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.

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.

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.

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.

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.

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.

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.

Probing the catalytic mechanism of Escherichia coli amine oxidase using mutational variants and a reversible inhibitor as a substrate analogue.

Copper amine oxidases are homodimeric enzymes containing one Cu(2+) ion and one 2,4,5-trihydroxyphenylalanine quinone (TPQ) per monomer. Previous studies with the copper amine oxidase from Escherichia coli (ECAO) have elucidated the structure of the active site and established the importance in catalysis of an active-site base, Asp-383. To explore the early interactions of substrate with enzyme, we have used tranylcypromine (TCP), a fully reversible competitive inhibitor, with wild-type ECAO and with the active-site base variants D383E and D383N. The formation of an adduct, analogous to the substrate Schiff base, between TCP and the TPQ cofactor in the active site of wild-type ECAO and in the D383E and D383N variants has been investigated over the pH range 5.5-9.4. For the wild-type enzyme, the plot of the binding constant for adduct formation (K(b)) against pH is bell-shaped, indicating two pK(a)s of 5.8 and approximately 8, consistent with the preferred reaction partners being the unprotonated active-site base and the protonated TCP. For the D383N variant, the reaction pathway involving unprotonated base and protonated TCP cannot occur, and binding must follow a less favoured pathway with unprotonated TCP as reactant. Surprisingly, for the D383E variant, the K(b) versus pH behaviour is qualitatively similar to that of D383N, supporting a reaction pathway involving unprotonated TCP. The TCP binding data are consistent with substrate binding data for the wild type and the D383E variant using steady-state kinetics. The results provide strong support for a protonated amine being the preferred substrate for the wild-type enzyme, and emphasize the importance of the active-site base, Asp-383, in the primary binding event.

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.

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.

Reaction of lysyl oxidase with trans-2-phenylcyclopropylamine.

trans-2-Phenylcyclopropylamine hydrochloride (tranylcypromine; TCP) was found to be both an inhibitor and a substrate of lysyl oxidase, the enzyme which oxidizes peptidyl lysine in elastin and collagen to initiate cross-linking in these proteins. The reaction of TCP with this enzyme was further characterized in view of the potential interference that chronic administration of this antidepressant compound may exert on the development and repair of connective tissues. In contrast to the irreversible and/or competitive inhibitors of lysyl oxidase previously described, TCP noncompetitively and reversibly inhibited the oxidation of both alkylamine and elastin substrates with Ki values of 386 and 375 microM, respectively. The noncompetitive mode of interaction affected the accessibility of the active site to productive amine substrates since the reductive trapping of n-hexylamine to lysyl oxidase was largely prevented by the presence of TCP. It was of additional interest that lysyl oxidase catalyzed a limited degree of conversion of TCP to cinnamaldehyde accompanied by the production of hydrogen peroxide. The lack of significant incorporation of protein-bound tritium accompanying reduction of the enzyme-TCP complex with [3H]NaBH4 argued against the formation of a Schiff base between the enzyme and the cinnamaldehyde product as the basis of the inhibitory effect. Spectral evidence was also obtained for an additional interaction between TCP and lysyl oxidase that was independent of the inhibitory effect of TCP. Cyclopropylamine, lacking the benzene moiety of TCP, inhibited lysyl oxidase irreversibly and competitively, and was not a substrate, pointing toward a defining role for the benzene moiety in the interaction of TCP with lysyl oxidase.

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.

Insights into the mechanisms of action of the MAO inhibitors phenelzine and tranylcypromine: a review.

Although the non-selective monoamine oxidase inhibitors phenelzine and tranylcypromine have been used for many years, much still remains to be understood about their mechanisms of action. Other factors, in addition to the inhibition of monoamine oxidase and the subsequent elevation of brain levels of the catecholamines and 5-hydroxytryptamine, may contribute to the overall pharmacological profiles of these drugs. This review also considers the effects on brain levels of amino acids and trace amines, uptake and release of neurotransmitter amines at nerve terminals, receptors for amino acids and amines, and enzymes other than monoamine oxidase, including enzymes involved in metabolism of other drugs. The possible contributions of metabolism and stereochemistry to the actions of these monoamine oxidase inhibitors 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.

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.

[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.

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.

N-(2-cyanoethyl)tranylcypromine, a potential prodrug of tranylcypromine: its disposition and interaction with catecholamine neurotransmitters in brain.

The disposition of the N-cyanoethyl analogue of tranylcypromine (TCP) and the TCP formed from it have been studied in the rat brain following intraperitoneal (ip) administration (0.1 mmol/kg) and the resultant data compared with those obtained following an equimolar dose of TCP. Brain concentrations of the neurotransmitter amines dopamine (DA) and noradrenaline (NA) have also been determined, as well as the percentage inhibition of monoamine oxidase (MAO) types A and B. Our results indicate that the N-cyanoethyl analogue may be a useful prodrug of TCP, providing lower but more sustained concentrations of TCP in brain. Brain levels of DA were increased in a similar pattern after CE-TCP or TCP. Brain levels of NA were decreased by TCP at most time intervals, while CE-TCP produced a much less pronounced effect. Both CE-TCP and TCP inhibited MAO-A and MAO-B, with maximum inhibition occurring 60 min after CE-TCP dosing and 30 min after dosing with TCP, times at which brain concentrations of CE-TCP and TCP were at the maximum.

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.