Inhibitor Deprenyl Research Articles

Head-to-head comparison of [18F]-Flortaucipir, [18F]-MK-6240 and [18F]-PI-2620 postmortem binding across the spectrum of neurodegenerative diseases

We and others have shown that [18F]-Flortaucipir, the most validated tau PET tracer thus far, binds with strong affinity to tau aggregates in Alzheimer's (AD) but has relatively low affinity for tau aggregates in non-AD tauopathies and exhibits off-target binding to neuromelanin- and melanin-containing cells, and to hemorrhages. Several second-generation tau tracers have been subsequently developed. [18F]-MK-6240 and [18F]-PI-2620 are the two that have garnered most attention. Our recent data indicated that the binding pattern of [18F]-MK-6240 closely parallels that of [18F]-Flortaucipir. The present study aimed at the direct comparison of the autoradiographic binding properties and off-target profile of [18F]-Flortaucipir, [18F]-MK-6240 and [18F]-PI-2620 in human tissue specimens, and their potential binding to monoamine oxidases (MAO). Phosphor-screen and high resolution autoradiographic patterns of the three tracers were studied in the same postmortem tissue material from AD and non-AD tauopathies, cerebral amyloid angiopathy, synucleopathies, transactive response DNA-binding protein 43 (TDP-43)-frontotemporal lobe degeneration and controls. Our results show that the three tracers show nearly identical autoradiographic binding profiles. They all strongly bind to neurofibrillary tangles in AD but do not seem to bind to a significant extent to tau aggregates in non-AD tauopathies pointing to their limited utility for the in vivo detection of non-AD tau lesions. None of them binds to lesions containing β-amyloid, α-synuclein or TDP-43 but they all show strong off-target binding to neuromelanin and melanin-containing cells, as well as weaker binding to areas of hemorrhage. The autoradiographic binding signals of the three tracers are only weakly displaced by competing concentrations of selective MAO-B inhibitor deprenyl but not by MAO-A inhibitor clorgyline suggesting that MAO enzymes do not appear to be a significant binding target of any of them. These findings provide relevant insights for the correct interpretation of the in vivo behavior of these three tau PET tracers.

Dihydroxyphenylacetaldehyde Lowering Treatment Improves Locomotor and Neurochemical Abnormalities in the Rat Rotenone Model: Relevance to the Catecholaldehyde Hypothesis for the Pathogenesis of Parkinson's Disease.

The catecholaldehyde hypothesis for the pathogenesis of Parkinson's disease centers on accumulation of 3,4-dihydroxyphenylacetaldehyde (DOPAL) in dopaminergic neurons. To test the hypothesis, it is necessary to reduce DOPAL and assess if this improves locomotor abnormalities. Systemic administration of rotenone to rats reproduces the motor and central neurochemical abnormalities characterizing Parkinson's disease. In this study, we used the monoamine oxidase inhibitor (MAOI) deprenyl to decrease DOPAL production, with or without the antioxidant N-acetylcysteine (NAC). Adult rats received subcutaneous vehicle, rotenone (2 mg/kg/day via a minipump), or rotenone with deprenyl (5 mg/kg/day i.p.) with or without oral NAC (1 mg/kg/day) for 28 days. Motor function tests included measures of open field activity and rearing. Striatal tissue was assayed for contents of dopamine, DOPAL, and other catechols. Compared to vehicle, rotenone reduced locomotor activity (distance, velocity and rearing); increased tissue DOPAL; and decreased dopamine concentrations and inhibited vesicular sequestration of cytoplasmic dopamine and enzymatic breakdown of cytoplasmic DOPAL by aldehyde dehydrogenase (ALDH), as indicated by DA/DOPAL and DOPAC/DOPAL ratios. The addition of deprenyl to rotenone improved all the locomotor indices, increased dopamine and decreased DOPAL contents, and corrected the rotenone-induced vesicular uptake and ALDH abnormalities. The beneficial effects were augmented when NAC was added to deprenyl. Rotenone evokes locomotor and striatal neurochemical abnormalities found in Parkinson's disease, including DOPAL buildup. Administration of an MAOI attenuates these abnormalities, and NAC augments the beneficial effects. The results indicate a pathogenic role of DOPAL in the rotenone model and suggest that treatment with MAOI+NAC might be beneficial for Parkinson's disease treatment.

125I]INFT: Synthesis and Evaluation of a New Imaging Agent for Tau Protein in Post-Mortem Human Alzheimer's Disease Brain.

Aggregation of Tau protein into paired helical filaments causing neurofibrillary tangles (NFT) is a neuropathological feature in Alzheimer's disease (AD). This study aimed to develop and evaluate the effectiveness of a novel radioiodinated tracer, 4-[125I]iodo-3-(1H-pyrrolo[2,3-c]pyridine-1-yl)pyridine ([125I]INFT), for binding to Tau protein in postmortem human AD brain. Radiosynthesis of [125I]INFT was carried out using electrophilic destannylation by iodine-125 and purified chromatographically. Computational modeling of INFT binding on Tau fibril was compared with IPPI. In vitro, autoradiography studies were conducted with [125I]INFT for Tau in AD and cognitively normal (CN) brains. [125I]INFT was produced in >95% purity. Molecular modeling of INFT revealed comparable binding energies to IPPI at site-1 of the Tau fibril with an affinity of IC50 = 7.3 × 10-8 M. Binding of [125I]INFT correlated with the presence of Tau in the AD brain, confirmed by anti-Tau immunohistochemistry. The ratio of average grey matter (GM) [125I]INFT in AD versus CN was found to be 5.9, and AD GM/white matter (WM) = 2.5. Specifically bound [125I]INFT to Tau in AD brains was displaced by IPPI (>90%). Monoamine oxidase inhibitor deprenyl had no effect and clorgyline had little effect on [125I]INFT binding. [125I]INFT is a less lipophilic imaging agent for Tau in AD.

Pharmacological Modulation of Behaviour, Serotonin and Dopamine Levels in Daphnia magna Exposed to the Monoamine Oxidase Inhibitor Deprenyl.

This study assessed the effects of the monoamine oxidase (MAO) inhibitor deprenyl in Daphnia magna locomotor activity. The mechanisms of action of deprenyl were also determined by studying the relationship between behaviour, MAO activity and neurotransmitter levels. Modulation of the D. magna monoamine system was accomplished by 24 h exposure to two model psychotropic pharmaceuticals with antagonistic and agonistic serotonin signalling properties: 10 mg/L of 4-chloro-DL-phenylalanine (PCPA) and 1 mg/L of deprenyl, respectively. Contrasting behavioural outcomes were observed for deprenyl and PCPA reflected in decreased basal locomotor activity and enhanced habituation for the former compound and delayed habituation for the latter one. Deprenyl exposure inhibited monoamine oxidase (MAO) activity and increased the concentrations of serotonin, dopamine and the dopamine metabolite 3-methoxytyramine in whole D. magna extracts. Our findings indicate that D. magna is a sensitive and useful nonvertebrate model for assessing the effects of short-term exposure to chemicals that alter monoamine signalling changes.

Improved Synthesis of [11C]COU and [11C]PHXY, Evaluation of Neurotoxicity, and Imaging of MAOs in Rodent Heart.

The radiotracers [11C]COU and [11C]PHXY are potential PET imaging agents for in vivo studies of monoamine oxidases (MAOs), as previously shown in rodent and primate brain. One-pot, automated methods for the radiosynthesis of [11C]PHXY and [11C]COU were developed to provide reliable and improved radiochemical yields. Although derived from the structure of the neurotoxin MPTP, COU did not exhibit in vivo neurotoxicity to dopaminergic nerve terminals in the mouse brain as assayed by losses of VMAT2 radioligand binding. PET imaging studies in rats demonstrated that both [11C]COU and [11C]PHXY exhibit retention in cardiac tissues that can be blocked by pretreatment with the MAO inhibitors deprenyl (MAO-B) and pargyline (MAO-A and -B). In addition to prior neuroimaging applications, [11C]COU and [11C]PHXY are thus also of interest for studies of MAO enzymatic activity and imaging of sympathetic nerve density in heart.

Development and evaluation of [125 I]IPPI for Tau imaging in postmortem human Alzheimer's disease brain.

Alzheimer's disease (AD) is a neurodegenerative disease characterized by aggregation of Tau protein into paired helical filaments causing neurofibrillary tangles (NFT) in the brain. The aim of this study was to develop and evaluate the effectiveness of a novel radioiodinated tracer, 6-[125 I]iodo-3-(1H-pyrrolo[2,3-c]pyridine-1-yl)isoquinoline ([125 I]IPPI), for binding to Tau protein (Ki=0.75nM) in postmortem human brain (AD and cognitively normal (CN). Radiosynthesis of [125 I]IPPI was carried out by radioiododestannylation and purified chromatographically. Computational modeling studies of IPPI and MK-6240 binding on Tau fibril were evaluated. In vitro autoradiography studies were carried out with [3 H]PIB for Aβ plaques and [125 I]IPPI for Tau in AD and CN brains and evaluate drug effects. [125 I]IPPI was produced in >95% purity. Molecular modeling of IPPI revealed binding energies of IPPI (-7.8, -8.1, -8.2, -7.5 Kcal/mol) at the four sites were comparable to MK-6240 (-8.7, -8.5, -8.3, -7.5 Kcal/mol). Ratio of average grey matter (GM) [125 I]IPPI in AD versus CN was found to be 7.31 (p=.07) and AD GM/ white matter (WM) = 4.35 (p=.09). Ratio of average GM/WM [125 I]IPPI in CN was 1.21. Binding of [125 I]IPPI correlated with the presence of Tau, confirmed by anti-Tau Dako A0024. Specifically bound [125 I]IPPI to Tau in AD brains was displaced by MK-6240 and IPPI (>90%). Monoamine oxidase inhibitors (MAO) inhibitors deprenyl and clorgyline effected [125 I]IPPI binding at >1µM concentrations. [125 I]IPPI exhibited high binding in human AD frontal cortex and anterior cingulate and is a suitable radioiodinated ligand for Tau imaging.

Binding of [18F]AV1451 in post mortem brain slices of semantic variant primary progressive aphasia patients

PurposeIn vivo tau-PET tracer retention in the anterior temporal lobe of patients with semantic variant primary progressive aphasia (SV PPA) has consistently been reported. This is unexpected as the majority of these patients have frontotemporal lobar degeneration TDP (FTLD-TDP).MethodsWe conducted an in vitro [18F]AV1451 autoradiography binding study in five cases with a clinical diagnosis of SV PPA constituting the range of pathologies (i.e., three FTLD-TDP, one Alzheimer’s disease (AD), and one Pick’s disease (PiD)). Binding was compared with two controls without neurodegeneration, two typical AD, one corticobasal syndrome with underlying AD, and one frontotemporal dementia behavioral variant with FTLD-TDP. The effect of blocking with the authentic reference material and with the MAO-B inhibitor deprenyl was assessed. Immunohistochemistry was performed on adjacent cryosections.ResultsAbsence of specific [18F]AV1451 binding was observed for all three SV PPA FTLD-TDP cases. The absence of binding in controls as well as the successful blocking with authentic AV1451 in cases with tauopathy demonstrated specificity of the [18F]AV1451 signal for tau. The specific [18F]AV1451 binding was highest in AD, followed by PiD. This binding colocalized with the respective tau lesions and could not be blocked by deprenyl. Similar pilot findings were obtained with [18F]THK5351.ConclusionIn vitro autoradiography showed no [18F]AV1451 binding in SV PPA due to FTLD-TDP, while specific binding was present in SV PPA due to AD and PiD. The discrepancy between in vitro and in vivo findings remains to be explained. The discordance is not related to [18F]AV1451 idiosyncrasies as [18F]THK5351 findings were similar.

STUDIES TO EVALUATE THE PUTATIVE BINDING OF THE TAU POSITRON EMISSION TOMOGRAPHY TRACER 18F-AV-1451 TO MONOAMINE OXIDASE-B (MAO-B)

Although MAO-B inhibitors selegiline (deprenyl) and rasagiline have been reported not to block 18F-AV-1451 binding in clinical studies, other researchers have reported 3H-AV-1451 binding to MAO-B with nanomolar affinity in in vitro binding studies. In light of these contrasting data, we conducted an extensive set of experiments to investigate potential MAO-B liability for 18F-AV-1451. Equilibrium dissociation constants (Kd) for compound binding to recombinant MAO-B were determined by filtration binding. Nonspecific binding was defined as the binding of the ligand to control microsomes lacking MAO-B. Bound ligand was measured by Liquid Chromatography - Mass Spectrometry (LC-MS) for cold compounds and by gamma counter for F18-ligands. IC50s for each compound were determined in an LC-MS Safinamide:MAO-B competition binding assay. 18F-AV-1451 autoradiography blocking studies were performed on normal tissue with MAO-A/B inhibitors using mild washing conditions. No direct binding of AV-1451 to recombinant MAO-B was detected by radioligand binding or by LC-MS for 1 nM to 15 μM AV-1451. Using the same conditions, the binding of a control MAO-B ligand safinamide was determined to be 57 nM Kd. Evidence of potential AV-1451 interaction with recombinant MAO-B was observed by the weak inhibition by AV-1451 of the binding of safinamide to MAO-B (1.3 μM IC50). By autoradiography, 18F-AV-1451 binding is observed only on tau rich AD tissue and not on normal control tissue when stringent wash conditions are used (i.e. 30% and 70% EtOH) . However, when mild aqueous wash conditions are used, some off-target binding is observed on both AD and normal tissue. Weak blocking of off target 18F-AV-1451 binding on normal tissue was observed for MAO-B inhibitors deprenyl and safinamide (IC50 > 10 μM). There is limited evidence of AV-1451 binding to MAO-B that would impact in vivo 18F-AV-1451 PET imaging as demonstrated by the lack of direct in vitro binding of AV-1451 to recombinant MAO-B, the weak inhibition by AV-1451 of safinamide: MAO-B binding, and the reported lack of effect of MAO-B inhibitor treatment on 18F-AV-1451 PET signal in patients treated with selegiline or rasagiline.

Autoradiography validation of novel tau PET tracer [F-18]-MK-6240 on human postmortem brain tissue

[F-18]-MK-6240, a novel tau positron emission tomography (PET) tracer recently discovered for the in vivo detection of neurofibrillary tangles, has the potential to improve diagnostic accuracy in the detection of Alzheimer disease. We have examined regional and substrate-specific binding patterns as well as possible off-target binding of this tracer on human brain tissue to advance towards its validation. We applied [F-18]-MK-6240 phosphor screen and high resolution autoradiography to postmortem samples from patients with a definite pathological diagnosis of Alzheimer disease, frontotemporal lobar degeneration-tau (Pick’s disease, progressive supranuclear palsy and corticobasal degeneration), chronic traumatic encephalopathy, frontotemporal lobar degeneration-Tar DNA-binding protein 43 (TDP-43), dementia with Lewy bodies, cerebral amyloid angiopathy and elderly controls free of pathologic changes of neurodegenerative disease. We also directly compared the binding properties of [F-18]-MK-6240 and [F-18]-AV-1451 in human tissue, and examined potential nonspecific binding of both tau tracers to monoamine oxidases (MAO) by using autoradiography in the presence of selective monoamine oxidase A (MAO-A) and monoamine oxidase B (MAO-B) inhibitors. Our data indicate that MK-6240 strongly binds to neurofibrillary tangles in Alzheimer disease but does not seem to bind to a significant extent to tau aggregates in non-Alzheimer tauopathies, suggesting that it may have a limited utility for the in vivo detection of these pathologies. There is no evidence of binding to lesions containing β-amyloid, α-synuclein or TDP-43. In addition, we identified MK-6240 strong off-target binding to neuromelanin and melanin-containing cells, and some weaker binding to areas of hemorrhage. These binding patterns are nearly identical to those previously reported by our group and others for [F-18]-AV-1451. Of note, [F-18]-MK-6240 and [F-18]-AV-1451 autoradiographic binding signals were only weakly displaced by competing concentrations of selective MAO-B inhibitor deprenyl but not by MAO-A inhibitor clorgyline, suggesting that MAO enzymes do not appear to be a significant binding target of any of these two tracers. Together these novel findings provide relevant insights for the correct interpretation of in vivo [F-18]-MK-6240 PET imaging.

Monoamine Oxidase Activity in the Hepatopancreas of the Kamchatka Crab Paralithodes camtschaticus: a Substrate–Inhibitor Specificity

A study of substrate–inhibitor specificity of mitochondrial monoamine oxidase (MAO) in the hepatopancreas of the adult Kamchatka crab Paralithodes camtschaticus revealed specific catalytic properties of the enzyme. On the one hand, crab hepatopancreas MAO, like its classical hepatic counterpart, can deaminate tyramine, tryptamine, dopamine, serotonin, noradrenalin, benzylamine, β-phenylethylamine and N-methylhistamine but shows no sensitivity to 10 mM semicarbazide. On the other hand, MAO deaminates histamine but not putrescine, two classical diamine oxidase (DAO) substrates. It was established that MAO activity was several times higher toward benzylamine, β-phenylethylamine and N-methylhistamine than toward serotonin and noradrenalin. MAO was also found to be almost 500 times more sensitive to its selective inhibitor deprenyl than to chlorogilyn. A substrate–inhibitory analysis with the use of deprenyl and chloroginyl provides an indirect evidence for the existence of a sole MAO molecular form in the Kamchatka crab hepatopancreas.

Development of Novel Monoamine Oxidase-B (MAO-B) Inhibitors with Reduced Blood-Brain Barrier Permeability for the Potential Management of Noncentral Nervous System (CNS) Diseases.

Studies indicate that MAO-B is induced in peripheral inflammatory diseases. To target peripheral tissues using MAO-B inhibitors that do not permeate the blood-brain barrier (BBB) the MAO-B-selective inhibitor deprenyl was remodeled by replacing the terminal acetylene with a CO2H function, and incorporating a para-OCH2Ar motif (compounds 10a-s). Further, in compound 32 the C-2 side chain corresponded to CH2CN. In vitro, 10c, 10j, 10k, and 32 were identified as potent reversible MAO-B inhibitors, and all four compounds were more stable than deprenyl in plasma, liver microsomal, and hepatocyte stability assays. In vivo, they demonstrated greater plasma bioavailability. Assessment of in vitro BBB permeability showed that compound 10k is a P-glycoprotein (P-gp) substrate and 10j displayed mild interaction. Importantly, compounds 10c, 10j, 10k, and 32 displayed significantly reduced BBB permeability after intravenous, subcutaneous, and oral administration. These polar MAO-B inhibitors are pertinent leads for evaluation of efficacy in noncentral nervous system (CNS) inflammatory disease models.

Partial reversal of the effort-related motivational effects of tetrabenazine with the MAO-B inhibitor deprenyl (selegiline): Implications for treating motivational dysfunctions

People with depression and Parkinsonism frequently show effort-related motivational symptoms, such as anergia, psychomotor retardation, and fatigue. Tasks that assess effort-related choice are being used as animal models of these motivational symptoms. The present studies characterized the ability of monoamine oxidase (MAO) inhibitors with varying selectivity profiles to reverse the low effort bias induced by the monoamine storage inhibitor tetrabenazine. Tetrabenazine produces depressive symptoms in humans, and because of its selective inhibition of VMAT-2, it preferentially depletes DA at low doses. Effort-based decision making is studied with tasks offering choices between high effort options leading to highly valued reinforcers vs. low effort/low reward options. Tetrabenazine shifted choice behavior, reducing selection of fixed ratio 5 lever pressing, but increasing intake of the concurrently available but less preferred lab chow. These effects of 0.75mg/kg tetrabenazine were attenuated by co-administration of the MAO-B inhibitor deprenyl (selegiline). The ability of deprenyl to reverse the effects of tetrabenazine was marked by an inverted-U shaped dose response curve, with the middle dose (2.5mg/kg) being effective. In contrast, neither the MAO-A selective antagonist moclobemide nor the nonselective drug pargyline reversed the effects of tetrabenazine, and moclobemide decreased lever pressing when administered alone. Deprenyl was originally developed as an antiparkinsonian drug, but it also has been shown to have antidepressant effects in humans and induce antidepressant-like effects in classical rodent models of depression. These studies have implications for the potential use of MAO-B inhibitors as treatments for the motivational symptoms of depression and Parkinsonism.

The monoamine-oxidase B inhibitor deprenyl increases selection of high-effort activity in rats tested on a progressive ratio/chow feeding choice procedure: Implications for treating motivational dysfunctions

Motivated behaviors often are characterized by a high degree of behavioral activation and work output, and organisms frequently make effort-related decisions based upon cost/benefit analyses. Moreover, people with depression and other disorders frequently show effort-related motivational symptoms, such as anergia, psychomotor retardation, and fatigue. Tasks measuring effort-related choice are being used as animal models of these motivational symptoms. The present studies characterized the ability of the monoamine oxidase –B (MAO-B) inhibitor deprenyl (selegiline) to enhance selection of high-effort lever pressing in rats tested on a concurrent progressive ratio (PROG)/chow feeding choice task. Deprenyl is widely used as an antiparkinsonian drug, but it also has been shown to have antidepressant effects in humans, and to induce antidepressant-like effects in traditional rodent models of depression. Systemic administration of deprenyl (1.5–12.0 mg/kg IP) shifted choice behavior, significantly increasing markers of PROG lever pressing at a moderate dose (6.0 mg/kg), and decreasing chow intake at 6.0 and 12.0 mg/kg. Intracranial injections of deprenyl into nucleus accumbens (2.0 and 4.0 μg) also increased PROG lever pressing and decreased chow intake. Microdialysis studies showed that the dose of deprenyl that was effective at increasing PROG lever pressing (6.0 mg/kg) also significantly elevated extracellular dopamine in nucleus accumbens. Thus, similar to the well-known antidepressant bupropion, deprenyl is capable of increasing selection of high-effort PROG lever pressing at doses that increase extracellular dopamine in nucleus accumbens. These studies have implications for the potential use of MAO-B inhibitors as treatments for the motivational symptoms of depression and Parkinsonism.

Comparative binding properties of the tau PET tracers THK5117, THK5351, PBB3, and T807 in postmortem Alzheimer brains

BackgroundThe aim of this study was to compare the binding properties of several tau positron emission tomography tracers—THK5117, THK5351, T807 (also known as AV1451; flortaucipir), and PBB3—head to head in the same human brain tissue.MethodsBinding assays were performed to compare the regional distribution of 3H-THK5117 and 3H-THK5351 in postmortem tissue from three Alzheimer’s disease (AD) cases and three control subjects in frontal and temporal cortices as well as in the hippocampus. Competition binding assays between THK5351, THK5117, PBB3, and T807, as well as off-target binding of THK5117 and T807 toward monoamine oxidase B (MAO-B), were performed using binding assays in brain homogenates and autoradiography of three AD cases.ResultsRegional binding of 3H-THK5117 and 3H-THK5351 was similar, except in the temporal cortex, which showed higher 3H-THK5117 binding. Saturation studies demonstrated two binding sites for 3H-THK5351 (Kd1 = 5.6 nM, Bmax = 76 pmol/g; Kd2 = 1 nM, Bmax = 40 pmol/g). Competition studies in the hippocampus between 3H-THK5351 and unlabeled THK5351, THK5117, and T807 revealed super-high-affinity sites for all three tracers (THK5351 Ki = 0.1 pM; THK5117 Ki = 0.3 pM; T807 Ki = 0.2 pM) and an additional high-affinity site (THK5351 Ki = 16 nM; THK5117 Ki = 20 nM; T807 Ki = 78nM). 18F-T807, 11C-THK5351, and 11C-PBB3 autoradiography of large frozen sections from three AD brains showed similar regional binding for the three tracers, with lower binding intensity for 11C-PBB3. Unlabeled THK5351 and T807 displaced 11C-THK5351 to a similar extent and a lower extent, respectively, compared with 11C-PBB3. Competition with the MAO-B inhibitor 3H-l-deprenyl was observed for THK5117 and T807 in the hippocampus (THK5117 Ki = 286 nM; T807 Ki = 227 nM) and the putamen (THK5117 Ki = 148 nM; T807 Ki = 135 nM). 3H-THK5351 binding was displaced using autoradiography competition with unlabeled THK5351 and T807 in cortical areas by 70–80% and 60–77%, respectively, in the basal ganglia, whereas unlabeled deprenyl displaced 3H-THK5351 binding by 40% in the frontal cortex and 50% in the basal ganglia.ConclusionsTHK5351, THK5117, and T807 seem to target similar binding sites, but with different affinities, whereas PBB3 seems to target its own binding site. Both THK5117 and T807 demonstrated off-target binding in the hippocampus and putamen with a ten times lower binding affinity to the MAO-B inhibitor deprenyl compared with 3H-THK5351.

Seasonal effects of the monoamine oxidase inhibitor deprenyl but not the tricyclic antidepressant imipramine in rats bred for helplessness

Objective: Seasonal variations in monoaminergic function may underlie seasonal affective disorder, a subtype of major depression. Here, we examined whether antidepressant drugs which regulate monoaminergic function exhibit seasonal effects in an animal model of depression, congenital helplessness. Material and Method: Rats selectively bred for helplessness were required to press a lever to turn off a foot-shock before and after chronic treatment with the tricyclic antidepressant imipramine (10 mg/kg) or the monoamine oxidase inhibitor deprenyl (10 mg/kg). Control rats received saline. Different groups of rats were tested in summer-fall and spring over the course of two years. Results: Congenitally helpless (cH) rats that were treated with imipramine pressed the lever more often than controls in fall and in spring, indicative of antidepressant effects regardless of season. By contrast, cH rats treated with deprenyl pressed the lever more often in summer-fall than in spring, suggestive of seasonal drug effects on helplessness behavior. Deprenyl significantly attenuated the lever-pressing deficit in both seasons when compared to saline controls. Moreover, cH rats treated with deprenyl but not imipramine increased the number of lever presses over trials, indicative of negative reinforcement learning. Conclusion: The present data are the first to show seasonal variations in antidepressant drug effects that are possibly linked to changes in dopamine neurotransmission. The data support the view that we must take seasonality into account when evaluating the efficacy of antidepressant compounds.

Rats bred for helplessness exhibit positive reinforcement learning deficits which are not alleviated by an antidepressant dose of the MAO-B inhibitor deprenyl

Principles of negative reinforcement learning may play a critical role in the etiology and treatment of depression. We examined the integrity of positive reinforcement learning in congenitally helpless (cH) rats, an animal model of depression, using a random ratio schedule and a devaluation-extinction procedure. Furthermore, we tested whether an antidepressant dose of the monoamine oxidase (MAO)-B inhibitor deprenyl would reverse any deficits in positive reinforcement learning. We found that cH rats (n=9) were impaired in the acquisition of even simple operant contingencies, such as a fixed interval (FI) 20 schedule. cH rats exhibited no apparent deficits in appetite or reward sensitivity. They reacted to the devaluation of food in a manner consistent with a dose–response relationship. Reinforcer motivation as assessed by lever pressing across sessions with progressively decreasing reward probabilities was highest in congenitally non-helpless (cNH, n=10) rats as long as the reward probabilities remained relatively high. cNH compared to wild-type (n=10) rats were also more resistant to extinction across sessions. Compared to saline (n=5), deprenyl (n=5) reduced the duration of immobility of cH rats in the forced swimming test, indicative of antidepressant effects, but did not restore any deficits in the acquisition of a FI 20 schedule. We conclude that positive reinforcement learning was impaired in rats bred for helplessness, possibly due to motivational impairments but not deficits in reward sensitivity, and that deprenyl exerted antidepressant effects but did not reverse the deficits in positive reinforcement learning.

The MAO-B inhibitor deprenyl reduces the oral tremor and the dopamine depletion induced by the VMAT-2 inhibitor tetrabenazine

Tetrabenazine (TBZ) is prescribed for the treatment of chorea associated with Huntington’s disease. Via inhibition of the vesicular monoamine transporter (VMAT-2), TBZ blocks dopamine (DA) storage and depletes striatal DA; this drug also has been shown to induce Parkinsonian motor side effects in patients. Recently, TBZ was shown to induce tremulous jaw movements (TJMs) in rats and mice. TJMs are an oral tremor that has many of the characteristics of Parkinsonian tremor in humans. The present study focused upon the ability of the well-estabilished antiparkinsonian agent deprenyl to attenuate the behavioral and neurochemical effects of 2.0mg/kg TBZ. Deprenyl is a selective and irreversible inhibitor of monoamine oxidase-B, and administration of deprenyl produced a dose-related suppression of TBZ-induced TJMs. A second experiment employed in vivo microdialysis to examine extracellular DA levels in the ventrolateral striatum, the neostriatal region most closely associated with the production of TJMs, after administration of TBZ and deprenyl. Consistent with the behavioral data, TBZ alone produced a biphasic effect on extracellular DA, with an initial increases followed by a prolonged decrease during the period in which TJMs are displayed. Co-administration of deprenyl with TBZ increased DA levels compared to rats treated with TBZ alone. These results provide support for use of TBZ as a rodent model of Parkinsonism, and future studies should utilize this model to evaluate putative anti-Parkinsonian agents.

The VMAT-2 inhibitor tetrabenazine affects effort-related decision making in a progressive ratio/chow feeding choice task: reversal with antidepressant drugs.

Behavioral activation is a fundamental feature of motivation, and organisms frequently make effort-related decisions based upon evaluations of reinforcement value and response costs. Furthermore, people with major depression and other disorders often show anergia, psychomotor retardation, fatigue, and alterations in effort-related decision making. Tasks measuring effort-based decision making can be used as animal models of the motivational symptoms of depression, and the present studies characterized the effort-related effects of the vesicular monoamine transport (VMAT-2) inhibitor tetrabenazine. Tetrabenazine induces depressive symptoms in humans, and also preferentially depletes dopamine (DA). Rats were assessed using a concurrent progressive ratio (PROG)/chow feeding task, in which they can either lever press on a PROG schedule for preferred high-carbohydrate food, or approach and consume a less-preferred lab chow that is freely available in the chamber. Previous work has shown that the DA antagonist haloperidol reduced PROG work output on this task, but did not reduce chow intake, effects that differed substantially from those of reinforcer devaluation or appetite suppressant drugs. The present work demonstrated that tetrabenazine produced an effort-related shift in responding on the PROG/chow procedure, reducing lever presses, highest ratio achieved and time spent responding, but not reducing chow intake. Similar effects were produced by administration of the subtype selective DA antagonists ecopipam (D1) and eticlopride (D2), but not by the cannabinoid CB1 receptor neutral antagonist and putative appetite suppressant AM 4413, which suppressed both lever pressing and chow intake. The adenosine A2A antagonist MSX-3, the antidepressant and catecholamine uptake inhibitor bupropion, and the MAO-B inhibitor deprenyl, all reversed the impairments induced by tetrabenazine. This work demonstrates the potential utility of the PROG/chow procedure as a rodent model of the effort-related deficits observed in depressed patients.

Metabolism of 1-Methyl-4-phenyl-1,2,3,6-tetrahydropyridine by Mitochondrion-targeted Cytochrome P450 2D6: IMPLICATIONS IN PARKINSON DISEASE

1-Methyl-4-phenyl-1,2,3,6-tetrahydropyridine (MPTP) is a neurotoxic side product formed in the chemical synthesis of desmethylprodine opioid analgesic, which induces Parkinson disease. Monoamine oxidase B, present in the mitochondrial outer membrane of glial cells, catalyzes the oxidation of MPTP to the toxic 1-methyl-4-phenylpyridinium ion (MPP(+)), which then targets the dopaminergic neurons causing neuronal death. Here, we demonstrate that mitochondrion-targeted human cytochrome P450 2D6 (CYP2D6), supported by mitochondrial adrenodoxin and adrenodoxin reductase, can efficiently catalyze the metabolism of MPTP to MPP(+), as shown with purified enzymes and also in cells expressing mitochondrial CYP2D6. Neuro-2A cells stably expressing predominantly mitochondrion-targeted CYP2D6 were more sensitive to MPTP-mediated mitochondrial respiratory dysfunction and complex I inhibition than cells expressing predominantly endoplasmic reticulum-targeted CYP2D6. Mitochondrial CYP2D6 expressing Neuro-2A cells produced higher levels of reactive oxygen species and showed abnormal mitochondrial structures. MPTP treatment also induced mitochondrial translocation of an autophagic marker, Parkin, and a mitochondrial fission marker, Drp1, in differentiated neurons expressing mitochondrial CYP2D6. MPTP-mediated toxicity in primary dopaminergic neurons was attenuated by CYP2D6 inhibitor, quinidine, and also partly by monoamine oxidase B inhibitors deprenyl and pargyline. These studies show for the first time that dopaminergic neurons expressing mitochondrial CYP2D6 are fully capable of activating the pro-neurotoxin MPTP and inducing neuronal damage, which is effectively prevented by the CYP2D6 inhibitor quinidine.

Synthesis of (E)-8-(3-Chlorostyryl)caffeine Analogues Leading to 9-Deazaxanthine Derivatives as Dual A2A Antagonists/MAO-B Inhibitors

A systematic modification of the caffeinyl core and substituents of the reference compound (E)-8-(3-chlorostyryl)caffeine led to the 9-deazaxanthine derivative (E)-6-(4-chlorostyryl)-1,3,5,-trimethyl-1H-pyrrolo[3,2-d]pyrimidine-2,4-(3H,5H)-dione (17f), which acts as a dual human A(2a) antagonist/MAO-B inhibitor (K(i)(A(2A)) = 260 nM; IC(50)(MAO-B) = 200 nM; IC(50)(MAO-A) = 10 μM) and dose dependently counteracts haloperidol-induced catalepsy in mice from 30 mg/kg by the oral route. The compound is the best balanced A(2A) antagonist/MAO-B inhibitor reported to date, and it could be considered as a new lead in the field of anti-Parkinson's agents. A number of analogues of 17f were synthesized and qualitative SARs are discussed. Two analogues of 17f, namely 18b and 19a, inhibit MAO-B with IC(50) of 68 and 48 nM, respectively, being 5-7-fold more potent than the prototypical MAO-B inhibitor deprenyl (IC(50) = 334 nM).