Transdermal selegiline: the new generation of monoamine oxidase inhibitors

The Mechanisms Underlying the Pharmacological Effects of GuiPi Decoction on Major Depressive Disorder based on Network Pharmacology and Molecular Docking

BACKGROUND AND AIM

Major Depressive Disorder (MDD) is a common affective disorder. GuiPi decoction (GPD) is used to treat depression in China, Japan, and Korea. However, its effective ingredients and antidepressant mechanisms remain unclear. We attempted to reveal the potential mechanisms of GPD in the treatment of MDD by network pharmacology and molecular docking. In addition, we conducted an enzymatic activity assay to validate the results of molecular docking.

METHODS

GPD-related compounds and targets, and MDD-related targets were retrieved from databases and literature. The herb-compound-target network was constructed by Cytoscape. The protein- protein interaction network was built using the STRING database to find key targets of GPD on MDD. Enrichment analysis of shared targets was analyzed by MetaCore database to obtain the potential pathway and biological process of GPD on MDD. The main active compounds treating MDD were screened by molecular docking. The PDE4s inhibitors were screened and verified by an enzyme activity assay.

RESULTS

GPD contained 1222 ingredients and 190 potential targets for anti-MDD. Possible biological processes regulated by GPD were neurophysiological processes, blood vessel morphogenesis, Camp Responsive Element Modulator (CREM) pathway, and Androgen Receptor (AR) signaling crosstalk in MDD. Potential pathways in MDD associated with GPD include neurotransmission, cell differentiation, androgen signaling, and estrogen signaling. Fumarine, m-cresol, quercetin, betasitosterol, fumarine, taraxasterol, and lupeol in GPD may be the targets of SLC6A4, monoamine oxidase A (MAOA), DRD2, OPRM1, HTR3A, Albumin (ALB), and NTRK1, respectively. The IC50 values of trifolin targeting Phosphodiesterase (PDE) 4A and girinimbine targeting PDE4B1 were 73.79 μM and 31.86 μM, respectively. The IC50 values of girinimbine and benzo[a]carbazole on PDE4B2 were 51.62 μM and 94.61 μM, respectively.

CONCLUSION

Different compounds in GPD may target the same protein, and the same component in GPD can target multiple targets. These results suggest that the effects of GPD on MDD are holistic and systematic, unlike the pattern of one drug-one target.

The Psychopharmacology Algorithm Project at the Harvard South Shore Program: An Update on Unipolar Nonpsychotic Depression

BACKGROUND

The Psychopharmacology Algorithm Project at the Harvard South Shore Program presents evidence-based recommendations considering efficacy, tolerability, safety, and cost. Two previous algorithms for unipolar nonpsychotic depression were published in 1993 and 1998. New studies over the last 20 years suggest that another update is needed.

METHODS

The references reviewed for the previous algorithms were reevaluated, and a new literature search was conducted to identify studies that would either support or alter the previous recommendations. Other guidelines and algorithms were consulted. We considered exceptions to the main algorithm, as for pregnant women and patients with anxious distress, mixed features, or common medical and psychiatric comorbidities.

SUMMARY

For inpatients with severe melancholic depression and acute safety concerns, electroconvulsive therapy (or ketamine if ECT refused or ineffective) may be the first-line treatment. In the absence of an urgent indication, we recommend trialing venlafaxine, mirtazapine, or a tricyclic antidepressant. These may be augmented if necessary with lithium or T3 (triiodothyronine). For inpatients with non-melancholic depression and most depressed outpatients, sertraline, escitalopram, and bupropion are reasonable first choices. If no response, the prescriber (in collaboration with the patient) has many choices for the second trial in this algorithm because there is no clear preference based on evidence, and there are many individual patient considerations to take into account. If no response to the second medication trial, the patient is considered to have a medication treatment-resistant depression. If the patient meets criteria for the atypical features specifier, a monoamine oxidase inhibitor could be considered. If not, reconsider (for the third trial) some of the same options suggested for the second trial. Some other choices can also considered at this stage. If the patient has comorbidities such as chronic pain, obsessive-compulsive disorder, attention-deficit/hyperactivity disorder, or posttraumatic stress disorder, the depression could be secondary; evidence-based treatments for those disorders would then be recommended.

Antidepressant-lnduced Liver Injury

Objective:

To review principles of drug-induced liver injury (DILI), summarize characteristics of antidepressant-mediated liver Injury, and provide recommendations for monitoring and management.

Data Sources:

A search relating to antidepressant-induced liver injury was performed using MEDLINE (1966–March 2007). Search terms included antidepressant, cholestasis, hepatotoxicity, jaundice, liver injury, toxic hepatitis, and transaminases. Reference citations not Identified in the initial database search were also utilized.

Study Selection and Data Extraction:

All English-language case reports, letters, and review articles identified from the data sources were used. Case reports and letters relating to hepatotoxicity from antidepressant overdose were excluded.

Data Synthesis:

Antidepressant-induced liver injury described in published cases were of the idiopathic type and, by definition, cannot be predicted based on dose or specific risk factors. Paroxetine had the largest number of cases within the selective serotonin-reuptake inhibitor class. Nefazodone, a serotonin–norepinephrine reuptake inhibitor, appeared to have the most serious cases and is the only antidepressant agent that carries a Food and Drug Administration Black Box Warning regarding hepatotoxiciiy. The tricyclic antidepressants and monoamine oxidase Inhibitors are capable of producing hepatotoxicity, but fewer cases with these agents have been reported in the past 15 years, possibly due to a decline in their use. Causality has not been well established in all reports due to the concurrent use of other drugs and/or underlying liver disease.

Conclusions:

Most antidepressant agents have the potential to produce idiopathic liver injury. There is no way to prevent idiopathic DILI, but the severity of the reaction may be minimized with prompt recognition and early withdrawal of the agent. The clinician must be careful to provide ongoing therapy of the underlying depressive disorder and be aware of possible drug discontinuation syndromes should potential hepatotoxicity be suspected.

Major Depressive Disorder: Understanding the Significance of Residual Symptoms and Balancing Efficacy with Tolerability

INTRODUCTION

Major depressive disorder is a complex and frequent psychiatric condition that poses significant challenges to both the patients who experience it and the physicians who treat them. The goal of therapy is for patients to achieve remission, which requires identifying and measuring symptoms at the outset and throughout treatment to document both response and resistance to treatment. A number of validated instruments are available both for diagnosis of and response to treatment. Many factors affect a patient's ability to achieve remission, but although many patients do achieve remission, a significant number continue to have residual symptoms that cause functional impairment.

METHODS

Review of the literature for treatment of major depression, including mechanisms of action, individualized treatment optimization, residual symptom reduction, and minimization of side effects.

RESULTS

For sustained remission, all symptoms must be treated until they are undetectable. Patients who do not achieve remission after adequate treatment trials should be evaluated for adherence to treatment, as well as comorbid psychiatric and medical disorders. In these cases, consideration should be given to changing therapy by switching, combining, or augmenting initial therapy, as well as referring some patients to a psychiatrist for treatment with specialized modalities. Linking symptoms with malfunctioning brain circuits and neurotransmitters provides a targeted approach for achieving sustained remission. Neurobiology also provides a rational basis for combination therapy in patients with treatment-resistant depression, because it can aid selection of different drugs with different mechanisms of action or of multifunctional/multimodal antidepressant drugs that target more than 1 molecular mechanism.

DISCUSSION

Recent advances and better understanding of neurobiology provide a rational basis for individualizing treatment of patients with major depression.

Efficacy and safety of selegiline transdermal system (STS) for the atypical subtype of major depressive disorder: pooled analysis of 5 short-term, placebo-controlled trials

OBJECTIVE

The objective of the present study is to investigate the efficacy and safety of the selegiline transdermal system (STS) in major depressive disorder (MDD) with atypical features.

METHODS

This was a post-hoc analysis of 5 short-term trials. The atypical subtype was defined as the presence of at least 1 item with a score of 2 or greater from items 22-26 on the 28-item Hamilton Depression Rating Scale (HAMD-28), and a maximum score of 1 point for items 6 (insomnia late), 12 (somatic symptoms, gastrointestinal), and 16 (loss of weight) to exclude vegetative features of melancholic depression. The mean changes of HAMD-28 total score from baseline to the endpoint (response rate defined as ≥50% reduction in HAMD-28 scores and remission rate defined as ≤10 HAMD-28 total score at the treatment endpoint) were compared between atypical and nonatypical groups.

RESULTS

In this analysis, 352 subjects (STS = 168 vs placebo = 184) met the definition of atypical subtype at baseline. STS (n = 641) significantly decreased HAMD-28 total score compared with placebo (n = 648) from beginning to end of treatment (-10.7 ± 9.3 vs -9.4 ± 9.3; p = 0.014). STS showed comparable efficacy in patients with the atypical subtype compared with the nonatypical subtype for placebo-subtracted mean change in HAMD-28 total score (-2.11 ± 1.01 vs. -1.0 ± 0.60; p = 0.34), odds ratio (OR) for response (1.41 vs 1.23, p = 0.62), and OR for remission (1.77 vs 1.18, p = 0.22).

CONCLUSION

STS appears to be comparably efficacious and tolerable in atypical and nonatypical subtypes of MDD. Adequately powered, controlled, clinical trials are necessary to confirm our findings.

Combining QSAR classification models for predictive modeling of human monoamine oxidase inhibitors

Due to their role in the metabolism of monoamine neurotransmitters, MAO-A and MAO-B present a significant pharmacological interest. For instance the inhibitors of human MAO-B are considered useful tools for the treatment of Parkinson Disease. Therefore, the rational design and synthesis of new MAOs inhibitors is considered of great importance for the development of new and more effective treatments of Parkinson Disease. In this work, Quantitative Structure Activity Relationships (QSAR) has been developed to predict the human MAO inhibitory activity and selectivity. The first step was the selection of a suitable dataset of heterocyclic compounds that include chromones, coumarins, chalcones, thiazolylhydrazones, etc. These compounds were previously synthesized in one of our laboratories, or elsewhere, and their activities measured by the same assays and for the same laboratory staff. Applying linear discriminant analysis to data derived from a variety of molecular representations and feature selection algorithms, reliable QSAR models were built which could be used to predict for test compounds the inhibitory activity and selectivity toward human MAO. This work also showed how several QSAR models can be combined to make better predictions. The final models exhibit significant statistics, interpretability, as well as displaying predictive power on an external validation set made up of chromone derivatives with unknown activity (that are being reported here for first time) synthesized by our group, and coumarins recently reported in the literature.

Comparison of the cutaneous iontophoretic delivery of rasagiline and selegiline across porcine and human skin in vitro

The objective was to investigate the anodal iontophoresis of the MAO-B inhibitors rasagiline (RAS) and selegiline (SEL) across porcine and human skin in vitro. Passive delivery of RAS and SEL from aqueous solution was minimal; however, increasing current density from 0.1 to 0.3 and 0.5 mA/cm(2) produced a linear increase in steady-state iontophoretic flux (J(ss,RAS)=49.1i(d)+27.9 (r(2)=0.96) and J(ss,SEL)=27.8i(d)+25.8 (r(2)=0.98)). In the absence of background electrolyte, a four-fold change in donor concentration (10, 20 and 40 mM) did not produce a statistically significant increase in cumulative permeation of either drug after iontophoresis at 0.5mA/cm(2) for 7h. Co-iontophoresis of acetaminophen confirmed that electromigration was the dominant transport mechanism for both drugs (∼90%). Total iontophoretic delivery of RAS and SEL across porcine and human skin in vitro was statistically equivalent (RAS: 1512.7 ± 163.7 and 1523.6 ± 195.9 μg/cm(2), respectively, and SEL: 1268.7 ± 231.2 and 1298.3 ± 253.3 μg/cm(2), respectively). Transport efficiencies for RAS and SEL were good (ranged from 6.81 to 8.50 and 2.86 to 3.61%, respectively). Furthermore, the delivery efficiency, i.e., the fraction of the drug in the formulation that was delivered was very high (>56% at 0.5 mA/cm(2)). Cumulative permeation of RAS and SEL from carbopol gels, potential drug reservoirs for iontophoretic systems, was 891.5 ± 148.3 and 626.6 ± 162.4 μg/cm(2), respectively; this was less than from solution and was tentatively attributed to either different partitioning or slower drug diffusion in the gel matrix. The results demonstrated that therapeutic amounts of rasagiline and selegiline could be easily delivered by transdermal iontophoresis with simple gel patches of modest surface area.

Transdermal iontophoretic delivery of selegiline hydrochloride, in vitro

Transdermal iontophoretic delivery of selegiline hydrochloride (SH) across dermatomed human skin was studied. Electrochemical stability and various factors affecting the skin permeation were investigated. SH was stable under the influence of an electrical field. The permeation of SH was very low by passive delivery (2.29 ± 0.05 µg/cm²/h) as compared to iontophoresis at 0.5 mA/cm² (65.10 ± 5.04 µg/cm²/h). An increase in drug concentration from 1 to 20 mg/mL increased the iontophoretic flux by 13-fold. Optimal pH and salt (NaCl) concentration for iontophoretic delivery of SH were found to be pH 5 and 100 mM, respectively. Overall, with 20 mg/mL SH and a current density of 0.4 mA/cm², a maximum flux of 305.5 µg/cm²/h was obtained. Based on reported pharmacokinetic parameters, input target delivery rate to achieve effective plasma concentration of SH (2.2 ng/mL) was calculated. With a surface area of 40 cm², iontophoretic delivery can provide six to seven times higher levels of SH than the target delivery rate, which enables lowering of the dose and/or patch surface area. Further in vivo studies will be required to prove the efficacy of ionophoresis for enhanced delivery of SH.

Atypical depression: a comprehensive review

Despite several decades of research, the characteristics distinguishing atypical depression from other depressive subtypes remain ambiguous. Multiple lines of evidence support the designation of atypical depression as a scientifically and clinically relevant subtype, including differences in hormonal responses, brain laterality, psychological profile and psychiatric co-morbidity and differential treatment response. The evolution of the diagnostic criteria for atypical depression has led to the designation of mood reactivity as the cardinal feature, and the research supporting this conclusion is reviewed. This paper also reviews the evidence for the drug treatment of atypical depression, with a particular focus on research related to the superior efficacy of monoamine oxidase inhibitors (MAOIs) compared with tricyclic antidepressants (TCAs). Data relevant to the efficacy of newer antidepressants, including selective serotonin reuptake inhibitors (SSRIs), serotonin-noradrenaline (norepinephrine) reuptake inhibitors, transdermal selegiline and other new agents for atypical depression, are discussed. In summary, the diagnostic reliability and validity of atypical depression still remain elusive and open to further evolution. Currently available findings suggest that atypical depression has preferential response to MAOIs over TCAs. More data are required to determine the efficacy of newer agents relative to MAOIs and TCAs, although limited studies have shown a non-inferior efficacy and better tolerability of newer agents such as SSRIs compared with those of MAOIs and TCAs. Finally, future directions for research include further refinement of the diagnostic criteria for atypical depression, and clarification of the role of newer antidepressants in the treatment of this subtype with evidence from randomized, controlled trials.

Selegiline transdermal system: a novel treatment option for major depressive disorder

BACKGROUND

The use of monoamine oxidase inhibitors has declined owing to the risk of hypertensive crisis following the consumption of tyramine-rich foods and the consequent need for dietary tyramine restriction. However, owing to their superior efficacy in treating depression, continued efforts have been made to develop more selective and reversible monoamine oxidase inhibitors. Oral selegiline, at low doses, is a selective monoamine oxidase B (MAO-B) inhibitor, but at higher doses it loses its selectivity and can potentially interact with tyramine. Unfortunately, antidepressant effects of selegiline have been observed only at higher doses. The selegiline transdermal system was developed to deliver sustained selegiline blood concentrations sufficient to selectively inhibit MAO-A and MAO-B in the brain, producing antidepressant effects, without substantially inhibiting MAO-A in the gastrointestinal tract, thereby reducing the risk of hypertensive crisis.

OBJECTIVES

This article reviews the basic pharmacology, as well as efficacy and safety data of selegiline transdermal system for the treatment of depression.

CONCLUSIONS

Selegiline transdermal system is safe and effective in treating major depressive disorder at the dose range of 6 - 12 mg/24 h, without the need for dietary precautions at the 6 mg/24 h dose. No cases of hypertensive crisis were reported in clinical trials, even without dietary restrictions.

Monoamine oxidase inhibitors: a modern guide to an unrequited class of antidepressants

Monoamine oxidase inhibitors (MAOIs) currently have a "bad rap" and are thus infrequently used in psychopharmacology, even by experienced clinicians. Misinformation about the dietary and drug interactions of MAOIs is widespread, whereas pragmatic tips for utilizing MAOIs to minimize risks and to maximize therapeutic actions are largely lacking in the contemporary literature. While clearly not first-line treatments, MAOIs, in the hands of experienced and well-informed clinicians, can be a powerful therapeutic intervention for patients with depression, panic disorder, and other anxiety disorders who have failed first-line treatments. This article focuses on the pharmacologic mechanisms of MAOIs, since an understanding of these mechanisms may provide a rationale to empower experts to expand their use of these agents. Discussed here are not only the mechanisms of therapeutic action of MAOIs, but also the mechanisms explaining their side effects, including hypertensive interactions with dietary tyramine (so-called "cheese reactions") and drug interactions that can lead to hypertensive reactions with some drugs and serotonin toxicities with others. This article also provides practical tips on how to use MAOIs, including debunking certain myths and giving specific guidance about which foods and drugs to avoid. Those with no previous interest in MAOIs may discover in this article a new "secret weapon" to add to their therapeutic armamentarium for patients who fail to respond to the better-known agents.

Selegiline transdermal system: current awareness and promise

Many monoamine oxidase inhibitors (MAOIs) have been used to treat major depressive disorder (MDD). However, the prescription of MAOIs has decreased considerably as a result of side effects such as tyramine-induced hypertensive crisis, which is also known as the 'Cheese Effect'. The drug delivery system itself can affect the bioavailability of certain drugs, which might influence the efficacy and tolerability of medications, as well as improve the compliance and reduce the incidence of recurrence and relapse. Therefore, there is a need for advanced drug delivery techniques that can evade the potentially hazardous toxic effects of the parent compound, including extended-release oral, cutaneous, intravesical and intravaginal routes, etc. In this context, the selegiline transdermal system (STS, EMSAM) was introduced with improved side effect profiles and efficacy compared with the conventional form of the selegiline oral tablet. STS allows the targeted inhibition of the monoamine A (MAO-A) and MAO-B isoenzymes with minimal effects on the MAO-A in the gastrointestinal and hepatic systems. Hence, STS can reduce the risk of interactions with tyramine-rich foods. Many fundamental clinical and preclinical studies have reported that 6 mg/24 h of STS is effective against MDD without the need for dietary restrictions with an equal efficacy and improved safety profile. In addition, STS might benefit MDD patients with atypical features or who are resistant to other antidepressants. Overall, familiarity with the properties and indications of STS will have the clinicians another option of biological treatments for MDD patients but subsequent more data including actual post-market clinical experiences will be mandatory.

Differential effects of selegiline on glucose synthesis in rabbit kidney-cortex tubules and hepatocytes. In vitro and in vivo studies

The action of selegiline, a selective and irreversible inhibitor of monoamine oxidase B, commonly applied in the therapy of Parkinson's disease, on glucose formation was investigated in isolated rabbit hepatocytes and kidney-cortex tubules, maintaining the whole body glucose homeostasis via gluconeogenic pathway activity. An intensive hepatic metabolism of selegiline resulted in formation of selegiline-N-oxide, desmethylselegiline, methamphetamine and amphetamine, whereas during slow degradation of the drug in freshly isolated renal tubules selegiline-N-oxide was mainly produced. At 100 microM concentration selegiline markedly diminished glucose synthesis in isolated renal tubules incubated with dihydroxyacetone or alanine+glycerol+octanoate (by about 60 and 30%, respectively), while at 5 microM concentration a similar degree of inhibition was achieved in renal tubules grown in primary culture under the same conditions (about 40 and 60%, respectively). Moreover, desmethylselegiline and selegiline-N-oxide considerably diminished glucose production in renal tubules whereas selegiline and its metabolites did not affect gluconeogenesis in hepatocytes. Contrary to control animals, following selegiline administration to alloxan-diabetic rabbits for 8 days (10 mg kg(-1) body wt. daily) the blood glucose and serum creatinine levels were significantly diminished, suggesting a decrease in renal gluconeogenesis and improvement of kidney functions. Since in renal tubules selegiline induced a decline in the intracellular levels of gluconeogenic intermediates and ATP content accompanied by a decrease in oxygen consumption in both kidney-cortex and hepatic mitochondria it seems possible that its inhibitory action on renal gluconeogenesis might result from an impairment of mitochondrial function, while an intensive selegiline metabolism in hepatocytes causes decrease of its concentration and in consequence no inhibition of gluconeogenesis. In view of these observations it is likely that an increased risk of selegiline-induced hypoglycemia might be expected particularly in patients exhibiting an impairment of liver function and following transdermal administration of this drug, i.e. under conditions of increased serum selegiline concentrations.

Selegiline transdermal system: in the treatment of major depressive disorder

The monamine oxidase (MAO) inhibitor selegiline is selective for MAO-B at the low oral dosages used in the treatment of Parkinson's disease. However, MAO-A is also inhibited at the high oral dosages needed to effectively treat depression (not an approved indication), necessitating a tyramine-restricted diet. The selegiline transdermal system was designed to deliver antidepressant drug concentrations to the CNS, without substantially impairing small intestine MAO-A activity. At the target dose of 6 mg/24 hours, tyramine dietary restrictions are not needed. Short-term treatment with fixed (6 mg/24 hours) or flexible (6, 9 or 12 mg/24 hours) doses of selegiline transdermal system was superior to placebo on most measures of antidepressant activity in 6- or 8-week, randomised, double-blind, multicentre studies in adult outpatients with major depressive disorder (MDD). Likewise, long-term treatment with a fixed dose of selegiline transdermal system 6 mg/24 hours was superior to placebo as maintenance therapy in a 52-week, randomised, double-blind, multicentre, relapse-prevention trial in patients with MDD. Selegiline transdermal system therapy was generally well tolerated in placebo-controlled studies; application site reactions, mostly of mild to moderate severity, were the most commonly reported adverse events. The incidence of sexual adverse effects and weight gain was low and similar to that with placebo.

Pharmacokinetic studies of (-)-deprenyl and some of its metabolites in mouse

(-)-Deprenyl is a selective irreversible inhibitor of MAO-B. The parent compound is responsible for the enzyme inhibitory effect, but its metabolites are also playing a role in the complex pharmacological activity of the substance. In the present studies male NMRI mice were treated orally, subcutaneously, intraperitoneally and intravenously with 5 mg/kg of (-)-deprenyl. The time related changes of the plasma concentrations of the parent compound and its main metabolites (methamphetamine, desmethyl-deprenyl and amphetamine) were determined by GC/ MSD technique. The main pharmacokinetic parameters (C(max), t(max), t1/2beta, AUC(0-6), AUC(0-infinity)) have been calculated. (-)-Deprenyl is well absorbed after oral and parental treatment. The peak concentrations (C(max)) were reached at 15 min after treatment and the absorption was followed by a fast elimination (t1/2beta < or = 2h). (-)-Deprenyl has an intensive "first pass" metabolism after oral treatment; only 25% of the parent compound reaches the systemic circulation. Increased bioavailability was detected after subcutaneous (87.1%) and intraperitoneal (78.7%) administration. The main metabolic pathway of (-)-deprenyl is the N-depropargylation, leading to the formation of methamphetamine. N-demethylation of (-)-deprenyl leads to formation of desmethyl-deprenyl. Amphetamine is produced from both former metabolites. After oral treatment the plasma concentrations of methamphetamine are higher during the first 6 h than that of (-)-deprenyl, while the opposite was found after parental treatment. The results indicate, that (-)-deprenyl, a potent MAO-B inhibitor, might induce a different spectrum of activity (e.g. antidepressant), when it is administered parenterally (transdermally). The new spectrum can be due to the special pharmacokinetic behaviour of the inhibitor.

Monoamine oxidase inhibitory coumarins from the aerial parts ofDictamnus albus

The methanol extract from the aerial parts of Dictamnus albus was active in inhibiting monoamine oxidase (MAO) from the mouse brain. Activity-guided fractionation led to the isolation of four known coumarins, 7-(6'R-hydroxy-3', 7'-dimethyl-2'E, 7'-octadienyloxy) coumarin (1), auraptene (2), umbelliferone (3), and xanthotoxin (4), as active compounds along with an inactive alkaloid, skimmianine (5). Compounds 1 and 2 inhibited MAO activity in a concentration-dependent manner with IC50 values of 0.7 and 1.7 microM, respectively. Compounds 1 and 2 showed a slight and potently selective inhibitory effect against MAO-B (IC50 0.5 and 0.6 microM, respectively) compared to MAO-A (IC50 1.3 and 34.6 microM, respectively). According to kinetic analyses derived by Lineweaver-Burk reciprocal plots, compounds 1 and 2 exhibited a competitive inhibition to MAO-B.