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PubMed1989

Psychiatric morbidity, platelet monoamine oxidase and tribulin output in headache.

A significantly higher proportion of patients with headache showed scores in the psychopathological range of the General Health Questionnaire (GHQ) compared with controls, with ratings particularly high on the anxiety and depression subscales. Across the whole group, there was a significant negative correlation between platelet monoamine oxidase (MAO) activity and GHQ score overall, and with the anxiety and depression subscales. There was a significant positive correlation between platelet MAO activity and urinary output of the endogenous MAO inhibitor, tribulin. Within the migraine group, there was a significant negative correlation between tribulin output and GHQ score. These findings suggest that the biochemical nature of the anxiety associated with migraine may differ from that in other conditions such as generalized anxiety disorder where high platelet MAO activity and high tribulin output have been reported.

Affective Symptoms↗
PubMedDate not supplied

[Mechanistic study of monoamine oxidase: significance for MAO A and MAO B in situ].

MAO A and MAO B follow the same chemical mechanism to oxidise primary, secondary, and tertiary amines, but they are distinguished by differences in their substrate and inhibitor specificities and in their kinetic behaviour. Studies on the purified enzymes show that monoamine oxidases are unusual enzymes because certain amine substrates accelerate the oxidative half-reaction (much more in A than in B) and because substrate binding induces an enormous positive shift in the redox potential of the flavin. The molecular basis of these features is still unknown, as is the structure of the active site, information necessary for national drug design. This article reviews the biochemistry of MAO in general and speculates about what the kinetic and thermodynamic properties observed in the isolated enzymes mean for the catalytic expression of their amine oxidase activities in vivo. Specific and distinct physiological roles for MAO A and MAO B are probable because they are expressed in different proportions in different cell types and their expression varies in development and ageing. Molecular localization techniques can now be used to measure the levels of MAO in specific cell types rather than a region of mixed cells. When this information is combined with the kinetic constants, it will be possible to construct numerical models to predict the metabolism of a given amine by a particular cell which should help in understanding the role of amines in development and perhaps also the role of the endogenous inhibitors in altering levels of bioactive amines.

Catalysis↗
PubMed1985

Tribulin: an endogenous monoamine oxidase inhibitor/benzodiazepine receptor ligand.

Tribulin is a low molecular weight inhibitor both of monoamine oxidase and of benzodiazepine receptor binding. It has been highly purified from human urine and has also been isolated from human plasma and animal brain. Its structure is still unknown but its properties do not appear to correspond with any known monoamine or benzodiazepine receptor binding inhibitor. Tribulin output has been found to be increased in a variety of states associated with stress and anxiety, including lactate-induced panic attacks, alcohol or benzodiazepine withdrawal and generalized anxiety disorder.

Animals↗
PubMed1992

Chondrocytic monoamine oxidase activity in the development of natural murine osteoarthritis.

Most of the male STR/ORT mice develop osteoarthritis (OA) involving the medial tibial plateau. A peculiarity of two chondroprotective drugs is the presence of a nitrogen atom so that cleavage of the molecule could generate a molecule that might act as an inhibitor of monoamine oxidase (MAO). Direct examination showed abnormal localization of MAO in the potentially osteoarthritic cartilage indicating possible abnormal response to catecholamines. In normal cartilage, the direct effect of excessive concentration of adrenaline caused considerable oedema, as measured by microscopic interferometry. It is therefore suggested that the excess of water found in the matrix of osteoarthritic cartilage may be related to disturbance of the MAO activity.

Animals↗
PubMed1996

Effects of some anxiogenic agents on rat brain monoamine oxidase (MAO) A and B inhibitory (tribulin) activity.

Anxiogenic agents, yohimbine, pentylenetetrazole (PTZ), quinine, bufotenine, flumazenil and isatin were administered (ip) to rats at doses known to induce anxiety in this species. All the drugs exhibited anxiogenic response on the elevated plus-maze and induced a parallel increase in endogenous brain monoamine oxidase (MAO) inhibitory (tribulin) activity. The intensity of the drug-induced anxiety was fairly well correlated with the magnitude of increase in the MAO A inhibitory component of tribulin but not so with its MAO B inhibitory component. Thus, in the doses used, the degree of anxiogenic activity was PTZ > yohimbine > bufotenine > quinine > isatin > flumazenil, in terms of % entries on the open arms of the maze, whereas the magnitude of endogenous MAO A inhibition was PTZ > yohimbine > bufotenine > quinine > flumazenil > isatin. The results indicate that the MAO A inhibitory component of tribulin, rather than its MAO B inhibitory component, may be responsible for the postulated function of tribulin as an endogenous marker of anxiety.

Animals↗
PubMed1976

The relationship between acetylator status and inhibition of monoamine oxidase, excretion of free drug and antidepressant response in depressed patients on phenelzine.

This study was designed to examine the hypothesis that phenelzine is metabolized by polymorphic acetylation and that its effects are dependent on acetylator status. 30 depressed inpatients were given a 3-week course of phenelzine 30 mg t.i.d. The antidepressant effect, the degree of inhibition of monoamine oxidase and the amount of free phenelzine excreted in the urine were all significantly greater in slow acetylators than in fast. These findings strongly support the hypothesis.

Acetylation↗
PubMed2001

Monoamine oxidase inhibitory activity of some Hypericum species native to South Brazil.

The total methanol crude extracts and petroleum ether, chloroform, and methanol fractions obtained from Hypericum species, H. caprifoliatum, H. carinatum, H. connatum, H. cordatum, H. myrianthum, H. piriai, H. polyanthemum and H. brasiliense, all native to South Brazil, were assayed for monoamine oxidase A (MAO A) and MAO B inhibitory activity in rat brain mitochondrial preparations at concentrations ranging from 1 to 20microg mL(-1). Three benzopyrans, HP1 (6-isobutyryl-5,7-dimethoxy-2,2-dimethylbenzopyran), HP2 (7-hydroxy-6-isobutyryl-5-methoxy-2,2-dimethylbenzopyran) and HP3 (5-hydroxy-6-isobutyryl-7-methoxy-2,2dimethylbenzopyran) isolated from H. polyanthemum were also tested at maximal concentrations of 150, 150 and 75/microM, respectively. The lipophilic extracts of H. polyanthemum, H. caprifoliatum and H. piriai displayed MAO A inhibitory activity greater than 50%. Among the benzopyrans, only HP3 showed significant activity, with an IC50 value of 22 microM. The total methanol crude extracts of aerial parts from H. carinatum, H. connatum, H. cordatum, H. polyanthemum and H. piriai were evaluated for antidepressant activity in the Porsolt's forced swimming test in Wistar rats (270 mg kg(-1) day(-1); i.p); however, none of them showed activity.

Animals↗
PubMed1975

Diamine oxydase in rabbit small intestine: separations from a soluble monoamine oxidase, properties and pathophysiological significance in intestinal ischemia.

From all mammals investigated so far only in rabbits diamine oxidase could not be detected in any tissue except the gut. Thus this species was chosen for studying the physiological and pathophysiological function of this enzyme in the gastrointestinal tract. By gel filtration on Sephadex G 50 and G 200 the enzyme was purified 100-fold, separated from a soluble monoamine oxidase, and the properties of the two enzymes were determined. Diamine oxidase from rabbit small intestine deaminated putrecine (Km = 1.3 times 10(-4) M, pH-optimum 6.4-6.9) and histamine (Km = 8 times 10(-5) M, pH-optimum 7.5), but not serotonin, and was inhibited by aminoguanidine, but not by pargyline. Soluble monoamine oxidase from rabbit small intestine catabolized serotonin (Km = 1.8 times 10(-4) M, pH-optimum 8.8) but not putrescine and histamine, and was inhibited by pargyline, but not by aminoguanidine. Based on its properties in vitro intestinal diamine oxidase could inactivate the vasoactive biogenic amine histamine in vivo. To confirm this hypothesis, in rabbits the small intestine was damaged severely by inducing total intestinal ischemia, which occurs as mesenteric infarction also in human subjects and is accompanied by histamine release. Treatment with aminoguanidine and ischemia killed the animals 3-times faster than ischemia alone, which supported our hypothesis on a protective role of intestinal diamine oxidase against histamine.

Animals↗
PubMed1990

1-Methyl-4-phenyl-1,2,3,6-tetrahydropyridine- and 1-methyl-4-(2'-ethylphenyl)-1,2,3,6-tetrahydropyridine-induced toxicity in PC12 cells: role of monoamine oxidase A.

The toxicity of 1-methyl-4-phenyl-1,2,3,6-tetrahydropyridine (MPTP), 1-methyl-4-(2'-ethylphenyl)-1,2,3,6-tetrahydropyridine (2'Et-MPTP), and their corresponding pyridinium species was studied in the rat pheochromocytoma PC12 cell line. MPTP and its analogues are known to be metabolized by monoamine oxidase (MAO) to dihydropyridinium intermediates which are further transformed, either enzymatically or spontaneously, into pyridinium species. MAO activity in PC12 cells is almost exclusively of the A form, and 2'Et-MPTP is a good substrate for both MAO-A and MAO-B. In contrast, MPTP is a poor substrate for MAO-A, but a good substrate for MAO-B. 2'Et-MPTP caused considerably more cell death than MPTP in the PC12 cells. However, 1-methyl-4-(2'-ethylphenyl)pyridinium and 1-methyl-4-phenylpyridinium, the corresponding pyridinium species formed from 2'Et-MPTP and MPTP, respectively, were equipotent as toxins. The toxic effects of the tetrahydropyridines and their corresponding pyridiniums were both concentration- and time-dependent. Measurements of the levels of the pyridinium species formed and the remaining tetrahydropyridine in the media indicated that 2'Et-MPTP was converted about five to seven times more readily into its toxic pyridinium species than was MPTP. There was, moreover, an excellent correlation between amount of pyridinium formed and cell death. There was also a parallel between the capacity of clorgyline and pargyline, irreversible MAO inhibitors, to decrease the formation of the pyridinium species and their capacity to protect against the toxic actions of the tetrahydropyridines. These data are consistent with the concept that the MAO-A-dependent formation of the pyridinium species from the tetrahydropyridine is a prerequisite for toxicity in PC12 cells.

1-Methyl-4-phenyl-1,2,3,6-tetrahydropyridine↗
PubMed1987

Comparison of the effects of two 1-methyl-4-phenyl-1,2,3,6-tetrahydropyridine analogs, 1-methyl-4-(2-thienyl)-1,2,3,6-tetrahydropyridine and 1-methyl-4-(3-thienyl)-1,2,3,6-tetrahydropyridine, on monoamine oxidase in vitro and on dopamine in mouse brain.

1-Methyl-4-(2-thienyl)-1,2,3,6-tetrahydropyridine (2-MTTP) and 1-methyl-4-(3-thienyl)-1,2,3,6-tetrahydropyridine were compared with 1-methyl-4-phenyl-1,2,3,6-tetrahydropyridine (MPTP) with respect to their interactions with MAO (monoamine oxidase) in vitro and their ability to produce persistent depletion of striatal dopamine and its metabolites, 3,4-dihydroxyphenylacetic acid and homovanillic acid, in mice. Both 2-MTTP and 1-methyl-4-(3-thienyl)-1,2,3,6-tetrahydropyridine were like MPTP in being potent, competitive inhibitors of MAO-A (MAO type A) and weak, noncompetitive inhibitors of MAO-B (MAO type B) in vitro. 2-MTTP resulted in persistent depletion of striatal dopamine, 3,4-dihydroxyphenylacetic acid and homovanillic acid 1 week after the last of four daily injections to mice although 2-MTTP was less than one-fourth as potent as MPTP. The other isomer, 1-methyl-4-(3-thienyl)-1,2,3,6-tetrahydropyridine, failed to deplete dopamine or its metabolites in mouse striatum. Dopamine and its metabolites were also depleted in mouse nucleus accumbens by 2-MTTP and by MPTP; however, norepinephrine in frontal cortex was depleted by MPTP but not by 2-MTTP. The depletion of dopamine, 3,4-dihydroxyphenylacetic acid and homovanillic acid by 2-MTTP was prevented by pretreatment with deprenyl, a selective inhibitor of MAO-B, or with EXP 561, a dopamine uptake inhibitor, just as the depletion by MPTP was prevented. Mouse brain MAO oxidized 2-MTTP in vitro less rapidly than it oxidized MPTP; deprenyl was a potent inhibitor of the oxidation of both substrates, suggesting that MAO-B oxidizes both 2-MTTP and MPTP.(ABSTRACT TRUNCATED AT 250 WORDS)

1-Methyl-4-phenyl-1,2,3,6-tetrahydropyridine↗
PubMedDate not supplied

Remarkable effect of selegiline (L-deprenyl), a selective monoamine oxidase type-B inhibitor, in a patient with severe refractory depression: a case report.

A 34-year-old man presented with severe refractory depression. He had failed to respond to various antidepressants, augmentation therapy with lithium carbonate, and modified electroconvulsive therapy. Switching from amoxapine 150 mg/day to selegiline 7.5 mg/day, a selective monoamine oxidase type-B inhibitor, produced a dramatic reduction in hypobulia and lassitude, leading to a complete remission of all depressive symptoms. The patient reverted to his former position at work after an interval of approximately 3 years. Although the biologic basis of the antidepressant effect of selegiline in this patient is unknown, it is suggested that the enhancement of dopaminergic neurotransmission or elevation of brain-derived neurotrophic factor levels in the brain by administration of selegiline is involved in the recovery of this patient from severe refractory depression. This report indicates the antidepressant effect of selegiline in a refractory depressed patient.

Adult↗
PubMed2005

Eugenol and its structural analogs inhibit monoamine oxidase A and exhibit antidepressant-like activity.

Eugenol (1) is an active principle of Rhizoma acori graminei, a medicinal herb used in Asia for the treatment of symptoms reminiscent of Alzheimer's disease (AD). It has been shown to protect neuronal cells from the cytotoxic effect of amyloid beta peptides (Abetas) in cell cultures and exhibit antidepressant-like activity in mice. Results from this study show that eugenol inhibits monoamine oxidase A (MAOA) preferentially with a K(i)=26 microM. It also inhibits MAOB but at much higher concentrations (K(i)=211 microM). In both cases, inhibition is competitive with respect to the monoamine substrate. Survey of compounds structurally related to eugenol has identified a few that inhibit MAOs more potently. Structure activity relationship reveals structural features important for MAOA and MAOB inhibition. Molecular docking experiments were performed to help explain the SAR outcomes. Four of these compounds, two (1, 24) inhibiting MAOA selectively and the other two (19, 21) inhibiting neither MAOA nor MAOB, were tested for antidepressant-like activity using the forced swim test in mice. Results suggest a potential link between the antidepressant activity of eugenol and its MAOA inhibitory activity.

Animals↗
PubMed2004

Neuroprotection by monoamine oxidase B inhibitors: a therapeutic strategy for Parkinson's disease?

Parkinsonism (PD) is a neurodegenerative disorder of the brain resulting in dopamine deficiency caused by the progressive death of dopaminergic neurons. PD is characterized by a combination of rigidity, poverty of movement, tremor and postural instability. Selegiline is a selective and irreversible propargylamine type B monoamine oxidase (MAO-B) inhibitor. This drug, which inhibits dopamine metabolism, has been effectively used in the treatment of PD. However, its therapeutic effects are compromised by its many neurotoxic metabolites. To circumvent this obstacle, a novel MAO-B inhibitor, rasagiline, was developed. Paradoxically, the neuroprotective mechanism of propargylamines in different neuronal models appears to be independent of MAO-B inhibition. Recent investigations into the neuroprotective mechanism of propargylamines indicate that glyceraldehyde-3-phosphate dehydrogenase (GAPDH), MAO-B and/or other unknown proteins may represent pivotal proteins in the survival of the injured neurons. Delineation of the mechanism(s) involved in the neuroprotective effects exerted by MAO-B inhibitors may provide the key to preventive novel therapeutic modalities.

Animals↗
PubMed1994

Inhibition of monoamine oxidase by clorgyline analogues.

N-Methyl-N-propargyl-3-(4-phenoxy)phenoxypropylamine, an analogue of the MAO-A-selective irreversible inhibitor clorgyline in which the 2,4-dichloro- substitution in clorgyline was replaced by a 2-H atom and a 4-phenoxy group, has been synthesised and assessed as an inhibitor of monoamine oxidase (MAO). This compound proved to be a time-dependent irreversible inhibitor of both MAO-A and -B. However, unlike clorgyline, it was selective towards MAO-B, both in its initial, non-covalent, binding to the enzyme and as an irreversible inhibitor. In order to assess the influence of side-chain length on inhibitory potency, analogues were synthesised in which the side-chain was reduced to 2 CH2 units (N-methyl-N-propargyl-2- (4-phenoxy)phenoxyethylamine) or increased to 4 CH2 units (N-methyl-N-propargyl-4-(4- phenoxy)phenoxybutylamine). Both these compounds were also time-dependent irreversible inhibitors with selectivity towards MAO-B. In the case of the initial, non-covalent, inhibition all these compounds were competitive inhibitors of MAO-A, with respect to the amine substrate, and the affinity for inhibitor binding increased with carbon chain length. In contrast the compounds were all mixed inhibitors of MAO-B. The competitive element of this inhibition (measured by Kis) was similar for the 2 and 3 carbon-chain compounds but decreased markedly when the chain-length was increased to 4 carbons. The uncompetitive inhibition (measured by Kii) decreased as the carbon chain-length was increased from 2 to 3, but there was no significant further change when the length was increased to 4 carbons. The time-dependent irreversible inhibition (measured as the IC50 values after 60 min enzyme-inhibitor preincubation) showed that the potency towards MAO-A increased when the side-chain length was increased from 2 to 3 carbons but that there was no significant difference between the 3 and 4 carbon-chain compounds. In the case of MAO-B inhibition, the 2 and 3 carbon-chain compounds had similar inhibitory potencies but this increased substantially when the chain length was increased to 4 carbons. The significance of the inhibitory behaviour of these compounds is discussed in terms of the structure-activity relationships of mechanism-based irreversible MAO inhibitors.

Chemical Phenomena↗
PubMed1989

Neuropathological changes in the caudate nucleus elicited by MPTP and their prevention by monoamine oxidase inhibition.

MPTP (1-methyl-4-phenyl-1,2,3,6-tetrahydropyridine), a neurotoxin producing parkinsonism, causes an obvious reduction in tyrosine hydroxylase (TH) activity in the caudate nucleus. This depletion of TH activity is due to degeneration of TH-positive punctate dopaminergic terminals. The disappearance of these terminals unmasks the presence of long branching, varicose preterminal fibers, which may be sprouting after degeneration of their terminal arborizations. Glial cells, normally sparse with delicate processes, undergo intense increase in number and a robust hypertrophy. All of these changes are prevented completely by administration of deprenyl, a monoamine oxidase inhibitor, before and after MPTP. These neuropathological effects are additional manifestations of the dopaminergic neurotoxicity induced by MPTP. The metabolism of MPTP, which is blocked by monoamine oxidase inhibition, is apparently necessary for the expression of toxicity in the brain by this neurotoxin.

Animals↗
PubMed1984

[Monoamine oxidase and diamine oxidase activity of the tissues of rats in the convulsive phase of oxygen poisoning].

Monoamine oxidase type A activity with substrate serotonine and type B with substrate p-nitrophenylethylamine decreases is rats' brain, liver, heart and blood during oxygen convulsions. Substrate specificity of the enzyme type A alters in all tissues studied. Diamine oxidase activity decreases in brain, lungs and liver approximately in 2 times and increases in blood at 48%. Histamine content increases in all tissues in 3-4 times, in blood--in 12 times. The role of observed changes in the mechanism of oxygen intoxication is discussed.

Amine Oxidase (Copper-Containing)↗
PubMed1986

Interactions of the neurotoxic amine 1-methyl-4-phenyl-1,2,3,6-tetrahydropyridine with monoamine oxidases.

1-Methyl-4-phenyl-1,2,3,6-tetrahydropyridine (MPTP), a thermal breakdown product of a meperidine-like narcotic used by drug abusers as a heroin substitute, produces Parkinsonian symptoms in humans and primates. The nigrostriatal toxicity is not due to MPTP itself but to one or more oxidation products resulting from the action of monoamine oxidase (MAO) on this tertiary allylamine. Both MAO A and B catalyse the oxidation of MPTP to the 1-methyl-4-phenyl-2,3-dihydropyridinium species (MPDP+), which undergoes further oxidation to the fully aromatic 1-methyl-4-phenylpyridinium species (MPP+). These bio-oxidations are blocked by selective inhibitors of MAO A and B. Additionally, MPTP, MPDP+ and MPP+ are competitive inhibitors of MAO A and B. The A form of the enzyme is particularly sensitive to this type of reversible inhibition. Both MAO A and B also are irreversibly inactivated by MPTP and MPDP+, but not by MPP+. This inactivation obeys the characteristics of a mechanism-based or 'suicide' process. The inactivation, which is accompanied by the incorporation of radioactivity from methyl-labelled MPTP, is likely to result from covalent modification of the enzyme.

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