Neuroinflammation in L-DOPA-induced dyskinesia: beyond the immune function.

Neuroinflammation is a main component of Parkinson's disease (PD) neuropathology, where unremitting reactive microglia and microglia-secreted soluble molecules such as cytokines, contribute to the neurodegenerative process as part of an aberrant immune reaction. Besides, pro-inflammatory cytokines, predominantly TNF-α, play an important neuromodulatory role in the healthy and diseased brain, being involved in neurotransmitter metabolism, synaptic scaling and brain plasticity. Recent preclinical studies have evidenced an exacerbated neuroinflammatory reaction in the striatum of parkinsonian rats that developed dyskinetic responses following L-DOPA administration. These findings prompted investigation of non-neuronal mechanisms of L-DOPA-induced dyskinesia (LID) involving glial cells and glial-secreted soluble molecules. Hence, besides the classical mechanisms of LID that include abnormal corticostriatal neurotransmission and maladaptive changes in striatal medium spiny neurons (MSNs), here we review studies supporting a role of striatal neuroinflammation in the development of LID, with a focus on microglia and the pro-inflammatory cytokine TNF-α. Moreover, we discuss several mechanisms that have been involved in the development of LID, which are directly or indirectly under the control of TNF-α, and might be abnormally affected by its chronic overproduction and release by microglia in PD. It is proposed that TNF-α may contribute to the altered neuronal responses occurring in LID by targeting receptor trafficking and function in MSNs, but also dopamine synthesis in preserved dopaminergic terminals and serotonin metabolism in serotonergic neurons. Therapeutic approaches specifically targeting glial-secreted cytokines may represent a novel target for preventing or treating LID.

Exogenous corticosterone reduces L-DOPA-induced dyskinesia in the hemi-parkinsonian rat: role for interleukin-1beta.

While the etiology of Parkinson's disease (PD) remains unknown, there is overwhelming evidence that neuroinflammation plays a critical role in the progressive loss of dopamine (DA) neurons. Because nearly all persons suffering from PD receive l-DOPA, it is surprising that inflammation has not been examined as a potential contributor to the abnormal involuntary movements (AIMs) that occur as a consequence of chronic l-DOPA treatment. As an initial test of this hypothesis, we examined the effects of exogenously administered corticosterone (CORT), an endogenous anti-inflammatory agent, on the expression and development of l-DOPA-induced dyskinesia (LID) in unilateral DA-depleted rats. To do this, male Sprague-Dawley rats received unilateral medial forebrain bundle 6-hydroxydopamine lesions. Three weeks later, l-DOPA primed rats received acute injections of CORT (0-3.75 mg/kg) prior to l-DOPA to assess the expression of LID. A second group of rats was used to examine the development of LID in l-DOPA naïve rats co-treated with CORT and l-DOPA for 2 weeks. AIMs and rotations were recorded. Exogenous CORT dose-dependently attenuated both the expression and development of AIMs without affecting rotations. Real-time reverse-transcription polymerase chain reaction of striatal tissue implicated a role for interleukin-1 (IL-1) beta in these effects as its expression was increased on the lesioned side in rats treated with l-DOPA (within the DA-depleted striatum) and attenuated with CORT. In the final experiment, interleukin-1 receptor antagonist (IL-1ra) was microinjected into the striatum of l-DOPA-primed rats to assess the impact of IL-1 signaling on LID. Intrastriatal IL-1ra reduced the expression of LID without affecting rotations. These findings indicate a novel role for neuroinflammation in the expression of LID, and may implicate the use of anti-inflammatory agents as a potential adjunctive therapy for the treatment of LID.

Serum-soluble interleukin-2 receptors in neuroleptic-naive schizophrenic subjects and in medicated schizophrenic subjects with and without tardive dyskinesia.

There is a growing body of literature suggesting that some schizophrenic subjects have evidence of immune activation. One marker that has been consistently elevated in studies is the serum-soluble interleukin-2 receptor (SIL-2R). This article reports the results of 2 experiments: the first compares concentrations of serum SIL-2R in neuroleptic-naive schizophrenic patients and matched controls, and the second study contrasts serum SIL-2R concentrations in medicated schizophrenic subjects with and without tardive dyskinesia. Serum SIL-2R concentrations were elevated in neuroleptic-naive schizophrenic subjects as compared with controls (1705.7 (SD 1124.2) U/ml vs 739.8 (SD 325.5) U/ml). Medicated subjects with tardive dyskinesia had increased serum SIL-2R levels (2385.5 (SD 1822.0) U/ml) compared with medicated subjects without tardive dyskinesia (1259.6 (SD 1365.3) U/ml). Thus, elevations in serum SIL-2R levels are present prior to neuroleptic treatment, and there may be an association between serum SIL-2Rs and tardive dyskinesia.

Serum antibodies to nicotinic acetylcholine receptors in schizophrenic patients.

Although elevated serum levels of antibodies to the nicotinic acetylcholine receptor (nAChR) have been reported in neuroleptic treated patients with tardive dyskinesia, such antibodies have not been determined in comparable nondyskinetic patients. Using a toxin-binding inhibition assay, we examined serum anti-nAChR antibody levels in 17 DSM-III-R chronic schizophrenic patients, seven of whom had persistent tardive dyskinesia, and 10 normal controls. On the average, anti-nAChR antibody levels were significantly higher in schizophrenic patients than in normal controls, but but not differ between patients with and without tardive dyskinesia and was not related to age, sex, or duration of illness in patients.

Human leucocyte antigens and tardive dyskinesia.

HLA status was assessed in matched groups of schizophrenics, 20 with and 20 without tardive dyskinesia. The antigen frequencies were also compared with that in a control sample. The anticipated excess of HLA-B44 was not confirmed. Pooled data displayed a shortfall of HLA-Cw7 and an excess of HLA-B44 in schizophrenics relative to population controls.

HLA antigens in tardive dyskinesia.

Fifty-three male, Caucasian, neuroleptic-treated patients with chronic schizophrenia were examined for the presence of tardive dyskinesia (TD) and were tissue typed. The group with TD (n = 25) was compared to the group without TD (n = 28). HLA-DR4 was more prevalent in the group with TD than in the group without TD, with a relative risk of 3.04 for TD with HLA-DR4 present, although this finding is not statistically significant when corrected for the number of nonparametric comparisons. Other investigations reported an association between HLA-B44 and TD, or between HLA-B44 and neuroleptic-induced parkinsonism. Potential explanations relating the findings of these investigations are discussed.

Immunogenetic markers in chlorpromazine-induced tardive dyskinesia.

The presence and severity of tardive dyskinesia were determined in 66 patients with chronic psychiatric disorders treated with chlorpromazine. The patients were classified according to the presence of antinuclear antibodies, the lupus anticoagulant, and the HLA antigen Bw44. The severity of orofacial dyskinesia was estimated using the Rockland Research Institute Scale. Patients with autoantibodies and the Bw44 antigen had higher tardive dyskinesia scores than those with AAB without the Bw44 antigen and also patients without autoantibodies regardless of their HLA phenotype (P less than 0.01). These studies suggest that the presence of autoantibodies in association with the HLA Bw44 antigen is related to, and can be a predictor of, neurological complications of long-term chlorpromazine therapy.