Increased vulnerability of parkin knock down PC12 cells to hydrogen peroxide toxicity: the role of salsolinol and NM-salsolinol.

Abstract Dopamine-derived neurotoxins, 1-methyl-4-phenyl-1,2,3,4-tetrahydroisoquinoline (salsolinol) and 1( R ),2( N )-dimethyl-6,7-dihydroxy-1,2,3,4-tetrahydroisoquinoline ( N M-salsolinol) are the two most possible 1-methyl-4-phenyl-1,2,3,6-tetrahydropyridine (MPTP)-like endogenous neurotoxin candidates that involved in the pathogenesis of Parkinson’s disease (PD). The levels of endogenously synthesized salsolinol and N M-salsolinol are increased in the cerebrospinal fluid (CSF) of PD patients. Both of them lead to neurotoxicity in dopaminergic cells by inhibiting mitochondrial electron transport chain. To study the role of salsolinol and N M-salsolinol in Parkin deficiency-induced dopaminergic cell damage, we determined the cellular level of oxidative stress, the formation of salsolinol and N M-salsolinol, the level of mitochondrial damage and cell viability with/without the presence of exogenous H 2 O 2 using differentiated dopaminergic PC12 cells. Our data show that parkin knock down elevates cellular oxidative stress, salsolinol and N M-salsolinol levels, which are responsible for the higher cell mortality in Parkin-deficient cells upon exposure to exogenous H 2 O 2 . The level of mitochondrial membrane potential loss, cristae disruption and the release of cytochrome c increased significantly along with the increased level of salsolinol and N M-salsolinol, whereas compared to parkin knock down cells in the presence of H 2 O 2 , the mitochondrial damage and higher cell mortality were both diminished when the levels of salsolinol and N M-salsolinol was reduced. The results not only indicate the elevated level of salsolinol and N M-salsolinol, but also reveal the potential role of salsolinol and N M-salsolinol in parkin knock down-induced cell vulnerability. We assume that parkin deficiency is the trigger of excessive oxidative stress, elevated endogenous neurotoxin levels and mitochondrial damage, which eventually results in cell death of dopaminergic cells.