Monoamine Oxidase B Inhibitory Activity Research Articles

A structural approach to investigate halogen substituted MAO-B inhibitors using QSAR modeling, molecular dynamics, and conceptual DFT analysis

Halogenated inhibitors showed robust, reversible, and selective monoamine oxidase-B (MAO-B) inhibitory efficacy in candidates that were derived from them. Our team has previously synthesized and assessed a panel of halogenated chalcones and coumarin for the study on MAO-B inhibition. The aim of this study was to build GA-MLR based QSAR models and predictive 3D Pharmacophore models, as well as to investigate the relationship between halogenated derivatives and MAO-B inhibitory activity. The robust statistical significance in the parameter (R2 = 0.78 and Q2 = 0.69) was demonstrated. Best Hypo1 contains one hydrophobic and two aromatic rings. The lead molecule for quantum mechanics was performed, and it was revealed that it would bind to proteins and provide stability. To determine the stability of the ligand-enzyme complex, a thorough molecular dynamics analysis of the lead compounds was accomplished.

Two dimensional-QSAR and molecular dynamics studies of a selected class of aldoxime- and hydroxy-functionalized chalcones as monoamine oxidase-B inhibitors

Candidates generated from unsaturated ketone (chalcone) demonstrated as strong, reversible and specific monoamine oxidase-B (MAO-B) inhibitory activity. For the research on MAO-B inhibition, our team has synthesized and evaluated a panel of aldoxime-chalcone ethers (ACE) and hydroxylchalcones (HC). The MAO-B inhibitory activity of several candidates is in the micro- to nanomolar range in these series. The purpose of this research was to develop predictive QSAR models and look into the relation between MAO-B inhibition by aldoxime and hydroxyl-functionalized chalcones. It was shown that the molecular descriptors ETA Shape P, MDEO-12, ETA dBetaP, SpMax1 Bhi and ETA EtaP B are significant in the inhibitory action of the MAO-B target. Using the current 2D QSAR models, potential chalcone-based MAO-B inhibitors might be created. The lead molecules were further analyzed by the detailed molecular dynamics study to establish the stability of the ligand–enzyme complex. Communicated by Ramaswamy H. Sarma

Design, synthesis, biological activity, molecular docking, and molecular dynamics of novel benzimidazole derivatives as potential AChE/MAO-B dual inhibitors.

To develop new acetylcholinesterase (AChE)-monoamine oxidase-B (MAO-B) dual inhibitors against Alzheimer's disease, the benzimidazole ring, which has a propargyl side chain with previously proven selective MAO-B inhibitory activity, was used as the main structure. Moreover, like donepezil, it was thought that the enzyme AChE would provide π-π interactions with the peripheral anionic side in this structure. Piperazine derivatives were chosen for the cationic active site. The synthesis of the compounds was carried out in five steps. The structures of the compounds were determined using 1 H-NMR (nuclear magnetic resonance), 13 C-NMR, and high-resolution mass spectrometry spectroscopic methods. First, the in vitro AChE, butyrylcholinesterase (BChE), MAO-A, and MAO-B inhibitory potentials of the obtained compounds were investigated. As a result of activity tests, compounds 5b, 5e, 5g, and 5h showed inhibitory activity against AChE; compounds 5e and 5g showed inhibitory activity against MAO-B. None of the compounds showed inhibitory activity against BChE or MAO-A. Compounds 5e and 5g showed dual inhibition. Among these compounds, compound 5g had inhibition potential similar to that of donepezil and selegiline. For compound 5g, further kinetic studies and Aβ-plaque inhibitory potentials were investigated using in vitro methods. Molecular docking studies were performed using both AChE and hMAO-B crystals to elucidate the compound's interactions with the enzyme active site. The binding modes of the compound on AChE were fully elucidated by molecular dynamics studies.

Design, synthesis and biological evaluation of potential anti-AD hybrids with monoamine oxidase B inhibitory and iron-chelating effects

A series of active hybrids combining 3-hydroxypyridin-4(1H)-one and coumarin pharmacophores were designed and synthesized as potential agents for the treatment of Alzheimer's disease (AD). All the compounds exhibited excellent iron-chelating activities (pFe3+ = 14.8–19.2) and showed favorable monoamine oxidase B (MAO-B) inhibitory effects compared to the reference drug Pargyline (IC50 = 86.9 nM). Among them, compound 11 g displayed the best MAO-B inhibitory activity with an IC50 value of 99.3 nM. Molecular docking analysis showed that compound 11 g could enter the entrance cavity and substrate cavity of MAO-B. Furthermore, the compound 11 g had an excellent antioxidant effect and was capable of protecting from the amyloid-β1-42 (Aβ1-42) induced PC12 cell damage. In silico tools were applied for predicting the blood–brain barrier (BBB) penetration and compound 11 g was proved to overcome the brain exposure challenge. In the mice behavioral study, compound 11 g significantly ameliorated cognitive impairment induced by Scopolamine. More importantly, compound 11 g displayed favorable pharmacokinetic profiles in a rat model. In summary, compound 11 g, with both anti-MAO-B and iron-chelating ability, was proved to be a promising potential anti-AD agent for further optimization.

Rational design, synthesis and biological evaluation of novel multitargeting anti-AD iron chelators with potent MAO-B inhibitory and antioxidant activity

A series of (3-hydroxypyridin-4-one)-coumarin hybrids were developed and investigated as potential multitargeting candidates for the treatment of Alzheimer's disease (AD) through the incorporation of iron-chelating and monoamine oxidase B (MAO-B) inhibition. This combination endowed the hybrids with good capacity to inhibit MAO-B as well as excellent iron-chelating effects. The pFe3+ values of the compounds were ranging from 16.91 to 20.16, comparable to more potent than the reference drug deferiprone (DFP). Among them, compound 18d exhibited the most promising activity against MAO-B, with an IC50 value of 87.9 nM. Moreover, compound 18d exerted favorable antioxidant activity, significantly reversed the amyloid-β1-42 (Aβ1-42) induced PC12 cell damage. More importantly, 18d remarkably ameliorated the cognitive dysfunction in a scopolamine-induced mice AD model. In brief, a series of hybrids with potential anti-AD effect were successfully obtained, indicating that the design of iron chelators with MAO-B inhibitory and antioxidant activities is an attractive strategy against AD progression.

8-Propyl-6H-[1,3]dioxolo[4,5-g]chromen-6-one: A new coumarin with monoamine oxidase B inhibitory activity and possible anti-parkinsonian effects

Parkinson’s disease is a common neurodegenerative disorder. In this study, the monoamine oxidase inhibitory activity and potential anti-parkinsonian effects of 8-propyl-6H-[1,3]dioxolo[4,5-g]chromen-6-one (FCS303), a new synthetic coumarin, were evaluated. To do this, we used the reserpine model of Parkinson’s disease, an assay of levodopa/carbidopa potentiation, the catalepsy model of haloperidol, and an in vitro assay against monoamine oxidase (MAO) activity. Additionally, lipid peroxidation and protein carbonyl group quantification was performed in mice brain homogenates previously treated with haloperidol. FCS303 inhibited monoamine oxidase B (MAO-B) with an IC50 of 5.46 ± 0.36 µM; however, there was no effect on monoamine oxidase A (MAO-A). The oral administration of FCS303 led to a significant reversal of hypokinesia in the reserpine model (at 24 h, doses of 100 and 200 mg/kg) and in the levodopa/carbidopa potentiation assay (at 2 and 24 h, dose of 200 mg/kg). In addition, FCS303 (100 mg/kg) showed anti-cataleptic activity against haloperidol. FCS303 (50 mg/kg) significantly decreased lipid peroxidation and protein carbonyl quantification. These results suggest that FCS303 could present anti-parkinsonian activity related to MAO-B inhibitory activity.

Synthesis of natural product-like polyprenylated phenols and quinones: Evaluation of their neuroprotective activities

Twenty-seven natural product-like polyprenylated phenols and quinones were synthesized and their neuroprotective activity was tested using human monoamine oxidase B (MAO-B) and SH-SY5Y cells. Eight compounds inhibited MAO-B (IC50 values < 25 μM) and the inhibition mode and molecular docking of two (8c and 16c) were investigated. Compounds inhibiting MAO-B activity were additionally tested for their ability to protect SH-SY5Y cells from peroxide injury. Three derivatives (3c, 8c and 16c) exhibited both MAO-B inhibitory and neuroprotective activity. A structure activity-relationship study showed that a phenolic hydroxyl group and a longer side chain are important for both activities.

Dual-target anti-Alzheimer’s disease agents with both iron ion chelating and monoamine oxidase-B inhibitory activity

MAO-B leads to an increase in the levels of hydrogen peroxide and oxidative free radicals, which contribute to the aetiology of the AD. Thus, both iron ion chelators and MAO-B inhibitors can be used to treat AD. Taking the coumarin derivatives and hydroxypyridinones as the lead compounds, a series of dual-target hybrids were designed and synthesised by Click Chemistry. The compounds were biologically evaluated for their iron ion chelating and MAO-B inhibitory activity. Most of the compounds displayed excellent iron ion chelating activity and moderate to good anti-MAO-B activity. Compounds 27b and 27j exhibited the most potent MAO-B inhibitory activity, with IC50 values of 0.68 and 0.86 μM, respectively. In summary, these dual-target compounds have the potential anti-AD activity.

Synthesis and evaluation of biaryl derivatives for structural characterization of selective monoamine oxidase B inhibitors toward Parkinson’s disease therapy

Benzyloxyphenyl moiety is a common structure of highly potent, selective and reversible inhibitors of monoamine oxidase B (MAO-B), safinamide and sembragiline. We synthesized 4-(benzyloxy)phenyl and biphenyl-4-yl derivatives including halogen substituents on the terminal aryl unit. In addition, we modified the carbon linker between amine group and the biaryl linked unit. Among synthesized compounds, 12c exhibited the most potent and selective MAO-B inhibitory effect (hMAO-B IC50: 8.9 nM; >10,000-fold selectivity over MAO-A) as a competitive inhibitor. In addition, 12c showed greater MAO-B inhibitory activity and selectivity compared to well-known MAO-B inhibitors such as selegiline, safinamide and sembragiline. In the MPTP-induced mouse model of Parkinson’s disease (PD), 12c significantly protected the tyrosine hydroxylase (TH)-immunopositive DAergic neurons and attenuated the PD-associated behavioral deficits. This study suggests characteristic structures as a MAO-B inhibitor that may provide a good insight for the development of therapeutic agents for PD.

Substantial protection against MPTP-associated Parkinson's neurotoxicity in vitro and in vivo by anti-cancer agent SU4312 via activation of MEF2D and inhibition of MAO-B

We have previously demonstrated the unexpected neuroprotection of the anti-cancer agent SU4312 in cellular models associated with Parkinson's disease (PD). However, the precise mechanisms underlying its neuroprotection are still unknown, and the effects of SU4312 on rodent models of PD have not been characterized. In the current study, we found that the protection of SU4312 against 1-methyl-4-phenylpyridinium ion (MPP+)-induced neurotoxicity in PC12 cells was achieved through the activation of transcription factor myocyte enhancer factor 2D (MEF2D), as evidenced by the fact that SU4312 stimulated myocyte enhancer factor 2 (MEF2) transcriptional activity and prevented the inhibition of MEF2D protein expression caused by MPP+, and that short hairpin RNA (ShRNA)-mediated knockdown of MEF2D significantly abolished the neuroprotection of SU4312. Additionally, Western blotting analysis revealed that SU4312 potentiated pro-survival PI3-K/Akt pathway to down-regulate MEF2D inhibitor glycogen synthase kinase-3beta (GSK3β). Furthermore, using the in vivo PD model of C57BL/6 mice insulted with 1-methyl-4-phenyl-1,2,3,6-tetrahydropyridine (MPTP), we found that intragastrical administration of SU4312 (0.2 and 1 mg/kg) greatly ameliorated Parkinsonian motor defects, and restored protein levels of MEF2D, phosphorylated-Ser473-Akt and phosphorylated-Ser9-GSK3β. Meanwhile, SU4312 effectively reversed the decrease in protein expression of tyrosine hydroxylase in substantia nigra pars compacta dopaminergic neurons, inhibited oxidative stress, maintained mitochondrial biogenesis and partially prevented the depletion of dopamine and its metabolites. Very encouragingly, SU4312 was able to selectively inhibit monoamine oxidase-B (MAO-B) activity both in vitro and in vivo, with an IC50 value of 0.2 μM. These findings suggest that SU4312 provides therapeutic benefits in cellular and animal models of PD, possibly through multiple mechanisms including enhancement of MEF2D through the activation of PI3-K/Akt pathway, maintenance of mitochondrial biogenesis and inhibition of MAO-B activity. SU4312 thus may be an effective drug candidate for the prevention or even modification of the pathological processes of PD.

Sembragiline: A Novel, Selective Monoamine Oxidase Type B Inhibitor for the Treatment of Alzheimer's Disease.

Monoamine oxidase B (MAO-B) has been implicated in the pathogenesis of Alzheimer's disease (AD) and other neurodegenerative disorders. Increased MAO-B expression in astroglia has been observed adjacent to amyloid plaques in AD patient brains. This phenomenon is hypothesized to lead to increased production of hydrogen peroxide and reactive oxygen species (ROS), thereby contributing to AD pathology. Therefore, reduction of ROS-induced oxidative stress via inhibition of MAO-B activity may delay the progression of the disease. In the present study we report the pharmacological properties of sembragiline, a novel selective MAO-B inhibitor specifically developed for the treatment of AD, and on its effect on ROS-mediated neuronal injury and astrogliosis in MAO-B transgenic animals. Sembragiline showed potent and long-lasting MAO-B-selective inhibition and did not inhibit MAO-A at doses where full inhibition of MAO-B was observed. Such selectivity should translate into a favorable clinical safety profile. Indeed, sembragiline neither induced the serotonin syndrome when administered together with the serotonin precursor l-5-hydroxytryptophan in combination with antidepressants such as fluoxetine, nor potentiated the pressor effect of tyramine. Additionally, in experiments using a transgenic animal model conditionally overexpressing MAO-B in astroglia, sembragiline protected against neuronal loss and reduced both ROS formation and reactive astrogliosis. Taken together, these findings warrant further investigation of the potential therapeutic benefit of MAO-B inhibitors in patients with AD and other neurologic disorders.

Subnanomolar indazole-5-carboxamide inhibitors of monoamine oxidase B (MAO-B) continued: indications of iron binding, experimental evidence for optimised solubility and brain penetration

Pharmacological and physicochemical studies of N-unsubstituted indazole-5-carboxamides (subclass I) and their structurally optimised N1-methylated analogues (subclass II), initially developed as drug and radioligand candidates for the treatment and diagnosis of Parkinson’s disease (PD), are presented. The compounds are highly brain permeable, selective, reversible, and competitive monoamine oxidase B (MAO-B) inhibitors with improved water-solubility and subnanomolar potency (pIC50 >8.8). Using a well-validated, combined X-ray/modelling technology platform, we performed a semi-quantitative analysis of the binding modes of all compounds and investigated the role of the indazole N1 position for their MAO-B inhibitory activity. Moreover, compounds NTZ-1006, 1032, and 1441 were investigated for their ability to bind Fe2+ and Fe3+ ions using UV-visible spectroscopy.

Synthesis and biological evaluation of novel propargyl amines as potential fluorine-18 labeled radioligands for detection of MAO-B activity

The aim of this project was to synthesize and evaluate three novel fluorine-18 labeled derivatives of propargyl amine as potential PET radioligands to visualize monoamine oxidase B (MAO-B) activity.The three fluorinated derivatives of propargyl amine ((S)-1-fluoro-N,4-dimethyl-N-(prop-2-ynyl)-pent-4-en-2-amine (5), (S)-N-(1-fluoro-3-(furan-2-yl)propan-2-yl)-N-methylprop-2-yn-1-amine (10) and (S)-1-fluoro-N,4-dimethyl-N-(prop-2-ynyl)pentan-2-amine (15)) were synthesized in multi-step organic syntheses. IC50 values for inhibition were determined for compounds 5, 10 and 15 in order to determine their specificity for binding to MAO-B. Compound 5 inhibited MAO-B with an IC50 of 664±48.08nM. No further investigation was carried out with this compound. Compound 10 inhibited MAO-B with an IC50 of 208.5±13.44nM and compound 15 featured an IC50 of 131.5±0.71nM for its MAO-B inhibitory activity. None of the compounds inhibited MAO-A activity (IC50 > 2μM).The fluorine-18 labeled analogues of the two higher binding affinity compounds (10 and 15) (S)-N-(1-[18F]fluoro-3-(furan-2-yl)propan-2-yl)-N-methylprop-2-yn-1-amine (16) and (S)-1-[18F]fluoro-N,4-dimethyl-N-(prop-2-ynyl)pentan-2-amine (18) were both prepared from the corresponding precursors 9A, 9B and 14A, 14B by a one-step fluorine-18 nucleophilic substitution reaction. Autoradiography experiments on human postmortem brain tissue sections were performed with 16 and 18. Only compound 18 demonstrated a high selectivity for MAO-B over MAO-A and was, therefore, chosen for further examination by PET in a cynomolgus monkey.The initial uptake of 18 in the monkey brain was 250% SUV at 4min post injection. The highest uptake of radioactivity was observed in the striatum and thalamus, regions with high MAO-B activity, whereas lower levels of radioactivity were detected in the cortex and cerebellum. The percentage of unchanged radioligand 18 was 30% in plasma at 90min post injection.In conclusion, compound 18 is a selective inhibitor of MAO-B in vitro and demonstrated a MAO-B specific binding pattern in vivo by PET in monkey. It can, therefore, be considered as a candidate for further investigation in human by PET.

Monoamine oxidase B (MAO-B) inhibition by active principles from Uncaria rhynchophylla

Attenuation of monoamine oxidase B (MAO-B) activity may provide protection against oxidative neurodegeneration. For this reason, inhibition of MAO-B activity is used as part of the treatment of Parkinson's and Alzheimer's patients. The hook of Uncaria rhynchophylla (Miq.) Jacks. (Rubiaceae) is a traditional Chinese herbal drug that is generally used to treat convulsive disorders. In this study, the fractionation and purification of Uncaria rhynchophylla extracts using a bioguided assay isolated two known compounds, (+)-catechin and (−)-epicatechin. The compounds inhibited MAO-B, as measured by an assay of rat brain MAO-B separated by electrophoresis on a 7.5% native polyacrylamide gel. The IC 50 values of (+)-catechin and (−)-epicatechin were 88.6 and 58.9 μM, respectively, and inhibition occurred in a dose-dependent manner, as measured by the fluorescence method. The Lineweaver–Burk plot revealed K i values for (+)-catechin and (−)-epicatechin of 74 and 21 μM, respectively. This suggests that these two compounds, isolated here for the first time from Uncaria rhynchophylla, might be able to protect against neurodegeneration in vitro, and, therefore, the molecular mechanism deserves further study. This finding may also increase interest in the health benefits of Uncaria rhynchophylla.

Is 10 milligrams selegiline essential as an adjunct therapy for the symptomatic treatment of Parkinson's disease?

Selegiline is used as an adjunct to levodopa in the symptomatic treatment of Parkinson's disease (PD). The normal daily dose of selegiline is 10 mg administered orally. This study, based on monoamine oxidase-B (MAO-B) inhibition, investigates whether a reduction in selegiline dose can provide the same beneficial effects seen with a 10-mg dose. The inhibition of platelet MAO-B activity against multiple dosing of selegiline (2.5, 5, and 7.5 mg) was predicted from the data obtained from literature (0.5, 1.0, 1.5, and 10 mg). A pharmacokinetic-pharmacodynamic model for selegiline was also developed. The data suggested that by 96 hours (four doses) the inhibition of platelet MAO-B activity is approximately 95% after a daily dose of 2.5 mg selegiline, whereas it takes only 48 hours (two doses) for doses of 5 mg and 7.5 mg to achieve this degree of inhibition. The pharmacokinetic-pharmacodynamic model was best described by a sigmoidal Emax model with an effect compartment. Based on the inhibition of MAO-B activity, a reduction in daily oral dose of selegiline appears possible without compromising the therapeutic effect. Therefore, lower doses of selegiline should be tested in clinical trials.

Antitumor effect of l-deprenyl in rats with carcinogen-induced mammary tumors

Deprenyl, a monoamine oxidase-B (MAO-B) inhibitor, has a wide range of pharmacological properties that are beneficial therapeutically in the treatment of human neurodegenerative diseases. Recent studies have demonstrated that deprenyl possesses a neuroprotective function that is not dependent on its MAO-B inhibitory activity. The focus of the present study was to investigate whether prolonged treatment of young Sprague–Dawley female rats with deprenyl before and after 9,10-dimethyl-1,2-benzanthracene (DMBA) administration would inhibit the development of mammary tumors by exerting a neuroprotective effect on the tuberoinfundibular dopaminergic (TIDA) neurons in the medial basal hypothalamus (MBH). For this purpose, the concentrations of catecholamines, indoleamine and their metabolites were measured in the MBH by high-performance liquid chromatography (HPLC) at the end of the treatment period. Female Sprague–Dawley rats (28–29 days old) were treated intraperitoneally with saline, or 0.25 or 2.5 mg of deprenyl/kg b.w. daily for 4 weeks prior to the administration of DMBA. Following the administration of DMBA, the rats were treated with saline or deprenyl daily for 27 weeks. At the end of the treatment period, there was a significant reduction in the tumor incidence and tumor number in rats that received 2.5 mg/kg deprenyl before and after the administration of DMBA and also in rats that were treated with 2.5 mg/kg deprenyl following DMBA. There also was a significant decrease in tumor number in rats that were treated with 0.25 mg/kg deprenyl during the entire treatment period of 31 weeks. Body weight increased throughout the treatment period with no significant differences between the groups. Treatment of rats with 2.5 mg of deprenyl following the administration of DMBA and also during the entire treatment period resulted in a significant decrease in the concentrations of the metabolites of norepinephrine (NE), dopamine (DA) and serotonin (5-HT) in the MBH, but there were no significant alterations in the concentrations of NE, DA and 5-HT in the MBH. These results suggest that the administration of deprenyl blocked the development of mammary tumors in part by inhibiting the metabolism of catecholamines and indoleamine and possibly by conferring a neuroprotective effect on the TIDA neurons in the MBH, especially at 0.25 mg/kg of deprenyl.

Metabolism of the newer antidepressants. An overview of the pharmacological and pharmacokinetic implications.

Several chemically unrelated agents has been developed and introduced in the past decade, to supplement the earlier antidepressants. These include inhibitors of the reuptake of serotonin [the selective serotonin reuptake inhibitors (SSRI)] or noradrenaline (reboxetine) or both (milnacipran and venlafaxine), as well as drugs with distinct neurochemical profiles such as mirtazapine, nefazodone, moclobemide and tianeptine. Like the earlier drugs, these newer antidepressants are almost totally biotransformed before excretion, except for milnacipran whose clearance appears to be due equally to both urinary excretion and metabolism. Sometimes--as in the case of moclobemide--up to 20 metabolites have been identified in body fluids. In some cases, however, only a few metabolites have been detected, and a substantial proportion of the dose remains unaccounted for (e.g. fluoxetine and fluvoxamine). Metabolism generally proceeds through sequential or parallel oxidative pathways. These may be affected to varying degrees by physiological and pathological factors and those mediated by cytochrome P450 (CYP) 2D6 and CYP2C19 through genetic polymorphism. Some are influenced by chirality (e.g. the dealkylation of citalopram and fluoxetine), although information on this aspect of disposition is still lacking for other drugs existing as racemates (e.g. mirtazapine and tianeptine) and milnacipran, which is probably a mixture of 4 stereoisomers. Others again are saturable within the therapeutic range of doses (e.g. some pathways of metabolism of fluoxetine, fluvoxamine, nefazodone, paroxetine and venlafaxine). This may explain the individual variability with all these drugs which, from the pharmacokinetic point of view, is the same as with tricyclic agents. Our knowledge of the isoenzymes involved in the various oxidation pathways and their relevance for potential drug interactions varies from a considerable amount for most of the SSRI and nefazodone, to minimal for reboxetine and tianeptine. This information is useful for predicting the pharmacokinetic interactions mediated through inhibition of specific isoenzymes. This would be better appreciated if the enzymatic mechanisms involved in the biotransformation of the metabolite(s), and their role in drug interactions, were also known. This information is still lacking for some drugs, although metabolites may exhibit in vitro inhibitory potencies of similar to (paroxetine and its M2 metabolite as inhibitors of CYP2D6) or even greater than that of the parent drug (norfluoxetine is more potent than fluoxetine as an inhibitor of CYP3A3/4, and in view of the longer half-life (t1/2) of the metabolite the potential for interactions may persist for weeks after discontinuation of the parent drug). While we do know something about the biological activity of the metabolites of some of these drugs, we know very little about others. With few exceptions this knowledge refers only to the major metabolite(s) and regards the main in vitro effects as exerted by the parent drug. However, in vitro potency and selectivity may not translate directly into in vivo, and either major or minor metabolites may have characteristic in vitro and in vivo properties. For example, unlike the parent drug some minor ring-opened metabolites of moclobemide have monoamine oxidase-B inhibitory activity in the rat, and the nefazodone metabolite m-chlorophenyl-piperazine shows activity on 5-HT2C receptors in rats and humans. Data on the brain-to-blood partition of metabolites compared with their parent drug are available only in a few cases. They are still not known for the main metabolites of fluvoxamine, milnacipran, mirtazapine, moclobemide, nefazodone, paroxetine, reboxetine and venlafaxine, despite the fact that total blood concentrations do not always reflect the metabolite: parent drug ratio in brain. Thus, in most cases, we do not really know what part hepatic metabolism plays in the overall effect of the administered parent drug.

The relationship between isatin and monoamine oxidase-B inhibitory activity in urine

We have investigated the correlation between urinary isatin concentration and MAO-B inhibitory activity. A sensitive enzyme-linked immunosorbent assay (ELISA) for the measurement of isatin in urine was developed. There was a strong correlation between isatin concentrations determined by this method and the established GC/MS technique. In two sets of urine samples from healthy individuals (N = 63 and N = 21), we have shown that there is no significant correlation between isatin concentration and MAO-B inhibitory activity (r = − 0.1013 and − 0.1597, respectively). Based upon IC50 measures, the concentration of isatin in normal urine (N = 10) was 3– 5 times less than that which could account for the detected MAO-B inhibitory activity. Furthermore, Lineweaver-Burk plots from urine samples (N = 12) compared with isatin showed that the inhibition by isatin was competitive whereas urine samples could elicit either mixed or non-competitive inhibition. We conclude that the MAO-B inhibitory activity in urine cannot be attributed to isatin alone and another inhibitor(s) appears to be present.

Effect of long-term treatment with L-deprenyl on the age-dependent microanatomical changes in the rat hippocampus

Chronic treatment with L-deprenyl increases both mean and maximum life span and improves cognitive functions in the aged rat. The present study was designed to evaluate whether long-term treatment with L-deprenyl at a dosage not inhibiting the monoamine oxidase-B (MAO-B) (1.25 mg/kg/day) or inhibiting the enzyme activity (5 mg/kg/day) had any effect on the age-dependent microanatomical changes in the rat hippocampus. The hippocampus was chosen in view of its key role in learning and memory functions. Treatment with L-deprenyl started at 19 months and lasted until the 24th month of age. Age-matched untreated rats were used as a control, whereas 11-month-old rats were used as an adult reference group. The number of nerve cell and glial fibrillary acidic protein-immunoreactive astrocyte profiles in the CA 1 and CA 3 fields of the hippocampus and in the dentate gyrus was decreased and increased, respectively in aged compared with adult rats. Treatment with 5 mg/kg/day, but not with 1.25 mg/kg/day L-deprenyl increased the number of neuronal profiles and decreased the number of astrocytes in the hippocampus of aged rats. The density of zinc stores in the associative intrahippocampal pathway of mossy fibres, which was decreased in aged animals, was increased after treatment with the two doses of L-deprenyl. Lipofuscin accumulation within the cytoplasm of pyramidal neurons of the hippocampus was reduced dose dependently by l-deprenyl treatment. These results suggest that long-term treatment with l-deprenyl is able to counter the expression of age-dependent microanatomical changes in the rat hippocampus. These effects seem only partially correlated with the MAO-B inhibitory activity of l-deprenyl.