NAD(P)H
quinone oxidoreductase 1 (NQO1) can metabolize
dopamine-derived
quinones (
DAQ) and absence of NQO1 due to the NQO1*2 polymorphism has been suggested to be a risk factor for
Parkinson's disease. In order to define whether NQO1 plays a protective role in
dopamine toxicity, we have examined the potential role of NQO1 in the SK-N-MC human
neuroblastoma cell line. SK-N-MC cells were stably transfected with NQO1 to generate stable clones with NQO1 enzymatic activity of 245 nmol/mgmin while vector control and parental cells had NQO1 activities of less than 12 nmol/mgmin. Incubation of
dopamine for 24 h in both parental and vector control SK-N-MC cells resulted in 85% and 72% cell death as assessed by
annexin-V/
propidium iodide analysis. In agreement, 88% and 84% of parental and vector control cells, respectively underwent loss of mitochondrial membrane potential (
MMP) assessed by
tetramethylrhodamine ethyl
ester. In contrast, NQO1-transfected cells were resistant to
dopamine toxicity and both cell death and loss of
MMP were markedly abrogated in NQO1-transfected SK-N-MC cells. When
dopamine was added to medium,
oxygen uptake could be detected indicating autoxidation with concomitant formation of
oxygen radicals and
quinones. However,
dopamine-induced cell death was not affected by the inclusion of either
superoxide dismutase or
catalase suggesting that
superoxide and
hydrogen peroxide were not involved in toxicity.
Quinones formed in medium may exert toxicity extracellularly or intracellularly but the protective role of NQO1 argues for an intracellular mechanism. In summary, transfection of SK-N-MC cells with NQO1 protects against
dopamine-induced toxicity.