Brain Mitochondrial Monoamine Oxidase Research Articles

Kinetics of Inhibition of Monoamine Oxidase Using Curcumin and Ellagic Acid.

Background:Curcumin and ellagic are the natural polyphenols having a wide range of pharmacological actions. They have been reported to have their use in various neurological disorders.Objective:This study was aimed to evaluate the effect of curcumin and ellagic acid on the activity of monoamine oxidase (MAO), the enzyme responsible for metabolism of monoamine neurotransmitters which are pivotal for neuronal development and function.Materials and Methods:The in vitro effects of these selected polyphenols on MAO activities in mitochondria isolated from rat brains were examined. Brain mitochondria were assayed for MAO type-B (MAO-B) using benzylamine as substrates. Rat brain mitochondrial MAO preparation was used to study the kinetics of enzyme inhibition using double reciprocal Lineweaver–Burk plot.Results:MAO activity was inhibited by curcumin and ellagic acid; however, higher half maximal inhibitory concentrations of curcumin (500.46 nM) and ellagic acid (412.24 nM) were required compared to the known MAO-B inhibitor selegiline. It is observed that the curcumin and ellagic acid inhibit the MAO activity with both the competitive and noncompetitive type of inhibitions.Conclusions:Curcumin and ellagic acid can be considered a possible source of MAO inhibitor used in the treatment of Parkinson's and other neurological disorders.SUMMARY Monoamine oxidase (MAO) is involved in a variety of neurological disorders including Parkinson's disease (PD)Curcumin and ellagic acid inhibit the monoamine oxidase activityEllagic acid revealed more potent MAO type-B (MAO-B) inhibitory activity than curcuminKinetic studies of MAO inhibition using different concentrations of curcumin and ellagic acid were plotted as double reciprocal Lineweaver–Burk plotThe mode of inhibition of both compounds toward MAO-B is mixed (competitive and uncompetitive) type of inhibition with both the competitive and noncompetitive type of inhibitions. Abbreviations used: MAO: Monoamine oxidase, IC50: Higher half maximal inhibitory concentrations, PD: Parkinson's disease, LB: Lewy bodies, SNpc: Substantia nigra pars compacta, ROS: Reactive oxygen species, SG: Selegiline, DMC: demethoxycurcumin, BDMC: Bisdemethoxycurcumin.

Antidepressant-like Activity of Andrographis paniculata in Type-2 Diabetic Rats

Pharmacological observations suggesting antidepressants-like efficacy of a medicinally used Andrographis paniculata extract (AP) in type-2 diabetic are presented in this communication. Efficacies of 10 daily oral doses of 50, 100 and 200 mg/kg/day AP and 15 mg/kg/day imipramine were compared in behavioral despair and learned helplessness tests using type-2 diabetic rats, and bio- and neuro-chemical alterations in the brain tissue of treated animals subjected to learned helplessness test were quantified. Significant imipramine like antidepressant activity of AP was observed even after its lowest daily tested (50 mg/kg/day) in both behavioral tests used, and such efficacy of the extract dose dependently increased with its increasing dose. Imipramine like effects of AP in elevating lower hippocampal levels of norepinephrine, dopamine, and serotonin observed in diabetic rats towards normal values were also observed after its 50 mg/kg/day doses and such efficacy of the extract increased also with its increasing daily doses. Levels of all the three monoamines quantified in 100 mg/kg/day AP treated diabetic rats were significantly higher than those of the non-diabetic animals. Imipramine had no significant effects on body weight losses, hyperglycemia, insulin deficiency, lower catalase and superoxide dismutase activities and higher lipid peroxides in the frontal cortex, and mitochondrial monoamine oxidase activities observed in diabetic animals. All such quantified biochemical and other pathologies observed in diabetic were significantly antagonized even by 50 mg/kg daily oral doses of AP, and its efficacies always increased with its increasing daily doses. These observations strongly suggest that AP could be an herbal alternative for treatments of diabesity-associated depression resistant to imipramine like antidepressants, and that antidepressants like efficacy of the extract is most probably due to its inhibitory effects on brain mitochondrial monoamine oxidase activities. The observed beneficial of AP on brain oxidative status could be indicative of its neuro-protective potentials as well. In any case its minimal effective doses for all such efficacies should be below or around 50 mg/kg/day.

Kinetics of Inhibition of Monoamine Oxidase Using Cymbopogon martinii (Roxb.) Wats.: A Potential Antidepressant Herbal Ingredient with Antioxidant Activity

The study was designed to evaluate the antioxidant activity and effect of Cymbopogon martinii (Roxb.) Wats. (Poaceae) leaves on the activity of monoamine oxidase and kinetics of enzyme inhibition. Ethanol extract of C. martinii and rat brain mitochondrial monoamine oxidase preparation ware used to study the kinetics of enzyme inhibition using double reciprocal Lineweaver-Burk plot. The DPPH was used as a source of free radical to evaluate antioxidant potential. It is observed that, the ethanolic extract of C. martinii inhibits the monoamine oxidase activity with competitive mode of inhibition. The V(max) (0.01 mM/min) remained constant while, K(m) varied from 21.00±1.1, 43.33±1.5 and 83.33±1.4 mM for 100-500 μg/ml concentration of C. martinii. The K(i) values were calculated to be 90.00±0.87, 75.00±0.69, 68.18±0.68 μg for 100-500 μg/ml concentration of C. martini. It also shows a significant DPPH (1,1-diphenyl-2-picryl hydrazine) radical scavenging (IC(50)=0.34±0.05 mg/ml) and reducing activity (IC(50)=0.70±0.22 mg/ml). The C. martini can be considered as a possible source of MAO inhibitor used in the treatment of depression and other neurological disorders.

Xanthone derivatives as inhibitors for monoamine oxidase

Various xanthone derivatives were tested for in vitro inhibition of monoamine oxidase (MAO) in the mitochondrial fraction from rat brain and mouse liver. 1,6-Dihydroxyxanthone and 1,3,6-trihydroxyxanthone exhibited much potent inhibitory activity toward rat brain mitochondrial MAO (type A). On the other hand, 1,3,7-trihydroxyxanthone showed great potency for inhibition of mouse liver mitochondrial MAO (type B). These results indicate that 1,3,6-trihydroxyxanthone and 1,3,7-trihydroxyxanthone were rather specific inhibitors of type A MAO and type B MAO, respectively. 1,3-Dihydroxy-6-alkoxyxanthones containing alkoxy residues with carbon number 1 to 8 were synthesized and compared for their inhibitory activity toward rat brain mitochondrial MAO. Among them, 6-ethoxy-, 6-propyloxy-, and 6-butyloxy-derivatives were potent inhibitors, and especially, 1,3-dihydroxy-6-propyloxyxanthone was the most inhibitory. Lineweaver–Burk plot analysis demonstrates that these xanthone derivatives inhibited MAO in a competitive and reversible manner. Spectroscopic examinations suggest that complex formation between the flavin moiety and a xanthone derivative could be involved at least partly in their inhibitory action.

Effects of long-term treatment with dicyclic, tricyclic, tetracyclic, and noncyclic antidepressant drugs on monoamine oxidase activity in mouse brain

1. 1. The individual long-term effects of the antidepressant drugs zimeldine, viloxazine, imipramine, amitriptyline, nortriptyline, maprotiline, or nomifensine, on brain mitochondrial monoamine oxidase (MAO) activity, were studied in mice that were given daily intraperitoneal injections (30 mg/kg) of these reagents for 4 weeks. 2. 2. Both the A-form (MAO-A) and B-form (MAO-B) of MAO were inhibited after long-term administration of all the drugs except nortriptyline (MAO-A was not affected) and maprotiline (neither MAO-A nor MAO-B were affected). 3. 3. Kinetic analysis showed a significant decrease in V max values, and an increase in K m values for MAO-B during treatment. 4. 4. All seven drugs are competitive inhibitors of MAO-A, noncompetitive inhibitors of MAO-B, and were more potent in vitro for MAO-B. 5. 5. MAO-A was inhibited by the following drugs (in ascending order of potency): nortriptyline, amitriptyline, imipramine, maprotiline, zimeldine, nomifensine, and viloxazine. 6. 6. MAO-B was inhibited by the following drugs (in ascending order of potency): nortriptyline, imipramine, maprotiline, amitriptyline, zimeldine, nomifensine, and viloxazine.

Synthesis and selective monoamine oxidase B-inhibiting properties of 1-methyl-1,2,3,6-tetrahydropyrid-4-yl carbamate derivatives: potential prodrugs of (R)- and (S)-nordeprenyl.

The results of previous studies have established that the monoamine oxidase-catalyzed oxidation of 1-methyl-1,2,3,6-tetrahydropyridyl derivatives bearing heteroatom substituents at C-4 generates 2,3-dihydropyridinium intermediates that undergo spontaneous hydrolysis to release the C-4 substituent and form the amino enone 1-methyl-2,3-dihydro-4-pyridone. We have attempted to adapt this metabolic pathway to the preparation of amine-containing prodrugs that may target the central nervous system which is rich in monoamine oxidase A and B. In this paper we report the synthesis and the in vitro and in vivo metabolic fate of the tetrahydropyridyl carbamate derivatives which are designed to release (S)- and (R)-nordeprenyl. These carbamates are selective monoamine oxidase A substrates. An ex vivo assay has shown that the R-enantiomer is an effective and selective inhibitor of brain mitochondrial monoamine oxidase B.

Changes in monoamine oxidase activity in mouse brain associated with d-methamphetamine dependence and withdrawal

The long-term effects of d-methamphetamine (MP, 5 mg/kg) on brain mitochondrial monoamine oxidase (MAO) activity were studied in mice given MP intraperitoneally daily for 4 weeks. The MAO activities decreased when serotonin (5-HT) and dopamine (DA) were used as substrates. A marked elevation in MAO activity was seen during MP withdrawal when 5-HT, DA, β-phenylethylamine (β-PEA) and norepinephrine (NE) were used as substrates. The kinetics of MAO showed a significant decrease in K m values, but no significant change in V max values during MP withdrawal, despite the presence of NE. The K m and V max values increased when NE was the substrate. Inhibition of MAO by MP or its metabolites (amphetamine, p-hydroxyamphetamine and p-hydroxymethamphetamine) increased with the use of the following substrates in the order: DA, 5-HT, NE and β-PEA.

Potent in vivo but not in vitro inhibition of monoamine oxidase by 3-chloro-α-phenylpyrazinemethanol

3-Chloro-α-phenylpyrazinemethanol (3-CPM) inhibited monoamine oxidase (MAO) types A and B in vivo in mouse brain, heart and liver. The inhibition was dose-dependent at doses of 0.3–32 mg/kg i.p. and occurred within 1 h after the compound was injected, 3-CPM was a very weak inhibitor of mouse brain mitochondrial MAO activity in vitro, even when preincubated with the enzyme; MAO-A was inhibited only about 50% at a high concentration of 3-CPM (1 mM), and MAO-B was inhibited even less. After a 10 mg/kg i.p. dose of 3-CPM in mice, both MAO-A and MAO-B were inhibited at day 1, but activity had largely recovered within a few days in brain, liver and heart. 3-CPM at doses of 1, 3, 10 and 32 mg/kg i.p. caused dose-dependent antagonism of the depletion of striatal dopamine and of cortical norepinephrine by 1-methyl-4-phenyl-1,2,3,6-tetrahydropyridine. 3-CPM is therefore a potent inhibitor of MAO-A and of MAO-B in mice in vivo despite its weak effect on the enzyme in vitro. A metabolite of the drug may be involved in the in vivo effects.

In vitro and in vivo effect of chloropromazine, imipramine and lithium chloride on monoamine oxidase activity in rat brain mitochondria.

Chloropromazine (CPZ) and imipramine at a concentration of 1 x 10(-3) M inhibit rat brain mitochondrial monoamine oxidase activity in vitro by 70 and 55% respectively, while lithium, even at a concentration of 0.05 M, inhibits the activity of this enzyme very negligibly (4%). In vivo, these drugs at a dose level of 56 mg CPZ, 76 mg imipramine and 76 mg lithium chloride/Kg body wt., did not cause any observable variation from normal in brain mitochondrial monoamine oxidase activity.

1-methyl substituent and stereochemical effects of 2-phenylcyclopropylamines on the inhibition of rat brain mitochondrial monoamine oxidase A and B

(E)-2-Phenylcyclopropylamine ((E)-TCP), (Z)-2-phenylcyclopropylamine ((Z)-TCP), (E)-1-methyl-2-phenylcyclopropylamine ((E)-MTCP), and (Z)-1-methyl-2-phenylcyclopropylamine ((Z)-MTCP) were synthesized and used to determine to what extent 1-methyl substitution and stereochemistry of 2-phenylcyclopropylamines affect inhibition of monoamine oxidase (MAO). Inhibition of rat brain mitochondrial MAO-A and B by the compounds were measured using serotonin and benzylamine as the substrate, respectively and IC50 values obtained with 95% confidence limits by the method of computation. For the inhibition of MAO-A, (E)-MTCP (IC50=6.2×10−8M) was found to be 37 times more potent than (Z)-MTCP (IC50=2.3×10−6 M), whereas the activity of (E)-TCP (IC50=2.9×10−7 M) was slightly less than that of (Z)-TCP (IC50=2.3×10−7 M). Similarly, for the inhibition of MAO-B, (E)-MTCP (IC50=6.3×10−8 M) was 7 times more potent than (Z)-MTCP (IC50=4.7×10−7 M) and (E)-TCP (IC50=7.8×10−8 M), 0.6 times as potent as (Z)-TCP (IC50=4.4×10−8 M). The results suggested that while without 1-methyl group, potency of a (Z)-isomer was comparable to that of (E)-isomer, the methyl group in its (Z)-position was very unfavorable to the inhibition of MAO and that in its (E)-position, the methyl group contributed positively to the potency as found by the fact that (E)-MTCP was 1–5 times more potent than (E)-TCP. In view of the selective inhibition of MAO-A or B, all compounds elicited 4–10 times higher preference for the inhibition of MAO-B over MAO-A and 1-methyl substitution as well as the stereochemical factors did not significantly influence the selectivity.

Dual enzyme-activated irreversible inhibition of monoamine oxidase

( E)-β-Fluoromethylene- m-tyrosine and related amino acids were synthesized from acetophenone derivatives and shown to be dual enzyme-activated inhibitors of monoamine oxidase. These substances are decarboxylated by hog kidney aromatic l-amino acid decarboxylase liberating ( E)-β-fluoromethylene- m-tyramine derivatives which, in turn, are enzyme-activated inhibitors of rat brain mitochondrial monoamine oxidase.

Phospholipid dependency of carp brain and liver mitochondrial monoamine oxidase

1. The effects of lipid-protein interactions on carp brain and liver mitochondrial MAO with respect to substrate and inhibitor preference, thermostability and Arrhenius parameters were studied and compared. 2. Treatment with phospholipase A 2, C or D decreased MAO activities towards 5-hydroxytryptamine (5-HT), β-phenylethylamine and tyramine similarly, accompanied by great changes in their apparent affinities for MAO, but not by changes in V max values. 3. Minimum phospholipid binding to mitochondria might be essential for enzyme activity. 4. Among these activities, 5-HT deamination was the most sensitive to the changes in mitochondrial phospholipids and bulk lipid phase transition (fluidity). 5. Sensitivity of MAO to clorgyline or l-deprenyl was not affected by these phospholipase treatments. 6. Of the phospholipids tested, only phosphatidylinositol significantly activated MAO activity towards 5-HT in both intact and phospholipase-treated mitochondria.

Membrane lipid environment of carp brain and liver mitochondrial monoamine oxidase

1. Delipidation of carp liver mitochondria by treatment with methyl ethyl ketone (MEK) or Triton X-100 and then perchlorate greatly reduced MAO activities. 2. Treatment with only Triton X-100 resulted in less reduction in activity. 3. The K m values of the remaining activities were similar regardless of these treatments. 4. The sensitivities towards clorgyline and l-deprenyl of the remaining activity in the Triton X-100-treated residue and the phospholipase C-treated carp brain mitochondria were found to be unchanged, but those of the activity remaining in the MEK-treated residue were similarly decreased. 5. No evidence was obtained suggesting conversion of carp MAO to either MAO-A or MAO-B by the modification of the mitochondrial lipid environment by the treatments employed.

Detection of a new series of monoamine oxidase inhibitors.

A new series of monoamine oxidase (MAO) inhibitors structurally analogous to tetrazolo [5, 1-a] phthalazine (Tetra-P) was detected using rat brain mitochondrial MAO. In the tricyclic group, naphtetrazole (NTE) indicated a marked potency of MAO inhibition almost equal to that of iproniazid, and naphtriazole (NTR) showed similar potency as did Tetra-P. The nonselective and competitive inhibition for both types, MAO-A and MAO-B, was observed in some Tetra-P analogues.

Alterations in monoamine oxidase activity after single and repeated exposure of rats to chlorphentermine

Monoamine oxidase (MAO) activity was determined in rat tissues following in vivo treatments with chlorphentermine (CP). Oxidation of seven amine substrates by liver, lung or brain mitochondrial MAO was investigated at 2 h after a single i.p. injection (60 mg/kg) or after repeated injection (once daily for 3 days, 20 mg/kg, i.p.). Deamination of the type A substrates, norepinephrine, serotonin and octopamine, was decreased significantly in liver, lung and brain after both single and repeated injections. Oxidative deamination of tyramine and dopamine (type A + B substrates) was also lowered in all organs after single and repeated exposure to CP, but to a lesser degree than the type A substrates. However, oxidation of the type B substrates, benzylamine and tryptamine, was unaffected by CP administration in comparison to control. These data indicate that CP is a specific inhibitor of mitochondrial MAO, form A.

MDL 72145, an enzyme-activated irreversible inhibitor with selectivity for monoamine oxidase type B.

MDL 72145, (E)-2-(3',4'-dimethoxyphenyl)-3-fluoroallylamine hydrochloride, was designed and synthesised as a potential enzyme-activated irreversible inhibitor of monoamine oxidase (MAO). In vitro, the compound displayed time-dependent pseudo-first-order irreversible inhibitory characteristics with high selectivity for the B form of rat brain mitochondrial MAO. At 10 degrees C the Ki and tau 50 values for the B enzyme were 40 microM and 1.7 min, respectively, while these same kinetic constants for the A enzyme were 131 microM and 14.5 min, respectively. Selective protection against inactivation of the two forms of MAO by MDL 72145 was obtained by preincubating the enzyme with suitable concentrations of the selective A and B substrates, 5-hydroxytryptamine and benzylamine.

Activation of monoamine oxidase by high molecular weight fractions of human plasma.

The activation of human platelet monoamine oxidase (MAO) and rat brain mitochondrial MAO ( RBM -MAO) by human plasma were studied. The deamination of two different substrates, tyramine and phenethylamine (PEA) was investigated. The increase in MAO activity in the presence of human plasma can be explained by the observed decrease in the apparent Km for the amine (tyramine, PEA). This activation pattern was the same both for human platelet MAO and RBM -MAO. The activating properties of human plasma were recovered in high molecular weight fractions after gel filtration.

Characteristics of mitochondrial and synaptosomal monoamine oxidase in monkey brain.

Enzymic properties of monoamine oxidase (MAO) from monkey brain were studied. High MAO activity was observed in the mesencephalon and dienecephalon of the brain. Highest activity in every region of the brain was found with tyramine as a substrate. Monkey brain mitochondrial MAO showed a different substrate specificity and different Km and Vmax values than the enzyme from mice, rats, guinea pigs and rabbits. The pH activity curves were all bell-shaped, but the pH optima were remarkably different with the various substrates used. The activities of various substrates at pH 7.2 were compared with those at the pH optimum. At the pH optima, the activity was about 1.2-fold higher with tyramine and dopamine, 2-fold higher with beta-phenylethylamine (beta-PEA) and 3-fold higher with serotonin (5-HT) and benzylamine. These results were almost similar when synaptosomes from monkey brain were used. MAO activities with 5-HT and beta-PEA were strongly inhibited by much lower concentrations of clorgyline and deprenyl, respectively. Plateau-shaped inhibition curves by these inhibitors were obtained with tyramine as the substrate. These results indicate that both the A- and B-form of MAO appear to be uniformly distributed in monkey brain, and the A-form of MAO represents approximately 35% and 50% of the total MAO activity in mitochondria and synaptosomes, respectively.

Characteristics of Mitochondrial and Synaptosomal Monoamine Oxidase in Monkey Brain

Enzymic properties of monoamine oxidase (MAO) from monkey brain were studied. High MAO activity was observed in the mesencephalon and die-ncephalon of the brain. Highest activity in every region of the brain was found with tyramine as a substrate. Monkey brain mitochondrial MAO showed a different substrate specificity and different Km and Vmax values than the enzyme from mice, rats, guinea pigs and rabbits. The pH activity curves were all bell-shaped, but the pH optima were remarkably different with the various substrates used. The activities of various substrates at pH 7.2 were compared with those at the pH optimum. At the pH optima, the activity was about 1.2-fold higher with tyramine and dopamine, 2-fold higher with β-phenylethylamine (β-PEA) and 3-fold higher with serotonin (5-HT) and benzylamine. These results were almost similar when synaptosomes from monkey brain were used. MAO activities with 5-HT and β-PEA were strongly inhibited by much lower concentrations of clorgyline and deprenyl, respectively. Plateau-shaped inhibition curves by these inhibitors were obtained with tyramine as the substrate. These results indicate that both the A- and B-form of MAO appear to be uniformly distributed in monkey brain, and the A-form of MAO represents approximately 35% and 50% of the total MAO activity in mitochondria and synaptosomes, respectively.

Catalytic properties of carp brain monoamine oxidase in delipidated and reconstituted mitochondrial membranes

A possible role of membrane phospholipids in catalytic properties of carp brain mitochondrial monoamine oxidase (MAO) in both intact and delipidated membranes were studied before and after addition of some phospholipids. Deaminations of 5-HT and tyramine were greatly decreased by treatment with either phospholipase A2, C or D, but that of PEA was to a lesser extent. The sensitivity of MAO in the delipidated preparation to clorgyline and deprenyl was similar to that in the intact one; however, the amount of 3H-pargyline bound to MAO was found to be about half, and the Km values for the three substrates were extremely increased after delipidation. Among phospholipids tested, phosphatidylinositol(PI) most effectively and dose-dependently activated activity towards 5-HT in both intact and delipidated mitochondria, but the inhibitor sensitivity of MAO and the Km values for these substrates were not changed as compared before and after the PI addition. As a result, delipidation accounts for loss of activity through decreases in both the Km values and amount of active enzyme, but some phospholipids activate MAO activity without altering affinities towards substrates and selective MAO inhibitors.