Monoamine transporter inhibitors and norepinephrine reduce dopamine-dependent iron toxicity in cells derived from the substantia nigra

Abstract

The role of dopamine in iron uptake into catecholaminergic neurons, and dopamine oxidation to aminochrome and its one-electron reduction in iron-mediated neurotoxicity, was studied in RCSN-3 cells, which express both tyrosine hydroxylase and monoamine transporters. The mean +/- SD uptake of 100 muM (FeCl3)-Fe-59 in RCSN-3 cells was 25 +/- 4 pmol per min per mg, which increased to 28 +/- 8 pmol per min per mg when complexed with dopamine (Fe(III)-dopamine). This uptake was inhibited by 2 muM nomifensine (43% p < 0.05), 100 muM imipramine (62% p < 0.01), 30 muM reboxetine (71% p < 0.01) and 2 mM dopamine (84% p < 0.01). The uptake of Fe-59-dopamine complex was Na+, Cl- and temperature dependent. No toxic effects in RCSN-3 cells were observed when the cells were incubated with 100 muM FeCl3 alone or complexed with dopamine. However, 100 muM Fe(III)-dopamine in the presence of 100 muM dicoumarol, an inhibitor of DT-diaphorase, induced toxicity (44% cell death; p < 0.001), which was inhibited by 2 muM nomifensine, 30 muM reboxetine and 2 mM norepinephrine. The neuroprotective action of norepinephrine can be explained by (1) its ability to form complexes with Fe3+, (2) the uptake of Fe-norepinephrine complex via the norepinephrine transporter and (3) lack of toxicity of the Fe-norepinephrine complex even when DT-diaphorase is inhibited. These results support the proposed neuroprotective role of DT-diaphorase and norepinephrine.