Styrene inhibits monoamine oxidase A, but not monoamine oxidase B in monkey brain mitochondria

The effects of styrene on mitochondrial monoamine oxidase (MAO) activity in rat and monkey brains were compared in vitro. After preincubation at 25 degrees C for 20 min with 1 mM styrene monomer MAO-A activity in monkey brain was inhibited potently using 5-HT (for MAO-A substrate), but MAO-B activity in monkey brain and platelets were slightly inhibited using beta-PEA (for MAO-B substrate). Styrene monomer also competitively inhibited MAO-A activity in a dose-dependent manner. MAO-A in monkey brain was inhibited by styrene in ascending order of potency: styrene trimer>styrene dimer>styrene monomer. In contrast styrene monomer slightly inhibited both MAO-A and MAO-B activities in rat brain mitochondria. In the present study styrene monomer potently inhibits MAO-A activity, but not MAO-B activity, in monkey brain mitochondria in vitro. These results indicate the inhibiting action of styrene differs depending on animal species and MAO isoforms.     

The effect of monoamine oxidase A and B inhibitors on rat serum prolactin

Serum prolactin levels were assayed in rats treated with specific inhibitors of monoamine oxidase (MAO) A or B. Monoamine oxidase A was inhibited by MD780515, clorgyline and Lilly 51641, and MAO B by pargyline and deprenyl (all at 10 mg/kg, p.o.). Serum prolactin levels were significantly reduced 1 hour after treatment with MAO A inhibitors, but were unaltered by MAO B inhibitors. The time-course of the reduction in serum prolactin did not correspond to that of MAO A inhibition. When rats were treated with clorgyline, serum prolactin returned to control values by 6 hr after treatment, whereas MAO A was inhibited by 92–94% over the whole period. At a time when MAO A inhibitors produced no change in serum prolactin (5 hr after treatment) they abolished the rise in serum prolactin induced by reserpine (5 mg/kg, i.p.), indicating a continuing absence of MAO A activity in the neurones regulating prolactin release. Monoamine oxidase B inhibitors did not alter the effect of reserpine on serum prolactin. Possible reasons for the rapid recovery of serum prolactin levels are discussed.     

Effects of a monoamine oxidase A inhibitor,FLA 668 (+) on the adrenergic mechanisms of the dog saphenous vein

Summary FLA 668(+)[(S)-(+)-4-amino-2, -dimethylethylphenethylamine (+)-hydrogen bitartrate] selectively inhibited MAO type A in homogenates of dog saphenous vein, with a IC₅₀ of 1 mol/l for MAO A and >1 mmol/l for MAO B.At concentrations of 1 mol/l and higher, FLA 668(+) progressively decreased the formation of deaminated metabolites by saphenous vein strips incubated with³H-noradrenaline, with a preferential action on DOPEG formation. Normetanephrine formation increased but this increase did not wholly compensate for the reduction in the formation of deaminated metabolites.FLA 668(+) caused increased reactivity of saphenous vein strips to noradrenaline and markedly reduced the accumulation of³H-noradrenaline in the incubated tissue; both effects were still evident in the presence of clorgyline. After cocaine, FLA 668(+) caused no further increase in sensitivity.It is concluded that FLA 668(+) is, in the saphenous vein of the dog, a selective inhibitor of MAO type A and that it exerts a cocaine-like effect.Part of the results were presented to the Amine Oxidases: a Cambridge workshop (Caramona et al. 1984). Supported by INIC (Centro de Farmacologia e Biopatologia Quimica da Universidade to Porto)with a grant from the Portuguese-Spanish Academic Exchange Service     

Some interrelated properties of A and B form monoamine oxidase in monkey brain mitochondria

The multiplicity of monoamine oxidase (MAO) in monkey brain was studied by comparing the relationship between the selective substrates of MAO and the pH-activity curves obtained using these substrates. When mitochondrial and A-form MAO were used as the enzyme preparations with serotonin (5-HT) and norepinephrine (NE), preferential substrates for A-form MAO, the pH optima were 8.8 and 7.8 with 5-HT and 8.5 and 7.2 with NE. These substrates were also oxidized by B-form MAO after changing the pH of the incubation medium (shift to alkaline); these pH optima were 9.0 and 8.2, respectively. When common substrates of MAO were used (tyramine, octopamine, dopamine and tryptamine), the pH activity curves obtained were all broad and bell-shaped with pH optima for the 3 species of enzyme (mitochondria, A-form and B-form MAO) at 8.0, 7.8, and 8.0 with tyramine; 8.3, 7.5, and 8.5 with octopamine; 7.8, 7.5, and 8.5 with dopamine; and 8.0, 8.3, and 6.9 with tryptamine, respectively. The pH optima were 6.6 with beta-phenylethylamine (beta-PEA) and 9.0 with benzylamine, preferential substrates for B-form MAO, for either mitochondria or B-form MAO. The Km values obtained for tryptamine and beta-PEA were lower than those for the other substrates of MAO, regardless of the enzyme preparations. The Km and Vmax values of both forms MAO for 5-HT and NE were similar to those of the A-form MAO. The differences in the Km and Vmax values of the A-form MAO and B-form MAO for common substrates were comparable. Tyramine, octopamine and dopamine were substrates for both forms MAO, with only a slight preference for B-form MAO over A-form MAO. However, tryptamine may be deaminated predominantly by A-form MAO.     

Orientation of oxazolidinones in the active site of monoamine oxidase

Oxazolidinone inhibitors of monoamine oxidase (MAO) and oxazolidinone antibacterials are two distinct classes of drug, often with linear structures and overlapping activities for some derivatives. By synthesizing novel dimerised derivatives with identical substitution of the two C-5 side chains, we have obtained experimental evidence for the orientation of oxazolidinones in the active site of MAO A. Two types of spectral changes, either increasing the absorbance at 510 nm or decreasing it at 495 nm depending on the group nearest to the flavin cofactor, were seen on ligand binding to MAO A. Side chain derivatives with amine substituents are very poor substrates so that it was possible to examine the spectral change due to binding of a substrate before reduction of the flavin occurred. Binding of these amino derivative substrates to MAO A induced a spectral change characterized by a strong decrease in absorbance at 495 nm. These substrates reduced the enzyme fully without any trace of a semiquinone intermediate. Only oxazolidinone inhibitors with a bromo-imidazole substituent increased the yield of semiquinone intermediate obtained during chemical reduction. In accord with the experimental data, results of docking experiments showed that binding of the oxazolidinone ring in the aromatic cage close to the flavin was favored and that the nitrogen of the derivatives that were substrates was within van der Waals distance of N-5 of the flavin.     

The monoamine oxidase B inhibitor deprenyl potentiates phenylethylamine behaviour in rats without inhibition of catecholamine metabolite formation.

The drug l-deprenyl has been reported to have antidepressant properties, and in the present study three possible mechanisms of action were investigated in animal experiments. l-Deprenyl, which is a type B monoamine oxidase (MAO) inhibitor, was compared to clorgyline, an MAO A inhibitor with regard to its inhibitory effect on the formation of three major catecholamine metabolites, homovanillic acid (HVA), dihydroxyphenylacetic acid (DOPAC) and 3-methoxy-4-hydroxyphenylglycol (MOPEG) in the rat brain in vivo. Apart from a difference in dose levels the two drugs showed no difference in the dose--response pattern of all three metabolites. Clorgyline inhibited the formation of HVA, DOPAC and MOPEG with an ED50 of about 0.2 mg/kg s.c. and l-deprenyldopamine and noradrenaline are formed by the same type of monoamine oxidase(s), probably type A, in the rat brain in vivo. Antidepressant properties of l-deprenyl therefore seem to be independent of catecholamine deamination. l-Deprenyl but not clorgyline (2 or 8 mg/kg s.c.) potentiated the stereotyped sniffing behaviour induced by beta-phenylethylamine, a specific substrate for type B monoamine oxidase. This result is discussed in relation to a new hypothesis of phenylethylamine and dopamine involvement in depression. l-Deprenyl was 10,000 times less potent than DMI as inhibitor of noradrenaline uptake in crude synaptosomes from the occipital cortex of rat brain. Inhibition of noradrenaline uptake was therefore excluded as a possible mechanism for the antidepressant action of l-deprenyl.     

The effect of reserpine and monoamine oxidase inhibitors on paradoxical sleep in the monkey

Summary Three Macaca, mulatta monkeys were administered parenteral reserpine (0.25 mg/kg), iproniazid (50 mg/kg), and tranylcypromine (2 mg/kg) in a counterbalanced design for seven days. All-night EEG sleep recordings were obtained prior to and during drug administration.Reserpine significantly increased the amount of paradoxical sleep, and decreased the latency to paradoxical sleep onset. Iproniazid significantly decreased the amount of paradoxical sleep and increased the latency to its onset. Tranylcypromine significantly increased the latency to paradoxical sleep onset, but did not decrease the amount of paradoxical sleep.The results are similar to the effect these drugs have on sleep in man, and sleep patterns after reserpine are similar to the sleep patterns of certain patients with psychotic depressive illness, suggesting that the common sleep patterns may in both cases represent an underlying deficiency of noradrenalin.     

Interactions of tricyclic antidepressant drugs with human and rat monoamine oxidase type B

Summary The effect of tricyclic antidepressant drugs on the deamination of phenylethylamine and benzylamine by monoamine oxidase (MAO) type B was investigated in vitro in human brain cortex, human platelet, and rat brain preparations. These drugs inhibited MAO activity as expected; however, an atypical biphasic response was observed with the tertiary amine tricyclic, clomipramine, and, to a somewhat lesser extent, with two other tertiary amine tricyclics, imipramine and amitriptyline, when benzylamine was used as the substrate in human tissue preparations. This atypical biphasic pattern was not found when we used the secondary amine antidepressant drugs, desipramine, desmethylclomipramine, or fluoxetine, or used phenylethylamine as the substrate, or used rat rather than human brain tissue. For the tricyclics exhibiting normal inhibition patterns, the same rank order of inhibition was observed with benzylamine as a substrate in all three types of tissue; however with phenylethylamine, differences in inhibition were found between rat and human tissues. These tricyclic-MAO interactional data suggest that secondary and tertiary amine tricyclics interact differently with human MAO type B, that rat and human MAO type B are not functionally identical, and also support other data that phenylethylamine and benzylamine are deaminated by different mechanisms. Send offprint requests to A. A. Reid at the above address     

锌对幼鼠脑发育及金属硫蛋白表达影响的实验研究

本实验从哺乳期建立大鼠常锌(ZN)、低锌(ZD)及高锌(ZE)动物模型。采用荧光标记及间接免疫荧光法以流式细胞仪检测皮层和海马神经细胞的增殖程度、DNA及蛋白质含量、金属硫蛋白(MT)表达水平,同时利用电镜技术和免疫组化技术分别观测了皮层和海马的超微结构及MT在脑组织内的分布。结果提示:缺锌及高锌均可影响脑组织生长发育及MT表达。饲料锌水平与脑组织MT表达密切相关,锌过低或过高都可引起MT表达的失代偿,使MT失去对脑组织内游离Zn~(2+)水平的调节能力,造成脑生长发育障碍。因此,在神经系统发育关键时期机体保持适当锌摄入量是非常必要的。     

Inhibition by Zn(2+) of A-form monoamine oxidase in monkey brain mitochondria

The effects of ZnSO(4) on mitochondrial monoamine oxidase (MAO) activity in monkey brain were compared with those in rat and rabbit, in vitro. After preincubation at 25 degrees C for 20 min with 1 microM ZnSO(4), MAO-A activity in monkey brain was about 50% using serotonin (5-HT) as a substrate, and the inhibition was proportional to the concentration of ZnSO(4). However, ZnSO(4) had no effect on MAO-B activity in monkey brain using beta-phenylethylamine (beta-PEA) as a substrate. The inhibition by ZnSO(4) of MAO-A activity was competitive and reversible. CdSO(4) also inhibits MAO-A, but not MAO-B in monkey brain mitochondria. ZnSO(4) did not inhibit either MAO-A or MAO-B activity in rat and rabbit brain mitochondria. These results indicate that the inhibiting action of Zn(2+) differs depending on animal species. In monkey brain mitochondria, MAO-A was highly sensitive to Zn(2+) and MAO-B was less sensitive. These results also suggest that Zn(2+) may regulate the level of catecholamine content in monkey brain.     

Selective inhibition of the a form of monoamine oxidase by 4-dimethylamino-α-methylphenylalkylamine derivatives in the rat

The inhibitory effects on monoamine oxidase (MAO) of some dimethylamino-α-phenylalkylamine derivatives were examined in a rat brain mitochondrial preparation in vitro and in rat brain slices following oral administration. In the in vitro assay the compounds were shown to be selective inhibitors of the A form of MAO, being 100–600 limes more potent in inhibiting the deamination of [¹⁴C]5-hydroxytryptamine than that of [¹⁴C]phenetylamine. Using an ex vivo brain slice technique it was found that the new compounds were reversible and very selective inhibitors of type A MAO in the rat brain and the most potent compounds (FLA 405, 314, 336 and 558) were equipotent with clorgyline. The compounds increased the monoamine concentrations in whole rat brain, particularly that of 5-hydroxytryptamine, in the same dose range which produced MAO inhibition. Some of the new compounds, e.g. FLA 336 and FLA 717, caused only weak potentiation of the vaso-pressor effect of orally administered tyramine.     

Effects of three monoamine oxidase inhibitors on ethanol preference in mice

These experiments investigated the effects of pargyline, N-[2-(o-Chlorophenoxy)-ethyl]-cyclopropylamine (Lilly 51641), and nialamide on voluntary ethanol consumption of C57BL/6J mice. Both pargyline and Lilly 51641 reduced ethanol preference; in contrast, nialamide did not affect preference, despite the fact that it inhibited MAO activity by more than 90%. A subsequent experiment determined that both pargyline and Lilly 51641 produced substantially greater elevations in acetaldehyde levels than did nialamide. It is suggested that increased acetaldehyde is the mechanism responsible for the reduction in ethanol preference observed with pargyline and Lilly 51641.     

Effects of d-methamphetamine on monkey brain monoamine oxidase, in vivo and in vitro

A and B form MAO activities in mitochondria and synaptosome were measured in the brain of monkeys administered d-methamphetamine (d-MP) 2 mg/kg, i.m., daily for 7 days. When mitochondria were used as an enzyme preparation, the Km and Vmax values decreased with 5-HT (serotonin for A-form MAO substrate) and beta-phenylethylamine (beta-PEA for B-form MAO substrate), while in the synaptosome, a significant increase of the Km and Vmax values was observed with 5-HT and dopamine as substrates. The mitochondrial MAO treated with d-MP was inhibited strongly by clorgyline and deprenyl with beta-PEA as a substrate, while synaptosomal MAO was highly sensitive to these MAO inhibitors with 5-HT as a substrate. MP and amphetamine (AP) were found in brain mitochondrial and synaptosomal preparations of monkeys administered 2 mg/kg d-MP, i.m. daily for 7 days; MP and AP contents were 5.05 +/- 0.22 pg/mg protein and 37.3 +/- 3.8 ng/mg protein in mitochondria and 2.35 +/- 0.35 pg/mg protein and 46.4 +/- 1.5 ng/mg protein in synaptosomes, respectively. MAO was inhibited by MP and its metabolites, AP p-hydroxymethamphetamine (OH-MP) and p-hydroxyamphetamine (OH-AP), with 5-HT, beta-PEA and dopamine as substrates, in vitro. MP and its metabolites were more potent inhibitors of A-form MAO than B-form MAO.     

Effects of co-administration of a selective serotonin reuptake inhibitor and monoamine oxidase inhibitors on 5-HT-related behavior in rats

5-hydroxytryptamine (5-HT) syndrome is a dangerous condition of 5-HT excess that can occur in the case of co-administration of a monoamine oxidase (MAO) inhibitor and a serotonin reuptake inhibitor (SSRI). The goal of the present study was to investigate the effects of acute administration of MAO inhibitors and subchronic administration of fluvoxamine on 5-HT-related behaviors (head shaking and 5-HT syndrome) in rats treated with 5-hydroxytryptophan (5-HTP). Administration of the non-selective MAO inhibitor, pargyline, and the selective MAO-A inhibitor, clorgyline, resulted in 5-HT syndrome in 5-HTP-treated rats, and subchronic co-administration of fluvoxamine intensified the syndrome. However, administration of the selective MAO-B inhibitor, selegiline, did not induce 5-HT syndrome with or without subchronic fluvoxamine co-administration. These data suggest that non-selective MAO and selective MAO-A inhibitors can induce 5-HT syndrome in humans when co-administered with SSRI. Further, the risk of 5-HT syndrome may be lower with the selective MAO-B inhibitor, selegiline.     

无机汞对大鼠脑单胺类神经递质代谢的影响

用大鼠脑组织匀浆、游离脑细胞和脑细胞亚组分作实验材料，较全面地观察了氯化汞对单胺类神经递质含量及其合成、释放、摄取、降解等重要代谢环节的影响。结果表明，汞通过抑制脑线粒体外膜单胺氧化酶使得脑组织中５－羟色胺、多巴胺、去甲肾上腺素含量增高，５－羟吲哚乙酸含量下降，呈良好的剂量－效应关系；汞还明显改变了游离脑细胞对单胺类神经递质的释放和摄取能力。     

Synthesis and biological evaluation of enantiomerically pure pyrrolyl-oxazolidinones as a new class of potent and selective monoamine oxidase type A inhibitors

Due to the key role played by monoamine oxidases (MAOs) in the metabolism of neurotransmitters, MAO inhibitors (MAOIs) represent an useful tool for the treatment of several neurological diseases. Among selective MAOIs, MAO-A inhibitors (e.g. clorgyline) are used as antidepressant and antianxiety drugs and are claimed to protect neuronal cells against apoptosis, and selective MAO-B inhibitors (e.g. L-deprenyl) can be used in the treatment of Parkinson's disease either alone or in combination with L-DOPA. However, they engender covalent bonds with the active site of the enzyme and induce irreversible inhibition; moreover, they tend to lose their initial selectivity at high dosages or with repeated administrations. Phenyloxazolidinones belong to third-generation-MAOIs, characterized by a selective and reversible inhibition of the enzyme. Among these molecules, the most representative are toloxatone and befloxatone, two selective and reversible MAO-A inhibitors used in therapy as antidepressant drugs. Going on our searches on CNS potentially active compounds containing a pyrrole moiety we prepared 3-(1H-pyrrol-1-yl)-2-oxazolidinones (1) and isomeric 3-(1H-pyrrol-2-and -3-yl)-2-oxazolidinones (2 and 3) as anti-MAO agents. Such derivatives resulted selective and reversible MAO-A inhibitors. The most potent compound is (R)-5-methoxymethyl-3-(1H-pyrrol-1-yl)-2-oxazolidinone (1b), endowed with very high potency (K(iMAO-A) = 4.9 nM) and A-selectivity (A-selectivity = 10,200, about 116-fold greater than that of befloxatone).     

当归注射液对老年小鼠脑、肝脏MAO-B活性的影响

当归注射液不同剂量给老年小鼠灌胃,每天1次,连用4周,可显著降低老年小鼠脑、肝脏MAO-B活性。结果提示、当归注射液具有延缓衰老作用。     

The effects of hydergine on the MAO activity of the aged and adult rat brain

Despite the fact that hydergine has been used in the treatment of dementia for many years, its mechanism of action is still not clear. Current studies imply that the major effect of hydergine may be the modulation of synaptic neurotransmission rather than solely increasing blood flow as was once thought. A prominent feature that accompanies aging is an increase in monoamine oxidase (MAO) levels which results in decreased availability of catecholamines in the synaptic cleft. The aim of this study was to determine the effects of hydergine on the MAO activity in different brain regions (cortex, olfactory bulb, hypothalamus, hippocampus, striatum, cerebellum) of old (30 months) and adult (12 months) male Sprague-Dawley rats. In cortex and olfactory bulb MAO levels were higher in the aged group. In hippocampus and hypothalamus hydergine treatment caused significant decreases in MAO levels. An interaction between age and hydergine treatment was observed in the hypothalamus, hippocampus and cerebellum. The hydergine effect was more pronounced in the aged group in the hypothalamus and cerebellum, and more pronounced in the adult in the hippocampus. Our findings imply that increased brain MAO activity in aging can be modified by hydergine treatment in some brain regions.     

The effect of selective type A or type B monoamine oxidase inhibition on the intrasynaptosomal deamination of (3H)serotonin in rat spinal cord tissue

Summary The degree to which the type A and type B forms of monoamine oxidase participate in the intraneuronal deamination of (³H)serotonin (5-HT) was examined in synaptosomal-rich fractions of rat spinal cord tissue. Synaptosomes were labeled with (³H)5-HT and superfused with physiological buffers containing selective concentrations of a type A (clorgyline) or a type B (deprenyl) MAO inhibitor. The efflux of (³H)5-HT and newly-formed (³H)5-hydroxyindoleacetic acid (5-HIAA) was determined and compared to controls over time. In control samples, a slight decline in (³H)5-HT efflux occurred over the experimental superfusion period. However, a stable formation and efflux of (³H)5-HIAA was seen during this same period of time. When clorgyline was added to the superfusion buffer, a rapid decline in superfusate levels of (³H)5-HIAA was observed. Similar experiments in the presence of deprenyl were without effect. In order to elevate cytoplasmic concentrations of (³H)5-HT and therefore increase its chances for interaction with nerve terminal MAO, reserpine was added to the superfusion buffer. Reserpine caused a greater than 3-fold increase in (³H)5-HIAA formation with no change in (³H)5-HT efflux. Clorgyline inhibited this increase in (³H)5-HIAA formation but deprenyl was again without effect. In the presence of clorgyline, reserpine also caused an increase in (³H)5-HT efflux. These results strongly support the notion that 5-HT deamination within rat spinal cord nerve terminals occurs primarily, if not exclusively, through an interaction with type A MAO.Abbreviations 5-HT 5-hydroxytryptamine, serotonin - MAO monoamine oxidase - 5-HIAA 5-hydroxyindoleacetic acid Supported in part by N.I.H. grants GM 30002, 5-T32-GM 07039, and the West Virginia University Medical Corporation. L. M. B. was supported by a Swiger Fellowship