Endogenous urinary monoamine oxidase inhibitor excretion in Parkinson's disease and other neurological disorders

Summary In this study, urinary output of both neutral (tribulin) and basic monoamine oxidase inhibitory activity was measured in parkinsonian patients, other neurological patients and controls. No significant differences in output were found between these different groups. In general, tribulin output rose with age, in parallel with known changes in monoamine oxidase B activity.     

Platelet monoamine oxidase activity and psychopathy

Platelet monoamine oxidase (MAO) activity appears to be correlated to certain diagnostic subgroups and symptom patterns. A group of criminal offenders hospitalized for forensic psychiatric assessment were studied. Male nurses and construction workers were used as controls. Patients who were diagnosed as psychopaths according to the criteria of Cleckley had significantly lower platelet MAO activity than the control group of construction workers.     

Platelet and fibroblast monoamine oxidase in alcoholism

Monoamine oxidase (MAO) activity has been reported to be low in platelets (MAO B) and brain (MAO A and B) of some patients with alcoholism compared to control subjects. Whether the decreased platelet MAO activity found in alcoholism is secondary to the effect of alcohol or exists before alcohol abuse is not clear. The hypothesis that altered MAO A activity is determined by an abnormality in the genetic regulation of the enzyme can be tested by measuring MAO A activity in human fibroblasts cultured under controlled conditions. We first studied the kinetic parameters of platelet MAO B activity in patients hospitalized for treatment of alcoholism. Vmax was 38% lower in the patients (n = 14) than in normal controls (n = 22), but the enzyme affinity (Km) for the substrate tyramine was unchanged. Patients with the five lowest levels of platelet MAO activity had MAO activity measured from fibroblasts cultured from skin punch biopsies. Their fibroblast MAO activity was within the normal range, showing a dissociation between platelet MAO B and fibroblast MAO A activities and suggesting that MAO A activity is not low for genetic reasons in alcoholic subjects who do have low platelet MAO B activity.     

Characterization of monoamine oxidase activity during early stages of quail embryogenesis

Catecholamines and other biogenic amines may play a role in early embryogenesis in addition to functioning as neurotransmitters after neuronal differentiation. Regulation of amine levels is mediated by several different parameters including activity levels of degradative enzymes. Since monoamine oxidase (EC 1.4.3.4) is the primary degradative enzyme for these biogenic amines, we have begun to characterize MAO activity during quail embryogenesis. Our results demonstrate that MAO activity is present at all stages of development examined (stages 2–22) and that the MAO specific activity levels are highest during the earliest stages (stages 2–6). Two types of MAO activity similar to adult avian and mammalian MAO-A and MAO-B have been demonstrated by differential clorgyline sensitivity of tryptamine deamination. In addition, SDS-PAGE of embryonic quail [³H]pargyiine-labeled MAO demonstrates that the quail MAO-A and MAO-B flavin-containing subunits have apparent molecular weights of 63,000 and 62,000 respectively.We have begun to assess the functional significance of embryonic quail MAO activity by daily injection of MAO inhibitors (clorgyline or clorgyline plus deprenyl) into fertilized eggs. Clorgyline injection selectively and completely inhibited MAO-A activity, while injection of clorgyline and deprenyl inhibited both MAO-A and MAO-B activities when embryos were assayed after either 2 or 7 days of embryonic development. This paradigm will allow a detailed examination of the effects of MAO inhibition on the developing embryo.     

MDL 72,974: a potent and selective enzyme-activated irreversible inhibitor of monoamine oxidase type B with potential for use in Parkinson's disease

Summary MDL 72,974, (E)-2-(4-fluorophenethyl)-3-fluoroallylamine, was designed to be a selective inhibitor of monoamine oxidase type B (MAO-B). In vitro, the compound inhibits rat brain mitochondrial MAO in a concentration and time-dependent fashion and shows marked selectivity for the B form (IC₅₀=680 and 3.6nM for MAO-A and MAO-B, respectively). After oral administration to rats, the compound shows preferential inhibition of brain MAO-B with ED₅₀ values of 8 and 0.18 mg/kg p.o. for the A and B forms, respectively. Selectivity is retained on repeat dosing. MDL 72,974 did not significantly potentiate the cardiovascular effects of intraduodenually-administered tyramine in anaesthetized rats and had only minor indirect sympathominatic effects in the pithed rat. At MAO-B selective doses the neurotoxic effect of MPTP in mice was blocked.Part of this work was presented at the 7th European Winter Conference on Brain Research (Zreika et al., 1987).     

Platelet monoamine oxidase molecular activity in demented patients

Blood platelet monoamine oxidase activity, as well as other platelet enzyme activities, have been studied in several neuropsychiatric disorders in an attempt to identify biochemical markers of altered brain function. In this study, we determined both total and molecular monoamine oxidase activity in platelets derived from demented patients, which showed significantly greater enzyme activity than those of the controls. It therefore seems that the high degree of monoamine oxidase activity depends on the increased intrinsic activity of individual enzyme molecules. A significant positive correlation was found between monoamine oxidase activity and the severity of illness, which suggests that monoamine oxidase activity may be a state-dependent marker of neurodegeneration. These findings are discussed with reference to the central nervous system biochemical abnormalities of demented subjects: it may be that Alzheimer-type dementia involves some central biochemical changes that are reflected in certain peripheral tissues (e.g. platelets), or a systemic derangement that also affects the brain.

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Sommario L'attività monoamino-ossidasica (MAO) piastrinica, come pure altre attività enzimatiche trombocitarie, sono state studiate in varie patologie neuropsichiatriche, allo scopo di identificare indici biochimici di un alterato funzionamento cerebrale. In questo lavoro abbiamo determinato l'attività MAO totale e quella molecolare in piastrine di pazienti affetti da demenza tipo Alzheimer, riscontrandone un aumento significativo rispetto ai controlli. Sembra, pertanto, che elevati livelli di attività MAO dipendano da un incremento dell'attività intrinseca delle singole molecole di enzima. Abbiamo osservato vieppiù una correlazione significativa tra attività MAO e gravità di malattia: l'attività MAO quindi può considerarsi, relativamente ad eventi neurodegenerativi, un indice di stato. Questi risultati vengono discussi in riferimento alle alterazioni biochimiche del sistema nervoso centrale occorrenti in pazienti con demenza tipo Alzheimer: può verificarsi che in questa condizione morbosa talune modificazioni biochimiche centrali si riflettano a livello periferico (ad es. nelle piastrine), oppure che alterazioni sistemiche si associno ad un interessamento cerebrale.

     

Substrate-typic changes of platelet monoamine oxidase activity in sub-types of schizophrenia

Summary Monoamine oxidase (MAO) activity has been measured in the platelets of controls (n=42) and schizophrenic patients (n=49) of three subtypes, using -phenylethylamine, p-tyramine, and tryptamine as substrates. Characteristic differences of MAO activity were observed between platelets of patients and controls; the differences were substrate-typic: decreased enzyme activity was found with all three substrates in platelets of the parnaoid subtype. With tryptamine, MAO activity was decreased in the platelets of all three sub-types of schizophrenia. With p-tyramine, MAO was low in patients with affective psychoses and paranoid schizophrenia.The value of MAO activity measurements as a means for distinguishing sub-types of schizophrenic disorders is improved by using two substrates; tryptamine and p-tyramine. Possible mechanisms of the substrate-typic changes of platelet MAO activity in schizophrenia are discussed.     

Electrophoresis of platelet monoamine oxidase in schizophrenia and manic-depressive illness

Monoamine oxidase is an important enzyme in the catabolism of biogenic amines and can be measured in human platelets. Platelet MAO has been reported to be reduced in schizophrenic and manicdepressive patients, though other reports are contradictory. The present study evaluated the possibility that qualitative genetic enzyme abnormalities of MAO could be responsible for the different enzyme activities of platelet MAO in different populations. However, polyacrylamide gel electrophoresis of platelet MAO from 10 manic-depressive, 12 schizophrenic, and 11 normal individuals did not reveal any genetic mutant forms.     

Brain gamma-aminobutyrate transaminase and monoamine oxidase activities in suicide victims

Summary The activity of gamma-aminobutyrate aminotransferase (GABA-T) and monoamine oxidase (MAOA and-B) was measured in 42 postmortem human brains. Three brain regions (frontal cortex, cingulate cortex and hypothalamus) from 23 controls without known neurological or psychiatric disorder and from 19 suicide victims were analysed. The suicide victims were classified according to the use of violent and non-violent methods and to the presence or absence of a known history of depressive disorder. No difference was found between the series of suicide victims and the control subjects with regard to GABA-T activity. Carbon monoxide poisoning and death by drug overdose, however, were found to reduce the activity. The MAO-B activity did not differ between the groups. With MAO-A, however, a significant elevation (t=2.01;P<0.05) was found in the hypothalamic region of the suicide victims. The difference seemed to be confined to the subgroup of suicides with a record of depressive disorder.     

Effect of aging on lazabemide binding,monoamine oxidase activity and monoamine metabolites in human frontal cortex

Summary Age-related modifications of monoamine oxidase-A and -B (MAO-A and MAO-B) and amine metabolite concentrations were studied in human frontal cortex taken postmortem from 22 subjects of various ages (21–75 years). Qualitative and quantitative analysis for MAO-B was provided by kinetic studies with a specific radioligand, [³H]lazabemide. The data demonstrated a significant (P < 0.05) positive correlation between the density of [³H]lazabemide binding sites (B_max) and age of the subject, without showing an apparent modification in the dissociation constant (K_D) of the radioligand. In parallel experiments, MAO-B but not MAO-A activity was shown to correlate with age (P < 0.05). The concentrations of the amine metabolites 4-hydroxy-3-methoxyphenylacetic acid (HVA), 5-hydroxyindole-3-acetic acid (5-HIAA), 3,4-dihydroxyphenylacetic acid (DOPAC), 4-hydroxy-3-methoxyphenylglycol (MHPG) and 3,4-dihydroxyphenylglycol (DHPG) were all devoid of a correlation with age. Neither did the concentrations of these metabolites relate to the respective subject's MAO-B enzymatic activity nor to [³H]lazabemide B_max. A correlation, though rather weak, was obtained between MAO-A activity and MHPG concentration (P=0.045). The MAO-A and -B enzyme characteristics in subjects who had committed suicide (n=9) did not differ from those of subjects deceased for other causes (n=13). Among the measured monoamine metabolites the concentrations of DOPAC and HVA were higher in the suicide versus control group (P < 0.05). The present data confirm in a direct manner that the increase in MAO-B activity in aging brain is due to an enhancement of the number of active sites of the enzyme and not through modifications of its kinetic characteristics. Furthermore, that neither the characteristics nor the activity of the enzyme are changed in the frontal cortex of suicide victims compared to control subjects.     

Purification and characterization of tribulin,an endogenous inhibitor of monoamine oxidase and of benzodiazepine receptor binding

Summary A low molecular weight fraction of human urine (<500 daltons) which both inhibits monoamine oxidase and benzodiazepine binding to central and peripheral receptors has been purified by ethyl acetate extractions, HPLC and thin layer chromatography. This material extracted equally well at acid and basic pH and was insoluble in heptane. It competitively inhibited binding of³H-clonazepam, a central benzodiazepine receptor agonist and, in addition, displaced³H-Ro 5-4864, a specific peripheral benzodiazepine receptor ligand, from its binding sites. It showed no GABA shift with the benzodiazepine receptor antagonist, Ro-15 1788. MAO A and B were inhibited approximately equipotently and the material competitively inhibited tyramine oxidation by rat liver. It was stable on boiling and is unlikely to be a peptide.     

Postmortem monoamine oxidase enzyme kinetics in the frontal cortex of suicide victims and controls

ABSTRACT– Serotonin, a preferred monoamine oxidase (MAO) A substrate may be deficient centrally in suicide victims. In postmortem samples of frontal cortex from suicide victims we demonstrated receptor changes in the serotonergic system supportive of this hypothesis. These changes were not accompanied in this series of brain samples by alterations in either MAO A or B enzyme kinetics. Thus brain MAO A is not a useful indicator of altered serotonergic function in suicide victims. We did confirm an age-related increase in cortical MAO B but not MAO A enzyme concentrations in both controls and suicide victims.     

Quantitative distribution of monoamine oxidase A in brainstem monoamine nuclei is normal in major depression

An abnormal expression of noradrenergic proteins (e.g., tyrosine hydroxylase, norepinephrine transporters) in the locus coeruleus has recently been demonstrated in subjects with major depression and/or victims of suicide. Monoamine oxidase A (MAO-A) is a key enzyme in the catabolism of biogenic amines and is expressed in brain noradrenergic neurons. In this study, the binding of [3H]Ro41-1049 to MAO-A was measured by quantitative autoradiography at multiple levels along the rostral-caudal axis of the noradrenergic locus coeruleus from subjects with major depression and age- and postmortem interval-matched control subjects who were psychiatrically normal. [3H]Ro41-1049 binding to MAO-A was unevenly distributed along the axis of the locus coeruleus, paralleling an uneven number of neuromelanin-containing (noradrenergic) neurons throughout the nucleus. Accordingly, there was a significant correlation between the number of neuromelanin-containing neurons per section and the specific binding of [3H]Ro41-1049 at any particular level of the locus coeruleus in control subjects (r(2)=0.25; p<0.001) and in subjects with major depression (r(2)=0.14; p<0. 001). Moderate levels of [3H]Ro41-1049 binding were observed in regions surrounding the locus coeruleus, including the central gray and the dorsal and median raphe nuclei. No significant differences in [3H]Ro41-1049 binding to MAO-A were observed at any level of the locus coeruleus, or raphe nuclei, comparing subjects with major depression to psychiatrically normal control subjects. These findings demonstrate that the pathophysiology of major depression is not likely to involve abnormalities in MAO-A.     

Variations in activity and inhibition with pH: the protonated amine is the substrate for monoamine oxidase,but uncharged inhibitors bind better

Summary It has been accepted that, as required mechanistically, the neutral form of the amine is the substrate for monoamine oxidase, despite the amine pK _a of above 9.5. The pH dependence of the kinetic parameters for kynuramine oxidation by purified human MAO-A and for phenylethylamine oxidation by MAO-B in granulocytes at pH values from 5 to 10 was consistent with the protonated amine being used. Deprotonation of a group of pK _a = 7.1 in MAO-B and pK _a = 7.5 ± 0.1 (n = 4) in MAO-A was important for efficient catalysis. The K_i values for two oxazolidinone inhibitors of MAO-A gave opposite pH-dependence indicating that the uncharged form of each inhibitor bound better than the charged form. Decreased pH induced a blue shift in the spectral maximum of MAO-A indicative of a more hydrophobic environment around the flavin, and also influenced the redox properties of the flavin.     

单胺氧化酶B基因微卫星多态与帕金森病的相关分析

目的 研究上海地区汉族人群中单胺氧化酶B(MAOB)基因第二内含子中鸟嘌呤、胸腺嘧啶(GT)二碱基重复的微卫星多态位点与帕金森病(Parkinson’s disease，PD)易患性之间的关系。方法 采用扩增片段长度多态法(Amp—FLP)，在上海汉族人群中选择67例散发PD患者为PD组和204名健康者为对照组，运用微卫星荧光标记—半自动基因分型技术精确计算出微卫星等位基因片段大小，进而分析该多态在PD易患性中的作用。结果 该位点短片段(≤170bp)等位基因的分布在：PD组中明显高于与对照组(x^2=11．28，P=0．001)，而172bp等位基因在PD组中亦明显低于与对照组(x^2=5．16，P=0．023)。结论 MAOB基因GT二碱基重复多态位点与本组PD患者的易患性有关。     

Serotonergic effects of isatin: an endogenous MAO inhibitor related to tribulin

Summary A study of the acute effects of isatin, an endogenous MAO inhibitor related to tribulin, on rat brain serotonergic function was undertaken. A single dose of isatin significantly increased 5-HT concentrations in the hypothalamus and cortex but did not significantly alter 5-HIAA concentrations. Synaptosomal 5-HT uptake was unaffected but there was a trend for the number of³H-ketanserin binding sites was to be decreased. The results of the study are discussed in terms of the relationship of isatin to tribulin and their possible causal role in stress.     

Selective reduction of monoamine oxidase A and B in the frontal cortex of subordinate rats

We have previously shown that subordination causes a reduction in the levels of 5-hydroxytryptamine and dopamine selectively in the frontal cortex [6]. These monoamines are catabolised mainly by the enzyme monoamine oxidase (MAO) which exists in two isoforms. MAO-A and MAO-B. The present study was carried out to determine whether there is any change in the activity of these two iso-enzymes induced by subordination and if any such alteration is confined to the frontal cortex. The animal model of dominance-subordination used was a worker-parasite paradigm in male Wistar rats. The enzyme activities were measured in five brain regions, the frontal cortex, entorhinal cortex, hippocampus, hypothalamus and striatum, using kynuramine as the substrate. Clorgyline and -deprenyl were used in vitro to block the activities of MAO-A and MAO-B, respectively. There was a significant (P < 0.001) reduction in the activity of MAO-A as well as MAO-B selectively in the frontal cortex of the subordinate animals. This finding may suggest a reduced neurotransmitter turnover in the serotonergic and dopaminergic neurons terminating in the frontal cortex.     

Platelet monoamine oxidase activity and behavioral response to pharmacotherapy in psychiatric patients

Platelet monoamine oxidase (MAO) levels were determined for drug-free psychiatric inpatients who were subsequently treated with neuroleptics, tricyclics, or lithium. Weekly, time-sampled recordings of specific behaviors were also made during both drug-free and medication periods. Significant correlations were obtained between MAO levels and changes in behavior scores subsequent to drug administration. For six of the seven recorded behaviors, correlations for patients treated with lithium vs. tricyclics were in the opposite direction. The results suggest that MAO levels, measured during a drug-free period, can predict some of the behavioral responses to antidepressant medications.     

Association analysis of the functional monoamine oxidase A gene promotor polymorphism in migraine

Summary. Migraine affects about 15% of the adult population. Serotonergic and dopaminergic systems are believed to be involved in its pathophysiology. One of the key enzymes in the degradation of serotonin and to a lesser extent of dopamine is monoamine oxidase A (MAO-A). In this study we investigated a functionally relevant gene-linked polymorphic repetitive sequence (LPR) located approximately 1.2kb upstream of the ATG codon in the MAO-A-promotor gene. 119 patients with migraine and 229 controls were tested. The allelic distribution of the controls and the migraine patients did not show significant differences with respect to the low- and high-activity alleles. Moreover, effectiveness of the potent serotonergic antimigraine agents, triptans, which are metabolized by MAO-A, was clinically not affected by the MAO-A-LPR in our patients. These findings thus indicate that there is no association between the functional MAO-A-LPR and susceptibility to migraine.