Effect of MAO-B inhibitors on MPP+ toxicity in Vivo

Type-B monoamine oxidase inhibitors in neurological diseases: clinical applications based on preclinical findings

Type-B monoamine oxidase inhibitors, encompassing selegiline, rasagiline, and safinamide, are available to treat Parkinson's disease. These drugs ameliorate motor symptoms and improve motor fluctuation in the advanced stages of the disease. There is also evidence supporting the benefit of type-B monoamine oxidase inhibitors on non-motor symptoms of Parkinson's disease, such as mood deflection, cognitive impairment, sleep disturbances, and fatigue. Preclinical studies indicate that type-B monoamine oxidase inhibitors hold a strong neuroprotective potential in Parkinson's disease and other neurodegenerative diseases for reducing oxidative stress and stimulating the production and release of neurotrophic factors, particularly glial cell line-derived neurotrophic factor, which support dopaminergic neurons. Besides, safinamide may interfere with neurodegenerative mechanisms, counteracting excessive glutamate overdrive in basal ganglia motor circuit and reducing death from excitotoxicity. Due to the dual mechanism of action, the new generation of type-B monoamine oxidase inhibitors, including safinamide, is gaining interest in other neurological pathologies, and many supporting preclinical studies are now available. The potential fields of application concern epilepsy, Duchenne muscular dystrophy, multiple sclerosis, and above all, ischemic brain injury. The purpose of this review is to investigate the preclinical and clinical pharmacology of selegiline, rasagiline, and safinamide in Parkinson's disease and beyond, focusing on possible future therapeutic applications.

Promising biomarkers and therapeutic targets for the management of Parkinson's disease: recent advancements and contemporary research

Parkinson's disease (PD) is one of the progressive neurological diseases which affect around 10 million population worldwide. The clinical manifestation of motor symptoms in PD patients appears later when most dopaminergic neurons have degenerated. Thus, for better management of PD, the development of accurate biomarkers for the early prognosis of PD is imperative. The present work will discuss the potential biomarkers from various attributes covering biochemical, microRNA, and neuroimaging aspects (α-synuclein, DJ-1, UCH-L1, β-glucocerebrosidase, BDNF, etc.) for diagnosis, recent development in PD management, and major limitations with current and conventional anti-Parkinson therapy. This manuscript summarizes potential biomarkers and therapeutic targets, based on available preclinical and clinical evidence, for better management of PD.

Melatonin Analogues Potently Inhibit MAO-B and Protect PC12 Cells against Oxidative Stress

Monoamine oxidase B (MAO-B) metabolizes dopamine and plays an important role in oxidative stress by altering the redox state of neuronal and glial cells. MAO-B inhibitors are a promising therapeutical approach for Parkinson’s disease (PD). Herein, 24 melatonin analogues (3a–x) were synthesized as novel MAO-B inhibitors with the potential to counteract oxidative stress in neuronal PC12 cells. Structure elucidation, characterization, and purity of the synthesized compounds were performed using ¹H-NMR, ¹³C-NMR, HRMS, and HPLC. At 10 µM, 12 compounds showed >50% MAO-B inhibition. Among them, compounds 3n, 3r, and 3u–w showed >70% inhibition of MAO-B and IC₅₀ values of 1.41, 0.91, 1.20, 0.66, and 2.41 µM, respectively. When compared with the modest selectivity index of rasagiline (II, a well-known MAO-B inhibitor, SI > 50), compounds 3n, 3r, 3u, and 3v demonstrated better selectivity indices (SI > 71, 109, 83, and 151, respectively). Furthermore, compounds 3n and 3r exhibited safe neurotoxicity profiles in PC12 cells and reversed 6-OHDA- and rotenone-induced neuronal oxidative stress. Both compounds significantly up-regulated the expression of the anti-oxidant enzyme, heme oxygenase (HO)-1. Treatment with Zn(II)-protoporphyrin IX (ZnPP), a selective HO-1 inhibitor, abolished the neuroprotective effects of the tested compounds, suggesting a critical role of HO-1 up-regulation. Both compounds increased the nuclear translocation of Nrf2, which is a key regulator of the antioxidative response. Taken together, these data show that compounds 3n and 3r could be further exploited for their multi-targeted role in oxidative stress-related PD therapy.

Protective effect of selegiline on cigarette smoke-induced oxidative stress and inflammation in rat lungs in vivo

Background

Cigarette smoke (CS)-induced build-up of oxidative stress is the leading cause of chronic obstructive pulmonary disease (COPD). Monoamine oxidases (MAOs) are novel sources of reactive oxygen species (ROS) due to the production of hydrogen peroxide (H₂O₂). However, it remains unclear whether MAO signaling is involved in CS-induced oxidative stress in vivo. This study aimed at investigating the impact of selegiline, a selective MAO-B inhibitor, on CS-induced lung oxidative stress and inflammation in vivo and its underlying mechanism.

Methods

Sprague Dawley rats were randomly divided into four groups: saline plus sham air (Saline/air), saline plus cigarette smoke (Saline/CS), selegiline plus sham air (Slg/air) and selegiline plus cigarette smoke (Slg/CS). Rats from Saline/air and Saline/CS groups were intraperitoneally injected with saline (2 mL/kg body weight) while rats from Slg/air and Slg/CS groups were injected with selegiline (2 mg/kg body weight) about 30 min prior to exposure daily. The Saline/air and Slg/air groups were exposed to atmospheric air while the Saline/CS and Slg/CS groups were exposed to mainstream CS generated from the whole body inExpose smoking system (SCIREQ, Canada) for twice daily (each for 1 hour with 20 cigarettes). After 7 days, rats were sacrificed to collect bronchoalveolar lavage (BAL) and lung tissues for the measurement of oxidative/anti-oxidative and inflammatory/anti-inflammatory makers respectively.

Results

CS caused significant elevation of MAO-B activity, reduction of total antioxidant capacity (T-AOC) and rGSH/GSSG ratio, and enhancement of superoxide dismutase (SOD) activity in rat lung. Selegiline significantly only reversed CS-induced elevation of MAO-B activity and reduction of rGSH/GSSG ratio. The CS-induced elevation of heme oxygenase-1 (HO-1) and NAD(P)H quinone dehydrogenase 1 (NQO1) expression via nuclear factor erythroid 2-related factor 2 (Nrf2) was also reversed by selegiline. Despite of CS-induced increase in total cell counts, especially the number of macrophages, selegiline had no effect. Selegiline attenuated CS-induced elevation of pro-inflammatory mediators (CINC-1, MCP-1 and IL-6) and restored CS-induced reduction of anti-inflammatory mediator IL-10 in BAL, which was driven through MAPK and NF-κB.

Conclusions

Inhibition of MAO-B may provide a promising therapeutic strategy for CS-mediated oxidative stress and inflammation in acute CS-exposed rat lungs.

Substantial protection against MPTP-associated Parkinson's neurotoxicity in vitro and in vivo by anti-cancer agent SU4312 via activation of MEF2D and inhibition of MAO-B

We have previously demonstrated the unexpected neuroprotection of the anti-cancer agent SU4312 in cellular models associated with Parkinson's disease (PD). However, the precise mechanisms underlying its neuroprotection are still unknown, and the effects of SU4312 on rodent models of PD have not been characterized. In the current study, we found that the protection of SU4312 against 1-methyl-4-phenylpyridinium ion (MPP⁺)-induced neurotoxicity in PC12 cells was achieved through the activation of transcription factor myocyte enhancer factor 2D (MEF2D), as evidenced by the fact that SU4312 stimulated myocyte enhancer factor 2 (MEF2) transcriptional activity and prevented the inhibition of MEF2D protein expression caused by MPP⁺, and that short hairpin RNA (ShRNA)-mediated knockdown of MEF2D significantly abolished the neuroprotection of SU4312. Additionally, Western blotting analysis revealed that SU4312 potentiated pro-survival PI3-K/Akt pathway to down-regulate MEF2D inhibitor glycogen synthase kinase-3beta (GSK3β). Furthermore, using the in vivo PD model of C57BL/6 mice insulted with 1-methyl-4-phenyl-1,2,3,6-tetrahydropyridine (MPTP), we found that intragastrical administration of SU4312 (0.2 and 1 mg/kg) greatly ameliorated Parkinsonian motor defects, and restored protein levels of MEF2D, phosphorylated-Ser473-Akt and phosphorylated-Ser9-GSK3β. Meanwhile, SU4312 effectively reversed the decrease in protein expression of tyrosine hydroxylase in substantia nigra pars compacta dopaminergic neurons, inhibited oxidative stress, maintained mitochondrial biogenesis and partially prevented the depletion of dopamine and its metabolites. Very encouragingly, SU4312 was able to selectively inhibit monoamine oxidase-B (MAO-B) activity both in vitro and in vivo, with an IC₅₀ value of 0.2 μM. These findings suggest that SU4312 provides therapeutic benefits in cellular and animal models of PD, possibly through multiple mechanisms including enhancement of MEF2D through the activation of PI3-K/Akt pathway, maintenance of mitochondrial biogenesis and inhibition of MAO-B activity. SU4312 thus may be an effective drug candidate for the prevention or even modification of the pathological processes of PD.

Indole-Substituted Benzothiazoles and Benzoxazoles as Selective and Reversible MAO-B Inhibitors for Treatment of Parkinson's Disease

To develop novel, selective, and reversible MAO-B inhibitors for safer treatment of Parkinson's disease, benzothiazole and benzoxazole derivatives with indole moiety were designed and synthesized. Most of the synthesized compounds showed inhibitory activities against MAO-B and selectivity over MAO-A. The most active compound was compound 5b, 6-fluoro-2-(1-methyl-1H-indol-5-yl)benzo[d]thiazole with an IC₅₀ value of 28 nM with no apparent effect on MAO-A activity at 10 μM. Based on the reversibility assay, compound 5b turned out to be fully reversible with over 95% of recovery of enzyme activity after washout of the compound. Compound 5b showed a reasonable stability in human liver microsomes and did not affect the activities of CYP isozymes, suggesting an absence of high-risk drug-drug interaction. In an in vivo MPTP-induced animal model of Parkinson's disease, oral administration of compound 5b showed neuroprotection of nigrostriatal dopaminergic neurons as revealed by tyrosine hydroxylase staining and prevention of MPTP-induced parkinsonism as revealed by motor behavioral assay of vertical grid test. In summary, the novel, reversible, and selective MAO-B inhibitor compound 5b was synthesized and characterized. We propose compound 5b as an effective therapeutic compound for relieving parkinsonism.

Defining the Role of the Monoamine Oxidase-B Inhibitors for Parkinson's Disease

Inhibitors of monoamine oxidase-B (MAO-B) occupy an important place in the treatment of Parkinson's disease. Selegiline was the first MAO-B to be used therapeutically, while rasagiline is a second-generation drug with higher potency and selectivity. Safinamide is an investigational MAO-B inhibitor with non-dopaminergic properties that may provide advantages over its predecessors. As a class, MAO-B inhibitors are safe and well tolerated and provide symptomatic benefit both as monotherapy and in combination with other antiparkinsonian medications from early to late stages of disease. In combination with levodopa, MAO-B inhibitors may improve motor fluctuations and allow for lower total doses of levodopa. Patient characteristics and preferences can be important factors in deciding between agents. As a class, MAO-B inhibitors have shown promise as disease-modifying agents, but the clinical trial evidence to date has not been strong enough to afford them such a label. Future research may help further elucidate their relative merits and clarify their role in altering disease progression.

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.

Multi target neuroprotective and neurorestorative anti-Parkinson and anti-Alzheimer drugs ladostigil and m30 derived from rasagiline

Present anti-PD and -AD drugs have limited symptomatic activity and devoid of neuroprotective and neurorestorative property that is needed for disease modifying action. The complex pathology of PD and AD led us to develop several multi-target neuroprotective and neurorestorative drugs with several CNS targets with the ability for possible disease modifying activity. Employing the pharmacophore of our anti-parkinson drug rasagiline (Azilect, N-propagrgyl-1-R-aminoindan), we have developed a series of novel multi-functional neuroprotective drugs (A) [TV-3326 (N-propargyl-3R-aminoindan-5yl)-ethyl methylcarbamate)], with both cholinesterase-butyrylesterase and brain selective monoamine-oxidase (MAO) A/B inhibitory activities and (B) the iron chelator-radical scavenging-brain selective monoamine oxidase (MAO) A/B inhibitor and M30 possessing the neuroprotective and neurorescuing propargyl moiety of rasagiline, as potential treatment of AD, DLB and PD with dementia. Another series of multi-target drugs (M30, HLA-20 series) which are brain permeable iron chelators and potent selective brain MAO inhibitors were also developed. These series of drugs have the ability of regulating and processing amyloid precursor protein (APP) since APP and alpha-synuclein are metaloproteins (iron-regulated proteins), with an iron responsive element 5"UTR mRNA similar to transferring and ferritin. Ladostigil inhibits brain acetyl and butyrylcholinesterase in rats after oral doses. After chronic but not acute treatment, it inhibits MAO-A and -B in the brain. Ladostigil acts like an anti-depressant in the forced swim test in rats, indicating a potential for anti-depressant activity. Ladostigil prevents the destruction of nigrostriatal neurons induced by infusion of neurotoxin MPTP in mice. The propargylamine moiety of ladostigil confers neuroprotective activity against cytotoxicity induced by ischemia and peroxynitrite in cultured neuronal cells. The multi-target iron chelator M30 has all the properties of ladostigil and similar neuroprotective activity to ladostigil, but is not a ChE inhibitor. M30 has a neurorestorative activity in post-lesion of nigrostriatal dopamine neurons in MPTP, lacatcystin and 6-hydroxydopamine animal models of PD. The neurorestorative activity is related to the ability of the drug to activate hypoxia inducing factor (HIF) which induces the production of such neurotrophins as brain-derived neurotrophic factor (BDNF), vascular endothelial growth factor (VEGF) and erythropoietin as well as glia-derived neurotrophic factor (GDNF). The unique multiple actions of ladostigil and M30 make the potentially useful drugs for the treatment of dementia with Parkinsonian-like symptoms and depression.

Medical management of Parkinson's disease: focus on neuroprotection

Neuroprotection refers to the protection of neurons from excitotoxicity, oxidative stress and apoptosis as principal mechanisms of cell loss in a variety of diseases of the central nervous system. Our interest in Parkinson’s disease (PD) treatment is focused on drugs with neuroprotective properties in preclinical experiments and evidence-based efficacy in human subjects. To this date, neuroprotection has never been solidly proven in clinical trials but recent adequate markers and/or strategies to study and promote this important goal are described. A myriad of compounds with protective properties in cell cultures and animal models yield to few treatments in clinical practice. At present, markers of neuronal vitality, disease modifying effects and long term clinical stability are the elements searched for in clinical trials. This review highlights new strategies to monitor patients with PD. Currently, neuroprotection in subjects has not been solidly achieved for selegiline and pramipexole; however, a recent rasagiline trial design is showing new indications of disease course modifying effects. In neurological practice, it is of utmost importance to take into account the potential neuroprotection exerted by a treatment in conjunction with its symptomatic efficacy.

(-)-Deprenyl inhibits vascular hyperpermeability after hemorrhagic shock

Recent studies from our laboratory demonstrated the involvement of endothelial cell reactive oxygen species (ROS) formation and activation of apoptotic signaling in vascular hyperpermeability after hemorrhagic shock (HS). The objective of this study was to determine if (-)-deprenyl, an antioxidant with antiapoptotic properties, would attenuate HS-induced vascular hyperpermeability. In rats, HS was induced by withdrawing blood to reduce the MAP to 40 mmHg for 60 min followed by resuscitation for 60 min. To study hyperpermeability, we injected the rats with fluorescein isothiocyanate--albumin (50 mg/kg), and the changes in integrated optical intensity of the mesenteric postcapillary venules were obtained intravascularly and extravascularly using intravital microscopy. Mitochondrial ROS formation and mitochondrial transmembrane potential (DeltaPsim) were studied using dihydrorhodamine 123 and JC-1, respectively. Mitochondrial release of cytochrome c was determined using enzyme-linked immunosorbent assay and caspase-3 activity by a fluorometric assay. Parallel studies were performed in rat lung microvascular endothelial cells using proapoptotic BAK as inducer of hyperpermeability. Hemorrhagic shock induced vascular hyperpermeability, mitochondrial ROS formation, DeltaPsim decrease, cytochrome c release, and caspase-3 activation (P G 0.05). (-)-Deprenyl (0.15 mg/kg) attenuated all these effects (P < 0.05). Similarly in rat lung microvascular endothelial cells, (-)-deprenyl attenuated BAK peptide-induced monolayer hyperpermeability (P < 0.05), ROS formation, DeltaPsim decrease, cytochrome c release (P<0.05), and caspase-3 activation (P < 0.05). The protective effects of (-)-deprenyl on vascular barrier functions may be due to its protective effects on DeltaPsim, thereby preventing mitochondrial release of cytochrome c and caspase-3--mediated disruption of endothelial adherens junctions.

Antidepressants reveal differential effect against 1-methyl-4-phenylpyridinium toxicity in differentiated PC12 cells

Treatment of depression may ameliorate the cognitive disability and motor slowness in Parkinson's disease. It has been shown that antidepressants, including fluoxetine, may attenuate or exacerbate neuronal cell death. The present study assessed the effect of antidepressants (amitriptyline, tranylcypromine and fluoxetine) against the toxicity of 1-methyl-4-phenylpyridinium (MPP(+)) in relation to the mitochondria-mediated cell death process in differentiated PC12 cells. Amitriptyline and tranylcypromine attenuated the MPP(+)-induced cell death that may be associated with mitochondrial membrane permeability change and oxidative stress. Both compounds prevented the loss of the mitochondrial transmembrane potential, over-expression of Bax, reduction in Bcl-2 level, cytochrome c release, caspase-3 activation, formation of reactive oxygen species and depletion of GSH. The inhibitory effect of tranylcypromine was greater than that of amitriptyline on the basis of concentration. In contrast, fluoxetine revealed a toxic effect and exhibited an additive effect against the toxicity of MPP(+). Results show that amitriptyline and tranylcypromine may attenuate the MPP(+) toxicity by suppressing the mitochondrial membrane permeability change that leads to cytochrome c release and subsequent caspase-3 activation. The effects seem to be associated with the inhibitory action on the formation of reactive oxygen species and the depletion of GSH. In contrast, fluoxetine seems to exert an additive toxic effect against neuronal cell damage by increasing mitochondrial damage and oxidative stress.

Neural progenitor cells are protected against MPTP by MAO-B inhibitors

Neurotoxic effects of MPTP on the nigrostriatal dopaminergic system are thought to be initiated by 1-methyl-4-phenylpyridinium (MPP+), a metabolite formed by the monoamine oxidase (MAO)-B-mediated oxidation of MPTP. We previously reported that the administration of MPTP induced apoptosis in migrating neuroblasts (neural progenitor cells, NPCs) in adult mice. To determine whether MAO-B is also involved in the neurotoxicity of MPTP to NPCs, this study looked at the effects of MAO B inhibitors, R(-)-deprenyl (deprenyl) and N-(2-aminoethyl)-4-chlorobenzamide (Ro 16-6491), both of which protect the dopaminergic system against MPTP. Few apoptotic cells were found in saline- or MAO-B inhibitor-treated animals but MPTP markedly induced apoptosis in the subventricular zone (SVZ) and rostral migratory stream (RMS) after 1 day. When mice were pretreated with deprenyl or Ro 16-6491, not only nigrostriatal dopamine levels but also NPCs were significantly protected against MPTP. In addition, MPTP-induced apoptosis was found in both juvenile (postnatal 21 days) and older (12 months old) mice, suggesting NPCs to be different from the dopamine system, which has been thought to exhibit age-dependent susceptibility to MPTP.

Genetic findings in Parkinson's disease and translation into treatment: a leading role for mitochondria?

Parkinson's disease (PD) is a progressive neurodegenerative movement disorder and in most patients its aetiology remains unknown. Molecular genetic studies in familial forms of the disease identified key proteins involved in PD pathogenesis, and support a major role for mitochondrial dysfunction, which is also of significant importance to the common sporadic forms of PD. While current treatments temporarily alleviate symptoms, they do not halt disease progression. Drugs that target the underlying pathways to PD pathogenesis, including mitochondrial dysfunction, therefore hold great promise for neuroprotection in PD. Here we summarize how the proteins identified through genetic research (alpha-synuclein, parkin, PINK1, DJ-1, LRRK2 and HTRA2) fit into and add to our current understanding of the role of mitochondrial dysfunction in PD. We highlight how these genetic findings provided us with suitable animal models and critically review how the gained insights will contribute to better therapies for PD.

Neurodegeneration and peroxidases

Alzheimer's disease (AD), Parkinson's disease (PD) and amyotrophic lateral sclerosis (ALS) are neurodegenerative diseases that affect different parts of the central nervous system. However, a review of the literature indicates that certain biochemical reactions involved in neurodegeneration in these three diseases are quite similar and could be partly identical. This article critically examines the similarities and, based on data from our own and other laboratories, proposes a novel explanation for neurodegeneration in these three diseases. We identified about 20 commonalities that exist in the neurodegenerative process of each disease. We hypothesize that there are two enzyme-catalyzed pathways that operate in affected neurons: an oxidative pathway leading to destruction of various neuronal proteins and lipids, and an apoptotic pathway which the body normally uses to remove unwanted and dysfunctional cells. Data from many laboratories indicate that oxidative reactions are primarily responsible for neurodegeneration, whereas apoptosis may well be a secondary response to the presence of neurons that have already been severely damaged by oxidative reactions. Attempts to inhibit apoptosis for the purpose of attenuating progression of these diseases may therefore be only of marginal benefit. Specific oxidative reactions within affected neurons led us to propose that one or more heme peroxidases may be the catalyst(s) involved in oxidation of proteins and lipids. Support for this proposal is provided by the recent finding that amyloi-beta peptide may act as a peroxidase in AD. Possible participation of the peroxidase activity of cytochrome c, herein designated as cytochrome c(px) to distinguish it from yeast cytochrome c peroxidase, is discussed. Of special interest is our recent finding that many compounds that cause attenuation of neurodegeneration are inhibitors of the peroxidase activity of cytochrome c. Several inhibitors were subsequently identified as suicide substrates. Such inhibitors could be ideally suited for targeted clinical approaches aimed at arresting progression of neurodegeneration. Finally, it is possible that immobilized yet still active peroxidase(s) may be present in protein aggregates in AD, PD, and ALS. This activity could be the catalyst for the slow, self-perpetuating and irreversible degeneration of affected neurons that occurs over long periods of time in these neurodegenerative diseases.

Treatment consideration and manifest complexity in comorbid neuropsychiatric disorders

Psychiatric disorders may co-occur in the same individual. These include, for example, substance abuse or obsessive-compulsive disorder with schizophrenia, and movement disorders or epilepsy with affective dysfunctional states. Medications may produce iatrogenic effects, for example cognitive impairments that co-occur with the residual symptoms of the primary disorder being treated. The observation of comorbid disorders in some cases may reflect diagnostic overlap. Impulsivity, impulsiveness or impulsive behaviour is implicated in a range of diagnostic conditions including substance abuse, affective disorder and obsessive-compulsive disorder. These observations suggest a need to re-evaluate established diagnostic criteria and disorder definitions, focusing instead on symptoms and symptom-profiles.

Novel pharmacological targets for the treatment of Parkinson's disease

Dopamine deficiency, caused by the degeneration of nigrostriatal dopaminergic neurons, is the cause of the major clinical motor symptoms of Parkinson's disease. These symptoms can be treated successfully with a range of drugs that include levodopa, inhibitors of the enzymatic breakdown of levodopa and dopamine agonists delivered by oral, subcutaneous, transcutaneous, intravenous or intra-duodenal routes. However, Parkinson's disease involves degeneration of non-dopaminergic neurons and the treatment of the resulting predominantly non-motor features remains a challenge. This review describes the important recent advances that underlie the development of novel dopaminergic and non-dopaminergic drugs for Parkinson's disease, and also for the motor complications that arise from the use of existing therapies.

Movement disorders: neurodevelopment and neurobehavioural expression

Braak and co-workers have recently shown that movement disorders such as Parkinson's disease develop progressively over years with early neuronal losses in brainstem regions caudal to the substantia nigra. The relevance of this finding to notions of comorbidity between movement disorders and psychiatric symptoms was recognised at the recent meeting concerning, "Implications of Comorbidity for the Etiology and Treatment of Neuropsychiatric Disorders" held in Oct. 2005 in Mazagon, Spain. The identification of stages in the early development of neurodegenerative disorders appeared to unify multiple, diverse findings. These included: novel therapeutic innovations for Parkinson's disease, Alzheimer's disease and depression in the aged; the neurochemical ontogeny of drug-induced oral dyskinesias; the types of chemical agents abused in neuropsychiatric states; postnatal iron overload effects upon the functional and interactive role of dopaminergic and noradrenergic pathways that contribute to the expression of movement disorders; and the spectrum of motor symptoms expressed in schizophrenia and attention deficit hyperactivity disorder and the eventual treatment of these disorders. A continued focus on a number of neuropsychiatric diseases as progressive disorders may lead to further advances in understanding their etiology and in developing better therapeutics.

L-deprenyl protects against rotenone-induced, oxidative stress-mediated dopaminergic neurodegeneration in rats

The present study investigated oxidative damage and neuroprotective effect of the antiparkinsonian drug, L-deprenyl in neuronal death produced by intranigral infusion of a potent mitochondrial complex-I inhibitor, rotenone in rats. Unilateral stereotaxic intranigral infusion of rotenone caused significant decrease of striatal dopamine levels as measured employing HPLC-electrochemistry, and loss of tyrosine hydroxylase immunoreactivity in the perikarya of ipsilateral substantia nigra (SN) neurons and their terminals in the striatum. Rotenone-induced increases in the salicylate hydroxylation products, 2,3- and 2,5-dihydroxybenzoic acid indicators of hydroxyl radials in mitochondrial P2 fraction were dose-dependently attenuated by L-deprenyl. L-deprenyl (0.1-10mg/kg; i.p.) treatment dose-dependently attenuated rotenone-induced reductions in complex-I activity and glutathione (GSH) levels in the SN, tyrosine hydroxylase immunoreactivity in the striatum or SN as well as striatal dopamine. Amphetamine-induced stereotypic rotations in these rats were also significantly inhibited by deprenyl administration. The rotenone-induced elevated activities of cytosolic antioxidant enzymes superoxide dismutase and catalase showed further significant increase following L-deprenyl. Our findings suggest that unilateral intranigral infusion of rotenone reproduces neurochemical, neuropathological and behavioral features of PD in rats and L-deprenyl can rescue the dopaminergic neurons from rotenone-mediated neurodegeneration in them. These results not only establish oxidative stress as one of the major causative factors underlying dopaminergic neurodegeneration as observed in Parkinson's disease, but also support the view that deprenyl is a potent free radical scavenger and an antioxidant.

Comparison of the Protective Effect of Indole beta-carbolines and R-(-)-deprenyl Against Nitrogen Species-Induced Cell Death in Experimental Culture Model of Parkinson's Disease

Background

The membrane permeability transition of mitochondria has been suggested to be involved in toxic and oxidative forms of cell injury. Mitochondrial dysfunction is considered to play a critical role in neurodegeneration in Parkinson's disease. Despite the suggestion that indole β-carbolines may be neurotoxic, these compounds provide a protective effect against cytotoxicity of other neurotoxins. In addition, the effect of indole β-carbolines on change in the mitochondrial membrane permeability due to reactive nitrogen species (RNS), which may lead to cell death, has not been clarified.

Methods

Differentiated PC12 cells were used as the experimental culture model for the investigation of neuronal cell injury, which occurs in Parkinson's disease. The effect of indole β-carbolines (harmalol and harmine) on differentiated PC12 cells against toxicity of S-nitroso-N-acetyl-DL-penicillamine (SNAP) was determined by measuring the effect on the change in transmembrane potential, cytochrome c release, formation of ROS, GSH contents, caspase-3 activity and cell viability, and was compared to that of R-(-)-deprenyl.

Results

Specific inhibitors of caspases (z-LEHD.fmk, z-DQMD.fmk) and antioxidants (N-acetylcysteine, dithiothreitol, melatonin, carboxy-PTIO and uric acid) depressed cell death in PC12 cells due to SNAP. β-Carbolines and R-(-)-deprenyl attenuated the SNAP-induced cell death and GSH depletion concentration dependently with a maximal inhibitory effect at 25-50 µM. The compounds inhibited the nuclear damage, decrease in mitochondrial transmembrane potential, cytochrome c release and formation of reactive oxygen species caused by SNAP in PC12 cells. β-Carbolines and R-(-)-deprenyl attenuated the H₂O₂-induced cell death and depletion of GSH.

Conclusions

The results suggest that indole β-carbolines attenuate the SNAP-induced viability loss in PC12 cells by inhibition of change in the mitochondrial membrane permeability, which may be caused by free radicals. Indole β-carbolines appear to exert a protective effect against the nitrogen species-mediated neuronal cell injury in Parkinson's disease comparable to R-(-)-deprenyl.

Antioxidant effect of phenelzine on MPP+-induced cell viability loss in differentiated PC12 cells

Phenelzine, deprenyl, and antioxidants (SOD, catalase, ascorbate, or rutin) reduced the loss of cell viability in differentiated PC12 cells treated with 250 microM MPP+, whereas N-acetylcysteine and dithiothreitol did not inhibit cell death. Phenelzine reduced the condensation and fragmentation of nuclei caused by MPP+ in PC12 cells. Phenelzine and deprenyl prevented the MPP+-induced decrease in mitochondrial membrane potential, cytochrome c release, formation of reactive oxygen species, and depletion of GSH in PC12 cells. Phenelzine revealed a scavenging action on hydrogen peroxide and reduced the hydrogen peroxide-induced cell death in PC12 cells, whereas deprenyl did not depress the cytotoxic effect of hydrogen peroxide. Both compounds reduced the iron and EDTA-mediated degradation of 2-deoxy-D-ribose degradation. The results suggest that phenelzine attenuates the MPP+-induced viability loss in PC12 cells by reducing the alteration of mitochondrial membrane permeability that seems to be mediated by oxidative stress.

N-methylated beta-carbolines protect PC12 cells from cytotoxic effect of MPP+ by attenuation of mitochondrial membrane permeability change

Opening of the mitochondrial permeability transition pore has been recognized to be involved in cell death. The present study investigated the effect of beta-carbolines (harmaline and harmalol) on the MPP(+)-induced change in the mitochondrial membrane permeability and cell death in differentiated PC12 cells. beta-Carbolines and antioxidants (superoxide dismutase, catalase, ascorbate or rutin) prevented the loss of cell viability in PC12 cells treated with 250 microM MPP(+), while the effects of N-acetylcysteine and dithiothreitol were not observed. beta-Carbolines reduced the condensation and fragmentation of nuclei caused by MPP(+) in PC12 cells. beta-Carbolines alone did not exhibit a significant cytotoxic effect on PC12 cells. beta-Carbolines (50 microM) inhibited the decrease in mitochondrial transmembrane potential, cytochrome c release, activation of caspase-3, formation of reactive oxygen species (ROS) and depletion of GSH caused by MPP(+) in PC12 cells. beta-Carbolines reduced the hydrogen peroxide- or SIN-1-induced cell death in PC12 cells. The results suggest that beta-carbolines may attenuate the MPP(+)-induced viability loss in PC12 cells by inhibition of change in the mitochondrial membrane permeability and by antioxidant effect.

A novel cholinesterase and brain-selective monoamine oxidase inhibitor for the treatment of dementia comorbid with depression and Parkinson's disease

Degeneration of cholinergic cortical neurons is one of the main reasons for the cognitive deficit in dementia of the Alzheimer type (AD) and in dementia with Lewy bodies (DLB). Many subjects with AD and DLB have extrapyramidal dysfunction and depression resulting from degeneration of dopaminergic, noradrenergic and serotoninergic neurons. We prepared a novel drug, TV-3326 (N-propargyl-3R-aminoindan-5yl)-ethyl methylcarbamate), with both cholinesterase (ChE) and monoamine oxidase (MAO) inhibitory activity, as potential treatment of AD and DLB. TV-3326 inhibits brain acetyl and butyrylcholinesterase (BuChE) in rats after oral doses of 10-100 mg/kg. After chronic but not acute treatment, it inhibits MAO-A and -B in the brain by more than 70% but has almost no effect on these enzymes in the small intestine in rats and rabbits. The brain selectivity results in minimal potentiation of the pressor response to oral tyramine. TV-3326 acts like other antidepressants in the forced swim test in rats, indicating a potential for antidepressant activity. Chronic treatment of mice with TV-3326 (26 mg/kg) prevents the destruction of nigrostriatal neurons by the neurotoxin MPTP (N-methyl-4-phenyl-1,2,3,6-tetrahydropyridine). In addition to ChE and MAO inhibition, the propargylamine moiety of TV-3326 confers neuroprotective activity against cytotoxicity induced by ischemia and peroxynitrite in cultured neuronal cells that results from prevention of the fall in mitochondrial membrane potential and antiapoptotic activity. These unique multiple actions of TV-3326 make it a potentially useful drug for the treatment of dementia with Parkinsonian-like symptoms and depression.

Neuroprotection by monoamine oxidase B inhibitors: a therapeutic strategy for Parkinson's disease?

Parkinsonism (PD) is a neurodegenerative disorder of the brain resulting in dopamine deficiency caused by the progressive death of dopaminergic neurons. PD is characterized by a combination of rigidity, poverty of movement, tremor and postural instability. Selegiline is a selective and irreversible propargylamine type B monoamine oxidase (MAO-B) inhibitor. This drug, which inhibits dopamine metabolism, has been effectively used in the treatment of PD. However, its therapeutic effects are compromised by its many neurotoxic metabolites. To circumvent this obstacle, a novel MAO-B inhibitor, rasagiline, was developed. Paradoxically, the neuroprotective mechanism of propargylamines in different neuronal models appears to be independent of MAO-B inhibition. Recent investigations into the neuroprotective mechanism of propargylamines indicate that glyceraldehyde-3-phosphate dehydrogenase (GAPDH), MAO-B and/or other unknown proteins may represent pivotal proteins in the survival of the injured neurons. Delineation of the mechanism(s) involved in the neuroprotective effects exerted by MAO-B inhibitors may provide the key to preventive novel therapeutic modalities.

Neuroprotective effect of the monoamine oxidase inhibitor PF 9601N [N-(2-propynyl)-2-(5-benzyloxy-indolyl) methylamine] on rat nigral neurons after 6-hydroxydopamine-striatal lesion

Monoamine oxidase B (MAO-B) inhibitors are potentially useful in the therapeutic treatment of Parkinson's disease. L-Deprenyl has been shown to slow nigrostriatal tract degeneration in human idiopathic Parkinsonism and to be an effective neuroprotector in experimental 1-methyl-4-phenyl-1,2,3,6-tetrahydropyridine toxicity models. However, L-amphetamine and (-)methamphetamine, the metabolites generated by L-deprenyl, can have adverse and severe side-effects. Therefore, the search for new MAO-B inhibitors without potential amphetamine-like properties is a matter of great therapeutic interest. The present report is the first to describe the neuroprotective effect--following chronic intraperitoneal (i.p.) treatment--of a novel and non-amphetaminic MAO-B inhibitor, [N-(2-propynyl)-2-(5-benzyloxy-indolyl) methylamine] (PF 9601N), on the neurodegeneration of nigral dopaminergic neurons caused by administration of intrastriatal 6-hydroxydopamine (6-OHDA). Two groups of six animals were unilaterally injected with 6-OHDA in the right striatum. One group was treated daily with 60 mg/kg PF 9601N i.p., starting before stereotaxic lesion and continuing for 18 days thereafter. The other group was treated with vehicle solution. Coronal slabs including the substantia nigra pars compacta (SNpc) were processed for tyrosine hydroxylase immunohistochemistry (TH). The number of TH positive (TH+) neurons in the SNpc was 60% lower in 6-OHDA lesioned rats. However, the loss of TH+ neurons in the SNpc was only 30% in PF 9601N i.p.-treated animals. Therefore, treatment with the specific MAO-B inhibitor significantly reduced the 6-OHDA-induced degeneration to about 50%.

Deprenyl protects from MPTP-induced Parkinson-like syndrome and glutathione oxidation in rat striatum

An intrastriatal injection with 18.8 nmoles of the neurotoxic agent 1-methyl-4-phenyl-1,2,3,6-tetrahydropyridine (MPTP) induced in rats a progressive parkinsonism characterized by a major loss of striatum dopamine (DA) levels and an increased turnover of this neurotransmitter 96 h after the administration. In addition, the intrastriatal administration of MPTP produced an alteration in various behavioral markers of motor activity. Loss of DA was accompanied by a significant decrease of reduced glutathione (GSH) and an increase in GSH oxidation in the striatum. When deprenyl (10 mg/kg) was i.p. administered 2 h before the intrastriatal injection of MPTP, DA, GSH, glutathione redox status and the indexes of motor activity were not altered. These results show that MPTP increases striatum oxidative stress leading to cellular and in vivo degenerative changes which are prevented by pretreatment with deprenyl.