Sal synthase induced cytotoxicity of PC12 cells through production of the dopamine metabolites salsolinol and N-methyl-salsolinol.

As a catechol isoquinoline, salsolinol (Sal) is widely distributed in mammalian brains, and is increased in the cerebrospinal fluid (CSF) and urine of Parkinsonian patients. Sal can be metabolized to N-methyl-salsolinol (NM-Sal), an MPP+-like neurotoxin, and impairs the function of dopaminergic neurons, causing the clinical symptoms of Parkinson's disease (PD). Sal synthase, which catalyzes the production of Sal from dopamine and acetaldehyde, may be the important enzyme in the metabolism of catechol isoquinolines (CTIQs). Previously, our work demonstrated the existence of Sal synthase in rat brain and identified its amino acid sequence. However, the biological function of Sal synthase has not been thoroughly explored, especially its role in dopaminergic neuronal degeneration. In this study, we tried to clarify the catalytic role of Sal synthase in the formation of CTIQs which are endogenous neurotoxins in the mammalian brain. Furthermore, the cytotoxicity of Sal synthase was also observed in dopaminergic PC12 cells. The results demonstrated that Sal synthase overexpression can increase the level of Sal and NM-Sal, and ultimately cause mitochondria damage and apoptosis.