Abstract

Treatment of human neuroblastoma SH-SY5Y cells with 1 mm1-methyl-4-phenylpyridinium (MPP⁺) for 3 days induced production of reactive oxygen species (ROS), followed by caspase-3 activation, cleavage of poly(ADP-ribose) polymerase (PARP), and apoptotic cell death with DNA fragmentation and characteristic morphological changes (condensed chromatin and fragmented nuclei). Simultaneous treatment with 1 mm talipexole slightly inhibited the MPP⁺-induced ROS production and apoptotic cell death. In contrast, pretreatment with 1 mm talipexole for 4 days markedly protected the cells against MPP⁺-induced apoptosis. However, this protective effect might not be mediated by dopamine receptors. The talipexole pretreatment induced an increase in antiapoptotic Bcl-2 protein level but had no effect on levels of proapoptotic Bax, Bak, and Bad. It also inhibited MPP⁺-induced ROS production, p53 expression, and cleavages of caspase-3 and PARP. Similarly, pramipexole pretreatment increased Bcl-2 and inhibited MPP⁺-induced apoptosis. Although pretreatment with bromocriptine also had a protective effect against MPP⁺-induced apoptosis, it had no effect on the protein levels of Bcl-2 family members. On the other hand,N ⁶,2′-O-dibutyryl cAMP or calphostin C induced a decreased Bcl-2 level and enhanced MPP⁺-induced cell death. These results suggest that talipexole has dual actions: (1) it directly scavenges ROS, affording slight protection against MPP⁺-induced apoptosis, and (2) it induces Bcl-2 expression, thereby affording more potent protection, if it is administrated before MPP⁺. Pramipexole has similar effects, whereas bromocriptine seems to exhibit the former but not the latter effect.