Dopamine Catabolism and Parkinson's Disease: Role of a Reactive Aldehyde Intermediate

Doorn, Jonathan A.

doi:10.1002/9783527628100.ch29

Endogenous Toxins 2009

DOI: 10.1002/9783527628100.ch29

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Dopamine Catabolism and Parkinson's Disease: Role of a Reactive Aldehyde Intermediate

Jonathan A. Doorn

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“…This can be explained by the K m value of each enzyme; ALDH has a K m for DOPAL of low micromolar to high nanomolar concentrations, while the K m of AKR for DOPAL is between 10-30 μM(82)(83)(84). These results indicate that as DOPAL concentration increases, ALDH would become overwhelmed, and AKR would compensate to help decrease levels of this reactive intermediate.…”

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Covalent modification and inhibition of tyrosine hydroxylase by 3,4-dihydroxyphenylacetaldehyde, an endogenously produced neurotoxin relevant to Parkinson's disease

Vermeer¹

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Parkinson's disease (PD) is a prevalent neurodegenerative disorder which affects over a million people in the United States. This disease is marked by the selective loss of dopaminergic neurons in the substantia nigra, leading to a decrease in the important neurotransmitter dopamine (DA), which is essential for the initiation and execution of coordinated movement. Currently, the exact pathogenesis behind PD is unknown, but there is evidence that both exogenous causes, such as pesticides and metals, as well as endogenous causes, such as reactive oxygen species or reactive metabolism intermediates, may play a role in the onset and progression of the disease. DA is catabolized by monoamine oxidase to 3,4-dihydroxyphenylacetaldehyde (DOPAL), which is further metabolized by aldehyde dehydrogenase and aldehyde reductase to the acid and alcohol products, respectively. Studies have demonstrated the reactivity of DOPAL with peptides and proteins, leading to covalent modification which may be detrimental to protein action. Furthermore, studies have shown that DOPAL is toxic, leading to a decrease in cell viability. Due to this, it was of interest to further study DOPAL and how it may play a role in the onset and progression of PD.It was of particular interest to determine protein targets of DOPAL modification.Until recently, no protein targets were identified and the cellular consequence of elevated DOPAL had not been fully studied. It has been previously shown that the important enzyme, tyrosine hydroxylase (TH) is inhibited by other catechols, including DA. This enzyme catalyzes the rate-limiting step in DA synthesis, oxidizing tyrosine to L-DOPA which is further metabolized to DA. Therefore, it was of interest to determine the effect of DOPAL on TH activity. It was hypothesized that DOPAL modifies and inhibits TH, leading to a decrease in the production of L-DOPA and DA. This work employed the use of a dopaminergic cell model (PC6-3 cells), to positively identify TH as a protein target of DOPAL modification. It also used both cell lysate as well as PC6-3 cell studies to investigate the effect of DOPAL modification on TH activity. Mass spectrometry was also utilized to determine sites of protein modification on TH.Results show that TH is potently inhibited by DOPAL modification, leading to a significant decrease in both L-DOPA and DA. Furthermore, DOPAL inhibition appears to be slowly-irreversible, with enzyme activity showing a time-and concentration-dependent recovery after preincubation with DOPAL. A novel cloning and purification procedure was used to obtain human recombinant TH, which was used in mass spectrometry studies in which five sites of DOPAL modification were discovered. Furthermore, a real-time assay for TH activity was developed using a plate reader to spectrophotometrically observe the formation of L-DOPA over time. These data demonstrate the toxicity and potent enzyme inhibition by DOPAL and implicate DOPAL as a neurotoxin relevant in the pathogenesis of PD. Abstract Approved __________________________ ...

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Covalent modification and inhibition of tyrosine hydroxylase by 3,4-dihydroxyphenylacetaldehyde, an endogenously produced neurotoxin relevant to Parkinson's disease

Vermeer¹

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Dopamine Catabolism and Parkinson's Disease: Role of a Reactive Aldehyde Intermediate

Cited by 1 publication

References 71 publications

Covalent modification and inhibition of tyrosine hydroxylase by 3,4-dihydroxyphenylacetaldehyde, an endogenously produced neurotoxin relevant to Parkinson's disease

Covalent modification and inhibition of tyrosine hydroxylase by 3,4-dihydroxyphenylacetaldehyde, an endogenously produced neurotoxin relevant to Parkinson's disease

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