Metabolites Of Selegiline Research Articles

Selegiline (L-Deprenyl) Mitigated Oxidative Stress, Cognitive Abnormalities, and Histopathological Change in Rats: Alternative Therapy in Transient Global Ischemia.

Selegiline (L-deprenyl) is the major drug which is used in the treatment of Parkinson's disease because of its neurotrophic and antiapoptotic properties. Previous studies suggested that low dose of L-methamphetamine (L-METH) caused lower mortality rate in patients with severe traumatic brain injury. As L-methamphetamine is one of the metabolites of selegiline, the present study aims to examine whether L-deprenyl can improve cognitive, biochemical, and histopathological injury in animal model of transient global ischemia. The animals were randomized in ten groups orally gavaged three times a week for 28days. Then, novel object recognition (NOR) was conducted to assess their behavioral abnormality. After scarification of the rats, their brains were divided into two sections to measure oxidative stress parameters and perform pathological evaluations in rats. Our data revealed the involvement of oxidative stress, behavioral despair, and pathological data in transient global ischemia rats. Significant recovery in cognitive behavior, oxidative stress biomarker, and number of dead cell in histopathological assay was observed in rats treated with 1,2 and 4mg/kg of selegiline. So, selegiline appears to be useful in alternative therapy of transient global ischemia.

Detection of l-Methamphetamine and l-Amphetamine as Selegiline Metabolites.

Selegiline (SE) is a selective, irreversible monoamine oxidase-B inhibitor, used for reducing symptoms in early-stage Parkinson's disease. The metabolites of SE include l-methamphetamine, l-amphetamine and desmethylselegiline (DSE). The stereoisomers of SE metabolites, d-methamphetamine and d-amphetamine are highly addictive psychostimulants and some of the most abused drugs in South Korea. In order to differentiate medical SE users form illicit methamphetamine abusers, it is important to distinguish between the l-isomers and d-isomers in urine samples. A 52-year-old male, seemingly under the influence of intoxication and demonstrating abnormal behavior, was reported to the police. The initial urine test using a methamphetamine detection kit demonstrated a positive result. Given the initial results, the police officer requested a further analysis of the urine sample. The urine sample was screened using headspace-solid phase microextraction-gas chromatography-mass spectrometry (HS-SPME-GC-MS). Both methamphetamine and amphetamine were detected, in addition to SE and DSE. To quantitate methamphetamine and amphetamine by HS-SPME-GC-MS, we performed a standard addition method due to the matrix effect of the case sample. Consistent with previous studies, our results indicated that the ratio of amphetamine to methamphetamine was 0.27, which was in the range of SE ingestion. Furthermore, we confirmed l-methamphetamine and l-amphetamine by chiral derivatization using (R)-(-)-α-methoxy-α-(trifluoromethyl) phenylacetyl chloride.

Identification of Methamphetamine Abuse and Selegiline Use： Chiral Analysis of Methamphetamine and Amphetamine in Urine

To study the content variation of selegiline and its metabolites in urine, and based on actual cases, to explore the feasibility for the identification of methamphetamine abuse and selegiline use by chiral analysis. The urine samples were tested by chiral separation and LC-MS/MS method using CHIROBIOTIC™ V2 chiral liquid chromatography column. The chiral analysis of methamphetamine and amphetamine were performed on the urine samples from volunteers of selegiline use and drug addicts whom suspected taking selegiline. After 5 mg oral administration, the positive test time of selegiline in urine was less than 7 h. The mass concentrations of R（-）-methamphetamine and R（-）-amphetamine in urine peaked at 7 h which were 0.86 μg/mL and 0.18 μg/mL and couldn't be detected after 80 h and 168 h, respectively. The sources of methamphetamine and amphetamine in the urine from the drug addicts whom suspected taking selegiline were analysed successfully by present method. The chiral analysis of methamphetamine and amphetamine, and the determination of selegiline's metabolites can be used to distinguish methamphetamine abuse from selegiline use.

Electrochemical generation of selegiline metabolites coupled to mass spectrometry

The metabolic pathways of selegiline (a drug used for the treatment of early-stage Parkinson's disease) were analyzed by electrochemical oxidation with application of the flow electrochemical cell consisting of three electrodes (ROXY™, Antec, the Netherlands). Two types of working electrodes were applied: glassy carbon (GC) and boron-doped diamond (BDD). The potential applied at working electrode and composition of the solvent were optimized for the best conditions for oxidation and identification processes. All products were directly analyzed on-line by mass spectrometry. For further characterization of electrochemical oxidation products, the novel approach involving reversed phase chromatography linked to mass spectrometry with dielectric barrier discharge ionization (DBDI-MS) was used. In this manuscript, we report a novel technique for simulation of drug metabolism by electrochemical system (EC) connected to liquid chromatography (LC) and dielectric barrier discharge ionization (DBDI) mass spectrometry (MS) for direct on-line detection of electrochemical oxidation products. Here, we linked LC/DBDI-MS system with an electrochemical flow cell in order to study metabolic pathways via identification of drug metabolites generated electrochemically. The DBDI source has never been used before for identification of psychoactive metabolites generated in an electrochemical flow cell. Our knowledge on the biological background of xenobiotics metabolism and its influence on human body is constantly increasing, but still many mechanisms are not explained. Nowadays, metabolism of pharmaceuticals is mainly studied using liver cells prepared from animals or humans. Cytochrome P450, present in microsomes, is primarily responsible for oxidative metabolism of xenobiotics. It was also shown, that breakdown of popular medicines may be successfully simulated by electrochemistry under appropriate conditions. The presented experiments allow for comparison of these two entirely distinct techniques using selegiline as the model xenobiotic with well-described metabolic pathway in human body. The obtained results for selegiline oxidation show that it is possible to generate the most important selegiline metabolites present in human body – some of them with psychoactive properties, such as methamphetamine and amphetamine. These metabolites, serving as an evidence of the xenobiotic intake, can also be produced, among a larger group of metabolites, by incubation of selegiline with rat and human liver microsomes. The EC/LC/DBDI-MS system provides novel, promising platform for drugs screening of the phase I metabolism. The metabolites can be detected directly by MS or collected and separated by liquid chromatography.

Metabolism of Selegiline [(-)-Deprenyl)

Selegiline (1) [(-)-deprenyl] is used to treat patients with Parkinson's disease. Nevertheless, in much higher doses it has beneficial effects in depression, and dementia of the aged patients. Selegiline (1) undergoes a complex metabolic pathway. Its major metabolites include (-)-desmethyldeprenyl (2), (-)-methamphetamine (3) and (-)-amphetamine (4), deprenyl-N-oxide (5) and formaldehyde (6) as a small metabolic fragment. In addition, more than 40 minor metabolites of selegiline (1) have also been either detected or proposed by investigators and researchers. This review analyses the pharmacological activity, generation pathway and the detection method of the major metabolites of selegiline (1).

Inhibition of Bupropion Metabolism by Selegiline: Mechanism-Based Inactivation of Human CYP2B6 and Characterization of Glutathione and Peptide Adducts

Selegiline, the R-enantiomer of deprenyl, is used in the treatment of Parkinson's disease. Bupropion, an antidepressant, often used to treat patients in conjunction with selegiline, is metabolized primarily by CYP2B6. The effect of selegiline on the enzymatic activity of human cytochrome CYP2B6 in a reconstituted system and its effect on the metabolism of bupropion were examined. Selegiline was found to be a mechanism-based inactivator of the 7-ethoxy-4-(trifluoromethyl)coumarin O-deethylation (7-EFC) activity of CYP2B6 as well as bupropion metabolism. The inactivations were time-, concentration-, and NADPH-dependent and were characterized by K(I) values of 0.14 and 0.6 μM, k(inact) values of 0.022 and 0.029 min⁻¹, and t(½) values of 31.5 and 24 min, respectively. In standard inhibition assays, selegiline increased the K(m) of CYP2B6 for bupropion from 10 to 92 μM and decreased the k(cat) by ∼50%. The reduced carbon-monoxide difference spectrum revealed over a 50% loss in the cytochrome P450 spectrum in the inactivated sample, with no loss in heme, and there was ∼70% loss in enzyme activity. Trapping of the reactive metabolite using GSH led to the identification of a GSH-selegiline conjugate with a m/z 528 that could be explained by hydroxylation of selegiline followed by the addition of glutathione to the propargyl moiety after oxygenation to form the ketene intermediate. Liquid chromatography-tandem mass spectrometry analysis of the labeled protein following digestion with trypsin revealed the peptide ⁶⁴DVFTVHLGPR⁷³ as the peptide modified by the reactive metabolite of selegiline and the site of adduct formation is Asp64.

A critical review of evidence for preclinical differences between rasagiline and selegiline

Monoamine oxidase M (MAO-B) inhibitors are used in the symptomatic treatment of Parkinson’s disease (PD) as they prolong the availability and activity of endogenous dopamine in the striatum by blocking its degradation. Two MAO-B inhibitors, rasagiline and selegiline, are currently licensed in Europe and North America. The differences between these agents at the clinical and preclinical level have been much debated. This review critically explores the evidence for preclinical differences between rasagiline and selegiline, and discusses the relevance of these differences for the treatment in PD.Rasagiline is about 10 times more potent in the inhibition of MAO-B than selegiline in ex vivo studies. To achieve similar potency in the clinical setting the doses were adapted. At their selective MAO-B inhibitory dosages, rasagiline and selegiline do not produce the “cheese reaction” and do not cause a potentiation of the effects of L-DOPA combined with the decarboxylase inhibitor carbidopa on blood pressure or heart rate in conscious rats. However, in pithed rats, selegiline but not rasagiline increased noradrenaline and adrenaline release, and pulse rate, and potentiated dopamine pressor response at MAO-B selective dose. It is believed that this difference is the result of their different chemical structure that gives rise to different metabolites with distinct pharmacological properties. Whether this difference is relevant for the clinic in regard to the occurrence of cardiovascular adverse drug reactions is not known, because, it is not known at what concentrations l-amphetamine and l-methamphetamine exert a sympathomimetic effect in vivo, and whether such concentrations are achieved in the blood of PD patients.Rasagiline is superior to selegiline in its potency to prevent spontaneous cell death seen in cell culture, and to reduce accelerated cell death following serum deprivation in vitro. In addition, rasagiline is more effective in regard to its ability to reverse changes in mitochondrial function that lead to apoptosis. Finally, in the lactacystin-treated mouse, rasagiline exerts a neurorestorative effect where selegiline has none. These effects were considered to be independent of the ability of both agents to inhibit MAO-B. It was concluded that these superior effects of rasagiline are attributable to additive effects of the parent active substance and its major metabolite, 1-R-aminoindan, and to possible neurotoxic effects of l-methamphetamine, one metabolite of selegiline. However, it is not known at what concentrations these compounds may exert any protective and neurotoxic effect, respectively, in vivo, and whether respective concentrations are achieved in the brain of PD patients.

Detection of <i>Levorotatory</i> Methamphetamine and <i>Levorotatory</i> Amphetamine in Urine after Ingestion of an Overdose of Selegiline

In this study, we measured the urine concentrations of methamphetamine and amphetamine as metabolites of selegiline after ingestion of an overdose of selegiline. A patient who had developed Parkinson disease took selegiline in a suicide attempt. Analysis by gas chromatography-mass spectrometry (GC-MS) with trifluoroacetic acid-derivatization revealed the presence of methamphetamine and amphetamine in the patient's urine at concentrations of 0.62 microg/ml and 0.25 microg/ml, respectively. To determine the stereospecificity of the methamphetamine and amphetamine, a urine sample was analyzed by GC-MS after derivatization with N-(trifluoroacetyl)-l-prolyl chloride. The methamphetamine and amphetamine were levorotatory in form. The ratio of the methamphetamine to amphetamine concentration in the urine was 2.5. This value is consistent with other case reports of ingestion of selegiline, which suggests that the methamphetamine to amphetamine concentration ratio in urine is useful information for indicating use of selegiline.

Selegiline Is a Mechanism-Based Inactivator of CYP2A6 Inhibiting Nicotine Metabolism in Humans and Mice

Selegiline (l-deprenyl) is in clinical treatment trials as a potential smoking cessation drug. We investigated the affect of selegiline and its metabolites on nicotine metabolism. In mice, selegiline was a potent inhibitor of nicotine metabolism in hepatic microsomes and cDNA-expressed CYP2A5; the selegiline metabolites desmethylselegiline, l-methamphetamine, and l-amphetamine, also inhibited nicotine metabolism. Pretreatment with selegiline and desmethylselegiline increased inhibition (IC(50)) in microsomes by 3.3- and 6.1-fold, respectively. In mice in vivo, selegiline increased AUC (90.7 +/- 5.8 versus 57.4 +/- 5.3 ng/h/ml, p < 0.05), decreased clearance (4.6 +/- 0.4 versus 7.3 +/- 0.3 ml/min, p < 0.05), and increased elimination half-life (12.5 +/- 6.3 versus 6.6 +/- 1.4 min, p < 0.05) of nicotine. In vitro, selegiline was a potent inhibitor of human nicotine metabolism in hepatic microsomes and cDNA-expressed CYP2A6; desmethylselegiline and l-amphetamine also inhibited nicotine metabolism. Selegiline preincubation increased inhibition in microsomes (3.7-fold) and CYP2A6 (14.8-fold); the K(i) for CYP2A6 was 4.2 muM. Selegiline dose- and time-dependently inhibited nicotine metabolism by CYP2A6 (K(i) = 15.6 +/- 2.7 muM; k(inact) = 0.34 +/- 0.04 min(-1)), and the inhibition was irreversible in the presence of NADPH, indicating that it is a mechanism-based inhibitor of CYP2A6. Thus, inhibition of mouse nicotine metabolism by selegiline was competitive in vitro and significantly increased plasma nicotine in vivo. In humans, where selegiline is both a competitive and mechanism-based inhibitor, it is likely to have even greater effects on in vivo nicotine metabolism. Our findings suggest that an additional potential mechanism of selegiline in smoking cessation is through inhibition of nicotine metabolism.

L-Methamphetamine and selective MAO inhibitors decrease morphine-reinforced and non-reinforced behavior in rats; Insights towards selegiline's mechanism of action

Selegiline is an inhibitor of type B monoamine oxidase (MAO) with psychostimulant effects that can decrease morphine-reinforced and non-reinforced responding. The present study was undertaken to compare the effects of MAO inhibition and treatment with l-methamphetamine, the major psychostimulant metabolite of selegiline, on these behaviors. After rats acquired a stable pattern of morphine self-administration under a progressive ratio schedule, chronic treatment was initiated with vehicle, l-methamphetamine, clorgyline (a selective inhibitor of MAO-A), or rasagiline (a selective inhibitor of MAO-B); with both MAO inhibitors administered at a dose selective for one MAO isoform and a higher dose that inhibited both isoforms. Rats were evaluated for up to four cycles of opiate dependence maintained by morphine self-administration and withdrawal during which extinction responding was recorded. Most behavioral measures (92.4%) did not differ in animals evaluated during an initial and subsequent cycles of dependence and withdrawal. All active treatments attenuated non-reinforced responding during extinction. Morphine reinforcement was also decreased by each of the three active treatments, but greater and more prolonged effects were observed following inhibition of MAO-B with rasagiline. Responding during either cue- or morphine-induced reinstatement was attenuated by either clorgyline or rasagiline administered at nonselective doses, but not by either compound administered at selective dose levels. Treatment with l-methamphetamine did not produce significant effects on cue-induced reinstatement, but decreased non-reinforced responding during morphine-induced reinstatement. These findings indicate that morphine reinforcement and different non-reinforced behaviors differ greatly in their susceptibility to modification by psychostimulant treatment or MAO inhibition.

In vitro formation of selegiline-N-oxide as a metabolite of selegiline in human, hamster, mouse, rat, guinea-pig, rabbit and dog

It is well established in the litrature, that selegiline is metabolised to its N-dealkylated metabolites, N-desmethylselegiline, methamphetamine and amphetamine. However, most studies on selegiline metabolism did not characterize the species differences in the formation of the metabolites. Therefore, in this study, we investigated the in vitro metabolism of selegiline in liver microsomes of different species. In addition, to the previously well-characterized metabolites, selegiline-N-oxide (selegiline-NO) was found to be formed as a metabolite of selegiline in rat liver microsomal preparation. The results of experiments with liver microsomes from other species indicated species differences in the rate and extent of formation of selegiline-NO. The dog and hamster liver microsomal preparations were the most active in terms of selegiline-NO production, whereas little selegiline was metabolized to its N-oxide in human liver microsomes. When selegiline-NO was incubated with rat liver microsomes, no metabolism occurred. When a short incubation time was applied in selegiline expriments no increase in the amount of selegiline-NO was detected. Accordingly, it was clear that selegiline was not metabolized to the N-dealkylated or N,N-bis-dealkylated compounds via selegiline-NO. Studies with different isoenzyme inhibitors indicated that the formation of selegiline-NO might be catalyzed at least partly by cytochrome P450 (CYP) 2D6 and CYP3A4. With the exception of hamster microsomes in the microsomal preparations in vitro, the formation of the R,S-stereoisomer of selegiline-NO was preferred.

Chiral Characterization and Quantification of Deprenyl-N-oxide and Other Deprenyl Metabolites in Rat Urine by Capillary Electrophoresis

Chiral capillary electrophoresis has been validated for the quantitative analysis of R-(-)-deprenyl (selegiline) and seven of its metabolites, among them the diastereomeric pair of selegiline-N-oxide in rat urine. Linear calibration curves were obtained over the concentration range: 0.5–100 μM for selegiline, N-desmethylselegiline, methamphetamine, amphetamine, and selegiline-N-oxides, and from 0.1-100 μM for para-hydroxylated derivatives of N-desmethylselegiline, methamphetamine, and amphetamine. The inter and intra-assay precision and accuracy varied by <15% for all analytes at concentrations of 2.5, 10 and 25 μM, and <20% at the lower limit of quantification (0.5 or 0.1 μM). The sample extraction procedure was optimised, and sample recoveries ranged: 80–111% and 74–91% at concentrations of 1 and 10 μM, respectively. The extracted urine samples retained quantitative accuracy for at least 5 days after storage at 4 °C. The validated method was used for in vivo metabolism studies in rats treated with either single or repeated dose of selegiline, or selegiline-N-oxide. Stereoselective N-oxidation of selegiline and rapid urinary excretion of selegiline-N-oxides have been observed. The most abundant metabolites of selegiline were the desalkylated and para-hydoxylated derivatives excreted in both conjugated and unconjugated forms in rat urine.

Contrasting neuroprotective and neurotoxic actions of respective metabolites of anti-Parkinson drugs rasagiline and selegiline

The anti-Parkinson selective irreversible monoamine oxidase B inhibitor drugs, rasagiline and selegiline, have been shown to possess neuroprotective activities in cell culture and in vivo models. While rasagiline is metabolized to its major metabolite aminoindan, selegiline gives rise to l-methamphetamine. Cultured PC-12 cells in absence of serum and nerve growth factor (NGF) die by an apoptotic process. Pretreatment of PC12 cells in absence of serum and NGF for 24 h with either rasagiline (1 μM) or selegiline (1 μM) is neuroprotective and anti-apoptotic as determined by Eliza and MTT tests. However, while aminoindan (1 μM), the major metabolite of rasagiline does not interfere with the neuroprotective activities of rasagiline or selegiline in PC-12 cells deprived of serum and NGF, the major metabolite of selegiline, l-methamphetamine (1 μM), inhibits them. In contrast to l-methamphetamine, aminoindan is itself is neuroprotective in this system. Recently it has been demonstrated that rasagiline directly activates PKC-MAP kinase pathway by a concentration and time dependent phosphorylation of p42 and p44 MAP kinase. In the present studies the neuroprotective activity of rasagiline is blocked by ERK inhibitor, PD98059 (20 μM), suggesting the involvement of PKC-MAP kinase pathway in the neuroprotection. These findings may have implication for the possible disease modifying action of rasagiline in treatment of Parkinson's disease.

Urinary excretion of selegiline N -oxide, a new indicator for selegiline administration in man

1. The metabolism of selegiline (SG) has been studied by investigating the timecourse of urinary excretion of SG and its metabolites using high-performance liquid chromatography-electrospray ionization mass spectrometry (LC-ESI MS) in combination with solid-phase extraction. 2. The excretion profiles of SG and its four major metabolites, selegiline- N -oxide (SGO), N -desmethylselegiline (DM-SG), methamphetamine (MA) and amphetamine (AP), were investigated in six healthy volunteers after oral administrations of SG hydrochloride in a single dose of 2.5 or 7.5mg, and a repeat twice-daily dose of 5.0 mg day -1 (for 3 days). 3. The cumulative amount of SGO excreted within approximately the first 8-12h was comparable with MA, and the amount in the first 72 h was 2.0-7.8 times larger (2.8-13.2% of the dose) than that of DM-SG. 4. These results demonstrate that SGO can be used in place of DM-SG, which is known to be a main specific metabolite of SG, as a new indicator for the discrimination of SG use compared with MA abuse.

Incorporation of selegiline metabolites into hair after oral selegiline intake.

We have previously shown that melanin in human hair has a great impact on the incorporation of codeine into hair. The present study on 10 subjects was performed to investigate whether or not these findings could also be extrapolated to other therapeutic drugs. We chose selegiline because it metabolizes to two commonly abused central stimulants, methamphetamine and amphetamine. The results would therefore also be of interest when studying the intake of such drugs and their incorporation into human hair. Selegiline and metabolites were determined by gas chromatography-mass spectrometry, total melanin by spectrophotometry, and pyrrole-tricarboxylic acid by high-performance liquid chromatography with ultraviolet detection. Our results show strong positive exponential relationships (y = e(x)) between melanin and the metabolites, which for methamphetamine improved by normalizing for plasma area under the curve. We conclude that the major metabolites of selegiline can be detected in hair up to four weeks after a single oral dose and that the incorporation closely relates to the melanin contents.

Multiple-dose pharmacokinetics of selegiline and desmethylselegiline suggest saturable tissue binding.

The goal of this study was to examine the multiple-dose pharmacokinetics of selegiline and its metabolites desmethylselegiline, 1-methamphetamine, and 1-amphetamine after oral administration of selegiline HCl. Twelve healthy volunteers received 10 mg of selegiline HCl once daily for 8 days. The pharmacokinetic profiles of selegiline and the metabolites were examined from serum samples for 24 hours (i.e., the dosing interval, tau) on days 1, 4, and 8. The results indicated significant apparent accumulation of selegiline and desmethylselegiline during the 8-day period of selegiline administration. The AUC tau S of selegiline and desmethylselegiline were increased 2.7 fold (p < 0.001) and 1.5 fold (p < 0.001), respectively, from day 1 to day 8. However, the half-lives of selegiline (range, 1.5-3.5 h) and desmethylselegiline (range, 3.4-5.3 h) were found to be relatively short. Accordingly, the short half-lives of these compounds failed to predict the apparent accumulation. With both of the 1-amphetamine metabolites of selegiline, steady state was reached by day 4. We suggest that the most likely explanation for the apparent accumulation of selegiline and desmethylselegiline was the saturation of the MAO-B binding sites in tissues, although decreased first-pass metabolism of selegiline cannot be ruled out. The observed increase in selegiline and desmethylselegiline concentrations on multiple dosing is not likely to significantly increase the pharmacodynamic effect or adverse effects of selegiline compared with what has been found after a single 10-mg dose.

Stereoselective analyses of selegiline metabolites: possible urinary markers for selegiline therapy

The stereoselective analysis of selegiline metabolites in human urine and plasma by gas chromatography using the chiral column with the non-chiral reagent was investigated for the differentiation of selegiline therapy from the methamphetamine (MA) abuse. This method gave clear separations of MA and amphetamine (AM) isomers without any artifactual optical-opposite peaks due to the reagent. After the administration of selegiline tablets, desmethylselegiline (DMS), MA and AM were observed as (−)-isomers in the urine and plasma. Within the first 48 h after dosing, approximately 40% of selegiline administered was excreted in urine as these three metabolites. The parent drug, selegiline, was not detected in any urine or plasma samples. On the other hand, MA and AM were observed only as (+)-isomers in the urine of MA abusers. For the distinction of selegiline users from street MA abusers in urinalysis, (−)-DMS, a specific metabolite of selegiline, was not a suitable marker. (−)-DMS rapidly disappeared from urine and was excreted only 1% of the given dose. By the moment analysis with the trapezoidal integration, the mean residence times of (−)-DMS in plasma and urine were 2.7 and 3.8 h, respectively, which were 5–20 times shorter than those of (−)-MA or (−)-AM. The values of AM/MA in the urine increased from 0.24 to 0.67 ( r=0.857) along with time after the selegiline administration. This ratio was not a sufficient marker to differentiate selegiline users from MA abusers, although the values of AM/MA in 74% of MA abusers were less than 0.24. The present GC technique improved the chiral analyses of MA and AM. This chiral analysis is the most useful technique to avoid the misinterpretation in the discrimination between clinical selegiline therapy and illicit MA use.

Desmethylselegiline, a Metabolite of Selegiline, Is an Irreversible Inhibitor of Monoamine Oxidase Type B in Humans

Selegiline, an irreversible and selective inhibitor of monoamine oxidase type B (MAO-B), is metabolized into desmethylselegiline, levomethamphetamine, and levoamphetamine. In animal experiments, desmethylselegiline also has been shown to be an irreversible inhibitor of MAO-B. This study investigated the inhibitory potential of MAO-B and the pharmacokinetics of desmethylselegiline in humans. A double-blind, crossover trial was performed to compare the effects of a single dose (10 mg) of selegiline or desmethylselegiline on MAO-B platelet activity. The urinary excretion of phenylethylamine, which is considered to be a parameter of MAO-B inhibition, also was measured. The concentrations of selegiline, desmethylselegiline, and their metabolites were measured in plasma after administration of the two compounds. Ten healthy volunteers participated in the study. There was a clear inhibition of platelet MAO-B by both compounds. Desmethylselegiline caused a 63.7 +/- 12.7% inhibition of platelet MAO-B compared with 96.4 +/- 3.9% caused by selegiline. The maximal inhibition by desmethylselegiline was reached significantly later after desmethylselegiline (time to reach maximal inhibition [tmax], 27 +/- 20 hours) than after selegiline administration (tmax, 1.4 +/- 1.4 hours). The platelet MAO-B activity returned to baseline levels within 2 weeks, thus reflecting the irreversible nature of the inhibition by both compounds. The cumulative 48-hour excretion of phenylethylamine was 33% lower after desmethylselegiline than after selegiline administration. All three major metabolites of selegiline could be detected in plasma after selegiline administration. Levoamphetamine was the only metabolite of desmethylselegiline. The area under the concentration-time curve from time 0 to 24 hours (AUC0-24) of desmethylselegiline was 33 times higher than that of selegiline, suggesting a better bioavailability of desmethylselegiline. Desmethylselegiline is an orally active, irreversible inhibitor of MAO-B and could possibly be used to treat Parkinson's disease in the same way as selegiline.

Determination of Desmethyl- Selegiline, Methamphetamine and Amphetamine - The Main Metabolites of Selegiline in Plasma by HPLC After Derivatization

Determination of desmethylselegiline, methamphetamine and amphetamine in plasma requires a very sensitive and selective method. These substances are metabolites of the MAO-inhibitor selegiline. This is the first published HPLC method which is able to determine these three substances down to a limit of quantification of 0.2 ng/mL human plasma. After extraction as free bases into an organic solvent and reextraction as salts into an inorganic acid all three substances and an internal standard (phentermine) are derivatized for fluorescence detection after reversed phase chromatography. The recovery is better than 90 % for all substances. The linearity in the range tested (0.2 – 15 ng for each substance/mL plasma) is very good indeed. The precision and accuracy is usually smaller than 5 %. Pharmacokinetic results are presented.

Selegiline percutaneous absorption in various species and metabolism by human skin.

A Selegiline Transdermal System (STS) is under development for indications which may not be optimally or safely treated with oral selegiline. Studies were conducted to evaluate the in vitro penetration and skin metabolism of selegiline in order to better understand the toxicological findings and the observed plasma levels of selegiline and its metabolites in animals and man. In vitro penetration studies were conducted in four different species (male hairless mice, male and female rats, female dog and male Micropig) and compared to human skin. In another study, viable human skin was used to estimate the extent of metabolism of selegiline by human skin using Franz diffusion cells. Results indicated that female dog and male Micropig skin were reasonable animal models for 24 hour in vitro selegiline penetration through human skin. Penetration of selegiline through rat skin and hairless mouse skin was 2-fold and 3-fold higher than through human skin, respectively. Metabolism was negligible in human skin. Selegiline metabolites (L-methamphetamine and N-desmethylselegiline but not L-amphetamine) were detected at all time points but the extent of selegiline metabolism was negligible. The cumulative 24 hour in vitro selegiline permeation from a 1.83 mg/cm2 STS through human skin was 5.0 mg. This was similar to the in vivo permeation in humans as assessed by residual patch analysis. The similarity of dog and human skin permeation results support the use of the dog as a species for evaluating the toxicology of transdermally-administered selegiline. Selegiline is not metabolized cutaneously and hence the metabolic profile following STS administration is likely due to hepatic metabolism only.