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PubMed1998

A functional polymorphism in the monoamine oxidase A gene promoter.

We describe a new polymorphism upstream of the gene for monoamine oxidase A (MAOA), an important enzyme in human physiology and behavior. The polymorphism, which is located 1.2 kb upstream of the MAOA coding sequences, consists of a 30-bp repeated sequence present in 3, 3.5, 4, or 5 copies. The polymorphism is in linkage disequilibrium with other MAOA and MAOB gene markers and displays significant variations in allele frequencies across ethnic groups. The polymorphism has been shown to affect the transcriptional activity of the MAOA gene promoter by gene fusion and transfection experiments involving three different cell types. Alleles with 3.5 or 4 copies of the repeat sequence are transcribed 2-10 times more efficiently than those with 3 or 5 copies of the repeat, suggesting an optimal length for the regulatory region. This promoter region polymorphism may be useful as both a functional and an anonymous genetic marker for MAOA.

Adult↗

PubMed1992

Displacement of in vivo binding of [3H]brofaromine to rat intestinal monoamine oxidase A by orally administered tyramine.

The reversibility of the interaction of inhibitors with monoamine oxidase (MAO) is thought to provide a safety valve with respect to tyramine potentiation. We sought experimental evidence for this concept by studying the binding of orally administered [3H]brofaromine to the A-form of MAO in the rat ileum. Specific binding, defined by pretreatment with 10 mg/kg clorgyline p.o., amounted to 70-90% of total binding between 30 min and 6 h after administration of the radioligand. Brofaromine and clorgyline dose dependently displaced [3H]brofaromine with ED50 values of about 0.2 mg/kg when administered orally after the radioligand; so did orally administered tyramine in doses relevant for tyramine potentiation in the rat. It was also found that tyramine was relatively more effective in partially MAO-inhibited rats. The data suggest that the concept of reversibility functioning as a safety valve with respect to the potentially hazardous effects of tyramine ingestion is realistic.

Administration, Oral↗

PubMed1986

Monoamine oxidase: an important intracellular regulator of gastrin release in the rat.

The role of monoamine oxidase (MAO) in the meal-induced or amino acid-induced release of gastrin was investigated. Rats that were pretreated with the nonspecific MAO inhibitor nialamide (200 mg/kg) showed a greater rise in meal-induced serum gastrin than did untreated controls. In vitro experiments demonstrated that gastrin secretion from dispersed antral G cells in response to a stimulatory dose of phenylalanine or methylbenzylamine (10 mM) was markedly enhanced if the cells were treated with nialamide. Studies with the more specific MAO inhibitors clorgyline and deprenyl indicated that antral mucosa contained predominantly type A activity. Inhibition of MAO type A with clorgyline, both in vivo and in vitro, resulted in a greater release of gastrin after stimulation by a meal or phenylalanine. It is concluded that MAO may play an important role in the regulation of gastrin release from the G cell by partially controlling the level of amines within the cell.

Animals↗

PubMed1986

Studies of monoamine oxidase and semicarbazide-sensitive amine oxidase. II. Inhibition by alpha-methylated substrate-analogue monoamines, alpha-methyltryptamine, alpha-methylbenzylamine and two enantiomers of alpha-methylbenzylamine.

The alpha-methylated substrate-analogue monoamines, dl-alpha-methyltryptamine, dl-alpha-methylbenzylamine and two optical isomers of alpha-methylbenzylamine, were shown to be inhibitors of rat lung semicarbazide-sensitive amine oxidase (SSAO), with dl-alpha-methyltryptamine being the most potent and d-alpha-methylbenzylamine, the least. The three compounds, dl-alpha-methyltryptamine and the two isomers of alpha-methylbenzylamine also inhibited rat brain monoamine oxidase (MAO)-A and -B with a greater selectivity towards MAO-A. Preincubation of rat lung and brain homogenates with either of these compounds revealed that the inhibition of MAO and SSAO is reversible. The modes of inhibition of MAO-A and -B were competitive with the substrates tested. However, inhibition of SSAO by dl-alpha-methyltryptamine was found to be a mixed type (with a Ki value of 47 microM) and those by the racemic form and two isomers of alpha-methylbenzylamine were non-competitive (with Ki values of 90 microM for the racemic compound, 1070 microM for the d-isomer and 72 microM for the l-isomer). The present results indicate that SSAO can recognize optical isomers and that some alpha-methylated monoamines tested in the present study inhibit SSAO with properties different from those as MAO inhibitors.

Animals↗

PubMed1978

A rapid and sensitive assay for monoamine oxidase activity.

Based on the Berthelot reaction, a new sensitive and rapid procedure for monoamine oxidase (MAO) determination with substrate tyramine has been developed. The saturation with oxygen and the separation of ammonia from the substrate were omitted. At the end of incubation the samples were deproteinized with ethanol and consecutive centrifugation. The newly-formed ammonia is converted into the coloured compound indophenol, using the procedure of Fenton (1962). The indophenol concentration, respectively NH3 is determined by spectrophotometry at 625 nm, and calculated by comparison with a set of standard amounts of NH3. The enzyme activity is expressed as nanomoles ammonia, formed by 1 mg protein for 1 min. The method was tested for studying the relationship between the enzyme activity, time of incubation and protein concentration, as well as the effect of pargyline. The kinetics of MAO, using both liver and brain mitochondria as enzyme material was also studied. Considering the specificity, simplicity, versatility and rapid performance, the new method showed several advantages in comparison with the other known methods for MAO determination.

Animals↗

PubMed1996

Differential inhibition of neuronal and extraneuronal monoamine oxidase.

This study examined whether the neuronal and extraneuronal sites of action of two monoamine oxidase (MAO) inhibitors, l-deprenyl and debrisoquin, could be distinguished by their effects on plasma concentrations of catecholamine metabolites. Plasma concentrations of the intraneuronal deaminated metabolite of norepinephrine, dihydroxyphenylglycol (DHPG), were decreased by 77% after debrisoquin and by 64% after l-deprenyl administration. Plasma concentrations of the extraneuronal O-methylated metabolite of norepinephrine, normetanephrine, were increased substantially more during treatment with l-deprenyl than with debrisoquin (255% compared to a 27% increase). The comparable decreases in plasma concentrations of DHPG indicate a similar inhibition of intraneuronal MAO by both drugs. Much larger increases in normetanephrine after l-deprenyl than after debrisoquin are consistent with a site of action of the latter drug directed at the neuronal rather than the extraneuronal compartment. Thus, differential changes in deaminated and O-methylated amine metabolites allows identification of neuronal and extraneuronal sites of action of MAO inhibitors.

Adult↗

PubMed1995

Localization of I2-imidazoline binding sites on monoamine oxidases.

Imidazoline binding sites (IBS) were proposed to be responsible for some of the pharmacological and therapeutic activities of imidazoline and related compounds and have been classified into two subtypes, I1BS and I2BS. Convergent studies attribute a role in central blood pressure regulation to the I1BS. In contrast, the function of I2BS remains unknown. In the present study, by combining biochemical and molecular biology approaches, we show that 1) microsequencing of I2BS purified from rabbit kidney mitochondria allowed the recovery of four peptide sequence stretches displaying up to 85.7% similarity with human, rat, and bovine monoamine oxidases (MAO)-A and -B; 2) I2BS and MAO displayed identical biophysical characteristics as their activities, measured by [3H]idazoxan binding and [14C]tyramine oxidation, respectively, could not be separated using various chromatographic procedures; and 3) heterologous expression of human placenta MAO-A and human liver MAO-B in yeast, inherently devoid of I2BS and MAO activities, led to the coexpression of [3H]idazoxan binding sites displaying ligand-recognition properties typical of I2BS. These results show definitely that I2BS is located on both MAO-A and -B. The fact that I2BS ligands inhibited MAO activity independently of the interaction with the catalytic region suggests that I2BS might be a previously unknown MAO regulatory site.

Amino Acid Sequence↗

PubMed1982

The monoamine oxidase and catechol-O-methyltransferase activities in the dog liver.

The activity of monoamine oxidase (MAO) and catechol-O-methyltransferase (COMT) was investigated in the liver of anesthetized dogs. The MAO activity was determined by means of the method described by Wurtman and Axelrod (1963, Biochem. Pharmacol. 12: 1439-1440) using tryptamine as a substrate. The activity of COMT was assayed with the method of Axelrod (1962, Methods in Enzymology, Vol. 5. Academic Press, New York) in the presence of epinephrine bitartrate as a substrate. The average values for the activity of MAO and COMT were found to be 57.7 nmol . min-1 . g-1 of liver and 101.8 nmol . min-1 . g-1 of liver, respectively. No significant difference in the enzyme activity was observed among various samples obtained from distinct zones (peripheral and central) and lobes at different time of sample collections. The results suggest the homogeneous distribution of MAO and COMT in the dog liver. The striking difference in the COMT activity in the dog liver as compared with that reported by others for the cat liver is probably due to a species difference between these two animals.

Animals↗

PubMed1977

Effects of thyroid hormones on the evolution of monoamine oxidase activity in the brain and heart of the developing rat.

The evolution of monoamine oxidase (MAO) activity towards tryptamine has been studied from birth to 20 days post-natal in the brain and heart of male rats. Hyperthyroidism was induced by thyroxine injections and hypothyroidism by PTU administration. The results are expressed per unit of fresh weight and per unit of protein weight. Cardiac MAO is higher in the hyperthyroid animals than in controls as soon as 5 days following birth; the difference between the 2 groups increases until 20 days. The deficiency in thyroid hormones, on the other hand, was followed by a slight decrease in the cardiac enzyme, this decrease reflecting the general deficit in protein synthesis. Brain MAO is not affected by hyperthyroidism, but a clear deficit follows PTU administration. This deficit is significant beginning at 10 days and the difference between the 2 groups increases up to 20 days. The effects of PTU-induced hypothyroidism can be corrected by thyroxine injections. Except for the decrease in the level of cardiac enzyme in hypothyroid animals, all the effects on MAO activity are independent of the total protein content of both organs.

Animals↗

PubMed1996

Involvement of monoamine oxidase and noradrenaline uptake in the positive chronotropic effects of apigenin in rat atria.

In rat isolated atria spontaneously beating and labelled with [3H]noradrenaline, exposure to the flavonoid apigenin increased the atrial rate in a concentration-dependent manner (0.01-30 microM). This increase was accompanied by a reduction of 60% in the uptake of [3H]noradrenaline as well as by a modification in the pattern of [3H]noradrenaline and metabolites spontaneously released. Sixty minutes after exposure to 30 microM apigenin, the proportion of unmetabolized [3H]noradrenaline increased from 11% to 45% of the total products collected in the organ bath whereas the tritiated O-methylated deaminated metabolites decreased from 33% to 14% of the total efflux. A small but significant decrease in the outflow of [3H]3,4-dihydroxymandelic acid as well as a tendency to a decrease in the efflux of [3H]3,4-dihydroxyphenylglycol was also observed. Furthermore, apigenin inhibited in a concentration-dependent manner the activity of monoamine oxidase in the rat atrial homogenates. The calculated IC50 (7.7 microM) was within the range that produced 50% of the maximal increase in atrial rate. It is concluded that apigenin possesses the property to increase the atrial rate, probably as a result of a reduction in noradrenaline uptake as well as in monoamine oxidase activity.

Animals↗

PubMed1992

Thrombocyte monoamine oxidase activity and behavior deviances in adolescence.

The frequencies of patients with low thrombocyte monoamine oxidase (MAO) activity (defined as having an activity lower than 1 SD below the mean of a respective control group) were studied in 100 consecutive cases admitted to a clinic for child and youth psychiatry. 41 boys and 26 girls (group I) had behavior disorders, attention deficit disorders and/or alcohol and hashish abuse according to DSM III R. 16 boys and 17 girls had other diagnoses (group II). None of the 2 male patient groups differed significantly from the controls. A significantly higher percentage of the girls in group I had low activity of platelet MAO than in the control group (p = 0.015), while the girls in group II did not differ from the controls. Acting out, antisocial behavior and abuse is less accepted in women than in men. Therefore, the girls in the present study might be either more psychiatrically disturbed or have more deviant personalities than the boys, which might explain why our hypothesis about a lower thrombocyte MAO activity in the adolescents with externalizing symptoms (group I) was verified only in the girls.

Acting Out↗

PubMed1987

Alterations in monoamine oxidase activity of the mouse brain and liver after mixed neutron-gamma irradiation.

Monoamine oxidase (MAO) plays an important role in the metabolism of neuro-transmitter biogenic amines. Its activity was determined in mouse brain and liver after exposure to different kinds of ionizing radiation and after pretreatment with a radioprotective agent. After a lethal dose of mixed neutron-gamma irradiation the MAO activity decreased in the brain and increased in the liver. In contrast, after a lethal dose of 60Co-gamma irradiation enzyme activity was considerably increased in the brain while in the liver it increased like after mixed neutron-gamma irradiation. AET (S2-aminoethyl-isothiuronium-Br X HBr), when administered in a radio-protective dose, inhibited MAO activity in the brain, while it increased in the liver. Even more marked changes of enzyme activity were observed in both brain and liver after AET pretreatment and mixed neutron-gamma irradiation. On the basis of the results it is suggested that different kinds of ionizing radiation lead to different types of lipid peroxidation in the lipid environment surrounding MAO, an event leading to altered enzyme activity. AET itself inhibited MAO in the brain and increased the activity in the liver but did not prevent the alterations caused by ionizing radiation in enzyme activity.

Animals↗

PubMed1979

Effect of narcotics on monoamine oxidase activity of mouse brain.

The effect of morphine, levorphanol and methadone on the monoamine oxidase (MAO) activity of mouse brain was studied. Both methadone and levorphanol produced a concentration-dependent inhibition of whole brain mitochondrial MAO in vitro with an IC50 of approximately 7.4 x 10(-4) for levorphanol and 2.5 x 10(-6)M for methadone. Methadone also produced a 60% inhibition of the MAO activity of the hippocampus, a 32% inhibition of the striatal and hypothalamic enzyme, a 30% inhibition of liver, and a 20 and 23% inhibition of the cerebral cortex and cerebellum, respectively. Naloxone did not antagonize this effect of methadone. In contrast, morphine had little effect in vitro except at very high concentrations where it was inhibitory. This was not linear with concentration and no IC50 could be estimated. This would imply that the inhibition by morphine is non-specific. When acutely administered to mice, morphine and methadone, again differed. Methadone produced a slight but significant inhibition of whole brain MAO and a 34% inhibition of the striatal enzyme. Morphine, on the other hand, produced a marked enhancement in the activity of the striatal enzyme. Since this action could not be demonstrated in vitro, it would suggest that the in vivo effect of morphine is indirect resulting from an alteration of some other modulating system.

Animals↗

PubMed1981

Elevation of epinephrine concentration in rat brain by LY51641, a selective inhibitor of type A monoamine oxidase.

LY51641, N-[2-(o-chlorophenoxy)ethyl]cyclopropylamine hydrochloride, selectively inhibited type A monoamine oxidase (MAO) (measured with 10 microM 14C-serotonin as substrate) without inhibiting type B MAO (measured with 12.5 microM 14C-phenylethylamine as substrate) in rat brain. The inhibition of type A MAO was accompanied by an increase in epinephrine concentration in hypothalamus. Although the absolute concentration of epinephrine in rat hypothalamus is low relative to norepinephrine and dopamine, the percentage increase in epinephrine after LY51641 was greater than the percentage increase in dopamine or norepinephrine. The inhibition of type A MAO activity and increase in hypothalamic epinephrine concentration following a single 30 mg/kg dose of LY51641 persisted for at least 10 days. Both effects were seen at doses as low as 0.03 mg/kg of LY51641. A 0.2 mg/kg dose of LY51641 given daily for 5 days retained selectivity in inhibiting type A MAO and increased epinephrine concentration. Two analogs of LY51641 of differing selectivity elevated epinephrine concentration to a degree related to percentage inhibition of type A MAO, and the effect of LY51641 was antagonized by pretreatment with harmaline, a short-acting reversible inhibitor of type A MAO. These findings support earlier evidence that in rat hypothalamus, epinephrine oxidation occurs by type A not type B MAO.

Animals↗

PubMed1994

Monoamine oxidase inhibitory effects of some 4-aminophenethylamine derivatives.

The in vitro and ex vivo monoamine oxidase (MAO) inhibitory effects of (+/-)4-dimethylamino-alpha-methyl-phenethylamine (4-DMAA) and (+/-)4-methylamino-alpha-methyl-phenethylamine (4-MAA) were reassessed, in comparison with the previously unstudied achiral parent compound, 4-dimethyl-aminophenethylamine (4-DMAPEA) and with a salt of 4-DMAA enriched in the levo isomer, ("-")-4-DMAA, using amiflamine [S-(+)-4-dimethylamino-alpha,2-dimethylphenethylamine] as positive control. The in vitro studies confirmed that 4-amino-alpha-methylphenethylamine derivatives are highly selective and reversible MAO-A inhibitors. Furthermore, ("-")-4DMAA was less active than the racemic mixture. The side chain-unsubstituted compound, 4-DMAPEA, proved to be a nonselective and reversible MAO inhibitor. The ex vivo results, in which catecholamines, serotonin (5-HT) and their metabolites were measured in two brain regions after i.p. administration, confirmed the results obtained in vitro. These results are consistent with the suggestion that the 4-amino group contributes to MAO inhibitory effects of alpha-methyl-phenethylamines, and show that the presence and orientation of an alpha-methyl side chain substituent may be important when determining the potency and selectivity of these compounds. All compounds tested could be quantified by HPLC with electrochemical detection.

Animals↗

PubMed1981

Differences in the structure of A and B forms of human monoamine oxidase.

[3H]Pargyline-labeled polypeptides associated with the A and B types of monoamine oxidase (MAO) activity in human tissues were analyzed by sodium dodecyl sulfate--polyacrylamide gel electrophoresis (SDS-PAGE). [3H]Pargyline was bound to MAO A in a crude mitochondrial fraction from the placental trophoblast of a male newborn and to MAO B in blood platelets from the umbilical vein of the same newborn. [3H]Pargyline was also bound to MAO A and B in a crude mitochondrial fraction from cultured skin fibroblasts of a male adult and to MAO B in blood platelets from the same individual. Specific labeling of proteins associated with type A or type B activity in fibroblast cells was achieved by preincubation with selective B or A inhibitors, respectively. For all tissues, SDS-PAGE of [3H]pargyline-bound samples revealed a labeled protein band of apparent molecular weight 63,000 for MAO A and 60,000 for MAO B. When SDS-solubilized, [3H]pargyline-labeled MAO A and B proteins from the same male newborn were subjected to limited proteolysis and one-dimensional peptide mapping in SDS gels, different patterns of [3H]pargyline-labeled peptides were obtained. These findings indicate that distinct enzyme molecules are associated with the A and B types of human MAO activity.

Adult↗

PubMedDate not supplied

The effects of continuous light and darkness on the activity of monoamine oxidase A and B in the hypothalamus, ovaries and uterus of rats.

For assessing monoamine oxidase (MAO-A and -B) activities in the hypothalamus, ovaries and uterus, mature female rats were exposed to either continuous light or dark over 6 weeks. Confirming previous studies, continuous light induced constant estrus in all animals. The majority of animals kept under continuous dark during the six weeks remained mostly in diestrus with estrus appearing sporadically. The endocrinological function of the ovaries was disturbed by continuous light, which resulted in the development of polycystic ovaries, their morphological appearance being not significantly affected by continuous dark. Hypothalamic MAO-A activity was markedly reduced under the influence of both light (p < 0.05) and dark (p < 0.01). The activity of hypothalamic MAO-B was reduced only under the influence of dark (p < 0.01). In the ovaries, no significant differences were detected in either MAO-A or -B activity as a result of these environmental manipulations. In the uterus of rats exposed to continuous light which developed polycystic ovaries, MAO-A activity was significantly lower (p < 0.05) in comparison to either intact controls or rats exposed to continuous dark. These results demonstrate that chronic changes in photoperiodicity may considerably influence MAO-A activity and to a lesser extent MAO-B activity dependent on the tissue studied.

Animals↗

PubMed2006

An association study of catechol-O-methyltransferase and monoamine oxidase A polymorphisms and personality traits in Koreans.

Catechol-O-methyltransferase (COMT) and monoamine oxidase A (MAOA) are both involved in the degradation of various biogenic amines which have been hypothesized to have a relationship with personality traits. The present study investigated the possible relationships between the genotypes of COMT Val158Met and MAOA-uVNTR polymorphisms and personality traits measured by the Temperament and Character Inventory (TCI). We recruited 286 normal, unrelated Korean subjects (138 males and 148 females). There were no associations between the COMT Val158Met genotypes or the TCI subscales in the male subjects. However, a significant correlation was observed between the COMT genotype and harm avoidance (HA, F=6.0, p=0.003) in females. Post hoc analyses showed that the subjects with the Met/Met genotype had the lowest mean HA (HA=13.8+/-5.7, p=0.02), Val/Met group had an intermediate mean HA score (HA=16.3+/-7.0, p=0.02), and Val/Val group had the highest mean HA value (HA=19.6+/-7.0, p=0.02). There were no associations between the MAOA-uVNTR and the TCI subscales in either the male or female subjects. These results suggest that genetic variants of the COMT Val158Met gene may play a role in HA in Korean females but not in males.

Adult↗