Deprenyl administration in man: a selective monoamine oxidase B inhibitor without the 'cheese effect'

Antioxidant therapy in Parkinson's disease

It is postulated that endogenous oxidative mechanisms are a major factor in the continuing death of dopaminergic neurons and the progression of Parkinson's disease. Scientific evidence in support of, and negating, the free radical auto-toxicity and dopamine toxicity concepts is reviewed. There is conflicting evidence whether free radicals are involved in the toxicity of 1-methyl-4-phenyl-1,2,3,6-tetrahydropyridine (MPTP) and attempts to prevent the toxicity of MPTP with antioxidant therapy have had variable results. The oxidation of dopamine by monoamine oxidase produces toxic metabolites however animal studies with high dose longterm levodopa and MPTP have failed to show clear evidence for autoxidation. Firm supportive evidence is obtained from the monoamine oxidase B inhibitor experience which demonstrated a block of the toxicity of MPTP in animals and probable prolongation of the course of human Parkinson's disease. The scientific data available is inconclusive but there is significant hope of retarding progressive catecholaminergic neuron degenerative changes by augmenting the free radical scavenging system with antioxidants (such as Vitamin E) and slowing catecholamine oxidation by monoamine oxidase B inhibition. Careful clinical trials with these agents must be performed.

The current status of monoamine oxidase and its inhibitors

The enzyme monoamine oxidase (MAO) plays an important role in the inactivation of both dietary amines and also of neurotransmitter amines. A study of the properties of irreversible inhibitors of this enzyme suggests that the enzyme exists in two broad types--MAO-A and MAO-B. Although irreversible inhibitors of MAO were once widely used as antidepressant agents, they fell from favour because of adverse reactions after the ingestion of amine-containing foodstuffs ("the cheese reaction"). However, these inhibitors (phenelzine and tranylcypromine) are probably best for the treatment of atypical depression providing the patient is aware of dietary reactions. A new series of reversible, MAO-A selective inhibitors are being developed which do not exhibit serious dietary interactions. These reversible inhibitors show promise as rapidly acting antidepressant agents. An atypical irreversible MAO-B selective inhibitor, selegiline (deprenyl) does not exhibit an adverse reaction on the ingestion of amine-containing foods. This drug has been used as an adjuvant in the treatment of Parkinson's disease since it allows the dose of L-dopa to be reduced by approximately 25%. More important, selegiline may slow the degeneration of dopaminergic neurons that is characteristic of Parkinson's disease.

N-propargylbenzylamine, a major metabolite of pargyline, is a potent inhibitor of monoamine oxidase type B in rats in vivo: a comparison with deprenyl

In an effort to explore the contribution of the metabolites of pargyline towards the in vivo inhibition of monoamine oxidase (MAO), the effects of pargyline and its major metabolites on the production and metabolism of a number of biogenic amines were studied in rats. The administration of pargyline gave rise to three major ethyl acetate extractable metabolites: benzylamine, N-methylbenzylamine and N-propargylbenzylamine (NPB). Only NPB demonstrated in vivo monoamine oxidase inhibitory properties at an acute dose of 30 mg kg-1. The acute effects of pargyline, NPB, and deprenyl on urine and brain concentrations of a number of biogenic amines (phenylethylamine (PEA), m- and p-tyramine, noradrenaline (NA), dopamine, and 5-hydroxytryptamine (5-HT) and their metabolites were evaluated. Increased urine and brain concentrations of PEA were considered to represent in vivo inhibition of type B MAO while decreased concentrations of NA and 5-HT metabolites were regarded as indicators of an in vivo inhibition of MAO type A. NPB, like deprenyl and pargyline, significantly increased urine and brain PEA while only pargyline reduced 5-HT metabolism, suggesting that the metabolism of pargyline to NPB may contribute towards the MAO type B inhibitory effects of pargyline in vivo. Since the therapeutic benefits of MAO inhibitors in clinical practice usually require some period of chronic treatment, the chronic effects of repeated 14 daily doses of the above MAO inhibitors on central and peripheral biogenic amines were evaluated at the following times: during treatment, one day and five days after termination of treatment. The biochemical changes observed during the course of chronic NPB, pargyline and deprenyl treatments generally follow the expected in vitro characteristics of these drugs, but the detailed changes observed suggest clear differences. For example, the in vivo effect of pargyline on urine 5-hydroxyindoleacetic acid excretion was considerably weaker than its effect on the excretion of NA and dopamine metabolites. These changes are opposite to the in vitro effects of pargyline on 5-HT, dopamine and NA oxidative deamination. Inhibitions of the metabolism of all the amines studied were clearly observed during chronic MAOI treatments, but these effects were less evident five days after the end of treatment, suggesting an almost normal metabolism of biogenic amines. It is concluded that while MAO inhibitors may be the primary compound responsible for MAO inhibition, the effects of their metabolites in some cases may also play equally important roles in the regulation of monoamines both in the periphery and the brain. Thus, as demonstrated here, NPB was found to be as potent as pargyline and deprenyl with regard to its in vivo MAO type B inhibitory properties.

Cognitive effects of L-deprenyl in Alzheimer's disease

Monoamine neurotransmitter systems, along with cholinergic systems, are known to play important roles in cognition, and are disrupted in at least some patients with dementia of the Alzheimer type (DAT). This suggests that monoamine-enhancing drugs might ameliorate cognitive symptoms in certain patients with DAT. L-Deprenyl is a monoamine oxidase (MAO) inhibitor which may selectively inhibit MAO-B at low doses, while at high doses it nonselectively inhibits MAO-A as well as MAO-B. We studied its effects on several types of cognitive function in 17 patients with DAT. Two doses of L-deprenyl (10 mg/day and 40 mg/day) and placebo were compared in a double-blind, serial treatment design. Episodic learning and memory, knowledge memory, attention, recognition, and performance on a continuous performance task were assessed at baseline and under these drug and placebo conditions. Statistically significant improvement was noted in performance on an episodic memory and learning task requiring complex information processing and sustained conscious effort during treatment with L-deprenyl 10 mg/day. Knowledge memory, intrusions, and other cognitive functions relevant to DAT were not altered by L-deprenyl at either dose.

MAO inhibitors in mental disease: their current status

Available MAOIs seem to be mainly indicated for the heterogeneous group of patients with depressive syndromes. Although groups of patients with all the recognized major subtypes of depression (including "endogenous depression") probably respond in varying degrees, MAOIs appear to be particularly indicated for out-patients with "neurotic depression" complicated by panic disorder or hysteroid dysphoria, which involves repeated episodes of depressed mood in response to feeling rejected. MAOIs can also be effective in several anxiety syndromes, in particular panic disorder. Other reports have claimed success in a variety of other syndromes including bulimia, anorexia nervosa, obsessive-compulsive neurosis, atypical facial pain and some other types of chronic pain, childhood attention deficit disorder and delusions of infestation by parasites. The nature of any underlying personality disorder is an important response variable and the assessment of personality should be encouraged in further studies. The development of new drugs raises the prospect of a range of MAOIs targeted at specific patient populations. Tranylcypromine also merits further investigation as clinical experience suggests that it can produce a dramatic response in some patients with phenelzine-resistant disorders. This may be due, at least in part, to its amphetamine-like effects.

The effects of amiflamine, a reversible MAO-A inhibitor, on the first pass metabolism of tyramine in dog intestine

The effects of amiflamine on tyramine deamination were studied using isolated loops of intestine in anesthetized dogs. In the pretreatment experiment, dogs were dosed with amiflamine (3.5 mg/kg/day) once daily for 3 days, with the study being carried out 3 hr after the final dose. [14C] Tyramine (50 mg and 50 microCi) in 10 ml of normal saline was introduced into the isolated loops of gut, and tyramine and p-hydroxyphenylacetic acid in the venous blood were separated by HPLC and measured by scintillation spectrometry. In the untreated dogs, approximately 15% of the tyramine passed through the gut wall unchanged. When tyramine and amiflamine (0.06 to 3.5 mg/kg) were administered simultaneously to the gut loop, about 27 to 65% of the tyramine passed through the gut wall unchanged. On the contrary, after pretreatment with amiflamine for 3 days, percentage of tyramine passing through the gut wall was not increased in comparison with the control. These results suggest that pretreatment with amiflamine does not produce drug concentrations in the lining cells of the gut sufficient to effectively inhibit the deamination of oral tyramine, which is administered at least 3 hr after the final dose of amiflamine.

Monoamine oxidase activity and monoamine metabolism in brains of parkinsonian patients treated with l-deprenyl

Monoamine oxidase (MAO) type A and type B were measured using kynuramine, 3,4-dihydroxyphenylethylamine (dopamine, DA), and 5-hydroxytryptamine (5-HT, serotonin) in 20 brain areas. The highest activities were found in the striatum (caudate nucleus, putamen, globus pallidus, and substantia nigra), hypothalamus, and c-mammilare. The ratio of DA to 5-HT deamination varied in the different regions, being in favor of DA in the striatum. With kynuramine as the substrate IC50 values of a number of inhibitors indicated that l-deprenyl was far more potent an inhibitor of human brain MAO than clorgyline or harmaline. N-Desmethylpropargylindane hydrochloride (AGN 1135) was also shown to have MAO-B inhibitory selectivity similar to that of l-deprenyl. Brains obtained at autopsy from l-deprenyl-treated Parkinsonian patients showed that, whereas MAO-B was fully inhibited by the therapeutic doses of l-deprenyl, substantial MAO-A activity was still evident. These results are matched by the significant increases of DA noted in caudate nucleus, globus pallidus, putamen, and substantia nigra and the unaltered 5-HT and 5-hydroxyindoleacetic acid (5-HIAA) in the same regions. These data indicate that the therapeutic actions of l-deprenyl may lie in its selective inhibition of MAO-B resulting in increased brain levels of DA formed from L-dihydroxyphenylacetic acid (L-DOPA).

The functional consequences of inhibition of monoamine oxidase type B: comparison of the pharmacological properties of L-deprenyl and MDL 72145

The pharmacological properties of two selective inhibitors of monoamine oxidase (MAO) type B, L-deprenyl and MDL 72145 [(E)-2-(3,4-dimethoxyphenyl)-3-fluoroallylamine, HCl], have been investigated in rats and mice in relation to their effects on MAO. Selective inhibition of MAO B achieved following 18 h pretreatment with L-deprenyl and/or MDL 72145 did not per se lead to prominent pharmacological activity; no effects were seen in the mouse "Behavioural Despair" test, hypothermia induced by reserpine in mice was neither prevented nor reversed and there was no change in the cardiovascular responsiveness of the pithed rat to tyramine, noradrenaline or stimulation of the spinal sympathetic outflow. L-Deprenyl differed from MDL 72145 in that short term treatment with this drug caused positive effects in the "Behavioural Despair" test, reversal of reserpine hypothermia, indirect sympathomimetic stimulation of blood pressure and heart rate in the pithed rat and ipsilateral rotation in rats with unilateral nigro-striatal lesions. Qualitatively similar effects were seen with dexamphetamine. The marked difference between the pharmacological effects of MDL 72145 and L-deprenyl despite equivalent inhibition of MAO B suggests that many of the pharmacological actions of L-deprenyl result from its amphetamine-like sympathomimetic properties. MDL 72145 can, therefore, be considered a more reliable tool with which to explore the functional importance of MAO B inhibition in experimental animals and man.

Attempts to attenuate the 'cheese effect'. Combined drug therapy in depressive illness

Although earlier results, employing intravenous tyramine challenge, had indicated that a tricyclic antidepressant plus monoamine oxidase inhibitor drug combination might be free from the 'cheese effect', the experiments reported here, involving oral tyramine challenge during the combined therapy, showed that relaxation of a tyramine-free diet during such a drug regimen might be unsafe. Preliminary observations indicated that combined (-)-deprenyl plus nonselective monoamine oxidase inhibitor therapy might lead to an unacceptable degree of orthostatic hypotension without reduction in tyramine sensitivity.

The neuropharmacological profile of N-methyl-N-propargyl-2-aminotetralin: a potent monoamine oxidase inhibitor

N-methyl-N-propargyl-2-aminotetralin (N-0425), a semi rigid analogue of deprenyl was found to be a potent inhibitor of monoamine oxidase type-A and -B. The MAO inhibitory potency was determined in in-vitro, ex-vivo and in-vivo experiments for racemic N-0425 and for both enantiomers, and compared with deprenyl. Racemic N-0425 and (-)N-0425 were found to inactivate both MAO-A and -B to about the same extent in rat brain homogenates, whereas (+)N-0425 was 10 times more potent in inhibiting MAO-B than MAO-A under in-vitro conditions. The latter compound was almost 3 times less active than (-)deprenyl with respect to inactivation of MAO-B. In ex-vivo experiments it was shown that (+/-)- and (+)N-0425 inhibited rat striatal MAO-B activity almost completely 2 h after a dose of 0.01 mmol/kg ip, whereas both compounds produced a much less rapid inactivation of type-A MAO, which was about 65% after 23 h. No potentiation of the tyramine induced increase in systolic blood pressure was found in normotensive rats following doses up to 0.01 mmol/kg ip of racemic N-0425, but a potentiation was observed after a higher dose of 0.04 mmol/kg. Levels of dopamine and noradrenaline were both increased in rat frontal cortex after the administration of N-0425, which can be interpreted as a reflection of MAO inactivation.(ABSTRACT TRUNCATED AT 250 WORDS)

Modification of blood pressure and nictitating membrane response to sympathetic amines by selective monoamine oxidase inhibitors, types A and B, in the cat

The selective monoamine oxidase (MAO) inhibitors clorgyline, selegiline and AGN 1135 did not cause a change in responses of the cat nictitating membrane to preganglionic sympathetic nerve stimulation at 5 Hz. Both selective MAO-A and MAO-B inhibitors markedly potentiated nictitating membrane contractions in response to beta-phenylethylamine (PEA). However, the responses to tyramine were unchanged. The pressor responses to tyramine were potentiated by the selective MAO-A inhibitor clorgyline (2 mg kg-1) but not by selegiline (1.0 mg kg-1) and AGN 1135 (1.5 mg kg-1), selective MAO-B inhibitors. At the doses used selegiline and AGN 1135 caused a near total selective inhibition of liver and brain MAO-B, while clorgyline inhibited MAO-A only in the brain. AGN 1135, like selegiline, could be a useful drug in potentiating the action of L-DOPA in Parkinson's disease.

Increased life expectancy resulting from addition of L-deprenyl to Madopar treatment in Parkinson's disease: a longterm study

In an open, uncontrolled study the longterm (9 years) effect of treatment with Madopar alone (n = 377) or in combination with l-deprenyl (selegiline, selective monoamine oxidase type B inhibitor) (n = 564) have been compared in Parkinsonian patients. In patients who lost their response to conventional Madopar therapy the addition of l-deprenyl resulted in a significant recouping of levodopa effect. The survival analysis revealed a significant increase of life expectancy in Madopar--l-deprenyl group regardless of the fact whether or not the significant demographic differences between the two groups were taken into account. Although the mechanism underlying this action of l-deprenyl is not known, the results are interpreted as indicating l-deprenyl's ability to prevent or retard the degeneration of striatal dopaminergic neurons. l-Deprenyl is the first anti-Parkinson drug having such a property. This hypothesis is not far fetched since l-deprenyl selectively prevents the degeneration of striatal dopaminergic neurons induced in animals by the illicit drug 1-methyl-4-phenyl-1,2,3,6-tetrahydropyridine (MPTP). Since latter compound is known to cause Parkinsonism in man and primates or Parkinson-like neurochemical and pathological changes in other animals the implications of the present study involving monoamine oxidase activity and l-deprenyl are apparent.

The facilitation of dopaminergic activity in the aged brain by (-)deprenyl. A proposal for a strategy to improve the quality of life in senescence

In the aging brain there is a loss of neurons compensated for by a proliferation of glial cells. Because of the increased B-type monoamine oxidase (MAO) activity present in the glia, dopaminergic and 'trace aminergic' modulation in the brain declines in senescence. The significant increase of the incidence of depression in the elderly, the age-dependent decline in male sexual vigor and the frequent appearance of parkinsonian symptoms in the latter decades of life might be attributed to a decrease of dopamine and 'trace amines' in the brain. The outlines of a drug strategy to counteract these biochemical lesions of aging by chronic administration of (-)deprenyl (Jumex, Eldepryl), a selective inhibitor of B-type MAO, which facilitates dopaminergic and 'trace-aminergic' activity in the brain, are forwarded. The restitution and long-term maintenance of full scale sexual activity in aged male rats continuously treated with (-)deprenyl and the clinical observation that this drug prolongs in a statistically significant manner, the duration of the Parkinson's disease support the view that (-)deprenyl may improve deteriorating functions due to dopamine deficiency in the aging brain.

Biochemical effects of L-deprenyl in atypical depressives

To examine the biochemical effects of 10-30 mg/day L-deprenyl, measurement of 24-hr urinary output of phenylethylamine (PEA), 3-methoxy 4-hydroxy phenylethyleneglycol (MHPG), and L-deprenyl's amphetamine metabolites were carried out before and during the treatment of atypical depressives. Platelet monoamine oxidase (MAO) activity was also assessed. With L-deprenyl 10-30 mg/day, the expected MAO B inhibition occurred, as indicated by significant increase in urinary PEA excretion and virtual disappearance of platelet MAO activity. Twenty-five to 33% of the daily dose of L-deprenyl was recovered as urinary methamphetamine or amphetamine. Excretion of MHPG was significantly decreased with L-deprenyl 10-20 mg/day. Overall, the results suggest that L-deprenyl's antidepressant effects are mediated by some mechanism other than, or in addition to, MAO B inhibition.

Tyramine pressor sensitivity changes during deprenyl treatment

Deprenyl has previously been reported to be a selective monoamine oxidase (MAO) type B inhibitor, which is associated with little or no enhancement of the pressor effects of tyramine. Employing an intravenous steady-state tyramine infusion technique, the effects of different doses of deprenyl and, for comparison, the mixed inhibitor tranylcypromine on the pressor response to tyramine were studied in 11 depressed patients. After 3 weeks of treatment, deprenyl produced dose-proportionate increases in tyramine sensitivity at all three doses (10, 30, and 60 mg/day) when compared to placebo baseline tyramine responses. While only a modest (3.7-fold) increase in tyramine sensitivity was found with the 10 mg/day deprenyl dose, the increase in tyramine sensitivity at the 60 mg/day dose of deprenyl (22-fold) approached that found with tranylcypromine. Reductions in plasma 3-methoxy,4-hydroxyphenylglycol (MHPG), used as a possible index of in vivo MAO-A inhibition, were highly correlated with increases in tyramine pressor sensitivity (r = 0.82). The data suggest that deprenyl acts as a relatively selective MAO-B inhibitor at low doses, but that this selectivity is lost at higher doses, resulting in a significant "crossover" inhibition of MAO-A and increased tyramine pressor sensitivity.

A controlled study of a specific MAO A reversible inhibitor (R011-1163) and amitriptyline in depressive illness

A double blind comparative study of amitriptyline and a new reversible MAO A inhibitor R011-1163 was conducted in 25 depressed inpatients over 4 weeks. Response to treatment was assessed with the Hamilton depression rating scale, the Carroll depression self rating scale and the Visual analogue scale. Both drugs produced significant changes in depressive symptomatology (P less than 0.01, MANOVA) and there were no statistically significant differences between drugs (P greater than 0.05 MANOVA). Side effects were of mild to moderate severity with dry mouth the most commonly reported side effect of amitriptyline and vague, generalised headache in patients, treated with R011-1163.

Selective inhibition by amiflamine of monoamine oxidase type A in rat brain, liver and duodenum

Amiflamine (FLA 336(+)), N-desmethylamiflamine (FLA 788(+)) and N,N-didesmethylamiflamine (FLA 668(+)) were examined for their monoamine oxidase (MAO) inhibitory effects in rat brain, liver and duodenum and were compared with the irreversible inhibitors clorgyline and (-)-deprenyl. The potency of each FLA compound was the same in each tissue both in vitro and after oral administration with either serotonin or tyramine as substrate. The in vitro effect of FLA 788(+) was 2-6 times stronger than that of amiflamine although the compounds were equipotent after oral administration. FLA 668(+) was 2-3 times less potent than amiflamine in vitro and had very poor activity after oral administration. The deamination of phenethylamine was weakly affected by the three FLA compounds. Clorgyline inhibited strongly the deamination of serotonin and tyramine in the duodenum after oral administration, being 1,000 times more potent than in the brain and the liver. Similar results were obtained for (-)-deprenyl which, however, was more potent in inhibiting the deamination of phenethylamine than that of serotonin and tyramine. Amiflamine was a reversible MAO inhibitor with no MAO inhibitory capacity 24 h after a single oral dose. On the other hand the irreversible inhibitor clorgyline had a maximal effect on brain MAO 48 h after a single dose while the inhibitory effect in the duodenum had almost disappeared. The influence of amiflamine on the excretion of acid and basic metabolites of orally administered 14C-tyramine (58 mumol/kg) in rat was examined.(ABSTRACT TRUNCATED AT 250 WORDS)

L-deprenyl plus L-phenylalanine in the treatment of depression

The antidepressive efficacy of 1-deprenyl (5-10 mg daily) plus 1-phenylalanine (250 mg/day) has been evaluated in 155 unipolar depressed patients. Both oral and intravenous administration showed beneficial effects in 90% of outpatients and 80.5% of inpatients. It is concluded that this combined treatment has a potent antidepressive action based on the accumulation of 1-phenylethylamine in the brain.

Pressor sensitivity to tyramine in patients with headache: relationship to platelet monoamine oxidase and to dietary provocation

The pressor responses to oral and intravenous tyramine were not different from controls in migrainous patients with or without a history of attacks triggered by foods. However, patients who reported a dietary trigger were more likely to develop headache after tyramine administration than those without such a dietary history. Pressor responses to intravenous tyramine in patients with cluster headache were indistinguishable from controls. A group of five males with platelet monoamine oxidase activity one standard deviation or more below that of male controls required less intravenous tyramine to raise blood pressure by 30 mm Hg than males with monoamine oxidase levels within one standard deviation of the controls. This finding suggests that platelet monoamine oxidase activity to some extent reflects that of total body monoamine oxidase A plus B.

Tyramine-induced noradrenaline release from rat brain slices: prevention by (-)-deprenyl

Clorgyline (1 and 10 microM) and (+)-deprenyl (10 microM) both significantly potentiated the tyramine (100 microM)-induced release of [3H]-noradrenaline from rat cerebral cortex slices. (-)-Deprenyl (50 microM) significantly reduced it, while lower concentrations had no effect on noradrenaline release. However, in combination, 1 microM (-)-deprenyl blocked the release-facilitating action of 1 microM clorgyline, and 10 microM (-)-deprenyl that of 10 microM (+)-deprenyl. Low concentrations of (+)- and (-)-deprenyl (1 and 10 microM), both selectively inhibited phenylethylamine oxidation by monoamine oxidase B. Higher concentrations of (-)-deprenyl (20 and 50 microM) also inhibited 5-hydroxytryptamine oxidation by monoamine oxidase A. Clorgyline (1 and 10 microM) inhibited both enzymes. Thus, the effects of these drugs on noradrenaline-release cannot be explained solely in terms of irreversible inhibition of monoamine oxidase A and B, and other possible mechanisms are discussed. If the brain-slice model faithfully mirrors the sequence of events manifesting peripherally as the tyramine hypertensive response ('cheese effect'), then it is possible that low doses of (-)-deprenyl, administered with antidepressant monoamine oxidase inhibitors, can prevent this adverse reaction.

Monoamine oxidase inhibitors and their pharmacological significance

The role of deprenyl, a selective monoamine oxidase B inhibitor, in the treatment of Parkinson's disease has been evaluated with special reference to the multiple pharmacological actions of the monoamine oxidase-inhibitory group of drugs.

Deprenyl (selegiline): the history of its development and pharmacological action

Deprenyl inhibits MAO-B selectively in different animal species and in man. Its safety margin is remarkable. We were able to block MAO-B activity in the brain selectively in vivo in four species (mouse, rat, cat, dog) with s.c. administration of 0.17-0.31% of LD50. The usual oral dose range in clinical practice, 5-20 mg daily (0.05-0.2 mg/kg), is about ten times lower than the orally active dose in the rat. Deprenyl proved to be safe drug in man. Neither hypertensive reactions nor the need for any special dietary care were ever encountered during long-term (2-8 years) daily administration of the drug. The most important effect of deprenyl in the brain is the sensitization of dopaminergic neurons to physiological and pharmacological influences, but in contrast to levodopa or bromocrytine, deprenyl does not elicit an acute increase in dopaminergic activity. The effect of deprenyl is due, on the one hand, to the inhibition of MAO-B and, on the other hand, to inhibition of the uptake of dopamine. In agreement with its peculiar spectrum of pharmacological activity, deprenyl proved to be a useful adjuvant to levodopa alone or in combination with a peripheral decarboxylase inhibitor. In addition, a supplement of deprenyl in Parkinson's disease led to significant prolongation of the duration of the illness. This has not been observed so far with other antiparkinsonian drugs. The dopamine content of the human caudate nucleus decreases by 13% per decade over the age of 45. The hypothesis has been put forward that the significant increase of incidence of depression in the elderly, the age-dependent decline in male sexual vigour and the frequent appearance of parkinsonian symptoms in the later decades of life might be attributed to a decrease of dopamine and 'trace amines' in the brain. The possibility of countering these biochemical lesions of ageing by long-term administration of deprenyl, a selective inhibitor of MAO-B which facilitates dopaminergic and 'trace-aminergic' activity in the brain, and is a safe drug in man, is considered in detail.

L-Deprenil, a selective monoamine oxidase type B inhibitor, in the treatment of depression: a double blind evaluation

In a double blind controlled study, 14 affectively ill patients (2 bipolars, 12 unipolars) were randomly allocated to L-Deprenil treatment (an irreversible selective MAO-B inhibitor without "cheese effect") and 13 patients (3 bipolars, 10 unipolars) to placebo only. Patients on L-Deprenil showed a significantly greater clinical improvement than placebo patients. A positive relationship was found between clinical improvement and degree of platelet MAO inhibition in patients treated with L-Deprenil.

Intestinal metabolism of tyramine by both forms of monoamine oxidase in the rat

The two forms of monoamine oxidase (MAO) in rat intestine and brain homogenates were found to have different Km and Vmax values towards tyramine. The Km values for the A-form of the enzyme towards this substrate were around 120 microM in both cases, whereas the values for the B-form were about 240 microM. As a consequence, the ratio of activities (MAO-A: MAO-B) towards tyramine are dependent upon the substrate concentration. The MAO-A-selective inhibitors, toloxatone and cimoxatone, were found to be competitive inhibitors of the oxidation of tyramine by the A-form of this enzyme in the rat intestine, with Ki values of 3.4 microM and 3.7 nM respectively. The significance of these results in relation to the "cheese effect", a pressor response to tyramine after monoamine oxidase inhibition, are discussed.

Effect of selective monoamine oxidase inhibition by clorgyline and deprenyl on the norepinephrine receptor-coupled adenylate cyclase system in rat cortex

The consequences of selective monoamine oxidase (MAO) inhibition on the norepinephrine(NE)-sensitive adenylate cyclase system were determined in slices of rat cerebral cortex. The chronic administration of clorgyline, which selectively inhibited the activity of MAO-A, caused a significant decrease in the responsiveness of the noradrenergic cyclic AMP-generating system. The noradrenergic subsensitivity was accompanied by a significant decrease in the density of beta-adrenoceptors, as measured by 3H-dihydroalprenolol (DHA) binding, without altering the Kd value. However, selective inhibition of MAO-B by deprenyl did not alter the sensitivity of the cyclic AMP-generating system to NE or the specific DHA binding. The basal levels of cyclic AMP in the cortex were unaltered by the drugs. Since inhibition of MAO-A, but not MAO-B, increases the availability of NE, the results support the hypothesis that a persistent NE-receptor interaction is one of the prerequisites for the in vivo densitization of the NE-sensitive adenylate cyclase and the concomitant down-regulation of the number of beta-adrenoceptors in brain.

Relationship between tyramine potentiation and selective inhibition of monoamine oxidase types A and B in the rat vas deferens

1 The degree of selective monoamine oxidase (MAO) inhibition produced by (-)-deprenyl, clorgyline, LY51641 and tranylcypromine was examined in relation to modification of tyramine and noradrenaline contractile responses of the rat isolated vas deferens. 2 All inhibitors possessed reversible alpha-adrenoceptor blocking activity, determined against noradrenaline on the denervated vas deferens. For LY51641 and tranylcypromine, antagonism was competitive, with pA2 values of 6.17 and 5.16. 3 Clorgyline, LY51641 and (-)-deprenyl (10(-5) M) inhibited the tyramine response while present in the organ bath: LY51641, which was the most potent as an alpha-adrenoceptor blocker, produced this effect at 10(-6) M. Responses to tyramine and noradrenaline were potentiated on wishing out the inhibitors, but noradrenaline potentiation was seen only when tyramine had been present in the system. 4 Tranylcypromine (10(-6) M) potentiated responses to noradrenaline and tyramine while present in the organ bath. 5 Potentiation of tyramine responses by clorgyline and LY51641 occurred at 91% and 64% inhibition of MAO type A respectively, although full potentiation of the tyramine response was elicited only when substantial inhibition of both enzyme types occurred. Selective inhibition of MAO type B by 67% (with deprenyl) was not associated with tyramine potentiation.

Cardiovascular changes in response to selective monoamine oxidase inhibition in the rat

Chronic (21 days) treatment with the selective monoamine oxidase (MAO)-A inhibitor clorgyline, but not with the MAO-B inhibitor deprenyl in pithed rats leads to increased blood pressure responses to sympathetic stimulation and intravenous tyramine, and to elevated unstimulated heart rates. No significant changes are observed in plasma catecholamine responses to sympathetic stimulation, nor in beta-adrenoreceptor numbers in heart ventricles. These findings suggest that the hypotensive effects of MAO inhibitors result from central nervous system rather than peripheral nervous system alterations.

Phenylacetic acid in human body fluids: high correlation between plasma and cerebrospinal fluid concentration values

In a group of six Parkinsonian patients and 13 "controls" with non-Parkinsonian neurological disease, there was a high correlation between both free and conjugated phenylacetic acid concentrations in plasma and cerebrospinal fluid taken at about the same time. This compound is the major metabolite of phenylethylamine, the production of which may be disturbed in a number of neuropsychiatric illnesses. Thus plasma measurements might be employed clinically to provide an estimate of central changes in phenylethylamine economy. A small but significantly higher proportion of conjugated phenylacetic acid was present in the plasma (but not cerebrospinal fluid) of Parkinsonians compared with controls.

The contribution of amphetamine metabolites of (-)-deprenyl to its antiparkinsonian properties

Although (-)-deprenyl is known to be metabolized to methamphetamine and amphetamine, two small-scale double-blind trials indicate that neither metabolite contributes to all therapeutic benefit conferred by this drug in certain patients with Parkinson's disease: the manipulation of urinary pH, which alters the rate of excretion of these metabolites, failed to change the response pattern; substitution of a metabolite mixture for active drug caused a falling off in benefit.

The acetylenic monoamine oxidase inhibitors clorgyline, deprenyl, pargyline and J-508: their properties and applications

The article presents a short review of some of the properties of the acetylenic inhibitors of monoamine oxidase currently under investigation: clorgyline, (—)-deprenyl, pargyline and J-508. Their substrate-selective inactivation, mechanism of inhibition, titration and pharmacology with respect to monoamine oxidase are critically discussed.

Selective acetylenic 'suicide' and reversible inhibitors of monoamine oxidase types A and B

1 A number of aromatic-N-propargyl (acetylenic) compounds and indoleamines were tested for their inhibitory action on monoamine oxidase (MAO) type A and type B using the substrates 5-hydroxytryptamine (5-HT), beta-phenylethylamine (PEA) and dopamine. 2 Structure activity studies with aromatic-N-propragyl (acetylenic) derivatives have shown that MAO inhibitory potency is least dependent on the aromatic portion of the compounds. N-methylated propargyl derivatives are the most active and replacement of the methyl group with a higher alkyl or aromatic group results in significant reduction of activity. The triple bond in the N-propargyl portion is absolutely essential for activity and must be beta-to the nitrogen. It is the acetylenic group that gives these compounds their irreversible MAO inhibitory property. 3 The present study has indicated that since the acetylenic compounds resemble the enzyme substrates the distance between the aromatic ring and the N-propargyl terminal is crucial in designating the type A or type B MAO inhibitory property. For MAO type A inhibition, a distance equivalent to at least three carbon units is required, while for the inhibition of the B type enzyme this distance can be 1 or 2 carbon units. 4 The compounds AGN-1133 and AGN-1135 show most promise in Parkinson's disease or as anti-depressants because of their irreversible selective type B MAO inhibition in vitro and in vivo. 5 A number of indoleamine derivatives were found to be reversible selective type A inhibitors.

Tyramine antagonistic properties of AGN 1135, an irreversible inhibitor of monoamine oxidase type B

1 The effects of the irreversible monoamine oxidase (MAO) inhibitors, AGN 1133, AGN 1135 and (-)-deprenyl, on tyramine and noradrenaline responses and uptake of [3H]-metaraminol were investigated in the isolated vas deferens of the rat. Uptake of [3H]-metaraminol and [3H]-octopamine was compared in mouse vas deferens. The modification of tyramine and noradrenaline-induced pressor responses by AGN 1133 and AGN 1135 was examined in anaesthetized rats and cats. 2 AGN 1133 (7.5 x 10(-6)M) greatly potentiated responses to tyramine in the rat isolated vas deferens. Both AGN 1135 and (-)-deprenyl inhibited tyramine responses selectively at concentrations above 10(-5)M (which caused almost complete inhibition of MAO types A and B) but tyramine responses were potentiated on washing out the inhibitors. 3 AGN 1135 (10(-4)M) and (-)-deprenyl (10-5)M) inhibited [3H]-metaraminol uptake by about 20% in rat and mouse vas deferens; neither inhibitor affected [3H]-octopamine uptake in mouse vas deferens. Desmethylimipramine (10(-6)M) inhibited amine uptake by more than 70%. 4 AGN 1133 (1.5 mg/kg) potentiated pressor responses to tyramine in rats and cats whereas AGN 1135 (1.5 mg/kg) did not. 5 AGN 1135 possesses tyramine antagonistic activity which is qualitatively similar to that of (-)-deprenyl but which cannot satisfactorily be explained by inhibition of neuronal or granula amine uptake.

Tyramine infusions and selective monoamine oxidase inhibitor treatment. I. Changes in pressor sensitivity

The enhanced sensitivity to the pressor effects of tyramine, an indirect-aging sympathomimetic found abundantly in the diet, is a well-known potentially dangerous side effect occurring during treatment with commonly used non-selective monoamine oxidase (MAO) inhibitors. The effects of treatment with the selective MAO-A inhibitor clorgyline and the partially selective MAO-B inhibitors pargyline and deprenyl on tyramine's pressor effects were studied in depressed patients using an IV steady-state tyramine infusion technique. After 4 weeks of treatment, clorgyline produced a significantly greater increase in tyramine sensitivity in comparison to a medication-free baseline (29-fold) than did pargyline (12-fold) or deprenyl (1.7-fold). The pressor effects of tyramine were significantly prolonged after cessation of infusion during both clorgyline and pargyline, but not deprenyl treatment. These data from IV tyramine administrations suggest that intestinal MAO inhibition is not the major determinant of the enhanced tyramine pressor sensitivity produced by clorgyline and pargyline.

Tyramine infusions and selective monoamine oxidase inhibitor treatment. II. Interrelationships among pressor sensitivity changes, platelet MAO inhibition, and plasma MHPG reduction

The relationship between changes in IV tyramine pressor sensitivity accompanying selective monoamine oxidase (MAO) inhibitor treatment and estimates of MAO-A and MAO-B inhibition in vivo were studied. Reductions in platelet MAO activity provided an index of MAO-B inhibition, while changes in plasma 3-methoxy-4-hydroxyphenethylene glycol (MHPG) were used as an hypothesized reflection of MAO-A inhibition. Chronic treatment with the MAO-A inhibitor clorgyline and the MAO-B inhibitor pargyline showed significant inhibition of the alternate MAO enzyme as well, although this crossover effect was greater for pargyline than clorgyline. The MAO-B inhibitor deprenyl appeared to maintain the greatest degree of MAO inhibition selectivity in vivo. Tyramine pressor sensitivity changes accompanying administration of the MAO inhibitors were highly correlated with decreases in plasma MHPG (r = 0.92), supporting our previous data indicating the rank order of clorgyline greater than pargyline greater than deprenyl for enhancement of tyramine pressor sensitivity and, thus, suggesting that tyramine potentiation is primarily a function of MAO-A rather than MAO-B inhibition. Changes in plasma MHPG are suggested to provide a potentially useful clinical index of in vivo MAO-A inhibition.

Is the failure of (-)deprenyl, a selective monoamine oxidase B inhibitor, to alleviate depression related to freedom from the cheese effect?

The selective monoamine oxidase (MAO) B inhibitor (-)deprenyl failed to produce any greater benefit than placebo in a limited double-blind trial conducted in depressive patients. Its relative freedom from the so-called cheese effect was confirmed, however, in drug-treated patients challenged IV with tyramine. There is evidence to suggest that this cheese effect, a facilitated tyramine-induced hypertensive response, is pharmacologically distinct from MAO inhibition proper. Thus, it is conceivable that its central counterpart, an enhanced noradrenaline release due to the access of traces of tyramine to the CNS, is a prerequisite for any therapeutic benefit obtainable with the MAO-inhibitory drugs in general.