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PubMed1999

Schizophrenia, monoamine oxidase activity, and cigarette smoking.

Reduced monoamine oxidase activity has been proposed as a marker for vulnerability to schizophrenia. Reduced monamine oxidase activity has also been shown to occur in cigarette smokers. This study compared monamine oxidase activity level in a matched group of patients with schizophrenia who smoked with a group who did not. Lower levels of monoamine oxidase activity were found in the smokers and this is the likely explanation for the low levels hypothesized as a marker for schizophrenia.

Adult↗
PubMed1976

Molecular turnover numbers of different forms of mitochondrial monoamine oxidase in rat.

Molecular turnover numbers of the different forms of monoamine oxidase in rat liver were estimated for serotonin, tyramine and beta-phenylethylamine by titration with irreversible inhibitors. The 'A' form was found to have a much higher turnover number for serotonin and a lower turnover number for beta-phenylethylamine than the 'B' form, while the turnover numbers for tyramine were in the same order of magnitude for both forms. The monoamine oxidase in the liver was found to have a significantly higher molecular turnover for tyramine and beta-phenylethylamine than that in the brain, heart and kidney. It was calculated that the 'A' form of monoamine oxidase amounted to about 20% and the 'B' form to about 80% of the total amount of monoamine oxidase in the rat liver mitochondrial preparation. The number of molecules per mitochondrion was also calculated.

Animals↗
PubMed1979

On hepatic mitochondrial monoamine oxidase activity in lipid deficiency.

A marked decrease in liver mitochondrial monoamine oxidase activity was noticed in rats fed a fat-free diet as compared with that of their controls. In lipid-deprived rats, the specific activity of this enzyme was very low towards different substrates studied. The activity of kynurenine 3-monooxygenase, which like monoamine oxidase is localized on the mitochondrial outer membrane, was similarly depressed under conditions of lipid deprivation. On the other hand no major changes were observed in the activity of the inner membrane enzyme, kynurenine amino-transferase. Mitochondria from fat-free diet-fed rats were deficient in essential fatty acids whereas no appreciable variations were found in the relative proportions of phospholipids in comparison with those of control mitochondria. Mitochondrial monoamine oxidase activity of the deficient rats retained its sensitivities to inhibitor drugs like clorgyline and deprenyl. No changes were noticeable in the substrate specificity of monoamine oxidase in these rats. When we switched the fat-free diet-fed rats to a diet supplemented with a source of essential fatty acids, there was an elevation in the activities of both monoamine oxidase and kynurenine 3-monooxygenase, their levels approaching those of the control rats.

Animals↗
PubMed2000

Hydrogen peroxide generation by monoamine oxidases in rat white adipocytes: role on cAMP production.

In rat, white adipocytes monoamine oxidases (EC 1.4.3.4.) generate hydrogen peroxide (H(2)O(2)). Recent studies suggested that, in addition to its toxic features, H(2)O(2) may behave as a cell second messenger. In the present study, using fluorimetric and chemiluminescence (CL) assays, we showed that tyramine degradation by monoamine oxidases in intact adipocytes resulted in the concentration-dependent generation of H(2)O(2). In addition, we found that, in the presence of low tyramine concentrations, forskolin-dependent cAMP production was significantly increased as compared to that of the control and this increase was prevented by the monoamine oxidase inhibitor pargyline or by the H(2)O(2) trapping system homovanillic acid-peroxidase. Finally, we demonstrated that tyramine degradation by monoamine oxidases increased the ability of isoproterenol to induce cell lipolysis. Taken together, these data suggest that H(2)O(2) produced during substrate degradation by monoamine oxidases may participate in the regulation of adipocyte metabolism.

Adipocytes↗
PubMed1964

MONOAMINE OXIDASE INHIBITORS: AUGMENTATION OF PRESSOR EFFECTS OF PERORAL TYRAMINE.

Monoamine oxidase inhibitors markedly enhance the oral pressor potency of tyramine by preventing it from being destroyed by the monoamine oxidase normally present in liver and intestine. Since certain types of cheese contain high concentrations of tyramine, they should not be eaten by patients during treatment with a monoamine oxidase inhibitor.

Blood Pressure↗
PubMedDate not supplied

[Study of monoamine oxidase from human placenta mitochondria by the chemoluminescence method].

The activity of monoamine oxidase from human placenta mitochondria was determined with 2-phenylethylamine and benzylamine as substrates by the generation of hydrogen peroxide in a conjugated luminol-peroxidase system, using the chemiluminescence method. The monoamine oxidase was found to oxidize at a high rate MAO substrates and revealed high sensitivity to clorgyline, a specific inhibitor of monoamine oxidase type A. It was shown that the use of the chemiluminescence technique for determining the monoamine oxidase activity gives the results that are fully consistent with those obtained by other methods.

Female↗
PubMed1982

Immunological studies of human monoamine oxidases.

Antisera have been raised against monoamine oxidase preparations from human placenta and platelets. These antisera have been employed to characterize membrane-bound enzyme from a variety of human sources including liver, heart, and brain. The comparisons were based on a displacement radioimmunoassay system with soluble placental monoamine oxidase, previously labelled specifically with [3H]pargyline, as antigen. All forms of enzyme investigated demonstrated immunological cross reaction; however, the placental enzyme appeared to possess determinants not exhibited by the enzyme from the platelets or other tissues examined.

Blood Platelets↗
PubMed1999

High expression of monoamine oxidases in human white adipose tissue: evidence for their involvement in noradrenaline clearance.

The clearance of plasma adrenaline and noradrenaline by human adipose tissue suggests the expression of the catecholamine-degrading enzyme monoamine oxidases and of catecholamine transport systems in adipocytes. In the present study, we identified and characterized the monoamine oxidases and an extraneuronal noradrenaline transporter expressed in human adipocytes. Enzyme assays using the monoamine oxidase A/B substrate [14C]tyramine showed that abdominal and mammary human adipocytes contain one of the highest monoamine oxidase activities in the body. Characterization of the enzyme isoforms by inhibition profiles of [14C]tyramine oxidation and Western and Northern blot analyses showed that mRNAs and proteins related to both monoamine oxidases A and B were expressed in adipocytes. Quantification of each enzyme isoform performed by enzyme assay and Western blot showed that monoamine oxidase A was predominant, representing 70-80% of the total enzyme activity. In uptake experiments, the monoamine oxidase substrate [3H]noradrenaline was transported into white adipocytes (Vmax 0.81+/-0.3 nmol/30 min/100 mg of lipid, Km 235+/-104 microM). The inhibition of [3H]noradrenaline uptake by specific inhibitors indicated that white human adipocytes contain an extraneuronal-type noradrenaline transporter. Competition studies of [14C]tyramine oxidation showed that noradrenaline is metabolized by monoamine oxidases in intact cells. In conclusion, the concomitant expression of monoamine oxidases and of a noradrenaline transporter in human white adipocytes supports the role of the adipose tissue in the clearance of peripheral catecholamines. These results suggest that adipocytes should be considered as a previously unknown potential target of drugs acting on monoamine oxidases and noradrenaline transporters.

Adipose Tissue↗
PubMed1985

The present status of monoamine oxidase inhibitors.

The present status of monoamine oxidase inhibitors in the treatment of depression is reviewed. With adequate doses they are effective antidepressants, but dosages have in the past been too low. Provided proper dietary precautions are taken, the incidence of fatality from dietary interactions is very small and should not deter doctors from using these drugs, especially in those depressed patients who do not respond to tricyclic-type antidepressants. The present status of combining monoamine oxidase inhibitors with tricyclics is discussed, as are the newer specific inhibitors particularly clorgyline and deprenyl.

Acetylation↗
PubMed1982

Clorgyline and deprenyl insensitive monoamine oxidase in rat brain soluble fraction.

A substantial percentage of monoamine oxidase activity was found in the soluble fraction of rat brain homogenates. The enzyme was not inhibited in vivo by high doses of clorgyline and deprenyl (12 mg/kg for 2 hr). Monoamine oxidase activity associated with the soluble fraction did not show the usual biphasic dose-response kinetics with clorgyline when kynuramine was used as the substrate. The present data show that there may be a new form of monoamine oxidase associated with the soluble fraction of the cell which has properties different from the two well-known monoamine oxidases A and B.

Animals↗
PubMed2006

Transdermal selegiline: the new generation of monoamine oxidase inhibitors.

The clinical use of monoamine oxidase inhibitors (MAOIs) has declined due to concerns about food and drug interactions and waning physician experience. Evidence indicates that MAOIs are effective in depressive disorders, in particular depression with atypical features. Efforts to address safety issues have led to the development of more selective and reversible MAOIs, such as moclobemide. Selegiline, a selective monoamine oxidase B inhibitor, has been approved for the adjunctive treatment of Parkinson's disease at low doses. At higher doses, oral selegiline is also effective in major depressive disorder (MDD) but loses its selectivity and has the potential for tyramine interactions. To overcome these problems, a transdermal formulation of selegiline, the selegiline transdermal system (STS), was developed with novel pharmacokinetic and pharmacodynamic properties. Compared with oral administration, transdermal selegiline leads to sustained plasma concentrations of the parent compound, increasing the amount of drug delivered to the brain and decreasing metabolite production. In addition, STS allows targeted inhibition of central nervous system monoamine A (MAO-A) and monoamine B isoenzymes with minimal effects on MAO-A in the gastrointestinal and hepatic systems, thereby reducing the risk of interactions with tyramine-rich foods (the "cheese-reaction"). Clinical trials have found 6 mg/24 hours of STS to be effective in MDD without the need for dietary restrictions. The efficacy and safety profile of STS supports its use in MDD. It is possible that STS may demonstrate benefit in MDD with atypical features or MDD resistant to other antidepressants. However, more research is needed. Clinicians should familiarize themselves with the properties and indications for the new generation of MAOIs.

Administration, Cutaneous↗
PubMed1994

Dopamine metabolism in the guinea pig striatum: role of monoamine oxidase A and B.

These studies were carried out to determine whether the greater abundance of monoamine oxidase B in the guinea pig affects the actions of (-)-deprenyl on dopamine metabolism in whole tissue or in extracellular fluid. The administration of (-)-deprenyl in doses that do not affect monoamine oxidase A activity (1-4 mg kg-1, 2 h) increases striatal 2-phenylethylamine and dopamine concentrations and reduces 3,4-dihydroxyphenylacetic acid. No effects were observed on striatal homovanillic acid, 5-HT and 5-hydroxyindole acetic acid. Inhibition of monoamine oxidase A with clorgyline with doses up to 8 mg kg-1 (2 h) does not affect striatal 2-phenylethylamine but increases dopamine and 5-HT concentrations and reduces 3,4-dihydroxyphenyl-acetic acid and 5-hydroxyindole acetic acid. (-)-Deprenyl (2-4 mg kg-1) did not change the extracellular concentrations of dopamine but the higher dose produced a limited reduction in extracellular 3,4-dihydroxyphenylacetic acid. Inhibition of monoamine oxidase A and monoamine oxidase B with pargyline (75 mg kg-1, 2 h) significantly increased the levels of extracellular dopamine and reduced those of their acid metabolites. These results show that in the guinea pig striatum inhibition of monoamine oxidase B by (-)-deprenyl impairs the metabolism of dopamine in the whole tissue but does not produce a marked increase in extracellular dopamine.

3,4-Dihydroxyphenylacetic Acid↗
PubMed1987

Effects of nondenaturating zwitterionic detergent CHAPS, 3-[(3-cholamido propyl) dimethyl ammonio]-1-propanesulfonate, on rat liver mitochondrial and microsomal monoamine oxidase.

It has been reported that monoamine oxidase (MAO) activity (EC1.4.3.4) and, in general, enzymes possessing cationic substrates, were activated and inhibited by anionic and cationic detergents, respectively. In order to examine this hypothesis, the effect of the zwitterionic detergent CHAPS 3-[(3-cholamido propyl) dimethyl ammonio]-1-propanesulphonate was studied in comparison with the effects of cationic, anionic, and non-ionic detergents. The non-denaturating zwitterionic detergent CHAPS was used to solubilise rat liver monoamine oxidase MAO (EC1.4.3.4) of mitochondrial and microsomal origin; the solubilisation conditions, purification, inhibition and kinetic studies were then determined. These results are compared with those previously obtained with the non-ionic detergent Triton X-100, which would also be expected to have no net charge, and are interpreted in terms of specific ionic effects.

Animals↗
PubMed1982

Platelet monoamine oxidase: specific activity and turnover number in headache.

Monoamine oxidase turnover numbers (molecules of substrate converted to product per minute per active site) have been calculated for the human platelet enzyme using [3H]pargyline. Headache patients with high and low monoamine oxidase specific activities relative to controls were found to have turnover numbers very close to those for controls. This finding suggests that their specific activities vary because of differences in the concentration of active monoamine oxidase molecules, rather than differences in the ability of those enzyme molecules to catalyse the deamination reaction.

Binding Sites↗
PubMed1988

Strain differences in systemic 1-methyl-4-phenyl-1,2,3,6-tetrahydropyridine neurotoxicity in mice correlate best with monoamine oxidase activity at the blood-brain barrier.

We measured monoamine oxidase activity in the cerebral cortex, striatum and brain microvessels of two mouse strains that differ in their susceptibility to systemic 1-methyl-4-phenyl-1,2,3,6-tetrahydropyridine (MPTP) neurotoxicity using specific pargyline binding and the rate of MPTP oxidation in vitro. We correlated these measurements with the results of in vivo experiments on: (i) the effect of MPTP on the striatal content of dopamine and its metabolites, and (ii) the regional brain accumulation of MPTP and its metabolites after systemic administration of tritiated MPTP. Results of the in vivo experiments do not correlate well with monoamine oxidase activity in the cerebral cortex and striatum, but correlate well with the inverse of monoamine oxidase activity in brain microvessels from the two strains of mice. These results support our hypothesis that monoamine oxidase activity in brain microvessels have an important role, as part of the "biochemical" blood-brain barrier, in obstructing MPTP entry into the brain.

1-Methyl-4-phenyl-1,2,3,6-tetrahydropyridine↗
PubMed1979

Histochemical characterization of monoamine oxidase in ependyma of rat hypothalamus.

Monoamine oxidase (MAO) activity has been demonstrated histochemically in rat hypothalamic ependyma using the sulphate-tetrazolium and coupled peroxidatic techniques with tryptamine, tyramine, 5-hydroxytryptamine and benzylamine as substrates. Both methods were applied to cryostat sections with and without exposure to selective amine oxidase inhibitors, including the selective A-MAO inhibitor clorgyline, and the B-MAO inhibitor deprenyl. Our results show that both cuboidal-columnar and tanycyte ependyma contain one or more forms of MAO not generally present in the hypothalamus. It is suggested that ependymal MAO may form an amine-barrier system modulating the movement and effect within the hypothalamus of specific cerebrospinal fluid or blood monoamines.

Animals↗
PubMed1987

Stopped-flow studies on the mechanism of oxidation of N-methyl-4-phenyltetrahydropyridine by bovine liver monoamine oxidase B.

The kinetic mechanism of monoamine oxidase B involves either a binary or a ternary complex, depending on the substrate. In this study, stopped-flow kinetic data provide direct evidence for ternary complexes not only of reduced enzyme, oxygen, and product but also of reduced enzyme, oxygen, and substrate, both for benzylamine and for the tertiary amine 1-methyl-4-phenyl-1,2,3,6-tetrahydropyridine (MPTP). However, the mechanism for a given substrate is not exclusive but, rather, is determined by competition between the alternate pathways as a result of different rate constants for the oxidation of the reduced enzyme, the reduced enzyme-product complex, and the reduced enzyme-substrate complex, as well as the different dissociation constants for the complexes. Comparison of the rate constants obtained from the stopped-flow studies with steady-state data indicates that the overall rate of reaction for the oxidation of MPTP by monoamine oxidase is dominated by the reductive step, but for benzylamine the steady-state rate is determined by a complex function of the rates of both the reductive and oxidative half-reactions.

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