Hepatic and extrahepatic metabolism of deprenyl, a selective monoamine oxidase (MAO) B inhibitor, of amphetamines in rats: sex and strain differences

The effect of deprenyl and isatin administration to mice on the proteomic profile of liver isatin-binding proteins

Isatin (indol-2,3-dione) is an endogenous indole found in the brain, peripheral tissues and biological body fluids of humans and animals. Its wide spectrum of biological activity is realized via interaction with numerous isatin-binding proteins; these include proteins playing an important role in the development of neurodegenerative pathology. In the context of the neuroprotective effect, the effect of isatin is comparable to the effects of deprenyl, a pharmacological agent used for treatment of Parkinson's disease. In this study, the effects of the course of deprenyl (1 mg/kg) and isatin (20 mg/kg) administration for 21 days on the profile of the isatin-binding proteins of the liver of mice have been investigated. Proteomic profiling of liver isatin-binding proteins of control mice by means of 5-aminocaproylisatin as an affinity ligand resulted in identification of 105 proteins. Treatment of animals with a low dose of isatin slightly decreased (up to 91), while injections of deprenyl slightly increased (up to 120) the total number of isatin-binding proteins. 75 proteins were common for all three groups; they represented from 62.5% (in deprenyl treated mice) and 71% (in control mice), to 82% (isatin treated mice) of the total number of identified liver isatin-binding proteins. Proteomic analysis of the isatin-binding proteins of mice treated with isatin (20 mg/kg) or deprenyl (1 mg/kg) for 21 days revealed a representative group of proteins (n=30) that were sensitive to the administration of these substances. Taking into account the previously obtained results, it is reasonable to suggest that the change in the profile of isatin-binding proteins may be attributed to accumulation of isatin and deprenyl in the liver and interaction with target proteins prevents their subsequent binding to the affinity sorbent. In this context, the identified isatin-binding liver proteins of control animals that do not bind to the affinity sorbent (immobilized isatin analogue) after treatment of animals with either deprenyl or isatin appear to be specific targets directly interacting with isatin in vivo.

Sex differences in baseline and drug-induced behavioural responses in classical behavioural tests

Behavioural pharmacology relies on animal models which are primarily validated using the male laboratory rat. Many researchers solely employ male animals in studies; this is primarily due to concerns about the impact of variations in the female estrous cycle on behavioural responses. The objective of the present study therefore was to examine whether sex has any effect in some commonly employed behavioural pharmacology tests. Male and female Sprague Dawley rats were examined in the following behavioural pharmacology tests: diazepam (DZP) effects on anxiolytic behaviour in the elevated plus maze (EPM); desipramine (DMI) effects on immobility time in the forced swim test (FST); amphetamine (AMP) and apomorphine (APO) effects on locomotor activity in the homecage monitoring apparatus (HCMA). Baseline investigations revealed that females were more active than males in all three tests. DZP increased open arm time and entries for males but not for females. Similarly, significant reduction in immobility time with DMI was found for males in the FST, with no effect observed in females. There was a significant effect of AMP dose on distance moved for both sexes; the peak locomotor stimulating effects were seen following 1-2 mg kg⁻¹ AMP doses for males, while 0.5 mg kg⁻¹ produced the greatest effect in females. APO impaired locomotor activity in both sexes. These results demonstrate that male and female rats respond differently to psychotropic drugs. The absence of female responses to the effects of DZP and DMI in the EPM and FST respectively was due to the high baseline activity levels seen with females; thus behavioural tests must be designed to account for sex differences in baseline behaviours to allow for unambiguous extrapolation of the results.

R-deprenyl: pharmacological spectrum of its activity

Deprenyl has been discovered by Knoll and co-workers. The R-enantiomer of deprenyl (selegiline) is a selective and irreversible inhibitor of the B-isoform of monoamine oxidase (MAO-B) enzyme. Due to its dopamine potentiating and possible neuroprotective properties it has an established role in the treatment of parkinsonian patients. By inhibiting MAO-B enzyme, R-deprenyl decreases the formation of hydrogen peroxide, alleviating the oxidative stress also reduced by increased expression of antioxidant enzymes (superoxide dismutases and catalase) reported during chronic treatment. It was shown to prevent the detrimental effects of neurotoxins like MPTP and DSP-4. R-Deprenyl elicits neuroprotective and neuronal rescue activities in concentrations too low to inhibit MAO-B. It is extensively metabolized and some of the metabolites possess pharmacological activities, thus their contribution to neuroprotective properties was also suggested. The recently identified deprenyl-N-oxide is extensively studied in our laboratory. Effects other than neuroprotection, like influencing cell adhesion and proliferation cannot be neglected.

Metabolic transformation plays a primary role in the psychostimulant-like discriminative-stimulus effects of selegiline [(R)-(-)-deprenyl]

l-Deprenyl [selegiline, (R)-(-)-deprenyl] is a selective inhibitor of monoamine oxidase B (MAO-B) used in the treatment of Parkinson's disease and proposed as an antidepressant and an aid for cigarette-smoking cessation and treatment of psychostimulant abuse. Beneficial therapeutic effects of (R)-(-)-deprenyl may also result from indirect actions. Brain levels of dopamine and beta-phenylethylamine (beta-PEA), a behaviorally active endogenous trace amine, increase after (R)-(-)-deprenyl treatment due to MAO-B blockade and (R)-(-)-deprenyl is metabolized to (R)-(-)-methamphetamine and (R)-(-)-amphetamine, suggesting that (R)-(-)-deprenyl may have psychostimulant-like behavioral effects. Indeed, (R)-(-)-deprenyl produces psychostimulant-like discriminative-stimulus effects in experimental animals. Here, we tested the hypothesis that psychostimulant-like behavioral effects of (R)-(-)-deprenyl are mainly mediated by its metabolites. Male Fisher F344 rats were trained to discriminate i.p. injection of 1.0 mg/kg (S)-(+)-methamphetamine or 10.0 mg/kg cocaine from injection of saline using two-lever choice schedules of food delivery or stimulus shock termination. When (R)-(-)-deprenyl was tested by substitution, it had (S)-(+)-methamphetamine- and cocaine-like discriminative-stimulus effects, but only at doses of 10 to 30 mg/kg, doses 10 to 20 times higher than those selective for MAO-B inhibition. Ro 16-6491 [N-(2-aminoethyl)-4-chlorobenzamide hydrochloride], a selective inhibitor of MAO-B enzyme activity without psychoactive metabolites, had no psychostimulant-like discriminative effects. In addition, blockade of (R)-(-)-deprenyl's metabolism with SKF 525A (beta-DEAE-diphenylpropylacetate hydrochloride; 50 mg/kg i.p.) reduced or eliminated (R)-(-)-deprenyl's psychostimulant-like discriminative effects. When beta-PEA synthesis was blocked by NSD 1015 (m-hydroxy-benzyl-hydrazine; 30 mg/kg i.p.), there was a modest reversal of (R)-(-)-deprenyl's psychostimulant-like discriminative effects under some conditions, indicating a facilitatory modulation of the psychostimulant-like discriminative effects of (R)-(-)-deprenyl metabolites by elevated levels of beta-PEA under certain conditions.

Effects of selegiline on antioxidant systems in the nigrostriatum in rat

Selegiline, a therapeutic agent of Parkinson's disease, is known to have neuroprotective properties that may involve its regulatory effects on antioxidant enzymes. We evaluated effects of selegiline on activities of catalase (CAT), Cu,Zn-superoxide dismutase (SOD1) and Mn-SOD (SOD2) in the striatum, cortex and hippocampus of 8- and 25-week-old rats, and on SOD activities and glutathione levels in mesencephalic slice cultures. Selegiline (2 mg/kg) significantly increased CAT and SOD2 activities in the striatum, but not in the cortex and hippocampus, of 25-week-old rats. In contrast, selegiline failed to increase CAT and SOD activities in three brain regions of 8-week-old rats, whereas L: -dopa significantly increased SOD1 activity in the striatum. In slice cultures, selegiline increased SOD1 and SOD2 activities with a maximal effective concentration of 10(-8) and 10(-10) M, respectively. Moreover, selegiline significantly increased glutathione level. These results suggest that selegiline can decrease oxidative stress in nigrostriatum by augmenting various antioxidant systems, each of which responds optimally to different concentrations of selegiline.

Comparative studies on the cytochrome p450-associated metabolism and interaction potential of selegiline between human liver-derived in vitro systems

Selegiline was used as a model compound in a project aimed at comparing, evaluating, and integrating different in vitro approaches for the prediction of cytochrome p450 (p450)-catalyzed hepatic drug metabolism in humans (EUROCYP). Metabolic predictions were generated using homology modeling, cDNA-expressed p450 enzymes, human liver microsomes, primary cultured human hepatocytes, and precision-cut human liver slices. All of the in vitro systems correctly indicated the formation of two dealkylated metabolites, desmethylselegiline and methamphetamine. The metabolic instability of selegiline was demonstrated by all of the in vitro systems studied. Estimates of clearance varied from 16 l/h to 223 l/h. With the exception of one approach, all systems underpredicted the in vivo clearance in humans (236 l/h). Despite this, all approaches successfully classified selegiline as a high clearance compound. Homology modeling suggested the participation of CYP2B6 in the demethylation of selegiline and of CYP2D6 in the depropargylation of the drug. Studies with recombinant expressed enzymes and with human hepatic microsomal fraction supported the involvement of CYP2B6 but not of CYP2D6. These techniques also suggested the involvement of CYP1A2, CYP2C8, and CYP2C19 in the biotransformation of selegiline. In vitro, CYP2B6 was the most active form of p450 involved in selegiline metabolism. Metabolism by several enzymes operating in parallel implies a low interaction potential for the drug. None of the techniques alone was able to predict all aspects of the metabolic and kinetic behavior of selegiline in vivo. However, when used as an integrated package, all significant characteristics were predictable.

Why (--)deprenyl prolongs survivals of experimental animals: increase of anti-oxidant enzymes in brain and other body tissues as well as mobilization of various humoral factors may lead to systemic anti-aging effects

(--)Deprenyl, a monoamine oxidase B (MAO B) inhibitor is known to upregulate activities of anti-oxidant enzymes such as superoxide dismutase (SOD) and catalase (CAT) in brain dopaminergic regions. The drug is also the sole chemical which has been repeatedly shown to increase life spans of several animal species including rats, mice, hamsters and dogs. Further, the drug was recently found to enhance anti-oxidant enzyme activities not only in brain dopaminergic regions but also in extra-brain tissues such as the heart, kidneys, adrenal glands and the spleen. We and others have also observed mobilization of many humoral factors (interferone (INF)-gamma, tumor necrosis factor (TNF)-alpha, interleukine (IL)-1beta,2,6, trophic factors, etc.) and enhancement of natural killer (NK) cell functions by (-)deprenyl administration. An apparent extension of life spans of experimental animals reported in the past may be better explained by these new observations that (-)deprenyl upregulate SOD and CAT activities not only in the brain but also in extra-brain vital organs and involve anti-tumorigenic as well as immunomodulatory effect as well. These combined drug effects may lead to the protection of the homeostatic regulations of the neuro-immuno-endocrine axis of an organism against aging.

Pharmacological interventions in aging and age-associated disorders: potentials of propargylamines for human use

Past studies including our own have confirmed that chronic administration of deprenyl can prolong life spans of at least four different animal species. Pretreatment with the drug for several weeks increases activities of superoxide dismutase (SOD) and catalase (CAT) in selective brain regions. An up-regulation of antioxidant enzyme activities can also be induced in organs such as the heart, kidney, spleen, and adrenal gland, and all are accompanied by an increase in mRNA levels for SODs in these organs. The effect of deprenyl on enzyme activities has a dose-effect relationship of a typical inverted U shape. A similar inverted U shape also has emerged for the drug's effect on survival of animals. An apparent parallelism observed between these two effects of the drug seems to support our contention that the up-regulation of antioxidant enzymes is at least partially responsible for the life-prolonging effect on animals. Further, when a clinically applied dose of the drug for patients with Parkinson's disease was given to monkeys, SOD and CAT activities were increased in striatum of these monkeys, which suggests potential for the drug's applicability to humans. The drug was also found to increase concentrations of cytokines such as interleukin-1beta (IL-1beta) and tumor necrosis factor-alpha (TNF-alpha) in the above rat organs. Together with past reports demonstrating that deprenyl increases natural killer (NK) cell functions and interferon-gamma, and prevents the occurrence of malignant tumors in rodents and dogs, the mobilization of these humoral factors may therefore be included as possible mechanisms of action of deprenyl for its diverse antiaging and life-prolonging effects. The potentials of propargylamines, (-)deprenyl in particular, for human use as antiaging drugs remain worthy of exploration in the future.

Common properties for propargylamines of enhancing superoxide dismutase and catalase activities in the dopaminergic system in the rat: implications for the life prolonging effect of (-)deprenyl

(-)Deprenyl has been reported to prolong the life span of different animal species. Further, the drug effectively increases antioxidant enzyme activities such as superoxide dismutase (SOD) and catalase (CAT) in brain dopaminergic regions. We have found that the effect of the drug on antioxidant enzyme activities is highly dose dependent, increasing with an increasing dose, however, a higher dose becomes less effective and an excessive dose becomes adversely effective. Most importantly, an optimal dose for the effect varies widely depending on animal species, strain, sex, age and duration of the treatment, which may at least partly explain discrepancies reported among different studies in the past. From the parallelism of the dose-effect relationship of the drug between life span extension and increasing endogenous antioxidant enzyme activity, we have suggested that the above two effects of (-)deprenyl may be causally related. This review summarizes our past series of studies and also reports our very recent observation that other propargylamines such as rasagiline and (R)-N-(2-heptyl)-N-methylpropagylamine (R-2HMP) also share the property of enhancing antioxidant enzyme activities. Further, our most recent study has found that these propargylamines increase antioxidant enzyme activities not only in brain dopaminergic regions but in extra-brain dopaminergic tissues such as the heart and kidneys. These observations are discussed in relation to the life prolonging effect of (-)deprenyl reported in the past.

Biotransformation of xenobiotics by amine oxidases

Although the cytochrome P450 (CYP) system ranks first in terms of catalytic versatility and the wide range of xenobiotics it detoxifies or activates to reactive intermediates, the contribution of amine oxidases and in particular of monoamine oxidases (MAOs) to the metabolism of xenobiotics is far from negligible but has been largely neglected. In this review on the involvement of amine oxidases in the metabolism of xenobiotics, the major characteristics reported for the CYP system (protein, reaction, tissue distribution, subcellular localisation, substrates, inhibitors, inducers, genetic polymorphism, impact of different physiopathological conditions on the activity, turnover) will be compared, whenever possible, with the corresponding characteristics of amine oxidases (MAOs in particular). The knowledge of the involvement of MAO-A, -B or both in the metabolism of a drug allows us to predict interactions with selective or non-selective MAO inhibitors (e.g. the metabolism of a drug deaminated by both forms of MAO is not necessarily inhibited in vivo by a selective MAO-A or -B inhibitor). If a drug is metabolized by MAOs, competitive interactions can occur with other drugs that are MAO substrates, e.g. with beta-adrenoceptor agonists and antagonists, prodrugs of dopamine, serotonin 5-HT1-receptor agonists as well as with primaquine, flurazepam and citalopram. Moreover, the knowledge of the involvement of MAOs in the metabolism of a drug may suggest possible, although not obligatory, interactions with tyramine-containing food or drink, with over the counter medicines sold to relieve the symptoms of coughs and colds (generally containing the indirectly-acting sympathomimetic amine phenylpropanolamine) or with phenylephrine-containing preparations. Finally, biotransformation by amine oxidases, as by CYP, does not always lead to detoxication but can produce toxic compounds.

Effects of MAO inhibitors upon MPTP mice chronically treated with suprathreshold doses of L-dopa

Groups of mice were administered either saline or 1-methyl-4-phenyl-1,2,3,6-tetrahydropyridine (MPTP) (2 X 40 mg / kg, s.c., separated by a 24-hour interval) 4-6 weeks prior to behavioural testing. At testing, all the MPTP-injected mice were repeatedly administered L-dopa (20 mg / kg, s.c., five times each week, Monday-Friday), by applying a procedure that induced a severe reduction of motor activity parameters from Day 1 to Day 25. Control (uninjected mice) received only saline and were retained only for neurochemical analysis. In each of three experiments, following the reduction of the activity-stimulating effects of L-dopa by repeated administration, a restorative effect of different monoamine oxidase (MAO) inhibitors was tested by co-administration of the test compounds (irreversible MAO-B inhibitor, reversible MAO-A inhibitors, or irreversible MAO-A / mixed MAO inhibitors) with L-dopa (20 mg / kg). In each case the MAO inhibitor was injected 60 min prior to L-dopa. L-Deprenyl (3 or 10 mg / kg, s.c.), in combination with L-dopa, reinstated locomotion and total activity, but not rearing, dose-dependently, in L-dopa-tolerant mice. The reversible MAO-A inhibitors, amiflamine and alpha-ethyltryptamine, in combination with L-dopa, reinstated locomotion and total activity, leaving rearing unaffected; Ro 41-1049 (3 mg / kg, s.c.) restored all three parameters of activity; locomotor activity was restored by all three doses (1, 3, and 10 mg / kg, s.c.). On the other hand, neither the irreversible MAO-A inhibitor, clorgyline, nor the mixed MAO inhibitor, phenelzine, produced any directly effective restorative increments. Neurochemical analysis confirmed the severe striatal dopamine depletion of MPTP-treated mice. These results demonstrate a synergistic and restorative action of combining certain MAO inhibitors, namely the reversible MAO-A inhibitors, with the suprathreshold dose of L-dopa in MPTP-treated, L-dopa-tolerant mice.

Cytochrome P450-dependent N-dealkylation of L-deprenyl in C57BL mouse liver microsomes: effects of in vivo pretreatment with ethanol, phenobarbital, beta-naphthoflavone and L-deprenyl

The monoamine oxidase inhibitor L-deprenyl [(-)-deprenyl, selegiline] is an effective therapeutic agent for improving early symptoms of idiopathic Parkinson's disease. It appears to exert this action independently of its inhibition of monoamine oxidase B (MAO-B) and some of its metabolites are thought to contribute. Cytochrome P450 (CYP) activities are known to give rise to L-deprenyl metabolites that may affect the dopaminergic system. In order to clarify the interactions of L-deprenyl with these enzymes, C57BL mice were treated with L-deprenyl, ethanol, phenobarbital or beta-naphthoflavone to induce different CYP isozymes. After preincubation of L-deprenyl with liver microsomes from control or treated mice, the metabolites were analysed by a GLC method. L-deprenyl (10 mg/kg i.p. for 3 days) caused a significant decrease in total CYP levels (0.315+/-0.019, L-deprenyl; 0.786+/-0.124, control, nmol/mg protein) and CYP2E1-associated p-nitrophenol hydroxylase activity (0.92+/-0.04 vs. 1.17+/-0.06 nmol/min/mg). Both phenobarbital and ethanol increased the N-depropynylation activity towards L-deprenyl that leads to the formation of methamphetamine (4. 11+/-0.64, phenobarbital; 4.77+/-1.15, ethanol; 1.77+/-0.34, control, nmol/min/mg). Ethanol alone increased the N-demethylation rate of L-deprenyl, that results in formation of nordeprenyl (3.99+/-0.68, ethanol; 1.41+/-0.31, control, nmol/min/mg). Moreover, the N-dealkylation pathways of deprenyl are inhibited by 4-methylpyrazole and disulfiram, two CYP2E1 inhibitors. None of the other treatments modified L-deprenyl metabolism. These findings indicate that mainly CYP2E1 and to a lesser extent CYP2B isozymes are involved in L-deprenyl metabolism. They also suggest that, by reducing CYP content, L-deprenyl treatment may impair the metabolic disposition of other drugs given in combination regimens.

Restoration and putative protection in Parkinsonism

Synergistic antiparkinsonian actions of different classes of putative therapeutic agents co-administered with a subthreshold dose of L-3,4-dihydroxyphenylalanine (L-Dopa) (5 mg/kg) in drug-naive 1-methyl-4-phenyl-1,2,3,6-tetrahydropyridine (MPTP)-treated mice as well as the restorative actions of those compounds in suprathreshold L-Dopa-tolerant MPTP-treated mice subjected to "wearing-off" of L-Dopa efficacy were assessed in a series of experiments. The classes of compounds studied included the noncompetitive NMDA antagonists, memantine, amantadine and MK-801, the anticonvulsive and putative anticonvulsive agents, lamotrigine, FCE 26743, phenytoin, the monoamine oxidase inhibitors, L-Deprenyl, amiflamine, alpha-ethyltryptamine, clorgyline and guanfacine. In this final case, the restorative effects of clonidine and guanfacine were antagonized by the alpha(2)-adrenoceptor antagonist, yohimbine, but not the alpha(1)-adrenoceptor antagonist, prazosin. Within each class of potentially therapeutic agents a differential restorative efficacy was obtained, but the combination of different doses of apomorphine with clonidine failed to restore motor activity. Finally, the neuroprotective actions of acute and subchronic administration of the nitrone spin-trapping compound, alpha-phenyl-tert-butyl nitrone upon the spontaneous motor behaviour and striatal dopamine concentrations of MPTP-treated mice was examined.

Association of cytochrome P450 induction with oxidative stress in vivo as evidenced by 3-hydroxylation of salicylate

1. Previous studies have shown that formation of 2,3-dihydroxybenzoate (2,3-DHB) from salicylate in vivo is a sensitive and specific marker of *OH radical generation, since 2,3-DHB is formed exclusively by *OH radicals, whereas both *OH radicals and cytochrome P450 (CYP) contribute to the production of 2,5-DHB. In the present study the salicylate-hydroxylation assay was used to examine whether CYP induction by the administration of dexamethasone, phenobarbital or beta-naphthoflavone to the male rat led to oxidative stress in vivo. 2. Dexamethasone was used under conditions that induced an approximately 50-fold induction of CYP P4503A expression in liver microsomal protein. Treatment with dexamethasone caused a 17.2-fold increase in 2,3-DHB plasma concentration compared with control animals. An increase in total hydroxylated salicylate (2,3-DHB plus 2,5-DHB) of 133.5 micromol/l plasma was produced, of which--assuming that the attack by *OH in position 3 or 5 of salicylate occurs at a similar rate--10.9 micromol/l were due to *OH radical attack and 122.6 micromol/l due to metabolism by CYP. 3. Phenobarbital led to a 4.7-fold increase in 2,3-DHB plasma concentration under conditions that induced CYP P4502B and 3A. An increase in total hydroxylated salicylate of 34.3 micromol/l plasma was observed, 2.0 micromol/l due to *OH radical attack and 32.3 micromol/l due to metabolism by cytochrome P450. 4. In contrast to dexamethasone and phenobarbital, beta-naphthoflavone did not cause a significant increase in 2,3-DHB plasma concentrations. 5. SKF 525A, a mixed-function oxidase inhibitor, caused a significant reduction of mean 2,5-DHB plasma concentration by 35% (p < 0.001), whereas 2,3-DHB was not significantly reduced, indicating that in contrast to the situation after induction by dexamethasone or phenobarbital, *OH radical generation by constitutive CYP contributes only to a minor degree to total in vivo *OH radical generation. 6. This study shows for the first time, to the authors' knowledge, that induction of some (but not all) P450s is associated with the production of hydroxyl radicals in vivo.

Biotransformation of deprenyl enantiomers

Rats were treated with either (-)- or (+)-deprenyl, and the metabolites extracted from the plasma, liver, kidney and heart homogenates were studied by chiral capillary electrophoresis (CE). Stereoselective dealkylation of both optical isomers with the formation of desmethyldeprenyl (DD), methamphetamine (MA), and amphetamine (A) was found. (-)-MA appears to be the main metabolite of (-)-D, and (+)-A for (+)-D. This suggests that the enantiomers undergo a different dealkylation process.

Gas-chromatographic study on the stereoselectivity of deprenyl metabolism

The metabolism and urinary elimination of both (-)-deprenyl and (+)-deprenyl have been studied. Gas-chromatographic analysis with mass specific detection indicated that the metabolism of (-)-deprenyl results in a large excess of methamphetamine compared to amphetamine, while the metabolism of (+)-deprenyl gave nearly equal amounts of amphetamine and methamphetamine. A novel deprenyl metabolite, phenylacetone, was also identified in our studies.

Urinary excretion of deprenyl metabolites

(+)-Deprenyl metabolites in rat's urine, such as nordeprenyl. methamphetamine amphetamine and p-hydroxy. methamphetamine were identified by HPLC-MS. After oral administration of 10 mg of pure (-)- and (+)-deprenyl to human volunteers, their urine was analyzed by gas chromatography. The concentration of methamphetamine was found to be overwhelming in the case of the (-)-isomer, while amphetamine and methamphetamine were excreted in equal amounts when (+)-deprenyl was administered. The metabolic processes of deprenyl resulted in metabolites possessing different lipophilicity, as it has been shown by planar displacement chromatography.

Absorption and presystemic metabolism of selegiline hydrochloride at different regions in the gastrointestinal tract in healthy males

PURPOSE

The absorption and disposition of selegiline (SEL) and its metabolites N-desmethylselegiline (DMS), L-methamphetamine (MET), and L-amphetamine (AMP) were assessed in 8 healthy male volunteers at proximal and distal regions of the intestine relative to oral administration (in the stomach) to determine if intestinal site dependence contributed to the erratic oral absorption of selegiline hydrochloride which is manifest as low and variable bioavailability.

METHODS

An open-label, four-way crossover, single dose pharmacokinetic study comparing the bioavailability of 10 mg selegiline hydrochloride administered to healthy young males as a solution by the oral route (in the stomach) and by a nasoenteric tube to the following three sites: duodenum, jejunum and terminal ileum was conducted. Infusions were administered over a 1 minute interval and a two week washout was observed between treatments. Samples were taken over 96 hours and analyzed by LC/MS/MS.

RESULTS

Selegiline exposure was greatest following administration to the stomach (approximately 150% > duodenum or jejunum) and least in the terminal ileum (approximately 33% less than duodenum or jejunum). Duodenal and jejunal sites were equivocal based on selegiline absorption and subsequent metabolism. While both AMP and MET exposure was equivalent at all dosing sites, DMS exposure was less (approximately 18%) at the terminal ileum.

CONCLUSIONS

The oral absorption of selegiline is neither permeability-limited or intestinal site-dependent. Stomach absorption may bypass presystemic metabolism. The reduced DMS exposure at the terminal ileum is consistent with the theorized presystemic formation of DMS via luminal P450 enzymes and the density of these enzymes in the duodenum and jejunum relative to the ileum. AMP and MET metabolites were insensitive to dosing site consistent with their hepatic formation. The true magnitude of these effects would require multiple dosing as single dose pharmacokinetics do not predict the extent of multiple dose selegiline exposure.

Long term treatment with (-)deprenyl reduces the optimal dose as well as the effective dose range for increasing antioxidant enzyme activities in old mouse brain

C57BL mice of the male sex received different doses of (-)deprenyl (0.25, 0.5, 1.0 mg/kg per injection 3 times a week, s.c.) for 3 months beginning at the age of 26 months. At the age of 29 months, animals were sacrificed and superoxide dismutase (SOD) and catalase (CAT) activities were examined in several brain regions. The dose of 0.5 mg/kg (3 times a week) was most effective in increasing SOD and CAT activities in S. nigra, striatum and cerebral cortex but not in hippocampus or cerebellum. The dose of 0.25 mg/kg was also effective in increasing enzyme activities, but the effect was much lower than the dose of 0.5 mg/kg. The magnitudes of increase in enzyme activities with the dose of 0.5 mg/kg, however, were generally much lower than respective values we previously found in animals treated with (-)deprenyl for only 3 weeks. The highest dose of 1.0 mg/kg had negligible effect. Enzyme activities in all groups of animals that were examined 2 weeks after the last (-)deprenyl dose were practically the same as respective control values. Together with the results from our previous study with short term (-)deprenyl treatment in old mice, these results replicate our previous findings in old female rats. We showed that longer term treatment with (-)deprenyl reduces the optimal dose for increasing antioxidant enzyme activities by a factor of 5 to 10. The present study further indicates that longer term treatment with (-)deprenyl also reduces the effective dose range of (-)deprenyl as well as the magnitude of increase of enzyme activities. If the effect of (-)deprenyl for increasing these antioxidant enzyme activities in selective brain regions is causally related to its effect of increasing average life expectancies of animals, the selection of a proper dose of the drug may be a critical factor for life span studies in which the drug, is administered for more than one year.

Synergistic interactions between COMT-/MAO-inhibitors and L-Dopa in MPTP-treated mice

Four experiments were performed to investigate the anti-akinesia effects of combining a sub-threshold dose (5 mg/kg, s.c.) of L-Dopa with different doses and combinations of COMT and MAO inhibitors upon the hypokinesia observed in MPTP-treated mice. Ro 40-7592 (1 and 3 mg/kg, s.c.), a novel COMT inhibitor, 60 min before L-Dopa reinstated both locomotion and rearing during a 2-hr interval after L-Dopa in MPTP mice; control mice were unaffected. The combination of Ro 40-7592 (3 mg/kg, s.c.) and pargyline (5 mg/kg, s.c.), a MAO inhibitor, with L-Dopa produced increases in both the peak effect and duration of action indicating a distinct potentiation of the effects of Ro 40-7592 by pargyline. L-Deprenyl, a MAOB inhibitor, together with L-Dopa, restored locomotion and rearing behaviour at all three doses applied (1, 3 and 10 mg/kg, s.c.); in control mice, motor activity was stimulated at the higher doses (3 and 10 mg/kg, s.c.), independent of L-Dopa administration. Combining L-Deprenyl (3 mg/kg, s.c.) with Ro 40-7592 (3 mg/kg, s.c.) one hr before L-Dopa to MPTP mice potentiated the restorative effects of each compound by itself, although no increase in peak effect was obtained. In the control mice, L-Deprenyl plus Ro 40-7592 or L-Deprenyl, by itself, stimulated motor activity following injection of L-Dopa. Marked dopamine (DA) depletions in the striatum of MPTP-treated mice were evident. The present results demonstrate that the effects of the COMT/MAO inhibitors in combination, and in conjunction with L-Dopa (at a dose that was without effect by itself), were well in excess of a summation of their individual effects. It was concluded therefore that a synergism of the restorative, anti-akinesic action of these compounds in MPTP-treated mice could offer a broader therapeutic spectrum in the treatment of Parkinson's disorder.

(-)Deprenyl increases the life span as well as activities of superoxide dismutase and catalase but not of glutathione peroxidase in selective brain regions in Fischer rats

(-)Deprenyl, a MAO-B inhibitor that is also known to be effective for symptoms of Parkinson's disease, when injected subcutaneously (sc) in male Fischer-344 rats at a dose of 0.5 mg/kg per day (3 times a week) from 18 months of age, significantly increased the remaining life expectancy. The average life span after 24 months was 34% greater in treated rats than in saline-treated control animals. Furthermore, a short-term (3 wk) continuous sc infusion of deprenyl significantly increased activities of superoxide dismutase and catalase but not of glutathione peroxidase in selective brain regions such as s. nigra, striatum, and cerebral cortex, but not in hippocampus or cerebellum, or the liver. The optimal dose for increasing these activities, however, differed greatly depending on the sex and age of animals, with a 10-fold lower value for young female than male rats. Interestingly, aging caused an increase and a decrease in the optimal dose in female and male rats, respectively. In addition, treatment for a longer term tended to reduce the optimal dosage in the same animal group. The results clearly demonstrate that deprenyl increases antioxidant enzyme activities in selective brain regions. If this effect of deprenyl is causally related to its life-prolonging effect, the dosage to be used for any life span study would be a critical factor, with the dosage differing widely depending on sex, age of animal, and mode and duration of drug administration.

Chronic L-deprenyl or L-amphetamine: equal cognitive enhancement, unequal MAO inhibition

The effect of chronic (4 month), subcutaneous injections of saline, L-deprenyl (0.25 mg/kg), or L-amphetamine (0.25 mg/kg) on the acquisition of a learned spatial habit in a modified Morris Water Maze was investigated in middle aged rats. Injections, given three times weekly starting at 6 months of age, were continued during behavioral testing, which occurred at 10 months of age. The cognitive performance of the middle aged rats was compared to that of 2-month-old control rats. Twenty-four hours after the last behavioral test, the rats were sacrificed and their brains were removed, dissected, and frozen in liquid nitrogen. The activities of MAO-A and MAO-B in the lateral cortex were determined. Results indicate that rats in the L-deprenyl group, the L-amphetamine group, and the young control group all learned the water maze task equally rapidly and significantly faster than rats in the saline group. MAO-A did not differ among the saline, amphetamine, and young control rats, but MAO-B was significantly higher in the middle aged saline and L-amphetamine rats than in the young controls. Both MAO-A and MAO-B activities were significantly lower in the L-deprenyl group than in the other three groups. This indicates that low-dose L-deprenyl can also inhibit MAO-A following chronic SC administration. Moreover, the improved cognitive performance produced by L-deprenyl may not be due to its ability to inhibit MAO-B, but rather to some other effect such as the activation of growth factors.(ABSTRACT TRUNCATED AT 250 WORDS)

Deprenyl alters behavior and caudate dopamine through an amphetamine-like action

In vivo microdialysis was used to concurrently measure the behavioral and caudate dopamine (DA) responses to the alleged irreversible type B monoamine oxidase inhibitor deprenyl. The effects were contrasted to those of the type A monoamine oxidase inhibitor, clorgyline. Consistent with its effects as an irreversible monoamine oxidase inhibitor, clorgyline produced an increase in DA concentration that remained elevated for at least 6 h. In contrast, the deprenyl-induced elevation in DA concentration occurred more rapidly, achieved a higher peak response, and then returned to baseline within 2 h following drug administration. The two drugs also produced distinctive changes in DA metabolite levels. Whereas the pattern of clorgyline-induced effects were consistent with irreversible monoamine oxidase inhibition, deprenyl produced an amphetamine-like response profile. Further, deprenyl but not clorgyline significantly increased locomotor activity. These results suggest that deprenyl does not augment caudate DA levels through monoamine oxidase inhibition. Rather, the pattern of its effects on caudate DA dynamics and behavior supports previous evidence that deprenyl produces its effects through its metabolism to amphetamine-like substances.

Pharmacokinetics and metabolism of selegiline

Selegiline is readily absorbed from the gastrointestinal tract. It is distributed rapidly into the tissues, including the brain. It is the L-form of selegiline that is an active MAO-B inhibitor, the D-(+)-form being 25 times less active. Selegiline is metabolised into L-(-)-desmethylselegiline (DES), L-(-)-amphetamine (A) and L-(-)-methamphetamine (MA), mainly in the liver. We measured the steady state concentrations of the metabolites in the serum and cerebrospinal fluid (CSF) of patients with Parkinson's or Alzheimer's diseases who were on continuous selegiline therapy. The mean concentrations in serum and CSF were similar, and were not affected by the addition of levodopa. The mean concentrations of patients with Alzheimer's or Parkinson's disease were 6.5 +/- 2.5 ng/ml for A, 14.7 +/- 6.5 ng/ml for MA and 0.9 +/- 0.7 ng/ml for DES. The metabolites of selegiline were excreted in urine, and the recovery as metabolites was 87%. Due to the stereospecificity and the low CSF concentrations of the (-)amphetamine metabolites during the therapy with 10 mg selegiline, these metabolites do not seem to contribute significantly to the clinical efficacy of selegiline.