Study of the neurotransmitter dopamine and the neurotoxin 6-hydroxydopamine by electrospray ionization coupled with tandem mass spectrometry

Selective C–C and C–N bond activation in dopamine and norepinephrine under deep ultraviolet laser irradiation

Selective C–C bond and C–N bond activation in dopamine and norepinephrine is analyzed utilizing deep-ultraviolet laser ionization mass spectrometry (DUV-LIMS).

Levodopa activates apoptosis signaling kinase 1 (ASK1) and promotes apoptosis in a neuronal model: implications for the treatment of Parkinson's disease

Oxidative stress is implicated in the etiology of Parkinson's disease (PD), the second most common neurodegenerative disease. PD is treated with chronic administration of l-3,4-dihydroxyphenylalanine (levodopa, L-DOPA), and typically, increasing doses are used during progression of the disease. Paradoxically, L-DOPA is a pro-oxidant and induces cell death in cellular models of PD through disruption of sulfhydryl homeostasis involving loss of the thiol-disulfide oxidoreductase functions of the glutaredoxin (Grx1) and thioredoxin (Trx1) enzyme systems [Sabens, E. A., Distler, A. M., and Mieyal, J. J. (2010) Biochemistry 49 (12), 2715-2724]. Considering this loss of both Grx1 and Trx1 activities upon L-DOPA treatment, we sought to elucidate the mechanism(s) of L-DOPA-induced apoptosis. In other contexts, both the NFκB (nuclear factor κB) pathway and the ASK1 (apoptosis signaling kinase 1) pathway have been shown to be regulated by both Grx1 and Trx1, and both pathways have been implicated in cell death signaling in model systems of PD. Moreover, mixed lineage kinase (MLK) has been considered as a potential therapeutic target for PD. Using SHSY5Y cells as model dopaminergic neurons, we found that NFκB activity was not altered by L-DOPA treatment, and the selective MLK inhibitor (CEP-1347) did not protect the cells from L-DOPA. In contrast, ASK1 was activated with L-DOPA treatment as indicated by phosphorylation of its downstream mitogen-activated protein kinases (MAPK), p38 and JNK. Chemical inhibition of either p38 or JNK provided protection from L-DOPA-induced apoptosis. Moreover, direct knockdown of ASK1 protected from L-DOPA-induced neuronal cell death. These results identify ASK1 as the main pro-apoptotic pathway activated in response to L-DOPA treatment, implicating it as a potential target for adjunct therapy in PD.

Clinical outcomes in Menkes disease patients with a copper-responsive ATP7A mutation, G727R

Menkes disease is a fatal neurodegenerative disorder of infancy caused by defects in an X-linked copper transport gene, ATP7A. Evidence from a recent clinical trial indicates that favorable response to early treatment of this disorder with copper injections involves mutations that retain some copper transport capacity. In three unrelated infants, we identified the same mutation, G727R, in the second transmembrane segment of ATP7A that complemented a Saccharomyces cerevisiae copper transport mutant, consistent with partial copper transport activity. Quantitative reverse transcription-polymerase chain reaction studies showed approximately normal levels of ATP7A(G727R) transcript in two patients' fibroblasts compared to wild-type controls, but Western blot analyses showed markedly reduced quantities of ATP7A, suggesting post-translational degradation. We confirmed the latter by comparing degradation rates of mutant and wild-type ATP7A via cyclohexamide treatment of cultured fibroblasts; half-life of the G727R mutant was 2.9h and for the wild-type, 11.4h. We also documented a X-box binding protein 1 splice variant in G727R cells-known to be associated with the cellular misfolded protein response. Patient A, diagnosed 6 months of age, began treatment at 228days (7.6 months) of age. At his current age (2.5 years), his overall neurodevelopment remains at a 2- to 4-month level. In contrast, patient B and patient C were diagnosed in the neonatal period, began treatment within 25 days of age, and show near normal neurodevelopment at their current ages, 3years (patient B), and 7 months (patient C). The poor clinical outcome in patient A with the same missense mutation as patient A and patient B with near normal oucomes, confirms the importance of early medical intervention in Menkes disease and highlights the critical potential benefit of newborn screening for this disorder.

Neonatal diagnosis and treatment of Menkes disease

BACKGROUND

Menkes disease is a fatal neurodegenerative disorder of infancy caused by diverse mutations in a copper-transport gene, ATP7A. Early treatment with copper injections may prevent death and illness, but presymptomatic detection is hindered by the inadequate sensitivity and specificity of diagnostic tests. Exploiting the deficiency of a copper enzyme, dopamine-beta-hydroxylase, we prospectively evaluated the diagnostic usefulness of plasma neurochemical levels, assessed the clinical effect of early detection, and investigated the molecular bases for treatment outcomes.

METHODS

Between May 1997 and July 2005, we measured plasma dopamine, norepinephrine, dihydroxyphenylacetic acid, and dihydroxyphenylglycol in 81 infants at risk. In 12 newborns who met the eligibility criteria and began copper-replacement therapy within 22 days after birth, we tracked survival and neurodevelopment longitudinally for 1.5 to 8 years. We characterized ATP7A mutations using yeast complementation, reverse-transcriptase-polymerase-chain-reaction analysis, and immunohistochemical analysis.

RESULTS

Of 81 infants at risk, 46 had abnormal neurochemical findings indicating low dopamine-beta-hydroxylase activity. On the basis of longitudinal follow-up, patients were classified as affected or unaffected by Menkes disease, and the neurochemical profiles were shown to have high sensitivity and specificity for detecting disease. Among 12 newborns with positive screening tests who were treated early with copper, survival at a median follow-up of 4.6 years was 92%, as compared with 13% at a median follow-up of 1.8 years for a historical control group of 15 late-diagnosis and late-treatment patients. Two of the 12 patients had normal neurodevelopment and brain myelination; 1 of these patients had a mutation that complemented a Saccharomyces cerevisiae copper-transport mutation, indicating partial ATPase activity, and the other had a mutation that allowed some correct ATP7A splicing.

CONCLUSIONS

Neonatal diagnosis of Menkes disease by plasma neurochemical measurements and early treatment with copper may improve clinical outcomes. Affected newborns who have mutations that do not completely abrogate ATP7A function may be especially responsive to early copper treatment. (ClinicalTrials.gov number, NCT00001262.)

Decomposition of protonated noradrenaline and normetanephrine assisted by NH2 migration studied by electrospray tandem mass spectrometry and molecular orbital calculations

As part of a research program on neurotransmitters in a biological fluid, the fragmentations characterising catecholamines protonated under electrospray ionisation (ESI) conditions, under low collision energy in a triple-quadrupole mass spectrometer, were investigated. The decompositions of protonated noradrenaline (VH) and normetanephrine (VIH) were studied. Both precursor ions eliminate first H2O at very low collision energy, and the fragmentations of [MH-H2O]+ occur at higher collision energy. The breakdown graphs of [MH-H2O]+ ions, with collision energy varying from 0-40 eV in the laboratory frame, are presented. [VIH-H2O]+ ions lose competitively NH3 and CH3OH. For [VH-H2O]+ the loss of NH3 is dominant while H2O is eliminated at very low abundance at all collision energies. All of these secondary fragmentations are followed at higher collision energies by elimination of CO. These fragmentations are interpreted by means of ab initio calculations up to the B3LYP/6-311+G(2d,2p) level of theory. The elimination of H2O requires first the isomerisation of N-protonated forms, chosen as energy references, to O-protonated forms. The isomerisation barriers are calculated to be lower than 81 kJ/mol above the N-protonated forms. The elimination of NH3 from [MH-H2O]+ requires first the migration, via a cyclisation, of the amine function from the linear chain to the aromatic ring in order to prevent the formation of unstable disubstituted carbocations in the ring. The barriers associated with the loss of NH3 are located 220 and 233 kJ/mol above VH and 219 kJ/mol above VIH. The energy barrier for the loss of ROH is located 236 and 228 kJ/mol above VH and VIH, respectively. The absence of ions corresponding to [VH-2H2O]+ is due to a parasitic mechanism with an activation barrier lower than 236 kJ/mol that leads to a stable species unable to fragment, thus preventing the second loss of H2O. Losses of CO following the secondary fragmentations involve activation barriers higher than 330 kJ/mol.

Fragmentation mechanisms of protonated benzylamines. Electrospray ionisation-tandem mass spectrometry study and ab initio molecular orbital calculations

Our research into neurotransmitters in a biological fluid presented an opportunity to investigate the fragmentations under low collision energy characterising benzyl-amines protonated under electrospray ionisation (ESI) conditions in a triple quadrupole mass spectrometer. In this work we present the breakdown graphs of protonated 3,4-dihydroxybenzylamine, DHBAH(+), and 3-methoxy, 4-hydroxybenzylamine, HMBAH(+), at various source temperatures and various pressures in the collision cell, the collision energy varying from 0 to 46 eV in the laboratory frame. Both parent ions eliminate first NH(3) at very low collision energy. The fragmentations of [MH - NH(3)](+) occur at high collision energy and are quite different for DHBAH(+) and HMBAH(+): formation of [MH - NH(3) - H(2)O - CO](+) for the former; formation of the radical cation [MH - NH(3) - CH(3)](+.) for the latter. These fragmentations are interpreted by means of ab initio calculations up to the B3LYP/6-311+G(2d,2p) level of theory. The successive losses of H(2)O and CO involve first the rearrangement in two steps of benzylic ions formed by loss of NH(3) into tropylium ions. The transition states associated with this rearrangement are very high in energy (about 400 kJ mol(-1) above MH(+)) explaining (i). the absence of an ion corresponding to [DHBAH - NH(3) - H(2)O](+). The determining steps associated with the losses of H(2)O and with H(2)O + CO are located lower in energy than the transition states associated with the isomerisation of benzylic ions into tropylium ions; explaining (ii). the formation of the radical cation [MH - NH(3) - CH(3)](+.). The homolytic cleavage of CH(3)-O requires less energy than does the rearrangement.