Pivotal Role of Fyn Kinase in Parkinson's Disease and Levodopa-Induced Dyskinesia: a Novel Therapeutic Target?

The exact etiology of Parkinson's disease (PD) remains obscure, although many cellular mechanisms including α-synuclein aggregation, oxidative damage, excessive neuroinflammation, and dopaminergic neuronal apoptosis are implicated in its pathogenesis. There is still no disease-modifying treatment for PD and the gold standard therapy, chronic use of levodopa is usually accompanied by severe side effects, mainly levodopa-induced dyskinesia (LID). Hence, the elucidation of the precise underlying molecular mechanisms is of paramount importance. Fyn is a tyrosine phospho-transferase of the Src family nonreceptor kinases that is highly implicated in immune regulation, cell proliferation and normal brain development. Accumulating preclinical evidence highlights the emerging role of Fyn in key aspects of PD and LID pathogenesis: it may regulate α-synuclein phosphorylation, oxidative stress-induced dopaminergic neuronal death, enhanced neuroinflammation and glutamate excitotoxicity by mediating key signaling pathways, such as BDNF/TrkB, PKCδ, MAPK, AMPK, NF-κB, Nrf2, and NMDAR axes. These findings suggest that therapeutic targeting of Fyn or Fyn-related pathways may represent a novel approach in PD treatment. Saracatinib, a nonselective Fyn inhibitor, has already been tested in clinical trials for Alzheimer's disease, and novel selective Fyn inhibitors are under investigation. In this comprehensive review, we discuss recent evidence on the role of Fyn in the pathogenesis of PD and LID and provide insights on additional Fyn-related molecular mechanisms to be explored in PD and LID pathology that could aid in the development of future Fyn-targeted therapeutic approaches.

Ameliorative effects of a phosphodiesterase 10A inhibitor, MR1916 on L-DOPA-induced dyskinesia in parkinsonian rats.

BACKGROUND: Dopamine replacement therapy using L-3,4-dihydroxyphenylalanine (L-DOPA) is a gold standard treatment in patients with Parkinson's disease (PD); however, chronic administration of L-DOPA causes excessive involuntary movements called L-DOPA-induced dyskinesia. Therefore, the novel pharmacological treatment is needed. METHODS: We examined the antidyskinetic effect of a phosphodiesterase 10A (PDE10A) inhibitor, MR1916 and a currently available antidyskinetic drug, amantadine in unilateral 6-OHDA lesioned rats exhibited stably dyskinesia after chronic administration of L-DOPA. We also examined the influence of MR1916 and amantadine on the improvement of forelimb akinesia induced by L-DOPA using stepping test in unilateral 6-OHDA lesioned rats. RESULTS: MR1916 (0.03‒0.3 mg/kg, po) reduced L-DOPA-induced dyskinesia in a dose-dependent manner and showed significant effects at doses of 0.1 and 0.3 mg/kg, while amantadine (40 mg/kg, sc) had no remarkable effects. Neither MR1916 (0.03‒0.3 mg/kg, po) nor amantadine (40 mg/kg, sc) affected the antiparkinsonian effects induced by L-DOPA in unilateral 6-OHDA lesioned rats. CONCLUSIONS: These results indicate that MR1916 specifically reduces L-DOPA-induced dyskinesia without affecting the antiparkinsonian effect of L-DOPA in parkinsonian rats.

Polymorphisms of Catechol-O-Methyl Transferase (COMT) Gene in Vulnerability to Levodopa-Induced Dyskinesia.

PURPOSE: Parkinson's disease (PD), a common neurodegenerative disorder, is usually treated with Levodopa (L-DOPA). The use of this drug, however, is severely limited by the development of side effects of the motor system: Levodopa-induced dyskinesia (LID). The aim of this study is to investigate the association between seven COMT gene single-nucleotide polymorphisms (SNPs) and the development of LID in patients with PD. METHODS: 232 Caucasian patients with PD were investigated. 212 patients with PD received Levodopa therapy. Dyskinesia was assessed with the use of the Abnormal Involuntary Movement Scale (AIMS).  Genotyping was carried out on seven SNPs of the COMT gene (rs4680, rs6269, rs4633, rs4818, rs769224, rs165774, rs174696) using a real-time PCR method, and blind to the clinical status of the subjects. RESULTS: We found association between four SNPs, rs165774, rs4818, rs4633, rs4680, and LID. When the duration of disease was added as a covariate in regression analysis, however, the results did not reach statistical significance. Only the additive model for rs165774 was found to be close to be statistical significance (OR = 1.627 [0.976-2.741], permutation p = 0.057). CONCLUSIONS: The results failed to clearly support a contribution of the studied polymorphisms; this may be related to a dominant relationship with the disease duration confounding the effect on the prevalence of LID.

Understanding the role of glycogen synthase kinase-3 in L-DOPA-induced dyskinesia in Parkinson's disease.

INTRODUCTION: Levodopa (L-DOPA) is the most commonly used drug for Parkinson's disease (PD), but its long-term use is associated with various complications, including L-DOPA-induced dyskinesia (LID). Many studies have suggested that L-DOPA neurotoxicity and LID are associated with glycogen synthase kinase-3 (GSK-3) activation. Areas covered: LID is caused by striatal dopamine (DA) denervation in PD and pulsatile L-DOPA treatment. These factors lead to dysregulated DA transmission, abnormal intracellular signaling and transcription factors in striatal neurons, and altered gene expression and plasticity at corticostriatal synapses. The mechanisms of L-DOPA toxicity involve oxidative stress, L-DOPA oxidation to quinone, mitochondrial dysfunction, and α-synuclein. GSK-3 has been suggested to play key roles in all the mechanisms associated of L-DOPA toxicity and LID in PD. Expert opinion: GSK-3 plays critical roles in L-DOPA-induced neurotoxicity, and the development of specific methods to inhibit GSK-3 function may help prevent L-DOPA neurotoxicity and LID in PD. However, balanced GSK-3 inhibition and less ß-catenin degradation is essential for preventing LID, because too much GSK-3 inhibition increases ß-catenin levels, which is related to cancers.

The Kinase Fyn As a Novel Intermediate in L-DOPA-Induced Dyskinesia in Parkinson's Disease.

Dopamine replacement therapy with L-DOPA is the treatment of choice for Parkinson's disease; however, its long-term use is frequently associated with L-DOPA-induced dyskinesia (LID). Many molecules have been implicated in the development of LID, and several of these have been proposed as potential therapeutic targets. However, to date, none of these molecules have demonstrated full clinical efficacy, either because they lie downstream of dopaminergic signaling, or due to adverse side effects. Therefore, discovering new strategies to reduce LID in Parkinson's disease remains a major challenge. Here, we have explored the tyrosine kinase Fyn, as a novel intermediate molecule in the development of LID. Fyn, a member of the Src kinase family, is located in the postsynaptic density, where it regulates phosphorylation of the NR2B subunit of the N-methyl-D-aspartate (NMDA) receptor in response to dopamine D1 receptor stimulation. We have used Fyn knockout and wild-type mice, lesioned with 6-hydroxydopamine and chronically treated with L-DOPA, to investigate the role of Fyn in the induction of LID. We found that mice lacking Fyn displayed reduced LID, ΔFosB accumulation and NR2B phosphorylation compared to wild-type control mice. Pre-administration of saracatinib (AZD0530), an inhibitor of Fyn activity, also significantly reduced LID in dyskinetic wild-type mice. These results support that Fyn has a critical role in the molecular pathways affected during the development of LID and identify Fyn as a novel potential therapeutic target for the management of dyskinesia in Parkinson's disease.

Effects of prolonged neuronal nitric oxide synthase inhibition on the development and expression of L-DOPA-induced dyskinesia in 6-OHDA-lesioned rats.

It is well known that nitric oxide (NO) interacts with dopamine (DA) within the striatal circuitry. The anti-dyskinetic properties of NO synthase (NOS) inhibitors demonstrate the importance of NO in L-3,4-dihydroxyphenylalanine (L-DOPA)-induced dyskinesia (LID). Here, we investigated the ability of a daily co-treatment of the preferential neuronal NOS (nNOS) inhibitor, 7-nitroindazole (7-NI, 30 mg/kg), with L-DOPA (30 mg/kg) to counteract LID in unilaterally 6-OHDA-lesioned rats. We analyzed striatal nNOS-expressing interneurons, DA and 5-HT neurochemistry in the striatum and alterations of the Fos-B/ΔFosB expression in the corticostriatal, nigrostriatal and mesolimbic pathways. Prolonged administration of 7-NI inhibited the manifestation of chronic L-DOPA treatment-induced abnormal involuntary movements (AIMs). LID was associated with an up-regulation in the number of nNOS-expressing interneurons in the lateral but not medial striatum. nNOS inhibition reduced the number of nNOS-expressing interneurons. The anti-dyskinetic effects of 7-NI correlated with a reduction in DA and 5-HT turnover in the striatum. At postsynaptic striatal sites, 7-NI prevented L-DOPA-induced Fos-B/ΔFosB up-regulation in the motor cortex, nucleus accumbens and striatum. Finally, 7-NI blocked Fos-B/ΔFosB expression in nicotinamide adenine dinucleotide phosphate diaphorase (NADPH-d)-positive interneurons in the striatum. These results provide further evidence of the molecular mechanisms by which NOS-inhibiting compounds attenuate LID. The involvement of NO with DA and 5-HT neurochemistry may contribute to the understanding of this new, non-dopaminergic therapy for the management of LID.

Association study indicates a protective role of phosphatidylinositol-4-phosphate-5-kinase against tardive dyskinesia.

BACKGROUND: Tardive dyskinesia is a disorder characterized by involuntary muscle movements that occur as a complication of long-term treatment with antipsychotic drugs. It has been suggested to be related to a malfunctioning of the indirect pathway of the motor part of the cortical-striatal-thalamic-cortical circuit, which may be caused by oxidative stress-induced neurotoxicity. METHODS: The purpose of our study was to investigate the possible association between phosphatidylinositol-4-phosphate-5-kinase type IIa (PIP5K2A) function and tardive dyskinesia in 491 Caucasian patients with schizophrenia from 3 different psychiatric institutes in West Siberia. The Abnormal Involuntary Movement Scale was used to assess tardive dyskinesia. Individuals were genotyped for 3 single nucleotide polymorphisms in PIP5K2A gene: rs10828317, rs746203, and rs8341. RESULTS: A significant association was established between the functional mutation N251S-polymorphism of the PIP5K2A gene (rs10828317) and tardive dyskinesia, while the other 2 examined nonfunctional single nucleotide polymorphisms were not related. CONCLUSIONS: We conclude from this association that PIP5K2A is possibly involved in a mechanism protecting against tardive dyskinesia-inducing neurotoxicity. This corresponds to our hypothesis that tardive dyskinesia is related to neurotoxicity at striatal indirect pathway medium-sized spiny neurons.

Inhibition of adenylyl cyclase type 5 prevents L-DOPA-induced dyskinesia in an animal model of Parkinson's disease.

The dopamine precursor L-3,4-dihydroxyphenylalanine (L-DOPA) is widely used as a therapeutic choice for the treatment of patients with Parkinson's disease. However, the long-term use of L-DOPA leads to the development of debilitating involuntary movements, called L-DOPA-induced dyskinesia (LID). The cAMP/protein kinase A (PKA) signaling in the striatum is known to play a role in LID. However, from among the nine known adenylyl cyclases (ACs) present in the striatum, the AC that mediates LID remains unknown. To address this issue, we prepared an animal model with unilateral 6-hydroxydopamine lesions in the substantia nigra in wild-type and AC5-knock-out (KO) mice, and examined behavioral responses to short-term or long-term treatment with L-DOPA. Compared with the behavioral responses of wild-type mice, LID was profoundly reduced in AC5-KO mice. The behavioral protection of long-term treatment with L-DOPA in AC5-KO mice was preceded by a decrease in the phosphorylation levels of PKA substrates ERK (extracellular signal-regulated kinase) 1/2, MSK1 (mitogen- and stress-activated protein kinase 1), and histone H3, levels of which were all increased in the lesioned striatum of wild-type mice. Consistently, FosB/ΔFosB expression, which was induced by long-term L-DOPA treatment in the lesioned striatum, was also decreased in AC5-KO mice. Moreover, suppression of AC5 in the dorsal striatum with lentivirus-shRNA-AC5 was sufficient to attenuate LID, suggesting that the AC5-regulated signaling cascade in the striatum mediates LID. These results identify the AC5/cAMP system in the dorsal striatum as a therapeutic target for the treatment of LID in patients with Parkinson's disease.

A genetic dissection of antipsychotic induced movement disorders.

BACKGROUND: Antipsychotic medications (APM) are the first line pharmacological treatment for psychotic disorders and other behavioral disorders. Nevertheless, their use causes a number of side effects, including extrapyramidal symptoms (EPS). EPS decrease the efficacy of the antipsychotic treatments by causing poorer compliance to the treatment, stigma and a poorer quality of life for patients. Genetic studies hold the potential to unravel the molecular underpinnings of the EPS induced by APM but results are not conclusive and are far to be used in clinical practice despite decades of research. A more sophisticated selection of the list of genetic mutations explaining the genetic variance of EPS induced by APM could help in the definition of a personalized treatments for patients. Moreover, it would increase the quality of the current treatments with APM. METHODS: We reviewed the literature searching for the genetic association studies focused on dystonia, parkinsonism, akathisia and tardive dyskinesia. Moreover, we reviewed the current biological knowledge of the APM induced side effects. Finally, we provide a reasoned list of candidate genes and their genetic variations, with the aim of identifying a list of candidates for APM induced EPS genetic investigations. RESULTS: Variations located within PIK3CA (phosphoinositide-3- kinase, catalytic, alpha polypeptide), PLA2G4A (phospholipase A2, group IVA, cytosolic, calcium-dependent), PRKCA (protein kinase C, alpha), PRKACG (Phosphatidylinositol-4,5-bisphosphate 3-kinase 110 kDa catalytic subunit gamma), ERK-1 (extracellular signalregulated kinase 1 (MAPK3)), ERK-2 (extracellular signal-regulated kinase 2 (MAPK1)), GNAS (guanine nucleotide binding protein (G protein), alpha stimulating activity polypeptide 1), PLCB1 (phospholipase C, beta 1 (phosphoinositide-specific)) and ITPR1 (inositol 1,4,5-triphosphate receptor type 1) were found to be relevant for APM induced EPS. Some of the genes are classical candidates for this kind of research, others were never investigated. For each of these genes we provide a list of variations that balances the limitations of multitesting with the advantages of the tagging approach. CONCLUSIONS: We undertook a review of the literature about the APM induced EPM to provide some rational genetic candidates to be tested in further genetic investigations.

DRD2 haplotype is associated with dyskinesia induced by levodopa therapy in Parkinson's disease patients.

AIM: Dyskinesia and motor fluctuation are frequent and serious complications of chronic levodopa therapy in patients with Parkinson's disease. Since genetic factors could play a role in determining the occurrence of these problems, the aim of the present study was to investigate whether possible functional polymorphisms among DRD2 and ANKK1 genes are associated with the risk of developing dyskinesia and motor fluctuations in Parkinson's disease patients. PATIENTS & METHODS: One hundred and ninety nine patients in treatment with levodopa were genotyped for the -141CIns/Del, rs2283265, rs1076560, C957T, TaqIA and rs2734849 polymorphisms at the DRD2/ANKK1 gene region. RESULTS: Carriers of the TTCTA haplotype showed an increased risk for the presence of dyskinesia (p = 0.007; 1.538 [95% CI: 1.126-2.101]). CONCLUSION: Our data suggest an influence of the DRD2/ANKK1 gene region on levodopa-induced dyskinesia.

Neuronal nitric oxide synthase inhibition attenuates the development of L-DOPA-induced dyskinesia in hemi-Parkinsonian rats.

Long-term treatment with the dopamine precursor levodopa (l-DOPA) frequently induces dyskinesia in Parkinson's disease patients, which is a major complication of this therapy. Previous studies using animal models show that repeated administration of l-DOPA results in alterations of some signaling molecules, including ΔFosB, phospho-DARPP32 and phosoho-GluA1 (also referred to as GluR1 or GluR-A) AMPA receptor subunits. Moreover, an in vivo microdialysis study showed that l-DOPA increases nitric oxide (NO) production in the striatum. However, it is not known whether NO is involved in the development of dyskinesia. The present study examined the effects of NOS inhibitors on the development of l-DOPA-induced dyskinesia in the rats. Dyskinesia symptoms were triggered by daily administration of l-DOPA for 3-4weeks in unilateral 6-hydroxydopamine lesioned rats. Repeated treatments, 30min prior l-DOPA administration, of the nonselective NOS inhibitor, N(G)-nitro-l-arginine methyl ester, and the nNOS inhibitor 7-nitroindazole, but not the inducible NOS inhibitor aminoguanidine, attenuated the development of l-DOPA-induced dyskinesia. In agreement with the behavioral analysis, 7-nitroindazole reduced the l-DOPA-induced increases in ΔFosB, phospho-DARPP32 and phospho-GluA1 AMPA receptor subunit levels in the striatum of 6-hydroxydopamine-lesioned rats. Furthermore, aminoguanidine did not affect ΔFosB or phospho-GluA1 AMPA receptor subunit levels. These findings suggest that nNOS-derived NO is involved in the development of l-DOPA-induced dyskinesia through a post-synaptic mechanism.

L-DOPA-induced dyskinesia in hemiparkinsonian rats is associated with up-regulation of adenylyl cyclase type V/VI and increased GABA release in the substantia nigra reticulata.

L-DOPA treatment induces abnormal involuntary movements (AIMs) in Parkinson's patients and experimental animals. We examined the relationship between the development of AIMs (dyskinesia) and changes in [(3)H]-GABA release and cAMP signaling in striatonigral terminals of rats with unilateral 6-OHDA lesions. Analysis of AIMs scores in hemiparkinsonian rats treated with L-DOPA for 20 days was fitted by the sum of two Gaussian distributions showing the presence of two populations: one with mild and the other with severe dyskinesia. cAMP signaling was evaluated in the two populations by determining changes in cAMP formation, Gα(olf) and adenylyl cyclase type V/VI levels. In animals that were not treated with L-DOPA, all the parameters were significantly increased in the denervated side. In the animals that had mild dyskinesia, L-DOPA treatment normalized these parameters. In contrast, in the animals in which l-DOPA treatment induced severe dyskinesia all the parameters, except for Gα(olf) levels, were significantly higher in the denervated side. Similarly, D1-stimulated [(3)H]-GABA release was not elevated in L-DOPA-treated animals with mild dyskinesia but was increased in animals with severe dyskinesia. Changes in Gα(olf) and adenylyl cyclase type V/VI levels in the striatum paralleled the response in the SNr. The linkage between the changes in [(3)H]-GABA release and cAMP activity was further evaluated with the selective adenylyl cyclase V/VI antagonist NKY80. This inhibitor blocked the increases of both [(3)H]-GABA release and cAMP production. These results indicate that increased expression of adenylyl cyclase V/VI is a major determinant of increased GABAergic transmission in the substantia nigra pars reticulata of animals in which L-DOPA induces severe dyskinesia.

Inhibition of phosphodiesterases rescues striatal long-term depression and reduces levodopa-induced dyskinesia.

The aim of the present study was to evaluate the role of the nitric oxide/cyclic guanosine monophosphate pathway in corticostriatal long-term depression induction in a model of levodopa-induced dyskinesia in experimental parkinsonism. Moreover, we have also analysed the possibility of targeting striatal phosphodiesterases to reduce levodopa-induced dyskinesia. To study synaptic plasticity in sham-operated rats and in 6-hydroxydopamine lesioned animals chronically treated with therapeutic doses of levodopa, recordings from striatal spiny neurons were taken using either intracellular recordings with sharp electrodes or whole-cell patch clamp techniques. Behavioural analysis of levodopa-induced abnormal involuntary movements was performed before and after the treatment with two different inhibitors of phosphodiesterases, zaprinast and UK-343664. Levodopa-induced dyskinesia was associated with the loss of long-term depression expression at glutamatergic striatal synapses onto spiny neurons. Both zaprinast and UK-343664 were able to rescue the induction of this form of synaptic plasticity via a mechanism requiring the modulation of intracellular cyclic guanosine monophosphate levels. This effect on synaptic plasticity was paralleled by a significant reduction of abnormal movements following intrastriatal injection of phosphodiesterase inhibitors. Our findings suggest that drugs selectively targeting phosphodiesterases can ameliorate levodopa-induced dyskinesia, possibly by restoring physiological synaptic plasticity in the striatum. Future studies exploring the possible therapeutic effects of phosphodiesterase inhibitors in non-human primate models of Parkinson's disease and the involvement of striatal synaptic plasticity in these effects remain necessary to validate this hypothesis.

Locomotor response to L-DOPA in reserpine-treated rats following central inhibition of aromatic L-amino acid decarboxylase: further evidence for non-dopaminergic actions of L-DOPA and its metabolites.

L-DOPA is the most widely used treatment for Parkinson's disease. The anti-parkinsonian and pro-dyskinetic actions of L-DOPA are widely attributed to its conversion, by the enzyme aromatic L-amino acid decarboxylase (AADC), to dopamine. We investigated the hypothesis that exogenous L-DOPA can induce behavioural effects without being converted to dopamine in the reserpine-treated rat-model of Parkinson's disease. A parkinsonian state was induced with reserpine (3 mg/kg s.c.). Eighteen hours later, the rats were administered L-DOPA plus the peripherally acting AADC inhibitor benserazide (25 mg/kg), with or without the centrally acting AADC inhibitor NSD1015 (100 mg/kg). L-DOPA/benserazide alone reversed reserpine-induced akinesia (4158+/-1125 activity counts/6 h, cf vehicle 1327+/-227). Addition of NSD1015 elicited hyperactive behaviour that was approximately 7-fold higher than L-DOPA/benserazide (35755+/-5226, P<0.001). The hyperactivity induced by L-DOPA and NSD1015 was reduced by the alpha(2C) antagonist rauwolscine (1 mg/kg) and the 5-HT(2C) agonist MK212 (5 mg/kg), but not by the D2 dopamine receptor antagonist remoxipride (3 mg/kg) or the D1 dopamine receptor antagonist SCH23390 (1 mg/kg). These data suggest that L-DOPA, or metabolites produced via routes not involving AADC, might be responsible for the generation of at least some L-DOPA actions in reserpine-treated rats.

The roles of striatal serotonin and L -amino-acid decarboxylase on L-DOPA-induced Dyskinesia in a Hemiparkinsonian rat model.

The administration of L: -DOPA is the standard treatment for Parkinson's disease (PD). However, the symptomatic relief provided by long-term administration may be compromised by L: -DOPA-induced dyskinesia (LID) that presents as adverse fluctuations in motor responsiveness and progressive loss of motor control. In the later stages of PD, raphestriatal serotonin neurons compensate for the loss of nigrostriatal dopamine (DA) neurons by converting and releasing DA derived from exogenous L: -DOPA. Since the serotonin system does not have an autoregulatory mechanism for DA, raphe-mediated striatal DA release may fluctuate dramatically and precede the development of LID. The 6-hydroxydopamine lesioned rats were treated with L: -DOPA (6 mg/kg) and benserazide (15 mg/kg) daily for 3 weeks to allow for the development of abnormal involuntary movement score (AIMs). In rats with LID, chronic treatment with L: -DOPA increased striatal DA levels compared with control rats. We also observed a relative increase in the expression of striatal L: -amino-acid decarboxylase (AADC) in LID rats, even though tyrosine hydroxylase (TH) expression did not increase. The administration of L: -DOPA also increased striatal serotonin immunoreactivity in LID rats compared to control rats. Striatal DA and 5-hydroxytryptamine (5-HT) levels were negatively correlated in L: -DOPA-treated rats. These results of this study reveal that 5-HT contributes to LID. Striatal DA positively influences LID, while 5-HT is negatively associated with LID. Finally, we suggest that by strategic modification of the serotonin system it may be possible to attenuate the adverse effects of chronic L: -DOPA therapy in PD patients.

Expression of catechol-O-methyltransferase in the brain and periphery of normal and MPTP-treated common marmosets.

Catechol-O-methyltransferase (COMT) inhibition is widely used to potentiate the effects of levodopa in Parkinson's disease but the effects of nigral dopaminergic cell loss and levodopa treatment on COMT activity are not known. The present study investigated the expression of COMT in the brain and liver of normal common marmosets, and animals treated with MPTP and those treated with levodopa to induce dyskinesia. Reverse transcript PCR demonstrated the expression of COMT mRNA in the liver, cortex and striatum of normal marmosets. Using Western blotting, the presence of two subunits of COMT protein, membrane bound COMT (MB-COMT) and soluble COMT (S-COMT), was shown in the liver, cortex and striatum of normal marmosets. Quantitative analysis of the MB-COMT and S-COMT subunit bands showed that there was no significant difference in the density of bands in MPTP treated marmosets or those exposed to levodopa compared to normal animals. COMT immunoreactivity was expressed in many brain regions including the cortex and striatum. No difference in COMT staining intensity was observed between normal, MPTP exposed or MPTP plus levodopa treated animals. COMT immunostaining was present in most striatal neurones and it was occasionally seen in glial cells. The data from present study demonstrated the expression of COMT mRNA and protein in the brain of common marmoset contrary to a previous report that it is not expressed in this species. COMT activity appears unaffected by loss of the dopaminergic nigro-striatal pathway and levodopa treatment.

Missense polymorphisms in three oxidative-stress enzymes (GSTP1, SOD2, and GPX1) and dyskinesias in Russian psychiatric inpatients from Siberia.

Neuronal degeneration due to oxidative stress (OS) has been proposed as a mechanism for tardive dyskinesia (TD) pathogenesis. Cellular defense mechanisms against OS may involve detoxification enzymes (e.g., glutathione peroxidase-1, GPX1; superoxide dismutase-2, SOD2 [also commonly known as MnSOD]; and glutathione S-transferase P1, GSTP1). Several pharmacogenetic studies have examined TD and OS in different ethnic groups, but not in Russians. Here we report the association between orofaciolingual (TDof) and limb-truncal dyskinesias (TDlt) and polymorphisms of GSTP1 (Ile105Val), MnSOD (Ala-9Val), and GPX1 (Pro197Leu) genes in 146 Russian inpatients from Siberia. We applied AIMS instrument to rate dyskinesias. Two-part model analyses, logistic and multivariate parametric regressions were applied to assess the effects of different variables (e.g., genotype, age, gender, and medication use). Our analyses do not suggest that Pro197Leu (GPX1) is associated with TD. However, our analyses suggest that the 105Val-allele of Ile105Val (GSTP1) may be associated with a lower risk and a severity of TDof and TDlt and that Ile105Val pharmacogenetics may be different in Slavonic Caucasians from that in American Caucasians. Furthermore, we find evidence for an association between Ala-9Val (MnSOD) and TDof, but not TDlt. Subject to further replication, our findings extend the available knowledge on the pharmacogenetics of TD and oxidative stress.

Cyp2d6*3, *4, *5 and *6 polymorphisms and antipsychotic-induced extrapyramidal side-effects in patients receiving antipsychotic therapy.

1. The aim of the present study was to examine the relationship between CYP2D6 polymorphisms and the risk of antipsychotic (AP)-induced extrapyramidal symptoms (EPS) in patients receiving AP treatment. The allele status for CYP2D6*3, CYP2D6*4, CYP2D6*5 and CYP2D6*6 was determined in 267 patients receiving AP therapy. Seventy-nine cases presenting with EPS (Simpson-Angus Scale 3) and 188 controls without EPS (Simpson-Angus > 3) took part in the study. 2. We found a non-significant over-representation of poor metaboliser genotypes among cases, but a significant association between the mutant homozygous genotype for CYP2D6*4 (odds ratio (OR) 4.1, 95% confidence interval (CI) 1.01-16, permutated P value 0.01) and the heterozygous genotype for CYP2D6*6 (OR 5.4, 95% CI 1.13-18, permutated P value 0.003) and the risk of suffering EPS. 3. These results suggest that the CYP2D6 genotype may be a contributory factor in the development of EPS in patients undergoing AP therapy.

Prolonged kynurenine 3-hydroxylase inhibition reduces development of levodopa-induced dyskinesias in parkinsonian monkeys.

Increased glutamatergic activity is believed to play a significant role in the development of levodopa-induced dyskinesias (LID). LID may therefore be attenuated by a reduction in glutamatergic function. This was tested pharmacologically in MPTP monkeys by increasing the formation of kynurenic acid (KYNA), a tryptophan metabolite that inhibits glutamate release and also blocks NMDA receptors directly. KYNA synthesis was stimulated by prolonged systemic administration of the kynurenine 3-hydroxylase inhibitor Ro 61-8048. Four MPTP cynomolgus monkeys received l-dopa (LD; 100mg) with benserazide (25 mg) for one month. Progressively, all these animals developed LID. Four other MPTP monkeys received Ro 61-8048 (50mg/kg) daily 3 h before administration of LD/benserazide for one month. The addition of Ro 61-8048 reduced the development of LID but did not affect the antiparkinsonian efficacy of LD. Moreover, Ro 61-8048 administration caused sustained increases in serum kynurenine and KYNA concentrations, which reverted to basal values 24 h after the last treatment. This effect of Ro 61-8048 was less pronounced in the CSF. These results demonstrate that long-lasting elevation of KYNA levels caused by prolonged inhibition of kynurenine 3-hydroxylase is associated with a significant reduction in LID but does not compromise the benefits of chronic LD therapy.