Enantio-selective inhibition of (1R,9S)- and (1S,9R)-beta-hydrastines on dopamine biosynthesis in PC12 cells.

The inhibitory effects of (1R,9S)- and (1S,9R)-enantiomers of beta-hydrastine (BHS) on dopamine biosynthesis in PC12 cells were investigated. (1R,9S)-BHS decreased the intracellular dopamine content with the IC50 value of 14.3 microM at 24 h, but (1S,9R)-BHS did not. (1R,9S)-BHS was not cytotoxic at concentrations up to 250 microM towards PC12 cells. In these conditions, (1R,9S)-BHS inhibited tyrosine hydroxylase (TH) activity mainly in a concentration-dependent manner (33% inhibition at 20 microM) and decreased TH mRNA level in PC12 cells. The inhibitory patterns of dopamine content and TH activity by (1R,9S)-BHS showed similar behavioral curves. (1R,9S)-BHS at 10-50 microM also reduced the intracellular cyclic AMP level and Ca2+ concentration. In addition, treatment of L-DOPA at 20-50 microM for 24 h increased the intracellular dopamine content to 198-251% compared with the control in PC12 cells. However, the increase in dopamine levels induced by L-DOPA (20-50 microM) was reduced when L-DOPA was combined with (1R,9S)-BHS (10-50 microM). These results indicate that (1R,9S)-BHS, but not (1S,9R)-BHS, reduced dopamine content and L-DOPA-induced increase in dopamine content, in part, through the inhibition of TH activity and TH gene expression in PC12 cells: thus, (1R,9S)-BHS proved to have a function to regulate dopamine biosynthesis.