Iproniazid

Monoamine—Oxidase Inhibitors. In the mid-1950s, tuberculosis patients with depression being treated with iproniazid (42) were occasionally reported to become euphoric. This observation led to the discovery of irreversible monoamine—oxidase (MAO) inhibiting properties. Hydrazine and nonhydrazine-related MAO inhibitors were subsequentiy shown to be antidepressants (122). Three other clinically effective irreversible MAO inhibitors have been approved for treatment of major depression phenelzine (43), isocarboxazid (44), and tranylcypromine (45). 

Monoamine Oxidase Inhibitors. MAOIs inactivate the enzyme MAO, which is responsible for the oxidative deamination of a variety of endogenous and exogenous substances. Among the endogenous substances are the neurotransmitters, norepinephrine, dopamine, and serotonin. The prototype MAOI is iproniazid [54-92-2] (25), originally tested as an antitubercular dmg and a close chemical relative of the effective antitubercular, isoniazid [54-85-3] (26). Tubercular patients exhibited mood elevation, although no reHef of their tuberculosis, following chronic administration of iproniazid. In... 

Iproniazid (isonicotinic acid 2-isopropylhydrazide) phosphate [305-33-9] M 277.2, m 178-179 , 180-182°, pKesj 3.5 (free base). Crystd from H2O and Me2CO. Free base has m 113-114° from C6Hg/pet ether. 

Thus, condensation of isoniazide with acetone at the basic nitrogen gives the corresponding Shiff base (8). Catalytic reduction affords the antidepressant, iproniazid (9). Addition of the same basic nitrogen to methyl acrylate by Michael condensation leads to the 3-amino ester (10). This is converted to the amide, nialamide (11), on heating with benzylamine. 

Acute treatment with nonselective MAO inhibitors (iproniazid, tranylcypromine, phenelzine), as a consequence of inhibiting both forms of the enzyme, increase, brain levels of all monoamines (phenylethylamine, tryptamine, methylhistamine aminergic neurotransmitters (dopamine, noradr enaline, adrenaline and serotonin). By contrast MAO-A inhibitors (clorgyline) increase serotonin and noradrenaline, while MAO-B inhibitors (selegiline, rasagiline) increase brain levels... 

Iproniazid was among the first psychotropic antidepressants to be discovered and introduced into the clinic. Although this inhibitor and others that followed... 

As early as 1961, the first generation of MAO inhibitors (iproniazid, isocarboxazide) were employed for the treatment of Parkinson s disease (PD). However, because of the severe side effects, such as cheese reaction, they were abandoned. The realization that the basal ganglia (extrapyramidal region) of human brain contained mostly MAO-B, which metabolized... 

C(,H7NjO 54-85-3) see Glyconiazide Iproniazid Nialamide Pasiniazid Streptoniazid isonicotinamidc... 

A link between the central monoamines, 5-hydroxytryptamine (5-HT) and noradrenaline, and depression was forged some 40 years ago and arose from clinical experience with the drugs, reserpine and iproniazid. At that time, reserpine was used as an... 

In contrast, iproniazid, introduced in 1951 for treatment of tuberculosis, induced euphoria and was described as a psychic energiser . In fact, these patients, when given iproniazid, could become quite disruptive and this action was regarded as an undesirable side-effect However, its beneficial effects in depression were soon recognised and it was regarded as the first effective antidepressant drug. Studies of peripheral sympathetic neurons, later extended to noradrenergic neurons in the brain, showed that iproniazid irreversibly inhibits the catalytic enzyme, monoamine oxidase (MAO). Because only cytoplasmic monoamines are accessible to MAO, inhibition of this enzyme first increases the concentration of the pool of soluble transmitter but this leads to a secondary increase in the stores of vesicle-bound transmitter i.e. the pool available for impulse-evoked release (Fillenz and Stanford 1981). 

Iproniazid also prevents the reserpine syndrome in rats. Reserpine blocks vesicular uptake of monoamines which, as a consequence, leak from the storage vesicles into the cytosol. Although these monoamines would normally be metabolised by MAO, they are conserved when a MAO inhibitor (MAOI) is present, and so co-administration of reserpine and a MAOI leads to accumulation of monoamines in the neuronal cytosol. It is now known that, when the concentration of cytoplasmic monoamines is increased in this way, they are exported to the synapse on membrane-bound monoamine transporters. The ensuing increase in monoamine transmission, despite the depletion of the vesicular pool, presumably accounts for the effects of iproniazid on the behaviour of reserpine-pretreated rats. 

With the exception of tranylcypromine (a phenylcycloalkylamine), the first MAOIs (e.g. iproniazid, isoniazid, phenelzine, isocarboxazid) were derivatives of hydrazine (originally used as a rocket fuel) (Fig. 20.2). All are irreversible inhibitors of the enzyme and restoration of MAO activity requires the synthesis of new enzyme. 

Huang, J.T., and Ho, B.T. The effect of pretreatment with iproniazid on the behavioral activities of P-phenethylamine in rats. 

Doxepine, Amitriptyline, Imipramine, Iproniazid, Pheniprazine Depression and anxiety... 

In 1957, Nathan Kline, Harry Loomer and John Saunders, at the Rockland State Hospital in Orangeburg, New York, reported the first influential assessment of iproniazid as a psychic energizer on non-tubercular psychiatric patients, some of whom were suffering from depression. According to their report, about two-thirds of patients showed a measurable response to the drug. This is about the same response rate that is reported for clinical... 

It is important to note that claims for the effectiveness of iproniazid and imipramine were not based on placebo-controlled clinical trials. Instead, they were based on clinical impressions.6 In discovering the antidepressant effects of imipramine, Kuhn did not even use precise measurement, rating scales or statistics. His claim was that precise measurement led to stagnation rather than progress in medicine, and he preferred to rely on his extensive medical experience and artistic imagination instead.7... 

Despite the weakness of the data, the idea that iproniazid and imipramine were effective antidepressants came to be widely accepted. This is not really surprising, in the context of the times. In the 1950s and 1960s, the power of the placebo effect was just beginning to be recognized, and placebo-controlled clinical trials were rare. New treatments were often accepted on the basis of clinical experience and the testimony of experts in the field. 

Iproniazid and imipramine seemed to work as antidepressants, but how did they achieve their effects It would be another decade before the chemical-imbalance theory was launched. In 1965, Joseph Schildkraut at the National Institute of Mental Health in Washington, DC, published a groundbreaking paper in which he argued that depression was caused by a deficiency of the neurotransmitter norepinephrine in the gaps between neurons in the brain.8 Two years later Alec Coppen, a physician at West Park Hospital in Surrey, published another version of the chemical-imbalance theory. His version differed from Schildkraut s in that it put most of the blame on a different neurotransmitter, emphasizing serotonin rather than norepinephrine as the neurotransmitter that was lacking.9... 

Against this backdrop, researchers reported evidence that iproniazid, the antitubercular drug that was to become the first antidepressant, might increase norepinephrine and serotonin levels in the brain. How did it have this effect Recall that some of the neurotransmitter molecules released by a neuron are destroyed by enzymes in the synaptic cleft between the sending presynaptic neuron and the receiving postsynaptic neuron. When the neurotransmitter is a monoamine - like norepinephrine and serotonin - this process is called monoamine oxidase (MAO). As early as 1952 researchers at the Northwestern University Medical School in Chicago reported that iproniazid inhibited the oxidation of monoamines. This meant that iproniazid was a... 

Here then is the logic behind the first version of the chemical-imbalance theory. Iproniazid is a monamine oxidase inhibitor - it inhibits the oxidation of norepinephrine and serotonin in the synapses, thereby leaving more of these neurotransmitters available in the brain. When depressed people take iproniazid, they get better. Therefore insufficient norepinephrine and/or serotonin causes depression.12... 

There was a problem with this first version of the biochemical theory of depression. Iproniazid was not the only drug that had been reported to be effective as an antidepressant. Imipramine, the drug that had been tested by the Swiss psychiatrist Roland Kuhn, seemed to have similar effects. But imipramine is not an MAOI it does not inhibit the destruction of neurotransmitters in the synapse. So if antidepressants worked by inhibiting monoamine oxidase, why was imipramine effective How could its apparent effectiveness be reconciled with the chemical-imbalance theory ... 

Like the articles indicating that iproniazid and imipramine functioned as antidepressants, the conclusion that reserpine makes people depressed was based on clinical reports, rather than controlled trials. 

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