Lipid peroxidation products inhibit dopamine catabolism yielding aberrant levels of a reactive intermediate.
Recent work indicates that oxidative stress is a factor in Parkinson's disease (PD); however, it is unknown how this condition causes selective dopaminergic cell death. The neurotransmitter dopamine (DA) has been implicated as an endogenous neurotoxin to explain the selective neurodegeneration. DA undergoes catabolism by monoamine oxidase (MAO) to the reactive intermediate 3,4-dihydroxyphenylacetaldehyde (DOPAL), which is further oxidized to 3,4-dihydroxyphenylacetic (DOPAC) acid via mitochondrial aldehyde dehydrogenase (ALDH). Previous studies found DOPAL to be more toxic than DA, and the major lipid peroxidation products, that is, 4-hydroxynonenal (4HNE) and malondialdehyde (MDA), potently inhibit ALDH. The hypothesis of this work is that lipid peroxidation products inhibit DOPAL oxidation, yielding aberrant levels of the reactive aldehyde intermediate. Treatment of striatal synaptosomes with 2-100 microM 4HNE or 2-50 microM MDA impaired DOPAL oxidation, resulting in elevated [DOPAL]. The aberrant concentration of DOPAL yielded an increase in protein modification by the DA-derived aldehyde, evident via staining of proteins with nitroblue tetrazolium (NBT). Pretreatment of synaptosomes with an MAO inhibitor significantly decreased NBT staining. On the basis of NBT staining, the order of protein reactivity for DA and metabolites was found to be DOPAL>>DOPAC>DA. Mass spectrometric analysis of a model peptide reacted with DOPAL revealed the adduct to be a Schiff base product. In summary, these data demonstrate the sensitivity of DA catabolism to the lipid peroxidation products 4HNE and MDA even at low, physiologic levels and suggest a mechanistic link between oxidative stress and generation of aberrant levels of an endogenous and protein reactive dopaminergic toxin relevant to PD.
Rees
Jennifer N
JN
Division of Medicinal and Natural Products Chemistry, College of Pharmacy, University of Iowa, Iowa City 52242, USA.
Florang
Virginia R
VR
Anderson
David G
DG
Doorn
Jonathan A
JA
D015102:3,4-Dihydroxyphenylacetic Acid / Q000031:analogs & derivatives* / Q000378:metabolism; D000447:Aldehydes / Q000494:pharmacology*; D000818:Animals; D003342:Corpus Striatum / Q000187:drug effects / Q000378:metabolism; D003432:Cross-Linking Reagents / Q000494:pharmacology*; D004298:Dopamine / Q000378:metabolism*; D004305:Dose-Response Relationship, Drug; D004336:Drug Antagonism; D004791:Enzyme Inhibitors / Q000494:pharmacology; D015227:Lipid Peroxidation; D008315:Malondialdehyde / Q000494:pharmacology*; D018384:Oxidative Stress / Q000187:drug effects / Q000502:physiology; D051381:Rats; D017207:Rats, Sprague-Dawley; D013574:Synaptosomes / Q000187:drug effects / Q000378:metabolism
D000447:Aldehydes; D003432:Cross-Linking Reagents; D004791:Enzyme Inhibitors; D015102:3,4-Dihydroxyphenylacetic Acid; D008315:Malondialdehyde; C007430:3,4-dihydroxyphenylacetaldehyde; C027576:4-hydroxy-2-nonenal; D004298:Dopamine