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Biomedical subjects

M Da Prada

Publications and source records attributed to M Da Prada.

At least 55 records · Page 3Linked to original sources
PubMed1990

Simple automated high-performance liquid chromatographic column-switching technique for the measurement of dopa and 3-O-methyldopa in plasma.

A reliable assay procedure for the determination of 3,4-dihydroxyphenyl-L-alanine (dopa) and its O-methylated metabolite 3-O-methyldopa (3-OMD) is described. Supernatants from deproteinized plasma samples were directly injected into a column-switching system, allowing on-line prepurification of the samples by cation-exchange chromatography followed by reversed-phase high-performance liquid chromatography with electrochemical detection. With this method, the detector response was linear from endogenous levels of dopa and 3-OMD up to microgram concentrations. This technique combines the simplicity of direct injection methods with advantages of procedures using a sample clean-up. It represents a valid tool for the rapid and accurate measurement of large numbers of plasma samples in animals treated with levodopa and in clinical trials with new levodopa formulations.

Animals↗
PubMed1990

Binding of [3H]dihydrotetrabenazine and [125I]azidoiodoketanserin photoaffinity labeling of the monoamine transporter of platelet 5-HT organelles.

The carrier for 5-hydroxytryptamine (5-HT) of the 5-HT storage organelles of blood platelets was characterized by [3H]dihydrotetrabenazine binding and [125I]azidoiodokentanserin photoaffinity labeling. [3H]Dihydrotetrabenazine bound with high affinity to membrane preparations from different animal species. The [3H]dihydrotetrabenazine Bmax value was about 10-fold higher in rabbit (9.4 +/- 1.3 pmol/mg protein) than in human, rat and guinea-pig preparations (Bmax values = 1.1 +/- 0.2, 1.2 +/- 0.1 and 0.52 +/- 0.06 pmol/mg protein, respectively). After rabbit platelet subcellular fractionation, [3H]dihydrotetrabenazine binding was highly enriched in the fraction corresponding to pure 5-HT organelles, whereas ligand binding was much lower in the other subcellular fractions. Conversely, [3H]paroxetine binding sites were more concentrated in the lower density fractions, with no binding to the 5-HT granules. In competition experiments, [3H]dihydrotetrabenazine binding to human platelet membranes and rabbit platelet 5-HT organelles was markedly inhibited by the benzo[a]quinolizine derivatives, tetrabenazine and Ro 4-1284, and by ketanserin. In isolated rabbit platelet 5-HT organelles, reserpine showed a relatively high IC50 (930 nM), but the presence of ATP increased its potency about 10-fold. Paroxetine, methysergide and carrier substrates had little or no effect. After photoaffinity labeling of rabbit 5-HT granules with [125I]azidoiodoketanserin, the radioactivity was incorporated into several polypeptides. The presence of Ro 4-1284, reserpine and ketanserin prevented the labeling of a polypeptide of 85 kDa. The data obtained suggest that this protein represents a component of the granular carrier which binds [3H]dihydrotetrabenazine.

Affinity Labels↗
PubMed1990

From moclobemide to Ro 19-6327 and Ro 41-1049: the development of a new class of reversible, selective MAO-A and MAO-B inhibitors.

This study describes the serendipitous discovery of moclobemide, a short-acting MAO-A inhibitor which is in an advanced stage of clinical development as an antidepressant. The short duration of action of this MAO inhibitor containing a morpholine ring moiety is due to the complete reversibility (probably by metabolism of the inhibitory molecular species) of MAO-A inhibition. Since moclobemide is much more effective in vivo than expected from its in vitro activity, investigations to identify a possible metabolite(s) more active as MAO-A inhibitor than the parent compound were carried out. The study of the MAO inhibitory characteristics of several known and putative moclobemide metabolites did not allow the identification of a potent MAO-A inhibitor but led to the discovery of Ro 16-6491, a potent MAO-B inhibitor of novel chemical structure. Systematic chemical modification of the aromatic ring system of Ro 16-6491 finally provided Ro 19-6327 and Ro 41-1049 which are highly selective and reversible inhibitors of MAO-B and MAO-A, respectively. Tritiated derivatives of Ro 19-6327 and Ro 41-1049 were used in binding studies to elucidate their mechanisms of action and to study their cellular distribution by quantitative enzyme radioautography.

Animals↗
PubMed1990

Monoamine oxidase inhibition by moclobemide and 2-amino-ethyl carboxamide derivatives: mode of action and kinetic characteristics.

The selective, reversible inhibitors of monoamine oxidase (MAO) moclobemide and Ro 41-1049 (selective for MAO-A), as well as of Ro 16-6491 and Ro 19-6327 (selective for MAO-B) inhibited the enzyme with an initial competitive phase, followed by a time-dependent inhibition of MAO. Ro 41-1049, Ro 16-6491 and Ro 19-6327, being activated by MAO into reversible adducts, fit into the classification as mechanism-based inhibitors. Conversely, since no product formation was observed after incubation of tissue homogenates with moclobemide, this drug probably belongs to the class of the "slow-binding" MAO inhibitors.

Animals↗
PubMed1990

MAO-B inhibition in rabbit tissues and in human platelets by Ro 19-6327 shows similar time-course.

In rabbits, 3 mg/kg Ro 19-6327 p.o., induced complete monoamine oxidase type B (MAO-B) inhibition in striatum, cerebral cortex, liver and platelets for about 12 h. In healthy human volunteers complete inhibition of platelet MAO was obtained with only 5 mg Ro 19-6327. After 40 and 200 mg Ro 19-6327 the duration of complete MAO-B inhibition was prolonged to 12 and 24 hours, respectively. Changes in brain MAO-B in humans after Ro 19-6327 are likely to be faithfully reflected by platelet MAO activity.

Animals↗
PubMed1990

Molecular neuroanatomy of MAO-A and MAO-B.

A selective, quantitative and high resolution technique (in vitro and in vivo enzyme radioautography) has been used to reveal the tissue distribution and abundance of MAO-A and MAO-B in the central nervous system and peripheral organs in the rat. The in vitro approach was also used to map the enzymes in human post-mortem brain. Furthermore, using in situ hybridization histochemistry, locus coeruleus and raphé neurons in the human brain were found to code for MAO-A and MAO-B respectively and not vice versa.

Animals↗
PubMed1990

Monoclonal antibodies recognizing both soluble and membrane bound catechol-O-methyltransferase.

Both cytosolic, soluble and membrane-bound catechol-O-methyl-transferase (COMT) from pig and rat liver or kidney were recognized by mouse monoclonal antibodies (MAbs) raised against soluble COMT isolated from pig liver. In ELISA, the MAbs Co 16 and Co 54 reacted better with the pig than with the rat enzyme. The MAb Co 60 showed good reactivity with both pig and rat COMT. In addition, all three MAbs recognize the soluble (23 kDa) as well as the membrane-bound (26 kDa) forms of the COMT enzyme.

Animals↗
PubMed1990

Ro 40-7592: inhibition of COMT in rat brain and extracerebral tissues.

A random biochemical screening followed by lead optimization culminated in the discovery of Ro 40-7592 3,4-dihydroxy-4'-methyl-5-nitrobenzophenone). Ro 40-7592 was found to inhibit COMT in a competitive fashion both in the CNS and in the periphery (Ki for the liver enzyme = 30 nM). Ro 40-7592 (30 mg/kg p.o.) combined with benserazide (15 mg/kg p.o.) and a low dose of L-DOPA (10 mg/kg p.o.) almost completely blocked (for about 6 h) the formation of 3-O-methyldopa (3-OMD) in brain and plasma, producing a long-lasting increase of L-DOPA in plasma and a parallel marked increase of L-DOPA and dopamine in the brain. Ro 40-7592, combined with peripheral decarboxylase inhibitors and L-DOPA (as in Madopar and Sinemet), will offer substantial advantages in the therapy of Parkinson's disease, i.e. enhanced bioavailability and prolonged plasma half-life of L-DOPA, pronounced DOPA sparing effect and blockade of 3-OMD formation.

Animals↗
PubMed1990

Effect of selective and reversible MAO inhibitors on dopamine outflow in rat striatum: a microdialysis study.

The effect of reversible inhibitors of the monoamine oxidase type A (MAO-A), moclobemide (Aurorix) and Ro 41-1049 (20 mg/kg i.p. each), as well as of reversible inhibitors of the MAO type B (MAO-B), Ro 19-6327 (1 mg/kg i.p.), on the outflow of dopamine (DA), 3,4-dihydroxyphenylacetic acid (DOPAC) and homovanillic acid (HVA) was studied in the rat by transstriatal microdialysis. Reversible MAO-A inhibitors markedly increased the output of DA and concomitantly decreased the output of DOPAC and HVA. These effects were absent with the highly selective MAO-B inhibitor Ro 19-6327.

3,4-Dihydroxyphenylacetic Acid↗
PubMed1990

The effects of lifelong treatment with MAO inhibitors on amino acid levels in rat brain.

In a previous paper a possible relationship had been suggested to exist between age-induced changes in total MAO activity and amino acid levels in some rat brain areas. To further investigate the possible involvement of MAO activity in changes of brain amino acid levels with aging, moclobemide and Ro 19-6327, short acting MAO-A and MAO-B inhibitors, respectively, were administered to female Wistar rats for their whole life-span. Brain amino acid levels in animals treated with MAO inhibitors were compared to those of young and old nontreated rats. The age-induced changes in brain amino acid concentrations found in the present study were in good agreement with those previously reported. Treatment with both moclobemide and Ro 19-6327 was found to restore taurine and serine concentrations in cortex and glutamine concentrations in cerebellum, to the same values as in young rats, to decrease cerebellum concentrations of serine and to increase taurine concentrations in hypothalamus. Administration of moclobemide brought aspartate concentrations in accumbens and cortex back to the same values as in young rats. A similar effect was observed on hypothalamus glutamate concentrations in rats treated with Ro 19-6327. Some possible causes and consequences of the correction of age-induced brain amino acid levels by chronic administration of MAO inhibitors are discussed.

Aging↗
PubMed1990

Some basic aspects of reversible inhibitors of monoamine oxidase-A.

A novel class of antidepressants is emerging with considerable therapeutic potential: reversible inhibitors of monoamine oxidase type A (RIMA). Moclobemide (Aurorix) is a representative RIMA. It is a fully and rapidly reversible inhibitor of MAO-A with a correspondingly intermediate duration of action in vivo. It is free of hepatotoxicity and produces a much weaker potentiation of the tyramine pressor effect than the classical irreversible MAO inhibitors. Interaction of MAO inhibitors and monoamine reuptake inhibitors with tyramine is discussed on the basis of experiments in conscious rats. The issue of tyramine content of foods and beverages has been reinvestigated and its relevance for treatment with RIMA antidepressants is discussed. Recently observed antihypoxic (neuroprotective) effects of moclobemide suggest new indications for this compound.

3,4-Dihydroxyphenylacetic Acid↗
PubMed1990

Comparison of monoamine oxidase-A inhibition by moclobemide in vitro and ex vivo in rats.

Inhibition of MAO activity was measured in rat brain homogenates using 5-HT as MAO-A substrate and phenylethylamine as MAO-B substrate. Moclobemide rather selectively inhibited MAO-A. Its inhibitory potency is rather low, like that of toloxatone, whereas clorgyline, harmaline, cimoxatone and brofaromine were all found to be at least 100 times more potent. Phenelzine, isocarboxazid and tranylcypromine were nonspecific, inhibiting MAO-A and MAO-B to about the same extent. The same drugs were also tested ex vivo. Here again moclobemide preferentially inhibited MAO-A; it was equipotent to clorgyline and brofaromine in these tests, and 2-4 times as potent as cimoxatone and harmaline. Moclobemide is a relatively weak MAO-A inhibitor in vitro and yet more potent in vivo than other reversible inhibitors, suggesting that the compound may be converted in vivo to an active form. Nevertheless, it has not been possible so far to identify activated derivatives, and recent findings that moclobemide markedly inhibits liver MAO-A within 5 min of an intravenous injection strongly suggests that the compound itself is responsible for the inhibition.

Animals↗
PubMed1990

Short-lasting and reversible inhibition of monoamine oxidase-A by moclobemide.

In ex vivo experiments, the time course of monoamine oxidase-A (MAO-A) inhibition after 10 mg/kg oral moclobemide was virtually the same for whole rat brains and liver: the onset was rapid, the maximum effect was obtained in 15 min, and the duration of action was short (about 16 h) compared with several days for the irreversible MAO inhibitors. The time course of MAO-B inhibition was peculiar: almost complete inhibition was obtained in the time only between the first and second hours, whereas in the whole brain, or various brain areas, maximum MAO-B inhibition (40%) did not occur until 2 h after drug administration. Inhibition in other peripheral organs, such as kidney and small intestine, was of even shorter duration (3 h). After even marked MAO-A inhibition in the liver by moclobemide, the activity recovered within about 4 h when the homogenate was dialysed against water or buffer at 37 degrees C. This rapid recovery is temperature-dependent and does not occur at 18 degrees C. The substance causing the marked inhibition of MAO-A activity when moclobemide is given is probably itself inactivated by the enzyme (reversibility by metabolism). It is expected that more insight into the mechanism of action of moclobemide will be obtained from the use of highly purified preparations of the MAO-A isoenzyme.

Animals↗
PubMed1990

Hypotensive action and weak potentiation of tyramine effect by moclobemide in rats.

Moclobemide belongs to a new class of reversible, selective monoamine oxidase-A (MAO-A) inhibitors; it is clinically well tolerated and has little liability to potentiate tyramine pressor effects. Measurement of blood pressure and heart rate in conscious, freely moving rats showed only a slight, nonsignificant decrease in mean arterial pressure in normotensive animals. However, in spontaneously hypertensive rats, moclobemide significantly decreased blood pressure by 20 mmHg within 30 min of oral intake of 30 mg/kg. In the same animals, heart rate was decreased by 20%; normal values returned after 2-3 h. Tyramine alone in oral doses up to 15 mg/kg had no effect on blood pressure in normotensive rats, and after treatment with 30 mg/kg moclobemide, tyramine at 5 mg/kg did not alter mean arterial pressure, whereas there was a significant increase after doses of tranylcypromine, toloxatone and brofaromine. Higher doses of tyramine (10-20 mg/kg) following moclobemide led to a rise of 30-40 mmHg in pressure, but this had disappeared within 20 min. This effect was almost completely eliminated by desipramine, suggesting that coadministration of a norepinephrine uptake inhibitor with a reversible MAO inhibitor is likely to reduce the risk of tyramine-induced hypertensive crisis. Thus, the authors conclude that moclobemide exerts only a slight hypotensive action in hypertensive rats, and differs from other MAO inhibitors in potentiating the pressor effect of tyramine only weakly.

Administration, Oral↗
PubMed1990

Species-specific biotransformation of moclobemide: a comparative study in rats and humans.

This study measured plasma concentration of moclobemide and 2 of its active metabolites in the rat after oral doses of 30 mg/kg moclobemide. The secondary amine metabolite Ro 16-3177 was found in rat plasma at all times investigated (up to 3 weeks); the peak concentration of 200 ng/ml was reached 15 min after administration of moclobemide. The primary amine 16-6491 was found after only 30 min at about 40 ng/ml, and remained at about one half to one third the level of the secondary amine. Unchanged moclobemide appeared in much higher concentrations than the metabolites initially, but declined rapidly to about the same level as Ro 16-3177 by 3 h. In the humans, peak concentrations of moclobemide were reached more slowly than in the rats, and neither of the amine metabolites was found in human plasma at any time. Metabolism of moclobemide, as has been shown for other morpholine compounds, is quantitatively different in rats and humans. Since the concentration of Ro 16-6491 in human plasma remains below the limit of detection, only a very weak inhibition of MAO-B is produced in human platelets, and moclobemide can thus be considered a selective MAO-A inhibitor in humans.

Administration, Oral↗