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Results for “MONOAMINE OXIDASE”

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At least 145 records · Page 8Linked to original sources
PubMed1995

Hydrogen peroxide (H2O2) production by monoamine oxidase in rat tissues using endogenous catecholamines as substrates. A comparison of catalytic monoamine oxidase histochemistry and recently published catechol-O-methyltransferase immunohistochemistry.

Histochemical studies on hydrogen peroxide (H2O2) production by monoamine oxidase (MAOX) using xenobiotic (foreign) catecholamines such as tryptamine or tyramine as substrates may not reveal the true H2O2-production capacity of this enzyme and the potential co-localization and cooperation of MAOX with catechol-O-methyltransferase (COMT), the other catecholamine-degrading enzyme. Therefore, in the present study the catecholamine hormones adrenaline (epinephrine) and noradrenaline (norepinephrine) and the catecholamine neurotransmitter noradrenaline as well as the COMT metabolites metanephrine and normetanephrine, which are likely to be the more important MAOX substrates, were used for MAOX visualization in many rat tissues with a cerium-diaminobenzidine-H2O2-Co method. Adrenaline and noradrenaline were autooxidized by Ce3+ and could not be employed; with metanephrine or normetanephrine as substrates MAOX produced considerable amounts of H2O2 in many cells and tissues. Comparisons with immunohistochemical COMT-data for rats from the literature show that MAOX and COMT are co-localized or not. Therefore, different from our current knowledge in rats COMT and MAOX either co-operate in catecholamine degradation or they degrade the respective catecholamines alone.

Animals↗
PubMed1977

[Studies on monoamine oxidase. (Report 37) Effects of oxygen concentration on rat liver and brain monoamine oxidase (author's transl)].

MAO activity in rat brain mitochondria with tyramine as substrate at 100% oxygen concentration was three times as much as that at 20%. When serotonin served as substrate, difference in activities between the two oxygen concentrations was not significant. Similar results were obtained when rat liver MAO was used as the enzyme source. At 100% oxygen concentration, pargyline showed the most potent inhibition of MAO activity in liver mitochondria with tyramine as substrate, but inhibitions caused by pheniprazine and harmaline were not remarkable. At 100% oxygen concentration, harmaline showed the most potent inhibition of MAO activity in the liver when serotonin served as substrate, while inhibitions of the MAO activity by pargyline and pheniprazine were weak. At 20% oxygen concentration, harmaline showed the most potent inhibition of MAO activity in the brain when serotonin was used as substrate. These inhibitions were studied using Lineweaver-Burk plots. Pargyline revealed a noncompetitive inhibition to MAO activity in liver and brain with tyramine and serotonin as substrate, harmaline a competitive inhibition to MAO activity in liver and brain with tyramine as substrate, while noncompetitive inhibition to MAO activity in liver and brain was evident when serotonin was used as the substrate.

Animals↗
PubMed2006

Forebrain-specific expression of monoamine oxidase A reduces neurotransmitter levels, restores the brain structure, and rescues aggressive behavior in monoamine oxidase A-deficient mice.

Previous studies have established that abrogation of monoamine oxidase (MAO) A expression leads to a neurochemical, morphological, and behavioral specific phenotype with increased levels of serotonin (5-HT), norepinephrine, and dopamine, loss of barrel field structure in mouse somatosensory cortex, and an association with increased aggression in adults. Forebrain-specific MAO A transgenic mice were generated from MAO A knock-out (KO) mice by using the promoter of calcium-dependent kinase IIalpha (CaMKIIalpha). The presence of human MAO A transgene and its expression were verified by PCR of genomic DNA and reverse transcription-PCR of mRNA and Western blot, respectively. Significant MAO A catalytic activity, autoradiographic labeling of 5-HT, and immunocytochemistry of MAO A were found in the frontal cortex, striatum, and hippocampus but not in the cerebellum of the forebrain transgenic mice. Also, compared with MAO A KO mice, lower levels of 5-HT, norepinephrine, and DA and higher levels of MAO A metabolite 5-hydroxyindoleacetic acid were found in the forebrain regions but not in the cerebellum of the transgenic mice. These results suggest that MAO A is specifically expressed in the forebrain regions of transgenic mice. This forebrain-specific differential expression resulted in abrogation of the aggressive phenotype. Furthermore, the disorganization of the somatosensory cortex barrel field structure associated with MAO A KO mice was restored and became morphologically similar to wild type. Thus, the lack of MAO A in the forebrain of MAO A KO mice may underlie their phenotypes.

Animals↗
PubMed1989

A controlled study of the antidepressant efficacy and side effects of (-)-deprenyl. A selective monoamine oxidase inhibitor.

Monoamine oxidase (MAO) inhibitors are effective antidepressants whose use is limited because of unwanted side effects and the possibility of a tyramine-induced hypertensive crisis (cheese reaction). (-)-Deprenyl (the official nonproprietary name for this substance is selegiline), a selective MAO type B inhibitor, may be safer and have fewer side effects, but its antidepressant efficacy is uncertain. A double-blind placebo-controlled study was carried out in depressed outpatients who were treated with (-)-deprenyl in an MAO type B selective dose range and at a higher nonselective dose range. (-)-Deprenyl did not have a statistically significant antidepressant effect after three weeks of treatment at doses of 10 mg/d. However, after six weeks and at higher doses (averaging about 30 mg/d for the second three weeks), (-)-deprenyl was superior to placebo in antidepressant effect with a positive response rate of 50% vs 13.6% and with a 41% reduction in the Hamilton Depression Rating Scale mean score vs 10% in the placebo-treated group. No hypertensive crises were seen. The rate of occurrence of side effects with (-)-deprenyl was no greater than with placebo. It was concluded that (-)-deprenyl is an effective antidepressant in a dose range where it is distinguished by the absence of many of the side effects typical of nonselective MAO inhibitors.

Adult↗
PubMed1994

Some kinetic properties of guinea pig liver monoamine oxidase.

Titration of monoamine oxidase activity in isolated guinea pig liver mitochondria with clorgyline and assay of remaining activity with tyramine yielded biphasic inhibition curves. The position of the plateaus obtained with mitochondria from four animals, indicated that the B form of monoamine oxidase accounted for 30% to 70% of the tyramine deaminating activity. Benzylamine deamination was selectively inhibited by (-)-deprenyl. However, benzylamine and other amines which are selective substrates for the B form of monoamine oxidase from the rat, were deaminated at only low rates by the guinea pig liver enzyme. Guinea pig liver contains a monoamine oxidase-B which is unusual in that although it exhibits apparently normal sensitivity to selective irreversible inhibitors, it has a low catalytic activity with substrates which the enzyme from rat liver deaminates rapidly.

Animals↗
PubMed1977

Localization, purification and substrate specificity of monoamine oxidase.

Bovine kidney monoamine oxidase (amine:oxygen oxidoreductase (deaminating) (flavin-containing), EC 1.4.3.4) has been purified to one band on disc electrophoresis, and is shown to be localized in the intra- and extramitochondrial membrane. Kinetic models have been used to determine the effect of different substances on the enzyme activity. This enzyme shows a very high substrate specificity. It is suggested that phenol ring and one hydrogen atom each on the methylene and amine groups are responsible for the enzyme activity. N-methylbenzylamine exhibits a homotropic negative cooperative effect which is also supported by the n and Rs values. Benzylhydrazine is apparently a good substrate unlike phenylhydrazine, semicarbazide, harmaline and alpha- and beta-naphthol which show an inhibitory effect on the enzyme activity. Methylamine has no effect. It is suggested that the enzyme may have different sites or different conformations for different substrates. The results of this communication demonstrate bovine kidney monoamine oxidase to be different from monoamine oxidase from other sources.

Animals↗
PubMed1989

Inhibition of monoamine oxidase by moclobemide: effects on monoamine metabolism and secretion of anterior pituitary hormones and cortisol in healthy volunteers.

1. Single oral doses (100, 200 and 300 mg) of moclobemide, a reversible inhibitor of monoamine oxidase (MAO) with predominant effects on the A-type of the enzyme, were administered to eight young, healthy male volunteers in a double-blind, random-order, placebo-controlled study. The investigation was thereafter continued in an open fashion by administering a single 10 mg dose of the MAO-B inhibitor deprenyl to the same subjects. 2. Deamination of catecholamines was powerfully and dose-dependently inhibited by moclobemide, as evidenced by up to 40% decreases in the urinary excretion of deaminated catecholamine metabolites, corresponding increases in the excretion of non-deaminated, methylated metabolites, and up to 79% average decreases in the plasma concentration of 3,4-dihydroxyphenylglycol (DHPG), a deaminated metabolite of noradrenaline (NA), and up to 75% average decreases in the plasma concentrations of 3,4-dihydroxyphenylacetic acid (DOPAC), a deaminated metabolite of dopamine. The urinary excretion of 5-hydroxyindoleacetic acid (5-HIAA) was only slightly reduced. In contrast, deprenyl, in a dose which almost totally inhibited MAO-B activity in blood platelets, did not appreciably affect the plasma concentrations of DHPG or DOPAC. 3. Due to the rapid, reversible, dose-dependent and MAO-A specific effect of moclobemide on plasma concentrations of DHPG, it is suggested that DHPG in plasma may be a useful indicator of the magnitude and duration of MAO-A inhibition in man. 4. Sympatho-adrenal function at rest was not significantly altered by moclobemide, as judged by unchanged plasma catecholamine concentrations and stable blood pressure and heart rate recordings. 5. Monoamine oxidase type B activity in blood platelets was slightly (less than 30%) and transiently inhibited after moclobemide. 6. The secretion of prolactin was dose-dependently stimulated by moclobemide, whereas the plasma concentrations of growth hormone (hGH) and cortisol remained unchanged.

3,4-Dihydroxyphenylacetic Acid↗
PubMed1986

The effect of chronic ozone exposure on lung benzo(a)pyrene oxidase, benzphetamine demethylase and monoamine oxidase.

Adult male Fischer 344 rats were exposed either to clean air or to a mixture of clean air and 0.5ppm ozone for up to one year. These populations were sampled after three and six months and when the exposure was completed. The activity of several oxidative enzymes in these rat lungs were compared. Although there was no significant increase in the ability of pulmonary microsomes to oxidize benzo[alpha]pyrene after three months of exposure to ozone, this activity and the oxidative demethylation of benzphetamine were increased after six months and a year of exposure. Aside from these enzymatic changes, electrophoretic analysis indicated that the microsomes from ozone exposed rats were enriched with a protein with an apparent molecular weight of 68,000. The activity of the two isoenzymic forms of monoamine oxidase, MAO A and MAO B, were also measured, and neither activity was affected by the ozone exposure.

Animals↗
PubMed2005

Novel multifunctional neuroprotective iron chelator-monoamine oxidase inhibitor drugs for neurodegenerative diseases: in vitro studies on antioxidant activity, prevention of lipid peroxide formation and monoamine oxidase inhibition.

Iron-dependent oxidative stress, elevated levels of iron and of monoamine oxidase (MAO)-B activity, and depletion of antioxidants in the brain may be major pathogenic factors in Parkinson's disease, Alzheimer's disease and related neurodegenerative diseases. Accordingly, iron chelators, antioxidants and MAO-B inhibitors have shown efficacy in a variety of cellular and animal models of CNS injury. In searching for novel antioxidant iron chelators with potential MAO-B inhibitory activity, a series of new iron chelators has been designed, synthesized and investigated. In this study, the novel chelators were further examined for their activity as antioxidants, MAO-B inhibitors and neuroprotective agents in vitro. Three of the selected chelators (M30, HLA20 and M32) were the most effective in inhibiting iron-dependent lipid peroxidation in rat brain homogenates with IC50 values (12-16 microM), which is comparable with that of desferal, a prototype iron chelator that is not has orally active. Their antioxidant activities were further confirmed using electron paramagnetic resonance spectroscopy. In PC12 cell culture, the three novel chelators at 0.1 microM were able to attenuate cell death induced by serum deprivation and by 6-hydroxydopamine. M30 possessing propargyl, the MAO inhibitory moiety of the anti-Parkinson drug rasagiline, displayed greater neuroprotective potency than that of rasagiline. In addition, in vitro, M30 was a highly potent non-selective MAO-A and MAO-B inhibitor (IC50 < 0.1 microM). However, HLA20 was more selective for MAO-B but had poor MAO inhibition, with an IC50 value of 64.2 microM. The data suggest that M30 and HLA20 might serve as leads in developing drugs with multifunctional activities for the treatment of various neurodegenerative disorders.

Animals↗