Dopamine toxicity in neuroblastoma cells: role of glutathione depletion byL-BSO and apoptosis

Dopamine (DA), while an essential neurotransmitter, is also a known neuroto xin that potentially plays an etiologic role in several neurodegenerative d iseases. DA metabolism and oxidation readily produce reactive oxygen specie s (ROS) and DA can also be oxidized to a reactive quinone via spontaneous, enzyme-catalyzed or metal-enhanced reactions. A number of these reactions a re cytotoxic, yet the precise mechanisms by which DA leads to cell death re main unknown. In this study, the neuroblastoma cell line, SK-N-SH, was util ized to examine DA toxicity under varying oxidant states. Cells pretreated with the glutathione (GSH)-depleting compound, L-buthionine sulfoximine (L- BSO), exhibited enhanced sensitivity to DA compared to controls (non-GSH-de pleted cells). Furthermore, in cells pretreated with L-BSO, the addition of ascorbate (250 mu M) afforded significant protection against DA-induced to xicity, while pyruvate (500 mu M) had no protective effect. To further char acterize the possibility that DA is associated with oxidative stress, addit ional studies were carried out with manganese (30 mu M) as a pro-oxidant. M anganese and DA (200 mu M); although not cytotoxic when individually admini stered to SK-N-SH cells, had a synergistic action on cytotoxicity. Finally, morphological and molecular markers of programmed cell death (apoptosis) w ere observed in cells treated with DA and L-BSO. These markers included mem brane blebbing and internucleosomal DNA fragmentation. These results sugges t that DA toxicity is tightly linked to intracellular oxidant/antioxidant l evels, and that environmental factors, such as excessive Mn exposure, may m odulate cellular sensitivity to DA. (C) 2000 Published by Elsevier Science B.V. All rights reserved.