Pargyline prevents MPTP-induced parkinsonism in primates

Synthesis of propargylamine: pioneering a green path with non-conventional KA2 coupling approach

The KA2 coupling reaction is a well-explored and versatile method for forming C-C bonds in synthetic chemistry. It is composed of ketone, amine, and alkyne, which play a major role in the synthesis of propargylamines, known for their diverse biological activities and are used in treating neurogenetical disorders. The KA2 coupling is highly challenging due to the low reactivity of ketimines toward nucleophilic attacks with metal acetylide intermediates formed by activating the C-H bond of the alkyne. Despite predominant studies conducted on thermal conditions for KA2 coupling reactions, green and sustainable approaches like non-conventional methods still have a lot to achieve. This review article provides a comprehensive introduction to the non-conventional approach in the KA2 coupling reaction, outlining its mechanisms and exploring future aspects.

Mitochondrial transplantation exhibits neuroprotective effects and improves behavioral deficits in an animal model of Parkinson's disease

Mitochondria are essential organelles for cell survival that manage the cellular energy supply by producing ATP. Mitochondrial dysfunction is associated with various human diseases, including metabolic syndromes, aging, and neurodegenerative diseases. Among the diseases related to mitochondrial dysfunction, Parkinson's disease (PD) is the second most common neurodegenerative disease and is characterized by dopaminergic neuronal loss and neuroinflammation. Recently, it was reported that mitochondrial transfer between cells occurred naturally and that exogenous mitochondrial transplantation was beneficial for treating mitochondrial dysfunction. The current study aimed to investigate the therapeutic effect of mitochondrial transfer on PD in vitro and in vivo. The results showed that PN-101 mitochondria isolated from human mesenchymal stem cells exhibited a neuroprotective effect against 1-methyl-4-phenylpyridinium, 6-hydroxydopamine and rotenone in dopaminergic cells and ameliorated dopaminergic neuronal loss in the brains of C57BL/6J mice injected 30 ​mg/kg of methyl-4-phenyl-1,2,3,6-tetrahydropyridine (MPTP) intraperitoneally. In addition, PN-101 exhibited anti-inflammatory effects by reducing the expression of pro-inflammatory cytokines in microglial cells and suppressing microglial activation in the striatum. Furthermore, intravenous mitochondrial treatment was associated with behavioral improvements during the pole test and rotarod test in the MPTP-induced PD mice. These dual effects of neuroprotection and anti-neuroinflammation support the potential for mitochondrial transplantation as a novel therapeutic strategy for PD.

The specific NQO2 inhibitor, S29434, only marginally improves the survival of dopamine neurons in MPTP-intoxicated mice

Over the years, evidence has accumulated on a possible contributive role of the cytosolic quinone reductase NQO2 in models of dopamine neuron degeneration induced by parkinsonian toxin, but most of the data have been obtained in vitro. For this reason, we asked the question whether NQO2 is involved in the in vivo toxicity of MPTP, a neurotoxin classically used to model Parkinson disease-induced neurodegeneration. First, we show that NQO2 is expressed in mouse substantia nigra dopaminergic cell bodies and in human dopaminergic SH-SY5Y cells as well. A highly specific NQO2 inhibitor, S29434, was able to reduce MPTP-induced cell death in a co-culture system of SH-SY5Y cells with astrocytoma U373 cells but was inactive in SH-SY5Y monocultures. We found that S29434 only marginally prevents substantia nigra tyrosine hydroxylase+ cell loss after MPTP intoxication in vivo. The compound produced a slight increase of dopaminergic cell survival at day 7 and 21 following MPTP treatment, especially with 1.5 and 3 mg/kg dosage regimen. The rescue effect did not reach statistical significance (except for one experiment at day 7) and tended to decrease with the 4.5 mg/kg dose, at the latest time point. Despite the lack of robust protective activity of the inhibitor of NQO2 in the mouse MPTP model, we cannot rule out a possible role of the enzyme in parkinsonian degeneration, particularly because it is substantially expressed in dopaminergic neurons.

Measurement of MAO Enzymatic Activity by Spectrophotometric Direct Assays

MAO activity measurement can be monitored by direct peroxidase-free assays following different spectroscopy methods. Typically, these are assays that follow the conversion of different MAO substrates into its corresponding products monitored in either absorbance or fluorescence. Herein, we describe the assays for enzyme activity assessment with MAO B and particularly the MAO A substrate kynuramine, as well as the MAO B substrate benzylamine. Moreover, we also describe MAO activity determination using the tertiary amine substrate allyl amine 1-methyl-4-(1-methyl-1 H-pyrrol-2-yl)-1,2,3,6-tetrahydropyridine (MMTP). These are very useful methods for the investigation of MAO inhibitory activity by molecules known to be HRP-interfering. In the present chapter we demonstrate the application of these methods in MAO activity and Michaelis-Menten curve determinations as well as inhibitory activity experiments.

The evaluation of N-propargylamine-2-aminotetralin as an inhibitor of monoamine oxidase

Monoamine oxidase B (MAO-B) inhibitors are established therapy for Parkinson's disease and act, in part, by blocking the MAO-catalysed metabolism of dopamine in the brain. Two propargylamine-containing MAO-B inhibitors, selegiline [(R)-deprenyl] and rasagiline, are currently used in the clinic for this purpose. These compounds are mechanism-based inactivators and, after oxidative activation, form covalent adducts with the FAD co-factor. An important consideration is that selegiline and rasagiline display specificity for MAO-B over the MAO-A isoform thus reducing the risk of tyramine-induced changes in blood-pressure. In the interest of discovering new propargylamine MAO inhibitors, the present study synthesises racemic N-propargylamine-2-aminotetralin (2-PAT), a compound that may be considered as both a six-membered ring analogue of rasagiline and a semi-rigid N-desmethyl ring-closed analogue of selegiline. The in vitro human MAO inhibition properties of this compound were measured and the results showed that 2-PAT is a 20-fold more potent inhibitor of MAO-A (IC₅₀ = 0.721 µM) compared to MAO-B (IC₅₀ = 14.6 µM). Interestingly, dialysis studies found that 2-PAT is a reversible MAO-A inhibitor, while acting as an inactivator of MAO-B. Since reversible MAO-A inhibitors are much less liable to potentiate tyramine-induced side effects than MAO-A inactivators, it is reasonable to suggest that 2-PAT could be a useful and safe therapeutic agent for disorders such as Parkinson's disease and depression.

A Biocatalytic Platform for the Synthesis of Enantiopure Propargylic Alcohols and Amines

Propargylic alcohols and amines are versatile building blocks in organic synthesis. We demonstrate a straightforward enzymatic cascade to synthesize enantiomerically pure propargylic alcohols and amines from readily available racemic starting materials. In the first step, the peroxygenase from Agrocybe aegerita converted the racemic propargylic alcohols into the corresponding ketones, which then were converted into the enantiomerically pure alcohols using the (R)-selective alcohol dehydrogenase from Lactobacillus kefir or the (S)-selective alcohol dehydrogenase from Thermoanaerobacter brokii. Moreover, an enzymatic Mitsunobu-type conversion of the racemic alcohols into enantiomerically enriched propargylic amines using (R)-selective amine transaminase from Aspergillus terreus or (S)-selective amine transaminase from Chromobacterium violaceum was established. The one-pot two-step cascade reaction yielded a broad range of enantioenriched alcohol and amine products in 70–99% yield.

Monoamine Oxidase Inhibitors: From Classic to New Clinical Approaches

Monoamine oxidases (MAOs) are involved in the oxidative deamination of different amines and neurotransmitters. This pointed them as potential targets for several disorders and along the last 70 years a wide variety of MAO inhibitors have been developed as successful drugs for the treatment of complex diseases, being the first drugs approved for depression in the late 1950s. The discovery of two MAO isozymes (MAO-A and B) with different substrate selectivity and tissue expression patterns led to novel therapeutic approaches and to the development of new classes of inhibitors, such as selective irreversible and reversible MAO-B inhibitors and reversible MAO-A inhibitors. Significantly, MAO-B inhibitors constitute a widely studied group of compounds, some of them approved for the treatment of Parkinson's disease. Further applications are under development for the treatment of Alzheimer's disease, amyotrophic lateral sclerosis, and cardiovascular diseases, among others. This review summarizes the most important aspects regarding the development and clinical use of MAO inhibitors, going through mechanistic and structural details, new indications, and future perspectives. Monoamine oxidases (MAOs) catalyze the oxidative deamination of different amines and neurotransmitters. The two different isozymes, MAO-A and MAO-B, are located at the outer mitochondrial membrane in different tissues. The enzymatic reaction involves formation of the corresponding aldehyde and releasing hydrogen peroxide (H₂O₂) and ammonia or a substituted amine depending on the substrate. MAO's role in neurotransmitter metabolism made them targets for major depression and Parkinson's disease, among other neurodegenerative diseases. Currently, these compounds are being studied for other diseases such as cardiovascular ones.

A green approach for A3-coupling reactions: an experimental and theoretical study on NHC silver and gold catalysts

N-heterocyclic carbene silver and gold complexes active in A3-coupling (aldehyde–alkyne–amine) reactions in green conditions.

Synthesis, Characterization, Catalytic Activity, and DFT Calculations of Zn(II) Hydrazone Complexes

Two new Zn(II) complexes with tridentate hydrazone-based ligands (condensation products of 2-acetylthiazole) were synthesized and characterized by infrared (IR) and nuclear magnetic resonance (NMR) spectroscopy and single crystal X-ray diffraction methods. The complexes 1, 2 and recently synthesized [ZnL³(NCS)₂] (L³ = (E)-N,N,N-trimethyl-2-oxo-2-(2-(1-(pyridin-2-yl)ethylidene)hydrazinyl)ethan-1-aminium) complex 3 were tested as potential catalysts for the ketone-amine-alkyne (KA²) coupling reaction. The gas-phase geometry optimization of newly synthesized and characterized Zn(II) complexes has been computed at the density functional theory (DFT)/B3LYP/6–31G level of theory, while the highest occupied molecular orbital and lowest unoccupied molecular orbital (HOMO and LUMO) energies were calculated within the time-dependent density functional theory (TD-DFT) at B3LYP/6-31G and B3LYP/6-311G(d,p) levels of theory. From the energies of frontier molecular orbitals (HOMO–LUMO), the reactivity descriptors, such as chemical potential (μ), hardness (η), softness (S), electronegativity (χ) and electrophilicity index (ω) have been calculated. The energetic behavior of the investigated compounds (1 and 2) has been examined in gas phase and solvent media using the polarizable continuum model. For comparison reasons, the same calculations have been performed for recently synthesized [ZnL³(NCS)₂] complex 3. DFT results show that compound 1 has the smaller frontier orbital gap so, it is more polarizable and is associated with a higher chemical reactivity, low kinetic stability and is termed as soft molecule.

[The role of inhibitors of COMT and MAO-B in the therapy of Parkinson's disease]

Inhibitors of COMT and MAO-B are well established in the pharmacotherapy of Parkinson's disease (PD). MAO-B inhibitors are used as monotherapy as well as in combination with levodopa, whereas COMT inhibitors exert their effects only in conjungtion with levodopa. Both classes of compounds prolong the response duration of levodopa and optimise its clinical benefit. As a result, the ON-times are prolonged significantly. In the past, MAO-B inhibitors were also adminstered for neuroprotection; however, despite convincing scientific reasoning in support of neuroprotective effects, these could not be substantiated in clinical studies performed so far.

Salidroside ameliorates Parkinson's disease by inhibiting NLRP3-dependent pyroptosis

Parkinson's disease (PD) is a common age-related neurodegenerative movement disorder, which is mainly due to the loss of dopaminergic neurons. Pyroptosis is a new programmed cell death characterized by NLR Family Pyrin Domain Containing 3 (NLRP3)-dependent, IL-1β, IL-18 and Gasdermin D. Salidroside (Sal) has been reported to have neuro-protective effect. However, the roles of pyroptosis and Sal on anti-pyroptosis in PD have not been elucidated. In this study, we tested underlying mechanisms of pyroptosis in PD and neuro-protective effects of Sal. We established 1-methyl-4-phenyl-1,2,3,6-tetrahydropyridine (MPTP)-induced C57BL/6J mice and C57BL/10ScNJ (TLR4-deficient mice) in vivo, MPTP-induced PC-12 and LPS-induced BV2 in vitro. We found that Sal could ameliorate MPTP-induced PD symptoms and reduce the levels of IL-1β, IL-18 and Gasdermin D, which are main hallmarks of pyroptosis. Further study indicated that Sal alleviated PD through inhibiting NLRP3-dependent pyroptosis. In conclusion, pyroptosis plays a key role in PD and Sal protects dopaminergic neurons by inhibiting NLRP3-dependent pyroptosis through: (1) indirectly reducing the production of NLRP3, pro-IL-1β and pro-IL-18 by inhibiting TLR4/MyD88/NF-κB signaling pathways, (2) directly suppressing pyroptosis through inhibiting TXNIP/NLRP3/caspase-1 signaling pathways. These results indicated that inhibiting pyroptosis or administration of Sal could be a novel therapeutic strategy for PD.

A pilot study on assessment of locomotor behavior using a video tracking system in minipigs

Pigs are often selected for large animal models including for neuroscience and behavioral research, because their anatomy and biochemistry are similar to those of humans. However, behavioral assessments, in combination with objective long-term monitoring, is difficult. In this study, we introduced an automated video tracking system which was previously used in rodent studies, for use with pig models. Locomotor behaviors (total distance, number of zone transitions, and velocity) were evaluated and their changes were validated by different 1-methyl-4-phenyl-1,2,3,6-tetrahydropyridine (MPTP) administration methods and dosing regimens. Three minipigs (23-29 kg) received subcutaneous or intravenous MPTP, either 1 or 3 times per week. Immediately after MPTP injection, the minipigs remained in a corner and exhibited reduced trajectory. In addition, the total distance travelled, number of zone transitions, and velocity were greatly reduced at every MPTP administration in all the minipigs, accompanying to increased resting time. However, the MPTP-induced symptoms were reversed when MPTP administration was terminated. In conclusion, this automated video-tracking system was able to monitor long-term locomotor activity and differentiate detailed alterations in large animals. It has the advantages of being easy to use, higher resolution, less effort, and more delicate tracking. Additionally, as our method can be applied to the animals' home pen, no habituation is needed.

Modern Catalysts in A3- Coupling Reactions

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Propargylamines are an important constituent of diverse, biologically active and industrially valuable compounds. These useful, convenient and effective compounds can be synthesized via the A3-coupling reactions between an aldehyde, amine, and alkyne in the presence of a catalyst. In the past years, most of the catalysts containing transition metals were applied in these reactions, but today, various heterogeneous catalysts, especially nanocatalysts are used. The purpose of this review was to introduce some modern catalysts for the A3-coupling reaction.

Zn-Catalyzed Multicomponent KA2 Coupling: One-Pot Assembly of Propargylamines Bearing Tetrasubstituted Carbon Centers

Tetrasubstituted propargylamines comprise a unique class of highly useful compounds, which can be accessed through the multicomponent coupling between ketones, amines, and alkynes (KA² coupling), an underexplored transformation. Herein, the development of a novel, highly efficient, and user-friendly catalytic system for the KA² coupling, based on the environmentally benign, inexpensive, and readily available zinc acetate, is described. This system is employed in the multicomponent assembly of unprecedented, tetrasubstituted propargylamines derived from structurally diverse, challenging, and even biorelevant substrates. Notable features of this protocol include the demonstration of the enhancing effect that neat conditions can have on catalytic activity, as well as the expedient functionalization of hindered, prochiral cyclohexanones, linear ketones, and interesting molecular scaffolds such as norcamphor and nornicotine.

Regulation of Monoamine Oxidase B Gene Expression: Key Roles for Transcription Factors Sp1, Egr1 and CREB, and microRNAs miR-300 and miR-1224

Monoamine oxidase B (MAO-B), a flavoenzyme located in the outer mitochondrial membrane, is involved in the catabolism of monoamines. Altered levels of MAO-B are associated with cardiovascular/neuronal diseases. However, molecular mechanisms of MAO-B gene regulation are partially understood. We undertook a systematic analysis of the MAO-B gene to identify the key transcriptional/post-transcriptional regulatory molecules. Expression of MAO-B promoter-reporter constructs in cultured cells identified the -144/+25-bp domain as the core promoter region. Stringent in silico analysis of this core promoter predicted binding sites for several transcription factors. Over-expression/down-regulation of transcription factors Sp1/Egr1/CREB increased/decreased the MAO-B promoter-reporter activity and endogenous MAO-B protein level. Electrophoretic mobility shift assays and ChIP assays provided evidence for interactions of Sp1/Egr1/CREB with the MAO-B promoter. MAOB transcript level also positively correlated with the transcript level of Sp1/Egr1/CREB in various human tissue samples. Computational predictions using multiple algorithms coupled with systematic functional analysis revealed direct interactions of the microRNAs miR-1224 and miR-300 with MAO-B 3'-UTR. Dopamine dose-dependently enhanced MAO-B transcript and protein levels via increased binding of CREB to MAO-B promoter and reduced miR-1224/miR-300 levels. 8-Bromo-cAMP and forskolin augmented MAO-B expression, whereas inhibition of PKA diminished the gene expression suggesting involvement of cAMP-PKA axis. Interestingly, Sp1/Egr1/CREB/miR-1224 levels correlate with MAO-B expression in rodent models of hypertension/MPTP-induced neurodegeneration, indicating their roles in governing MAO-B gene expression in these disease states. Taken together, this study elucidates the previously unknown roles of the transcription factors Sp1/Egr1/CREB and microRNAs miR-1224/miR-300 in regulating MAO-B gene expression under basal/disease states involving dysregulated catecholamine levels.

The MPTP Story

The identification of MPTP, a relatively simple compound which causes selective degeneration of the substantia nigra after systemic administration, has had an a significant impact on the understanding and treatment of Parkinson’s disease (PD) over the last 30 years. This article is prefaced by the intriguing “medical detective story” that lead to the discovery of the biological effects of MPTP in humans. The steps that lead to the unraveling its mechanism of action and their impact on research into pathways underlying nigrostriatal degeneration are reviewed. The impact of the animal models that have been developed utilizing MPTP is also described with a focus on the translational implications of MPTP-related research. These include use of MAO-B inhibitors aimed at neuroprotection in PD and the importance of a stable primate model for PD which was utilized to better understand the circuitry of the basal ganglia, and the identification of the subthalamic nucleus as a target for deep brain stimulation. Finally, the results of a broad range of epidemiologic studies aimed as assessing the impact of environmental factors in PD that have been inspired by MPTP are summarized, including the discovery of other neurotoxicants (rotenone and paraquat) with parkinsonogenic effects. Overall, this article attempts to describe how the discovery of this nigral neurotoxicant began, where it is currently, and what the future may hold.

Novel ferrocene-labeled propargyl amines via CuI multicomponent amination/alkynylation

An efficient synthesis of ferrocene-tagged propargyl amine derivatives via one-pot three-component domino amination/alkynylation in water is reported.

Efficient Gold(I) Acyclic Diaminocarbenes for the Synthesis of Propargylamines and Indolizines

Mononuclear gold(I) acyclic diaminocarbenes (ADCs) were prepared by the reaction of 1,2-cyclohexanediamine with the corresponding isocyanide complexes [AuCl(CNR)] (R = Cy, t Bu). The three-component coupling of aldehydes, amines, and alkynes was investigated by using these gold(I) ADC complexes. The new gold(I) metal complexes are highly efficient catalysts for the synthesis of propargylamines and indolizines in the absence of solvent and in mild conditions. This method affords the corresponding final products with excellent yields in short reaction times. Additionally, chiral gold(I) complexes with ADCs have been prepared and tried in the enantioselective synthesis of propargylamines.

Monoamine Oxidases

Monoamine oxidases A and B (MAO A and B) are mammalian flavoenzymes bound to the outer mitochondrial membrane. They were discovered almost a century ago and they have been the subject of many biochemical, structural and pharmacological investigations due to their central role in neurotransmitter metabolism. Currently, the treatment of Parkinson's disease involves the use of selective MAO B inhibitors such as rasagiline and safinamide. MAO inhibition was shown to exert a general neuroprotective effect as a result of the reduction of oxidative stress produced by these enzymes, which seems to be relevant also in non-neuronal contexts. MAOs were successfully expressed as recombinant proteins in Pichia pastoris, which allowed a thorough biochemical and structural characterization. These enzymes are characterized by a globular water-soluble main body that is anchored to the mitochondrial membrane through a C-terminal α-helix, similar to other bitopic membrane proteins. In both MAO A and MAO B the enzyme active site consists of a hydrophobic cavity lined by residues that are conserved in the two isozymes, except for few details that determine substrate and inhibitor specificity. In particular, human MAO B features a dual-cavity active site whose conformation depends on the size of the bound ligand. This article provides a comprehensive and historical review of MAOs and the state-of-the-art of these enzymes as membrane drug targets.

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.

Synthesis and Reactivity of Propargylamines in Organic Chemistry

Propargylamines are a versatile class of compounds which find broad application in many fields of chemistry. This review aims to describe the different strategies developed so far for the synthesis of propargylamines and their derivatives as well as to highlight their reactivity and use as building blocks in the synthesis of chemically relevant organic compounds. In the first part of the review, the different synthetic approaches to synthesize propargylamines, such as A³ couplings and C-H functionalization of alkynes, have been described and organized on the basis of the catalysts employed in the syntheses. Both racemic and enantioselective approaches have been reported. In the second part, an overview of the transformations of propargylamines into heterocyclic compounds such as pyrroles, pyridines, thiazoles, and oxazoles, as well as other relevant organic derivatives, is presented.

MPTP-Induced Modulation of Neurotransmitters in SH-SY5Y Human Neuroblastoma Cells

Neurotoxic effects of MPTP(1-methyl-4-phenyl-1, 2, 3, 6-tetrahydropyridine) were evaluated in vitro using a human neuronal cell line, SH-SY5Y, that contained features contributing to expression of MPTP toxicity in vivo, namely, a transport system for dopam ine (DA) and monam ine oxidase (MAO) activity. In this model system, MPTP was found to reduce levels of catecholamines (DA, norepinephrine, epinephrine), serotonin (5-HT), and the 5-HT metabolite 5-hydroxyindoleacetic acid (5-HIAA). MPTP enhanced 3H-DA release, which could contribute to the reduction in DA concentrations seen in these cells. In addition, MPTP inhibited MAO activity (Ki 2.26 X 10-5 M). Pretreatment with the MAO inhibitor pargy-line protected the cells from MPTP-induced alterations of catecholamines and the decrease in 5-HT. In this in vitro model, the cholinergic antagonists atro-pine and A-tubocurarine also protected cells from MPTP-induced alterations of catecholamines. The capability of cholinergic antagonists to prevent the MPTP-induced alterations of catecholamine concentrations suggests a possible cholinergic contribution to MPTP neurotoxicity in this cell line.

Parkinson's Disease: The Mitochondria-Iron Link

Mitochondrial dysfunction, iron accumulation, and oxidative damage are conditions often found in damaged brain areas of Parkinson's disease. We propose that a causal link exists between these three events. Mitochondrial dysfunction results not only in increased reactive oxygen species production but also in decreased iron-sulfur cluster synthesis and unorthodox activation of Iron Regulatory Protein 1 (IRP1), a key regulator of cell iron homeostasis. In turn, IRP1 activation results in iron accumulation and hydroxyl radical-mediated damage. These three occurrences-mitochondrial dysfunction, iron accumulation, and oxidative damage-generate a positive feedback loop of increased iron accumulation and oxidative stress. Here, we review the evidence that points to a link between mitochondrial dysfunction and iron accumulation as early events in the development of sporadic and genetic cases of Parkinson's disease. Finally, an attempt is done to contextualize the possible relationship between mitochondria dysfunction and iron dyshomeostasis. Based on published evidence, we propose that iron chelation-by decreasing iron-associated oxidative damage and by inducing cell survival and cell-rescue pathways-is a viable therapy for retarding this cycle.

Preferential Extracellular Generation of the Active Parkinsonian Toxin MPP+ by Transporter-Independent Export of the Intermediate MPDP+

AIMS

1-Methyl-4-phenyl-tetrahydropyridine (MPTP) is among the most widely used neurotoxins for inducing experimental parkinsonism. MPTP causes parkinsonian symptoms in mice, primates, and humans by killing a subpopulation of dopaminergic neurons. Extrapolations of data obtained using MPTP-based parkinsonism models to human disease are common; however, the precise mechanism by which MPTP is converted into its active neurotoxic metabolite, 1-methyl-4-phenyl-pyridinium (MPP(+)), has not been fully elucidated. In this study, we aimed to address two unanswered questions related to MPTP toxicology: (1) Why are MPTP-converting astrocytes largely spared from toxicity? (2) How does MPP(+) reach the extracellular space?

RESULTS

In MPTP-treated astrocytes, we discovered that the membrane-impermeable MPP(+), which is generally assumed to be formed inside astrocytes, is almost exclusively detected outside of these cells. Instead of a transporter-mediated export, we found that the intermediate, 1-methyl-4-phenyl-2,3-dihydropyridinium (MPDP(+)), and/or its uncharged conjugate base passively diffused across cell membranes and that MPP(+) was formed predominately by the extracellular oxidation of MPDP(+) into MPP(+). This nonenzymatic extracellular conversion of MPDP(+) was promoted by O2, a more alkaline pH, and dopamine autoxidation products.

INNOVATION AND CONCLUSION

Our data indicate that MPTP metabolism is compartmentalized between intracellular and extracellular environments, explain the absence of toxicity in MPTP-converting astrocytes, and provide a rationale for the preferential formation of MPP(+) in the extracellular space. The mechanism of transporter-independent extracellular MPP(+) formation described here indicates that extracellular genesis of MPP(+) from MPDP is a necessary prerequisite for the selective uptake of this toxin by catecholaminergic neurons.

Mitochondrial iron homeostasis and its dysfunctions in neurodegenerative disorders

Synthesis of the iron-containing prosthetic groups-heme and iron-sulfur clusters-occurs in mitochondria. The mitochondrion is also an important producer of reactive oxygen species (ROS), which are derived from electrons leaking from the electron transport chain. The coexistence of both ROS and iron in the secluded space of the mitochondrion makes this organelle particularly prone to oxidative damage. Here, we review the elements that configure mitochondrial iron homeostasis and discuss the principles of iron-mediated ROS generation in mitochondria. We also review the evidence for mitochondrial dysfunction and iron accumulation in Alzheimer's disease, Huntington Disease, Friedreich's ataxia, and in particular Parkinson's disease. We postulate that a positive feedback loop of mitochondrial dysfunction, iron accumulation, and ROS production accounts for the process of cell death in various neurodegenerative diseases in which these features are present.

Increased expression of the dopamine transporter leads to loss of dopamine neurons, oxidative stress and l-DOPA reversible motor deficits

The dopamine transporter is a key protein responsible for regulating dopamine homeostasis. Its function is to transport dopamine from the extracellular space into the presynaptic neuron. Studies have suggested that accumulation of dopamine in the cytosol can trigger oxidative stress and neurotoxicity. Previously, ectopic expression of the dopamine transporter was shown to cause damage in non-dopaminergic neurons due to their inability to handle cytosolic dopamine. However, it is unknown whether increasing dopamine transporter activity will be detrimental to dopamine neurons that are inherently capable of storing and degrading dopamine. To address this issue, we characterized transgenic mice that over-express the dopamine transporter selectively in dopamine neurons. We report that dopamine transporter over-expressing (DAT-tg) mice display spontaneous loss of midbrain dopamine neurons that is accompanied by increases in oxidative stress markers, 5-S-cysteinyl-dopamine and 5-S-cysteinyl-DOPAC. In addition, metabolite-to-dopamine ratios are increased and VMAT2 protein expression is decreased in the striatum of these animals. Furthermore, DAT-tg mice also show fine motor deficits on challenging beam traversal that are reversed with l-DOPA treatment. Collectively, our findings demonstrate that even in neurons that routinely handle dopamine, increased uptake of this neurotransmitter through the dopamine transporter results in oxidative damage, neuronal loss and l-DOPA reversible motor deficits. In addition, DAT over-expressing animals are highly sensitive to MPTP-induced neurotoxicity. The effects of increased dopamine uptake in these transgenic mice could shed light on the unique vulnerability of dopamine neurons in Parkinson's disease.

The interplay between iron accumulation, mitochondrial dysfunction, and inflammation during the execution step of neurodegenerative disorders

A growing set of observations points to mitochondrial dysfunction, iron accumulation, oxidative damage and chronic inflammation as common pathognomonic signs of a number of neurodegenerative diseases that includes Alzheimer’s disease, Huntington disease, amyotrophic lateral sclerosis, Friedrich’s ataxia and Parkinson’s disease. Particularly relevant for neurodegenerative processes is the relationship between mitochondria and iron. The mitochondrion upholds the synthesis of iron–sulfur clusters and heme, the most abundant iron-containing prosthetic groups in a large variety of proteins, so a fraction of incoming iron must go through this organelle before reaching its final destination. In turn, the mitochondrial respiratory chain is the source of reactive oxygen species (ROS) derived from leaks in the electron transport chain. The co-existence of both iron and ROS in the secluded space of the mitochondrion makes this organelle particularly prone to hydroxyl radical-mediated damage. In addition, a connection between the loss of iron homeostasis and inflammation is starting to emerge; thus, inflammatory cytokines like TNF-alpha and IL-6 induce the synthesis of the divalent metal transporter 1 and promote iron accumulation in neurons and microglia. Here, we review the recent literature on mitochondrial iron homeostasis and the role of inflammation on mitochondria dysfunction and iron accumulation on the neurodegenerative process that lead to cell death in Parkinson’s disease. We also put forward the hypothesis that mitochondrial dysfunction, iron accumulation and inflammation are part of a synergistic self-feeding cycle that ends in apoptotic cell death, once the antioxidant cellular defense systems are finally overwhelmed.

Update on the pharmacology of selective inhibitors of MAO-A and MAO-B: focus on modulation of CNS monoamine neurotransmitter release

Inhibitors of monoamine oxidase (MAO) were initially used in medicine following the discovery of their antidepressant action. Subsequently their ability to potentiate the effects of an indirectly-acting sympathomimetic amine such as tyramine was discovered, leading to their limitation in clinical use, except for cases of treatment-resistant depression. More recently, the understanding that: a) potentiation of indirectly-acting sympathomimetic amines is caused by inhibitors of MAO-A but not by inhibitors of MAO-B, and b) that reversible inhibitors of MAO-A cause minimal tyramine potentiation, has led to their re-introduction to clinical use for treatment of depression (reversible MAO-A inhibitors and new dose form MAO-B inhibitor) and treatment of Parkinson's disease (MAO-B inhibitors). The profound neuroprotective properties of propargyl-based inhibitors of MAO-B in preclinical experiments have drawn attention to the possibility of employing these drugs for their neuroprotective effect in neurodegenerative diseases, and have raised the question of the involvement of the MAO-mediated reaction as a source of reactive free radicals. Despite the long-standing history of MAO inhibitors in medicine, the way in which they affect neuronal release of monoamine neurotransmitters is still poorly understood. In recent years, the detailed chemical structure of MAO-B and MAO-A has become available, providing new possibilities for synthesis of mechanism-based inhibitors. This review describes the latest advances in understanding the way in which MAO inhibitors affect the release of the monoamine neurotransmitters dopamine, noradrenaline and serotonin (5-HT) in the CNS, with an accent on the importance of these effects for the clinical actions of the drugs.

Effects of the neurotoxin MPTP and pargyline protection on extracellular energy metabolites and dopamine levels in the striatum of freely moving rats

The neurotoxin MPTP is known to induce dopamine release and depletion of ATP in the striatum of rats. Therefore, we studied the changes induced by MPTP and pargyline protection both on striatal dopamine release and on extracellular energy metabolites in freely moving rats, using dual asymmetric-flow microdialysis. A dual microdialysis probe was inserted in the right striatum of rats. MPTP (25mg/kg, 15mg/kg, 10mg/kg) was intraperitoneally administered for three consecutive days. MAO-B inhibitor pargyline (15mg/kg) was systemically administered before neurotoxin administration. The first MPTP dose induced an increase in dialysate dopamine and a decrease of DOPAC levels in striatal dialysate. After the first neurotoxin administration, increases in striatal glucose, lactate, pyruvate, lactate/pyruvate (L/P) and lactate/glucose (L/G) ratios were observed. Subsequent MPTP administrations showed a progressive reduction of dopamine, glucose and pyruvate levels with a concomitant further increase in lactate levels and L/P and L/G ratios. At day 1, pargyline pre-treatment attenuated the MPTP-induced changes in all studied analytes. Starting from day 2, pargyline prevented the depletion of dopamine, glucose and pyruvate while reduced the increase of lactate, L/P ratio and L/G ratio. These in vivo results suggest a pargyline neuroprotection role against the MPTP-induced energetic impairment consequent to mitochondrial damage. This neuroprotective effect was confirmed by TH immunostaining of the substantia nigra.

Secalonic acid A protects dopaminergic neurons from 1-methyl-4-phenylpyridinium (MPP⁺)-induced cell death via the mitochondrial apoptotic pathway

Secalonic acid A (SAA) is a natural compound found in marine fungi. We have reported that SAA can attenuate the cytotoxicity of colchicine in rat cortical neurons. Whether SAA can also inhibit the neurotoxicity of 1-methyl-4-phenylpyridinium (MPP(+)) in dopaminergic neurons has not been investigated. Here, we show that pretreatment with 1 μM SAA significantly rescued tyrosine hydroxylase (TH)-positive neurons from MPP(+)-induced neurotoxicity in primary dopaminergic neuron culture. Moreover, SAA at doses of 0.15 mg/kg and 0.75 mg/kg increased the number of dopaminergic neurons and upregulated striatal dopamine in 1-methyl-4-phenyl-1,2,3,6-tetrahydropyridine (MPTP)-induced Parkinson's disease mice experiments. We also show that SAA significantly attenuated cytotoxicity induced by 2.5 mM MPP(+) in SH-SY5Y cells. These results indicate that the activation of JNK, p38 mitogen activated protein kinase (MAPK) and caspase-3 during apoptosis triggered by MPP(+) could be suppressed by SAA; on the other hand, an MPP(+)-induced increase in the expression of Bax in SH-SY5Y cells was blocked by SAA. These results indicate that inhibition of the phosphorylation of JNK and p38 MAPK, down-regulation of Bax expression, and suppression of caspase-3 activation are involved in the protective effects of SAA against MPP(+) toxicity in SH-SY5Y cells. SAA may rescue dopaminergic neurons from MPP(+)-induced cell death through the mitochondrial apoptotic pathway.

Mitochondrial dynamics in neurodegeneration

It has been only 15 years since studies began on the molecular mechanisms underlying mitochondrial fission and fusion using simple model organisms such as Drosophila, yeast, and Caenorhabditis elegans. Beyond the primary functions of mitochondrial fission and fusion in controlling organelle shape, size, and number, it became clear that these dynamic processes are also critical to regulating cell death, mitophagy, and organelle distribution. Now, studies suggest that prominent changes occur in mitochondrial dynamics in a broad array of neurodegenerative diseases, and there is substantial evidence suggesting a key role in disease pathogenesis because neurons are among the most energy-consuming cell types and have a highly developed cell shape. Here, we review the recent findings on mitochondrial dynamics in neurodegeneration.

Neurotoxin-induced impairment of biopterin synthesis and function: Initial stage of a Parkinson-like dopamine deficiency syndrome

Disorders of the function of the tyrosine hydroxylase play an important role in the occurrence of the Parkinson syndrome. The enzyme that catalyses the first, rate-limiting step in the biosynthesis to dopamine requires the cofactor tetrahydrobiopterin. This compound supplies the reduction equivalent for activation of molecular oxygen. Binding of the cofactor to the enzyme is affected by phosphorylation or dephosphorylation of the enzyme protein and, thereby, influences the activity. Nerve and chromaffin cells that synthesize dopamine, noradrenaline and serotonin are able to synthesize the cofactor tetrahydrobiopterin de novo from guanosine-triphosphate as a precursor. In patients suffering from Parkinson's disease a remarkable decrease in biopterin content was found in the brain. The function of the dopaminergic system was studied with an experimental Parkinson model. The antimetabolite 6-aminonicotinamide induces a dopamine deficit in the striatum with a significant slowdown in the utilization of this transmitter. The abolition of the 6-aminonicotinamide-induced muscular rigidity by l-DOPA and dopamine agonists implies that the antimetabolite produces a Parkinson-like syndrome in rats. There are reports on the molecular basis of this effect which are also important for understanding possible disturbances of the synthesis of biopterins. The effector 6-aminonicotinamide-adenine-dinucleotide-phosphate (6-ANADP), which blocks the pentose phosphate pathway, is formed by an enzymatic neurotoxic synthesis. The clonal cell line PC-12 was used to study the molecular basis of the disturbances occurring in the dopaminergic system. These cells contain all the enzymes for catecholamine synthesis, including those for the synthesis of the cofactor tetrahydrobiopterin. Addition of 6-aminonicotinamide to the culture medium resulted in the synthesis of the neurotoxic agent, 6-ANADP, by a glycohydrolase localized in the endoplasmic reticulum. The synthesis of biopterin was depressed after application of 6-aminonicotinamide. The decrease of intracellular tetrahydrobiopterin and total biopterin resulted in reduced DOPA production. The decreased content of biopterin cofactor synthesis was compensated for by the addition of the precursor sepiapterin, indicating that the NADPH-dependent reductases in biopterin synthesis were not inhibited by the antimetabolic nucleotide 6-ANADP. DOPA production was not fully normalized by sepiapterin. Addition of NADH to the medium resulted in a further increase of DOPA production, probably by activation of the recycling pathway. The first step in the synthesis of biopterin from GTP to 7,8-neopterin-triphosphate seems to be particularly sensitive to the action of exogenous neurotoxins. A further sensitive site of action in synthesis to the cofactor BH(4) concerns the function of the dihydropteridin-reductase, which recycles qBH(2) to BH(4). Neurotoxin-induced impairment of biopterin synthesis is probably a pathogenetically important disorder at the initial stage of Parkinson's disease.

Lack of CCR5 modifies glial phenotypes and population of the nigral dopaminergic neurons, but not MPTP-induced dopaminergic neurodegeneration

Constitutive expression of C-C chemokine receptor (CCR) 5 has been detected in astrocytes, microglia and neurons, but its physiological roles in the central nervous system are obscure. The bidirectional interactions between neuron and glial cells through CCR5 and its ligands were thought to be crucial for maintaining normal neuronal activities. No study has described function of CCR5 in the dopaminergic neurodegeneration in Parkinson's disease. In order to examine effects of CCR5 on 1-methyl-4-phenyl-1,2,3,6-tetrahydropyridine (MPTP)-induced dopaminergic neurodegeneration, we employed CCR5 wild type (WT) and knockout (KO) mice. Immunostainings for tyrosine hydroxylase (TH) exhibited that CCR5 KO mice had lower number of TH-positive neurons even in the absence of MPTP. Difference in MPTP (15mg/kg×4 times, 2hr interval)-mediated loss of TH-positive neurons was subtle between CCR5 WT and KO mice, but there was larger dopamine depletion, behavioral impairments and microglial activation in CCR5 deficient mice. Intriguingly, CCR5 KO brains contained higher immunoreactivity for monoamine oxidase (MAO) B which was mainly localized within astrocytes. In agreement with upregulation of MAO B, concentration of MPP+ was higher in the substantia nigra and striatum of CCR5 KO mice after MPTP injection. We found remarkable activation of p38 MAPK in CCR5 deficient mice, which positively regulates MAO B expression. These results indicate that CCR5 deficiency modifies the nigrostriatal dopaminergic neuronal system and bidirectional interaction between neurons and glial cells via CCR5 might be important for dopaminergic neuronal survival.

Vesicular monoamine transporters: structure-function, pharmacology, and medicinal chemistry

Vesicular monoamine transporters (VMAT) are responsible for the uptake of cytosolic monoamines into synaptic vesicles in monoaminergic neurons. Two closely related VMATs with distinct pharmacological properties and tissue distributions have been characterized. VMAT1 is preferentially expressed in neuroendocrine cells and VMAT2 is primarily expressed in the CNS. The neurotoxicity and addictive properties of various psychostimulants have been attributed, at least partly, to their interference with VMAT2 functions. The quantitative assessment of the VMAT2 density by PET scanning has been clinically useful for early diagnosis and monitoring of the progression of Parkinson's and Alzheimer's diseases and drug addiction. The classical VMAT2 inhibitor, tetrabenazine, has long been used for the treatment of chorea associated with Huntington's disease in the United Kingdom, Canada, and Australia, and recently approved in the United States. The VMAT2 imaging may also be useful for exploiting the onset of diabetes mellitus, as VMAT2 is also expressed in the β-cells of the pancreas. VMAT1 gene SLC18A1 is a locus with strong evidence of linkage with schizophrenia and, thus, the polymorphic forms of the VMAT1 gene may confer susceptibility to schizophrenia. This review summarizes the current understanding of the structure-function relationships of VMAT2, and the role of VMAT2 on addiction and psychostimulant-induced neurotoxicity, and the therapeutic and diagnostic applications of specific VMAT2 ligands. The evidence for the linkage of VMAT1 gene with schizophrenia and bipolar disorder I is also discussed.

Parkin degrades estrogen-related receptors to limit the expression of monoamine oxidases

Parkin, whose mutations cause Parkinson disease (PD), controls oxidative stress by limiting the expression of monoamine oxidases (MAO)--mitochondrial enzymes responsible for the oxidative de-amination of dopamine. Here, we show that parkin performed this function by increasing the ubiquitination and degradation of estrogen-related receptors (ERR), orphan nuclear receptors that play critical roles in the transcription regulation of many nuclear-encoded mitochondrial proteins. All three ERRs (α, β and γ) increased the transcription of MAOs A and B; the effects were abolished by parkin, but not by its PD-linked mutants. Parkin bound to ERRs and increased their ubiquitination and degradation. In fibroblasts from PD patients with parkin mutations or brain slices from parkin knockout mice, degradation of ERRs was significantly attenuated. The results reveal the molecular mechanism by which parkin suppresses the transcription of MAOs to control oxidative stress induced by dopamine oxidation.

Environmental factors and Parkinson's disease: a case-control study in Belgrade, Serbia

A case-control study was performed in Belgrade in order to investigate the association between Parkinson's disease (PD) and some environmental factors. During the period 2001-2005, 110 new PD cases and 220 hospital controls were interviewed. Cases and controls were matched by sex, age (+/-2 years), and place of residence (urban/rural). According to multivariate conditional logistic regression analysis, PD was positively asssociated with exposure to insecticides (odds ratio (OR) 3.22, 95% confidence interval (95% CI) 1.32-7.87), dyes (OR 25.33; 95% CI, 2.89-222.0), and naphtha and its derivates (OR 9.53; 95% CI, 1.04-86.96), and with gardening (OR 5.51; 95% CI, 3.04-10.01), well water drinking (OR 2.62; 95% CI, 1.40-4.90), and spring water drinking (OR 2.19; 95% CI, 1.15-4.16). Negative association was found for service-sector working (OR 0.15; 95% CI, 0.04-0.59). The results obtained did not changed after adjustment for smoking. The findings of the present study support the role of environmental factors in the occurence of PD.

Zonisamide reduces cell death in SH-SY5Y cells via an anti-apoptotic effect and by upregulating MnSOD

Zonisamide, originally known as an antiepileptic drug, has been approved in Japan as adjunctive therapy with levodopa for the treatment of Parkinson's disease (PD). Although zonisamide reduces neurotoxicity, the precise mechanism of this action is not known. Here, we show that zonisamide increases cell viability in SH-SY5Y cells via an anti-apoptotic effect and by upregulating levels of manganese superoxide dismutase (MnSOD). These results would give us novel evidences of PD treatment.

The comparative neuroanatomy and neurochemistry of zebrafish CNS systems of relevance to human neuropsychiatric diseases

Modulatory neurotransmitters which signal through G protein-coupled receptors control brain functions which deteriorate in degenerative brain diseases. During the past decade many of these systems have been mapped in the zebrafish brain. The main architecture of the systems in zebrafish brain resembles that of the mammals, despite differences in the development of the telencephalon and mesodiencephalon. Modulatory neurotransmitters systems which degenerate in human diseases include dopamine, noradrenaline, serotonin, histamine, acetylcholine and orexin/hypocretin. Although the number of G protein-coupled receptors in zebrafish is clearly larger than in mammals, many receptors have similar expression patterns, binding and signaling properties as in mammals. Distinct differences between mammals and zebrafish include duplication of the tyrosine hydroxylase gene in zebrafish, and presence of one instead of two monoamine oxidase genes. Zebrafish are sensitive to neurotoxins including MPTP, and exposure to this neurotoxin induces a decline in dopamine content and number of detectable tyrosine hydroxylase immunoreactive neurons in distinct nuclei. Sensitivity to important neurotoxins, many available genetic methods, rapid development and large-scale quantitative behavioral methods in addition to advanced quantitative anatomical methods render zebrafish an optimal organism for studies on disease mechanisms.