Molecular docking of inhibitors into monoamine oxidase B

Monoamine oxidase B (MAO-B) functions in the deamination of monoamines, including dopamine and norepinephrine. The search for MAO-B inhibitors increased following the discovery that the enzyme may be responsible for generating neurotoxins from various endogenous or exogenous compounds. Computational screening methods aid in the search for new inhibitors, but validation studies for specific software packages and receptors are necessary for effective application of these methods. In this study, DOCK 6.0.0 was used to dock a series of inhibitors to MAO-B. Included were studies of re-docking ligands into MAO-B crystal structures, after which a set of 30 compounds with known inhibition constants for MAO-B were docked, including 15 strong inhibitors and 15 weak inhibitors. Good agreement was observed between the top experimental inhibitors and the top ranked docking results, and key interactions between the ligands and receptor were identified.     

The therapeutic potential of monoamine oxidase inhibitors

Monoamine oxidase inhibitors were among the first antidepressants to be discovered and have long been used as such. It now seems that many of these agents might have therapeutic value in several common neurodegenerative conditions, independently of their inhibition of monoamine oxidase activity. However, many claims and some counter-claims have been made about the physiological importance of these enzymes and the potential of their inhibitors. We evaluate these arguments in the light of what we know, and still have to learn, of the structure, function and genetics of the monoamine oxidases and the disparate actions of their inhibitors.     

Structure-activity relationship and docking studies of thiazolidinedione-type compounds with monoamine oxidase B

The neuroprotective activity of pioglitazone and rosiglitazone in the MPTP parkinsonian mouse prompted us to evaluate a set of thiazolidinedione (TZD) type compounds for monoamine oxidase A and B inhibition activity. These compounds were able to inhibit MAO-B over several log units of magnitude (82 nM to 600 μM). Initial structure-activity relationship studies identified key areas to modify the aromatic substituted TZD compounds. Primarily, substitutions on the aromatic group and the TZD nitrogen were key areas where activity was enhanced within this group of compounds.     

The uptake of [14C]choline into synaptosomes in vitro

1. The uptake of [(14)C]choline into synaptosomes in vitro was investigated by a gel-filtration method. Synaptosomes incubated in a medium fortified with glucose and succinate rapidly take up [(14)C]choline. 2. A substantial proportion of the radioactivity taken up can be released by osmotic shock, and is recoverable as choline on a thin-layer chromatogram. This suggests that choline is taken up across the limiting membrane into the cytoplasmic compartment of the synaptosome. 3. The concentration of choline in the synaptosome has a dependence on the external concentration of choline that is similar to that in erythrocytes and mouse cerebral-cortex slices. The choline influx has two components, one that is linear and one that is saturable with increasing choline concentration. 4. Omission of Na(+) from the incubation medium, or addition of 100mm-K(+), inhibits choline uptake. Hemicholinium no. 3 is a powerful inhibitor of the choline uptake. 5. The similarity of the choline-uptake process in synaptosomes to that in erythrocytes and cortex slices indicates that the synaptosome limiting membrane is functionally competent in this respect.     

The insertion of monoamine oxidase A into the outer membrane of rat liver mitochondria.

Human monoamine oxidase A that had been synthesized in a reticulocyte lysate translation system was capable of binding to and inserting into either rat liver mitochondria or isolated mitochondrial outer membranes. The inserted form was as resistant to proteinase K as endogenous mitochondrial monoamine oxidase A. The insertion, but not the binding, of monoamine oxidase A was prevented by depleting the reaction mixture of either ATP (with apyrase) or ubiquitin (with purified antibodies against this polypeptide). Addition of ATP or ubiquitin, respectively, to these depleted mixtures restored the insertion of the enzyme. In the absence of mitochondria, in vitro synthesized monoamine oxidase A did not catalyze its own alkylation by the mechanism-based inhibitor, [3H]clorgyline. However, both monoamine oxidase A that had been membrane-inserted in vitro and monoamine oxidase A that had been bound to the mitochondria under conditions of ATP depletion catalyzed adduct formation. Furthermore, reaction of either clorgyline or another mechanism-based inhibitor, pargyline, with the membrane-bound enzyme during ATP depletion inhibited the insertion of monoamine oxidase A when ATP was restored. These observations indicate that monoamine oxidase A acquired a catalytically active conformation on interaction with the mitochondrial outer membranes prior to its ATP and ubiquitin-dependent insertion into the membrane.     

Anorectic activities of serotonin uptake inhibitors: correlation with their potencies at inhibiting serotonin uptake in vivo and 3H-mazindol binding in vitro

The mechanism of anorectic action of several serotonin uptake inhibitors was investigated by comparing their anorectic potencies with several biochemical and pharmacological properties and in reference to the novel compound SL 81.0385. The anorectic effect of the potent serotonin uptake inhibitor SL 81.0385 (ED50 = 4 mg/kg, i.p.) was potentiated by pretreatment with 5-hydroxytryptophan and blocked by the serotonin receptor antagonist metergoline. A good correlation (r = 0.98, p less than 0.01) was obtained between the ED50 values of anorectic action and the ED50 values of serotonin uptake inhibition in vivo (but not in vitro) for several specific serotonin uptake inhibitors. Most of the drugs tested displaced [3H]-mazindol from its binding to the anorectic recognition site in the hypothalamus, except the pro-drug zimelidine which was inactive (IC50 greater than 100 microM). Excluding zimelidine, a good correlation (r = 0.835, p less than 0.01) was obtained between the affinities of these drugs for [3H]-mazindol binding and their anorectic action indicating that their anorectic activity may be associated with an effect mediated through this site. Taken together these results suggest that the anorectic action of serotonin uptake inhibitors is directly associated to their ability to inhibit serotonin uptake and thus increasing the synaptic levels of serotonin. The interactions of these drugs with the anorectic recognition site labelled with [3H]-mazindol is discussed in connection with the serotonergic regulation of carbohydrate intake.     

The in vitro insertion of monoamine oxidase B into mitochondrial outer membranes

Bovine monoamine oxidase (MAO) B has been synthesized in vitro using a reticulocyte lysate translation system directed by bovine liver poly(A)+ RNA. The newly synthesized enzyme apparently lacks a cleavable N-terminal extension, but MAO B is readily incorporated into mitochondria or isolated mitochondrial outer membranes prepared from rat liver. ATP is not required for the binding of the newly synthesized enzyme to the outer membranes, but is necessary for the insertion of MAO B into these membrane vesicles. The ATP is not required to generate a mitochondrial membrane potential as assembly occurs under conditions that preclude either the formation or the maintenance of the potential. MAO B will bind to but not become incorporated into outer membrane vesicles which have been treated with trypsin, suggesting that the insertion of MAO B also depends on protein factors present on the outer membranes.