alpha-synuclein and catechol

3,4-Dihydroxyphenylacetaldehyde (DOPAL) is the focus of the catecholaldehyde hypothesis for the pathogenesis of Parkinson's disease and other Lewy body diseases. The catecholaldehyde is produced via oxidative deamination catalyzed by monoamine oxidase (MAO) acting on cytoplasmic dopamine. DOPAL is autotoxic, in that it can harm the same cells in which it is produced. Normally, DOPAL is detoxified by aldehyde dehydrogenase (ALDH)-mediated conversion to 3,4-dihydroxyphenylacetic acid (DOPAC), which rapidly exits the neurons. Genetic, environmental, or drug-induced manipulations of ALDH that build up DOPAL promote catecholaminergic neurodegeneration. A concept derived from the catecholaldehyde hypothesis imputes deleterious interactions between DOPAL and the protein alpha-synuclein (αS), a major component of Lewy bodies. DOPAL potently oligomerizes αS, and αS oligomers impede vesicular and mitochondrial functions, shifting the fate of cytoplasmic dopamine toward the MAO-catalyzed formation of DOPAL-destabilizing vicious cycles. Direct and indirect effects of DOPAL and of DOPAL-induced misfolded proteins could "freeze" intraneuronal reactions, plasticity of which is required for neuronal homeostasis. The extent to which DOPAL toxicity is mediated by interactions with αS, and vice versa, is poorly understood. Because of numerous secondary effects such as augmented spontaneous oxidation of dopamine by MAO inhibition, there has been insufficient testing of the catecholaldehyde hypothesis in animal models. The clinical pathophysiological significance of genetics, emotional stress, environmental agents, and interactions with numerous proteins relevant to the catecholaldehyde hypothesis are matters for future research. The imposing complexity of intraneuronal catecholamine metabolism seems to require a computational modeling approach to elucidate clinical pathogenetic mechanisms and devise pathophysiology-based, individualized treatments.

Topics: Aldehyde Dehydrogenase; Aldehydes; alpha-Synuclein; Animals; Catechols; Dopamine; Humans; Monoamine Oxidase; Monoamine Oxidase Inhibitors; Nerve Degeneration; Neurons; Oxidation-Reduction; Parkinson Disease; PC12 Cells; Rats

Parkinson's disease (PD) is a neurodegenerative disorder characterized by the presence of abnormal α-synuclein (αSyn) deposits in the brain. Alterations in metal homeostasis and metal-induced oxidative stress may play a crucial role in the aggregation of αSyn and, consequently, in the pathogenesis of PD. We have therefore investigated the capability of copper-αSyn6 and copper-αSyn15 peptide complexes, with the 1-6 and 1-15 terminal fragments of the protein, to promote redox reactions that can be harmful to other cellular components. The pseudo-tyrosinase activity of copper-αSyn complexes against catecholic (di-tert-butylcatechol (DTBCH2), 4-methylcatechol (4-MC)) and phenolic (phenol) substrates is lower compared to that of free copper(II). In particular, the rates (kcat) of DTBCH2 catalytic oxidation are 0.030 s(-1) and 0.009 s(-1) for the reaction promoted by free copper(II) and [Cu(2+)-αSyn15], respectively. On the other hand, HPLC/ESI-MS analysis of solutions of αSyn15 incubated with copper(II) and 4-MC showed that αSyn is competitively oxidized with remarkable formation of sulfoxide at Met1 and Met5 residues. Moreover, the sulfoxidation of methionine residues, which is related to the aggregation of αSyn, also occurs on peptides not directly bound to copper, indicating that external αSyn can also be oxidized by copper. Therefore, this study strengthens the hypothesis that copper plays an important role in oxidative damage of αSyn which is proposed to be strongly related to the etiology of PD.

Topics: alpha-Synuclein; Amino Acid Sequence; Catechols; Copper; Humans; Molecular Sequence Data; Oxidation-Reduction; Oxidative Stress; Parkinson Disease

Several studies have shown that catecholamines can inhibit the fibrillation of alpha-synuclein (alpha-Syn), a small presynaptic protein whose aggregation is believed to be a critical step in the etiology of Parkinson's disease and several other neurodegenerative disorders. However, the mechanism of this inhibition is uncertain. We show here that substoichiometric concentrations of 3,4-dihydroxyphenylacetic acid (DOPAC), a normal product of the metabolism of dopamine, can inhibit the fibrillation of alpha-Syn, due to non-covalent binding of DOPAC to alpha-Syn monomer. Intriguingly, the presence of alpha-Syn accelerates the spontaneous oxidation of DOPAC, and the oxidized form of DOPAC (the quinone) is responsible for the fibrillation inhibition. In addition, the presence of DOPAC leads to the oxidation of the methionine residues of alpha-Syn, probably due to the H(2)O(2) production as a by-product of DOPAC oxidation. The lack of fibrillation results from the formation of stable oligomers, which are very similar to those observed transiently at early stages of the alpha-Syn fibrillation. A possible explanation for this phenomenon is that DOPAC stabilizes the normally transient oligomers and prevents them from subsequent fibril formation. The analysis of the alpha-Syn Y39W variant suggests that DOPAC binds non-covalently to the same N-terminal region of alpha-Syn as lipid vesicles, probably in the vicinity of residue 39. In contrast to the compounds with 1,2-dihydroxyphenyl groups (DOPAC and catechol), their 1,4-dihydroxyphenyl isomers (hydroquinone and homogentisic acid) are able to modify alpha-Syn covalently, probably due to the less steric hindrance in the Michael addition.

Topics: 3,4-Dihydroxyphenylacetic Acid; alpha-Synuclein; Amyloid; Catechols; Homogentisic Acid; Hydroquinones; Microscopy, Electron, Transmission; Oxidation-Reduction; Protein Binding

Free radicals, including dopamine (DA)-oxidized metabolites, have long been implicated in pathogenesis of Parkinson's disease (PD). However, the relationships between such oxidative stresses and alpha-synuclein (alpha-S), a major constituent of Lewy bodies, remain unknown. In this study, we established neuronal cells that constitutively express alpha-S and tetracycline-regulated tyrosinase. While tyrosinase overexpression induced apoptosis, co-expression of wild type or A53T mutant human alpha-S with tyrosinase further exacerbated cell death. In this process, the formation of alpha-S oligomers and the reduction in mitochondrial membrane potential were demonstrated. This cellular model may reconstitute the pathological metabolism of alpha-S in the synucleinopathy and provide a useful tool to explore possible pathomechanisms of nigral degeneration in PD.

Topics: alpha-Synuclein; Apoptosis; Catechols; Cells, Cultured; Comet Assay; DNA Damage; Enzyme Activation; Gene Expression; Humans; Intracellular Membranes; Membrane Potentials; Mitochondrial Membranes; Mitogen-Activated Protein Kinases; Molecular Weight; Monophenol Monooxygenase; Multiprotein Complexes; Mutation; Nerve Degeneration; Oxidation-Reduction; Parkinson Disease