Involvement of dopamine D2/D3 receptors and BDNF in the neuroprotective effects of S32504 and pramipexole against 1-methyl-4-phenylpyridinium in terminally differentiated SH-SY5Y cells

Anti-parkinsonian agents possessing both D-2 and D-3 receptor agonist properties are neuroprotective against 1-methyl-4-phenylpyridinium (MPP+) toxicity in a variety of in vitro models. The mechanisms underlying protection by these D-2/D-3 receptor agonists remain poorly defined. To test if the D-3 receptor preferring agonists S32504 and pramipexole act through D-2 or D-3 receptors and via brain-derived neurotrophic factor (BDNF)-dependent pathways, we utilized a terminally differentiated neuroblastoma SH-SY5Y cell line exhibiting a dopaminergic phenotype. The cytotoxic effects of MPP+ (LD50 of 100 muM) were stereospecifically antagonized by S32504 (EC50 = 2.0 muM) and, less potently, by pramipexole (EC50 = 64.3 muM), but not by their inactive stereoisomers, R(+) pramipexole and S32601, respectively. Neuroprotective effects afforded by EC50 doses of S32504 and pramipexole were antagonized by the selective D-3 antagonists S33084, U99194A, and SB269652, and by the D-2/D-3 antagonist raclopride. However, the preferential D-2 receptor antagonist LY741626 was ineffective as was the D-1 antagonist SCH23390. BDNF (1 nM) potently protected against MPP+-induced neurotoxicity. Antibody directed against BDNF concentration-dependently blocked both the neuroprotective effects of BDNF and those of pramipexole and S32504 against MPP+. The protection afforded by BDNF was blocked by the P3K-AKT pathway inhibitor LY249002 and less so by the MEK/MAPKK pathway inhibitor PD98059. LY249002, but not PD98059, blocked the neuroprotective effects of pramipexole and S32504 against MPP+ toxicity. In conclusion, S32504 and, less potently, pramipexole show robust, stereospecific, and long-lasting neuroprotective effects against MPP+ toxicity that involve D-3 receptors. Their actions also reflect downstream recruitment of BDNF and via a PK3-AKT pathway. (C) 2004 Elsevier Inc. All rights reserved.