Monoamine oxidase inhibitory effects of some 4-aminophenethylamine derivatives

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.

The Kulinkovich Reaction in the Synthesis of Constrained N,N-Dialkyl Neurotransmitter Analogues

An intermolecular Ti(IV)-mediated cyclopropanation reaction has been used to synthesize substituted 2-phenylcyclopropylamines and constrained analogues of the neurotransmitters histamine and tryptamine. Many hydroxy- and methoxy-substituted phenylcyclopropylamines are known to inhibit monoamine oxidase and have been shown to mimic hallucinogens. These compounds were made in 1 to 5 steps from readily available starting materials.

An antisense oligonucleotide targeted at MAO-B attenuates rat striatal serotonergic neurotoxicity induced by MDMA

The present study was designed to elucidate the role of dopamine (DA) metabolism in the serotonergic neurotoxicity induced by 3,4-methylenedioxymethamphetamine (MDMA). An antisense (AS) oligonucleotide (ODN) sequence targeted at monoamine oxidase-B (MAO-B) was utilized to attenuate MAO-B activity prior to MDMA administration. Sprague-Dawley rats were surgically implanted with intracerebroventricular (icv) cannulae and received a continuous infusion of MAO-B AS-ODN via an osmotic minipump. Constant AS ODN infusion for 7 days at a rate of 0.5 microl/h (total daily dose 600 pmol) resulted in a 63% knockdown of MAO-B activity. MDMA (40 mg/kg, sc) produced a rise in body temperature within 1 h of MDMA administration and a reduction in striatal serotonin (5-HT) and 5-hydroxyindole acetic acid (5-HIAA) levels 7 days later. Pretreatment with the MAO-B AS ODN prior to MDMA attenuated this reduction in serotonergic markers, yet had no effect on MDMA-induced hyperthermia. Furthermore, in vivo microdialysis revealed that previous AS ODN treatment failed to alter the acute DA release induced by MDMA (10 mg/kg, sc) within the striatum. These results indicate that MAO-B plays an integral role in the development of MDMA-induced neurotoxicity while not affecting MDMA-induced hyperthermia or acute DA release.

The pharmacodynamic characterization of an antisense oligonucleotide against monoamine oxidase-B (MAO-B) in rat brain striatal tissue

1. The aim of our work was to pharmacodynamically characterize an antisense oligonucleotide sequence (5'-GCC AAA CTT TTG CAT GAC-3') against MAO-B, using qualitative and quantitative analyses as assessment measures. 2. Qualitative analysis using histochemical staining revealed that intracerebroventricular (ICV) administered antisense (100 picomoles twice daily x 3.5 days) eliminated all visibly detectable histochemical staining for MAO-B throughout the striatum 1, 12, and 24 h after the last antisense treatment. 3. Qualitative analysis using RT-PCR of the time course of MAO-B mRNA expression in the rat striatum following ICV administration of the antisense sequence showed that 12-24 h after the last administration there was a dramatic reduction in MAO-B mRNA expression in the striatum. The reverse and scrambled sequences generated no change in MAO-B mRNA at 1 or 24 h after the last treatment. 4. Quantitative analysis using the MAO-B selective substrate 4-dimethylamino-phenethylamine (DMAPEA) showed that the antisense sequence reduced MAO-B activity by more than 40%, which was comparable to a single 2 mg/kg, ip dose of L-deprenyl. 5. Quantitative analysis of neurotransmitter levels 24 h after the last treatment suggested that the antisense sequence did not produce any significant changes in neurotransmitter levels. 6. Potential mechanisms for enhancing the antisense response and the speculated potential of an antisense against MAO-B for studying neurotoxicity, Parkinson's disease, and the aging process are also discussed.

Dopaminergic pharmacology and antioxidant properties of pukateine, a natural product lead for the design of agents increasing dopamine neurotransmission

The dopaminergic and antioxidant properties of pukateine [(R)-11-hydroxy-1,2-methylenedioxyaporphine, PUK], a natural aporphine derivative, were analyzed in the rat central nervous system. At dopamine (DA) D1 ([3H]-SCH 23390) and D2 ([3H]-raclopride) binding sites, PUK showed IC50 values in the submicromolar range (0.4 and 0.6 microM, respectively). When the uptake of tritiated dopamine was assayed by using a synaptosomal preparation, PUK showed an IC50 = 46 microM. In 6-hydroxydopamine unilaterally denervated rats, PUK (8 mg/kg but not 4 mg/kg) elicited a significant contralateral circling, a behavior classically associated with a dopaminergic agonist action. When perfused through a microdialysis probe inserted into the striatum, PUK (340 microM) induced a significant increase in dopamine levels. In vitro experiments with a crude rat brain mitochondrial suspension showed that PUK did not affect monoamine oxidase activities, at concentrations as high as 100 microM. PUK potently (IC50 = 15 microM) and dose-dependently inhibited the basal lipid peroxidation of a rat brain membrane preparation. As a whole, PUK showed a unique profile of action, comprising an increase in extracellular DA, an agonist-like interaction with DA receptors, and antioxidant activity. Thus, PUK may be taken as a lead compound for the development of novel therapeutic strategies for Parkinson disease.

Monoamine oxidase inhibitory properties of some methoxylated and alkylthio amphetamine derivatives: structure-activity relationships

The monoamine oxidase (MAO) inhibitory properties of a series of amphetamine derivatives with different substituents at or around the para position of the aromatic ring were evaluated. In in vitro studies in which a crude rat brain mitochondrial suspension was used as the source of MAO, several compounds showed a strong (IC50 in the submicromolar range), selective, reversible, time-independent, and concentration-related inhibition of MAO-A. After i.p. injection, the compounds induced an increase of serotonin and a decrease of 5-hydroxyindoleacetic acid in the raphe nuclei and hippocampus, confirming the in vitro results. The analysis of structure-activity relationships indicates that: molecules with amphetamine-like structure and different substitutions on the aromatic ring are potentially MAO-A inhibitors; substituents at different positions of the aromatic ring modify the potency but have little influence on the selectivity; substituents at the para position such as amino, alkoxyl, halogens, or alkylthio produce a significant increase in the activity; the para-substituent must be an electron donor; bulky groups next to the para substituent lead to a decrease in the activity; substituents located at positions more distant on the aromatic ring have less influence and, even when the substituent is a halogen (Cl, Br), an increase in the activity of the compound is obtained. Finally, the MAO-A inhibitory properties of some of the compounds evaluated are discussed in relation to: (a) potential antidepressant activity, and (b) their reported hallucinogenic, neurotoxic, or anxiolytic effects.

Enzyme immunometric assay of thyroliberin (TRH)

An enzyme immunometric assay of thyroliberin (TRH) using monoclonal antibodies and a derivatization procedure is described. This assay, named SPIE-IA, involves a four step procedure after chemical derivatization of TRH and biological samples by diazotized APEA. Step 1: derivatized TRH was immunocaptured by a monoclonal anti-TRH antibody coated on a 96-well microtiter plate. Step 2: after washing, derivatized TRH was cross-linked via its amino group to the wells using glutaraldehyde. Step 3: washing and treatment with NaOH. Step 4: measurement of bound TRH using a monoclonal anti-TRH antibody labeled with acetylcholinesterase. The minimal detectable concentration was 0.1 pmol/ml: with a coefficient of variation less than 10% in the 0.156-10 pmol/ml range. This assay is 26-fold more sensitive and more specific than the competitive enzyme immunoassay using the same monoclonal capture antibody, derivatized TRH and TRH-acetylcholinesterase conjugate as tracer. Good correlation was observed between SPIE-IA and a sensitive competitive enzyme immunoassay using polyclonal antibodies.

Behavioral effects of the putative anxiolytic (+/-)-1-(2,5-dimethoxy-4-ethylthiophenyl)-2-aminopropane (ALEPH-2) in rats and mice

Behavioral effects of the phenethylamine derivative (+/-)-1-(2,5-dimethoxy-4-ethylthiophenyl)-2-aminopropane (ALEPH-2) were studied in mice and rats. Murine locomotor activity, measured with a photocell actometer, was markedly depressed following IP injection of 2 and 6 mg/kg of the drug. The same doses of the drug also decreased frequency and duration of head dipping and the number of rearings in the hole board apparatus. In the murine elevated plus maze 2 and 6 mg/kg of ALEPH-2 increased the percentage of both open arm entries and time. The total number of entries into the enclosed arms was not significantly affected by the drug. In the rat, 2-12 mg/kg ALEPH-2, IP, decreased photobeam counts in the actometer in a dose-dependent fashion. Both 2 and 4 mg/kg of the drug increased the percentage of open arm entries, but only the highest dose significantly increased the percentage of time spent on the open arms. The dose of 4 mg/kg ALEPH-2 also significantly decreased the total number of enclosed arm entries. Finally, in a recently developed model of anxiety and memory, the elevated T-maze, the doses of 2 and 4 mg/kg ALEPH-2 did not change inhibitory avoidance of the open arms. Nevertheless, the highest dose had an amnestic effect on this task, repeated 72 h later in the absence of drug. In addition, this dose significantly increased the latency to escape from the open arms and had an amnestic effect measured 72 h later. Overall, these results indicate that ALEPH-2 possesses anxiolytic, amnestic as well as sedative and/or motor depressant actions.