Adil J. Nazarali

Chronic tranylcypromine treatment induces functional α2-adrenoceptor down-regulation in rats

Abstract The effects of chronic (28 d Alzet 2002 osmotic mini-pumps) administration of antidepressant drugs on the functional sensitivity of α 2 -adrenoceptors and on monoamine oxidase activity has been assessed. Tranylcypromine, 4-fluorotranylcypromine and clorgyline (0.5–1.0 mg kg −1 ) induced a decrease in the motor-suppresant effects of clonidine (50 μg kg −1 ) observed at 9–10 and 23–24 days of drug administration. These effects were associated with marked decreases in type A (clorgyline) or type A and B monoamine oxidase activity (tranylcypromine and 4-fluorotranycylpromine). The results indicate that α 2 -adrenoceptor down-regulation is an early emergent feature of adaptive changes in noradrenaline systems induced by prolonged exposure to tranylcypromine.

Rapid analysis of β-phenylethylamine in tissues and body fluids utilizing pentafluorobenzoylation followed by electron-capture gas chromatography

A rapid, sensitive gas chromatographic procedure for analysis of beta-phenylethylamine is reported. The procedure involves extraction with a liquid ion-pairing compound, back-extraction with HCl, basification and reaction with pentafluorobenzoyl chloride under aqueous conditions. The pentafluorobenzoyl derivative of beta-phenylethylamine is then separated and analyzed on a gas chromatograph equipped with a capillary column and an electron-capture detector. The procedure produces a derivative which has good chromatographic properties and a high degree of stability. The method has been applied to analysis of beta-phenylethylamine in a variety of tissues and body fluids.

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.

Amphetamine in rat brain after intraperitoneal injection of N-alkylated analogues

Three N-alkylated analogues of amphetamine were administered intraperitoneally to male Sprague-Dawley rats and whole brain levels of amphetamine (AM) and the N-alkyl analogue were determined one hour after injection of the N-alkylated compounds. The drugs administered were the N-2-cyanoethyl-(I) (fenproporex), the N-3-chloropropyl-(II) (mefenorex) and the N-n-propyl-(III) derivatives of AM: the first two of these are used clinically as anorexiants, and the latter has been used extensively to study aspects of metabolism of AM-like compounds. Analysis of AM, I, II and III was performed using electron-capture gas chromatography with a capillary column after reaction of compounds with pentafluorobenzoyl chloride under aqueous conditions. In a second comparative study, equimolar doses (0.05 mMole/kg) of I or AM were administered intraperitoneally to the rats and brain levels determined after one hour. Results indicate extensive N-dealkylation occurs for compounds I, II and III in the rat.

Inhibition of ischemia-induced brain catecholamine alterations by clonidine.

The effect of clonidine, an alpha 2-agonist, on ischemia-induced alterations in brain catecholamine and metabolite levels was studied in Mongolian gerbils subjected to 180 min of unilateral cerebral ischemia. The gerbils were randomly assigned to four treatment groups: sham-operated or unilateral carotid lesion; each pretreated with clonidine 0.4 mg/kg IP, or untreated. All animals were neurologically assessed and categorized as asymptomatic, neurological deficit or seizure activity at the time of sacrifice. Hemispheric levels of noradrenaline (NA), dopamine (DA), homovanillic acid (HVA), and 3,4-dihydroxyphenylacetic acid (DOPAC) were measured using high pressure liquid chromatography with electrochemical detection. No changes from control were found in animals that remained asymptomatic regardless of treatment. In untreated gerbils that exhibited neurological deficits, marked reductions in both NA and DA and increases in HVA occurred in the ischemic hemisphere. These alterations were greater in gerbils that developed seizures during the observation period. Ischemic animals pretreated with clonidine did not show any significant alterations in catecholamine or metabolite levels from clonidine-treated, sham-operated controls in spite of the presence of neurological deficits. Although significant reductions in NA and DA still occurred in pretreated animals that developed seizures, the changes were markedly less than in untreated gerbils. These results indicate that alpha 2-adrenoceptor stimulation is an effective approach for inhibition of ischemia-induced brain catecholamine alterations, and thus may provide a useful method for assessing the role of catecholamine release in the production of acute ischemic neuronal damage.

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

Summarypara-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 ofp-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°C until time of analysis. Tissue levels ofp-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 ofp-OHTCP were present in both brain and heart after TCP and CE-TCP administration. Higher levels ofp-OHTCP were present in the brain than in the heart after TCP treatment, but this situation was reversed with the CE-TCP-treated rats. Sincep-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.

Chronic effects of tranylcypromine and 4-fluorotranylcypromine on regional brain monoamine metabolism in rats: A comparison with clorgyline

A regional analysis of brain amine and acid metabolite levels was conducted after chronic administration of the antidepressant tranylcypromine (0.5 mg/kg/day), of a novel fluorinated analog of this compound, and of clorgyline (1.0 mg/kg/day). These compounds were administered to male Sprague-Dawley rats for 28 days by subcutaneous infusion using osmotic minipumps (Alzet 2002). Levels of noradrenaline, 5-hydroxytryptamine, dopamine, and of the acid metabolites 5-hydroxyindole-3-acetic acid, 3,4-dihydroxyphenylacetic acid, and homovanillic acid were measured in the frontal cortex, nucleus accumbens, caudate nucleus, hippocampus, and hypothalamus. After 28 days of drug administration, sustained increases in amines and decreases in their acid metabolites were observed. Regional differences in these effects were minimal. These results are consistent with reports of sustained increases in brain amine concentrations following prolonged administration of other monoamine oxidase inhibitors.

Prodrugs of Trace Amines

The “trace” amines 2-phenylethylamine (Ia; PEA) and tryptamine (IIa; T) are endogenous CNS stimulants with rapid turnover rates. It has been suggested (Dewhurst, 1968; Sabelli and Mosnaim, 1974) that in depression there is a functional deficiency of one or both of these amines in the brain. Brain levels of PEA and T can be greatly increased in laboratory animals by the administration of monoamine oxidase (MAO)-inhibiting antidepressants (e.g. phenelzine, tranylcypromine) (Philips and Boulton, 1979) but this treatment is not selective and increases brain levels of other endogenous amines. To study the role of PEA and T in affective disorders, it is necessary to increase brain levels of individual endogenous amines and observe the biochemical and behavioural changes that result. Since MAO inhibitors which selectively inhibit the metabolism of individual brain amines do not exist, alternative methods of increasing brain levels of amines must be utilized. In our laboratory, we have investigated the usefulness of prodrugs with the hope that they may alter advantageously the pharmacokinetics of the amine released by the prodrug, such that brain levels of amine are increased, prolonged or better controlled.

Tranylcypromine and an N-Cyanoethyl Analogue: Effects on Brain Levels of the Trace Amines β-Phenylethylamine and Tryptamine

Imbalances in the neuronal homeostasis of the trace amines β-phenylethylamine (PE) and tryptamine (T) have been implicated in the aetiology of certain neuropsychiatry disorders, including depression (Dewhurst, 1984 for review). Tranylcypromine (TCP), a monoamine oxidase (MAO) inhibitor used clinically as an antidepressant, has been shown to elevate substantially brain concentrations of these trace amines (Philips and Boulton, 1979). A number of N-alkylated derivatives of TCP have been synthesized in our laboratories to test them as potential prodrugs of TCP. The prodrug N-(2-cyanoethyl)tranylcypromine (CE-TCP) was found to be a potent MAO inhibitor in its own right (Baker et al., 1984). A neurochemical study is now reported in which the effects of TCP and CE-TCP on brain levels of the trace amines PE and T are compared.