Selective acetylenic 'suicide' and reversible inhibitors of monoamine oxidase types A and B

Are Terminal Alkynes Necessary for MAO-A/MAO-B Inhibition? A New Scaffold Is Revealed

A versatile family of quaternary propargylamines was synthesized employing the KA2 multicomponent reaction, through the single-step coupling of a number of amines, ketones, and terminal alkynes. Sustainable synthetic procedures using transition metal catalysts were employed in all cases. The inhibitory activity of these molecules was evaluated against human monoaminoxidase (hMAO)-A and hMAO-B enzymes and was found to be significant. The IC50 values for hMAO-B range from 152.1 to 164.7 nM while the IC50 values for hMAO-A range from 765.6 to 861.6 nM. Furthermore, these compounds comply with Lipinski's rule of five and exhibit no predicted toxicity. To understand their binding properties with the two target enzymes, key interactions were studied using molecular docking, all-atom molecular dynamics (MD) simulations, and MM/GBSA binding free energy calculations. Overall, herein, the reported family of propargylamines exhibits promise as potential treatments for neurodegenerative disorders, such as Parkinson's disease. Interestingly, this is the first time a propargylamine scaffold bearing an internal alkyne has been reported to show activity against monoaminoxidases.

A comprehensive review of monoamine oxidase inhibitors as Anti-Alzheimer's disease agents: A review

Monoamine oxidases (MAO-A and MAO-B) are mammalian flavoenzyme, which catalyze the oxidative deamination of several neurotransmitters like norepinephrine, dopamine, tyramine, serotonin, and some other amines. The oxidative deamination produces several harmful side products like ammonia, peroxides, and aldehydes during the biochemical reaction. The concentration of biochemical neurotransmitter alteration in the brain by MAO is directly related with several neurological disorders like Alzheimer's disease and Parkinson's disease (PD). Activated MAO also contributes to the amyloid beta (Aβ) aggregation by two successive cleft β-secretase and γ-secretase of amyloid precursor protein (APP). Additionally, activated MAO is also involved in aggregation of neurofibrillary tangles and cognitive destruction through the cholinergic neuronal damage and disorder of the cholinergic system. MAO inhibition has general anti-Alzheimer's disease effect as a consequence of oxidative stress reduction prompted by MAO enzymes. In this review, we outlined and addressed recent understanding on MAO enzymes such as their structure, physiological function, catalytic mechanism, and possible therapeutic goals in AD. In addition, it also highlights the current development and discovery of potential MAO inhibitors (MAOIs) from various chemical scaffolds.

Designer drugs: a medicinal chemistry perspective (II)

During 2012-2018, the clandestine manufacture of new psychoactive substances (NPS) designed to circumvent substance control regulations increased exponentially worldwide, with concomitant increase in fatalities. This review focuses on three compound classes identified as synthetic opioids, synthetic amphetamines, and synthetic cannabinoids and highlights the medicinal chemistry precedents utilized by clandestine laboratories to develop new NPS with increased brain penetration, longer duration of action, and greater potency. Chemical approaches to illicit drug abuse treatment options, particularly for opioid use disorder, are also discussed.

Monoamine oxidase-B inhibitors as potential neurotherapeutic agents: An overview and update

Monoamine oxidase (MAO) inhibitors have made significant contributions and remain an indispensable approach of molecular and mechanistic diversity for the discovery of antineurodegenerative drugs. However, their usage has been hampered by nonselective and/or irreversible action which resulted in drawbacks like liver toxicity, cheese effect, and so forth. Hence, the search for selective MAO inhibitors (MAOIs) has become a substantial focus in current drug discovery. This review summarizes our current understanding on MAO-A/MAO-B including their structure, catalytic mechanism, and biological functions with emphases on the role of MAO-B as a potential therapeutic target for the development of medications treating neurodegenerative disorders. It also highlights the recent developments in the discovery of potential MAO-B inhibitors (MAO-BIs) belonging to diverse chemical scaffolds, arising from intensive chemical-mechanistic and computational studies documented during past 3 years (2015-2018), with emphases on their potency and selectivity. Importantly, readers will gain knowledge of various newly established MAO-BI scaffolds and their development potentials. The comprehensive information provided herein will hopefully accelerate ideas for designing novel selective MAO-BIs with superior activity profiles and critical discussions will inflict more caution in the decision-making process in the MAOIs discovery.

Monoamine oxidase inhibitors, and iron chelators in depressive illness and neurodegenerative diseases

In early 1920s, tyramine oxidase was discovered that metabolized tyramine and in 1933 Blaschko demonstrated that this enzyme also metabolized adrenaline, noradrenaline and dopamine. Zeller gave it the name monoamine oxidase (MAO) to distinguish it from the enzyme that oxidatively deaminated diamines. MAO was recognized as an enzyme of crucial interest to pharmacologists because it catalyzed the major inactivation pathway for the catecholamines (and, later, 5-hydroxytryptamine, as well). Within the few decade, the inhibitors of MAO were discovered and introduced for the treatment of depressive illness which was established clinically. However, the first clinical use exposed serious side effects, pharmacological interest in, and investigation of, MAO continued, resulting in the characterization of two forms, distinct forms, MAO-A and -B, and selective inhibitors for them. Selective inhibitors of MAO-B (selegiline, rasagiline and safinamide) have found a therapeutic role in the treatment of Parkinson's disease and reversible inhibitors of MAO-A offered antidepressant activity without the serious side effects of the earlier nonselective MAO inhibitors. Subsequent molecular pharmacological have also generated the concept of neuroprotection, reflecting the possibility of slowing, halting and maybe reversing, neurodegeneration in Parkinson's or Alzheimer's diseases. Increased levels of oxidative stress through the accumulation of iron in the Parkinsonian and Alzheimer brains has been suggested to be critical for the initiation and progress of neurodegeneration. Selective inhibition of brain MAO could contribute importantly to lowering such stress, preventing the formation of hydrogen peroxide. Interaction of Iron with hydrogen peroxide and lead to Fenton reaction and production of the most reactive radical, namely hydroxyl radical. There are complex interactions between free iron levels in brain and MAO, and cascade of neurotoxic events may have practical outcomes for depressive disorders and neurodegenerative diseases. As consequence recent novel therapeutic drugs for neurodegenerative diseases has led to the development of multi target drugs, that possess selective brain MAO A and B inhibitory moiety, iron chelating and antioxidant activities and the ability to increase brain levels of endogenous neurotrophins, such as BDNF, GDNF VEGF and erythropoietin and induce mitochondrial biogenesis.

Evidence for a Cyanine Link Between Propargylamine Drugs and Monoamine Oxidase Clarifies the Inactivation Mechanism

Successful propargylamine drugs such as deprenyl inactivate monoamine oxidase (MAO), a target in multi-faceted approaches to prevent neurodegeneration in the aging population, but the chemical structure and mechanism of the irreversible inhibition are still debated. We characterized the covalent cyanine structure linking the multi-target propargylamine inhibitor ASS234 and the flavin adenine dinucleotide in MAO-A using a combination of ultra-high performance liquid chromatography, spectroscopy, mass spectrometry, and computational methods. The partial double bond character of the cyanine chain gives rise to 4 interconverting geometric isomers of the adduct which were chromatographically separated at low temperatures. The configuration of the cyanine linker governs adduct stability with segments of much higher flexibility and rigidity than previously hypothesized. The findings indicate the importance of intramolecular electrostatic interactions in the MAO binding site and provide key information relevant to incorporation of the propargyl moiety into novel multi-target drugs. Based on the structure, we propose a mechanism of MAO inactivation applicable to all propargylamine inhibitors.

Privileged scaffolds as MAO inhibitors: Retrospect and prospects

This review aims to be a comprehensive, authoritative, critical, and readable review of general interest to the medicinal chemistry community because it focuses on the pharmacological, chemical, structural and computational aspects of diverse chemical categories as monoamine oxidase inhibitors (MAOIs). Monoamine oxidases (MAOs), namely MAO-A and MAO-B represent an enormously valuable class of neuronal enzymes embodying neurobiological origin and functions, serving as potential therapeutic target in neuronal pharmacotherapy, and hence we have coined the term "Neurozymes" which is being introduced for the first time ever. Nowadays, therapeutic attention on MAOIs engrosses two imperative categories; MAO-A inhibitors, in certain mental disorders such as depression and anxiety, and MAO-B inhibitors, in neurodegenerative disorders like Alzheimer's disease (AD) and Parkinson's disease (PD). The use of MAOIs declined due to some potential side effects, food and drug interactions, and introduction of other classes of drugs. However, curiosity in MAOIs is reviving and the recent developments of new generation of highly selective and reversible MAOIs, have renewed the therapeutic prospective of these compounds. The initial section of the review emphasizes on the detailed classification, structural and binding characteristics, therapeutic potential, current status and future challenges of the privileged pharmacophores. However, the chemical prospective of privileged scaffolds such as; aliphatic and aromatic amines, amides, hydrazines, azoles, diazoles, tetrazoles, indoles, azines, diazines, xanthenes, tricyclics, benzopyrones, and more interestingly natural products, along with their conclusive SARs have been discussed in the later segment of review. The last segment of the article encompasses some patents granted in the field of MAOIs, in a simplistic way.

Synthetic Aminoindanes: A Summary of Existing Knowledge

OBJECTIVES

Aminoindanes ("bath salts," a class of novel psychoactive substances, NPSs) increased rapidly in popularity on the recreational drug market, particularly after mephedrone and other synthetic cathinones were banned in the UK in 2010. Novel aminoindanes continue to emerge, but relatively little is known about their effects and risks. Their history, chemistry, pharmacology, behavioral effects, pharmacokinetics, and toxicity are reviewed in this paper.

METHODS

Scientific literature was searched on ISI Web of Knowledge: Web of Science (WoS) during June and July 2017, using English language terms: aminoindanes such as 5,6-methylenedioxy-2-aminoindane (MDAI), 5-iodo-2-aminoindane (5-IAI), 2-aminoindane (2-AI), 5,6-methylenedioxy-N-methyl-2-aminoindane (MDMAI), and 5-methoxy-6-methyl-2-aminoindane (MMAI). WoS was selected as it searches several databases simultaneously and has quality criteria for inclusion. For typical use and effects, Erowid, PsychonautWiki, Bluelight, and Drugs-Forum were searched; for legal status and epidemiology, the European Information System and Database on New Drugs (EDND) was used.

RESULTS

Aminoindanes were first synthesized for medical use, e.g., as anti-Parkinsonian drugs and later as a potential compound facilitating psychotherapy; however, they are now widely substituted for ecstasy. Their mechanisms of action (primarily via serotonin) mean that they may pose a significant risk of serotonin syndrome at high doses or when combined with other drugs. Fatally toxic effects have been observed both in the laboratory in animal studies and in clinic, where deaths related with aminoindanes have been reported.

CONCLUSION

Greater knowledge about aminoindanes is urgently required to decrease risks of fatal intoxication, and appropriate legislation is needed to protect public health without impeding research.

MAO-B inhibitors: multiple roles in the therapy of neurodegenerative disorders?

Monoamine oxidases play a central role in catecholamine catabolism in the central nervous system. The biochemical and pharmacological properties of inhibitors of the monoamine oxidase type B are reviewed. The evidence for biochemical activities distinct from their ability to inhibit MAO-B is discussed, including possible antioxidative and antiapoptotic activities of these agents. The significance of these properties for the pharmacological management of Parkinson's disease and the evidence for a neuroprotective effect of one such agent (selegiline) is also discussed.

Adjunctive therapy in Parkinson's disease: the role of rasagiline

Parkinson's disease is the second most common neurodegenerative disorder, currently affecting 1.5 million people in the US. In this review, we describe the diagnostic and pathological features of Parkinson's disease, as well as its clinical course. We then review pharmacologic treatments for the disease, with a particular focus on therapies adjunctive to levodopa and specifically the role of rasagiline. We review the four pivotal rasagiline trials, and discuss rasagiline and its use as adjunctive therapy for Parkinson's disease. Finally, we discuss potential side effects, drug interactions, and other practical aspects concerning the use of rasagiline in Parkinson's disease.

limited potentiation of blood pressure in response to oral tyramine by the anti-Parkinson brain selective multifunctional monoamine oxidase-AB inhibitor, M30

One of the limitations of non-selective monoamine oxidase (MAO) inhibitors as anti-depressant or anti-Parkinson drugs is their ability to potentiate the cardiovascular effect of oral tyramine, resulting from inhibition of systemic MAO-A and release of noradrenaline. We have investigated the cardiovascular effect of oral tyramine in response to the novel multifunctional, brain selective MAO-AB inhibitor, M30 [5-(N-methyl-N-propargylaminomethyl)-8-hydroxyquinoline], and compared it to the classical non-selective inhibitor tranylcypromine (TCP) in rats. We also measured MAO-A and B in the striatum, hippocampus, liver, and small intestine and determined brain levels of dopamine, noradrenaline, and serotonin. At the doses employed, intraperitoneal (i.p.) M30 (5 and 10 mg/kg) selectively inhibited brain MAO-A and B by more than 85%, with little inhibition of liver and small intestine enzymes while raising striatal levels of dopamine, noradrenaline, and serotonin. In contrast to TCP (10 mg/kg, i.p.), which fully inhibits both enzymes in the brain and systemic organs and significantly potentiates the tyramine pressor effect, M30 had a limited pressor effect as compared to it and controls. The limited potentiation of tyramine pressor effect by M30, its ability to raise brain levels of aminergic neurotransmitters together with its neuroprotective and neurorestorative activities make this drug potentially important as an anti-depressant and anti-Parkinsonian agent, for which it is being developed.

Rasagiline: A second-generation monoamine oxidase type-B inhibitor for the treatment of Parkinson's disease

PURPOSE

The pharmacology, pharmacokinetics, clinical efficacy, and safety of rasagiline are reviewed.

SUMMARY

Rasagiline is a novel, investigational propargylamine that irreversibly and selectively inhibits monoamine oxidase type B (MAO-B). Rasagiline demonstrates complete and selective inhibition of MAO-B and is at least five times more potent than selegiline. Unlike selegiline, which is metabolized to amphetamine derivatives, rasagiline is biotransformed to the nonamphetamine compound aminoindan. Clinical studies have revealed that rasagiline is associated with improved outcomes in patients with early Parkinson's disease (PD) and also reduces "off" time in patients with moderate to advanced PD with motor fluctuations. Rasagiline is rapidly absorbed by the gastrointestinal tract and readily crosses the blood-brain barrier. The optimal therapeutic dosage is 0.5-1 mg administered orally once daily. Rasagiline appears to be well tolerated, although elderly patients may be more prone to treatment-emergent adverse cardiovascular and psychiatric effects. At the recommended therapeutic dosage of up to 1 mg once daily, tyramine restriction is unnecessary. In addition to MAO-B inhibition, rasagiline has demonstrated neuroprotective properties in experimental laboratory models. The mechanisms whereby rasagiline exerts neuroprotective effects are multifactorial and include upregulation of cellular antioxidant activity and antiapoptotic factors.

CONCLUSION

Rasagiline is an investigational selective and irreversible inhibitor of MAO-B that has demonstrated efficacy and safety for the treatment of PD. Whether rasagiline is associated with clinically significant neuroprotection is the subject of ongoing clinical trials.

Novel multifunctional neuroprotective iron chelator-monoamine oxidase inhibitor drugs for neurodegenerative diseases: in vitro studies on antioxidant activity, prevention of lipid peroxide formation and monoamine oxidase inhibition

Iron-dependent oxidative stress, elevated levels of iron and of monoamine oxidase (MAO)-B activity, and depletion of antioxidants in the brain may be major pathogenic factors in Parkinson's disease, Alzheimer's disease and related neurodegenerative diseases. Accordingly, iron chelators, antioxidants and MAO-B inhibitors have shown efficacy in a variety of cellular and animal models of CNS injury. In searching for novel antioxidant iron chelators with potential MAO-B inhibitory activity, a series of new iron chelators has been designed, synthesized and investigated. In this study, the novel chelators were further examined for their activity as antioxidants, MAO-B inhibitors and neuroprotective agents in vitro. Three of the selected chelators (M30, HLA20 and M32) were the most effective in inhibiting iron-dependent lipid peroxidation in rat brain homogenates with IC50 values (12-16 microM), which is comparable with that of desferal, a prototype iron chelator that is not has orally active. Their antioxidant activities were further confirmed using electron paramagnetic resonance spectroscopy. In PC12 cell culture, the three novel chelators at 0.1 microM were able to attenuate cell death induced by serum deprivation and by 6-hydroxydopamine. M30 possessing propargyl, the MAO inhibitory moiety of the anti-Parkinson drug rasagiline, displayed greater neuroprotective potency than that of rasagiline. In addition, in vitro, M30 was a highly potent non-selective MAO-A and MAO-B inhibitor (IC50 < 0.1 microM). However, HLA20 was more selective for MAO-B but had poor MAO inhibition, with an IC50 value of 64.2 microM. The data suggest that M30 and HLA20 might serve as leads in developing drugs with multifunctional activities for the treatment of various neurodegenerative disorders.

Novel multifunctional neuroprotective iron chelator-monoamine oxidase inhibitor drugs for neurodegenerative diseases. In vivo selective brain monoamine oxidase inhibition and prevention of MPTP-induced striatal dopamine depletion

Several multifunctional iron chelators have been synthesized from hydroxyquinoline pharmacophore of the iron chelator, VK-28, possessing the monoamine oxidase (MAO) and neuroprotective N-propargylamine moiety. They have iron chelating potency similar to desferal. M30 is a potent irreversible rat brain mitochondrial MAO-A and -B inhibitor in vitro (IC50, MAO-A, 0.037 +/- 0.02; MAO-B, 0.057 +/- 0.01). Acute (1-5 mg/kg) and chronic [5-10 mg/kg intraperitoneally (i.p.) or orally (p.o.) once daily for 14 days]in vivo studies have shown M30 to be a potent brain selective (striatum, hippocampus and cerebellum) MAO-A and -B inhibitor. It has little effects on the enzyme activities of the liver and small intestine. Its N-desmethylated derivative, M30A is significantly less active. Acute and chronic treatment with M30 results in increased levels of dopamine (DA), serotonin(5-HT), noradrenaline (NA) and decreases in DOPAC (dihydroxyphenylacetic acid), HVA (homovanillic acid) and 5-HIAA (5-hydroxyindole acetic acid) as determined in striatum and hypothalamus. In the mouse MPTP (N-methy-4-phenyl-1,2,3,6-tetrahydropyridine) model of Parkinson's disease (PD) it attenuates the DA depleting action of the neurotoxin and increases striatal levels of DA, 5-HT and NA, while decreasing their metabolites. As DA is equally well metabolized by MAO-A and -B, it is expected that M30 would have a greater DA neurotransmission potentiation in PD than selective MAO-B inhibitors, for which it is being developed, as MAO-B inhibitors do not alter brain dopamine.

Clinical pharmacology of rasagiline: a novel, second-generation propargylamine for the treatment of Parkinson disease

Rasagiline is a novel second-generation propargylamine that irreversibly and selectively inhibits monoamine oxidase type B (MAO-B). For the management of Parkinson disease (PD), rasagiline is efficacious across the span of PD stages ranging from monotherapy in early disease to adjunctive treatment in patients with advancing disease and motor fluctuations. Rasagiline completely and selectively inhibits MAO-B with a potency 5 to 10 times greater than selegiline. Unlike the prototype propargylamine selegiline, which is metabolized to amphetamine derivatives, rasagiline is biotransformed to aminoindan, a non-amphetamine compound. Rasagiline is well tolerated with infrequent cardiovascular or psychiatric side effects, and at the recommended therapeutic dose of up to 1 mg once daily, tyramine restriction is unnecessary. In addition to MAO-B inhibition, the propargylamine chain also confers dose-related antioxidant and antiapoptotic effects, which have been associated with neuroprotection in multiple experimental models. Thus, in addition to symptomatic benefits, rasagiline offers the promise of clinically relevant neuroprotection.

Bifunctional drug derivatives of MAO-B inhibitor rasagiline and iron chelator VK-28 as a more effective approach to treatment of brain ageing and ageing neurodegenerative diseases

Degeneration of nigrostriatal dopamine neurons and cholinergic cortical neurones are the main pathological features of Parkinson's disease (PD) and for the cognitive deficit in dementia of the Alzheimer' type (AD) and in dementia with Lewy bodies (DLB), respectively. Many PD and DLB subjects have dementia and depression resulting from possible degeneration of cholinergic and noradrenergic and serotonergic neurons. On the other hand, AD patients may also develop extrapyramidal features as well as depression. In both PD and AD there is, respectively, accumulation of iron within the melanin containing dopamine neurons of pars compacta and with in the plaques and tangle. It has been suggested that iron accumulation may contribute to the oxidative stress induced apoptosis reported in both diseases. This may result from increased glia hydrogen peroxide producing monoamine oxidase (MAO) activity that can generate of reactive hydroxyl radical formed from interaction of iron and hydrogen peroxide. We have therefore prepared a series of novel bifunctional drugs from the neuroprotective-antiapoptotic antiparkinson monoamine oxidase B inhibitor, rasagiline, by introducing a carbamate cholinesterase (ChE) inhibitory moiety into it. Ladostigil (TV-3326, N-propargyl-3R-aminoindan-5yl)-ethyl methylcarbamate), has both ChE and MAO-AB inhibitory activity, as potential treatment of AD and DLB or PD subjects with dementia Being a brain selective MAO-AB inhibitor it has limited potentiation of the pressor response to oral tyramine and exhibits antidepressant activity similar to classical non-selective MAO inhibitor antidepressants by increasing brain serotonin and noradrenaline. Ladostigil inhibits brain acetyl and butyrylcholinesterase in rats and antagonizes scopolamine-induced inhibition of spatial learning. Ladostigil like MAO-B inhibitor it prevents MPTP Parkinsonism in mice model and retains the in vitro and in vivo neuroprotective activity of rasagiline. Ladostigil, rasagiline and other propargylamines have been demonstrated to have neuroprotective activity in several in vitro and in vivo models, which have been shown be associated with propargylamines moiety, since propargylamines itself possess these properties. The mechanism of neuroprotective activity has been attributed to the ability of propargylamines-inducing the antiapoptotic family proteins Bcl-2 and Bcl-xl, while decreasing Bad and Bax and preventing opening of mitochondrial permeability transition pore. Iron accumulates in brain regions associated with neurodegenerative diseases of PD, AD, amyotrophic lateral sclerosis and Huntington disease. It is thought to be involved in Fenton chemistry oxidative stress observed in these diseases. The neuroprotective activity of propargylamines led us to develop several novel bifunctional iron chelator from our prototype brain permeable iron chelators, VK-28, possessing propargylamine moiety (HLA-20, M30 and M30A) to iron out iron from the brain. These compounds have been shown to have iron chelating and monoamine oxidase A and B selective brain inhibitory and neuroprotective-antiapoptotic actions.

Cardiovascular activity of rasagiline, a selective and potent inhibitor of mitochondrial monoamine oxidase B: comparison with selegiline

Selegiline is used for treating Parkinson's disease. Despite its efficacy, the clinical use of selegiline in combination with l-dihydroxphenylalanine in Parkinsonian patients is hampered by cardiovascular complications, such as hypotension. This study was designed to compare in rats the cardiovascular effects of selegiline and rasagiline, their metabolites l-methamphetamine and aminoindan (TVP-136), respectively, and the second rasagiline metabolite non-monoamine oxidase (MAO) inhibitor TVP-1022 (N-propargyl-1S(-)aminoindan). Intravenous (i.v.) administration of selegiline and rasagiline (1 mg kg(-1)) to anaesthetized rats (thiobutabarbital, 100 mg kg(-1), i.p.) did not affect mean arterial pressure (MAP), carotid blood flow (CBF) or carotid vascular resistance (CVR). Selegiline (10 mg kg(-1), i.v.) decreased MAP, CBF and increased CVR. In contrast, rasagiline (10 mg kg(-1), i.v.) caused a small transient decrease in MAP, while CBF and CVR were unchanged. l-methamphetamine (1 mg kg(-1), i.v.) administration provoked a dramatic and long-lasting depressor response, decreased CBF and increased CVR. In contrast, injection of aminoindan or TVP-1022 at a similar dose produced gradual nonsignificant decreases in MAP and CBF. Chronic oral treatment (21 days) of awake rats with selegiline at 10 mg kg(-1) decreased systolic blood pressure (SBP), diastolic blood pressure (DBP), and MAP, whereas heart rate was unaffected. Since the effective MAO-B inhibitory and clinical dose of rasagiline is about one-tenth that of selegiline, administration of 1 mg kg(-1) day(-1) rasagiline resulted in moderate decreases in SBP, DBP, and MAP, which were significantly lower than those caused by the 10 mg kg(-1) day(-1) dose of selegiline. These findings indicate that rasagiline, when given at doses equivalent to selegiline, is less likely to be hypotensive.

Neuroprotective strategies in Parkinson's disease : an update on progress

In spite of the extensive studies performed on postmortem substantia nigra from Parkinson's disease patients, the aetiology of the disease has not yet been established. Nevertheless, these studies have demonstrated that, at the time of death, a cascade of events had been initiated that may contribute to the demise of the melanin-containing nigro-striatal dopamine neurons. These events include increased levels of iron and monoamine oxidase (MAO)-B activity, oxidative stress, inflammatory processes, glutamatergic excitotoxicity, nitric oxide synthesis, abnormal protein folding and aggregation, reduced expression of trophic factors, depletion of endogenous antioxidants such as reduced glutathione, and altered calcium homeostasis. To a large extent, the 1-methyl-4-phenyl-1,2,3,6-tetrahydropyridine (MPTP) and 6-hydroxydopamine (6-OHDA) animal models of Parkinson's disease confirm these findings. Furthermore, neuroprotection can be afforded in these models with iron chelators, radical scavenger antioxidants, MAO-B inhibitors, glutamate antagonists, nitric oxide synthase inhibitors, calcium channel antagonists and trophic factors. Despite the success obtained with animal models, clinical neuroprotection is much more difficult to accomplish. Although the negative studies obtained with the MAO-B inhibitor selegiline (deprenyl) and the antioxidant tocopherol (vitamin E) may have resulted from an inappropriate choice of drug (selegiline) or an inadequate dose (tocopherol), the niggling problem that still remains is why these drugs, and others, do work in animals while they fail in the clinic. One reason for this may be related to the fact that in normal human brains the number of dopaminergic neurons falls by around 3-5% every decade, while in Parkinson's disease this decline is greater. Brain autopsy studies have shown that by the time the disease is identified, some 70-75% of the dopamine-containing neurons have been lost. More sensitive reliable methods and clinical correlative markers are required to discern between confoundable symptomatic effects versus a possible neuroprotective action of drugs, namely, the ability to delay or forestall disease progression by protecting or rescuing the remaining dopamine neurons or even restoring those that have been lost.A number of other possibilities for the clinical failure of potential neuroprotectants also exist. First, the animal models of Parkinson's disease may not be totally reflective of the disease and, therefore, the chemical pathologies established in the animal models may not cause, or contribute to, the progression of the disease clinically. Second, because of the series of events occurring in neurodegeneration and our ignorance about which of these factors constitutes the primary event in the pathogenic process, a single drug may not be adequate to induce neuroprotection and, as a consequence, use of a cocktail of drugs may be more appropriate. The latter concept receives support from recent complementary DNA (cDNA) microarray gene expression studies, which show the existence of a gene cascade of events occurring in the nigrostriatal pathway of MPTP, 6-OHDA and methamphetamine animal models of Parkinson's disease. Even with the advent of powerful new tools such as genomics, proteomics, brain imaging, gene replacement therapy and knockout animal models, the desired end result of neuroprotection is still beyond our current capability.

PF 9601N [N-(2-propynyl)-2-(5-benzyloxy-indolyl) methylamine], a new MAO-B inhibitor, attenuates MPTP-induced depletion of striatal dopamine levels in C57/BL6 mice

Monoamine oxidase isoform B (MAO-B) is involved in Parkinson's disease (PD) induced by the 1-methyl-4-phenyl-1,2,3,6-tetrahydropyridine toxin (MPTP) in human and non-human-primate. MAO-B inhibitors, such as L-deprenyl have shown to prevent against MPTP-toxicity in different species, and it has been used in Parkinson therapy, however, the fact that it is metabolized to (-)-methamphetamine and (-)-amphetamine highlights the need to find out new MAO-B inhibitors without a structural amphetaminic moiety. In this context we herein report, for the first time, anywhere a novel non-amphetamine-like MAO-B inhibitor, PF 9601N, N-(2-propynyl)-2-(5-benzyloxy-indolyl) methylamine. This attenuates the MPTP-induced striatal dopamine depletion in young-adult and adult-old C57/BL mice, using different schedules of administration, and which behave "ex vivo" as a slightly more potent and selective MAO-B inhibitor than L-deprenyl, assayed for comparative purposes in the same experimental conditions. The MAO-B ID(50) values were calculated from the total MAO-B activity measured against [14C] phenylethylamine (22 microM) as substrate, at each inhibitor concentration. The MAO-B ID(50) values resulted to be 381 and 577 nmol/kg for PF 9601N and L-deprenyl, respectively. The intraperitoneally (i.p.) co-administration to young-adult C57/BL6 mice of MPTP (30 mg/kg), with different concentrations of PF 9601N or L-deprenyl (29.5-0.357 micromol/kg) showed a dose-dependent protective effect against striatal dopamine depletion, measuring the dopamine contents and its metabolites by HPLC. The ED(50) value proved to be 3.07 micromol/kg without any significant differences between either MAO-B inhibitor. Nevertheless, lower doses of PF 9601N (1.5 micromol/kg) were necessary to get almost total protection, without any change in the DOPAC and HVA content, when administered 2 h before MPTP (30 mg/kg), whereas partial protection (45%) against dopamine depletion was observed in the case of L-deprenyl. In both cases, MAO-B inhibition was a necessary condition in order to observe the protective effect. When adult-old (8-10 months) C57/BL6 mice were used, MPTP (25 mg/kg) administration induced 25 days later, an irreversible dopamine depletion. In these conditions, chronic administration with 0.15 micromol/kg of PF 9601N, before the toxin, every 24 h for 10 days, rendered almost total protection of dopamine depletion, whereas L-deprenyl yielded only 50% protection of the dopamine content, assayed in the same conditions. It is worth remarking, that in both cases MAO-B was not affected. From these results, it can be concluded that PF 9601N attenuates MPTP neurotoxicity "in vivo" better than L-deprenyl through different mechanisms, with special relevance to the protective effect, independent of MAO-B inhibition, observed in the irreversibly MPTP-lesioned adult-old mice. Therefore, this novel non-amphetamine MAO-B inhibitor could be potentially effective in PD therapy.

Novel dual inhibitors of AChE and MAO derived from hydroxy aminoindan and phenethylamine as potential treatment for Alzheimer's disease

Carbamate derivatives of N-propargylaminoindans (Series I) and N-propargylphenethylamines (Series II) were synthesized via multistep procedures from the corresponding hydroxy precursors. The respective rasagiline- and selegiline-related series were designed to combine inhibitory activities of both acetylcholine esterase (AChE) and monoamine oxidase (MAO) by virtue of their carbamoyl and propargylamine pharmacophores. Each compound was tested for these activities in vitro in order to find molecules with similar potencies against each enzyme. Compounds with such dual AChE and MAO inhibitory activities are expected to have potential for the treatment of Alzheimer's disease. The observed SAR also offers insight into the requirements of the active sites on these enzymes. A carbamate moiety was found to be essential for AChE inhibition, which was absent in the corresponding hydroxy precursors. The propargyl group caused 2-70-fold decrease in AChE inhibitory activity (depending on the position of the carbamoyl group) of Series I, but had little or no effect in Series II. Thus, the 6- and 7-carbamyloxyphenyls in Series I were either equipotent to, or slightly (2- to 5-fold) less active as AChE inhibitors than, the corresponding compounds in Series II, while the 4-carbamyloxyphenyls were more potent. The presence of the carbamate moiety in 6- and 7-carbamyloxyphenyls of Series I, considerably decreased MAO-A and -B inhibitory activity, compared to that of the parent hydroxy analogues, while the opposite was true for Series II. Thus, the 6- and 7-carbamyloxyphenyls in Series I were 2-3 orders of magnitude weaker MAO inhibitors while the 4- carbamyloxyphenyls were equipotent with the corresponding compounds in Series II. In both series, N-methylation of the propargylamine enhanced the MAO (A and B equally) inhibitory activities and decreased the AChE inhibitory activity. Two candidates belonging to the indan and tetralin ring systems (24c, 27b) and one phenethylamine (53d) were identified as possible leads for further development based on the following criteria: (a) comparable AChE and MAO-B inhibitory activities, (b) good to moderate AChE inhibitory activity, and (c) lack of strong MAO-A selectivity. However, it is likely that these compounds will be metabolized to the corresponding phenols, with inhibitory activities against AChE and/or MAO-A or -B, different from those of the parent carbamates. Thus, the apparent enzyme inhibition will be a result of the combined inhibition of all of these individual metabolites. The results of our ongoing in vivo screening programs will be published elsewhere.

Novel neuroprotective anti-Alzheimer drugs with anti-depressant activity derived from the anti-Parkinson drug, rasagiline

A number of studies have shown that the selective monoamine oxidase (MAO)-B inhibitor l-selegiline has neuroprotective activities in several cell culture systems and in vivo. The suggestion has been made that the propargyl moiety in this molecule may have some intrinsic neuroprotective activity not related to its ability to bind covalently to MAO B and inhibit it. We have therefore developed a number of novel drugs based on rasagiline (N-propargyl-1R-(+)-aminoindan), a potent anti-Parkinson-propargyl-containing MAO-B inhibitor drug with structural resemblance to selegiline, for the treatment of Alzheimer's disease. These drugs possess a carbamate moiety for cholinesterase (ChE), and a propargyl group for MAO inhibition. The R-enantiomer of these compounds (TV3326) has ChE and MAO inhibitory activities in vivo and retains the neuroprotective properties of rasagiline. It also exhibits anti-depressant activity in animal models. The S-enantiomer does not inhibit MAO and has no anti-depressant activity, but it has similar ChE inhibitory and neuroprotective activities. Thus MAO inhibition by propargylamines is not a pre-requisite for neuroprotection. Rather, propargylamines have some intrinsic neuroprotective property whose mechanism of action requires further elucidation.

Rat striatal monoamine oxidase-B inhibition by l-deprenyl and rasagiline: its relationship to 2-phenylethylamine-induced stereotypy and Parkinson's disease

Rats were injected intraperitoneally with varying doses of l-deprenyl (selegiline) followed 2h later by 30 mg kg(-1) 2-phenylethylamine (PEA), administered in the same way, and the stereotypic behavioural response elicited was assessed. l-Deprenyl alone at doses of up to 5 mg kg(-1) caused no significant behavioural response. Administration of PEA without prior l-deprenyl treatment resulted in only a modest increase in stereotypic behaviour and this was not significantly enhanced by the prior administration 1 mg kg(-1) l-deprenyl. When the administered dose of l-deprenyl was increased to 2.5 or 5 mgkg(-1), however, the stereotypic behavioural response to PEA was greatly potentiated and in the latter case persisted for 60 min. A dose of 2.5 mg kg(-1) l-deprenyl and 1 mg kg(-1) rasagiline was shown to result in over 90% inhibition of the monoamine oxidase (MAO)-B from rat liver and striatum, whereas the inhibition of MAO-A was about 60 and 40% in liver and striatum, respectively. The recovery of MAO-B activity in rat striatum and liver following a single i.p. injection of 5 mg kg(-1) l-deprenyl gave first-order rate constants of 1.80 and 7.15 h(-1), respectively, which corresponded to half-lives of 9.23 and 2.33 days. Similar results were obtained with rasagiline. The corresponding indices of stereotypic response to PEA (30 mg kg(-1); i.p.) during recovery from the single dose of l-deprenyl were initially high, but had started to decline by the third day after l-deprenyl treatment and was not significant after day 4. At that time, less than 20% of the striatal monoamine oxidase-B activity had been regained, whereas the recovery of the liver enzyme was about 65%. These data are discussed in terms of the suggested involvement of PEA potentiation in the anti-parkinsonian actions of l-deprenyl and rasagiline and the duration of the 'wash-out' period used in studies on the effects of l-deprenyl on patients with Parkinson's disease. The longer duration of the recovery of brain monoamine oxidase B after its selective inhibition and the corresponding behavioural responses of the animals to PEA at same time points, indicate that PEA may have a major pharmacological role in the mechanism of the antiParkinson action of l-deprenyl and rasagiline. Brain monoamine oxidase B inhibition has previously been shown to significantly increases brain PEA and which is capable of releasing dopamine endogenously or that formed from L-dopa.

Molecular basis of neuroprotective activities of rasagiline and the anti-Alzheimer drug TV3326 [(N-propargyl-(3R)aminoindan-5-YL)-ethyl methyl carbamate]

Rasagiline (N-propargyl-1-(R)-aminoindan) is a selective, irreversible monoamine oxidase B (MAO B) inhibitor which has been developed as an anti-Parkinson drug. In controlled monotherapy and as adjunct to L-dopa it has shown anti-Parkinson activity. In cell culture (PC-12 and neuroblastoma SH-SY5Y cells) it exhibits neuroprotective and anti-apoptotic activity against several neurotoxins (SIN-1, MPTP, 6-hydroxydopamine and N-methyl-(R)-salsolinol) and ischemia. In vivo, it reduces the sequelae of traumatic brain injury in mice and speeds their recovery. The neuroprotective activity of rasagaline does not result from MAO B inhibition, since its S-enantiomer, TVP1022, which has 1000-fold weaker MAO inhibitory activity, exhibits similar neuroprotective properties. Introduction of a carbamate moiety into the rasagiline molecule to confer cholinesterase inhibitory activity for the treatment of Alzheimer's disease, resulted in compounds TV3326 [(N-Propargyl-(3R)Aminoindan-5-YL)-Ethyl Methyl Carbamate] and its S-enantiomer TV3279 [(N-Propargyl-(3S)Aminoindan-5-YL)-Ethyl Methyl Carbamate], which retain the neuroprotective activities of rasagiline and TVP1022. They also antagonize scopolamine-induced impairments in spatial memory. In addition, TV3326 exhibits brain-selective MAO A and B inhibitory activity after chronic administration and has antidepressant-like activity in the forced swim test. This is associated with an increase in brain levels of serotonin. The anti-apoptotic activity of these propargylamine-containing derivatives may be related to their ability to delay the opening of voltage-dependent anion channels (VDAC), which are part of the mitochondrial permeability transition pore. The propargylamine moiety is responsible for the increase in the mitochondrial family of Bcl-2 proteins, prevention in the fall in mitochondrial membrane potential, prevention of the activation of caspase 3, and of translocation of glyceraldehyde-3-phosphate dehydrogenase from the cytoplasm to the nucleus. The latter processes are closely associated with neurotoxin-induced apoptosis. Rasagiline interacts with and prevents the binding of PKI 1195 to the pro-apoptotic peripheral benzodiazepine receptor, which together with Bcl-2, hexokinase, porin, and adenine nucleotide translocator constitutes part of the VDAC. Furthermore, rasagiline, TV3326 and TV3279 are able to influence the processing of amyloid precursor protein by activation of alpha-secretase and increasing the release of soluble alpha APP in rat PC-12 and human neuroblastoma SH-SY5Y cells and in rat and mice cortex and hippocampus. This process has been shown to involve the upregulation of PKC and MAP kinase. It is quite likely that the induction of Bcl-2 and activation of PKC by rasagiline and TV3326 is closely linked to the anti-apoptotic action of these drugs and their ability to process APP by activation of alpha-secretase.

Antiapoptotic properties of rasagiline, N-propargylamine-1(R)-aminoindan, and its optical (S)-isomer, TV1022

Rasagiline and structurally related propargylamines protected dopaminergic SH-SY5Y cells from apoptosis induced by 6-OHDA and peroxynitrite-generating SIN-1. It was suggested that the intracellular mechanism of the neuroprotection is related to the stabilization of mitochondrial membrane potential, as indicated by use of a fluorescent indicator, JC-1. The opening of the permeability transition pore (PTP) was prevented by rasagiline, even in isolated mitochondria. The activation of apoptotic cascade by the oxidative stress and neurotoxins, such as activation of caspase 3 and DNA fragmentation, was also inhibited by pretreatment with rasagiline. These propargylamines may prevent or rescue declining neurons induced by mitochondrial apoptotic cascade and may be applicable as "neuroprotective agents" in aging and age-related neurodegenerative disorders, such as Parkinson's and Alzheimer's diseases.

The anti-Parkinson drug rasagiline and its cholinesterase inhibitor derivatives exert neuroprotection unrelated to MAO inhibition in cell culture and in vivo

The antiapoptotic and neuroprotective activity of irreversible monoamine oxidase (MAO) B inhibitor, rasagiline [R(+)-N-propargyl-1-aminioindan], its S-isomer (TVP1022) and TV 3219, a novel anti-Alzheimer cholinesterase-MAO inhibitor drug derived from rasagiline were examined in PC12 cells cultures and in vivo. We found that these drugs have potent antiapoptotic and neuroprotective activities in response to serum and NGF withdrawal in partially neuronally differentiated PC12 cells and prevent the fall in mitochondrial membrane potential, the first step in cell death. Closed head injury studies in mice have shown that both rasagiline and TVP1022 are neuroprotective. All these compounds possess a propargyl moiety, which normally is responsible for irreversible inactivation of MAO, as is seen with rasagiline. However, neither TVP1022 nor TV3219 are MAO inhibitors, both share the antiapoptotic and neuroprotective actions of rasagiline, indicating that MAO inhibition is not a prerequisite for neuroprotection and that the propargyl moiety exhibits intrinsic neuroprotective pharmacological activity that requires identification.

Neurotoxins induce apoptosis in dopamine neurons: protection by N-propargylamine-1(R)- and (S)-aminoindan, rasagiline and TV1022

In Parkinson's disease, apoptosis was proposed to cause cell death in nigral dopamine neurons. An endogenous dopaminergic neurotoxin, N-methyl(R)salsolinol, stereo-selectively induced apoptosis in human neuroblastoma SH-SY5Y cells. In this paper the intracellular mechanism of apoptosis was studied using N-methyl(R)salsolinol, 6-hydroxydopamine and peroxynitrite as inducers of apoptosis. Apoptotic cascade was initiated by opening of mitochondrial permeability transition pore, as shown by collapse of mitochondrial membrane potential, deltapsim. Apoptosis was executed by caspase 3 activation, followed by DNA fragmentation, which was antagonized by overexpressed Bcl-2. Propargylamines were found to protect the cells from apoptosis, and rasagiline, a selective irreversible inhibitor of type B monoamine oxidase was the most potent to prevent the cell death. Rasagiline preserved deltapsim, which was proved also in isolated mitochondria, and rasagiline completely suppressed the activation of caspases and DNA fragmentation. These results suggest that mitochondria regulate apoptotic process, which may be a target of neuroprotection by rasagiline.

TV3326, a novel neuroprotective drug with cholinesterase and monoamine oxidase inhibitory activities for the treatment of Alzheimer's disease

TV3326, [(N-propargyl-(3R) aminoindan-5-yl)-ethyl methyl carbamate] is a novel aminoindan derivative of the selective irreversible monoamine oxidase (MAO)-B inhibitor, rasagiline (N-propargyl-(1R)-aminoindan), possessing both cholinesterase (ChE) and MAO-inhibitory activity. In doses of 35-100 micromoles/kg administered orally to rats, it inhibits ChE by 25-40% and antagonises scopolamine-induced impairments in spatial memory. After daily administration of 75 micromoles/kg for 2 weeks, TV3326 does not show any motor stimulant effects but significantly reduces immobility in the forced swim test, an action consistent with that of known antidepressants. This could result from more than 70% inhibition of both MAO-A and B in the brain that occurs under these conditions, since it is not shared by the S-isomer, TV3279, which does not block MAO. TV3326 also shows selectivity for brain MAO, even after 2 months of daily administration, with little or no effect on the enzyme in the intestinal tract and liver. This reduces the likelihood of it producing the "cheese effect" if administered with tyramine-containing foods or beverages. TV3326 and TV3279 protect against ischemia-induced cytotoxicity in PC12 cells and reduce the oedema, deficits in motor function and memory after closed head injury in mice. These neuroprotective effects do not result from MAO inhibition. The pharmacological actions of TV3326 could be of clinical importance for the treatment of AD, and the drug is currently in development for this purpose.

Rasagiline [N-propargyl-1R(+)-aminoindan], a selective and potent inhibitor of mitochondrial monoamine oxidase B

1. Rasagiline [N-propargyl-1R(+)-aminoindan], was examined for its monoamine oxidase (MAO) A and B inhibitor activities in rats together with its S(-)-enantiomer (TVP 1022) and the racemic compound (AGN-1135) and compared to selegiline (1-deprenyl). The tissues that were studied for MAO inhibition were the brain, liver and small intestine. 2. While rasagiline and AGN1135 are highly potent selective irreversible inhibitors of MAO in vitro and in vivo, the S(-) enantiomer is relatively inactive in the tissues examined. 3. The in vitro IC(50) values for inhibition of rat brain MAO activity by rasagiline are 4.43+/-0.92 nM (type B), and 412+/-123 nM (type A). The ED(50) values for ex vivo inhibition of MAO in the brain and liver by a single dose of rasagiline are 0.1+/-0.01, 0.042+/-0.0045 mg kg(-1) respectively for MAO-B, and 6.48+/-0.81, 2.38+/-0.35 mg kg(-1) respectively for MAO-A. 4. Selective MAO-B inhibition in the liver and brain was maintained on chronic (21 days) oral dosage with ED(50) values of 0.014+/-0.002 and 0.013+/-0.001 mg kg(-1) respectively. 5. The degree of selectivity of rasagiline for inhibition of MAO-B as opposed to MAO-A was similar to that of selegiline. Rasagiline was three to 15 times more potent than selegiline for inhibition of MAO-B in rat brain and liver in vivo on acute and chronic administration, but had similar potency in vitro. 6. These data together with lack of tyramine sympathomimetic potentiation by rasagiline, at selective MAO-B inhibitory dosage, indicate that this inhibitor like selegiline may be a useful agent in the treatment of Parkinson's disease in either symptomatic or L-DOPA adjunct therapy, but lack of amphetamine-like metabolites could present a therapeutic advantage for rasagiline.

New 2-[(5-methoxy-1-methylindolyl)]-alkylamine derivatives: the effect of branching and elongation of the side chain on MAO inhibition

A novel series of previously synthesised 2-[(5-methoxy-1-methylindolyl)]alkylamine derivatives were irreversible and time-dependent mechanism-based inhibitors of MAO. The effect of branching and elongation of the side chain was evaluated on the inhibitory potency towards MAO-A and MAO-B activities. The KI of the reversible step and the kinact of the irreversible one were determined in each case. The results obtained lead to the conclusion that neither the elongation nor the branching of the side chain improve the potency of the compounds as MAO inhibitors.

Determination of regions important for monoamine oxidase (MAO) A and B substrate and inhibitor selectivities

MAO-A and -B are defined by their substrate and inhibitor preferences. To determine which regions of the isoenzymes confer these preferences, we have constructed six chimeric MAO enzymes by reciprocally exchanging corresponding N-terminal, C-terminal, and internal segments of MAO-A and -B then determined the catalytic properties of these chimeric enzymes. N-terminal chimerics A45B and B36A were made by exchanging amino acid segments 1-45 and 1-36 of MAO-A and -B respectively. C-terminal chimerics A402B and B393A were made by exchanging amino acid segments 403-527 and 394-520 of MAO-A and -B respectively, and internal chimerics AB161-375A and BA152-366B were made by exchanging amino acid segments 161-375 and 152-366 of MAO-A and -B respectively. The enzymatic properties observed for the chimerics suggest that the exchanged internal regions but not the N- or C-terminal regions confer substrate and inhibitor preferences.

Effects of N-propargyl-1-(R)aminoindan (rasagiline) in models of motor and cognition disorders

N-propargyl-1-(R)aminoindan (rasagiline) is a new and selective irreversible MAO-B inhibitor, currently being considered as the mesylate salt for potential therapy in certain neurological disorders. It has been studied in animal models of cognition and motor dysfunction. Its ability to restore normal motor activity was determined in models of acute drug-induced dopaminergic dysfunction: Its effects in improving cognition and memory deficits was studied in adult and senescent rats that had been exposed to prolonged hypoxia, then subjected to the passive and active avoidance tests. In alpha-methyl-p-tyrosine (alpha-MpT)-induced hypokinesia (100-120 mg/kg, i.p.) pretreatment with rasagiline at 2.5 mg/kg i.p. restored motor activity to control level. But pretreatment with reserpine abolished the protective effect of rasagiline. Rasagiline at 0.5 mg/kg/day was protective against alpha-MpT also in hypoxia-lesioned rats. In haloperidol-induced catalepsy in rats (1.5 mg/kg, s.c.) or mice (4-6 mg/kg s.c.), rasagiline improved recovery of normal locomotion, gait and coordination at 0.4-2.4 mg/kg i.p. and 1.8-1.5 mg/kg i.p., respectively. In amphetamine-induced stereotypy (0.6 mg/kg s.c., rasagiline potentiated this effect at 1.5 mg/kg i.p. In hypoxia-induced impairment of memory and learning, rasagiline at 0.32-0.5 mg/kg/day per os improved performance of adult rats in passive and active avoidance, and of senescent rats in active avoidance. Selegiline was either ineffective or less effective at equivalent doses. Racemic N-propargyl-1-aminoindan (AGN-1135), besides being of lower potency, had a different dose-dependency than rasagiline in antagonizing haloperidol-induced catalepsy or alpha-MpT-induced hypokinesia. 1-(R)aminoindan ((R)AI), a metabolite of rasagiline, in relatively high doses produced effects that were distinct in certain respects from those of rasagiline.

Chronic TVP-1012 (rasagiline) dose--activity response of monoamine oxidases A and B in the brain of the common marmoset

The stereospecific form of the known acetylenic mechanism-based MAO-inhibitor AGN1135 (Rasagiline, TVP-1012) is devoid of sympathomimetic amphetamine-like properties. To evaluate the efficiency and selectivity of subcutaneous injections of TVP-1012 (dose range from 0.01 up to 10 mg/kg for 7 days) the activities of monoamine oxidases A and B (MAO-A,-B) were determined in different brain regions of the common marmoset. At a dose of 0.1 mg/kg TVP-1012, almost 80% of MAO-B activity is inhibited in all brain regions investigated (prefrontal and occipital cortex, cerebellum, caudate nucleus, putamen, nucleus accumbens). In contrast, MAO-A is not inhibited in putamen and nucleus accumbens. However, by increasing the TVP-1012 dose to 0.5 mg/kg, MAO-A is inhibited to a significant extent as well, concomitant to total inhibition of MAO-B. The results obtained indicate that TVP-1012 irreversibly inhibits both types of MAO in the common marmoset with selectivity for MAO-B at doses less than 0.5 mg/kg. TVP-1012 could be useful in studies requiring selective MAO-B inhibition without concomitant sympathomimetic amphetamine-like effects and could thus be of therapeutic interest for Parkinson's disease and retarded depression.

Increased striatal dopamine production from L-DOPA following selective inhibition of monoamine oxidase B by R(+)-N-propargyl-1-aminoindan (rasagiline) in the monkey

Striatal extracellular fluid concentrations of dopamine and metabolites in response to direct striatal administration of two L-DOPA boluses administered sequentially were determined in three rhesus monkeys during halothane anesthesia. Whereas in an initial microdialysis run, generation of dopamine was less following the second L-DOPA bolus than the first, in a subsequent run, in which the selective MAO-B inhibitor R(+)-N-propargyl-1-aminoindan (rasagiline) was administered systemically (0.2 mg/kg s.c.) between the two L-DOPA boluses, generation of dopamine was greater following the second bolus.

(R)(+)-N-propargyl-1-aminoindan (rasagiline) and derivatives: highly selective and potent inhibitors of monoamine oxidase B

(+)-N-Propargyl-1-aminoindan (rasagiline) and a series of derivatives have been synthesized and screened for monoamine oxidase inhibitory activity. Rasagiline and several analogues were found be highly selective and potent inhibitors of the B form of the enzyme in contrast to the levorotatory enantiomer which was not active. The results indicate that rasagiline has potential for the treatment of Parkinson's Disease. This compound is currently under development for that indication.

Clinical pharmacokinetics and pharmacodynamics of selegiline. An update

Selegiline is a selective inhibitor of monoamine oxidase-B (MAO-B) at a dose of 10 mg/day and is given to patients with Parkinson's disease as an adjunct to levodopa therapy. By inhibiting MAO-B, selegiline increases the dopamine levels in the substantia nigra. Selegiline also blocks dopamine re-uptake from the synaptic cleft, thus increasing the dopamine concentrations in the brain. At a dose of 10 mg/day, selegiline is devoid of 'cheese effect'. The pharmacokinetics of selegiline are highly variable. Following an oral dose of selegiline 10 mg, it is rapidly absorbed and metabolised to desmethylselegiline, levoamphetamine and levomethamphetamine. The mean peak plasma concentration (Cmax) is approximately 2 micrograms/L and the time to reach the peak is under an hour. The absolute bioavailability of selegiline is approximately 10%. It has an apparent volume of distribution of 1854 L. The oral clearance of selegiline (59 L/min) is many fold higher than the liver blood flow (1.5 L/min), indicating that extrahepatic processes are involved in the elimination of selegiline. The elimination half-life of selegiline is about 1.5 hours. Following multiple administration of selegiline 10 mg/day, the accumulation of both the parent compound and its metabolites have been reported. At least a 4-fold increase in the half-lives of selegiline and desmethylselegiline has been reported. There is at least a 3-fold increase in the Cmax and area under the concentration-time curve of selegiline with food. One of the metabolites of selegiline, desmethylselegiline, is believed to posses some MAO-B inhibitory property, though to a lesser extent than that of selegiline. Within 2 to 4 hours of an oral dose of selegiline 10 mg, 86% of the platelet MAO-B activity was inhibited and it took almost 2 weeks for platelet MAO-B activity to return to the baseline values. Transdermal administration of selegiline resulted in an increase in the plasma concentrations of selegiline and a decrease in the formation of its metabolites, indicating that the extensive first-pass effect is avoided when selegiline is given transdermally.

Kinetic studies of N-allenic analogues of tryptamine as monoamine oxidase inhibitors

A series of N-allenic analogues of tryptamine in which the side chain is located at the 2 position of the indole ring, but which differed in the ring and side-chain nitrogen substituents, were assayed kinetically as MAO A and MAO B inhibitors. All the compounds studied were mechanism-based inhibitors. The kinetic constants of each inhibition step Ki and ki, were determined for both MAO A and B. The data obtained indicated that these allenic derivatives show a greater selectivity and potency towards MAO A as inhibitors than the corresponding acetylenic derivatives.

Pharmacology and neuroprotective properties of rasagiline

Rasagiline [R(+)-N-propargyl-1-aminoindane] is a selective irreversible inhibitor of MAO-B which is not metabolised to amphetamine-like derivatives. Like deprenyl, when given to rats in a dose selective for inhibition of MAO-B, it does not affect striatal extracellular fluid dopamine levels, but when administered chronically (21 days) it increased striatal microdialysate dopamine without reduction in deaminated metabolites. Similarly to deprenyl, rasagiline (10(-6)M) increased the percentage of tyrosine hydroxylase positive cells in a primary culture of rat fetal mesencephalic cells (6 days in culture). Rasagiline, but not deprenyl, also increased the number of neurons per field in this organotypic culture.

Iododerivative of pargyline: a potential tracer for the exploration of monoamine oxidase sites by SPECT

Monoamine oxidases are important in the regulation of monoaminergic neurotransmission. An increase in monoamine oxidase B (MAO B) has been observed in some neurodegenerative diseases, and therefore quantification of cerebral MAO B activity by SPECT would be useful for the diagnosis and therapeutic follow-up of these disorders. We have developed an iodinated derivative of pargyline, a selective inhibitor of MAO B, in order to explore this enzyme by SPECT. Stable bromo and iodo derivatives of pargyline were synthesized and chemically characterized. The radioiodinated ligand [125I]-2-iodopargyline was obtained with high specific activity from the bromo precursor by nucleophilic exchange. Affinity and selectivity of 2-iodopargyline were tested in vitro. Biodistribution study of [125I]-2-iodopargyline was performed in rats. Radioiodinated ligand were obtained in a no-carrier-added form. 2-iodopargyline has a higher in vitro affinity for MAO B than pargyline. However, the in vitro selectivity for MAO B was better for pargyline than for 2-iodopargyline. Ex vivo autoradiographic studies and in vivo saturation studies with selective inhibitors of MAO showed that the cerebral biodistribution of [125I]-2-iodopargyline in the rat is consistent with high level binding to MAO B sites in the pineal gland and in the thalamus. In conclusion, 2-iodopargyline preferentially binds in vivo to MAO B sites with high affinity. However, its selectivity for MAO B in rats is not very high, whereas this ligand binds to a lesser extent to MAO A. It will be then of great value to evaluate the specificity of 2-iodopargyline in humans. This new ligand labeled with 123I should therefore be a suitable tool for SPECT exploration of MAO B in the human brain.

Synthesis and characterization of [125I]N-(2-aminoethyl)-4-iodobenzamide as a selective monoamine oxidase B inhibitor

We described the radiosynthesis of an analog of Ro 16-6491, [125I]N-(2-aminoethyl)-4-iodobenzamide, for SPECT exploration of the monoamine oxidase B (MAO-B) in human brain. The radiolabelling was carried out by nucleophilic exchange of the brominated precursor at solid-state phase in presence of ammonium sulphate. The radiochemical purity of radioiodinated product was higher than 95%. In comparison with Ro 16-6491, the in vitro studies showed a good selectivity of stable N-(2-aminoethyl)-4-iodobenzamide for MAO-B but a slightly lower affinity. Biodistribution studies in the rat showed a high and selective uptake of this compound in the pineal gland 1 h after i.v. injection. The cerebral uptake was low, but the coupling of [125I]N-(2-aminoethyl)-4-iodobenzamide with a lipophilic radical to enhance the passage through the blood-brain barrier can be envisaged.