ACTIVATION OF ENDOGENOUS ANTIOXIDANT DEFENSES IN NEURONAL CELLS PREVENTS FREE RADICAL-MEDIATED DAMAGE

Dopamine (DA) is oxidized to the neurotoxic prooxidant species H2O2, O H., and DA quinones, We tested whether dimethyl fumarate (DMF), an ele ctrophile shown to induce a pleiotropic antioxidant response in nonneu ronal cells, could reduce the toxicity of DA metabolites in neural cel ls. Treatment of the N18-RE-105 neuroblastoma-retina hybridoma cell li ne with 30-150 mu M dopamine led to cell death within 24 h, which incr eased steeply with dose, decreased with higher plating density, and wa s blocked by the H2O2-metabolizing enzyme catalase. Pretreatment with DMF (30 mu M, 24 h) significantly attenuated DA and H2O2 toxicity (40- 60%) but not that caused by the calcium ionophore ionomycin. DMF treat ment also elevated total intracellular GSH and increased activities of the antioxidant enzymes quinone reductase (QR), glutathione S-transfe rase (GST), glutathione reductase, and the pentose phosphate enzyme gl ucose-6-phosphate dehydrogenase. To assess the protective efficacy of QR and GST, a stable cell line was constructed in which these enzymes were overexpressed, Cell death in the overexpressing line was not sign ificantly different from that in a cell line expressing normal QR and GST activities, indicating that these two enzymes alone are insufficie nt for protection against DA toxicity. Although the relative importanc e of a single antioxidant enzyme such as QR or GST may be small, antio xidant inducers such as DMF may prove valuable as agents that elicit a broad-spectrum neuroprotective response.