Rasagiline, a suicide inhibitor of monoamine oxidases, binds reversibly to α-synuclein

Dietary Natural Flavonoids: Intervention for MAO-B Against Parkinson's Disease

Parkinson's disease (PD) stands as the second most common neurological disorder after Alzheimer's disease, primarily affecting the elderly population and significantly compromising their quality of life. The precise etiology of PD remains elusive, but recent research has shed light on potential factors, including the formation of α-synuclein aggregates, oxidative stress, neurotransmitter imbalances, and dopaminergic neurodegeneration in the substantia nigra pars compacta (SNpc) region of the brain, culminating in motor symptoms such as bradykinesia, akinesia, tremors, and rigidity. Monoamine oxidase (MAO) is an essential enzyme, comprising two isoforms, MAO-A and MAO-B, responsible for the oxidation of monoamines such as dopamine. Increased MAO-B activity is responsible for decreased dopamine levels in the SNpc region of mid brain which is remarkably associated with the pathogenesis of PD-like manifestations. Inhibitors of MAO-B enhance striatal neuronal responses to dopamine, making them valuable in treating PD, which involves dopamine deficiency. Clinically approved MAO-B inhibitors such as selegiline, L-deprenyl, pargyline, and rasagiline are employed in the management of neurodegenerative conditions associated with PD. Current therapeutic interventions including MAO-B inhibitors for PD predominantly aim to alleviate these motor symptoms but often come with a host of side effects that can be particularly challenging for the patients. While effective, they have limitations, prompting a search for alternative treatments, there is a growing interest in exploring natural products notably flavonoids as potential sources of novel MAO-B inhibitors. In line with that, the present review focuses on natural flavonoids of plant origin that hold promise as potential candidates for the development of novel MAO-B inhibitors. The discussion encompasses both in vitro and in vivo studies, shedding light on their potential therapeutic applications. Furthermore, this review underscores the significance of exploring natural products as valuable reservoirs of MAO-B inhibitors, offering new avenues for drug development and addressing the pressing need for improved treatments in PD-like pathological conditions. The authors of this review majorly explore the neuroprotective potential of natural flavonoids exhibiting notable MAO-B inhibitory activity and additionally multi-targeted approaches in the treatment of PD with clinical evidence and challenges faced in current therapeutic approaches.

The Bifunctional Dimer Caffeine-Indan Attenuates α-Synuclein Misfolding, Neurodegeneration and Behavioral Deficits after Chronic Stimulation of Adenosine A1 Receptors

We previously found that chronic adenosine A1 receptor stimulation with N6-Cyclopentyladenosine increased α-synuclein misfolding and neurodegeneration in a novel α-synucleinopathy model, a hallmark of Parkinson's disease. Here, we aimed to synthesize a dimer caffeine-indan linked by a 6-carbon chain to cross the blood-brain barrier and tested its ability to bind α-synuclein, reducing misfolding, behavioral abnormalities, and neurodegeneration in our rodent model. Behavioral tests and histological stains assessed neuroprotective effects of the dimer compound. A rapid synthesis of the 18F-labeled analogue enabled Positron Emission Tomography and Computed Tomography imaging for biodistribution measurement. Molecular docking analysis showed that the dimer binds to α-synuclein N- and C-termini and the non-amyloid-β-component (NAC) domain, similar to 1-aminoindan, and this binding promotes a neuroprotective α-synuclein "loop" conformation. The dimer also binds to the orthosteric binding site for adenosine within the adenosine A1 receptor. Immunohistochemistry and confocal imaging showed the dimer abolished α-synuclein upregulation and aggregation in the substantia nigra and hippocampus, and the dimer mitigated cognitive deficits, anxiety, despair, and motor abnormalities. The 18F-labeled dimer remained stable post-injection and distributed in various organs, notably in the brain, suggesting its potential as a Positron Emission Tomography tracer for α-synuclein and adenosine A1 receptor in Parkinson's disease therapy.

Toxic interactions between dopamine, α-synuclein, monoamine oxidase, and genes in mitochondria of Parkinson's disease

Parkinson's disease is characterized by its distinct pathological features; loss of dopamine neurons in the substantia nigra pars compacta and accumulation of Lewy bodies and Lewy neurites containing modified α-synuclein. Beneficial effects of L-DOPA and dopamine replacement therapy indicate dopamine deficit as one of the main pathogenic factors. Dopamine and its oxidation products are proposed to induce selective vulnerability in dopamine neurons. However, Parkinson's disease is now considered as a generalized disease with dysfunction of several neurotransmitter systems caused by multiple genetic and environmental factors. The pathogenic factors include oxidative stress, mitochondrial dysfunction, α-synuclein accumulation, programmed cell death, impaired proteolytic systems, neuroinflammation, and decline of neurotrophic factors. This paper presents interactions among dopamine, α-synuclein, monoamine oxidase, its inhibitors, and related genes in mitochondria. α-Synuclein inhibits dopamine synthesis and function. Vice versa, dopamine oxidation by monoamine oxidase produces toxic aldehydes, reactive oxygen species, and quinones, which modify α-synuclein, and promote its fibril production and accumulation in mitochondria. Excessive dopamine in experimental models modifies proteins in the mitochondrial electron transport chain and inhibits the function. α-Synuclein and familiar Parkinson's disease-related gene products modify the expression and activity of monoamine oxidase. Type A monoamine oxidase is associated with neuroprotection by an unspecific dose of inhibitors of type B monoamine oxidase, rasagiline and selegiline. Rasagiline and selegiline prevent α-synuclein fibrillization, modulate this toxic collaboration, and exert neuroprotection in experimental studies. Complex interactions between these pathogenic factors play a decisive role in neurodegeneration in PD and should be further defined to develop new therapies for Parkinson's disease.

Cell-Penetrating Peptides: Promising Therapeutics and Drug-Delivery Systems for Neurodegenerative Diseases

Currently, one of the most significant and rapidly growing unmet medical challenges is the treatment of neurodegenerative diseases such as Alzheimer's disease (AD) and Parkinson's disease (PD). This challenge encompasses the imperative development of efficacious therapeutic agents and overcoming the intricacies of the blood-brain barrier for successful drug delivery. Here we focus on the delivery aspect with particular emphasis on cell-penetrating peptides (CPPs), widely used in basic and translational research as they enhance drug delivery to challenging targets such as tissue and cellular compartments and thus increase therapeutic efficacy. The combination of CPPs with nanomaterials such as nanoparticles (NPs) improves the performance, accuracy, and stability of drug delivery and enables higher drug loads. Our review presents and discusses research that utilizes CPPs, either alone or in conjugation with NPs, to mitigate the pathogenic effects of neurodegenerative diseases with particular reference to AD and PD.

Dietary Restriction against Parkinson's Disease: What We Know So Far

Dietary restriction (DR) is defined as a moderate reduction in food intake while avoiding malnutrition. The beneficial effects of DR are being increasingly acknowledged in aging and in a series of age-related neurodegenerative disorders, for example, Parkinson's disease (PD). To date, the pathogenesis of PD remains elusive and there is no cure for it in spite of intensive research over decades. In this review, we summarize the current knowledge on the efficacy of DR on PD, focusing on the underlying mechanisms involving general metabolism, neuroendocrinolgy, neuroinflammation, gut microbiome, and so on. We anticipate that this review will provide future perspectives for PD prevention and treatment.

Neuroprotective Function of Rasagiline and Selegiline, Inhibitors of Type B Monoamine Oxidase, and Role of Monoamine Oxidases in Synucleinopathies

Synucleinopathies are a group of neurodegenerative disorders caused by the accumulation of toxic species of α-synuclein. The common clinical features are chronic progressive decline of motor, cognitive, behavioral, and autonomic functions. They include Parkinson’s disease, dementia with Lewy body, and multiple system atrophy. Their etiology has not been clarified and multiple pathogenic factors include oxidative stress, mitochondrial dysfunction, impaired protein degradation systems, and neuroinflammation. Current available therapy cannot prevent progressive neurodegeneration and “disease-modifying or neuroprotective” therapy has been proposed. This paper presents the molecular mechanisms of neuroprotection by the inhibitors of type B monoamine oxidase, rasagiline and selegiline. They prevent mitochondrial apoptosis, induce anti-apoptotic Bcl-2 protein family, and pro-survival brain- and glial cell line-derived neurotrophic factors. They also prevent toxic oligomerization and aggregation of α-synuclein. Monoamine oxidase is involved in neurodegeneration and neuroprotection, independently of the catalytic activity. Type A monoamine oxidases mediates rasagiline-activated signaling pathways to induce neuroprotective genes in neuronal cells. Multi-targeting propargylamine derivatives have been developed for therapy in various neurodegenerative diseases. Preclinical studies have presented neuroprotection of rasagiline and selegiline, but beneficial effects have been scarcely presented. Strategy to improve clinical trials is discussed to achieve disease-modification in synucleinopathies.

Adenosine A1 receptor ligands bind to α-synuclein: implications for α-synuclein misfolding and α-synucleinopathy in Parkinson's disease

Background

Accumulating α-synuclein (α-syn) aggregates in neurons and glial cells are the staples of many synucleinopathy disorders, such as Parkinson’s disease (PD). Since brain adenosine becomes greatly elevated in ageing brains and chronic adenosine A1 receptor (A1R) stimulation leads to neurodegeneration, we determined whether adenosine or A1R receptor ligands mimic the action of known compounds that promote α-syn aggregation (e.g., the amphetamine analogue 2-aminoindan) or inhibit α-syn aggregation (e.g., Rasagiline metabolite 1-aminoindan). In the present study, we determined whether adenosine, A1R receptor agonist N⁶-Cyclopentyladenosine (CPA) and antagonist 8-cyclopentyl-1,3-dipropylxanthine (DPCPX) could directly interact with α-syn to modulate α-syn aggregation and neurodegeneration of dopaminergic neurons in the substantia nigra (SN).

Methods

Nanopore analysis and molecular docking were used to test the binding properties of CPA and DPCPX with α-syn in vitro. Sprague–Dawley rats were administered with 7-day intraperitoneal injections of the A1R ligands and 1- and 2-aminoindan, and levels of α-syn aggregation and neurodegeneration were examined in the SN pars compacta and hippocampal regions using confocal imaging and Western blotting.

Results

Using nanopore analysis, we showed that the A1R agonists (CPA and adenosine) interacted with the N-terminus of α-syn, similar to 2-aminoindan, which is expected to promote a “knot” conformation and α-syn misfolding. In contrast, the A1R antagonist DPCPX interacted with the N- and C-termini of α-syn, similar to 1-aminoindan, which is expected to promote a “loop” conformation that prevents α-syn misfolding. Molecular docking studies revealed that adenosine, CPA and 2-aminoindan interacted with the hydrophobic core of α-syn N-terminus, whereas DPCPX and 1-aminoindan showed direct binding to the N- and C-terminal hydrophobic pockets. Confocal imaging and Western blot analyses revealed that chronic treatments with CPA alone or in combination with 2-aminoindan increased α-syn expression/aggregation and neurodegeneration in both SN pars compacta and hippocampus. In contrast, DPCPX and 1-aminoindan attenuated the CPA-induced α-syn expression/aggregation and neurodegeneration in SN and hippocampus.

Conclusions

The results indicate that A1R agonists and drugs promoting a “knot” conformation of α-syn can cause α-synucleinopathy and increase neuronal degeneration, whereas A1R antagonists and drugs promoting a “loop” conformation of α-syn can be harnessed for possible neuroprotective therapies to decrease α-synucleinopathy in PD.

Supplementary Information

The online version contains supplementary material available at 10.1186/s40035-022-00284-3.

Monoamine Oxidase-B Inhibitors for the Treatment of Parkinson's Disease: Past, Present, and Future

Monoamine oxidase-B (MAO-B) inhibitors are commonly used for the symptomatic treatment of Parkinson's disease (PD). MAO-B inhibitor monotherapy has been shown to be effective and safe for the treatment of early-stage PD, while MAO-B inhibitors as adjuvant drugs have been widely applied for the treatment of the advanced stages of the illness. MAO-B inhibitors can effectively improve patients' motor and non-motor symptoms, reduce "OFF" time, and may potentially prevent/delay disease progression. In this review, we discuss the effects of MAO-B inhibitors on motor and non-motor symptoms in PD patients, their mechanism of action, and the future development of MAO-B inhibitor therapy.

The art of suicidal molecular seduction for targeting drug resistance

The development of drug resistance is one of the most significant challenges of the current century in the pharmaceutical industry. Superinfections, cancer chemoresistance, and resistance observed in many non-infectious diseases are nullifying the efforts and monetary supplies, put in the advent of new drug molecules. Millions of people die because of this drug resistance developed gradually through extensive use of the drugs. Inherently, some drugs are less prone to become ineffective by drug resistance than others. Covalent inhibitors bind to their targets via a biologically permanent bound with their cognate receptor and therefore display more potent inhibiting characteristics. Suicide inhibitors or mechanism-based inhibitors are one of the covalent inhibitors, which require a pre-activation step by their targeting enzyme. This step accrues their selectivity and specificity with respect to other covalent inhibitors. After that pre-activation step, they produce an analogue of the transition state of the catalytic enzyme, which is practically incapable of dissociating from the enzyme. Suicide inhibitors, due to their high intrinsic affinity toward the related enzyme, are resistant to many mechanisms involved in the development of drug resistance and can be regarded as one of the enemies of this scientific hurdle. These inhibitors compete even with monoclonal antibodies in terms of their cost-effectiveness and efficacy.

Rasagiline and selegiline modulate mitochondrial homeostasis, intervene apoptosis system and mitigate α-synuclein cytotoxicity in disease-modifying therapy for Parkinson's disease

Parkinson's disease has been considered as a motor neuron disease with dopamine (DA) deficit caused by neuronal loss in the substantia nigra, but now proposed as a multi-system disorder associated with α-synuclein accumulation in neuronal and non-neuronal systems. Neuroprotection in Parkinson's disease has intended to halt or reverse cell death of nigro-striatal DA neurons and prevent the disease progression, but clinical studies have not presented enough beneficial results, except the trial of rasagiline by delayed start design at low dose of 1 mg/day only. Now strategy of disease-modifying therapy should be reconsidered taking consideration of accumulation and toxicity of α-synuclein preceding the manifest of motor symptoms. Hitherto neuroprotective therapy has been aimed to mitigate non-specific risk factors; oxidative stress, mitochondrial dysfunction, apoptosis, deficits of neurotrophic factors (NTFs), inflammation and accumulation of pathogenic protein. Future disease-modify therapy should target more specified pathogenic factors, including deregulated mitochondrial homeostasis, deficit of NTFs and α-synuclein toxicity. Selegiline and rasagiline, inhibitors of type B monoamine oxidase, have been proved to exhibit potent neuroprotective function: regulation of mitochondrial apoptosis system, maintenance of mitochondrial function, increased expression of genes coding antioxidant enzymes, anti-apoptotic Bcl-2 and pro-survival NTFs, and suppression of oligomerization and aggregation of α-synuclein and the toxicity in cellular and animal experiments. However, the present available pharmacological therapy starts too late to reverse disease progression, and future disease-modifying therapy should include also non-pharmacological complementary therapy during the prodromal stage.

A new MAP-Rasagiline conjugate reduces α-synuclein inclusion formation in a cell model

BACKGROUND

Parkinson's disease (PD) is the second most common neurodegenerative disease of the elderly. Current therapies are only symptomatic, and have no disease-modifying effect. Therefore, disease progresses continuously over time, presenting with both motor and non-motor features. The precise molecular basis for PD is still elusive, but the aggregation of the protein alpha-synuclein (α-syn) is a key pathological hallmark of the disease and is, therefore, a major focus of current research. Considering the intrinsic properties of cell-penetrating peptides (CPPs) for mediating drug delivery of neurotherapeutics across the blood brain barrier (BBB), these might open novel opportunities for the development of new solutions for the treatment of brain-related aspects of PD and other neurodegenerative disorders.

METHODS

Here, we synthesized solid-phase CPPs using an amphipathic model peptide (MAP) conjugated with the drug Rasagiline (RAS), which we named RAS-MAP, and evaluated its effect on α-syn inclusion formation in a human cell-based model of synucleinopathy.

RESULTS

We found that treatment with RAS-MAP at low concentrations (1-3 µM) reduced α-syn aggregation in cells.

CONCLUSIONS

For the first time, we report that conjugation of a current drug used in the therapy of PD with CPP reduces α-syn aggregation, which might prove beneficial in PD and other synucleinopathies.

Toward the discovery and development of effective modulators of α-synuclein amyloid aggregation

A host of human diseases, including Parkinson's disease and Dementia with Lewy bodies, are suspected to be directly linked to protein aggregation. Amyloid protein aggregates and oligomeric intermediates of α-synuclein are observed in synucleinopathies and considered to be mediators of cellular toxicity. Hence, α-synuclein has seen as one of the leading and most compelling targets and is receiving a great deal of attention from researchers. Nevertheless, there is no neuroprotective approach directed toward Parkinson's disease or other synucleinopathies so far. In this review, we summarize the available data concerning inhibitors of α-synuclein aggregation and their advancing towards clinical use. The compounds are grouped according to their chemical structures, providing respective insights into their mechanism of action, pharmacology, and pharmacokinetics. Overall, shared structure-activity elements are emerging, as well as specific binding modes related to the ability of the modulators to establish hydrophobic and hydrogen bonds interactions with the protein. Some molecules with encouraging in vivo data support the possibility of translation to the clinic.

α-Synuclein Heterocomplexes with β-Amyloid Are Increased in Red Blood Cells of Parkinson's Disease Patients and Correlate with Disease Severity

Neurodegenerative disorders (NDs) are characterized by abnormal accumulation/misfolding of specific proteins, primarily α-synuclein (α-syn), β-amyloid1-42 (Aβ1-42) and tau, in both brain and peripheral tissues. In addition to oligomers, the role of the interactions of α-syn with Aβ or tau has gradually emerged. Nevertheless, despite intensive research, NDs have no accepted peripheral markers for biochemical diagnosis. In this respect, Red Blood Cells (RBCs) are emerging as a valid peripheral model for the study of aging-related pathologies. Herein, a small cohort (N = 28) of patients affected by Parkinson's disease (PD) and age-matched controls were enrolled to detect the content of α-syn (total and oligomeric), Aβ1-42 and tau (total and phosphorylated) in RBCs. Moreover, the presence of α-syn association with tau and Aβ1-42 was explored by co-immunoprecipitation/western blotting in the same cells, and quantitatively confirmed by immunoenzymatic assays. For the first time, PD patients were demonstrated to exhibit α-syn heterocomplexes with Aβ1-42 and tau in peripheral tissues; interestingly, α-syn-Aβ1-42 concentrations were increased in PD subjects with respect to healthy controls (HC), and directly correlated with disease severity and motor deficits. Moreover, total-α-syn levels were decreased in PD subjects and inversely related to their motor deficits. Finally, an increase of oligomeric-α-syn and phosphorylated-tau was observed in RBCs of the enrolled patients. The combination of three parameters (total-α-syn, phosphorylated-tau and α-syn-Aβ1-42 concentrations) provided the best fitting predictive index for discriminating PD patients from controls. Nevertheless further investigations should be required, overall, these data suggest α-syn hetero-aggregates in RBCs as a putative tool for the diagnosis of PD.

Pharmacological aspects of the neuroprotective effects of irreversible MAO-B inhibitors, selegiline and rasagiline, in Parkinson's disease

The era of MAO-B inhibitors dates back more than 50 years. It began with Kálmán Magyar's outstanding discovery of the selective inhibitor, selegiline. This compound is still regarded as the gold standard of MAO-B inhibition, although newer drugs have also been introduced to the field. It was revealed early on that selective, even irreversible inhibition of MAO-B is free from the severe side effect of the non-selective MAO inhibitors, the potentiation of tyramine, resulting in the so-called 'cheese effect'. Since MAO-B is involved mainly in the degradation of dopamine, the inhibitors lack any antidepressant effect; however, they became first-line medications for the therapy of Parkinson's disease based on their dopamine-sparing activity. Extensive studies with selegiline indicated its complex pharmacological activity profile with MAO-B-independent mechanisms involved. Some of these beneficial effects, such as neuroprotective and antiapoptotic properties, were connected to its propargylamine structure. The second MAO-B inhibitor approved for the treatment of Parkinson's disease, rasagiline also possesses this structural element and shows similar pharmacological characteristics. The preclinical studies performed with selegiline and rasagiline are summarized in this review.

Looking at the recent advances in understanding α-synuclein and its aggregation through the proteoform prism

Despite attracting the close attention of multiple researchers for the past 25 years, α-synuclein continues to be an enigma, hiding sacred truth related to its structure, function, and dysfunction, concealing mechanisms of its pathological spread within the affected brain during disease progression, and, above all, covering up the molecular mechanisms of its multipathogenicity, i.e. the ability to be associated with the pathogenesis of various diseases. The goal of this article is to present the most recent advances in understanding of this protein and its aggregation and to show that the remarkable structural, functional, and dysfunctional multifaceted nature of α-synuclein can be understood using the proteoform concept.

Novel Dimer Compounds That Bind α-Synuclein Can Rescue Cell Growth in a Yeast Model Overexpressing α-Synuclein. A Possible Prevention Strategy for Parkinson's Disease

The misfolding of α-synuclein is a critical event in the death of dopaminergic neurons and the progression of Parkinson's disease. Previously, it was suggested that drugs, which bind to α-synuclein and form a loop structure between the N- and C-termini, tend to be neuroprotective, whereas others, which cause a more compact structure, tend to be neurotoxic. To improve the binding to α-synuclein, eight novel compounds were synthesized from a caffeine scaffold attached to (R,S)-1-aminoindan, (R,S)-nicotine, and metformin, and their binding to α-synuclein determined through nanopore analysis and isothermal titration calorimetry. The ability of the dimers to interact with α-synuclein in a cell system was assayed in a yeast model of PD which expresses an AS-GFP (α-synuclein-Green Fluorescent Protein) construct under the control of a galactose promoter. In 5 mM galactose this yeast strain will not grow and large cytoplasmic foci are observed by fluorescent microscopy. Two of the dimers, C₈-6-I and C₈-6-N, at a concentration of 0.1 μM allowed the yeast to grow normally in 5 mM galactose and the AS-GFP became localized to the periphery of the cell. Both dimers were superior when compared to the monomeric compounds. The presence of the dimers also caused the disappearance of preformed cytoplasmic foci. Nanopore analysis of C₈-6-I and C₈-6-N were consistent with simultaneous binding to both the N- and C-terminus of α-synuclein but the binding constants were only 10⁵ M^-1.

Behavior of α-synuclein-drug complexes during nanopore analysis with a superimposed AC field

Seven α-synuclein-drug complexes have been studied by nanopore analysis in which an AC field of 200 mV from 10 MHz to 1 GHz has been superimposed on the standard electrophoretic DC voltage of 100 mV. α-Synuclein has a large dipole moment and in the absence of drug the AC field causes the molecule to oscillate at the entrance to the pore and reduces its ability to translocate through the pore. Thus more bumping events are observed in the current blockade histograms. The binding of drugs to α-synuclein has a large effect on the event profiles depending on the region of α-synuclein to which the drugs bind. Caffeine and (-)-nicotine bind both the N- and C-termini causing the protein to adopt a loop conformation that allows translocation even in the AC field. Metformin, which binds only to the C-terminus also facilitates translocation. For these drugs there is good evidence that the AC field is causing the complex to dissociate as it enters the pore that has not been observed previously. In contrast, complexes with (+)-amphetamine that has an N-terminal binding site and cocaine that binds to the central region of the protein, show only small changes in the event profiles in an AC field.

Label-free nanopore single-molecule measurement of trypsin activity

Trypsin is the most important digestive enzyme produced in the pancreas, and is a useful biomarker for pancreatitis. In this work, a rapid and sensitive method for the quantitative determination of trypsin activity is developed by using a biological alpha-hemolysin protein nanopore. Due to its much larger molecular diameter than the narrow pore constriction, trypsin itself cannot transport through the alpha-hemolysin channel. Hence, an indirect trypsin detection method is developed by monitoring its proteolytic cleavage of a lysine-containing peptide substrate. Based on the current modulations produced by the translocation of the substrate degradation products in the nanopore, the activity levels of trypsin could be determined. The method is rapid and highly sensitive, with picomolar concentrations of trypsin detected in minutes. In addition, the effects of cation and temperature on the sensor sensitivity, trypsin inhibition, and serum sample analysis are also investigated.

BDNF levels are increased by aminoindan and rasagiline in a double lesion model of Parkinson׳s disease

The anti-Parkinsonian drug rasagiline is a selective, irreversible inhibitor of monoamine oxidase and is used in the treatment of Parkinson׳s disease (PD). Its postulated neuroprotective effects may be attributed to MAO inhibition, or to its propargylamine moiety. The major metabolite of rasagiline, aminoindan, has shown promising neuroprotective properties in vitro but there is a paucity of studies investigating in vivo effects of this compound. Therefore, we examined neuroprotective effects of rasagiline and its metabolite aminoindan in a double lesion model of PD. Male Fisher 344 rats received i.p. injections of the noradrenergic neurotoxin DSP-4 and intra-striatal stereotaxic microinjections of the dopamine neurotoxin 6-OHDA. Saline, rasagiline or aminoindan (3mg/kg/day s.c.) were delivered via Alzet minipumps for 4 weeks. Rats were then tested for spontaneous locomotion and a novel object recognition task. Following behavioral testing, brain tissue was processed for ELISA measurements of growth factors and immunohistochemistry. Double-lesioned rats treated with rasagiline or aminoindan had reduced behavioral deficits, both in motor and cognitive tasks compared to saline-treated double-lesioned rats. BDNF levels were significantly increased in the hippocampus and striatum of the rasagiline- and aminoindan-lesioned groups compared to the saline-treated lesioned group. Double-lesioned rats treated with rasagiline or aminoindan exhibited a sparing in the mitochondrial marker Hsp60, suggesting mitochondrial involvement in neuroprotection. Tyrosine hydroxylase (TH) immunohistochemistry revealed a sparing of TH-immunoreactive terminals in double-lesioned rats treated with rasagiline or aminoindan in the striatum, hippocampus, and substantia nigra. These data provide evidence of neuroprotection by aminoindan and rasagiline via their ability to enhance BDNF levels.

Drugs That Bind to α-Synuclein: Neuroprotective or Neurotoxic?

The misfolding of α-synuclein is a critical event in the death of dopaminergic neurons and the progression of Parkinson's disease. Drugs that bind to α-synuclein and form a loop structure between the N- and C-terminus tend to be neuroprotective, whereas others that cause a more compact structure tend to be neurotoxic. The binding of several natural products and other drugs that are involved in dopamine metabolism were investigated by nanopore analysis and isothermal titration calorimetry. The antinausea drugs, cinnarizine and metoclopramide, do not bind to α-synuclein, whereas amphetamine and the herbicides, paraquat and rotenone, bind tightly and cause α-synuclein to adopt a more compact conformation. The recreational drug, cocaine, binds to α-synuclein, whereas heroin and methadone do not. Metformin, which is prescribed for diabetes and is neuroprotective, binds well without causing α-synuclein to adopt a more compact conformation. Methylphenidate (ritalin) binds to sites in both the N- and C-terminus and causes α-synuclein to adopt a loop conformation. In contrast, amphetamine only binds to the N-terminus. Except for cinnarizine and metoclopramide, there is a good correlation between the mode of binding to α-synuclein and whether a drug is neuroprotective or neurotoxic.