Dopamine Transporter (DAT) Inhibitors Alleviate Specific Parkinsonian Deficits in Monkeys: Association with DAT Occupancy in Vivo

Striatal serotonin transporter gain-of-function in L-DOPA-treated, hemi-parkinsonian rats

L-DOPA is the standard treatment for Parkinson's disease (PD), but chronic treatment typically leads to L-DOPA-induced dyskinesia (LID). LID involves a complex interaction between the remaining dopamine (DA) system and the semi-homologous serotonin (5-HT) system. Since serotonin transporters (SERT) have some affinity for DA uptake, they may serve as a functional compensatory mechanism when DA transporters (DAT) are scant. DAT and SERT's functional contributions in the dyskinetic brain have not been well delineated. The current investigation sought to determine how DA depletion and L-DOPA treatment affect DAT and SERT transcriptional processes, translational processes, and functional DA uptake in the 6-hydroxydopamine-lesioned hemi-parkinsonian rat. Rats were counterbalanced for motor impairment into equally lesioned treatment groups then given daily L-DOPA (0 or 6 mg/kg) for 2 weeks. At the end of treatment, the substantia nigra was processed for tyrosine hydroxylase (TH) and DAT gene expression and dorsal raphe was processed for SERT gene expression. The striatum was processed for synaptosomal DAT and SERT protein expression and ex vivo DA uptake. Nigrostriatal DA loss severely reduced DAT mRNA and protein expression in the striatum with minimal changes in SERT. L-DOPA treatment, while not significantly affecting DAT or SERT alone, did increase striatal SERT:DAT protein ratios. Using ex vivo microdialysis, L-DOPA treatment increased DA uptake via SERT when DAT was depleted. Overall, these results suggest that DA loss and L-DOPA treatment uniquely alter DAT and SERT, revealing implications for monoamine transporters as potential biomarkers and therapeutic targets in the hemi-parkinsonian model and dyskinetic PD patients.

A systematic review of the potential effects of medications and drugs of abuse on dopamine transporter imaging using [123I]I-FP-CIT SPECT in routine practice

PURPOSE

In routine practice, dopamine transporter (DAT) imaging is frequently used as a diagnostic tool to support the diagnosis of Parkinson's disease or dementia with Lewy bodies. In 2008, we published a review on which medications and drugs of abuse may influence striatal [123I]I-FP-CIT binding and consequently may influence the visual read of an [123I]I-FP-CIT SPECT scan. We made recommendations on which drugs should be withdrawn before performing DAT imaging in routine practice. Here, we provide an update of the original work based on published research since 2008.

METHODS

We performed a systematic review of literature without language restriction from January 2008 until November 2022 to evaluate the possible effects of medications and drugs of abuse, including the use of tobacco and alcohol, on striatal DAT binding in humans.

RESULTS

The systematic literature search identified 838 unique publications, of which 44 clinical studies were selected. Using this approach, we found additional evidence to support our original recommendations as well as some new findings on potential effect of other medications on striatal DAT binding. Consequently, we updated the list of medications and drugs of abuse that may influence the visual read of [123I]I-FP-CIT SPECT scans in routine clinical practice.

CONCLUSION

We expect that a timely withdrawal of these medications and drugs of abuse before DAT imaging may reduce the incidence of false-positive reporting. Nevertheless, the decision to withdraw any medication must be made by the specialist in charge of the patient's care and considering the pros and cons of doing so.

Repurposing Benztropine, Natamycin, and Nitazoxanide Using Drug Combination and Characterization of Gastric Cancer Cell Lines

Gastric cancer (GC) ranked as the fifth most incident cancer in 2020 and the third leading cause of cancer mortality. Surgical prevention and radio/chemotherapy are the main approaches used in GC treatment, and there is an urgent need to explore and discover innovative and effective drugs to better treat this disease. A new strategy arises with the use of repurposed drugs. Drug repurposing coupled with drug combination schemes has been gaining interest in the scientific community. The main objective of this project was to evaluate the therapeutic effects of alternative drugs in GC. For that, three GC cell lines (AGS, MKN28, and MKN45) were used and characterized. Cell viability assays were performed with the reference drug 5-fluororacil (5-FU) and three repurposed drugs: natamycin, nitazoxanide, and benztropine. Nitazoxanide displayed the best results, being active in all GC cells. Further, 5-FU and nitazoxanide in combination were tested in MKN28 GC cells, and the results obtained showed that nitazoxanide alone was the most promising drug for GC therapy. This work demonstrated that the repurposing of drugs as single agents has the ability to decrease GC cell viability in a concentration-dependent manner.

Effects of daily Δ9-Tetrahydrocannabinol (THC) alone or combined with cannabidiol (CBD) on cognition-based behavior and activity in adolescent nonhuman primates

BACKGROUND

Daily use of marijuana is rising in adolescents, along with consumption of high potency marijuana products (high % Δ-9-tetrahydrocannabinol or THC). These dual, related trends have opened gaps in understanding the long-term effects of daily consumption of a high dose of THC in adolescents and whether a therapeutic dose of cannabidiol (CBD) modulates THC effects.

METHODS

Adolescent squirrel monkeys (Saimiri boliviensis) were treated daily for four months with vehicle (n = 4), a high THC dose (1 mg/kg i.m.; n = 4), or THC + CBD (1 mg/kg +3 mg/kg i.m.; n = 4), to investigate whether: (1) a daily high THC dose affects performance in tasks of cognition (repeated acquisition, discrimination reversal); (2) a daily high THC dose affects spontaneous behavior and day/night activity (3) tolerance develops to the behavioral effects of THC; (4) whether CBD modulates THC effects.

RESULTS

THC impaired performance of adolescent monkeys in a cognitive test initially, but not performance on a task of cognitive flexibility. THC reduced motor activity and increased sedentary behavior, with tolerance developing after weeks of daily treatment. Co-administered with THC, CBD did not modulate THC effects on cognitive performance, activity or tolerance, but prevented THC-induced emesis on the first day of daily treatment.

CONCLUSIONS

Daily high dosing with THC compromised performance on a task of cognition, and reduced activity in adolescent primates, with tolerance developing within weeks. Whether our observations are relevant to a broader range of cognitive tasks vital for daily function in human adolescents is uncertain.

In vitro binding affinity vs. in vivo site occupancy: A PET study of four diastereomers of dihydrotetrabenazine (DTBZ) in monkey brain

INTRODUCTION

In vivo imaging methods such as Positron Emission Tomography (PET) can be used to examine the relationship between in vitro binding affinity and in vivo occupancy of binding sites in the brain for new drug candidates. In this study, PET imaging in monkey brain was used to evaluate that correlation for a set of four diastereomers of the compound dihydrotetrabenazine (DTBZ), the pharmacologically active metabolite of the drug tetrabenazine.

METHODS

PET studies of DTBZ diastereomers were completed in a single monkey brain. In vivo occupancies (ED50) were estimated using multiple drug doses and the vesicular monoamine transporter 2 specific radioligand (+)-α-[11C] DTBZ, employing a test-retest sequence of control PET scan, drug administration and a second PET scan completed on a single day.

RESULTS

DTBZ has three chiral carbon centers and eight possible stereoisomers, and in vivo occupancy of the target site VMAT2 was observed only for the four diastereomers of DTBZ having the 11bR absolute configuration. The estimated in vivo occupancies (ED50 values from 0.023 to >3.15 mg/kg) correlated well (R2 = 0.95) with the in vitro binding affinities (Ki values of 4 to 600 nM for the VMAT2), and an even better correlation (R2 = 0.99) was found for the three isomers with in vitro binding affinities <100 nM.

CONCLUSIONS

If the physiochemical (MW, log P, pKa) or physiological (metabolism, transport, protein binding) properties of a set of drug stereoisomers are considered similar, the binding affinities determined from in vitro assays may predict the in vivo occupancies of the target binding site in the monkey brain.

Neuroprotection or Neurotoxicity of Illicit Drugs on Parkinson's Disease

Parkinson's Disease (PD) is currently the most rapid growing neurodegenerative disease and over the past generation, its global burden has more than doubled. The onset of PD can arise due to environmental, sporadic or genetic factors. Nevertheless, most PD cases have an unknown etiology. Chemicals, such as the anthropogenic pollutant 1-methyl-4-phenyl-1,2,3,6-tetrahydropyridine (MPTP) and amphetamine-type stimulants, have been associated with the onset of PD. Conversely, cannabinoids have been associated with the treatment of the symptoms'. PD and medical cannabis is currently under the spotlight, and research to find its benefits on PD is on-going worldwide. However, the described clinical applications and safety of pharmacotherapy with cannabis products are yet to be fully supported by scientific evidence. Furthermore, the novel psychoactive substances are currently a popular alternative to classical drugs of abuse, representing an unknown health hazard for young adults who may develop PD later in their lifetime. This review addresses the neurotoxic and neuroprotective impact of illicit substance consumption in PD, presenting clinical evidence and molecular and cellular mechanisms of this association. This research area is utterly important for contemporary society since illicit drugs' legalization is under discussion which may have consequences both for the onset of PD and for the treatment of its symptoms.

Antiparkinson Drug Benztropine Suppresses Tumor Growth, Circulating Tumor Cells, and Metastasis by Acting on SLC6A3/DAT and Reducing STAT3

Tumor growth, progression, and therapy resistance are crucial factors in the prognosis of cancer. The properties of three-dimensional (3D) tumor-like organoids (tumoroids) more closely resemble in vivo tumors compared to two-dimensionally cultured cells and are therefore effectively used for assays and drug screening. We here established a repurposed drug for novel anticancer research and therapeutics using a 3D tumoroid-based screening system. We screened six pharmacologically active compounds by using an original tumoroid-based multiplex phenotypic screening system with a matrix metalloproteinase 9 (MMP9) promoter-driven fluorescence reporter for the evaluation of both tumoroid formation and progression. The antiparkinson drug benztropine was the most effective compound uncovered by the screen. Benztropine significantly inhibited in vitro tumoroid formation, cancer cell survival, and MMP9 promoter activity. Benztropine also reduced the activity of oncogenic signaling transducers and trans-activators for MMP9, including STAT3, NF-κB, and β-catenin, and the properties of cancer stem cells/cancer-initiating cells. Benztropine and GBR-12935 directly targeted the dopamine transporter DAT/SLC6A3, whose genetic alterations such as amplification were correlated with poor prognosis for cancer patients. Benztropine also inhibited the tumor growth, circulating tumor cell (CTC) number, and rate of metastasis in a tumor allograft model in mice. In conclusion, we propose the repurposing of benztropine for anticancer research and therapeutics that can suppress tumor progression, CTC, and metastasis of aggressive cancers by reducing key pro-tumorigenic factors.

The Growing Problem of New Psychoactive Substances (NPS)

The term "new psychoactive substances" (NPS) can be defined as individual drugs in pure form or in complex preparations that are not scheduled under the Single Convention on Narcotic Drugs (1961) or the Convention on Psychotropic Substances (1971). NPS may be categorized by chemical structure, by psychoactive properties, by biological targets, or by source (plant, synthetic, or combined). The emergence of hundreds of NPS in the past decade is challenging for public health and drug policies globally. The novelty of NPS, their ambiguous legal status, ability to evade toxicological tests, swift adaptation to legal restrictions, global Internet marketing, and scant public knowledge of their adverse effects are among the key drivers of this twenty-first century phenomenon. Multi-disciplinary research in areas of biology, epidemiology, prevention, and web analytics are needed to develop effective responses in a domain capable of overwhelming current international conventions and national drug control policies. Ultimately, research-guided prevention education will fortify societies against this tidal wave.

Monoamine transporter contributions to l-DOPA effects in hemi-parkinsonian rats

l-DOPA is the standard treatment for Parkinson's disease (PD), but chronic treatment typically leads to abnormal involuntary movement or dyskinesia (LID) development. Although poorly understood, dyskinetic mechanisms involve a complex interaction between the remaining dopamine system and the semi-homologous serotonin and norepinephrine systems. Serotonin and norepinephrine transporters (SERT and NET, respectively) have affinity for dopamine uptake especially when dopamine transporters (DAT) are scant. Monoamine reuptake inhibitors have been reported to modulate l-DOPA's anti-parkinsonian effects, but DAT, SERT, and NET's contribution to dyskinesia has not been well delineated. The current investigation sought to uncover the differential expression and function of DAT, SERT, and NET in the l-DOPA-treated hemi-parkinsonian rat. Protein analysis of striatal monoamine transporters in unilateral sham or 6-hydroxydopamine-lesioned rats treated with l-DOPA (0 or 6 mg/kg) showed lesion-induced DAT loss and l-DOPA-induced gain in SERT:DAT and NET:DAT ratios in lesioned rats which positively correlated with dyskinesia expression, suggesting functional shifts among monoamine transporters in the dyskinetic state. SERT blockade with citalopram (3, 5 mg/kg) reduced LID while DAT and NET blockade with GBR-12909 (5, 10 mg/kg) and nisoxetine (5, 10 mg/kg), respectively, mildly exacerbated dyskinesia expression. Transporter inhibition did not significantly alter l-DOPA's ability to reverse motor deficit. Overall, DA and DAT loss with l-DOPA treatment appear to precipitate gain in SERT and NET function. Strong correlations with LID and direct behavioral comparisons of selective transporter blockade reveal novel implications for SERT, DAT, and NET as potential biomarkers and therapeutic targets in the hemi-parkinsonian model and dyskinetic PD patients.

2-Substituted 3β-Aryltropane Cocaine Analogs Produce Atypical Effects without Inducing Inward-Facing Dopamine Transporter Conformations

Previous structure-activity relationship studies indicate that a series of cocaine analogs, 3β-aryltropanes with 2β-diarylmethoxy substituents, selectively bind to the dopamine transporter (DAT) with nanomolar affinities that are 10-fold greater than the affinities of their corresponding 2α-enantiomers. The present study compared these compounds to cocaine with respect to locomotor effects in mice, and assessed their ability to substitute for cocaine (10 mg/kg, i.p.) in rats trained to discriminate cocaine from saline. Despite nanomolar DAT affinity, only the 2β-Ph2COCH2-3β-4-Cl-Ph analog fully substituted for cocaine-like discriminative effects. Whereas all of the 2β compounds increased locomotion, only the 2β-(4-ClPh)PhCOCH2-3β-4-Cl-Ph analog had cocaine-like efficacy. None of the 2α-substituted compounds produced either of these cocaine-like effects. To explore the molecular mechanisms of these drugs, their effects on DAT conformation were probed using a cysteine-accessibility assay. Previous reports indicate that cocaine binds with substantially higher affinity to the DAT in its outward (extracellular)- compared with inward-facing conformation, whereas atypical DAT inhibitors, such as benztropine, have greater similarity in affinity to these conformations, and this is postulated to explain their divergent behavioral effects. All of the 2β- and 2α-substituted compounds tested altered cysteine accessibility of DAT in a manner similar to cocaine. Furthermore, molecular dynamics of in silico inhibitor-DAT complexes suggested that the 2-substituted compounds reach equilibrium in the binding pocket in a cocaine-like fashion. These behavioral, biochemical, and computational results show that aryltropane analogs can bind to the DAT and stabilize outward-facing DAT conformations like cocaine, yet produce effects that differ from those of cocaine.

Classic Studies on the Interaction of Cocaine and the Dopamine Transporter

The dopamine transporter is responsible for recycling dopamine after release. Inhibitors of the dopamine transporter, such as cocaine, will stop the reuptake of dopamine and allow it to stay extracellularly, causing prominent changes at the molecular, cellular, and behavioral levels. There is much left to be known about the mechanism and site(s) of binding, as well as the effect that cocaine administration does to dopamine transporter-cocaine binding sites and gene expression which also plays a strong role in cocaine abusers and their behavioral characteristics. Thus, if more light is shed on the dopamine transporter-cocaine interaction, treatments for addiction and even other diseases of the dopaminergic system may not be too far ahead. As today's ongoing research expands on the shoulders of classic research done in the 1990s and 2000s, the foundation of core research done in that time period will be reviewed, which forms the basis of today's work and tomorrow's therapies.

Social behavioral changes in MPTP-treated monkey model of Parkinson's disease

Parkinsonian patients experience not only the physical discomfort of motor disorders but also the considerable psychological distress caused by cognitive deficits and behavioral disorders. These two factors can result in a disruption of social relationships during the symptomatic and even the presymptomatic motor states of the disease. However, it remains difficult, if not impossible, to evaluate social relationships in presymptomatic patients. The present study focused on the evaluation of social relationships within a group of female long-tailed macaques during presymptomatic and symptomatic motor states induced by Chronic Low-Dose (CLD) and then Chronic High-Dose (CHD) systemic administration of 1-methyl-4-phenyl-l,2,3,6-tetrahydropyridine (MPTP). Dopaminergic denervation within basal ganglia and cortical areas was evaluated using Positron Emission Tomography (PET) scans with (18)F-DOPA (6-[18F]-fluoro-L-3,4-dihydroxyphenylalanine) radiotracer. Interestingly, social behavioral changes could be identified in the presymptomatic motor state before any motor and/or cognitive impairment occurred. Stronger effects were observed in subordinate animals compared to dominant animals. From baseline state to CLD-presymptomatic motor state, the frequency of emitted affiliative and aggressive behaviors increased. From CLD-presymptomatic to CHD-presymptomatic motor states, the frequency of the three categories of social behaviors (aggressive, submissive and affiliative) decreased. At this time, quantitative data analysis in PET scans highlighted a dopaminergic denervation in the insula and the posterior caudate nucleus. Finally, the frequency of the three categories of social behaviors decreased during the stable-symptomatic motor state compared to baseline and presymptomatic motor states; this was also associated with motor and cognitive disorders and a dopaminergic denervation in all the evaluated cortical and subcortical structures.

Norepinephrine transporter inhibition with desipramine exacerbates L-DOPA-induced dyskinesia: role for synaptic dopamine regulation in denervated nigrostriatal terminals

Pharmacological dopamine (DA) replacement with Levodopa [L-dihydroxyphenylalanine (L-DOPA)] is the gold standard treatment of Parkinson's disease (PD). However, long-term L-DOPA treatment is complicated by eventual debilitating abnormal involuntary movements termed L-DOPA-induced dyskinesia (LID), a clinically significant obstacle for the majority of patients who rely on L-DOPA to alleviate PD-related motor symptoms. The manifestation of LID may in part be driven by excessive extracellular DA derived from L-DOPA, but potential involvement of DA reuptake in LID severity or expression is unknown. We recently reported that in 6-hydroxydopamine (6-OHDA)-lesioned striatum, norepinephrine transporter (NET) expression increases and may play a significant role in DA transport. Furthermore, L-DOPA preferentially inhibits DA uptake in lesioned striatum. Therefore, we hypothesized that desipramine (DMI), a NET antagonist, could affect the severity of LID in an established LID model. Whereas DMI alone elicited no dyskinetic effects in lesioned rats, DMI + L-DOPA-treated rats gradually expressed more severe dyskinesia compared with L-DOPA alone over time. At the conclusion of the study, we observed reduced NET expression and norepinephrine-mediated inhibition of DA uptake in the DMI + L-DOPA group compared with L-DOPA-alone group in lesioned striatum. LID severity positively correlated with striatal extracellular signal-regulated protein kinase phosphorylation among the three treatment groups, with increased ppERK1/2 in DMI + L-DOPA group compared with the L-DOPA- and DMI-alone groups. Taken together, these results indicate that the combination of chronic L-DOPA and NET-mediated DA reuptake in lesioned nigrostriatal terminals may have a role in LID severity in experimental Parkinsonism.

Animal models of Parkinson's disease: a gateway to therapeutics?

Parkinson's disease (PD) is a progressive, neurodegenerative disorder of unknown etiology, although a complex interaction between environmental and genetic factors has been implicated as a pathogenic mechanism of selected neuronal loss. A better understanding of the etiology, pathogenesis, and molecular mechanisms underlying the disease process may be gained from research on animal models. While cell and tissue models are helpful in unraveling involved molecular pathways, animal models are much better suited to study the pathogenesis and potential treatment strategies. The animal models most relevant to PD include those generated by neurotoxic chemicals that selectively disrupt the catecholaminergic system such as 6-hydroxydopamine; 1-methyl-1,2,3,6-tetrahydropiridine; agricultural pesticide toxins, such as rotenone and paraquat; the ubiquitin proteasome system inhibitors; inflammatory modulators; and several genetically manipulated models, such as α-synuclein, DJ-1, PINK1, Parkin, and leucine-rich repeat kinase 2 transgenic or knock-out animals. Genetic and nongenetic animal models have their own unique advantages and limitations, which must be considered when they are employed in the study of pathogenesis or treatment approaches. This review provides a summary and a critical review of our current knowledge about various in vivo models of PD used to test novel therapeutic strategies.

Dopamine transporter loss in 6-OHDA Parkinson's model is unmet by parallel reduction in dopamine uptake

The dopamine transporter (DAT) regulates synaptic dopamine (DA) in striatum and modulation of DAT can affect locomotor activity. Thus, in Parkinson's disease (PD), DAT loss could affect DA clearance and locomotor activity. The locomotor benefits of L-DOPA may be mediated by transport through monoamine transporters and conversion to DA. However, its impact upon DA reuptake is unknown and may modulate synaptic DA. Using the unilateral 6-OHDA rat PD model, we examined [(3)H]DA uptake dynamics in relation to striatal DAT and tyrosine hydroxylase (TH) protein loss compared with contralateral intact striatum. Despite >70% striatal DAT loss, DA uptake decreased only ∼25% and increased as DAT loss approached 99%. As other monoamine transporters can transport DA, we determined if norepinephrine (NE) and serotonin (5-HT) differentially modulated DA uptake in lesioned striatum. Unlabeled DA, NE, and 5-HT were used, at a concentration that differentially inhibited DA uptake in intact striatum, to compete against [(3)H]DA uptake. In 6-OHDA lesioned striatum, DA was less effective, whereas NE was more effective, at inhibiting [(3)H]DA uptake. Furthermore, norepinephrine transporter (NET) protein levels increased and desipramine was ∼two-fold more effective at inhibiting NE uptake. Serotonin inhibited [(3)H]DA uptake, but without significant difference between lesioned and contralateral striatum. L-DOPA inhibited [(3)H]DA uptake two-fold more in lesioned striatum and inhibited NE uptake ∼five-fold more than DA uptake in naïve striatum. Consequently, DA uptake may be mediated by NET when DAT loss is at PD levels. Increased inhibition of DA uptake by L-DOPA and its preferential inhibition of NE over DA uptake, indicates that NET-mediated DA uptake may be modulated by L-DOPA when DAT loss exceeds 70%. These results indicate a novel mechanism for DA uptake during PD progression and provide new insight into how L-DOPA affects DA uptake, revealing possible mechanisms of its therapeutic and side effect potential.

The noradrenaline transporter as site of action for the anti-Parkinson drug amantadine

Amantadine is an established antiparkinsonian drug with a still unclear molecular site of action. In vivo studies on rodents, in vitro studies on tissue of rodents as well as binding studies on post mortem human tissue implicate monoamine transporters and NMDA receptors. In order to re-examine its action at human variants of these proteins on intact cells we established cells stably expressing the human NR1/2A NMDA-receptor, noradrenaline transporter (NAT) or dopamine transporter (DAT) and tested the activity of amantadine in patch-clamp, uptake, release, and cytotoxicity experiments. Amantadine was less potent in blockade of NMDA-induced inward currents than in blockade of noradrenaline uptake and in induction of inward currents in NAT expressing cells. It was 30 times more potent in blocking uptake in NAT- than in DAT cells. Amantadine induced NAT-mediated release at concentrations of 10-100 μM in superfusion experiments and blocked NAT-mediated cytotoxicity of the parkinsonism inducing neurotoxin 1-methyl-4-phenyl-pyridinium (MPP(+)) at concentrations of 30-300 μM, whereas 300-1000 μM amantadine was necessary to block NMDA-receptor mediated cytotoxicity. Similar to amphetamine, amantadine was inactive at α(2A)-adrenergic receptors and induced reverse noradrenaline transport by NAT albeit with smaller effect size. Thus, amantadine acted as "amphetamine-like releaser" with selectivity for the noradrenergic system. These findings and differences with memantine, which had been reported as less efficient antiparkinsonian drug than amantadine but in our hands was significantly more potent at the NMDA-receptor, suggest contributions from a noradrenergic mechanism in the antiparkinsonian action of amantadine.

α-Synuclein synaptic pathology and its implications in the development of novel therapeutic approaches to cure Parkinson's disease

Parkinson's disease (PD) is characterized by a progressive loss of dopamine (DA) neurons of the nigrostriatal system and by the presence of Lewy bodies (LB), proteinaceous inclusions mainly composed of filamentous α-synuclein aggregates. Alpha-synuclein is a natively unfolded protein which plays a central role in the control of dopaminergic neuronal functions and which is thought to be critically implicated in PD pathophysiology. Indeed, besides the fact that α-synuclein is the main protein component of LB, genetic studies showed that mutations and multiplications of the α-synuclein gene are responsible for the onset of familial forms of PD. A large body of evidence indicates that α-synuclein pathology at dopaminergic synapses may underlie the onset of neuronal cell dysfunction and degeneration in the PD brain. Thus, since the available therapeutic approaches to cure this disease are still limited, we hypothesized that the analysis of the α-synuclein synaptic proteome/lipidome may represent a tool to identify novel potential therapeutic targets to cure this disorder. We thus performed a critical review of studies describing α-synuclein pathophysiology at synaptic sites in experimental models of PD and in this paper we outline the most relevant findings regarding the specific modulatory effects exerted by α-synuclein in the control of synaptic functions in physiological and pathological conditions. The conclusions of these studies allow to single out novel potential therapeutic targets among the α-synuclein synaptic partners. These targets may be considered for the development of new pharmacological and gene-based strategies to cure PD.

TRK-820, a selective kappa opioid receptor agonist, could effectively ameliorate L-DOPA-induced dyskinesia symptoms in a rat model of Parkinson's disease

Long-term therapy with L-3,4-dihydroxyphenylalanine (L-DOPA) in parkinsonian patients is known to lead to dyskinesia within a few years, and repeated administration of L-DOPA is also likely to alter the expression of kappa opioid receptors in the basal ganglia, especially the striatum and substantia nigra pars reticulata, suggesting that kappa opioid receptors might be deeply involved in motor functions. Therefore, effects of TRK-820 ((E)-N-[17-(cyclopropylmethyl)-4,5alpha-epoxy-3,14-dihydroxymorphinan-6beta-yl]-3-(furan-3-yl)-N-methylprop-2-enamide monohydrochloride), a selective kappa opioid receptor agonist, were investigated on rotational behavior in unilateral 6-hydroxydopamine (6-OHDA)-treated rats (hemi-parkinsonian rats) and on L-DOPA-induced dyskinesia produced by administering L-DOPA to hemi-parkinsonian rats for 3 weeks (dyskinesia rats). A single administration of subcutaneous TRK-820 significantly increased spontaneous ipsilateral rotational behavior of hemi-parkinsonian rats at 30 microg/kg though the efficacy was moderate and also significantly inhibited L-DOPA-induced dyskinesia at 10 and 30 microg/kg; this inhibition was reversed in the presence of nor-binaltorphimine, a kappa opioid receptor antagonist. In vivo microdialysis study, TRK-820 (30 microg/kg, s.c.) significantly inhibited L-DOPA-derived extracellular dopamine content in the 6-OHDA-treated striatum in dyskinesia rats, but not in hemi-parkinsonian rats. Moreover, the development of L-DOPA-induced dyskinesia was suppressed by the 3-week co-administration of TRK-820 (3 and 10 microg/kg, s.c.) with L-DOPA. These results have suggested that TRK-820 ameliorates L-DOPA-induced dyskinesia with a moderate anti-parkinsonian effect by inhibiting L-DOPA-induced excessive dopamine release through kappa opioid receptors only in dyskinesia rats; therefore, TRK-820 is expected to become a useful agent for the treatment of L-DOPA-induced dyskinesia.

Modafinil Occupies Dopamine and Norepinephrine Transporters in Vivo and Modulates the Transporters and Trace Amine Activity in Vitro

2-[(Diphenylmethyl) sulfinyl]acetamide (modafinil), prescribed principally to treat narcolepsy, is undergoing assessment for other neuropsychiatric disorders and medical conditions. The neurochemical substrates of modafinil are unresolved. We postulated that modafinil enhances wakefulness by modulating dopamine (DAT), norepinephrine (NET), or serotonin (SERT) transporter activities. In vivo, we determined DAT and NET occupancy by modafinil by positron emission tomography imaging; in vitro, we determined modafinil activity at the DAT, NET, SERT, and rhesus monkey trace amine receptor 1 (TA1). In rhesus monkey, modafinil occupancy of striatal DAT was detected by [(11)C]2beta-carbomethoxy-3beta-4-(fluorophenyl)tropane and of thalamic NET by [(11)C](S,S)-2-(alpha-(2-methoxyphenoxy)-benzyl)morpholine. In vitro, modafinil effects in DAT-human embryonic kidney (HEK), NET-HEK, and SERT-HEK cells were investigated alone or combined with the TA1 receptor. Modafinil (i.v.) occupied striatal DAT sites (5 mg/kg: 35 +/- 12%, n = 4; 8 mg/kg: 54 +/- 3%, n = 3). In thalamus, modafinil occupied NET sites (5 mg/kg: 16 +/- 7.8%, n = 6; 8 mg/kg: 44 +/- 12%; n = 2). In vitro, modafinil inhibited [(3)H]dopamine (IC(50) = 6.4 microM), [(3)H]norepinephrine (IC(50) = 35.6 microM), and [(3)H]serotonin (IC(50) > 500 microM) transport via the human DAT, NET, and SERT. Modafinil did not activate the TA1 receptor in TA1-HEK cells, but it augmented a monoamine transporter-dependent enhancement of phenethylamine activation of TA1 in TA1-DAT and TA1-NET cells, but not in TA1-SERT cells. The present data provide compelling evidence that modafinil occupies the DAT and NET in living brain of rhesus monkeys and raise the possibility that modafinil affects wakefulness by interacting with catecholamine transporters in brain.