NF-E2-related factor-2 (Nrf2), a
basic leucine zipper transcription factor, is involved in the expression of numerous detoxifying and
antioxidant genes via the antioxidant response element (ARE).
Apomorphine (
Apo), a dopamine D(1)/D(2) receptor agonist, is used for clinical
therapy of
Parkinson's disease. On the other hand, Apo is a potent radical scavenger and has protective effects on oxidative stress-induced cell death. Previously, we have reported that pretreatment of human
neuroblastoma SH-SY5Y cells with Apo enhances protection against
6-hydroxydopamine (6-OHDA)-induced cell death. In this study, we investigated whether the Nrf2-ARE system is involved in the protection by Apo. Pretreatment of SH-SY5Y cells with Apo suppressed 6-OHDA-induced cell death in a dose-dependent manner. However, neither
SCH23390, a
dopamine D(1) receptor antagonist, nor
sulpiride, a
dopamine D(2) receptor antagonist, prevented the protective effect of Apo. Apo stimulated the translocation of Nrf2 into the nucleus and the transactivation of the ARE. The expression of
heme oxygenase-1 (HO-1) was dose dependently induced by Apo. Moreover, we found that the activation of the ARE and the induction of HO-1
mRNA caused by Apo were suppressed in the presence of the
antioxidant N-acetylcysteine and also that Apo produced intracellular
reactive oxygen species (ROS), indicating that the low level of ROS produced by Apo may play a critical role in this phenomenon. Taken together, our findings suggest that not only the function as a radical scavenger but also the function as an Nrf2-ARE pathway activator may be involved in the
neuroprotective effects of Apo.