Monoamine Oxidase Inhibitors (MAOIs) in Psychiatric Practice: How to Use them Safely and Effectively

Monoamine oxidase inhibitors (MAOIs) were among the first licensed pharmacological treatments for patients with depression but over time have fallen out of mainstream clinical use. This has led to a loss of clinician training opportunities and reduced availability of MAOIs for prescribing. This article provides a concise and practical overview of how to use MAOIs safely and effectively in psychiatric practice. We consider the history of MAOIs, why they are not used more frequently, their mechanisms of action, availability, indications and efficacy, general tolerability, withdrawal symptoms, and safety considerations (including hypertensive reactions and serotonin syndrome). Practical advice is given in terms of dietary restrictions, interactions with other medications (both prescribed and non-prescribed), and how prescribers can stop and switch MAOIs, both within the drug class and outside of it. We also provide advice on choice of MAOI and treatment sequencing. Lastly, we consider emerging directions and potential additional indications.

Performance of Force-Field- and Machine Learning-Based Scoring Functions in Ranking MAO-B Protein-Inhibitor Complexes in Relevance to Developing Parkinson's Therapeutics

Monoamine oxidase B (MAOB) is expressed in the mitochondrial membrane and has a key role in degrading various neurologically active amines such as benzylamine, phenethylamine and dopamine with the help of Flavin adenine dinucleotide (FAD) cofactor. The Parkinson’s disease associated symptoms can be treated using inhibitors of MAO-B as the dopamine degradation can be reduced. Currently, many inhibitors are available having micromolar to nanomolar binding affinities. However, still there is demand for compounds with superior binding affinity and binding specificity with favorable pharmacokinetic properties for treating Parkinson’s disease and computational screening methods can be majorly recruited for this. However, the accuracy of currently available force-field methods for ranking the inhibitors or lead drug-like compounds should be improved and novel methods for screening compounds need to be developed. We studied the performance of various force-field-based methods and data driven approaches in ranking about 3753 compounds having activity against the MAO-B target. The binding affinities computed using autodock and autodock-vina are shown to be non-reliable. The force-field-based MM-GBSA also under-performs. However, certain machine learning approaches, in particular KNN, are found to be superior, and we propose KNN as the most reliable approach for ranking the complexes to reasonable accuracy. Furthermore, all the employed machine learning approaches are also computationally less demanding.

How antidepressants work: cautionary conclusions based on clinical and laboratory studies of the longer-term consequences of antidepressant drug treatment

Time-dependent alterations in the functional activity of adrenergic and serotonergic neurotransmitter systems and, in particular, a frequently observed down-regulation of brain beta-adrenoceptors have been implicated in antidepressant drug effects. Current studies of catecholamine and serotonin neurotransmitter systems suggest that the net physiological output changes in neuroendocrine responses, blood pressure, sleep and motor activity which follow various antidepressant treatments in psychiatric patients, normal controls and different experimental animals are not indicative of a common response pattern to all therapeutically effective agents. Rather, antidepressant treatment effects differ according to many variables, including the pre-existing state of the organism (e.g. depressed, stressed or normal), the species, the duration of treatment and the particular brain or peripheral circuits investigated. Examples are cited from our studies of the effects of monoamine oxidase inhibitors and other antidepressants on noradrenergic-serotonergic interactions that affect melatonin release and other neuroendocrine responses, on some additional functional end-points, and on depressive mood and other symptoms in patients with depression or other tricyclic-responsive disorders. These examples illustrate the complexity found in attempts to identify a unitary mechanism of antidepressant drug action.

Spline-fitting with a genetic algorithm: a method for developing classification structure-activity relationships

Classification methods allow for the development of structure-activity relationship models when the target property is categorical rather than continuous. We describe a classification method which fits descriptor splines to activities, with descriptors selected using a genetic algorithm. This method, which we identify as SFGA, is compared to the well-established techniques of recursive partitioning (RP) and soft independent modeling by class analogy (SIMCA) using five series of compounds: cyclooxygenase-2 (COX-2) inhibitors, benzodiazepine receptor (BZR) ligands, estrogen receptor (ER) ligands, dihydrofolate reductase (DHFR) inhibitors, and monoamine oxidase (MAO) inhibitors. Only 1-D and 2-D descriptors were used. Approximately 40% of compounds in each series were assigned to a test set, "cherry-picked" from the complete set such that they lie outside the training set as much as possible. SFGA produced models that were more predictive for all but the DHFR set, for which SIMCA was most predictive. RP gave the least predictive models for all but the MAO set. A similar trend was observed when using training and test sets to which compounds were randomly assigned and when gradually eliminating compounds from the (designed) training set. The stability of models was examined for the random and reduced sets, where stability means that classification statistics and the selected descriptors are similar for models derived from different sets. Here, SIMCA produced the most stable models, followed by SFGA and RP. We show that a consensus approach that combines all three methods outperforms the single best model for all data sets.

A high-throughput monoamine oxidase inhibition assay using liquid chromatography with tandem mass spectrometry

A highly efficient method utilizing liquid chromatography with tandem mass spectrometry (LC/MS/MS) was developed and employed for high-throughput screening of compounds for monoamine oxidase (MAO) inhibition. The method used kynuramine as a common substrate for both MAO-A and MAO-B in incubations, and the 4-hydroxyquinoline (4-HQ) resulting from deamination of kynuramine followed by intramolecular condensation was analyzed using LC/MS/MS; formation of 4-HQ was used as the marker of MAO activity to evaluate the effects of test compounds. Isocratic liquid chromatography was applied to reduce the run time to 2 min. Because of the high specificity and sensitivity of detection of 4-HQ by LC/MS/MS, this method was able to use MAO enzymes at very low concentrations and to perform short incubations; as a result, consumable cost was minimized, and sample preparations were completely avoided. The inhibition data are highly reproducible, and the IC(50) values determined by the method are in good agreement with literature values. The results suggest that this method is very robust and can be used as a generic approach to screen for MAO inhibitors in drug discovery.

Monoamine oxidase inhibitors. A perspective on their use in the elderly

Monoamine oxidase inhibitors (MAOIs) are mainly used in psychiatry for the treatment of depressive disorders and in neurology for the treatment of Parkinson's disease. While the classical, nonselective and nonreversible MAOIs, such as phenelzine and tranylcypromine, are characterised by the risk of inducing a hypertensive crisis when dietary tyramine is ingested, the selective monoamine oxidase-B (MAO-B) inhibitor selegiline (deprenyl) and, even more so, the selective and reversible monoamine oxidase-A (MAO-A) inhibitor moclobemide, are free from this potential interaction. Drug tolerability data for the elderly show that moclobemide is one of the most well tolerated compounds. Selegiline, especially when used in combination with levodopa, can cause anorexia, dry mouth, dyskinesia and, most problematic, orthostatic hypotension. For the traditional MAOIs, phenelzine and tranylcypromine, published data are insufficient to be able to give a conclusive tolerability statement regarding the use of these compounds in elderly people. Although orthostatic hypotension occurs in most patients treated with traditional MAOIs, the incidence in elderly patients with depression does not appear to be greater than that reported with tricyclic antidepressants.

Antidepressant drug selection: criteria and options

The dilemma of developing new medications rationally--as opposed to discovering them through serendipity--is to create an optimal balance between the number of mechanisms of action needed for the widest spectrum of antidepressant activity while maximizing safety and tolerability. Newer antidepressants, such as serotonin selective reuptake inhibitors (SSRIs) and venlafaxine, have a wider therapeutic index than the older tricyclic antidepressants. Fewer types of adverse effects and a reduction in the potential for pharmacodynamic interactions are the distinct benefits of all the newer targeted antidepressants, such as venlafaxine, SSRIs, and bupropion, in comparison with older drugs. However, there are important differences among the newer antidepressants in terms of effects of P450 enzymes, dose-response curves for antidepressant response and adverse effects, and dosing schedules. One of the main benefits of having a wide array of options is the evidence that there may be different forms of the illness, which respond to different mechanisms of action. More research is needed to test this concept and to develop predictors of differential responsiveness.

Spontaneous hypertensive reactions with monoamine oxidase inhibitors

Despite long-standing concerns over hypertensive reactions, monoamine oxidase inhibitors (MAOIs) have grown in popularity and are now used in a variety of psychiatric disorders. The risk of hypertensive episodes is less than 1%. This is most likely the result of careful dietary instructions and prudent prescribing of concomitant medications. The possibility exists of spontaneous or unprovoked hypertensive crises in patients receiving MAOIs. In this report, we review the literature on spontaneous hypertensive episodes and present a case report. There has been a total of 11 cases described in six separate reports. We discuss the possible mechanism, risk factors, treatment, and safety of rechallenging the patients with the MAOI. Further research is needed to clarify this reaction. For now, it remains a rare but worrisome phenomenon. It should stand as an additional source of concern for clinicians who are already well aware of the risk of hypertensive episodes in patients receiving MAOIs.

Dopamine metabolism and neurotransmission in primate brain in relationship to monoamine oxidase A and B inhibition

The "cheese effect", potentiation of sympathomimetic action of indirectly acting amines such as tyramine, the main side effect of irreversible non-selective and selective monoamine oxidase (MAO) A inhibitors, has largely been eliminated in the new generation of reversible selective MAO-A and B and irreversible MAO-B inhibitors. These selective inhibitors are demonstrating unique pharmacology and initial controlled clinical studies are providing evidence to support their action as anti-depressants and anti-Parkinson's disease drugs and possibly as neuroprotectors. Thirty years of experience with non-selective MAO inhibitors has resulted in a better understanding and management of the new generation of MAO inhibitors. Because of their selective action on the specific forms of MAO, which results in selective elevation of brain noradrenaline and serotonin on the one hand and dopamine and phenylethylamine on the other, it is hoped that these drugs will be able to elucidate the functional roles of MAO-A and B subtypes with regards to dopamine metabolism in the human brain.

The functional consequences of inhibition of monoamine oxidase type B: comparison of the pharmacological properties of L-deprenyl and MDL 72145

The pharmacological properties of two selective inhibitors of monoamine oxidase (MAO) type B, L-deprenyl and MDL 72145 [(E)-2-(3,4-dimethoxyphenyl)-3-fluoroallylamine, HCl], have been investigated in rats and mice in relation to their effects on MAO. Selective inhibition of MAO B achieved following 18 h pretreatment with L-deprenyl and/or MDL 72145 did not per se lead to prominent pharmacological activity; no effects were seen in the mouse "Behavioural Despair" test, hypothermia induced by reserpine in mice was neither prevented nor reversed and there was no change in the cardiovascular responsiveness of the pithed rat to tyramine, noradrenaline or stimulation of the spinal sympathetic outflow. L-Deprenyl differed from MDL 72145 in that short term treatment with this drug caused positive effects in the "Behavioural Despair" test, reversal of reserpine hypothermia, indirect sympathomimetic stimulation of blood pressure and heart rate in the pithed rat and ipsilateral rotation in rats with unilateral nigro-striatal lesions. Qualitatively similar effects were seen with dexamphetamine. The marked difference between the pharmacological effects of MDL 72145 and L-deprenyl despite equivalent inhibition of MAO B suggests that many of the pharmacological actions of L-deprenyl result from its amphetamine-like sympathomimetic properties. MDL 72145 can, therefore, be considered a more reliable tool with which to explore the functional importance of MAO B inhibition in experimental animals and man.