Single dose of tranylcypromine increases human plasma melatonin

Methylene blue and its analogues as antidepressant compounds

Methylene Blue (MB) is considered to have diverse medical applications and is a well-described treatment for methemoglobinemias and ifosfamide-induced encephalopathy. In recent years the focus has shifted to MB as an antimalarial agent and as a potential treatment for neurodegenerative disorders such as Alzheimer's disease. Of interest are reports that MB possesses antidepressant and anxiolytic activity in pre-clinical models and has shown promise in clinical trials for schizophrenia and bipolar disorder. MB is a noteworthy inhibitor of monoamine oxidase A (MAO-A), which is a well-established target for antidepressant action. MB is also recognized as a non-selective inhibitor of nitric oxide synthase (NOS) and guanylate cyclase. Dysfunction of the nitric oxide (NO)-cyclic guanosine monophosphate (cGMP) cascade is strongly linked to the neurobiology of mood, anxiety and psychosis, while the inhibition of NOS and/or guanylate cyclase has been associated with an antidepressant response. This action of MB may contribute significantly to its psychotropic activity. However, these disorders are also characterised by mitochondrial dysfunction and redox imbalance. By acting as an alternative electron acceptor/donor MB restores mitochondrial function, improves neuronal energy production and inhibits the formation of superoxide, effects that also may contribute to its therapeutic activity. Using MB in depression co-morbid with neurodegenerative disorders, like Alzheimer's and Parkinson's disease, also represents a particularly relevant strategy. By considering their physicochemical and pharmacokinetic properties, analogues of MB may provide therapeutic potential as novel multi-target strategies in the treatment of depression. In addition, low MAO-A active analogues may provide equal or improved response with a lower risk of adverse effects.

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.

Effect of methylene blue and related redox dyes on monoamine oxidase activity; rat pineal content of N-acetylserotonin, melatonin, and related indoles; and righting reflex in melatonin-primed frogs

The ability of methylene blue (MB) to inhibit the nitric oxide-induced stimulation of N-methyl-D-aspartate receptors has been suggested as a possible mechanism of MB's clinical antidepressant action. This study evaluated the alternative/additional mechanisms of the antidepressant effect of MB on biochemical and behavior levels. Selective inhibition of monoamine oxidase type A (MAO-A) is widely accepted as a major mechanism of the clinical antidepressant effect. MB and the related redox dyes toluidine blue O (TBO), thionine (TN), brilliant cresyl blue (BCB), and toluylene blue (TB) were reversible competitive inhibitors of both MAO-A and MAO-B and were highly selective toward MAO-A. TBO was the most potent inhibitor, followed by TN, BCB, MB, and TB. The dyes studied increased rat pineal N-acetylserotonin (NAS) and melatonin content, in accordance with our previous observations of the stimulating effect of selective inhibition of MAO-A on pineal melatonin biosynthesis. The redox dyes exerted antidepressant-like activity in frogs; that is, they suppressed the righting reflex in melatonin-primed frogs. This study's results indicate that selective inhibition of MAO-A might mediate the clinical antidepressant effect of MB through NAS stimulation and melatonin biosynthesis.

An investigation of the effect of immediate and extended release venlafaxine on nocturnal melatonin and cortisol release in healthy adult volunteers

The secretion of the hormone melatonin is particularly robust to the effect of pharmacological agents. Medications may alter melatonin levels through either altering adrenergic activity or affecting liver enzymes involved in melatonin metabolism. The aim of this study was to investigate the effect of venlafaxine, a third generation antidepressant with known adrenergic properties on melatonin secretion. A further aim of the study was to investigate the correlation between plasma and salivary measures on this medication. Eight healthy adult participants (four males, four females) took part in this double blind placebo controlled randomised trial. Participants were tested on 3 nights after taking venlafaxine XR (75 mg), venlafaxine IR (75 mg) or placebo. Participants were placed in a darkened room between 1900 and 0300 h and regular temperature readings, blood and saliva samples were drawn to assess melatonin and cortisol secretion in each condition. There was no significant effect of venlafaxine IR or XR on melatonin concentrations in plasma or saliva and no effects on other circadian parameters including cortisol and temperature. It was notable that the correlation between plasma and salivary melatonin levels became poor after drug treatment. These results indicate that at low doses the mixed serotonergic and noradrenergic drug venlafaxine has no effect on nocturnal melatonin concentrations.

Reversible and selective inhibitors of monoamine oxidase A in the treatment of depressed elderly patients

The treatment of depression in the elderly population needs a thorough and careful work-up and an aggressive therapeutic approach. Any treatment initiative in this population often becomes difficult because of accompanying physical illness, concomitant medication, possible degenerative changes in central nervous system and age-related altered metabolic status. Despite unevenness in research findings, pharmacological treatment remains the mainstay of management of depression among elderly people. Currently available antidepressants, although effective, are problematic because of the increased vulnerability of the elderly to side effects. Recent research efforts to improve the efficacy and safety of drug treatment of depression resulted in development of reversible and selective monoamine oxidase inhibitors of the isoenzyme A (RIMA), with antidepressant efficacy comparable to tricyclic antidepressants and newer generation antidepressants. RIMAs include moclobemide, brofaromine, toloxatone and cimoxatone. Moclobemide is the most investigated available RIMA for therapeutic use at present. Its absorption and disposition in elderly individuals do not differ significantly from those in young healthy volunteers and depressed patients. The results of present clinical studies show that, in elderly depressed patients, moclobemide is at least as effective as other antidepressants. Its particular advantage is, however, that it is as well tolerated in elderly people as in younger people. There are only few significant adverse events, and they are generally less frequent and less severe than those with TCAs. An additional attribute of moclobemide seems also to be its beneficial effect on cognitive functions.

Comparison of the effects of acute fluvoxamine and desipramine administration on melatonin and cortisol production in humans

1. Acute administration of the specific serotonin uptake inhibitor, fluvoxamine (100 mg at 16.00 h), markedly increased nocturnal plasma melatonin concentrations, with high levels extending into the morning hours. 2. Acute administration of the noradrenaline uptake inhibitor, desipramine (DMI) (100 mg at 16.00 h), increased evening plasma melatonin concentrations. 3. Both drug treatments increased the duration of melatonin secretion, fluvoxamine significantly delaying the offset time and DMI significantly advancing the onset time. 4. The stimulatory effect of DMI on plasma melatonin was mirrored by increased urinary 6-sulphatoxymelatonin (aMT6s) excretion. 5. On the contrary, there was no correlation between plasma melatonin and urinary aMT6s concentrations following fluvoxamine treatment, suggesting that fluvoxamine may inhibit the metabolism of melatonin. 6. Treatment with DMI increased plasma cortisol concentrations in the evening and early morning, treatment with fluvoxamine increased plasma cortisol at 03.00 h, 10.00 h and 11.00 h. 7. The drug treatments affected different aspects of the nocturnal plasma melatonin profile suggesting that the amplitude of the melatonin rhythm may depend upon serotonin availability and/or melatonin metabolism whilst the onset of melatonin production depends upon noradrenaline availability.

Clorgyline effect on pineal melatonin biosynthesis in adrenalectomized rats pretreated with 6-hydroxydopamine

The response to administration of the specific monoamine oxidase A (MAO-A) blocker clorgyline was investigated in adult male Sprague-Dawley rats which were adrenalectomized four days prior to treatment or were additionally sympathectomized as newborns by injection of 6-hydroxydopamine. In both groups, the contents of pineal indoles melatonin and N-acetylserotonin were augmented, and the contents of 5-hydroxyindoleacetic acid and 5-hydroxyindoletryptophol decreased 90 min following clorgyline injections when compared to rats receiving saline. The observed responses were less pronounced in rats both adrenalectomized and sympathectomized. The results are in line with the hypothesis that preservation from oxidation of both MAO-A substrates, noradrenaline and serotonin, upon clorgyline administration contributes to the observed increase in melatonin biosynthesis thought to be associated with the anti-depressant effects of MAO inhibition.

Chronopharmacological study of moclobemide effect on the rat pineal melatonin biosynthesis

The chronopharmacological hypothesis of the mechanism of the antidepressant effect of MAO-A inhibitors predicts that clinical efficacy depends upon the time of the day at which the drugs are administered. In the present study moclobemide (10 mg/kg, s.c.) injected at the end of the light phase advanced the onset of the nighttime increase of the rat pineal melatonin biosynthesis while the same dose of drug injected at the end of the dark phase delayed the daytime decrease of melatonin biosynthesis. The results obtained suggest that the timing of MAO-A inhibitor administration should be considered in clinical practice.

Effects of indirectly acting 5-HT receptor agonists on circulating melatonin levels in rats

Because circulating melatonin levels are generally thought to be under the strict control of pineal N-acetyltransferase, little attention has been paid to the impact of an altered availability of serotonin (5-HT) on melatonin formation. In order to see whether melatonin synthesis is stimulated by an increased availability of free, cytosolic 5-HT, we studied the effects of 5-HT precursors, 5-HT releasers and reuptake inhibitors and of monoamine oxidase inhibitors, alone and in combination, on circulating melatonin levels in experimental animals. The administration of tryptophan and 5-HT-releasing drugs (fenfluramine, +/- 3,4-methylenedioxymethamphetamine) to rats caused a dose- and time-dependent elevation of circulating melatonin levels during the day and night. This increase in melatonin was further enhanced by inhibition of monoamine oxidase. The elevation of plasma melatonin caused by 5-HT-releasing drugs was prevented by prior administration of fluoxetine. Monoamine oxidase inhibitors and fluoxetine alone had no effect on circulating melatonin levels. These findings indicate that the administration of indirectly acting 5-HT receptor agonists which increase the free cytoplasmic pool of 5-HT may also elevate circulating melatonin levels. The results of this study suggest that the rate of pineal melatonin synthesis is dependent on the free cytoplasmic pool of 5-HT in pinealocytes and that the drug-induced elevation of this pool stimulates melatonin formation and increases circulating melatonin levels. At least some of the effects of indirectly acting 5-HT receptor agonists, e.g. on sleep, mood, food intake, pain perception, and neuroendocrine secretion, may therefore be mediated by the elevation of circulating melatonin and the subsequent activation of central melatonin receptors.

Nialamide, an MAO inhibitor, increases urinary excretion of endogenously produced bufotenin in man

Nialamide, an MAO inhibitor, was given per os (PO) to a normal man who volunteered in two separate trials (total intake 300 mg and 1000 mg, respectively), and his bufotenin excretion was followed by consecutive urine samples. In both experiments the excretion rose well above the values measured from the same test subject when not taking nialamide (median 0.089 nmol/mmol creatinine, range 0.002-1.78). At its highest, the excretion was 16.5 nmol/mmol creatinine, and the maximum urinary output was 495 nmoles (56 micrograms) in 24 hr. The levels of bufotenin in plasma required for the excretion of the latter amounts are not far from those that produce psychic symptoms in man.

Effect of different photoperiods on the diurnal rhythm of 5-methoxytryptamine in the pineal gland of golden hamsters (Mesocricetus auratus)

This study tested the photo-dependency of the rhythmic synthesis of 5-methoxytryptamine (5-MT) in the pineal gland of golden hamsters. After pargyline administration, pineal 5-methoxytryptamine and melatonin were measured by HPLC in male golden hamsters kept under short and long photoperiod. In both photoperiodic regimes, a clear 5-MT rhythm was observed which fitted a sinusoidal function with high values occurring during the daytime and low values occurring during the night-time. The duration of the low night-time levels was clearly proportional to the length of the dark phase. A marked rhythm of melatonin synthesis was also seen with low daytime levels and high night-time values. An inverse relationship between 5-MT and melatonin levels was observed. Thus, after pargyline administration, the rhythms of 5-MT and melatonin in the pineal gland of golden hamsters are photoperiod-dependent and show a reciprocal relationship.

The response of the pineal melatonin biosynthesis to the selective MAO-A inhibitor, clorgyline, in young and middle-aged rats

1. Clorgyline increased pineal melatonin and N-acetylserotonin (NAS) and decreased 5-hydroxyindoleacetic acid (5-HIAA) content in 3 and 12 months of age male Sprague-Dawley rats kept under 12:12 h light: dark schedule. Exposure to light for 24 h before clorgyline administration resulted in additional elevation of NAS and melatonin. NAS and melatonin levels after clorgyline injections were significantly higher while 5-HIAA levels were significantly lower in young than in middle-aged rats. 2. The 5-HIAA/5-HT ratio (index of monoamine oxidase activity) was higher in middle-aged than in young rats suggesting the lesser degree of clorgyline-induced inhibition of MAO-A in old than in young rats. 3. It is suggested that melatonin response to a single dose of the selective MAO-A inhibitor might be used for the assessment of the aging changes of the rat (and human) pineals.

Differential effects of indolepyruvic acid and 5-hydroxytryptophan on indole metabolism in the pineal gland of the rat during the light-dark cycle

The effect of two serotonin precursors, 5-hydroxytryptophan (5-OH-TRP) and indolepyruvic acid (IPA), a tryptophan ketoanalogue, on rat pineal indole metabolism during the light-dark cycle was investigated. 5-OH-TRP drastically increased the production of 5-hydroxyindoleacetic acid at a dose of only 10 mg/kg, whereas 50-100 mg/kg was needed to reach higher serotonin levels. It had no effect on the pathway leading to the production of N-acetylserotonin and melatonin. IPA, on the other hand, led to a marked dose-related increase in tryptophan, 5-OH-TRP, serotonin and 5-OH-indoleacetic acid, and was also active on N-acetylserotonin and melatonin synthesis in both phases. The different behaviour of these two substances with regard to melatonin synthesis was also confirmed by their effects on N-acetyltransferase, since IPA increased, whereas 5-OH-TRP decreased its activity. These data suggest that an increase in serotonin does not necessarily lead to an increase in melatonin, and that IPA may in fact induce this effect by altering the activity on N-acetyltransferase, which is regarded as a key enzyme in pineal hormone synthesis.

Moclobemide, an inhibitor of MAO-A, does not increase daytime plasma melatonin levels in normal humans

1. Plasma melatonin concentrations were determined after administration of single oral doses (100, 200 and 300 mg) of moclobemide, a reversible inhibitor of monoamine oxidase (MAO) with predominant effects on the A-type of the enzyme, to eight young, healthy male volunteers in a double-blind, random-order, placebo-controlled study. The investigation was later continued in an open fashion by giving a single 10 mg dose of the MAO-B inhibitor deprenyl to the same subjects. 2. Neither drug had any effects on plasma melatonin levels, in spite of very marked MAO-A inhibition after moclobemide (as evidenced by up to 79% average decreases in the plasma concentrations of 3,4-dihydroxyphenylglycol, a deaminated metabolite of noradrenaline) and over 90% inhibition of MAO-B activity in blood platelets after deprenyl. 3. It is concluded that daytime human plasma melatonin levels do not accurately reflect MAO-A inhibition in acute drug studies.

Does moclobemide stimulate melatonin synthesis as the other selective MAO-A inhibitors do?

It has been reported that selective MAO-A inhibitors, clorgyline and brofaromine, but not the MAO-B inhibitors, deprenyl and pargyline, stimulated rat pineal melatonin synthesis in humans and animals. Recent studies, however, found no effect of moclobemide, a selective MAO-A inhibitor, on human plasma melatonin levels. Present study found that in vitro moclobemide produced very weak stimulation of rat pineal NAT activity. However, in vivo moclobemide induced a significant increase of rat pineal NAS and melatonin content, and a dramatic decrease of 5-HIAA content (HPLC-fluorimetric procedure). Moclobemide's effect on melatonin and related indoles could be detected as early as 30 min after the injection and lasted, at least, for 2 h. The possible reasons for discrepancies between human and animal data are discussed.

Melatonin: a new probe in psychiatric investigation?

The pineal gland, Descartes' seat of the soul, was variously considered until recently as a somewhat mysterious vestigial organ, or simply a good neuroradiological marker. The former point of view arose partly out of ignorance and the curious mythical associations related to its function as a ‘third eye’ in some lower vertebrates. The latter is due to the calcification which is present in most adult human pineal glands.

Chemical sympathectomy and clorgyline-induced stimulation of rat pineal melatonin synthesis

The response to administration of the specific monoamine oxidase A (MAO-A) blocker clorgyline was investigated in adult male Sprague-Dawley rats which were sympathectomized by injection of the false neurotransmitter 6-hydroxydopamine as newborns. In intact animals which served as controls, the contents of pineal indoles melatonin, serotonin, 5-hydroxytryptophan were augmented, and the content of 5-hydroxyindoleacetic acid decreased 90 min following clorgyline injections when compared to saline receiving rats. Sympathectomized animals exhibited similar responses but these were less pronounced. It is suggested that blocking of the oxidation of both MAO-A substrates, noradrenaline and serotonin, upon clorgyline administration results in the observed increase in melatonin synthesis which is thought to contribute to the antidepressant effects of MAO inhibition.

Plasma melatonin levels in depressed patients before and after treatment with antidepressant medication

Daytime melatonin was measured by radioimmunoassay in 113 depressed outpatients before and after treatment with imipramine, mianserin, phenelzine, and placebo. At baseline, elevation of daytime melatonin values above expected levels suggests nonspecificity of the assay. After 6 weeks of treatment, melatonin levels were somewhat lower in patients on imipramine, mianserin, and placebo and slightly increased in patients treated with phenelzine. Changes in melatonin levels during treatment were significantly different for phenelzine compared with the other treatments. These findings are consistent with alterations in beta-adrenergic functioning or changes in serotonin levels.

Melatonin plasma response to MAO inhibitor: influence on human pineal activity?

Strong negative correlation has been observed between nighttime (physiological) elevation of plasma melatonin and plasma melatonin increase induced by a single dose of MAO inhibitor, tranylcypromine. The possible use of acute plasma melatonin response to MAO inhibitor as a functional test for the evaluation of human pineal activity is discussed.

Effect of brofaromine and pargyline on human plasma melatonin concentrations

1. Plasma melatonin was used to determine the influence of two monoamine oxidase inhibitor drugs in 11 normal subjects. 2. Acute oral administration of the selective reversible MAO-A inhibitor brofaromine but not of the - in low doses - selective MAO-B inhibitor pargyline increased daytime melatonin with large variations in onset, degree and duration. 3. Further investigation of this selective action on melatonin might help to better understand the action of the therapeutically effective antidepressive therapy with selective MAO-A inhibitors.