The effect of nicotine and nicotine+monoamine oxidase inhibitor on the value of alcohol.

Alcohol is the most commonly abused drug in the USA and many people suffer from alcohol use disorder. Many factors are associated with alcohol use disorder, but the causal role of comorbid nicotine use has not been extensively considered. Nicotine has reward-enhancing properties and may increase the value of alcohol. Monoamine oxidase inhibition increases nicotine self-administration and may increase the reward-enhancing effects of nicotine. We assessed the effect of nicotine and nicotine in combination with a commonly used monoamine oxidase inhibitor (tranylcypromine) on the value of alcohol using a progressive ratio schedule of reinforcement in rats. Nicotine administration increased the breakpoint for alcohol, but nicotine in combination with tranylcypromine decreased the breakpoint for alcohol. The current study adds to previous research showing that nicotine increases the value of alcohol. This finding has important implications for the etiology of addiction because of the comorbidity of smoking with many drugs of abuse. The finding that nicotine in combination with tranylcypromine reduces the value of alcohol warrants further investigation.

Structural basis of drug binding to CYP46A1, an enzyme that controls cholesterol turnover in the brain.

Cytochrome P450 46A1 (CYP46A1) initiates the major pathway of cholesterol elimination from the brain and thereby controls cholesterol turnover in this organ. We determined x-ray crystal structures of CYP46A1 in complex with four structurally distinct pharmaceuticals; antidepressant tranylcypromine (2.15 Å), anticonvulsant thioperamide (1.65 Å), antifungal voriconazole (2.35 Å), and antifungal clotrimazole (2.50 Å). All four drugs are nitrogen-containing compounds that have nanomolar affinity for CYP46A1 in vitro yet differ in size, shape, hydrophobicity, and type of the nitrogen ligand. Structures of the co-complexes demonstrate that each drug binds in a single orientation to the active site with tranylcypromine, thioperamide, and voriconazole coordinating the heme iron via their nitrogen atoms and clotrimazole being at a 4 Å distance from the heme iron. We show here that clotrimazole is also a substrate for CYP46A1. High affinity for CYP46A1 is determined by a set of specific interactions, some of which were further investigated by solution studies using structural analogs of the drugs and the T306A CYP46A1 mutant. Collectively, our results reveal how diverse inhibitors can be accommodated in the CYP46A1 active site and provide an explanation for the observed differences in the drug-induced spectral response. Co-complexes with tranylcypromine, thioperamide, and voriconazole represent the first structural characterization of the drug binding to a P450 enzyme.

Advances pertaining to the pharmacology and interactions of irreversible nonselective monoamine oxidase inhibitors.

Recent advances clarifying the pharmacology and interactions of irreversible nonselective monoamine oxidase inhibitors that have not been considered in depth lately are discussed. These new data elucidate aspects of enzyme inhibition and pharmacokinetic interactions involving amine oxidases, cytochrome P450 enzymes, aminotransferases (transaminases), and decarboxylases (carboxy-lyases) and the effects of tyramine. Phenelzine and tranylcypromine remain widely available, and many publications have data relevant to this review. Their effect on CYP 450 enzymes is less than many newer drugs. Tranylcypromine only inhibits CYP 450 2A6 (selectively and potently). Phenelzine has no reported interactions, but, like isoniazid, weakly and irreversibly inhibits CYP 450 2C19 and 3A4 in vitro. It might possibly be implicated in interactions (as isoniazid is). Phenelzine has some clinically relevant inhibitory effects on amine oxidases, aminotransferases, and decarboxylases, and it lowers pyridoxal phosphate levels. It commonly causes pyridoxal deficiency, weight gain, sedation, and sexual dysfunction, but only rarely causes hepatic damage and failure, or neurotoxicity. The adverse effects and difficulties with monoamine oxidase inhibitors are less than previously believed or estimated, including a lower risk of hypertension, because the tyramine content in foods is now lower. Potent norepinephrine reuptake inhibitors have a strong protective effect against tyramine-induced hypertension. The newly discovered trace amine-associated receptors probably mediate the pressor response. The therapeutic potential of tranylcypromine and L-dopa in depression and Parkinson disease is worthy of reassessment. Monoamine oxidase inhibitors are not used to an extent proportionate with their benefits; medical texts and doctors' knowledge require a major update to reflect the evidence of recent advances.

Enhancement of drug affinity for cell membranes by conjugation with lipoamino acids II. Experimental and computational evidence using biomembrane models.

Lipoamino acids (LAAs) are promoieties able to enhance the amphiphilicity of drugs, facilitating their interaction with cell membranes. Experimental and computational studies were carried out on two series of lipophilic amide conjugates between a model drug (tranylcypromine, TCP) and LAA or alkanoic acids containing a short, medium or long alkyl side chain (C-4 to C-16). The effects of these compounds were evaluated by monolayer surface tension analysis and differential scanning calorimetry using dimyristoylphosphatidylcholine monolayers and liposomes as biomembrane models. The experimental results were related to independent calculations to determine partition coefficient and blood-brain partitioning. The comparison of TCP-LAA conjugates with the related series of TCP alkanoyl amides confirmed that the ability to interact with the biomembrane models is not due to the mere increase of lipophilicity, but mainly to the amphipatic nature and the kind of LAA residue.

trans-2-phenylcyclopropylamine is a substrate for and inactivator of horseradish peroxidase.

Horseradish peroxidase (HRP) is well known for mediating the electron-transfer oxidation of electron-rich aromatic 'donors' such as phenols and anilines, but has not been described to oxidize aliphatic amines. We here confirm the inability of HRP to oxidize typical aliphatic amines, even those which would exist significantly as free bases at the operative pH. In contrast, trans-2-phenylcyclopropylamine (2-PCPA) is both a substrate (turnover product is cinnamaldehyde) and a time-dependent inactivator of HRP. These activities of 2-PCPA are consistent with either a concerted or rapid sequential one-electron-oxidation/ring-opening to give an intermediate capable of covalent binding to the enzyme. 2-PCPA is the first known example of a simple aliphatic amine which serves as a substrate for HRP under turnover conditions.

cis-Cyclopropylamines as mechanism-based inhibitors of monoamine oxidases.

Cyclopropylamines, inhibitors of monoamine oxidases (MAO) and lysine-specific demethylase (LSD1), provide a useful structural scaffold for the design of mechanism-based inhibitors for treatment of depression and cancer. For new compounds with the less common cis relationship and with an alkoxy substituent at the 2-position of the cyclopropyl ring, the apparent affinity determined from docking experiments revealed little difference between the enantiomers. Using the racemate, kinetic parameters for the reversible and irreversible inhibition of MAO were determined. No inhibition of LSD1 was observed. For reversible inhibition, most compounds gave high IC50 values with MAO A, but sub-micromolar values with MAO B. After pre-incubation of the cyclopropylamine with the enzyme, the inhibition was irreversible for both MAO A and MAO B, and the activity was not restored by dilution. Spectral changes during inactivation of MAO A included bleaching at 456 nm and an increased absorbance at 400 nm, consistent with flavin modification. These derivatives are MAO B-selective irreversible inhibitors that do not show inhibition of LSD1. The best inhibitor was cis-N-benzyl-2-methoxycyclopropylamine, with an IC50 of 5 nm for MAO B and 170 nm for MAO A after 30 min pre-incubation. This cis-cyclopropylamine is over 20-fold more effective than tranylcypromine, so may be studied as a lead for selective inhibitors of MAO B that do not inhibit LSD1.

Pharmacokinetics of tranylcypromine in patients who are depressed: relationship to cardiovascular effects.

We investigated the pharmacokinetics of tranylcypromine, as well as the relationship between plasma levels of this agent and its effects on blood pressure and pulse rate. Tranylcypromine was absorbed rapidly after oral dosing, with the peak level being attained within 0.67 to 3.50 hours. Absorption was biphasic in seven of nine subjects. Elimination of tranylcypromine also was rapid, with a t 1/2 between 1.54 and 3.15 hours. From 2 to 7 hours after dosing, standing systolic and diastolic blood pressures were lowered and standing pulse was raised, compared with baseline. Onset of the effect on standing systolic blood pressure was correlated with the time of peak plasma tranylcypromine concentration. Maximum orthostatic drop of blood pressure and rise of pulse rate occurred 2 hours after dosing. Mean plasma tranylcypromine concentrations were correlated with mean orthostatic drop of systolic blood pressure and rise of pulse rate. Patients who have clinically significant hypotensive reactions to this agent may benefit from changes in their dose regimen aimed at minimizing peak tranylcypromine levels.

Medical implications from the crystal structure of a copper-containing amine oxidase complexed with the antidepressant drug tranylcypromine.

The X-ray crystal structure of the copper-containing quinoprotein amine oxidase from E. coli has been determined in complex with the antidepressant drug tranylcypromine to 2.4 A resolution. The drug is a racemic mix of two enantiomers, but only one is seen bound to the enzyme. The other enantiomer is not acting as a substrate for the enzyme as no catalytic activity was detected when the enzyme was initially exposed to the drug. The inhibition of human copper amine oxidases could be a source of side-effects in its use as an antidepressant to inhibit the flavin-containing monoamine oxidases in the brain.

A gas chromatographic procedure for separation and quantitation of the enantiomers of the antidepressant tranylcypromine.

A novel assay procedure has been developed that allows for the separation and quantification of the enantiomers of the monoamine oxidase inhibitor tranylcypromine (TCP) in brain and liver of rats. The analytical method involves extraction of the drug from rat tissue with an organic solvent. TCP is then derivatized with S-(-)-N-(trifluoroacetyl)-prolyl chloride to allow gas chromatographic analysis of the resulting diastereoisomers. Conditions for analysis by a gas chromatograph equipped with a nitrogen-phosphorus detector and a capillary column are described. The method has been applied to the separation and quantification of the enantiomers of TCP in samples of brain and liver of rats that had been injected with this drug alone and after pretreatment with iprindole, a drug known to block aromatic ring hydroxylation.

Stereoisomery and the release of the adrenergic neurotransmitter by indirectly acting sympathomimetics.

The isolated right rat atrium was used to investigate the chronotropic effects of dl-tranylcypromine and its d- and l-isomers. The concentration-effect curves of the three compounds were similar. The response of the preparation to the three drugs was completely blocked by pretreatment of the animal with reserpine, thus indicating an indirect effect of the drugs by the release of the natural mediator. Cocaine present in the bathing fluid partially antagonized the effect of dl-tranylcypromine and its isomers. It is concluded that the accumulation of the different forms of the drug by neural structures and the subsequent release of the neurotransmitter are not stereospecific processes. Furthermore it is suggested that the efflux of the neurotransmitter in the rat atrium may be carrier-mediated, and that this process is inhibited by cocaine.

Two cases of fatal intoxication due to tranylcypromine overdose.

Two cases of death following the ingestion of tranylcypromine are presented. High concentrations of tranylcypromine were determined in blood, urine, and liver by gas-liquid chromatography. Tranylcypromine was extracted from buffered blood with n-butyl chloride. The evaporated extract was derivatized with trifluoroacetic anhydride and analyzed by gas chromatography with nitrogen-phosphorus selective detection. The method was linear in blood over the range 0.5-20 mg/L with a limit of quantitation of about 0.2 mg/L.

One fatal and one nonfatal intoxication with tranylcypromine. Absence of amphetamines as metabolites.

Two very different cases of overdose with tranylcypromine are presented. One clinical case involving the ingestion of 400 mg tranylcypromine with suicidal intention and one fatality with a suspicion of possible tranylcypromine overdose were examined. Both cases showed similar blood concentrations (0.5 and 0.7 mg/L, respectively), but the clinical case exhibited only mild symptoms of intoxication. The fatality showed no other drugs that could provide an explanation for the death of a 40-year-old male except tranylcypromine. Consideration of the drug concentrations in the fatality in relation to the case findings and other reported data indicates the tranylcypromine overdose as the probable cause of death, despite the low blood concentration. In addition, we looked for evidence of amphetamine as a putative metabolite in both cases. No amphetamines were detected in the overdose cases reported here.

[Effect of cicletanine on prostacyclin generation in vivo]. / Effet du ciclétanine sur la génération de prostacycline in vivo.

The administration of arachidonic acid to live rabbits if followed by the generation of prostacyclin and/or thromboxane. Cicletanine increased the production of prostacyclin in a first group of rabbits and amplified the prostacyclin/thromboxane ratio in a second group of the thromboxane type. The most probable mechanism for this action is activation of prostacyclin synthase by cicletanine. This was confirmed in the in vivo model by a study of the platelet-vascular wall interaction: tranylcyprominE, a prostacyclin synthase inhibitor, increased the interaction. Under these experimental conditions, cicletanine inhibited the effect of tranylcypromine and completely restored the enzymatic activity of prostacyclin synthase.

Tranylcypromine isomers and Parkinson's disease: new aspects of an old drug.

The tranylcypromine stereoisomers have been investigated in a series of comparative trials in Parkinsons' disease and the results indicate that doses below 3 mg/day, of the (+)-isomer in particular, are effective as adjuvant anti-parkinsonian therapy. Biochemical results, monitoring platelet monoamine oxidase (MAO) activity and plasma concentrations of drugs and phenylethylamine, an MAO substrate, showed such low doses of the (+)-isomer to inhibit MAO without inducing the hypertensive reaction sometimes observed at higher dosage. These findings, along with the observation of substantial pharmacokinetic differences between the two isomers are discussed, particularly in relation to reports on their efficacy in depressive illness.

Para-hydroxytranylcypromine: presence in rat brain and heart following administration of tranylcypromine and an N-cyanoethyl analogue.

para-Hydroxytranylcypromine (p-OHTCP) has recently been unequivocally identified in our laboratory as a metabolite of the antidepressant tranylcypromine (TCP). In the study reported here, we have determined brain and heart levels of p-OHTCP in the rat after intraperitoneal administration of a 0.1 mmol/kg dose of TCP or N-(2-cyanoethyl)tranylcypromine (CE-TCP). The animals were killed at 5, 15, 30, 60, 120 or 240 min after drug administration and the tissues (brain and heart) rapidly dissected out. The tissues were frozen in isopentane on solid carbon dioxide and stored at -20 degrees C until time of analysis. Tissue levels of p-OHTCP, TCP and CE-TCP were determined after aqueous pentafluorobenzoylation by conducting analyses with a gas-liquid chromatograph equipped with a fused silica (SE-54) capillary column and an electron-capture detector. Our results show that substantial concentrations of p-OHTCP were present in both brain and heart after TCP and CE-TCP administration. Higher levels of p-OHTCP were present in the brain than in the heart after TCP treatment, but this situation was reversed with the CE-TCP-treated rats. Since p-OHTCP has been shown to retain some MAO-inhibiting properties and to have effects on uptake of catecholamines and serotonin it could therefore contribute to the pharmacological profile of TCP.

Hydrazine and amphetamine binding to amine oxidases: old drugs with new prospects.

Tranylcypromine (TCP), an amphetamine, is a reversible inhibitor of copper-containing amine oxidases. We have solved the structure of the complex of TCP with the amine oxidase from E. coli (ECAO) and shown that only the (+)-enantiomer of TCP binds. Kinetic studies on 2-phenylethylamine and TCP binding to wild-type ECAO and mutational variants fully support the model in which binding of the protonated amine is the first step in the catalytic cycle. Hydrazines are irreversible inhibitors of copper-containing amine oxidases. Binding of hydrazines leads to an adduct ("Adduct 1") with a chromophore at 430 nm which converts at higher pH to another adduct ("Adduct 2") with a chromophore at 520 nm. We have determined the structures of Adduct 1 and 2 for 2-hydrazinopyridine reacted with ECAO. It has been found that Adduct 1 corresponds to the hydrazone and azo tautomers whilst Adduct 2 corresponds to the azo tautomer coordinated to the active site copper. The implications of these results in developing more specific drugs are discussed.

The biotransformation of tranylcypromine by Cunninghamella echinulata.

When incubated alone for 7 days with the fungus Cunninghamella echinulata, tranylcypromine was extensively metabolized. As observed in mammalian systems, N-acetyltranylcypromine was the major metabolite recovered along with lesser amounts of 4-hydroxytranylcypromine, as its N,O-diacetyl derivative. The rate and extent of tranylcypromine biotransformation was affected by whether incubation was on either 30 degrees or flat brackets with a gyratory shaker. There is a strong association between the rate of biotransformation and the utilization of glucose, formation of ammonia, and pH. The slowest rates of biotransformation and metabolic response were observed with the large fungal pellets formed during incubation on flat brackets. These findings raise the possibility that, as in mammalian systems, fungal metabolism of xenobiotics can be affected by nutrient and environmental conditions.