to neurons. Indeed, DA causes apoptotic
Fig. 3 Mass spectroscopy of wild-type of SNCA. MS/MS spectrum of m/z 1295.4 at the ion (upper panel). MS/MS spectrum of m/z 1433.2 at the ion. After interaction of His residue, the MW of HNE is 138.
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cell death as shown by morphological nuclear changes and DNA fragmentation [15–17]. DA and its metabolites seem to exert cytotoxicity mainly by generating highly reactive quinones through auto-oxidation. On the other hand, the toxicity of levodopa and DA may be due to the generation of reactive oxygen species (ROS) that could disrupt cellular integrity, causing cell death. Thus SNCA is involved in DA metabolism and aberrant regulation of DA is accompanied by accumulation of oxidative levodopa/DA metabolites. Recently, SNCA multiplications in FPD have been reported in two and three families with genomic triplication and duplication, respectively, and even through a single case [18–23]. The findings suggest that overproduction of SNCA is one of the most important factors in this type of FPD. Clinical phenotypes of multiplication of SNCA are PD, PD with dementia (PDD), and dementia with Lewy bodies (DLB). Clinical symptoms, including age at onset, could be associated with copy numbers of SNCA. Therefore, overproduction of wild-type SNCA may result in phenotypes of PD, PDD, and DLB, suggesting that regulation of SNCA protein levels is central to the etiology of these phenotypes. In this regard, SNCA involvement in oxidative stress plays an important role in the pathogenesis of PD. Levodopa has the potential to auto-oxidize from a catechol to a quinone and to generate other ROS. Thus, levodopa itself may contribute to the pathogenesis of PD via oxidative stress. Both overt toxicity and neuroprotective effects of levodopa, both in vivo and in vitro, have been described in several studies investigating whether levodopa may accelerate or delay progression of human PD. However, levodopa is the most effective drug for PD. Therefore, further studies will be needed to develop new therapies with a neuroprotective strategy. Conflict of interest The authors have no conflict of interest to report. No funding applicable. References [1] Dexter DT, Carter CJ, Wells FR, Javoy-Agid F, Agid Y, Lees A, et al. Basal lipid peroxidation in substantia nigra is increased in Parkinson’s disease. J Neurochem 1989;2:381–9. [2] Sian J, Dexter DT, Lees AJ, Daniel S, Agid Y, Javoy-Agid F, et al. Alterations in glutathione levels in Parkinson’s disease and other neurodegenerative disorders affecting basal ganglia. Ann Neurol 1994;36:348–55. [3] Dexter DT, Carayon A, Vidailhet M, Ruberg M, Agid F, Agid Y, et al. Decreased ferritin levels in brain in Parkinson’s disease. J Neurochem 1990;55:16–20. [4] Shastry BS. Neurodegenerative disorders of protein aggregation. Neurochem Int 2003;43:1–7.
[5] Fahn S, Oakes D, Shoulson I, Kieburtz K, Rudolph A, Lang A, et al. Levodopa and the progression of Parkinson’s disease. N Engl J Med 2004;351:2498–508. [6] Spillantini MG, Schmidt ML, Lee VM, Trojanowski JQ, Jakes R, Goedert M. Alpha-synuclein in Lewy bodies. Nature 1997;388:839– 40. [7] Maroteaux L, Campanelli JT, Scheller RH. Synuclein: a neuronspecific protein localized to the nucleus and presynaptic nerve terminal. J Neurosci 1988;8:2804–15. [8] Uversky VN, Gillespie JR, Fink AL. Why are “natively unfolded” proteins unstructured under physiologic conditions? Proteins 2000;41: 415–27. [9] Weinreb PH, Zhen W, Poon AW, Conway KA, Lansbury PT, Jr. NACP, a protein implicated in Alzheimer’s disease and learning, is natively unfolded. Biochemistry 1996;35:13709–15. [10] Kubo S, Nemani VM, Chalkley RJ, Anthony MD, Hattori N, Mizuno Y et al. A combinatorial code for the interaction of alpha-synuclein with membranes. J Biol Chem 2005;280:31664–72. [11] Zhu M, Li J, Fink AL. The association of alpha-synuclein with membranes affects bilayer structure, stability, and fibril formation. J Biol Chem 2003;278:40186–97. [12] Davidson WS, Jonas A, Clayton DF, George JM. Stabilization of alpha-synuclein secondary structure upon binding to synthetic membranes. J Biol Chem 1998;273:9443–9. [13] Qin Z, Hu D, Han S, Reaney SH, Di Monte DA, Fink AL. Effect of 4-hydroxy-2-nonenal modification on alpha-synuclein aggregation. J Biol Chem 2007;282:5862–70. [14] Trostchansky A, Lind S, Hodara R, Oe T, Blair IA, Ischiropoulos H, et al. Interaction with phospholipids modulates alpha-synuclein nitration and lipid-protein adduct formation. Biochem J 2006;393:343–9. [15] Emdadul Haque M, Asanuma M, Higashi Y, Miyazaki I, Tanaka K, Ogawa N. Apoptosis-inducing neurotoxicity of dopamine and its metabolites via reactive quinone generation in neuroblastoma cells. Biochim Biophys Acta 2003;1619:39–52. [16] Hastings TG, Lewis DA, Zigmond MJ. Role of oxidation in the neurotoxic effects of intrastriatal dopamine injections. Proc Natl Acad Sci USA 1996;93:1956–61. [17] Jones DC, Gunasekar PG, Borowitz JL, Isom GE. Dopamine-induced apoptosis is mediated by oxidative stress and Is enhanced by cyanide in differentiated PC12 cells. J Neurochem 2000;74:2296–304. [18] Ikeuchi T, Kakita A, Shiga A, Kasuga K, Kaneko H, Tan CF, et al. Patients homozygous and heterozygous for SNCA duplication in a family with parkinsonism and dementia. Arch Neurol 2008;65:514–9. [19] Ahn TB, Kim SY, Kim JY, Park SS, Lee DS, Min HJ, et al. AlphaSynuclein gene duplication is present in sporadic Parkinson disease. Neurology 2008;70:43–9. [20] Chartier-Harlin MC, Kachergus J, Roumier C, Mouroux V, Douay X, Lincoln S, et al. Alpha-synuclein locus duplication as a cause of familial Parkinson’s disease. Lancet 2004;364:1167–9. [21] Pals P, Lincoln S, Manning J, Heckman M, Skipper L, Hulihan M, et al. Alpha-synuclein promoter confers susceptibility to Parkinson’s disease. Ann Neurol 2004;56:591–5. [22] Nishioka K, Hayashi S, Farrer MJ, Singleton AB, Yoshino H, Imai H, et al. Clinical heterogeneity of alpha-synuclein gene duplication in Parkinson’s disease. Ann Neurol 2006;59:298–309. [23] Singleton AB, Farrer M, Johnson J, Singleton A, Hague S, Kachergus J, et al. Alpha-synuclein locus triplication causes Parkinson’s disease. Science 2003;302:841.
Toxic effects of dopamine metabolism in Parkinson’s disease Nobutaka Hattori a, *, Mei Wang a , Hikari Taka b , Tsutomu Fujimura b , Asako Yoritaka a , Shin-ichiro Kubo a , Hideki Mochizuki a a Department
of Neurology and b Biochemical Research Center, Division of Proteomics and Biomolecular Sciences, Juntendo University School of Medicine, 2-1-1 Hongo, Bunkyo, Tokyo 113-8421, Japan
Abstract Levodopa is the most effective medication for Parkinson’s disease (PD). In contrast, there is evidence that levodopa and its metabolites such as dopa/dopamine quinone are toxic for nigral neurons based on in vitro studies. Moreover, there is growing evidence that oxidative stress and mitochondrial dysfunction contribute the pathogenesis of PD. Thus, studies for oxidative stress give us good information for elucidating the pathogenesis of PD. In this regard, it is mandatory to develop markers such as 4-hydroxy-nonenal (HNE). HNE is a product of lipid peroxidation. Indeed, immunohistochemical studies have revealed that HNE-modified proteins accumulate within ragged red fibers (RRFs). This finding indicated that mitochondrial impairment may be linked to oxidative stress. Moreover, HNE-modified proteins accumulate in nigral neurons. In PD, mitochondrial dysfunction such as complex I deficiency has also been reported. In addition, HNE can modify α-synuclein (SNCA). Subsequently, this modification may trigger the aggregation of this protein. At a minimum, this modification could be associated with oligomer formation or fibrillation of SNCA. © 2008 Elsevier Ltd. All rights reserved. Keywords: 4-Hydroxy-nonenal; Parkinson’s disease; Oxidative stress; Levodopa; Mitochondrial dysfunctions
1. Introduction Since the discovery of levodopa therapy, the prognosis of Parkinson’s disease (PD) has improved. However, it is clear that long-term treatment with levodopa can induce motor fluctuations such as wearing off and levodopa-induced dyskinesia. Moreover, despite continuing levodopa therapy, the signs and symptoms of parkinsonism worsen progressively. In addition, dopaminergic neurons in the substantia nigra are particularly vulnerable to oxidative stress. Indeed, studies on post-mortem brains from PD patients indicate increased lipid peroxidation [1], decreased glutathione [2], abnormalities in iron homeostasis [3], and protein aggregation [4]. There is evidence that oxidative stress contributes to the pathogenesis of PD. Levodopa is the most effective medication for management of this disorder. Although there are controversies * Correspondence to: N. Hattori, Department of Neurology, Juntendo University School of Medicine, 2-1-1 Hongo, Bunkyo, Tokyo 113-8421, Japan. Tel.: +81-3-3813-3111 ext. 3321; Fax: +81-3-5800-0547. E-mail address: [email protected] 1353-8020/$ – see front matter © 2008 Elsevier Ltd. All rights reserved.
about whether levodopa is toxic for PD patients, recent studies, such as the ELLDOPA study, indicate that levodopa is not toxic for nigral neurons [5]. The ELLDOPA study was designed to determine if levodopa affected the progression of PD. This double-blind randomized study showed that subjects treated with levodopa for 40 weeks had less severe parkinsonism than placebo-treated subjects, even after a 2week washout of medications, with the highest dose group showing the greatest benefit, suggesting that levodopa may actually have neuroprotective value. However, the study did not conclusively demonstrate slowing of disease progression, because the same result could have arisen from a long-lasting symptomatic benefit of levodopa. In this paper, we review the role of the toxic effects of dopamine (DA) metabolism in PD. 2. Familial PD gene product, α-synuclein, and oxidative stress Seven causative genes and four chromosomal loci for familial PD (FPD) have been identified. Among them, α-
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synuclein (SNCA) is a key molecule to understand the mechanisms of Lewy body formation since it is a major component of the inclusions [6]. SNCA is a small, highly conserved protein that is abundant in various regions of the brain [7] and is natively unfolded [8,9]. It is associated with membranous function such as lipid rafts [10]. We recently found that an interaction with lipid rafts is crucial for the normal, pre-synaptic localization of SNCA. In addition, we have also found that SNCA binds directly to artificial membranes whose lipid composition mimics that of lipid rafts. The binding of SNCA to these raft-like liposomes requires acidic phospholipids, with a preference for phosphatidylserine (PS). Interestingly, a variety of synthetic PS with defined acyl chains does not support binding when used individually. Rather, the interaction with SNCA requires a combination of PS with oleic (18:1) and polyunsaturated (either 20:4 or 22:6) fatty acyl chains, suggesting a role for phase separation within the membrane. Furthermore, SNCA binds with higher affinity to artificial membranes with the PS head group on the polyunsaturated fatty acyl chain rather than on the oleoyl side chain, indicating a stringent combinatorial code for the interaction of SNCA with membranes. In agreement with the membrane-related functions, SNCA has seven repeats of 11 residues in the N-terminal half of the molecule with a consensus sequence of KTKEGV. Taken together, the binding potential with lipid rafts for SNCA revealed that SNCA undergoes a conformational change from an unstructured monomer in solution to an α-helical membrane-bound protein [11,12]. There is growing evidence that oxidative stress and mitochondrial respiratory failure with attendant decrease in energy output are implicated in nigral neuronal death in PD. It is not known, however, which cellular elements (neurons or glial cells) are major targets of oxygen-mediated damage. 4-Hydroxy-2-nonenal (HNE) was shown earlier to react with proteins to form stable adducts that can be used as
markers of oxidative stress-induced cellular damage. Indeed, HNE-modified proteins accumulate within ragged red fibers in mitochondrial myopathies (unpublished data) (Fig. 1). Abnormal mitochondria accumulate within the fibers. This finding indicates that mitochondrial dysfunction could be associated with oxidative stress such as lipid peroxidation. In previous work, we reported the results of immunochemical studies using polyclonal antibodies directed against HNEprotein conjugates to label the site of oxidative damage in PD patients and control subjects. On average, 58% of nigral neurons were positively stained for HNE-modified proteins in PD; in contrast, only 9% of nigral neurons were positive in the control subjects. The difference was statistically significant (Mann-Whitney U test, p < 0.01). In contrast to the substantia nigra, oculomotor neurons in the same midbrain sections showed no or only weak staining for HNE-modified proteins in both PD and control subjects. Young control subjects did not show any immunostaining; however, aged control subjects showed weak staining in the oculomotor nucleus, suggesting age-related accumulation of HNE-modified proteins in neurons. Our results indicate the presence of oxidative stress within nigral neurons in PD, and this oxidative stress may contribute to nigral cell death. HNE is one of the highly reactive aldehydes. This molecule forms covalent adducts including HNE-cysteine (Cys), HNE-histidine (His), and HNE-lysine (Lys) via the Michael reaction. Thus, SNCA is a good target of HNE, since SNCA has a single site of His residue at position 50 and 15 Lys residues. Recently, Qin and colleagues reported the effects of the interaction of HNE with SNCA. They concluded that HNE modification of SNCA resulted in a major conformational change involving increased βsheet formation [13]. HNE-modification of SNCA led to inhibition of fibrillation in an HNE concentration-dependent manner. Furthermore, they found that the addition of HNEmodified oligomer to primary mesencephalic cultures caused
Fig. 1 Immunohistochemistry for HNE-modified proteins. Arrows show immunoreactivities for HNE-modified proteins. Bar indicates 100 μm. SDH, succinate dehydrogenese.
N. Hattori et al. / Parkinsonism and Related Disorders 15, Supplement 1 (2009) S35–S38
S37
Fig. 2 Aggregation of SNCA with the increase of HNE concentration in vitro. HNE-SNCA aggregation was observed after incubation of both HNE and SNCA recombinant proteins. The aggregation was shown in an HNE concentration-dependent manner. Panels A and B show the treatments without and with HNE incubation, respectively.
marked neurotoxicity. We also investigated the interaction of HNE with SNCA (unpublished data). The MS/MS spectrum mass showed HNE modified SNCA at His residue (His50) as in previous studies [14] (unpublished data) (Fig. 2). It is possible that HNE can modify SNCA at the sites of the 15 Lys residues. However, we could not detect modification at Lys residues due to the labile reaction between Lys residues and HNE. Alternatively, it could be due to trypsin digestion. Moreover, incubation of HNE with SNCA at pH 7.8 and 37°C resulted in covalent modification of the protein and the
amount of HNE modified proteins increased with increasing HNE concentration (Fig. 3). It remains unclear why dopaminergic neurons of the substantia nigra are selectively vulnerable in PD patients. Considering the specificity of the lesions in PD, it is possible that the high oxidative state associated with DA metabolism may cause deterioration of dopaminergic neurons. The mechanism underlying increased oxidative stress may involve DA itself, because oxidation of cytosolic levodopa/DA may be deleterious to neurons. Indeed, DA causes apoptotic
Fig. 3 Mass spectroscopy of wild-type of SNCA. MS/MS spectrum of m/z 1295.4 at the ion (upper panel). MS/MS spectrum of m/z 1433.2 at the ion. After interaction of His residue, the MW of HNE is 138.
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cell death as shown by morphological nuclear changes and DNA fragmentation [15–17]. DA and its metabolites seem to exert cytotoxicity mainly by generating highly reactive quinones through auto-oxidation. On the other hand, the toxicity of levodopa and DA may be due to the generation of reactive oxygen species (ROS) that could disrupt cellular integrity, causing cell death. Thus SNCA is involved in DA metabolism and aberrant regulation of DA is accompanied by accumulation of oxidative levodopa/DA metabolites. Recently, SNCA multiplications in FPD have been reported in two and three families with genomic triplication and duplication, respectively, and even through a single case [18–23]. The findings suggest that overproduction of SNCA is one of the most important factors in this type of FPD. Clinical phenotypes of multiplication of SNCA are PD, PD with dementia (PDD), and dementia with Lewy bodies (DLB). Clinical symptoms, including age at onset, could be associated with copy numbers of SNCA. Therefore, overproduction of wild-type SNCA may result in phenotypes of PD, PDD, and DLB, suggesting that regulation of SNCA protein levels is central to the etiology of these phenotypes. In this regard, SNCA involvement in oxidative stress plays an important role in the pathogenesis of PD. Levodopa has the potential to auto-oxidize from a catechol to a quinone and to generate other ROS. Thus, levodopa itself may contribute to the pathogenesis of PD via oxidative stress. Both overt toxicity and neuroprotective effects of levodopa, both in vivo and in vitro, have been described in several studies investigating whether levodopa may accelerate or delay progression of human PD. However, levodopa is the most effective drug for PD. Therefore, further studies will be needed to develop new therapies with a neuroprotective strategy. Conflict of interest The authors have no conflict of interest to report. No funding applicable. References [1] Dexter DT, Carter CJ, Wells FR, Javoy-Agid F, Agid Y, Lees A, et al. Basal lipid peroxidation in substantia nigra is increased in Parkinson’s disease. J Neurochem 1989;2:381–9. [2] Sian J, Dexter DT, Lees AJ, Daniel S, Agid Y, Javoy-Agid F, et al. Alterations in glutathione levels in Parkinson’s disease and other neurodegenerative disorders affecting basal ganglia. Ann Neurol 1994;36:348–55. [3] Dexter DT, Carayon A, Vidailhet M, Ruberg M, Agid F, Agid Y, et al. Decreased ferritin levels in brain in Parkinson’s disease. J Neurochem 1990;55:16–20. [4] Shastry BS. Neurodegenerative disorders of protein aggregation. Neurochem Int 2003;43:1–7.
[5] Fahn S, Oakes D, Shoulson I, Kieburtz K, Rudolph A, Lang A, et al. Levodopa and the progression of Parkinson’s disease. N Engl J Med 2004;351:2498–508. [6] Spillantini MG, Schmidt ML, Lee VM, Trojanowski JQ, Jakes R, Goedert M. Alpha-synuclein in Lewy bodies. Nature 1997;388:839– 40. [7] Maroteaux L, Campanelli JT, Scheller RH. Synuclein: a neuronspecific protein localized to the nucleus and presynaptic nerve terminal. J Neurosci 1988;8:2804–15. [8] Uversky VN, Gillespie JR, Fink AL. Why are “natively unfolded” proteins unstructured under physiologic conditions? Proteins 2000;41: 415–27. [9] Weinreb PH, Zhen W, Poon AW, Conway KA, Lansbury PT, Jr. NACP, a protein implicated in Alzheimer’s disease and learning, is natively unfolded. Biochemistry 1996;35:13709–15. [10] Kubo S, Nemani VM, Chalkley RJ, Anthony MD, Hattori N, Mizuno Y et al. A combinatorial code for the interaction of alpha-synuclein with membranes. J Biol Chem 2005;280:31664–72. [11] Zhu M, Li J, Fink AL. The association of alpha-synuclein with membranes affects bilayer structure, stability, and fibril formation. J Biol Chem 2003;278:40186–97. [12] Davidson WS, Jonas A, Clayton DF, George JM. Stabilization of alpha-synuclein secondary structure upon binding to synthetic membranes. J Biol Chem 1998;273:9443–9. [13] Qin Z, Hu D, Han S, Reaney SH, Di Monte DA, Fink AL. Effect of 4-hydroxy-2-nonenal modification on alpha-synuclein aggregation. J Biol Chem 2007;282:5862–70. [14] Trostchansky A, Lind S, Hodara R, Oe T, Blair IA, Ischiropoulos H, et al. Interaction with phospholipids modulates alpha-synuclein nitration and lipid-protein adduct formation. Biochem J 2006;393:343–9. [15] Emdadul Haque M, Asanuma M, Higashi Y, Miyazaki I, Tanaka K, Ogawa N. Apoptosis-inducing neurotoxicity of dopamine and its metabolites via reactive quinone generation in neuroblastoma cells. Biochim Biophys Acta 2003;1619:39–52. [16] Hastings TG, Lewis DA, Zigmond MJ. Role of oxidation in the neurotoxic effects of intrastriatal dopamine injections. Proc Natl Acad Sci USA 1996;93:1956–61. [17] Jones DC, Gunasekar PG, Borowitz JL, Isom GE. Dopamine-induced apoptosis is mediated by oxidative stress and Is enhanced by cyanide in differentiated PC12 cells. J Neurochem 2000;74:2296–304. [18] Ikeuchi T, Kakita A, Shiga A, Kasuga K, Kaneko H, Tan CF, et al. Patients homozygous and heterozygous for SNCA duplication in a family with parkinsonism and dementia. Arch Neurol 2008;65:514–9. [19] Ahn TB, Kim SY, Kim JY, Park SS, Lee DS, Min HJ, et al. AlphaSynuclein gene duplication is present in sporadic Parkinson disease. Neurology 2008;70:43–9. [20] Chartier-Harlin MC, Kachergus J, Roumier C, Mouroux V, Douay X, Lincoln S, et al. Alpha-synuclein locus duplication as a cause of familial Parkinson’s disease. Lancet 2004;364:1167–9. [21] Pals P, Lincoln S, Manning J, Heckman M, Skipper L, Hulihan M, et al. Alpha-synuclein promoter confers susceptibility to Parkinson’s disease. Ann Neurol 2004;56:591–5. [22] Nishioka K, Hayashi S, Farrer MJ, Singleton AB, Yoshino H, Imai H, et al. Clinical heterogeneity of alpha-synuclein gene duplication in Parkinson’s disease. Ann Neurol 2006;59:298–309. [23] Singleton AB, Farrer M, Johnson J, Singleton A, Hague S, Kachergus J, et al. Alpha-synuclein locus triplication causes Parkinson’s disease. Science 2003;302:841.