Showing papers on "Monoamine oxidase B published in 2002"

Structure of human monoamine oxidase B, a drug target for the treatment of neurological disorders

Abstract: Monoamine oxidase B (MAO B) is a mitochondrial outermembrane flavoenzyme that is a well-known target for antidepressant and neuroprotective drugs. We determined the structure of the human enzyme to 3 A resolution. The enzyme binds to the membrane through a C-terminal transmembrane helix and apolar loops located at various positions in the sequence. The electron density shows that pargyline, an analog of the clinically used MAO B inhibitor, deprenyl, binds covalently to the flavin N5 atom. The active site of MAO B consists of a 420 A(3)-hydrophobic substrate cavity interconnected to an entrance cavity of 290 A(3). The recognition site for the substrate amino group is an aromatic cage formed by Tyr 398 and Tyr 435. The structure provides a framework for probing the catalytic mechanism, understanding the differences between the B- and A-monoamine oxidase isoforms and designing specific inhibitors.

Propargylamines Induce Antiapoptotic New Protein Synthesis in Serum- and Nerve Growth Factor (NGF)-Withdrawn, NGF-Differentiated PC-12 Cells

Abstract: (-)-Deprenyl and structurally related propargylamines increase neuronal survival independently of monoamine oxidase B (MAO-B) inhibition, in part by decreasing apoptosis. We found that deprenyl and two other propargylamines, one of which does not inhibit monoamine oxidase B, increased survival in trophically withdrawn 6-day nerve growth factor (NGF)- and 9-day NGF-differentiated PC-12 cells but not in NGF naive or 3-day NGF-differentiated PC-12 cells. Four days of prior NGF exposure were required for the propargylamine-mediated antiapoptosis. Studies using actinomycin D, cycloheximide, and camptothecin revealed that the maintenance of both transcription and translation, particularly between 2 and 6 h after trophic withdrawal, was required for propargylamine-mediated antiapoptosis. Metabolic labeling of newly synthesized proteins for two-dimensional protein gel autoradiography and scintillation counting showed that the propargylamines either increased or reduced the levels of new synthesis or induced de novo synthesis of a number of different proteins, most notably proteins in the mitochondrial and nuclear subfractions. Western blotting for whole cell or subcellular fraction lysates showed that the timing of new protein synthesis changes or subcellular redistribution of apoptosis-related proteins induced by the propargylamines were appropriate to antiapoptosis. The apoptosis-related proteins included superoxide dismutases (SOD1 and SOD2), glutathione peroxidase, c-JUN, and glyceraldehyde-3-phosphate dehydrogenase. Most notable were the prevention of apoptotic decreases in BCL-2 levels and increases in mitochondrial BAX levels. In general, (-)-deprenyl-related propargylamines appear to reduce apoptosis by altering the levels or subcellular localization of proteins that affect mitochondrial membrane permeability, scavenge oxidative radicals, or participate in specific apoptosis signaling pathways.

Investigation of the functional effect of monoamine oxidase polymorphisms in human brain.

Abstract: Monoamine oxidase A and monoamine oxidase B (MAOA and MAOB) have been suggested to play a role in psychiatric disorders and/or behavioral traits. We have investigated whether different polymorphisms can account for variations in enzyme activity and/or mRNA levels in human brain. Whereas several association studies have been reported previously, this is the first study of the functional effect of MAO DNA variants in human brain. Four polymorphic changes were analyzed: a VNTR located in the MAOA promoter, a VNTR located in the first intron of the MAOA gene, and two single nucleotide polymorphisms located in exon 8 of MAOA and in intron 13 of MAOB. We studied the association of the variants and the resulting haplotypes, with expression levels and enzyme activities of both monoamine oxidases in human cortical brain autopsies. We did not find a significant association of any single MAOA polymorphism with expression levels or enzyme activity in human brain. We did, however, find an association of a particular haplotype with MAOA enzyme levels (P=0.03). Our results suggest that a novel functional polymorphism that affects enzyme activity in human brain may exist in MAOA. For MAOB, we found a significant association (P=0.02) between the MAOB intron 13 alleles and different levels of MAOB enzyme activity in human brain. We postulate that there may be a cis-regulatory element in linkage disequilibrium with the B-SNP13 polymorphisms that alters MAOB enzyme activity in human brain.

Effect of Long‐Term Treatment with Selective Monoamine Oxidase A and B Inhibitors on Dopamine Release from Rat Striatum In Vivo

Abstract: Acute inhibition of monoamine oxidase B (MAO-B) in the rat does not affect striatal dopamine (DA) metabolism, but chronic MAO-B inhibition with deprenyl has been reported to increase the release of striatal DA, as shown using in vitro techniques. To see whether chronic MAO-B inhibition also causes an increase in DA release in vivo, rats were treated for 21 days with either deprenyl (0.25 mg/kg), TVP-1012 [R(+)-N-propargyl-1-aminoindan mesylate; 0.05 mg/kg], an irreversible inhibitor of MAO-B that is not metabolized to amphetamines, clorgyline (0.2 mg/kg), or saline (all doses once daily by subcutaneous injection). Concentric 4-mm-long microdialysis probes were implanted in the left striatum under pentobarbital/chloral hydrate anesthesia on day 21, and microdialysate DA, 3,4, dihydroxyacetic acid (DOPAC), and 4-hydroxy-3-methoxyphenyl acetic acid (HVA) were determined in the conscious animals on day 22. Baseline levels of DA were as follows: control, 0.34 +/- 0.04 (n = 13); deprenyl, 0.88 +/- 0.10 (n = 8, p < 0.01); TVP-1012, 0.94 +/- 0.20 (n = 7, p < 0.01); clorgyline, 0.90 +/- 0.12 (n = 7, p < 0.01) pmol/20 min. Levels of DOPAC and HVA were reduced only in the clorgyline-treated group. The incremental release of DA induced by depolarizing concentration of K+ (100 mM bolus of KCl in perfusate) was significantly greater in clorgyline- and deprenyl-treated rats and elevated (nonsignificantly) in TVP-1012-treated rats. Chronic treatment with the MAO-B inhibitors reduced striatal MAO-B activity by 90%, with 15% (TVP-1012) or 40% (deprenyl) inhibition of MAO-A. Clorgyline inhibited MAO-A by 95%, with 30% inhibition of MAO-B. A single dose of deprenyl (0.25 mg/kg, 24 h before microdialysis) had no significant effect on striatal efflux of DA. The results show that DA metabolism was reduced only by clorgyline, whereas neuronal release of DA was enhanced by both MAO-A and MAO-B inhibitors on chronic administration. The enhanced DA release by chronic MAO-B inhibition does not appear to be dependent on production of amphetamine-like metabolites of the inhibitor. Possible mechanisms for the release-enhancing effect of the MAO-B inhibitors include elevation in levels of endogenous beta-phenylethylamine, or an inhibition of DA reuptake, which develops only on chronic administration, because both deprenyl and TVP-1012 have only very weak effects on amine uptake in acute experiments.

l‐3,4‐Dihydroxyphenylalanine‐Induced Dopamine Release in the Striatum of Intact and 6‐Hydroxydopamine‐Treated Rats: Differential Effects of Monoamine Oxidase A and B Inhibitors

Abstract: Administration of l-DOPA (50 mg/kg) elicits a significant increase in extracellular dopamine in striata of rats treated with the catecholaminergic neurotoxin 6-hydroxydopamine but not in striata of intact rats. To assess the role of dopaminergic nerve terminals in determining the effects of exogenous l-DOPA on extracellular dopamine levels in striatum, we examined the relative contributions of monoamine oxidase A and monoamine oxidase B to the catabolism of dopamine synthesized from exogenous l-DOPA. Extracellular concentrations of dopamine and its catabolite, 3,4-dihydroxyphenylacetic acid, were monitored with in vivo dialysis in striata of intact rats and of rats with unilateral 6-hydroxydopamine lesions of striatal dopamine. Clorgyline (2 mg/kg), an inhibitor of monoamine oxidase A, significantly increased dopamine and decreased 3,4-dihydroxyphenylacetic acid in intact but not in dopamine-depleted striata. Inhibition of monoamine oxidase B with either l-deprenyl (1 mg/kg) or Ro 19-6327 (1 mg/kg) did not significantly affect dopamine or 3,4-dihydroxyphenylacetic acid in striata of intact or dopamine-depleted rats. In intact rats, administration of clorgyline in conjunction with l-DOPA produced a >20-fold increase in dopamine and prevented the l-DOPA-induced increase in 3,4-dihydroxyphenylacetic acid. Although both l-deprenyl and Ro 19-6327 administered in combination with l-DOPA elicited a small but significant increase in dopamine, levels of 3,4-dihydroxyphenylacetic acid were not affected. In rats pretreated with 6-hydroxydopamine, clorgyline had no significant effect on the increases in dopamine and 3,4-dihydroxyphenylacetic acid elicited by l-DOPA. Furthermore, neither l-deprenyl nor Ro 19-6327 affected l-DOPA-induced increases in dopamine and 3,4-dihydroxyphenylacetic acid in dopamine-depleted striata. The present findings indicate that deamination by monoamine oxidase A is the primary mechanism for catabolism of striatal dopamine, both under basal conditions and after administration of exogenous l-DOPA. Loss of dopaminergic terminals eliminates this action of monoamine oxidase A but does not enhance deamination by monoamine oxidase B. These data support a model in which exogenous l-DOPA elicits enhanced extracellular accumulation of dopamine in the dopamine-depleted striatum because some transmitter synthesis occurs at nondopaminergic sites and the dopamine terminals that normally take up and catabolize this pool of transmitter are absent.

Developmental expression of monoamine oxidases A and B in the central and peripheral nervous systems of the mouse.

Abstract: Monoamine oxidases A (MAOA) and B (MAOB) are key players in the inactivation pathway of biogenic amines. Their cellular localization has been well established in the mature brain, but nothing is known concerning the localization of both enzymes during development. We have combined in situ hybridization and histochemistry to localize MAOA and MAOB in the developing nervous system of mice. Our observations can be summarized as five key features. (1) MAOA is tightly linked to catecholaminergic traits. MAOA is expressed in all noradrenergic and adrenergic neurons early on, and in several dopaminergic cell groups such as the substantia nigra. MAOA is also expressed in all the neurons that display a transient tyrosine hydroxylase expression in the brainstem and the amygdala and in neurons with transient dopamine-β-hydroxylase expression in the cranial sensory ganglia. (2) MAOA and MAOB are coexpressed in the serotoninergic neurons of the raphe from E12 to P7. During postnatal life, MAOA expression declines, whereas MAOB expression remains stable. (3) MAOA is transiently expressed in the cholinergic motor nuclei of the hindbrain, and MAOB is expressed in the forebrain cholinergic neurons. (4) MAOA- and MAOB-expressing neurons are also detected in structures that do not contain aminergic neurons, such as the thalamus, hippocampus, and claustrum. (5) Starting at birth, MAOB expression is found in a variety of nonneuronal cells, the choroid plexus, the ependyma, and astrocytes. These localizations are of importance for understanding the effects of monoaminergic transmission during development. J. Comp. Neurol. 442:331–347, 2002. © 2002 Wiley-Liss, Inc.

Evidence for a genetic association between monoamine oxidase A and restless legs syndrome

Abstract: Background: Impairment in the central dopaminergic system has been consistently suggested as an etiologic factor in restless legs syndrome (RLS). Objective: To investigate a possible role for the MAOA and MAOB genes in RLS using a population-based association study. Methods: In addition to a dinucleotide repeat located within the second intron of the MAOB gene, a functional variable number of tandem repeat (VNTR) polymorphism recently identified in the MAOA gene promoter region was examined, using 96 extensively characterized patients and 200 control subjects matched for ethnic background. The relationship between variation at these loci and several clinical features was also considered. Results: Pertaining to the MAOA gene, females with the high activity allele had a greater risk (OR: 2.0; 95% CI: 1.06 to 3.77) of being affected with RLS than females carrying the low activity alleles. The authors did not observe this association among the male subjects (OR: 0.98; 95% CI: 0.31 to 3.14). Interestingly, females carrying the high transcription alleles showed a longer sleep onset latency (U = 163.5; p = 0.015) and exhibited a higher movement index during the Suggested Immobilization Test (Student’s t -test = −2.02; p = 0.048). No differences were observed regarding the MAOB gene in our sample. Conclusions: The high activity allele of the MAOA gene may represent a modifying factor involved in the severity of RLS manifestations in females.

Striatal Dopamine Metabolism in Monoamine Oxidase B‐Deficient Mice : A Brain Dialysis Study

Abstract: We have studied striatal dopamine (DA) metabolism in monoamine oxidase (MAO) B-deficient mice using brain microdialysis. Baseline DA levels were similar in wild-type and knock-out (KO) mice. Administration of a selective MAO A inhibitor, clorgyline (2 mg/kg), increased DA levels and decreased levels of its metabolites in all mice, but a selective MAO B inhibitor, l-deprenyl (1 mg/ kg), had no effect. Administration of 10 and 50 mg/kg L-DOPA, the precursor of DA, increased the levels of DA similarly in wild-type and KO mice. The highest dose of L-DOPA (100 mg/kg) produced a larger increase in DA in KO than wild-type mice. This difference was abolished by pretreating wild-type mice with l-deprenyl. These results suggest that in mice, DA is only metabolized by MAO A under basal conditions and by both MAO A and B at high concentrations. This is in contrast to the rat, where DA is always metabolized by MAO A regardless of concentration.

l-(−)-Desmethylselegiline, a Metabolite of Selegiline [l-(−)-Deprenyl], Protects Mesencephalic Dopamine Neurons from Excitotoxicity In Vitro

Abstract: Selegiline [L-(-)-deprenyl], a monoamine oxidase B inhibitor, has been used in the treatment of Parkinson's disease as a putative neuroprotective agent. Selegiline is metabolized rapidly in the gastrointestinal tract and liver to desmethylselegiline (DMS) and methamphetamine. We have previously shown that selegiline protects dopamine neurons in mesencephalic cultures from toxicity resulting from activation of glutamate receptors. In the present study we examined whether DMS has similar neuroprotective effects. Our data show that DMS protects dopamine neurons from N-methyl-D-aspartate receptor-mediated excitotoxic damage. The efficacy of DMS is greater than that of selegiline, as it can cause protection at lower concentrations and provide significantly greater levels of protection at the same concentrations. Our results suggest that DMS might be the active compound responsible for the neuroprotective properties of selegiline.

MAOB intron 13 and COMT codon 158 polymorphisms, cigarette smoking, and the risk of PD

Abstract: Background: A polymorphism (G to A transition) in intron 13 of the mitochondrial enzyme monoamine oxidase B ( MAOB ) gene may modify, alone or by interacting with the catechol- O -methyltransferase (COMT LL ) genotype (low enzymatic activity), the risk of idiopathic PD. Also, the association between never smoking and PD risk may be present only in people with the MAOB G allele. Methods: The authors studied two ongoing prospective cohorts—the Nurses’ Health Study (121,700 women aged 30 to 55 in 1976) and the Health Professionals’ Follow-up Study (51,529 men aged 40 to 75 in 1986). They identified new PD cases through 1996, selected random control subjects matched on age and study cohort, and obtained DNA samples from blood or buccal smears from 85% of the eligible cases and 84% of the control subjects. They included genotypes from 214 cases and 449 control subjects, all Caucasian. Results: The odds ratio of PD was 1.2 (95% CI 0.9, 1.7) for MAOB genotypes G/GG/GA compared with genotypes A/AA, and 1.1 (0.7, 1.8) for COMT genotypes LL compared with HH. The odds ratio (95% CI) was 1.7 (0.7, 3.9) for those with MAOB G/GG and COMT LL genotypes compared with those with MAOB A/AA and COMT HH . There was a strong association between never smoking and PD risk in all groups defined by MAOB and COMT genotypes. Conclusion: The findings do not support a major role of the MAOB intron 13 polymorphism in the development of PD, either by itself or by interacting with smoking.

Lazabemide, a selective, reversible monoamine oxidase B inhibitor, as an aid to smoking cessation.

Abstract: Background Previous research has shown that smokers have reduced brain and platelet monoamine oxidase B (MAOB) activity. This is probably due to some components of tobacco smoke. When smokers quit, MAOB activity returns to normal. Reduced MAO activity may increase nicotine's addictive potential. Aims To assess whether lazabemide, a reversible selective MAOB inhibitor, promotes smoking cessation. Study design Double-blind, randomized, placebo-controlled, multicenter phase II study. Placebo, lazabemide 100 mg/day and 200 mg/day were administered for 8 weeks. This was a dose finding, proof-of-concept, exploratory study. Setting General practices and anti-smoking clinics in France and Belgium. Participants Smokers smoking ≥15 cigarettes per day and motivated to quit. Main outcome measure Sustained abstinence during the last 4 weeks of the study. Findings The study was discontinued prematurely by the sponsor before randomization of the planned 420 smokers because of liver toxicity observed in other indications. Data of 330 randomized subjects could be analysed. Sustained abstinence during the last 4 weeks of treatment was 9%, 11% and 17% in the intent-to-treat population [P for trend: 0.036 (one-sided)]; 11%, 14% and 21% in the intent-to-treat population of smokers without those excluded because of discontinuation of the study [n = 262, P for trend: 0.02 (one-sided)], and 19%, 27% and 35% in completers [P for trend: 0.03 (one-sided)], in the placebo, lazabemide 100 mg/day and lazabemide 200 mg/day groups, respectively. Point prevalence abstinence (intent-to-treat population) at the end of treatment (week 8) was 17%, 19% and 30% in the placebo, lazabemide 100 mg/day and lazabemide 200 mg/day groups, respectively (placebo vs. lazabemide 200 mg/day: P = 0.01, one-sided). No treatment emergent major adverse event occurred. More nausea and insomnia were reported with lazabemide than with placebo. Conclusions MAOB inhibitors are promising treatments as an aid in smoking cessation. There may be an interest to develop MAOB inhibitors with an acceptable toxicity profile. Further studies may associate MAOB inhibitors with nicotine replacement therapies to increase therapeutic efficacy.

Case-Control study of dopamine transporter-1, monoamine oxidase-B, and catechol-O-methyl transferase polymorphisms in Parkinson's disease

Abstract: We investigated the association of Parkinson's disease (PD) with dopamine transporter-1 (DAT1), monoamine oxidase-B (MAO-B), and catechol-O-methyltransferase (COMT) gene polymorphisms. Overall, we observed no significant association of PD with the DAT1-3'-variable numbers of tandem repeats, the MAO-B-(GT)(n), and the COMT-Val108Met gene polymorphisms in a sample of 319 unrelated PD cases and 196 control subjects. Analyses stratified by sex, age at examination, family history of PD, and ethnic origin also yielded negative findings, with three exceptions. We found statistically significant associations of PD with MAO-B polymorphisms in older patients and with a COMT polymorphism in younger subjects and in women. These significant differences at the two-tailed alpha level of 0.05 and restricted to subgroup analyses may have a biological basis or may be chance findings.

Gender difference in the interaction of smoking and monoamine oxidase B intron 13 genotype in Parkinson's disease

Abstract: We tested for gender-specific interactions between smoking and genetic polymorphisms of monoamine oxidase B (MAO-B) intron 13 (G or A allele), monoamine oxidase A (MAO-A) EcoRV (Y or N allele), and dopamine D2 recepor (DRD2) Taq1B (B1 or B2 allele) in a case-control study of 186 incident idiopathic Parkinson’s disease (PD) cases and 296 age- and gender-matched controls. The odds ratios (ORs) for PD risk for ever smokers versus never smokers were 0.27 (95% CI: 0.13–0.58) for men of genotype G, and 1.26 (0.60–2.63) for men of genotype A (interaction χ2=8.14, P=0.004). In contrast, for women, the OR for ever smokers versus never smokers were 0.62 (95% CI: 0.25–1.34) and 0.64 (95% CI: 0.18–2.21) for women of genotype GG/GA and AA, respectively (interaction χ2=0.001, P=0.975). No interactions were detected between smoking and either MAO-A EcoRV or DRD2 Taq1B genotypes. These results suggest that a strong gender difference exists with respect to the modifying effect of MAO-B genotype on the smoking association with PD.

Neurochemical and Neuroprotective Effects of Some Aliphatic Propargylamines: New Selective Nonamphetamine‐Like Monoamine Oxidase B Inhibitors

Abstract: Aliphatic N-propargylamines have recently been discovered to be highly potent, selective, and irreversible monoamine oxidase B (MAO-B) inhibitors. N-Methyl-N-(2-pentyl)propargylamine (M-2-PP) and N-methyl-N-(2-hexyl) propargylamine (2-HxMP), for example, are approximately fivefold more potent than I-deprenyl at inhibiting mouse brain MAO-B activity following oral administration. These inhibitors are nonaromatic compounds and are chemically quite different from other known MAO-B inhibitors. Some of their neurochemical and neuroprotective properties have been evaluated and compared with those of I-deprenyl. We have confirmed that these new inhibitors selectively inhibit MAO-B activity both in vitro and in vivo. 2-Phenylethylamine levels were substantially increased following administration of M-2-PP, but the levels of dopamine, 3,4-dihydroxyphenylacetic acid, homovanillic acid, 5-hydroxytryptamine, and 5-hydroxyindoleacetic acid were not affected except at high, nonselective doses. Chronic oral administration of I-deprenyl and M-2-PP causes selective inhibition of MAO-B activity and increases dopamine levels in mouse caudate. M-2-PP, like I-deprenyl, has been shown to be potent in protecting against MPTP-induced damage in the mouse. N-(2-Chloroethyl)-N-ethyl-2-bromobenzylamine (DSP-4), a noradrenaline neurotoxin, is not an MAO substrate. Its noradrenaline-depleting effects were substantially mitigated by I-deprenyl as well as by M-2-PP and 2-HxMP in the mouse hippocampus. Administration of 2-phenylethylamine, however, failed to reverse the effect of DSP-4. The neuroprotective effect of M-2-PP and 2-HxMP is apparently unrelated to the uptake of DSP-4.

Influence of C terminus on monoamine oxidase A and B catalytic activity.

Abstract: Monoamine oxidase (MAO) A and B play important roles in the metabolism of neurotransmitters and dietary amines. The domains important for enzyme specificities were studied by construction of chimeric MAOA/B enzymes. Exchange of the N-terminal 45 amino acids of MAOA with the N-terminal 36 residues of MAOB (chimeric enzymes B 36 A and A 45 B) resulted in the same substrate and inhibitor sensitivities as the wild-type MAOA or B. Thus, the N terminus may not be responsible for MAOA or B enzyme specificities. When MAOB C-terminal residues 393-520 were replaced with MAOA C-terminal residues 402-527 (chimeric B 393 A) catalytic activity was not detectable. Chimeric B 393 A consists of eight residues with different charges, three less proline residues (458, 476, and 490), and one additional proline at 518 compared with wild-type MAOB. These differences may have induced conformational changes and affected MAOB catalytic activity. Thus, the C terminus of MAOB is critical for maintaining MAOB in an active form. It is interesting that when the C terminus of MAOA was switched with MAOB (chimeric A 402 B), little effect was observed on MAOA catalytic activity. This new information is valuable for further studies of the structure and function relationship of this important enzyme.

PET imaging of monoamine oxidase B in peripheral organs in humans.

Abstract: Monoamine oxidase (MAO) regulates neurotransmitter concentration in the brain and is also an important detoxifying enzyme in peripheral organs. It occurs in 2 subtypes, MAO A and MAO B. Their relative ratios in different organs are variable, depending on the particular organ and species, making it difficult to extrapolate measures from animals to humans. The purpose of this study was to investigate the feasibility of imaging MAO B in peripheral organs in humans with PET. Methods: Nine healthy subjects (7 males, 2 females; mean age ± SD, 37 ± 7 y) received 2 dynamic PET studies of the torso area 2 h apart with 11C-l-deprenyl and deuterium-substituted 11C-l-deprenyl (11C-l-deprenyl-D2). Time-activity curves for heart, lungs, liver, kidneys, and spleen and arterial plasma input were measured for each study. The uptake at plateau and the incorporation quotient (IQ = uptake/plasma input) as well as model terms K1 (which is a function of blood flow) and k3 and λk3 (which are kinetic terms proportional to MAO B) were compared to identify organs that showed reduced values with deuterium substitution (deuterium isotope effect) characteristic of MAO B. In addition, a sensitivity analysis compared the 2 tracers with respect to their ability to quantify MAO B. Results: Heart, lungs, kidneys, and spleen showed a robust deuterium isotope effect on uptake, IQ, k3, and λk3. The arterial plasma input function was significantly larger for 11C-l-deprenyl-D2 than for 11C-l-deprenyl. Liver time-activity curves were not affected by deuterium substitution and model terms could not be estimated. In organs showing an isotope effect, λk3 showed the rank order: kidneys ≥ heart > lungs = spleen. A sensitivity analysis showed that 11C-l-deprenyl-D2 is a better index of MAO activity than 11C-l-deprenyl. Conclusion: This study demonstrates that (a) the deuterium isotope effect is useful in assessing the binding specificity of labeled deprenyl to peripheral MAO B; (b) MAO B can be visualized and quantified in the heart, lungs, kidneys, and spleen but not in the liver; (c) with the exception of the liver, which cannot be measured, MAO B activity is highest in the kidneys and heart; and (d) quantitation in organs having high levels of MAO B is improved by the use of 11C-l-deprenyl-D2, similar to prior studies on the brain. This study indicates that 11C-l-deprenyl-D2 will be useful for measuring the effects of different variables, including tobacco smoke exposure on MAO B activity in peripheral organs in humans.