Monoamine oxidase inhibitors from rhizoma of Coptis chinensis

Three protoberberine alkaloids jatrorrhizine, berberine and palmatine were isolated from the monoamine oxidase (MAO) inhibitory fraction of the methanol extract of Coptis chinensis rhizoma. Jatrorrhizine was shown to inhibit non-competitively both MAO-A and -B from rat brain mitochondria with the IC50 values of 4 and 62 microM, respectively. Berberine only competitively inhibited MAO-A with an IC50 values of 126 microM whereas palmatine exhibited, up to 200 microM, no inhibition on any type of the enzyme. The structure-activity relationship was briefly discussed.     

In-vivo and in-vitro assessment of the free-radical-scavenger activity of Ginkgo flavone glycosides at high concentration

Free radicals are involved in numerous skin diseases, especially inflammatory reactions and photosenescence. To identify possible free-radical scavenging by an original terpene-free Ginkgo biloba extract containing 33% Ginkgo flavone glycosides, mostly quercetin and kaempferol derivatives, we studied its activity by means of in-vitro and in-vivo experiments, using superoxide dismutase (SOD) as a positive control. By means of an in-vitro electron-spin resonance (ESR) assay we compared the activity of the Ginkgo extract with that of its two aglycones, quercetin and kaempferol. Quercetin and Ginkgo extract had significant antioxidant properties without pro-oxidant effect. In contrast, kaempferol, above an optimum antioxidant concentration, behaved as a pro-oxidant. The in-vivo experiments were conducted on an anti-inflammatory model. The cutaneous blood flux which reflects the skin inflammatory level was recorded by means of a laser Doppler perfusion imager. The data confirmed the free-radical-scavenging property of both Ginkgo extract and SOD. The Ginkgo extract significantly inhibited (37%) cutaneous blood flux to the same extent as SOD. These data confirmed the antioxidant property of Ginkgo extract. A complementary spin-trapping technique would enable identification of the free radicals involved. This Ginkgo extract should be useful for protection of the skin against free radicals.     

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.     

The effect of DSP-4 (N-[2-chloroethyl]-N-ethyl-2-bromobenzylamine) on monoamine oxidase activities in tissues of the rat

The in vitro inhibition of monoamine oxidase (MAO) in rat liver, and of the clorgyline-resistant amine oxidase (CRAO) in rat heart and aorta, by DSP-4 (N-[2-chloroethyl]-N-ethyl-2-bromobenzylamine) has been studied. Inhibition of each enzyme activity was independent of prolonged preincubation, was reversed by dialysis, and also Ackermann-Potter plots were consistent with reversible inhibition. Simple linear competitive inhibition of MAO-A and MAO-B was observed, with Ki values of 6 x 10(-6) and 8 x 10(-5) M, respectively. CRAO was inhibited in a mixed, non-competitive manner (Ki of 3.2 x 10(-5) and 7.8 x 10(-6) M in heart and aorta, respectively) which conformed to a kinetic model in which the binding of DSP-4 to CRAO increased the affinity of substrate binding, but prevented product formation. The possible significance of these results for the in vivo actions of the drug is discussed.     

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。     

Novel monoamine oxidase inhibitors, 3-(2-aminoethoxy)-1,2-benzisoxazole derivatives, and their differential reversibility

Although possible usefulness of non-selective monoamine oxidase (MAO) inhibitors for Parkinson's disease therapy has been suggested in the literature, MAO inhibitors whose inhibition is reversible and have dual action to both MAO-A and -B subtypes is not available yet. Subtype selectivity and reversibility of a series of novel MAO inhibitors, 3-(2-aminoethoxy)-1,2-benzisoxazole derivatives, were studied. Several dual MAO inhibitors, which inhibit both MAO-A and -B, were obtained. When administered to mice, their effects were generally reversible. Among the derivatives, RS-1636 and RS-1653 had much longer duration of brain MAO-B inhibition than that of MAO-A. In vitro, the inhibited MAO-A activity by these compounds was partially recovered by buffer change at 4 degrees C, while little MAO-B activity was recovered. Although it is not fully elucidated yet, the reversibility of these inhibitors is probably determined primarily by this dissociation profile. This unique differential reversibility indicates that optimization of the balance of actions can be achieved by differentiating reversibility to each target molecule.     

Ginkgo biloba leaf extract reverses amyloid beta-peptide-induced isoprostane production in rat brain in vitro

Isoprostanes are prostaglandin (PG) isomers generated from oxygen radical peroxidation of arachidonic acid, which are reliable markers of membrane oxidative damage. Aging is characterized by an imbalance between the generation of reactive oxygen species and antioxidant detoxification pathways. Ginkgo biloba leaf extract is reputed as a neuroprotective antioxidant agent. We have tested the effects of a Ginkgo biloba extract {containing 24.1 % flavonoids and 181 % terpene lactones [bilobalide (0.542 %), ginkgolide A (0.570 %), ginkgolide B (0.293 %), ginkgolide C (0.263 %), and ginkgolide J (0.138 %)]} on the production of 8-iso-PGF2alpha from rat brain synaptosomes obtained from young (3 months old) or aged (12 and 24 months old) rats, both in the basal state and after oxidative stress induced by either hydrogen peroxide or amyloid beta-peptide. Our findings show that Ginkgo biloba extract pretreatment is able to completely reverse both basal and hydrogen peroxide-stimulated isoprostane production (IC50 of 81.92 microM and 31.89 microM, respectively). Amyloid beta-peptide-induced isoprostane production was also inhibited, both in young and aged rats, to a level even lower than that in unstimulated synaptosomes. This suggests that the oxygen radical scavenging properties of the Ginkgo biloba extract are fully effective in young, as well as in old rats, showing a greater inhibition of isoprostane production in the latter.     

Characterization of phentermine and related compounds as monoamine oxidase (MAO) inhibitors

Phentermine was shown in the 1970s to inhibit the metabolism of serotonin by monoamine oxidase (MAO), but never was labeled as an MAO inhibitor; hence, it was widely used in combination with fenfluramine, and continues to be used, in violation of their labels, with other serotonin uptake blockers. We examined the effects of phentermine and several other unlabeled MAO inhibitors on MAO activities in rat lung, brain, and liver, and also the interactions of such drugs when administered together. Rat tissues were assayed for MAO-A and -B, using serotonin and beta-phenylethylamine as substrates. Phentermine inhibited serotonin-metabolizing (MAO-A) activity in all three tissues with K(i) values of 85-88 microM. These potencies were similar to those of the antidepressant MAO inhibitors iproniazid and moclobemide. When phentermine was mixed with other unlabeled reversible MAO inhibitors (e.g. pseudoephedrine, ephedrine, norephedrine; estradiol benzoate), the degree of MAO inhibition was additive. The cardiac valvular lesions and primary pulmonary hypertension that have been reported to be associated with fenfluramine-phentermine use may have resulted from the intermittent concurrent blockage of both serotonin uptake and metabolism.     

缺氧缺血新生鼠脑损伤后银杏叶对Nogo-A蛋白表达的影响

目的 探讨银杏叶对新生大鼠缺氧缺血性脑损伤后Nogo-A表达的影响.方法 72只7d龄SD大鼠随机分为银杏叶治疗组、对照组和假手术组,应用免疫组化的方法观察银杏叶对脑组织Nogo-A表达的影响.结果 脑组织Nogo-A的表达在对照组和银杏叶治疗组3d开始增高,21 d达到最高峰,对照组增高幅度最大,其平均光密度值与假手...     

Enzymic and molecular characteristics of a new form of monoamine oxidase, distinct from form-A and form-B

The present study was undertaken to clarify the enzymic and molecular properties of monoamine oxidase (MAO) in carp brain. In particular, its sensitivities to selective MAO inhibitors, kinetic properties and molecular weight were compared with those of the enzyme in carp liver. The selective and potent MAO-A and MAO-B inhibitors FLA 788(+), FLA 336(+), MD 780236 and benzylcyanide caused dose-dependent inhibitions of MAO activity in both carp brain and liver; the inhibition curves were all single-sigmoidal, and the degrees of inhibition of the activities towards 5-hydroxytryptamine (5-HT, selective MAO-A substrate), tyramine (substrate for both forms of MAO) and beta-phenylethylamine (PEA, selective MAO-B substrate) were similar. This was also the case for inhibition of activity in carp brain by the irreversible and selective MAO-A and MAO-B inhibitors clorgyline and I-deprenyl, indicating the presence in both preparations of a single MAO which differs from either form of MAO. Studies on the substrate specificities and Km values for these three substrates and the inhibitory effects of some compounds suggested that the enzymic characters of MAO in carp preparations were similar and that these enzymes might be FAD-containing enzymes, like MAO in various mammals. By labelling the preparations with radioactive pargyline and then subjecting them to sodium dodecyl sulfate electrophoresis, the apparent molecular weights of carp brain and liver MAO were estimated as 60,000 daltons. The same value was also obtained for rat brain and liver mitochondrial MAO-B. These results indicate that by the present definitions of MAO-A and MAO-B, MAO in carp brain and liver is similar to, but distinct from, both these forms of MAO.     

A monoamine oxidase-B inhibitor, MD 780236, metabolized essentially by the A form of the enzyme in the rat

In-vivo studies on the metabolism of [14C]MD 780236 a short-acting selective type B MAO inhibitor in the rat showed the acid to be the major metabolite in plasma and urine, whereas it was minor in brain, where the alcohol was the major metabolite. Pretreatment with SKF 525-A did not modify the metabolite profile in brain, but benserazide decreased the alcohol. Pretreatment with (-)-selegiline had no effect, but clorgyline or clorgyline with (-)-selegiline significantly decreased the alcohol and increased the primary amine metabolite in brain. In-vivo results suggest that MAO-A is the enzyme responsible for the metabolism of MD 780236. This was confirmed by in-vitro studies. Rat brain homogenates extensively metabolized the drug, with the aldehyde being the major metabolite formed (28% of the total radioactivity in the incubation mixture after 60 min incubation). The acid (12%) was more important than the alcohol (4%) in-vitro. The addition of all metabolites originating from possible MAO activity gave 46% when the incubation was carried out at pH 7.4 and 82% at pH 8.8. The presence of NADPH or NAD+ did not alter the relative amounts of metabolites formed. Total metabolites originating from MAO activity in the presence of (-)-selegiline accounted for 40% of total radioactivity, whereas in the presence of clorgyline they accounted for 8% and in the presence of both clorgyline and (-)-selegiline they were reduced to 3%, compared with 45% in controls. As a further proof of the importance of MAO-A in the metabolism of MD 780236, rats were pretreated with clorgyline 1 h before the drug and MAO-B inhibition measured at different times ex-vivo in brain and liver. The short-lasting phase of inhibition of MAO-B disappeared after pretreatment with clorgyline, and inhibition at 24 h was as high as that at 1 h. These results demonstrate the importance of the A form of MAO for the metabolism of MD 780236.     

Effect of lamotrigine on the activities of monoamine oxidases A and B in vitro and on monoamine disposition in vivo

Recent clinical evidence indicates that the broad spectrum anticonvulsant drug lamotrigine is effective against the depressive phase of bipolar illness and the difficult to treat rapid cycling form of the disorder. However, the molecular mechanism underlying this therapeutic action remains uncertain. Given that inhibition of the A-type of monoamine oxidase (MAO) is a proven antidepressant mechanism, we investigated the effects of lamotrigine on MAO activities in vitro and on monoamine disposition in vivo. In vitro, lamotrigine inhibited rat brain MAO activities with Ki values (MAO-A, 15 microM; MAO-B, 18 microM) potentially within the therapeutic range for this drug. The effects of lamotrigine on the MAO-A activities of rat brain and human liver preparations were almost identical suggesting minimal species or tissue variation. In contrast, there was no (MAO-A) or minimal (MAO-B) reduction in brain MAO activities when assayed ex vivo following the administration of lamotrigine to rats. In vivo brain microdialysis failed to detect meaningful alterations in extracellular hippocampal or frontal cortex monoamine concentrations. Furthermore, lamotrigine did not modulate oral tyramine-induced hypertension in rats or 5-hydroxytryptophan-induced head shaking in mice, providing strong evidence that the drug does not perturb monoamine metabolism in vivo. The absence of observable effects of lamotrigine on monoamine disposition in vivo may be explained by the competitive and highly reversible nature of the interaction of lamotrigine with MAO isoforms. Thus, altered monoamine metabolism in vivo is unlikely to account for the antidepressant action of the drug in bipolar depression.     

Effects of Ginkgolide B and Ginkgo biloba extract on local cerebral glucose utilization in the awake adult rat

The effects of the extract of the leaves of Ginkgo biloba and of one of its major components, Ginkgolide B, on local cerebral glucose utilization (LCGU) have been studied in the awake adult rat. Ginkgolide B (10 mg/kg i.p.) had no significant effect on LCGU in 38 brain regions studied. In contrast, the Ginkgo biloba extract (150 mg/kg i.p. in 3 divided doses) produced significant and widespread decreases in LCGU in 21 brain regions (range 3–26% reduction). These results demonstrate that Ginkgo biloba is able to reduce brain glucose utilization, but that the substance responsible for this effect may not be Ginkgolide B.     

Relationship between extracellular 5-hydroxytryptamine and behaviour following monoamine oxidase inhibition and L-tryptophan.

1. The present study investigates the effects of selective and a non-selective monoamine oxidase (MAO) inhibitors combined with L-tryptophan on MAO-A and -B activity, hypothalamic extracellular 5-hydroxytryptamine (5-HT) in vivo and the occurrence of the 5-HT behavioural syndrome. 2. Selective inhibition of intraneuronal MAO-A with MDL 72394 (0.5 mg kg-1, i.p.) had no effect on extracellular 5-HT and following administration of L-tryptophan (50 mg kg-1, i.p.) the 5-HT behavioural syndrome was not induced. 3. Selective inhibition of MAO-A at all sites with clorgyline (5 mg kg-1, i.p.) increased extracellular 5-HT but did not induce the 5-HT behavioural syndrome when combined with L-tryptophan administration. 4. Selective inhibition of MAO-B with selegiline (10 mg kg-1, i.p.) had no effect on extracellular 5-HT and the 5-HT behavioural syndrome was not observed after L-tryptophan administration. 5. Inhibition of MAO-A and -B with a higher and therefore non-selective, dose of MDL 72394 (2 mg kg-1) markedly increased extracellular 5-HT but failed to induce the 5-HT behavioural syndrome after L-tryptophan administration. 6. Inhibition of MAO-A and -B at all sites in the brain (tranylcypromine 20 mg kg-1, i.p. or clorgyline 5 mg kg-1 plus selegiline 10 mg kg-1) increased extracellular 5-HT and induced the behavioural syndrome on administration of L-tryptophan. 7. The results demonstrate that inhibition of MAO-A and -B both within amine neurones and elsewhere in the brain is essential for the development of the 5-HT behavioural syndrome.(ABSTRACT TRUNCATED AT 250 WORDS)     

Selective influences of age and thyroid hormones on type A monoamine oxidase of the rat heart.

The specific actiivty of rat heart MAO, towards both tyramine and benzylamine as substrates, was found to increase with the age of the animal, and also after administration of (-)-thyroxine to young male rats. Conversely, enzyme activity was decreased in animals made hypothyroid by including 2-thiouracil in their diet. However, with both age and altered thyroid status, relatively greater changes in the deamination of tyramine rather than in that of benzylamine, were obtained. Clorgyline and deprenyl, used as inhibitors of rat heart MAO, indicated that tyramine is metabolized solely by MAO-A, whereas benzylamine is a substrate for both MAO-A and -B, and also a clorgyline- and deprenyl-resistant enzymic activity. The proportional contribution of MAO-A, -B and the clorgyline-resistant enzyme towards the total benzylamine deamination in the rat heart was found to vary with the age and with altered thyroid status of the animal in such a way that selective changes in the activity of MAO-A appear to be largely responsible for the overall changes in the specific activity of rat heart MAO which occur in response to these developmental factors.     

Inhibition of rat brain monoamine oxidase activity by cerebral anti-ischemic agent, ifenprodil

Ifenprodil, which is clinically used as a cerebral vasodilator, inhibited rat brain type A (MAO-A) and type B (MAO-B) monoamine oxidase activity. It did not, however, affect rat lung semicarbazide-sensitive amine oxidase. The degree of inhibition of either form of MAO was not changed by 30 min preincubation of the enzyme preparations at 37 degrees C with ifenprodil. Modes of inhibition of MAO-A and MAO-B by ifenprodil were competitive towards oxidation of their respective substrates, 5-hydroxytryptamine and benzylamine, with Ki values of 75 microM for inhibition of MAO-A and 110 microM for inhibition of MAO-B.     

Monoamine oxidase inhibitory naphthoquinones from the roots ofLithospermum erythrorhizon

Activity-guided fractionation of a hexane-soluble extract of the roots of Lithospermum erythrorhizon, using a mouse brain monoamine oxidase (MAO) inhibition assay, led to the isolation of two known naphthoquinones, acetylshikonin and shikonin, and a furylhydroquinone, shikonofuran E. These compounds were shown to inhibit MAO with IC50 values of 10.0, 13.3, and 59.1 microM, respectively. Although no specificity for MAO-A and MAO-B was shown by acetylshikonin and shikonin, a Lineweaver-Burk plot analysis indicated that the inhibition was competitive for both MAO-A and MAO-B activity.     

Zinc benzoate, a contaminating environmental compound derived from polystyrene resin inhibits A-type monoamine oxidase

The contaminants in deionized and distilled water (DDI water) boiled with polystyrene resin inhibited A-type monoamine oxidase (MAO, MAO-A preferentially deaminates serotonin and norepinephrine and regulates these amines concentration) activity in monkey brain mitochondria. To identify these contaminants, we attempted measurements by HPLC, FT-IR and NMR. The compound inhibiting MAO-A activity was zinc benzoate. Although it potently inhibited MAO-A activity, zinc benzoate did not effect MAO-B in monkey brain mitochondria. It also reversibly and competitively inhibited MAO-A activity in a dose-dependent manner. Zinc benzoate, however, did not inhibit either MAO-A or -B activities in rat brain mitochondria. These results indicate that zinc benzoate, which inhibits MAO-A activity, is easily incorporated in DDI water by boiling polystyrene and also may be a contaminating environmental chemical compound that alters the levels of serotonin and norepinephrine in the central nervous system.     

Studies of monoamine oxidase and semicarbazide-sensitive amine oxidase. I. Inhibition by a selective monoamine oxidase-B inhibitor, MD 780236

In vitro studies of the effect of MD 780236, a selective monoamine oxidase (MAO)-B inhibitor, on a semicarbazide-sensitive amine oxidase (SSAO) in rat testis and lung showed that this compound dose-dependently inhibited SSAO activity. The extents of inhibition of MAO-A, -B and SSAO in these two rat tissues by this compound after 30 min of preincubation were found to be MAO-B greater than MAO-A greater than SSAO. This selectivity was also evident in preparations without preincubation. Degree of inhibition of SSAO was not significantly influenced by pretreatment with either 10(-3) M clorgyline, I-deprenyl or 10(-4) M SKF 525A. Inhibition of SSAO was not enhanced by varying the time of preincubation of the enzyme and the compound, indicating direct action on and reversible inhibition of SSAO. The inhibition of SSAO by MD 780236 was non-competitive with or without preincubation, with a K1 value of 110 muM. Although MD 780236 is a selective and "suicide substrate" inhibitor of MAO-B, these present results indicate that this compound may also inhibit SSAO activity, but by a mechanism different from that for MAO-B. These findings confirm an earlier hypothesis that compounds that inhibit both MAO and SSAO have totally different modes of action on these two different amine oxidases.     

Inhibition of rat brain monoamine oxidase activities by psoralen and isopsoralen: implications for the treatment of affective disorders

Psoralen and isopsoralen, furocoumarins isolated from the plant Psoralea corylifolia L., were demonstrated to exhibit in vitro inhibitory actions on monoamine oxidase (MAO) activities in rat brain mitochondria, preferentially inhibiting MAO-A activity over MAO-B activity. This inhibition of enzyme activities was found to be dose-dependent and reversible. For MAO-A, the IC50 values are 15.2 +/- 1.3 microM psoralen and 9.0 +/- 0.6 microM isopsoralen. For MAO-B, the IC50 values are 61.8 +/- 4.3 microM psoralen and 12.8 +/- 0.5 microM isopsoralen. Lineweaver-Burk transformation of the inhibition data indicates that inhibition by both psoralen and isopsoralen is non-competitive for MAO-A. The Ki values were calculated to be 14.0 microM for psoralen and 6.5 microM for isopsoralen. On the other hand, inhibition by both psoralen and isopsoralen is competitive for MAO-B. The Ki values were calculated to be 58.1 microM for psoralen and 10.8 microM for isopsoralen. These inhibitory actions of psoralen and isopsoralen on rat brain mitochondrial MAO activities are discussed in relation to their toxicities and their potential applications to treat affective disorders.