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Dopamine Section
Dopamine and quinone
(28 References)
Asanuma, M., I. Miyazaki, et al. (2003). "Dopamine- or L-DOPA-induced neurotoxicity: the role of dopamine quinone formation and tyrosinase in a model of Parkinson's disease." Neurotox Res 5(3): 165-76.
Dopamine (DA)- or L-dihydroxyphenylalanine-(L-DOPA-) induced neurotoxicity is thought to be involved not only in adverse reactions induced by long-term L-DOPA therapy but also in the pathogenesis of Parkinson's disease. Numerous in vitro and in vivo studies concerning DA- or L-DOPA-induced neurotoxicity have been reported in recent decades. The reactive oxygen or nitrogen species generated in the enzymatical oxidation or auto-oxidation of an excess amount of DA induce neuronal damage and/or apoptotic or non-apoptotic cell death; the DA-induced damage is prevented by various intrinsic and extrinsic antioxidants. DA and its metabolites containing two hydroxyl residues exert cytotoxicity in dopaminergic neuronal cells mainly due to the generation of highly reactive DA and DOPA quinones which are dopaminergic neuron-specific cytotoxic molecules. DA and DOPA quinones may irreversibly alter protein function through the formation of 5-cysteinyl-catechols on the proteins. For example, the formation of DA quinone-alpha-synuclein consequently increases cytotoxic protofibrils and the covalent modification of tyrosine hydroxylase by DA quinones. The melanin-synthetic enzyme tyrosinase in the brain may rapidly oxidize excess amounts of cytosolic DA and L-DOPA, thereby preventing slowly progressive cell damage by auto-oxidation of DA, thus maintainng DA levels. Since tyrosinase also possesses catecholamine-synthesizing activity in the absence of tyrosine hydroxylase (TH), the double-edged synthesizing and oxidizing functions of tyrosinase in the dopaminergic system suggest its potential for application in the synthesis of DA, instead of TH in the degeneration of dopaminergic neurons, and in the normalization of abnormal DA turnover in the long-term L-DOPA-treated Parkinson's disease patients.
Cavalieri, E. L., K. M. Li, et al. (2002). "Catechol ortho-quinones: the electrophilic compounds that form depurinating DNA adducts and could initiate cancer and other diseases." Carcinogenesis 23(6): 1071-7.
Catechol estrogens and catecholamines are metabolized to quinones, and the metabolite catechol (1,2-dihydroxybenzene) of the leukemogenic benzene can also be oxidized to its quinone. We report here that quinones obtained by enzymatic oxidation of catechol and dopamine with horseradish peroxidase, tyrosinase or phenobarbital-induced rat liver microsomes react with DNA by 1,4-Michael addition to form predominantly depurinating adducts at the N-7 of guanine and the N-3 of adenine. These adducts are analogous to the ones formed with DNA by enzymatically oxidized 4-catechol estrogens (Cavalieri,E.L., et al. (1997) PROC: Natl Acad. Sci., 94, 10937). The adducts were identified by comparison with standard adducts synthesized by reaction of catechol quinone or dopamine quinone with deoxyguanosine or adenine. We hypothesize that mutations induced by apurinic sites, generated by the depurinating adducts, may initiate cancer by benzene and estrogens, and some neurodegenerative diseases (e.g. Parkinson's disease) by dopamine. These data suggest that there is a unifying molecular mechanism, namely, formation of specific depurinating DNA adducts at the N-7 of guanine and N-3 of adenine, that could initiate many cancers and neurodegenerative diseases.
Cavalieri, E. L., E. G. Rogan, et al. (2002). "Initiation of cancer and other diseases by catechol ortho-quinones: a unifying mechanism." Cell Mol Life Sci 59(4): 665-81.
Exposure to estrogens is a risk factor for breast and other human cancers. Initiation of breast, prostate and other cancers has been hypothesized to result from reaction of specific estrogen metabolites, catechol estrogen-3,4-quinones, with DNA to form depurinating adducts at the N-7 of guanine and N-3 of adenine by 1,4-Michael addition. The catechol of the carcinogenic synthetic estrogen hexestrol, a hydrogenated derivative of diethylstilbestrol, is metabolized to its quinone, which reacts with DNA to form depurinating adducts at the N-7 of guanine and N-3 of adenine. The catecholamine dopamine and the metabolite catechol (1,2-dihydroxybenzene) of the leukemogen benzene can also be oxidized to their quinones, which react with DNA to form predominantly analogous depurinating adducts. Apurinic sites formed by depurinating adducts are converted into tumor-initiating mutations by error-prone repair. These mutations could initiate cancer by estrogens and benzene, and Parkinson's disease by the neurotransmitter dopamine. These data suggest a unifying molecular mechanism of initiation for many cancers and neurodegenerative diseases and lay the groundwork for designing strategies to assess risk and prevent these diseases.
Choi, H. J., S. W. Kim, et al. (2003). "Dopamine-dependent cytotoxicity of tetrahydrobiopterin: a possible mechanism for selective neurodegeneration in Parkinson's disease." J Neurochem 86(1): 143-52.
Parkinson's disease is a neurodegenerative disorder associated with selective loss of dopaminergic neurons in the substantia nigra. While the underlying cause of this cell death is poorly understood, oxidative stress is thought to play a role. We have previously shown that tetrahydrobiopterin (BH4), an obligatory co-factor for tyrosine hydroxylase (TH), exerts selective toxicity on dopamine-producing cells and that this is prevented by antioxidants. This study shows that BH4-induced dopaminergic cell death is primarily mediated by dopamine, evidenced by findings that (i) BH4 toxicity is increased in proportion to cellular dopamine content; (ii) non-dopaminergic cells become susceptible to BH4 upon exposure to dopamine; and (iii) depletion of dopamine attenuates BH4 toxicity in dopamine-producing cells. BH4 causes lipid peroxidation, suggesting involvement of oxidative stress but the toxicity does not require enzymatic oxidation of dopamine. Instead, it seems to involve formation of quinone product(s) because (i) the cell death is attenuated by exposure to or induction of quinone reductase and (ii) BH4-treated cells show increased formation of protein-bound quinones, which is inhibited by thiol antioxidants. These data taken together suggest that the presence of both BH4 and dopamine is important in rendering dopaminergic cells vulnerable and that this involves formation of reactive dopamine quinone products.
Corpillo, D., F. Valetti, et al. (2003). "Induction and characterization of a novel amine oxidase from the yeast Kluyveromyces marxianus." Yeast 20(5): 369-79.
An amine oxidase from the yeast Kluyveromyces marxianus was induced, purified and completely characterized; it was shown to belong to the class of copper-containing amine oxidases (E.C. 1.4.3.6). The enzyme was induced by putrescine and, very strongly, by copper(II); structural-functional characterization of the enzyme was performed, including determination of molecular weight, glycosylation, copper and TPQ content, isoelectric point, K(M) and k(CAT) (with benzylamine as substrate), pH, temperature and ionic strength effect on catalysis, substrate and inhibitor specificity. A 700 bp clone was isolated containing the cDNA that encodes for the C-terminus of the enzyme; the amino acid sequence deduced (the first available for a benzylamine oxidase from yeast) was compared to that of other copper amine oxidases from microorganisms and higher organisms. From the results obtained, the putrescine/benzylamine oxidase from Kluyveromyces marxianus was found to have a good homology with other enzymes of this class from microorganisms, and particularly with AO I from Aspergillus niger. Nonetheless, some features resulted closer to those of animal amine oxidases and histaminases. Some potential biotechnological applications are proposed. The cDNA Accession No. is AJ320485.
Elmore, B. O., J. A. Bollinger, et al. (2002). "Human kidney diamine oxidase: heterologous expression, purification, and characterization." J Biol Inorg Chem 7(6): 565-79.
Human kidney diamine oxidase has been overexpressed as a secreted enzyme under the control of a metallothionein promoter in Drosophila S2 cell culture. This represents the first heterologous overexpression and purification of a catalytically active, recombinant mammalian copper-containing amine oxidase. A rapid and highly efficient purification protocol using chromatography on heparin affinity, hydroxyapatite, and gel filtration media allows for the recovery of large quantities of the recombinant enzyme, which is judged to be greater than 98% homogenous by SDS/PAGE. The availability of large quantities of highly purified enzyme makes it now possible to investigate the spectroscopic, mechanistic, functional, and structural properties of this human enzyme at the molecular level. Visible absorption, circular dichroism, electron paramagnetic resonance, and resonance Raman spectroscopic results are presented. The recombinant enzyme contains the cofactors 2,4,5-trihydroxyphenylalaninequinone and copper at stoichiometries of up to 1.1 and 1.5 mol per mol homodimer, respectively. In addition, tightly bound and stoichiometric calcium ions were identified and proposed to occupy a second metal-binding site. The apparent molecular weight of the recombinant protein, determined by analytical ultracentrifugation, suggests 20-26% glycosylation by weight. Detailed kinetic studies indicate the preferred substrates (k(cat)/K(M)) of human diamine oxidase are, in order, histamine, 1-methylhistamine, and putrescine, with K(M) values of 2.8, 3.4, and 20 microM, respectively. These results, demonstrating the substrate preference for histamine and 1-methylhistamine, were unanticipated given the available literature. The pH dependence of k(cat) for putrescine oxidation gives two apparent p K(a) values at 6.0 and 8.2. Tissue-specific expression of the human diamine oxidase gene was investigated using an mRNA array. The relevance of this work to earlier work and the suggested physiological roles of the human enzyme are discussed.
Emdadul Haque, M., M. Asanuma, et al. (2003). "Apoptosis-inducing neurotoxicity of dopamine and its metabolites via reactive quinone generation in neuroblastoma cells." Biochim Biophys Acta 1619(1): 39-52.
Neurotoxic properties of L-dopa and dopamine (DA)-related compounds were assessed in human neuroblastoma SH-SY5Y cells with reference to their structural relationship. L-Dopa and its metabolites containing two free hydroxyl residues on their benzene ring showed toxicity in the cell, which was prevented by superoxide dismutase (SOD) and reduced glutathione (GSH), but not by catalase. Furthermore, a synthetic derivative of DA, 3-hydroxy-4-methoxyphenethylamine (HMPE) containing methoxy residue at position 4 in the benzene ring, exerted partial cytotoxicity, which was not prevented by SOD, GSH or catalase. However, the metabolites containing methoxy residue at position 3 failed to show a toxic effect in the SH-SY5Y cells. Moreover, DA induced apoptotic cell death, which was observed by nuclear and terminal deoxynucleotidyl transferase-mediated dUTP nick end-labeling (TUNEL) staining and measurement of caspase-3 activity; this compound up-regulated apoptotic factor p53 while down-regulating anti-apoptotic factor Bcl-2. In the cell-free in vitro electron spin resonance (ESR) spectrometry, DA possessing two hydroxyl groups showed generation of DA-semiquinone radicals, which were markedly prevented by addition of SOD or GSH but not by catalase. On the other hand, methylation of one of the hydroxyl residues on the benzene ring of DA converted DA to an unoxidizable compound (3-MT or HMPE), and caused it to lose the property to produce semiquinone radicals. It has been previously reported that SOD acting as a superoxide:semiquinone oxidoreductase prevents quinone formation, and that reduced GSH through forming a complex with DA-quinone prevents quinone binding to the thiol group of the intact protein. Therefore, the present results suggest that DA and its metabolites containing two hydroxyl residues exert cytotoxicity mainly due to generation of highly reactive quinones.
Eppler, B. and R. Dawson, Jr. (2002). "Cytoprotective role of taurine in a renal epithelial cell culture model." Biochem Pharmacol 63(6): 1051-60.
Taurine (TAU) is a sulfur-containing amino acid that has been shown to decrease during aging and is believed to be important for cytoprotection. A decrease in TAU could exacerbate the accumulation of free radical-induced damage that may lead to cell death during the aging process. We have shown previously that TAU directly inhibits dopamine (DA) and (-)-3-(3,4-dihydroxyphenyl)-L-alanine (L-dopa) oxidation. Experiments were conducted to establish a cytoprotective role for TAU. Porcine renal epithelial cells were treated for 1 hr with iron and catecholamines (L-dopa and DA) to produce cytotoxicity by a free radical and quinone mechanism in the absence and presence of 10 or 20mM TAU. Viability assays, protein, and DNA measurements were performed after a 24hr recovery period. In some experiments, cells were extracted immediately after the insult for DA and TAU content measurements using high performance liquid chromatography with electrochemical detection. Catecholamine-induced cytotoxicity caused a 50% loss in cell viability, and 10 or 20mM TAU provided significant protection from cytotoxicity and maintained the functional integrity of the cells. Photomicrographs showed attenuation in cell loss and swelling in the presence of TAU. Pretreatment with 1mM TAU followed by exposure to iron and L-dopa in the presence of 1mM TAU caused a moderate but non-significant increase in cell survival. These data conclusively show that TAU can play a cytoprotective role in the LLC-PK(1) cell culture model.
Gasowska, B., H. Wojtasek, et al. (2002). "Redox reaction between amino-(3,4-dihydroxyphenyl)methyl phosphonic acid and dopaquinone is responsible for the apparent inhibitory effect on tyrosinase." Eur J Biochem 269(16): 4098-104.
Amino-(3,4-dihydroxyphenyl)methyl phosphonic acid, the phosphonic analog of 3,4-dihydroxyphenylglycine, had been previously reported as a potent inhibitor of tyrosinase. The mechanism of the apparent enzyme inhibition by this compound has now been established. Amino-(3,4-dihydroxyphenyl)methyl phosphonic acid turned out to be a substrate and was oxidized to o-quinone, which evolved to a final product identified as 3,4-dihydroxybenzaldehyde, the same as for 3,4-dihydroxyphenylglycine. Monohydroxylated compounds (amino-(3-hydroxyphenyl)methyl phosphonic acid and amino-(4-hydroxyphenyl)methyl phosphonic acid) were not oxidized, neither was 4-hydroxy-l-phenylglycine. However, the relatively high Km for amino-(3,4-dihydroxyphenyl)methyl phosphonic acid (0.52 mm) indicated that competitive inhibition could not entirely explain the previously reported strong inhibitory effect (Ki = 50 and 97 micro m for tyrosine and 3-(3,4-dihydroxyphenyl)alanine (Dopa) as substrates, respectively). Neither was the enzyme covalently inactivated to a significant degree. Spectroscopic and electrochemical analysis of the oxidation of a mixture of Dopa and the inhibitor demonstrated that the phosphonic compound reduced dopaquinone back to Dopa, thus diminishing and delaying the formation of dopachrome. This produces an apparent strong inhibitory effect when the reaction is monitored spectrophotometrically at 475 nm. In this peculiar case Dopa acts as a redox shuttle mediating the oxidation of the shorter phosphonic homolog. Decomposition of the phosphonic o-quinone to 3,4-dihydroxybenzaldehyde drives the reaction against the slightly unfavorable difference in redox potentials.
Goto, Y. and J. P. Klinman (2002). "Binding of dioxygen to non-metal sites in proteins: exploration of the importance of binding site size versus hydrophobicity in the copper amine oxidase from Hansenula polymorpha." Biochemistry 41(46): 13637-43.
Copper amine oxidases (CAOs) contain 2,4,5-trihydroxyphenylalanyl quinone (TPQ) and a copper ion in their active sites, catalyzing amine oxidation to aldehyde and ammonia concomitant with the reduction of molecular oxygen to hydrogen peroxide. Kinetic studies on the CAO from bovine serum (BSAO) [Su and Klinman (1999) Biochemistry 37, 12513-12525] and the recent reports on the cobalt substituted form of the enzyme from Hansenula polymorpha (HPAO) [Mills and Klinman (2000) J. Am. Chem. Soc. 122, 9897-9904, and Mills et al. (2002) Biochemistry, 41, 10577-10584] support pre-binding of molecular oxygen prior to a rate-limiting electron transfer from the reduced form of TPQ (p-aminohydroquinone form) to dioxygen. Although there is significant sequence homology between BSAO and HPAO, k(cat)/K(m)(O2) for BSAO under the optimal condition is one order of magnitude lower than that for HPAO. From a comparison of amino acid sequences for BSAO and HPAO, together with the X-ray crystal structure of HPAO, a plausible dioxygen pre-binding site has been identified that involves Y407, L425, and M634 in HPAO; the latter two residues are altered in BSAO to A490 and T695. To determine which of these residues plays a greater role in dioxygen chemistry, k(cat)/K(m)(O2) was determined in HPAO for the M634 --> T and L425 --> A mutants. The L425 --> A mutation does not alter k(cat)/K(m)(O2) to a large extent, whereas the M634 --> T decreased k(cat)/K(m)(O2) by one order of a magnitude, creating a catalyst that is similar to BSAO. A series of mutants at M634 (to F, L, and Q) were, therefore, prepared in HPAO and characterized with regard to k(cat)/K(m)(O2) as a function of pH. Structure reactivity correlations show a linear relationship of rate with side chain volume, rather than hydrophobicity, indicating that dioxygen reactivity increases with the bulk of the residue at position 634. This site also shows specificity for O2, in relation to the co-gas N2, since substitution of the inert gas N2 by either Ar or He has no effect on measured rates. In particular, He gas is expected to have little affinity for protein at 1 atmospheric pressure, implying little or no binding by N2 as well.
Green, E. L., N. Nakamura, et al. (2002). "Rates of oxygen and hydrogen exchange as indicators of TPQ cofactor orientation in amine oxidases." Biochemistry 41(2): 687-96.
This study presents the first detailed examination by resonance Raman (RR) spectroscopy of the rates of solvent exchange for the C5 and C3 positions of the TPQ cofactor in several wild-type copper-containing amine oxidases and mutants of the amine oxidase from Hansenula polymorpha (HPAO). On the basis of crystal structure analysis and differing rates of C5 [double bond] O and C3 [bond] H exchange within the enzyme systems, but equally rapid rates of C5 [double bond] O and C3 [bond] H exchange in a TPQ model compound, it is proposed that these data can be used to determine the TPQ cofactor orientation within the active site of the resting enzyme. A rapid rate of C5 [double bond] O exchange (t(1/2) < 30 min) and a slow (t(1/2) = 6 h) to nonexistent rate of C3 [bond] H exchange was observed for wild-type HPAO, the amine oxidase from Arthrobacter globiformis, pea seedling amine oxidase at pH 7.1, and the E406Q mutant of HPAO. This pattern is ascribed to a productive TPQ orientation, with the C5 [double bond] O near the substrate-binding site and the C3 [bond] H near the Cu. In contrast, a slow rate of C5 [double bond] O exchange (t(1/2) = 1.6-3.3 h) coupled with a fast rate of C3 [bond] H exchange (t(1/2) < 30 min) was observed for the D319E and D319N catalytic base mutants of HPAO and for PSAO at pH 4.6 (t(1/2) = 4.5 h for C5 [double bond] O exchange). This pattern identifies a flipped orientation, involving 180 degrees rotation about the C alpha-C beta bond, which locates the C3 [bond] H near the substrate-binding site and the C5 double bond] O near the Cu. Finally, fast rates of both C5 [double bond] O and C3 [bond] H exchange (t(1/2) < 30 min) were observed for the amine oxidase from Escherichia coli and the N404A mutant of HPAO, suggesting a mobile cofactor, with multiple TPQ orientations between productive and flipped. These results demonstrate that opposing sides of the TPQ ring possess different degrees of solvent accessibility and that the rates of C5 [double bond] O and C3 [bond] H exchange can be used to predict the TPQ cofactor orientation in the resting forms of these enzymes.
Grima, G., B. Benz, et al. (2003). "Dopamine-induced oxidative stress in neurons with glutathione deficit: implication for schizophrenia." Schizophr Res 62(3): 213-24.
Glutathione (GSH) is the main non-protein antioxidant and plays a critical role in protecting cells from damage by reactive oxygen species (ROS) generated by dopamine (DA) metabolism. We reported a decrease of GSH levels ([GSH]) in CSF and in prefrontal cortex in vivo in schizophrenics [Eur. J. Neurosci. 12 (2000) 3721]. A GSH deficit may lead to membrane peroxidation and microlesions around dopaminergic terminals, resulting in loss of connectivity. To test this hypothesis, we studied the effect of DA in cultured cortical neurons with low [GSH]. DA alone decreased [GSH] by 40%. This effect appears to result from direct conjugation of DA semiquinone/quinone with GSH. Ethacrynic acid (EA) decreased [GSH] in a concentration-dependent manner. When added to EA, DA further lowers [GSH]. As this additional decrease is blocked by superoxide dismutase (SOD) or D(1)/D(2) receptor antagonists, it likely involves the generation of superoxide via activation of DA receptors. It also reduces the mitochondrial membrane potential. Most interestingly, a significant decrease in number of neuronal processes (spines analogous) was induced by 24-h application of DA only in low [GSH]. These data, compatible with our hypothesis, is consistent with the dendritic spines reduction reported in schizophrenia and could be related to abnormalities in synaptic connectivity.
Kim, M., T. Okajima, et al. (2002). "X-ray snapshots of quinone cofactor biogenesis in bacterial copper amine oxidase." Nat Struct Biol 9(8): 591-6.
The quinone cofactor TPQ in copper amine oxidase is generated by posttranslational modification of an active site tyrosine residue. Using X-ray crystallography, we have probed the copper-dependent autooxidation process of TPQ in the enzyme from Arthrobacter globiformis. Apo enzyme crystals were anaerobically soaked with copper; the structure determined from this crystal provides a view of the initial state: the unmodified tyrosine coordinated to the bound copper. Exposure of the copper-bound crystals to oxygen led to the formation of freeze-trapped intermediates; structural analyses indicate that these intermediates contain dihydroxyphenylalanine quinone and trihydroxyphenylalanine. These are the first visualized intermediates during TPQ biogenesis in copper amine oxidase.
Klinman, J. P. (2003). "The multi-functional topa-quinone copper amine oxidases." Biochim Biophys Acta 1647(1-2): 131-7.
The mature copper amine oxidases (CAOs) contain a tyrosine-derived 2,4,5-trihydroxyphenylalanyl quinone (topa quinone or TPQ) and a cupric ion in close proximity. Through a combination of structural, spectroscopic and kinetic analyses, a chemical mechanism for the self-processing of an active site tyrosine to TPQ has been proposed. Once formed, TPQ acts as a switch between the heterolytic transformation of amine substrates to aldehydes, via a pyridoxal phosphate-like Schiff base complex, and one electron chemistry involving reduction of molecular oxygen. The relationship between the biogenetic and catalytic processes is discussed.
Lee, C. S., E. H. Song, et al. (2003). "Combined effect of dopamine and MPP+ on membrane permeability in mitochondria and cell viability in PC12 cells." Neurochem Int 43(2): 147-54.
The present study examined the combined effect of dopamine and 1-methyl-4-phenylpyridinium (MPP(+)) on the membrane permeability in isolated brain mitochondria and on cell viability in PC12 cells. MPP(+) increased effect of dopamine against the swelling, membrane potential, and Ca(2+) transport in isolated mitochondria, which was not inhibited by the addition of antioxidant enzymes (SOD and catalase). Dopamine or MPP(+) caused the decrease in transmembrane potential, increase in reactive oxygen species, depletion of GSH, and cell death in PC12 cells. Antioxidant enzymes reduced each effect of dopamine and MPP(+) against PC12 cells. Co-addition of dopamine and MPP(+) caused the decrease in the transmembrane potential and increase in the formation of reactive oxygen species in PC12 cells, in which they showed an additive effect. Dopamine plus MPP(+)-induced the depletion of GSH and cell death in PC12 cells were not decreased by the addition of antioxidant enzymes, rutin, diethylstilbestrol, and ascorbate. Melanin caused a cell viability loss in PC12 cells. The N-acetylcysteine, N-phenylthiourea, and 5-hydroxyindole decreased the cell death and the formation of dopamine quinone and melanin induced by co-addition of dopamine and MPP(+), whereas deprenyl and chlorgyline did not show an inhibitory effect. The results suggest that co-addition of dopamine and MPP(+) shows an enhancing effect on the change in mitochondrial membrane permeability and cell death, which may be accomplished by toxic quinone and melanin derived from the MPP(+)-stimulated dopamine oxidation.
Li, Y. and Z. Cao (2002). "The neuroprotectant ebselen inhibits oxidative DNA damage induced by dopamine in the presence of copper ions." Neurosci Lett 330(1): 69-73.
Ebselen (2-phenyl-1,2-benzisoselenazol-3(2H)-one), a seleno-organic compound with glutathione peroxidase-like activity, has been shown to be protective against brain ischemic injury and Parkinson's disease. This study was undertaken to investigate the protective effects of ebselen on oxidative DNA damage induced by dopamine in the presence of copper ions. Incubation of phiX-174 plasmid DNA with micromolar dopamine in the presence of Cu(II) resulted in a concentration-dependent induction of DNA strand breaks. Both a Cu(II)/Cu(I) redox cycle and H(2)O(2) formation were critically involved in the induction of DNA strand breaks by the dopamine/Cu(II) system. The presence of ebselen at micromolar concentrations led to a marked concentration-dependent inhibition of DNA strand breaks induced by the dopamine/Cu(II) system. Further studies showed that ebselen did not affect either the Cu(II)-mediated oxidation of dopamine to dopamine quinone or the reduction of Cu(II) to Cu(I) by dopamine. Instead, the presence of ebselen resulted in a marked decrease in the levels of H(2)O(2) derived from the Cu(II)-mediated oxidation of dopamine. Taken together, our results demonstrate for the first time that ebselen is able to inhibit the dopamine/Cu(II)-induced oxidative DNA damage, which appears to be attributable to the ability of ebselen to decrease the levels of H(2)O(2) derived from the dopamine/Cu(II) system. Since oxidative DNA damage has been implicated in the pathogenesis of various neurodegenerative diseases, the inhibition of oxidative DNA damage by ebselen may be responsible, at least partially, for its neuroprotective activities observed in both humans and experimental animals.
Mure, M., S. A. Mills, et al. (2002). "Catalytic mechanism of the topa quinone containing copper amine oxidases." Biochemistry 41(30): 9269-78.
Park, S., T. J. Geddes, et al. (2003). "Dopamine Prevents Nitration of Tyrosine Hydroxylase by Peroxynitrite and Nitrogen Dioxide: IS NITROTYROSINE FORMATION AN EARLY STEP IN DOPAMINE NEURONAL DAMAGE?" J Biol Chem 278(31): 28736-42.
Peroxynitrite and nitrogen dioxide (NO2) are reactive nitrogen species that have been implicated as causal factors in neurodegenerative conditions. Peroxynitrite-induced nitration of tyrosine residues in tyrosine hydroxylase (TH) may even be one of the earliest biochemical events associated with 1-methyl-4-phenyl-1,2,3,6-tetrahydropyridine-induced damage to dopamine neurons. Exposure of TH to peroxynitrite or NO2 results in nitration of tyrosine residues and modification of cysteines in the enzyme as well as inactivation of catalytic activity. Dopamine (DA), its precursor 3,4-dihydroxyphenylalanine, and metabolite 3,4-dihydroxyphenylacetic acid completely block the nitrating effects of peroxynitrite and NO2 on TH but do not relieve the enzyme from inhibition. o-Quinones formed in the reaction of catechols with either peroxynitrite or NO2 react with cysteine residues in TH and inhibit catalytic function. Using direct, real-time evaluation of tyrosine nitration with a green fluorescent protein-TH fusion protein stably expressed in intact cells (also stably expressing the human DA transporter), DA was also found to prevent NO2-induced nitration while leaving TH activity inhibited. These results show that peroxynitrite and NO2 react with DA to form quinones at the expense of tyrosine nitration. Endogenous DA may therefore play an important role in determining how DA neurons are affected by reactive nitrogen species by shifting the balance of their effects away from tyrosine nitration and toward o-quinone formation.
Pedrosa, R. and P. Soares-da-Silva (2002). "Oxidative and non-oxidative mechanisms of neuronal cell death and apoptosis by L-3,4-dihydroxyphenylalanine (L-DOPA) and dopamine." Br J Pharmacol 137(8): 1305-13.
1. The present study was designed to evaluate the nature of intervening agents in L-DOPA- and dopamine-induced neurotoxicity in Neuro-2A cells. 2. In the absence of cells and in conditions of light protection, at 37 degrees C, L-DOPA or dopamine (1 mM) in culture medium degraded spontaneously in a time-dependent manner, this being prevented by ascorbic acid (200 microM) and other antioxidants, namely glutathione (1 mM), N-acetyl-L-cysteine (1 mM), sodium metabisulphite (200 microM), but not N-ter-butyl-alpha-phenylnitrone (1 mM) and deferoxamine (100 microM). 3. The viability of Neuro-2A cells declined following treatment with L-DOPA or dopamine in a concentration- and time-dependent manner. The decrease in cell viability by L-DOPA (10+/-4% of control) or dopamine (15+/-4% of control) was markedly attenuated by antioxidants (ascorbic acid, glutathione, N-acetyl-L-cysteine and sodium metabisulphite). Autoxidation of L-DOPA or dopamine was accompanied by the formation of H(2)O(2) in a time-dependent manner, this being completely prevented by ascorbic acid at 24 h or markedly reduced at 48 h. 4. Protective effects of 100 U ml(-1) catalase (40+/-1% of control) against L-DOPA-induced cell death were lower than those conferred by 200 microM ascorbic acid (70+/-3% of control). Catalase-induced protection (59+/-5% of control) against dopamine-induced cell death was similar to that conferred by 200 microM ascorbic acid (57+/-4% of control). L-DOPA-induced neuronal cell death was also accompanied by increases in caspase-3 activity, this being insensitive to ascorbic acid. Dopamine-induced increase in caspase-3 activity occurred only when autoxidation of the amine was prevented by ascorbic acid. 5. It is suggested that in addition to generation of H(2)O(2) and quinone formation, L-DOPA- and dopamine-induced cell death may result from induction of apoptosis, as evidenced by increases in caspase-3 activity. Dopamine per se induces apoptosis by a mechanism independent of oxidative stress, as evidenced by the fact that increases in caspase-3 activity occurred only when autoxidation of the amine was prevented.
Picada, J. N., N. Schroder, et al. (2002). "Differential neurobehavioral deficits induced by apomorphine and its oxidation product, 8-oxo-apomorphine-semiquinone, in rats." Eur J Pharmacol 443(1-3): 105-11.
Apomorphine is a potent dopamine receptor agonist, which has been used in the therapy of Parkinson's disease. It has been proposed that apomorphine and other dopamine receptor agonists might induce neurotoxicity mediated by their quinone and semiquinone oxidation derivatives. The aim of the present study was to evaluate the possible neurobehavioral effects of apomorphine and its oxidation derivative, 8-oxo-apomorphine-semiquinone (8-OASQ). Adult female Wistar rats were treated with a systemic injection of apomorphine (0.05 or 0.5 mg/kg) or 8-OASQ (0.05 or 0.5 mg/kg) 20 min before behavioral testing. Apomorphine and 8-OASQ induced differential impairing effects on short- and long-term retention of an inhibitory avoidance task. Apomorphine, but not 8-OASQ, dose-dependently impaired habituation to a novel environment. The memory-impairing effects could not be attributed to reduced nociception or other nonspecific behavioral alterations, since neither apomorphine nor 8-OASQ affected footshock reactivity or behavior during exploration of an open field. The results suggest that oxidation products of dopamine or dopamine receptor agonists might induce cognitive deficits.
Pietrangeli, P., S. Nocera, et al. (2003). "Is the catalytic mechanism of bacteria, plant, and mammal copper-TPQ amine oxidases identical?" Biochim Biophys Acta 1647(1-2): 152-6.
This short review is mostly concerned with the work carried out in Rome on the copper amine oxidase from bovine serum (BSAO). The first target was the copper oxidation state and its relationship with the organic cofactor. It was found that copper is not reduced on reaction with amines under anaerobic conditions or along the catalytic cycle and that it is not within bonding distance of the quinone cofactor. The copper stability in the oxidised state was supported by BSAO ability to oxidise benzylhydrazine, a slow substrate, in the presence of N,N-diethyldithiocarbamate (DDC) and by the substantial catalytic activity of Co(2+)-substituted BSAO. Parallel work established that only one subunit of the dimeric enzyme readily binds reagents of the carbonyl group. Flexible hydrazides with a long aromatic tail were found to be highly specific inhibitors, suggesting the presence of an extended hydrophobic region at the catalytic site. A study by stopped-flow transient spectroscopy and steady state kinetics led to the formulation of a simplified, yet complete and consistent, catalytic mechanism for BSAO that was compared with that available for lentil seedling amine oxidase (LSAO). As in other copper amine oxidases, BSAO is inactivated by H(2)O(2) produced in the catalytic reaction, while the cofactor is stabilised in its reduced state. A conserved tyrosine hydrogen-bonded to the cofactor might be oxidised.
Prabhakar, R., P. E. Siegbahn, et al. (2003). "A theoretical study of the dioxygen activation by glucose oxidase and copper amine oxidase." Biochim Biophys Acta 1647(1-2): 173-8.
Glucose oxidase (GO) and copper amine oxidase (CAO) catalyze the reduction of molecular oxygen to hydrogen peroxide. If a closed-shell cofactor (like FADH(2) in GO and topaquinone (TPQ) in CAO) is electron donor in dioxygen reduction, the formation of a closed-shell species (H(2)O(2)) is a spin forbidden process. Both in GO and CAO, formation of a superoxide ion that leads to the creation of a radical pair is experimentally suggested to be the rate-limiting step in the dioxygen reduction process. The present density functional theory (DFT) studies suggest that in GO, the creation of the radical pair induces a spin transition by spin orbit coupling (SOC) in O(2)(-)(rad), whereas in CAO, it is induced by exchange interaction with the paramagnetic metal ion (Cu(II)). In the rate-limiting step, this spin-transition is suggested to transform the O(2)(-)(rad)-FADH(2)(+)(rad) radical pair in GO and the Cu(II)-TPQ (triplet) species in CAO, from a triplet (T) to a singlet (S) state. For CAO, a mechanism for the O[bond]O cleavage step in the biogenesis of TPQ is also suggested.
Riobo, N. A., F. J. Schopfer, et al. (2002). "The reaction of nitric oxide with 6-hydroxydopamine: implications for Parkinson's disease." Free Radic Biol Med 32(2): 115-21.
Oxidation of catecholamines is suggested to contribute to oxidative stress in Parkinson's disease. Nitric oxide (*NO) is able to oxidize cyclic compounds like ubiquinol; moreover, recent lines of evidence proposed a direct role of *NO and its by-product peroxynitrite in the pathophysiology of Parkinson's disease. The aim of this study was to analyze the potential reaction between 6-hydroxydopamine, a classic inducer of Parkinson's disease, and *NO. The results showed that *NO reacts with the deprotonated form of 6-hydroxydopamine at pH 7 and 37 degrees C with a second-order rate constant of 1.5 x 10(3) M(-1) x s(-1) as calculated by the rate of *NO decay measured with an amperometric sensor. Accordingly, the rates of formation of 6-hydroxy-dopamine quinone were dependent on *NO concentration. The coincubation of *NO and 6-hydroxydopamine with either bovine serum albumin or alpha-synuclein led to tyrosine nitration of the protein, in a concentration dependent-manner and sensitive to superoxide dismutase. These findings suggest the formation of peroxynitrite during the redox reactions following the interaction of 6-hydroxydopamine with *NO. The implications of this reaction for in vivo models are discussed in terms of the generation of reactive nitrogen and oxygen species within a propagation process that may play a significant role in neurodegenerative diseases.
Saysell, C. G., W. S. Tambyrajah, et al. (2002). "Probing the catalytic mechanism of Escherichia coli amine oxidase using mutational variants and a reversible inhibitor as a substrate analogue." Biochem J 365(Pt 3): 809-16.
Copper amine oxidases are homodimeric enzymes containing one Cu(2+) ion and one 2,4,5-trihydroxyphenylalanine quinone (TPQ) per monomer. Previous studies with the copper amine oxidase from Escherichia coli (ECAO) have elucidated the structure of the active site and established the importance in catalysis of an active-site base, Asp-383. To explore the early interactions of substrate with enzyme, we have used tranylcypromine (TCP), a fully reversible competitive inhibitor, with wild-type ECAO and with the active-site base variants D383E and D383N. The formation of an adduct, analogous to the substrate Schiff base, between TCP and the TPQ cofactor in the active site of wild-type ECAO and in the D383E and D383N variants has been investigated over the pH range 5.5-9.4. For the wild-type enzyme, the plot of the binding constant for adduct formation (K(b)) against pH is bell-shaped, indicating two pK(a)s of 5.8 and approximately 8, consistent with the preferred reaction partners being the unprotonated active-site base and the protonated TCP. For the D383N variant, the reaction pathway involving unprotonated base and protonated TCP cannot occur, and binding must follow a less favoured pathway with unprotonated TCP as reactant. Surprisingly, for the D383E variant, the K(b) versus pH behaviour is qualitatively similar to that of D383N, supporting a reaction pathway involving unprotonated TCP. The TCP binding data are consistent with substrate binding data for the wild type and the D383E variant using steady-state kinetics. The results provide strong support for a protonated amine being the preferred substrate for the wild-type enzyme, and emphasize the importance of the active-site base, Asp-383, in the primary binding event.
Shepard, E. M., J. Smith, et al. (2002). "Towards the development of selective amine oxidase inhibitors. Mechanism-based inhibition of six copper containing amine oxidases." Eur J Biochem 269(15): 3645-58.
Four substrate analogs, 4-(2-naphthyloxy)-2-butyn-1-amine (1), 1,4-diamino-2-chloro-2-butene (2), 1,6-diamino-2,4-hexadiyne (3), and 2-chloro-5-phthalimidopentylamine (4) have been tested as inhibitors against mammalian, plant, bacterial, and fungal copper-containing amine oxidases: bovine plasma amine oxidase (BPAO), equine plasma amine oxidase (EPAO), pea seedling amine oxidase (PSAO), Arthrobacter globiformis amine oxidase (AGAO), Escherichia coli amine oxidase (ECAO), and Pichia pastoris lysyl oxidase (PPLO). Reactions of 1,4-diamino-2-butyne with selected amine oxidases were also examined. Each substrate analog contains a functional group that chemical precedent suggests could produce mechanism-based inactivation. Striking differences in selectivity and rates of inactivation were observed. For example, between two closely related plasma enzymes, BPAO is more sensitive than EPAO to 1 and 3, while the reverse is true for 2 and 4. In general, inactivation appears to arise in some cases from TPQ cofactor modification and in other cases from alkylation of protein residues in a manner that blocks access of substrate to the active site. Notably, 1 completely inhibits AGAO at stoichiometric concentrations and is not a substrate, but is an excellent substrate of PSAO and inhibition is observed only at very high concentrations. Structural models of 1 in Schiff base linkage to the TPQ cofactor in AGAO and PSAO (for which crystal structures are available) reveal substantial differences in the degree of interaction of bound 1 with side-chain residues, consistent with the widely divergent activities. Collectively, these results suggest that the development of highly selective amine oxidase inhibitors is feasible.
Siraki, A. G. and P. J. O'Brien (2002). "Prooxidant activity of free radicals derived from phenol-containing neurotransmitters." Toxicology 177(1): 81-90.
It has been suggested that biogenic amines may partake in neurodegenerative disease processes by causing oxidative stress. In the following, we present evidence showing for the first time that biogenic amines can form prooxidant radicals when metabolized. The order of prooxidant activity of neurotransmitter phenols or hydroxyindoles in catalyzing beta-nicontinamide adenine dinucleotide (reduced) (NADH) or cysteine cooxidation found when metabolically activated by peroxidase/H(2)O(2) was tyramine>N-acetyltyrosine>tyrosine>serotonin>N-acetylserotonin, 5-hydroxyindoleacetic acid (5-HIAA). This order likely reflects the reactivity of the phenoxyl radicals (for phenols) as extensive oxygen activation accompanied the NADH oxidation and only catalytic amounts of H(2)O(2) were required. The low reactivity of the hydroxyindoles suggests that the redox potential of the radical (semiquinone-imine radical?) was too low to oxidize NADH and/or that the radical dimerization rate was too rapid. The order of catalytic effectiveness for phenolic or hydroxyindole neurotransmitters in catalyzing ascorbate cooxidation on the otherhand, was N-acetylserotonin>serotonin>5-HIAA>>tyramine>N-acetyltyrosine>tyrosine. The first formed hydroxyindole radical product was likely the active cooxidizing species formed from hydroxyindoles. The order for catecholamine catalytic effectiveness in catalyzing NADH or ascorbate cooxidation rate was N-acetyldopamine>3,4-dihydroxyphenylacetic acid (DOPAC)>dopamine>norepinephrine>(-)-3,4-dihydroxyphenylalanine (L-DOPA)>epinephrine which correlated with the second-order rate constant for the peroxidase/H(2)O(2) catalyzed oxidation of the catecholamines. However, the total amount of NADH oxidized was proportional to the amount of H(2)O(2) added and was not accompanied by oxygen uptake, suggesting that NADH was oxidized by the o-quinone metabolite formed by semiquinone radical disproportionation. These results show that biogenic amines form prooxidant radicals, when metabolized by peroxidase, cooxidize cellular antioxidants (ascorbate, NADH, or cysteine).
Slepneva, I. A., D. A. Komarov, et al. (2003). "Influence of fungal infection on the DOPA-semiquinone and DOPA-quinone production in haemolymph of Galleriamellonella larvae." Biochem Biophys Res Commun 300(1): 188-91.
The formation of reactive oxygen metabolites in haemolymph of Galleria mellonella larvae was studied by ESR spectroscopy. The inhibition of the production of the reactive oxygen metabolites of DOPA in haemolymph under the action of fungal infection was shown using spin trap 1-hydroxy-3-carboxy-pyrrolidine. This inhibition correlated with decrease of phenoloxidase activity in haemolymph of infected insects. Simultaneously, the decrease of production of DOPA-semiquinone was detected using method of spin stabilization by diamagnetic metal ions. Moreover, it was shown that the formation of DOPA-quinone was slowed down in haemolymph of infected insects. Our results suggest that the DOPA-derived quinones/semiquinones may be involved in immune response of insects as part of its defense mechanism.
Teismann, P., K. Tieu, et al. (2003). "Cyclooxygenase-2 is instrumental in Parkinson's disease neurodegeneration." Proc Natl Acad Sci U S A 100(9): 5473-8.
Parkinson's disease (PD) is a neurodegenerative disorder of uncertain pathogenesis characterized by the loss of the nigrostriatal dopaminergic neurons, which can be modeled by the neurotoxin 1-methyl-4-phenyl-1,2,3,6-tetrahydropyridine (MPTP). Increased expression of cyclooxygenase type 2 (COX-2) and production of prostaglandin E(2) have been implicated in neurodegeneration in several pathological settings. Here we show that COX-2, the rate-limiting enzyme in prostaglandin E(2) synthesis, is up-regulated in brain dopaminergic neurons of both PD and MPTP mice. COX-2 induction occurs through a JNKc-Jun-dependent mechanism after MPTP administration. We demonstrate that targeting COX-2 does not protect against MPTP-induced dopaminergic neurodegeneration by mitigating inflammation. Instead, we provide evidence that COX-2 inhibition prevents the formation of the oxidant species dopamine-quinone, which has been implicated in the pathogenesis of PD. This study supports a critical role for COX-2 in both the pathogenesis and selectivity of the PD neurodegenerative process. Because of the safety record of the COX-2 inhibitors, and their ability to penetrate the blood-brain barrier, these drugs may be therapies for PD.