Amphetamine Derivatives as Monoamine Oxidase Inhibitors

Amphetamine and its derivatives exhibit a wide range of pharmacological activities, including psychostimulant, hallucinogenic, entactogenic, anorectic, or antidepressant effects. The mechanisms of action underlying these effects are usually related to the ability of the different amphetamines to interact with diverse monoamine transporters or receptors. Moreover, many of these compounds are also potent and selective monoamine oxidase inhibitors. In the present work, we review how structural modifications on the aromatic ring, the amino group and/or the aliphatic side chain of the parent scaffold, modulate the enzyme inhibitory properties of hundreds of amphetamine derivatives. Furthermore, we discuss how monoamine oxidase inhibition might influence the pharmacology of these compounds.

Characterization of a Novel Drosophila SERT Mutant: Insights on the Contribution of the Serotonin Neural System to Behaviors

A better comprehension on how different molecular components of the serotonergic system contribute to the adequate regulation of behaviors in animals is essential in the interpretation on how they are involved in neuropsychiatric and pathological disorders. It is possible to study these components in "simpler" animal models including the fly Drosophila melanogaster, given that most of the components of the serotonergic system are conserved between vertebrates and invertebrates. Here we decided to advance our understanding on how the serotonin plasma membrane transporter (SERT) contributes to serotonergic neurotransmission and behaviors in Drosophila. In doing this, we characterized for the first time a mutant for Drosophila SERT (dSERT) and additionally used a highly selective serotonin-releasing drug, 4-methylthioamphetamine (4-MTA), whose mechanism of action involves the SERT protein. Our results show that dSERT mutant animals exhibit an increased survival rate in stress conditions, increased basal motor behavior, and decreased levels in an anxiety-related parameter, centrophobism. We also show that 4-MTA increases the negative chemotaxis toward a strong aversive odorant, benzaldehyde. Our neurochemical data suggest that this effect is mediated by dSERT and depends on the 4-MTA-increased release of serotonin in the fly brain. Our in silico data support the idea that these effects are explained by specific interactions between 4-MTA and dSERT. In sum, our neurochemical, in silico, and behavioral analyses demonstrate the critical importance of the serotonergic system and particularly dSERT functioning in modulating several behaviors in Drosophila.

Role of the Cys Loop and Transmembrane Domain in the Allosteric Modulation of α4β2 Nicotinic Acetylcholine Receptors

Allosteric modulators of pentameric ligand-gated ion channels are thought to act on elements of the pathways that couple agonist binding to channel gating. Using α4β2 nicotinic acetylcholine receptors and the α4β2-selective positive modulators 17β-estradiol (βEST) and desformylflustrabromine (dFBr), we have identified pathways that link the binding sites for these modulators to the Cys loop, a region that is critical for channel gating in all pentameric ligand-gated ion channels. Previous studies have shown that the binding site for potentiating βEST is in the C-terminal (post-M4) region of the α4 subunit. Here, using homology modeling in combination with mutagenesis and electrophysiology, we identified the binding site for potentiating dFBr on the top half of a cavity between the third (M3) and fourth transmembrane (M4) α-helices of the α4 subunit. We found that the binding sites for βEST and dFBr communicate with the Cys loop, through interactions between the last residue of post-M4 and Phe¹⁷⁰ of the conserved FPF sequence of the Cys loop, and that these interactions affect potentiating efficacy. In addition, interactions between a residue in M3 (Tyr³⁰⁹) and Phe¹⁶⁷, a residue adjacent to the Cys loop FPF motif, also affect dFBr potentiating efficacy. Thus, the Cys loop acts as a key control element in the allosteric transduction pathway for potentiating βEST and dFBr. Overall, we propose that positive allosteric modulators that bind the M3-M4 cavity or post-M4 region increase the efficacy of channel gating through interactions with the Cys loop.

Neonicotinic analogues: selective antagonists for α4β2 nicotinic acetylcholine receptors

Nicotine is an agonist of nicotinic acetylcholine receptors (nAChRs) that has been extensively used as a template for the synthesis of α4β2-preferring nAChRs. Here, we used the N-methyl-pyrrolidine moiety of nicotine to design and synthesise novel α4β2-preferring neonicotinic ligands. We increased the distance between the basic nitrogen and aromatic group of nicotine by introducing an ester functionality that also mimics acetylcholine (Fig. 2). Additionally, we introduced a benzyloxy group linked to the benzoyl moiety. Although the neonicotinic compounds fully inhibited binding of both [α-(125)I]bungarotoxin to human α7 nAChRs and [(3)H]cytisine to human α4β2 nAChRs, they were markedly more potent at displacing radioligand binding to human α4β2 nAChRs than to α7 nAChRs. Functional assays showed that the neonicotinic compounds behave as antagonists at α4β2 and α4β2α5 nAChRs. Substitutions on the aromatic ring of the compounds produced compounds that displayed marked selectivity for α4β2 or α4β2α5 nAChRs. Docking of the compounds on homology models of the agonist binding site at the α4/β2 subunit interfaces of α4β2 nAChRs suggested the compounds inhibit function of this nAChR type by binding the agonist binding site.

Synthesis, 5-hydroxytryptamine1A receptor affinity and docking studies of 3-[3-(4-aryl-1-piperazinyl)-propyl]-1H-indole derivatives

A series of 3-[3-(4-aryl-1-piperazinyl)-propyl]-1H-indole derivatives (12a-h) was synthesized and evaluated for binding affinity at the human 5-hydroxytryptamine(1A) receptor (5-HT(1A)R) compounds (12b) and (12h) showed the highest 5-HT(1A) receptor affinity (IC(50)=15 nM). Molecular docking studies with all the compounds in a homology model of 5-HT(1A) showed that the main interaction anchoring the ligand in the receptor was a charge-reinforced bond between the protonated nitrogen atom (N-4) of the piperazine ring and Aspartate(3.32).

Aminochrome induces disruption of actin, alpha-, and beta-tubulin cytoskeleton networks in substantia-nigra-derived cell line

In previous studies, we observed that cells treated with aminochrome obtained by oxidizing dopamine with oxidizing agents dramatically changed cell morphology, thus posing the question if such morphological changes were dependent on aminochrome or the oxidizing agents used to produce aminochrome. Therefore, to answer this question, we have now purified aminochrome on a CM-Sepharose 50-100 column and, using NMR studies, we have confirmed that the resulting aminochrome was pure and that it retained its structure. Fluorescence microscopy with calcein-AM and transmission electron microscopy showed that RCSN-3 cells presented an elongated shape that did not change when the cells were incubated with 50 muM aminochrome or 100 muM dicoumarol, an inhibitor of DT-diaphorase. However, the cell were reduced in size and the elongated shape become spherical when the cells where incubated with 50 muM aminochrome in the presence of 100 muM dicoumarol. Under these conditions, actin, alpha-, and beta-tubulin cytoskeleton filament networks became condensed around the cell membrane. Actin aggregates were also observed in cells processes that connected the cells in culture. These results suggest that aminochrome one-electron metabolism induces the disruption of the normal morphology of actin, alpha-, and beta-tubulin in the cytoskeleton, and that DT-diaphorase prevents these effects.

Naphthylisopropylamine and N-benzylamphetamine derivatives as monoamine oxidase inhibitors

A series of naphthylisopropylamine and N-benzyl-4-methylthioamphetamine derivatives were evaluated as monoamine oxidase inhibitors. Their potencies were compared with those of a series of amphetamine derivatives, to test if the increase of electron richness of the aromatic ring and overall size of the molecule might improve their potency as enzyme inhibitors. Molecular dockings were performed to gain insight regarding the binding mode of these inhibitors and rationalize their different potencies. In the case of naphthylisopropylamine derivatives, the increased electron-donating capacity and size of the aromatic moiety resulting from replacement of the phenyl ring of amphetamine derivatives by a naphthalene system resulted in more potent compounds. In the other case, extension of the arylisopropylamine molecule by N-benzylation of the amino group led to a decrease in potency as monoamine oxidase inhibitors.