Marine natural products with monoamine oxidase (MAO) inhibitory activity

CONTEXT

Research interest in monoamine oxidase (MAO) as a promising drug target for neurodegenerative diseases has a long history. However, efforts to develop MAO inhibitors (MAOIs) from marine sources have been limited, despite the increasing number of interesting marine natural products.

OBJECTIVE

To review the potential of marine natural products as MAOIs source, including their activities and selectivity on MAO.

METHODS

Public databases such as SciFinder, MarinLit and PubMed were systematically searched from 1991 until Dec 2019. MAO and MAOI were the key terms searched combined with marine natural products and marine.

RESULTS

Six classes of marine natural products with good selectivity between the two MAO subtypes were organized with their selectivity and sources.

CONCLUSIONS

This is the first review to investigate the potential of marine natural products as MAOIs source. Despite the small number of known MAOIs from marine sources, marine natural products are potential leads for the further development of MAOI drugs with novel chemical frames and good selectivity.

Design and synthesis of novel 2-pyrazoline-1-ethanone derivatives as selective MAO inhibitors

Thirty seven novel 2-pyrazoline-1-ethanone derivatives were designed, synthesized and evaluated as selective hMAO inhibitors. Among them, compounds 7h (IC50=2.40 μM) and 12c (IC50=2.00 μM) exhibited best inhibitory activity and selectivity against hMAO-A, surpassing that of the positive control Clorgyline (IC50=2.76 μM). Based on selective activity of hMAO-A, SAR analysis showed that the order of N1 substituent contribution was bromo (3)>piperidinyl (4)>morpholinyl (5)>imidazolyl (6), and compounds with electron-withdrawing substituents (-F, -Cl) at C3 or C5 phenyl ring of 2-pyrazoline nucleus dedicated stronger MAO-A inhibitory activity. Molecular docking showed that compounds 7h and 12c were nicely bound to hMAO-A via two hydrogen bonds (SER209, GLU216), one Pi-Pi interaction and three hydrogen bonds (SER209, GLU216, TYR69), one Sigma-Pi interaction, respectively. In addition, the substituent at C3 position of 2-pyrazoline with the N1 acetyl has little effect on MAO-A inhibitory activity. These data support further studies to assess rational design of more efficiently selective hMAO inhibitors in the future.

Monoamine neurocircuitry in depression and strategies for new treatments

Extensive studies showed that monoaminergic neurotransmission that involves serotonin (5-HT), norepinephrine (NE) and dopamine (DA) exerts major influence on brain circuits concerned by the regulation of mood, reactivity to psychological stress, self-control, motivation, drive, and cognitive performance. Antidepressants targeting monoamines directly affect the functional tone of these circuits, notably in limbic and frontocortical areas, and evidence has been provided that this action plays a key role in their therapeutic efficacy. Indeed, at least some of functional changes detected by functional magnetic resonance imaging in emotion- and cognitive-related circuits such as the one involving limbic-cortical-striatal-pallidal-thalamic connections in depressed patients can be reversed by monoamine-targeted antidepressants. However, antidepressants acting selectively on only one monoamine, such as selective inhibitors of 5-HT or NE reuptake, alleviate depression symptoms in a limited percentage of patients, and are poorly effective to prevent recurrence. Thorough investigations for the last 30 years allowed the demonstration of the existence of functional interactions between 5-HT, NE and DA systems, and the identification of the specific receptors involved. In particular, 5-HT systems were shown to exert negative influence on NE and DA systems through 5-HT2A and 5-HT2C receptor- mediated mechanisms, respectively. On the other hand, complex positive and negative influences of NE system on 5-HT neurotransmission are mediated through α1- and α2-adrenergic receptors, respectively. These data provided a rationale for the design of new, multimodal, therapeutic strategies involving drugs acting not only at the "historical" targets such as the 5-HT and/or the NE transporter, but also at other molecular targets to improve their efficacy and their tolerability.