Effects of asimilobine on dopamine biosynthesis and l-DOPA-induced cytotoxicity in PC12 cells

Abstract

The effects of asimilobine, an aporphine isoquinoline alkaloid, on dopamine biosynthesis and l-DOPA-induced cytotoxicity in PC12 cells were investigated. Asimilobine at concentration ranges of 0.05–0.2 μM showed a significant inhibition of intracellular dopamine levels for 24 h in a concentration-dependent manner with an IC₅₀ value of 0.13 μM. Asimilobine at 0.15 μM inhibited tyrosine hydroxylase (TH) and aromatic l-amino acid decarboxylase (AADC) activities at 24 h (73.2% inhibition of TH activity): the inhibition of TH activity was stronger and longer than that of AADC activity. Asimilobine also decreased TH mRNA levels and intracellular cyclic AMP levels, but not the basal Ca^2 +  concentrations. In addition, asimilobine at 0.05–5.0 μM, but not 10 μM, did not alter cell viability toward PC12 cells. A non-cytotoxic asimilobine (0.15 μM) associated with l-DOPA (20, 50, and 100 μM) for 24 h inhibited l-DOPA-induced increases in dopamine levels and enhanced l-DOPA-induced cell death when compared with l-DOPA alone. These results suggest that asimilobine inhibits dopamine biosynthesis by mainly reducing the TH activity and TH mRNA expression, and enhances l-DOPA-induced cytotoxicity in PC12 cells.

Keywords:

• asimilobine
• dopamine biosynthesis
• tyrosine hydroxylase
• l-DOPA-induced cytotoxicity
• PC12 cells

Acknowledgements

This work was supported by the Korean Research Foundation Grant funded by the Korean Government (MOEHRD) (The Regional Research Universities Program/Chungbuk BIT Research-Oriented University Consortium) (2007) and the financial support by the Program of Research Center for Bioresource and Health, MOPS and ITEP (2007).