FIBROBLASTS THAT EXPRESS AROMATIC AMINO-ACID DECARBOXYLASE HAVE INCREASED SENSITIVITY TO THE SYNERGISTIC CYTOTOXICITY OF L-DOPA AND MANGANESE

Manganism, a neurodegenerative disease that can follow chronic exposur e to Mn, has been associated with lesions in the basal ganglia and dep letion of dopamine and its metabolites in this brain region. Herein, w e have tested the hypothesis that oxidation of catechols is a critical component of Mn-induced cytotoxicity. To eliminate confounding metabo lic pathways, a nonneuronal cell line, Chinese hamster ovary (CHO) fib roblasts, was transfected with a cDNA for bovine aromatic amino acid d ecarboxylase, and a high expressing clone was isolated (CHO/AADC). Exp osure of wild-type (CHO/WT) or CHO/ AADC cultures to L-dopa (62 to 500 mu M) resulted in intracellular accumulation of L-dopa or L-dopa and dopamine, respectively, that was concentration-dependent. Intracellula r catechol levels in CHO/AADC cells were double those in CHO/WT cultur es. No dopac was identified intra- or extracellularly. Addition of MnC l2 (125 to 500 mu M) resulted in cytotoxicity that progressed with inc reasing concentrations of L-dopa or Mn. Neither L-dopa nor MnCl, alone was toxic at these concentrations, and cytotoxicity was completely ab rogated by substitution of L-tyrosine for L-dopa. Although CHO/AADC cu ltures were more sensitive than CHO/WT to L-dopa and Mn, this was comp letely accounted for by the differences in intracellular catechol leve ls between the two cell lines. Preformed melanin or dopac were low-pot ency cytotoxins only at high MnCl2 concentrations. These results indic ate that Mn and intracellular L-dopa and dopamine, but not extracellul ar dopac or melanin, are potent synergistic cytotoxins. (C) 1994 Acade mic Press, Inc.