Alterations of serotonin neurotransmission and inhibition of mouse-killing behavior: III. Effects of minaprine, CM 30366 and SR 95191

Three closely related aminopyridazine derivatives: minaprine [3-(2-morpholino-ethylamino)-4-methyl-6-phenyl pyridazine, dihydrochloride], CM 30366 [3-(2-morpholino-ethylamino)-4-methyl-6-(4-hydroxyphenyl) pyridazine, hydrobromide] and SR 95191 [3-(2-morpholino-ethylamino)-4-cyano-6-phenyl pyridazine] were examined for their inhibitory effects on mouse-killing behavior (MKB). Three groups of killer rats were used: spontaneous killer rats (K rats) and nonkillers which became killers following para-chlorophenylalanine (PCPA) treatment or electrolytical destruction of the dorsal and median raphe nuclei. When given intraperitoneally (IP), the three drugs inhibited MKB of K rats without sedation. When given orally, minaprine showed no antimuricidal effect in K rats. After chronic IP administration of minaprine, MKB inhibition in K rats decreased after 25 days of treatment, probably because serotonin receptors became subsensitive. Minaprine and SR 95191, a derivative of minaprine, are inhibitors of type A monoamine oxidase (MAO), whereas CM 30366, a metabolite of minaprine, has no effect on MAO activity. SR 95191 displayed a similar MKB inhibition in the three groups of killer rats, and in this respect, it behaved like other type A MAO inhibitors. Minaprine and CM 30366 were less efficient in their antimuricidal effect in PCPA-treated and raphe-lesioned killer rats as compared with spontaneous killer rats. Moreover, the time courses of MKB inhibition and MAO A inhibition by minaprine did not correlate. The effects of minaprine on MKB seemed not related in a simple way to an alteration of serotonin level through MAO A inhibition, and rise the question of an alternative mechanism of antimuricidal action, until now unknown.     

Biochemical effects of minaprine on striatal dopaminergic neurons in rats

The biochemical effects of minaprine, a new psychotropic drug, were investigated on striatal dopaminergic neurons in the rat. Minaprine did not displace [³H]spiperone in-vitro binding from striatal membranes but had clear effects on dopamine (DA) metabolites. Homovanillic acid (HVA) and dihydroxyphenylacetic acid (DOPAC) were significantly decreased in a dose-dependent manner after intraperitoneal administration of minaprine 30 min before killing. In rats injected with minaprine 15 mg kg⁻¹ i.p. at different intervals, the decrease in striatal HVA and DOPAC was time-dependent and a concomitant rise in 3-methoxytryramine (3-MT) concentrations was observed. The maximum of these effects was reached 30 min after minaprine. When administered 5 min after a monoamineoxidase (MAO) inhibitor (pargyline, 100 mg kg⁻¹ i.p.) and 30 min before killing, minaprine did not affect pargyline-induced changes in HVA, DOPAC and 3-MT levels. This together with other data suggests that minaprine affects DA metabolism by acting, at least partially, at presynaptic level through in-vivo inhibition of MAO activity.     

N-propargylbenzylamine, a major metabolite of pargyline, is a potent inhibitor of monoamine oxidase type B in rats in vivo: a comparison with deprenyl.

In an effort to explore the contribution of the metabolites of pargyline towards the in vivo inhibition of monoamine oxidase (MAO), the effects of pargyline and its major metabolites on the production and metabolism of a number of biogenic amines were studied in rats. The administration of pargyline gave rise to three major ethyl acetate extractable metabolites: benzylamine, N-methylbenzylamine and N-propargylbenzylamine (NPB). Only NPB demonstrated in vivo monoamine oxidase inhibitory properties at an acute dose of 30 mg kg-1. The acute effects of pargyline, NPB, and deprenyl on urine and brain concentrations of a number of biogenic amines (phenylethylamine (PEA), m- and p-tyramine, noradrenaline (NA), dopamine, and 5-hydroxytryptamine (5-HT) and their metabolites were evaluated. Increased urine and brain concentrations of PEA were considered to represent in vivo inhibition of type B MAO while decreased concentrations of NA and 5-HT metabolites were regarded as indicators of an in vivo inhibition of MAO type A. NPB, like deprenyl and pargyline, significantly increased urine and brain PEA while only pargyline reduced 5-HT metabolism, suggesting that the metabolism of pargyline to NPB may contribute towards the MAO type B inhibitory effects of pargyline in vivo. Since the therapeutic benefits of MAO inhibitors in clinical practice usually require some period of chronic treatment, the chronic effects of repeated 14 daily doses of the above MAO inhibitors on central and peripheral biogenic amines were evaluated at the following times: during treatment, one day and five days after termination of treatment. The biochemical changes observed during the course of chronic NPB, pargyline and deprenyl treatments generally follow the expected in vitro characteristics of these drugs, but the detailed changes observed suggest clear differences. For example, the in vivo effect of pargyline on urine 5-hydroxyindoleacetic acid excretion was considerably weaker than its effect on the excretion of NA and dopamine metabolites. These changes are opposite to the in vitro effects of pargyline on 5-HT, dopamine and NA oxidative deamination. Inhibitions of the metabolism of all the amines studied were clearly observed during chronic MAOI treatments, but these effects were less evident five days after the end of treatment, suggesting an almost normal metabolism of biogenic amines. It is concluded that while MAO inhibitors may be the primary compound responsible for MAO inhibition, the effects of their metabolites in some cases may also play equally important roles in the regulation of monoamines both in the periphery and the brain.(ABSTRACT TRUNCATED AT 400 WORDS)     

Rasagiline [N-propargyl-1R(+)-aminoindan], a selective and potent inhibitor of mitochondrial monoamine oxidase B

1. Rasagiline [N-propargyl-1R(+)-aminoindan], was examined for its monoamine oxidase (MAO) A and B inhibitor activities in rats together with its S(-)-enantiomer (TVP 1022) and the racemic compound (AGN-1135) and compared to selegiline (1-deprenyl). The tissues that were studied for MAO inhibition were the brain, liver and small intestine. 2. While rasagiline and AGN1135 are highly potent selective irreversible inhibitors of MAO in vitro and in vivo, the S(-) enantiomer is relatively inactive in the tissues examined. 3. The in vitro IC(50) values for inhibition of rat brain MAO activity by rasagiline are 4.43+/-0.92 nM (type B), and 412+/-123 nM (type A). The ED(50) values for ex vivo inhibition of MAO in the brain and liver by a single dose of rasagiline are 0.1+/-0.01, 0.042+/-0.0045 mg kg(-1) respectively for MAO-B, and 6.48+/-0.81, 2.38+/-0.35 mg kg(-1) respectively for MAO-A. 4. Selective MAO-B inhibition in the liver and brain was maintained on chronic (21 days) oral dosage with ED(50) values of 0.014+/-0.002 and 0.013+/-0.001 mg kg(-1) respectively. 5. The degree of selectivity of rasagiline for inhibition of MAO-B as opposed to MAO-A was similar to that of selegiline. Rasagiline was three to 15 times more potent than selegiline for inhibition of MAO-B in rat brain and liver in vivo on acute and chronic administration, but had similar potency in vitro. 6. These data together with lack of tyramine sympathomimetic potentiation by rasagiline, at selective MAO-B inhibitory dosage, indicate that this inhibitor like selegiline may be a useful agent in the treatment of Parkinson's disease in either symptomatic or L-DOPA adjunct therapy, but lack of amphetamine-like metabolites could present a therapeutic advantage for rasagiline.     

Selective acetylenic 'suicide' and reversible inhibitors of monoamine oxidase types A and B.

1 A number of aromatic-N-propargyl (acetylenic) compounds and indoleamines were tested for their inhibitory action on monoamine oxidase (MAO) type A and type B using the substrates 5-hydroxytryptamine (5-HT), beta-phenylethylamine (PEA) and dopamine. 2 Structure activity studies with aromatic-N-propragyl (acetylenic) derivatives have shown that MAO inhibitory potency is least dependent on the aromatic portion of the compounds. N-methylated propargyl derivatives are the most active and replacement of the methyl group with a higher alkyl or aromatic group results in significant reduction of activity. The triple bond in the N-propargyl portion is absolutely essential for activity and must be beta-to the nitrogen. It is the acetylenic group that gives these compounds their irreversible MAO inhibitory property. 3 The present study has indicated that since the acetylenic compounds resemble the enzyme substrates the distance between the aromatic ring and the N-propargyl terminal is crucial in designating the type A or type B MAO inhibitory property. For MAO type A inhibition, a distance equivalent to at least three carbon units is required, while for the inhibition of the B type enzyme this distance can be 1 or 2 carbon units. 4 The compounds AGN-1133 and AGN-1135 show most promise in Parkinson's disease or as anti-depressants because of their irreversible selective type B MAO inhibition in vitro and in vivo. 5 A number of indoleamine derivatives were found to be reversible selective type A inhibitors.     

Minaprine, a new drug with antidepressant properties

Minaprine is a new psychotropic drug which has recently proved to be effective in the treatment of various depressive states. In rodents, minaprine exhibits an atypical spectrum of antidepressant and dopaminomimetic activities. Thus in mice minaprine antagonizes the effects of reserpine, decreases immobility time in the behavioural despair test and potentiates the effects of 5-HTP; in rats it antagonizes muricidal behaviour (blocked by PCPA or raphectomy). However, minaprine does not affect yohimbine lethality and does not induce anticholinergic effects in mice. Minaprine also activates central dopaminergic transmission. Thus at low doses the drug antagonizes neuroleptic-induced catalepsy and induces stereotypies in rats. These stereotypies are blocked by neuroleptics. In addition, minaprine (like apomorphine) induces contralateral turning in mice with a unilateral lesion of the striatum, whereas d-amphetamine induces ipsilateral rotations. Unlike classical dopaminomimetic drugs, minaprine does not stimulate locomotor activity in rats. The mechanisms by which minaprine exerts its effects are still unclear, since in vitro minaprine does not affect monoamine uptake or release and does not interact with monoamine receptors. In vivo, minaprine (acute doses) increases 5-HT, decreases 5-HIAA levels in various brain areas and weakly and reversibly inhibits type A MAO; subacute treatments lead to a decrease in the number of 5-HT1 and 5-HT2 receptors. In addition, in the striatum the drug decreases HVA and DOPAC, and increases 3-MT levels, without affecting DA levels. Minaprine also weakly displaces (3H)-spiperone from striatal D2 receptors and increases striatal ACh levels. Finally, minaprine fails to affect brain NA or MHPG levels in acute doses and does not modify beta receptor density in subacute treatment. Thus minaprine appears to be a chemically and pharmacologically original antidepressant drug which activates both 5-HT- and DA-mediated transmission but which is devoid of NAergic and anticholinergic effects. This latter statement is confirmed by the good cardiovascular tolerance of minaprine in dog, monkey and humans, and by the lack of "tricyclic-like" anticholinergic side-effects in man.     

Novel dual inhibitors of AChE and MAO derived from hydroxy aminoindan and phenethylamine as potential treatment for Alzheimer's disease

Carbamate derivatives of N-propargylaminoindans (Series I) and N-propargylphenethylamines (Series II) were synthesized via multistep procedures from the corresponding hydroxy precursors. The respective rasagiline- and selegiline-related series were designed to combine inhibitory activities of both acetylcholine esterase (AChE) and monoamine oxidase (MAO) by virtue of their carbamoyl and propargylamine pharmacophores. Each compound was tested for these activities in vitro in order to find molecules with similar potencies against each enzyme. Compounds with such dual AChE and MAO inhibitory activities are expected to have potential for the treatment of Alzheimer's disease. The observed SAR also offers insight into the requirements of the active sites on these enzymes. A carbamate moiety was found to be essential for AChE inhibition, which was absent in the corresponding hydroxy precursors. The propargyl group caused 2-70-fold decrease in AChE inhibitory activity (depending on the position of the carbamoyl group) of Series I, but had little or no effect in Series II. Thus, the 6- and 7-carbamyloxyphenyls in Series I were either equipotent to, or slightly (2- to 5-fold) less active as AChE inhibitors than, the corresponding compounds in Series II, while the 4-carbamyloxyphenyls were more potent. The presence of the carbamate moiety in 6- and 7-carbamyloxyphenyls of Series I, considerably decreased MAO-A and -B inhibitory activity, compared to that of the parent hydroxy analogues, while the opposite was true for Series II. Thus, the 6- and 7-carbamyloxyphenyls in Series I were 2-3 orders of magnitude weaker MAO inhibitors while the 4- carbamyloxyphenyls were equipotent with the corresponding compounds in Series II. In both series, N-methylation of the propargylamine enhanced the MAO (A and B equally) inhibitory activities and decreased the AChE inhibitory activity. Two candidates belonging to the indan and tetralin ring systems (24c, 27b) and one phenethylamine (53d) were identified as possible leads for further development based on the following criteria: (a) comparable AChE and MAO-B inhibitory activities, (b) good to moderate AChE inhibitory activity, and (c) lack of strong MAO-A selectivity. However, it is likely that these compounds will be metabolized to the corresponding phenols, with inhibitory activities against AChE and/or MAO-A or -B, different from those of the parent carbamates. Thus, the apparent enzyme inhibition will be a result of the combined inhibition of all of these individual metabolites. The results of our ongoing in vivo screening programs will be published elsewhere.     

BCEF0083抗单胺氧化酶作用的研究

目的　研究一种白僵菌代谢产物提取物 (BCEF0 0 83)对单胺氧化酶 (MAO)的抑制作用。方法　提取动物脑组织重线粒体应用荧光分光光度计法检测MAO活性 ;采用大、小鼠体内外给药研究BCEF抗MAO作用的量效、时效关系 ,应用林 -贝氏法测定MAOKm值。结果　小鼠BCEF 50 0mg·kg- 1 ,ig给药后 0 5hMAO活性已有抑制 ,2～ 8h活性抑制明显 ,一次给药后 72h抑制作用基本消失 ;小鼠BCEF50 0、40 0、2 0 0、1 0 0、50、2 5mg·kg- 1 ,ig后 2h取脑组织测MAO活性 ,BCEF对MAO活性的抑制呈现一定的量效关系。BCEF体外给药对大鼠脑组织MAO活性的抑制随药物浓度增加而增强 ,BCEF体外给药对MAO A、MAO B抑制的IC50 (95 %可信限 )分别为 1 2 8 88(82 70～ 2 0 0 86)mg·L- 1 、1 84 1 4 (1 56 1 7～ 2 1 7 1 1 )mg·L- 1 ;BCEF对MAO A ,B抑制呈混合型抑制作用 ,Km值分别为 1 1 97、 8 1 3μmol·L- 1 。结论　BCEF0 0 83体内外给药对大、小鼠脑组织MAO活性具有抑制作用     

Selective inhibition by amiflamine of monoamine oxidase type A in rat brain,liver and duodenum

Summary Amiflamine (FLA 336(+)), N-desmethylamiflamine (FLA 788(+)) and N,N-didesmethylamiflamine (FLA 668(+)) were examined for their monoamine oxidase (MAO) inhibitory effects in rat brain, liver and duodenum and were compared with the irreversible inhibitors clorgyline and (-)-deprenyl. The potency of each FLA compound was the same in each tissue both in vitro and after oral administration with either serotonin or tyramine as substrate. The in vitro effect of FLA 788(+) was 2–6 times stronger than that of amiflamine although the compounds were equipotent after oral administration. FLA 668(+) was 2–3 times less potent than amiflamine in vitro and had very poor activity after oral administration. The deamination of phenethylamine was weakly afected by the three FLA compounds. Clorgyline inhibited strongly the deamination of serotonin and tyramine in the duodenum after oral administration, being 1,000 times more potent than in the brain and the liver. Similar results were obtained for (-)-deprenyl which, however, was more potent in inhibiting the deamination of phenethylamine than that of serotonin and tyramine. Amiflamine was a reversible MAO inhibitor with no MAO inhibitory capacity 24 h after a single oral dose. On the other hand the irreversible inhibitor clorgyline had a maximal effect on brain MAO 48 h after a single dose while the inhibitory effect in the duodenum had almost disappeared. The influence of amiflamine on the excretion of acid and basic metabolites of orally administered ¹⁴C-tyramine (58 mol/kg) in rat was examined. Amiflamine, at doses that strongly inhibited MAO-A in rat brain, only slightly affected the excretion of ¹⁴C-labelled acid in urine during 6 and 24 h after the tyramine administration. The results in this study suggest that other factors than a low interaction with intestinal MAO may be of importance for the low tyramine potentiating effect obtained after oral administration of amiflamine.     

次黄嘌呤对单胺氧化酶的抑制作用

实验证明给小鼠po次黄嘌呤25～500 mg/kg时,对肝和脑中单胺氧化酶B(MAOB)活性的抑制作用与剂量成明显的量—效关系,对MAO-A活性的抑制较弱,且无明显的量—效关系。给小鼠一次po次黄嘌呤500 mg/kg,于给药后16h,对MAO抑制作用最明显。sc时,对肝中MAO活性抑制也以给药后16 h最明显,但对脑中MAO活性抑制不明显。离体实验证明,次黄嘌呤对MAO-B的抑制为竞争性,对MAO-A则为混合型抑制。     

Circulating and brain metabolites of minaprine in the baboon

A mixture of 15N-labelled, 14C-labelled and unlabelled minaprine was administered orally to three baboons, and metabolites in blood, urine and brain investigated. Biological samples were extracted with dichloromethane and the radioactive components extracted were analysed by t.l.c. and autoradiography. Compounds identified by comparing their physiochemical properties with those of synthetic standards and by g.l.c.-mass spectrometry were minaprine, 3-[2-(3-oxo)morpholino-ethylamino]-4-methyl-6-phenylpyridazine, 3-amino-4-methyl-6-phenylpyridazine, 3-[2-(aminoethyl)ethylamino]-4-methyl-6-phenylpyridazine, p-hydroxyminaprine and minaprine N-oxide. In addition to the urinary metabolites, two circulating metabolites were detected: metabolite A, 3-[2-(3-oxo)morpholino-ethylamino]-4-methyl-6-phenylpyridazine, and metabolite B (unidentified). All circulating metabolites appeared very early in blood, confirming the rapid and extensive metabolism of the drug. Metabolites A, B and 3 (p-hydroxyminaprine) were the major metabolites present in plasma. The parent drug was not the major circulating form, and was present in a higher concentration in erythrocytes than in plasma. Erythrocytes might act as a reservoir of the drug and could explain the relatively slow blood clearance of minaprine despite its rapid metabolism. The qualitative metabolic profile in brain tissue was similar to that in blood.     

EFFECT OF STYRENE ON MONOAMINE OXIDASE B ACTIVITY IN RAT BRAIN

Previous studies have indicated that workers exposed to styrene present a decreased activity of platelet monoamine oxidase B (MAO B), suggesting that this biochemical assay may represent a biomarker for styrene-induced neurotoxicity. This study was undertaken to determine whether exposure to styrene would cause changes in MAO B activity in the target organ-the brain. Groups of rats were exposed to styrene by inhalation at concentrations of 300 ppm for 4 wk or 50 ppm for 13 wk. Both treatments caused significant decreases of MAO B activity in several brain areas, while MAO A activity was not affected. Decreases in MAO B activity were also found in brainstem of rats given styrene (400 mg/ kg) or styrene oxide (100 mg/ kg) by ip injection for 2 wk. Styrene, styrene oxide, and other styrene metabolites (mandelic acid, phenylglyoxylic acid, and styrene glycol) had no direct inhibitory effect on brain MAO B activity when tested in vitro. These results indicate that exposure to low concentrations of styrene alters MAO B activity in rat brain, suggesting that the observed changes in human platelets may reflect alterations in the nervous system.     

Inhibitory potency of some isatin analogues on human monoamine oxidase A and B.

Isatin is an endogenous compound which acts as a selective inhibitor of monoamine oxidase (MAO) B. In this study a range of isatin analogues were tested for their in vitro inhibition of human MAO A and B. Most of the analogues were less potent than isatin. Hydroxylation of the aromatic ring changed the inhibitory potency in favour of MAO A, with 5-hydroxyisatin being a potent and selective MAO A inhibitor (IC50 8 microM). Isatinic acid, which is formed reversibly from isatin at alkaline pH, showed no inhibition.     

Inhibition of brain mitochondrial monoamine oxidases by the endogenous compound 5-hydroxyoxindole

5-Hydroxyoxindole is a recently identified endogenous compound. Its physiological role remains unclear but certain evidence exists, that it may share some regulatory properties with isatin, a known endogenous inhibitor of monoamine oxidase (MAO) type B (MAO-B). In this study several oxidized indoles were tested for their in vitro inhibition of MAO type A (MAO-A) and B of rat brain non-synaptic mitochondria. 5-Hydroxyoxindole was less potent MAO-A inhibitor (IC50 56.8 microM) than isatin (31.8 microM) and especially 5-hydroxyisatin (6.5 microM), but it was the only highly selective MAO-A inhibitor among the all compounds studied (IC50 MAO-A:IC50 MAO-B = 0.044). Thus, the in vitro data suggest that MAO-A may represent potential target for 5-hydroxyoxindole.     

串果藤中甘草素和异甘草素对大鼠单胺氧化酶的体外抑制作用(英文)

目的:研究串果藤中甘草素和异甘草素体外对单胺氧化酶A型和B型的抑制作用.方法:根据不同的离心速度制备大鼠全脑粗线粒体作为单胺氧化酶的酶源;分别以5-羟基[侧链-2-~(14)C]色胺肌酸硫酸盐([~(14)C]5-HT)和2-苯基[1-~(14)C]乙基胺盐酸盐([~(14)C]β-PEA)为单胺氧化酶A型和B型放射性底物,用液体闪烁技术,研究甘草素和异甘草素酶抑制作用和抑制类型.结果:甘草素和异甘草素对单胺氧化酶A型和B型均具有抑制作用,呈良好的量效关系,对单胺氧化酶A型的IC_(50)(95％的可信限)分别为32(26-36)μmol/L和13.9(12.8-15.6)μmol/L,对单胺氧化酶B型的IC_(50)值分别为104.6(89.0-118.9)μmol/L和47.2(39.5-54.5)μmol/L.酶抑制特征曲线显示甘草素和异甘草素对单胺氧化酶A型呈非竞争性抑制,K_i值分别为31.5μmol/L和14.3μmol/L,而对单胺氧化酶B型呈混合竞争性抑制,K_i值分别为164.7μmol/L和62.2μmol/L,K_I值分别为15.2μmol/L和9.3μmol/L.结论:甘草素和异甘草素体外对单胺氧化酶A型呈非竞争性抑制作用,对单胺氧化酶B型呈混合竞争性抑制作用.     

Disposition and metabolism of minaprine in the rat

After iv. injection (5 mg/kg) to rats, minaprine is cleared rapidly from plasma with an elimination t 1/2 of 34 min. After the same dose but given orally the drug is rapidly absorbed from the rat gastrointestinal tract. The ratio of the area under the curves (AUC) of the parent drug indicates low bioavailability (5%). Two metabolites of minaprine (M3 and M5) appeared rapidly in rat plasma and far exceed minaprine concentrations. Other known urinary metabolites of the drug were undetectable in rat plasma and brain within the limits of the sensitivity of the method. Minaprine rapidly enters the central nervous system and then distributes almost evenly in various regions beyond the blood/brain barrier. It concentrates in brain tissue reaching concentrations two-three times those in plasma. It metabolites enter the brain less rapidly and their brain AUC never reached 50% of the plasma AUC.     

Monoamine oxidase inhibitory components from the roots ofSophora flavescens

In our search for monoamine oxidase (MAO) inhibitors from natural resources, we found that the methanol extract of the roots of Sophora flavescens showed an inhibitory effect on mouse brain monoamine oxidase (MAO). Bioactivity-guided isolation of the extract yielded two known flavonoids, formononetin (1) and kushenol F (2), as active compounds along with three inactive compounds, oxymatrine (3), trifolirhizin (4), and beta-sitosterol (5). Formononetin (1) and kushenol F (2) showed significant inhibitory effects on MAO in a dose-dependent manner with IC50 values of 13.2 and 69.9 microM, respectively. Formononetin (1) showed a slightly more potent inhibitory effect against MAO-B (IC50: 11.0 microM) than MAO-A (IC50: 21.2 microM). Kushenol F (2) also preferentially inhibited the MAO-B activity than MAO-A activity with the IC50 values of 63.1 and 103.7 microM, respectively.     

1-N-substituted thiocarbamoyl-3-phenyl-5-thienyl-2-pyrazolines: synthesis and evaluation as MAO inhibitors

Twelve new 1-N-substituted thiocarbomoyl-3-phenyl-5-thienyl-2-pyrazoline derivatives were synthesized and evaluated their for antidepressant, anxiogenic and mammalian monoamine oxidase (MAO)-A and Binhibitory activities by in vivo and in vitro tests. MAO was isolated and purified from the mitochondrial pellet of bovine liver homogenates and human platelets. All of the new compounds inhibited the total MAO activity of liver homogenates and the inhibition was found to be time-dependent. Four compounds (3 i-3 l) inhibited MAO-B selectively and irreversibly in a classical non-competitive manner with IC(50) values in the range of 22.00-91.50 microM. The rest of the compounds appeared to be non-selective reversible inhibitors. It was suggested that the p-methoxy group on the phenyl ring in the compounds increased the inhibitory effect and selectivity toward MAO-B. The reversible and unselective inhibition of MAO by the remaining compounds was suggested to be related to their properties of acting ability to act as both as substrate and inhibitor at the same time. However, none of the novel compounds showed antidepressant activity as expected suggesting formation of inactive metabolites. We conclude that the compounds appeared as which functioned as selective MAO-B inhibitors might have promising features as therapeutic properties in the treatment of Parkinson disease. In vivo studies are needed to verify this hypothesis.     

N-methyl,N-propargyl-2-aminotetralins:novel dopamine agonists with monoamine oxidase inhibiting properties

A series of mono- (5 and 7) and dihydroxylated (5,6 and 6,7)N-methyl,N-propargyl-2-aminotetralins were studied with respect to their dopamine agonistic and monoamine oxidase inhibitory activities. MAO inhibition was found to be reduced by hydroxylation of the aromatic ring. Among the hydroxylated compounds the 7-OH analogue was the most potent inhibitor in in vitro and ex vivo experiments. Both catecholic structures were equipotent with apomorphine as displacers of the specific in vitro binding of [3H]NPA to rat striatal homogenates. Moreover, the catecholic analogues had a potency comparable to that of apomorphine in the gamma-butyrolactone model whereas the monohydroxy analogues were less active. On the basis of their effectiveness to induce stereotypy in rats and to reverse reserpine-induced hypomotility in mice (both used as indices of postsynaptic dopamine receptor stimulation) the catecholic compounds were more potent than the monohydroxy analogues but much less active than apomorphine. Dopamine agonistic activity was also reflected in decreased HVA levels in the striatum whilst effects on striatal 3-MT levels reflected the balance between dopamine agonistic (decrease in 3-MT) and MAO inhibitory (increase in 3-MT) activity of the various compounds. It was concluded that both the mono- and dihydroxylated compounds have MAO inhibiting and dopamine agonistic activities. The MAO inhibitory activity predominated within the monohydroxy structures whereas the dopamine agonistic effect was predominant for the catecholic compounds. It would thus appear that, at least for the 2-aminotetralins, it is difficult to prepare an analogue which combines a high degree of both MAO inhibitory and DA agonistic activity.     

Pharmacological and biochemical actions of the hemolytic agents acetylphenylhydrazine and phenylhydrazine on monoamine oxidase in the rat

The injection of normal rats with the hemolytic agents acetylphenylhydrazine (APHZ) and phenylhydrazine (PHZ) rapidly produces a long-lasting inhibition of monoamine oxidase (MAO). The effect is more pronounced in liver than in brain at the dosage levels used, viz. 80 mg/kg body weight. APHZ inhibits liver MAO more actively than does an equivalent dose of PHZ. The former compound causes 65–75 per cent inhibition of activity by 24 hr after injeption, whereas PHZ inhibits by about 40 per cent at 24 hr and 50 per cent at 2 days. On the other hand, PHZ is slightly more active than APHZ against the rat brain enzyme in vivo. Equal doses of PHZ and APHZ cause 39 and 30 per cent inhibition, respectively, after 2 days. The inhibitory effects of APHZ in vivo are enhanced in riboflavin-deficient rats. Both drugs inhibit MAO in vitro in an immediate, irreversible, non-competitive manner; inhibition is independent of pH. PHZ is more active than APHZ against rat liver MAO. Concentrations of the respective chemicals which cause 50 per cent inhibition in vitro after 15 min of pre-incubation with the enzyme at 37° and pH7.0 are about 1.6 × 10^?5 M and 3.6 × 10^?5 M. Kynuramine protects MAO against inhibition by APHZ but not PHZ. Cyanide is active in enhancing the inhibitory action of both substances on MAO in vitro.