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PubMedDate not supplied

[Oxidative modification of monoamine oxidase].

Oxidative modification of monoamine oxidases (MAO) accompanied by alteration of their substrate specificity and sensitivity to specific inhibitors was discovered by Professor V.Z. Gorkin more than 30 years ago. The mechanism of this phenomenon includes oxidation of SH groups of the enzyme. Oxidative modification of MAO is also accompanied by increased sensitivity to limited proreolysis. Modification of MAO was found in many pathological states, however, elucidation of biological role of this phenomenon requires further investigations.

Animals↗
PubMed1980

Delusional misidentification and platelet monoamine oxidase.

Recently, reduced platelet monoamine oxidase (MAO) activity was demonstrated in two cases of paranoid schizophrenia exhibiting Capgras' syndrome. The present authors report platelet MAO studies in an additional patient with the Delusion of Doubles. In this case, one of delusional hyperidentification (false recognition), decreased platelet MAO activity compared with normal controls was detected. The patient, while not schizophrenic, showed platelet MAO activity comparable with that of a chronic schizophrenic control group. The possible significance of the findings are discussed.

Adult↗
PubMed1979

Human platelet monoamine oxidase activity in glaucoma.

Monoamine oxidase (MAO, E.C. 1.4.3.4) activity was determined by spectrophotofluorimetric assay of the reaction product of the artificial substrate kynuramine in platelets from venous blood samples from 50 outpatients with glaucomas and 47 sex- and age-matched controls. No significant differences were found between MAO activity in control subjects and that in subjects with glaucomas grouped according to diagnostic subcategories. Irrespective of ocular disease, women had significantly higher enzyme activity than men. Age-related changes in platelet MAO were inconsistent.

Adult↗
PubMed1992

Mitochondrial targeting signal of rat liver monoamine oxidase B is located at its carboxy terminus.

Monoamine oxidase B, a typical intrinsic protein of the outer mitochondrial membrane, has an uncleavable targeting signal and is inserted into the membrane without proteolytic maturation. To investigate the region responsible for targeting the enzyme to the outer mitochondrial membrane, various mutated proteins were expressed in cultured mammalian cells, and the distributions of the expressed proteins were analyzed by immunofluorescence microscopy and subcellular fractionation. Deletion of the carboxy-terminal 28 amino acids of monoamine oxidase B abolished the transfer of the enzyme to mitochondria, while the deletion of the amino-terminal 55 amino acids had no effect on the transfer to mitochondria. The existence of the targeting signal at the carboxy-terminal portion of the enzyme was confirmed by using hybrid proteins in which the amino- or carboxy-terminal portion of the enzyme was fused to the hydrophilic portion of cytochrome b5. The fused protein with the carboxy-terminal 29 amino acid residues of monoamine oxidase B was localized in mitochondria, whereas that with 10 amino acids remained in the cytoplasm. These results indicate that the targeting signal of monoamine oxidase B is present within its carboxy-terminal 29 amino acid residues.

Animals↗
PubMed1987

Species differences in lung mitochondrial monoamine oxidase activities.

Pulmonary mitochondrial monoamine oxidase (MAO) activity was examined in preparations from rat, rabbit and guinea-pig with 12 different amines as substrates: serotonin, norepinephrine, and octopamine (type A specific); tryptamine, benzylamine, 5-methoxytryptamine, 5-methyltryptamine, p-methoxyphenylethylamine, and 3,4-dimethoxyphenethylamine (type B specific); and tyramine, dopamine and 3-methoxytyramine (type A + B specific). The oxidation of type A and type A + B substrates was greater in guinea-pig lung mitochondria than in rat or rabbit preparations. Except for benzylamine, the oxidation of type B substrates was similar in all three species. Benzylamine was not oxidized by guinea-pig lung mitochondria but was actively metabolized by rat and rabbit preparations.

Animals↗
PubMed1997

Potential latent nitrogen mustard derivatives designed to target monoamine oxidase rich cells.

The monoamine oxidases A and B (MAO-A and MAO-B) catalyze the alpha-carbon oxidation of a variety of 4-substituted 1-methyl-1,2,3,6-tetrahydropyridine derivatives to yield the corresponding 2,3-dihydropyridinium species. When the substituent at C-4 of the tetrahydropyridine moiety is a carbamoyloxy functionality, the resulting dihydropyridinium metabolite undergoes spontaneous hydrolytic cleavage to yield 1-methyl-5,6-dihydro-4-pyridone, CO2, and the corresponding secondary amine. In this paper we summarize our efforts to exploit this metabolic pathway to develop latent nitrogen mustard derivatives related to the oxazaphosphorine antitumor agent cyclophosphamide which may target MAO-A and/or MAO-B rich cells.

Animals↗
PubMed1989

The pharmacology of reversible monoamine oxidase inhibitors.

The older monoamine oxidase inhibitors (MAOIs) are mechanism-based, irreversible inhibitors of MAO; most inhibit both the A and B forms of MAO. Several of the drugs are hydrazine derivatives which have non-specific effects other than MAO inhibition. These properties convey disadvantages, which may be seen as serious, though infrequent, adverse events--the 'cheese effect', hepatotoxicity, amphetamine-like activity, orthostatic hypotension and anticholinergic effects. New, reversible MAOIs stem from a variety of chemical classes and are more specific in their effects, with relatively rapid onset of action, direct relationship between plasma concentration and pharmacological effect, and no prolonged carry-over phenomena.

Administration, Oral↗
PubMedDate not supplied

A promoter polymorphism in the monoamine oxidase A gene and its relationships to monoamine metabolite concentrations in CSF of healthy volunteers.

Concentrations of monoamine metabolites (MM) in lumbar cerebrospinal fluid (CSF) have been used extensively as indirect estimates of monoamine turnover in the brain. We investigated possible relationships between a putative functional promoter polymorphism in the monoamine oxidase A (MAOA) gene and CSF concentrations of homovanillic acid (HVA), 5-hydroxyindoleacetic acid (5-HIAA), and 3-methoxy-4-hydroxyphenylglycol (MHPG) in healthy volunteers (n=88). Among women (n=37), those carrying at least one copy of the alleles associated with more efficient transcription displayed higher concentrations of HVA (p=0.01) and 5-HIAA (p=0.01). In men (n=51), however, there was a tendency in the opposite direction. The results suggest that MAOA genotypes may participate differentially in the regulation of dopamine and serotonin turnover rates under presumed steady state in the central nervous system. The results should be interpreted with caution until replicated because of the limited sample size.

Adult↗
PubMed1997

The influence of estrogen on monoamine oxidase activity.

The enzyme monoamine oxidase (MAO) has generated considerable interest as a biological marker. The serendipitous discovery that iproniazid was a weak MAO inhibitor (MAOI) led to the development and widespread use of MAOIs as antidepressants in the early 1950s. The-discovery of the two isoenzymes of MAO has led to the development of selective MAOIs that may have a more favorable side-effect profile. The regulation of MAO is multifactorial, and there is evidence that it involves estrogens. Improvement in mood and cognition reported in women on estrogen replacement therapy may also involve changes in MAO activity. The literature in this regard is reviewed here, and possible implications of the effects of estrogens on MAO activity are discussed.

Alzheimer Disease↗
PubMed1983

Monoamine oxidase activity in diabetes.

Monoamine oxidase (MAO) activities were measured in platelets from insulin-dependent and non-insulin-dependent diabetic subjects and in platelets from nondiabetic controls. Circulating levels of glycosylated hemoglobin (HbA1) were determined simultaneously. Mean MAO activities were not significantly different in any of these groups. MAO activity did not relate to the age of the individual, but mean values for females were higher than mean values for males in healthy controls and in insulin-dependent diabetics. In this study mean HbA1 levels were higher in female than in male diabetics. There was no relationship between MAO activity and HbA, level when results for males and females were analyzed separately.

Adolescent↗
PubMed2000

The genotype of human transcription factor AP-2beta is associated with platelet monoamine oxidase B activity.

Platelet monoamine oxidase B (MAO; EC 1.4.3.4.) activity is stable in the individual and is mainly genetically regulated. Levels of MAO-B in platelets have repeatedly been shown to be associated with personality traits. We have recently also demonstrated an association between the genotype of AP-2beta to a variety of personality traits as well as binge-eating disorder. In the present study we have analysed blood samples from 158 males and 64 females with regard to platelet MAO activity and genotype of transcription factor AP-2beta. In both sexes homozygotes for the long allele [CAAA](5) were significantly associated with low platelet MAO activity P<0.0001 (males) and P=0.0158 (females). This study represents a novel approach to increase the understanding about the molecular mechanisms for how the MAOB gene is regulated in blood cells and how this regulation is linked to personality traits.

Alleles↗
PubMed1980

Brain and skeletal muscle monoamine oxidase activity in schizophrenia.

Monoamine oxidase (MAO) activity has been studied in postmortem brain specimens from chronic schizophrenics and comparison groups by various laboratories. There is no evidence for decreased MAO activity in the brains of the schizophrenic patients, but many possible sources of error in postmortem studies make the conclusions of these studies less than definitive. However, since almost complete inhibition of brain MAO activity appears necessary before it has any functional significance, reduced brain MAO activity is unlikely to have any significance for the pathogenesis of psychosis. Brain and platelet MAO activities in man have been found not to be significantly correlated with each other. There is some evidence neuroleptic drugs may inhibit human brain MAO activity in vitro, but indirect evidence from spinal fluid and postmortem studies is not consistent with this. Decreased MAO activity has been found in the skeletal muscle of various types of psychotic patients compared to normal controls. This suggests decreased MAO activity in peripheral tissues may be a nonspecific marker for vulnerability to the development of psychopathology.

Antipsychotic Agents↗
PubMed2004

Immobilized enzyme reactors based upon the flavoenzymes monoamine oxidase A and B.

Monoamine oxidase (MAO) catalyzes the oxidative deamination of amines. The enzyme exists in two forms, MAO-A and MAO-B, which differ in substrate specificity and sensitivity to various inhibitors. Membrane fractions containing either expressed MAO-A or MAO-B have been non-covalently immobilized in the hydrophobic interface of an immobilized artificial membrane (IAM) liquid chromatographic stationary phase. The MAO-containing stationary phases were packed into glass columns to create on-line immobilized enzyme reactors (IMERs) that retained the enzymatic activity of the MAO. The resulting MAO-IMERs were coupled through a switching valve to analytical high performance liquid chromatographic columns. The multi-dimensional chromatographic system was used to characterize the MAO-A (MAO-A-IMER) and MAO-B (MAO-B-IMER) forms of the enzyme including the enzyme kinetic constants associated with enzyme/substrate and enzyme/inhibitor interactions as well as the determination of IC(50) values. The results of the study demonstrate that the MAO-A-IMER and the MAO-B-IMER can be used for the on-line screening of substances for MAO-A and MAO-B substrate/inhibitor properties.

Bioreactors↗
PubMed1993

The deduced amino acid sequences of human platelet and frontal cortex monoamine oxidase B are identical.

Monoamine oxidases (MAOs) A and B play important roles in the metabolism of neuroactive, vasoactive amines. Human platelets contain only MAO B, often used as an indicator of brain MAO B. The validity of this model remained to be evaluated. This report describes the molecular cloning of human MAO B from frontal cortex and platelets. Two overlapping PCR-amplified clones of human platelet MAO B and four PCR-amplified clones of human frontal cortex MAO B covering the entire coding region were sequenced using five internal oligomers and M13 reverse and forward primers. The nucleotide sequences of human MAO B cDNA from platelet and frontal cortex were identical to that of human liver MAO B except for three nucleotides that differed in frontal cortex: nucleotides 440 A-->G, 794 C-->T, and 825 C-->T. Whether or not these differences are artifactual, all three represent silent mutations, which would not alter the amino acid of the encoded polypeptides. Thus, the deduced amino acid sequences of MAO B from frontal cortex, platelet, and liver are identical. These findings indicate the validity of using platelet MAO B mRNA as a marker for brain MAO B and provide a new approach to study the role of brain MAO B in humans.

Amino Acid Sequence↗
PubMed1992

Molecular properties of monoamine oxidases A and B.

Monoamine oxidases A and B (MAO-A and B) catalyze the oxidative catabolism of biogenic amines and xenobiotics. Investigation of these mitochondrial membrane proteins shows that they differ in substrate preference, inhibitor specificity, tissue and neuronal cell distribution, immunological properties, and nucleotide and deduced amino acid sequences. Comparisons of MAO-A and B from the human, bovine, and rat species show strikingly high similarity (85-88%) in the amino acid sequences of each enzyme. Furthermore, three regions in MAO-A and B have sequence identities across species of 78, 88, and 86%. These regions correspond to a nucleotide-binding site near the N-terminal end that is found in the vast majority of enzymes that require flavin adenine dinucleotide (FAD), a region of unknown function, and the FAD-binding site toward the C-terminal end. Genomic clones of MAO-B which span almost the entire gene (greater than 40 kb) have been isolated, restriction mapped, and partially sequenced. Likewise, genomic clones of MAO-A that correspond to the 3'-flanking region have also been investigated. Current studies which focus on identification of the promoter and regulatory sequences should help to establish why MAO-A and B are localized in different subsets of neurons in brain.

Chromosome Mapping↗
PubMed1996

Tyramine content of previously restricted foods in monoamine oxidase inhibitor diets.

Traditional monoamine oxidase inhibitors (MAOIs) remain an important class of drugs for a variety of psychiatric conditions, including depressive illnesses, anxiety, and eating disorders. It was the objective of this study to refine the MAOI diet by determining the tyramine content of a variety of untested and "controversial" foods that continue to appear on MAOI diet-restricted food lists. A secondary objective of the study was to evaluate the effect of freshness on the tyramine content of some foods. Fifty-one food samples were evaluated for tyramine content by liquid chromatography. Food samples included a selection of sausages, beverages, sliced meat products, including chicken liver, and some fruits, including raspberries, bananas, and banana peels. Foods that were found to have dangerously high concentrations of tyramine (> or = 6 mg/serving) included chicken liver aged 9 days (63.84 mg/30 g), air-dried sausage (7.56 g/30 g), soy sauce (0.941 mg/ml), and sauerkraut (7.75 mg/250 g). Of the foods analyzed in this study, only those with high tyramine content per serving should continue to be absolutely restricted. All other foods are either safe for consumption or safe in moderation. The data provided should be combined with the data from other similar analytical studies to develop a list of foods that should be absolutely restricted. A more accurate list of restricted foods may enhance patient dietary compliance.

Diet Therapy↗
PubMed1997

A key amino acid responsible for substrate selectivity of monoamine oxidase A and B.

Monoamine oxidase (MAO) oxidizes biologically important amines including neurotransmitters and plays a central role in the regulation of intracellular level of these amines. Two distinct forms of MAO (MAO A and MAO B) were defined based on differences in substrate and inhibitor specificities. We earlier reported that the region between about residues 120 and 220 of rat MAO is responsible for determination of the substrate selectivity of MAO A and B (Tsugeno, Y. Hirashiki, I., Ogata, F., and Ito, A. (1995) J. Biochem. (Tokyo) 118, 974-980). To determine the essential amino acids in this region that participate in substrate recognition, a series of mutant enzymes in which amino acid residues that are conserved among various species but are different between the two forms of the enzyme were replaced with the corresponding amino acids of the counterpart and were engineered from the cDNAs of rat liver MAO A and B, and affinities for several substrates were examined. A single mutation in which Phe-208 in MAO A was substituted by the corresponding residue of Ile in MAO B was sufficient to convert the A-type substrate selectivity, and the reverse was exactly the case. Phe at this position was replaceable with Tyr for the A-type specificity and Ile was replaceable with Val and Ala for the B-type. Thus, aromatic and aliphatic residues seem to contribute to render substrate selectivity of MAO A and MAO B, respectively.

Amino Acid Sequence↗
PubMed1987

L-deprenyl in Alzheimer's disease. Preliminary evidence for behavioral change with monoamine oxidase B inhibition.

Since monoamine neurotransmitter disturbances exist in some cases of dementia of the Alzheimer's type (DAT), monoamine-enhancing drugs may ameliorate some symptoms of DAT. L-Deprenyl is a monoamine oxidase (MAO) inhibitor that is generally free of undesired effects. At low doses (10 mg/d) it selectively inhibits MAO-B, an enzyme whose level is elevated in the brains of patients with DAT who are studied post mortem. At higher doses it has more complex effects, including inhibition of MAO-A plus MAO-B. We administered 10 mg/d and 40 mg/d of L-deprenyl to 17 patients with DAT in a double-blind, placebo-controlled, serial treatment. Total Brief Psychiatric Rating Scale scores decreased significantly during 10-mg/d treatment, with decreases in measures of anxiety/depression, tension, and excitement. Approximately one half of the patients' conditions were judged to be improved clinically, with evidence of increased activity and social interaction along with reduced tension and retardation. Similar but smaller changes were observed during 40-mg/d treatment. The behavioral changes were associated with improvement in performance on a complex cognitive task requiring sustained effort. There were minimal physiologic and side effects. The greater effect of low-dose L-deprenyl therapy suggests that it is the inhibition of MAO-B, and not MAO-A, that may be important in the behavioral effects of L-deprenyl administration to patients with DAT.

Adult↗