Increased Divalent Metal Transporter 1 Expression Might Be Associated with the Neurotoxicity of l-DOPA

Abstract

Based on the available data, we speculated that changes in brain iron metabolism induced by L-DOPA might be associated with the neurotoxicity of L-DOPA. To investigate this possibility, the effects of L-DOPA on the expression of iron influx proteins [transferrin receptor (TfR) and divalent metal transporter 1 (DMT1)], iron efflux protein (ferroportin 1), and iron uptake in C6 glioma cells were determined in this study using Northern blot and Western blot analysis and the calcein method. The findings showed that treatment of C6 cells with different concentrations of L-DOPA (0 -100 M) did not affect the expression of mRNA and protein of TfR and DMT1 with iron-responsive element (ϩIRE) and protein of ferroportin 1. However, a significant increase in the expression of DMT1(ϪIRE) mRNA and protein was found in cells treated, respectively, with 10 and 30 M L-DOPA (mRNA) and 1, 5, 10 and 30 M L-DOPA (protein). The increase in DMT(ϪIRE) protein induced by L-DOPA treatment was in parallel with the increase in DMT(ϪIRE) mRNA. The levels of DMT1(ϪIRE) mRNA and protein peaked in the cells treated with 10 M L-DOPA and then decreased progressively with increasing concentrations of L-DOPA. Further study demonstrated that treatment of the cells with 10 M L-DOPA induced a significant increase in ferrous uptake by C6 glioma cells. The findings suggested that the increased DMT1(ϪIRE) expression might be partly associated with the neurotoxicity of L-DOPA. Clinical relevance of the findings needs to be investigated further.Parkinson's disease (PD) is a progressive neurodegenerative disorder characterized mainly by degeneration of dopamine-containing neurons. The affected sections of the brain are therefore deprived of adequate amounts of the neurotransmitter dopamine (Foley, 2000). Because dopamine itself cannot access the brain directly, its natural precursor, L-DOPA, is used in clinical treatment of patients with PD. L-DOPA remains the most effective treatment for the symptomatic control of PD (Dunnett and Björklund, 1999;LeWitt and Nyholm, 2004). However, it was reported that long-term administration of high oral doses could cause drug-induced involuntary movements, on-off fluctuation of efficacy, and dyskinesias (Jenner and Brin, 1998;Foster and Hoffer, 2004).The causes of the long-term side effects caused by L-DOPA treatment of PD are not yet completely known. Based on available data, we speculated that changes in brain iron metabolism induced by L-DOPA might be associated with neurotoxicity or side effects of L-DOPA. First, it has been suggested that changes in trace metal concentrations in the brain may be related to the long-term toxicity of L-DOPA (Weiner et al., 1978). Second, a clinical study (Boll et al., 1999) demonstrated that L-DOPA can significantly affect brain ceruloplasmin, a major factor in the regulation of regional brain iron content and that cerebrospinal fluid ferroxidase (CP) in L-DOPA-treated patients with PD was significantly higher than that in patients with PD who were not This work was supported ...

L-DOPA Neurotoxicity Is Mediated by Up-Regulation of DMT1−IRE Expression

“…A pathological study of postmortem brain tissue showed that the levels of iron storage protein ferritin were significantly lower in several brain regions of PD patients treated with L-DOPA than those in the age-matched control patients [9]. In a recent study, we demonstrated that L-DOPA induces a significant increase in the expression of divalent metal transporter 1 without iron-response element (DMT1−IRE), but not divalent metal transporter 1 with iron-response element (DMT1+IRE), TfR1 or Fpn1, and a remarkable increase in ferrous uptake in cells [10].…”

“…Based on our recent findings [10], together with the potential role of DMT1−IRE in neuronal iron uptake [10], [22] and the well-known function of iron in the generation of reactive oxygen species, we hypothesized that the upregulation of DMT1−IRE might play a critical role in the development of L-DOPA neurotoxicity. In the present study, efforts were made to test this hypothesis.…”

Role of hepcidin in murine brain iron metabolism

“…Recent reports on the role of divalent metal transporter 1 (DMT1), ceruloplasmin (CP), hephaestin (HP), and ferroportin1 (Fpn1) in brain iron transport represent important advances in our understanding of the physiology and pathophysiology of brain iron metabolism. A recent study reported that the treatment of C6 glioma cells with different concentrations of l -DOPA significantly increased the expression of DMT1 (-IRE) mRNA and protein, and enhanced uptake of ferrous iron [6]. These findings suggest that increased DMT1 expression might be associated with the neurotoxicity of l -DOPA.…”

Hepcidin Treatment Modulates the Expression of Divalent Metal Transporter-1, Ceruloplasmin, and Ferroportin-1 in the Rat Cerebral Cortex and Hippocampus

“…Iron levels are tightly controlled in the brain and chronically elevated or reduced iron levels have toxic effects [19]. Elevated neuronal iron levels play a role in the neurodegenerative mechanisms that underlie Alzheimer's and Parkinson's disease [8,21] very likely by producing toxic amounts of free radicals [20,26,27]. It is feasible that a lack of control of iron levels in the brain is linked to disturbed FPN1 or Hepc expression.…”

“…Iron levels in the brain are of central importance for neuronal function and survival. Increased levels of iron is considered to be responsible for the neurotoxic properties of Ldopa [8]. Iron-generated hydroxyl radicals are neurotoxic [9], and elevated iron levels are considered to play a role in the neurodegenerative mechanisms that underlie Alzheimer's and Parkinson's disease [10].…”