Increased oxidative stress in dopaminergic neurons has been implicated as a causative factor in Parkinson's disease (PD). The catechols DOPA dopamine and DOPAC generated in these cells can undergo oxidation to produce aggressive oxygen species and reactive arylating quinones which are capable of cellular damage. We have characterized a null polymorphism in the NQO1 gene (NQO1 *2) and individuals carrying the variant NQO1 *2 allele have been found to be at a markedly increased risk of PD relative to control individuals emphasizing the role of NQO1 as a risk factor for PD. PD has also been associated with inhibition of the ubiquitin-proteasomal system (UPS). Inhibition of the UPS by aggregated proteins in neurodegenerative disease leads to increased oxidative stress. Since oxidative stress can result in the misfolding and aggregation of proteins resulting in further frustration of the UPS, a picture is beginning to emerge where both oxidative stress and UPS inhibition are part of a vicious cycle and are important factors in the etiology of PD.In this proposal, we will test the following hypotheses; 1) that NQO1 protects cells against reactive arylating quinones and oxidizing species generated during metabolism of DOPA, dopamine and DOPAC. We will use dopaminergic cells, mechanism based inhibitors of NQO1 and an isogenic cellular model developed in our lab to explore the role of NQOl in these studies; 2) that DOPA, dopamine or DOPAC derived o-quinones contribute to UPS inhibition and that NQO1 protects against this inhibitory effect; 3) that NQO1 protects against oxidative stress generated as a result of inhibition of the UPS. UPS inhibition in cells will be achieved by the use of both chemical proteasome inhibitors and by transfection of mutant forms of alpha-synuclein which have been associated with PD and inhibit the UPS by mechanisms involving protein aggregation and 4) that mutant NQO1*2 protein, which is normally rapidly degraded by the UPS, generates oxygen radicals leading to increased oxidative stress. The ability of mutant NQO1 *2 protein to generate oxygen radicals becomes particularly important under conditions where the UPS is inhibited and the protein accumulates.

Agency
National Institute of Health (NIH)
Institute
National Institute of Neurological Disorders and Stroke (NINDS)
Type
Research Project (R01)
Project #
1R01NS044613-01
Application #
6533442
Study Section
Alcohol and Toxicology Subcommittee 4 (ALTX)
Program Officer
Sheehy, Paul A
Project Start
2002-07-01
Project End
2007-06-30
Budget Start
2002-07-01
Budget End
2003-06-30
Support Year
1
Fiscal Year
2002
Total Cost
$344,090
Indirect Cost
Name
University of Colorado Denver
Department
Pharmacology
Type
Schools of Pharmacy
DUNS #
065391526
City
Aurora
State
CO
Country
United States
Zip Code
80045
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Zafar, Khan Shoeb; Siegel, David; Ross, David (2006) A potential role for cyclized quinones derived from dopamine, DOPA, and 3,4-dihydroxyphenylacetic acid in proteasomal inhibition. Mol Pharmacol 70:1079-86
Zafar, K S; Inayat-Hussain, S H; Siegel, D et al. (2006) Overexpression of NQO1 protects human SK-N-MC neuroblastoma cells against dopamine-induced cell death. Toxicol Lett 166:261-7
Ross, David (2004) Quinone reductases multitasking in the metabolic world. Drug Metab Rev 36:639-54
Siegel, David; Gustafson, Daniel L; Dehn, Donna L et al. (2004) NAD(P)H:quinone oxidoreductase 1: role as a superoxide scavenger. Mol Pharmacol 65:1238-47
Ross, David; Siegel, David (2004) NAD(P)H:quinone oxidoreductase 1 (NQO1, DT-diaphorase), functions and pharmacogenetics. Methods Enzymol 382:115-44