Modification of tyrosine hydroxylase activity by chloral derived beta-carbolines in vitro

Beta-carbolines have been suggested to be involved in the pathogenesis of Parkinson's disease as a result of their structural similarity to the neurotoxin N -methyl-4-phenyl-1,2,3,6-tetrahydropyridine (MPTP). The chloral-derived beta-carboline derivative 1-trichloromethyl-1,2,3,4-tetrahydro-beta-carboline (TaClo) causes cell loss in neuronal and glial cell cultures and induces a slowly developing neurodegenerative process in rats. In our experiments, effects of TaClo and its derivatives 2-methyl-TaClo (2-Me-TaClo), and 1-dichloromethylene-1,2,3,4-tetrahydro-beta-carboline (1-CCl(2) -THbetaC) on tyrosine hydroxylase (TH) activity were investigated in TH assays using homogenate preparations of the rat nucleus accumbens and recombinant human TH (hTH1). TH activity was determined in vitro by measuring l-DOPA production with HPLC-ECD. Using homogenate preparations, TaClo, 2-Me-TaClo, and 1-CCl(2) -THbetaC inhibited TH in concentrations of 0.1 mm, while 1-CCl(2) -THbetaC in low concentrations enhanced TH activity. When TH was activated by PACAP-27, TaClo, 2-Me-TaClo, or 1-CCl(2) -THbetaC also inhibited activated enzyme activity in high concentrations. However, in the case of 2-Me-TaClo and 1-CCl(2) -THbetaC a biphasic effect was observed with a marked increase of TH activity in the nanomolar range. In our experiments using recombinant hTH1, TaClo, 2-Me-TaClo, or 1-CCl(2) -THbetaC did not modify enzyme activity. After activation of hTH1 by PKA all the tetrahydro-beta-carbolines investigated in this study decreased l-DOPA formation. We suggest that these beta-carbolines modulate dopamine synthesis by interacting with a protein kinase TH-activating system.