Differential Toxicity of 6-Hydroxydopamine in SH-SY5Y HumanNeuroblastoma Cells and Rat Brain Mitochondria: ProtectiveRole of Catalase and Superoxide Dismutase

Oxidative stress and mitochondrial dysfunctionare two pathophysiological factors often associated with theneurodegenerative process involved in Parkinson’s disease(PD). Although, 6-hydroxydopamine (6-OHDA) is able tocause dopaminergic neurodegeneration in experimentalmodels of PD by an oxidative stress-mediated process, theunderlying molecular mechanism remains unclear. It hasbeen established that some antioxidant enzymes such ascatalase (CAT) and superoxide dismutase (SOD) are oftenaltered in PD, which suggests a potential role of theseenzymes in the onset and/or development of this multifac-torial syndrome. In this study we have used high-resolutionrespirometry to evaluate the effect of 6-OHDA on mito-chondrial respiration of isolated rat brain mitochondria andthe lactate dehydrogenase cytotoxicity assay to assess thepercentage of cell death induced by 6-OHDA in humanneuroblastoma cell line SH-SY5Y. Our results show that6-OHDA affects mitochondrial respiration by causing areduction in both respiratory control ratio (IC 50 = 200 ± 15 nM)and state 3respiration(IC 50 = 192 ± 17 nM), withnosignificanteffectsonstate4 o .Aninhibitionintheactivityof both complex I and V was also observed. 6-OHDA alsocaused cellular death in human neuroblastoma SH-SY5Ycells (IC 50 = 100 ± 9 l M). Both SOD and CAT have beenshowntoprotectagainstthetoxiceffectscausedby6-OHDAon mitochondrial respiration. However, whereas SOD pro-tects against 6-OHDA-induced cellular death, CAT enhan-ces its cytotoxicity. The here reported data suggest that bothsuperoxideanionandhydroperoxylradicalcouldaccountfor6-OHDA toxicity. Furthermore, factors reducing the rate of 6-OHDA autoxidation to its p -quinone appear to enhance itscytotoxicity.