Search PubMed⌕ Search

Biomedical subjects

M Da Prada

Publications and source records attributed to M Da Prada.

At least 73 records · Page 4Linked to original sources
PubMed1990

Characterization of the binding of [3H]Ro 41-1049 to the active site of human monoamine oxidase-A.

The novel reversible and selective inhibitor of monoamine oxidase-A (MAO-A) Ro 41-1049 [N-(2-aminoethyl)-5-(m-fluorophenyl)-4-thiazole carboxamide HCl] shows inhibition characteristics similar to those of the structurally related reversible MAO-B inhibitors Ro 16-6491 and Ro 19-6327. In the present study, tritiated Ro 41-1049 was used as a high affinity ligand to study the binding characteristics of this inhibitor to MAO-A and its interactions with the enzyme. An homogeneous population of high affinity binding sites for [3H]Ro 41-1049 was found in membrane preparations from human frontal cortex and placenta (Kd = 16.5 +/- 1.4 and 64.4 +/- 19.2 nM, respectively). In frontal cortex the Bmax value for [3H]Ro 41-1049 (2.6 +/- 0.4 pmol/mg of protein) was about one third of the Bmax calculated for the MAO-B-selective ligand [3H]Ro 16-6491. The density of [3H]Ro 41-1049 binding sites in human placenta varied greatly in the different tissue samples investigated, showing an average Bmax of 101.7 +/- 36.5 pmol/mg of protein. Apparent binding equilibrium was reached after 1 hr of incubation at 37 degrees. At this temperature the binding was reversible, with a dissociation t 1/2 of about 35 min. At lower temperatures the radioactivity dissociation was much slower. Among the various drugs tested, only inhibitors of MAO-A were able to effectively prevent [3H]Ro 41-1049 specific binding. As previously reported for the MAO-B ligands [3H]Ro 16-6491 and [3H]Ro 19-6327, the analysis of the membrane-bound radioactivity showed that [3H]Ro 41-1049 was entirely recovered in the form of its aldehyde derivative, indicating that Ro 41-1049 was deaminated by MAO-A. The existence of a Ro 41-1049 adduct reversibly bound to the enzyme active site might explain the inhibition mechanism of this compound. The exposure of the radioligand-enzyme complex to NaBH3CN at pH 4.5 caused the irreversible covalent incorporation of about 70% of the specifically bound radioactivity into a 60-kDa polypeptide. This incorporation was dependent on the pH and on the amount of NaBH3CN added. The presence of MAO-A- but not MAO-B-selective inhibitors prevented the covalent incorporation of [3H]Ro 41-1049. The present results indicate that [3H]Ro 41-1049 is incorporated into a subunit of MAO-A, in the presence of NaBH3CN, and modifies a protein domain that is essential for the enzyme activity.(ABSTRACT TRUNCATED AT 400 WORDS)

Affinity Labels↗
PubMed1989

[3H]Ro 19-6327: a reversible ligand and affinity labelling probe for monoamine oxidase-B.

This study demonstrated the existence of specific binding sites for [3H]Ro 19-6327 in human platelet membranes. This compound is a novel, time-dependent inhibitor of monoamine oxidase type B (MAO-B) and is structurally closely related to [3H]Ro 16-6491. The density of the sites labelled with high affinity by [3H]Ro 19-6327 was similar to that observed in previous studies with [3H]Ro 16-6491 as ligand. Binding was reversible at 20 degrees C and showed a relatively slow dissociation (t1/2 = 220 min). The dissociation rate was markedly decreased (t1/2 = greater than 24h) at 0 degrees C. MAO-B, but not MAO-A inhibitors, effectively prevented the binding of [3H]Ro 19-6327. Like [3H]Ro 16-6491, [3H]Ro 19-6327 is recognized as a substrate by MAO-B, being eventually deaminated by the enzyme. Since the deaminated aldehyde derivative of Ro 19-6327 did not inhibit MAO-B, a still unidentified reversible adduct, formed at the MAO-B active site, might explain the high potency and selectivity of [3H]Ro 19-6327. Incubation of the radioligand-enzyme complex from platelet and brain membranes with NaBH3CN and acetic acid (to pH 4.5) caused the irreversible incorporation of the radioactivity into a single polypeptide as shown by SDS-PAGE analysis. This polypeptide had a molecular weight identical to that of the MAO-B subunit, i.e. 58,000. The presence of unlabelled MAO-B inhibitors in the incubation mixture prevented the covalent incorporation of [3H]Ro 19-6327. The irreversible MAO-B inhibitor, [3H] pargyline, labelled a protein with a molecular weight identical to the protein labelled by [3H]Ro 19-6327.(ABSTRACT TRUNCATED AT 250 WORDS)

Affinity Labels↗
PubMed1989

[Comparison of the new MAO-A inhibitors moclobemide, brofaromine and toloxatone with tranylcypromine in an animal experiment: significance for clinical practice].

The rat studies presented in this manuscript show that the new non-hydrazine compounds moclobemide, brofaromine and toloxatone have a profile typical of monoamine oxidase-A (MAO-A) inhibitors. These inhibitors are short-acting (16-24 h), reversible, non-hepatotoxic and have only low liability to potentiate tyramine pressor effects (cheese-effect). The present results in rats and the clinical trials provide evidence that moclobemide is an orally active MAO-A inhibitor which, due to its remarkably low tyramine potentiating pressor effects and to its lack of anticholinergic activity, has a very attractive pharmacological profile. In contrast to moclobemide, tranylcypromine is an irreversible and mixed MAO-A and MAO-B inhibitor with long-lasting effects. This hydrazine derivative is not devoid of hepatotoxic effects and markedly potentiates tyramine pressor effects. Moclobemide, being a particularly safe MAO-A inhibitor, seems to be an effective new compound for the therapy of exogenous and endogenous depressive states.

3,4-Dihydroxyphenylacetic Acid↗
PubMed1989

Preclinical profiles of the novel reversible MAO-A inhibitors, moclobemide and brofaromine, in comparison with irreversible MAO inhibitors.

Acceptance into clinical practice of monoamine oxidase (MAO) antidepressants requires unequivocal evidence that novel, non-hepatotoxic and reversible MAO-A inhibitors carry little or no risk of inducing severe hypertensive crises (cheese effect). This study summarizes the most relevant preclinical aspects which differentiate the novel reversible MAO-A inhibitors moclobemide and brofaromine, from previous irreversible MAO inhibitors of the old generation, particularly phenelzine and tranylcypromine. Moclobemide and brofaromine bear no chemical relation to irreversible inhibitors such as hydrazine derivatives (phenelzine) or aminocyclopropyl derivatives (tranylcypromine). Experiments in rats show that moclobemide and brofaromine increase the level of serotonin (5-hydroxytryptamine) and decrease that of 3,4-dihydroxyphenylacetic acid for only 16-24 hours. In vitro, moclobemide and brofaromine behave as mechanism-based, enzyme-activated inhibitors since their intrinsic inhibitory activity increases with the duration of their interaction with the enzyme in tissue homogenates. In contrast to irreversible monoamine oxidase inhibitors, which are much more potent in vitro than in vivo, moclobemide has the characteristic to be virtually equipotent in vitro and in vivo. MAO-A inhibition induced by moclobemide in the rat in vivo was rapidly reversed by simply incubating liver homogenates at 37 degrees C in the absence of the inhibitor, indicating a rapid metabolic inactivation of moclobemide in vitro. This reversibility is a distinctive feature of moclobemide, when compared with brofaromine or irreversible MAO inhibitors. Hepatotoxicity is not an inherent property of MAO inhibitors indeed, moclobemide or brofaromine, due to their chemical structures, cannot be converted into isopropyl hydrazine, the hepatotoxic metabolite of iproniazid suspected to induce liver necrosis. Results from preclinical and clinical investigations demonstrate that moclobemide and brofaromine, in contrast to tranylcypromine and phenelzine, very weakly potentiate the pressor effects of orally administered tyramine. In conclusion, the reversible MAO-A inhibitors moclobemide and brofaromine, due to their well-documented safety characteristics, to their lack of anticholinergic-effects and to their good tolerability, will provide innovative tools for clarifying the role of MAO-A inhibitors in the treatment of endogenous and atypical depressive states.

Animals↗
PubMed1989

Pre-clinical pharmacology of moclobemide. A review of published studies.

The novel antidepressant, moclobemide, is a reversible inhibitor of monoamine oxidase (MAO) preferentially of monoamine oxidise-A (MAO-A); it emerged for study out of a series of lipid-lowering agents. In spite of its weak MAO-A inhibition in vitro, moclobemide is a potent inhibitor of MAO-A, in vivo; its in vivo activity is of short duration, in contrast to the extremely long-lasting inhibition, e.g. by tranylcypromine. Moclobemide only slightly potentiates the pressor effect of oral tyramine in freely moving rats, again in contrast to tranylcypromine; it is not anti-cholinergic and is free of hepatotoxicity. Published evidence on the preclinical pharmacology is reviewed.

Animals↗
PubMed1989

Neurochemical profile of moclobemide, a short-acting and reversible inhibitor of monoamine oxidase type A.

Moclobemide belongs to a new generation of short-acting, reversible, monoamine oxidase (MAO) inhibitors. In vitro (rat brain homogenates) moclobemide inhibits MAO-A selectively with lower potency than many of the reference MAO inhibitors. However, when measured ex vivo in the rat, the potency of moclobemide is similar to that of reference compounds. In vivo the drug induces a dose-dependent, short-lasting (8-16 hr) and preferential inhibition of MAO-A in the brain and both MAO-A and MAO-B inhibition in extracerebral organs (liver, small intestine and kidney). In the extracerebral tissues of the rat moclobemide induces marked peripheral MAO-B inhibition due to rapid and extensive biotransformation of its morpholine ring. The active molecular species is probably the metabolite Ro 16-6491. The moderate MAO-B inhibition measured after moclobemide intake in human platelets indicates that only minor amounts of Ro 16-6491 are formed in humans. Virtually all metabolites of moclobemide so far identified have been tested in vitro and ex vivo in the rat and proved to be either equipotent or, mostly, less effective than moclobemide as MAO-A inhibitors. In liver homogenates of moclobemide-treated rats MAO-A activity recovers during dialysis or simple incubation at 37 degrees C, suggesting a biodegradation of moclobemide and/or the moclobemide-derived active metabolite(s) by MAO itself or a slow dissociation of the active inhibitory species from the enzyme. Similar to other MAO-A inhibitors, moclobemide induces an increase in the rat brain levels of 5-hydroxytryptamine, norepinephrine and dopamine and a concomitant decrease of their deaminated metabolites. These effects are of short duration (8-16 hr) and parallel the time course of MAO-A inhibition. Moclobemide administered subchronically down-regulates beta adrenoceptors as shown by binding experiments with brain cortical membranes using dihydroalprenolol as ligand. In vitro MAO inhibition by moclobemide is specific in that the compound does not affect other amine oxidases or monoamine uptake mechanisms; furthermore, it does not interact with various neurotransmitter or drug receptor sites. In conclusion, a large body of preclinical evidence characterizes moclobemide as a short-acting and reversible MAO-inhibitor. The neurochemical profile of moclobemide indicates clearly that this nonhydrazine nonhepatotoxic MAO-A inhibitor represents a novel and safe drug for treatment of affective disorders.

1-Methyl-4-phenyl-1,2,3,6-tetrahydropyridine↗
PubMed1989

Pharmacological profile of moclobemide, a short-acting and reversible inhibitor of monoamine oxidase type A.

The novel antidepressant moclobemide is a reversible inhibitor of monoamine oxidase (MAO), preferentially of type A. Moclomide was active in three animal models considered predictive for antidepressant activity: 1) it prevented dose-dependently akinesia and blepharospasm induced in mice and rats by Ro 4-1284, a short-acting amine releasing agent. Prevention of akinesia by moclobemide also depended upon the dose of Ro 4-1284. For comparison also, effects of cimoxatone, harmaline, tranylcypromine and clorgyline are presented: 2) in cats, it selectively and dose-dependently suppressed rapid eye movement sleep without disturbing the sleep-wakefulness cycle; and 3) in the behavioral despair test in mice, it decreased the immobility score to a similar degree as amitriptyline or imipramine. In addition, moclobemide potentiated 5-hydroxytryptophan-induced stereotypies in rats with a potency similar to cimoxatone and with a duration of action of less than 24 hr. Moclobemide had almost no effect on the spontaneous behavior in mice, rats, cats and monkeys. Only in higher doses, marginal sedation and slight impairment in motor performance were seen. Moclobemide did not prevent pilcarpine-induced salivation in mice, demonstrating the absence of anticholinergic activity. Blood pressure and heart rate of freely moving, spontaneously hypertensive rats were only slightly decreased for less than 3 hr. Moclobemide moderately potentiated the pressor effect of p.o. tyramine in rats. In conclusion, the reversible MAO inhibitor moclobemide is active in animal models sensitive to all major drugs used in the treatment of depression. In contrast to imipramine-like antidepressants, it lacks anticholinergic activity and it differs from classic MAO inhibitors by potentiating only weakly the pressor effect of p.o. tyramine.

2H-Benzo(a)quinolizin-2-ol, 2-Ethyl-1,3,4,6,7,11b-↗
PubMed1988

Dopamine D2 receptor stimulation inhibits inositol phosphate generating system in rat striatal slices.

Previous studies on the transduction mechanisms triggered by dopamine receptor stimulation have established that both D1 and D2 subtypes of dopamine receptors are linked to the adenylate cyclase system, the former in a stimulatory and the latter in an inhibitory manner. The present report provides the first evidence that stimulation of D2 receptors in rat brain tissue affects the turnover of polyphosphoinositides, as revealed by changes of the content of inositol phosphates. We found that the basal level of [3H]inositol trisphosphate, [3H]inositol bisphosphate and [3H]inositol monophosphate decreased following the stimulation of the D2 receptor. The rank order of potency was quinpirole (IC50 5 nM) greater than lisuride (IC50 8 nM) greater than RU 24213 (IC50 50 nM) greater than dopamine (IC50 200 nM). In contrast, selective D1 receptor stimulation by fenoldopam did not alter the inositol monophosphate, inositol bisphosphate and inositol trisphosphate content. The quinpirole effect was prevented by selective D2 antagonists, such as domperidone and L-sulpiride (both 5 microM) while it was unaffected by the selective D1 antagonist SCH 23390 (100 nM) and by the pharmacologically inactive D-isomer of sulpiride. Our data indicate that the activation of striatal D2 receptors leads to the inhibition of inositol phosphate production.

Animals↗
PubMed1988

Platelets as a model for neurones?

The multiple biochemical and pharmacological similarities existing between blood platelets and 5-hydroxytryptamine (5-HT)-containing neurones of the CNS point to the platelets as a reliable model for the biochemical characterization of 5-HT releasers and uptake blockers which interfere with the storage and the active carrier mechanism of 5-HT in the neurones, respectively. In addition, the affinity displayed by dopamine and by dopaminergic neurotoxin MPP+ for the platelet 5-HT transport and storage indicates also some similarities between platelets and the dopaminergic system of the CNS. Since human platelets contain almost exclusively monoamine oxidase type B (MAO-B), they can be used as a source for the purification and characterization of this human enzyme. Human platelets thus offer an excellent peripheral model to indirectly assess the degree and duration of MAO-B inhibition occurring in the CNS. To date, knowledge of the many biochemical mechanisms underlying platelet physiology is still fragmentary. In fact, the functional role of binding sites located on the platelet cytoplasmic membrane, i.e. their coupling to a specific transmembrane signalling mechanism, is still in need of a precise biochemical and physiological characterization.

Animals↗
PubMed1988

Effect of moclobemide, a new reversible monoamine oxidase inhibitor, on absorption and pressor effect of tyramine.

We determined in healthy subjects the pressor effect and the plasma level of free tyramine in response to intravenous and oral tyramine doses before and after therapeutic doses (3 X 100 mg/day) of moclobemide, a new reversible, preferential type A monoamine oxidase (MAO) inhibitor. In fasting subjects moclobemide increased the pressor effect of intravenously and orally administered tyramine; the tyramine dose-pressor curve was shifted to the left by factors of 2.4 and 4.1, respectively. No increase in systolic blood pressure occurred at free plasma tyramine concentrations lower than 70 ng/ml before, and 20 ng/ml after, moclobemide. Peak plasma tyramine concentrations increased dose-dependently after oral tyramine; after moclobemide similar peak plasma concentrations of tyramine were obtained with 2.6 times smaller doses of tyramine. Thus, the potentiation by moclobemide of the pressor effect of oral tyramine appears to be due to inhibition of tyramine first-pass metabolism, as well as to inhibition of tyramine catabolism by MAO within adrenergic nerve terminals. The peak concentrations of free tyramine in plasma and the concomitant increase of systolic blood pressure were significantly (p less than 0.01) smaller when tyramine was administered with a meal (before or after moclobemide) than when given with tap water. We conclude that at doses of 3 X 100 mg/day moclobemide induces only a mild potentiation of the pressor effect of tyramine. This potentiation is virtually absent under natural conditions when tyramine is given with a meal.

Absorption↗
PubMed1988

[3H]Ro 16-6491, a selective probe for affinity labelling of monoamine oxidase type B in human brain and platelet membranes.

[3H]Ro 16-6491 [N-(2-aminoethyl)-p-chlorobenzamide HCl], a reversible "mechanism-based" inhibitor of monoamine oxidase (MAO) type B, binds selectively and with high affinity to the active site of MAO-B in brain and platelet membranes. Under normal conditions, the binding of [3H]Ro 16-6491 is fully reversible. However, [3H]Ro 16-6491 could be irreversibly bound (covalently) to membranes by the addition of the reducing agent NaBH3CN to the sample and adjusting to pH 4.5 with acetic acid. No irreversible labelling occurred in the absence of NaBH3CN and at neutral pH. The presence of the irreversible MAO-B inhibitor l-deprenyl completely abolished the irreversible labelling of the membranes by [3H]Ro 16-6491. The selective inactivation of MAO-B, e.g., by l-deprenyl prevented the covalent incorporation of [3H]Ro 16-6491 whereas selective inhibition of the MAO-A by clorgyline was without effect. The covalent linkage to membranes of unlabelled Ro 16-6491 and Ro 19-6327 (a selective and reversible MAO-B inhibitor closely related to Ro 16-6491) after the addition of NaBH3CN at pH 4.5 irreversibly inactivated MAO-B activity whereas MAO-A activity was unaffected. Sodium dodecyl sulfate-polyacrylamide gel electrophoretic analysis of labelled membranes showed that [3H]Ro 16-6491 was incorporated into a single polypeptide with a molecular mass identical to the one labelled by [3H]pargyline (58 kilodaltons). Our results indicate that the polypeptide that is covalently labelled by [3H]Ro 16-6491 corresponds to one of the two MAO-B subunits.(ABSTRACT TRUNCATED AT 250 WORDS)

Affinity Labels↗
PubMed1988

Tyramine pressor effect in man: studies with moclobemide, a novel, reversible monoamine oxidase inhibitor.

The pressor effect of tyramine (TYR) administered i.v. and orally was measured in healthy volunteers during treatment with different therapeutic doses of moclobemide, a new, reversible, preferential type A monoamine oxidase inhibitor. With moclobemide 3 X 100 mg/day the systolic blood pressure (SBP) increase produced by TYR administered i.v. was potentiated 2.4-fold and that in response to TYR p.o. in the fasting state was increased 4.1-fold, as determined from equieffective TYR doses before and during moclobemide treatment. Peak concentrations of free TYR in plasma after oral doses of TYR were increased 2.6-fold, and a 2.5-fold smaller plasma TYR concentration produced the same SBP rise as before moclobemide treatment. No SBP increase was observed at plasma TYR concentrations below 20 ng/ml or after p.o. TYR does smaller than 80 mg. The potentiation of the pressor effect of i.v. TYR by single moclobemide doses up to 300 mg had disappeared 24 hrs after moclobemide administration. Peak TYR plasma concentration and concomitant SBP increments were considerably smaller when TYR was administered with a meal than when administered as a bolus with tap water, 2.1 times higher oral TYR doses being required to achieve similar peak TYR plasma concentration as in the fasting condition. The pressor effect of TYR was further, but only slightly, increased during treatment with moclobemide 3 x 200 mg/day, however SBP rises were again significantly smaller when TYR was given together with a meal. In contrast, tranylcypromine produced a 20 to 40-fold potentiation of the pressor effect of oral TYR and this potentiation was only slightly smaller when TYR was given with a meal. In conclusion the potentiation by moclobemide of the pressor response to oral TYR corresponds roughly to a fourfold left shift of the TYR dose-pressor response curve and is about 10 times less marked than after tranylcypromine. In real life situations, the ingestion of TYR in amounts less than 100 mg is highly unlikely to produce a clinically relevant blood pressure elevation.

Adult↗
PubMed1988

On tyramine, food, beverages and the reversible MAO inhibitor moclobemide.

The pathways for the biosynthesis and metabolism of tyramine are described as a basis for the discussion of the interaction between MAO inhibitors and tyramine. While a role of endogenous tyramine in the antidepressant action of MAO inhibitors remains purely hypothetical at this time, the mechanisms leading to the potentiation of the tyramine pressor effect ("cheese effect") are well known. Experiments in animals and man have provided concordant quantitative information on the effect of irreversible and some novel reversible MAO inhibitors on the presystemic disposition of orally ingested tyramine and on the noradrenaline-releasing action of tyramine in noradrenergic nerve terminals. There is a profound difference in the magnitude of tyramine potentiation between the irreversible inhibitor tranylcypromine and the reversible inhibitor moclobemide. A systematic analysis of the tyramine content of current European food and beverage is reported and serves as a rational basis for providing advice to patients on moclobemide. Most of the food and beverages analyzed contain less tyramine than previously reported and a few rules concerning rare cheeses with high tyramine content are sufficient to eliminate the risk of hypertensive crises.

Animals↗
PubMed1987

Effects of diethyl ether, halothane, ketamine and urethane on sympathetic activity in the rat.

The present paper describes the effects of different general anaesthetics on plasma catecholamine (CA) concentrations taken as biochemical index of peripheral sympathetic activity. In chronically catheterized rats, diethyl ether, ketamine and urethane increased plasma adrenaline (A) and noradrenaline (NA) concentrations, indicating that these drugs stimulate both neurosympathetic and adrenomedullary functions. These effects appear to be centrally mediated, since ganglionic blockade or spinal transection completely counteracted the diethyl ether- and ketamine-induced increases in plasma CA levels. Halothane induced a transient decrease in circulating A and an increase in NA. These results support the concept that general anaesthetics may have different effects on sympathetic function. Arterial blood pressure and heart rate were also measured to look for possible correlations with peripheral sympathetic activity. The enhanced release of peripheral CAs seemed to be the determining factor for increasing blood pressure and heart rate with ketamine only. In the other instances the activation of the peripheral sympathetic system appeared to maintain homeostasis by counterbalancing the various depressive effects of anaesthetics on the cardiovascular system.

Anesthetics↗
PubMed1987

Short-acting novel MAO inhibitors: in vitro evidence for the reversibility of MAO inhibition by moclobemide and Ro 16-6491.

The inhibition of monoamine oxidase (MAO) in rat liver and brain by the short-acting MAO-A inhibitors moclobemide (Ro 11-1163 = p-chloro-N-[2-morpholinoethyl]benzamide) and brofaremine and by the short-acting MAO-B inhibitors Ro 16-6491 (N-[2-aminoethyl]-p-chloro-benzamide) and almoxatone, administered p.o. at roughly equieffective doses 2 h before decapitation, was investigated for its reversibility under various in vitro conditions. MAO A activity in liver homogenates, inhibited by moclobemide (300 mumol/kg) to approx. 15% of control, time dependently recovered during 0.5 to 2 h of incubation at 37 degrees C, irrespective of whether the homogenates were prepared and incubated in distilled water or Krebs-Ringer buffer (KRB). Dialysis of such homogenates for 4 h in distilled water at 37 degrees C (but not at 13 degrees C) led to a complete return of the MAO activity. In liver homogenates from rats pretreated with brofaremine (30 mumol/kg), dialysis for 4 h at 37 degrees C against distilled water caused only little recovery of the MAO activity. Likewise, MAO-B inhibited by Ro 16-6491 (30 mumol/kg) to approx. 4% of control returned to almost control activity after 4 h of dialysis at 37 degrees C, while inhibition induced by almoxatone (30 mumol/kg) was little or not reversed at all. In brain homogenates prepared in, and dialysed against, distilled water or KRB at 37 degrees C (but not at 13 degrees C), MAO-A inhibited by moclobemide (100-300 mumol/kg) to approx. 15% of control, partially (KRB) or almost completely (dist. water) returned to control activity after 4 h of dialysis.(ABSTRACT TRUNCATED AT 250 WORDS)

Animals↗