Dialkyldithiocarbamates inhibit tyrosine hydroxylase activity in PC12 cells and in fibroblasts that express tyrosine hydroxylase

Abstract

Dithiocarbamates and CS₂ have been associated with neurobehavioural changes suggestive of central dopaminergic dysfunction. Diethyldithiocarbamate (DEDC), dimethyldithiocarbamate (DMDC), and methyldithiocarbamate (MDC) were examined for their ability to inhibit tyrosine hydroxylase (TH) activity in PC12 cells and transfected CHO fibroblasts that expressed TH ($\text{CHO}\text{TH}$) activity when tetrahydrobiopterin (BH₄) was added to medium. DEDC or DMDC did not significantly alter viability of PC12 cells or $\text{CHO}\text{TH}$ cells at ≤100 μM for 18 h; the EC50 for each compound was approximately 5 mM in both cell lines. In contrast, the EC50 for MDC was 41 or 74 μM in PC12 or $\text{CHO}\text{TH}$ cultures, respectively. There was no change in immunodetectable levels of TH in PC12 or $\text{CHO}\text{TH}$ cells following exposure to subcytotoxic concentrations of dithiocarbamates. DEDC and DMDC (5 to 100 μM) produced concentration-dependent reductions in PC12 cell dopamine and dopac levels as well as in dopa levels in $\text{CHO}\text{TH}$ cultures. Reduction of PC12 catechols was not due to altered vesicular storage. In vitro PC12 TH activity was 80.2 ± 3.4% or 82.4 ± 2.9% of control following exposure to 100 μM DEDC or DMDC, respectively, and was not fully restored by incubation with Fe²⁺. These results show that DEDC and DMDC, but not MDC, are low potency cytotoxins that decrease TH activity in cultured cells through mechanisms other than inhibition of BH₄ biosynthesis or iron chelation.