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PubMed1983

Monoamine oxidase in adult Ascaridia galli.

Monoamine oxidase (MAO), catalysing oxidative deamination of biogenic monoamines, has been detected in adult Ascaridia galli. MAO was present in mitochondria and deaminated noradrenaline at the maximal rate, although serotonin, adrenaline, tyramine and dopamine were also degraded but more slowly. Of the organs studied, the body wall, female reproductive organ and intestine, the body wall (containing neuronal structures) showed highest MAO activity. Km value for chick ascarid mitochondrial MAO using tyramine as substrate was 1.66 X 10(-3) M and it was most active at 2.5 mM tyramine concentration, pH 7.5 and 40 degrees C. MAO of A. galli appeared to be thermolabile as nearly 80% of its activity was lost when the incubation temperature was increased 5 degrees above optimum.

Animals↗
PubMed1983

Intestinal metabolism of tyramine by both forms of monoamine oxidase in the rat.

The two forms of monoamine oxidase (MAO) in rat intestine and brain homogenates were found to have different Km and Vmax values towards tyramine. The Km values for the A-form of the enzyme towards this substrate were around 120 microM in both cases, whereas the values for the B-form were about 240 microM. As a consequence, the ratio of activities (MAO-A: MAO-B) towards tyramine are dependent upon the substrate concentration. The MAO-A-selective inhibitors, toloxatone and cimoxatone, were found to be competitive inhibitors of the oxidation of tyramine by the A-form of this enzyme in the rat intestine, with Ki values of 3.4 microM and 3.7 nM respectively. The significance of these results in relation to the "cheese effect", a pressor response to tyramine after monoamine oxidase inhibition, are discussed.

Animals↗
PubMed1988

Reciprocal changes in striatal dopamine and beta-phenylethylamine induced by reserpine in the presence of monoamine oxidase inhibitors.

Recent studies have demonstrated that selective monoamine oxidase inhibition may induce changes in brain beta-phenylethylamine availability following lesions. The present study used this approach to re-assess the possible effects of reserpine on striatal concentrations of beta-phenylethylamine and of other amines and selected metabolites. Mice were injected with pargyline (2,200 mg kg-1, 4 h), clorgyline (2 mg kg-1, 2 h) or (-)deprenyl (2 mg kg-1, 2 h) alone or in combination with reserpine (1, 10 mg kg-1, 2 h). Increases in beta-phenylethylamine accumulation were observed in the presence of both (-)deprenyl or pargyline respectively after reserpine except in the case of combined 200 mg kg-1 of pargyline plus 1 mg kg-1 of reserpine. In this condition, a minimal dopamine decrease was observed (to 80% of the concentration of pargyline-treated controls). Increases in beta-phenylethylamine concentration were not observed with reserpine alone (1 or 10 mg kg-1). In the latter condition, the concentrations of beta-phenylethylamine remained at control values due to the activity of monoamine oxidase B. Changes in p-tyrosine, 5-hydroxytryptamine or tryptophan did not consistently accompany increases in beta-phenylethylamine accumulation. Increased beta-phenylethylamine accumulation was always accompanied by the decreases in dopamine induced by reserpine in mice with either non-selective (200 mg kkg-1 pargyline) or type B monoamine oxidase inhibition (2 mg kg-1 pargyline or deprenyl). These data suggest that although the changes in beta-phenylethylamine accumulation may not be due simply to p-tyrosine availability they are related to dopamine levels in the intact striatum.

Animals↗
PubMed1993

Monoamine oxidase inhibitors inhibit [3H]quinpirole binding in rat striatal membranes.

This study describes interactions of monoamine oxidase inhibitors at binding sites labeled by [3H]quinpirole, a putatively selective ligand for dopamine D2-like receptors, in in vitro binding assays in rat brain. Monoamine oxidase inhibitors potently and competitively inhibited equilibrium binding of [3H]quinpirole in homogenate binding assays with the following rank order of potencies: clorgyline > or = Ro 41-1049 > pargyline > (-)-deprenyl > (+)-deprenyl > Ro 16-6491 > iproniazid. This rank order of potencies does not correlate with the potencies of these drugs at monoamine oxidase-A or monoamine oxidase-B, sigma site(s) or dopamine receptors. Monoamine oxidase inhibitors did not alter the ability of quinpirole to compete for [3H]spiperone binding. Quinpirole did not inhibit monoamine oxidase-A or monoamine oxidase-B activity and had low affinity (200 nM) for sigma site(s). These data suggest a potential novel binding site for [3H]quinpirole in rat brain and/or an alternative site of action for the antidepressant effects of monoamine oxidase inhibitors.

Animals↗
PubMed1983

Comparison of monoamine oxidase in golden hamster islets and insulinoma.

We compared the properties of monoamine oxidase (MAO) in hamster islets and insulinomas. The tryptamine concentration at which the monoamine oxidase velocity was half maximal (Km) was higher in islets than insulinomas; the maximal velocity (Vmax) of monoamine oxidase was greater in islets than insulinomas. Both islet and insulinoma are more sensitive to inhibition by pargyline than clorgyline. After pargyline administration the monoamine oxidase activity of insulinoma returns faster than activity of islets. This may occur because both synthesis of new MAO in pre-existing cells and formation of new cells occurs in the insulinoma.

Adenoma, Islet Cell↗
PubMed1989

Stress reduces in vivo inhibition of monoamine oxidase by phenelzine in rat brain.

The level of inhibition of rat whole brain monoamine oxidase activity produced by the irreversible monoamine oxidase inhibitor phenelzine has been studied with or without concurrent cold restraint stress. We have found that phenelzine caused significantly less enzyme inhibition when given during a period of stress than during a control period. Thus, stress can reduce the in vivo potency of MAO inhibitors. This would be compatible with an increased production of the reversible, endogenous monoamine oxidase inhibitor, tribulin, competing for the active site of the enzyme.

Animals↗
PubMed1983

Selective effects on catalysis by the multiple forms of monoamine oxidase produced by interactions of acidic phospholipids with mitochondrial membranes.

The effect of acidic phospholipids on the A and B multiple forms of membrane-bound mitochondrial monoamine oxidase has been investigated by incubating liposomes with isolated rat liver mitochondrial outer membrane preparations at lipid:protein ratios of 0.01 to 1. A strong inhibition of monoamine oxidase B was observed with phosphatidylserine and a moderate activation of monoamine oxidase A with phosphatidylinositol, while cardiolipin had no significant effect on either form. The specificity of phosphatidylserine inhibition for monoamine oxidase B was also confirmed in mitochondrial outer membrane isolated from tissues containing exclusively the A or B form of the enzyme (human placenta and bovine liver). Levels of incorporation were comparable for all the phospholipids and tissues studied and could not account for the different effects observed. Inhibition of monoamine oxidase B was found to be similar in an intact mitochondria preparation to that observed in the isolated outer membrane. A recent report of activation of both monoamine oxidase forms in delipidated whole mitochondria by the acidic phospholipids was re-examined and found to involve release of monoamine oxidase from the mitochondria. The details of the effects of phosphatidylserine and phosphatidylinositol on membrane-bound monoamine oxidase are consistent with the concept of the multiple forms as two distinct peptides, and suggest a second possible mode of in vivo regulation of substrate specificity.

Animals↗
PubMed1979

Immunochemical characterization of monoamine oxidase from human liver, placenta, platelets and brain cortex.

1. Antiserum raised to purified human liver monoamine oxidase was used to characterize the monoamine oxidase from human liver, brain cortex, placenta and platelets. 2. Antibodies to monoamine oxidase were purified by adsorption with a mitochondrial preparation. 3. Monoamine oxidase was present in liver particle-free supernatant as measured by enzyme activity and immunodiffusion. 4. Multiple precipitin lines were obtained on immunodiffusion analysis against the purified liver enzyme. It is proposed that this is due to either aggregation or to differential lipid binding. 5. The results suggest that the functionally different enzymes found in liver, brain cortex, platelets and placenta are immunochemically related and may be identical.

Antigens↗
PubMed1987

Effects of different monoamine oxidase inhibitors on the metabolism of L-dopa in the rat brain.

The influence of monoamine oxidases A and B on the metabolism of dopamine or the expanded dopamine pool following L-dopa administration remains unclear. This study found that treatment of Sprague-Dawley rats with monoamine oxidase inhibitors strongly affected L-dopa metabolism in the brain, but the influence varied with each individual inhibitor. In animals pretreated with pargyline or clorgyline, L-dopa administration led to huge accumulations of dopamine and significantly raised central norepinephrine concentrations. In contrast, similar L-dopa injections in deprenyl-pretreated rats caused only a moderate rise in dopamine and no change in norepinephrine. There seems to be little relationship between the degree of monoamine oxidase inhibition and the accumulation of catecholamines and their metabolites in the rat brain. The effects of monoamine oxidase inhibitors on dopamine accumulation appeared to occur outside the catecholaminergic neurons since in the animals pretreated with 6-hydroxydopamine, which decreased significantly the content of brain catecholamines, dopamine accumulation following L-dopa administration still remained considerable. On the other hand, the influence of monoamine oxidase inhibitors on brain norepinephrine concentrations seemed to originate in the noradrenergic neurons because norepinephrine increase was greatly reduced in rats treated with 6-hydroxydopamine but was restored when the treatment with 6-hydroxydopamine was accompanied by desimipramine which specifically protects noradrenergic stores.

Animals↗
PubMed1981

[Monoamine oxidase activity in the brain during adaptation to cold and simultaneous exposure to cold and hyperbaric oxygenation].

One--day cold exposure decreases the monoamine oxidase type A activity by 52--54% (serotonin and noradrenaline substrates); the monoamine oxidase type B activity by 14%. Three--day cold exposure leaves the monoamine oxidase type B activity unchanged and decreases the monoamine oxidase type A activity by 29--32%; the enzyme of the latter type acquires the ability for deamination of glucosamine, putrescine and GABA. Under cold adaptation (45 days, 2 degrees C) the monoamine oxidase type A activity remains reduced as on the 3rd day, the type B activity decreases by 19%; enzyme substrate specificity does not change at all. Preliminary cold adaptation prevents alteration of the monoamine oxidase substrate specificity under hyperbaric oxygenation.

Acclimatization↗
PubMed1982

Bovine liver mitochondrial monoamine oxidase is not an iron-dependent enzyme.

It has been reported that rat liver monoamine oxidase is an iron-dependent enzyme. Calculations from reported data suggest that rat liver monoamine oxidase contains 2 g atoms of iron/mol of enzyme. However, our data over a 16-year period show that our purified bovine liver monoamine oxidase does not contain sufficient iron to justify being considered an iron protein. In order to ensure the correctness of the iron content, two microchemical analyses and atomic absorption spectroscopy were used to determine the iron content of wet ashed samples. The iron content was also determined during successive steps of enzyme purification and was found to decrease rather than increase. Monoamine oxidase, being a hydrophobic outer membrane enzyme, is very difficult to purify and detailed tests for homogeneity are necessary. Our preparations show a single band when examined by sodium dodecyl sulfate-polyacrylamide disc electrophoresis and behave as a pure protein by end group analysis. Thus, bovine liver monoamine oxidase is not an iron-dependent enzyme.

Animals↗
PubMed2006

Isolation and characterization of a monoamine oxidase B selective inhibitor from tobacco smoke.

It is well established that tobacco smokers have reduced levels of monoamine oxidase activities both in the brain and peripheral organs. Furthermore, extensive evidence suggests that smokers are less prone to develop Parkinson's disease. These facts, plus the observation that inhibition of monoamine oxidase B protects against the parkinsonian inducing effects of the nigrostriatal neurotoxin 1-methyl-4-phenyl-1,2,3,6-tetrahydropyridine, have prompted studies to identify monoamine oxidase inhibitors in the tobacco plant and tobacco cigarette smoke. Our previous efforts on cured tobacco leaf extracts have led to the characterization of 2,3,6-trimethyl-1,4-naphthoquinone, a non-selective monoamine oxidase inhibitor, and farnesylacetone, a selective monoamine oxidase B inhibitor. We now have extended these studies to tobacco smoke constituents. Fractionation of the smoke extracts has confirmed and extended the qualitative results of an earlier report [J. Korean Soc. Tob. Sci.1997, 19, 136] demonstrating the inhibitory activity of the terpene trans,trans-farnesol on rat brain MAO-B. In the present study, K(i) values for the inhibition of human, baboon, monkey, dog, rat, and mouse liver MAO-B have been determined. Noteworthy is the absence of inhibitory effects on human placental MAO-A and beef liver MAO-B. A limited structure-activity relationship study of analogs of trans,trans-farnesol is reported. Although the health hazards associated with the use of tobacco products preclude any therapeutic opportunities linked to smoking, these results suggest the possibility of identifying novel structures of compounds that could lead to the development of neuroprotective agents.

Animals↗
PubMedDate not supplied

[Use of bacterial luciferase for determining monoamine oxidase activity].

A bioluminescence assay is proposed for measuring monoamine oxidase activity in different biological specimens (platelets, mitochondria). The assay is based on the bioluminescent reaction catalysed by bacterial luciferase and coupled to monoamine oxidase. Two modifications of the bioluminescence assay were used. In the first case, the bioluminescent system was added to monoamine oxidase preincubated with the substrates, while in the second case, all the components of the coupled enzymatic systems were directly mixed in a cell. The proposed bioluminescence assay is simple, highly sensitive and rapid, and could be especially useful for biomedical examinations.

Animals↗
PubMed1994

Increased monoamine oxidase B activity in plaque-associated astrocytes of Alzheimer brains revealed by quantitative enzyme radioautography.

The aetiology and pathogenesis of Alzheimer's disease are currently poorly understood, but symptomatic disease is associated with amyloid plaques, neurofibrillary tangles, neuronal loss and numerous alterations of neurotransmitter systems in the CNS. Monoamine oxidase type B is known to be increased in Alzheimer diseased brains. The distribution and abundance of catalytic sites for monoamine oxidases A and B in post mortem human brains of 11 Alzheimer disease cases and five age-matched controls were investigated by quantitative enzyme radioautography. Using tritiated monoamine oxidase inhibitors (Ro41-1049 and lazabemide)--as high affinity substrates selective for monoamine oxidases A and B, respectively--it was found that monoamine oxidase B activity increased up to three-fold exclusively in temporal, parietal and frontal cortices of Alzheimer disease cases compared with controls. This increase was restricted to discrete patches (approximately 185 microns in diameter) which occupied approximately 12% of the cortical areas examined. In other brain regions (hippocampal formation >> caudate-putamen > cerebellum), patches of [3H]lazabemide-enriched binding were less abundant. [3H]Ro41-1049 binding (i.e. monoamine oxidase A) was unchanged in all tissues of diseased versus control brains. The monoamine oxidase B-enriched patches in all cortical regions correlated, in their distribution and frequency, with glial fibrillary acidic protein-immunoreactive clusters of astrocytes. Diffuse and mature beta-amyloid-immunoreactive senile plaques as well as patches of high density binding of [3H]PK-11195--a high-affinity ligand for peripheral-type (mitochondrial) benzodiazepine binding sites in microglia/macrophages--were found throughout Alzheimer diseased cortices. The up-regulation of monoamine oxidase B in plaque-associated astrocytes in Alzheimer's disease--in analogy to its proposed role in neurodegenerative disorders such as Parkinson's disease--might, indirectly, be a potential source of cytotoxic free radicals. Lazabemide, a selective reversible monoamine oxidase B inhibitor, is currently under clinical evaluation for the treatment of Parkinson's and Alzheimer's diseases. We conclude that enzyme radioautography with [3H]lazabemide is a reliable high resolution assay for plaque-associated astroglioses in Alzheimer's disease. Its clinical diagnostic utility for positron emission tomography or single photon emission computer tomography studies is being investigated.

Aged↗
PubMed1996

[Monoamine oxidase inhibitors in psychiatry. Status of current knowledge].

With the introduction of moclobemide as the first reversible and selective inhibitor of monoamine oxidase (type A), the therapeutic principle of monoamine oxidase inhibition gained new importance. In this paper the clinical pharmacology, efficacy and side effects of traditional monoamine oxidase inhibitors and specifically of tranylcypromine as an example) are compared with those of the reversible and selective monoamine oxidase inhibitors (as exemplified by moclobemide).

Antidepressive Agents↗